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

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.

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.

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.

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.