BMP-2 controls alkaline phosphatase expression and osteoblast mineralization by a Wnt autocrine loop

An allograft generated from adult stem cells and their secreted products efficiently fuses vertebrae in immunocompromised athymic rats and inhibits local immune responses

BACKGROUND CONTEXT

Spine pain and the disability associated with it are epidemic in the United States. According to the National Center for Health Statistics, more than 650,000 spinal fusion surgeries are performed annually in the United States, and yet there is a failure rate of 15%-40% when standard methods employing current commercial bone substitutes are used. Autologous bone graft is the gold standard in terms of fusion success, but the morbidity associated with the procedure and the limitations in the availability of sufficient material have limited its use in the majority of cases. A freely available and immunologically compatible bone mimetic with the properties of live tissue is likely to substantially improve the outcome of spine fusion procedures without the disadvantages of autologous bone graft.

PURPOSE

This study aimed to compare a live human bone tissue analog with autologous bone grafting in an immunocompromised rat model of posterolateral fusion.

DESIGN/SETTING

This is an in vitro and in vivo preclinical study of a novel human stem cell-derived construct for efficacy in posterolateral lumbar spine fusion.

METHODS

Osteogenically enhanced human mesenchymal stem cells (OEhMSCs) were generated by exposure to conditions that activate the early stages of osteogenesis. Immunologic characteristics of OEhMSCs were evaluated in vitro. The secreted extracellular matrix from OEhMSCs was deposited on a clinical-grade gelatin sponge, resulting in bioconditioned gelatin sponge (BGS). Bioconditioned gelatin sponge was used alone, with live OEhMSCs (BGS+OEhMSCs), or with whole human bone marrow (BGS+hBM). Efficacy for spine fusion was determined by an institutionally approved animal model using 53 nude rats.

RESULTS

Bioconditioned gelatin sponge with live OEhMSCs did not cause cytotoxicity when incubated with immunologically mismatched lymphocytes, and OEhMSCs inhibited lymphocyte expansion in mixed lymphocyte assays. Bioconditioned gelatin sponge with live OEhMSC and BGS+hBM constructs induced profound bone growth at fusion sites in vivo, with a comparable rate of fusion with syngeneic bone graft (negative [0 of 10], BGS alone [0 of 10], bone graft [7 of 10], BGS+OEhMSC [10 of 15], and BGS+hBM [8 of 8]).

CONCLUSIONS

Collectively, these studies demonstrate that BGS+OEhMSC constructs possess low immunogenicity and drive vertebral fusion with efficiency matching syngeneic bone graft in rodents. We also demonstrate that BGS serves as a promising scaffold for spine fusion when combined with hBM.

Latest perspectives on macrophages in bone homeostasis

Knowledge about macrophages residing in the bone, also known as osteal macrophages or osteomacs, is still limited. A hallmark of this peculiar myeloid population is the expression of macrophage markers distinct from the markers found on osteoclast surface. In bone, osteomacs are in contact with osteoblasts, where they are involved in regulating bone homeostasis. However, additional macrophage subtypes already present in the bone marrow or recruited from the blood circulation could have further functions, which could be all important for the maintenance of the bone architecture and its associated functions. Indeed, bone marrow macrophages have been found to eliminate apoptotic cells, particularly apoptotic osteoblasts through a process named efferocytosis. This phagocytic process plays an essential role in bone tissue homeostasis and new bone formation. In addition, bone marrow macrophages can influence the hematopoietic stem cell (HSC) niches. They contribute to the regulation of the HSC progenitor cell maintenance, mobilization, and function. To do so, macrophages secrete cytokines in steady state or during stress conditions. These cytokines influence hematopoiesis either by a direct effect on HSCs or through the control of stromal cells that are essential for the HSC niches. Interestingly, the similarities between the niches for HSCs and the niche for metastatic tumor cells support the possibility that bone-resident macrophages could control the homing of tumor cells and their proliferation within the bone. In general, macrophage role during metastatic processes is well described; however, their direct involvement in bone metastasis is a rising research area. In this review, we will highlight the macrophage functions in the skeleton, in the maintenance of the HCS niches, and their importance in bone metastasis.

Bmp Induces Osteoblast Differentiation through both Smad4 and mTORC1 Signaling

The bone morphogenetic protein (Bmp) family of secreted molecules has been extensively studied in the context of osteoblast differentiation. However, the intracellular signaling cascades that mediate the osteoblastogenic function of Bmp have not been fully elucidated. By profiling mRNA expression in the bone marrow mesenchymal progenitor cell line ST2, we discover that BMP2 induces not only genes commonly associated with ossification and mineralization but also genes important for general protein synthesis. We define the two groups of genes as mineralization related versus protein anabolism signatures of osteoblasts. Although it induces the expression of several Wnt genes, BMP2 activates the osteogenic program largely independently of de novo Wnt secretion. Remarkably, although Smad4 is necessary for the activation of the mineralization-related genes, it is dispensable for BMP2 to induce the protein anabolism signature, which instead critically depends on the transcription factor Atf4. Upstream of Atf4, BMP2 activates mTORC1 to stimulate protein synthesis, resulting in an endoplasmic reticulum stress response mediated by Perk. Thus, Bmp signaling induces osteoblast differentiation through both Smad4- and mTORC1-dependent mechanisms.

Mechanisms of Cdc42-mediated rat MSC differentiation on micro/nano-textured topography

Micro/nano-textured titanium surface topography promotes osteoblast differentiation and the Wnt/β-catenin signaling pathway. However, the response of rat bone mesenchymal stem cells (MSCs) to micro/nano-textured topography, and the underlying mechanisms of its effects, are not well understood. We hypothesized that cell division cycle 42 protein (Cdc42), a key member of the Rho GTPases family, may regulate rat MSCs morphology and osteogenic differentiation by micro/nano-textured topography, and that crosstalk between Cdc42 and Wnt/β-catenin is the underlying mechanism. To confirm the hypothesis, we first tested rat MSCs' morphology, cytoskeleton, and osteogenic differentiation on micro/nano-textured topography. We then examined the cells' Wnt pathway and Cdc42 signaling activity. The results show that micro/nano-textured topography enhances MSCs' osteogenic differentiation. In addition, the cells' morphology and cytoskeletal reorganization were dramatically different on smooth surfaces and micropitted/nanotubular topography. Ligands of the canonical Wnt pathway, as well as accumulation of β-catenin in the nucleus, were up-regulated by micro/nano-textured topography. Cdc42 protein expression was markedly increased under these conditions; conversely, Cdc42 silencing significantly depressed the enhancement of MSCs osteogenic differentiation by micro/nano-textured topography. Moreover, Cdc42si attenuated p-GSK3β activation and resulted in β-catenin cytoplasmic degradation on the micro/nano-textured topography. Our results indicate that Cdc42 is a key modulator of rat MSCs morphology and cytoskeletal reorganization, and that crosstalk between Cdc42 and Wnt/β-catenin signaling though GSK3β regulates MSCs osteogenic differentiation by implant topographical cues.

STATEMENT OF SIGNIFICANCE

Topographical modification at micro- and nanoscale is widely applied to enhance the tissue integration properties of biomaterials. However, the response of bone mesenchymal stem cells (MSCs) to the micro/nano-textured topography and the underlying mechanisms are not well understood. This study shows that the micropitted/nanotubular hierarchical topography produced by etching and anodic oxidation treatment drives fusiform cell morphology, cytoskeletal reorganization as well as better MSCs osteogenic differentiation. The cross-talk between Cdc42 pathway and Wnt/β-catenin pathway though GSK3β modulates the osteoinductive effect of the micro/nano-textured topography on MSCs. This finding sheds light on a novel mechanism involved in micro/nano-textured surface-mediated MSCs osteogenic differentiation and is a major step in the development of new surface modifications aiming to accelerate and enhance the process of osseointegration.

