Fractalkine is a novel chemoattractant for rheumatoid arthritis fibroblast-like synoviocyte signaling through MAP kinases and Akt

Aging Microglia and Their Impact in the Nervous System

Aging is the greatest risk factor for neurodegenerative diseases. Microglia are the resident immune cells in the central nervous system (CNS), playing key roles in its normal functioning, and as mediators for age-dependent changes of the CNS, condition at which they generate a hostile environment for neurons. Transforming Growth Factor β1 (TGFβ1) is a regulatory cytokine involved in immuneregulation and neuroprotection, affecting glial cell inflammatory activation, neuronal survival, and function. TGFβ1 signaling undergoes age-dependent changes affecting the regulation of microglial cells and can contribute to the pathophysiology of neurodegenerative diseases. This chapter focuses on assessing the role of age-related changes on the regulation of microglial cells and their impact on neuroinflammation and neuronal function, for understanding age-dependent changes of the nervous system.

Age-dependent changes on fractalkine forms and their contribution to neurodegenerative diseases

The chemokine fractalkine (FKN, CX3CL1), a member of the CX3C subfamily, contributes to neuron-glia interaction and the regulation of microglial cell activation. Fractalkine is expressed by neurons as a membrane-bound protein (mCX3CL1) that can be cleaved by extracellular proteases generating several sCX3CL1 forms. sCX3CL1, containing the chemokine domain, and mCX3CL1 have high affinity by their unique receptor (CX3CR1) which, physiologically, is only found in microglia, a resident immune cell of the CNS. The activation of CX3CR1contributes to survival and maturation of the neural network during development, glutamatergic synaptic transmission, synaptic plasticity, cognition, neuropathic pain, and inflammatory regulation in the adult brain. Indeed, the various CX3CL1 forms appear in some cases to serve an anti-inflammatory role of microglia, whereas in others, they have a pro-inflammatory role, aggravating neurological disorders. In the last decade, evidence points to the fact that sCX3CL1 and mCX3CL1 exhibit selective and differential effects on their targets. Thus, the balance in their level and activity will impact on neuron-microglia interaction. This review is focused on the description of factors determining the emergence of distinct fractalkine forms, their age-dependent changes, and how they contribute to neuroinflammation and neurodegenerative diseases. Changes in the balance among various fractalkine forms may be one of the mechanisms on which converge aging, chronic CNS inflammation, and neurodegeneration.

Chemokines and chemokine receptors as promising targets in rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disease that commonly causes inflammation and bone destruction in multiple joints. Inflammatory cytokines, such as IL-6 and TNF-α, play important roles in RA development and pathogenesis. Biological therapies targeting these cytokines have revolutionized RA therapy. However, approximately 50% of the patients are non-responders to these therapies. Therefore, there is an ongoing need to identify new therapeutic targets and therapies for patients with RA. In this review, we focus on the pathogenic roles of chemokines and their G-protein-coupled receptors (GPCRs) in RA. Inflamed tissues in RA, such as the synovium, highly express various chemokines to promote leukocyte migration, tightly controlled by chemokine ligand-receptor interactions. Because the inhibition of these signaling pathways results in inflammatory response regulation, chemokines and their receptors could be promising targets for RA therapy. The blockade of various chemokines and/or their receptors has yielded prospective results in preclinical trials using animal models of inflammatory arthritis. However, some of these strategies have failed in clinical trials. Nonetheless, some blockades showed promising results in early-phase clinical trials, suggesting that chemokine ligand-receptor interactions remain a promising therapeutic target for RA and other autoimmune diseases.

The monocyte-to-osteoclast transition in rheumatoid arthritis: Recent findings

Rheumatoid arthritis (RA) is an autoimmune disease characterized by joint inflammation leading to joint destruction and deformity. The crucial role of osteoclasts in the bone erosion in RA has been demonstrated. Deregulated osteoclastogenesis which is affected by environmental factors including the inflammatory state, as well as genetic and epigenetic factors, is one of hallmarks of RA pathogenesis. An enhanced-monocyte-to-osteoclast transition plays an important role in osteoclast upregulation in RA because under specific stimuli, circulating monocytes might migrate to a specific location in the bones and fuse with each other to become mature multinucleated osteoclasts. To understand the mechanism of bone damage in RA and to develop novel treatments targeting osteoclast upregulation, it is important to clarify our understanding of the monocyte-to-osteoclast transition in RA. Several potential targets which inhibit both inflammation and osteoclastogenesis, as well as regulators that affect the monocyte-to-osteoclast transition have been revealed by recent studies. Here, we review the factors affecting osteoclastogenesis in RA, summarize the anti-osteoclastogenic effects of current RA treatments, and identify promising therapeutic targets relating to both inflammation and osteoclastogenesis.

CX3CL1/fractalkine regulates the differentiation of human peripheral blood monocytes and monocyte-derived dendritic cells into osteoclasts

Osteoclast differentiation is promoted under inflammatory conditions and osteoclasts play a major role in bone destruction in rheumatoid arthritis (RA). Chemokine (C-X3-C motif) ligand 1 (CX3CL1), also known as fractalkine, functions as a chemoattractant and adhesion molecule, and is involved in the pathogenesis of RA. The blockade of CX3CL1 inhibits the migration of macrophages and osteoclast precursor cells into the inflamed synovium. In the present study, we investigated the direct stimulatory effects of CX3CL1 on osteoclast differentiation from human peripheral blood monocytes and monocyte-derived dendritic cells. A stimulation with CX3CL1 significantly promoted osteoclast differentiation from CD16^- monocytes and also monocyte-derived dendritic cells induced by macrophage colony-stimulating factor (M-CSF) and receptor activator of NF-κB ligand (RANKL). On the other hand, CD16⁺ monocytes treated with M-CSF and RANKL did not differentiate into osteoclasts, even with CX3CL1. Calcium resorption was significantly increased by monocyte-derived osteoclasts, but not by dendritic cell-derived osteoclasts, following the addition of CX3CL1. The present results suggest that CX3CL1 directly regulates osteoclast differentiation. CX3CL1 may play important roles in the pathogenesis of RA, not only through the accumulation of inflammatory cells, but also through osteoclastogenesis.

Regulation and biological functions of the CX3CL1-CX3CR1 axis and its relevance in solid cancer: A mini-review

CX3CL1 is a transmembrane protein from which a soluble form can be generated by proteolytic shedding. Membranal and soluble forms of CX3CL1 exhibit different functions, although both bind to the CX3CR1 chemokine receptor. The CX3CL1-CX3CR1 axis mediates the adhesion of leukocytes and is also involved in cell survival and recruitment of immune cell subpopulations. The function of CX3CL1 is finely tuned by cytokines and transcription factors regulating its expression and post-translational modifications. On homeostasis, the CX3CL1-CX3CR1 axis participates in the removal of damaged neurons and neurogenesis, and it is also involved on several pathological contexts. The CX3CL1-CX3CR1 axis induces several cellular responses relevant to cancer such as proliferation, migration, invasion and apoptosis resistance. In this review, we address biological aspects of this molecular axis with important therapeutic potential, emphasizing its role in cancer, one of the most prevalent chronic diseases which significantly affect the quality of life and life expectancy of patients.

