Serum levels of novel noggin and sclerostin-immune complexes are elevated in ankylosing spondylitis

Psoriasis, bone and bowel: a comprehensive review and new insights

Psoriasis is a chronic immune-mediated disorder affecting about 2% of the population worldwide which is associated with significant morbidity. The disease usually presents as raised, well-demarcated erythematous plaques with adherent silvery scales. Psoriasis can appear at any age but it has two peaks occurring at 15–20 and 55–60 years of age. It affects males and females equally. Despite the multitude of investigations about psoriasis and even development of drugs with satisfactory results, its pathogenesis is not fully understood yet and its course is unpredictable. Various environmental triggers, e.g., obesity, stress and drugs may induce disease in genetically susceptible patients. Although psoriasis was considered primarily as a disease of the skin, more investigations have been revealed its systemic nature. Psoriatic arthritis (PsA) may complicate up to one-third of cases of psoriasis vulgaris (PV). Also, the association between psoriasis and a variety of other immune-mediated disorders such as inflammatory bowel disease (IBD) and celiac disease (CD) has been confirmed in various studies. Moreover, a growing body of evidences indicates that psoriasis shares some common histological and phenotypical properties with the spectrum of osteoimmunological diseases such as Paget’s disease of bone (PDB). Thus, exploring the common molecular and genetic mechanisms underlying psoriasis and related disorders is of paramount importance for better elucidating disease pathogenesis and designing more targeted treatments.

Potential Roles for B cells and Autoantibodies in Ankylosing Spondylitis

Ankylosing spondylitis (AS) is a chronic inflammatory rheumatic disease that predominantly affects young males. AS is a condition in which the spine and sacroiliac joints become inflamed. More specifically, most AS patients experience spine malformations over time, resulting in functional incapability. The etiopathogenesis of AS is a complex combination of genetic predisposition and environmental factors. Extensive studies on AS have revealed the central role of genetics and immune reactions in its etiology. However, an utmost agreement has yet to be created. The available evidence suggests that both autoinflammation and T-cell-mediated autoimmune processes have significant roles in the disease process of AS. So far, B cells have obtained moderately little attention in AS pathogenesis, primarily because of the absence of disease-defining autoantibodies. However, against general dogma, evidence is mounting showing B cell involvement. Disruptions depict this in circulating B cell populations, the increased expression of immunoglobulin (Ig)G, IgA, and IgM, and B cell infiltration within the axial skeleton of AS patients. Meanwhile, compared to many other inflammatory autoimmune disorders, AS has no disease-specific autoantibodies that help disease diagnosis. This study has provided an overview of the B lymphocytes and antibodies' role in AS pathogenesis. It also introduces autoantibodies that can be the prognosis and diagnosis biomarkers of AS.

Osteoimmunology of Spondyloarthritis

The mechanisms underlying the development of bone damage in the context of spondyloarthritis (SpA) are not completely understood. To date, a considerable amount of evidence indicates that several developmental pathways are crucially involved in osteoimmunology. The present review explores the biological mechanisms underlying the relationship between inflammatory dysregulation, structural progression, and osteoporosis in this diverse family of conditions. We summarize the current knowledge of bone biology and balance and the foundations of bone regulation, including bone morphogenetic protein, the Wnt pathway, and Hedgehog signaling, as well as the role of cytokines in the development of bone damage in SpA. Other areas surveyed include the pathobiology of bone damage and systemic bone loss (osteoporosis) in SpA and the effects of pharmacological treatment on focal bone damage. Lastly, we present data relative to a survey of bone metabolic assessment in SpA from Italian bone specialist rheumatology centers. The results confirm that most of the attention to bone health is given to postmenopausal subjects and that the aspect of metabolic bone health may still be underrepresented. In our opinion, it may be the time for a call to action to increase the interest in and focus on the diagnosis and management of SpA.

Uncovering the Underworld of Axial Spondyloarthritis

Axial spondyloarthritis (axial-SpA) is a multifactorial disease characterized by inflammation in sacroiliac joints and spine, bone reabsorption, and aberrant bone deposition, which may lead to ankylosis. Disease pathogenesis depends on genetic, immunological, mechanical, and bioenvironmental factors. HLA-B27 represents the most important genetic factor, although the disease may also develop in its absence. This MHC class I molecule has been deeply studied from a molecular point of view. Different theories, including the arthritogenic peptide, the unfolded protein response, and HLA-B27 homodimers formation, have been proposed to explain its role. From an immunological point of view, a complex interplay between the innate and adaptive immune system is involved in disease onset. Unlike other systemic autoimmune diseases, the innate immune system in axial-SpA has a crucial role marked by abnormal activity of innate immune cells, including γδ T cells, type 3 innate lymphoid cells, neutrophils, and mucosal-associated invariant T cells, at tissue-specific sites prone to the disease. On the other hand, a T cell adaptive response would seem involved in axial-SpA pathogenesis as emphasized by several studies focusing on TCR low clonal heterogeneity and clonal expansions as well as an interindividual sharing of CD4/8 T cell receptors. As a result of this immune dysregulation, several proinflammatory molecules are produced following the activation of tangled intracellular pathways involved in pathomechanisms of axial-SpA. This review aims to expand the current understanding of axial-SpA pathogenesis, pointing out novel molecular mechanisms leading to disease development and to further investigate potential therapeutic targets.

Anti-tumor necrosis factor alpha treatment does not influence serum levels of the markers associated with radiographic progression in ankylosing spondylitis

OBJECTIVES

The study aimed to determine the levels of change of the markers related to radiographic progression, such as Dickkopf-1 (DKK-1), sclerostin (SOST), bone morphogenetic protein (BMP)-2 and -4, and interleukin (IL)-17 and -23, in ankylosing spondyloarthritis (AS) during anti-tumor necrosis factor alpha (TNF-α) treatment.

PATIENTS AND METHODS

Fifty-three anti-TNF-α naïve AS patients (34 males, 19 females; median: 38 years; range, 20 to 52 years) refractory to conventional treatments meeting the modified New York criteria or Assessment of SpondyloArthritis International Society classification criteria were enrolled to this cross-sectional, controlled study between October 2015 and January 2017. Fifty healthy volunteers (35 males, 15 females; median: 36 years; range, 18 to 55 years) with similar age and sex characteristics were recruited. Serum DKK-1, BMP-2, BMP-4, SOST, IL-17, and IL-23 levels were measured in both groups. The serum levels of the markers were measured again after about two years (mean follow-up duration of 21.7±6.4 months) in AS patients who started anti-TNF-α treatment. Demographic, clinical characteristics, and laboratory parameters were recorded. The disease activity at the time of inclusion was assessed through the Bath Ankylosing Spondylitis Disease Activity Index.

