In vivo analysis of Wnt signaling in bone

LDL receptor-related protein 5 rs648438 polymorphism is associated with the risk of skeletal fluorosis

To investigate the potential association between LRP5 rs648438 polymorphism and the risk of skeletal fluorosis (SF) was evaluated in a cross-sectional case-control study conducted in Shanxi, China, in 2019. A total of 973 individuals were enrolled in this study, in which cases and controls were 346 and 627, respectively. SF was diagnosed according to the standard WS/192-2008 (China). The LRP5 rs648438 was detected by the multiple PCR and sequencing. LRP5 rs648438 was found to follow a dominant genetic model using a web-based SNP-STATS software. Logistic regression analysis found that the TC/CC genotype of LRP5 rs648438 might be a protective factor for SF. When stratified by gender, this protective effect of TC/CC genotype in rs648438 was pronounced in males. There was an interaction between gender and rs648438 on risk of SF. Our study suggested that TC/CC genotype of rs648438 might be a protective factor for water-drinking-type skeletal fluorosis, especially in male participants.

Advances in additive manufacturing of polycaprolactone based scaffolds for bone regeneration

Critical sized bone defects are difficult to manage and currently available clinical/surgical strategies for treatment are not completely successful. Polycaprolactone (PCL) which is a biodegradable and biocompatible thermoplastic can be 3D printed using medical images into patient specific bone implants. The excellent mechanical properties and low immunogenicity of PCL makes it an ideal biomaterial candidate for 3D printing of bone implants. Though PCL suffers from the limitation of being bio-inert. Here we describe the use of PCL as a biomaterial for 3D printing for bone regeneration, and advances made in the field. The specific focus is on the different 3D printing techniques used for this purpose and various modification that can enhance bone regeneration following the development pathways. We further describe the effect of various scaffold characteristics on bone regeneration both in vitro and the translational assessment of these 3D printed PCL scaffolds in animal studies. The generated knowledge will help understand cell-material interactions of 3D printed PCL scaffolds, to further improve scaffold chemistry and design that can replicate bone developmental processes and can be translated clinically.

Role of irisin in bone diseases

Bone diseases are common among middle-aged and elderly people, and harm to activities of daily living (ADL) and quality of life (QOL) for patients. It is crucial to search for key regulatory factors associated with the development of bone diseases and explore potential therapeutic targets for bone diseases. Irisin is a novel myokine that has been discovered in recent years. Accumulating evidence indicates that irisin has beneficial effects in the treatment of various diseases such as metabolic, cardiovascular and neurological disorders, especially bone-related diseases. Recent studies had shown that irisin plays the role in various bone diseases such as osteoarthritis, osteoporosis and other bone diseases, suggesting that irisin may be a potential molecule for the prevention and treatment of bone diseases. Therefore, in this review, by consulting the related domestic and international literature of irisin and bone diseases, we summarized the specific regulatory mechanisms of irisin in various bone diseases, and provided a systematic theoretical basis for its application in the diagnosis and treatment of the bone diseases.

Changes in Bone Metabolism in Patients with Rheumatoid Arthritis during Tumor Necrosis Factor Inhibitor Therapy

Tumor necrosis factor alpha (TNF-α), which enhances osteoclast activity and bone resorption, is one of the key inflammation mediators in rheumatoid arthritis (RA). The aim of this study was to assess the influence of yearlong TNF-α inhibitor application on bone metabolism. The study sample comprised 50 female patients with RA. Analyses involved the osteodensitometry measurements obtained using a "Lunar" type apparatus and the following biochemical markers from serum: procollagen type 1 N-terminal propeptide (P1NP), beta crosslaps C-terminal telopeptide of collagen type I (b-CTX) by ECLIA method, total and ionized calcium, phosphorus, alkaline phosphatase, parathyroid hormone and vitamin D. Analyses revealed changes in bone mineral density (BMD) at L1-L4 and the femoral neck, with the difference in mean BMD (g/cm²) not exceeding the threshold of statistical significance (p = 0.180; p = 0.502). Upon completion of 12-month therapy, a significant increase (p < 0.001) in P1NP was observed relative to b-CTX, with mean total calcium and phosphorus values following a decreasing trend, while vitamin D levels increased. These results suggest that yearlong application of TNF inhibitors has the capacity to positively impact bone metabolism, as indicated by an increase in bone-forming markers and relatively stable BMD (g/cm²).

Regulation of bone health through physical exercise: Mechanisms and types

Osteoporosis, characterized by bone mineral density reduction, bone mass loss, increased bone fragility, and propensity to fractures, is a common disease in older individuals and one of the most serious health problems worldwide. The imbalance between osteoblasts and osteoclasts results in the predominance of bone resorption and decreased bone formation. In recent years, it has been found that regular and proper exercise not only helps prevent the occurrence of osteoporosis but also adds benefits to osteoporosis therapy; accordingly, bone homeostasis is closely associated with mechanical stress and the intricate crosstalk between osteoblasts and osteoclasts. In this review, we summarize the mechanisms of exercise on osteoporosis and provide new proposals for the prevention and treatment of osteoporosis.

Canonical Wnt signaling enhances pro-inflammatory response to titanium by macrophages

Biomaterial characteristics like surface roughness and wettability can determine the phenotype of macrophages following implantation. We have demonstrated that inhibiting Wnt ligand secretion abolishes macrophage polarization in vitro and in vivo; however, the role of canonical Wnt signaling in macrophage activation in response to physical and chemical biomaterial cues is unknown. The aim of this study was to understand whether canonical Wnt signaling affects the response of macrophages to titanium (Ti) surface roughness or wettability in vitro and in vivo. Activating canonical Wnt signaling increased expression of toll-like receptors and interleukin receptors and secreted pro-inflammatory cytokines and reduced anti-inflammatory cytokines on Ti, regardless of surface properties. Inhibiting canonical Wnt signaling reduced pro-inflammatory cytokines on all Ti surfaces and increased anti-inflammatory cytokines on rough or rough-hydrophilic Ti. In vivo, activating canonical Wnt signaling increased total macrophages, pro-inflammatory macrophages, and T cells and decreased anti-inflammatory macrophages on both smooth and rough-hydrophilic implants. Functionally, canonical Wnt activation increases pro-inflammatory macrophage response to cell and cell-extracellular matrix lysates. These results demonstrate that activating canonical Wnt signaling primes macrophages to a pro-inflammatory phenotype that affects their response to Ti implants in vitro and in vivo.

Expression of Wnt signaling agonists and antagonists in periodontitis and healthy subjects, before and after non-surgical periodontal treatment: A systematic review

Periodontitis is a preventable and treatable multifactorial chronic inflammatory disease that can lead to irreversible periodontal destruction and tooth loss. Wnt signaling and its regulators play an important role in periodontal inflammation, destruction, regeneration, and reconstruction. This systematic review aimed at investigating the involvement of Wnt signaling agonists and antagonists in periodontitis and healthy subjects, before and after periodontal treatment. Electronic searches were carried out using MEDLINE/PubMed, EMBASE, and Cochrane Library databases in addition to hand searches. Studies having different designs assessing the levels of Wnt signaling antagonist and agonist levels in gingival crevicular fluid, serum, and tissue in patients diagnosed with periodontitis or gingivitis, compared with healthy individuals were included. In addition, studies compared these levels in periodontitis patients before and after non-surgical periodontal therapy were also eligible. Sixteen studies met the eligibility criteria. Sclerostin (SOST) has been mainly investigated in the literature (8 publications). Sclerostin (5 studies), Wnt-5a (2 studies), secreted frizzled-related protein 1 (SFRP1) (3 studies), and β-catenin (3 studies) show increased levels in periodontitis compared with periodontal health. Strong correlations between marker levels and periodontal clinical parameters were identified for SOST (5 studies), SFRP1 (2 studies), and β-catenin (2 studies). SOST (3 studies) and SFRP1 (1 study) levels significantly decrease following non-surgical periodontal treatment. The present systematic review demonstrated an association between Wnt signaling agonist and antagonist levels and periodontitis. Wnt agonists and antagonists may serve as valuable diagnostic and prognostic markers for periodontitis onset and progression. Further case-control and longitudinal studies should be conducted for different Wnt signaling agonists and antagonists.

RecQ Helicase Somatic Alterations in Cancer

Named the “caretakers” of the genome, RecQ helicases function in several pathways to maintain genomic stability and repair DNA. This highly conserved family of enzymes consist of five different proteins in humans: RECQL1, BLM, WRN, RECQL4, and RECQL5. Biallelic germline mutations in BLM, WRN, and RECQL4 have been linked to rare cancer-predisposing syndromes. Emerging research has also implicated somatic alterations in RecQ helicases in a variety of cancers, including hematological malignancies, breast cancer, osteosarcoma, amongst others. These alterations in RecQ helicases, particularly overexpression, may lead to increased resistance of cancer cells to conventional chemotherapy. Downregulation of these proteins may allow for increased sensitivity to chemotherapy, and, therefore, may be important therapeutic targets. Here we provide a comprehensive review of our current understanding of the role of RecQ DNA helicases in cancer and discuss the potential therapeutic opportunities in targeting these helicases.

bFGF-Loaded Mesoporous Silica Nanoparticles Promote Bone Regeneration Through the Wnt/β-Catenin Signalling Pathway

Background

Bone defects remain an unsolved clinical problem due to the lack of effective osteogenic induction protocols. Nanomaterials play an important role in bone defect repair by stimulating osteogenesis. However, constructing an effective bioactive nanomaterial remains a substantial challenge.

