Session Title: Rheumatoid Arthritis: Human Etiology and Pathogenesis II
Session Type: Abstract Submissions (ACR)
Background/Purpose: Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease which causes progressive joint destruction. In spite of the modern medications including biologic reagents, it is still hard to cure RA completely. A line of evidence suggests that synovial fibroblasts (SFs) play an important role in the pathogenesis of RA. RASFs produce matrix-degrading enzymes and promote bone and cartilage destruction. Recent advances have revealed that epigenetic mechanisms including histone modifications are important regulators in gene transcription. We have hypothesized that aberrant epigenetic regulations might cause long-lasting synovitis in RA.
Methods: Human SFs were enzymatically isolated from knee articular synovial tissues removed at the time of joint replacement from patients with RA or osteoarthritis (OA) as a control. We compared matrix metalloproteinases (MMPs) gene expression by quantitative RT-PCR (qRT-PCR) and histone methylation in their promoters by chromatin immunoprecipitation (ChIP) assay in RASFs and OASFs. Interleukin-6 (IL-6) is an inflammatory cytokine and has been proved to be involved in the pathogenesis of RA. It was unknown whether IL-6 affected MMPs gene transcription, so we stimulated SFs with IL-6 and/or soluble IL-6 receptor α (sIL-6Rα) and examined the change in MMPs gene expression by qRT-PCR. IL-6 induces Signal Transducer and Activator of Transcription 3 (STAT3) activation. To elucidate the mechanisms of IL-6 dependent MMPs gene transcriptional activation in RASFs, we investigated cell surface expressions of IL-6 receptor (gp130 and IL-6Rα) by flow cytometry, phospho-STAT3 (p-STAT3) expression by immunoblotting, and STAT3 binding to the MMP1, 3, 9, and 13 promoters by ChIP assay.
Results: MMP1, 3, 9, and 13 mRNA levels were significantly higher in RASFs than in OASFs. Tri-methylation of histone 3 lysine 4 (H3K4me3) is associated with active gene transcription and tri-methylation of histone 3 lysine 27 (H3K27me3) with gene silencing. The amounts of H3K4me3 significantly increased whereas those of H3K27me3 substantially decreased in the MMP1, 3, 9, and 13 promoters in RASFs. These data showed that histone methylation was correlated with MMP1, 3, 9, and 13 gene transcriptional activation in RASFs. Then, MMP1, 3, and 13 but not MMP9 mRNA levels significantly increased at 24 hr after stimulation with IL-6 (100 ng/ml) and sIL6Rα (100 ng/ml) in RASFs. Cell surface expressions of gp130 and IL-6Rα were comparable and STAT3 was similarly phosphorylated after stimulation with IL-6 and sIL-6Rα in RASFs and OASFs. STAT3 strongly associated with the MMP1, 3, and 13 promoters but not the MMP9 promoter in RASFs. Together, it was suggested that STAT3 binding to their promoters resulted in MMP1, 3, and 13 gene transcriptional activation after stimulation with IL-6 and sIL-6Rα in RASFs.
Conclusion: Characteristic histone methylation is associated with IL-6 dependent MMPs gene transcriptional activation and possibly arthritogenic properties of RASFs.
T. T. Wada,
Y. F. Asanuma,
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/altered-histone-methylation-is-associated-with-il-6-dependent-matrix-metalloproteinases-gene-transcriptional-activation-in-rheumatoid-arthritis-synovial-fibroblasts/