RESULTS

Serum DKK-1, SOST, IL-17, and IL-23 levels in the AS group before anti-TNF-a treatment were significantly higher compared to the control group (p<0.01 for DKK-1, p<0.001 for others). There was no difference regarding serum BMP-4 levels, whereas BMP-2 levels were significantly higher in the control group (p<0.01). Forty (75.47%) AS patients had serum marker levels measured after anti-TNF-α treatment. No significant change was observed in the serum levels of these 40 patients measured 21.7±6.4 months after the initiation of anti-TNF-α treatment (p>0.05 for all).

CONCLUSION

In AS patients, there was no change in DKK-1/SOST, BMP, and IL-17/23 cascade with anti-TNF-α treatment. This finding may suggest that these pathways act independently of each other, and their local effects are not influenced by systemic inflammation.

How Has Molecular Biology Enhanced Our Undertaking of axSpA and Its Management

PURPOSE

This review aims at investigating pathophysiological mechanisms in spondyloarthritis (SpA). Analysis of genetic factors, immunological pathways, and abnormalities of bone metabolism lay the foundations for a better understanding of development of the axial clinical manifestations in patients, allowing physician to choose the most appropriate therapeutic strategy in a more targeted manner.

RECENT FINDINGS

In addition to the contribution of MHC system, findings emerged about the role of non-HLA genes (as ERAP1 and 2, whose inhibition could represent a new therapeutic approach) and of epigenetic mechanisms that regulate the expression of genes involved in SpA pathogenesis. Increasing evidence of bone metabolism abnormalities secondary to the activation of immunological pathways suggests the development of various bone anomalies that are present in axSpA patients. SpA are a group of inflammatory diseases with a multifactorial origin, whose pathogenesis is linked to the genetic predisposition, the action of environmental risk factors, and the activation of immune response. It is now well known how bone metabolism leads to long-term structural damage via increased bone turnover, bone loss and osteoporosis, osteitis, erosions, osteosclerosis, and osteoproliferation. These effects can exist in the same patient over time or even simultaneously. Evidence suggests a cross relationship among innate immunity, autoimmunity, and bone remodeling in SpA, making treatment approach a challenge for rheumatologists. Specifically, treatment targets are consistently increasing as new drugs are upcoming. Both biological and targeted synthetic drugs are promising in terms of their efficacy and safety profile in patients affected by SpA.

Immune mechanism of low bone mineral density caused by ankylosing spondylitis based on bioinformatics and machine learning

Background and Objective: This study aims to find the key immune genes and mechanisms of low bone mineral density (LBMD) in ankylosing spondylitis (AS) patients.

Methods: AS and LBMD datasets were downloaded from the GEO database, and differential expression gene analysis was performed to obtain DEGs. Immune-related genes (IRGs) were obtained from ImmPort. Overlapping DEGs and IRGs got I-DEGs. Pearson coefficients were used to calculate DEGs and IRGs correlations in the AS and LBMD datasets. Louvain community discovery was used to cluster the co-expression network to get gene modules. The module most related to the immune module was defined as the key module. Metascape was used for enrichment analysis of key modules. Further, I-DEGs with the same trend in AS and LBMD were considered key I-DEGs. Multiple machine learning methods were used to construct diagnostic models based on key I-DEGs. IID database was used to find the context of I-DEGs, especially in the skeletal system. Gene–biological process and gene-pathway networks were constructed based on key I-DEGs. In addition, immune infiltration was analyzed on the AS dataset using the CIBERSORT algorithm.

Results: A total of 19 genes were identified I-DEGs, of which IFNAR1, PIK3CG, PTGER2, TNF, and CCL3 were considered the key I-DEGs. These key I-DEGs had a good relationship with the hub genes of key modules. Multiple machine learning showed that key I-DEGs, as a signature, had an excellent diagnostic performance in both AS and LBMD, and the SVM model had the highest AUC value. Key I-DEGs were closely linked through bridge genes, especially in the skeletal system. Pathway analysis showed that PIK3CG, IFNAR1, CCL3, and TNF participated in NETs formation through pathways such as the MAPK signaling pathway. Immune infiltration analysis showed neutrophils had the most significant differences between case and control groups and a good correlation with key I-DEG.

Conclusion: The key I-DEGs, TNF, CCL3, PIK3CG, PTGER2, and IFNAR1, can be utilized as biomarkers to determine the risk of LBMD in AS patients. They may affect neutrophil infiltration and NETs formation to influence the bone remodeling process in AS.

Serum BMP-2 and BMP-4 levels and their relationship with disease activity in patients with rheumatoid arthritis and ankylosing spondylitis

Objectives

This study aims to investigate the levels of bone morphogenic proteins (BMPs), one of the pathways affecting bone turnover in these diseases, and to investigate their relationship with disease activity.

Patients and methods

Between September 2013 and July 2015, a total of 100 ankylosing spondylitis (AS) patients (53 males, 48 females; median age: 40 years; range, 18 to 62 years), 58 rheumatoid arthritis (RA) patients (25 males, 33 females; median age: 40.5 years; range, 26 to 59 years), and 102 age- and sex-matched healthy controls (55 males, 47 females; median age: 38 years; range, 18 to 55 years) were included in the study. In all groups, serum BMP-2 and BMP-4 levels were measured using enzyme-linked immunosorbent assay (ELISA). Demographic data (age, sex, duration of disease) and acute phase reactants of the patients at the final visit were recorded. Disease activity was assessed through the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and Ankylosing Spondylitis Disease Activity Score C-Reactive Protein (ASDAS-CRP) for AS patients and through the Disease Activity Score-28-CRP (DAS-28-CRP) for RA patients.

Results

The median BMP-2 values were found to be significantly higher in the RA group compared to the other groups and in the control group compared to the AS group (p<0.001 for both). There was no significant difference between the groups in terms of median BMP-4 values (p>0.05). No significant relationship was found between serum BMP-2 and BMP-4 levels and disease activity in both AS and RA patients, while there was a weak positive correlation between erythrocyte sedimentation rate and CRP levels with BMP-2 level in RA patients (p=0.014, r=0.320 and p=0.029, r=0.287, respectively).

Conclusion

Our study results suggest that the BMP pathway may have different dual effects in AS and RA patients depending on the underlying pathogenesis, and that local effects are more prominent than serum levels.

The Role of Sclerostin in Bone Diseases

Sclerostin has been identified as an important regulator of bone homeostasis through inhibition of the canonical Wnt-signaling pathway, and it is involved in the pathogenesis of many different skeletal diseases. Many studies have been published in the last few years regarding sclerostin’s origin, regulation, and mechanism of action. The ongoing research emphasizes the potential therapeutic implications of sclerostin in many pathological conditions with or without skeletal involvement. Antisclerostin antibodies have recently been approved for the treatment of osteoporosis, and several animal studies and clinical trials are currently under way to evaluate the effectiveness of antisclerostin antibodies in the treatment of other than osteoporosis skeletal disorders and cancer with promising results. Understanding the exact role of sclerostin may lead to new therapeutic approaches for the treatment of skeletal disorders.

