Runx2 regulates FGF2-induced Bmp2 expression during cranial bone development

Mandible development under gestational protein restriction: cellular and molecular mechanisms

Insufficient evidence regarding how maternal undernutrition affects craniofacial bone development persists. With its unique focus on the impact of gestational protein restriction on calvaria and mandible osteogenesis, this study aims to fill, at least in part, this gap. Female mice were mated and randomized into NP (normal protein) or LP (low protein) groups. On the 18th gestational day (GD), male embryos were collected and submitted to microtomography (µCT), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), PCR, and autophagy dynamic analyses. The study shows that the LP offspring exhibited lower body mass than the NP group, with µCT analysis revealing no volumetric differences in fetus's head. EDS analysis showed lower calcium and higher phosphorus percentages in mandibles and calvaria. SEM assessment evidenced higher hydroxyapatite crystal-like (HC) deposition on the calvaria surface in LP fetus. Conversely, lower HC deposition was observed on the mandible surface, suggesting delayed matrix mineralization in LP fetuses with a higher percentage of collagen fibers in the mandible bone. The autophagy process was reduced in the mesenchyme of LP fetuses. PCR array analysis of 84 genes revealed 27 genes with differential expression in the LP progeny-moreover, increased mRNA levels of Akt1, Mtor, Nfkb, and Smad1 in the LP offspring. In conclusion, the results suggest that gestational protein restriction anticipated bone differentiation in utero, before 18GD, where this process is reduced compared to the control, leading to the reduction in bone area at 15 postnatal day previously observed. These findings provide insights into the molecular and cellular mechanisms of mandible development and suggest potential implications for the Developmental Origins of Health and Disease (DOHaD).

Simvastatin-loaded 3D aerogel scaffolds promote bone regeneration

BACKGROUND

It is imperative to design a suitable material for bone regeneration that emulates the microstructure and compositional framework of natural bone while mitigating the shortcomings of current repair materials.

OBJECTIVE

The aim of the study is to synthesize a 3D aerogel scaffold composed of PLCL/gelatin electro-spun nanofiber loaded with Simvastatin and investigate its biocompatibility as well as its performance in cell proliferation and ossification differentiation.

METHODS

PLCL/gelatin nanofibers were fabricated in coaxial electrospinning with simvastatin added. Fibers were fragmented, pipetted into molds, frozen, and dried. The morphology of fibers and contact angles in 4 groups of PLCL, PLCL@S, 3D-PLCL, and 3D-PLCL@S was observed and compared. MC3T3-E1 cells were planted at the four materials to observe cell growth status, and ALP and ARS tests were conducted to compare the ossification of cells.

RESULTS

TEM scanning showed the coaxial fiber of the inner PLCL and outer gelatin. The mean diameter of the PLCL/gelatin fibers is 561 ± 95 nm and 631 ± 103 nm after the drug loading. SEM showed the fibers in the 3D-PLCL@S group were more curled and loose with more space interlaced. The contact angle in this group was 27.1°, the smallest one. Drug release test demonstrated that simvastatin concentration in the 3D-PLCL@S could remain at a relatively high level compared to the control group. The cell proliferation test showed that MC3T3-EI cells could embed into the scaffold deeply and exhibit higher viability in the 3D-PLCL@S group than other groups. The ossification tests of ALP and ARS also inferred that the 3D-PLCL@S scaffold could offer a better osteogenic differentiation matrix.

CONCLUSION

The PLCL/gelatin aerogel scaffold, when loaded with Simvastatin, demonstrates a more pronounced potential in enhancing osteoblast proliferation and osteogenic differentiation. We hypothesize that this scaffold could serve as a promising material for addressing bone defects.

Joint multi-ancestry and admixed GWAS reveals the complex genetics behind human cranial vault shape

The cranial vault in humans is highly variable, clinically relevant, and heritable, yet its genetic architecture remains poorly understood. Here, we conduct a joint multi-ancestry and admixed multivariate genome-wide association study on 3D cranial vault shape extracted from magnetic resonance images of 6772 children from the ABCD study cohort yielding 30 genome-wide significant loci. Follow-up analyses indicate that these loci overlap with genomic risk loci for sagittal craniosynostosis, show elevated activity cranial neural crest cells, are enriched for processes related to skeletal development, and are shared with the face and brain. We present supporting evidence of regional localization for several of the identified genes based on expression patterns in the cranial vault bones of E15.5 mice. Overall, our study provides a comprehensive overview of the genetics underlying normal-range cranial vault shape and its relevance for understanding modern human craniofacial diversity and the etiology of congenital malformations.

RUNX2 Regulates Osteoblast Differentiation via the BMP4 Signaling Pathway

RUNX2 is a master osteogenic transcription factor, and mutations in RUNX2 cause the inherited skeletal disorder cleidocranial dysplasia (CCD). Studies have revealed that RUNX2 is not only a downstream target of the bone morphogenetic protein (BMP) pathway but can also regulate the expression of BMPs. However, the underlying mechanism of the regulation of BMPs by RUNX2 remains unknown. In this project, we diagnosed a CCD patient with a 7.86-Mb heterozygous deletion on chromosome 6 containing all exons of RUNX2 by multiplex ligation-dependent probe amplification (MLPA) and whole-genome sequencing (WGS). Bone marrow mesenchymal stem cells (BMSCs) were further extracted from patient alveolar bone fragments (CCD-BMSCs), an excellent natural model to explore the possible mechanism. The osteogenic differentiation ability of CCD-BMSCs was severely affected by RUNX2 heterozygous deletion. Also, BMP4 decreased most in BMP ligands, and CHRDL1, a BMP antagonist, was abnormally elevated in CCD-BMSCs. Furthermore, BMP4 treatment essentially rescued the osteogenic capacity of CCD-BMSCs, and RUNX2 overexpression reversed the abnormal expression of BMP4 and CHRDL1. Notably, we constructed CRISPR/Cas9 Runx2^+/m MC3T3-E1 cells, which simulated a variant in CCD-BMSCs, to exclude the interference of other gene deletions and the heterogeneity of the genetic background of primary cells, and verified all findings from the CCD-BMSCs. Moreover, the luciferase reporter experiment showed that RUNX2 could inhibit the transcription of CHRDL1. Through immunofluorescence, the inhibitory effect of CHRDL1 on BMP4/Smad signaling was confirmed in MC3T3-E1 cells. These results revealed that RUNX2 regulated the BMP4 pathway by inhibiting CHRDL1 transcription. We collectively identified a novel RUNX2/CHRDL1/BMP4 axis to regulate osteogenic differentiation and noted that BMP4 might be a valuable therapeutic option for treating bone diseases.

The Role of Growth Factors in Bioactive Coatings

With increasing obesity and an ageing population, health complications are also on the rise, such as the need to replace a joint with an artificial one. In both humans and animals, the integration of the implant is crucial, and bioactive coatings play an important role in bone tissue engineering. Since bone tissue engineering is about designing an implant that maximally mimics natural bone and is accepted by the tissue, the search for optimal materials and therapeutic agents and their concentrations is increasing. The incorporation of growth factors (GFs) in a bioactive coating represents a novel approach in bone tissue engineering, in which osteoinduction is enhanced in order to create the optimal conditions for the bone healing process, which crucially affects implant fixation. For the application of GFs in coatings and their implementation in clinical practice, factors such as the choice of one or more GFs, their concentration, the coating material, the method of incorporation, and the implant material must be considered to achieve the desired controlled release. Therefore, the avoidance of revision surgery also depends on the success of the design of the most appropriate bioactive coating. This overview considers the integration of the most common GFs that have been investigated in in vitro and in vivo studies, as well as in human clinical trials, with the aim of applying them in bioactive coatings. An overview of the main therapeutic agents that can stimulate cells to express the GFs necessary for bone tissue development is also provided. The main objective is to present the advantages and disadvantages of the GFs that have shown promise for inclusion in bioactive coatings according to the results of numerous studies.

