Background: Apoptosis is a major cause of ischemic heart dysfunction. Apelin, the endogenous ligand for the G-protein-coupled APJ receptor, has been reported to exert cardioprotective effects during myocardial injury. The aim of this study was to investigate the effects of apelin on apoptosis of rat cardiomyocytes induced by glucose deprivation (GD) and study the related signaling pathway.
Methods: Apelin and APJ mRNA expression were determined by RT-PCR in neonatal rat cardiomyocytes during different durations of GD. Cardiomyocyte apoptosis was detected by annexin V-FITC/propidium iodide (PI) staining after GD for 12 hours with or without apelin-13 (10 and 100 nmol/L) pretreatment. Protein levels of Akt and the mammalian target of rapamycin (mTOR) as well as cell apoptosis were detected in the presence or absence of LY294002 (a phosphatidylinositol 3-kinases (PI3K) inhibitor) or rapamycin (a mTOR inhibitor).
Results: Apelin mRNA expression was up-regulated when cardiomyocytes were exposed to GD for 6, 12, 18, and 24 hours compared with the base level (P > 0.05, P < 0.01, P < 0.01, P < 0.01). However, when cardiomyocytes were exposed to GD for up to 36 hours, apelin mRNA expression was 17% lower than the base level (P < 0.05). APJ mRNA expression paralleled that of apelin. Apelin-13 pretreatment at 100 nmol/L significantly inhibited GD-induced cardiomyocyte apoptosis (P < 0.05) and increased Akt and mTOR phosphorylation (P < 0.01, P < 0.01). At the same time apelin-13 (100 nmol/L) up-regulated Bcl-2 protein expression and down-regulated Bax and cleaved caspase-3 expression (P < 0.01, P < 0.05, P < 0.05). The anti-apoptotic effect of apelin-13 was blocked by LY294002 (P < 0.01) but not by rapamycin.
Conclusions: The endogenous apelin-APJ system is compensatorily up-regulated and ultimately down-regulated following sustained myocardial ischemia. Apelin protects against ischemic cardiomyocyte apoptosis via activation of the PI3K/Akt pathway.