Identification of Regulatory Factors and Prognostic Markers in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the progressive degeneration of motor neurons, leading to muscle atrophy, paralysis and even death. Immune disorder, redox imbalance, autophagy disorder, and iron homeostasis disorder have been shown to play critical roles in the pathogenesis of ALS. However, the exact pathogenic genes and the underlying mechanism of ALS remain unclear. The purpose of this study was to screen for pathogenic regulatory genes and prognostic markers in ALS using bioinformatics methods. We used Gene Ontology (GO) analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, gene set enrichment analysis (GSEA), and expression regulation network analysis to investigate the function of differentially expressed genes in the nerve tissue, lymphoid tissue, and whole blood of patients with ALS. Our results showed that the up-regulated genes were mainly involved in immune regulation and inflammation, and the down-regulated genes were mainly involved in energy metabolism and redox processes. Eleven up-regulated transcription factors (CEBPB, CEBPD, STAT5A, STAT6, RUNX1, REL, SMAD3, GABPB2, FOXO1, PAX6, and FOXJ1) and one down-regulated transcription factor (NOG) in the nerve tissue of patients with ALS likely play important regulatory roles in the pathogenesis of ALS. Based on construction and evaluation of the ALS biomarker screening model, cluster analysis of the identified characteristic genes, univariate Cox proportional hazards regression analysis, and the random survival forest algorithm, we found that MAEA, TPST1, IFNGR2, and ALAS2 may be prognostic markers regarding the survival of ALS patients. High expression of MAEA, TPST1, and IFNGR2 and low expression of ALAS2 in ALS patients may be closely related to short survival of ALS patients. Taken together, our results indicate that immune disorders, inflammation, energy metabolism, and redox imbalance may be the important pathogenic factors of ALS. CEBPB, CEBPD, STAT5A, STAT6, RUNX1, REL, SMAD3, GABPB2, FOXO1, PAX6, FOXJ1, and NOG may be important regulatory factors linked to the pathogenesis of ALS. MAEA, TPST1, IFNGR2, and ALAS2 are potential important ALS prognostic markers. Our findings provide evidence on the pathogenesis of ALS, potential targets for the development of new drugs for ALS, and important markers for predicting ALS prognosis.

The comparison of effects of balneotherapy, water-based and land-based exercises on disease activity, symptoms, sleep quality, quality of life and serum sclerostin level in patients with ankylosing spondylitis: A prospective, randomized study

Objectives

This study aims to compare the effects of balneotherapy, water-based exercise (WBE), and land-based exercise (LBE) on disease activity, symptoms, sleep quality, quality of life, and serum sclerostin level (SSL) in patients with ankylosing spondylitis (AS).

Patients and methods

Between January 2019 and January 2020, a total of 60 patients (35 males, 25 females; mean age: 40.9±11.2 years; range, 18 to 55 years) who were diagnosed with AS were randomly divided into the balneotherapy (n=20), WBE (n=20), and LBE (n=20) groups (20 sessions of treatment in groups of five to six patients). The patients were evaluated before treatment and at 4 and 12 weeks using the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Bath Ankylosing Spondylitis Functional Index (BASFI), Bath Ankylosing Spondylitis Metrology Index (BASMI), Ankylosing Spondylitis Disease Activity Score-C-reactive protein (ASDAS-CRP), Maastricht Ankylosing Spondylitis Enthesitis Score (MASES), Ankylosing Spondylitis Quality of Life (ASQoL) Scale, Fatigue Severity Scale (FSS), and Pittsburg Sleep Quality Index (PSQI), and SSL were measured.

Results

Statistically significant improvements in the BASDAI, BASFI, MASES, BASMI, ASQoL, FSS, and ASDAS-CRP scores were observed in all groups at 4 and 12 weeks of follow-up (p<0.05). A significant improvement in sleep latency was seen in the balneotherapy and WBE groups. Changes in SSL were not statistically significant in any group (p>0.05).

Conclusion

Balneotherapy, WBE, and LBE are effective in the treatment of AS, and the beneficial effects may last for at least 12 weeks.

B Cell Involvement in the Pathogenesis of Ankylosing Spondylitis

Extensive research into ankylosing spondylitis (AS) has suggested the major role of genetics, immune reactions, and the joint-gut axis in its etiology, although an ultimate consensus does not yet exist. The available evidence indicates that both autoinflammation and T-cell-mediated autoimmune processes are actively involved in the disease process of AS. So far, B cells have received relatively little attention in AS pathogenesis; this is largely due to a lack of conventional disease-defining autoantibodies. However, against prevailing dogma, there is a growing body of evidence suggestive of B cell involvement. This is illustrated by disturbances in circulating B cell populations and the formation of auto-reactive and non-autoreactive antibodies, along with B cell infiltrates within the axial skeleton of AS patients. Furthermore, the depletion of B cells, using rituximab, displayed beneficial results in a subgroup of patients with AS. This review provides an overview of our current knowledge of B cells in AS, and discusses their potential role in its pathogenesis. An overarching picture portrays increased B cell activation in AS, although it is unclear whether B cells directly affect pathogenesis, or are merely bystanders in the disease process.

Ankylosing spondylitis: an autoimmune or autoinflammatory disease?

Ankylosing spondylitis (AS) is a chronic inflammatory disorder of unknown aetiology. Unlike other systemic autoimmune diseases, in AS, the innate immune system has a dominant role characterized by aberrant activity of innate and innate-like immune cells, including γδ T cells, group 3 innate lymphoid cells, neutrophils, mucosal-associated invariant T cells and mast cells, at sites predisposed to the disease. The intestine is involved in disease manifestations, as it is at the forefront of the interaction between the mucosal-associated immune cells and the intestinal microbiota. Similarly, biomechanical factors, such as entheseal micro-trauma, might also be involved in the pathogenesis of the articular manifestation of AS, and sentinel immune cells located in the entheses could provide links between local damage, genetic predisposition and the development of chronic inflammation. Although these elements might support the autoinflammatory nature of AS, studies demonstrating the presence of autoantibodies (such as anti-CD74, anti-sclerostin and anti-noggin antibodies) and evidence of activation and clonal expansion of T cell populations support an autoimmune component to the disease. This Review presents the evidence for autoinflammation and the evidence for autoimmunity in AS and, by discussing the pathophysiological factors associated with each, aims to reconcile the two hypotheses.

