The Effect And Mechanism Of Wnt/β-catenin Signaling Pathway In Myocardial Adaptation To Chronic Hypoxia

ObjectiveResearchs showed that exposured to moderate oxygen lack triggers defence mechanisms to adapt to reduced oxygen supply and cardioprotective programs,however,the mechanisms by which hearts adapt to chronic hypoxia remain unknown.To examine the role and mechanism of Wnt/β-catenin signaling pathway in adaptation to chronic hypoxia we identified and characterized β-catenin,bcl-2,survivin in H9c2 cells exposed to 5% O2 at different time points,and detected the expression level of β-catenin in myocardial tissue from children with cyanotic congenital heart disease.Method(1)Embryonic rat-heart-derived H9c2 cells were exposed to 5% O2 for 72 h,expression of β-catenin,bcl-2 and survivin mRNA or protein at different time points were measured by using Western blotting and Real-time PCR,the cells were cultured under normal conditions as control group.(2)Samples from the auricle of right atrium were collected from children with acyanotic(n=23)and cyanotic(n=15)congenital heart disease before the cardiopulmonary bypass was established during heart surgery.The level and site of the protein expression of β-catenin were examined by Western blotting and immunohistochemistry.Then analyze the relationship between age and the level of β-catenin.Results(1)Time course experiments showed that after 12 h,24 h,and 36 h of hypoxia,β-catenin mRNA significantly increased compared with control group(P<0.05、P<0.01、P<0.05),but significantly declined at 48 h and 72 h(P<0.05).(2)Western blotting showed that compared with control group,expression of β-catenin protein was significantly increased at 6h,12 h,24 h and 36 h(P<0.001,P<0.05,P<0.01,P<0.001)and got peak at 36 h.Level of β-catenin significantly reduced at 48 h and 72 h compared with 36 h(P<0.001),and reached the same level as control group.(3)Expression of bcl-2 mRNA was significantly increased after 6h,12 h compared with control group(P<0.001),gradually declined thereafter.Bcl-2 mRNA level was significantly reduced at 36 h.Expression of bcl-2 protein was significantly increased at 6 h,12 h,24 h(P<0.001,P<0.001,P<0.001).(4)Level of survivin mRNA was significantly increased at 24 h compared with control group(P<0.001).Expression level of survivin protein raised significantly at 12 h,24 h and got peak at 24 h(P<0.001,P<0.001).(5)Level of β-catenin protein in cyanotic group was lower than that in acyanotic group(P<0.001).Expression level of β-catenin decrease with the increase of their age both in two groups(P<0.001,P<0.001),and β-catenin in cyanotic group was lower compared with acyanotic group at same age(P<0.05,P<0.001,P<0.01).Conclusions(1)Activation of Wnt/β-catenin signaling pathway may contribute to H9c2 cells adaptation to chronic hypoxia partly through upregulate anti-apoptosis genes expression to promote cell survival.(2)Wnt/β-catenin signaling pathway is unlikely to be an important mechanism for heart adaptation to chronic hypoxia in cyanotic congenital heart disease.