Transcriptional regulation of the osterix (Osx, Sp7) promoter by tumor necrosis factor identifies disparate effects of mitogen-activated protein kinase and NF kappa B pathways

The effect of Rsk2 on TNFα-mediated bone loss in the TMJ and craniofacial skeleton

OBJECTIVES

This study aims to investigate the impact of the pro-osteoblastogenic ERK-activated ribosomal S6 kinase (Rsk2) on Tumor necrosis factor (TNF)α-induced bone loss in the craniofacial system, focusing on its role in rheumatoid arthritis (RA). The objective is to understand whether Rsk2, previously shown to have protective effects in long bones against TNFα-induced bone resorption, exhibits similar effects in the craniofacial region.

MATERIALS

, and Methods. The study compares mice with TNFα overexpression, Rsk2 knockout mice, and a combination of TNFα, and Rsk2 knockout mice using detailed micro-computed tomography coupled with landmark based morphometric analysis, and classical histology. The overall skull morphology, mandible shape, and the temporomandibular joint were examined. Additionally, histological sections were utilized to examine the synovial membrane.

RESULTS

Combining TNFα, and Rsk2 deficiency does not further alter overall skull shape compared to TNFα alone. TNFα overexpression shortens the mandibular ramus, exacerbated by Rsk2 absence. Micro-computed tomography (µCT) reveals significant temporomandibular joint damage from TNFα, independent of Rsk2. However, histological sections show increased synovial membrane thickness with TNFα, heightened in the absence of Rsk2.

CONCLUSIONS

Rsk2 mitigates TNFα-induced effects on mandibular ramus length in the craniofacial system but has limited impact on the temporomandibular joint, except for synovial membrane thickness. Overall, Rsk2 demonstrates a weaker preventive effect on TNFα-induced craniofacial bone loss compared to its established role in the appendicular skeleton.

CLINICAL RELEVANCE

This study highlights regional differences in Rsk2's protective mechanisms, emphasizing the need for further exploration of the underlying mechanisms for these disparities. Understanding these regional differences can be crucial for the development of targeted therapeutic interventions.

Fam102a translocates Runx2 and Rbpjl to facilitate Osterix expression and bone formation

Bone remodeling maintains the robustness of the bone tissue by balancing bone resorption by osteoclasts and bone formation by osteoblasts. Although these cells together play a crucial role in bone remodeling, only a few reports are available on the common factors involved in the differentiation of the two types of cells. Here, we show family with sequence similarity 102 member A (Fam102a) as a bone-remodeling factor that positively regulates both osteoclast and osteoblast differentiation. Fam102a regulates osteoblast differentiation by controlling recombination signal binding protein for immunoglobulin κ J region-like (Rbpjl). The Fam102a-Rbpjl axis promotes the nuclear translocation of transcription factors and enhances the expression of Osterix, a transcription factor essential for osteoblast differentiation. The deletion of Fam102a or a functional mutation in Rbpjl leads to osteopenia accompanied by reduced osteoblastic bone formation. Thus, the Fam102a-Rbpjl axis plays an important role in osteoblasts and this finding provides insights into bone remodeling.

Antimicrobial peptides in bone regeneration: mechanism and potential

INTRODUCTION

Antimicrobial peptides (AMPs) are small-molecule peptides with a unique antimicrobial mechanism. Other notable biological activities of AMPs, including anti-inflammatory, angiogenesis, and bone formation effects, have recently received widespread attention. These remarkable bioactivities, combined with the unique antimicrobial mechanism of action of AMPs, have led to their increasingly important role in bone regeneration.

AREAS COVERED

In this review, on the one hand, we aimed to summarize information about the AMPs that are currently used for bone regeneration by reviewing published literature in the PubMed database. On the other hand, we also highlight some AMPs with potential roles in bone regeneration and their possible mechanisms of action.

EXPERT OPINION

The translation of AMPs to the clinic still faces many problems, but their unique antimicrobial mechanisms and other conspicuous biological activities suggest great potential. An in-depth understanding of the structure and mechanism of action of AMPs will help us to subsequently combine AMPs with different carrier systems and perform structural modifications to reduce toxicity and achieve stable release, which may be a key strategy for facilitating the translation of AMPs to the clinic.

Targeted postnatal knockout of Sclerostin using a bone-targeted adeno-associated viral vector increases bone anabolism and decreases canalicular density

PURPOSE

The creation of murine gene knockout models to study bone gene functions often requires the resource intensive crossbreeding of Cre transgenic and gene-floxed strains. The developmental versus postnatal roles of genes can be difficult to discern in such models. For example, embryonic deletion of the Sclerostin (Sost) gene establishes a high-bone mass phenotype in neonatal mice that may impact on future bone growth. To generate a postnatal skeletal knockout of Sost in adult mice, this study used a single injection of a bone-targeted recombinant adeno-associated virus (rAAV) vector.

METHODS

8-week-old Sost^flox/flox mice were injected with saline (control) or a single injection containing 5 × 10¹¹ vg AAV8-Sp7-Cre vector. Ai9 fluorescent Cre reporter mice were dosed in parallel to confirm targeting efficiency. After 6 weeks, detailed bone analysis was performed via microCT, biomechanical testing, and bone histology on vertebral and long bone specimens.

RESULTS

The AAV8-Sp7-Cre vector induced widespread persistent recombination in the bone compartment. Regional microCT analyses revealed significant increases in bone with vector treatment. In the L3 vertebrae, Sost^flox/flox:AAV-Cre showed a 22 % increase in bone volume and 21 % in trabecular bone fraction compared to controls; this translated to a 17 % increase in compressive strength. In the tibiae, Sost^flox/flox:AAV-Cre led to small but statistically significant increases in cortical bone volume and thickness. These were consistent with a 25 % increase in mineral apposition rate, but this did not translate into increased four-point bending strength. Ploton silver nitrate stain on histological sections revealed an unexpected increase in canalicular density associated with Sost ablation.

CONCLUSION

This report demonstrates a proof-of-concept that the AAV8-Sp7-Cre vector can efficiently produce postnatal skeletal knockout mice using gene-floxed strains. This technology has the potential for broad utility in the bone field with existing conditional lines. These data also confirm an important postnatal role for Sost in regulating bone homeostasis, consistent with prior studies using neutralizing Sclerostin antibodies, and highlights a novel role of Sost in canalicular remodeling.

The regulatory role and therapeutic application of pyroptosis in musculoskeletal diseases

Pyroptosis is a controlled form of inflammatory cell death characterized by inflammasome activation, pore formation, and cell lysis. According to different caspases, pyroptosis can be divided into canonical, non-canonical, and other pathways. The role of pyroptosis in disease development has been paid more attention in recent years. The trigger factors of pyroptosis are often related to oxidative stress and proinflammatory substances, which coincide with the pathological mechanism of some diseases. Pyroptosis directly leads to cell lysis and death, and the release of cytosolic components and proinflammatory cytokines affects cell activity and amplifies the inflammatory response. All the above are involved in a series of basic pathological processes, such as matrix degradation, fibrosis, and angiogenesis. Since these pathological changes are also common in musculoskeletal diseases (MSDs), emerging studies have focused on the correlations between pyroptosis and MSDs in recent years. In this review, we first summarized the molecular mechanism of pyroptosis and extensively discussed the differences and crosstalk between pyroptosis, apoptosis, and necrosis. Next, we elaborated on the role of pyroptosis in some MSDs, including osteoarthritis, rheumatoid arthritis, osteoporosis, gout arthritis, ankylosing spondylitis, intervertebral disc degeneration, and several muscle disorders. The regulation of pyroptosis could offer potential therapeutic targets in MSDs treatment. Herein, the existing drugs and therapeutic strategies that directly or indirectly target pyroptosis pathway components have been discussed in order to shed light on the novel treatment for MSDs.