Preparation, Characterization and in vitro/in vivo Evaluation of Lovastatin-Loaded PLGA Microspheres by Local Administration for Femoral Head Necrosis

Background

The present work is an effort to develop a novel locally injection LVTT-loaded PLGA microspheres (LVTT-PLGA-MS) on the treatment of rabbits with femoral head necrosis (FHN).

Methods

LVTT-loaded PLGA microspheres (LVTT-PLGA MS) were prepared by an emulsion-solvent evaporation method. The physicochemical properties of LVTT-PLGA-MS were investigated to ensure that they have good qualities and are suitable for local delivery. In vitro drug release behavior of MS was also studied compared with free LVTT. In vivo, we also studied the pharmacokinetics and pharmacodynamics of MS in rabbits with the optimized formulation.

Results

In this study, we used the emulsion-solvent evaporation method to prepare LVTT-PLGA MS. Scanning electron microscopy demonstrated that the LVTT-PLGA MS were regular, round in shape and relatively unified size distributions were selected. The mean PS was 12.3±2.1 µm. The drug-loading rate (27.6% ± 2.9%) was calculated for three batches of MS. The thermogram of LVTT-PLGA MS showed an endothermic peak at 98.3°C, revealing that LVTT existed in MS in an uncrystallized rather than a crystallized form. In the release study, LVTT-PLGA MS is observed linear prolonging drug release rates for more than 21 days without initial burst release. The pharmacodynamic results confirmed that the LVTT-PLGA MS had a good and lasting improvement effect against femoral head necrosis.

Conclusion

Our results demonstrated that LVTT-PLGA MS has the potential for being a local delivery system.

RUNX2-modifying enzymes: therapeutic targets for bone diseases

RUNX2 is a master transcription factor of osteoblast differentiation. RUNX2 expression in the bone and osteogenic front of a suture is crucial for cranial suture closure and membranous bone morphogenesis. In this manner, the regulation of RUNX2 is precisely controlled by multiple posttranslational modifications (PTMs) mediated by the stepwise recruitment of multiple enzymes. Genetic defects in RUNX2 itself or in its PTM regulatory pathways result in craniofacial malformations. Haploinsufficiency in RUNX2 causes cleidocranial dysplasia (CCD), which is characterized by open fontanelle and hypoplastic clavicles. In contrast, gain-of-function mutations in FGFRs, which are known upstream stimulating signals of RUNX2 activity, cause craniosynostosis (CS) characterized by premature suture obliteration. The identification of these PTM cascades could suggest suitable drug targets for RUNX2 regulation. In this review, we will focus on the mechanism of RUNX2 regulation mediated by PTMs, such as phosphorylation, prolyl isomerization, acetylation, and ubiquitination, and we will summarize the therapeutics associated with each PTM enzyme for the treatment of congenital cranial suture anomalies.

Temporally Altered miRNA Expression in a Piglet Model of Hypoxic Ischemic Brain Injury

Hypoxic ischemic encephalopathy (HIE) is the most frequent cause of acquired infant brain injury. Early, clinically relevant biomarkers are required to allow timely application of therapeutic interventions. We previously reported early alterations in several microRNAs (miRNA) in umbilical cord blood at birth in infants with HIE. However, the exact timing of these alterations is unknown. Here, we report serial changes in six circulating, cross-species/bridging biomarkers in a clinically relevant porcine model of neonatal HIE with functional analysis. Six miRNAs—miR-374a, miR-181b, miR-181a, miR-151a, miR-148a and miR-128—were significantly and rapidly upregulated 1-h post-HI. Changes in miR-374a, miR-181b and miR-181a appeared specific to moderate-severe HI. Histopathological injury and five miRNAs displayed positive correlations and were predictive of MRS Lac/Cr ratios. Bioinformatic analysis identified that components of the bone morphogenic protein (BMP) family may be targets of miR-181a. Inhibition of miR-181a increased neurite length in both SH-SY5Y cells at 1 DIV (days in vitro) and in primary cultures of rat neuronal midbrain at 3 DIV. In agreement, inhibition of miR-181a increased expression of BMPR2 in differentiating SH-SY5Y cells. These miRNAs may therefore act as early biomarkers of HIE, thereby allowing for rapid diagnosis and timely therapeutic intervention and may regulate expression of signalling pathways vital to neuronal survival.

The Epstein-Barr Virus-Encoded EBNA1 Protein Activates the Bone Morphogenic Protein (BMP) Signalling Pathway to Promote Carcinoma Cell Migration

The Epstein-Barr virus (EBV)-encoded nuclear antigen 1 (EBNA1) protein is expressed in all virus-associated malignancies, where it performs an essential role in the maintenance, replication and transcription of the EBV genome. In recent years, it has become apparent that EBNA1 can also influence cellular gene transcription. Here, we demonstrate that EBNA1 is able to stimulate the expression of the Transforming growth factor-beta (TGFβ) superfamily member, bone morphogenic protein 2 (BMP2), with consequential activation of the BMP signalling pathway in carcinoma cell lines. We show that BMP pathway activation is associated with an increase in the migratory capacity of carcinoma cells, an effect that can be ablated by the BMP antagonist, Noggin. Gene expression profiling of authentic EBV-positive nasopharyngeal carcinoma (NPC) tumours revealed the consistent presence of BMP ligands, established BMP pathway effectors and putative target genes, constituting a prominent BMP “signature” in this virus-associated cancer. Our findings show that EBNA1 is the major viral-encoded protein responsible for activating the BMP signalling pathway in carcinoma cells and supports a role for this pathway in promoting cell migration and possibly, metastatic spread.

The transcriptional regulator MEIS2 sets up the ground state for palatal osteogenesis in mice

Haploinsufficiency of Meis homeobox 2 (MEIS2), encoding a transcriptional regulator, is associated with human cleft palate, and Meis2 inactivation leads to abnormal palate development in mice, implicating MEIS2 functions in palate development. However, its functional mechanisms remain unknown. Here we observed widespread MEIS2 expression in the developing palate in mice. Wnt1Cre -mediated Meis2 inactivation in cranial neural crest cells led to a secondary palate cleft. Importantly, about half of the Wnt1Cre ;Meis2f/f mice exhibited a submucous cleft, providing a model for studying palatal bone formation and patterning. Consistent with complete absence of palatal bones, the results from integrative analyses of MEIS2 by ChIP sequencing, RNA-Seq, and an assay for transposase-accessible chromatin sequencing identified key osteogenic genes regulated directly by MEIS2, indicating that it plays a fundamental role in palatal osteogenesis. De novo motif analysis uncovered that the MEIS2-bound regions are highly enriched in binding motifs for several key osteogenic transcription factors, particularly short stature homeobox 2 (SHOX2). Comparative ChIP sequencing analyses revealed genome-wide co-occupancy of MEIS2 and SHOX2 in addition to their colocalization in the developing palate and physical interaction, suggesting that SHOX2 and MEIS2 functionally interact. However, although SHOX2 was required for proper palatal bone formation and was a direct downstream target of MEIS2, Shox2 overexpression failed to rescue the palatal bone defects in a Meis2-mutant background. These results, together with the fact that Meis2 expression is associated with high osteogenic potential and required for chromatin accessibility of osteogenic genes, support a vital function of MEIS2 in setting up a ground state for palatal osteogenesis.

