Inhibition of Sumoylation Alleviates Oxidative Stress-induced Retinal Pigment Epithelial Cell Senescence and Represses Proinflammatory Gene Expression

Purpose: Advanced age is the largest risk factor for age-related macular degeneration (AMD). Sumoylation is a reversible post-translational modification that conjugates small peptide, small ubiquitin-like modifier (SUMO), to a target protein. Dysregulation of sumoylation is recently found to be critically involved in several age-related disorders. However, the effects of sumoylation during retina senescence and aging remains elusive. This study is aimed to investigate the function and regulation of sumoylation pathway in the aging retina and premature senescent retinal pigment epithelial (RPE) cells.

Methods: 1.5- and 10-month C57/B6 mice were used for comparative aging study. Both ARPE primary cultures and ARPE-19 cells were used for assay systems. The qRT-PCR was used for analysis of mRNA expression. Western blot and immunofluorescence were used to analyze the protein expression. Cell flow cytometry was used for cell cycle progression analysis. RPE barrier function and senescent-associated β-galactosidase (SA β-gal) activity were analyzed to measure cellular senescence.

Results: We show that the expression of SUMO enzymes and global protein sumoylation were downregulated in the aging mouse retina, and in the oxidative stress (OS) -induced premature senescent RPE cells. Dramatical altered distribution of SUMO E1, E2 and E3 enzymes were observed during RPE senescence. Inhibition of sumoylation alleviated OS-induced cell senescence in RPE cells, as indicated by decreased p21 and p53 expression and decreased percentage of cell cycle arrest at G0/G1 phase. Intriguingly, inhibition of SUMO E1 repressed the expression of proinflammatory cytokine and chemokine in the premature senescent RPE cells. However, inhibition of sumoylation did not prevent DNA damage during the OS-induced RPE senescence process.

Conclusions: Our data indicate sumoylation critically regulates retina and RPE aging and that targeting sumoylation process may provide potential therapeutic strategy for AMD treatment.