Promote Osteoclast Formation Research Articles

Development of a novel hyaluronic acid/alginate/RANKL degradable microneedle patch for accelerating bone remodeling and orthodontic tooth movement through promoting osteoclastogenesis

The prolonged duration of orthodontic treatment remains a significant concern for both orthodontists and patients. In this study, we developed a degradable microneedle (MN) patch composed of hyaluronic acid (HA) and sodium alginate (SA) for the delivery of receptor activator of nuclear factor-kappa B ligand (RANKL) to accelerate tooth movement. This MN patch which was crosslinked by calcium chloride (CaCl2) exhibits adequate mechanical properties and favorable in vitro mucosal insertion ability. Moreover, the MN patch can achieve the sustained release of RANKL and maintain the biological stability of RANKL protein after one month of storage at −20 °C, 4 °C, or 37 °C. In vitro experiments using RAW264.7 cells indicated that the HA/SA/RANKL MN possessed excellent biocompatibility and could effectively induce osteoclast differentiation. In vivo application of the HA/SA/RANKL MN in rat models showed a remarkable effect in promoting osteoclast formation and accelerating tooth movement. These findings suggest that the degradable HA/SA/RANKL MN holds significant potential for enhancing tooth movement efficiency.

Erythropoietin regulates osteoclast formation via up-regulating PPARγ expression

Erythropoietin (EPO), expressed in red blood progenitor cells, primarily regulates erythropoiesis by binding to its receptor. Besides anemia, recent studies have identified new therapeutic indications for EPO that are not connected to red blood cell formation. Elevated EPO levels harm bone homeostasis in adult organisms and are associated with increased osteoclast; however, the underlying molecular mechanisms remain unclear. This study demonstrated that EPO enhanced osteoclast differentiation and bone resorption in vitro. We showed that EPO promoted osteoclast formation by up-regulating PPARγ expression through activating the Jak2/ERK signaling pathway. Consistently, PPARγ antagonists rescued the hyperactivation of osteoclasts due to EPO, while PPARγ agonists reversed the EMP9-mediated decrease in osteoclast differentiation. Further, exposing female mice to EPO for two months led to a decrease in bone mass and increased osteoclast numbers. The present results suggested that EPO promotes osteoclastogenesis by regulating the Jak2/ERK/ PPARγ signaling pathway. From a clinical perspective, the risk of compromised bone health should be considered when using EPO to treat anemia in post-operative patients with intertrochanteric fractures of the femur, as it could significantly impact the patient’s recovery and quality of life.

Is there an effect of anti-TNF-α drugs on Chronic Periodontitis in subjects with Rheumatoid Arthritis? A Scoping Review

Chronic periodontitis (CP) is a multi-factorial disease affecting the periodontium, which destroys the alveolar bone and its supporting structures, eventually leading to tooth loss. Rheumatoid arthritis (RA), a chronic inflammatory disorder, affects the joints and causes their destruction, leading to disability. Although CP is essentially a microbial infection, it triggers the destructive host response that destroys the periodontal tissues and produces systemic consequences. Likewise, RA is an autoimmune disorder that causes bone resorption due to the release of inflammatory mediators, such as tumor necrosis factor-alpha (TNF-α) and interleukin (IL)-1β, which induce monocyte chemoattractant protein-1 (MCP-1) and lytic enzymes that promote osteoclast formation and phagocytosis. Lately, anti-TNF-α drugs have been studied for their cytokine-blocking ability. They bind to TNF-α and block its biological effects with marked improvement in clinical and laboratory inflammatory parameters. However, there is only minuscule information about their effects on CP. Purpose: This review evaluated the role of anti-TNF-α drugs on CP in subjects with RA. Methods: A systematic search of databases like Medline (Pubmed), Embase, Scopus, and Web of Science and manual search yielded 48 studies, of which 7 were selected based on the inclusion criteria. Results: It was observed that anti-TNF-α drugs significantly inhibited TNF-α activity in RA and produced a positive effect on the periodontal parameters. However, some studies concluded that there was no direct influence of anti-TNF-α drugs on CP parameters. Conclusion: Anti-TNF-α drugs may be a plausible modality for managing CP associated with RA. These agents may be helpful in CP owing to their anti-inflammatory effect. Moreover, improvement of RA, may indirectly enhance the manual dexterity required for maintaining oral hygiene in these patients with resultant improvement of periodontal health. However, more evidence supporting this is needed; hence, future clinical trials in humans are imperative.