Methods

In this study, mesoporous silica nanoparticles (MSNs) were prepared and used as nanocarriers for basic fibroblast growth factor (bFGF). The characteristics and biological properties of the synthetic bFGF@MSNs were tested. The osteogenic effects of the particles on the behavior of MC3T3-E1 cells were investigated in vitro. In addition, the differentially expressed genes during induction of osteogenesis were analyzed by transcriptomic sequencing. Radiological and histological observations were carried out to determine bone regeneration capability in a distal femur defect model.

Results

Achieving bFGF sustained release, bFGF@MSNs had uniform spherical morphology and good biocompatibility. In vitro osteogenesis induction experiments showed that bFGF@MSNs exhibited excellent osteogenesis performance, with upregulation of osteogenesis-related genes (RUNX2, OCN, Osterix, ALP). Transcriptomic sequencing revealed that the Wnt/β-catenin signalling pathway could be activated in regulation of biological processes. In vivo, bone defect repair experiments showed enhanced bone regeneration, as indicated by radiological and histological analysis, after the application of bFGF@MSNs.

Conclusion

bFGF@MSNs can promote bone regeneration by activating the Wnt/β-catenin signalling pathway. These particles are expected to become a potential therapeutic bioactive material for clinical application in repairing bone defects in the future.

Naringin Promotes Osteogenic/Odontogenic Differentiation of Dental Pulp Stem Cells via Wnt/β-Catenin

Purpose

This investigation intended to unravel the effect and mechanism of naringin on the proliferation and osteogenic differentiation of human dental pulp stem cells (hDPSCs).

Methods

hDPSCs were induced to differentiate, and the degree of cell differentiation was observed by alizarin red staining, Oil Red O staining, and Alcian blue staining. hDPSCs were treated with 0, 20, 40, and 80 μmol/L naringin for 48 h, respectively. The proliferation rate and chemotaxis of the cells were measured by MTT and transwell assay, alkaline phosphatase (ALP) activity and osteogenic differentiation degree by ALP staining and alizarin red staining, and gene expression of osteogenic markers by qRT-PCR. Additionally, western blot was performed to test the levels of Wnt/β-catenin signaling-related proteins in hDPSCs.

Results

The isolated hDPSCs with spindle-shaped morphology had good differentiation capability. Further experiments confirmed naringin-caused increases in the proliferation rate and migration ability of hDPSCs. In addition, compared with the control group, naringin-treated cells had strong ALP activity and ossification levels and higher expression of Runx2, OPN, DSPP, and DMP1. The western blot results showed that naringin significantly activated Wnt/β-catenin signaling in hDPSCs.

Conclusion

Taken together, naringin enhances the proliferation, migration, and osteogenesis of hDPSCs through stimulating Wnt/β-catenin signaling pathway.

The osteocyte as a signaling cell

Osteocytes, former osteoblasts encapsulated by mineralized bone matrix, are far from being passive and metabolically inactive bone cells. Instead, osteocytes are multifunctional and dynamic cells capable of integrating hormonal and mechanical signals and transmitting them to effector cells in bone and in distant tissues. Osteocytes are a major source of molecules that regulate bone homeostasis by integrating both mechanical cues and hormonal signals that coordinate the differentiation and function of osteoclasts and osteoblasts. Osteocyte function is altered in both rare and common bone diseases, suggesting that osteocyte dysfunction is directly involved in the pathophysiology of several disorders affecting the skeleton. Advances in osteocyte biology initiated the development of novel therapeutics interfering with osteocyte-secreted molecules. Moreover, osteocytes are targets and key distributors of biological signals mediating the beneficial effects of several bone therapeutics used in the clinic. Here we review the most recent discoveries in osteocyte biology demonstrating that osteocytes regulate bone homeostasis and bone marrow fat via paracrine signaling, influence body composition and energy metabolism via endocrine signaling, and contribute to the damaging effects of diabetes mellitus and hematologic and metastatic cancers in the skeleton.

Adipsin promotes bone marrow adiposity by priming mesenchymal stem cells

Background

Marrow adipose tissue (MAT) has been shown to be vital for regulating metabolism and maintaining skeletal homeostasis in the bone marrow (BM) niche. As a reflection of BM remodeling, MAT is highly responsive to nutrient fluctuations, hormonal changes, and metabolic disturbances such as obesity and diabetes mellitus. Expansion of MAT has also been strongly associated with bone loss in mice and humans. However, the regulation of BM plasticity remains poorly understood, as does the mechanism that links changes in marrow adiposity with bone remodeling.

Methods

We studied deletion of Adipsin, and its downstream effector, C3, in C57BL/6 mice as well as the bone-protected PPARγ constitutive deacetylation 2KR mice to assess BM plasticity. The mice were challenged with thiazolidinedione treatment, calorie restriction, or aging to induce bone loss and MAT expansion. Analysis of bone mineral density and marrow adiposity was performed using a μCT scanner and by RNA analysis to assess adipocyte and osteoblast markers. For in vitro studies, primary bone marrow stromal cells were isolated and subjected to osteoblastogenic or adipogenic differentiation or chemical treatment followed by morphological and molecular analyses. Clinical data was obtained from samples of a previous clinical trial of fasting and high-calorie diet in healthy human volunteers.

Results

We show that Adipsin is the most upregulated adipokine during MAT expansion in mice and humans in a PPARγ acetylation-dependent manner. Genetic ablation of Adipsin in mice specifically inhibited MAT expansion but not peripheral adipose depots, and improved bone mass during calorie restriction, thiazolidinedione treatment, and aging. These effects were mediated through its downstream effector, complement component C3, to prime common progenitor cells toward adipogenesis rather than osteoblastogenesis through inhibiting Wnt/β-catenin signaling.

Conclusions

Adipsin promotes new adipocyte formation and affects skeletal remodeling in the BM niche. Our study reveals a novel mechanism whereby the BM sustains its own plasticity through paracrine and endocrine actions of a unique adipokine.

Funding

This work was supported by the National Institutes of Health T32DK007328 (NA), F31DK124926 (NA), R01DK121140 (JCL), R01AR068970 (BZ), R01AR071463 (BZ), R01DK112943 (LQ), R24DK092759 (CJR), and P01HL087123 (LQ).

FOXQ1 promotes the osteogenic differentiation of bone mesenchymal stem cells via Wnt/β-catenin signaling by binding with ANXA2

BACKGROUND

This study investigated the role of Forkhead box Q1 (FOXQ1) in the osteogenic differentiation of bone mesenchymal stem cells.

METHODS

Mouse bone mesenchymal stem cells (mBMSCs) were transfected with lentivirus to generate Foxq1-overexpressing mBMSCs, Foxq1-suppressed mBMSCs, and mBMSC controls. The activity of osteogenic differentiation was evaluated with alizarin red staining, alkaline phosphatase activity assay, and RT-qPCR. Wnt/β-catenin signaling activities were compared among groups by TOPFlash/FOPFlash assay, immunofluorescence staining, and western blot assay of beta-catenin (CTNNB1). Coimmunoprecipitation mass spectrometry was also carried out to identify proteins binding with FOXQ1.

RESULTS

Our data showed that FOXQ1 expression was positively correlated with the osteogenic differentiation of the mBMSCs. FOXQ1 also promoted the nuclear translocation of CTNNB1 in the mBMSCs, enhancing Wnt/β-catenin signaling, which was also shown to be essential for the osteogenic differentiation-promoting effect of FOXQ1 in the mBMSCs. Annexin A2 (ANXA2) was bound with FOXQ1, and its depletion reversed the promoting effect of FOXQ1 on Wnt/β-catenin signaling.

CONCLUSION

These results showed that FOXQ1 binds with ANXA2, promoting Wnt/β-catenin signaling in bone mesenchymal stem cells, which subsequently promotes osteogenic differentiation.

