Synergistic inhibition of Wnt pathway by HIF-1α and osteoblast-specific transcription factor osterix (Osx) in osteoblasts

Spontaneous Spheroids of hUC-MSCs Regulate Osteogenic Differentiation for Enhancing Osteogenesis

Stem cells play a critical role in the regeneration process by proliferating and differentiating to form new bone tissue. However, stem cells tend to lose their stemness and pluripotency during in vitro expansion, resulting in reduced bone regeneration capacity after osteogenic induction. Our aim is to enhance the osteogenic impact of human umbilical cord-derived mesenchymal stromal cells (hUC-MSCs) through spontaneous spheroid in vitro. The pluripotency and osteogenesis-related genes up-regulated in hUC-MSCs can be enhanced in spontaneous spheroids in vitro. For in vivo testing, spontaneous spheroids were transplanted into mice using beta-tricalcium phosphate as a scaffold. Transplant samples were stained using hematoxylin and eosin (HE), immunohistochemistry, and TRAP staining. The samples showed new bone formation, upregulated SP7 and OCN expression, and more vigorous bone metabolism in the Sph-OI group than the other groups. However, new bone formation was mainly immature bone. Overall, our findings demonstrate that hUC-MSC spheroids possess remarkable pluripotency, with the spontaneous spheroids formed following osteogenic induction exhibiting enhanced osteogenic differentiation potential and bone regeneration capacity. However, optimizing the osteogenic differentiation process and elucidating the underlying mechanisms of bone regeneration are critical scientific issues that urgently need to be addressed to enable its application in bone regeneration.

WDR36 inhibits the osteogenic differentiation and migration of periodontal ligament stem cells

BACKGROUND

Periodontitis is an inflammatory disease caused by the host's immune response and various interactions between pathogens, which lead to the loss of connective tissue and bone. In recent years, mesenchymal stem cell (SC) transplantation technology has become a research hotspot, which can form periodontal ligament, cementum, and alveolar bone through proliferation and differentiation.

AIM

To elucidate the regulatory effects of WD repeat-containing protein 36 (WDR36) on the senescence, migration, and osteogenic differentiation of periodontal ligament SCs (PDLSCs).

METHODS

The migration and chemotaxis of PDLSCs were detected by the scratch-wound migration test and transwell chemotaxis test. Alkaline phosphatase (ALP) activity, Alizarin red staining, calcium content, and real-time reverse transcription polymerase chain reaction (RT-qPCR) of key transcription factors were used to detect the osteogenic differentiation function of PDLSCs. Cell senescence was determined by senescence-associated β-galactosidase staining.

RESULTS

The 24-hour and 48-hour scratch-wound migration test and 48-hour transwell chemotaxis test showed that overexpression of WDR36 inhibited the migration/chemotaxis of PDLSCs. Simultaneously, WDR36 depletion promoted the migration/chemotaxis of PDLSCs. The results of ALP activity, Alizarin red staining, calcium content, and RT-qPCR showed that overexpression of WDR36 inhibited the osteogenic differentiation of PDLSCs, and WDR36 depletion promoted the osteogenic differentiation of PDLSCs. Senescence-associated β-galactosidase staining showed that 0.1 μg/mL icariin (ICA) and overexpression of WDR36 inhibited the senescence of PDLSCs, and WDR36 depletion promoted the osteogenic differentiation of PDLSCs.

CONCLUSION

WDR36 inhibits the migration and chemotaxis, osteogenic differentiation, and senescence of PDLSCs; 0.1 μg/mL ICA inhibits the senescence of PDLSCs. Therefore, WDR36 might serve as a target for periodontal tissue regeneration and the treatment of periodontitis.

Hypoxia Promotes the Stemness of Mesangiogenic Progenitor Cells and Prevents Osteogenic but not Angiogenic Differentiation

The stem cell niche in the bone marrow is a hypoxic environment, where the low oxygen tension preserves the pluripotency of stem cells. We have identified mesangiogenic progenitor cells (MPC) exhibiting angiogenic and mesenchymal differentiation capabilities in vitro. The effect of hypoxia on MPC has not been previously explored. In this study, MPCs were isolated from volunteers' bone marrow and cultured under both normoxic and hypoxic conditions (3% O2). MPCs maintained their characteristic morphology and surface marker expression (CD18 + CD31 + CD90-CD73-) under hypoxia. However, hypoxic conditions led to reduced MPC proliferation in primary cultures and hindered their differentiation into mesenchymal stem cells (MSCs) upon exposure to differentiative medium. First passage MSCs derived from MPC appeared unaffected by hypoxia, exhibiting no discernible differences in proliferative potential or cell cycle. However, hypoxia impeded the subsequent osteogenic differentiation of MSCs, as evidenced by decreased hydroxyapatite deposition. Conversely, hypoxia did not impact the angiogenic differentiation potential of MPCs, as demonstrated by spheroid-based assays revealing comparable angiogenic sprouting and tube-like formation capabilities under both hypoxic and normoxic conditions. These findings indicate that hypoxia preserves the stemness phenotype of MPCs, inhibits their differentiation into MSCs, and hampers their osteogenic maturation while leaving their angiogenic potential unaffected. Our study sheds light on the intricate effects of hypoxia on bone marrow-derived MPCs and their differentiation pathways.

Differential but complementary roles of HIF-1α and HIF-2α in the regulation of bone homeostasis

Bone is a highly dynamic tissue undergoing continuous formation and resorption. Here, we investigated differential but complementary roles of hypoxia-inducible factor (HIF)-1α and HIF-2α in regulating bone remodeling. Using RNA-seq analysis, we identified that specific genes involved in regulating osteoblast differentiation were similarly but slightly differently governed by HIF-1α and HIF-2α. We found that increased HIF-1α expression inhibited osteoblast differentiation via inhibiting RUNX2 function by upregulation of Twist2, confirmed using Hif1a conditional knockout (KO) mouse. Ectopic expression of HIF-1α via adenovirus transduction resulted in the increased expression and activity of RANKL, while knockdown of Hif1a expression via siRNA or osteoblast-specific depletion of Hif1a in conditional KO mice had no discernible effect on osteoblast-mediated osteoclast activation. The unexpected outcome was elucidated by the upregulation of HIF-2α upon Hif1a overexpression, providing evidence that Hif2a is a transcriptional target of HIF-1α in regulating RANKL expression, verified through an experiment of HIF-2α knockdown after HIF-1α overexpression. The above results were validated in an ovariectomized- and aging-induced osteoporosis model using Hif1a conditional KO mice. Our findings conclude that HIF-1α plays an important role in regulating bone homeostasis by controlling osteoblast differentiation, and in influencing osteoclast formation through the regulation of RANKL secretion via HIF-2α modulation.

Cell signaling and transcriptional regulation of osteoblast lineage commitment, differentiation, bone formation, and homeostasis

The initiation of osteogenesis primarily occurs as mesenchymal stem cells undergo differentiation into osteoblasts. This differentiation process plays a crucial role in bone formation and homeostasis and is regulated by two intricate processes: cell signal transduction and transcriptional gene expression. Various essential cell signaling pathways, including Wnt, BMP, TGF-β, Hedgehog, PTH, FGF, Ephrin, Notch, Hippo, and Piezo1/2, play a critical role in facilitating osteoblast differentiation, bone formation, and bone homeostasis. Key transcriptional factors in this differentiation process include Runx2, Cbfβ, Runx1, Osterix, ATF4, SATB2, and TAZ/YAP. Furthermore, a diverse array of epigenetic factors also plays critical roles in osteoblast differentiation, bone formation, and homeostasis at the transcriptional level. This review provides an overview of the latest developments and current comprehension concerning the pathways of cell signaling, regulation of hormones, and transcriptional regulation of genes involved in the commitment and differentiation of osteoblast lineage, as well as in bone formation and maintenance of homeostasis. The paper also reviews epigenetic regulation of osteoblast differentiation via mechanisms, such as histone and DNA modifications. Additionally, we summarize the latest developments in osteoblast biology spurred by recent advancements in various modern technologies and bioinformatics. By synthesizing these insights into a comprehensive understanding of osteoblast differentiation, this review provides further clarification of the mechanisms underlying osteoblast lineage commitment, differentiation, and bone formation, and highlights potential new therapeutic applications for the treatment of bone diseases.

