Claudin 11 regulates bone homeostasis via bidirectional EphB4-EphrinB2 signaling

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.

Poly(ethylenimine)-Cyclodextrin-Based Cationic Polymer Mediated HIF-1α Gene Delivery for Hindlimb Ischemia Treatment

Hindlimb ischemia is a common disease worldwide featured by the sudden decrease in limb perfusion, which usually causes a potential threat to limb viability and even amputation or death. Revascularization has been defined as the gold-standard therapy for hindlimb ischemia. Considering that vascular injury recovery requires cellular adaptation to the hypoxia, hypoxia-inducible factor 1 α (HIF-1α) is a potential gene for tissue restoration and angiogenesis. In this manuscript, effective gene delivery vector PEI-β-CD (PC) was reported for the first application in the hindlimb ischemia treatment to deliver HIF-1α plasmid in vitro and in vivo. Our in vitro finding demonstrated that PC/HIF-1α-pDNA could be successfully entered into the cells and mediated efficient gene transfection with good biocompatibility. More importantly, under hypoxic conditions, PC/HIF-1α-pDNA could up-regulate the HUEVC cell viability. In addition, the mRNA levels of VEGF, Ang-1, and PDGF were upregulated, and transcriptome results also demonstrated that the cell-related function of response to hypoxia was enhanced. The therapeutic effect of PC/HIF-1α-pDNA was further estimated in a murine acute hindlimb ischemia model, which demonstrated that intramuscular injection of PC/HIF-1α-pDNA resulted in significantly increased blood perfusion and alleviation in tissue damage, such as tissue fibrosis and inflammation. The results provide a rationale that HIF-1α-mediated gene therapy might be a practical strategy for the treatment of limb ischemia.

Comprehensive Analysis of SLC35A2 in Pan-Cancer and Validation of Its Role in Breast Cancer

Purpose

Elucidation of the oncogenic role of SLC35A2 in human tumors and the potential function and clinical significance in breast cancer.

Methods

Pan-cancer analysis was performed via various bioinformatics tools to explain the pathogenic role of SLC35A2. A prognostic nomogram was also developed based on the SLC35A2 expression and clinicopathological characteristics in breast cancer patients. In addition, the role of SLC35A2 was validated in breast cancer by in vivo and in vitro experiments.

Results

SLC35A2 expression is increased in 27 tumor types, and its high expression is substantially correlated with poor prognosis in patients with a variety of cancers. Receiver operating characteristic (ROC) curves showed that SLC35A2 expression levels could accurately distinguish most tumor tissues from normal tissues. High SLC35A2 expression was linked to increased immune infiltration in myeloid-derived suppressor cells (MDSC), as well as immune checkpoints, ferroptosis-related genes, tumor mutational burden (TMB), and microsatellite instability (MSI). SLC35A2 may be involved in tumorigenesis by regulating the glycosylation process. Furthermore, multivariate Cox analysis showed that SLC35A2 was an independent prognostic factor for breast cancer. And the nomogram model had good predictive accuracy for the prognosis of breast cancer patients. Meanwhile, cellular experiments demonstrated that knockdown of SLC35A2 could significantly inhibit the proliferation, migration and invasion of breast cancer cells, while increasing the protein level of E-cadherin and decreasing N-cadherin. A nude mouse xenograft model showed that inhibition of SLA35A2 expression could significantly inhibit tumor growth.

Conclusion

SLC35A2 has good diagnostic and prognostic values in multiple cancers and is closely related to tumor immune infiltration. In addition, SLA35A2 as an oncogene in breast cancer may be involved in the progression of epithelial mesenchymal transition (EMT).

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.

Low-intensity pulsed ultrasound regulates osteoblast-osteoclast crosstalk via EphrinB2/EphB4 signaling for orthodontic alveolar bone remodeling

