Vascular endothelial growth factor (VEGF) directly enhances osteoclastic bone resorption and survival of mature osteoclasts

Vascular endothelial growth factor I/D variant and postmenopausal osteoporosis risk in the Turkish population

INTRODUCTION

Postmenopausal osteoporosis (PMOP) is a common metabolic bone disorder manifested by low bone mineral density and increased fracture risks in postmenopausal women. Vascular endothelial growth factor (VEGF) has been shown to play an important role in bone formation. In this study, we investigated the potential association between the VEGF insertion/deletion (I/D) variant (rs35569394) and PMOP in a cohort of postmenopausal Turkish women.

METHODS

This study included 300 women, including 150 PMOP patients and 150 healthy postmenopausal women. A T score was used in the diagnosis of OP. DNA was extracted from all subjects. The VEGF I/D polymorphism was analyzed by the PCR method. The Hardy-Weinberg equilibrium (HWE) test and odds ratio (OR) were analyzed, considering CI 95% and p ≤ 0.05.

RESULTS

The mean age of patients aged between 40 and 74 was 60.32 ± 8.65. The frequency of the I/I, I/D, and D/D genotypes was 7.34% versus 6.66%; 67.33% versus 65.34%; and 25.33% versus 28%, in patients and the control group, respectively. The allele frequencies were I: 41% (patients) and 39.4% (controls); D: 59% (patients) and 60.66% (controls). There was no statistically significant difference in the VEGF - 2549 I/D allele and genotype distribution between patients with PMOP and control subjects (p = 0.349, p = 0.864, respectively).

CONCLUSION

Our results showed that the VEGF I/D variant was not a significant factor in the development of PMOP in a Turkish population sample. These findings need confirmation in other ethnic populations.

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.

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.

In Vitro Cytotoxicity of Antiresorptive and Antiangiogenic Compounds on Oral Tissues Contributing to MRONJ: Systematic Review

BACKGROUND

Invasive dental treatment in patients exposed to antiresorptive and antiangiogenic drugs can cause medication-related osteonecrosis of the jaw (MRONJ). Currently, the exact pathogenesis of this disease is unclear.

METHODS

In March 2022, Medline (Ovid), Embase (Ovid), Scopus, and Web of Science were screened to identify eligible in vitro studies investigating the effects of antiresorptive and antiangiogenic compounds on orally derived cells.

RESULTS

Fifty-nine articles met the inclusion criteria. Bisphosphonates were used in 57 studies, denosumab in two, and sunitinib and bevacizumab in one. Zoledronate was the most commonly used nitrogen-containing bisphosphonate. The only non-nitrogen-containing bisphosphonate studied was clodronate. The most frequently tested tissues were gingival fibroblasts, oral keratinocytes, and alveolar osteoblasts. These drugs caused a decrease in cell proliferation, viability, and migration.

CONCLUSIONS

Antiresorptive and antiangiogenic drugs displayed cytotoxic effects in a dose and time-dependent manner. Additional research is required to further elucidate the pathways of MRONJ.

Zoledronate/Anti-VEGF Neutralizing Antibody Combination Administration Increases Osteal Macrophages in a Murine Model of MRONJ Stage 0-like Lesions

The pathophysiology, pathogenesis, histopathology, and immunopathology of medication-related osteonecrosis of the jaw (MRONJ) Stage 0 remain unclear, although 50% of MRONJ Stage 0 cases could progress to higher stages. The aim of this study was to investigate the effects of zoledronate (Zol) and anti-vascular endothelial cell growth factor A (VEGFA) neutralizing antibody (Vab) administration on polarization shifting of macrophage subsets in tooth extraction sockets by creating a murine model of MRONJ Stage 0-like lesions. Eight-week-old, female C57BL/6J mice were randomly divided into 4 groups: Zol, Vab, Zol/Vab combination, and vehicle control (VC). Subcutaneous Zol and intraperitoneal Vab administration were performed for 5 weeks with extraction of both maxillary first molars 3 weeks after drug administration. Euthanasia was conducted 2 weeks after tooth extraction. Maxillae, tibiae, femora, tongues, and sera were collected. Structural, histological, immunohistochemical, and biochemical analyses were comprehensively performed. Tooth extraction sites appeared to be completely healed in all groups. However, osseous healing and soft tissue healing of tooth extraction sites were quite different. The Zol/Vab combination significantly induced abnormal epithelial healing, and delayed connective tissue healing due to decreased rete ridge length and thickness of the stratum granulosum and due to decreased collagen production, respectively. Moreover, Zol/Vab significantly increased necrotic bone area with increased numbers of empty lacunae compared with Vab and VC. Most interestingly, Zol/Vab significantly increased the number of CD169⁺ osteal macrophages (osteomacs) in the bone marrow and decreased F4/80+ macrophages, with a slightly increased ratio of F4/80⁺CD38⁺ M1 macrophages compared to VC. These findings are the first to provide new evidence of the involvement of osteal macrophages in the immunopathology of MRONJ Stage 0-like lesions.

Circulating Extracellular Vesicles Express Receptor Activator of Nuclear Factor κB Ligand and Other Molecules Informative of the Bone Metabolic Status of Mouse Models of Experimentally Induced Osteoporosis

Extracellular vesicles (EVs) are potent means of cell-to-cell communication. They are released in biological fluids, including blood, urine, and saliva, and can be exploited to identify new biomarkers of diseases. We hypothesized that EVs contain molecular cargos involved in bone metabolism, possibly mirroring biological differences between postmenopausal and disuse osteoporosis. We tested this hypothesis in primary murine osteoblasts subjected to steroid depletion or to unloading, and in the serum of animal models of osteoporosis induced by ovariectomy or hindlimb tail suspension. EVs were isolated by ultracentrifugation and analysed by transmission electron microscopy, cytofluorimetry, immunoblotting and RT-PCR. Large-scale analyses were performed by Real-Time arrays and Proteome Profiler™ Antibody arrays. Finally, precise titration of analytes was carried out by ELISA assay. In vitro, we confirmed an increased release of EVs enriched in surface RANKL by primary mouse osteoblasts subjected to steroid depletion or simulated microgravity compared to controls. In vivo, circulating EVs isolated from the sera of control female mice expressed RANKL along with other genes associated with bone metabolism. Serum EVs from ovariectomized or hindlimb tail-suspended mice showed distinct molecular profiles. They expressed RANKL with different kinetics, while transcriptomic and proteomic profiles uncovered unique molecular signatures that discriminated the two conditions, unveiling exclusive molecules expressed in time- and osteoporosis type-dependent manner. These results suggest that circulating EVs could represent a new tool for monitoring the onset and the progression of diverse types of the disease in mice, paving the way for their exploitation to diagnose human osteoporosis in liquid biopsies.

Effects of Linagliptin and Pioglitazone on Fracture Healing in an Experimental Type 2 Diabetes Rat Model

AIM

Our study aimed to examine the effects of Linagliptin, Pioglitazone, and their combination on fracture healing in a diabetes rat femur fracture model.

MATERIAL AND METHODS

Type 2 diabetes mellitus (T2DM) induced rats were randomly divided into four groups: non-treated diabetes group (TD), Pioglitazone group (P), Linagliptin group (L), and Pioglitazone and Linagliptin group (PL). Daily oral dosage of pioglitazone (10 mg/kg/day), linagliptin (10 mg/kg/day), and their combination were administered. Femur fractures were stabilized intramedullary. At weeks 2 and 6, rats were sacrificed for evaluation radiologically, biomechanically, histopathologically, histomorphometrically, and immunohistochemically.

RESULTS

Flexural strength of the L and PL groups were significantly higher compared to the P group. The highest healing score was in the L group and lowest in the P group, while the highest inflammation score was in the P group and lowest in the L group. A cluster of differentiation (CD) CD 34 reactivity was highest in the L group and lowest in the PL group.

CONCLUSION

Linagliptin treatment significantly increased histological healing scores, callus volume, biomechanical strength, and vascularity, however, minimized the inflammatory process, which was increased by pioglitazone. The combination of linagliptin and pioglitazone restored BMD and increased biomechanical strength. Linagliptin monotherapy is rarely indicated; hence, T2DM patients with a high risk of bone fractures can be considered for combined therapy of pioglitazone and linagliptin.

