The Paradox of Bone Formation and Bone Loss in Ankylosing Spondylitis: Evolving New Concepts of Bone Formation and Future Trends in Management

Itaconate is a metabolic regulator of bone formation in homeostasis and arthritis

OBJECTIVES

Bone remodelling is a highly dynamic process dependent on the precise coordination of osteoblasts and haematopoietic-cell derived osteoclasts. Changes in core metabolic pathways during osteoclastogenesis, however, are largely unexplored and it is unknown whether and how these processes are involved in bone homeostasis.

METHODS

We metabolically and transcriptionally profiled cells during osteoclast and osteoblast generation. Individual gene expression was characterised by quantitative PCR and western blot. Osteoblast function was assessed by Alizarin red staining. immunoresponsive gene 1 (Irg1)-deficient mice were used in various inflammatory or non-inflammatory models of bone loss. Tissue gene expression was analysed by RNA in situ hybridisation.

RESULTS

We show that during differentiation preosteoclasts rearrange their tricarboxylic acid cycle, a process crucially depending on both glucose and glutamine. This rearrangement is characterised by the induction of Irg1 and production of itaconate, which accumulates intracellularly and extracellularly. While the IRG1-itaconate axis is dispensable for osteoclast generation in vitro and in vivo, we demonstrate that itaconate stimulates osteoblasts by accelerating osteogenic differentiation in both human and murine cells. This enhanced osteogenic differentiation is accompanied by reduced proliferation and altered metabolism. Additionally, supplementation of itaconate increases bone formation by boosting osteoblast activity in mice. Conversely, Irg1-deficient mice exhibit decreased bone mass and have reduced osteoproliferative lesions in experimental arthritis.

CONCLUSION

In summary, we identify itaconate, generated as a result of the metabolic rewiring during osteoclast differentiation, as a previously unrecognised regulator of osteoblasts.

Intermittent administration of PTH for the treatment of inflammatory bone loss does not enhance entheseal pathological new bone formation

OBJECTIVE

To investigate the effect of intermittent parathyroid hormone (iPTH) administration on pathological new bone formation during treatment of ankylosing spondylitis-related osteoporosis.

METHODS

Animal models with pathological bone formation caused by hypothetical AS pathogenesis received treatment with iPTH. We determined the effects of iPTH on bone loss and the formation of pathological new bone with micro-computed tomography (micro-CT) and histological examination. In addition, the tamoxifen-inducible conditional knockout mice (CAGGCre-ERTM; PTHflox/flox, PTH-/-) was established to delete PTH and investigate the effect of endogenous PTH on pathological new bone formation.

RESULTS

iPTH treatment significantly improved trabecular bone mass in the modified collagen-induced arthritis (m-CIA) model and unbalanced mechanical loading models. Meanwhile, iPTH treatment did not enhance pathological new bone formation in all types of animal models. Endogenous PTH deficiency had no effects on pathological new bone formation in unbalanced mechanical loading models.

CONCLUSION

Experimental animal models of AS treated with iPTH show improvement in trabecular bone density, but not entheseal pathological bone formation，indicating it may be a potential treatment for inflammatory bone loss does in AS.

SPI1 Regulates the Progression of Ankylosing Spondylitis by Modulating TLR5 via NF-κB Signaling

Ankylosing spondylitis (AS) is an autoimmune disease which associated with inflammation of the spinal joints. Enhanced osteogenic differentiation was observed in AS; however, the underlying mechanism remains undefined. A cohort of AS (n = 15) and patients with traumatic fracture (n = 15) were recruited to this study. Fibroblasts were isolated, and characterized by H&E and immunocytochemistry (ICC) analysis. The expression and secretion of key molecules were detected by qRT-PCR, western blot, immunofluorescence (IF), and ELISA. Calcium deposition and alkaline phosphatase (ALP) activity were monitored by Alizarin Red S and ALP staining. The direct association between Spi-1 proto-oncogene (SPI1) and toll-like receptor 5 (TLR5) promoter was assessed by ChIP assay. AS fibroblasts was successfully isolated and exhibited osteogenic differentiation potentials. SPI1 was elevated in AS fibroblasts, and silencing of SPI1 inhibited osteogenic differentiation of AS fibroblasts. Mechanistic study showed that SPI1 acted as a transcriptional activator of TLR5. Knockdown of TLR5 suppressed osteogenic differentiation of AS fibroblasts via nuclear factor kappa B (NF-κB) signaling. Rescue experiments revealed that overexpression of TLR5 reversed SPI1 knockdown-suppressed osteogenic differentiation via NF-κB signaling. SPI1 regulated the progression of AS by modulating TLR5 via NF-κB signaling.

Abnormal kynurenine level contributes to the pathological bone features of ankylosing spondylitis

OBJECTIVE

Ankylosing spondylitis (AS) exhibits paradoxical bone features typically characterized by new bone formation and systemic bone loss. Although abnormal kynurenine (Kyn), a tryptophan metabolite, has been closely linked to the disease activity of AS, the distinct role of its pathological bone features remains unknown.

METHODS

Kynurenine sera level was collected from healthy control (HC; n = 22) and AS (n = 87) patients and measured by ELISA. In the AS group, we analyzed and compared the Kyn level based on the modified stoke ankylosing spondylitis spinal score (mSASSS), MMP13, and OCN. Under osteoblast differentiation, the treatment with Kyn in AS-osteoprogenitors conducted cell proliferation, alkaline phosphatase activity, bone mineralization-related alizarin red s (ARS), von kossa (VON), hydroxyapatite (HA) staining, and mRNA expression markers (ALP, RUNX2, OCN, and OPG) for bone formation. TRAP and F-actin staining was used for osteoclast formation of mouse osteoclast precursors.