Sphingosine-1-phosphate/S1PR2-mediated signaling triggers Smad1/5/8 phosphorylation and thereby induces Runx2 expression in osteoblasts

Sphingosine-1-phosphate (S1P) is a signaling sphingolipid that also plays crucial roles in bone regeneration. Recently, we reported that the S1P receptors S1PR1 and S1PR2 were mainly expressed in osteoblast-like cells, and that the S1P/S1PR1 signaling pathway up-regulated osteoprotegerin and osteoblast differentiation. However, the involvement of S1P/S1PR2 signaling in osteoblast differentiation is not well understood. Here we investigate the role of S1P/S1PR2-mediated signaling in osteoblast differentiation and clarify the underlying signaling mechanisms. We found that an S1P/S1PR2/Gi-independent signaling pathway activated RhoA activity, leading to phosphorylation of Smad1/5/8 in mouse osteoblast-like MC3T3-E1 cells and primary osteoblasts. Furthermore, this signaling pathway promoted nuclear translocation of Smad4, and increased the amount of Smad6/7 protein in the nucleus. S1P also up-regulated runt-related transcription factor 2 (Runx2) expression through S1PR2/RhoA/ROCK/Smad1/5/8 signaling. Moreover, we found that S1P partially triggered S1PR2/RhoA/ROCK pathway leading to bone formation in vivo. These findings suggest that S1P induces RhoA activity, leading to the phosphorylation of Smad1/5/8, thereby promoting Runx2 expression and differentiation in osteoblasts. Our findings describe novel molecular mechanisms in S1P/S1PR2-mediated osteoblast differentiation that could aid future studies of bone regeneration.

Dioxinodehydroeckol Enhances the Differentiation of Osteoblasts by Regulating the Expression of Phospho-Smad1/5/8

Lack of bone formation-related health problems are a major problem for the aging population in the modern world. As a part of the ongoing trend of developing natural substances that attenuate osteoporotic bone loss conditions, dioxinodehydroeckol (DHE) from edible brown alga Ecklonia cava was tested for its effects on osteoblastogenic differentiation in MC3T3-E1 pre-osteoblasts. DHE was observed to successfully enhance osteoblast differentiation, as indicated by elevated cell proliferation, alkaline phosphatase activity, intracellular cell mineralization, along with raised levels of osteoblastogenesis indicators at the concentration of 20 μM. Results suggested a possible intervening of DHE on the bone morphogenetic protein (BMP) signaling pathway, according to elevated protein levels of BMP-2, collagen-I, and Smads. In addition, the presence of DHE was also able to raise the phosphorylated extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) levels which are also activated by the BMP signaling pathway. In conclusion, DHE is suggested to be a potential bioactive compound against bone loss that could enhance osteoblastogenesis with a suggested BMP pathway interaction.

Real-Time Analysis of Endogenous Wnt Signalling in 3D Mesenchymal Stromal Cells

Wnt signalling has been implicated in the regulation of stem cell self-renewal and differentiation; however, the majority of in vitro studies are carried out using monolayer 2D culture techniques. Here, we used mesenchymal stromal cell (MSC) EGFP reporter lines responsive to Wnt pathway activation in a 3D spheroid culture system to mimic better the in vivo environment. Endogenous Wnt signalling was then investigated under basal conditions and when MSCs were induced to undergo osteogenic and adipogenic differentiation. Interestingly, endogenous Wnt signalling was only active during 3D differentiation whereas 2D cultures showed no EGFP expression throughout an extended differentiation time-course. Furthermore, exogenous Wnt signalling in 3D adipogenic conditions inhibited differentiation compared to unstimulated controls. In addition, suppressing Wnt signalling by Dkk-1 restored and facilitated adipogenic differentiation in MSC spheroids. Our findings indicate that endogenous Wnt signalling is active and can be tracked in 3D MSC cultures where it may act as a molecular switch in adipogenesis. The identification of the signalling pathways that regulate MSCs in a 3D in vivo-like environment will advance our understanding of the molecular mechanisms that control MSC fate.

Mechanical Vibration Mitigates the Decrease of Bone Quantity and Bone Quality of Leptin Receptor-Deficient Db/Db Mice by Promoting Bone Formation and Inhibiting Bone Resorption

Leptin, a major hormonal product of adipocytes, is involved in regulating appetite and energy metabolism. Substantial studies have revealed the anabolic actions of leptin on skeletons and bone cells both in vivo and in vitro. Growing evidence has substantiated that leptin receptor-deficient db/db mice exhibit decreased bone mass and impaired bone microstructure despite several conflicting results previously reported. We herein systematically investigated bone microarchitecture, mechanical strength, bone turnover and its potential molecular mechanisms in db/db mice. More importantly, we also explored an effective approach for increasing bone mass in leptin receptor-deficient animals in an easy and noninvasive manner. Our results show that deterioration of trabecular and cortical bone microarchitecture and decreases of skeletal mechanical strength-including maximum load, yield load, stiffness, energy, tissue-level modulus and hardness-in db/db mice were significantly ameliorated by 12-week, whole-body vibration (WBV) with 0.5 g, 45 Hz via micro-computed tomography (μCT), three-point bending, and nanoindentation examinations. Serum biochemical analysis shows that WBV significantly decreased serum tartrate-resistant acid phosphatase 5b (TRACP5b) and CTx-1 levels and also mitigated the reduction of serum osteocalcin (OCN) in db/db mice. Bone histomorphometric analysis confirmed that decreased bone formation-lower mineral apposition rate, bone formation rate, and osteoblast numbers in cancellous bone-in db/db mice were suppressed by WBV. Real-time PCR assays show that WBV mitigated the reductions of tibial alkaline phosphatase (ALP), OCN, Runt-related transcription factor 2 (RUNX2), type I collagen (COL1), BMP2, Wnt3a, Lrp6, and β-catenin mRNA expression, and prevented the increases of tibial sclerostin (SOST), RANK, RANKL, RANL/osteoprotegerin (OPG) gene levels in db/db mice. Our results show that WBV promoted bone quantity and quality in db/db mice with obvious anabolic and anticatabolic effects. This study not only enriches our basic knowledge about bone quality and bone turnover mechanisms in leptin receptor-deficient animals, but also advances our understanding of the skeletal sensitivity of leptin-resistant db/db mice in response to external mechanical stimulation. © 2016 American Society for Bone and Mineral Research.

Factors Influencing Early Dental Implant Failures

The purpose of the present study was to assess the influence of local and systemic factors on the occurrence of dental implant failures up to the second-stage surgery (abutment connection). This retrospective study is based on 2,670 patients who received 10,096 implants and were consecutively treated with implant-supported prostheses between 1980 and 2014 at 1 specialist clinic. Several anatomic-, patient-, health-, and implant-related factors were collected. Descriptive statistics were used to describe the patients and implants. Univariate and multivariate logistic regression models were used at the patient level as well as the implant level to evaluate the effect of explanatory variables on the failure of implants up to abutment connection. A generalized estimating equation method was used for the implant-level analysis to account for the fact that repeated observations (several implants) were available for a single patient. Overall, 642 implants (6.36%) failed, of which 176 (1.74%) in 139 patients were lost up to second-stage surgery. The distribution of implants in sites of different bone quantities and qualities was quite similar between implants lost up to and after abutment connection. Smoking and the intake of antidepressants were the statistically significant predictors in the multivariate model (ClinicalTrials.gov NCT02369562).

