Fraktalkine – ein proinflammatorisches Chemokin bei rheumatoider Arthritis

Fractalkine (CX3CL1), so far the only member of the CX3C class of chemokines, and its receptor, CX3CR1, are strongly expressed in the chronically inflamed synovial tissue of patients with rheumatoid arthritis (RA). Due to the specific binding of Fractalkine to its receptor, many proinflammatory reactions involved in the pathogenesis of RA are triggered. Functionally, fractalkine plays an important proinflammatory role in RA pathogenesis as characterized by induction of synovial angiogenesis, chemotaxis, activation of monocytes and T cells as well as the stimulation of proliferation and synthesis of matrix degrading enzymes (matrix metalloproteinases, MMP) in synovial fibroblasts. Fractalkine thus may represent a novel target molecule for therapeutic intervention in RA.     

Fractalkine in rheumatoid arthritis and allied conditions

Abstract

Leukocyte adhesion and trafficking at the endothelium requires both adhesion molecules and chemotactic factors. Fractalkine (CX3C) is a unique chemokine, and is expressed on tumor necrosis factor-α- and interleukin-1-activated endothelial cells (ECs). Fractalkine receptor, CX3CR1, is expressed on NK cells, monocytes, and some portion of CD4- and CD8-positive T cells. Interactions between fractalkine and CX3CR1 can mediate not only chemotaxis, but also cell adhesion in the absence of substrates for other adhesion molecules. Furthermore, fractalkine activates NK cells, leading to increased cytotoxicity and interferon-γ production. Recently, accumulating evidence has shown that fractalkine is involved in the pathogenesis of rheumatoid arthritis and allied conditions. This review examines new concepts underlying fractalkine-mediated leukocyte migration and tissue damage, focusing primarily on the pathophysiological roles of fractalkine in rheumatic diseases.     

Fractalkine in rheumatoid arthritis and allied conditions

Leukocyte adhesion and trafficking at the endothelium requires both adhesion molecules and chemotactic factors. Fractalkine (CX3C) is a unique chemokine, and is expressed on tumor necrosis factor-α- and interleukin-1-activated endothelial cells (ECs). Fractalkine receptor, CX3CR1, is expressed on NK cells, monocytes, and some portion of CD4- and CD8-positive T cells. Interactions between fractalkine and CX3CR1 can mediate not only chemotaxis, but also cell adhesion in the absence of substrates for other adhesion molecules. Furthermore, fractalkine activates NK cells, leading to increased cytotoxicity and interferon-γ production. Recently, accumulating evidence has shown that fractalkine is involved in the pathogenesis of rheumatoid arthritis and allied conditions. This review examines new concepts underlying fractalkine-mediated leukocyte migration and tissue damage, focusing primarily on the pathophysiological roles of fractalkine in rheumatic diseases.     

Proinflammatory role of fractalkine (CX3CL1) in rheumatoid arthritis

OBJECTIVE: Fractalkine (CX3CL1) represents the sole member of the so-called CX3C chemokines. In rheumatoid arthritis (RA), functional studies suggest a role for this chemokine in monocyte chemotaxis and angiogenesis in the rheumatoid synovium. We analyzed the expression of fractalkine within different T cell subsets of the peripheral blood and expression of its receptor CX3CR1 within the rheumatoid synovium to further characterize its pathogenic role in RA. METHODS: Peripheral blood mononuclear cells (PBMC) were isolated from 17 patients with RA and analyzed by flow cytometry in comparison to healthy blood donors. To identify the T helper cell cytokine profile of fractalkine-expressing cells, flow cytometric analysis of PBMC was performed after stimulation with PMA and ionomycin. Expression of fractalkine and its receptor was characterized in RA synovium by immunohistochemistry and laser capture microdissection microscopy. RESULTS: Flow cytometric analysis of fractalkine-expressing T cell subsets revealed a low proportion of fractalkine-expressing CD4+ and CD8+ T cells in both RA patients and controls. In addition, fractalkine was predominantly expressed in CD4+ T cells with a Th1-type cytokine expression profile. In RA synovium, fractalkine was detected in synovial macrophages, dendritic cells, endothelial cells, and a small proportion of T cells. The fractalkine receptor CX3CR1 was found in synovial macrophages, dendritic cells, and T cells as well as in synovial fibroblasts. Fractalkine stimulation of cultured synovial fibroblasts resulted in a marked upregulation of matrix metalloproteinase-2 (MMP-2) production. CONCLUSION: The results suggest that fractalkine may represent a Th1-type chemokine. Upregulation of MMP-2 production in synovial fibroblasts upon fractalkine stimulation in vitro supports the hypothesis of a proinflammatory role of this chemokine in RA.     

