Role of autophagy in attenuating myocardial ischemia-reperfusion injury induced by endoplasmic reticulum stress preconditioning with low dose of tunicamycin

Abstract

Objective To investigate the role of autophagy in reducing myocardial ischemia reperfusion (I/R) injury by endoplasmic reticulum stress preconditioning induced by low dose of tunicamycin (TM). Methods Fifty male SD rats were randomly divided into five groups: sham group; I/R group; TM group (the rats received TM treatment 30 minutes before LAD ligation); 3-MA-1 group (the rats received intraperitoneal injection of TM and vein injection of autophagy inhibition 30 minutes before LAD ligation); 3-MA-2 group (the rats received intraperitoneal injection of TM and intravenous injection of 3-MA before reperfusion). I/R model was used ligation of left anterior descending coronary artery and reperfusion 2 h. Creatine kinase isozyme (CK-MB) and lactate dehydrogenase (LDH) activities were measured by colorimetry after thoracotomy and 2 hours after reperfusion. Cardiac apoptosis was observed by TdT-mediated dUTP nick end labeling (TUNEL) and the expression of autophagy protein Beclin-1 and LC3-Ⅱ/LC3-Ⅰ was detected by Western blotting. Results CK-MB and LDH activity at 2 hours after reperfusion were lower in TM group than in I/R group (t=2.672, 2.834, P 0.05). The apoptotic index of Sham group, I/R group, TM group, 3-MA-1 group and 3-MA-2 group were (2.5±0.3)%, (27.9 ±3.1)%, (13.4±1.6)%, (26.4±2.9)% and (9.4±0.8)% respectively. TM group and 3-MA-2 group were lower than I/R group (t=3.695, 3.587, P 0.05). At 2 hours after reperfusion, Beclin-1, LC3-Ⅱ/LC3-Ⅰ in I/R group, TM group, 3-MA-1 group and 3-MA-2 group were higher than those in Sham group (t=4.047, 3.773, 3.738, 2.542, P<0.05; t=3.447, 3.363, 3.169, 2.527, P<0.05), while those in TM group, 3-MA-1 group and 3-MA-2 group were lower than those in I/R group (t=2.671, 3.150, 3.357, P<0.05; LC3-Ⅱ/LC3-Ⅰ比较: t=2.479, 3.263, 3.351, P<0.05). Conclusion Autophagy plays an important role in the process of myocardial ischemia reperfusion injury. ERS preconditioning induced by low dose of TM can induce moderate autophagy during ischemia, help maintain the homeostasis of myocardial cells, and produce a certain degree of myocardial protection. Key words: Myocardial ischemia reperfusion injury; Endoplasmic reticulum stress; Preconditioning; Tunicamycin; Autophagy