The Pathophysiological Sequence of Glucocorticoid-Induced Osteonecrosis of the Femoral Head in Male Mice

Bioinformatics analysis of PANoptosis regulators in the diagnosis and subtyping of steroid-induced osteonecrosis of the femoral head

In this study, we aimed to investigate the involvement of PANoptosis, a form of regulated cell death, in the development of steroid-induced osteonecrosis of the femoral head (SONFH). The underlying pathogenesis of PANoptosis in SONFH remains unclear. To address this, we employed bioinformatics approaches to analyze the key genes associated with PANoptosis. Our analysis was based on the GSE123568 dataset, allowing us to investigate both the expression profiles of PANoptosis-related genes (PRGs) and the immune profiles in SONFHallowing us to investigate the expression profiles of PRGs as well as the immune profiles in SONFH. We conducted cluster classification based on PRGs and assessed immune cell infiltration. Additionally, we used the weighted gene co-expression network analysis (WGCNA) algorithm to identify cluster-specific hub genes. Furthermore, we developed an optimal machine learning model to identify the key predictive genes responsible for SONFH progression. We also constructed a nomogram model with high predictive accuracy for assessing risk factors in SONFH patients, and validated the model using external data (area under the curve; AUC = 1.000). Furthermore, we identified potential drug targets for SONFH through the Coremine medical database. Using the optimal machine learning model, we found that 2 PRGs, CASP1 and MLKL, were significantly correlated with the key predictive genes and exhibited higher expression levels in SONFH. Our analysis revealed the existence of 2 distinct PANoptosis molecular subtypes (C1 and C2) within SONFH. Importantly, we observed significant variations in the distribution of immune cells across these subtypes, with C2 displaying higher levels of immune cell infiltration. Gene set variation analysis indicated that C2 was closely associated with multiple immune responses. In conclusion, our study sheds light on the intricate relationship between PANoptosis and SONFH. We successfully developed a risk predictive model for SONFH patients and different SONFH subtypes. These findings enhance our understanding of the pathogenesis of SONFH and offer potential insights into therapeutic strategies.

HIF-1α in cartilage homeostasis, apoptosis, and glycolysis in mice with steroid-induced osteonecrosis of the femoral head

With the prevalence of coronavirus disease 2019, the administration of glucocorticoids (GCs) has become more widespread. Treatment with high-dose GCs leads to a variety of problems, of which steroid-induced osteonecrosis of the femoral head (SONFH) is the most concerning. Since hypoxia-inducible factor 1α (HIF-1α) is a key factor in cartilage development and homeostasis, it may play an important role in the development of SONFH. In this study, SONFH models were established using methylprednisolone (MPS) in mouse and its proliferating chondrocytes to investigate the role of HIF-1α in cartilage differentiation, extracellular matrix (ECM) homeostasis, apoptosis and glycolysis in SONFH mice. The results showed that MPS successfully induced SONFH in vivo and vitro, and MPS-treated cartilage and chondrocytes demonstrated disturbed ECM homeostasis, significantly increased chondrocyte apoptosis rate and glycolysis level. However, compared with normal mice, not only the expression of genes related to collagens and glycolysis, but also chondrocyte apoptosis did not demonstrate significant differences in mice co-treated with MPS and HIF-1α inhibitor. And the effects observed in HIF-1α activator-treated chondrocytes were similar to those induced by MPS. And HIF-1α degraded collagens in cartilage by upregulating its downstream target genes matrix metalloproteinases. The results of activator/inhibitor of endoplasmic reticulum stress (ERS) pathway revealed that the high apoptosis rate induced by MPS was related to the ERS pathway, which was also affected by HIF-1α. Furthermore, HIF-1α affected glucose metabolism in cartilage by increasing the expression of glycolysis-related genes. In conclusion, HIF-1α plays a vital role in the pathogenesis of SONFH by regulating ECM homeostasis, chondrocyte apoptosis, and glycolysis.

Research progress in the pathogenesis of hormone-induced femoral head necrosis based on microvessels: a systematic review

Hormonal necrosis of the femoral head is caused by long-term use of glucocorticoids and other causes of abnormal bone metabolism, lipid metabolism imbalance and blood microcirculation disorders in the femoral head, resulting in bone trabecular fracture, bone tissue necrosis collapse, and hip dysfunction. It is the most common type of non-traumatic necrosis of the femoral head, and its pathogenesis is complex, while impaired blood circulation is considered to be the key to its occurrence. There are a large number of microvessels in the femoral head, among which H-type vessels play a decisive role in the "angiogenesis and osteogenesis coupling", and thus have an important impact on the occurrence and development of femoral head necrosis. Glucocorticoids can cause blood flow injury of the femoral head mainly through coagulation dysfunction, endothelial dysfunction and impaired angiogenesis. Glucocorticoids may inhibit the formation of H-type vessels by reducing the expression of HIF-1α, PDGF-BB, VGEF and other factors, thus causing damage to the "angiogenesis-osteogenesis coupling" and reducing the ability of necrosis reconstruction and repair of the femoral head. Leads to the occurrence of hormonal femoral head necrosis. Therefore, this paper reviewed the progress in the study of the mechanism of hormone-induced femoral head necrosis based on microvascular blood flow at home and abroad, hoping to provide new ideas for the study of the mechanism of femoral head necrosis and provide references for clinical treatment of femoral head necrosis.

[α2-macroglobulin alleviates glucocorticoid-induced avascular necrosis of the femoral head in mice by promoting proliferation, migration and angiogenesis of vascular endothelial cells]

OBJECTIVE

To explore the mechanism underlying the protective effect of α2-macroglobulin (A2M) against glucocorticoid-induced femoral head necrosis.

METHODS

In a human umbilical vein endothelial cell (HUVEC) model with injuries induced by gradient concentrations of dexamethasone (DEX; 10-8-10-5 mol/L), the protective effects of A2M at 0.05 and 0.1 mg/mL were assessed by examining the changes in cell viability, migration, and capacity of angiogenesis using CCK-8 assay, Transwell and scratch healing assays and angiogenesis assay. The expressions of CD31 and VEGF-A proteins in the treated cells were detected using Western blotting. In BALB/c mouse models of avascular necrosis of the femoral head induced by intramuscular injections of methylprednisolone, the effects of intervention with A2M on femoral trabecular structure, histopathological characteristics, and CD31 expression were examined with Micro-CT, HE staining and immunohistochemical staining.

RESULTS

In cultured HUVECs, DEX treatment significantly reduced cell viability, migration and angiogenic ability in a concentration- and time-dependent manner (P<0.05), and these changes were obviously reversed by treatment with A2M in positive correlation with A2M concentration (P<0.05). DEX significantly reduced the expression of CD31 and VEGF-A proteins in HUVECs, while treatment with A2M restored CD31 and VEGF-A expressions in the cells (P<0.05). The mouse models of femoral head necrosis showed obvious trabecular damages in the femoral head, where a large number of empty lacunae and hypertrophic fat cells could be seen and CD31 expression was significantly decreased (P<0.05). A2M treatment of the mouse models significantly improved trabecular damages, maintained normal bone tissue structures, and increased CD31 expression in the femoral head (P<0.05).

CONCLUSION

A2M promotes proliferation, migration, and angiogenesis of DEX-treated HUVECs and alleviates methylprednisolone-induced femoral head necrosis by improving microcirculation damages and maintaining microcirculation stability in the femoral head.

Preparation of genetically or chemically engineered exosomes and their therapeutic effects in bone regeneration and anti-inflammation

The treatment of bone or cartilage damage and inflammation-related diseases has been a long-standing research hotspot. Traditional treatments such as surgery and cell therapy have only displayed limited efficacy because they can't avoid potential deterioration and ensure cell activity. Recently, exosomes have become a favorable tool for various tissue reconstruction due to their abundant content of proteins, lipids, DNA, RNA and other substances, which can promote bone regeneration through osteogenesis, angiogenesis and inflammation modulation. Besides, exosomes are also promising delivery systems because of stability in the bloodstream, immune stealth capacity, intrinsic cell-targeting property and outstanding intracellular communication. Despite having great potential in therapeutic delivery, exosomes still show some limitations in clinical studies, such as inefficient targeting ability, low yield and unsatisfactory therapeutic effects. In order to overcome the shortcomings, increasing studies have prepared genetically or chemically engineered exosomes to improve their properties. This review focuses on different methods of preparing genetically or chemically engineered exosomes and the therapeutic effects of engineering exosomes in bone regeneration and anti-inflammation, thereby providing some references for future applications of engineering exosomes.

The protective role of vitamins C and E in steroid-induced femoral head osteonecrosis: An experimental study in rats

OBJECTIVES

This study aimed to determine whether vitamin C (VC) and vitamin E (VE) can effectively protect the femoral head and reduce the risk of developing osteonecrosis in rats that have been treated with steroids.

MATERIALS AND METHODS

The study was conducted on 30 young adult male Sprague-Dawley rats (mean weight: 356±18 g; range, 330 to 375 g), which were randomly assigned to one of five groups. The control group received saline solution, while the other groups were given lipopolysaccharide/methylprednisolone (LPS/MPS) to induce osteonecrosis. Three groups in which osteonecrosis was induced were also intraperitoneally administered either VC, VE, or both once a day for four weeks. Intracardiac blood samples were taken at the end of the fourth week for biochemical examination, and the rats were then sacrificed under general anesthesia. After sacrification, right femurs were removed for histopathological, immunohistochemical, and radiologic examinations.