Effects of Improper Mechanical Force on the Production of Sonic Hedgehog, RANKL, and IL-6 in Human Periodontal Ligament Cells In Vitro.

Improper mechanical stress may induce side effects during orthodontic treatment. If the roots and alveolar bones are extensively resorbed following excess mechanical stress, unplanned tooth mobility and inflammation can occur. Although multiple factors are believed to contribute to the development of side effects, the cause is still unknown. Sonic hedgehog (Shh), one of the hedgehog signals significantly associated with cell growth and cancer development, promotes osteoclast formation in the jawbone. Shh may be associated with root and bone resorptions during orthodontic treatment. In this study, we investigated the relationships between Shh, RANKL, and IL-6 in human periodontal ligament (hPDL) cells exposed to improper mechanical force. Weights were placed on hPDL cells and human gingival fibroblasts (HGFs) for an optimal orthodontic force group (1.0 g/cm2) and a heavy orthodontic force group (4.0 g/cm2). A group with no orthodontic force was used as a control group. Real-time PCR, SDS-PAGE, and Western blotting were performed to examine the effects of orthodontic forces on the expression of Shh, RANKL, and IL-6 at 2, 4, 6, 8, 12, and 24 h after the addition of pressure. The protein expression of Shh was not clearly induced by orthodontic forces of 1.0 and 4.0 g/cm2 compared with the control in HGFs and hPDL cells. In contrast, RANKL and IL-6 gene and protein expression was significantly induced by 1.0 and 4.0 g/cm2 in hPDL cells for forces lasting 6~24 h. However, neither protein was expressed in HGFs. RANKL and IL-6 expressions in response to orthodontic forces and in the control were clearly inhibited by Shh inhibitor RU-SKI 43. Shh did not directly link to RANKL and IL-6 for root and bone resorptions by orthodontic force but was associated with cell activities to be finally guided by the production of cytokines in hPDL cells.

Cigarette smoke promotes IL-6-dependent lung cancer migration and osteolytic bone metastasis.

Lung cancer stands as a major contributor to cancer-related fatalities globally, with cigarette smoke playing a pivotal role in its development and metastasis. Cigarette smoke is also recognized as a risk factor for bone loss disorders like osteoporosis. However, the association between cigarette smoke and another bone loss disorder, lung cancer osteolytic bone metastasis, remains largely uncertain. Our Gene Set Enrichment Analysis (GSEA) indicated that smokers among lung cancer patients exhibited higher expression levels of bone turnover gene sets. Both The Cancer Genome Atlas (TCGA) database and our clinic samples demonstrated elevated expression of the osteolytic factor IL-6 in ever-smokers with bone metastasis among lung cancer patients. Our cellular experiments revealed that benzo[α]pyrene (B[α]P) and cigarette smoke extract (CSE) promoted IL-6 production and cell migration in lung cancer. Activation of the PI3K, Akt, and NF-κB signaling pathways was involved in cigarette smoke-augmented IL-6-dependent migration. Additionally, cigarette smoke lung cancer-secreted IL-6 promoted osteoclast formation. Importantly, blocking IL-6 abolished cigarette smoke-facilitated lung cancer osteolytic bone metastasis in vivo. Our findings provide evidence that cigarette smoke is a risk factor for osteolytic bone metastasis. Thus, inhibiting IL-6 may be a valuable therapeutic strategy for managing osteolytic bone metastasis in lung cancer patients who smoke.

