Histone Methylation and STAT‐3 Differentially Regulate Interleukin‐6–Induced Matrix Metalloproteinase Gene Activation in Rheumatoid Arthritis Synovial Fibroblasts

Abstract

Objective. Synovial fibroblasts (SFs) produce matrix-degrading enzymes that cause joint destruction in rheumatoid arthritis (RA). Epigenetic mechanisms play a pivotal role in autoimmune diseases. This study was undertaken to elucidate the epigenetic mechanism that regulates the transcription of matrix metalloproteinases (MMPs) in RASFs.Methods. MMP gene expression and histone methylation profiles in the MMP promoters were examined in RASFs. The effect of WD repeat domain 5 (WDR5) silencing on histone methylation and MMP gene expression in RASFs was analyzed. MMP gene expression, surface expression of the interleukin-6 (IL-6) receptor, phosphorylation of STAT-3, and binding of STAT-3 in the MMP promoters were investigated in RASFs stimulated with IL-6.Results. The MMP-1, MMP-3, MMP-9, and MMP-13 genes were actively transcribed in RASFs. Correspondingly, the level of histone H3 trimethylated at lysine 4 (H3K4me3) was elevated, whereas that of H3K27me3 was suppressed in the MMP promoters in RASFs. The decrease in H3K4me3 via WDR5 small interfering RNA reduced the levels of messenger RNA for MMP-1, MMP-3, MMP-9, and MMP-13 in RASFs. Interestingly, IL-6 signaling significantly increased the expression of MMP-1, MMP-3, and MMP-13, but not MMP-9, in RASFs. Although the IL-6 signaling pathway was similarly active in RASFs and osteoarthritis SFs, STAT-3 bound to the MMP-1, MMP-3, and MMP-13 promoters, but not the MMP-9 promoter, after IL-6 stimulation in RASFs.Conclusion. Our findings indicate that histone methylation and STAT-3 regulate spontaneous and IL-6-induced MMP gene activation in RASFs. The combination of chromatin structure and transcription factors may regulate distinct arthritogenic properties of RASFs.Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease that results in progressive joint destruction and is difficult to treat effectively (1). Several lines of evidence suggest that synovial fibroblasts (SFs) are characterized by an activated and aggressive phenotype with a tumor-like appearance and play a major role in the pathogenesis of RA (2). RASFs produce a variety of proteolytic enzymes, such as matrix metalloproteinases (MMPs) and cathepsins. These enzymes degrade articular cartilage, which is mainly composed of an extracellular matrix (ECM) that consists of proteoglycans and type II collagen (3).The MMPs are a family of zinc-dependent endopeptidases that have the catalytic extracellular activity of degrading the ECM components in a neutral pH environment (4). Twenty-three human MMPs have been identified and grouped into different subfamilies, including the collagenases, gelatinases, stromelysins, matrilysins, and membrane-type MMPs, according to

Elevated Wall Tension Initiates Interleukin-6 Expression and Abdominal Aortic Dilation

“…Additional flow cytometric analysis of cells expressing the myeloid lineage marker CD11b + along with the murine mature macrophage marker F4/80 detected increased aortic macrophage accumulation under conditions of continuous IL-6 infusion, presumably due to local MCP-1 production and secretion. Since these cells are the documented source of several matrix metalloproteinases (MMPs) and cathepsins (Cts) known to be instrumental in AAA development, 34,35 and more specifically, that MMP-9 and Cts contain a STAT3 binding site in their promoter regions, 36,37 the medial accumulation of macrophages supports the pivotal role of the IL-6-STAT3 pathway in pathophysiology of aortic remodeling. Furthermore, accumulation of macrophages with an anti-inflammatory phenotype, frequently referred to as M2 or nonclassical macrophages, may be directed by the IL-6-STAT3 pathway with potential for subsequent profibrotic contribution to account for not only increased wall thickness but also elevated lumen diameter.…”

The Histone Modification Code in the Pathogenesis of Autoimmune Diseases

“…Matrix metalloproteinases (MMPs) degrade articular cartilage and play an important role in joint destruction in RA. The expression of MMP-1, MMP-3, MMP-9, and MMP-13 is high in RASFs and the levels of the active histone marker H3K4me3 are increased, whereas those of the repressive histone marker H3K27me3 are decreased in the MMP promoters in RASFs [84]. Because WD (tryptophan-aspartate) repeat domain 5 (WDR5) is a core subunit of the complex proteins associated with SET1 (COMPASS) or COMPASS-like complexes that catalyze H3K4 methylation, WDR5 is required for the generation of H3K4me3.…”

Matrix Metalloproteinase Gene Activation Resulting from Disordred Epigenetic Mechanisms in Rheumatoid Arthritis

“…RASFs secrete various proteases, including MMPs that degrade ECM components, mainly proteoglycans and collagens, of articular cartilage in the affected joints [100]. Since MMP-1, MMP-3, MMP-9, and MMP-13 expression is upregulated in RASFs, MMPs are considered to play a critical role in the degeneration of cartilage in RA joints [17]. MMP-1 (collagenase 1) and MMP-13 (collagenase 3) cleave collagens, whereas MMP-3 (stromelysin 1) and MMP-9 (gelatinase B) target proteoglycans that are comprised of aggrecan.…”

“…IL-6 is another pro-inflammatory cytokine that is associated with the pathogenesis of RA [16]. Recently, IL-6 was also reported to induce MMP gene activation through the binding of signal transducer and activator of transcription (STAT) 3 to MMP promoters in RA synovial fibroblasts (SFs) [17]. Epigenetic changes have been shown to affect chromatin structure without a change in DNA sequence itself.…”