Background: The limited regenerative potential of periodontal tissue remains a challenge in orthodontic treatment, especially with respect to alveolar bone remodeling. The dynamic balance between the bone formation of osteoblasts and the bone resorption of osteoclasts controls bone homeostasis. The osteogenic effect of low-intensity pulsed ultrasound (LIPUS) is widely accepted, so LIPUS is expected to be a promising method for alveolar bone regeneration. Osteogenesis is regulated by the acoustic mechanical effect of LIPUS, while the cellular perception, transduction mode and response regulation mechanism of LIPUS stimuli are still unclear. This study aimed to explore the effects of LIPUS on osteogenesis by osteoblast-osteoclast crosstalk and the underlying regulation mechanism. Methods: The effects of LIPUS on orthodontic tooth movement (OTM) and alveolar bone remodeling were investigated via rat model by histomorphological analysis. Mouse bone marrow mesenchymal stem cells (BMSCs) and bone marrow monocytes (BMMs) were purified and used as BMSC-derived osteoblasts and BMM-derived osteoclasts, respectively. The osteoblast-osteoclast co-culture system was used to evaluate the effect of LIPUS on cell differentiation and intercellular crosstalk by Alkaline phosphatase (ALP), Alizarin Red S (ARS), tartrate-resistant acid phosphatase (TRAP) staining, real-time quantitative PCR, western blotting and immunofluorescence. Results: LIPUS was found to improve OTM and alveolar bone remodeling in vivo, promote differentiation and EphB4 expression in BMSC-derived osteoblasts in vitro, particularly when cells were directly co-cultured with BMM-derived osteoclasts. LIPUS enhanced EphrinB2/EphB4 interaction between osteoblasts and osteoclasts in alveolar bone, activated the EphB4 receptor on osteoblasts membrane, transduced LIPUS-related mechanical signals to the intracellular cytoskeleton, and gave rise to the nuclear translocation of YAP in Hippo signaling pathway, thus regulating cell migration and osteogenic differentiation. Conclusions: This study shows that LIPUS modulates bone homeostasis by osteoblast-osteoclast crosstalk via EphrinB2/EphB4 signaling, which benefits the balance between OTM and alveolar bone remodeling.

Osteoblast Jmjd3 regulates osteoclastogenesis via EphB4 and RANKL signalling

BACKGROUND

Osteoblasts suppress osteoclastogenesis during the reversal phase of bone remodelling and the mechanism needs to be further investigated. Here, we investigated the role of histone demethylase Jumonji domain-containing 3 (Jmjd3) in osteoblasts on regulating osteoclastogenesis.

METHODS

Jmjd3 expression was silenced in osteoblasts. Osteoblasts and osteoclasts were co-cultured in direct or indirect contact ways, and osteoclastogenesis was determined by tartrate-resistant acid phosphatase (TRAP) staining and Western blotting. Additionally, Ephrin receptor B4 (EphB4) and receptor activator of nuclear factor-kappa Β ligand (RANKL) expression were quantified in osteoblasts via real-time PCR, Western blotting, and enzyme-linked immunosorbent assay. Subsequently, EphB4 was overexpressed in osteoblasts and RANKL expression and osteoclastogenesis was quantified.

RESULTS

Osteoclastogenesis and marker protein expression levels was promoted when osteoclasts were co-cultured with Jmjd3-silenced osteoblasts. Silencing of Jmjd3 expression in osteoblasts decreased EphB4 expression, owing to suppression of demethylation of H3K27me3 on the promoter region of EphB4. Whereas RANKL expression was upregulated in Jmjd3-silenced osteoblasts. Overexpression of EphB4 in osteoblasts inhibited osteoclastogenesis and RANKL expression.

CONCLUSION

Jmjd3 in osteoblasts is a crucial regulator of osteoblast-to-osteoclast communication through EphB4-EphrinB2, RANKL-RANK and EphB4-RANKL signalling axes, suggesting the pivotal role of Jmjd3 in bone remodelling process in bone destruction disease such as chronic apical periodontitis.

CLDN6 inhibits breast cancer metastasis through WIP-dependent actin cytoskeleton-mediated autophagy

BACKGROUND

As a breast cancer suppressor gene, CLDN6 overexpression was found to inhibit breast cancer metastasis in our previous studies, but the specific mechanism remains unclear. This study aimed to clarify the role and mechanism of CLDN6 in inhibiting breast cancer metastasis.

METHODS

Western blot, immunofluorescence and transmission electron microscopy were performed to detect autophagy. Wound healing, transwell assays and lung metastasis mouse models were used to examine breast cancer metastasis. Phalloidin staining and immunofluorescent staining were used to observe actin cytoskeleton. mRNA seq, RT-PCR, western blot, chromatin immunoprecipitation, dual luciferase reporter assay, co-immunoprecipitation and immunofluorescence were performed to define the molecular mechanism. The expression levels and clinical implication of CLDN6, WIP and LC3 in breast cancer tissues were evaluated using immunohistochemistry.