Up regulated expression of fractalkine/CX3CL1 and CX3CR1 in patients with systemic sclerosis

BACKGROUND: Fractalkine expressed on endothelial cells mediates activation and adhesion of leucocytes expressing its receptor, CX(3)CR1. Soluble fractalkine exhibits chemotactic activity for leucocytes expressing CX(3)CR1. OBJECTIVE: To determine the role of fractalkine and its receptor in systemic sclerosis (SSc) by assessing their expression levels in patients with this disease. METHODS: The expression of fractalkine and CX(3)CR1 in the skin and lung tissues was immunohistochemically examined. Circulating soluble fractalkine levels were examined by enzyme linked immunosorbent assay (ELISA). Blood samples from patients with SSc were stained for CX(3)CR1 with flow cytometric analysis. RESULTS: CX(3)CR1 levels on peripheral monocytes/macrophages and T cells were found to be raised in patients with diffuse cutaneous SSc. The numbers of cells expressing CX(3)CR1, including monocytes/macrophages, were increased in the lesional skin and lung tissues from patients with diffuse cutaneous SSc. Fractalkine was strongly expressed on endothelial cells in the affected skin and lung tissues. Soluble fractalkine levels were significantly raised in sera and were associated with raised erythrocyte sedimentation rates, digital ischaemia, and severity of pulmonary fibrosis. CONCLUSIONS: Up regulated expression of fractalkine and CX(3)CR1 cooperatively augments the recruitment of mononuclear cells expressing CX(3)CR1 into the affected tissue of SSc, leading to inflammation and vascular injury.     

T cell costimulation by fractalkine-expressing synoviocytes in rheumatoid arthritis

OBJECTIVE: Patients with rheumatoid arthritis (RA) accumulate prematurely aged T cells that have acquired a new profile of regulatory receptors. Many of the de novo-expressed receptors are typically found on natural killer cells, including CX(3)CR1, the receptor for the chemokine fractalkine (FKN). This study explored whether interactions between CX(3)CR1 and FKN are relevant for T cell functions in rheumatoid synovitis. METHODS: FKN expression was examined by real-time polymerase chain reaction and immunohistochemistry. CX(3)CR1 expression on peripheral blood T cells was analyzed by flow cytometry. T cell activation was quantified by determining proliferative responses, interferon-gamma (IFNgamma) secretion, and granule release. Fibroblast-like synoviocyte (FLS)/T cell adhesion was measured by the retention of 5-carboxyfluorescein diacetate succinimidyl ester-labeled T cells on FLS monolayers. RESULTS: FKN was expressed on cultured synovial fibroblasts and hyperplastic synoviocytes in the rheumatoid tissue. Among CD4+ T cells, only senescent CD28- T cells were positive for CX(3)CR1 (P < 0.001). Such CD4+,CD28-,CX(3)CR1+ T cells strongly adhered to FLS, with soluble FKN blocking the interaction. FKN expressed on FLS costimulated T cell-activating signals and amplified proliferation, IFNgamma production, and expulsion of cytoplasmic granules. CONCLUSION: Senescent CD4+ T cells that accumulate in rheumatoid arthritis aberrantly express CX(3)CR1. FKN, which is membrane-anchored on synoviocytes, enhances CD4+ T cell adhesion, provides survival signals, and costimulates the production of proinflammatory cytokines as well as the release of granules. By virtue of their altered receptor profile, senescent CD4+ T cells receive strong stimulatory signals from nonprofessional antigen-presenting cells in the synovial microenvironment.     