Non-Canonical WNT5A Signaling Through RYK Contributes to Aggressive Phenotype of the Rheumatoid Fibroblast-Like Synoviocytes

We hypothesized that WNT5A could contribute to the enhanced migration and invasiveness of rheumatoid arthritis fibroblast-like synoviocytes (RA FLS), which is one of the incompletely understood aspects of the RA FLS aggressive phenotype. This hypothesis is based on the previous evidence of a WNT5A role in both, RA and cell migration. Migration and invasion of RA FLS were assessed after incubation with recombinant Wnt5a (rWnt5a) or silencing of the endogenous WNT5A expression. The expression of WNT5A, WNT receptors, cytokines, chemokines, and metalloproteinases was quantified with RT-PCR. The WNT pathway was explored with gene silencing, antibody and pharmacological inhibition followed by migration assays and phosphoprotein western blots. Here, we reported that rWnt5a promoted migration and invasion of RA FLS, whereas knockdown of the endogenous WNT5A reduced them. These effects were specific to the RA FLS since they were not observed in FLS from osteoarthritis (OA) patients. Also, rWnt5a induced the expression of IL6, IL8, CCL2, CXCL5, MMP1, MMP3, MMP9, and MMP13 from baseline or potentiating the TNF induction, WNT5A signaling required the RYK receptor and was mediated through the WNT/Ca²⁺ and the ROCK pathway. These pathways involved the RYK and ROCK dependent activation of the p38, ERK, AKT, and GSK3β kinases, but not the activation of JNK. Together these findings indicate that WNT5A contributes to the enhanced migration and invasiveness of RA FLS through RYK and the specific activation of ROCK and downstream kinases.

CX3CR1 regulates angiogenesis and activation of pro-angiogenic factors and triggers macrophage accumulation in experimental hepatopulmonary syndrome model

OBJECTIVE

Prevalence of hepatopulmonary syndrome (HPS) ranges from 4% to 47% in patients with cirrhosis. This study aimed to explore possible relationship between CX3CR1 and angiogenesis or macrophage accumulation in pathological process of HPS.

MATERIAL AND METHODS

Wide-type C57Bl/6 mice were divided into WT-sham, WT-common bile duct ligation (WT-CBDL), WT-CBDL plus antibody (WT-CBDL+Ab) and WT-CBDL plus Bevacizumab. The CX3CR1^GFP/GFP mice were grouping into CX3CR1 GFP/GFP-sham, CX3CR1 GFP/GFP-CBDL and CX3CR1 GFP/GFP-CBDL+Bevacizumab group. Intrapulmonary expression of Akt, pAkt, ERK, pERK, iNOS, VEGF, PDGF was measured using biological technology. Hematoxylin-eosin (H&E) staining and immunohistochemical analysis were used to evaluate changes of pulmonary tissues including pathological abnormality, angiogenesis and macrophage accumulation.

RESULTS

Blockade CX3CR1 pathway inhibited angiogenesis, macrophage accumulation and pathological changes of lung tissues. Blockade of CX3CR1 pathway reduced pAkt, pERK, iNOS, PDGF and VEGF activation. CX3CR1 contributed to the process of angiogenesis and activate the pro-angiogenic factors. CX3CR1 deficiency obviously reduced the macrophage accumulation. Inhibition of VEGF by Bevacizumab improved intrapulmonary angiogenesis and pathological changes of lung tissues. Inhibition of VEGF by Bevacizumab retarded the production of pAKt, PDGF, and iNOS. Inhibition of VEGF by Bevacizumab reduced CX3CL1 production.

CONCLUSION

CX3CR1 could regulate the angiogenesis and activation of pro-angiogenic factors, including pAKT, pERK, iNOS, VEGF and PDGF in the process of hepato-pulmonary syndrome. Moreover, CX3CR1 could also contribute to the macrophage accumulation.

Rationale for and clinical development of anti-fractalkine antibody in rheumatic diseases

Introduction: Rheumatic diseases are inflammatory diseases that damage target organs via multiple subsets of immune cells. Fractalkine (FKN) acts as chemoattractant as well as adhesion molecule. It contributes to the pathogenesis of rheumatoid arthritis (RA) and other rheumatic diseases through multiple mechanisms: the migration of monocytes and cytotoxic effector T cells, the proliferation and activation of fibroblast-like synoviocytes, angiogenesis, and osteoclastogenesis. FKN has potential as a new therapeutic target, and clinical trials on anti-FKN monoclonal antibodies for RA are ongoing. FKN-targeted therapy has been developed and a humanized anti-FKN monoclonal antibody is currently being tested in phase 2 clinical trials. Areas covered: This review summarizes accumulated evidence on the involvement of FKN in RA and other rheumatic diseases, including systemic lupus erythematosus (SLE), systemic sclerosis, inflammatory myositis, Sjögren's syndrome (SS), osteoarthritis, and systemic vasculitis. Expert opinion: A phase 1/2a clinical trial on anti-FKN demonstrated its safety, tolerability, and clinical efficacy. Anti-FKN therapy has potential in the treatment of atherosclerosis and interstitial lung diseases associated with RA. Based on recent findings, other rheumatic diseases, including SLE, polymyositis/dermatomyositis, and SS, may also be treated using anti-FKN therapy.

Meta-Analysis of Transcriptomic Data of Dorsolateral Prefrontal Cortex and of Peripheral Blood Mononuclear Cells Identifies Altered Pathways in Schizophrenia

Schizophrenia (SCZ) is a psychiatric disorder characterized by both positive and negative symptoms, including cognitive dysfunction, decline in motivation, delusion and hallucinations. Antipsychotic agents are currently the standard of care treatment for SCZ. However, only about one-third of SCZ patients respond to antipsychotic medications. In the current study, we have performed a meta-analysis of publicly available whole-genome expression datasets on Brodmann area 46 of the brain dorsolateral prefrontal cortex in order to prioritize potential pathways underlying SCZ pathology. Moreover, we have evaluated whether the differentially expressed genes in SCZ belong to specific subsets of cell types. Finally, a cross-tissue comparison at both the gene and functional level was performed by analyzing the transcriptomic pattern of peripheral blood mononuclear cells of SCZ patients. Our study identified a robust disease-specific set of dysfunctional biological pathways characterizing SCZ patients that could in the future be exploited as potential therapeutic targets.

Role of Chemokines and Chemokine Receptors in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is one of the most prevalent autoimmune diseases and a prototypic inflammatory disease, affecting the small joints of the hands and feet. Chemokines and chemokine receptors play a critical role in RA pathogenesis via immune cells recruitment. Several chemokines and chemokine receptors are abundant in the peripheral blood and in the local inflamed joints of RA. Furthermore, synthetic and biologics disease modifying anti rheumatic drugs have been reported to affect chemokines expression. Thus, many studies have focused on targeting chemokines and chemokine receptors, where some have shown positive promising results. However, most of the chemokine blockers in human trials of RA treatment displayed some failures that can be attributed to several reasons in their structures and binding affinities. Nevertheless, targeting chemokines will continue to be under development, in order to improve their therapeutic potentials in RA and other autoimmune diseases. In this review we provide an up-to-date knowledge regarding the role of chemokines and chemokine receptors in RA with an emphasis on their activities on immune cells. We also discussed the effects of drugs targeting those molecules in RA. This knowledge might provide impetus for developing new therapeutic modalities to treat this chronic disease.

Andrographolide Benefits Rheumatoid Arthritis via Inhibiting MAPK Pathways

Andrographolide (AD) is the main compound distributed in medicinal herb Andrographis paniculata and exhibits anti-inflammatory activity. AD has been used for the treatment of multiple inflammatory diseases. However, the therapeutic value of AD on human rheumatoid arthritis (RA) remains unclear. In this study, we investigated the effects of AD on collagen-induced arthritis (CIA) and human RA synovial fibroblasts (RA-SFs). CIA mice were treated with AD (dissolved in 0.5% CMC-Na, 100 mg/kg per day) or vehicle (0.5% CMC-Na) daily by oral gavage for 2 weeks. The arthritis severity and joint destruction were assessed. Serum anti-collagen II antibody (anti-CII Abs) and cytokines were determined by ELISA. TNFα-stimulated human RA-SFs were treated with varying doses of AD for in vitro investigation. Results showed that AD significantly attenuated the arthritis severity and joint damage. AD treatment significantly reduced the production of serum anti-CII, TNFα, IL-1β, and IL-6. In vitro, AD decreased the secretion of IL-1β and IL-6 from TNFα-stimulated RA-SFs in a dose-dependent manner. AD treatment reduced the TNFα-induced phosphorylation of p38 MAPK and ERK1/2 in a dose-dependent manner. Thus, our findings suggest that AD confers protective effects on autoimmune arthritis through inhibiting MAPK pathways.