Contrary Roles of Wnt/β-Catenin Signaling in BMP9-Induced Osteogenic and Adipogenic Differentiation of 3T3-L1 Preadipocytes

Our previous study revealed that 3T3-L1 preadipocytes can differentiate to either osteoblasts or adipocytes in response to bone morphogenic protein 9 (BMP9). In the present study, we try to further investigate whether the Wnt/β-catenin signaling plays a crucial role in this process. It was found that BMP9 effectively activated the Wnt/β-catenin signaling, and induced the expression levels of certain canonical Wnt ligands and their receptors in preadipocytes. Exogenous expression of β-catenin, Wnt1, Wnt3a, and Wnt10b potentiated BMP9-induced alkaline phosphatase (ALP) activity, while β-catenin knockdown or Dickkopf 1 (Dkk1) diminished BMP9-induced ALP activity. Moreover, it was demonstrated that β-catenin overexpression promoted BMP9-induced mineralization, and increased the expression levels of late osteogenic markers osteopontin and osteocalcin. Furthermore, β-catenin inhibited BMP9-induced lipid accumulation and the adipogenic marker adipocyte fatty acid binding protein (aP2). The cell-implantation assay results identified that β-catenin not only augmented BMP9-induced ectopic bone formation, but also blocked adipogenesis in vivo. Mechanistically, it was found that β-catenin and BMP9 synergistically stimulated the osteogenic transcription factors runt-related transcription factor 2 (Runx2) and Osterix (OSX). However, BMP9-induced adipogenic transcription factors, peroxisome proliferator-activated receptor γ (PPARγ) and CCAAT enhancer-binding protein α (C/EBPα), were inhibited by β-catenin. Therefore, these findings suggested that the Wnt/β-catenin signaling, potentially via the modulation of osteogenic and adipogenic transcriptional factors, exerts an opposite effect on BMP9-induced osteogenic and adipogenic differentiation in preadipocytes.

DNA methylation and gene expression of sFRP2, sFRP4, Dkk 1, and Wif1 during osteoblastic differentiation of bone marrow derived mesenchymal stem cells

OBJECTIVES

Bone marrow derived mesenchymal stem cells (BMSCs) are an irresistible choice for use in stem cell therapy and regenerative medicine. BMSCs osteoblastic differentiation is also important in bone development, diseases, malignancies, and cancers studies. Wnt signaling pathway antagonists, Dickkopf-1 (Dkk 1), Secreted Frizzled-Related Proteins (sFRPs), and Wnt Inhibitory Factor 1 (Wif1) play important roles in inducing osteoblastic differentiation. This study is the first to investigate the association between DNA methylation and gene expression of Dkk1, sFRP2, sFRP4, and Wif1 during BMSCs osteoblastic differentiation.

METHODS

Human BMSCs were isolated and characterized using flow cytometry. Then, cells were treated with osteo-differentiation medium for three weeks. Alizarin red S staining and polymerase chain reaction (PCR) (alkaline phosphatase/osteocalcin) were performed for confirmation. The expression of Dkk 1, sFRP2, sFRP4, and Wif1 genes was evaluated at days 7, 14, and 21 using real-time PCR. Methylation-specific PCR (MSP) was performed to detect the methylation status of the promoters of the genes.

RESULTS

Data showed significant decreases (P < 0.05) during various days of BMSCs differentiation, while the promoters of the genes remained mostly un-methylated.

CONCLUSIONS

The down-regulation of Dkk 1, sFRP2, sFRP4, and Wif1 regulates various stages of human BMSCs during osteoblastic differentiation. DNA methylation does not interfere in the down-regulation of these genes, except for Wif1. We propose that the Wnt antagonist gene promoters should remain un-methylated during osteoblastic differentiation of BMSCs and that the down-regulation of these genes may contribute to other epigenetic mechanisms, other than DNA methylation, which implicitly indicates the role of DNA methylation in osteogenic cancers.

Inhibition of Axin1 in osteoblast precursor cells leads to defects in postnatal bone growth through suppressing osteoclast formation

Axin1 is a negative regulator of β-catenin signaling and its role in osteoblast precursor cells remains undefined. In the present studies, we determined changes in postnatal bone growth by deletion of Axin1 in osteoblast precursor cells and analyzed bone growth in newborn and postnatal Axin1Osx mice and found that hypertrophic cartilage area was largely expanded in Axin1Osx KO mice. A larger number of chondrocytes and unabsorbed cartilage matrix were found in the bone marrow cavity of Axin1Osx KO mice. Osteoclast formation in metaphyseal and subchondral bone areas was significantly decreased, demonstrated by decreased TRAP-positive cell numbers, associated with reduction of MMP9- and cathepsin K-positive cell numbers in Axin1Osx KO mice. OPG expression and the ratio of Opg to Rankl were significantly increased in osteoblasts of Axin1Osx KO mice. Osteoclast formation in primary bone marrow derived microphage (BMM) cells was significantly decreased when BMM cells were cultured with conditioned media (CM) collected from osteoblasts derived from Axin1Osx mice compared with BMM cells cultured with CM derived from WT mice. Thus, the loss of Axin1 in osteoblast precursor cells caused increased OPG and the decrease in osteoclast formation, leading to delayed bone growth in postnatal Axin1Osx KO mice.

Ethanol Inhibits Mesenchymal Stem Cell Osteochondral Lineage Differentiation Due in Part to an Activation of Forkhead Box Protein O-Specific Signaling

BACKGROUND

During bone fracture repair, resident mesenchymal stem cells (MSCs) differentiate into chondrocytes, to form a cartilaginous fracture callus, and osteoblasts, to ossify the collagen matrix. Our laboratory previously reported that alcohol administration led to decreased cartilage formation within the fracture callus of rodents and this effect was mitigated by postfracture antioxidant treatment. Forkhead box protein O (FoxO) transcription factors are activated in response to intracellular reactive oxygen species (ROS), and alcohol has been shown to increase ROS. Activation of FoxOs has also been shown to inhibit canonical Wnt signaling, a necessary pathway for MSC differentiation. These findings have led to our hypothesis that alcohol exposure decreases osteochondrogenic differentiation of MSCs through the activation of FoxOs.

METHODS

Primary rat MSCs were treated with ethanol (EtOH) and assayed for FoxO expression, FoxO activation, and downstream target expression. Next, MSCs were differentiated toward osteogenic or chondrogenic lineages in the presence of 50 mM EtOH and alterations in osteochondral lineage marker expression were determined. Lastly, osteochondral differentiation experiments were repeated with FoxO1/3 knockdown or with FoxO1/3 inhibitor AS1842856 and osteochondral lineage marker expression was determined.

RESULTS

EtOH increased the expression of FoxO3a at mRNA and protein levels in primary cultured MSCs. This was accompanied by an increase in FoxO1 nuclear localization, FoxO1 activation, and downstream catalase expression. Moreover, EtOH exposure decreased expression of osteogenic and chondrogenic lineage markers. FoxO1/3 knockdown restored proosteogenic and prochondrogenic lineage marker expression in the presence of 50 mM EtOH. However, FoxO1/3 inhibitor only restored proosteogenic lineage marker expression.

CONCLUSIONS

These data show that EtOH has the ability to inhibit MSC differentiation, and this ability may rely, at least partially, on the activation of FoxO transcription factors.

Vasoactive Intestinal Peptide Stimulates Bone Marrow-Mesenchymal Stem Cells Osteogenesis Differentiation by Activating Wnt/β-Catenin Signaling Pathway and Promotes Rat Skull Defect Repair

Bone defect regeneration is a complex process that involves the coordination of a variety of different type of cells. As bone tissues are innervated and rich in nerve fibers, the neuropeptides released from various never fibers could regulate bone development, metabolism, and remodeling. Among all the neuropeptides, vasoactive intestinal peptide (VIP) could modulate the functions of both osteoblasts and osteoclasts, and may play a vital role in bone marrow mesenchymal stem cell (BMSC) osteogenesis during bone repair. In this study, we investigated the role of VIP in bone formation and the mechanisms of VIP in mediating BMSC osteogenic differentiation, and its possibility in clinical application of bone defect reconstruction. Our in vitro study results indicated that VIP promoted BMSC osteogenic differentiation by activating Wnt/β-catenin signaling pathway in BMSCs. VIP could also stimulate tube formation of EA.hy926 endothelial cell and increase vascular endothelial growth factor (VEGF) expression in BMSCs. Furthermore, in the rat skull defect model, VIP-conjugated functionalized hydrogel significantly enhanced cranial bone defect repair compared with the control group, with increased bone formation and angiogenesis. Taken together, as a member of neuropeptides, VIP could promote the BMSCs osteogenesis and angiogenesis differentiation in vitro and stimulate bone repair in vivo by activating Wnt/β-catenin signaling pathway. The knowledge obtained from this study emphasized the close association between innervation and bone repair process, and VIP may be a potential therapeutic agent for augmenting bone repair.

Adjuvant drug-assisted bone healing: Part III - Further strategies for local and systemic modulation

In this third in a series of reviews on adjuvant drug-assisted bone healing, further approaches aiming at influencing the healing process are discussed. Local and systemic modulation of bone metabolism is pursued with use of a number of drugs with completely different indications, which are characterized by a pleiotropic spectrum of action. These include drugs used to treat lipid disorders (HMG-CoA reductase inhibitors), hypertension (ACE inhibitors), osteoporosis (bisphosphonates), cancer (proteasome inhibitors) and others. Potential applications to enhance bone healing are discussed.

