Wnt signaling in bone development and disease: making stronger bone with Wnts

Exercise and Peak Bone Mass

PURPOSE OF REVIEW

The main goal of this narrative review is to assess whether physical activity (PA) influences peak bone mass and fracture risk.

RECENT FINDINGS

Several randomized controlled trials (RCT) show that short-term PA intervention programs in childhood improve the accrual of bone mineral. There are now also long-term controlled PA intervention studies demonstrating that both boys and girls with daily school PA through puberty gain higher bone mineral content (BMC) and bone mineral density (BMD) and greater bone size than boys and girls with school PA 1-2 times/week. These benefits seem to be followed by a gradual reduction in expected fracture rates, so that in children with daily school PA, the incidence rate ratio (IRR) after 8 years is less than half that expected by age. Daily school PA from before to after puberty is associated with beneficial gains in bone traits and gradually lower relative fracture risk.

Regulation of Wnt Signaling through Ubiquitination and Deubiquitination in Cancers

The Wnt signaling pathway plays important roles in embryonic development, homeostatic processes, cell differentiation, cell polarity, cell proliferation, and cell migration via the β-catenin binding of Wnt target genes. Dysregulation of Wnt signaling is associated with various diseases such as cancer, aging, Alzheimer’s disease, metabolic disease, and pigmentation disorders. Numerous studies entailing the Wnt signaling pathway have been conducted for various cancers. Diverse signaling factors mediate the up- or down-regulation of Wnt signaling through post-translational modifications (PTMs), and aberrant regulation is associated with several different malignancies in humans. Of the numerous PTMs involved, most Wnt signaling factors are regulated by ubiquitination and deubiquitination. Ubiquitination by E3 ligase attaches ubiquitins to target proteins and usually induces proteasomal degradation of Wnt signaling factors such as β-catenin, Axin, GSK3, and Dvl. Conversely, deubiquitination induced by the deubiquitinating enzymes (DUBs) detaches the ubiquitins and modulates the stability of signaling factors. In this review, we discuss the effects of ubiquitination and deubiquitination on the Wnt signaling pathway, and the inhibitors of DUBs that can be applied for cancer therapeutic strategies.

Analyzing Genome-Wide Association Study Dataset Highlights Immune Pathways in Lip Bone Mineral Density

Osteoporosis is a common complex human disease. Until now, large-scale genome-wide association studies (GWAS) using single genetic variant have reported some novel osteoporosis susceptibility variants. However, these risk variants only explain a small proportion of osteoporosis genetic risk, and most genetic risk is largely unknown. Interestingly, the pathway analysis method has been used in investigation of osteoporosis mechanisms and reported some novel pathways. Until now, it remains unclear whether there are other risk pathways involved in BMD. Here, we selected a lip BMD GWAS with 301,019 SNPs in 5,858 Europeans, and conducted a gene-based analysis (SET SCREEN TEST) and a pathway-based analysis (WebGestalt). On the gene level, BMD susceptibility genes reported by previous GWAS were identified to be the top 10 significant signals. On the pathway level, we identified 27 significant KEGG pathways. Three immune pathways including T cell receptor signaling pathway (hsa04660), complement and coagulation cascades (hsa04610), and intestinal immune network for IgA production (hsa04672) are ranked the top three significant signals. Evidence from the PubMed and Google Scholar databases further supports our findings. In summary, our findings provide complementary information to these nine risk pathways.

Frizzled-4 is required for normal bone acquisition despite compensation by Frizzled-8

The activation of the Wnt/β-catenin signaling pathway is critical for skeletal development but surprisingly little is known about the requirements for the specific frizzled (Fzd) receptors that recognize Wnt ligands. To define the contributions of individual Fzd proteins to osteoblast function, we profiled the expression of all 10 mammalian receptors during calvarial osteoblast differentiation. Expression of Fzd4 was highly upregulated during in vitro differentiation and therefore targeted for further study. Mice lacking Fzd4 in mature osteoblasts had normal cortical bone structure but reduced cortical tissue mineral density and also exhibited an impairment in the femoral trabecular bone acquisition that was secondary to a defect in the mineralization process. Consistent with this observation, matrix mineralization, markers of osteoblastic differentiation, and the ability of Wnt3a to stimulate the accumulation of β-catenin were reduced in cultures of calvarial osteoblasts deficient for Fzd4. Interestingly, Fzd4-deficient osteoblasts exhibited an increase in the expression of Fzd8 both in vitro and in vivo, which suggests that the two receptors may exhibit overlapping functions. Indeed, ablating a single Fzd8 allele in osteoblast-specific Fzd4 mutants produced a more severe effect on bone acquisition. Taken together, our data indicate that Fzd4 is required for normal bone development and mineralization despite compensation from Fzd8.

Cross-Species RNA-Seq Study Comparing Transcriptomes of Enriched Osteocyte Populations in the Tibia and Skull

Local site-specific differences between bones in different regions of the skeleton account for their different properties and functions. To identify mechanisms behind these differences, we have performed a cross-species study comparing RNA transcriptomes of cranial and tibial osteocytes, from bones with very different primary functions and physiological responses, collected from the same individual mouse, rat, and rhesus macaque. Bioinformatic analysis was performed to identify 32 genes changed in the same direction between sites and shared across all three species. Several well-established key genes in bone growth and remodeling were upregulated in the tibias of all three species (BMP7, DKK1, FGF1, FRZB, SOST). Many of them associate or crosstalk with the Wnt signaling pathway. These results suggest Wnt signaling-related candidates for different control of regulatory mechanisms in bone homeostasis in the skull and tibia and indicate a different balance between genetically determined structure and feedback mechanisms to strains induced by mechanical loading at the different sites.

A transcriptional and post-transcriptional dysregulation of Dishevelled 1 and 2 underlies the Wnt signaling impairment in type I Gaucher disease experimental models

Bone differentiation defects have been recently tied to Wnt signaling alterations occurring in vitro and in vivo Gaucher disease (GD) models. In this work, we provide evidence that the Wnt signaling multi-domain intracellular transducers Dishevelled 1 and 2 (DVL1 and DVL2) may be potential upstream targets of impaired beta glucosidase (GBA1) activity by showing their misexpression in different type 1 GD in vitro models. We also show that in Gba mutant fish a miR-221 upregulation is associated with reduced dvl2 expression levels and that in type I Gaucher patients single-nucleotide variants in the DVL2 3′ untranslated region are related to variable canonical Wnt pathway activity. Thus, we strengthen the recently outlined relation between bone differentiation defects and Wnt/β-catenin dysregulation in type I GD and further propose novel mechanistic insights of the Wnt pathway impairment caused by glucocerebrosidase loss of function.

Defective WNT signaling may protect from articular cartilage deterioration - a quantitative MRI study on subjects with a heterozygous WNT1 mutation

OBJECTIVE

WNT signaling is of key importance in chondrogenesis and defective WNT signaling may contribute to the pathogenesis of osteoarthritis and other cartilage diseases. Biochemical composition of articular cartilage in patients with aberrant WNT signaling has not been studied. Our objective was to assess the knee articular cartilage in WNT1 mutation-positive individuals using a 3.0T MRI unit to measure cartilage thickness, relaxation times, and texture features.

DESIGN

Cohort comprised mutation-positive (N = 13; age 17-76 years) and mutation-negative (N = 13; 16-77 years) subjects from two Finnish families with autosomal dominant WNT1 osteoporosis due to a heterozygous missense mutation c.652T>G (p.C218G) in WNT1. All subjects were imaged with a 3.0T MRI unit and assessed for cartilage thickness, T2 and T1ρ relaxation times, and T2 texture features contrast, dissimilarity and homogeneity of T2 relaxation time maps in six regions of interest (ROIs) in the tibiofemoral cartilage.

RESULTS

All three texture features showed opposing trends with age between the groups in the medial tibiofemoral cartilage (P = 0.020-0.085 for the difference of the regression coefficients), the mutation-positive individuals showing signs of cartilage preservation. No significant differences were observed in the lateral tibiofemoral cartilage. Cartilage thickness and means of T2 relaxation time did not differ between groups. Means of T1ρ relaxation time were significantly different in one ROI but the regression analysis displayed no differences.

