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Background: Cholesteatoma is a benign epithelial lesion that affects the middle ear or mastoid process, causing otorrhea and hearing impairment. Currently, the pathogenesis of temporal bone injury in middle ear cholesteatoma remains elusive, hindering the development of effective treatment strategies., Methods and Results: We examined the expression of transcription factor AP-2-beta (TFAP2B) and its downstream factor silent mating type information regulation 2 homolog 1 (SIRT1) in clinical samples from patients with middle ear cholesteatoma and analyzed the potential correlation between TFAP2B expression and clinical conditions. The findings revealed a significant down-regulation of TFAP2B and SIRT1 in patients diagnosed with middle ear cholesteatoma (p < 0.01), and TFAP2B expression was negatively correlated with the clinical manifestations of hearing impairment and bone destruction. We further explored the role of TFAP2B in the differentiation of RAW 264.7 cells into osteoclasts induced by receptor activator of nuclear factor kappa B ligand (RANKL) in vitro. TFAP2B overexpression significantly inhibited, while TFAP2B knockdown promoted osteoclast differentiation of RAW264.7 cells. Further investigation suggested that TFAP2B positively regulated SIRT1 (p < 0.01) and negatively regulated NF-κB activation. Finally, we demonstrated that TFAP2B transcriptionally regulated SIRT, which inhibited the activation of the NF-κB signaling pathway by reducing the acetylation level of the p65 subunit, thereby suppressing osteoclast differentiation., Conclusions: TFAP2B/SIRT1 plays a crucial role in regulating osteoclast differentiation in middle ear cholesteatoma. The downregulation of TFAP2B/SIRT1 triggers enhanced osteoclast differentiation, which may contribute to one of the mechanisms underlying bone destruction in middle ear cholesteatoma., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2025. Published by Elsevier Inc.)

Introduction: Uncoupled bone remodeling in the subchondral bone (SB) has recently been considered as an important process in the progression of knee osteoarthritis (KOA). In this study, we aimed to investigate changes in SB and articular cartilage using a mouse model of destabilization of the medial meniscus (DMM) and determine the effects of bone metabolism on KOA progression., Methods: DMM or sham surgery was performed on the left knees of 40-week-old male wild-type (WT) mice and Tsukuba hypertensive mice (THM), which exhibit high-turnover bone metabolism. Bone volume/tissue volume (BV/TV) and bone mineral density (BMD) in the medial tibial SB were measured longitudinally in vivo using μCT at 0 (immediately after surgery), 1, 2, 4, 8, and 12 weeks postoperatively. Concurrently, histological evaluations of the articular cartilage in the medial tibial plateau were conducted. Furthermore, the number of endo-periosteal tartrate-resistant acid phosphatase-positive osteoclasts, trabecular RANKL-positive osteocytes, and osteocytes in the trabeculae were measured at 0, 1, 2, and 4 weeks., Results: In the WT + DMM group, BV/TV and BMD in the SB significantly decreased with time, whereas cartilage degeneration significantly increased. In the THM + DMM group, these changes in BMD and cartilage degeneration were significantly pronounced. Interestingly, in the THM + DMM group, BV/TV significantly decreased up to 4 weeks but then began to increase, although BMD continued to decrease until the 12-week mark. The number of osteoclasts and the percentage of RANKL-positive osteocytes per total number of osteocytes within the total trabecular bone area (%) in the WT + DMM group significantly increased with time, with a significant difference between the WT + DMM and WT + sham groups at 4 weeks. The number of osteocytes in the WT + DMM group significantly decreased with time, and the difference between the WT + DMM and WT + sham groups was significant at 4 weeks postoperatively. These histological changes were significantly enhanced in the THM + DMM group., Conclusions: The results indicate that early-stage osteocyte death in the SB and RANKL-mediated osteoclastic SB loss precede histological cartilage degeneration and contribute to uncoupled bone remodeling at the later stage. Acceleration of disease processes in the THM + DMM group suggests that high-turnover bone metabolism is a potential risk factor for KOA. Maintaining SB integrity and avoiding continuous SB overload may be key strategies for mitigating disease progression., Competing Interests: Declarations. Ethics approval and consent to participate: All animal experimental procedures were performed in accordance with the guidelines of the National Institutes of Health and the institutional rules for the use and care of laboratory animals at Kindai University. All procedures were approved by the Experimental Animal Welfare Committee of Kindai University (approval number: KAME-2022-008). Consent to participate was not required. Consent for publication: Not applicable. Competing interests: The authors declare that they have no competing interests., (© 2025. The Author(s).)

Background/aim: Bone destruction caused by oral cancer severely impacts patient quality of life. This study aimed to clarify the role of angiogenin (ANG) in osteoclastogenesis and oral cancer-induced bone destruction., Materials and Methods: Recombinant ANG was used to assess its effects on osteoclast formation and bone resorption activity in bone marrow cultures. ANG-knockdown oral squamous carcinoma HSC-2 cells (ANG-RNAi) were transplanted into intramedullary cavities of femurs. Bone destruction was radiologically analyzed, while angiogenesis and osteoclast induction in the surrounding area of the transplanted lesion were histologically examined., Results: Recombinant ANG promoted osteoclast formation and bone resorption activity. Transplantation of ANG-RNAi cells significantly reduced tumor growth and bone destruction properties compared to transplantation of control cells. Histological analysis revealed lower angiogenesis and fewer osteoclast induction in the ANG-RNAi cells-transplanted group., Conclusion: ANG mediates oral cancer-induced bone destruction by promoting osteoclast formation and resorption. These findings suggest that ANG could be a potential therapeutic target for suppressing tumor growth, angiogenesis, and bone destruction in oral cancer therapy., (Copyright © 2025 International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved.)

