Bradykinin receptors and EphB2/EphrinB2 pathway in response to high glucose-induced osteoblast dysfunction and hyperglycemia-induced bone deterioration in mice

Imbalanced EphB4/EphrinB2 Signaling Modulates Bone Resorption in Periodontitis Induced by Porphyromonas gingivalis

Periodontitis, a chronic infectious disease in periodontal tissues, is characterized by an imbalance of alveolar bone resorption and remodeling, which eventually results in tooth loosening and even tooth loss. The etiology of periodontitis is polymicrobial synergy and dysbiosis, in which Porphyromonas gingivalis (P. gingivalis) is one of the primary pathogens responsible for periodontitis progression. The interplay of EphrinB2/EphB4 is crucial for osteoblast-osteoclast communication during bone remodeling and healing. This study investigates the mechanism of EphB4/EphrinB2 transduction modulating osteogenesis inhibition and bone resorption in periodontitis induced by P. gingivalis. An in vivo model of chronic periodontitis provoked by P. gingivalis was constructed, the inflammation and bone resorption were evaluated. The expression of EphB4 and EphrinB2 proteins in periodontal tissues was detected, which was also evaluated, respectively, in osteoblasts and osteoclasts infected with P. gingivalis in vitro. Then, a simulated coculture model of osteoblasts and osteoclasts was established to activate the forward and reverse pathways of EphB4/EphrinB2 with P. gingivalis infection. This study showed that P. gingivalis infection promoted alveolar bone resorption in rats and enhanced EphB4 and EphrinB2 expression in periodontal tissues. EphB4 and molecules associated with osteogenesis in osteoblasts infected with P. gingivalis were inhibited, while EphrinB2 and osteoclast differentiation-related markers in osteoclasts were activated. In conclusion, this study suggested that EphB4/EphrinB2 proteins were involved in alveolar bone remodeling in the process of periodontitis induced by P. gingivalis infection. Moreover, attenuated EphB4/EphrinB2 with P. gingivalis infection weakened osteoblast activity and enhanced osteoclast activity.

Association of sarcopenia with osteoporosis in Chinese patients with type 2 diabetes

BACKGROUND

People with type 2 diabetes mellitus (T2DM) present a higher tendency to develop sarcopenia and osteoporosis compared with the normal population. Currently, osteoporosis screening has been frequently performed among T2DM patients, but sarcopenia screening is relatively less, and the association between the two diseases remains unclear. Herein, this study aims to determine the association between sarcopenia and osteoporosis in Chinese T2DM patients.

METHODS

This was a retrospective study of 678 patients with T2DM in the First Affiliated Hospital of Wenzhou Medical University. The bone mineral density (BMD) and muscle mass were measured by using dual-energy X-ray absorptiometry scanning. The diagnostic criteria of sarcopenia referred to the consensus by the Asia Working Group for Sarcopenia (AWGS).

RESULT

Among T2DM patients, the proportion of the sarcopenia population complicated with osteoporosis was higher than that of the non-sarcopenia (30.9% vs. 8.6% in men and 46.9% vs. 33.9% in women), but only significantly in men. The BMD of the hip and femoral neck was positively correlated with skeletal muscle mass index (SMI), grip strength, and gait speed (P < 0.01). After adjusting all covariates, the association between sarcopenia and BMD showed odds ratios of 0.43 (95% CI:0.28-0.66) for the femoral neck and 0.49 (95% CI:0.32-0.73) for the hip.

CONCLUSIONS

The BMD of the hip and femoral neck in T2DM patients is related to sarcopenia-related indicators and represents an independent protective factor for sarcopenia. To reduce the risk of falls, fractures, and weakness, it is necessary to take sarcopenia assessment in people with T2DM and osteopenia/osteoporosis.

