Grafting of fibroblasts isolated from the synovial membrane of rheumatoid arthritis (RA) patients induces chronic arthritis in SCID mice-A novel model for studying the arthritogenic role of RA fibroblasts in vivo

Matrix-mediated activation of murine fibroblast-like synoviocytes

Fibroblast-like synoviocytes (FLS) are key cells promoting cartilage damage and bone loss in rheumatoid arthritis (RA). They are activated to assume an invasive and migratory phenotype. While mechanisms of FLS activation are unknown, evidence suggests that pre-damaged extracellular matrix (ECM) of the cartilage can trigger FLS activation. Integrin α11β1 might be involved in the activation, as it is increased in RA patients and hTNFtg mice, an RA mouse model. We treated murine chondrocytes with TNFα to produce a damaged, RA-like matrix. Comparison to healthy chondrocyte matrix revealed decreased ECM proteins, e.g. collagens and proteoglycans, increased matrix-degrading proteins and elevated levels of inflammatory cytokines. FLS responded to the damaged chondrocyte matrix with a matrix-remodeling and pro-inflammatory phenotype characterized by a gene signature involved in matrix degradation and increased production of CLL11 and CCL19. Damaged chondrocyte matrix stimulated increased Itga11 expression in FLS, correlating with the increased α11β1 amounts in RA patients. FLS deficient in integrin α11β1 released lower amounts of inflammation-associated cytokines. Our results demonstrate differences in healthy and RA-like chondrocyte ECM and distinctly different responses of wt FLS to damaged versus healthy ECM.

Redefinition of Synovial Fibroblasts in Rheumatoid Arthritis

The breakdown of immune tolerance and the rise in autoimmunity contribute to the onset of rheumatoid arthritis (RA), driven by significant changes in immune components. Recent advances in single-cell and spatial transcriptome profiling have revealed shifts in cell distribution and composition, expanding our understanding beyond molecular-level changes in inflammatory cytokines, autoantibodies, and autoantigens in RA. Surprisingly, synovial fibroblasts (SFs) play an active immunopathogenic role rather than remaining passive bystanders in RA, with notable alterations in their subpopulation distribution and composition. This study examines these changes in SF heterogeneity, assesses their impact on RA progression, and elucidates the immune characteristics and functions of SF subsets in the RA autoimmunity, encompassing both intrinsic and adaptive immunity. Additionally, this review discusses therapeutic strategies targeting immune SF subsets, highlighting the potential of future interventions in SF phenotypic reprogramming. Overall, this review redefines the role of SFs in RA and suggests targeting SF phenotypic reprogramming and its upstream molecules as a promising therapeutic approach to restore immune balance and modulate immune tolerance in RA.

Mitochondrial Dysfunction Affects the Synovium of Patients with Rheumatoid Arthritis and Osteoarthritis Differently

There is growing evidence regarding the role of mitochondrial dysfunction in osteoarthritis (OA) and rheumatoid arthritis (RA). However, quantitative comparison of synovial mitochondrial derangements in these main arthritis forms is missing. A prospective clinical study was conducted on adult patients undergoing knee surgery. Patients were allocated into RA and OA groups based on disease-specific clinical scores, while patients without arthritis served as controls. Synovial samples were subjected to high-resolution respirometry to analyze mitochondrial functions. From the total of 814 patients, 109 cases were enrolled into the study (24 RA, 47 OA, and 38 control patients) between 1 September 2019 and 31 December 2021. The decrease in complex I-linked respiration and dyscoupling of mitochondria were characteristics of RA patients, while both arthritis groups displayed reduced OxPhos activity compared to the control group. However, no significant difference was found in complex II-related activity between the OA and RA groups. The cytochrome C release and H₂O₂ formation were increased in both arthritis groups. Mitochondrial dysfunction was present in both arthritis groups; however, to a different extent. Consequently, mitochondrial protective agents may have major benefits for arthritis patients. Based on our current study, we recommend focusing on respiratory complex I in rheumatoid arthritis research.

Expression levels of CXCR4 and CXCL12 in patients with rheumatoid arthritis and its correlation with disease activity

The present study aimed to investigate the expression levels of C-X-C motif chemokine receptor 4 (CXCR4) and CXC ligand 12 (CXCL12) in patients with rheumatoid arthritis (RA) and the correlation with disease activity. In total, 60 patients with RA were selected as the study group, comprising of 28 patients in active-stage and 32 patients in remission-stage. In addition, 60 patients with osteoarthritis were selected as the control group. Western blotting and ELISA were used to detect the expression of CXCR4 and CXCL12, respectively. The Spearman's correlation test was used to analyze correlations between CXCR4 and CXCL12, and erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), disease activity score 28 (DAS28) scores and rheumatoid factor (RF). The present results suggested that CXCR4 and CXCL12 expression levels in the serum and joint synovial fluid of the study group were significantly higher compared with the control group (P<0.05). Moreover, CXCR4 and CXCL12 expression levels in the RA-active group were higher compared with the remission (P<0.05) and control groups (P<0.01). The Pearson test results suggested that the expression levels of CXCR4 and CXCL12 in the serum and joint synovial fluid of patients with RA had a positive correlation with the ESR, CRP, RF and DAS28 scores (P<0.05). CXCL12 and CXCR4 were highly expressed in the serum and joint synovial fluid of patients with RA, and these expression levels were positively correlated with ESR, CRP, RF and DAS28 scores. Therefore, these clinical parameters may be used as indicators to evaluate the disease activity of patients with RA.