CONCLUSIONS

Our results show less age-related cartilage deterioration in the WNT1 mutation-positive than the mutation-negative subjects. This suggests, that the WNT1 mutation may alter cartilage turnover and even have a potential cartilage-preserving effect.

The role of osteoblasts in energy homeostasis

Osteoblasts are specialized mesenchymal cells that synthesize bone matrix and coordinate the mineralization of the skeleton. These cells work in harmony with osteoclasts, which resorb bone, in a continuous cycle that occurs throughout life. The unique function of osteoblasts requires substantial amounts of energy production, particularly during states of new bone formation and remodelling. Over the last 15 years, studies have shown that osteoblasts secrete endocrine factors that integrate the metabolic requirements of bone formation with global energy balance through the regulation of insulin production, feeding behaviour and adipose tissue metabolism. In this article, we summarize the current understanding of three osteoblast-derived metabolic hormones (osteocalcin, lipocalin and sclerostin) and the clinical evidence that suggests the relevance of these pathways in humans, while also discussing the necessity of specific energy substrates (glucose, fatty acids and amino acids) to fuel bone formation and promote osteoblast differentiation.

Skeletal phenotype/genotype in progressive pseudorheumatoid chondrodysplasia

BACKGROUND

Axial and extra-axial deceleration in function and progressive joint pain with subsequent development of antalgic gait associated with swellings, and stiffness of the joints with loss of the physiological spine biomechanics were the natural history in this group of patients. Clinical and radiological phenotypes have been analysed carefully to further understand the aetiology behind.

METHODS

Seven patients (three children around the age of 9-11 and one child of 17 years old). Three adults aging 25, 30, 33 and 40 years old were seen and examined. The paediatric group of patients were initially diagnosed with myopathy followed later by juvenile rheumatoid arthritis in other institutions. Clinical and imaging documentation were collected in our departments, followed by mutation screening, was carried out by bidirectional sequencing of the WISP3 gene.

RESULTS

Clinical and radiological phenotypic studies confirmed the diagnosis of progressive pseudorheumatoid chondrodysplasia. A constellation of abnormalities such as early senile hyperostosis of the spine (Forestier disease), osteoarthritis of the hips showed progressive diminution and irregularities of the hip joint spaces associated with progressive capital femoral epiphyseal dysplasia and coxa vara have been encountered. Loss-of-function homozygous mutations (c.667T>G, p.Cys223Gly) and (c.170C>A, p.Ser57*) in the WISP3 gene were identified in our patients.

CONCLUSION

The definite diagnosis was not defined via vigorous myopathic and rheumatologic investigations. Detailed clinical examination and skeletal survey, followed by genotypic confirmation, were our fundamental pointers to rule out the false diagnosis of juvenile rheumatoid arthritis and rheumatoid polyarthritis in the adult group of patients. We wish to stress that the clinical/radiological phenotype is the baseline tool to establish a definite diagnosis and to guide the geneticist toward proper genotype.Key Points•Joint pain and difficulties in walking/climbing the stairs are characteristic features encountered in early childhood. False diagnosis of juvenile rheumatoid arthritis can be made at this point.•False positive-like muscular wasting resembling myopathy results in ensuing vigorous troublesome investigations.•Flattened vertebral bodies associated with defective ossification of the anterior end plates are characteristic features of progressive pseudorheumatoid chondrodysplasia.•Joint expansions, which are usually accompanied by narrowing of the articular ends of the appendicular skeletal system, show a clear radiological phenotype of pseudorheumatoid chondrodysplasia.

Rapamycin attenuates articular cartilage degeneration by inhibiting β-catenin in a murine model of osteoarthritis

Purpose: To investigate whether systemic injection of rapamycin attenuates articular cartilage degeneration by inhibiting β-catenin in a murine model of osteoarthritis (OA). Materials and methods: Ten-week-old male C57BL/6j wild-type (WT) mice and SOST-knockout (SOST^-/-) mice were randomized to a sham group, a vehicle-treated group, and a rapamycin-treated group. Mice in the vehicle-treated group underwent destabilizing of the medial meniscus (DMM) in the right knee, and were then treated with vehicle. Mice in the rapamycin treatment group underwent DMM and were treated with rapamycin. Safranin O-Fast green staining and Osteoarthritis Research Society International (OARSI) modified Mankin score were used to evaluate the histopathological features of the articular cartilage in the knee. The expression of light chain 3 (LC3) was evaluated by immunofluorescence, whereas the expression of ATG5, matrix metallopeptidase 13 (MMP-13), vascular endothelial growth factor (VEGF), sclerostin, and β-catenin were evaluated by immunohistochemistry. TUNEL staining was used to determine apoptosis of chondrocytes. Results: In vehicle-treated mice when compared with mice in the sham group, the OARSI scores, expression of MMP-13, VEGF, sclerostin, β-catenin, and chondrocyte apoptosis were significantly increased, whereas the expression of LC3 and ATG5 were significantly decreased. A systemic injection of rapamycin activated chondrocyte autophagy, which increased the expression of LC3 and ATG-5, and reduced OARSI scores, the expression of β-catenin, MMP-13, and VEGF, and chondrocyte apoptosis in rapamycin treated mice when compared with vehicle-treated mice. Conclusions: Systemic injection of rapamycin attenuated articular cartilage degeneration by inhibiting β-catenin in a murine model of OA.

Interleukin-35 stimulates tumor necrosis factor-α activated osteoblasts differentiation through Wnt/β-catenin signaling pathway in rheumatoid arthritis

Interleukin (IL)-35 plays an important role in the pathogenesis of rheumatoid arthritis (RA), which is characterized by tumor necrosis factor (TNF)-α activated bone loss beginning early and persisting over time. The aim of this study was to explore the effects and signaling pathway of IL-35 on osteoblasts differentiation in MC3T3E1 cells and TNF-α activated MC3T3E1 cells. A microenvironment was established with low concentration and short-term treatment of TNF-α to mimic inflammatory activated osteoblasts of RA in vitro. The role of IL-35 on osteoblasts proliferation and apoptosis were assessed using cell counting kit (CCK)-8 assay and flow cytometry, respectively. Alkaline phosphatase (ALP) activity was measured by p-nitrophenyl phosphate assay. Extracellular matrix mineralization was measured by Alizarin red S staining. Osteoprotegerin (OPG) and receptor activator of nuclear factor-κB ligand (RANKL) in response to IL-35 were investigated using real-time polymerase chain reaction and western blot analysis. Wnt/β-catenin signaling pathway in osteoblasts was investigated. In basal and TNF-α activated osteoblasts, IL-35 promoted proliferation and inhibited apoptosis. Basal and TNF-α activated ALP activity and mineralization in vitro was increased stimulated by IL-35. Furthermore, IL-35 increased the basal and TNF-α activated OPG expression and decreased basal and TNF-α activated RANKL expression. Blocking Wnt/β-catenin signaling pathway with Dickkopf (Dkk)-1 inhibited the osteogenic effects of IL-35. IL-35 stimulates basal and TNF-α activated osteoblasts differentiation through the Wnt/β-catenin signaling pathway, thus highlighting the IL-35 for pharmaceutical and medicinal applications for treating RA bone loss.

Adenosine A2A receptor (A2AR) activation triggers Akt signaling and enhances nuclear localization of β-catenin in osteoblasts

Osteoblast differentiation and proliferation are regulated by several modulators, among which are adenosine A_2A receptors (A2ARs) and Wingless/Integrated-β-catenin pathways. Cytosolic β-catenin stabilization promotes its nuclear translocation and transcriptional activity. In the present study, we seek to determine whether there is a connection between A2AR stimulation and cellular β-catenin levels in osteoblasts. Osteoblast precursor cell line (MC3T3-E1) and primary murine osteoblasts were treated with CGS21680, a highly selective A2AR agonist. We analyzed cellular content and nuclear translocation of phosphorylated (p)-serine 552 (S552) β-catenin in response to A2AR stimulation in MC3T3-E1 cells, in both wild-type and A2AR knockout (A2AKO) mice. Moreover, we measured cellular β-catenin levels in MC3T3-E1 cells transfected with scrambled or protein kinase B (Akt) small interfering RNA following A2AR activation. CGS21680 (1 μM) stimulated an increase in both the cellular content and nuclear translocation of p-S552 β-catenin after 15 min of incubation. A2AR activation had no tangible effect on the cellular β-catenin level either in A2AKO mice or in osteoblasts with diminished Akt content. Our findings demonstrate an interaction between A2AR, β-catenin, and Akt signaling in osteoblasts. The existence of such a crosstalk has significant repercussions in the development of novel therapeutic approaches targeting medical conditions associated with reduced bone density.-Borhani, S., Corciulo, C., Larranaga-Vera, A., Cronstein, B. N. Adenosine A_2A receptor (A2AR) activation triggers Akt signaling and enhances nuclear localization of β-catenin in osteoblasts.

