Ankylosing enthesitis, dactylitis, and onychoperiostitis in male DBA/1 mice: a model of psoriatic arthritis

50 years of spondyloarthritis: a look back and a look ahead

PURPOSE OF REVIEW

It is now 50 years since the concept of spondyloarthritis was introduced by Moll, Wright and co-authors from Leeds, UK. This review will review the original concept and mark significant milestones over the last 50 years while looking ahead to developments in the future.

RECENT FINDINGS

While the diseases included under this rubric in the original description may have changed the core conditions remain and are still characterized by axial inflammation as a common feature. Imaging, animal models, genetics and immunology have contributed to our knowledge of the pathogenesis and classification of these diseases and have led to the development of more effective treatments.

SUMMARY

Future developments, facilitated by large research consortia, will help build on our current knowledge and will help clarify disease heterogeneity and provide insights into new therapeutic pathways.

An update of murine models and their methodologies in immune-mediated joint damage and pain research

Murine models have played an indispensable role in the understanding of rheumatic and musculoskeletal disorders (RMD), elucidating the genetic, endocrine and biomechanical pathways involved in joint pathology and associated pain. To date, the available models in RMD can be classified as induced or spontaneous, both incorporating transgenic alternatives that improve specific insights. It is worth noting that the selection of the most appropriate model together with the evaluation of their specific characteristics and technical capabilities are crucial when designing the experiments. Furthermore, it is also imperative to consistently adhere to the ethical standards concerning animal experimentation. Recognizing the inherent limitation that any model can entirely encapsulates the complexity of the pathophysiology of these conditions, the aim of this review is to provide an updated overview on the methodology of current murine models in major arthropathies and their immune-mediated pathways, addressing to basic, translational and pharmacological research in joint damage and pain.

Fibroblast Insights into the Pathogenesis of Ankylosing Spondylitis

Purpose of the Review

Emerging evidence has shown that ankylosing spondylitis fibroblasts (ASFs) act as crucial participants in inflammation and abnormal ossification in ankylosing spondylitis (AS). This review examines the investigations into ASFs and their pathological behavior, which contributes to inflammatory microenvironments and abnormal bone formation. The review spans the period from 2000 to 2023, with a primary focus on the most recent decade. Additionally, the review provides an in-depth discussion on studies on ASF ossification at the cellular level.

Recent Findings

ASFs organize immune functions by recruiting immune cells and influencing their differentiation and activation, thus mediate the inflammatory response in the early phase of disease. ASFs promote joint destruction at sites of cartilage and actively promote abnormal ossification by recruiting osteoblasts, differentiation into myofibroblasts or ossification directly. Many signaling pathways and cytokines such as Wnt signaling and BMP/TGF-β signaling are involved in ASF ossification.

Summary

ASFs play a key role in AS inflammation and osteogenesis. Further studies are required to elucidate molecular mechanisms behind that and provide new targets and directions for AS diagnosis and treatment from a new perspective of fibroblasts.

Therapeutic Efficacy of Mesenchymal Stem/Stromal Cell Small Extracellular Vesicles in Alleviating Arthritic Progression by Restoring Macrophage Balance

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by joint inflammation and damage, often associated with an imbalance in M1/M2 macrophages. Elevated levels of anti-inflammatory M2 macrophages have been linked to a therapeutic response in RA. We have previously demonstrated that mesenchymal stem/stromal cell small extracellular vesicles (MSC-sEVs) promote M2 polarization and hypothesized that MSC-sEVs could alleviate RA severity with a concomitant increase in M2 polarization. Here, we treated a mouse model of collagen-induced arthritis (CIA) with MSC-sEVs. Relative to vehicle-treated CIA mice, both low (1 μg) and high (10 μg) doses of MSC-sEVs were similarly efficacious but not as efficacious as Prednisolone, the positive control. MSC-sEV treatment resulted in statistically significant reductions in disease progression rate and disease severity as measured by arthritic index (AI), anti-CII antibodies, IL-6, and C5b-9 plasma levels. There were no statistically significant differences in the treatment outcome between low (1 μg) and high (10 μg) doses of MSC-sEVs. Furthermore, immunohistochemical analysis revealed that concomitant with the therapeutic efficacy, MSC-sEV treatment increased anti-inflammatory M2 macrophages and decreased pro-inflammatory M1 macrophages in the synovium. Consistent with increased M2 macrophages, histopathological examination also revealed reduced inflammation, pannus formation, cartilage damage, bone resorption, and periosteal new bone formation in the MSC-sEV-treated group compared to the vehicle group. These findings suggest that MSC-sEVs are potential biologic disease-modifying antirheumatic drugs (DMARDs) that can help slow or halt RA joint damage and preserve joint function.

Immune-mediated inflammatory diseases: Common and different pathogenic and clinical features

The term "immune-mediated inflammatory diseases (IMIDs)" refers to several inflammatory pathologies of multifactorial etiology and involving either simultaneously or sequentially more organs. IMIDs share some common pathogenic mechanisms, which account for some similarities in the clinical course and the impact that these diseases may have on other organs and systems of the body. However, there are some differences in the IMID-associated pathological process, including the synthesis and function of multiple inflammatory cytokines, which are supposed to perpetuate the tissue-damaging inflammation. This justifies the different indications and responsiveness to corticosteroids, immunosuppressors, small molecules, and biologics. Many individuals with IMIDs are, however, intolerant, or unresponsive to the current drugs, thus suggesting the necessity of novel therapeutic approaches, such as the combination of compounds that either inhibit more immuno-inflammatory networks selectively or simultaneously suppress inflammatory signals and activate counter-regulatory pathways. In this article, we highlight the most relevant features of IMIDs and discuss how clinicians can combat the detrimental immune response in such disorders.

Biology and therapeutic potential of mesenchymal stem cell extracellular vesicles in axial spondyloarthritis

Axial spondyloarthritis (AxSpA) is a chronic, inflammatory, autoimmune disease that predominantly affects the joints of the spine, causes chronic pain, and, in advanced stages, may result in spinal fusion. Recent developments in understanding the immunomodulatory and tissue-differentiating properties of mesenchymal stem cell (MSC) therapy have raised the possibility of applying such treatment to AxSpA. The therapeutic effectiveness of MSCs has been shown in numerous studies spanning a range of diseases. Several studies have been conducted examining acellular therapy based on MSC secretome. Extracellular vesicles (EVs) generated by MSCs have been proven to reproduce the impact of MSCs on target cells. These EVs are associated with immunological regulation, tissue remodeling, and cellular homeostasis. EVs' biological effects rely on their cargo, with microRNAs (miRNAs) integrated into EVs playing a particularly important role in gene expression regulation. In this article, we will discuss the impact of MSCs and EVs generated by MSCs on target cells and how these may be used as unique treatment strategies for AxSpA.