The Eph/Ephrin system in primary bone tumor and bone cancer pain

The family of Eph receptor tyrosine kinases and their Ephrin ligands system constitutes a bidirectional signaling pathway. Eph/Ephrin system coordinate a wide spectrum of pathologic processes during development, metastasis, prognosis, drug resistance and angiogenesis in carcinogenesis. Chemotherapy, surgery and radiotherapy are the most commonly used clinical treatments for primary bone tumors. Therefore, surgical resection is often unable to completely eliminate the tumor, and this is the main cause of metastasis and postoperative recurrence. A growing body of literature has been published lately revitalizing our scientific interest towards the role of Eph/Ephrins in pathogenesis and the treatment of bone tumor and bone cancer pain. This study mainly reviewed the roles of Eph/Ephrin system that has both tumor-suppressing and -promoting roles in primary bone tumors and bone cancer pain. Understanding the intracellular mechanisms of Eph/Ephrin system in tumorigenesis and metastasis of bone tumors might provide a foundation for the development of Eph/Ephrin targeted anti-cancer therapy.

Yi Shen Juan Bi Pill alleviates bone destruction in inflammatory arthritis under postmenopausal conditions by regulating ephrinB2 signaling

Yi Shen Juan Bi Pill (YSJB) is a traditional Chinese medicine (TCM) formulation that has a therapeutic effect upon rheumatoid arthritis (RA), but how YSJB affects bone destruction in arthritis under postmenopausal conditions is not known. We evaluated the therapeutic role of YSJB in bone destruction in postmenopausal arthritis, We used collagen-induced arthritis (CIA) rats who had been ovariectomized (OVX) as models and explored the possible mechanism from the synovium and bone marrow (BM). Arthritis was generated after ovariectomy or sham surgery for 12 weeks. After 14 days of primary immunization, rats were administered YSJB or estradiol valerate (EV) for 28 days. YSJB could prevent bone destruction in the inflamed joints of rats in the OVX + CIA group. CIA promoted osteoclast differentiation significantly in the synovial membrane according to tartrate resistant acid phosphatase (TRACP) staining, and OVX tended to aggravate the inflammatory reaction of CIA rats according to hematoxylin-and-eosin staining. Immunohistochemistry revealed that the synovium did not have significant changes in erythropoietin-producing hepatocellular interactor (ephrin)B2 or erythropoietin-producing hepatocellular (eph) B4 expression after YSJB treatment, but YSJB treatment reduced nuclear factor of activated T cells (NFATc)1 expression. The BM of rats in the OVX + CIA exhibited remarkable increases in the number of osteoclasts and NFATc1 expression, as well as significantly reduced expression of ephrinB2 and ephB4 compared with the CIA group and sham group. YSJB treatment reduced NFATc1 expression significantly but also increased ephrinB2 expression in the BM markedly. These data suggest that YSJB exhibit a bone-protective effect, it may be a promising therapeutic strategy for alleviating bone destruction in arthritis under postmenopausal conditions, and one of the mechanisms is associated with the modulation of ephrinB2 signaling.

ED-71 inhibited osteoclastogenesis by enhancing EphrinB2-EphB4 signaling between osteoclasts and osteoblasts in osteoporosis

BACKGROUND

Osteoporosis is a degenerative skeletal disease essentially caused by bone remodeling disorder. EphrinB2-EphB4 signaling play critical regulatory roles in bone remodeling via communication between osteoclasts and osteoblasts. Eldecalcitol (ED-71), a new vitamin D analog, is a high-potential drug for treating osteoporosis; however, its mechanism has yet to be determined. This study aims to investigate whether EphrinB2-EphB4 signal mediates the process of osteoporosis improved by ED-71.

MATERIALS AND METHODS

An ovariectomized (OVX) rat model was constructed in vivo. ED-71 at 30 ng/kg was orally administered once daily for 8 weeks. Osteoclast activity and EphrinB2-EphB4 expression were evaluated by hematoxylin and eosin staining, tartrate-resistant acid phosphatase (TRAP) staining, and immunohistochemical staining. The mRNA levels of oxidation stress factors in the bone tissue were tested by reverse transcription polymerase chain reaction (RT-PCR). An H₂O₂-stimulated model in vitro was established to simulate the status of osteoporosis. Osteoclastogenesis and associated protein were detected by TRAP staining, F-actin ring formation assay, PCR, and Western blot analysis. EprhrinB2 and EphB4 levels were determined by immunofluorescence, PCR, and Western blot analysis. EprhrinB2 small-interfering RNA knocked down the EprhrinB2 in osteoclasts, and an EphB4 antibody blocked EphB4 in osteoblasts.

