Cell-matrix signals specify bone endothelial cells during developmental osteogenesis

Programmed surface platform orchestrates anti-bacterial ability and time-sequential bone healing for implant-associated infection

Implant-associated infection (IAI) has become an intractable challenge in clinic. The healing of IAI is a complex physiological process involving a series of spatiotemporal connected events. However, existing titanium-based implants in clinic suffer from poor antibacterial effect and single function. Herein, a versatile surface platform based on the presentation of sequential function is developed. Fabrication of titania nanotubes and poly-γ-glutamic acid (γ-PGA) achieves the efficient incorporation of silver ions (Ag+) and the pH-sensitive release in response to acidic bone infection microenvironment. The optimized PGA/Ag platform exhibits satisfactory biocompatibility and converts macrophages from pro-inflammatory M1 to pro-healing M2 phenotype during the subsequent healing stage, which creates a beneficial osteoimmune microenvironment and promotes angio/osteogenesis. Furthermore, the PGA/Ag platform mediates osteoblast/osteoclast coupling through inhibiting CCL3/CCR1 signaling. These biological effects synergistically improve osseointegration under bacterial infection in vivo, matching the healing process of IAI. Overall, the novel integrated PGA/Ag surface platform proposed in this study fulfills function cascades under pathological state and shows great potential in IAI therapy.

Skeletal pathology in mouse models of Gould syndrome is partially alleviated by genetically reducing TGFβ signaling

Skeletal defects are hallmark features of many extracellular matrix (ECM) and collagen-related disorders. However, a biological function in bone has never been defined for the highly evolutionarily conserved type IV collagen. Collagen type IV alpha 1 (COL4A1) and alpha 2 (COL4A2) form α1α1α2 (IV) heterotrimers that represent a fundamental basement membrane constituent present in every organ of the body, including the skeleton. COL4A1 and COL4A2 mutations cause Gould syndrome, a variable and clinically heterogenous multisystem disorder generally characterized by the presence of cerebrovascular disease with ocular, renal, and muscular manifestations. We have previously identified elevated TGFβ signaling as a pathological insult resulting from Col4a1 mutations and demonstrated that reducing TGFβ signaling ameliorate ocular and cerebrovascular phenotypes in Col4a1 mutant mouse models of Gould syndrome. In this study, we describe the first characterization of skeletal defects in Col4a1 mutant mice that include a developmental delay in osteogenesis and structural, biomechanical and vascular alterations of mature bones. Using distinct mouse models, we show that allelic heterogeneity influences the presentation of skeletal pathology resulting from Col4a1 mutations. Importantly, we found that TGFβ target gene expression is elevated in developing bones from Col4a1 mutant mice and show that genetically reducing TGFβ signaling partially ameliorates skeletal manifestations. Collectively, these findings identify a novel and unsuspected role for type IV collagen in bone biology, expand the spectrum of manifestations associated with Gould syndrome to include skeletal abnormalities, and implicate elevated TGFβ signaling in skeletal pathogenesis in Col4a1 mutant mice.

Loss of Hdac4 in Osteoprogenitors Impairs Postnatal Trabecular and Cortical Bone Formation, Resulting in a Dwarfism and Osteopenia Phenotype in Mice

HDAC4 is a class II histone deacetylation protein with a well-characterized role in chondrocyte differentiation and skeletal development, and dysregulated expression or haploinsufficiency of Hdac4 leads to skeletal formation and malformation disorders. The early lethality of hdac4 ablation mice hindered further investigation of its role in postnatal bone growth and development. Therefore, this study aims to investigate the significant role of Hdac4 in postnatal endochondral bone development using two mouse models with conditional deletion of Hdac4 in Sp7-expressing osteoprogenitors or chondrocytes and monitored postnatal bone development. The phenotype of Acan-CreERT2; Hdac4fl/fl mice largely resembled that of conventional Hdac4-/- mice. But phenotypic characterizations of mice with Hdac4 inactivation in Sp7-expressing osteoprogenitors (Sp7-Cre; Hdac4fl/fl) showed dwarfism with body and limb shortening and remarkable skeletal defects. Micro-computed tomography analysis of tibias further demonstrated that loss of Hdac4 expression impaired bone formation and microarchitecture, mainly characterized by dysplasia of trabecular and cortical bone in young mice. Our in vivo and in vitro data support a crucial role for Hdac4 in regulating osteoblast proliferation and differentiation, bone matrix protein production, angiogenesis, and ultimately trabecular and cortical bone formation. Moreover, RNA-seq analysis implicated Hdac4 in the regulation of key genes and pathways necessary to affect the accumulation of extracellular matrix, biological processes related to signal transduction, and skeletal growth. Collectively, our data show that postnatal expression of Hdac4 in Sp7-expressing osteoprogenitors provides essential regulatory oversight of endochondral bone formation, bone morphology, and homeostasis.

Type-H endothelial cell protein Clec14a orchestrates osteoblast activity during trabecular bone formation and patterning

Type-H capillary endothelial cells control bone formation during embryogenesis and postnatal growth but few signalling mechanisms underpinning this influence have been characterised. Here, we identify a highly expressed type-H endothelial cell protein, Clec14a, and explore its role in coordinating osteoblast activity. Expression of Clec14a and its ligand, Mmrn2 are high in murine type-H endothelial cells but absent from osteoblasts. Clec14a-/- mice have premature condensation of the type-H vasculature and expanded distribution of osteoblasts and bone matrix, increased long-bone length and bone density indicative of accelerated skeletal development, and enhanced osteoblast maturation. Antibody-mediated blockade of the Clec14a-Mmrn2 interaction recapitulates the Clec14a-/- phenotype. Endothelial cell expression of Clec14a regulates osteoblast maturation and mineralisation activity during postnatal bone development in mice. This finding underscores the importance of type-H capillary control of osteoblast activity in bone formation and identifies a novel mechanism that mediates this vital cellular crosstalk.

Deferoxamine Accelerates Mandibular Condylar Neck Fracture Early Bone Healing by Promoting Type H Vessel Proliferation

BACKGROUND

Condylar fractures (CFs) are a common type of maxillofacial trauma, especially in adolescents. Conservative treatment of CF avoids the possible complications of surgical intervention, but prolongs the patient's suffering because of the requirement for extended intermaxillary fixation. Therefore, the development of a new strategy to accelerate the rate of fracture healing to shorten the period of conservative treatment is of great clinical importance.

OBJECTIVE

To investigate the potential of deferoxamine (DFO) in promoting the healing process of CF in adolescent mice.

METHODS

Thirty-two 4-week-old male C57BL/6J mice were randomly assigned to four groups: vehicle + sham group, vehicle + CF group, DFO + sham group and DFO + CF group. After constructing the mandibular CF model, mandibular tissue samples were collected respectively at 1, 2 and 4 weeks postoperatively. Radiographic and histomorphometric analyses were employed to assess bone tissue healing and vascular formation.

RESULTS

Deferoxamine was observed to promote the early bone healing of fracture, both radiologically and histomorphometrically. Furthermore, this enhancement of condylar neck fracture healing was attributed to the upregulation of the hypoxia-inducible factor-1α (HIF-1α) signalling pathway while facilitating the formation of type H vessels. In addition, DFO did not produce significant effects on the condylar neck between vehicle + sham and DFO + sham group.

CONCLUSION

The application of the HIF-1α inducer DFO can enhance type H vessels expansion thereby accelerating condylar neck fracture healing.

The evolving hematopoietic niche during development

Mammalian hematopoietic stem cells (HSCs) emerge from the hemogenic endothelium in the major embryonic arteries. HSCs undergo a complex journey first migrating to the fetal liver (FL) and from there to the fetal bone marrow (FBM), where they mostly remain during adult life. In this process, a pool of adult HSCs is produced, which sustains lifelong hematopoiesis. Multiple cellular components support HSC maturation and expansion and modulate their response to environmental and developmental cues. While the adult HSC niche has been extensively studied over the last two decades, the niches present in the major embryonic arteries, FL, FBM and perinatal bone marrow (BM) are poorly described. Recent investigations highlight important differences among FL, FBM and adult BM niches and emphasize the important role that inflammation, microbiota and hormonal factors play regulating HSCs and their niches. We provide a review on our current understanding of these important cellular microenvironments across ontogeny. We mainly focused on mice, as the most widely used research model, and, when possible, include relevant insights from other vertebrates including birds, zebrafish, and human. Developing a comprehensive picture on these processes is critical to understand the earliest origins of childhood leukemia and to achieve multiple goals in regenerative medicine, such as mimicking HSC development in vitro to produce HSCs for broad transplantation purposes in leukemia, following chemotherapy, bone marrow failure, and in HSC-based gene therapy.