Impaired osteogenic differentiation associated with connexin43/microRNA-206 in steroid-induced avascular necrosis of the femoral head

Connexin(Cx)43 and microRNA(miR)-206 play an important role in osteogenesis. However, their role in steroid-induced femoral head osteonecrosis (SANFH) is still ambiguous. The present study aimed to establish a rabbit model and investigate osteogenesis in steroid-induced femoral head osteonecrosis occurring via Cx43/miR-206 and the changes of Wnt/β-catenin signal pathway-related proteins. A total of 72 adult New Zealand white rabbits were divided randomly into a model group (Group A) and a control group (Group B) of 36 rabbits each. Group A was injected intravenously with lipopolysaccharide (10μg/kg body weight, once per day). After 48h, three injections of methylprednisolone (MPS; 20mg/kg body weight) were administered intramuscularly at 24-hour intervals. Group B were fed and housed under identical conditions but received saline injections. All animals were sacrificed at two, four, and eight weeks from the first MPS injection. Typical early osteonecrosis symptoms were observed in Group A. The expression of miR-206 in Group A was significantly higher than that of Group B. The mRNA and protein levels of Cx43, β-catenin, runt-related transcription factor 2, and alkaline phosphatase gradually decreased while Dickkopf-1 (Dkk-1) gradually increased in Group A compared with Group B. These findings indicated that Cx43/miR-206 is involved in the pathogenesis of early stage SANFH and may be associate with Wnt/β-catenin signal pathway.

Biodegradable Mg-Cu alloys with enhanced osteogenesis, angiogenesis, and long-lasting antibacterial effects

A series of biodegradable Mg-Cu alloys is designed to induce osteogenesis, stimulate angiogenesis, and provide long-lasting antibacterial performance at the same time. The Mg-Cu alloys with precipitated Mg2Cu intermetallic phases exhibit accelerated degradation in the physiological environment due to galvanic corrosion and the alkaline environment combined with Cu release endows the Mg-Cu alloys with prolonged antibacterial effects. In addition to no cytotoxicity towards HUVECs and MC3T3-E1 cells, the Mg-Cu alloys, particularly Mg-0.03Cu, enhance the cell viability, alkaline phosphatase activity, matrix mineralization, collagen secretion, osteogenesis-related gene and protein expressions of MC3T3-E1 cells, cell proliferation, migration, endothelial tubule forming, angiogenesis-related gene, and protein expressions of HUVECs compared to pure Mg. The favorable osteogenesis and angiogenesis are believed to arise from the release of bioactive Mg and Cu ions into the biological environment and the biodegradable Mg-Cu alloys with osteogenesis, angiogenesis, and long-term antibacterial ability are very promising in orthopedic applications.

Turning Bone Morphogenetic Protein 2 (BMP2) on and off in Mesenchymal Cells

The concentration, location, and timing of bone morphogenetic protein 2 (BMP2, HGNC:1069, GeneID: 650) gene expression must be precisely regulated. Abnormal BMP2 levels cause congenital anomalies and diseases involving the mesenchymal cells that differentiate into muscle, fat, cartilage, and bone. The molecules and conditions that influence BMP2 synthesis are diverse. Understandably, complex mechanisms control Bmp2 gene expression. This review includes a compilation of agents and conditions that can induce Bmp2. The currently known trans-regulatory factors and cis-regulatory elements that modulate Bmp2 expression are summarized and discussed. Bone morphogenetic protein 2 (BMP2, HGNC:1069, GeneID: 650) is a classical morphogen; a molecule that acts at a distance and whose concentration influences cell behavior. In mesenchymal cells, the concentration of BMP2 influences myogenesis, adipogenesis, chondrogenesis, and osteogenesis. Because the amount, timing, and location of BMP2 synthesis influence the allocation of cells to muscle, fat, cartilage, and bone, the mechanisms that regulate the Bmp2 gene are crucial. Key early mesodermal events that require precise Bmp2 regulation include heart specification and morphogenesis. Originally named for its osteoinductive properties, healing fractures requires BMP2. The human Bmp2 gene also has been linked to osteoporosis and osteoarthritis. In addition, all forms of pathological calcification in the vasculature and in cardiac valves involve the pro-osteogenic BMP2. The diverse tissues, mechanisms, and diseases influenced by BMP2 are too numerous to list here (see OMIM: 112261). However, in all BMP2-influenced pathologies, changes in the behavior and differentiation of pluripotent mesenchymal cells are a recurring theme. Consequently, much effort has been devoted to identifying the molecules and conditions that influence BMP2 synthesis and the complex mechanisms that control Bmp2 gene expression. This review begins with an overview of the Bmp2 gene's chromosomal neighborhood and then summarizes and evaluates known regulatory mechanisms and inducers.

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.

TGF-β and BMP signaling in osteoblast, skeletal development, and bone formation, homeostasis and disease

Transforming growth factor-beta (TGF-β) and bone morphogenic protein (BMP) signaling has fundamental roles in both embryonic skeletal development and postnatal bone homeostasis. TGF-βs and BMPs, acting on a tetrameric receptor complex, transduce signals to both the canonical Smad-dependent signaling pathway (that is, TGF-β/BMP ligands, receptors, and Smads) and the non-canonical-Smad-independent signaling pathway (that is, p38 mitogen-activated protein kinase/p38 MAPK) to regulate mesenchymal stem cell differentiation during skeletal development, bone formation and bone homeostasis. Both the Smad and p38 MAPK signaling pathways converge at transcription factors, for example, Runx2 to promote osteoblast differentiation and chondrocyte differentiation from mesenchymal precursor cells. TGF-β and BMP signaling is controlled by multiple factors, including the ubiquitin–proteasome system, epigenetic factors, and microRNA. Dysregulated TGF-β and BMP signaling result in a number of bone disorders in humans. Knockout or mutation of TGF-β and BMP signaling-related genes in mice leads to bone abnormalities of varying severity, which enable a better understanding of TGF-β/BMP signaling in bone and the signaling networks underlying osteoblast differentiation and bone formation. There is also crosstalk between TGF-β/BMP signaling and several critical cytokines’ signaling pathways (for example, Wnt, Hedgehog, Notch, PTHrP, and FGF) to coordinate osteogenesis, skeletal development, and bone homeostasis. This review summarizes the recent advances in our understanding of TGF-β/BMP signaling in osteoblast differentiation, chondrocyte differentiation, skeletal development, cartilage formation, bone formation, bone homeostasis, and related human bone diseases caused by the disruption of TGF-β/BMP signaling.

Sclerostin expression in bone tumours and tumour-like lesions

AIMS

To assess the immunophenotypic and mRNA expression of sclerostin in human skeletal tissues and in a wide range of benign and malignant bone tumours and tumour-like lesions.

METHODS AND RESULTS

Sclerostin expression was evaluated by immunohistochemistry and quantitative polymerase chain reaction (PCR). In lamellar and woven bone, there was strong sclerostin expression by osteocytes. Osteoblasts and other cell types in bone were negative. Hypertrophic chondrocytes in the growth plate and mineralized cartilage cells in zone 4 of hyaline articular cartilage strongly expressed sclerostin, but most chondrocytes in hyaline cartilage were negative. In primary bone-forming tumours, including osteosarcomas, there was patchy expression of sclerostin in mineralized osteoid and bone. Sclerostin staining was seen in woven bone in fibrous dysplasia, in osteofibrous dysplasia, and in reactive bone formed in fracture callus, in myositis ossificans, and in the wall of solitary bone cysts and aneurysmal bone cysts. Sclerostin was expressed by hypertrophic chondrocytes in osteochondroma and chondroblasts in chondroblastoma, but not by tumour cells in other bone tumours, including myeloma and metastatic carcinoma. mRNA expression of sclerostin was identified by quantitative PCR in osteosarcoma specimens and cell lines.

CONCLUSIONS

Sclerostin is an osteocyte marker that is strongly expressed in human woven and lamellar bone and mineralizing chondrocytes. This makes it a useful marker with which to identify benign and malignant osteogenic tumours and mineralizing cartilage tumours, such as chondroblastomas and other lesions in which there is bone formation.