How Does Lifestyle Affect Hematopoiesis and the Bone Marrow Microenvironment?

Lifestyle factors are modifiable behavioral factors that have a significant impact on health and longevity. Diet-induced obesity and physical activity/exercise are two prevalent lifestyle factors that have strong relationships to overall health. The mechanisms linking obesity to negative health outcomes and the mechanisms linking increased participation in physical activity/exercise to positive health outcomes are beginning to be elucidated. Chronic inflammation, due in part to overproduction of myeloid cells from hematopoietic stem cells (HSCs) in the bone marrow, is an established mechanism responsible for the negative health effects of obesity. Recent work has shown that exercise training can reverse the aberrant myelopoiesis present in obesity in part by restoring the bone marrow microenvironment. Specifically, exercise training reduces marrow adipose tissue, increases HSC retention factor expression, and reduces pro-inflammatory cytokine levels in the bone marrow. Other, novel mechanistic factors responsible for these exercise-induced effects, including intercellular communication using extracellular vesicles (EVs), is beginning to be explored. This review will summarize the recent literature describing the effects of exercise on hematopoiesis in individuals with obesity and introduce the potential contribution of EVs to this process.

Role of NLRP3 Inflammasome in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by multi-articular, symmetrical and invasive arthritis resulting from immune system abnormalities involving T and B lymphocytes. Although significant progress has been made in the understanding of RA pathogenesis, the underlying mechanisms are not fully understood. Recent studies suggest that NLRP3 inflammasome, a regulator of inflammation, might play an important role in the development of RA. There have been increasing clinical and pre-clinical evidence showing the treatment of NLRP3/IL-1β in inflammatory diseases. To provide a foundation for the development of therapeutic strategies, we will briefly summarize the roles of NLRP3 inflammasome in RA and explore its potential clinical treatment.

Transcriptomic Analysis Provides Insights to Reveal the bmp6 Function Related to the Development of Intermuscular Bones in Zebrafish

Intermuscular bones (IBs) are small, hard-boned spicules located in the muscle tissue that mainly exist in the myosepta of lower teleosts, which hurt the edibleness and economic value of fish. The study of the development of IBs is very important for freshwater aquaculture fish, but the molecular mechanism of its formation and the key regulatory genes remain unclear. In this study, we first constructed two types of zebrafish mutants (the mutants losing IBs and the mutants with partial deletion of IBs) by knocking out bmp6. We then carried out a transcriptomic analysis to reveal the role of bmp6 in the developmental mechanism of IBs; we used the caudal musculoskeletal tissues of these mutants and wild-type zebrafish at three development stages (20, 45, and 60 dph) to perform transcriptomic analysis. The results showed that the deficiency of bmp6 upregulated sik1 and activated the TNF-A signaling via the NF-KB pathway, which inhibited the development of osteoblasts and promoted osteoclast formation, thereby inhibiting the formation of IBs. These results provided insights to understand the role of bmp6 in the development of IBs in zebrafish and are useful for selective breeding of IBs in cyprinids.

The Multiple Biological Functions of Dipeptidyl Peptidase-4 in Bone Metabolism

Dipeptidyl peptidase-4 (DPP4) is a ubiquitously occurring protease involved in various physiological and pathological processes ranging from glucose homeostasis, immunoregulation, inflammation to tumorigenesis. Recently, the benefits of DPP4 inhibitors as novel hypoglycemic agents on bone metabolism have attracted extensive attraction in many studies, indicating that DPP4 inhibitors may regulate bone homeostasis. The effects of DPP4 on bone metabolism are still unclear. This paper thoroughly reviews the potential mechanisms of DPP4 for interaction with adipokines, bone cells, bone immune cells, and cytokines in skeleton system. This literature review shows that the increased DPP4 activity may indirectly promote bone resorption and inhibit bone formation, increasing the risk of osteoporosis. Thus, bone metabolic balance can be improved by decreasing DPP4 activities. The substantial evidence collected and analyzed in this review supports this implication.

YY2 Promotes Osteoblast Differentiation by Upregulating Osterix Transcriptional Activity

Yin Yang 2 (YY2) is a paralog of YY1, a well-known multifunctional transcription factor containing a C-terminal zinc finger domain. Although the role of YY1 in various biological processes, such as the cell cycle, cell differentiation and tissue development, is well established, the function of YY2 has not been fully determined. In this study, we investigated the functional role of YY2 during osteoblast differentiation. YY2 overexpression and knockdown increased and decreased osteoblast differentiation, respectively, in BMP4-induced C2C12 cells. Mechanistically, YY2 overexpression increased the mRNA and protein levels of Osterix (Osx), whereas YY2 knockdown had the opposite effect. To investigate whether YY2 regulates Osx transcription, the effect of YY2 overexpression and knockdown on Osx promoter activity was evaluated. YY2 overexpression significantly increased Osx promoter activity in a dose-dependent manner, whereas YY2 knockdown had the opposite effect. Furthermore, vectors containing deletion and point mutations were constructed to specify the regulation site. Both the Y1 and Y2 sites were responsible for YY2-mediated Osx promoter activation. These results indicate that YY2 is a positive regulator of osteoblast differentiation that functions by upregulating the promoter activity of Osx, a representative osteogenic transcription factor in C2C12 cells.

Network Pharmacological Study on Mechanism of the Therapeutic Effect of Modified Duhuo Jisheng Decoction in Osteoporosis

BACKGROUND

Modified Duhuo Jisheng Decoction (MDHJSD) is a traditional Chinese medicine prescription for the treatment of osteoporosis (OP), but its mechanism of action has not yet been clarified. This study aims to explore the mechanism of MDHJSD in OP through a combination of network pharmacology analysis and experimental verification.

METHODS

The active ingredients and corresponding targets of MDHJSD were acquired from the Traditional Chinese Medicine System Pharmacology (TCMSP) database. OP-related targets were acquired from databases, including Genecards, OMIM, Drugbank, CTD, and PGKB. The key compounds, core targets, major biological processes, and signaling pathways of MDHJSD that improve OP were identified by constructing and analysing the relevant networks. The binding affinities between key compounds and core targets were verified using AutoDock Vina software. A rat model of ovariectomized OP was used for the experimental verification.

RESULTS

A total of 100 chemical constituents, 277 targets, and 4734 OP-related targets of MDHJSD were obtained. Subsequently, five core components and eight core targets were identified in the analysis. Pathway enrichment analysis revealed that overlapping targets were significantly enriched in the tumour necrosis factor-alpha (TNF-α) signaling pathway, an inflammation signaling pathway, which contained six of the eight core targets, including TNF-α, interleukin 6 (IL-6), transcription factor AP-1, mitogen-activated protein kinase 3, RAC-alpha serine/threonine-protein kinase, and caspase-3 (CASP3). Molecular docking analysis revealed close binding of the six core targets of the TNF signaling pathway to the core components. The results of experimental study show that MDHJSD can protect bone loss, inhibit the inflammatory response, and downregulate the expression levels of TNF-α, IL-6, and CASP3 in ovariectomized rats.

CONCLUSION

The mechanism of MDHJSD in the treatment of OP may be related to the regulation of the inflammatory response in the bone tissue.