Levofloxacin induces differential effects in the transcriptome between the gut, peripheral and axial joints in the Spondyloarthritis DBA/1 mice: Improvement of intestinal dysbiosis and the overall inflammatory process

To analyze the effect of levofloxacin-induced intestinal microbiota modifications on intestinal, joint, and systemic inflammation in the DBA/1 mice with spontaneous arthritis. The study included two groups of mice, one of which received levofloxacin. The composition and structure of the microbiota were determined in the mice's stool using 16S rRNA sequencing; the differential taxa and metabolic pathway between mice treated with levofloxacin and control mice were also defied. The effect of levofloxacin was evaluated in the intestines, hind paws, and spines of mice through DNA microarray transcriptome and histopathological analyses; systemic inflammation was measured by flow cytometry. Levofloxacin decreased the pro-inflammatory bacteria, including Prevotellaceae, Odoribacter, and Blautia, and increased the anti-inflammatory Muribaculaceae in mice's stool. Histological analysis confirmed the intestinal inflammation in control mice, while in levofloxacin-treated mice, inflammation was reduced; in the hind paws and spines, levofloxacin also decreased the inflammation. Microarray showed the downregulation of genes and signaling pathways relevant in spondyloarthritis, including several cytokines and chemokines. Levofloxacin-treated mice showed differential transcriptomic profiles between peripheral and axial joints and intestines. Levofloxacin decreased the expression of TNF-α, IL-23a, and JAK3 in the three tissues, but IL-17 behaved differently in the intestine and the joints. Serum TNF-α was also reduced in levofloxacin-treated mice. Our results suggest that the microbiota modification aimed at reducing pro-inflammatory and increasing anti-inflammatory bacteria could potentially be a coadjuvant in treating inflammatory arthropathies.

Inflammatory Foot Involvement in Spondyloarthritis: From Tarsitis to Ankylosing Tarsitis

Spondyloarthritis (SpA) is a group that includes a wide spectrum of clinically similar diseases manifested by oligoarticular arthritis and axial or peripheral ankylosis. Although axial SpA is predominant in Caucasians and adult-onset patients, juvenile-onset and Latin American patients are characterized by severe peripheral arthritis and particularly foot involvement. The peripheral involvement of SpA can vary from tarsal arthritis to the most severe form named ankylosing tarsitis (AT). Although the cause and etiopathogenesis of axSpA are often studied, the specific characteristics of pSpA are unknown. Several animal models of SpA develop initial tarsitis and foot ankylosis as the main signs, emphasizing the role of foot inflammation in the overall SpA spectrum. In this review, we attempt to highlight the clinical characteristics of foot involvement in SpA and update the knowledge regarding its pathogenesis, focusing on animal models and the role of mechanical forces in inflammation.

Complexity of enthesitis and new bone formation in ankylosing spondylitis: current understanding of the immunopathology and therapeutic approaches

Despite increasing availability of treatments for spondyloarthritis (SpA) including tumour necrosis factor (TNF) and interleukin-17 (IL-17) inhibitors, there is no established treatment that abates new bone formation (NBF) in ankylosing spondylitis (AS), a subset of SpA. Recent research on TNF has revealed the increased level of transmembrane TNF in the joint tissue of SpA patients compared to that of rheumatoid arthritis patients, which appears to facilitate TNF-driven osteo-proliferative changes in AS. In addition, there is considerable interest in the central role of IL-23/IL-17 axis in type 3 immunity and the therapeutic potential of blocking this axis to ameliorate enthesitis and NBF in AS. AS immunopathology involves a variety of immune cells, including both innate and adoptive immune cells, to orchestrate the immune response driving type 3 immunity. In response to external stimuli of inflammatory cytokines, local osteo-chondral progenitor cells activate intra-cellular anabolic molecules and signals involving hedgehog, bone morphogenetic proteins, receptor activator of nuclear factor kappa-B ligand, and Wnt pathways to promote NBF in AS. Here, we provide an overview of the current immunopathology and future directions for the treatment of enthesitis and NBF associated with AS.

Incidence and severity of G6PI-induced arthritis are not increased in genetically distinct mouse strains upon aging

Background

The incidence of rheumatoid arthritis is correlated with age. In this study, we analyzed the association of the incidence and severity of glucose-6-phosphate isomerase (G6PI)-induced arthritis with age in two different mouse strains.

Methods

Young and very old mice from two different arthritis-susceptible wild-type mouse strains were analyzed after a single subcutaneous injection of G6PI s.c. The metabolism and the function of synoviocytes were analyzed in vitro, the production of bioactive lipid mediators by myeloid cells and synoviocytes was assessed in vitro and ex vivo by UPLC-MS-MS, and flow cytometry was used to verify age-related changes of immune cell composition and function.

Results

While the severity of arthritis was independent from age, the onset was delayed in old mice. Old mice showed common signs of immune aging like thymic atrophy associated with decreased CD4⁺ effector T cell numbers. Despite its decrease, the effector T helper (Th) cell compartment in old mice was reactive and functionally intact, and their Tregs exhibited unaltered suppressive capacities. In homeostasis, macrophages and synoviocytes from old mice produced higher amounts of pro-inflammatory cyclooxygenase (COX)-derived products. However, this functional difference did not remain upon challenge in vitro nor upon arthritis reactions ex vivo.

Conclusion

While old mice show a higher baseline of inflammatory functions, this does not result in increased reaction towards self-antigens in arthritis-susceptible mouse strains. Together, our data from two different mouse strains show that the susceptibility for G6PI-induced arthritis is not age-dependent.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-021-02596-7.

The Role of the IL-23/IL-17 Axis in Disease Initiation in Spondyloarthritis: Lessons Learned From Animal Models

Spondyloarthritis (SpA) is a spectrum of chronic inflammatory joint diseases that frequently presents with inflammation of the axial skeleton, peripheral joints, entheses, skin, and gut. Understanding SpA pathogenesis has been proven challenging due to the limited availability of human target tissues. In recent years, the interleukin (IL)-23/IL-17 pathway has been implicated in the pathogenesis of SpA, in addition to the Tumor Necrosis Factor Alpha (TNF-α) cytokine. The underlying molecular mechanisms by which the IL-23/IL-17 pathway triggers disease initiation, both in the joints as well as at extra-musculoskeletal sites, are not precisely known. Animal models that resemble pathological features of human SpA have provided possibilities for in-depth molecular analyses of target tissues during various phases of the disease, including the pre-clinical initiation phase of the disease before arthritis and spondylitis are clinically present. Herein, we summarize recent insights gained in SpA animal models on the role of the IL-23/IL-17 pathway in immune activation across affected sites in SpA, which include the joint, entheses, gut and skin. We discuss how local activation of the IL-23/IL-17 axis may contribute to the development of tissue inflammation and the onset of clinically manifest SpA. The overall aim is to provide the reader with an overview of how the IL-23/IL-17 axis could contribute to the onset of SpA pathogenesis. We discuss how insights from animal studies into the initiation phase of disease could instruct validation studies in at-risk individuals and thereby provide a perspective for potential future preventive treatment.

Psoriatic Dactylitis: Current Perspectives and New Insights in Ultrasonography and Magnetic Resonance Imaging

Dactylitis, one of the most typical features of psoriatic arthritis (PsA), is the diffuse swelling of the digits and is determined by the involvement of different anatomic structures, including: the subcutaneous fibrous tissue “accessory pulley” system; flexor tendons, with their related structures; the articular synovium; the small enthesis of the hands. Dactylitis is currently considered both a marker of disease activity and severe prognosis and its importance in PsA is emphasized by the inclusion in the classification criteria of PsA. This review focuses on the role of imaging in the management of PsA patients with dactylitis in clinical practice and in a research setting. Furthermore, imaging could be a valuable tool to assist in unravelling some of the underlying mechanisms of the onset and chronicization of dactylitis in PsA patients.

