The role of Wnt proteins in arthritis

Extracellular PPM1A promotes mineralization of osteoblasts differentiation in ankylosing spondylitis via the FOXO1A-RUNX2 pathway

Protein phosphatase magnesium-dependent 1A (PPM1A), serine/threonine protein phosphatase, in sera level was increased in patients with ankylosing spondylitis (AS). Preosteoblasts were differentiated actively to matured osteoblasts by intracellular PPM1A overexpression. However, it was unclear whether extracellular PPM1A contributes to the excessive bone-forming activity in AS. Here, we confirmed that PPM1A and runt-related transcription factor 2 (RUNX2) were increased in facet joints of AS. During osteoblasts differentiation, exogenous PPM1A treatment showed increased matrix mineralization in AS-osteoprogenitor cells accompanied by induction of RUNX2 and factor forkhead box O1A (FOXO1A) protein expressions. Moreover, upon growth condition, exogenous PPM1A treatment showed an increase in RUNX2 and FOXO1A protein expression and a decrease in phosphorylation at ser256 of FOXO1A protein in AS-osteoprogenitor cells, and positively regulated promoter activity of RUNX2 protein-binding motif. Mechanically, exogenous PPM1A treatment induced the dephosphorylation of transcription factor FOXO1A protein and translocation of FOXO1A protein into the nucleus for RUNX2 upregulation. Taken together, our results suggest that high PPM1A concentration promotes matrix mineralization in AS via the FOXO1A-RUNX2 pathway.

MicroRNAs-mediated regulation pathways in rheumatic diseases

Rheumatoid arthritis (RA) and ankylosing spondylitis (AS) are two common rheumatic disorders marked by persistent inflammatory joint disease. Patients with RA have osteodestructive symptoms, but those with AS have osteoproliferative manifestations. Ligaments, joints, tendons, bones, and muscles are all affected by rheumatic disorders. In recent years, many epigenetic factors contributing to the pathogenesis of rheumatoid disorders have been studied. MicroRNAs (miRNAs) are small, non-coding RNA molecules implicated as potential therapeutic targets or biomarkers in rheumatic diseases. MiRNAs play a critical role in the modulation of bone homeostasis and joint remodeling by controlling fibroblast-like synoviocytes (FLSs), chondrocytes, and osteocytes. Several miRNAs have been shown to be dysregulated in rheumatic diseases, including miR-10a, 16, 17, 18a, 19, 20a, 21, 27a, 29a, 34a, 103a, 125b, 132, 137, 143, 145, 146a, 155, 192, 203, 221, 222, 301a, 346, and 548a.The major molecular pathways governed by miRNAs in these cells are Wnt, bone-morphogenic protein (BMP), nuclear factor (NF)-κB, receptor activator of NF-κB (RANK)-RANK ligand (RANKL), and macrophage colony-stimulating factor (M-CSF) receptor pathway. This review aimed to provide an overview of the most important signaling pathways controlled by miRNAs in rheumatic diseases.

Wnt Signaling Pathway: A Comprehensive Review

Wnt signaling is an evolutionary cell-to-cell coordination mechanism and it is highly critical for a variety of physiological processes of an organism's body, including stem cell regeneration, proliferation, division, migration, polarity of a cell, determining fate of the cell and specification of neural crest, neural symmetry and morphogenesis. Wnts are extracellular secreted glycol proteins, consisted of a family of 19 human proteins that represent the complex nature of the regulatory structure and physiological efficiency of signaling. Moreover, a Wnt/β-catenin-dependent pathway and the β-catenin-independent pathway that is further classified into the Planar Cell Polarity and Wnt/Ca²⁺ pathways have been established as key signaling nodes downstream of the frizzled (Fz/Fzd) receptor, and these nodes are extensively analyzed at biochemical and molecular levels. Genetic and epigenetic activities that ultimately characterize the pathway and its subsequent responses contribute to Wnt-β-catenin signaling pathway hypo or hyper-activation and is associated with the variety of human disorders progression most significantly cancers. Recognizing how this mechanism operates is crucial to the advancement of cancer prevention therapies or regenerative medicine methods. This article is protected by copyright. All rights reserved.

Effects of targeted therapies on bone in rheumatic and musculoskeletal diseases

Generalized bone loss (osteoporosis) and fragility fractures can occur in rheumatic and musculoskeletal diseases including rheumatoid arthritis and spondyloarthritis (SpA; including ankylosing spondylitis and psoriatic arthritis). In addition, rheumatoid arthritis can involve localized, periarticular bone erosion and, in SpA, local (pathological) bone formation can occur. The RANK-RANKL-osteoprotegerin axis and the Wnt-β-catenin signalling pathway (along with its inhibitors sclerostin and Dickkopf 1) have been implicated in inflammatory bone loss and formation, respectively. Targeted therapies including biologic DMARDs and Janus kinase (JAK) inhibitors can stabilize bone turnover and inhibit radiographic joint damage, and potentially also prevent generalized bone loss. Targeted therapies interfere at various points in the mechanisms of local and generalized bone changes in systemic rheumatic diseases, and they effect biomarkers of bone resorption and formation, bone mass and risk of fragility fractures. Studies on the effects of targeted therapies on rates of fragility fracture are scarce. The efficacy of biologic DMARDs for arresting bone formation in axial SpA is debated. Improved understanding of the most relevant therapeutic targets and identification of important targeted therapies could lead to the preservation of bone in inflammatory rheumatic and musculoskeletal diseases.

Effects of one-year tofacitinib therapy on bone metabolism in rheumatoid arthritis

Janus kinase (JAK) inhibitors are used to treat rheumatoid arthritis (RA). We assessed the effects of tofacitinib on bone density and bone markers in association with clinical and laboratory parameters in RA. Tofacitinib stabilized bone density and resulted in a positive balance of bone turnover.

INTRODUCTION

Janus kinase (JAK) inhibitors emerged as new therapeutic options in rheumatoid arthritis (RA). We have little information on how it affects areal and volumetric bone mineral density (BMD) and bone turnover markers. The aim of this study was to assess the effects of 1-year tofacitinib therapy on bone metabolism in RA.

METHODS

Thirty RA patients with active disease were treated with either 5 mg bid or 10 mg bid tofacitinib for 12 months. We determined DAS28, CRP, IgM rheumatoid factor (RF), and anti-cyclic citrullinated peptide (CCP) levels, as well as serum levels of sclerostin, osteocalcin (OC), P1NP, DKK-1, OPG, RANKL, and 25-hydroxy-vitamin D3. Areal and volumetric BMD were assessed by DXA and peripheral quantitative CT (QCT), respectively.

RESULTS

Twenty-six patients (13 on each arm) completed the study. Tofacitinib was clinically effective by suppressing DAS28, CRP, and HAQ. This was accompanied by the attenuation of further bone loss. Tofacitinib therapy significantly increased OC, OPG, and vitamin D3, while decreased CTX levels (p < 0.05). Age and multiple bone markers (OC, CTX, P1NP, RANKL) inversely correlated with L2-4 and femoral neck BMD by DXA. CRP, DAS28, and RANKL inversely determined volumetric BMD by QCT. Age, CRP, anti-CCP, and DKK-1 influenced the effects of tofacitinib therapy on BMD changes.

CONCLUSIONS

One-year tofacitinib treatment stabilized BMD in RA patients and resulted in a positive balance of bone turnover as indicated by bone biomarkers. Further studies are needed to evaluate the potential beneficial effects of JAK inhibitors on inflammatory bone loss.

