Ralph A Nixon, M.D., Ph.D.

Developmental ethanol enhances histone methyl transferase-mediated epigenetic modification
Basavaraj B.S.; Saito M.; Kumar A.; Nixon R.A.; Verin A.D.; Umapathy N.S.; Subbanna S.
2011 ;35:119A-119A, Alcoholism: clinical & experimental research
Ethanol administration to neonatal animals leads to a significant loss of cells in various regions of the brain, including the hippocampus, and impairs long-term potentiation (LTP), which is a physiological correlate of memory. Chromatin remodeling by histone modification plays an important role in several aspects of long-term cellular plasticity, including neuronal differentiation, learning and memory, drug addiction and neurodegeneration. Dimethylation of histone-3 Lys 9 (H3K9me2) correlates with transcriptional silencing, and trimethylation of histone-3 Lys 4 (H3K4me3) is linked to active transcription. Recently, histone (H3) methylation was implicated in the regulation of chromatin remodeling in the nervous system and the process of long-term memory storage. Postnatal ethanol-induces neurodegeneration in rodents, although the molecular mechanisms by which this occurs and physiological consequences are largely limited. In the current study, we show the participation of specific histone methyl transferase mediated dimethylation of histone-3 at lysine 4 in neonatal one or more brain regions. The results suggest that postnatal ethanol-induces robust apoptotic neurodegeneration as indicated by enhanced active caspase-3 immunoreactivity as well as electron microscope ultra structural features in hippocampus, cortex and cerebellum. These conditions resulted in enhanced expression of H3K9 specific histone methyl transferase (G9a/ b) mRNA and protein in a dose and time dependent manner. This is followed by enhanced dimethylation of H3K9 in hippocampus, cortex and cerebellum, although dual immunofluorescence histochemistry reveals that active caspase-3 positive neurons show diminishing immunoreactivity against H3K9me2. The results collectively suggest that developmental ethanol not only induces neurodegeneration but also enhances H3K9 dimethylation through histone methyl transferase, G9a/b. The current finding highlights the histone methylation mediated epigenetic modification as a valuable target in the therapy for fetal alcohol spectrum disorders
— id: 146274, year: 2011, vol: 35, page: 119A, stat: Journal Article,

Upregulation of select rab GTPases in cholinergic basal forebrain neurons in mild cognitive impairment and Alzheimer's disease
Ginsberg, Stephen D; Mufson, Elliott J; Alldred, Melissa J; Counts, Scott E; Wuu, Joanne; Nixon, Ralph A; Che, Shaoli
2011 Oct;42(2):102-110, Journal of chemical neuroanatomy
Endocytic system dysfunction is one of the earliest disturbances that occur in Alzheimer's disease (AD), and may underlie the selective vulnerability of cholinergic basal forebrain (CBF) neurons during the progression of dementia. Herein we report that genes regulating early and late endosomes are selectively upregulated within CBF neurons in mild cognitive impairment (MCI) and AD. Specifically, upregulation of rab4, rab5, rab7, and rab27 was observed in CBF neurons microdissected from postmortem brains of individuals with MCI and AD compared to age-matched control subjects with no cognitive impairment (NCI). Upregulated expression of rab4, rab5, rab7, and rab27 correlated with antemortem measures of cognitive decline in individuals with MCI and AD. qPCR validated upregulation of these select rab GTPases within microdissected samples of the basal forebrain. Moreover, quantitative immunoblot analysis demonstrated upregulation of rab5 protein expression in the basal forebrain of subjects with MCI and AD. The elevation of rab4, rab5, and rab7 expression is consistent with our recent observations in CA1 pyramidal neurons in MCI and AD. These findings provide further support that endosomal pathology accelerates endocytosis and endosome recycling, which may promote aberrant endosomal signaling and neurodegeneration throughout the progression of AD
— id: 136996, year: 2011, vol: 42, page: 102, stat: Journal Article,

Lysosomal Proteolysis Inhibition Selectively Disrupts Axonal Transport of Degradative Organelles and Causes an Alzheimer's-Like Axonal Dystrophy
Lee, Sooyeon; Sato, Yutaka; Nixon, Ralph A
2011 May 25;31(21):7817-7830, Journal of neuroscience
In the hallmark neuritic dystrophy of Alzheimer's disease (AD), autophagic vacuoles containing incompletely digested proteins selectively accumulate in focal axonal swellings, reflecting defects in both axonal transport and autophagy. Here, we investigated the possibility that impaired lysosomal proteolysis could be a basis for both of these defects leading to neuritic dystrophy. In living primary mouse cortical neurons expressing fluorescence-tagged markers, LC3-positive autophagosomes forming in axons rapidly acquired the endo-lysosomal markers Rab7 and LAMP1 and underwent exclusive retrograde movement. Proteolytic clearance of these transported autophagic vacuoles was initiated after fusion with bidirectionally moving lysosomes that increase in number at more proximal axon levels and in the perikaryon. Disrupting lysosomal proteolysis by either inhibiting cathepsins directly or by suppressing lysosomal acidification slowed the axonal transport of autolysosomes, late endosomes, and lysosomes and caused their selective accumulation within dystrophic axonal swellings. Mitochondria and other organelles lacking cathepsins moved normally under these conditions, indicating that the general functioning of the axonal transport system was preserved. Dystrophic swellings induced by lysosomal proteolysis inhibition resembled in composition those in several mouse models of AD and also acquired other AD-like features, including immunopositivity for ubiquitin, amyloid precursor protein, and hyperphosphorylated neurofilament proteins. Restoration of lysosomal proteolysis reversed the affected movements of proteolytic Rab7 vesicles, which in turn essentially cleared autophagic substrates and reversed the axonal dystrophy. These studies identify the AD-associated defects in neuronal lysosomal proteolysis as a possible basis for the selective transport abnormalities and highly characteristic pattern of neuritic dystrophy associated with AD
— id: 132892, year: 2011, vol: 31, page: 7817, stat: Journal Article,

Autophagy failure in Alzheimer's disease-locating the primary defect
Nixon RA; Yang DS
2011 Jul;43(1):38-45, Neurobiology of disease
Autophagy, the major degradative pathway for organelles and long-lived proteins, is essential for the survival of neurons. Mounting evidence has implicated defective autophagy in the pathogenesis of several major neurodegenerative diseases, particularly Alzheimer's disease (AD). A continuum of abnormalities of the lysosomal system has been identified in neurons of the AD brain, including pathological endocytic pathway responses at the very earliest disease stage and a progressive disruption of autophagy leading to the massive buildup of incompletely digested substrates within dystrophic axons and dendrites. In this review, we examine research on autophagy in AD and evaluate evidence addressing the specific step or steps along the autophagy pathway that may be defective. Current evidence strongly points to disruption of substrate proteolysis within autolysosomes for the principal mechanism underlying autophagy failure in AD. In the most common form of familial early onset AD, mutant presenilin 1 disrupts autophagy directly by impeding lysosomal proteolysis while, in other forms of AD, autophagy impairments may involve different genetic or environmental factors. Attempts to restore more normal lysosomal proteolysis and autophagy efficiency in mouse models of AD pathology have yielded promising therapeutic effects on neuronal function and cognitive performance, demonstrating the relevance of autophagy failure to the pathogenesis of AD and the potential of autophagy modulation as a therapeutic strategy
— id: 126480, year: 2011, vol: 43, page: 38, stat: Journal Article,

The Myosin Va Head Domain Binds to the Neurofilament-L Rod and Modulates Endoplasmic Reticulum (ER) Content and Distribution within Axons
Rao, Mala V; Mohan, Panaiyur S; Kumar, Asok; Yuan, Aidong; Montagna, Lee; Campbell, Jabbar; Espreafico, Enilza M; Julien, Jean P; Nixon, Ralph A
2011 ;6(2):e17087-e17087, PLoS ONE
The neurofilament light subunit (NF-L) binds to myosin Va (Myo Va) in neurons but the sites of interaction and functional significance are not clear. We show by deletion analysis that motor domain of Myo Va binds to the NF-L rod domain that forms the NF backbone. Loss of NF-L and Myo Va binding from axons significantly reduces the axonal content of ER, and redistributes ER to the periphery of axon. Our data are consistent with a novel function for NFs as a scaffold in axons for maintaining the content and proper distribution of vesicular organelles, mediated in part by Myo Va. Based on observations that the Myo Va motor domain binds to intermediate filament (IF) proteins of several classes, Myo Va interactions with IFs may serve similar roles in organizing organelle topography in different cell types
— id: 126479, year: 2011, vol: 6, page: e17087, stat: Journal Article,

Sensory Network Dysfunction, Behavioral Impairments, and Their Reversibility in an Alzheimer's beta-Amyloidosis Mouse Model
Wesson DW; Borkowski AH; Landreth GE; Nixon RA; Levy E; Wilson DA
2011 Nov 2;31(44):15962-15971, Journal of neuroscience
The unique vulnerability of the olfactory system to Alzheimer's disease (AD) provides a quintessential translational tool for understanding mechanisms of synaptic dysfunction and pathological progression in the disease. Using the Tg2576 mouse model of beta-amyloidosis, we show that aberrant, hyperactive olfactory network activity begins early in life, before detectable behavioral impairments or comparable hippocampal dysfunction and at a time when amyloid-beta (Abeta) deposition is restricted to the olfactory bulb (OB). Hyperactive odor-evoked activity in the piriform cortex (PCX) and increased OB-PCX functional connectivity emerged at a time coinciding with olfactory behavior impairments. This hyperactive activity persisted until later in life when the network converted to a hyporesponsive state. This conversion was Abeta-dependent, because liver-X receptor agonist treatment to promote Abeta degradation rescued the hyporesponsive state and olfactory behavior. These data lend evidence to a novel working model of olfactory dysfunction in AD and, complimentary to other recent works, suggest that disease-relevant network dysfunction is highly dynamic and region specific, yet with lasting effects on cognition and behavior
— id: 145504, year: 2011, vol: 31, page: 15962, stat: Journal Article,

Mechanisms of neural and behavioral dysfunction in Alzheimer's disease
Wesson, Daniel W; Nixon, Ralph A; Levy, Efrat; Wilson, Donald A
2011 Jun;43(3):163-179, Molecular neurobiology
This review critically examines progress in understanding the link between Alzheimer's disease (AD) molecular pathogenesis and behavior, with an emphasis on the impact of amyloid-beta. We present the argument that the AD research field requires more multifaceted analyses into the impacts of Alzheimer's pathogenesis which combine simultaneous molecular-, circuit-, and behavior-level approaches. Supporting this argument is a review of particular research utilizing similar, 'systems-level' methods in mouse models of AD. Related to this, a critique of common physiological and behavioral models is made-highlighting the likely usefulness of more refined and specific tools in understanding the relationship between candidate molecular pathologies and behavioral dysfunction. Finally, we propose challenges for future research which, if met, may greatly extend our current understanding of how AD molecular pathology impacts neural network function and behavior and possibly may lead to refinements in disease therapeutics
— id: 131960, year: 2011, vol: 43, page: 163, stat: Journal Article,

Declining phosphatases underlie aging-related hyperphosphorylation of neurofilaments
Yang, Dun-Sheng; Lee, Ju-Hyun; Vinod, K Yaragudri; Stavrides, Philip; Amin, Niranjana D; Pant, Harish C; Nixon, Ralph A
2011 Nov;32(11):2016-2029, Neurobiology of aging
Cytoskeletal protein phosphorylation is frequently altered in neuropathologic states but little is known about changes during normal aging. Here we report that declining protein phosphatase activity, rather than activation of kinases, underlies aging-related neurofilament hyperphosphorylation. Purified PP2A or PP2B dephosphorylated the heavy neurofilament (NFH) subunit or its extensively phorphorylated carboxyl-terminal domain in vitro. In cultured primary hippocampal neurons, inhibiting either phosphatase induced NFH phosphorylation without activating known neurofilament kinases. Neurofilament phosphorylation in the mouse CNS, as reflected by levels of the RT-97 phosphoepitope associated with late axon maturation, more than doubled during the 12-month period after NFH expression plateaued at p21. This was accompanied by declines in levels and activity of PP2A but not PP2B, and no rise in activities of neurofilament kinases (Erk1,2, cdk5 and JNK1,2). Inhibiting PP2A in mice in vivo restored brain RT-97 to levels seen in young mice. Declining PP2A activity, therefore, can account for rising neurofilament phosphorylation in maturing brain, potentially compounding similar changes associated with adult-onset neurodegenerative diseases
— id: 138382, year: 2011, vol: 32, page: 2016, stat: Journal Article,

Therapeutic effects of remediating autophagy failure in a mouse model of Alzheimer disease by enhancing lysosomal proteolysis
Yang, Dun-Sheng; Stavrides, Philip; Mohan, Panaiyur S; Kaushik, Susmita; Kumar, Asok; Ohno, Masuo; Schmidt, Stephen D; Wesson, Daniel W; Bandyopadhyay, Urmi; Jiang, Ying; Pawlik, Monika; Peterhoff, Corrinne M; Yang, Austin J; Wilson, Donald A; St George-Hyslop, Peter; Westaway, David; Mathews, Paul M; Levy, Efrat; Cuervo, Ana M; Nixon, Ralph A
2011 Jul 1;7(7):788-789, Autophagy
The extensive autophagic-lysosomal pathology in Alzheimer disease (AD) brain has revealed a major defect: in the proteolytic clearance of autophagy substrates. Autophagy failure contributes on several levels to AD pathogenesis and has become an important therapeutic target for AD and other neurodegenerative diseases. We recently observed broad therapeutic effects of stimulating autophagic-lysosomal proteolysis in the TgCRND8 mouse model of AD that exhibits defective proteolytic clearance of autophagic substrates, robust intralysosomal amyloid-beta peptide (Abeta) accumulation, extracellular beta-amyloid deposition and cognitive deficits. By genetically deleting the lysosomal cysteine protease inhibitor, cystatin B (CstB), to selectively restore depressed cathepsin activities, we substantially cleared Abeta, ubiquitinated proteins and other autophagic substrates from autolysosomes/lysosomes and rescued autophagic-lysosomal pathology, as well as reduced total Abeta40/42 levels and extracellular amyloid deposition, highlighting the underappreciated importance of the lysosomal system for Abeta clearance. Most importantly, lysosomal remediation prevented the marked learning and memory deficits in TgCRND8 mice. Our findings underscore the pathogenic significance of autophagic-lysosomal dysfunction in AD and demonstrate the value of reversing this dysfunction as an innovative therapeautic strategy for AD
— id: 134440, year: 2011, vol: 7, page: 788, stat: Journal Article,

Reversal of autophagy dysfunction in the TgCRND8 mouse model of Alzheimer's disease ameliorates amyloid pathologies and memory deficits
Yang, Dun-Sheng; Stavrides, Philip; Mohan, Panaiyur S; Kaushik, Susmita; Kumar, Asok; Ohno, Masuo; Schmidt, Stephen D; Wesson, Daniel; Bandyopadhyay, Urmi; Jiang, Ying; Pawlik, Monika; Peterhoff, Corrinne M; Yang, Austin J; Wilson, Donald A; St George-Hyslop, Peter; Westaway, David; Mathews, Paul M; Levy, Efrat; Cuervo, Ana M; Nixon, Ralph A
2011 Jan;134(Pt 1):258-277, Brain
Autophagy, a major degradative pathway for proteins and organelles, is essential for survival of mature neurons. Extensive autophagic-lysosomal pathology in Alzheimer's disease brain contributes to Alzheimer's disease pathogenesis, although the underlying mechanisms are not well understood. Here, we identified and characterized marked intraneuronal amyloid-beta peptide/amyloid and lysosomal system pathology in the Alzheimer's disease mouse model TgCRND8 similar to that previously described in Alzheimer's disease brains. We further establish that the basis for these pathologies involves defective proteolytic clearance of neuronal autophagic substrates including amyloid-beta peptide. To establish the pathogenic significance of these abnormalities, we enhanced lysosomal cathepsin activities and rates of autophagic protein turnover in TgCRND8 mice by genetically deleting cystatin B, an endogenous inhibitor of lysosomal cysteine proteases. Cystatin B deletion rescued autophagic-lysosomal pathology, reduced abnormal accumulations of amyloid-beta peptide, ubiquitinated proteins and other autophagic substrates within autolysosomes/lysosomes and reduced intraneuronal amyloid-beta peptide. The amelioration of lysosomal function in TgCRND8 markedly decreased extracellular amyloid deposition and total brain amyloid-beta peptide 40 and 42 levels, and prevented the development of deficits of learning and memory in fear conditioning and olfactory habituation tests. Our findings support the pathogenic significance of autophagic-lysosomal dysfunction in Alzheimer's disease and indicate the potential value of restoring normal autophagy as an innovative therapeutic strategy for Alzheimer's disease
— id: 126481, year: 2011, vol: 134, page: 258, stat: Journal Article,

The contributions of myelin and axonal caliber to transverse relaxation time in shiverer and neurofilament-deficient mouse models
Dyakin, Victor V; Chen, Yuanxin; Branch, Craig A; Yuan, Aidong; Rao, Mala; Kumar, Asok; Peterhoff, Corrinne M; Nixon, Ralph A
2010 Jul 1;51(3):1098-1105, Neuroimage
White matter disorders can involve injury to myelin or axons but the respective contribution of each to clinical course is difficult to evaluate non-invasively. Here, to develop a paradigm for further investigations of axonal pathology by MRI, we compared two genetic mouse models exhibiting relatively selective axonal or myelin deficits using quantitative MRI relaxography of the transverse relaxation times (T2) in vivo and ultrastructural morphometry. In HM-DKO mice, which lack genes encoding the heavy (NF-H) and medium (NF-M) subunits of neurofilaments, neurofilament content of large myelinated axons of the central nervous system (CNS) is markedly reduced in the absence of changes in myelin thickness and volume. In shiverer mutant mice, which lack functional myelin basic protein, CNS myelin sheath formation is markedly reduced but neurofilament content is normal. We observed increases in T2 in nearly all white matter in shiverer mice compared to their wild type, while more subtle increases in T2 were observed in HM-DKO in the corpus callosum. White matter T2 was generally greater in shiverer mice than HM-DKO mice. Ultrastructural morphometry of the corpus callosum, which exhibited the greatest T2 differences, confirmed that total cross-sectional area occupied by axons was similar in the two mouse models and that the major ultrastructural differences, determined by morphometry, were an absence of myelin and larger unmyelinated axons in shiverer mice and absence of neurofilaments in HM-DKO mice. Our findings indicate that T2 is strongly influenced by myelination state and axonal volume, while neurofilament structure within the intra-axonal compartment has a lesser effect upon single compartment T2 estimates
— id: 126489, year: 2010, vol: 51, page: 1098, stat: Journal Article,

Microarray analysis of hippocampal CA1 neurons implicates early endosomal dysfunction during Alzheimer's disease progression
Ginsberg, Stephen D; Alldred, Melissa J; Counts, Scott E; Cataldo, Anne M; Neve, Rachael L; Jiang, Ying; Wuu, Joanne; Chao, Moses V; Mufson, Elliott J; Nixon, Ralph A; Che, Shaoli
2010 Nov 15;68(10):885-893, Biological psychiatry
BACKGROUND: Endocytic dysfunction and neurotrophin signaling deficits may underlie the selective vulnerability of hippocampal neurons during the progression of Alzheimer's disease (AD), although there is little direct in vivo and biochemical evidence to support this hypothesis. METHODS: Microarray analysis of hippocampal CA1 pyramidal neurons acquired via laser capture microdissection was performed using postmortem brain tissue. Validation was achieved using real-time quantitative polymerase chain reaction and immunoblot analysis. Mechanistic studies were performed using human fibroblasts subjected to overexpression with viral vectors or knockdown via small interference RNA. RESULTS: Expression levels of genes regulating early endosomes (rab5) and late endosomes (rab7) are selectively upregulated in homogeneous populations of CA1 neurons from individuals with mild cognitive impairment and AD. The levels of these genes are selectively increased as antemortem measures of cognition decline during AD progression. Hippocampal quantitative polymerase chain reaction and immunoblot analyses confirmed increased levels of these transcripts and their respective protein products. Elevation of select rab GTPases regulating endocytosis paralleled the downregulation of genes encoding the neurotrophin receptors TrkB and TrkC. Overexpression of rab5 in cells suppressed TrkB expression, whereas knockdown of TrkB expression did not alter rab5 levels, suggesting that TrkB downregulation is a consequence of endosomal dysfunction associated with elevated rab5 levels in early AD. CONCLUSIONS: These data support the hypothesis that neuronal endosomal dysfunction is associated with preclinical AD. Increased endocytic pathway activity, driven by elevated rab GTPase expression, may result in long-term deficits in hippocampal neurotrophic signaling and represent a key pathogenic mechanism underlying AD progression
— id: 114169, year: 2010, vol: 68, page: 885, stat: Journal Article,

Regional Selectivity of rab5 and rab7 Protein Upregulation in Mild Cognitive Impairment and Alzheimer's Disease
Ginsberg, Stephen D; Mufson, Elliott J; Counts, Scott E; Wuu, Joanne; Alldred, Melissa J; Nixon, Ralph A; Che, Shaoli
2010 ;22(2):631-639, Journal of Alzheimer's Disease
Endocytic alterations are one of the earliest changes to occur in Alzheimer's disease (AD), and are hypothesized to be involved in the selective vulnerability of specific neuronal populations during the progression of AD. Previous microarray and real-time quantitative PCR experiments revealed an upregulation of the early endosomal effector rab5 and the late endosome constituent rab7 in the hippocampus of people with mild cognitive impairment (MCI) and AD. To assess whether these select rab GTPase gene expression changes are reflected in protein levels within selectively vulnerable brain regions (basal forebrain, frontal cortex, and hippocampus) and relatively spared areas (cerebellum and striatum), we performed immunoblot analysis using antibodies directed against rab5 and rab7 on postmortem human brain tissue harvested from cases with a premortem clinical diagnosis of no cognitive impairment (NCI), MCI, and AD. Results indicate selective upregulation of both rab5 and rab7 levels within basal forebrain, frontal cortex, and hippocampus in MCI and AD, which also correlated with Braak staging. In contrast, no differences in protein levels were found in the less vulnerable cerebellum and striatum. These regional immunoblot assays are consistent with single cell gene expression data, and provide protein-based evidence for endosomal markers contributing to the vulnerability of cell types within selective brain regions during the progression of AD
— id: 114587, year: 2010, vol: 22, page: 631, stat: Journal Article,

Alzheimer's-related endosome dysfunction in Down syndrome is Abeta-independent but requires APP and is reversed by BACE-1 inhibition
Jiang, Ying; Mullaney, Kerry A; Peterhoff, Corrinne M; Che, Shaoli; Schmidt, Stephen D; Boyer-Boiteau, Anne; Ginsberg, Stephen D; Cataldo, Anne M; Mathews, Paul M; Nixon, Ralph A
2010 Jan 26;107(4):1630-1635, Proceedings of the National Academy of Sciences of the United States of America
An additional copy of the beta-amyloid precursor protein (APP) gene causes early-onset Alzheimer's disease (AD) in trisomy 21 (DS). Endosome dysfunction develops very early in DS and AD and has been implicated in the mechanism of neurodegeneration. Here, we show that morphological and functional endocytic abnormalities in fibroblasts from individuals with DS are reversed by lowering the expression of APP or beta-APP-cleaving enzyme 1 (BACE-1) using short hairpin RNA constructs. By contrast, endosomal pathology can be induced in normal disomic (2N) fibroblasts by overexpressing APP or the C-terminal APP fragment generated by BACE-1 (betaCTF), all of which elevate the levels of betaCTFs. Expression of a mutant form of APP that cannot undergo beta-cleavage had no effect on endosomes. Pharmacological inhibition of APP gamma-secretase, which markedly reduced Abeta production but raised betaCTF levels, also induced AD-like endosome dysfunction in 2N fibroblasts and worsened this pathology in DS fibroblasts. These findings strongly implicate APP and the betaCTF of APP, and exclude Abeta and the alphaCTF, as the cause of endocytic pathway dysfunction in DS and AD, underscoring the potential multifaceted value of BACE-1 inhibition in AD therapeutics
— id: 126490, year: 2010, vol: 107, page: 1630, stat: Journal Article,

Cystatin C rescues degenerating neurons in a cystatin B-knockout mouse model of progressive myoclonus epilepsy
Kaur, Gurjinder; Mohan, Panaiyur; Pawlik, Monika; DeRosa, Steven; Fajiculay, Jay; Che, Shaoli; Grubb, Anders; Ginsberg, Stephen D; Nixon, Ralph A; Levy, Efrat
2010 Nov;177(5):2256-2267, American journal of pathology
In vitro studies have shown that cystatin C (CysC) is neuroprotective. Here we demonstrate that CysC is neuroprotective in vivo, in a mouse model of the inherited neurodegenerative disorder, progressive myoclonic epilepsy type 1 (EPM1). Loss-of-function mutations in the cystatin B (CysB) gene, an intracellular cysteine protease inhibitor, lead to this human disease. A CysB-knockout (CysBKO) mouse model develops symptoms that mimic EPM1. CysB deficiency in these mice results in enhanced cathepsin B and D activities, indicating lysosomal dysfunction. We show that expression of CysC is enhanced in the brains of CysBKO mice. Crossbreeding of CysBKO mice with either CysC-overexpressing transgenic mice or CysC-knockout mice demonstrates that clinical symptoms and neuropathologies, including motor coordination disorder, cerebellar atrophy, neuronal loss in the cerebellum and cerebral cortex, and gliosis caused by CysB deficiency, are rescued by CysC overexpression and exacerbated by CysC deficiency. Thus, CysC effectively rescues the CysB loss-of-function mutations, facilitating the reversal of pathophysiological changes and suggesting a novel therapeutic intervention for patients with EPM1 and other neurodegenerative disorders
— id: 126484, year: 2010, vol: 177, page: 2256, stat: Journal Article,

Lysosomal proteolysis and autophagy require presenilin 1 and are disrupted by Alzheimer-related PS1 mutations
Lee, Ju-Hyun; Yu, W Haung; Kumar, Asok; Lee, Sooyeon; Mohan, Panaiyur S; Peterhoff, Corrinne M; Wolfe, Devin M; Martinez-Vicente, Marta; Massey, Ashish C; Sovak, Guy; Uchiyama, Yasuo; Westaway, David; Cuervo, Ana Maria; Nixon, Ralph A
2010 Jun 25;141(7):1146-1158, Cell
Macroautophagy is a lysosomal degradative pathway essential for neuron survival. Here, we show that macroautophagy requires the Alzheimer's disease (AD)-related protein presenilin-1 (PS1). In PS1 null blastocysts, neurons from mice hypomorphic for PS1 or conditionally depleted of PS1, substrate proteolysis and autophagosome clearance during macroautophagy are prevented as a result of a selective impairment of autolysosome acidification and cathepsin activation. These deficits are caused by failed PS1-dependent targeting of the v-ATPase V0a1 subunit to lysosomes. N-glycosylation of the V0a1 subunit, essential for its efficient ER-to-lysosome delivery, requires the selective binding of PS1 holoprotein to the unglycosylated subunit and the Sec61alpha/oligosaccharyltransferase complex. PS1 mutations causing early-onset AD produce a similar lysosomal/autophagy phenotype in fibroblasts from AD patients. PS1 is therefore essential for v-ATPase targeting to lysosomes, lysosome acidification, and proteolysis during autophagy. Defective lysosomal proteolysis represents a basis for pathogenic protein accumulations and neuronal cell death in AD and suggests previously unidentified therapeutic targets
— id: 126485, year: 2010, vol: 141, page: 1146, stat: Journal Article,

Proteomic identification of sorting nexin 6 as a negative regulator of BACE1-mediated APP processing
Okada, Hirokazu; Zhang, Wenzhu; Peterhoff, Corrinne; Hwang, Jeremy C; Nixon, Ralph A; Ryu, Sung H; Kim, Tae-Wan
2010 Aug;24(8):2783-2794, FASEB journal
The beta-site APP cleaving enzyme-1 (BACE1) mediates the first cleavage of the beta-amyloid precursor protein (APP) to yield the amyloid beta-peptide (Abeta), a key pathogenic agent in Alzheimer's disease (AD). Using a proteomic approach based on in-cell chemical cross-linking and tandem affinity purification (TAP), we herein identify sorting nexin 6 (SNX6) as a BACE1-associated protein. SNX6, a PX domain protein, is a putative component of retromer, a multiprotein cargo complex that mediates the retrograde trafficking of the cation-independent mannose-6-phosphate receptor (CI-MPR) and sortilin. RNA interference suppression of SNX6 increased BACE1-dependent secretion of soluble APP (sAPPbeta) and cell-associated fragments (C99), resulting in increased Abeta secretion. Furthermore, SNX6 reduction led to elevated steady-state BACE1 levels as well as increased retrograde transport of BACE1 in the endocytic pathway, suggesting that SNX6 modulates the retrograde trafficking and basal levels of BACE1, thereby regulating BACE1-mediated APP processing and Abeta biogenesis. Our study identifies a novel cellular pathway by which SNX6 negatively modulates BACE1-mediated cleavage of APP
— id: 126488, year: 2010, vol: 24, page: 2783, stat: Journal Article,

Amyloid-independent mechanisms in Alzheimer's disease pathogenesis
Pimplikar, Sanjay W; Nixon, Ralph A; Robakis, Nikolaos K; Shen, Jie; Tsai, Li-Huei
2010 Nov 10;30(45):14946-14954, Journal of neuroscience
Despite the progress of the past two decades, the cause of Alzheimer's disease (AD) and effective treatments against it remain elusive. The hypothesis that amyloid-beta (Abeta) peptides are the primary causative agents of AD retains significant support among researchers. Nonetheless, a growing body of evidence shows that Abeta peptides are unlikely to be the sole factor in AD etiology. Evidence that Abeta/amyloid-independent factors, including the actions of AD-related genes, also contribute significantly to AD pathogenesis was presented in a symposium at the 2010 Annual Meeting of the Society for Neuroscience. Here we summarize the studies showing how amyloid-independent mechanisms cause defective endo-lysosomal trafficking, altered intracellular signaling cascades, or impaired neurotransmitter release and contribute to synaptic dysfunction and/or neurodegeneration, leading to dementia in AD. A view of AD pathogenesis that encompasses both the amyloid-dependent and -independent mechanisms will help fill the gaps in our knowledge and reconcile the findings that cannot be explained solely by the amyloid hypothesis
— id: 126483, year: 2010, vol: 30, page: 14946, stat: Journal Article,

Ubiquilin functions in autophagy and is degraded by chaperone-mediated autophagy
Rothenberg, Cara; Srinivasan, Deepa; Mah, Leann; Kaushik, Susmita; Peterhoff, Corrine M; Ugolino, Janet; Fang, Shengyun; Cuervo, Ana Maria; Nixon, Ralph A; Monteiro, Mervyn J
2010 Aug 15;19(16):3219-3232, Human molecular genetics
Autophagy is the process by which organelles and portions of the cytoplasm are degraded in lysosomes. Several different forms of autophagy are known that are distinguishable chiefly by the mode in which cargo is delivered to the lysosome for degradation. Ubiquilin was recently reported to regulate macroautophagy, the form of autophagy in which cytosolic cargo is packaged in a double-membrane structure or autophagosome that fuses with lysosomes for degradation. We confirm here using different morphological and biochemical procedures that ubiquilin is present in autophagosomes in HeLa cells and in brain and liver tissue of mouse. Coimmunoprecipitation studies indicated that ubiquilin binds the autophagosome marker LC3 in a complex and that reduction of ubiquilin expression reduces autophagosome formation, which correlates with a reduction in maturation of LC3-I to the LC3-II form of the protein. We found that ubiquilin is degraded during both macroautophagy and during chaperone-mediated autophagy (CMA), the latter of which involves the active transport of proteins into lysosomes. We discuss the implication of this degradation in mediating cross-talk between macroautophagy and CMA. Finally, we demonstrate that ubiquilin protects cells against starvation-induced cell death propagated by overexpression of mutant Alzheimer's disease PS2N141I protein and green fluorescent protein (GFP)-huntingtin exon-1 fusion protein containing 74 polyglutamines
— id: 126486, year: 2010, vol: 19, page: 3219, stat: Journal Article,

Rapamycin induces autophagic flux in neurons
Rubinsztein, David C; Nixon, Ralph A
2010 Dec 7;107(49):E181-E181, Proceedings of the National Academy of Sciences of the United States of America
— id: 126482, year: 2010, vol: 107, page: E181, stat: Journal Article,

Induction of autophagy by cystatin C: a mechanism that protects murine primary cortical neurons and neuronal cell lines
Tizon, Belen; Sahoo, Susmita; Yu, Haung; Gauthier, Sebastien; Kumar, Asok R; Mohan, Panaiyur; Figliola, Matthew; Pawlik, Monika; Grubb, Anders; Uchiyama, Yasuo; Bandyopadhyay, Urmi; Cuervo, Ana Maria; Nixon, Ralph A; Levy, Efrat
2010 ;5(3):e9819-e9819, PLoS ONE
Cystatin C (CysC) expression in the brain is elevated in human patients with epilepsy, in animal models of neurodegenerative conditions, and in response to injury, but whether up-regulated CysC expression is a manifestation of neurodegeneration or a cellular repair response is not understood. This study demonstrates that human CysC is neuroprotective in cultures exposed to cytotoxic challenges, including nutritional-deprivation, colchicine, staurosporine, and oxidative stress. While CysC is a cysteine protease inhibitor, cathepsin B inhibition was not required for the neuroprotective action of CysC. Cells responded to CysC by inducing fully functional autophagy via the mTOR pathway, leading to enhanced proteolytic clearance of autophagy substrates by lysosomes. Neuroprotective effects of CysC were prevented by inhibiting autophagy with beclin 1 siRNA or 3-methyladenine. Our findings show that CysC plays a protective role under conditions of neuronal challenge by inducing autophagy via mTOR inhibition and are consistent with CysC being neuroprotective in neurodegenerative diseases. Thus, modulation of CysC expression has therapeutic implications for stroke, Alzheimer's disease, and other neurodegenerative disorders
— id: 109506, year: 2010, vol: 5, page: e9819, stat: Journal Article,

Olfactory dysfunction correlates with amyloid-beta burden in an Alzheimer's disease mouse model
Wesson, Daniel W; Levy, Efrat; Nixon, Ralph A; Wilson, Donald A
2010 Jan 13;30(2):505-514, Journal of neuroscience
Alzheimer's disease often results in impaired olfactory perceptual acuity-a potential biomarker of the disorder. However, the usefulness of olfactory screens to serve as informative indicators of Alzheimer's is precluded by a lack of knowledge regarding why the disease impacts olfaction. We addressed this question by assaying olfactory perception and amyloid-beta (Abeta) deposition throughout the olfactory system in mice that overexpress a mutated form of the human amyloid-beta precursor protein. Such mice displayed progressive olfactory deficits that mimic those observed clinically-some evident at 3 months of age. Also, at 3 months of age, we observed nonfibrillar Abeta deposition within the olfactory bulb-earlier than deposition within any other brain region. There was also a correlation between olfactory deficits and the spatial-temporal pattern of Abeta deposition. Therefore, nonfibrillar, versus fibrillar, Abeta-related mechanisms likely contribute to early olfactory perceptual loss in Alzheimer's disease. Furthermore, these results present the odor cross-habituation test as a powerful behavioral assay, which reflects Abeta deposition and thus may serve to monitor the efficacy of therapies aimed at reducing Abeta
— id: 126491, year: 2010, vol: 30, page: 505, stat: Journal Article,

Should olfactory dysfunction be used as a biomarker of Alzheimer's disease?
Wesson, Daniel W; Wilson, Donald A; Nixon, Ralph A
2010 May;10(5):633-635, Expert review of neurotherapeutics
— id: 126487, year: 2010, vol: 10, page: 633, stat: Journal Article,

Endocannabinoid system: emerging role from neurodevelopment to neurodegeneration
Basavarajappa, Balapal S; Nixon, Ralph A; Arancio, Ottavio
2009 Apr;9(4):448-462, Mini reviews in medicinal chemistry
The endocannabinoid system, including endogenous ligands ('endocannabinoids' ECs), their receptors, synthesizing and degrading enzymes, as well as transporter molecules, has been detected from the earliest stages of embryonic development and throughout pre- and postnatal development. ECs are bioactive lipids, which comprise amides, esters and ethers of long chain polyunsaturated fatty acids. Anandamide (N-arachidonoylethanolamine; AEA) and 2-arachidonoylglycerol (2-AG) are the best studied ECs, and act as agonists of cannabinoid receptors. Thus, AEA and 2-AG mimic several pharmacological effects of the exogenous cannabinoid delta9-tetrahydrocannabinol (Delta(9)-THC), the psychoactive principle of cannabis sativa preparations like hashish and marijuana. Recently, however, several lines of evidence have suggested that the EC system may play an important role in early neuronal development as well as a widespread role in neurodegeneration disorders. Many of the effects of cannabinoids and ECs are mediated by two G protein-coupled receptors (GPCRs), CB1 and CB2, although additional receptors may be implicated. Both CB1 and CB2 couple primarily to inhibitory G proteins and are subject to the same pharmacological influences as other GPCRs. This new system is briefly presented in this review, in order to put in a better perspective the role of the EC pathway from neurodevelopment to neurodegenerative disorders, like Alzheimer's disease, Parkinson's disease, Huntington's disease, and multiple sclerosis. In addition, the potential exploitation of antagonists of CB1 receptors, or of inhibitors of EC metabolism, as next-generation therapeutics is discussed
— id: 126495, year: 2009, vol: 9, page: 448, stat: Journal Article,

In vivo MRI identifies cholinergic circuitry deficits in a Down syndrome model
Chen, Yuanxin; Dyakin, Victor V; Branch, Craig A; Ardekani, Babak; Yang, Dunsheng; Guilfoyle, David N; Peterson, Jesse; Peterhoff, Corrinne; Ginsberg, Stephen D; Cataldo, Anne M; Nixon, Ralph A
2009 Sep;30(9):1453-1465, Neurobiology of aging
In vivo quantitative magnetic resonance imaging (MRI) was employed to detect brain pathology and map its distribution within control, disomic mice (2N) and in Ts65Dn and Ts1Cje trisomy mice with features of human Down syndrome (DS). In Ts65Dn, but not Ts1Cje mice, transverse proton spin-spin (T(2)) relaxation time was selectively reduced in the medial septal nucleus (MSN) and in brain regions that receive cholinergic innervation from the MSN, including the hippocampus, cingulate cortex, and retrosplenial cortex. Basal forebrain cholinergic neurons (BFCNs) in the MSN, identified by choline acetyltransferase (ChAT) and nerve growth factor receptors p75(NTR) and TrkA immunolabeling were reduced in Ts65Dn brains and in situ acetylcholinesterase (AChE) activity was depleted distally along projecting cholinergic fibers, and selectively on pre- and postsynaptic profiles in these target areas. T(2) effects were negligible in Ts1Cje mice that are diploid for App and lack BFCN neuropathology, consistent with the suspected relationship of this pathology to increased App dosage. These results establish the utility of quantitative MRI in vivo for identifying Alzheimer's disease-relevant cholinergic changes in animal models of DS and characterizing the selective vulnerability of cholinergic neuron subpopulations
— id: 86660, year: 2009, vol: 30, page: 1453, stat: Journal Article,

Age-dependent dysregulation of brain amyloid precursor protein in the Ts65Dn Down syndrome mouse model
Choi, Jennifer H K; Berger, Jason D; Mazzella, Matthew J; Morales-Corraliza, Jose; Cataldo, Anne M; Nixon, Ralph A; Ginsberg, Stephen D; Levy, Efrat; Mathews, Paul M
2009 Sep;110(6):1818-1827, Journal of neurochemistry
Individuals with Down syndrome develop beta-amyloid deposition characteristic of early-onset Alzheimer's disease (AD) in mid-life, presumably because of an extra copy of the chromosome 21-located amyloid precursor protein (App) gene. App mRNA and APP metabolite levels were assessed in the brains of Ts65Dn mice, a mouse model of Down syndrome, using quantitative PCR, western blot analysis, immunoprecipitation, and ELISAs. In spite of the additional App gene copy, App mRNA, APP holoprotein, and all APP metabolite levels in the brains of 4-month-old trisomic mice were not increased compared with the levels seen in diploid littermate controls. However starting at 10 months of age, brain APP levels were increased proportional to the App gene dosage imbalance reflecting increased App message levels in Ts65Dn mice. Similar to APP levels, soluble amino-terminal fragments of APP (sAPPalpha and sAPPbeta) were increased in Ts65Dn mice compared with diploid mice at 12 months but not at 4 months of age. Brain levels of both Abeta40 and Abeta42 were not increased in Ts65Dn mice compared with diploid mice at all ages examined. Therefore, multiple mechanisms contribute to the regulation towards diploid levels of APP metabolites in the Ts65Dn mouse brain
— id: 126493, year: 2009, vol: 110, page: 1818, stat: Journal Article,

Complexes of amyloid-beta and cystatin C in the human central nervous system
Mi, Weiqian; Jung, Sonia S; Yu, Haung; Schmidt, Stephen D; Nixon, Ralph A; Mathews, Paul M; Tagliavini, Fabrizio; Levy, Efrat
2009 ;18(2):273-280, Journal of Alzheimer's Disease
A role for cystatin C (CysC) in the pathogenesis of Alzheimer's disease (AD) has been suggested by the genetic linkage of a CysC gene (CST3) polymorphism with late-onset AD, the co-localization of CysC with amyloid-beta (Abeta) in AD brains, and binding of CysC to soluble Abeta in vitro and in mouse models of AD. This study investigates the binding between Abeta and CysC in the human central nervous system. While CysC binding to soluble Abeta was observed in AD patients and controls, a SDS-resistant CysC/Abeta complex was detected exclusively in brains of neuropathologically normal controls, but not in AD cases. The association of CysC with Abeta in brain from control individuals and in cerebrospinal fluid reveals an interaction of these two polypeptides in their soluble form. The association between Abeta and CysC prevented Abeta accumulation and fibrillogenesis in experimental systems, arguing that CysC plays a protective role in the pathogenesis of AD in humans and explains why decreases in CysC concentration caused by the CST3 polymorphism or by specific presenilin 2 mutations can lead to the development of the disease. Thus, enhancing CysC expression or modulating CysC binding to Abeta have important disease-modifying effects, suggesting a novel therapeutic intervention for AD
— id: 126494, year: 2009, vol: 18, page: 273, stat: Journal Article,

Olfactory Perceptual Correlates of b-Amyloid Plaque Burden in Alzheimer's Disease Mouse Models
Wesson, DW; Levy, E; Nixon, RA; Wilson, DA
2009 SEP ;34(7):A26-A27, Chemical Senses
— id: 101941, year: 2009, vol: 34, page: A26, stat: Journal Article,

Sniffing out a function for prion proteins
Wilson, Donald A; Nixon, Ralph A
2009 Jan;12(1):7-8, Nature neuroscience
— id: 94316, year: 2009, vol: 12, page: 7, stat: Journal Article,

Monitoring autophagy in Alzheimer's disease and related neurodegenerative diseases
Yang, Dun-Sheng; Lee, Ju-Hyun; Nixon, Ralph A
2009 ;453:111-144, Methods in enzymology
This chapter describes detailed methods to monitor autophagy in neurodegenerative disorders, especially in Alzheimer's disease. Strategies to assess the competence of autophagy-related mechanisms in disease states ideally incorporate analyses of human disease and control tissues, which may include brain, fibroblasts, or other peripheral cells, in addition to animal and cell models of the neurodegenerative disease pathology and pathobiology. Cross-validation of pathophysiological mechanisms in the diseased tissues is always critical. Because of the cellular heterogeneity of the brain and the differential vulnerability of the neural cells in a given disease state, analyses focus on regional comparisons of affected and unaffected regions or cell populations within a particular brain region and include ultrastructural, immunological, and cell and molecular biological approaches
— id: 96862, year: 2009, vol: 453, page: 111, stat: Journal Article,

Neurofilaments form a highly stable stationary cytoskeleton after reaching a critical level in axons
Yuan, Aidong; Sasaki, Takahiro; Rao, Mala V; Kumar, Asok; Kanumuri, Vivek; Dunlop, David S; Liem, Ronald K; Nixon, Ralph A
2009 Sep 9;29(36):11316-11329, Journal of neuroscience
The ultrastructural view of the axonal cytoskeleton as an extensively cross-linked network of neurofilaments (NFs) and other cytoskeletal polymers contrasts with the dynamic view suggested by axonal transport studies on cytoskeletal elements. Here we reconcile these perspectives by showing that neurons form a large NF network along axons which is unequivocally stationary, metabolically stable, and maintained by NFs and nonfilamentous subunit assemblies undergoing slow transport by intermittent rapid movements and pauses. In mouse primary cortical neurons transfected with EGFP-NFL, formation of this stationary NF network requires a critical level of NFs, which explains its absence in NF-poor developing neurons studied previously. Most NFs at proximal axon regions were in a stationary structure coexisting with a smaller pool of moving EGFP-NFL assemblies that were mainly nonfilamentous. Distally along the same axon, EGFP-labeled NFL was much less abundant, and we detected only short filaments moving bidirectionally by slow transport (rapid movements and pauses) as previously described. In living mice, >25% of radiolabeled newly synthesized NFs remained in optic axons after slowly transported NFs had exited. Retained NF remained fixed over several months in a nonuniform distribution and exhibited exceptionally slow turnover (t(1/2) >2.5 months), implying that, at steady state, >90% of NFs in mature optic axons comprise the stationary cytoskeleton and <10% are undergoing slow transport. These findings reconcile in vitro and in vivo axonal transport observations, showing that slowly transported NFs or subunit oligomers are precursors to a highly stable stationary cytoskeletal network that supports mature axons
— id: 126492, year: 2009, vol: 29, page: 11316, stat: Journal Article,