Loss of p62 impairs bone turnover and inhibits PTH-induced osteogenesis

The p62 (also named sequestosome1/SQSTM1) is multidomain and multifunctional protein associated with several physiological and pathological conditions. A number of studies evidenced an involvement of p62 on the disruptive bone scenarios due to its participation in the inflammatory/osteoclastogenic pathways. However, so far, information regarding the function of p62 in the fine-tuned processes underpinning the bone physiology are not well-defined and are sometime discordant. We, previously, demonstrated that the intramuscular administration of a plasmid coding for p62 was able to contrast bone loss in a mouse model of osteopenia. Here, in vitro findings showed that the p62 overexpression in murine osteoblasts precursors enhanced their maturation while the p62 depletion by a specific siRNA, decreased osteoblasts differentiation. Consistently, the activity of osteoblasts from p62^-/- mice was reduced compared with wild-type. Also, morphometric analyses of bone from p62 knockout mice revealed a pathological phenotype characterized by a lower turnover that could be explained by the poor Runx2 protein synthesis in absence of p62. Furthermore, we demonstrated that the parathyroid hormone (PTH) regulates p62 expression and that the osteogenic effects of this hormone were totally abrogated in osteoblasts from p62-deficient mice. Therefore, these findings, for the first time, highlight the important role of p62 both for the basal and for PTH-stimulated bone remodeling.

Positive role of calcium phosphate ceramics regulated inflammation in the osteogenic differentiation of mesenchymal stem cells

Recently, researches have confirmed the crucial role of inflammatory response in Ca-P ceramic-induced osteogenesis, however, the underlying mechanism has not yet been fully understood. In this study, BCP and β-TCP ceramics were used as material models to investigate the effect of physicochemical properties on inflammatory response in vitro. The results showed that BCP and β-TCP could support macrophages attachment, proliferation, and spreading favorably, as well as promote gene expressions of inflammatory related cytokines (IL-1, IL-6, MCP-1, and TNF-α) and growth factors (TGF-β, FGF, PDGF, VEGF, IGF, and EGF). BCP showed a facilitating function on the gene expressions earlier than β-TCP. Further coculture experiments performed in vitro demonstrated that the CMs containing various increased cytokines for macrophages pre-culture could significantly promote MSCs osteogenic differentiation, which was confirmed by the gene expressions of osteogenic specific markers and the intracellular OCN product accumulation under the stimulation of BCP and β-TCP ceramics. Further evidence was found from the formation of mineralized nodules in BCM and TCM. In addition, this study showed a concise relationship between Ca-P ceramic induced inflammation and its osteoinductivity that the increased cytokines and growth factors from macrophages could promote MSCs osteogenic differentiation.

Fibroblast growth factors in skeletal development

Fibroblast growth factors (FGFs) and their receptors (FGFRs) are expressed throughout all stages of skeletal development. In the limb bud and in cranial mesenchyme, FGF signaling is important for formation of mesenchymal condensations that give rise to bone. Once skeletal elements are initiated and patterned, FGFs regulate both endochondral and intramembranous ossification programs. In this chapter, we review functions of the FGF signaling pathway during these critical stages of skeletogenesis, and explore skeletal malformations in humans that are caused by mutations in FGF signaling molecules.

A tale of two cities: The genetic mechanisms governing calvarial bone development

The skull bones must grow in a coordinated, three-dimensional manner to coalesce and form the head and face. Mammalian skull bones have a dual embryonic origin from cranial neural crest cells (CNCC) and paraxial mesoderm (PM) and ossify through intramembranous ossification. The calvarial bones, the bones of the cranium which cover the brain, are derived from the supraorbital arch (SOA) region mesenchyme. The SOA is the site of frontal and parietal bone morphogenesis and primary center of ossification. The objective of this review is to frame our current in vivo understanding of the morphogenesis of the calvarial bones and the gene networks regulating calvarial bone initiation in the SOA mesenchyme.

Clinical and radiological findings in a severe case of cleidocranial dysplasia

Cleidocranial dysplasia (CCD) is a rare congenital autosomal dominant condition, causing hypoplasia of the clavicle, abnormal formation of teeth, skeletal and craniofacial bones. CCD is caused by the mutation of RUNX2/CBFA1 present in the short arm of chromosome 6 at position 21.1, a transcription factor essential for the formation of teeth, cartilage and bone. Patients with CCD show the classical features of excessive mobility of the shoulder bone, lack of resorption of the deciduous teeth, failure to erupt permanent teeth, multiple impacted and supernumerary teeth, and open fontanelle and sutures of the skull. In this article we report a case of CCD in a 16-year-old male patient, with an aim to highlight the clinical, radiological and recommended treatment guidelines.

Conditional deletion of Bmp2 in cranial neural crest cells recapitulates Pierre Robin sequence in mice

Bone morphogenetic protein (BMP) signaling plays a crucial role in the development of craniofacial organs. Mutations in numerous members of the BMP signaling pathway lead to several severe human syndromes, including Pierre Robin sequence (PRS) caused by heterozygous loss of BMP2. In this study, we generate mice carrying Bmp2-specific deletion in cranial neural crest cells using floxed Bmp2 and Wnt1-Cre alleles to mimic PRS in humans. Mutant mice exhibit severe PRS with a significantly reduced size of craniofacial bones, cleft palate, malformed tongue and micrognathia. Palate clefting is caused by the undescended tongue that prevents palatal shelf elevation. However, the tongue in Wnt1-Cre;Bmp2^f/f mice does not exhibit altered rates of cell proliferation and apoptosis, suggesting contribution of extrinsic defects to the failure of tongue descent. Further studies revealed obvious reduction in cell proliferation and differentiation of osteogenic progenitors in the mandible of the mutants, attributing to the micrognathia phenotype. Our study illustrates the pathogenesis of PRS caused by Bmp2 mutation, highlights the crucial role of BMP2 in the development of craniofacial bones and emphasizes precise coordination in the morphogenesis of palate, tongue and mandible during embryonic development.

Evaluation of osteoblast differentiation and function when cultured on mesoporous bioactive glass adsorbed with testosterone

Mesoporous bioactive glass (MBG), a kind of porous materials with great osteoconductive and osteoinductive ability, shows promising application in bone tissue engineering due to its high specific surface area, orderly channel structure, and large pore volume. Here we reported that the proliferation, differentiation, and mineralization were promoted in MC3T3-E1 cells cultured on MBG which adsorbed with testosterone (MBG/T). We found that transcriptional activity of Runx2 which is a critical transcription factor is increased in MC3T3-E1 cells cultured on MBG/T. Intriguingly, we observed that ERK phosphorylation was enhanced in MC3T3-E1 cells cultured on MBG/T. We showed that activated Runx2 in MC3T3-E1 cells cultured on MBG/T is through Erk1/2 phosphorylation. Consistent with this result, we also found that the expression of osteoblastic marker genes were increased. Therefore, we concluded that osteoblast differentiation and mineralization was enhanced after cells cultured on MBG/T through Erk1/2-activated Runx2 pathway. Our findings provided that MBG/T is a potential material in the process of bone repair.