Carboxy-Terminal Cementum Protein 1-Derived Peptide 4 (cemp1-p4) Promotes Mineralization through wnt/β-catenin Signaling in Human Oral Mucosa Stem Cells

Human cementum protein 1 (CEMP1) is known to induce cementoblast and osteoblast differentiation and alkaline phosphatase (ALP) activity in human periodontal ligament-derived cells in vitro and promotes bone regeneration in vivo. CEMP1's secondary structure analysis shows that it has a random-coiled structure and is considered an Intrinsic Disordered Protein (IDP). CEMP1's short peptide sequences mimic the biological capabilities of CEMP1. However, the role and mechanisms of CEMP1's C-terminal-derived synthetic peptide (CEMP1-p4) in the canonical Wnt/β-catenin signaling pathway are yet to be described. Here we report that CEMP1-p4 promotes proliferation and differentiation of Human Oral Mucosa Stem Cells (HOMSCs) by activating the Wnt/β-catenin pathway. CEMP1-p4 stimulation upregulated the expression of β-catenin and glycogen synthase kinase 3 beta (GSK-3B) and activated the transcription factors TCF1/7 and Lymphoid Enhancer binding Factor 1 (LEF1) at the mRNA and protein levels. We found translocation of β-catenin to the nucleus in CEMP1-p4-treated cultures. The peptide also penetrates the cell membrane and aggregates around the cell nucleus. Analysis of CEMP1-p4 secondary structure revealed that it has a random-coiled structure. Its biological activities included the induction to nucleate hydroxyapatite crystals. In CEMP1-p4-treated HOMSCs, ALP activity and calcium deposits increased. Expression of Osterix (OSX), Runt-related transcription factor 2 (RUNX2), Integrin binding sialoproptein (IBSP) and osteocalcin (OCN) were upregulated. Altogether, these data show that CEMP1-p4 plays a direct role in the differentiation of HOMSCs to a "mineralizing-like" phenotype by activating the β-catenin signaling cascade.

RECQ DNA Helicases and Osteosarcoma

The RECQ family of DNA helicases is a conserved group of enzymes that plays an important role in maintaining genomic stability. Humans possess five RECQ helicase genes, and mutations in three of them - BLM, WRN, and RECQL4 - are associated with the genetic disorders Bloom syndrome, Werner syndrome, and Rothmund-Thomson syndrome (RTS), respectively. These syndromes share overlapping clinical features, and importantly they are all associated with an increased risk of cancer. Patients with RTS have the highest specific risk of developing osteosarcoma compared to all other cancer predisposition syndromes; therefore, RTS serves as a relevant model to study the pathogenesis and molecular genetics of osteosarcoma. The "tumor suppressor" function of the RECQ helicases continues to be an area of active investigation. This chapter will focus primarily on the known cellular functions of RECQL4 and how these may relate to tumorigenesis, as well as ongoing efforts to understand RECQL4's functions in vivo using animal models. Understanding the RECQ pathways will provide insight into avenues for novel cancer therapies in the future.

Loss of Dkk-1 in Osteocytes Mitigates Alveolar Bone Loss in Mice With Periodontitis

Background: Periodontitis is a highly prevalent infection-triggered inflammatory disease that results in bone loss. Inflammation causes bone resorption by osteoclasts, and also by suppression of bone formation via increase of Dickkopf-1 (Dkk-1), an inhibitor of Wnt signaling. Here, we tested the hypothesis that osteocytic Dkk-1 is a key factor in the pathogenesis of periodontitis-induced alveolar bone loss (ABL).

Methods: Twelve-week-old female mice with a constitutive deletion of Dkk-1 specifically in osteocytes (Dkk-1^fl/fl;Dmp1:Cre) were subjected to experimental periodontitis (EP). Cre-negative littermates served as controls. EP was induced by placing a ligature around the upper 2nd left molar, the contralateral side was used as control. Mice were killed after 11 days and maxillae removed for micro-CT and histological analyses. The mRNA expression of Dkk-1, Runx2, Osteocalcin, OPG, RANKL, RANKL/OPG ratio, LEF-1, and TCF-7 were assessed in maxillae, while mRNA expressions of TNF and IL-1 were evaluated on gingiva using real-time PCR. Blood samples were collected for Dkk-1, CTX, and P1NP measurement by ELISA.

Results: The deletion of Dkk-1 in osteocytes prevented ABL in mice with EP, compared to Cre-negative control mice with EP. Micro-CT analysis showed a significant reduction of bone loss (−28.5%) in EP Dkk-1^fl/fl;Dmp1:Cre-positive mice compared to their littermate controls. These mice showed a greater alveolar bone volume, bone mineral density, trabecular number, and trabecular thickness after EP when compared to the Cre-negative controls. The local expression in maxillae as well as the serum levels of Dkk-1 were reduced in Dkk-1^fl/fl;Dmp1:Cre-positive mice with EP. The transgenic mice submitted to EP showed increase of P1NP and reduction of CTX-I serum levels, and increase of TCF-7 expression. Histological analysis displayed less inflammatory infiltrates, a reduction of TNF and IL-1 expressions in the gingiva and fewer osteoclasts in Cre-positive animals with EP. Moreover, in mice with EP, the osteocytic deletion of Dkk-1 enhanced bone formation due to increased expressions of Runx2 and Osteocalcin and decreased expression of RANKL in maxillae.

Conclusion: In summary, Dkk-1 derived from osteocytes plays a crucial role in ABL in periodontitis.

MicroRNA-155 inhibition up-regulates LEPR to inhibit osteoclast activation and bone resorption via activation of AMPK in alendronate-treated osteoporotic mice

Osteoporosis is characterized by a progressive increase in bone fragility, leading to low bone mass and structural deterioration of bone tissue. MicroRNA-155 (miR-155) is highly expressed in osteoporosis. Thus, the current study aimed to investigate the effect of miR-155 on the inhibition of osteoclast activation and bone resorption by targeting leptin receptor (LEPR) through the adenosine monophosphate activated protein kinase (AMPK) pathway in alendronate-treated osteoporotic mice. An osteoporosis mouse model was established to examine the bone tension and bone density and the expression of miR-155 in osteoclasts. Binding sites between miR-155 and LEPR were verified. Osteoclasts in the treatment group were transfected with different mimic, inhibitor, vector, or siRNA for subsequent experiments. The expression of miR-155, LEPR, AMPK, p-AMPK, RANKL, OPG, M-CSF, RANK, TRAP, Bax, Bcl-2, and the contents of TNF-α and IL-1β were all examined. The proliferation and bone resorption of osteoclasts were also detected. Mice with osteoporosis exhibited decreased bone density and bone tension, along with elevated expression of miR-155. LEPR was verified as a target gene of miR-155. Down-regulated miR-155 was found to increase the expression of LEPR, AMPK, p-AMPK, OPG, Bax, decrease expression of TNF-α, IL-1β, RANKL, M-CSF, RANK, TRAP, Bcl-2, inhibit the cell proliferation and bone resorption of osteoclasts. Taken together, decreased miR-155 up-regulated LEPR via activation of AMPK, which ultimately repressed osteoclast activation and bone resorption of osteoclasts in alendronate-treated osteoporotic mice.

Sclerostin injection enhances orthodontic tooth movement in rats

OBJECTIVE

It was aimed to investigate the in vivo effects of local injection of sclerostin protein on orthodontic tooth movement.

DESIGN

A total of 48 rats underwent orthodontic mesialization of the maxillary first molars on both sides. Local injection was given at the compression side in the alveolar bone on both maxillary sides, with sclerostin protein carried by hydrogel on one side, and the same volume of normal saline carried by hydrogel on the other side serving as the control. After two weeks, the tooth movement amount and effects on the periodontium were assessed through micro-computed tomography (μCT) analysis, tartrate-resistant acid phosphatase (TRAP) staining and immunohistochemistry (IHC) analysis.

RESULTS

After two weeks of intervention, tooth movement was significantly greater in the 4 μg/kg and 20 μg/kg sclerostin injection groups, compared to the control. Analysis of the furcation area of the maxillary first molar showed that the 20 μg/kg group had significantly decreased BV/TV. At the compression side, the number of TRAP-positive osteoclasts was significantly increased in 20 μg/kg group compared to the control. The expression of RANKL was statistically higher in all the sclerostin groups, while the expression of OPG was statistically lower in the 4 μg/kg and 20 μg/kg groups, compared to the control. At the tension side, the expression of RUNX2 and COL-1 was statistically higher in the 20 μg/kg group compared to the control.

CONCLUSIONS

Local injection of sclerostin protein in the alveolar bone at the compression side accelerates OTM in rats by promoting osteoclastogenesis.

Why SNP rs227584 is associated with human BMD and fracture risk? A molecular and cellular study in bone cells

A large number of SNPs significant for osteoporosis (OP) had been identified by genome-wide association studies. However, the underlying association mechanisms were largely unknown. From the perspective of protein phosphorylation, gene expression regulation, and bone cell activity, this study aims to illustrate association mechanisms for representative SNPs of interest. We utilized public databases and bioinformatics tool to identify OP-associated SNPs which potentially influence protein phosphorylation (phosSNPs). Associations with hip/spine BMD, as well as fracture risk, in human populations for one significant phosSNP, that is, rs227584 (major/minor allele: C/A, EAS population) located in C17orf53 gene, were suggested in prior meta-analyses. Specifically, carriers of allele C had significant higher BMD and lower risk of low-trauma fractures than carriers of A. We pursued to test the molecular and cellular functions of rs227584 in bone through osteoblastic cell culture and multiple assays. We identified five phosSNPs significant for OP (P < 0.01). The osteoblastic cells, which was transfected with wild-type C17orf53 (allele C at rs227584, P126), demonstrated specific interaction with NEK2 kinase, increased expression levels of osteoblastic genes significantly (OPN, OCN, COL1A1, P < 0.05), and promoted osteoblast growth and ALP activity, in contrast to those transfected with mutant C17orf53 (allele A at rs227584, T126). In the light of the consistent evidences between the present functional study in human bone cells and the prior association studies in human populations, we conclude that the SNP rs227584, via altering protein-kinase interaction, regulates osteoblastic gene expression, influences osteoblast growth and activity, hence to affect BMD and fracture risk in humans.