Transmembrane protein 64 modulates prostate tumor progression by regulating Wnt3a secretion

Wnt3a is a glycosylated ligand that activates the β-catenin-dependent signaling pathway. Wnt signaling is also important in the prostate tumor microenvironment, and Wnt proteins secreted by the tumor stroma promote resistance to therapy. Bioactive Wnt3a production requires a number of dedicated factors in the secretory cell, but their coordinated functions are not fully understood. We previously reported transmembrane protein 64 (Tmem64) as a novel regulator of the Wnt/β-catenin signaling pathway, which is correlated with β-catenin regulation. In the present study, the role of Tmem64 in prostate cancer cells was investigated by modulating Wnt3a secretion. Overexpression of Tmem64 inhibited Wnt3a secretion and Lef/Tcf-sensitive transcription. By contrast, a Tmem64 mutation deleting the protein's transmembrane region restored Wnt3a secretion. Notably, Tmem64 protein and mRNA in PC3 cells were significantly overexpressed compared with that observed in LNCaP and DU145 cells. In a mouse metastasis model intracardially injected with PC3 cells, Tmem64 expression was downregulated in the metastatic spine and mandible lesions compared with in the primary injection regions. However, Wnt3a was strongly expressed in the metastatic spine and mandible lesions. Collectively, these findings suggest that Tmem64 is involved in the metastatic progression of prostate cancer cells by regulating Wnt3a secretion.

Mechanical Stress Modulates the RANKL/OPG System of Periodontal Ligament Stem Cells via α7 nAChR in Human Deciduous Teeth: An In Vitro Study

The aim of this study was to investigate the mechanism by which periodontal ligament stem cells (PDLSCs) modulate root resorption of human deciduous teeth under mechanical stress. In this investigation, the PDLSCs were derived from deciduous and permanent teeth at different stages of root resorption. A cyclic hydraulic pressure was applied on the PDLSCs to mimic chewing forces in the oral environment. The cultured cells were characterized using osteogenic and adipogenic differentiation assays, quantitative real-time polymerase chain reaction (qRT-PCR), and Western blotting analysis. The PDLSCs exhibited the ability to induce osteoclast differentiation under certain mechanical stresses. As the expressions of RUNX2, alkaline phosphatase (ALP), and osteoprotegerin (OPG) were significantly reduced, the receptor activator of the nuclear factor kappa-B ligand (RANKL) was upregulated increasing the RANKL/OPG ratio. Under hydrodynamic pressure at 0-135 kPa, the expressions of alpha 7 nicotinic acetylcholine receptors (α7 nAChR), p-GSK-3β, and active-β-catenin were markedly upregulated in PDLSCs from unresorbed deciduous teeth. Treatment with the α7 nAChR inhibitor alpha-bungarotoxin (α-BTX) and the Wnt pathway inhibitor DKK1 may reverse the mechanical stress inducing upregulation of RANKL and reduction of RUNX2, ALP, and OPG. Alizarin red staining confirmed these results. The mechanical stress applied on the deciduous tooth PDLSCs can induce osteoclastic effects through upregulation of α7 nAChR and activation of the canonical Wnt pathway. It can be suggested that chewing forces may play a major role at the beginning of the physiological root resorption of deciduous teeth.

SHP2 regulates intramembranous ossification by modifying the TGFβ and BMP2 signaling pathway

SHP2 is a ubiquitously expressed protein tyrosine phosphatase, which is involved in many signaling pathways to regulate the skeletal development. In endochondral ossification, SHP2 is known to modify the osteogenic fate of osteochondroprogenitors and to impair the osteoblastic transdifferentiation of hypertrophic chondrocytes. However, how SHP2 regulates osteoblast differentiation in intramembranous ossification remains incompletely understood. To address this question, we generated a mouse model to ablate SHP2 in the Prrx1-expressing mesenchymal progenitors by using "Cre-loxP"-mediated gene excision and examined the development of calvarial bone, in which the main process of bone formation is intramembranous ossification. Phenotypic characterization showed that SHP2 mutants have severe defects in calvarial bone formation. Cell lineage tracing and in situ hybridization data showed less osteoblast differentiation of mesenchymal cells and reduced osteogenic genes expression, respectively. Further mechanistic studies revealed enhanced TGFβ and suppressed BMP2 signaling in SHP2 ablated mesenchymal progenitors and their derivatives. Our study uncovered the critical role of SHP2 in osteoblast differentiation through intramembranous ossification and might provide a potential target to treat craniofacial skeleton disorders.

Wnt Pathway in Bone Repair and Regeneration - What Do We Know So Far

Wnt signaling plays a central regulatory role across a remarkably diverse range of functions during embryonic development, including those involved in the formation of bone and cartilage. Wnt signaling continues to play a critical role in adult osteogenic differentiation of mesenchymal stem cells. Disruptions in this highly-conserved and complex system leads to various pathological conditions, including impaired bone healing, autoimmune diseases and malignant degeneration. For reconstructive surgeons, critically sized skeletal defects represent a major challenge. These are frequently associated with significant morbidity in both the recipient and donor sites. The Wnt pathway is an attractive therapeutic target with the potential to directly modulate stem cells responsible for skeletal tissue regeneration and promote bone growth, suggesting that Wnt factors could be used to promote bone healing after trauma. This review summarizes our current understanding of the essential role of the Wnt pathway in bone regeneration and repair.

[Bone mechanobiology, an emerging field: a review]

INTRODUCTION

Mechanobiology, at the interface between biology and biophysics, studies the impact of mechanical forces on tissues, cells and biomolecules. The application of orthodontic forces, followed by induced tooth displacement, is a striking example of its clinical application.

OBJECTIVE

The purpose of this article was to compile a review of the literature on the subject of mechanobiology; from its detection at bone level to the presentation of stimulated intracellular pathways.

MATERIALS AND METHODS

The literature search was conducted on the Pubmed database in April 2018, with associations of the terms "mechanobiology", "orthodontics", "cell culture", "physiopathology".

RESULTS

Three major areas of research were selected: highlighting of the phenomenon and its application in the field of bone biology; the cellular effectors of mechanobiology and its clinical applications. The use of mechanobiology in dentofacial orthopedics opens up a new field of reflection for clinicians regarding future advances in orthodontics.

Human ex vivo 3D bone model recapitulates osteocyte response to metastatic prostate cancer

Prostate cancer (PCa) is the second leading cause of cancer deaths among American men. Unfortunately, there is no cure once the tumor is established within the bone niche. Although osteocytes are master regulators of bone homeostasis and remodeling, their role in supporting PCa metastases remains poorly defined. This is largely due to a lack of suitable ex vivo models capable of recapitulating the physiological behavior of primary osteocytes. To address this need, we integrated an engineered bone tissue model formed by 3D-networked primary human osteocytes, with conditionally reprogrammed (CR) primary human PCa cells. CR PCa cells induced a significant increase in the expression of fibroblast growth factor 23 (FGF23) by osteocytes. The expression of the Wnt inhibitors sclerostin and dickkopf-1 (Dkk-1), exhibited contrasting trends, where sclerostin decreased while Dkk-1 increased. Furthermore, alkaline phosphatase (ALP) was induced with a concomitant increase in mineralization, consistent with the predominantly osteoblastic PCa-bone metastasis niche seen in patients. Lastly, we confirmed that traditional 2D culture failed to reproduce these key responses, making the use of our ex vivo engineered human 3D bone tissue an ideal platform for modeling PCa-bone interactions.

