CCL2/CCR2 and CX3CL1/CX3CR1 chemokine axes and their possible involvement in age-related macular degeneration

The causes of age-related macular degeneration (AMD) are not well understood. Due to demographic shifts in the industrialized world a growing number of people will develop AMD in the coming decades. To develop treatments it is essential to characterize the disease's pathogenic process. Over the past few years, numerous studies have focused on the role of chemotactic cytokines, also known as chemokines. Certain chemokines, such as CCL2 and CX3CL1, appear to be crucial in subretinal microglia and macrophage accumulation observed in AMD, and participate in the development of retinal degeneration as well as in choroidal neovascularization. This paper reviews the possible implications of CCL2 and CX3CL1 signaling in AMD. Expression patterns, single nucleotide polymorphisms (SNPs) association studies, chemokine and chemokine receptor knockout models are discussed. Future AMD treatments could target chemokines and/or their receptors.     

CX3CL1/CX3CR1 Axis Contributes to Angiotensin II-Induced Vascular Smooth Muscle Cell Proliferation and Inflammatory Cytokine Production

Angiotensin II (Ang II) dysregulation has been determined in many diseases. The CX3CL1/CX3CR1 axis, which has a key role in cardiovascular diseases, is involved in the proliferation and inflammatory cytokine production of vascular smooth muscle cells (VSMCs). In this study, we aim to explore whether Ang II has a role in the expression of CX3CL1/CX3CR1, thus contributing to the proliferation and pro-inflammatory status of VSMCs. Cultured mouse aortic VSMCs were stimulated with 100 nmol/L of Ang II, and the expression of CX3CR1 was assessed by western blot. The results demonstrated that Ang II significantly up-regulated CX3CR1 expression in VSMCs and induced the production of reactive oxygen species (ROS) and the phosphorylation of p38 MAPK. Inhibitors of NADPH oxidase, ROS, and AT1 receptor significantly reduced Ang II-induced CX3CR1 expression. Targeted disruption of CX3CR1 by transfection with siRNA significantly attenuated Ang II-induced VSMC proliferation as well as down-regulated the expression of proliferating cell nuclear antigen (PCNA). Furthermore, CX3CR1-siRNA suppressed the effect of Ang II on stimulating Akt phosphorylation. Besides, the use of CX3CR1-siRNA decreased inflammatory cytokine production induced by Ang II treatment. Our results indicate that Ang II up-regulates CX3CR1 expression in VSMCs via NADPH oxidase/ROS/p38 MAPK pathway and that CX3CL1/CX3CR1 axis contributes to the proliferative and pro-inflammatory effects of Ang II in VSMCs.     

Fkn及其受体CX3CR1

不规则趋化因子 (Fkn)是趋化因子家族的新成员 ,既有膜结合形式又有游离形式 ,兼具粘附分子和趋化因子的活性。Fkn及其受体CX3CR1在白细胞及众多组织器官如神经组织、心脏、肾脏、皮肤等均有表达 ,可望成为疾病防治的新靶点     

Chemokines and common variable immunodeficiency; possible contribution of the fractalkine system (CX3CL1/CX3CR1) to chronic inflammation

Common variable immunodeficiency (CVID) is a heterogeneous syndrome characterized by defective immunoglobulin production and high frequency of bacterial infections, autoimmunity and manifestations of chronic inflammation. The chemokine Fractalkine (CX3CL1) and its receptor CX3CR1 is suggested to play an important role in the pathogenesis of several inflammatory disorders. We hypothesized that enhanced CX3CL1/CX3CR1 interaction could be involved in the chronic inflammation characterising subgroups of CVID. CVID patients were characterized by raised plasma levels of CX3CLl and enhanced expression of its corresponding receptor CX3CR1 on CD4(+) and CD8(+) T cells, including both CD45RA(+) and CD45RA(-) subsets. CX3CR1 expression was particularly enhanced in patients characterized by chronic inflammation in vivo. The high expression of the receptor in CVID patients was accompanied by enhanced chemotactic, adhesive, and other inflammatory cell responses to stimulation with CX3CL1. Our findings suggest that increased CX3CL1/CX3CR1 interaction could contribute to the inflammatory phenotype seen in subgroups of CVID patients.     

