Inhibiting mTOR enhanced Cardiac STAT3 Phosphorylation at Site Ser 727 and Attenuated Myocardial Ischemia Reperfusion Injury in Diabetic Rats

Background: Reduced levels of myocardial STAT3 activity in diabetic hearts may contribute to the increased susceptibility to ischemia-reperfusion injury (I/RI). The protein mammalian target of rapamycin (mTOR) can regulate metabolism and cell processes and plays major roles in the dynamics of I/RI. However, the role of mTOR in regulation of myocardial STAT3 and thereby affect myocardial I/RI in diabetes at relatively late stages of the disease is unknown. Methods: Diabetes was induced by Streptozotocin in Sprague-Dawley rats. Myocardial I/RI was achieved with coronary occlusion for 30 minutes and reperfusion for 2 hours in absence or presence of the mTOR inhibitor rapamycin. In vitro cardiomyocyte hypoxia/re-oxygenation (H/R) was established within H9C2 cells. Results: In diabetic rats, the levels of troponin-I (Tn-I), lipid peroxidation products 15-F2t-Isoprostane (15-F2t-Iso) and MDA, and the expression of protein mTOR were all significantly increased,and SOD releasing, the expression of protein phosphorylation of STAT3(p-STAT3-Ser727) were both significantly decreased compared to non-diabetic rats. Myocardial I/RI significantly increased the infract size (IS) and further increased the mTOR activation and decreased p-STAT3-Ser727 compared to diabetic rats. The selective mTOR inhibitor rapamycin reversed these changes and conferred cardioprotective effect. In H9C2 cells, high glucose (HG) significantly increased lactic dehydrogenase (LDH) release, apoptosis cells, ROS release, activation of mTOR, and decreased p-STAT3-Ser727. H/R further increased cellular injury, mTOR knock-down significantly reduced H/R injury. Conclusion: Myocardial mTOR was enhanced in diabetes and contributed to I/RI. mTOR inhibition attenuated myocardial I/RI through increasing p-STAT3-Ser727.