Gut microbiota-microRNA interactions in ankylosing spondylitis

Ankylosing spondylitis (AS) is a chronic autoimmune inflammatory disability that is part of the rheumatic disease group of spondyloarthropathies. AS commonly influences the joints of the axial skeleton. The contributions to AS pathogenesis of genetic susceptibility (particularly HLA-B27 and ERAP-1) and epigenetic modifications, like non-coding RNAs, as well as environmental factors, have been investigated over the last few years. But the fundamental etiology of AS remains elusive to date. The evidence summarized here indicates that in the immunopathogenesis of AS, microRNAs and the gut microbiome perform critical functions. We discuss significant advances in the immunological mechanisms underlying AS and address potential cross-talk between the gut microbiome and host microRNAs. This critical interaction implicates a co-evolutionary symbiotic link between host immunity and the gut microbiome.

Axial Spondyloarthritis: Current Advances, Future Challenges

Axial spondyloarthritis (axSpA) is a chronic inflammatory joint disease with a predilection for the spine. It affects young adults and has the potential to have a major impact on quality of life, not only because of the chronic pain and fatigue, but also because of the potential for marked disability related to spinal ankylosis. Early detection of axSpA remains a major challenge, for which there is a heightened sense of urgency since it has been shown that earlier intervention with biologics can alter the progression of radiographic change in the spine. Advances in the genetics of axSpA have highlighted a number of candidate genes conferring susceptibility to the disease, but there is evidence of environmental factors playing a role as well. Recently studies in both clinical and experimental axSpA have implicated alterations in the gut microbiome as playing a key role, and the immunology of the gut-joint axis is becoming better understood. The unmet needs which are shaping the research agenda include improvement in early case identification, sensitive and specific biomarkers which could accurately reflect disease activity and severity, improved understanding of the common pathways of inflammation in the skin, eye and gut in axSpA, and novel therapeutic targets which could have curative potential.

Anti-IL-17A treatment reduces serum inflammatory, angiogenic and tissue remodeling biomarkers accompanied by less synovial high endothelial venules in peripheral spondyloarthritis

Spondyloarthritis (SpA) is characterized by inflammation and new bone formation. The exact pathophysiology underlying these processes remains elusive. We propose that the extensive neoangiogenesis in SpA could play a role both in sustaining/enhancing inflammation and in new bone formation. While ample data is available on effects of anti-TNF on angiogenesis, effects of IL-17A blockade on serum markers are largely unknown. We aimed to assess the impact of secukinumab (anti-IL-17A) on synovial neoangiogenesis in peripheral SpA, and how this related to changes in inflammatory and tissue remodeling biomarkers. Serum samples from 20 active peripheral SpA patients included in a 12 week open-label trial with secukinumab were analyzed for several markers of angiogenesis and tissue remodeling. Synovial biopsies taken before and after treatment were stained for vascular markers. Serum levels of MMP-3, osteopontin, IL-6 (all P < 0.001), IL-31, S100A8, S100A9, Vascular Endothelial Growth Factor A (VEGF-A), IL-33, TNF-α (all P < 0.05) decreased significantly upon anti-IL17A treatment. Secukinumab treatment resulted in a decrease in the number of synovial high endothelial venules and lymphoid aggregate score. These results indicate that anti-IL-17A not only diminishes inflammation, but also impacts angiogenesis and tissue remodeling/new bone formation. This may have important implications for disease progression and/or structural damage.

Revisiting the gut-joint axis: links between gut inflammation and spondyloarthritis

Gut inflammation is strongly associated with spondyloarthritis (SpA), as exemplified by the high prevalence of inflammatory bowel disease (IBD) and the even higher occurrence of subclinical gut inflammation in patients with SpA. The gut-joint axis of inflammation in SpA is further reinforced by similarities in immunopathogenesis at both anatomical sites and by the clinical success of therapies blocking TNF and IL-23 in IBD and in some forms of SpA. Many genetic risk factors are shared between SpA and IBD, and changes in the composition of gut microbiota are seen in both diseases. Current dogma is that inflammation in SpA initiates in the gut and leads to joint inflammation; however, although conceptually attractive, some research does not support this causal relationship. For example, therapies targeting IL-17A are efficacious in the joint but not the gut, and interfering with gut trafficking by targeting molecules such as α4β7 in IBD can lead to onset or flares of SpA. Several important knowledge gaps remain that must be addressed in future studies. Determining the true nature of the gut-joint axis has real-world implications for the treatment of patients with co-incident IBD and SpA and for the repurposing of therapeutics from one disease to the other.

An update on serum biomarkers to assess axial spondyloarthritis and to guide treatment decision

Axial spondyloarthritis (axSpA) is a group of debilitating, chronic, rheumatic conditions characterized by inflammation and new bone formation, mainly involving the spine and the sacroiliac joints. The lack of biomarkers in axSpA is well known. Despite significant treatment advances in recent years thanks to the introduction of drugs with a new mode of action, such as new biologic and targeted synthetic disease-modifying antirheumatic drugs, no relevant improvement in the identification of disease biomarkers has been achieved. Common parameters, such as erythrocyte sedimentation rate and C-reactive protein, which are routinely used to measure systemic inflammation, are the sole markers available to date and are not adequate to assess disease activity in all patients. The aim of this study is to review the most promising serum biomarkers that may help treatment decision in axSpA via a proper assessment of disease activity and identification of negative prognostic factors.

Lipocalin 2 links inflammation and ankylosis in the clinical overlap of inflammatory bowel disease (IBD) and ankylosing spondylitis (AS)

Background

Little is known about the mechanisms underlying the clinical overlap between gut inflammation and joint ankylosis, as exemplified by the concurrence of inflammatory bowel diseases (IBD) and ankylosing spondylitis (AS). As dysbiosis may serve as a common contributor, the anti-microbial pleiotropic factor lipocalin 2 could be a potential mediator due to its roles in inflammation and bone homeostasis.

Methods

Baseline colonic pathology was conducted in the ank/ank mouse model. Serum lipocalin 2 was analyzed by ELISA, in ank/ank mutants versus C3FeB6-A/A^w-jwt/wt, in patients with concurrent AS-IBD, AS alone, IBD alone, or mechanical back pain, and in healthy controls. In the ank/ank mouse model, the expression of nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) was examined by real-time PCR. Intraperitoneal injection was done with the PPARγ agonist rosiglitazone or antagonist bisphenol A diglycidyl ether for four consecutive days. Serum levels of lipocalin 2 were examined on the sixth day.

Results

This study showed that the ank/ank mice with fully fused spines had concurrent colonic inflammation. By first using the ank/ank mouse model with progressive ankylosis and subclinical colonic inflammation, confirmed in patients with concurrent AS and IBD, elevated circulating lipocalin 2 levels were associated with the coexisting ankylosis and gut inflammation. The intracellular pathway of lipocalin 2 was further investigated with the ank/ank mouse model involving PPARγ. Colonic expression of PPARγ was negatively associated with the degree of gut inflammation. The PPARγ agonist rosiglitazone treatment significantly upregulated the serum levels of lipocalin 2, suggesting a potential regulatory role of PPARγ in the aberrant expression of lipocalin 2.

