Fibroblast-like synoviocytes in inflammatory arthritis pathology: the emerging role of cadherin-11

Cyclophilin A secreted from fibroblast-like synoviocytes is involved in the induction of CD147 expression in macrophages of mice with collagen-induced arthritis

Background

Cyclophilin A (CypA), a member of the immunophilin family, is a ubiquitously distributed intracellular protein. Recent studies have shown that CypA is secreted by cells in response to inflammatory stimuli. Elevated levels of extracellular CypA and its receptor, CD147 have been detected in the synovium of patients with RA. However, the precise process of interaction between CypA and CD147 in the development of RA remains unclear. This study aimed to investigate CypA secretion from fibroblast-like synoviocytes (FLS) isolated from mice with collagen-induced arthritis (CIA) and CypA-induced CD147 expression in mouse macrophages.

Findings

CIA was induced by immunization with type II collagen in mice. The expression and localization of CypA and CD147 was investigated by immunoblotting and immunostaining. Both CypA and CD147 were highly expressed in the joints of CIA mice. CD147 was expressed in the infiltrated macrophages in the synovium of CIA mice. In vitro, spontaneous CypA secretion from FLS was detected and this secretion was increased by stimulation with lipopolysaccharide. CypA markedly increased CD147 levels in macrophages.

Conclusions

These findings suggest that an interaction in the synovial joints between extracellular CypA and CD147 expressed by macrophages may be involved in the mechanisms underlying the development of arthritis.

Rheumatoid Fibroblast-like Synoviocytes Downregulate Foxp3 Expression by Regulatory T Cells Via GITRL/GITR Interaction

Fibroblast-like synoviocytes (FLS) colocalize with leukocyte infiltrates in rheumatoid synovia. Proinflammatory leukocytes are known to amplify inflammation by signaling to FLS, but crosstalk between FLS and regulatory T cells (Tregs) remains uncharacterized. To address this possibility, we cocultured FLS lines derived from arthritic mice with Tregs. FLS that expressed the ligand for glucocorticoid-induced TNF receptor family-related gene (GITR) decreased expression of Foxp3 and GITR in Tregs in a contact-dependent manner. This effect was abolished by blocking antibody to GITR. On the other hand, the Tregs caused the FLS to increase IL-6 production. These results demonstrate that inflamed FLS license Tregs to downregulate Foxp3 expression via the GITRL/GITR interaction while the Tregs induce the FLS to increase their production of IL-6. Our findings suggest that the interaction between FLS and Tregs dampens the anti-inflammatory activity of Tregs and amplifies the proinflammatory activity of FLS, thereby exacerbating inflammatory arthritis.

The use of anti-COX2 siRNA coated onto PLGA nanoparticles loading dexamethasone in the treatment of rheumatoid arthritis

In drug delivery systems, some genes have the potential to interrupt unnecessary gene expression in specific target cells. In this study, two types of drug, glucocorticoids and siRNA, were co-delivered into conditioned cells to inhibit the expression of unnecessary genes and proteins involved in arthritis. To deliver the two factors into a human chondrocyte cell line (C28/I2), dexamethasone was first loaded into PLGA nanoparticles, and then drug-loaded PLGA nanoparticles were complexed with poly(ethyleneimine) (PEI)/siRNA. To test the co-delivery of siRNA and dexamethasone into chondrocytes, cells were transfected with green fluorescence protein siRNA (GFP siRNA) and drugs. After transfection with GFP siRNA, 70% reduction of C28/I2 cells demonstrated GFP expression, whereas MOCK carrying PLGA nanoparticles and PLGA nanoparticles without siRNA showed no differences of GFP expressions. COX-2 and iNOS productions in C28/I2 cells were examined after TNF-α pre-treatment to induce expression of arthritis-related molecules in vitro. The reduction of gene and protein expression associated with arthritis by transfection with dexamethasone-loaded and COX-2 siRNA-complexed PLGA nanoparticles was evaluated by RT-PCR, real time-qPCR, immunoblotting, immunohistochemistry, and immunofluorescence imaging.

Transcriptional profiling of stroma from inflamed and resting lymph nodes defines immunological hallmarks

Lymph node stromal cells (LNSCs) closely regulate immunity and self-tolerance, yet key aspects of their biology remain poorly elucidated. Here, comparative transcriptomic analyses of mouse LNSC subsets demonstrated the expression of important immune mediators, growth factors and previously unknown structural components. Pairwise analyses of ligands and cognate receptors across hematopoietic and stromal subsets suggested a complex web of crosstalk. Fibroblastic reticular cells (FRCs) showed enrichment for higher expression of genes relevant to cytokine signaling, relative to their expression in skin and thymic fibroblasts. LNSCs from inflamed lymph nodes upregulated expression of genes encoding chemokines and molecules involved in the acute-phase response and the antigen-processing and antigen-presentation machinery. Poorly studied podoplanin (gp38)-negative CD31(-) LNSCs showed similarities to FRCs but lacked expression of interleukin 7 (IL-7) and were identified as myofibroblastic pericytes that expressed integrin α(7). Together our data comprehensively describe the transcriptional characteristics of LNSC subsets.

