Mechanism Of Cardiac Aging Mediated By Advanced Glycation End Products Binding To MD2-TLR4

Objective: To investigate whether advanced glycation end products(AGEs)can mediate chronic inflammation,myocardial remodeling and chronic heart failure through myeloid differentiation 2(MD2)-toll like receptor 4(TLR4)pathway in the elderly.Method: In vivo,12 SD rats were divided into control group(3 months old)and old group(24 months old)with 6 rats in each group.The results of HE,Masson staining were compared between the two groups to observe the arrangement of myocardium and judge the degree of fibrosis.The echocardiography were performed to evaluate the changes of cardiac function.The ELISA method was employed to test serum AGEs-MD2 complex,interleukin-6(IL-6)and N terminal pro B type natriuretic peptide(NT-pro BNP)in rats.Western blot and RT-PCR were used to detect the expression of MD2,TLR4 and their downstream signals in myocardium.In vitro,H9C2 cells were divided into four groups: normal control group,AGEs group,normal + MD2 inhibitor group,AGEs + MD2 inhibitor group.The ELISA method was employed to test the absorbance of AGEs-MD2 complex of H9C2.Western blot and RT-PCR were used to determine the expression of myeloid differentiation factor 88(My D88)and inflammatory factors(IL-6、tumor necrosis factor-α(TNF-α)).In the population study,48 patients were enrolled.21 patients aged < 65 years old were included in the control group,and 27 patients aged≥65 years old were in the old group.The differences of AGEs-MD2 levels between two groups were compared.And the correlations between AGEs-MD2 level and age,IL-6,NT-pro BNP,E/A were evaluated.Result: In vivo,the absorbance of serum AGEs-MD2 complex at OD450 in the old group was higher than that in the control group(P < 0.01).The expression levels of IL-6and NT-pro BNP in serum were significantly higher than those in young group(P <0.01).The results of echocardiography showed that left ventricular end-diastolic dimension(LVDD)and left ventricular end-systolic dimension(LVSD)of the old group were higher than those of the control group,while values of E/A were lower.Compared with the control group,the myocardial cells in the old group were hypertrophic and disordered.There was much myocardial fibrosis in the old group.Compared with the control group,the m RNA levels of My D88,IL-6 in myocardium increased in the old group(P < 0.05),while the level of inhibitor of nuclear factor kappa-B alpha(Ik Bα)decreased.The protein expression levels of AGEs,TLR4 and MD2 were also higher in the old group(P < 0.05).In vitro,the absorbance of AGEs-MD2 complex at OD450 in the AGEs group was higher than other three groups(P < 0.05).At the protein level,the expression of My D88 in the AGEs group was higher than the other groups(P < 0.01).The m RNA levels of IL-6 and TNF-α also increased in the AGEs group(P < 0.05).In the population study,after adjusting for serum creatinine level,serum AGEs-MD2 level in the old group still remained higher than that in the young group,which was positively correlated with age,serum IL-6 level serum NT-pro BNP level and negatively correlated with value of E/A(P < 0.05).Conclusion: During aging,AGEs accumulate in the body,which mediate chronic inflammation and further cause myocardial fibrosis,myocardial remodeling,chronic heart failure through classic inflammatory pathway of MD2-TLR4-My D88.To a certain extent,MD2 inhibitor could block this effect.Cardiac function is correlated with the level of AGEs-MD2 in human plasma.