Effects of nitrite exposure on metamorphosis and skeletal development of Bufo gargarizans

Nitrite, as a part of nitrogen cycle, is one of the most common toxic compounds in aquatic ecosystems. Since skeletal development is an essential process during amphibian metamorphosis, exposure of larval amphibians to nitrite might disrupt skeletal development. To evaluate whether nitrite affects skeletal development of amphibian larvae, Bufo gargarizans larvae at Gs26 were exposed to 10, 100, 500 and 1000 μg/L nitrite-nitrogen (NO₂-N) in the present study. The metamorphosis rate, body weight, body length, forelimb length and hindlimb length of B. gargarizans exposed to NO₂-N were decreased. The microscopic structures of thyroid gland were altered under NO₂-N exposure at Gs42. The skeletal lengths of the humerus, femur and fibulare of tadpole at Gs42 were significantly reduced under 100, 500 and 1000 μg/L NO₂-N treatment groups, and the lengths of humerus, tibia-fibula and tibiale of tadpole at Gs46 were significantly reduced under 1000 μg/L NO₂-N treatment groups. In addition, the expression levels of thyroid hormone (TH) and endochondral ossification-related genes of tadpoles at Gs42 and Gs46 were tested by qRT-PCR. Overall, NO₂-N exposure could affect the expressions of these genes and then may influence the activity and function of thyroid gland, further disturbing the amphibian metamorphosis and skeletal development of amphibian larvae.

Insights Into the Role of Mitochondria in Vascular Calcification

Vascular calcification (VC) is a growing burden in aging societies worldwide, and with a significant increase in all-cause mortality and atherosclerotic plaque rupture, it is frequently found in patients with aging, diabetes, atherosclerosis, or chronic kidney disease. However, the mechanism of VC is still not yet fully understood, and there are still no effective therapies for VC. Regarding energy metabolism factories, mitochondria play a crucial role in maintaining vascular physiology. Discoveries in past decades signifying the role of mitochondrial homeostasis in normal physiology and pathological conditions led to tremendous advances in the field of VC. Therapies targeting basic mitochondrial processes, such as energy metabolism, damage in mitochondrial DNA, or free-radical generation, hold great promise. The remarkably unexplored field of the mitochondrial process has the potential to shed light on several VC-related diseases. This review focuses on current knowledge of mitochondrial dysfunction, dynamics anomalies, oxidative stress, and how it may relate to VC onset and progression and discusses the main challenges and prerequisites for their therapeutic applications.

The vascularization paradox of non-union formation

Despite major research efforts to elucidate mechanisms of non-union formation, failed fracture healing remains a common complication in orthopedic surgery. Adequate vascularization has been recognized as a crucial factor for successful bone regeneration, as newly formed microvessels guarantee the supply of the callus tissue with vital oxygen, nutrients, and growth factors. Accordingly, a vast number of preclinical studies have focused on the development of vascularization strategies to stimulate fracture repair. However, recent evidence suggests that stimulation of blood vessel formation is an oversimplified approach to support bone regeneration. This review discusses the role of vascularization during bone regeneration and delineates a phenomenon, for which we coin the term “the vascularization paradox of non-union-formation”. This view is based on the results of a variety of experimental studies that suggest that the callus tissue of non-unions is indeed densely vascularized and that pro-angiogenic mediators, such as vascular endothelial growth factor, are sufficiently expressed at the facture site. By gaining further insights into the molecular and cellular basis of non-union vascularization, it may be possible to develop more optimized treatment approaches or even prevent the non-union formation in the future.

A Reassessment of the Barrier Effect of the Physis against Metaphyseal Osteosarcoma: A Comprehensive Pathological Study with Its Radiological and Clinical Follow-Up Correlations

Osteosarcoma is a primary malignant bone tumor usually arising at the metaphysis of long bones, particularly around the knee. The physis has been regarded as a barrier capable of blocking tumor extension, thus allowing it to preserve their epiphysis and therefore improve functional results. With the objective of clarifying how effective the physis is as a barrier to tumor spread, a large series of skeletally immature patients with osteosarcoma were reviewed. From 452 metaphyseal osteosarcomas a selection of 282 cases in which the tumor was close or crossing the physis were carried out. This sub-sample was split into two groups according to the surgical treatment (epiphyseal preservation or not). The specimens obtained by resection were studied, and the physeal and metaphyseal areas were studied by multiple sections. Immunostaining against VEGF of physis was obtained in selected cases. In about half of the patients affected by metaphyseal malignant bone tumors, the growth plate and epiphysis were not compromised by the tumor. Three sequential invasive growth patterns of an osteosarcoma in its relationship with the physis could be distinguished. An intense angiogenesis and osteoclastic reaction could be observed in the growth plate in the free zone between the tumor and the physis. The local recurrence incidence was lower in the epiphyseal preservation treated patients than it was in the conventional treatment (8% vs. 12%). Most local recurrences appeared in the first 2 years. The overall survival of patients treated with epiphyseal preservation was better than that of the patients treated without preserving the epiphysis (73% vs. 59%; p = 0.03) at a mean follow-up of 18 years. We have described an angiogenic and osteoclastic reaction in the base of the growth plate in the proximity of the advance front of the tumor, which could facilitate the osteosarcoma invasion. It is also shown that the preoperative imaging method for examination is a valid approach for the decision to carry out epiphyseal preservation. Finally, we concluded that epiphyseal preservation combined with protective chemotherapy is an excellent clinical approach for selected patients with metaphyseal osteosarcoma.

Systematic review of medication related osteonecrosis of the jaw (MRONJ) in patients undergoing only antiangiogenic drug therapy: surgery or conservative therapy?

Osteonecrosis of the jaw is a severe adverse condition affecting patients exposed to specific types of medications. Previous studies have highlighted that osteonecrosis of the jaw is triggered by invasive dental procedures and can be very challenging to manage, especially in patients with cancer. The primary aim of this review was to analyse all available evidence on the management (surgical and/or conservative) of medication related osteonecrosis of the jaws (MRONJ) in patients with a history of antiangiogenic drugs therapy and who had not been previously exposed to any antiresorptive drug treatments. A multi-database search (PubMed, MEDLINE, EMBASE and CINAHL) was performed to identify related multi-language papers published from January 2003 until November 2020. Data were extracted from relevant papers and analysed according to the outcomes selected in this review. The search generated 28 studies eligible for the analysis. The total number of patients included in the analysis was 36. Sixteen patients were treated with anti-vascular endothelial growth factor drugs (anti-VEGF) while the remaining patients were administered a combination of antiangiogenic drugs. The most common MRONJ site was the mandible in 29 patients. MRONJ recurrence after treatment was only reported in six patients, the majority of which were treated conservatively. The data reviewed confirmed that an invasive procedure was the most common trigger of MRONJ with relatively high frequency of postoperative recurrence following treatment. However, due to the low quality of available research in the literature, it is difficult to draw a definitive conclusion on the validity of the presented treatment to manage patients affected by MRONJ associated with angiogenic therapy.

Skeletal regeneration for segmental bone loss: Vascularised grafts, analogues and surrogates

Massive segmental bone defects (SBD) are mostly treated by removing the fibula and transplanting it complete with blood supply. While revolutionary 50 years ago, this remains the standard treatment. This review considers different strategies to repair SBD and emerging potential replacements for this highly invasive procedure. Prior to the technical breakthrough of microsurgery, researchers in the 1960s and 1970s had begun to make considerable progress in developing non autologous routes to repairing SBD. While the breaktthrough of vascularised bone transplantation solved the immediate problem of a lack of reliable repair strategies, much of their prior work is still relevant today. We challenge the assumption that mimicry is necessary or likely to be successful and instead point to the utility of quite crude (from a materials technology perspective), approaches. Together there are quite compelling indications that the body can regenerate entire bone segments with few or no exogenous factors. This is important, as there is a limit to how expensive a bone repair can be and still be widely available to all patients since cost restraints within healthcare systems are not likely to diminish in the near future. STATEMENT OF SIGNIFICANCE: This review is significant because it is a multidisciplinary view of several surgeons and scientists as to what is driving improvement in segmental bone defect repair, why many approaches to date have not succeeded and why some quite basic approaches can be as effective as they are. While there are many reviews of the literature of grafting and bone repair the relative lack of substantial improvement and slow rate of progress in clinical translation is often overlooked and we seek to challenge the reader to consider the issue more broadly.