RESULTS

Kyn sera level was significantly elevated in the AS group compared to the HC. In addition, Kyn sera level was correlated with mSASSS (r = 0.03888, p = 0.067), MMP13 (r = 0.0327, p = 0.093), and OCN (r = 0.0436, p = 0.052). During osteoblast differentiation, treatment with Kyn exhibited no difference in cell proliferation and alkaline phosphate (ALP) activity for bone matrix maturation but promoted ARS, VON, and HA staining for bone mineralization. Interestingly, osteoprotegerin (OPG) and OCN expressions of AS-osteoprogenitors were augmented in the Kyn treatment during differentiation. In growth medium, Kyn treatment of AS-osteoprogenitors resulted in induction of OPG mRNA, protein expression, and Kyn-response genes (AhRR, CYP1b1, and TIPARP). Secreted OPG proteins were observed in the supernatant of AS-osteoprogenitors treated with Kyn. Notably, the supernatant of Kyn-treated AS-osteoprogenitors interrupted the RANKL-mediated osteoclastogenesis of mouse osteoclast precursor such as TRAP-positive osteoclast formation, NFATc1 expression, and osteoclast differentiation markers.

CONCLUSION

Our results revealed that elevated Kyn level increased the bone mineralization of osteoblast differentiation in AS and decreased RANKL-mediated osteoclast differentiation by inducing OPG expression. Out study have implication for potential coupling factors linking osteoclast and osteoblast where abnormal Kyn level could be involved in pathological bone features of AS.

Rotating Magnetic Field Mitigates Ankylosing Spondylitis Targeting Osteocytes and Chondrocytes via Ameliorating Immune Dysfunctions

Ankylosing spondylitis (AS) is clinically characterized by bone fusion that is induced by the pathological formation of extra bone. Unfortunately, the fundamental mechanism and related therapies remain unclear. The loss of SHP-2 (encoded by Ptpn11) in CD4-Cre;Ptpn11^f/f mice resulted in the induction of AS-like pathological characteristics, including spontaneous cartilage and bone lesions, kyphosis, and arthritis. Hence, this mouse was utilized as an AS model in this study. As one of the basic physical fields, the magnetic field (MF) has been proven to be an effective treatment method for articular cartilage degeneration. In this study, the effects of a rotating magnetic field (RMF; 0.2 T, 4 Hz) on an AS-like mouse model were investigated. The RMF treatment (2 h/d, 0.2 T, 4 Hz) was performed on AS mice from two months after birth until the day before sampling. The murine specimens were subjected to transcriptomics, immunomics, and metabolomics analyses, combined with molecular and pathological experiments. The results demonstrated that the mitigation of inflammatory deterioration resulted in an increase in functional osteogenesis and a decrease in dysfunctional osteolysis due to the maintenance of bone homeostasis via the RANKL/RANK/OPG signaling pathway. Additionally, by regulating the ratio of CD4+ and CD8+ T-cells, RMF treatment rebalanced the immune microenvironment in skeletal tissue. It has been observed that RMF interventions have the potential to alleviate AS, including by decreasing pathogenicity and preventing disease initiation. Consequently, RMF, as a moderately physical therapeutic strategy, could be considered to alleviate the degradation of cartilage and bone tissue in AS and as a potential option to halt the progression of AS.

Evaluating the relationship between ankylosing spondylitis and periodontal disease: a case-control study

OBJECTIVES

This study aimed to determine the possible relationship between periodontal disease and ankylosing spondylitis (AS) by evaluating clinical periodontal measurements and gingival crevicular fluid (GCF) levels of sclerostin, interleukin-1β (IL-1ß), and matrix metalloproteinase-8 (MMP-8) levels.

MATERIALS AND METHODS

Twenty-eight patients with AS (AS group) and 28 systemically healthy controls (C group) were enrolled in this study. Full-mouth periodontal measurements: plaque index, bleeding on probing (BOP), probing pocket depth (PPD), and clinical attachment level (CAL) measurements were obtained from all patients. AS-related parameters were included in the data analyses. An enzyme-linked immunosorbent assay determined GCF IL-1β, MMP-8, and sclerostin levels.

RESULTS

There were no significant differences in the clinical periodontal measurements between the two groups (p > 0.05). Interestingly, patients with AS had significantly lower GCF sclerostin levels than the C group (p < 0.05). But there were no statistical differences in the GCF levels of IL-1ß and MMP-8 between the two groups (p > 0.05). Serum C-reactive protein (CRP) levels strongly correlated with both BOP (r = 0.497, p < 0.05) and PPD (r = 0.570, p < 0.05) in the AS group. Bath AS Metrology Index (BASMI) also positively correlated with both BOP (r = 0.530, p < 0.05) and CAL (r = 0.568, p < 0.05). Similarly, Maastrıcht Ankylosing Spondylitis Enthesis Score (MASES) strongly correlated with both BOP (r = 0.487, p < 0.05) and CAL (r = 0.522, p < 0.05).

CONCLUSION

These results suggest that the patient's systemic condition may influence local sclerostin levels in GCF, and the strong correlations between periodontal measurements and AS-related parameters may indicate an interrelationship between inflammatory periodontal disease and AS.

CLINICAL RELEVANCE

The present study provides important information concerning the relationship between periodontal disease and ankylosing spondylitis.

TRIAL REGISTRATION

Thai Clinical Trials.gov (TCTR20200908001) (08. September 2020).

Survivin; a novel therapeutic target that correlates with survival of autoreactive T lymphocytes obtained from patients with ankylosing spondylitis

Ankylosing spondylitis (AS) is progressive immune-mediated arthritis. Persistent autoreactivity of T cells with an up-regulated Survivin expression is strongly implicated in AS immunopathogenesis. Besides, Survivin can inhibit proapoptotic caspase 9 activations. Moreover, microRNAs are small non-coding RNAs that are dysregulated in various diseases, in which their altered expression could modulate Survivin expression. The primary goal of this study was to assess the role of Survivin and its-targeting microRNAs in the immunopathogenesis of AS disease. For this aim, peripheral blood mononuclear cells (PBMCs) were isolated from 15 patients with AS and healthy matched controls using Ficoll-Hypaque. T cells were obtained using the magnetic-activated cell sorting (MACS) method. After that, the expression levels of Survivin, Caspase 9, and specific miRNAs were determined using qT-qPCR. Also, the expression of Survivin and Caspase 9 at protein levels was determined by western blotting. Then, the isolated T cells were co-cultured with interleukin (IL)-2 and muromonab-CD3 (OKT-3) for active-induced cell death (AICD) induction, Survivin siRNA for inhibition of Survivin expression, and their combination to assess the implication of Survivin expression in autoreactive T lymphocytes' resistance to apoptosis by determining the rate of apoptosis by Flowcytometry assay. The results showed that Survivin was up-regulated while Caspase 9 was downregulated in patients with AS. It was also revealed that microRNAs that directly or indirectly target the Survivin mRNA were dysregulated in patients with AS. It was also revealed that T cells obtained from AS patients were more resistant to apoptosis induction than those obtained from healthy people. In summary, the results obtained from this study showed that dysregulation of Survivin and Survivin-targeting miRNAs in T lymphocytes obtained from AS patients contribute to their resistance to apoptosis, suggesting the future development of targeted therapies for AS.

