The complement system drives local inflammatory tissue priming by metabolic reprogramming of synovial fibroblasts.

Arthritis typically involves recurrence and progressive worsening at specific predilection sites, but the checkpoints between remission and persistence remain unknown. Here, we defined the molecular and cellular mechanisms of this inflammation-mediated tissue priming. Re-exposure to inflammatory stimuli caused aggravated arthritis in rodent models. Tissue priming developed locally and independently of adaptive immunity. Repeatedly stimulated primed synovial fibroblasts (SFs) exhibited enhanced metabolic activity inducing functional changes with intensified migration, invasiveness and osteoclastogenesis. Meanwhile, human SF from patients with established arthritis displayed a similar primed phenotype. Transcriptomic and epigenomic analyses as well as genetic and pharmacological targeting demonstrated that inflammatory tissue priming relies on intracellular complement C3- and C3a receptor-activation and downstream mammalian target of rapamycin- and hypoxia-inducible factor 1α-mediated metabolic SF invigoration that prevents activation-induced senescence, enhances NLRP3 inflammasome activity, and in consequence sensitizes tissue for inflammation. Our study suggests possibilities for therapeutic intervention abrogating tissue priming without immunosuppression.

PU.1 controls fibroblast polarization and tissue fibrosis.

Fibroblasts are polymorphic cells with pleiotropic roles in organ morphogenesis, tissue homeostasis and immune responses. In fibrotic diseases, fibroblasts synthesize abundant amounts of extracellular matrix, which induces scarring and organ failure. By contrast, a hallmark feature of fibroblasts in arthritis is degradation of the extracellular matrix because of the release of metalloproteinases and degrading enzymes, and subsequent tissue destruction. The mechanisms that drive these functionally opposing pro-fibrotic and pro-inflammatory phenotypes of fibroblasts remain unknown. Here we identify the transcription factor PU.1 as an essential regulator of the pro-fibrotic gene expression program. The interplay between transcriptional and post-transcriptional mechanisms that normally control the expression of PU.1 expression is perturbed in various fibrotic diseases, resulting in the upregulation of PU.1, induction of fibrosis-associated gene sets and a phenotypic switch in extracellular matrix-producing pro-fibrotic fibroblasts. By contrast, pharmacological and genetic inactivation of PU.1 disrupts the fibrotic network and enables reprogramming of fibrotic fibroblasts into resting fibroblasts, leading to regression of fibrosis in several organs.

Unmet need in rheumatology: reports from the Advances in Targeted Therapies meeting, 2023.

The Advances in Targeted Therapies meets annually, convening experts in the field of rheumatology to both provide scientific updates and identify existing scientific gaps within the field. To review the major unmet scientific needs in rheumatology. The 23rd annual Advances in Targeted Therapies meeting convened with more than 100 international basic scientists and clinical researchers in rheumatology, immunology, infectious diseases, epidemiology, molecular biology and other specialties relating to all aspects of immune-mediated inflammatory diseases. We held breakout sessions in five rheumatological disease-specific groups including: rheumatoid arthritis (RA), psoriatic arthritis (PsA), axial spondyloarthritis (axSpa), systemic lupus erythematosus (SLE), systemic sclerosis (SSc) and vasculitis, and osteoarthritis (OA). In each group, experts were asked to identify and prioritise current unmet needs in clinical and translational research. An overarching theme across all disease states is the continued need for clinical trial design innovation with regard to therapeutics, endpoint and disease endotypes. Within RA, unmet needs comprise molecular classification of disease pathogenesis and activity, pre-/early RA strategies, more refined pain profiling and innovative trials designs to deliver on precision medicine. Continued scientific questions within PsA include evaluating the genetic, immunophenotypic, clinical signatures that predict development of PsA in patients with psoriasis, and the evaluation of combination therapies for difficult-to-treat disease. For axSpA, there continues to be the need to understand the role of interleukin-23 (IL-23) in pathogenesis and the genetic relationship of the IL-23-receptor polymorphism with other related systemic inflammatory diseases (eg, inflammatory bowel disease). A major unmet need in the OA field remains the need to develop the ability to reliably phenotype and stratify patients for inclusion in clinical trials. SLE experts identified a number of unmet needs within clinical trial design including the need for allowing endpoints that reflect pharmacodynamic/functional outcomes (eg, inhibition of type I interferon pathway activation; changes in urine biomarkers). Lastly, within SSc and vasculitis, there is a lack of biomarkers that predict response or disease progression, and that allow patients to be stratified for therapies. There remains a strong need to innovate clinical trial design, to identify systemic and tissue-level biomarkers that predict progression or response to therapy, endotype disease, and to continue developing therapies and therapeutic strategies for those with treatment-refractory disease. This document, based on expert consensus, should provide a roadmap for prioritising scientific endeavour in the field of rheumatology.