Conclusions

In summary, lipocalin 2 modulated by PPARγ could be a potential pathway involved in concurrent inflammation and ankylosis in AS and IBD.

Biomarkers in Inflammatory Bowel Disease-Associated Spondyloarthritis: State of the Art and Unmet Needs

Inflammatory bowel disease-associated spondyloarthritis is a systemic disease characterized by the chronic inflammation of both the gastrointestinal tract and the musculoskeletal system. Since inflammatory bowel disease-associated spondyloarthritis has been associated with a significant diagnostic delay, which may lead to poor quality of life and progression of joint damage, efforts to discover new reliable and noninvasive diagnostic biomarkers have been made. We reviewed the state of the art of biomarker research in inflammatory bowel disease-associated spondyloarthritis, showing that to date it has been largely unsatisfactory. Only a few of the biomarkers that have been investigated are likely to enter the clinical practice upon further validation in independent cohorts. The research of new and innovative biomarkers for inflammatory bowel disease-associated spondyloarthritis is warranted.

Autoantibodies in Spondyloarthritis, Focusing on Anti-CD74 Antibodies

Spondyloarthritis (SpA) is an inflammatory rheumatic disease with diverse clinical presentation. The diagnosis of SpA remains a big challenge in daily clinical practice because of the limitation in specific biomarkers of SpA, more biomarkers are still needed for SpA diagnosis and disease activity monitoring. In the past, SpA was considered predominantly as auto-inflammatory disease vs. autoimmune disease. However, in recent years several researches demonstrated a broad autoantibody response in SpA patients. Study also indicated that mice lack of ZAP70 in T cell develop SpA featured inflammation. These studies indicated the autoimmune features of SpA and gave rise to the potential use of autoantibody in SpA management. In this article, we reviewed recent reports of autoantibodies associated with SpA patients, revealing the autoimmune features of SpA, suggesting the hypothesis that SpA was also an autoimmune disease, studies about the autoimmune features might provide more insights in the pathogenesis of SpA. In addition, as there are two opposite conclusions in the role of anti-CD74 autoantibody in the diagnosis of SpA, we also gave our own data on the diagnostic value of anti-CD74 in Chinese SpA patients. Though our data indicated that anti-CD74 might not be a good biomarker for SpA diagnosis in Asian people, CD74 was still a good molecule target in the research of SpA pathogenesis.

Anti-SIRT1 autoantibody is elevated in ankylosing spondylitis: a potential disease biomarker

Background

Little is known about the presence of specific autoantibodies in ankylosing spondylitis (AS), an immune-mediated inflammatory disease. The object of this study was to explore potential autoantibody profiles in AS patients.

Results

Levels of anti-SIRT1 autoantibodies were significantly higher in AS (P < 0.001) and psoriatic arthritis (PsA) (P < 0.01) patients but not rheumatoid arthritis (RA) patients compared with healthy controls. Additionally, titers of anti-NAD-dependent protein deacetylase sirtuin-1(SIRT1) antibodies were significantly higher in AS patients than in RA (P < 0.05) and PsA (P < 0.05) patients. Moreover, levels of anti-SIRT1 (P < 0.001) antibodies were significantly higher during the first year in patients with hip joint involvement. The anti-SIRT1 antibody positivity rate was 18.9% in AS patients.

Conclusions

Our findings indicate that anti-SIRT1 autoantibodies may serve as a marker for diagnosing AS and predicting hip joint involvement at an early stage.

Electronic supplementary material

The online version of this article (10.1186/s12865-018-0280-x) contains supplementary material, which is available to authorized users.

Increased serum levels of MIC1/GDF15 correlated with bone erosion in spondyloarthritis: A pilot study

INTRODUCTION

To assess the association between growth differentiation factor-15 (GDF15) and radiographic features including bone marrow edema and bone erosion in Spondyloarthritis (SpA).

METHODS

Patients with SpA (n = 120) receiving treatment in the Guangdong General Hospital, China, between August 2012 and December 2016 were retrospectively included. Serum of patients and healthy controls (n = 30) were collected and GDF15 levels were measured using ELISA. Inflammation was assessed by C-reactive protein (CRP), and magnetic resonance imaging (MRI) of the sacroiliac joint using Spondyloarthritis Research Consortium of Canada score and a method of dichotomy to assess fat metaplasia, bone erosion, and ankylosis. Radiographs of the pelvis were scored using the modified New York (mNY) score.

RESULTS

Serum GDF15 levels were higher in SpA patients compared to controls (503.52 ± 222.92 vs. 190.86 ± 104.18 pg/mL, P < .0001). Patients who suffered from bone erosion on MRI had higher levels of GDF15 (525.72 [186.33, 801.62]vs. 428.06 [255.15, 670.98] pg/mL, P = .0375). There was a positive correlation between serum GDF15 and CRP (r = 0.5442, P < .0001). Moreover, GDF15 levels were related to CRP levels (r = 0.5658, P < .0001) in those X-ray scores were III, according to 1984mNY criteria. Receiver operating characteristic (ROC) analysis showed that GDF15 levels above 501.98pg/mL could predict presence of bone erosion on MRI.

CONCLUSION

The present study suggested that serum GDF15 levels are higher in SpA patients than in healthy controls. The GDF15 level was correlated with CRP and may be a surrogate biomarker in bone erosion.

Sclerostin rather than Dickkopf-1 is associated with mSASSS but not with disease activity score in patients with ankylosing spondylitis

OBJECTIVE

To determine the serum levels of Dickkopf-1 (DKK-1) and sclerostin, as well as their correlations with the structural damage assessed by modified stoke ankylosing spondylitis spine score (mSASSS) and the disease activity evaluated by ankylosing spondylitis disease activity score (ASDAS) in patients with ankylosing spondylitis (AS).

METHODS

Eighty-eight AS patients, 26 rheumatoid arthritis (RA) patients, and 26 age- and gender-matched healthy controls (HC) were collected from rheumatic clinic of the Second Affiliated Hospital of Zhejiang University, School of Medicine, between March 2015 and July 2015. Demographic data, parameters of ASDAS, and image evaluations of spine (i.e., mSASSS) were collected. The serum levels of DKK-1 and sclerostin were measured using commercially available ELISA kits.

RESULTS

Both DKK-1 and sclerostin were significantly higher in the AS patients than in the controls (1855 ± 84.58 vs. 1406 ± 99.76 pg/ml and 106 ± 6.75 vs. 62.78 ± 6.39 pmol/l, respectively, P < 0.05). The correlation analysis suggested a negative correlation between serum sclerostin and mSASSS (P = 0.019, r² = 0.062). DKK-1 had a trend of positive correlation with mSASSS, but was not statistically significant (P > 0.05). There was no association between the serum levels of DKK-1 or sclerostin and disease activity assessed by ASDAS (P > 0.05). DKK-1 and sclerostin had a negative correlation (P = 0.013, r² = 0.07).