Spondyloarthritis and the Human Leukocyte Antigen (HLA)-B*27 Connection

Heritability of Spondyloarthritis (SpA) is highlighted by several familial studies and a high association with the presence of human leukocyte antigen (HLA)-B^*27. Though it has been over four decades since the association of HLA-B^*27 with SpA was first determined, the pathophysiological roles played by specific HLA-B^*27 allotypes are not fully understood. Popular hypotheses include the presentation of arthritogenic peptides, triggering of endoplasmic reticulum (ER) stress by misfolded HLA-B^*27, and the interaction between free heavy chains or heavy chain homodimers of HLA-B^*27 and immune receptors to drive IL-17 responses. Several non-HLA susceptibility loci have also been identified for SpA, including endoplasmic reticulum aminopeptidases (ERAP) and those related to the IL-23/IL-17 axes. In this review, we summarize clinical aspects of SpA including known characteristics of gut inflammation, enthesitis and new bone formation and the existing models for understanding the association of HLA-B^*27 with disease pathogenesis. We also examine newer insights into the biology of HLA class I (HLA-I) proteins and their implications for expanding our understanding of HLA-B^*27 contributions to SpA pathogenesis.

Exploring IL-17 in spondyloarthritis for development of novel treatments and biomarkers

Spondyloarthritis (SpA) is an umbrella term describing a family of chronic inflammatory rheumatic diseases. These diseases are characterised by inflammation of the axial skeleton, peripheral joints, and entheseal insertion sites throughout the body which can lead to structural joint damage including formation of axial syndesmophytes and peripheral osteophytes. Genetic evidence, preclinical and clinical studies indicate a clear role of interleukin (IL)- 23 and IL-17 as mediators in SpA pathogenesis. Targeting the IL-23/-17 pathways seems an efficient strategy for treatment of SpA patients, and despite the remaining challenges the pathway holds great promise for further advances and improved therapeutic opportunities. Much research is focusing on serological markers and imaging strategies to correctly diagnose patients in the early stages of SpA. Biomarkers may facilitate personalised medicine tailored to each patient's specific disease to optimise treatment efficacy and to monitor therapeutic response. This narrative review focuses on the IL-17 pathway in SpA-related diseases with emphasis on its role in pathogenesis, current approved IL-17 inhibitors, and the need for biomarkers reflecting core disease pathways for early diagnosis and measurement of disease activity, prognosis, and response to therapy.

Lessons on SpA pathogenesis from animal models

Understanding the complex mechanisms underlying a disorder such as spondyloarthritis (SpA) may benefit from studying animal models. Several suitable models have been developed, in particular to investigate the role of genetic factors predisposing to SpA, including HLA-B27, ERAP1, and genes related to the interleukin (IL)-23/IL-17 axis. One of the best examples of such research is the HLA-B27 transgenic rat model that fostered the emergence of original theories regarding HLA-B27 pathogenicity, including dysregulation of innate immunity, contribution of the adaptive immune system to chronic inflammation, and influence of the microbiota on disease development. Very recently, a new model of HLA-B27 transgenic Drosophila helped to expand further some of those theories in an unexpected direction involving the TGFβ/BMP family of mediators. On the other hand, several spontaneous, inducible, and/or genetically modified mouse models-including SKG mouse, TNF^ΔARE mouse and IL-23-inducible mouse model of SpA-have highlighted the importance of TNFα and IL-23/IL-17 axis in the development of SpA manifestations. Altogether, those animal models afford not only to study disease mechanism but also to investigate putative therapeutic targets.

Aberrant upregulation of CaSR promotes pathological new bone formation in ankylosing spondylitis

Pathological new bone formation is a typical pathological feature in ankylosing spondylitis (AS), and the underlying molecular mechanism remains elusive. Previous studies have shown that the calcium‐sensing receptor (CaSR) is critical for osteogenic differentiation while also being highly involved in many inflammatory diseases. However, whether it plays a role in pathological new bone formation of AS has not been reported. Here, we report the first piece of evidence that expression of CaSR is aberrantly upregulated in entheseal tissues collected from AS patients and animal models with different hypothetical types of pathogenesis. Systemic inhibition of CaSR reduced the incidence of pathological new bone formation and the severity of the ankylosing phenotype in animal models. Activation of PLCγ signalling by CaSR promoted bone formation both in vitro and in vivo. In addition, various inflammatory cytokines induced upregulation of CaSR through NF‐κB/p65 and JAK/Stat3 pathways in osteoblasts. These novel findings suggest that inflammation‐induced aberrant upregulation of CaSR and activation of CaSR‐PLCγ signalling in osteoblasts act as mediators of inflammation, affecting pathological new bone formation in AS.

Bone phenotypes in rheumatology - there is more to bone than just bone

Osteoarthritis, rheumatoid arthritis, psoriatic arthritis, and ankylosing spondylitis, all have one clear common denominator; an altered turnover of bone. However, this may be more complex than a simple change in bone matrix and mineral turnover. While these diseases share a common tissue axis, their manifestations in the area of pathology are highly diverse, ranging from sclerosis to erosion of bone in different regions. The management of these diseases will benefit from a deeper understanding of the local versus systemic effects, the relation to the equilibrium of the bone balance (i.e., bone formation versus bone resorption), and the physiological and pathophysiological phenotypes of the cells involved (e.g., osteoblasts, osteoclasts, osteocytes and chondrocytes). For example, the process of endochondral bone formation in chondrocytes occurs exists during skeletal development and healthy conditions, but also in pathological conditions. This review focuses on the complex molecular and cellular taxonomy of bone in the context of rheumatological diseases that alter bone matrix composition and maintenance, giving rise to different bone turnover phenotypes, and how biomarkers (biochemical markers) can be applied to potentially describe specific bone phenotypic tissue profiles.

Inhibition of Ras GTPases prevents Collagen-Induced Arthritis by Reducing the Generation of Pathogenic CD4+ T Cells and the Hyposialylation of Autoantibodies

OBJECTIVE

RasGTPases are master regulators of multiple intracellular signaling cascades. Perturbation of this pathway has been implicated in the pathogenesis of rheumatoid arthritis (RA). In this study we aimed to define the therapeutic potential of a novel RasGTPases inhibitor, farnesylthiosalicylate (FTS), in the preclinical mouse model of collagen-induced arthritis (CIA) and better delineate its immunomodulatory effects both ex vivo and in the mouse.

METHODS

We analyzed in vitro the immunomodulatory effects of FTS on various CD4⁺ T-cell functions such as activation, proliferation, T-helper polarization, and production of proinflammatory cytokines. Using the CIA model, we further determined the efficacy of FTS to inhibit clinical, histopathologic, and diverse immunological outcomes of arthritis.

RESULTS

FTS treatment of CD4⁺ T cells in vitro effectively targeted distinct kinases (extracellular signal-regulated kinase 1/2, p38, protein kinase B/AKT, and mammalian target of rapamycin), the production of interleukin (IL)-17A, IL-22, and granulocyte-macrophage colony-stimulating factor, and Th17 polarization. FTS therapy in the mouse CIA model significantly reduced clinical disease severity and joint inflammation/damage by histology. Importantly, FTS suppressed the in vivo induction of splenic IL-17⁺ IL-22⁺ Th17 cells and the secretion of proinflammatory cytokines. The production of pathogenic autoantibodies and their abnormal hyposialylation was significantly attenuated by FTS therapy. Importantly, in vivo generation of collagen type-II specific effector CD4⁺ T cells was likewise repressed by FTS therapy.

CONCLUSION

The RasGTPases inhibitor FTS attenuates the production of proinflammatory cytokines by in vitro-activated T cells and is a potent immunomodulatory compound in the CIA model, primarily targeting the generation of autoreactive Th17 cells and the production of autoantibodies and their subsequent pathogenic hyposialylation.