Dystrophic serotonergic axons in neurodegenerative diseases
Azmitia, Efrain C; Nixon, Ralph
2008 Jun 27;1217C:185-194, Brain research
Neurodegenerative diseases such as Parkinson's disease (PD), frontal lobe dementia (FLD) and diffuse Lewy-body dementia (DLBD) have diverse neuropathologic features. Here we report that serotonin fibers are dystrophic in the brains of individuals with these three diseases. In neuropathologically normal (control) brains (n=3), serotonin axons immunoreactive (IR) with antibodies against the serotonin transporter (5-HTT) protein were widely distributed in cortex (entorhinal and dorsolateral prefrontal), hippocampus and rostral brainstem. 5-HTT-IR fibers-of-passage appeared thick, smooth, and unbranched in medial forebrain bundle, medial lemniscus and cortex white matter. The terminal branches were fine, highly branched and varicose in substantia nigra, hippocampus and cortical gray matter. In the diseased brains, however, 5-HTT-IR fibers in the forebrain were reduced in number and were frequently bulbous, splayed, tightly clustered and enlarged. Morphometric analysis revealed significant differences in the size distribution of the 5-HTT-IR profiles in dorsolateral prefrontal area between neurodegenerative diseases and controls. Our observations provide direct morphologic evidence for degeneration of human serotonergic axons in the brains of patients with neurodegenerative diseases despite the limited size (n=3 slices for each region (3) from each brain (4), total slices was n=36) and the lack of extensive clinical characterization of the analyzed cohort. This is the first report of dystrophic 5-HTT-IR axons in postmortem human tissue
— id: 79132, year: 2008, vol: 1217C, page: 185, stat: Journal Article,

Autophagy induction and autophagosome clearance in neurons: relationship to autophagic pathology in Alzheimer's disease
Boland, Barry; Kumar, Asok; Lee, Sooyeon; Platt, Frances M; Wegiel, Jerzy; Yu, W Haung; Nixon, Ralph A
2008 Jul 2;28(27):6926-6937, Journal of neuroscience
Macroautophagy, a major pathway for organelle and protein turnover, has been implicated in the neurodegeneration of Alzheimer's disease (AD). The basis for the profuse accumulation of autophagic vacuoles (AVs) in affected neurons of the AD brain, however, is unknown. In this study, we show that constitutive macroautophagy in primary cortical neurons is highly efficient, because newly formed autophagosomes are rapidly cleared by fusion with lysosomes, accounting for their scarcity in the healthy brain. Even after macroautophagy is strongly induced by suppressing mTOR (mammalian target of rapamycin) kinase activity with rapamycin or nutrient deprivation, active cathepsin-positive autolysosomes rather than LC3-II-positive autophagosomes predominate, implying efficient autophagosome clearance in healthy neurons. In contrast, selectively impeding late steps in macroautophagy by inhibiting cathepsin-mediated proteolysis within autolysosomes with cysteine- and aspartyl-protease inhibitors caused a marked accumulation of electron-dense double-membrane-limited AVs, containing cathepsin D and incompletely degraded LC3-II in perikarya and neurites. Similar structures accumulated in large numbers when fusion of autophagosomes with lysosomes was slowed by disrupting their transport on microtubules with vinblastine. Finally, we find that the autophagic vacuoles accumulating after protease inhibition or prolonged vinblastine treatment strongly resembled AVs that collect in dystrophic neurites in the AD brain and in an AD mouse model. We conclude that macroautophagy is constitutively active and highly efficient in healthy neurons and that the autophagic pathology observed in AD most likely arises from impaired clearance of AVs rather than strong autophagy induction alone. Therapeutic modulation of autophagy in AD may, therefore, require targeting late steps in the autophagic pathway
— id: 96865, year: 2008, vol: 28, page: 6926, stat: Journal Article,

Down syndrome fibroblast model of Alzheimer-related endosome pathology: accelerated endocytosis promotes late endocytic defects
Cataldo, Anne M; Mathews, Paul M; Boiteau, Anne Boyer; Hassinger, Linda C; Peterhoff, Corrinne M; Jiang, Ying; Mullaney, Kerry; Neve, Rachael L; Gruenberg, Jean; Nixon, Ralph A
2008 Aug;173(2):370-384, American journal of pathology
Endocytic dysfunction is an early pathological change in Alzheimer's disease (AD) and Down's syndrome (DS). Using primary fibroblasts from DS individuals, we explored the interactions among endocytic compartments that are altered in AD and assessed their functional consequences in AD pathogenesis. We found that, like neurons in both AD and DS brains, DS fibroblasts exhibit increased endocytic uptake, fusion, and recycling, and trafficking of lysosomal hydrolases to rab5-positive early endosomes. Moreover, late endosomes identified using antibodies to rab7 and lysobisphosphatidic acid increased in number and appeared as enlarged, perinuclear vacuoles, resembling those in neurons of both AD and DS brains. In control fibroblasts, similar enlargement of rab5-, rab7-, and lysobisphosphatidic acid-positive endosomes was induced when endocytosis and endosomal fusion were increased by expression of either a rab5 or an active rab5 mutant, suggesting that persistent endocytic activation results in late endocytic dysfunction. Conversely, expression of a rab5 mutant that inhibits endocytic uptake reversed early and late endosomal abnormalities in DS fibroblasts. Our results indicate that DS fibroblasts recapitulate the neuronal endocytic dysfunction of AD and DS, suggesting that increased trafficking from early endosomes can account, in part, for downstream endocytic perturbations that occur in neurons in both AD and DS brains
— id: 95387, year: 2008, vol: 173, page: 370, stat: Journal Article,

Guidelines for the use and interpretation of assays for monitoring autophagy in higher eukaryotes
Klionsky, Daniel J; Abeliovich, Hagai; Agostinis, Patrizia; Agrawal, Devendra K; Aliev, Gjumrakch; Askew, David S; Baba, Misuzu; Baehrecke, Eric H; Bahr, Ben A; Ballabio, Andrea; Bamber, Bruce A; Bassham, Diane C; Bergamini, Ettore; Bi, Xiaoning; Biard-Piechaczyk, Martine; Blum, Janice S; Bredesen, Dale E; Brodsky, Jeffrey L; Brumell, John H; Brunk, Ulf T; Bursch, Wilfried; Camougrand, Nadine; Cebollero, Eduardo; Cecconi, Francesco; Chen, Yingyu; Chin, Lih-Shen; Choi, Augustine; Chu, Charleen T; Chung, Jongkyeong; Clarke, Peter G H; Clark, Robert S B; Clarke, Steven G; Clave, Corinne; Cleveland, John L; Codogno, Patrice; Colombo, Maria I; Coto-Montes, Ana; Cregg, James M; Cuervo, Ana Maria; Debnath, Jayanta; Demarchi, Francesca; Dennis, Patrick B; Dennis, Phillip A; Deretic, Vojo; Devenish, Rodney J; Di Sano, Federica; Dice, J Fred; Difiglia, Marian; Dinesh-Kumar, Savithramma; Distelhorst, Clark W; Djavaheri-Mergny, Mojgan; Dorsey, Frank C; Droge, Wulf; Dron, Michel; Dunn, William A Jr; Duszenko, Michael; Eissa, N Tony; Elazar, Zvulun; Esclatine, Audrey; Eskelinen, Eeva-Liisa; Fesus, Laszlo; Finley, Kim D; Fuentes, Jose M; Fueyo, Juan; Fujisaki, Kozo; Galliot, Brigitte; Gao, Fen-Biao; Gewirtz, David A; Gibson, Spencer B; Gohla, Antje; Goldberg, Alfred L; Gonzalez, Ramon; Gonzalez-Estevez, Cristina; Gorski, Sharon; Gottlieb, Roberta A; Haussinger, Dieter; He, You-Wen; Heidenreich, Kim; Hill, Joseph A; Hoyer-Hansen, Maria; Hu, Xun; Huang, Wei-Pang; Iwasaki, Akiko; Jaattela, Marja; Jackson, William T; Jiang, Xuejun; Jin, Shengkan; Johansen, Terje; Jung, Jae U; Kadowaki, Motoni; Kang, Chanhee; Kelekar, Ameeta; Kessel, David H; Kiel, Jan A K W; Kim, Hong Pyo; Kimchi, Adi; Kinsella, Timothy J; Kiselyov, Kirill; Kitamoto, Katsuhiko; Knecht, Erwin; Komatsu, Masaaki; Kominami, Eiki; Kondo, Seiji; Kovacs, Attila L; Kroemer, Guido; Kuan, Chia-Yi; Kumar, Rakesh; Kundu, Mondira; Landry, Jacques; Laporte, Marianne; Le, Weidong; Lei, Huan-Yao; Lenardo, Michael J; Levine, Beth; Lieberman, Andrew; Lim, Kah-Leong; Lin, Fu-Cheng; Liou, Willisa; Liu, Leroy F; Lopez-Berestein, Gabriel; Lopez-Otin, Carlos; Lu, Bo; Macleod, Kay F; Malorni, Walter; Martinet, Wim; Matsuoka, Ken; Mautner, Josef; Meijer, Alfred J; Melendez, Alicia; Michels, Paul; Miotto, Giovanni; Mistiaen, Wilhelm P; Mizushima, Noboru; Mograbi, Baharia; Monastyrska, Iryna; Moore, Michael N; Moreira, Paula I; Moriyasu, Yuji; Motyl, Tomasz; Munz, Christian; Murphy, Leon O; Naqvi, Naweed I; Neufeld, Thomas P; Nishino, Ichizo; Nixon, Ralph A; Noda, Takeshi; Nurnberg, Bernd; Ogawa, Michinaga; Oleinick, Nancy L; Olsen, Laura J; Ozpolat, Bulent; Paglin, Shoshana; Palmer, Glen E; Papassideri, Issidora; Parkes, Miles; Perlmutter, David H; Perry, George; Piacentini, Mauro; Pinkas-Kramarski, Ronit; Prescott, Mark; Proikas-Cezanne, Tassula; Raben, Nina; Rami, Abdelhaq; Reggiori, Fulvio; Rohrer, Barbel; Rubinsztein, David C; Ryan, Kevin M; Sadoshima, Junichi; Sakagami, Hiroshi; Sakai, Yasuyoshi; Sandri, Marco; Sasakawa, Chihiro; Sass, Miklos; Schneider, Claudio; Seglen, Per O; Seleverstov, Oleksandr; Settleman, Jeffrey; Shacka, John J; Shapiro, Irving M; Sibirny, Andrei; Silva-Zacarin, Elaine C M; Simon, Hans-Uwe; Simone, Cristiano; Simonsen, Anne; Smith, Mark A; Spanel-Borowski, Katharina; Srinivas, Vickram; Steeves, Meredith; Stenmark, Harald; Stromhaug, Per E; Subauste, Carlos S; Sugimoto, Seiichiro; Sulzer, David; Suzuki, Toshihiko; Swanson, Michele S; Tabas, Ira; Takeshita, Fumihiko; Talbot, Nicholas J; Talloczy, Zsolt; Tanaka, Keiji; Tanaka, Kozo; Tanida, Isei; Taylor, Graham S; Taylor, J Paul; Terman, Alexei; Tettamanti, Gianluca; Thompson, Craig B; Thumm, Michael; Tolkovsky, Aviva M; Tooze, Sharon A; Truant, Ray; Tumanovska, Lesya V; Uchiyama, Yasuo; Ueno, Takashi; Uzcategui, Nestor L; van der Klei, Ida; Vaquero, Eva C; Vellai, Tibor; Vogel, Michael W; Wang, Hong-Gang; Webster, Paul; Wiley, John W; Xi, Zhijun; Xiao, Gutian; Yahalom, Joachim; Yang, Jin-Ming; Yap, George; Yin, Xiao-Ming; Yoshimori, Tamotsu; Yu, Li; Yue, Zhenyu; Yuzaki, Michisuke; Zabirnyk, Olga; Zheng, Xiaoxiang; Zhu, Xiongwei; Deter, Russell L
2008 Feb 16;4(2):151-175, Autophagy
Research in autophagy continues to accelerate,(1) and as a result many new scientists are entering the field. Accordingly, it is important to establish a standard set of criteria for monitoring macroautophagy in different organisms. Recent reviews have described the range of assays that have been used for this purpose.(2,3) There are many useful and convenient methods that can be used to monitor macroautophagy in yeast, but relatively few in other model systems, and there is much confusion regarding acceptable methods to measure macroautophagy in higher eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers of autophagosomes versus those that measure flux through the autophagy pathway; thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from fully functional autophagy that includes delivery to, and degradation within, lysosomes (in most higher eukaryotes) or the vacuole (in plants and fungi). Here, we present a set of guidelines for the selection and interpretation of the methods that can be used by investigators who are attempting to examine macroautophagy and related processes, as well as by reviewers who need to provide realistic and reasonable critiques of papers that investigate these processes. This set of guidelines is not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to verify an autophagic response
— id: 96866, year: 2008, vol: 4, page: 151, stat: Journal Article,

Neurofilament tail phosphorylation: identity of the RT-97 phosphoepitope and regulation in neurons by cross-talk among proline-directed kinases
Lee, Ju-Hyun; Pareek, Tej K; Jaffee, Howard; Boland, Barry; Vinod, K Yaragudri; Amin, Niranjana; Kulkarni, Ashok B; Pant, Harish C; Nixon, Ralph A
2008 Oct;107(1):35-49, Journal of neurochemistry
As axons myelinate, establish a stable neurofilament network, and expand in caliber, neurofilament proteins are extensively phosphorylated along their C-terminal tails, which is recognized by the monoclonal antibody, RT-97. Here, we demonstrate in vivo that RT-97 immunoreactivity (IR) is generated by phosphorylation at KSPXK or KSPXXXK motifs and requires flanking lysines at specific positions. extracellular signal regulated kinase 1,2 (ERK1,2) and pERK1,2 levels increase in parallel with phosphorylation at the RT-97 epitope during early postnatal brain development. Purified ERK1,2 generated RT-97 on both KSP motifs on recombinant NF-H tail domain proteins, while cdk5 phosphorylated only KSPXK motifs. RT-97 epitope generation in primary hippocampal neurons was regulated by extensive cross-talk among ERK1,2, c-Jun N-terminal kinase 1,2 (JNK1,2) and cdk5. Inhibition of both ERK1,2 and JNK1,2 completely blocked RT-97 generation. Cdk5 influenced RT-97 generation indirectly by modulating JNK activation. In mice, cdk5 gene deletion did not significantly alter RT-97 IR or ERK1,2 and JNK activation. In mice lacking the cdk5 activator P35, the partial suppression of cdk5 activity increased RT-97 IR by activating ERK1,2. Thus, cdk5 influences RT-97 epitope generation partly by modulating ERKs and JNKs, which are the two principal kinases regulating neurofilament phosphorylation. The regulation of a single target by multiple protein kinases underscores the importance of monitoring other relevant kinases when the activity of a particular one is blocked
— id: 96864, year: 2008, vol: 107, page: 35, stat: Journal Article,

Neurodegenerative lysosomal disorders- a continuum from development to late age
Nixon, Ralph A; Yang, Dun-Sheng; Lee, Ju-Hyun
2008 Sep-Oct;4(5):590-599, Autophagy
Neuronal survival requires continuous lysosomal turnover of cellular constituents delivered by autophagy and endocytosis. Primary lysosomal dysfunction in inherited congenital 'lysosomal storage' disorders is well known to cause severe neurodegenerative phenotypes associated with accumulations of lysosomes and autophagic vacuoles (AVs). Recently, the number of inherited adult-onset neurodegenerative diseases caused by proteins that regulate protein sorting and degradation within the endocytic and autophagic pathways has grown considerably. In this Perspective, we classify a group of neurodegenerative diseases across the lifespan as disorders of lysosomal function, which feature extensive autophagic-endocytic-lysosomal neuropathology and may share mechanisms of neurodegeneration related to degradative failure and lysosomal destabilization. We highlight Alzheimer's disease as a disease within this group and discuss how each of the genes and other risk factors promoting this disease contribute to progressive lysosomal dysfunction and neuronal cell death
— id: 79133, year: 2008, vol: 4, page: 590, stat: Journal Article,

Anesthesia-induced hyperphosphorylation detaches 3-repeat tau from microtubules without affecting their stability in vivo
Planel, Emmanuel; Krishnamurthy, Pavan; Miyasaka, Tomohiro; Liu, Li; Herman, Mathieu; Kumar, Asok; Bretteville, Alexis; Figueroa, Helen Y; Yu, Wai Haung; Whittington, Robert A; Davies, Peter; Takashima, Akihiko; Nixon, Ralph A; Duff, Karen E
2008 Nov 26;28(48):12798-12807, Journal of neuroscience
In Alzheimer's disease, tau is hyperphosphorylated, which is thought to detach it from microtubules (MTs), induce MT destabilization, and promote aggregation. Using a previously described in vivo model, we investigated whether hyperphosphorylation impacts tau function in wild-type and transgenic mice. We found that after anesthesia-induced hypothermia, MT-free tau was hyperphosphorylated, which impaired its ability to bind MTs and promote MT assembly. MT-bound tau was more resistant to hyperphosphorylation compared with free tau and tau did not dissociate from MTs in wild-type mice. However, 3-repeat tau detached from MT in the transgenic mice. Surprisingly, dissociation of tau from MTs did not lead to overt depolymerization of tubulin, and there was no collapse, or disturbance of axonal MT networks. These results indicate that, in vivo, a subpopulation of tau bound to MTs does not easily dissociate under conditions that extensively phosphorylate tau. Tau remaining on the MTs under these conditions is sufficient to maintain MT network integrity
— id: 96863, year: 2008, vol: 28, page: 12798, stat: Journal Article,

Marked calpastatin (CAST) depletion in Alzheimer's disease accelerates cytoskeleton disruption and neurodegeneration: neuroprotection by CAST overexpression
Rao, Mala V; Mohan, Panaiyur S; Peterhoff, Corrinne M; Yang, Dun-Sheng; Schmidt, Stephen D; Stavrides, Philip H; Campbell, Jabbar; Chen, Yuanxin; Jiang, Ying; Paskevich, Peter A; Cataldo, Anne M; Haroutunian, Vahram; Nixon, Ralph A
2008 Nov 19;28(47):12241-12254, Journal of neuroscience
Increased activity of calpains is implicated in synaptic dysfunction and neurodegeneration in Alzheimer's disease (AD). The molecular mechanisms responsible for increased calpain activity in AD are not known. Here, we demonstrate that disease progression is propelled by a marked depletion of the endogenous calpain inhibitor, calpastatin (CAST), from AD neurons, which is mediated by caspase-1, caspase-3, and calpains. Initial CAST depletion focally along dendrites coincides topographically with calpain II and ERK 1/2 activation, tau cleavage by caspase-3, and tau and neurofilament hyperphosphorylation. These same changes, together with cytoskeletal proteolysis and neuronal cell death, accompany CAST depletion after intrahippocampal kainic acid administration to mice, and are substantially reduced in mice overexpressing human CAST. Moreover, CAST reduction by shRNA in neuronal cells causes calpain-mediated death at levels of calcium-induced injury that are sublethal to cells normally expressing CAST. Our results strongly support a novel hypothesis that CAST depletion by multiple abnormally activated proteases accelerates calpain dysregulation in AD leading to cytoskeleton disruption and neurodegeneration. CAST mimetics may, therefore, be neuroprotective in AD
— id: 94362, year: 2008, vol: 28, page: 12241, stat: Journal Article,

Inhibition of calpains improves memory and synaptic transmission in a mouse model of Alzheimer disease
Trinchese, Fabrizio; Fa', Mauro; Liu, Shumin; Zhang, Hong; Hidalgo, Ariel; Schmidt, Stephen D; Yamaguchi, Hisako; Yoshii, Narihiko; Mathews, Paul M; Nixon, Ralph A; Arancio, Ottavio
2008 Aug;118(8):2796-2807, Journal of clinical investigation
Calpains are calcium-dependent enzymes that determine the fate of proteins through regulated proteolytic activity. Calpains have been linked to the modulation of memory and are key to the pathogenesis of Alzheimer disease (AD). When abnormally activated, calpains can also initiate degradation of proteins essential for neuronal survival. Here we show that calpain inhibition through E64, a cysteine protease inhibitor, and the highly specific calpain inhibitor BDA-410 restored normal synaptic function both in hippocampal cultures and in hippocampal slices from the APP/PS1 mouse, an animal model of AD. Calpain inhibition also improved spatial-working memory and associative fear memory in APP/PS1 mice. These beneficial effects of the calpain inhibitors were associated with restoration of normal phosphorylation levels of the transcription factor CREB and involved redistribution of the synaptic protein synapsin I. Thus, calpain inhibition may prove useful in the alleviation of memory loss in AD
— id: 95386, year: 2008, vol: 118, page: 2796, stat: Journal Article,

Neuronal apoptosis and autophagy cross talk in aging PS/APP mice, a model of Alzheimer's disease
Yang, Dun-Sheng; Kumar, Asok; Stavrides, Philip; Peterson, Jesse; Peterhoff, Corrine M; Pawlik, Monika; Levy, Efrat; Cataldo, Anne M; Nixon, Ralph A
2008 Sep;173(3):665-681, American journal of pathology
Mechanisms of neuronal loss in Alzheimer's disease (AD) are poorly understood. Here we show that apoptosis is a major form of neuronal cell death in PS/APP mice modeling AD-like neurodegeneration. Pyknotic neurons in adult PS/APP mice exhibited apoptotic changes, including DNA fragmentation, caspase-3 activation, and caspase-cleaved alpha-spectrin generation, identical to developmental neuronal apoptosis in wild-type mice. Ultrastructural examination using immunogold cytochemistry confirmed that activated caspase-3-positive neurons also exhibited chromatin margination and condensation, chromatin balls, and nuclear membrane fragmentation. Numbers of apoptotic profiles in both cortex and hippocampus of PS/APP mice compared with age-matched controls were twofold to threefold higher at 6 months of age and eightfold higher at 21 to 26 months of age. Additional neurons undergoing dark cell degeneration exhibited none of these apoptotic features. Activated caspase-3 and caspase-3-cleaved spectrin were abundant in autophagic vacuoles, accumulating in dystrophic neurites of PS/APP mice similar to AD brains. Administration of the cysteine protease inhibitor, leupeptin, promoted accumulation of autophagic vacuoles containing activated caspase-3 in axons of PS/APP mice and, to a lesser extent, in those of wild-type mice, implying that this pro-apoptotic factor is degraded by autophagy. Leupeptin-induced autophagic impairment increased the number of apoptotic neurons in PS/APP mice. Our findings establish apoptosis as a mode of neuronal cell death in aging PS/APP mice and identify the cross talk between autophagy and apoptosis, which influences neuronal survival in AD-related neurodegeneration
— id: 86556, year: 2008, vol: 173, page: 665, stat: Journal Article,

Axonal transport rates in vivo are unaffected by tau deletion or overexpression in mice
Yuan, Aidong; Kumar, Asok; Peterhoff, Corrinne; Duff, Karen; Nixon, Ralph A
2008 Feb 13;28(7):1682-1687, Journal of neuroscience
Elevated tau expression has been proposed as a possible basis for impaired axonal transport in Alzheimer's disease. To address this hypothesis, we analyzed the movement of pulse radiolabeled proteins in vivo along retinal ganglion cell (RGC) axons of mice that lack tau or overexpress human tau isoforms. Here, we show that the global axonal transport rates of slow and fast transport cargoes in axons are not significantly impaired when tau expression is eliminated or increased. In addition, markers of slow transport (neurofilament light subunit) and fast transport (snap25) do not accumulate in retinas and are distributed normally along optic axons in mice that lack or overexpress tau. Finally, ultrastructural analyses revealed no abnormal accumulations of vesicular organelles or neurofilaments in RGC perikarya or axons in mice overexpressing or lacking tau. These results suggest that tau is not essential for axonal transport and that transport rates in vivo are not significantly affected by substantial fluctuations in tau expression
— id: 94106, year: 2008, vol: 28, page: 1682, stat: Journal Article,

Cortical plasticity in Alzheimer's disease in humans and rodents
Battaglia, Fortunato; Wang, Hoau-Yan; Ghilardi, M Felice; Gashi, Eleonora; Quartarone, Angelo; Friedman, Eitan; Nixon, Ralph A
2007 Dec 15;62(12):1405-1412, Biological psychiatry
BACKGROUND: The aim of this study was to determine whether neocortical long-term potentiation (LTP) is deficient in patients with Alzheimer's disease (AD) and in amyloid precursor protein (APP)/presenilin-1 (PS1) mice, an AD animal model. We then ascertained whether this deficit might be paralleled by functional abnormalities of N-methyl-D-aspartate (NMDAR) glutamate receptors. METHODS: We studied neocortical LTP-like plasticity in 10 patients with mild-to-moderate AD and 10 age-matched normal controls using paired associative stimulation (PAS). We assessed neocortical (medial prefrontal cortex and primary motor cortex) and hippocampal LTP in brain slices of symptomatic APP/PS1 mice. NMDAR composition and signaling as well as synaptic calcium influx were determined in motor, prefrontal and hippocampal cortices of APP/PS1 mice. RESULTS: Both AD patients and transgenic animals showed a deficit in NMDAR-dependent forms of neocortical plasticity. Biochemical analysis showed impaired NMDAR function in symptomatic APP/PS1 mice. CONCLUSIONS: Neocortical plasticity is impaired in both patients with AD and APP/PS1 mice. The results of our biochemical studies point to impaired NMDAR function as the most likely cause for the neocortical plasticity deficit in AD
— id: 96868, year: 2007, vol: 62, page: 1405, stat: Journal Article,

Quantitative MRI reveals aging-associated T2 changes in mouse models of Alzheimer's disease
Falangola, M F; Dyakin, V V; Lee, S P; Bogart, A; Babb, J S; Duff, K; Nixon, R; Helpern, J A
2007 May;20(3):343-351, NMR in biomedicine
In this study, we used MRI to analyze quantitative parametric maps of transverse (T(2)) relaxation times in a longitudinal study of transgenic mice expressing mutant forms of amyloid precursor protein (APP), presenilin (PS1), or both (PS/APP), modeling aspects of Alzheimer's disease (AD). The main goal was to characterize the effects of progressive beta-amyloid accumulation and deposition on the biophysical environment of water and to investigate if these measurements would provide early indirect evidence of AD pathological changes in the brains of these mice. Our results demonstrate that at an early age before beta-amyloid deposition, only PS/APP mice show a reduced T(2) in the hippocampus and cortex compared with wild-type non-transgenic (NTg) controls, whereas a statistically significant within-group aging-associated decrease in T(2) values is seen in the cortex and hippocampus of all three transgenic genotypes (APP, PS/APP, and PS) but not in the NTg controls. In addition, for animals older than 12 months, we confirmed our previous report that only the two genotypes that form amyloid plaques (APP and PS/APP) have significantly reduced T(2) values compared with NTg controls. Thus, T(2) changes in these AD models can precede amyloid deposition or even occur in AD models that do not deposit beta-amyloid (PS mice), but are intensified in the presence of amyloid deposition
— id: 91355, year: 2007, vol: 20, page: 343, stat: Journal Article,

Alzheimer's presenilin 1 modulates sorting of APP and its carboxyl-terminal fragments in cerebral neurons in vivo (vol 102, pg 619, 2007)
Gandy, S; Zhang, YW; Ikin, A; Schmidt, SD; Bogush, A; Levy, E; Sheffield, R; Nixon, RA; Liao, FF; Mathews, PM; Xu, HX; Ehrlich, ME
2007 NOV ;103(3):1272-1272, Journal of neurochemistry
— id: 74687, year: 2007, vol: 103, page: 1272, stat: Journal Article,

Alzheimer's presenilin 1 modulates sorting of APP and its carboxyl-terminal fragments in cerebral neurons in vivo
Gandy, Sam; Zhang, Yun-wu; Ikin, Annat; Schmidt, Stephen D; Bogush, Alexey; Levy, Efrat; Sheffield, Roxanne; Nixon, Ralph A; Liao, Francesca-Fang; Mathews, Paul M; Xu, Huaxi; Ehrlich, Michelle E
2007 Aug;102(3):619-626, Journal of neurochemistry
Studies in continuously cultured cells have established that familial Alzheimer's disease (FAD) mutant presenilin 1 (PS1) delays exit of the amyloid precursor protein (APP) from the trans-Golgi network (TGN). Here we report the first description of PS1-regulated APP trafficking in cerebral neurons in culture and in vivo. Using neurons from transgenic mice or a cell-free APP transport vesicle biogenesis system derived from the TGN of those neurons, we demonstrated that knocking-in an FAD-associated mutant PS1 transgene was associated with delayed kinetics of APP arrival at the cell surface. Apparently, this delay was at least partially attributable to impaired exit of APP from the TGN, which was documented in the cell-free APP transport vesicle biogenesis assay. To extend the study to APP and carboxyl terminal fragment (CTF) trafficking to cerebral neurons in vivo, we performed subcellular fractionation of brains from APP transgenic mice, some of which carried a second transgene encoding an FAD-associated mutant form of PS1. The presence of the FAD mutant PS1 was associated with a slight shift in the subcellular localization of both holoAPP and APP CTFs toward iodixanol density gradient fractions that were enriched in a marker for the TGN. In a parallel set of experiments, we used an APP : furin chimeric protein strategy to test the effect of artificially forcing TGN concentration of an APP : furin chimera that could be a substrate for beta- and gamma-cleavage. This chimeric substrate generated excess Abeta42 when compared with wildtype APP. These data indicate that the presence of an FAD-associated mutant human PS1 transgene is associated with redistribution of the APP and APP CTFs in brain neurons toward TGN-enriched fractions. The chimera experiment suggests that TGN-enrichment of a beta-/gamma-secretase substrate may play an integral role in the action of mutant PS1 to elevate brain levels of Abeta42
— id: 95391, year: 2007, vol: 102, page: 619, stat: Journal Article,

Cystatin C inhibits amyloid-beta deposition in Alzheimer's disease mouse models
Mi, Weiqian; Pawlik, Monika; Sastre, Magdalena; Jung, Sonia S; Radvinsky, David S; Klein, Andrew M; Sommer, John; Schmidt, Stephen D; Nixon, Ralph A; Mathews, Paul M; Levy, Efrat
2007 Dec;39(12):1440-1442, Nature genetics
Using transgenic mice expressing human cystatin C (encoded by CST3), we show that cystatin C binds soluble amyloid-beta peptide and inhibits cerebral amyloid deposition in amyloid-beta precursor protein (APP) transgenic mice. Cystatin C expression twice that of the endogenous mouse cystatin C was sufficient to substantially diminish amyloid-beta deposition. Thus, cystatin C has a protective role in Alzheimer's disease pathogenesis, and modulation of cystatin C concentrations may have therapeutic implications for the disease
— id: 95389, year: 2007, vol: 39, page: 1440, stat: Journal Article,

Autophagy, amyloidogenesis and Alzheimer disease
Nixon, Ralph A
2007 Dec 1;120(Pt 23):4081-4091, Journal of cell science
Autophagy is the sole pathway for organelle turnover in cells and is a vital pathway for degrading normal and aggregated proteins, particularly under stress or injury conditions. Recent evidence has shown that the amyloid beta peptide is generated from amyloid beta precursor protein (APP) during autophagic turnover of APP-rich organelles supplied by both autophagy and endocytosis. Abeta generated during normal autophagy is subsequently degraded by lysosomes. Within neurons, autophagosomes and endosomes actively form in synapses and along neuritic processes but efficient clearance of these compartments requires their retrograde transport towards the neuronal cell body, where lysosomes are most concentrated. In Alzheimer disease, the maturation of autophagolysosomes and their retrograde transport are impeded, which leads to a massive accumulation of ;autophagy intermediates' (autophagic vacuoles) within large swellings along dystrophic and degenerating neurites. The combination of increased autophagy induction and defective clearance of Abeta-generating autophagic vacuoles creates conditions favorable for Abeta accumulation in Alzheimer disease
— id: 96867, year: 2007, vol: 120, page: 4081, stat: Journal Article,

Neuronal macroautophagy: from development to degeneration
Boland, Barry; Nixon, Ralph A
2006 Oct-Dec;27(5-6):503-519, Molecular aspects of medicine
Macroautophagy, a lysosomal pathway responsible for the turnover of organelles and long-lived proteins, has been regarded mainly as an inducible process in neurons, which is mobilized in states of stress and injury. New studies show, however, that macroautophagy is also constitutively active in healthy neurons and is vital to cell survival. Neurons in the brain, unlike cells in the periphery, are protected from large-scale autophagy induction because they can use several different energy sources optimally, receive additional nutrients and neurotrophin support from glial cells, and benefit from hypothalamic regulation of peripheral nutrient supplies. Due to its exceptional efficiency, constitutive autophagy in healthy neurons proceeds in the absence of easily detectable autophagic vacuole intermediates. These intermediates can accumulate rapidly, however, when late steps in the autophagic process are blocked. Autophagic vacuoles also accumulate abnormally in affected neurons of several major neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease, where they have been linked to various aspects of disease pathogenesis including neuronal cell death. The build-up of autophagic vacuoles in these neurological disorders and others may reflect either heightened autophagy induction, impairment in later digestive steps in the autophagy pathway, or both. Determining the basis for AV accumulation is critical for understanding the pathogenic significance of autophagy in a given pathologic state and for designing possible therapies based on modulating autophagy. In this review, we discuss the special features of autophagy regulation in the brain, its suspected roles in neurodevelopment and plasticity, and recent progress toward understanding how dysfunctional autophagy contributes to neurodegenerative disease.
— id: 72833, year: 2006, vol: 27, page: 503, stat: Journal Article,

Potential compensatory responses through autophagic/lysosomal pathways in neurodegenerative diseases
Butler, David; Nixon, Ralph A; Bahr, Ben A
2006 Jul-Sep;2(3):234-237, Autophagy
Intracellular protein degradation decreases with age, altering the important balance between protein synthesis and breakdown. Slowly, protein accumulation events increase causing axonopathy, synaptic deterioration, and subsequent cell death. As toxic species accumulate, autophagy-lysosomal protein degradation pathways are activated. Responses include autophagic vacuoles that degrade damaged cellular components and long-lived proteins, as well as enhanced levels of lysosomal hydrolases. Although such changes correlate with neuronal atrophy in age-related neurodegenerative disorders and in related models of protein accumulation, the autophagic/lysosomal responses appear to be compensatory reactions. Recent studies indicate that protein oligomerization/ aggregation induces autophagy and activates lysosomal protein degradation in an attempt to clear toxic accumulations. Such compensatory responses may delay cell death and account for the gradual nature of protein deposition pathology that can extend over months/years in model systems and years/decades in the human diseases. Correspondingly, enhancement of compensatory pathways shifts the balance from pathogenesis to protection. Positive modulation of protein degradation processes represents a strategy to promote clearance of toxic accumulations and to slow the synaptopathogenesis and associated cognitive decline in aging-related dementias.
— id: 72830, year: 2006, vol: 2, page: 234, stat: Journal Article,

Characterization of erasin (UBXD2): a new ER protein that promotes ER-associated protein degradation
Liang, Jing; Yin, Chaobo; Doong, Howard; Fang, Shengyun; Peterhoff, Corrine; Nixon, Ralph A; Monteiro, Mervyn J
2006 Oct 1;119(Pt 19):4011-4024, Journal of cell science
Ubiquitin regulator-X (UBX) is a discrete protein domain that binds p97/valosin-containing protein (VCP), a molecular chaperone involved in diverse cell processes, including endoplasmic-reticulum-associated protein degradation (ERAD). Here we characterize a human UBX-containing protein, UBXD2, that is highly conserved in mammals, which we have renamed erasin. Biochemical fractionation, immunofluorescence and electron microscopy, and protease protection experiments suggest that erasin is an integral membrane protein of the endoplasmic reticulum and nuclear envelope with both its N- and C-termini facing the cytoplasm or nucleoplasm. Localization of GFP-tagged deletion derivatives of erasin in HeLa cells revealed that a single 21-amino-acid sequence located near the C-terminus is necessary and sufficient for localization of erasin to the endoplasmic reticulum. Immunoprecipitation and GST-pulldown experiments confirmed that erasin binds p97/VCP via its UBX domain. Additional immunoprecipitation assays indicated that erasin exists in a complex with other p97/VCP-associated factors involved in ERAD. Overexpression of erasin enhanced the degradation of the ERAD substrate CD3delta, whereas siRNA-mediated reduction of erasin expression almost completely blocked ERAD. Erasin protein levels were increased by endoplasmic reticulum stress. Immunohistochemical staining of brain tissue from patients with Alzheimer's disease and control subjects revealed that erasin accumulates preferentially in neurons undergoing neurofibrillary degeneration in Alzheimer's disease. These results suggest that erasin may be involved in ERAD and in Alzheimer's disease.
— id: 72831, year: 2006, vol: 119, page: 4011, stat: Journal Article,

Autophagy in neurodegenerative disease: friend, foe or turncoat?
Nixon, Ralph A
2006 Sep;29(9):528-535, Trends in neurosciences
Autophagy, a lysosomal pathway for degrading organelles and long-lived proteins, is becoming recognized as a key adaptive response that can preclude death in stressed or diseased cells. However, during development strong induction of autophagy in specific cell populations mediates a type of programmed cell death that has distinctive 'autophagic' morphology and a requirement for autophagy activity. The recent identification of autophagosomes in neurons in a growing number of neurodegenerative disorders has, therefore, sparked controversy about whether these structures are contributing to neuronal cell death or protecting against it. Emerging evidence supports the view that induction of autophagy is a neuroprotective response and that inadequate or defective autophagy, rather than excessive autophagy, promotes neuronal cell death in most of these disorders. In this review, we consider possible mechanisms underlying autophagy-associated cell death and their relationship to pathways mediating apoptosis and necrosis.
— id: 72829, year: 2006, vol: 29, page: 528, stat: Journal Article,

Lysosomal system pathways: genes to neurodegeneration in Alzheimer's disease
Nixon, Ralph A; Cataldo, Anne M
2006 ;9(3 Suppl):277-289, Journal of Alzheimer's Disease
The identification of cathepsins in amyloid-beta plaques revealed broad dysfunction of the lysosomal system in Alzheimer's disease (AD). Coinciding with the discovery that proteolysis is required to generate the Abeta-peptide, these findings heralded an era of intense investigation on proteases in neurodegeneration. This review traces lysosomal system pathology from its early characterization to its origins within two pathways leading to the lysosome, the endocytic and autophagic pathways. An understanding has grown about how these two pathways are adversely influenced by normal brain aging and by genetic and environmental risk factors for AD, resulting in increased susceptibility of neurons to injury, amyloidogenesis, and neurodegeneration
— id: 126496, year: 2006, vol: 9, page: 277, stat: Journal Article,

Increased App expression in a mouse model of Down's syndrome disrupts NGF transport and causes cholinergic neuron degeneration
Salehi, Ahmad; Delcroix, Jean-Dominique; Belichenko, Pavel V; Zhan, Ke; Wu, Chengbiao; Valletta, Janice S; Takimoto-Kimura, Ryoko; Kleschevnikov, Alexander M; Sambamurti, Kumar; Chung, Peter P; Xia, Weiming; Villar, Angela; Campbell, William A; Kulnane, Laura Shapiro; Nixon, Ralph A; Lamb, Bruce T; Epstein, Charles J; Stokin, Gorazd B; Goldstein, Lawrence S B; Mobley, William C
2006 Jul 6;51(1):29-42, Neuron
Degeneration of basal forebrain cholinergic neurons (BFCNs) contributes to cognitive dysfunction in Alzheimer's disease (AD) and Down's syndrome (DS). We used Ts65Dn and Ts1Cje mouse models of DS to show that the increased dose of the amyloid precursor protein gene, App, acts to markedly decrease NGF retrograde transport and cause degeneration of BFCNs. NGF transport was also decreased in mice expressing wild-type human APP or a familial AD-linked mutant APP; while significant, the decreases were less marked and there was no evident degeneration of BFCNs. Because of evidence suggesting that the NGF transport defect was intra-axonal, we explored within cholinergic axons the status of early endosomes (EEs). NGF-containing EEs were enlarged in Ts65Dn mice and their App content was increased. Our study thus provides evidence for a pathogenic mechanism for DS in which increased expression of App, in the context of trisomy, causes abnormal transport of NGF and cholinergic neurodegeneration.
— id: 72832, year: 2006, vol: 51, page: 29, stat: Journal Article,

Deleting the phosphorylated tail domain of the neurofilament heavy subunit does not alter neurofilament transport rate in vivo
Yuan, Aidong; Nixon, Ralph A; Rao, Mala V
2006 Jan 30;393(2-3):264-268, Neuroscience letters
Phosphorylation of the carboxyl tail domains of the neurofilament heavy (NF-H) and middle molecular weight (NF-M) subunits has been proposed to regulate the axonal transport of neurofilaments. To test this hypothesis, we recently constructed mice lacking the extensively phosphorylated NF-H tail domain (NF-HtailDelta) and showed that the transport rate of neurofilaments in optic axons is unaltered in the absence of this domain [M.V. Rao, M.L. Garcia, Y. Miyazaki, T. Gotow, A. Yuan, S. Mattina, C.M. Ward, N.A. Calcutt, Y. Uchiyama, R.A. Nixon, D.W. Cleveland, Gene replacement in mice reveals that the heavily phosphorylated tail of neurofilament heavy subunit does not affect axonal caliber or the transit of cargoes in slow axonal transport, J. Cell Biol. 158 (2002) 681-693]. However, Shea et al. proposed that deletion of NF-H carboxyl-terminal region accelerates the transport of a subpopulation of neurofilaments based on minor differences between tail-deleted and control mice in our axonal transport analysis. Here, we present additional evidence that neurofilament transport rate is unchanged after deleting the phosphorylated NF-H tail domain, establishing unequivocally that the NF-H tail domain alone does not regulate the rate of neurofilament transport in optic axons in vivo. Possible roles for tail domains as cross-bridges between a neurofilament and its neighbors or other cytoskeletal elements is discussed
— id: 60252, year: 2006, vol: 393, page: 264, stat: Journal Article,

Alpha-internexin is structurally and functionally associated with the neurofilament triplet proteins in the mature CNS
Yuan, Aidong; Rao, Mala V; Sasaki, Takahiro; Chen, Yuanxin; Kumar, Asok; Liem, Ronald K H; Eyer, Joel; Peterson, Alan C; Julien, Jean-Pierre; Nixon, Ralph A
2006 Sep 27;26(39):10006-10019, Journal of neuroscience
Alpha-internexin, a neuronal intermediate filament protein implicated in neurodegenerative disease, coexists with the neurofilament (NF) triplet proteins (NF-L, NF-M, and NF-H) but has an unknown function. The earlier peak expression of alpha-internexin than the triplet during brain development and its ability to form homopolymers, unlike the triplet, which are obligate heteropolymers, have supported a widely held view that alpha-internexin and neurofilament triplet form separate filament systems. Here, we demonstrate, however, that despite a postnatal decline in expression, alpha-internexin is as abundant as the triplet in the adult CNS and exists in a relatively fixed stoichiometry with these subunits. Alpha-internexin exhibits transport and turnover rates identical to those of triplet proteins in optic axons and colocalizes with NF-M on single neurofilaments by immunogold electron microscopy. Alpha-internexin also coassembles with all three neurofilament proteins into a single network of filaments in quadruple-transfected SW13vim(-) cells. Genetically deleting NF-M alone or together with NF-H in mice dramatically reduces alpha-internexin transport and content in axons throughout the CNS. Moreover, deleting alpha-internexin potentiates the effects of NF-M deletion on NF-H and NF-L transport. Finally, overexpressing a NF-H-LacZ fusion protein in mice induces alpha-internexin and neurofilament triplet to aggregate in neuronal perikarya and greatly reduces their transport and content selectively in axons. Our data show that alpha-internexin and the neurofilament proteins are functionally interdependent. The results strongly support the view that alpha-internexin is a fourth subunit of neurofilaments in the adult CNS, providing a basis for its close relationship with neurofilaments in CNS diseases associated with neurofilament accumulation
— id: 94108, year: 2006, vol: 26, page: 10006, stat: Journal Article,

Medical bioremediation: prospects for the application of microbial catabolic diversity to aging and several major age-related diseases
de Grey, Aubrey D N J; Alvarez, Pedro J J; Brady, Roscoe O; Cuervo, Ana Maria; Jerome, W Gray; McCarty, Perry L; Nixon, Ralph A; Rittmann, Bruce E; Sparrow, Janet R
2005 Aug;4(3):315-338, Ageing research reviews
Several major diseases of old age, including atherosclerosis, macular degeneration and neurodegenerative diseases are associated with the intracellular accumulation of substances that impair cellular function and viability. Moreover, the accumulation of lipofuscin, a substance that may have similarly deleterious effects, is one of the most universal markers of aging in postmitotic cells. Reversing this accumulation may thus be valuable, but has proven challenging, doubtless because substances resistant to cellular catabolism are inherently hard to degrade. We suggest a radically new approach: augmenting humans' natural catabolic machinery with microbial enzymes. Many recalcitrant organic molecules are naturally degraded in the soil. Since the soil in certain environments - graveyards, for example - is enriched in human remains but does not accumulate these substances, it presumably harbours microbes that degrade them. The enzymes responsible could be identified and engineered to metabolise these substances in vivo. Here, we survey a range of such substances, their putative roles in age-related diseases and the possible benefits of their removal. We discuss how microbes capable of degrading them can be isolated, characterised and their relevant enzymes engineered for this purpose and ways to avoid potential side-effects.
— id: 72834, year: 2005, vol: 4, page: 315, stat: Journal Article,

