The effect of transforming growth factor-beta on fibroblast cell proliferation in intact connective tissue in vitro

Transforming growth factor-beta (TGF-beta) has varying effects on cell proliferation, stimulating some cell types while inhibiting others. Its effect on proliferation has mostly been assessed in cell cultures without consideration for the influence of a tissue matrix. In the present investigation we studied the effect of TGF-beta on fibroblast cell proliferation in intact connective tissue in vitro using the membranous part of the rat mesentery. Mesenteric membranes were spread over the hole of a cytocentrifuge paper, incubated in vitro, and exposed to various concentrations of TGF-beta with or without serum added. At designated times after incubation, the specimens were fixed, spread out on microscope slides, and stained by the Feulgen reaction. Cell proliferation was estimated by counting mitoses in fibroblasts and mesothelial cells and by DNA cytometry of fibroblast nuclei using computer assisted image analyses. Higher concentrations of TGF-beta significantly increased proliferation estimated as either the percentage of cells in the S+G2 phase of the cell cycle or the mitotic index when serum was added. In medium without serum, TGF-beta did slightly, but not significantly, increase proliferation. The results show that TGF-beta stimulates connective tissue cell proliferation dose-dependently in intact connective tissue in vitro and that addition of serum to the medium is a prerequisite for optimal stimulation.