Osterix induces Col1a1 gene expression through binding to Sp1 sites in the bone enhancer and proximal promoter regions

Regulation of osteogenesis and angiogenesis by cobalt, manganese and strontium doped apatitic materials for functional bone tissue regeneration

Strontium, cobalt, and manganese ions are present in the composition of bone and useful for bone metabolism, even when combined with calcium phosphate in the composition of biomaterials. Herein we explored the possibility to include these ions in the composition of apatitic materials prepared through the cementitious reaction between ion-substituted calcium phosphate dibasic dihydrate, CaHPO4·2H2O (DCPD) and tetracalcium phosphate, Ca4(PO4)2O (TTCP). The results of the chemical, structural, morphological and mechanical characterization indicate that cobalt and manganese exhibit a greater delaying effect than strontium (about 15 at.%) on the cementitious reaction, even though they are present in smaller amounts within the materials (about 0.8 and 4.5 at.%, respectively). Furthermore, the presence of the foreign ions in the apatitic materials leads to a slight reduction of porosity and to enhancement of compressive strength. The results of biological tests show that the presence of strontium and manganese, as well as calcium, in the apatitic materials cultured in direct contact with human mesenchymal stem cells (hMSCs) stimulates their viability and activity. In contrast, the apatitic material containing cobalt exhibits a lower metabolic activity. All the materials have a positive effect on the expression of Vascular Endothelial Growth Factor (VEGF) and Von Willebrand Factor (vWF). Moreover, the apatitic material containing strontium induces the most significant reduction in the differentiation of preosteoclasts into osteoclasts, demonstrating not only osteogenic and angiogenic properties, but also ability to regulate bone resorption.

Update on the Genetics of Osteogenesis Imperfecta

Osteogenesis imperfecta (OI) is a heterogeneous heritable skeletal dysplasia characterized by bone fragility and deformity, growth deficiency, and other secondary connective tissue defects. OI is now understood as a collagen-related disorder caused by defects of genes whose protein products interact with collagen for folding, post-translational modification, processing and trafficking, affecting bone mineralization and osteoblast differentiation. This review provides the latest updates on genetics of OI, including new developments in both dominant and rare OI forms, as well as the signaling pathways involved in OI pathophysiology. There is a special emphasis on discoveries of recessive mutations in TENT5A, MESD, KDELR2 and CCDC134 whose causality of OI types XIX, XX, XXI and XXI, respectively, is now established and expends the complexity of mechanisms underlying OI to overlap LRP5/6 and MAPK/ERK pathways. We also review in detail new discoveries connecting the known OI types to each other, which may underlie an eventual understanding of a final common pathway in OI cellular and bone biology.

Stiff extracellular matrix drives the differentiation of mesenchymal stem cells toward osteogenesis by the multiscale 3D genome reorganization

Extracellular matrix (ECM) stiffness is a major driver of stem cell fate. However, the involvement of the three-dimensional (3D) genomic reorganization in response to ECM stiffness remains unclear. Here, we generated comprehensive 3D chromatin landscapes of mesenchymal stem cells (MSCs) exposed to various ECM stiffness. We found that there were more long-range chromatin interactions, but less compartment A in MSCs cultured on stiff ECM than those cultured on soft ECM. However, the switch from compartment B in MSCs cultured on soft ECM to compartment A in MSCs cultured on stiff ECM included genes encoding proteins primarily enriched in cytoskeleton organization. At the topologically associating domains (TADs) level, stiff ECM tends to have merged TADs on soft ECM. These merged TADs on stiff ECM include upregulated genes encoding proteins enriched in osteogenesis, such as SP1, ETS1, and DCHS1, which were validated by quantitative real-time polymerase chain reaction and found to be consistent with the increase of alkaline phosphatase staining. Knockdown of SP1 or ETS1 led to the downregulation of osteogenic marker genes, including COL1A1, RUNX2, ALP, and OCN in MSCs cultured on stiff ECM. Our study provides an important insight into the stiff ECM-mediated promotion of MSC differentiation towards osteogenesis, emphasizing the influence of mechanical cues on the reorganization of 3D genome architecture and stem cell fate.

Macrophage-derived apoptotic bodies impair the osteogenic ability of osteoblasts in periodontitis

OBJECTIVES

Periodontitis is induced by the imbalance between osteoblast and osteoclast activity, which leads to periodontal tissue destruction. Macrophages play a vital role in periodontitis. However, the hypoxic periodontal environment will also induce macrophage apoptosis within a short time. Apoptotic bodies (ABs) are the major products generated from apoptotic cells, but whether macrophage-derived ABs play a regulatory role as their mother cells in periodontitis remains unknown. In the present study, we aimed to investigate the effects of ABs on osteoblasts.

METHOD

ABs derived from hypoxia-induced macrophages were co-cultured with osteoblasts and the impact of ABs on osteoblast differentiation in vitro was assessed. In vivo, periodontitis model was established and macrophages-derived ABs were injected into the gingival sulcus. The effects of ABs on periodontal bone resorption were determined.

RESULTS

The results showed that ABs significantly inhibit osteoblast differentiation and promoted alveolar bone resorption in periodontitis. MicroRNA (miRNAs) array analysis was performed and revealed that miR-483-5p is the key miRNA in ABs. Dual luciferase reporter assays were performed and confirmed that miR-483-5p targeted Col1A1 mRNA and attenuated its expression.

CONCLUSION

Macrophage-derived ABs inhibit osteoblast differentiation via the transfer of miR-483-5p, which downregulates Col1A1 expression and finally suppresses osteogenic activity.

External Mechanical Stability Regulates Hematoma Vascularization in Bone Healing Rather than Endothelial YAP/TAZ Mechanotransduction

Bone fracture healing is regulated by mechanobiological cues. Both, extracellular matrix (ECM) deposition and microvascular assembly determine the dynamics of the regenerative processes. Mechanical instability as by inter-fragmentary shear or compression is known to influence early ECM formation and wound healing. However, it remains unclear how these external cues shape subsequent ECM and microvascular network assembly. As transcriptional coactivators, the mechanotransducers yes-associated protein 1 (YAP)/transcriptional coactivator with PDZ-binding motif (TAZ) translate physical cues into downstream signaling events, yet their role in sprouting angiogenesis into the hematoma after injury is unknown. Using bone healing as model system for scar-free regeneration, the role of endothelial YAP/TAZ in combination with tuning the extrinsic mechanical stability via fracture fixation is investigated. Extrinsically imposed shear across the gap delayed hematoma remodeling and shaped the morphology of early collagen fiber orientations and microvascular networks, suggesting that enhanced shear increased the nutrient exchange in the hematoma. In contrast, endothelial YAP/TAZ deletion has little impact on the overall vascularization of the fracture gap, yet slightly increases the collagen fiber deposition under semi-rigid fixation. Together, these data provide novel insights into the respective roles of endothelial YAP/TAZ and extrinsic mechanical cues in orchestrating the process of bone regeneration.

Roles of SP/KLF transcription factors in odontoblast differentiation: From development to diseases

OBJECTIVES

A zinc-finger transcription factor family comprising specificity proteins (SPs) and Krüppel-like factor proteins (KLFs) plays an important role in dentin development and regeneration. However, a systematic regulatory network involving SPs/KLFs in odontoblast differentiation has not yet been described. This review examined the expression patterns of SP/KLF gene family members and their current known functions and mechanisms in odontoblast differentiation, and discussed prospective research directions for further exploration of mechanisms involving the SP/KLF gene family in dentin development.

MATERIALS AND METHODS

Relevant literature on SP/KLF gene family members and dentin development was acquired from PubMed and Web of Science.

RESULTS

We discuss the expression patterns, functions, and related mechanisms of eight members of the SP/KLF gene family in dentin development and genetic disorders with dental problems. We also summarize current knowledge about their complementary or synergistic actions. Finally, we propose future research directions for investigating the mechanisms of dentin development.