CONCLUSION

In the present study, the expressions of serum DKK-1 and sclerostin were independent of disease activity. Sclerostin was negatively correlated with the mSASSS, which suggests that sclerostin may be a potential marker indicating the spine ossification process in AS. The specific mechanism remains to be investigated.

Stress proteins in the pathogenesis of spondyloarthritis

Spondyloarthritis is an autoinflammatory rheumatic disease in which arthritis and osteoproliferation lead the patients who suffer from it to chronic disability. This disease is associated with the expression of class I MHC molecule HLA-B27, which tends to be misfolded in the endoplasmic reticulum and, therefore, expressed in aberrant forms. This phenomena lead to endoplasmic reticulum stress, which in time, evokes a whole response to cellular injury. Under these conditions, the molecules involved in restoring cell homeostasis play a key role. Such is the case of the "heat-shock proteins", which usually regulate protein folding, but also have important immunomodulatory functions, as well as some roles in tissue modeling. In this review, we attempt to summarize the involvement of cell stress and heat-shock proteins in the homeostatic disturbances and pathological conditions associated with this disease.

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.

Sclerostin and Antisclerostin Antibody Serum Levels Predict the Presence of Axial Spondyloarthritis in Patients with Inflammatory Bowel Disease

OBJECTIVE

The early diagnosis of inflammatory bowel disease (IBD)-associated spondyloarthritis (SpA/IBD) in patients affected by IBD represents a major topic in clinical practice; in particular, to date there are no available serum biomarkers revealing the presence of joint inflammation in these patients. Sclerostin (SOST), an antagonist of the Wnt/β-catenin pathway, and antisclerostin-immunoglobulin G (anti-SOST-IgG) have been recently studied in patients with ankylosing spondylitis (AS) as a putative marker of disease activity.

METHODS

SOST and anti-SOST-IgG serum levels were assayed in 125 patients with IBD, 85 with axial or peripheral SpA, and in control groups (patients with AS and rheumatoid arthritis, and healthy individuals). The diagnostic performance in discriminating the presence of SpA/IBD was assessed for both candidate biomarkers.

RESULTS

Patients affected by SpA/IBD with axial involvement displayed significantly lower levels of SOST and higher levels of anti-SOST-IgG compared to patients with only peripheral arthritis, IBD, and controls. Moreover, SOST and anti-SOST-IgG serum levels were inversely correlated and were associated with the duration of articular symptoms. Both biomarkers showed good accuracy in predicting the presence of axial SpA in patients with IBD.

CONCLUSION

We demonstrated that in patients with IBD, SOST and anti-SOST-IgG might represent novel biomarkers to assess the presence of axial joint involvement. Moreover, the development of anti-SOST-IgG and the subsequent decrease of SOST serum levels could play a role in the pathogenesis of SpA/IBD.

Macrophage Migration Inhibitory Factor Induces Inflammation and Predicts Spinal Progression in Ankylosing Spondylitis

OBJECTIVE

To investigate the role of macrophage migration inhibitory factor (MIF) in the pathogenesis of ankylosing spondylitis (AS).

METHODS

Patients who met the modified New York criteria for AS were recruited for the study. Healthy volunteers, rheumatoid arthritis patients, and osteoarthritis patients were included as controls. Based on the annual rate of increase in modified Stoke AS Spine Score (mSASSS), AS patients were classified as progressors or nonprogressors. MIF levels in serum and synovial fluid were quantitated by enzyme-linked immunosorbent assay. Predictors of AS progression were evaluated using logistic regression analysis. Immunohistochemical analysis of ileal tissue was performed to identify MIF-producing cells. Flow cytometry was used to identify MIF-producing subsets, expression patterns of the MIF receptor (CD74), and MIF-induced tumor necrosis factor (TNF) production in the peripheral blood. MIF-induced mineralization of osteoblast cells (SaOS-2) was analyzed by alizarin red S staining, and Western blotting was used to quantify active β-catenin levels.

RESULTS

Baseline serum MIF levels were significantly elevated in AS patients compared to healthy controls and were found to independently predict AS progression. MIF levels were higher in the synovial fluid of AS patients, and MIF-producing macrophages and Paneth cells were enriched in their gut. MIF induced TNF production in monocytes, activated β-catenin in osteoblasts, and promoted the mineralization of osteoblasts.

CONCLUSION

Our findings indicate an unexplored pathogenic role of MIF in AS and a link between inflammation and new bone formation.

Axial spondyloarthritis

The term axial spondyloarthritis covers both patients with non-radiographic and radiographic axial spondyloarthritis, which is also termed ankylosing spondylitis. The disease usually starts in the third decade of life with a male to female ratio of two to one for radiographic axial spondyloarthritis and of one to one for non-radiographic axial spondyloarthritis. More than 90% heritabilty has been estimated, the highest genetic association being with HLA-B27. The pathogenic role of HLA-B27 is still not clear although various hypotheses are available. On the basis of evidence from trials the cytokines tumour necrosis factor (TNF)-α and interleukin-17 appear to have a relevant role in pathogenesis. The mechanisms of interaction between inflammation and new bone formation is still not completely understood but clarification will be important for the prevention of long-term structural damage of the bone. The development of new criteria for classification and for screening of patients with axial spondyloarthritis have been crucial for the early indentification and treatment of such patients, with MRI being the most important existing imaging method. Non-steroidal anti-inflammatory drugs and TNF blockers are effective therapies. Blockade of interleukin-17 is a new and relevant treatment option.

Sclerostin expression and functions beyond the osteocyte

Sclerostin, the product of the SOST gene, is a secreted inhibitor of Wnt signaling that is produced by osteocytes to regulate bone formation. While it is often considered an osteocyte-specific protein, SOST expression has been reported in numerous other cell types, including hypertrophic chondrocytes and cementocytes. Of interest, SOST/sclerostin expression is altered in certain pathogenic conditions, including osteoarthritis and rheumatic joint disease, and it is unclear whether sclerostin plays a protective role or whether sclerostin may mediate disease pathogenesis. Therefore, as anti-sclerostin antibodies are being developed for the treatment of osteoporosis, it is important to understand the functions of sclerostin beyond the regulation of bone formation.