Osteoporosis (OP) is a bone metabolic disease caused by decreased bone mass leading to destruction of bone microstructure. Treatment of OP is characterized by a lifelong nature, causing extreme financial and psychological burdens to patients. Hormonal abnormalities, cellular autophagy, Ferroptosis, and oxidative stress are all part of the intricate and varied pathophysiology of OP. Recent research has revealed that mitochondrial dysfunction is a significant factor in the onset and progression of OP. By regulating bone marrow mesenchymal stem cell differentiation through various signaling pathways and cytokines, abnormal mitochondrial energy metabolism brought on by oxidative stress processes impacts osteoblast and osteoclast proliferation and differentiation, causing an imbalance in bone metabolism that ultimately results in OP. Therefore, one possible method to prevent and manage OP may be to use mitochondria as a carrier to trigger osteogenic differentiation of bone marrow mesenchymal stem cells from mitochondrial energy consumption, oxidative stress, autophagy, and osteoclast death. In order to offer some theoretical references and therapeutic approaches for the clinical prevention and treatment of OP, we will examine the pathophysiology of OP from mitochondrial dysfunction in this work., Competing Interests: Declaration of competing interest The authors declare that they have no conflicts of interest., (Copyright © 2025 Elsevier B.V. All rights reserved.)

Rheumatoid arthritis (RA) is a chronic autoimmune disease that can cause destruction of cartilage and bone's extracellular matrix. Bromodomain 4 (BRD4), as a transcriptional and epigenetic regulator, plays a key role in cancer and inflammatory diseases. While, the role of BRD4 in bone destruction in RA has not been extensively reported. Our study aimed to investigate the effect of BRD4 on the bone destruction in RA and, further, its mechanism in the pathogenesis of the disease. In this study, receiving approval from the Ethical Committee of the Affiliated Hospital of Qingdao University, we evaluated synovial tissues from patients with RA and OA for BRD4 expression through advanced techniques such as immunohistochemistry, quantitative real-time PCR (qRT-PCR), and Western blotting. We employed a collagen-induced arthritis (CIA) mouse model to assess the therapeutic efficacy of the BRD4 inhibitor JQ1 on disease progression and bone destruction, supported by detailed clinical scoring and histological examinations. Further, in vitro osteoclastogenesis assays using RAW264.7 macrophages, facilitated by TRAP staining and resorption pit assays, provided insights into the mechanistic effects of JQ1 on osteoclast function. Statistical analysis was rigorously conducted using SPSS, applying Kruskal-Wallis, one-way ANOVA, and Student's t-tests to validate the data. In our study, we found that BRD4 expression significantly increased in the synovial tissues of RA patients and the ankle joints of CIA mice, with JQ1, a BRD4 inhibitor, effectively reducing inflammation, arthritis severity (p < 0.05), and bone erosion. Treatment with JQ1 not only improved bone mass and structural integrity in CIA mice but also downregulated osteoclast-related gene expression and the RANKL/RANK signaling pathway, indicating a suppression of osteolysis. Furthermore, in vitro assays demonstrated that JQ1 markedly inhibited osteoclast differentiation and function, underscoring the pivotal role of BRD4 in osteoclastogenesis and its potential as a target for therapeutic intervention in RA-induced bone destruction. Our study concludes that targeting BRD4 with the inhibitor JQ1 significantly mitigates inflammation and bone destruction in rheumatoid arthritis, suggesting that inhibition of BRD4 may be a potential therapeutic strategy for the treatment of bone destruction in RA., Competing Interests: Declarations. Competing interest: The authors declare no competing interests. Ethical approval: All patients recruited in this study provided informed consent for participation. The animal experimental procedures complied with the National Research Council’s Guide for the Care and Use of Laboratory Animals. The research protocols were approved by the Ethical Committee of the Affiliated Hospital of Qingdao University (Ethical committee number: QYFYWZLL26707) and the Ethical Committee of Animal Experiments of Qingdao University (Ethical committee number: AHQU-MAL20210428). Consent for publication: All authors gave their consent for publication and have no conflicts of interest., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Periodontitis is the sixth most common disease worldwide and is closely associated with various systemic diseases, impacting overall health. It is characterized by the over-differentiation and activity of osteoclasts, leading to increased bone resorption and subsequent bone loss. Current treatments for bone loss are not ideal, highlighting the need for new targeted therapeutic strategies. Dectin-2, a member of the C-type lectin receptor (CLR) family, has recently been reported to play an important role in immune regulation, but its role in osteoclastogenesis has not been documented. This study identified a significant upregulation of Dectin-2 expression during osteoclast differentiation through single-cell sequencing and transcriptomic analysis. Knocking down Dectin-2 significantly inhibits the differentiation of RAW264.7 cells and bone marrow-derived macrophages (BMDMs) into osteoclasts, while overexpressing Dectin-2 enhances osteoclast differentiation and function. Mechanistically, transcriptomic analysis indicates that Dectin-2 deficiency disrupts redox homeostasis and affects the MAPK signaling pathway. Furthermore, the study demonstrates that Dectin-2 promotes osteoclastogenesis via the Syk/NOX2/ROS/MAPK signaling axis. In vivo, Dectin-2 knockout mice show reduced osteoclast numbers and decreased alveolar bone resorption in a periodontitis model. In conclusion, these findings suggest that Dectin-2 is a key regulatory factor in osteoclast-mediated bone resorption and may serve as a promising therapeutic target for bone diseases characterized by osteoclast overactivity, such as periodontitis., Competing Interests: Declaration of competing interest The authors have declared no conflict of interest., (Copyright © 2025 Elsevier Inc. All rights reserved.)

