Activation of liver X receptor alleviates ocular inflammation in experimental autoimmune uveitis

Purpose: To investigate whether a synthetic LXR Agonist TO901317 (TO90) ameliorates ocular inflammation in a mouse model of experimental autoimmune uveitis (EAU) and to explore its underlying mechanism.

Methods: EAU was induced with subcutaneous injection of IRBP161-180 peptide (SGIPYIISYLHPGNTILHVD) in B10.RIII mice. TO90 (50 mg/kg/d) or vehicle was administrated orally for successive 16 days or 8 days as prevention or effector phase, respectively. The severity of EAU was evaluated with clinical and histological scores. The levels of LXRs, NF-κB subunit p65, and an LXR target gene ABCA1 in the retina were detected with Real-Time PCR and Western blotting. The expressions of proinflammatory genes, including TNF-α, IL-1β, IL-6, MCP-1, IFN-γ, and IL-17, were detected by Real-Time PCR. IRBP-specific lymphocyte proliferation was detected by MTT. Intracellular IFN-γ and IL-17 in CD4(+) T cells were measured by flow cytometry.

Results: We found both LXRα and LXRβ were expressed in mouse retina. After administering TO90 orally to B10.RIII mice, the expression of LXRα but not LXRβ was upregulated in the naïve mice. Compared with naïve mice, LXRα expression was increased in vehicle and TO90-treated EAU mice, but the LXRβ expression was unchanged. The protein level of ABCA1 was enhanced in TO90-treated naïve and EAU mice but was unchanged in vehicle-treated EAU mice, suggesting activation of LXRα by TO90 is ligand dependent. TO90-mediated activation of LXRα improved the clinical and morphological scores in EAU mice. Meanwhile, activation of LXRα decreased the expressions of proinflammatory cytokines, including TNF-α, IL-1β, IL-6, MCP-1, IFN-γ, and IL-17 in the retina. TO90 treatment inhibited IRBP-specific immune responses. The proportions of Th1 and Th17 expressing IFN-γ and IL-17 were reduced in TO90-treated EAU mice in both prevention and effector phases. Furthermore, TO90 significantly downregulated the expressions of an NF-κB subunit p65 at the protein and mRNA levels.

Conclusions: TO90 activates LXRα and potently attenuates ocular inflammation in EAU. Alleviation of ocular inflammation could partially result from inhibition of the NF-κB signaling pathway. TO90 reduces IFN-γ and IL-17 expression in both prevention and treatment scenarios. Our data suggest that the LXR Agonist may become a novel class of therapeutic agent for autoimmune uveitis.