Calcific Aortic Valve Disease: a Developmental Biology Perspective

PURPOSE OF REVIEW

This review aims to highlight the past and more current literature related to the multifaceted pathogenic programs that contribute to calcific aortic valve disease (CAVD) with a focus on the contribution of developmental programs.

RECENT FINDINGS

Calcification of the aortic valve is an active process characterized by calcific nodule formation on the aortic surface leading to a less supple and more stiffened cusp, thereby limiting movement and causing clinical stenosis. The mechanisms underlying these pathogenic changes are largely unknown, but emerging studies have suggested that signaling pathways common to valvulogenesis and bone development play significant roles and include Transforming Growth Factor-β (TGF-β), bone morphogenetic protein (BMP), Wnt, Notch, and Sox9. This comprehensive review of the literature highlights the complex nature of CAVD but concurrently identifies key regulators that can be targeted in the development of mechanistic-based therapies beyond surgical intervention to improve patient outcome.

BMP signaling regulates the skeletal and connective tissue differentiation during caudal fin regeneration in sailfin molly (Poecilia latipinna)

Caudal fin regeneration in sailfin molly, Poecilia latipinna (Lesueur 1821) involves an initial wound healing stage, followed by blastema that is formed of fast proliferating cells. In order to replicate the lost fin, correct differentiation of the blastemal cells into various tissues is the prime essence. Among the molecular signals governing proper differentiation of blastemal cells, members of the bone morphogenetic protein (BMP) family are crucial. Herein, we investigated the specific effects of inhibition of BMP signaling using LDN193189 on skeletal and connective tissue formation in the regenerating tail fin of P. latipinna during early differentiation phase. It was observed that BMP inhibition leads to reduction in the length of regeneration, which can be correlated with compromised proliferation of blastemal cells. Decreased expression of cell proliferation marker like pcna together with reduced BrdU positive cells consolidate the above observation. Further, histological analysis revealed stunted progression of skeletal tissues and this correlated with the reduced expression of sox9, runx2 and dlx5, Osc and Osn genes in response to BMP inhibition. Also, defective bone patterning was observed due to BMP inhibition, which was associated with diminished levels of shh, ptc-1, gli2 and other BMP ligands. Moreover, histochemical analysis revealed that collagen, one of the most prominent components of connective tissue, was formed below par in treated fin tissues which was subsequently confirmed by biochemical and transcript level analyses. Overall our results highlight the importance of the BMP pathway in proper differentiation of skeletal and connective tissues during the differentiation stage of regenerating caudal fin.

Enhanced osteogenesis and angiogenesis by mesoporous hydroxyapatite microspheres-derived simvastatin sustained release system for superior bone regeneration

Biomaterials with both excellent osteogenic and angiogenic activities are desirable to repair massive bone defects. In this study, simvastatin with both osteogenic and angiogenic activities was incorporated into the mesoporous hydroxyapatite microspheres (MHMs) synthesized through a microwave-assisted hydrothermal method using fructose 1,6-bisphosphate trisodium salt (FBP) as an organic phosphorous source. The effects of the simvastatin-loaded MHMs (S-MHMs) on the osteogenic differentiation of rat bone marrow mesenchymal stem cells (rBMSCs) and angiogenesis in EA.hy926 cells were investigated. The results showed that the S-MHMs not only enhanced the expression of osteogenic markers in rBMSCs but also promoted the migration and tube formation of EA.hy926 cells. Furthermore, the S-MHMs were incorporated into collagen matrix to construct a novel S-MHMs/collagen composite scaffold. With the aid of MHMs, the water-insoluble simvastatin was homogenously incorporated into the hydrophilic collagen matrix and presented a sustained release profile. In vivo experiments showed that the S-MHMs/collagen scaffolds enhanced the bone regeneration and neovascularization simultaneously. These results demonstrated that the water-insoluble simvastatin could be incorporated into the MHMs and maintained its biological activities, more importantly, the S-MHMs/collagen scaffolds fabricated in this study are of immense potential in bone defect repair by enhancing osteogenesis and angiogenesis simultaneously.

Comparison between mandibular and femur derived bone marrow stromal cells: osteogenic and angiogenic potentials in vitro and bone repairing ability in vivo

M-BMSCs contains stronger osteogenic and angiogenic potentials, and better bone repairing ability.

Alpinia officinarum Stimulates Osteoblast Mineralization and Inhibits Osteoclast Differentiation

Alpinia officinarum rhizome has been used as a traditional herbal remedy to treat inflammatory and internal diseases. Based on the previously observed inhibitory effect of A. officinarum rhizome in an arthritis model, we evaluated whether a water extract of A. officinarum rhizome (WEAO) would enhance in vitro osteoblast mineralization using calvarial osteoblast precursor cells or would inhibit in vitro osteoclast differentiation and bone resorption using bone marrow derived macrophages. In osteoblasts, WEAO enhanced the mRNA levels of transcription factor (runt-related transcription factor 2, smad1, smad5, and junB) and marker (bone morphogenetic protein-2, collagen type 1alpha1, and osteocalcin) genes related to osteoblast mineralization, consistent with increased alizarin red S staining intensity. WEAO markedly inhibited osteoclast differentiation by suppressing the receptor activator for nuclear factor-[Formula: see text]B ligand-induced downregulation of inhibitor of DNA binding 2 and V-maf musculoaponeurotic fibrosarcoma oncogene homolog B and the phosphorylation of c-Jun N-terminal kinase, p38, nuclear factor-[Formula: see text]B, c-Src, and Bruton's tyrosine kinase to induce nuclear factor of activated T cells cytoplasmic 1 expression. WEAO also suppressed the resorbing activity of mature osteoclasts by altering actin ring formation. Therefore, the results of this study demonstrate that WEAO stimulates osteoblast mineralization and inhibits osteoclast differentiation. Thus, WEAO may be a promising herbal candidate to treat or prevent pathological bone diseases by regulating the balance between osteoclast and osteoblast activity.

Recombinant human bone morphogenetic protein-2 suspended in fibrin glue enhances bone formation during distraction osteogenesis in rabbits

INTRODUCTION

Bone morphogenetic protein-2 (BMP-2) has high potential for bone formation, but its in vivo effects are unpredictable due to the short life time. This study was designed to evaluate the effects of recombinant human (rh) BMP-2 suspended in fibrin on bone formation during distraction osteogenesis (DO) in rabbits.

MATERIAL AND METHODS

The in vitro release kinetics of rhBMP-2 suspended in fibrin was tested using an enzyme-linked immunosorbent assay. Unilateral tibial lengthening for 10 mm was achieved in 48 rabbits. At the completion of osteodistraction, vehicle, fibrin, rhBMP-2 or rhBMP-2 suspended in fibrin (rhBMP-2 + fibrin) was injected into the center of the lengthened gap, with 12 animals in each group. Eight weeks later, the distracted callus was examined by histology, micro-CT and biomechanical testing. Radiographs of the distracted tibiae were taken at both 4 and 8 weeks after drug treatment.