Loss of the WNT9a ligand aggravates the rheumatoid arthritis-like symptoms in hTNF transgenic mice

Agonists and antagonists of the canonical Wnt signaling pathway are modulators of pathological aspects of rheumatoid arthritis (RA). Their activity is primarily modifying bone loss and bone formation, as shown in animal models of RA. More recently, modulation of Wnt signaling by the antagonist Sclerostin has also been shown to influence soft-tissue-associated inflammatory aspects of the disease pointing towards a role of Wnt signaling in soft-tissue inflammation as well. Yet, nothing is known experimentally about the role of Wnt ligands in RA. Here we provide evidence that altering Wnt signaling at the level of a ligand affects all aspects of the rheumatoid arthritic disease. WNT9a levels are increased in the pannus tissue of RA patients, and stimulation of synovial fibroblasts (SFB) with tumor necrosis factor (TNF) leads to increased transcription of Wnt9a. Loss of Wnt9a in a chronic TNF-dependent RA mouse model results in an aggravation of disease progression with enhanced pannus formation and joint destruction. Yet, loss of its activity in the acute K/BxN serum-transfer induced arthritis (STIA) mouse model, which is independent of TNF signaling, has no effect on disease severity or progression. Thus, suggesting a specific role for WNT9a in TNF-triggered RA. In synovial fibroblasts, WNT9a can activate the canonical Wnt/β-catenin pathway, but it can also activate P38- and downregulate NFκB signaling. Based on in vitro data, we propose that loss of Wnt9a creates a slight proinflammatory and procatabolic environment that boosts the TNF-mediated inflammatory response.

Wnt/β-catenin signaling may induce senescence of chondrocytes in osteoarthritis

Osteoarthritis (OA) is an autoimmune disease associated with increasing age. Typically, chondrocyte senescence is believed to serve an important role in the development and progression of OA. However, the specific mechanisms underlying chondrocyte senescence have not been fully addressed. The present study hypothesized that the Wnt/β-catenin signaling may represent a major regulator of chondrocyte senescence. In addition, the acetylated levels of p53 and sirtuin-1 (SIRT-1) were examined as putative markers for chondrocyte senescence, since activation of p53 is considered an important step in the regulation of senescence. The Wnt/β-catenin signaling pathway was activated using LiCl and inhibited using the Wnt signaling pathway inhibitor, dickkopf-1 (DKK1) in order to evaluate the role of this pathway in the development of OA. Senescent cells were detected using the senescence-associated indicator acidic senescence-associated β-galactosidase (SA-β-gal). The effects of p53 and p16 on chondrocyte senescence were assessed via activation of Wnt/β-catenin signaling using Wnt-1. In addition, β-catenin was transfected into chondrocytes to induce activation of the Wnt/β-catenin signaling pathway. Finally, a rabbit model of OA was used to assess whether the observed effects on the Wnt/β-catenin signaling pathway and the induction of chondrocyte senescence were perpetuated. Activation of Wnt/β-catenin signaling increased the expression levels of SA-β-gal, p53, p16 and acetylated p53. Transfection of β-catenin in chondrocytes increased the expression levels of acetylated p53 and decreased the expression levels of SIRT-1, which in turn deacetylated p53 and modulated its activity. Finally, the role of the Wnt/β-catenin signaling pathway was confirmed in the development of OA using a rabbit model with this condition. The present study suggested that activation of the Wnt/β-catenin signaling pathway promoted chondrocyte senescence, through downregulation of SIRT-1 and increased the expression of acetylated p53.

Therapeutic potential of enhancer of zeste homolog 2 in autoimmune diseases

Introduction: Autoimmune diseases (ADs) are idiopathic and heterogeneous disorders with contentious pathophysiology. Great strides have been made in epigenetics and its involvement in ADs. Zeste homolog 2 (EZH2) has sparked extensive interest because of its pleiotropic roles in distinct pathologic contexts.Areas covered: This review summarizes the epigenetic functions and the biological significance of EZH2 in the etiology of rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), type 1 diabetes (T1D), inflammatory bowel disease (IBD), multiple sclerosis (MS), and systemic sclerosis (SSc). A brief recapitulation of the therapeutic potential of EZH2 targeting is provided.Expert opinion: There are questions marks and controversies surrounding the feasibility and safety of EZH2 targeting; it is recommended in RA and SLE, but queried in T1D, IBD, MS, and SSc. Future work should focus on contrast studies, systematic analyses and preclinical studies with optimizing methodologies. Selective research studies conducted in a stage-dependent manner are necessary because of the relapsing-remitting clinical paradigms.

Conditional Activation of NF-κB Inducing Kinase (NIK) in the Osteolineage Enhances Both Basal and Loading-Induced Bone Formation

Studies from global loss-of-function mutants suggest that alternative NF-κB downstream of NF-κB inducing kinase (NIK) is a cell-intrinsic negative regulator of osteogenesis. However, the interpretation of the osteoblast and/or osteocyte contribution to the bone phenotype is complicated by simultaneous osteoclast defects in these models. Therefore, we turned to a transgenic mouse model to investigate the direct role of NIK in the osteolineage. Osx-Cre;NT3 animals (NT3-Cre +), which bear a constitutively active NIK allele (NT3) driven by Osx-Cre, were compared with their Cre-negative, Control (Ctrl) littermates. NT3-Cre + mice had elevated serum P1NP and CTX levels. Despite this high turnover state, µCT showed that constitutive activation of NIK resulted in a net increase in basal bone mass in both cortical and cancellous compartments. Furthermore, NT3-Cre + mice exhibited a greater anabolic response following mechanical loading compared with controls. We next performed RNA-Seq on nonloaded and loaded tibias to elucidate possible mechanisms underlying the increased bone anabolism seen in NT3-Cre + mice. Hierarchical clustering revealed two main transcriptional programs: one loading-responsive and the other NT3 transgene-driven. Gene ontology (GO) analysis indicated a distinct upregulation of receptor, kinase, and growth factor activities including Wnts, as well as a calcium-response signature in NT3-Cre + limbs. The promoters of these GO-term associated genes, including many known to be bone-anabolic, were highly enriched for multiple κB recognition elements (κB-RE) relative to the background frequency in the genome. The loading response in NT3-Cre + mice substantially overlapped (>90%) with Ctrl. Surprisingly, control animals had 10-fold more DEGs in response to loading. However, most top DEGs shared between genotypes had a high incidence of multiple κB-RE in their promoters. Therefore, both transcriptional programs (loading-responsive and NT3 transgene-driven) are modulated by NF-κB. Our studies uncover a previously unrecognized role for NF-κB in the promotion of both basal and mechanically stimulated bone formation. © 2019 American Society for Bone and Mineral Research.

Inhibition of tumor necrosis factor-alpha (TNF-alpha) in patients with early rheumatoid arthritis results in acute changes of bone modulators

OBJECTIVE

Dicckopf-1 (Dkk-1) is a potent inhibitor of the Wnt canonical pathway. In rheumatoid arthritis (RA), Dkk-1 is upregulated by tumor necrosis factor-α (TNF). Certolizumab pegol (CMZ) is a biologic TNF-inhibitor (TNFi) effective in RA and slows radiographic progression. Data on the immediate effects (≤1-8 weeks) of TNFi on Wnt modulators are lacking. This study investigated the acute influence of TNFi treatment on Wnt modulators (Dkk-1 and sclerostin) and bone turnover markers (BTM), including intact N-terminal propeptide of collagen type I (PINP) and C-terminal telopeptide of type I collagen (CTX-I).

METHODS

This longitudinal, uncontrolled study involved female RA patients with inadequate response to conventional methotrexate who underwent treatment with CMZ. ESR, Dkk-1, sclerostin, BTM, parathyroid hormone (PTH), and 25OH-vitamin D levels were evaluated at baseline, week 1, week 4, and week 8. Radiographs of the hands and feet were obtained at baseline and the total and erosion scores were assessed using the Simple Erosion Narrowing Score method (SENS).

RESULTS

Seventeen patients were enrolled. Dkk-1 and CTX-I significantly decreased after one week of treatment with CMZ (-49.1 ± 17.1% and -25.0 ± 20.6%, respectively, p < 0.01), whereas PINP increased (+43.2 ± 31.5%, p < 0.01). These changes persisted at week 4 and 8.

CONCLUSIONS

Our study showed that TNF-alpha inhibition with CMZ promptly results in a rapid decline of serum Dkk-1 levels, alongside decreased bone resorption and increased bone formation.