Bone Remodeling and the Role of TRAF3 in Osteoclastic Bone Resorption

Skeletal health is maintained by bone remodeling, a process in which microscopic sites of effete or damaged bone are degraded on bone surfaces by osteoclasts and subsequently replaced by new bone, which is laid down by osteoblasts. This normal process can be disturbed in a variety of pathologic processes, including localized or generalized inflammation, metabolic and endocrine disorders, primary and metastatic cancers, and during aging as a result of low-grade chronic inflammation. Osteoclast formation and activity are promoted by factors, including cytokines, hormones, growth factors, and free radicals, and require expression of macrophage-colony stimulating factor (M-CSF) and receptor activator of NF-κB ligand (RANKL) by accessory cells in the bone marrow, including osteoblastic and immune cells. Expression of TNF receptor-associated factor 6 (TRAF6) is required in osteoclast precursors to mediate RANKL-induced activation of NF-κB, which is also necessary for osteoclast formation and activity. TRAF3, in contrast is not required for osteoclast formation, but it limits RANKL-induced osteoclast formation by promoting proteasomal degradation of NF-κB-inducing kinase in a complex with TRAF2 and cellular inhibitor of apoptosis proteins (cIAP). TRAF3 also limits osteoclast formation induced by TNF, which mediates inflammation and joint destruction in inflammatory diseases, including rheumatoid arthritis. Chloroquine and hydroxychloroquine, anti-inflammatory drugs used to treat rheumatoid arthritis, prevent TRAF3 degradation in osteoclast precursors and inhibit osteoclast formation in vitro. Chloroquine also inhibits bone destruction induced by ovariectomy and parathyroid hormone in mice in vivo. Mice genetically engineered to have TRAF3 deleted in osteoclast precursors and macrophages develop early onset osteoporosis, inflammation in multiple tissues, infections, and tumors, indicating that TRAF3 suppresses inflammation and tumors in myeloid cells. Mice with TRAF3 conditionally deleted in mesenchymal cells also develop early onset osteoporosis due to a combination of increased osteoclast formation and reduced osteoblast formation. TRAF3 protein levels decrease in bone and bone marrow during aging in mice and humans. Development of drugs to prevent TRAF3 degradation in immune and bone cells could be a novel therapeutic approach to prevent or reduce bone loss and the incidence of several common diseases associated with aging.

GH prevents adipogenic differentiation of mesenchymal stromal stem cells derived from human trabecular bone via canonical Wnt signaling

The imbalance between osteogenesis and adipogenesis, which naturally accompanies bone marrow senescence, may contribute to the development of bone-associated diseases, like osteoporosis. In the present study, using primary human mesenchymal stromal cells (hMSCs) isolated from trabecular bone, we assessed the possible effect of GH on hMSC differentiation potential into adipocytes. GH (5 ng/ml) significantly inhibited the lipid accumulation in hMSCs cultured for 14 days in lipogenic medium. GH decreased the expression of the adipogenic genes, CCAAT/enhancer-binding protein alpha (C/EBPα) and adiponectin (ADN) as well as the expression of two lipogenesis-related enzymes, lipoprotein lipase (LPL) and acethylCoA carboxylase (ACACA). In parallel, GH induced an increase in the gene expression and protein levels of osterix (OSX) and osteoprotegerin (OPG). These effects were ascribed to enhanced Wnt signaling as GH significantly reduced Wnt inhibitors, Dickkopf 1 (DKK1) and the secreted frizzled protein 2 (SFRP2), and increased the expression of an activator of Wnt, Wnt3. Accordingly, the expression of β-catenin and its nuclear levels were raised. Wnt involvement in GH anti-adipogenic effect was further confirmed by the silencing of β-catenin. In silenced hMSC, both the inhibitory effect of GH on the expression of the adipogenic genes, ADN and C/EBPα and the lipogenesis enzymes LPL and ACACA, were prevented together with the stimulatory effect of GH on the osteogenic genes OSX and OPG. The present study supports the hypothesis that when GH secretion declines as in aging, the fat in the bone-marrow cavities increases and the osteogenic capacity of the MSC pool is reduced due to a decrease in Wnt signaling.

The Expanding Life and Functions of Osteogenic Cells: From Simple Bone-Making Cells to Multifunctional Cells and Beyond

During the last three decades, important progress in bone cell biology and in human and mouse genetics led to major advances in our understanding of the life and functions of cells of the osteoblast lineage. Previously unrecognized sources of osteogenic cells have been identified. Novel cellular and molecular mechanisms controlling osteoblast differentiation and senescence have been determined. New mechanisms of communications between osteogenic cells, osteocytes, osteoclasts, and chondrocytes, as well as novel links between osteogenic cells and blood vessels have been identified. Additionally, cells of the osteoblast lineage were shown to be important components of the hematopoietic niche and to be implicated in hematologic dysfunctions and malignancy. Lastly, unexpected interactions were found between osteogenic cells and several soft tissues, including the central nervous system, gut, muscle, fat, and testis through the release of paracrine factors, making osteogenic cells multifunctional regulatory cells, in addition to their bone-making function. These discoveries considerably enlarged our vision of the life and functions of osteogenic cells, which may lead to the development of novel therapeutics with immediate applications in bone disorders. © 2017 American Society for Bone and Mineral Research.

Role of TCF/LEF Transcription Factors in Bone Development and Osteogenesis

Bone formation occurs by two distinct mechanisms, namely, periosteal ossification and endochondral ossification. In both mechanisms, osteoblasts play an important role in the secretion and mineralization of bone-specific extracellular matrix. Differentiation and maturation of osteoblasts is a prerequisite to bone formation and is regulated by many factors. Recent experiments have shown that transcription factors play an important role in regulating osteoblast differentiation, proliferation, and function. Osteogenesis related transcription factors are the central targets and key mediators of the function of growth factors, such as cytokines. Transcription factors play a key role in the transformation of mesenchymal progenitor cells into functional osteoblasts. These transcription factors are closely linked with each other and in conjunction with bone-related signaling pathways form a complex network that regulates osteoblast differentiation and bone formation. In this paper, we discuss the structure of T-cell factor/lymphoid enhancer factor (TCF/LEF) and its role in embryonic skeletal development and the crosstalk with related signaling pathways and factors.

GSK-3β inhibition suppresses instability-induced osteolysis by a dual action on osteoblast and osteoclast differentiation

Currently, there are no medications available to treat aseptic loosening of orthopedic implants. Using osteoprotegerin fusion protein (OPG-Fc), we previously blocked instability-induced osteoclast differentiation and peri-prosthetic osteolysis. Wnt/β-catenin signaling, which regulates OPG secretion from osteoblasts, also modulates the bone tissue response to mechanical loading. We hypothesized that activating Wnt/β-catenin signaling by inhibiting glycogen synthase kinase-3β (GSK-3β) would reduce instability-induced bone loss through regulation of both osteoblast and osteoclast differentiation. We examined effects of GSK-3β inhibition on regulation of RANKL and OPG in a rat model of mechanical instability-induced peri-implant osteolysis. The rats were treated daily with a GSK-3β inhibitor, AR28 (20 mg/kg bw), for up to 5 days. Bone tissue and blood serum were assessed by qRT-PCR, immunohistochemistry, and ELISA on days 3 and 5, and by micro-CT on day 5. After 3 days of treatment with AR28, mRNA levels of β-catenin, Runx2, Osterix, Col1α1, and ALP were increased leading to higher osteoblast numbers compared to vehicle-treated animals. BMP-2 and Wnt16 mRNA levels were downregulated by mechanical instability and this was rescued by GSK-3β inhibition. Osteoclast numbers were decreased significantly after 3 days of GSK-3β inhibition, which correlated with enhanced OPG mRNA expression. This was accompanied by decreased serum levels of TRAP5b on days 3 and 5. Treatment with AR28 upregulated osteoblast differentiation, while osteoclastogenesis was blunted, leading to increased bone mass by day 5. These data suggest that GSK-3β inactivation suppresses osteolysis through regulating both osteoblast and osteoclast differentiation in a rat model of instability-induced osteolysis.