Application of a non-linear image registration algorithm to quantitative analysis of T2 relaxation time in transgenic mouse models of AD pathology
Falangola, M F; Ardekani, B A; Lee, S-P; Babb, J S; Bogart, A; Dyakin, V V; Nixon, R; Duff, K; Helpern, J A
2005 May 15;144(1):91-97, Journal of neuroscience methods
Transgenic mouse models have been essential for understanding the pathogenesis of Alzheimer's disease (AD) including those that model the deposition process of beta-amyloid (Abeta). Several laboratories have focused on research related to the non-invasive detection of early changes in brains of transgenic mouse models of Alzheimer's pathology. Most of this work has been performed using regional image analysis of individual mouse brains and pooling the results for statistical assessment. Here we report the implementation of a non-linear image registration algorithm to register anatomical and transverse relaxation time (T2) maps estimated from MR images of transgenic mice. The algorithm successfully registered mouse brain magnetic resonance imaging (MRI) volumes and T2 maps, allowing reliable estimates of T2 values for different regions of interest from the resultant combined images. This approach significantly reduced the data processing and analysis time, and improved the ability to statistically discriminate between groups. Additionally, 3D visualization of intra-regional distributions of T2 of the resultant registered images provided the ability to detect small changes between groups that otherwise would not be possible to detect
— id: 56353, year: 2005, vol: 144, page: 91, stat: Journal Article,

Histological co-localization of iron in Abeta plaques of PS/APP transgenic mice
Falangola, Maria F; Lee, Sang-Pil; Nixon, Ralph A; Duff, Karen; Helpern, Joseph A
2005 Feb;30(2):201-205, Neurochemical research
This study confirms the presence of iron, co-localized with Abeta plaques, in PS/APP mouse brain, using Perls' stain for Fe3+ supplemented by 3,3'-diaminobenzidine (DAB) and Abeta immunohistochemistry in histological brains sections fixed with formalin or methacarn. In this study, the fixation process and the slice thickness did not interfere with the Perls' technique. The presence of iron in beta-amyloid plaques in PS/APP transgenic mice, a model of Alzheimer's disease (AD) pathology, may explain previous reports of reductions of transverse relaxation time (T2) in MRI studies and represent the source of the intrinsic Abeta plaque MR contrast in this model
— id: 55764, year: 2005, vol: 30, page: 201, stat: Journal Article,

Dissociated phenotypes in presenilin transgenic mice define functionally distinct gamma-secretases
Mastrangelo, Peter; Mathews, Paul M; Chishti, M Azhar; Schmidt, Stephen D; Gu, Yongjun; Yang, Jing; Mazzella, Matthew J; Coomaraswamy, Janaky; Horne, Patrick; Strome, Bob; Pelly, Heather; Levesque, Georges; Ebeling, Chris; Jiang, Ying; Nixon, Ralph A; Rozmahel, Richard; Fraser, Paul E; St George-Hyslop, Peter; Carlson, George A; Westaway, David
2005 Jun 21;102(25):8972-8977, Proceedings of the National Academy of Sciences of the United States of America
Gamma-secretase depends on presence of presenilins (PS), Nct, Aph-1, and PEN-2 within a core complex. This endoproteolytic activity cleaves within transmembrane domains of amyloid-beta precursor protein (APP) and Notch, and familial Alzheimer's disease (FAD) mutations in PS1 or PS2 genes shift APP cleavage from production of amyloid-beta (Abeta) 40 peptide to greater production of Abeta42. Although studies in PS1/PS2-deficient embryonic cells define overlapping activities for these proteins, in vivo complementation of PS1-deficient animals described here reveals an unexpected spectrum of activities dictated by PS1 and PS2 alleles. Unlike PS1 transgenes, wild-type PS2 transgenes expressed in the mouse CNS support little Abeta40 or Abeta42 production, and FAD PS2 alleles support robust production of only Abeta42. Although wild-type PS2 transgenes failed to rescue Notch-associated skeletal defects in PS1 hypomorphs, a 'gained' competence in this regard was apparent for FAD alleles of PS2. The range of discrete and divergent processing activities in mice reconstituted with different PS genes and alleles argues against gamma-secretase being a single enzyme with intrinsically relaxed substrate and cleavage site specificities. Instead, our studies define functionally distinct gamma-secretase variants. We speculate that extrinsic components, in combination with core complexes, may tailor functional variants of this enzyme to their preferred substrates
— id: 95396, year: 2005, vol: 102, page: 8972, stat: Journal Article,

Endosome function and dysfunction in Alzheimer's disease and other neurodegenerative diseases
Nixon, Ralph A
2005 Mar;26(3):373-382, Neurobiology of aging
Endocytosis is universally important in cell function. In the brain, the roles of endosomes are relatively more complex due to the unique polar morphology of neurons and specialized needs for inter-cellular communication. New evidence shows that endosome function is altered in a surprising range of neurodegenerative disorders, including in several inherited neurologic disorders where the causative mutations occur in genes that regulate endosome function. In Alzheimer's disease (AD), endosome abnormalities are among the earliest neuropathologic features to develop and have now been closely linked to genetic risk factors for AD, including APP triplication in Trisomy 21 (Down syndrome, DS) and ApoE4 genotype in sporadic AD. Recent findings on endosome regulation and developmental and late-onset neurodegenerative disease disorders are beginning to reveal how endocytic pathway impairment may lead to neuronal dysfunction and cell death in these disorders and may also promote amyloidogenesis in AD
— id: 51387, year: 2005, vol: 26, page: 373, stat: Journal Article,

Extensive involvement of autophagy in Alzheimer disease: an immuno-electron microscopy study
Nixon, Ralph A; Wegiel, Jerzy; Kumar, Asok; Yu, Wai Haung; Peterhoff, Corrinne; Cataldo, Anne; Cuervo, Ana Maria
2005 Feb;64(2):113-122, Journal of neuropathology & experimental neurology
The accumulation of lysosomes and their hydrolases within neurons is a well-established neuropathologic feature of Alzheimer disease (AD). Here we show that lysosomal pathology in AD brain involves extensive alterations of macroautophagy, an inducible pathway for the turnover of intracellular constituents, including organelles. Using immunogold labeling with compartmental markers and electron microscopy on neocortical biopsies from AD brain, we unequivocally identified autophagosomes and other prelysosomal autophagic vacuoles (AVs), which were morphologically and biochemically similar to AVs highly purified from mouse liver. AVs were uncommon in brains devoid of AD pathology but were abundant in AD brains particularly, within neuritic processes, including synaptic terminals. In dystrophic neurites, autophagosomes, multivesicular bodies, multilamellar bodies, and cathepsin-containing autophagolysosomes were the predominant organelles and accumulated in large numbers. These compartments were distinguishable from lysosomes and lysosomal dense bodies, previously shown also to be abundant in dystrophic neurites. Autophagy was evident in the perikarya of affected neurons, particularly in those with neurofibrillary pathology where it was associated with a relative depletion of mitochondria and other organelles. These observations provide the first evidence that macroautophagy is extensively involved in the neurodegenerative/regenerative process in AD. The striking accumulations of immature AV forms in dystrophic neurites suggest that the transport of AVs and their maturation to lysosomes may be impaired, thereby impeding the suspected neuroprotective functions of autophagy
— id: 50295, year: 2005, vol: 64, page: 113, stat: Journal Article,

Autophagy and its possible roles in nervous system diseases, damage and repair
Rubinsztein, David C; DiFiglia, Marian; Heintz, Nathaniel; Nixon, Ralph A; Qin, Zheng-Hong; Ravikumar, Brinda; Stefanis, Leonidas; Tolkovsky, Aviva
2005 Apr;1(1):11-22, Autophagy
Increased numbers of autophagosomes/autophagic vacuoles are seen in a variety of physiological and pathological states in the nervous system. In many cases, it is unclear if this phenomenon is the result of increased autophagic activity or decreased autophagosome-lysosome fusion. The functional significance of autophagy and its relationship to cell death in the nervous system is also poorly understood. In this review, we have considered these issues in the context of acute neuronal injury and a range of chronic neurodegenerative conditions, including the Lurcher mouse, Alzheimer's, Parkinson's, Huntington's and prion diseases. While many issues remain unresolved, these conditions raise the possibility that autophagy can have either deleterious or protective effects depending on the specific situation and stage in the pathological process.
— id: 72828, year: 2005, vol: 1, page: 11, stat: Journal Article,

Tissue processing prior to protein analysis and amyloid-beta quantitation
Schmidt, Stephen D; Jiang, Ying; Nixon, Ralph A; Mathews, Paul M
2005 ;299:267-278, Methods in molecular biology
Amyloid-containing tissue, whether from human patients or an animal model of a disease, is typically characterized by various biochemical and immunohistochemical techniques, many of which are described in detail in this volume. In this chapter, we describe a straightforward technique for the homogenization of tissue prior to these analyses. The technique is particularly well-suited for performing a large number of different biochemical analyses on a single mouse brain hemisphere. Starting with this homogenate, multiple characterizations can be done, including Western blot analysis and isolation of membrane-associated proteins, both of which are described here. Additional analyses can readily be performed on the tissue homogenate, including the ELISA quantitation of Abeta in the brain of a transgenic mouse model of beta-amyloid deposition. The ELISA technique is described in detail in the following chapter
— id: 56368, year: 2005, vol: 299, page: 267, stat: Journal Article,

ELISA method for measurement of amyloid-beta levels
Schmidt, Stephen D; Nixon, Ralph A; Mathews, Paul M
2005 ;299:279-297, Methods in molecular biology
The neuritic plaque in the brain of Alzheimer's disease (AD) patients consists of an amyloid composed primarily of Abeta, an approx 4-kDa peptide derived from the amyloid precursor protein. Multiple lines of evidence suggest that Abeta plays a key role in the pathogenesis of the disease, and potential treatments that target Abeta production and/or Abeta accumulation in the brain as beta-amyloid are being aggressively pursued. Methods to quantitate the Abeta peptide are, therefore, invaluable to most studies aimed at a better understanding of the molecular etiology of the disease and in assessing potential therapeutics. Although other techniques have been used to measure Abeta in the brains of AD patients and beta-amyloid-depositing transgenic mice, the enzyme-linked immunosorbent assay (ELISA) is one of the most commonly used, reliable, and sensitive methods for quantitating the Abeta peptide. Here we describe methods for the recovery of both soluble and deposited Abeta from brain tissue and the subsequent quantitation of the peptide by sandwich ELISA
— id: 56369, year: 2005, vol: 299, page: 279, stat: Journal Article,

Macroautophagy--a novel Beta-amyloid peptide-generating pathway activated in Alzheimer's disease
Yu, W Haung; Cuervo, Ana Maria; Kumar, Asok; Peterhoff, Corrinne M; Schmidt, Stephen D; Lee, Ju-Hyun; Mohan, Panaiyur S; Mercken, Marc; Farmery, Mark R; Tjernberg, Lars O; Jiang, Ying; Duff, Karen; Uchiyama, Yasuo; Naslund, Jan; Mathews, Paul M; Cataldo, Anne M; Nixon, Ralph A
2005 Oct 10;171(1):87-98, Journal of cell biology
Macroautophagy, which is a lysosomal pathway for the turnover of organelles and long-lived proteins, is a key determinant of cell survival and longevity. In this study, we show that neuronal macroautophagy is induced early in Alzheimer's disease (AD) and before beta-amyloid (Abeta) deposits extracellularly in the presenilin (PS) 1/Abeta precursor protein (APP) mouse model of beta-amyloidosis. Subsequently, autophagosomes and late autophagic vacuoles (AVs) accumulate markedly in dystrophic dendrites, implying an impaired maturation of AVs to lysosomes. Immunolabeling identifies AVs in the brain as a major reservoir of intracellular Abeta. Purified AVs contain APP and beta-cleaved APP and are highly enriched in PS1, nicastrin, and PS-dependent gamma-secretase activity. Inducing or inhibiting macroautophagy in neuronal and nonneuronal cells by modulating mammalian target of rapamycin kinase elicits parallel changes in AV proliferation and Abeta production. Our results, therefore, link beta-amyloidogenic and cell survival pathways through macroautophagy, which is activated and is abnormal in AD
— id: 60255, year: 2005, vol: 171, page: 87, stat: Journal Article,

Alzheimer amyloid precursor aspartyl proteinase activity in CHAPSO homogenates of Spodoptera frugiperda cells
Carter, Troy L; Verdile, Giuseppe; Groth, David; Bogush, Alexey; Thomas, Stefani; Shen, Patrick; Fraser, Paul E; Mathews, Paul; Nixon, Ralph A; Ehrlich, Michelle E; Kwok, John B J; St George-Hyslop, Peter; Schofield, Peter; Li, Yueming; Yang, Austin; Martins, Ralph N; Gandy, Sam
2004 Oct-Dec;18(4):261-263, Alzheimer disease & associated disorders
Presenilins are polytopic, integral proteins that control intramembranous proteolysis at the 'gamma-' and 'epsilon-' cleavage sites of the Alzheimer amyloid-beta precursor protein (APP) to yield amyloid-beta peptide (Abeta) and the APP intracellular domain (AICD). We have overexpressed a constitutively active, pathogenic form of PS1 (known as PS1 Delta exon 9) together with its substrate, APP-C99, in Spodoptera frugiperda (Sf9) cells. Sf9 cells have been reported to lack endogenous gamma-secretase, an unexpected finding since there exists an insect homologue of PS1. In our hands, neither intact insect cells coexpressing PS1 Delta exon 9/APP-C99 nor the aqueous homogenates of these cells displayed obvious products of the gamma- or epsilon-secretase reactions, as reported. Surprisingly, when APP-C99-expressing cells were homogenized in 3[(3-cholamidopropyl) dimethylammonio]-2-hydroxypropanesulfonic acid (CHAPSO), a detergent known to support gamma-secretase activity, subsequent incubation led to the accumulation of an AICD-like peptide (AICD-L). Aspartyl proteinase inhibitors were effective in preventing the appearance of AICD-L, but inhibitors of other classes of proteinases were ineffective. Immunoprecipitation-mass spectrometry of AICD-L revealed its identity as the minor of the two known AICDs
— id: 55765, year: 2004, vol: 18, page: 261, stat: Journal Article,

Abeta localization in abnormal endosomes: association with earliest Abeta elevations in AD and Down syndrome
Cataldo, Anne M; Petanceska, Suzana; Terio, Nicole B; Peterhoff, Corrinne M; Durham, Robert; Mercken, Marc; Mehta, Pankaj D; Buxbaum, Joseph; Haroutunian, Vahram; Nixon, Ralph A
2004 Nov-Dec;25(10):1263-1272, Neurobiology of aging
Early endosomes are a major site of amyloid precursor protein (APP) processing and a convergence point for molecules of pathologic relevance to Alzheimer's disease (AD). Neuronal endosome enlargement, reflecting altered endocytic function, is a disease-specific response that develops years before the earliest stage of AD and Down syndrome (DS). We examined how endocytic dysfunction is related to Abeta accumulation and distribution in early stage AD and DS. We found by ELISA and immunocytochemistry that the appearance of enlarged endosomes coincided with an initial rise in soluble Abeta40 and Abeta42 peptides, which preceded amyloid deposition. Double-immunofluorescence using numerous Abeta antibodies showed that intracellular Abeta localized principally to rab5-positive endosomes in neurons from AD brains and was prominent in enlarged endosomes. Abeta was not detectable in neurons from normal controls and was diminished after amyloid deposition in neuropathologically confirmed AD. These studies support growing evidence that endosomal pathology contributes significantly to Abeta overproduction and accumulation in sporadic AD and in AD associated with DS and may signify earlier disease-relevant disturbances of the signaling functions of endosomes
— id: 61153, year: 2004, vol: 25, page: 1263, stat: Journal Article,

Presenilin mutations in familial Alzheimer disease and transgenic mouse models accelerate neuronal lysosomal pathology
Cataldo, Anne M; Peterhoff, Corrinne M; Schmidt, Stephen D; Terio, Nicole B; Duff, Karen; Beard, Margaret; Mathews, Paul M; Nixon, Ralph A
2004 Aug;63(8):821-830, Journal of neuropathology & experimental neurology
The neuronal lysosomal system is a major degradative pathway, induced by cell stress and closely linked to Alzheimer disease (AD) and other neurodegenerative diseases. Here, we show that mutations of presenilin (PS) 1 and 2, which cause familial early-onset AD (FAD), induce more severe lysosomal system neuropathology in humans than does sporadic AD (SAD). Cathepsin D and B levels were higher in PS-FAD neocortex than in SAD and, unlike neurons in SAD, expressed higher levels of the cation-independent mannose-6-phosphate receptor. Lysosomal pathology was also evident in more populations of neurons in PS-FAD brains, including the less vulnerable neurons in laminae II and IV and affected neurons contained high numbers of hydrolase-positive vesicular compartments with a broader range of abnormal morphology. In transgenic mice expressing mutant amyloid precursor protein (APPswe), introducing mutant PSI significantly upregulated the lysosomal system in neocortical and hippocampal neurons. This upregulation, though milder in severity, resembled that seen in human PS-FAD. Accumulation of hydrolases in dystrophic neurites in senile plaques was particularly strong, suggesting that amyloid deposition may be a stimulus for local mobilization of the lysosomal system. PS1 mice lacking the APPswe transgene also had a mild lysosomal response in some neuronal populations, which was not seen in the APPswe mice. Our findings suggest that presenilin mutations have amyloid-independent effects on the lysosomal system, which are synergistic with the lysosomal system pathology that is associated with beta-amyloid
— id: 95397, year: 2004, vol: 63, page: 821, stat: Journal Article,

MRI assessment of neuropathology in a transgenic mouse model of Alzheimer's disease
Helpern, Joseph A; Lee, Sang-Pil; Falangola, Maria F; Dyakin, Victor V; Bogart, Adam; Ardekani, Babak; Duff, Karen; Branch, Craig; Wisniewski, Thomas; de Leon, Mony J; Wolf, Oliver; O'Shea, Jacqueline; Nixon, Ralph A
2004 Apr;51(4):794-798, Magnetic resonance in medicine
The cerebral deposition of amyloid beta-peptide, a central event in Alzheimer's disease (AD) pathogenesis, begins several years before the onset of clinical symptoms. Noninvasive detection of AD pathology at this initial stage would facilitate intervention and enhance treatment success. In this study, high-field MRI was used to detect changes in regional brain MR relaxation times in three types of mice: 1). transgenic mice (PS/APP) carrying both mutant genes for amyloid precursor protein (APP) and presenilin (PS), which have high levels and clear accumulation of beta-amyloid in several brain regions, starting from 10 weeks of age; 2). transgenic mice (PS) carrying only a mutant gene for presenilin (PS), which show subtly elevated levels of Abeta-peptide without beta-amyloid deposition; and 3). nontransgenic (NTg) littermates as controls. The transverse relaxation time T(2), an intrinsic MR parameter thought to reflect impaired cell physiology, was significantly reduced in the hippocampus, cingulate, and retrosplenial cortex, but not the corpus callosum, of PS-APP mice compared to NTg. No differences in T(1) values or proton density were detected between any groups of mice. These results indicate that T(2) may be a sensitive marker of abnormalities in this transgenic mouse model of AD
— id: 42285, year: 2004, vol: 51, page: 794, stat: Journal Article,

Co-expressed presenilin 1 NTF and CTF form functional gamma-secretase complexes in cells devoid of full-length protein
Laudon, Hanna; Mathews, Paul M; Karlstrom, Helena; Bergman, Anna; Farmery, Mark R; Nixon, Ralph A; Winblad, Bengt; Gandy, Samuel E; Lendahl, Urban; Lundkvist, Johan; Naslund, Jan
2004 Apr;89(1):44-53, Journal of neurochemistry
Abstract The enzyme gamma-secretase catalyzes the intramembrane proteolytic cleavage that generates the amyloid beta-peptide from the beta-amyloid precursor protein. The presenilin (PS) protein is one of the four integral membrane protein components of the mature gamma-secretase complex. The PS protein is itself subjected to endoproteolytic processing, generating stable N- and C-terminal fragment (NTF and CTF, respectively) heterodimers. Here we demonstrate that coexpression of PS1 NTF and CTF functionally mimics expression of the full-length PS1 protein and restores gamma-secretase activity in PS-deficient mammalian cells. The coexpressed fragments re-associate with each other inside the cell, where they also interact with nicastrin, another gamma-secretase complex component. Analysis of gamma-secretase activity following the expression of mutant forms of NTF and CTF, under conditions bypassing endoproteolysis, indicated that the putatively catalytic Asp257 and Asp385 residues have a direct effect on gamma-secretase activity. Moreover, we demonstrate that expression of the wild-type CTF rescues endoproteolytic cleavage of C-terminally truncated PS1 molecules that are otherwise uncleaved and inactive. Recovery of cleavage is critically dependent on the integrity of Asp385. Taken together, our findings indicate that ectopically expressed NTF and CTF restore functional gamma-secretase complexes and that the presence of full-length PS1 is not a requirement for proper complex assembly
— id: 42252, year: 2004, vol: 89, page: 44, stat: Journal Article,

Visualization of beta-amyloid plaques in a transgenic mouse model of Alzheimer's disease using MR microscopy without contrast reagents
Lee, Sang-Pil; Falangola, Maria F; Nixon, Ralph A; Duff, Karen; Helpern, Joseph A
2004 Sep;52(3):538-544, Magnetic resonance in medicine
The visualization of beta-amyloid plaque deposition in brain, a key feature of Alzheimer's disease (AD), is important for the evaluation of disease progression and the efficacy of therapeutic interventions. In this study, beta-amyloid plaques in the PS/APP transgenic mouse brain, a model of human AD pathology, were detected using MR microscopy without contrast reagents. beta-Amyloid plaques were clearly visible in the cortex, thalamus, and hippocampus of fixed brains of PS/APP mice. The distribution of plaques identified by MRI was in excellent agreement with those found in the immunohistological analysis of the same brain sections. It was also demonstrated that image contrast for beta-amyloid plaques was present in freshly excised nonfixed brains. Furthermore, the detection of beta-amyloid plaques was achieved with a scan time as short as 2 hr, approaching the scan time considered reasonable for in vivo imaging
— id: 47817, year: 2004, vol: 52, page: 538, stat: Journal Article,

Autophagy in Alzheimer's disease pathogenesis
Nixon, RA; Yu, WH; Cuervo, AM; Cataldo, AM; Mathews, PM; Yang, DS; Zheng, P; Peterhoff, CM; Kumar, A; Jiang, Y; Peterson, J; Schmidt, SD; Mohan, P; Duff, K; Hassinger, L; Wegiel, J; Lamb, B
2004 JUL ;25(10):S70-S71, Neurobiology of aging
— id: 47716, year: 2004, vol: 25, page: S70, stat: Journal Article,

Niemann-Pick Type C disease and Alzheimer's disease: the APP-endosome connection fattens up
Nixon, Ralph A
2004 Mar;164(3):757-761, American journal of pathology
Niemann-Pick Type C (NPC) is an inherited neurodegenerative disease of childhood and adolescence that develops from a failure of cholesterol trafficking within the endosomal-lysosomal pathway. Although NPC differs in major respects from Alzheimer's disease (AD), intriguing parallels exist in the cellular pathology of these two diseases, including neurofibrillary tangle formation, prominent lysosome system dysfunction, and influences of apolipoprotein E epsilon4 genotype. Added to these similarities are new findings that some neuronal populations develop abnormalities of endosomes resembling those seen at the earliest stages of AD and also accumulate beta-cleaved amyloid precursor protein (APP) and Abeta peptides within endosomes. In this commentary, the common features of endosome dysfunction are reviewed. Emerging evidence that endosome dysfunction may lead to beta-amyloidogenic APP processing or neurodegeneration by several different means is discussed
— id: 42286, year: 2004, vol: 164, page: 757, stat: Journal Article,

Overexpression of human cystatin C in transgenic mice does not affect levels of endogenous brain amyloid Beta Peptide
Pawlik, Monika; Sastre, Magdalena; Calero, Miguel; Mathews, Paul M; Schmidt, Stephen D; Nixon, Ralph A; Levy, Efrat
2004 ;22(1-2):13-18, Journal of molecular neuroscience
Cystatin C, an inhibitor of cysteine proteases, colocalizes with amyloid beta (Abeta) in parenchymal and vascular amyloid deposits in brains of Alzheimer's disease (AD) patients, suggesting that cystatin C has a role in AD. Cystatin C also colocalizes with beta amyloid precursor protein (betaAPP) in transfected cultured cells. In vitro analysis of the association between the two proteins revealed that binding of cystatin C to full-length betaAPP does not affect the level of Abeta secretion. Here we studied the effect of in vivo overexpression of cystatin C on the levels of endogenous brain Abeta. We have generated lines of transgenic mice expressing either wild-type human cystatin C or the Leu68Gln variant that forms amyloid deposits in the cerebral vessels of Icelandic patients with hereditary cerebral hemorrhage, under control sequences of the human cystatin C gene. Western blot analysis of brain homogenates was used to select lines of mice expressing various levels of the transgene. Analysis of Abeta40 and Abeta42 concentrations in the brain showed no difference between transgenic mice and their nontransgenic littermates. Thus, in vivo overexpression of human cystatin C does not affect Abeta levels in mice that do not deposit Abeta
— id: 42253, year: 2004, vol: 22, page: 13, stat: Journal Article,

Amyloid-beta deposition is associated with decreased hippocampal glucose metabolism and spatial memory impairment in APP/PS1 mice
Sadowski, Marcin; Pankiewicz, Joanna; Scholtzova, Henrieta; Ji, Yong; Quartermain, David; Jensen, Catrin H; Duff, Karen; Nixon, Ralph A; Gruen, Rand J; Wisniewski, Thomas
2004 May;63(5):418-428, Journal of neuropathology & experimental neurology
In Alzheimer disease (AD) patients, early memory dysfunction is associated with glucose hypometabolism and neuronal loss in the hippocampus. Double transgenic (Tg) mice co-expressing the M146L presenilin 1 (PS1) and K670N/M671L, the double 'Swedish' amyloid precursor protein (APP) mutations, are a model of AD amyloid-beta deposition (Abeta) that exhibits earlier and more profound impairments of working memory and learning than single APP mutant mice. In this study we compared performance on spatial memory tests, regional glucose metabolism, Abeta deposition, and neuronal loss in APP/PS1, PS1, and non-Tg (nTg) mice. At the age of 2 months no significant morphological and metabolic differences were detected between 3 studied genotypes. By 8 months, however, APP/PS1 mice developed selective impairment of spatial memory, which was significantly worse at 22 months and was accompanied by reduced glucose utilization in the hippocampus and a 35.8% dropout of neurons in the CA1 region. PS1 mice exhibited a similar degree of neuronal loss in CA1 but minimal memory deficit and no impairment of glucose utilization compared to nTg mice. Deficits in 22 month APP/PS1 mice were accompanied by a substantially elevated Abeta load, which rose from 2.5% +/- 0.4% at 8 months to 17.4% +/- 4.6%. These findings implicate Abeta or APP in the behavioral and metabolic impairments in APP/PS1 mice and the failure to compensate functionally for PS1-related hippocampal cell loss
— id: 44514, year: 2004, vol: 63, page: 418, stat: Journal Article,

Binding of cystatin C to Alzheimer's amyloid beta inhibits in vitro amyloid fibril formation
Sastre, Magdalena; Calero, Miguel; Pawlik, Monika; Mathews, Paul M; Kumar, Asok; Danilov, Vlatko; Schmidt, Stephen D; Nixon, Ralph A; Frangione, Blas; Levy, Efrat
2004 Oct;25(8):1033-1043, Neurobiology of aging
The colocalization of cystatin C, an inhibitor of cysteine proteases, with amyloid beta (Abeta) in parenchymal and vascular amyloid deposits in brains of Alzheimer's disease (AD) patients may reflect cystatin C involvement in amyloidogenesis. We therefore sought to determine the association of cystatin C with Abeta. Immunofluorescence analysis of transfected cultured cells demonstrated colocalization of cystatin C and beta amyloid precursor protein (betaAPP) intracellularly and on the cell surface. Western blot analysis of immunoprecipitated cell lysate or medium proteins revealed binding of cystatin C to full-length betaAPP and to secreted betaAPP (sbetaAPP). Deletion mutants of betaAPP localized the cystatin C binding site within betaAPP to the Abeta region. Cystatin C association with betaAPP resulted in increased sbetaAPP but did not affect levels of secreted Abeta. Analysis of the association of cystatin C and Abeta demonstrated a specific, saturable and high affinity binding between cystatin C and both Abeta(1-42) and Abeta(1-40). Notably, cystatin C association with Abeta results in a concentration-dependent inhibition of Abeta fibril formation
— id: 46126, year: 2004, vol: 25, page: 1033, stat: Journal Article,

Calpain mediates calcium-induced activation of the erk1,2 MAPK pathway and cytoskeletal phosphorylation in neurons: relevance to Alzheimer's disease
Veeranna; Kaji T; Boland B; Odrljin T; Mohan P; Basavarajappa BS; Peterhoff C; Cataldo A; Rudnicki A; Amin N; Li BS; Pant HC; Hungund BL; Arancio O; Nixon RA
2004 Oct;165(3):795-805, American journal of pathology
Aberrant phosphorylation of the neuronal cytoskeleton is an early pathological event in Alzheimer's disease (AD), but the underlying mechanisms are unclear. Here, we demonstrate in the brains of AD patients that neurofilament hyperphosphorylation in neocortical pyramidal neurons is accompanied by activation of both Erk1,2 and calpain. Using immunochemistry, Western blot analysis, and kinase activity measurements, we show in primary hippocampal and cerebellar granule (CG) neurons that calcium influx activates calpain and Erk1,2 and increases neurofilament phosphorylation on carboxy terminal polypeptide sites known to be modulated by Erk1,2 and to be altered in AD. Blocking Erk1,2 activity either with antisense oligonucleotides to Erk1,2 mRNA sequences or by specifically inhibiting its upstream activating kinase MEK1,2 markedly reduced neurofilament phosphorylation. Calpeptin, a cell-permeable calpain inhibitor, blocked both Erk1,2 activation and neurofilament hyperphosphorylation at concentrations that inhibit calpain-mediated cleavage of brain spectrin. By contrast, inhibiting Erk1,2 with U-0126, a specific inhibitor of Mek1,2, had no appreciable effect on ionomycin-induced calpain activation. These findings demonstrate that, under conditions of calcium injury in neurons, calpains are upstream activators of Erk1,2 signaling and are likely to mediate in part the hyperphosphorylation of neurofilaments and tau seen at early stages of AD as well as the neuron survival-related functions of the MAP kinase pathway
— id: 46128, year: 2004, vol: 165, page: 795, stat: Journal Article,

Aging, gender and APOE isotype modulate metabolism of Alzheimer's Abeta peptides and F-isoprostanes in the absence of detectable amyloid deposits
Yao, Jun; Petanceska, Suzana S; Montine, Thomas J; Holtzman, David M; Schmidt, Stephen D; Parker, Carolyn A; Callahan, Michael J; Lipinski, William J; Bisgaier, Charles L; Turner, Brian A; Nixon, Ralph A; Martins, Ralph N; Ouimet, Charles; Smith, Jonathan D; Davies, Peter; Laska, Eugene; Ehrlich, Michelle E; Walker, Lary C; Mathews, Paul M; Gandy, Sam
2004 Aug;90(4):1011-1018, Journal of neurochemistry
Aging and apolipoprotein E (APOE) isoform are among the most consistent risks for the development of Alzheimer's disease (AD). Metabolic factors that modulate risk have been elusive, though oxidative reactions and their by-products have been implicated in human AD and in transgenic mice with overt histological amyloidosis. We investigated the relationship between the levels of endogenous murine amyloid beta (Abeta) peptides and the levels of a marker of oxidation in mice that never develop histological amyloidosis [i.e. APOE knockout (KO) mice with or without transgenic human APOEepsilon3 or human APOEepsilon4 alleles]. Aging-, gender-, and APOE-genotype-dependent changes were observed for endogenous mouse brain Abeta40 and Abeta42 peptides. Levels of the oxidized lipid F2-isoprostane (F2-isoPs) in the brains of the same animals as those used for the Abeta analyses revealed aging- and gender-dependent changes in APOE KO and in human APOEepsilon4 transgenic KO mice. Human APOEepsilon3 transgenic KO mice did not exhibit aging- or gender-dependent increases in F2-isoPs. In general, the changes in the levels of brain F2-isoPs in mice according to age, gender, and APOE genotype mirrored the changes in brain Abeta levels, which, in turn, paralleled known trends in the risk for human AD. These data indicate that there exists an aging-dependent, APOE-genotype-sensitive rise in murine brain Abeta levels despite the apparent inability of the peptide to form histologically detectable amyloid. Human APOEepsilon3, but not human APOEepsilon4, can apparently prevent the aging-dependent rise in murine brain Abeta levels, consistent with the relative risk for AD associated with these genotypes. The fidelity of the brain Abeta/F2-isoP relationship across multiple relevant variables supports the hypothesis that oxidized lipids play a role in AD pathogenesis, as has been suggested by recent evidence that F2-isoPs can stimulate Abeta generation and aggregation
— id: 56111, year: 2004, vol: 90, page: 1011, stat: Journal Article,

Autophagic vacuoles are enriched in amyloid precursor protein-secretase activities: implications for beta-amyloid peptide over-production and localization in Alzheimer's disease
Yu, W H; Kumar, A; Peterhoff, C; Shapiro Kulnane, L; Uchiyama, Y; Lamb, B T; Cuervo, A M; Nixon, R A
2004 Dec;36(12):2531-2540, International journal of biochemistry & cell biology
In Alzheimer's disease (AD), the neuropathologic hallmarks of beta-amyloid deposition and neurofibrillary degeneration are associated with early and progressive pathology of the endosomal-lysosomal system. Abnormalities of autophagy, a major pathway to lysosomes for protein and organelle turnover, include marked accumulations of autophagy-related vesicular compartments (autophagic vacuoles or AVs) in affected neurons. Here, we investigated the possibility that AVs contain the proteases and substrates necessary to cleave the amyloid precursor protein (APP) to A beta peptide that forms beta-amyloid, a key pathogenic factor in AD. AVs were highly purified using a well-established metrizamide gradient procedure from livers of transgenic YAC mice overexpressing wild-type human APP. By Western blot analysis, AVs contained APP, beta C
— id: 61278, year: 2004, vol: 36, page: 2531, stat: Journal Article,

Calpain inhibitors, a treatment for Alzheimer's disease: position paper
Battaglia, Fortunato; Trinchese, Fabrizio; Liu, Shumin; Walter, Sean; Nixon, Ralph A; Arancio, Ottavio
2003 ;20(3):357-362, Journal of molecular neuroscience
Calpains modulate processes that govern the function and metabolism of proteins key to the pathogenesis of Alzheimer's disease, including tau and amyloid precursor protein. Because activation of the calpain system might contribute to the impairment of synaptic transmission in Alzheimer's disease, we are currently testing the hypotheses that a treatment with calpain inhibitors might restore normal cognition and synaptic transmission in a transgenic model of Alzheimer's disease, the APP (K670N:M671L)/PS1(M146L) mouse. Findings derived from these studies will provide a novel approach to cognitive enhancement in Alzheimer's disease
— id: 40067, year: 2003, vol: 20, page: 357, stat: Journal Article,

App gene dosage modulates endosomal abnormalities of Alzheimer's disease in a segmental trisomy 16 mouse model of down syndrome
Cataldo, Anne M; Petanceska, Suzana; Peterhoff, Corrinne M; Terio, Nicole B; Epstein, Charles J; Villar, Angela; Carlson, Elaine J; Staufenbiel, Matthias; Nixon, Ralph A
2003 Jul 30;23(17):6788-6792, Journal of neuroscience
Altered neuronal endocytosis is the earliest known pathology in sporadic Alzheimer's disease (AD) and Down syndrome (DS) brain and has been linked to increased Abeta production. Here, we show that a genetic model of DS (trisomy 21), the segmental trisomy 16 mouse Ts65Dn, develops enlarged neuronal early endosomes, increased immunoreactivity for markers of endosome fusion (rab5, early endosomal antigen 1, and rabaptin5), and endosome recycling (rab4) similar to those in AD and DS individuals. These abnormalities are most prominent in neurons of the basal forebrain, which later develop aging-related atrophy and degenerative changes, as in AD and DS. We also show that App, one of the triplicated genes in Ts65Dn mice and human DS, is critical to the development of these endocytic abnormalities. Selectively deleting one copy of App or a small portion of the chromosome 16 segment containing App from Ts65Dn mice eliminated the endosomal phenotype. Overexpressing App at high levels in mice did not alter early endosomes, implying that one or more additional genes on the triplicated segment of chromosome 16 are also required for the Ts65Dn endosomal phenotype. These results identify an essential role for App gene triplication in causing AD-related endosomal abnormalities and further establish the pathogenic significance of endosomal dysfunction in AD
— id: 40068, year: 2003, vol: 23, page: 6788, stat: Journal Article,

Rab5-stimulated up-regulation of the endocytic pathway increases intracellular beta-cleaved amyloid precursor protein carboxyl-terminal fragment levels and Abeta production
Grbovic, Olivera M; Mathews, Paul M; Jiang, Ying; Schmidt, Stephen D; Dinakar, Ravi; Summers-Terio, Nicole B; Ceresa, Brian P; Nixon, Ralph A; Cataldo, Anne M
2003 Aug 15;278(33):31261-31268, Journal of biological chemistry
We previously identified abnormalities of the endocytic pathway in neurons as the earliest known pathology in sporadic Alzheimer's disease (AD) and Down's syndrome brain. In this study, we modeled aspects of these AD-related endocytic changes in murine L cells by overexpressing Rab5, a positive regulator of endocytosis. Rab5-transfected cells exhibited abnormally large endosomes immunoreactive for Rab5 and early endosomal antigen 1, resembling the endosome morphology seen in affected neurons from AD brain. The levels of both Abeta40 and Abeta42 in conditioned medium were increased more than 2.5-fold following Rab5 overexpression. In Rab5 overexpressing cells, the levels of beta-cleaved amyloid precursor protein (APP) carboxyl-terminal fragments (betaCTF), the rate-limiting proteolytic intermediate in Abeta generation, were increased up to 2-fold relative to APP holoprotein levels. An increase in beta-cleaved soluble APP relative to alpha-cleaved soluble APP was also observed following Rab5 overexpression. BetaCTFs were co-localized by immunolabeling to vesicular compartments, including the early endosome and the trans-Golgi network. These results demonstrate a relationship between endosomal pathway activity, betaCTF generation, and Abeta production. Our findings in this model system suggest that the endosomal pathology seen at the earliest stage of sporadic AD may contribute to APP proteolysis along a beta-amyloidogenic pathway
— id: 48176, year: 2003, vol: 278, page: 31261, stat: Journal Article,

Setback for an Alzheimer's disease vaccine: Lessons learned
Mathews, Paul M; Nixon, Ralph A
2003 Jul 8;61(1):7-8, Neurology
— id: 36835, year: 2003, vol: 61, page: 7, stat: Journal Article,

The calpains in aging and aging-related diseases
Nixon, Ralph A
2003 Oct;2(4):407-418, Ageing research reviews
Calpains are a family of calcium-dependent cysteine proteases under complex cellular regulation. By making selective limited proteolytic cleavages, they modulate the activity of enzymes, including key signaling molecules, and induce specific cytoskeletal rearrangements, accounting for their roles in cell motility, signal transduction, vesicular trafficking and structural stabilization. Calpain activation has been implicated in various aging phenomena and diseases of late life, including cataract formation, erythrocyte senescence, diabetes mellitus type 2, hypertension, arthritis, and neurodegenerative disorders. The early and pervasive involvement of calpains in Alzheimer's disease potentially influences the development of beta-amyloid and tau disturbances and their consequences for neurodegeneration and neuronal cell loss
— id: 40066, year: 2003, vol: 2, page: 407, stat: Journal Article,

Cdk5 is a key factor in tau aggregation and tangle formation in vivo
Noble W; Olm V; Takata K; Casey E; Mary O; Meyerson J; Gaynor K; LaFrancois J; Wang L; Kondo T; Davies P; Burns M; Veeranna; Nixon R; Dickson D; Matsuoka Y; Ahlijanian M; Lau LF; Duff K
2003 May 22;38(4):555-565, Neuron
Tau aggregation is a common feature of neurodegenerative diseases such as Alzheimer's disease, and hyperphosphorylation of tau has been implicated as a fundamental pathogenic mechanism in this process. To examine the impact of cdk5 in tau aggregation and tangle formation, we crossed transgenic mice overexpressing the cdk5 activator p25, with transgenic mice overexpressing mutant (P301L) human tau. Tau was hyperphosphorylated at several sites in the double transgenics, and there was a highly significant accumulation of aggregated tau in brainstem and cortex. This was accompanied by increased numbers of silver-stained neurofibrillary tangles (NFTs). Insoluble tau was also associated with active GSK. Thus, cdk5 can initiate a major impact on tau pathology progression that probably involves several kinases. Kinase inhibitors may thus be beneficial therapeutically
— id: 60993, year: 2003, vol: 38, page: 555, stat: Journal Article,

Overexpression of human cystatin C in transgenic mice does not affect levels of endogenous brain amyloid beta peptide
Pawlik, M; Sastre, M; Calero, M; Mathews, PM; Schmidt, SD; Nixon, RA; Levy, E
2003 FEB ;22(1-2):13-18, Journal of molecular neuroscience
Cystatin C, an inhibitor of cysteine proteases, colocalizes with amyloid beta (Abeta) in parenchymal and vascular amyloid deposits in brains of Alzheimer's disease (AD) patients, suggesting that cystatin C has a role in AD. Cystatin C also colocalizes with beta amyloid precursor protein (betaAPP) in transfected cultured cells. In vitro analysis of the association between the two proteins revealed that binding of cystatin C to full-length betaAPP does not affect the level of Abeta secretion. Here we studied the effect of in vivo overexpression of cystatin C on the levels of endogenous brain Abeta. We have generated lines of transgenic mice expressing either wild-type human cystatin C or the Leu68Gln variant that forms amyloid deposits in the cerebral vessels of Icelandic patients with hereditary cerebral hemorrhage, under control sequences of the human cystatin C gene. Western blot analysis of brain homogenates was used to select lines of mice expressing various levels of the transgene. Analysis of Abeta40 and Abeta42 concentrations in the brain showed no difference between transgenic mice and their nontransgenic littermates. Thus, in vivo overexpression of human cystatin C does not affect Abeta levels in mice that do not deposit Abeta
— id: 42508, year: 2003, vol: 22, page: 13, stat: Journal Article,

In vivo reduction of amyloid-{beta} by a mutant copper transporter
Phinney, Amie L; Drisaldi, Bettina; Schmidt, Stephen D; Lugowski, Stan; Coronado, Veronica; Liang, Yan; Horne, Patrick; Yang, Jing; Sekoulidis, Joannis; Coomaraswamy, Janaky; Chishti, M Azhar; Cox, Diane W; Mathews, Paul M; Nixon, Ralph A; Carlson, George A; St George-Hyslop, Peter; Westaway, David
2003 Nov 25;100(24):14193-14198, Proceedings of the National Academy of Sciences of the United States of America
Cu ions have been suggested to enhance the assembly and pathogenic potential of the Alzheimer's disease amyloid-beta (Abeta) peptide. To explore this relationship in vivo, toxic-milk (txJ) mice with a mutant ATPase7b transporter favoring elevated Cu levels were analyzed in combination with the transgenic (Tg) CRND8 amyloid precursor protein mice exhibiting robust Abeta deposition. Unexpectedly, TgCRND8 mice homozygous for the recessive txJ mutation examined at 6 months of age exhibited a reduced number of amyloid plaques and diminished plasma Abeta levels. In addition, homozygosity for txJ increased survival of young TgCRND8 mice and lowered endogenous CNS Abeta at times before detectable increases in Cu in the CNS. These data suggest that the beneficial effect of the txJ mutation on CNS Abeta burden may proceed by a previously undescribed mechanism, likely involving increased clearance of peripheral pools of Abeta peptide
— id: 40065, year: 2003, vol: 100, page: 14193, stat: Journal Article,

The neurofilament middle molecular mass subunit carboxyl-terminal tail domains is essential for the radial growth and cytoskeletal architecture of axons but not for regulating neurofilament transport rate
Rao, Mala V; Campbell, Jabbar; Yuan, Aidong; Kumar, Asok; Gotow, Takahiro; Uchiyama, Yasuo; Nixon, Ralph A
2003 Dec 8;163(5):1021-1031, Journal of cell biology
The phosphorylated carboxyl-terminal 'tail' domains of the neurofilament (NF) subunits, NF heavy (NF-H) and NF medium (NF-M) subunits, have been proposed to regulate axon radial growth, neurofilament spacing, and neurofilament transport rate, but direct in vivo evidence is lacking. Because deletion of the tail domain of NF-H did not alter these axonal properties (Rao, M.V., M.L. Garcia, Y. Miyazaki, T. Gotow, A. Yuan, S. Mattina, C.M. Ward, N.S. Calcutt, Y. Uchiyama, R.A. Nixon, and D.W. Cleveland. 2002. J. Cell Biol. 158:681-693), we investigated possible functions of the NF-M tail domain by constructing NF-M tail-deleted (NF-MtailDelta) mutant mice using an embryonic stem cell-mediated 'gene knockin' approach that preserves normal ratios of the three neurofilament subunits. Mutant NF-MtailDelta mice exhibited severely inhibited radial growth of both motor and sensory axons. Caliber reduction was accompanied by reduced spacing between neurofilaments and loss of long cross-bridges with no change in neurofilament protein content. These observations define distinctive functions of the NF-M tail in regulating axon caliber by modulating the organization of the neurofilament network within axons. Surprisingly, the average rate of axonal transport of neurofilaments was unaltered despite these substantial effects on axon morphology. These results demonstrate that NF-M tail-mediated interactions of neurofilaments, independent of NF transport rate, are critical determinants of the size and cytoskeletal architecture of axons, and are mediated, in part, by the highly phosphorylated tail domain of NF-M
— id: 40064, year: 2003, vol: 163, page: 1021, stat: Journal Article,