Prevalence and Factors of Osteoporosis and High Risk of Osteoporotic Fracture in Patients with Ankylosing Spondylitis: A Multicenter Comparative Study of Bone Mineral Density and the Fracture Risk Assessment Tool

Background: We investigated the prevalence of and the factors associated with a high risk of osteoporotic fractures in Korean patients with ankylosing spondylitis (AS). Methods: This was a multicenter, retrospective study including 219 AS patients from five university hospitals; the control group was selected by matching age and sex with those of the AS patients. The fracture risk was evaluated based on bone mineral density (BMD) measured by dual-energy X-ray absorptiometry and the fracture risk assessment tool (FRAX) with/without BMD. Results: The mean age of the patients was 47.6 years, and 144 (65.8%) patients were men. According to the WHO criteria and FRAX with/without BMD, the candidates for pharmacological treatment were 44 (20.1%), 20 (13.2%), and 23 (15.1%) patients, respectively, significantly more than those in the healthy control group. Among them, the proportion of patients receiving osteoporosis treatment was 39.1–75%. In logistic regression analysis, menopause was an independent factor for the high risk of fracture according to the WHO criteria and FRAX with/without BMD. C-reactive protein level (odds ratio (OR) 3.8 and OR 6) and glucocorticoid use (OR 1.5 and OR 1.7) were associated with a high risk of osteoporotic fracture based on FRAX without BMD and osteoporosis diagnosed according to the WHO criteria. Conclusions: Our study suggests that both FRAX and WHO criteria may be complementary for treatment decisions to reduce osteoporotic fractures in patients with AS.

Interleukin-35 promotes Breg expansion and interleukin-10 production in CD19+ B cells in patients with ankylosing spondylitis

OBJECTIVE

IL-35 is a potent immunosuppressive and anti-inflammatory cytokine, consisting of a p35 subunit and an Epstein-Barr virus-induced gene 3 (EBI3) subunit, which suppresses CD4⁺ effector T cell proliferation and promotes regulatory T cell (Treg) expansion. However, the effects of IL-35 on regulatory B cells (Bregs) in ankylosing spondylitis (AS) have not been explored. The present study aimed (i) to measure serum IL-35 levels and the percentages of Bregs in the peripheral blood of patients with AS and (ii) to explore their relationships in the pathogenesis of AS.

METHODS

A total of 77 patients with AS (AS group), including 47 inactive AS and 30 active AS cases, and 59 healthy controls (HCs) were enrolled into this study. The serum levels of IL-35 and IL-10 were detected by ELISA, and the mRNA levels of p35 and EBI3 were measured by RT-qPCR. The percentages of CD19⁺CD24^hiCD38^hi and CD19⁺CD24^hiCD27⁺ Bregs and IL-35 receptor (IL-12Rβ2, IL-27Rα and gp130), IL-10, p-STAT1, p-STAT3, and p-STAT4 in CD19⁺ B cells were detected by flow cytometry. The correlations between IL-35 levels and percentages of Bregs were analyzed by determining Pearson's correlation coefficient. The effect of IL-35 on Bregs was determined by mix-culture of recombinant (r) IL-35 with peripheral blood mononuclear cells (PBMCs).

RESULTS

The serum IL-35 and IL-10 levels, p35 and EBI3 mRNA levels, and the percentages of CD19⁺CD24^hiCD38^hi and CD19⁺CD24^hiCD27⁺ Bregs were significantly lower in AS patients than those in HCs. In addition, the percentages of CD19⁺CD24^hiCD38^hi and CD19⁺CD24^hiCD27⁺ Bregs in active AS patients were significantly lower than those in inactive AS patients. The serum IL-35 levels were positively correlated with the percentages of CD19⁺CD24^hiCD38^hi and CD19⁺CD24^hiCD27⁺ Bregs in AS patients. IL-12Rβ2 and IL-27Rα, but not gp130 subunit, were expressed in CD19⁺ B cells in AS patients. RIL-35 could effectively promote CD19⁺CD24^hiCD38^hi Breg expansion and IL-10 production. Meanwhile, rIL-35 also promoted the expression of IL-12Rβ2 and IL-27Rα and the phosphorylation of STAT1 and STAT3 in CD19⁺ B cells.

CONCLUSION

These results demonstrated that reduced IL-35 production may be associated with Bregs defects in AS patients. RIL-35 induced the proliferation of CD19⁺CD24^hiCD38^hi Bregs and IL-10 production, suggesting that IL-35 may serve as a reference for further investigation to develop novel treatments for AS. Key Points • Our study investigated the effects of IL-35 on Bregs in AS patients. • We found the serum IL-35, IL-10 levels, and the percentages of CD19⁺CD24^hiCD38^hi and CD19⁺CD24^hiCD27⁺ Bregs were significantly lower in AS patients. • The serum IL-35 levels were positively correlated with the percentages of CD19⁺CD24^hiCD38^hi and CD19⁺CD24^hiCD27⁺ Bregs in AS patients. • Recombinant IL-35 could effectively promote CD19⁺CD24^hiCD38^hi Breg expansion and IL-10 production.

Risk Factors for Spinal Structural Damage in a Chinese Cohort With Ankylosing Spondylitis

OBJECTIVES

A cross-sectional study was conducted in 270 Chinese patients with ankylosing spondylitis (AS) in order to identify potential risk factors for severity of spinal structural damage.

METHODS

Two hundred seventy AS patients fulfilled the Modified New York Criteria. Computed tomography (CT) was used to scan sacroiliac and hip joints, and radiography was used to scan anteroposterior and lateral lumbar spine, as well as lateral cervical spine. Bath Ankylosing Spondylitis Radiology Index and modified Stoke Ankylosing Spondylitis Spine Score (mSASSS) were scored in duplicate.