RESULTS

ED-71 prevented bone loss and decreased the number of osteoclasts in vivo relative to the OVX group. In addition, the bone tissue of OVX rat displayed as an increased level of oxidation stress, which could be inhibited by ED-71. In vitro, in the simulation of osteoporosis with H₂O₂, ED-71 reversed the increase H₂O₂-induced oxidative stress. ED-71 then inhibited osteoclastogenesis and osteoclast function, accompanied by increased EphrinB2 expression in osteoclasts. Notably, EphrinB2 knockdown reversed the inhibitory effect of ED-71 on osteoclasts. ED-71 also enhanced EphB4 expression in osteoblasts in vivo and in vitro. Further research showed that ED-71 inhibited osteoclastogenesis in co-culture systems, which was weakened by blocking EphB4 in osteoblasts.

CONCLUSIONS

ED-71 inhibited osteoclastogenesis by enhancing EphrinB2-EphB4 signaling between osteoclasts and osteoblasts, preventing osteoporosis. This theory explains the role of ED-71 in the treatment of osteoporosis.

The Effect of the Angiotensin-Converting Enzyme Inhibitor on Bone Health in Castrated Hypertensive Rats Is Mediated via the Kinin-Kallikrein System

Background

In previous studies, angiotensin-converting enzyme inhibitor (ACEI) use was associated with increased bone loss, while an angiotensin II type I receptor blocker had no effect on bone loss in elder subjects, which suggested that the effect of ACEI on bone loss was not mediated through the classical renin-angiotensin system. In this study, we set to investigate whether the effect of ACEI on bone deterioration was mediated via the kinin-kallikrein system.

Methods

Six-month-old male and female spontaneously hypertensive rats were used. The effect of captopril on blood pressure, serum Ang II, and bradykinin concentration was measured in intact rats. Ovariectomy and orchidectomy were performed to establish an osteoporosis model in female and male rats, respectively. Captopril and the bradykinin receptor blocker icatibant (HOE140) were administered after operation for 12 weeks. Serum Ang II and bradykinin concentration, bone turnover markers, bone mineral density (BMD), and bone microarchitecture were evaluated. Femur samples were subjected to a mechanical test.

Results

Captopril decreased blood pressure and serum Ang II concentration and increased serum bradykinin concentration in intact rats (P < 0.05). After castration, captopril decreased serum Ang II concentration (P < 0.05); in female rats, icatibant increased serum Ang II concentration (P < 0.05). Captopril increased serum bradykinin concentration (P < 0.05); in male rats, icatibant decreased serum bradykinin concentration (P < 0.05). Captopril increased the rat urine deoxypyridinoline-creatinine ratio (DPD/Cr) and serum osteocalcin concentration (P < 0.05). Icatibant decreased urine DPD/Cr in male rats (P < 0.05) and increased osteocalcin concentration in female rats (P < 0.05). Captopril increased cancellous BMD in castrated hypertensive rats (P < 0.05), and icatibant further increased cancellous BMD (P < 0.05), which was due to the increased trabecular bone number. In mechanical testing, ACEI increased bone strength (P < 0.05), and icatibant further improved it (P < 0.05).

Conclusion

ACEI decreased bone deterioration in both male and female hypertensive rats, and the bradykinin receptor blocker further decreased bone deterioration.

NAD(P)H autofluorescence lifetime imaging enables single cell analyses of cellular metabolism of osteoblasts in vitro and in vivo via two-photon microscopy

