Age-related changes in fibre differentiation of rat lens epithelial explants exposed to fibroblast growth factor

Abstract

Epithelial cells explanted from neonatal rat lenses undergo changes characteristic of fibre differentiation when cultured with neural retina, neural retina-conditioned medium (RCM), or acidic and basic fibroblast growth factor (FGF). In neonates fibre differentiation is marked by cell elongation, the accummulation of α-crystallin, and the appearance of β- and γ-crystallins. To analyze the fibre differentiation response of lens epithelial cells in later life, we compared the fibre differentiation responses of lens epithelia from 3-, 10- and 21-day- 14-week-, and 6-month-old rats to basic fibroblast growth factor (bFGF). Explants of the central epithelium were used to maintain consistency between ages. Crystallin composition of explants was analyzed by immunofluorescence and ELISA methods. Only explants from 3-day-old rats demonstrated any ability to synthesize γ-crystallin in response to bFGF. Central lens epithelia explanted from rats up to 14 weeks old accumulated α- and β-crystallins when exposed to bFGF. The onset of crystallin accumulation, however, was increasingly delayed, and the amount of crystallin accumulated by the end of the culture period declined as the age of the donor rat increased. The diminished ability of lens epithelial explants from older rats to undergo fibre specific changes in response to bFGF is also demonstrated in the reduced degree of morphological changes characteristic of fibre differentiation. Cell elongation and multilayering in response to bFGF was observed in explants from 3-day-old rats but was substantially reduced in explants from from 14-week-old rats. Explants from 6-month-old rats failed to demonstrate any evidence of morphological change or crystallin accumulation in response to bFGF. Therefore as the rat ages cells from the central lens epithelium progressively lose the capacity to undergo events characteristic of fibre differentiation in response to bFGF.