RESULTS

We demonstrated that CLDN6 inhibited breast cancer metastasis through autophagy in vitro and vivo. We unraveled a novel mechanism that CLDN6 regulated autophagy via WIP-dependent actin cytoskeleton assembly. Through its PDZ-binding motif, overexpressed CLDN6 interacted with JNK and upregulated JNK/c-Jun pathway. C-Jun promoted WIP expression at the transcriptional level. Notably, we observed c-Jun transcriptionally upregulated CLDN6 expression, and there was a positive feedback loop between CLDN6 and JNK/c-Jun. Finally, we found that CLDN6, WIP and LC3 expression correlated with each other, and WIP expression was significantly associated with lymph node metastasis of breast cancer patients.

CONCLUSIONS

The data provide a new insight into the inhibitory effects of CLDN6-mediated autophagy on breast cancer metastasis, and revealed the new mechanism of CLDN6 regulating autophagy through WIP-dependent actin cytoskeleton. Our findings enrich the theoretical basis for CLDN6 as a potential biomarker for breast cancer diagnosis and therapy.

Histological functions of parathyroid hormone on bone formation and bone blood vessels

BACKGROUND

The intermittent administration of parathyroid hormone (PTH) has been prescribed to osteoporotic patients due to its bone anabolic effects. In addition to its actions on bone cells, PTH appears to affect bone-specific blood vessels. These blood vessels are derived from bone marrow sinusoids, which express EphB4, a hallmark of veinous vascular endothelial cells. Given the presence of osteo-vascular interactions, it is important to elucidate the effects of PTH on bone cells and blood vessels in murine models.

HIGHLIGHTS

PTH stimulates preosteoblastic proliferation and osteoblastic bone formation. The former appears to be directly affected by PTH, whereas the latter requires osteoclast-mediated coupling. The administration of PTH through high-frequency dosage schemes accelerates bone turnover featuring remodeling-based bone formation, whereas low-frequency schemes cause mainly remodeling-based and partly modeling-based bone formation. Normally, many blood vessels lack alpha smooth muscle actin (αSMA)-immunoreactive vascular muscle cells surrounding basement membranes, indicating them being capillaries. However, PTH administration increases the number of blood vessels surrounded by αSMA-positive cells. These αSMA-positive cells spread out of blood vessels and express alkaline phosphatase and c-kit, suggesting their potential to differentiate into osteogenic and vascular endothelial/perivascular cells. Unlike bone cells, αSMA-positive cells did not appear in the periphery of blood vessels in the kidney and liver, and the thickness of the tunica media did not change regardless of PTH administration.

CONCLUSION

Based on the results of the study and presence of osseous-vascular interactions, PTH appears to influence not only osteoblastic cells, but also blood vessels in bone.

Transcriptome analysis reveals the mechanism of stromal cell-derived factor-1 and exendin-4 synergistically promoted periodontal ligament stem cells osteogenic differentiation

Stromal cell-derived factor-1 (SDF-1) and Exendin-4 (EX-4) play beneficial roles in promoting periodontal ligament stem cells (PDLSCs) osteogenic differentiation, while the detailed mechanism has not been clarified. In this study, we aimed to evaluate the biological mechanism of SDF-1 and EX-4 alone or synergistic application in regulating PDLSCs differentiation by RNA-sequencing (RNA-seq). A total of 110, 116 and 109 differentially expressed genes (DEGs) were generated in osteogenic medium induced PDLSCs treated by SDF-1, EX-4, and SDF-1+EX-4, respectively. The DEGs in SDF-1 group were enriched in signal transduction related signaling pathways; the DEGs in EX-4 group were enriched in metabolism and biosynthesis-related pathways; and the DEGs generated in SDF-1+EX-4 group were mainly enriched in RNA polymerase II transcription, cell differentiation, chromatin organization, protein phosphorylation pathways. Based on Venn analysis, a total of 37 specific DEGs were identified in SDF-1+EX-4 group, which were mainly enriched in negative regulation of autophagy and cellular component disassembly signaling pathways. Short time-series expression miner (STEM) analysis grouped all expressed genes of PDLSCs into 49 clusters according to the dynamic expression patterns and 25 genes, including NRSN2, CHD9, TUBA1A, distributed in 10 gene clusters in SDF-1+EX-4 treated PDLSCs were significantly up-regulated compared with the SDF-1 and EX-4 alone groups. The gene set enrichment analysis indicated that SDF-1 could amplify the role of EX-4 in regulating varied signaling pathways, such as type II diabetes mellitus and insulin signaling pathways; while EX-4 could aggravate the effect of SDF-1 on PDLSCs biological roles via regulating primary immunodeficiency, tight junction signaling pathways. In summary, our study confirmed that SDF-1 and EX-4 combined application could enhance PDLSCs biological activity and promote PDLSCs osteogenic differentiation by regulating the metabolism, biosynthesis and immune-related signaling pathways.