Spontaneous onset of TNFα-triggered colonic inflammation depends on functional T lymphocytes, S100A8/A9 alarmins, and MHC H-2 haplotype

Recently, we established a doxycycline-inducible human tumor necrosis factor alpha (TNFα)-transgenic mouse line, ihTNFtg. Non-induced young and elderly mice showed low but constitutive expression of hTNFα due to promoter leakiness. The persistently present hTNFα stimulated endogenous pro-inflammatory mouse mS100A8/A9 alarmins. Secreted mS100A8/A9 in turn induced the expression and release of mouse mTNFα. The continuous upregulation of pro-inflammatory mTNFα and mS100A8/A9 proteins, due to their mutual expression dependency, gradually led to increased levels in colon tissue and blood. This finally exceeded the threshold levels tolerated by the healthy organism, leading to the onset of intestinal inflammation. Here, recombinant hTNFα functioned as an initial trigger for the development of chronic inflammation. Crossing ihTNFtg mice with S100A9^KO mice lacking active S100A8/A9 alarmins or with Rag1^KO mice lacking T and B lymphocytes completely abrogated the development of colonic inflammation, despite the still leaky hTNFα promoter. Furthermore, both the intensity of the immune response and the strength of immunosuppressive Treg induction was found to depend on the major histocompatibility complex (MHC) genetic composition. In summary, the onset of intestinal inflammation in elderly mice depends on at least four factors that have to be present simultaneously: TNFα upregulation, S100A8/A9 protein expression, functional T lymphocytes and genetic composition, with the MHC haplotype being of central importance. Only joint action of these factors leads to chronic intestinal inflammation, while absence of any of these determinants abrogates the development of the autoimmune disorder. © 2020 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Disease Characteristics, Quality of Life, and Work Productivity by Enthesitis Site: Real-world Data From the US Corrona Psoriatic Arthritis/Spondyloarthritis Registry

OBJECTIVE

To assess the effect of clinical enthesitis by body site in patients with psoriatic arthritis (PsA).

METHODS

Adults with PsA enrolled in the Corrona Psoriatic Arthritis/Spondyloarthritis Registry (March 2013-March 2018) were included. Enthesitis at enrollment was assessed by the Spondyloarthritis Research Consortium of Canada Enthesitis Index and classified by affected sites (upper, lower, or both). Disease activity (e.g., Clinical Disease Activity Index, Clinical Disease Activity Index for PsA), patient-reported outcomes (PRO; e.g., patient-reported pain and fatigue), and work productivity were compared between those with and without enthesitis using t- or Wilcoxon rank-sum tests for continuous variables and chi-square or Fisher exact tests for categorical variables. The association of enthesitis with disease activity and PRO measures versus no enthesitis was modeled using multivariable-adjusted linear or logistic regression.

RESULTS

Of 2003 patients with PsA, 391 (19.5%) had enthesitis: 80 (20.5%) in upper sites only; 137 (35.0%) in lower sites only; and 174 (44.5%) in both. Regardless of location, disease activity and PRO were worse in patients with versus without enthesitis. In adjusted models, the presence of enthesitis at any site was significantly associated with worse disease activity versus no enthesitis. Enthesitis in lower or both upper and lower sites was associated with higher pain and fatigue scores and greater work impairment versus no enthesitis.

CONCLUSION

Patients with clinical enthesitis had worse disease activity regardless of enthesitis location versus those without enthesitis, and patients with enthesitis in lower or both upper and lower sites had worse pain, fatigue, and work impairment.

Tendon and ligament mechanical loading in the pathogenesis of inflammatory arthritis

Mechanical loading is an important factor in musculoskeletal health and disease. Tendons and ligaments require physiological levels of mechanical loading to develop and maintain their tissue architecture, a process that is achieved at the cellular level through mechanotransduction-mediated fine tuning of the extracellular matrix by tendon and ligament stromal cells. Pathological levels of force represent a biological (mechanical) stress that elicits an immune system-mediated tissue repair pathway in tendons and ligaments. The biomechanics and mechanobiology of tendons and ligaments form the basis for understanding how such tissues sense and respond to mechanical force, and the anatomical extent of several mechanical stress-related disorders in tendons and ligaments overlaps with that of chronic inflammatory arthritis in joints. The role of mechanical stress in 'overuse' injuries, such as tendinopathy, has long been known, but mechanical stress is now also emerging as a possible trigger for some forms of chronic inflammatory arthritis, including spondyloarthritis and rheumatoid arthritis. Thus, seemingly diverse diseases of the musculoskeletal system might have similar mechanisms of immunopathogenesis owing to conserved responses to mechanical stress.

Pathophysiology, assessment and treatment of psoriatic dactylitis

Dactylitis is diffuse swelling of the digits that is usually related to an underlying inflammatory or infiltrative disorder. Psoriatic arthritis (PsA) is the most common severe disease thought to cause dactylitis. Our understanding of the pathogenesis of PsA-related dactylitis comes from experimental animal models of PsA-like disease, as well as advances in imaging and other clinical studies. Clinical trials in PsA have increasingly included dactylitis as an important secondary outcome measure. These studies indicate that cytokines drive multi-locus microanatomical pan-digital pathology. Given the importance of pro-inflammatory cytokines, the pathogenesis of dactylitis is best understood as an initial aberrant innate immune response to biomechanical stress or injury, with subsequent adaptive immune mechanisms amplifying the dactylitis inflammatory response. Regarding the treatment of dactylitis, no studies have been conducted using dactylitis as the primary outcome measure, and the current knowledge comes from analysis of dactylitis as a secondary outcome measure.

Reporters of TCR signaling identify arthritogenic T cells in murine and human autoimmune arthritis

How arthritis-causing T cells trigger rheumatoid arthritis (RA) is not understood since it is difficult to differentiate T cells activated by inflammation in arthritic joints from those activated through their T cell antigen receptor (TCR) by self-antigens. We developed a model to identify and study antigen-specific T cell responses in arthritis. Nur77—a specific marker of TCR signaling—was used to identify antigen-activated T cells in the SKG arthritis model and in patients with RA. Nur77 could distinguish highly arthritogenic and autoreactive T cells in SKG mice. The enhanced autoreactivity was associated with increased interleukin-6 (IL-6) receptor signaling, likely contributing to their arthritogenicity. These data highlight a functional correlate between Nur77 expression, arthritogenic T cell populations, and heightened IL-6 sensitivity in SKG mice with translatable implications for human RA.

How pathogenic cluster of differentiation 4 (CD4) T cells in rheumatoid arthritis (RA) develop remains poorly understood. We used Nur77—a marker of T cell antigen receptor (TCR) signaling—to identify antigen-activated CD4 T cells in the SKG mouse model of autoimmune arthritis and in patients with RA. Using a fluorescent reporter of Nur77 expression in SKG mice, we found that higher levels of Nur77-eGFP in SKG CD4 T cells marked their autoreactivity, arthritogenic potential, and ability to more readily differentiate into interleukin-17 (IL-17)–producing cells. The T cells with increased autoreactivity, nonetheless had diminished ex vivo inducible TCR signaling, perhaps reflective of adaptive inhibitory mechanisms induced by chronic autoantigen exposure in vivo. The enhanced autoreactivity was associated with up-regulation of IL-6 cytokine signaling machinery, which might be attributable, in part, to a reduced amount of expression of suppressor of cytokine signaling 3 (SOCS3)—a key negative regulator of IL-6 signaling. As a result, the more autoreactive GFP^hi CD4 T cells from SKGNur mice were hyperresponsive to IL-6 receptor signaling. Consistent with findings from SKGNur mice, SOCS3 expression was similarly down-regulated in RA synovium. This suggests that despite impaired TCR signaling, autoreactive T cells exposed to chronic antigen stimulation exhibit heightened sensitivity to IL-6, which contributes to the arthritogenicity in SKG mice, and perhaps in patients with RA.

