Effects And Mechanisms Of Tumor Necrosis Factor Receptor Type 1-associated Protein On Cardiac Remodeling Induced By Pressure Overload

Part I Loss of TRADD attenuates pressure overload-induced cardiac hypertrophy through regulating TAK1/P38 MAPK signalling in miceObjective We investigated the role of tumour necrosis factor receptor(TNFR)-associated death domain(TRADD)on pressure overload-induced cardiac hypertrophy and the underlying molecular mechanisms by using a TRADD deficiency mice model.Methods 6-8-week wild-type and TRADD knockout mice were performed to transverse aorta constriction(TAC)or sham operation(6-8 mice for each group).14 days after TAC,cardiac function was measured by echocardiography,as well as by pathological and molecular analyses of heart samples.The expressions of cardiac hypertrophic and fibrotic markers were detected by q PCR.Phosphorylated and total TAK1,Akt,and p38 MAPK levels were examined by Western blotting.Results The ratios of lung or heart/body weight,wall thickness/ chamber diameter of left ventricular and cross area of cardiomyocyte were significantly reduced in TRADD knockout(KO)mice than those of wild-type mice after TAC.Moreover,cardiac hypertrophic and fibrotic markers were downregulated in TRADD knockout mice than those of wild-type mice following TAC.Protein expression analysis showed phosphorylated TAK1,p38 MAPK and AKT were upregulated after TAC in both wild-type and TRADD KO mice,phosphorylation of TAK1 and p38 MAPK was reduced more remarkablely after TRADD deficiency,while phosphorylated AKT expression was similar between TRADD KO and wild-type mice following TAC.Conclusion Our data suggest that TRADD KO blunts pressure overload-induced cardiac hypertrophy through mediating TAK1/p38 MAPK but not AKT phosphorylation in mice.Part II Cardiac-specific Traf2 overexpression enhances cardiac hypertrophy through activating AKT/GSK3? signalingObjective Tumor necrosis factor superfamily ligands provoke a dilated cardiac phenotype signal through a common scaffolding protein termed tumor necrosis factor receptor-associated factor 2(Traf2);however,Traf2 signaling in the adult mammalian cardiac hypertrophy is not fully understood.Thisstudy was aimed to identify the effect of Traf2 on cardiac hypertrophy and the underlying mechanisms.Methods A significant up-regulation of Traf2 expression was observed in mice failing hearts.To further investigate the role of Traf2 in cardiac hypertrophy,we used cultured neonatal rat cardiomyocytes with gain and loss of Traf2 function and cardiac-specific Traf2-overexpressing transgenic(TG)mice.In cultured cardiomyocytes,Traf2 positively regulated angiotensin II(Ang II)-mediated hypertrophic growth,as detected by [3H]-Leucine incorporation,cardiac myocyte area,and hypertrophic marker protein levels.Cardiac hypertrophy in vivo was produced by constriction of transverse aortic(TAC)in TG mice and their wild-type controls.The extent of cardiac hypertrophy was evaluated by echocardiography as well as by pathological and molecular analyses of heart samples.Results Traf2 overexpression in the heart remarkably enhanced cardiac hypertrophy,left ventricular dysfunction in mice in response to TAC.Further analysis of the signaling pathway in vitro and in vivo suggested that these adverse effects of Traf2 were associated with the activation of AKT/glycogen synthase kinase 3?(GSK3?).Conclusion The present study demonstrates that Traf2 serves as a novel mediator that enhanced cardiac hypertrophy by activating AKT/GSK3? signaling.Part III Olmesartan ameliorates pressure overload-induced cardiac remodeling through inhibition of TAK1/p38 signaling in miceAims Many studies have demonstrated the potent effects of ARB administration on heart failure.However,the mechanism of the potent effects of ARB on cardiac remodeling is less well understood.We investigated the role of Olmesartan on the fibrosis and hypertrophy in mouse heart.Methods We employed TAC surgery,a mouse model of chronic cardiac failure.All the mice were separated into three groups: the sham group,TAC group and TAC plus Olmesartan group(given Olmesartan treatment after TAC).We analyzed left ventricle remodeling,and function by echocardiography or pathology.We further detected the level of marker genes involved in fibrosis and hypertrophy and in cultured neonatal rat cardiac fibroblasts and myocytes infected by constitutively active TAK1 and p38 MAPK.After TAC,all the mice developed hypertrophy,worse cardiac function and malignant remodeling in left ventricle.Results(1)Olmesartan attenuates pathological cardiac remodeling induced by pressure overload.We performed TAC surgery on 8-to 10-week-old mice.Fromour echocardiographic results,PWs of the mice are significantly higher in TAC and TAC + Olmesartan groups than that of sham mice.Masson's trichrome stain and HE staining also suggested the inhibitory effect of Olmesartan on heart remodeling induced by TAC.These results indicate that administration of Olmesartan improved left ventricular function by ameliorating cardiac fibrosis and hypertrophy.(2)Olmesartan abrogated TAK1/p38 MAPK Signaling activated by TAC.We examined activation of the mitogen-activated protein kinase(MAPK)pathway in the pressure overload model.Thephosphorylated levels of TAK1,p38,AKT,and ERK1/2were markedly increased by TAC in the hearts.In vitro cardiomyocyte studies further suggested that TAK1 and p38 phosphorylation levels were attenuated after the treatment of Olmesartan in response to Ang II.(3)Olmesartan inhibits Ang II-induced cardiac hypertrophy through TAK1/p38 in vitro.in vitro experiment showed that overexpression of active TAK1 and p38(Ad-?n TAK1 and Ad-ca MKK3b)by infection of cardiomyocytes promoted Ang II-induced hypertrophic responses such as the increment in ANP,BNP,?-MHC expression aswell as [3H]-Leucine incorporation.(4)Olmesartan inhibits collagen synthesis induced by TGF?1 through TAK1/p38 in vitro.Ad-?n TAK1 and Ad-ca MKK3 b enhanced TGF?1-induced [3H]-Proline incorporation,TGF?3 and collagen I/III m RNA expression.Conclusions Olmesartan suppresses p38 expression by negatively interfering with some cellular proteins.Therefore,TAK1 is a candidate target which may be crucial to heart fibrosis.The regulator of TAK1-related molecules including p38,which is involved in fibrogenesis,can be crucial for the target therapy of the heart remodeling or hear failure.