TRANSFORMING GROWTH-FACTOR-BETA-1 PROMOTES CONTRACTION OF COLLAGEN GEL BY BOVINE CORNEAL FIBROBLASTS THROUGH DIFFERENTIATION OF MYOFIBROBLASTS

PURPOSE. TO determine whether the ability of transforming growth facto r-beta (TGF-beta) to influence the contractile activity of corneal fib roblasts depends on their differentiation into myofibroblasts. METHODS . Bovine corneal fibroblasts were cultured on collagen gel in MED 5 me dium (F-12 nutrient mixture supplemented with 5% fetal bovine serum) w ith or without TGF-beta 1 (0.01-10 ng/ml). To evaluate the corneal fib roblast-derived contraction of collagen gel, the thickness of the gel was measured daily for 6 days. The total number of cells on the gel wa s counted with a Coulter counter. The detection of alpha-smooth muscle actin (alpha-SMA), a marker for myofibroblasts, on these cells was pe rformed immunocytochemically by using a mouse monoclonal antibody agai nst alpha-SMA. The number of myofibroblasts (alpha-SMA-positive cells) was determined. RESULTS. The control gels containing bovine corneal f ibroblasts that were cultured with the MED 5 medium alone significantl y contracted to 72.3 +/- 1.2% of their original thickness after 6 days . TGF-beta 1 increased the contraction of collagen gel mediated by bov ine corneal fibroblasts in a dose-dependent manner. Approximately 0.2% of the cells on the control gels cultured with MED 5 medium alone wer e alpha-SMA positive. TGF-beta 1 significantly increased the expressio n of alpha-SMA in a dose-dependent manner. There was no significant co rrelation between the thickness of the collagen gel and the total numb er of cells. However, there was a significant negative correlation bet ween the thickness of collagen gel and the number of myofibroblasts. C ONCLUSIONS. TGF-beta 1 increased the contractile activity of bovine co rneal fibroblasts and their ability to differentiate into myofibroblas ts. Because contractile activity was correlated with differentiation, the influence of TGF-beta 1 on corneal fibroblast-induced collagen gel contraction may depend on the promotion of myofibroblast differentiat ion.