Abstract
OBJECTIVE: Previously, we reported that pattern-recognition receptors (PRRs) such as TLRs and NOD2 contribute to the pathogenesis of rheumatoid arthritis (RA). Now, we analyzed the expression, regulation and function of the PRR NOD1 in RA synovial fibroblasts (RASFs) and its interaction with other PRRs. METHODS: Expression of NOD1 was analyzed by immunohistochemistry in RA, psoriasis arthritis, gout and OA synovial tissues. RASFs and monocyte-derived macrophages (MDMs) were stimulated with Tri-DAP, Pam3, PIC, LPS, heat inactivated bacteria, TNF-α or IL-1β. IL-6, CCL5, MMPs, NODs and TLRs were measured by Real-time PCR and/or ELISA. NOD1 and NOD2 were silenced with target specific siRNA. Phosphorylation of IRAK1 was measured by Western blot. RESULTS: In RA synovium, expression of NOD1 protein was significantly increased compared to OA synovium. There was similar basal expression of NOD1 in RASFs, OASFs, healthy controls PBMCs and MDMs. TLR3 stimulation further up-regulated NOD1 expression in RASFs. Expression of IL-6, CCL5, MMPs, TLR2 and NOD2 was significantly up-regulated in RASFs by stimulation with the NOD1 ligand. There was a synergistic effect in IL-6 production by stimulation with NOD1 and TLR2 ligands and NOD1 and TLR4 ligands. Silencing of NOD1, but not NOD2 decreased IL-6 levels after TLR2 and IL-1β stimulation and blocked phosphorylation of IRAK1. CONCLUSION: NOD1 is strongly expressed in synovial tissues from RA patients in different cell types. Our data indicate that NOD1 alone and in interaction with other inflammatory activators plays an important role in the chronic and destructive joint inflammation in RA.
Yokota, K