Impact of muscle biopsy on the clinical decision-making process in patients with suspected idiopathic inflammatory myopathy.

BACKGROUND: The significance of muscle biopsy as a diagnostic tool in idiopathic inflammatory myopathies (IIM) remains elusive. We aimed to determine the diagnostic weight that has been given to muscle biopsy in patients with suspected IIM, particularly in terms of clinical diagnosis and therapeutic decisions. MATERIAL AND METHODS: In this retrospective multicentric study, we analyzed muscle biopsy results of adult patients with suspected IIM referred to a tertiary center between January 1, 2007, and October 31, 2021. Information regarding referral department, suspected diagnosis, biopsy site, demographic, clinical, laboratory data, and imaging results were extracted. Statistical analyses included the level of agreement between suspected and histological diagnosis and calculation of diagnostic performance (positive and negative predictive values, positive and negative likelihood ratios, sensitivity, and specificity of muscle biopsy in relation to clinical diagnosis and/or treatment initiation). Performance was tested in different strata based on clinical pre-test probability. RESULTS: Among 758 muscle biopsies, IIM was histologically compatible in 357/758 (47.1%) cases. Proportion of IIM was higher if there was a solid clinical pre-test probability (64.3% vs. 42.4% vs. 48% for high, medium and low pre-test probability). Sensitivity and specificity of muscle biopsy were highest (82%) when the diagnosis by the clinician was used as outcome scenario. Negative predictive value was only moderate (between 63% and 80%) and lowest if autoantibodies were positive (35%). CONCLUSION: In patients with clinically suspected IIM, approximately 50% of biopsies revealed features indicative of IIM. Diagnostic performance of muscle biopsy was moderate to high depending on clinical pre-test probability.

Cytokine-directed cellular cross-talk imprints synovial pathotypes in rheumatoid arthritis.

INTRODUCTION: Structural reorganisation of the synovium with expansion of fibroblast-like synoviocytes (FLS) and influx of immune cells is a hallmark of rheumatoid arthritis (RA). Activated FLS are increasingly recognised as a critical component driving synovial tissue remodelling by interacting with immune cells resulting in distinct synovial pathotypes of RA. METHODS: Automated high-content fluorescence microscopy of co-cultured cytokine-activated FLS and autologous peripheral CD4+ T cells from patients with RA was established to quantify cell-cell interactions. Phenotypic profiling of cytokine-treated FLS and co-cultured T cells was done by flow cytometry and RNA-Seq, which were integrated with publicly available transcriptomic data from patients with different histological synovial pathotypes. Computational prediction and knock-down experiments were performed in FLS to identify adhesion molecules for cell-cell interaction. RESULTS: Cytokine stimulation, especially with TNF-α, led to enhanced FLS-T cell interaction resulting in cell-cell contact-dependent activation, proliferation and differentiation of T cells. Signatures of cytokine-activated FLS were significantly enriched in RA synovial tissues defined as lymphoid-rich or leucocyte-rich pathotypes, with the most prominent effects for TNF-α. FLS cytokine signatures correlated with the number of infiltrating CD4+ T cells in synovial tissue of patients with RA. Ligand-receptor pair interaction analysis identified ICAM1 on FLS as an important mediator in TNF-mediated FLS-T cell interaction. Both, ICAM1 and its receptors were overexpressed in TNF-treated FLS and co-cultured T cells. Knock-down of ICAM1 in FLS resulted in reduced TNF-mediated FLS-T cell interaction. CONCLUSION: Our study highlights the role of cytokine-activated FLS in orchestrating inflammation-associated synovial pathotypes providing novel insights into disease mechanisms of RA.

