Calpain-induced light scattering in young rat lenses is enhanced by UV-B

The purpose of this study is to determine if UV-B enhances light scattering after proteolysis of crystallins by calpains, and to determine if lens-specific calpain Lp82 is involved, along with m-calpain, in the mechanism of in vitro precipitation. Lens soluble proteins from young rats were hydrolyzed for 24 hr by endogenous lens calpains, and the proteins were further incubated for up to 7 days with periodic irradiation by UV-B. Light scattering was measured daily at 405 nm. SDS-PAGE and immunoblotting assessed proteolysis of crystallins, activation of calpains, and formation of high molecular weight aggregations. Appreciable light scattering occurred in lens soluble proteins after proteolysis of crystallins by m-calpain and Lp82. UV-B markedly enhanced this light scattering and the formation of higher molecular weight aggregates consisting of proteolyzed alpha- and beta- and intact gamma-crystallins. Calpain inhibitor E64 and antioxidants DTE or GSH prevented the light scattering. These results show that calpain-induced light scattering is enhanced by the natural oxidant UV-B. Activation of Lp82, along with m-calpain, contributed to the light scattering. The linkage between proteolysis and oxidation is important because both oxidation and truncation of crystallins are found in aged human lenses, which are constantly exposed to UV irradiation.