Defective neurofilament transport in mouse models of amyotrophic lateral sclerosis: a review
Rao, Mala V; Nixon, Ralph A
2003 Jul;28(7):1041-1047, Neurochemical research
Neurofilament proteins synthesized in the cell body of neurons are assembled and transported into axons, where they influence axon radial growth, axonal transport, and nerve conduction velocities. In diseased states, neurofilaments accumulate in cell bodies and proximal axons of affected neurons, and these lesions are characteristic of many neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD), spinal muscular atrophy (SMA), Charcot-Marie-Tooth disease type 2 (CMT2), and hereditary sensory motor neuropathy. Although the molecular mechanisms that contribute to these accumulations are not yet identified, transgenic mouse models are beginning to provide insight into the role of neurofilament transport in disease-related dysfunction of neurons. This review addresses axonal transport in mouse models of ALS and the special significance of neurofilament transport in this disease
— id: 60267, year: 2003, vol: 28, page: 1041, stat: Journal Article,

Hypothesis for a common basis for neuroprotection in glaucoma and Alzheimer's disease: anti-apoptosis by alpha-2-adrenergic receptor activation
Tatton, William; Chen, David; Chalmers-Redman, Ruth; Wheeler, Larry; Nixon, Ralph; Tatton, Nadine
2003 Apr;48 Suppl 1:S25-S37, Survey of ophthalmology
Recent studies have suggested glaucomatous loss of retinal ganglion cells and their axons in Alzheimer's disease. Amyloid beta peptides and phosphorylated tau protein have been implicated in the selective regional neuronal loss and protein accumulations characteristic of Alzheimer's disease. Similar protein accumulations are not present on glaucomatous retinal ganglion cells. Neurons die in both Alzheimer's disease and glaucoma by apoptosis, although the signaling pathways for neuronal degradation appear to differ in the two diseases. Alzheimer's disease features a loss of locus ceruleus noradrenergic neurons, which send axon terminals to the brain regions suffering neuronal apoptosis and results in reductions in noradrenaline in those regions. Activation of alpha-2 adrenergic receptors reduces neuronal apoptosis, in part through a protein kinase B (Akt)-dependent signaling pathway. Loss of noradrenaline innervation facilitates neuronal apoptosis in Alzheimer's disease models and may act similarly in glaucoma. Alpha-2 adrenergic receptor agonists offer the potential to slow the neuronal loss in both diseases by compensating for lost noradrenaline innervation
— id: 61273, year: 2003, vol: 48 Suppl 1, page: S25, stat: Journal Article,

Neurofilament transport in vivo minimally requires hetero-oligomer formation
Yuan, Aidong; Rao, Mala V; Kumar, Asok; Julien, Jean-Pierre; Nixon, Ralph A
2003 Oct 15;23(28):9452-9458, Journal of neuroscience
Neurofilament assembly requires at minimum the polymerization of neurofilament light chain (NF-L) with either neurofilament medium chain (NF-M) or neurofilament heavy chain (NF-H) subunits, but requirements for their axonal transport have long been controversial. Using a gene deletion approach, we generated mice containing only NF-L or NF-M. In vivo pulse radiolabeling analyses in retinal ganglion cell neurons revealed that NF-L alone is incapable of efficient transport, whereas nearly one-half of the normal level of NF-M is transported along optic axons in the absence of the other triplet subunits. Under these conditions, however, NF-M transport is completely abolished by deleting alpha-internexin. Our results strongly suggest that efficient neurofilament protein transport in vivo minimally requires hetero-oligomer formation. They also show that NF-M can partner with intermediate filament proteins other than the NF-H and NF-L subunits in neurons to support slow transport and possibly other functions of neuronal intermediate filaments
— id: 39029, year: 2003, vol: 23, page: 9452, stat: Journal Article,

Study of the endosomal-lysosomal system in APPswe/PS1 transgenic mice
Zamora, E; Borchelt, DR; Jankowsky, K; Cataldo, AM; Nixon, RA; Troncoso, JC
2003 MAY ;62(5):552-552, Journal of neuropathology & experimental neurology
— id: 38570, year: 2003, vol: 62, page: 552, stat: Journal Article,

Calpain activation in neurodegenerative diseases: confocal immunofluorescence study with antibodies specifically recognizing the active form of calpain 2
Adamec, Emil; Mohan, Panaiyur; Vonsattel, Jean P; Nixon, Ralph A
2002 Jul;104(1):92-104, Acta neuropathologica
The calcium-activated protease calpain cleaves a variety of biologically important proteins and serves, therefore, as a key regulator of many cellular functions. Activation of both main isoforms, calpain 1 and calpain 2, was demonstrated previously in Alzheimer's disease. In this report, antibodies specifically recognizing the active form of calpain 2 were used to investigate calpain 2 activation in a broad range of neurodegenerative diseases, utilizing multiple-label confocal immunofluorescence imaging. With rare exceptions, the active form of calpain 2 was found in colocalization with hyperphosphorylated tau protein. Aggregates of mutated huntingtin, alpha-synuclein, or unidentified protein in motor neuron disease type of frontotemporal dementia were always negative. These findings indicate that calpain 2 activation is not a general response to protein aggregation. In tauopathies, more pathological inclusions were labeled for hyperphosphorylated tau than for activated calpain 2. The extent of colocalization varied in both a disease-specific and cell-type specific manner. The active form of calpain 2 was detected in 50-75% of tau neurofibrillary pathology in Alzheimer's disease, Alzheimer neurofibrillary changes and Down's syndrome, as well as in the accompanying Alzheimer-type tau pathology in diffuse Lewy bodies disease, progressive supranuclear palsy, and corticobasal degeneration. For glial cells, only 10-25% of tuft-shaped astrocytes, glial plaques, or coiled bodies contained activated calpain 2. The majority of Pick bodies were negative. The association of calpain 2 activation with hyperphosphorylated tau might be the result of an attempt by the calpain proteolytic system to degrade the tau protein aggregates. Alternatively, calpain 2 could be directly involved in tau hyperphosphorylation by modulating protein kinase activities. Overall, these results provide evidence of the important role of the calpain proteolytic system in the pathogenesis of neurodegenerative diseases with tau neurofibrillary pathology
— id: 32532, year: 2002, vol: 104, page: 92, stat: Journal Article,

P301L tauopathy: confocal immunofluorescence study of perinuclear aggregation of the mutated protein
Adamec, Emil; Murrell, Jill R; Takao, Masaki; Hobbs, Wendy; Nixon, Ralph A; Ghetti, Bernardino; Vonsattel, Jean P
2002 Aug 15;200(1-2):85-93, Journal of the neurological sciences
The clinical and neuropathological features in the P301L tauopathy have been described in several kindreds. In this study, we present findings in two previously unreported patients, evaluated both genetically, neuropathologically, and with multiparametric confocal immunofluorescence. The patients were female, with age 65 and 75 years old, respectively. Both exhibited clinical symptoms of frontotemporal dementia (FTD). Marked atrophy of the frontal and temporal lobes with moderate atrophy of the remaining cerebral and brain stem structures was present. The substantia nigra was pale. The atrophic neocortical regions exhibited neuronal loss, marked gliosis, status spongiosus, and occasional ballooned neurons. By light microscopy, the most striking findings were argyrophilic perinuclear rings, frequently with an attached small inclusion (mini Pick-like body), especially prominent in dentate granule cells, entorhinal and temporal cortices, and to a lesser extent in CA1. These structures were immunopositive for tau protein (Tau-2, AT-8, PHF-1, MC-1). Numerous astrocytic plaques, tuft-shaped astrocytes, coiled bodies, and dystrophic neurites were also present. Confocal immunofluorescence with a P301L-specific antibody directly demonstrated the presence of the mutated protein in the PHF-1 positive aggregates. The mutated tau protein (4-repeat tau) was detected in the mini Pick-like bodies, indicating an important biochemical difference between these inclusions and classical Pick bodies (3-repeat tau). Additionally, since 4-repeat tau protein is not normally present in dentate granule cells, this result also suggests an abnormality in the mRNA splicing mechanisms. The structural features of the involvement of proteolytic systems in this tauopathy were assessed by immunohistochemistry for the active form of calpain II (C-27) and ubiquitin. Colocalization of PHF-1 positive aggregates with C-27 points to the possible involvement of calpain in tau protein hyperphosphorylation. Absence of immunostaining for ubiquitin indicates possible dysfunction of the ubiquitin-proteasome system in this tauopathy
— id: 32531, year: 2002, vol: 200, page: 85, stat: Journal Article,

Calpain inhibitors: a treatment for Alzheimer's disease
Di Rosa, Gabriella; Odrijin, Tatjana; Nixon, Ralph A; Arancio, Ottavio
2002 Aug-Oct;19(1-2):135-141, Journal of molecular neuroscience
Activation of the calpain system might contribute to the impairment of synaptic transmission inAlzheimer's disease (AD) (Liu et al., 1999; Rapoport, 1999; Selkoe, 1994). Calpains regulate the function of many proteins by limited proteolysis and initiate the complete degradation of other proteins. In particular, they modulate processes that govern the function and metabolism of proteins key to the pathogenesis of AD, including tau and amyloid precursor protein (APP). (Xie and Johnson, 1998; Wang, 2000). We have found that overexpression of APP(K670M:N671L) and PS1(M146L) proteins in hippocampal cultures derived from transgenic mice causes an increase in the frequency of spontaneous release of neurotransmitter. We have also found that calpain immunoreactive clusters are co-localized with immunoreactivity for the vesicle-associated presynaptic marker, synaptophysin. Moreover, application of calpain inhibitor reduces the frequency of spontaneous release of neurotransmitter. Therefore, we have hypothesized that calpains might contribute to the increase in transmitter release. Based on this hypothesis, we propose to test whether it is possible to restore normal synaptic transmission between cells derived from the transgenic model of AD by using calpain inhibitors. The transgenic mouse model also shows spatial learning impairment, a phenomenon that is thought to be associated with plastic changes at synaptic level. Therefore, we will also test whether we can rescue the learning impairment through a treatment with calpain inhibitors
— id: 32533, year: 2002, vol: 19, page: 135, stat: Journal Article,

Alzheimer's disease-related overexpression of the cation-dependent mannose 6-phosphate receptor increases Abeta secretion: role for altered lysosomal hydrolase distribution in beta-amyloidogenesis
Mathews, Paul M; Guerra, Carolyn B; Jiang, Ying; Grbovic, Olivera M; Kao, Benjamin H; Schmidt, Stephen D; Dinakar, Ravi; Mercken, Marc; Hille-Rehfeld, Annette; Rohrer, Jack; Mehta, Pankaj; Cataldo, Anne M; Nixon, Ralph A
2002 Feb 15;277(7):5299-5307, Journal of biological chemistry
Prominent endosomal and lysosomal changes are an invariant feature of neurons in sporadic Alzheimer's disease (AD). These changes include increased levels of lysosomal hydrolases in early endosomes and increased expression of the cation-dependent mannose 6-phosphate receptor (CD-MPR), which is partially localized to early endosomes. To determine whether AD-associated redistribution of lysosomal hydrolases resulting from changes in CD-MPR expression affects amyloid precursor protein (APP) processing, we stably transfected APP-overexpressing murine L cells with human CD-MPR. As controls for these cells, we also expressed CD-MPR trafficking mutants that either localize to the plasma membrane (CD-MPRpm) or to early endosomes (CD-MPRendo). Expression of CD-MPR resulted in a partial redistribution of a representative lysosomal hydrolase, cathepsin D, to early endosomal compartments. Turnover of APP and secretion of sAPPalpha and sAPPbeta were not altered by overexpression of any of the CD-MPR constructs. However, secretion of both human Abeta40 and Abeta42 into the growth media nearly tripled in CD-MPR- and CD-MPRendo-expressing cells when compared with parental or CD-MPRpm-expressing cells. Comparable increases were confirmed for endogenous mouse Abeta40 in L cells expressing these CD-MPR constructs but not overexpressing human APP. These data suggest that redistribution of lysosomal hydrolases to early endocytic compartments mediated by increased expression of the CD-MPR may represent a potentially pathogenic mechanism for accelerating Abeta generation in sporadic AD, where the mechanism of amyloidogenesis is unknown
— id: 48164, year: 2002, vol: 277, page: 5299, stat: Journal Article,

Calpain Activity Regulates the Cell Surface Distribution of Amyloid Precursor Protein. INHIBITION OF CALPAINS ENHANCES ENDOSOMAL GENERATION OF beta -CLEAVED C-TERMINAL APP FRAGMENTS
Mathews, Paul M; Jiang, Ying; Schmidt, Stephen D; Grbovic, Olivera M; Mercken, Marc; Nixon, Ralph A
2002 Sep 27;277(39):36415-36424, Journal of biological chemistry
In murine L cells, treatment with calpeptin or calpain inhibitor III increased Abeta42, but not Abeta40, secretion in a dose-dependent fashion. This correlated with an increase in the levels of amyloid precursor protein (APP) carboxyl-terminal fragments (CTFs). Immunoprecipitation with novel mAbs directed against the carboxyl-terminus of APP or specific for the beta-cleaved CTF showed that generation of both alpha- and beta-cleaved CTFs increase proportionately following inhibition of calpains. Pulse-chase metabolic labeling confirmed that inhibiting calpains increases the production of alpha- and beta-cleaved APP metabolites. Immunolabeling showed greater betaCTF signal in calpeptin-treated cells, primarily in small vesicular compartments that were shown to be predominantly endosomal by colocalization with early endosomal antigen 1. A second mAb, which recognizes an extracellular/luminal epitope found on both APP and betaCTFs, gave more cell surface labeling of calpeptin-treated cells than control cells. Quantitative binding of this antibody confirmed that inhibiting calpains caused a partial redistribution of APP to the cell surface. These results demonstrate that 1) calpain inhibition results in a partial redistribution of APP to the cell surface, 2) this redistribution leads to an increase in both alpha- and beta-cleavage without changing the ratio of alphaCTFs/betaCTFs, and 3) the bulk of the betaCTFs in the cell are within early endosomes, confirming the importance of this compartment in APP processing
— id: 32534, year: 2002, vol: 277, page: 36415, stat: Journal Article,

Cell and molecular neuropathology of Alzheimer's disease
Nixon RA
Neuropsychopharmacology : the fifth generation of progress Philadelphia : Lippincott Williams & Wilkins, 2002,
— id: 4406, year: 2002, vol: , page: ?, stat: Chapter,

Neural circuitry and signaling in dementia and Alzheimer's Disease
Nixon RA
Brain circuitry and signaling in psychiatry: basic science and clinical implications Washington DC : American Psychiatric Publishing, 2002,
— id: 2655, year: 2002, vol: , page: 201, stat: Chapter,

Myosin Va binding to neurofilaments is essential for correct myosin Va distribution and transport and neurofilament density
Rao, Mala V; Engle, Linda J; Mohan, Panaiyur S; Yuan, Aidong; Qiu, Dike; Cataldo, Anne; Hassinger, Linda; Jacobsen, Stephen; Lee, Virginia M-Y; Andreadis, Athena; Julien, Jean-Pierre; Bridgman, Paul C; Nixon, Ralph A
2002 Oct 28;159(2):279-290, Journal of cell biology
The identification of molecular motors that modulate the neuronal cytoskeleton has been elusive. Here, we show that a molecular motor protein, myosin Va, is present in high proportions in the cytoskeleton of mouse CNS and peripheral nerves. Immunoelectron microscopy, coimmunoprecipitation, and blot overlay analyses demonstrate that myosin Va in axons associates with neurofilaments, and that the NF-L subunit is its major ligand. A physiological association is indicated by observations that the level of myosin Va is reduced in axons of NF-L-null mice lacking neurofilaments and increased in mice overexpressing NF-L, but unchanged in NF-H-null mice. In vivo pulse-labeled myosin Va advances along axons at slow transport rates overlapping with those of neurofilament proteins and actin, both of which coimmunoprecipitate with myosin Va. Eliminating neurofilaments from mice selectively accelerates myosin Va translocation and redistributes myosin Va to the actin-rich subaxolemma and membranous organelles. Finally, peripheral axons of dilute-lethal mice, lacking functional myosin Va, display selectively increased neurofilament number and levels of neurofilament proteins without altering axon caliber. These results identify myosin Va as a neurofilament-associated protein, and show that this association is essential to establish the normal distribution, axonal transport, and content of myosin Va, and the proper numbers of neurofilaments in axons
— id: 32536, year: 2002, vol: 159, page: 279, stat: Journal Article,

Gene replacement in mice reveals that the heavily phosphorylated tail of neurofilament heavy subunit does not affect axonal caliber or the transit of cargoes in slow axonal transport
Rao, Mala V; Garcia, Michael L; Miyazaki, Yukio; Gotow, Takahiro; Yuan, Aidong; Mattina, Salvatore; Ward, Chris M; Calcutt, Nigel A; Uchiyama, Yasuo; Nixon, Ralph A; Cleveland, Don W
2002 Aug 19;158(4):681-693, Journal of cell biology
The COOH-terminal tail of mammalian neurofilament heavy subunit (NF-H), the largest neurofilament subunit, contains 44-51 lysine-serine-proline repeats that are nearly stoichiometrically phosphorylated after assembly into neurofilaments in axons. Phosphorylation of these repeats has been implicated in promotion of radial growth of axons, control of nearest neighbor distances between neurofilaments or from neurofilaments to other structural components in axons, and as a determinant of slow axonal transport. These roles have now been tested through analysis of mice in which the NF-H gene was replaced by one deleted in the NF-H tail. Loss of the NF-H tail and all of its phosphorylation sites does not affect the number of neurofilaments, alter the ratios of the three neurofilament subunits, or affect the number of microtubules in axons. Additionally, it does not reduce interfilament spacing of most neurofilaments, the speed of action potential propagation, or mature cross-sectional areas of large motor or sensory axons, although its absence slows the speed of acquisition of normal diameters. Most surprisingly, at least in optic nerve axons, loss of the NF-H tail does not affect the rate of transport of neurofilament subunits
— id: 32535, year: 2002, vol: 158, page: 681, stat: Journal Article,

Alleles at the Nicastrin locus modify presenilin 1- deficiency phenotype
Rozmahel, Richard; Mount, Howard T J; Chen, Fusheng; Nguyen, Van; Huang, Jean; Erdebil, Serap; Liauw, Jennifer; Yu, Gang; Hasegawa, Hiroshe; Gu, YongJun; Song, You-Qiang; Schmidt, Stephen D; Nixon, Ralph A; Mathews, Paul M; Bergeron, Catherine; Fraser, Paul; Westaway, David; St George-Hyslop, Peter
2002 Oct 29;99(22):14452-14457, Proceedings of the National Academy of Sciences of the United States of America
Presenilin 1 (PS1), presenilin 2, and nicastrin form high molecular weight complexes that are necessary for the endoproteolysis of several type 1 transmembrane proteins, including amyloid precursor protein (APP) and the Notch receptor, by apparently similar mechanisms. The cleavage of the Notch receptor at the 'S3-site' releases a C-terminal cytoplasmic fragment (Notch intracellular domain) that acts as the intracellular transduction molecule for Notch activation. Missense mutations in the presenilins cause familial Alzheimer's disease by augmenting the 'gamma-secretase' cleavage of APP and overproducing one of the proteolytic derivatives, the Abeta peptide. Null mutations in PS1 inhibit both gamma-secretase cleavage of APP and S3-site cleavage of the Notch receptor. Mice lacking PS1 function have defective Notch signaling and die perinatally with severe skeletal and brain deformities. We report here that a genetic modifier on mouse distal chromosome 1, coinciding with the locus containing Nicastrin, influences presenilin-mediated Notch S3-site cleavage and the resultant Notch phenotype without affecting presenilin-mediated APP gamma-site cleavage. Two missense substitutions of residues conserved among vertebrates have been identified in nicastrin. These results indicate that Notch S3-site cleavage and APP gamma-site cleavage are distinct presenilin-dependent processes and support a functional interaction between nicastrin and presenilins in vertebrates. The dissociation of Notch S3-site and APP gamma-site cleavage activities will facilitate development of gamma-secretase inhibitors for treatment of Alzheimer's disease
— id: 32537, year: 2002, vol: 99, page: 14452, stat: Journal Article,

Murine A beta co-deposition in transgenic mice: Analyses with species-specific antibodies and comparison of human and murine A beta 42 : A beta 40 ratios
Schmidt, S; Jiang, Y; Duff, KEK; Nixon, RA; Mathews, PM; Herzig, MC; Jucker, M; Chishti, MA; Westaway, D; Mercken, M; Staufenbiel, M
2002 Jul-Aug;23(1):920-, Neurobiology of aging
— id: 32422, year: 2002, vol: 23, page: 920, stat: Journal Article,

Mature glycosylation and trafficking of nicastrin modulate its binding to presenilins
Yang, Dun-Sheng; Tandon, Anurag; Chen, Fusheng; Yu, Gang; Yu, Haung; Arawaka, Shigeki; Hasegawa, Hiroshi; Duthie, Monika; Schmidt, Stephen D; Ramabhadran, Triprayer V; Nixon, Ralph A; Mathews, Paul M; Gandy, Samuel E; Mount, Howard T J; St George-Hyslop, Peter; Fraser, Paul E
2002 Aug 2;277(31):28135-28142, Journal of biological chemistry
Nicastrin is an integral component of the high molecular weight presenilin complexes that control proteolytic processing of the amyloid precursor protein and Notch. We report here that nicastrin is most probably a type 1 transmembrane glycoprotein that is expressed at moderate levels in the brain and in cultured neurons. Immunofluorescence studies demonstrate that nicastrin is localized in the endoplasmic reticulum, Golgi, and a discrete population of vesicles. Glycosidase analyses reveal that endogenous nicastrin undergoes a conventional, trafficking-dependent maturation process. However, when highly expressed in transfected cells, there is a disproportionate accumulation of the endo-beta-N-acetylglucosaminidase H-sensitive, immature form, with no significant increase in the levels of the fully mature species. Immunoprecipitation revealed that presenilin-1 interacts preferentially with mature nicastrin, suggesting that correct trafficking and co-localization of the presenilin complex components are essential for activity. These findings demonstrate that trafficking and post-translational modifications of nicastrin are tightly regulated processes that accompany the assembly of the active presenilin complexes that execute gamma-secretase cleavage. These results also underscore the caveat that simple overexpression of nicastrin in transfected cells may result in the accumulation of large amounts of the immature protein, which is apparently unable to assemble into the active complexes capable of processing amyloid precursor protein and Notch
— id: 62376, year: 2002, vol: 277, page: 28135, stat: Journal Article,

Multiple-label immunocytochemistry for the evaluation of nature of cell death in experimental models of neurodegeneration
Adamec E; Yang F; Cole GM; Nixon RA
2001 Jul;7(3):193-202, Brain research protocols
A prominent feature of neurodegenerative diseases is a loss of specific neuronal populations. The pathophysiological mechanisms responsible are, however, poorly understood. Primary cultures of rodent embryonic neurons represent a useful experimental system for investigation of molecular pathways of neurodegeneration and mechanisms of cell death. Here, we report a technique utilizing triple-label immunocytochemistry with confocal immunofluorescence detection designed to simultaneously assess multiple parameters of cell injury in individual hippocampal neurons in primary culture. This method combines detection of DNA damage (TUNEL or Klenow assay) with double-label immunocytochemistry for the activated form of caspase-3 or, alternatively, caspase-cleaved actin (fractin), and microtubule-associated protein-2 (MAP-2) or beta-tubulin. The combined evaluation of the form of nuclear damage (karyorrhexis, pyknosis), the presence or absence of activated caspase-3, and the extent of the damage to cell cytoskeleton, allows for precise assessment of the extent of injury and the mode of cell death (apoptosis, oncosis) for individual neurons
— id: 25413, year: 2001, vol: 7, page: 193, stat: Journal Article,

Endocytic disturbances distinguish among subtypes of Alzheimer's disease and related disorders
Cataldo, A; Rebeck, GW; Ghetti, B; Hulette, C; Lippa, C; Van Broeckhovan, C; Van Duijn, C; Cras, P; Bogdanovic, N; Bird, T; Peterhoff, C; Nixon, R
2001 Nov;50(5):661-665, Annals of neurology
The endocytic pathway is important in amyloid precursor protein (APP) processing and beta -amyloid formation. Our studies have shown that endocytic pathway activation is a prominent and early feature of neurons in vulnerable regions of the brain in sporadic Alzheimer's disease. We report that endocytic pathway abnormalities are present not only in neurons, but in cerebral endothelia in Alzheimer's disease caused by certain APP mutations. The presence or absence of endocytic abnormalities distinguish subtypes of familial Alzheimer's disease linked to APP mutations from presenilin mutations, supporting the notion that different cellular pathways are involved in the altered processing of APP leading to increased beta -amyloid generation in certain of these different Alzheimer's disease subtypes
— id: 28208, year: 2001, vol: 50, page: 661, stat: Journal Article,

In vivo detection of neuropathology in an animal model of Alzheimer's disease by magnetic resonance imaging
Helpern, J. A.; Wisniewski, T.; Duff, K.; Dyakin, V.; de Leon, M.; Ardekani, B.; Wolf, O.; Branch, C.; O'Shea, J.; Wegiel, J.; Nixon, R. A.
2001 ;27(1):1217-343, Abstracts (Society for Neuroscience)
The cerebral deposition of amyloid beta-peptide, a central event in Alzheimer's disease (AD) pathogenesis, begins several years before the onset of clinical symptoms. Non-invasive detection of AD pathology at this initial stage would facilitate intervention and enhance treatment success. Here, we demonstrate the ability of high field strength MRI to detect regional brain volume reductions and ventricular enlargement in the PS-APP transgenic mouse model of AD more sensitively than histopathologic analysis by unbiased stereology. Moreover, the transverse relaxation time T2, an intrinsic MR parameter thought to reflect impaired cell physiology, was altered substantially in cortical regions containing beta-amyloid but only slightly in cerebellum, which contains little beta-amyloid. MR measures were also minimally altered in mice expressing mutant presenilin-1, which do not deposit beta-amyloid, supporting the view that the MR abnormalities in PS-APP mice are partly related to amyloid beta-peptide deposition. These results set the stage for MRI to aid in the early diagnosis of AD and the evaluation of potential therapies in transgenic animal models and in patients
— id: 97624, year: 2001, vol: 27, page: 1217, stat: Journal Article,

Accelerated A-beta generation in a cell model of Alzheimer's disease-related endosomal-lysomal system upregulation
Mathews PM; Guerra CB; Jiang Y; Kao BH; Dinakar R; Mehta P; Cataldo AM; Nixon RA
Alzheimer's disease: advances in etiology, pathogenesis and therapeutics Chichester: Wiley, 2001,
— id: 2653, year: 2001, vol: , page: 461, stat: Chapter,

The neuronal endosomal-lysosomal system in Alzheimer's disease
Nixon RA; Mathews PM; Cataldo AM
2001 Feb;3(1):97-107, Journal of Alzheimer's Disease
Robust activation of the neuronal lysosomal system and cellular pathways converging on the lysosome, such as the endocytic and autophagic pathways, are prominent neuropathological features of Alzheimer's disease. Disturbances of the neuronal endocytic pathway, which are one of the earliest known intracellular changes occurring in Alzheimer's disease and Down syndrome, provide insight into how beta-amyloidogenesis might be promoted in sporadic Alzheimer's disease, the most prevalent and least well understood form of the disease. Primary lysosomal system dysfunction in inherited disorders is commonly associated with prominent neurological phenotypes and neurodegeneration. New studies now directly implicate lysosomal cathepsins as proteases capable of initiating, as well as executing, cell death programs. These and other studies support the view that the progressive alterations of lysosomal system function in Alzheimer's disease have broad relevance to the neurodegenerative processes occurring during the disease
— id: 32538, year: 2001, vol: 3, page: 97, stat: Journal Article,

In vivo perturbation of lysosomal function promotes neurodegeneration in the PS1m146V/APPPK67ON,M671L mouse model of Alzheimer's disease pathology
Nixon RA; Mathews PM; Cataldo AM; Mohan PS; Schmidt SD; Duff K; Berg M; Marks N; Peterhoff C; Sershen H
Alzheimer's disease: advances in etiology, pathogenesis and therapeutics Chichester: Wiley, 2001,
— id: 2654, year: 2001, vol: , page: , stat: Chapter,

Neurofilaments
Nixon RA; Rao MV
Encyclopedia of molecular medicine Chichester : Wiley, 2001,
— id: 2724, year: 2001, vol: , page: 1589, stat: Chapter,

Experimental aging of the lysosomal system promotes neurodegeneration in the PS/APP mouse model of Alzheimer's disease pathology
Nixon, R. A.; Mathews, P. M.; Cataldo, A. M.; Mohan, P. S.; Marks, N.; Duff, K.; Berg, M.; Schmidt, S. D.; Jacobsen, S. P.; Jiang, Y.; Sershen, H.
2001 ;27(1):925-925, Abstracts (Society for Neuroscience)
The lysosomal system (LS) is markedly activated in vulnerable neuronal populations early in Alzheimer's disease, although lysosomes become less efficient degradative compartments as neurons become more compromised. LS dysfunction, especially altered activity of the lysosomal protease cathepsin D, has been implicated in cell death initiation under various apoptotic conditions in vivo and in vitro. In this study, we observed that cathepsin D content increases nearly 3-fold in the human neocortex during normal aging while lysosomal cysteine protease activities decrease. By contrast, during aging in the mouse, this protease imbalance and other aging-related changes of the LS, such as lipofuscin accumulation, are minimal in these cortical areas. However, when leupeptin (a cysteine protease inhibitor) was infused intraventricularly, an imbalance of cathepsins similar to that in the aging human brain was induced. This was accompanied by changes associated with cell senescence, including ceroid-lipofuscin accumulation and alterations of tau proteolysis. In PSM146L/APPSWE transgenic mice, super-imposition of this aging-related cathepsin imbalance accentuated preexisting LS abnormalities to the level seen in AD brain and also induced neuronal atrophy and neurodegeneration. The minimal degree of 'lysosomal aging' seen in old mice, compared to that in humans, may partly explain the mild neurodegenerative phenotypes in transgenic models of AD pathology. In addition, these studies provide in vivo evidence relating altered lysosomal function to neurodegeneration
— id: 115690, year: 2001, vol: 27, page: 925, stat: Journal Article,

Up-regulation of the lysosomal system in experimental models of neuronal injury: implications for Alzheimer's disease
Adamec E; Mohan PS; Cataldo AM; Vonsattel JP; Nixon RA
2000 ;100(3):663-675, Neuroscience
Previous studies established that the populations of neurons that frequently degenerate in Alzheimer's disease exhibit robust up-regulation of the lysosomal system. In this study, we investigated alterations of the lysosomal system during different forms of experimental injury in rat hippocampal neurons in culture, utilizing a combination of immunocytochemical and biochemical methods. Using triple-label immnocytochemistry for activated caspase-3, fragmentation of DNA and the microtubule-associated protein-2, we characterized treatment paradigms as models of the apoptotic (staurosporine, camptothecin), the oncotic (high-dose menadione, glutamate), and the mixed apoptotic and oncotic (low-dose menadione) pathways of neuronal death. Slowly developing apoptotic or slowly developing mixed apoptotic and oncotic forms of neuronal injury were associated with substantial increases in the number and size of cathepsin D-positive vesicles (late endosomes and mature lysosomes) as determined by immunocytochemistry, and elevated levels of cathepsin D by western blotting. In agreement with our previous findings in Alzheimer's disease, where lysosomal system activation was not restricted to overtly degenerating neurons, up-regulation of this system was also detected quite early during the course of experimental neuronal injury, preceding the development of dystrophic neurites, nuclear segmentation or fragmentation of DNA. These findings implicate lysosomal system activation, both in Alzheimer's disease and in experimental models of neuronal injury, as an important event associated with early stages of neurodegeneration
— id: 24717, year: 2000, vol: 100, page: 663, stat: Journal Article,

Morphological and biochemical assessment of DNA damage and apoptosis in Down syndrome and Alzheimer disease, and effect of postmortem tissue archival on TUNEL
Anderson AJ; Stoltzner S; Lai F; Su J; Nixon RA
2000 Jul-Aug;21(4):511-524, Neurobiology of aging
We have previously shown that Alzheimer disease (AD) brain exhibits terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) for DNA damage and morphological evidence for apoptosis. Down syndrome (DS) is a neurodegenerative disorder that exhibits significant neuropathological parallels with AD. In accordance with these parallels and the need to clarify the mechanism of cell death in DS and AD, we investigated two principal issues in the present study. First, we investigated the hypothesis that TUNEL labeling for DNA damage and morphological evidence for apoptosis is also present in the DS brain. All DS cases employed had a neuropathological diagnosis of AD. Analysis of these cases showed that DS brain exhibits a significant increase in the number of TUNEL-labeled nuclei relative to controls matched for age, Postmortem Delay, and Archival Length, and that a subset of TUNEL-positive nuclei exhibits apoptotic morphologies. We also report that Archival Length in 10% formalin can significantly affect TUNEL labeling in postmortem human brain, and therefore, that Archival Length must be controlled for as a variable in this type of study. Second, we investigated whether biochemical evidence for the mechanism of cell death in DS and AD could be detected. To address this question we employed pulsed-field gel electrophoresis (PFGE) as a sensitive method to evaluate DNA integrity. Although apoptotic oligonucleosomal laddering has not previously been observed in AD, PFGE of DNA from control, DS and AD brain in the present study revealed evidence of high molecular weight DNA fragmentation indicative of apoptosis. This represents biochemical support for an apoptotic mechanism of cell death in DS and AD
— id: 24725, year: 2000, vol: 21, page: 511, stat: Journal Article,

Endocytic pathway abnormalities precede amyloid beta deposition in sporadic Alzheimer's disease and Down syndrome: differential effects of APOE genotype and presenilin mutations
Cataldo AM; Peterhoff CM; Troncoso JC; Gomez-Isla T; Hyman BT; Nixon RA
2000 Jul;157(1):277-286, American journal of pathology
Endocytosis is critical to the function and fate of molecules important to Alzheimer's disease (AD) etiology, including the beta protein precursor (betaPP), amyloid beta (Abeta) peptide, and apolipoprotein E (ApoE). Early endosomes, a major site of Abeta peptide generation, are markedly enlarged within neurons in the Alzheimer brain, suggesting altered endocytic pathway (EP) activity. Here, we show that neuronal EP activation is a specific and very early response in AD. To evaluate endocytic activation, we used markers of internalization (rab5, rabaptin 5) and recycling (rab4), and found that enlargement of rab5-positive early endosomes in the AD brain was associated with elevated levels of rab4 immunoreactive protein and translocation of rabaptin 5 to endosomes, implying that both endocytic uptake and recycling are activated. These abnormalities were evident in pyramidal neurons of the neocortex at preclinical stages of disease when Alzheimer-like neuropathology, such as Abeta deposition, was restricted to the entorhinal region. In Down syndrome, early endosomes were significantly enlarged in some pyramidal neurons as early as 28 weeks of gestation, decades before classical AD neuropathology develops. Markers of EP activity were only minimally influenced by normal aging and other neurodegenerative diseases studied. Inheritance of the epsilon4 allele of APOE, however, accentuated early endosome enlargement at preclinical stages of AD. By contrast, endosomes were normal in size at advanced stages of familial AD caused by mutations of presenilin 1 or 2, indicating that altered endocytosis is not a consequence of Abeta deposition. These results identify EP activation as the earliest known intraneuronal change to occur in sporadic AD, the most common form of AD. Given the important role of the EP in Abeta peptide generation and ApoE function, early endosomal abnormalities provide a mechanistic link between EP alterations, genetic susceptibility factors, and Abeta generation and suggest differences that may be involved in Abeta generation and beta amyloidogenesis in subtypes of AD
— id: 24726, year: 2000, vol: 157, page: 277, stat: Journal Article,

A beta peptide immunization reduces behavioural impairment and plaques in a model of Alzheimer's disease
Janus C; Pearson J; McLaurin J; Mathews PM; Jiang Y; Schmidt SD; Chishti MA; Horne P; Heslin D; French J; Mount HT; Nixon RA; Mercken M; Bergeron C; Fraser PE; St George-Hyslop P; Westaway D
2000 Dec 21-28;408(6815):979-982, Nature
Much evidence indicates that abnormal processing and extracellular deposition of amyloid-beta peptide (A beta), a proteolytic derivative of the beta-amyloid precursor protein (betaAPP), is central to the pathogenesis of Alzheimer's disease (reviewed in ref. 1). In the PDAPP transgenic mouse model of Alzheimer's disease, immunization with A beta causes a marked reduction in burden of the brain amyloid. Evidence that A beta immunization also reduces cognitive dysfunction in murine models of Alzheimer's disease would support the hypothesis that abnormal A beta processing is essential to the pathogenesis of Alzheimer's disease, and would encourage the development of other strategies directed at the 'amyloid cascade'. Here we show that A beta immunization reduces both deposition of cerebral fibrillar A beta and cognitive dysfunction in the TgCRND8 murine model of Alzheimer's disease without, however, altering total levels of A beta in the brain. This implies that either a approximately 50% reduction in dense-cored A beta plaques is sufficient to affect cognition, or that vaccination may modulate the activity/abundance of a small subpopulation of especially toxic A beta species
— id: 24772, year: 2000, vol: 408, page: 979, stat: Journal Article,

Brain expression of presenilins in sporadic and early-onset, familial Alzheimer's disease
Mathews PM; Cataldo AM; Kao BH; Rudnicki AG; Qin X; Yang JL; Jiang Y; Picciano M; Hulette C; Lippa CF; Bird TD; Nochlin D; Walter J; Haass C; Levesque L; Fraser PE; Andreadis A; Nixon RA
2000 Oct;6(10):878-891, Molecular medicine
BACKGROUND: Mutations in the presenilin proteins cause early-onset, familial Alzheimer's disease (FAD). MATERIALS AND METHODS: We characterized the cellular localization and endoproteolysis of presenilin 2 (PS2) and presenilin 1 (PS1) in brains from 25 individuals with presenilin-mutations causing FAD, as well as neurologically normal individuals and individuals with sporadic Alzheimer's disease (AD). RESULTS: Amino-terminal antibodies to both presenilins predominantly decorated large neurons. Regional differences between the broad distributions of the two presenilins were greatest in the cerebellum, where most Purkinje cells showed high levels of only PS2 immunoreactivity. PS2 endoproteolysis in brain yielded multiple amino-terminal fragments similar in size to the PS1 amino-terminal fragments detected in brain. In addition, two different PS2 amino-terminal antibodies also detected a prominent 42 kDa band that may represent a novel PS2 form in human brain. Similar to PS1 findings, neither amino-terminal nor antiloop PS2 antibodies revealed substantial full-length PS2 in brain. Immunocytochemical examination of brains from individuals with the N141I PS2 mutation or eight different PS1 mutations, spanning the molecule from the second transmembrane domain to the large cytoplasmic loop domain, revealed immunodecoration of no senile plaques and only neurofibrillary tangles in the M139I PS1 mutation stained with PS1 antibodies. CONCLUSIONS: Overall presenilin expression and the relative abundance of full-length and amino-terminal fragments in presenilin FAD cases were similar to control cases and sporadic AD cases. Thus, accumulation of full-length protein or other gross mismetabolism of neither PS2 nor PS1 is a consequence of the FAD mutations examined
— id: 25504, year: 2000, vol: 6, page: 878, stat: Journal Article,

A "protease activation cascade" in the pathogenesis of Alzheimer's disease
Nixon RA
2000 ;924(4):117-131, Annals of the New York Academy of Sciences
A pathway to Alzheimer's disease (AD) relevant to sporadic AD pathogenesis is described that involves the early and progressive activation of proteolytic systems including, but not limited to, the calpain-calpastatin and endosomal-lysosomal systems. Activation of these proteolytic systems is initiated by normal brain aging and is propelled by the genetic and environmental factors known to increase AD risk. Recent studies show how cathepsins and calpains, acting directly or indirectly through other proteolytic pathways and cellular signaling cascades, may promote beta-amyloidogenesis, neurofibrillary pathology, as well as mediate neurodegeneration in AD
— id: 25503, year: 2000, vol: 924, page: 117, stat: Journal Article,

The endosomal-lysosomal system of neurons in Alzheimer's disease pathogenesis: a review
Nixon RA; Cataldo AM; Mathews PM
2000 Oct;25(9-10):1161-1172, Neurochemical research
A prominent feature of brain pathology in Alzheimer's disease is a robust activation of the neuronal lysosomal system and major cellular pathways converging on the lysosome, namely, endocytosis and autophagy. Recent studies that identify a disturbance of the endocytic pathway as one of the earliest known manifestation of Alzheimer's disease provide insight into how beta-amyloidogenesis might be promoted in sporadic Alzheimer's disease, the most prevalent and least well understood form of the disease. Primary lysosomal dysfunction has historically been linked to neurodegeneration. New data now directly implicate cathepsins as proteases capable of initiating, as well as executing, cell death programs in certain pathologic states. These and other studies support the view that the progressive alterations of lysosomal function observed during aging and Alzheimer's disease contribute importantly to the neurodegenerative process in Alzheimer's disease
— id: 24724, year: 2000, vol: 25, page: 1161, stat: Journal Article,

The pathobiology of tau protein in neurodegenerative diseases
Nixon, RA; Duff, K; Matsuoka, Y
2000 APR 15 ;47(8):7S-7S, Biological psychiatry
— id: 54653, year: 2000, vol: 47, page: 7S, stat: Journal Article,

Local control of neurofilament accumulation during radial growth of myelinating axons in vivo. Selective role of site-specific phosphorylation
Sanchez I; Hassinger L; Sihag RK; Cleveland DW; Mohan P; Nixon RA
2000 Nov 27;151(5):1013-1024, Journal of cell biology
The accumulation of neurofilaments required for postnatal radial growth of myelinated axons is controlled regionally along axons by oligodendroglia. Developmentally regulated processes previously suspected of modulating neurofilament number, including heavy neurofilament subunit (NFH) expression, attainment of mature neurofilament subunit stoichiometry, and expansion of interneurofilament spacing cannot be primary determinants of regional accumulation as we show each of these factors precede accumulation by days or weeks. Rather, we find that regional neurofilament accumulation is selectively associated with phosphorylation of a subset of Lys-Ser-Pro (KSP) motifs on heavy neurofilament subunits and medium-size neurofilament subunits (NFMs), rising >50-fold selectively in the expanding portions of optic axons. In mice deleted in NFH, substantial preservation of regional neurofilament accumulation was accompanied by increased levels of the same phosphorylated KSP epitope on NFM. Interruption of oligodendroglial signaling to axons in Shiverer mutant mice, which selectively inhibited this site-specific phosphorylation, reduced regional neurofilament accumulation without affecting other neurofilament properties or aspects of NFH phosphorylation. We conclude that phosphorylation of a specific KSP motif triggered by glia is a key aspect of the regulation of neurofilament number in axons during axonal radial growth
— id: 24723, year: 2000, vol: 151, page: 1013, stat: Journal Article,

DNA strand breaks in Alzheimer's disease
Adamec E; Vonsattel JP; Nixon RA
1999 Dec 4;849(1-2):67-77, Brain research
The goal of this study was to investigate the presence of DNA damage in Alzheimer's disease (AD) utilizing independent assays for three different types of DNA strand breaks. Sections from hippocampi of AD brains, brains with Alzheimer neurofibrillary changes (Ch) from non-demented individuals, and controls (C) were labeled with (1) the TUNEL assay to identify blunt-ended and 3' protruding termini of breaks in double-stranded DNA, (2) the Klenow assay to detect single-stranded and double-stranded breaks with protruding 5' termini, and (3) the Apostain assay which utilizes a monoclonal antibody to single-stranded DNA and is based on the decreased stability of apoptotic DNA to thermal denaturation caused by DNA breaks. The highest incidence of nuclei positive for either molecular form of DNA strand breaks was detected in AD, followed by Ch, and controls (C). In either AD and Ch, the incidence of TUNEL- or Klenow-positive nuclei did not differ significantly, but was higher than the incidence of Apostain-positive nuclei. With all three assays, the highest incidence of positive nuclei was in the molecular layer of CA1. In the majority of nuclei positive for either the Klenow or the Apostain assay, the product of the labeling reaction was localized either to the periphery of the nucleus or to distinct clumps of chromatin (or both). With the TUNEL assay, the majority of positive nuclei were diffusely labeled. In both AD and Ch, the individual positive nuclei were labeled with both the Klenow and the TUNEL assays. The results indicate high incidence of nuclei with either double-stranded or single-stranded DNA breaks in AD, which, for the forms detectable with the Klenow or TUNEL assays, were colocalized
— id: 24727, year: 1999, vol: 849, page: 67, stat: Journal Article,

