Restoring mitochondrial calcium uniporter expression in diabetic mouse heart improves mitochondrial calcium handling and cardiac function

Diabetes mellitus is a growing health care problem, resulting in significant cardiovascular morbidity and mortality. Diabetes also increases the risk for heart failure (HF) and decreased cardiac myocyte function, which are linked to changes in cardiac mitochondrial energy metabolism. The free mitochondrial calcium level ([Ca2+](m)) is fundamental in activating the mitochondrial respiratory chain complexes and ATP production and is also known to regulate pyruvate dehydrogenase complex (PDC) activity. The mitochondrial calcium uniporter (MCU) complex (MCUC) plays a major role in mediating mitochondrial Ca2+ import, and its expression and function therefore have a marked impact on cardiac myocyte metabolism and function. Here, we investigated MCU's role in mitochondrial Ca2+ handling, mitochondrial function, glucose oxidation, and cardiac function in the heart of diabetic mice. We found that diabetic mouse hearts exhibit altered expression of MCU and MCUC members and a resulting decrease in [Ca2+](m), mitochondrial Ca2+ uptake, mitochondrial energetic function, and cardiac function. Adeno-associated virus-based normalization of MCU levels in these hearts restored mitochondrial Ca2+ handling, reduced PDC phosphorylation levels, and increased PDC activity. These changes were associated with cardiac metabolic reprogramming toward normal physiological glucose oxidation. This reprogramming likely contributed to the restoration of both cardiac myocyte and heart function to nondiabetic levels without any observed detrimental effects. These findings support the hypothesis that abnormal mitochondrial Ca2+ handling and its negative consequences can be ameliorated in diabetes by restoring MCU levels via adeno-associated virus-based MCU transgene expression.