Alpha-smooth muscle actin expression in cultured lens epithelial cells.

PURPOSE Lens epithelial cells transdifferentiate to myofibroblasts during the formation of anterior subcapsular cataracts and secondary cataracts. One of the defining characteristics of myofibroblasts is the expression of alpha-smooth muscle actin (alpha-SMA). This study investigated some of the factors that influence alpha-SMA expression in lens epithelial cells. METHODS Bovine, rabbit, and human lens epithelial explants or cells were cultured with or without serum. Immunohistochemistry and immunoblotting were used to detect and quantitate alpha-SMA expression. RESULTS Cells from all species studied expressed alpha-SMA in primary explant culture with or without serum. Immunostaining for alpha-SMA first appeared in a diffuse granular pattern, then accumulated at the cell cortex, and eventually was detected along stress fibers. When lens epithelial cells migrated onto cell-free regions of the capsule or were transferred to a plastic culture dish, alpha-SMA expression increased significantly. Expression of alpha-SMA positively correlated with cell size and cell migration. CONCLUSIONS Expression of alpha-SMA is a common feature of cultured mammalian lens epithelial cells. Because alpha-SMA expression occurred without the addition of exogenous factors, the fibrosis seen in anterior subcapsular cataracts or secondary cataracts may reflect the intrinsic properties of lens epithelial cells. Interaction between lens epithelial cells and their substratum appears to be an important regulator of myofibroblast formation. Understanding the factors that regulate alpha-SMA expression in lens epithelial cells could lead to the development of methods for preventing secondary cataracts and anterior subcapsular cataracts.