Isoform-specific translocation of protein kinase C following glutamate administration in primary hippocampal neurons
Buchner K; Adamec E; Beermann ML; Nixon RA
1999 Feb 5;64(2):222-235, Brain research. Molecular brain research
High concentrations of glutamate, the major excitatory neurotransmitter in the mammalian brain, lead to intracellular calcium overload resulting in excitotoxic damage and death of neurons. Since protein kinase C (PKC) is involved in neuronal degeneration resulting from cerebral ischemia and from glutamate excitotoxicity, we investigated the effect of glutamate on changes in the cellular distribution of various PKC isoforms in cultured hippocampal neurons in comparison with the effects elicited by the PKC activator phorbol ester. Out of the expressed PKC isoforms alpha, gamma,varepsilon,zeta and lambda only the conventional isoforms PKC alpha and gamma responded to glutamate. Using subcellular fractionation and Western blotting with isoform-specific antibodies and immunocytochemical localization with confocal laser scanning microscopy, we observed that phorbol ester and glutamate have different effects on PKC isoform redistribution: Whereas phorbol ester resulted in translocation of PKC alpha and PKC gamma toward a membrane fraction, the glutamate-mediated rise in intracellular calcium concentration induced a translocation mainly toward a detergent-insoluble, cytoskeletal fraction. Immunocytochemical analysis revealed an isoform-specific translocation following glutamate treatment: PKC gamma was translocated mainly to cytoplasmic, organelle-like structures, whereas PKC alpha redistributed to the plasma membrane and into the cell nucleus. The latter result is of special interest, as it indicates that nuclear PKC may play a role in processes of excitotoxic cell damage
— id: 24729, year: 1999, vol: 64, page: 222, stat: Journal Article,

APOE genotype and gender effects on Alzheimer disease in 100 adults with Down syndrome
Lai F; Kammann E; Rebeck GW; Anderson A; Chen Y; Nixon RA
1999 Jul 22;53(2):331-336, Neurology
BACKGROUND: Alzheimer disease (AD) neuropathology is present in Down syndrome (DS) after age 35, but dementia onset varies from ages 40 to 70 years. Because of small sample sizes and nonuniform determination of dementia, previous studies produced differing results on the influence of APOE subtypes on AD in DS. OBJECTIVE: To determine the influence of the APOE genotype and gender on development of AD in adults with DS to ascertain similarities with AD in the general population. METHODS: A total of 100 adults with DS (ages 35 to 79 years), almost all of whom were longitudinally assessed by neurologists, underwent APOE genotyping. Dementia onset was determined using criteria applied from the Tenth International Classification of Mental and Behavioral Disorders. This cohort contains the largest number of DS subjects with dementia (n = 57) in a single study, thus increasing reliability of the results. RESULTS: The epsilon2 allele frequency was 4% in those with dementia versus 13% in those without dementia (p = 0.03); epsilon4 allele frequency was 18% in those with dementia versus 13% in those without dementia (p = 0.45). Using APOE-epsilon3/3 as the reference group, the risk ratio for the development of AD at any given time was 0.34 for the APOE-epsilon2/3 group (p = 0.04) and 1.44 for the APOE-epsilon(3/4,4/4) group (p = 0.25). Women were 1.77 times as likely to dement as men at any given point in time (p = 0.04). CONCLUSIONS: The epsilon2 allele confers a protective effect, and women with DS have an increased risk for AD, as in the general population. In this sample, epsilon4 does not confer a significantly increased risk for AD in DS
— id: 24728, year: 1999, vol: 53, page: 331, stat: Journal Article,

Developmental expression of wild-type and mutant presenilin-1 in hippocampal neurons from transgenic mice: evidence for novel species-specific properties of human presenilin-1
Levesque L; Annaert W; Craessaerts K; Mathews PM; Seeger M; Nixon RA; Van Leuven F; Gandy S; Westaway D; St George-Hyslop P; De Strooper B; Fraser PE
1999 Aug;5(8):542-554, Molecular medicine
Presenilins 1 (PS1) and 2 (PS2) are multispanning transmembrane proteins associated with familial Alzheimer disease (FAD). They are developmentally regulated, being expressed at highest levels during neuronal differentiation and are sustained at a lower level throughout life. We investigated the distribution and metabolism of endogenous murine PS1 as well as human wild-type (wtPS1) and the familial AD Met146Leu (M146L) mutant presenilins in dissociated cultures of hippocampal neurons derived from control and transgenic mice. We found that the PS1 endoproteolytic fragments and, to a lesser extent, the full-length protein, were expressed as early as day 3 post-plating. Both species increased until the cells were fully differentiated at day 12. Confocal microscopy revealed that presenilin is present in the Golgi and endoplasmic reticulum and, as in punctate, vesicle-like structures within developing neurites and growth cones. Using a human-specific PS1 antibody, we were able to independently examine the distribution of the transgenic protein which, although similar to the endogenous, showed some unique qualities. These included (i) some heterogeneity in the proteolytic fragments of human PS1; (ii) significantly reduced levels of full-length human PS1, possibly as a result of preferential processing; and (iii) a more discrete intracellular distribution of human PS1. Colocalization with organelle-specific proteins revealed that PS1 was located in a diffuse staining pattern in the MAP2-positive dendrites and in a punctate manner in GAP43-positive axons. PS1 showed considerable overlap with GAP43, particularly at the growth cones. Similar patterns of PS1 distribution were detected in cultures derived from transgenic animals expressing human wild-type or mutant presenilins. The studies demonstrate that mutant presenilins are not grossly different in their processing or distribution within cultured neurons, which may represent more physiological models as compared to transfection systems. Our data also suggest that the molecular pathology associated with PS1 mutations results from subtle alterations in presenilin function, which can be further investigated using these transgenic neuronal cell culture models
— id: 24709, year: 1999, vol: 5, page: 542, stat: Journal Article,

Psychopathology
Meissner, W. W; Vaillant, George E; Nemiah, John C; Otto, Michael W; Pollack, Mark H; Jenike, Michael A; Rosenbaum, Jerrold F; Tsuang, Ming T; Faraone, Stephen V; Green, Alan I; Rothschild, Anthony J; Gunderson, Anthony G; Nixon, Ralph A; Albert, Marilyn S; Rogers, Malcolm S; Fricchione, Gregory; Reich, Peter; Grinspoon, Lester; Bakalar, James; Weiss, Roger; Herzog, David B; Becker, Anne E
The Harvard guide to psychiatry Cambridge, MA, US: Belknap Press/Harvard University Press. xiv, 856pp,
(from the book) 'Theories of Personality' / W. W. Meissner / 'Defense Mechanisms' / George E. Vaillant / 'The Psychodynamic Basis of Psychopathology' / John C. Nemiah / 'Anxiety Disorders and Their Treatment' / Michael W. Otto, Mark H. Pollack, Michael A. Jenike and Jerrold F. Rosenbaum / 'Schizophrenia and Other Psychotic Disorders' / Ming T. Tsuang, Stephen V. Faraone and Alan I. Green / 'Mood Disorders' / Anthony J. Rothschild / 'Personality Disorders' / John G. Gunderson / 'Disorders of Cognition' / Ralph A. Nixon and Marilyn S. Albert / 'Psychosomatic Medicine and Consultation-Liaison Psychiatry' / Malcolm P. Rogers, Gregory Fricchione and Peter Reich / 'Substance Use Disorders' / Lester Grinspoon, James Bakalar and Roger Weiss / 'Eating Disorders' / David B. Herzog and Anne E. Becker
— id: 2725, year: 1999, vol: , page: 171, stat: Chapter,

Neurofilaments
Nixon RA
Encyclopedia of molecular biology New York : Wiley, 1999,
— id: 2658, year: 1999, vol: , page: 1589, stat: Chapter,

Disorders of cognition
Nixon RA; Albert MS
Harvard guide to modern psychiatry Cambridge MA : Belknap Press of Harvard University Press, 1999,
— id: 4407, year: 1999, vol: , page: 328, stat: Chapter,

Calpains in the pathogenesis of Alzheimer's disease
Nixon RA; Mohan PS
Calpain: pharmacology and toxicology of calcium-dependent protease Philadelphia : Taylor & Francis, 1999,
— id: 2660, year: 1999, vol: , page: 267, stat: Chapter,

Serine-23 is a major protein kinase A phosphorylation site on the amino-terminal head domain of the middle molecular mass subunit of neurofilament proteins
Sihag RK; Jaffe H; Nixon RA; Rong X
1999 Feb;72(2):491-499, Journal of neurochemistry
We have shown previously that phosphate groups on the amino-terminal head domain region of the middle molecular mass subunit of neurofilament proteins (NF-M) are added by second messenger-dependent protein kinases. Here, we have identified Ser23 as a specific protein kinase A phosphorylation site on the native NF-M subunit and on two synthetic peptides, S1 (14RRVPTETRSSF24) and S2 (21RSSFSRVSGSPSSGFRSQSWS41), localized within the amino-terminal head domain region. Ser23 was identified as a phosphorylation site on the 32P-labeled alpha-chymotryptic peptide that carried >80% of the 32P-phosphates incorporated into the NF-M subunit by protein kinase A. The synthetic peptides S1 and S2 were phosphorylated 18 and two times more efficiently by protein kinase A than protein kinase C, respectively. Neither of the peptides was phosphorylated by casein kinase II. The sequence analyses of the chemically modified phosphorylated serine residues showed that Ser23 was the major site of phosphorylation for protein kinase A on both S1 and S2 peptides. Low levels of incorporation of 32P-phosphates into Ser22, Ser28, and Ser32 by protein kinase A were also observed. Protein kinase C incorporated 32P-phosphates into Ser22, Ser23, Ser25, Ser28, Ser32, and a threonine residue, but none of these sites could be assigned as a major site of phosphorylation. Analyses of the phosphorylated synthetic peptides by liquid chromatography-tandem mass spectrometry also showed that protein kinase A phosphorylated only one site on peptide S1 and that ions with up to four phosphates were detected on peptide S2. Analysis of the data from the tandem ion trap mass spectrometry by using the computer program PEPSEARCH did not unequivocally identify the specific sites of phosphorylation on these serine-rich peptides. Our data suggest that Ser23 is a major protein kinase A-specific phosphorylation site on the amino-terminal head region of the NF-M subunit. Phosphorylation of Ser23 on the NF-M subunit by protein kinase A may play a regulatory role in neurofilament assembly and/or the organization of neurofilaments in the axon
— id: 24730, year: 1999, vol: 72, page: 491, stat: Journal Article,

Calpain I activation in rat hippocampal neurons in culture is NMDA receptor selective and not essential for excitotoxic cell death
Adamec E; Beermann ML; Nixon RA
1998 Feb;54(1):35-48, Brain research. Molecular brain research
Administration of glutamate (100 microM) to primary cultures of rat hippocampal neurons for 1 h led to calpain I activation as determined by monitoring the extent of spectrin breakdown with the antibodies designed to specifically recognize the calpain I-mediated spectrin breakdown products. Based on the studies with subtype selective antagonists of glutamate receptors, glutamate caused calpain I activation specifically through the activation of the NMDA receptor. In parallel experiments, the magnitude and the temporal profiles of Ca2+ rise were determined by Fura-2 microfluorimetry. Ca2+ influx through voltage-sensitive Ca2+ channels, even though leading to substantial Ca2+ rise, did not by itself activate calpain I. These results indicate that for calpain I activation, the source of Ca1+ influx is more important than the magnitude of Ca2+ rise. Glutamate-mediated calpain I activation was fully blocked by preincubation (30 min) of the cultures with calpain inhibitor I, calpain inhibitor II, or calpeptin (all 10 microM). The presence of calpain inhibitors did not, however, in any way ameliorate the massive excitotoxicity resulting from 16 h exposure to glutamate, indicating that calpain I activation and excitotoxicity are not causally related events. Similarly, preincubation with any of the tested calpain inhibitors was detrimental to the clearance of neuritic from a 10-min exposure to glutamate. Additionally, the presence of calpain inhibitors was detrimental to the clearance of neuritic varicosities resulting from a short-term sublethal exposure to glutamate, suggesting that a physiological level of calpain I activation might actually play an important homeostatic role in the restoration of normal cytoskeletal organization
— id: 25147, year: 1998, vol: 54, page: 35, stat: Journal Article,

Developmental regulation of the recovery process following glutamate-induced calcium rise in rodent primary neuronal cultures
Adamec E; Didier M; Nixon RA
1998 Jun 15;108(1-2):101-110, Brain research. Developmental brain research
CNS neurons exhibit a profound, maturation-dependent increase in the vulnerability to injury. Little is, however, known about the cellular mechanisms involved. This study investigated the developmental influence on the ability to recover the resting concentration of free cytoplasmic Ca2+ ([Ca2+]i) following stimulation with 100 microM glutamate in hippocampal and cerebellar granule cells in culture. Primary neurons were exposed to glutamate for either 1 min or 10 min. Hippocampal neurons were evaluated at 7, 12-14, and 17-19 days in vitro (DIV), and cerebellar granule cells were tested at 8-9 or 15-16 DIV. In hippocampal neurons, either an increased age in culture or longer drug exposure were both associated with less efficient [Ca2+]i recovery. Additionally, for both 1-min and 10-min drug exposure, increased age in culture was the primary determinant of the development of secondary [Ca2+]i destabilization followed by a very variable recovery patterns. Similar to hippocampal neurons, older cerebellar granule cells also recovered less efficiently from glutamate-mediated [Ca2+]i rise. The difference in the extent of recovery was not directly influenced by the magnitude of the [Ca2+]i rise, since cerebellar granule cells recovered from both high or low [Ca2+]i rise with similar kinetic profiles. Overall, the results presented in this study implicate the age in culture as an important influencing factor of both the less efficient recovery from glutamate-induced Ca2+ load and the development of secondary [Ca2+]i destabilizations. The progressive, maturation-dependent, decrease in the ability to recover from Ca2+ load might represent a potentially important mechanism contributing to the increased vulnerability of fully developed neurons to injury
— id: 25175, year: 1998, vol: 108, page: 101, stat: Journal Article,

The proteolytic fragments of the Alzheimer's disease-associated presenilin-1 form heterodimers and occur as a 100-150-kDa molecular mass complex
Capell A; Grunberg J; Pesold B; Diehlmann A; Citron M; Nixon R; Beyreuther K; Selkoe DJ; Haass C
1998 Feb 6;273(6):3205-3211, Journal of biological chemistry
Mutations in the presenilin (PS) genes are linked to early onset familial Alzheimer's disease (FAD). PS-1 proteins are proteolytically processed by an unknown protease to two stable fragments of approximately 30 kDa (N-terminal fragment (NTF)) and approximately 20 kDa (C-terminal fragment (CTF)) (Thinakaran, G., Borchelt, D. R., Lee, M. K., Slunt, H. H., Spitzer, L., Kim, G., Ratovitsky, T., Davenport, F., Nordstedt, C., Seeger, M., Hardy, J., Levey, A. I., Gandy, S. E., Jenkins, N. A., Copeland, N. G., Price, D. L., and Sisodia, S. S. (1996) Neuron 17, 181-190). Here we show that the CTF and NTF of PS-1 bind to each other. Fractionating proteins from 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid-extracted membrane preparations by velocity sedimentation reveal a high molecular mass SDS and Triton X-100-sensitive complex of approximately 100-150 kDa. To prove if both proteolytic fragments of PS-1 are bound to the same complex, we performed co-immunoprecipitations using multiple antibodies specific to the CTF and NTF of PS-1. These experiments revealed that both fragments of PS-1 occur as a tightly bound non-covalent complex. Upon overexpression, unclipped wild type PS-1 sediments at a lower molecular weight in glycerol velocity gradients than the endogenous fragments. In contrast, the non-cleavable, FAD-associated PS-1 Deltaexon 9 sediments at a molecular weight similar to that observed for the endogenous proteolytic fragments. This result may indicate that the Deltaexon 9 mutation generates a mutant protein that exhibits biophysical properties similar to the naturally occurring PS-1 fragments. This could explain the surprising finding that the Deltaexon 9 mutation is functionally active, although it cannot be proteolytically processed (Baumeister, R., Leimer, U., Zweckbronner, I., Jakubek, C., Grunberg, J., and Haass, C. (1997) Genes & Function 1, 149-159; Levitan, D., Doyle, T., Brousseau, D., Lee, M., Thinakaran, G., Slunt, H., Sisodia, S., and Greenwald, I. (1996) Proc. Natl. Acad. Sci. U. S. A. 93, 14940-14944). Formation of a high molecular weight complex of PS-1 composed of both endogenous PS-1 fragments may also explain the recent finding that FAD-associated mutations within the N-terminal portion of PS-1 result in the hyperaccumulation not only of the NTF but also of the CTF (Lee, M. K., Borchelt, D. R., Kim, G., Thinakaran, G., Slunt, H. H., Ratovitski, T., Martin, L. J., Kittur, A., Gandy, S., Levey, A. I., Jenkins, N., Copeland, N., Price, D. L., and Sisodia, S. S. (1997) Nat. Med. 3, 756-760). Moreover, these results provide a model to understand the highly regulated expression and processing of PS proteins
— id: 7520, year: 1998, vol: 273, page: 3205, stat: Journal Article,

Altered gene expression for calpain/calpastatin system in motor neuron degeneration (Mnd) mutant mouse brain and spinal cord
Li J; Nixon R; Messer A; Berman S; Bursztajn S
1998 Jan;53(1-2):174-186, Brain research. Molecular brain research
The calcium-activated neutral proteases (CANP, calpains) have been implicated in both acute and chronic neurodegenerative processes. In the present study, we analyzed the in situ mRNA expression of calpain I and II and their endogenous inhibitor, calpastatin, in the motor neuron degeneration (Mnd) mutant mouse, which exhibits progressive dysfunction of the spinal cord and brain. As the disease progresses, the mutants show increasingly pronounced motor abnormalities which coincide with swelling of the spinal motor neurons, neocortex, hippocampal CA regions and cerebellar Purkinje cells. In situ hybridization studies show that the Mnd mice have a significantly higher level of calpain I, calpain II and calpastatin than the congenic controls in the following brain regions and cell types: hippocampal CA3 region, pyramidal cells, cerebellar Purkinje cells and spinal cord motor neurons. However, no differences in calpain or calpastatin mRNA levels are observed in glial and cerebellar granule cells of Mnd and control mice. Western blots and competitive RT-PCR analyses of brain and spinal cord homogenates are confirmative. Such altered gene expression in specific cell types of brain and spinal cord suggests the involvement of the calpain/calpastatin system
— id: 25173, year: 1998, vol: 53, page: 174, stat: Journal Article,

Dynamic behavior and organization of cytoskeletal proteins in neurons: reconciling old and new findings
Nixon RA
1998 Oct;20(10):798-807, Bioessays
Neurons are faced with the formidable challenge of having to assemble most of their cytoskeleton at axonal sites far removed from the protein synthetic machinery in the perikaryon. Their achievement seems all the more impressive now that new evidence is showing that the cytoskeleton may vary markedly in size and composition along the axon and exhibit striking regional specializations. Further complexity is contributed to this structure by a growing assortment of cytoskeleton-associated proteins that cross-link the various fibrous elements and stabilize cytoskeletal architecture. Much of the dynamic behavior of cytoskeletal proteins and polymers in axons is locally controlled. This regulation involves, in part, a system of protein kinases and phosphatases modulated by both intercellular and intracellular signals. Conceptual models of slow axonal transport have evolved to accommodate these new findings
— id: 7713, year: 1998, vol: 20, page: 798, stat: Journal Article,

The slow axonal transport debate
Nixon RA
1998 Mar;8(3):100-100, Trends in cell biology
— id: 25179, year: 1998, vol: 8, page: 100, stat: Journal Article,

The slow axonal transport of cytoskeletal proteins
Nixon RA
1998 Feb;10(1):87-92, Current opinion in cell biology
Once presumed to be relatively uniform, the axonal cytoskeleton can vary markedly in size and composition along its length. New studies emphasize the interactiveness of neurofilaments and identify a family of cytoskeletal proteins that may cross-link the various cytoskeletal polymers of the axon, and anchor this network to the membrane skeleton. These and other findings support a model of the axonal cytoskeleton as a stationary but dynamic structure. Current evidence continues to support the possibility that axonally transported polymers/oligomers and/or monomers may serve as precursors to the cytoskeleton in different situations. Although the motors for slow transport of cytoskeletal proteins remain elusive, possible candidates are emerging
— id: 7712, year: 1998, vol: 10, page: 87, stat: Journal Article,

Immunocytochemistry of formalin-fixed human brain tissues: microwave irradiation of free-floating sections
Shiurba RA; Spooner ET; Ishiguro K; Takahashi M; Yoshida R; Wheelock TR; Imahori K; Cataldo AM; Nixon RA
1998 Jan;2(2):109-119, Brain research protocols
Formalin fixation, the chemical process in which formaldehyde binds to cells and tissues, is widely used to preserve human brain specimens from autolytic decomposition. Ultrastructure of cellular and mitochondrial membranes is markedly altered by vesiculation, but this does not interfere with diagnostic evaluation of neurohistology by light microscopy. Serious difficulties are encountered, however, when immunocytochemical staining is attempted. Antigens that are immunoreactive in unfixed frozen sections and protein extracts appear to be concealed or destroyed in formalin-fixed tissues. In dilute aqueous solution, formaldehyde is in equilibrium with methylene glycol and its polymeric hydrates, the balance by far in favor of methylene glyco. Carbonylic formaldehyde is a reactive electrophilic species well known for crosslinking functional groups in tissue proteins, nucleic acids, and polysaccharides. Some of its methylene crosslinks are readily hydrolyzed. Others are stable and irreversible. During immunostaining reactions, intra- and inter-molecular links between macromolecules limit antibody permeation of tissue sections, alter protein secondary structure, and reduce accessibility of antigenic determinants . Accordingly, immunoreactivity is diminished for many antigens. Tissues are rapidly penetrated by methylene glycol, but formaldehyde binding to cellular constituents is relatively slow, increasing progressively until equilibrium is reached. In addition, prolonged storage in formalin may result in acidification of human brain specimens. Low pH favors dissociation of methylene glycol into formaldehyde, further reducing both classical staining and antigen detectability. Various procedures have been devised to counter the antigen masking effects of formaldehyde. Examples include pretreatment of tissue sections with proteases, formic acid, or ultrasound. Recently, heating of mounted sections in ionic salt solution by microwave energy was found to restore many antigens. Theory and practice of microwave antigen retrieval are covered extensively in the handbook Microwave Cookbook for Microscopists. A concise overview of microwave methods in the neurosciences has been published, and clinical applications have been reviewed. In this context, it should be noted that fresh tissues may be stabilized for immunocytochemistry by reversible, non-chemical binding processes such as cryosectioning after microwave treatment and freeze-drying. Thus, it may be possible to enhance immunostaining for some antigens by microwave irradiation of unfixed as well as fixed specimens. Parameters to be optimized for microwave retrieval of specific antigens include temperature, irradiation time, tissue buffer composition, salt concentration, and pH. Temperature, irradiation time, and pH are key variables. With this in mind, an optimal method was developed for retrieval of a wide variety of antigens in human brain tissues. Typical microwave protocols employ elevated temperatures that may reach 100 degrees C, where denaturation causes irreversible uncoiling and disruption of protein secondary and tertiary structures. Under these conditions, stable covalent bonds securing methylene crosslinks between polypeptides remain intact, but more reactive links formed by Schiff bases may be hydrolyzed. Resultant conformational changes presumably expose buried loops of continuous amino acids and protruding regions, increasing accessibility of their epitopes. Protein denaturation seems to be a reasonable explanation for the effects of microwaves on antigen retrieval. This idea is supported by the observation that denaturing solutions such as 6 M urea increase immunoreactivity of some antigens. Still, the molecular basis of these effects remains unresolved, in part due to the complex chemistry of formaldehyde reactions with tissue constituents. Indeed, some methylene bridges between similar groups such as NH2 and NH may be hydrolyzed by washing fixed tissues in distilled wa
— id: 25148, year: 1998, vol: 2, page: 109, stat: Journal Article,

Neuropathology of preclinical and clinical late-onset Alzheimer's disease
Troncoso JC; Cataldo AM; Nixon RA; Barnett JL; Lee MK; Checler F; Fowler DR; Smialek JE; Crain B; Martin LJ; Kawas CH
1998 May;43(5):673-676, Annals of neurology
We report on the neuropathological examinations of a 74-year-old woman with Alzheimer's disease (AD) and of her 47-year-old nondemented daughter. The brain of the mother showed fully developed pathological changes of AD. By contrast, the brain of the daughter revealed only perineuronal deposition of diffuse amyloid in cerebral cortex and striking abnormalities of the endosomal-lysosomal system, without neurofibrillary, glial, or microglial changes. These observations suggest that amyloid deposition and endosomal-lysosomal changes are early events in late-onset AD and that they may precede the onset of dementia by several decades
— id: 25174, year: 1998, vol: 43, page: 673, stat: Journal Article,

Caspase-mediated fragmentation of calpain inhibitor protein calpastatin during apoptosis
Wang KK; Posmantur R; Nadimpalli R; Nath R; Mohan P; Nixon RA; Talanian RV; Keegan M; Herzog L; Allen H
1998 Aug 15;356(2):187-196, Archives of biochemistry & biophysics. ABB
Two cysteine protease families (caspase and calpain) participate in apoptosis. Here we report that the endogenous calpain inhibitor calpastatin is fragmented by caspase(s) to various extents during early apoptosis in two cell types. In anti-fas or staurosporine-treated Jurkat T-cells, the high-molecular-weight form (HMW) of calpastatin (apparent Mr 110 K) was extensively degraded to immunoreactive fragments of Mr 75 K and 30 K In apoptotic SH-SY5Y human neuroblastoma cells, HMW calpastatin was degraded to a major immunoreactive fragment of 75 K. In both cell types, fragmentation of HMW calpastatin was blocked by a caspase-specific inhibitor carbobenzoxy-Asp-CH2OC(O)-2,6-dichlorobenzene. In vitro translated HMW calpastatin was sensitive to proteolysis by recombinant caspase-1, -3, and -7. By contrast, in vitro translated LMW calpastatin (which lacks domains L and I) was cleaved into multiple fragments only by caspase-1 and was relatively resistant to caspase-3, -7, and other caspases tested. Consistently with that, purified erythroid LMW calpastatin was also highly susceptible to caspase-1 digestion. Recombinant human calpastatin spanning domain I through III (CAST(DI-III)) was found cleaved by caspase-1 at at least three sites, located in either the A or the C helix of domains I and III (ALDD137*L, LSSD203*F and ALAD404*S), while only a single site (ALDD137*L) was cleaved by caspase-3. These findings suggest that both HMW and LMW calpastatins are more vulnerable to caspase-1 than to caspase-3. Surprisingly, both erythroid LMW calpastatin and recombinant CAST(DI-III) fragmented by caspase-1 suffered only a less than twofold reduction of inhibitory activity toward calpain. We propose that the proteolysis of calpastatin in early apoptosis might have yet unidentified effects on the cross-talk between the two protease systems.
— id: 7948, year: 1998, vol: 356, page: 187, stat: Journal Article,

Acute rise in the concentration of free cytoplasmic calcium leads to dephosphorylation of the microtubule-associated protein tau
Adamec E; Mercken M; Beermann ML; Didier M; Nixon RA
1997 May 16;757(1):93-101, Brain research
The objective of this study was to asses the response of the microtubule-associated protein tau to acute rise in the concentration of free cytoplasmic calcium ([Ca2+]i) in rat cortical neurons and mouse cerebellar granule cells in culture. One-hour exposure to glutamate (100 microM), N-methyl-D-aspartate (100 microM), KCl (50 mM), and ionomycin (5 microM) led to tau protein dephosphorylation as indicated by an appearance of additional faster moving bands on Western immunoblots with a phosphorylation-independent antibody and an increase in the tau-1 immunoreactivity associated with the appearance of an additional faster moving band. Lowering the extracellular concentration of Ca2+ to less than 1 microM fully prevented the drug-induced tau protein dephosphorylation indicating a dependence on Ca2+ influx from the extracellular environment. Administration of okadaic acid (inhibitor of phosphatase 1/2A) simultaneously with the above mentioned drugs decreased the drug-mediated dephosphorylation. Pre-incubation with okadaic acid fully prevented the dephosphorylation. Treatment with cypermethrin (inhibitor of phosphatase 2B) was without effect when administered either alone, simultaneously with the drugs, or pre-incubated. These findings indicate that, independently of the influx pathway, [Ca2+]i elevation leads to dephosphorylation of the microtubule-associated protein tau and implicate phosphatase 1 and/or 2A in the process
— id: 25152, year: 1997, vol: 757, page: 93, stat: Journal Article,

Cellular expression and proteolytic processing of presenilin proteins is developmentally regulated during neuronal differentiation
Capell A; Saffrich R; Olivo JC; Meyn L; Walter J; Grunberg J; Mathews P; Nixon R; Dotti C; Haass C
1997 Dec;69(6):2432-2440, Journal of neurochemistry
We have determined the expression of the Alzheimer's disease-associated proteins presenilin-1 and presenilin-2 in primary cultures of rat hippocampal neurons. Neurons highly express presenilin-1 and presenilin-2, whereas both proteins were not detected in astrocytes. Further, we have analyzed the subcellular localization and expression in rat hippocampal neurons during development. Although presenilin proteins were localized predominantly to the endoplasmic reticulum in nonneuronal cells transfected with presenilin cDNAs, in neurons, presenilin proteins were also found in compartments not staining with antibodies to grp78(BiP). Presenilin-1 and presenilin-2 were predominantly detected in vesicular structures within the somatodendritic compartment with much less expression in axons. Polarized distribution of presenilin-1 and presenilin-2 differs slightly, with more presenilin-2 expressed in axons compared with presenilin-1. Presenilin expression was found to be developmentally regulated. Presenilin expression strongly increased during neuronal differentiation until full morphological polarization and then declined. No full-length presenilin-1 or presenilin-2 could be detected within cell lysates. At early developmental stages the expected approximately 34-kDa N-terminal proteolytic fragment of presenilin-1 and the approximately 38-kDa fragment of presenilin-2 were detected. Later during differentiation we predominantly detected a approximately 38-kDa fragment for presenilin-1 and a approximately 42-kDa fragment for presenilin-2. By epitope mapping, we show that these slower migrating peptides represent N-terminal proteolytic fragments, cleaved C-terminal to the conventional site of processing. It is noteworthy that both presenilin-1 and presenilin-2 undergo alternative proteolytic cleavage at the same stage of neuronal differentiation. Regulation of presenilin expression and proteolytic processing might have implications for the pathological as well as the biological function of presenilins during aging in the human brain
— id: 24765, year: 1997, vol: 69, page: 2432, stat: Journal Article,

Increased neuronal endocytosis and protease delivery to early endosomes in sporadic Alzheimer's disease: neuropathologic evidence for a mechanism of increased beta-amyloidogenesis
Cataldo AM; Barnett JL; Pieroni C; Nixon RA
1997 Aug 15;17(16):6142-6151, Journal of neuroscience
The early endosome is the first vacuolar compartment along the endocytic pathway. It is the site of internalization and initial processing of amyloid precursor protein (APP) and apolipoprotein E (ApoE), two proteins of etiological importance in Alzheimer's disease, and a putative site of beta-amyloid peptide (Abeta) formation. Here, we identify early endosomes in human pyramidal neurons, using specific compartmental markers and morphometry, and show that in Alzheimer's disease individual endosomes display up to 32-fold larger volumes than the normal average. Endosomal enlargement contributed to an average 2.5-fold larger total endosomal volume per neuron, implying a marked increase in endocytic activity. Endosomal alterations were evident in most pyramidal neurons in Alzheimer brain, detectable at early stages of the disease but absent in several other neurodegenerative disorders examined. In addition, mature and proenzyme forms of the proteases cathepsin B and cathepsin D, a candidate APP secretase, were identified in most early endosomes in Alzheimer brains but were detectable in only a minor proportion of endosomes in normal brain. Expression of the cation-dependent 46 kDa mannose 6-phosphate receptor was elevated in pyramidal neurons of Alzheimer brains, which could be a possible basis for the altered cathepsin trafficking pattern. Enhanced endocytic activity, coupled with increased trafficking to endosomes of proteases, which may have the ability under pathological conditions to generate Abeta, constitutes a potential mechanism by which beta-amyloidogenesis may become accelerated in sporadic AD and also be subject to influences by ApoE
— id: 25150, year: 1997, vol: 17, page: 6142, stat: Journal Article,

Calpains and calpastatin in SH-SY5Y neuroblastoma cells during retinoic acid-induced differentiation and neurite outgrowth: comparison with the human brain calpain system
Grynspan F; Griffin WB; Mohan PS; Shea TB; Nixon RA
1997 May 1;48(3):181-191, Journal of neuroscience research
Calpains have importance in human neurodegenerative disease pathogenesis, but these mechanisms are difficult to study in postmortem tissues. To establish a cellular model of the human calpain and calpastatin system, we characterized calpain I, calpain II, and calpastatin in SH-SY5Y human neuroblastoma cells in relation to their counterparts in human brain and investigated their expression and activity after inducing cellular differentiation with retinoic acid (RA), a physiological effector of normal brain development. Calpain I in both SH-SY5Y cells and human brain existed in the cytosolic and particulate fractions as three isoforms (80, 78, and 76 kDa) and exhibited atypical isoelectric focusing behavior. Calpain II in SH-SY5Y cells, as in human brain, migrated as a single predominantly cytosolic 76-kDa protein with an isoelectric point ranging from 5.9 to 6.3. Calpastatin from both sources was also 90% cytosolic. In the cells it was composed of four discrete bands, ranging in molecular weight from 110 to 127 kDa. Levels of activated (76 and 78 kDa) and precursor (80 kDa) calpain I isoforms rose 54% (P < 0.0001) in the particulate fraction and 26% (P < 0.0001) in the soluble fraction after 3 days of RA exposure. Because levels and activity of calpastatin remain unchanged during the first 7 days of RA exposure, the increased abundance of calpain I implies a net activation of the calpain system during differentiation. Calpain I activation may contribute to the remodeling of cell shape and neurite extension/retraction associated with neuronal differentiation
— id: 24718, year: 1997, vol: 48, page: 181, stat: Journal Article,

Active site-directed antibodies identify calpain II as an early-appearing and pervasive component of neurofibrillary pathology in Alzheimer's disease
Grynspan F; Griffin WR; Cataldo A; Katayama S; Nixon RA
1997 Jul 25;763(2):145-158, Brain research
Calpain proteases influence intracellular signaling pathways and regulate cytoskeleton organization, but the neuronal and pathological roles of individual isoenzymes are unknown. In Alzheimer's disease (AD), the activated form of calpain I is significantly increased while the fate of calpain II has been more difficult to address. Here, calpain II antibodies raised to different sequences within a cryptic region around the active site, which becomes exposed during protease activation, were shown immunohistochemically to bind extensively to neurofibrillary tangles (NFT), neuritic plaques, and neuropil threads in brains from individuals with AD. Additional 'pre-tangle' granular structures in neurons were also intensely immunostained, indicating calpain II mobilization at very early stages of NFT formation. Total levels of calpain II remained constant in the prefrontal cortex of AD patients but were increased 8-fold in purified NFT relative to levels of calpain I. These results implicate activated calpain II in neurofibrillary degeneration, provide further evidence for the involvement of the calpain system in AD pathogenesis, and imply that neuronal calcium homeostasis is altered in AD
— id: 25149, year: 1997, vol: 763, page: 145, stat: Journal Article,

Triton-soluble phosphovariants of the heavy neurofilament subunit in developing and mature mouse central nervous system
Shea TB; Dahl DC; Nixon RA; Fischer I
1997 Jun 15;48(6):515-523, Journal of neuroscience research
The low abundance of soluble neurofilament (NF) subunits in mature axons has suggested that newly synthesized NF proteins rapidly assemble into highly stable polymers and associate with the Triton X-100-insoluble cytoskeleton. The dynamic nature of these subunit associations in vivo remains unresolved, and the applicability of this assembly model to NFs in other neuronal compartments or to developing neurons is unknown. Here, we report that a unique pool of Triton X-100-soluble, extensively phosphorylated, high molecular weight NF subunits (NF-H, or H-200) are abundantly expressed in the mouse CNS during early postnatal development and persist in the perikaryal compartment of some mature neurons. Triton-soluble H-200 subunits appeared at postnatal day 14 (P14) and remained high through P60, beyond which the percentage declined to marginal levels by P120. Medium and low molecular weight NF (NF-M and NF-L, respectively) were at all times only detectable within the cytoskeleton. Comparison of soluble and cytoskeleton-associated H-200 immunoreactivity indicated that certain phosphorylation-dependent epitopes were confined to the cytoskeleton. Pulse-chase radiolabeling analyses in optic pathway demonstrated that some Triton-soluble NF-H subunits are extensively phosphorylated within retinal perikarya before they are incorporated into Triton-insoluble structures. These findings indicate that the assembly behaviors of NF-H differ substantially from those of NF-M and NF-L, and that the interaction of NF-H with NFs may be more dynamic than is generally recognized, especially during brain development and within specific compartments of mature neurons
— id: 25151, year: 1997, vol: 48, page: 515, stat: Journal Article,

Colocalization of lysosomal hydrolase and beta-amyloid in diffuse plaques of the cerebellum and striatum in Alzheimer's disease and Down's syndrome
Cataldo AM; Barnett JL; Mann DM; Nixon RA
1996 Jun;55(6):704-715, Journal of neuropathology & experimental neurology
The lysosomal hydrolases, cathepsin D (Cat D) and beta-hexosaminidase A (HEX), which are normally intracellular enzymes, colocalize with beta-amyloid in a subgroup of diffuse plaques in the cerebellum and striatum of individuals with Alzheimer's disease or Down's syndrome. Using specific antisera in combination with single- and double-label immunocytochemical techniques, extracellular hydrolase was detected in 30 to 40% of the diffuse plaques in the cerebellar molecular layer and nearly all of the diffuse plaques in the striatum. In both Alzheimer's disease and Down's syndrome, about 5 to 10% of the cerebellar Purkinje cells contained abnormally increased numbers of hydrolase-positive lysosomes despite their normal appearance by conventional histologic stains. Occasional atrophic Purkinje cells identified by Nissl stain were intensely immunostained. By confocal imaging analysis, abnormal hydrolase-laden Purkinje cell dendrites were seen coursing through some hydrolase-positive plaques and were continuous with dendritic branches that terminated within deposits of extracellular hydrolase and beta-amyloid. In the striatum, intensely immunostained abnormal-appearing neurons were commonly associated with extracellular deposits of hydrolase immunoreactivity and beta-amyloid within diffuse plaques and in the less commonly seen classical plaques. In both brain regions, other hydrolase-negative beta-amyloid deposits were seen, these being associated with blood vessels. The presence of HEX immunoreactivity in neurons, but not in glia, and its abundance in plaques support earlier studies, suggesting that neurons are the principal source of plaque hydrolase. An endosomal-lysosomal system upregulation, with increased hydrolase expression and extracellular enzyme deposition in plaques, is, like beta-amyloid deposition, an early marker of metabolic dysfunction potentially related to primary etiologic events in Alzheimer's disease and Down's syndrome
— id: 25155, year: 1996, vol: 55, page: 704, stat: Journal Article,

Abnormalities of the endosomal-lysosomal system in Alzheimer's disease: relationship to disease pathogenesis
Cataldo AM; Hamilton DJ; Barnett JL; Paskevich PA; Nixon RA
1996 ;389(7):271-280, Advances in experimental medicine & biology
— id: 25158, year: 1996, vol: 389, page: 271, stat: Journal Article,

Properties of the endosomal-lysosomal system in the human central nervous system: disturbances mark most neurons in populations at risk to degenerate in Alzheimer's disease
Cataldo AM; Hamilton DJ; Barnett JL; Paskevich PA; Nixon RA
1996 Jan;16(1):186-199, Journal of neuroscience
Specific antibodies and cytochemical markers combined with several imaging and morphometric techniques were used to characterize the endosomal-lysosomal system in mature neurons of the normal human central nervous system and to quantitate changes in its function in Alzheimer's disease. Compartments containing cathespin D (Cat D) and other acid hydrolases included a major subpopulation of mature lysosomes lacking mannose-6-phosphate receptors (MPR) and smaller populations of late endosomes (MPR-positive) and lipofuscin granules (MPR-negative). Antibodies to the pro-isoform of Cat D decorated perinuclear vacuolar compartments corresponding to late endosomes. Neurons and glia contained lysosomes with differing complements of acid hydrolases, implying different processing capabilities. Endosome/lysosome number per unit volume of cytoplasm was relatively well conserved within populations of normal neurons. By contrast, in morphometric analyses of Alzheimer's disease brains, 80-93% of pyramidal cells in the prefrontal cortex (laminae III or V) and hippocampus (CA2, CA3) displayed two- to eightfold higher numbers of hydrolase-positive vacuolar compartments than did corresponding cell populations in age-matched normal brains. Only 5-10% of cerebellar Purkinje cells, a less vulnerable population, showed the same statistically significant elevations. Most affected in these brain regions and in subcortical areas seemed otherwise normal by conventional histological staining and ultrastructural inspection. That both lysosomal and pro-Cat D- and MPR-positive endosomal compartments increased in number demonstrates that the endosomal-lysosomal system is activated markedly in vulnerable neuronal populations of Alzheimer's disease brains and implies that endocytosis or autophagy or both are accelerated persistently at an early stage of cellular compromise, greatly surpassing the degree of activity associated with normal aging. Early activation of the endosomal-lysosomal system represents a biological event potentially linking major etiological factors in Alzheimer's disease, including defective membrane proteins, apolipoprotein E function, and altered amyloid precursor protein processing
— id: 25159, year: 1996, vol: 16, page: 186, stat: Journal Article,

DNA strand breaks induced by sustained glutamate excitotoxicity in primary neuronal cultures
Didier M; Bursztajn S; Adamec E; Passani L; Nixon RA; Coyle JT; Wei JY; Berman SA
1996 Apr 1;16(7):2238-2250, Journal of neuroscience
We developed a new approach to study single- and double-stranded DNA breaks during chronic, moderate excitotoxicity resulting from the inhibition of the glutamate transporter in cerebellar granule cell primary cultures. A 24 hr treatment of 2-week-old cultures with L-alpha-amino adipate (LAA), an inhibitor of the cerebellar glutamate uptake transporter, caused a gradual extracellular accumulation of endogenous glutamate that induced reversible morphological change of granule neurons but no neuronal cell death despite sustained, but moderate, elevations of the free intracellular calcium concentrations. Nick translation experiments on isolated nuclei or cells from cerebellar cultures chronically exposed to LAA revealed increased radioactive nucleotide incorporation indicative of DNA nicking. This LAA effect was dose-dependent and suppressed by NMDA receptor antagonists. Cultures treated for 24 hr with LAA and subjected to in situ nick translation showed an intense nuclear labeling of neurons but not glia, which could be abolished by MK801. A similar labeling was also observed in altered nuclei of granule neurons acutely exposed to high glutamate concentrations or undergoing an apoptotic cell death. Although the TUNEL labeling method detected no DNA double-strand breaks in LAA-treated cerebellar cultures, it displayed clear evidence of DNA damage during acute glutamate excitotoxicity or during apoptosis. However, Southern blot analysis of nuclear DNA revealed a DNA laddering only in apoptotic cell death. Our results demonstrate that DNA damage, characterized by DNA single-strand breaks, is an early event in chronic, moderate excitotoxicity. This type of DNA degradation, which appears before any nuclear morphological changes, is distinct from the massive DNA single- and/or double-strand damages observed during acute glutamate excitotoxicity or apoptosis
— id: 25157, year: 1996, vol: 16, page: 2238, stat: Journal Article,

mu-calpain activation and calpain-mediated cytoskeletal proteolysis following traumatic brain injury
Kampfl A; Posmantur R; Nixon R; Grynspan F; Zhao X; Liu SJ; Newcomb JK; Clifton GL; Hayes RL
1996 Oct;67(4):1575-1583, Journal of neurochemistry
Increasing evidence suggests that excessive activation of the calcium-activated neutral protease mu-calpain could play a major role in calcium-mediated neuronal degeneration after acute brain injuries. To further investigate the changes of the in vivo activity of mu-calpain after unilateral cortical impact injury in vivo, the ratio of the 76-kDa activated isoform of mu-calpain to its 80-kDa precursor was measured by western blotting. This mu-calpain activation ratio increased to threefold in the pellet of cortical samples ipsilateral to the injury site at 15 min, 1 h, 3 h, and 6 h after injury and returned to control levels at 24-48 h after injury. We also investigated the effect of mu-calpain activation on proteolysis of the neuronal cytoskeletal protein alpha-spectrin. Immunoreactivity for alpha-spectrin breakdown products was detectable within 15 min after injury in cortical samples ipsilateral to the injury site. The levels of alpha-spectrin breakdown products increased in a biphasic manner, with a large increase between 15 min and 6 h after injury, followed by a smaller increase between 6 and 24 h after the insult. No further accumulation of alpha-spectrin breakdown products was observed between 24 and 48 h after injury. Histopathological examinations using hematoxylin and eosin staining demonstrated dark, shrunken neurons within 15 min after traumatic brain injury. No evidence of mu-calpain autolysis, calpain-mediated alpha-spectrin degradation, or hematoxylin and eosin neuronal pathology was detected in the contralateral cortex. Although mu-calpain autolysis and cytoskeletal proteolysis occurred concurrently with early morphological alterations, evidence of calpain-mediated proteolysis preceded the full expression of evolutionary histopathological changes. Our results indicate that rapid and persistent mu-calpain activation plays an important role in cortical neuronal degeneration after traumatic brain injury. Our data also suggest that specific inhibitors of calpain could be potential therapeutic agents for the treatment of traumatic brain injury in vivo
— id: 25172, year: 1996, vol: 67, page: 1575, stat: Journal Article,