Histochemical assessment on the cellular interplay of vascular endothelial cells and septoclasts during endochondral ossification in mice

This study was aimed to verify the cellular interplay between vascular endothelial cells and surrounding cells in the chondro-osseous junction of murine tibiae. Many CD31-positive endothelial cells accompanied with Dolichos Biflorus Agglutinin lectin-positive septoclasts invaded into the hypertrophic zone of the tibial epiphyseal cartilage. MMP9 immunoreactive cytoplasmic processes of vascular endothelial cells extended into the transverse partitions of cartilage columns. In contrast, septoclasts included several large lysosomes which indicate the incorporation of extracellular matrices despite no immunopositivity for F4/80-a hallmark of macrophage/monocyte lineage. In addition, septoclasts were observed in c-fos-/- mice but not in Rankl-/- mice. Unlike c-fos-/- mice, Rankl-/- mice showed markedly expanded hypertrophic zone and the irregular shape of the chondro-osseous junction. Immunoreactivity of platelet-derived growth factor-bb, which involved in angiogenic roles in the bone, was detected in not only osteoclasts but also septoclasts at the chondro-osseous junction. Therefore, septoclasts appear to assist the synchronous vascular invasion of endothelial cells at the chondro-osseous junction. Vascular endothelial cells adjacent to the chondro-osseous junction possess endomucin but not EphB4, whereas those slightly distant from the chondro-osseous junction were intensely positive for both endomucin and EphB4, while being accompanied with ephrinB2-positive osteoblasts. Taken together, it is likely that vascular endothelial cells adjacent to the chondro-osseous junction would interplay with septoclasts for synchronous invasion into the epiphyseal cartilage, while those slightly distant from the chondro-osseous junction would cooperate with osteoblastic activities presumably by mediating EphB4/ephrinB2.

MINI-ABSTRACT

Our original article demonstrated that vascular endothelial cells adjacent to the chondro-osseous junction would interplay with septoclasts for synchronous invasion into the epiphyseal cartilage, while those slightly distant from the chondro-osseous junction would cooperate with osteoblastic activities presumably by mediating EphB4/ephrinB2. (A figure that best represents your paper is Fig. 5c).

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.

Adverse Impact of Heavy Metals on Bone Cells and Bone Metabolism Dependently and Independently through Anemia

Mounting evidence is revealing that heavy metals can incur disordered bone homeostasis, leading to the development of degenerative bone diseases, including osteoporosis, osteoarthritis, degenerative disk disease, and osteomalacia. Meanwhile, heavy metal-induced anemia has been found to be intertwined with degenerative bone diseases. However, the relationship and interplay among these adverse outcomes remain elusive. Thus, it is of importance to shed light on the modes of action (MOAs) and adverse outcome pathways (AOPs) responsible for degenerative bone diseases and anemia under exposure to heavy metals. In the current Review, the epidemiological and experimental findings are recapitulated to interrogate the contributions of heavy metals to degenerative bone disease development which may be attributable dependently and independently to anemia. A few likely mechanisms are postulated for anemia-independent degenerative bone diseases, including dysregulated osteogenesis and osteoblastogenesis, imbalanced bone formation and resorption, and disturbed homeostasis of essential trace elements. By contrast, remodeled bone microarchitecture, inhibited erythropoietin production, and disordered iron homeostasis are speculated to account for anemia-associated degenerative bone disorders upon heavy metal exposure. Together, this Review aims to elaborate available literature to fill in the knowledge gaps in understanding the detrimental effects of heavy metals on bone cells and bone homeostasis through different perspectives.