Gene-gene interactions of the Wnt/β-catenin signaling pathway in knee osteoarthritis

This study was designed to investigate whether genetic polymorphisms of the Wnt/β-catenin signaling pathway and its interactions are involved in the development of knee osteoarthritis (KOA). Patients with KOA (n = 131) and healthy individuals (n = 190) with different ancestry from two Mexican populations (Mexico City and Guadalajara City) were analyzed. Twenty-five SNPs from thirteen genes (WISP1, DKK1, SOST, FRZB, LRP1, LRP4, LRP5, LRP6, GSKB, ADAMTS5, GDF5, FMN2 and COL11A1) involved in the Wnt/β-catenin signaling pathway were genotyped. Genetic and allelic frequencies and gene-gene interactions were performed for this study. After adjusting for age, sex, BMI and admixture, significant associations were found for five SNPs in Mexico City: LRP6 rs12314259 (G/G genotype OR 0.22, P = 0.029; and G allele OR 0.48, P = 0.022), SOST rs851054 (C/T genotype OR 0.42, P = 0.027; and T allele OR 0.62, P = 0.026), FMN2 rs986690 (G/A genotype OR 0.42, P = 0.034; and A allele OR 0.50, P = 0.015), FRZB rs409238 (A/G genotype, OR 2.41, P = 0.022), and COL11A1 rs2615977 (A/C genotype OR 2.39, P = 0.024); no associations for Guadalajara City were found. With respect to gene-gene interactions, the pairwise interactions of WISP1-COL11A1, COL11A1-FRZB, FRZB-SOST and WISP1-FMN2 make it possible to visualize the synergistic or antagonistic effect of their genotypes or alleles in both populations. These results suggest that gene-gene interactions in the Wnt/β-catenin signaling pathway play a role in the etiology of KOA.

Comparison of peripheral quantitative computed tomography forearm bone density versus DXA in rheumatoid arthritis patients and controls

Rheumatoid arthritis (RA) has been associated with osteoporosis. Quantitative computed tomography (QCT) is capable of assessing bone density and composition. We found lower bone density in RA compared to controls. Age and RA duration influenced bone density. QCT may be useful to assess bone metabolism in RA.

INTRODUCTION

RA is associated with generalized and periarticular osteoporosis. In addition to DXA that determines areal bone mineral density (BMD), peripheral QCT also detects volumetric BMD. QCT differentiates between total, trabecular, and cortical BMD. Here, we compared DXA and QCT in RA patients and healthy controls.

METHODS

BMD of 57 female RA patients and 32 age-matched healthy female controls were assessed by DXA. QCT of the forearm ultradistal region was also performed. Densitometry data were correlated with age, disease duration, disease activity, serum CRP, and anti-CCP levels.

RESULTS

Total bone density (310.4 ± 79.7 versus 354.0 ± 54.1 mg/cm³; p = 0.007) and attenuation (0.37 ± 0.05 versus 0.40 ± 0.03 1/cm; p = 0.001), trabecular density (157.6 ± 57.0 versus 193.8 ± 48.7 mg/cm³; p = 0.005) and attenuation (0.28 ± 0.03 versus 0.32 ± 0.04 1/cm; p < 0.0001), and cortical density (434.3 ± 115.8 versus 492.5 ± 64.0 mg/cm³; p = 0.006) and attenuation (0.44 ± 0.07 versus 0.47 ± 0.04 1/cm; p = 0.004) were significantly lower in RA. Both lumbar and femoral neck BMD, as well as T-scores, were significantly lower in RA versus controls (p < 0.001 in all cases). In RA, total and cortical QCT attenuation and density were associated with age, the presence of RA, and their combination. In contrast, trabecular density and attenuation were only affected by the presence of the disease but not by age. Also in RA, total trabecular and cortical density as determined by QCT significantly correlated with lumbar and/or femoral neck BMD as measured by DXA. Finally, anti-CCP seropositivity was associated with lower trabecular density and attenuation.

CONCLUSIONS

Both DXA and QCT may be suitable to study bone metabolism in RA. Areal BMD determined by DXA may correlate with volumetric bone density measured by QCT. Moreover, trabecular osteoporosis may be associated by the underlying autoimmune-inflammatory disease, while cortical osteoporosis may rather be age-related.

Synovium-Derived MicroRNAs Regulate Bone Pathways in Rheumatoid Arthritis

Articular bone erosion in rheumatoid arthritis (RA) is mediated by the interaction between inflammation and pathways regulating bone metabolism. Inflammation promotes osteoclastogenesis and also inhibits osteoblast function, further contributing to the persistence of erosions. MicroRNAs (miRNAs) are important regulators of skeletal remodeling and play a role in RA pathogenesis. We therefore determined the expression of miRNAs in inflamed synovial tissue and the role they play in pathways regulating osteoblast and osteoclast function. Using the serum transfer mouse model of RA in C57BL/6 mice, we performed Fluidigm high-throughput qPCR-based screening of miRNAs from nonarthritic and arthritic mice. Global gene expression profiling was also performed on Affymetrix microarrays from these same synovial samples. miRNA and mRNA expression profiles were subjected to comparative bioinformatics. A total of 536 upregulated genes and 417 downregulated genes were identified that are predicted targets of miRNAs with reciprocal expression changes. Gene ontology analysis of these genes revealed significant enrichment in skeletal pathways. Of the 22 miRNAs whose expression was most significantly changed (p < 0.01) between nonarthritic and arthritic mice, we identified their targets that both inhibit and promote bone formation. These miRNAs are predicted to target Wnt and BMP signaling pathway components. We validated miRNA array findings and demonstrated that secretion of miR-221-3p in exosomes was upregulated by synovial fibroblasts treated with the proinflammatory cytokine TNF. Overexpression of miR-221-3p suppressed calvarial osteoblast differentiation and mineralization in vitro. These results suggest that miRNAs derived from inflamed synovial tissues may regulate signaling pathways at erosion sites that affect bone loss and potentially also compensatory bone formation. © 2016 American Society for Bone and Mineral Research.

Correlation of blood bone turnover biomarkers and Wnt signaling antagonists with AS, DISH, OPLL, and OYL

Background

Wnt signaling plays an important role in development and maintenance of many organs and tissues. The most-studied secreted Wnt inhibitors are sclerostin (SOST), Dickkopf-related protein 1 (DKK-1), and secreted frizzled related protein 1 (SFRP-1) which play important roles in bone turnover. The present study investigated the relationship between serum Wnt inhibitors and diseases with excessive ossification structures, such as ossification of posterior longitudinal ligament (OPLL), ankylosing spondylitis (AS), diffuse idiopathic skeletal hyperostosis (DISH), and ossification of yellow ligament (OYL).

Methods

Twenty-five patients with AS, DISH, OPLL, or OYL were recruited in this study. Fasting peripheral blood samples were collected from all patients and nine controls. Various biomarkers of bone turnover including osteocalcin (OSC), osteoprotegerin (OPG), SFRP-1, DKK-1, and SOST were investigated.

Results

Our data showed that serum levels of OSC were higher, but Dkk-1 levels were lower in AS, DISH, OPLL, and OYL patients than those in the controls. Serum levels of SFRP-1 were significantly higher in DISH patients than those in the controls. Serum levels of SOST were significantly higher in DISH and OPLL patients than both levels in the controls. Serum levels of OPG were lower in AS patients than those in the controls. Serum levels of OSC were higher in the OPLL patients than those in the AS patients. Serum levels of DKK-1, SFRP-1, SOST, and OPG were not significantly different between the different disease groups.

Conclusions

In this exploratory study, both OSC and DKK-1 levels are correlated with the clinical conditions associated with excessive ossification, indicating that blood OSC and DKK-1 levels may serve as diagnostic biomarkers for AS, DISH, OPLL, and OYL. These findings may also help discover potential drug therapies for management of these diseases in the future.

Emerging Role and Therapeutic Implication of Wnt Signaling Pathways in Autoimmune Diseases

The Wnt signaling pathway plays a key role in many biological aspects, such as cellular proliferation, tissue regeneration, embryonic development, and other systemic effects. Under a physiological condition, it is tightly controlled at different layers and arrays, and a dysregulated activation of this signaling has been implicated into the pathogenesis of various human disorders, including autoimmune diseases. Despite the fact that therapeutic interventions are available for ameliorating disease manifestations, there is no curative therapy currently available for autoimmune disorders. Increasing lines of evidence have suggested a crucial role of Wnt signaling during the pathogenesis of many autoimmune diseases; in addition, some of microRNAs (miRNAs), a class of small, noncoding RNA molecules capable of transcriptionally regulating gene expression, have also recently been demonstrated to possess both physiological and pathological roles in autoimmune diseases by regulating the Wnt signaling pathway. This review summarizes currently our understanding of the pathogenic roles of Wnt signaling in several major autoimmune disorders and miRNAs, those targeting Wnt signaling in autoimmune diseases, with a focus on the implication of the Wnt signaling as potential biomarkers and therapeutic targets in immune diseases, as well as miRNA-mediated regulation of Wnt signaling activation in the development of autoimmune diseases.

