Open AccessExpression, regulation, and signaling of the pattern‐recognition receptor nucleotide‐binding oligomerization domain 2 in rheumatoid arthritis synovial fibroblasts
Author(s) -
Ospelt Caroline,
Brentano Fabia,
Jüngel Astrid,
Rengel Yvonne,
Kolling Christoph,
Michel Beat A.,
Gay Renate E.,
Gay Steffen
Publication year - 2009
Publication title -
arthritis & rheumatism
Language(s) - English
Resource type - Journals
eISSN - 1529-0131
pISSN - 0004-3591
DOI - 10.1002/art.24226
Subject(s) - synovial membrane , microbiology and biotechnology , nod , muramyl dipeptide , small interfering rna , matrix metalloproteinase , receptor , tumor necrosis factor alpha , electrophoretic mobility shift assay , arthritis , chemistry , biology , gene expression , immunology , transfection , immune system , biochemistry , gene
Objective Since pattern‐recognition receptors (PRRs), in particular Toll‐like receptors (TLRs), were found to be overexpressed in the synovium of rheumatoid arthritis (RA) patients and to play a role in the production of disease‐relevant molecules, we sought to determine the expression, regulation, and function of the PRR nucleotide‐binding oligomerization domain 2 (NOD‐2) in RA. Methods Expression of NOD‐2 in synovial tissues was analyzed by immunohistochemistry. Expression and induction of NOD‐2 in RA synovial fibroblasts (RASFs) were measured by conventional and real‐time polymerase chain reaction (PCR) analyses. Levels of interleukin‐6 (IL‐6) and IL‐8 were measured by enzyme‐linked immunosorbent assay (ELISA) and expression of matrix metalloproteinases (MMPs) by ELISA and/or real‐time PCR. NOD‐2 expression was silenced with small interfering RNA. Western blotting with antibodies against phosphorylated and total p38, JNK, and ERK, as well as inhibitors of p38, JNK, and ERK was performed. Activation of NF‐κB was measured by electrophoretic mobility shift assay. Results NOD‐2 was expressed by fibroblasts and macrophages in the synovium of RA patients, predominantly at sites of invasion into articular cartilage. In cultured RASFs, no basal expression of messenger RNA for NOD‐2 was detectable, but was induced by poly(I‐C), lipopolysaccharide, and tumor necrosis factor α. After up‐regulation of NOD‐2 by TLR ligands, its ligand muramyl dipeptide (MDP) increased the expression of IL‐6 and IL‐8 via p38 and NF‐κB. Stimulation with MDP further induced the expression of MMP‐1, MMP‐3, and MMP‐13. Conclusion Not only TLRs, but also the PRR NOD‐2 is expressed in the synovium of RA patients, and activation of NOD‐2 acts synergistically with TLRs in the production of proinflammatory and destructive mediators. Therefore, NOD‐2 might contribute to the initiation and perpetuation of chronic, destructive inflammation in RA.