SPI1 exacerbates iron accumulation and promotes osteoclast formation through inhibiting the expression of Hepcidin

BackgroundOsteoporosis (OP) can be caused by an overactive osteoclastic function. Anti-osteoporosis considerable therapeutic effects in tissue repair and regeneration because bone resorption is a unique osteoclast function. In this study, we mainly explored the underlying mechanisms of osteoclasts' effects on osteoporosis. MethodsRAW264.7 cells were used and induced toward osteoclast and iron accumulation by M-CSF and RANKL administration. We investigated Hepcidin and divalent metal transporter 1 (DMT1) on iron accumulation and osteoclast formation in an ovariectomy (OVX)-induced osteoporosis. Osteoporosis was induced in mice by OVX, and treated with Hepcidin (10, 20, 40, 80 mg/kg, respectively) and overexpression of DMT1 by tail vein injection. Hepcidin, SPI1, and DMT1 were detected by immunohistochemical staining, western blot and RT-PCR. The bioinformatics assays, luciferase assays, and Chromatin Immunoprecipitation (ChIP) verified that Hepcidin was a direct SPI1 transcriptional target. Iron accumulation was detected by laser scanning confocal microscopy, Perl's iron staining and iron content assay. The formation of osteoclasts was assessed using tartrate-resistant acid phosphatase (TRAP) staining. ResultsWe found that RAW264.7 cells differentiated into osteoclasts when exposed to M-CSF and RANKL, which increased the protein levels of osteoclastogenesis-related genes, including c-Fos, MMP9, and Acp5. We also observed higher concentration of iron accumulation when M-CSF and RANKL were administered. However, Hepcidin inhibited the osteoclast differentiation cells and decreased intracellular iron concentration primary osteoclasts derived from RAW264.7. Spi-1 proto-oncogene (SPI1) transcriptionally repressed the expression of Hepcidin, increased DMT1, facilitated the differentiation and iron accumulation of mouse osteoclasts. Overexpression of SPI1 significantly declined luciferase activity of HAMP promoter and increased the enrichment of HAMP promoter. Furthermore, our results showed that Hepcidin inhibited osteoclast differentiation and iron accumulation in mouse osteoclasts and OVX mice. ConclusionTherefore, the study revealed that SPI1 could inhibit Hepcidin expression contribute to iron accumulation and osteoclast formation via DMT1 signaling activation in mouse with OVX.

Optimization of small molecule degraders and antagonists for targeting estrogen receptor based on breast cancer: current status and future.

The estrogen receptor (ER) is a classical receptor protein that plays a crucial role in mediating multiple signaling pathways in various target organs. It has been shown that ER-targeting therapies inhibit breast cancer cell proliferation, enhance neuronal protection, and promote osteoclast formation. Several drugs have been designed to specifically target ER in ER-positive (ER+) breast cancer, including selective estrogen receptor modulators (SERM) such as Tamoxifen. However, the emergence of drug resistance in ER+ breast cancer and the potential side effects on the endometrium which has high ER expression has posed significant challenges in clinical practice. Recently, novel ER-targeted drugs, namely, selective estrogen receptor degrader (SERD) and selective estrogen receptor covalent antagonist (SERCA) have shown promise in addressing these concerns. This paper provides a comprehensive review of the structural functions of ER and highlights recent advancements in SERD and SERCA-related small molecule drugs, especially focusing on their structural optimization strategies and future optimization directions. Additionally, the therapeutic potential and challenges of novel SERDs and SERCAs in breast cancer and other ER-related diseases have been discussed.

