MicroRNA-146a-5p Protects Retinal Ganglion Cells Through Reducing Neuroinflammation in Experimental Glaucoma

Neuroinflammation plays important roles in retinal ganglion cell (RGC) degeneration in glaucoma. MicroRNA‐146 (miR‐146) has been shown to regulate inflammatory response in neurodegenerative diseases. In this study, whether and how miR‐146 could affect RGC injury in chronic ocular hypertension (COH) experimental glaucoma were investigated. We showed that in the members of miR‐146 family only miR‐146a‐5p expression was upregulated in COH retinas. The upregulation of miR‐146a‐5p was observed in the activated microglia and Müller cells both in primary cultured conditions and in COH retinas, but mainly occurred in microglia. Overexpression of miR‐146a‐5p in COH retinas reduced the levels pro‐inflammatory cytokines and upregulated the levels of anti‐inflammatory cytokines, which were further confirmed in the activated primary cultured microglia. Transfection of miR‐146a‐5p mimic increased the percentage of anti‐inflammatory phenotype in the activated BV2 microglia, while transfection of miR‐146a‐5p inhibitor resulted in the opposite effects. Transfection of miR‐146a‐5p mimic/agomir inhibited the levels of interleukin‐1 receptor associated kinase (IRAK1) and TNF receptor associated factor 6 (TRAF6) and phosphorylated NF‐κB subunit p65. Dual luciferase reporter gene assay confirmed that miR‐146a‐5p could directly target IRAK1 and TRAF6. Moreover, downregulation of IRAK1 and TRAF6 by siRNA techniques or blocking NF‐κB by SN50 in cultured microglia reversed the miR‐146a‐5p inhibitor‐induced changes of inflammatory cytokines. In COH retinas, overexpression of miR‐146a‐5p reduced RGC apoptosis, increased RGC survival, and partially rescued the amplitudes of photopic negative response. Our results demonstrate that overexpression of miR‐146a‐5p attenuates RGC injury in glaucoma by reducing neuroinflammation through downregulating IRAK1/TRAF6/NF‐κB signaling pathway in microglia.