Intracellular VEGF regulates the balance between osteoblast and adipocyte differentiation

Using network pharmacology and molecular docking technology, proteomics and experiments were used to verify the effect of Yigu decoction (YGD) on the expression of key genes in osteoporotic mice

BACKGROUND

Yigu decoction (YGD) is a traditional Chinese medicine prescription for the treatment of osteoporosis, although many clinical studies have confirmed its anti-OP effect, but the specific mechanism is still not completely clear.

METHODS

In this study, through the methods of network pharmacology and molecular docking, the material basis and action target of YGD in preventing and treating OP were analyzed, and the potential target and mechanism of YGD in preventing and treating OP were clarified by TMT quantitative protein and experiment.

RESULTS

Network pharmacology and molecular docking revealed that the active components of YGD were mainly stigmasterol and flavonoids. Molecular docking mainly studied the strong binding ability of stigmasterol to the target. Animal proteomics verified the related mechanism of YGD in preventing and treating OP. Based on the KEGG enrichment of network pharmacology and histology, our animal experiments in vivo verified that YGD may play a role in the treatment of OP by mediating hif1- α/vegf/glut1 signal pathway.

CONCLUSIONS

YGD prevention and treatment of OP may be achieved by interfering with multiple targets. This study confirmed that it may promote osteoblast proliferation and protect osteoblast function by up-regulating the expression of proteins related to HIF signal pathway.

Mechanisms Underlying Medication-Related Osteonecrosis of the Jaw

OBJECTIVE

Medication-related osteonecrosis of the jaw (MRONJ) is a rare but debilitating disease characterized by a progressive necrosis of jaw bones in patients who have received anti-resorptive or anti-angiogenic therapies. Unfortunately, we still have no validated preventive or pharmaceutical interventions to help these patients, primarily due to our limited understanding of MRONJ pathogenesis. Here, we offer an extensive review of recent studies relevant to MRONJ pathogenesis. We present a hypothesis regarding the coupling of bone resorption and angiogenesis that relies on osteoblast-derived, matrix-bound vascular endothelial growth factors to explain why ONJ is associated with both anti-resorptive and anti-angiogenic agents.

METHODS

A narrative review was conducted by searching databases, including PubMed, Scopus, Google Scholar, and Web of Science, to retrieve relevant reports.

RESULTS

Reduced bone resorption leads to reduced angiogenesis, and vice versa, creating a vicious cycle that ultimately results in ischemic necrosis of the jaw. Additionally, we suggest that reduced angiogenesis, induced by anti-resorptive or anti-angiogenic agents, aggravates bacterial infection-induced bone necrosis, explaining why the jaw bone is particularly susceptible to necrosis.

CONCLUSION

Our novel hypothesis will facilitate the advancement of future research and the development of more targeted approaches to managing MRONJ.

Skeletal stem and progenitor cells in bone physiology, ageing and disease

Skeletal stem cells (SSCs) and related progenitors with osteogenic potential, collectively termed skeletal stem and/or progenitor cells (SSPCs), are crucial for providing osteoblasts for bone formation during homeostatic tissue turnover and fracture repair. Besides mediating normal bone physiology, they also have important roles in various metabolic bone diseases, including osteoporosis. SSPCs are of tremendous interest because they represent prime future targets for osteoanabolic therapies and bone regenerative medicine. Remarkable progress has been made in characterizing various SSC and SSPC populations in postnatal bone. SSPCs exist in the periosteum and within the bone marrow stroma, including subsets localizing around arteriolar and sinusoidal blood vessels; they can display osteogenic, chondrogenic, adipogenic and/or fibroblastic potential, and exert critical haematopoiesis-supportive functions. However, much remains to be clarified. By the current markers, bona fide SSCs are commonly contained within broader SSPC populations characterized by considerable heterogeneity and overlap, whose common versus specific functions in health and disease have not been fully unravelled. Here, we review the present knowledge of the identity, fates and relationships of SSPC populations in the postnatal bone environment, their contributions to bone maintenance, the changes observed upon ageing, and the effect of metabolic diseases such as osteoporosis and diabetes mellitus.

Mapping the spatial atlas of the human bone tissue integrating spatial and single-cell transcriptomics

Bone is a multifaceted tissue requiring orchestrated interplays of diverse cells within specialized microenvironments. Although significant progress has been made in understanding cellular and molecular mechanisms of component cells of bone, revealing their spatial organization and interactions in native bone tissue microenvironment is crucial for advancing precision medicine, as they govern fundamental signaling pathways and functional dependencies among various bone cells. In this study, we present the first integrative high-resolution map of human bone and bone marrow, using spatial and single-cell transcriptomics profiling from femoral tissue. This multi-modal approach discovered a novel bone formation-specialized niche enriched with osteoblastic lineage cells and fibroblasts and unveiled critical cell-cell communications and co-localization patterns between osteoblastic lineage cells and other cells. Furthermore, we discovered a novel spatial gradient of cellular composition, gene expression and signaling pathway activities radiating from the trabecular bone. This comprehensive atlas delineates the intricate bone cellular architecture and illuminates key molecular processes and dependencies among cells that coordinate bone metabolism. In sum, our study provides an essential reference for the field of bone biology and lays the foundation for advanced mechanistic studies and precision medicine approaches in bone-related disorders.

Fluorinated Porcine Bone-Derived Hydroxyapatite Promotes Vascularized Osteogenesis by Coordinating Human Bone Marrow Mesenchymal Stem Cell/Human Umbilical Vein Endothelial Cell Complexes

Biogenic hydroxyapatite is known for its osteoinductive potential due to its similarity to human bone and biocompatibility, but insufficient vascularization compared to autogenous bone during early implantation limits bone integration and osteogenesis. Fluorine has been shown to improve hydroxyapatite's mechanical properties and the coupling of osteogenic and angiogenic cells. In this study, fluorine-modified biogenic hydroxyapatite (FPHA) with varying fluorine concentrations was prepared and tested for its ability to promote vascularized osteogenesis. FPHA prepared in this study retained the natural porous structure of biological cancellous bone and released F- ions when immersed in cell culture medium. The extraction solutions of FPHA0.25 and FPHA0.50 promoted the formation of capillary-like tubes by human umbilical vein endothelial cells (HUVECs), with FPHA0.25 significantly upregulating vegf mRNA and VEGF protein levels in co-cultured human bone marrow mesenchymal stem cells (HBMSCs). Additionally, FPHA0.25 and FPHA0.50 upregulated pdgf-bb mRNA and PDGF-BB protein levels in HUVECs. In vivo experiments using a rabbit cranial defect model demonstrated that FPHA0.25 promoted early bone formation and angiogenesis in the defect area, enhanced VEGF secretion, and increased PDGFR-β expression in endothelial and mesenchymal cells. These findings suggest that fluorine-modified biogenic hydroxyapatite with an optimal fluorine concentration (FPHA0.25) may offer a promising strategy to enhance the body's innate bone-healing potential by accelerating vascularization.

Stem cell secretome restore the adipo-osteo differentiation imbalance in diabetic dental pulp-derived mesenchymal stem cells

Background

Mesenchymal stem cells (MSCs) from type 2 diabetes mellitus (T2DM) individuals exhibit increased adipogenesis and decreased osteogenesis. We investigated the potential of adipose tissue-derived MSCs (ADMSCs) secretome obtained from healthy individuals in restoring the tumor necrosis factor-α (TNF-α) mediated imbalance in the adipo/osteogenic differentiation in the dental pulp-derived MSCs obtained from T2DM individuals (dDPMSCs).

Methods

dDPMSCs were differentiated into adipocytes and osteocytes using a standard cocktail in the presence of (a) induction cocktail, (b) induction cocktail + TNF-α, and (c) induction cocktail+ TNF-α + ADMSCs-secretome (50%) for 15 and 21 days resp. Differentiated adipocytes and osteocytes were stained by oil red O and alizarin red and analyzed by using ImageJ software. Molecular expression of the key genes involved was analyzed by using reverse-transcription polymerase chain reaction (RT-PCR).

Results

Treatment of TNF-α augmented the adipogenesis (9571 ± 765 vs. 19,815 ± 1585 pixel, p < 0.01) and decreased the osteogenesis (15,603 ± 1248 vs. 11,894 ± 951 pixel, p < 0.05) of dDPMSCs as evidenced by the oil red O and alizarin red staining respectively. Interestingly, dDPMSCs differentiated along with TNF-α and 50% ADMSCs secretome exhibited enhanced osteogenesis (11,894 ± 951 vs. 41,808 ± 3344 pixel, p < 0.01) and decreased adipogenesis (19,815 ± 1585 vs. 4480 ± 358 pixel, p < 0.01). Additionally, dDPMSCs differentiated along with ADMSCs secretome exhibited decreased expression of PPARg (p < 0.01), C/EBPa (p < 0.05), and FAS (p < 0.01) whereas mRNA expression of Runx2 (p < 0.05), Osterix (p < 0.01), and OCN (p < 0.05) was upregulated as revealed by the RT-PCR analysis.