Characterization of genetically engineered mouse models carrying Col2a1-cre-induced deletions of Lrp5 and/or Lrp6

Mice carrying Collagen2a1-cre-mediated deletions of Lrp5 and/or Lrp6 were created and characterized. Mice lacking either gene alone were viable and fertile with normal knee morphology. Mice in which both Lrp5 and Lrp6 were conditionally ablated via Collagen2a1-cre-mediated deletion displayed severe defects in skeletal development during embryogenesis. In addition, adult mice carrying Collagen2a1-cre-mediated deletions of Lrp5 and/or Lrp6 displayed low bone mass suggesting that the Collagen2a1-cre transgene was active in cells that subsequently differentiated into osteoblasts. In both embryonic skeletal development and establishment of adult bone mass, Lrp5 and Lrp6 carry out redundant functions.

Wnt/β-catenin signaling plays a key role in the development of spondyloarthritis

Spondyloarthritis (SpA) is a group of diseases consisting of psoriatic arthritis (PsA), reactive arthritis, arthritis related to inflammatory bowel disease (a subgroup of juvenile idiopathic arthritis), and ankylosing spondylitis (the prototype of SpA). Axial bone formation and the combination of concurrent erosion and new bone formation are specific characteristics of SpA disease. The use of antiproinflammatory cytokines, such as inhibitors of tumor necrosis factor α (TNF-α), appears to be the greatest advance in the treatment of SpA over the past 20 years. However, TNF-α blockers do not halt new bone formation. Recent clinical observations and animal studies demonstrate that Wnt signaling proteins and natural Wnt inhibitors, such as DKK1 and sclerostin, are likely to play important roles in the process of ankylosis in SpA, and could potentially serve as therapeutic targets for the treatment of SpA.

Polymorphic variation of hypoxia inducible factor-1 A (HIF1A) gene might contribute to the development of knee osteoarthritis: a pilot study

Background

Osteoarthritis (OA) is a multifactorial degenerative condition of the whole joint with a complex pathogenesis whose development and progression is significantly mediated by interactions between the joint cartilage and articular tissues, particularly, proinflammatory mediators and oxidative stress, which results in cartilage deterioration and subchondral bone destruction. HIF-1 alpha regulates oxygen homeostasis in hypoxic tissues such as joint cartilage; efficiency of transcriptional activity of the HIF1A gene is strongly influenced by the presence of polymorphic variants. Given the loss of articular cartilage and with intention to restore damaged tissue, WISP-1 participates in the development of subchondral bone; further, its expression is highly increased in chondrocytes of OA patients. The aim of this study was to evaluate gene frequencies of HIF1A and WISP1 polymorphisms in Mexican patients suffering from knee OA.

Methods

We determined HIF1A rs11549465 (P582S), rs11549467 (A588T), and rs2057482 (C191T), and WISP1 rs2929970 (A2364G) polymorphisms in 70 Mexican patients with knee OA and compare them to those present in 66 ethnically matched healthy controls. Genotyping for these polymorphisms was performed by Real-Time PCR using TaqMan probes.

Results

Gene frequencies exhibited a significant increase of the CC genotype of rs11549465 polymorphism in knee OA patients as compared with those present in controls (P = 0.003 OR = 5.7, 95 % CI = 1.7–21.6); CT genotype and T allele showed decreased frequency in the knee OA group vs. the controls (P = 0.003 OR = 0.2, CI = 0.05–0.6; and P = 0.004 OR = 0.2, CI = 0.05–0.65, respectively). Allele frequencies of the other polymorphic variants were similar in both patients and controls.

Conclusions

These results suggest that the presence of the rs11549465 SNP (HIF1A) plays a role protective in the loss of articular cartilage in our population, and offers the possibility to further study the molecular mechanisms within cartilage and subchondral bone.

Electronic supplementary material

The online version of this article (doi:10.1186/s12891-015-0678-z) contains supplementary material, which is available to authorized users.

Chronic Periodontitis Is Associated With Spinal Dysmobility in Patients With Ankylosing Spondylitis

BACKGROUND

Although microbes have been suggested to play a role in the pathogenesis of ankylosing spondylitis (AS), several studies present contradictory results regarding the association between AS and chronic periodontitis (CP).

METHODS

Clinical, laboratory, and medication data were collected from 84 patients with AS and 84 age- and sex-matched controls. Periodontal measurements, including probing depths (PDs), clinical attachment loss (AL), serum anti-Porphyromonas gingivalis titers, and the detection of P. gingivalis DNA in gingival crevicular fluid, were recorded. All participants with periodontitis with PD ≥4 to <7 mm received scaling and root planing and were re-evaluated at 12 weeks; those still exhibiting periodontitis with PD of ≥4 to <7 mm at 12 weeks were followed at 24 weeks.

RESULTS

The prevalence of moderate-to-severe CP was not different between patients with AS and controls (70.2% versus 66.6%). The P. gingivalis detection rate was not different between patients with AS and controls or between patients with AS receiving and not receiving anti-tumor necrosis factor (TNF)-α agents. However, CP was positively associated with impaired spinal mobility of patients with AS in multivariate analyses. After periodontal treatment, PD and AL levels were improved in both groups, but the change was significantly greater in patients with AS than in controls. Patients with AS receiving anti-TNF-α agents exhibited a greater improvement in PD and AL than those who did not.

CONCLUSIONS

Although AS was not associated with the presence of CP, CP was associated positively with the severity of spinal dysmobility in Korean patients with AS. These results suggest that periodontitis can have a negative effect on axial movement in AS.

Agrin mediates chondrocyte homeostasis and requires both LRP4 and α-dystroglycan to enhance cartilage formation in vitro and in vivo

Objectives

Osteoarthritis (OA) is a leading cause of disability for which there is no cure. The identification of molecules supporting cartilage homeostasis and regeneration is therefore a major pursuit in musculoskeletal medicine. Agrin is a heparan sulfate proteoglycan which, through binding to low-density lipoprotein receptor-related protein 4 (LRP4), is required for neuromuscular synapse formation. In other tissues, it connects the cytoskeleton to the basement membrane through binding to α-dystroglycan. Prompted by an unexpected expression pattern, we investigated the role and receptor usage of agrin in cartilage.

Methods

Agrin expression pattern was investigated in human osteoarthritic cartilage and following destabilisation of the medial meniscus in mice. Extracellular matrix (ECM) formation and chondrocyte differentiation was studied in gain and loss of function experiments in vitro in three-dimensional cultures and gain of function in vivo, using an ectopic cartilage formation assay in nude mice. Receptor usage was investigated by disrupting LRP4 and α-dystroglycan by siRNA and blocking antibodies respectively.

Results

Agrin was detected in normal cartilage but was progressively lost in OA. In vitro, agrin knockdown resulted in reduced glycosaminoglycan content, downregulation of the cartilage transcription factor SOX9 and other cartilage-specific ECM molecules. Conversely, exogenous agrin supported cartilage differentiation in vitro and ectopic cartilage formation in vivo. In the context of cartilage differentiation, agrin used an unusual receptor repertoire requiring both LRP4 and α-dystroglycan.

Conclusions

We have discovered that agrin strongly promotes chondrocyte differentiation and cartilage formation in vivo. Our results identify agrin as a novel potent anabolic growth factor with strong therapeutic potential in cartilage regeneration.