Synovial tissue biopsy analysis: unlocking the hidden secrets to personalised medicine?

Rheumatoid arthritis is an immune-mediated inflammatory disease of the synovium. Yet we still lack robust tissue-specific (synovial) biomarkers that are able to guide clinical decisions and stratify patients according to their disease subgroup and predicted response to treatment. The EULAR Synovitis Study Group and the OMERACT synovial tissue biopsy (STB) Special Interests Group have undertaken a consensus exercise to identify factors that are important for the standardisation of STB handling and analytical procedures in two situations—clinical practice and translational research.

Induction of chronic destructive arthritis in SCID mice by arthritogenic fibroblast-like synoviocytes derived from mice with antigen-induced arthritis

Background

Fibroblast-like synoviocytes (FLSs) from patients with rheumatoid arthritis (RA) are autonomously activated to maintain inflammation and joint destruction in co-transplantation models. To elucidate inducing mechanisms involved in this altered behavior, the arthritogenic potential of FLSs from murine antigen-induced arthritis (AIA) were investigated in a transfer model.

Methods

FLSs were isolated, expanded in vitro, and transferred into knee joint cavities of severe combined immunodeficient (SCID) mice. Their arthritogenic capacity was assessed by monitoring joint swelling and evaluation of histological parameters 70 to 100 days after transfer.

Results

FLSs from AIA mice were able to transfer arthritis into recipient SCID mice. FLS transfer induced a chronic arthritis with recruitment of inflammatory cells and marked cartilage destruction. Long-lasting inflammation was not required for imprinting of arthritogenicity in FLSs since cells isolated from acute arthritic joints were fully competent to transfer arthritis. We also observed arthritogenic potential in FLSs isolated from contralateral non-arthritic joints in our monoarticular arthritis model.

Conclusions

We show that the transformation of FLSs into arthritogenic cells occurs early in arthritis development. This challenges current hypotheses on the role of these cells in arthritis pathogenesis and opens up the way for further mechanistic studies.

Identification of a transitional fibroblast function in very early rheumatoid arthritis

OBJECTIVES

Synovial fibroblasts actively regulate the inflammatory infiltrate by communicating with neighbouring endothelial cells (EC). Surprisingly, little is known about how the development of rheumatoid arthritis (RA) alters these immunomodulatory properties. We examined the effects of phase of RA and disease outcome (resolving vs persistence) on fibroblast crosstalk with EC and regulation of lymphocyte recruitment.

METHODS

Fibroblasts were isolated from patients without synovitis, with resolving arthritis, very early RA (VeRA; symptom ≤12 weeks) and established RA undergoing joint replacement (JRep) surgery. Endothelial-fibroblast cocultures were formed on opposite sides of porous filters. Lymphocyte adhesion from flow, secretion of soluble mediators and interleukin 6 (IL-6) signalling were assessed.

RESULTS

Fibroblasts from non-inflamed and resolving arthritis were immunosuppressive, inhibiting lymphocyte recruitment to cytokine-treated endothelium. This effect was lost very early in the development of RA, such that fibroblasts no longer suppressed recruitment. Changes in IL-6 and transforming growth factor beta 1 (TGF-β1) signalling appeared critical for the loss of the immunosuppressive phenotype. In the absence of exogenous cytokines, JRep, but not VeRA, fibroblasts activated endothelium to support lymphocyte.

CONCLUSIONS

In RA, fibroblasts undergo two distinct changes in function: first a loss of immunosuppressive responses early in disease development, followed by the later acquisition of a stimulatory phenotype. Fibroblasts exhibit a transitional functional phenotype during the first 3 months of symptoms that contributes to the accumulation of persistent infiltrates. Finally, the role of IL-6 and TGF-β1 changes from immunosuppressive in resolving arthritis to stimulatory very early in the development of RA. Early interventions targeting 'pathogenic' fibroblasts may be required in order to restore protective regulatory processes.

DKK1 expression by synovial fibroblasts in very early rheumatoid arthritis associates with lymphocyte adhesion in an in vitro flow co-culture system

BACKGROUND

Synovial fibroblasts play a key role in joint destruction and regulation of the inflammatory infiltrate in established rheumatoid arthritis (RA). The mechanisms by which this occurs in the earliest stages of RA are largely unknown. We investigated the role of Dickkopf-related protein 1 (DKK1) produced by synovial fibroblasts of patients with very early rheumatoid arthritis (VeRA).