FOXO3 is involved in the tumor necrosis factor-driven inflammatory response in fibroblast-like synoviocytes.

Fibroblast-like synoviocytes (FLS) are major contributors to joint inflammation in rheumatoid arthritis (RA). Forkhead box O 3 (FOXO3) perturbations in immune cells are increasingly linked to RA pathogenesis. Here, we show that FOXO3 is distinctly inactivated/phosphorylated in the FLS of rheumatoid synovitis. In vitro, stimulation of FLS with tumor necrosis factor-alpha α (TNFα) induced a rapid and sustained inactivation of FOXO3. mRNA profiling revealed that the inactivation of FOXO3 is important for the sustained pro-inflammatory interferon response to TNFα (CXCL9, CXCL10, CXCL11, and TNFSF18). Mechanistically, our studies demonstrate that the inactivation of FOXO3 results from TNF-induced downregulation of phosphoinositide-3-kinase-interacting protein 1 (PIK3IP1). Thus, we identified FOXO3 and its modulator PIK3IP1 as a critical regulatory circuit for the inflammatory response of the resident mesenchymal cells to TNFα and contribute insight into how the synovial tissue brings about chronic inflammation that is driven by TNFα.

Targeted inhibition of Janus kinases abates interfon gamma-induced invasive behaviour of fibroblast-like synoviocytes.

Objectives: The aim was to explore the function of the T-cell cytokine IFNγ for mesenchymal tissue remodelling in RA and to determine whether IFNγ signalling controls the invasive potential of fibroblast-like synoviocytes (FLS). Methods: To assess architectural responses, FLS were cultured in three-dimensional micromasses. FLS motility was analysed in migration and invasion assays. Signalling events relevant to cellular motility were defined by western blots. Baricitinib and small interfering RNA pools were used to suppress Janus kinase (JAK) functions. Results: Histological analyses of micromasses revealed unique effects of IFNγ on FLS shape and tissue organization. This was consistent with accelerated migration upon IFNγ stimulation. Given that cell shape and cell motility are under the control of the focal adhesion kinase (FAK), we next analysed its activity. Indeed, IFNγ stimulation induced the phosphorylation of FAK-Y925, a phosphosite implicated in FAK-mediated cell migration. Small interfering RNA knockdown of JAK2, but not JAK1, substantially abrogated FAK activation by IFNγ. Correspondingly, IFNγ-induced FAK activation and invasion of FLS was abrogated by the JAK inhibitor, baricitinib. Conclusion: Our study contributes insight into the synovial response to IFNγ and reveals JAK2 as a potential therapeutic target for FLS-mediated joint destruction in arthritis, especially in RA.

Relation of Nailfold Capillaries and Autoantibodies to Mortality in Patients With Raynaud Phenomenon.

BACKGROUND: In incipient Raynaud phenomenon, nailfold capillaroscopy and autoantibody tests are obtained to screen for an emerging connective tissue disease. Whether the presence of abnormal nailfold capillaries and autoantibodies are related to mortality in patients with incipient Raynaud phenomenon is not known. METHODS AND RESULTS: In 2958 consecutive patients (78% women, median age 45 years) with incipient Raynaud phenomenon without previously known connective tissue disease, nailfold capillaroscopy and laboratory tests for antinuclear antibodies (ANA) and ANA subsets were obtained at initial presentation. During a median follow-up period of 9.3 years, 227 women (9.9% of female patients) and 129 men (20% of male patients) with Raynaud phenomenon died. In comparison with a demographically matched standard population, survival was poorer in patients with Raynaud phenomenon (log-rank test P<0.0001). In patients with Raynaud phenomenon, mortality was higher in men than in women (P<0.0001, Cox proportional hazards model). In women, the presence of abnormal nailfold capillaries, ANA, and anti-Scl-70 antibodies were related to an increase in all-cause mortality. The conjoint presence of abnormal nailfold capillaries and autoantibodies was associated with the highest mortality rates. In men, abnormal nailfold capillaries, and ANA and ANA subsets, as well, were not related to survival. In both sexes, patients' age and serum creatinine were associated with mortality. CONCLUSIONS: In Raynaud phenomenon, male sex, age, and serum creatinine are related to mortality. Abnormal nailfold capillaries and autoantibodies are associated with an increase in all-cause mortality in female patients, but not in male patients with Raynaud phenomenon.

