Intestinal fibroblasts regulate intestinal epithelial cell proliferation via hepatocyte growth factor

Although the presence of subepithelial intestinal fibroblasts has been well recognized, the effects of fibroblasts on intestinal epithelial cell (IEC) growth are incompletely understood. In vitro studies were undertaken to evaluate the effects of fibroblasts on the proliferation of model IEC lines. IECs (Caco-2, T84, and IEC-6) were grown alone or in the presence of human intestinal (CCD-18), lung (CCD-37), or skin explant-derived fibroblasts. Cocultures were carried out directly on irradiated fibroblasts or by Transwell coculture technique with fibroblasts and epithelial cells separated by a porous filter. Cell proliferation was assessed by [3H]thymidine incorporation and cell counts. Hepatocyte growth factor (HGF) and c-met transcript expression in IECs and fibroblasts was examined by RT-PCR and Northern blotting; protein expression was evaluated by immunoblotting. Intestinal as well as lung and skin fibroblasts substantially stimulated proliferation of Caco-2, T84, and IEC-6 cells in both direct and Transwell cocultures. In addition, fibroblast-conditioned medium stimulated IEC proliferation, suggesting a paracrine mechanism. Anti-human HGF-neutralizing antibodies blocked the growth-promoting effects in both fibroblasts and fibroblast-conditioned medium. Recombinant human HGF dose dependently promoted IEC proliferation. HGF mRNA and protein expression was restricted to fibroblasts. High levels of c-met expression were found in Caco-2 and T84 cells; in contrast, expression in fibroblasts was weak. In summary, fibroblasts stimulate IEC proliferation through a paracrine mechanism mediated predominantly by HGF.