CONCLUSIONS

The SP/KLF gene family plays a vital role in tooth development. Studying the complex complementary or synergistic interactions between SPs/KLFs is helpful for understanding the process of odontoblast differentiation. Applications of single-cell and spatial multi-omics may provide a more complete investigation of the mechanism involved in dentin development.

The bone transcription factor Osterix controls extracellular matrix- and node of Ranvier-related gene expression in oligodendrocytes

Oligodendrocytes are the primary producers of many extracellular matrix (ECM)-related proteins found in the CNS. Therefore, oligodendrocytes play a critical role in the determination of brain stiffness, node of Ranvier formation, perinodal ECM deposition, and perineuronal net formation, all of which depend on the ECM. Nevertheless, the transcription factors that control ECM-related gene expression in oligodendrocytes remain unknown. Here, we found that the transcription factor Osterix (also known as Sp7) binds in proximity to genes important for CNS ECM and node of Ranvier formation and mediates their expression. Oligodendrocyte-specific ablation of Sp7 changes ECM composition and brain stiffness and results in aberrant node of Ranvier formation. Sp7 is known to control osteoblast maturation and bone formation. Our comparative analyses suggest that Sp7 plays a conserved biological role in oligodendrocytes and in bone-forming cells, where it mediates brain and bone tissue stiffness by controlling expression of ECM components.

MiR-29b Downregulation by p53/Sp1 Complex Plays a Critical Role in Bleb Scar Formation After Glaucoma Filtration Surgery

Purpose

To investigate the function and mechanism of tumor protein p53 in pathological scarring after glaucoma filtration surgery (GFS) using human Tenon's fibroblasts (HTFs) and a rabbit GFS model.

Methods

The expression of p53 in bleb scarring after GFS and transforming growth factor-β (TGF-β)-induced HTFs (myofibroblasts [MFs]) was examined by western blot and immunochemical analysis. The interaction between p53 and specificity protein 1 (Sp1) was investigated by immunoprecipitation. The role of p53 and Sp1 in the accumulation of collagen type I alpha 1 chain (COL1A1) and the migration of MFs was evaluated by western blot, quantitative real-time polymerase chain reaction (qRT-PCR), wound healing, and Transwell assay. The regulatory mechanisms among p53/Sp1 and miR-29b were detected via qRT-PCR, western blot, luciferase reporter assay, and chromatin immunoprecipitation assay. The therapeutic effect of mithramycin A, a specific inhibitor of Sp1, on scarring formation was evaluated in a rabbit GFS model.

Results

p53 was upregulated in bleb scar tissue and MFs. p53 and Sp1 form a transcription factor complex that induces the accumulation of COL1A1 and promotes the migration of MFs through downregulation of miR-29b, a known suppressor of COL1A1. The p53/Sp1 axis inhibits miR-29b expression by the direct binding promoter of the miR-29b gene. Mithramycin A treatment attenuated bleb scar formation in vivo.

Conclusions

The p53/Sp1/miR-29b signaling pathway plays a critical role in bleb scar formation after GFS. This pathway could be targeted for therapeutic intervention of pathological scarring after GFS.

Translational Relevance

Our research indicates that inhibition of p53/Sp1/miR-29b is a promising therapeutic strategy for preventing post-GFS pathological scarring.

Cannabidiol and Cannabigerol, Nonpsychotropic Cannabinoids, as Analgesics that Effectively Manage Bone Fracture Pain and Promote Healing in Mice

Bone fractures are among the most prevalent musculoskeletal injuries, and pain management is an essential part of fracture treatment. Fractures heal through an early inflammatory phase, followed by repair and remodeling. Nonsteroidal anti-inflammatory drugs (NSAIDs) are not recommended for fracture pain control as they potently inhibit the inflammatory phase and, thus, impair the healing. Opioids do not provide a better alternative for several reasons, including abuse potential. Accordingly, there is an unmet clinical need for analgesics that effectively ameliorate postfracture pain without impeding the healing. Here, we investigated the analgesic efficacy of two nonpsychotropic cannabinoids, cannabidiol (CBD) and cannabigerol (CBG), in a mouse model for tibial fracture. Mice with fractured tibiae exhibited increased sensitivity to mechanical, cold, and hot stimuli. Both CBD and CBG normalized pain sensitivity to all tested stimuli, and their analgesic effects were comparable to those of the NSAIDs. Interestingly, CBD and CBG promoted bone healing via multiple mechanisms during the early and late phases. During the early inflammatory phase, both cannabinoids increased the abundance of periosteal bone progenitors in the healing hematoma and promoted the osteogenic commitment of these progenitors. During the later phases of healing, CBD and CBG accelerated the fibrocartilaginous callus mineralization and enhanced the viability and proliferation of bone and bone-marrow cells. These effects culminated in higher bone volume fraction, higher bone mineral density, and improved mechanical quality of the newly formed bone. Together, our data suggest CBD and CBG as therapeutic agents that can replace NSAIDs in managing postfracture pain as both cannabinoids exert potent analgesic effects and, at the same time, promote bone healing. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Sumecton reinforced gelatin-based scaffolds for cell-free bone regeneration

Bone tissue engineering has risen to tackle the challenges of the current clinical need concerning bone fractures that is already considered a healthcare system problem. Scaffold systems for the repair of this tissue have yielded different combinations including biomaterials with nanotechnology or biological agents. Herein, three-dimensional porous hydrogels were engineered based on gelatin as a natural biomaterial and reinforced with synthetic saponite nanoclays. Scaffolds were biocompatible and shown to enhance the inherent properties of pristine ones, in particular, proved to withstand pressures similar to load-bearing tissues. Studies with murine mesenchymal stem cells found that scaffolds had the potential to proliferate and promote cell differentiation. In vivo experiments were conducted to gain insight about the ability of these cell-free scaffolds to regenerate bone, as well as to determine the role that these nanoparticles in the scaffold could play as a drug delivery system. SDF-1 loaded scaffolds showed the highest percentage of bone formation, which was corroborated by osteogenic markers and new blood vessels. Albeit a first attempt in the field of synthetic nanosilicates, these results suggest that the designed constructs may serve as delivery platforms for biomimetic agents to mend bony defects, circumventing high doses of therapeutics and cell-loading systems.

Assembling the Puzzle Pieces. Insights for in Vitro Bone Remodeling

As a highly dynamic organ, bone changes during throughout a person's life. This process is referred to as 'bone remodeling' and it involves two stages - a well-balanced osteoclastic bone resorption and an osteoblastic bone formation. Under normal physiological conditions bone remodeling is highly regulated that ensures tight coupling between bone formation and resorption, and its disruption results in a bone metabolic disorder, most commonly osteoporosis. Though osteoporosis is one of the most prevalent skeletal ailments that affect women and men aged over 40 of all races and ethnicities, currently there are few, if any safe and effective therapeutic interventions available. Developing state-of-the-art cellular systems for bone remodeling and osteoporosis can provide important insights into the cellular and molecular mechanisms involved in skeletal homeostasis and advise better therapies for patients. This review describes osteoblastogenesis and osteoclastogenesis as two vital processes for producing mature, active bone cells in the context of interactions between cells and the bone matrix. In addition, it considers current approaches in bone tissue engineering, pointing out cell sources, core factors and matrices used in scientific practice for modeling bone diseases and testing drugs. Finally, it focuses on the challenges that bone regenerative medicine is currently facing.

SP7: from Bone Development to Skeletal Disease

PURPOSE OF REVIEW

The purpose of this review is to summarize the different roles of the transcription factor SP7 in regulating bone formation and remodeling, discuss current studies in investigating the causal relationship between SP7 mutations and human skeletal disease, and highlight potential therapeutic treatments that targeting SP7 and the gene networks that it controls.

RECENT FINDINGS

Cell-type and stage-specific functions of SP7 have been identified during bone formation and remodeling. Normal bone development regulated by SP7 is strongly associated with human bone health. Dysfunction of SP7 results in common or rare skeletal diseases, including osteoporosis and osteogenesis imperfecta with different inheritance patterns. SP7-associated signaling pathways, SP7-dependent target genes, and epigenetic regulations of SP7 serve as new therapeutic targets in the treatment of skeletal disorders. This review addresses the importance of SP7-regulated bone development in studying bone health and skeletal disease. Recent advances in whole genome and exome sequencing, GWAS, multi-omics, and CRISPR-mediated activation and inhibition have provided the approaches to investigate the gene-regulatory networks controlled by SP7 in bone and the therapeutic targets to treat skeletal disease.