MicroRNA-146a governs fibroblast activation and joint pathology in arthritis.

Synovial fibroblasts are key cells orchestrating the inflammatory response in arthritis. Here we demonstrate that loss of miR-146a, a key epigenetic regulator of the innate immune response, leads to increased joint destruction in a TNF-driven model of arthritis by specifically regulating the behavior of synovial fibroblasts. Absence of miR-146a in synovial fibroblasts display a highly deregulated gene expression pattern and enhanced proliferation in vitro and in vivo. Deficiency of miR-146a induces deregulation of tumor necrosis factor (TNF) receptor associated factor 6 (TRAF6) in synovial fibroblasts, leading to increased proliferation. In addition, loss of miR-146a shifts the metabolic state of fibroblasts towards glycolysis and augments the ability of synovial fibroblasts to support the generation of osteoclasts by controlling the balance of osteoclastogenic regulatory factors receptor activator of NF-κB ligand (RANKL) and osteoprotegerin (OPG). Bone marrow transplantation experiments confirmed the importance of miR-146a in the radioresistant mesenchymal compartment for the control of arthritis severity, in particular for inflammatory joint destruction. This study therefore identifies microRNA-146a as an important local epigenetic regulator of the inflammatory response in arthritis. It is a central element of an anti-inflammatory feedback loop in resident synovial fibroblasts, who are orchestrating the inflammatory response in chronic arthritis. MiR-146a restricts their activation, thereby preventing excessive tissue damage during arthritis.

The RNA-binding protein HuR/ELAVL1 regulates IFN-ß mRNA abundance and the type I IFN response.

Secretion of type I interferon (IFN) is the first cellular reaction to invading pathogens. Despite the protective function of these cytokines, an excessive response to their action can contribute to serious pathologies, such as autoimmune diseases. Transcripts of most cytokines contain adenylate-uridylate (A/U)-rich elements (AREs) that make them highly unstable. RNA-binding proteins (RBPs) are mediators of the regulatory mechanisms that determine the fate of mRNAs containing AREs. Here, we applied an affinity proteomic approach and identified lethal, abnormal vision, drosophila-like 1 (ELAVL1)/Hu antigen R (HuR) as the predominant RBP of the IFN-ß mRNA ARE. Reduced expression or chemical inhibition of HuR severely hampered the type I IFN response in various cell lines and fibroblast-like synoviocytes isolated from joints of rheumatoid arthritis patients. These results define a role for HuR as a potent modulator of the type I IFN response. Taken together, HuR could be used as therapeutic target for diseases where type I IFN production is exaggerated.

Amino Acids Fueling Fibroblast-Like Synoviocyte Activation and Arthritis By Regulating Chemokine Expression and Leukocyte Migration.