Expression and function of β-arrestin 2 stimulated by IL-1β in human fibroblast-like synoviocytes and the effect of paeoniflorin

The aim of this study was to explore the expression and function of β-arrestin 2 in human fibroblast-like synoviocytes (FLS) stimulated by IL-1β and the effect of paeoniflorin (Pae). We isolated and cultured human FLS, which were stimulated by IL-1β. The FLS proliferations were detected by [3H] thymidine incorporation. The level of cAMP stimulated by IL-1β on different times was investigated by radioimmunoassay, and the activity of PKA was measured by luminescent kinase assay. The expression of β-arrestin 2 was measured by western blot. We found that the human FLS proliferation increased apparently in 24 h, and the activities of PKA and cAMP accumulation increased significantly in 6 h after stimulated by IL-1β, while cAMP accumulation and the activities of PKA decreased especially in 24 h when the expression of β-arrestin 2 increased significantly. Decreased cAMP accumulation and the increased expression of β-arrestin 2 may reveal a positive correlation with the FLS proliferation. Pae (10(-5), 10(-6), 10-7 mol•L(-1)) in vitro could suppress the FLS proliferation and the high expression of β-arrestin 2. The expression of β-arrestin 2 may have a positive correlation with the human FLS proliferation, while the activities of PKA and cAMP accumulation have a negative correlation with the proliferation. The increased β-arrestin 2 may down-regulate cAMP-PKA signaling pathway and promote FLS proliferation. Pae may suppress the expression of β-arrestin 2 and up-regulate cAMP-PKA signaling, which may be one of the mechanisms for the effects of Pae on inhibiting human FLS proliferation.

Rheumatoid arthritis and anaesthesia

There has been a great deal of progress in our understanding and management of rheumatoid arthritis in recent years. The peri-operative management of rheumatoid arthritis patients can be challenging and anaesthetists need to be familiar with recent developments and potential risks of this multi system disease.

Hyaluronan within fascia in the etiology of myofascial pain

The layers of loose connective tissue within deep fasciae were studied with particular emphasis on the histochemical distribution of hyaluronan (HA). Samples of deep fascia together with the underlying muscles were taken from neck, abdomen and thigh from three fresh non-embalmed cadavers. Samples were stained with hematoxylin-eosin, Azan-Mallory, Alcian blue and a biotinylated HA-binding protein specific for HA. An ultrasound study was also performed on 22 voluntary subjects to analyze the thickness of these deep fasciae and their sublayers. The deep fascia presented a layer of HA between fascia and the muscle and within the loose connective tissue that divided different fibrous sublayers of the deep fascia. A layer of fibroblast-like cells that stained prominently with Alcian blue stain was observed. It was postulated that these are cells specialized for the biosynthesis of the HA-rich matrix. These cells we have termed "fasciacytes", and may represent a new class of cells not previously recognized. The ultrasound study highlighted a mean thickness of 1.88 mm of the fascia lata, 1.68 mm of the rectus sheath, and 1.73 mm of the sternocleidomastoid fascia. The HA within the deep fascia facilitates the free sliding of two adjacent fibrous fascial layers, thus promoting the normal function associated with the deep fascia. If the HA assumes a more packed conformation, or more generally, if the loose connective tissue inside the fascia alters its density, the behavior of the entire deep fascia and the underlying muscle would be compromised. This, we predict, may be the basis of the common phenomenon known as "myofascial pain."

Cadherin-11 regulates fibroblast inflammation

Fibroblasts are important participants in inflammation. Although not leukocytes, their capacity to produce cytokines, chemokines, and other inflammatory factors locally in tissues suggests that they can contribute to inflammatory diseases. For example, fibroblasts in a rheumatoid arthritis (RA) joint are a dominant source of IL-6 and RANKL in the synovium, both of which are therapeutic targets for inflammation and bone erosion. Previously, we found that fibroblasts can be targeted by mAb directed against cadherin-11 (cad-11), a mesenchymal cadherin that fibroblasts selectively express. Targeting cad-11 significantly reduced inflammation as assessed by joint swelling and clinical inflammation scores. However, the mechanism by which anti-cad-11 reduced inflammation was not known. Here, we show that cad-11 engagement induces synovial fibroblasts to secret proinflammatory cytokines including IL-6. Cad-11 engagement strongly synergized with TNF-α and IL-1β in the induction of IL-6. Importantly, cad-11 activated MAP kinases and NF-κB for IL-6 induction. IL-6 levels in ankles of inflamed joints were reduced in cad-11 mutant mice compared to wild-type mice with inflammatory arthritis. Thus, we suggest that cad-11 modulates synovial fibroblasts to evoke inflammatory factors that may contribute to the inflammatory process in RA.