Dual Oxidase Maturation Factor 1 Positively Regulates RANKL-Induced Osteoclastogenesis via Activating Reactive Oxygen Species and TRAF6-Mediated Signaling

Receptor activator of NF-κB ligand (RANKL) induces generation of intracellular reactive oxygen species (ROS), which act as second messengers in RANKL-mediated osteoclastogenesis. Dual oxidase maturation factor 1 (Duoxa1) has been associated with the maturation of ROS-generating enzymes including dual oxidases (Duox1 and Duox2). In the progression of osteoclast differentiation, we identified that only Duoxa1 showed an effective change upon RANKL stimulation, but not Duox1, Duox2, and Duoxa2. Therefore, we hypothesized that Duoxa1 could independently act as a second messenger for RANKL stimulation and regulate ROS production during osteoclastogenesis. Duoxa1 gradually increased during RANKL-induced osteoclastogenesis. Using siRNA or retrovirus transduction, we found that Duoxa1 regulated RANKL-stimulated osteoclast formation and bone resorption positively. Furthermore, knockdown of Duoxa1 decreased the RANKL-induced ROS production. During Duoxa1-related control of osteoclastogenesis, activation of tumor necrosis factor receptor-associated factor 6 (TRAF6)-mediated early signaling molecules including MAPKs, Akt, IκB, Btk, Src and PLCγ2 was affected, which sequentially modified the mRNA or protein expression levels of key transcription factors in osteoclast differentiation, such as c-Fos and NFATc1, as well as mRNA expression of osteoclast-specific markers. Overall, our data indicate that Duoxa1 plays a crucial role in osteoclastogenesis via regulating RANKL-induced intracellular ROS production and activating TRAF6-mediated signaling.

Securinine suppresses osteoclastogenesis and ameliorates inflammatory bone loss

Securinine (Sec) is a naturally derived compound separated from the roots of Securinega suffruticosa, which has long been used as a herbal medicine. Sec is widely known as a GABA receptor antagonist, it is also known as an innate immune cell agonist and has been reported to increase macrophage activity and promote monocyte maturation. On the basis of these studies, we investigated the effect of Sec on osteoclast differentiation and bone resorbing function. We have found that Sec inhibits RANKL-induced osteoclast differentiation, fusion, actin ring formation, and bone resorbing function by the inhibition of gene expression associated with each stage. Moreover, Sec significantly suppressed osteoclastogenesis by decreasing the phosphorylation of p38, Akt, JNK, IκB, and PLCγ2, in pathways involved in early osteoclastogenesis as well as through the subsequent suppression of c-Fos and NFATc1. Finally, Sec effectively protected bone loss induced by the excessive inflammatory responses and activity of osteoclasts in vivo by a micro-CT and histological analysis. In conclusion, our findings suggest that Sec may be a promising drug for bone metabolic diseases such as osteoporosis, which is associated with the excessive activity of osteoclasts.

Icariin Alleviates Glucocorticoid-Induced Osteoporosis through EphB4/Ephrin-B2 Axis

PURPOSE

Glucocorticoid (GC) is the most important risk factor for osteoporosis (OP); in the present study, we examined the potential mechanism of icariin, a natural bioactive compound isolated from the traditional Chinese herbal Epimedium, for GC-induced OP to explore its potential therapeutic effect.

METHODS

We used a GC-induced OP mice model and treated with icariin. Pathological changes were measured by H&E staining, and the effects of icariin on osteoblasts and osteoclasts were measured by immunohistochemistry (IHC) staining and western blot (WB) analyses, while trabecular bone parameters were detected by micro-CT imaging in vivo.

RESULTS

The results showed that in GC-induced OP symptoms, icariin treatment significantly increased the density of the trabecular bone when exposed to GC, revealed by H&E staining and micro-CT imaging. IHC staining showed that GC-induced OP had a lower EphB4 expression and higher Ephrin-B2 expression, but icariin could promote EphB4 while suppressing Ephrin-B2 expression. The WB results also provided evidence of the same protein expression trend, showing that the osteoblast marker OCN and the EphB4 downstream factor RhoA in the GC group were decreased, while both OCN and RhoA expression were significantly increased and the Ephrin-B2 downstream factor Grb4 in in GC group was increased after icariin treatment.

CONCLUSION

Icariin could improve the characteristics of OP through regulating the balance of the EphB4/Ephrin-B2 pathway. Further preclinical trial is needed to provide certainty of clinical benefits for OP patients.