Bone as a Target Organ in Rheumatic Disease: Impact on Osteoclasts and Osteoblasts

Dysregulated bone remodeling occurs when there is an imbalance between bone resorption and bone formation. In rheumatic diseases, including rheumatoid arthritis (RA) and seronegative spondyloarthritis, systemic and local factors disrupt the process of physiologic bone remodeling. Depending upon the local microenvironment, cell types, and local mechanical forces, inflammation results in very different effects on bone, promoting bone loss in the joints and in periarticular and systemic bone in RA and driving bone formation at enthesial and periosteal sites in diseases such as ankylosing spondylitis (AS), included within the classification of axial spondyloarthritis. There has been a great deal of interest in the role of osteoclasts in these processes and much has been learned over the past decade about osteoclast differentiation and function. It is now appreciated that osteoblast-mediated bone formation is also inhibited in the RA joint, limiting the repair of erosions. In contrast, osteoblasts function to produce new bone in AS. The Wnt and BMP signaling pathways have emerged as critical in the regulation of osteoblast function and the outcome for bone in rheumatic diseases, and these pathways have been implicated in both bone loss in RA and bone formation in AS. These pathways provide potential novel approaches for therapeutic intervention in diseases in which inflammation impacts bone.

Causes and consequences of endoplasmic reticulum stress in rheumatic disease

Rheumatic diseases represent a heterogeneous group of inflammatory conditions, many of which involve chronic activation of both innate and adaptive immune responses by multiple genetic and environmental factors. These immune responses involve the secretion of excessive amounts of cytokines and other signalling mediators by activated immune cells. The endoplasmic reticulum (ER) is the cellular organelle that directs the folding, processing and trafficking of membrane-bound and secreted proteins, including many key components of the immune response. Maintaining homeostasis in the ER is critical to cell function and survival. Consequently, elaborate mechanisms have evolved to sense and respond to ER stress through three main signalling pathways that together comprise the unfolded protein response (UPR). Activation of the UPR can rapidly resolve the accumulation of misfolded proteins, direct permanent changes in the size and function of cells during differentiation, and critically influence the immune response and inflammation. Recognition of the importance of ER stress and UPR signalling pathways in normal and dysregulated immune responses has greatly increased in the past few years. This Review discusses several settings in which ER stress contributes to the pathogenesis of rheumatic diseases and considers some of the therapeutic opportunities that these discoveries provide.

Idiopathic Acquired Osteosclerosis in a Middle-Aged Woman With Systemic Lupus Erythematosus

Widely distributed osteosclerosis is an unusual radiographic finding with multiple causes. A 42-year-old premenopausal Spanish woman gradually acquired dense bone diffusely affecting her axial skeleton and focally affecting her proximal long bones. Systemic lupus erythematosus (SLE) diagnosed in adolescence had been well controlled. She had not fractured or received antiresorptive therapy, and she was hepatitis C virus antibody negative. Family members had low bone mass. Lumbar spine bone mineral density (BMD) measured by dual-photon absorptiometry (DPA) at age 17 years, while receiving glucocorticoids, was 79% the average value of age-matched controls. From ages 30 to 37 years, dual-energy X-ray absorptiometry (DXA) BMD Z-scores steadily increased in her lumbar spine from +3.8 to +7.9, and in her femoral neck from -1.4 to -0.7. Serum calcium and phosphorus levels were consistently normal, 25-hydroxyvitamin D (25OHD) <20 ng/mL, and parathyroid hormone (PTH) sometimes slightly increased. Her reduced estimated glomerular filtration rate (eGFR) was 38 to 55 mL/min. Hypocalciuria likely reflected positive mineral balance. During increasing BMD, turnover markers (serum bone-specific alkaline phosphatase [ALP], procollagen type 1 N propeptide [P1NP], osteocalcin [OCN], and carboxy-terminal cross-linking telopeptide of type 1 collagen [CTx], and urinary amino-terminal cross-linking telopeptide of type 1 collagen [NTx and CTx]) were 1.6- to 2.8-fold above the reference limits. Those of bone formation seemed increased more than those of resorption. FGF-23 was slightly elevated, perhaps from kidney disease. Serum osteoprotegerin (OPG) and TGFβ1 levels were normal, but sclerostin (SOST) and receptor activator of nuclear factor kappa-B ligand (RANKL) were elevated. Serum multiplex biomarker profiling confirmed a high level of SOST and RANKL, whereas Dickkopf-1 (DKK-1) seemed low. Matrix metalloproteinases-3 (MMP-3) and -7 (MMP-7) were elevated. Iliac crest biopsy revealed tetracycline labels, no distinction between thick trabeculae and cortical bone, absence of peritrabecular fibrosis, few osteoclasts, and no mastocytosis. Then, for the past 3 years, BMD Z-scores steadily decreased. Skeletal fluorosis, mastocytosis, myelofibrosis, hepatitis C-associated osteosclerosis, multiple myeloma, and aberrant phosphate homeostasis did not explain her osteosclerosis. Mutation analysis of the LRP5, LRP4, SOST, and osteopetrosis genes was negative. Microarray showed no notable copy number variation. Perhaps her osteosclerosis reflected an interval of autoimmune-mediated resistance to SOST and/or RANKL. © 2016 American Society for Bone and Mineral Research.

Imbalance Between Bone Morphogenetic Protein 2 and Noggin Induces Abnormal Osteogenic Differentiation of Mesenchymal Stem Cells in Ankylosing Spondylitis

OBJECTIVE

To study the osteogenic differentiation capacity of bone marrow-derived mesenchymal stem cells (BM-MSCs) from patients with ankylosing spondylitis (AS) and to investigate the mechanisms of abnormal osteogenic differentiation of BM-MSCs in AS.

METHODS

BM-MSCs from healthy donors (HD-MSCs) and patients with AS (AS-MSCs) were cultured in osteogenic differentiation medium for 0-21 days, after which their osteogenic differentiation capacity was determined using alizarin red S and alkaline phosphatase assays. Gene expression levels of osteoblastic markers and related cytokines were detected by high-throughput quantitative reverse transcription-polymerase chain reaction. Enzyme-linked immunosorbent assay was performed to detect protein levels of bone morphogenetic protein 2 (BMP-2) and Noggin in the cell culture supernatant. The activation of Smad1/5/8 and MAPK signaling pathways was measured by Western blotting. The balance between BMP-2 and Noggin expression was regulated using lentiviruses encoding short hairpin RNA and exogenous Noggin, respectively, which enabled evaluation of how this balance affected osteogenic differentiation of AS-MSCs.

RESULTS

AS-MSCs outperformed HD-MSCs in osteogenic differentiation capacity. During osteogenic differentiation, AS-MSCs secreted more BMP-2 but less Noggin, accompanied by an overactivation of Smad1/5/8 and ERK-1/2. When the Noggin concentration was increased or BMP-2 expression was inhibited, the abnormal osteogenic differentiation of AS-MSCs was rectified. In addition, the balance between BMP-2 and Noggin secretion was restored.