The Bioactive Compounds of Epimedium and Their Potential Mechanism of Action in Treating Osteoporosis: A Network Pharmacology and Experimental Validation Study

Osteoporosis is a global health challenge characterized by bone loss and microstructure deterioration, which urgently requires the development of safer and more effective treatments due to the significant adverse effects and limitations of existing drugs for long-term treatment. Traditional Chinese medicine, like Epimedium, offers fewer side effects and has been used to treat osteoporosis, yet its active compounds and pharmacological mechanisms remain unclear. In this study, 65 potential active compounds, 258 potential target proteins, and 488 pathways of Epimedium were identified through network pharmacology analysis. Further network analysis and review of the literature identified six potential active compounds and HIF-1α for subsequent experimental validation. In vitro experiments confirmed that 2″-O-RhamnosylIcariside II is the most effective compound among the six potential active compounds. It can promote osteoblast differentiation, bind with HIF-1α, and inhibit both HIF-1α gene and protein expression, as well as enhance COL1A1 protein expression under hypoxic conditions. In vivo experiments demonstrated its ability to improve bone microstructures and reduce bone loss by decreasing bone marrow adipose tissue, enhancing bone formation, and suppressing HIF-1α protein expression. This study is the first to describe the therapeutic effects of 2-O-RhamnosylIcariside II on osteoporosis, which was done, specifically, through a mechanism that targets and inhibits HIF-1α. This study provides a scientific basis for the clinical application of Epimedium and offers a new candidate drug for the treatment of osteoporosis. Additionally, it provides new evidence supporting HIF-1α as a therapeutic target for osteoporosis.

Hypoxia inducible factor-1α related mechanism and TCM intervention in process of early fracture healing

As a common clinical disease, fracture is often accompanied by pain, swelling, bleeding as well as other symptoms and has a high disability rate, even threatening life, seriously endangering patients' physical and psychological health and quality of life. Medical practitioners take many strategies for the treatment of fracture healing, including Traditional Chinese Medicine (TCM). In the early stage of fracture healing, the local fracture is often in a state of hypoxia, accompanied by the expression of hypoxia inducible factor-1α (HIF-1α), which is beneficial to wound healing. Through literature mining, we thought that hypoxia, HIF-1α and downstream factors affected the mechanism of fracture healing, as well as dominated this process. Therefore, we reviewed the local characteristics and related signaling pathways involved in the fracture healing process and summarized the intervention of TCM on these mechanisms, in order to inspirit the new strategy for fracture healing, as well as elaborate on the possible principles of TCM in treating fractures based on the HIF molecular mechanism.

HIF-1α and periodontitis: Novel insights linking host-environment interplay to periodontal phenotypes

Periodontitis, the sixth most prevalent epidemic disease globally, profoundly impacts oral aesthetics and masticatory functionality. Hypoxia-inducible factor-1α (HIF-1α), an oxygen-dependent transcriptional activator, has emerged as a pivotal regulator in periodontal tissue and alveolar bone metabolism, exerts critical functions in angiogenesis, erythropoiesis, energy metabolism, and cell fate determination. Numerous essential phenotypes regulated by HIF are intricately associated with bone metabolism in periodontal tissues. Extensive investigations have highlighted the central role of HIF and its downstream target genes and pathways in the coupling of angiogenesis and osteogenesis. Within this concise perspective, we comprehensively review the cellular phenotypic alterations and microenvironmental dynamics linking HIF to periodontitis. We analyze current research on the HIF pathway, elucidating its impact on bone repair and regeneration, while unraveling the involved cellular and molecular mechanisms. Furthermore, we briefly discuss the potential application of targeted interventions aimed at HIF in the field of bone tissue regeneration engineering. This review expands our biological understanding of the intricate relationship between the HIF gene and bone angiogenesis in periodontitis and offers valuable insights for the development of innovative therapies to expedite bone repair and regeneration.

HIF-1α increases the osteogenic capacity of ADSCs by coupling angiogenesis and osteogenesis via the HIF-1α/VEGF/AKT/mTOR signaling pathway

BACKGROUND

Stabilization and increased activity of hypoxia-inducible factor 1-α (HIF-1α) can directly increase cancellous bone formation and play an essential role in bone modeling and remodeling. However, whether an increased HIF-1α expression in adipose-derived stem cells (ADSCs) increases osteogenic capacity and promotes bone regeneration is not known.

RESULTS

In this study, ADSCs transfected with small interfering RNA and HIF-1α overexpression plasmid were established to investigate the proliferation, migration, adhesion, and osteogenic capacity of ADSCs and the angiogenic ability of human umbilical vein endothelial cells (HUVECs). Overexpression of HIF-1α could promote the biological functions of ADSCs, and the angiogenic ability of HUVECs. Western blotting showed that the protein levels of osteogenesis-related factors were increased when HIF-1α was overexpressed. Furthermore, the influence of upregulation of HIF-1α in ADSC sheets on osseointegration was evaluated using a Sprague-Dawley (SD) rats implant model, in which the bone mass and osteoid mineralization speed were evaluated by radiological and histological analysis. The overexpression of HIF-1α in ADSCs enhanced bone remodeling and osseointegration around titanium implants. However, transfecting the small interfering RNA (siRNA) of HIF-1α in ADSCs attenuated their osteogenic and angiogenic capacity. Finally, it was confirmed in vitro that HIF-1α promotes osteogenic differentiation and the biological functions in ADSCs via the VEGF/AKT/mTOR pathway.

CONCLUSIONS

This study demonstrates that HIF-1α has a critical ability to promote osteogenic differentiation in ADSCs by coupling osteogenesis and angiogenesis via the VEGF/AKT/mTOR signaling pathway, which in turn increases osteointegration and bone formation around titanium implants.

Depletion of enhancer zeste homolog 2 (EZH2) directs transcription factors associated with T cell differentiation through epigenetic regulation of Yin Yang 1(YY1) in combating non-small cell lung cancer (NSCLC)

Non-Small Cell Lung Cancer (NSCLC) is the leading cause of death in all countries alike. In the current study, we have found out that Histone H3Lys4trimethylation is abnormal on YY1 in CD4⁺T Helper (T_H) cells of NSCLC patients which is evident by Histone H3Lys27 trimethylation mediated via EZH2. We investigated the status of Yin Yang 1 (YY1) and the involvement of certain transcription factors that lead to tumorigenesis after depleting endogenous EZH2 in vitro by CRISPR/Cas9 in the CD4⁺T_H1-or-T_H2-polarized cells isolated initially as CD4⁺T_H0 cells from the PBMC of the control subjects and patients suffering from NSCLC. After depletion of endogenous EZH2, RT-qPCR based mRNA expression analysis showed that there was an increase in the expression of T_H1 specific genes and a decrease in the expression of T_H2 specific genes in NSCLC patients CD4⁺T_H cells. We can conclude that this group of NSCLC patients may have the tendency at least in vitro to elucidate adaptive/protective immunity through the depletion of endogenous EZH2 along with the reduction in the expression of YY1. Moreover, depletion of EZH2 not only suppressed the CD4⁺CD25⁺FOXP3⁺Regulatory T cells (Treg) but also it aided the generation of CD8⁺Cytotoxic T Lymphocytes (CTL) which were involved in killing of the NSCLC cells. Thus the transcription factors involved in EZH2 mediated T cell differentiation linked to malignancies offers us an appealing avenue of targeted therapeutic intervention for NSCLC.

Intracellular glucose starvation inhibits osteogenic differentiation in human periodontal ligament cells

BACKGROUND

Periodontal ligament cells (PDLCs), as mesenchymal cells in the oral cavity, are closely linked to periodontal tissue regeneration. However, the effect of local glucose deficiency on periodontal tissue regeneration, such as immediately post-surgery, remains unknown.

OBJECTIVE

In the present study, we investigated the effect of a low-glucose environment on the proliferation and osteogenic differentiation of PDLCs.

MATERIALS AND METHODS

We used media with five glucose concentrations (100, 75, 50, 25, and 0 mg/dL) and focused on the effects of a low-glucose environment on the proliferation, osteogenic differentiation, and autophagy of PDLCs. Additionally, we focused on changes in lactate production in a low-glucose environment and investigated the involvement of lactate with AZD3965, a monocarboxylate transporter-1 (MCT-1) inhibitor.

RESULTS

The low-glucose environment inhibited PDLCs proliferation, migration, and osteogenic differentiation, and induced the expression of the autophagy-related factors LC3 and p62. Lactate and ATP production were decreased under low-glucose conditions. The addition of AZD3965 (MCT-1 inhibitor) in normal glucose conditions caused a similar trend as in low-glucose conditions on PDLCs.

CONCLUSION

Our results suggest lactate production through glucose metabolism in the osteogenic differentiation of PDLCs. A low-glucose environment decreased lactate production, inhibiting cell proliferation, migration, and osteogenic differentiation and inducing autophagy in PDLCs.