The Multifunctional Role of the Chemokine System in Arthritogenic Processes

PURPOSE OF REVIEW

The involvement of chemokines and their receptors in the genesis and perpetuation of rheumatoid arthritis, spondyloarthritis, and osteoarthritis has been clearly recognized for a long time. Nevertheless, the complexity of their contribution to these diseases is now becoming evident and this review focuses on published evidence on their mechanism of action.

RECENT FINDINGS

Studies performed on patients and in vivo models have identified a number of chemokine-mediated pathways involved in various aspects of arthritogenic processes. Chemokines promote leukocyte infiltration and activation, angiogenesis, osteoclast differentiation, and synoviocyte proliferation and activation and participate to the generation of pain by regulating the release of neurotransmitters. A number of chemokines are expressed in a timely controlled fashion in the joint during arthropathies, regulating all the aspects of inflammation as well as the equilibrium between damage and repair and between relief and pain. Thus, the targeting of specific chemokine/chemokine receptor interactions is considered a promising tool for therapeutic intervention.

Fractalkine/CX3CR1 induces apoptosis resistance and proliferation through the activation of the AKT/NF-κB cascade in pancreatic cancer cells

Fractalkine (FKN, CX3CL1) is highly expressed in a majority of malignant solid tumours. Fractalkine is the only known ligand for CX3CR1. In this study, we performed an analysis to determine the effects of fractalkine/CX3CR1 on modulating apoptosis and explored the related mechanisms. The expression of fractalkine/CX3CR1 was detected by immunohistochemistry and western blotting. The levels of AKT/p-AKT, BCL-xl, and BCL-2 were detected by western blotting. Then, the effects of exogenous and endogenous fractalkine on the regulation of tumour apoptosis and proliferation were investigated. The mechanism of fractalkine/CX3CR1 on modulating apoptosis in cancer cells through the activation of AKT/NF-κB/p65 signals was evaluated. The effect of fractalkine on regulating cell cycle distribution was also tested. Fractalkine, AKT/p-AKT, and apoptotic regulatory proteins BCL-xl and BCL-2 were highly expressed in human pancreatic cancer tissues. In vitro, fractalkine/CX3CR1 promoted proliferation and mediated resistance to apoptosis in pancreatic cancer cells. The antiapoptotic effect of fractalkine was induced by the activation of AKT/NF-κB/p65 signalling in pancreatic cancer cells. The NF-κB/p65 contributes to promote the expressions of BCL-xl and BCL-2 and reduce caspase activity, thereby inhibiting apoptotic processes. Treatment with fractalkine resulted in the enrichment of pancreatic cancer cells in S phase with a concomitant decrease in the number of cells in G1 phase. The present study demonstrated the function of fractalkine in the activation of the AKT/NF-κB/p65 signalling cascade and mediation of apoptosis resistance in pancreatic cancer cells. Fractalkine/CX3CR1 could serve as a diagnostic marker and as a potential target for chemotherapy in early stage pancreatic cancer. Pancreatic cancer is characterized by local recurrence, neural invasion, or distant metastasis. The present study demonstrated the overexpression of fractalkine/CX3CR1 in pancreatic cancer tissues, indicating its important role in the tumourigenesis of pancreatic cancer, and suggested that the overexpression of fractalkine/CX3CR1 could serve as a diagnostic marker for pancreatic cancer. Moreover, we reveal the mechanism that fractalkine functions on the activation of the AKT/NF-κB/p65 signalling cascade and regulation of the antiapoptosis process in pancreatic cancer cells. Fractalkine/CX3CR1 could serve as an effective therapeutic target of chemotherapeutic and biologic agents in early stage pancreatic cancer.

HIV Infection and Compromised Mucosal Immunity: Oral Manifestations and Systemic Inflammation

Mucosal surfaces account for the vast majority of HIV transmission. In adults, HIV transmission occurs mainly by vaginal and rectal routes but rarely via oral route. By contrast, pediatric HIV infections could be as the result of oral route by breastfeeding. As such mucosal surfaces play a crucial role in HIV acquisition, and spread of the virus depends on its ability to cross a mucosal barrier. HIV selectively infects, depletes, and/or dysregulates multiple arms of the human immune system particularly at the mucosal sites and causes substantial irreversible damage to the mucosal barriers. This leads to microbial products translocation and subsequently hyper-immune activation. Although introduction of antiretroviral therapy (ART) has led to significant reduction in morbidity and mortality of HIV-infected patients, viral replication persists. As a result, antigen presence and immune activation are linked to “inflammaging” that attributes to a pro-inflammatory environment and the accelerated aging process in HIV patients. HIV infection is also associated with the prevalence of oral mucosal infections and dysregulation of oral microbiota, both of which may compromise the oral mucosal immunity of HIV-infected individuals. In addition, impaired oral immunity in HIV infection may predispose the patients to periodontal diseases that are associated with systemic inflammation and increased risk of cardiovascular diseases. The purpose of this review is to examine existing evidence regarding the role of innate and cellular components of the oral cavity in HIV infection and how HIV infection may drive systemic hyper-immune activation in these patients. We will also discuss current knowledge on HIV oral transmission, HIV immunosenescence in relation to the oral mucosal alterations during the course of HIV infection and periodontal disease. Finally, we discuss oral manifestations associated with HIV infection and how HIV infection and ART influence the oral microbiome. Therefore, unraveling how HIV compromises the integrity of the oral mucosal tissues and innate immune components of the oral cavity and its association with induction of chronic inflammation are critical for the development of effective preventive interventions and therapeutic strategies.

HIV Infection and Compromised Mucosal Immunity: Oral Manifestations and Systemic Inflammation

Mucosal surfaces account for the vast majority of HIV transmission. In adults, HIV transmission occurs mainly by vaginal and rectal routes but rarely via oral route. By contrast, pediatric HIV infections could be as the result of oral route by breastfeeding. As such mucosal surfaces play a crucial role in HIV acquisition, and spread of the virus depends on its ability to cross a mucosal barrier. HIV selectively infects, depletes, and/or dysregulates multiple arms of the human immune system particularly at the mucosal sites and causes substantial irreversible damage to the mucosal barriers. This leads to microbial products translocation and subsequently hyper-immune activation. Although introduction of antiretroviral therapy (ART) has led to significant reduction in morbidity and mortality of HIV-infected patients, viral replication persists. As a result, antigen presence and immune activation are linked to "inflammaging" that attributes to a pro-inflammatory environment and the accelerated aging process in HIV patients. HIV infection is also associated with the prevalence of oral mucosal infections and dysregulation of oral microbiota, both of which may compromise the oral mucosal immunity of HIV-infected individuals. In addition, impaired oral immunity in HIV infection may predispose the patients to periodontal diseases that are associated with systemic inflammation and increased risk of cardiovascular diseases. The purpose of this review is to examine existing evidence regarding the role of innate and cellular components of the oral cavity in HIV infection and how HIV infection may drive systemic hyper-immune activation in these patients. We will also discuss current knowledge on HIV oral transmission, HIV immunosenescence in relation to the oral mucosal alterations during the course of HIV infection and periodontal disease. Finally, we discuss oral manifestations associated with HIV infection and how HIV infection and ART influence the oral microbiome. Therefore, unraveling how HIV compromises the integrity of the oral mucosal tissues and innate immune components of the oral cavity and its association with induction of chronic inflammation are critical for the development of effective preventive interventions and therapeutic strategies.