METHODS

Fibroblasts were isolated from the disease-modifying anti-rheumatic drug-naive Birmingham early arthritis cohort of patients with new onset of clinically apparent arthritis and inflammatory symptoms of ≤12 weeks' duration, who at follow-up had either resolving arthritis or RA. Endothelial fibroblast co-cultures were formed using porous filters, and lymphocyte adhesion to co-cultures was assessed using phase-contrast microscopy. DKK1 gene expression and secretion were quantified by quantitative polymerase chain reaction and enzyme-linked immunosorbent assay, respectively.

RESULTS

Synovial fibroblasts from patients with VeRA expressed significantly higher levels of DKK1 messenger RNA than those from patients with resolving arthritis. A similar trend was observed for DKK1 protein secretion. In co-culture constructs, more DKK1 tended to be secreted in co-cultures incorporating fibroblasts from VeRA than in co-cultures from non-inflamed joints and resolving arthritis. DKK1 secretion during co-culture positively correlated with lymphocyte adhesion.

CONCLUSIONS

Alterations in DKK1 could be involved in the pathogenesis and perpetuation of the inflammatory response in the earliest clinically apparent stages of RA.

Preclinical good laboratory practice-compliant safety study to evaluate biodistribution and tumorigenicity of a cartilage advanced therapy medicinal product (ATMP)

BACKGROUND

The clinical development of advanced therapy medicinal products (ATMPs), a new class of drugs, requires initial safety studies that deviate from standard non-clinical safety protocols. The study provides a strategy to address the safety aspects of biodistribution and tumorigenicity of ATMPs under good laboratory practice (GLP) conditions avoiding cell product manipulation. Moreover, the strategy was applied on a human ATMP for cartilage repair.

METHODS

The testing strategy addresses biodistribution and tumorigenicity using a multi-step analysis without any cell manipulation to exclude changes of test item characteristics. As a safeguard measurement for meeting regulatory expectations, the project design and goals were discussed continuously with the regulatory authority using a staggered scientific advice concept. Subsequently, the strategy was applied to co.don chondrosphere® (huChon spheroid), a tissue-engineered matrix-free ATMP of human normal chondrocytes. In both the biodistribution and tumorigenicity studies, huChon spheroids were implanted subcutaneously into 40 immunodeficient mice. Biodistribution was studied 1 month after implantation. A skin disc containing the huChon spheroid, two surrounding skin rings and selected organs were analyzed by validated, gender-specific, highly-sensitive triplex qPCR and by immunohistochemistry (IHC).

RESULTS

No human DNA was detected in distant skin rings and analyzed organs. IHC revealed no direct or indirect indications of cell migration. Tumorigenicity was assessed 6 months after huChon spheroid implantation by palpation, macroscopic inspection, histology and IHC. No mice from the huChon spheroid group developed a tumor at the implantation site. In two mice, benign tumors were detected that were negative for HLA-ABC, suggesting that they were of spontaneous murine origin.

CONCLUSIONS

In summary, the presented strategy using a multi-step analysis was confirmed to be suitable for safety studies of ATMPs.

Characterization of the murine myeloid precursor cell line MuMac-E8

Starting point for the present work was the assumption that the cell line MuMac-E8 represents a murine cell population with stem cell properties. Preliminary studies already pointed to the expression of stem-cell associated markers and a self-regenerative potential of the cells. The cell line MuMac-E8 should be examined for their differential stage within stem cell hierarchy. MuMac-E8 cells were derived from a chimeric mouse model of arthritis. It could be shown that MuMac-E8 cells express mRNA of some genes associated with pluripotent stem cells (Nanog, Nucleostemin), of genes for hematopoietic markers (EPCR, Sca-1, CD11b, CD45), for the mesenchymal marker CD105 and of genes for the neural markers Pax-6 and Ezrin. In methylcellulose and May-Grünwald-Giemsa staining, hematopoietic colonies were obtained but the hematopoietic system of lethally irradiated mice could not be rescued. Osteogenic differentiation was not detectable. Thus, it became evident that MuMac-E8 represents not a stem cell line. However, MuMac-E8 cells expressed several myeloid surface markers (i.e. CD11b, F4/80, CD14, CD64), showed phagocytosis and is capable of producing nitric oxide. Thus, this cell line seems to be arrested an advanced stage of myeloid differentiation. Adherence data measured by impedance-based real-time cell analysis together with cell morphology data suggested that MuMac-E8 represents a new macrophage precursor cell line exhibiting weak adherence. This cell line is suitable as an in-vitro model for testing of macrophage functions. Moreover, it might be also useful for differentiation or reprogramming studies.

