Growth factors influence contractility and alpha-smooth muscle actin expression in bovine lens epithelial cells

To determine whether basic fibroblast growth factor (bFGF) and transforming growth factor-beta 2 (TGF-beta 2) influence the contractile activity and the expression of alpha-smooth muscle actin (alpha-SMA) in bovine lens epithelial cells (LECs). To examine whether modulation of contractile activity by these growth factors depends on changes of alpha-SMA expression.

Bovine LECs were cultured in collagen gel in MED 5 medium (F-12 nutrient mixture supplemented with 5% fetal bovine serum) with or without bFGF (1 to 100 ng/ml) or TGF-beta 2 (0.01 to 10 ng/ml). To evaluate collagen gel contraction, the longest and shortest diameters of the gels were measured daily for 7 days, and the area was determined. Detection of alpha-SMA in the gels was performed immunohistochemically using a mouse monoclonal antibody against alpha-SMA. The percentage of alpha-SMA-positive cells to the total number of cells was determined.

Control gels cultured with MED 5 medium alone contracted to 15.8% +/- 3.4% of their original area after 7 days. TGF-beta 2 significantly increased this contraction in a dose-dependent manner, whereas bFGF significantly decreased it. Approximately 30% of cells in the control gels were alpha-SMA positive. TGF-beta 2 significantly increased the alpha-SMA positivity dose dependently, whereas bFGF significantly decreased it. The percent positivity for alpha-SMA and the gel area showed a significant negative correlation.

TGF-beta 2 increased collagen gel contraction and alpha-SMA expression in bovine LECs, whereas bFGF decreased these parameters. Because collagen gel contraction was correlated with alpha-SMA expression, the modulation of LEC contractile activity by growth factors may be related to an effect on alpha-SMA.