Conclusion

ADMSCs secretome from healthy individuals restore the TNF-α influenced differentiation fate of dDPMSCs and therefore can be explored for T2DM clinical management in the future.

Laponite modified methacryloyl gelatin hydrogel with controlled release of vascular endothelial growth factor a for bone regeneration

Reconstruction of bone defects has long been a major clinical challenge. Limited by the various shortcomings of conventional treatment like autologous bone grafting and inorganic substitutes, the development of novel bone repairing strategies is on top priority. Injectable biomimetic hydrogels that deliver stem cells and growth factors in a minimally invasive manner can effectively promote bone regeneration and thus represent a promising alternative. Therefore, in this study, we designed and constructed an injectable nanocomposite hydrogel co-loaded with Laponite (Lap) and vascular endothelial growth factor (VEGF) through a simplified and convenient scheme of physical co-mixing (G@Lap/VEGF). The introduced Lap not only optimized the injectability of GelMA by the electrostatic force between the nanoparticles, but also significantly delayed the release of VEGF-A. In addition, Lap promoted high expression of osteogenic biomarkers in mesenchymal stem cells (MSCs) and enhanced the matrix mineralization. Besides, VEGF-A exerted chemotactic effects recruiting endothelial progenitor cells (EPCs) and inducing neovascularization. Histological and micro-CT results demonstrated that the critical-sized calvarial bone defect lesions in the SD rats after treated with G@Lap/VEGF exhibited significant in vivo bone repairing. In conclusion, the injectable G@Lap/VEGF nanocomposite hydrogel constructed in our study is highly promising for clinical transformation and applications, providing a convenient and simplified scheme for clinical bone repairing, and contributing to the further development of the injectable biomimetic hydrogels.

Advances in osteoimmunomodulation of biomaterials after intrabone implantation: focus on surface hydrophilicity

Biomaterials intended for intrabone implantation are extensively utilized in orthopedic and dental applications. Their surface properties, particularly hydrophilicity, significantly influence the biological interactions surrounding the implant, ultimately determining the implant's in vivo fate. Recently, the role of osteoimmunomodulation in these implantable biomaterials has been recognized for its importance in regulating biomaterial-mediated osteogenesis. Consequently, it is imperative to elucidate the correlation between hydrophilicity and the immune response for the development of osteoimmunomodulatory implants. Herein, this review highlights recent advances in osteoimmunomodulation of biomaterials after intrabone implantation from a novel perspective-surface hydrophilicity, and summarizes the series of immune reactions and subsequent bone remodeling that occur in response to hydrophilic implants, focusing on protein adsorption, the behaviors of major immune cells, and osteoimmunomodulation-enhanced angiogenesis and osteogenesis. Hydrophilic biomaterials have the capacity to alter the surrounding immune microenvironment and accelerate the process of material-tissue bonding, thereby facilitating the successful integration of biomaterials with tissue. Collectively, the authors hope that this article provides strategies for modulating hydrophilicity to achieve osteoimmunomodulatory performance and further promotes the development of novel implantable biomaterials for orthopedic and dental applications.

Seaweed-derived etherified carboxymethyl cellulose for sustainable tissue engineering

Biodegradability, biocompatibility, abundant supply from renewable sources, and affordability are the outstanding properties of cellulose that have prompted substantial studies into its potential in biomedical applications. Beyond terrestrial sources of cellulose, seaweeds have attracted much attention as a potential source of cellulose because they are widely available. Cellulose and its byproducts may be extracted from various macroalgae species, including red, green, and brown algae. The extracted cellulose's qualities vary depending on the algae species, age, and extraction process utilized. Cellulose's characteristics are enhanced through chemical modifications, specifically etherification and esterification, which substitute functional groups for hydroxyl groups, yielding a range of products, including cellulose acetate (CA), cellulose nitrate, cellulose sulfate, methylcellulose, and carboxymethyl cellulose (CMC). The ability to modify CMC characteristics for particular applications is explored through techniques including grafting processes mixing, and cross-linking with other polymers. Moreover, tissue engineering is given significant consideration in the growing use of CMC and its altered forms in biological applications. These alterations allow for the production of scaffolds that promote tissue regeneration and cell proliferation, enabling CMC-based scaffolds for various tissue engineering uses. This review provides a comprehensive overview of CMC's properties, modifications, and potential in tissue engineering.

Paracrine signals influence patterns of fibrocartilage differentiation in a lyophilized gelatin hydrogel for applications in rotator cuff repair

Rotator cuff injuries present a clinical challenge for repair due to current limitations in functional regeneration of the native tendon-to-bone enthesis. A biomaterial that can regionally instruct unique tissue-specific phenotypes offers potential to promote enthesis repair. We have recently demonstrated the mechanical benefits of a stratified triphasic biomaterial made up of tendon- and bone-mimetic collagen scaffold compartments connected via a continuous hydrogel, and we now explore the potential of a biologically favorable enthesis hydrogel for this application. Here we report in vitro behavior of human mesenchymal stem cells (hMSCs) within thiolated gelatin (Gel-SH) hydrogels in response to chondrogenic stimuli as well as paracrine signals derived from MSC-seeded bone and tendon scaffold compartments. Chondrogenic differentiation media promoted upregulation of cartilage and entheseal fibrocartilage matrix markers COL2, COLX, and ACAN as well as the enthesis-associated transcription factors SCX, SOX9, and RUNX2 in hMSCs within Gel-SH. Similar effects were observed in response to TGF-β3 and BMP-4, enthesis-associated growth factors known to play a role in entheseal development and maintenance. Conditioned media generated by hMSCs seeded in tendon- and bone-mimetic collagen scaffolds influenced patterns of gene expression regarding enthesis-relevant growth factors, matrix markers, and tendon-to-bone transcription factors for hMSCs within the material. Together, these findings demonstrate that a Gel-SH hydrogel provides a permissive environment for enthesis tissue engineering and highlights the significance of cellular crosstalk between adjacent compartments within a spatially graded biomaterial.

Growth factor-functionalized titanium implants for enhanced bone regeneration: A review

Titanium and titanium alloys are widely favored materials for orthopedic implants due to their exceptional mechanical properties and biological inertness. The additional benefit of sustained local release of bioactive substances further promotes bone tissue formation, thereby augmenting the osseointegration capacity of titanium implants and attracting increasing attention in bone tissue engineering. Among these bioactive substances, growth factors have shown remarkable osteogenic and angiogenic induction capabilities. Consequently, researchers have developed various physical, chemical, and biological loading techniques to incorporate growth factors into titanium implants, ensuring controlled release kinetics. In contrast to conventional treatment modalities, the localized release of growth factors from functionalized titanium implants not only enhances osseointegration but also reduces the risk of complications. This review provides a comprehensive examination of the types and mechanisms of growth factors, along with a detailed exploration of the methodologies used to load growth factors onto the surface of titanium implants. Moreover, it highlights recent advancements in the application of growth factors to the surface of titanium implants (Scheme 1). Finally, the review discusses current limitations and future prospects for growth factor-functionalized titanium implants. In summary, this paper presents cutting-edge design strategies aimed at enhancing the bone regenerative capacity of growth factor-functionalized titanium implants-a significant advancement in the field of enhanced bone regeneration.

Expression of the HIF-1α/VEGF pathway is upregulated to protect alveolar bone density reduction in nasal-obstructed rats

BACKGROUND

Hypoxia and mouth breathing are closely related to maxillofacial bone metabolism and are characteristic of obstructive sleep apnea-hypopnea syndrome (OSAHS). Being key factors in the hypoxia response, hypoxia-inducible factor 1α (HIF-1α) and HIF-responsive gene vascular endothelial growth factor (VEGF) are essential for bone remodeling. This study focuses on the role of the HIF-1α/VEGF pathway in alveolar bone metabolism during OSAHS.

MATERIALS AND METHODS

36 three-week-old male Wistar rats were divided into three groups: twelve control rats, twelve bilateral nasal obstructed (BNO) rats, twelve BNO rats treated with intraperitoneal injection of Dimethyloxalylglycine (DMOG). After two weeks, the microstructure and bone mineral density (BMD) of alveolar bone were evaluated using micro-computed tomography (micro-CT). The expressions of HIF-1α and VEGF in the alveolar bone were then assessed via immunohistochemistry staining, quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot. Alkaline phosphatase (ALP) staining and Alizarin red S staining were performed to evaluate osteogenesis of bone marrow-derived mesenchymal stem cells (BMSCs).

RESULTS

Significant reductions in alveolar bone density were noted in BNO rats. Bilateral nasal obstruction increased the expressions of HIF-1α and VEGF in alveolar bone. With upregulation of HIF-1α/VEGF via DMOG, alveolar bone density of BNO rats increased. Furthermore, DMOG promoted the osteogenic differentiation of BMSCs by stabilizing the HIF-1α protein and increasing the expression of VEGF.

CONCLUSION

Bilateral nasal obstruction changes alveolar bone structure and leads to a reduction in alveolar bone density. Moreover, the expression of the HIF-1α/VEGF signaling pathway increases to protect alveolar bone density reduction in BNO rats.