The Chemokine CX3CL1 (Fractalkine) and its Receptor CX3CR1: Occurrence and Potential Role in Osteoarthritis

Chemokines are molecules able to induce chemotaxis of monocytes, neutrophils, eosinophils, lymphocytes and fibroblasts. The complex chemokine acts in many physiological and pathological phenomena, including those occurring in the articular cartilage. To date, chemokine CX3CL1 (fractalkine) is the only member of the CX3C class of chemokines with well-documented roles in endothelial cells. CX3CL1 is a unique chemokine that combines properties of chemoattractant and adhesion molecule. The main roles of CX3CL1 include promotion of leukocyte binding and adhesion as well as activation of the target cells. The soluble chemokine domain of CX3CL1 is chemotactic for T cells and monocytes. CX3CL1 acts via its receptor, CX3CR1, which belongs to a family of G protein-coupled receptors. Stimulation of CX3CR1 activates both CX3CL1-dependent and integrin-dependent migrations of cells with synergistically augmented adhesion. Genetic polymorphisms of CX3CR1 may significantly modify the biological roles of CX3CL1, especially in pathologic conditions. Osteoarthritis (OA) is the most common joint disease, affecting approximately 7–8 % of the general population. Development of OA is largely driven by low-grade local background inflammation involving chemokines. The importance of CX3CL1/CX3CR1 signalling in the pathophysiology of OA is still under investigation. This paper, based on a review of the literature, updates and summarises the current knowledge about CX3CL1/CX3CR1 in OA and indicates possible interactions with a potential for therapeutic targeting.     

Interleukin-34 accelerates intrauterine adhesions progress related to CX3CR1+ monocytes/macrophages

Intrauterine adhesions (IUA) are characterized by endometrial fibrosis and impose a great challenge for female reproduction. IL-34 is profoundly involved in various fibrotic diseases through regulating the survival, proliferation, and differentiation of monocytes/macrophages. However, it remains unclear how IL-34 regulates monocytes/macrophages in context of IUA. Here, we showed that the expression level of IL-34 and the amount of CX3CR1+ monocytes/macrophages were significantly increased in endometrial tissues of IUA patients. IL-34 promoted the differentiation of monocytes/macrophages, which express CX3CR1 via CSF-1R/P13K/Akt pathway in vitro. Moreover, IL-34-induced CX3CR1+ monocytes/macrophages promoted the differentiation of endometrial stromal cells into myofibroblasts. Of note, IL-34 caused endometrial fibrosis and increased the amount of CX3CR1+ monocytes/macrophages in endometrial tissues in vivo. IL-34 modulated endometrial fibrosis by regulating monocytes/macrophages since the elimination of endometrial monocytes/macrophages significantly suppressed the profibrotic function of IL-34. Finally, blocking of IL-34 in the LPS-IUA model resulted in the improvement of endometrial fibrosis and decreased number of CX3CR1+ monocytes/macrophages. Our studies uncover the novel mechanism of interaction between IL-34-induced CX3CR1+ monocytes/macrophages and endometrial stromal cells in endometrial fibrosis pathogenesis, and highlight IL-34 as a critical target for treating IUA.     

Association study between the CX3CR1 gene and asthma

CX3CR1, a fractalkine receptor, mediates cell-adhesive and migratory functions in inflammation. Based on CX3CR1 expression observed in bronchial tissues of asthmatic subjects, we hypothesized that genetic variation at this locus may affect susceptibility to asthma. We carried out an association study and a haplotypic analysis with selected polymorphisms of the CX3CR1 in a familial asthmatic sample from a founder population. Genetic analyses performed by FBAT software showed five CX3CR1 single nucleotide polymorphisms (rs938203, rs2669849, rs1050592, T280M and V249I) with significant associations between their common alleles and asthma (P<0.004) in a dominant model. A haplotype formed with common alleles of rs1050592, T280M and V249I is also overtransmitted in asthmatic subjects (P=0.005) under a dominant model. The associations of V249I and rs2669849 have been validated in an independent case-control sample. For V249I, odds ratios (OR) are 2.16 (common homozygous) and 2.11 (heterozygous) in dominant model (P=0.031). For rs2669849, OR are 2.75 (common homozygous) and 1.86 (heterozygous) in additive model (P=0.007) and dominant model (P=0.059). These results suggest an asthma protective effect of the minor alleles in healthy control carriers. Further functional studies of CX3CR1 are needed to document its role in the pathophysiology of asthma.     