Two-photon fluorescence lifetime microscopy (2P-FLIM) is a non-invasive optical technique that can obtain cellular metabolism information based on the intrinsic autofluorescence lifetimes of free and enzyme-bound NAD(P)H, which reflect the metabolic state of single cells within the native microenvironment of the living tissue. NAD(P)H 2P-FLIM was initially performed in bone marrow stromal cell (BMSC) cultures established from Col (I) 2.3GFP or OSX-mCherry mouse models, in which osteoblastic lineage cells were labelled with green or red fluorescence protein, respectively. Measurement of the mean NAD(P)H lifetime, τ_M, demonstrated that osteoblasts in osteogenic media had a progressively increased τ_M compared to cells in regular media, suggesting that osteoblasts undergoing mineralization had higher NAD⁺/NAD(P)H ratio and may utilize more oxidative phosphorylation (OxPhos). In vivo NAD(P)H 2P-FLIM was conducted in conjunction with two-photon phosphorescence lifetime microscopy (2P-PLIM) to evaluate cellular metabolism of GFP⁺ osteoblasts as well as bone tissue oxygen at different locations of the native cranial bone in Col (I) 2.3GFP mice. Our data showed that osteocytes dwelling within lacunae had higher τ_M than osteoblasts at the bone edge of suture and marrow space. Measurement of pO₂ showed poor correlation of pO₂ and τ_M in native bone. However, when NAD(P)H 2P-FLIM was used to examine osteoblast cellular metabolism at the leading edge of the cranial defects during repair in Col (I) 2.3GFP mouse model, a significantly lower τ_M was recorded, which was associated with lower pO₂ at an early stage of healing, indicating an impact of hypoxia on energy metabolism during bone tissue repair. Taken together, our current study demonstrates the feasibility of using non-invasive optical NAD(P)H 2P-FLIM technique to examine cellular energy metabolism at single cell resolution in living animals. Our data further support that both glycolysis and OxPhos are being used in the osteoblasts, with more mature osteoblasts exhibiting higher ratio of NAD⁺/NAD(P)H, indicating a potential change of energy mode during differentiation. Further experiments utilizing animals with genetic modification of cellular metabolism could enhance our understanding of energy metabolism in various cell types in living bone microenvironment.

Effects of Incretin-Related Diabetes Drugs on Bone Formation and Bone Resorption

Patients with type 2 diabetes have an increased risk of fracture compared to the general population. Glucose absorption is accelerated by incretin hormones, which induce insulin secretion from the pancreas. The level of the incretin hormone, glucagon-like peptide-1 (GLP-1), shows an immediate postprandial increase, and the circulating level of intact GLP-1 is reduced rapidly by dipeptidyl peptidase-4 (DPP-4)-mediated inactivation. Therefore, GLP-1 receptor agonists and DPP-4 inhibitors are effective in the treatment of type 2 diabetes. However, these incretin-related diabetic agents have been reported to affect bone metabolism, including bone formation and resorption. These agents enhance the expression of bone markers, and have been applied to improve bone quality and bone density. In addition, they have been reported to suppress chronic inflammation and reduce the levels of inflammatory cytokine expression. Previously, we reported that these incretin-related agents inhibited both the expression of inflammatory cytokines and inflammation-induced bone resorption. This review presents an overview of current knowledge regarding the effects of incretin-related diabetes drugs on osteoblast differentiation and bone formation as well as osteoclast differentiation and bone resorption. The mechanisms by which incretin-related diabetes drugs regulate bone formation and bone resorption are also discussed.

Pharmic Activation of PKG2 Alleviates Diabetes-Induced Osteoblast Dysfunction by Suppressing PLCβ1-Ca2+-Mediated Endoplasmic Reticulum Stress

As reported in our previous study, cinaciguat can improve implant osseointegration in type 2 diabetes mellitus (T2DM) rats by reactivating type 2 cGMP-dependent protein kinase (PKG2), but the downstream mechanisms remain unclear. In the present study, we investigated the favorable effect of cinaciguat on primary rat osteoblast, which was cultivated on titanium disc under vitro T2DM conditions (25 mM glucose and 200 μM palmitate), and clarified the therapeutic mechanism by proteomic analysis. The results demonstrated that T2DM medium caused significant downregulation of PKG2 and induced obvious osteoblast dysfunction. And overexpression of PKG2 by lentivirus and cinaciguat could promote cell proliferation, adhesion, and differentiation, leading to decreased osteoblasts injury. Besides, proteomic analysis revealed the interaction between PKG2 and phospholipase Cβ1 (PLCβ1) in the cinaciguat addition group, and we further verified that upregulated PKG2 by cinaciguat could inhibit the activation of PLCβ1, then relieve intracellular calcium overload, and suppress endoplasmic reticulum (ER) stress to ameliorate osteoblast functions under T2DM condition. Collectively, these findings provided the first detailed mechanisms responsible for cinaciguat provided a favorable effect on promoting osseointegration in T2DM and demonstrated a new insight that diabetes mellitus-induced the aberrations in PKG2-PLCβ1-Ca²⁺-ER stress pathway was one underlying mechanism for poor osseointegration.

