Impaired FGF10 Signaling and Epithelial Development in Experimental Lung Hypoplasia With Esophageal Atresia

The interactions between fibroblast growth factors (FGF) and their receptors have important roles in mediating mesenchymal-epithelial cell interactions during embryogenesis. In particular, Fgf10 is predicted to function as a regulator of brain, lung and limb development on the basis of its spatiotemporal expression pattern in the developing embryo. To define the role of Fgf10, we generated Fgf10-deficient mice. Fgf10-/- mice died at birth due to the lack of lung development. Trachea was formed, but subsequent pulmonary branching morphogenesis was disrupted. In addition, mutant mice had complete truncation of the fore- and hindlimbs. In Fgf10-/- embryos, limb bud formation was initiated but outgrowth of the limb buds did not occur; however, formation of the clavicles was not affected. Analysis of the expression of marker genes in the mutant limb buds indicated that the apical ectodermal ridge (AER) and the zone of polarizing activity (ZPA) did not form. Thus, we show here that Fgf10 serves as an essential regulator of lung and limb formation.

Chronic obstructive pulmonary disease (COPD) is characterized by chronic airway inflammation that is greater in patients with advanced disease. We asked whether there is a link between the severity of disease and the reduction in histone deacetylase (HDAC) activity in the peripheral lung tissue of patients with COPD of varying severity. HDAC is a key molecule in the repression of production of proinflammatory cytokines in alveolar macrophages. HDAC activity and histone acetyltransferase (HAT) activity were determined in nuclear extracts of specimens of surgically resected lung tissue from nonsmokers without COPD, patients with COPD of varying severity, and patients with pneumonia or cystic fibrosis. Alveolar macrophages from nonsmokers, smokers, and patients with COPD and bronchial-biopsy specimens from nonsmokers, healthy smokers, patients with COPD, and those with mild asthma were also examined. Total RNA extracted from lung tissue and macrophages was used for quantitative reverse-transcriptase-polymerase-chain-reaction assay of HDAC1 through HDAC8 and interleukin-8. Expression of HDAC2 protein was quantified with the use of Western blotting. Histone-4 acetylation at the interleukin-8 promoter was evaluated with the use of a chromatin immunoprecipitation assay. Specimens of lung tissue obtained from patients with increasing clinical stages of COPD had graded reductions in HDAC activity and increases in interleukin-8 messenger RNA (mRNA) and histone-4 acetylation at the interleukin-8 promoter. The mRNA expression of HDAC2, HDAC5, and HDAC8 and expression of the HDAC2 protein were also lower in patients with increasing severity of disease. HDAC activity was decreased in patients with COPD, as compared with normal subjects, in both the macrophages and biopsy specimens, with no changes in HAT activity, whereas HAT activity was increased in biopsy specimens obtained from patients with asthma. Neither HAT activity nor HDAC activity was changed in lung tissue from patients with cystic fibrosis or pneumonia. Patients with COPD have a progressive reduction in total HDAC activity that reflects the severity of the disease. Copyright 2005 Massachusetts Medical Society.

During mouse lung morphogenesis, the distal mesenchyme regulates the growth and branching of adjacent endoderm. We report here that fibroblast growth factor 10 (Fgf10) is expressed dynamically in the mesenchyme adjacent to the distal buds from the earliest stages of lung development. The temporal and spatial pattern of gene expression suggests that Fgf10 plays a role in directional outgrowth and possibly induction of epithelial buds, and that positive and negative regulators of Fgf10 are produced by the endoderm. In transgenic lungs overexpressing Shh in the endoderm, Fgf10 transcription is reduced, suggesting that high levels of SHH downregulate Fgf10. Addition of FGF10 to embryonic day 11.5 lung tissue (endoderm plus mesenchyme) in Matrigel or collagen gel culture elicits a cyst-like expansion of the endoderm after 24 hours. In Matrigel, but not collagen, this is followed by extensive budding after 48-60 hours. This response involves an increase in the rate of endodermal cell proliferation. The activity of FGF1, FGF7 and FGF10 was also tested directly on isolated endoderm in Matrigel culture. Under these conditions, FGF1 elicits immediate endodermal budding, while FGF7 and FGF10 initially induce expansion of the endoderm. However, within 24 hours, samples treated with FGF10 give rise to multiple buds, while FGF7-treated endoderm never progresses to bud formation, at all concentrations of factor tested. Although exogenous FGF1, FGF7 and FGF10 have overlapping activities in vitro, their in vivo expression patterns are quite distinct in relation to early branching events. We conclude that, during early lung development, localized sources of FGF10 in the mesoderm regulate endoderm proliferation and bud outgrowth.