title: The pattern-recognition receptor nucleotide-binding oligomerization domain--containing protein 1 promotes production of inflammatory mediators in rheumatoid arthritis synovial fibroblasts.
abstract: OBJECTIVE
  Pattern-recognition receptors (PRRs), such as Toll-like receptors (TLRs) and nucleotide-binding oligomerization domain-containing protein 2 (NOD-2), have been shown to contribute to the pathogenesis of rheumatoid arthritis (RA). The aim of this study was to analyze the expression, regulation, and function of the PRR NOD-1 in RA synovial fibroblasts (RASFs), and to examine its interaction with other PRRs.
  
  
  METHODS
  Expression of NOD-1 was analyzed by immunohistochemistry in synovial tissue from RA patients, psoriatic arthritis patients, gout patients, and osteoarthritis (OA) patients. RASFs and human monocyte-derived macrophages (HMDMs) were stimulated with L-alanyl-γ-D-glutamyl-meso-diaminopimelic acid, palmitoyl-3-cysteine-serine-lysine-4, poly(I-C), lipopolysaccharide, heat-inactivated bacteria, tumor necrosis factor α (TNFα), or interleukin-1β (IL-1β). Expression levels of IL-6, CCL5, matrix metalloproteinases (MMPs), NODs, and TLRs were measured by real-time reverse transcription-polymerase chain reaction and/or enzyme-linked immunosorbent assay. NOD-1 and NOD-2 were silenced with target-specific small interfering RNA. Phosphorylation of IL-1 receptor-associated kinase 1 (IRAK-1) was measured by Western blotting.
  
  
  RESULTS
  Expression of NOD-1 protein was significantly increased in RA synovium compared to OA synovium. The basal expression of NOD-1 was similar in RASFs, OASFs, healthy control peripheral blood mononuclear cells, and healthy control HMDMs. Stimulation of RASFs with TLR-3 up-regulated the expression of NOD-1. Expression of IL-6, CCL5, MMPs, TLR-2, and NOD-2 was significantly up-regulated in RASFs by stimulation with the NOD-1 ligand. A synergistic effect on IL-6 production was observed in cells stimulated with NOD-1 and TLR-2 ligands or NOD-1 and TLR-4 ligands. Silencing of NOD-1, but not NOD-2, decreased the levels of IL-6 in RASFs after stimulation with TLR-2 and IL-1β, and blocked the phosphorylation of IRAK-1.
  
  
  CONCLUSIONS
  NOD-1 is strongly expressed in different cell types in the synovial tissue of patients with RA. These results indicate that NOD-1, either alone or interacting with other inflammatory mediators, can play an important role in the chronic and destructive inflammation of the joints in RA.
authors.affiliation: University Hospital Zurich, Zurich Center of Integrative Human Physiology, and University of Zurich, Zurich, Switzerland.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Yokota
authors.forename: Takashi
authors.initials: T
authors.lastname: Miyazaki
authors.forename: Hossein
authors.initials: H
authors.lastname: Hemmatazad
authors.forename: Renate E
authors.initials: RE
authors.lastname: Gay
authors.forename: Christoph
authors.initials: C
authors.lastname: Kolling
authors.forename: Ursula
authors.initials: U
authors.lastname: Fearon
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Suzuki
authors.forename: Toshihide
authors.initials: T
authors.lastname: Mimura
authors.forename: Steffen
authors.initials: S
authors.lastname: Gay
authors.forename: Caroline
authors.initials: C
authors.lastname: Ospelt
mesh_terms: D015535:Arthritis, Psoriatic / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D001172:Arthritis, Rheumatoid / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D002478:Cells, Cultured; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D015870:Gene Expression; D006073:Gout / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D006801:Humans; D007155:Immunologic Factors / Q000494:pharmacology; D018836:Inflammation Mediators / Q000378:metabolism*; D053473:Nod2 Signaling Adaptor Protein / Q000235:genetics / Q000378:metabolism*; D010003:Osteoarthritis / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D013583:Synovial Membrane / Q000378:metabolism* / Q000473:pathology
chemical_list: D007155:Immunologic Factors; D018836:Inflammation Mediators; C429018:NOD2 protein, human; D053473:Nod2 Signaling Adaptor Protein