Effects of Long-Term Odanacatib Treatment on Bone Gene Expression in Ovariectomized Adult Rhesus Monkeys: Differentiation From Alendronate

Similar efficacy of the cathepsin K inhibitor odanacatib (ODN) and the bisphosphonate alendronate (ALN) in reducing bone turnover markers and increasing bone mineral density in spine and hip were previously demonstrated in ovariectomized (OVX)-monkeys treated for 20 months in prevention mode. Here, we profiled RNA from tibial metaphysis and diaphysis of the same study using Affymetrix microarrays, and selected 204 probe sets (p < 0.001, three-group ANOVA) that were differentially regulated by ODN or ALN versus vehicle. Both drugs produced strikingly different effects on known bone-related genes and pathways at the transcriptional level. Although ALN either reduced or had neutral effects on bone resorption-related genes, ODN significantly increased the expression of osteoclast genes (eg, APC5, TNFRSF11A, CTSK, ITGB3, and CALCR), consistent with previous findings on the effects of this agent in enhancing the number of nonresorbing osteoclasts. Conversely, ALN reduced the expression of known bone formation-related genes (eg, TGFBR1, SPP1, RUNX2, and PTH1R), whereas ODN either increased or had neutral effects on their expression. These differential effects of ODN versus ALN on bone resorption and formation were highly correlative to the changes in bone turnover markers, cathepsin K (Catk) target engagement marker serum C-terminal cross-linked telopeptide (1-CTP) and osteoclast marker tartrate resistant acid phosphatase isoform 5b (TRAP5b) in the same monkeys. Overall, the molecular profiling results are consistent with the known pharmacological actions of these agents on bone remodeling and clearly differentiate the molecular mechanisms of ODN from the bisphosphonates.

Gene array analysis of neural crest cells identifies transcription factors necessary for direct conversion of embryonic fibroblasts into neural crest cells

Neural crest cells (NC cells) are multipotent cells that emerge from the edge of the neural folds and migrate throughout the developing embryo. Although the gene regulatory network for generation of NC cells has been elucidated in detail, it has not been revealed which of the factors in the network are pivotal to directing NC identity. In this study we analyzed the gene expression profile of a pure NC subpopulation isolated from Sox10-IRES-Venus mice and investigated whether these genes played a key role in the direct conversion of Sox10-IRES-Venus mouse embryonic fibroblasts (MEFs) into NC cells. The comparative molecular profiles of NC cells and neural tube cells in 9.5-day embryos revealed genes including transcription factors selectively expressed in developing trunk NC cells. Among 25 NC cell-specific transcription factor genes tested, SOX10 and SOX9 were capable of converting MEFs into SOX10-positive (SOX10+) cells. The SOX10+ cells were then shown to differentiate into neurons, glial cells, smooth muscle cells, adipocytes and osteoblasts. These SOX10+ cells also showed limited self-renewal ability, suggesting that SOX10 and SOX9 directly converted MEFs into NC cells. Conversely, the remaining transcription factors, including well-known NC cell specifiers, were unable to convert MEFs into SOX10+ NC cells. These results suggest that SOX10 and SOX9 are the key factors necessary for the direct conversion of MEFs into NC cells.

Summary: In this study, we identified the transcription factors specifically expressed in developing neural crest cells, and showed that SOX10 and SOX9 directly converted fibroblasts into neural crest cells.

The cartilage extracellular matrix as a transient developmental scaffold for growth plate maturation

The cartilage growth plate is a specialized developmental tissue containing characteristic zonal arrangements of chondrocytes. The proliferative and differentiative states of chondrocytes are tightly regulated at all stages including the initial limb bud and rudiment cartilage stages of development, the establishment of the primary and secondary ossification centers, development of the growth plates and laying down of bone. A multitude of spatio-temporal signals, including transcription factors, growth factors, morphogens and hormones, control chondrocyte maturation and terminal chondrocyte differentiation/hypertrophy, cell death/differentiation, calcification and vascular invasion of the growth plate and bone formation during morphogenetic transition of the growth plate. This involves hierarchical, integrated signaling from growth and factors, transcription factors, mechanosensory cues and proteases in the extracellular matrix to regulate these developmental processes to facilitate progressive changes in the growth plate culminating in bone formation and endochondral ossification. This review provides an overview of selected components which have particularly important roles in growth plate biology including collagens, proteoglycans, glycosaminoglycans, growth factors, proteases and enzymes.

Molecular Regulation of Adipogenesis and Potential Anti-Adipogenic Bioactive Molecules

Adipogenesis is the process by which precursor stem cells differentiate into lipid laden adipocytes. Adipogenesis is regulated by a complex and highly orchestrated gene expression program. In mammalian cells, the peroxisome proliferator-activated receptor γ (PPARγ), and the CCAAT/enhancer binding proteins (C/EBPs) such as C/EBPα, β and δ are considered the key early regulators of adipogenesis, while fatty acid binding protein 4 (FABP4), adiponectin, and fatty acid synthase (FAS) are responsible for the formation of mature adipocytes. Excess accumulation of lipids in the adipose tissue leads to obesity, which is associated with cardiovascular diseases, type II diabetes and other pathologies. Thus, investigating adipose tissue development and the underlying molecular mechanisms is vital to develop therapeutic agents capable of curbing the increasing incidence of obesity and related pathologies. In this review, we address the process of adipogenic differentiation, key transcription factors and proteins involved, adipogenic regulators and potential anti-adipogenic bioactive molecules.

Cell-free 3D scaffold with two-stage delivery of miRNA-26a to regenerate critical-sized bone defects

MicroRNAs (miRNAs) are being developed to enhance tissue regeneration. Here we show that a hyperbranched polymer with high miRNA-binding affinity and negligible cytotoxicity can self-assemble into nano-sized polyplexes with a 'double-shell' miRNA distribution and high transfection efficiency. These polyplexes are encapsulated in biodegradable microspheres to enable controllable two-stage (polyplexes and miRNA) delivery. The microspheres are attached to cell-free nanofibrous polymer scaffolds that spatially control the release of miR-26a. This technology is used to regenerate critical-sized bone defects in osteoporotic mice by targeting Gsk-3β to activate the osteoblastic activity of endogenous stem cells, thus addressing a critical challenge in regenerative medicine of achieving cell-free scaffold-based miRNA therapy for tissue engineering.

Mulberry water extract regulates the osteoblast/osteoclast balance in an ovariectomic rat model

Mulberry has favorable antioxidant ability.

Expression of osterix Is Regulated by FGF and Wnt/β-Catenin Signalling during Osteoblast Differentiation

Osteoblast differentiation from mesenchymal cells is regulated by multiple signalling pathways. Here we have analysed the roles of Fibroblast Growth Factor (FGF) and canonical Wingless-type MMTV integration site (Wnt/β-Catenin) signalling pathways on zebrafish osteogenesis. We have used transgenic and chemical interference approaches to manipulate these pathways and have found that both pathways are required for osteoblast differentiation in vivo. Our analysis of bone markers suggests that these pathways act at the same stage of differentiation to initiate expression of the osteoblast master regulatory gene osterix (osx). We use two independent approaches that suggest that osx is a direct target of these pathways. Firstly, we manipulate signalling and show that osx gene expression responds with similar kinetics to that of known transcriptional targets of the FGF and Wnt pathways. Secondly, we have performed ChIP with transcription factors for both pathways and our data suggest that a genomic region in the first intron of osx mediates transcriptional activation. Based upon these data, we propose that FGF and Wnt/β-Catenin pathways act in part by directing transcription of osx to promote osteoblast differentiation at sites of bone formation.