The role of magnesium in the pathogenesis of osteoporosis

Magnesium (Mg), a nutritional element which is essential for bone development and mineralization, has a role in the progression of osteoporosis. Osteoporosis is a multifactorial disease characterized by significant deterioration of bone microstructure and bone loss. Mg deficiency can affect bone structure in an indirect way through the two main regulators of calcium homeostasis (parathyroid hormone and vitamin D). In human osteoblasts (OBs), parathyroid hormone regulates the expression of receptor activator of nuclear factor-κ B ligand (RANKL) and osteoprotegerin (OPG) to affect osteoclast (OC) formation. In addition, Mg may also affect the vitamin D3 -mediated bone remodeling activity. vitamin D3 usually coordinates the activation of the OB and OC. The unbalanced activation OC leads to bone resorption. The RANK/RANKL/OPG axis is considered to be a key factor in the molecular mechanism of osteoporosis. Mg participates in the pathogenesis of osteoporosis by affecting the regulation of parathyroid hormone and vitamin D levels to affect the RANK/RANKL/OPG axis. Different factors affecting the axis and enhancing OC function led to bone loss and bone tissue microstructure damage, which leads to the occurrence of osteoporosis. Clinical research has shown that Mg supplementation can alleviate the symptoms of osteoporosis to some extent.

Endothelial cell signature in muscle stem cells validated by VEGFA-FLT1-AKT1 axis promoting survival of muscle stem cell

Endothelial and skeletal muscle lineages arise from common embryonic progenitors. Despite their shared developmental origin, adult endothelial cells (ECs) and muscle stem cells (MuSCs; satellite cells) have been thought to possess distinct gene signatures and signaling pathways. Here, we shift this paradigm by uncovering how adult MuSC behavior is affected by the expression of a subset of EC transcripts. We used several computational analyses including single-cell RNA-seq (scRNA-seq) to show that MuSCs express low levels of canonical EC markers in mice. We demonstrate that MuSC survival is regulated by one such prototypic endothelial signaling pathway (VEGFA-FLT1). Using pharmacological and genetic gain- and loss-of-function studies, we identify the FLT1-AKT1 axis as the key effector underlying VEGFA-mediated regulation of MuSC survival. All together, our data support that the VEGFA-FLT1-AKT1 pathway promotes MuSC survival during muscle regeneration, and highlights how the minor expression of select transcripts is sufficient for affecting cell behavior.

N6-Methyladenosine in Cell-Fate Determination of BMSCs: From Mechanism to Applications

The methylation of adenosine base at the nitrogen-6 position is referred to as "N6-methyladenosine (m6A)" and is one of the most prevalent epigenetic modifications in eukaryotic mRNA and noncoding RNA (ncRNA). Various m6A complex components known as "writers," "erasers," and "readers" are involved in the function of m6A. Numerous studies have demonstrated that m6A plays a crucial role in facilitating communication between different cell types, hence influencing the progression of diverse physiological and pathological phenomena. In recent years, a multitude of functions and molecular pathways linked to m6A have been identified in the osteogenic, adipogenic, and chondrogenic differentiation of bone mesenchymal stem cells (BMSCs). Nevertheless, a comprehensive summary of these findings has yet to be provided. In this review, we primarily examined the m6A alteration of transcripts associated with transcription factors (TFs), as well as other crucial genes and pathways that are involved in the differentiation of BMSCs. Meanwhile, the mutual interactive network between m6A modification, miRNAs, and lncRNAs was intensively elucidated. In the last section, given the beneficial effect of m6A modification in osteogenesis and chondrogenesis of BMSCs, we expounded upon the potential utility of m6A-related therapeutic interventions in the identification and management of human musculoskeletal disorders manifesting bone and cartilage destruction, such as osteoporosis, osteomyelitis, osteoarthritis, and bone defect.

Sphingosine-1-phosphate promotes osteogenesis by stimulating osteoblast growth and neovascularization in a vascular endothelial growth factor-dependent manner

Sphingosine-1-phosphate (S1P) plays multiple roles in bone metabolism and regeneration. Here, we have identified a novel S1P-regulated osteoanabolic mechanism functionally connecting osteoblasts (OBs) to the highly specialized bone vasculature. We demonstrate that S1P/S1PR3 signaling in OBs stimulates vascular endothelial growth factor a (VEGFa) expression and secretion to promote bone growth in an autocrine and boost osteogenic H-type differentiation of bone marrow endothelial cells in a paracrine manner. VEGFa-neutralizing antibodies and VEGF receptor inhibition by axitinib abrogated OB growth in vitro and bone formation in male C57BL/6J in vivo following S1P stimulation and S1P lyase inhibition, respectively. Pharmacological S1PR3 inhibition and genetic S1PR3 deficiency suppressed VEGFa production, OB growth in vitro, and inhibited H-type angiogenesis and bone growth in male mice in vivo. Together with previous work on the osteoanabolic functions of S1PR2 and S1PR3, our data suggest that S1P-dependent bone regeneration employs several nonredundant positive feedback loops between OBs and the bone vasculature. The identification of this yet unappreciated aspect of osteoanabolic S1P signaling may have implications for regular bone homeostasis as well as diseases where the bone microvasculature is affected such as age-related osteopenia and posttraumatic bone regeneration.

Zhuang-Gu-Fang intervenes vasculogenic and osteogenic coupling in GK rats through Notch1/Noggin/VEGF pathway

Background

Zhuang-Gu-Fang (ZGF) has been proved to treat osteoporosis in ovariectomized rats by increasing osteogenic related factors Leptin, Ghrelin and Peptide YY(PYY). However, the mechanism of ZGF in the treatment of diabetic osteoporosis (DOP) remains unclear. The aim of this study was to explore the therapeutic effect of ZGF on DOP and its potential molecular mechanism.

Methods

Using GK rats as models, the pharmacodynamic effects of ZGF on bone loss were evaluated by hematoxylin-eosin (H&E) staining and micro-computed.tomography (micro-CT). The expression levels of CD31 and endomucin (Emcn) were detected by immunofluorescence to assess the role of ZGF in angiogenic osteogenic coupling. Finally, real-time quantitative PCR (RT-PCR) and Western Blot (WB)were used to detect the expression levels of osteogenic and angiogenesis-related genes and proteins Notch1, Noggin and vascular endothelial growth factor (VEGF).

Results

Administration of ZGF demonstrated a significant mitigation of bone loss attributable to elevated glucose levels. H&E staining and micro-CT showed that ZGF notably improved the integrity of the trabecular and cortical bone microarchitecture. Moreover, ZGF was found to augment the density of type H vessels within the bone tissue, alongside elevating the expression levels of Osterix, a transcription factor pivotal for bone formation. Furthermore, our findings suggest that ZGF facilitates the activation of the Notch1/Noggin/VEGF pathway, indicating a potential mechanism through which ZGF exerts its osteoprotective effects.

Conclusion

Our results suggest that ZGF potentially facilitates the formation of type H vessels through the Notch1/Noggin/VEGF pathway. This action not only enhances angiogenic-osteogenic coupling but also contributes to the improvement of bone structure and density. Consequently, ZGF emerges as a promising therapeutic agent for the prevention and management of DOP, offering a novel approach by leveraging angiogenesis-dependent osteogenesis.

The emerging role of the gut microbiome in cancer cell plasticity and therapeutic resistance

Resistance to therapeutic agents is one of the major challenges in cancer therapy. Generally, the focus is given to the genetic driver, especially the genetic mutation behind the therapeutic resistance. However, non-mutational mechanisms, such as epigenetic modifications, and TME alteration, which is mainly driven by cancer cell plasticity, are also involved in therapeutic resistance. The concept of plasticity mainly relies on the conversion of non-cancer stem cells (CSCs) to CSCs or epithelial-to-mesenchymal transition via different mechanisms and various signaling pathways. Cancer plasticity plays a crucial role in therapeutic resistance as cancer cells are able to escape from therapeutics by shifting the phenotype and thereby enhancing tumor progression. New evidence suggests that gut microbiota can change cancer cell characteristics by impacting the mechanisms involved in cancer plasticity. Interestingly, gut microbiota can also influence the therapeutic efficacy of anticancer drugs by modulating the mechanisms involved in cancer cell plasticity. The gut microbiota has been shown to reduce the toxicity of certain clinical drugs. Here, we have documented the critical role of the gut microbiota on the therapeutic efficacy of existing anticancer drugs by altering the cancer plasticity. Hence, the extended knowledge of the emerging role of gut microbiota in cancer cell plasticity can help to develop gut microbiota-based novel therapeutics to overcome the resistance or reduce the toxicity of existing drugs. Furthermore, to improve the effectiveness of therapy, it is necessary to conduct more clinical and preclinical research to fully comprehend the mechanisms of gut microbiota.

[Research progress on mechanism of traumatic brain injury promoting fracture healing]

Objective

To summarize the research progress on the mechanism related to traumatic brain injury (TBI) to promote fracture healing, and to provide theoretical basis for clinical treatment of fracture non-union.