Indirubin inhibits the migration, invasion, and activation of fibroblast-like synoviocytes from rheumatoid arthritis patients

OBJECTIVES

To evaluate the inhibition of indirubin in FLSs migration, invasion, activation, and proliferation in RA FLSs.

METHODS

The levels of IL-6 and IL-8 in cultural supernatants were measured by ELISA. RA FLS migration and invasion in vitro were measured by the Boyden chamber method and the scratch assay. Signal transduction protein expression was measured by western blot. FLS proliferation was detected by Edu incorporation. F-actin was measured by immunofluorescence staining.

RESULTS

We found that indirubin reduced migration, invasion, inflammation, and proliferation in RA FLSs. In addition, we demonstrated that indirubin inhibited lamellipodium formation during cell migration. To gain insight into molecular mechanisms, we evaluated the effect of indirubin on PAK1 and MAPK activation. Our results indicated that indirubin inhibited the activity of PAK1 and MAPK.

CONCLUSIONS

Our observations suggest that indirubin may be protective against joint destruction in RA by regulating synoviocyte migration, invasion, activation, and proliferation.

Role of protein arginine methyltransferase 5 in inflammation and migration of fibroblast-like synoviocytes in rheumatoid arthritis

To probe the role of protein arginine methyltransferase 5 (PRMT5) in regulating inflammation, cell proliferation, migration and invasion of fibroblast‐like synoviocytes (FLSs) from patients with rheumatoid arthritis (RA). FLSs were separated from synovial tissues (STs) from patients with RA and osteoarthritis (OA). An inhibitor of PRMT5 (EPZ015666) and short interference RNA (siRNA) against PRMT5 were used to inhibit PRMT5 expression. The standard of protein was measured by Western blot or immunofluorescence. The excretion and genetic expression of inflammatory factors were, respectively, estimated by enzyme‐linked immunosorbent assay (ELISA) and real‐time polymerase chain reaction (PCR). Migration and invasion in vitro were detected by Boyden chamber assay. FLSs proliferation was detected by BrdU incorporation. Increased PRMT5 was discovered in STs and FLSs from patients with RA. In RA FLSs, the level of PRMT5 was up‐regulated by stimulation with IL‐1β and TNF‐α. Inhibition of PRMT5 by EPZ015666 and siRNA‐mediated knockdown reduced IL‐6 and IL‐8 production, and proliferation of RA FLSs. In addition, inhibition of PRMT5 decreased in vitro migration and invasion of RA FLSs. Furthermore, EPZ015666 restrained the phosphorylation of IκB kinaseβ and IκBα, as well as nucleus transsituation of p65 as well as AKT in FLSs. PRMT5 regulated the production of inflammatory factors, cell proliferation, migration and invasion of RA FLS, which was mediated by the NF‐κB and AKT pathways. Our data suggested that targeting PRMT5 to prevent synovial inflammation and destruction might be a promising therapy for RA.

Cathepsin S contributes to microglia-mediated olfactory dysfunction through the regulation of Cx3cl1-Cx3cr1 axis in a Niemann-Pick disease type C1 model

Microglia can aggravate olfactory dysfunction by mediating neuronal death in the olfactory bulb (OB) of a murine model of Niemann-Pick disease type C1 (NPC1), a fatal neurodegenerative disorder accompanied by lipid trafficking defects. In this study, we focused on the crosstalk between neurons and microglia to elucidate the mechanisms underlying extensive microgliosis in the NPC1-affected brain. Microglia in the OB of NPC1 mice strongly expressed CX3C chemokine receptor 1 (Cx3cr1), a specific receptor for the neural chemokine C-X3-C motif ligand 1 (Cx3cl1). In addition, a high level of Cx3cl1 was detected in NPC1 mouse-derived CSF due to enhanced catalytic activity of Cathepsin S (Ctss), which is responsible for Cx3cl1 secretion. Notably, nasal delivery of Cx3cl1 neutralizing antibody or Ctss inhibitor could inhibit the Cx3cl1-Cx3cr1 interaction and support neuronal survival through the suppression of microglial activation, leading to an improvement in the olfactory function in NPC1 mice. Relevant in vitro experiments revealed that intracellular cholesterol accumulation could act as a strong inducer of abnormal Ctss activation and, in turn, stimulated the Cx3cl1-Cx3cr1 axis in microglia via p38 mitogen-activated protein kinase signaling. Our data address the significance of Cx3cl1-Cx3cr1 interaction in the development of microglial neurotoxicity and suggest that Ctss is a key upstream regulator. Therefore, this study contributes to a better understanding of the crosstalk between neurons and microglia in the development of the neurodegeneration and provides a new perspective for the management of olfactory deficits and other microglia-dependent neuropathies. GLIA 2016;64:2291-2305.

Rheumatoid Arthritis, Immunosenescence and the Hallmarks of Aging

Age is the most important risk factor for the development of infectious diseases, cancer and chronic inflammatory diseases including rheumatoid arthritis (RA). The very act of living causes damage to cells. A network of molecular, cellular and physiological maintenance and repair systems creates a buffering capacity against these damages. Aging leads to progressive shrinkage of the buffering capacity and increases vulnerability. In order to better understand the complex mammalian aging processes, nine hallmarks of aging and their interrelatedness were recently put forward.

RA is a chronic autoimmune disease affecting the joints. Although RA may develop at a young age, the incidence of RA increases with age. It has been suggested that RA may develop as a consequence of premature aging (immunosenescence) of the immune system. Alternatively, premature aging may be the consequence of the inflammatory state in RA. In an effort to answer this chicken and egg conundrum, we here outline and discuss the nine hallmarks of aging, their contribution to the pre-aged phenotype and the effects of treatment on the reversibility of immunosenescence in RA.

Fractalkine (CX3CL1): a biomarker reflecting symptomatic severity in patients with knee osteoarthritis

BACKGROUND

Elevated serum and synovial fluid (SF) fractalkine (CX3CL1) levels have been detected in patients with knee osteoarthritis (OA). The current study was carried out to investigate the association between serum and SF fractalkine levels with symptomatic severity in patients with knee OA.

METHOD

One hundred ninety-three patients with OA and 182 healthy controls were enrolled in this study. The symptomatic severity was assessed by the Western Ontario McMaster University Osteoarthritis scores.

RESULTS

Fractalkine levels in SF and serum were both positively associated with self-reported greater pain and physical disability.

CONCLUSIONS

Fractalkine in SF and serum may serve as a biomarker for reflecting symptomatic severity. Therapeutic interventions that target fractalkine signaling pathways to delay OA-related symptoms deserve further study.

Protein Inhibitor of Activated STAT3 Regulates Migration, Invasion, and Activation of Fibroblast-like Synoviocytes in Rheumatoid Arthritis

The aggressive phenotype displayed by fibroblast-like synoviocytes (FLSs) is a critical factor of cartilage destruction in rheumatoid arthritis (RA). Increased FLSs migration and subsequent degradation of the extracellular matrix are essential to the pathology of RA. Protein inhibitor of activated STAT (PIAS), whose family members include PIAS1, PIAS2 (PIASx), PIAS3, and PIAS4 (PIASy), play important roles in regulating various cellular events, such as cell survival, migration, and signal transduction in many cell types. However, whether PIAS proteins have a role in the pathogenesis of RA is unclear. In this study, we evaluated the role of PIAS proteins in FLSs migration, invasion, and matrix metalloproteinases (MMPs) expression in RA. We observed increased expression of PIAS3, but not PIAS1, PIAS2, or PIAS4, in FLSs and synovial tissues from patients with RA. We found that PIAS3 knockdown by short hairpin RNA reduced migration, invasion, and MMP-3, MMP-9, and MMP-13 expression in FLSs. In addition, we demonstrated that PIAS3 regulated lamellipodium formation during cell migration. To gain insight into molecular mechanisms, we evaluated the effect of PIAS3 knockdown on Rac1/PAK1 and JNK activation. Our results indicated that PIAS3-mediated SUMOylation of Rac1 controlled its activation and modulated the Rac1 downstream activity of PAK1 and JNK. Furthermore, inhibition of Rac1, PAK1, or JNK decreased migration and invasion of RA FLSs. Thus, our observations suggest that PIAS3 suppression may be protective against joint destruction in RA by regulating synoviocyte migration, invasion, and activation.