Fractalkine与肾脏疾病

随着人们预期寿命的增加和糖尿病肾病发病率的增长,肾脏疾病将给社会带来巨大挑战。Frac-talkine(CX3CL1)是目前已知惟一的CX3C-趋化因子,它既可作为趋化因子,也可作为黏附因子,CX3CR1是其特异受体。关于Fractalkine与肾脏疾病之间的研究近年来有许多进展,本文综述了这方面的一些文献。     

CX3CR1基因多态性与冠心病的相关性

目的 研究Fractalkine受体CX3CR1基因多态性(249V/I和280T/M)与冠心病的相关性.方法 应用聚合酶链反应限制片长多态性方法对139例冠心病患者和90例对照者的CX3CR1基因多态性进行分析,比较CX3CR1基因多态性在两组之间的差异性.结果 等位基因I249在对照组中的分布频率明显高于冠心病组(P<0.05);冠心病组280T/M基因型和等位基因频率分布与对照组比较无显著性差异(P>0.05).结论 Fractalkine受体CX3CR1等位基因I249变异可能与冠心病的发病危险性下降有关,CX3CR1基因多态性与中国南方汉族人群冠心病的发生存在相关性.     

Fractalkine and CX3CR1 are involved in the recruitment of intraepithelial lymphocytes of intrahepatic bile ducts

Fractalkine is a chemokine with both chemoattractant and cell-adhesive functions, and in the intestine it is involved with its receptor CX3CR1 in the chemoattraction and recruitment of intraepithelial lymphocytes. We examined the pathophysiological roles of fractalkine and CX3CR1 in normal and diseased bile ducts. Expression of fractalkine and CX3CR1 were examined in liver tissues from patients with primary biliary cirrhosis (17 cases) and controls (9 cases of primary sclerosing cholangitis, 10 cases of extrahepatic biliary obstruction, 20 cases of chronic viral hepatitis C, and 18 cases of histologically normal livers). Expression of fractalkine in biliary epithelial cells (BECs) in response to cytokine treatments was examined using a human cholangiocarcinoma cell line (HuCC-T1) and human intrahepatic BEC line. The chemotaxis of CX3CR1-expressing monocytes (THP-1) toward fractalkine was assayed using chemotaxis chambers. Fractalkine messenger RNA/protein were expressed on BECs of normal and diseased bile ducts, and their expression was upregulated in injured bile ducts of primary biliary cirrhosis. CX3CR1 was expressed on infiltrating mononuclear cells in portal tracts and on CD3(+), CD4(+), and CD8(+) intraepithelial lymphocytes of injured bile ducts in primary biliary cirrhosis. Fractalkine messenger RNA expression was upregulated in two cultured BECs on treatment with lipopolysaccharide and Th1-cytokines (interleukin 1beta, interferon gamma, and tumor necrosis factor alpha). THP-1 cells showed chemotaxis toward fractalkine secreted by cultured cells. In conclusion, Th1-cytokine predominance and lipopolysaccharide in the microenvironment of injured bile ducts resulting from primary biliary cirrhosis induce the upregulation of fractalkine expression in BECs, followed by the chemoattraction of CX3CR1-expressing mononuclear cells, including CD4(+) and CD8(+) T cells, and their adhesion to BECs and the accumulation of biliary intraepithelial lymphocytes.     

Polymorphisms of Fractalkine receptor CX3CR1 and plasma levels of its ligand CX3CL1 in colorectal cancer patients