Semaphorin 4D Promotes Osteoclast Formation but Inhibits Osteoblast Formation: Implication in Bisphosphonate-Related Osteonecrosis of the Jaw

Introduction: Bisphosphonates are widely used for the treatment of osteoporosis, which could cause osteonecrosis of the jaw (also known as bisphosphonate-related osteonecrosis of the jaw [BRONJ]). Currently, there is no effective treatment for BRONJ. Here, we investigated the role of human recombinant semaphorin 4D (Sema4D) in BRONJ in vitro. Methods: MG-63 and RAW264.7 cells were used to determine the effects of Sema4D on BRONJ. Osteoclast and osteoblast were differentiated by treatment with 50 ng/mL RANKL for 7 days. In vitro BRONJ model was induced by treatment with ZOL (2.5 μ<sc>m</sc>). The development of osteoclasts and osteoblasts was evaluated using ALP activity and ARS staining. qRT-PCR was used to measure the genes relative expression involved in the development of osteoclasts and osteoblasts. In addition, ZOL decreased TRAP-positive area; TRAP protein and mRNA expression were determined using Western blot and qTR-PCR. Results: ZOL treatment remarkedly suppressed Sema4D expression in RAW264.7 cells. Moreover, ZOL reduced TRAP-positive area and TRAP protein and mRNA expression. In parallel, genes involved in osteoclast formation were reduced by ZOL treatment. In contrast, osteoclast apoptosis was increased by ZOL treatment. Recombinant human Sema4D significantly abolished these effects of ZOL. In addition, ALP activity was reduced by recombinant human Sema4D. Discussions: Genes involved in osteoblast formation were decreased by recombinant human Sema4D in a dose-dependent manner. We demonstrated that ZOL treatment inhibited Sema4D expression in RAW264.7 cells. Conclusion: Recombinant human Sema4D treatment can effectively alleviate ZOL-induced inhibition of osteoclast formation and apoptosis and promote osteoblast formation.

TRAF-STOP alleviates osteoclastogenesis in periodontitis.

The enhanced osteoclastogenesis contributes to alveolar bone resorption in periodontitis, which increases the risk of tooth loss. To reduce bone destruction, the inhibition of osteoclast development is proposed as a feasible treatment. CD40L-CD40-TRAF6 signal transduction plays a crucial role in inflammation, but how it regulates osteoclast activity in periodontitis has not been elucidated. In this study, we showed the potential role of CD40L-CD40-TRAF6 signaling in periodontitis. CD40L obviously promoted osteoclast formation and bone resorption capacity in vitro. Mechanistically, we found that osteoclastogenesis was enhanced by the overexpression of NFATc1 and NF-κB activation. Importantly, osteoclast activity was effectively suppressed by TRAF-STOP, a small molecular inhibitor of TRAF6. Furthermore, local injection of TRAF-STOP-loaded injectable PLGA-PEG-PLGA hydrogel could alleviate ligation-induced periodontitis in vivo. Taken together, TRAF-STOP shows promising clinical efficacy in periodontitis through alleviating osteoclastogenesis.

Association of RANKL and EGFR gene expression with bone metastases in patients with metastatic non-small cell lung cancer.

Bone metastases are frequent in patients with non-small cell lung cancer (NSCLC). The receptor activator of Nuclear Factor κB (RANK)/RANK ligand (RANKL)/osteoprotegerin (OPG) pathway is important in bone metastases development. Furthermore, epidermal growth factor receptor (EGFR) signaling promotes osteoclast formation and stimulation. The understanding of the biological mechanism of bone metastases development might have implications for treatment strategies. Therefore, we studied whether there is an association between EGFR, RANKL, RANK and OPG gene expression in the tumor and presence of bone metastases in patients with NSCLC. From an updated multicenter study, including patients with EGFR mutated (EGFR+), Kirsten rat sarcoma (KRAS+) and EGFR/KRAS wildtype metastatic NSCLC, all patients with available formalin-fixed paraffin-embedded (FFPE) tumor samples were selected. Ribonucleic Acid (RNA) was isolated from these samples and gene expressions of EGFR, RANKL, OPG and RANKL were determined via quantitative Polymerase Chain Reaction (qPCR). Data on demographics, histology and molecular subtyping, sample origin, presence of bone metastasis, SREs and bone progression were collected. Primary endpoint was relation between EGFR, RANK, RANKL, OPG gene expression, RANKL: OPG ratio and bone metastases. In 73/335 (32% EGFR+, 49% KRAS+, 19% EGFR/KRAS wildtype) samples from unique patients, gene expression analysis could be performed. Of these 73 patients, 46 (63%) had bone metastases at diagnosis or developed bone metastases during the disease course. No association was found between EGFR expression and presence of bone metastases. Patients with bone metastases had a significantly higher RANKL expression and RANKL: OPG ratio compared to those without. An increased RANKL: OPG ratio resulted in a 1.65x increased risk to develop bone metastases, especially in the first 450 days after diagnosis of metastatic NSCLC. Increased RANKL gene expression and RANKL: OPG ratio, but not EGFR expression, was associated with presence of bone metastases. Additionally, an increased RANKL: OPG gene ratio was associated with a higher incidence of bone metastases development.