CONCLUSION

The results of this study demonstrate that an imbalance between BMP-2 and Noggin secretion induces abnormal osteogenic differentiation of AS-MSCs. These findings reveal a mechanism of pathologic osteogenesis in AS and provide a new perspective on inhibiting pathologic osteogenesis by regulating the balance between BMP-2 and Noggin.

Detection of novel diagnostic antibodies in ankylosing spondylitis: An overview

Ankylosing spondylitis (AS) is a debilitating, chronic, rheumatic disease characterized by inflammation and new bone formation resulting in fusion of the spine and sacroiliac joints. Since early treatment is impeded by a delayed diagnosis, it is highly important to find new biomarkers that improve early diagnosis and may also contribute to a better assessment of disease activity, prognosis and therapy response in AS. Because of the absence of rheumatoid factor, AS was long assumed to have a seronegative character and antibodies are thus not considered a hallmark of the disease. However, emerging evidence suggests plasma cells and autoantibodies to be involved in the disease course. In this review, the role of B cells and antibodies in AS is discussed. Furthermore, an overview is provided of antibodies identified in AS up till now, and their diagnostic potential. Many of these antibody responses were based on small study populations and further validation is lacking. Moreover, most were identified by a hypothesis-driven approach and thus limited to antibodies against targets that are already known to be involved in AS pathogenesis. Hence, we propose an unbiased approach to identify novel diagnostic antibodies. The already successfully applied techniques cDNA phage display and serological antigen selection will be used to identify antibodies against both known and new antigen targets in AS plasma. These newly identified antibodies will enhance early diagnosis of AS and provide more insight into the underlying disease pathology, resulting in a more effective treatment strategy and eventually an improved disease outcome.

Autoinflammation and HLA-B27: Beyond Antigen Presentation

HLA-B27 associated disorders comprise a group of inflammatory conditions which have in common an association with the HLA class I molecule, HLA-B27. Given this association, these diseases are classically considered disorders of adaptive immunity. However, mounting data are challenging this assumption and confirming that innate immunity plays a more prominent role in pathogenesis than previously suspected. In this review, the concept of autoinflammation is discussed and evidence is presented from human and animal models to support a key role for innate immunity in HLA-B27 associated disorders.

Clinical Utility of Biomarkers in IBD

There is no gold standard for the diagnosis and monitoring of inflammatory bowel diseases (IBD). Biomarkers are useful tools for the management of patients suffering from IBD. However, they should be used only when their additional information is useful for clinical decision-making. In principal, four situations during the management of an individual IBD patient can be discriminated from a clinical standpoint in which biomarkers provide useful information. First, biomarkers may be helpful when the diagnosis of IBD is established and aid in the discrimination between ulcerative colitis (UC) and Crohn's disease (CD) is necessary. Second, biomarkers may be helpful in the prognostic evaluation of IBD severity or disease behavior and for early decisions on the best treatment. The third situation in which biomarkers are useful is the evaluation of disease activity during the disease course, for monitoring and for guidance of ongoing treatment. Finally, the fourth typical situation when biomarkers are of value is after surgery to predict or diagnose a relapse of the disease. From a clinical point of view, it may be more useful to discuss specific biomarkers and their individual value and impact in these four prototypic situations than to sum up advantages and disadvantages for each biomarker isolated from the clinical situation. Therefore, this overview is structured in chapters reflecting those four typical situations during the disease course of IBD patents to critically evaluate the potential and value of each of the biomarkers in the specific situation.

Bone morphogenetic proteins in inflammation, glucose homeostasis and adipose tissue energy metabolism

Bore morphogenetic proteins (BMPs) are members of the transforming growth factor (TGF)-β superfamily, a group of secreted proteins that regulate embryonic development. This review summarizes the effects of BMPs on physiological processes not exclusively linked to the musculoskeletal system. Specifically, we focus on the involvement of BMPs in inflammatory disorders, e.g. fibrosis, inflammatory bowel disease, anchylosing spondylitis, rheumatoid arthritis. Moreover, we discuss the role of BMPs in the context of vascular disorders, and explore the role of these signalling proteins in iron homeostasis (anaemia, hemochromatosis) and oxidative damage. The second and third parts of this review focus on BMPs in the development of metabolic pathologies such as type-2 diabetes mellitus and obesity. The pancreatic beta cells are the sole source of the hormone insulin and BMPs have recently been implicated in pancreas development as well as control of adult glucose homeostasis. Lastly, we review the recently recognized role of BMPs in brown adipose tissue formation and their consequences for energy expenditure and adiposity. In summary, BMPs play a pivotal role in metabolism beyond their role in skeletal homeostasis. However, increased understanding of these pleiotropic functions also highlights the necessity of tissue-specific strategies when harnessing BMP action as a therapeutic target.

Update on ankylosing spondylitis: current concepts in pathogenesis

Ankylosing spondylitis is an insidiously progressive and debilitating form of arthritis involving the axial skeleton. The long delay in diagnosis and insufficient response to currently available therapeutics both advocate for a greater understanding of disease pathogenesis. Genome-wide association studies of this highly genetic disease have implicated specific immune pathways, including the interleukin (IL)-17/IL-23 pathway, control of nuclear factor kappa B (NF-κB) activation, amino acid trimming for major histocompatibility complex (MHC) antigen presentation, and other genes controlling CD8 and CD4 T cell subsets. The relevance of these pathways has borne out in animal and human subject studies, in particular, the response to novel therapeutic agents. Genetics and the findings of autoantibodies in ankylosing spondylitis revisit the question of autoimmune vs. autoinflammatory etiology. As environmental partners to genetics, recent attention has focused on the roles of microbiota and biomechanical stress in initiating and perpetuating inflammation. Herein, we review these current developments in the investigation of ankylosing spondylitis pathogenesis.

The genetic basis of ankylosing spondylitis: new insights into disease pathogenesis

Ankylosing spondylitis (AS) is a complex disease involving multiple risk factors, both genetic and environmental. AS patients are predominantly young men, and the disease is characterized by inflammation and ankylosis, mainly at the cartilage–bone interface and enthesis. HLA-B27 has been known to be the major AS-susceptibility gene for more than 40 years. Despite advances made in the past few years, progress in the search for non-human leukocyte antigen susceptibility genes has been hampered by the heterogeneity of the disease. Compared to other complex diseases, such as inflammatory bowel disease (IBD), fewer susceptibility loci have been identified in AS. Furthermore, non-major histocompatibility-complex susceptibility loci discovered, such as ERAP1 and IL23R, are likely contributors to joint inflammation. Identification and confirmation of functional variants remains a significant challenge of investigations involving genome-wide association studies (GWAS). It remains unclear why none of the AS-susceptibility genes identified in GWAS appear to be directly involved in the ankylosing process. Numerous reviews have recently been published on the genetics of AS. Therefore, aside from a brief summary of what AS GWAS has successfully achieved thus far, this review will focus on directions that could address unanswered questions raised by GWAS.