Collagen Synthesis by Normal and Fibrotic Human Lung Fibroblasts and the Effect of Transforming Growth Factor-β

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Abstract
Collagen accumulation is a major feature of pulmonary fibrosis and other fibrotic lesions. We have studied the synthesis of collagens in fibroblasts cultured from normal and fibrotic human lung specimens and evaluated how it is affected by transforming growth factor-.beta. (TGF-.beta.). Fibroblasts were obtained from normal and fibrotic adult human lungs (n = 11; normal = 6, idiopathic pulmonary fibrosis = 5). They were exposed to TGF-.beta. and pulse-labeled with [3H]proline and [3H]glycine. Collagen production was measured as bacterial collagenase-susceptible radioactivity, and collagen mRNA levels were determined by a solution hybridization assay using labeled procollagen .alpha.1[1] cDNA clone HF677 as probe. Synthesis of collagen types I, III, and V were assessed after separating them by DEAE-cellulose chromatography and SDS-polyacrylamide gel electrophoresis. The results showed that both normal and fibrotic lung fibroblasts synthesized similar amounts of collagen. Type I was the major collagen species synthesized by both normal and fibrotic cell types, and the relative proportion of type I, III, and V collagens was similar in both cell types. TGF-.beta. caused a two to fourfold increase in stimulation of collagen production and collagen mRNA levels, and no differences were detected in the response of normal and fibrotic lung fibroblasts. All collagen types were stimulated by the TGF-.beta.. TGF-.beta. did not increase fibroblast proliferation and the majority of normal and fibrotic lung cells exposed to TGF-.beta. remained in G1 phase of the cell cycle. We conclude that fibroblasts of normal and fibrotic human lungs synthesize similar amounts of collagens. TGF-.beta. stimulates collagen production to the same extent in both cell strains and, in both of these fibroblast types, changes in collagen production appear to be mediated through collagen mRNA levels.