Successes and failures of chemokine-pathway targeting in rheumatoid arthritis

Chemokines and chemokine receptors are involved in leukocyte recruitment and angiogenesis underlying the pathogenesis of rheumatoid arthritis (RA) and other inflammatory rheumatic diseases. Numerous chemokines, along with both conventional and atypical cell-surface chemokine receptors, are found in inflamed synovia. Preclinical studies carried out in animal models of arthritis involving agents targeting chemokines and chemokine receptors have yielded promising results. However, most human trials of treatment of RA with antibodies and synthetic compounds targeting chemokine signalling have failed to show clinical improvements. Chemokines can have overlapping actions, and their activities can be altered by chemical modification or proteolytic degradation. Effective targeting of chemokine pathways must take acount of these properties, and can also require high levels of receptor occupancy by therapeutic agents to prevent signalling. CCR1 is a promising target for chemokine-receptor blockade.

HIF-2α-induced chemokines stimulate motility of fibroblast-like synoviocytes and chondrocytes into the cartilage-pannus interface in experimental rheumatoid arthritis mouse models

Introduction

Pannus formation and resulting cartilage destruction during rheumatoid arthritis (RA) depends on the migration of synoviocytes to cartilage tissue. Here, we focused on the role of hypoxia-inducible factor (HIF)-2α-induced chemokines by chondrocytes in the regulation of fibroblast-like synoviocyte (FLS) migration into the cartilage-pannus interface and cartilage erosion.

Methods

Collagen-induced arthritis (CIA), K/BxN serum transfer, and tumor necrosis factor-α transgenic mice were used as experimental RA models. Expression patterns of HIF-2α and chemokines were determined via immunostaining, Western blotting and RT-PCR. FLS motility was evaluated using transwell migration and invasion assays. The specific role of HIF-2α was determined via local deletion of HIF-2α in joint tissues or using conditional knockout (KO) mice. Cartilage destruction, synovitis and pannus formation were assessed via histological analysis.

Results

HIF-2α and various chemokines were markedly upregulated in degenerating cartilage and pannus of RA joints. HIF-2α induced chemokine expression by chondrocytes in both primary culture and cartilage tissue. HIF-2α -induced chemokines by chondrocytes regulated the migration and invasion of FLS. Local deletion of HIF-2α in joint tissues inhibited pannus formation adjacent to cartilage tissue and cartilage destruction caused by K/BxN serum transfer. Furthermore, conditional knockout of HIF-2α in cartilage blocked pannus formation in adjacent cartilage but not bone tissue, along with inhibition of cartilage erosion caused by K/BxN serum transfer.

Conclusion

Our findings suggest that chemokines induced by IL-1β or HIF-2α in chondrocytes regulate pannus expansion by stimulating FLS migration and invasion, leading to cartilage erosion during RA pathogenesis.

Inhibitory effects of niclosamide on inflammation and migration of fibroblast-like synoviocytes from patients with rheumatoid arthritis

OBJECTIVES

This study evaluated the anti-inflammatory effect of niclosamide in tumor necrosis factor (TNF)-α-stimulated human rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLS) and inhibitory effects on migration and invasion in RA FLS and investigated the signal mechanism, and further explored the treatment activity of niclosamide on collagen-induced arthritis (CIA).

METHODS

The levels of interleukin (IL)-1β, IL-6, IL-8, IL-10,IL-17A and interferon (IFN)-γ in cultural supernatants were measured by multiplex cytokine assay kits. RA FLS migration and invasion in vitro were measured by the Boyden chamber method and the scratch assay. Signal transduction proteins expression was measured by western blot. The in vivo suppressive effects of niclosamide were elucidated on CIA in a mouse model.

RESULTS

Niclosamide reduced the secretion of IL-1β, IL-6, IL-8, IL-17A and IFN-γ from TNF-α-induced RA FLS in a dose-dependent manner. Niclosamide inhibits FBS-induced migration and invasion and exhibits F-actin alterations in RA FLS. Niclosamide decreased the phosphorylation of c-Jun N-terminal kinase and ERK in TNF-α-stimulated RA FLS and blocked TNF-α-induced IKK, IκBα phosphorylation and translocation of p65. Niclosamide treatments reduced the severity of CIA model.

CONCLUSIONS

Our data suggest for the first time that niclosamide posses the anti-inflammatory effect in RA both in vitro and in vivo.

Increased phosphorylation of ezrin is associated with the migration and invasion of fibroblast-like synoviocytes from patients with rheumatoid arthritis

OBJECTIVE

Increasing evidence indicates that the cytoskeletal protein ezrin may play a critical role in cell motility. This study aims to investigate the role of ezrin in regulating the migration and invasion of fibroblast-like synoviocytes (FLSs) from patients with RA.

METHODS

Synovial tissues were obtained from 12 patients with RA and 6 with OA, and then FLSs were separated from synovial tissues. The expression of ezrin and phosphorylated ezrin (p-ezrin) was examined by Western blotting or IF staining. A specific inhibitor of ezrin phosphorylation and small interference RNA-mediated ezrin knockdown were used to inhibit the phosphorylation of ezrin. Migration and invasion of FLSs in vitro were measured by the Boyden chamber assay.

RESULTS

Increased expression of p-ezrin protein was found in synovial tissue and FLSs in patients with RA compared with patients with OA. Stimulation with TNF-α and IL-1β increased ezrin phosphorylation in RA FLSs. Inhibition of p-ezrin protein by a specific inhibitor of phosphorylation of ezrin and small interfering RNA-mediated knockdown reduced in vitro migration and invasion, as well as actin stress fibre formation in RA FLS. Furthermore, rho kinase and p38 mitogen-activated protein kinase (MAPK) signal pathways were involved in the phosphorylation of ezrin and invasion of RA FLSs.

CONCLUSION

Increased expression of p-ezrin may contribute to aberrant aggressive behaviours of RA FLSs, which are mediated by rho kinase and the p38 MAPK pathway. This suggests a novel strategy targeting phosphorylation of ezrin to prevent synovial invasiveness and joint destruction in RA.

Role of ADAM-17, p38 MAPK, cathepsins, and the proteasome pathway in the synthesis and shedding of fractalkine/CX₃ CL1 in rheumatoid arthritis

OBJECTIVE

To evaluate the mechanism of fractalkine (FKN)/CX3 CL1 synthesis and shedding in rheumatoid arthritis synovial fibroblasts (RASFs) and in rat adjuvant-induced arthritis (AIA).

METHODS

The effect of tumor necrosis factor α (TNFα) and/or interferon-γ (IFNγ) on FKN synthesis and shedding in human RASFs was determined over time by immunostaining, quantitative reverse transcription-polymerase chain reaction, and Western blotting. The role of protease enzymes and signaling pathways was evaluated using chemical inhibitors and small interfering RNA (siRNA). The activity of 20S proteasome in the lysates and the DNA binding of NF-κB/p65 in the nuclear fractions were evaluated. The in vivo relevance of these findings was examined in rat AIA.

