Protein alterations in age-related cataract associated with a persistent hyaloid vascular system in senescence-accelerated mouse (SAM).

The occurrence of age-related cataract associated with a persistent hyaloid vascular system is the most prominent feature in SAMP9, an inbred strain of Senescence-accelerated Mouse. To examine the cataractogenesis, we analysed protein changes in the process of cataract formation in the lens. The cataractous lenses showed a striking decrease in water-soluble protein content, in contrast to increases in the amount of water insoluble protein. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and Western blots of water-soluble protein in the cataractous lenses showed additional high molecular weight beta-crystallin proteins of about 43 kDa, concomitant with decreased amounts of 29-kDa and 31-kDa beta-crystallins and 21-kDa gamma-crystallin, as compared with findings in normal lenses. Although there was no apparent difference between the patterns of SDS-PAGE of urea-soluble and urea-insoluble proteins isolated from cataractous and normal lenses, slightly increased reactivity of bands around 43 kDa against anti-beta-crystallin antibody was observed in cataractous lenses. The calcium content was elevated and activity of transglutaminase was increased in the cataractous lenses. While the molecular weight of beta-crystallin polymers cross-linked in vitro by exogenous transglutaminase was not completely compatible with those of high molecular weight beta-crystallins observed in the cataractous lenses, these findings do suggest the contribution of this enzyme to production of high molecular weight beta-crystallins and to insolubilization of these proteins in the cataractous lenses in SAMP9.