Indirect mitogenic effect of transforming growth factor-beta on cell proliferation of subconjunctival fibroblasts

To understand the mechanism of fibrosis after filtering surgery for glaucoma, the effect of transforming growth factor-beta (TGF-beta) was studied in subconjunctival fibroblasts (SCFs). TGF-beta, universal inhibitor of cell proliferation, stimulates the cell proliferation of fibroblasts. SCFs were evaluated for their production of TGF-beta and fibroblast growth factor 2 (FGF-2) to determine whether TGF-beta may be an indirect mitogen acting through the induction of an endogenous growth factor, or factors, that then acts as the direct mitogen in an autocrine manner.

Cell proliferation was determined either by counting cell numbers or by analyzing the incorporation of [3H]thymidine into DNA. The synthesis of TGF-beta and FGF-2 was analyzed by immunoprecipitation and immunoblotting.

TGF-beta 1, TGF-beta 2, and TGF-beta 3 stimulated the cell proliferation of SCFs in a dose-dependent manner. The media conditioned by SCFs, which were subsequently activated by acid, stimulated cell proliferation of corneal stromal fibroblasts. When the acid-activated media conditioned by SCFs were immunoprecipitated, respectively, either with anti-TGF-beta 1 and TGF-beta 2 antibodies or with anti-TGF-beta 3 antibody, TGF-beta s, with an apparent molecular size of 25 kDa, were detected, whereas SCFs produced an 80-kDa latent form of TGF-beta 1. Interestingly, SCFs produced and secreted an 18-kDa extracellular isoform of FGF-2, the synthesis of which is further stimulated by TGF-beta 1 and TGF-beta 3, respectively, whereas the neutralizing antibody to FGF-2 and the FGF-2-specific antisense oligonucleotide primers inhibited the stimulatory activities of TGF-beta 1 in SCFs.

These findings indicate that SCFs produce TGF-beta and FGF-2 and that FGF-2 seems to be the direct stimulator of TGF-beta-mediated cell proliferation in SCFs.