Methods

The research literature on TBI to promote fracture healing at home and abroad was reviewed, the role of TBI in fracture healing was summarized from three aspects of nerves, body fluids, and immunity, to explore new ideas for the treatment of fracture non-union.

Results

Numerous studies have shown that fracture healing is faster in patients with fracture combined with TBI than in patients with simple fracture. It is found that the expression of various cytokines and hormones in the body fluids of patients with fracture and TBI is significantly higher than that of patients with simple fracture, and the neurofactors released by the nervous system reaches the fracture site through the damaged blood-brain barrier, and the chemotaxis and aggregation of inflammatory cells and inflammatory factors at the fracture end of patients with combined TBI also differs significantly from those of patients with simple fracture. A complex network of humoral, neural, and immunomodulatory networks together promote regeneration of blood vessels at the fracture site, osteoblasts differentiation, and inhibition of osteoclasts activity.

Conclusion

TBI promotes fracture healing through a complex network of neural, humoral, and immunomodulatory, and can treat fracture non-union by intervening in the perifracture microenvironment.

Novel Strategies for Spatiotemporal and Controlled BMP-2 Delivery in Bone Tissue Engineering

Bone morphogenetic protein-2 (BMP-2) has been commercially approved by the Food and Drug Administration for use in bone defects and diseases. BMP-2 promotes osteogenic differentiation of mesenchymal stem cells. In bone tissue engineering, BMP-2 incorporated into scaffolds can be used for stimulating bone regeneration in organoid construction, drug testing platforms, and bone transplants. However, the high dosage and uncontrollable release rate of BMP-2 challenge its clinical application, mainly due to the short circulation half-life of BMP-2, microbial contamination in bone extracellular matrix hydrogel, and the delivery method. Moreover, in clinical translation, the requirement of high doses of BMP-2 for efficacy poses challenges in cost and safety. Based on these, novel strategies should ensure that BMP-2 is delivered precisely to the desired location within the body, regulating the timing of BMP-2 release to coincide with the bone healing process, as well as release BMP-2 in a controlled manner to optimize its therapeutic effect and minimize side effects. This review highlights improvements in bone tissue engineering applying spatiotemporal and controlled BMP-2 delivery, including molecular engineering, biomaterial modification, and synergistic therapy, aiming to provide references for future research and clinical trials.

Type H vessels: functions in bone development and diseases

Type H vessels are specialized blood vessels found in the bone marrow that are closely associated with osteogenic activity. They are characterized by high expression of endomucin and CD31. Type H vessels form in the cancellous bone area during long bone development to provide adequate nutritional support for cells near the growth plate. They also influence the proliferation and differentiation of osteoprogenitors and osteoclasts in a paracrine manner, thereby creating a suitable microenvironment to facilitate new bone formation. Because of the close relationship between type H vessels and osteogenic activity, it has been found that type H vessels play a role in the physiological and pathological processes of bone diseases such as fracture healing, osteoporosis, osteoarthritis, osteonecrosis, and tumor bone metastasis. Moreover, experimental treatments targeting type H vessels can improve the outcomes of these diseases. Here, we reviewed the molecular mechanisms related to type H vessels and their associated osteogenic activities, which are helpful in further understanding the role of type H vessels in bone metabolism and will provide a theoretical basis and ideas for comprehending bone diseases from the vascular perspective.

Mechanism of Liuwei Dihuang Pills in treating osteoporosis based on network pharmacology

Osteoporosis is a prevalent age-related disease that poses a significant public health concern as the population continues to age. While current treatments have shown some therapeutic benefits, their long-term clinical efficacy is limited by a lack of stable curative effects and significant adverse effects. Traditional Chinese Medicine has gained attention due to its positive curative effects and fewer side effects. Liuwei Dihuang Pill has been found to enhance bone mineral density in patients with osteoporosis and rats, but the underlying mechanism is not yet clear. To shed more light on this problem, this study aims to explore the pharmacological mechanism of Liuwei Dihuang Pill in treating osteoporosis using network pharmacology and molecular docking. The findings indicate that Liuwei Dihuang Pills treat osteoporosis through various targets and channels. Specifically, it mainly involves TNF, IL17, and HIF-1 signaling pathways and helps regulate biological processes such as angiogenesis, apoptosis, hypoxia, and gene expression. Furthermore, molecular docking demonstrates excellent binding properties between the drug components and key targets. Therefore, this study offers a theoretical foundation for understanding the pharmacological mechanism and clinical application of Liuwei Dihuang Pills in treating osteoporosis more comprehensively.

Andrographolide and pterostilbene inhibit adipocyte differentiation by downregulating PPARγ through different regulators

Adipogenesis involves commitment of stem cells and their differentiation into mature adipocytes. It is tightly regulated by hormones, nutrients and adipokines. Many natural compounds are being tested for their anti-adipogenic activity which can be attributed to apoptosis induction in adipocytes, blocking adipocyte differentiation, or inhibiting intracellular triglyceride synthesis and accumulation. In this study, we have determined molecular mechanism of two phytocompounds: andrographolide (AN) and pterostilbene (PT) during differentiation of the human MSCs into adipocyte. Interestingly, AN upregulates miR27a, whereas, PT upregulated SIRT1 which inhibits the expression of PPARγ. Thus, our results clearly demonstrate that both AN and PT inhibited adipogenesis by blocking a surge of reactive oxygen species (ROS) during differentiation and inhibiting expression of crucial transcription factors like SREBP1c and PPARγ.

VEGF dose controls the coupling of angiogenesis and osteogenesis in engineered bone

Vascular endothelial growth factor-A (VEGF) physiologically regulates both angiogenesis and osteogenesis, but its application in bone tissue engineering led to contradictory outcomes. A poorly understood aspect is how VEGF dose impacts the coordination between these two processes. Taking advantage of a unique and highly tunable platform, here we dissected the effects of VEGF dose over a 1,000-fold range in the context of tissue-engineered osteogenic grafts. We found that osteo-angiogenic coupling is exquisitely dependent on VEGF dose and that only a tightly defined dose range could stimulate both vascular invasion and osteogenic commitment of progenitors, with significant improvement in bone formation. Further, VEGF dose regulated Notch1 activation and the induction of a specific pro-osteogenic endothelial phenotype, independently of the promotion of vascular invasion. Therefore, in a therapeutic perspective, fine-tuning of VEGF dose in the signaling microenvironment is key to ensure physiological coupling of accelerated vascular invasion and improved bone formation.

Hydrogel scaffolds in bone regeneration: Their promising roles in angiogenesis

Bone tissue engineering (BTE) has become a hopeful potential treatment strategy for large bone defects, including bone tumors, trauma, and extensive fractures, where the self-healing property of bone cannot repair the defect. Bone tissue engineering is composed of three main elements: progenitor/stem cells, scaffold, and growth factors/biochemical cues. Among the various biomaterial scaffolds, hydrogels are broadly used in bone tissue engineering owing to their biocompatibility, controllable mechanical characteristics, osteoconductive, and osteoinductive properties. During bone tissue engineering, angiogenesis plays a central role in the failure or success of bone reconstruction via discarding wastes and providing oxygen, minerals, nutrients, and growth factors to the injured microenvironment. This review presents an overview of bone tissue engineering and its requirements, hydrogel structure and characterization, the applications of hydrogels in bone regeneration, and the promising roles of hydrogels in bone angiogenesis during bone tissue engineering.

Simulated microgravity affects stroma-dependent ex vivo myelopoiesis

Microgravity is known negatively affect physiology of living beings, including hematopoiesis. Dysregulation of hematopoietic cells and supporting stroma relationships in bone marrow niche may be in charge. We compared the efficacy of ex vivo expansion of hematopoietic stem and progenitor cells (HSPCs) in presence of native or osteocommitted MSCs under simulated microgravity (Smg) using Random Positioning Machine (RPM). In comparison with 1 g, a decrease of MSC-associated HSPCs and an increase of floating HSPCs was observed after 7 days of Smg exposure. Among floating HSPCs, primitive progenitors were presented by late CD34⁺/133^-. Total CFUs as well as erythroid (BFU-E) and granulocytic (CFU-G) numbers were lower. MSC-associated primitive HSPCs demonstrated increased proportion of late CD34⁺/133^- in expense of early CD34^-/133⁺. Osteo-MSCs preferentially supported late primitive CD34⁺ and more committed HSPCs as followed from increase of CFUs, and CD235a⁺ erythroid progenitors. Under Smg, an increased VEGF, eotaxin, and GRO-a levels, and a decrease in RANTES were found in the osteo-MSC-HSPC co-cultures. IL-6,-8, -13, G-CSF, GRO-a, MCP-3, MIP-1b, VEGF increased in co-culture with osteo-MSCs vs intact MSCs. Based on the findings, the misbalance between primitive/committed HSPCs and a decrease in hematopoiesis-supportive activity of osteocommitted cells are supposed to underline hematopoietic disorders during space flights.

