Keratinocyte Growth Factor and Embryonic Rat Lung Morphogenesis

We examined possible roles of keratinocyte growth factor (KGF) and hepatocyte growth factor (HGF) in lung morphogenesis. By polymerase chain reaction, transcripts for both KGF and its receptor were detected early (rat gestational days 16 and 14, respectively) and their abundance increased during lung morphogenesis. To evaluate possible role of KGF in lung morphogenesis, day 14 lung explants were cultured in Dulbecco's modified Eagle medium + 10% fetal calf serum for 1 to 4 days in the presence (5-50 ng/ml) or absence of KGF (control). KGF (at 25 and 50 ng/ml) induced a marked reduction in the number of terminal branches and distension of the distal epithelium into cyst-like structures. These effects of exogenous KGF were progressively diminished by increasing concentrations of anti-KGF (2-16 μg/ml). Electron microscopic examination revealed that the epithelial cells of the cystic structures contained lamellar bodies, and were therefore type II cells and/or their progenitors. Northern blot analysis showed higher expression of surfactant protein C (SP-C) mRNA (a marker for alveolar epithelial type II cells) in KGF-treated fetal lungs. In situ hybridization of the KGF-treated lungs revealed that the SP-C mRNA-expressing cells were arranged distally in the form of linear arrays, a pattern distinctly different from that in control lungs. Acidic fibroblast growth factor, which also binds KGF receptors, in the presence of heparin mimicked the effect of KGF on branching. Transforming growth factor-β₁ (TGF-β1) inhibited branching of fetal lungs in culture, and this effect dominated over that induced by KGF. Blocking of endogenous HGF with antibodies or addition of HGF to cultures of fetal lung explants had no significant effect on branching or growth. In conclusion, KGF markedly influences branching, and epithelial growth, differentiation, and patterning during lung morphogenesis.