An unexpected lack of difference in superoxide/H2O2 production rates in isolated heart and skeletal muscle mitochondria from a mouse model of Barth Syndrome

Abstract

Barth Syndrome (BTHS) is a rare X-linked genetic disorder caused by mutations in tafazzin and characterized by loss of cardiolipin and severe cardiomyopathy. Mitochondrial superoxide/H2O2 production has been implicated in the cardiomyopathy observed in different BTHS models. There are at least 11 mitochondrial sites that produce superoxide/H2O2 at significant rates. Which of these sites generate oxidants at excessive rates in BTHS is unknown. Here, we measured the maximum capacity of superoxide/H2O2 production from each site in mitochondria isolated from heart and skeletal muscle of the tafazzin knockdown mice (tazkd) at 3, 7 and 12 months of age. Strikingly, the superoxide/H2O2 production capacities of these sites were overall indistinguishable between tazkd mice and their wildtype littermates across the time points analyzed. The only exception was site GQ in glycerol phosphate dehydrogenase, which was increased in the skeletal muscle of 7 months old tazkd mice. Mitochondrial superoxide/H2O2 production was also measured ex vivo during the oxidation of a complex mixture of substrates mimicking either heart or skeletal muscle cytosol and was found to be indistinguishable between wildtype and tazkd mice. However, we consistently measured decreased FAD-linked respiration in mitochondria isolated from tazkd mice. We conclude that the maximum capacity and ex vivo rates of superoxide/H2O2 production were not increased in mitochondria isolated from heart and skeletal muscle of tazkd mice, despite reduced oxidative capacity. Therefore, it seems unlikely that mitochondrial oxidants contribute to the development of cardiomyopathy in tazkd mice. These observations raise questions about the involvement of mitochondrial oxidants in BTHS pathology.