RESULTS

The results showed that the mean trabecular number increased significantly in the VC+VE group. There was a substantial decrease observed in the mean trabecular separation within the LPS/MPS group compared to the control group, although trabecular separation decreased in all three vitamin groups compared to the LPS/MPS group. The surface area/bone volume was significantly increased in the VC+VE group compared to the LPS/MPS group. Histological, immunohistochemical, and radiological examinations showed that the administration of VC and VE significantly reduced oxidative stress, inflammation, and microvascular dysfunction in rats with steroid-induced femoral head osteonecrosis.

CONCLUSION

This study suggests that VC, VE, and particularly VC+VE have a protective effect on the femoral head in rats with steroid-induced femoral head osteonecrosis. These findings may lead to new treatment options for patients.

Apocynin exerts cytoprotective effects on dexamethasone-induced osteoblasts by inhibiting oxidative stress through the Nrf2 signalling pathway

Steroid-induced femoral head necrosis (SIFHN) is a serious clinical complication that is caused by prolonged or excessive use of glucocorticoids (GCs). Osteoblast apoptosis and osteogenic differentiation dysfunction caused by GC-induced oxidative stress and mitochondrial impairment are strongly implicated in SIFHN. Apocynin (APO) is a kind of acetophenone extracted from an herb. In recent years, APO has received much attention for its antiapoptotic and antioxidant properties. This study aimed to investigate whether APO could protect against SIFHN and explore the mechanism. In our study, low-dose APO had no toxic effects on osteoblasts and restored dexamethasone (Dex)-treated osteoblasts by improving survival, inhibiting OS and restoring mitochondrial dysfunction. Mechanistically, APO alleviated Dex-induced osteoblast injury by activating the Nrf2 pathway, and the use of ML385 to block Nrf2 significantly eliminated the protective effect of APO. In addition, APO could reduce the formation of empty lacunae, restore bone mass and promote the expression of Nrf2 in SIFHN rats. In conclusion, APO protects osteoblasts from Dex-induced oxidative stress and mitochondrial dysfunction through activation of the Nrf2 pathway and may be a beneficial drug for the treatment of SIFHN.

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.

Effect of whole body vibration therapy in the rat model of steroid-induced osteonecrosis of the femoral head

Background: Steroid-induced Osteonecrosis of the Femoral Head (SIONFH) is a skeletal disease with a high incidence and a poor prognosis. Whole body vibration therapy (WBVT), a new type of physical training, is known to promote bone formation. However, it remains unclear whether WBVT has a therapeutic effect on SIONFH. Materials and methods: Thirty adult male and female Sprague-Dawley (SD) rats were selected and randomly assigned to three experimental groups: the control group, the model group, and the mechanical vibration group, respectively. SIONFH induction was achieved through the combined administration of lipopolysaccharides (LPS) and methylprednisolone sodium succinate for injection (MPS). The femoral head samples underwent hematoxylin and eosin (H&E) staining to visualize tissue structures. Structural parameters of the region of interest (ROI) were compared using Micro-CT analysis. Immunohistochemistry was employed to assess the expression levels of Piezo1, BMP2, RUNX2, HIF-1, VEGF, CD31, while immunofluorescence was used to examine CD31 and Emcn expression levels. Results: The H&E staining results revealed a notable improvement in the ratio of empty lacuna in various groups following WBVT intervention. Immunohistochemical analysis showed that the expression levels of Piezo1, BMP2, RUNX2, HIF-1, VEGF, and CD31 in the WBVT group exhibited significant differences when compared to the Model group (p < 0.05). Additionally, immunofluorescence analysis demonstrated statistically significant differences in CD31 and Emcn expression levels between the WBVT group and the Model group (p < 0.05). Conclusion: WBVT upregulates Piezo1 to promote osteogenic differentiation, potentially by enhancing the HIF-1α/VEGF axis and regulating H-vessel angiogenesis through the activation of the Piezo1 ion channel. This mechanism may lead to improved blood flow supply and enhanced osteogenic differentiation within the femoral head.

Bone and the Unfolded Protein Response: In Sickness and in Health

Differentiation and optimal function of osteoblasts and osteoclasts are contingent on synthesis and maintenance of a healthy proteome. Impaired and/or altered secretory capacity of these skeletal cells is a primary driver of most skeletal diseases. The endoplasmic reticulum (ER) orchestrates the folding and maturation of membrane as well as secreted proteins at high rates within a calcium rich and oxidative organellar niche. Three ER membrane proteins monitor fidelity of protein processing in the ER and initiate an intricate signaling cascade known as the Unfolded Protein Response (UPR) to remediate accumulation of misfolded proteins in its lumen, a condition referred to as ER stress. The UPR aids in fine-tuning, expanding and/or modifying  the cellular proteome, especially in specialized secretory cells, to match everchanging physiologic cues and metabolic demands. Sustained activation of the UPR due to chronic ER stress, however, is known to hasten cell death and drive pathophysiology of several diseases. A growing body of evidence suggests that ER stress and an aberrant UPR may contribute to poor skeletal health and the development of osteoporosis. Small molecule therapeutics that target distinct components of the UPR may therefore have implications for developing novel treatment modalities relevant to the skeleton. This review summarizes the complexity of UPR actions in bone cells in the context of skeletal physiology and osteoporotic bone loss, and highlights the need for future mechanistic studies to develop novel UPR therapeutics that mitigate adverse skeletal outcomes.

Tanshinone I alleviates steroid-induced osteonecrosis of femoral heads and promotes angiogenesis: in vivo and in vitro studies

BACKGROUND

The impaired blood supply to the bones is an important pathological feature of steroid-induced osteonecrosis of the femoral head (SIONFH). Danshen is a Chinese herb that shows therapeutic effects on SIONFH, but the effects of one of its major bioactive constituents, Tanshinone I (TsI), on SIONFH remain unknown. Here, we evaluated the effects of TsI on SIONFH, particularly focusing on its effects on angiogenesis, in in vivo and in vitro research.

METHODS

SIONFH was induced in Sprague-Dawley rats by an intramuscular injection of methylprednisolone (40 mg/kg) in combination with an intraperitoneal injection of lipopolysaccharide (20 μg/kg). Morphological alterations of the femoral head were observed by dual-energy X-ray absorptiometry and HE staining. Western blot, qRT-PCR, and immunohistochemical/immunofluorescence staining were used to determine gene expression.

RESULTS

TsI (10 mg/kg) alleviated bone loss and rescued the expression of angiogenesis-related molecules (CD31, VWF, VEGF, and VEGFR2) in the femoral heads of SIONFH rats. Notably, TsI rescued the down-regulated expression of SRY-box transcription factor 11 (SOX11) in CD31⁺ endothelial cells in the femoral heads of SIONFH rats. In vitro studies showed that TsI preserved the dexamethasone-harmed angiogenic property (migration and tube formation) of human umbilical vein cells (EA.hy926), suppressed dexamethasone-induced cell apoptosis, reduced pro-apoptotic proteins (cytosolic cytochrome C, Bax, and caspase 3/9) and increased anti-apoptotic protein Bcl-2, whereas silencing of SOX11 reversed these beneficial effects.

CONCLUSIONS

This study demonstrates that TsI alleviates SIONFH and promotes angiogenesis by regulating SOX11 expression. Our work would provide new evidence for the application of TsI to treat SIONFH.

Administration of necrostatin-1 ameliorates glucocorticoid-induced osteonecrosis of the femoral head in rats

Glucocorticoid (GC)-induced osteonecrosis of the femoral head (ONFH) is a serious complication of glucocorticoid treatment and is characterized by dysfunctional bone reconstruction at necrotic sites. Our previous study confirmed the protective potential of necrostatin-1, a selective blocker of necroptosis, in glucocorticoid-induced osteoporosis. In this study, rat models of GC-induced ONFH were established to evaluate the effects of necrostatin-1 on osteonecrotic changes and repair processes. Osteonecrosis was verified by histopathological staining. An analysis of trabecular bone architecture was performed to evaluate osteogenesis in the osteonecrotic zone. Then, necroptotic signaling molecules such as RIP1 and RIP3 were examined by immunohistochemistry. Histopathological observations indicated that necrostatin-1 administration reduced the incidence of osteonecrosis and the osteogenic response in subchondral areas. Additionally, bone histomorphometry demonstrated that necrostatin-1 intervention could restore bone reconstruction in the necrotic zone. The protective mechanism of necrostatin-1 was related to the inhibition of RIP1 and RIP3. Necrostatin-1 administration alleviated GC-induced ONFH in rats by attenuating the formation of necrotic lesions, recovering the function of osteogenesis, and suppressing glucocorticoid-induced osteocytic necroptosis by inhibiting the expression of RIP1 and RIP3.

Bone tissue engineering for treating osteonecrosis of the femoral head

Osteonecrosis of the femoral head (ONFH) is a devastating and complicated disease with an unclear etiology. Femoral head-preserving surgeries have been devoted to delaying and hindering the collapse of the femoral head since their introduction in the last century. However, the isolated femoral head-preserving surgeries cannot prevent the natural progression of ONFH, and the combination of autogenous or allogeneic bone grafting often leads to many undesired complications. To tackle this dilemma, bone tissue engineering has been widely developed to compensate for the deficiencies of these surgeries. During the last decades, great progress has been made in ingenious bone tissue engineering for ONFH treatment. Herein, we comprehensively summarize the state-of-the-art progress made in bone tissue engineering for ONFH treatment. The definition, classification, etiology, diagnosis, and current treatments of ONFH are first described. Then, the recent progress in the development of various bone-repairing biomaterials, including bioceramics, natural polymers, synthetic polymers, and metals, for treating ONFH is presented. Thereafter, regenerative therapies for ONFH treatment are also discussed. Finally, we give some personal insights on the current challenges of these therapeutic strategies in the clinic and the future development of bone tissue engineering for ONFH treatment.