Hypoxia Pathway in Osteoporosis: Laboratory Data for Clinical Prospects

The hypoxia pathway not only regulates the organism to adapt to the special environment, such as short-term hypoxia in the plateau under normal physiological conditions, but also plays an important role in the occurrence and development of various diseases such as cancer, cardiovascular diseases, osteoporosis. Bone, as a special organ of the body, is in a relatively low oxygen environment, in which the expression of hypoxia-inducible factor (HIF)-related molecules maintains the necessary conditions for bone development. Osteoporosis disease with iron overload endangers individuals, families and society, and bone homeostasis disorder is linked to some extent with hypoxia pathway abnormality, so it is urgent to clarify the hypoxia pathway in osteoporosis to guide clinical medication efficiently. Based on this background, using the keywords "hypoxia/HIF, osteoporosis, osteoblasts, osteoclasts, osteocytes, iron/iron metabolism", a matching search was carried out through the Pubmed and Web Of Science databases, then the papers related to this review were screened, summarized and sorted. This review summarizes the relationship and regulation between the hypoxia pathway and osteoporosis (also including osteoblasts, osteoclasts, osteocytes) by arranging the references on the latest research progress, introduces briefly the application of hyperbaric oxygen therapy in osteoporosis symptoms (mechanical stimulation induces skeletal response to hypoxic signal activation), hypoxic-related drugs used in iron accumulation/osteoporosis model study, and also puts forward the prospects of future research.

Bone marrow mesenchymal stem cell's exosomes as key nanoparticles in osteogenesis and bone regeneration: specific capacity based on cell type

Today, communities and their health systems are facing with several challenges associated with the population ageing. Growing number of bone disorders is one of the most serious consequences of aging. According to the reports bone disorders won't just affect the elderly population. Mesenchymal stem cells (MSCs) are multipotent cells that could be derived from a variety of tissues including bone marrow, Wharton's Jelly, adipose tissue, and others. MSCs have been utilized in different researches in the field of regenerative medicine because of their immunosuppression and anti-inflammatory mechanisms (like: inhibiting the activity of antigen presenting cells, and suppressing the activity of T lymphocyte cells, macrophages, and so on.), migration to injured areas, and participation in healing processes. Bone marrow mesenchymal stem cells (BMMSCs) are a type of these cells which can be commonly used in bone research with the promising results. These cells function by releasing a large number of extracellular vesicles (EVs). Exosomes are the most major EVs products produced by BMMSCs. They have the same contents and properties as their parent cells; however, these structures don't have the defects of cell therapy. Proteins (annexins, tetraspannins, etc.), lipids (cholesterol, phosphoglycerides, etc.), nucleic acids (micro-RNAs, and etc.) and other substances are found in exosomes. Exosomes affect target cells, causing them to change their function. The features of BMMSC exosomes' mechanism in osteogenesis and bone regeneration (like: effects on other MSCs, osteoblasts, osteoclasts, and angiogenesis) and also the effects of their micro-RNAs on osteogenesis are the subject of the present review.

Hypoxia-Inducible Factors Signaling in Osteogenesis and Skeletal Repair

Sufficient oxygen is required to maintain normal cellular and physiological function, such as a creature’s development, breeding, and homeostasis. Lately, some researchers have reported that both pathological hypoxia and environmental hypoxia might affect bone health. Adaptation to hypoxia is a pivotal cellular event in normal cell development and differentiation and in pathological settings such as ischemia. As central mediators of homeostasis, hypoxia-inducible transcription factors (HIFs) can allow cells to survive in a low-oxygen environment and are essential for the regulation of osteogenesis and skeletal repair. From this perspective, we summarized the role of HIF-1 and HIF-2 in signaling pathways implicated in bone development and skeletal repair and outlined the molecular mechanism of regulation of downstream growth factors and protein molecules such as VEGF, EPO, and so on. All of these present an opportunity for developing therapies for bone regeneration.

Systematic review on the application of 3D-bioprinting technology in orthoregeneration: current achievements and open challenges

BACKGROUND

Joint degeneration and large or complex bone defects are a significant source of morbidity and diminished quality of life worldwide. There is an unmet need for a functional implant with near-native biomechanical properties. The potential for their generation using 3D bioprinting (3DBP)-based tissue engineering methods was assessed. We systematically reviewed the current state of 3DBP in orthoregeneration.

METHODS

This review was performed using PubMed and Web of Science. Primary research articles reporting 3DBP of cartilage, bone, vasculature, and their osteochondral and vascular bone composites were considered. Full text English articles were analyzed.

RESULTS

Over 1300 studies were retrieved, after removing duplicates, 1046 studies remained. After inclusion and exclusion criteria were applied, 114 articles were analyzed fully. Bioink material types and combinations were tallied. Cell types and testing methods were also analyzed. Nearly all papers determined the effect of 3DBP on cell survival. Bioink material physical characterization using gelation and rheology, and construct biomechanics were performed. In vitro testing methods assessed biochemistry, markers of extracellular matrix production and/or cell differentiation into respective lineages. In vivo proof-of-concept studies included full-thickness bone and joint defects as well as subcutaneous implantation in rodents followed by histological and µCT analyses to demonstrate implant growth and integration into surrounding native tissues.

CONCLUSIONS

Despite its relative infancy, 3DBP is making an impact in joint and bone engineering. Several groups have demonstrated preclinical efficacy of mechanically robust constructs which integrate into articular joint defects in small animals. However, notable obstacles remain. Notably, researchers encountered pitfalls in scaling up constructs and establishing implant function and viability in long term animal models. Further, to translate from the laboratory to the clinic, standardized quality control metrics such as construct stiffness and graft integration metrics should be established with investigator consensus. While there is much work to be done, 3DBP implants have great potential to treat degenerative joint diseases and provide benefit to patients globally.

Deciphering Obesity-Related Gene Clusters Unearths SOCS3 Immune Infiltrates and 5mC/m6A Modifiers in Ossification of Ligamentum Flavum Pathogenesis

BACKGROUND

Ossification of ligamentum flavum (OLF) is an insidious and debilitating heterotopic ossifying disease with etiological heterogeneity and undefined pathogenesis. Obese individuals predispose to OLF, whereas the underlying connections between obesity phenotype and OLF pathomechanism are not fully understood. Therefore, this study aims to explore distinct obesity-related genes and their functional signatures in OLF.

METHODS

The transcriptome sequencing data related to OLF were downloaded from the GSE106253 in the Gene Expression Omnibus (GEO) database. The obesity-related differentially expressed genes (ORDEGs) in OLF were screened, and functional and pathway enrichment analysis were applied for these genes. Furthermore, protein-protein interactions (PPI), module analysis, transcription factor enrichment analysis (TFEA), and experiment validation were used to identify hub ORDEGs. The immune infiltration landscape in OLF was depicted, and correlation analysis between core gene SOCS3 and OLF-related infiltrating immune cells (OIICs) as well as 5mC/m6A modifiers in OLF was constructed.

RESULTS

Ninety-nine ORDEGs were preliminarily identified, and functional annotations showed these genes were mainly involved in metabolism, inflammation, and immune-related biological functions and pathways. Integrative bioinformatic algorithms determined a crucial gene cluster associated with inflammatory/immune responses, such as TNF signaling pathway, JAK-STAT signaling pathway, and regulation of interferon-gamma-mediated signaling. Eight hub ORDEGs were validated, including 6 down-regulated genes (SOCS3, PPARG, ICAM-1, CCL2, MYC, and NT5E) and 2 up-regulated genes (PTGS2 and VEGFA). Furthermore, 14 differential OIICs were identified by ssGSEA and xCell, and SOCS3 was overlapped to be the core gene, which was associated with multiple immune infiltrates (dendritic cells, macrophage, and T cells) and six m6A modifiers as well as four 5mC regulators in OLF. Reduced SOCS3 and FTO expression and up-regulated DNMT1 level in OLF were validated by Western blotting.

CONCLUSION

This study deciphered immune/inflammatory signatures of obesity-related gene clusters for the first time, and defined SOCS3 as one core gene. The crosstalk between 5mC/m6A methylation may be a key mediator of SOCS3 expression and immune infiltration. These findings will provide more insights into molecular mechanisms and therapeutic targets of obesity-related OLF.

The Cellular Choreography of Osteoblast Angiotropism in Bone Development and Homeostasis

Interaction between endothelial cells and osteoblasts is essential for bone development and homeostasis. This process is mediated in large part by osteoblast angiotropism, the migration of osteoblasts alongside blood vessels, which is crucial for the homing of osteoblasts to sites of bone formation during embryogenesis and in mature bones during remodeling and repair. Specialized bone endothelial cells that form "type H" capillaries have emerged as key interaction partners of osteoblasts, regulating osteoblast differentiation and maturation and ensuring their migration towards newly forming trabecular bone areas. Recent revolutions in high-resolution imaging methodologies for bone as well as single cell and RNA sequencing technologies have enabled the identification of some of the signaling pathways and molecular interactions that underpin this regulatory relationship. Similarly, the intercellular cross talk between endothelial cells and entombed osteocytes that is essential for bone formation, repair, and maintenance are beginning to be uncovered. This is a relatively new area of research that has, until recently, been hampered by a lack of appropriate analysis tools. Now that these tools are available, greater understanding of the molecular relationships between these key cell types is expected to facilitate identification of new drug targets for diseases of bone formation and remodeling.

