SAT0353 STAT3 PHOSPHORYLATION IS INVOLVED IN THE DEVELOPMENTS OF INFLAMMATORY ARTHRITIS, ENTHESITIS, AND NEW BONE FORMATION IN ANKYLOSING SPONDYLITIS

Background: Ankylosing Spondylitis (AS) is a chronic inflammatory rheumatic disease, which is characterized by the enthesitis, peripheral arthritis, and chronic inflammation of the spine, leading to bony ankylosis. Signal transducer and activator of transcription (STAT) family proteins are latent cytoplasmic transcription factors that convey signals to the nucleus. It is activated by IL-6, IL-23, and IL-22 through JAK-mediated phosphorylation. Moreover, genetic studies implicate interleukin-23 (IL-23) receptor signal, including STAT3 in the development of AS. IL-17A has recently emerged as a potential target that regulates the extensive inflammation and abnormal bone formation observed in AS. It was reported that STAT3 is a regulatory factor that induces Th17 cell development from naive CD4 T cells. Objectives: The aim of this study is to investigate whether the STAT3 phosphorylation (stat3-p) inhibitor has a therapeutic effect on inflammation and new bone formation in AS. Methods: Eight weeks after curdlan injection, SKG mice were treated with stat3-p inhibitor or mock as a control. Clinical and histologic scores for arthritis and enthesitis were evaluated. Synovial fluid mononuclear cells (SFMC) samples were obtained from AS patients. Inflammatory cytokine producing cells were analyzed using flow cytometry. Bone tissue samples were obtained from the facet joints of patients with AS at surgery. Primary bone-derived cells (BdCs) were isolated and cultured. The osteogenic differentiation was assessed in vitro for 3 weeks using ALP activity, Alizarin red S (ARS), Type I collagen, von kossa, and hydroxyapatite stains. Statistical analysis was performed using Prism 5.0 Software. A p < 0.05 was considered statistically significant. Results: The stat3-p inhibitor significantly suppressed peripheral arthritis and enthesitis in SKG mice (figure 1). Inflammatory infiltration around the tendon–bone insertion site and along the tendon, as well as bony involvement were all reduced in stat3-p inhibitor-treated mice compared to control mice. We found that the levels of IFN-±, IL-17, TNF-± were higher in AS Synovial fluid. A significantly decreased frequencies of IFN-±, IL-17, TNF-± producing cells in AS SFMC were shown after stat3-p inhibitor treatment (P < 0.01). In vitro experiment of bone formation, the stat3-p inhibitor suppressed ALP activity. In addition, there were significant decrease in Alizarin red S (ARS), Type I collagen, von kossa staining scores due to stat3-p inhibitor at a concentration of 5 μM. Light intensity of hydroxyapatite staining was also decreased by stat3-p inhibitor in a dose dependent manner (figure 2). Intriguingly, the stat3-p inhibitor suppressed osteogenesis in both early phase and late phase in AS-BdCs, down-regulating osteoblast-involved genes. Conclusion: The stat3-p inhibitor had beneficial effects on reducing inflammation and new bone formation in AS animal model. In addition, stat3-p inhibitor suppressed bone formation in vitro experiment. These findings suggest that the stat3-p inhibitor could be a potential therapeutic agent for AS. References: [1]Arthritis Res Ther 2018;20:115. [2]Nat Med 2012;18:1069-76. [3]Rheumatology (Oxford) 2017;56:488-493. [4]Nat Rev Immunol. 2011;11:239–50. [5]J Exp Med 2005;201:949–60. Acknowledgments: None Disclosure of Interests: None declared