Structure-based virtual screening for discovery of paederosidic acid from Paederia scandens as novel P2Y14R antagonist

BackgroundThe activation of P2Y14 receptor (P2Y14R) promotes osteoclast formation and causes neuropathic pain, exhibiting possible link to osteoarthritis (OA). Given lack of P2Y14R antagonist, the present study aims to search a novel P2Y14R antagonist with low toxicity and high activity from natural products as a possible drug candidate in treatment of OA. MethodsThe role of P2Y14R on OA was verified using P2Y14R knockout (KO) rats. Molecular docking virtual screening strategy and activity test in P2Y14R stably-expressed HEK293 cells were used to screen target compound from natural product library. The MM/GBSA free energy calculation/decomposition technique was used to determine the principal interaction mechanism. Next, the binding of target compound to P2Y14R was examined using cellular thermal shift assay and drug affinity responsive target stability test. Finally, the therapeutic effect of target compound was performed in monosodium iodoacetate (MIA)-induced OA mouse model. To verify whether the effect of target compound was attributed to P2Y14R, we establish the osteoarthritis model in P2Y14R KO mice to perform pharmacodynamic evaluation. Importantly, to investigate the potential mechanism by which target compound attenuate OA, expressions of the major transcription factors involved in osteoclast differentiation were detected by western blot, while markers of nerve damage in dorsal root ganglion (DRG) were evaluated by RT-qPCR and immunofluorescence techniques. ResultsDeficiency of P2Y14R alleviated pain behavior and cartilage destruction in MIA-induced OA rats. 14 natural compounds were screened by Glide docking-based virtual screening, among which paederosidic acid exhibited the highest antagonistic activity to P2Y14R with IC50 of 8.287 μM. As a bioactive component extracted from Paederia scandens, paederosidic acid directly interacted with P2Y14R to enhance the thermostability and decrease the protease sensitivity of target protein, which significantly inhibited receptor activator for nuclear factor-κB ligand (RANKL)-mediated osteoclastogenesis. More importantly, paederosidic acid suppressed osteoclast formation by downregulating expressions of NFAT2 and ATP6V0D2, as well as relieved neuropathic pain by decreasing expressions of CGRP, CSF1 and galanin in DRG. ConclusionsPaederosidic acid targeted P2Y14R to improve OA through alleviating osteoclast formation and neuropathic pain, which provided an available strategy for developing novel drug leads for treatment of OA.

USP7 promotes the osteoclast differentiation of CD14+ human peripheral blood monocytes in osteoporosis via HMGB1 deubiquitination.