Worldwide research trends on femur head necrosis (2000-2021): a bibliometrics analysis and suggestions for researchers

Background

Osteonecrosis of the femoral head (ONFH) is a common and stubborn disease. The main causes are venous stasis of the femoral head, arterial blood supply damage, bone cell and bone marrow death, and bone tissue necrosis and subsequent repair obstacles. Over the past 22 years, the number of papers on ONFH has, overall, continued to increase.

Methods

Using bibliometrics, we investigated the trends, frontiers, and hotspots of global scientific output in the past 22 years. We searched Science Citation Index Expanded (SCIE) of the Web of Science Core Collection (WoSCC) and retrieved information associated with papers and records published between 2000 and 2021. We used VOSviewer and CiteSpace to conduct bibliometric analysis and visual analysis on the overall distribution of annual output, major countries, active institutions, journals, authors, commonly cited literature, and keywords. The impact and quality of the papers were assessed using the global citation score (GCS).

Results

We retrieved a total of 2006 articles and reviews. Over the past 22 years, the number of publications (NP) increased. China ranked first in terms of NP, while the United States had the highest h-index and the highest number of citations (NC). Shanghai Jiao Tong University and International Orthopaedics were the institution and periodical, respectively. The paper written by Mont et al. in 2006 had the highest total GCS score, at 379. The top three keywords were "ischemic necrosis", "osteonecrosis", and "hip joint". Although there was a fluctuation in publications associated with ONFH, overall, the NP increased. China was the most prolific in this area, while the United States was the most influential country. The top 3 authors in terms of NP were Zhang, Motomura, and Zhao. Areas of focus in ONFH over recent years include signal pathway, genetic differentiation, glucocorticoid-induced osteogenesis, induced ischemic necrosis and osteogenesis.

Conclusions

Our bibliometrics analysis revealed the research hotspots and rapid development trends of ONFH research in the past 22 years. The most critical indicators [researchers, countries, research institutions, and journals publishing osteonecrosis of the femoral head (ONFH) research] relevant to the research hotspots in the field of ONFH research were analyzed.

Advances in experimental models of osteonecrosis of the femoral head

Background

Osteonecrosis of the femoral head (ONFH) is a devastating disease affecting young adults, resulting in significant pain, articular surface collapse, and disabling dysfunction. ONFH can be divided into two broad categories: traumatic and non-traumatic. It has been established that ONFH results from an inadequate blood supply that causes the death of osteocytes and bone marrow cells. Nonetheless, the precise mechanism of ONFH remains to be elucidated. In this regard, preclinical animal and cell models to study ONFH have been established to assess the efficacy of various modalities for preventing and treating ONFH. Nevertheless, it should be borne in mind that many models do not share the same physiologic and metabolic characteristics as humans. Therefore, it is necessary to establish a reproducible model that better mimics human disease.

Methods

We systematically reviewed the literatures in regard to ONFH experimental models over the past 30 years. The search was performed in PubMed and Web of Science. Original animal, cell studies with available full-text were included. This review summarizes different methods for developing animal and cell experimental models of ONFH. The advantages, disadvantages and success rates of ONFH models are also discussed. Finally, we provide experimental ONFH model schemes as a reference.

Results

According to the recent literatures, animal models of ONFH include traumatic, non-traumatic and traumatic combined with non-traumatic models. Most researchers prefer to use small animals to establish non-traumatic ONFH models. Indeed, small animal-based non-traumatic ONFH modeling can more easily meet ethical requirements with large samples. Otherwise, gradient concentration or a particular concentration of steroids to induce MSCs or EPCs, through which researchers can develop cell models to study ONFH.

Conclusions

Glucocorticoids in combination with LPS to induce ONFH animal models, which can guarantee a success rate of more than 60% in large samples. Traumatic vascular deprivation combines with non-traumatic steroids to induce ONFH, obtaining success rates ranging from 80% to 100%. However, animals that undergo vascular deprivation surgery may not survive the glucocorticoid induction process. As for cell models, 10-6mol/L Dexamethasone (Dex) to treat bone marrow stem cells, which is optimal for establishing cell models to study ONFH.

The translational potential of this article

This review aims to summarize recent development in experimental models of ONFH and recommended the modeling schemes to verify new models, mechanisms, drugs, surgeries, and biomaterials of ONFH to contribute to the prevention and treatment of ONFH.

Human umbilical cord mesenchymal stem cells prevent glucocorticoid-induced osteonecrosis of the femoral head by promoting angiogenesis

The impairment of angiogenesis is an outstanding pathogenic characteristic of glucocorticoid (GC)-induced osteonecrosis of the femoral head (ONFH). Human umbilical cord mesenchymal stem cells (hUC-MSCs) have been used in several diseases models, which were reported to be involved in the angiogenesis. However, whether hUC-MSCs suppress the GC-induced ONFH via promoting angiogenesis is still unclear. hUC-MSCs were isolated from the Wharton's jelly using the explant culture method. A GC-induced ONFH model was established in vitro and in vivo. The angiogenesis, proliferation and migration ability of HMECs were determined using the tube-forming, CCK-8, transwell and scratching assays in vitro. The protective role of hUC-MSCs in GC-induced ONFH was evaluated using micro-CT scanning and histological, immunohistochemical (IHC) and Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) assays in vivo. The results showed that hUC-MSCs treatment improved the tube-forming, proliferation and migration ability of HMECs in vitro. Moreover, hUC-MSCs treatment enhanced the integrity of trabecular bone of the femoral head, and the tube-forming ability in vivo. hUC-MSCs prevent the femoral head against necrosis and damage caused by GCs though promoting angiogenesis.

Sequential Release of Panax Notoginseng Saponins and Osteopractic Total Flavone from Poly (L-Lactic Acid) Scaffold for Treating Glucocorticoid-Associated Osteonecrosis of Femoral Head

Glucocorticoids inhibit angiogenesis in the femoral head, which fails to nourish the bone tissue and leads to osteonecrosis. Restoring angiogenesis is not only essential for vessel formation, but also crucial for osteogenesis. Poly (L-lactic acid) (PLLA) is commonly used in the bone tissue engineering field. Panax notoginseng saponins (PNS) and osteopractic total flavone (OTF) promote angiogenesis and osteogenesis, respectively. We designed a sequentially releasing PLLA scaffold including PLLA loaded with OTF (inner layer) and PLLA loaded with PNS (outer layer). We assessed the osteogenic effect of angiogenesis in this scaffold by comparing it with the one-layered scaffold (PLLA embedded with OTF and PNS) in vivo. Results from the micro-CT showed that the data of bone mineral density (BMD), bone volume (BV), and percent bone volume (BV/TV) in the PO-PP group were significantly higher than those in the POP group (p < 0.01). Histological analyses show that the PO-PP scaffold exhibits better angiogenic and osteogenic effects compared with the one-layered scaffold. These might result from the different structures between them, where the sequential release of a bi-layer scaffold achieves the osteogenic effect of vascularization by initially releasing PNS in the outer layer. We further explored the possible mechanism by an immunohistochemistry analysis and an immunofluorescence assay. The results showed that the protein expressions of vascular endothelial growth factor (VEGF) and platelet endothelial cell adhesion molecule-1(CD31) in the PO-PP scaffold were significantly higher than those in the POP scaffold (p < 0.01); the protein expressions of osteocalcin (OCN), osteopontin (OPN), and alkaline phosphatase (ALP) in the PO-PP scaffold were significantly higher than those in the POP scaffold (p < 0.05). Upregulating the expressions of angiogenic and osteogenic proteins might be the possible mechanism.

Effects of Simvastatin on Cartilage Homeostasis in Steroid-Induced Osteonecrosis of Femoral Head by Inhibiting Glucocorticoid Receptor

Steroid-induced osteonecrosis of femoral head (SONFH) is one of the most common bone disorders in humans. Statin treatment is beneficial in preventing the development of SONFH through anti-inflammation effects and inhibition of the glucocorticoid receptor (GR). However, potential mechanisms of statin action remain to be determined. In this study, pulse methylprednisolone (MP) treatment was used to induce SONFH in broilers, and then MP-treated birds were administrated with simvastatin simultaneously to investigate the changes in cartilage homeostasis. Meanwhile, chondrocytes were isolated, cultured, and treated with MP, simvastatin, or GR inhibitor in vitro. The changes in serum homeostasis factors, cell viability, and expression of GR were analyzed. The results showed that the morbidity of SONFH in the MP-treated group increased significantly compared with the simvastatin-treated and control group. Furthermore, MP treatment induced apoptosis and high-level catabolism and low-level anabolism in vitro and vivo, while simvastatin significantly decreased catabolism and slightly recovered anabolism via inhibiting GR and the hypoxia-inducible factor (HIF) pathway. The GR inhibitor or its siRNA mainly affected the catabolism of cartilage homeostasis in vitro. In conclusion, the occurrence of SONFH in broilers was related to the activation of GR and HIF pathway, and imbalance of cartilage homeostasis. Simvastatin and GR inhibitor maintained cartilage homeostasis via GR and the HIF pathway.

