Time-dependent Changes Of Cardiac Performance, Gene Expression Profiles And Apoptosis In STZ-induced Diabetic Rat Model Of Acute Myocardial Infarction

Objective:In spite of numerous studies in diabetic animal models,to our knowledge,myocardial performance,especially time course study was never performed in untreated diabetic myocardial infarction(MI) rat model without reperfusion.Methods:In the present study,myocardial function and structure changes of myocardium were examined in untreated streptozotocin(STZ)-induced diabetic MI rat model without perfusion. DM was induced with a single intraperitoneal injection of STZ(65 mg/kg),and body weight was recorded and serum glucose levels were determined at baseline,day 3,day 7,day 30 and day 70 after STZ injection by using One Touch Sure Step test strips and meter(Life Scan,Johnson & Johnson,Warren NJ,USA).Ten weeks after DM induction without any therapy,the left anterior descending coronary artery of diabetic Sprague-Dawley rats was ligated to induce no-reperfusion MI model Tissue structure of myocardium,two-dimensional echocardiography,and hemodynamic studies were utilized to monitor the time course changes of above relating parameters up to 56 days.Results:Ten weeks after DM established,serum glucose levels were significantly higher in the diabetic rats(489±28mg/dl) than in the non-diabetic animals(112±13mg/dl,P＜0.001).Body weights were significantly lower in the diabetic rats(244.8±23.6g) than that of non-diabetic ones (516.3±48.6g,P＜0.001).TEM examination showed that the heart of diabetic rats contained increased lipid droplets and glycogen particles around mitochondria and scattered mitochondrial damage(swelling and disrupted cristae);in addition,cardiac muscle fibers were identified to be crumbly in the majority of the diabetic rats,and the basal lamina of regional small vessels was thicker in some regions.After AMI,Diabetic rats experienced lower survival rate in both acute phase(1,7 and 14 days) and chronic phase(28 and 56 days) compared with non-diabetic rats at corresponding time points.During 56 days after myocardial infarction,worse left ventricular function(EF 37.3±5.4 vs.48.8±4.1,P＜0.01 and FS 17.0±1.4 vs.23.7±2.5,P＜0.05) and larger the left ventricular diameter(increased LVEDD 47.5±5.2%vs.26.8±4.9%,P＜0.001) were identified in diabetic rats than in non-diabetics.Furthermore,diabetic rats showed more serious myocardial fibrosis by quantification of fibrosis area in the remote zone of left ventricular free wall compared with non-diabetic ones at 28 and 56 days after MI(Masson's quantitation 10.3%±1.5%vs.3.8%±0.9%,P＜0.001 and 17.5%±2.1%vs.9.8%±1.2%,P＜0.001).Conclusion:The different patterns of the pathophysiologic changes in the untreated STZ-induced diabetic MI rat model without reperfusion might suggest that in the early phase after AMI,LV diastolic dysfunction may account for the higher incidence of HF and death,while in the prolonged phase,both LV dysfunction and accelerated cardiac remodeling can be the motivation. Objective:To study the time-dependent effects of genetic changes in untreated Streptozotocin (STZ)-induced diabetic rat with MI.Methods:The left anterior descending coronary arteries were ligated 10 weeks after DM induction without any therapy and reperfusion.Microarray analysis and real time-PCR were utilized to monitor the time-dependent genetic changes in the remote zone of LV up to 56 days.Results:The gene expression related to cardiac remodeling in the remote zone was quite different as time elapses between both groups.Total 1221 genes were found to be differentially expressed between diabetics and non-diabetics,770 unregulated and 451 downregulated, involving in glucose metabolism,fatty acid metabolism,extracellular matrix,apoptosis, oxido-reductase activity,phosphoprotein phosphatase activity,etc.The gene expression at 1 and 7 days post acute MI in diabetic and non-diabetic group was similar,while such changes at day 14 in diabetic rats were comparable to both 14 and 28 days in non-diabetic rats;moreover,the pattern of gene expression at day 28 and 56 in diabetic rats was similar to the ones at day 56 in non-diabetic rats,which may indicate that upregulation of the genes was found one-two weeks earlier in diabetic rats than in non-diabetic rats.In primary examination,164 genes(118 named) were found to be candidates for hierarchical analysis,such as leucine-rich PPR-motif containing (interleukin-6 signaling pathway),procollagen typeⅠandⅢ,fibronectin-1,RT1,and TIMP-1,etc.Conclusion:The present data support that diabetes upregulates remodeling-related gene,which may be responsible for the worse outcomes in diabetes than in non-diabetes after myocardial infarction. Objective:To examine whether diabetes is associated with enhanced cardiomyocyte apoptosis and thus interferes with the post-infarction remodelling process in myocardium in rat.Methods:Ten weeks after intravenous streptozotocin(diabetic groups) or citrate buffer(controls) injection,myocardial infarction was produced by ligation of left descending coronary artery.Level of cardiomyocyte apoptosis was quantified by TUNEL method;Bax and Bcl-2 proteins were determined by western blot method;CTGF and caspase-3 were quantitated by real time-PCR.Results:The number of apoptotic cardiomyocytes was higher in diabetic than in non-diabetic rats after 10 weeks of DM induction(apototic index,3.2±0.5 vs.1.4±0.3,P<0.01).At 1d(20.1±1.8 vs.16.9±1.5,P<0.05),7d(16.1±1.7 vs.12.9±1.3,P<0.01),14d(16.1±1.7 vs.13.1±1.4,P<0.05), 28d(15.2±1.8 vs.11.9±1.5,P<0.01) and 56d(16.3±1.6 vs.9.6±1.2,P<0.001) after myocardial infarction,the apoptotic indices in the border zone of infarction area was higher in the diabetic as compared to non-diabetic rats.Correspondingly,Bax,connective tissue growth factor and caspase-3 expression were increased in diabetic compared with non-diabetic rats with myocardial infarction,whereas Bcl-2 expression was decreased.Conclusion:Apoptotic myocyte loss could be an important mechanism contributing to progressive dilatation of the heart and poor prognosis after myocardial infarction in diabetes.