RESULTS

One hundred eighty-three patients had low mSASSS (mSASSS, <10), and 87 patients had high mSASSS (mSASSS, ≥10). Univariate analysis revealed that AS age of onset, body mass index (BMI), smoking duration, duration of symptoms, diagnostic delay, hip involvement, and sacroiliitis grade were significantly associated with the risk of having high mSASSS after adjustment (all p's < 0.05). Hip involvement interacted significantly with BMI and smoking duration in a graded manner. Particularly, relative to patients with low BMI-negative hip involvement, those with high BMI-negative hip involvement, low BMI-positive hip involvement, and high BMI-positive hip involvement had a 1.94-fold, 3.29-fold, and 5.07-fold increased risk of high mSASSS (95% confidence interval, 0.84-4.47, 1.37-7.89, and 1.97-13.06, p = 0.118, 0.008, and 0.001, respectively). Finally, a nomogram graph based on 7 significant risk factors was generated with substantial prediction accuracy (concordance index, 0.906).

CONCLUSIONS

We have identified 7 potential risk factors for the severity of spinal structural damage in Chinese AS patients. Importantly, positive hip involvement, combined with high BMI or long smoking duration, was associated with a remarkably increased risk of having severe spinal structural damage.

Anti-Osteogenic Effect of Danshensu in Ankylosing Spondylitis: An in Vitro Study Based on Integrated Network Pharmacology

Ankylosing spondylitis (AS) is a chronic inflammatory disease characterized by abnormal bone metabolism, with few effective treatments available. Danshensu [3-(3,4-dihydroxy-phenyl) lactic acid) is a bioactive compound from traditional Chinese medicine with a variety of pharmacologic effects. In the present study, we investigated the pharmacologic effect and molecular mechanism of Danshensu in AS. Potential targets of Danshensu were identified in four drugs-genes databases; and potential pharmacologic target genes in AS were identified in three diseases-genes databases. Differentially expressed genes related to AS were obtained from the Gene Expression Omnibus database. Overlapping targets of Danshensu and AS were determined and a disease–active ingredient–target interaction network was constructed with Cytoscape software. Enrichment analyses of the common targets were performed using Bioconductor. To test the validity of the constructed network, an in vitro model was established by treating osteoblasts from newborn rats with low concentrations of tumor necrosis factor (TNF)-α. Then, the in vitro model and AS fibroblasts were treated with Danshensu (1–10 μM). Osteogenesis was evaluated by alkaline phosphatase staining and activity assay, alizarin red staining, quantitative PCR, and western blotting. We identified 2944 AS-related genes and 406 Danshensu targets, including 47 that were common to both datasets. The main signaling pathways associated with the targets were the c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK) pathways. A low concentration of TNF-α (0.01 ng/ml) promoted the differentiation of osteoblasts; this was inhibited by Danshensu, which had the same effect on AS fibroblasts but had the opposite effect on normal osteoblasts. Danshensu also decreased the phosphorylation of JNK and ERK in AS fibroblasts. There results provide evidence that Danshensu exerts an anti-osteogenic effect via suppression of JNK and ERK signaling, highlighting its therapeutic potential for the treatment of AS.

Targeting chondrocytes for arresting bony fusion in ankylosing spondylitis

Bony fusion caused by pathological new bone formation manifests the clinical feature of ankylosing spondylitis (AS). However, the underlying mechanism remains elusive. Here we discovered spontaneous kyphosis, arthritis and bony fusion in mature CD4-Cre;Ptpn11^f/f mice, which present the pathophysiological features of AS. A population of CD4-Cre-expressing proliferating chondrocytes was SHP2 deficient, which could differentiate into pre-hypertrophic and hypertrophic chondrocytes. Functionally, SHP2 deficiency in chondrocytes impeded the fusion of epiphyseal plate and promoted chondrogenesis in joint cavity and enthesis. Mechanistically, aberrant chondrocytes promoted ectopic new bone formation through BMP6/pSmad1/5 signaling. It is worth emphasizing that such pathological thickness of growth plates was evident in adolescent humans with enthesitis-related arthritis, which could progress to AS in adulthood. Targeting dysfunctional chondrogenesis with Smo inhibitor sonidegib significantly alleviated the AS-like bone disease in mice. These findings suggest that blockade of chondrogenesis by sonidegib would be a drug repurposing strategy for AS treatment.

Current treatments cannot significantly alleviate the radiographic progression in ankylosing spondylitis (AS), which results in joints stiffness and bony fusion of AS. Smo inhibitor sonidegib retards the pathological new bone formation in AS through targeting dysfunctional chondrogenesis.

Immunological Changes in Peripheral Blood of Ankylosing Spondylitis Patients during Anti-TNF-α Therapy and Their Correlations with Treatment Outcomes

Tumor necrosis factor-α (TNF-α) inhibitors are the main types of biological conventional synthetic disease-modifying antirheumatic drugs and have efficacy in treating ankylosing spondylitis (AS) which is not sensitive for nonsteroidal anti-inflammatory drug. However, the impact of TNF-α inhibitors on immune cells in patients with AS is still clearly undefined, and the impact of immune cells on treatment response is also largely elusive. This study is aimed at evaluating the longitudinal changes of circulating immune cells after anti-TNF-α therapy and their associations with treatment response in AS patients. Thirty-five AS patients receiving the treatment of anti-TNF-α therapy were included into this prospective observational study. The frequencies of immune cells including Th1, Th2, Th17, regulatory T cell (Treg), T follicular helper cell (Tfh), and regulatory B cell (Breg) in the peripheral blood were measured by flow cytometry at baseline and 4 time points after therapy. The difference in the circulating immune cells between responders and nonresponders was compared. This study suggested that anti-TNF-α therapy could significantly reduce circulating proinflammatory immune cells such as Th17 and Tfh, but significantly increased the percentages of circulating Treg and Breg. Moreover, circulating Breg may be a promising predictor of response to anti-TNF-α therapy in AS patients.