Shikonin mitigates ovariectomy-induced bone loss and RANKL-induced osteoclastogenesis via TRAF6-mediated signaling pathways

BACKGROUND

Postmenopausal osteoporosis results from estrogen withdrawal and is characterized mainly by bone resorption. Shikonin is a bioactive constitute of Chinese traditional herb which plays a role in antimicrobial and antitumor activities. The study was designed to investigate the role of shikonin on postmenopausal osteoporosis and explore its underlying mechanisms.

METHODS

Immunofluorescence staining was performed to evaluate the effects of shikonin on actin ring formation. The expression levels of the nuclear factor kappa-B (NF-κB) and mitogen-activated protein kinase (MAPK) pathway were determined by Western blot analysis. To determine whether shikonin influences the receptor activator of nuclear factor-κB ligand (RANKL)-induced association between receptor activator of NF-κB (RANK) and tumor necrosis factor receptor associated factor 6 (TRAF6), immunofluorescence staining and immunoprecipitation experiments were performed. During our validation model, histomorphometric examination and micro-computed tomography (CT) were conducted to assess the morphology of osteoporosis.

RESULTS

Shikonin prevented bone loss by inhibiting osteoclastogenesis in vitro and improving bone loss in ovariectomized mice in vivo. At the molecular level, Western blot analysis indicated that shikonin inhibited the phosphorylation of inhibitor of NF-κB (IκB), P50, P65, extracellular regulated protein kinases (ERK), c-Jun N-terminal kinase (JNK), and P38. Interaction of TRAF6 and RANK was prevented, and downstream MAPK and NF-κB signaling pathways were downregulated.

CONCLUSION

Osteoclastic bone resorption was reduced in the presence of shikonin in vitro and in vivo. Shikonin is a promising candidate for treatment of postmenopausal osteoporosis.

Novel Role for Claudin-11 in the Regulation of Osteoblasts via Modulation of ADAM10-Mediated Notch Signaling

The claudin (Cldn) family comprises 27 members of 20 to 34 kDa transmembrane tight junction proteins. In addition to Cldns' established canonical role as barriers controlling paracellular flow of molecules, a distinct noncanonical role for them as mediators of cell signaling is now emerging. In our studies evaluating Cldn family expression levels during osteoblast differentiation, Cldn-11 showed the largest increase (60-fold). Immunohistochemistry studies revealed high Cldn-11 expression in trabecular (Tb) bone lining cells. Micro-CT analysis of femurs and vertebrae of Cldn-11 knock-out (KO) mice at 12 weeks of age exhibited a 40% (p < 0.01) reduction in Tb bone volume adjusted for tissue volume compared with control mice, a change caused by significant reductions in Tb number and thickness and increase in Tb separation. Histomorphometry and serum biomarker studies revealed that reduced bone formation, not increased resorption, is the cause for reduced Tb bone volume in the Cldn-11 KO mice. Cldn-11 KO osteoblasts expressed reduced ALP and BSP, whereas Cldn-11 overexpression in MC3T3-E1 cells increased expression of ALP and BSP. Mechanistically, Cldn-11 interacted with tetraspanin (Tspan)3 in osteoblasts, and Tspan3 knockdown reduced osteoblast differentiation. Because members of the Tspan family regulate cell functions via Notch signaling, we evaluated whether Cldn-11/Tspan3 regulates Notch signaling in osteoblasts. Accordingly, Notch targets Hey1 and Hey2 were significantly upregulated in Cldn-11 overexpressing cultures but downregulated in both Cldn-11 KO and Tspan3 knockdown osteoblasts. Because ADAM10 has been shown to interact with Tspan family members to regulate Notch signaling, we evaluated whether Cldn-11 regulates ADAM10 expression. Cldn-11 overexpressing cells express more mature ADAM10, and an ADAM10 inhibitor blocked the Cldn-11 effect on osteoblast differentiation. Based on these data, we propose Cldn-11 as a novel component of an osteoblast cell surface protein complex, comprising Tspan3 and ADAM10, which regulates Notch signaling and cell differentiation. © 2019 American Society for Bone and Mineral Research.

