Increased Mitochondrial Calpain-1 Is an Important Mechanism Contributing to Mitochondrial ROS Generation in Cardiac Diseases
Both calpain activation and excessive mitochondrial reactive oxygen species (mtROS) have been implicated in the pathogenesis of cardiac diseases. We investigated whether and how calpain regulates mtROS generation in mediating cardiac diseases. In mouse models of streptozotocin-induced type-1 diabetes and lipopolysaccharides- induced sepsis, we show that the protein levels of calpain-1 and calpain activities in mitochondria were significantly elevated in diabetic and septic hearts. The elevation of mitochondrial calpain-1 correlated with an increase in mtROS generation and oxidative damage. Importantly, cardiomyocyte-specific deletion of capns1 disrupted calpain-1 and calpain-2 in the heart and prevented mtROS generation in both septic and diabetic mouse hearts. As a consequence, cardiomyopathic changes (e.g. cardiac apoptosis, hypertrophy and fibrosis) and myocardial dysfunction were attenuated in diabetic or septic capns1 knockout mice compared with their wild-type littermates. Mechanistically, we demonstrate that mitochondrial calpain-1 directly targeted and cleaved ATP synthase subunit-alpha (ATP5A1), leading to a reduction in ATP synthase activity in diabetic hearts and septic hearts, and that up-regulation of ATP5A1 restored ATP synthase activity, prevented mtROS generation and reduced cardiomyopathic changes in type-1 diabetic mice and in septic mice. In addition, selective inhibition of mtROS with mitochondria-targeted antioxidant mito-TEMPO prevented mtROS production and intracellular oxidative stress, reduced cardiomyopathic changes and improved myocardial function in mouse models of type-1 and type-2 diabetes. These in vivo data were recapitulated in cultured cardiomyocytes stimulated with diabetic and septic conditions. In summary, we have provided strong evidence demonstrating that calpain-1 accumulation in mitochondria disrupts ATP synthase through the proteolysis of ATP5A1 and promotes mtROS generation, both of which contribute to diabetic cardiomyopathy and septic cardiomyopathy. Given that mitochondrial calpains also increase and contribute to myocardial injury in ischemic hearts, our findings suggest that increased mitochondrial calpain-1 may be a common mechanism contributing to mtROS generation and myocardial injury in the pathogenesis of cardiac diseases. Thus, targeted inhibition of mitochondrial calpain may be a potentially effective therapy for cardiac diseases.
ATP synthase, calpain, cardiac disease, cardiomyopathy, diabetes, mitochondria, reactive oxygen species, sepsis
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