Background and aims The chemokine Fractalkine/CX3CL1, which is expressed by epithelial cells within normal colorectal mucosa and in colorectal cancer (CRC), is thought to have a crucial role in colorectal mucosal immunity by recruiting leucocytes via the receptor CX3CR1. The purpose of this study was to investigate two single-nucleotide polymorphisms of the Fractalkine receptor/CX3CR1 gene, V249I and T280M, in CRC to find out whether they occur more often in patients with CRC than in non-CRC individuals. In the search for tumour markers, we also intended to determine whether plasma levels of Fractalkine were correlated with parameters such as Dukes’ stage, tumour localisation, gender and age in CRC patients. Materials and methods Genomic deoxyribonucleic acid from 223 CRC patients and 229 controls was amplified by polymerase chain reaction, and the polymorphisms were detected by the restriction fragment length polymorphism analysis. Fractalkine/CX3CL1 was analysed in plasma from 62 CRC patients and 78 controls using enzyme-linked immunosorbent assay. Results The variant V249I was significantly different in genotype and allelic distribution between CRC patients and control subjects, P = 0.028 and P = 0.048, respectively. We also found that individuals with the I249 allele in homozygote state were less frequent in the CRC group (3.1%) compared with controls (9.2%; P = 0.008). No significant difference was observed regarding Fractalkine/CX3CL1 levels in plasma between patients and the control group. Conclusion Our results suggest that the lack of the allele I249 of the CX3CR1 gene may play a partial or minor role in CRC and that plasma Fractalkine/CX3CL1 does not seem to be a useful tumour marker that reflects the disease outcome of CRC.     

Fractalkine in vascular biology: from basic research to clinical disease

Fractalkine (now also called CX3CL1) is a unique chemokine that functions not only as a chemoattractant but also as an adhesion molecule and is expressed on endothelial cells activated by proinflammatory cytokines, such as interferon-gamma and tumor necrosis factor-alpha. The fractalkine receptor, CX3CR1, is expressed on cytotoxic effector lymphocytes, including natural killer (NK) cells and cytotoxic T lymphocytes, which contain high levels of intracellular perforin and granzyme B, and on macrophages. Soluble fractalkine causes migration of NK cells, cytotoxic T lymphocytes, and macrophages, whereas the membrane-bound form captures and enhances the subsequent migration of these cells in response to secondary stimulation with other chemokines. Furthermore, stimulation through membrane-bound fractalkine activates NK cells, leading to increased cytotoxicity and interferon-gamma production. Recently, accumulating evidence has shown that fractalkine is involved in the pathogenesis of various clinical disease states or processes, such as atherosclerosis, glomerulonephritis, cardiac allograft rejection, and rheumatoid arthritis. In addition, polymorphisms in CX3CR1, which reduce its binding activity to fractalkine, have been reported to increase the risk of HIV disease and to reduce the risk of coronary artery disease. This review will examine new concepts underlying fractalkine-mediated leukocyte migration and tissue damage, focusing primarily on the pathophysiological roles of fractalkine in various clinical conditions, especially in atherosclerosis and vascular injury.     

Regulation of CX3CL1/fractalkine expression in endothelial cells

CX3CL1/fractalkine is a chemokine with a unique CX3C motif. Fractalkine is synthesized in endothelial cells as a membrane protein, and the N-terminal domain containing a CX3C motif is cleaved and secreted. CX3CR1, the specific receptor for fractalkine, is expressed in monocytes and lymphocytes. Membrane-bound fractalkine works as an adhesion molecule for these leukocytes and the secreted form as a chemotactic factor. Fractalkine is produced by endothelial cells stimulated with tumor necrosis factor-alpha, interleukin-1 (IL-1), lipopolysaccharide and interferon-gamma. Expression of fractalkine in endothelial cells is inhibited by the soluble form of IL-6 receptor-alpha, 15-deoxy-Delta(12,14)-prostaglandin J(2), and hypoxia. The expression of fractalkine is tightly regulated and fractalkine plays an important role in the interaction between leukocytes and endothelial cells.     

Fractalkine: a survivor's guide: chemokines as antiapoptotic mediators

Chemokines are a family of low-molecular-weight proteins essential to the directed migration of cells under homeostatic and pathological conditions. Fractalkine (CX3CL1) is an unusual chemokine that can act as either a soluble or membrane-bound mediator and signals through the G protein-coupled chemokine receptor CX3CR1, expressed on monocytes, natural killer cells, T cells, and smooth muscle cells. Accumulating evidence suggests that fractalkine, in addition to its role in chemotaxis and adhesion of leukocytes, supports the survival of multiple cell types during homeostasis and inflammation. This review presents the evidence obtained from several disease models implying an antiapoptotic function for fractalkine and shows how this is relevant to the pathology of atherosclerosis and other vascular diseases. We discuss whether the key role of fractalkine, unlike other chemokines, is the promotion of cell survival and whether this has implications for vascular disease.     