Lnc Tmem235 promotes repair of early steroid-induced osteonecrosis of the femoral head by inhibiting hypoxia-induced apoptosis of BMSCs

Bone marrow mesenchymal stem cells (BMSCs) have been used in the treatment of early steroid-induced osteonecrosis of the femoral head (SONFH). However, the hypoxic microenvironment in the osteonecrotic area leads to hypoxia-induced apoptosis of transplanted BMSCs, which limits their efficacy. Therefore, approaches that inhibit hypoxia-induced apoptosis of BMSCs are promising for augmenting the efficacy of BMSC transplantation. Our present study found that under hypoxia, the expression of the long noncoding RNA (Lnc) transmembrane protein 235 (Tmem235) was downregulated, the expression of Bcl-2-associated X protein was upregulated, the expression of B-cell lymphoma-2 protein was downregulated, and the apoptotic rate of BMSCs was over 70%. However, overexpression of Lnc Tmem235 reversed hypoxia-induced apoptosis of BMSCs and promoted their survival. These results demonstrated that Lnc Tmem235 effectively inhibited hypoxia-induced apoptosis of BMSCs. Mechanistically, we found that Lnc Tmem235 exhibited competitive binding to miR-34a-3p compared with BIRC5 mRNA, which is an inhibitor of apoptosis; this competitive binding relieved the silencing effect of miR-34a-3p on BIRC5 mRNA to ultimately inhibit hypoxia-induced apoptosis of BMSCs by promoting the expression of BIRC5. Furthermore, we cocultured BMSCs overexpressing Lnc Tmem235 with xenogeneic antigen-extracted cancellous bone to construct tissue-engineered bone to repair a model of early SONFH in vivo. The results showed that overexpression of Lnc Tmem235 effectively reduced apoptosis of BMSCs in the hypoxic microenvironment of osteonecrosis and improved the effect of BMSC transplantation. Taken together, our findings show that Lnc Tmem235 inhibited hypoxia-induced apoptosis of BMSCs by regulating the miR-34a-3p/BIRC5 axis, thus improving the transplantation efficacy of BMSCs for treating early SONFH.

HIF-1α Regulates Bone Homeostasis and Angiogenesis, Participating in the Occurrence of Bone Metabolic Diseases

In the physiological condition, the skeletal system's bone resorption and formation are in dynamic balance, called bone homeostasis. However, bone homeostasis is destroyed under pathological conditions, leading to the occurrence of bone metabolism diseases. The expression of hypoxia-inducible factor-1α (HIF-1α) is regulated by oxygen concentration. It affects energy metabolism, which plays a vital role in preventing bone metabolic diseases. This review focuses on the HIF-1α pathway and describes in detail the possible mechanism of its involvement in the regulation of bone homeostasis and angiogenesis, as well as the current experimental studies on the use of HIF-1α in the prevention of bone metabolic diseases. HIF-1α/RANKL/Notch1 pathway bidirectionally regulates the differentiation of macrophages into osteoclasts under different conditions. In addition, HIF-1α is also regulated by many factors, including hypoxia, cofactor activity, non-coding RNA, trace elements, etc. As a pivotal pathway for coupling angiogenesis and osteogenesis, HIF-1α has been widely studied in bone metabolic diseases such as bone defect, osteoporosis, osteonecrosis of the femoral head, fracture, and nonunion. The wide application of biomaterials in bone metabolism also provides a reasonable basis for the experimental study of HIF-1α in preventing bone metabolic diseases.

Vitamin B2 Prevents Glucocorticoid-Caused Damage of Blood Vessels in Osteonecrosis of the Femoral Head

Osteonecrosis of the femoral head (ONFH) is a disorder that can cause collapse of the femoral head. The damage and dysfunction of femoral head microvascular endothelial cells are related to the pathogenesis of glucocorticoid-induced ONFH. Reports suggest that vitamin B₂ can promote osteoblast differentiation and prevent low bone mineral density and prevent reperfusion oxidative injury. To explore the effect and possible molecular mechanism of vitamin B₂ on the ONFH and Human Umbilical Vein Endothelial Cells (HUVECs), we performed a rat model of ONFH by dexamethasone. The rats were randomly divided into four groups: control group, vitamin B₂ group, dexamethasone group, and dexamethasone combined with vitamin B₂ treatment group. HUVECs were used to further prove the role and mechanism of vitamin B₂ in vitro. In patients, according to immunohistochemical and qRT-PCR of the femoral head, the angiogenic capacity of the ONFH femoral head is compromised. In vivo, it showed that vitamin B₂ could inhibit glucocorticoid-induced ONFH-like changes in rats by suppressing cell apoptosis, promoting the regeneration of blood vessels, and increasing bone mass. According to in vitro results, vitamin B₂ could induce the migration of HUVECs, enhance the expression of angiogenesis-related factors, and inhibit glucocorticoid-induced apoptosis. The underlying mechanism may be that vitamin B₂ activates the PI3K signaling pathway. Vitamin B₂ alleviated dexamethasone-induced ONFH, and vitamin B₂ could promote the proliferation and migration of HUVECs and inhibit their apoptosis by activating the PI3K/Akt signaling pathway. Vitamin B₂ may be a potentially effective treatment for ONFH.

11β-Hydroxysteroid Dehydrogenase Type 1 within Osteoclasts Mediates the Bone Protective Properties of Therapeutic Corticosteroids in Chronic Inflammation

Therapeutic glucocorticoids (GCs) are powerful anti-inflammatory tools in the management of chronic inflammatory diseases such as rheumatoid arthritis (RA). However, their actions on bone in this context are complex. The enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) is a mediator of the anti-inflammatory actions of therapeutic glucocorticoids (GCs) in vivo. In this study we delineate the role of 11β-HSD1 in the effects of GC on bone during inflammatory polyarthritis. Its function was assessed in bone biopsies from patients with RA and osteoarthritis, and in primary osteoblasts and osteoclasts. Bone metabolism was assessed in the TNF-tg model of polyarthritis treated with oral GC (corticosterone), in animals with global (TNF-tg11βKO), mesenchymal (including osteoblast) (TNF-tg11βflx/tw2cre) and myeloid (including osteoclast) (TNF-tg11βflx/LysMcre) deletion. Bone parameters were assessed by micro-CT, static histomorphometry and serum metabolism markers. We observed a marked increase in 11β-HSD1 activity in bone in RA relative to osteoarthritis bone, whilst the pro-inflammatory cytokine TNFα upregulated 11β-HSD1 within osteoblasts and osteoclasts. In osteoclasts, 11β-HSD1 mediated the suppression of bone resorption by GCs. Whilst corticosterone prevented the inflammatory loss of trabecular bone in TNF-tg animals, counterparts with global deletion of 11β-HSD1 were resistant to these protective actions, characterised by increased osteoclastic bone resorption. Targeted deletion of 11β-HSD1 within osteoclasts and myeloid derived cells partially reproduced the GC resistant phenotype. These data reveal the critical role of 11β-HSD1 within bone and osteoclasts in mediating the suppression of inflammatory bone loss in response to therapeutic GCs in chronic inflammatory disease.

Knockdown of HDAC9 Inhibits Osteogenic Differentiation of Human Bone Marrow Mesenchymal Stem Cells Partially by Suppressing the MAPK Signaling Pathway

Background

Histone deacetylase 9 (HDAC9) is a member of the HDAC gene family that plays essential roles in the organization of transcriptional regulation by catalyzing deacetylation of histone proteins. However, the effects of HDAC9 on osteonecrosis of femoral head (ONFH) have not been investigated. The present study aimed to reveal whether histone deacetylase 9 (HDAC9) regulated osteogenic differentiation.

Methods

A lentiviral knockdown HDAC9 model was established in hBMSCs. Osteoblast-specific gene expression, such as Runx2, OCN was examined by qRT-PCR and Western blot, respectively. Though transcriptome sequencing and enrichment analysis, related signal pathways caused by down-regulation of HDAC9 were screened. The effect of HDAC9 on MAPK signaling pathway was determined by Western blot. Eventually, tert-Butylhydroquinone (tBHQ) was used to examine the effect of MAPK activation on osteogenesis in HDAC9 knockdown hBMSCs.

Results

A lentiviral knockdown HDAC9 model was successfully established in hBMSCs. HDAC9 knockdown significantly inhibited osteoblast-specific gene expression, such as runt-related transcription factor 2 (Runx2), osteocalcin (OCN) and mineral deposition in vitro. Moreover, a total of 950 DEGs were identified in HDAC9-knockdown hBMSCs. We discovered that the MAPK signaling pathway might be related to this process by pathway enrichment analysis. HDAC9 knockdown significantly reduced the expression level of phosphorylated extracellular signal-regulated kinase 1/2 (pERK1/2). Finally, the decreased osteogenesis due to HDAC9 knockdown was partly rescued by a MAPK signaling pathway activator.

Conclusion

Taken together, these results suggest that HDAC9 knockdown inhibits osteogenic differentiation of hBMSCs, partially through the MAPK signaling pathway. HDAC9 may serve as a potential target for the treatment of ONFH.