Effects of Ureaplasma urealyticum lipid-associated membrane proteins on rheumatoid arthritis synovial fibroblasts

Objectives

As an infectious agent might play a role in rheumatoid arthritis (RA) development, this study investigated effects of Ureaplasma urealyticum lipid-associated membrane proteins (UuLAMPs) on RA synovial fibroblast (RASF) proliferation, and tumour necrosis factor (TNF)-α and interleukin (IL)-1β production by THP-1 macrophages. Possible immunogenic proteins in UuLAMPs were identified.

Methods

RASFs were cultured from synovial tissue from donors with RA. Serum samples from donors with/without RA and with/without U. urealyticum infection were used for immunogenicity analyses. THP-1 macrophages served as a model for synovial macrophages. TNF-α and IL-1β mRNA levels were assessed using reverse transcription–polymerase chain reaction; protein levels were estimated using enzyme-linked immunosorbent assay. UuLAMPs underwent separation and Western blot analyses.

Results

UuLAMPs (0.025–0.4 µg/ml) stimulated RASF proliferation in a dose- and time-dependent manner, and increased TNF-α and IL-1β levels in THP-1 macrophages. Several immunogenic UuLAMPs were identified, but antibodies to a 25 kDa protein were only found in RA patients with U. urealyticum infection.

Conclusions

UuLAMPs might induce RASF proliferation and proinflammatory cytokine secretion in synovium from RA patients. A 25 kDa U. urealyticum protein might act as a cross-reactive antigen.

Rheumatoid and pyrophosphate arthritis synovial fibroblasts induce osteoclastogenesis independently of RANKL, TNF and IL-6

Bone destruction is a common feature of inflammatory arthritis and is mediated by osteoclasts, the only specialized cells to carry out bone resorption. Aberrant expression of receptor activator of nuclear factor kappa β ligand (RANKL), an inducer of osteoclast differentiation has been linked with bone pathology and the synovial fibroblast in rheumatoid arthritis (RA). In this manuscript, we challenge the current concept that an increase in RANKL expression governs osteoclastogenesis and bone destruction in autoimmune arthritis. We isolated human fibroblasts from RA, pyrophosphate arthropathy (PPA) and osteoarthritis (OA) patients and analyzed their RANKL/OPG expression profile and the capacity of their secreted factors to induce osteoclastogenesis. We determined a 10-fold increase of RANKL mRNA and protein in fibroblasts isolated from RA relative to PPA and OA patients. Peripheral blood mononuclear cells (PBMC) from healthy volunteers were cultured in the presence of RA, PPA and OA synovial fibroblast conditioned medium. Osteoclast differentiation was assessed by expression of tartrate-resistant acid phosphatase (TRAP), vitronectin receptor (VNR), F-actin ring formation and bone resorption assays. The formation of TRAP(+), VNR(+) multinucleated cells, capable of F-actin ring formation and lacunar resorption in synovial fibroblast conditioned medium cultures occured in the presence of osteoprotegerin (OPG) a RANKL antagonist. Osteoclasts did not form in these cultures in the absence of macrophage colony stimulating factor (M-CSF). Our data suggest that the conditioned medium of pure synovial fibroblast cultures contain inflammatory mediators that can induce osteoclast formation in human PBMC independently of RANKL. Moreover inhibition of the TNF or IL-6 pathway was not sufficient to abolish osteoclastogenic signals derived from arthritic synovial fibroblasts. Collectively, our data clearly show that alternate osteoclastogenic pathways exist in inflammatory arthritis and place the synovial fibroblast as a key regulatory cell in bone and joint destruction, which is a hallmark of autoimmune arthritis.

Identification and evaluation of novel synovial tissue biomarkers in rheumatoid arthritis by laser scanning cytometry

Introduction

Suitable biomarkers are essential for therapeutic strategies in personalized medicine in terms of diagnosis as well as of prognosis. With highly specific biomarkers, it is possible, for example, to identify patients with poor prognosis, which enables early intervention and intensive treatment. The aim of this study was to identify and validate biomarkers and possible combinations for a prospective use in immunoscintigraphy, which may improve diagnosis of rheumatoid arthritis (RA) patients with consideration of inflammatory activity in the affected joints. Therefore, we tested several monoclonal antibodies (mAbs) directed against cellular-surface molecules on cells likely to be involved in the pathogenesis of RA.

Methods

Synovial tissue from patients with long-standing RA (accompanied by synovitis with varying states of current activity) and patients with acute non-RA arthritis were stained for surface molecules on different cell types by using fluorochrome-labeled antibodies. Tissue analysis was done by laser scanning cytometry (LSC), and statistical evaluation, by discriminant analysis and ROC analysis.