A Histologic, Histomorphometric, and Immunohistochemical Evaluation of Anorganic Bovine Bone and Injectable Biphasic Calcium Phosphate in Humans: A Randomized Clinical Trial

Following trauma, chronic periapical process, or tooth extraction, a large loss of bone volume is noticed during the healing process. To facilitate the placement of dental implants, various surgical procedures are used for an optimal alveolar ridge profile, while maintaining adequate bone dimensions. The main aim of this study was to determine the healing ability (histologically and immunohistologically) of alveolar bone defects during augmentation with two different biomaterials: injectable biphasic calcium phosphate (BCP) and anorganic bovine bone (ABB). Thirty-eight subjects were randomly divided into two groups. The first group received the tested bone substitute biomaterial (BSB), i.e., BCP (maxresorb inject®), and the second group received an alternative to the gold standard, i.e., ABB (Bio-Oss®). The histopathological, histomorphometric, and immunohistochemical analyses gave comparable results for these bone substitute materials in terms of newly formed bone: (BCP: 39.91 ± 8.49%, ABB: 41.73 ± 13.99%), residual biomaterial (BCP: 28.61 ± 11.38%, ABB: 31.72 ± 15.52%), and soft tissue (BCP: 31.49 ± 11.09%, ABB: 26.54 ± 7.25%), with no significant difference found between the groups (p < 0.05, t-test), proving that BCP is equally suitable and successful for alveolar bone regeneration.

Gene Expression in MC3T3-E1 Cells Treated with Diclofenac and Methylprednisolone

Nonsteroidal anti-inflammatory drugs (NSAIDs) and glucocorticoids (GCs) are often used to treat articular-skeletal disorders. The extended use of NSAIDs and GCs have adverse effects on bone metabolism, reducing bone quality and impairing fracture healing. In the present study, we used mouse pre-osteoblast cells MC3T3-E1 to demonstrate the effects of diclofenac (DF) and methylprednisolone (MP) on cell proliferation and gene expression. Cells were incubated with three doses of DF or MP: 0.5 µM, 5 µM, and 50 µM. MP decreased cell viability even after 24 h, but DF inhibited cell viability after only seven days of treatment. The cells were lysed after one, two, three, and seven days of treatment, and gene expression was analyzed by reverse transcription and quantitative PCR (RT-qPCR) assays. DF did not significantly affect the expression of the osteogenic marker genes. MP modified the expression of Osx, Runx, and Col1a1. We concluded that MP is a more potent inhibitor of mouse pre-osteoblast differentiation and viability than is DF. Our results suggest that prolonged DF treatment could be less harmful to osteoblasts than MP treatment.

Multi-omics analysis reveals the pathogenesis of db/db mice diabetic kidney disease and the treatment mechanisms of multi-bioactive compounds combination from Salvia miltiorrhiza

Diabetic kidney disease (DKD) is a common diabetic complication. Salvia miltiorrhiza has significant therapeutic effects on diabetes complications, although the mechanism remains unclear. Here, biochemical indicators and pathological changes were used to screen out the optimal Salvia miltiorrhiza multi-bioactive compounds combination. Metabolomics, transcriptomics and proteomics were used to explore the pathogenesis of DKD. RT-PCR and parallel reaction monitoring targeted quantitative proteome analysis were utilized to investigate treatment mechanisms of the optimal Salvia miltiorrhiza multi-bioactive compounds combination. The db/db mice showed biochemical abnormalities and renal lesions. The possible metabolic pathways were steroid hormone biosynthesis and sphingolipid metabolism. The 727 differential genes found in transcriptomics were associated with biochemical indicators via gene network to finally screen 11 differential genes, which were mainly key genes of TGF-β/Smad and PI3K/Akt/FoxO signaling pathways. Salvia miltiorrhiza multi-bioactive compounds combination could significantly regulate the Egr1, Pik3r3 and Col1a1 genes. 11 differentially expressed proteins involved in the two pathways were selected, of which 9 were significantly altered in db/db mice compared to db/m mice. Salvia miltiorrhiza multi-bioactive compounds combination could callback Q9DBM2, S4R1W1, Q91Y97, P47738, A8DUK4, and A2ARV4. In summary, Salvia miltiorrhiza multi-bioactive compounds combination may ameliorate kidney injury in diabetes through regulation of TGF-β/Smad and PI3K/Akt/FoxO signaling pathways.

Cathelicidin LL-37 improves bone metabolic balance in rats with ovariectomy-induced osteoporosis via the Wnt/beta-catenin pathway

Osteoporosis is a bone disease characterized by low bone mineral density (BMD) and impaired bone microarchitecture due to the abnormal activity of osteoclasts. Cathelicidins are antimicrobial peptides present in the lysosomes of macrophages and polymorphonuclear leukocytes. LL-37, a cathelicidin, induces various biological effects, including modulation of the immune system, angiogenesis, wound healing, cancer growth, as well as inflammation, and bone loss. A previous study reported direct involvement of LL-37 suppressing osteoclastogenesis in humans. Here, we examined the role of LL-37 in the treatment of osteoporosis using an ovariectomy (OVX) rat model. Our results showed that LL-37 significantly reduced bone loss and pathological injury in OVX rats with osteoporosis. Furthermore, we found that LL-37 significantly increased the activity of the Wnt/beta-catenin pathway in OVX rats with osteoporosis, including the increased expression of beta-catenin, Osterix (Osx), and Runt-related transcription factor 2 (Runx2), whereas XAV-939, an inhibitor of the Wnt/beta-catenin pathway, significantly blocked the effects of LL-37 on bone loss and abnormal bone metabolism. Altogether, our findings suggested that LL-37 exerted a protective role in regulating bone loss and abnormal bone metabolism in rats with osteoporosis by activating the Wnt/beta-catenin pathway.

Sp7 Action in the Skeleton: Its Mode of Action, Functions, and Relevance to Skeletal Diseases

Osteoblast differentiation is a tightly regulated process in which key transcription factors (TFs) and their target genes constitute gene regulatory networks (GRNs) under the control of osteogenic signaling pathways. Among these TFs, Sp7 works as an osteoblast determinant critical for osteoblast differentiation. Following the identification of Sp7 and a large number of its functional studies, recent genome-scale analyses have made a major contribution to the identification of a "non-canonical" mode of Sp7 action as well as "canonical" ones. The analyses have not only confirmed known Sp7 targets but have also uncovered its additional targets and upstream factors. In addition, biochemical analyses have demonstrated that Sp7 actions are regulated by chemical modifications and protein-protein interaction with other transcriptional regulators. Sp7 is also involved in chondrocyte differentiation and osteocyte biology as well as postnatal bone metabolism. The critical role of SP7 in the skeleton is supported by its relevance to human skeletal diseases. This review aims to overview the Sp7 actions in skeletal development and maintenance, particularly focusing on recent advances in our understanding of how Sp7 functions in the skeleton under physiological and pathological conditions.

Enamel matrix derivative expedites osteogenic differentiation of BMSCs via Wnt/β-catenin pathway in high glucose microenvironment

INTRODUCTION

The influence of enamel matrix derivative (EMD) on proliferation and osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) was explored in high glucose (HG) microenvironment with interaction of Wnt/β-catenin pathway.

MATERIALS AND METHODS

Extraction of BMSCs from Sprague-Dawley rats, culture, and identification were manifested. The cells were treated with different concentration of EMD in HG to figure out the most available concentration for proliferation and osteogenic differentiation. Then, observation of cell growth curve and cell cycle changes, and detection of Osterix, runt-related transcription factor 2 (Runx2), COL-I, early osteogenic indexes, Calcium salt deposition, and β-catenin protein in Wnt/β-catenin pathway were assured. After adding Wnt/β-catenin pathway inhibitor (XAV-939) in the cells with osteogenesis induction, detection of binding of β-catenin to Osterix was clarified.

