Interleukin-17A Induces IL-1β Secretion From RPE Cells Via the NLRP3 Inflammasome

PURPOSE. Inflammasome activation and IL-1 beta production have been proposed to have an important role in age-related macular degeneration (AMD). Growing evidence is emerging for involvement of interleukin-17A (IL-17A) in AMD pathogenesis. We investigated the effects of IL-17A on the activation of inflammasome and production of IL-1 beta in primary human RPE cells. METHODS. Primary human RPE cells were isolated and cultured for the following experiments. Expression patterns of IL-17 receptor A (IL-17RA), IL-17 receptor C (IL-17RC), and ACT1 were analyzed by RT-PCR, flow cytometry, and immunofluorescence. IL-17A was added to the cell cultures, and cytokine expression, signaling pathways, and inflammasome machinery were investigated using real-time RT-PCR, ELISA, Western blot, flow cytometry, and small interfering RNA. RESULTS. Retinal pigment epithelial cells constitutively expressed IL-17RA, IL-17RC, and ACT1. IL-17A upregulated the mRNA levels of pro-IL-1 beta, IL-8, CCL2, and CCL20, as well as the protein level of IL-1 beta. IL-17A induced the phosphorylation of Akt, Erk1/2, p38 MAPK, and NF-kappa B p65 in RPE cells. Blocking NF-kappa B attenuated IL-17A-induced expression of pro-IL-1 beta mRNA. IL-17A enhanced pro-caspase-1 and NLRP3 mRNA expression. Inhibiting caspase-1 activity and silencing NLRP3 decreased IL-1 beta secretion, confirming NLRP3 as the IL-17A-responsive inflammasome on the posttranscriptional level. The mechanism of IL-17A-triggered NLRP3 activation and subsequent IL-1 beta secretion was found to involve the generation of reactive oxygen species. CONCLUSIONS. Our results suggest that IL-17A triggers a key inflammatory mediator, IL-1 beta, from RPE cells, via NLRP3 inflammasome activation, holding therapeutic potential for AMD.