Effects of sarcoplasmic reticulum calcium ATPase 2a overexpression on endoplasmic reticulum stress in cardiomyocytes

Abstract

To investigate the effects of sarcoplasmic reticulum calcium ATPase 2a (SERCA2a) overexpression on the endoplasmic reticulum stress (ERS). Ventricular cardiomyocytes were obtained from a neonatal rat, cultured, and then randomly divided into 6 groups: normal control group; hypoxia group cultured in an airtight chamber gassed with 95% N(2)/5% CO2 at 37 degrees C for 72 hours so as to induce ERS; tunicamycin group treated with 10 microg/ml tunicamycin so as to induce ERS too; SERCA2a group transfected with recombinant adenovirus expressing the target gene SERCA2a (rAd-SERCA2a); SERCA2a + hypoxia group; and SERCA2a + tunicamycin group. Western blotting was used to detect the protein expression of SERCA2a, and glucose-regulated protein 78 (GRP78) and C/EBP homologous protein (CHOP), both the ERS markers. Flow cytometry was used to detect the apoptosis of the cardiomyocytes, and trypan blue staining was used to detect the survival rate of the cardiomyocytes. (1) The GRP78 expression level of the hypoxia group was 5.1 times as high as that of the control group, and the CHOP expression level of the hypoxia group was 2.5 times as high as hat of the control group. The GRP78 expression level of the tunicamycin group was 4.9 times as high as that of the control group, and the CHOP expression level of the tunicamycin group was 3.1 times as high as hat of the control group. SERCA2a overexpression was found to relieve the expression of GRP78 induced by hypoxia and tunicamycin (49.1% and 50.4% decrease respectively), and to inhibit the activation of CHOP (52.7% and 66.1% decrease respectively). (2) In comparison with the hypoxia group, the protein expression levels of GRP78 and CHOP of the SERCA2a overexpression + hypoxia group were significantly lower by 49.1% and 52.7% respectively, the apoptotic rate was significantly lower by 66.0%, and the cardiomyocyte survival rate was significantly higher by 13.4% (all P < 0.05). Compared with the tunicamycin group, the protein expression levels of GRP78 and CHOP of the SERCA2a overexpression + tunicamycin group were significantly lower by 50.4% and 66.1% respectively, the apoptotic rate was significantly lower by 54.0%, and the cardiomyocyte survival rate was significantly higher by 6.7% (all P < 0.05). SERCA2a overexpression attenuates ERS induced by hypoxia or tunicamycin, and protects cardiomyocytes against ERS-mediated cellular injury.