RESULTS

Via identification BMSCs cultured in vitro was qualified. Different concentrations of EMD could accelerate cell proliferation in HG and osteogenesis induction, and 75 μg/mL EMD had the best effect. The HG augmented BMSCs proliferation and the propidium iodide index of flow cytometry cycle was elevated in HG, which were strengthened via the EMD. After BMSCs' osteogenesis induction, Osterix, Runx2, CoL-1, early osteogenic indexes, and calcium salt deposition were reduced, but elevated via EMD. β-Catenin was the lowest in the HG, but elevated after EMD. After addition of XAV-939, reduction of β-catenin and the downstream (Osterix and Runx2) were manifested. Detection of binding protein bands was in β-catenin and Osterix of the HG after EMD treatment.

CONCLUSION

EMD may facilitate the osteogenic differentiation of BMSCs via activating the Wnt/β-catenin pathway in HG.

Differences in pathways contributing to thyroid hormone effects on postnatal cartilage calcification versus secondary ossification center development

The proximal and distal femur epiphyses of mice are both weight-bearing structures derived from chondrocytes but differ in development. Mineralization at the distal epiphysis occurs in an osteoblast-rich secondary ossification center (SOC), while the chondrocytes of the proximal femur head (FH), in particular, are directly mineralized. Thyroid hormone (TH) plays important roles in distal knee SOC formation, but whether TH also affects proximal FH development remains unexplored. Here, we found that TH controls chondrocyte maturation and mineralization at the FH in vivo through studies in thyroid stimulating hormone receptor (Tshr^-/-) hypothyroid mice by X-ray, histology, transcriptional profiling, and immunofluorescence staining. Both in vivo and in vitro studies conducted in ATDC5 chondrocyte progenitors concur that TH regulates expression of genes that modulate mineralization (Ibsp, Bglap2, Dmp1, Spp1, and Alpl). Our work also delineates differences in prominent transcription factor regulation of genes involved in the different mechanisms leading to proximal FH cartilage calcification and endochondral ossification at the distal femur. The information on the molecular pathways contributing to postnatal cartilage calcification can provide insights on therapeutic strategies to treat pathological calcification that occurs in soft tissues such as aorta, kidney, and articular cartilage.

Experimental and molecular docking studies of estrogen-like and anti-osteoporosis activity of compounds in Fructus Psoraleae

ETHNOPHARMACOLOGICAL RELEVANCE

Fructus Psoraleae (FP), dry mature fruits of Cullen corylifolium (L.) Medik., has been used clinically to treat kidney yang deficiency-induced impotence, asthma and cold pain in waist and knee caused by kidney deficiency. A study of the source of the significant kidney-enhancing effect of FP revealed that it may be due to its strong estrogen-like activity.

AIM OF THE STUDY

This study aimed to investigate the estrogen-like activity of the FP extract and 13 bioactive compounds in it, as well as the mechanisms underlying their estrogen-like and anti-osteoporosis activities.

MATERIALS AND METHODS

The estrogen-like activities of the 75% ethanol-only FP extract, and 75% ethanol plus petroleum ether, ethyl acetate, n-butanol or water FP extracts were each measured using Cell Counting Kit-8 (CCK-8) and luciferase reporter gene assays. The compounds were identified by high-performance liquid chromatography analysis. The activation of estrogen receptor signaling by the compounds was compared with that by estradiol (E₂) using the molecular docking software MOE-Dock 2008.10. The activation of the ER-Wnt-β-catenin signaling pathway was investigated using an alkaline phosphatase (ALP) assay, qPCR analysis and Western blot analysis.

RESULTS

The results revealed that the 75% ethanol plus ethyl acetate extract showed the highest estrogen-like activity among the four 75% ethanol extract fractions (further extracted with petroleum ether, ethyl acetate, n-butanol or water). Some compounds in FP showed strong estrogenic effect and anti-osteoporosis activity, and activated the Wnt-β-catenin pathway. The isoflavone compound was the most active.

CONCLUSIONS

This study demonstrated that FP has a strong estrogen-like activity and some of its component compounds have anti-osteoporosis activity by activating the ER-Wnt-β-catenin signaling pathway. Our detections provide a new insight into the mechanisms underlying the estrogen-like and anti-osteoporosis activities of FP, as well as a better understanding of structure effects.

LncRNA, PLXDC2-OT promoted the osteogenesis potentials of MSCs by inhibiting the deacetylation function of RBM6/SIRT7 complex and OSX specific isoform

Bone regeneration and remodeling are complex physiological processes that are regulated by key transcription factors. Understanding the regulatory mechanism of key transcription factors on the osteogenic differentiation of mesenchymal stem cells (MSCs) is a key issue for successful bone regeneration and remodeling. In the present study, we investigated the regulatory mechanism of the histone deacetylase Sirtuin 7 (SIRT7) on the key transcription factor OSX and osteogenesis of MSCs. In this study, we found that SIRT7 knockdown increased ALP activity and in vitro mineralization and promoted the expression of the osteogenic differentiation markers DSPP, DMP1, BSP, OCN, and the key transcription factor OSX in MSCs. In addition, SIRT7 could associate with RNA binding motif protein 6 (RBM6) to form a protein complex. Moreover, RBM6 inhibited ALP activity, the expression of DSPP, DMP1, BSP, OCN, and OSX in MSCs, and the osteogenesis of MSCs in vivo. Then, the SIRT7/RBM6 protein complex was shown to downregulate the level of H3K18Ac in the OSX promoter by recruiting SIRT7 to the OSX promoter and inhibiting the expression of OSX isoforms 1 and 2. Furthermore, lncRNA PLXDC2-OT could associate with the SIRT7/RBM6 protein complex to diminish its binding and deacetylation function in the OSX promoter and its inhibitory function on OSX isoforms 1 and 2 and to promote the osteogenic potential of MSCs.

How miR-31-5p and miR-33a-5p Regulates SP1/CX43 Expression in Osteoarthritis Disease: Preliminary Insights

Osteoarthritis (OA) is a degenerative bone disease that involved micro and macro-environment of joints. To date, there are no radical curative treatments for OA and novel therapies are mandatory. Recent evidence suggests the role of miRNAs in OA progression. In our previous studies, we demonstrated the role of miR-31-5p and miR-33a families in different bone regeneration signaling. Here, we investigated the role of miR-31-5p and miR-33a-5p in OA progression. A different expression of miR-31-5p and miR-33a-5p into osteoblasts and chondrocytes isolated from joint tissues of OA patients classified in based on different Kellgren and Lawrence (KL) grading was highlighted; and through a bioinformatic approach the common miRNAs target Specificity proteins (Sp1) were identified. Sp1 regulates the expression of gap junction protein Connexin43 (Cx43), which in OA drives the modification of i) osteoblasts and chondrocytes genes expression, ii) joint inflammation cytokines releases and iii) cell functions. Concerning this, thanks to gain and loss of function studies, the possible role of Sp1 as a modulator of CX43 expression through miR-31-5p and miR-33a-5p action was also evaluated. Finally, we hypothesize that both miRNAs cooperate to modulate the expression of SP1 in osteoblasts and chondrocytes and interfering, consequently, with CX43 expression, and they might be further investigated as new possible biomarkers for OA.

Recent Advances of Osterix Transcription Factor in Osteoblast Differentiation and Bone Formation

With increasing life expectations, more and more patients suffer from fractures either induced by intensive sports or other bone-related diseases. The balance between osteoblast-mediated bone formation and osteoclast-mediated bone resorption is the basis for maintaining bone health. Osterix (Osx) has long been known to be an essential transcription factor for the osteoblast differentiation and bone mineralization. Emerging evidence suggests that Osx not only plays an important role in intramembranous bone formation, but also affects endochondral ossification by participating in the terminal cartilage differentiation. Given its essentiality in skeletal development and bone formation, Osx has become a new research hotspot in recent years. In this review, we focus on the progress of Osx's function and its regulation in osteoblast differentiation and bone mass. And the potential role of Osx in developing new therapeutic strategies for osteolytic diseases was discussed.

