Mindong Ren, PhD

As the signature phospholipid of mitochondria membranes, cardiolipin owes its reputation in large part to the important mitochondrial proteins it associates with. The list of proteins that bind cardiolipin with high affinity is long and includes, among others, the respiratory complexes I, III, IV, and V, the carrier family (ADP?ATP-carrier, phosphate carrier, uncoupling protein), and two peripheral membrane proteins (cytochrome c and creatine kinase). By stabilizing higher order assemblies of respiratory complexes, called supercomplexes, with the major ADP/ATP carrier, cardiolipin significantly improves the efficiency and adaptability of the oxidative phosphorylation machinery. It is thus not surprising that derangements of cardiolipin metabolism are associated with a plethora of pathological states including ischemia/reperfusion injury, heart failure, inherited and diabetic cardiomyopathy, and cancer. However, the precise role of cardiolipin in these complex diseases has been mainly a matter of speculation. It is this gap in our understanding of cardiolipin?s role in health and disease that our research aims to fill. To simplify the matter, we chose to study Barth syndrome (BTHS), an inherited cardiomyopathy with its primary defect in cardiolipin metabolism. BTHS is caused by mutations in tafazzin gene, which lead to severe cardiolipin deficiency. Previously, using a Drosophila model, we established the causal role of cardiolipin deficiency in the pathogenesis of the disease and showed that cardiolipin deficiency disrupts the supramolecular organization of ATP synthase in mitochondria and diminishes the mitochondrial respiratory activity. In tafazzin-deficient mammalian cells in culture, we demonstrated that diminished mitochondrial respiratory activity is accompanied by elevated ROS production. Overall, the emerging pathogenic pathway is that of cardiolipin deficiency → abnormal mitochondrial supercomplex assembly → reduced mitochondrial oxygen consumption rate and elevated reactive oxygen species (ROS) production → cardiomyopathy. Recently, we characterized an inducible tafazzin-knockdown transgenic mouse model and showed that it recapitulates all the salient features of the cardiomyopathy in BTHS. We are carrying out systematic investigations of the pathogenic mechanism of BTHS-associated cardiomyopathy in this model. The outcome of this project will be significant because new understanding gained from this model will not only elucidate the pathogenesis of BTHS but also shed light on the mechanisms of common diseases such as diabetic cardiomyopathy and heart failure, where cardiolipin deficiency has been implicated as an important contributing factor.