Simulated remote ischemic preconditioning inhibits Smad2 and enhances post‐hypoxic autophagy and survival of H9c2 cells

Abstract

BackgroundCardiomyocyte apoptosis is considered as one the major forms of cell deaths of myocardial ischemia/reperfusion (I/R) injury. Remote ischemic preconditioning (RIPC) protects the cardiomyocytes from I/R injury that involves the enhancement of autophagy, but the underlying mechanism and especially the relationship with apoptosis has not been delineated. Smad2 is an important autophagy regulatory protein, but its role in RIPC is unknown.MethodsRat cardiac myoblast H9c2 cells hypoxia/reoxygenation (H/R) injury model was established with 6 hours of hypoxia followed by 12 hours of normoxia reoxygenation to mimic I/R injury. The cells in the conditioning group were exposed to 3 cycles of 10 minutes of alternating nitrogen‐flushed hypoxia and reoxygenation as stimulated RIPC (sRIPC) 24 hours before inducing prolonged H/R. The cell viability, oxidative damage, inflammatory markers, expressions of apoptosis and autophagy‐related proteins were assessed.ResultsH/R caused significant cell injury in untreated control H9c2 cells that was associated reduced autophagy (reduction in the ratio of LC3‐II to LC3‐I) and sRIPC enhanced post‐hypoxic cell survival, reduced reactive oxygen species formation and oxidative damage manifested as increased lipid peroxidation product Malondialdehyde (MDA), inhibited Smad2 transcriptional repressor activity, activated Beclin‐1 and autophagy but reduced apoptotic cell death (all p < 0.05).ConclusionsIt is concluded that inhibition of Smad2 and the subsequent activation of autophagy may represent a mechanism by which sRIPC attenuate post‐hypoxic cardiomyocyte injury.Support or Funding InformationFunding: This study was supported by grants NSFC(81800245 and 81670770), and in part by Health and Medical Research Fund (HMRF, 05161826)