Circulating miRNAs in bone health and disease

microRNAs have evolved as important regulators of multiple biological pathways essential for bone homeostasis, and microRNA research has furthered our understanding of the mechanisms underlying bone health and disease. This knowledge, together with the finding that active or passive release of microRNAs from cells into the extracellular space enables minimal-invasive detection in biofluids (circulating miRNAs), motivated researchers to explore microRNAs as biomarkers in several pathologic conditions, including bone diseases. Thus, exploratory studies in cohorts representing different types of bone diseases have been performed. In this review, we first summarize important molecular basics of microRNA function and release and provide recommendations for best (pre-)analytical practices and documentation standards for circulating microRNA research required for generating high quality data and ensuring reproducibility of results. Secondly, we review how the genesis of bone-derived circulating microRNAs via release from osteoblasts and osteoclasts could contribute to the communication between these cells. Lastly, we summarize evidence from clinical research studies that have investigated the clinical utility of microRNAs as biomarkers in musculoskeletal disorders. While previous reviews have mainly focused on diagnosis of primary osteoporosis, we have also included studies exploring the utility of circulating microRNAs in monitoring anti-osteoporotic treatment and for diagnosis of other types of bone diseases, such as diabetic osteopathy, bone degradation in inflammatory diseases, and monogenetic bone diseases.

Adipokines and Chronic Rheumatic Diseases: from Inflammation to Bone Involvement

Besides its well-known role as energy storage tissue, adipose tissue is a biologically active tissue that can also be considered as an endocrine organ, as it is able to secrete adipokines. These bioactive factors, similar in structure to cytokines, are involved in several physiological and pathological conditions, such as glucose homeostasis, angiogenesis, blood pressure regulation, control of food intake, and also inflammation and bone homeostasis via endocrine, paracrine, and autocrine mechanisms. Given their pleiotropic functions, the role of adipokines has been evaluated in chronic rheumatic osteoarticular inflammatory diseases, particularly focusing on their effects on inflammatory and immune response and on bone alterations. Indeed, these diseases are characterized by different bone complications, such as local and systemic bone loss and new bone formation. The aim of this review is to summarize the role of adipokines in rheumatoid arthritis, ankylosing spondylitis, psoriatic arthritis, osteoarthritis, and osteoporosis, especially considering their role in the pathogenesis of bone complications typical of these conditions.

Novel immune cell phenotypes in spondyloarthritis pathogenesis

Spondyloarthritis (SpA) is a heterogeneous group of chronic inflammatory diseases of unknown etiology. Over time, the plethora of cellular elements involved in its pathogenesis has progressively enriched together with the definition of specific cytokine pathways. Recent evidence suggests the involvement of new cellular mediators of inflammation in the pathogenesis of SpA or new subgroups of known cellular mediators. The research in this sense is ongoing, and it is clear that this challenge aimed at identifying new cellular actors involved in the perpetuation of the inflammatory process in AxSpA is not a mere academic exercise but rather aims to define a clear cellular hierarchy. Such a definition could pave the way for new targeted therapies, which could interfere with the inflammatory process and specific pathways that trigger immune system dysregulation and stromal cell activity, ultimately leading to significant control of the inflammation and new bone formation in a significant number of patients. In this review, we will describe the recent advances in terms of new cellular actors involved in the pathogenesis of SpA, focusing our attention on stromal cells and innate and adaptive immunity cells.

Factors influencing peak bone mass gain

Bone mass is a key determinant of osteoporosis and fragility fractures. Epidemiologic studies have shown that a 10% increase in peak bone mass (PBM) at the population level reduces the risk of fracture later in life by 50%. Low PBM is possibly due to the bone loss caused by various conditions or processes that occur during adolescence and young adulthood. Race, gender, and family history (genetics) are responsible for the majority of PBM, but other factors, such as physical activity, calcium and vitamin D intake, weight, smoking and alcohol consumption, socioeconomic status, age at menarche, and other secondary causes (diseases and medications), play important roles in PBM gain during childhood and adolescence. Hence, the optimization of lifestyle factors that affect PBM and bone strength is an important strategy to maximize PBM among adolescents and young people, and thus to reduce the low bone mass or osteoporosis risk in later life. This review aims to summarize the available evidence for the common but important factors that influence bone mass gain during growth and development and discuss the advances of developing high PBM.

Conventional disease-modifying antirheumatic drugs therapy may not slow spinal radiographic progression in ankylosing spondylitis: results from an 18-year longitudinal dataset

Objectives:

The clinical benefit of conventional disease-modifying antirheumatic drugs (cDMARDs) for treating ankylosing spondylitis (AS) is generally limited to improvements in peripheral arthritis. However, cDMARDs could be conditionally considered as alternatives to established drugs for improving axial manifestations in exceptional circumstances. However, there are few studies of the impact of cDMARDs on radiographic progression outcomes. Therefore, we investigated the effectiveness of cDMARDs on radiographic progression in AS.

Methods:

Among 1280 AS patients at a single hospital from 2000 to 2018, 301 who had been treated with sulfasalazine (SSZ) or methotrexate (MTX) were enrolled. For each patient, the entire follow-up period was split into 1-year intervals. Each interval was classified as either an “on-cDMARD” interval, which was a period of treatment with SSZ alone, MTX alone, or a combination of SSZ and MTX, or an “off-cDMARD” interval, which was a period without cDMARD treatment. Radiographic progression was scored using the modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS). The relationship between cDMARD use and radiographic progression within the intervals, defined as the rate of mSASSS progression, was investigated using linear models with adjustment for potential confounding covariates and for clustering among observations from the same patient.

Results:

The 732 on-cDMARD intervals and 1027 off-cDMARD intervals were obtained from enrolled patients. In multivariable regression analysis, there was no significant association between cDMARDs and the rate of mSASSS progression (β = −0.081, p = 0.418). The mean adjusted mSASSS change per year was 0.610 from on-cDMARD intervals and 0.691 from off-cDMARD intervals.

Conclusion:

Treatment with cDMARDs may not reduce radiographic progression in AS patients.