Role of the Interaction of Tumor Necrosis Factor-α and Tumor Necrosis Factor Receptors 1 and 2 in Bone-Related Cells

Tumor necrosis factor-α (TNF-α) is a pleiotropic cytokine expressed by macrophages, monocytes, and T cells, and its expression is triggered by the immune system in response to pathogens and their products, such as endotoxins. TNF-α plays an important role in host defense by inducing inflammatory reactions such as phagocytes and cytocidal systems activation. TNF-α also plays an important role in bone metabolism and is associated with inflammatory bone diseases. TNF-α binds to two cell surface receptors, the 55kDa TNF receptor-1 (TNFR1) and the 75kDa TNF receptor-2 (TNFR2). Bone is in a constant state of turnover; it is continuously degraded and built via the process of bone remodeling, which results from the regulated balance between bone-resorbing osteoclasts, bone-forming osteoblasts, and the mechanosensory cell type osteocytes. Precise interactions between these cells maintain skeletal homeostasis. Studies have shown that TNF-α affects bone-related cells via TNFRs. Signaling through either receptor results in different outcomes in different cell types as well as in the same cell type. This review summarizes and discusses current research on the TNF-α and TNFR interaction and its role in bone-related cells.

Role of the major histocompatibility complex class II protein presentation pathway in bone immunity imbalance in postmenopausal osteoporosis

Bone immunity regulates osteoclast differentiation and bone resorption and is a potential target for the treatment of postmenopausal osteoporosis (PMOP). The molecular network between bone metabolism and the immune system is complex. However, the molecular mechanism underlying the involvement of the major histocompatibility complex class II (MHC-II) molecule protein presentation pathway in PMOP remains to be elucidated. The MHC-II molecule is a core molecule of the protein presentation pathway. It is combined with the processed short peptide and presented to T lymphocytes, thereby activating them to become effector T cells. T-cell-derived inflammatory factors promote bone remodeling in PMOP. Moreover, the MHC-II molecule is highly expressed in osteoclast precursors. MHC-II transactivator (CIITA) is the main regulator of MHC-II gene expression and the switch for protein presentation. CIITA is also a major regulator of osteoclast differentiation and bone homeostasis. Therefore, we hypothesized that the MHC-II promotes osteoclast differentiation, providing a novel pathogenic mechanism and a potential target for the treatment of PMOP.

The Role of Immune Microenvironment in Maxillofacial Bone Homeostasis

Maxillofacial bone defects are common medical problems caused by congenital defects, necrosis, trauma, tumor, inflammation, and fractures non-union. Maxillofacial bone defects often need bone graft, which has many difficulties, such as limited autogenous bone supply and donor site morbidity. Bone tissue engineering is a promising strategy to overcome the above-mentioned problems. Osteoimmunology is the inter-discipline that focuses on the relationship between the skeletal and immune systems. The immune microenvironment plays a crucial role in bone healing, tissue repair and regeneration in maxillofacial region. Recent studies have revealed the vital role of immune microenvironment and bone homeostasis. In this study, we analyzed the complex interaction between immune microenvironment and bone regeneration process in oral and maxillofacial region, which will be important to improve the clinical outcome of the bone injury treatment.

Cytokine-scavenging nanodecoys reconstruct osteoclast/osteoblast balance toward the treatment of postmenopausal osteoporosis

Imbalance between osteoblasts and osteoclasts accounts for the incidence and deterioration of postmenopausal osteoporosis. Abnormally elevated RANKL and TNF-α levels after menopause promote osteoclast formation and inhibit osteoblast differentiation, respectively. Here, nanodecoys capable of scavenging RANKL and TNF-α were developed from preosteoclast (RAW 264.7 cell) membrane–coated poly(lactic-co-glycolic acid) (PLGA) nanoparticles, which inhibited osteoporosis and maintained bone integrity. The nanodecoys effectively escaped from macrophage capture and enabled prolonged blood circulation after systemic administration. The abundant RANK and TNF-α receptor (TNF-αR) on the cell membranes effectively neutralized RANKL and TNF-α to prevent osteoclastogenesis and promote osteoblastogenesis, respectively, thus reversing the progression of osteoporosis in the ovariectomized (OVX) mouse model. These biomimetic nanodecoys provide an effective strategy for reconstructing the osteoclast/osteoblast balance and hold great potentials for the clinical management of postmenopausal osteoporosis.

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.

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.

T-Cell Mediated Inflammation in Postmenopausal Osteoporosis

Osteoporosis is the most prevalent metabolic bone disease that affects half the women in the sixth and seventh decade of life. Osteoporosis is characterized by uncoupled bone resorption that leads to low bone mass, compromised microarchitecture and structural deterioration that increases the likelihood of fracture with minimal trauma, known as fragility fractures. Several factors contribute to osteoporosis in men and women. In women, menopause - the cessation of ovarian function, is one of the leading causes of primary osteoporosis. Over the past three decades there has been growing appreciation that the adaptive immune system plays a fundamental role in the development of postmenopausal osteoporosis, both in humans and in mouse models. In this review, we highlight recent data on the interactions between T cells and the skeletal system in the context of postmenopausal osteoporosis. Finally, we review recent studies on the interventions to ameliorate osteoporosis.

Bone Marrow Mesenchymal Stromal Cells in Multiple Myeloma: Their Role as Active Contributors to Myeloma Progression

Multiple myeloma (MM) is a hematological malignancy of plasma cells that proliferate and accumulate within the bone marrow (BM). Work from many groups has made evident that the complex microenvironment of the BM plays a crucial role in myeloma progression and response to therapeutic agents. Within the cellular components of the BM, we will specifically focus on mesenchymal stromal cells (MSCs), which are known to interact with myeloma cells and the other components of the BM through cell to cell, soluble factors and, as more recently evidenced, through extracellular vesicles. Multiple structural and functional abnormalities have been found when characterizing MSCs derived from myeloma patients (MM-MSCs) and comparing them to those from healthy donors (HD-MSCs). Other studies have identified differences in genomic, mRNA, microRNA, histone modification, and DNA methylation profiles. We discuss these distinctive features shaping MM-MSCs and propose a model for the transition from HD-MSCs to MM-MSCs as a consequence of the interaction with myeloma cells. Finally, we review the contribution of MM-MSCs to several aspects of myeloma pathology, specifically to myeloma growth and survival, drug resistance, dissemination and homing, myeloma bone disease, and the induction of a pro-inflammatory and immunosuppressive microenvironment.

P53 regulation of osteoblast differentiation is mediated through specific microRNAs

In order to understand the role of the p53 tumor suppressor gene in microRNA expression during osteoblast differentiation, we used a screen to identify microRNAs that were altered in a p53-dependent manner. MicroRNAs from MC3T3-E1 preosteoblasts were isolated from day 0 (undifferentiated) and day 4 (differentiating) and compared to a p53 deficient MC3T3-E1 line treated similarly. Overall, one fourth of all the microRNAs tested showed a reduction of 0.6 fold, and a similar number of them were increased 1.7 fold with differentiation. P53 deficiency caused 40% reduction in expression of microRNAs in differentiating cells, while a small percent (0.03%) showed an increase. Changes in microRNAs were validated using real-time PCR and two microRNAs were selected for further analysis (miR-34b and miR-140). These two microRNAs were increased significantly during differentiation but showed a dramatic reduction in expression in a p53 deficient state. Stable expression of miR-34b and miR-140 in MC3T3-E1 cells resulted in decreases in cell proliferation rates when compared to control cells. There was a 4-fold increase in p53 levels with miR-34b expression and a less dramatic increase with miR-140. Putative target binding sites for bone specific transcription factors, Runx2 and Osterix, were found for miR-34b, while Runx2, beta catenin and type 1 collagen were found to be miR-140 targets. Western blot analyses and functional assays for the transcription factors Runx2, Osterix and Beta-catenin confirmed microRNA specific interactions. These studies provide evidence that p53 mediated regulation of osteoblast differentiation can also occur through specific microRNAs such as miR-34b and miR-140 that also directly target important bone specific genes.

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The p53 tumor suppressor gene regulates microRNA expression during in vitro osteoblast differentiation.