RESULTS

It was found that fibrin prolonged the life span of rhBMP-2 in vitro with sustained release during 17 days. The rhBMP-2 + fibrin treated animals showed the best results in bone mineral density, bone volume fraction, cortical bone thickness by micro-CT evaluation and mechanical properties by the three-point bending test when compared to the other groups (p < 0.05). In histological images, rhBMP-2 + fibrin treatment showed increased callus formation and better gap bridging compared to the other groups.

CONCLUSIONS

The results of this study suggest that fibrin holds promise to be a good carrier of rhBMP-2, and rhBMP-2 suspended in fibrin showed a stronger promoting effect on bone formation during DO in rabbits.

Polycomb PRC2 complex mediates epigenetic silencing of a critical osteogenic master regulator in the hippocampus

During hippocampal neuron differentiation, the expression of critical inducers of non-neuronal cell lineages must be efficiently silenced. Runx2 transcription factor is the master regulator of mesenchymal cells responsible for intramembranous osteoblast differentiation and formation of the craniofacial bone tissue that surrounds and protects the central nervous system (CNS) in mammalian embryos. The molecular mechanisms that mediate silencing of the Runx2 gene and its downstream target osteogenic-related genes in neuronal cells have not been explored. Here, we assess the epigenetic mechanisms that mediate silencing of osteoblast-specific genes in CNS neurons. In particular, we address the contribution of histone epigenetic marks and histone modifiers on the silencing of the Runx2/p57 bone-related isoform in rat hippocampal tissues at embryonic to adult stages. Our results indicate enrichment of repressive chromatin histone marks and of the Polycomb PRC2 complex at the Runx2/p57 promoter region. Knockdown of PRC2 H3K27-methyltransferases Ezh2 and Ezh1, or forced expression of the Trithorax/COMPASS subunit Wdr5 activates Runx2/p57 mRNA expression in both immature and mature hippocampal cells. Together these results indicate that complementary epigenetic mechanisms progressively and efficiently silence critical osteoblastic genes during hippocampal neuron differentiation.

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.

Skp2 inhibits osteogenesis by promoting ubiquitin-proteasome degradation of Runx2

Osteogenic transcription factor Runx2 is essential for osteoblast differentiation. The activity of Runx2 is tightly regulated at transcriptional as well as post-translational level. However, regulation of Runx2 stability by ubiquitin mediated proteasomal degradation by E3 ubiquitin ligases is little-known. Here, for the first time we demonstrate that Skp2, an SCF family E3 ubiquitin ligase negatively targets Runx2 by promoting its polyubiquitination and proteasome dependent degradation. Co-immunoprecipitation studies revealed that Skp2 physically interacts with Runx2 both in a heterologous as well as physiologically relevant system. Functional consequences of Runx2-Skp2 physical interaction were then assessed by promoter reporter assay. We show that Skp2-mediated downregulation of Runx2 led to reduced Runx2 transactivation and osteoblast differentiation. On the contrary, inhibition of Skp2 restored Runx2 levels and promoted osteoblast differentiation. We further show that Skp2 and Runx2 proteins are co-expressed and show inverse relation in vivo such as in lactating, ovariectomized and estrogen-treated ovariectomized animals. Together, these data demonstrate that Skp2 targets Runx2 for ubiquitin mediated degradation and hence negatively regulate osteogenesis. Therefore, the present study provides a plausible therapeutic target for osteoporosis or cleidocranial dysplasia caused by the heterozygous mutation of Runx2 gene.

Transcriptional regulation of gilthead seabream bone morphogenetic protein (BMP) 2 gene by bone- and cartilage-related transcription factors

Bone morphogenetic protein (BMP) 2 belongs to the transforming growth factor β (TGFβ) superfamily of cytokines and growth factors. While it plays important roles in embryo morphogenesis and organogenesis, BMP2 is also critical to bone and cartilage formation. Protein structure and function have been remarkably conserved throughout evolution and BMP2 transcription has been proposed to be tightly regulated, although few data is available. In this work we report the cloning and functional analysis of gilthead seabream BMP2 promoter. As in other vertebrates, seabream BMP2 gene has a 5′ non-coding exon, a feature already present in DPP gene, the fruit fly ortholog of vertebrate BMP2 gene, and maintained throughout evolution. In silico analysis of seabream BMP2 promoter revealed several binding sites for bone and cartilage related transcription factors (TFs) and their functionality was evaluated using promoter-luciferase constructions and TF-expressing vectors. Runt-related transcription factor 3 (RUNX3) was shown to negatively regulate BMP2 transcription and combination with the core binding factor β (CBFβ) further reduced transcriptional activity of the promoter. Although to a lesser extent, myocyte enhancer factor 2C (MEF2C) had also a negative effect on the regulation of BMP2 gene transcription, when associated with SRY (sex determining region Y)-box 9 (SOX9b). Finally, v-ets avian erythroblastosis virus E26 oncogene homolog 1 (ETS1) was able to slightly enhance BMP2 transcription. Data reported here provides new insights toward the better understanding of the transcriptional regulation of BMP2 gene in a bone and cartilage context.

Fibroblast growth factor signaling in skeletal development and disease

Fibroblast growth factor (FGF) signaling pathways are essential regulators of vertebrate skeletal development. FGF signaling regulates development of the limb bud and formation of the mesenchymal condensation and has key roles in regulating chondrogenesis, osteogenesis, and bone and mineral homeostasis. This review updates our review on FGFs in skeletal development published in Genes & Development in 2002, examines progress made on understanding the functions of the FGF signaling pathway during critical stages of skeletogenesis, and explores the mechanisms by which mutations in FGF signaling molecules cause skeletal malformations in humans. Links between FGF signaling pathways and other interacting pathways that are critical for skeletal development and could be exploited to treat genetic diseases and repair bone are also explored.

Craniosynostosis, psychomotor retardation, and facial dysmorphic features in a Spanish patient with a 4q27q28.3 deletion

CASE REPORT

We describe an unusual clinical case with an 11-Mb deletion at 4q27 (chr4: 123094652-134164491), craniosynostosis (CS), mild psychomotor retardation, and facial dysmorphic features. This deletion involves 18 genes; FGF2, NUDT6, and SPRY1 are primarily or secondarily implicated in human cranial bone and sagittal suture development and could play an important role in CS.

CONCLUSIONS

Clinicians should always contemplate genetic studies in patients with syndromic CS. Mutational targeted genetic testing is appropriate for patients with classical or specific CS syndrome. Nevertheless, array comparative genomic hybridization (array CGH) should be considered as a first-line test in nontypical syndromic CS phenotype. Cytogenetic studies are decisive for genetic counseling indeed.

