Endogenous Galectin-9 Suppresses Apoptosis in Human Rheumatoid Arthritis Synovial Fibroblasts.

Galectin-9 (Gal9) has been postulated to have anti-inflammatory properties based on the ability of exogenous Gal9 to induce apoptosis in synovial fibroblasts in animal models of rheumatoid arthritis (RA). Here we aimed to assess the potential role of endogenous Galectins, including Gal9, in the inflammatory pathology of the RA synovium in humans. Firstly expression of Galectins 1-9 was determined in synovial fibroblasts (RASF) and dermal fibroblasts (DF) isolated from RA patients, the latter representing a non-inflamed site. We then further challenged the cells with pro-inflammatory TLR agonists and cytokines and assessed Galectin expression. Gal9 was found to be differentially and abundantly expressed in RASF compared to DF. Agonists of TLR3 and TLR4, along with IFNgamma were also found to induce Gal9 expression in RASF. siRNA was then used to knock-down Gal9 expression in RASF and the effects of this on apoptosis and cell viability were assessed. Increased apoptosis was observed in RASF following Gal9 knock-down. We conclude that, unlike exogenous Gal9, endogenous Gal9 is protective against apoptosis and enhances synovial fibroblast viability suggesting that its role in RA is both pathogenic and pro-inflammatory.

Galectin 3 induces a distinctive pattern of cytokine and chemokine production in rheumatoid synovial fibroblasts via selective signaling pathways.

OBJECTIVE: High expression of galectin 3 at sites of joint destruction in rheumatoid arthritis (RA) suggests that galectin 3 plays a role in RA pathogenesis. Previous studies have demonstrated the effects of galectins on immune cells, such as lymphocytes and macrophages. This study was undertaken to investigate the hypothesis that galectin 3 induces proinflammatory effects in RA by modulating the pattern of cytokine and chemokine production in synovial fibroblasts. METHODS: Matched samples of RA synovial and skin fibroblasts were pretreated with galectin 3 or tumor necrosis factor alpha (TNFalpha), and the levels of a panel of cytokines, chemokines, and matrix metalloproteinases (MMPs) were determined using enzyme-linked immunosorbent assays and multiplex assays. Specific inhibitors were used to dissect signaling pathways, which were confirmed by Western blotting and NF-kappaB activation assay. RESULTS: Galectin 3 induced secretion of interleukin-6 (IL-6), granulocyte-macrophage colony-stimulating factor, CXCL8, and MMP-3 in both synovial and skin fibroblasts. By contrast, galectin 3-induced secretion of TNFalpha, CCL2, CCL3, and CCL5 was significantly greater in synovial fibroblasts than in skin fibroblasts. TNFalpha blockade ruled out autocrine TNFalpha-stimulated induction of chemokines. The MAPKs p38, JNK, and ERK were necessary for IL-6 production, but phosphatidylinositol 3-kinase (PI 3-kinase) was required for selective CCL5 induction. NF-kappaB activation was required for production of both IL-6 and CCL5. CONCLUSION: Our findings indicate that galectin 3 promotes proinflammatory cytokine secretion by tissue fibroblasts. However, galectin 3 induces the production of mononuclear cell-recruiting chemokines uniquely from synovial fibroblasts, but not matched skin fibroblasts, via a PI 3-kinase signaling pathway. These data provide further evidence of the role of synovial fibroblasts in regulating the pattern and persistence of the inflammatory infiltrate in RA and suggest a new and important functional consequence of the observed high expression of galectin 3 in the rheumatoid synovium.

Functional TLR9 modulates bone marrow B cells from rheumatoid arthritis patients.

TLR9 recognizes unmethylated CpG-rich, pathogen-derived DNA sequences and represents the component of the innate immune system that heavily influences adaptive immunity and may contribute to the immunological disturbances in rheumatoid arthritis (RA). Accumulating data indicate that BM of RA patients participates in the pathogenesis of this disease as a site of proinflammatory cytokines overproduction and lymphocytes activation. Here, we investigated the functionality of TLR9 and its role in the modulation of RA BM B-cell functions. We report that BM B cells isolated from RA patients express TLR9 at the mRNA and protein levels acquired at the stage of preB/immature B-cell maturation. Stimulation of BM CD20(+) B cells by CpG-containing oligodeoxynucleotide-enhanced expression of activation markers (CD86 and CD54) triggered IL-6 and TNF-alpha secretion and cell proliferation. Significantly higher levels of eubacterial DNA encoding 16S-rRNA were found in BM samples from RA than osteoarthritis patients. Moreover, RA BM B cells exerted higher expression of CD86 than their osteoarthritis counterparts, suggesting their in situ activation via TLR9. Thus, our data indicate that TLR9 may participate in direct activation and proliferation of B cells in BM, and therefore could play a role in the pathogenesis of RA.

Prolonged, granulocyte-macrophage colony-stimulating factor-dependent, neutrophil survival following rheumatoid synovial fibroblast activation by IL-17 and TNFalpha.

INTRODUCTION: A surprising feature of the inflammatory infiltrate in rheumatoid arthritis is the accumulation of neutrophils within synovial fluid and at the pannus cartilage boundary. Recent findings suggest that a distinct subset of IL-17-secreting T-helper cells (TH17 cells) plays a key role in connecting the adaptive and innate arms of the immune response and in regulating neutrophil homeostasis. We therefore tested the hypothesis that synovial fibroblasts bridge the biological responses that connect TH17 cells to neutrophils by producing neutrophil survival factors following their activation with IL-17. METHODS: IL-17-expressing cells in the rheumatoid synovium, and IL-17-expressing cells in the peripheral blood, and synovial fluid were examined by confocal microscopy and flow cytometry, respectively. Peripheral blood neutrophils were cocultured either with rheumatoid arthritis synovial fibroblasts (RASF) or with conditioned medium from RASF that had been pre-exposed to recombinant human IL-17, TNFalpha or a combination of the two cytokines. Neutrophils were harvested and stained with the vital mitochondrial dye 3,3'-dihexyloxacarbocyanine iodide before being enumerated by flow cytometry. RESULTS: TH17-expressing CD4+ cells were found to accumulate within rheumatoid synovial tissue and in rheumatoid arthritis synovial fluid. RASF treated with IL-17 and TNFalpha (RASFIL-17/TNF) effectively doubled the functional lifespan of neutrophils in coculture. This was entirely due to soluble factors secreted from the fibroblasts. Specific depletion of granulocyte-macrophage colony-stimulating factor from RASFIL-17/TNF-conditioned medium demonstrated that this cytokine accounted for approximately one-half of the neutrophil survival activity. Inhibition of phosphatidylinositol-3-kinase and NF-kappaB pathways showed a requirement for both signalling pathways in RASFIL-17/TNF-mediated neutrophil rescue. CONCLUSION: The increased number of neutrophils with an extended lifespan found in the rheumatoid synovial microenvironment is partly accounted for by IL-17 and TNFalpha activation of synovial fibroblasts. TH17-expressing T cells within the rheumatoid synovium are likely to contribute significantly to this effect.