Inhibition of Cdk5 Ameliorates Skeletal Bone Loss in Glucocorticoid-Treated Mice

Glucocorticoids (GCs) are widely used to treat inflammatory diseases. However, their long-term use leads to glucocorticoid-induced osteoporosis, increasing morbidity and mortality. Both anabolic and anti-resorptive drugs are used to counteract GC-induced bone loss, however, they are expensive and/or have major side effects. Therefore, identifying new targets for cost-effective, small-molecule inhibitors is essential. We recently identified cyclin-dependent kinase 5 (Cdk5) as a suppressor of osteoblast differentiation and showed that its inhibition with roscovitine promoted osteoblastogenesis, thus improving the skeletal bone mass and fracture healing. Here, we assessed whether Cdk5 knockdown or inhibition could also reverse the GC-mediated suppression of osteoblast differentiation, bone loss, and fracture healing. We first demonstrated that Cdk5 silencing abolished the dexamethasone (Dex)-induced downregulation of alkaline phosphatase (Alp) activity, osteoblast-specific marker gene expression (Runx2, Sp7, Alpl, and Bglap), and mineralization. Similarly, Cdk5 inhibition rescued Dex-induced suppression of Alp activity. We further demonstrated that Cdk5 inhibition reversed prednisolone (Pred)-induced bone loss in mice, due to reduced osteoclastogenesis rather than improved osteoblastogenesis. Moreover, we revealed that Cdk5 inhibition failed to improve Pred-mediated impaired fracture healing. Taken together, we demonstrated that Cdk5 inhibition with roscovitine ameliorated GC-mediated bone loss but did not reverse GC-induced compromised fracture healing in mice.

Effects of immunosuppressants on T-cell dynamics: Understanding from a generic coarse-grained immune network model

Long-term immunosuppressive therapy is a drug regimen often used to lower aggressive immune responses in various chronic inflammatory diseases. However, such long-term therapy leading to immune suppression may trigger other adverse reactions in the immune system. The rising concern regarding the optimal dose and duration of such treatment has motivated us to understand non-classical immunomodulatory responses induced by various immunosuppressive steroid and secosteroid drugs such as glucocorticoid and vitamin D supplements. The immunomodulatory actions of such immunosuppressants (that govern the adaptive immune response) are often mediated through their characteristic control over CD4+ T-cells involving pro- and antiinflammatory T-cells. Several early studies attempted to decode temporal and dose-dependent behaviors of such pro- and anti-inflammatory T-cells using the chemical dynamics approach. We first summarize these early works. Then, we develop a minimal coarse-grained kinetic network model to capture the commonality in their immunomodulatory functions. This generic model successfully reproduces the characteristic dynamical features, including the clinical latency period in long-term T-cell dynamics. The temporal behavior of T-cells is found to be sensitive to specific rate parameters and doses of immunosuppressants. The steady-state analysis reflects the transition from an early classified weakly regulated (autoimmune-prone) immune state to a strongly regulated state (immunocompromised state), separated by an intervening state of moderate/balanced regulation. An optimal dose and duration are essential in rescuing balanced immune regulation. This review elucidates how developing a simple generic coarse-grained immune network model may provide immense information that helps diagnose inefficacy in adaptive immune function before and after administering immunosuppressants such as glucocorticoid or vitamin D.

Sequential Epiphyseal Cartilage Changes of Femoral Heads in C57BL/6 Female Mice Treated with Excessive Glucocorticoids

OBJECTIVE

Excessive use of glucocorticoids (GCs) may cause adverse effects on the skeletal system in children. However, only a few studies have reported the effects of GCs on the epiphyseal cartilage. This study aimed to uncover the subsequent epiphyseal cartilage changes of immature femoral heads after excessive GC treatment in a mouse model and explain the pathological changes preliminarily.

DESIGN

Female C57BL/6 mice were divided into control and model (excessive GC treatment) groups. The structure of the femoral heads was evaluated by using micro-computed tomography, hematoxylin-eosin staining, and safranin staining analyses. Immunohistochemistry was used to detect angiogenesis and cartilage metabolism. Western blotting and TUNEL staining were used to examine epiphyseal cartilage chondrocyte apoptosis. Primary chondrocytes were isolated from the femoral heads of healthy mice for in vitro studies. The effects of GCs on chondrocyte apoptosis and metabolism were determined by flow cytometry and Western blotting.

RESULTS

The epiphyseal cartilage ossification had started at 4 weeks posttreatment in a portion of mice; the ossification presented as a sequential process in the model group, while the epiphyseal cartilage maintained an unossified state in the control group. Vascular invasion into the epiphyseal cartilage of the model mice was observed at 4 weeks posttreatment. GCs induced chondrocyte apoptosis and altered chondrocyte metabolism in the epiphyseal cartilage.

CONCLUSIONS

The epiphyseal cartilage ossification accelerated in the femoral heads of female C57BL/6 mice after excessive GC treatment. Increased chondrocyte apoptosis, altered chondrocyte metabolism, as well as increased vascular invasion, are the potential factors influencing epiphyseal cartilage ossification.

[Progress of developmental mechanism of subtype H vessels in osteonecrosis of the femoral head]

Objective

To review the research progress of subtype H vessels in the occurrence and development of osteonecrosis of the femoral head (ONFH).

Methods

The relevant domestic and foreign literature was extensively reviewed. The histological features, biological mechanism of subtype H vessels involved in promoting of osteogenesis, and the role and application of the subtype H vessels in ONFH were summarized.

Results

The subtype H vessel is a newly discovered bone vessel, mainly distributed in metaphysis and subperiosteum, highly expressing endomucin and CD31. The subtype H vessel has a dense arrangement of Runx2 ⁺ early osteoprogenitors, collagen type Ⅰα ⁺ osteoblast cells, and Osterix ⁺ osteoprogenitors that have the ability to induce osteogenesis and angiogenesis. Factors such as platelet-derived growth factor BB, slit guidance ligand 3, hypoxia inducible factor 1α, Notch signaling pathway, and vascular endothelial growth factor are involved in the mechanism of subtype H vessels in promoting osteogenesis.

Conclusion

Subtype H vessels play an important role in the regulation of angiogenesis and osteogenesis during bone tissue repair and reconstruction. The discovery of subtype H vessels provides new insights into the molecular and cellular mechanisms of osteogenesis and angiogenesis coupling. In the future, new techniques targeting the regulation of subtype H blood vessels may become a promising method for the treatment of ONFH.

The psychobiological links between chronic stress-related diseases, periodontal/peri-implant diseases, and wound healing

Chronic stress is a relevant disease to periodontal practice, encompassing 25%-28% of the US population (American Psychological Association 2015). While it is well established that chronic psychologic stress can have significant deleterious systemic effects, only in recent decades have we begun to explore the biochemical, microbial, and physiologic impacts of chronic stress diseases on oral tissues. Currently, chronic stress is classified as a "risk indicator" for periodontal disease. However, as the evidence in this field matures with additional clinically controlled trials, more homogeneous data collection methods, and a better grasp of the biologic underpinnings of stress-mediated dysbiosis, emerging evidence suggests that chronic stress and related diseases (depression, anxiety) may be significant contributing factors in periodontal/peri-implant disease progression and inconsistent wound healing following periodontal-related therapeutics. Ideal solutions for these patients include classification of the disease process and de-escalation of chronic stress conditions through coping strategies. This paper also summarizes periodontal/implant-related therapeutic approaches to ensure predictable results for this specific patient subpopulation.

Porous copper- and lithium-doped nano-hydroxyapatite composite scaffold promotes angiogenesis and bone regeneration in the repair of glucocorticoids-induced osteonecrosis of the femoral head

Glucocorticoids-induced osteonecrosis of the femoral head (GIONFH) is a common refractory disease. In the present study, we aimed to synthesize the nano-hydroxyapatite-copper-lithium (Cu-Li-nHA) composite porous scaffold to promote osteogenesis and angiogenesis functions to repair GIONFH by regulating the Wnt/β-catenin and HIF-1α/VEGF pathways. The physicochemical property of the scaffold was characterized and their osteogenic and angiogenic effects were tested through a serial of experimentsin vitroandin vivo. Results showed that 0.25% Cu-Li-nHA scaffolds possessed the highest mechanical and biocompatibilityin vitro. Then the 0.25% Cu-Li-nHA scaffolds significantly enhanced the new bone formation on defects in GIONFH rabbitsin vivo. Moreover, the scaffold could increase the expression of osteogenic and angiogenic factors along with the activation of factors in Wnt/β-catenin and HIF-1α/VEGF pathwaysin vitroandin vivo. In conclusion, the 0.25% Cu-Li-nHA scaffold could improve the osteogenesis and angiogenesis by upregulating the Wnt/β-catenin and HIF-1α/VEGF pathways which benefited to repair the GIONFH in rabbit models.

Comprehensive analysis of pivotal biomarkers, immune cell infiltration and therapeutic drugs for steroid-induced osteonecrosis of the femoral head

Steroid-induced osteonecrosis of the femoral head (SONFH) is a progressive disease that leads to an increased disability rate. This study aimed to ascertain biomarkers, infiltrating immune cells, and therapeutic drugs for SONFH. The gene expression profile of the GSE123568 dataset was downloaded from the Gene Expression Omnibus (GEO) database. The differentially expressed genes (DEGs) were identified using the NetworkAnalyst platform. Functional enrichment, protein-protein interaction network (PPI), and module analyses were performed using Metascape tools. An immune cell abundance identifier was used to explore immune cell infiltration. Furthermore, hub genes were identified based on maximal clique centrality (MCC) evaluation using cytoHubba application and confirmed by qRT-PCR using clinical samples. Finally, the L1000 platform was used to determine potential drugs for SONFH treatment. The SONFH mouse model was used to determine the therapeutic effects of aspirin. In total, 429 DEGs were identified in SONFH samples. Functional enrichment analysis showed that these DEGs were enriched in myeloid leukocyte activation and osteoclast differentiation processes. A set of nine immune cell types was confirmed to be markedly different between the SONFH and control samples. All 10 hub genes were significantly highly expressed in the serum of SONFH patients, as shown by qRT-PCR. Finally, the therapeutic effect of aspirin on SONFH was examined in animal experiments. Taken together, our data revealed the hub genes and infiltrating immune cells in SONFH, and we also screened potential drugs for use in SONFH treatment.

