Age-related cataracts in α3Cx46-knockout mice are dependent on a calpain 3 isoform

PURPOSE. Previous studies have demonstrated that in 129 alpha 3Cx46(-/-) mice, age-related nuclear cataract is formed. In the present study, a more in vivo-relevant model was generated to test the hypothesis that the calpain 3 gene is involved in age-related nuclear cataractogenesis in alpha 3Cx46 knockout mice. METHODS. To test the hypothesis that the calpain 3 gene is involved in age-related nuclear cataractogenesis in a3Cx46 knockout mice, 129 alpha 3Cx46(-/-) and CAPN3(-/-) mice were mated to generate homozygous double-knockout (dKO) mice. Lenses from the mice were examined by visual observation, laser scan analysis, and histologic and biochemical methods. RESULTS. In the absence of the CAPN3 gene, the formation of a cataract was delayed, and its appearance was changed to a more diffuse, pulverulent type. Unlike in the 129 alpha 3Cx46(-/-) mouse, cleavage of gamma-crystallin was not detected in the dKO mouse. In both 129 alpha 3Cx46(-/-) and dKO mice, total Ca2+ increased. CONCLUSIONS. The present study shows for the first time that calpain 3 is necessary for the formation of age-dependent nuclear cataracts in alpha 3Cx46(-/-) mice. Evidence that the calpain 3 gene is directly involved in, or part of the pathway that leads to, gamma-crystallin cleavage is presented. These results are consistent with the hypothesis that the loss of alpha 3Cx46 leads to increased levels of Ca2+ ions, and this increase activates the CAPN3 isoform, Lp82/85, which results in the formation of a nuclear cataract.