OBJECTIVE: We analyzed the impact of amino acid (AA) availability on the inflammatory response in arthritis. METHODS: We stimulated rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLSs) with tumor necrosis factor (TNF) in the presence or absence of proteinogenic AAs and measured their response by QuantSeq 3' messenger RNA sequencing, quantitative polymerase chain reaction, and enzyme-linked immunosorbent assay. Signal transduction events were determined by Western blot. We performed K/BxN serum transfer arthritis in mice receiving a normal and a low-protein diet and analyzed arthritis clinically and histologically. RESULTS: Deprivation of AAs decreased the expression of a specific subset of genes, including the chemokines CXCL10, CCL2, and CCL5 in TNF-stimulated FLSs. Mechanistically, the presence of AAs was required for the TNF-induced activation of an interferon regulatory factor 1 (IRF1)-STAT1 signaling circuit that drives the expression of chemotactic factors. The expression of IRF1 and the IRF1-dependent gene set in FLSs was highly correlated with the presence of inflammatory cells in human RA, emphasizing the important role of this AA-dependent pathway in inflammatory cell recruitment to the synovial tissue. Finally, we show that mice receiving a low-protein diet expressed less IRF1 in the inflamed synovium and consequently developed reduced clinical and histologic signs of arthritis. CONCLUSION: AA deprivation reduces the severity of arthritis by suppressing the expression of IRF1-STAT1-driven chemokines, which are crucial for leukocyte recruitment to the arthritic joint. Overall, our study provides novel insights into critical determinants of inflammatory arthritis and may pave the way for dietary intervention trials in RA.

Interferon signals and monocytic sensitization of the interferon-γ signaling pathway in the peripheral blood of patients with rheumatoid arthritis.

OBJECTIVE: Both type I interferons (IFNα and IFNß) and type II IFN (IFNγ) signal via pSTAT-1. Immunohistochemistry and the gene expression signatures of rheumatoid arthritis (RA) synovial tissue suggest an activated IFN/STAT-1 signaling pathway. The aim of this study was to determine the systemic activity of the IFN/STAT-1 signaling pathway in the peripheral blood cells of patients with RA. METHODS: Fluorocytometry or quantitative polymerase chain reaction was used to measure the expression of STAT-1, pSTAT-1, and IFN-inducible genes (monokine induced by interferon-γ [MIG], interferon-γ-inducible protein 10 [IP-10], and 2',5'-oligoadenylate synthetase [OAS]) in the peripheral blood mononuclear cells (PBMCs) and purified CD14+ peripheral blood monocytes of patients with RA and healthy control subjects. PBMCs were also incubated for 48 hours with IFNs and several other cytokines to investigate influences on STAT-1 levels. To examine the significance of STAT-1 activation in RA monocytes after stimulation with IFNγ, the expression of pSTAT-1 and of the IFNγ-inducible chemokine MIG was measured using fluorocytometry. RESULTS: Levels of STAT-1 were significantly increased in peripheral lymphocytes and monocytes from patients with RA compared with those from healthy control subjects. STAT-1 levels correlated well with RA disease activity, as measured by the Disease Activity Score in 28 joints and the Clinical Disease Activity Index. Furthermore, STAT-1 messenger RNA expression in RA CD14+ monocytes correlated with the expression of other IFN-target genes, such as IP-10, OAS, or MIG. In RA PBMCs, STAT-1 expression was increased not only by IFNs but also by tumor necrosis factor. RA monocytes demonstrated a considerably higher increase in pSTAT-1 and MIG levels upon IFNγ stimulation when compared with monocytes from control subjects, indicating that RA monocytes are more sensitive to IFNγ stimulation. CONCLUSION: In addition to supporting the role of IFNs in systemic proinflammatory activity, the results of this study further suggest preactivation of the IFNγ/STAT-1 signaling pathway, especially in RA monocytes.

COVID-19 as a putative trigger of anti-MDA5-associated dermatomyositis with acute respiratory distress syndrome (ARDS) requiring lung transplantation, a case report.

