Aβ-Induced Senescent Retinal Pigment Epithelial Cells Create a Proinflammatory Microenvironment in AMD

PURPOSE. Chronic inflammation is implicated in the pathogenesis of AMD. The source of chronic inflammation is often attributed to the progressive activation of immune cells over time. However, recent studies have shown that senescent cells can alter tissue microenvironment via secretion of growth factors, proteases, and inflammatory cytokines and might be an additional source of chronic inflammation. We hypothesized that altered secretory pattern in A beta-induced senescent RPE cells may contribute to compromised RPE barrier integrity and chronic inflammation in AMD. METHODS. Senescence was assessed by measuring the SA-beta-Galactosidase activity, the expressions of p16(INK4a) and ATM, and cell cycle analysis. Expressions of IL-8 and MMPs were analyzed by RT-PCR, ELISA, and gelatin zymography. The barrier structures of RPE cells were detected by actin-tracker, ZO-1, claudin-19, occludin immunochemistry, and Western blot; barrier function was analyzed by measuring transepithelial resistance (TER) and transepithelial diffusion rate of FITC-dextran. For inhibitory studies, MMP-9 was inhibited by RNA interference strategy. RESULTS. A beta promotes RPE cells to enter senescence and secrete higher concentrations of IL-8 and MMP-9. Secretion of MMP-9 is associated with compromised barrier integrity and with processing of IL-8 to a more activated form. Silence of MMP-9 preserved the barrier integrity of senescent RPE cells. CONCLUSIONS. The altered secretory phenotype of senescent RPE cells may contribute to age-related inflammation in AMD.