The role of vascular and lymphatic networks in bone and joint homeostasis and pathology

The vascular and lymphatic systems are integral to maintaining skeletal homeostasis and responding to pathological conditions in bone and joint tissues. This review explores the interplay between blood vessels and lymphatic vessels in bones and joints, focusing on their roles in homeostasis, regeneration, and disease progression. Type H blood vessels, characterized by high expression of CD31 and endomucin, are crucial for coupling angiogenesis with osteogenesis, thus supporting bone homeostasis and repair. These vessels facilitate nutrient delivery and waste removal, and their dysfunction can lead to conditions such as ischemia and arthritis. Recent discoveries have highlighted the presence and significance of lymphatic vessels within bone tissue, challenging the traditional view that bones are devoid of lymphatics. Lymphatic vessels contribute to interstitial fluid regulation, immune cell trafficking, and tissue repair through lymphangiocrine signaling. The pathological alterations in these networks are closely linked to inflammatory joint diseases, emphasizing the need for further research into their co-regulatory mechanisms. This comprehensive review summarizes the current understanding of the structural and functional aspects of vascular and lymphatic networks in bone and joint tissues, their roles in homeostasis, and the implications of their dysfunction in disease. By elucidating the dynamic interactions between these systems, we aim to enhance the understanding of their contributions to skeletal health and disease, potentially informing the development of targeted therapeutic strategies.

Vascular smooth muscle cell-derived exosomes promote osteoblast-to-osteocyte transition via β-catenin signaling

Blood vessel growth and osteogenesis in the skeletal system are coupled; however, fundamental aspects of vascular function in osteoblast-to-osteocyte transition remain unclear. Our study demonstrates that vascular smooth muscle cells (VSMCs), but not endothelial cells, are sufficient to drive bone marrow mesenchymal stromal cell-derived osteoblast-to-osteocyte transition via β-catenin signaling and exosome-mediated communication. We found that VSMC-derived exosomes are loaded with transcripts encoding proteins associated with the osteocyte phenotype and members of the WNT/β-catenin signaling pathway. In contrast, endothelial cell-derived exosomes facilitated mature osteoblast differentiation by reprogramming the TGFB1 gene family and osteogenic transcription factors osterix (SP7) and RUNX2. Notably, VSMCs express significant levels of tetraspanins (CD9, CD63, and CD81) and drive the intracellular trafficking of exosomes with a lower membrane zeta potential than those from other cells. Additionally, the high ATP content within these exosomes supports mineralization mechanisms, as ATP is a substrate for alkaline phosphatase. Osteocyte function was further validated by RNA sequencing, revealing activity in genes related to intermittent mineralization and sonic hedgehog signaling, alongside a significant increase in TNFSF11 levels. Our findings unveil a novel role of VSMCs in promoting osteoblast-to-osteocyte transition, thus offering new insights into bone biology and homeostasis, as well as in bone-related diseases. Clinically, these insights could pave the way for innovative therapeutic strategies targeting VSMC-derived exosome pathways to treat bone-related disorders such as osteoporosis. By manipulating these signaling pathways, it may be possible to enhance bone regeneration and improve skeletal health in patients with compromised bone structure and function.

Hydrogel Use in Osteonecrosis of the Femoral Head

Osteonecrosis of the femoral head (ONFH) is a vascular disease of unknown etiology and can be categorized mainly into two types: non-traumatic and traumatic ONFH. Thus, understanding osteogenic-angiogenic coupling is of prime importance in finding a solution for the treatment of ONFH. Hydrogels are biomaterials that are similar to the extracellular matrix (ECM). As they are able to mimic real tissue, they meet one of the most important rules in tissue engineering. In ONFH studies, hydrogels have recently become popular because of their ability to retain water and their adjustable properties, injectability, and mimicry of natural ECM. Because bone regeneration and graft materials are very broad areas of research and ONFH is a complex situation including bone and vascular systems, and there is no settled treatment strategy for ONFH worldwide, in this review paper, we followed a top-down approach by reviewing (1) bone and bone grafting, (2) hydrogels, (3) vascular systems, and (4) ONFH and hydrogel use in ONFH with studies in the literature which show promising results in limited clinical studies. The aim of this review paper is to provide the reader with general information on every aspect of ONFH and to focus on the hydrogel used in ONFH.

Mussel-Derived and Bioclickable Peptide Mimic for Enhanced Interfacial Osseointegration via Synergistic Immunomodulation and Vascularized Bone Regeneration

Inadequate osseointegration at the interface is a key factor in orthopedic implant failure. Mechanistically, traditional orthopedic implant interfaces fail to precisely match natural bone regeneration processes in vivo. In this study, a novel biomimetic coating on titanium substrates (DPA-Co/GFO) through a mussel adhesion-mediated ion coordination and molecular clicking strategy is engineered. In vivo and in vitro results confirm that the coating exhibits excellent biocompatibility and effectively promotes angiogenesis and osteogenesis. Crucially, the biomimetic coating targets the integrin α2β1 receptor to promote M2 macrophage polarization and achieves a synergistic effect between immunomodulation and vascularized bone regeneration, thereby maximizing osseointegration at the interface. Mechanical push-out tests reveal that the pull-out strength in the DPA-Co/GFO group is markedly greater than that in the control group (79.04 ± 3.20 N vs 31.47 ± 1.87 N, P < 0.01) and even surpasses that in the sham group (79.04 ± 3.20 N vs 63.09 ± 8.52 N, P < 0.01). In summary, the novel biomimetic coating developed in this study precisely matches the natural process of bone regeneration in vivo, enhancing interface-related osseointegration and showing considerable potential for clinical translation and applications.

Skeletal stem and progenitor cells in bone development and repair

Bone development, growth, and repair are complex processes involving various cell types and interactions, with central roles played by skeletal stem and progenitor cells. Recent research brought new insights into the skeletal precursor populations that mediate intramembranous and endochondral bone development. Later in life, many of the cellular and molecular mechanisms determining development are reactivated upon fracture, with powerful trauma-induced signaling cues triggering a variety of postnatal skeletal stem/progenitor cells (SSPCs) residing near the bone defect. Interestingly, in this injury context, the current evidence suggests that the fates of both SSPCs and differentiated skeletal cells can be considerably flexible and dynamic, and that multiple cell sources can be activated to operate as functional progenitors generating chondrocytes and/or osteoblasts. The combined implementation of in vivo lineage tracing, cell surface marker-based cell selection, single-cell molecular analyses, and high-resolution in situ imaging has strongly improved our insights into the diversity and roles of developmental and reparative stem/progenitor subsets, while also unveiling the complexity of their dynamics, hierarchies, and relationships. Albeit incompletely understood at present, findings supporting lineage flexibility and possibly plasticity among sources of osteogenic cells challenge the classical dogma of a single primitive, self-renewing, multipotent stem cell driving bone tissue formation and regeneration from the apex of a hierarchical and strictly unidirectional differentiation tree. We here review the state of the field and the newest discoveries in the origin, identity, and fates of skeletal progenitor cells during bone development and growth, discuss the contributions of adult SSPC populations to fracture repair, and reflect on the dynamism and relationships among skeletal precursors and differentiated cell lineages. Further research directed at unraveling the heterogeneity and capacities of SSPCs, as well as the regulatory cues determining their fate and functioning, will offer vital new options for clinical translation toward compromised fracture healing and bone regenerative medicine.

Research progress of the mechanisms and applications of ginsenosides in promoting bone formation

BACKGROUND

Bone deficiency-related diseases caused by various factors have disrupted the normal function of the skeleton and imposed a heavy burden globally, urgently requiring potential new treatments. The multi-faceted role of compounds like ginsenosides and their interaction with the bone microenvironment, particularly osteoblasts can promote bone formation and exhibit anti-inflammatory, vascular remodeling, and antibacterial properties, holding potential value in the treatment of bone deficiency-related diseases and bone tissue engineering.

