| Research backgroundDiabetic cardiomyopathy is a specific cardiomyopathy caused by diabetes mellitus,and differes from coronary heart disease,hypertensive heart disease.Diabetic cardiomyopathy shows reduced ventricular compliance,blocked ventriclar diastolic filling and systolic dysfunction.Myocardial cells can be directly injured by hyperglycemia and metabolic disorder,which will induce diabetic cardiomyopathy.Therefore all patients with diabetic cardiovascular complications combine with diabetic cardiomyopathy.Different from myocardial necrosis in acute myocardial infraction patients,cardiomyocytes hypertrophy and myocardial interstitial fibrosis,myocardial cells apoptosis plays the major role in chronic myocardial pathologic changes of diabetes mellitus[1,2].It is the key to inhibit cardiomyocyte apoptosis to prevent diabetic cardiomyopathy.Adiponectin is one of the highest concentrational adipokines in blood serum,and has also been suggested to be a protective factor for cardiovascular system.Previous researches have indicated that up-regulated expression of APPL1,the key protein of adiponectin pathway,will improve diabetic cardiomyopathy [3].Activating APPL1-AMPK axis and inhibiting NF-?B expression shows the protective benefit to cardiovascular system by adiponectin pathway [4,5].Meanwhile,we have proved that PPARα as a important downstream protein of AMPK,can inhibite NF-?B to participate in the inhibiting of cardiocytes apoptosis [6].These research results indicated that “APPL1-AMPK-PPARα” axis did exist in adiponectin signal pathway and played a significant role in cardiomyocytes apoptosis inhitition of diabetic cardiomyopathy.Recent reports have demonstrated that glucagon-like peptide-1(GLP-1)agonists showed the protective effect to cardiovascular system.GLP-1 can stimulate the secretion of adiponectin and decrease cardiomyocyte apoptosis independent of glucose reduction [7-9].Some researchers indicated the cardiomyocytes protective effect of GLP-1 was closely related to activated adiponectin signal pathway.So,we suppose that GLP-1 activate adiponectin signal pathway “APPL1-AMPK-PPARα” axis to inhibit cardiomyocyte apoptosis.For verifying our hypothsis,we finish clinical,diabetic animal model and primary myocardial cells tests.Firstly,we collected the type 2 diabetes to analyze the relationship between adiponectin and heart function.Then,we used streptozotocin injection and high-fat diet to construct type 2 diabetes rat model,and intervened by Exenatide to investigate the effect and mechanism of Exenatide on diabetic cardiomyopathy.Lastly,for removal of the hypoglycemic and antilipemic effect of Exenatide,we investigate the effect and mechanism of Exenatide on the apoptosis of primary myocardial cells.ObjectiveTo investigate the relationship between serum adiponectin and heart function of type 2 diabetes and discuss the effect and mechanism of Exenatide to improve diabetic cardiomyocytes apoptosis.Methods1.In clinic try,we collected clinical data of type 2 diabetes and normal examination population,dectected their serum high weight molecular adiponectin and insulin concentration in fasting vein blood by ELISA,and analysed the patients’ heart function by contrast enhancement magnetic resinance;2.In animal try,we used streptozotocin(STZ)injection and high-fat diet to constructed type 2 diabetes rat model and divided the rats into control group(C group),diabetes group(D group),diabetes with insulin treatment group(DI group)and diabetes with Exenatide treatment group(DE group).Then keep feeding for 12 weeks,drawed the iliac vein blood of rats to detect serum high molecular weight adiponectin(HMW-ADN)and insulin by ELISA,measured hemodynamics by multimedia biosignal recorder,detected myocardial cells apoptosis rate by TUNEL.We also dissected the cardiac tissue to test the expression of APPL1,p-AMPK/T-AMPK,PPARα and NF-?B by immunohistochemistry and western blotting.3.In cells try,we cultivated primary cardiomyocytes and divided the cells into control group(C group),diabetic group(D group),diabetic + exenatide treatment group(DE group),diabetic + exenatide treatment + APPL1 overexpression group(OE group),and diabetic + exenatide treatment + APPL1 blockage group(BL group).The apoptosis rate of cells was detected by TUNEL,the