Bioinformatics Analysis of the Molecular Mechanism of Aging on Fracture Healing

Increasing age negatively affects different phases of bone fracture healing. The present study aimed to explore underlying mechanisms related to bone fracture repair in the elderly. GSE17825 public transcriptome data from the Gene Expression Omnibus database were used for analysis. First, raw data were normalized and differentially expressed genes (DEGs) were identified. Next, Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) analyses were implemented to evaluate pathways and DEGs. A protein-protein interaction (PPI) network was then constructed. A total of 726, 861, and 432 DEGs were identified between the young and elderly individuals at 1, 3, and 5 days after fracture, respectively. The results of GO, KEGG, and PPI network analyses suggested that the inflammatory response, Wnt signaling pathway, vascularization-associated processes, and synaptic-related functions of the identified DEGs are markedly enriched, which may account for delayed fracture healing in the elderly. These findings provide valuable clues for investigating the effects of aging on fracture healing but should be validated through further experiments.

Targeting the Wnt/β-catenin pathway in human osteosarcoma cells

Aberrant activation of Wnt signaling has been implicated in human osteosarcoma, which may provide a genetic vulnerability that can be targeted in osteosarcoma treatment. To test whether Wnt activation is necessary for osteosarcoma growth, colony formation, invasion, and metastasis, we treated human osteosarcoma cells with a small molecule inhibitor of Wnt/β-catenin, PRI-724, which suppresses Wnt/β-catenin-mediated transcription. We found increased protein levels of endogenous active-β-catenin in five human osteosarcoma cell lines. Treatment with PRI-724 was sufficient to inhibit human osteosarcoma 143B and SJSA-1 cell proliferation. Suppressed Wnt signaling was confirmed by decreased protein levels of the Wnt target Cyclin D1. Furthermore, we revealed significant inhibitory effects on cell migration, invasion, and colony formation in the human osteosarcoma cells. Using deposited data from next generation sequencing studies, we analyzed somatic mutations and gene expression of components in the Wnt/β-catenin pathway. We found somatic mutations and upregulated gene expression of many components in the Wnt/ β-catenin pathway, indicating activated Wnt signaling. Taken together, our results illustrate the critical role of Wnt/β-catenin signaling in human osteosarcoma pathogenesis and growth, as well as the therapeutic potential of Wnt inhibitors in the treatment of human osteosarcoma.

Design, synthesis and structure-activity relationship optimization of phenanthridine derivatives as new Wnt/β-catenin signalling pathway agonists

Phenanthridine derivativeHLY78 has previously been identified as the first Wnt/β-catenin signalling pathway agonist that targets the DAX domain of axin. However, due to the relatively weak activation on the Wnt/β-catenin signalling pathway, HLY78 is insufficient for further pharmacological study. Herein, the structural optimization of HLY78 and analyses of the structure-activity relationships (SARs) of HLY78-derived phenanthridine derivatives as agonists of the Wnt/β-catenin signalling pathway are presented. In this work, 36 derivatives were designed and synthesized with some derivatives exhibiting stronger Wnt activity than the activity of HLY78. In particular, one of them, 8-((1,3-dimethy-pyrazol-5-yl)methoxy)-5-ethyl-4-methyl-5,6-dihydro-phenanthridin-9-ol, exhibited strong Wnt active activity and is 10 times more potent than HLY78. The following SAR analysis suggests that a pyrazole group, especially at the C-8 position, is important for Wnt activation; a methyl group at the C-4position seems to be more beneficial for Wnt activation than ethyl; and oxidation of the C-6 position reduces the Wnt activation.

Fatty acid metabolism by the osteoblast

The emergence of bone as an endocrine organ able to influence whole body metabolism, together with comorbid epidemics of obesity, diabetes, and osteoporosis, have prompted a renewed interest in the intermediary metabolism of the osteoblast. To date, most studies have focused on the utilization of glucose by this specialized cell, but the oxidation of fatty acids results in a larger energy yield. Osteoblasts express the requisite receptors and catabolic enzymes to take up and then metabolize fatty acids, which appears to be required during later stages of differentiation when the osteoblast is dedicated to matrix production and mineralization. In this article, we provide an overview of fatty acid β-oxidation and highlight studies demonstrating that the skeleton plays a significant role in the clearance of circulating lipoproteins and non-esterified fatty acids. Additionally, we review the requirement for long-chain fatty acid metabolism during post-natal bone development and the effects of anabolic stimuli on fatty acid utilization by osteoblasts. These recent findings may help to explain the skeletal manifestations of human diseases associated with impaired lipid metabolism while also providing additional insights into the metabolic requirements of skeletal homeostasis.

LRP5 gene polymorphisms and radiographic joint damage in rheumatoid arthritis patients

Rheumatoid arthritis (RA) is characterized by increased bone resorption and impaired bone formation. Osteoblast function is regulated by the canonical LRP5/Wnt/β-catenin pathway. Bone mineral density and RA joint destruction are partially inherited. In line with this, we found significant associations between LRP5 SNPs (p.A1330V, p.N740N, p.V667M) and RA radiographic damage severity.

INTRODUCTION

Increased bone resorption and impaired bone formation characterize rheumatoid arthritis (RA). Canonical Wnt/β-catenin pathway, signalled by lipoprotein receptor-related protein-5 (LRP5), regulates osteoblast function. Since bone mineral density (BMD) and RA joint destruction are partially inherited, we studied their association with LRP5 single nucleotide polymorphisms (SNPs).

METHODS

Clinical data and peripheral blood for biomarkers assessment and LRP5 genotyping were collected from 208 RA patients. Hands and feet X-rays were scored [modified Sharp/van der Heijde Score (SHS), joint space narrowing (JSN), and erosion scores]. Lumbar spine, total left proximal femur, and left hand BMD were assessed by dual-energy X-ray absorptiometry (DXA).

RESULTS

TT genotypes for p.A1330V and p.N740N LRP5 SNPs associated with total SHS, erosion score, and hands erosion score; the same for p.A1330V with feet JSN score and p.N740N with hands total score. AG genotype for p.V667M associated with sclerostin and hands JSN score. Femoral BMD associated with TC genotype for p.N740N. Multiple test correction precluded a few of these associations. Among V667M-N740N-A1330V haplotypes: GTT associated with higher feet JSN score (OR = 3.80; p = 0.016) and ATT with higher JSN score (OR = 4.60; p = 0.032), hands total score (OR = 5.65; p = 0.022), and total SHS (OR = 6.74; p = 0.024).

CONCLUSION

Significant associations between LRP5 SNPs (p.A1330V, p.N740N, and p.V667M) and the severity of radiographic damage reinforce the evidence of bone destruction heritability in RA.

Efficient synthesis of new phenanthridine Wnt/β-catenin signaling pathway agonists

Previously, HLY78, a lycorine derivative, was identified as the first Wnt/β-catenin signaling agonist through binding to the DAX domain of Axin, a scaffold of Wnt/β-catenin complex. In this study, to obtain more potent Wnt/β-catenin agonist, the structure optimization of HLY78 was carried out by design and synthesis of six phenanthridine derivatives, which afforded five active ones. In particular, 8,9-bis((1,3-dimethyl-1H-pyrazol)methoxy)-5-ethyl-4-methyl-5,6-dihydrophenanthridine showed the most potent activity (0.15/μM) that was increased nearly 30 times as that of the lead HLY78. These compounds may be valuable in future pharmacological or biological studies.