High resolution intravital photoacoustic microscopy reveals VEGF-induced bone regeneration in mouse tibia

Osteogenesis and angiogenesis are essential for bone homeostasis and repair. Newly formed vessels convey osteogenic progenitors during bone regeneration. However, the lack of continuous and label-free visualization of the bone microvasculature has resulted in little understanding of the neovascular dynamics. Here, we take advantage of optical-resolution photoacoustic microscopy (ORPAM) for label-free, intravital, long-term observation of the bone vascular dynamics, including angiogenesis, remodeling and quantified angiogenic effect of locally-applied vascular endothelial growth factor (VEGF) in the murine tibial defect model. We employed ex vivo confocal microscopy and micro-computed tomography (micro-CT) imaging to verify the positive role of VEGF treatment. VEGF treatment increased the concentration of total hemoglobin, vascular branching, and vascular density, which correlated with more osteoprogenitors and increased bone formation within the defect. These data demonstrated ORPAM as a useful imaging tool that detected functional capillaries to understand hemodynamics, and revealed the effectiveness of locally delivered therapeutic agents with sufficient sensitivity, contributing to the understanding of spatiotemporal regulatory mechanisms on blood vessels during bone regeneration.

Vascularized Tissue Organoids

Tissue organoids hold enormous potential as tools for a variety of applications, including disease modeling and drug screening. To effectively mimic the native tissue environment, it is critical to integrate a microvasculature with the parenchyma and stroma. In addition to providing a means to physiologically perfuse the organoids, the microvasculature also contributes to the cellular dynamics of the tissue model via the cells of the perivascular niche, thereby further modulating tissue function. In this review, we discuss current and developing strategies for vascularizing organoids, consider tissue-specific vascularization approaches, discuss the importance of perfusion, and provide perspectives on the state of the field.

Exosomal miR-29a Derived from Bone Marrow Mesenchymal Stem Cells Promotes Mouse Bone Development and Formation

Bone undergoes constant remodeling during development, and the maintenance of its function requires a dynamic balance between bone formation and resorption by osteoclasts. With unique bone resorption capabilities, as large multinucleated cells, osteocytes participate in bone remodeling and they are produced by the mononuclear/macrophage cells under activation of Wnt and Runx2. The mechanism underlying osteogenesis remains unclear. We investigated the impact of exosomal miR-29a derived from BMSCs on bone development and formation. In this study, BMSCs were transfected and then injected into mice followed by analysis of femur and skull development and regeneration by HE staining and CT scanning, and the expression of DKK1, Runx-2, and osteogenic biomarkers (Osterix, Satb2, ALP, and BSP) by western blot and RT-qPCR. Compared with mice in miR-29a inhibitor group, the femur and skull of mice in miRNA NC group were more complete. miR-29a derived from BMSCs induced a decrease of DKK1 expression and increase of the expression of β-catenin and osteogenic transcription factors. In conclusion, this study demonstrates that BMSC-derived exosomes miR-29a facilitates osteogenesis in mice through inhibition of DKK1 expression.

Bibliometric and visual analysis of mesenchymal stem cells in the treatment of osteoporosis based on CiteSpace software

BACKGROUND

The focus of research in the treatment of osteoporosis (OP) has evolved from promoting bone formation and inhibiting bone resorption to current stem cell therapy. Due to their multipotent differentiation properties, mesenchymal stem cells (MSCs) can repair degenerated bones through transplantation, and have become a new method for the treatment of OP.

METHODS

Relevant literatures included in the Web of Science database core collection database from 2012 to 2021 were retrieved. CiteSpace software was used to analyze the cooperative relationship among authors, journals, institutions, and countries, and to analyze the co-citation situation of the literature. And performed co-occurrence analysis, cluster analysis and burst analysis of keywords, draw visual maps and analyzed the results.

RESULTS

A total of 2100 papers were included, and the number of papers published from 2012 to 2021 was on the rise. A total of 484 authors were included, and 176 authors published more than 3 papers. The high-yield authors were mainly represented by YAN JIN and BO GAO. A total of 99 journals were included, and the journal with the most publications was J BONE MINER RES. A total of 787 institutions were included, and the institution with the largest number of publications was Shanghai Jiao Tong University. A total of 65 countries were included. The country with the largest number of publications was China, and the United States had the highest centrality. The co-citation analysis of the literature found 2 articles with high citation frequency and high centrality. The main research direction was the mechanism of MSCs in the treatment of osteoporosis. A total of 133 keywords were included, and the hot keywords were osteogenic differentiation, expression, proliferation, bone marrow, etc.

CONCLUSIONS

The research hotspots in this field mainly focused on the mechanism of bone regeneration, proliferation and osteogenic differentiation of bone marrow MSCs, and the expression of osteogenic-related genes. The future research trends in this field are predicted to be the mechanism of action of microRNA and long non-coding RNA on MSCs and their relationship with OP, the mechanism of MSCs adipogenic and osteogenic differentiation, and tissue engineering scaffolds applications.

Paracrine and Autocrine Effects of VEGF Are Enhanced in Human eMSC Spheroids

The mechanisms underlying the therapeutic potential of MSCs are the focus of intense research. We studied human MSCs isolated from desquamated endometrium (eMSCs), which, as previously shown, have high regenerative potential in various disease models. The aim was to evaluate the role of secreted VEGF in stimulating angiogenesis and maintaining eMSC viability and migration, which is important for improving the therapeutic properties of MSCs. We compared three eMSC cultures differing in the level of VEGF secretion: 3D spheroids, monolayer eMSCs, and monolayer eMSCs with VEGF knockdown. Spheroid eMSCs produced higher amounts of VEGF and had the strongest paracrine effect on HUVEC. eMSCs with VEGF knockdown did not stimulate angiogenesis. Monolayered eMSCs expressed VEGFR1, while spheroid eMSCs expressed both VEGFR1 and VEGFR2 receptors. The knockdown of VEGF caused a significant decrease in the viability and migration of eMSCs. eMSCs from 3D spheroids enhanced proliferation and migration in response to exogenous VEGF, in contrast to monolayered eMSCs. Our results suggest that the VEGF-VEGFR1 loop appears to be autocrine-involved in maintaining the viability of eMSCs, and VEGFR2 expression enhances their response to exogenous VEGF, so the angiogenic potential of eMSC can be up- or downregulated by intrinsic VEGF signals.

Ginsenoside Rg1 interferes with the progression of diabetic osteoporosis by promoting type H angiogenesis modulating vasculogenic and osteogenic coupling

Ginsenoside Rg1 (Rg1) has been demonstrated to have antidiabetic and antiosteoporotic activities. The aim of this study was to investigate the protective effect of Rg1 against diabetic osteoporosis and the underlying mechanism. In vitro, we found that Rg1 increased the number of osteoprogenitors and alleviated high glucose (HG) induced apoptosis of osteoprogenitors by MTT assays and flow cytometry. qRT‒PCR and western blot analysis suggested that Rg1 can also promote the secretion of vascular endothelial growth factor (VEGF) by osteoprogenitors and promote the coupling of osteogenesis and angiogenesis. Rg1 can also promote the proliferation of human umbilical vein endothelial cells (HUVECs) cultured in high glucose, enhance the angiogenic ability of endothelial cells, and activate the Notch pathway to promote endothelial cells to secrete the osteogenesis-related factor Noggin to regulate osteogenesis, providing further feedback coupling of angiogenesis and osteogenesis. Therefore, we speculated that Rg1 may have similar effects on type H vessels. We used the Goto-Kakizaki (GK) rat model to perform immunofluorescence staining analysis on two markers of type H vessels, Endomucin (Emcn) and CD31, and the osteoblast-specific transcription factor Osterix, and found that Rg1 stimulates type H angiogenesis and bone formation. In vivo experiments also demonstrated that Rg1 promotes VEGF secretion, activates the Noggin/Notch pathway, increases the level of coupling between type H vessels and osteogenesis, and improves the bone structure of GK rats. All of these data reveal that Rg1 is a promising candidate drug for treating diabetic osteoporosis as a potentially bioactive molecule that promotes angiogenesis and osteointegration coupling.

