Background/Purpose: Ankylosing spondylitis (AS) is a chronic inflammatory disease characterized by enthesitis in axial joints, bone erosion near the entheses, and subsequent irreversible ankylosis due to new bone formation. Although AS has a strong association with HLA-B27, its occurrence in HLA-B27-negative individuals suggests the involvement of epigenetic factors. Decitabine is a DNA methylation inhibitor that induces demethylation and reactivation of silenced genes and is used to treat myelodysplastic syndromes. This study aimed to evaluate the effects of decitabine in a mouse model of spondyloarthritis.

Methods: Spondyloarthritis was induced in SKG mice by intraperitoneal injection of β-glucan under SPF conditions. Mice were treated weekly with either decitabine (1 mg/kg/week) or vehicle. Body weight and arthritis scores were monitored until week 12. At week 12, and histological analysis was performed on the limb joints, spine, and tail. At weeks 4, 8, and 12, splenic T cell subsets and cytokine production were analyzed by flow cytometry. DNA methylation analysis was performed on the achilles tendon to identify genes with suppressed methylation by decitabine. Furthermore, to assess the functional effects of decitabine in vitro, splenocyte supernatants from arthritic mice were co-cultured with decitabine, and production of IL-17 and TGF-β was evaluated.

Results: Mice treated with decitabine showed significantly improved arthritis scores compared to the control (vehicle) group. Histological scores of the limb joints and tail at week 12 were significantly improved as assessed by both H&E and toluidine blue staining. Flow cytometry of splenocytes revealed a significant suppression of IL-17 production in mice at weeks 4 and 8. Although the number of regulatory T cells (CD4+CD25⁺FOXP3⁺) remained unchanged in mice sacrificed at week 12, PD-1 expression on Tregs was significantly reduced. DNA methylation analysis of the Achilles tendon at week 12 revealed significant demethylation of the FOXP3 and IL17rd genes. In vitro experiments showed that stimulation of splenocyte supernatants with IL-2 and anti-CD3/CD28 antibodies, followed by co-culture with decitabine, resulted in a significant increase in TGF-β production as measured by ELISA. After additional 24-hour stimulation with PMA/ionomycin, IL-17 production tended to be suppressed in the decitabine-treated cultures.

Conclusion: DNA methylation inhibitors may alleviate systemic symptoms and arthritis in a mouse model of spondyloarthritis by suppressing IL-17 production and enhancing Treg function.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/investigation-of-dna-methylation-inhibition-in-a-mouse-model-of-ankylosing-spondylitis/