Ubiquitination of Ku70 by Parkin promotes apoptosis of lens epithelial cells

Oxidative damage-triggered apoptosis in lens epithelial cells is considered as a main risk factor in the pathogenesis of age-related cataracts. Ku70 is a key factor in the DNA repair process of double-strand breaks. In the present study, we aimed to investigate the role of Ku70 and its related E3 ubiquitin ligase in lens epithelial cell apoptosis. The levels of Ku70 in the anterior lens capsules of human cataracts and Emory mice were lower compared to controls. H2O2 treatment resulted in decreased expression of Ku70 through accelerating Ku70 ubiquitination. Parkin, an E3 ubiquitin ligase, could interact with Ku70 and promote the ubiquitination and degradation of this protein. In addition, ubiquitinated Ku70 was regulated by ubiquitin-proteasome, autophagy-lysosome and mitophagy pathways. Ectopic expression of Ku70 protected SRA01/04 cells from H2O2-induced apoptosis, whereas silencing Ku70 exhibited the opposite trend. Co-transfected with Parkin non-ubiquitinatable Ku70 mutant could maintain its anti-apoptosis ability, whereas wild-type Ku70 failed. Moreover, Ku70 might facilitate mitochondrial fusion by increasing the expression of Mitofusin 1/2. The present study revealed that Parkin-mediated Ku70 ubiquitination facilitated H2O2-induced lens epithelial cell apoptosis through alleviating mitochondrial fusion, which could provide potential targets for age-related cataract treatment.

Automated summary

Oxidative damage-triggered apoptosis in lens epithelial cells is a main risk factor in age-related cataract pathogenesis. Ku70 and its related E3 ubiquitin ligase play a role in lens epithelial cell apoptosis. Ku70 levels were lower in cataracts and Emory mice, and oxidative stress decreased Ku70 expression through ubiquitination. Parkin, an E3 ubiquitin ligase, interacted with Ku70 and promoted its ubiquitination and degradation. Ubiquitinated Ku70 was regulated by ubiquitin-proteasome, autophagy-lysosome, and mitophagy pathways. Ku70 overexpression protected cells from apoptosis, while Ku70 silencing had the opposite effect. Non-ubiquitinatable Ku70 mutant maintained its anti-apoptosis ability, in contrast to wild-type Ku70. Ku70 may also facilitate mitochondrial fusion. Overall, this study demonstrated the role of Parkin-mediated Ku70 ubiquitination in oxidative stress-induced lens epithelial cell apoptosis, providing potential targets for age-related cataract treatment.