VEGFA from osteoblasts is not required for lamellar bone formation following tibial loading

The relationship between osteogenesis and angiogenesis is complex. Normal bone development requires angiogenesis, mediated by vascular endothelial growth factor A (VEGFA). Studies have demonstrated through systemic inhibition or genetic modification that VEGFA is indispensable for several types of bone repair, presumably via its role in supporting angiogenesis. But a direct role for VEGFA within osteoblasts, in the absence of angiogenesis, has also been suggested. To address the question of whether VEGFA from osteoblasts supports bone formation directly, we applied anabolic loading to induce lamellar bone formation in mice, a process shown to be independent of angiogenesis. We hypothesized that VEGFA from osteoblasts is required for lamellar bone formation. To test this hypothesis, we applied axial tibial compression to inducible Cre/LoxP mice from three lines. Vegfafl/fl mice were crossed with Ubiquitin C (UBC), Osterix (Osx) and Dentin-Matrix Protein 1 (DMP1) Cre-ERT2 mice to target all cells, (pre)osteoblast-lineage cells, and mature osteoblasts and osteocytes, respectively. Genotype effects were determined by comparing control (Vegfafl/fl) and Cre+ (VegfaΔ) mice for each line. At 5 months of age tamoxifen was injected for 5 days followed by a 3-week clearance prior to loading. Female and male mice (N = 100) were loaded for 5 days to peak forces to engender -3100 με peak compressive strain and processed for dynamic histomorphometry (day 12). Percent MS/BS increased 20-70 % as a result of loading, with no effect of genotype in Osx or Dmp1 lines. In contrast, the UBC groups had a significant decrease in relative periosteal BFR/BS in VegfaΔ vs. Vegfafl/fl mice. The UBC line did not have any cortical bone phenotype in non-loaded femurs. In summary, dynamic histomorphometry data confirmed that tibial loading induces lamellar bone formation. Contrary to our hypothesis, there was no decrease in loading-induced bone formation in the Osx or Dmp1 lines in the absence of VEGFA. There was a decrease in bone formation in the UBC line where all cells were targeted. This result indicates that VEGFA from a non-osteoblast cell source supports loading-induced lamellar bone formation, although osteoblast/osteocyte VEGFA is dispensable. These findings support a paracrine model whereby non-osteoblast VEGFA supports lamellar bone formation, independent of angiogenesis.

Taohong Siwu Decoction Promotes Osteo-Angiogenesis in Fractures by Regulating the HIF-1α Signaling Pathway

Background

Vascular damage is a major consequence of bone fracture. Taohong Siwu decoction (TSD) can raise the expression of vascular endothelial growth factor (VEGF) in fracture healing. However, its molecular mechanism in promoting angiogenesis is still unknown. The aim of this study was to investigate the potential mechanisms of TSD in the regulation of osteo-angiogenesis in fracture healing.

Methods

A rat tibial fracture model was established. After low- (4.5 g·kg⁻¹), medium- (9 g·kg⁻¹), and high-dose TSD (18 g·kg⁻¹) and panax notoginsenoside (25 mg kg⁻¹) treatment, hematoxylin-eosin staining was employed to visualize pathological changes in bone tissues. The levels of cytokines (interleukin (IL)-2, tumor necrosis factor-α (TNF-α), IL-6, and IL-1β), thromboxane B2 (TXB2), and 6 ketone prostaglandin F1α (6-Keto-PGF1α) were quantified by enzyme-linked immunosorbent assay (ELISA). Immunofluorescence was used to identify the rat aortic endothelial cells (RAECs). Control serum, 10% TSD-containing serum, and 10% TSD-containing serum combined with hypoxia-inducible factor-1α (HIF-1α) inhibitor were used to treat the RAECs and rat osteoblasts. Transwell migration assay was utilized to examine the migration of the RAECs. The Matrigel tubulogenesis assay was used for the assessment of angiogenesis. The expression of angiogenesis- (von Hippel-Lindau tumor suppressor (VHL), HIF-1α, VEGF, angiopoietin-2 (Ang-2), and pVHL) and osteogenesis-related (alkaline phosphatase (ALP), runt-related transcription factor 2 (Runx2), and osteopontin-1 (OPN-1)) protein and gene was detected by western blot and quantitative real-time PCR (qRT-PCR).

Results

Compared with the model group, TSD increased the trabecular bone areas, numbers, and thicknesses in fractured rats. In the plasma, the levels of cytokines and TXB2 in the middle- and high-dose TSD group were significantly lower than those in the model group (P < 0.01). The 6-keto-PGF1α content was increased by middle- and high-dose TSD intervention (P < 0.01). Compared to the control serum group, the angiogenesis and migration of the RAECs were enhanced in the TSD group (P < 0.001). The expression of HIF-1α, VEGF, and Ang-2 in the TSD group upregulated significantly (P < 0.001). VHL and pVHL were inhibited under TSD-containing serum treatment (P < 0.001). ALP, Runx2, and OPN-1 were increased obviously in the TSD group (P < 0.001). Nevertheless, the HIF-1α inhibitor reversed these changes (P < 0.001).

Conclusion

TSD promotes angiogenesis and osteogenesis by regulating the HIF-1α signaling pathway. Meanwhile, it can effectively reduce the risk of inflammation and improve blood circulation.

Loss of Vhl alters trabecular bone loss during S. aureus osteomyelitis in a cell-specific manner

Osteomyelitis, or bone infection, is a major complication of accidental trauma or surgical procedures involving the musculoskeletal system. Staphylococcus aureus is the most frequently isolated pathogen in osteomyelitis and triggers significant bone loss. Hypoxia-inducible factor (HIF) signaling has been implicated in antibacterial immune responses as well as bone development and repair. In this study, the impact of bone cell HIF signaling on antibacterial responses and pathologic changes in bone architecture was explored using genetic models with knockout of either Hif1a or a negative regulator of HIF-1α, Vhl. Deletion of Hif1a in osteoblast-lineage cells via Osx-Cre (Hif1aΔOB ) had no impact on bacterial clearance or pathologic changes in bone architecture in a model of post-traumatic osteomyelitis. Knockout of Vhl in osteoblast-lineage cells via Osx-Cre (VhlΔOB ) caused expected increases in trabecular bone volume per total volume (BV/TV) at baseline and, intriguingly, did not exhibit an infection-mediated decline in trabecular BV/TV, unlike control mice. Despite this phenotype, bacterial burdens were not affected by loss of Vhl. In vitro studies demonstrated that transcriptional regulation of the osteoclastogenic cytokine receptor activator of NF-κB ligand (RANKL) and its inhibitor osteoprotegerin (OPG) is altered in osteoblast-lineage cells with knockout of Vhl. After observing no impact on bacterial clearance with osteoblast-lineage conditional knockouts, a LysM-Cre model was used to generate Hif1aΔMyeloid and VhlΔMyeloid mouse models to explore the impact of myeloid cell HIF signaling. In both Hif1aΔMyeloid and VhlΔMyeloid models, bacterial clearance was not impacted. Moreover, minimal impacts on bone architecture were observed. Thus, skeletal HIF signaling was not found to impact bacterial clearance in our mouse model of post-traumatic osteomyelitis, but Vhl deletion in the osteoblast lineage was found to limit infection-mediated trabecular bone loss, possibly via altered regulation of RANKL-OPG gene transcription.

Advances in the superhydrophilicity-modified titanium surfaces with antibacterial and pro-osteogenesis properties: A review

In recent years, the rate of implant failure has been increasing. Microbial infection was the primary cause, and the main stages included bacterial adhesion, biofilm formation, and severe inhibition of implant osseointegration. Various biomaterials and their preparation methods have emerged to produce specific implants with antimicrobial or bactericidal properties to reduce implant infection caused by bacterial adhesion and effectively promote bone and implant integration. In this study, we reviewed the research progress of bone integration promotion and antibacterial action of superhydrophilic surfaces based on titanium alloys. First, the adverse reactions caused by bacterial adhesion to the implant surface, including infection and bone integration deficiency, are briefly introduced. Several commonly used antibacterial methods of titanium alloys are introduced. Secondly, we discuss the antibacterial properties of superhydrophilic surfaces based on ultraviolet photo-functionalization and plasma treatment, in contrast to the antibacterial principle of superhydrophobic surface morphology. Thirdly, the osteogenic effects of superhydrophilic surfaces are described, according to the processes of osseointegration: osteogenic immunity, angiogenesis, and osteogenic related cells. Finally, we discuss the challenges and prospects for the development of this superhydrophilic surface in clinical applications, as well as the prominent strategies and directions for future research.

Femoral Skeletal Perfusion is Reduced in Male Mice with Type 1 Diabetes

The bone vasculature and blood flow are critical for bone modeling, remodeling, and regeneration. Vascular complications are one of the major health concerns of people with type 1 diabetes (T1D). Moreover, people with T1D have lower bone mineral density and increased bone fragility. The goal of this study was to understand whether bone perfusion was altered in a mouse model of T1D and how this related to changes in bone mass. T1D was induced via the administration of streptozotocin in 12-week-old C57BL/6NHsd male mice. The assessment of bone perfusion utilized the injection of fluorescent microspheres with assessment of levels in the bone. Femoral blood flow and VEGF-A expression in the cortical bone shafts were lower in the T1D mice, compared to healthy controls, in this pattern followed that of changes in bone mass. These data demonstrate a possible association between reduced skeletal perfusion and reduced bone mass in the setting of T1D.

