The Role Of Helix B Surface Peptide On Diabetic Cardiomyopathy And The Possible Mechanism

Background Diabetes mellitus(DM)is a complex metabolic disorder with the characteristics of high incidence,high disability rate and high mortality rate.The cardiovascular complications caused by diabetes always lead to the deaths of diabetic patients.Diabetes and related complications are piling pressure on the already overburdened health and medical system,ranking diabetes as a top medical issue around the world.Erythropoietin(EPO)is a hormone mainly secreted by the kidney.Its erythropoietic effect has long been known to medical workers and it has been applied clinically for the amemia treatment.Intriguingly,recent studies indicate that despite its erythropoietic effect,EPO also has tissue protective properties.EPO could exert protective effects on an array of organs such as heart,brain and kidney.However,due to the high doses needed to attain tissue protection and its erythropoietic effect,EPO can lead to increased risks of thrombosis,stroke and hypertension.Thus,the clinical use of EPO is substantially limited.Helix B surface peptide,an 11-amino acid peptide,is derived from EPO.HBSP mimics the hydrophilic surface of helix B of EPO.HBSP could bind exclusively to the inner repair receptor(EPOR-βCR),thus exhibiting potent tissue protective property on a diversity oforgans like the brain,heart,kidney,retina,etc.Amazingly,HBSP is capable of protecting tissues without causing erythropoietic effect.AMPK is widely distributed in eukaryotes.It is a multi-functional protein that participates in many biological processes such as metabolism and autophagy.Researches showed that HBSP could alleviate the ischemia-reperfusion injury of mouse kidney by the activation of APMK-dependent autophagy.Nonetheless,it remains need to be elucidated whether HBSP could alleviate the diabetic cardiomyopathy caused by type 1 diabetes.Studies showed that cardiac autophagy was diminished in the mouse model of diabetic cardiomyopathy induced by STZ,which indicated that diminished cardiac autophagy was related to the diabetic cardiomyopathy caused by type 1 diabetes.Currently,there is no report about the relationship of HBSP and diabetic cardiomyopathy in type 1 diabetes mice.Objectives In order to investigate the role of HBSP on diabetic cardiomyopathy,type 1 diabetes was induced by intraperitoneal injections of STZ.Cardiac function,interstitial fibrosis and apoptosis of cardiomyocyte were determined.The ultrastructure and autophagy of cardiomyocytes were examined.To investigate the possible mechanism,the mitochondrial membrane potential,apoptosis and autophagy of H9C2 cells were examined in the presence of high glucose or HBSP.Methods STZ was employed to induce type 1 diabetes mice models,which were later successfully into mice models of diabetic cardiomyopathy.Cardiac function of mice was determined by echocardiography.The expressions of TNF-ɑ and IL-6 were examined by ELISA.The ultrastructure of cardiomyocytes was examined by TEM.Cardiac interstitial fibrosis was determined by Sirius red staining.Western blotting and LC3 immunofluorescence were used to examine the expressions of autophagy related proteins.H9C2 cells were incubated in DMEM with high doses(33m M)of glucose for 48 h,in the presence or absence of HBSP(100u M),the autophagy inhibitor 3-MA(10m M),the autophagy inducer rapamycin(Rapa,100 n M)or the AMPK inhibitor compound c(CC,10 m M).JC-1 Assay Kit was used to examine the mitochondrial membrane potential.Theapoptosis was determined by terminal deoxvnucleotidy1 transferase-mediated d UTP nick-end labeling(TUNEL)assay.Western blotting was used to evaluate the expression of p62,LC3 Ⅱ/Ⅰ,phosphorylation of AMPK,and m TOR.Results Compared with the CON group,the cardiac function of DCM group was impaired while the apoptosis and expressions of TNF-ɑ and IL-6 were increased;The cardiac interstitial fibrosis of DCM mice was increased while the cardiac autophagy was decreased.The ultrastructure of myocardia was impaired in the DCM group.The administration of HBSP could attenuate the above-mentioned changes.High glucose treatment could increase the apoptosis,the expression of p62 and the phosphorylation of m TOR of H9C2 cells while lowered the expression of LC3Ⅱ/Ⅰ,the mitochondrial membrane potential and the phosphorylation of AMPK of H9C2 cells.These above-mentioned changes could be partly reversed by HBSP.Rapamycin had the similar effect of HBSP.3-MA or CC partly abolished the effect of HBSP.Conclusion In vivo and in vitro experiments show that HBSP plays a protective role on diabetic cardiomyopathy induced by type 1 diabetes.The possible mechanism might be the activation of AMPK-dependent autophagy.