Regional differences in gene expression for calcium activated neutral proteases (calpains) and their endogenous inhibitor calpastatin in mouse brain and spinal cord
Li J; Grynspan F; Berman S; Nixon R; Bursztajn S
1996 Jun;30(2):177-191, Journal of neurobiology
The family of calpains (CANP or calcium activated neutral proteases) and their endogenous inhibitor calpastatin have been implicated in many neural functions; however, functional distinctions between the major calpain isoforms, calpain I and II, have not been clearly established. In the present study we analyzed the gene expression patterns for calpain I and II and calpastatin in mouse brain and spinal cord by measuring both their mRNA and protein levels. Our results show that the overall mRNA level measured by competitive reverse transcription polymerase chain reaction for calpain II is 15-fold higher and for calpastatin is three-fold higher than that for calpain I. Overall, both mRNA and protein expression levels for the calpains and calpastatin showed no significant difference between the spinal cord and the brain. The cellular distributions of mRNA for calpain I or calpastatin, measured by in situ hybridization, are relatively uniform throughout the brain. In contrast, calpain II gene expression is selectively higher in certain neuron populations including pyramidal neurons of the hippocampus and the deep neocortical layers, Purkinje cells of cerebellum, and motor neurons of the spinal cord. The motor neurons were the most enriched in calpain message. Motor neurons possessed 10-fold more calpain II mRNA than any other spinal cord cell type. The differential distribution of the two proteases in the brain and the spinal cord at the mRNA level indicates that the two calpain genes are differentially regulated, suggesting that they play different physiological roles in neuronal activities and that they may participate in the pathogenesis of certain regional neurological degenerative diseases
— id: 25171, year: 1996, vol: 30, page: 177, stat: Journal Article,

Oligodendroglia regulate the regional expansion of axon caliber and local accumulation of neurofilaments during development independently of myelin formation
Sanchez I; Hassinger L; Paskevich PA; Shine HD; Nixon RA
1996 Aug 15;16(16):5095-5105, Journal of neuroscience
Axon caliber may be influenced by intrinsic neuronal factors and extrinsic factors related to myelination. To understand these extrinsic influences, we studied how axon-caliber expansion is related to changes in neurofilament and microtubule organization as axons of retinal ganglion cells interact with oligodendroglia and become myelinated during normal mouse brain development. Caliber expanded and neurofilaments accumulated only along regions of the axon invested with oligodendroglia. Very proximal portions of axons within a region of the optic nerve from which oligodendrocytes are excluded remained unchanged. More distally, these axons rapidly expanded an average of fourfold as soon as they were recruited to become myelinated between postnatal days 9 and 120. Unmyelinated axons remained unchanged. Axons ensheathed by oligodendroglial processes, but not yet myelinated, were intermediate in caliber and neurofilament number. That oligodendrocytes can trigger regional caliber expansion in the absence of myelin was confirmed using three strains of mice with different mutations that prevent myelin formation but allow wrapping of some axons by oligodendroglial processes. Unmyelinated axons persistently wrapped by oligodendrocytes showed full axon caliber expansion, neurofilament accumulation, and appropriately increased lateral spacing between neurofilaments. Thus, signals from oligodendrocytes, independent of myelin formation, are sufficient to induce full axon radial growth primarily by triggering local accumulation and reorganization of the neurofilament network
— id: 25154, year: 1996, vol: 16, page: 5095, stat: Journal Article,

Calcium influx into human neuroblastoma cells induces ALZ-50 immunoreactivity: involvement of calpain-mediated hydrolysis of protein kinase C
Shea TB; Spencer MJ; Beermann ML; Cressman CM; Nixon RA
1996 Apr;66(4):1539-1549, Journal of neurochemistry
Calcium influx into SH-SY5Y human neuroblastoma cells after ionophore treatment or transient permeabilization in calcium-containing medium increased ALZ-50 immunoreactivity markedly. This increase was prevented by inhibitors active against calpain or against protein kinase C (PKC), suggesting that both of these enzymes were required to mediate the effect of calcium influx on ALZ-50 immunoreactivity. Treatment with PKC activator TPA increased ALZ-50 immunoreactivity in the absence of calcium influx or after intracellular delivery of the specific calpain inhibitor calpastatin, indicating that the influence of PKC was downstream from that of calpain. Calcium influx also resulted in mu-calpain autolysis (one index of calpain activation) and the transient appearance of PKM (i.e., free PKC catalytic subunits, generated by calpain-mediated cleavage of the regulatory and catalytic PKC domains). Inhibition of calpain within intact cells resulted in a dramatic increase in steady-state levels of total tau (migrating at 46-52 kDa) but resulted in a relatively minor increase in 68-kDa ALZ-50-immunoreactive tau isoforms. Although calcium influx into intact cells resulted in accumulation of ALZ-50 immunoreactivity, total tau levels were, by contrast, rapidly depleted. Incubation of isolated fractions with calpain in the presence of calcium indicated that ALZ-50-immunoreactive tau isoforms were more resistant to calpain-mediated proteolysis than were non-ALZ-50 reactive tau isoforms. These data therefore indicate that calpain may regulate tau levels directly via proteolysis and indirectly through PKC activation. A consequence of the latter action is altered tau phosphorylation, perhaps involving one or more kinase cascades, and the preferential accumulation of ALZ-50-immunoreactive tau isoforms due to their relative resistance to degradation. These findings provide a basis for the possibility that disregulation of calcium homeostasis may contribute to the pathological levels of conversion of tau to A68 by hyperactivation of the calpain/PKC system
— id: 25156, year: 1996, vol: 66, page: 1539, stat: Journal Article,

Immunocytochemistry of tau phosphoserine 413 and tau protein kinase I in Alzheimer pathology
Shiurba RA; Ishiguro K; Takahashi M; Sato K; Spooner ET; Mercken M; Yoshida R; Wheelock TR; Yanagawa H; Imahori K; Nixon RA
1996 Oct 21;737(1-2):119-132, Brain research
One unique phosphorylation site consistently found in paired helical filament tau, serine 413, is modified by tau protein kinase I/glycogen synthase kinase-3 beta but no other known tau kinase. Here we present immunocytochemistry from Alzheimer's disease brains showing that focal subpopulations of hippocampal CA1 pyramidal neurons and neuritic plaques are strongly reactive for tau protein kinase I/glycogen synthase kinase-3 beta and tau phosphoserine 413 in early stages of pathology. Colocalization of these epitopes suggests that tau protein kinase I/glycogen synthase kinase-3 beta abnormally phosphorylates tau and is in a position to disrupt neuronal metabolism in anatomical areas vulnerable to Alzheimer's disease
— id: 25153, year: 1996, vol: 737, page: 119, stat: Journal Article,

Gene expression and cellular content of cathepsin D in Alzheimer's disease brain: evidence for early up-regulation of the endosomal-lysosomal system
Cataldo AM; Barnett JL; Berman SA; Li J; Quarless S; Bursztajn S; Lippa C; Nixon RA
1995 Mar;14(3):671-680, Neuron
In Alzheimer's disease brains, more than 90% of pyramidal neurons in lamina V and 70% in lamina III displayed 2- to 5-fold elevated levels of cathepsin D (Cat D) mRNA by in situ hybridization compared with neurologically normal controls. Most of these cells appeared histologically normal. The less vulnerable nonpyramidal neuron population in lamina IV had relatively normal message levels. Neuronal populations expressing more Cat D mRNA also displayed quantitatively increased Cat D immunoreactive protein. Cat D mRNA expression was only moderately increased in astrocytes. Degenerating neurons exhibited intense immunoreactivity but lowered Cat D mRNA levels. The upregulation of Cat D synthesis and accumulation of hydrolase-laden lysosomes indicate an early activation of the endosomal-lysosomal system in vulnerable neuronal populations, possibly reflecting early regenerative or repair processes. These abnormalities also represent a basis for altered regulation of amyloid precursor protein processing
— id: 25164, year: 1995, vol: 14, page: 671, stat: Journal Article,

Limited proteolytic processing of the mature form of cathepsin D in human and mouse brain: postmortem stability of enzyme structure and activity
Compaine A; Schein JD; Tabb JS; Mohan PS; Nixon RA
1995 Oct-Nov;27(4-5):385-396, Neurochemistry international
The mature form of cathepsin D (Cat D), purified to homogeneity from postmortem human brain or mouse brain, behaved as a 42-kDa protein in its native state but revealed additional proteolytic processing under denaturing conditions. Human brain Cat D was composed of a 30-32 kDa heavy chain and a protein doublet consisting of 14 and 15 kDa light chains. Mouse Cat D, which closely resembled the human enzyme in amino acid composition, existed mainly as the uncleaved 42-kDa protein, but up to 40% existed as a complex of 30-32 kDa and 12-14 kDa chains. The 3:1 ratio of light to heavy (30-32 kDa) chains suggested processing of some 30-kDa chains. Cleavage of the 42-kDa chain could not be induced autolytically. Human brain Cat D had a 2-3-fold higher specific activity than the mouse enzyme but shared other properties, including similar biphasic pH optima (peaks at pH 3.30 and 4.2), Km values for methemoglobin and inhibitor profiles. Human Cat D displayed the same polypeptide chain composition when purified from brains differing in postmortem interval (3-28 h). Fresh SH-SY5Y human neuroblastoma cells analyzed on Western blots with anti-Cat D antibodies also displayed only cleaved forms of mature Cat D. Furthermore, brain Cat D isolated from mice stored after death for 5, 15 or 30 h at 25 degrees C contained the same molar ratios of cleaved and uncleaved enzyme found in fresh mouse brain . Cat D activity was stable in human brains with postmortem intervals up to 27 h and stored frozen for up to 3 years. Similarly, total Cat D activity was essentially unchanged in brains of mice subjected to stimulated postmortem conditions for 0.5-4.2 h, although 20% of the total soluble brain protein became insoluble during this postmortem interval. These results demonstrate a remarkable postmortem stability of Cat D and strongly suggest that limited proteolytic cleavage of mature brain Cat D is an in vivo event, the extent of which varies markedly in different species
— id: 24719, year: 1995, vol: 27, page: 385, stat: Journal Article,

Proteolysis of protein kinase C: mM and microM calcium-requiring calpains have different abilities to generate, and degrade the free catalytic subunit, protein kinase M
Cressman CM; Mohan PS; Nixon RA; Shea TB
1995 Jul 3;367(3):223-227, FEBS letters
Limited proteolysis of protein kinase C (PKC) by calpain under cell free conditions cleaves the regulatory and catalytic PKC subunits, generating a free, co-factor independent catalytic subunit, termed PKM. In the present study, we demonstrate distinct differences in the rate, nature, and lipid-sensitivity of PKC and PKM proteolysis by microM and mM calcium-requiring calpain isozymes (mu calpain or m calpain, respectively). PKC is a preferred substrate for m calpain; not even a 100-fold increase in mu calpain was capable of degrading PKC as fast as in calpain. PKM was generated by both m and mu calpains, but was itself rapidly degraded by m calpain and therefore was only transiently detectable. By contrast, PKM was formed but not degraded by mu calpain, and persisted in the presence of mu calpain long after all PKC had been degraded. Phosphatidyl serine (PS) inhibited PKC hydrolysis by m calpain yet enhanced PKC hydrolysis by mu calpain. The ability of either calpain isoenzyme to degrade [14C]azocasein was unaffected by PS, suggesting that the influence of PS was on PKC conformation. These findings point towards distinct roles for mu and m calpain in PKC regulation
— id: 24720, year: 1995, vol: 367, page: 223, stat: Journal Article,

Three distinct axonal transport rates for tau, tubulin, and other microtubule-associated proteins: evidence for dynamic interactions of tau with microtubules in vivo
Mercken M; Fischer I; Kosik KS; Nixon RA
1995 Dec;15(12):8259-8267, Journal of neuroscience
Microtubule-associated proteins (MAPs), such as tau, modulate neuronal shape and process outgrowth by influencing the stability and organization of microtubules. The dynamic nature of MAP-microtubule interactions in vivo, however, is poorly understood. Here, we have assessed the stability of these interactions by investigating the synthesis and axoplasmic transport of tau in relation to that of tubulin and other MAPs within retinal ganglion cells of normal adult mice in vivo. Using immunoprecipitation and Western blot analysis with anti-tau monoclonal and polyclonal antibodies, we unequivocally identified in optic axons a family of 50-60 kDa tau isoforms and a second 90-95 KDa tau family, the members of which were shown to contain the domain of tau encoded by exon 4A. To measure the rates of translocation of tau proteins in vivo, we injected mice with 35S-methionine intravitreously and, after 6-30 d, quantitated the radiolabeled tau isoforms immunoprecipitated from eight consecutive 1.1 mm segments of the nerve and optic tract and separated by electrophoresis. Linear regression analysis of protein transport along optic axons showed that the tau isoforms advanced at a rate of 0.2-0.4 mm/d, and other radiolabeled MAPs, identified by their association with taxol-stabilized microtubules, moved three- to fivefold more rapidly. By contrast, tubulins advanced at 0.1-0.2 mm/d, significantly more slowly than tau or other MAPs. These studies establish that tau is not cotransported with tubulin or microtubules, indicating that associations of tau with microtubules within axons are not as stable as previously believed. Our findings also reveal differences among various MAPs in their interactions with microtubules and provide evidence that assembly and reorganization of the microtubule network is an active process even after axons establish connections and fully mature
— id: 25160, year: 1995, vol: 15, page: 8259, stat: Journal Article,

Differential sensitivity to proteolysis by brain calpain of adult human tau, fetal human tau and PHF-tau
Mercken M; Grynspan F; Nixon RA
1995 Jul 10;368(1):10-14, FEBS letters
Reduced turn-over of tau by calpains is a possible mechanism to facilitate the incorporation into paired helical filaments (PHFs) in Alzheimer's disease. The present study shows that the differently phosphorylated fetal tau isoforms are all rapidly proteolysed to an equal extent by human brain m-calpain. This result argues against the hypothesis that this type of fetal phosphorylation is involved in reducing tau turn-over by calpain in Alzheimer's disease. Adult and fetal tau fragments in vitro generated by m-calpain, but not trypsin, cathepsin D or chymotrypsin resemble the post-mortem in situ degradation patterns, suggesting a possible role for calpains in tau metabolism in vivo. Tau incorporated into PHFs was considerably more resistant to proteolysis by calpain which can help to explain the persistence of these structures in Alzheimer's disease
— id: 25163, year: 1995, vol: 368, page: 10, stat: Journal Article,

Purification and properties of high molecular weight calpastatin from bovine brain
Mohan PS; Nixon RA
1995 Feb;64(2):859-866, Journal of neurochemistry
Calcium-activated neutral proteases (calpains) are regulated by specific endogenous protein inhibitors, the calpastatins, which are widely distributed in mammalian tissues. Calpastatins from different species or in various tissues from the same species exhibit considerable size heterogeneity on sodium dodecyl sulfate (SDS) gels, reflecting both transcriptional and posttranslational regulation. This heterogeneity has complicated previous biochemical characterizations. In this study, we purified bovine brain calpastatin to homogeneity. The inhibitor was purified 2,463-fold from a cytosolic fraction of fresh bovine cerebral cortex by chromatographies on diethylaminoethyl cellulose, Ultrogel AcA44, phenyl-Sepharose, concanavalin A-Sepharose, and Q-Sepharose. The major calpastatin displayed a native molecular mass of 250-300 kDa by gel filtration and was composed of 125-kDa polypeptide chains by SDS-polyacrylamide gel electrophoresis (SDS-PAGE). Small amounts of a 68-kDa calpastatin fragment were detected particularly in molecules exhibiting smaller native molecular mass (250 kDa). When electroeluted from SDS gels, the 125- and 68-kDa polypeptides each inhibited calpain. The purified protein was strongly immunoreactive toward antibodies raised against a synthetic peptide, CEKLGEKEETIPPDYR, shown to be a conserved repetitive motif in the calpastatin gene or a recombinant polypeptide corresponding to domains L and 1 of human calpastatin. Calpastatins purified from bovine and human erythrocytes exhibited molecular masses of 78 and 68 kDa, respectively, by SDS-PAGE. Both erythrocyte calpastatins reacted strongly with antibodies against the conserved sequence but not with antibodies raised against domains L and 1 of human calpastatin, indicating that the erythrocyte inhibitors lack these two domains.(ABSTRACT TRUNCATED AT 250 WORDS)
— id: 24721, year: 1995, vol: 64, page: 859, stat: Journal Article,

The endosoma-lysosomal system in Alzheimer disease
Nixon RA; Cataldo AM
1995 Feb;:?-?, ICOP newsletter (International Committee on Proteolysis)
— id: 25205, year: 1995, vol: , page: ?, stat: Journal Article,

The endosomal-lysosomal system of neurons: new roles
Nixon RA; Cataldo AM
1995 Nov;18(11):489-496, Trends in neurosciences
The repertoire of the lysosomal system extends beyond its function in degrading biologic macromolecules for energy and recycling purposes. Controlled shifts in lysosomal activity help neurons to regulate their cytoplasmic volume and to remodel local cellular domains. Newly identified regulatory controls over targeting to lysosomes and the limited proteolytic actions of 'lysosomal' hydrolases, together with other recent findings, are suggesting potential roles for the endosomal-lysosomal system in modifying functions of specific proteins, acquiring nutrients essential for growth and repair, influencing the output of secretory products, and helping neurons to modulate trophic signals. The prominent involvement of the endosomal-lysosomal system in Alzheimer's disease and other major pathologies has redoubled interest in how this system serves neurons
— id: 25178, year: 1995, vol: 18, page: 489, stat: Journal Article,

Elevated levels of the endosomal-lysosomal proteinase cathepsin D in cerebrospinal fluid in Alzheimer disease
Schwagerl AL; Mohan PS; Cataldo AM; Vonsattel JP; Kowall NW; Nixon RA
1995 Jan;64(1):443-446, Journal of neurochemistry
Lysosomal hydrolases are normally intracellular enzymes but are abundant extracellularly within senile plaques in Alzheimer disease and in other conditions where beta-amyloid accumulates. To examine whether acid hydrolases released from abnormal hydrolase-laden neurons are detectable in CSF, we measured levels of the major aspartic proteinase of lysosomes, cathepsin D (Cat D), in ventricular CSF collected after death from 30 patients with Alzheimer disease, 14 patients with Huntington disease, and seven patients with other neurodegenerative diseases. The levels of Cat D-immunoreactive protein, expressed as micrograms per milliliter of protein, determined by western blot immunoassay using a polyclonal antiserum against human brain Cat D, were more than fourfold higher in the Alzheimer patients than in the other patient groups (p < 0.0005). Cat D activity, assayed separately against [14C]methemoglobin at pH 3.2, was also significantly elevated but less than Cat D content. The lower specific activity of Cat D in Alzheimer CSF therefore indicated that the abnormally accumulated Cat D included a high proportion of inactive enzyme. These results indicate that abnormal Cat D release from affected neurons into the extracellular space is an active, ongoing process in Alzheimer brain. In addition, the levels of this enzyme and possibly other lysosomal hydrolases in CSF may prove to be useful biological markers of Alzheimer disease
— id: 24722, year: 1995, vol: 64, page: 443, stat: Journal Article,

Aluminum treatment of intact neuroblastoma cells alters neurofilament subunit phosphorylation, solubility, and proteolysis
Shea TB; Beermann ML; Nixon RA
1995 Sep;26(1):1-14, Molecular & chemical neuropathology
Addition of 400 microM AlCl3 to the culture medium for 72 h has been previously shown to induce perikaryal whorls of intermediate-sized filaments in intact mouse NB2a/d1 neuroblastoma cells. Immunoblot analyses demonstrated that in vivo treatment of cells with aluminum induced the de novo appearance of extensively phosphorylated NF-H isoforms in cytoskeletons of undifferentiated cells and increased levels of these isoforms in differentiated cells. Neurofilament subunits isolated from intact cells treated with aluminum were resistant to dephosphorylation in vitro by alkaline phosphatase and to in vitro degradation by endogenous calcium-dependent protease(s). These alterations were accompanied by a greater tendency of neurofilaments to form insoluble aggregates after isolation. These findings demonstrate direct effects of aluminum on neurofilament subunits within intact neuronal cells similar to those previously demonstrated following in vitro exposure of isolated neurofilaments to aluminum
— id: 25161, year: 1995, vol: 26, page: 1, stat: Journal Article,

Enhancement of neurite outgrowth following calpain inhibition is mediated by protein kinase C
Shea TB; Cressman CM; Spencer MJ; Beermann ML; Nixon RA
1995 Aug;65(2):517-527, Journal of neurochemistry
We examined the interdependence of calpain and protein kinase C (PKC) activities on neurite outgrowth in SH-SY-5Y human neuroblastoma cells. SH-SY-5Y cells elaborated neurites when deprived of serum or after a specific thrombin inhibitor, hirudin, was added to serum-containing medium. The extent of neurite outgrowth under these conditions was enhanced by treatment of cells with the cell-permeant cysteine protease inhibitors N-acetyl-leucyl-leucyl-norleucinal ('C1') and calpeptin or by the phospholipid-mediated intracellular delivery of either a recombinant peptide corresponding to a conserved inhibitory sequence of human calpastatin or a neutralizing anti-calpain antisera. Calpain inhibition in intact cells was confirmed by immunoblot analysis showing inhibition of calpain autolysis and reduced proteolysis of the known calpain substrates fodrin and microtubule-associated protein 1. The above inhibitory peptides and antiserum did not induce neurites in medium containing serum but lacking hirudin, suggesting that increased surface protein adhesiveness is a prerequisite for enhancement of neurite outgrowth by calpain inhibition. Treatment of cells with the PKC inhibitor H7, staurosporine, or sphingosine induced neurite outgrowth independently of serum concentration. Because calpain is thought to regulate PKC activity, we examined this potential interrelationship during neurite outgrowth. Simultaneous treatment with calpain and PKC inhibitors did not produce additive or synergistic effects on neurite outgrowth. PKC activation by 2-O-tetradecanoylphorbol 13-acetate (TPA) prevented and reversed both neurite initiation by serum deprivation and its enhancement by calpain inhibitors. Treatment of cells with the calpain inhibitor C1 retarded PKC down-regulation following TPA treatment. Cell-free analyses demonstrated the relative specificity of various protease and kinase inhibitors for calpain and PKC and confirmed the ability of millimolar calcium-requiring calpain to cleave the SH-SY-5Y PKC regulatory subunit from the catalytic subunit, yielding a free catalytic subunit (protein kinase M). These findings suggest that the influence of PKC on neurite outgrowth is downstream from that of surface adhesiveness and calpain activity
— id: 25162, year: 1995, vol: 65, page: 517, stat: Journal Article,

Degenerative changes in epinephrine tonic vasomotor neurons in Alzheimer's disease
Burke WJ; Galvin NJ; Chung HD; Stoff SA; Gillespie KN; Cataldo AM; Nixon RA
1994 Oct 24;661(1-2):35-42, Brain research
The C-1 region in the rostral ventral lateral medulla contains mainly epinephrine (Epi) neurons. These neurons are the tonic vasomotor center of the brain. We previously demonstrated changes in the enzymatic activity of phenylethanolamine N-methyltransferase (PNMT) in axon terminals and cell bodies of Epi neurons from the medulla of Alzheimer's disease (AD) brains. In this study, we investigated the perikarya of C-1 neurons for the morphometric, immunohistochemical and histochemical changes that are seen in severely affected regions of Alzheimer brain. The mean areas and size distributions of C-1 neurons from 6 AD and 6 neurologically normal patients were compared using the Wilcoxon rank sum test and Kolmogorov-Smirnov z tests respectively. Additional brain sections from the C-1 region of AD and control individuals were stained with cresyl violet or immunostained with antibodies to the lysosomal hydrolase cathepsin D, Tau-2, Alz-50 and beta-amyloid protein. The average area of C-1 neurons in AD brains was decreased 18.3% (P < 0.001) compared to the areas of the same cell population in age-matched control brains. A shift toward smaller sized C-1 neurons was seen in the AD cases. Nissl stain demonstrated a central chromatolytic appearance in 3.7% of AD neurons sampled. No beta-amyloid deposits were detected histologically or immunocytochemically in the C-1 region of AD brains. Both Tau-2 and Alz-50 immunoreactivity was observed in occasional (1%) C-1 neurons from AD brains but not in controls. A small proportion (30%) of the C-1 neurons showing atrophy displayed increased cathepsin D immunoreactivity.(ABSTRACT TRUNCATED AT 250 WORDS)
— id: 25166, year: 1994, vol: 661, page: 35, stat: Journal Article,

Lysosomal abnormalities in degenerating neurons link neuronal compromise to senile plaque development in Alzheimer disease
Cataldo AM; Hamilton DJ; Nixon RA
1994 Mar 21;640(1-2):68-80, Brain research
Antibodies to the lysosomal hydrolases, cathepsins B and D and beta-hexosaminidase A, revealed alterations of the endosomal-lysosomal system in neurons of the Alzheimer disease brain, which preceded evident degenerative changes and became marked as atrophy, neurofibrillary pathology, or chromatolysis developed. At the earliest stages of cell atrophy, hydrolase-positive lysosomes accumulated at the basal pole and then massively throughout the perikarya and proximal and proximal dendrites of affected pyramidal neurons in Alzheimer prefrontal cortex and hippocampus, far exceeding the changes of normal aging. Secondary lysosomes as well as tertiary residual bodies (lysosomes/lipofuscin) increased implying stimulated, autophagocytosis and lysosomal system activation. Less affected brain regions, such as the thalamus, displayed similar though less extensive alterations. Certain thalamic neurons exhibited a distinctive lysosome-related abnormality characterized by the presence of cell surface blebs of varying size and number filled with intense hydrolase immunoreactivity. At more advanced stages of degeneration in still intact neurons, hydrolase-positive lipofuscin, particularly in the form of abnormally large aggregates, nearly filled the cytoplasm. Similar lipofuscin aggregates were observed in abundance in the extracellular space following cell lysis and were usually associated with deposits of the beta-amyloid protein. Degenerating neurons and their processes were the major source of these aggregates within senile plaques which contained high concentrations of acid hydrolases. We have shown in previous studies that these lysosomal hydrolases in plaques are enzymatically-active. The persistence of lysosomal structures in the brain parenchyma after neurons have degenerated is a striking and potentially diagnostic feature of Alzheimer disease which has not been observed, to our knowledge, in other degenerative diseases. The lysosomal response in degenerating Alzheimer neurons represents a probable link between an early activation of the lysosomal system in at-risk, normal-appearing neurons and the end-stage contribution of lysosomes to senile plaque formation and emphasizes a slowly progressive disturbance of the lysosomal system throughout the development of Alzheimer disease
— id: 25169, year: 1994, vol: 640, page: 68, stat: Journal Article,

Neuronal degenerative mechanisms as clues to pathogenesis and treatment of Alzheimer's disease
Nixon RA
1994 ;15 Suppl 2(4):S61-S65, Neurobiology of aging
— id: 25177, year: 1994, vol: 15 Suppl 2, page: S61, stat: Journal Article,

Free radicals, proteolysis, and the degeneration of neurons in Alzheimer disease: how essential is the beta-amyloid link?
Nixon RA; Cataldo AM
1994 Jul-Aug;15(4):463-469, Neurobiology of aging
— id: 25176, year: 1994, vol: 15, page: 463, stat: Journal Article,

[32P]orthophosphate and [35S]methionine label separate pools of neurofilaments with markedly different axonal transport kinetics in mouse retinal ganglion cells in vivo
Nixon RA; Lewis SE; Mercken M; Sihag RK
1994 Nov;19(11):1445-1453, Neurochemical research
Newly synthesized neurofilament proteins become highly phosphorylated within axons. Within 2 days after intravitreously injecting normal adult mice with [32P]orthophosphate, we observed that neurofilaments along the entire length of optic axons were radiolabeled by a soluble 32P-carrier that was axonally transported faster than neurofilaments. 32P-incorporation into neurofilament proteins synthesized at the time of injection was comparatively low and minimally influenced the labeling pattern along axons. 32P-incorporation into axonal neurofilaments was considerably higher in the middle region of the optic axons. This characteristic non-uniform distribution of radiolabel remained nearly unchanged for at least 22 days. During this interval, less than 10% of the total 32P-labeled neurofilaments redistributed from the optic nerve to the optic tract. By contrast, newly synthesized neurofilaments were selectively pulse-labeled in ganglion cell bodies by intravitreous injection of [35S]methionine and about 60% of this pool translocated by slow axoplasmic transport to the optic tract during the same time interval. These findings indicate that the steady-state or resident pool of neurofilaments in axons is not identical to the newly synthesized neurofilament pool, the major portion of which moves at the slowest rate of axoplasmic transport. Taken together with earlier studies, these results support the idea that, depending in part on their phosphorylation state, transported neurofilaments can interact for short or very long periods with a stationary but dynamic neurofilament lattice in axons
— id: 25165, year: 1994, vol: 19, page: 1445, stat: Journal Article,

Phosphorylation on carboxyl terminus domains of neurofilament proteins in retinal ganglion cell neurons in vivo: influences on regional neurofilament accumulation, interneurofilament spacing, and axon caliber
Nixon RA; Paskevich PA; Sihag RK; Thayer CY
1994 Aug;126(4):1031-1046, Journal of cell biology
The high molecular weight subunits of neurofilaments, NF-H and NF-M, have distinctively long carboxyl-terminal domains that become highly phosphorylated after newly formed neurofilaments enter the axon. We have investigated the functions of this process in normal, unperturbed retinal ganglion cell neurons of mature mice. Using in vivo pulse labeling with [35S]methionine or [32P]orthophosphate and immunocytochemistry with monoclonal antibodies to phosphorylation-dependent neurofilament epitopes, we showed that NF-H and NF-M subunits of transported neurofilaments begin to attain a mature state of phosphorylation within a discrete, very proximal region along optic axons starting 150 microns from the eye. Ultrastructural morphometry of 1,700-2,500 optic axons at each of seven levels proximal or distal to this transition zone demonstrated a threefold expansion of axon caliber at the 150-microns level, which then remained constant distally. The numbers of neurofilaments nearly doubled between the 100- and 150-microns level and further increased a total of threefold by the 1,200-microns level. Microtubule numbers rose only 30-35%. The minimum spacing between neurofilaments also nearly doubled and the average spacing increased from 30 nm to 55 nm. These results show that carboxyl-terminal phosphorylation expands axon caliber by initiating the local accumulation of neurofilaments within axons as well as by increasing the obligatory lateral spacing between neurofilaments. Myelination, which also began at the 150-microns level, may be an important influence on these events because no local neurofilament accumulation or caliber expansion occurred along unmyelinated optic axons. These findings provide evidence that carboxyl-terminal phosphorylation triggers the radial extension of neurofilament sidearms and is a key regulatory influence on neurofilament transport and on the local formation of a stationary but dynamic axonal cytoskeletal network
— id: 25168, year: 1994, vol: 126, page: 1031, stat: Journal Article,

Calcium-activated neutral proteinase (calpain) system in aging and Alzheimer's disease
Nixon RA; Saito KI; Grynspan F; Griffin WR; Katayama S; Honda T; Mohan PS; Shea TB; Beermann M
1994 Dec 15;747(3):77-91, Annals of the New York Academy of Sciences
Calpains (CANPs) are a family of calcium-dependent cysteine proteases under complex cellular regulation. By making selective limited proteolytic cleavages, they activate or alter the regulation of certain enzymes, including key protein kinases and phosphatases, and induce specific cytoskeletal rearrangements, accounting for their suspected involvement in intracellular signaling, vesicular trafficking, and structural stabilization. Calpain activity has been implicated in various aging phenomena, including cataract formation and erythrocyte senescence. Abnormal activation of the large stores of latent calpain in neurons induces cell injury and is believed to underlie neurodegeneration in excitotoxicity, Wallerian degeneration, and certain other neuropathologic states involving abnormal calcium influx. In Alzheimer's disease, we found the ratio of activated calpain I to its latent precursor isoform in neocortex to be threefold higher than that in normal individuals and those with Huntington's or Parkinson's disease. Immunoreactivity toward calpastatin, the endogenous inhibitor of calpain, was also markedly reduced in layers II-V of the neocortex in Alzheimer's disease. The excessive calpain system activation suggested by these findings represents a potential molecular basis for synaptic loss and neuronal cell death in the brain in Alzheimer's disease given the known destructive actions of calpain I and its preferential neuronal and synaptic localization. In surviving cells, persistent calpain activation may also contribute to neurofibrillary pathology and abnormal amyloid precursor protein trafficking/processing through its known actions on protein kinases and the membrane skeleton. The degree of abnormal calpain activation in the brain in Alzheimer's disease strongly correlated with the extent of decline in levels of secreted amyloid precursor protein in brain. Cytoskeletal proteins that are normally good calpain substrates become relatively calpain resistant when they are hyperphosphorylated, which may contribute to their accumulation in neurofibrillary tangles. As a major effector of calcium signals, calpain activity may mirror disturbances in calcium homeostasis and mediate important pathologic consequences of such disturbances
— id: 25180, year: 1994, vol: 747, page: 77, stat: Journal Article,

Secretion of amyloid precursor protein and laminin by cultured astrocytes is influenced by culture conditions
Shea TB; Beermann ML; Honda T; Nixon RA
1994 Feb 1;37(2):197-207, Journal of neuroscience research
Although normally quiescent, astrocytes in the adult brain respond to various types of brain injury by rapidly dividing, swelling, extending cellular processes, and expressing increased amounts of glial fibrillary acidic protein (GFAP). These phenomena are collectively referred to as 'astrogliosis.' Similarly, astroglia in primary culture stop dividing when they attain confluency, yet, as seen in situ, they retain their proliferative capacity for extended periods and resume rapid division when subcultured. To examine the impact of glial division on secretion of neurite-promoting factors, conditioned medium (CM) was removed from subconfluent, newly confluent, and long-term confluent ('aged') neonatal rat astrocyte cultures, and from aged confluent cultures that had been repassaged, 'lesioned' (scraping with a rubber policeman), or triturated 3 days before harvest. Secretion of neurite-promoting factor(s) by glial cells into these CM was then assayed by treating neuroblastoma cultures with these various CM and quantitating neurite elaboration. Extensive neurite sprouting was elicited by CM from cultures just reaching confluency and from repassaged, lesioned, or triturated cultures. CM from aged confluent cultures did not induce sprouting. These results indicate that secretion of neurite-promoting factor(s) is regulated by glial division, and suggest that gliosis in situ may contribute to neurite sprouting by similar mechanisms. Immunoblot analysis demonstrated the presence in CM of varying amounts of laminin and amyloid precursor protein (APP), including isoforms containing the Kunitz-type protease inhibitor domain. CM from subconfluent cultures contained trace amounts of these proteins, but CM from cultures just reaching confluency contained significant amounts. Although CM from aged cultures contained barely detectable levels of either protein, trituration or repassage of aged cultures dramatically increased secretion of these proteins. APP- and laminin-enriched CM fractions promoted neuritogenesis to a similar level as respective unfractionated CM; anti-APP and anti-laminin antisera blocked this effect. Purified human brain APP promoted neuritogenesis when added to non-conditioned medium and aged CM. Increased secretion of APP and laminin therefore mediates at least a portion of CM-induced neuronal sprouting; these proteins may perform analogous functions during astrogliosis in situ
— id: 25170, year: 1994, vol: 37, page: 197, stat: Journal Article,

Evidence for the association of protein 4.1 immunoreactive forms with neurofibrillary tangles in Alzheimer's disease brains
Sihag RK; Wang LW; Cataldo AM; Hamlin M; Cohen CM; Nixon RA
1994 Sep 5;656(1):14-26, Brain research
The formation of neurofibrillary tangles (NFTs) and paired-helical filaments (PHFs) in Alzheimer's disease (AD) reflects a major disorganization of the cytoskeleton. The role of the neuronal membrane skeleton in the development of these abnormalities has not previously been investigated. In this study, we used 9 antibodies raised against the erythrocyte membrane skeleton protein 4.1 (P4.1) for immunocytochemical and immunoblot analyses to investigate whether or not the brain homologues of this protein were constituents of NFTs or PHFs. Our results show that 7 of the 9 monospecific antibodies against the human and pig erythrocyte P4.1 stained NFTs in the prefrontal cortex and hippocampus of AD brains. The P4.1 antibodies used here did not cross-react with tau protein isolated from AD brain, and preabsorption of these antibodies with tau protein did not cause loss of NFT staining. In age-matched control brains, these P4.1 antibodies stained neuronal cell bodies or nuclei. Six of the antibodies also stained isolated NFTs but the SDS-insoluble NFTs were immunostained only by two of the P4.1 antibodies. By using inositol hexaphosphate affinity chromatography and immunoblot analysis, we identified a 68-kDa protein as the most likely brain analogue of P4.1. When SDS-extracted proteins from the isolated NFTs were immunoblotted, a 50-kDa band was immunostained. The 68-kDa and 50-kDa proteins were not stained by tau protein and neurofilament subunit NF-H antibodies, that strongly stained NFTs. We conclude that brain protein 4.1 isoform(s) are constituents of NFTs in AD
— id: 25167, year: 1994, vol: 656, page: 14, stat: Journal Article,

Thyrotropin response to thyrotropin-releasing hormone in patients with dementia of the Alzheimer type
Albert M; Jenike M; Nixon R; Nobel K
1993 Feb 15;33(4):267-271, Biological psychiatry
Eleven patients with senile dementia of the Alzheimer type and 11 age-matched control subjects were given the thyrotropin-releasing hormone (TRH) test. The two groups did not differ with respect to peak thyrotropin (TSH) response or TSH levels at baseline, 20, 30, and 45 min after TRH injection. There were significant differences between the groups on Hamilton Depression Rating Scale scores (p < 0.03), although neither group met clinical criteria for depression. Items that were significantly different pertained to depressed mood, loss of interest, loss of insight, suicidal ideation, and obsessional symptoms
— id: 25502, year: 1993, vol: 33, page: 267, stat: Journal Article,

Differential expression and subcellular localization of protein kinase C alpha, beta, gamma, delta, and epsilon isoforms in SH-SY5Y neuroblastoma cells: modifications during differentiation
Leli U; Shea TB; Cataldo A; Hauser G; Grynspan F; Beermann ML; Liepkalns VA; Nixon RA; Parker PJ
1993 Jan;60(1):289-298, Journal of neurochemistry
A decrease in protein kinase C activity caused either by treatment with inhibitors, such as staurosporine or H-7, or by prolonged exposure to phorbol diesters has been proposed to be involved in the early events of SH-SY5Y neuroblastoma cell differentiation. Because eight distinct isoforms of protein kinase C with discrete subcellular and tissue distributions have been described, we determined which isoforms are present in SH-SY5Y cells and studied their modifications during differentiation. The alpha, beta 1, delta, and epsilon isoforms were present in SH-SY5Y cells, as well as in rat brain. Protein kinase C-alpha and -beta 1 were the most abundant isoforms in SH-SY5Y cells, and immunoreactive protein kinase C-delta and -epsilon were present in much smaller amounts than in rat brain. Subcellular fractionation and immunocytochemistry demonstrated that all four isoforms are distributed bimodally in the cytoplasm and the membranes. Immunocytochemical analysis showed that the alpha isoform is associated predominantly with the plasma membrane and the processes extended during treatment with 12-tetradecanoyl-13-acetyl-beta-phorbol or staurosporine, and that protein kinase C-epsilon is predominantly membrane-bound. Its localization did not change during differentiation. Western blots of total SH-SY5Y cell extracts and of subcellular fractions probed with isoform-specific polyclonal antibodies showed that when SH-SY5Y cells acquired a morphologically differentiated phenotype, protein kinase C-alpha and -epsilon decreased, and protein kinase C-beta 1 did not change. These data suggest distinct roles for the different protein kinase C isoforms during neuronal differentiation, as well as possible involvement of protein kinase alpha and epsilon in neuritogenesis
— id: 25500, year: 1993, vol: 60, page: 289, stat: Journal Article,

The regulation of neurofilament protein dynamics by phosphorylation: clues to neurofibrillary pathobiology
Nixon RA
1993 Jan;3(1):29-38, Brain pathology
Neurofilament proteins are continuously modified during their lifetime by a succession of protein kinases and phosphatases. Site-specific phosphorylation or dephosphorylation within different polypeptide domains of each neurofilament subunit is now believed to regulate such behaviors of neurofilaments as subunit polymerization and exchange, axonal transport, interactions with other cytoskeletal proteins and degradation. Local regulation of phosphorylation events could account for variations in the size, morphology and dynamics of the neurofilament network in different regions of the neuron. The apparent greater plasticity of the neurofilament network in regions like the perikaryon, initial segment and nodes along the axon may provide some insight into the vulnerability of these regions in neurofibrillary disease
— id: 25501, year: 1993, vol: 3, page: 29, stat: Journal Article,

Abnormalities of lysosomal proteolysis in neurons in Alzheimer's disease and Down's syndrome: possible relationship to b-amyloid deposition
Nixon RA; Cataldo A; Mann DMA; Paskevich PA; Hamilton DJ; Wheelock TR
Alzheimer's disease: advances in clinical and basic research New York : Wiley, 1993,
— id: 2730, year: 1993, vol: , page: 441, stat: Chapter,

The lysosomal system in neuronal cell death: a review
Nixon RA; Cataldo AM
1993 May 28;679(2):87-109, Annals of the New York Academy of Sciences
The lysosomal system has often been considered a prominent morphologic marker of distressed or dying neurons. Lysosomes or their constituent hydrolases have been viewed in different neuropathologic states as either initiators and direct agents of cell death, agents of cellular repair and recompensation, effectors of end-stage cellular dissolution, or autolytic scavengers of cellular debris. Limited data and limitations of methodology often do not allow these potential roles to be discriminated. In all forms of neurodegeneration, it may be presumed that lysosomes ultimately rupture and release various hydrolases that promote cell autolysis during the final stages of cellular disintegration. Beyond this perhaps universal contribution to cell death, the degree to which the lysosomal system may be involved in neurodegenerative states varies considerably. In many conditions, morphologic evidence for activation of the lysosomal system is minimal or undetectable. In other cases, lysosomal activation is evident only when other morphologic signs of cell injury are also present. This level of participation may be viewed as either an attempt by the neuron to compensate for or repair the injury or a late-stage event leading to cell dissolution. The early involvement of the lysosomal system in neurodegeneration occurs most commonly in the form of intraneuronal accumulations of abnormal storage profiles or residual bodies (tertiary lysosomes). Very often the lysosomal involvement can be traced to a primary defect or dysfunction of lysosomal components or to accelerated or abnormal membrane breakdown that leads to the buildup of modified digestion-resistant substrates within lysosomes. Because they are often striking, changes in the lysosomal system are a sensitive morphologic indicator of certain types of metabolic distress; however, whether they reflect a salutary response of a compromised neuron or a mechanism to promote cell death and removal of debris from the brain remains to be established for most conditions. Factors that may influence the lysosomal response during lethal neuronal injury include species differences, stage of neuronal development, duration of injury and pace of cell death. The lysosomal system may be more closely coupled to certain forms of neuronal cell death in lower vertebrate or invertebrate systems than in mammalian systems
— id: 25497, year: 1993, vol: 679, page: 87, stat: Journal Article,

Widespread activation of calcium-activated neutral proteinase (calpain) in the brain in Alzheimer disease: a potential molecular basis for neuronal degeneration
Saito K; Elce JS; Hamos JE; Nixon RA
1993 Apr 1;90(7):2628-2632, Proceedings of the National Academy of Sciences of the United States of America
Calcium-activated neutral proteinases (CANPs or calpains) are believed to be key enzymes in intracellular signaling cascades and potential mediators of calcium-induced neuronal degeneration. To investigate their involvement in Alzheimer disease, we identified three isoforms of muCANP (calpain I) in human postmortem brain corresponding to an 80-kDa precursor and two autolytically activated isoforms (78 and 76 kDa). As an index of changes in the in vivo activity of muCANP in Alzheimer disease, the ratio of the 76-kDa activated isoform of muCANP to its 80-kDa precursor was measured by immunoassay in selected brain regions from 22 individuals with Alzheimer disease and 18 normal controls. This muCANP activation ratio was elevated 3-fold in the prefrontal cortex from patients with Alzheimer disease but not from patients with Huntington disease. The activation ratio was also significantly elevated, but to a lesser degree, in brain regions where Alzheimer pathology is milder and has not led to overt neuronal degeneration. These findings indicate that muCANP activation is not simply a consequence of cellular degeneration but may be associated with dysfunction in many neurons before gross structural changes occur. The known influences of CANPs on cytoskeleton and membrane dynamics imply that persistent CANP activation may contribute to neurofibrillary pathology and abnormal amyloid precursor protein processing prior to causing synapse loss or cell death in the most vulnerable neuronal populations. Pharmacological modulation of the CANP system may merit consideration as a potential therapeutic strategy in Alzheimer disease
— id: 25498, year: 1993, vol: 90, page: 2628, stat: Journal Article,

Specificity of calcium-activated neutral proteinase (CANP) inhibitors for human mu CANP and mCANP
Saito K; Nixon RA
1993 Feb;18(2):231-233, Neurochemical research
We investigated the relative inhibition of purified human mu CANP and mCANP by five cysteine proteinase inhibitors including N-acetyl-Leu-Leu-nor-leucinal (C-I) and N-acetyl-Leu-Leu-methioninal (C-II), calpeptin, E64, and leupeptin. Based on IC50 measurements, calpeptin and C-I were stronger inhibitors by one to two orders of magnitude than C-II, leupeptin or E64. None of the five inhibitors, however, exhibited greater specificity for human mu CANP or mCANP. These results indicate that, although the inhibition of a given cellular event by these compounds may suggest CANP involvement, effects on mu CANP cannot be discriminated from those on mCANP
— id: 25499, year: 1993, vol: 18, page: 231, stat: Journal Article,