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miR34b and miR140 targets include several bone specific markers such as runx2, beta catenin, type 1 collagen and osterix.

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miR34b and miR140 overexpression inhibits osteoblast cell proliferation.

Transcriptional response of human articular chondrocytes treated with fibronectin fragments: an in vitro model of the osteoarthritis phenotype

OBJECTIVE

Fibronectin is a matrix protein that is fragmented during cartilage degradation in osteoarthritis (OA). Treatment of chondrocytes with fibronectin fragments (FN-f) has been used to model OA in vitro, but the system has not been fully characterized. This study sought to define the transcriptional response of chondrocytes to FN-f, and directly compare it to responses traditionally observed in OA.

DESIGN

Normal human femoral chondrocytes isolated from tissue donors were treated with either FN-f or PBS (control) for 3, 6, or 18 h. RNA-seq libraries were compared between time-matched FN-f and control samples in order to identify changes in gene expression over time. Differentially expressed genes were compared to a published OA gene set and used for pathway, transcription factor motif, and kinome analysis.

RESULTS

FN-f treatment resulted in 3,914 differentially expressed genes over the time course. Genes that are up- or downregulated in OA were significantly up- (P < 0.00001) or downregulated (P < 0.0004) in response to FN-f. Early response genes were involved in proinflammatory pathways, whereas many late response genes were involved in ferroptosis. The promoters of upregulated genes were enriched for NF-κB, AP-1, and IRF motifs. Highly upregulated kinases included CAMK1G, IRAK2, and the uncharacterized kinase DYRK3, while growth factor receptors TGFBR2 and FGFR2 were downregulated.

CONCLUSIONS

FN-f treatment of normal human articular chondrocytes recapitulated many key aspects of the OA chondrocyte phenotype. This in vitro model is promising for future OA studies, especially considering its compatibility with genomics and genome-editing techniques.

Multifactorial effects of hyperglycaemia, hyperinsulinemia and inflammation on bone remodelling in type 2 diabetes mellitus

Bones undergo continuous cycles of bone remodelling that rely on the balance between bone formation and resorption. This balance allows the bone to adapt to changes in mechanical loads and repair microdamages. However, this balance is susceptible to upset in various conditions, leading to impaired bone remodelling and abnormal bones. This is usually indicated by abnormal bone mineral density (BMD), an indicator of bone strength. Despite this, patients with type 2 diabetes mellitus (T2DM) exhibit normal to high BMD, yet still suffer from an increased risk of fractures. The activity of the bone cells is also altered as indicated by the reduced levels of bone turnover markers in T2DM observed in the circulation. The underlying mechanisms behind these skeletal outcomes in patients with T2DM remain unclear. This review summarises recent findings regarding inflammatory cytokine factors associated with T2DM to understand the mechanisms involved and considers potential therapeutic interventions.

Loss of interleukin-10 exacerbates early Type-1 diabetes-induced bone loss

Type-1 diabetes (T1D) increases systemic inflammation, bone loss, and risk for bone fractures. Levels of the anti-inflammatory cytokine interleukin-10 (IL-10) are decreased in T1D, however their role in T1D-induced osteoporosis is unknown. To address this, diabetes was induced in male IL-10 knockout (KO) and wild-type (WT) mice. Analyses of femur and vertebral trabecular bone volume fraction identified bone loss in T1D-WT mice at 4 and 12 weeks, which in T1D-IL-10-KO mice was further reduced at 4 weeks but not 12 weeks. IL-10 deficiency also increased the negative effects of T1D on cortical bone. Osteoblast marker osterix was decreased, while osteoclast markers were unchanged, suggesting that IL-10 promotes anabolic processes. MC3T3-E1 osteoblasts cultured under high glucose conditions displayed a decrease in osterix which was prevented by addition of IL-10. Taken together, our results suggest that IL-10 is important for promoting osteoblast maturation and reducing bone loss during early stages of T1D.

Stepwise strategy for generating osteoblasts from human pluripotent stem cells under fully defined xeno-free conditions with small-molecule inducers

Clinically relevant human induced pluripotent stem cell (hiPSC) derivatives require efficient protocols to differentiate hiPSCs into specific lineages. Here we developed a fully defined xeno-free strategy to direct hiPSCs toward osteoblasts within 21 days. The strategy successfully achieved the osteogenic induction of four independently derived hiPSC lines by a sequential use of combinations of small-molecule inducers. The induction first generated mesodermal cells, which subsequently recapitulated the developmental expression pattern of major osteoblast genes and proteins. Importantly, Col2.3-Cherry hiPSCs subjected to this strategy strongly expressed the cherry fluorescence that has been observed in bone-forming osteoblasts in vivo. Moreover, the protocol combined with a three-dimensional (3D) scaffold was suitable for the generation of a xeno-free 3D osteogenic system. Thus, our strategy offers a platform with significant advantages for bone biology studies and it will also contribute to clinical applications of hiPSCs to skeletal regenerative medicine.

Pyroptosis in Osteoblasts: A Novel Hypothesis Underlying the Pathogenesis of Osteoporosis

Osteoporosis has become a worldwide disease characterized by a reduction in bone mineral density and the alteration of bone architecture leading to an increased risk of fragility fractures. And an increasing number of studies have indicated that osteoblasts undergo a large number of programmed death events by many different causes in osteoporosis and release NLRP3 and interleukin (e.g., inflammatory factors), which play pivotal roles in contributing to excessive differentiation of osteoclasts and result in exaggerated bone resorption. NLRP3 is activated during pyroptosis and processes the precursors of IL-1β and IL-18 into mature forms, which are released into the extracellular milieu accompanied by cell rupture. All of these compounds are the classical factors of pyroptosis. The cellular effects of pyroptosis are commonly observed in osteoporosis. Although many previous studies have focused on the pathogenesis of these inflammatory factors in osteoporosis, pyroptosis has not been previously evaluated. In this review, pyroptosis is proposed as a novel hypothesis of osteoporosis pathogenesis for the first time, thus providing a new direction for the treatment of osteoporosis in the future.

Sexual dimorphisms in adult human neural, mesoderm-derived, and neural crest-derived stem cells

Sexual dimorphisms contribute, at least in part, to the severity and occurrence of a broad range of neurodegenerative, cardiovascular, and bone disorders. In addition to hormonal factors, increasing evidence suggests that stem cell-intrinsic mechanisms account for sex-specific differences in human physiology and pathology. Here, we discuss sex-related intrinsic mechanisms in adult stem cell populations, namely mesoderm-derived stem cells, neural stem cells (NSCs), and neural crest-derived stem cells (NCSCs), and their implications for stem cell differentiation and regeneration. We particularly focus on sex-specific differences in stem cell-mediated bone regeneration, in neuronal development, and in NSC-mediated neuroprotection. Moreover, we review our own recently published observations regarding the sex-dependent role of NF-κB-p65 in neuroprotection of human NCSC-derived neurons and sex differences in NCSC-related disorders, so-called neurocristopathies. These observations are in accordance with the increasing evidence pointing toward sex-specific differences in neurocristopathies and degenerative diseases like Parkinson's disease or osteoporosis. All findings discussed here indicate that sex-specific variability in stem cell biology may become a crucial parameter for the design of future treatment strategies.