Glucose Metabolism in Osteoblasts in Healthy and Pathophysiological Conditions

Bone tissue in vertebrates is essential to performing movements, to protecting internal organs and to regulating calcium homeostasis. Moreover, bone has also been suggested to contribute to whole-body physiology as an endocrine organ, affecting male fertility; brain development and cognition; and glucose metabolism. A main determinant of bone quality is the constant remodeling carried out by osteoblasts and osteoclasts, a process consuming vast amounts of energy. In turn, clinical conditions associated with impaired glucose metabolism, including type I and type II diabetes and anorexia nervosa, are associated with impaired bone turnover. As osteoblasts are required for collagen synthesis and matrix mineralization, they represent one of the most important targets for pharmacological augmentation of bone mass. To fulfill their function, osteoblasts primarily utilize glucose through aerobic glycolysis, a process which is regulated by various molecular switches and generates adenosine triphosphate rapidly. In this regard, researchers have been investigating the complex processes of energy utilization in osteoblasts in recent years, not only to improve bone turnover in metabolic disease, but also to identify novel treatment options for primary bone diseases. This review focuses on the metabolism of glucose in osteoblasts in physiological and pathophysiological conditions.

Eph-Ephrin Signaling Mediates Cross-Talk Within the Bone Microenvironment

Skeletal integrity is maintained through the tightly regulated bone remodeling process that occurs continuously throughout postnatal life to replace old bone and to repair skeletal damage. This is maintained primarily through complex interactions between bone resorbing osteoclasts and bone forming osteoblasts. Other elements within the bone microenvironment, including stromal, osteogenic, hematopoietic, endothelial and neural cells, also contribute to maintaining skeletal integrity. Disruption of the dynamic interactions between these diverse cellular systems can lead to poor bone health and an increased susceptibility to skeletal diseases including osteopenia, osteoporosis, osteoarthritis, osteomalacia, and major fractures. Recent reports have implicated a direct role for the Eph tyrosine kinase receptors and their ephrin ligands during bone development, homeostasis and skeletal repair. These membrane-bound molecules mediate contact-dependent signaling through both the Eph receptors, termed forward signaling, and through the ephrin ligands, referred to as reverse signaling. This review will focus on Eph/ ephrin cross-talk as mediators of hematopoietic and stromal cell communication, and how these interactions contribute to blood/ bone marrow function and skeletal integrity during normal steady state or pathological conditions.

The role of EphB4/ephrinB2 signaling in root repair after orthodontically-induced root resorption

INTRODUCTION

This study aimed to investigate the effect of EphB4/ephrinB2 signaling on orthodontically-induced root resorption repair and the possible molecular mechanism behind it.

METHODS

Seventy-two 6-week-old male Wistar rats were randomly divided into 3 groups: blank control group, physiological regeneration group (PHY), and EphB4 inhibitor local injection group (INH). A root repair model was built on experimental rats of the PHY and INH groups. The animals in the INH groups received a daily periodontal local injection of EphB4 inhibitor NVP-BHG712, whereas the blank control group and PHY groups received only the vehicle.

RESULTS

Histologic staining and microcomputed tomography analysis showed that root regeneration was inhibited in the INH group compared with the PHY group with a greater number of osteoclasts. Immunohistochemical staining showed active EphB4/ephrinB2 signaling activities during root regeneration. The cementogenesis-related factors cementum attachment protein, alkaline phosphatase, osteopontin, and runt-related transcription factor 2, and osteoclastic-related factors RANKL and osteoprotegerin were affected by regulated EphB4/ephrinB2 signaling.

CONCLUSIONS

These findings demonstrated that the EphB4/ephrinB2 signaling might be a promising therapeutic target for novel therapeutic approaches to reduce orthodontically-induced root resorption through enhancement of cementogenesis.