Trisomy of human chromosome 21 (Ts21) individuals present with a spectrum of low bone mineral density (BMD) that predisposes this vulnerable group to skeletal injuries. To determine the bone regenerative capacity of Down syndrome (DS) mice, male and female Dp16 and Ts65Dn DS mice underwent amputation of the digit tip (the terminal phalanx (P3)). This is a well-established mammalian model of bone regeneration that restores the amputated skeletal segment and all associated soft tissues. P3 amputation was performed in 8-week-old male and female DS mice and WT controls and followed by in vivo μCT, histology and immunofluorescence. Following P3 amputation, the bone degradation phase was attenuated in both Dp16 and Ts65Dn males. In Dp16 males, P3 regeneration was delayed but complete by 63 days post amputation (DPA); however, male Ts65Dn exhibited attenuated regeneration by 63 DPA. In both Dp16 and Ts65Dn female DS mice, P3 regenerates were indistinguishable from WT by 42 DPA. In Ts65Dn males, osteoclasts and eroded bone surface were significantly reduced, and osteoblast number significantly decreased in the regenerating digit. In Ts65Dn females, no significant differences were observed in any osteoclast or osteoblast parameter. Like Ts21 individuals and DS mice with sex differences in bone mass, these data expand the characteristic sexually dimorphism to include bone resorption and regeneration in response to skeletal injury in Ts65Dn mice. These observations suggest that sex differences contribute to the poor bone healing of DS and compound the increased risk of bone injury in the Ts21 population., Competing Interests: Declaration of competing interest The authors declare that they have no conflict of interest., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Regulatory-B-cells (Bregs) modulate immune-homeostasis. Variations in the number and function of Bregs have been associated with various immune-related ailments, highlighting the importance of Bregs under inflammatory-conditions. Previously, we discovered the anti-osteoclastogenic-potential of Bregs. However, the crucial role of Bregs in the onset and progression of post-menopausal osteoporosis (PMO) has never been explored. Interestingly, our temporal-kinetic study demonstrated that Bregs have a compromised dynamics and functionality which further contributes to inception and the progression of the inflammatory bone loss condition in the PMO. Our ex-vivo findings further elucidate a significant reduction in the immunomodulatory and anti-osteoclastogenic functions of Bregs under the estrogen deficient post-menopausal osteoporotic conditions. The current study for the first time reports the crucial role of dysregulated-Bregs (both functionally and numerically), in the development of PMO. Our findings thereby provide a novel concept for immuno-therapeutically targeting "Bregs", for effective management and treatment of post-menopausal osteoporosis in the long run., Competing Interests: Declaration of competing interest The authors have no disclosures or conflicts of interest to declare., (Copyright © 2025 Elsevier B.V. All rights reserved.)

Objective: Rheumatoid arthritis (RA) is a chronic inflammatory disorder that causes joint damage, including cartilage degradation and bone erosion. Bone morphogenetic protein 9 (BMP9), a member of the TGF-β superfamily, plays a key role in osteogenesis and tissue repair. However, its role in bone erosion and inflammation in RA remains underexplored. This study aims to evaluate BMP9's therapeutic potential in RA, focusing on its effects on bone destruction, osteogenesis, and inflammation., Materials and Methods: In this study, BMP9 expression was analyzed in synovial tissues from RA and osteoarthritis patients and in the ankle joints of collagen-induced arthritis (CIA) mice using immunohistochemistry, qRT-PCR, and Western blotting. The therapeutic effect of BMP9 on bone destruction was evaluated in a CIA mouse model through micro-CT imaging, histological analysis, and clinical scoring. Osteogenic differentiation was assessed by alkaline phosphatase and Alizarin Red S staining, while osteoclast activity was examined through tartrate-resistant acid phosphatase staining. Fluorescence double-labeling was used to track new bone formation. Data were analyzed using (Statistical Package for the Social Sciences) SPSS, and appropriate statistical tests were performed to determine significance., Results: In this study, BMP9 expression was significantly down-regulated in the synovial tissue of RA patients and in the ankle joints of CIA mice. BMP9 treatment in CIA mice ameliorated joint inflammation, as shown by reduced limb swelling, lower arthritis index, and improved tissue morphology. Furthermore, BMP9 significantly alleviated bone loss, as evidenced by increased bone mineral density and trabecular structure. However, BMP9 treatment did not significantly impact osteoclastogenesis or bone resorption. BMP9 also enhanced bone mineralization and formation, as shown by increased mineral apposition rate and bone formation rate. Additionally, BMP9 promoted osteogenic differentiation of synovial cells, enhancing alkaline phosphatase activity and mineral nodule formation. These results suggest that BMP9 has a protective effect on joint inflammation and bone loss in RA, potentially through promoting bone formation without influencing osteoclast activity., Conclusion: Our study concludes that targeting BMP9 alleviates inflammation and promotes osteogenic differentiation in RA, highlighting BMP9 as a promising therapeutic target for addressing bone destruction in RA., Competing Interests: Declarations. Ethics approval and consent to participate: All participants in this study gave informed consent prior to their inclusion. The animal experiments were conducted in accordance with the National Research Council's Guide for the Care and Use of Laboratory Animals. The study protocols were approved by the Ethical Committee of the Affiliated Hospital of Qingdao University and the Animal Experimentation Ethics Committee of Qingdao University. Consent for publication: All authors gave their consent for publication and have no conflicts of interest. Competing interests: The authors declare that they have no competing interests., (© 2025. The Author(s).)

Introduction: B-cell lymphoma 6 (Bcl6) inhibits osteoclast differentiation in vitro; however, its role in orthodontic tooth movement (OTM) remains unclear. This study aimed to investigate the role of Bcl6 in OTM of rat molars., Materials and Methods: OTM was performed on the maxillary first molars of male rats using nickel-titanium coil springs (25 gf) for 14 days with or without local injection of FX1 (50 mg/kg), a Bcl6 inhibitor (n = 10 per group). Micro-computed tomography (CT) images were used to analyse OTM distance and bone morphometric parameters. Immunohistochemistry (IHC) determined Bcl6 expression and tartrate-resistant acid phosphatase staining (TRAP) staining assessed osteoclast differentiation. TRAP staining, and reverse transcription-quantitative polymerase chain reaction determined the effect of FX1 (1 μM) on in vitro rat osteoclast differentiation. The effect of FX1 on cell proliferation and Smad4 expression in periodontal ligament (PDL) cells was determined., Results: Administration of FX1 significantly increased OTM distance and decreased the bone/tissue volume compared with vehicle treatment. IHC staining showed that the vehicle-OTM group had higher expression of Bcl6 than the FX1-OTM group. The number of osteoclasts on the compression side was significantly higher in the FX1-OTM group than that in the vehicle-OTM group. FX1 enhanced osteoclast differentiation and expression of Nfatc1, Dc-stamp, and Ctsk mRNA in osteoclasts in vitro. FX1 significantly promotes PDL cell proliferation in vivo and in vitro., Limitations: We evaluated only 14 days of OTM., Conclusions: Bcl6 may play an important role in OTM via modulation of osteoclast differentiation and PDL cell proliferation., (© The Author(s) 2025. Published by Oxford University Press on behalf of the European Orthodontic Society. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Osteolytic lesions and pathological fractures are hallmark manifestations of multiple myeloma (MM), profoundly influencing the quality of life and self-care ability of MM patients. By analyzing transcriptome data and single-cell RNA-seq data from our center and the GEO database, a subset of MM cells with high expression levels of chemokine CXCL7 was identified. This subset of MM cells possesses a high capacity for proliferation and activation of osteoclast signaling pathway. CXCL7 might be a crucial regulator of osteolytic damage in MM. Subsequently, the association between the expression level of CXCL7 and pathological fractures in patients was investigated, and the impact of CXCL7 on MM proliferation was confirmed both in vivo and in vitro. A mouse xenograft tumor model was established through intravenous injection of myeloma cell lines based on the homing ability of plasma cells. Moreover, the mechanism by which CXCL7 promotes the activation of osteoclast signaling pathways in MM was explored. Our findings reveal that elevated CXCL7 levels significantly enhance MM cell proliferation, increasing the risk of pathological fractures in MM patients. Additionally, our mouse xenograft tumor model demonstrated that CXCL7 can induce femoral fractures and reduce bone mineral density. Concurrently, it was discovered that CXCL7 could activate the JAK/STAT3 pathway via CXCR2 and upregulate the expression levels of MMP13 and C-myc, facilitating MM cell proliferation and activation of the osteoclast signaling pathway. Our study offers novel insights into the pathogenic mechanism of osteolytic lesions and implies that targeting CXCL7 may present a new therapeutic avenue for MM., Competing Interests: Competing interests: The authors declare no competing interests. Ethics approval and consent to participate: The study was approved by the Ethics Committee of Fudan University Zhong Hospital (Observation Research Cohort of Plasma Cell Diseases in Zhongshan Hospital, Registration Number: B2017-031R)) and complied with the principles of the Helsinki Accord. Bone marrow samples were collected from all subjects, with patient consent, and stored in the tissue bank at Fudan University Zhongshan Hospital. The animal experiments were approved by the Animal Ethics Committee of Zhongshan Hospital Fudan University., (© 2025. The Author(s).)