Inhibitory Effects of Combined Bone Morphogenetic Protein 2, Vascular Endothelial Growth Factor, and Basic Fibroblast Growth Factor on Osteoclast Differentiation and Activity

Bone morphogenetic protein 2 (BMP-2), vascular endothelial growth factor (VEGF), and basic fibroblast growth factors (bFGF) are important regulators of bone development and bone remodeling involving the coordination of osteoblast-mediated bone formation and osteoclast-mediated bone resorption. The synergistic promotions of these growth factors on osteogenesis in the appropriate combination have been confirmed by a lot of studies, but the effect of this combined application on osteoclastogenesis still remains ambiguous. On the basis of comparing the osteoclastic potentials under stimulation of BMP-2, VEGF, or bFGF alone, this study focused on their combined effects on the differentiation and activity of osteoclasts. Our results showed that osteoclastogenesis was enhanced to some extent under the stimulation of BMP-2, VEGF, or bFGF alone, and the potential of these three growth factors to stimulate osteoclastogenesis was VEGF > BMP-2 > bFGF. However, the treatment with the combination of BMP-2 (50 ng/mL), VEGF (1 ng/mL), and bFGF (10 ng/mL), the most suitable dose combination for osteogenesis optimized in our previous study, weakened osteoclast differentiation confirmed by smaller tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells, lower TRAP activity, and lower expression of dendritic cell-specific transmembrane protein, an important molecule regulating osteoclast fusion. Moreover, BMP-2, VEGF, and bFGF in combination also moderately inhibited the bone-resorbing activity of mature osteoclasts by suppressing the expression of osteoclast-specific genes cathepsin K, and matrix metalloproteinase-9. The underlying molecular mechanisms involved the suppression of the receptor activator of nuclear factor-κB ligand-induced c-Fos levels and the activation of nuclear factor of activated T cells c1, two major transcription factors in osteoclast differentiation. Taken together, our study showed that the combination of BMP-2 (50 ng/mL), VEGF (1 ng/mL), and bFGF (10 ng/mL) promoted osteoblastogenesis but inhibited osteoclastogenesis. Thus, the simultaneous use of BMP-2 (50 ng/mL), VEGF (1 ng/mL), and bFGF (10 ng/mL) in an appropriate combination might improve efficacious bone regeneration in a clinical setting. Impact statement Few studies have addressed the combined effects of multiple growth factors on osteoclasts. This study demonstrated that the simultaneous use of bone morphogenetic protein 2 (BMP-2; 50 ng/mL), vascular endothelial growth factor (VEGF; 1 ng/mL), and basic fibroblast growth factors (bFGF; 10 ng/mL), the most suitable dose combination for osteogenesis optimized in our previous study, showed inhibitory effects on the differentiation and activity of osteoclasts. Our results suggest that the growth factor signaling pathways in osteoclasts may interact with each other. Furthermore, this study could provide new insights into the optimal application of BMP-2, VEGF, and bFGF for bone repair and regeneration.

Integrative analyses reveal RNA regulatory network in Ti particles induced inflammation

Introduction Wear particles induced inflammatory osteolysis is the most important initiating factors in the mechanism of aseptic loosening. However, the molecular network changes in this process remain largely elusive. Methods Here, we performed whole transcriptome analysis using Ti particles induced RAW264.7 cell model to identify specific genes and pathways. Results Sequencing results totally identified 159 mRNAs, 96 lncRNAs, 31 circRNAs, and 12 miRNAs were significantly differently expressed. Of these, we selected two of each RNA for qRT-PCR validation and the results were highly consistent with the RNA-seq data. GSEA analysis shows that upregulated gene sets were related to the three classical inflammation pathway, cytokine–cytokine receptor interaction, TNF, and NF-kappa B signaling pathway. The enriched genes included not only IL-1β and TNF- α, which were independently verified before sequencing, but also other inflammatory osteolysis-related genes such as Mmp9, Fas, and Ccl2. Co-differentially expressed RNAs were employed to construct the ceRNA co-regulatory network. Conclusion: The results revealed that 4 lncRNAs and 2 circRNAs formed a regulatory network to simultaneously regulate miR-3065-3p targeting Myo18a. The present study helps to comprehensively understand the molecular mechanisms and regulatory interaction networks during early inflammatory response.

Targeting thymidine phosphorylase as a potential therapy for bone loss associated with periprosthetic osteolysis

Macrophages are generally thought to play a key role in the pathogenesis of aseptic loosening through initiating periprosthetic inflammation and pathological bone resorption. The aim of this study was to identify macrophage-derived factors that promote osteoclast differentiation and periprosthetic bone destruction. To achieve this, we examined the effects of 12 macrophage-derived factors that were identified by RNA-seq analysis of stimulated macrophages on osteoclast differentiation. Surprisingly, thymidine phosphorylase (TYMP) was found to trigger significant number of osteoclasts that exhibited resorbing activities on dentine slices. Functionally, TYMP knockdown reduced the number of osteoclasts in macrophages that had been stimulated with polyethylene debris. TYMP were detected in serum and synovial tissues of patients that had been diagnosed with aseptic loosening. Moreover, the administration of TYMP onto calvariae of mice induced pathological bone resorption that was accompanied by an excessive infiltration of inflammatory cells and osteoclasts. The RNA-seq for TYMP-induced-osteoclasts was then performed in an effort to understand action mode of TYMP. TYMP stimulation appeared to activate the tyrosine kinase FYN signaling associated with osteoclast formation. Oral administration of saracatinib, a FYN kinase inhibitor, significantly suppressed formation of bone osteolytic lesions in a polyethylene debris-induced osteolysis model. Our findings highlight a novel molecular target for therapeutic intervention in periprosthetic osteolysis.

Vascular Endothelial Growth Factor Biology and Its Potential as a Therapeutic Target in Rheumatic Diseases

Rheumatic diseases constitute a diversified group of diseases distinguished by arthritis and often involve other organs. The affected individual has low quality of life, productivity even life-threatening in some severe conditions. Moreover, they impose significant economic and social burdens. In recent years, the patient outcome has been improved significantly due to clearer comprehension of the pathology of rheumatic diseases and the effectiveness of "treat to target" therapies. However, the high cost and the adverse effects are the concerns and full remissions are not often observed. One of the main processes that contributes to the pathogenesis of rheumatic diseases is angiogenesis. Vascular endothelial growth factor (VEGF), a central mediator that regulates angiogenesis, has different isoforms and functions in various physiological processes. Increasing evidence suggests an association between the VEGF system and rheumatic diseases. Anti-VEGF and VEGF receptor (VEGFR) therapies have been used to treat several cancers and eye diseases. This review summarizes the current understanding of VEGF biology and its role in the context of rheumatic diseases, the contribution of VEGF bioavailability in the pathogenesis of rheumatic diseases, and the potential implications of therapeutic approaches targeting VEGF for these diseases.

Insights into the mechanism of vascular endothelial cells on bone biology

In the skeletal system, blood vessels not only function as a conduit system for transporting gases, nutrients, metabolic waste, or cells but also provide multifunctional signal molecules regulating bone development, regeneration, and remodeling. Endothelial cells (ECs) in bone tissues, unlike in other organ tissues, are in direct contact with the pericytes of blood vessels, resulting in a closer connection with peripheral connective tissues. Close-contact ECs contribute to osteogenesis and osteoclastogenesis by secreting various cytokines in the paracrine or juxtacrine pathways. An increasing number of studies have revealed that extracellular vesicles (EVs) derived from ECs can directly regulate maturation process of osteoblasts and osteoclasts. The different pathways focus on targets at different distances, forming the basis of the intimate spatial and temporal link between bone tissue and blood vessels. Here, we provide a systematic review to elaborate on the function of ECs in bone biology and its underlying mechanisms based on three aspects: paracrine, EVs, and juxtacrine. This review proposes the possibility of a therapeutic strategy targeting blood vessels, as an adjuvant treatment for bone disorders.

Interleukin-35 Is Involved in Angiogenesis/Bone Remodeling Coupling Through T Helper 17/Interleukin-17 Axis

OBJECTIVE

Osteoporosis is a common metabolic bone disease mainly involving bone remodeling and blood vessels. The current study aimed to explore the suppressive role of interleukin (IL)-35 in nuclear factor kappa-B ligand receptor activator (RANKL) and macrophage colony stimulating factor (M-CSF)-induced osteoclastogenesis and angiogenesis in osteoclasts.