Correlation of Osteoporosis in Patients With Newly Diagnosed Type 2 Diabetes: A Retrospective Study in Chinese Population

This study aimed to explore the risk factors attributed to osteoporosis in newly type 2 diabetes mellitus (T2DM) patients. This study aimed to recruit 244 T2DM patients and 218 non-diabetic controls. We collected demographic characteristics, medical history, bone mineral density and biomarkers including bone specific alkaline phosphatase (BALP), osteocalcin, N-terminal peptide of type I procollagen (P1NP), tartrate-resistant acid phosphatase 5b (TRCAP-5b), β-Cross Laps of type I collagen-containing cross-linked C-telopeptide (β-CTX), 25-hydroxyvitamin D, parathyroid hormone were recorded or detected. Bone mineral density (BMD) was our primary outcome. Based on the result of BMD, we divided both the control group and T2DM group into three subgroups: normal bone mass, osteopenia and osteoporosis. In control group, we found age, sex, menopausal status, BMI, P1NP, BALP, TRACP-5b, osteocalcin, and corrected serum calcium are differential among three subgroups. In T2DM group, we found age, sex, menopausal status, drinking status, BMI, HbA1c, TRACP-5b and OC were differential among three subgroups. In T2DM and control groups, age, female, postmenopausal status, BALP, TRACP-5b and osteocalcin were positively correlated while BMI was negatively correlated with osteoporosis. In control group, β-CTX was positively correlated with osteoporosis. In T2DM group, HbA1c and corrected serum calcium concentration were positively correlated with osteoporosis. After further adjustment of age, BMI in male, TRACP-5b was positively correlated with the risk of osteoporosis in newly diagnosed T2DM. After adjusted of age, BMI and menopausal status in female, OC was positively correlated with the risk of osteoporosis in newly diagnosed T2DM and controls. In female T2DM, BALP and P1NP were positively correlated with the risk of osteoporosis. In conclusion, age, BMI and menopausal status are common risk factors for osteoporosis in diabetic and non-diabetic patients, however TRACP-5b, BALP and osteocalcin are special risk factors for osteoporosis in newly diagnosed T2DM patients but not non-diabetic patients, which may be applied to identify osteoporosis risk in T2DM patients, but this result needs to be proven with fracture data.

Osteocytes and Diabetes: Altered Function of Diabetic Osteocytes

PURPOSE OF REVIEW

Diabetes mellitus is a prevalent chronic disease affecting millions of people in the world. Bone fragility is a complication found in diabetic patients. Although osteoblasts and osteoclasts are directly affected by diabetes, herein we focus on how the diabetic state-based on hyperglycemia and accumulation of advanced glycation end products among other features-impairs osteocyte functions exerting deleterious effects on bone.

RECENT FINDINGS

In the last years, several studies described that diabetic conditions cause morphological modifications on lacunar-canalicular system, alterations on osteocyte mechanoreceptors and intracellular pathways and on osteocyte communication with other cells through the secretion of proteins such as sclerostin or RANKL. This article gives an overview of events occurring in diabetic osteocytes. In particular, mechanical responses seem to be seriously affected in these conditions, suggesting that mechanical sensibility could be a target for future research in the field.

Impact of diabetes mellitus simulations on bone cell behavior through in vitro models

Diabetes mellitus (DM) is related to impaired bone healing and an increased risk of bone fractures. While it is recognized that osteogenic differentiation and the function of osteoblasts are suppressed in DM, the influence of DM on osteoclasts is still unclear. Hyperglycemia and inflammatory environment are the hallmark of DM that causes dysregulation of various pro-inflammatory cytokines and alternated gene expression in periodontal ligament cells, osteoblasts, osteocytes, osteoclasts, and osteoclast precursors. A methodological review on conceptual and practical implications of in vitro study models is used for DM simulation on bone cells. Several major databases were screened to find literature related to the study objective. Published literature within last 20 years that used in vitro DM-simulated models to study how DM affects the cellular behavior of bone cells were selected for this review. Studies utilizing high glucose and serum acquired from diabetic animals are the mainly used methods to simulate the diabetic condition. The combination with various simulating factors such as lipopolysaccharide (LPS), hydrogen peroxide (H₂O₂), and advanced glycation end products (AGEs) have been reported in diabetic situations in vitro, as well. Through screening procedure, it was evident DM-simulated conditions exerted negative impact on bone-related cells. However, inconsistent results were found among different reported studies, which could be due to variation in culture conditions, concentrations of the stimulating factors and cell lineage, etc. This manuscript has concisely reviewed currently existing DM-simulated in vitro models and provides valuable insights of detailed components in simulating DM conditions in vitro. Studies using DM-simulated microenvironment revealed that in vitro simulation negatively impacted periodontal ligament cells, osteoblasts, osteocytes, osteoclasts, and osteoclast precursors. Contrarily, studies also indicated beneficial influence on bone-related cells when such conditions are reversed.