Curcumin alleviates glucocorticoid-induced osteoporosis through the regulation of the Wnt signaling pathway

It is known that prolonged glucocorticoid (GC) treatment results in osteoporosis. This study aimed to evaluate the protective effects of curcumin on the bones of rats with dexamethasone (DXM)-induced osteoporosis. In the present study, rats were administered DXM for 60 days to induce osteoporosis, and they were then treated with curcumin (100 mg/kg/day) for a further 60 days. H&E staining was used to observe the pathological changes in the femurs. Serum osteocalcin levels and collagen-type I fragments (CTX) were examined as bone metabolism markers. The results revealed that treatment with curcumin attenuated DXM-induced bone injury in femurs, increased the serum levels of osteocalcin and decreased the levels of CTX. In addition, in in vitro experiments, primary rat osteoblasts treated with curcumin at 0.5, 1 and 2 µM were exposed to 100 nM DXM. An MTT assay was used to determine the proliferative ability of the cells. Alkaline phosphatase activity, and the mRNA expression levels of runt-related transcription factor 2 (Runx2), osterix, osteocalcin, collagen, type 1, alpha 1 (Col1A1) and osteonectin were detected to assess transcription factor-associated osteogenic differentiation. The mRNA and protein expression levels of osteoprotegerin (OPG) and receptor activator for nuclear factor-kappa B ligand (RANKL) were detected to assess cytokine-associated osteoclastogenesis. The results demonstrated that curcumin prevented the DXM-induced inhibition of the proliferative ability of the osteoblasts in a dose-dependent manner. In addition, curcumin upregulated the mRNA expression levels of transcription factors that favor osteoblast differentiation and increased the ratio of OPG to RANKL. Moreover, the effects of curcumin on the Wnt signaling pathway were also investigated. RT-qPCR and western blot analysis demonstrated that the Wnt signaling pathway, which was inhibited by DXM, was re-activated upon treatment with curcumin. Immunofluorescence staining revealed that curcumin restored the intranuclear staining of β-catenin in the DXM-stimulated osteoblasts. Collectively, our data demonstrate that curcumin may be a potential therapeutic agent for the treatment of GC-induced osteoporosis.

Positive skeletal effect of two ingredients of Psoralea corylifolia L. on estrogen deficiency-induced osteoporosis and the possible mechanisms of action

Estrogen replacement therapy (ERT) is utilized as a major regime for treatment of postmenopausal osteoporosis at present. However, long-term supplement of estrogen may cause uterine hyperplasia and hypertension leading to a high risk of endometrial cancer and breast cancer. Psoralea corylifolia L. has long been used as tonic and food additives in many countries. Previous studies had found two ingredients in P. corylifolia L.: bavachin and bakuchiol exhibited osteoblastic activity. The present study was designed to investigate the protective effect of bakuchiol and bavachin on ovariectomy-induced bone loss and explore the possible mechanism. In vivo, bakuchiol and bavachin could prevented estrogen deficiency-induced bone loss in ovariectomized rats without uterotrophic activity. In vitro studies suggested that bakuchiol and bavachin induced primary human osteoblast differentiation by up-regulating the Wnt signalling pathway. This study suggests that such a bone-protective role makes them a promising and safe estrogen supplement for the ERT.

Effect of low-level mechanical vibration on osteogenesis and osseointegration of porous titanium implants in the repair of long bone defects

Emerging evidence substantiates the potential of porous titanium alloy (pTi) as an ideal bone-graft substitute because of its excellent biocompatibility and structural properties. However, it remains a major clinical concern for promoting high-efficiency and high-quality osseointegration of pTi, which is beneficial for securing long-term implant stability. Accumulating evidence demonstrates the capacity of low-amplitude whole-body vibration (WBV) in preventing osteopenia, whereas the effects and mechanisms of WBV on osteogenesis and osseointegration of pTi remain unclear. Our present study shows that WBV enhanced cellular attachment and proliferation, and induced well-organized cytoskeleton of primary osteoblasts in pTi. WBV upregulated osteogenesis-associated gene and protein expression in primary osteoblasts, including OCN, Runx2, Wnt3a, Lrp6 and β-catenin. In vivo findings demonstrate that 6-week and 12-week WBV stimulated osseointegration, bone ingrowth and bone formation rate of pTi in rabbit femoral bone defects via μCT, histological and histomorphometric analyses. WBV induced higher ALP, OCN, Runx2, BMP2, Wnt3a, Lrp6 and β-catenin, and lower Sost and RANKL/OPG gene expression in rabbit femora. Our findings demonstrate that WBV promotes osteogenesis and osseointegration of pTi via its anabolic effect and potential anti-catabolic activity, and imply the promising potential of WBV for enhancing the repair efficiency and quality of pTi in osseous defects.

Titanium Oxide: A Bioactive Factor in Osteoblast Differentiation

Titanium and titanium alloys are currently accepted as the gold standard in dental applications. Their excellent biocompatibility has been attributed to the inert titanium surface through the formation of a thin native oxide which has been correlated to the excellent corrosion resistance of this material in body fluids. Whether this titanium oxide layer is essential to the outstanding biocompatibility of titanium surfaces in orthopedic biomaterial applications is still a moot point. To study this critical aspect further, human fetal osteoblasts were cultured on thermally oxidized and microarc oxidized (MAO) surfaces and cell differentiation, a key indicator in bone tissue growth, was quantified by measuring the expression of alkaline phosphatase (ALP) using a commercial assay kit. Cell attachment was similar on all the oxidized surfaces although ALP expression was highest on the oxidized titanium alloy surfaces. Untreated titanium alloy surfaces showed a distinctly lower degree of ALP activity. This indicates that titanium oxide clearly upregulates ALP expression in human fetal osteoblasts and may be a key bioactive factor that causes the excellent biocompatibility of titanium alloys. This result may make it imperative to incorporate titanium oxide in all hard tissue applications involving titanium and other alloys.

Nanogel-Mediated RNAi Against Runx2 and Osx Inhibits Osteogenic Differentiation in Constitutively Active BMPR1A Osteoblasts

Trauma-induced heterotopic ossification (HO) and fibrodysplasia ossificans progressiva (FOP) are acquired and genetic variants of pathological bone formation occurring in soft tissues. Conventional treatment modalities target the inflammatory processes preceding bone formation. We investigated the development of a prophylaxis for heterotopic bone formation by addressing the biological basis for HO - dysregulation in the bone morphogenetic protein (BMP) signaling pathway. We previously reported the synthesis of cationic nanogel nanostructured polymers (NSPs) for efficient delivery of short interfering ribonucleic acids (siRNAs) and targeted gene silencing. Results suggested that nanogel:siRNA weight ratios of 1:1 and 5:1 silenced Runx2 and Osx gene expression in primary mouse osteoblasts with a constitutively active (ca) BMP Receptor 1A (BMPR1A) by the Q233D mutation. Repeated RNAi treatments over 14 days significantly inhibited alkaline phosphatase activity in caBMPR1A osteoblasts. Hydroxyapatite (HA) deposition was diminished over 28 days in culture, though complete suppression of HA deposition was not achieved. Outcome data suggested minimal cytotoxicity of nanogel-based RNAi therapeutics, and the multistage disruption of BMP-induced bone formation processes. This RNAi based approach to impeding osteoblastic differentiation and subsequent bone formation may form the basis of a clinical therapy for heterotopic bone formation.

Bone morphogenetic protein signaling in bone homeostasis

Bone morphogenetic proteins (BMPs) are cytokines belonging to the transforming growth factor-β (TGF-β) superfamily. They play multiple functions during development and tissue homeostasis, including regulation of the bone homeostasis. The BMP signaling pathway consists in a well-orchestrated manner of ligands, membrane receptors, co-receptors and intracellular mediators, that regulate the expression of genes controlling the normal functioning of the bone tissues. Interestingly, BMP signaling perturbation is associated to a variety of low and high bone mass diseases, including osteoporosis, bone fracture disorders and heterotopic ossification. Consistent with these findings, in vitro and in vivo studies have shown that BMPs have potent effects on the activity of cells regulating bone function, suggesting that manipulation of the BMP signaling pathway may be employed as a therapeutic approach to treat bone diseases. Here we review the recent advances on BMP signaling and bone homeostasis, and how this knowledge may be used towards improved diagnosis and development of novel treatment modalities. This article is part of a Special Issue entitled "Muscle Bone Interactions".