METHODS

Osteoclasts differentiation were induced by incubation of mouse leukemic monocyte/macrophage cell line RAW264.7 cells in the presence of RANKL and M-CSF and was assessed with tartrate-resistant acid phosphatase (TRAP) staining assay. The viability and apoptosis of RAW264.7 was measured using CCK-8 assay and flow cytometry, respectively. The expression of angiogenic genes and proteins were measured using RT-PCR, Western blots and ELISA. The inhibition of Th17/IL-17 axis was examined using plumbagin, which was demonstrated as an IL-17A related signaling pathway inhibitor.

RESULTS

IL-35 inhibited the viability of RAW264.7 cells and promoted the apoptosis of RAW264.7 cells in a dose-dependent manner. Furthermore, IL-35 dose-dependently suppressed the expression of angiogenic markers including VEGF and its receptor. The suppressive effect of IL-35 was confirmed through the activation of Th17/IL-17 axis.

CONCLUSIONS

We demonstrated for the first time the immuno-suppressive function of IL-35 on RANKL and M-CSF-induced osteoclastogenesis and angiogenesis through Th17/IL-17 axis. Therapeutic approach involving augmentation of IL-35 regulatory response may serve as a novel treatment option for osteoporosis, especially by suppressing bone resorption and angiogenesis.

Bone Vasculature and Bone Marrow Vascular Niches in Health and Disease

Bone vasculature and bone marrow vascular niches supply oxygen, nutrients, and secrete angiocrine factors required for the survival, maintenance, and self-renewal of stem and progenitor cells. In the skeletal system, vasculature creates nurturing niches for bone and blood-forming stem cells. Blood vessels regulate hematopoiesis and drive bone formation during development, repair, and regeneration. Dysfunctional vascular niches induce skeletal aging, bone diseases, and hematological disorders. Recent cellular and molecular characterization of the bone marrow microenvironment has provided unprecedented insights into the complexity, heterogeneity, and functions of the bone vasculature and vascular niches. The bone vasculature is composed of distinct vessel subtypes that differentially regulate osteogenesis, hematopoiesis, and disease conditions in bones. Further, bone marrow vascular niches supporting stem cells are often complex microenvironments involving multiple different cell populations and vessel subtypes. This review provides an overview of the emerging vascular cell heterogeneity in bone and the new roles of the bone vasculature and associated vascular niches in health and disease. © 2020 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

The effect of TNF-α on osteoblasts in metal wear-induced periprosthetic bone loss

Aims

This study aimed to examine the effects of tumour necrosis factor-alpha (TNF-α) on osteoblasts in metal wear-induced bone loss.

Methods

TNF-α immunoexpression was examined in periprosthetic tissues of patients with failed metal-on-metal hip arthroplasties and also in myeloid MM6 cells after treatment with cobalt ions. Viability and function of human osteoblast-like SaOs-2 cells treated with recombinant TNF-α were studied by immunofluorescence, terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL) assay, western blotting, and enzyme-linked immunosorbent assay (ELISA).

Results

Macrophages, lymphocytes, and endothelial cells displayed strong TNF-α immunoexpression in periprosthetic tissues containing metal wear debris. Colocalization of TNF-α with the macrophage marker CD68 and the pan-T cell marker CD3 confirmed TNF-α expression in these cells. Cobalt-treated MM6 cells secreted more TNF-α than control cells, reflecting the role of metal wear products in activating the TNF-α pathway in the myeloid cells. While TNF-α did not alter the immunoexpression of the TNF-receptor 1 (TNF-R1) in SaOs-2 cells, it increased the release of the soluble TNF-receptor 1 (sTNF-R1). There was also evidence for TNF-α-induced apoptosis. TNF-α further elicited the expression of the endoplasmic reticulum stress markers inositol-requiring enzyme (IRE)-1α, binding-immunoglobulin protein (BiP), and endoplasmic oxidoreductin1 (Ero1)-Lα. In addition, TNF-α decreased pro-collagen I α 1 secretion without diminishing its synthesis. TNF-α also induced an inflammatory response in SaOs-2 cells, as evidenced by the release of reactive oxygen and nitrogen species and the proinflammatory cytokine vascular endothelial growth factor.

Conclusion

The results suggest a novel osteoblastic mechanism, which could be mediated by TNF-α and may be involved in metal wear debris-induced periprosthetic bone loss.

Cite this article: Bone Joint Res 2020;9(11):827–839.

Effects of VEGF on Prefabricated Vascularized Bone Allografts in Rats

BACKGROUND

 Massive bone defects after wide resection of malignant bone tumors or a serious injury require treatment using vascularized bone grafts. Although cadaveric bone allografts combined with vascularized bone autografts are currently thought to be ideal in terms of size and durability, this treatment requires the scarification of healthy bone tissue. In a previous study, we attempted to improve this situation by prefabricating a vascularized bone allograft in recipient rats. In this study, we added vascular endothelial growth factor (VEGF)-containing hydroxyapatite/collagen composite (HAp/Col) to a prefabricated vascularized bone allograft to stimulate angiogenesis, which is known to be important for bone formation.

METHODS

 Sprague Dawley rats (n = 50) were used as donors and Wistar rats (n = 50) as recipients. All rats were 9 weeks old. The recipient rats were divided into five groups according to the use of vascular bundles, HAp/Col, and an additive substance (VEGF). The bone allografts collected from the donors were transplanted into the thigh region of the recipients, and a saphenous vein and 10 μg HAp/Col with VEGF were inserted into the bone allografts through the slit. After 4 weeks, the transplanted bone allografts were harvested, and histologic and genetic evaluations were performed in relation to bone formation and resorption.

RESULTS

 The results showed that, compared with the control group, the implantation of the vascular bundles and VEGF-containing HAp/Col significantly stimulated angiogenesis and bone formation in the rats with the bone allografts. However, histological and genetic evaluations of bone resorption revealed that resorption was not observed in any group.

CONCLUSION

 These results suggest that VEGF-containing HAp/Col effectively stimulates angiogenesis and bone formation, but not bone resorption, in prefabricated vascularized bone allografts. This method could therefore become a useful tool for treating large bone defects.

Current and novel therapeutic targets in the treatment of rheumatoid arthritis

Rheumatoid arthritis (RA), a multifactorial disease characterized by synovitis, cartilage destruction, bone erosion, and periarticular decalcification, finally results in impairment of joint function. Both genetic and environmental factors are risk factors in the development of RA. Unwanted side effects accompany most of the current treatment strategies, and around 20-40% of patients with RA do not clinically benefit from these treatments. The unmet need for new treatment options for RA has prompted research in the development of novel agents acting through physiologically and pharmacologically relevant targets. Here we discuss in detail three critical pathways, Janus kinase/signal transducer and activator of transcription (JAK/STAT), Th17, and hypoxia-inducible factor (HIF), and their roles as unique therapeutic targets in the field of RA. Some of the less developed but potential targets like nucleotide-binding and oligomerization domain-like receptor containing protein 3 (NLRP3) inflammasome and histone deacetylase 1 (HDAC1) are also discussed.

Vasoinhibin reduces joint inflammation, bone loss, and the angiogenesis and vasopermeability of the pannus in murine antigen-induced arthritis

Increased permeability and growth (angiogenesis) of blood vessels play a key role in joint swelling and pannus formation in inflammatory arthritis, a family of diseases influenced by reproductive hormones. The hormone prolactin (PRL) protects against joint inflammation, pannus formation, and bone destruction in adjuvant-induced arthritis and these effects may involve its proteolytic conversion to vasoinhibin, a PRL fragment that inhibits angiogenesis and vasopermeability. Here, we show that the intra-articular injection of an adeno-associated virus type-2 (AAV2) vector encoding vasoinhibin reduced joint inflammation, the hyperplasia, vascular density, and vasopermeability of the pannus, and the loss of bone in mice subjected to antigen-induced arthritis. In agreement, the AAV2 vasoinhibin vector reduced the expression of proinflammatory cytokines (interleukin-1β, interleukin-6), an endothelial cell marker (platelet endothelial cell-adhesion molecule 1), and proangiogenic molecules [vascular endothelial growth factor (VEGF), VEGF receptor 2, and hypoxia-inducible factor 1α] in the arthritic joint. Also, vasoinhibin reduced the synovial vasopermeability induced by the intra-articular injection of VEGF in healthy mice. Finally, vasoinhibin signals by blocking the phosphorylation/activation of endothelial nitric oxide synthase (eNOS) at Ser1179 and the AAV2 vasoinhibin vector inhibited the enhanced phosphorylation of eNOS Ser1179 in the arthritic joint. We conclude that vasoinhibin reduces joint inflammation and bone loss in arthritis by inhibiting pannus angiogenesis and vasopermeability via the blockage of VEGF-induced eNOS activation. These findings suggest the potential therapeutic benefit of AAV2-mediated vasoinhibin gene delivery in arthritis.