Developmental pathways hijacked by osteosarcoma

Cancer of any type often can be described by an arrest, alteration or disruption in the normal development of a tissue or organ, and understanding of the normal counterpart's development can aid in understanding the malignant state. This is certainly true for osteosarcoma and the normal developmental pathways that guide osteoblast development that are changed in the genesis of osteogenic sarcoma. A carefully regulated crescendo-decrescendo expression of RUNX2 accompanies the transition from mesenchymal stem cell to immature osteoblast to mature osteoblast. This pivotal role is controlled by several pathways, including bone morphogenic protein (BMP), Wnt/β-catenin, fibroblast growth factor (FGF), and protein kinase C (PKC). The HIPPO pathway and its downstream target YAP help to regulate proliferation of immature osteoblasts and their maturation into non-proliferating mature osteoblasts. This pathway also helps regulate expression of the mature osteoblast protein osteocalcin. YAP also regulates expression of MT1-MMP, a membrane-bound matrix metalloprotease responsible for remodeling the extracellular matrix surrounding the osteoblasts. YAP, in turn, can be regulated by the ERBB family protein Her-4. Osteosarcoma may be thought of as a cell held at the immature osteoblast stage, retaining some of the characteristics of that developmental stage. Disruptions of several of these pathways have been described in osteosarcoma, including BMP, Wnt/b-catenin, RUNX2, HIPPO/YAP, and Her-4. Further, PKC can be activated by several receptor tyrosine kinases implicated in osteosarcoma, including the ERBB family (EGFR, Her-2 and Her-4 in osteosarcoma), IGF1R, FGF, and others. Understanding these functions may aid in the understanding the mechanisms underpinning clinical observations in osteosarcoma, including both the lytic and blastic phenotypes of tumors, the invasiveness of the disease, and the tendency for treated tumors to ossify rather than shrink. Through a better understanding of the relationship between normal osteoblast development and osteosarcoma, we may gain insights into novel therapeutic avenues and improved outcomes.

Expression of glucagon-like peptide-1 receptor and glucose‑dependent insulinotropic polypeptide receptor is regulated by the glucose concentration in mouse osteoblastic MC3T3-E1 cells

Glucose-dependent insulinotropic polypeptide receptor (GIPR) and glucagon-like peptide-1 receptor (GLP‑1R) are incretin receptors that play important roles in regulating insulin secretion from pancreatic β cells. Incretin receptors are also thought to play a potential role in bone metabolism. Osteoblasts in animals and humans express GIPR; however, the presence of GLP-1R in these cells has not been reported to date. Thus, the aim of this study was to determine whether GLP-1R and GIPR are expressed in osteoblastic cells, and whether their expression levels are regulated by the extracellular glucose concentration. Mouse osteoblastic MC3T3-E1 cells were cultured in medium containing normal (5.6 mM) or high (10, 20 or 30 mM) glucose concentrations, with or without bone morphogenetic protein-2 (BMP-2). RT-PCR, western blot analysis and immunofluorescence were carried out to determine GIPR and GLP-1R mRNA and protein expression levels. Cell proliferation was also assessed. The GLP-1R and GIPR mRNA expression levels were higher in the MC3T3-E1 cells cultured in medium containing high glucose concentrations with BMP-2 compared with the cells cultured in medium containing normal glucose concentrations with or without BMP-2. GLP-1R protein expression increased following culture in high-glucose medium with BMP-2 compared with culture under normal glucose conditions. However, the cellular localization of GLP-1R was not affected by either glucose or BMP-2. In conclusion, our data demonstrate that the expression of GLP-1R and GIPR is regulated by glucose concentrations in MC3T3-E1 cells undergoing differentiation induced by BMP-2. Our results reveal the potential role of incretins in bone metabolism.

FGF-2 enhances Runx-2/Smads nuclear localization in BMP-2 canonical signaling in osteoblasts

Bone morphogenetic protein 2 (BMP-2) is one of the most potent regulators of osteoblast differentiation and bone formation. R-Smads (Smads 1/5/8) are the major transducers for BMPs receptors and, once activated, they are translocated in the nucleus regulating transcription target genes by interacting with various transcription factors. Runx-2 proteins have been shown to interact through their C-terminal segment with Smads and this interaction is required for in vivo osteogenesis. In particular, recruitment of Smads to intranuclear sites is Runx-2 dependent, and Runx-2 factor may accommodate the dynamic targeting of signal transducer to active transcription sites. Previously, we have shown, by in vitro and in vivo experiments, that BMP-2 up-regulated FGF-2 which is important for the maximal responses of BMP-2 in bone. In this study, we found that endogenous FGF2 is necessary for BMP-2 induced nuclear accumulation and co-localization of Runx-2 and phospho-Smads1/5/8, while Runx/Smads nuclear accumulation and co-localization was reduced in Fgf2-/- osteoblasts. Based on these novel data, we conclude that the impaired nuclear accumulation of Runx-2 in Fgf2-/- osteoblasts reduces R-Smads sub-nuclear targeting with a consequent decreased expression of differentiating markers and impaired bone formation in Fgf2 null mice.

Integration of multiple signaling pathways determines differences in the osteogenic potential and tissue regeneration of neural crest-derived and mesoderm-derived calvarial bones

The mammalian skull vault, a product of a unique and tightly regulated evolutionary process, in which components of disparate embryonic origin are integrated, is an elegant model with which to study osteoblast biology. Our laboratory has demonstrated that this distinct embryonic origin of frontal and parietal bones confer differences in embryonic and postnatal osteogenic potential and skeletal regenerative capacity, with frontal neural crest derived osteoblasts benefitting from greater osteogenic potential. We outline how this model has been used to elucidate some of the molecular mechanisms which underlie these differences and place these findings into the context of our current understanding of the key, highly conserved, pathways which govern the osteoblast lineage including FGF, BMP, Wnt and TGFβ signaling. Furthermore, we explore recent studies which have provided a tantalizing insight into way these pathways interact, with evidence accumulating for certain transcription factors, such as Runx2, acting as a nexus for cross-talk.

BMP signaling in development and diseases: a pharmacological perspective

Bone morphogenetic protein (BMP) signaling has been implicated in several processes during embryonic development and in adult tissue homeostasis. Maintenance of many organs such as skin, intestinal villi, bones and bone marrow requires continuous regeneration and subsequent differentiation of stem cells in order to maintain organ shape and size necessary for proper functioning. Although BMPs were initially identified as osteogenic factors present in demineralized bone capable of inducing ectopic bone formation, it is now evident that BMPs perform several other functions during embryonic development as well as during the adult life of an organism. Many disorders have been linked to either the BMPs or the molecules functioning downstream of BMP signaling pathway. This review summarizes the existing literature describing the role of BMP signaling during embryonic development and in adult tissue homeostasis to provide a perspective on pharmacological interventions of BMP signaling pathway to mitigate several disease conditions.

Cross-talk between FGF and other cytokine signalling pathways during endochondral bone development

FGF (fibroblast growth factor)/FGFR (FGF receptor) signalling plays an essential role in both endochondral and intramembranous bone development. FGF signalling pathways are important for the earliest stages of limb development and throughout skeletal development. The activity and the outcome of this signalling pathway during bone development are also influenced by many other intracellular and extracellular signals. In this review, we focus on the interplay between FGF signalling and other pathways, which is tightly regulated both spatially and temporally during endochondral skeletal development.

Runx2 mediates epigenetic silencing of the bone morphogenetic protein-3B (BMP-3B/GDF10) in lung cancer cells

Background

The Runt-related transcription factor Runx2 is essential for bone development but is also implicated in progression of several cancers of breast, prostate and bone, where it activates cancer-related genes and promotes invasive properties. The transforming growth factor β (TGF-β) family member bone morphogenetic protein-3B (BMP-3B/GDF10) is regarded as a tumor growth inhibitor and a gene silenced in lung cancers; however the regulatory mechanisms leading to its silencing have not been identified.