Mediators of inflammation and bone remodeling in rheumatic disease

Remodeling of bone is a continuous process that occurs throughout life. Under normal physiologic conditions, bone-resorbing osteoclasts and bone-forming osteoblasts are tightly coupled and regulated to ensure proper balance, such that there is no net change in bone mass. However, inflammation perturbs normal bone homeostasis. The impact of inflammation on bone is dependent upon the anatomic site affected, cell types, factors and cytokines present in the local microenvironment, and local mechanical forces. Cytokines are central to the pathogenesis of inflammation-induced bone loss and contribute to the uncoupling of osteoclast-mediated bone resorption and osteoblast-mediated bone formation, thereby disrupting normal remodeling. In this review, we will discuss the effects of cytokines on bone in two settings, rheumatoid arthritis and spondyloarthritis, a disease category that includes ankylosing spondylitis, psoriatic arthritis, reactive arthritis, inflammatory bowel disease, and juvenile onset spondyloarthropathy. The outcome for bone in these disease settings is quite different, and an understanding of the pathogenic mechanisms leading to the net impact on bone has been essential in developing new therapeutic approaches to bone health in these diseases.

BMP-2 Enhances Lgr4 Gene Expression in Osteoblastic Cells

Osteoporosis is one of the most prevalent diseases and the number of patients suffering from this disease is soaring due to the increase in the aged population in the world. The severity of bone loss in osteoporosis is based on the levels of impairment in the balance between bone formation and bone resorption, two arms of the bone metabolism, and bone remodeling. However, determination of bone formation levels is under many layers of control that are as yet fully defined. Bone morphogenetic protein (BMP) plays a key role in regulation of bone formation while its downstream targets are still incompletely understood. Lgr4 gene encodes an orphan receptor and has been identified as a genetic determinant for bone mass in osteoporotic patients. Here, we examine the effects of BMP on the expression of Lgr4 in osteoblastic cells. Lgr4 gene is expressed in an osteoblastic cell line, MC3T3E1 in a time dependent manner during the culture. BMP treatment enhances Lgr4 mRNA expression at least in part via transcriptional event. When Lgr4 mRNA is knocked down, the levels of BMP-induced increase in alkaline phosphatase (Alp) activity and Alp mRNA are suppressed. BMP enhancement of Lgr4 gene expression is suppressed by FGF and reversed by dexamethasone. BMP also enhances Lgr4 expression in primary cultures of calvarial osteoblasts. These data indicate that Lgr4 gene is regulated by BMP and is required for BMP effects on osteoblastic differentiation. J. Cell. Physiol. 231: 887-895, 2016. © 2015 Wiley Periodicals, Inc.

Wnt/β-catenin signaling in bone marrow niche

The bone marrow (BM) niche is a specific physiological environment for hematopoietic and non-hematopoietic stem cells (HSCs). Several signaling pathways (including Wnt/β-catenin) regulate various aspects of stem cell growth, function and death in the BM niche. In addition, the canonical Wnt pathway is crucial for directing self-renewal and differentiation as important mechanisms in many types of stem cells. We review the role of the Wnt/β-catenin pathway in the BM niche and its importance in stem cells. Relevant literature was identified by a PubMed search (1997-2014) of English-language literature by using the following keywords: BM niche, Wnt/β-catenin signaling, osteoblast, osteoclast and bone disease. The Wnt/β-catenin pathway regulates the stability of the β-catenin proto-oncogene. The stabilized β-catenin then translocates to the nucleus, forming a β-catenin-TCF/LEF complex regulating the transcription of specific target genes. Stem cells require β-catenin to mediate their response to Wnt signaling for maintenance and transition from the pluripotent state during embryogenesis. In adult stem cells, Wnt signaling functions at various hierarchical levels to contribute to the specification of the diverse tissues. Aberrant Wnt/β-catenin signaling and its downstream transcriptional regulators are observed in several malignant stem cells and human cancers. Because Wnt signaling can maintain stem cells and cancer cells, the ability to modulate the Wnt pathway either positively or negatively may be of therapeutic relevance. The controlled activation of Wnt signaling might allow us to enhance stem and progenitor cell activity when regeneration is needed.

Tissue alkaline phosphatase is involved in lipid metabolism and gene expression and secretion of adipokines in adipocytes

BACKGROUND

Alkaline phosphatases are dimeric hydrolytic enzymes that dephosphorylate nucleotides and proteins. AP-TNAP is found primarily in skeletal tissues were it plays a major role in the mineralization of the extracellular matrix and bone formation.

METHODS

In this study we found through conventional and real time PCR assays that Alpl, the gene encoding for AP-TNAP is expressed in adipose tissue and in 3 T3-F442A adipocytes. We evaluated, using RNAi its role in adipocyte metabolism, and its cytoplasmic location by immunohistochemistry.

RESULTS

Alpl is highly expressed late in adipogenesis during adipose terminal differentiation. Knocking down Alpl increased the expression of the genes encoding for glycerophosphate dehydrogenase, and for the adipokines adiponectin, and FABP4 (aP2) but decreased that of leptin, and it also increased secretion of FABP4; these 3 proteins are important in adipocyte systemic signaling and insulin sensitivity. Inhibition of alkaline phosphatase activity in adipocytes by levamisole reduced lipolysis and the expression of various lipogenic genes. We found the enzyme intracytoplasmically, forming aggregates in close surroundings of the lipid droplets during lipolysis.

CONCLUSIONS

We suggest that AP-TNAP activity is involved in lipid and energy metabolism of fat cells, and it might regulate glucose metabolism and insulin sensitivity via adipokine synthesis and secretion.

GENERAL SIGNIFICANCE

The activity of AP-TNAP might have a critical role in the energy balance of the adipocyte, probably participating in obesity and metabolic syndrome.

Cell seeding density is a critical determinant for copolymer scaffolds-induced bone regeneration

Constructs intended for bone tissue engineering (TE) are influenced by the initial cell seeding density. Therefore, the objective of this study was to determine the effect of bone marrow stromal stem cells (BMSCs) density loaded onto copolymer scaffolds on bone regeneration. BMSCs were harvested from rat's bone marrow and cultured in media with or without osteogenic supplements. Cells were seeded onto poly(l‐lactide‐co‐ε‐caprolactone) [poly(LLA‐co‐CL)] scaffolds at two different densities: low density (1 × 10⁶ cells/scaffold) or high density (2 × 10⁶ cells/scaffold) using spinner modified flasks and examined after 1 and 3 weeks. Initial attachment and spread of BMSC onto the scaffolds was recorded by scanning electron microscopy. Cell proliferation was assessed by DNA quantification and cell differentiation by quantitative real‐time reverse transcriptase‐polymerized chain reaction analysis (qRT‐PCR). Five‐millimeter rat calvarial defects (24 defects in 12 rats) were implanted with scaffolds seeded with either low or high density expanded with or without osteogenic supplements. Osteogenic supplements significantly increased cell proliferation (p < 0.001). Scaffolds seeded at high cell density exhibited higher mRNA expressions of Runx2 p = 0.001, Col1 p = 0.001, BMP2 p < 0.001, BSP p < 0.001, and OC p = 0.013. More bone was formed in response to high cell seeding density (p = 0.023) and high seeding density with osteogenic medium (p = 0.038). Poly (LLA‐co‐CL) scaffolds could be appropriate candidates for bone TE. The optimal number of cells to be loaded onto scaffolds is critical for promoting Extracellular matrix synthesis and bone formation. Cell seeding density and osteogenic supplements may have a synergistic effect on the induction of new bone. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 103A: 3649–3658, 2015.

