Effects Of Dexamethasone On Lung Morphogenesis And Wnt Signal Transduction Pathway In Lung Of Offspring

Objective:Antenatal Dexamethasone(DEX)therapy can induce pneum dysplasia.Fetal lung development is effected by many signal transduction pathways.Among them,Wnt pathway has been shown to play important roles in the development of lung by regulating cell differentiation, proliferation and polarity.To investigate the effects of DEX on lung morphogenesis and Wnt signal transduction,premature rat models were used to compare the effects of various dosages and courses of DEX therapy on antenatal rat fetal lung development.Methods:Twenty pregnant rats were given the medicin through five defferent ways,and the fetal rats were divided into five groups randomly. For the small dose and large dose single course DEX groups, intraperitoneal(i.p)0.5ml saline on the 16^th,17^thday and i.p with 0.4 mg/kg and 0.8 mg/kg DEX respectively on the 18^thday of gestation.For the small dose and large dose multiple courses DEX groups,i.p with 0.4 mg/kg and 0.8 mg/kg DEX respectively on the 16^th,17^th,18^thday of gestation.For the control group,each of the four rats was i.p with 0.5ml saline on the 16^th,17^thand 18^thday of gestation.On the 19^thday of gestation,cesarean section were performed and the histological structures of fetal rat lungs of each pregnant rat were observed with light microscope and electronmicroscopy.The RT-PCR,Western-Blot and immunohistochemistry methods were used to detect the mRNA and protein level of Wnts,glycogen synthasekinase 3β(GSK-3β)and β-catenin genes.Results:1.Under the light microscope,less alveolar numbers,larger alveolar spaces and thinner alveolar septums(P＜0.01)were showed in the DEX groups compared with the control group.2.Under electron microscopy,lamellar body and cellular organs such as bioblast in endochylema of the DEX groups were more common compared with the control group.Lamellar body in the DEX groups was more anachromasis and condensed compared with the control group.With the increased DEX usage of the doses and courses,the basement membrane showed from completing to discontinuation, from uniform to anisouniform.3.RT-PCR results:the mRNA level of Wnt7b andβ-catenin genes were significantly enhanced in study groups compared with those of the control group(P＜0.05)While the expressions of Wnt5a,GSK-3βwere downregulated in study groups compared with controls (P＜0.05).But there was no statistic difference in the expressions of Wnt2 between the DEX groups and control group.4.Western-blot results:the expressions of GSK-3βprotein in cytoplasm of the study groups reduced gradually(P＜0.05)whileβ-catenin's in cytoplasm reduced(P＜0.01)andβ-catenin's in the nucleus enhanced(P＜0.01).5.Immunohistochemistry results:β-catenin was expressed in mesenchyme and pulmonary alveolus in the control group.The expressions ofβ-catenin in control group were lower compared with the DEX groups(P＜0.05).GSK-3βwas also expressed in mesenchyme and pulmonary alveolus in the control group.The expressions ofβ-catenin in the control group were much higher compared with the DEX groups(P＜0.05).Conclusions:1.Antenatal DEX therapy can improve the fetal lung development.Even the small and single dosage of DEX may induce the fetal lung mature. Increasing the doses and courses of DEX not only improves the level of the fetal lung development,but also has negative effect on rat fetal lung morphogenesis.For example,reduction in alveolar numbers, alteration of alveolar space and septum.The basement membrane showed from completing to discontinuation,from uniform to anisouniform.These changes caused the cell differentiation, proliferation,and polarity,even the interactions between basement membrane and mesenchyme.2.Antenatal DEX therapy changed the expressions of the mRNA and the protein of Wnt7b,Wnt 5a,β-catenin and GSK-3βgenes in the 19^th day of rat embryos.3.Wnt pathway may involved in the effects of DEX therapy on rat fetal lung morphogenesis.