The effects of mineral trioxide aggregate on osteo/odontogenic potential of mesenchymal stem cells: a comprehensive and systematic literature review

The significance of dental materials in dentin-pulp complex tissue engineering is undeniable. The mechanical properties and bioactivity of mineral trioxide aggregate (MTA) make it a promising biomaterial for future stem cell-based endodontic therapies. There are numerous in vitro studies suggesting the low cytotoxicity of MTA towards various types of cells. Moreover, it has been shown that MTA can enhance mesenchymal stem cells' (MSCs) osteo/odontogenic ability. According to the preferred reporting items for systematic reviews and meta-analyses (PRISMA), a literature review was conducted in the Medline, PubMed, and Scopus databases. Among the identified records, the cytotoxicity and osteo/odontoblastic potential of MTA or its extract on stem cells were investigated. Previous studies have discovered the differentiation-inducing potential of MTA on MSCs, providing a background for dentin-pulp complex cell therapies using the MTA, however, animal trials are needed before moving into clinical trials. In conclusion, MTA can be a promising candidate dental biomaterial for futuristic stem cell-based endodontic therapies.

Cannabidiol induces osteoblast differentiation via angiopoietin1 and p38 MAPK

In this study, we report the potential of cannabidiol, one of the major cannabis constituents, for enhancing osteoblastic differentiation in U2OS and MG-63 cells. Cannabidiol increased the expression of Angiopoietin1 and the enzyme activity of alkaline phosphatase in U2OS and MG-63. Invasion and migration assay results indicated that the cell mobility was activated by cannabidiol in U2OS and MG-63. Western blotting analysis showed that the expression of tight junction related proteins such as Claudin1, Claudin4, Occuludin1, and ZO1 was increased by cannabidiol in U2OS and MG-63. Alizarin Red S staining analysis showed that calcium deposition and mineralization was enhanced by cannabidiol in U2OS and MG-63. Western blotting analysis indicated that the expression of osteoblast differentiation related proteins such as distal-less homeobox 5, bone sialoprotein, osteocalcin, type I collagen, Runt-related transcription factor 2 (RUNX2), osterix (OSX), and alkaline phosphatase was time dependently upregulated by cannabidiol in U2OS and MG-63. Mechanistically, cannabidiol-regulated osteoblastic differentiation in U2OS and MG-63 by strengthen the protein-protein interaction among RUNX2, OSX, or the phosphorylated p38 mitogen-activated protein kinase (MAPK). In conclusion, cannabidiol increased Angiopoietin1 expression and p38 MAPK activation for osteoblastic differentiation in U2OS and MG-63 suggesting that cannabidiol might provide a novel therapeutic option for the bone regeneration.

The Transcription Factor HAND1 Is Involved in Cortical Bone Mass through the Regulation of Collagen Expression

Temporal and/or spatial alteration of collagen family gene expression results in bone defects. However, how collagen expression controls bone size remains largely unknown. The basic helix-loop-helix transcription factor HAND1 is expressed in developing long bones and is involved in their morphogenesis. To understand the functional role of HAND1 and collagen in the postnatal development of long bones, we overexpressed Hand1 in the osteochondroprogenitors of model mice and found that the bone volumes of cortical bones decreased in Hand1^Tg/+;Twist2-Cre mice. Continuous Hand1 expression downregulated the gene expression of type I, V, and XI collagen in the diaphyses of long bones and was associated with decreased expression of Runx2 and Sp7/Osterix, encoding transcription factors involved in the transactivation of fibril-forming collagen genes. Members of the microRNA-196 family, which target the 3' untranslated regions of COL1A1 and COL1A2, were significantly upregulated in Hand1^Tg/+;Twist2-Cre mice. Mass spectrometry revealed that the expression ratios of alpha 1(XI), alpha 2(XI), and alpha 2(V) in the diaphysis increased during postnatal development in wild-type mice, which was delayed in Hand1^Tg/+;Twist2-Cre mice. Our results demonstrate that HAND1 regulates bone size and morphology through osteochondroprogenitors, at least partially by suppressing postnatal expression of collagen fibrils in the cortical bones.

Epidrugs: novel epigenetic regulators that open a new window for targeting osteoblast differentiation

Efficient osteogenic differentiation of mesenchymal stem cells (MSCs) is a critical step in the treatment of bone defects and skeletal disorders, which present challenges for cell-based therapy and regenerative medicine. Thus, it is necessary to understand the regulatory agents involved in osteogenesis. Epigenetic mechanisms are considered to be the primary mediators that regulate gene expression during MSC differentiation. In recent years, epigenetic enzyme inhibitors have been used as epidrugs in cancer therapy. A number of studies mentioned the role of epigenetic inhibitors in the regulation of gene expression patterns related to osteogenic differentiation. This review attempts to provide an overview of the key regulatory agents of osteogenesis: transcription factors, signaling pathways, and, especially, epigenetic mechanisms. In addition, we propose to introduce epigenetic enzyme inhibitors (epidrugs) and their applications as future therapeutic approaches for bone defect regeneration.

Nanomaterials-based Cell Osteogenic Differentiation and Bone Regeneration

With the rapid development of nanotechnology, various nanomaterials have been applied to bone repair and regeneration. Due to the unique chemical, physical and mechanical properties, nanomaterials could promote stem cells osteogenic differentiation, which has great potentials in bone tissue engineering and exploiting nanomaterials-based bone regeneration strategies. In this review, we summarized current nanomaterials with osteo-induction ability, which could be potentially applied to bone tissue engineering. Meanwhile, the unique properties of these nanomaterials and their effects on stem cell osteogenic differentiation are also discussed. Furthermore, possible signaling pathways involved in the nanomaterials- induced cell osteogenic differentiation are also highlighted in this review.

Evaluation of the Genetic Association and mRNA Expression of the COL1A1, BMP2, and BMP4 Genes in the Development of Otosclerosis

Background: Otosclerosis (OTSC) is a genetically heterogeneous disorder, characterized by abnormal bone growth in the middle ear, affecting the stapes bone. Previous studies have shown that single nucleotide polymorphisms (SNPs) of the COL1A1, BMP2, and BMP4 genes are linked to susceptibility of OTSC, musculoskeletal degenerative diseases, and bone remodeling. Aims: To evaluate the genetic association and expression levels of COL1A1, BMP2, and BMP4 genes with OTSC in the Indian population. Methods: A total of 320 otosclerotic and 320 control samples were screened for four SNPs (rs1107946, rs11327935, rs2269336, and rs1800012) of the COL1A1 gene; rs3178250 of the BMP2 gene; and rs17563 of the BMP4 gene using single-strand conformation polymorphism analysis, and restriction fragment length polymorphism analyses. Genotypic, haplotypic, and linkage disequilibrium analyses were performed to assess the potential associations of these SNPs with OTSC. COL1A1, BMP2, and BMP4 mRNA expression levels were analyzed by semiquantitative RT-PCR and real-time PCR. Results: Genotypes of two SNPs, rs1800012 and rs17563, were found to be associated with OTSC (the rs1800012 GT genotype, p = 0.0022, OR = 0.481; and the rs17563 TC genotype, p = 0.0225, OR = 1.471). Haplotypic analyses revealed that the COL1A1 haplotype G-T-C-T (p = 0.021) was significantly increased among controls. Functional studies revealed an unexpected decrease in mRNA expression of COL1A1 but an increased expression of the BMP2 and BMP4 genes in otosclerotic stapes tissues. Conclusions: Our findings suggest that OTSC is a heterogeneous disorder, but that the GT genotype of the rs1800012 locus is protective and that the TC genotype at the rs17563 locus is a risk factor. In addition, our studies indicate that changes in the expression of the COL1A1, BMP2, and BMP4 genes may contribute to the genetic susceptibility of OTSC by regulating their mRNA levels.