Approximately one-third of advanced renal cell carcinoma (RCC) patients develop osteolytic bone metastases, leading to skeletal complications. In this review, we first provide a comprehensive perspective of seminal studies on bone metastasis of RCC describing the main molecular modulators and growth factor signaling pathways most important for the RCC-stimulated osteoclast-mediated bone destruction. We next focus on newer developments revealing with in-depth details, the bidirectional interplay between renal cancer cells and the immune and stromal microenvironment that can through epigenetic reprogramming, profoundly affect the behaviors of transformed cells. Understanding their mechanistic interactions is of paramount importance for advancing both fundamental and translational research. These new investigations into the landscape of RCC-bone metastasis offer novel insights and identify potential avenues for future therapeutic interventions., (© 2024 The Author(s). International Journal of Cancer published by John Wiley & Sons Ltd on behalf of UICC.)

Fibroblast-like synoviocytes (FLSs) and osteoclasts are central cells in the maintenance of joint homeostasis. Rheumatoid arthritis (RA) is a chronic inflammatory disease of joints that induces cytokine-activated FLSs and progressive bone erosion. Interactions between FLSs and other cells, such as T cells and B cells, have been recognized in the development of RA. Here we hypothesized that calcium released from bone by mature osteoclasts might activate FLSs, which are also affected by inflammatory cytokines in the inflamed synovium. Osteoclastogenesis occurs in the presence of cytokine-stimulated FLS medium, and calcium released from the bone disc activates FLS migration. We first investigated the calcium and cytokine feedback loop between FLSs and osteoclast maturation. Moreover, by addressing the role of the sodium-bicarbonate cotransporter NBCn1 in osteoclastogenesis, we found that the inhibition of NBCn1 attenuated the infinite calcium and cytokine feedback loop between FLSs and osteoclasts. In a collagen-induced arthritis mouse model, the inhibition of NBC reduced the RA pathological phenotype and bone resorption area in the femur. These results suggest that modulation of the crosstalk between FLSs and osteoclasts by inhibiting the calcium and cytokine feedback loop could be considered to develop pioneering strategies to combat RA severity and dysregulated bone homeostasis., Competing Interests: Competing interests: The authors declare no competing interests. Ethics: All procedures related to synovial fluid collection were performed in accordance with the Declaration of Helsinki. The study was approved by the institutional review board of Gil Medical Center (GAIRB-2019-018)., (© 2025. The Author(s).)

Bone is a unique organ crucial for locomotion, mineral metabolism, and hematopoiesis. It maintains homeostasis through a balance between bone formation by osteoblasts and bone resorption by osteoclasts, which is regulated by the basic multicellular unit (BMU). Abnormal bone metabolism arises from an imbalance in the BMU. Osteoclasts, derived from the monocyte-macrophage lineage, are regulated by the RANKL-RANK-OPG system, which is a key factor in osteoclast differentiation. RANKL activates osteoclasts through its receptor RANK, while OPG acts as a decoy receptor that inhibits RANKL. In trabecular bone, high turnover involves rapid bone formation and resorption, influenced by conditions such as malignancy and inflammatory cytokines that increase RANKL expression. Cortical bone remodeling, regulated by aged osteocytes expressing RANKL, is less understood, despite ongoing research into how Rett syndrome, characterized by MeCP2 abnormalities, affects RANKL expression. Balancing trabecular and cortical bone involves mechanisms that preserve cortical bone, despite overall bone mass reduction due to aging or oxidative stress. Research into genes like sFRP4, which modulates bone mass, highlights the complex regulation by BMUs. The roles of the RANKL-RANK-OPG system extend beyond bone, affecting processes such as aortic valve formation and temperature regulation, which highlight the interconnected nature of biological research., (© 2024 The Author(s). Pathology International published by Japanese Society of Pathology and John Wiley & Sons Australia, Ltd.)