The endothelium-bone axis in development, homeostasis and bone and joint disease

Blood vessels form a versatile transport network that is best known for its critical roles in processes such as tissue oxygenation, metabolism and immune surveillance. The vasculature also provides local, often organ-specific, molecular signals that control the behaviour of other cell types in their vicinity during development, homeostasis and regeneration, and also in disease processes. In the skeletal system, the local vasculature is actively involved in both bone formation and resorption. In addition, blood vessels participate in inflammatory processes and contribute to the pathogenesis of diseases that affect the joints, such as rheumatoid arthritis and osteoarthritis. This Review summarizes the current understanding of the architecture, angiogenic growth and functional properties of the bone vasculature. The effects of ageing and pathological conditions, including arthritis and osteoporosis, are also discussed.

Exosomes from miRNA-378-modified adipose-derived stem cells prevent glucocorticoid-induced osteonecrosis of the femoral head by enhancing angiogenesis and osteogenesis via targeting miR-378 negatively regulated suppressor of fused (Sufu)

Background

Local ischemia and defective osteogenesis are implicated in the progression of glucocorticoid (GC)-induced osteonecrosis of the femoral head (ONFH). Recent studies have revealed that exosomes released from adipose-derived stem cells (ASCs) play important roles in ONFH therapy. The present study aimed to investigate whether exosomes derived from miR-378-overexpressing ASCs (miR-378-ASCs-Exos) could promote angiogenesis and osteogenesis in GC-induced ONFH.

Methods

In vitro, we investigated the osteogenic potential of miR-378-ASCs-Exos on bone marrow stromal cells (BMSCs) by alkaline phosphatase staining and western blotting. The angiogenic effects of miR-378-ASCs-Exos on human umbilical vein endothelial cells (HUVECs) were examined by evaluating their proliferation, migration, and tube-forming analyses. We identified the underlying mechanisms of miR-378 in osteogenic and angiogenic regulation. In addition, an ONFH rat model was established to explore the effects of miR-378-ASCs-Exos through histological and immunohistochemical staining and micro-CT in vivo.

Results

Administration of miR-378-ASCs-Exos improved the osteogenic and angiogenic potentials of BMSCs and HUVECs. miR-378 negatively regulated the suppressor of fused (Sufu) and activated Sonic Hedgehog (Shh) signaling pathway, and recombinant Sufu protein reduced the effects triggered by miR-378-ASCs-Exos. In vivo experiments indicated that miR-378-ASCs-Exos markedly accelerated bone regeneration and angiogenesis, which inhibited the progression of ONFH.

Conclusion

Our study indicated that miR-378-ASCs-Exos enhances osteogenesis and angiogenesis by targeting Sufu to upregulate the Shh signaling pathway, thereby attenuating GC-induced ONFH development.

Management of glucocorticoid-induced osteoporosis

Long-term glucocorticoid (GC) therapy is frequently indicated to treat autoimmune and chronic inflammatory diseases in daily clinical practice. Two of the most devastating untoward effects are bone loss and fractures. Doses as low as 2.5 mg of prednisone for more than 3 months can impair bone integrity. Population at risk is defined based on the dose and duration of GC therapy and should be stratified according to FRAX (Fracture Risk Assessment Tool), major osteoporotic fracture, prior fractures, and bone mineral density values (BMD). General measures include to prescribe the lowest dose of GC to control the underlying disease for the shortest possible time, maintain adequate vitamin D levels and calcium intake, maintain mobility, and prescribe a bone acting agent in patients at high risk of fracture. These agents include oral and intravenous bisphosphonates, denosumab, and teriparatide.

Osteoclasts protect bone blood vessels against senescence through the angiogenin/plexin-B2 axis

Synthetic glucocorticoids (GCs), one of the most effective treatments for chronic inflammatory and autoimmune conditions in children, have adverse effects on the growing skeleton. GCs inhibit angiogenesis in growing bone, but the underlying mechanisms remain unclear. Here, we show that GC treatment in young mice induces vascular endothelial cell senescence in metaphysis of long bone, and that inhibition of endothelial cell senescence improves GC-impaired bone angiogenesis with coupled osteogenesis. We identify angiogenin (ANG), a ribonuclease with pro-angiogenic activity, secreted by osteoclasts as a key factor for protecting the neighboring vascular cells against senescence. ANG maintains the proliferative activity of endothelial cells through plexin-B2 (PLXNB2)-mediated transcription of ribosomal RNA (rRNA). GC treatment inhibits ANG production by suppressing osteoclast formation in metaphysis, resulting in impaired endothelial cell rRNA transcription and subsequent cellular senescence. These findings reveal the role of metaphyseal blood vessel senescence in mediating the action of GCs on growing skeleton and establish the ANG/PLXNB2 axis as a molecular basis for the osteoclast-vascular interplay in skeletal angiogenesis.

[Experimental study on improvement of osteonecrosis of femoral head with exosomes derived from miR-27a-overexpressing vascular endothelial cells]

OBJECTIVE

To investigate whether exosomes derived from miR-27a-overexpressing human umbilical vein endothelial cells (HUVECs)-exo (miR-27a) can promote bone regeneration and improve glucocorticoids (GC) induced osteonecrosis of femoral head (ONFH) (GC-ONFH).

METHODS

The exo (miR-27a) were intended to be constructed and identified by transmission electron microscopy, nanoparticle tracking analysis, Western blot, and real-time fluorescent quantitative PCR (qRT-PCR). qRT-PCR was used to evaluate the effect of exo (miR-27a) in delivering miR-27a to osteoblasts (MC3T3-E1 cells). Alkaline phosphatase staining, alizarin red staining, and qRT-PCR were used to evaluate its effect on MC3T3-E1 cells osteogenesis. Dual-luciferase reporter (DLRTM) assay was used to verify whether miR-27a targeting Dickkopf WNT signaling pathway inhibitor 2 (DKK2) was a potential mechanism, and the mechanism was further verified by qRT-PCR, Western blot, and alizarin red staining in MC3T3-E1 cells. Finally, the protective effect of exo (miR-27a) on ONFH was verified by the GC-ONFH model in Sprague Dawley (SD) rats.

RESULTS

Transmission electron microscopy, nanoparticle tracking analysis, Western blot, and qRT-PCR detection showed that exo (miR-27a) was successfully constructed. exo (miR-27a) could effectively deliver miR-27a to MC3T3-E1 cells and enhance their osteogenic capacity. The detection of DLRTM showed that miR-27a promoted bone formation by directly targeting DDK2. Micro-CT and HE staining results of animal experiments showed that tail vein injection of exo (miR-27a) improved the osteonecrosis of SD rat GC-ONFH model.

CONCLUSION

exo (miR-27a) can promote bone regeneration and protect against GC-ONFH to some extent.

Hypoxia Enhanced Bone Regeneration Through the HIF-1α/β-Catenin Pathway in Femoral Head Osteonecrosis

BACKGROUND

Osteonecrosis of the femoral head (ONFH) is a common disease. Transplantation of bone marrow stem cells (BMSCs) is a promising method to treat ONFH but is impeded by the low survival rate and deficiency of cell bioactivity.

METHODS

We performed hypoxic preprocessing to treat BMSCs and assessed cell viability, apoptosis, differentiation, and growth factor expression in vitro. Subsequently, we constructed the ONFH model and delivered hypoxia-pretreated BMSCs to the rabbit femoral head after core decompression surgery, evaluating its effects on bone regeneration and ONFH repair. Six weeks later, micro-computed tomography (CT) and histopathology were performed to evaluate ONFH repair.

RESULTS

Our findings demonstrated that hypoxic preprocessing promoted the viability of BMSCs, increased the expression of hypoxia-inducible factor-1 alpha (HIF-1α), vascular endothelial growth factor (VEGF), alkaline phosphatase (ALP), calcium deposition, and enhanced the formation of vessels-shaped structures. In an in vivo study, micro-CT observations demonstrated that the bone volume was increased in the hypoxia BMSCs group. Histological examination revealed reduced cellular apoptosis, lower empty lacunae rate, enhanced bone formation, and stronger trabecular bone in the hypoxia BMSCs group when compared with those transplanted with normoxia treated BMSCs. Additionally, immunological assessment of the hypoxia BMSCs group demonstrated increased expression of HIF-1α and β-catenin, as well as increased VEGF, ALP, osteocalcin (OCN), and collagen type I (Col-1).

CONCLUSIONS

Collectively, our findings indicated that hypoxia stimulated angiogenesis and bone regeneration via the HIF-1/β-catenin pathway in BMSCs and that the delivery of hypoxia-pretreated BMSCs contributed to the treatment of early ONFH.

CircCDR1as Suppresses Bone Microvascular Endothelial Cell Activity and Angiogenesis Through Targeting miR-135b/ FIH-1 Axis

Objective

The current study investigated the role of CircCDR1as on angiogenesis of bone microvascular endothelial cells (BMECs) isolated from non‐traumatic ONFH.

