Astragaloside Ⅳ Inhibits Autophagy Through PI3K/AKT/mTOR Pathway And Reduces Myocardial Hypertrophy In Rats

Objective: To investigate the effect and mechanism of Astragaloside Ⅳ(ASⅣ)on autophagy in simulated hemodynamic overload.Methods: Through conducting echocardiography,hematoxylin-eosin(HE)staining and wheat germ agglutinin(WGA)immunefluorescence on the SD rats,the cardiac morphological changes of the rats were observed.The expression of rat atrial natriuretic peptide(ANP)was observed by the immunohistochemical method,and enzyme linked immunosorbent assay(ELISA)was applied to determine the brain natriuretic peptide(BNP)of rats.The western blot(WB)method was used to determine the expressions of key proteins of autophagy and underlying signal pathway,including autophagy related microtubule-associated protein 1 light chain 3(LC3),autophagy related 5homolog(ATG5)and phosphatidylinositol-3-kinase(PI3K)/protein dinase B(AKT)/ Mammlian target of rapamycin(mTOR)pathway in rat myocardium.The therapeutic effect of ASⅣ on cardiac hypertrophy and its influence on autophagy were evaluated.Results:1.Compared with the sham operation group,the weight of the heart in the model group treated with abdominal aortic coarctation(AAC)was increased.HE staining indicated disordered arrangement of cardiomyocytes,and the cross section of myocytes showed the hypertrophic myocardial cell nucleus in obviously irregular shapes.After abdominal aortic constriction(AAC)in rats was treated with ASⅣ,the cardiomyocytes were arranged orderly,the shape of myocardial cell nucleus was regular,the heart weight was reduced,the heart weight index(HWI)and heart weight/tibia length(HW/TL)ratio were decreased.The higher the dose required,the lower the heart weight.Compared with the sham operation group,the WGA immunofluorescence staining of the model group indicated that AAC surgery significantly increased the cross-sectional area of cardiomyocytes(P<0.05).ASⅣ exposure decreased the cross-sectional area of myocardial cells in AAC rats in a significant dose-dependent manner(P<0.05),without significant difference between the sham operation group and the ASⅣ control group.2.According to Masson staining,significant myocardial fibrosis was observed in the model group as compared with the sham operation group(P<0.05);the myocardial fibrosis was significantly relieved in AAC rats after ASⅣ treatment(P<0.05);no significant difference was found between the sham operation group and the ASⅣ control group.3.Compared with the sham operation group,the expressions of ANP in myocardial cells and the serum BNP in rats of the model group were significantly up-regulated(P<0.05).After ASⅣ treatment,the expressions of ANP and BNP in AAC rats declined dose-dependently,and there was no significant difference between the sham operation group and the ASⅣ control group.4.Echocardiographic measurement including left ventricular posterior wall depth(LVPWd),interventricular septal thickness at diastole(ⅣSd),left ventricular internal diameter at end-diastole(LVIDd)levels were significantly increased and left ventricular ejection fraction(LVEF)was significantly decreased(P<0.05)in the model group as compared with sham group.All the indexs were improved after ASⅣ treatment(P<0.05).There was no significant difference between the sham operation group and the ASⅣ control group.Compared with the sham operation group,the rats in the model group experienced significantly increased levels of left ventricular posterior wall depth(LVPWd),interventricular septal thickness at diastole(ⅣSd)and left ventricular internal diameter at end-diastole(LVIDd),while significantly decreased level of left ventricular ejection fraction(LVEF)(P<0.05).All the indexes were improved after ASⅣ treatment(P<0.05).The comparison of the sham operation group and the ASⅣ control group was not statistically significant(P>0.05).5.The expressions of LC3 and ATG5 went up in the AAC group as compared with the sham operation group(P<0.05),and this trend could be reversed by ASⅣ.Moreover,with the increase of the ASⅣ dose,the expressions of LC3 and ATG5 were decreased dose-dependently,with the difference being statistically significant(P<0.05).No difference was found in the expressions of LC3 and ATG5 between AAC rats and the rats in the ASⅣ control group.6.As compared with the control group,the expressions of phospho-PI3K(p-PI3K),phospho-AKT(p-AKT)and phospho-mTOR(p-mTOR)in AAC rats decreased significantly,with the difference being statistically significant(P<0.05).After ASⅣ treatment,the expressions of the above proteins in AAC rats increased dose-dependently.There was no significant difference between the sham operation group and the ASⅣ group in terms of the expressions of p-PI3 K,p-AKT and p-mTOR.Conclusion:1.ASⅣ can relieve AAC-induced cardiac hypertrophy,myocardial fibrosis and improve cardiac function.2.ASⅣ can reverse myocardial fibrosis and improve cardiac functions by activating PI3K/AKT/mTOR signal pathway.