Fibroblast growth factor-2 and receptor-1alpha(IIIc) regulate postnatal rat lung cell apoptosis.

RATIONALE Fibroblast growth factor receptor-1alpha(IIIc) [FGF-R1alpha(IIIc)] regulates recovery of neonatal rat lung growth, after 95% oxygen-mediated growth arrest. Its role in normal postnatal alveologenesis is unknown. OBJECTIVE To determine if FGF-R1alpha(IIIc) regulates normal postnatal alveologenesis. METHODS Truncated soluble FGF-R1alpha(IIIc) or neutralizing antibodies to FGF-1 or FGF-2 were injected intraperitoneally into 3-d-old rats. The pups were killed at Day 7 for studies of alveolar development. MEASUREMENTS AND MAIN RESULTS Injected, truncated soluble FGF-R1alpha(IIIc) inhibited phosphorylation of the endogenous FGF-R1, and downstream pathway, and paradoxically increased lung DNA content and tissue fraction while inhibiting lung cell DNA synthesis. The increase in tissue thickness was due to reduced apoptosis, as indicated by reductions in cleaved effector caspases 3 and 7. Inhibition of the intrinsic apoptosis pathway was suggested by decreases in the proapoptotic protein Bax and mitochondrial cytochrome c release, and an increase in the antiapoptotic protein Bcl-x(L). Injected antibodies to FGF-1 and FGF-2 had no effect on DNA synthesis, but both increased Bcl-x(L) content and decreased cytochrome c release and cleaved caspase-7 protein expression. However, only injection of the antibody to FGF-2 replicated the increased tissue fraction and inhibited apoptosis observed with the injection of truncated soluble FGF-R1alpha(IIIc). CONCLUSIONS Inhibition of ligand binding, most likely of FGF-2, to the FGF-R1alpha(IIIc) inhibits normal postnatal lung cell apoptosis.