Role of ANTXR1 in the regulation of RANKL-induced osteoclast differentiation and function

Anthrax toxin receptor 1 (ANTXR1) is a transmembrane protein with an extracellular domain which is deeply associated with the process of bone formation and plays an important role in angiogenesis. However, there have been no reports investigating the effects of ANTXR1 on bone metabolism mediated by the two types of bone cells, osteoclasts, and osteoblasts. The aim of this study is to reveal the role of ANTXR1 in the differentiation and function of osteoclasts and osteoblasts. We found that ANTXR1 positively regulated the receptor activator of nuclear factor kappa B ligand (RANKL)-induced osteoclast differentiation and bone resorption with no effects on osteoblast differentiation by performing gain- and loss-of-function studies. During ANTXR1-mediated regulation of osteoclastogenesis, phosphorylation of early signal transducers such as c-Jun N-terminal kinase (JNK), Akt, inhibitor of kappa B (IκB), and phospholipase C gamma 2 (PLCγ2) was affected, which in turn altered the mRNA and protein levels of c-Fos and nuclear factor of activated T cells cytoplasmic 1 (NFATc1). In addition, genetic manipulation of ANTXR1 in bone marrow macrophages (BMMs) modulated the capillary-like tube formation in HUVECs via secretion of two angiogenic factors, matrix metalloproteinase-9 (MMP-9) and vascular endothelial growth factor-A (VEGF-A). These results elucidated the importance of ANTXR1 in osteoclast differentiation and functional activity, as well as, osteoclast-mediated angiogenesis of endothelial cells. Taken together, we propose that ANTXR1 might be a promising candidate for gene therapy for bone metabolic diseases and further, might potentially serve as an important biomarker in the field of bone metastasis associated with vascularization.

The Natural Product 6-Gingerol Inhibits Inflammation-Associated Osteoclast Differentiation via Reduction of Prostaglandin E₂ Levels

The natural product 6-gingerol, a major bioactive component of the rhizome of ginger (Zingiber officinale), is known to have several beneficial effects on health, including anti-inflammatory activity. The present study aimed to investigate the effects of 6-gingerol on osteoclast differentiation associated with inflammation. 6-Gingerol inhibited osteoclast differentiation in co-cultures of osteoblasts and osteoclast precursor cells in response to the pro-inflammatory cytokine, interleukin (IL)-1. However, it did not affect osteoclast precursor differentiation into osteoclasts induced by the receptor activator of nuclear factor-κB ligand (RANKL), a key cytokine causing osteoclast differentiation. 6-Gingerol inhibited IL-1-induced RANKL expression in osteoblasts, and the addition of RANKL to the co-cultures overcame 6-gingerol-mediated inhibition of osteoclast differentiation. It also suppressed IL-1-induced prostaglandin E₂ (PGE₂) production in osteoblasts, and the addition of exogenous PGE₂ reversed 6-gingerol-mediated inhibition of IL-induced RANKL expression in osteoblasts and osteoclast differentiation in the co-cultures. We found that 6-gingerol reduced PGE₂ levels by suppressing enzymatic activities of cyclooxygenase and PGE synthase, which cooperatively catalyze the conversion of arachidonic acid to PGE₂. Our findings demonstrate that 6-gingerol inhibits IL-1-induced osteoclast differentiation via suppression of RANKL expression in osteoblasts though reduction of PGE₂ levels, suggesting its potential use in treating inflammatory bone destruction associated with excessive PGE₂ production.

Magnolol Inhibits Osteoclast Differentiation via Suppression of RANKL Expression

Magnolol, a compound from the traditional Korean herb Magnolia sp., has been exhaustively investigated as a therapeutic agent against several diseases including systemic and local inflammation. We examined the effects of magnolol on osteoclastic differentiation associated with inflammation. Magnolol markedly reduced interleukin (IL)-1-induced osteoclast formation in co-cultures of murine osteoblasts and bone marrow cells, whereas it had no effect on receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast formation in bone marrow macrophage cultures. In osteoblasts, magnolol markedly inhibited both the up-regulation of RANKL expression and the production of prostaglandin E₂ (PGE₂) in response to IL-1 treatment. Addition of exogenous PGE₂ reversed the inhibitory effects of magnolol on IL-1-induced RANKL expression in osteoblasts and osteoclast formation in co-cultures. Magnolol inhibited IL-1-induced PGE₂ production, at least in part by suppressing cyclooxygenase-2 (COX-2) expression. Taken together, these results demonstrate that magnolol inhibits IL-1-induced RANKL expression in osteoblasts through suppression of COX-2 expression and PGE₂ production, resulting in inhibition of osteoclast differentiation in co-cultures.