Down-regulation of Wnt signal pathway in nitrofen-induced hypoplastic lung

PurposeThe pathogenesis of pulmonary hypoplasia associated with congenital diaphragmatic hernia is poorly understood. Recently, it has been reported that Wnt signaling pathway plays a critical role in branching lung morphogenesis. Mice lacking Wnt7b gene die soon after birth because of respiratory failure and display severe lung hypoplasia. Wnt2 gene is expressed in the distal airway during development. To test the hypothesis that Wnt-mediated signaling is altered in nitrofen-induced hypoplastic lungs, we examined the expression of Wnt genes and Wnt target gene, BMP4 in normal and nitrofen-treated lungs.Materials and MethodsFetal rat lungs of normal (n = 24) and nitrofen-treated (n = 24) dams were harvested on embryonic day (E)15, E17, E19, and E21. The expression of GATA6, the Wnt genes (Wnt7b, Wnt2), and BMP4 was analyzed in each lung by real-time reverse transcription polymerase chain reaction.ResultsThe gene expression of Wnt7b, Wnt2, and BMP4 on E15 was significantly reduced (P < .05) in lungs from nitrofen-treated animals compared with normal lungs. The expression level of GATA6, which has been reported to transactivate Wnt7b expression, was also significantly reduced (P < .05) in lungs from the nitrofen group.ConclusionOur results provide evidence for the first time that the Wnt signaling pathway is down-regulated in nitrofen-induced hypoplastic lungs in the early stages of lung development. Decreased expression of GATA6 may account for the down-regulation of Wnt signal pathway. These data suggest that the down-regulation of Wnt signaling pathway may disrupt branching lung morphogenesis, resulting in pulmonary hypoplasia in the nitrofen rat model of congenital diaphragmatic hernia.