RESULTS

In RASFs, stimulation with the combination of TNFα and IFNγ induced cellular expression of FKN within 24 hours. Activation of ADAM-17, but not ADAM-10, partly mediated the proteolytic shedding and release of soluble FKN (sFKN) following TNFα/IFNγ stimulation for 24-72 hours. Compared with control siRNA, ADAM-17 siRNA markedly inhibited TNFα/IFNγ-induced sFKN production (by ∼33%). TNFα/IFNγ-induced sFKN release was markedly suppressed by inhibitors of ADAM-17, p38 MAPK, proteasome, or cathepsin inhibitor but not by inhibitors of caspase 3 or calpain. TNFα/IFNγ-induced proteasome activity also correlated with rapid degradation of IκBα and p38 MAPK phosphorylation. In vivo findings showed increased FKN expression in the joints of rats with AIA, which correlated with increased expression of ADAM-17 and phospho-p38 MAPK.

CONCLUSION

Our results provide new understanding of the role of ADAM-17, p38 MAPK, cathepsins, and the proteasome pathway in FKN expression and shedding. Regulating these pathways may suppress FKN-mediated inflammation and tissue destruction.

Wen Luo Yin inhibits angiogenesis in collagen-induced arthritis rat model and in vitro

ETHNOPHARMACOLOGICAL RELEVANCE AND AIM OF THE STUDY

Wen Luo Yin (WLY) is a traditional Chinese formula, which has the traditional use of scattering cold pathogen, draining dampness, freeing the flow of network vessels and relieving pains. It is extensively used in the treatment of rheumatoid arthritis (RA) patients for more than 2000 years, but its actions on angiogenesis of RA have not been clarified. The present study aims to determine the anti-angiogenic activity of WLY on collagen-induced arthritis (CIA) rat model and in human fibroblast-like synoviocytes of RA (HFLS-RA) and human umbilical vein endothelial cells (HUVEC).

MATERIALS AND METHODS

For in vivo experiment, arthritis was induced by immunization with bovine II collagen in DA rats. Treatment with WLY (3.45, 6.9, 13.8 g/kg, p.o., daily), or vehicle began from day 1 to day 28 of first immunization. The arthritis score, arthritis incidence, microfocal computed tomography analysis and histopathology evaluation of inflamed joints were assessed. Angiogenesis was measured by synovial vessel density with immunohistochemistry and histomorphometric analysis in synovial membrane tissues of joints. For in vitro experiments, HFLS-RA and HUVEC were used. Assays to determine HFLS-RA migration and adhesion were performed in the presence of vascular endothelial growth factor (VEGF)165 or interleukin (IL)-1β and/or the WLY (8, 16, 32 mg/ml). Angiogenesis was assessed by measuring the migration, adhesion, and tube formation of HUVEC. Further the effect of treatment with WLY on expression levels of angiogenic activators in sera of CIA rats and in IL-1β-induced HFLS-RA were evaluated by enzyme linked immunosorbent assay.

RESULTS

WLY significantly decreased the arthritis score and arthritis incidence, and inhibited inflammation, pannus formation, cartilage and bone destruction of inflamed joints in CIA rats. More interestingly, doses of 3.45-13.8 g/kg WLY could markedly reduce the capillaries, small, medium and large vessel density in synovial membrane tissues of inflamed joints. Moreover, WLY suppressed the VEGF-induced chemotactic migration of HFLS-RA and HUVEC, and inhibited matrigel-induced cell adhesion of them. It also disrupted tube formation of HUVEC on matrigel. Furthermore, WLY significantly reduced the expression of angiogenic activators including tumor necrosis factor-α, IL-1β, IL-17, VEGF, VEGFR, angiopoietin (Ang)-1, Ang-2 and Ang-2 receptor in sera of CIA rats and/or in IL-1β-induced HFLS-RA/HUVEC.

CONCLUSIONS

Our data suggest for the first time that WLY posses the anti-angiogenic effect in RA both in vivo and in vitro by downregulating angiogenic activators.

Human cytomegalovirus chemokine receptor US28 induces migration of cells on a CX3CL1-presenting surface

Human cytomegalovirus (HCMV)-encoded G protein-coupled-receptor US28 is believed to participate in virus dissemination through modulation of cell migration and immune evasion. US28 binds different CC chemokines and the CX3C chemokine CX3CL1. Membrane-anchored CX3CL1 is expressed by immune-activated endothelial cells, causing redirection of CX3CR1-expressing leukocytes in the blood to sites of infection. Here, we used stable transfected cell lines to examine how US28 expression affects cell migration on immobilized full-length CX3CL1, to model how HCMV-infected leukocytes interact with inflamed endothelium. We observed that US28-expressing cells migrated more than CX3CR1-expressing cells when adhering to immobilized CX3CL1. US28-induced migration was G protein-signalling dependent and was blocked by the phospholipase Cβ inhibitor U73122 and the intracellular calcium chelator BAPTA-AM. In addition, migration was inhibited in a dose-dependent manner by competition from CCL2 and CCL5, whereas CCL3 had little effect. Instead of migrating, CX3CR1-expressing cells performed ‘dancing-on-the-spot’ movements, demonstrating that anchored CX3CL1 acts as a strong tether for these cells. At low receptor expression levels, however, no significant difference in migration potential was observed when comparing the migration of CX3CR1- and US28-expressing cells. Thus, these data showed that, in contrast to CX3CR1, which promotes efficient cell capture upon binding to anchored CX3CL1, US28 acts to increase the migration of cells upon binding to the same ligand. Overall, this indicates that infected cells probably move more than uninfected cells in inflamed tissues with high CX3CL1 expression, with soluble chemokines affecting the final migration.

Inhibitory effects of simvastatin on migration and invasion of rheumatoid fibroblast-like synoviocytes by preventing geranylgeranylation of RhoA

To investigate the effect of simvastatin on the migration and invasion of fibroblast-like synoviocytes (FLS) from patients with rheumatoid arthritis (RA) and its cellular signal mechanisms, FLS from active RA patients were stimulated with 3 % FBS or GM-CSF in the presence or absence of simvastatin. Cells migration and invasion in vitro were measured by the Boyden chamber method. RhoA activity was assessed by a pull-down assay. Matrix metalloproteinases-2 (MMP-2) activity was evaluated by zymography. Simvastatin inhibits FBS- or GM-CSF-induced migration in a dose-dependent manner by RA FLS, and this inhibitory effect is independent of cell apoptosis. We also found that simvastatin suppressed in vitro invasion, adhesion, MMP-2 activity, cytoskeletal reorganization and RhoA activation. Furthermore, mevalonate or GGPP treatment reversed the inhibitory effect of simvastatin not only on migration and invasion in vitro but also on RhoA activation, and inhibition of RhoA by specific siRNA transfection reduced migration, adhesion and invasion of RA FLS. This study shows that simvastatin reduces RA FLS migration and invasion through the prevention of protein geranylgeranylation and RhoA activation. These findings provide a novel evidence that statin may be benefit for preventing RA arthritic destruction, and also indicate that RhoA may be a new target for the modulation of RA FLS migration and invasion.

Total flavonoids of Bidens bipinnata L. a traditional Chinese medicine inhibits the production of inflammatory cytokines of vessel endothelial cells stimulated by sera from Henoch-Schönlein purpura patients

OBJECTIVES

Bidens bipinnata L. is well known as a traditional antipyretic, anti-inflammatory and anti-rheumatic medicine in China. This study was designed to evaluate the role of total extracted flavonoids from B. bipinnata (TFB) in inhibiting the production of inflammatory cytokines.