Association of Anabolic Effect of Calcitriol with Osteoclast-Derived Wnt 10b Secretion

Canonical Wnt (Wingless/Integrated) signaling is crucial in bone development and the Wnt ligand can promote osteoblast differentiation from mesenchymal progenitor cells. Calcitriol, an active vitamin D3, is used clinically for treatment of secondary hyperparathyroidism (SHPT) in chronic kidney disease (CKD) patients. The bone effects of calcitriol in SHPT remains uncertain. We hypothesized that calcitriol improves bone mass by suppressing osteoclast activity, and simultaneously promoting Wnt ligand secretion. We designed a cross-sectional study in maintenance hemodialysis patients to explore the effects of calcitriol on different bone turnover markers and specifically emphasized the Wnt 10b levels. Then, we explored the source of Wnt 10b secretion by using osteoclasts and osteoblasts treated with calcitriol in cell culture studies. Finally, we explored the effects of calcitriol on bone microarchitectures in CKD mice, using the 5/6 nephrectomy CKD animal model with analysis using micro-computed tomography. Calcitriol promoted the growth of both trabecular and cortical bones in the CKD mice. Wnt 10b and Procollagen 1 N-terminal Propeptide (P1NP) significantly increased, but Tartrate-resistant acid phosphatase 5b (Trap 5b) significantly decreased in the calcitriol-treated maintenance hemodialysis patients. Calcitriol enhanced Wnt 10b secretion from osteoclasts in a dose-dependent manner. Treatment of SHPT with calcitriol improved the bone anabolism by inhibiting osteoclasts and promoting osteoblasts that might be achieved by increasing the Wnt 10b level.

A Review of FOXI3 Regulation of Development and Possible Roles in Cancer Progression and Metastasis

Development and cancer share a variety of functional traits such as EMT, cell migration, angiogenesis, and tissue remodeling. In addition, many cellular signaling pathways are noted to coordinate developmental processes and facilitate aspects of tumor progression. The Forkhead box superfamily of transcription factors consists of a highly conserved DNA binding domain, which binds to specific DNA sequences and play significant roles during adult tissue homoeostasis and embryogenesis including development, differentiation, metabolism, proliferation, apoptosis, migration, and invasion. Interestingly, various studies have implicated the role of key Fox family members such as FOXP, FOXO, and FOXA during cancer initiation and metastases. FOXI3, a member of the Forkhead family affects embryogenesis, development, and bone remodeling; however, no studies have reported a role in cancer. In this review, we summarize the role of FOXI3 in embryogenesis and bone development and discuss its potential involvement in cancer progression with a focus on the bone metastasis. Moreover, we hypothesize possible mechanisms underlying the role of FOXI3 in the development of solid tumor bone metastasis.

Microenvironmental Regulation of Chondrocyte Plasticity in Endochondral Repair-A New Frontier for Developmental Engineering

The majority of fractures heal through the process of endochondral ossification, in which a cartilage intermediate forms between the fractured bone ends and is gradually replaced with bone. Recent studies have provided genetic evidence demonstrating that a significant portion of callus chondrocytes transform into osteoblasts that derive the new bone. This evidence has opened a new field of research aimed at identifying the regulatory mechanisms that govern chondrocyte transformation in the hope of developing improved fracture therapies. In this article, we review known and candidate molecular pathways that may stimulate chondrocyte-to-osteoblast transformation during endochondral fracture repair. We also examine additional extrinsic factors that may play a role in modulating chondrocyte and osteoblast fate during fracture healing such as angiogenesis and mineralization of the extracellular matrix. Taken together the mechanisms reviewed here demonstrate the promising potential of using developmental engineering to design therapeutic approaches that activate endogenous healing pathways to stimulate fracture repair.

MicroRNA-185 inhibits the growth and proliferation of osteoblasts in fracture healing by targeting PTH gene through down-regulating Wnt/β -catenin axis: In an animal experiment

Fracture healing is a repair process of a mechanical discontinuity loss of force transmission, and pathological mobility of bone. Increasing evidence suggests that microRNA (miRNA) could regulate chondrocyte, osteoblast, and osteoclast differentiation and function, indicating miRNA as key regulators of bone formation, resorption, remodeling, and repair. Hence, during this study, we established a right femur fracture mouse model to explore the effect microRNA-185 (miR-185) has on osteoblasts in mice during fracture healing and its underlying mechanism. After successfully model establishment, osteoblasts were extracted and treated with a series of mimics or inhibitors of miR-185, or siRNA against PTH. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) and western blot analysis were performed to determine the levels of miR-185, PTH, β-catenin and Wnt5b. Cell viability, cycle distribution and apoptosis were detected by means of MTT and flow cytometry assays. Dual luciferase reporter gene assay verified that PTH is a target gene of miR-185. Osteoblasts transfected with miR-185 mimics or siRNA against PTH presented with decreased levels of PTH, β-catenin and Wnt5b which indicated that miR-185 blocks the Wnt/β -catenin axis by inhibiting PTH. Moreover, miR-185 inhibitors promoted the osteoblast viability and reduced apoptosis with more cells arrested at the G1 stage. MiR-185 mimics were observed to have inhibitory effects on osteoblasts as opposed to those induced by miR-185 inhibitors. Above key results indicated that suppression of miR-185 targeting PTH could promote osteoblast growth and proliferation in mice during fracture healing through activating Wnt/β -catenin axis.

Discovery of a small-molecule inhibitor of Dvl-CXXC5 interaction by computational approaches

The Wnt/β-catenin signaling pathway plays a significant role in the control of osteoblastogenesis and bone formation. CXXC finger protein 5 (CXXC5) has been recently identified as a negative feedback regulator of osteoblast differentiation through a specific interaction with Dishevelled (Dvl) protein. It was reported that targeting the Dvl-CXXC5 interaction could be a novel anabolic therapeutic target for osteoporosis. In this study, complex structure of Dvl PDZ domain and CXXC5 peptide was simulated with molecular dynamics (MD). Based on the structural analysis of binding modes of MD-simulated Dvl PDZ domain with CXXC5 peptide and crystal Dvl PDZ domain with synthetic peptide-ligands, we generated two different pharmacophore models and applied pharmacophore-based virtual screening to discover potent inhibitors of the Dvl-CXXC5 interaction for the anabolic therapy of osteoporosis. Analysis of 16 compounds selected by means of a virtual screening protocol yielded four compounds that effectively disrupted the Dvl-CXXC5 interaction in the fluorescence polarization assay. Potential compounds were validated by fluorescence spectroscopy and nuclear magnetic resonance. We successfully identified a highly potent inhibitor, BMD4722, which directly binds to the Dvl PDZ domain and disrupts the Dvl-CXXC5 interaction. Overall, CXXC5-Dvl PDZ domain complex based pharmacophore combined with various traditional and simple computational methods is a promising approach for the development of modulators targeting the Dvl-CXXC5 interaction, and the potent inhibitor BMD4722 could serve as a starting point to discover or design more potent and specific the Dvl-CXXC5 interaction disruptors.

Endocrine-disrupting chemicals, epigenetics, and skeletal system dysfunction: exploration of links using bisphenol A as a model system

Early life exposures to endocrine-disrupting chemicals (EDCs) have been associated with physiological changes of endocrine-sensitive tissues throughout postnatal life. Although hormones play a critical role in skeletal growth and maintenance, the effects of prenatal EDC exposure on adult bone health are not well understood. Moreover, studies assessing skeletal changes across multiple generations are limited. In this article, we present previously unpublished data demonstrating dose-, sex-, and generation-specific changes in bone morphology and function in adult mice developmentally exposed to the model estrogenic EDC bisphenol A (BPA) at doses of 10 μg (lower dose) or 10 mg per kg bw/d (upper dose) throughout gestation and lactation. We show that F1 generation adult males, but not females, developmentally exposed to bisphenol A exhibit dose-dependent reductions in outer bone size resulting in compromised bone stiffness and strength. These structural alterations and weaker bone phenotypes in the F1 generation did not persist in the F2 generation. Instead, F2 generation males exhibited greater bone strength. The underlying mechanisms driving the EDC-induced physiological changes remain to be determined. We discuss potential molecular changes that could contribute to the EDC-induced skeletal effects, with an emphasis on epigenetic dysregulation. Furthermore, we assess the necessity of intact sex steroid receptors to mediate these effects. Expanding future assessments of EDC-induced effects to the skeleton may provide much needed insight into one of the many health effects of these chemicals and aid in regulatory decision making regarding exposure of vulnerable populations to these chemicals.

