title: Tumor necrosis factor α induces sustained signaling and a prolonged and unremitting inflammatory response in rheumatoid arthritis synovial fibroblasts.
abstract: OBJECTIVE
  The nonresolving character of synovial inflammation in rheumatoid arthritis (RA) is a conundrum. To identify the contribution of fibroblast-like synoviocytes (FLS) to the perpetuation of synovitis, we investigated the molecular mechanisms that govern the tumor necrosis factor α (TNFα)-driven inflammatory program in human FLS.
  
  
  METHODS
  FLS obtained from the synovial tissues of patients with RA or osteoarthritis were stimulated with TNFα and assayed for gene expression and cytokine production by real-time quantitative reverse transcription-polymerase chain reaction analysis and enzyme-linked immunosorbent assay. NF-κB signaling was evaluated by Western blotting. Histone acetylation, chromatin accessibility, and NF-κB p65 and RNA polymerase II (Pol II) occupancy at the interleukin-6 (IL-6) promoter were measured by chromatin immunoprecipitation and restriction enzyme accessibility assays.
  
  
  RESULTS
  In FLS, TNFα induced prolonged transcription of messenger RNA (mRNA) for IL-6 and progressive accumulation of IL-6 protein over 4 days. Similarly, induction of mRNA for CXCL8/IL-8, CCL5/RANTES, matrix metalloproteinase 1 (MMP-1), and MMP-3 after TNFα stimulation was sustained for several days. This contrasted with the macrophage response to TNFα, which characteristically involved a transient increase in the expression of proinflammatory genes. In FLS, TNFα induced prolonged activation of NF-κB signaling and sustained transcriptional activity, as indicated by increased histone acetylation, chromatin accessibility, and p65 and Pol II occupancy at the IL-6 promoter. Furthermore, FLS expressed low levels of the feedback inhibitors A20-binding inhibitor of NF-κB activation 3 (ABIN-3), IL-1 receptor-associated kinase M (IRAK-M), suppressor of cytokine signaling 3 (SOCS-3), and activating transcription factor 3 (ATF-3), which terminate inflammatory responses in macrophages.
  
  
  CONCLUSIONS
  TNFα signaling is not effectively terminated in FLS, which leads to an uncontrolled inflammatory response. The results suggest that prolonged and sustained inflammatory responses by FLS in response to synovial TNFα contribute to the persistence of synovial inflammation in RA.
authors: Hospital for Special Surgery and Weill Cornell Graduate School of Medical Sciences, New York, New York 10021, USA.
authors: Angela
authors: A
authors: Lee
authors: Yu
authors: Y
authors: Qiao
authors: Galina
authors: G
authors: Grigoriev
authors: Janice
authors: J
authors: Chen
authors: Kyung-Hyun
authors: KH
authors: Park-Min
authors: Sung Ho
authors: SH
authors: Park
authors: Lionel B
authors: LB
authors: Ivashkiv
authors: George D
authors: GD
authors: Kalliolias
mesh_terms: D001172:Arthritis, Rheumatoid / Q000150:complications / Q000235:genetics / Q000378:metabolism*; D016022:Case-Control Studies; D002478:Cells, Cultured; D016207:Cytokines / Q000235:genetics / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism*; D020869:Gene Expression Profiling; D006801:Humans; D007249:Inflammation / Q000150:complications / Q000235:genetics / Q000378:metabolism*; D018836:Inflammation Mediators / Q000378:metabolism*; D008264:Macrophages / Q000378:metabolism; D010003:Osteoarthritis / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013583:Synovial Membrane / Q000166:cytology / Q000378:metabolism*; D015533:Transcriptional Activation; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
chemical_list: D016207:Cytokines; D018836:Inflammation Mediators; D014409:Tumor Necrosis Factor-alpha