Oxidative and Antioxidative Stress Linked Biomarkers in Ankylosing Spondylitis: A Systematic Review and Meta-analysis

Objective. Ankylosing spondylitis (AS) is a chronic inflammatory disease that affects the axial skeleton, leading to joint disability. Our study aims at investigating the change of oxidative and antioxidative stress linked biomarkers in AS. Methods. This systematic review and meta-analysis was performed following the Preferred Reporting Items of Systematic Reviews and Meta-Analyses (PRISMA) statement. PubMed, Web of Science, and Cochrane Library databases till May 2020 were searched. Only articles published in English were included. Two reviewers screened relevant studies, extracted data, and assessed the quality of included studies using the Newcastle-Ottawa scale independently. Either random or fixed effect model was adopted base on the heterogeneity testing by $I^2$ statistic. Standardized mean difference (SMD) and 95% confidence intervals (CI) of oxidative and antioxidative markers were calculated. $p$ value <0.05 was considered statistically significant. Results. A total of 22 studies including 931 AS patients and 917 healthy controls met the selection criteria. Significantly increased levels of all oxidative stress markers except myeloperoxidase, and significantly decreased levels of total antioxidant status ( $\text{SMD}=-1.19$ , 95% CI -2.35 to -0.03, $p=0.044$ ) and paraoxonase 1( $\text{SMD}=-1.01$ , 95% CI -1.78 to -0.24, $p=0.010$ ) in serum were observed in AS patients when compared with healthy controls. However, there were no significant differences of all oxidative and anti-oxidative stress biomarkers in erythrocytes. Additionally, the levels of malondialdehyde ( $\text{SMD}=0.51$ , 95% CI 0.21 to 0.81, $p=0.001$ ) and advanced oxidation protein products ( $\text{SMD}=0.95$ , 95% CI 0.58 to 1.31, $p<0.001$ ) in serum were significantly higher in active patients when compared with inactive AS patients. Conclusion. This meta-analysis demonstrated an overall increase of oxidative markers and decrease of antioxidative markers in AS, suggesting that oxidative stress may play an important role in the pathogenesis of AS.

TNF‑α treatment increases DKK1 protein levels in primary osteoblasts via upregulation of DKK1 mRNA levels and downregulation of miR‑335‑5p

Elucidation of the underlying mechanisms governing osteogenic differentiation is of significant importance to the improvement of therapeutics for bone-related inflammatory diseases. Tumor necrosis factor-α (TNF-α) is regarded as one of the major agents during osteogenic differentiation in an inflammatory environment. miR-335-5p post-transcriptionally downregulates the Dickkopf WNT signaling pathway inhibitor 1 (DKK1) protein level by specifically binding to the DKK1 3′UTR and activating Wnt signaling. The role of miR-335-5p in TNF-α-induced post-transcriptional regulation of DKK1 remains to be elucidated. In the present study, the mRNA and protein levels of DKK1 and the level of miR-335-5p were determined in MC3T3-E1 cells and the primary calvarial osteoblasts treated with or without TNF-α. The role of NF-κB signaling in TNF-α-induced post-transcriptional regulation of DKK1 was also evaluated. The present study determined that although TNF-α treatment exhibited cell-specific effects on DKK1 mRNA expression, the stimulation of TNF-α time- and concentration-dependently upregulated the protein levels of DKK1. In primary calvarial osteoblasts, the decreased miR-335-5p level induced by TNF-α-activated NF-κB signaling served an important role in mediating the post-transcriptional regulation of DKK1 by TNF-α treatment. In MC3T3-E1 cells, the post-transcriptional regulation of DKK1 by TNF-α treatment was more complicated and involved other molecular signaling pathways in addition to the NF-κB signaling. In conclusion, TNF-α treatment served an important role in the post-transcriptional regulation of DKK1 expression, which requires further investigation. The results of the present study not only provided new insights into the regulatory effects of miR-335-5p on osteogenic differentiation in an inflammatory microenvironment, but may also promote the development of potential therapeutic strategies for the treatment of bone-related inflammatory diseases.

Measuring bone density in axial spondyloarthropathy: Time to turn things on their side?

AIM

Osteoporosis in axial spondyloarthropathy (axSpA) is difficult to accurately diagnose due to osteoproliferation of the spine interfering with conventional (anteroposterior, AP) dual-energy X-ray absorptiometry (DXA). This study compares AP and lateral projections of DXA when assessing bone mineral density (BMD) of the spine and investigates the impact of osteoproliferation on AP DXA.

METHOD

In this cross-sectional study, structured standardized assessments collected demographic, clinical, laboratory and radiographic data. DXA assessed BMD of the spine using PA and lateral projections. Hip BMD was assessed in the usual manner. World Health Organization (WHO) criteria assessed prevalence of low BMD. Incorporating lateral DXA in the bone health assessment of axSpA was investigated. SPSS was used for statistical analysis.

RESULTS

A total of 100 patients had paired AP and lateral DXA studies: 78% were male, mean (SD) age 52 (12) years. BMD of the spine measured by AP projection was significantly higher than BMD measured by lateral projection (mean difference 0.34 g/cm² , 95% CI 0.30-0.37). More patients had low BMD with lateral compared to AP projection (47% vs 16%, P = .01). At the hip, 34% of patients had low BMD. Disease duration, body mass index and radiographic severity independently predicted a difference between AP and lateral measurements of the spine.

CONCLUSION

Lateral DXA of the spine is unaffected by osteoproliferation of the spine in axSpA and detects significantly more cases of low BMD than conventional AP DXA. Lateral DXA should be included in BMD assessment of patients with axSpA.

Wnt Signaling and Biological Therapy in Rheumatoid Arthritis and Spondyloarthritis

The Wnt signaling pathway plays a key role in several biological processes, such as cellular proliferation and tissue regeneration, and its dysregulation is involved in the pathogenesis of many autoimmune diseases. Several evidences support its role especially in bone complications of rheumatic diseases. In Rheumatoid Arthritis (RA), the Wnt signaling is implicated in systemic and localized bone loss, while available data of its role in Spondyloarthritis (SpA) are conflicting. In the last few decades, the quality of life of rheumatic patients has been dramatically improved by biological therapy, targeting cytokines involved in the pathogenesis of these diseases like tumor necrosis factor (TNF)α, interleukin (IL)-1, IL-6, IL-17. In this review, we reviewed the role of Wnt signaling in RA and SpA, focusing on the effect of biological therapy on this pathway and its possible clinical implications.