The regulatory roles of Notch in osteocyte differentiation via the crosstalk with canonical Wnt pathways during the transition of osteoblasts to osteocytes

Osteocytes comprise more than 90% of the cells in bone and are differentiated from osteoblasts via an unknown mechanism. Recently, it was shown that Notch signaling plays an important role in osteocyte functions. To gain insights into the mechanisms underlying the functions of Notch in regulating the transition of osteoblasts to osteocytes, we performed a luciferase assay by cloning the proximal E11 and dentin matrix acidic phosphoprotein 1 (DMP1) promotor regions into pGluc-Basic 2 vectors, which were subsequently transfected into the IDG-SW3 (osteocytes), MC3T3 (osteoblasts) and 293T (non-osteoblastic cells) cell lines. Two approaches were used to activate Notch signaling in vitro. One was a Notch1 extracellular antibody-coated cell culture plate, and the other was transfection of a Hairy/Enhancer of Split 1 (Hes1) overexpression vector. The interaction between the Notch and Wnt signaling pathways was probed by assessing the expression of a series of phosphorylated proteins involved in the cascade of both signaling pathways. Our data suggested that Notch signaling regulates E11 expression through Hes1 activity, while Hes1 solely did not initiate the expression of DMP1. The regulatory function of E11 by Hes1 was not observed in the 293T cell line, indicating a cell context-dependent manner of the Notch signaling pathway. Additionally, we found that Notch inhibited Wnt signaling at the late differentiation stage of osteocytes by both directly repressing phosphorylated Akt and preventing the nuclear aggregation of β-catenin. These findings provide profound understandings of Notch's regulatory function in osteocyte differentiation.

Antagonizing miR-218-5p attenuates Wnt signaling and reduces metastatic bone disease of triple negative breast cancer cells

Wnt signaling is implicated in bone formation and activated in breast cancer cells promoting primary and metastatic tumor growth. A compelling question is whether osteogenic miRNAs that increase Wnt activity for bone formation are aberrantly expressed in breast tumor cells to support metastatic bone disease. Here we report that miR-218-5p is highly expressed in bone metastases from breast cancer patients, but is not detected in normal mammary epithelial cells. Furthermore, inhibition of miR-218-5p impaired the growth of bone metastatic MDA-MB-231 cells in the bone microenvironment in vivo. These findings indicate a positive role for miR-218-5p in bone metastasis. Bioinformatic and biochemical analyses revealed a positive correlation between aberrant miR-218-5p expression and activation of Wnt signaling in breast cancer cells. Mechanistically, miR-218-5p targets the Wnt inhibitors Sclerostin (SOST) and sFRP-2, which highly enhances Wnt signaling. In contrast, delivery of antimiR-218-5p decreased Wnt activity and the expression of metastasis-related genes, including bone sialoprotein (BSP/IBSP), osteopontin (OPN/SPP1) and CXCR-4, implicating a Wnt/miR-218-5p regulatory network in bone metastatic breast cancer. Furthermore, miR-218-5p also mediates the Wnt-dependent up-regulation of PTHrP, a key cytokine promoting cancer-induced osteolysis. Antagonizing miR-218-5p reduced the expression of PTHrP and Rankl, inhibited osteoclast differentiation in vitro and in vivo, and prevented the development of osteolytic lesions in a preclinical metastasis model. We conclude that pathological elevation of miR-218-5p in breast cancer cells activates Wnt signaling to enhance metastatic properties of breast cancer cells and cancer-induced osteolytic disease, suggesting that miR-218-5p could be an attractive therapeutic target for preventing disease progression.

Expanding the clinical and molecular spectrum of PRMT7 mutations: 3 additional patients and review

Protein arginine methyltransferase 7 (PRMT7) is a member of a family of enzymes that catalyze the transfer of methyl groups from S-adenosyl-l-methionine to nitrogen atoms on arginine residues. Arginine methylation is involved in multiple biological processes, such as signal transduction, mRNA splicing, transcriptional control, DNA repair, and protein translocation. Currently, 7 patients have been described harboring compound heterozygous or homozygous variants in the PRMT7 gene, causing a novel intellectual disability syndrome, known as SBIDDS syndrome (Short Stature, Brachydactyly, Intellectual Developmental Disability, and Seizures). We report on 3 additional patients from 2 consanguineous families with severe/moderate intellectual disability, short stature, brachydactyly and dysmorphisms. Exome sequencing revealed 2 novel homozygous mutations in PRMT7. Our findings expand the clinical and molecular spectrum of homozygous PRMT7 mutations, associated to the SBIDDS syndrome, showing a possible correlation between the type of mutation and the severity of the phenotype.

IGFBP7 regulates the osteogenic differentiation of bone marrow-derived mesenchymal stem cells via Wnt/β-catenin signaling pathway

Insulin-like growth factor-binding protein 7 (IGFBP7), a low-affinity IGF binder, may play an important role in bone metabolism. However, its function in osteogenic differentiation of human bone marrow-derived mesenchymal stem cells (BMSCs) remains unclear. Therefore, we investigated its effects on osteogenic differentiation. Overexpression of IGFBP7 enhanced the expression of osteo-specific genes and proteins, and IGFBP7 knockdown decreased osteogenesis-specific markers. More mineral deposits and higher alkaline phosphatase activity were observed after the up-regulation of IGFBP7. Moreover, β-catenin levels were up-regulated by the overexpression of IGFBP7 or the addition of extracellular IGFBP7 protein and were reduced by the depletion of IGFBP7. The increase in osteogenic differentiation due to the overexpression of IGFBP7 was partially decreased by specific Wnt/β-catenin signaling inhibitors. Using a rat tibial osteotomy model, a sheet of IGFBP7-overexpressing BMSCs improved bone healing, as demonstrated by imaging, biomechanical, and histologic analyses. Taken together, these findings indicate that IGFBP7 regulates the osteogenic differentiation of BMSCs partly via the Wnt/β-catenin signaling pathway.-Zhang, W., Chen, E., Chen, M., Ye, C., Qi, Y., Ding, Q., Li, H., Xue, D., Gao, X., Pan, Z. IGFBP7 regulates the osteogenic differentiation of bone marrow-derived mesenchymal stem cells via Wnt/β-catenin signaling pathway.

MiR 376c inhibits osteoblastogenesis by targeting Wnt3 and ARF-GEF-1 -facilitated augmentation of beta-catenin transactivation

Wnt signaling pathway plays important role in all aspects of skeletal development which include chondrogenesis, osteoblastogenesis, and osteoclastogenesis. Induction of the Wnt-3 signaling pathway promotes bone formation while inactivation of the pathway leads to bone related disorders like osteoporosis. Wnt signaling thus has become a desired target to treat osteogenic disorders. MicroRNAs (miRNAs) represent an important category of elements that interact with Wnt signaling molecules to regulate osteogenesis. Here, we show that miR-376c, a well-characterized tumor suppressor which inhibits cell proliferation and invasion in osteosarcoma by targeting to transforming growth factor-alpha, suppresses osteoblast proliferation, and differentiation. Over-expression of miR-376c inhibited osteoblast differentiation, whereas inhibition of miR-376c function by antimiR-376c promoted expression of osteoblast-specific genes, alkaline phosphatase (ALP) activity, and matrix mineralization. Target prediction analysis tools and experimental validation by luciferase 3' UTR reporter assay along with qRT-PCR identified Wnt-3 and ARF-GEF-1 as direct targets of miR-376c. It was seen that over-expression of miR-376c leads to repression of canonical Wnt/β-catenin signaling. Our overall results suggest that miR-376c targets Wnt-3 and ARF-GEF-1 suppresses ARF-6 activation which prevents the release of β-catenin and its transactivation thereby inhibiting osteoblast differentiation. Although miR-376c is known to be a tumor repressor; we have identified a second complementary function of miR-376c where it inhibits Wnt-3-mediated osteogenesis and promotes bone loss.

