Expression and function of EZH2 in synovial fibroblasts: epigenetic repression of the Wnt inhibitor SFRP1 in rheumatoid arthritis

Abstract

OBJECTIVES: /st> To study the expression, regulation and function of the histone methyltransferase enhancer of zeste homologue 2 (EZH2) in synovial fibroblasts (SF) from patients with rheumatoid arthritis (RA) and osteoarthritis (OA). METHODS: /st> SF were obtained from RA and OA patients undergoing joint surgery. Expression levels were assessed by quantitative real-time PCR and western blot. Kinase inhibitors and reporter gene assays were employed to study signalling pathways. Functional analyses included EZH2 overexpression by plasmid transfection and gene silencing by small interfering RNA. Chromatin immunoprecipitation assay was used to analyse histone methylation within distinct promoter regions. RESULTS: /st> By studying the expression and function of EZH2 in SF the authors found that EZH2 is overexpressed in rheumatoid arthritis synovial fibroblasts (RASF) and further induced by tumour necrosis factor alpha through the nuclear factor kappa B and Jun kinase pathways. As a target gene of EZH2 the authors identified secreted frizzled-related protein 1 (SFRP1), an inhibitor of Wnt signalling, which is associated with the activation of RASF, and show that SFRP1 expression correlates with the occupation of its promoter with activating and silencing histone marks. CONCLUSIONS: /st> These data strongly suggest that the chronic inflammatory environment of the RA joint induces EZH2 and thus might cause changes in the epigenetic programmes of SF. Expression and function of EZH2 in synovial fibroblasts: epigenetic repression of the Wnt inhibitor SFRP1 in rheumatoid arthritis ResultsBy studying expression and function of EZH2 in SF we found that EZH2 is overexpressed in RASF and further induced by tumour necrosis factor alpha through the NF-B and Jun kinase pathways. As a target gene of EZH2 we identified secreted frizzled related protein (SFRP)1, an inhibitor of Wnt signalling, which is associated with the activation of RASF, and show that SFRP1 expression correlates with the occupation of its promoter with activating and silencing histone marks. ConclusionsOur data strongly suggest that the chronic inflammatory environment of the RA joint induces EZH2and, thus, might cause changes in the epigenetic programmes of SF.

Epigenome Analysis Reveals TBX5 as a Novel Transcription Factor Involved in the Activation of Rheumatoid Arthritis Synovial Fibroblasts

“…The ChIP assay was done as described previously (15). The primers used for qPCR are shown in Table I.…”

Epigenetics Changes in the RA Synovium

“…Expression of retrotransposons often occurs in cancer cells, and is connected to loss of methylation in transformed cells [64]. The expression of LINE-1 in RA DR3 decreased Promoter hypermethylation [66] Histone acetylation HDAC4 MMP-1 increased Increased H4 acetylation at MMP1 promoter [93] Histone methylation EZH2 sFRP1 decreased Changes in H3 methylation at sFRP1 promoter [95] synovium therefore strongly supports the hypothesis of similar epigenetic changes occurring in RA.…”

“…Expression of the histone methyltransferase enhancer of Zeste homolog 2 (EZH2) is higher in RASFs compared to OASFs and was connected to decreased expression of the secreted frizzledrelated protein 1 (sFRP1) [95]. Since sFRP1 is a major inhibitor of the wnt signalling pathway, which is intrinsically activated in RASFs, also this study provides evidence for a potential link of epigenetic histone modifications and the activated phenotype of RASFs [96].…”

Epigenetics in autoimmune diseases: Pathogenesis and prospects for therapy

“…Hypermethylation also silences the expression of the DKK1 and SFRP1, which are antagonists of Wnt signaling, permitting the profibrotic pathway in RA and SSc [38,39]. These findings suggest that epigenetic mechanisms might mediate the fibrotic manifestations of RA and SSc.…”

“…Synovial fibroblasts from patients with RA show increased histone methyltransferase EZH2 which could silence SFRP1 gene expression and thereby abrogate its inhibitory role on aberrant collagen deposition by such fibroblasts [39].…”