EZH2 deficiency attenuates Treg differentiation in rheumatoid arthritis

The chromatin modifier enhancer of zeste homolog 2 (EZH2) methylates lysine 27 of histone H3 (H3K27) and regulates T cell differentiation. However, the potential role of EZH2 in the pathogenesis of rheumatoid arthritis (RA) remains elusive. We analyzed EZH2 expression in PBMC, CD4⁺ T cells, CD19⁺ B cell, and CD14⁺ monocytes from active treatment-naïve RA patients and healthy controls (HC). We also suppressed EZH2 expression using EZH2 inhibitor GSK126 and measured CD4⁺ T cell differentiation, proliferation and apoptosis. We further examined TGFβ-SMAD and RUNX1 signaling pathways in EZH2-suppressed CD4⁺ T cells. Finally, we explored the regulation mechanism of EZH2 by RA synovial fluid and fibroblast-like synoviocyte (FLS) by neutralizing key proinflammatory cytokines. EZH2 expression is lower in PBMC and CD4⁺ T cells from RA patients than those from HC. EZH2 inhibition suppressed regulatory T cells (Tregs) differentiation and FOXP3 transcription, and downregulated RUNX1 and upregulated SMAD7 expression in CD4⁺ T cells. RA synovial fluid and fibroblast-like synoviocytes suppressed EZH2 expression in CD4⁺ T cells, which was partially neutralized by anti-IL17 antibody. Taken together, EZH2 in CD4⁺ T cells from RA patients was attenuated, which suppressed FOXP3 transcription through downregulating RUNX1 and upregulating SMAD7 in CD4⁺ T cells, and ultimately suppressed Tregs differentiation. IL17 in RA synovial fluid might promote downregulation of EZH2 in CD4⁺ T cells. Defective EZH2 in CD4⁺ T cells might contribute to Treg deficiency in RA.