Differential effects of aqueous and vitreous on fiber differentiation and extracellular matrix accumulation in lens epithelial explants.

PURPOSE Results from this and other laboratories strongly suggest that differences in the properties of the ocular media that bathe cells in the anterior and posterior regions of the lens contribute to its normal growth patterns and polarity. The aim of this study was to compare the effects of aqueous and vitreous on the morphology of lens epithelial explants, with particular attention to changes associated with fiber differentiation. METHODS Light and electron microscopy were used to assess rat lens epithelial explants cultured with bovine aqueous or vitreous. Immunohistochemistry was used to detect fiber-specific crystallins and extracellular matrix components, and synthesis of extracellular matrix was investigated by autoradiography. RESULTS Vitreous, but not aqueous, induced morphologic changes characteristic of fiber differentiation, which included cell elongation, organelle loss, and the appearance of ball and socket junctions, as well as the accumulation of beta-crystallin. In addition, vitreous stimulated the synthesis and organization of a distinct basement membrane on explants that resembled the lens capsule, both structurally (regular layers of basal laminae) and immunologically (reactive for laminin and heparan sulphate proteoglycan). CONCLUSIONS Only one of the ocular media, the posteriorly located vitreous, induced lens epithelial explants to undergo morphologic events characteristic of fiber differentiation. This provides further support for the hypothesis that anteroposterior patterns of cellular responses in the lens are caused by differences in the ocular media. The observation that vitreous also stimulated the synthesis and assembly of capsule-like extracellular matrix suggests that vitreous contains factors that may influence lens capsule formation in situ.