A functional map of genomic HIF1α-DNA complexes in the eye lens revealed through multiomics analysis

BACKGROUND

During eye lens development the embryonic vasculature regresses leaving the lens without a direct oxygen source. Both embryonically and throughout adult life, the lens contains a decreasing oxygen gradient from the surface to the core that parallels the natural differentiation of immature surface epithelial cells into mature core transparent fiber cells. These properties of the lens suggest a potential role for hypoxia and the master regulator of the hypoxic response, hypoxia-inducible transcription factor 1 (HIF1), in the regulation of genes required for lens fiber cell differentiation, structure and transparency. Here, we employed a multiomics approach combining CUT&RUN, RNA-seq and ATACseq analysis to establish the genomic complement of lens HIF1α binding sites, genes activated or repressed by HIF1α and the chromatin states of HIF1α-regulated genes.

RESULTS

CUT&RUN analysis revealed 8375 HIF1α-DNA binding complexes in the chick lens genome. One thousand one hundred ninety HIF1α-DNA binding complexes were significantly clustered within chromatin accessible regions (χ2 test p < 1 × 10- 55) identified by ATACseq. Formation of the identified HIF1α-DNA complexes paralleled the activation or repression of 526 genes, 116 of which contained HIF1α binding sites within 10kB of the transcription start sites. Some of the identified HIF1α genes have previously established lens functions while others have novel functions never before examined in the lens. GO and pathway analysis of these genes implicate HIF1α in the control of a wide-variety of cellular pathways potentially critical for lens fiber cell formation, structure and function including glycolysis, cell cycle regulation, chromatin remodeling, Notch and Wnt signaling, differentiation, development, and transparency.

CONCLUSIONS

These data establish the first functional map of genomic HIF1α-DNA complexes in the eye lens. They identify HIF1α as an important regulator of a wide-variety of genes previously shown to be critical for lens formation and function and they reveal a requirement for HIF1α in the regulation of a wide-variety of genes not yet examined for lens function. They support a requirement for HIF1α in lens fiber cell formation, structure and function and they provide a basis for understanding the potential roles and requirements for HIF1α in the development, structure and function of more complex tissues.

Effect of edaravone on pregnant mice and their developing fetuses subjected to placental ischemia

Growing evidence indicates that reduced uterine perfusion pressure (RUPP) triggers the cascade of events leading to preeclampsia. Edaravone is a powerful free radical scavenger used for the treatment of ischemia/reperfusion diseases due to its anti-oxidative stress and anti-inflammatory properties. Here we investigate the effect of edaravone (3 mg/kg) on different maternal and fetal outcomes of RUPP-induced placental ischemia mice model. RUPP surgery was performed on gestation day (GD) 13 followed by edaravone injection from GD14 to GD18, sacrifice day. The results showed that edaravone injection significantly decreased the maternal blood pressure (113.2 ± 2.3 mmHg) compared with RUPP group (131.5 ± 1.9 mmHg). Edaravone increased fetal survival rate (75.4%) compared with RUPP group (54.4%), increased fetal length, weights, and feto-placental ratio (7.2 and 5.7 for RUPP and RUPP-Edaravone groups, respectively) compared with RUPP group. In addition, RUPP resulted in many fetal morphological abnormalities as well as severe delayed ossification, however edaravone decreased the morphological abnormalities and increased the ossification of the fetal endoskeleton. Edaravone improved the histopathological structure of the maternal kidney and heart as well as decreased the elevated blood urea and creatinine levels (31.5 ± 0.15 mg/dl (RUPP), 25.6 ± 0.1 mg/dl (RUPP+edaravone) for urea and 5.4 ± 0.1 mg/dl (RUPP), 3.5 ± 0.1 mg/dl (RUPP+edaravone) for creatinine) and decreased cleaved caspase-3 expression in the maternal kidney. In conclusion, this study demonstrated that our RUPP mice model recapitulated preeclampsia symptoms and edaravone injection ameliorated most of these abnormalities suggesting its effectiveness and potential application in preeclampsia treatment regimes.

Functionalized Polycaprolactone/Hydroxyapatite Composite Microspheres for Promoting Bone Consolidation in a Rat Distraction Osteogenesis Model

Distraction osteogenesis (DO) is an ideal model to study bone regeneration. The major limitation is the relatively long period required for new bone consolidation. Here, we investigated whether the application of polycaprolactone (PCL) and hydroxyapatite (HA) composite microspheres could enhance bone formation in DO. Pure PCL microspheres and composite PCL and 10% HA microspheres were synthesized. Bone mesenchymal stem cells isolated from green fluorescent protein rats (GFP-rBMSCs) were cultured with microspheres in a rotary bioreactor system. Scanning electron microscopy was used to examine the microstructures. Osteogenic differentiation of rBMSCs was confirmed. Moreover, PCL/HA (20 mg) and PCL (20 mg) were locally administered into the distraction gap in the rat DO model toward the end of the distraction period. Imaging detection, mechanical and histological examinations were performed to assess the quality of the 4-week regenerates. Results showed that the microspheres were of uniform size and monodisperse. After incubation with rBMSCs in culture, PCL/HA microspheres showed a better ability for cell adhesion and osteogenic differentiation compared with PCL microspheres. In vivo, bone volume/total tissue volume, bone mineral density, and mechanical properties of the new callus were significantly higher in the PCL/HA group compared with the PCL group. Histological analyses confirmed improved bone formation and vascularization in PCL/HA group. We presented an effective protocol for the generation of functionalized microspheres and demonstrated implantation of PCL/HA microspheres into the distraction regenerate could significantly enhance bone consolidation. Thus, the application of PCL/HA composite microspheres may be a novel approach for promoting bone regeneration. This article is protected by copyright. All rights reserved © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:961-971, 2020.

Effects of different oxygen concentrations on the proliferation, survival, migration, and osteogenic differentiation of MC3T3-E1 cells

In physiological and pathological environments, the concentration of oxygen around osteoblasts varies widely. No studies have systematically evaluated the effects of different oxygen concentrations on the proliferation, survival, migration, and osteogenic differentiation of osteoblasts. In this study, we cultured the osteoblast precursor cell line MC3T3-E1 in small individual chambers with oxygen concentrations of 1%, 3%, 6%, 9%, and 21%. Cell proliferation was evaluated by the proliferation index test and EdU staining. To test cell survival, a live/dead assay was performed. A tablet scratch assay was performed to detect the migratory ability of the cells. Bone nodule formation experiments and immunofluorescence and Western blotting analyses of osteogenic-related proteins were performed to assess the osteogenic differentiation of the cells. We found that the proliferation and osteogenic differentiation ability of MC3T3-E1 cells in different oxygen concentrations were both approximately bell-shaped curves and that the optimal oxygen concentrations were approximately 6% and 9%, respectively. The live/dead assay showed that the survival of MC3T3-E1 cells in different oxygen concentrations was affected by the amount of serum. The tablet scratch experiment showed that there was greater cell migration with oxygen concentrations of 1%, 3%, and 21% than with oxygen concentrations of 6% and 9%. Our results have significant reference value for the intervention of the pathological processes involving osteoblasts, such as fracture, osteoporosis, and some vascular diseases. These results also have an important guiding role for the new scientific idea that osteoblasts can function as treatment cells to repair bone defects.

Hypoxia Signaling in the Skeleton: Implications for Bone Health

PURPOSE OF REVIEW

We reviewed recent literature on oxygen sensing in osteogenic cells and its contribution to development of a skeletal phenotype, the coupling of osteogenesis with angiogenesis and integration of hypoxia into canonical Wnt signaling, and opportunities to manipulate oxygen sensing to promote skeletal repair.

RECENT FINDINGS

Oxygen sensing in osteocytes can confer a high bone mass phenotype in murine models; common and unique targets of HIF-1α and HIF-2α and lineage-specific deletion of oxygen sensing machinery suggest differentia utilization and requirement of HIF-α proteins in the differentiation from mesenchymal stem cell to osteoblast to osteocyte; oxygen-dependent but HIF-α-independent signaling may contribute to observed skeletal phenotypes. Manipulating oxygen sensing machinery in osteogenic cells influences skeletal phenotype through angiogenesis-dependent and angiogenesis-independent pathways and involves HIF-1α, HIF-2α, or both proteins. Clinically, an FDA-approved iron chelator promotes angiogenesis and osteogenesis, thereby enhancing the rate of fracture repair.

