The time relation between autophagy and myocardium ischemia (MI) has never been documented. Therefore, the present study was conducted to find out the exact timings and specific roles that AMP-activated protein kinase (AMPK)-mTOR signaling pathway plays on autophagy and apoptosis in rats' ischemic heart. 36 male Sprague Dawley (SD) rats were divided randomly into control and MI groups (each = 6). MI models were created by ligating left anterior descending artery (LAD) of rat hearts and the right myocardium were harvested at 0.5 h, 1 h, 3 h, 6 h, 12 h after ischimia. Expressions of Phosphorylated-AMPK (p-AMPK) and Phosphorylated-mTOR (p-mTOR) were determined by immunohistochemistry (IHC), western blotting (WB) and quantitative real-time PCR (Q-PCR) methods. LC3 expression was determined by WB and Q-PCR. The level of cell apoptosis was measured by the terminal deoxynucleotidyl transferase-mediated dUTP-nick end labeling (TUNEL) method. p-AMPK was activated significantly in ischemic myocardium and its expression at MI groups showed a time dependent pattern with a fluctuating pattern compared to the control group. p-AMPK levels were seen to rise at 0.5 h followed by a fall at 1 h after MI, which again gradually peaked at 6 h and finally decreased at 12 h. While, p-mTOR levels suggested a constant declining trend with time. Autophagy related protein LC3 had a sustained up-regulation with time. TUNEL method suggested that apoptosis increased at 0.5 h, then decreased at 1 h and 3 h after MI and finally showed a continuous rising trend. Activation of protective autophagy that occured during the initial phases of ischemic insults was within 6 hours. When the ischemia was prolonged, after 6 hours, although autophagy increased, cardiomyocyte death followed via the activation of apoptosis. Thus, limiting autophagy within 6 hours would give us double benefits. It would prevent the death related autophagy and prevent apoptotic cellular death. This 6 hours time period could serve as a landmark for therapeutic application for achieving cardioprotection from ischemic insults.
Keywords: AMPK; LC3; Myocardium ischemia; apoptosis; autophagy; mTOR; timings.