PURPOSE

This review summarizes the interaction between ginsenosides and osteoblasts and the bone microenvironment in bone formation, including vascular remodeling and immune regulation, as well as their therapeutic potential and toxicity in the broad treatment applications of bone deficiency-related diseases and bone tissue engineering, to provide novel insights and treatment strategies.

METHODS

The literature focusing on the mechanisms and applications of ginsenosides in promoting bone formation before March 2024 was searched in PubMed, Web of Science, Google Scholar, Scopus, and Science Direct databases. Keywords such as "phytochemicals", "ginsenosides", "biomaterials", "bone", "diseases", "bone formation", "microenvironment", "bone tissue engineering", "rheumatoid arthritis", "periodontitis", "osteoarthritis", "osteoporosis", "fracture", "toxicology", "pharmacology", and combinations of these keywords were used.

RESULTS

Ginsenoside monomers regulate signaling pathways such as WNT/β-catenin, FGF, and BMP/TGF-β, stimulating osteoblast generation and differentiation. It exerts angiogenic and anti-inflammatory effects by regulating the bone surrounding microenvironment through signaling such as WNT/β-catenin, NF-κB, MAPK, PI3K/Akt, and Notch. It shows therapeutic effects and biological safety in the treatment of bone deficiency-related diseases, including rheumatoid arthritis, osteoarthritis, periodontitis, osteoporosis, and fractures, and bone tissue engineering by promoting osteogenesis and improving the microenvironment of bone formation.

CONCLUSION

The functions of ginsenosides are diverse and promising in treating bone deficiency-related diseases and bone tissue engineering. Moreover, potential exists in regulating the bone microenvironment, modifying biomaterials, and treating inflammatory-related bone diseases and dental material applications. However, the mechanisms and effects of some ginsenoside monomers are still unclear, and the lack of clinical research limits their clinical application. Further exploration and evaluation of the potential of ginsenosides in these areas are expected to provide more effective methods for treating bone defects.

Role of miRNA-regulated type H vessel formation in osteoporosis

Osteoporosis (OP) is a chronic systemic bone metabolism disease characterized by decreased bone mass, microarchitectural deterioration, and fragility fractures. With the demographic change caused by long lifespans and population aging, OP is a growing health problem. The role of miRNA in the pathogenesis of OP has also attracted widespread attention from scholars in recent years. Type H vessels are unique microvessels of the bone and have become a new focus in the pathogenesis of OP because they play an essential role in osteogenesis-angiogenesis coupling. Previous studies found some miRNAs regulate type H vessel formation through the regulatory factors, including platelet-derived growth factor-BB (PDGF-BB), hypoxia-inducible factor 1α (HIF-1α), vascular endothelial growth factor (VEGF), and so on. These findings help us gain a more in-depth understanding of the relationship among miRNAs, type H vessels, and OP to find a new perspective on treating OP. In the present mini-review, we will introduce the role of type H vessels in the pathogenesis of OP and the regulation of miRNAs on type H vessel formation by affecting regulatory factors to provide some valuable insights for future studies of OP treatment.

Exosomes: A New Hope for Angiogenesis-Mediated Bone Regeneration

Bone is a metabolically dynamic structure that is generally remodeled throughout the lifetime of an individual but often causes problems with increasing age. A key player for bone development and homeostasis, but also under pathological conditions, is the bone vasculature. This complex system of arteries, veins, and capillaries forms distinct structures where each subset of endothelial cells has important functions. Starting with the basic process of angiogenesis and bone-specific blood vessel formation, coupled with initial bone formation, the importance of different vascular structures is highlighted with respect to how these structures are maintained or changed during homeostasis, aging, and pathological conditions. After exemplifying the current knowledge on bone vasculature, this review will move on to exosomes, a novel hotspot of scientific research. Exosomes will be introduced starting from their discovery via current isolation procedures and state-of-the-art characterization to their role in bone vascular development, homeostasis, and bone regeneration and repair while summarizing the underlying signal transduction pathways. With respect to their role in these processes, especially mesenchymal stem cell-derived extracellular vesicles are of interest, which leads to a discussion on patented applications and an update on ongoing clinical trials. Taken together, this review provides an overview of bone vasculature and bone regeneration, with a major focus on how exosomes influence this intricate system, as they might be useful for therapeutic purposes in the near future.

Targeting adipocyte ESRRA promotes osteogenesis and vascular formation in adipocyte-rich bone marrow

Excessive bone marrow adipocytes (BMAds) accumulation often occurs under diverse pathophysiological conditions associated with bone deterioration. Estrogen-related receptor α (ESRRA) is a key regulator responding to metabolic stress. Here, we show that adipocyte-specific ESRRA deficiency preserves osteogenesis and vascular formation in adipocyte-rich bone marrow upon estrogen deficiency or obesity. Mechanistically, adipocyte ESRRA interferes with E2/ESR1 signaling resulting in transcriptional repression of secreted phosphoprotein 1 (Spp1); yet positively modulates leptin expression by binding to its promoter. ESRRA abrogation results in enhanced SPP1 and decreased leptin secretion from both visceral adipocytes and BMAds, concertedly dictating bone marrow stromal stem cell fate commitment and restoring type H vessel formation, constituting a feed-forward loop for bone formation. Pharmacological inhibition of ESRRA protects obese mice against bone loss and high marrow adiposity. Thus, our findings highlight a therapeutic approach via targeting adipocyte ESRRA to preserve bone formation especially in detrimental adipocyte-rich bone milieu.

Plasminogen activator inhibitor-1 is involved in glucocorticoid-induced decreases in angiogenesis during bone repair in mice

INTRODUCTION

Glucocorticoids delay fracture healing and induce osteoporosis. Angiogenesis plays an important role in bone repair after bone injury. Plasminogen activator inhibitor-1 (PAI-1) is the principal inhibitor of plasminogen activators and an adipocytokine that regulates metabolism. However, the mechanisms by which glucocorticoids delay bone repair remain unclear.

MATERIALS AND METHODS

Therefore, we herein investigated the roles of PAI-1 and angiogenesis in glucocorticoid-induced delays in bone repair after femoral bone injury using PAI-1-deficient female mice intraperitoneally administered dexamethasone (Dex).

RESULTS

PAI-1 deficiency significantly attenuated Dex-induced decreases in the number of CD31-positive vessels at damaged sites 4 days after femoral bone injury in mice. PAI-1 deficiency also significantly ameliorated Dex-induced decreases in the number of CD31- and endomucin-positive type H vessels and CD31-positive- and endomucin-negative vessels at damaged sites 4 days after femoral bone injury. Moreover, PAI-1 deficiency significantly mitigated Dex-induced decreases in the expression of vascular endothelial growth factor as well as hypoxia inducible factor-1α, transforming growth factor-β1, and bone morphogenetic protein-2 at damaged sites 4 days after femoral bone injury.

CONCLUSION

The present results demonstrate that Dex-reduced angiogenesis at damaged sites during the early bone-repair phase after femoral bone injury partly through PAI-1 in mice.

The design of an RGD in situ sustained delivery system utilizing scallop byssal protein through genetic engineering

Although bioactive peptides enhancing bone healing have demonstrated effectiveness in treating bone defects, in vivo instability poses a challenge to their clinical application. Currently reported peptide delivery systems do not meet the demands of bone tissue repair regarding stability and peptide release efficacy. Herein, the self-assembling recombinant chimeric protein (Sbp5-2RGD) is developed by genetic engineering with cell adhesion peptide RGD as the targeted peptide and a newly discovered scallop byssal-derived protein Sbp5-2 that can assemble into wet stable films as the structural domain. In vitro studies show that the Sbp5-2RGD film exhibits excellent extensibility and biocompatibility. In vitro and in vivo degradation experiments demonstrate that the film remains stable due to the layer-by-layer degradation mode, resulting in sustained delivery of RGD in situ for up to 4 weeks. Consequently, the film can effectively promote osteogenesis, which accelerates bone defect healing and the implants osseointegration. Cell-level studies further show that the film up-regulates the expression of genes and proteins (ALP, OCN, OSX, OPN, RUNX2, VEGF) associated with osteogenesis and angiogenesis. Overall, this novel protein film represents an intelligent platform for peptide immobilization, protection, and release through its self-assembly, dense structure, and degradation mode, providing a therapeutic strategy for bone repair.

