Rapamycin protects heart from ischemia/reperfusion injury independent of autophagy by activating PI3 kinase-Akt pathway and mitochondria K_ATP channel

Objectives : The purpose of this study was to investigate potential roles of rapamycin, a macrocytic lactone produced by Streptomyces hygroscopicus, in myocardial ischemia/reperfusion (I/R) injury. Methods: Male Wistar rats were pretreated with three different doses of rapamycin (0.25, 2, and 5 mg/kg). Then, isolated rat hearts were exposed to 40 min of global ischemia followed by 120 min of reperfusion using a Langendorff apparatus. Western blot analysis was used to examine changes in the expression levels of ERK_1/2 and Akt kinases and LC₃ –II/I (a marker of autophagy). The area of myocardial infarction and cardiac function were evaluated. Results : Our results demonstrated that rapamycin mediates cardioprotection in a dosedependent manner in isolated rat hearts during myocardial I/R injury. Significant a autophagy was induced by rapamycin during I/R. Both, the mitochondrial K_ATP -channel blocker 5-hydroxydecanoate (5-HD) and the PI3K inhibitor LY294002 (LY) abolished the protection afforded by rapamycin completely, while the inhibitors alone did not influence the infarct size in control hearts. However, the ERK1/2 inhibitor PD98059(PD) and the blocker of autophagy 3-methyladenine (3-MA) had no effect on rapamycin-mediated cardioprtection. Conclusions: Cardioprotection afforded by rapamycin involves the PI3K pathway and the activation of mitochondrial K_ATP -channels, but is independent of rapamycin-induced autophagy. This study may have significant impact on clinical practice.