Decreased chaperone activity of α-crystallin in selenite cataract may result from selenite-induced aggregation

Abstract

Purpose. To investigate the role of chaperone activity of α-crystallin in selenite-induced cataract formation. Methods. Selenite cataract was induced in Sprague-Dawley rats by five subcutaneous injections of sodium selenite over a 20-day period starting at 8-10 days postpartum. α-Crystallin was separated from the rat lenses by size-exclusion chromatography. Bovine αL-crystallin and βL-crystallin were isolated for studies in vitro, and for the chaperone assays. The protective effects of both αH-and αL-crystallin were measured spectrophotometrically in four different assay procedures including the thermally induced aggregation of catalase and βL-crystallin, and the fructation-and heat-induced inactivation of catalase. The bovine αL-crystallin was incubated with different concentrations of sodium selenite for 72h and then its chaperone activity against heat-induced βL-crystallin aggregation was assayed. The aggregation of selenite-treated αL-crystallin was analysed by molecular sieve high-performance liquid chromatography (HPLC). Results. The protection of αH-crystallin was less than that of αL-crystallin in both normal and cataractous lenses. The chaperone activities of both αH-and αL-crystallin in selenite cataract were decreased compared with normal lenses. The protection provided by both αH-crystallin and αL-crystallin against the thermal aggregation of catalase was much greater than their protection against thermally and chemically induced inactivation. HPLC analysis demonstrated aggregation of α-crystallin by sodium selenite after 24h incubation in a dose-dependent fashion. Conclusion. The chaperone activity of α-crystallin presented parallel patterns of activity with different methods, further supporting the view that the different assays measure essentially the same property. The decreased chaperone activity of α-crystallin in selenite cataract may result from selenite-induced aggregation.