Stem cell-based therapy for human diseases

Recent advancements in stem cell technology open a new door for patients suffering from diseases and disorders that have yet to be treated. Stem cell-based therapy, including human pluripotent stem cells (hPSCs) and multipotent mesenchymal stem cells (MSCs), has recently emerged as a key player in regenerative medicine. hPSCs are defined as self-renewable cell types conferring the ability to differentiate into various cellular phenotypes of the human body, including three germ layers. MSCs are multipotent progenitor cells possessing self-renewal ability (limited in vitro) and differentiation potential into mesenchymal lineages, according to the International Society for Cell and Gene Therapy (ISCT). This review provides an update on recent clinical applications using either hPSCs or MSCs derived from bone marrow (BM), adipose tissue (AT), or the umbilical cord (UC) for the treatment of human diseases, including neurological disorders, pulmonary dysfunctions, metabolic/endocrine-related diseases, reproductive disorders, skin burns, and cardiovascular conditions. Moreover, we discuss our own clinical trial experiences on targeted therapies using MSCs in a clinical setting, and we propose and discuss the MSC tissue origin concept and how MSC origin may contribute to the role of MSCs in downstream applications, with the ultimate objective of facilitating translational research in regenerative medicine into clinical applications. The mechanisms discussed here support the proposed hypothesis that BM-MSCs are potentially good candidates for brain and spinal cord injury treatment, AT-MSCs are potentially good candidates for reproductive disorder treatment and skin regeneration, and UC-MSCs are potentially good candidates for pulmonary disease and acute respiratory distress syndrome treatment.

The osteo-angiogenic signaling crosstalk for bone regeneration: harmony out of complexity

In recent years it has been increasingly appreciated that blood vessels are not simply suppliers of nutrients and oxygen, but actually play an exquisite regulatory role in bone development and repair. A specialized kind of endothelium, named type H because of its high expression of CD31 and Endomucin, constitutes anatomically defined vessels in proximity of the epiphyseal growth plate. Type H endothelium regulates the proliferation and differentiation of both osteoblasts and osteoclasts through the secretion of angiocrine signals and is a hub for the bidirectional molecular crosstalk between the different cell populations of the osteogenic microenvironment. Type H vessels are a key target for current translational approaches aiming at coupling angiogenesis and osteogenesis for bone repair. Open questions remain about their presence and features in notstereotyped tissues, like engineered osteogenic grafts, and the opportunities for their clinical stimulation by pharmacological treatments.

Upregulation of osteoprotegerin inhibits tert-butyl hydroperoxide-induced apoptosis of human chondrocytes

Necrosis of the femoral head (NFH) is an orthopedic disease characterized by a severe lack of blood supply to the femoral head and a marked increase in intraosseous pressure. NFH is associated with numerous factors, such as alcohol consumption and hormone levels. The present study focused on the expression levels of osteoprotegerin (OPG) in NFH and the effect of OPG overexpression on chondrocyte apoptosis. The results demonstrated that OPG expression was markedly decreased in the femoral head of patients with NFH compared with normal femoral heads. Lentivirus-mediated overexpression of OPG in human chondrocytes reversed the decrease in cell viability and the increase in reactive oxygen species production induced by an oxidative stress-inducing factor, tert-butyl hydroperoxide. Flow cytometry and TUNEL assays revealed that OPG overexpression inhibited the apoptosis of chondrocytes. In addition, it was revealed that OPG exerted its anti-apoptotic effect mainly by promoting Bcl-2 expression and Akt phosphorylation and inhibiting caspase-3 cleavage and Bax expression. The present study revealed that OPG may be an important regulator of NFH.

Bone Marrow Mesenchymal Stem Cell-Exosomes (BMSC-ExO) Promote Osteogenic Differentiation In Vitro and Osteogenesis In Vivo by Regulating miR-318/Runt-Related Transcription Factor 2 (RUNX2)

Primary osteoporosis (PMOP) is characterized by bone mass reduction and bone microstructure destruction, increased bone fragility and prone to fracture, which is partially caused by ovarian dysfunction and decreased estrogen content. Bone marrow mesenchymal stem cell exosomes (BMSC-ExO) can improve PMOP. In this study, BMSC-EXO was used to study the role and function of miR-318 and Runx2 in PMOP. Human osteogenitor cells were isolated from PMOP patients with primary osteoporosis. After BMSC-exo treatment, miR-318 and Runx 2 level was tested by RT-qPCR and Western blot. In addition, mice in OVX group were treated with BMSC-ExO (bilateral ovaries were removed) to observe the effect of BMSC-ExO on bone tissue. Our results showed that BMSC-exo treatment significantly decreased miR-318 level, upregulated RUNX2 expression and increased ALP activity. In addition, BMSC-exo administration ameliorated the declined bone mass and bone formation in osteoporotic femurs in OVX mice. In conclusion, BMSC-Exo enhances Runx2 levels by down-regulation of miR-318, thereby promoting osteogenic differentiation of osteogenitor cells, providing new potential therapeutic targets for treating PMOP.

Discovery of surface biomarkers for cell mechanophenotype via an intracellular protein-based enrichment strategy

Cellular mechanophenotype is often a defining characteristic of conditions like cancer malignancy/metastasis, cardiovascular disease, lung and liver fibrosis, and stem cell differentiation. However, acquiring living cells based on mechanophenotype is challenging for conventional cell sorters due to a lack of biomarkers. In this study, we demonstrate a workflow for surface protein discovery associated with cellular mechanophenotype. We sorted heterogeneous adipose-derived stem/stromal cells (ASCs) into groups with low vs. high lamin A/C, an intracellular protein linked to whole-cell mechanophenotype. Proteomic data of enriched groups identified surface protein candidates as potential biochemical proxies for ASC mechanophenotype. Select surface biomarkers were used for live-cell enrichment, with subsequent single-cell mechanical testing and lineage-specific differentiation. Ultimately, we identified CD44 to have a strong inverse correlation with whole-cell elastic modulus, with CD44lo cells exhibiting moduli three times greater than that of CD44hi cells. Functionally, these stiff and soft ASCs showed enhanced osteogenic and adipogenic differentiation potential, respectively. The described workflow can be replicated for any phenotype with a known correlated intracellular protein, allowing for the acquisition of live cells for further characterization, diagnostics, or therapeutics.

Smoking Impairs Hematoma Formation and Dysregulates Angiogenesis as the First Steps of Fracture Healing

Bone fracture healing is an overly complex process in which inflammation, osteogenesis, and angiogenesis are tightly coupled, and delayed fracture repair is a very common health risk. One of the major causes of delayed healing is the formation of insufficient vasculature. Precise regulation of blood vessels in bone and their interplay with especially osteogenic processes has become an emerging topic within the last years; nevertheless, regulation of angiogenesis in (early) diseased fracture repair is still widely unknown. Here, we aim to develop an in vitro model for the analysis of early fracture healing which also enables the analysis of angiogenesis as a main influencing factor. As smoking is one of the main risk factors for bone fractures and developing a delay in healing, we model smoking and non-smoking conditions in vitro to analyze diverging reactions. Human in vitro fracture hematomas mimicking smokers' and non-smokers' hematomas were produced and analyzed regarding cell viability, inflammation, osteogenic and chondrogenic differentiation, and angiogenic potential. We could show that smokers' blood hematomas were viable and comparable to non-smokers. Smokers' hematomas showed an increase in inflammation and a decrease in osteogenic and chondrogenic differentiation potential. When analyzing angiogenesis, we could show that the smokers' hematomas secrete factors that drastically reduced HUVEC proliferation and tube formation. With an angiogenesis array and gene expression analysis, we could identify the main influencing factors: Anpgt1/2, Tie2, and VEGFR2/3. In conclusion, our model is suitable to mimic smoking conditions in vitro showing that smoking negatively impacts early vascularization of newly formed tissue.

A novel natural-derived tilapia skin collagen mineralized with hydroxyapatite as a potential bone-grafting scaffold

Collagen is widely used in medical field because of its excellent biocompatibility and bioactivity. To date, collagen for biomedical use is always derived from bovine or swine. The purpose of this study was to evaluate collagen-based biomaterials from non-mammalian donors for bone repair. Thus, tilapia skin collagen-hydroxyapatite (T-col/HAp) scaffolds were fabricated in three different proportions and then cross-linked with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide-N-hydroxysuccinimide (EDC-NHS). The scaffolds were evaluated for their microstructure, chemical and physical properties, mechanical strength and degradability. Then the in vitro responses of bone mesenchymal stem cells (BMSCs) to the scaffolds were investigated in terms of cellular proliferation, differentiation, and mineralization. At last, the scaffolds were implanted into rat skull critical defections to investigate the potential of osteogenic activities. As a result, the pore sizes and the porosities of the scaffolds were approximately 106.67–196.67 μm and 81.5%–66.7%. Pure collagen group showed a mechanical strength of 0.065 MPa, and the mechanical strength was significantly enhanced almost 17 times and 32 times in collagen/HAp ratio 1:4 and 1:9 groups. In vitro studies revealed the most prominent and healthy growth of BMSCs in collagen/HAp ratio 1:4 group. All the scaffolds showed certain osteogenic activities and those loaded with small amount of hydroxyapatite showed the strongest bioactivities. The micro-CT showed that the critical bone defect was almost filled with generated bone 6 months after implantation in collagen/HAp ratio 1:4 group. The biomechanics tests further confirmed the highest generated bone strength was in the collagen/HAp ratio 1:4 group. This study indicated aquatic collagen might be a potential alternative for type I collagen from mammals in bone tissue engineering. The combination of collagen and inorganic materials was also important and appropriate inorganic component loading can achieve both osteogenic quality and osteogenic efficiency to a certain extent.