Abnormal osteoclast and osteoblast differentiation is an essential pathological process in osteoporosis. As an important deubiquitinase enzyme, ubiquitin-specific peptidase 7 (USP7) participates in various disease processes through posttranslational modification. However, the mechanism by which USP7 regulates osteoporosis remains unknown. Herein, we aimed to investigate whether USP7 regulates abnormal osteoclast differentiation in osteoporosis. The gene expression profiles of blood monocytes were preprocessed to analyze the differential expression of USP genes. CD14+ peripheral blood mononuclear cells (PBMCs) were isolated from whole blood collected from osteoporosis patients (OPs) and healthy donors (HDs), and the expression pattern of USP7 during the differentiation of CD14+ PBMCs into osteoclasts was detected by western blotting. The role of USP7 in the osteoclast differentiation of PBMCs treated with USP7 siRNA or exogenous rUSP7 was further investigated by the F-actin assay, TRAP staining and western blotting. Moreover, the interaction between high-mobility group protein 1 (HMGB1) and USP7 was investigated by coimmunoprecipitation, and the regulation of the USP7-HMGB1 axis in osteoclast differentiation was further verified. Osteoporosis in ovariectomized (OVX) mice was then studied using the USP7-specific inhibitor P5091 to identify the role of USP7 in osteoporosis. The bioinformatic analyses and CD14+ PBMCs from osteoporosis patients confirmed that the upregulation of USP7 was associated with osteoporosis. USP7 positively regulates the osteoclast differentiation of CD14+ PBMCs in vitro. Mechanistically, USP7 promoted osteoclast formation by binding to and deubiquitination of HMGB1. In vivo, P5091 effectively attenuates bone loss in OVX mice. We demonstrate that USP7 promotes the differentiation of CD14+ PBMCs into osteoclasts via HMGB1 deubiquitination and that inhibition of USP7 effectively attenuates bone loss in osteoporosis in vivo.The translational potential of this article:The study reveals novel insights into the role of USP7 in the progression of osteoporosis and provides a new therapeutic target for the treatment of osteoporosis.

Metastatic prostate cancer‐derived extracellular vesicles facilitate osteoclastogenesis by transferring the CDCP1 protein

Bone metastases are still incurable and result in the development of clinical complications and decreased survival for prostate cancer patients. Recently, a number of studies have shown that extracellular vesicles (EVs) play important roles in tumour progression. Here, we show that EVs from metastatic prostate cancer cells promote osteoclast formation in the presence of receptor activator of NF-κB ligand (RANKL). EV characterization followed by functional siRNA screening identified CUB-domain containing protein 1 (CDCP1), a transmembrane protein, as an inducer of osteoclastogenesis. Additionally, CDCP1 expression on plasma-derived EVs was upregulated in bone metastatic prostate cancer patients. Our findings elucidate the effect of EVs from metastatic prostate cancer cells on osteoclast formation, which is promoted by CDCP1 located on EVs. Furthermore, our data suggested that CDCP1 expression on EVs might be useful to detect bone metastasis of prostate cancer.

Crucial Role of Lysine-Specific Histone Demethylase 1 in RANKL-Mediated Osteoclast Differentiation.

Epigenetic regulators are involved in osteoclast differentiation. This study proposes that the inhibitors of epigenetic regulators could be effective in the treatment of osteoporosis. This study identified GSK2879552, a lysine-specific histone demethylase 1 (LSD1) inhibitor, as a candidate for the treatment of osteoporosis from epigenetic modulator inhibitors. We investigate the function of LSD1 during RANKL-induced osteoclast formation. LSD1 small-molecule inhibitors effectively inhibit the RANKL-induced osteoclast differentiation in a dose-dependent manner. LSD1 gene knockout in macrophage cell line Raw 264.7 also inhibits RANKL-mediated osteoclastogenesis. LSD1-inhibitor-treated primary macrophage cells and LSD1 gene knockout Raw 264.7 cells failed to show actin ring formation. LSD1 inhibitors prevent the expression of RANKL-induced osteoclast-specific genes. They also downregulated the protein expression of osteoclast-related markers in osteoclastogeneses, such as Cathepsin K, c-Src, and NFATc1. Although LSD1 inhibitors were shown to reduce the in vitro demethylation activity of LSD1, they did not modulate the methylation of Histone 3 K4 and K9 during osteoclastogenesis. The ovariectomy (OVX)-induced osteoporosis model revealed that GSK2879552 slightly restores OVX-induced cortical bone loss. LSD1 can be employed as a positive regulator to promote osteoclast formation. Hence, inhibition of LSD1 activities is a potential target for preventing bone diseases characterized by excessive osteoclast activities.