MicroRNA-663 activates the canonical Wnt signaling through the adenomatous polyposis coli suppression

Rheumatoid arthritis (RA) is a symmetrical polyarticular autoimmune disease of unknown etiology. In this present study, we observed that the adenomatous polyposis coli (APC) expression is down-regulated and the expression of microRNA (miR)-663 increased significantly in synovium from RA patients compared with control. Target gene prediction for miR-663 revealed that the mRNA of APC gene, which is a member of the canonical Wnt signaling pathway, has a miR-663 binding site in its 3'-untranslated region (3'UTR). The result showed that increased miR-663 suppressed the APC expression significantly, and this down-regulation of APC expression triggered the activation of canonical Wnt signaling through accumulation of β-catenin in fibroblast-like synoviocytes (FLS). In addition, increased miR-663 induced the FLS proliferation and the expression MMP3 and fibronectin during disease development. Therefore, miR-663 can be considered as a critical regulator of RA pathogenesis and can be utilized for developing miRNA-based therapeutic agents for RA patients.

Kinetics of gene expression and bone remodelling in the clinical phase of collagen-induced arthritis

Introduction

Pathological bone changes differ considerably between inflammatory arthritic diseases and most studies have focused on bone erosion. Collagen-induced arthritis (CIA) is a model for rheumatoid arthritis, which, in addition to bone erosion, demonstrates bone formation at the time of clinical manifestations. The objective of this study was to use this model to characterise the histological and molecular changes in bone remodelling, and relate these to the clinical disease development.

Methods

A histological and gene expression profiling time-course study on bone remodelling in CIA was linked to onset of clinical symptoms. Global gene expression was studied with a gene chip array system.

Results

The main histopathological changes in bone structure and inflammation occurred during the first two weeks following the onset of clinical symptoms in the joint. Hereafter, the inflammation declined and remodelling of formed bone dominated.

Global gene expression profiling showed simultaneous upregulation of genes related to bone changes and inflammation in week 0 to 2 after onset of clinical disease. Furthermore, we observed time-dependent expression of genes involved in early and late osteoblast differentiation and function, which mirrored the histopathological bone changes. The differentially expressed genes belong to the bone morphogenetic pathway (BMP) and, in addition, include the osteoblast markers integrin-binding sialoprotein (Ibsp), bone gamma-carboxyglutamate protein (Bglap1), and secreted phosphoprotein 1 (Spp1). Pregnancy-associated protein A (Pappa) and periostin (Postn), differentially expressed in the early disease phase, are proposed to participate in bone formation, and we suggest that they play a role in early bone formation in the CIA model. Comparison to human genome-wide association studies (GWAS) revealed differential expression of several genes associated with human arthritis.

Conclusions

In the CIA model, bone formation in the joint starts shortly after onset of clinical symptoms, which results in bony fusion within one to two weeks. This makes it a candidate model for investigating the relationship between inflammation and bone formation in inflammatory arthritis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0531-7) contains supplementary material, which is available to authorized users.

A possible mechanism in DHEA-mediated protection against osteoarthritis

Dehydroepiandrosterone (DHEA) and its ester form, DHEA-S, are the most abundant steroids in human plasma. Our previous studies showed that DHEA protects against osteoarthritis (OA). The aim of this paper was to explore the possible mechanisms that underlie DHEA-mediated protection against OA. We tested the expression of β-catenin, it was increased significantly in OA. Rabbit cartilage was treated with various concentrations of DHEA in both IL-1β-induced rabbit chondrocytes and in rabbit cartilage from the anterior cruciate ligament transaction-induced OA model. We found DHEA decreased the expression of β-catenin. Then we further activated Wnt/β-catenin signaling by β-catenin transfection and inactivated it by the inhibitor Dickkopf1 in chondrocytes to reveal its role in the pathogenesis of OA. It turns out the protective effect of DHEA was significantly decreased when Wnt/β-catenin signaling was activated, while inactivating Wnt/β-catenin signaling enhanced the effects of DHEA. Therefore, we hypothesize that DHEA probably exerted its chondroprotective effect by regulating Wnt/β-catenin signaling. Our findings demonstrate the critical role of Wnt/β-catenin signaling in DHEA-mediated protection against OA.

Differentiation between osteoarthritis and psoriatic arthritis: implications for pathogenesis and treatment in the biologic therapy era

Rheumatologists have long considered OA and PsA as two completely distinct arthropathies. This review highlights how some forms of generalized OA and PsA may afflict the same entheseal-associated anatomical territories. While degeneration or inflammation may be clearly discernible at the two extremes, there may be a group of patients where differentiation is impossible. Misdiagnosis of a primary degeneration-related pathology as being part of the PsA spectrum could lead to apparent failure of disease-modifying agents, including apparent anti-TNF and apparent IL23/17 axis therapy failure. This is not a reflection of poor clinical acumen, but rather a failure to appreciate that the pathological process overlaps in the two diseases. Whether the category of OA-PsA overlap disease exists or whether it represents the co-occurrence of two common arthropathies that afflict the same anatomical territories has implications for the optimal diagnosis and management of both OA and PsA.

Childhood abuse is associated with methylation of multiple loci in adult DNA

Background

Childhood abuse is associated with increased adult disease risk, suggesting that processes acting over the long-term, such as epigenetic regulation of gene activity, may be involved. DNA methylation is a critical mechanism in epigenetic regulation. We aimed to establish whether childhood abuse was associated with adult DNA methylation profiles.

Methods

In 40 males from the 1958 British Birth Cohort we compared genome-wide promoter DNA methylation in blood taken at 45y for those with, versus those without, childhood abuse (n = 12 vs 28). We analysed the promoter methylation of over 20,000 genes and 489 microRNAs, using MeDIP (methylated DNA immunoprecipitation) in triplicate.

Results

We found 997 differentially methylated gene promoters (311 hypermethylated and 686 hypomethylated) in association with childhood abuse and these promoters were enriched for genes involved in key cell signaling pathways related to transcriptional regulation and development. Using bisulfite-pyrosequencing, abuse-associated methylation (MeDIP) at the metalloproteinase gene, PM20D1, was validated and then replicated in an additional 27 males. Abuse-associated methylation was observed in 39 microRNAs; in 6 of these, the hypermethylated state was consistent with the hypomethylation of their downstream gene targets. Although distributed across the genome, the differentially methylated promoters associated with child abuse clustered in genome regions of at least one megabase. The observations for child abuse showed little overlap with methylation patterns associated with socioeconomic position.

Conclusions

Our observed genome-wide methylation profiles in adult DNA associated with childhood abuse justify the further exploration of epigenetic regulation as a mediating mechanism for long-term health outcomes.

Pustulotic arthro-osteitis associated with palmoplantar pustulosis

Palmoplantar pustulosis (PPP) is a chronic inflammatory disorder characterized by sterile pustules predominantly involving the palms and soles of middle-aged women. PPP frequently develops or exacerbates following focal infections, such as tonsillitis, odontogenic infection and sinusitis, either with or without arthralgia and/or extra-palmoplantar lesions. Pustulotic arthro-osteitis (PAO) is a joint comorbidity of PPP, most often affecting the anterior chest wall. PAO is sometimes regarded as the same entity as synovitis, acne, pustulosis, hyperostosis and osteitis (SAPHO) syndrome, and may be a subtype or incomplete type of SAPHO syndrome; however, there are several differences. In Japanese patients, PPP with PAO is frequently seen, whereas SAPHO syndrome in the true meaning is rare. A difference of incidence depending on race suggests that different genetic backgrounds may be responsible for susceptibility to these disorders. Bacterial infection, especially Propionibacterium acnes, is suggested to play an important role in the pathogenesis of SAPHO syndrome. P. acnes is responsible for acne, however, bacterium is unassociated with PPP skin lesions which are characterized by sterile pustules. On the other hand, PAO is frequently triggered by focal infection, and treatment of focal infection results in dramatic effects on the release of joint pain. This paper reviews current insights into the clinicopathophysiology of PAO, and discusses its possible mechanisms in comparison with SAPHO syndrome.

Regulation of lubricin/superficial zone protein by Wnt signalling in bovine synoviocytes

Lubricin, homologous to superficial zone protein (SZP), functions as a boundary lubricant in articular cartilage and plays an essential role in the maintenance of joint function and homeostasis. Wnt signalling plays a key role in joint development, including synovial joint formation, and several Wnt proteins are expressed in the synovium and articular cartilage in arthritis. The aim of this study was to determine the role of Wnt signalling on SZP accumulation in synoviocytes. Isolated synoviocytes from bovine knee joints were cultured with Wnt proteins (Wnt-3a and Wnt-5a) and antagonists or agonists of the Wnt-β-catenin pathway or Wnt-Ca(2+) pathway in serum-free chemically defined medium. SZP accumulation in the culture medium was determined by enzyme-linked immunosorbent assay. Wnt-3a suppressed SZP accumulation via a Wnt-β-catenin-dependent pathway. In contrast, Wnt-5a stimulated SZP accumulation via a β-catenin independent pathway. The present investigation provides novel insights into the role of the Wnt signalling pathways in SZP accumulation in synoviocytes and their roles in the homeostasis of normal joints.

