DNA methylation inhibitor decitabine ameliorates spondyloarthritis by suppressing Th17 responses and epigenetically upregulating VIPR1 in SKG mice

Abstract Background Spondyloarthritis (SpA) is a chronic inflammatory disorder characterized by enthesitis of axial and peripheral joints. Although genetic factors, bacterial infection, dysbiosis, and mechanical stress contribute to its development, the role of epigenetic regulation remains poorly understood. DNA methylation has been implicated in immune dysregulation, and the DNA methyltransferase inhibitor, decitabine (DAC), has demonstrated therapeutic effects in autoimmune disease models. This study aimed to evaluate the effect of DAC in the SpA-resembling SKG/Jcl (SKG) mouse model and elucidate the immunological mechanisms. Methods SpA-like arthritis was induced in SKG mice via intraperitoneal injection of curdlan (1,3-β-glucan aggregates). DAC (1 mg/kg) was administered weekly. Arthritis severity and histopathological changes were evaluated in the limb joints and tail, and histopathological enthesitis scores were assessed in the limb joints. Splenic T-cell profiles were analyzed by flow cytometry. CD4⁺ T cells were stimulated in vitro with DAC to assess cytokine production. To investigate epigenetic regulation, reduced representation bisulfite sequencing (RRBS) and RNA-seq were performed on Achilles tendon tissue containing enthesis. Local expression of IL-17 and vasoactive intestinal peptide receptor 1 (VIPR1) in peripheral entheses was assessed by immunohistochemistry. Results DAC treatment significantly reduced arthritis severity and improved histopathological findings, including synovial hyperplasia, inflammatory cell infiltration, bone erosion, and cartilage loss. Peripheral enthesitis at the Achilles tendon insertion sites was also reduced. Flow cytometric analysis demonstrated that the DAC-treated group reduced IL-17 A expression in splenic CD4⁺ T cells during the early phase (weeks 4–8) and decreased PD-1 expression in regulatory T cells (Tregs) at week 12. In vitro, DAC suppressed IL-17 A secretion and enhanced TGF-β production in stimulated splenic CD4⁺ T cells. Integrated RRBS and RNA-seq analyses identified Vipr1 as a DAC-responsive gene, showing significant hypomethylation (Δmethylation ≥ − 25%) and concordant transcriptional upregulation (log₂FC > 1) in the entheses of DAC-treated mice. Immunohistochemical analysis of the ankle entheses revealed decreased IL-17 A expression and increased VIPR1 expression. Conclusions DAC ameliorated SpA in SKG mice, possibly through suppression of Th17 responses and epigenetic upregulation of Vipr1 , and may be associated with improved Treg-associated regulation. These findings highlight an important role of DNA methylation in SpA pathogenesis.