Background: Breast cancer exhibits high incidence and mortality among women, with distant metastasis, especially bone metastasis, being the leading cause of death. Despite advances in adjuvant therapies, bone metastasis remains a challenge for patient survival and quality of life. Exosomes, small vesicles capable of mediating intercellular communication, play a crucial role in tumor metastasis., Results: This study investigated the role of tumor-derived exosomal long noncoding RNA (lncRNA)-MIR193BHG in breast cancer bone metastasis. LncRNA-MIR193BHG was delivered to osteoclasts via exosomes and promoted osteoclast formation and activity by targeting the miR-489-3p/DNA methyltransferase 3A (DNMT3A) signaling axis, thereby accelerating breast cancer-induced osteolysis. Knockdown experiments demonstrated that reducing the levels of exosomal lncRNA-MIR193BHG significantly inhibited osteoclast differentiation and bone resorption, which was confirmed both in vitro and in vivo. Additionally, mechanistic studies revealed that lncRNA-MIR193BHG acted as a competitive endogenous RNA (ceRNA) interacting with miR-489-3p, regulating DNMT3A expression and subsequently affecting osteoclast differentiation., Conclusions: These findings suggest that lncRNA-MIR193BHG plays a critical regulatory role in breast cancer bone metastasis, and the lncRNA-MIR193BHG/miR-489-3p/DNMT3A signaling axis could be a potential target for the treatment of breast cancer bone metastasis. Future studies should further explore the broader applicability of this mechanism and its clinical feasibility., Competing Interests: Declarations. Ethics approval and consent to participate: All procedures involving animal care and use were approved by Institutr Of Analysis And Testing, Beijing Academy Of Science And Technology(Beijing Center for Physical&Chemical Analysis)Application for Laboratory Animal Welfare and Ethical review and followed the National Policy on the Use of Laboratory Animals. Consent for publication: All authors agreed to this publication. Competing interests: The authors declare that they have no competing interests., (© 2025. The Author(s).)

Extracellular vesicles (EVs), particularly exosomes (EXOs) of various skeletal and stem cells, were shown to delay osteoarthritis (OA) progression, and apoptotic bodies (ABs), another EV subtype, of osteoclasts showed osteoanabolic actions and were involved in the osteoclastic-regulation of local bone formation. Moreover, this study demonstrates that microvesicles (MVs) released by osteoclasts displayed potent pro-chondrogenic, pro-osteogenic, and anti-inflammatory activities. These activities were unique to osteoclastic MVs and were not shared by osteoclastic ABs and EXOs or MVs of other cell types. Because chronic synovial inflammation, progressive articular cartilage erosion, abnormal subchondral bone remodeling, and inability to regenerate articular cartilage are key etiologies of OA, we postulate that the foregoing activities of osteoclastic MVs could simultaneously target multiple etiologies of OA and could thereby be an effective therapy for OA. Accordingly, this study sought to assess the feasibility of an osteoclastic MV-based strategy for OA with a mouse tibial plateau injury model of OA. Briefly, tibial plateau injuries were created on the right knees of adult C57BL/6J mice, MVs were intraarticularly injected into the injured joints biweekly, and the OA progression was monitored histologically at five weeks post-injury. The MV treatment reduced the OA-induced losses of articular cartilage area and thickness, decreased irregularity in the articular cartilage surface, reduced loss of gliding/intermediate zone of articular cartilage, reduced osteophyte formation, suppressed synovial inflammation, and decreased the OARSI OA score. In summary, treatment with osteoclastic MVs delayed or reversed OA progression. Thus, this study supports the feasibility of an osteoclastic MV-based therapy for OA.

Background: Osteosarcoma (OS) is one of the most common primary malignant bone tumors, primarily originating from mesenchymal tissue. It is notorious for its high invasiveness, high disability rate, high mortality rate, and poor prognosis. In most primary and metastatic malignant tumors, bone destruction can promote cancer progression, which is closely related to osteoclast activation and the imbalance between osteoblasts and osteoclasts. A large number of studies confirmed that osteoclasts are an important part of OS, which play an active role in destroying bone homeostasis and promoting the progress of OS. Therefore, we conducted a detailed study of osteoclasts at the single cell level, aiming to find new OS therapeutic targets to prevent tumor progression and local spread., Methods: We analyzed the single-cell sequencing data of OS patients and usedMonocle2, Cytotrace, and Slingshot software to analyze the pseudo-sequential trajectory during OS progression. CellChat was used to reveal the communication between cells. PySCENIC was used to identify active transcription factors in osteoclasts. Finally, we further demonstrated the results by RT-qPCR analysis, CCK-8 assay, wound healing assay, Transwell assay, etc., Results: Through the analysis of single-cell sequencing data in OS, we identified a highly specific subgroup, C2MKI67+ Osteoclast. The key signaling pathway APP and the top 1 transcription factor PPARG in this subgroup played essential roles in osteoclast proliferation and differentiation. Given the pivotal role of osteoclasts in OS progression, we speculated that these signaling pathways and transcription factors could emerge as novel therapeutic targets, offering innovative strategies for OS treatment., Conclusion: This study enhanced our understanding of OS and osteoclasts through scRNA-seq. Furthermore, we discovered that PPARG amplifies osteoclast activation and proliferation, resulting in excessive bone resorption and degradation of the bone matrix, thereby creating a favorable environment for tumor cell proliferation and growth. By innovatively targeting PPARG, it affected osteoclast proliferation and thus affected tumor progression; this work offered new insights and directions for the clinical treatment of OS patients., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2025 Sun, Zhang, Xiahou, Zhao and Liang.)

Craniometaphyseal dysplasia (CMD), a rare craniotubular disorder, occurs in an autosomal dominant (AD) or autosomal recessive (AR) form. CMD is characterized by hyperostosis of craniofacial bones and metaphyseal flaring of long bones. Many patients with CMD suffer from neurological symptoms. The pathogenesis of CMD is not fully understood. Treatment is limited to craniofacial surgery. Here, we report a knock in (KI) mouse model for AR CMD carrying a Cx43 R239Q mutation. Cx43 KI/KI mice replicate typical features of AR CMD, including thickening of craniofacial bones, club-shaped femurs, and widened diaphyseal cortical bones. Female Cx43 KI/KI mice display remarkably more bone overgrowth than male Cx43 KI/KI mice as they age. In contrast to Cx43 +/+ littermates, Cx43 KI/KI mice exhibit periosteal bone deposition and increased osteoclast (OC) numbers in the endosteum of long bones. Although formation of resting OCs in Cx43 +/+ and Cx43 KI/KI mice is comparable, the actively resorbing Cx43 KI/KI OCs have reduced resorption on bone chips. Cx43 KI/KI mice display reduced osteocyte dendrites. RNA from Cx43 KI/KI femoral cortical bones show reduced expression levels of Sost, Tnf-α, IL-1β, Esr1, Esr2, and a lower Rankl/Opg ratio. Moreover, the Cx43 R239Q mutation results in altered spatial expression of Cx43 protein and mild reduction of gap junction and hemichannel activity. The distinct phenotype seen in Cx43 KI/KI mice but not in Cx43 ablation models suggests that Cx43 loss-of-function is unlikely the main cause of AR CMD. Additional studies are required to investigate new roles of CMD-mutant Cx43., Competing Interests: Competing interests: The authors declare no competing interests., (© 2025. The Author(s).)

