Cardiomyocyte-derived adiponectin is biologically active in protecting against myocardial ischemia-reperfusion injury

Adiponectin (APN) has traditionally been viewed as an adipocyte-specific endocrine molecule with cardioprotective effects. Recent studies suggest that APN is also expressed in cardiomyocytes. However, biological significances of this locally produced APN remain completely unknown. The aim of this study was to investigate the pathological and pharmacological significance of cardiac-derived APN in cardiomyocyte pathology. Adult cardiomyocytes from wild-type littermates (WT) or gene-deficient mice were pretreated with vehicle (V) or rosiglitazone (RSG) for 6 h followed by simulated ischemia-reperfusion (SI/R, 3 h/12 h). Compared with WT cardiomyocytes, myocytes from APN knockout (APN-KO) mice sustained greater SI/R injury, evidenced by greater oxidative/nitrative stress, caspase-3 activity, and lactate dehydrogenase (LDH) release (P < 0.05). Myocytes from adiponectin receptor 1 knockdown (AdipoR1-KD) or AdipoR1-KD/AdipoR2-KO mice had slightly increased SI/R injury, but the difference was not statistically significant. RSG significantly (P < 0.01) increased APN mRNA and protein expression, upregulated AdipoR1/AdipoR2 expression, reduced SI/R-induced apoptosis, and decreased LDH release in WT cardiomyocytes. However, the anti-oxidative/anti-nitrative and cell protective effects of RSG were completely lost in APN-KO cardiomyocytes (P > 0.05 vs. vehicle group), although a comparable degree of AdipoR1/AdipoR2 upregulation was observed. The upregulatory effect of RSG on APN mRNA and protein expression was significantly potentiated in AdipoR1-KD/AdipoR2-KO cardiomyocytes. However, the cellular protective effects of RSG were significantly blunted, although not completely lost, in these cells. These results demonstrated that cardiomyocyte APN is biologically active in protecting cells against SI/R injury. Moreover, this locally produced APN achieves its protective effect primarily through paracrine/autocrine activation of APN receptors.