Upregulation of fibroblast growth factor receptor 2 and 3 in the late stages of fetal lung development in the nitrofen rat model

Abstract

Nitrofen model of congenital diaphragmatic hernia (CDH) has been widely used to investigate the pathogenesis of pulmonary hypoplasia (PH). Fibroblast growth factor (FGF) signaling pathway plays a fundamental role in fetal lung development. FGF7 and FGF10, which are critical for lung morphogenesis, have been reported to be downregulated in nitrofen-induced PH. FGF signaling is mediated by a family of four single transmembrane receptors, FGFR1-4. FGFR2 and FGFR3 have been shown to be expressed predominantly in the late stages of developing lungs. In addition, the upregulation of FGFR2 gene expression has been associated with severe defects in lung development and resulted in arrested alveologenesis similar to PH seen in the nitrofen model. Furthermore, FGFR3(-/-)FGFR4(-/-) double mutants showed thinner mesenchyme and larger air spaces. We designed this study to test the hypothesis that FGFR gene expression is upregulated in the late stages of lung development in the nitrofen CDH model. Pregnant rats were exposed to either olive oil or nitrofen on day 9 of gestation (D9). Cesarean section was performed and fetuses were harvested on D18 and D21. Fetal lungs were divided into three groups: control, nitrofen without CDH [CDH(-)], and nitrofen with CDH [CDH(+)] (n = 24 at each time-point). Pulmonary gene expression levels of FGFR1-4 were analyzed by real-time RT-PCR. Immunohistochemistry was also performed to evaluate protein expression/distribution at each time-point. The relative messenger RNA expression levels of pulmonary FGFR2 and FGFR3 on D21 were significantly increased in CDH(-) (6.38 ± 1.93 and 7.84 ± 2.86, respectively) and CDH(+) (7.09 ± 2.50 and 7.25 ± 3.43, respectively) compared to controls (P < 0.05 and P < 0.01, respectively), whereas no significant alteration was observed on D18. There were no differences in FGFR1 and FGFR4 expression at both time-points. Increased immunoreactivity of FGFR2 and FGFR3, mainly in the distal epithelium and mesenchyme, was observed in the nitrofen-induced hypoplastic lungs on D21 compared to controls. Upregulation of FGFR2 and FGFR3 pulmonary gene expression in the late stages of fetal lung development may disrupt FGFR-mediated alveologenesis resulting in PH in the CDH model.