BACKGROUND: Autoimmune disease following COVID-19 has been studied intensely since the beginning of the pandemic. Growing evidence indicates that SARS-CoV-2 infection, by virtue of molecular mimicry can lead to an antigen-mediated cross-reaction promoting the development of a plethora of autoimmune spectrum diseases involving lungs and extrapulmonary tissues alike. In both COVID-19 and autoimmune disease, the immune self-tolerance breaks, leading to an overreaction of the immune system with production of a variety of autoantibodies, sharing similarities in clinical manifestation, laboratory, imaging, and pathology findings. Anti-Melanoma Differentiation-Associated gene 5 dermatomyositis (anti-MDA5 DM) comprises a rare subtype of systemic inflammatory myopathies associated with characteristic cutaneous features and life-threatening rapidly progressive interstitial lung disease (RP-ILD). The production of anti-MDA5 autoantibodies was proposed to be triggered by viral infections. CASE PRESENTATION: A 20-year-old male patient with polyarthritis, fatigue and exertional dyspnea was referred to our department. An elevated anti-MDA5 autoantibody titer, myositis on MRI, ground glass opacifications on lung CT and histological features of Wong-type dermatomyositis were confirmed, suggesting the diagnosis of an anti-MDA5 DM. Amid further diagnostic procedures, a serologic proof of a recent SARS-CoV-2 infection emerged. Subsequently, the patient deteriorated into a fulminant respiratory failure and an urgent lung transplantation was performed, leading to remission ever since (i.e. 12 months as of now). CONCLUSIONS: We report a unique case of a patient with a new-onset anti-MDA5 DM with fulminant ARDS emerging in a post-infectious stage of COVID-19, who underwent a successful lung transplantation and achieved remission. Given the high mortality of anti-MDA5 DM associated RP-ILD, we would like to highlight that the timely recognition of this condition and urgent therapy initiation are of utmost importance.

Dysbalance of angiogenic and angiostatic mediators in patients with mixed connective tissue disease.

OBJECTIVE: Vascular disease is common in mixed connective tissue disease (MCTD). The aim of the present study was to investigate, whether dysbalance of angiogenic and angiostatic factors occurs in MCTD. METHODS: In all, 38 patients with MCTD, and 40 patients with systemic sclerosis (SSc) for comparison, were included. Four centres contributed to this cross-sectional analysis. A total of 66 healthy volunteers were used as controls. The serum levels of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF) and endostatin were determined by ELISA. For comparisons between controls and patients with MCTD and detection of associations of serum levels with dichotomous clinical parameters in patients with MCTD the Mann-Whitney test was used. RESULTS: Serum levels of the angiogenic factor VEGF were significantly elevated in patients with MCTD and SSc. Significantly increased levels of the angiostatic factor endostatin were also detected in MCTD, but not in SSc. No differences were observed for bFGF. Levels of VEGF were higher in patients with MCTD with pulmonary arterial hypertension (PAH), acrosclerosis and myositis. In multivariate linear regression analysis, an additive model of PAH, myositis and lymphadenopathy accounted for 79% of the variability of the VEGF levels (r=0.889). CONCLUSIONS: Molecular factors modulating angiogenic responses are dysregulated in patients with MCTD and SSc with increases of VEGF in MCTD and SSc and selective upregulation of endostatin in MCTD. Furthermore, high serum levels of VEGF might characterise patients with MCTD with a more severe course of the disease with increased prevalence of PAH and myositis.

Synovial fibroblasts self-direct multicellular lining architecture and synthetic function in three-dimensional organ culture.

OBJECTIVE: To define the intrinsic capacity of fibroblast-like synoviocytes (FLS) to establish a 3-dimensional (3-D) complex synovial lining architecture characterized by the multicellular organization of the compacted synovial lining and the elaboration of synovial fluid constituents. METHODS: FLS were cultured in spherical extracellular matrix (ECM) micromasses for 3 weeks. The FLS micromass architecture was assessed histologically and compared with that of dermal fibroblast controls. Lubricin synthesis was measured via immunodetection. Basement membrane matrix and reticular fiber stains were performed to examine ECM organization. Primary human and mouse monocytes were prepared and cocultured with FLS in micromass to investigate cocompaction in the lining architecture. Cytokine stimuli were applied to determine the capacity for inflammatory architecture rearrangement. RESULTS: FLS, but not dermal fibroblasts, spontaneously formed a compacted lining architecture over 3 weeks in the 3-D ECM micromass organ cultures. These lining cells produced lubricin. FLS rearranged their surrounding ECM into a complex architecture resembling the synovial lining and supported the survival and cocompaction of monocyte/macrophages in the neo-lining structure. Furthermore, when stimulated by cytokines, FLS lining structures displayed features of the hyperplastic rheumatoid arthritis synovial lining. CONCLUSION: This 3-D micromass organ culture method demonstrates that many of the phenotypic characteristics of the normal and the hyperplastic synovial lining in vivo are intrinsic functions of FLS. Moreover, FLS promote survival and cocompaction of primary monocytes in a manner remarkably similar to that of synovial lining macrophages. These findings provide new insight into inherent functions of the FLS lineage and establish a powerful in vitro method for further investigation of this lineage.