Methods

Forty corticosteroid‐induced ONFH patients received THA were enrolled in our study. Expressions of CircCDR1as, miR‐135b, and FIH‐1 were detected by qRT‐PCR in affected necrosis tissue and non‐affected normal tissue. Bone microvascular endothelial cells (BMEC) were isolated from six patients and treated with 0.1 mg/mL hydrocortisone to establish a GC‐damaged model of BMECs. Circ CDR1as plasmid and miR‐135b mimic were transfected into BMECs. BMEC proliferation was assessed using MTT assays. The migration ability of cells was detected by scratch‐wound assays. Matrigel assay was performed to detect angiogenesis in vitro. Western blot assay was used to detect HIF‐1α, VEGF, and FIH‐1 expressions. FISH, RNA pull down, RIP, and luciferase assay were carried out to determine the interaction of CircCDR1as, miR‐135b, and FIH‐1.

Results

CircCDR1as was upregulated(2.02 ± 0.30 vs. 1.00 ± 0.10,P < 0.001) whereas miR‐135b was downregulated (0.55 ± 0.12 vs. 1.00 ± 0.10,P < 0.001) in affected tissues than in non‐affected tissues. Expression of CircCDR1as and FIH‐1 were negatively associated with miR‐135b in affected tissues (CircCDR1as with miR‐135b: r = −0.506, P < 0.001; FIH‐1 with miR‐135b r = −0.510, P < 0.001). Total blood tubule density was increased when CircCDR1as was silenced compared with NC (P < 0.01 vs. NC). The number of migrated BMECs were significantly increased in CircCDR1as silencing group compared with NC group (P < 0.05 vs. NC). In addition, CircCDR1as plasmids transfection increased the protein expressions of FIH‐1 (P < 0.05 vs. NC) and reduced the HIF‐1α as well as VEGF expression compared with NC group (P < 0.05 vs. NC). FISH, RNA pull down, RIP, and luciferase assay identified that FIH‐1 was a target of miR‐135b and could be modulated by CircCDR1as.

Conclusion

CircCDR1as decreases angiogenesis and proliferation of BMECs by sponging miR‐135b and upregulate FIH‐1.

Preclinical studies on pleiotropic functions of erythropoietin on bone healing

Erythropoietin (ЕPО) is a glycoprotein hormone, mainly known for its haemopoietic function. For orthopaedics, its pleiotropic effects – osteogenic and angiogenic potential, are of primary interest. The exact mechanism of EPO action is still unclear. The effects of EPO on bone healing were investigated through experiments with rats, mice, rabbits and pigs. Each of used models for experimental bone defects (calvarial models, long bone segmental defects, posterolateral spinal fusion and corticosteroid-induced femoral head osteonecrosis) has specific advantages and flaws. Obtaining specific and correct results is largely dependent on the used model. The brief evaluation of models could serve for standardisation of preclinical studies on bone regeneration.

Association of ABCB1 and CYP450 Gene Polymorphisms and their DNA Methylation Status with Steroid-Induced Osteonecrosis of the Femoral Head in the Chinese Population

Objective: Osteonecrosis of the femoral head (ONFH) is a severe pathological state with multiple etiologies. Steroid hormone metabolism-related genes play an important role in ONFH. The aim of this study was to investigate the relationships between polymorphisms of the drug-metabolizing enzyme gene, cytochrome P450 (CYP450), and the drug transporter gene, ATP-binding cassette subfamily B member 1 (ABCB1), as well as their DNA methylation status with the pathogenesis of steroid-induced ONFH. Methods: In this case-control study, we evaluated five single nucleotide polymorphisms (SNPs) in two genes in a Han Chinese population, including 79 patients with steroid-induced ONFH and 114 persons who took steroids but did not develop steroid-induced ONFH. SNPs were genotyped by the improved multiplex ligation detection reaction. MethylTarget technology was used to ascertain the methylation status at two CpG islands in the ABCB1 gene for statistical analysis. Finally, interactions between the SNPs and the CpG site's methylation levels were statistically analyzed by methylation quantitative trait locus. Results: We found that the T allele of the CYP450 rs2242480 locus was associated with steroid-induced ONFH risk reduction (odds ratio [OR] = 0.598, 95% confidence interval [CI]: 0.360-0.992, p = 0.046). In the genetic model analysis, the T allele of the rs2032582 locus in the ABCB1 gene was associated with a reduced risk of steroid-induced ONFH under the dominant model (OR = 0.465, 95% CI: 0.223-0.972, p = 0.042). The CpG sites with significant differences (p < 0.05) in methylation levels between the cases and controls were ABCB1_1_192…ABCB1_2_43. A total of 14 pairs of linear regression tests between SNPs and methylation sites demonstrated statistical significance (p < 0.05). Conclusions: This study provides evidence for two steroid-induced ONFH susceptibility genes (ABCB1, CYP450) in the Han Chinese population.

Blood Vessels and Vascular Niches in Bone Development and Physiological Remodeling

Recent advances in our understanding of blood vessels and vascular niches in bone convey their critical importance in regulating bone development and physiology. The contribution of blood vessels in bone functions and remodeling has recently gained enormous interest because of their therapeutic potential. The mammalian skeletal system performs multiple functions in the body to regulate growth, homeostasis and metabolism. Blood vessels provide support to various cell types in bone and maintain functional niches in the bone marrow microenvironment. Heterogeneity within blood vessels and niches indicate the importance of specialized vascular niches in regulating skeletal functions. In this review, we discuss physiology of bone vasculature and their specialized niches for hematopoietic stem cells and mesenchymal progenitor cells. We provide clinical and experimental information available on blood vessels during physiological bone remodeling.

Effects of hypoxia environment on osteonecrosis of the femoral head in Sprague-Dawley rats

INTRODUCTION

Osteonecrosis of the femoral head (ONFH) is a disease in which the blood supply of the femoral head is interrupted or damaged, resulting in joint dysfunction. Hypoxic environments increase the expression of EPO, VEGF, and HIF causes vascular proliferation and increases the blood supply. It also causes the organism to be in a state of hypercoagulability and increases thrombosis. Therefore, the purpose of this study was to explore the occurrence of ONFH after the use of glucocorticoids (GCs) under conditions of hypoxia tolerance for a long time.

MATERIALS AND METHODS

Sprague-Dawley rats were fed in a hypobaric hypoxic chamber at an altitude of 4000 m, the whole blood viscosity, and plasma viscosity were determined to analyze the blood flow and hemagglutination. Western blotting, polymerase chain reaction, and immunohistochemistry were used to detect EPO, VEGF, CD31, and osteogenesis related proteins. Femoral head angiography was used to examine the local blood supply and micro-CT scanning was used to detect the structure of the bone trabecula.

RESULTS

Under hypoxic environments, the expression of EPO and VEGF increased, which increased the local blood supply of the femoral head, but due to more severe thrombosis, the local blood supply of the femoral head decreased.

CONCLUSIONS

Hypoxic environments can aggravate ONFH in SD rats; this aggravation may be related to the hypercoagulable state of the blood. We suggest that long-term hypoxia should be regarded as one of the risk factors of ONFH and we need to conduct a more extensive epidemiological investigation on the occurrence of ONFH in hypoxic populations.

Combined Pharmacotherapy with Alendronate and Desferoxamine Regulate the Bone Resorption and Bone Regeneration for Preventing Glucocorticoids-Induced Osteonecrosis of the Femoral Head

Background

Osteonecrosis of the femoral head (ONFH) is a challenge for surgeons and is still without effective treatment method. This study is aimed at evaluating the combined pharmacotherapy with alendronate and desferoxamine for preventing glucocorticoid-induced osteonecrosis of the femoral head (GIOFH) and evaluating the efficacy of the combined medicine in regulating the bone resorption and bone regeneration.

Materials and Methods

Thirty-six rats were randomly assigned to three groups: group A received alendronate and desferoxamine (n = 12), group B received alendronate only (n = 12), and group C acted as the control group received placebo (n = 12). All rats induced the GIOFH using methylprednisolone combined with lipopolysaccharide. Eight weeks later, all rats were killed and their tissues were subjected to radiographic and histological analyses.

Results

According to the results, alendronate administration improved the trabecular thickness and separation in micro-CT analysis but had no significant evidence in increasing the bone area and decreasing the ratio of osteocyte lacunae in histological analysis when compared with the control group. Meanwhile, the alendronate group had more OCs, but less OCN and VEGF levels along with decreased p-AKT, HIF-1α, RANKL, and NFATc1 expressions than the control group. For comparison, alendronate combined with DFO further improved the bone volume, trabecular number, trabecular separation, and trabecular thickness with lower ratio of osteocyte lacunae and OC number, higher expression of OCN and VEGF and upregulated signal factors of HIF-1α and β-catenin, and decreased RANKL and NFATc1.

Conclusion

Combined pharmacotherapy with alendronate and desferoxamine provide significant effects in regulating the bone resorption and bone regeneration for preventing GIOFN.