METHODS

Human umbilical vein endothelial cells (HUVEC) were used to examine the effect of TFB on the production of inflammatory cytokines. The supernatant interleukin (IL)-8, tumour necrosis factor (TNF)-α and nitric oxide (NO) levels of HUVEC were measured with ELISA methods. Nuclear factor-kappaB (NF-κB) and fractalkine expression was evaluated by RT-PCR and Western blot methods, respectively.

KEY FINDINGS

We observed that IL-8, TNF-α and NO release of HUVEC incubated with sera from active Henoch-Schönlein purpura (HSP) was significantly increased. TFB intervention may significantly suppressed the supernatant IL-8, TNF-α and NO levels of HUVEC. Similarly, TFB obviously suppressed the NF-κB and fractalkine mRNA and protein expression.

CONCLUSIONS

These results suggested that TFB may be useful for improving microvascular inflammation in HSP patients.

Role of p21-activated kinase 1 in regulating the migration and invasion of fibroblast-like synoviocytes from rheumatoid arthritis patients

OBJECTIVE

To investigate the role of p21-activated kinase 1 (PAK1) in regulating migration, invasion and MMP expression in RA fibroblast-like synoviocytes (FLS).

METHODS

RA FLS migration and invasion in vitro were measured by the Boyden chamber method. Invasion of RA FLS into cartilage was detected in the severe combined immunodeficiency (SCID) mouse co-implantation model of RA in vivo. PAK1 and MT1-MMP expression were examined by western blotting. ELISA was used to measure the production and activity of MMPs.

RESULTS

Phosphorylated PAK1 (p-PAK1) protein expression was increased in ex vivo synovial membrane cells from RA patients. Stimulation with IL-1β or TNF-α up-regulated p-PAK1 expression. Inhibition of PAK1 by transfection with dominant negative PAK1 mutant (dnPAK1) reduced in vitro migration and invasion of RA FLS. In the SCID mouse model, RA FLS invasion into cartilage was attenuated by transfection with dnPAK1 in vivo. PAK1 regulated IL-1β-induced production and activity of MMP-13 and MT1-MMP. Inhibition of MMP-13 or MT1-MMP activity also reduced RA FLS invasion. Furthermore, dnPAK1 transfection inhibited c-Jun N-terminal kinase (JNK) activation, but did not affect the activities of extracellular signal-regulated kinases and p38. Inhibition of the JNK activity by chemical inhibitor significantly reduced the migration, invasion and production of MMP-13 and MT1-MMP.

CONCLUSION

PAK1 plays an important role in regulating the migration, invasion and production and activity of MMPs in RA FLS, which is mediated by the JNK pathway. This suggests a novel strategy targeting PAK1 to prevent joint destruction of RA.

Pathological role of fractalkine/CX3CL1 in rheumatic diseases: a unique chemokine with multiple functions

Understanding rheumatic diseases from the perspective of chemokine biology has shaped and will continue to shape our approach for targeted drug design. Among different kinds of chemokines, fractalkine/CX3CL1 has been found to play an important role in inflammation, portraying unique functional, and structural characteristics. This review summarizes the emerging role of fractalkine/CX3CL1 from a functional and clinical perspective and provides evidence to validate it as a potential therapeutic target in rheumatic diseases such as rheumatoid arthritis, Sjögren's syndrome, systemic lupus erythematosus, scleroderma, as well as diseases related to vascular inflammation. From this, recent studies investigating potential therapeutic agents against fractalkine/CX3CL1's role in pathology have shown promise.

Activation of human fibroblast-like synoviocytes by uric acid crystals in rheumatoid arthritis

Hyperuricemia-mediated uric acid crystal formation may cause joint inflammation and provoke the destruction of joints through the activation of inflammasome-mediated innate immune responses. However, the immunopathological effects and underlying intracellular regulatory mechanisms of uric acid crystal-mediated activation of fibroblast-like synoviocytes (FLS) in rheumatoid arthritis (RA) have not been elucidated. Therefore, we investigated the in vitro effects of monosodium urate crystals, alone or in combination with the inflammatory cytokines tumor-necrosis factor (TNF)-α or interleukin (IL)-1β, on the activation of human FLS from RA patients and normal control subjects and the underlying intracellular signaling mechanisms of treatment with these crystals. Monosodium urate crystals were able to significantly increase the release of the inflammatory cytokine IL-6, the chemokine CXCL8 and the matrix metalloproteinase (MMP)-1 from both normal and RA-FLS (all P<0.05). Moreover, the additive or synergistic effect on the release of IL-6, CXCL8 and MMP-1 from both normal and RA-FLS was observed following the combined treatment with monosodium urate crystals and TNF-α or IL-1β. Further experiments showed that the release of the measured inflammatory cytokine, chemokine and MMP-1 stimulated by monosodium urate crystals were differentially regulated by the intracellular activation of extracellular signal-regulated kinase and c-Jun N-terminal kinase pathways but not the p38 mitogen-activated protein kinase pathway. Our results therefore provide a new insight into the uric acid crystal-activated immunopathological mechanisms mediated by distinct intracellular signal transduction pathways leading to joint inflammation in RA.

Arthritis is associated with T-cell-induced upregulation of Toll-like receptor 3 on synovial fibroblasts

Introduction

Toll-like receptors (TLRs) are likely to play crucial roles in the pathogenesis of rheumatoid arthritis (RA). The aim of this study was to determine the key TLRs in synovium and explore their roles in the activation of fibroblast-like synoviocytes (FLSs) mediated by T cells in arthritis.

Methods

Pristane-induced arthritis (PIA) was established by subcutaneous injection with pristane at the base of the rat's tail. TLR expression in synovium from PIA rats was detected at different time points by performing real-time PCR. Polyinosinic:polycytidylic acid (poly(I:C)) was intra-articularly administrated to PIA rats, and arthritis was monitored macroscopically and microscopically. Synovial TLR3 was detected by immunohistochemical staining. Rat FLSs were stimulated with pristane-primed T cells or pristane-primed, T-cell conditioned medium. The intervention of TLR3 in FLSs was achieved by specific short-hairpin RNA (shRNA) or an antibody. The migration ability of FLSs was measured by using the scratch test, and gene expression was detected by using real-time PCR. FLSs from RA patients were stimulated with various cytokines and TLR ligands, and TLR3 expression was detected by performing real-time PCR. In addition, with different concentrations of poly(I:C) stimulation, TLR3 expression of FLSs from RA patients and patients with osteoarthritis (OA) was compared.

Results

Synovium TLR3 displayed early and persistent overexpression in PIA rats. TLR3 was expressed in FLSs, and local treatment with poly(I:C) synergistically aggravated the arthritis. Rat FLSs co-cultured with pristane-primed T cells showed strengthened migration ability and significant upregulation of TLR3, IFN-β, IL-6 and matrix metalloproteinase 3 (MMP3) expression, which could also be induced by pristane-primed, T-cell conditioned medium. The upregulation of cytokines and MMPs was blocked by shRNA or TLR3 antibodies. In RA FLSs with cytokine or TLR ligand stimulation, TLR3 expression exhibited remarkable upregulation. Furthermore, RA FLSs showed higher reactivity than OA FLSs to poly(I:C).

Conclusions

TLR3 in the synovium of PIA rats was overexpressed, and activation of the TLR3 signaling pathway could aggravate this arthritis. The induction of TLR3 in FLSs resulted from T cell-derived inflammatory stimulation and could further mediate FLS activation in arthritis. We conclude that TLR3 upregulation of FLSs activated by T cells results in articular inflammation.