Enhancement of bone regeneration with the accordion technique via HIF-1α/VEGF activation in a rat distraction osteogenesis model

Axial micromotion of bone fragments promotes callus formation and bone healing during the process of distraction osteogenesis (DO). This study investigated the effects of the combined axial compression and distraction (accordion) technique on bone regeneration in rat DO model. Male Sprague-Dawley rats (n = 62) underwent right tibial transverse osteotomy and were randomly divided into four groups after lengthening: control (no manipulation) and three experimental groups assigned on the basis of the period of accordion manoeuvres in the consolidation phase (Groups 1, 2, and 3 with accordion technique applied at Weeks 1, 3, and 5, respectively). Animals were terminated at 1 week after each accordion phase (i.e., Weeks 2, 4, and 6). Callus formation was monitored by X-ray radiography; new bone quality was evaluated by microcomputed tomography, histological analysis, and mechanical testing. Serum levels of hypoxia-inducible factor (HIF)-1α and vascular endothelial growth factor (VEGF) were measured. Callus formation after accordion manoeuvre at Week 3 (Group 2) increased significantly over time of consolidation. The microcomputed tomography and mechanical analysis revealed Group 2 had more newly formed bone and superior mechanical properties in contrast to the other groups at termination. Histomorphological and immunohistochemical analyses confirmed a greater degree of osteogenesis and angiogenesis corresponding to increased serum levels of HIF-1α and VEGF in Group 2. The accordion technique was effective in promoting bone consolidation via activation of HIF-1α/VEGF during DO. The accordion technique may be used in the middle phase of bone consolidation to promote bone formation in patients undergoing DO treatment.

Lactate induces osteoblast differentiation by stabilization of HIF1α

Aerobic glycolysis is involved in osteoblast differentiation induced by Wnt signaling or PTH treatment. However, it is still unclear whether lactate, the end product of aerobic glycolysis, plays any role in osteoblast differentiation. Herein we report that in cultures of osteoblast-lineage cells, lactate promoted alkaline phosphatase-positive cell formation, increased the activity of alkaline phosphatase, and induced the expression of osteocalcin. This osteoblast differentiation-inducing effect of lactate can be inhibited by blocking its entry into cells with MCT1 siRNA or inhibitors, and by interfering with its metabolism by using specific siRNAs for LDHB and PDH. Moreover, lactate stabilized HIF1α expression and inhibited HIF1α activity, with BAY87-2243 lowering the osteoblast differentiation-inducing effect of lactate. Thus, these findings reveal an unrecognized role for aerobic glycolysis in osteoblast differentiation via its end product, lactate.

Use of Imaging Techniques to Illuminate Dynamics of Hematopoietic Stem Cells and Their Niches

Continuous generation of blood cells over an organism's lifetime is supported by hematopoietic stem/progenitor cells (HSPCs) capable of producing all hematopoietic cell subtypes. Adult mammalian HSPCs are localized to bone marrow and regulated by their neighboring microenvironment, or "niche." Because interactions of HSPCs with their niches are highly dynamic and complex, the recent development of imaging technologies provides a powerful new tool to understand stem cell/niche biology. In this review, we discuss recent advances in our understanding of dynamic HSPC/niche interactions during development, homeostasis, disease states or aging with a focus on studies advanced by imaging analysis. We also summarize methods to visualize HSPCs and niche cells in vivo, including use of HSPC reporter mice and chemical probes. Findings emerging from these investigations could suggest novel therapies for diseases and aging.

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.

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

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

STATEMENT OF SIGNIFICANCE

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

Human fetal mesenchymal stem cell secretome enhances bone consolidation in distraction osteogenesis

BACKGROUND

Distraction osteogenesis (DO) is one of the most dramatic reconstructive techniques for inducing bone regeneration, but it involves an undesirably long period for bone consolidation. Developing innovative approaches to enhance bone consolidation is a burning need. Human fetal mesenchymal stem cells (hFMSCs) have been shown to express more primitive developmental genes than those of human adult mesenchymal stem cells (hAMSCs), which is a preferable source for cell therapy and tissue regeneration. In the present study, we investigated the immunogenicity of using the human mesenchymal stem cell (MSC) secretome on rat cells, the effects of secretome on osteogenic differentiation of rat bone marrow-derived MSCs (rBMSCs), and the potential application of hFMSC secretome in promoting bone consolidation in a rat DO model.

METHODS

Secretome was collected from MSC culture and was used to treat rBMSCs. Following secretome treatment, cell proliferation, alkaline phosphatase staining, Alizarin Red S staining, and mRNA expression of osteogenic differentiation-related genes (including ALP, Runx2, OCN, OPN, and Osx) in the rBMSCs were checked, as well as mixed rat peripheral blood lymphocyte reaction. hFMSC secretome was injected locally into the regenerates from the end of lengthening every 3 days in the rat DO model, until termination. The regenerates were subject to weekly x-rays, micro-computed tomography (μCT) and mechanical testing examination. The bone quality was assessed by histology and immunohistochemistry examinations.

RESULTS

Compared to the secretome from rBMSCs and hAMSCs, hFMSC secretome had the best osteogenic induction ability and low immunogenicity. hFMSC secretome with different doses showed no effect on cell viability. hFMSC secretome at the dose of 100 μg/μl could significantly increase the expression of alkaline phosphatase and all the osteogenic marker genes, as well as the amount of calcium deposits in the rBMSCs. Finally, the local application of hFMSC secretome in distraction regenerates in a rat DO model significantly improved bone consolidation according to the results of μCT, mechanical test, and histological and immunohistochemistry analysis.

CONCLUSIONS

The current study demonstrated that hFMSC secretome promotes osteogenesis of rBMSCs and bone consolidation during DO. hFMSC secretome may be a new therapeutic strategy to enhance bone consolidation in patients undergoing DO treatment.

Targeting the hypoxic response in bone tissue engineering: A balance between supply and consumption to improve bone regeneration

Bone tissue engineering is a promising therapeutic alternative for bone grafting of large skeletal defects. It generally comprises an ex vivo engineered combination of a carrier structure, stem/progenitor cells and growth factors. However, the success of these regenerative implants largely depends on how well implanted cells will adapt to the hostile and hypoxic host environment they encounter after implantation. In this review, we will discuss how hypoxia signalling may be used to improve bone regeneration in a tissue-engineered construct. First, hypoxia signalling induces angiogenesis which increases the survival of the implanted cells as well as stimulates bone formation. Second, hypoxia signalling has also angiogenesis-independent effects on mesenchymal cells in vitro, offering exciting new possibilities to improve tissue-engineered bone regeneration in vivo. In addition, studies in other fields have shown that benefits of modulating hypoxia signalling include enhanced cell survival, proliferation and differentiation, culminating in a more potent regenerative implant. Finally, the stimulation of endochondral bone formation as a physiological pathway to circumvent the harmful effects of hypoxia will be briefly touched upon. Thus, angiogenic dependent and independent processes may counteract the deleterious hypoxic effects and we will discuss several therapeutic strategies that may be combined to withstand the hypoxia upon implantation and improve bone regeneration.

Wnt5a is a key target for the pro-osteogenic effects of iron chelation on osteoblast progenitors

Iron overload due to hemochromatosis or chronic blood transfusions has been associated with the development of osteoporosis. However, the impact of changes in iron homeostasis on osteoblast functions and the underlying mechanisms are poorly defined. Since Wnt signaling is a critical regulator of bone remodeling, we aimed to analyze the effects of iron overload and iron deficiency on osteoblast function, and further define the role of Wnt signaling in these processes. Therefore, bone marrow stromal cells were isolated from wild-type mice and differentiated towards osteoblasts. Exposure of the cells to iron dose-dependently attenuated osteoblast differentiation in terms of mineralization and osteogenic gene expression, whereas iron chelation with deferoxamine promoted osteogenic differentiation in a time- and dose-dependent manner up to 3-fold. Similar results were obtained for human bone marrow stromal cells. To elucidate whether the pro-osteogenic effect of deferoxamine is mediated via Wnt signaling, we performed a Wnt profiler array of deferoxamine-treated osteoblasts. Wnt5a was amongst the most highly induced genes. Further analysis revealed a time- and dose-dependent induction of Wnt5a being up-regulated 2-fold after 48 h at 50 μM deferoxamine. Pathway analysis using specific inhibitors revealed that deferoxamine utilized the phosphatidylinositol-3-kinase and nuclear factor of activated T cell pathways to induce Wnt5a expression. Finally, we confirmed the requirement of Wnt5a in the deferoxamine-mediated osteoblast-promoting effects by analyzing the matrix mineralization of Wnt5a-deficient cells. The promoting effect of deferoxamine on matrix mineralization in wild-type cells was completely abolished in Wnt5a^-/- cells. Thus, these data demonstrate that Wnt5a is critical for the pro-osteogenic effects of iron chelation using deferoxamine.