Epigenetic drugs as new therapy for tumor necrosis factor-α-compromised bone healing

Impaired bone regeneration by excess inflammation leads to failure of bone healing. Current therapies display limited benefits making new treatments imperative. Our recent discoveries of the anti-inflammatory characteristics of bromodomain and extra terminal domain (BET) inhibitors, N-methylpyrrolidone (NMP) and N,N-Dimethylacetamide (DMA), implicate possible therapeutic use of epigenetic drugs in inflammation-impaired bone healing. Here, we investigated the effects of NMP and DMA on osteogenesis in vitro and ex vivo under the influence of TNFα, a key cytokine responsible for impaired fracture healing. NMP and DMA pre-treatment recovered TNFα-inhibited expression of essential osteoblastic genes, Alp, Runx2, and Osterix as well as mineralization in multipotent stem cells, but not in pre-osteoblasts and calvarial osteoblasts. The mechanism of action involves the recovery of TNFα-suppressed BMP-induced Smad signaling and the reduction of TNFα-triggered ERK pathway. In addition, ERK inhibitor treatment diminished the effect of TNFα on osteogenesis, which reinforces the role of ERK pathway in the adverse effect of TNFα. Furthermore, endochondral ossification was analyzed in an ex vivo bone culture model. TNFα largely abrogated BMP-promoted growth of mineralized bone while pre-treatment of NMP and DMA prevented the deleterious effect of TNFα. Taken together, these data shed light on developing low- affinity epigenetic drugs as new therapies for inflammation-compromised bone healing.

Targeting Adeno-Associated Virus Vectors for Local Delivery to Fractures and Systemic Delivery to the Skeleton

A panel of 18 recombinant adeno-associated virus (rAAV) variants, both natural and engineered, constitutively expressing Cre recombinase under the cytomegalovirus early enhancer/chicken β actin (CAG) promoter, were screened for their ability to transduce bone in Ai9 fluorescent reporter mice. Transgenic Cre-induced tdTomato expression served as a measure of transduction efficiency and alkaline phosphatase (AP) activity as an osteoblastic marker. Single injections of AAV8, AAV9, and AAV-DJ into midshaft tibial fractures yielded robust tdTomato expression in the callus. Next, the bone cell-specific promoters Sp7 and Col2.3 were tested to restrict Cre expression in an alternate model of systemic delivery by intravenous injection. Although CAG promoter constructs packaged into AAV8 produced high levels of tdTomato in the bone, liver, heart, spleen, and kidney, bone-specific promoter constructs restricted Cre expression to osseous tissues. AAV variants were further tested in vitro in a human osteoblast cell line (hFOB1.19), measuring GFP reporter expression by flow cytometry after 72 h. AAV2, AAV5, and AAV-DJ showed the highest transduction efficiency. In summary, we produced AAV vectors for selective and high-efficiency in vivo gene delivery to murine bone. The AAV8-Sp7-Cre vector has significant practical applications for inducing gene deletion postnatally in floxed mouse models.

Wnt4 signaling mediates protective effects of melatonin on new bone formation in an inflammatory environment

Growing evidence shows that the inhibitory effect of inflammatory cytokines on new bone formation by osteogenic precursor cells is a critical cause of net bone-density reduction. Melatonin has been proven to be a potential therapeutic candidate for osteoporosis. However, whether it is capable of antagonizing the suppressing effect of inflammatory cytokines on osteogenic precursor cells is so far elusive. In this study, using the cell culture system of human bone marrow stromal cells and MC3T3-E1 preosteoblasts, we recorded the following vital observations that provided insights of melatonin-induced bone formation: 1) melatonin induced bone formation in both normal and inflammatory conditions; 2) Wnt4 was essential for melatonin-induced bone formation in inflammatory stimulation; 3) melatonin- and Wnt4-induced bone formation occurred via activation of β-catenin and p38-JNK MAPK pathways by interaction with a distinct frizzled LDL receptor-related protein complex; 4) melatonin suppressed the inhibitory effect of NF-κB on osteogenesis in a Wnt4-dependent manner; and 5) melatonin induced Wnt4 expression through the ERK1/2-Pax2-Egr1 pathway. In summary, we showed a novel mechanism of melatonin-induced bone formation in an inflammatory environment. Melatonin-induced Wnt4 expression is essential for its osteoinductive effect and the inhibitory effect of NF-κB on bone formation. Our novel findings may provide useful information for its potential translational application.-Li, X., Li, Z., Wang, J., Li, Z., Cui, H., Dai, G., Chen, S., Zhang, M., Zheng, Z., Zhan, Z., Liu, H. Wnt4 signaling mediates protective effects of melatonin on new bone formation in an inflammatory environment.

Ctrp4, a new adipokine, promotes the differentiation of osteoblasts

Recent evidence suggests that adipokines are involved in the regulation of bone metabolism. Ctrp4 is a newly discovered member of the adipokine CTRP family. Studies have shown that Ctrp4 is involved in the regulation of tumor cell inflammatory signaling pathways and acts on the hypothalamus to regulate food intake, but its role in osteoblasts is not yet clear. In this study, we found that the expression of Ctrp4 in bone tissue was significantly decreased in the tail-suspended mouse, while that in ovariectomized-simulated osteoporosis mice decreased similarly, indicating that Ctrp4 was involved in osteogenesis regulation. We further isolated Alp-positive osteoblasts from the femur of tail-suspended rats and confirmed that the expression of Ctrp4, Bglap and Alp was down-regulated in the process of bone loss caused by tail suspension. In the process of inducing osteoblastic differentiation in vitro, Ctrp4 interfering significantly inhibited the expression of Alp and Bglap. In addition, inhibition of Ctrp4 resulted in decreased alkaline phosphatase expression and less alizarin red staining, indicating that Ctrp4 promoted osteogenic differentiation and osteoblasts mineralization. In conclusion, our results suggest that Ctrp4 is involved in bone metabolism regulation and promotes osteoblast differentiation, which may become a potential target for future intervention in bone metabolic diseases.

Myeloma Bone Disease: Update on Pathogenesis and Novel Treatment Strategies

Bone disease, including osteolytic lesions and/or osteoporosis, is a common feature of multiple myeloma (MM). The consequences of skeletal involvement are severe pain, spinal cord compressions, and bone fractures, which have a dramatic impact on patients’ quality of life and, ultimately, survival. During the past few years, several landmark studies significantly enhanced our insight into MM bone disease (MBD) by identifying molecular mechanisms leading to increased bone resorption due to osteoclast activation, and decreased bone formation by osteoblast inhibition. Bisphosphonates were the mainstay to prevent skeletal-related events in MM for almost two decades. Excitingly, the most recent approval of the receptor activator of NF-kappa B ligand (RANKL) inhibitor, denosumab, expanded treatment options for MBD, for patients with compromised renal function, in particular. In addition, several other bone-targeting agents, including bone anabolic drugs, are currently in preclinical and early clinical assessment. This review summarizes our up-to-date knowledge on the pathogenesis of MBD and discusses novel state-of-the-art treatment strategies that are likely to enter clinical practice in the near future.

Expression of the ectodomain-releasing protease ADAM17 is directly regulated by the osteosarcoma and bone-related transcription factor RUNX2

Osteoblast differentiation is controlled by transcription factor RUNX2 which temporally activates or represses several bone-related genes, including those encoding extracellular matrix proteins or factors that control cell-cell, and cell-matrix interactions. Cell-cell communication in the many skeletal pericellular micro-niches is critical for bone development and involves paracrine secretion of growth factors and morphogens. This paracrine signaling is in part regulated by "A Disintegrin And Metalloproteinase" (ADAM) proteins. These cell membrane-associated metalloproteinases support proteolytic release ("shedding") of protein ectodomains residing at the cell surface. We analyzed microarray and RNA-sequencing data for Adam genes and show that Adam17, Adam10, and Adam9 are stimulated during BMP2 mediated induction of osteogenic differentiation and are robustly expressed in human osteoblastic cells. ADAM17, which was initially identified as a tumor necrosis factor alpha (TNFα) converting enzyme also called (TACE), regulates TNFα-signaling pathway, which inhibits osteoblast differentiation. We demonstrate that Adam17 expression is suppressed by RUNX2 during osteoblast differentiation through the proximal Adam17 promoter region (-0.4 kb) containing two functional RUNX2 binding motifs. Adam17 downregulation during osteoblast differentiation is paralleled by increased RUNX2 expression, cytoplasmic-nuclear translocation and enhanced binding to the Adam17 proximal promoter. Forced expression of Adam17 reduces Runx2 and Alpl expression, indicating that Adam17 may negatively modulate osteoblast differentiation. These findings suggest a novel regulatory mechanism involving a reciprocal Runx2-Adam17 negative feedback loop to regulate progression through osteoblast differentiation. Our results suggest that RUNX2 may control paracrine signaling through regulation of ectodomain shedding at the cell surface of osteoblasts by directly suppressing Adam17 expression.

