Effect of extracellular matrix on proliferation and differentiation of porcine lens epithelial cells

Background: Proliferation and differentiation of lens epithelial cells (LECs) are important mechanisms of secondary cataract formation. After extracapsular cataract extraction the extracellular matrix (ECM) around the remaining LECs is altered compared with the intact lens. This study investigated the effects of different ECMs on cell proliferation and alpha-smooth muscle actin (alpha-SMA) expression, a marker for myofibroblasts, in cultured porcine LECs. Methos: Porcine LECs were cultured for 3 days (cell proliferation assay) or 4 days (alpha-SMA expression) on wells and glass cover slips, respectively, coated with laminin, fibronectin, type I collagen or type IV collagen. LECs cultured on uncoated wells or cover slips served as control. Proliferative response was measured by [H-3]-thymidine incorporation into DNA. alpha-SMA was detected immunocytochemically with a mouse monoclonal antibody, and the relative numbers of alpha-SMA-positive cells were calculated. Statistical analysis was performed using Student's unpaired t-test. Results: Cell proliferation was significantly increased by coating with fibronectin (10,320.5 +/- 6,073 counts per minute; p < 0.0001) (mean +/- SD), type I collagen (12,507.3 +/- 3,914.2 CPM; p < 0.0001) and type IV collagen (9,591.4 +/- 4,088 CPM; p < 0.0001) compared with control (1,876.5 +/- 998 CPM), whereas coating with laminin had no effect (1,760.8 +/- 812.6 CPM; p=0.7271). The ratio of alpha-SMA-positive LECs cultured on uncoated cover slips for a period of 4 days was 12.2 +/- 3.51%. This ratio was significantly increased by coating with fibronectin (24.3 +/- 4.56%; p=0.0001) and type I collagen (21.2 +/- 8.48%; p=0.0142). Coating with laminin (9.8 +/- 3.67%; p=0.1682) and type IV collagen (9.0 +/- 7.09 %; p=0.2491) slightly decreased alpha-SMA expression, but this effect was not statistically significant. Conclusions: Fibronectin and type I collagen stimulated both cell proliferation and alpha-SMA expression in cultured porcine LECs. Because fibronectin and type I collagen are not normally present in the adult lens, their possible introduction into the lens capsule after cataract surgery may play a critical role in the development of posterior capsule opacification.