Notch signaling represses hypoxia-inducible factor-1α-induced activation of Wnt/β-catenin signaling in osteoblasts under cobalt-mimicked hypoxia

The modification of Wnt and Notch signaling pathways by hypoxia, and its association with osteoblast proliferation and apoptosis remain to be fully elucidated. To investigate Wnt-Notch crosstalk, and its role in hypoxia-induced osteoblast proliferation and apoptosis regulation, the present study investigated the effects of cobalt-mimicked hypoxia on the mouse pre-osteoblast-like cell line, MC3T3-E1, when the Notch signals were repressed using a γ-secretase inhibitor DAPT. The data showed that the cobalt-mimicked hypoxia suppressed cell proliferation under normal conditions, but increased cell proliferation under conditions of Notch repression, in a concentration-dependent manner. The results of western blot and reverse transcription-quantitative polymerase chain reaction analyses showed that the cobalt treatment increased the levels of activated β-catenin protein and the expression levels of the target genes, axis inhibition protein 2 and myelocytomatosis oncogene, under DAPT-induced Notch repression. However, no significant changes were found in the expression levels of the Notch intracellular domain protein or the Notch target gene, hes1. In a β-catenin gene-knockdown experiment, the proliferation of the MC3T3-E1 cells under hypoxia were decreased by DAPT treatment, and knockdown of the expression of hypoxia-inducible factor-1α (HIF-1α) suppressed the cobalt-induced increase in Wnt target gene levels. No significant difference in cell proliferation rate was found following DAPT treatment when the expression of HIF-1α was knocked down. The results of the present study showed the opposing effects of Wnt and Notch signaling under cobalt-mimicked hypoxia, which were partially regulated by HIF-1α, The results also showed that osteoblast proliferation was dependent on Wnt-Notch signal crosstalk.

Strong effect of SNP rs4988300 of the LRP5 gene on bone phenotype of Caucasian postmenopausal women

The purpose of this study was to identify relationships between single nucleotide polymorphisms (SNPs) in the genes of the Wnt pathway and bone mineral density (BMD) of postmenopausal women. We chose this pathway due to its importance in bone metabolism that was underlined in several studies. DNA samples of 932 Hungarian postmenopausal women were studied. First, their BMD values at different sites (spine, total hip) were measured, using a Lunar Prodigy DXA scanner. Thereafter, T-score values and the patients' body mass indices (BMIs) were calculated, while information about the fracture history of the sample population was also collected. We genotyped nine SNPs of the following three genes: LRP5, GPR177, and SP7, using a Sequenom MassARRAY Analyzer 4 instrument. The genomic DNA samples used for genotyping were extracted from the buccal mucosa of the subjects. Statistical analyses were carried out using the SPSS 21 and R package. The results of this analysis showed a significant association between SNP rs4988300 of the LRP5 gene and total hip BMD values. We could not reveal any associations between the markers of GPR177, SP7, and bone phenotypes. We found no effect of these genotypes on fracture risk. We could demonstrate a significant gene-gene interaction between two SNPs of LRP5 (rs4988300 and rs634008, p = 0.009) which was lost after Bonferroni correction. We could firmly demonstrate a significant association between rs4988300 of the LRP5 gene and bone density of the hip on the largest homogeneous postmenopausal study group analyzed to date. Our finding corroborates the relationship between LRP5 genotype and bone phenotype in postmenopausal women, however, the complete mechanism of this relationship requires further investigations.

Adipocytes exert lipotoxic effects on osteoblast through activating hypoxia signaling pathway in vitro

This study aimed to investigate the effect of adipocytes on osteoblastic bone formation in vitro. The differentiated and undifferentiated 3T3-L1 cells were co-cultured with primary calvarial osteoblasts. At 48 h, proliferated osteoblasts decreased significantly after co-culture with differentiated preadipocytes as compared to those co-cultured with undifferentiated preadipocytes; at 7 days, the expressions of bone formation-related genes decreased in osteoblasts co-cultured with differentiated preadipocytes; at 14 days, osteoblasts mineralization also decreased significantly after co-culture with differentiated preadipocytes. To further determine whether the decreased proliferation and mineralization were related to the hypoxia signaling pathway, the expressions of hypoxia related-genes were detected. Results showed the expressions of these genes significantly increased after co-culture with differentiated preadipocytes. NF-κB and IL-6 expressions were also up-regulated in osteoblasts co-cultured with differentiated preadipocytes. Osteoblasts from Hif1α(f/f) mice showed increased proliferation and mineralization after co-culture with adipocytes transfected with adenoviral-cre, accompanied by up-regulated expressions of bone formation-related genes and down-regulated expressions of NF-κB and IL-6. These results demonstrated that adipocytes exert a negative effect on the proliferation and mineralization of osteoblasts via up-regulating the expressions of hypoxia-related genes, and NF-κB and IL-6 may impair the osteoblastic bone formation.

Protective effect of Edaravone against hypoxia-induced cytotoxicity in osteoblasts MC3T3-E1 cells

Edaravone is a newly developed clinical medicine for the treatment of acute cerebral infarction. Reduced blood supply to bones (hypoxia) has been involved in the pathological development of osteoporosis. In this study, we investigated the effect of Edaravone and its latent mechanism on hypoxia-induced cell toxicity in MC3T3-E1 cells. Cell viability was determined by the 3-(4,5-dimethyl-thiazol-2yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. Intracellular reactive oxygen species (ROS) and nitric oxide (NO) were determined by the fluorescence dyes 2',7'-dichlorofluorescein diacetate (DCFH-DA) and 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate (DAF-FM DA), respectively. mRNA and proteins were determined by real-time polymerase chain reaction and Western blot analysis, respectively. Edaravone significantly restored the hypoxia-induced reduction of MC3T3-E1 cell viability and inhibited lactate dehydrogenase release. In addition, we found that Edaravone inhibits the generation of ROS and NO. Hoechst staining results indicated that the nuclear condensation characteristic of apoptosis was increased in MC3T3-E1 cells after hypoxia exposure, which was significantly suppressed by Edaravone treatment. Mechanistically, we found that Edaravone markedly reduced the expression of cleaved caspase-3 and blunted the release of cytochrome c. These findings strongly suggested that Edaravone suppresses hypoxia-induced cytotoxicity in MC3T3-E1 cells. The pleiotropic effects of Edaravone on hypoxia exposure in osteoblasts suggest potential antiosteoporosis mechanisms of Edaravone.

COX2 is involved in hypoxia-induced TNF-α expression in osteoblast

Bone regeneration involves a series of events in a coordinated manner, including recruitment of mesenchymal stem cells, induction of immune response, inflammatory activity and vascular ingrowth. The microenvironment of bone regeneration is hypoxic. Low oxygen tension (hypoxia) promotes the upregulation of several signaling molecules. The primary mediating factor is the hypoxia-inducible factor-1 (HIF-1). Hypoxia stimulates the expression of a variety of cytokines from inflammatory cells, fibroblasts, endothelial cells, and osteoblasts. TNF-α is a key proinflammatory cytokine. The molecular events involved in osteoblast dysfunction under hypoxia are not fully understood. This study determined the effects of hypoxia on TNF-α in osteoblasts, and molecular mechanisms were explored. We observed that hypoxia induced TNF-α expression in a time-dependent manner in osteoblasts. Experiments using a potent HIF-1α activator DFO demonstrated that hypoxia-induced TNF-α was mediated by HIF-1-α. In addition, this study showed that hypoxia activated cyclooxygenase-2 (COX2) expression along with TNF-α. Inhibition experiments using COX2 inhibitor N398 indicated that COX2 was involved in hypoxia-mediated TNF-α expression, and this observation was further confirmed by Small interfering RNA against COX2. On the other hand, TNF-α didn’t lead to the activation of COX2 expression. We conclude that COX2 is involved in hypoxia-induced TNF-α expression in osteoblast.

Hypoxia mimetic deferoxamine influences the expression of histone acetylation- and DNA methylation-associated genes in osteoblasts

PURPOSE OF THE STUDY

Sufficient oxygen supply to bone tissue is essential for normal bone development and efficient bone repair. Hypoxia and hypoxia-inducible factor 1α (HIF1α) signaling pathway have been shown to exhibit profound effects on proliferation, differentiation as well as gene and protein expression in osteoblasts, osteoclasts and mesenchymal stem cells; however, as epigenetic mechanisms also perform an important regulatory role in these cells, our aim was to elucidate whether hypoxia mimetic deferoxamine could influence epigenetic mechanisms in bone cells by modulating the gene expression levels of chromatin-modifying enzymes.