Predominant ultrasonographic extracapsular changes in symptomatic psoriatic dactylitis: results from a multicenter cross-sectional study comparing symptomatic and asymptomatic hand dactylitis

OBJECTIVE

Despite diffuse digital swelling, dactylitis may sometimes be asymptomatic. The objective of this study was to compare the clinical and ultrasonographic features of symptomatic with asymptomatic psoriatic arthritis (PsA) dactylitis.

METHODS

One hundred and twenty-five hand dactylitis were evaluated in a multicenter cross-sectional study for the presence of pain, subjective functional limitation, and tenderness (4-points scale) with the calculation of a Leeds Dactylitis Index (LDI) score. Fingers were subsequently investigated using high-frequency ultrasound (US) both in gray-scale (GS) and power Doppler (PD), for the presence and grading of flexor tenosynovitis, soft tissue edema, subcutaneous PD signal (PDUS), extensor tendon involvement, and joints synovitis. Clinical and US characteristics of symptomatic dactylitic fingers were compared with the asymptomatic dactylitic ones.

RESULTS

Symptomatic fingers (n = 80) had a significantly lower dactylitis duration compared to asymptomatic fingers (n = 36) (p < 0.001). Values of LDI, patient VAS-pain, and VAS-functional score were significantly higher in fingers with symptomatic dactylitis (p < 0.001 and p = 0.010, respectively). Symptomatic dactylitis had a higher prevalence of flexor tenosynovitis of grade > 2, soft tissue edema and subcutaneous PDUS signal (p < 0.001). Asymptomatic dactylitis showed a greater prevalence of joint synovitis (both in GS and in PD) than symptomatic dactylitis (p < 0.001).

CONCLUSIONS

Digital tenderness and pain are linked to US tenosynovitis of grade > 2 and extra synovial abnormalities and conversely asymptomatic dactylitis is associated with joint-based synovitis.Key Points• Digital tenderness and local pain in psoriatic arthritis dactylitis are strongly associated with flexor tenosynovitis of grade> 2, soft tissue edema, and subcutaneous PD signal.• In psoriatic arthritis, asymptomatic dactylitis showed a greater prevalence of joint synovitis than symptomatic dactylitis.• In psoriatic arthritis, ultrasound inflammatory abnormalities are present in about 70% of cold dactylitis which is linked for disease chronicity.• In psoriatic arthritis, the flexor tendon and adjacent soft tissues play a significant role in symptomatic dactylitis.

The effect of anti-IL-6 receptor antibody for the treatment of McH-lpr/lpr-RA1 mice that spontaneously developed destructive arthritis and enthesitis

Background

McH-lpr/lpr-RA1 mice are a new strain of mice which spontaneously develop destructive arthritis and enthesitis in the ankle. There is no published data that drug treatment has been trialed on these mice. This study examined the effect of the mouse anti-IL-6 receptor antibody, MR16–1, for the treatment of arthritis and enthesitis in McH-lpr/lpr-RA1 mice.

Methods

Male McH-lpr/lpr-RA1 mice were randomly divided into control and treatment groups. MR16–1 was administered from 10 weeks of age for the treatment group. Saline was applied for the control group. The drug was administered once a week, at an initial dose of 2 mg, then maintained at 0.5 mg once per week thereafter. The effects were evaluated by the histopathological synovitis score, in vivo imaging using indocyanine green liposomes, and analysis of the gene expression of inflammatory cytokines.

Results

Tissue analyses were carried out at 14, 17 and 20 weeks of age. The synovitis scores of treated groups were significantly lower compared with those of the control group at 14 and 17 weeks of age. The kappa coefficient was 0.77. However, progression of entheseal ossification persisted in the MR16–1 treated group. In vivo imaging using indocyanine green liposomes showed significant decreases in signal intensities of treated groups at week 14, but no significant differences were observed at week 18. Blood serum amyloid A levels in treated groups were significantly lower at 17 weeks of age. The gene expression levels of Tnf and Il17 were also significantly lower in MR16–1 treated groups.

Conclusions

Administration of the anti-IL-6 receptor antibody is effective for the treatment of synovitis and bone destruction of McH-lpr/lpr-RA1 mice. McH-lpr/lpr-RA1 mice may be a suitable experimental model for the development of new treatments for destructive arthritis and enthesitis. IL-6 signal blockade could contribute to the treatment of destructive arthritis, and further studies should be carried out to confirm its potential in the prevention of enthesopathy developed to ossification.

Sacroiliac Joint Ankylosis in Young Spondyloarthritis Patients Receiving Biologic Therapy: Observation of Serial Magnetic Resonance Imaging Scans

OBJECTIVE

To assess the temporal relationship between initiating biologic therapy and magnetic resonance imaging (MRI) scores of inflammation and structural damage in young patients with spondyloarthritis.

METHODS

A local adolescent/young adult patient rheumatology database was searched for patients ages 12-24 years who had evidence of sacroiliitis on MRI and a clinical diagnosis of enthesitis-related arthritis (ERA) with axial involvement or nonradiographic axial spondyloarthritis. Patients treated with tumor necrosis factor inhibitor (TNFi) therapy who had undergone a minimum of 1 MRI scan before and 2 MRI scans after starting TNFi therapy (over ≥2 years) were included. Images of the sacroiliac joints were scored for inflammation and structural abnormalities (including erosions, fat metaplasia, and fusion). The effects of TNFi therapy and of time since initiation of TNFi therapy on inflammation and structural abnormalities were assessed using a mixed-effects regression analysis.

RESULTS

Twenty-nine patients (ages 12-23 years) with ERA or nonradiographic axial spondyloarthritis who underwent TNFi therapy were included. Inflammation scores were significantly lower in patients receiving TNFi treatment (P = 0.013), but there was no significant effect of time from TNFi initiation on inflammation (P = 0.125). Conversely, there was no significant effect of active TNFi treatment on fusion scores (P = 0.308), but fusion scores significantly increased with time from TNFi initiation (P < 0.001); a similar positive relationship between time since biologic start and fat metaplasia scores was observed.

CONCLUSION

TNFi therapy failed to prevent the eventual development of joint ankylosis in this cohort of young patients with spondyloarthritis, despite a substantial reduction in inflammation with TNFi therapy.

Advances in understanding the pathophysiology of spondyloarthritis

Progressive understanding of the underlying pathophysiology of axial spondyloarthritis has successfully translated into innovative therapeutic strategies and successful management of patients in the clinic. This review summarizes the key roles of the pro-inflammatory cytokines tumor necrosis factor and interleukin-17 in the onset and progression of disease and how these cytokines are instrumental in shaping the concept that enthesitis is a key feature of axial spondyloarthritis. Advances in immunological technologies have led to the important insight that different cell populations, part of both the innate and adaptive immune system, play a key role in axial spondyloarthritis. In addition to inflammation, structural damage to the axial skeleton, in particular progressive ankylosis of the sacroiliac joints and the spine, is key to the outcome of patients. Novel data integrate the role of pro-inflammatory cytokines and enthesitis in this context.

