ABSTRACT
Indoleamine 2,3-dioxygenase (IDO) is a key negative regulator of immune responses and has been implicated in tumor tolerance, autoimmune disease and asthma. IDO was detected in the joint synovial tissue in the inflammatory microenvironment of rheumatoid arthritis (RA), but IDO expression in joint synovial tissue is not sufficient to overcome the inflamed synovial environment. This study aimed to unravel the mechanisms involving the failure to activate tolerogenic IDO in the inflamed joint. We demonstrate that both poly (I:C) and lipopolysaccharide (LPS) induce expression of IDO in synovial fibroblasts. However, inflammatory cytokines such as IL-17, TNF-alpha, IL-12, IL-23 and IL-16 did not induce IDO expression. Poly (I:C) appeared to induce higher IDO expression than did LPS. Surprisingly, toll-like receptor (TLR)4-mediated IDO expression was upregulated after depletion of myeloid differentiation primary response protein 88 (MyD88) in synovial fibroblasts using small interfering RNA (siRNA). IDO, TLR3 and TLR4 were highly expressed in synovial tissue of RA patients compared with that of osteoarthritis patients. In addition, RA patients with severe disease activity had higher levels of expression of IDO, TLR3 and TLR4 in the synovium than patients with mild disease activity. These data suggest that upregulation of IDO expression in synovial fibroblasts involves TLR3 and TLR4 activation by microbial constituents. We showed that the mechanisms responsible for IDO regulation primarily involve MyD88 signaling in synovial fibroblasts, as demonstrated by siRNA-mediated knockdown of MyD88.
Subject(s)
Humans , Adaptor Proteins, Vesicular Transport/genetics , Arthritis, Rheumatoid/metabolism , Blotting, Western , Cells, Cultured , Fibroblasts/drug effects , Immunohistochemistry , Indoleamine-Pyrrole 2,3,-Dioxygenase/genetics , Interleukin-12/pharmacology , Interleukin-16/pharmacology , Interleukin-17/pharmacology , Interleukin-23/pharmacology , Lipopolysaccharides/pharmacology , Myeloid Differentiation Factor 88/genetics , Poly I-C/pharmacology , Polymerase Chain Reaction , RNA, Small Interfering/genetics , Synovial Membrane/cytology , Toll-Like Receptor 4/genetics , Tumor Necrosis Factor-alpha/pharmacologyABSTRACT
OBJECTIVE: Interleukin-15 (IL-15) recruits and activates synovial T cells, and IL-15 plays an important role in amplifying and perpetuating inflammation in the pathogenesis of rheumatoid arthritis (RA). Stromal cell-derived factor-1 (SDF-1) is a potent chemoattractant for memory T cells in the inflamed RA synovium. This study investigated the effect of IL-15 on SDF-1 production in RA fibroblast-like synoviocytes (FLS). METHODS: The expressions of IL-15 and SDF-1 were determined from the synovium of patients with RA and osteoarthritis (OA) by performing immunohistochemistry. The expressions of SDF-1 was measured from the RA FLS that were cultured with IL-15 and IL-17 by real-time RT-PCR and ELISA. The SDF-1 expression was also measured, via ELISA, from the RA FLS stimulated by IL-15 together with the inhibitors of such intracellular signal molecules as phosphatidylinositol 3-kinase (PI 3-kinase, LY294002), STAT3 (AG490), MAP Kinase (PD98059), NF-kappaB (parthenolide) and activator protein 1 (AP-1, curcumin). RESULTS: IL-15 and SDF-1 were mainly expressed in the RA synovium compared to that of the OA synovium. IL-15 increased the SDF-1 expressions and it, and had an additive effect with IL-17 on the SDF-1 expressions in the cultured RA FLS. The IL-15 induced increase of the SDF-1 expression in the cultured RA FLS was blocked by the inhibitors of PI 3-kinase, NF-kappaB and AP-1. CONCLUSION: The SDF-1 expression was increased in the RA synovium and it was up-regulated by IL-15 in the RA FLS through the PI 3-kinase, NF-kappaB, and AP-1 pathways. These results imply that the IL-15 induced increase of the SDF-1 expressions may be involved in the immunopathogenesis of RA.