The Protective Effect of Luteolin in Glucocorticoid-Induced Osteonecrosis of the Femoral Head

Glucocorticoid-induced osteonecrosis of the femoral head (GIONFH) is a frequently occurring type of nontraumatic osteonecrosis. A failure of the timely treatment can eventually result in the collapse of the subchondral bone structure. Luteolin (Lut), a compound extracted from Rhizoma Drynariae, is reported to possess multiple pharmacological properties including anticancer, antioxidant, antiapoptosis, and antiinflammatory properties. However, whether Lut has a protective effect on the development of GIONFH remains unclear. In this study, we evaluated the effect of Lut on Dexamethasone (Dex)-induced STAT1/caspase3 pathway in vitro and evaluated GIONFH model in vivo. In vitro, Lut inhibited the upregulation of Dex-induced phospho-STAT1, cleaved caspase9, and cleaved caspase3. In addition, Lut inhibited Dex-induced expression of Bax and cytochrome c and increased the expression of B cell lymphoma-2(Bcl-2). In vivo, Lut decreased the proportion of empty lacunae in rats with GIONFH. Taken together, these findings indicate that Lut may have therapeutic potential in the treatment of GIONFH. Further, this effect might be achieved by suppressing mitochondrial apoptosis of osteoblasts via inhibition of STAT1 activity.

Pinocembrin alleviates glucocorticoid-induced apoptosis by activating autophagy via suppressing the PI3K/Akt/mTOR pathway in osteocytes

Glucocorticoids are widely used in clinical practice, but are associated with potentially severe side effects like glucocorticoid-induced osteoporosis (GIOP) and glucocorticoid-associated osteonecrosis of the femoral head (GA-ONFH). Glucocorticoid-induced osteocyte apoptosis plays critical roles in the pathological processes of both GIOP and GA-ONFH. Pinocembrin is a natural flavonoid that may exert protective effects on osteocytes. The present study investigated the effects of pinocembrin on glucocorticoid-induced apoptosis of murine long bone osteocyte Y4 (MLO-Y4) cells and sought to elucidate the underlying molecular mechanism. We found that pinocembrin attenuated glucocorticoid-induced cell viability injury and apoptosis of MLO-Y4 cells. Moreover, pinocembrin increased Beclin-1 and LC3B-II level, but decreased p62 expression, suggesting that pinocembrin activates autophagy in glucocorticoid-treated MLO-Y4 cells. The protective effects of pinocembrin on glucocorticoid-induced apoptosis of MLO-Y4 cells were mimicked by a known stimulator of autophagy but prevented by a known inhibitor of autophagy. Pinocembrin also suppressed the PI3K/Akt/mTOR signaling pathway, which regulates cell autophagy, in glucocorticoid-treated MLO-Y4 cells. In conclusion, the results indicate that pinocembrin alleviates glucocorticoid-induced osteocyte apoptosis by activating autophagy via suppressing the PI3K/Akt/mTOR pathway. Pinocembrin may represent a potential natural agent for preventing and treating GIOP and GA-ONFH.

Nontraumatic Osteonecrosis of the Femoral Head: Where Do We Stand Today?: A 5-Year Update

➢. Clinicians should exercise a high level of suspicion in at-risk patients (those who use corticosteroids, consume excessive alcohol, have sickle cell disease, etc.) in order to diagnose osteonecrosis of the femoral head in its earliest stage. ➢. Nonoperative treatment modalities have generally been ineffective at halting progression. Thus, nonoperative treatment is not appropriate in early stages when one is attempting to preserve the native joint, except potentially on rare occasions for small-sized, medially located lesions, which may heal without surgery. ➢. Joint-preserving procedures should be attempted in early-stage lesions to save the femoral head. ➢. Cell-based augmentation of joint-preserving procedures continues to show promising results, and thus should be considered as an ancillary treatment method that may improve clinical outcomes. ➢. The outcomes of total hip arthroplasty in the setting of osteonecrosis are excellent, with results similar to those in patients who have an underlying diagnosis of osteoarthritis.

Glucocorticoid-induced osteoporosis update

PURPOSE OF REVIEW

Steroid-induced osteoporosis or glucocorticoid-induced osteoporosis (GIOP) is a common form of secondary osteoporosis and is a cause of increased morbidity and mortality. The pathogenesis of GIOP includes decreased bone formation and increased bone resorption. Clinicians can rely on several effective medications for the treatment and prevention of GIOP, including antiresorptive drugs (i.e. bisphosphonates) and bone anabolic drugs (i.e. teriparatide).

RECENT FINDINGS

Recent studies have further highlighted that GIOP is a major public health concern and have provided new insights on the pathogenesis of GIOP, in particular, the dose-dependent effects of glucocorticoids on bone. New evidence on the real-world effectiveness of established GIOP therapies have been recently published as well as the results of the 24-months denosumab randomized controlled trial in GIOP.

SUMMARY

GIOP and fragility fractures are important adverse events related to the long-term use of glucocorticoids. Recent studies have provided additional data on the epidemiology and pathogenesis of GIOP and on the efficacy and effectiveness of GIOP therapies.

Steroid-induced osteonecrosis of the femoral head reveals enhanced reactive oxygen species and hyperactive osteoclasts

Steroid-induced osteonecrosis of the femoral head (ONFH) is a progressive bone disorder which typically results in femoral head collapse and hip joint dysfunction. It is well-accepted that abnormal osteoclast activity contributes to loss of bone structural integrity and subchondral fracture in ONFH. However, the pathophysiologic mechanisms underlying the recruitment and hyperactivation of osteoclasts in ONFH remain incompletely understood. We assessed the changes of reactive oxygen species (ROS) level and subsequent osteoclast alterations in steroid-induced osteonecrotic femoral heads from both patients and rat ONFH models. When compared with healthy neighboring bone, the necrotic region of human femoral head was characterized by robust up-regulated expression of osteoclast-related proteins [cathepsin K and tartrate-resistant acid phosphatase(TRAP)] but pronounced down-regulation of antioxidant enzymes (catalase, γ-glutamylcysteine synthetase [γ-GCSc], and superoxide dismutase 1 [SOD1]). In addition, the ratio of TNFSF11 (encoding RANKL)/TNFRSF11B (encoding OPG) was increased within the necrotic bone. Consistently, in rat ONFH models induced by methylprednisolone (MPSL) and imiquimod (IMI), significant bone loss in the femoral head was observed, attributable to increased numbers of TRAP positive osteoclasts. Furthermore, the decreased expression of antioxidant enzymes observed by immunoblotting was accompanied by increased ex-vivo ROS fluorescence signals of dihydroethidium (DHE) in rat ONFH models. Therefore, this study lends support to the rationale that antioxidant agents may be a promising therapeutic avenue to prevent or mitigate the progression of steroid-induced ONFH by inhibiting ROS level and hyperactive osteoclasts.

Silencing MicroRNA-137-3p, which Targets RUNX2 and CXCL12 Prevents Steroid-induced Osteonecrosis of the Femoral Head by Facilitating Osteogenesis and Angiogenesis

The main pathogenesis of steroid-induced osteonecrosis of the femoral head (SONFH) includes decreased osteogenic capacity of bone marrow-derived mesenchymal stem cells (BMSCs) and damaged blood supply to the femoral head. MicroRNAs (miRNAs) have been shown to play prominent roles in SONFH development. However, there is no report that a specific miRNA targeting two genes in two different pathogenic pathways has been applied to this disease. The present study investigated the effects of transplantation of miR-137-3p-silenced BMSCs on the prevention and early treatment of SONFH. First, western blotting and dual luciferase assays were employed to verify that miR-137-3p directly targets Runx2 and CXCL12. Then, silencing of miR-137-3p was found to facilitate osteogenic differentiation of BMSCs, which was confirmed by alkaline phosphatase (ALP) staining, alizarin red staining and qRT-PCR. Silencing of miR-137-3p also promoted angiogenesis by human umbilical vein endothelial cells (HUVECs) in the presence or absence of glucocorticoids. Thereafter, overexpression of Runx2 and CXCL12 without the 3′ untranslated region (3′UTR) partially rescued the effects of miR-137-3p on osteogenesis and angiogenesis, respectively. This finding further supported the hypothesis that miR-137-3p exerts its functions partly by regulating the genes, Runx2 and CXCL12. We also demonstrated that SONFH was partially prevented by transplantation of miR-137-3p-silenced BMSCs into a rat model. Micro-CT and histology showed that the transplantation of miR-137-3p-silenced BMSCs significantly improved bone regeneration. Additionally, the results of enzyme-linked immunosorbent assays (ELISA) and flow cytometry suggested that stromal cell-derived factor-1α (SDF-1α) and endothelial progenitor cells (EPCs) participated in the process of vascular repair. Taken together, these findings show that silencing of miR-137-3p directly targets the genes, Runx2 and CXCL12, which can play critical roles in SONFH repair by facilitating osteogenic differentiation and mobilizing EPCs.

Type H blood vessels in bone modeling and remodeling

In the mammalian skeletal system, osteogenesis and angiogenesis are intimately linked during bone growth and regeneration in bone modeling and during bone homeostasis in bone remodeling. Recent studies have expanded our knowledge about the molecular and cellular mechanisms responsible for coupling angiogenesis and bone formation. Type H vessels, termed such because of high expression of Endomucin (Emcn) and CD31, have recently been identified and have the ability to induce bone formation. Factors including platelet-derived growth factor type BB (PDGF-BB), slit guidance ligand 3 (SLIT3), hypoxia-inducible factor 1-alpha (HIF-1α), Notch, and vascular endothelial growth factor (VEGF) are involved in the coupling of angiogenesis and osteogenesis. This review summarizes the current understanding of signaling pathways that regulate type H vessels and how type H vessels modulate osteogenesis. Further studies dissecting the regulation and function of type H vessels will provide new insights into the role of bone vasculature in the metabolism of the skeleton. We also discuss considerations for therapeutic approaches targeting type H vessels to promote fracture healing, prevent pathological bone loss, osteonecrosis, osteoarthritis, and bone metastases.