Molecular genetics of osteosarcoma

Osteosarcoma is the predominant form of bone cancer, affecting mostly adolescents. Recent progress made in molecular genetic studies of osteosarcoma has changed our view on the cause of the disease and ongoing therapeutic approaches for patients. As we draw closer to gaining more complete catalogs of candidate cancer driver genes in common forms of cancer, the landscape of somatic mutations in osteosarcoma is emerging from its first phase. In this review, we summarize recent whole genome and/or whole exome genomic studies, and then put these findings in the context of genetic hallmarks of somatic mutations and mutational processes in human osteosarcoma. One of the lessons learned here is that the extent of somatic mutations and complexity of the osteosarcoma genome are similar to that of common forms of adult cancer. Thus, a much higher number of samples than those currently obtained are needed to complete the catalog of driver mutations in human osteosarcoma. In parallel, genetic studies in other species have revealed candidate driver genes and their roles in the genesis of osteosarcoma. This review also summarizes newly identified drivers in genetically engineered mouse models (GEMMs) and discusses our understanding of the impact of nature and number of drivers on tumor latency, subtypes, and metastatic potentials of osteosarcoma. It is becoming apparent that a synergistic team composed of three drivers (one 'first driver' and two 'synergistic drivers') may be required to generate an animal model that recapitulates aggressive osteosarcoma with a short latency. Finally, new cancer therapies are urgently needed to improve survival rate and quality of life for osteosarcoma patients. Several vulnerabilities in osteosarcoma are illustrated in this review to exemplify the opportunities for next generation molecularly targeted therapies. However, much work remains in order to complete our understanding of the somatic mutation basis of osteosarcoma, to develop reliable animal models of human disease, and to apply this information to guide new therapeutic approaches for reducing morbidity and mortality of this rare disease.

Childhood cancer chemotherapy-induced bone damage: pathobiology and protective effects of resveratrol and other nutraceuticals

Intensive cancer chemotherapy causes significant bone loss, for which the mechanisms remain unclear and effective treatments are lacking. This is a significant issue particularly for childhood cancers, as the most common ones have a >75% cure rate following chemotherapy; there is an increasing population of survivors who live with chronic bone defects. Studies suggest that these defects are the result of reduced bone from increased marrow fat formation and increased bone resorption following chemotherapy. These changes probably result from altered expression/activation of regulatory molecules or pathways regulating skeletal cell formation and activity. Treatment with methotrexate, an antimetabolite commonly used in childhood oncology, has been shown to increase levels of proinflammatory/pro-osteoclastogenic cytokines (e.g., enhanced NF-κB activation), leading to increased osteoclast formation and bone resorption, as well as to attenuate Wnt signaling, leading to both decreased bone and increased marrow fat formation. In recent years, understanding the mechanisms of action and potential health benefits of selected nutraceuticals, including resveratrol, genistein, icariin, and inflammatory fatty acids, has led to preclinical studies that, in some cases, indicate efficacy in reducing chemotherapy-induced bone defects. We summarize the supporting evidence.

Polycaprolactone nanofiber scaffold enhances the osteogenic differentiation potency of various human tissue-derived mesenchymal stem cells

BACKGROUND

Polycaprolactone (PCL) has been regarded as a promising synthetic material for bone tissue engineering application. Owing to its unique biochemical properties and great compatibility, PCL fibers have come to be explored as a potential delivering scaffold for stem cells to support bone regeneration during clinical application.

METHODS

The human derived mesenchymal stem cells (MSCs) were obtained from umbilical cord (UC), bone marrow (BM), and adipose tissue (AD), respectively. The osteogenic differentiation potency of various human MSCs on this novel synthetic biomaterial was also investigated in vitro.

RESULTS

Here, we illustrated that those human UC-, BM-, and AD-derived MSCs exhibited fibroblast-like morphology and expressed characteristic markers. Impressively, PCL nanofiber scaffold could support those MSC adhesion and proliferation. Long-term culture on PCL nanofiber scaffold maintained the viability as well as accelerated the proliferation of those three different kinds of human MSCs. More importantly, the osteogenic differentiation potency of those human MSCs was increased significantly by culturing on PCL nanofiber scaffold. Of note, BM-derived MSCs demonstrated greater differentiation potency among the three kinds of MSCs. The Wnt/β-catenin and Smad3 signaling pathways contributed to the enhanced osteogenesis of human MSCs, which was activated consistently by PCL nanofiber scaffold.

CONCLUSIONS

The utilization of PCL nanofiber scaffold would provide a great application potential for MSC-based bone tissue repair by enhancing the osteogenic differentiation of human MSCs.

Dickkopf-1 is involved in BMP9-induced osteoblast differentiation of C3H10T1/2 mesenchymal stem cells

Bone morphogenetic protein 9 (BMP9) is a potent inducer of osteogenic differentiation of mesenchymal stem cells. The Wnt antagonist Dickkopf-1 (Dkk1) is involved in skeletal development and bone remodeling. Here, we investigated the role of Dkk1 in BMP9-induced osteogenic differentiation of MSCs. We found that overexpression of BMP9 induced Dkk1 expression in a dose-dependent manner, which was reduced by the P38 inhibitor SB203580 but not the ERK inhibitor PD98059. Moreover, Dkk1 dramatically decreased not only BMP9-induced alkaline phosphatase (ALP) activity but also the expression of osteocalcin (OCN) and osteopontin (OPN) and matrix mineralization of C3H10T1/2 cells. Furthermore, exogenous Dkk1 expression inhibited Wnt/β-catenin signaling induced by BMP9. Our findings indicate that Dkk1 negatively regulates BMP9-induced osteogenic differentiation through inhibition of the Wnt/β-catenin pathway and it could be used to optimize the therapeutic use of BMP9 and for bone tissue engineering. [BMB Reports 2016; 49(3): 179-184]

Alcohol-related deficient fracture healing is associated with activation of FoxO transcription factors in mice

The process of fracture healing is complex, and poor or incomplete healing remains a significant health problem. Proper fracture healing relies upon resident mesenchymal stem cell (MSC) differentiation into chondrocytes and osteoblasts, which are necessary for callus formation and ossification. Alcohol abuse is a leading contributor to poor fracture healing. Although the mechanism behind this action is unknown, excessive alcohol consumption is known to promote systemic oxidative stress. The family of FoxO transcription factors is activated by oxidative stress, and FoxO activation antagonizes Wnt signaling, which regulates mesenchymal stem cell differentiation. We hypothesize that alcohol exposure increases oxidative stress leading to deficient fracture repair by activating FoxO transcription factors within the fracture callus which disrupts chondrogenesis of mesenchymal stem cells. Our laboratory has developed an experimental model of delayed fracture union in mice using ethanol administration. We have found that ethanol administration significantly decreases external, cartilaginous callus formation, and hallmarks of endochondral ossification, and these changes are concomitant with increases in FoxO expression and markers of activation in fracture callus tissue of these mice. We were able to prevent these alcohol-induced effects with the administration of the antioxidant n-acetyl cysteine (NAC), suggesting that alcohol-induced oxidative stress produces the perturbed endochondral ossification and FoxO expression. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:2106-2115, 2016.

Effects of the overexpression of IFITM5 and IFITM5 c.-14C>T mutation on human osteosarcoma cells

The present study aimed to investigate the effects of overexpression of interferon-induced transmembrane protein 5 (IFITM5) and IFITM5 c.-14C>T mutation on osteogenic differentiation, and the proliferation, migration and invasion of SaOS2 cells. SaOS2 cells were transfected with plasmids containing wild type IFITM5 (W) or IFITM5 containing the c.-14C>T mutation (MU). The mRNA and protein expression levels of IFITM5 in SaOS2 cells were respectively detected by reverse transcription quantitative polymerase chain reaction and western blotting. The proliferative, migratory and invasive ability of SaOS2 cells was also examined. In addition, the expression levels of osteogenic differentiation markers alkaline phosphatase (ALP), osteocalcin (OCN) and runt-related transcription factor 2 (Runx2) were detected. Mineralized nodules were detected by Alizarin Red S staining and were quantified by measuring absorbance. The mRNA and protein expression levels of IFITM5 were high in cells transfected with IFITM5 and IFITM5 c.-14C>T mutation, and were higher in cells transfected with IFITM5 c.-14C>T mutation. There was no difference in proliferation between the control group (C) and the W and MU groups. However, overexpression of IFITM5 and IFITM5 c.-14C>T mutation increased apoptotic rate, decreased invasive capacity, increased the expression of ALP, OCN and Runx2, and increased the number of mineralized nodules following osteogenic induction. In addition, compared with C and W groups, cells transfected with IFITM5 c.-14C>T mutation exhibited decreased migratory ability. In conclusion, overexpression of IFITM5 and IFITM5 c.-14C>T mutation promotes tumor cell apoptosis, inhibits tumor invasion and promotes osteogenic differentiation. These findings may provide a theoretical basis for the development of a novel treatment method that targets IFITM5, and provides a platform for the potential treatment of human osteosarcoma.