Cell-cell interactions in rheumatoid arthritis synovium

Understanding the pathogenesis of joint inflammation and destruction in rheumatoid arthritis involves dissection of the cellular and molecular interactions that occur in synovial tissue. Development of effective targeted therapies has been based on progress in achieving such insights. Safer and more specific approaches to treatment could flow from discovery of cell-cell interaction pathways that are specific to inflammation of the joint and less important in the defense against systemic infection. This article highlights selected cell-cell interactions in rheumatoid arthritis synovium that may be worthy of evaluation as future therapeutic targets.

Anti-neuropilin-1 peptide inhibition of synoviocyte survival, angiogenesis, and experimental arthritis

OBJECTIVE

To delineate the role of neuropilin-1 (NP-1), a vascular endothelial growth factor receptor (VEGFR), in rheumatoid inflammation and to determine whether blockade of NP-1 could suppress synoviocyte survival and angiogenesis.

METHODS

VEGF(111-165) peptide, which encompasses the NP-1 binding domain of VEGF(165), was generated by cleaving VEGF(165) with plasmin. The effect of this peptide on the interaction between VEGF(165) and its receptor was determined by (125)I-VEGFR binding assay. Assays to determine synoviocyte apoptosis, adhesion, and migration were performed in the presence of VEGF(165) and/or the peptide. VEGF(165)-induced angiogenesis was assessed by measuring the proliferation, tube formation, and wounding migration of endothelial cells (ECs). Mice were immunized with type II collagen to induce experimental arthritis.

RESULTS

VEGF(111-165) peptide specifically inhibited the binding of (125)I-VEGF(165) to NP-1 on rheumatoid synoviocytes and ECs. The peptide eliminated the VEGF(165)-mediated increase in synoviocyte survival and activation of p-ERK and Bcl-2. The peptide also completely inhibited a VEGF(165)-induced increase in synoviocyte adhesion and migration. In addition, the anti-NP-1 peptide blocked VEGF(165)-stimulated proliferation, capillary tube formation, and wounding migration of ECs in vitro. VEGF(165)-induced neovascularization in a Matrigel plug in mice was also blocked by treatment with the peptide. Finally, subcutaneous injection of anti-NP-1 peptide suppressed arthritis severity and autoantibody formation in mice with experimental arthritis and inhibited synoviocyte hyperplasia and angiogenesis in arthritic joints.

CONCLUSION

Anti-NP-1 peptide suppressed VEGF(165)-induced increases in synoviocyte survival and angiogenesis, and thereby blocked experimental arthritis. Our findings suggest that anti-NP-1 peptide could be useful in alleviating chronic arthritis.

Fractalkine-induced endothelial cell migration requires MAP kinase signaling

BACKGROUND/AIMS

Angiogenesis is a well-established characteristic in the rheumatoid arthritis (RA) synovial pannus. We have previously demonstrated that fractalkine (Fkn/ CX3CL1) expression is significantly increased in the RA joint and that fractalkine induces angiogenesis. In this work we studied mechanisms through which Fkn functions as an angiogenic mediator.

METHODS

Human microvascular endothelial cells (HMVECs) and human umbilical vein endothelial cells (HUVECs) were stimulated with Fkn and analyzed by Western blotting or stained with Alexa Fluor 488 phalloidin for F-actin to characterize the time frame of cytoskeletal rearrangement. Fkn-induced HUVEC chemotaxis was performed in the presence and absence of MAP kinase inhibitors.

RESULTS

Phalloidin staining of F-actin revealed significant cytoskeletal rearrangements in HUVECs and HMVECs starting as early as 10 min after Fkn stimulation. Western blotting demonstrated that HUVEC and HMVEC stimulation with Fkn for 1-30 min resulted in phosphorylation of JNK. Fkn also induces significant phosphorylation of Erk 1/2 in HUVECs over a time course ranging from 1 to 15 min. A somewhat similar time course (5-15 min) was detected for Erk 1/2 phosphorylation in HMVECs. Inhibitors of either JNK or Erk 1/2 nearly abolish Fkn-induced HUVEC migration.

CONCLUSIONS

We demonstrate that Fkn induces significant alterations in cytoskeletal structure and specifically activates the MAP kinases, JNK and Erk 1/2, both of which appear necessary for endothelial cell migration. Our results suggest that the endogenous Fkn present in the RA joint may induce angiogenesis through activation of the JNK and Erk 1/2 pathways.

Correlation of CX3CL1 and CX3CR1 Levels with Response to Infliximab Therapy in Patients with Rheumatoid Arthritis

Objective.

To examine the relation between serum chemokine levels and patient responsiveness to infliximab, and the influence of infliximab administration on serum chemokine levels.

Methods.

Serum levels of the chemokines CX3CL1, CXCL8, CCL3, and CXCL10 were quantified prior to (at baseline) and after 30 weeks of treatment with infliximab in 20 patients using enzyme-linked immunosorbent assays. Disease status was assessed using the Disease Activity Score (DAS28). The response to infliximab was classified according to the European League Against Rheumatism (EULAR) response criteria.

Results.

By 30 weeks, infliximab produced a significant overall reduction in DAS28 among the 20 patients with RA, although only 12 achieved a good to moderate response based on EULAR response criteria. A significant reduction in CX3CL1 was seen in the responsive group, although infliximab treatment had no significant effect on the serum levels of the other 3 chemokines. Comparison of patients with lower (< 2000 pg/ml) and higher (≥ 2000 pg/ml) basal CX3CL1 levels revealed that DAS28, erythrocyte sedimentation rate, C-reactive protein, and CX3CL1 levels were all significantly diminished by infliximab in RA patients with lower basal CX3CL1 levels, but not in those with higher basal levels. In addition, cell-surface expression of CX3CR1 protein in peripheral blood CD8+CD3+ T cells and mRNA expression of CX3CR1 in lymphocytes were both significantly downregulated after infliximab treatment in the responsive group.

Conclusion.

Our results suggest that the CX3CL1-CX3CR1 system in patients with active RA may be sensitive to anti-tumor necrosis factor-α therapy, and confirm that CX3CL1 plays a crucial role in the pathogenesis of RA.

Fractalkine functions as a chemoattractant for osteoarthritis synovial fibroblasts and stimulates phosphorylation of mitogen-activated protein kinases and Akt

Fractalkine (FKN/CX3CL1) has been detected in synovial fluids from osteoarthritis (OA) patients. Additionally, low-level expression of the FKN receptor, CX3CR1, has been demonstrated in OA synovial lining. This study aimed to determine a biological function for this ligand/receptor pair in OA and to assess a potential signalling mechanism for FKN in this predominant synovial lining cell type, using chemotaxis assays, Western blotting and F-actin staining. Chemotaxis assays demonstrate that the chemokine domain of FKN effectively induces migration of OA fibroblasts. Consistent with this finding, visualization of F-actin demonstrates that 1 or 10 nM FKN induces noticeable reorganization of cytoskeletal structure in OA fibroblasts after 30 min stimulation with a maximal enhancement at approximately 2 h. In addition, Western blotting analysis demonstrates that FKN stimulates phosphorylation of the mitogen-activated protein (MAP) kinases p38, c-Jun N-terminal kinase (JNK) and extracellular-regulated kinase (ERK) 1/2 as well as the serine-threonine kinase Akt at Ser 473 and Thr 308. All these phosphorylation events occur in a time-dependent manner, with little or no activation within 1 min, and maximal activation occurring typically between 5 and 30 min. Moreover, inhibition of ERK 1/2 significantly reduces FKN-induced OA fibroblast migration. These results suggest that FKN is a novel chemoattractant for OA fibroblasts, consistent with FKN-induced alterations in cytoskeletal structure. In addition, FKN induces OA fibroblast signalling via the MAP kinases p38, JNK and ERK 1/2, as well as Akt.

[Fractalkine--a proinflammatory chemokine in rheumatoid 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.