Ischemic postconditioning confers cardioprotection through adiponectin-dependent mitochondrial STAT3 activation in mice

Abstract

INTRODUCTION: Signal transducer and activator of transcription 3 (STAT3) plays a key role in postconditioning (IPo) mediated protection against myocardial ischemia reperfusion injury, but the mechanism by which IPo activates STAT3 is unknown. Adiponectin (APN), a protein with anti-ischemic properties, activates STAT3. We hypothesized that IPo activates mitochondrial STAT3 (MitoSTAT3) via APN signaling. METHODS AND RESULTS: Wild type (WT) and APN knockout (KO) mice were either sham operated or subjected to 30 min of coronary artery occlusion followed by 2 hours of reperfusion with or without IPo (3 cycles of 10 seconds reperfusion and 10 seconds reocclusion; n=8/group). At the end of reperfusion, KO mice exhibited more severe myocardial injury evidenced as increased infarct size (% of area at risk) 49.2±2.0 vs WT 39.4±3.5, P<0.01; plasma troponin I (ng/ml): KO 72.8±7.6 vs WT 45.7±4.0, P<0.01; worse cardiac function (lower dP/dtmax and end-systolic pressure-volume relation, P<0.05); more severely impaired mitochondrial function (reductions in complex IV and complex V protein expression) and more severe reduction of MitoSTAT3 phosphorylation (activation) at site Ser727, P<0.01. IPo significantly attenuated post-ischemic cardiac injury and dysfunction with a concomitant increase in phosphorylated MitoSTAT3 and attenuation of mitochondrial dysfunction in WT (all P<0.05) but not in KO mice. In cultured cardiac H9C2 cells, hypoxic postconditioning (HPo, 3 cycles of 5 min hypoxia and 5 min reoxygenation) significantly attenuated hypoxia/reoxygenation (HR, 3 hours hypoxia/3 hours reoxygenation) induced cell injury (increased apoptotic cell death as % of HR): HR 100.2±0.4 vs HPo 78.2±4.8, P<0.05) and reduced mitochondrial transmembrane potential (% total cells, HR 37.2±4.9 vs HPo 23.5±3.7, P<0.01). APN, adiponectin receptor 1 (AdipoR1), or STAT3 gene knockdown but not AdipoR2 gene knockdown, respectively, abolished HPo cellular protection (all P<0.05 vs. HPo). APN supplementation (10μg/ml) restored HPo protection in cells with APN knockdown but not in cells with AdipoR1or STAT3 gene knockdown. CONCLUSION: Adiponectin and AdipoR1 signaling are required for IPo to activate myocardial mitochondrial STAT3 to confer cardioprotection.