Prostate cancer, as one of the most prevalent malignant tumors in men, seriously affects the prognosis and survival of patients due to its extremely high rate of bone metastasis. This study investigated the effect of Polyphyllin VI (PPVI) on metastatic bone disease for the first time in prostate cancer, focusing on its impact on osteoclast and tumor cell. In vitro studies utilized TRAP staining, ghost pen cyclic peptide staining, and bone resorption assays to evaluate the differentiation and function of receptor activator of nuclear factor-κB ligand (RANKL) induced and RM-1 conditional medium (CM) induced osteoclasts. The colony formation assay, wound healing assay, and Transwell assay were employed to analyze tumor cell proliferation, migration, and invasion in vitro. Flow cytometry was used to detect the cycling and apoptosis of tumor cells in vitro. Western Blot and PCR assays were conducted to assess the expression of genes. In vivo, micro-CT, hematoxylin-eosin staining, and immunohistochemical staining evaluated the impact of PPVI on bone destruction and tumor growth in a mouse model of tumor tibial metastasis. The study results indicated that PPVI effectively inhibited osteoclast differentiation, suppresses tumor cell proliferation, migration, and invasion in vitro, and induces apoptosis and G2/M phase arrest. In vivo, PPVI not only inhibits the growth of metastatic tumors but also mitigates the resulting bone destruction. These results suggest that PPVI holds significant potential as an alternative treatment for prostate cancer with bone metastasis, providing insights into its molecular mechanisms and therapeutic efficacy., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

Background: Undifferentiated carcinoma (UC) is a rare subtype of pancreatic cancer distinguished from UC with osteoclast-like giant cells (UC-OGC) in 2019, affecting interpretation of literature that does not distinguish these subtypes. We sought to identify translationally relevant differences between these 2 variants and compared with pancreatic ductal adenocarcinoma., Methods: We characterized clinical and multiomic differences between UC (n = 32) and UC-OGC (n = 15) using DNA sequencing, RNA sequencing, and multiplex immunofluorescence and compared these findings with pancreatic ductal adenocarcinoma., Results: Characteristics at diagnosis were similar between UC and UC-OGC, though the latter was more resectable (P = .009). Across all stages, median overall survival was shorter for UC than for UC-OGC (0.4 years vs 10.8 years, respectively; P = .003). This shorter survival was retained after stratification by resection, albeit without statistical significance (1.8 years vs 11.9 years, respectively; P = .08). In a subset of patients with available tissue, the genomic landscape was similar among UC (n = 9), UC-OGC (n = 5), and pancreatic ductal adenocarcinoma (n = 159). Bulk RNA sequencing was deconvoluted and, along with multiplex immunofluorescence in UC (n = 13), UC-OGC (n = 5), and pancreatic ductal adenocarcinoma (n = 16), demonstrated statistically significantly increased antigen-presenting cells, including M2 macrophages and natural killer cells, and decreased cytotoxic and regulatory T cells in UC and UC-OGC vs pancreatic ductal adenocarcinoma. Findings were similar between UC and UC-OGC , except for decreased regulatory T cells in UC-OGC (P = .04)., Conclusions: In this series, UC was more aggressive than UC-OGC, with these variants having more antigen-presenting cells and fewer regulatory T cells than pancreatic ductal adenocarcinoma, suggesting potential for immune-modulating therapies in the treatment of these pancreatic cancer subtypes., (© The Author(s) 2024. Published by Oxford University Press.)

Iron overload leads to apoptosis and increased expression of receptor activator of nuclear factor kappa-Β ligand (RANKL) in osteocytes, which in turn accelerates osteoclastogenesis. Since osteocytes are the main RANKL producers, we hypothesized that apoptotic osteocytes increase RANKL expression in osteocytes, which in turn stimulates osteoclastogenesis and bone resorption. In this study, alendronate or IG9402, a bisphosphonate (BP) analog which does not inhibit bone resorption, inhibited iron overload-induced osteocyte apoptosis and increased RANKL expression. Both BPs also prevented osteoblast apoptosis but did not inhibit the increase in osteoblastic RANKL. Alendronate, but not IG9402, prevented the increase in osteoclastogenesis and serum levels of the bone resorption marker C-telopeptide of type I collagen (CTX) in iron-overloaded mice. Alendronate also prevented the iron overload-induced reduction in femoral bone mineral density, disruption of bone microstructure, and weakness of bone strength. Although IG9402 did not prevent bone loss due to iron overload, it partially prevented reduction of strength, suggesting that osteocyte viability contributes to the maintenance of bone strength. In conclusion, although osteocyte apoptosis in the presence of iron overload leads to an increase in osteocytic RANKL production. However, blocking these events was not sufficient to inhibit iron overload-induced osteoclastogenesis and bone loss., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Iron is an essential element for physiological cellular processes, but is toxic in excess. Iron overload diseases are commonly associated with low bone mass. Increased bone resorption by osteoclasts as well as decreased bone formation by osteoblasts have been implicated in bone loss under iron overload conditions. However, the exact contribution of individual cell types has not yet been formally tested. In this study, we aimed to investigate the role of osteoclast precursors in iron overload-induced bone loss. To that end, we used clodronate liposomes to deplete phagocytic cells (including macrophages and osteoclast precursors) in male C57BL/6J mice that were exposed to ferric derisomaltose. Bone microarchitecture and bone turnover were assessed after 4 weeks. The application of clodronate resulted in the efficient depletion of circulating myeloid-lineage cells by about 70%. Depletion of osteoclast precursors mitigated iron overload-induced trabecular bone loss at the lumbar vertebrae and distal femur. While clodronate treatment led to a profound inhibition of bone turnover in control mice, it significantly reduced osteoclast numbers in iron-treated mice without further impacting the bone formation rate or serum PINP levels. Our observations suggest that even though bone formation is markedly suppressed by iron overload, osteoclasts also play a key role in iron overload-induced bone loss and highlight them as potential therapeutic targets., (© 2024 The Author(s). IUBMB Life published by Wiley Periodicals LLC on behalf of International Union of Biochemistry and Molecular Biology.)

