Effect of noise stress on the expression of myocardial glucose-regulated protein 78 and C/EBP-homologous protein and its relationships with myocardial remodeling in rats

Objective To study the expression of glucose-regulated protein 78（GRP78） and C/EBP-homologous protein（CHOP） in myocardial cells in rat noise-induced stress model and explore the relationship between these changes and the myocardial remodeling.Methods Forty male SD rats were divided randomly into two groups: the noise group（n=20）,the control group（n=20）.According to the different exposure time,the noise group was further divided into 4 groups: 2 weeks noise（n=5）,4 weeks noise（n=5）,6 weeks noise（n=5） and 8 weeks noise group（n=5）.Mean blood pressure（MBP） was measured through carotid cannulation.IVST,LPWT,EF and E/A were assessed by B-ultrasound.The left ventricular mass（LVM） and body mass（BM） were measured and LVMI（LVM/BM）was calculated.Immunohistochemistry and Western blot were used to evaluate the protein levels of GRP78 and CHOP.TUNNEL was used to detect the apoptosis in cardiac myocyte.Results ①The MBP in noise group was significantly higher than that in control group（P＜0.01）;②The IVST,LVPWT and LVMI increased by 29%,33%,38% in 4 week;29%,29%,33% in 6 weeks;23%,30%,26% in 8 weeks exposure group compared with control group（P＜0.05）.While E/A and EF value in noise group decreased at week 2 and week 6 respectively;③The expression of GRP78 in cardiac myocyte increased,reached its peak at week 4,and then declined.The protein level of CHOP was increased in a time-dependent manner.The expression of CHOP in noise groups was higher than the corresponding control group（P＜0.01）.Furthermore,the apoptosis in cardiac myocyte in noise groups also increased.Conclusion Noise stress could activate RES in myocyte.The abnormal expressions of GRP78 and CHOP could damage cardiac myocytes and increase apoptosis,which could be part of the potential mechanisms for hypertension,myocyte remodeling induced by noise stress.