Activated human T cells directly induce osteoclastogenesis from human monocytes: possible role of T cells in bone destruction in rheumatoid arthritis patients

OBJECTIVE: To elucidate the direct role of human T cells in the induction of osteoclastogenesis in rheumatoid arthritis (RA), by studying human monocytes and the pathogenetic roles of receptor activator of nuclear factor kappaB ligand (RANKL), RANK, and osteoprotegerin (OPG). METHODS: Synovial tissue obtained at total knee replacement was stained immunohistologically using anti-RANKL, CD3, and CD4 antibodies. Synovial fluid was obtained from patients with RA, osteoarthritis (OA), gout, or trauma. Concentrations of the soluble form of RANKL (sRANKL) and OPG in the synovial fluid were measured by enzyme-linked immunosorbent assay. Activated T cells from peripheral blood mononuclear cells (PBMC) of healthy volunteers were cultured with human monocytes from PBMC. RESULTS: Immunostaining of the synovial tissue of RA patients demonstrated that RANKL-positive cells were detected in a subset of fibroblast-like synoviocytes and infiltrating mononuclear cells. Double immunostaining revealed that RANKL-positive cells were detected in a subset of CD3+ cells and CD4+ cells. An increased concentration of sRANKL and a decreased concentration of OPG were detected in synovial fluid from RA patients. The ratio of the concentration of sRANKL to that of OPG was significantly higher in synovial fluid of RA patients than in synovial fluid of patients with OA or gout. The activated T cells expressing RANKL induced osteoclastogenesis from autologous peripheral monocytes. The role of RANKL in this osteoclastogenetic process was confirmed by dose-dependent inhibition by OPG. CONCLUSION: The present study is the first to demonstrate osteoclastogenesis using human-derived T cells and monocytes. In addition, the present findings suggest that excess production of RANKL by activated T cells increases the level of sRANKL in synovial fluid and may contribute to osteoclastic bone resorption in RA patients.     

Fractalkine mediates T cell-dependent proliferation of synovial fibroblasts in rheumatoid arthritis

OBJECTIVE: In rheumatoid arthritis (RA), synovial fibroblasts proliferate excessively, eventually eroding bone and cartilage. The aim of this study was to examine the mechanisms through which CD4 T cells, the dominant lymphocyte population in patients with rheumatoid synovitis, regulate synoviocyte proliferation. METHODS: Fibroblast-like synoviocyte (FLS) lines were established from rheumatoid synovium. CD4 T cells from patients with RA and age-matched control subjects were cultured on FLS monolayers. FLS proliferation was quantified by cytometry, using carboxyfluorescein succinimidyl ester staining or microscopic enumeration of PKH26-stained FLS. Surface expression of the fractalkine (FKN) receptor CX(3)CR1 was monitored by fluorescence-activated cell sorting. The induction of CX(3)CR1 and its ligand FKN in FLS was quantified by real-time polymerase chain reaction. RESULTS: The proliferation of FLS was significantly increased in the presence of CD4 T cells from patients with RA compared with control T cells. CD4+,CD28- T cells were particularly effective in supporting FLS growth, inducing a 25-fold expansion compared with a 5-fold expansion induced by CD4+,CD28+ T cells. The growth-promoting activity of CD4+,CD28- T cells was mediated through CX(3)CR1, a chemokine receptor expressed on both T cells and FLS. Anti-CX(3)CR1 antibodies inhibited T cell production of tumor necrosis factor alpha (TNFalpha) and suppressed FLS proliferation. TNFalpha amplified the expansion of FLS by enhancing their expression of CX(3)CR1 and FKN. CONCLUSION: FKN-CX(3)CR1 receptor-ligand interactions regulate FLS growth and FLS-dependent T cell function. FLS stimulate autocrine growth by releasing FKN and triggering the activity of their own CX(3)CR1. This growth-promotion loop is amplified by TNFalpha produced by CX(3)CR1-expressing T cells upon stimulation by FKN-expressing FLS. These data assign a critical role to FKN and its receptor in fibroblast proliferation and pannus formation in RA.