Dendritic cells modified to express fractalkine/CX3CL1 in the treatment of preexisting tumors

Fractalkine (CX3CL1) is a unique membrane-bound CX3C chemokine that serves as a potent chemoattractant for lymphocytes. The hypothesis of this study is that dendritic cells (DC) genetically modified ex vivo to overexpress fractalkine would enhance the T cell-mediated cellular immune response with a consequent induction of anti-tumor immunity to suppress tumor growth. To prove this hypothesis, established tumors of different mouse cancer cells (B16-F10 melanoma, H-2b, and Colon-26 colon adenocarcinoma, H-2d) were treated with intratumoral injection of bone marrow-derived DC that had been modified in vitro with an RGD fiber-mutant adenovirus vector expressing mouse fractalkine (Ad-FKN). In both tumor models tested, treatment of tumor-bearing mice with Ad-FKN-transduced DC gave rise to a significant suppression of tumor growth along with survival advantages in the treated mice. Immunohistochemical analysis of tumors treated with direct injection of Ad-FKN-transduced DC demonstrated that the treatment prompted CD8+ T cells and CD4+ T cells to accumulate in the tumor milieu, leading to activation of immune-relevant processes. Consistent with the finding, the intratumoral administration of Ad-FKN-transduced DC evoked tumor-specific cytotoxic T lymphocytes, which ensued from in vivo priming of Th1 immune responses in the treated host. In addition, the anti-tumor effect provided by intratumoral injection of Ad-FKN-transduced DC was completely abrogated in CD4+ T cell-deficient mice as well as in CD8+ T cell-deficient mice. These results support the concept that genetic modification of DC with a recombinant fractalkine adenovirus vector may be a useful strategy for cancer immunotherapy protocols.     

Hypertrophy of the ligament flavum in degenerative lumbar stenosis associated with the increased expression of fractalkine (CX3CL1)/CX3CR1 chemokine

Abstract

Fractalkine (CX3CL1) and its receptor (CX3CR1) comprise a chemokine system involved in leukocyte recruitment and adhesion in chronic inflammatory disease, but its role in spinal diseases is unknown. The purpose of this study is to investigate the role of CX3CL1/CX3CR1 chemokine on hypertrophy of the ligamentum flavum (LF) in degenerative lumbar stenosis (DLS) compared with that of non-degenerative spinal condition (NDS) of the lumbar spine and correlation between expression of CX3CL1/CX3CR1 chemokine and thickness of LF. The mRNA concentrations of CX3CL1/CX3CR1 chemokine were analyzed in the surgically obtained LF specimens from DLS (n?=?10) and NDS (n?=?11) by real-time PCR. The localization of CX3CL1/CX3CR1 chemokine within the LF was determined using immunohistochemical study. Plasma levels of soluble FKN (sFKN) were measured by enzyme-linked immunosorbent assay, respectively. The thickness of the LF was measured with axial T1-weighted MRI. The cells that express CX3CL1/CX3CR1 chemokine ratio in the LF observed in DLS group were substantially higher than in NDS group. In ELISA, the plasma levels of sFKN was significantly increased in DLS compared with patients in the other groups (p?=?0.006). There was greater CX3CL1/CX3CR1 expression in DLS as quantified by RT-PCR (p?=?0.004, 0.010). Thickness of LF in patients was significantly correlated with serum CX3CL1 level (R^2?=?0.824, p?=?0.003) and with mRNA expression of CX3CL1/CX3CR1 (R^2?=?0.671, p?=?0.000) (R^2?=?0.514, p?=?0.001). This study identified for the first time that increases in CX3CL1 and CX3CR1-expressing cells are significantly related to LF hypertrophy.     

CX3CL1/fractalkine在肺动脉高压过程中的表达变化及葛根素的干预作用

目的: 观察趋化因子CX₃CL1/fractalkine(FKN)在野百合碱诱导的肺动脉高压大鼠模型中的变化并探讨葛根素的干预效应。方法: 复制大鼠肺动脉高压模型,随机分为溶剂对照组(C组)、野百合碱造模组(M组)和葛根素干预组(M+P组)。测量并比较各组肺动脉平均压(mPAP)、右心室平均压(mRVP)、颈动脉平均压(mCAP)、右心室游离壁(RV)和左心室加室间隔(LV＋S)重量比。观察肺细小动脉显微结构变化,测定肺细小动脉管壁面积/管总面积(WA/TA)、肺细小动脉中膜厚度(PAMT),测定血浆可溶性fractalkine(sFKN)浓度,肺细小动脉FKN蛋白,肺组织FKN mRNA的表达。结果: M组mPAP、mRVP、RV/(LV+S)、WA/TA和PAMT显著高于C组(P<0.01),M+P组RV/(LV+S)、WA/TA和PAMT较M组显著降低(P<0.01),M组血浆sFKN、肺组织FKN mRNA和肺动脉壁FKN含量显著大于C组(P<0.01),M+P组显著降低(P<0.05),sFKN与PAMT呈正相关(r＝0.719,P<0.01),与RV/(LV+S)呈正相关(r＝0.685,P<0.01)。结论: 葛根素具有抑制FKN表达、肺动脉高压发展和肺血管结构重建的作用。     