Multiple analyses of large-scale genome-wide association study highlight new risk pathways in lumbar spine bone mineral density

Osteoporosis is a common human complex disease. It is mainly characterized by low bone mineral density (BMD) and low-trauma osteoporotic fractures (OF). Until now, a large proportion of heritability has yet to be explained. The existing large-scale genome-wide association studies (GWAS) provide strong support for the investigation of osteoporosis mechanisms using pathway analysis. Recent findings showed that different risk pathways may be involved in BMD in different tissues. Here, we conducted multiple pathway analyses of a large-scale lumbar spine BMD GWAS dataset (2,468,080 SNPs and 31,800 samples) using two published gene-based analysis software including ProxyGeneLD and the PLINK. Using BMD genes from ProxyGeneLD, we identified 51 significant KEGG pathways with adjusted P<0.01. Using BMD genes from PLINK, we identified 38 significant KEGG pathways with adjusted P<0.01. Interestingly, 33 pathways are shared in both methods. In summary, we not only identified the known risk pathway such as Wnt signaling, in which the top GWAS variants are significantly enriched, but also highlight some new risk pathways. Interestingly, evidence from further supports the involvement of these pathways in MBD.

FilaminA and Formin2 regulate skeletal, muscular, and intestinal formation through mesenchymal progenitor proliferation

The effects of actin dependent molecular mechanisms in coordinating cellular proliferation, migration and differentiation during embryogenesis are not well-understood. We have previously shown that actin-binding Filamin A (FlnA) and actin-nucleating Formin 2 (Fmn2) influence the development of the brain causing microcephaly in mice. In this study, we broaden this phenotype to explore the effects of these two proteins in the development of extra-CNS organ systems, including the gut, muscle, and skeleton. We observed defects in rib and sternum midline closure leading to thoracoabdominal schisis in FlnA+Fmn2 knockout mice, reminiscent of the pentalogy of Cantrell syndrome. These mice exhibit shortened guts, as well as thinned thoracic muscle mass. Immunostaining showed these changes are partially caused by a decrease in the number of presumptive mesenchymal proliferating cells with loss of either FlnA or FlnA+Fmn2. This proliferation defect appears to be in part due to delayed differentiation in these regions. While both FlnA and FlnA+Fmn2 mice show reduced cell death relative to WT control, increased caspase staining was seen in the double null relative to FlnA null suggesting that this could also contribute to the FlnA+Fmn2 phenotype. Therefore FlnA and Fmn2 are likely essential to cell proliferation, differentiation and cell death in a variety of tissues and organs, further reiterating the importance of vesicle trafficking in regulation of development.

Induced GnasR201H expression from the endogenous Gnas locus causes fibrous dysplasia by up-regulating Wnt/β-catenin signaling

Fibrous dysplasia (FD; Online Mendelian Inheritance in Man no. 174800) is a crippling skeletal disease caused by activating mutations of the GNAS gene, which encodes the stimulatory G protein Gα_s FD can lead to severe adverse conditions such as bone deformity, fracture, and severe pain, leading to functional impairment and wheelchair confinement. So far there is no cure, as the underlying molecular and cellular mechanisms remain largely unknown and the lack of appropriate animal models has severely hampered FD research. Here we have investigated the cellular and molecular mechanisms underlying FD and tested its potential treatment by establishing a mouse model in which the human FD mutation (R201H) has been conditionally knocked into the corresponding mouse Gnas locus. We found that the germ-line FD mutant was embryonic lethal, and Cre-induced Gnas FD mutant expression in early osteochondral progenitors, osteoblast cells, or bone marrow stromal cells (BMSCs) recapitulated FD features. In addition, mosaic expression of FD mutant Gα_s in BMSCs induced bone marrow fibrosis both cell autonomously and non-cell autonomously. Furthermore, Wnt/β-catenin signaling was up-regulated in FD mutant mouse bone and BMSCs undergoing osteogenic differentiation, as we have found in FD human tissue previously. Reduction of Wnt/β-catenin signaling by removing one Lrp6 copy in an FD mutant line significantly rescued the phenotypes. We demonstrate that induced expression of the FD Gα_s mutant from the mouse endogenous Gnas locus exhibits human FD phenotypes in vivo, and that inhibitors of Wnt/β-catenin signaling may be repurposed for treating FD and other bone diseases caused by Gα_s activation.

Reverse engineering development: Crosstalk opportunities between developmental biology and tissue engineering

The fields of developmental biology and tissue engineering have been revolutionized in recent years by technological advancements, expanded understanding, and biomaterials design, leading to the emerging paradigm of "developmental" or "biomimetic" tissue engineering. While developmental biology and tissue engineering have long overlapping histories, the fields have largely diverged in recent years at the same time that crosstalk opportunities for mutual benefit are more salient than ever. In this perspective article, we will use musculoskeletal development and tissue engineering as a platform on which to discuss these emerging crosstalk opportunities and will present our opinions on the bright future of these overlapping spheres of influence. The multicellular programs that control musculoskeletal development are rapidly becoming clarified, represented by shifting paradigms in our understanding of cellular function, identity, and lineage specification during development. Simultaneously, advancements in bioartificial matrices that replicate the biochemical, microstructural, and mechanical properties of developing tissues present new tools and approaches for recapitulating development in tissue engineering. Here, we introduce concepts and experimental approaches in musculoskeletal developmental biology and biomaterials design and discuss applications in tissue engineering as well as opportunities for tissue engineering approaches to inform our understanding of fundamental biology. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2356-2368, 2017.

Exercise and bone health across the lifespan

With ageing, bone tissue undergoes significant compositional, architectural and metabolic alterations potentially leading to osteoporosis. Osteoporosis is the most prevalent bone disorder, which is characterised by progressive bone weakening and an increased risk of fragility fractures. Although this metabolic disease is conventionally associated with ageing and menopause, the predisposing factors are thought to be established during childhood and adolescence. In light of this, exercise interventions implemented during maturation are likely to be highly beneficial as part of a long-term strategy to maximise peak bone mass and hence delay the onset of age- or menopause-related osteoporosis. This notion is supported by data on exercise interventions implemented during childhood and adolescence, which confirmed that weight-bearing activity, particularly if undertaken during peripubertal development, is capable of generating a significant osteogenic response leading to bone anabolism. Recent work on human ageing and epigenetics suggests that undertaking exercise after the fourth decade of life is still important, given the anti-ageing effect and health benefits provided, potentially occurring via a delay in telomere shortening and modification of DNA methylation patterns associated with ageing. Exercise is among the primary modifiable factors capable of influencing bone health by preserving bone mass and strength, preventing the death of bone cells and anti-ageing action provided.

The association between parathyroid hormone 1‑34 and the Wnt/β‑catenin signaling pathway in a rat model of osteoarthritis

The aim of the current study was to determine the effect of parathyroid hormone (PTH) 1‑34 on cartilage degeneration, and the association between PTH 1‑34 and factors associated with the Wnt/β‑catenin pathway following anterior cruciate ligament and medial meniscectomy‑induced osteoarthritis (OA) in rats. A total of 64 Sprague‑Dawley rats were randomly divided into the following four groups: Sham‑operated rats with normal saline (NS)‑treatment (n=16); anterior cruciate ligament transection with partial medial meniscectomy (ACLT + MMx) rats with NS‑treatment (n=16); sham‑operated rats treated with PTH 1‑34 (n=16); and ACLT + MMx rats treated with PTH 1‑34 (n=16). PTH (15 µg/kg/day) was administered via subcutaneous injection 5 days per week from the first postoperative day for 2 or 6 weeks. Staining with hematoxylin and eosin and safranin O, and a scoring system modified by Mankin were used to assess the histopathological features of cartilage. The present study detected the expression of PTH 1 receptor (PTH1R), sclerostin, dickkopf Wnt signaling pathway inhibitor 1 (DKK1), β‑catenin and runt‑related transcription factor 2 (RUNX2) in cartilage by immunohistochemical analysis to determine the association between PTH 1‑34 and factors associated with the Wnt/β‑catenin pathway. Reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) was performed to detect the mRNA expression levels of PTH1R and β‑catenin in cartilage. Histological analysis demonstrated that cartilage degeneration was present post‑surgery and gradually increased over time. PTH 1‑34 reduced the Mankin scores in ACLT + MMx rats compared with the NS‑treated ACLT + MMx rats. Immunohistochemistry and RT‑qPCR analysis demonstrated that, in cartilage, PTH 1‑34 treatment increased the mRNA expression and protein levels of PTH1R and β‑catenin, and decreased protein levels of sclerostin, DKK1 and RUNX2 in ACLT + MMx rats compared with the NS‑treated ACLT + MMx group. The present study demonstrated that PTH 1‑34 upregulated the Wnt/β‑catenin signaling pathway and that PTH1‑34 downregulated RUNX2 through an alternative pathway to the Wnt/β‑catenin signaling pathway, in a rat model of OA.

