Effects Of Cycloastragenol On Cardiac Fibrosis Induced By Isoproterenol In Mice

Cardiac fibrosis(CF),one of the main manifestations of cardiac remodeling,is an important pathological process in the development of many cardiovascular diseases.Pathological alterations of CF characterized by the excessive deposition of extracellular matrix(ECM)in the interstitial space of the heart,which cause an increased stiffness and reduced compliance.As a consequence,heart performance is impaired;thereby leading eventually to various heart diseases such as cardiac arrhythmias,heart failure.Therefore,the prevention of CF is particularly important for the treatment of a variety of cardiovascular diseases.However,there are currently no effective measures of treating CF because the specific pathogenesis is still unclear.Cycloastrogenol(CAG)is an active substance extracted from the root of Astragalus.Many studies have shown that CAG is of potential pharmacological effects to ameliorate heart dysfunction and remodeling through anti-oxidation,anti-myocardial ischemia,promoting autophagy in cardiomyocytes.However,whether CAG protects cardiomyocytes against pathological stimulation-induced fibrosis remains elusive.This study was designed to investigate the effects of CAG on isoproterenol(ISO)-induced heart dysfunction in mice and the possible mechanisms involved in.The main results were as follows:At the H9c2 cell level,it was demonstrated that ISO stimulation induced cardiomyocyte hypertrophy and increased the expression of hypertrophic genes.The CAG pretreatment and the co-treatment of ISO with CAG significantly reduced the expression of hypertrophic genes and alleviated cardiomyocyte hypertrophy.C57BL/6J mice were successively intraperitoneal injected with ISO for 4weeks,and echocardiography was used to evaluate the heart function.The results showed that the cardiac function of the ISO group was significantly impaired compared with the control group.The specific manifestations were that the left ventricular ejection fraction(EF%)and the left ventricular fractional shortening(FS%)were significantly decreased,respectively.While pretreatment of mice with CAG,the impairment of cardiac function caused by ISO stimulation was significantly alleviated.Histopathological section examination showed that ISO stimulation caused significantly cardiomyocyte hypertrophy and fibrosis,while CAG treatment abated remarkably these phenomena.Further results showed that ISO stimulation caused oxidative stress in the heart,evidenced by the increase of NADPH oxidases 4(NOX4)and inducible nitric oxide synthase(i NOS).In contrast,CAG pretreatment reduced the level of oxidative stress in the heart by reducing the expression of NOX4 and i NOS.In addition,ISO stimulation increased the expression of inflammatory factors including TNF-α and IL-1β,which in turn activated NF-κB through a kinase-mediated phosphorylation cascade involving a high-molecular-mass kinase complex.CAG pretreatment however,inhibited the activation of the inflammatory signaling pathway by reducing the expression of their genes and proteins.Increasing studies have linked both inflammatory activation and cellular oxidative stress to an elevation of the expression of transforming growth factor-β(TGF-β)in variety tissues.As a key factor in cardiac fibrosis,TGF-β plays a critical role in promoting the transdifferentiation of fibroblasts to myofibroblasts.As a major producer of ECM in the heart,enhanced synthesis of ECM derived from myofibroblast may trigger the progression of pathological cardiac fibrosis.Our results demonstrated that the expression of TGF-βin the heart was elevated upon ISO stimulation,and subsequently a series of reactions induced fibrosis through increasing in the expression of collagen 1 and collagen 3(Col-1,3).Interestingly,CAG pretreatment reduced remarkably the content of collagen in the heart by down regulating the expression of TGF-β.In summary,this study proved that CAG alleviated significantly heart dysfunction and fibrosis by reducing the activation of oxidative stress and inflammatory pathway,and TGF-β-mediated the accumulation of ECM.