adiponectin level in the cell culture fluid by ELISA,and the expression levels of APPL1,p-AMPK,PPARα and NF-κB by Western-blotting.Results:1.Clinical research: We collect 30 type 2 diabetes mellitus patients(D group)and 30 normal examination population(N group),the age,gender,height,weight of all participants have no difference except diabetic duration.Compared with N group,the Hb A1 c,fasting blood glucose(FBG),HOMA-IR and TG of DM group patients were obviously elevated,but the high density lipoprotein(HDL)and C-peptide level were significantly decreased(P<0.05).The serum insulin,TC,and LDL have no difference in two groups’ patients(P>0.05).The HMW-AND concentration,left ventricular end-diastolic volume(EDV),left ventricular end-systolic volume(ESV),left ventricular stroke volume(SV)are 14.90±3.26mg/L,65.84±9.67 ml/m2,24.25±5.51 ml/m2,38.40±4.75 ml/m2.Compared with N group population,the HMW-AND concentration of D group patients(10.83±2.81mg/L),EDV(59.70±7.26ml/m2),SV(34.77±6.48ml/m2)is obviously depressed,the ESV(29.00±6.60 ml/m2)is obviously increased.All the differences are statistically significant(P<0.05).Correlation analysis shows that the serum HMW-AND concentration of DM group patients is related to SV[r=0.376,p=0.041].2.Animal research: We successfully constructed the diabetes rats model by low-dose streptozotocin and high-fat diet.After intervening with insulin or Exenatide,the blood glucose decreased and serum insulin level raised significantly in DI and DE group than D group(P <0.05).But the blood glucose was no difference in DI and DE group.The adiponectin concentrate of C group was 0.52±0.06μg/l.Compared with C group,the adiponectin concentrate of D group(0.47±0.04μg/l)and DI group(0.47±0.03μg/l)were significantly depressed,but the adiponectin concentrate of DE group(0.76±0.03μg/l)is obviously increased,and all of the differences were statistically significant(P<0.05).Compared with C group about the apoptosis rate(6.14% ± 2.32%),D group(55.71% ± 3.84%)and DI group(43.91% ± 4.23%)were both apparently elevated,But interestingly,the apoptosis rate of DE group(27.43% ± 3.63%)was statistically depressed when compared with DI group.The left ventricular systolic pressure(LVSP)and left ventricular end-diastolic pressure(LVEDP)of C group rats were 126.25±4.59 mm Hg and 10.38 ± 0.93 mm Hg.Compared with C group,the LVSP of D group rats(105.87±4.08 mmHg)and DI group rats(107.19±4.09 mm Hg)are obviously depressed,LVEDP of D group(17.62 ± 1.74 mm Hg)and DI group(17.48±1.49 mm Hg)were obviously elevated(P<0.05).Compared with DI group,the LVSP of DE group rats(119.11±5.11 mm Hg)is significantly elevated,however the LVEDP(13.64 ± 1.25 mm Hg)is decreased(P<0.05).The APPL1,P-AMPK,PPARα and NF-?B expression level of C group rats’ cardiac tissue were 0.75±0.03,0.94±0.02,1.89±0.03,0.35±0.05.Compared with C group,the APPL1,P-AMPK,PPARα expression level of D group and DI group rats’ cardiac tissue were both elevated,but the NF-?B expression level were depressed.Compared with D and DI group rats,the APPL1,P-AMPK,PPARα expression level of DE group rats’ cardiac tissue were 0.65± 0.02,0.78±0.04,1.72±0.05,both significantly increased,but inversely,the expression level of NF-?B is 0.58±0.09,obviously decreased(P<0.05).3.Cell research: Compared with the C group,the apoptosis rate of cardiomyocytes(34%~42%)was markedly increased in D group,the HMW-AND level(6.72±0.32 ng/ml)was evidently decreased.Compared with the D group,the apoptosis rate of cardiomyocytes(20~29%)was markedly decreased in the DE group.Compared with the DE group,the apoptosis rate of cardiomyocytes(18~24%)was decreased in the OE group(P<0.05).In the BL group,the HMW-AND level(9.30±.34ng/m)was evidently elevated(P<0.05)and the apoptosis rate of cardiomyocytes(43~52%)was increased,as compared with the D group.The tendency of APPL1,p-AMPK,PPARα and NF-κB expression were similar to aninal research results.ConclusionThe systolic and diastolic dysfunction was related to the decrease of serum high molecular weight adiponectin in T2 DM.Treatment with Exinatide can increase the expression level of adiponectin in blood and myocardial cells by autocrine,and activate the “APPL1-AMPK-PPARα axis”,then inhibit activation of NF-?B and cardiacmyocyte apoptosis,improve the diabetic heart function. |
