IGFBP-4 Gene Overexpression in the Nitrofen-Induced Hypoplastic Lung

Abstract

The precise mechanism of pulmonary hypoplasia (HP) associated with congenital diaphragmatic hernia (CDH) remains unclear. Insulin-like growth factors (IGFs) play an essential role in fetal lung development through IGF receptors (IGFRs) by regulating cellular proliferation, differentiation and survival. It has been reported that the expression of genes involved in IGF-IGFR signaling is altered in the nitrofen-induced hypoplastic lung during the later stages of lung development. IGF-binding proteins (IGFBPs) control bioavailability, activity and disruption of IGFs through the high affinity IGFBP/IGF complexes. IGFBP-4 is a key inhibitor of IGF-IGFR signaling-mediated cell proliferation. It has been revealed that cell proliferation in fetal lung fibroblasts is inhibited by increased IGFBP-4 production. We hypothesized that IGFBP-4 gene expression is increased during the later stages of lung development in the nitrofen-induced CDH lung. Pregnant Sprague-Dawley rats were exposed to either olive oil or nitrofen on day 9 (D9) of gestation. Fetuses were harvested by cesarean section on D18 and D21. Fetal lungs were divided into 3 groups: control, nitrofen without CDH [CDH(-)] and nitrofen with CDH [CDH(+)] (n=24 at each time point). Relative mRNA levels of IGFBP-4 were determined using real-time RT-PCR. Immunohistochemistry was performed to evaluate the protein expression of IGFBP-4. The relative expression levels of IGFBP-4 mRNA were significantly increased in CDH(-) and CDH(+) groups on D18 and D21 compared to controls. Immunohistochemistry showed increased IGFBP-4 expression in mesenchymal compartments on D18 and D21 in hypoplastic lungs compared to controls. Overexpression of pulmonary IGFBP-4 during the later stages of lung development may contribute to pulmonary hypoplasia in the nitrofen-induced CDH model by inhibiting IGF-mediated cell proliferation.