A Unique Triculture Model to Study Osteoblasts, Osteoclasts, and Endothelial Cells

IMPACT STATEMENT

In this article, we first developed a new medium to culture together primary human osteoblastic, osteoclastic, and endothelial cells (ECs) chosen to represent the three major bone cell tissues. Indeed, no study has been conducted on primary human cells and on the phenotype/activity retention of these three primary human cell types. Thus, we established an original triculture model with osteoblastic, osteoclastic, and ECs, where not only both cell phenotype and cell activity were maintained but also cell culture homeostasis. These promising results will permit further investigations to create in vitro conditions to mimic the bone microenvironment and analyze cell interactions in ex vivo studies.

Osteocyte-Related Cytokines Regulate Osteoclast Formation and Bone Resorption

The process of bone remodeling is the result of the regulated balance between bone cell populations, namely bone-forming osteoblasts, bone-resorbing osteoclasts, and the osteocyte, the mechanosensory cell type. Osteoclasts derived from the hematopoietic stem cell lineage are the principal cells involved in bone resorption. In osteolytic diseases such as rheumatoid arthritis, periodontitis, and osteoporosis, the balance is lost and changes in favor of bone resorption. Therefore, it is vital to elucidate the mechanisms of osteoclast formation and bone resorption. It has been reported that osteocytes express Receptor activator of nuclear factor κΒ ligand (RANKL), an essential factor for osteoclast formation. RANKL secreted by osteocytes is the most important factor for physiologically supported osteoclast formation in the developing skeleton and in pathological bone resorption such as experimental periodontal bone loss. TNF-α directly enhances RANKL expression in osteocytes and promotes osteoclast formation. Moreover, TNF-α enhances sclerostin expression in osteocytes, which also increases osteoclast formation. These findings suggest that osteocyte-related cytokines act directly to enhance osteoclast formation and bone resorption. In this review, we outline the most recent knowledge concerning bone resorption-related cytokines and discuss the osteocyte as the master regulator of bone resorption and effector in osteoclast formation.

Osteoclast-derived exosomal let-7a-5p targets Smad2 to promote the hypertrophic differentiation of chondrocytes

The invasion of osteoclasts into the cartilage via blood vessels advances the process of endochondral ossification, and dysregulation of dynamic intercellular interactions results in skeletal dysplasias. Although the regulation of osteoclasts by growth plate chondrocytes has been reported in detail, the effect of osteoclasts on chondrocytes remains to be determined. In this study, ATDC5 cells and bone marrow mesenchymal stem cells were differentiated into chondrocytes and treated with conditioned medium obtained from bone marrow macrophages differentiated to osteoclast precursors and osteoclasts. Exosomes were inhibited in conditioned medium or isolated directly from osteoclasts to further determine whether osteoclast-derived exosomes play an important role in chondrocyte hypertrophy. Additionally, exosomal miRNAs were detected, and let-7a-5p was selected as an miRNA with significantly increased expression in osteoclast-derived exosomes. Experiments were performed to verify the potential target Smad2 and investigate how let-7a-5p affected chondrocytes. The results suggest that both osteoclast precursors and osteoclasts promote chondrocyte hypertrophy and that the promotive effect of osteoclasts is more significant than that of osteoclast precursors. Osteoclast-derived exosomes promote the hypertrophic differentiation of chondrocytes. Moreover, osteoclast-derived exosomal let-7a-5p inhibits Smad2 to decrease the transforming growth factor-β-induced inhibition of chondrocyte hypertrophy. Our research reveals the role of osteoclasts in the regulation of chondrocytes and provides insights into the highly coordinated intercellular process of endochondral ossification.

The expression of extracellular matrix metalloproteinase inducer (EMMPRIN) in the compression area during orthodontic relapse

OBJECTIVE

This study investigated the expression of extracellular matrix metalloproteinase inducer (EMMPRIN) in the compression area during orthodontic relapse in rat molars.

MATERIALS AND METHODS

Thirty Wistar rats (6 weeks old) underwent orthodontic tooth movement (OTM) of the left first maxillary molar for 21 days, followed by removal of the force device. The contralateral maxillary molar served as a control with no mechanical force stimuli. Animals were sacrificed at 0, 1, 3, 7, and 14 days of relapse after force withdrawal. Tooth relapse and alveolar bone parameters were measured using microcomputed tomography (micro-CT). Maxilla sections were obtained for haematoxylin and eosin (HE), immunohistochemical staining [EMMPRIN, nuclear factor kappa B ligand (RANKL) and vascular endothelial growth factor (VEGF)] and tartrate-resistant acid phosphatase (TRAP). Correlation analyses were then performed.

RESULTS

After force removal, nearly 79.88% of the total relapse occurred within the initial 3 days. The number of osteoclasts clearly increased while the alveolar bone density decreased on the pressure side on Day 3 of relapse. Moreover, the EMMPRIN expression level significantly increased on Day 1, peaked up on Day 3 and decreased on Days 7 and 14. Statistically, a strong positive correlation was found between EMMRPIN expression and the osteoclast number and RANKL and VEGF expression.

CONCLUSION

EMMPRIN was highly expressed on the pressure side during the orthodontic tooth relapse, which could be involved in osteoclastogenesis and alveolar bone resorption in association with RANKL and VEGF expression.

Zoledronate Inhibits Osteoclast Differentiation via Suppressing Vascular Endothelial Growth Factor Receptor 2 Expression

Bisphosphonate-related osteonecrosis of the jaw (ONJ) is a major oral complication; however, its pathogenesis remains unclear. Impairment of osteoclast differentiation by bisphosphonates may be associated with the pathogenesis of ONJ. In our previous study, we reported that the expression of the gene encoding nuclear factor of activated T cells c1 (NFATc1), a known osteoclast differentiation marker, was significantly silenced by zoledronate, a bisphosphonate, in mouse osteoclast precursor cells (mOCPCs) using cDNA microarray. In the present study, the expression value of the NFATc1 gene was regarded as a cut-off and genes whose expression value was significantly decreased compared with that of the NFATc1 gene were extracted in mOCPCs. For validation, CD11b-positive (CD11b+) cells were used, which were purified from human peripheral blood mononuclear cells as human OCPCs. A total of 19 genes were identified; sequential expression analysis revealed that the gene encoding vascular endothelial growth factor receptor 2 (VEGFR2) was frequently silenced by zoledronate in CD11b+ cells. Furthermore, the number of tartrate-resistant acid phosphatase-positive multinucleated cells was decreased by VEGFR2 suppression using a VEGFR2 neutralizing antibody. Zoledronate inhibits human osteoclast differentiation via suppressing VEGFR2 expression. These results suggest that low expression of VEGFR2 in OCPCs may be involved in the pathogenesis of zoledronate-induced ONJ. The understanding of the role of VEGFR2 on bone remodeling is important to elucidate the pathogenesis of bisphosphonate-related ONJ.

Deciphering novel chemotherapy and its impact on dentistry

In the last few decades, the number of targeted chemotherapies approved for cancer treatment and undergoing clinical trials has risen. In comparison to conventional chemotherapy, targeted therapies (TTs) act on specific molecular targets involved in cancer development and progression, with reduced detrimental effects to normal tissues. TTs have now been recognised as key treatments in a number of common cancers, including solid tumours and haematological malignancies. The number of patients undergoing novel cancer treatment will continue to increase, and a significant population will likely present to the dental environment. This paper aims to provide an insight into TTs currently available, including monoclonal antibodies, fusion proteins, tyrosine kinase inhibitors, histone deacetylase inhibitors, mammalian target of rapamycin inhibitors, phosphoinositide 3-kinase inhibitors, proteasome inhibitors and hedgehog pathway inhibitors. The mechanisms of action, indications for use and how to identify the medications will be summarised. Dental implications of these novel therapies include medication-related osteonecrosis of the jaw, delayed healing, immunosuppression and thrombocytopenia. These will be discussed to ensure oral healthcare providers are aware of their impact in a dental setting.