Symptomatic psoriatic dactylitis is associated with ultrasound determined extra-synovial inflammatory features and shorter disease duration

OBJECTIVES

To explore the link between ultrasonographic features of dactylitis in psoriatic arthritis (PsA) and symptoms, digital tenderness and duration of dactylitis.

METHODS

Forty-eight cases of PsA dactylitis were investigated using high frequency ultrasound (US) both in grey scale (GS) and Power Doppler (PD), evaluating the presence and the degree of flexor tenosynovitis, peri-tendinous oedema, subcutaneous PD, extensor tendon involvement, GS synovitis and intra-articular PD signal (PDS) of the involved digits. Patients were compared according to the presence of local pain and digital tenderness, the duration of dactylitis and the concomitant treatment.

RESULTS

The presence of pain/tenderness was positively associated with US GS flexor tenosynovitis of grade > 2 (p < 0.001), PD-flexor tenosynovitis (p < 0.001), peri-tendinous oedema (p < 0.001) and subcutaneous PDS (p < 0.001); moreover, it was negatively associated with GS synovitis (p < 0.001) and intra-articular PD (p < 0.001). The same positive and negative association with US findings were found comparing patients with duration of dactylitis shorter or longer than the median (24 weeks) (p < 0.001 for all comparisons).

CONCLUSIONS

Pain and digital tenderness are linked to dactylitis duration and earlier lesions are associated with extra synovial inflammatory changes. These findings suggest a hitherto unappreciated extra synovial basis for symptoms in PsA dactylitis.

The Early Phases of Ankylosing Spondylitis: Emerging Insights From Clinical and Basic Science

In our paper, we discuss how the early phases of ankylosing spondylitis (AS) are linked to peri-firbocartilagenous osteitis in the sacroiliac joint and entheseal bone related anchoring sites. This skeletal proclivity is linked to an abnormal immunological response to skeletal biomechanical stress and associated microdamage. A key event in the early stages of AS appears to be the association with subclinical Crohn's-like colitis with this gut inflammation being pivotal to the osteitis reaction. Whether this osteitis is consequent to non-specific intestinal innate immune activation or adaptive immune responses against specific microbiotal or self-antigens is unknown. Recurrent iritis is an HLA-B27 associated feature that may predate AS and pursues a course independent of joint involvement, and points toward the pivotal role of organ specific immunology over generalized systemic immune responses in disease expression. Human genetics and animal model studies strongly incriminate the IL23/17 axis and TNF-α in disease pathogenesis. Preliminary work shows a strong convergence of innate immune cells including type 3 innate lymphoid-cells (ILC3) and γδ T-cells in skin, gut, entheseal, and eye inflammation. Despite the HLA-B27 association, the role of adaptive immunity, especially CD8+ T-cells mediated responses remains unproven and alternative theories have been proposed. The emerging non-dependence of axial inflammation on IL-23 but dependence on IL-17A is an unexpected new twist that awaits full explanation. In this mini-review, we discuss the key events in the early stages of human AS from clinical and basic science aspects, which could be crucial for attempted disease prevention studies in at risk subjects.

A model of chronic enthesitis and new bone formation characterized by multimodal imaging

Enthesitis is a key feature of several different rheumatic diseases. Its pathophysiology is only partially known due to the lack of access to human tissue and the shortage of reliable animal models for enthesitis. Here, we aimed to develop a model that mimics the effector phase of enthesitis and reliably leads to inflammation and new bone formation. Enthesitis was induced by local injection of monosodium urate (MSU) crystals into the metatarsal entheses of wild-type (WT) or oxidative-burst-deficient (Ncf1**) mice. Quantitative variables of inflammation (edema, swelling) and vascularization (tissue perfusion) were assessed by magnetic resonance imaging (MRI), bone-forming activity by [¹⁸F]-fluoride positron emission tomography (PET), and destruction of cortical bone and new bone formation by computed tomography (CT). Non-invasive imaging was validated by histochemical and histomorphometric analysis. While injection of MSU crystals into WT mice triggered transient mild enthesitis with no new bone formation, Ncf1** mice developed chronic enthesitis accompanied by massive enthesiophytes. In MRI, inflammation and blood flow in the entheses were chronically increased, while PET/CT showed osteoproliferation with enthesiophyte formation. Histochemical analyses showed chronic inflammation, increased vascularization, osteoclast differentiation and bone deposition in the affected entheseal sites. Herein we describe a fast and reliable effector model of chronic enthesitis, which is characterized by a combination of inflammation, vascularization and new bone formation. This model will help to disentangle the molecular pathways involved in the effector phase of enthesitis.

Inflammation Intensity-Dependent Expression of Osteoinductive Wnt Proteins Is Critical for Ectopic New Bone Formation in Ankylosing Spondylitis

OBJECTIVE

To investigate the molecular mechanism underlying inflammation-related ectopic new bone formation in ankylosing spondylitis (AS).

METHODS

Spinal tissues and sera were collected from patients with AS and healthy volunteers and examined for the expression of Wnt proteins. An in vitro cell culture system mimicking the local inflammatory microenvironment of bone-forming sites was established to study the relationship between inflammation and Wnt expression, the regulatory mechanism of inflammation-induced Wnt expression, and the role of Wnt signaling in new bone formation. Modified collagen-induced arthritis (CIA) and proteoglycan-induced spondylitis (PGIS) animal models were used to confirm the key findings in vivo.

RESULTS

The levels of osteoinductive Wnt proteins were increased in sera and spinal ligament tissues from patients with AS. Constitutive low-intensity tumor necrosis factor (TNF) stimulation, but not short-term or high-intensity TNF stimulation, induced persistent expression of osteoinductive Wnt proteins and subsequent bone formation through NF-κB (p65) and JNK/activator protein 1 (c-Jun) signaling pathways. Furthermore, inhibition of either the Wnt/β-catenin or Wnt/protein kinase Cδ (PKCδ) pathway significantly suppressed new bone formation. The increased expression of Wnt proteins was confirmed in both the modified CIA and PGIS models. A kyphotic and ankylosing phenotype of the spine was seen during long-term observation in the modified CIA model. Inhibition of either the Wnt/β-catenin or Wnt/PKCδ signaling pathway significantly reduced the incidence and severity of this phenotype.

CONCLUSION

Inflammation intensity-dependent expression of osteoinductive Wnt proteins is a key link between inflammation and ectopic new bone formation in AS. Activation of both the canonical Wnt/β-catenin and noncanonical Wnt/PKCδ pathways is required for inflammation-induced new bone formation.

Bone Disease in Axial Spondyloarthritis

Axial spondyloarthritis is a chronic inflammatory skeletal disorder with an important burden of disease, affecting the spine and sacroiliac joints and typically presenting in young adults. Ankylosing spondylitis, diagnosed by the presence of structural changes to the skeleton, is the prototype of this disease group. Bone disease in axial spondyloarthritis is a complex phenomenon with the coexistence of bone loss and new bone formation, both contributing to the morbidity of the disease, in addition to pain caused by inflammation. The skeletal structural changes respectively lead to increased fracture risk and to permanent disability caused by ankylosis of the sacroiliac joints and the spine. The mechanism of this new bone formation leading to ankylosis is insufficiently known. The process appears to originate from entheses, specialized structures that provide a transition zone in which tendon and ligaments insert into the underlying bone. Growth factor signaling pathways such as bone morphogenetic proteins, Wnts, and Hedgehogs have been identified as molecular drivers of new bone formation, but the relationship between inflammation and activation of these pathways remains debated. Long-standing control of inflammation appears necessary to avoid ankylosis. Recent evidence and concepts suggest an important role for biomechanical factors in both the onset and progression of the disease. With regard to new bone formation, these processes can be understood as ectopic repair responses secondary to inflammation-induced bone loss and instability. In this review, we discuss the clinical implications of the skeletal changes as well as the underlying molecular mechanisms, the relation between inflammation and new bone formation, and the potential role of biomechanical stress.