Establishment of a human three-dimensional chip-based chondro-synovial coculture joint model for reciprocal cross talk studies in arthritis research.

Rheumatoid arthritis is characterised by a progressive, intermittent inflammation at the synovial membrane, which ultimately leads to the destruction of the synovial joint. The synovial membrane as the joint capsule's inner layer is lined with fibroblast-like synoviocytes that are the key player supporting persistent arthritis leading to bone erosion and cartilage destruction. While microfluidic models that model molecular aspects of bone erosion between bone-derived cells and synoviocytes have been established, RA's synovial-chondral axis has not yet been realised using a microfluidic 3D model based on human patient in vitro cultures. Consequently, we established a chip-based three-dimensional tissue coculture model that simulates the reciprocal cross talk between individual synovial and chondral organoids. When co-cultivated with synovial organoids, we could demonstrate that chondral organoids induce a higher degree of cartilage physiology and architecture and show differential cytokine response compared to their respective monocultures highlighting the importance of reciprocal tissue-level cross talk in the modelling of arthritic diseases.

Lasp1 regulates adherens junction dynamics and fibroblast transformation in destructive arthritis.

The LIM and SH3 domain protein 1 (Lasp1) was originally cloned from metastatic breast cancer and characterised as an adaptor molecule associated with tumourigenesis and cancer cell invasion. However, the regulation of Lasp1 and its function in the aggressive transformation of cells is unclear. Here we use integrative epigenomic profiling of invasive fibroblast-like synoviocytes (FLS) from patients with rheumatoid arthritis (RA) and from mouse models of the disease, to identify Lasp1 as an epigenomically co-modified region in chronic inflammatory arthritis and a functionally important binding partner of the Cadherin-11/ß-Catenin complex in zipper-like cell-to-cell contacts. In vitro, loss or blocking of Lasp1 alters pathological tissue formation, migratory behaviour and platelet-derived growth factor response of arthritic FLS. In arthritic human TNF transgenic mice, deletion of Lasp1 reduces arthritic joint destruction. Therefore, we show a function of Lasp1 in cellular junction formation and inflammatory tissue remodelling and identify Lasp1 as a potential target for treating inflammatory joint disorders associated with aggressive cellular transformation.

Cadherin-11 provides specific cellular adhesion between fibroblast-like synoviocytes.

Cadherins are integral membrane proteins expressed in tissue-restricted patterns that mediate homophilic intercellular adhesion. During development, they orchestrate tissue morphogenesis and, in the adult, they determine tissue integrity and architecture. The synovial lining is a condensation of fibroblast-like synoviocytes (FLS) and macrophages one to three cells thick. These cells are embedded within the extracellular matrix, but the structure is neither an epithelium nor an endothelium. Previously, the basis for organization of the synovium into a tissue was unknown. Here, we cloned cadherin-11 from human rheumatoid arthritis (RA)-derived FLS. We developed L cell transfectants expressing cadherin-11, cadherin-11 fusion proteins, and anti-cadherin-11 mAb. Cadherin-11 was found to be expressed mainly in the synovial lining by immunohistologic staining of human synovium. FLS adhered to cadherin-11-Fc, and transfection of cadherin-11 conferred the formation of tissue-like sheets and lining-like structures upon fibroblasts in vitro. These findings support a key role for cadherin-11 in the specific adhesion of FLS and in synovial tissue organization and behavior in health and RA.