Osteoblast versus Adipocyte: Bone Marrow Microenvironment-Guided Epigenetic Control

The commitment and differentiation of bone marrow mesenchymal stem cells (MSCs) is tightly controlled by the local environment ensuring lineage differentiation balance and bone homeostasis. However, pathological conditions linked with osteoporosis have changed the bone marrow microenvironment, shifting MSCs’ fate to favor adipocytes over osteoblasts, and consequently leading to decreased bone mass with marrow fat accumulation. Multiple questions related to the underlying mechanisms remain to be answered. As recent findings have confirmed the fundamental role of the epigenetic mechanism in connecting environmental signals with gene expression and stem cell differentiation, a regulatory network in the bone marrow microenvironment, epigenetic modulation, gene expression, and MSC differentiation begins to emerge. This review discusses how pathological environmental factors affect MSCs’ fate by epigenetic modulating lineage-specific genes. We conclude that manipulating local environments and/or the epigenetic regulatory machinery that target the adipocyte differentiation pathway might be a therapeutic implication of bone loss diseases such as osteoporosis.

Altered Bone Remodeling in Psoriatic Disease: New Insights and Future Directions

Psoriatic arthritis (PsA) is an inflammatory rheumatic disorder that occurs in patients with psoriasis and predominantly affects musculoskeletal structures, skin, and nails. The etiology of PsA is not well understood but evidence supports an interplay of genetic, immunologic, and environmental factors which promote pathological bone remodeling and joint damage in PsA. Localized and systemic bone loss due to increased activity of osteoclasts is well established in PsA based on animal models and translational studies. In contrast, the mechanisms responsible for pathological bone remodeling in PsA remain enigmatic although new candidate molecules and pathways have been identified. Recent reports have revealed novel findings related to bone erosion and pathologic bone formation in PsA. Many associated risk factors and contributing molecular mechanisms have also been identified. In this review, we discuss new developments in the field, point out unresolved questions regarding the pathogenetic origins of the wide array of bone phenotypes in PsA, and discuss new directions for investigation.

ATF3 mediates the inhibitory action of TNF-α on osteoblast differentiation through the JNK signaling pathway

Tumor necrosis factor (TNF)-α, which is a proinflammatory cytokine, inhibits osteoblast differentiation under diverse inflammatory conditions. Activating transcription factor 3 (ATF3), which is a member of the ATF/cAMP response element-binding protein family of transcription factors, has been implicated in the regulation of cell proliferation and differentiation. However, the precise interactions between ATF3 and the TNF-α signaling pathway in the regulation of osteoblast differentiation remain unclear. In this study, we examined the role of ATF3 in the TNF-α-mediated inhibition of osteoblast differentiation and investigated the signaling pathways involved. The treatment of cells with TNF-α downregulated osteogenic markers, but significantly upregulated the expression of Atf3. The inhibition of Atf3 by small interfering RNAs rescued osteogenesis, which was inhibited by TNF-α. Conversely, the enforced expression of Atf3 enhanced the TNF-α-mediated inhibition of osteoblast differentiation, as revealed by the measurement of osteogenic markers and alkaline phosphatase staining. Mechanistically, TNF-α-induced Atf3 expression was significantly suppressed by the inhibition of the c-Jun N-terminal kinase (JNK) pathway. Furthermore, the overexpression of Atf3 did not affect the rescue effect that inhibiting TNF-α expression using a JNK inhibitor had on alkaline phosphatase activity and mineralization. Taken together, these results indicate that ATF3 mediates the inhibitory action of TNF-α on osteoblast differentiation and that the TNF-α-activated JNK pathway is responsible for the induction of Atf3 expression.

TNF-α inhibits SATB2 expression and osteoblast differentiation through NF-κB and MAPK pathways

Although the mechanisms of Tumor necrosis factor alpha (TNF-α) on facilitating osteoclast differentiation and bone resorption is well known, the mechanisms behind the suppression of the osteoblast differentiation from mesenchymal stem cells (MSCs) are still poorly understood. In this study, we observed a negative correlation between TNF-α levels and the expression of special AT-rich sequence-binding protein 2 (SATB2), a critical osteoblastogenesis transcription factor, in ovariectomy (OVX)-induced bone loss and IL-1-induced arthritis animal model. We found that TNF-α treatment inhibited mesenchymal cell line C2C12 osteoblast differentiation and sharply decreased BMP2-induced SATB2 expression. Upon TNF-α treatment, the activity of smad1/5/8 was inhibited, by contrast, extracellular signal-regulated kinase-1/2 (ERK1/2) and P38 was increased in C2C12 cells, the inhibitor of ERK1/2 (U0126) was found to abrogate the TNF-α inhibition of SATB2 expression. Furthermore, the NF-κB signaling pathway in C2C12 cells was significantly activated by the treatment of TNF-α, and TNF-α induced NF-κB directly binds to SATB2 promoter to suppress its expression. These results suggest that TNF-α suppresses SATB2 expression through activating NF-κB and MAPK signaling and depressing smad1/5/8 signaling, which contributes to the inhibition of osteoblast differentiation and might be potential therapeutic targets for inflammation-induced bone loss.

Tet-Mediated DNA Demethylation Is Required for SWI/SNF-Dependent Chromatin Remodeling and Histone-Modifying Activities That Trigger Expression of the Sp7 Osteoblast Master Gene during Mesenchymal Lineage Commitment

Here we assess histone modification, chromatin remodeling, and DNA methylation processes that coordinately control the expression of the bone master transcription factor Sp7 (osterix) during mesenchymal lineage commitment in mammalian cells. We find that Sp7 gene silencing is mediated by DNA methyltransferase1/3 (DNMT1/3)-, histone deacetylase 1/2/4 (HDAC1/2/4)-, Setdb1/Suv39h1-, and Ezh1/2-containing complexes. In contrast, Sp7 gene activation involves changes in histone modifications, accompanied by decreased nucleosome enrichment and DNA demethylation mediated by SWI/SNF- and Tet1/Tet2-containing complexes, respectively. Inhibition of DNA methylation triggers changes in the histone modification profile and chromatin-remodeling events leading to Sp7 gene expression. Tet1/Tet2 silencing prevents Sp7 expression during osteoblast differentiation as it impairs DNA demethylation and alters the recruitment of histone methylase (COMPASS)-, histone demethylase (Jmjd2a/Jmjd3)-, and SWI/SNF-containing complexes to the Sp7 promoter. The dissection of these interconnected epigenetic mechanisms that govern Sp7 gene activation reveals a hierarchical process where regulatory components mediating DNA demethylation play a leading role.

