Epigenetics contributes to the pathogenesis of immune-mediated diseases like rheumatoid arthritis (RA). Here we show the first comprehensive epigenomic characterization of RA fibroblast-like synoviocytes (FLS), including histone modifications (H3K27ac, H3K4me1, H3K4me3, H3K36me3, H3K27me3, and H3K9me3), open chromatin, RNA expression and whole-genome DNA methylation. To address complex multidimensional relationship and reveal epigenetic regulation of RA, we perform integrative analyses using a novel unbiased method to identify genomic regions with similar profiles. Epigenomically similar regions exist in RA cells and are associated with active enhancers and promoters and specific transcription factor binding motifs. Differentially marked genes are enriched for immunological and unexpected pathways, with “Huntington’s Disease Signaling” identified as particularly prominent. We validate the relevance of this pathway to RA by showing that Huntingtin-interacting protein-1 regulates FLS invasion into matrix. This work establishes a high-resolution epigenomic landscape of RA and demonstrates the potential for integrative analyses to identify unanticipated therapeutic targets.

Objective. Tofacitinib (CP-690,550) is a novel JAK inhibitor that is currently in clinical trials for the treatment of rheumatoid arthritis (RA). The aim of this study was to examine the effects of tofacitinib in vitro and in vivo in RA, in order to elucidate the role of JAK in the disease process.Methods. CD4؉ T cells, CD14؉ monocytes, and synovial fibroblasts (SFs) were purified from the synovium and peripheral blood of patients with RA and were evaluated for the effect of tofacitinib on cytokine production and cell proliferation. For in vivo analysis, synovium and cartilage samples obtained from patients with RA were implanted in immunodeficient mice (SCID-HuRAg mice), and tofacitinib was administered via an osmotic minipump.Results. Tofacitinib treatment of CD4؉ T cells originating from synovium and peripheral blood inhibited the production of interleukin-17 (IL-17) and interferon-␥ (IFN␥) in a dose-dependent manner, affecting both proliferation and transcription, but had no effect on IL-6 and IL-8 production. Tofacitinib did not affect IL-6 and IL-8 production by RASFs and CD14؉ monocytes. However, conditioned medium from CD4؉ T cells cultured with tofacitinib inhibited IL-6 production by RASFs and IL-8 production by CD14؉ monocytes. Treatment of SCID-HuRAg mice with tofacitinib decreased serum levels of human IL-6 and IL-8 and markedly suppressed invasion of synovial tissue into cartilage. Conclusion. Tofacitinib directly suppressed the production of IL-17 and IFN␥ and the proliferation of CD4؉ T cells, resulting in inhibition of IL-6 production by RASFs and IL-8 production by CD14؉ cells and decreased cartilage destruction. In CD4؉ T cells, presumably Th1 and Th17 cells, JAK plays a crucial role in RA synovitis.

Results. The number of osteoclast-like cells was decreased and expression of cathepsin K and nuclear factor of activated T cells c1 (NF-ATc1) was downregulated by the addition of either MSCs or a conditioned medium obtained from MSCs. Osteoprotegerin (OPG) was constitutively produced by MSCs and inhibited osteoclastogenesis. However, osteoclast differentiation was not fully recovered upon treatment with either anti-OPG antibody or OPG small interfering RNA, suggesting that OPG had only a partial role in the inhibitory effect of MSCs. Moreover, bone-resorbing activity of osteoclast-like cells was partially recovered by addition of anti-OPG antibody into the conditioned medium.Conclusion. The present results indicate that human MSCs constitutively produce OPG, resulting in inhibition of osteoclastogenesis and expression of NFATc1 and cathepsin K in the absence of cell-cell contact. Therefore, we conclude that human MSCs exert a suppressive effect on osteoclastogenesis, which may be beneficial in inhibition of joint damage in RA.

Multiple cytokines play a pivotal role in the pathogenesis of rheumatoid arthritis (RA). The appropriate intracellular signalling pathways must be activated via cytokine receptors on the cell surface, and the tyrosine kinases transduce the first 'outside to in' signals to be phosphorylated after receptor binding to its ligand. Among them, members of the Janus kinase (JAK) family are essential for the signalling pathways of various cytokines and are implicated in the pathogenesis of RA. The in vitro, ex vivo and in vivo effects of a JAK inhibitor CP-690,550 (tofacitinib) for the treatment of RA are reported. In vitro experiments indicated that the effects of tofacitinib were mediated through suppression of interleukin 17 (IL-17) and interferon γ production and proliferation of CD4 T cells, presumably Th1 and Th17. A treatment study was conducted in the severe combined immunodeficiency (SCID)-HuRAg mice, an RA animal model using SCID mice implanted with synovium and cartilage from patients. Tofacitinib reduced serum levels of human IL-6 and IL-8 in the mice and also reduced synovial inflammation and invasion into the implanted cartilage. A phase 2 double-blind study using tofacitinib was carried out in Japanese patients with active RA and inadequate response to methotrexate (MTX). A total of 140 patients were randomised to tofacitinib 1, 3, 5, 10 mg or placebo twice daily and the American College of Rheumatology 20% improvement criteria (ACR20) response rate at week 12, a primary end point, was significant for all tofacitinib treatment groups. Thus, an orally available tofacitinib in combination with MTX was efficacious and had a manageable safety profile. Tofacitinib at 5 and 10 mg twice a day appears suitable for further evaluation to optimise the treatment of RA.

The PTPN11 gene, encoding the tyrosine phosphatase SHP-2, is overexpressed in rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLS) compared with osteoarthritis (OA) FLS and promotes RA FLS invasiveness. Here, we explored the molecular basis for PTPN11 overexpression in RA FLS and the role of SHP-2 in RA pathogenesis. Using computational methods, we identified a putative enhancer in PTPN11 intron 1, which contained a glucocorticoid receptor– binding (GR-binding) motif. This region displayed enhancer function in RA FLS and contained 2 hypermethylation sites in RA compared with OA FLS. RA FLS stimulation with the glucocorticoid dexamethasone induced GR binding to the enhancer and PTPN11 expression. Glucocorticoid responsiveness of PTPN11 was significantly higher in RA FLS than OA FLS and required the differentially methylated CpGs for full enhancer function. SHP-2 expression was enriched in the RA synovial lining, and heterozygous Ptpn11 deletion in radioresistant or innate immune cells attenuated K/BxN serum transfer arthritis in mice. Treatment with SHP-2 inhibitor 11a-1 reduced RA FLS migration and responsiveness to TNF and IL-1β stimulation and reduced arthritis severity in mice. Our findings demonstrate how abnormal epigenetic regulation of a pathogenic gene determines FLS behavior and demonstrate that targeting SHP-2 or the SHP-2 pathway could be a therapeutic strategy for RA.