MATERIALS AND METHODS

Osteoblast cell line HOS was exposed to deferoxamine, a widely used hypoxia mimetic, and expression profile of 40 genes associated with histone acetylation, deacetylation and DNA methylation was determined using quantitative real time polymerase chain reaction (qPCR) array followed by individual qPCR analyses. In addition, genes associated with hypoxia response, RANK/RANKL/OPG system, WNT/β-catenin signaling pathway and oxidative stress were also analyzed.

RESULTS

We observed induced expression of histone deacetylase 9 (HDAC9) and suppressed expression of K(lysine) acetyltransferase 5 (KAT5) and DNA methyltransferase 3A (DNMT3A) demonstrating for the first time that expression of genes encoding chromatin-modifying enzymes could be influenced by hypoxia mimetic in HOS cells.

CONCLUSIONS

Based on our results we can conclude that hypoxia mimetic deferoxamine influences expression of histone acetylation- and DNA methylation-associated genes in osteoblasts and that further studies of hypoxia-induced epigenetic changes in bone cells should be undertaken.

The effects of secretion factors from umbilical cord derived mesenchymal stem cells on osteogenic differentiation of mesenchymal stem cells

Factors synthesized by mesenchymal stem cells (MSCs) contain various growth factors, cytokines, exosomes and microRNAs, which may affect the differentiation abilities of MSCs. In the present study, we investigated the effects of secretion factors of human umbilical cord derived mesenchymal stem cells (hUCMSCs) on osteogenesis of human bone marrow derived MSCs (hBMSCs). The results showed that 20 μg/ml hUCMSCs secretion factors could initiate osteogenic differentiation of hBMSCs without osteogenic induction medium (OIM), and the amount of calcium deposit (stained by Alizarin Red) was significantly increased after the hUCMSCs secretion factors treatment. Real time quantitative reverse transcription-polymerase chain reaction (real time qRT-PCR) demonstrated that the expression of osteogenesis-related genes including ALP, BMP2, OCN, Osterix, Col1α and Runx2 were significantly up-regulated following hUCMSCs secretion factors treatment. In addition, we found that 10 μg hUCMSCs secretion factors together with 2×10(5) hBMSCs in the HA/TCP scaffolds promoted ectopic bone formation in nude mice. Local application of 10 μg hUCMSCs secretion factors with 50 μl 2% hyaluronic acid hydrogel and 1×10(5) rat bone marrow derived MSCs (rBMSCs) also significantly enhanced the bone repair of rat calvarial bone critical defect model at both 4 weeks and 8 weeks. Moreover, the group that received the hUCMSCs secretion factors treatment had more cartilage and bone regeneration in the defect areas than those in the control group. Taken together, these findings suggested that hUCMSCs secretion factors can initiate osteogenesis of bone marrow MSCs and promote bone repair. Our study indicates that hUCMSCs secretion factors may be potential sources for promoting bone regeneration.

Kinetics of gene expression and bone remodelling in the clinical phase of collagen-induced arthritis

Introduction

Pathological bone changes differ considerably between inflammatory arthritic diseases and most studies have focused on bone erosion. Collagen-induced arthritis (CIA) is a model for rheumatoid arthritis, which, in addition to bone erosion, demonstrates bone formation at the time of clinical manifestations. The objective of this study was to use this model to characterise the histological and molecular changes in bone remodelling, and relate these to the clinical disease development.

Methods

A histological and gene expression profiling time-course study on bone remodelling in CIA was linked to onset of clinical symptoms. Global gene expression was studied with a gene chip array system.

Results

The main histopathological changes in bone structure and inflammation occurred during the first two weeks following the onset of clinical symptoms in the joint. Hereafter, the inflammation declined and remodelling of formed bone dominated.

Global gene expression profiling showed simultaneous upregulation of genes related to bone changes and inflammation in week 0 to 2 after onset of clinical disease. Furthermore, we observed time-dependent expression of genes involved in early and late osteoblast differentiation and function, which mirrored the histopathological bone changes. The differentially expressed genes belong to the bone morphogenetic pathway (BMP) and, in addition, include the osteoblast markers integrin-binding sialoprotein (Ibsp), bone gamma-carboxyglutamate protein (Bglap1), and secreted phosphoprotein 1 (Spp1). Pregnancy-associated protein A (Pappa) and periostin (Postn), differentially expressed in the early disease phase, are proposed to participate in bone formation, and we suggest that they play a role in early bone formation in the CIA model. Comparison to human genome-wide association studies (GWAS) revealed differential expression of several genes associated with human arthritis.

Conclusions

In the CIA model, bone formation in the joint starts shortly after onset of clinical symptoms, which results in bony fusion within one to two weeks. This makes it a candidate model for investigating the relationship between inflammation and bone formation in inflammatory arthritis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0531-7) contains supplementary material, which is available to authorized users.

Osterix controls cementoblast differentiation through downregulation of Wnt-signaling via enhancing DKK1 expression

Osterix (Osx), a transcriptional factor essential for osteogenesis, is also critical for in vivo cellular cementum formation. However, the molecular mechanism by which Osx regulates cementoblasts is largely unknown. In this study, we initially demonstrated that overexpression of Osx in a cementoblast cell line upregulated the expression of markers vital to cementogenesis such as osteopontin (OPN), osteocalcin (OCN), and bone sialoprotein (BSP) at both mRNA and protein levels, and enhanced alkaline phosphatase (ALP) activity. Unexpectedly, we demonstrated a sharp increase in the expression of DKK1 (a potent canonical Wnt antagonist), and a great reduction in protein levels of β-catenin and its nuclear translocation by overexpression of Osx. Further, transient transfection of Osx reduced protein levels of TCF1 (a target transcription factor of β-catenin), which were partially reversed by an addition of DKK1. We also demonstrated that activation of canonical Wnt signaling by LiCl or Wnt3a significantly enhanced levels of TCF1 and suppressed the expression of OPN, OCN, and BSP, as well as ALP activity and formation of extracellular mineralized nodules. Importantly, we confirmed that there were a sharp reduction in DKK1 and a concurrent increase in β-catenin in Osx cKO mice (crossing between the Osx loxP and 2.3 Col 1-Cre lines), in agreement with the in vitro data. Thus, we conclude that the key role of Osx in control of cementoblast proliferation and differentiation is to maintain a low level of Wnt-β-catenin via direct up-regulation of DKK1.

Down regulation of Wnt signaling mitigates hypoxia-induced chemoresistance in human osteosarcoma cells

Osteosarcoma (OS) is the most common type of solid bone cancer and remains the second leading cause of cancer-related death for children and young adults. Hypoxia is an element intrinsic to most solid-tumor microenvironments, including that of OS, and is associated with resistance to therapy, poor survival, and a malignant phenotype. Cells respond to hypoxia through alterations in gene expression, mediated most notably through the hypoxia-inducible factor (HIF) class of transcription factors. Here we investigate hypoxia-induced changes in the Wnt/β-catenin signaling pathway, a key signaling cascade involved in OS pathogenesis. We show that hypoxia results in increased expression and signaling activation of HIF proteins in human osteosarcoma cells. Wnt/β-catenin signaling is down-regulated by hypoxia in human OS cells, as demonstrated by decreased active β-catenin protein levels and axin2 mRNA expression (p<0.05). This down-regulation appears to rely on both HIF-independent and HIF-dependent mechanisms, with HIF-1α standing out as an important regulator. Finally, we show that hypoxia results in resistance of human OS cells to doxorubicin-mediated toxicity (6–13 fold increase, p<0.01). These hypoxic OS cells can be sensitized to doxorubicin treatment by further inhibition of the Wnt/β-catenin signaling pathway (p<0.05). These data support the conclusion that Wnt/β-catenin signaling is down-regulated in human OS cells under hypoxia and that this signaling alteration may represent a viable target to combat chemoresistant OS subpopulations in a hypoxic niche.

Hypoxia modulates the phenotype of osteoblasts isolated from knee osteoarthritis patients, leading to undermineralized bone nodule formation

Objective

To investigate the role of hypoxia in the pathology of osteoarthritic (OA) bone by exploring its effect on the phenotype of isolated primary osteoblasts from patients with knee OA.

Methods

OA bone samples were collected at the time of elective joint replacement surgery for knee or hip OA. Normal bone samples were collected postmortem from cadaver donors. Primary osteoblasts were isolated from knee OA bone chips and cultured under normoxic or hypoxic (2% O₂) conditions. Alkaline phosphatase activity was quantified using an enzymatic assay, and osteopontin and prostaglandin E₂ (PGE₂) production was assayed by enzyme-linked immunosorbent assay. Total RNA was extracted from bone and osteoblasts, and gene expression was profiled by quantitative reverse transcription–polymerase chain reaction.