Neutrophil extracellular trap-associated carbamylation and histones trigger osteoclast formation in rheumatoid arthritis

ObjectiveNeutrophil infiltration into the synovial joint is a hallmark of rheumatoid arthritis (RA), a disease characterised by progressive bone erosion. However, the mechanisms by which neutrophils participate in bone destruction...

Immunohistochemical analysis of the distribution of RANKL: a case of disseminated carcinomatosis of bone marrow as the first presentation of relapse in curatively resected colorectal cancer.

Poorly differentiated adenocarcinoma of colorectal carcinoma (CRC) is a rare condition with poor prognosis. In this report, we describe a case of a 69-year-old man who underwent laparoscopic low anterior resection after being diagnosed with stage IIIB CRC. At 10months post-operation, he developed fever and loss of appetite. Laboratory examination revealed > 120.0μg/dL fibrin degradation products and > 60.0μg/dL D-dimer. Bone marrow (BM) examination showed malignant epithelioid infiltrate with CK20 and CDX2 expression, leading to diagnosis of disseminated carcinomatosis of BM, which is rare in CRC and indicative of widespread disease throughout the body. Furthermore, immunohistochemistry revealed high expression of receptor activator of nuclear factor κB ligand (RANKL) in tumor cells, including budding cells of CRC and BM tissues. Thus, RANKL expression, which is known to indicate metastatic behavior of cancer cells, may play a critical role in promoting osteoclast formation, which has been associated with the pathogenesis of BM lesions.

Nox4 promotes osteoblast differentiation through TGF-beta signal pathway.

NADPH oxidase 4 (Nox4) is the main source of reactive oxygen species, which promote osteoclast formation and lead to bone loss, thereby causing osteoporosis. However, the role of Nox4 in osteoblasts during early development remains unclear. We used zebrafish to study the effect of Nox4 deletion on bone mineralization in early development. nox4-/- zebrafish showed decreased bone mineralization during early development and significantly reduced numbers of osteoblasts, osteoclasts, and chondrocytes. Transcriptome sequencing showed that the TGF-β signaling pathway was significantly disrupted in nox4-/- zebrafish. Inhibiting TGF-β signaling rescued the abnormal bone development caused by nox4 deletion and increased the number of osteoblasts. We used Saos-2 human osteosarcoma cells to confirm our results, which clarified the role of Nox4 in human osteoblasts. Our results demonstrate the mechanism of reduced bone mineralization in early development and provide a basis for the clinical treatment of osteoporosis.

Roles of osteoclast-associated receptor in rheumatoid arthritis and osteoarthritis.

Osteoclast-associated receptor (OSCAR) is a member of the leukocyte receptor complex (LRC)-encoded protein family, which is characterized by the presence of immunoglobulin (Ig)-like domains. OSCAR recognizes collagen and was first identified as a co-stimulatory receptor that is needed for complete osteoclast differentiation. However, it is now clear that OSCAR is also expressed by multiple immune cells that participate in many innate and adaptive immune cell activities. We also showed recently that chondrocytes express OSCAR. Our and other studies suggest that OSCAR participates in the pathogenesis of two common joint diseases, namely, rheumatoid arthritis (RA) and osteoarthritis (OA). Specifically, OSCAR promotes osteoclast formation and therefore bone erosion in RA while in OA, it triggers chondrocyte death, thereby inducing cartilage fragility. Significantly, blocking the interaction of OSCAR with its collagen ligand can markedly reduce these activities in vitro and in vivo. Thus, this novel approach may have therapeutic potential for joint diseases.