Altered Bone Remodeling in Psoriatic Disease: New Insights and Future Directions

Psoriatic arthritis (PsA) is an inflammatory rheumatic disorder that occurs in patients with psoriasis and predominantly affects musculoskeletal structures, skin, and nails. The etiology of PsA is not well understood but evidence supports an interplay of genetic, immunologic, and environmental factors which promote pathological bone remodeling and joint damage in PsA. Localized and systemic bone loss due to increased activity of osteoclasts is well established in PsA based on animal models and translational studies. In contrast, the mechanisms responsible for pathological bone remodeling in PsA remain enigmatic although new candidate molecules and pathways have been identified. Recent reports have revealed novel findings related to bone erosion and pathologic bone formation in PsA. Many associated risk factors and contributing molecular mechanisms have also been identified. In this review, we discuss new developments in the field, point out unresolved questions regarding the pathogenetic origins of the wide array of bone phenotypes in PsA, and discuss new directions for investigation.

ENTHESITIS AND PSORIATIC ONYCHOPATHY AS A FACTOR FOR PREDICTION OF PSORIATIC ARTHRITIS IN PSORIASIS

Psoriatic arthritis is a psoriasis-related spondyloarthropathy that occurs in 20–30 % of patients with psoriasis. Psoriatic arthritis affects the patient’s quality of life indicators and are more often associated with disabilities of working age than psoriasis skin form. Nail psoriasis has been proposed as a predictor for the development of psoriatic arthritis. The inflammation involving the entheses, called enthesitis, is an early inflammatory change seen in psoriatic arthritis, and nail changes appear to result from the close relationship between the nail and the enthesis of the distal interphalangeal extensor tendon, one of the main entheseal compartments affected in psoriatic arthritis. Various imaging studies have demonstrated that there is a considerable proportion of undiagnosed psoriatic arthritis among patients with psoriasis. Since early detection and treatment of psoriatic arthritis could, ultimately, allow the prevention of clinical and radiologic progression of the disease, there is the need to establish clinical indicators to detect this risk.

No evidence for a direct role of HLA-B27 in pathological bone formation in axial SpA

Objective

The strong genetic association between HLA-B27 and ankylosing spondylitis has been known for over 40 years. HLA-B27 positivity is possibly associated with severity of ankylosis. We studied the in vitro and in vivo impact of HLA-B27 in models of chondrogenesis and osteogenesis.

Methods

Different in vitro differentiation systems were used to mimic endochondral and direct bone formation. ATDC5 cells and primary human periosteum-derived cells (hPDCs) were transduced with lentiviral vectors expressing HLA-B27 or HLA-B7. These cells and limb bud cells (from HLA-B27 transgenic and wild-type (WT) mice) were cultured in micromasses. To study direct osteogenesis in hPDCs, cells were cultured as monolayers and stimulated with osteogenic media. Chondrogenesis (COL2, ACAN, COL10) and osteogenesis (OSC, ALP, RUNX2) marker expression was studied by quantitative RT-PCR. Colorimetric tests were performed to measure proteoglycans, mineralization and collagens. Collagen antibody-induced arthritis (CAIA) was induced in HLA-B27 transgenic and WT mice. Clinical scoring and µCTs were performed. Statistical analyses were performed by two-way ANOVA.

Results

There was no difference in chondrogenesis markers or in colorimetric tests between HLA-B27⁺ and HLA-B7⁺ micromasses. Expression of osteogenesis markers and Alizarin red staining was comparable in the HLA-B27⁺ and the HLA-B7⁺ hPDCs in monolayers. HLA-B27 transgenic mice showed more severe arthritis compared with WT mice in the CAIA model. µCT analysis showed no increased bone formation in HLA-B27 transgenic mice.

Conclusion

HLA-B27 seems to enhance joint inflammation in the CAIA model. We could not document a direct effect of HLA-B27 on chondrogenesis or osteogenesis.

Association of ERAP1, IL23R and PTGER4 Polymorphisms with Radiographic Severity of Ankylosing Spondylitis

Background:

Radiographic severity of ankylosing spondylitis (AS) shows such great variance that some patients never develop syndesmophytes throughout the entire disease span, whereas some develop bamboo spine relatively early.

Objective:

To study the association between ERAP1, IL23R and PTGER4 single nucleotide polymorphisms (SNPs) and radiographic severity in AS patients.

Methods:

rs27044 and rs30187 (ERAP1), rs11209032 (IL23R) and rs10440635 (PTGER4) SNPs were genotyped in 235 AS patients fulfilling the modified New York criteria. Patients were classified as mild- and severe-AS according to modified Stoke AS spinal score (mSASSS). Mild-AS is defined as having mSASSS of “0” following at least 10 years of disease duration. Severe-AS is defined as having mSASSS of >20 (patients with mild vertebral changes (i.e. squaring or erosions) were omitted for clear stratification) regardless of disease duration.

Results:

The genotype distributions and allele frequencies of ERAP1 rs27044 and rs30187, IL23R rs11209032 and PTGER4 rs10440635 SNPs were similar in mild- (n=171, mSASSS=0, 55.6% HLA-B27 positive) and severe-AS patients (n=64, mSASSS=48.5±17.8, 73.4% HLA-B27 positive). After adjustment for clinical differences between groups (gender, disease duration, HLA-B27 and smoking status) by logistic regression analysis, none of the alleles in the investigated SNPs were found to be associated with radiographic severity of AS.

Conclusion:

In radiographically well-categorized AS patients, ERAP1 rs27044 and rs30187, IL23R rs11209032 and PTGER4 rs10440635 SNPs are not found to be associated with radiographic severity of AS.

The osteogenic potential of ligament fibroblasts is greater in ankylosing spondylitis patients than in patients with osteoarthritis

BACKGROUND

The goal of the present study was to investigate the osteogenic potential of ligament fibroblasts from patients with ankylosing spondylitis (AS).

MATERIALS AND METHODS

Ligament fibroblasts were isolated from tissues harvested from AS patients and patients with aseptic necrosis of the femoral head (ANFH) who had undergone total hip arthroplasty (THA). Cells were cultured in osteogenic induction medium (OIM) with or without bone morphogenetic protein 2 (BMP-2) for 30 days. During this time, the levels of alkaline phosphatase (ALP) and osteocalcin (OC) were determined as markers of osteogenesis.

RESULTS

Ligament fibroblasts isolated from patients with AS exhibited significantly greater potential for differentiation than those isolated from patients with osteoarthritis (ANFH).

CONCLUSION

These findings illuminate osteogenesis as a new pathway for studying the mechanism underlying ankylosis in AS patients. Factors which cause localized stromal remodeling at the enthesis significantly influence formation of new bone and further research is required to determine the mechanisms responsible for the osteogenic potential of enthesis cells and ligament fibroblasts in AS patients.

