Abstract P125: A Novel Role for Survivin in Insulin-induced Inhibition of Myocardial Apoptosis in Ischemic/reperfused Heart
Objectives: Insulin reduces post-ischemic myocardial apoptotic death, but the mechanism remains unclear. Survivin, an anti-apoptotic protein has recently found participating in vascular repair. This study aimed to test the hypothesis that the up-regulation of survivin by insulin may play a role in the antiapoptotic and cardioprotective effects in the ischemic/reperfused (I/R) heart, and further investigate the signaling mechanism involved.
Methods: Isolated adult Sprague-Dawley rat hearts were subjected to 30 min regional ischemia and 3 h of reperfusion. The hearts were randomized to receive insulin, insulin plus LY294002 (specific inhibitor of PI3K), or insulin plus rapamycin (specific inhibitor of mTOR) at the start of reperfusion. To further confirm the correlation between survivin and myocardial survival in vitro, cardiomyocytes were infected with adenovirus encoding survivin or transfected with siRNA targeting survivin. Phosphorylation of Akt, mTOR, p70S6K and the expression of protein survivin were determined and infarct size was assessed using TTC staining, cardiomyocytes apoptosis were evaluated after reperfusion by TUNEL staining and DNA laddering.
Results: I/R increased myocardial survivin expression. Insulin reperfusion (10−7 mol/L) resulted in a 4.2-fold increase in survivin expression (P<0.01 vs. I/R alone), which was almost completely blocked by LY294002. Both of the mTOR phosphorylation and survivin expression were inhibited in the group of insulin reperfusion plus LY294002. Rapamycin reperfusion did not change Akt phosphorylation but partially inhibited survivin expression (16.7±1.2 vs. 9.8±1.6, P<0.01 vs. I/R+Ins), which indicated a cardioprotective effect of survivin and a possible PI3K/Akt/mTOR/SVV signaling pathway during I/R. Moreover, over-expressed survivin provides protection against stimulated ischemia reperfusion induced cardiomyocyte apoptosis, while targeting survivin blunted the anti-apoptotic effect of insulin.
Conclusion: This study demonstrates that insulin up-regulates myocardial survivin expression, partly at least, via PI3-kinase-mTOR mechanism, which contributes to the anti-apoptotic effect of insulin in the I/R heart.