Circaea mollis Siebold & Zucc. Alleviates postmenopausal osteoporosis in a mouse model via the BMP-2/4/Runx2 pathway

Background

Circaea mollis Sieb. & Zucc. has been used as a traditional herbal medicine in Hani Ethnopharmacy and possesses anti-arthritic activities. This study aimed to investigate the effect of Circaea mollis Siebold & Zucc on postmenopausal osteoporosis.

Methods

For in vitro study, MCF7 breast cancer cells and MC3T3-E1 pre-osteoblast cells were utilized to estimate estrogenic and osteogenic activity. Osteoblastic markers were measured by western blot and real-time PCR. For in vivo study, female mature C57BL/6 mice were ovariectomized and oral administrated with 10 mg/kg and 40 mg/kg of EECM respectively.

Results

EtOH extract of Circaea mollis Siebold & Zucc. (EECM) increased alkaline phosphatase activity and osteoblast marker levels at day 7 during differentiation of mouse preosteoblasts. EECM reduced osteoclast differentiation and bone resorption in an osteoblast-osteoclast primary co-culture system. In ovariectomized mice, EECM prevented the decrease in bone mineral density and recovered OSX and Runx2 via BMP2/4, Smad1/5/9 and p38.

Conclusions

The results suggest that EECM may be effective in preventing bone loss, offering a promising alternative for the nutritional management of postmenopausal osteoporosis.

Cholinergic control of bone development and beyond

There is ample evidence that cholinergic actions affect the health status of bones in vertebrates including man. Nicotine smoking, but also exposure to pesticides or medical drugs point to the significance of cholinergic effects on bone status, as reviewed here in Introduction. Then, we outline processes of endochondral ossification, and review respective cholinergic actions. In Results, we briefly summarize our in vivo and in vitro studies on bone development of chick and mouse [1,2], including (i) expressions of cholinergic components (AChE, BChE, ChAT) in chick embryo, (ii) characterisation of defects during skeletogenesis in prenatal ChE knockout mice, (iii) loss-of-function experiments with beads soaked in cholinergic components and implanted into chicken limb buds, and finally (iv) we use an in vitro mesenchymal 3D-micromass model that mimics cartilage and bone formation, which also had revealed complex crosstalks between cholinergic, radiation and inflammatory mechanisms [3]. In Discussion, we evaluate non-cholinergic actions of cholinesterases during bone formation by considering: (i) how cholinesterases could function in adhesive mechanisms; (ii) whether and how cholinesterases can form bone-regulatory complexes with alkaline phosphatase (ALP) and/or ECM components, which could regulate cell division, migration and adhesion. We conclude that cholinergic actions in bone development are driven mainly by classic cholinergic, but non-neural cycles (e.g., by acetylcholine); in addition, both cholinesterases can exert distinct ACh-independent roles. Considering their tremendous medical impact, these results bring forward novel research directions that deserve to be pursued.

Metformin coordinates osteoblast/osteoclast differentiation associated with ischemic osteonecrosis

In this study, we aimed to identify a candidate drug that can activate endogenous Angiopoietin 1 (Ang1) expression via drug repositioning as a pharmacological treatment for avascular osteonecrosis. After incubation with 821 drugs from the Food and Drug Administration (FDA)-approved drug library, Ang1 expression in U2OS cell culture media was examined by ELISA. Metformin, the first-line medication for treatment of type 2 diabetes, was selected as a candidate for in vitro and in vivo experimental evaluation. Ang1 was induced, and alkaline phosphatase activity was increased by metformin treatment in U2OS and MG63 cells. Wound healing and migration assay showed increased osteoblastic cell mobility by metformin treatment in U2OS and MG63 cells. Metformin upregulated expression of protein markers for osteoblastic differentiation in U2OS and MG63 cells but inhibited osteoclastic differentiation in Raw264.7 cells. Metformin (25 mg/kg) protected against ischemic necrosis in the epiphysis of the rat femoral head by maintaining osteoblast/osteocyte function and vascular density but inhibiting osteoclast activity in the necrotic femoral head. These findings provide novel insight into the specific biomarkers that are targeted and regulated by metformin in osteoblast differentiation and contribute to understanding the effects of these FDA-approved small-molecule drugs as novel therapeutics for ischemic osteonecrosis.

Chronic Intermittent Hypobaric Hypoxia Enhances Bone Fracture Healing

The effect of chronic intermittent hypobaric hypoxia (CIHH) on bone fracture healing is not elucidated. The present study aimed to investigate the role of CIHH on bone fracture healing and the mechanism. The Sprague-Dawley rats were randomly divided into the CIHH group and control group and monitored for 2, 4, or 8 weeks after femoral fracture surgery. Bone healing efficiency was significantly increased in the CIHH group as evidenced by higher high-density bone volume fractions, higher bone mineral density, higher maximum force, and higher stiffness. Histologically, the CIHH group exhibited superior bone formation, endochondral ossification, and angiogenic ability compared with the control group. The expression of HIF-1α and its downstream signaling proteins VEGF, SDF-1/CXCR4 axis were increased by the CIHH treatment. Moreover, the expression of RUNX2, osterix, and type I collagen in the callus tissues were also up-regulated in the CIHH group. In conclusion, our study demonstrated that CIHH treatment improves fracture healing, increases bone mineral density, and increases bone strength via the activation of HIF-1α and bone production-related genes.

Verification of osteoblast differentiation on airborne-particle abrasion, large-grit, acid-etched surface of titanium implants regulated by yes-associated protein and transcriptional coactivator with PDZ-binding motif

Although airborne-particle abrasion, large-grit, acid-etched (SLA) surface technology can promote implant osseointegration; its mechanism remains unclear. By preparing the SLA titanium (Ti) plate (SLA Ti) and Polished Ti plate (Polished Ti), this experiment investigates the expression and distribution of the Yes-associated protein (YAP) and transcriptional coactivator with the PDZ-binding motif (TAZ) in MC3T3-E1 cells. In addition, gene YAP and TAZ silencing on the SLA Ti was conducted to observe changes in the osteoblast differentiation markers, runt-related transcription factor-2 (Runx2) and bone sialoprotein (BSP). The results demonstrated that SLA Ti surface microtopography could induce YAP/TAZ's transfer from the cytoplasm to the nuclei of MC3T3-E1 cells. The expression of YAP/TAZ increased in terms of mRNA and protein. After silencing the YAP/TAZ genes, Runx2 and BSP decreased, suggesting that YAP/TAZ plays an important regulatory role in this process. Meanwhile, the results also showed that SLA microtopography enhanced the expression of integrins α1, α2, and β1. After silencing the integrin α1, α2, and β1 genes, YAP and TAZ decreased in terms of mRNA and protein. Therefore, this experiment was the first to confirm that SLA surface microtopography facilitates osteoblast differentiation by regulating YAP/TAZ and confirms that the process can be related to integrins α1, α2, and β1.

From skeletal development to the creation of pluripotent stem cell-derived bone-forming progenitors

Bone has many functions. It is responsible for protecting the underlying soft organs, it allows locomotion, houses the bone marrow and stores minerals such as calcium and phosphate. Upon damage, bone tissue can efficiently repair itself. However, healing is hampered if the defect exceeds a critical size and/or is in compromised conditions. The isolation or generation of bone-forming progenitors has applicability to skeletal repair and may be used in tissue engineering approaches. Traditionally, bone engineering uses osteochondrogenic stem cells, which are combined with scaffold materials and growth factors. Despite promising preclinical data, limited translation towards the clinic has been observed to date. There may be several reasons for this including the lack of robust cell populations with favourable proliferative and differentiation capacities. However, perhaps the most pertinent reason is the failure to produce an implant that can replicate the developmental programme that is observed during skeletal repair. Pluripotent stem cells (PSCs) can potentially offer a solution for bone tissue engineering by providing unlimited cell sources at various stages of differentiation. In this review, we summarize key embryonic signalling pathways in bone formation coupled with PSC differentiation strategies for the derivation of bone-forming progenitors.This article is part of the theme issue 'Designer human tissue: coming to a lab near you'.