[Tumor necrosis factor-α regulates the osteogenic differentiation of bone marrow mesenchymal stem cells in chronic periodontitis]

Bone marrow mesenchymal stem cells (BMSCs) and ideal adult stem cells for alveolar bone regeneration considerably help restore the structure and function of the periodontium and promote the healing of periodontal disease. Thus, BMSC features, especially the mechanism of osteogenic differentiation, has recently become a research hotspot. Tumor necrosis factor-α (TNF-α), which is the main factor in the periodontal inflammatory microenvironment, is directly related to the osteogenic differentiation of BMSCs. Exploring the TNF-α-regulated differentiation mechanism of BMSCs aids in the search for new treatment targets. Such investigation also promotes the development of stem cell therapy for periodontal diseases. This article aims to describe the potential of TNF-α in regulating the osteogenic differentiation of stem cells.

Loss of Cbl-PI3K interaction modulates the periosteal response to fracture by enhancing osteogenic commitment and differentiation

The periosteum contains multipotent skeletal progenitors that contribute to bone repair. The signaling pathways regulating the response of periosteal cells to fracture are largely unknown. Phosphatidylinositol-3 Kinase (PI3K), a prominent lipid kinase, is a major signaling protein downstream of several factors that regulate osteoblast differentiation. Cbl is an E3 ubiquitin ligase and a major adaptor protein that binds to the p85 regulatory subunit and modulates PI3K activity. Substitution of tyrosine 737 to phenylalanine (Y737F) in Cbl abolishes the interaction between Cbl and p85 subunit without affecting the Cbl's ubiquitin ligase function. Here, we investigated the role of PI3K signaling during the very early stages of fracture healing using Osterix^RFP reporter mice. We found that the absence of PI3K regulation by Cbl resulted in robust periosteal thickening, with increased proliferation of periosteal cells. While the multipotent properties of periosteal progenitors to differentiate into chondrocytes and adipocytes did not change, osteogenic differentiation in the absence of Cbl-PI3K interaction was highly augmented. The increased stability and nuclear localization of Osterix observed in periosteal cells lacking Cbl-PI3K interaction may explain this enhanced osteogenic differentiation since the expression of Osterix transcriptional target genes including osteocalcin and BSP are increased in YF cells. Overall, our findings highlight a hitherto unexplored and novel role for Cbl and PI3K in modulating the osteogenic response of periosteal cells during the early stages of fracture repair.

NF-κB as a Therapeutic Target in Inflammatory-Associated Bone Diseases

Inflammation is a defensive mechanism for pathogen clearance and maintaining tissue homeostasis. In the skeletal system, inflammation is closely associated with many bone disorders including fractures, nonunions, periprosthetic osteolysis (bone loss around orthopedic implants), and osteoporosis. Acute inflammation is a critical step for proper bone-healing and bone-remodeling processes. On the other hand, chronic inflammation with excessive proinflammatory cytokines disrupts the balance of skeletal homeostasis involving osteoblastic (bone formation) and osteoclastic (bone resorption) activities. NF-κB is a transcriptional factor that regulates the inflammatory response and bone-remodeling processes in both bone-forming and bone-resorption cells. In vitro and in vivo evidences suggest that NF-κB is an important potential therapeutic target for inflammation-associated bone disorders by modulating inflammation and bone-remodeling process simultaneously. The challenges of NF-κB-targeting therapy in bone disorders include: (1) the complexity of canonical and noncanonical NF-κB pathways; (2) the fundamental roles of NF-κB-mediated signaling for bone regeneration at earlier phases of tissue damage and acute inflammation; and (3) the potential toxic effects on nontargeted cells such as lymphocytes. Recent developments of novel inhibitors with differential approaches to modulate NF-κB activity, and the controlled release (local) or bone-targeting drug delivery (systemic) strategies, have largely increased the translational application of NF-κB therapy in bone disorders. Taken together, temporal modulation of NF-κB pathways with the combination of recent advanced bone-targeting drug delivery techniques is a highly translational strategy to reestablish homeostasis in the skeletal system.

DHEA promotes osteoblast differentiation by regulating the expression of osteoblast-related genes and Foxp3(+) regulatory T cells

Several studies have reported that dehydroepiandrosterone (DHEA) promotes osteoblast proliferation and inhibits osteoblast apoptosis and that DHEA inhibits osteoclast maturation. However, whether DHEA regulates osteoblast differentiation remains unclear. The present study first examined the effect of DHEA on bone morphology in vivo. DHEA was found to increase bone volume (BV), bone mineral density (BMD), and the number of trabeculae in bone (Th.N) and it was found to decrease trabecular spacing in bone (Th.sp) in ovariectomized (OVX) mice. Next, the effect of DHEA on osteoblast differentiation was examined in vitro and osteoblastogenesis-related marker genes, such as Runx2, Osterix, Collagen1, and Osteocalcin, were also detected. DHEA increased osteoblast production in mesenchymal stem cells (MSCs) cultured in osteoblastogenic medium, and DHEA increased the expression of Runx2 and osterix, thereby increasing the expression of osteocalcin and collagen1. Immune cells and bone interact, so changes in immune cells were detected in vivo. DHEA increased the number of Foxp3(+) regulatory T cells (Tregs) in the spleen but it did not affect CTLA-4 or IL-10. When MSCs were treated with DHEA in the presence of Tregs, alkaline phosphatase (ALP) activity increased. Osteoblasts and adipocytes are both generated by MSCs. If osteoblast differentiation increases, adipocyte differentiation will decrease, and the reverse also holds true. DHEA was found to increase the number of adipocytes in osteoblastogenic medium but it had no effect on the number of adipocytes and expression of PPARγ mRNA in adipogenic medium. This finding suggests that osteoblasts may be involved in adipocyte production. In conclusion, the current results suggest that DHEA can improve postmenopausal osteoporosis (PMO) by up-regulating osteoblast differentiation via the up-regulation of the expression of osteoblastogenesis-related genes and via an increase in Foxp3(+) Tregs.

Ossotide promotes cell differentiation of human osteoblasts from osteogenesis imperfecta patients by up-regulating miR-145

Ossotide as an effective bone formation compound preparation has been proved to promote osteoblasts differentiation. MiR-145 is significantly decreased in osteogenesis imperfecta (OI) patients, but it is still unknown whether ossotide performed its effect by regulating miR-145. In this study, we investigated the effect of ossotide on regulating miR-145 expression and osteoblasts differentiation. The primary osteoblasts cells were isolated from OI patients and then cultured with different concentrations (0, 25, 50, 100, 200μg/l) of ossotide. The cell proliferation was detected with CCK-8 Elisa kit after ossotide treatment. The level of miR-145 expression was determined using qRT-PCR. In order to study whether ossotide up regulated miR-145, miR-145 mimic and miR-145 inhibitor were used to up regulate and down regulate the miR-145 levels in osteoblasts. The expressions of Runx2, Osx, β-catenin, TCF-1 were detected using Western blot and qRT-PCR. We observed that miR-145 was up regulated by ossotide treatment in miR-145 mimic or miR-145 inhibitor treated osteoblasts. What's more, up regulated miR-145 increased the expression of osteoblasts differentiation regulated protein Runx2 and Osx. In addition, Wnt signaling related β-catenin, TCF-1 were activated by up-regulated miR-145 which was induced by ossotide treatment. In summary, ossotide induced cell differentiation and Wnt signaling activation in osteoblasts by up regulating miR-145.

The effects of dopamine receptor 2 expression on B cells on bone metabolism and TNF-α levels in rheumatoid arthritis

Background

Dopamine receptor 2 (DR2) expressions on B cells from Rheumatoid arthritis (RA) patients has been found to be negatively correlated with disease activity and can potentially predict the response to treatment. This study aimed to investigate the role of B cell DR2 expression on bone remodeling in RA.