Results

Here we show that Runx2 is highly expressed in lung cancer cells and downregulates BMP-3B. This inverse relationship between Runx2 and BMP-3B expression is further supported by increased expression of BMP-3B in mesenchymal cells from Runx2 deficient mice. The ectopic expression of Runx2, but not DNA binding mutant Runx2, in normal lung fibroblast cells and lung cancer cells resulted in suppression of BMP-3B levels. The chromatin immunoprecipitation studies identified that the mechanism of Runx2-mediated suppression of BMP-3B is due to the recruitment of Runx2 and histone H3K9-specific methyltransferase Suv39h1 to BMP-3B proximal promoter and a concomitant increase in histone methylation (H3K9) status. The knockdown of Runx2 in H1299 cells resulted in decreased histone H3K9 methylation on BMP-3B promoter and increased BMP-3B expression levels. Furthermore, co-immunoprecipitation studies showed a direct interaction of Runx2 and Suv39h1 proteins. Phenotypically, Runx2 overexpression in H1299 cells increased wound healing response to TGFβ treatment.

Conclusions

Our studies identified BMP-3B as a new Runx2 target gene and revealed a novel function of Runx2 in silencing of BMP-3B in lung cancers. Our results suggest that Runx2 is a potential therapeutic target to block tumor suppressor gene silencing in lung cancer cells.

Erythroid promoter confines FGF2 expression to the marrow after hematopoietic stem cell gene therapy and leads to enhanced endosteal bone formation

Fibroblast growth factor-2 (FGF2) has been demonstrated to be a promising osteogenic factor for treating osteoporosis. Our earlier study shows that transplantation of mouse Sca-1(+) hematopoietic stem/progenitor cells that are engineered to express a modified FGF2 leads to considerable endosteal/trabecular bone formation, but it also induces adverse effects like hypocalemia and osteomalacia. Here we report that the use of an erythroid specific promoter, β-globin, leads to a 5-fold decrease in the ratio of serum FGF2 to the FGF2 expression in the marrow cavity when compared to the use of a ubiquitous promoter spleen focus-forming virus (SFFV). The confined FGF2 expression promotes considerable trabeculae bone formation in endosteum and does not yield anemia and osteomalacia. The avoidance of anemia in the mice that received Sca1(+) cells transduced with FGF2 driven by the β-globin promoter is likely due to attenuation of high-level serum FGF2-mediated stem cell mobilization observed in the SFFV-FGF2 animals. The prevention of osteomalacia is associated with substantially reduced serum Fgf23/hypophosphatemia, and less pronounced secondary hyperparathyroidism. Our improved stem cell gene therapy strategy represents one step closer to FGF2-based clinical therapy for systemic skeletal augmentation.

Prevention of premature fusion of calvarial suture in GLI-Kruppel family member 3 (Gli3)-deficient mice by removing one allele of Runt-related transcription factor 2 (Runx2)

Mutations in the gene encoding the zinc finger transcription factor GLI3 (GLI-Kruppel family member 3) have been identified in patients with Grieg cephalopolysyndactyly syndrome in which premature fusion of calvarial suture (craniosynostosis) is an infrequent but important feature. Here, we show that Gli3 acts as a repressor in the developing murine calvaria and that Dlx5, Runx2 type II isoform (Runx2-II), and Bmp2 are expressed ectopically in the calvarial mesenchyme, which results in aberrant osteoblastic differentiation in Gli3-deficient mouse (Gli3(Xt-J/Xt-J)) and resulted in craniosynostosis. At the same time, enhanced activation of phospho-Smad1/5/8 (pSmad1/5/8), which is a downstream mediator of canonical Bmp signaling, was observed in Gli3(Xt-J/Xt-J) embryonic calvaria. Therefore, we generated Gli3;Runx2 compound mutant mice to study the effects of decreasing Runx2 dosage in a Gli3(Xt-J/Xt-J) background. Gli3(Xt-J/Xt-J) Runx2(+/-) mice have neither craniosynostosis nor additional ossification centers in interfrontal suture and displayed a normalization of Dlx5, Runx2-II, and pSmad1/5/8 expression as well as sutural mesenchymal cell proliferation. These findings suggest a novel role for Gli3 in regulating calvarial suture development by controlling canonical Bmp-Smad signaling, which integrates a Dlx5/Runx2-II cascade. We propose that targeting Runx2 might provide an attractive way of preventing craniosynostosis in patients.

Integration of BMP, Wnt, and notch signaling pathways in osteoblast differentiation

Bone marrow-derived mesenchymal stem cells (MSCs) are multipotent progenitors that can commit to osteoblast, chondrocyte, adipocyte, and several other lineages. The proper utilization of stem cells for clinical applications requires an integrated understanding of multiple signal inputs that control maintenance of stemness, proliferation, commitment, and differentiation. Various signaling pathways have been implicated in the regulation of MSC differentiation; however, complexities of pathway interactions, as well as seemingly contradictory results in the literature, create an often confusing and disjointed knowledge base. Several recent publications explore the integration of signaling pathways such as BMP, Wnt, Notch, Hedgehog, and Fibroblast Growth Factors in MSC osteoblast differentiation. The transcription factor Cbfa1/Runx2 has been implicated in these pathways as a potential focal point for signaling integration. This review will outline the current understanding of these pathways and indicate where both spatiotemporal effects during differentiation and comparable experimental conditions need to be considered in order to clarify the outcome(s) of differing regulatory levels of these signaling pathways.

FGF/FGFR signaling in bone formation: progress and perspectives

Fibroblast growth factors (FGFs) are important molecules that control bone formation. FGF act by activating FGF receptors (FGFRs) and downstream signaling pathways that control cells of the osteoblast lineage. Recent advances have been made in the identification of FGF/FGFR signaling pathways that control osteogenesis. Indeed, studies of mouse and human models provided novel insights into the signaling pathways that control bone formation. Genomic studies also highlighted the implication of molecular targets of FGF/FGFR signaling regulating osteoblastogenesis. Recent studies further revealed the important role of crosstalks between FGF/FGFR signaling and other signaling pathways in the regulation of osteogenesis. Finally, the importance of the mechanisms modulating FGFR degradation in the control of osteoblast differentiation has been recently revealed. This short review summarizes the recently described mechanisms underlying FGF/FGFR signaling that are involved in the control of osteoblastogenesis. This knowledge may have potential therapeutic implications in skeletal disorders characterized by abnormal bone formation.

TGF-β and BMP signaling in osteoblast differentiation and bone formation

Transforming growth factor-beta (TGF-β)/bone morphogenic protein (BMP) signaling is involved in a vast majority of cellular processes and is fundamentally important throughout life. TGF-β/BMPs have widely recognized roles in bone formation during mammalian development and exhibit versatile regulatory functions in the body. Signaling transduction by TGF-β/BMPs is specifically through both canonical Smad-dependent pathways (TGF-β/BMP ligands, receptors and Smads) and non-canonical Smad-independent signaling pathway (e.g. p38 mitogen-activated protein kinase pathway, MAPK). Following TGF-β/BMP induction, both the Smad and p38 MAPK pathways converge at the Runx2 gene to control mesenchymal precursor cell differentiation. The coordinated activity of Runx2 and TGF-β/BMP-activated Smads is critical for formation of the skeleton. Recent advances in molecular and genetic studies using gene targeting in mice enable a better understanding of TGF-β/BMP signaling in bone and in the signaling networks underlying osteoblast differentiation and bone formation. This review summarizes the recent advances in our understanding of TGF-β/BMP signaling in bone from studies of genetic mouse models and human diseases caused by the disruption of TGF-β/BMP signaling. This review also highlights the different modes of cross-talk between TGF-β/BMP signaling and the signaling pathways of MAPK, Wnt, Hedgehog, Notch, and FGF in osteoblast differentiation and bone formation.