IL-17 in the immunopathogenesis of spondyloarthritis

Spondyloarthritis (SpA) is a term that refers to a group of inflammatory diseases that includes psoriatic arthritis, axial SpA and nonradiographic axial SpA, reactive arthritis, enteropathic arthritis and undifferentiated SpA. The disease subtypes share clinical and immunological features, including joint inflammation (peripheral and axial skeleton); skin, gut and eye manifestations; and the absence of diagnostic autoantibodies (seronegative). The diseases also share genetic factors. The aetiology of SpA is still the subject of research by many groups worldwide. Evidence from genetic, experimental and clinical studies has accumulated to indicate a clear role for the IL-17 pathway in the pathogenesis of SpA. The IL-17 family consists of IL-17A, IL-17B, IL-17C, IL-17D, IL-17E and IL-17F, of which IL-17A is the best studied. IL-17A is a pro-inflammatory cytokine that also has the capacity to promote angiogenesis and osteoclastogenesis. Of the six family members, IL-17A has the strongest homology with IL-17F. In this Review, we discuss how IL-17A and IL-17F and their cellular sources might contribute to the immunopathology of SpA.

Low bone mineral density of vertebral lateral projections can predict spinal radiographic damage in patients with ankylosing spondylitis

OBJECTIVES

To investigate the association between bone mineral status and spinal radiographic damage in patients with ankylosing spondylitis (AS) and determine whether bone mineral status can predict further spinal radiographic damage after 2 years.

METHODS

Bone mineral density (BMD) of the lumbar spine (anteroposterior and lateral projections), femoral neck, and total hip and trabecular bone score (TBS) of the lumbar spine were measured in AS patients (n = 54) who fulfilled the modified New York criteria. Spinal radiographic damage was scored on cervical and lumbar spine radiographs using modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS) at baseline and after 2 years. Simple and multiple linear regression analyses were performed to examine predictors of spinal radiographic damage.

RESULTS

Patients with advanced AS exhibited low BMD on lumbar spine lateral projections, femoral neck, and total hip and low TBS. Low vertebral bone mass at baseline, assessed by BMD of the lateral projections or TBS, was independently associated with baseline mSASSS. After 2 years, mSASSS change from baseline was significantly associated with high baseline mSASSS, high baseline erythrocyte sedimentation rate and C-reactive protein (CRP) levels, and low baseline BMD of the lumbar spine lateral projections. The best predictive model for spinal radiographic progression consisted of baseline mSASSS, baseline CRP, and low BMD of lateral lumbar spine (area under curve = 0.826).

CONCLUSIONS

BMD at vertebral lateral projections and TBS were inversely associated with baseline mSASSS in AS patients. Low BMD at vertebral lateral projections, as well as baseline mSASSS and inflammatory markers, might predict spinal radiographic damage in AS.Key Points• Vertebral bone mineral density of lateral projections and trabecular bone score are inversely associated with baseline mSASSS in patients with ankylosing spondylitis.• Baseline mSASSS, inflammatory markers, and low vertebral bone mineral density might predict spinal radiographic progression in patients with ankylosing spondylitis.

Serum miR-21 expression correlates with radiographic progression but also low bone mineral density in patients with ankylosing spondylitis: a cross-sectional study

Increased expressions of miR-21 have been detected in ankylosing spondylitis (AS) patients. The current study was performed to examine the serum miR-21 expression with radiographic severity in AS patients, which was determined based on the modified New York (NY) criteria for sacroiliac joints assessment and modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS) system for spine involvement. Bone mineral density at lumbar 1–4 and femoral neck were examined by dual-energy absorptiometry (DXA). Serum miR-21 expressions were determined by quantitative real-time PCR, and receiver operating characteristic curve analysis was performed to identify the diagnostic value of miR-21 expression levels regarding the NY criteria. Elevated levels of serum miR-21 expressions were detected in AS patients compared with healthy controls. AS patients with modified NY grade 4 showed significantly higher miR-21 expression than grade 3 and grade 2. AS patients with spinal syndesmophytes had significantly higher serum miR-21 expressions than non-syndesmophyte patients. Increased miR-21 expressions were significantly related to the disease radiographic severity. In addition, serum miR-21 expressions were negatively associated with lumbar 1–4 and femoral neck bone mineral density. In summary, serum miR-21 expressions were related to structural damage and radiological progression in AS, indicating that miR-21 may act as a switch between inflammation and new bone information and regulate different signal ways between lesioned enthesis and trabecular bone.

Evaluation of serum fibroblast growth factor-23 in patients with axial spondyloarthritis and its association with sclerostin, inflammation, and spinal damage

The mechanisms underlying new bone formation in individuals with axial spondyloarthritis (axSpA) remain unclear; however, low levels of sclerostin (SOST) may be associated with development of syndesmophytes in those with ankylosing spondylitis (AS). Expression of fibroblast growth factor-23 (FGF-23), another osteocyte factor, is high in those with osteoporosis and chronic renal failure, but levels in those with axSpA are unknown. To evaluate serum FGF-23 and SOST levels in axSpA patients, and to assess their relationship with inflammation and structural damage. In total, 109 axSpA patients (55 with AS and 54 with non-radiographic axSpA) and 57 healthy control (HC) subjects were included in the analysis. Serum concentrations of FGF-23 and SOST were measured and correlation analysis was performed. The presence of syndesmophytes and the modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS) were used to assess structural damage. Levels of serum FGF-23 in axSpA patients were significantly higher than those in HCs [median (interquartile range-IQR) FGF-23 level, pg/ml; AxSpA = 144 (82.3-253.2), HC = 107 (63.3-192.8), p = 0.010]; however, there was no difference in SOST levels. FGF-23 levels correlated with the erythrocyte sedimentation rate (ESR) (r = 0.265, p = 0.006) and serum C-reactive protein (CRP) level (r = 0.229, p = 0.010). In the axSpA, SOST levels correlated negatively with mSASSS (r = - 0.283, p = 0.007), whereas those in the AS group correlated negatively with CRP (r = - 0.426, p = 0.001). Serum FGF-23 levels were high in axSpA patients. Increased FGF-23 was associated with inflammation, but not with SOST levels or disease activity. SOST correlated negatively with both inflammation and structural damage.

Structural damage and motion rhythm of the spine and hip during trunk lateral bending in ankylosing spondylitis patients with mild to moderate radiographic signs

BACKGROUND

Ankylosing spondylitis causes structural damage and motion restriction in spine. The study was designed to assess structural damage and incoordination pattern between the spine and hip during trunk lateral bending in ankylosing spondylitis.