Plastic pollution is becoming more and more serious, and microplastics (MPs) formed by degradation from plastics significantly threaten the health of animals and humans. However, it remains unknown how MPs interfere with bone homeostasis by regulating the function of bone marrow mesenchymal stem cells (BMSCs). In order to simulate the toxic impacts of long-term low-dose MPs on the skeletal system, we constructed a 6-month drinking water model of mice exposed to MPs. We found that the bone microstructure in the femur of mice exposed to MPs was destroyed, the quantity of bone trabeculae decreased sharply and the bone mass decreased significantly, accompanied by the decrease of bone formation and the activation of osteoclasts. In addition, RNA sequencing showed NF-κB pathway was activated in MPs-treated BMSCs, manifested as significantly up-regulated inflammatory factors, accelerated the senescence of BMSCs, and inhibited their osteogenic differentiation and extracellular mineralization. Senescent BMSCs induced by MPs led to the overproduction of RANKL, which contributed to the production of more osteoclasts. Importantly, the administration of NF-κB inhibitors in vivo markedly diminished MPs-induced BMSCs senescence and impaired osteogenic differentiation. Meanwhile, the secretion of RANKL caused by MPs was reversed, and osteoclast formation was significantly reduced. In summary, our data innovatively reveal the core mechanism of MPs in bone balance. By promoting the NF-κB signaling pathway, it significantly accelerates the aging of BMSCs, causes a decrease in bone formation, and promotes osteoclast formation through RANKL., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Regulatory T cells (Tregs) are immune regulatory T cells that are vital for controlling inflammation. The role of Tregs in inflammatory diseases namely psoriatic arthritis (PsA) is still poorly understood. The underlying reason being a lack of robust unbiased analysis to test the immune regulatory phenotype of human Tregs. Here, we propose that checkpoint receptors can identify functional Tregs in PsA. Using unbiased BD Rhapsody single-cell analysis, we have analyzed the expression pattern of checkpoint receptors in Tregs and found that PsA Tregs are enriched in the expression of CTLA4, TIGIT, PD-1, and GITR while TIM3 was downregulated. Furthermore, PD-1 + Tregs in PsA had an increased type 1 phenotype and expressed the protease asparaginyl endopeptidase. By harnessing the PD-1 signaling pathway and inhibiting asparaginyl endopeptidase, PsA Treg function was significantly enhanced in in vitro suppressor assays. Next, we interrogated the cell interaction pathways of Tregs in PsA and found a diminished crosstalk with circulating osteoclast precursors through the CD244-CD48 coreceptor pathways. Therapeutically, PsA Treg function could be enhanced by modulating PD-1 and osteoclast interactions. Our study suggests that unconventional immune cell crosstalk with Tregs is severely diminished in PsA., Competing Interests: Conflict of interest The authors declare that they have no conflicts of interest with the contents of this article., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Hyperactivation of osteoclasts has been identified as a significant etiological factor in several bone resorption-related disorders, including osteoporosis, periodontitis, arthritis, and bone metastasis of tumors. It has been demonstrated that the severity of these diseases is influenced by lipids that regulate osteoclast differentiation and activity through specific signaling pathways and cytokine levels. The regulatory mechanisms of different types of lipids on osteoclastogenesis vary across diverse disease contexts in bone resorption regulated by osteoclasts. This review presents an overview of the mechanisms underlying osteoclast formation and summarizes the pathways through which various lipids regulate osteoclastogenesis in different pathological contexts. We also discuss effective therapeutic strategies for osteolytic diseases based on modulation of lipid metabolism., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2025 Elsevier Inc. All rights reserved.)

Background: Bone is the most frequent site of metastasis for breast cancer (BC). Metastatic BC cells interact with bone cells, including osteoclasts and osteoblasts, creating a cancer niche where they seed and proliferate. MicroRNAs (miRNAs) are regulators of breast-to-bone metastasis progression. MiR-24-2-5p has previously been shown to have roles in both breast cancer progression and inhibition of osteogenic differentiation. However, a direct link between miR-24-2-5p activity and the onset of bone metastasis remains ill-defined., Methods: Analysis of the expression of miR-24 forms (miR-24-2-5p, miR-24-3p, miR-24-1-5p) in the serum from early-stage BC patients at baseline (time of surgery) was conducted. MiR-24-2-5p overexpression in BC cells (NW1, a luc2-positive subpopulation of MDA-MB-231, and MCF7) was obtained by miRNA mimic transfection or lentivirus transduction. MiR-24-2-5p downregulation in BC cells (ZR-75-1, T-47D, SK-BR-3) was obtained by miRNA inhibitor transfection. Cell proliferation, migration and/or invasion assays were performed to assess BC cell functions after modulation of miR-24-2-5p expression. An animal model was used to assess the effect of miR-24-2-5p overexpression on early BC metastasis formation, as judged by bioluminescence imaging, and on bone remodelling, following measurement of circulating bone resorption (CTX-I) and bone formation (P1NP) markers. The effect of conditioned medium from miR-24-2-5p-overexpressing BC cells on human and murine osteoclast differentiation was investigated. Endogenous miR-24-2-5p expression levels were also quantified during murine osteoclast differentiation. RNA-sequencing (RNA-seq) analysis of BC cells was performed to evaluate transcriptomic changes associated with miR-24-2-5p overexpression. Selected modulated transcripts upon miR-24-2-5p overexpression were further validated by real-time qPCR., Results: Low expression levels of miR-24-2-5p, but not other miR-24 forms (miR-24-3p, miR-24-1-5p), in the serum from early-stage BC patients were associated with a high risk to develop future (bone) metastases. MiR-24-2-5p was also present in small extracellular vesicles secreted from BC cells. Forced expression of miR-24-2-5p in BC cells (NW1, MCF7) reduced their malignant traits (migration, invasion, and proliferation) in vitro. Furthermore, miR-24-2-5p overexpression in NW1 cells reduced metastasis, particularly in bone, and decreased bone turnover in vivo. RNA-seq and real-time qPCR analyses of NW1 and MCF7 cells overexpressing miR-24-2-5p showed the downregulation of common transcripts (CNNM4, DCTD, FMR1, PIGS, HLA-A, ICK, SH3BGRL2, WDFY, TRAF9B, IL6ST, PEX10, TRIM59). The conditioned medium from BC cells overexpressing miR-24-2-5p decreased human and murine osteoclast differentiation in vitro. Additionally, endogenous miR-24-2-5p expression levels in murine bone marrow-derived monocytes decreased during their differentiation into osteoclasts, further suggesting an inhibitory role for miR-24-2-5p during osteoclastogenesis., Conclusion: MiR-24-2-5p exerts multiple protective roles in the early steps of BC bone metastasis by reducing malignant BC cell traits and tumour cell dissemination in bone, as well as by reducing the differentiation of precursors into mature osteoclasts., Competing Interests: Declarations. Ethical approval: Animal studies were carried out in accordance with local guidelines and UK Home Office approval under project licenses 70/8964 and P99922A2E, University of Sheffield, Sheffield, UK. For peripheral blood mononuclear cells of healthy donors, the procedure was approved by the Ethical Committee of Campus Bio-Medico University of Rome (Prot. 21/15 OSS), in accordance with the Declaration of Helsinki principles. Competing interests: The authors declare no competing interests., (© 2024. The Author(s).)