Hand Bone Loss in Patients with Psoriatic Arthritis: Posthoc Analysis of IMPACT II Data Comparing Infliximab and Placebo

Objective.

In rheumatoid arthritis (RA), anti-tumor necrosis factor (anti-TNF) treatment is shown to reduce but not to arrest the rate of hand bone loss. This has not been assessed in psoriatic arthritis (PsA). Our objective was to examine changes in cortical hand bone density in patients with PsA treated with placebo or infliximab (IFX).

Methods.

Patients in IMPACT II (Induction and Maintenance Psoriatic Arthritis Clinical Trial 2) were randomized to placebo or IFX. After Week 24, all received IFX. In a subset of 120 patients, cortical hand bone density was assessed at Weeks 0, 24, and 54 by digital X-ray radiogrammetry (dxr-BMD) on the same radiographs scored for joint damage.

Results.

Changes from baseline to 24 weeks in dxr-BMD were −0.30% (SD 1.1%) in the placebo group and −0.08% (SD 1.4%) in the IFX group (p = 0.63). Between baseline and 54 weeks the changes were −0.71% (SD 2.1%) in the placebo group and 0.15% (SD 1.7%) in the IFX group (p = 0.07), and between 24 and 54 weeks −0.41% (SD 1.4%) and 0.23% (SD 0.8%), respectively (p = 0.05). No significant correlation was found between change in dxr-BMD and radiographic damage.

Conclusion.

This pilot study indicates that hand bone loss in PsA patients treated with anti-TNF can be arrested. Assessment of hand bone density may thus be a potential outcome measure for bone involvement and a response variable to treatment in PsA.

Sclerostin is expressed in articular cartilage but loss or inhibition does not affect cartilage remodeling during aging or following mechanical injury

OBJECTIVE

Sclerostin plays a major role in regulating skeletal bone mass, but its effects in articular cartilage are not known. The purpose of this study was to determine whether genetic loss or pharmacologic inhibition of sclerostin has an impact on knee joint articular cartilage.

METHODS

Expression of sclerostin was determined in articular cartilage and bone tissue obtained from mice, rats, and human subjects, including patients with knee osteoarthritis (OA). Mice with genetic knockout (KO) of sclerostin and pharmacologic inhibition of sclerostin with a sclerostin-neutralizing monoclonal antibody (Scl-Ab) in aged male rats and ovariectomized (OVX) female rats were used to study the effects of sclerostin on pathologic processes in the knee joint. The rat medial meniscus tear (MMT) model of OA was used to investigate the pharmacologic efficacy of systemic Scl-Ab or intraarticular (IA) delivery of a sclerostin antibody-Fab (Scl-Fab) fragment.

RESULTS

Sclerostin expression was detected in rodent and human articular chondrocytes. No difference was observed in the magnitude or distribution of sclerostin expression between normal and OA cartilage or bone. Sclerostin-KO mice showed no difference in histopathologic features of the knee joint compared to age-matched wild-type mice. Pharmacologic treatment of intact aged male rats or OVX female rats with Scl-Ab had no effect on morphologic characteristics of the articular cartilage. In the rat MMT model, pharmacologic treatment of animals with either systemic Scl-Ab or IA injection of Scl-Fab had no effect on lesion development or severity.

CONCLUSION

Genetic absence of sclerostin does not alter the normal development of age-dependent OA in mice, and pharmacologic inhibition of sclerostin with Scl-Ab has no impact on articular cartilage remodeling in rats with posttraumatic OA.

Tetrandrine Inhibits the Wnt/ β -Catenin Signalling Pathway and Alleviates Osteoarthritis: An In Vitro and In Vivo Study

There is currently no effective drug treatment for the early phase of osteoarthritis (OA), one of the most common senile diseases. The goal of this study was to investigate the protective effect of the tetrandrine (Tet) on OA, in vitro and in vivo. In an in vitro experiment, quantitative real-time polymerase chain reaction (qRT-PCR) was used to investigate changes in gene expression upon the addition of Tet in chondrocytes processed with IL-1β; changes in protein profiles were assessed by Western blotting. In vivo, to determine whether Tet has the protective effects on articular cartilage, a rabbit anterior cruciate ligament transaction model of OA was established. Expression of matrix metalloproteinase and β-catenin genes increased significantly, while that of tissue inhibitor of metalloproteinase-1 decreased significantly in the OA group both in vivo and in chondrocytes. However, the changes of expression were reversed by Tet, and there was less cartilage degradation in vivo compared with the OA group, as assessed by histological and macroscopic observations. Thus, Tet may play a useful role in the treatment of OA through the Wnt/β-catenin signalling pathway and has potential for the treatment of OA.

MeCP2 modulates the canonical Wnt pathway activation by targeting SFRP4 in rheumatoid arthritis fibroblast-like synoviocytes in rats

Rheumatoid arthritis (RA) is an autoimmune disease characterized by the rheumatoid factor and anti-citrullinated peptide antibody (ACPA) against common autoantigens that are widely expressed within and outside the joints. Many factors participate in the pathogenesis of RA, such as cytokine imbalance, Wnt pathway activation, matrix production, and osteoprotegerin on osteoclasts. Fibroblast-like synoviocytes (FLS) activation has an important role in RA pathogenesis. The methyl-CpG-binding protein (MeCP2) which promoted repressed chromatin structure was selectively detected in synovium of diseased articular in rats. Overexpression of this protein results in an up-regulation of global methylation levels and transcriptional suppression of specific genes. There were increased MeCP2 and decreased secreted frizzled-related protein 4 (SFRP4) in synovium as well as the FLS isolated from the synovium of RA rats. Knockdown of MeCP2 using siRNA technique enhanced SFRP4 expression in both mRNA and protein levels in FLS. These results indicated that epigenetic modification was involved in differential expression of SFRP4. To further explore the underlying molecular mechanisms, we hypothesized that the SFRP4 down-regulation in synovium was caused by DNA methylation. Treatment of FLS with DNA methylation inhibitor 5-Aza-2'-deoxycytidine (5-azadC) blocked the cell proliferation and increased the SFRP4 expression. Increased SFRP4 down-regulated the key gene β-catenin, the downstream effectors gene ccnd1 and fibronectin expression in canonical Wnt pathway at the same time. MeCP2 and DNA methylation may provide molecular mechanisms for canonical Wnt pathway activation in RA. Combination of 5-azadC and MeCP2 may be a promising treatment strategy for individuals with RA in which SFRP4 is inactivated.

Biomarkers and cytokines of bone turnover: extensive evaluation in a cohort of patients with ankylosing spondylitis

Background

Ankylosing spondylitis (AS) is a chronic inflammatory disease of spine and sacroiliac joints; it is characterized by new bone formation, and the disease processes can be accompanied by osteoporosis. In the present study, we investigated changes in bone mineral density (BMD) and in the levels of various bone turnover-related biomarkers and cytokines in a cohort of AS patients, with regard to clinical parameters, disease activity, and treatment regimen.

Methods

55 AS patients and 33 healthy controls included in the study. Spinal mobility was assessed by the Bath Ankylosing Spondylitis Metrology Index (BASMI), and radiologic changes were scored by the Bath Ankylosing Spondylitis Radiologic Index (BASRI). Patients were also evaluated with the Bath Ankylosing Spondylitis Functional Index (BASFI) and the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI). Bone mineral density (BMD) assessed by dual energy X-ray absorptiometry. Various biomarkers and cytokines of bone turnover including osteoprotegerin (OPG), serum band 5 tartrate-resistant acid phosphatase (TRAP-5), soluble receptor activator of nuclear factor kappa-B ligand (sRANKL), secreted frizzled-related protein 1 (sFRP-1), Dickkopf-related protein 1 (DKK-1), and sclerostin were studied.