The Recombinant Protein EphB4-Fc Changes the Ti Particle-Mediated Imbalance of OPG/RANKL via EphrinB2/EphB4 Signaling Pathway and Inhibits the Release of Proinflammatory Factors In Vivo

Aseptic loosening caused by wear particles is one of the common complications after total hip arthroplasty. We investigated the effect of the recombinant protein ephB4-Fc (erythropoietin-producing human hepatocellular receptor 4) on wear particle-mediated inflammatory response. In vitro, ephrinB2 expression was analyzed using siRNA-NFATc1 (nuclear factor of activated T-cells 1) and siRNA-c-Fos. Additionally, we used Tartrate-resistant acid phosphatase (TRAP) staining, bone pit resorption, Enzyme-linked immunosorbent assay (ELISA), as well as ephrinB2 overexpression and knockdown experiments to verify the effect of ephB4-Fc on osteoclast differentiation and function. In vivo, a mouse skull model was constructed to test whether the ephB4-Fc inhibits osteolysis and inhibits inflammation by micro-CT, H&E staining, immunohistochemistry, and immunofluorescence. The gene expression of ephrinB2 was regulated by c-Fos/NFATc1. Titanium wear particles activated this signaling pathway to the promoted expression of the ephrinB2 gene. However, ephrinB2 protein can be activated by osteoblast membrane receptor ephB4 to inhibit osteoclast differentiation. In in vivo experiments, we found that ephB4 could regulate Ti particle-mediated imbalance of OPG/RANKL, and the most important finding was that ephB4 relieved the release of proinflammatory factors. The ephB4-Fc inhibits wear particle-mediated osteolysis and inflammatory response through the ephrinB2/EphB4 bidirectional signaling pathway, and ephrinB2 ligand is expected to become a new clinical drug therapeutic target.

High glucose inhibits osteogenic differentiation and proliferation of MC3T3‑E1 cells by regulating P2X7

Diabetes mellitus adversely affects human bones and increases the risk of developing osteoporosis. In the present study, treatment with 30 mmol/l glucose was used to establish a high glucose (HG) cell model in vitro. Plasmids were used to overexpress the P2X purinoceptor 7 (P2X7) gene. Brilliant blue G and (4‑benzoyl‑benzoyl)‑ATP were used as a P2X7 antagonist and agonist, respectively. Proliferation of osteogenic MC3T3‑E1 cells and alkaline phosphatase (ALP) activity were determined using MTT and colorimetric assays, respectively. Alizarin Red S was used to assess calcification of MC3T3‑E1 cells. Western blotting and reverse transcription‑quantitative PCR were performed to determine protein and mRNA expression levels. The results demonstrated that HG inhibited MC3T3‑E1 cell proliferation and P2X7 expression, reduced calcification, and downregulated the expression levels of ALP and osteocalcin (Ocn) in MC3T3‑E1 cells. Overexpression of P2X7 in HG conditions increased calcification and proliferation, and upregulated the levels of ALP and Ocn in MC3T3‑E1 cells. Inhibition of P2X7 downregulated the expressions of ALP and Ocn in MC3T3‑E1 cells under HG conditions. Therefore, the present results indicated that HG caused damage to osteogenic MC3T3‑E1 cells. Thus, P2X7 may be a regulatory factor that may be used to counteract the effects of HG on osteogenesis.

Inhibition on angiotensin-converting enzyme exerts beneficial effects on trabecular bone in orchidectomized mice

BACKGROUND

This study aimed to study the osteo-preservative effects of captopril, an inhibitor on angiotensin-converting enzyme (ACE), on bone mass, micro-architecture and histomorphology as well as the modulation of captopril on skeletal renin-angiotensin system (RAS) and regulators for bone metabolism in mice with bilateral orchidectomy.

METHODS

The orchidectomized (ORX) mice were orally administered with vehicle or captopril at low dose (10mg/kg) and high dose (50mg/kg) for six weeks. The distal femoral end, the proximal tibial head and the lumbar vertebra (LV) were stained by hematoxylin and eosin, Safranin O/Fast Green and masson-trichrome. Micro-computed tomography was performed to measure bone mineral density (BMD).