Variation in lipid mediator and cytokine levels during mouse femur fracture healing

Fracture healing is regulated by a variety of inflammatory mediators and growth factors which act over time to regenerate the injured tissue. This study used a mouse femur fracture model to quantify the temporal expression pattern of lipid mediators, cytokines, and related mRNAs during healing. Cyclooxygenase (COX-1 and COX-2) and 5-lipoxygenase (5-LO) derived lipid mediators, cytokines, and mRNA levels were quantified using mass spectrometry (LC-MS/MS), bead-based multiplex assays (xMAP), and quantitative PCR of cDNA (RTqPCR), respectively. Our analysis found that, the early inflammatory response (between 0 and 4 days after fracture) in the mouse femur fracture model coincided with elevated levels of COX-derived lipid mediators and inflammatory cytokines but with decreased levels of 5-LO-derived lipid mediators. Further, the COX-derived lipid mediators remained elevated for at least 7 days after fracture, suggesting that the COX-derived lipid mediators have additional functions during later phases of the fracture healing response. Differences were also found between mRNA levels and corresponding cytokines and lipid mediator levels, supporting a role for post-transcriptional regulation of gene expression. The temporal changes in fracture callus lipid mediator levels and inflammatory cytokines support a general positive role for inflammatory cytokines and COX-derived lipid mediators on fracture healing and a general negative role for 5-lipoxygenase derived lipid mediators during the initial stages of repair. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1883-1893, 2016.

Sclerostin antibody prevented progressive bone loss in combined ovariectomized and concurrent functional disuse

Osteoporosis is characterized by low bone mass and compromised trabecular architecture, and is commonly occurred in post-menopausal women with estrogen deficiency. In addition, prolonged mechanical unloading, i.e., long term bed rest, can exaggerate the bone loss. Sclerostin is a Wnt signaling antagonist and acts as a negative regulator for bone formation. A sclerostin-neutralizing antibody (Scl-Ab) increased bone mineral density in women with postmenopausal osteoporosis and healthy men. The objective of this study was to characterize the condition of bone loss in ovariectomized (OVX) rats with concurrent mechanical unloading and evaluate the effect of sclerostin antibody treatment in mitigating the prospective severe bone loss conditions in this model. Four-month-old OVX- or sham-operated female SD rats were used in this study. They were subjected to functional disuse induced by hind-limb suspension (HLS) or free ambulance after 2days of arrival. Subcutaneous injections with either vehicle or Scl-Ab at 25mg/kg were made twice per week for 5weeks from the time of HLS. μCT analyses demonstrated a significant decrease in distal metaphyseal trabecular architecture integrity with HLS, OVX and HLS+OVX (bone volume fraction decreased by 29%, 71% and 87% respectively). The significant improvements of various trabecular bone parameters (bone volume fraction increased by 111%, 229% and 297% respectively as compared with placebo group) with the administration of Scl-Ab are associated with stronger mechanical property and increased bone formation by histomorphometry. These results together indicate that Scl-Ab prevented the loss of trabecular bone mass and cortical bone strength in OVX rat model with concurrent mechanical unloading. The data suggested that monoclonal sclerostin-neutralizing antibody represents a promising therapeutic approach for severe osteoporosis induced by estrogen deficiency with concurrent mechanical unloading.

sFRP4-dependent Wnt signal modulation is critical for bone remodeling during postnatal development and age-related bone loss

sFRP4 is an extracellular Wnt antagonist that fine-tunes its signal activity by direct binding to Wnts. Bone fragility under oxidative stress by diabetes and aging is partly related to the suppression of the Wnt signal through upregulated sFRP4. Here, to explore the functions of sFRP4 as a balancer molecule in bone development and remodeling, we analyzed the sFRP4 knock-in mouse strain. X-gal and immunohistochemically stained signals in sFRP4-LacZ heterozygous mice were detectable in restricted areas, mostly in osteoblasts and osteoclasts, of the femoral diaphysis after neonatal and postnatal stages. Histological and μCT analyses showed increased trabecular bone mass with alteration of the Wnt signal and osteogenic activity in sFRP4 mutants; this augmented the effect of the buildup of trabecular bone during the ageing period. Our results indicate that sFRP4 plays a critical role in bone development and remodeling by regulating osteoblasts and osteoclasts, and that its functional loss prevents age-related bone loss in the trabecular bone area. These findings imply that sFRP4 functions as a key potential endogenous balancer of the Wnt signaling pathway by efficiently having direct influence on both bone formation and bone absorption during skeletal bone development and maintenance through remodeling.

Tanshinol Rescues the Impaired Bone Formation Elicited by Glucocorticoid Involved in KLF15 Pathway

Decreased bone formation is responsible for the pathogenesis of glucocorticoid- (GC-) induced osteoporosis (GIO), while the mechanism remains to be elucidated. The aim was to investigate how natural antioxidant tanshinol attenuates oxidative stress and rescues impaired bone formation elicited by GC in Sprague-Dawley rats and in C2C12 cells and/or MC3T3-E1 cells. The results showed that tanshinol prevented bone loss and decreased biomechanical characteristics and suppressed reduction of biomarkers related to osteogenesis in GIO rats. Further study revealed that tanshinol reversed decrease of transcription activity of Osterix-luc and rescued impairment of osteoblastic differentiation and bone formation involved in induction of KLF15 mRNA. Meanwhile, tanshinol diminished inhibition of protein expression of β-catenin and Tcf4 and transcription activity of Tcf4-luc induced by GC, especially under conditions of KLF siRNA in vitro. Additionally, tanshinol attenuated increase of reactive oxygen species (ROS) generation, phosphorylation of p66^Shc expression, TUNEL-positive cells, and caspase-3 activity elicited by KLF15 under conditions of GC. Taken together, the present findings suggest that tanshinol attenuated the decrease of bone formation and bone mass and bone quality elicited by GC involved in KLF15/Wnt signaling transduction and counteracted GC-evoked oxidative stress and subsequent cell apoptosis involved in KLF15/p66^Shc pathway cascade.

Aluminum trichloride inhibits osteoblastic differentiation through inactivation of Wnt/β-catenin signaling pathway in rat osteoblasts

Exposure to aluminum (Al) suppresses bone formation. Osteoblastic differentiation plays a key role in the process of bone formation. However, the effect of Al on osteoblastic differentiation is still controversial, and the mechanism remains unclear. To investigate the effect of Al on osteoblastic differentiation and whether Wnt signaling pathway was involved in it, the primary rat osteoblasts were exposed to 1/40 IC50, 1/20 IC50 and 1/10 IC50 of aluminum trichloride (AlCl3) for 24h, respectively. The activity analysis of alkaline phosphate, qRT-PCR analysis of type I collagen, alkaline phosphate, Wnt3a and Dkk-1, Western blot analysis of p-GSK3β, GSK3β and β-catenin protein and Immunofluorescence staining for β-catenin suggested that AlCl3 inhibited osteoblastic differentiation and Wnt/β-catenin pathway. Moreover, we found exogenous Wnt3a application reversed the inhibitory effect of AlCl3 on osteoblastic differentiation, accompanied by activating the Wnt/β-catenin pathway. Taken together, these findings suggest that AlCl3 inhibites osteoblastic differentiation through inactivation of Wnt/β-catenin pathway in osteoblasts.

All-trans retinoic acid modulates Wnt3A-induced osteogenic differentiation of mesenchymal stem cells via activating the PI3K/AKT/GSK3β signalling pathway

Osteogenic differentiation of mesenchymal stem cells (MSCs) is a vital process for the maintenance of healthy bone tissue and is mediated by numerous factors. Canonical Wnt signalling is essential for MSC osteogenic differentiation, and it interacts with several nuclear receptors, including the retinoic acid receptor, vitamin D receptor, and glucocorticoid receptor. Here, we explored whether Wnt3A and all-trans-retinoic acid (ATRA) play synergistic roles in MSC osteogenic differentiation. We found that ATRA potentiated the Wnt3A-induced expression of early and late osteogenic markers as well as matrix mineralization and further confirmed the phenomena using foetal limb explant culture and MSC implantation experiments. Mechanistically, ATRA cooperated with Wnt3A to induce β-catenin translocation from cell-cell contacts into the cytosol and nucleus, thereby activating Wnt/β-catenin signalling. Additionally, Wnt3A attenuated ATRA-induced Cyp26a1 expression, inhibiting the degradation of ATRA into its oxidative forms. β-catenin silencing abolished the stimulatory effect of ATRA on Wnt3A-induced alkaline phosphatase (ALP) activity and reversed its inhibitory effect on Cyp26a1 expression. Furthermore, ATRA and Wnt3A synergistically promoted AKT phosphorylation, enhancing β-catenin-dependent transcription through GSK3β inhibition or direct β-catenin phosphorylation at Ser552. This event was largely abolished by LY294002 pre-treatment, suggesting that ATRA and Wnt3A at least partially promote osteogenic differentiation via activating the PI3K/AKT/GSK3β signalling pathway. Thus, crosstalk between the Wnt/β-catenin and retinoic acid signalling pathways may be an effective therapeutic target for bone diseases, such as osteoporosis.

Osteocytes and Skeletal Pathophysiology

For many years, osteocytes have been the forgotten bone cells and considered as inactive spectators buried in the bone matrix. We now know that osteocytes detect and respond to mechanical and hormonal stimuli to coordinate bone resorption and bone formation. Osteocytes are currently considered a major source of molecules that regulate the activity of osteoclasts and osteoblasts, such as RANKL and sclerostin; and genetic and pharmacological manipulations of either molecule markedly affect bone homeostasis. Besides playing a role in physiological bone homeostasis, accumulating evidence supports the notion that dysregulation of osteocyte function and alteration of osteocyte life-span underlies the pathophysiology of skeletal disorders characterized by loss bone mass and increased bone fragility, as well as the damaging effects of cancer in bone. In this review, we highlight some of these investigations and discuss novel observations that demonstrate that osteocytes, far from being passive cells entombed in the bone, are critical for bone function and maintenance.