Role of osteoclasts in oral homeostasis and jawbone diseases

The jawbone is a unique structure as it serves multiple functions in mastication. Given the fact that the jawbone is remodeled faster than other skeletal bones, bone cells in the jawbone may respond differently to local and systemic cues to regulate bone remodeling and adaptation. Osteoclasts are bone cells responsible for removing old bone, playing an essential role in bone remodeling. Although bone resorption by osteoclasts is required for dental tissue development, homeostasis and repair, excessive osteoclast activity is associated with oral skeletal diseases such as periodontitis. In addition, antiresorptive medications used to prevent bone homeostasis of tumors can cause osteonecrosis of the jaws that is a major concern to the dentist. Therefore, understanding of the role of osteoclasts in oral homeostasis under physiological and pathological conditions leads to better targeted therapeutic options for skeletal diseases to maintain patients' oral health. Here, we highlight the unique features of the jawbone compared to the long bone and the involvement of osteoclasts in the jawbone-specific diseases.

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.

The influence of leukocyte-platelet-rich plasma on accelerated orthodontic tooth movement in rabbits

Objective

To determine the effects of a local injection of leukocyte-platelet-rich plasma (L-PRP) on orthodontic tooth movement in rabbits.

Methods

Twenty-three male New Zealand white rabbits were included in a split-mouth design. Tooth movement with a 100-g nickel-titanium closed-coil spring was performed on the maxillary first premolars. L-PRP was injected submucosally at the buccal and lingual areas of the first premolar in one random side of the maxilla and the other side served as the control and received normal saline. The amount of tooth movement was assessed on three-dimensional digital models on days 0, 3, 7, 14, 21, and 28. Histological findings and osteoclast numbers were examined on day 0 as the baseline and on days 7, 14, and 28.

Results

The L-PRP group showed significantly greater cumulative tooth movement at all observed periods. However, a significantly higher rate of tooth movement was observed only on days 0–7 and 7–14. The osteoclast numbers were significantly increased in the L-PRP group on days 7 and 14.

Conclusions

Local injection of L-PRP resulted in a transient increase in the rate of tooth movement and higher osteoclast numbers.

Bone biology in postnatal Wistar rats following hypoxia-reoxygenation

Hypoxia response pathways have a central role in normal and abnormal bone biology but the effect of systemic hypoxia-reoxygenation on bone is not clear. Following hypoxic exposure, aberrant synthesis, folding and trafficking of proteins has been reported to occur, which can result in endoplasmic reticulum (ER) stress and may finally cause cell death. This study aimed to examine the effect of systemic hypoxia-reoxygenation injury on bone biology in postnatal rats. Immunoexpression of HIF-1α and VEGF was upregulated in femurs of newborn Wistar rats in response to systemic hypoxia-reoxygenation. Along with that, increased apoptosis of osteoblast precursors, osteoblasts, osteocytes and endothelial cells was observed in comparison to femurs of control animals by transmission electron microscopy, TUNEL staining and immunoexpression of cleaved caspase-3. The viability of osteoclasts was not affected. After hypoxia-reoxygenation, ER stress was observed in the osteoblasts and osteocytes as indicated by dilatation of the ER and enhanced immunoexpression of the ER stress marker GRP78. Localisation of collagen α1 immunoreaction was widespread in the bone matrix of control femurs but was confined to the osteoblasts and osteocytes in response to hypoxia-reoxygenation. In support of these findings, in vitro work showed reduced viability of osteoblast-like SaOs-2 cells and upregulation of GRP78 protein expression in them by western blotting following exposure to hypoxia. This suggests that systemic hypoxia-reoxygenation may disturb bone biology in postnatal Wistar rats by inducing ER stress and apoptosis in osteoblasts and osteocytes, without affecting the viability of osteoclasts. More in-depth research is needed to confirm causality between ER stress and apoptosis of osteoblasts and osteocytes.

Collagen XIII-derived ectodomain regulates bone angiogenesis and intracortical remodeling

Osteoporosis is the most common degenerative bone disease that occurs when the balance of bone production and resorption is perturbed. Loss of bone mass or alteration in its quality leads to significant weakening of the bones and subsequently to higher fracture risk. Collagen XIII (ColXIII) is a conserved transmembrane protein expressed in many mesenchymal tissues. Here we show that ColXIII is a regulator of bone remodeling niche. In this study, we found that ColXIII expression is significantly upregulated in osteoporotic patients. In view of that, we studied bone homeostasis in ColXIII-overexpressing mice (Col13a1^oe) up to 72 weeks of age and observed a cortical bone overgrowth followed by a drastic bone loss, together with increased bone vascularization. Moreover, our results demonstrate that the ColXIII-derived ectodomain enhances angiogenesis through β1-integrins and the JNK pathway. Consequently, these data suggest that ColXIII has a role in age-dependent cortical bone deterioration with possible implications for osteoporosis and fracture risk.

Targeting vascular endothelial growth factor ameliorates PMMA-particles induced inflammatory osteolysis in murine calvaria

Cytokines and growth factors mediate inflammatory osteolysis in response to particles released from bone implants. However, the mechanism by which this process develops is not entirely clear. Blood vessels and related factors may be required to deliver immune cells and soluble factors to the injury site. Therefore, in the current study we investigated if, vascular endothelial growth factor (VEGF), which is required for angiogenesis, mediates polymethylmethacrylate (PMMA) particles-induced osteolysis. Using bone marrow derived macrophages (BMMs) and ST2 stromal cell line, we show that PMMA particles increase VEGF expression. Further, using a murine calvarial osteolysis model, we found that PMMA injection over calvaria induce significant increase in VEGF expression as well as new vessel formation, represented by von Willebrand factor (vWF) staining. Co-treatment using a VEGF-neutralizing antibody abrogated expression of vWF, indicating decreased angiogenesis. Finally, VEGF neutralizing antibody reduced expression of Tumor necrosis factor (TNF) and decreased osteoclastogenesis induced by PMMA particles in calvariae. This work highlights the significance of angiogenesis, specifically VEGF, as key driver of PMMA particle-induced inflammatory osteolysis, inhibition of which attenuates this response.

The role of physical forces in osteoclastogenesis

The movements of life at every level from organs, tissues, cells to sub-cells, are all conducted in certain physical environments. In the human body, skeletal tissue among all connective tissues is influenced the most by physical forces. Studying the biological behavior of bone cells under different physical environments is helpful in further understanding bone homeostasis and metabolism. Among all bone cells, osteoclast (OC) and OC steered bone remodeling is one of the key points in bone metabolism. In the past few decades, people's understanding of OC was mostly limited to its involvement of bone resorption under physiological and pathological conditions. However, more and more studies started to focus on how physical forces affect the formation and differentiation of OC. This review tries to illustrate the knowledge up to date about how osteoclastogenesis is regulated by physical forces through direct and indirect ways, including fluid shear force, compressive force, and microgravity. The direct way describes the straightforward effects produced by different forces in osteoclastogenesis, whereas the indirect way describes the effects of different forces in osteoclastogenesis through regulation of other bone cells when a certain force is applied. Molecular mechanisms were analyzed and reviewed in both direct and indirect regulation by different forces. Finally, we discussed the status quo and tendency of related research, as well as other unresolved issues, and some future prospects.

Medication-related osteonecrosis of the jaw unrelated to bisphosphonates and denosumab-a review

The link between medication-related osteonecrosis of the jaw (MRONJ) and bone modulating drugs, such as bisphosphonates and denosumab, is well established, and the number of reported cases is increasing. The development of novel medications used in the treatment of cancer, as well as autoimmune and bone conditions, has led to more cases of MRONJ being reported. However, in addition to this group of medications, increasing numbers of new agents in cancer therapy, such as antiangiogenic agents, have also been implicated in the development of MRONJ. As these newer agents with similar mechanisms are routinely used, the numbers of reported cases will likely rise further. This article aims to identify and summarize the drugs implicated in MRONJ, besides bisphosphonates and denosumab. A wide range of medications classified as tyrosine kinase inhibitors, monoclonal antibodies, mammalian target of rapamycin inhibitors, radiopharmaceuticals, selective estrogen receptor modulators, and immunosuppressants have been implicated in MRONJ. It remains crucial that oral health care providers are aware of these new medications and their associated risks to manage their patients appropriately.