Results

The levels of TRAP-5, NTX, sRANKL, sclerostin, sFRP-1, DKK-1, and IFNγ, were similar between the patients and controls (p > 0.05), while BMD of femoral neck, and OPG levels were significantly lower in AS patients (p < 0.05). In a subgroup analysis, patients with active disease had significantly higher concentrations of OPG compared with the inactive group. Rest of the biomarkers and cytokines of bone turnover were similar between the active and inactive disease groups. Subgroup analysis of patients receiving anti-TNFα agents and conventional therapy revealed that OPG concentrations were significantly lower in the patients receiving biological drugs, while BAP and DKK-1 were significantly higher in the patients treated with conventional agents.

Conclusions

In this cross-sectional study we showed that OPG levels were significantly lower in AS patients compared to healthy subjects. On the other hand, the levels of wingless (Wnt) signal pathway inhibitors seem not altered. Ectopic bone formation in AS may be related to dysfunction of these molecules at the cellular level.

Sclerostin and Dickkopf-1 as therapeutic targets in bone diseases

The processes of bone growth, modeling, and remodeling determine the structure, mass, and biomechanical properties of the skeleton. Dysregulated bone resorption or bone formation may lead to metabolic bone diseases. The Wnt pathway plays an important role in bone formation and regeneration, and expression of two Wnt pathway inhibitors, sclerostin and Dickkopf-1 (DKK1), appears to be associated with changes in bone mass. Inactivation of sclerostin leads to substantially increased bone mass in humans and in genetically manipulated animals. Studies in various animal models of bone disease have shown that inhibition of sclerostin using a monoclonal antibody (Scl-Ab) increases bone formation, density, and strength. Additional studies show that Scl-Ab improves bone healing in models of bone repair. Inhibition of DKK1 by monoclonal antibody (DKK1-Ab) stimulates bone formation in younger animals and to a lesser extent in adult animals and enhances fracture healing. Thus, sclerostin and DKK1 are emerging as the leading new targets for anabolic therapies to treat bone diseases such as osteoporosis and for bone repair. Clinical trials are ongoing to evaluate the effects of Scl-Ab and DKK1-Ab in humans for the treatment of bone loss and for bone repair.

Perspectives of pharmacological treatment in otosclerosis

To review our current knowledge of the pathologic bone metabolism in otosclerosis and to discuss the possibilities of non-surgical, pharmacological intervention. Otosclerosis has been suspected to be associated with defective measles virus infection, local inflammation and consecutive bone deterioration in the human otic capsule. In the early stages of otosclerosis, different pharmacological agents may delay the progression or prevent further deterioration of the disease and consecutive hearing loss. Although effective anti-osteoporotic drugs have become available, the use of sodium fluoride and bisphosphonates in otosclerosis has not yet been successful. Bioflavonoids may relieve tinnitus due to otosclerosis, but there is no data available on long-term application and effects on sensorineural hearing loss. In the initial inflammatory phase, corticosteroids or non-steroidal anti-inflammatory drugs may be effective; however, extended systemic application may lead to serious side effects. Vitamin D administration may have effects on the pathological bone loss, as well as on inflammation. No information has been reported on the use of immunosuppressive drugs. Anti-cytokine targeted biological therapy, however, may be feasible. Indeed, one study on the local administration of infliximab has been reported. Potential targets of future therapy may include osteoprotegerin, RANK ligand, cathepsins and also the Wnt-β-catenin pathway. Finally, anti-measles vaccination may delay the progression of the disease and potentially decrease the number of new cases. In conclusion, stapes surgery remains to be widely accepted treatment of conductive hearing loss due to otosclerosis. Due to lack of solid evidence, the place of pharmacological treatment targeting inflammation and bone metabolism needs to be determined by future studies.

Adalimumab significantly reduces inflammation and serum DKK-1 level but increases fatty deposition in lumbar spine in active ankylosing spondylitis

AIM

To investigate whether adalimumab is effective for active ankylosing spondylitis (AS) patients and whether it has an impact on the formation of fatty deposition lesions (FDL) and serum Dickkopf homolog 1 (Dkk-1) level in AS patients.

METHOD

This was a randomized, double-blind, placebo-controlled study. Active AS patients received 40 mg adalimumab (n = 26) or placebo (n = 20) every other week during an initial 12-week double-blind period, and all switched to adalimumab treatment for another 12 weeks. Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Bath Ankylosing Spondylitis Function Index (BASFI), C-reactive protein (CRP), Ankylosing Spondylitis Disease Activity Scores (ASDAS) and serum DKK-1 levels were measured and magnetic resonance imaging (MRI) of both the lumbar spine and sacroiliac joints were obtained at baseline, week 12 and week 24. Spinal and sacroiliac joint inflammations were evaluated using the Spondyloarthritis Research Consortium of Canada (SPARCC) MRI index, and FDL were assessed in a dichotomous manner.

RESULTS

Obvious improvements in clinical assessments (BASDAI, BASFI, CRP and ASDAS reduced, all P < 0.05), as well as MRI inflammation measurements (both lumbar spine and sacroiliac joints SPARCC scores decreased, all P < 0.05) were shown in active AS patients treated by adalimumab for 12 weeks, but FDL in the lumbar spine seen by MRI increased significantly (P < 0.05) accompanied by decrease of serum DKK-1 levels (P < 0.05), while FDL remained stable after the treatment of placebo in AS patients.

CONCLUSION

Our study found that adalimumab was highly effective in reducing inflammation in active AS patients, but it was accompanied by the formation of FDL in the lumbar spine and decrease in serum DKK-1 levels.

Articular cartilage development: a molecular perspective

In this article, development of articular cartilage and endochondral ossification is reviewed, from the perspective of both morphologic aspects of histogenesis and molecular biology, particularly with respect to key signaling molecules and extracellular matrix components most active in cartilage development. The current understanding of the roles of transforming growth factor β and associated signaling molecules, bone morphogenic proteins, and molecules of the Wnt-β catenin system in chondrogenesis are described. Articular cartilage development is a highly conserved complex biological process that is dynamic and robust in nature, which proceeds well without incident or failure in all joints of most young growing individuals.

Activation of canonical Wnt signalling is required for TGF-β-mediated fibrosis

The transforming growth factor-β (TGF-β) signalling pathway is a key mediator of fibroblast activation that drives the aberrant synthesis of extracellular matrix in fibrotic diseases. Here we demonstrate a novel link between transforming growth factor-β and the canonical Wnt pathway. TGF-β stimulates canonical Wnt signalling in a p38-dependent manner by decreasing the expression of the Wnt antagonist Dickkopf-1. Tissue samples from human fibrotic diseases show enhanced expression of Wnt proteins and decreased expression of Dickkopf-1. Activation of the canonical Wnt pathway stimulates fibroblasts in vitro and induces fibrosis in vivo. Transgenic overexpression of Dickkopf-1 ameliorates skin fibrosis induced by constitutively active TGF-β receptor type I signalling and also prevents fibrosis in other TGF-β-dependent animal models. These findings demonstrate that canonical Wnt signalling is necessary for TGF-β-mediated fibrosis and highlight a key role for the interaction of both pathways in the pathogenesis of fibrotic diseases.

Aberrant activation of the TGF-β pathway leads to fibrotic disease. Distler and colleagues show that TGF-β-mediated fibrosis requires the decrease of Dickkopf-1, an antagonist of canonical Wnt signalling, suggesting that the two pathways interact for the manifestation of this disease.

