Role of Cardiolipin in ATP synthesis in mitochondria

Barth Syndrome is a hereditary disease where cardiomyopathy is the main cause of death during infancy and childhood. Mutations in the transacylase tafazzin cause depletion of the phospholipid cardiolipin. Cardiolipin is exclusive to mitochondria and makes up 20% of mitochondrial lipids. Depletion of this phospholipid in Barth Syndrome causes malformation and malfunction of mitochondria especially in oxidative tissues, most importantly in heart muscle. We used electron tomography to show that the cardiolipin depletion affects cristae formation in various Barth Syndrome model systems.

wild-type mitochondria

Slice from a tomogram from wild-type mitochondria

Barth syndrome mitodhondria

Slice from a tomogram from Barth syndrome mitochondria

Cardiolipin is suggested to concentrate in high curvature cristae regions and interact with mitochondrial protein complexes such as ATP synthase. We think that Barth Syndrome associated cardiolipin depletion may affect mitochondrial protein complexes. Indeed, we found that the spatial organization of the ATP synthase dimers is altered in cardiolipin depleted mitochondria.  For this study, we isolated mitochondria from indirect flight muscle of wild type, tafazzin or cardiolipin synthase knockout fruit fly models (WT, DTAZ and DCLS). After fragmenting mitochondria using sonication or freeze-thawing methods we have flash frozen samples on EM grids in liquid ethane. Using cryo electron tomography we obtained ATP synthase densities on mitochondrial fragments to compare their distribution in WT, DTAZ and DCLS mitochondria.

mitochondrial prep

Preparation of fragmented mitochondrial cristae from fruit flies for cryo-electron tomography

 

FoF1 distribution

Distribution of FoF1 ATP-synthase molecules identified in cryo-electron tomograms from isolated mitochondrial cristae. Flies with genetic knockout of cardiolipin synthase (CLS) or tafazzin(TAZ) have lower, more disorganized arrays of ATP-synthase molecules.