Results

Human OA bone tissue sections stained positively for carbonic anhydrase IX, a biomarker of hypoxia, and exhibited differential expression of genes that mediate the vasculature and blood coagulation as compared to those found in normal bone. Culture of primary osteoblasts isolated from knee OA bone under hypoxic conditions profoundly affected the osteoblast phenotype, including the expression of genes that mediate bone matrix, bone remodeling, and bone vasculature. Hypoxia also increased the expression of cyclooxygenase 2 and the production of PGE₂ by OA osteoblasts. Osteoblast expression of type II collagen α1 chain, angiopoietin-like 4, and insulin-like growth factor binding protein 1 was shown to be mediated by hypoxia-inducible factor 1α. Chronic hypoxia reduced osteoblast- mineralized bone nodule formation.

Conclusion

These findings demonstrate that hypoxia can induce pathologic changes in osteoblast functionality consistent with an OA phenotype, providing evidence that hypoxia is a key driver of OA pathology.

Sclerostin monoclonal antibody enhanced bone fracture healing in an open osteotomy model in rats

Sclerostin is a negative regulator of bone formation. Sclerostin monoclonal antibody (Scl-Ab) treatment promoted bone healing in various animal models. To further evaluate the healing efficiency of Scl-Ab in osteotomy healing, we investigated the time course effects of systemic administration of Scl-Ab on fracture repair in rat femoral osteotomy model. A total of 120 six-month-old male SD rats were subjected to transverse osteotomy at the right femur mid-shaft. Rats were treated with vehicle or Scl-Ab treatment for 3, 6, or 9 weeks. Fracture healing was evaluated by radiography, micro-CT, micro-CT based angiography, 4-point bending mechanical test and histological assessment. Scl-Ab treatment resulted in significantly higher total mineralized callus volume fraction, BMD and enhanced neovascularization. Histologically, Scl-Ab treatment resulted in a significant reduction in fracture callus cartilage at week 6 and increase in bone volume at week 9, associated with a greater proportion of newly formed bone area at week 6 and 9 by fluorescence microscopy. Mechanical testing showed significantly higher ultimate load in Scl-Ab treatment group at week 6 and 9. This study has demonstrated that Scl-Ab treatment enhanced bone healing in a rat femoral osteotomy model, as reflected in increased bone formation, bone mass and bone strength.

MiR-143 suppresses osteogenic differentiation by targeting Osterix

Osterix (Osx) is an essential transcription factor for osteoblast differentiation and bone formation. However, the knowledge of the regulation of Osx expression is poor. MicroRNAs (miRNAs), a class of small non-coding RNAs, play critical roles in numerous biological processes, including the proliferation, differentiation, and survival of cells and organisms. Herein, we aimed to explore the effect of miR-143 on Osx expression and osteogenic differentiation. miR-143, which was suppressor of the osteogenic differentiation of MC3T3-E1 cells, had decreased levels of expression during osteogenic differentiation. Moreover, Osx was identified to be a direct target of miR-143. Inhibition of Osx performed similar effect with miR-143 on osteogenic differentiation, while overexpression of Osx could partially reverse the suppressive effect of miR-143. Collectively, these data indicate that miR-143 is a novel regulator of Osx, and it might play an essential role in the regulation of osteogenic differentiation.

Prostate cancer derived prostatic acid phosphatase promotes an osteoblastic response in the bone microenvironment

Approximately 90 % of patients who die of prostate cancer (PCa) have bone metastases, often promoting osteoblastic lesions. We observed that 88 % of castration-resistant PCa (CRPC) bone metastases express prostatic acid phosphatase (PAP), a soluble secreted protein expressed by prostate epithelial cells in predominately osteoblastic (n = 18) or osteolytic (n = 15) lesions. Additionally, conditioned media (CM) of an osteoblastic PCa xenograft LuCaP 23.1 contained significant levels of PAP and promoted mineralization in mouse and human calvaria-derived cells (MC3T3-E1 and HCO). To demonstrate that PAP promotes mineralization, we stimulated MC3T3-E1 cells with PAP and observed increased mineralization, which could be blocked with the specific PAP inhibitor, phosphonic acid. Furthermore, the mineralization promoted by LuCaP 23.1 CM was also blocked by phosphonic acid, suggesting PAP is responsible for the mineralization promoting activity of LuCaP 23.1. In addition, gene expression arrays comparing osteoblastic to osteolytic CRPC (n = 14) identified betacellulin (BTC) as a gene upregulated during the osteoblastic response in osteoblasts during new bone formation. Moreover, BTC levels were increased in bone marrow stromal cells in response to LuCaP 23.1 CM in vitro. Because new bone formation does occur in osteoblastic and can occur in osteolytic CRPC bone metastases, we confirmed by immunohistochemistry (n = 36) that BTC was highly expressed in osteoblasts involved in new bone formation occurring in both osteoblastic and osteolytic sites. These studies suggest a role for PAP in promoting the osteoblastic reaction in CRPC bone metastases and identify BTC as a novel downstream protein expressed in osteoblasts during new bone formation.

Human stem cell osteoblastogenesis mediated by novel glycogen synthase kinase 3 inhibitors induces bone formation and a unique bone turnover biomarker profile in rats

Wnt activation by inhibiting glycogen synthase kinase 3 (GSK-3) causes bone anabolism in rodents making GSK-3 a potential therapeutic target for osteoporotic and osteolytic metastatic bone disease. To understand the wnt pathway related to human disease translation, the ability of 3 potent inhibitors of GSK-3 (AZD2858, AR79, AZ13282107) to 1) drive osteoblast differentiation and mineralisation using human adipose-derived stem cells (hADSC) in vitro; and 2) stimulate rat bone formation in vivo was investigated. Bone anabolism/resorption was determined using clinically relevant serum biomarkers as indicators of bone turnover and bone formation assessed in femurs by histopathology and pQCT/μCT imaging. GSK-3 inhibitors caused β-catenin stabilisation in human and rat mesenchymal stem cells, stimulated hADSC commitment towards osteoblasts and osteogenic mineralisation in vitro. AZD2858 produced time-dependent changes in serum bone turnover biomarkers and increased bone mass over 28 days exposure in rats. After 7 days, AZD2858, AR79 or AZ13282107 exposure increased the bone formation biomarker P1NP, and reduced the resorption biomarker TRAcP-5b, indicating increased bone anabolism and reduced resorption in rats. This biomarker profile was differentiated from anabolic agent PTH1-34 or the anti-resorptive Alendronate-induced changes. Increased bone formation in cortical and cancellous bone as assessed by femur histopathology supported biomarker changes. 14 day AR79 treatment increased bone mineral density and trabecular thickness, and decreased trabecular number and connectivity assessed by pQCT/μCT. GSK-3 inhibition caused hADSC osteoblastogenesis and mineralisation in vitro. Increased femur bone mass associated with changes in bone turnover biomarkers confirmed in vivo bone formation and indicated uncoupling of bone formation and resorption.

HIF-1α inhibits Wnt signaling pathway by activating Sost expression in osteoblasts

The nature of the cellular and molecular mechanisms for the transition of avascular cartilage replacement with bone during endochondral ossification remains poorly understood. One of the driving forces is hypoxia. As a master regulator of hypoxia, hypoxia-inducible factor-1α (HIF-1α) has been reported to couple angiogenesis to osteogenesis. Our recent study has demonstrated that osteoblast growth is inhibited under hypoxia and that HIF-1α cooperates with Osterix (Osx) to inhibit Wnt pathway. However, molecular mechanisms for inhibitory effects of HIF-1α on Wnt pathway are not well understood. In this study, our quantitative RT-PCR results revealed that the expression of a Wnt antagonist Sclerostin (Sost) was upregulated in osteoblasts during hypoxia while HIF-1α was upregulated. Treatment of desferrioxamine (DFO), a HIF-1α activator, led to further increase of Sost expression, suggesting that HIF-1α may activate Sost expression. The regulation of Sost gene expression by HIF-1α was then investigated. We performed loss-of-function experiments to examine Sost expression by using siRNA approach against HIF-1α, and found that the inhibition of HIF-1α by siRNA in osteoblasts led to the decrease of Sost expression. To address transcriptional regulation of Sost gene by HIF-1α, transient transfection assay was performed and showed that HIF-1α activated Sost-1 kb promoter reporter activity in a dose-dependent manner. To narrow down the minimal region of Sost promoter activated by HIF-1α, we generated a series of deletion mutants of Sost constructs. It was demonstrated that Sost-260 was the minimal region of Sost promoter for HIF-1α activation and that Sost-106 construct, which lack hypoxia response element, abolished HIF-1α-mediated Sost reporter activation. Gel shift assay showed that HIF-1 bound to the promoter sequence of Sost directly. These findings support our hypothesis that HIF-1α activates Sost expression. This study provides a novel molecular mechanism through which HIF-1α inhibits Wnt signaling in osteoblasts.