MicroRNAs regulate NLRP3 inflammasome activation by microglia and macrophages in retinal degeneration

Abstract

Purpose : Excessive NLRP3 inflammasome activation is implicated in several neuroinflammatory diseases including Age-Related Macular Degeneration (AMD). Activation of the NLRP3 inflammasome triggers the release of IL-1β and IL-18, amplifying the inflammatory response. Several microRNAs (miRNAs) have roles in regulating activation of the NLRP3 inflammasome, including miR-223 and miR-7, although their roles in modulating retinal inflammasomes have not been studied. We investigated the expression of miR-223 and miR-7 in the retina in parallel with inflammasome activation using a model of retinal degeneration.

Methods : C57BL/6J mice were exposed to 100K lux light for up to 7 days to induce photo-oxidative damage (PD). Eyes and retinas were collected for immunohistochemistry (NLRP3, F4/80) and qPCR for inflammasome genes (Nlrp3, Il-1β, Il-18, Casp1, Casp8) and miRNAs (miR-223, miR-7). In vitro, NLRP3 inflammasome activation in mouse N11 microglia were stimulated using LPS and ATP. Changes in inflammasome genes and miRNAs were correlated to NLRP3 and IL-1β protein expression.

Results : All inflammasome genes assayed (Nlrp3, Il-1β, Il-18, Casp1, and Casp8) were upregulated in the retina following PD, compared to dim-reared controls (P<0.05). Immunohistochemistry revealed that NLRP3 expression was localised to outer retinal F4/80+ microglia and macrophages (mononuclear phagocytes), which reached peak numbers at 5 days PD (P<0.05), concurrent with maximal photoreceptor cell death. Retinal miR-223 expression increased following PD, whereas miR-7 decreased in PD retinas (P<0.05). In N11 microglia, LPS and ATP stimulation induced the upregulation of all inflammasome genes (Nlrp3, Il-1β, Il-18, Casp1, and Casp8) and an increase in NLRP3 protein expression, compared to unstimulated controls (P<0.05). The expression levels of both miR-223 and miR-7 were upregulated concurrently with inflammasome activation in these cells (P<0.05).

Conclusions : The differential expression of miR-223 and miR-7 correlate with changes in inflammasome activation by microglia and macrophages in retinal degeneration. Further investigation using miRNA mimics or inhibitors to regulate the retinal inflammasome could be of therapeutic benefit for targeting NLRP3 inflammasome activation, a major feature of AMD pathogenesis.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.