Results

CD11b, HLA-DR, CD90, and CD64 revealed significant differences between tissues from patients with RA and acute non-RA arthritis. Especially with the expression of CD64, both patient cohorts could be discriminated with high sensitivity and specificity. RA classification was improved by simultaneously investigating the expression of two or three different surface proteins, such as HLA-DR, CD90, and CD29 in the tissue. The simultaneous analysis of CD64 together with CD304 or the combination of CD11b and CD38 was suitable for the identification of RA patients with high current activity in synovitis.

Conclusions

In this study, we showed that LSC is a novel reliable method in biomarker prevalidation in RA. Hence, identified mAbs in situ may allow their potential use in in vivo approaches. Moreover, we proved that biomarker-combination analysis resulted in better discrimination than did single-marker analysis. Combinations of these markers make a novel and reliable panel for the discrimination between RA and acute non-RA arthritis. In addition, further expedient combinations may be novel promising biomarker panels to identify current activity in synovitis in RA.

Ajulemic acid, a synthetic cannabinoid acid, induces an antiinflammatory profile of eicosanoids in human synovial cells

AIMS

To better understand mechanisms whereby Ajulemic acid (AjA), a synthetic antiinflammatory cannabinoid, promotes resolution of acute and chronic inflammation in animal models, we investigated its influence on cyclooxygenase 2 (COX2) expression and eicosanoid production in human fibroblast-like synovial cells (FLS).

MAIN METHODS

FLS isolated from tissue obtained at joint replacement surgery or cultured from synovial fluid were treated for 60 min with AjA (10-30 microM), then stimulated with tumor necrosis factor alpha (TNFalpha). COX2 mRNA was measured by hybridization/colorimetric assay of whole cell lysates collected 4 h after stimulation. To determine effects on arachidonic acid release, FLS were incubated with (14)C-arachidonic acid for 20 h then treated with AjA (8-32 microM). Arachidonic acid release was measured by scintillation counting. Prostaglandins (PG) were measured by enzyme linked immunosorbent assay (ELISA) in cell supernatants collected 4 and 24 h after stimulation.

KEY FINDINGS

AjA increased the steady state levels of COX2 mRNA in and arachidonic acid release from FLS. Treatment of FLS with AjA increased 15-deoxy-delta(12,14)-PGJ(2) (15d-PGJ(2)) production in a concentration dependent manner, but did not affect PGE(2) production significantly.

SIGNIFICANCE

The capacity of AjA to increase selectively and markedly 15d-PGJ(2), an eicosanoid which facilitates resolution of inflammation, suggests that AjA may have value as a therapeutic agent for the treatment of rheumatoid arthritis (RA) and other diseases characterized by acute and chronic inflammation.

Characterization of fibroblasts responsible for cartilage destruction in arthritis

In the pathogenesis of rheumatoid arthritis (RA), synovial fibroblasts (SF) play a key role as they secrete distinct patterns of cytokines and express variable levels of costimulatory and adhesion molecules. The murine fibroblast cell line LS48 has been shown to be invasive in the cartilage destruction models in vivo and in vitro. The purpose of this study was to examine in detail the LS48 phenotype, to obtain a better understanding of the SF-mediated cartilage destruction in RA. The destructive fibroblasts line LS48 and the nondestructive 3T3 cells were cultured and characterized with slide-based and flow cytometry, using antibodies against several adhesion molecules, immunological acting molecules, and marker proteins. The invasive LS48 fibroblasts are characterized by significantly higher expression of adhesion molecules such as CD47 (IAP), CD51 (integrin alpha V), CD61 (GPIIIa), and CD147 (EMMPRIN), and immunological acting molecules such as CD40 (Bp50), CD55 (DAF), and TLR-2. The results from the slide-based and flow cytometry analyses were exactly the same, except for the selected CD147 and TLR-2. This study demonstrated that the destructive fibroblast cell line LS48 has the characteristics of RA SFs. The high expression of specific costimulatory and adhesion molecules underlines the aberrant phenotype of these cells when compared with noninvasive fibroblasts. Furthermore, slide-based and flow cytometry complement each other in fibroblast phenotyping. Overall, this study shows that LS48 is an excellent tool to gain a deeper understanding of SF in RA.

Identification of genomic targets downstream of p38 mitogen-activated protein kinase pathway mediating tumor necrosis factor-alpha signaling

