Calpain Activity in the Sheep Lens

Abstract

Abstract: : Purpose:Cataract formation is often accompanied by a rise in calcium concentration in the lens and crystallin destruction causing light scattering and cataract. Calcium dependent proteases are thought to be responsible for crystallin proteolysis causing some cataracts. m-Calpain has been shown to proteolyse ß-crystallins in rodent and bovine lens. A line of sheep at Lincoln University inherit cataracts and offer a unique opportunity to study the mechanism of cataract initiation and progression in a lens. The purpose of this study was to show that the calpain family are active in the ovine lens. Methods:Casein zymography was performed on lenses from normal-eyed and cataractous sheep aged 40 days. Each lens had previously been dissected into cortical and nuclear fractions. Enzyme activity attributed to specific calpain activity was confirmed by Immunoblotting. Results:Both m- and µ-calpain activity was found in the soluble cortex fraction of the ovine lens. µ-Calpain activity was not detected in the nucleus fraction. In both fractions m-calpain had the greatest activity. A third much smaller band of activity was present in both fractions. This could be attributed to lens specific calpain Lp82, indicated by its position on the gel. Calpain activity was seen in normal and early cataract lenses. Conclusion:Both m- and µ-calpain activity are present in the ovine lens. m-Calpain is the dominant isozyme in both nuclear and cortical fractions. The different forms of calpain present could serve different functions relative to their abundance of activity.

Keywords: 399 enzymes/enzyme inhibitors • 338 cataract • 316 animal model