RESULTS

Treatment with captopril increased trabecular bone area at distal metaphysis of femur, proximal metaphysis of tibia and LV-4, moreover, high dose of captopril significantly elevated trabecular BMD of LV-2 and LV-5. The mRNA expressions of renin receptor, angiotensinogen, carbonic anhydrase II, matrix metalloproteinase-9, and tumor necrosis factor-alpha were significantly decreased in tibia of ORX mice following treatment with captopril. The administration with captopril enhanced the ratio of OPG/RANKL mRNA expression, the mRNA expression of transforming growth factor-beta and the protein expression of bradykinin receptor-1.

CONCLUSIONS

The inhibition on ACE by captopril exerts beneficial effects on trabecular bone of ORX mice. The therapeutic efficacy may be attributed to the regulation of captopril on local RAS and cytokines in bone.

Chronic hyperglycemia affects bone metabolism in adult zebrafish scale model

Type II diabetes mellitus is a metabolic disease characterized by chronic hyperglycemia that induce other pathologies including diabetic retinopathy and bone disease. The mechanisms implicated in bone alterations induced by type II diabetes mellitus have been debated for years and are not yet clear because there are other factors involved that hide bone mineral density alterations. Despite this, it is well known that chronic hyperglycemia affects bone health causing fragility, mechanical strength reduction and increased propensity of fractures because of impaired bone matrix microstructure and aberrant bone cells function. Adult Danio rerio (zebrafish) represents a powerful model to study glucose and bone metabolism. Then, the aim of this study was to evaluate bone effects of chronic hyperglycemia in a new type II diabetes mellitus zebrafish model created by glucose administration in the water. Fish blood glucose levels have been monitored in time course experiments and basal glycemia was found increased. After 1 month treatment, the morphology of the retinal blood vessels showed abnormalities resembling to the human diabetic retinopathy. The adult bone metabolism has been evaluated in fish using the scales as read-out system. The scales of glucose-treated fish didn't depose new mineralized matrix and shown bone resorption lacunae associated with an intense osteoclast activity. In addition, hyperglycemic fish scales have shown a significant decrease of alkaline phosphatase activity and increase of tartrate-resistant acid phosphatase activity, in association with alterations in other bone-specific markers. These data indicates an imbalance in bone metabolism, which leads to the osteoporotic-like phenotype visualized through scale mineral matrix staining. The zebrafish model of hyperglycemic damage can contribute to elucidate in vivo the molecular mechanisms of metabolic changes, which influence the bone tissues regulation in human diabetic patients.

Involvement of skeletal renin-angiotensin system and kallikrein-kinin system in bone deteriorations of type 1 diabetic mice with estrogen deficiency

AIMS

This study was aimed to investigate the involvement of skeletal renin-angiotensin system (RAS) and kallikrein-kinin system (KKS) in bone deteriorations of mice in response to the combination treatment of estrogen deficiency and hyperglycemia.

METHODS

The female C57BL/6J mice were sham-operated or ovariectomized with vehicle or streptozotocin (STZ) treatment. Two weeks later, the biochemistries in serum and urine were determined by standard colorimetric methods or ELISA. The H&E and TRAP staining were performed at the tibial proximal metaphysis. The polymerase chain reaction and immunoblotting were applied for molecular analysis on mRNA and protein expression.

RESULTS

The mice after treating with ovariectomy and STZ showed the decreased level of serum Ca and the increased level of serum PTH and urine Ca. The H&E staining showed trabecular bone abnormalities as demonstrated by the loss, disconnection and separation of trabecular bone network as well as the loss of chondrocytes and appearance of chondrocyte cluster at growth plate of tibia. The significant increase of matured osteoclast number was shown in group with double treatments. The combination treatment significantly up-regulated mRNA expression of AGT, ACE, renin receptor, MMP-9 and CAII, and protein expression of renin, and decreased the ratio of OPG/RANKL and the expression of bradykinin receptors in bone tissue.

CONCLUSION

Ovariectomy combined with STZ induction produced more detrimental actions on bone through the activation of local bone RAS and the down-regulation of bradykinin receptors, as compared to the respective single treatment.