USP5 facilitates diabetic retinopathy development by stabilizing ROBO4 via deubiquitination

Ubiquitin-specific proteases (USPs) have been proved to play important roles in the progression of diabetic retinopathy. In this study, we explored the role of USP5 and its possible mechanisms in diabetic retinopathy development. Cell proliferation, apoptosis, inflammation and oxidative stress were determined using CCK-8 assay, EdU staining assay, flow cytometry, and ELISA, respectively. The mRNA and protein expression of ROBO4 and USP5 were measured through RT-qPCR and western blot, respectively. Co-IP and deubiquitination assay were conducted to evaluate the interaction between ROBO4 and USP5. The results showed that high glucose (HG) stimulation significantly led to HRPE cell damage as described by suppressing proliferation, and promoting oxidative stress, inflammation and apoptosis. ROBO4 was markedly increased in diabetic retinopathy plasma samples and HG-triggered HRPE cells. Depletion of ROBO4 could alleviate HG-caused HRPE cell damage. USP5 was also significantly elevated in diabetic retinopathy plasma samples and HG-triggered HRPE cells. USP5 overexpression aggravated HG-induced HRPE cell damage. USP5 stabilized ROBO4 through deubiquitination. Moreover, USP5 knockdown decreased ROBO4 expression to mitigate HG-triggered cell damage in HRPE cells. USP5 stabilized ROBO4 via deubiquitination to repress cell proliferation, and facilitate inflammation, cell apoptosis and oxidative stress in HG-treated HRPE cells, thereby promoting the development of diabetic retinopathy.