Lung fibroblasts improve differentiation of rat type II cells in primary culture

Epithelial-mesenchymal interactions mediate prenatal lung morphogenesis and differentiation, yet little is known about their effects in the adult. In this study we have examined the influence of cocultured lung fibroblasts on rat alveolar type II cell differentiation in primary culture. Type II cell s that were cocultured with lung fibroblasts showed significant increases i n messenger RNA (mRNA) levels of surfactant protein (SP)-A, SP-B, SP-C, and SP-D. Metabolic labeling and immunohistochemistry demonstrated that these mRNAs were translated and processed. Addition of 10(-7) M dexamethasone (DE X) to cocultures antagonized the effects of the fibroblasts on SP-A and SP- C, but significantly augmented the effects on SP-B; expression of SP-D was unaffected. Coculture of type II cells with lung fibroblasts also increased acetate incorporation into phospholipids 10-fold, which was antagonized by DEX. Keratinocyte growth factor (KGF) mimicked the effects of lung fibrobl asts on SP gene expression, but KGF neutralizing antibodies only partially reduced the effects of lung fibroblasts. KGF increased acetate incorporatio n into surfactant phospholipids, and the addition of DEX augmented this res ponse. Together, our observations suggest that epithelial-mesenchymal inter actions affect type II cell differentiation in the adult lung, and that the se effects are partially mediated by KGF.