Abstract
Sex differences in cardiac ischemia/reperfusion (I/R) injury have been reported, but the mechanisms underlying these differences remain poorly understood. As mitochondrial Ca(2+) accumulation plays an important role in I/R injury, we examined whether sex specific differences occur. To monitor mitochondrial Ca(2+) in Langendorff perfused hearts, we used a genetically encoded, mitochondrially targeted Ca(2+) indicator (R-GECO1) delivered via an adeno-associated viral vector (AAV9). Male hearts accumulated significantly more mitochondrial Ca(2+) during 20 min of ischemia than female hearts. Interestingly, sex differences in Ca(2+) accumulation during ischemia were not observed in hearts from mice lacking the mitochondrial Ca(2+) uniporter (MCU), suggesting an important role for MCU. As nitric oxide (NO) and its posttranslational modification S-nitrosylation have been suggested to modulate sex differences in Ca(2+) homeostasis, we inhibited NO signaling in female hearts, which increased mitochondrial Ca(2+) accumulation, while treatment of male hearts with an NO donor reduced mitochondrial Ca(2+) levels, indicating that S-nitrosylation modulates Ca(2+) uptake during ischemia in a sex-dependent manner. Using a biotin-switch assay in isolated mitochondria, we found increased S-nitrosylation of MCU in females compared to males. Finally, isolated male mitochondria exposed to an NO donor exhibited reduced Ca(2+) uptake, comparable to untreated female mitochondria. Taken together, these findings suggest that S-nitrosylation of MCU reduces mitochondrial Ca(2+) uptake during ischemia, uncovering a new layer of redox regulated mitochondrial function, with sex as a critical determinant.