Transdifferentiation of Cultured Bovine Lens Epithelial Cells into Myofibroblast-like Cells by Serum Modulation

ABSTRACT

An after-cataract is caused by the proliferation of residual cells over the equator of the lens. These cells subsequently migrate to the posterior lens capsule, where they undergo aberrant differentiation into fiber-like cells or transdifferentiation into fibroblast-like cells. To study the precise molecular mechanisms of transdifferentiation, an attempt was made to establish an in vitro system, in which the lens epithelial cells (LECs) of the pre-equatorial zone could be transdifferentiated into fibroblast-like cells. The required conditions for culturing the LECs were identified as consisting of four phases; intact bovine explants, explant-cultured, serum-modulated and additionally modulated LECs. The LECs of each phase were compared by examining changes in the expression of the epithelial-mesenchymal transition (EMT) -related genes and changes in cellular morphology and adhesion. The explants that were cultured in a medium containing 10% fetal bovine serum (FBS) for 2 weeks, showed changes in the expression of the EMT-related genes, although the other explant-cultured cells maintained an epithelial morphology. To introduce a transition into mesenchymal cells, the explant cultures were subcultured in a medium containing 20% FBS for six passages. These cells displayed an elongated morphology and were able to grow and migrate in a similar way to fibroblast cells. The expression of the EMT-related genes, such as, extracellular matrix proteins and integrins, was altered. This was similar to the alteration of the 3-dimensional collagen gels model previously reported. During a further process of EMT by additional serum modulation, the inhibitory effect of disintegrin on cell adhesion was gradually decreased, integrin expression was differentially regulated and alpha-smooth muscle actin was post-translationally modified from the point of passage number six. Overall, it can be concluded that terminal transdifferentiation accompanies changes in the cytoskeletal proteins and cell surface molecules. These are modulated in systematic patterns of post-transcriptional and post-translational regulation and patterns of gene regulation, by the synergic effects of several transforming factors contained in serum. Therefore, posterior capsular opacification may also be accompanied by this molecular mechanism.