Inhibition of p38 MAPK suppresses the expression of proinflammatory cytokines such as TNF-alpha and IL-1 beta in macrophages and fibroblast-like synoviocytes (FLS). However, there have been no genomewide studies on the gene targets of p38 MAPK signaling in synoviocytes. Microarray technology was applied to generate a comprehensive analysis of all genes regulated by the p38 MAPK signaling pathway in FLS. Gene expression levels were measured with Agilent oligonucleotide microarrays. Four independent sets of mRNA modulated by TNF-alpha and vehicle were used to measure the change of gene expression due to TNF-alpha, and three experiments were done to ascertain the effect of SB-203580, a p38 MAPK inhibitor, on TNF-alpha-induced genes. Microarray data were validated by RT-quantitative polymerase chain reaction. One hundred forty-one significantly expressed genes were more than twofold upregulated by TNF-alpha. Thirty percent of these genes were downregulated by the p38 inhibitor SB-203580, whereas 67% of these genes were not significantly changed. The SB-203580-inhibited genes include proinflammatory cytokines such as interleukins and chemokines, proteases including matrix metallopeptidases, metabolism-related genes such as cyclooxygenases and phosphodiesterase, genes involved in signal transduction, and genes encoding for transcription factors, receptors, and transporters. Approximately one-third of the TNF-alpha-induced genes in FLS are regulated by the p38 MAPK signal pathway, showing that p38 MAPK is a possible target for suppressing proinflammatory gene expressions in rheumatoid arthritis.

A cell-cycle independent role for p21 in regulating synovial fibroblast migration in rheumatoid arthritis

Rheumatoid arthritis (RA) is characterized by synovial hyperplasia and destruction of cartilage and bone. The fibroblast-like synoviocyte (FLS) population is central to the development of pannus by migrating into cartilage and bone. We demonstrated previously that expression of the cell cycle inhibitor p21 is significantly reduced in RA synovial lining, particularly in the FLS. The aim of this study was to determine whether reduced expression of p21 in FLS could alter the migratory behavior of these cells. FLS were isolated from mice deficient in p21 (p21(-/-)) and were examined with respect to growth and migration. p21(-/-) and wild-type (WT) FLS were compared with respect to migration towards chemoattractants found in RA synovial fluid in the presence and absence of cell cycle inhibitors. Restoration of p21 expression was accomplished using adenoviral infection. As anticipated from the loss of a cell cycle inhibitor, p21(-/-) FLS grow more rapidly than WT FLS. In examining migration towards biologically relevant RA synovial fluid, p21(-/-) FLS display a marked increase (3.1-fold; p < 0.05) in migration compared to WT cells. Moreover, this effect is independent of the cell cycle since chemical inhibitors that block the cell cycle have no effect on migration. In contrast, p21 is required to repress migration as restoration of p21 expression in p21(-/-) FLS reverses this effect. Taken together, these data suggest that p21 plays a novel role in normal FLS, namely to repress migration. Loss of p21 expression that occurs in RA FLS may contribute to excessive invasion and subsequent joint destruction.

Anti-TNF Effects on Destructive Fibroblasts Depend on Mechanical Stress

Joint destruction in rheumatoid arthritis (RA) starts typically at sites of mechanically stressed inserts of the synovial membrane near the cartilage/bone border. In the therapy of RA, tumour necrosis factor (TNF) antagonists have rapidly emerged as a valuable class of anti-rheumatic agents that reduce joint destruction. The aim of this study was to investigate and profile genes involved in the interaction between articular movement and anti-TNF therapy in an in vitro model. Murine LS48 cells, an established substitute for invasive RA synovial fibroblasts, were cultured, stretched and/or treated with anti-TNF-alpha antibody for 24 h. RNA was isolated and gene transcript levels were determined using U74Av2 Affymetrix GeneChips to identify transcriptional events. Positive findings were verified by polymerase chain reaction (PCR). We identified 170 differentially regulated genes, including 44 of particular interest. Gene expression fell into different functional groups that can be explained by RA pathogenesis and experimental conditions. For 21 genes of the 44 of particular interest, regulation could be confirmed by real-time PCR. Remarkably, we found structural as well as functional genes differently regulated between stretched cells, anti-TNF-treated cells, and stretched cells treated with anti-TNF antibody. Additionally, we also found a large number of genes that are apparently not related to the experimental conditions. Mechanical exertion modulates gene expression and subsequently cellular response to anti-TNF therapy. Results in exerted cells correspond to current knowledge regarding RA pathogenesis and underline the relevance of our experimental approach. Finally, the central function of the interleukin-18 system in joint destruction could be confirmed by our findings.

Investigation of arthritic joint destruction by a novel fibroblast-based model

The key pathologic mechanism in rheumatoid arthritis (RA) is the destruction of cartilage by fibroblasts. In a severe combined immunodeficient (SCID) mouse model, this process can be modulated by gene transfer using invasive LS48 fibroblasts. This study aims to investigate the effect of interleukins (IL) -11 and -12 on cartilage destruction when transferred into LS48, and of IL-15 when transfected into non-invasive 3T3 cells; to compare three transduction systems (a lentiviral vector system, a retroviral vector system, and a particle-mediated gene transfer); and to establish an in vitro cartilage destruction system based on LS48 cells. Transduced fibroblasts were injected into SCID mice knee joints, and disease progression assessed microscopically. Distinctive morphologic pattern revealed invasion of fibroblasts into the articular cartilage by transfected, as well as non-transfected, LS48 cells. IL-12 and IL-15 did not alter swelling or cartilage destruction. Animals treated with IL-11-transfected cells showed reduced cartilage damage but no changes in swelling. Efficacy of gene transfer to establish transfected fibroblasts was shown to be >85% for lentiviral transfer, compared to <10% for retroviral transfer and gene gun. Furthermore, cells were co-incubated with porcine cartilage. Transduction of IL-11 led to a reduction of apoptosis in chondrocytes. These findings suggest that cartilage destruction by invasive fibroblasts can be modulated by gene transfer. Lentiviral vector systems offer the most effective approach for gene transduction. In vitro fibroblast/cartilage co-cultures present a convenient system for the assessment of novel therapeutic strategies toward reduction of articular destruction.