Transplantation of Cbfa1-overexpressing adipose stem cells together with vascularized periosteal flaps repair segmental bone defects

BACKGROUND

Segmental bone defect is still a challenge to orthopedic surgeons. Currently available therapies for segmental bone defects have some drawbacks. Tissue engineering using pluripotent stem cells is a new, promising method for bone repair. The present study aims to promote the effect of bone defect repair using the tissue engineered bone in combination with vascularized periosteal flaps.

METHODS

The adenoviral vector carrying Cbfa1 transduced rabbit adipose-derived mesenchymal stem cells and gene modified tissue engineering bone (GMB) were constructed. Rabbits with radial defects were implanted with the GMB together with vascularized periosteum (group A); or GMB with free periosteum (group B); or GMB (group C), and scaffold (group D). The bone repair effect was evaluated at 4, 8, or 12 wk, respectively, after the operations.

RESULTS

Cbfa1 proteins were strongly expressed in adipose stem cells (ADSCs) that formed a stratified network on the inner surface of the polylactic acid/ polycaprolacton (PLA/PCL) pores. Bone repair was well achieved in the rabbits treated with the Cbfa1-expressing ADSCs and vascularized flap that was markedly better than those treated with either Cbfa1-expressing ADSCs alone or with vascularized flap alone.

CONCLUSIONS

Combination with implanting the Cbfa1 gene-modified tissue-engineered bone and vascularized periosteum can better repair the segmental bone defects by stimulating osteogenesis, osteoinduction, and osteoconduction than using either one of the approaches.

Administration of BMP2/7 in utero partially reverses Rubinstein-Taybi syndrome-like skeletal defects induced by Pdk1 or Cbp mutations in mice

Mutations in the coactivator CREB-binding protein (CBP) are a major cause of the human skeletal dysplasia Rubinstein-Taybi syndrome (RTS); however, the mechanism by which these mutations affect skeletal mineralization and patterning is unknown. Here, we report the identification of 3-phosphoinositide-dependent kinase 1 (PDK1) as a key regulator of CBP activity and demonstrate that its functions map to both osteoprogenitor cells and mature osteoblasts. In osteoblasts, PDK1 activated the CREB/CBP complex, which in turn controlled runt-related transcription factor 2 (RUNX2) activation and expression of bone morphogenetic protein 2 (BMP2). These pathways also operated in vivo, as evidenced by recapitulation of RTS spectrum phenotypes with osteoblast-specific Pdk1 deletion in mice (Pdk1osx mice) and by the genetic interactions observed in mice heterozygous for both osteoblast-specific Pdk1 deletion and either Runx2 or Creb deletion. Finally, treatment of Pdk1osx and Cbp+/- embryos with BMPs in utero partially reversed their skeletal anomalies at birth. These findings illustrate the in vivo function of the PDK1-AKT-CREB/CBP pathway in bone formation and provide proof of principle for in utero growth factor supplementation as a potential therapy for skeletal dysplasias.

Enhanced bone regeneration with sequential delivery of basic fibroblast growth factor and sonic hedgehog

BACKGROUND

Bone regeneration approaches that mimic the natural processes of bone repair have generated significant attention. We hypothesized that early delivery of an angiogenic factor combined with sustained exposure to an osteogenic factor would recapitulate the critical aspects of natural bone repair.

MATERIALS AND METHODS

Basic fibroblast growth factor (bFGF) and sonic hedgehog (Shh) were constructed to the recombinant adeno-associated virus, respectively (rAAV2-tet-off-bFGF and rAAV2-Shh). The previous viral vector allowed for regulation of the bFGF expression by the addition of doxycycline, a tetracycline analogue. These two viral vectors were used to cotransduce bone marrow-derived mesenchymal stem cells (BMSCs). Several osteogenic markers such as core-binding factor a-1, alkaline phosphatase and osteocalcin were detected by quantitative real-time reverse transcriptase polymerase chain reaction. Meanwhile, protein expressions of transgenes were measured by western blot. Furthermore, these cotransduced BMSCs were seeded on β-tricalcium phosphate (β-TCP) granules and then were implanted into the calvarium defect in a rat model. A sample of 30 Sprague-Dawley rats was divided into six groups (n=5); an 8-mm critical-sized bone defect was made in calvarium of all subjects. Each group was treated with various transgenic BMSCs and β-TCP composites; and the sixth group is the negative control which was implanted with nothing. At 4 weeks after treatment, the samples were evaluated with histological staining.

RESULTS

The expression of osteogenic marker mRNA had an increased tendency after two genes transduction (p<0.05). In addition, dramatically enhanced regeneration of critical-sized calvarial defects was observed in the groups which were implanted with two transgenic BMSCs and β-TCP composites. And in these experimental groups, bone areas and vascular densities were increased significantly (p<0.05) than other groups.

CONCLUSION

Sequential delivery of angiogenic and osteogenic factors likely has a synergistic effect, mimicking the molecular events of natural bone regeneration.

The influence of stereolithographic scaffold architecture and composition on osteogenic signal expression with rat bone marrow stromal cells

Scaffold design parameters, especially physical construction factors such as mechanical stiffness of substrate materials, pore size of 3D porous scaffolds, and channel geometry, are known to influence the osteogenic signal expression and subsequent differentiation of a transplanted cell population. In this study of photocrosslinked poly(propylene fumarate) (PPF) and diethyl fumarate (DEF) scaffolds, the effect of DEF incorporation ratio and pore size on the osteogenic signal expression of rat bone marrow stromal cells (BMSCs) was investigated. Results demonstrated that DEF concentrations and pore sizes that led to increased scaffold mechanical stiffness also upregulated osteogenic signal expression, including bone morphogenic protein-2 (BMP-2), fibroblast growth factors-2 (FGF-2), transforming growth factor-β1 (TGF-β1), vascular endothelial growth factor (VEGF), and Runx2 transcriptional factor. Similar scaffold fabrication parameters supported rapid BMSC osteoblastic differentiation, as demonstrated by increased alkaline phosphatase (ALP) and osteocalcin expression. When scaffolds with random architecture, fabricated by porogen leaching, were compared to those with controlled architecture, fabricated by stereolithography (SLA), results showed that SLA scaffolds with the highly permeable and porous channels also have significantly higher expression of FGF-2, TGF-β1, and VEGF. Subsequent ALP expression and osteopontin secretion were also significantly increased in SLA scaffolds. Based upon these results, we conclude that scaffold properties provided by additive manufacturing techniques such as SLA fabrication, particularly increased mechanical stiffness and high permeability, may stimulate dramatic BMSC responses that promote rapid bone tissue regeneration.