Identification of ceRNA networks in type H and L vascular endothelial cells through integrated bioinformatics methods

OBJECTIVES

Type H blood vessels are a subtype of bone-specific microvessels (CD31hiEmcnhi) that play an important regulatory role in the coupling of angiogenesis and osteogenesis. Despite reports on the distinct roles of type H and L vessels under physiological and pathological bone conditions, their genetic differences remain to be elucidated. This study aims to construct a competitive endogenous RNA (ceRNA) network of key gene for differencial expression (DE) in type H and L vascular endothelial cells (ECs) through integrated bioinformatic methods.

METHODS

We downloaded relevant raw data from the ArrayExpress and the Gene Expression Omnibus (GEO) database and used the Limma R-Bioconductor package to screen for DE lncRNAs, DE miRNAs, and DE mRNAs between type H and L vascular ECs. A total ceRNA network was constructed based on their interactions, followed by refinement using protein-protein interaction (PPI) networks to select upregulated and downregulated key genes. Enrichment analysis was performed on these key genes. Random validation was conducted using flow cytometry and real-time RT-PCR.

RESULTS

A total of 1 761 DE mRNAs, 187 DE lncRNAs, and 159 DE miRNAs were identified, and a comprehensive ceRNA network was constructed based on their interactions. Six upregulated (Itga5, Kdr, Tjp1, Pecam1, Cdh5, and Ptk2) and 2 downregulated (Csf1r and Il10) key genes were selected via PPI network to construct a subnetwork of ceRNAs related to these key genes. Upregulated key genes were mainly enriched in negative regulation of angiogenesis and vascular apoptosis. Results from flow cytometry and real-time RT-PCR were consistent with bioinformatics analysis.

CONCLUSIONS

This study proposes a ceRNA network associated with upregulated and downregulated type H and L vascular ECs based on selected key genes, providing new insights into the regulatory mechanisms of type H and L vascular ECs in bone metabolism.

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.

Integrative analyses of genetic characteristics associated with skeletal endothelial cells

The osseous vascular endothelium encompasses a vast intricate framework that regulates bone remodeling. Osteoporosis, an age-associated systemic bone disease, is characterized by the degeneration of the vascular architecture. Nevertheless, the precise mechanisms underpinning the metamorphosis of endothelial cells (ECs) with advancing age remain predominantly enigmatic. In this study, we conducted a systematic analysis of differentially expressed genes (DEGs) and the associated pathways in juvenile and mature femoral ECs, utilizing data sourced from the Gene Expression Omnibus (GEO) repositories (GSE148804) and employing bioinformatics tools. Through this approach, we successfully discerned six pivotal genes, namely Adamts1, Adamts2, Adamts4, Adamts14, Col5a1, and Col5a2. Subsequently, we constructed a miRNA-mRNA network based on miRNAs displaying differential expression between CD31hiEMCNhi and CD31lowEMCNlow ECs, utilizing online repositories for prediction. The expression of miR-466i-3p and miR-466i-5p in bone marrow ECs exhibited an inverse correlation with age. Our in vivo experiments additionally unveiled miR-466i-5p as a pivotal regulator in osseous ECs and a promising therapeutic target for age-related osteoporosis.

Transforming the Niche: The Emerging Role of Extracellular Vesicles in Acute Myeloid Leukaemia Progression

Acute myeloid leukaemia (AML) management remains a significant challenge in oncology due to its low survival rates and high post-treatment relapse rates, mainly attributed to treatment-resistant leukaemic stem cells (LSCs) residing in bone marrow (BM) niches. This review offers an in-depth analysis of AML progression, highlighting the pivotal role of extracellular vesicles (EVs) in the dynamic remodelling of BM niche intercellular communication. We explore recent advancements elucidating the mechanisms through which EVs facilitate complex crosstalk, effectively promoting AML hallmarks and drug resistance. Adopting a temporal view, we chart the evolving landscape of EV-mediated interactions within the AML niche, underscoring the transformative potential of these insights for therapeutic intervention. Furthermore, the review discusses the emerging understanding of endothelial cell subsets' impact across BM niches in shaping AML disease progression, adding another layer of complexity to the disease progression and treatment resistance. We highlight the potential of cutting-edge methodologies, such as organ-on-chip (OoC) and single-EV analysis technologies, to provide unprecedented insights into AML-niche interactions in a human setting. Leveraging accumulated insights into AML EV signalling to reconfigure BM niches and pioneer novel approaches to decipher the EV signalling networks that fuel AML within the human context could revolutionise the development of niche-targeted therapy for leukaemia eradication.

Hypoxia preconditioning of adipose stem cell-derived exosomes loaded in gelatin methacryloyl (GelMA) promote type H angiogenesis and osteoporotic fracture repair

The challenges posed by delayed atrophic healing and nonunion stand as formidable obstacles in osteoporotic fracture treatment. The processes of type H angiogenesis and osteogenesis emerge as pivotal mechanisms during bone regeneration. Notably, the preconditioning of adipose-derived stem cell (ADSC) exosomes under hypoxic conditions has garnered attention for its potential to augment the secretion and functionality of these exosomes. In the present investigation, we embarked upon a comprehensive elucidation of the underlying mechanisms of hypo-ADSC-Exos within the milieu of osteoporotic bone regeneration. Our findings revealed that hypo-ADSC-Exos harboured a preeminent miRNA, namely, miR-21-5p, which emerged as the principal orchestrator of angiogenic effects. Through in vitro experiments, we demonstrated the capacity of hypo-ADSC-Exos to stimulate the proliferation, migration, and angiogenic potential of human umbilical vein endothelial cells (HUVECs) via the mediation of miR-21-5p. The inhibition of miR-21-5p effectively attenuated the proangiogenic effects mediated by hypo-ADSC-Exos. Mechanistically, our investigation revealed that exosomal miR-21-5p emanating from hypo-ADSCs exerts its regulatory influence by targeting sprouly1 (SPRY1) within HUVECs, thereby facilitating the activation of the PI3K/AKT signalling pathway. Notably, knockdown of SPRY1 in HUVECs was found to potentiate PI3K/AKT activation and, concomitantly, HUVEC proliferation, migration, and angiogenesis. The culminating stage of our study involved a compelling in vivo demonstration wherein GelMA loaded with hypo-ADSC-Exos was validated to substantially enhance local type H angiogenesis and concomitant bone regeneration. This enhancement was unequivocally attributed to the exosomal modulation of SPRY1. In summary, our investigation offers a pioneering perspective on the potential utility of hypo-ADSC-Exos as readily available for osteoporotic fracture treatment.

Endothelial SMAD1/5 signaling couples angiogenesis to osteogenesis in juvenile bone

Skeletal development depends on coordinated angiogenesis and osteogenesis. Bone morphogenetic proteins direct bone formation in part by activating SMAD1/5 signaling in osteoblasts. However, the role of SMAD1/5 in skeletal endothelium is unknown. Here, we found that endothelial cell-conditional SMAD1/5 depletion in juvenile mice caused metaphyseal and diaphyseal hypervascularity, resulting in altered trabecular and cortical bone formation. SMAD1/5 depletion induced excessive sprouting and disrupting the morphology of the metaphyseal vessels, with impaired anastomotic loop formation at the chondro-osseous junction. Endothelial SMAD1/5 depletion impaired growth plate resorption and, upon long-term depletion, abrogated osteoprogenitor recruitment to the primary spongiosa. Finally, in the diaphysis, endothelial SMAD1/5 activity was necessary to maintain the sinusoidal phenotype, with SMAD1/5 depletion inducing formation of large vascular loops and elevated vascular permeability. Together, endothelial SMAD1/5 activity sustains skeletal vascular morphogenesis and function and coordinates growth plate remodeling and osteoprogenitor recruitment dynamics in juvenile mouse bone.

