A Novel Role Of Survivin In Insulin-induced Inhibition Of Myocardial Apoptosis In Ischemic/reperfused Rat Hearts

Background: Insulin inhibits ischemia/reperfusion-induced myocardial apoptosis through activation of survival signaling cascade including the phosphatidylinositol 3-kinase (PI3K)-Akt pathway. However, the downstream mechanism of PI3K remains elusive. Survivin (SVV) is an anti-apoptotic protein which has recently been found to participate in vascular protection, however, whether this molecule is expressed in the myocardium is unclear. This study is aimed at investigating whether SVV plays a role in the insulin-induced anti-apoptotic effect in the ischemic/reperfused (I/R) hearts, if yes, further determining the signaling mechanism involved.Methods and results: Isolated adult Sprague-Dawley rat hearts were subjected to 30 min regional ischemia followed by 2h, 3h and 4h reperfusion with or without insulin (10-7 mol/L). Survivin expression was detected with WB. Hearts were randomized to receive insulin in the presence or absence of the specific PI3K inhibitor LY294002, or mTOR inhibitor rapamycin at the onset of reperfusion. SVV expression, phosphorylation of Akt, and downstream molecular mTOR and p70S6K were determined. Infarct size was assessed using TTC staining, cardiomyocytes apoptosis were evaluated by TUNEL staining and DNA fragmentation. Furthermore, cardiomyocytes were transfected with adenovirus encoding SVV or siRNA targeting SVV to further investigate the relationship between insulin and SVV. Insulin reperfusion significantly up regulated myocardial SVV expression, reduced infarct size, inhibited cell apoptosis and resulted in a dramatic increase in mTOR and p70S6K phosphorylation as compared to the I/R group, which was blocked by pretreatment of PI3K inhibitor LY294002. mTOR specific inhibitor rapamycin reperfusion did not change Akt phosphorylation but significantly inhibited SVV expression, indicating a possible role of PI3K/Akt/mTOR/SVV signaling pathway in the cardio-protective effect of insulin. Moreover, over-expression of SVV offered protection against simulated I/R-induced cardiomyocyte apoptosis in vitro, while siRNA targeting SVV blunted the anti-apoptotic effect of insulin.Conclusion: These results provide the first evidence that elevated SVV expression contributes to the anti-apoptotic effect of insulin in I/R hearts through a PI3 kinase/Akt-dependent and mTOR-mediated mechanism.