METHODS

Twenty-three healthy adults and 39 adults with ankylosing spondylitis were recruited from a tertiary care medical centre. Patients with ankylosing spondylitis were divided into two subgroups: sacroiliitis or lumbar-level syndesmophytes (n = 27) and thoracic or cervical-level syndesmophytes (n = 12). An inertia motion system was used to record three-dimensional kinematic data during trunk lateral bending.

FINDINGS

Significant differences were observed in lumbar spine syndesmophyte scores, sacroiliitis severity and Bath Ankylosing Spondylitis Metrology Index between the subgroups. The cervical supraspinous ligaments thickness revealed difference between the ankylosing spondylitis and control group, but the Glasgow Ultrasound Enthesitis Scoring System did not revealed difference. Motion analysis revealed that the ankylosing spondylitis group had a larger hip, cervical rotation and smaller lumbar-hip rhythm than the control group; however, the other motions of the spine and hip were smaller. The sacroiliitis or lumbar-level syndesmophytes group had the largest thoracic rotation among the three groups.

INTERPRETATION

The different lumbar-hip rhythm between ankylosing spondylitis patients depends on syndesmophyte formation levels. Cervical rotation, the Schober test, the chest expansion test, and lumbar-hip rhythm can indicate the levels of bone damage in ankylosing spondylitis. Clinical examination of ankylosing spondylitis should include kinematic measures of both the spine and hips in the early disease stage.

Understanding and managing secondary osteoporosis

INTRODUCTION

The term secondary osteoporosis (SO) identifies a reduction of bone mass related to a well-established disease or pharmacological agent. The identification of the underlying disease often represents a challenging situation in clinical practice.

AREAS COVERED

The prevalence of SO in the real world may vary, ranging from 17% to 80%; therefore, search for a form of SO represents a pillar when evaluating patients with osteoporosis. Guidelines for treatment of specific secondary forms of osteoporosis, such as glucocorticoid-induced osteoporosis, have been published even though often neglected in clinical practice. For the majority of SO, there are currently no specific guidelines concerning treatment with only few trials showing the effect of bone-active drugs on fracture risk reduction.

EXPERT OPINION

Healthcare professionals should be aware of the secondary forms of osteoporosis, in particular when the reason for reduced skeletal resistance is uncertain or when bone mineral density results are unsatisfactory in a patient compliant to therapy. In a few cases (such as, for example: no response to therapy, better classification of bone involvement in patients with kidney failure, suspicion of rare metabolic bone disease) bone biopsy is needed to investigate the patient. This review highlights recent advances in understanding and managing SO.

Protein inhibitor of activated STAT3 reduces peripheral arthritis and gut inflammation and regulates the Th17/Treg cell imbalance via STAT3 signaling in a mouse model of spondyloarthritis

Background

Spondyloarthritis (SpA) is chronic inflammatory arthritis, and interleukin (IL)-17 is crucial in SpA pathogenesis. Type 17 helper T (Th17) cells are one of major IL-17-secreting cells. Signal transducer and activator of transcription (STAT)-3 signaling induces Th17 differentiation. This study investigated the effects of protein inhibitor of activated STAT3 (PIAS3) on SpA pathogenesis. Curdlan was injected into SKG ZAP-70^W163C mice for SpA induction.

Methods

The PIAS3 or Mock vector was inserted into mice for 10 weeks. Clinical and histologic scores of the paw, spine, and gut were evaluated. The expression of IL-17, tumor necrosis factor-α (TNF-α), STAT3, and bone morphogenic protein (BMP) was measured. Confocal microscopy and flow cytometry were used to assess Th cell differentiation.

Results

PIAS3 significantly diminished the histologic scores of the paw and gut. PIAS3-treated mice displayed decreased expression of IL-17, TNF-α, and STAT3 in the paw, spine, and gut. BMP-2/4 expression was lower in the spines of PIAS3-treated mice. Th cell differentiation was polarized toward the upregulation of regulatory T cells (Tregs) and the downregulation of Th17 in PIAS3-treated mice.

Conclusion

PIAS3 had beneficial effects in mice with SpA by reducing peripheral arthritis and gut inflammation. Pro-inflammatory cytokines and Th17/Treg differentiation were controlled by PIAS3. In addition, BMPs were decreased in the spines of PIAS3-treated mice. These findings suggest that PIAS3 could have therapeutic benefits in patients with SpA.

Targeting tumor necrosis factor receptors in ankylosing spondylitis

Over the past two decades, considerable advances in our understanding of inflammatory and immune pathways have allowed for the growing use of targeted biologic therapy. Most notably, the introduction of tumor necrosis factor (TNF) inhibitors has dramatically changed the management of autoimmune inflammatory disorders, including ankylosing spondylitis (AS). Despite the efficacy of TNF inhibitors documented in multiple clinical trials, anti-TNF therapy in AS is far from foolproof; it is associated with serious adverse effects and limited response to therapy in some patients. Moreover, specific questions regarding the role of TNF as a mediator of AS remain unanswered. Therefore, additional efforts are needed in order to better understand the role of TNF in the pathogenesis of AS and to develop safer and more effective treatment strategies. The purpose of this review is to better the understanding of the physiologic and pathogenic roles of TNF signaling in the course of AS. Relevant TNF biology and novel approaches to TNF blockade in AS are discussed.

Bone remodeling induced by mechanical forces is regulated by miRNAs

The relationship between mechanical force and alveolar bone remodeling is an important issue in orthodontics because tooth movement is dependent on the response of bone tissue to the mechanical force induced by the appliances used. Mechanical cyclical stretch (MCS), fluid shear stress (FSS), compression, and microgravity play different roles in the cell differentiation and proliferation involved in bone remodeling. However, the underlying mechanisms are unclear, particularly the molecular pathways regulated by non-coding RNAs (ncRNAs) that play essential roles in bone remodeling. Amongst the various ncRNAs, miRNAs act as post-transcriptional regulators that inhibit the expression of their target genes. miRNAs are considered key regulators of many biologic processes including bone remodeling. Here, we review the role of miRNAs in mechanical force-induced bone metabolism.