Disease‐associated, differentially hypermethylated regions have been reported in rheumatoid arthritis (RA), but no DNA methyltransferase inhibitors have been evaluated in either RA or any animal models of RA. The present study was conducted to evaluate the therapeutic potential of 5′‐azacytidine (5′‐azaC), a DNA methyltransferase inhibitor, and explore the cellular and gene regulatory networks involved in the context of autoimmune arthritis.

A disease‐associated genome‐wide DNA methylation profile was explored by methylated CpG island recovery assay–chromatin immunoprecipitation (ChIP) in arthritic B cells. Mice with proteoglycan‐induced arthritis (PGIA) were treated with 5′‐azaC. The effect of 5′‐azaC on the pathogenesis of PGIA was explored by measuring serum IgM and IgG1 antibody levels using enzyme‐linked immunosorbent assay, investigating the efficiency of class‐switch recombination (CSR) and Aicda gene expression using real‐time quantitative polymerase chain reaction, monitoring germinal center (GC) formation by immunohistochemistry, and determining alterations in B cell subpopulations by flow cytometry. The 5′‐azaC–induced regulation of the Aicda gene was explored using RNA interference, ChIP, and luciferase assays.

We explored arthritis‐associated hypermethylated regions in mouse B cells and demonstrated that DNA demethylation had a beneficial effect on autoimmune arthritis. The 5′‐azaC–mediated demethylation of the epigenetically inactivated Ahr gene resulted in suppressed expression of the Aicda gene, reduced CSR, and compromised GC formation. Ultimately, this process led to diminished IgG1 antibody production and amelioration of autoimmune arthritis in mice.

DNA hypermethylation plays a leading role in the pathogenesis of autoimmune arthritis and its targeted inhibition has therapeutic potential in arthritis management.