Regulation of Proliferation, Differentiation and Functions of Osteoblasts by Runx2

Runx2 is essential for osteoblast differentiation and chondrocyte maturation. During osteoblast differentiation, Runx2 is weakly expressed in uncommitted mesenchymal cells, and its expression is upregulated in preosteoblasts, reaches the maximal level in immature osteoblasts, and is down-regulated in mature osteoblasts. Runx2 enhances the proliferation of osteoblast progenitors by directly regulating Fgfr2 and Fgfr3. Runx2 enhances the proliferation of suture mesenchymal cells and induces their commitment into osteoblast lineage cells through the direct regulation of hedgehog (Ihh, Gli1, and Ptch1), Fgf (Fgfr2 and Fgfr3), Wnt (Tcf7, Wnt10b, and Wnt1), and Pthlh (Pthr1) signaling pathway genes, and Dlx5. Runx2 heterozygous mutation causes open fontanelle and sutures because more than half of the Runx2 gene dosage is required for the induction of these genes in suture mesenchymal cells. Runx2 regulates the proliferation of osteoblast progenitors and their differentiation into osteoblasts via reciprocal regulation with hedgehog, Fgf, Wnt, and Pthlh signaling molecules, and transcription factors, including Dlx5 and Sp7. Runx2 induces the expression of major bone matrix protein genes, including Col1a1, Spp1, Ibsp, Bglap2, and Fn1, in vitro. However, the functions of Runx2 in differentiated osteoblasts in the expression of these genes in vivo require further investigation.

The Deletion of Hdac4 in Mouse Osteoblasts Influences Both Catabolic and Anabolic Effects in Bone

Histone deacetylase 4 (Hdac4) is known to control chondrocyte hypertrophy and bone formation. We have previously shown that parathyroid hormone (PTH) regulates many aspects of Hdac4 function in osteoblastic cells in vitro; however, in vivo confirmation was previously precluded by preweaning lethality of the Hdac4-deficient mice. To analyze the function of Hdac4 in bone in mature animals, we generated mice with osteoblast lineage-specific knockout of Hdac4 (Hdac4^ob-/- ) by crossing transgenic mice expressing Cre recombinase under the control of a 2.3-kb fragment of the Col1a1 promoter with mice bearing loxP-Hdac4. The Hdac4^ob-/- mice survive to adulthood and developed a mild skeletal phenotype. At age 12 weeks, they had short, irregularly shaped and stiff tails due to smaller tail vertebrae, with almost no growth plates. The tibial growth plate zone was also thinned, and Mmp13 and Sost mRNAs were increased in the distal femurs of Hdac4^ob-/- mice. Immunohistochemistry showed that sclerostin was elevated in Hdac4^ob-/- mice, suggesting that Hdac4 inhibits its gene and protein expression. To determine the effect of PTH in these mice, hPTH (1-34) or saline were delivered for 14 days with subcutaneously implanted devices in 8-week-old female Hdac4^ob-/- and wild-type (Hdac4^fl/fl ) mice. Serum CTX, a marker of bone resorption, was increased in Hdac4^ob-/- mice with or without PTH treatment. Tibial cortical bone volume/total volume (BV/TV), cortical thickness (Ct.Th), and relative cortical area (RCA) were decreased in Hdac4^ob-/- mice, but PTH caused no further decrease in Hdac4^ob-/- mice. Tibial trabecular BV/TV and thickness were not changed significantly in Hdac4^ob-/- mice but decreased with PTH treatment. These results indicate that Hdac4 inhibits bone resorption and has anabolic effects via inhibiting Mmp13 and Sost/sclerostin expression. Hdac4 influences cortical bone mass and thickness and knockout of Hdac4 prevents the catabolic effect of PTH in cortical bone. © 2018 American Society for Bone and Mineral Research.

SRC kinase inhibition with saracatinib limits the development of osteolytic bone disease in multiple myeloma

Multiple myeloma (MM)-associated osteolytic bone disease is a major cause of morbidity and mortality in MM patients and the development of new therapeutic strategies is of great interest. The proto-oncogene SRC is an attractive target for such a strategy. In the current study, we investigated the effect of treatment with the SRC inhibitor saracatinib (AZD0530) on osteoclast and osteoblast differentiation and function, and on the development of MM and its associated bone disease in the 5TGM.1 and 5T2MM murine MM models. In vitro data showed an inhibitory effect of saracatinib on osteoclast differentiation, polarization and resorptive function. In osteoblasts, collagen deposition and matrix mineralization were affected by saracatinib. MM cell proliferation and tumor burden remained unaltered following saracatinib treatment and we could not detect any synergistic effects with drugs that are part of standard care in MM. We observed a marked reduction of bone loss after treatment of MM-bearing mice with saracatinib as reflected by a restoration of trabecular bone parameters to levels observed in naive control mice. Histomorphometric analyses support that this occurs through an inhibition of bone resorption. In conclusion, these data further establish SRC inhibition as a promising therapeutic approach for the treatment of MM-associated osteolytic bone disease.

p53 inhibits SP7/Osterix activity in the transcriptional program of osteoblast differentiation

Osteoblast differentiation is achieved by activating a transcriptional network in which Dlx5, Runx2 and Osx/SP7 have fundamental roles. The tumour suppressor p53 exerts a repressive effect on bone development and remodelling through an unknown mechanism that inhibits the osteoblast differentiation programme. Here we report a physical and functional interaction between Osx and p53 gene products. Physical interaction was found between overexpressed proteins and involved a region adjacent to the OSX zinc fingers and the DNA-binding domain of p53. This interaction results in a p53-mediated repression of OSX transcriptional activity leading to a downregulation of the osteogenic programme. Moreover, we show that p53 is also able to repress key osteoblastic genes in Runx2-deficient osteoblasts. The ability of p53 to suppress osteogenesis is independent of its DNA recognition ability but requires a native conformation of p53, as a conformational missense mutant failed to inhibit OSX. Our data further demonstrates that p53 inhibits OSX binding to their responsive Sp1/GC-rich sites in the promoters of their osteogenic target genes, such as IBSP or COL1A1. Moreover, p53 interaction to OSX sequesters OSX from binding to DLX5. This competition blocks the ability of OSX to act as a cofactor of DLX5 to activate homeodomain-containing promoters. Altogether, our data support a model wherein p53 represses OSX-DNA binding and DLX5-OSX interaction, and thereby deregulates the osteogenic transcriptional network. This mechanism might have relevant roles in bone pathologies associated to osteosarcomas and ageing.

17β-estradiol attenuates ovariectomy‑induced bone deterioration through the suppression of the ephA2/ephrinA2 signaling pathway

The present study aimed to investigate whether 17β-estradiol (E2) exerts protective effects on bone deterioration induced by ovariectomy (OVX) through the ephA2/ephrinA2 signaling pathway in rats. Female rats were subjected to OVX, sham surgeryor OVX+E2 treatment. Levels of biomarkers were measured in serum and urine. Hematoxylin and eosin staining was performed on paraffin-embedded bone sections. Expression of genes and proteins was analyzed by reverse transcription-quantitative polymerase chain reaction and western blotting, respectively. Bone mineral density (BMD) was analyzed by dual-energy X-ray absorptiometry. Trabecular bone microarchitecture was also evaluated. Osteoclastogenesis was induced by in vitro culturing with mouse receptor activator of nuclear factor κB ligand (RANKL) and macrophage colony-stimulating factor 1. small interfering RNA was designed to knockdown ehpA2 receptor and its ligand ephrinA2. Results of the present study demonstrated that E2 had suppressive effects on OVX-induced body weight gain and bone turnover factors in serum and urine. E2 inhibited the bone resorption function of osteoclasts by inhibiting the production of tartrate-resistant acid phosphatase-5b and RANKL, and induced bone formation function of osteoblasts by prompting runt-related transcription factor 2, Sp7 transcription factor and collagen alpha-1(I) chain expression in bone marrow cells. E2 treatment significantly increased the tibia BMD and prevented the deterioration of trabecular microarchitecture compared with the OVX group. Moreover, E2 significantly decreased the OVX-stimulated expression of ephA2 and ephrinA2. EphA2 or ephrin A2 knockdown significantly suppressed osteoclastogenesis in vitro. In conclusion, E2 can attenuate OVX-induced bone deterioration partially through the suppression of the ephA2/ephrinA2 signaling pathway. Therefore EphA2/ephrinA2 signaling pathway may be a potential target for osteoporosis treatment.

