Irisin Alleviates Autoimmune Uveitis Through Promoting Retinal Microglial M1 to M2 Phenotypic Polarization Mediated...

Irisin, proteolytically cleaved from Fndc5 protein, has been identified as an exercise-related hormone. Here, we investigated the irisin levels in aqueous humor and its involvement in the pathogenesis of uveitis. The results revealed that the irisin level in the aqueous humor was significantly decreased in Vogt-Koyanagi-Harada (VKH), and Behcet uveitis (BU) patients, and was negatively correlated with TNF-α in BU patients. Exogenous supplementation of irisin alleviated scores of experimental autoimmune uveitis (EAU) clinically and pathologically and suppressed the proportion of Th1 and Th17 cells in spleen. Fndc5^-/- EAU mice exhibited more severe inflammatory manifestations with increased microglial activation in the retina. Irisin could mitigate M1 microglia and promote M2 microglia polarization. RNA sequencing of the retina showed that HIF-1α pathway was significantly enriched in Fndc5^-/- EAU mice. HIF-1α pathway inhibitor significantly rescued EAU severity, associated with a decreased M1 microglial polarization in the retina of Fndc5^-/- mice. In conclusion, we highlighted that irisin could alleviate uveitis by inhibiting Th1 and Th17 cells and reducing M1 microglial polarization via HIF-1α pathway.