Effect of UV-A light on the chaperone-like properties of young and old lens alpha-crystallin.

Purpose: To study the damaging effect of UV-A irradiation on the chaperone-like properties of alpha-crystallin and the subsequent recovery process of young and old bovine lenses.

Methods: Young and old bovine lenses were kept in organ culture. After 24 hours of incubation they were irradiated with UV-A at 365 nm, and optical quality measurements were performed during the experiments (192 hours). alpha-Crystallin and alpha1-, alphaA2-, alphaB1-, and alphaB2-crystallin subunits were analyzed, separated by gel filtration and cation exchange chromatography, respectively, after different culture times. Protein patterns were obtained after two-dimensional (2-D) gel electrophoresis. Chaperone-like activity was determined on the basis of insulin B-chain and betaL-crystallin aggregation assays. Aggregation of alpha-crystallin was analyzed, tryptophan fluorescence measurements were performed, and alpha-crystallin mRNA levels were determined.

Results: The water-soluble alpha-crystallin obtained from old lenses compared with young lenses after UV irradiation had decreased chaperone activity, a higher molecular weight, and increased loss of tryptophan fluorescence. Moreover, alpha-crystallin mRNA virtually disappeared, whereas extra spots on the 2-D protein pattern appeared, possibly because of deamidation.

Conclusions: alpha-Crystallin obtained from old lenses is more affected by irradiation than alpha-crystallin derived from young lenses. Moreover, it appeared that alphaB-crystallin from UV-treated old lenses compared with control lenses was less susceptible to UV-A than alphaA-crystallin. It may well be that alphaB-crystallin protects alphaA-crystallin in vivo.