Background/Purpose: Although a number of epigenetic alterations have been revealed in rheumatoid arthritis (RA), it remained an open question whether these epimutations play role in RA etiology or are consequences of the pathogenesis. We investigated how arthritis-specific DNA methylation events could contribute to the dysregulation of a gene regulatory network leading to increased autoantibody production, and development of polyarthritis in a mouse model of RA.

Methods: In B cells isolated from arthritic mice, DNA methylation profile changes were explored by methylated CpG island recovery assay (MIRA-chip). Disease-associated gene expression patterns were also investigated using microarray platforms and quantitative reverse transcription PCR (RT-qPCR). DNA methyltransferase inhibitor, 5`-Azacitidine (Aza) was employed to reactivate hypermethylated genes in cell cultures and animal studies. Gene expression changes were monitored using RT–qPCR and Western blotting. Mice with proteoglycan-induced arthritis (PGIA) were treated with Aza and its effects were followed in B cells by flow cytometry, histochemistry, RT-qPCR and ELISA. ShRNA expressing plasmid constructs were constructed and introduced into cell cultures for targeted silencing of gene of interest.

Results: A group of promoters with arthritis-specific DNA methylation profile was identified by MIRA-chip. The promoter region of AhR transcription factor encoding gene was differentially methylated in B cells isolated from arthritic mice, which de novo hypermethylation resulted in downregulated expression of AhR. Selective inhibition of DNA methylation restored AhR expression, which was associated by reduced expression of post-recombinant IgG1 in B cells and low level of IgG1 in sera of Aza treated animals. AhR directly regulates genes are implicated in germinal center formation within secondary lymph nodes. Aza treatment provided significant protection against disease onset, and abolished inflammatory reactions in synovial joints of arthritic mice.

Conclusion: AhR is a master regulator of IgG maturation and its epigenetic inactivation by DNA methylation significantly contributes to RA pathogenesis. Targeted reactivation of AhR employing DNA methylation may have therapeutic potential for treatment of polyarthritis.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/arthritis-associated-dna-hypermethylation-provokes-increased-antibody-expression-in-mouse-model-of-rheumatoid-arthritis/