Alleviation of Experimental Arthritis in SKG Mice through Nr4a1 Agonization

Yoichi Nakayama¹Ryosuke Hiwa^1*Ayaka Okubo¹Mikihito Shoji¹Mirei Shirakashi¹HIDEAKI TSUJI¹Koji Kitagori²Ran Nakashima¹Shuji Akizuki¹Hajime Yoshifuji¹Akio Morinobu¹

• ¹Department of Rheumatology and Clinical Immunology, Kyoto University Graduate School of Medicine, Kyoto, Japan
• ²Occupational Welfare Division, Agency for Health, Safety and Environment, Kyoto University, Kyoto, Japan

Introduction: Rheumatoid arthritis (RA), a chronic autoimmune disease, is characterized by CD4⁺ T cell-mediated synovial inflammation, with T helper (Th)17 cells being implicated in RA pathogenesis. Nr4a1 is an orphan nuclear receptor functioning as a negative regulator of T cell activation and central tolerance. Cytosporone B (CsnB) is a small-molecule agonist of Nr4a1 and can exert immunomodulatory effects. However, its efficacy in T cell-driven autoimmune arthritis remains unclear. This study aimed to investigate the therapeutic effect of CsnB-mediated Nr4a1 agonization on RA development in SKG mice and evaluate its impact on T cell function. Methods: The SKG mouse model of T cell-dependent chronic arthritis was constructed via zymosan A induction. The mice were intraperitoneally treated with CsnB, and disease severity and immune cell populations were evaluated by clinical scoring and flow cytometry. In vitro assays were performed to examine T cell antigen receptor (TCR)-induced T cell activation and Th17 differentiation. Additionally, RNA sequencing was performed to profile transcriptomic changes in CD4⁺ T cells following TCR stimulation. Results: CsnB markedly attenuated arthritis development and reduced the population of effector memory and Th17 cells in the spleen and synovium. Furthermore, in vitro assay results showed that CsnB suppressed T cell activation, downregulated interleukin (IL)-2 and activation markers, and repressed inflammatory gene expression. CsnB inhibited Th17 differentiation and IL-6– signal transducer and activator of transcription 3 signaling by reducing CD130 (Il6st) expression. Discussion: Altogether, the findings of this study showed that CsnB, one of the agonists of Nr4a1, suppressed TCR-driven T cell activation and Th17 differentiation, thereby ameliorating autoimmune arthritis in SKG mice. These findings highlight the potential of Nr4a1 as an immunotherapeutic target in T cell-mediated autoimmune arthritis, particularly in RA subsets characterized by TCR signaling dysfunction.