Tensile Stress-Activated and Exosome-Transferred YAP/TAZ-Notch Circuit Specifies Type H Endothelial Cell for Segmental Bone Regeneration

The Ilizarov technique has been continuously innovated to utilize tensile stress (TS) for inducing a bone development-like regenerative process, aiming to achieve skeletal elongation and reconstruction. However, it remains uncertain whether this distraction osteogenesis (DO) process induced by TS involves the pivotal coupling of angiogenesis and osteogenesis mediated by type H endothelial cells (THECs). In this study, it is demonstrated that the Ilizarov technique induces the formation of a metaphysis-like architecture composed of THECs, leading to segmental bone regeneration during the DO process. Mechanistically, cell-matrix interactions-mediated activation of yes-associated protein (YAP)/transcriptional co-activator with PDZ-binding motif (TAZ) transcriptionally upregulates the expression of Notch1 and Delta-like ligand 4, which act as direct positive regulators of THECs phenotype, in bone marrow endothelial cells (BMECs) upon TS stimulation. Simultaneously, the Notch intracellular domain enhances YAP/TAZ activity by transcriptionally upregulating YAP expression and stabilizing TAZ protein, thus establishing the YAP/TAZ-Notch circuit. Additionally, TS-stimulated BMECs secrete exosomes enriched with vital molecules in this positive feedback pathway, which can be utilized to promote segmental bone defect healing, mimicking the therapeutic effects of Ilizarov technique. The findings advance the understanding of TS-induced segmental bone regeneration and establish the foundation for innovative biological therapeutic strategies aimed at activating THECs.

Reduction of the trans-cortical vessel was associated with bone loss, another underlying mechanism of osteoporosis

RATIONALE

Numerous studies have established a robust association between bone morrow microvascular diseases and osteoporosis. This study sought to investigate the relationship between alterations in trans-cortical vessel (TCVs) and the onset of osteoporosis in various mouse models.

METHODS

Aged mice, ovariectomized mice, and db/db mice, were utilized as osteoporosis models. TCVs in the tibia were detected using tissue clearing and light sheet fluorescence microscopy imaging. Femurs bone mass were analyzed using micro-CT scanning. Correlations between the number of TCVs and bone mass were analyzed using Pearson correlation analysis.

RESULTS

All osteoporosis mouse models showed a significant reduction in the number of TCVs compared to the control group. Correlation analysis revealed a positive association between the number of TCVs and bone mass. TCVs were also expressed high levels of CD31 and EMCN proteins as type H vessels.

CONCLUSIONS

This study underscores a consistent correlation between the number of TCVs and bone mass. Moreover, TCVs may serve as a potential biomarker for bone mass evaluation.

The impact of gut microbial signals on hematopoietic stem cells and the bone marrow microenvironment

Hematopoietic stem cells (HSCs) undergo self-renewal and differentiation in the bone marrow, which is tightly regulated by cues from the microenvironment. The gut microbiota, a dynamic community residing on the mucosal surface of vertebrates, plays a crucial role in maintaining host health. Recent evidence suggests that the gut microbiota influences HSCs differentiation by modulating the bone marrow microenvironment through microbial products. This paper comprehensively analyzes the impact of the gut microbiota on hematopoiesis and its effect on HSCs fate and differentiation by modifying the bone marrow microenvironment, including mechanical properties, inflammatory signals, bone marrow stromal cells, and metabolites. Furthermore, we discuss the involvement of the gut microbiota in the development of hematologic malignancies, such as leukemia, multiple myeloma, and lymphoma.

A Dose-Dependent Spatiotemporal Response of Angiogenesis Elicited by Zn Biodegradation during the Initial Stage of Bone Regeneration

Zinc (Zn) plays a crucial role in bone metabolism and imbues biodegradable Zn-based materials with the ability to promote bone regeneration in bone trauma. However, the impact of Zn biodegradation on bone repair, particularly its influence on angiogenesis, remains unexplored. This study reveals that Zn biodegradation induces a consistent dose-dependent spatiotemporal response in angiogenesis,both in vivo and in vitro. In a critical bone defect model, an increase in Zn release intensity from day 3 to 10 post-surgery is observed. By day 10, the CD31-positive area around the Zn implant significantly surpasses that of the Ti implant, indicating enhanced angiogenesis. Furthermore,angiogenesis exhibits a distance-dependent pattern closely mirroring the distribution of Zn signals from the implant. In vitro experiments demonstrate that Zn extraction fosters the proliferation and migration of human umbilical vein endothelial cells and upregulates the key genes associated with tube formation, such as HIF-1α and VEGF-A, peaking at a concentration of 22.5 µM. Additionally, Zn concentrations within the range of 11.25-45 µM promote the polarization of M0-type macrophages toward the M2-type, while inhibiting polarization toward the M1-type. These findings provide essential insights into the biological effects of Zn on bone repair, shedding light on its potential applications.

Blood and bones: Mechanical cues and Hippo signaling drive vascular invasion during limb formation

Although mechanical cues are known to influence the postnatal skeleton, the impact of bone cell mechano-transduction on early skeletal development remains less clear. In this issue of Developmental Cell, Collins et al. (2023) report that YAP/TAZ deletion in osteoblast precursors reduces Cxcl12 expression, leading to defects in bone vascularization.

YAP and TAZ couple osteoblast precursor mobilization to angiogenesis and mechanoregulation in murine bone development

Fetal bone development occurs through the conversion of avascular cartilage to vascularized bone at the growth plate. This requires coordinated mobilization of osteoblast precursors with blood vessels. In adult bone, vessel-adjacent osteoblast precursors are maintained by mechanical stimuli; however, the mechanisms by which these cells mobilize and respond to mechanical cues during embryonic development are unknown. Here, we show that the mechanoresponsive transcriptional regulators Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ) spatially couple osteoblast precursor mobilization to angiogenesis, regulate vascular morphogenesis to control cartilage remodeling, and mediate mechanoregulation of embryonic murine osteogenesis. Mechanistically, YAP and TAZ regulate a subset of osteoblast-lineage cells, identified by single-cell RNA sequencing as vessel-associated osteoblast precursors, which regulate transcriptional programs that direct blood vessel invasion through collagen-integrin interactions and Cxcl12. Functionally, in 3D human cell co-culture, CXCL12 treatment rescues angiogenesis impaired by stromal cell YAP/TAZ depletion. Together, these data establish functions of the vessel-associated osteoblast precursors in bone development.

YBX1 promotes type H vessel-dependent bone formation in an m5C-dependent manner

RNA-binding proteins (RBPs) interact with RNA and ubiquitously regulate RNA transcripts during their life cycle, playing a fundamental role in the progression of angiogenesis-related diseases. In the skeletal system, endothelium-dependent angiogenesis is indispensable for bone formation. However, the role of RBPs in endothelium-dependent bone formation is unclear. Here, we show that RBP-Y-box-binding protein 1 (YBX1) was strongly reduced in the bone vasculature of ovariectomy (OVX) mice. Endothelial cell-specific deletion of Ybx1 impaired CD31-high, endomucin-high (CD31hiEMCNhi) endothelium morphology and resulted in low bone mass whereas Ybx1 overexpression promoted angiogenesis-dependent osteogenesis and ameliorated bone loss. Mechanistically, YBX1 deletion disrupted CD31, EMCN, and bone morphogenetic protein 4 (BMP4) stability in an m5C-dependent manner and blocked endothelium-derived BMP4 release, thereby inhibiting osteogenic differentiation of bone mesenchymal stromal cells. Administration of recombinant BMP4 protein restored impaired bone formation in Ybx1 deletion mice. Tail vein injection of CD31-modified polyethylene glycol-poly (lactic-co-glycolic acid) carrying sciadopitysin, a natural YBX1 agonist, pharmacologically partially reversed CD31hiEMCNhi vessels' decline and improved bone mass in both OVX and aging animals. These findings demonstrated the role of RBP-YBX1 in angiogenesis-dependent bone formation and provided a therapeutic approach for ameliorating osteoporosis.