Methotrexate ameliorates T cell dependent autoimmune arthritis and encephalomyelitis but not antibody induced or fibroblast induced arthritis

OBJECTIVE

To investigate the mode of action of methotrexate (MTX) in different types of models for rheumatoid arthritis (RA) and multiple sclerosis (MS).

METHODS

Models for RA and MS were selected known to have different pathogenesis--that is, fibroblast induced arthritis in SCID mice, collagen induced arthritis (CIA), anticollagen II antibody induced arthritis (CAIA), and experimental autoimmune encephalomyelitis (EAE) in (Balb/c x B10.Q)F1 and B10.Q mice, and Pristane induced arthritis in DA rats (PIA). The MTX treatment was started 1 day after the onset of disease and continued for 14 days to compare effects on the different models.

RESULTS

All models known to be critically dependent on T cell activation (CIA, PIA, and EAE) were effectively down regulated by titrated doses of MTX. In contrast, no effects were seen on fibroblast induced arthritis or CAIA. No effects were seen on the levels of anticollagen II antibodies in the CIA experiment.

CONCLUSION

The data show that MTX has strong ameliorative effect on both classical models of RA, like CIA and PIA, but also on a model for MS, EAE. It also suggests that MTX operates only in diseases which are preceded by, and dependent on, T cell activation. A comparison of CAIA and CIA suggested that MTX operates independently of arthritogenic antibodies. These results demonstrate that different animal models reflect the complexity of the corresponding human diseases and suggest that several models should be used for effective screening of new therapeutic agents.

Fibroblast-like synoviocytes derived from patients with rheumatoid arthritis show the imprint of synovial tissue heterogeneity: evidence of a link between an increased myofibroblast-like phenotype and high-inflammation synovitis

OBJECTIVE

Given the heterogeneity of gene expression patterns and cellular distribution between rheumatoid arthritis (RA) synovial tissues, we sought to determine whether this variability was also reflected at the level of the fibroblast-like synoviocyte (FLS) cultured from RA synovial tissues.

METHODS

Gene expression profiles in FLS cultured from synovial tissues obtained from 19 RA patients were analyzed using complementary DNA microarrays and hierarchical cluster analysis. To validate the subclassification, we performed prediction analysis and principal components analysis. Genes that differed significantly in their expression between FLS cultures were selected using Statistical Analysis of Microarrays software. Real-time quantitative polymerase chain reaction was performed to validate the microarray data. Immunocytochemistry was applied to study the expression of the genes of interest in FLS and synovial tissues.

RESULTS

Hierarchical clustering identified 2 main groups of FLS characterized by distinctive gene expression profiles. FLS from high-inflammation synovial tissues revealed increased expression of a transforming growth factor beta/activin A-inducible gene profile that is characteristic of myofibroblasts, a cell type considered to be involved in wound healing, whereas increased production of growth factor (insulin-like growth factor 2/insulin-like growth factor binding protein 5) appeared to constitute a characteristic feature of FLS derived from low-inflammation synovial tissues. The molecular feature that defines the myofibroblast-like phenotype was reflected as an increased proportion of myofibroblast-like cells in the heterogeneous FLS population. Myofibroblast-like cells were also found upon immunohistochemical analysis of synovial tissue.

CONCLUSION

Our findings support the notion that heterogeneity between synovial tissues is reflected in FLS as a stable trait, and provide evidence of a possible link between the behavior of FLS and the inflammation status of RA synovium.

