Mitochondrial PKC-ε deficiency promotes I/R-mediated myocardial injury via GSK3-dependent mitochondrial permeability transition pore opening

Mitochondrial fission is critically involved in cardiomyocyte apoptosis, which has been considered as one of the leading causes of ischaemia/reperfusion (I/R)-induced myocardial injury. In our previous works, we demonstrate that aldehyde dehydrogenase-2 (ALDH2) deficiency aggravates cardiomyocyte apoptosis and cardiac dysfunction. The aim of this study was to elucidate whether ALDH2 deficiency promotes mitochondrial injury and cardiomyocyte death in response to I/R stress and the underlying mechanism. I/R injury was induced by aortic cross-clamping for 45 min. followed by unclamping for 24 hrs in ALDH2 knockout (ALDH2(-/-)) and wild-type (WT) mice. Then myocardial infarct size, cell apoptosis and cardiac function were examined. The protein kinase C (PKC) isoform expressions and their mitochondrial translocation, the activity of dynamin-related protein 1 (Drp1), caspase9 and caspase3 were determined by Western blot. The effects of N-acetylcysteine (NAC) or PKC- shRNA treatment on glycogen synthase kinase-3 (GSK-3) activity and mitochondrial permeability transition pore (mPTP) opening were also detected. The results showed that ALDH2(-/-) mice exhibited increased myocardial infarct size and cardiomyocyte apoptosis, enhanced levels of cleaved caspase9, caspase3 and phosphorylated Drp1. Mitochondrial PKC-epsilon translocation was lower in ALDH2(-/-) mice than in WT mice, and PKC- was the opposite. Further data showed that mitochondrial PKC isoform ratio was regulated by cellular reactive oxygen species (ROS) level, which could be reversed by NAC pre-treatment under I/R injury. In addition, PKC-epsilon inhibition caused activation of caspase9, caspase3 and Drp1Ser(616) in response to I/R stress. Importantly, expression of phosphorylated GSK-3 (inactive form) was lower in ALDH2(-/-) mice than in WT mice, and both were increased by NAC pre-treatment. I/R-induced mitochondrial translocation of GSK-3 was inhibited by PKC- shRNA or NAC pre-treatment. In addition, mitochondrial membrane potential ((m)) was reduced in ALDH2(-/-) mice after I/R, which was partly reversed by the GSK-3 inhibitor (SB216763) or PKC- shRNA. Collectively, our data provide the evidence that abnormal PKC-epsilon/PKC- ratio promotes the activation of Drp1 signalling, caspase cascades and GSK-3-dependent mPTP opening, which results in mitochondrial injury-triggered cardiomyocyte apoptosis and myocardial dysfuction in ALDH2(-/-) mice following I/R stress.