Itaconate alleviates autoimmune uveitis by boosting FOXP3 and blocking succinate-driven inflammation

Introduction/Rationale: We recently reported the activation of the Irg1/itaconate axis in promoting inflammation resolution during ocular infectious disease. This study aims to determine the immunomodulatory role of itaconate in the pathogenesis of experimental autoimmune uveitis (EAU).

Methods: EAU was induced in wild-type (WT) or Irg1 KO (knock out) mice by immunization with IRBP. Disease severity was assessed based on fundus examination and retinal function testing. Ocular tissues (retina and cornea), splenocytes, and cervical lymph nodes were harvested at 21 days post-immunization. Flow cytometry was used to determine the frequencies of myeloid and lymphoid cells. In vitro studies were performed using mouse splenocytes, and challenged with IRBP in the presence or absence of succinate and 4-octyl itaconate. ELISA and qPCR assays were performed to measure inflammatory mediators.

Results: Our data show that Irg1 KO mice developed severe EAU. The exacerbated EAU in Irg1 KO mice is accompanied by increased frequencies of myeloid cells, specifically macrophages, as well as pathogenic Th17 cells. The elevated frequency of these immune cell infiltrations coincided with a decrease in regulatory T cells. Additionally, Irg1 KO mice exhibited increased levels of succinate and its receptor. The in vitro experiments using splenocytes from Irg1 KO mice or succinate treatment in WT mice revealed decreased regulatory T cells and Foxp3 expression. However, in splenocytes (Irg1 KO) treated with 4-OI, the regulatory T cell numbers and Foxp3 expression were restored. Moreover, the 4-OI treatment significantly suppressed the levels of inflammatory mediators and succinate.

Conclusion: Our study demonstrates that Krebs cycle metabolites regulate innate and adaptive immune responses during EAU. Itaconate derivative supplementation exerts anti-inflammatory effects, inhibits succinate expression, and promotes the regulatory cells, indicating its therapeutic potential in treating ocular inflammation during autoimmune uveitis.