Methods

Patients with RA (n = 14) or osteoarthritis (OA; n = 12), and healthy controls (n = 12) were recruited for this study. Dopamine receptor (DR) 2 expression was assessed using flow cytometry. Pro-inflammatory cytokines, including interleuin(IL)-1β, IL-6, IL-17, and tumor necrosis factor(TNF)-α, and bone turnovers, including osteocalcin (OC),serum procollagen type I N propeptide (PINP), C-terminal telopeptide of type I collagen (β-CTX), collagen type I cross-linked telopeptide (ICTP), as well as matrix metalloproteinase-3 (MMP-3) and osteoprotegerin (OPG) were measured by electrochemiluminescence, chemiluminescence, or enzyme-linked immunosorbent assay. DR2 expression on synovial B cells from 4 RA patients and 3 OA patients was detected by immunofluorescence.

Results

There were more DR2⁺CD19⁺ B cells in synovial tissues from RA patients than in those from OA patients. The frequency of peripheral B cells that expressed DR2 was positively correlated with plasma TNF-α level. Levels of ICTP and MMP-3 were significantly higher, and OPG were lower in RA patients compared to those in the OA group and healthy controls (all P < 0.05).

Conclusion

The frequency of B cells that expressed DR2 showed a correlation with levels of the pro-inflammatory cytokine TNF-α. DR2⁺CD19⁺ B cells in synovial tissues might have a role in bone metabolism and TNF-α production.

Gout increases risk of fracture: A nationwide population-based cohort study

There is still debate on whether high uric acid increases bone mineral density (BMD) against osteoporotic fracture or bone resorption caused by gout inflammation. This study aimed to evaluate whether gout offers a protective effect on bone health or not. We conducted a nationwide population-based retrospective cohort study to evaluate the association between gout history and risk factors of fracture.A retrospective cohort study was designed using the claim data from Longitudinal Health Insurance Database (LHID). A total of 43,647 subjects with gout and a cohort of 87,294 comparison subjects without gout were matched in terms of age and sex between 2001 and 2009, and the data were followed until December 31, 2011. The primary outcome of the study was the fracture incidence, and the impacts of gout on fracture risks were analyzed using the Cox proportional hazards model.After an 11-year follow-up period, 6992 and 11,412 incidents of fracture were reported in gout and comparison cohorts, respectively. The overall incidence rate of fracture in individuals with gout was nearly 23%, which was higher than that in individuals without gout (252 vs 205 per 10,000 person-years) at an adjusted hazard ratio of 1.17 (95% confidence interval = 1.14-1.21). Age, sex, and fracture-associated comorbidities were adjusted accordingly. As for fracture locations, patients with gout were found at significant higher fracture risks for upper/lower limbs and spine fractures. In gout patient, the user of allopurinol or benzbromarone has significantly lower risk of facture than nonusers.Gout history is considered as a risk factor for fractures, particularly in female individuals and fracture sites located at the spine or upper/lower limbs.

Anti-IL-20 monoclonal antibody promotes bone fracture healing through regulating IL-20-mediated osteoblastogenesis

Bone loss and skeletal fragility in bone fracture are caused by an imbalance in bone remodeling. The current challenge in bone fracture healing is to promote osteoblastogenesis and bone formation. We aimed to explore the role of IL-20 in osteoblastogenesis, osteoblast differentiation and bone fracture. Serum IL-20 was significantly correlated with serum sclerostin in patients with bone fracture. In a mouse model, anti-IL-20 monoclonal antibody (mAb) 7E increased bone formation during fracture healing. In vitro, IL-20 inhibited osteoblastogenesis by upregulating sclerostin, and downregulating osterix (OSX), RUNX2, and osteoprotegerin (OPG). IL-20R1 deficiency attenuated IL-20-mediated inhibition of osteoblast differentiation and maturation and reduced the healing time after a bone fracture. We conclude that IL-20 affects bone formation and downregulates osteoblastogenesis by modulating sclerostin, OSX, RUNX2, and OPG on osteoblasts. Our results demonstrated that IL-20 is involved in osteoregulation and anti-IL-20 mAb is a potential therapeutic for treating bone fracture or metabolic bone diseases.

The Role of Bone Marrow Microenvironment in Governing the Balance between Osteoblastogenesis and Adipogenesis

In the adult bone marrow, osteoblasts and adipocytes share a common precursor called mesenchymal stem cells (MSCs). The plasticity between the two lineages has been confirmed over the past decades, and has important implications in the etiology of bone diseases such as osteoporosis, which involves an imbalance between osteoblasts and adipocytes. The commitment and differentiation of bone marrow (BM) MSCs is tightly controlled by the local environment that maintains a balance between osteoblast lineage and adipocyte. However, pathological conditions linked to osteoporosis can change the BM microenvironment and shift the MSC fate to favor adipocytes over osteoblasts, and consequently decrease bone mass with marrow fat accumulation. This review discusses the changes that occur in the BM microenvironment under pathological conditions, and how these changes affect MSC fate. We suggest that manipulating local environments could have therapeutic implications to avoid bone loss in diseases like osteoporosis.

Role of Cbl-PI3K Interaction during Skeletal Remodeling in a Murine Model of Bone Repair

Mice in which Cbl is unable to bind PI3K (YF mice) display increased bone volume due to enhanced bone formation and repressed bone resorption during normal bone homeostasis. We investigated the effects of disrupted Cbl-PI3K interaction on fracture healing to determine whether this interaction has an effect on bone repair. Mid-diaphyseal femoral fractures induced in wild type (WT) and YF mice were temporally evaluated via micro-computed tomography scans, biomechanical testing, histological and histomorphometric analyses. Imaging analyses revealed no change in soft callus formation, increased bony callus formation, and delayed callus remodeling in YF mice compared to WT mice. Histomorphometric analyses showed significantly increased osteoblast surface per bone surface and osteoclast numbers in the calluses of YF fractured mice, as well as increased incorporation of dynamic bone labels. Furthermore, using laser capture micro-dissection of the fracture callus we found that cells lacking Cbl-PI3K interaction have higher expression of Osterix, TRAP, and Cathepsin K. We also found increased expression of genes involved in propagating PI3K signaling in cells isolated from the YF fracture callus, suggesting that the lack of Cbl-PI3K interaction perhaps results in enhanced PI3K signaling, leading to increased bone formation, but delayed remodeling in the healing femora.

Sharpin Controls Osteogenic Differentiation of Mesenchymal Bone Marrow Cells

The cytosolic protein Sharpin is a component of the linear ubiquitin chain assembly complex, which regulates NF-κB signaling in response to specific ligands, such as TNF-α. Its inactivating mutation in chronic proliferative dermatitis mutation (Cpdm) mice causes multiorgan inflammation, yet this phenotype is not transferable into wild-type mice by hematopoietic stem cell transfer. Recent evidence demonstrated that Cpdm mice additionally display low bone mass, and that this osteopenia is corrected by Tnf deletion. Because the cellular mechanism underlying this pathology, however, was still undefined, we performed a thorough skeletal phenotyping of Cpdm mice on the basis of nondecalcified histology and cellular and dynamic histomorphometry. We show that the trabecular and cortical osteopenia in Cpdm mice is solely explained by impaired bone formation, whereas osteoclastogenesis is unaffected. Consistently, Cpdm primary calvarial cells display reduced osteogenic capacity ex vivo, and the same was observed with CD11b(-) bone marrow cells. Unexpectedly, short-term treatment of these cultures with TNF-α did not reveal an impaired molecular response in the absence of Sharpin. Instead, genome-wide and gene-specific expression analyses revealed that Cpdm mesenchymal cells display increased responsiveness toward TNF-α-induced expression of specific cytokines, such as CXCL5, IL-1β, and IL-6. Therefore, our data not only demonstrate that the skeletal defects of Cpdm mice are specifically caused by impaired differentiation of osteoprogenitor cells, they also suggest that increased cytokine expression in mesenchymal bone marrow cells contributes to the inflammatory phenotype of Cpdm mice.