Effects Of Atorvastatin On Myocardial Endoplasmic Reticulum Stress In Diabetic Rats

Objectives To investigate the effect of atorvastatin on the expression of endoplasmic reticulum stress(ERS)related ATF6/CHOP/PUMA signal pathway in the myocardium of type 2 diabetes mellitus(T2DM)rats,and to explore the mechanism of atorvastatin on preventing myocardial damage in diabetic cardiomyopathy(DC).Methods 50 Wistar rats were randomly divided into normal control group(NC group)and experimental group.The rats in NC group were fed with normal diet,while rats in experimental group with high-fat dietary and a single intraperitoneal injection of streptozotocin(STZ,25mg/kg)to establish T2 DM models.Fasting blood glucose(FBG)was examined at 3,7 and 14 days after STZ injection,and the rats with results of equal or higher than 16.7mmol/L in every examination and typical manifestations of diabetes were confirmed as T2 DM models.T2 DM rats were fed with HFD continually.Those rats were confirmed as DC models,when cardiac function detected by echocardiography was abnormal.The DC rats were randomly separated into diabetic cardiomyopathy group(DC group),low-dose atorvastatin treatment group(AtoL group),middle-dose atorvastatin treatment group(AtoM group)and high-dose atorvastatin treatment group(AtoH group).All rats were sacrificed after 12 weeks of drug intervention.The basic informations,such as body weight,active status,eating and drinking,were observed and recorded during the experiment.FBG,TC,TG,LDL-C,HDL-C and NT-proBNP were examined to understand the changes of metabolism and cardiac function of rats.Left ventricular end diastolic diameter(LVEDd),left ventricular end systolic diameter(LVEDs)and left ventricular ejection fraction(LVEF)were measured by echocardiography.HE and Masson staining were used to observe the pathological changes and fibrosis of myocardial.Myocardial cell apoptosis was evaluated through TUNEL staining.78-kd glucose-regulated protein(GRP78)and CCAAT/enhancer binding protein homologous protein(CHOP)expression lelves were tested by immunohistochemical staining.Western blotting technology was used to detect the protein expression levels of ERS related factors,GRP78,CHOP,activating transcription factor 6(ATF6)and P53 up-regulate modulator of apoptosis(PUMA).Results 1 The basic informations of rats: In DC group,body weight was significantly lower than that of the NC group,while heart weight/body weight ratio(HW/BW)was higher than that of the NC group(P<0.01).Compared with DC group,the body weight in Ato group gradually increased,whereas HW/BW decreased.Moreover,these effects were in a dose-dependent manner,so the change of AtoH group was significantly different from that of DC group(P<0.01).2 Changes of biochemical indexes in rats: The FBG in NC group was normal.Compared with NC group,FBG in DC group significantly increased(P<0.01),but no statistical difference in Ato group compared with DC group(P>0.01).TC,TG,LDL-C and HDL-C in group NC were normal,while TC,TG and LDL-C-C in DC group increased,HDL-C decreased significantly compared with NC group(P<0.01).There was no prominent difference in AtoL and AtoM group compared with DC group(P>0.01),however,in AtoH group,HDL-C was higher and TC,TG and LDL-C were lower than those in DC group(P<0.01).3 Changes of cardiac function in rats: At the end of the experiment,compared with NC group,LVEDd,LVEDs and NT-proBNP increased significantly in DC group,and LVEF decreased(P<0.01).There was no statistical difference between AtoL group and DC group(P>0.01).However,in both the AtoM and AtoH group,LVEDd,LVEDs and NT-proBNP decreased,and the LVEF was increased,compared with DC group,these changes were in a dose-dependent manner(P<0.01).4 HE staining: The myocardial cells in NC group arranged neatly and densely,cell structure was clear,and nucleus size was uniform.In DC group,cardiac muscle cells were fractured and arranged in disorder,sparsely.Cardiomyocyte are hypertrophic,nuclears’ size was different,intercellular substance was wide,and massive inflammatory cells were observed.The pathological changes in Ato group were improved in a dose-dependent manner.5 Masson staining: Compared with the NC group,massive collagen fibers were found in the myocardium tissues in the DC group.The collagenous fibers in the Ato group decreased gradually with the increased drug dosage.6 TUNEL staining: Apoptosis Index(AI)increased significantly in the DC group compared with the NC group(P<0.01),which decreased in the Ato group gradually with the increased drug dosage compared with the DC group(P<0.01).7 Immunohistochemistry staining: The expression signals of GRP78 and CHOP are shades of brown particles.A large number of brown granules were found in the cytoplasm in the DC group,and the immunohistochemical score(IHS)was significantly higher than that in the NC group(P<0.01).The expression signals of GRP78 and CHOP in the Ato group decreased with the increased drug dosage(P<0.01).8 Western blotting analysis: Compared with NC group,The expressions of GRP78,ATF6,CHOP and PUMA increased significantly in DC group(P<0.01),which was decreased gradually with the increased drug dosage in the Ato group(P<0.01).Conclusions 1 Cardiomyocyte apoptosis mediated by ERS related ATF6/CHOP/PUMA signaling pathway may be involved in the development of DC.2 Atorvastatin may play a cardioprotective role in DC by inhibiting the apoptosis of cardiomyocytes mediated by ERS related ATF6/CHOP/PUMA signaling pathway in a dose-dependent manner.3 Atorvastatin can improve the cardiac function of DC rats by decreasing the apoptosis rate of myocardial cells,reducing the pathological injury and fibrosis of myocardial tissue,and inhibiting myocardial hypertrophy.