Postconditioning with Calreticulin Attenuates Myocardial Ischemia/Reperfusion Injury and Improves Autophagic Flux

BACKGROUND: Impaired autophagic flux contributes to cardiomyocyte death in ischemia/reperfusion (I/R) injury. Restoring the impaired autophagic flux by using agents may be a promising strategy that alleviates myocardial I/R injury. The present study aimed to evaluate the effect of exogenous calreticulin (CRT) postconditioning on impaired autophagic flux induced by hypoxia/reoxygenation (H/R) injury in H9c2 cells. METHODS: Rat myocardial I/R injury model was prepared. CRT postconditionging was fulfilled by an intraperitoneal injection of CRT (0.5 mg/kg body weight) 5 min before reperfusion. Hemodynamics, serum lactate dehydrogenase (LDH) activity and Cardiac troponin T (TnT) content, and infarct size were measured. The H/R injury model of H9c2 cells was prepared. CRT postconditioning was performed by adding 25 pg/mL CRT to the medium at the onset of reoxygenation. Cell death rate, lactate dehydrogenase (LDH) leakage, intracellular reactive oxygen species (ROS), and malondialdehyde (MDA) were assessed. Autophagic flux was monitored by mRFP-GFP-LC3 adenovirus infection. The number of autophagosomes and autolysosomes in cells were determined by counting the fluorescence dots. Western blot assay was used to determine the expression of autophagy-related proteins. RESULTS: CRT postconditionging improved cardiac function, reduced serum LDH activity and TnT content, and limited myocardial infarct size after myocardial I/R injury in rat. H/R induced H9c2 cells injury and autophagosomes accumulation in cells. CRT postconditioning attenuated H/R-induced cell death, LDH leakage, and the increase of intracellular ROS and MDA. Meanwhile, CRT postconditioning suppressed H/R-induced excessive formation of autophagosomes, as shown by a decrease of autophagosomes and the ratio of LC3-II/LC3-I, LC3-II, and Beclin1. It also improved H/R-induced impaired autophagosomes clearance, as shown by an increase of autolysosomes and the level of LAMP-2, and a decrease of the level of p62. CONCLUSION: These findings suggested that CRT postconditioning reduced myocardial I/R injury. CRT postconditioning also inhibited the excessive formation of autophagosomes, promoted the clearance of autophagosomes, and resorted the autophagic flux, consequently reduced the H/R injury in H9c2 cells.