Fenofibrate decreases the bone quality by down regulating Runx2 in high-fat-diet induced Type 2 diabetes mellitus mouse model

Background

This study is to investigate the effect of fenofibrate on the bone quality of Type 2 diabetes mellitus (T2DM) mouse model.

Methods

T2DM mouse model was induced by high-fat-diet, and the mice were treated with fenofibrate (100 mg/kg) (DIO-FENO) or PBS (DIO-PBS) for 4 weeks. The bone microstructure and biomechanical properties of femora were analyzed by micro-CT and 3-Point bending test. The protein expression was detected by immunohistochemical staining and Western blot. The cell apoptosis was evaluated by TUNEL staining. The Bcl2, caspase 3, and osteoblast marker genes were detected by RT-qPCR.

Results

The biomechanical properties of bones from DIO-FENO group were significantly lower than those in the control and DIO-PBS groups. Besides, the trabecular number was lower than those of the other groups, though the cortical porosity was decreased compared with that of DIO-PBS group because of the increase of apoptotic cells. The expression of osteocalcin and collagen I were decreased after treatment with fenofibrate in T2DM mice. Moreover, the cell viability was decreased after treated with different concentrations of fenofibrate, and the expression of Runx2 decreased after treated with high dose of fenofibrate.

Conclusion

Fenofibrate decreases the bone quality of T2DM mice through decreasing the expression of collagen I and osteocalcin, which may be resulted from the down regulation of Runx2 expression.

Osteogenesis imperfecta: new genes reveal novel mechanisms in bone dysplasia

Osteogenesis imperfecta (OI) is a skeletal dysplasia characterized by fragile bones and short stature and known for its clinical and genetic heterogeneity which is now understood as a collagen-related disorder. During the last decade, research has made remarkable progress in identifying new OI-causing genes and beginning to understand the intertwined molecular and biochemical mechanisms of their gene products. Most cases of OI have dominant inheritance. Each new gene for recessive OI, and a recently identified gene for X-linked OI, has shed new light on its (often previously unsuspected) function in bone biology. Here, we summarize the literature that has contributed to our current understanding of the pathogenesis of OI.

Zinc finger transcription factor Sp7/Osterix acts on bone formation and regulates col10a1a expression in zebrafish

Sp7/Osterix as a zinc finger transcription factor is expressed specifically in osteoblasts. Embryonic lethality of Sp7 knockout mice, however, has prevented from examining the functions of Sp7 in osteoblast and bone formation in live animals. Here we used TALEN, a versatile genome-editing tool, to generate one zebrafish sp7 mutant line. Homozygous sp7-/- mutant zebrafish are able to survive to adulthood. Alizarin Red staining and Micro-CT analysis showed that sp7-/- larvae and adult fish fail to develop normal opercula, and display curved tail fins and severe craniofacial malformation, while Alcian Blue staining showed no obvious cartilage defects in sp7-/- fish. Quantitative RT-PCR showed that a number of osteoblast markers including spp1, phex, col1ala, and col1a1b are significantly down-regulated in sp7-/- fish. Furthermore, col10a1a, whose ortholog is the cartilage marker in mice, was shown to be a novel downstream gene of Sp7 as an osteoblast marker in zebrafish. Together, these results suggest that Sp7 is required for zebrafish bone development and zebrafish sp7 mutants provide animal models for investigating novel aspects of bone development.

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.

Salidroside accelerates fracture healing through cell-autonomous and non-autonomous effects on osteoblasts

Salidroside (SAL), a major active component of Rhodiola rosea L., exhibits diverse pharmacological effects. However, the direct roles of SAL in fracture healing remain largely unknown. Here, we demonstrate that SAL significantly promotes proliferation by altering the cell-cycle distribution of osteoblastic cells. SAL also greatly stimulates osteoblast differentiation and mineralization by inducing the expression of Runx2 and Osterix. In addition to its osteoblast-autonomous effects, SAL can activate the HIF-1α pathway coupling of angiogenesis and osteogenesis through cell-non-autonomous effects. Our in vitro results suggest that SAL significantly up-regulates HIF-1α expression at the mRNA and protein levels. Furthermore, the nuclear translocation and transcriptional activity of HIF-1α and the HIF-responsive gene VEGF increase following SAL treatment. Our mechanistic study revealed that the regulation of osteoblastic proliferation and HIF-1α expression partly involves MAPK/ERK and PI3K/Akt signaling. Our in vivo analysis also demonstrated that SAL can promote angiogenesis within the callus and accelerate fracture healing. Thus, SAL promotes skeletal regeneration in cell-autonomous and cell-non-autonomous ways and might be a potential therapy for accelerating fracture healing.

RNA-binding protein SAMD4 regulates skeleton development through translational inhibition of Mig6 expression

Protein translation regulation has essential roles in inflammatory responses, cancer initiation and the pathogenesis of several neurodegenerative disorders. However, the role of the regulation of protein translation in mammalian skeleton development has been rarely elaborated. Here we report that the lack of the RNA-binding protein sterile alpha motif domain containing protein 4 (SAMD4) resulted in multiple developmental defects in mice, including delayed bone development and decreased osteogenesis. Samd4-deficient mesenchymal progenitors exhibit impaired osteoblast differentiation and function. Mechanism study demonstrates that SAMD4 binds the Mig6 mRNA and inhibits MIG6 protein synthesis. Consistent with this, Samd4-deficient cells have increased MIG6 protein level and knockdown of Mig6 rescues the impaired osteogenesis in Samd4-deficient cells. Furthermore, Samd4-deficient mice also display chondrocyte defects, which is consistent with the regulation of MIG6 protein level by SAMD4. These findings define SAMD4 as a previously unreported key regulator of osteoblastogenesis and bone development, implying that regulation of protein translation is an important mechanism governing skeletogenesis and that control of protein translation could have therapeutic potential in metabolic bone diseases, such as osteoporosis.

ZBTB16 as a Downstream Target Gene of Osterix Regulates Osteoblastogenesis of Human Multipotent Mesenchymal Stromal Cells

Human multipotent mesenchymal stromal cells (hMSCs) possess the ability to differentiate into osteoblasts, and they can be utilized as a source for bone regenerative therapy. Osteoinductive pretreatment, which induces the osteoblastic differentiation of hMSCs in vitro, has been widely used for bone tissue engineering prior to cell transplantation. However, the molecular basis of osteoblastic differentiation induced by osteoinductive medium (OIM) is still unknown. Therefore, we used a next-generation sequencer to investigate the changes in gene expression during the osteoblastic differentiation of hMSCs. The hMSCs used in this study possessed both multipotency and self-renewal ability. Whole-transcriptome analysis revealed that the expression of zinc finger and BTB domain containing 16 (ZBTB16) was significantly increased during the osteoblastogenesis of hMSCs. ZBTB16 mRNA and protein expression was enhanced by culturing the hMSCs with OIM. Small interfering RNA (siRNA)-mediated gene silencing of ZBTB16 decreased the activity of alkaline phosphatase (ALP); the expression of osteogenic genes, such as osteocalcin (OCN) and bone sialoprotein (BSP), and the mineralized nodule formation induced by OIM. siRNA-mediated gene silencing of Osterix (Osx), which is known as an essential regulator of osteoblastic differentiation, markedly downregulated the expression of ZBTB16. In addition, chromatin immunoprecipitation (ChIP) assays showed that Osx associated with the ZBTB16 promoter region containing the GC-rich canonical Sp1 sequence, which is the specific Osx binding site. These findings suggest that ZBTB16 acts as a downstream transcriptional regulator of Osx and can be useful as a late marker of osteoblastic differentiation. J. Cell. Biochem. 117: 2423-2434, 2016. © 2016 Wiley Periodicals, Inc.