Subject(s)
Humans , Arthritis, Rheumatoid , Enzyme-Linked Immunosorbent Assay , Fibroblasts , Immunohistochemistry , Inflammation , Interleukin-15 , Interleukin-17 , Memory , NF-kappa B , Osteoarthritis , Phosphatidylinositol 3-Kinase , Phosphatidylinositol 3-Kinases , Phosphotransferases , Synovial Membrane , T-Lymphocytes , Transcription Factor AP-1ABSTRACT
OBJECTIVE: Interleukin-15 (IL-15) recruits and activates synovial T cells, and IL-15 plays an important role in amplifying and perpetuating inflammation in the pathogenesis of rheumatoid arthritis (RA). Stromal cell-derived factor-1 (SDF-1) is a potent chemoattractant for memory T cells in the inflamed RA synovium. This study investigated the effect of IL-15 on SDF-1 production in RA fibroblast-like synoviocytes (FLS). METHODS: The expressions of IL-15 and SDF-1 were determined from the synovium of patients with RA and osteoarthritis (OA) by performing immunohistochemistry. The expressions of SDF-1 was measured from the RA FLS that were cultured with IL-15 and IL-17 by real-time RT-PCR and ELISA. The SDF-1 expression was also measured, via ELISA, from the RA FLS stimulated by IL-15 together with the inhibitors of such intracellular signal molecules as phosphatidylinositol 3-kinase (PI 3-kinase, LY294002), STAT3 (AG490), MAP Kinase (PD98059), NF-kappaB (parthenolide) and activator protein 1 (AP-1, curcumin). RESULTS: IL-15 and SDF-1 were mainly expressed in the RA synovium compared to that of the OA synovium. IL-15 increased the SDF-1 expressions and it, and had an additive effect with IL-17 on the SDF-1 expressions in the cultured RA FLS. The IL-15 induced increase of the SDF-1 expression in the cultured RA FLS was blocked by the inhibitors of PI 3-kinase, NF-kappaB and AP-1. CONCLUSION: The SDF-1 expression was increased in the RA synovium and it was up-regulated by IL-15 in the RA FLS through the PI 3-kinase, NF-kappaB, and AP-1 pathways. These results imply that the IL-15 induced increase of the SDF-1 expressions may be involved in the immunopathogenesis of RA.
Subject(s)
Humans , Arthritis, Rheumatoid , Enzyme-Linked Immunosorbent Assay , Fibroblasts , Immunohistochemistry , Inflammation , Interleukin-15 , Interleukin-17 , Memory , NF-kappa B , Osteoarthritis , Phosphatidylinositol 3-Kinase , Phosphatidylinositol 3-Kinases , Phosphotransferases , Synovial Membrane , T-Lymphocytes , Transcription Factor AP-1ABSTRACT
BACKGROUND/AIMS: This study was undertaken to identify the intracellular signaling pathway involved in induction of macrophage migration inhibitory factor (MIF) in human rheumatoid arthritis (RA) synovial fibroblasts. METHODS: Human RA synovial fibroblasts were treated with concanavalin A (ConA), various cytokines, and inhibitors of signal transduction molecules. The production of MIF by synovial fibroblasts was measured in culture supernatants by ELISA. The expression of MIF mRNA was determined using reverse transcriptase polymerase chain reaction (RT-PCR) and real-time PCR. Phosphorylation of p38 mitogen-activated protein (MAP) kinase in synovial fibroblasts was confirmed using Western blotting. The expression of MIF and p38 MAP kinase in RA synovium was determined using dual immunohistochemistry. RESULTS: The production of MIF by RA synovial fibroblasts increased in a dose-dependent manner after ConA stimulation. MIF was also induced by interferon-gamma, CD40 ligand, interleukin-15, interleukin-1beta, tumor necrosis factor-alpha, and transforming growth factor-beta. The production of MIF by RA synovial fibroblasts was significantly reduced after inhibition of p38 MAP kinase. The expression of MIF and p38 MAP kinase was upregulated in the RA synovium compared with the osteoarthritis synovium. CONCLUSIONS: These results suggest that MIF production was induced through a p38 MAP-kinase-dependent pathway in RA synovial fibroblasts.