Osteoclast-related markers in the hip joint fluid with subchondral insufficiency fracture of the femoral head

Similar to the radiological findings in rapidly destructive arthrosis of the hip joint (RDA), subchondral insufficiency fracture of the femoral head (SIF) can result in progressive femoral head collapse of unknown etiology. We thus examined the osteoclast activity of hip joint fluid in SIF with progressive collapse in comparison with that in RDA. Twenty-nine hip joint fluid samples were obtained intraoperatively with whole femoral heads from 12 SIF patients and 17 RDA patients. SIF cases were classified into subgroups based on the presence of ≥2 mm collapse on preoperative radiographs: SIF with progressive collapse (n = 5) and SIF without progressive collapse (n = 7). The levels of tartrate-resistant acid phosphatase (TRACP)-5b, interleukin-8, vascular endothelial growth factor (VEGF), and matrix metalloproteinase (MMP)-9 were measured. The number of multinuclear giant cells at the subchondral region was histopathologically assessed using mid-coronal slice of each femoral head specimen. The median levels of all markers and the median number of multinuclear giant cells in SIF with progressive collapse were significantly higher than those in SIF without progressive collapse, while there were no significant differences in SIF with progressive collapse versus RDA. Regression analysis showed that the number of multinuclear giant cells was positively correlated with the level of TRACP-5b in joint fluid. The present study demonstrated the possible association of increased osteoclast activity with the existing condition of progressive collapse in SIF, which was quite similar to the findings in RDA, indicating that increased osteoclast activity may reflect the condition of progressive collapse in SIF as well as RDA. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2987-2995, 2018.

Transcriptome analyses reveal molecular mechanisms that regulate endochondral ossification in amphibian Bufo gargarizans during metamorphosis

BACKGROUND

A developmental transition from aquatic to terrestrial existence is one of the most important events in the evolution of terrestrial vertebrates. Amphibian metamorphosis is a classic model to study this transition. The development of the vertebrate skeleton can reflect its evolutionary history. Endochondral ossification serves a vital role in skeletal development. Thus, we sought to unravel molecular mechanisms that regulate endochondral ossification during Bufo gargarizans metamorphosis.

METHODS

The alizarin red-alcian blue double staining method was used to visualize the skeletal development of B. gargarizans during metamorphosis. RNA sequencing (RNA-seq) was used to explore the transcriptome of B. gargarizans in four key developmental stages during metamorphosis. Real-time quantitative PCR (RT-qPCR) was used to validate the expression patterns of endochondral ossification related genes.

RESULTS

Endochondral ossification increased gradually in skeletal system of B. gargarizans during metamorphosis. A total of 137,264 unigenes were assembled and 44,035 unigenes were annotated. 10,352 differentially expressed genes (DEGs) were further extracted among four key developmental stages. In addition, 28 endochondral ossification related genes were found by searching for DEG libraries in B. gargarizans. Of the 28 genes, 10 genes were validated using RT-qPCR.

CONCLUSIONS

The exquisite coordination of the 28 genes is essential for regulation of endochondral ossification during B. gargarizans metamorphosis.

GENERAL SIGNIFICANCE

The present study will not only provide an invaluable genomic resource and background for further research of endochondral ossification in amphibians but will also aid in enhancing our understanding of the evolution of terrestrial vertebrates.

CYR61/CCN1 Regulates Sclerostin Levels and Bone Maintenance

CYR61/CCN1 is a matricellular protein that resides in the extracellular matrix, but serves regulatory rather than structural roles. CYR61/CCN1 is found in mineralized tissues and has been shown to influence bone healing in vivo and osteogenic differentiation in vitro. In this study we generated Cyr61 bone-specific knockout mice to examine the physiological role of CYR61/CCN1 in bone development and maintenance in vivo. Extensive analysis of Cyr61 conditional knockout mice showed a significant decrease in both trabecular and cortical bone mass as compared to WT littermates. Our data suggest that CYR61/CCN1 exerts its effects on mature osteoblast/osteocyte function to modulate bone mass. Specifically, changes were observed in osteocyte/osteoblast expression of RankL, VegfA, and Sost. The increase in RankL expression was correlated with a significant increase in osteoclast number; decreased VegfA expression was correlated with a significant decrease in bone vasculature; increased Sost expression was associated with decreased Wnt signaling, as revealed by decreased Axin2 expression and increased adiposity in the bone marrow. Although the decreased number of vascular elements in bone likely contributes to the low bone mass phenotype in Cyr61 conditional knockout mice, this cannot explain the observed increase in osteoclasts and the decrease in Wnt signaling. We conducted in vitro assays using UMR-106 osteosarcoma cells to explore the role CYR61/CCN1 plays in modulating Sost mRNA and protein expression in osteocytes and osteoblasts. Overexpression of CYR61/CCN1 can suppress Sost expression in both control and Cyr61 knockout cells, and blocking Sost with siRNA can rescue Wnt responsiveness in Cyr61 knockout cells in vitro. Overall, our data suggest that CYR61/CCN1 modulates mature osteoblast and osteocyte function to regulate bone mass through angiogenic effects as well as by modulating Wnt signaling, at least in part through the Wnt antagonist Sost. © 2018 American Society for Bone and Mineral Research.

MALAT1 enhanced the proliferation of human osteoblasts treated with ultra‑high molecular weight polyethylene by targeting VEGF via miR‑22‑5p

Osteolysis associated with an implanted prosthesis is the major cause of failure in prosthesis implantation, and a severe public health issue worldwide. The type of bone metabolism associated with this disorder has been a major focus for improving the outcomes of patients with osteolysis. The role of metastasis-associated lung adenocarcinoma transcript 1 (MALAT1; a member of the long coding RNA family) during the onset of osteolysis and the related molecular regulatory mechanism in ultra-high molecular weight polyethylene (UHMWPE)-treated hFOB 1.19 cells were investigated in the current study. The effect of MALAT1 knockdown on cell viability, cell apoptosis and osteolysis-associated signaling were also examined, and the interactions that occurred between MALAT1 and an anti-osteolysis molecule, microRNA (miR)-22-5p were investigated. Additionally, knockdown of vascular endothelial growth factor (VEGF) exerted similar biological effects as observed following miR-22-5p overexpression. The data showed that MALAT1 and pro-osteolysis indicators, receptor activator of nuclear factor-κB ligand (RANKL) and VEGF were upregulated in clinical interface membrane samples. Knockdown of MALAT1 inhibited the growth of UHMWPE-treated hFOB 1.19 cells, and this effect was associated with the upregulation of OPG, and downregulation of RANKL and VEGF. Results of a dual luciferase assay confirmed the interaction between VEGF and miR-22-5p, and also between MALAT1 and miR-22-5p. Additionally, subsequent assays indicated that overexpression of MALAT1 suppressed the anti-osteolysis effect of miR-22-5p, which would further induce VEGF expression. The data indicated that MALAT1 has an in port ant role in the onset of osteolysis via its ability to induce RANKL expression and inhibit the effect of miR-22-5p.

Roles of VEGF-Flt-1 signaling in malignant behaviors of oral squamous cell carcinoma

Background

Vascular endothelial growth factor (VEGF) is a highly specific signaling protein for vascular endothelial cells that plays a critical role in tumor growth and invasion through angiogenesis, and may contribute to cell migration and activation of pre-osteoclasts, osteoclasts and some tumor cells.

Objectives

We aimed to clarify the detailed roles of VEGF-Flt-1 signaling in bone invasion of oral squamous cell carcinoma (OSCC) cells.

Results

Forty-two (42) of 54 cases with gingival SCC (77.8%) strongly expressed VEGF, and had a significantly increased number of Flt-1+ osteoclasts (p<0.01) and more aggressive bone invasion (p<0.05). PlGF, a ligand of Flt-1, induced osteoclastogenesis in single culture of bone marrow cells (BMCs), and inhibition of Flt-1-signaling by VEGF tyrosine kinase inhibitor and It’s down stream (Akt and ERK1/2) inhibitos reduced osteoclastogenesis in PlGF-stimulated BMCs (p<0.01). In molecular level, PlGF stimulation significantly upregulated RANKL expression in Flt-1-expressing HSC2 cells via phosphorylation of Akt and ERK1/2. In the co-culture of VEGF-producing HSC2 cells and BMCs, number of TRAP-positive osteoclasts markedly increased (p<0.01). The osteoclastogenesis was significantly inhibited by RANKL-neutralizing antibody (p<0.01) as well as by VEGF tyrosine kinase inhibitor (p<0.01) and it’s downstream (Akt and ERK1/2) inhibitors (p<0.01, p<0.05, respectively).