Compressive force regulates GSK-3β in osteoclasts contributing to alveolar bone resorption during orthodontic tooth movement in vivo

BackgroundOrthodontic tooth movement mainly depends on biological and mechanical reactions in the periodontium, such as the indispensable reconstruction process of the periodontal ligament and alveolar bone. To explore whether orthodontic compressive force can induce bone resorption during orthodontic tooth movement by regulating the GSK-3β/β-catenin pathway. MethodsWe established orthodontic tooth movement models in Sprague-Dawley rats. In addition, compressive force-induced bone resorption that occurred during orthodontic tooth movement was analyzed by HE staining and micro-CT. The number and distribution of osteoclasts were observed by TRAP staining. Furthermore, pressure-induced bone resorption mediated by the GSK-3β/β-catenin signaling pathway was analyzed by immunohistochemistry. ResultsAs shown by the micro-CT results, bone parameters, such as bone mineral density (BMD), the bone volume fraction (BV/TV), and trabecular thickness (Tb. Th), were significantly decreased under orthodontic compressive force stimulation, in contrast with the dramatically increased trabecular spacing (Tb. Sp). During the process of tooth movement, the compressive force can induce bone resorption on the side with the force, which increases the expression of phosphorylated Ser-GSK-3β and activation of the β-catenin signaling pathway. Additionally, downregulation of the GSK-3β activity further caused the downregulation of bone parameters, leading to bone loss. The TRAP staining and immunohistochemistry staining results indicated that orthodontic compressive force influenced osteoclast formation and the secretion of osteoclast-related cytokines, matrix metallopeptidase 9 (MMP-9) and receptor activator of nuclear factor-κB ligands (RANKLs), which is also related to the duration of orthodontic force. ConclusionsThese results indicated that the GSK-3β inhibitor can promote osteoclast formation on the side with orthodontic compressive force. In addition, the activation of the GSK-3β/β-catenin signaling pathway contributes to bone reconstruction caused by orthodontic compressive force. Therefore, the GSK-3β/β-catenin signaling pathway can be a potential target for further clinical applications.

Low levels of cadmium exposure affect bone by inhibiting Lgr4 expression in osteoblasts and osteoclasts

BackgroundCadmium exposure is associated with bone loss. However, the mechanisms involved have not yet been fully understood. Leucine-rich repeat containing GPCR-4 (LGR4) can bind with the receptor activator of nuclear factors κB ligand (RANKL) and inhibit osteoclast formation. In addition, Lgr4 plays an important role in maintaining osteoblast activity. In the present study the effect of cadmium exposure on bone was investigated in terms of Lgr4 expression. MethodsRaw 264.7 cells and primary osteoblasts were exposed to cadmium (0–60 nM/L). The effects of cadmium on osteoclast formation and osteoblast activity were investigated. Osteoclast differentiation-related (Traf6, NFATc1) and osteoblast-related (RANKL; osteoprotegerin, OPG) gene and protein expression were determined. Lgr4 expression in osteoclasts and osteoblasts were also determined. A rat model was established to show the effects of cadmium (50 mg/L) on bone loss and Lgr4 expression in vivo. ResultsCadmium exposure inhibited osteoblast activities and stimulated osteoclast formation. Cadmium exposure also inhibited Lgr4 expression in both osteoclasts and osteoblasts. Low dose of RANKL added to the culture medium could promote osteoclast formation in cadmium-pretreated RAW264.7 cells. Blocking Lgr4 in osteoclasts only slightly inhibited cadmium-induced osteoclast formation in cadmium-pretreated RAW264.7 cells. Cadmium significantly upregulated the AKT/ERK signaling pathway. An in vivo study showed that cadmium exposure promoted osteoclast formation and inhibited Lgr4 expression. ConclusionsOur data indicates that cadmium may induce bone loss by inhibiting Lgr4-related bone formation and promoting Lgr4-related osteoclast formation.