A novel model of fibroblast-mediated cartilage destruction

In rheumatoid arthritis (RA), fibroblasts have been shown to be crucial for disease progression as well as joint destruction. In the model of human/murine SCID arthritis, synovial explants as well as fibroblasts from human rheumatoid synovial membrane induce destructive arthritis in immunodeficient mice. Hereby, the underlying cartilage destruction is accomplished by murine fibroblasts. Therefore, murine destructive fibroblasts represent a promising tool to investigate destruction of articular cartilage and bone. In this context, a novel destructive murine fibroblast line (LS48) was examined for morphological, ultrastructural, immunological and functional cellular parameters. These cells were injected into knees of SCID mice. Subsequently, the animals were monitored for joint swelling and serological parameters of arthritis by radiological methods. Finally, cartilage destruction was assessed morphologically. Cultured LS48 cells exhibit characteristic features that resemble those of activated synovial fibroblasts in human RA. Expression levels of inducible nitric oxide synthase, interleukin-6, tumour necrosis factor-alpha and matrix metalloproteinases were comparable to those detected in invasive human fibroblasts. The instillation of 5 x 10(5) LS48 cells into the knee joints of SCID mice initiated a rapid progressive process, that caused cartilage destruction within 10 days, and morphological examinations revealed that articular cartilage was infiltrated by the fibroblasts injected previously. In summary, the intra-articular application of LS48 cells represents a rapid and highly reproducible model to investigate the initiation and progression of cartilage destruction in connection with RA therapy and represents an easy-to-handle animal model.

Ameliorative effect of ozone on cytokine production in mice injected with human rheumatoid arthritis synovial fibroblast cells

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by invasion of hyperplastic synovial cells and progressive joint destruction. Ozone therapy has been proposed as an immunomodulator and cellular metabolic activator which shows long-term anti-inflammatory effects and serves to reduce further the proinflammatory factors. We purified RA synovial fibroblast cells (RA-SFc) from patients and avoided contaminating macrophages by flow cytometry, then treated them with ozone. Following the observable decreased production of proinflammatory factors TNF-alpha, IL-1beta, and IL-6 from RA-SFc, we infused the cultured RA-SFc into joints of severe combined immunodeficiency mice. The mRNA and protein levels of the RA-SFc exposed to 3% and 5% ozone were the same. As a result, 3% and 5% ozone applied externally ameliorated the inflammatory reaction of RA without toxicity or serious side effects. Therefore, ozone injected into the knees of RA patients could become a valuable treatment, and we confirm the interactive mechanism between ozone and RA-SFc.

Functional analysis of an arthritogenic synovial fibroblast

Increasing attention has been directed towards identifying non-T-cell mechanisms as potential therapeutic targets in rheumatoid arthritis. Synovial fibroblast (SF) activation, a hallmark of rheumatoid arthritis, results in inappropriate production of chemokines and matrix components, which in turn lead to bone and cartilage destruction. We have demonstrated that SFs have an autonomous pathogenic role in the development of the disease, by showing that they have the capacity to migrate throughout the body and cause pathology specifically to the joints. In order to decipher the pathogenic mechanisms that govern SF activation and pathogenic potential, we used the two most prominent methods of differential gene expression analysis, differential display and DNA microarrays, in a search for deregulated cellular pathways in the arthritogenic SF. Functional clustering of differentially expressed genes, validated by dedicated in vitro functional assays, implicated a number of cellular pathways in SF activation. Among them, diminished adhesion to the extracellular matrix was shown to correlate with increased proliferation and migration to this matrix. Our findings support an aggressive role for the SF in the development of the disease and reinforce the perspective of a transformed-like character of the SF.

Cytokine mRNA and protein expression in primary-culture and repeated-passage synovial fibroblasts from patients with rheumatoid arthritis

Constitutive mRNA expression and secretion of proinflammatory and anti-inflammatory cytokines was comparatively analyzed in rheumatoid arthritis (RA) synovial fibroblasts (SFB), isolated from primary culture or derived by repeated passage; normal-skin fibroblasts were used as controls. First-passage RA-SFB (n = 3) secreted large amounts of IL-6 (15,800 +/- 2,110 pg/ml; mean +/- SEM), but only limited amounts of tumor necrosis factor (TNF)-alpha (22.1 +/- 1.1 pg/ml) or IL-10 (35.7 +/- 34.2 pg/ml; only one of three samples was positive). IL-1beta, IL-15, and IL-18 were not detectable at the protein level and showed very low mRNA levels by semiquantitative RT-PCR. In repeated-passage RA-SFB (tenth passage), protein secretion was significantly lower for IL-6 (one-twentieth of the initial level) and TNF-alpha (two-thirds), and markedly reduced for IL-10 (one-quarter, with only one of three samples positive). While the decrease of IL-10 protein from first to tenth passage was paralleled by a corresponding decrease of mRNA, the relative mRNA levels for IL-6 and TNF-alpha were actually increased (20-fold and 300-fold, respectively), indicating post-transcriptional and/or post-translational regulation of these cytokines. Due to highly variable levels among individual patients, however, no significant differences were observed for any cytokine mRNA between primary-culture and repeated-passage RA-SFB (ninth passage). Likewise, no significant differences were detectable between RA-SFB and normal-skin fibroblasts (primary-culture and repeated-passage). By producing high amounts of IL-6 and limited amounts of TNF-alpha, RA-SFB may contribute to the (im)balance of proinflammatory and anti-inflammatory cytokines in the inflamed joint.