Reassessing endothelial-to-mesenchymal transition in mouse bone marrow: insights from lineage tracing models

Endothelial cells (ECs) and bone marrow stromal cells (BMSCs) play crucial roles in supporting hematopoiesis and hematopoietic regeneration. However, whether ECs are a source of BMSCs remains unclear. Here, we evaluate the contribution of endothelial-to-mesenchymal transition to BMSC generation in postnatal mice. Single-cell RNA sequencing identifies ECs expressing BMSC markers Prrx1 and Lepr; however, this could not be validated using Prrx1-Cre and Lepr-Cre transgenic mice. Additionally, only a minority of BMSCs are marked by EC lineage tracing models using Cdh5-rtTA-tetO-Cre or Tek-CreERT2. Moreover, Cdh5+ BMSCs and Tek+ BMSCs show distinct spatial distributions and characteristic mesenchymal markers, suggestive of their origination from different progenitors rather than CDH5+ TEK+ ECs. Furthermore, myeloablation induced by 5-fluorouracil treatment does not increase Cdh5+ BMSCs. Our findings indicate that ECs hardly convert to BMSCs during homeostasis and myeloablation-induced hematopoietic regeneration, highlighting the importance of using appropriate genetic models and conducting careful data interpretation in studies concerning endothelial-to-mesenchymal transition.

Spatiotemporal Immunomodulation and Biphasic Osteo-Vascular Aligned Electrospun Membrane for Diabetic Periosteum Regeneration

Under diabetic conditions, blood glucose fluctuations and exacerbated immunopathological inflammatory environments pose significant challenges to periosteal regenerative repair strategies. Responsive immune regulation in damaged tissues is critical for the immune microenvironment, osteogenesis, and angiogenesis stabilization. Considering the high-glucose microenvironment of such acute injury sites, a functional glucose-responsive immunomodulation-assisted periosteal regeneration composite material-PLA（Polylactic Acid）/COLI(Collagen I）/Lipo(Liposome）-APY29 (PCLA)-is constructed. Aside from stimulating osteogenic differentiation, owing to the presence of surface self-assembled type I collagen in the scaffolds, PCLA can directly respond to focal area high-glucose microenvironments. The PCLA scaffolds trigger the release of APY29-loaded liposomes, shifting the macrophages toward the M2 phenotype, inhibiting the release of inflammatory cytokines, improving the bone immune microenvironment, and promoting osteogenic differentiation and angiogenesis. Bioinformatics analyses show that PCLA enhances bone repair by inhibiting the inflammatory signal pathway regulating the polarization direction and promoting osteogenic and angiogenic gene expression. In the calvarial periosteal defect model of diabetic rats, PCLA scaffolds induce M2 macrophage polarization and improve the inflammatory microenvironment, significantly accelerating periosteal repair. Overall, the PCLA scaffold material regulates immunity in fluctuating high-glucose inflammatory microenvironments, achieves relatively stable and favorable osteogenic microenvironments, and facilitates the effective design of functionalized biomaterials for bone regeneration therapy in patients with diabetes.

Recent advancement in vascularized tissue-engineered bone based on materials design and modification

Bone is one of the most vascular network-rich tissues in the body and the vascular system is essential for the development, homeostasis, and regeneration of bone. When segmental irreversible damage occurs to the bone, restoring its vascular system by means other than autogenous bone grafts with vascular pedicles is a therapeutic challenge. By pre-generating the vascular network of the scaffold in vivo or in vitro, the pre-vascularization technique enables an abundant blood supply in the scaffold after implantation. However, pre-vascularization techniques are time-consuming, and in vivo pre-vascularization techniques can be damaging to the body. Critical bone deficiencies may be filled quickly with immediate implantation of a supporting bone tissue engineered scaffold. However, bone tissue engineered scaffolds generally lack vascularization, which requires modification of the scaffold to aid in enhancing internal vascularization. In this review, we summarize the relationship between the vascular system and osteogenesis and use it as a basis to further discuss surgical and cytotechnology-based pre-vascularization strategies and to describe the preparation of vascularized bone tissue engineered scaffolds that can be implanted immediately. We anticipate that this study will serve as inspiration for future vascularized bone tissue engineered scaffold construction and will aid in the achievement of clinical vascularized bone.

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.

Vascular and lymphatic heterogeneity and age-related variations of dental pulps

OBJECTIVES

Dental pulp tissue is highly vascularized. However, age-related vascular changes of the dental pulp in mice and humans remain poorly understood. We modified a novel tissue clearing method, mapped the vasculature, pericytes, and perivascular matrix in the dental pulp via high-resolution 3D imaging.

METHODS

We isolated young and aged pulps from mouse teeth, and mapped vasculature through a high-resolution thick frozen sections imaging method and a modified tissue clearing method. Human dental pulps were also mapped for vasculature studying. Furthermore, young and aged human dental pulps were collected and were compared with mouse pulps through RNA- sequencing.

RESULTS

Five vascular subtypes of blood vessels were found in the mouse dental pulp, which constituted the arterioles-capillaries-venules network. The density of capillaries and venules of molars declined obviously in aged mice. Among the age-dependent changes in the perivascular pulp matrix, the perivascular macrophages remarkably increased, lymphatic capillaries increased, while the nerves and extracellular matrix remained unchanged. Furthermore, the vascular patterns of human formed a complex vascular network. Both mouse and human dental pulps exhibited an inflammaging state. TNF pathway and Rap1 pathway might become promising targets for combating inflammaging and promoting angiogenesis.

CONCLUSIONS

Five subtypes of blood vessels were identified within the dental pulp of mice. Notably, the density of capillaries and venules in pulps of aged mice was reduced. Furthermore, partial similarities were observed in the vascular patterns between the dental pulps of humans and mice. RNA-sequencing analysis revealed that both mouse and human dental pulps exhibit indications of an inflammaging state.

CLINICAL SIGNIFICANCE

This study may contribute to unraveling potential therapeutic targets in the pulp regeneration and treatment of relevant diseases in the elderly.

Type H vessels in osteogenesis, homeostasis, and related disorders

The vascular system plays a crucial role in bone tissue. Angiogenic and osteogenic processes are coupled through a spatial-temporal connection. Recent studies have identified three types of capillaries in the skeletal system. Compared with type L and E vessels, type H vessels express high levels of CD31 and endomucin, and function to couple angiogenesis and osteogenesis. Endothelial cells in type H vessels interact with osteolineage cells (e.g., osteoblasts, osteoclasts, and osteocytes) through cytokines or signaling pathways to maintain bone growth and homeostasis. In imbalanced bone homeostases, such as osteoporosis and osteoarthritis, it may be a new therapeutic strategy to regulate the endothelial cell activity in type H vessels to repair the imbalance. Here, we reviewed the latest progress in relevant factors or signaling pathways in coupling angiogenesis and osteogenesis. This review would contribute to further understanding the role and mechanisms of type H vessels in coupling angiogenic and osteogenic processes. Furthermore, it will facilitate the development of therapeutic approaches for bone disorders by targeting type H vessels.

Spatially multicellular variability of intervertebral disc degeneration by comparative single-cell analysis

Previous studies have revealed cellular heterogeneity in intervertebral discs (IVDs). However, the cellular and molecular alteration patterns of cell populations during degenerative progression remain to be fully elucidated. To illustrate the cellular and molecular alteration of cell populations in intervertebral disc degeneration (IDD), we perform single cell RNA sequencing on cells from four anatomic sites of healthy and degenerative goat IVDs. EGLN3+ StressCs, TGFBR3+ HomCs and GPRC5A+ RegCs exhibit the characteristics associated with resistance to stress, maintaining homeostasis and repairing, respectively. The frequencies and signatures of these cell clusters fluctuate with IDD. Notably, the chondrogenic differentiation programme of PROCR+ progenitor cells is altered by IDD, while notochord cells turn to stemness exhaustion. In addition, we characterise CAV1+ endothelial cells that communicate with chondrocytes through multiple signalling pathways in degenerative IVDs. Our comprehensive analysis identifies the variability of key cell clusters and critical regulatory networks responding to IDD, which will facilitate in-depth investigation of therapeutic strategies for IDD.