Proteases and protease inhibitors in Alzheimer's Disease pathogens
Banner CDB; Nixon RA
New York : NY Academy of Sciences, 1992,
— id: 639, year: 1992, vol: , page: , stat: ,

Distinct mechanisms of differentiation of SH-SY5Y neuroblastoma cells by protein kinase C activators and inhibitors
Leli U; Cataldo A; Shea TB; Nixon RA; Hauser G
1992 Apr;58(4):1191-1198, Journal of neurochemistry
Certain biological actions of phorbol esters cannot be duplicated by diacylglycerol (DAG). Thus, the human neuroblastoma cell line SH-SY5Y differentiates when exposed to 12-tetradecanoyl-13-acetyl-beta-phorbol (TPA) and protein kinase C (PKC) inhibitors, but not when exposed to DAG. To investigate the specific features of the phorbol diester molecule that might be responsible for these effects, we examined the extension of neurites, expression of neuron-specific enolase, and appearance and localization of phosphorylated high molecular weight neurofilament subunits (NF-H). TPA, 12-deoxy-13-tetradecanoyl-beta-phorbol, and staurosporine, but not DAG or 4-O-methyl-TPA, caused neurite outgrowth. Neuron-specific enolase was expressed in cells treated with TPA and 12-deoxy-13-tetradecanoyl-beta-phorbol but not with DAG, staurosporine, or 4-O-methyl-TPA. NF-H increased in the perikarya of cells treated with DAG and 4-O-methyl-TPA, in processes and to varying degrees in perikarya of TPA- and 12-deoxy-13-tetradecanoyl-beta-phorbol-treated cells, but much more in the processes than in the perikarya of staurosporine-differentiated cells. These findings and additional differences between the differentiation induced by TPA (a PKC activator) and staurosporine (a PKC inhibitor), including distinct morphology of the cell body and processes and time of appearance of the morphological phenotype, suggest that activators and inhibitors of PKC induce differentiation of SH-SY5Y cells by different mechanisms, and that the five-membered/seven-membered terpene ring region present in TPA must be intact for the induction of morphological differentiation
— id: 25492, year: 1992, vol: 58, page: 1191, stat: Journal Article,

Slow axonal transport
Nixon RA
1992 Feb;4(1):8-14, Current opinion in cell biology
New studies provide further evidence that the neuronal cytoskeleton is the product of a dynamic interplay between axonal transport processes and locally regulated assembly mechanisms. These data confirm that the axonal cytoskeleton in mammalian systems is largely stationary and is maintained by a smaller pool of moving subunits or polymers. Slow axonal transport in certain lower species, however, may exhibit quite different features
— id: 25495, year: 1992, vol: 4, page: 8, stat: Journal Article,

The lysosomal system in neurons. Involvement at multiple stages of Alzheimer's disease pathogenesis
Nixon RA; Cataldo AM; Paskevich PA; Hamilton DJ; Wheelock TR; Kanaley-Andrews L
1992 Dec 31;674(3):65-88, Annals of the New York Academy of Sciences
Disturbed lysosomal function may be implicated at several stages of Alzheimer's pathogenesis. Lysosomes and acid hydrolases accumulate in the majority of neocortical pyramidal neurons before typical degenerative changes can be detected, indicating that altered lysosome function is among the earliest markers of metabolic dysfunction in Alzheimer's disease. These early alterations could reflect accelerated membrane and protein turnover, defective lysosome or hydrolase function, abnormal lysosomal trafficking or any combination of these possibilities. Because APP is partly metabolized in lysosomes, early disturbances in lysosomal function could promote the production of abnormal and/or neurotoxic APP fragments within intact cells. Lysosomal abnormalities progressively worsen as neurons begin to degenerate. Based on existing literature on cell death, increased perturbation and instability of the lysosomal system may be expected to contribute to the atrophy and eventual lysis of the neuron. Finally, the release of hydrolase-filled lysosomes and lipofuscin aggregates from dying neurons accounts for the abundant deposition of enzymatically active acid hydrolases of all classes in the extracellular space--a phenomenon that may be unique to Alzheimer's disease. Acting on APP present in surrounding dystrophic neurites, cellular debris and astrocyte processes, dysregulated hydrolases may cleave APP in atypical sequential patterns, thereby generating self-aggregating protease-resistant APP fragments that can be only processed to beta-amyloid. Genetic mutations or posttranslational factors of APP should further enhance the generation of amyloidogenic fragments by a dysregulated lysosomal system. Given that very little, if any, beta-amyloid is detected intracellularly, yet extracellular beta-amyloid is very abundant, our data suggest that the final steps of APP processing and the generation of most beta-amyloid in the brain parenchyma occur extracellularly and may involve one or more lysosomal proteases
— id: 25488, year: 1992, vol: 674, page: 65, stat: Journal Article,

Dynamics of neuronal intermediate filaments: a developmental perspective
Nixon RA; Shea TB
1992 ;22(2):81-91, Cell motility & the cytoskeleton
— id: 25496, year: 1992, vol: 22, page: 81, stat: Journal Article,

Opposing influences of protein kinase activities on neurite outgrowth in human neuroblastoma cells: initiation by kinase A and restriction by kinase C
Shea TB; Beermann ML; Leli U; Nixon RA
1992 Nov;33(3):398-407, Journal of neuroscience research
The respective roles of cAMP-dependent protein kinase (protein kinase A [PKA]) and protein kinase C (PKC) in the early stages of neurite outgrowth were examined in SH-SY-5Y human neuroblastoma cells. Forskolin or dbcAMP, agents that increase intracellular cAMP levels, and intracellular delivery of PKA catalytic subunit induced neurite outgrowth. The PKA inhibitor, N-(2-guanidinoethyl)-5-isoquinolinesulfonamide (HA 1004), prevented the increases, and decreased further the percentage of cells possessing short, filopodia-like neurites in the absence of inducers. In contrast to effects on PKA activation, PKC activation by 12-0-tetradecanoylphorbol-13-acetate (TPA) reduced the percentage of filopodia-like neurites elaborated by otherwise untreated cells, and prevented neurite outgrowth induced by PKA activators. PKC inhibitors 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H7), staurosporine, and sphingosine induced neurite outgrowth. Neurites induced by PKA activation contained higher levels of tubulin immunoreactivity than those induced by PKC inhibition. Furthermore, PKA-induced neurites rapidly retracted in the presence of colchicine, while those elaborated following PKC inhibition were more resistant. These data suggest that neurites elaborated in response to PKA activation are dependent upon microtubule polymerization, and that neurite induction following PKC inhibition is mediated by a different mechanism. PKA activators and PKC inhibitors exerted additive effects on neurite outgrowth, suggesting that the distinct pathways regulated by these two kinases function cooperatively during neuritogenesis
— id: 25489, year: 1992, vol: 33, page: 398, stat: Journal Article,

Aluminum alters the electrophoretic properties of neurofilament proteins: role of phosphorylation state
Shea TB; Beermann ML; Nixon RA
1992 Feb;58(2):542-547, Journal of neurochemistry
Exposure of each of the three neurofilament proteins (NFPs) to AlCl3 resulted in their failure to migrate into sodium dodecyl sulfate (SDS)-containing gels. This effect was dependent on length of incubation (minimum, 2 h) and AlCl3 concentrations (minimum, 50 microM) and was not reversed by 20% SDS, 6 M urea, freeze-thawing, boiling, or extensive dialysis. The migration of vimentin and glial fibrillary acidic protein was not affected by AlCl3. The high-molecular-weight neurofilament subunit (NF-H) entered SDS-containing gels after exposure to aluminum lactate but migrated aberrantly as a long high-molecular-weight streak. Migration of the 160-kDa alpha-chymotryptic cleavage product of NF-H, which contains the higher phosphorylated tail domain, was also prevented from migrating into SDS-containing gels by AlCl3. Dephosphorylation of NF-H and the middle-molecular-weight neurofilament subunit (NF-M) eliminated these effects on gel migration. EDTA, EGTA, MgCl2, CaCl2, or FeCl3 had no effect on NF-H or NF-M migration; furthermore, preincubation with, or simultaneous exposure to, CaCl2 or FeCl3 did not alter the effect of AlCl3. One interpretation of these results is that Al3+ interacts with phosphate groups on extensively phosphorylated C-terminal sidearms of NFPs, resulting in intermolecular cross-linking. These findings demonstrate a direct effect of aluminum on NFPs and provide a possible mechanism for neurofilament accumulation in perikarya during aluminum intoxication
— id: 25493, year: 1992, vol: 58, page: 542, stat: Journal Article,

Complementary effects of laminin and protease inhibitors on neurite outgrowth and maintenance
Shea TB; Beermann ML; Nixon RA
1992 ;10:53-61, Neuroscience research communications
— id: 25505, year: 1992, vol: 10, page: 53, stat: Journal Article,

Sequential effects of astroglial-derived factors on neurite outgrowth: initiation by protease inhibitors and potentiation by extracellular matrix components
Shea TB; Beermann ML; Nixon RA
1992 Feb;31(2):309-317, Journal of neuroscience research
Astroglial-conditioned medium (GCM) induced two distinct, but intimately related, phases of neuritogenesis in NB2a/d1 neuroblastoma cells--a 'rapid-outgrowth,' unstable phase, and a delayed, relatively stable phase, which are apparently regulated by glial-derived protease inhibitors and laminin, respectively. The initial rapid outgrowth (less than 4 hr) may be mediated by inhibition of a thrombin-like protease, present as a serum component and/or adsorbed to the outer neuronal surface, since (1) a similar effect was obtained by serum removal or by adding the specific thrombin inhibitor, hirudin; (2) exogenous thrombin inhibited the rapid outgrowth of neurites by GCM; and (3) cell-free enzyme assays confirmed the presence of thrombin-inhibitory activity in GCM. Although neurites induced by removal of serum removal or hirudin addition are rapidly resorbed following serum replenishment or hirudin depletion, GCM-induced neurites continued to elongate after GCM removal, indicating that GCM contained additional neurite-promoting factors. Anti-laminin antiserum did not inhibit the initial elaboration of neurites by GCM but prevented their continued elongation. Anti-laminin antiserum had no affect on neurite outgrowth induced by serum deprivation. The more protracted, second phase of neurite outgrowth could also be achieved by the addition of soluble purified laminin to undifferentiated cells. Unlike neurites at 4 hr, neurites at 24 hr were no longer dependent on the protease inhibitors in GCM, since exogenous thrombin no longer caused them to retract. Simultaneous addition of thrombin and anti-laminin antiserum with GCM had identical inhibitory effects on continued neurite elaboration at 24 hr as did anti-laminin antiserum without thrombin.(ABSTRACT TRUNCATED AT 250 WORDS)
— id: 25494, year: 1992, vol: 31, page: 309, stat: Journal Article,

Microtubule-associated protein tau is required for axonal neurite elaboration by neuroblastoma cells
Shea TB; Beermann ML; Nixon RA; Fischer I
1992 Jul;32(3):363-374, Journal of neuroscience research
NB2a/d1 neuroblastoma cells constitutively express multiple isoforms of the microtubule-associated protein tau and incorporate this protein into the axonal neurites elaborated during serum deprivation. To examine whether or not tau played an essential role in axonal outgrowth, cells cultured in serum-free medium were treated at 24 h intervals with antisense- and sense-oriented cDNA oligonucleotides (25 or 36 mers that span or are upstream of tau initiation codon) and were simultaneously serum deprived. Oligonucleotide uptake was confirmed by determination of intracellular levels of radiolabeled oligonucleotides. Treatment for 48 h with tau antisense oligonucleotides reversibly inhibited the expression of tau and the number of neurite-bearing cells compared with treatment with sense oligonucleotides. By contrast, tubulin expression was not affected. When cells were treated with antisense oligonucleotide simultaneously with serum deprivation, the initial outgrowth of neurites was unaffected, but continued neurite elongation was prevented. By contrast, neurite outgrowth at 4 h was inhibited when cells were pretreated with tau antisense 24 h before serum deprivation. Furthermore, intracellular delivery of anti-tau antiserum prevented neurite outgrowth and, in cells that had previously been deprived of serum for 24 h, induced retraction of existing neurites. These findings indicate that both the initiation and the continued outgrowth of neurites are dependent on tau and that pre-existing cytoplasmic pools of tau can mediate initial neuritogenesis
— id: 25490, year: 1992, vol: 32, page: 363, stat: Journal Article,

Immunoassay and activity of calcium-activated neutral proteinase (mCANP): distribution in soluble and membrane-associated fractions in human and mouse brain
Takeuchi KH; Saito KI; Nixon RA
1992 Apr;58(4):1526-1532, Journal of neurochemistry
The millimolar form of calcium-activated neutral proteinase (mCANP) is generally regarded as a cytosolic enzyme in nonneuronal systems, although its subcellular localization in brain is less well established. To resolve conflicting reports on the localization of mCANP based on activity measurements, we developed an immunoassay for CANP and compared the content and activity of the molecule in soluble and membrane fractions of mouse and human brain. Western blot immunoassays, using two different antibodies specific for mCANP, demonstrated that mCANP content is 4.5 ng/g in human or mouse brain, about 0.0005% of the total protein. More than 95% of the total immunoreactive mCANP remained in the soluble fraction after 15,000 g centrifugation of the whole homogenate. mCANP activity was determined with [14C]azocasein as substrate after removing endogenous CANP inhibitor(s) by ion-exchange chromatography on DEAE-cellulose. Caseinolytic activity was detected only in fractions derived from the supernatant extract. The distribution of mCANP content and enzyme activity were unchanged when tissues were extracted with different concentrations of Triton X-100. These findings establish the usefulness and validity of the CANP immunoassay and demonstrate that mCANP in mouse and human brain is localized predominantly within the cytosol
— id: 25491, year: 1992, vol: 58, page: 1526, stat: Journal Article,

Lysosomal hydrolases of different classes are abnormally distributed in brains of patients with Alzheimer disease
Cataldo AM; Paskevich PA; Kominami E; Nixon RA
1991 Dec 15;88(24):10998-11002, Proceedings of the National Academy of Sciences of the United States of America
beta-Amyloid formation requires multiple abnormal proteolytic cleavages of amyloid precursor protein (APP), including one within its intramembrane domain. Lysosomes, which contain a wide variety of proteases (cathepsins) and other acid hydrolases, are major sites for the turnover of membrane proteins and other cell constituents. Using immunocytochemistry, immunoelectron microscopy, and enzyme histochemistry, we studied the expression and cellular distributions of 10 lysosomal hydrolases, including 4 cathepsins, in neocortex from patients with Alzheimer disease and control (non-Alzheimer-disease) individuals. In control brains, acid hydrolases were localized exclusively to intracellular lysosome-related compartments, and 8 of the 10 enzymes predominated in neurons. In Alzheimer disease brains, strongly immunoreactive lysosomes and lipofuscin granules accumulated markedly in the perikarya and proximal dendrites of many cortical neurons, some of which were undergoing degeneration. More strikingly, these same hydrolases were present in equally high or higher levels in senile plaques in Alzheimer disease, but they were not found extracellularly in control brains, including those from Parkinson or Huntington disease patients. At the ultrastructural level, hydrolase immunoreactivity in senile plaques was localized to extracellular lipofuscin granules similar in morphology to those within degenerating neurons. Two cathepsins that were undetectable in neurons were absent from senile plaques. These results show that lysosome function is altered in cortical neurons in Alzheimer disease. The presence of a broad spectrum of acid hydrolases in senile plaques indicates that lysosomes and their contents may be liberated from cells, principally neurons and their processes, as they degenerate. Because cathepsins can cleave polypeptide sites on APP relevant for beta-amyloid formation, their abnormal extracellular localization and dysregulation in Alzheimer disease can account for the multiple hydrolytic events in beta-amyloid formation. The actions of membrane-degrading acid hydrolases could also explain how the intramembrane portion of APP containing the C terminus of beta-amyloid becomes accessible to proteases
— id: 25484, year: 1991, vol: 88, page: 10998, stat: Journal Article,

Axonal transport of cytoskeletal proteins
Nixon RA
The neuronal cytoskeleton New York : Wiley-Liss, 1991,
— id: 2729, year: 1991, vol: , page: 283, stat: Chapter,

Lysosomal proteolysis in Alzheimer brain: possible roles in neuronal cell death and amyloid formation
Nixon RA; Cataldo AM
Frontiers of Alzheimer research New York : Excerpta Medica, 1991,
— id: 2732, year: 1991, vol: , page: 133, stat: Chapter,

Neurofilament phosphorylation: a new look at regulation and function
Nixon RA; Sihag RK
1991 Nov;14(11):501-506, Trends in neurosciences
Dynamic remodeling of cytoskeleton architecture is necessary for axonal growth and guidance, signal transduction and other fundamental aspects of neuron function. Protein phosphorylation plays a key part in these remodeling processes. Since neurofilaments are major cytoskeletal constituents and are among the most highly phosphorylated neuronal proteins, the control of their behavior serves as a possible model for understanding how phosphorylation regulates the many other phosphoproteins in the cytoskeleton. Recent studies show that neurofilament protein subunits are phosphorylated on both their amino-terminal head domains and carboxy-terminal tails by different protein kinases. This review considers the implications of this complex regulation for neurofilament function in normal neurons and in disease states characterized by neurofibrillary pathology
— id: 25485, year: 1991, vol: 14, page: 501, stat: Journal Article,

Multiple proteases regulate neurite outgrowth in NB2a/dl neuroblastoma cells
Shea TB; Beermann ML; Nixon RA
1991 Mar;56(3):842-851, Journal of neurochemistry
Mouse NB2a/dl neuroblastoma cells elaborate axonal neurites in response to various chemical treatments including dibutyryl cyclic AMP and serum deprivation. Hirudin, a specific inhibitor of thrombin, initiated neurite outgrowth in NB2a/dl cells cultured in the presence of serum; however, these neurites typically retracted within 24 h. The cysteine protease inhibitors leupeptin and N-acetyl-leucyl-leucyl-norleucinal (CI; preferential inhibitor of micromolar calpain but also inhibits millimolar calpain) at 10(-6) M considerably enhanced neurite outgrowth induced by serum deprivation, but could not induce neuritogenesis in the presence of serum. A third cysteine protease inhibitor, N-acetyl-leucyl-leucyl-methional (CII; preferential inhibitor of millimolar calpain but also inhibits micromolar calpain), had no detectable effects by itself. Cells treated simultaneously with hirudin and either leupeptin, CI, or CII elaborated stable neurites in the presence of serum. Cell-free enzyme assays demonstrated that hirudin inhibited thrombin but not calpain, CI and CII inhibited calpain but not thrombin, and leupeptin inhibited both proteases. These results imply that distinct proteolytic events, possibly involving more than one protease, regulate the initiation and subsequent elongation and stabilization of axonal neurites. Since the addition of exogenous thrombin or calpain to serum-free medium did not modify neurite outgrowth, the proteolytic events affected by these inhibitors may be intracellular or involve proteases distinct from thrombin or calpain
— id: 25487, year: 1991, vol: 56, page: 842, stat: Journal Article,

Evidence for site- and domain-specific phosphorylation of the 145-kDa neurofilament subunit in vivo
Sihag RK; Nixon RA
Cellular regulation by protein phosphorylation Berlin : Springer-Verlag, 1991,
— id: 2731, year: 1991, vol: , page: 465, stat: Chapter,

Identification of Ser-55 as a major protein kinase A phosphorylation site on the 70-kDa subunit of neurofilaments. Early turnover during axonal transport
Sihag RK; Nixon RA
1991 Oct 5;266(28):18861-18867, Journal of biological chemistry
The 70-kDa neurofilament protein subunit (NF-L) is phosphorylated in vivo on at least three sites (L1 to L3) (Sihag, R. K. and Nixon, R. A. (1989) J. Biol. Chem. 264, 457-464). The turnover of phosphate groups on NF-L during axonal transport was determined after the neurofilaments in retinal ganglion cells were phosphorylated in vivo by injecting mice intravitreally with [32P]orthophosphate. Two-dimensional phosphopeptide maps of NF-L from optic axons of mice 10 to 90 h after injection showed that radiolabel decreased faster from peptides L2 and L3 than from L1 as neurofilaments were transported. To identify phosphorylation sites on peptide L2, axonal cytoskeletons were phosphorylated by protein kinase A in the presence of heparin. After the isolated NF-L subunits were digested with alpha-chymotrypsin, 32P-peptides were separated by high performance liquid chromatography on a reverse-phase C8 column. Two-dimensional peptide mapping showed that the alpha-chymotrypsin 32P-peptide accepting most of the phosphates from protein kinase A migrated identically with the in vivo-labeled phosphopeptide L2. The sequence of this peptide (S-V-R-R-S-Y) analyzed by automated Edman degradation corresponded to amino acid residues 51-56 of the NF-L sequence. A synthetic 13-mer (S-L-S-V-R-R-S-Y-S-S-S-S-G) corresponding to amino acid residues 49-61 of NF-L was also phosphorylated by protein kinase A. alpha-Chymotryptic digestion of the 13-mer generated a peptide which contained most of the phosphates and co-migrated with the phosphopeptide L2 on two-dimensional phosphopeptide maps. Edman degradation of the phosphorylated 13-mer identified serine residue 55 which is located within a consensus phosphorylation sequence for protein kinase A as the major site of phosphorylation. Since protein kinase A-mediated phosphorylation influences intermediate filament assembly/disassembly in vitro, we propose that the phosphopeptide L2 region is a neurofilament-assembly domain and that the cycle of phosphorylation and dephosphorylation of Ser-55 on NF-L, which occurs relatively early after subunit synthesis in vivo, regulaaes a step in neurofilament assembly or initial interactions during axonal transport
— id: 25486, year: 1991, vol: 266, page: 18861, stat: Journal Article,

Neuroleptic-associated autoantibodies. A prevalence study
Canoso RT; de Oliveira RM; Nixon RA
1990 Apr 15;27(8):863-870, Biological psychiatry
Antinuclear antibodies (ANA), antiphospholipid antibodies (APA), rheumatoid factor (RF), and immunoglobulin (Ig) M levels were determined in 184 male chronic psychiatric patients on long-term therapy with neuroleptics, and in 35 age-matched normal male controls. The prevalence of one or more of these autoantibodies was 70% in the neuroleptic-treated patients and 9% in the normal controls. Polyclonal IgM elevation was frequently seen among patients treated with phenothiazines. There was a significant correlation between the presence of ANA, APA, and RF; ANA and APA were more frequently associated with CPZ therapy, but the prevalence of RF was high in all treatment groups. These findings suggest that antibodies against the Fc fragment of IgG are the most common autoantibody associated with neuroleptics. Alternatively, the presence of RF could be a common finding in patients with neuropsychiatric disorders
— id: 25480, year: 1990, vol: 27, page: 863, stat: Journal Article,

Enzymatically active lysosomal proteases are associated with amyloid deposits in Alzheimer brain
Cataldo AM; Nixon RA
1990 May;87(10):3861-3865, Proceedings of the National Academy of Sciences of the United States of America
The formation of beta-amyloid in the brains of individuals with Alzheimer disease requires the proteolytic cleavage of a membrane-associated precursor protein. The proteases that may be involved in this process have not yet been identified. Cathepsins are normally intracellular proteolytic enzymes associated with lysosomes; however, when sections from Alzheimer brains were stained by antisera to cathepsin D and cathepsin B, high levels of immunoreactivity were also detected in senile plaques. Extracellular sites of cathepsin immunoreactivity were not seen in control brains from age-matched individuals without neurologic disease or from patients with Huntington disease or Parkinson disease. In situ enzyme histochemistry of cathepsin D and cathepsin B on sections of neocortex using synthetic peptides and protein substrates showed that senile plaques contained the highest levels of enzymatically active cathepsin. At the ultrastructural level, cathepsin immunoreactivity in senile plaques was localized principally to lysosomal dense bodies and lipofuscin granules, which were extracellular. Similar structures were abundant in degenerating neurons of Alzheimer neocortex, and cathepsin-laden neuronal perikarya in various stages of disintegration could be seen within some senile plaques. The high levels of enzymatically competent lysosomal proteases abnormally localized in senile plaques represent evidence for candidate enzymes that may mediate the proteolytic formation of amyloid. We propose that amyloid precursor protein within senile plaques is processed by lysosomal proteases principally derived from degenerating neurons. Escape of cathepsins from the stringently regulated intracellular milieu provides a basis for an abnormal sequence of proteolytic cleavages of accumulating amyloid precursor protein
— id: 25478, year: 1990, vol: 87, page: 3861, stat: Journal Article,

Lysosomal proteinase antigens are prominently localized within senile plaques of Alzheimer's disease: evidence for a neuronal origin
Cataldo AM; Thayer CY; Bird ED; Wheelock TR; Nixon RA
1990 Apr 16;513(2):181-192, Brain research
To investigate the role of proteolysis in amyloid formation, we studied the localization of the proteolytic enzymes, cathepsin D and cathepsin B, in the prefrontal cerebral cortex and hippocampus of human postmortem brains from patients with Alzheimer's disease and from individuals free of neurological disease. In control and Alzheimer brains, cathepsin immunoreactivity within cells was localized to lysosome-related structures, which were particularly abundant in neuronal perikarya. In Alzheimer brain, cathepsin immunoreactivity was also heavily concentrated extracellularly within senile plaques. Cathepsin immunoreactivity associated with plaques was not confined to lysosomes and was distributed throughout the plaque. Isolated amyloid cores, however, were not immunostained. Cathepsin-laden perikarya of degenerating neurons were frequently seen within senile plaques and, in the more advanced stages of degeneration, cathepsin immunoreactivity was present throughout the cytoplasm. Other identified constituents of senile plaques appeared to be less significant sources of cathepsin immunoreactivity, including astrocytes, degenerating neurites, microglia and macrophages. These results demonstrate that lysosomal proteinases are major constituents of the senile plaque and that degenerating neuronal perikarya are a principal source of the cathepsin immunoreactivity. We propose that the unregulated action of extracellular cathepsins liberated from degenerating neurons may lead to abnormal processing of the amyloid precursor protein and to the formation of amyloid locally within senile plaques in Alzheimer's disease
— id: 25479, year: 1990, vol: 513, page: 181, stat: Journal Article,

Aluminum inhibits calpain-mediated proteolysis and induces human neurofilament proteins to form protease-resistant high molecular weight complexes
Nixon RA; Clarke JF; Logvinenko KB; Tan MK; Hoult M; Grynspan F
1990 Dec;55(6):1950-1959, Journal of neurochemistry
We studied the effects of aluminum salts on the degradation of human neurofilament subunits (NF-H, NF-M, and NF-L, the high, middle, and low molecular weight subunits, respectively) and other cytoskeletal proteins using calcium-activated neutral proteinase (calpain) purified from human brain. Calpain-mediated proteolysis of NF-L, tubulin, and glial fibrillary acidic protein (GFAP), three substrates that displayed constant digestion rates in vitro, was inhibited by AlCl3 (IC50 = 200 microM) and by aluminum lactate (IC50 = 400 microM). Aluminum salts inhibited proteolysis principally by affecting the substrates directly. After exposure to 400 microM aluminum lactate and removal of unbound aluminum, human cytoskeletal proteins were degraded two- to threefold more slowly by calpain. When cytoskeleton preparations were exposed to aluminum salt concentrations of 100 microM or higher, proportions of NF-M and NF-H formed urea-insoluble complexes of high apparent molecular mass, which were also resistant to proteolysis by calpain. Complexes of tubulin and of GFAP were not observed under the same conditions. Aluminum salts irreversibly inactivated calpain but only at high aluminum concentrations (IC50 = 1.2 and 2.1 mM for aluminum lactate and AlCl3, respectively), although longer exposure to the ion reduced by twofold the levels required for protease inhibition. These interactions of aluminum with neurofilament proteins and the effects on proteolysis suggest possible mechanisms for the impaired axoplasmic transport of neurofilaments and their accumulation in neuronal perikarya after aluminum administration in vivo
— id: 25476, year: 1990, vol: 55, page: 1950, stat: Journal Article,

Synthesis, axonal transport, and turnover of the high molecular weight microtubule-associated protein MAP 1A in mouse retinal ganglion cells: tubulin and MAP 1A display distinct transport kinetics
Nixon RA; Fischer I; Lewis SE
1990 Feb;110(2):437-448, Journal of cell biology
Microtubule-associated proteins (MAPs) in neurons establish functional associations with microtubules, sometimes at considerable distances from their site of synthesis. In this study we identified MAP 1A in mouse retinal ganglion cells and characterized for the first time its in vivo dynamics in relation to axonally transported tubulin. A soluble 340-kD polypeptide was strongly radiolabeled in ganglion cells after intravitreal injection of [35S]methionine or [3H]proline. This polypeptide was identified as MAP 1A on the basis of its co-migration on SDS gels with MAP 1A from brain microtubules; its co-assembly with microtubules in the presence of taxol or during cycles of assembly-disassembly; and its cross-reaction with well-characterized antibodies against MAP 1A in immunoblotting and immunoprecipitation assays. Glial cells of the optic nerve synthesized considerably less MAP 1A than neurons. The axoplasmic transport of MAP 1A differed from that of tubulin. Using two separate methods, we observed that MAP 1A advanced along optic axons at a rate of 1.0-1.2 mm/d, a rate typical of the Group IV (SCb) phase of transport, while tubulin moved 0.1-0.2 mm/d, a group V (SCa) transport rate. At least 13% of the newly synthesized MAP 1A entering optic axons was incorporated uniformly along axons into stationary axonal structures. The half-residence time of stationary MAP 1A in axons (55-60 d) was 4.6 times longer than that of MAP 1A moving in Group IV, indicating that at least 44% of the total MAP 1A in axons is stationary. These results demonstrate that cytoskeletal proteins that become functionally associated with each other in axons may be delivered to these sites at different transport rates. Stable associations between axonal constituents moving at different velocities could develop when these elements leave the transport vector and incorporate into the stationary cytoskeleton
— id: 25483, year: 1990, vol: 110, page: 437, stat: Journal Article,

Post-translational modification of alpha-tubulin by acetylation and detyrosination in NB2a/d1 neuroblastoma cells
Shea TB; Beermann ML; Nixon RA
1990 Feb 1;51(2):195-204, Brain research. Developmental brain research
Western blot analyses of total assembled microtubule fractions from NB2a/d1 neuroblastoma cells demonstrated that these cells are capable of post-translationally modifying alpha-tubulin by acetylation and detyrosination. Immunocytochemical analyses of NB2a/d1 cells differentiated with dbcAMP which had been processed under microtubule-stabilizing conditions demonstrated that all forms of alpha-tubulin were present throughout perikarya and neurites. By contrast, extraction of cells with Triton X-100 revealed a regional concentration of acetylated and detyrosinated alpha-tubulin subunits within axonal neurites, detectable in some cells after 3 days of differentiation and in nearly all cells after 7 days. Resistance of neurites to retraction following colchicine-treatment developed at a similar rate; furthermore, colchicine-resistant neurites contained intense acetylated alpha-tubulin immunoreactivity. We conclude that NB2a/d1 cells are capable of acetylating and detyrosinating alpha-tubulin subunits and that selective post-translational modification of alpha-tubulin subunits may be related to neuritic maturation
— id: 25482, year: 1990, vol: 51, page: 195, stat: Journal Article,

Dynamics of phosphorylation and assembly of the high molecular weight neurofilament subunit in NB2a/d1 neuroblastoma
Shea TB; Sihag RK; Nixon RA
1990 Nov;55(5):1784-1792, Journal of neurochemistry
In neuronal systems thus far studied, newly synthesized neurofilament subunits rapidly associate with the Triton-insoluble cytoskeleton and subsequently undergo extensive phosphorylation. However, in the present study we demonstrate by biochemical and immunological criteria that NB2a/d1 neuroblastoma cells also contain Triton-soluble, extensively phosphorylated 200-kDa high molecular weight neurofilament subunits (NF-H). High-speed centrifugation (100,000 g) of the Triton-soluble fraction for 1 h sedimented some, but not all, soluble NF-H subunits; immunoelectron microscopic analyses of the resulting pellet indicated that a portion of the NF-H subunits in this fraction are assembled into (Triton-soluble) neurofilaments. When cells were pulse labeled for 15 min with [35S]methionine, radiolabel was first associated with the Triton-soluble 200-kDa NF-H variants. Because only extensively phosphorylated NF-H subunits migrate at 200 kDa, whereas hypophosphorylated subunits migrate instead at 160 kDa, these findings suggest that some newly synthesized subunits were phosphorylated before they polymerized. In pulse-chase analyses, radiolabeled 200-kDa NF-H migrated into the 100,000 g particulate fraction of Triton-soluble extracts before its arrival in the Triton-insoluble cytoskeleton. Undifferentiated cells, which do not possess axonal neurites and lack a significant amount of Triton-insoluble, extensively phosphorylated NF-H, contain a sizeable pool of Triton-soluble extensively phosphorylated NF-H subunits and polymers. We interpret these data to indicate that the integration of newly synthesized NF-H into the cytoskeleton occurs in a progression of distinct stages, and that assembly of NF-H into neurofilaments and integration into the Triton-insoluble cytoskeleton are not prerequisites for the incorporation of certain phosphate groups on these polypeptides.(ABSTRACT TRUNCATED AT 250 WORDS)
— id: 25477, year: 1990, vol: 55, page: 1784, stat: Journal Article,

Phosphorylation of the amino-terminal head domain of the middle molecular mass 145-kDa subunit of neurofilaments. Evidence for regulation by second messenger-dependent protein kinases
Sihag RK; Nixon RA
1990 Mar 5;265(7):4166-4171, Journal of biological chemistry
To begin to understand the regulation and roles of neurofilament phosphorylation, we localized the phosphorylated domains on the 140-145-kDa neurofilament subunit (NF-M) and identified the protein kinases that may specifically phosphorylate the sites within these domains in vivo. Mouse retinal ganglion cells were labeled in vivo by injecting mice intravitreally with [32P]orthophosphate, and neurofilament-enriched fractions were obtained from the optic axons. Two-dimensional phosphopeptide map analysis of NF-M after digestion with alpha-chymotrypsin and trypsin revealed seven major (M8-M14) and at least eight minor (M1-M7 and M15) phosphopeptides. Two-dimensional phosphopeptide map analyses of NF-M phosphorylated in vitro by individual purified or endogenous axonal cytoskeleton-associated protein kinases showed that five peptides (M9-M13) were substrates for the heparin-sensitive second messenger-independent protein kinase(s). Protein kinase A and/or protein kinase C phosphorylated eight other peptides (M1-M8). Two alpha-chymotryptic peptides (C1 and C2) that were phosphorylated by protein kinase A but not by the endogenous independent kinase(s) were isolated by high performance liquid chromatography on a reverse-phase C8 column. Partial sequence analysis of peptides C1 (S R V S G P S ...) and C2 (S R G S P S T V S ...) showed that the peptides were localized on the head domain of NF-M at 25 and 41 residues from the amino terminus, respectively. Tryptic digest of peptide C1 (less than 12 kDa) generated the phosphopeptides M1-M6. Peptide C2 was a breakdown product of peptide C1. Since the polypeptide sites targeted by second messenger-independent kinase(s) associated with neurofilaments are localized on the carboxyl-terminal domain, separate aspects of NF-M function appear to be regulated by separate kinase systems that selectively phosphorylate head or tail domains of the polypeptide
— id: 25481, year: 1990, vol: 265, page: 4166, stat: Journal Article,

Fluoxetine versus trazodone in depressed geriatric patients
Falk WE; Rosenbaum JF; Otto MW; Zusky PM; Weilburg JB; Nixon RA
1989 Oct-Dec;2(4):208-214, Journal of geriatric psychiatry & neurology
A total of 27 subjects began active treatment in this double-blind study comparing the efficacy and safety of trazodone and fluoxetine in geriatric depressed patients, but only 13 completed 6 weeks on study medication. Both agents were effective according to weekly and endpoint analyses, and there was no evidence of significant effects on blood pressure, pulse, or weight. Separate analysis of patients who had received an adequate trial of medication indicated a trend toward relatively more fluoxetine-treated patients meeting clinical criteria for resolved depression
— id: 25471, year: 1989, vol: 2, page: 208, stat: Journal Article,

Calcium-activated neutral proteinases as regulators of cellular function. Implications for Alzheimer's disease pathogenesis
Nixon RA
1989 ;568(1):198-208, Annals of the New York Academy of Sciences
Evidence is emerging that calcium-activated neutral proteinases (CANPs) not only participate in intracellular protein turnover but help to regulate the functional reorganization of cytoskeletal proteins in response to calcium and second-messenger stimulation. The high concentration of CANPs in certain neurons has suggested prominent roles for this proteolytic system in neuronal and synaptic function. In addition to acting directly on specific constituents of the cytoplasmic and membrane-associated cytoskeletal networks, CANP may amplify its effects by modulating the activities of protein kinase C and possibly other kinases and phosphatases by limited proteolysis. Given its suspected involvement at the cytoskeleton-membrane interface, calcium-mediated proteolysis is an example of a metabolic process which, if impaired, could provide a unifying basis for the slow progressive development of diverse structural and functional abnormalities within neurons. The multiplicity of mechanisms regulating its activity makes the CANP system a vulnerable target for disruption from various sources. A working hypothesis is advanced that down-regulation (inhibition) of neuronal calcium-mediated proteolysis in Alzheimer's disease is one critical and early step in the development of neurofibrillary degeneration and altered membrane cytoskeleton dynamics, which leads to membrane injury, accumulation of abnormal proteins, and synaptic dysfunction
— id: 25475, year: 1989, vol: 568, page: 198, stat: Journal Article,

Early posttranslational modifications of the three neurofilament subunits in mouse retinal ganglion cells: neuronal sites and time course in relation to subunit polymerization and axonal transport
Nixon RA; Lewis SE; Dahl D; Marotta CA; Drager UC
1989 Mar;5(2):93-108, Brain research. Molecular brain research
We have characterized stages in the posttranslational processing of the three neurofilament subunits, High (NF-H), Middle (NF-M), and Low (NF-L), in retinal ganglion cells in vivo during the interval between synthesis in cell bodies within the retina and appearance of these polypeptides in axons at the level of the optic nerve (optic axons). Neurofilament proteins pulse-labeled by injecting mice intravitreally with [35S]methionine or [32P]orthophosphate, were isolated from Triton-soluble and Triton-insoluble fractions of the retina or optic axons by immunoprecipitation or immunoaffinity chromatography. Within 2 h after [35S]methionine injection, the retina contained neurofilament-immunoreactive radiolabeled proteins with apparent molecular weights of 160, 139, and 70 kDa, which co-migrated with subunits of axonal neurofilaments that were dephosphorylated in vitro with alkaline phosphatase. The two larger polypeptides were not labeled with [32P]orthophosphate, indicating that they were relatively unmodified forms of NF-H and NF-M. About 75% of the subunits were Triton-insoluble by 2 h after isotope injection, and this percentage increased to 98% by 6 h. Labeled neurofilament polypeptides appeared in optic axons as early as 2 h after injection. These subunits exhibited apparent molecular weights of 160, 139, and 70 kDa and were Triton-insoluble. The time of appearance of fully modified polypeptide forms differed for each subunit (2 h for NF-L, 6-18 h for NF-M, 18-24 h for NF-H) and was preceded by the transient appearance of intermediate forms. The modified radiolabeled subunits in optic axons 3 days after synthesis were heavily labeled with [32P]orthophosphate and exhibited the same apparent molecular weights as subunits of axonal neurofilaments (70 kDa, 145 and 140 kDa, and 195-210 kDa, respectively). Whole mounts of retina immunostained with monoclonal antibodies against NF-H in different states of phosphorylation demonstrated a transition from non-phosphorylated neurofilaments to predominantly phosphorylated ones within a region of the axon between 200 and 1000 microns downstream from the cell body. These experiments demonstrate that the addition of most phosphate groups to NF-M and NF-H takes place within a proximal region of the axon. The rapid appearance of modified forms of NF-L after synthesis may imply that processing of this subunit occurs at least partly in the cell body. The presence of a substantial pool of Triton-insoluble, unmodified subunits early after synthesis indicates that the heaviest incorporation of phosphate occurs after neurofilament proteins are polymerized.(ABSTRACT TRUNCATED AT 400 WORDS)
— id: 25473, year: 1989, vol: 5, page: 93, stat: Journal Article,

Appearance and localization of phosphorylated variants of the high molecular weight neurofilament protein in NB2a/d1 cytoskeletons during differentiation
Shea TB; Beermann ML; Nixon RA
1989 Nov 1;50(1):142-146, Brain research. Developmental brain research
We used immunoblot and immunocytochemical methodologies to characterize the appearance and intracellular localization of the high molecular weight neurofilament subunit (NF-H) within the Triton-insoluble cytoskeleton during the first 5 days of differentiation of mouse NB2a/d1 neuroblastoma cells. Hypophosphorylated and partially phosphorylated forms of NF-H were detected in cells before and throughout differentiation. By contrast, some extensively phosphorylated forms of NF-H were first detected on the third day of differentiation and at least one additional 200 kDa isoform was visualized in cytoskeletons only after five days of differentiation. Extensively phosphorylated forms of NF-H were restricted to axonal neurites; by contrast, hypophosphorylated and partially phosphorylated forms of NF-H were present throughout undifferentiated and differentiated cells
— id: 25470, year: 1989, vol: 50, page: 142, stat: Journal Article,

Aluminum salts induce the accumulation of neurofilaments in perikarya of NB2a/dl neuroblastoma
Shea TB; Clarke JF; Wheelock TR; Paskevich PA; Nixon RA
1989 Jul 17;492(1-2):53-64, Brain research
NB2a/dl neuroblastoma cells were exposed to aluminum chloride or aluminum lactate (0.1-1 mM) for 3 and 6 days. Additional cultures were exposed to aluminum salts as the cells were stimulated to elaborate axonal neurites by dibutyryl cyclic AMP. By phase-contrast microscopy, aluminum salts had no effect on the morphology of undifferentiated (NB2a(-] or differentiated (NB2a(+] cells, or on neuritic elaboration and maintenance. Silver straining by the Bielschowsky method, however, demonstrated argyrophilic accumulations in perikarya of many NB2a(-) and NB2a(+) cells treated with aluminum salts. At the ultrastructural level, whorls of intermediate filaments were the most prominent abnormalities in neuronal perikarya. Although phosphorylated high-molecular weight neurofilament subunits (NF-H) are normally detected by immunocytochemical analyses only within axonal neurites of NB2a/dl cells, aluminum salt treatment caused the detection of phosphorylated epitopes of NF-H within perikaryal of NB2a(-) and NB2a(+) cytoskeletons, suggesting that the argyrophilic filamentous accumulations are composed at least partly of phosphorylated NF-H
— id: 25472, year: 1989, vol: 492, page: 53, stat: Journal Article,

In vivo phosphorylation of distinct domains of the 70-kilodalton neurofilament subunit involves different protein kinases
Sihag RK; Nixon RA
1989 Jan 5;264(1):457-464, Journal of biological chemistry
A combination of in vivo and in vitro approaches were used to characterize phosphorylation sites on the 70,000-kilodalton (kDa) subunit of neurofilaments (NF-L) and to identify the protein kinases that are likely to mediate these modifications in vivo. Neurofilament proteins in a single class of neurons, the retinal ganglion cells, were pulse-labeled in vivo by injecting mice intravitreously with [32P]orthophosphate. Radiolabeled neurofilaments were isolated after they had advanced along optic axons, and the individual subunits were separated on sodium dodecyl sulfate-polyacrylamide gels. Two-dimensional alpha-chymotryptic phosphopeptide map analysis of NF-L revealed three phosphorylation sites: an intensely labeled peptide (L-1) and two less intensely labeled peptides (L-2 and L-3). The alpha-chymotryptic peptide L-1 was identified as the 11-kDa segment containing the C terminus of NF-L. The ability of these peptides to serve as substrates for specific protein kinases were examined by incubating neurofilament preparations with [gamma-32P]ATP in the presence of purified cAMP-dependent protein kinase or appropriate activators and/or inhibitors of endogenous cytoskeleton-associated protein kinases. The heparin-sensitive, calcium- and cyclic nucleotide-independent kinase associated with the cytoskeleton selectively phosphorylated L-1 and L-3 but had little, if any, activity toward L-2. When this kinase was inhibited with heparin, cAMP addition to the neurofilament preparation stimulated the phosphorylation of L-2, and addition of the purified catalytic subunit of cAMP-dependent protein kinase induced intense labeling of L-2. At higher labeling efficiencies, the exogenous kinase also phosphorylated L-3 and several sites at which labeling was not detected in vivo; however, L-1 was not a substrate. Calcium and calmodulin added to neurofilament preparations in the presence of heparin modestly stimulated the phosphorylation of L-1 and L-3, but not L-2, and the stimulation was reversed by trifluoperazine. The selective phosphorylation of different polypeptide domains on NF-L by second messenger-dependent and -independent kinases suggests multiple functions for phosphate groups on this protein
— id: 25474, year: 1989, vol: 264, page: 457, stat: Journal Article,