Small molecule inhibitors of the Dishevelled-CXXC5 interaction are new drug candidates for bone anabolic osteoporosis therapy

Bone anabolic agents promoting bone formation and rebuilding damaged bones would ideally overcome the limitations of anti‐resorptive therapy, the current standard prescription for osteoporosis. However, the currently prescribed parathyroid hormone (PTH)‐based anabolic drugs present limitations and adverse effects including osteosarcoma during long‐term use. Also, the antibody‐based anabolic drugs that are currently being developed present the potential limits in clinical application typical of macromolecule drugs. We previously identified that CXXC5 is a negative feedback regulator of the Wnt/β‐catenin pathway via its interaction with Dishevelled (Dvl) and suggested the Dvl–CXXC5 interaction as a potential target for anabolic therapy of osteoporosis. Here, we screened small‐molecule inhibitors of the Dvl–CXXC5 interaction via a newly established in vitro assay system. The screened compounds were found to activate the Wnt/β‐catenin pathway and enhance osteoblast differentiation in primary osteoblasts. The bone anabolic effects of the compounds were shown using ex vivo‐cultured calvaria. Nuclear magnetic resonance (NMR) titration analysis confirmed interaction between Dvl PDZ domain and KY‐02061, a representative of the screened compounds. Oral administration of KY‐02327, one of 55 newly synthesized KY‐02061 analogs, successfully rescued bone loss in the ovariectomized (OVX) mouse model. In conclusion, small‐molecule inhibitors of the Dvl–CXXC5 interaction that block negative feedback regulation of Wnt/β‐catenin signaling are potential candidates for the development of bone anabolic anti‐osteoporosis drugs.

Low-Density Lipoprotein Receptor-Related Proteins in Skeletal Development and Disease

The identification of the low-density lipoprotein receptor (LDLR) provided a foundation for subsequent studies in lipoprotein metabolism, receptor-mediated endocytosis, and many other fundamental biological functions. The importance of the LDLR led to numerous studies that identified homologous molecules and ultimately resulted in the description of the LDL-receptor superfamily, a group of proteins that contain domains also found in the LDLR. Subsequent studies have revealed that members of the LDLR-related protein family play roles in regulating many aspects of signal transduction. This review is focused on the roles of selected members of this protein family in skeletal development and disease. We present background on the identification of this subgroup of receptors, discuss the phenotypes associated with alterations in their function in human patients and mouse models, and describe the current efforts to therapeutically target these proteins to treat human skeletal disease.

Transcriptional regulation of Runx2 by HSP90 controls osteosarcoma apoptosis via the AKT/GSK-3β/β-catenin signaling

Osteosarcoma (OS) is the most malignant primary bone tumor in children and adolescents with limited treatment options and poor prognosis. Recently, aberrant expression of Runx2 has been found in OS, thereby contributing to the development, and progression of OS. However, the upstream signaling molecules that regulate its expression in OS remain largely unknown. In the present study, we first confirmed that the inhibition of HSP90 with 17-AAG caused significant apoptosis of OS cells via a caspase-3-dependent mechanism, and that inhibition or knockdown of HSP90 by 17-AAG or siRNAs significantly suppressed mRNA and protein expression of Runx2. Furthermore, we provided evidence that Runx2 was transcriptionally regulated by HSP90 when using MG132 and CHX chase assay. We also demonstrated that β-catenin was overexpressed in OS tissue, and that knockdown of β-catenin induced pronounced apoptosis of OS cells in the presence or absence of 17-AAG. Interestingly, this phenomenon was accompanied with a significant reduction of Runx2 and Cyclin D1 expression, indicating an essential role of Runx2/Cyclin D1 in 17-AAG-induced cells apoptosis. Moreover, we demonstrated that the apoptosis of OS cells induced by 17-AAG did require the involvement of the AKT/GSK-3β/β-catenin signaling pathway by using pharmacological inhibitor GSK-3β (LiCl) or siGSK-3β. Our findings reveal a novel mechanism that Runx2 is transcriptionally regulated by HSP90 via the AKT/GSK-3β/β-catenin signaling pathway, and by which leads to apoptosis of OS cells.

Impaired WNT signaling and the spine-Heterozygous WNT1 mutation causes severe age-related spinal pathology

BACKGROUND

WNT signaling plays a major role in bone and cartilage metabolism. Impaired WNT/β-catenin signaling leads to early-onset osteoporosis, but specific features in bone and other tissues remain inadequately characterized. We have identified two large Finnish families with early-onset osteoporosis due to a heterozygous WNT1 mutation c.652T>G, p.C218G. This study evaluated the impact of impaired WNT/β-catenin signaling on spinal structures.

METHODS

Altogether 18 WNT1 mutation-positive (age range 11-76years, median 49years) and 14 mutation-negative subjects (10-77years, median 43years) underwent magnetic resonance imaging (MRI) of the spine. The images were reviewed for spinal alignment, vertebral compression fractures, intervertebral disc changes and possible endplate deterioration. The findings were correlated with clinical data.

RESULTS

Vertebral compression fractures were present in 78% (7/9) of those aged over 50years but were not seen in younger mutation-positive subjects. All those with fractures had several severely compressed vertebrae. Altogether spinal compression fractures were present in 39% of those with a WNT1 mutation. Only 14% (2/14) mutation-negative subjects had one mild compressed vertebra each. The mutation-positive subjects had a higher mean spinal deformity index (4.0±7.3 vs 0.0±0.4) and more often increased thoracic kyphosis (Z-score>+2.0 in 33% vs 0%). Further, they had more often Schmorl nodes (61% vs 36%), already in adolescence, and their intervertebral discs were enlarged.

CONCLUSION

Compromised WNT signaling introduces severe and progressive changes to the spinal structures. Schmorl nodes are prevalent even at an early age and increased thoracic kyphosis and compression fractures become evident after the age of 50years. Therapies targeting the WNT pathway may be an effective way to prevent spinal pathology not only in those harboring a mutation but also in the general population with similar pathology.

In vitro effect of microRNA-107 targeting Dkk-1 by regulation of Wnt/β-catenin signaling pathway in osteosarcoma

BACKGROUND

The aim of the study was to explore the effects of microRNA-107 (miR-107) by targeting Dkk-1 on osteosarcoma (OS) via the Wnt/β-catenin signaling pathway.

METHODS

OS and adjacent tissues were collected from 67 patients diagnosed with OS. Expressions of miR-107, Dkk-1, LRP5, β-catenin, and c-Myc were detected by the quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting. The dual-luciferase reporter gene assay was performed to observe the relationship between miR-107 and Dkk-1.Transfected cells were divided into different investigating groups designated as Inhibitor, Mimic, siRNA, Inhibitor + siRNA, negative control (NC), and blank groups. qRT-PCR and Western blotting were used to detect expressions of miR-107, Dkk-1, β-catenin, Bcl-2, c-Myc, Caspase-3, and PARP. Cell counting kit-8 (CCK-8), flow cytometry (FCM), colony-formation efficiency (CFE), and subcutaneous tumorigenicity assays were all utilized for to determine cell proliferation, apoptosis, colony-forming, and tumorigenic abilities.

RESULTS

Dkk-1 is the target gene of miR-107. Decreased expressions of miR-107, LRP5, β-catenin, and c-Myc, and increased expressions of Dkk-1 were found in OS tissues. The Mimic and siRNA groups exhibited decreased proliferation rates, colony-forming abilities, and tumorigenicity and increased apoptosis rates, whereas the inhibitor group showed opposite trends when compared to the blank group. On the other hand, expressions of miR-107, LRP5, β-catenin, c-Myc, Caspase-3, and PARP were all elevated in the mimic group, whereas expressions of Dkk-1 and Bcl-2 were reduced; opposite trends were observed in the inhibitor group.

CONCLUSION

We conclude that miR-107 is likely to inhibit the occurrence and development of OS by down-regulating Dkk-1 via the Wnt/β-catenin signaling pathway, providing us with a new therapeutic target for the treatment of OS.