The tumour-associated glycoprotein podoplanin is expressed in fibroblast-like synoviocytes of the hyperplastic synovial lining layer in rheumatoid arthritis

Introduction

Activated fibroblast-like synoviocytes (FLSs) in rheumatoid arthritis (RA) share many characteristics with tumour cells and are key mediators of synovial tissue transformation and joint destruction. The glycoprotein podoplanin is upregulated in the invasive front of several human cancers and has been associated with epithelial-mesenchymal transition, increased cell migration and tissue invasion. The aim of this study was to investigate whether podoplanin is expressed in areas of synovial transformation in RA and especially in promigratory RA-FLS.

Methods

Podoplanin expression in human synovial tissue from 18 RA patients and nine osteoarthritis (OA) patients was assessed by immunohistochemistry and confirmed by Western blot analysis. The expression was related to markers of synoviocytes and myofibroblasts detected by using confocal immunofluoresence microscopy. Expression of podoplanin, with or without the addition of proinflammatory cytokines and growth factors, in primary human FLS was evaluated by using flow cytometry.

Results

Podoplanin was highly expressed in cadherin-11-positive cells throughout the synovial lining layer in RA. The expression was most pronounced in areas with lining layer hyperplasia and high matrix metalloproteinase 9 expression, where it coincided with upregulation of α-smooth muscle actin (α-sma). The synovium in OA was predominantly podoplanin-negative. Podoplanin was expressed in 50% of cultured primary FLSs, and the expression was increased by interleukin 1β, tumour necrosis factor α and transforming growth factor β receptor 1.

Conclusions

Here we show that podoplanin is highly expressed in FLSs of the invading synovial tissue in RA. The concomitant upregulation of α-sma and podoplanin in a subpopulation of FLSs indicates a myofibroblast phenotype. Proinflammatory mediators increased the podoplanin expression in cultured RA-FLS. We conclude that podoplanin might be involved in the synovial tissue transformation and increased migratory potential of activated FLSs in RA.

[Interleukins network in rheumatoid arthritis pathophysiology: beyond proinflammatory cytokines]

Rheumatoid arthritis (RA) is a systemic autoimmune disease characterized by synovitis and progressive destruction of the joint cartilage and underlying bone, together with diverse extra-articular manifestations. Cytokines act as soluble effector mediators of the inflammatory process. Therapeutic neutralization with monoclonal antibodies against the pro-inflammatory cytokines TNF-alpha and interleukin 1 (IL-1) has shown a clear efficacy on inflammation and clinical manifestations of RA, although a percentage of patients do not respond. This review covers new relevant cytokines in the RA physiopathology and potential biomarkers of inflammation. The current challenge is to develop biomarkers that enable an earlier diagnosis, as well as prognostic markers and new therapeutic candidates. Combined administration of several of these cytokines could eventually address a personalized treatment approach for each patient.

The changing face of rheumatoid arthritis: sustained remission for all?

Earlier diagnosis and treatment, plus biological therapies, have transformed the outlook for many patients with rheumatoid arthritis. In the future, new biomarkers for diagnosis, prognosis and therapeutic response will further improve outcomes. Additionally, preclinical diagnosis and tolerogenic therapies could provide sustained remission for some individuals, although ethical and societal challenges must also be addressed before rheumatoid arthritis becomes 'yesterday's disease'.

Rheumatoid arthritis progression mediated by activated synovial fibroblasts

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by synovial hyperplasia and progressive joint destruction. Rheumatoid arthritis synovial fibroblasts (RASFs) are leading cells in joint erosion and contribute actively to inflammation. RASFs show an activated phenotype that is independent of the inflammatory environment and requires the combination of several factors. Although new aspects regarding RASF activation via matrix degradation products, epigenetic modifications, inflammatory factors, Toll-like receptor (TLR) activation and others have recently been uncovered, the primary pathophysiological processes in early arthritis leading to permanent activation are mostly unknown. Here, we review new findings regarding RASF activation and their altered behavior that contribute to matrix destruction and inflammation as well as their potential to spread RA.