CX3CL1 up-regulation is associated with recruitment of CX3CR1+ mononuclear phagocytes and T lymphocytes in the lungs during cigarette smoke-induced emphysema

CX3CR1 is expressed on monocytes, dendritic cells, macrophages, subsets of T lymphocytes, and natural killer cells and functions in diverse capacities such as leukocyte adhesion, migration, and cell survival on ligand binding. Expression of the CX3CL1 gene, whose expression product is the sole ligand for CX3CR1, is up-regulated in human lungs with chronic cigarette smoke-induced obstructive lung disease. At present, it is unknown whether CX3CL1 up-regulation is associated with the recruitment and accumulation of immune cells that express CX3CR1. We show that mice chronically exposed to cigarette smoke up-regulate CX3CL1 gene expression, which is associated with an influx of CX3CR1⁺ cells in the lungs. The increase in CX3CR1⁺ cells is primarily comprised of macrophages and T lymphocytes and is associated with the development of emphysema. In alveolar macrophages, cigarette smoke exposure increased the expression of both CX3CR1 and CX3CL1 genes. The inducibility of CX3CR1 expression was not solely dependent on a chronic stimulus because lipopolysaccharide up-regulated CX3CR1 in RAW264.7 cells in vitro and in mononuclear phagocytes in vivo. Our findings suggest a mechanism by which macrophages amplify and promote CX3CR1⁺ cell accumulation within the lungs during both acute and chronic inflammatory stress. We suggest that one function of the CX3CR1-CX3CL1 pathway is to recruit and sustain divergent immune cell populations implicated in the pathogenesis of cigarette smoke-induced emphysema.     

Deleterious genetic influence of CX3CR1 genotypes on HIV-1 disease progression

We previously reported that patients homozygous for a specific mutation (M280) in the chemokine receptor CX3CR1 progressed to AIDS more rapidly than those with other genotypes. This deleterious effect would predict that a cohort of prevalent patients would be depleted in M280 carriers, because these patients would have disappeared before recruitment. This hypothesis is confirmed in this new study based on the French SEROCO cohort showing that patients homozygous for the M280 allele were rare among the seroprevalent group. These results may explain the conflicting results published on the impact of CX3CR1 polymorphism in seroconverters.     

Characterization of fractalkine (CX3CL1) and CX3CR1 in human coronary arteries with native atherosclerosis, diabetes mellitus, and transplant vascular disease

Background: Fractalkine is a novel chemokine that mediates both firm adhesion of leukocytes to the endothelium via CX3CR1 and leukocyte transmigration out of the bloodstream. Fractalkine has recently been shown to play a role in the pathogenesis of acute organ rejection. Since its expression is regulated by inflammatory agents such as LPS, IL-1, and TNF-, fractalkine involvement in atherosclerosis and transplant vascular disease (TVD) is of particular interest. In this study, we characterized the presence of fractalkine and its receptor CX3CR1 in human coronary arteries from normal, atherosclerotic, diabetic, and TVD settings. Method: Polyclonal rabbit antibodies were used to immunostain human fractalkine and CX3CR1 to localize their presence in transverse sections of the proximal left anterior descending and/or right coronary arteries. Slides were scored in a blinded fashion for intensity of staining (0 to 4+) and for localization in vessel walls. Results: Normal coronary arteries showed no fractalkine staining. In atherosclerotic coronary arteries, staining was localized to the intima, media, and adventitia. Within the media, fractalkine expression was seen in macrophages, foam cells, and smooth muscle cells (SMCs). Diabetic vessels showed similar staining patterns to atherosclerotic coronaries, with much stronger staining in the deep intima. Transplanted coronaries showed staining in the endothelium, intima, and adventitia in early disease, and intimal, medial, and adventitial staining in late disease. CX3CR1 staining was seen in the coronary arteries of all cases, with specific localization to regions with fractalkine staining. Conclusion: The distinctive staining patterns in native atherosclerosis, diabetes mellitus with atherosclerosis, and TVD indicate that the expression of fractalkine and CX3CR1 may be important in the pathogenesis of these diseases.