Investigation On The Expression Changes And Intervention Of TGF-β1/Smad Signaling Path-way In Myocardium Of Diabetes Rats

Objective:Diabetes mellitus (DM) is a chronic metabolic disorder characterized by hyperglycemia which is caused by insulin secretion defect and weakened biologi-cal action.Diabetic cardiomyopathy(DCM) is a distinct primary disease,independent of hypertension,coronary artery disease and other known myocardial diseases, char-acterized by extensive focal necrosis in myocardium which is caused by microan-giopathy and energy metabolic disorder.Myocardial fibrosis is one of the features of DCM. Transforming growth factor betal(TGF-β1) is a profibrotic cytokine and a common agent that plays an important role in the process of other factors leading to myocardial fibrosis. Smads proteins are the most important cytokins in the down-stream of TGF-β1, which transfer the information of TGF-β1from membrane to aim genes. Exenatide,a new drug that lowering glucose, is the agonist of glucagon-like peptide-1(GLP-1) receptor,which was synthesized recently.Recent studies have found that the receptor of GLP-1distributed exstensively besides the pancreas,and can pro-tect other organs.However,whether GLP-1receptor agonist can alleviate or reverse myocardial fibrosis is still unclear.Our study aims at observe the changes of myocar-dium structure and the collagen aggradation in DCM,and establishing a GLP-1inter-vention group to observe the changes of these indicators, so that to explore whether GLP-1have a protective effects on DCM myocardial fibrosis.Methods:36clean grade inbred Wistar rats, were raised in cages in specific pathogen-free conditions. Selected10of them randomly as normal control group(N group),fed with regular rodent feedstuff,Others with fatty and sugary feedstuff.8weeks later,STZ was injected into caudal vein to induce type2diabetes mellitus.22of the26were alive after that,and then randomly selected11of them as exenatide inter-vention group(EX group),and were subcutaneous injected exenatide everyday;the other11were subcutaneous injected by physiological saline in the same amount. Eventually,there were10rats left in each group. When the experiment was at the end:①Recorded body weight of the rats,tested the blood glucose,kept the blood samples to test glycosylated hemoglobin,cholesterol,triacylglyceride,high density lipoprotein cholesterol and then recorded the heart weight.②Heart samples were obtained for: HE staining:to observe the structural changes of heart tissue and collagen aggradation under light microscope; Western Blotting:to detect the protein expression of COL Ⅰ PPARa in each group;RT-PCR:to detect the mRNA expression of TGF-β1、Smad2、 Smad3、Smad7、COL Ⅰ、PPARα in each group.Results:(1) HE staining:N group had regular cardiac muscle fiber,cardiac in-terstitial and micrangium,fractured and rearranged cardiac muscle fiber and necrotic cardiomyocytes can not be seen. There were cardiomyocytes hypertrophy and some-times necrosis in DM group, besides inflammatory cells infiltration,and scattered pink collagen can be seen in cardiac interstitial. Heart damage in EX group were slighter than DM group, however,it didn’t recover to normal.(2) Western Blotting:compared with N group,there were more COLⅠ and less PPARα espressed in DM group(P<0.01);while in EX group,there were less COLⅠ and more PPARα expressed than DM group(P<0.01).(3)RT-PCR:DM group expressed more TGF-β1, Smad2, Smad3,COLⅠ but less Smad7and PPARα than N group (P<0.01);while EX group expressed less TGF-β1,Smad2,Smad3and COLⅠ but more Smad7and PPARα than DM group (P<0.01).(4)Pearson correlation analysis:The expression of TGF-β1was positively correlated with that of Smad2,Smad3,COLⅠ (r=0.639,0.736,0.638, P<0.01),but negatively correlated with Smad7and PPARα(r=-0.537,-0.501,P<0.01).Conclusions:(1) The expressions of TGF-β1,Smad2,Smad3,COL Ⅰ increased in DM group, while Smad7decreased,which suggested that abnormal expression of TGF-β1/Smad signal transduction pathway plays a role in the pathogenesis of inter-stitial fibrosis in DCM.(2)The pathological changes of myocardium in EX group were slighter than DM group and the deposition of collagen and the expression of TGF-β1,Smad2,Smad3,COL Ⅰ were suppressed in EX group while Smad7were acti-vated,which suggested that exenatide can relieve the interstitial fibrosis of DM rats by suppress TGF-β1/Smad signal transduction pathway.(3)The expression of PPARα in heart tissure was decreased in DM group and increased after exenatide treat-ment, which suggested the suppression of TGF-β1/Smad signal transduction pathway by exenatide may have something to do with the activation of PPARα.