The spatiotemporal heterogeneity of the biophysical microenvironment during hematopoietic stem cell development: from embryo to adult

Hematopoietic stem cells (HSCs) with the ability to self-renew and differentiate are responsible for maintaining the supply of all types of blood cells. The complex and delicate microenvironment surrounding HSCs is called the HSC niche and can provide physical, chemical, and biological stimuli to regulate the survival, maintenance, proliferation, and differentiation of HSCs. Currently, the exploration of the biophysical regulation of HSCs remains in its infancy. There is evidence that HSCs are susceptible to biophysical stimuli, suggesting that the construction of engineered niche biophysical microenvironments is a promising way to regulate the fate of HSCs in vitro and ultimately contribute to clinical applications. In this review, we introduced the spatiotemporal heterogeneous biophysical microenvironment during HSC development, homeostasis, and malignancy. Furthermore, we illustrated how these biophysical cues contribute to HSC behaviors, as well as the possible mechanotransduction mechanisms from the extracellular microenvironment into cells. Comprehending the important functions of these biophysical regulatory factors will provide novel approaches to resolve clinical problems.

Prostate cancer and bone: clinical presentation and molecular mechanisms

Prostate cancer (PCa) is an increasingly prevalent health problem in the developed world. Effective treatment options exist for localized PCa, but metastatic PCa has fewer treatment options and shorter patient survival. PCa and bone health are strongly entwined, as PCa commonly metastasizes to the skeleton. Since androgen receptor signaling drives PCa growth, androgen-deprivation therapy whose sequelae reduce bone strength constitutes the foundation of advanced PCa treatment. The homeostatic process of bone remodeling - produced by concerted actions of bone-building osteoblasts, bone-resorbing osteoclasts, and regulatory osteocytes - may also be subverted by PCa to promote metastatic growth. Mechanisms driving skeletal development and homeostasis, such as regional hypoxia or matrix-embedded growth factors, may be subjugated by bone metastatic PCa. In this way, the biology that sustains bone is integrated into adaptive mechanisms for the growth and survival of PCa in bone. Skeletally metastatic PCa is difficult to investigate due to the entwined nature of bone biology and cancer biology. Herein, we survey PCa from origin, presentation, and clinical treatment to bone composition and structure and molecular mediators of PCa metastasis to bone. Our intent is to quickly yet effectively reduce barriers to team science across multiple disciplines that focuses on PCa and metastatic bone disease. We also introduce concepts of tissue engineering as a novel perspective to model, capture, and study complex cancer-microenvironment interactions.

Central and peripheral tau retention modulated by an anti-tau antibody

Tau protein blood levels dependent on its distribution to peripheral organs and possible elimination from the body. Thus, the peripheral distribution of CSF-derived tau protein was explored, especially since there is a transition to blood-based biomarkers and the emerging idea that tau pathology may spread beyond brain. Near infrared fluorescence (NIRF) was mainly used to analyze tau (tau-NIRF) distribution after its intracisternal or intravenous injection. There was a striking uptake of blood- or CSF-derived tau-NIRF protein by the skeletal structures, liver, small intestine (duodenum), gall bladder, kidneys, urinary bladder, lymph nodes, heart, and spleen. In aging and in older APP/PS1 mice, tau uptake in regions, such as the brain, liver, and skeleton, was increased. In bone (femur) injected tau protein was associated with integrin-binding sialoprotein (IBSP), a major non-collagenous glycoprotein that is associated with mineralization. Tau-NIRF was cleared slowly from CSF via mainly across the cribriform plate, and cervical lymph nodes. In brain, some of the CSF injected tau protein was associated with NeuN-positive and PDGFRý-positive cells, which may explain its retention. The presence of tau in the bladders suggested excretion routes of tau. CSF anti-tau antibody increased CSF tau clearance, while blood anti-tau antibody decreased tau accumulation in the femur but not in liver, kidney, and spleen. Thus, the data show a body-wide distribution and retention of CSF-derived tau protein, which increased with aging and in older APP/PS1 mice. Further work is needed to elucidate the relevance of tau accumulation in each organ to tauopathy.

Sandblasted/Acid-Etched Titanium Surface Modified with Calcium Phytate Enhances Bone Regeneration in a High-Glucose Microenvironment by Regulating Reactive Oxygen Species and Cell Senescence

Hyperglycemia in patients with diabetes affect osteoblast function, leading to abnormal bone metabolism and implant failure. Adequate bone volume surrounding an implant is essential for osseointegration, which can be improved by implant surface modifications. In this study, titanium surfaces were hydrothermally treated with a mixture of phytic acid (PA) and calcium hydroxide to produce a calcium-decorated surface. The control group comprised pure titanium with a sandblasted/acid-etched (SLA) surface. The elemental composition, hydrophilicity, surface roughness, and morphology of the titanium surfaces were examined. Evaluation of in vitro osteogenic differentiation ability in a high-glucose environment using alkaline phosphatase (ALP) staining, ALP activity assays, Alizarin Red S staining, quantitative reverse transcription-polymerase chain reaction (qRT-PCR), and immunofluorescence staining revealed that Ca-PA-modified SLA titanium surfaces can promote osteogenic differentiation of human bone marrow mesenchymal stem cells (hBMSCs). Evaluation of oxidative stress and aging using reactive oxygen species (ROS), malondialdehyde (MDA), superoxide dismutase (SOD), and β-galactosidase staining revealed that Ca-PA-modified SLA titanium surfaces can reduce ROS production and ameliorate oxidative stress damage in hBMSCs. In vivo assessment of osteogenesis in a diabetic rat model revealed that Ca-PA coating promotes peri-implant osseointegration. Ca-PA-modified SLA titanium surface is a candidate for improving implant osseointegration in patients with diabetes.

Bone angiocrine factors

Angiogenesis in the bone is unique and involves distinctive signals. Whether they are created through intramembranous ossification or endochondral ossification, bones are highly vascularized tissues. Long bones undergo a sequence of processes known as endochondral osteogenesis. Angiogenesis occurs during the creation of endochondral bone and is mediated by a variety of cells and factors. An initially avascular cartilage template is invaded by blood vessels from the nearby subchondral bone thanks to the secreted angiogenic chemicals by hypertrophic chondrocytes. Vascular endothelial growth factor (VEGF), one of several angiogenic molecules, is a significant regulator of blood vessel invasion, cartilage remodeling, and ossification of freshly created bone matrix; chondrocyte proliferation and hypertrophy are facilitated by the production of VEGFA and VEGF receptor-2 (VEGFR-2), which is stimulated by fibroblast growth factors (FGFs). NOTCH signaling controls blood capillaries formation during bone maturation and regeneration, while hypoxia-inducible factor 1 alpha (HIF1-a) promotes chondrocyte development by switching to anaerobic metabolism. To control skeletal remodeling and repair, osteogenic cells release angiogenic factors, whereas endothelial cells secrete angiocrine factors. One of the better instances of functional blood vessels specialization for certain organs is the skeletal system. A subpopulation of capillary endothelial cells in the bone regulate the activity of osteoprogenitor cells, which in turn affects bone formation during development and adult homeostasis. Angiogenesis and osteogenesis are strictly connected, and their crosstalk is essential to guarantee bone formation and to maintain bone homeostasis. Additionally, pathological processes including inflammation, cancer, and aging include both bone endothelial cells and angiocrine factors. Therefore, the study and understanding of these mechanisms is fundamental, because molecules and factors involved may represent key targets for novel and advanced therapies.

Type H blood vessels in coupling angiogenesis-osteogenesis and its application in bone tissue engineering

One specific capillary subtype, termed type H vessel, has been found with unique functional characteristics in coupling angiogenesis with osteogenesis. Researchers have fabricated a variety of tissue engineering scaffolds to enhance bone healing and regeneration through the accumulation of type H vessels. However, only a limited number of reviews discussed the tissue engineering strategies for type H vessel regulation. The object of this review is to summary the current utilizes of bone tissue engineering to regulate type H vessels through various signal pathways including Notch, PDGF-BB, Slit3, HIF-1α, and VEGF signaling. Moreover, we give an insightful overview of recent research progress about the morphological, spatial and age-dependent characteristics of type H blood vessels. Their unique role in tying angiogenesis and osteogenesis together via blood flow, cellular microenvironment, immune system and nervous system are also summarized. This review article would provide an insight into the combination of tissue engineering scaffolds with type H vessels and identify future perspectives for vasculized tissue engineering research.

