Role of endoplasmic reticulum stress in Bim-mediated cardiomyocyte apoptosis induced by hypoxia

AIM: To investigate the role of endoplasmic reticulum stress( ERS) in the process of Bim-mediated cardiomyocyte apoptosis induced by hypoxia. METHODS: Cardiomyocytes were isolated from neonatal Sprague-Dawley rats aged 1 ~ 3 days,and primarily cultured in vitro. The antibody targeting α-striated muscle actin was used to identify the cardiomyocytes. The siRNAs targeting bim were transfected into cardiomyocytes with liposome,followed by detecting the expression of Bim by Western blotting. Cardiomyocytes were divided into five groups: blank control group,hypoxia group, hypoxia + liposome group,hypoxia + negative control siRNA group and hypoxia + Bim-siRNA group. The cell viability was determined by MTT assay,and the cell apoptotic rate and the intracellular calcium concentration were measured by flow cytometry. The protein expression of caspase-12 and inositol 1,4,5-triphosphate( IP 3) was detected by Western blotting. RESULTS: Immunohistochemical identification confirmed that rat cardiomyocytes were successfully cultured. Green fluorescence was observed in the cells transfected with negative control siRNA under fluorescence microscope. The expression of Bim was obviously inhibited after transfected with Bim-siRNAs and the silencing efficiency of Bim-siRNA-2 was the highest( 86. 73%). Compared with blank control group,the viability of cardiomyocytes in hypoxia group was significantly reduced( P 0. 05). Compared with hypoxia + negative control siRNA group,the viability of cardiomyocytes in hypoxia + Bim-siRNA group was significantly increased( P 0. 05). The apoptotic rate and the intracellular calcium concentration of cardiomyocytes were obviously increased in hypoxia group( P 0. 01),and were both decreased after bim silencing( P 0. 05 or P 0. 01). The expression of caspase-12 and IP 3 was up-regulated in hypoxia group( P 0. 05),and was downregulated after bim silencing( P 0. 05 or P 0. 01). CONCLUSION: Cardiomyocyte apoptosis induced by hypoxia can be inhibited by silencing the expression of bim gene. Caspase-12 and IP 3,as markers of ERS,may participate in the process of Bim-mediated cardiomyocyte apoptosis induced by hypoxia.