Multiple phosphorylated variants of the high molecular mass subunit of neurofilaments in axons of retinal cell neurons: characterization and evidence for their differential association with stationary and moving neurofilaments
Lewis SE; Nixon RA
1988 Dec;107(6 Pt 2):2689-2701, Journal of cell biology
The 200-kD subunit of neurofilaments (NF-H) functions as a cross-bridge between neurofilaments and the neuronal cytoskeleton. In this study, four phosphorylated NF-H variants were identified as major constituents of axons from a single neuron type, the retinal ganglion cell, and were shown to have characteristics with different functional implications. We resolved four major Coomassie Blue-stained proteins with apparent molecular masses of 197, 200, 205, and 210 kD on high resolution one-dimensional SDS-polyacrylamide gels of mouse optic axons (optic nerve and optic tract). Proteins with the same electrophoretic mobilities were radiolabeled within retinal ganglion cells in vivo after injecting mice intravitreally with [35S]methionine or [3H]proline. Extraction of the radiolabeled protein fraction with 1% Triton X-100 distinguished four insoluble polypeptides (P197, P200, P205, P210) with expected characteristics of NF-H from two soluble neuronal polypeptides (S197, S200) with few properties of neurofilament proteins. The four Triton-insoluble polypeptides displayed greater than 90% structural homology by two-dimensional alpha-chymotryptic iodopeptide map analysis and cross-reacted with four different monoclonal and polyclonal antibodies to NF-H by immunoblot analysis. Each of these four polypeptides advanced along axons primarily in the Group V (SCa) phase of axoplasmic transport. By contrast, the two Triton-soluble polypeptides displayed only a minor degree of alpha-chymotryptic peptide homology with the Triton-insoluble NF-H forms, did not cross-react with NF-H antibodies, and moved primarily in the Group IV (SCb) wave of axoplasmic transport. The four NF-H variants were generated by phosphorylation of a single polypeptide. Each of these polypeptides incorporated 32P when retinal ganglion cells were radiolabeled in vivo with [32P]orthophosphate and each cross-reacted with monoclonal antibodies specifically directed against phosphorylated epitopes on NF-H. When dephosphorylated in vitro with alkaline phosphatase, the four variants disappeared, giving rise to a single polypeptide with the same apparent molecular mass (160 kD) as newly synthesized, unmodified NF-H. The NF-H variants distributed differently along optic axons. P197 predominated at proximal axonal levels; P200 displayed a relatively uniform distribution; and P205 and P210 became increasingly prominent at more distal axonal levels, paralleling the distribution of the stationary neurofilament network.(ABSTRACT TRUNCATED AT 400 WORDS)
— id: 25464, year: 1988, vol: 107, page: 2689, stat: Journal Article,

Possible synergism between fluoxetine and lithium in refractory depression
Pope HG Jr; McElroy SL; Nixon RA
1988 Oct;145(10):1292-1294, American journal of psychiatry
Five depressed patients who had shown no improvement with trials of antidepressants from several chemical families, including fluoxetine, responded when lithium was given in conjunction with fluoxetine. Lithium augmentation of fluoxetine may represent a useful strategy in refractory depression
— id: 25466, year: 1988, vol: 145, page: 1292, stat: Journal Article,

Soluble, phosphorylated forms of the high molecular weight neurofilament protein in perikarya of cultured neuronal cells
Shea TB; Majocha RE; Marotta CA; Nixon RA
1988 Oct 17;92(3):291-297, Neuroscience letters
The high molecular weight subunit of neurofilaments (NF-H) in mouse NB2a/d1 neuroblastoma cells is extensively phosphorylated and exhibits an apparent molecular weight of 200 kDa by SDS gel electrophoresis. In this study, we observed that extensively phosphorylated NF-H variants exist as both Triton-soluble and -insoluble forms, which display different cellular distributions. Perikarya and neurites of differentiated NB2a/d1 cells were immunostained by a polyclonal antiserum (anti-NF-H) that specifically recognizes the extensively phosphorylated NF-H forms and a monoclonal antibody (SMI-31) that recognizes phosphorylated epitopes of neurofilament proteins (NFPs). When cells were extracted with Triton X-100 to remove soluble proteins, however, only axonal neurites remained immunoreactive. Immunoblot analyses established the specificity of anti-NF-H and SMI-31 and demonstrated that both Triton-soluble and -insoluble NF-H subunits exhibit an apparent molecular weight of 200 kDa. Incorporation of radiolabeled phosphate into Triton-soluble NF-H following incubation of intact NB2a/d1 cells with 32P-orthophosphate confirmed that the Triton-soluble form of NF-H is a phosphoprotein. Most NF-H subunits in the Triton-soluble fraction sedimented after centrifugation at 100,000 g for 1 h, indicating that they may be present as oligomers. The implications of these data for the development of neurofibrillary pathology are discussed
— id: 25465, year: 1988, vol: 92, page: 291, stat: Journal Article,

Differential distribution of vimentin and neurofilament protein immunoreactivity in NB2a/d1 neuroblastoma cells following neurite retraction distinguishes two separate intermediate filament systems
Shea TB; Nixon RA
1988 Jun 1;469(1-2):298-302, Brain research
Mouse NB2a/d1 cells assemble all 3 neurofilament protein subunits (NFPs) into the detergent-insoluble cytoskeleton and segregate phosphorylated forms of the 200-kDa subunit (NFP-H) within neurites when differentiation is induced with dibutyryl cyclic AMP (dbcAMP). Before and after differentiation, these cells also incorporate vimentin into both the perikaryal and neuritic cytoskeleton (Shea et al., 1988, Dev. Brain Res., submitted). To determine whether NFPs and vimentin constitute separate intermediate filament systems or exist as heteropolymers, we perturbed cytoskeletal architecture by inducing the retraction of neurites with colchicine. After cells were exposed to colchicine, vimentin immunoreactivity partitioned into perikarya in the form of fibrous whorls that did not cross-react with antisera to NFPs. By contrast, NFP immunoreactivity remained dispersed throughout the cell body following neurite retraction. We interpret these different responses to colchicine to indicate that NFPs and vimentin are assembled into separate intermediate filaments in NB2a/d1 cells
— id: 25469, year: 1988, vol: 469, page: 298, stat: Journal Article,

Neurofilament triplet proteins of NB2a/d1 neuroblastoma: posttranslational modification and incorporation into the cytoskeleton during differentiation
Shea TB; Sihag RK; Nixon RA
1988 Sep 1;471(1):97-109, Brain research
Induction of axonal neuritogenesis in NB2a/d1 cells was associated with an increased content of neurofilament proteins (NFPs) by immunoblot analysis. The major NFP subunits in differentiated [NB2a(+)] cells included microheterogenous forms with apparent molecular weights of 200-190 kDa (NFP-H), 143-142 kDa (NFP-M) and 70 kDa (NFP-L) on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Only NFP-L was detected in cytoskeletal preparations of undifferentiated [NB2a(-)] cells. All three NFPs of NB2a(+) cells incorporated 32P-orthophosphate in intact cells. A 160/155 kDa NFP-H immunoreactive polypeptide in NB2a(-) and NB2a(+) cells represented a relatively unmodified form of the 200 kDa NFP-H, since dephosphorylation of the 200 kDa NFP-H in vitro with alkaline phosphatase generated the 160/155 kDa forms. Triton-extracted NB2a(+) cells displayed NFP-H immunoreactivity in neurites and occasionally in perikaryal regions at the base of neurites. NFP-M was present throughout the neurites and somata of NB2a(+) cells, and was regularly detected in portions of perikarya in NB2a(-) cells. NFP-L immunoreactivity was distributed throughout the Triton-insoluble cytoskeleton of NB2a(-) and NB2a(+) cells. Immunocytochemical analyses revealed that extensively phosphorylated forms of NFP-H were largely restricted to the neurites of NB2a(+) cells, and less modified forms predominated throughout both perikarya and neurites of NB2a(-) and NB2a(+) cells
— id: 25467, year: 1988, vol: 471, page: 97, stat: Journal Article,

Phosphorylation of neurofilament proteins by protein kinase C
Sihag RK; Jeng AY; Nixon RA
1988 Jun 6;233(1):181-185, FEBS letters
The low molecular mass (70 kDa) subunit of neurofilaments (NF-L) contains at least three phosphorylation sites in vivo and is phosphorylated by multiple kinases in a site-specific manner [(1987) J. Neurochem. 48, S101; Sihag, R.K. and Nixon, R.A. submitted]. In this study, we observed that the three subunits of neurofilament proteins from retinal ganglion cell neurons are substrates for purified mouse brain protein kinase C. Two-dimensional alpha-chymotryptic phosphopeptide map analyses of the NF-L subunit demonstrated that protein kinase C phosphorylates four polypeptide sites, two of which incorporate phosphate when retinal ganglion cells are pulse-radiolabeled with [32P]orthophosphate in vivo
— id: 25468, year: 1988, vol: 233, page: 181, stat: Journal Article,

The axonal transport of cytoskeletal proteins: a reappraisal
Nixon RA
Axonal transport New York : Liss, 1987,
— id: 2726, year: 1987, vol: , page: 175, stat: Chapter,

Phosphorylation and dephosphorylation of neurofilament proteins in retinal ganglion cell neurons in vivo
Nixon RA; Lewis SE
1987 ;221(4):167-186, Advances in experimental medicine & biology
— id: 25463, year: 1987, vol: 221, page: 167, stat: Journal Article,

Phosphorylation and dephosphorylation of neurofilament proteins in retinal ganglion cell neurons in vivo
Nixon RA; Lewis SE
Molecular mechanisms of neuronal responsiveness New York : Plenum Press, 1987,
— id: 2727, year: 1987, vol: , page: 167, stat: Chapter,

Posttranslational modification of neurofilament proteins by phosphate during axoplasmic transport in retinal ganglion cell neurons
Nixon RA; Lewis SE; Marotta CA
1987 Apr;7(4):1145-1158, Journal of neuroscience
The progressive modification of newly synthesized neurofilament proteins (NFPs) during axoplasmic transport in mouse retinal ganglion cell (RGC) neurons was studied after RGC perikarya were pulse-labeled with 32P-orthophosphate or radiolabeled amino acids. The 3 NFP subunits, H(igh), M(iddle), and L(ow), were among a group of axonally transported proteins that incorporated high levels of 32P. Covalent addition of phosphate slowed the electrophoretic mobility of H and M on SDS polyacrylamide gels and shifted the charge of all 3 subunits toward more acidic pH values, thereby providing an index of the phosphorylation state of this radiolabeled population of NFPs. NFPs were extensively phosphorylated before they entered axons at the optic nerve level, and continued to be modified during transport along RGC axons at the optic nerve and tract level. H and M exhibited charge shifts of 0.2-0.6 units toward a more acidic pH during axoplasmic transport. The charge modifications became more prominent when NFPs reached distal axonal levels, which may indicate regional differences in the activity of this modification process along axons. By contrast, the L subunit became more basic in charge, consistent with decreases in the phosphorylation state during transport. Additional observations (Nixon and Lewis, 1986) that a considerable proportion of phosphate groups initially added to L and M were later removed as neurofilaments advanced along RGC axons support the notion that the changing phosphorylation state of NFP subunits during axoplasmic transport reflects a dynamic equilibrium between phosphorylation and dephosphorylation events. Topographical remodeling of phosphate groups on NFPs during axoplasmic transport is proposed as a possible mechanism for coordinating interactions between neurofilaments and other constituents, as these elements are transported and integrated into the axonal cytoskeleton
— id: 25462, year: 1987, vol: 7, page: 1145, stat: Journal Article,

A versatile transition metal salt reaction for a wide range of common biochemical reagents: an instantaneous and quantifiable color test
Fleming N; Nixon RA
1986 May 1;154(2):691-701, Analytical biochemistry
A rapid and sensitive spot test amenable to visual or spectrophotometric quantitation has been developed for a wide variety of biochemical reagents by utilizing the transition metal salt cupric chloride and its large number of related colored compounds. This assay is potentially a widely applicable multipurpose test for rapidly detecting the presence of unknown substances. Combination of the test sample with the working reagent results in the immediate formation of a distinctive colored product that may be precipitable. Some compounds require the further addition of sodium hydroxide in order to generate the distinctively colored product. Distinctive reactions occur with the following reagents, and their limit of visual detection is indicated in parentheses: ammonium bicarbonate (12.5 mM), ammonium acetate (25 mM), ammonium hydroxide (0.1%), ammonium sulfate (2%), ammonium persulfate (0.02 mM), L-(+)-cysteine (0.07 mM), dithiothreitol (DTT) (1.25 mM), EDTA (0.6 mM), ethylene glycol bis(beta-aminoethyl ether) N,N'-tetraacetic acid (5 mM), D-glucose (6 mM), glycerol (0.3%), imidazol (12.5 mM), DL-methionine (100 mM), mercaptoethanol (0.05%), sodium azide (19 mM, 0.1%), sodium dithionite (0.25%), sodium metabisulfite (25 mM), sodium nitrite (6.2 mM), sodium periodate (3.1 mM), sodium sulfite (12.5 mM), sodium thiosulfite (12.5 mM), sucrose (6 mM), and N,N,N',N'-tetramethylethylenediamine (0.05%). A distinctive exothermic reaction occurs with hydrogen peroxide, but without color change. Compounds reacting insignificantly include 50 mM Tris buffer, urea, N,N'-methylene bisacrylamide, sodium dodecyl sulfate, isopropyl alcohol, sodium fluoride, trichloroacetic acid, phenol, mannose, K2HPO4, guanidine HCl, chloramine-T, magnesium chloride, and boric acid, where the solids were tested at approximately 10 mg/ml. Spectrophotometric standard curves were developed for DTT and sodium azide utilizing the clear supernatants resulting from these reactions. Combinations of at least four reagents could be discriminated, as demonstrated with mixtures of glucose, sodium azide, EDTA, and DTT. In addition ammonium sulfate could be detected to a limit of 4% in the presence of protein, DTT, and EDTA in a 50 mM Tris buffer. Spot tests were developed which utilized reagent-impregnated filter paper and gave distinctive colored products on addition of 5 microliter of test sample
— id: 25457, year: 1986, vol: 154, page: 691, stat: Journal Article,

Fodrin degradation by calcium-activated neutral proteinase (CANP) in retinal ganglion cell neurons and optic glia: preferential localization of CANP activities in neurons
Nixon RA
1986 May;6(5):1264-1271, Journal of neuroscience
The activity of calcium-activated neutral proteinases (CANPs) toward endogenous substrates was measured in axons of retinal ganglion cell (RGC) neurons and separately in adjacent optic glia under in vitro conditions that preserved the ultrastructure and anatomic relationships between these cellular elements. RGC neurons and optic glia both expressed CANP activity. In contrast to RGC axons, which contained at least two CANP activities with calcium requirements in the millimolar (CANP A) and micromolar (CANP B) range (Nixon et al., 1985), CANP activity in optic glia was detectable only at millimolar calcium concentrations. When maximally activated, CANP(s) in optic glia exhibited a broad specificity for endogenous proteins but degraded larger proteins at a faster rate. The cytoskeletal protein fodrin (brain spectrin) was among the most susceptible endogenous substrates in RGC axons or glia. The similar properties of fodrin in neurons and glia, including its susceptibility to a purified millimolar calcium-sensitive brain CANP (mCANP), provided the basis for using this protein as a substrate to compare the relative activity of neuronal and glial CANPs in situ. Fodrin degradation mediated by CANPs proceeded at least 6 X more rapidly in intact RGC axons than in optic glia. Comparable differences in the relative degradation rates of the total neuronal and glial protein pools were also observed. These results indicate that the potential activity of CANPs is substantially greater in RGC neurons than in glia. The enormous potential activity and preferential localization of multiple CANP activities in RGC neurons support previously hypothesized roles for CANPs in the processing of axonally transported proteins and in the regulation of neuronal cytoskeletal dynamics and geometry.(ABSTRACT TRUNCATED AT 250 WORDS)
— id: 25458, year: 1986, vol: 6, page: 1264, stat: Journal Article,

Differential turnover of phosphate groups on neurofilament subunits in mammalian neurons in vivo
Nixon RA; Lewis SE
1986 Dec 15;261(35):16298-16301, Journal of biological chemistry
The phosphorylation and dephosphorylation of specific proteins was demonstrated directly in the intact vertebrate nervous system in vivo. By exploiting the neurons' ability to segregate a select group of cytoskeletal proteins from most other phosphorylated constituents of the cell by axoplasmic transport, we were able to examine the dynamics of phosphate turnover on neurofilament proteins in mouse retinal ganglion cell neurons simultaneously labeled with [32P]orthophosphate and [3H]proline in vivo. Three [3H]proline-labeled neurofilament protein (NFP) subunits, designated H (160-200 kDa), M (135-145 kDa), and L (68-70 kDa), entered optic axons in a mole:mole ratio similar to that of isolated axonal neurofilaments, supporting the notion that newly synthesized NFPs are transported along axons as assembled neurofilaments. NFP subunits incorporated high levels of 32P before reaching axonal sites at the level of the optic nerve. As neurofilaments were transported along axons, however, many initially incorporated [32P]phosphate groups were removed. Loss of these phosphate groups occurred to a different extent on each subunit. A minimum of 50-60 and 35-40% of the labeled phosphate groups was removed in a 5-day period from the L and M subunits, respectively. By contrast, the H subunit exhibited relatively little or no phosphate turnover during the same period. Dephosphorylation of L in axons is accompanied by a decrease in its net state of phosphorylation; changes in the phosphorylation state of H and M, however, also reflect ongoing addition of phosphates to these polypeptides during axonal transport (Nixon, R.A., Lewis, S.E., and Marotta, C.A. (1986) J. Neurosci., in press). The possibility is raised that dynamic rearrangements of phosphate topography on NFPs represent a mechanism to coordinate interactions of neurofilaments with other proteins as these elements are transported and incorporated into the stationary cytoskeleton along retinal ganglion cell axons
— id: 25454, year: 1986, vol: 261, page: 16298, stat: Journal Article,

Multiple fates of newly synthesized neurofilament proteins: evidence for a stationary neurofilament network distributed nonuniformly along axons of retinal ganglion cell neurons
Nixon RA; Logvinenko KB
1986 Feb;102(2):647-659, Journal of cell biology
We have studied the fate of neurofilament proteins (NFPs) in mouse retinal ganglion cell (RGC) neurons from 1 to 180 d after synthesis and examined the proximal-to-distal distribution of the newly synthesized 70-, 140-, and 200-kD subunits along RGC axons relative to the distribution of neurofilaments. Improved methodology for intravitreal delivery of [3H]proline enabled us to quantitate changes in the accumulation and subsequent decline of radiolabeled NFP subunits at various postinjection intervals and, for the first time, to estimate the steady state levels of NFPs in different pools within axons. Two pools of newly synthesized triplet NFPs were distinguished based on their kinetics of disappearance from a 9-mm 'axonal window' comprising the optic nerve and tract and their temporal-spatial distribution pattern along axons. The first pool disappeared exponentially between 17 and 45 d after injection with a half-life of 20 d. Its radiolabeled wavefront advanced along axons at 0.5-0.7 mm/d before reaching the distal end of the axonal window at 17 d, indicating that this loss represented the exit of neurofilament proteins composing the slowest phase of axoplasmic transport (SCa or group V) from axons. About 32% of the total pool of radiolabeled neurofilament proteins, however, remained in axons after 45 d and disappeared exponentially at a much slower rate (t 1/2 = 55 d). This second NFP pool assumed a nonuniform distribution along axons that was characterized proximally to distally by a 2.5-fold gradient of increasing radioactivity. This distribution pattern did not change between 45 and 180 d indicating that neurofilament proteins in the second pool constitute a relatively stationary structure in axons. Based on the relative radioactivities and residence time (or turnover) of each neurofilament pool in axons, we estimate that, in the steady state, more neurofilament proteins in mouse RGC axons may be stationary than are undergoing continuous slow axoplasmic transport. This conclusion was supported by biochemical analyses of total NFP content and by electron microscopic morphometric studies of neurofilament distribution along RGC axons. The 70-, 140-, and 200-kD subunits displayed a 2.5-fold proximal to distal gradient of increasing content along RGC axons. Neurofilaments were more numerous at distal axonal levels, paralleling the increased content of NFP.(ABSTRACT TRUNCATED AT 400 WORDS)
— id: 25460, year: 1986, vol: 102, page: 647, stat: Journal Article,

Multiple calcium-activated neutral proteinases (CANP) in mouse retinal ganglion cell neurons: specificities for endogenous neuronal substrates and comparison to purified brain CANP
Nixon RA; Quackenbush R; Vitto A
1986 May;6(5):1252-1263, Journal of neuroscience
Calcium-activated neutral proteinases (CANPs) and their specificities for axonally transported proteins were studied within intact axons of mouse retinal ganglion cell (RGC) neurons in vitro. Two CANP activities with markedly different properties were identified. CANP B, at endogenous calcium levels, selectively cleaved the 145,000 Da (145 kDa) neurofilament protein subunit to yield 143 and 140 kDa neurofilament proteins that are also major constituents of the axonal cytoskeleton. This process represents a posttranslational modification of the neurofilament protein subunit rather than the initial step in its degradation (Nixon et al., 1982, 1983). A second calcium-activated neutral proteinase activity, CANP A, appeared only when calcium levels in the incubating medium were 100 microM or higher. CANP A degraded most proteins in RGC axons but acted considerably more rapidly on high-molecular-weight species. In particular, a 290-320 kDa protein in the Group IV (SCb) phase of axoplasmic transport was degraded 3 X faster than other major axonal proteins, including neurofilament proteins and fodrin. When maximally expressed, CANP A activity represented an enormous proteolytic potential in RGC axons--more than 50% of the total axonal content of proteins larger than 60 kDa could be hydrolyzed within 5 min. The calcium requirements, inhibitor profile, and substrate specificity of CANP A were similar to those of mCANP, the major CANP of mouse brain purified to homogeneity, suggesting that these enzymes may be the same or highly related proteins. The existence in a single neuron type of two CANP activities with markedly different substrate specificities and enzymatic properties emphasizes the possible functional diversity of calcium-activated neutral proteinases in neurons. These functions include the posttranslational modification, as well as degradation of neuronal proteins
— id: 25459, year: 1986, vol: 6, page: 1252, stat: Journal Article,

The epidemiology of ipecac abuse
Pope HG Jr; Hudson JI; Nixon RA; Herridge PL
1986 Jan 23;314(4):245-246, New England journal of medicine
— id: 25461, year: 1986, vol: 314, page: 245, stat: Journal Article,

Calcium-activated neutral proteinase of human brain: subunit structure and enzymatic properties of multiple molecular forms
Vitto A; Nixon RA
1986 Oct;47(4):1039-1051, Journal of neurochemistry
Calcium-activated neutral proteinase (CANP) was purified 2,625-fold from postmortem human cerebral cortex by a procedure involving chromatography on diethylaminoethyl (DEAE)-cellulose, phenyl-Sepharose, Ultrogel AcA-44, and DEAE-Biogel A. The major active form of CANP exhibited a molecular weight of 94-100 kilodaltons (Kd) by gel filtration on Sephacryl 300 and consisted of 78-Kd and 27-Kd subunits. Two-dimensional gel electrophoresis resolved the small subunit into two molecular species with different isoelectric points. CANP degraded most human cytoskeletal proteins but was particularly active toward fodrin and the neurofilament protein subunits (145 Kd greater than 200 Kd greater than 70 Kd). The enzyme required 175 microM Ca2+ for half-maximal activation and 2 mM Ca2+ for optimal activity toward [methyl-14C]azocasein. Other divalent metal ions were poor activators of the enzyme, and some, including copper, lead, and zinc, strongly inhibited the enzyme. Aluminum, a neurotoxic ion that induces neurofilament accumulations in mammalian brain, inhibited the enzyme 47% at 1 mM and 100% at 5 mM. A second CANP form lacking the 27-Kd subunit was partially resolved from the 100-Kd heterodimer during DEAE-Biogel A chromatography. The 78-Kd monomer exhibited the same specific activity, calcium ion requirement, pH optimum, and specificity for cytoskeletal proteins as the 100-Kd heterodimer, suggesting that the 27-Kd subunit is not essential for the major catalytic properties of the enzyme. The rapid autolysis of the 27-Kd subunit to a 18-Kd intermediate when CANP is exposed to calcium may explain differences between our results and previous reports, which describe brain mCANP in other species as a 76-80-Kd monomer or a heterodimer containing 76-80-Kd and 17-20-Kd subunits. The similarity of the 100-Kd human brain CANP to CANPs in nonneural tissues indicates that the heterodimeric form is relatively conserved among various tissues and species
— id: 25456, year: 1986, vol: 47, page: 1039, stat: Journal Article,

Cerebrospinal fluid levels of angiotensin-converting enzyme, acetylcholinesterase, and dopamine metabolites in dementia associated with Alzheimer's disease and Parkinson's disease: a correlative study
Zubenko GS; Marquis JK; Volicer L; Direnfeld LK; Langlais PJ; Nixon RA
1986 Dec;21(14):1365-1381, Biological psychiatry
Mean levels of the two hydrolases angiotensin-converting enzyme (ACE) and acetylcholinesterase (AChE), the dopamine metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), and total protein concentration were examined in cerebrospinal fluid (CSF) samples from a group of patients with dementia of the Alzheimer's type, a group of comparably demented patients with Parkinson's disease, and a neurologically healthy elderly control group. Both pathological groups exhibited a significant decrease in the mean levels of ACE activity and DOPAC per milliliter and were distinguishable from one another based on mean CSH HVA levels. Unlike the Parkinson's disease group, whose mean concentration of HVA was lower than, but not significantly different from that of the control group, the mean HVA concentration of the Alzheimer's disease group was significantly elevated. In contrast, comparisons of the mean CSF AChE activity (expressed per milliliter or per milligram of protein) and CSF total protein concentration did not reveal significant differences for any of the groups. Independent of CSF protein concentration, ACE activity per milliliter exhibited a positive correlation with AChE activity per milliliter within the control and Parkinson's disease groups, whereas a statistically significant correlation for these CSF hydrolases was not observed within the Alzheimer's disease group. Thus, the CSF profiles for patients with mild dementias associated with Alzheimer's or Parkinson's disease differed by at least two neurochemical criteria. Based on the levels of ACE activity, DOPAC, and HVA per milliliter of CSF, two discriminant functions were derived and resulted in the correct classification of 71% of all subjects (n = 38) into Alzheimer's disease, Parkinson's disease, and neurologically healthy control groups
— id: 25455, year: 1986, vol: 21, page: 1365, stat: Journal Article,

Evidence for a stationary nonuniform network of neurofilaments along retinal ganglion cell axons
Nixon RA; Logvinenko KB; Fisher WH
1985 ;455:797-800, Annals of the New York Academy of Sciences
— id: 25506, year: 1985, vol: 455, page: 797, stat: Journal Article,

Captopril and teprotide as discriminators of angiotensin-converting enzyme activity in brain tissue
Zubenko GS; Nixon RA
1985 Sep 16;60(1):33-37, Neuroscience letters
Titrations of angiotensin-converting enzyme (ACE; E.C. 3.4.15.1) present in human serum, as well as in homogenates prepared from post-mortem human caudate or mouse (C57BL1/6J) whole brain tissue, were performed with the selective ACE inhibitors, captopril (SQ 14225) and teprotide (SQ 20881). ACE activity present in human serum was more sensitive to inhibition by either inhibitor than the activity present in the brain homogenates. The inhibition curves for the titration of the human serum activity by both inhibitors were sigmoidal while the inhibition curves for the ACE activity present in the brain homogenates were more complex. These results suggest that the brain homogenates contained: at least two species of enzyme activity with properties similar to ACE but with differing affinities for the inhibitors, or substances without ACE activity that are capable of competing with ACE for the binding of the inhibitors. Therefore, measurements of captopril or teprotide-sensitive peptidase activity as well as inhibitor-binding activity may not always reflect ACE concentrations in brain tissue
— id: 25452, year: 1985, vol: 60, page: 33, stat: Journal Article,

Cerebrospinal fluid levels of angiotensin-converting enzyme in Alzheimer's disease, Parkinson's disease and progressive supranuclear palsy
Zubenko GS; Volicer L; Direnfeld LK; Freeman M; Langlais PJ; Nixon RA
1985 Mar 4;328(2):215-221, Brain research
Angiotensin-converting enzyme (ACE, E.C. 3.4.15.1) has been identified as a normal constituent of human cerebrospinal fluid (CSF). ACE activity in CSF from adult subjects without known neurologic disorder correlated positively (P = 0.002) with age between 50 and 90 years. Patients with moderate degrees of senile dementia of the Alzheimer's type and comparably demented patients with Parkinson's disease or progressive supranuclear palsy exhibited mean levels of ACE activity that were decreased 41, 27 and 53% respectively, compared to the mean level in an age and sex-matched group of neurologically intact individuals. These results raise the possibility that ACE activity in CSF may be an index of neuronal dysfunction in certain central neurodegenerative disorders
— id: 25453, year: 1985, vol: 328, page: 215, stat: Journal Article,

Degradation of neurofilament proteins by purified human brain cathepsin D
Nixon RA; Marotta CA
1984 Aug;43(2):507-516, Journal of neurochemistry
Cathepsin D (CD) was purified to homogeneity from postmortem human cerebral cortex. Incubation of CD with human neurofilament proteins (NFPs) prepared by axonal flotation led to the rapid degradation of the 200,000, 160,000, and 70,000 NFP subunits (200K, 160K, and 70K) which had been separated by one- or two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Degradation was appreciable at enzyme activity-to-substrate protein ratios that were two- to threefold lower than those in unfractionated homogenates from cerebral cortex. Quantitative measurements of NFPs separated by PAGE revealed that, at early stages of digestion, the 160K NFP was somewhat more rapidly degraded than the 70K subunit while the 200K NFP had an intermediate rate of degradation. At sufficiently high enzyme concentrations, all endogenous proteins in human NF preparations were susceptible to the action of CD. Human brain CD also degraded cytoskeletal proteins in NF preparations from mouse brain with a similar specificity. To identify specific NFP break-down products, antisera against each of the major NFPs were applied to nitrocellulose electroblots of NFPs separated by two-dimensional SDS-PAGE. In addition to detecting the 200K, 160K, and 70K NFP in human NF preparations, the antisera also detected nonoverlapping groups of polypeptides resembling those in NF preparations from fresh rat brain. When human NF preparations were incubated with CD, additional polypeptides were released in specific patterns from each NFP subunit. Some of the immuno-cross-reactive fragments generated from NFPs by CD comigrated on two-dimensional gels with polypeptides present in unincubated preparations. These results demonstrate that NFPs and other cytoskeletal proteins are substrates for CD. The physiological significance of these findings and the possible usefulness of analyzing protein degradation products for establishing the action of proteinases in vivo are discussed
— id: 25449, year: 1984, vol: 43, page: 507, stat: Journal Article,

Proteases of human brain
Pope A; Nixon RA
1984 Mar;9(3):291-323, Neurochemical research
Growing appreciation of the multiple functions of proteolytic enzymes in intracellular protein degradation and post-translational modification, in the release of biologically active macromolecules and peptides from precursors and in cellular protein regulation and quality control has stimulated interest in proteases in neurobiology and neuropathology. In this article, the proteinases and peptidases thus far studied in the human central nervous system are reviewed with respect to their enzymology, anatomical and cytological distributions and contributions to neurological and psychiatric disease states. Though information concerning brain proteases in man is fragmentary, it suffices to establish the importance of these complex systems for advancing knowledge of human cerebral function in health and disease
— id: 25450, year: 1984, vol: 9, page: 291, stat: Journal Article,

Mood-elevating effect of captopril in depressed patients
Zubenko GS; Nixon RA
1984 Jan;141(1):110-111, American journal of psychiatry
The use of captopril, an inhibitor of angiotensin-converting enzyme and enkephalinase, was associated with substantial mood elevation in three depressed patients. Substances that may alter neuropeptide synthesis or degradation warrant further investigation as therapeutic agents in certain neuropsychiatric disorders
— id: 25451, year: 1984, vol: 141, page: 110, stat: Journal Article,

Proteolysis of neurofilaments
Nixon RA
Neurofilaments Minneapolis : Univ of Minnesota Press, 1983,
— id: 2728, year: 1983, vol: , page: 117, stat: Chapter,

Limited proteolytic modification of a neurofilament protein involves a proteinase activated by endogenous levels of calcium
Nixon RA; Brown BA; Marotta CA
1983 Sep 26;275(2):384-388, Brain research
Posttranslational modification of a structural protein by limited proteolysis is demonstrated for the first time in the nervous system. The 145,000 dalton subunit of neurofilaments in mouse retinal ganglion cell (RGC) axons is selectively converted in vitro to the major 143,000 and 140,000 dalton neurofilament subunits by a neutral proteinase that is activated by endogenous levels of calcium and is distinguishable from other known brain proteinases. The close similarities between this in vitro process and the previously observed modification of the 145,000 dalton neurofilament protein during axoplasmic transport in vivo suggest that the same enzymatic mechanism is involved. These findings imply that limited proteolysis is an active process along central axons in vivo and that this enzyme may play a specific role in the function of the neuronal cytoskeleton
— id: 25448, year: 1983, vol: 275, page: 384, stat: Journal Article,

Water intoxication, demeclocycline, and antidiuretic hormone -- reply
Nixon RA; Chin WW
1983 Jun;140(6):815-815, American journal of psychiatry
— id: 72840, year: 1983, vol: 140, page: 815, stat: Journal Article,

Posttranslational processing of alpha-tubulin during axoplasmic transport in CNS axons
Brown BA; Nixon RA; Marotta CA
1982 Jul;94(1):159-164, Journal of cell biology
Tubulin proteins in mouse retinal ganglion cell (RGC) neurons were analyzed to determine whether they undergo posttranslational processing during axoplasmic transport. Alpha- and beta-tubulin comprised heterogeneous proteins in the primary optic pathway (optic nerve and optic tract) when examined by two-dimensional (2D) PAGE. In addition, however, alpha-tubulin exhibited regional heterogeneity when consecutive 1.1-mm segments of the optic pathway were analyzed separately. In proximal segments, alpha-tubulin consisted of two predominant proteins separable by isoelectric point and several less abundant species. In more distal segments, these predominant proteins decreased progressively and the alpha-tubulin region of the gel was represented by less abundant multiple forms only; beta-tubulin region of the gel was represented by less abundant multiple forms only; beta-tubulin was the same in all segments. After intravitreal injection of [3H]proline to mice, radiolabeled alpha- and beta-tubulin heteroproteins were conveyed together at a rate of 0.1-0.2 mm/d in the slowest phase of axoplasmic transport. At 45 d postinjection, the distribution of radiolabeled heterogeneous forms a alpha- and beta-tubulin in consecutive segments of optic pathway resembled the distribution of unlabeled proteins by 2D PAGE, indicating that regional heterogeneity of tubulin arises during axonal transport. Peptide mapping studies demonstrated that the progressive alteration of alpha-tubulin revealed by PAGE analysis cannot be explained by contamination of the alpha-tubulin region by other proteins on gels. The results are consistent with the posttranslational processing of alpha-tubulin during axoplasmic transport. These observations, along with the accompanying report (J. Cell Biol., 1982, 94:150-158), provide additional evidence that CNS axons may be regionally specialized
— id: 25444, year: 1982, vol: 94, page: 159, stat: Journal Article,

Increased axonal proteolysis in myelin-deficient mutant mice
Nixon RA
1982 Feb 19;215(4535):999-1001, Science
Protein degradation within retinal ganglion cell axons in vitro is 50 to 110 percent faster than normal in mutant mice exhibiting deficiencies of myelin in the central nervous system. Proteolysis is increased proximally and distally within retinal ganglion cell axons of mice carrying the jumpy mutation or its allele, myelin synthesis deficiency, and is increased distally within those axons of quaking mice. The proteolytic defect is axon (neuron)-specific since the rate of protein degradation within glial cells is normal. Increased axonal proteolysis does not bear a simple relation to hypomyelination since shiverer, another mouse mutant deficient in central myelin, displayed normal rates of axonal protein degradation under the same conditions. These observations suggest an abnormal axon-glial interaction in mice with primary glial defects and raise the possibility that the functioning of histologically normal axons (neurons) may be altered in dysmyelinating diseases
— id: 25447, year: 1982, vol: 215, page: 999, stat: Journal Article,

Posttranslational modification of a neurofilament protein during axoplasmic transport: implications for regional specialization of CNS axons
Nixon RA; Brown BA; Marotta CA
1982 Jul;94(1):150-158, Journal of cell biology
— id: 25445, year: 1982, vol: 94, page: 150, stat: Journal Article,

Demeclocycline in the prophylaxis of self-induced water intoxication
Nixon RA; Rothman JS; Chin W
1982 Jun;139(6):828-830, American journal of psychiatry
Demeclocycline, a competitive inhibitor of antidiuretic hormone at renal tubules, was studied in a patient with the syndrome of psychosis, psychogenic polydipsia, and episodic water intoxication. Under double-blind, placebo-controlled conditions, demeclocycline substantially reduced the severity and frequency of hyponatremic episodes
— id: 25446, year: 1982, vol: 139, page: 828, stat: Journal Article,

Characterization and comparison of neurofilament proteins from rat and mouse CNS
Brown BA; Nixon RA; Strocchi P; Marotta CA
1981 Jan;36(1):143-153, Journal of neurochemistry
Rat and mouse CNS neurofilament proteins (NFPs) were characterized and compared, in terms of electrophoretic properties on polyacrylamide gels and by peptide mapping, with one another and with other co-purifying lower-molecular-weight CNS proteins, including alpha and beta tubulin. NFPs were partially purified by modification of the axon flotation procedure of Norton and co-workers and were demyelinated with Triton X-100. On one-dimensional SDS polyacrylamide gels the molecular weights of the triad of NFPs from both rat and mouse were approximately 200,000, 140,000, and 70,000. Prominent lower-molecular-weight proteins (63,000-16,000) as well as minor amounts of tubulin and actin were observed after gel electrophoresis. On two-dimensional gels (isoelectric focusing followed by SDS gel electrophoresis) each of the NFPs appeared to be composed of more than one component and the corresponding NFPs from rat and mouse had similar isoelectric points. Gel electrophoresis peptide mapping using Staphylococcus aureus V8 protease indicated the following: (1) the triad of NFPs of different sizes have different peptide maps; (2) alpha and beta tubulin have nonidentical digestion products, which are dissimilar to those of the NFPs; (3) other proteins that co-purify by the axon flotation procedure also have nonidentical peptide maps; and(4) the corresponding NFPs from rat and mouse have similar peptide maps. The co-purifying proteins examined in detail (63,000-49,000) do not appear to be derived by proteolytic cleavage of NFPs and may represent other cytoskeletal constituents
— id: 25443, year: 1981, vol: 36, page: 143, stat: Journal Article,

Protease activities in normal and schizophrenic human prefrontal cortex and white matter
Pope A; Amelotte JA; Belfer H; Nixon RA
1981 Oct;6(10):1043-1052, Neurochemical research
Endo- and exopeptidase activities have been measured post-mortem human prefrontal cortex and subjacent white matter to estimate their relative capabilities for protein and peptide degradation. Cathepsin D and three dipeptidases versus leucyl-glycine, glycyl-L-leucine and glycyl-glycine) were assayed in serial, microtome prepared frozen sections (+/- 125 micrograms fresh weight) and related to histological composition (Nissl stain), dry weight, total protein, and DNA content. RNA concentrations were similarly determined, serving as approximate indices of protein synthetic potential. Cathepsin D activity and RNA concentration were, respectively, threefold and twofold greater in cortical gray than in subcortical white matter. Each dipeptidase showed somewhat higher activity in white matter than in cortex. In both tissues the order of activities were: glycyl-leucine greater than glycyl-glycine greater than leucyl-glycine dipeptidase. The results are consistent with preferential localizations of cathepsin D in cortical neurons and dipeptidases in neuroglia. None of the four enzymes showed differences in activity in comparable cortex from six patients with chronic schizophrenia
— id: 25442, year: 1981, vol: 6, page: 1043, stat: Journal Article,

Protein degradation in the mouse visual system. I. Degradation of axonally transported and retinal proteins
Nixon RA
1980 Oct 27;200(1):69-83, Brain research
The analysis of proteolysis in the nervous system is complicated by the heterogeneity of cell types, extensive reutilization of liberated amino acids, and artifacts that may arise when the integrity of the tissue is disrupted during experimentation. For these reasons, changes in proteolytic activity that are observed during brain development and in neuropathological states may often be difficult to interpret. To minimize these problems, we have developed a technique that permits protein degradation to be investigated specifically within axons of the mouse retinal ganglion cells (RGC). In the present study, the method has been used to examine the degradation of proteins conveyed in the slow phases of axoplasmic transport. When adult C57Bl/6J mice were injected intravitreally with L-[3H]proline, labeled proteins within the primary optic pathway (optic nerve and tract) after 5 days were almost exclusively the slow phase axonal proteins. The rate of degradation of these proteins was then determined within the excised, but otherwise intact, optic pathway by measuring the release of acid soluble radioactivity at 37 degrees C in vitro. At physiological pH, the amino acids released by proteolysis were extensively reutilized. Unless amino acid reutilization was prevented, protein degradative rates were artifactually lowered 3-fold. At least two proteolytic systems within RGC axons actively degraded the slowly transported axonal proteins. A 'neutral' system, stimulated by exogenous calcium ions, was optimally active within the physiological pH range (pH 7.0--7.8). The rate of protein degradation at pH 7.4 was uniform along the RGC axon. An 'acidic' system was optimally active with the incubation was carried out at pH 3.8. This proteolytic activity was calcium-independent and exhibited a proximodistal gradient within the RCG axon with higher activity proximally. Similar proteolytic activities were present in isolated intact retinas but in different proportions. The half-lives of axonal and retinal proteins were comparable to CNS protein half-lives estimated in vivo by methods that take amino acid reutilization into account. These and other recent findings demonstrate the utility of this neuron-specific approach in characterizing proteolytic processes within one cell type that may otherwise be obscured by proteolytic events in other cells when brain tissue is analyzed by conventional methods
— id: 25441, year: 1980, vol: 200, page: 69, stat: Journal Article,

Genetic control of retinal ganglion cell projections
LaVail JH; Nixon RA; Sidman RL
1978 Dec 1;182(3):399-421, Journal of comparative neurology
We have assessed the effects of 15 pigmentation mutations on the development of retinal ganglion cell projections in mice in two ways: (1) by analyzing the pattern of innervation of the ipsilateral lateral geniculate nucleus as mapped in autoradiograms of brains of animals killed 12 days after intravitreal injection of 3H-proline into one eye and (2) by determining the ratio of axonally transported radioactive protein in the contralateral and ipsilateral optic tracts after similar intravitreal injections. Analysis of the ratio of transported protein in the two optic tracts provides a new and useful assay of the degree of decussation in experimental animals. The effects of the mutations on eye pigmentation, whole eye melanin content and relative tyrosinase activity also were examined. The degree of ipsilateral innervation generally correlates with the degree of pigmentation of the retinal pigment epithelium and with tyrosinase activity. However, discrepancies have been found in ch and ce mutants. In these animals the pigment epithelium is well pigmented, and the area of ipsilateral innervation in the lateral geniculate nucleus is extensive, despite a high ratio of label in contralateral to ipsilateral optic tracts and low tyrosinase activity. Furthermore, mice heterozygous for the c2J allele have pigmentation and optic projections that are normal even though tyrosinase is reduced to 40% of normal. The few anomalous results suggest that alternative or additional factors may control optic axon projections
— id: 25439, year: 1978, vol: 182, page: 399, stat: Journal Article,

Quinine sulfate for pain in the Guillain-Barre syndrome
Nixon RA
1978 Oct;4(4):386-387, Annals of neurology
— id: 25440, year: 1978, vol: 4, page: 386, stat: Journal Article,

Uptake and metabolism of intraventricularly administered piperidine and its effects on sleep and wakefulness in the rat
Nixon RA; Karnovsky ML
1977 Oct 14;134(3):501-511, Brain research
— id: 25438, year: 1977, vol: 134, page: 501, stat: Journal Article,

Neurotoxicity of a non-metabolizable amino acid, 1 -aminocyclopentane-1-carboxylic acid (ACPC): ACPC transport mechanisms in tissues
Nixon RA
1976 Mar 15;25(6):726-729, Biochemical pharmacology
— id: 25437, year: 1976, vol: 25, page: 726, stat: Journal Article,

Neurotoxicity of a non-metabolizable amino acid, 1-aminocyclopentane-1-carboxylic acid: regional protein levels and lipid composition of nervous tissue
Nixon RA
1976 Jul;27(1):237-244, Journal of neurochemistry
— id: 25436, year: 1976, vol: 27, page: 237, stat: Journal Article,

Neurotoxicity of a non-metabolizable amino acid, 1-aminocyclopentane-1-carboxylic acid: antagonism by amino acids in cultures of cerebellum
Nixon RA; Suva M; Wolf MK
1976 Jul;27(1):245-251, Journal of neurochemistry
— id: 25435, year: 1976, vol: 27, page: 245, stat: Journal Article,

Studies on the neurotoxicity of a non-metabolized amino acid, 1-aminocyclopentane-1-carboxylic acid
Nixon, Ralth Angus
[S.l. : s.n], 1974,
Thesis (Ph.D.) -- Harvard University, 1974
— id: 1334, year: 1974, vol: , page: , stat: ,

Volatile amines in mouse brain: a radioassay with picogram sensitivity
Nixon R
1972 Aug;48(2):460-470, Analytical biochemistry
— id: 25434, year: 1972, vol: 48, page: 460, stat: Journal Article,

Comparison of cerebral sphingolipid metabolism in vivo in "quaking" and normal mice
Nixon, R; Kanfer, J N
1971 Jan 22;10(2):71-79, Life sciences
— id: 25433, year: 1971, vol: 10, page: 71, stat: Journal Article,

Interaction of ribosomes and the cell envelope of Escherichia coli mediated by lysozyme
Patterson D; Weinstein M; Nixon R; Gillespie D
1970 Feb;101(2):584-591, Journal of bacteriology
— id: 25432, year: 1970, vol: 101, page: 584, stat: Journal Article,

Screening of Escherichia coli temperature-sensitive mutants by pretreatment with glucose starvation
Boyd D; Nixon R; Gillespie S; Gillespie D
1968 Mar;95(3):1040-1050, Journal of bacteriology
— id: 25431, year: 1968, vol: 95, page: 1040, stat: Journal Article,