Inflammation-driven bone formation in a mouse model of ankylosing spondylitis: sequential not parallel processes

Background

Ankylosing spondylitis (AS) is an immune-mediated arthritis particularly targeting the spine and pelvis and is characterised by inflammation, osteoproliferation and frequently ankylosis. Current treatments that predominately target inflammatory pathways have disappointing efficacy in slowing disease progression. Thus, a better understanding of the causal association and pathological progression from inflammation to bone formation, particularly whether inflammation directly initiates osteoproliferation, is required.

Methods

The proteoglycan-induced spondylitis (PGISp) mouse model of AS was used to histopathologically map the progressive axial disease events, assess molecular changes during disease progression and define disease progression using unbiased clustering of semi-quantitative histology. PGISp mice were followed over a 24-week time course. Spinal disease was assessed using a novel semi-quantitative histological scoring system that independently evaluated the breadth of pathological features associated with PGISp axial disease, including inflammation, joint destruction and excessive tissue formation (osteoproliferation). Matrix components were identified using immunohistochemistry.

Results

Disease initiated with inflammation at the periphery of the intervertebral disc (IVD) adjacent to the longitudinal ligament, reminiscent of enthesitis, and was associated with upregulated tumor necrosis factor and metalloproteinases. After a lag phase, established inflammation was temporospatially associated with destruction of IVDs, cartilage and bone. At later time points, advanced disease was characterised by substantially reduced inflammation, excessive tissue formation and ectopic chondrocyte expansion. These distinct features differentiated affected mice into early, intermediate and advanced disease stages. Excessive tissue formation was observed in vertebral joints only if the IVD was destroyed as a consequence of the early inflammation. Ectopic excessive tissue was predominantly chondroidal with chondrocyte-like cells embedded within collagen type II- and X-rich matrix. This corresponded with upregulation of mRNA for cartilage markers Col2a1, sox9 and Comp. Osteophytes, though infrequent, were more prevalent in later disease.

Conclusions

The inflammation-driven IVD destruction was shown to be a prerequisite for axial disease progression to osteoproliferation in the PGISp mouse. Osteoproliferation led to vertebral body deformity and fusion but was never seen concurrent with persistent inflammation, suggesting a sequential process. The findings support that early intervention with anti-inflammatory therapies will be needed to limit destructive processes and consequently prevent progression of AS.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0805-0) contains supplementary material, which is available to authorized users.

In vivo activation of Treg cells with a CD28 superagonist prevents and ameliorates chronic destructive arthritis in mice

Although regulatory T (Treg) cells are necessary to prevent autoimmune diseases, including arthritis, whether Treg cells can ameliorate established inflammatory disease is controversial. Using the glucose-6-phosphate isomerase (G6PI)-induced arthritis model in mice, we aimed to determine the therapeutic efficacy of increasing Treg cell number and function during chronic destructive arthritis. Chronic destructive arthritis was induced by transient depletion of Treg cells prior to immunization with G6PI. At different time points after disease induction, mice were treated with a CD28 superagonistic antibody (CD28SA). CD28SA treatment during the induction phase of arthritis ameliorated the acute signs of arthritis and completely prevented the development of chronic destructive arthritis. CD28SA treatment of mice with fully developed arthritis induced a significant reduction in clinical and histological signs of arthritis. When given during the chronic destructive phase of arthritis, 56 days after disease induction, CD28SA treatment resulted in a modest reduction of clinical signs of arthritis and a reduction in histopathological signs of joint inflammation. Our data show that increasing the number and activation of Treg cells by a CD28SA is therapeutically effective in experimental arthritis.

Presence of HLA-B27 is associated with changes of serum levels of mediators of the Wnt and hedgehog pathway

BACKGROUND

HLA-B27 is present in 5% of the Caucasian population and is strongly associated with the development of spondyloarthritis (SpA), a disease characterized by inflammation and substantial bone changes. We hypothesized that the presence of HLA-B27 in itself is associated with alterations of key regulatory of bone homeostasis.

METHODS

Sera of 241 individuals were assessed for the serum levels of Wnt pathway regulators, sclerostin and dickkopf (Dkk)-1 as well as Indian hedgehog (IHH) and collagen type I cleavage products (CTX1). Of the 151 HLA-B27+ subjects, 31 had SpA, 30 had anterior uveitis, 30 were healthy individuals and 60 healthy siblings of patients with SpA.

RESULTS

Sclerostin levels were significantly (P<0.001) lower in HLA-B27+ subjects (314±21pg/mL) compared to HLA-B27 negative controls (mean±SEM: 492±30pg/mL), no matter if subjects were either healthy, or affected by SpA or uveitis. Similar results were found for Dkk-1. No differences between the groups with respect to the bone resorption marker CTX1 were found. In contrast, IHH levels were significantly (P<0.001) higher in the carriers of HLA-B27 than in the negative controls.

CONCLUSIONS

Changes in key regulators of the Wnt pathway as well as IHH, a molecule regulating endochondral ossification, are found in HLA-B27 carriers, independent if they were healthy or affected by uveitis or SpA.

Optimal management of dactylitis in patients with psoriatic arthritis

Psoriatic arthritis (PsA) is an inflammatory arthropathy associated with cutaneous psoriasis, which is currently classified as a seronegative spondyloarthropathy. The presence of cutaneous psoriasis is important for correct and early diagnosis of PsA, because the onset of cutaneous lesions usually precedes the appearance of joint manifestation. Thus, dermatologists are able to detect the condition at its inception. PsA has several unique characteristics such as enthesopathy, dactylitis, and abnormal bone remodeling. In particular, dactylitis occurs on the easily observed sites such as digits, and is thus a significant indicator of PsA. It is important to observe not only the fingers but also the toes, because dactylitis involves both digits of the hands and feet. Recently, new ideas regarding the involvement of the interleukin (IL)-23/Th17 axis have emerged, and the dramatic effects of targeting therapies have highlighted the physiological roles of key cytokines such as tumor necrosis factor-α, IL-17A, and IL-23 in psoriasis. As recent insights are shedding light on the pathogenesis of PsA, understanding of the pathogenesis of dactylitis and enthesitis are also progressing. In this article, current views on the optimal management of dactylitis are discussed.

Axial spondyloarthritis

The term axial spondyloarthritis covers both non-radiographic disease and radiographic disease (also known as ankylosing spondylitis). Some studies have been performed to investigate the prevalence of axial spondyloarthritis, although most are limited to patients with radiographic disease. A strong genetic association has been shown between axial spondyloarthritis and human leukocyte antigen-B27 (HLA-B27), but the pathogenetic role of HLA-B27 has not yet been clarified. Tumour necrosis factor (TNF), IL-17, IL-23 and downstream pathways also seem to be important - based on the good results of therapies directed against these molecules - but their exact role in the inflammatory process is also not yet clear. Elucidating the interaction between osteoproliferation and inflammation will be crucial for the prevention of long-term structural damage of the bone. The development of new criteria for classification, diagnosis and screening of patients with axial spondyloarthritis will enable earlier intervention for this chronic inflammatory disease. MRI has become an important tool for the early detection of axial spondyloarthritis. NSAIDs and TNF blockers are effective therapies, including in the early non-radiographic stage. Therapeutic blockade of IL-17 or IL-23 seems to be a promising new treatment option. Tools for measuring quality of life in axial spondyloarthritis have become relevant to assess the impact that the disease has on patients. These diagnostic and therapeutic advances will continue to change the management of axial spondyloarthritis, and new insights into the disease pathogenesis will hopefully accelerate this process. For an illustrated summary of this Primer, visit: http://go.nature.com/51b1af.