purpose. Keratocytes give rise to fibroblasts and myofibroblasts in wounded cornea. It is well established that treatment of fibroblasts with transforming growth factor (TGF) β will induce myofibroblast differentiation. We investigated whether this differentiation could be reversed by the administration of fibroblast growth factor (FGF).

methods. Cultured corneal myofibroblasts were plated at 200 cells/mm 2, and cells were grown in DMEM/F12 containing (1) 10% FBS or (2) 10% FBS with FGF and heparin or (3) 1% FBS or (4) 1% FBS with TGF-β. As distinguished from the fibroblast phenotype, the myofibroblast phenotype was identified by the assembly of α-smooth muscle (SM) actin protein into the stress fiber cytoskeleton. To further characterize growth factor regulation of the two phenotypes, the phenotypic expression of TGF-β receptor types I and II, cadherins, and connexin 43 by immunocytochemistry, Western blot analysis, and immunoprecipitation and of α-SM actin mRNA in Northern blot analysis were evaluated.

results. Corneal myofibroblasts replated and grown in the presence of FGF-1 or FGF-2 (20 ng/ml) plus heparin (5 μg/ml) in 10% FBS medium had decreased expression of α-SM actin protein, TGF-β receptors, and cadherins. Thus, FGF–heparin decreased the myofibroblast phenotype and promoted the fibroblast phenotype. Administration of either 20 ng/ml FGF or 5 μg/ml heparin alone was not effective. Addition of TGF-β further enhanced the expression of α-SM actin mRNA and protein and cell surface expression of TGF-β receptors in myofibroblast cultures.

conclusions. FGF-1 or-2 and heparin promoted the fibroblast phenotype and reversed the myofibroblast phenotype. This finding supports the idea that corneal myofibroblasts and fibroblasts are alternative phenotypes rather than terminally differentiated cell types.