Epidermal growth factor enhances osteogenic differentiation of dental pulp stem cells in vitro

Introduction

Epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) play an important role in extracellular matrix mineralization, a complex process required for proper bone regeneration, one of the biggest challenges in dentistry. The purpose of this study was to evaluate the osteogenic potential of EGF and bFGF on dental pulp stem cells (DPSCs).

Material and methods

Human DPSCs were isolated using CD105 magnetic microbeads and characterized by flow cytometry. To induce osteoblast differentiation, the cells were cultured in osteogenic medium supplemented with EGF or bFGF at a low concentration. Cell morphology and expression of CD146 and CD10 surface markers were analyzed using fluorescence microscopy. To measure mineralization, an alizarin red S assay was performed and typical markers of osteoblastic phenotype were evaluated by RT-PCR.

Results

EGF treatment induced morphological changes and suppression of CD146 and CD10 markers. Additionally, the cells were capable of producing calcium deposits and increasing the mRNA expression to alkaline phosphatase (ALP) and osteocalcin (OCN) in relation to control groups (p < 0.001). However, bFGF treatment showed an inhibitory effect.

Conclusion

These data suggests that DPSCs in combination with EGF could be an effective stem cell-based therapy for bone tissue engineering applications in periodontics and oral implantology.

Heparin affects human bone marrow stromal cell fate: Promoting osteogenic and reducing adipogenic differentiation and conversion

Heparins are broadly used for the prevention and treatment of thrombosis and embolism. Yet, osteoporosis is considered to be a severe side effect in up to one third of all patients on long-term treatment. However, the mechanisms underlying this clinical problem are only partially understood. To investigate if heparin affects differentiation of skeletal precursors, we examined the effects of heparin on the osteogenic and adipogenic lineage commitment and differentiation of primary human bone marrow stromal cells (hBMSCs). Due to the known inverse relationship between adipogenesis and osteogenesis and the capacity of pre-differentiated cells to convert into the respective other lineage, we also determined heparin effects on osteogenic conversion and adipogenic differentiation/conversion. Interestingly, heparin did not only significantly increase mRNA expression and enzyme activity of the osteogenic marker alkaline phosphatase (ALP), but it also promoted mineralization during osteogenic differentiation and conversion. Furthermore, the mRNA expression of the osteogenic marker bone morphogenic protein 4 (BMP4) was enhanced. In addition, heparin administration partly prevented adipogenic differentiation and conversion demonstrated by reduced lipid droplet formation along with a decreased expression of adipogenic markers. Moreover, luciferase reporter assays, inhibitor experiments and gene expression analyses revealed that heparin had putative permissive effects on osteogenic signaling via the BMP pathway and reduced the mRNA expression of the Wnt pathway inhibitors dickkopf 1 (DKK1) and sclerostin (SOST). Taken together, our data show a rather supportive than inhibitory effect of heparin on osteogenic hBMSC differentiation and conversion in vitro. Further studies will have to investigate the net effects of heparin administration on bone formation versus bone resorption in vivo to unravel the molecular mechanisms of heparin-associated osteoporosis and reconcile conflicting experimental data with clinical observations.

Calycosin-7-O-β-d-glucopyranoside stimulates osteoblast differentiation through regulating the BMP/WNT signaling pathways

The isoflavone calycosin-7-O-β-d-glucopyranoside (CG) is a principal constituent of Astragalus membranaceus (AR) and has been reported to inhibit osteoclast development in vitro and bone loss in vivo. The aim of this study was to investigate the osteogenic effects of CG and its underlying mechanism in ST2 cells. The results show that exposure of cells to CG in osteogenic differentiation medium increases ALP activity, osteocalcin (Ocal) mRNA expression and the osteoblastic mineralization process. Mechanistically, CG treatment increased the expression of bone morphogenetic protein 2 (BMP-2), p-Smad 1/5/8, β-catenin and Runx2, all of which are regulators of the BMP- or wingless-type MMTV integration site family (WNT)/β-catenin-signaling pathways. Moreover, the osteogenic effects of CG were inhibited by Noggin and DKK-1 which are classical inhibitors of the BMP and WNT/β-catenin-signaling pathways, respectively. Taken together, the results indicate that CG promotes the osteoblastic differentiation of ST2 cells through regulating the BMP/WNT signaling pathways. On this basis, CG may be a useful lead compound for improving the treatment of bone-decreasing diseases and enhancing bone regeneration.

Skeletal tissue engineering using mesenchymal or embryonic stem cells: clinical and experimental data

INTRODUCTION

Mesenchymal stem cells (MSCs) can be obtained from a wide variety of tissues for bone tissue engineering such as bone marrow, adipose, birth-associated, peripheral blood, periosteum, dental and muscle. MSCs from human fetal bone marrow and embryonic stem cells (ESCs) are also promising cell sources.

AREAS COVERED

In vitro, in vivo and clinical evidence was collected using MEDLINE® (1950 to January 2014), EMBASE (1980 to January 2014) and Google Scholar (1980 to January 2014) databases.

EXPERT OPINION

Enhanced results have been found when combining bone marrow-derived mesenchymal stem cells (BMMSCs) with recently developed scaffolds such as glass ceramics and starch-based polymeric scaffolds. Preclinical studies investigating adipose tissue-derived stem cells and umbilical cord tissue-derived stem cells suggest that they are likely to become promising alternatives. Stem cells derived from periosteum and dental tissues such as the periodontal ligament have an osteogenic potential similar to BMMSCs. Stem cells from human fetal bone marrow have demonstrated superior proliferation and osteogenic differentiation than perinatal and postnatal tissues. Despite ethical concerns and potential for teratoma formation, developments have also been made for the use of ESCs in terms of culture and ideal scaffold.

2,4,5-Trimethoxyldalbergiquinol promotes osteoblastic differentiation and mineralization via the BMP and Wnt/β-catenin pathway

Dalbergia odorifera has been traditionally used as a medicine to treat many diseases. However, the role of 2,4,5-trimethoxyldalbergiquinol (TMDQ) isolated and extracted from D. odorifera in osteoblast function and the underlying molecular mechanisms remain poorly understood. The aim of this study was to investigate the effects and possible underlying mechanisms of TMDQ on osteoblastic differentiation of primary cultures of mouse osteoblasts as an in vitro assay system. TMDQ stimulated osteoblastic differentiation, as assessed by the alkaline phosphatase (ALP) activity, ALP staining, mineralized nodule formation, and the levels of mRNAs encoding the bone differentiation markers, including ALP, bone sialoprotein (BSP), osteopontin, and osteocalcin. TMDQ upregulated the expression of Bmp2 and Bmp4 genes, and increased the protein level of phospho-Smad1/5/8. Furthermore, TMDQ treatment showed the increased mRNA expression of Wnt ligands, phosphorylation of GSK3, and the expression of β-catenin protein. The TMDQ-induced osteogenic effects were abolished by Wnt inhibitor, Dickkopf-1 (DKK1), and bone morphogenetic protein (BMP) antagonist, noggin. TMDQ-induced runt-related transcription factor 2 (Runx2) expression was attenuatted by noggin and DKK1. These data suggest that TMDQ acts through the activation of BMP, Wnt/β-catenin, and Runx2 signaling to promote osteoblast differentiation, and we demonstrate that TMDQ could be a potential agent for the treatment of bone loss-associated diseases such as osteoporosis.