Conclusion

VEGF-Flt-1 signaling induces osteoclastogenesis in OSCC through two possible ways: 1) VEGF produced from OSCC cells can directly stimulate the Flt-1 pathway in preosteoclasts to induce migration to future bone resorbing area and differentiation into osteoclasts, and 2) VEGF-Flt-1 signaling upregulates RANKL expression in OSCC cells, which indirectly leads to osteoclast differentiation. Therefore, blocking of the VEGF-Flt-1 signaling may help inhibit bone invasion of OSCC.

It Takes Two to Tango: Coupling of Angiogenesis and Osteogenesis for Bone Regeneration

Bone regeneration is a complex process requiring highly orchestrated interactions between different cells and signals to form new mineralized tissue. Blood vessels serve as a structural template, around which bone development takes place, and also bring together the key elements for bone homeostasis into the osteogenic microenvironment, including minerals, growth factors and osteogenic progenitor cells. Vascular endothelial growth factor (VEGF) is the master regulator of vascular growth and it is required for effective coupling of angiogenesis and osteogenesis during both skeletal development and postnatal bone repair. Here, we will review the current state of knowledge on the molecular cross-talk between angiogenesis and osteogenesis. In particular, we will focus on the role of VEGF in coupling these two processes and how VEGF dose can control the outcome, addressing in particular: (1) the direct influence of VEGF on osteogenic differentiation of mesenchymal progenitors; (2) the angiocrine functions of endothelium to regulate osteoprogenitors; (3) the role of immune cells, e.g., myeloid cells and osteoclast precursors, recruited by VEGF to the osteogenic microenvironment. Finally, we will discuss emerging strategies, based on the current biological understanding, to ensure rapid vascularization and efficient bone formation in regenerative medicine.

Vascular Endothelial Growth Factor in Cartilage Development and Osteoarthritis

Genome wide studies indicate that vascular endothelial growth factor A (VEGF) is associated with osteoarthritis (OA), and increased VEGF expression correlates with increased disease severity. VEGF is also a chondrocyte survival factor during development and essential for bone formation, skeletal growth and postnatal homeostasis. This raises questions of how the important embryonic and postnatal functions of VEGF can be reconciled with an apparently destructive role in OA. Addressing these questions, we find that VEGF acts as a survival factor in growth plate chondrocytes during development but only up until a few weeks after birth in mice. It is also required for postnatal differentiation of articular chondrocytes and the timely ossification of bones in joint regions. In surgically induced knee OA in mice, a model of post-traumatic OA in humans, increased expression of VEGF is associated with catabolic processes in chondrocytes and synovial cells. Conditional knock-down of Vegf attenuates induced OA. Intra-articular anti-VEGF antibodies suppress OA progression, reduce levels of phosphorylated VEGFR2 in articular chondrocytes and synovial cells and reduce levels of phosphorylated VEGFR1 in dorsal root ganglia. Finally, oral administration of the VEGFR2 kinase inhibitor Vandetanib attenuates OA progression.

Biochemical Changes in the Niche Following Tumor Cell Invasion

Metastatic cancer is the leading cause of all cancer related deaths. Prostate cancer (PCa) metastasizes preferentially to the bone marrow, specifically within the endosteal niche. Endosteal cells secrete homing molecules that may recruit PCa cells to the bone marrow. Once there, the biochemical signature of this niche regulates PCa fate including cellular dormancy or cell cycle arrest, reactivation and resistance to chemotherapeutics. Growth factors, interleukins, adhesion molecules, as well as extra-cellular matrix proteins can collectively change the phenotype of PCa cells. Understanding the biochemical signature of endosteal niche parasitism by PCa is imperative for the establishment of new and innovative therapeutic strategies. This review seeks to summarize these important niche signatures and the potential therapeutic approaches to target metastatic PCa within the bone marrow hematopoietic stem cell (HSC) niche. J. Cell. Biochem. 118: 1956-1964, 2017. © 2016 Wiley Periodicals, Inc.

The Top 50 Most Cited Articles in Cartilage Regeneration

The aim of this study was to identify and analyze the top 50 most cited articles in cartilage regeneration. The impact of a scientific journal can be gauged by the total number of citations it has accrued. The top 50 most cited articles involving cartilage regeneration represent the most quoted level of evidence among this new subspecialty. This study aims to identify and analyze the 50 most cited articles in cartilage regeneration. The Web of Science™ citation indexing service was utilized to determine the most frequently cited articles published after 1956 containing “cartilage regeneration” in the “topic” or “title.” The 50 most cited articles were included. The number of citations, year of publication, country of article origin, article institution, journal of publication, publication format, and authorship were then calculated for each article. The span of citations ranged from 1287 to 203 citations, with a mean of 361.02 citations per article in question. The articles originated from 11 countries, with the United States contributing 34 articles, followed by Japan with 5 articles. The articles were distributed across 34 high-impact journals. Biomaterials was the journal with the highest number of publications (seven articles) followed by the Journal of Orthopaedic Research (three articles). Of the 50 articles, 2 were clinical observational studies, 47 concerned basic science, and 1 was review article. The most cited articles involving cartilage regeneration are detected in both experimental and clinical research fields. The high ratio of basic science to clinical articles reflects the infancy of this relatively new specialty and that further clinical research is required in this area.

Soluble Factors on Stage to Direct Mesenchymal Stem Cells Fate

Mesenchymal stem cells (MSCs) are multipotent stromal cells that are identified by in vitro plastic adherence, colony-forming capacity, expression of a panel of surface molecules, and ability to differentiate at least toward osteogenic, adipogenic, and chondrogenic lineages. They also produce trophic factors with immunomodulatory, proangiogenic, and antiapoptotic functions influencing the behavior of neighboring cells. On the other hand, a reciprocal regulation takes place; in fact, MSCs can be isolated from several tissues, and depending on the original microenvironment and the range of stimuli received from there, they can display differences in their essential characteristics. Here, we focus mainly on the bone tissue and how soluble factors, such as growth factors, cytokines, and hormones, present in this microenvironment can orchestrate bone marrow-derived MSCs fate. We also briefly describe the alteration of MSCs behavior in pathological settings such as hematological cancer, bone metastasis, and bone marrow failure syndromes. Overall, the possibility to modulate MSCs plasticity makes them an attractive tool for diverse applications of tissue regeneration in cell therapy. Therefore, the comprehensive understanding of the microenvironment characteristics and components better suited to obtain a specific MSCs response can be extremely useful for clinical use.

Dual growth factor delivery from biofunctionalized allografts: Sequential VEGF and BMP-2 release to stimulate allograft remodeling

Autografts have been shown to stimulate osteogenesis, osteoclastogenesis, and angiogenesis, and subsequent rapid graft incorporation. Large structural allografts, however, suffer from limited new bone formation and remodeling, both of which are directly associated with clinical failure due to non-unions, late graft fractures, and infections, making it a priority to improve large structural allograft healing. We have previously shown the osteogenic ability of a polymer-coated allograft that delivers bone morphogenetic protein-2 both in vitro and in vivo through both burst release and sustained release kinetics. In this study, we have demonstrated largely sequential delivery of bone morphogenetic protein-2 and vascular endothelial growth factor from the same coated allograft. Release data showed that loading both growth factors onto a polymeric coating with two different techniques resulted in short-term (95% release within 2 weeks) and long-term (95% release within 5 weeks) delivery kinetics. We have also demonstrated how released VEGF, traditionally associated with angiogenesis, can also provide a stimulus for allograft remodeling via resorption. Bone marrow derived mononuclear cells were co-cultured with VEGF released from the coated allograft and showed a statistically significant (p < 0.05) and dose dependent increase in the number of tartrate-resistant acid phosphatase-positive multinucleated osteoclasts. Functionality of these osteoclasts was assessed quantitatively and qualitatively by evaluating resorption pit area from both osteo-assay plates and harvested bone. Data indicated a statistically significant higher resorption area from the cells exposed to VEGF released from the allografts over controls (p < 0.05). These results indicate that by using different loading protocols temporal control can be achieved when delivering multiple growth factors from a polymer-coated allograft. Further, released VEGF can also stimulate osteoclastogenesis that may enhance allograft incorporation, and thus mitigate long-term clinical complications. © 2017 Orthopedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1086-1095, 2017.