Aberrant CXCR4 and β-catenin expression in osteosarcoma correlates with patient survival

To determine the clinical significance of C-X-C chemokine receptor type 4 (CXCR4) and β-catenin in osteosarcoma, their protein expression levels were assessed in 96 osteosarcoma and 20 osteochondroma cases using immunohistochemistry. Additionally, CXCR4 and β-catenin mRNA expression levels were measured in 16 fresh osteosarcoma and 16 adjacent healthy tissue samples using fluorescent reverse transcription-quantitative polymerase chain reaction (RT-qPCR). In the osteosarcoma samples, the positive CXCR4 protein expression rate was significantly higher than the rate in the osteochondroma samples (68.75 vs. 20.00%; P<0.01). Furthermore, β-catenin protein expression was detected in 61.46% of osteosarcoma cases and 25.00% of osteochondroma cases. Similarly, the RT-qPCR data identified increased CXCR4 and β-catenin mRNA expression levels in the osteosarcoma compared with adjacent control tissues. It was determined that CXCR4 (P<0.01) and β-catenin (P<0.05) expression were significantly associated with the clinical Enneking stage, metastasis and survival of osteosarcoma. Furthermore, multivariate analysis identified CXCR4 and β-catenin protein expression levels, as well as clinical stage and metastasis, as significant risk factors for survival in patients with osteosarcoma (P<0.05). In conclusion, the present study determined that CXCR4 and β-catenin are abnormally expressed in osteosarcoma tissues, and, therefore, may be important during osteosarcoma progression.

Role of the Parathyroid Hormone Type 1 Receptor (PTH1R) as a Mechanosensor in Osteocyte Survival

Osteocytes have a major role in the control of bone remodeling. Mechanical stimulation decreases osteocyte apoptosis and promotes bone accrual, whereas skeletal unloading is deleterious in both respects. PTH1R ablation or overexpression in osteocytes in mice produces trabecular bone loss or increases bone mass, respectively. The latter effect was related to a decreased osteocyte apoptosis. Here, the putative role of PTH1R activation in osteocyte protection conferred by mechanical stimulation was assessed. Osteocytic MLO-Y4 cells were subjected to mechanical stimuli represented by hypotonic shock (216 mOsm/kg) or pulsatile fluid flow (8 Hz, 10 dynes/cm(2)) for a short pulse (10 min), with or without PTH1R antagonists or after transfection with specific PTHrP or PTH1R siRNA. These mechanical stimuli prevented cell death induced within 6 hours by etoposide (50 μM), related to PTHrP overexpression; and this effect was abolished by the calcium antagonist verapamil (1 μM), a phospholipase C (PLC) inhibitor (U73122; 10 μM), and a PKA activation inhibitor, Rp-cAMPS (25 μM), in these cells. Each mechanical stimulus also rapidly induced β-catenin stabilization and nuclear ERK translocation, which were inhibited by the PTH1R antagonist PTHrP(7-34) (1 μM), or PTH1R siRNA, and mimicked by PTHrP(1-36) (100 nM). Mechanical stretching by hypotonic shock did not affect cAMP production but rapidly (<1 min) stimulated Ca(i)(2+) transients in PTH1R-overexpressing HEK-293 cells and in MLO-Y4 cells, in which calcium signaling was unaffected by the presence of a PTHrP antiserum or PTHrP siRNA but inhibited by knocking down PTH1R. These novel findings indicate that PTH1R is an important component of mechanical signal transduction in osteocytic MLO-Y4 cells, and that PTH1R activation by PTHrP-independent and dependent mechanisms has a relevant role in the prosurvival action of mechanical stimulus in these cells.

microRNA-103a functions as a mechanosensitive microRNA to inhibit bone formation through targeting Runx2

Emerging evidence indicates that microRNAs (miRNAs) play essential roles in regulating osteoblastogenesis and bone formation. However, the role of miRNA in osteoblast mechanotransduction remains to be defined. In this study, we aimed to investigate whether miRNAs regulate mechanical stimulation-triggered osteoblast differentiation and bone formation through modulation of Runx2, the master transcription factor for osteogenesis. We first investigated the role of mechanical loading both in a mouse model and in an osteoblast culture system and the outcomes clearly demonstrated that mechanical stimuli can regulate osteogenesis and bone formation both in vivo and in vitro. Using bioinformatic analyses and subsequent confirmation by quantitative real-time PCR (qRT-PCR), we found that multiple miRNAs that potentially target Runx2 were responding to in vitro mechanical stimulation, among which miR-103a was fully characterized. miR-103a and its host gene PANK3 were both downregulated during cyclic mechanical stretch (CMS)-induced osteoblast differentiation, whereas Runx2 protein expression was upregulated. Overexpression of miR-103a significantly decreased and inhibition of miR-103a increased Runx2 protein level, suggesting that miR-103a acts as an endogenous attenuator of Runx2 in osteoblasts. Mutation of putative miR-103a binding sites in Runx2 mRNA abolishes miR-103a-mediated repression of the Runx2 3'-untranslated region (3'UTR) luciferase reporter activity, suggesting that miR-103a binds to Runx2 3'UTR. Osteoblast marker gene profiling and osteogenic phenotype assays demonstrated that miR-103a negatively correlates with CMS-induced osteogenesis. Further, the perturbation of miR-103a also has a significant effect on osteoblast activity and matrix mineralization. More importantly, we found an inhibitory role of miR-103a in regulating bone formation in hindlimb unloading mice, and pretreatment with antagomir-103a partly rescued the osteoporosis caused by mechanical unloading. Taken together, our data suggest that miR-103a is the first identified mechanosensitive miRNA that regulates osteoblast differentiation by directly targeting Runx2, and therapeutic inhibition of miR-103a may be an efficient anabolic strategy for skeletal disorders caused by pathological mechanical loading.

Effects of toll-like receptors 3 and 4 in the osteogenesis of stem cells

Objective. To investigate the effects of Toll-like receptors in stem cell osteogenesis. Methods. Bone marrow mesenchymal stem cells (BMSCs) were divided into the blank group, the TLR-3 activated group, and the TLR-4 activated group. After 10 days' osteogenic-promoting culture, expression of type I collagen and osteocalcin was determined by Western blot. Osteoblasts (OBs) were also divided into three groups mentioned above. Alkaline phosphatase (ALP) and alizarin red staining were performed after 10 days' ossification-inducing culture. The expression of β-catenin was investigated by Western blot. Results. Both the TLR-3 and TLR-4 activated groups had increased expression of type I collagen and osteocalcin; the effect of TLR-4 was stronger. The intensity of alizarin red and ALP staining was strongest in the TLR-3 activated group and weakest in the TLR-4 activated group. Activation of TLR-4 decreased the expression of β-catenin, whilst activation of TLR-3 did not affect the expression of β-catenin. Discussion. This study suggested that both TLR-3 and -4 promoted differentiation of BMSCs to OBs. TLR-3 had an inducing effect on the ossification of OBs to osteocytes, whilst the effect of TLR-4 was the opposite because of its inhibitory effect on the Wnt signaling pathway.

Canonical Wnt signaling acts synergistically on BMP9-induced osteo/odontoblastic differentiation of stem cells of dental apical papilla (SCAPs)

Dental pulp/dentin regeneration using dental stem cells combined with odontogenic factors may offer great promise to treat and/or prevent premature tooth loss. Here, we investigate if BMP9 and Wnt/β-catenin act synergistically on odontogenic differentiation. Using the immortalized SCAPs (iSCAPs) isolated from mouse apical papilla tissue, we demonstrate that Wnt3A effectively induces early osteogenic marker alkaline phosphatase (ALP) in iSCAPs, which is reduced by β-catenin knockdown. While Wnt3A and BMP9 enhance each other's ability to induce ALP activity in iSCAPs, silencing β-catenin significantly diminishes BMP9-induced osteo/odontogenic differentiation. Furthermore, silencing β-catenin reduces BMP9-induced expression of osteocalcin and osteopontin and in vitro matrix mineralization of iSCAPs. In vivo stem cell implantation assay reveals that while BMP9-transduced iSCAPs induce robust ectopic bone formation, iSCAPs stimulated with both BMP9 and Wnt3A exhibit more mature and highly mineralized trabecular bone formation. However, knockdown of β-catenin in iSCAPs significantly diminishes BMP9 or BMP9/Wnt3A-induced ectopic bone formation in vivo. Thus, our results strongly suggest that β-catenin may play an important role in BMP9-induced osteo/ondontogenic signaling and that BMP9 and Wnt3A may act synergistically to induce osteo/odontoblastic differentiation of iSCAPs. It's conceivable that BMP9 and/or Wnt3A may be explored as efficacious biofactors for odontogenic regeneration and tooth engineering.