Skeletal-Vascular Interactions in Bone Development, Homeostasis, and Pathological Destruction

Bone is a highly vascularized organ that not only plays multiple roles in supporting the body and organs but also endows the microstructure, enabling distinct cell lineages to reciprocally interact. Recent studies have uncovered relevant roles of the bone vasculature in bone patterning, morphogenesis, homeostasis, and pathological bone destruction, including osteoporosis and tumor metastasis. This review provides an overview of current topics in the interactive molecular events between endothelial cells and bone cells during bone ontogeny and discusses the future direction of this research area to find novel ways to treat bone diseases.

Synergistic Effect of Magneto-Mechanical Bioengineered Stem Cells and Magnetic Field to Alleviate Osteoporosis

Therapeutic bioengineering based on stem cell therapy holds great promise in biomedical applications. However, the application of this treatment is limited in orthopedics because of their poor survival, weak localization, and low cell retention. In this work, magneto-mechanical bioengineered cells consisting of magnetic silica nanoparticles (MSNPs) and mesenchymal stem cells (MSCs) are prepared to alleviate osteoporosis. The magneto-mechanical bioengineered MSCs with spatial localization, cell retention, and directional tracking capabilities could be mediated by a guided magnetic field (MF) in vitro and in vivo. Furthermore, high uptake rates of the MSNPs ensure the efficient construction of magnetically controlled MSCs within 2 h. In conjunction with external MF, the magneto-mechanical bioengineered MSCs have the potential for the activation of the YAP/β-catenin signaling pathway, which could further promote osteogenesis, mineralization, and angiogenesis. The synergistic effects of MSNPs and guided MF could also decline bone resorption to rebalance bone metabolism in bone loss diseases. In vivo experiments confirm that the functional MSCs and guided MF could effectively alleviate postmenopausal osteoporosis, and the bone mass of the treated osteoporotic bones by using the bioengineered cells for 6 weeks is nearly identical to that of the healthy ones. Our results provide a new avenue for osteoporosis management and treatment, which contribute to the future advancement of magneto-mechanical bioengineering and treatment.

Warning regarding hematological toxicity of tamoxifen activated CreERT2 in young Rosa26CreERT2 mice

The Cre-lox system is a versatile and powerful tool used in mouse genetics. It allows spatial and/or temporal control of the deletion of a target gene. The Rosa26-CreERT2 (R26CreERT2) mouse model allows ubiquitous expression of CreERT2. Once activated by tamoxifen, CreERT2 will enter into the nuclei and delete floxed DNA sequences. Here, we show that intraperitoneal injection of tamoxifen in young R26CreERT2 mice leads to morbidity and mortality within 10 days after the first injection, in the absence of a floxed allele. Activation of CreERT2 by tamoxifen led to severe hematological defects, with anemia and a strong disorganization of the bone marrow vascular bed. Cell proliferation was significantly reduced in the bone marrow and the spleen resulting in the depletion of several hematopoietic cells. However, not all cell types or organs were affected to the same extent. We realized that many research groups are not aware of the potential toxicity of Cre recombinases, resulting in misinterpretation of the observed phenotype and in a waste of time and resources. We discuss the necessity to include tamoxifen injected CreERT2 controls lacking a floxed allele in experimental designs and to improve communication about the limitations of Cre-lox mouse models among the scientific community.

The enhanced visible light driven photocatalytic activity of zinc porphyrin/g-C3N4 nanosheet for efficient bacterial infected wound healing

Graphitic carbon nitride (g-C₃N₄) has received much attention as a metal-free polymeric two-dimensional photocatalyst for antibiotic-free antibacterial application. However, the weak photocatalytic antibacterial activity of pure g-C₃N₄ stimulated by visible light limits its applications. Herein, g-C₃N₄ is modified with Zinc (II) meso-tetrakis (4-carboxyphenyl) porphyrin (ZnTCPP) by amidation reaction to enhance the utilization of visible light and reduce the recombination of electron-hole pairs. The composite (ZP/CN) is used to treat bacterial infection under visible light irradiation with a high efficacy of 99.99% within 10 min due to the enhanced photocatalytic activity. Ultraviolet photoelectron spectroscopy and density flooding theory calculations indicate the excellent electrical conductivity between the interface of ZnTCPP and g-C₃N₄. The formed built-in electric field is responsible for the high visible photocatalytic performance of ZP/CN. In vitro and in vivo tests have demonstrated that ZP/CN not only possesses excellent antibacterial activity upon visible light irradiation, but also facilitates the angiogenesis. In addition, ZP/CN also suppresses the inflammatory response. Therefore, this inorganic-organic material can serve as a promising platform for effective healing of bacteria-infected wounds.

Effects of material nano-topography on the angiogenesis of type H vessels: Size dependence, cell heterogeneity and intercellular communication

Type H vessel, a vascular subtype in bone, is a critical regulator of osteogenesis, but how material properties affect this organ-specific vessel remains unknown. Here, titania nanotubes were fabricated on bone implant surface to investigate the effects of nano-topography on type H vessels. In vivo, surface nanotubes with 20-100 nm diameters promoted the angiogenesis of type H vessels and bone regeneration in mouse femurs to different extents, with the best effects induced by 70 nm diameter. In vitro, bone-specific endothelial cells (BECs) and artery endothelial cells (AECs) presented significantly different behaviors on the same material. Nanotubes with 20 nm small diameters significantly improved the adhesion, proliferation, type H differentiation of BECs and their paracrine function to regulate pre-osteoblasts (POBs), possibly via binding integrin β1 on the cell membrane, but these effects weakened when tube diameter increased, which conflicted with the results in vivo. Further study suggested that the better in vivo effects by larger diameters of 70-100 nm might be exerted indirectly through remodeling the regulation from POBs to BECs, highlighting the underappreciated indirect bio-effects of materials via intercellular communication. These suggest that nanoscale material topography makes significant impact on the angiogenesis of type H vessels, directly via binding integrins on the cell membrane of BECs and indirectly via modulating the regulation from osteoblastic cells to BECs, both in a size-dependent manner. Cells of the same type but from different tissues may show different responses to the same material, thus material properties should be tailored to the specific cell population. In research on material-tissue interactions, conclusions from in vitro experiments exposing a single type of cell to material might deviate from the truth in vivo, because materials may indirectly influence the targeted cells through modulating intercellular communication. These provide new insights into material-tissue interactions.

Dynamic crosstalk between hematopoietic stem cells and their niche from emergence to aging

The behavior of somatic stem cells is regulated by their niche. Interaction between hematopoietic stem cells (HSCs) and their niches are a representative model to understand stem cell-niche interplay. Here, we provide an overview of crosstalk between HSCs and their niches in bone marrow and extramedullary organs following the life journey of HSCs from emergence, development, maturation until aging. We highlight the unique differences of HSC niches in different life stages within various organs focusing on recent literature to propose new speculations and hypotheses.

Cellular niches for hematopoietic stem cells in bone marrow under normal and malignant conditions

Throughout adult life, most lineages of blood cells, including immune cells, are generated from hematopoietic stem cells (HSCs) in the bone marrow. HSCs are thought to require special microenvironments, termed niches, for their maintenance in the bone marrow; however, the identity of the HSC cellular niche has been a subject of long-standing debate. Although diverse candidates have been proposed so far, accumulated studies demonstrate that the bone marrow-specific population of fibroblastic reticular cells with long processes, termed CXC chemokine ligand 12-abundant reticular cells (which overlap strongly with leptin receptor-expressing cells), termed CAR/LepR⁺ cells, are the pivotal cellular component of niches for HSCs and lymphoid progenitors. Sinusoidal endothelial cells (ECs) are also important for hematopoietic homeostasis and regeneration. Hematopoiesis is altered dynamically by various stimuli such as inflammation, infection, and leukemia, all of which affect cellular niches and alter their function. Therefore, it is important to consider situations in which stimuli affect HSCs, either via direct interaction or indirectly via the hematopoietic niches. In this review, the dynamics of cellular niches in the steady state and disease are described, with a focus on CAR/LepR⁺ cells and ECs.