Hedgehog Signaling Controls Bone Homeostasis by Regulating Osteogenic/Adipogenic Fate of Skeletal Stem/Progenitor Cells in Mice

Skeletal stem/progenitor cells (SSPCs) can differentiate into osteogenic or adipogenic lineage. The mechanism governing lineage allocation of SSPCs is still not completely understood. Hedgehog (Hh) signaling plays an essential role in specifying osteogenic fate of mesenchymal progenitors during embryogenesis. However, it is still unclear whether Hh signaling is required for lineage allocation of SSPCs in postnatal skeleton, and whether its dysregulation is related to age-related osteoporosis. Here, we demonstrated that Hh signaling was activated in metaphyseal SSPCs during osteogenic differentiation in the adult skeleton, and its activity decreased with aging. Inactivation of Hh signaling by genetic ablation of Smo, a key molecule in Hh signaling, in Osx-Cre-targeted SSPCs and hypertrophic chondrocytes led to decreased bone formation and increased bone marrow adiposity, two key pathological features of age-related osteoporosis. Moreover, we found that the bone-fat imbalance phenotype caused by Smo deletion mainly resulted from aberrant allocation of SSPCs toward adipogenic lineage at the expense of osteogenic differentiation, but not due to accelerated transdifferentiation of chondrocytes into adipocytes. Mechanistically, we found that Hh signaling regulated osteoblast versus adipocyte fate of SSPCs partly through upregulating Wnt signaling. Thus, our results indicate that Hh signaling regulates bone homeostasis and age-related osteoporosis by acting as a critical switch of cell fate decisions of Osx-Cre-targeted SSPCs in mice and suggest that Hh signaling may serve as a potential therapeutic target for the treatment of osteoporosis and other metabolic bone diseases. © 2021 American Society for Bone and Mineral Research (ASBMR).

Gene expression analysis of subchondral bone, cartilage, and synovium in naturally occurring equine palmar/plantar osteochondral disease

Osteoarthritis (OA) is a disease of the entire joint but the relationship between pathological events in various joint tissues is poorly understood. We examined concurrent changes in bone, cartilage, and synovium in a naturally occurring equine model of joint degeneration. Joints (n = 64) were grossly assessed for palmar/plantar osteochondral disease (POD) in racehorses that required euthanasia for unrelated reasons and assigned a grade of 0 (n = 34), 1 (n = 17), 2 or 3 (n = 13) using a recognized grading scheme. Synovium, cartilage, and subchondral bone were collected for histological and gene expression analysis. Relations between POD grade, cartilage histological score, and gene expression levels were examined using one-way analysis of variance or Kruskal-Wallis test and Spearman's correlation coefficient with corrections for multiple comparisons. Cartilage histological score increased in joints with POD grade 1 (p = 0.002) and 2 or 3 (p < 0.001) compared to 0. At grade 1, expression of COL1A1, COL2A1, and MMP1 increased and BGN decreased in subchondral bone while expression of BGN and ACAN decreased in cartilage. These changes further progressed at grades 2 and 3. POD grades 2 and 3 were associated with decreased expression of osteoclast inhibitor OPG and increased markers of cartilage degeneration (MMP13, COL1A1). Expression of the vascular endothelial growth factor decreased with POD grade and negatively correlated with cartilage histological score. Synovium showed no histological or transcriptomic changes related to pathology grade. Cartilage degeneration in POD is likely to be secondary to remodeling of the subchondral bone. Limited activation of proinflammatory and catabolic genes and moderate synovial pathology suggests distinct molecular phenotype of POD compared with OA.

Suture Cells in a Mechanical Stretching Niche: Critical Contributors to Trans-sutural Distraction Osteogenesis

Trans-sutural distraction osteogenesis has been proposed as an alternative technique of craniofacial remodelling surgery for craniosynostosis correction. Many studies have defined the contribution of a series of biological events to distraction osteogenesis, such as changes in gene expression, changes in suture cell behaviour and changes in suture collagen fibre characteristics. However, few studies have elucidated the systematic molecular and cellular mechanisms of trans-sutural distraction osteogenesis, and no study has highlighted the contribution of cell-cell or cell-matrix interactions with respect to the whole expansion process to date. Therefore, it is difficult to translate largely primary mechanistic insights into clinical applications and optimize the clinical outcome of trans-sutural distraction osteogenesis. In this review, we carefully summarize in detail the literature related to the effects of mechanical stretching on osteoblasts, endothelial cells, fibroblasts, immune cells (macrophages and T cells), mesenchymal stem cells and collagen fibres in sutures during the distraction osteogenesis process. We also briefly review the contribution of cell-cell or cell-matrix interactions to bone regeneration at the osteogenic suture front from a comprehensive viewpoint.

Toward Marrow Adipocytes: Adipogenic Trajectory of the Bone Marrow Stromal Cell Lineage

Bone marrow contains precursor cells for osteoblasts and adipocytes in the stromal compartment. Bone marrow adipose tissue (BMAT) is an important constituent of the bone marrow that is particularly abundant in adults. BMAT is composed of the proximal "regulated" BMAT containing individual adipocytes interspersed within actively hematopoietic marrow, and the distal "constitutive" BMAT containing large adipocytes in the area of low hematopoiesis. Historically, bone marrow adipocytes were regarded as one of the terminal states of skeletal stem cells, which stand at the pinnacle of the lineage and possess trilineage differentiation potential into osteoblasts, chondrocytes and adipocytes. Recent single-cell RNA-sequencing studies uncover a discrete group of preadipocyte-like cells among bone marrow stromal cells (BMSCs), and recent mouse genetic lineage-tracing studies reveal that these adipocyte precursor cells possess diverse functions in homeostasis and regeneration. These adipogenic subsets of BMSCs are abundant in the central marrow space and can directly convert not only into lipid-laden adipocytes but also into skeletal stem cell-like cells and osteoblasts under regenerative conditions. It remains determined whether there are distinct adipocyte precursor cell types contributing to two types of BMATs. In this short review, we discuss the functions of the recently identified subsets of BMSCs and their trajectory toward marrow adipocytes, which is influenced by multiple modes of cell-autonomous and non-cell autonomous regulations.

Regulation of Methylase METTL3 on Fat Deposition

N6-methyladenosine (m6A) is the most prevalent and abundant type of internal post-transcriptional RNA modification in eukaryotic cells. METTL3 is a methylation modifying enzyme, which can directly or indirectly affect biological processes, such as RNA degradation, translation and splicing. In addition, it was found that 67% of 3'-UTR regions containing m6A sites had at least one miRNA binding site, and the number of m6A at 3'-UTR sites was closely related to the binding sites of miRNA. With the improvement of human living standards, obesity has become a very serious and urgent problem. The essence of obesity is the accumulation of excess fat. Exploring the origin and development mechanisms of adipocyte from the perspective of fat deposition has always been a hotspot in the field of adipocyte research. The aim of the present review is to focus on METTL3 regulating fat deposition through mRNA/adipocyte differentiation axis and pri-miRNA/pre-miRNA/target genes/adipocyte differentiation and to provide a theoretical basis according to the currently available literature for further exploring this association. This review may provide new insights for obesity, fat deposition disease and molecular breeding.

Osteoblast-derived EGFL6 couples angiogenesis to osteogenesis during bone repair

Rationale: Angiogenesis and osteogenesis are highly coupled processes which are indispensable to bone repair. However, the underlying mechanism(s) remain elusive. To bridge the gap in understanding the coupling process is crucial to develop corresponding solutions to abnormal bone healing. Epidermal growth factor-like protein 6 (EGFL6) is an angiogenic factor specifically and distinctively up-regulated during osteoblast differentiation. In contrast with most currently known osteoblast-derived coupling factors, EGFL6 is highlighted with little or low expression in other cells and tissues.

Methods: In this study, primary bone marrow mesenchymal stem cells (MSCs) and osteoblastic cell line (MC3T3-E1) were transduced with lentiviral silencing or overexpression constructs targeting EGFL6. Cells were induced by osteogenic medium, followed by the evaluation of mineralization as well as related gene and protein expression. Global and conditional knockout mice were established to examine the bone phenotype under physiological condition. Furthermore, bone defect models were created to investigate the outcome of bone repair in mice lacking EGFL6 expression.

Results: We show that overexpression of EGFL6 markedly enhances osteogenic capacity in vitro by augmenting bone morphogenic protein (BMP)-Smad and MAPK signaling, whereas downregulation of EGFL6 diminishes osteoblastic mineralization. Interestingly, osteoblast differentiation was not affected by the exogenous addition of EGFL6 protein, thereby indicating that EGFL6 may regulate osteoblastic function in an intracrine manner. Mice with osteoblast-specific and global knockout of EGFL6 surprisingly exhibit a normal bone phenotype under physiological conditions. However, EGFL6-deficiency leads to compromised bone repair in a bone defect model which is characterized by decreased formation of type H vessels as well as osteoblast lineage cells.

Conclusions: Together, these data demonstrate that EGFL6 serves as an essential regulator to couple osteogenesis to angiogenesis during bone repair.