Osteogenic Differentiation of Human and Ovine Bone Marrow Stromal Cells in response to β-Glycerophosphate and Monosodium Phosphate

Bone defects are severe burdens in clinics, and thus cell therapy offers an alternative strategy exploiting the features of bone marrow stromal cells (BMSCs). Sheep are a suitable orthopedic preclinical model for similarities with humans. This study compares the influence of two phosphate sources combined with bone morphogenetic protein-2 (BMP-2) on the osteogenic potential of human and ovine BMSCs. β-Glycerophosphate (β-GlyP) and monosodium phosphate (NaH2PO4) were used as organic and inorganic phosphate sources. Osteogenic differentiation of the BMSCs was assessed by calcified matrix, alkaline phosphatase (ALP) activity, and gene expression analysis. A higher calcified matrix deposition was detected in BMSCs cultured with NaH2PO4. Although no significant differences were detected among media for human BMSCs, β-GlyP with or without BMP-2 determined a positive trend in ALP levels compared to NaH2PO4. In contrast, NaH2PO4 had a positive effect on ALP levels in ovine BMSCs. β-GlyP better supported the expression of COL1A1 in human BMSCs, whereas all media enhanced RUNX2 and SPARC expression. Ovine BMSCs responded poorly to any media for RUNX2, COL1A1, and SPARC expression. NaH2PO4 improved calcified matrix deposition without upregulating the transcriptional expression of osteogenic markers. A further optimization of differentiation protocols needs to be performed to translate the procedures from preclinical to clinical models.

Molecular Aspects of Bone Resorption in β-Thalassemia Major

β-thalassemia is the most common single gene disorder worldwide, in which hemoglobin β-chain production is decreased. Today, the life expectancy of thalassemic patients is increased because of a variety of treatment methods; however treatment related complications have also increased. The most common side effect is osteoporosis, which usually occurs in early adulthood as a consequence of increased bone resorption. Increased bone resorption mainly results from factors such as delayed puberty, diabetes mellitus, hypothyroidism, ineffective hematopoiesis as well as hyperplasia of the bone marrow, parathyroid gland dysfunction, toxic effect of iron on osteoblasts, growth hormone (GH) and insulin-like growth factor-1 (IGF-1) deficiency. These factors disrupt the balance between osteoblasts and osteoclasts by interfering with various molecular mechanisms and result in decreased bone density.

Given the high prevalence of osteopenia and osteoporosis in thalassemic patients and complexity of their development process, the goal of this review is to evaluate the molecular aspects involved in osteopenia and osteoporosis in thalassemic patients, which may be useful for therapeutic purposes.

Bone morphogenetic protein 2-induced human dental pulp cell differentiation involves p38 mitogen-activated protein kinase-activated canonical WNT pathway

Both bone morphogenetic protein 2 (BMP2) and the wingless-type MMTV integration site (WNT)/β-catenin signalling pathway play important roles in odontoblast differentiation and dentinogenesis. Cross-talk between BMP2 and WNT/β-catenin in osteoblast differentiation and bone formation has been identified. However, the roles and mechanisms of the canonical WNT pathway in the regulation of BMP2 in dental pulp injury and repair remain largely unknown. Here, we demonstrate that BMP2 promotes the differentiation of human dental pulp cells (HDPCs) by activating WNT/β-catenin signalling, which is further mediated by p38 mitogen-activated protein kinase (MAPK) in vitro. BMP2 stimulation upregulated the expression of β-catenin in HDPCs, which was abolished by SB203580 but not by Noggin or LDN193189. Furthermore, BMP2 enhanced cell differentiation, which was not fully inhibited by Noggin or LDN193189. Instead, SB203580 partially blocked BMP2-induced β-catenin expression and cell differentiation. Taken together, these data suggest a possible mechanism by which the elevation of β-catenin resulting from BMP2 stimulation is mediated by the p38 MAPK pathway, which sheds light on the molecular mechanisms of BMP2-mediated pulp reparative dentin formation.

Role of bone morphogenetic protein-2 in osteogenic differentiation of mesenchymal stem cells

Bone mesenchymal stem cells (BMSCs) have been an area of interest in biomedical research and tissue engineering due to their diverse differentiation abilities. In osteogenesis, bone morphogenetic proteins (BMPs), particularly BMP-2, are important. However, the effect of BMP-2 on the osteogenetic capacity of BMSCs remains to be fully elucidated. In the present study, primary rat BMSCs were infected with a recombinant lentivirus carrying the BMP-2 gene (Lenti-BMP-2), and the effects of BMP-2 on the activity of alkaline phosphatase (ALP) on days 3, 7, 14 and 21, and on mineralization on day 21 were evaluated. In addition, the adhesive ability of BMP-2-overexpressed BMSCs was detected using an adhesion assay. Following forced expression of BMP-2 in the BMSCs, the levels of osteogenic genes, including osteopontin (OPN), osteocalcin (OC) and collagen type I (Col-I), were detected and the nuclear accumulation of Runt-related transcription factor (Runx)-2 and phosphorylated small mothers against decapentaplegic (p-Smad) 1/5/8 was also evaluated. The results demonstrated that the rat BMSCs had been isolated, cultured and passaged from Sprague-Dawley rat bone marrow successfully, and the third-generation BMSCs were identified using flow cytometry with CD29 staining. The osteogenetic phenotype of the BMSCs, expressing ALP and osteocalcin, was significantly induced by BMP-2, and the proliferation of the BMSCs was enhanced by BMP-2. Furthermore, the adhesive potential of the BMP-2-overexpressed BMSCs was increased, the expression levels of OPN, OCN and Col-Ie osteogenetic factors were upregulated and the nuclear accumulation of Runx-2 and p-Smads1/5/8 were increased significantly. These data suggested that BMP-2 may facilitate the osteogenetic differentiation of rat BMSCs and provide a favorable cell resource for tissue engineering.

Wnt3a signaling induces murine dental follicle cells to differentiate into cementoblastic/osteoblastic cells via an osterix-dependent pathway

BACKGROUND AND OBJECTIVE

Dental follicle cells, putative progenitor cells for cementoblasts, osteoblasts and periodontal ligament cells, interplay with Hertwig's epithelial root sheath (HERS) cells during tooth root formation, in which HERS is considered to have an inductive role in initiating cementogenesis by epithelial-mesenchymal interaction. However, the specific mechanisms controlling the cementoblast/osteoblast differentiation of dental follicle cells are not fully understood. Canonical Wnt signaling has been implicated in increased bone formation by controlling mesenchymal stem cell or osteoblastic cell functions. This study examined the possible expression of canonical Wnt ligand in HERS and the role of Wnt signaling during the cementoblast/osteoblast differentiation of dental follicle cells.

MATERIAL AND METHODS

The expression of Wnt3a, a representative canonical Wnt ligand, in HERS was assessed by immunohistochemistry. The differentiation and function of immortalized murine dental follicle cells were evaluated by measuring alkaline phosphatase (ALP, Alpl) activity and osteogenic gene expression.

RESULTS

We identified the expression of Wnt3a in HERS during mouse tooth root development by immunohistochemistry as well as in cultured human epithelial rest cells of Malassez by real-time polymerase chain reaction, while no expression of Wnt3a was detected in cultured dental mesenchymal cells. Exposure of immortalized murine dental follicle cells to Wnt3a-induced ALP activity as well as expression of the Alpl gene. Pretreatment of cells with Dickkopf-1, a potent canonical Wnt antagonist, markedly attenuated the effect of Wnt3a on ALP expression. Furthermore, Wnt3a induced transcriptional activity of runt-related transcription factor 2 (Runx2) and expression of osterix at gene and/or protein levels. Treatment with osterix-small interfering RNA significantly inhibited Wnt3a-induced ALP expression at gene and protein levels.

CONCLUSION

These findings suggest that HERS has a potential role in stimulating cementoblast/osteoblast differentiation of dental follicle cells via the Wnt/β-catenin signaling pathway.