The inflammatory reaction in rheumatoid arthritis (RA) is controlled by major epigenetic modifications that modulate the phenotype of synovial and immune cells. The aim of this work was to perform a systematic review focusing on miR expression, DNA methylation and histone modifications in RA. We demonstrated that, in human samples, the expressions of miR-155, miR-146a and miR-150 were significantly decreased while the expression of miR-410-3p was significantly increased in the RA group. Moreover, miR-146a significantly decreased pro-autoimmune IL-17 cytokine expression in RA. In a murine model, miR-34a inhibition can ameliorate the arthritis score. However, this evidence remain critically insufficient to support current therapeutic applications in RA patients.

CD248 (endosialin) belongs to a glycoprotein family that also includes thrombomodulin (CD141), CLEC14A, and CD93 (AA4) stem cell markers. We analyzed the regulated expression of CD248 in vitro using skin (HFFF) and synovial (FLS) mesenchymal stem cell lines, and in fluid and tissue samples of rheumatoid arthritis (RA) and osteoarthritis (OA) patients. Cells were incubated with either rhVEGF₁₆₅, bFGF, TGF-β1, IL1-β, TNF-α, TGFβ1, IFN-γ, or PMA (Phorbol ester). There was no statistically significant change in membrane expression. A soluble (s) form of cleaved CD248 (sCD248) was detected after cell treatment with IL1-β and PMA. Matrix metalloprotease (MMP) MMP-1 and MMP-3 mRNAs were significantly up-regulated by IL1-β and PMA. A broad MMP inhibitor blocked the release of soluble CD248. In RA synovial tissue, we identified CD90⁺ perivascular MSCs double-stained for CD248 and VEGF. High sCD248 levels were detected in synovial fluid from RA. In culture, subpopulations of CD90⁺ CD14⁻ RA MSCs were either identified as CD248⁺ or CD141⁺ cells but CD93⁻. CD248 is abundantly expressed by inflammatory MSCs and shed in an MMP-dependent manner in response to cytokines and pro-angiogenic growth factors. Both membrane-bound and soluble CD248 (acting as a decoy receptor) may contribute to RA pathogenesis.

Infection by arthritogenic alphaviruses (aavs) can lead to reactive arthritis, which is characterized by inflammation and persistence of the virus; however, its mechanisms remain ill-characterized. Intriguingly, it has been shown that viral persistence still takes place in spite of robust innate and adaptive immune responses, characterized notably by the infiltration of macrophages (sources of TNF-alpha) as well as T/NK cells (sources of IFN-gamma) in the infected joint. Aavs are known to target mesenchymal stem cells (MSCs) in the synovium, and we herein tested the hypothesis that the infection of MSCs may promote the expression of immunoregulators to skew the anti-viral cellular immune responses. We compared the regulated expression via human synovial MSCs of pro-inflammatory mediators (e.g., IL-1β, IL6, CCL2, miR-221-3p) to that of immunoregulators (e.g., IDO, TSG6, GAS6, miR146a-5p). We used human synovial tissue-derived MSCs which were infected with O’Nyong-Nyong alphavirus (ONNV, class II aav) alone, or combined with recombinant human TNF-α or IFN-γ, to mimic the clinical settings. We confirmed via qPCR and immunofluorescence that ONNV infected human synovial tissue-derived MSCs. Interestingly, ONNV alone did not regulate the expression of pro-inflammatory mediators. In contrast, IDO, TSG6, and GAS6 mRNA expression were increased in response to ONNV infection alone, but particularly when combined with both recombinant cytokines. ONNV infection equally decreased miR-146a-5p and miR-221-3p in the untreated cells and abrogated the stimulatory activity of the recombinant TNF-α but not the IFN-gamma. Our study argues for a major immunoregulatory phenotype of MSCs infected with ONNV which may favor virus persistence in the inflamed joint.

In rheumatoid arthritis (RA), activated synovial tissue-derived mesenchymal stem cells (MSC) acquire a pathogenic phenotype and produce pro-inflammatory cytokines, chemokines, metalloproteinases, pro-osteoclastic and pro-angiogenic factors. The acquisition of this aggressive phenotype might be due to modified expression of micro-RNAs. We aimed to clarify the role of specific micro-RNAs (miR-146a-5p, miR-221-3p, miR-34a-3p, miR-150, miR-203a-3p and miR-155-3p) in an in vitro model of RA. Methods: Micro-RNA expression was determined in RA patient plasma and in commercial human synovial tissue-derived MSC-like cells stimulated with a panel of pro-inflammatory mediators (poly I:C, TNF-α, IL-1β, IFN-γ) to mimic the rheumatoid arthritis pathogenic setting. Next, unstimulated cells or TNF-α stimulated cells were transfected with miR-146a-5p mimic or miR-221-3p mimic. Protein and/or mRNA expressions of chemokines, cytokines, VEGF, MMPs and RANKL were determined by ELISA or qRT-PCR. MiR-34a-3p, miR-146a-5p, miR-150, miR-221-3p and miR-203a-5p were upregulated in RA patient plasma versus healthy controls. Moreover, synovial tissue-derived MSC-like cells expressed miR-146a-5p and miR-221-3p in response to pro-inflammatory mediators. Overexpression of miR-146a-5p increased CCL2 and CXCL8 expression and miR-221-3p increased IL-1β and IL-6 expression in synovial tissue-derived MSC-like cells stimulated with TNF-α. Conclusion: Overexpression of miR-146a-5p and miR-221-3p might favour inflammation and participate in rheumatoid arthritis pathogenesis.