Wnt5a-Ror2 signaling between osteoblast-lineage cells and osteoclast precursors enhances osteoclastogenesis

The signaling molecule Wnt regulates bone homeostasis through β-catenin-dependent canonical and β-catenin-independent noncanonical pathways. Impairment of canonical Wnt signaling causes bone loss in arthritis and osteoporosis; however, it is unclear how noncanonical Wnt signaling regulates bone resorption. Wnt5a activates noncanonical Wnt signaling through receptor tyrosine kinase-like orphan receptor (Ror) proteins. We showed that Wnt5a-Ror2 signaling between osteoblast-lineage cells and osteoclast precursors enhanced osteoclastogenesis. Osteoblast-lineage cells expressed Wnt5a, whereas osteoclast precursors expressed Ror2. Mice deficient in either Wnt5a or Ror2, and those with either osteoclast precursor-specific Ror2 deficiency or osteoblast-lineage cell-specific Wnt5a deficiency showed impaired osteoclastogenesis. Wnt5a-Ror2 signals enhanced receptor activator of nuclear factor-κB (RANK) expression in osteoclast precursors by activating JNK and recruiting c-Jun on the promoter of the gene encoding RANK, thereby enhancing RANK ligand (RANKL)-induced osteoclastogenesis. A soluble form of Ror2 acted as a decoy receptor of Wnt5a and abrogated bone destruction in mouse arthritis models. Our results suggest that the Wnt5a-Ror2 pathway is crucial for osteoclastogenesis in physiological and pathological environments and represents a therapeutic target for bone diseases, including arthritis.

β-catenin is a central mediator of pro-fibrotic Wnt signaling in systemic sclerosis

OBJECTIVES

Pathologic fibroblast activation drives fibrosis of the skin and internal organs in patients with systemic sclerosis (SSc). β-catenin is an integral part of adherens junctions and a central component of canonical Wnt signaling. Here, the authors addressed the role of β-catenin in fibroblasts for the development of SSc dermal fibrosis.

METHODS

Nuclear accumulation of β-catenin in fibroblasts was assessed by triple staining for β-catenin, prolyl-4-hydroxylase-β and 4',6-diamidino-2-phenylindole (DAPI). The expression of Wnt proteins in the skin was analysed by real-time PCR and immunohistochemistry. Mice with fibroblast-specific stabilisation or fibroblast-specific depletion were used to evaluate the role of β-catenin in fibrosis.

RESULTS

The auhors found significantly increased nuclear levels of β-catenin in fibroblasts in SSc skin compared to fibroblasts in the skin of healthy individuals. The accumulation of β-catenin resulted from increased expression of Wnt-1 and Wnt-10b in SSc. The authors further showed that the nuclear accumulation of β-catenin has direct implications for the development of fibrosis: Mice with fibroblast-specific stabilisation of β-catenin rapidly developed fibrosis within 2 weeks with dermal thickening, accumulation of collagen and differentiation of resting fibroblasts into myofibroblasts. By contrast, fibroblast-specific deletion of β-catenin significantly reduced bleomycin-induced dermal fibrosis.

CONCLUSIONS

The present study findings identify β-catenin as a key player of fibroblast activation and tissue fibrosis in SSc. Although further translational studies are necessary to test the efficacy and tolerability of β-catenin/Wnt inhibition in SSc, the present findings may have clinical implications, because selective inhibitors of β-catenin/Wnt signaling have recently entered clinical trials.

Roles of β-catenin signaling in phenotypic expression and proliferation of articular cartilage superficial zone cells

The superficial zone (SFZ) of articular cartilage has unique structural and biomechanical features, is thought to promote self-renewal of articular cartilage, and is thus important for joint long-term function, but the mechanisms regulating its properties remain unclear. Previous studies revealed that Wnt/β-catenin signaling is continuously active in SFZ, indicating that it may be essential for SFZ function. Thus, we examined whether Wnt/β-catenin signaling regulates proliferation and phenotypic expression in SFZ cells. Using transgenic mice, we found that acute activation of Wnt/β-catenin signaling increases SFZ thickness, Proteoglycan 4 (Prg4, also called lubricin) expression and the number of slow-cell cycle cells, whereas conditional ablation of β-catenin causes the opposite. We developed a novel method to isolate SFZ cell-rich populations from the epiphyseal articular cartilage of neonatal mice, and found that the SFZ cells in culture exhibit a fibroblastic cytoarchitecture and higher Prg4 and Ets-related gene (Erg) expression and lower aggrecan expression compared with chondrocyte cultures. Gene array analyses indicated that SFZ cells have distinct gene expression profiles compared with underlying articular chondrocytes. Treatment of Wnt3a strongly stimulated SFZ cell proliferation and maintained strong expression of Prg4 and Erg, whereas ablation of β-catenin strongly impaired proliferation and phenotypic expression. When the cells were transplanted into athymic mice, they formed Prg4- and aggrecan-expressing cartilaginous masses attesting to their autonomous phenotypic capacity. Ablation of β-catenin caused a rapid loss of Prg4 gene expression and strong increases in expression of aggrecan and collagen 10, the latter being a trait of hypertrophic chondrocytes. Together, the data reveal that Wnt/β-catenin signaling is a key regulator of SFZ cell phenotype and proliferation, and may be as important for articular cartilage long-term function.

ANKH and susceptibility to and severity of ankylosing spondylitis

OBJECTIVE

Unconfirmed reports describe association of ankylosing spondylitis (AS) with several candidate genes including ANKH. Cellular export of inorganic pyrophosphate is regulated by the ANK protein, and mutant mice (ank/ank), which have a premature stop codon in the 3' end of the ank gene, develop severe ankylosis. We tested the association between single-nucleotide polymorphisms (SNP) in these genes and susceptibility to AS in a population of patients with AS. We investigated the role of these genes in terms of functional (BASFI) and metrological (BASMI) measures, and the association with radiological severity (mSASSS).

METHODS

Our study was conducted on 355 patients with AS and 95 ethnically matched healthy controls. AS was defined according to the modified New York criteria. Four SNP in ANKH (rs27356, rs26307, rs25957, and rs28006) were genotyped. Association analysis was performed using Cochrane-Armitage and linear regression tests for dichotomous and quantitative variables. Analyses of Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), BASFI, and mSASSS were controlled for sex and disease duration.

RESULTS

None of the 4 markers showed significant single-locus disease associations (p > 0.05), suggesting that ANKH was not a major determinant of AS susceptibility in our population. No association was observed between these SNP and age at symptom onset, BASDAI, BASFI, BASMI, or mSASSS.

CONCLUSION

These results confirm data in white Europeans that ANKH is probably not a major determinant of susceptibility to AS. ANKH polymorphisms do not markedly influence AS disease severity, as measured by BASMI and mSASSS.

WNT-3A modulates articular chondrocyte phenotype by activating both canonical and noncanonical pathways

A single Wnt can simultaneously activate different pathways with distinct and independent outcomes and reciprocal regulation in human articular chondrocytes.

Activation and disruption of Wnt/β-catenin signaling both result in cartilage breakdown via unknown mechanisms. Here we show that both WNT-3A and the Wnt inhibitor DKK1 induced de-differentiation of human articular chondrocytes through simultaneous activation of β-catenin–dependent and independent responses. WNT-3A activates both the β-catenin–dependent canonical pathway and the Ca²⁺/CaMKII noncanonical pathways, with distinct transcriptional targets. WNT-3A promotes cell proliferation and loss of expression of the chondrocyte markers COL2A1, Aggrecan, and SOX9; however, proliferation and AXIN2 up-regulation are downstream of the canonical pathway and are rescued by DKK1, whereas the loss of differentiation markers is CaMKII dependent. Finally, we showed that in chondrocytes, the Ca²⁺/CaMKII-dependent and β-catenin–dependent pathways are reciprocally inhibitory, thereby explaining why DKK1 can induce loss of differentiation through de-repression of the CaMKII pathway. We propose a novel model in which a single WNT can simultaneously activate different pathways with distinct and independent outcomes and with reciprocal regulation. This offers an opportunity for selective pharmacological targeting.

Bone damage in rheumatoid arthritis: mechanistic insights and approaches to prevention

In rheumatoid arthritis (RA), cells within the inflamed synovium and pannus elaborate a variety of cytokines, including tumor necrosis factor (TNF) alpha, interleukin (IL)-1, IL-6, and IL-17, that contribute to inflammation, and may directly affect bone. The receptor activator of NF-kappaB (RANK) ligand/RANK/osteoprotegerin pathway plays a critical role in regulating osteoclastogenesis in articular bone erosions in RA. Proinflammatory cytokines can modulate this pathway, and may also affect the ability of the osteoblast to repair bone at sites of articular erosion. In this review, the authors discuss the current understanding of pathogenic mechanisms of bone erosion in RA and examine current therapeutic approaches to prevent this damage.