Rheumatoid arthritis (RA) is a chronic autoimmune disorder marked by pain, inflammation, and discomfort in the synovial joints. It is critical to understand the pathological mechanisms of RA progression. MicroRNA-378 (miR-378) is highly expressed in the synovium of RA patients and positively correlated with disease severity, but its function and underlying mechanisms remain poorly understood. In this study, miR-378 transgenic (miR-378 high ) mice were used to construct the collagen-induced arthritis (CIA) model for exploring the role of miR-378 in RA development. miR-378 high CIA mice showed accelerated RA development, as evidenced by exaggerated joint swelling and bone structural deformities. More severe endoplasmic reticulum (ER) stress and the consequent angiogenesis and osteoclastogenesis were also activated in the synovial tissue and calcaneus, respectively, in the miR-378 high group, suggesting that ER plays a significant role in miR-378-mediated RA pathogenesis. Upon in vitro RA induction, fibroblast-like synoviocytes (FLSs) isolated from miR-378 high mice showed a higher expression level of ER stress markers. The conditioned medium (CM) from RA-FLSs of miR-378 high mice stimulated more intensive angiogenesis and osteoclastogenesis. The ER stress-related protein Crebrf was identified as a downstream target of miR-378. Crebrf knockdown diminished the promoting effect of miR-378 on ER stress, as well as its downstream angiogenesis and osteoclastogenesis activities. Tail vein injection of anti-miR-378 lentivirus in an established RA mouse model was shown to ameliorate RA progression. In conclusion, miR-378 amplified RA development by promoting ER stress and downstream angiogenesis and osteoclastogenesis, thus indicating that miR-378 may be a potential therapeutic target for RA treatment., Competing Interests: Competing interests: The authors declare no competing interests. Ethics approval and consent to participate: This study was carried out in accordance with the principles outlined in the Declaration of Helsinki. The Laboratory Animal Ethics Committee at the Chinese University of Hong Kong reviewed and approved all experimental procedures involving these animals., (© 2024. The Author(s).)

Sickle cell disease (SCD) is a severe hematological disorder characterized by erythrocyte sickling that causes significant morbidity and mortality. Skeletal complications of SCD include a high incidence of bone loss, especially in vertebrae, leading to fragility fractures that contribute to disease burden. Whether hydroxyurea (HU), a front-line therapy for SCD ameliorates bone disease has not been established. To investigate HU action on SCD-related vertebral defects, we used HU-treated "Townes" mice, an SCD animal model and performed high-resolution micro-computed tomography (µCT) imaging to resolve bone volume and micro-architectural structure of cortical and trabecular bone, the two major compartments contributing to bone mass and strength. Our data revealed that cortical bone was significantly diminished in the vertebrae of skeletally mature (representing adults) and immature (representing children) SCD mice, while only mature mice lost trabecular bone mass. Administration of HU ameliorated cortical bone loss in mature SCD mice, but paradoxically promoted trabecular bone decline in both groups. We further investigated the mechanisms of HU action in wild-type C57BL6/J mice. HU caused dose-dependent trabecular bone loss due to diminished osteoclast and osteoblast function, indicative of a low bone turnover state. Mechanistic investigations in vitro revealed that HU impeded osteoblast-progenitor proliferation and early differentiation, and diminished osteoclastogenic cytokine production, blunting osteoclast formation as well as the activity of mature osteoclasts. HU further, suppressed mitochondrial, but not glycolytic energy metabolism in both differentiating osteoblasts and differentiated osteoclasts. Collectively, these findings reveal that despite ameliorating cortical bone loss, HU inhibits trabecular bone formation and resorption, by suppressing mitochondrial energy metabolism and blunting the differentiation and/or activity of osteoblasts and osteoclasts. Together HU drives a low bone turnover state culminating in trabecular bone loss. Further investigation into HU's impact on bone in SCD patients is warranted for understanding and managing skeletal complications in this population., Competing Interests: Competing interests: The authors declare no competing interests. Ethics approval: Animal studies were approved by the Emory IACUC and performed in accordance with the approved protocols and in accordance with the National Institutes of Health’s Laboratory Guide for the Care and Use of Laboratory Animals., (© 2024. This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply.)

Breast cancer bone metastases increase fracture risk and are a major cause of morbidity and mortality among women. Upon colonization by tumor cells, the bone microenvironment undergoes profound reprogramming to support cancer progression, which disrupts the balance between osteoclasts and osteoblasts and leads to bone lesions. A deeper understanding of the processes mediating this reprogramming could help develop interventions for treating patients with bone metastases. Here, we demonstrated that osteocytes (Ot) in established breast cancer bone metastasis develop premature senescence and a distinctive senescence-associated secretory phenotype (SASP) that favors bone destruction. Single-cell RNA sequencing identified Ots from mice with breast cancer bone metastasis enriched in senescence, SASP markers, and pro-osteoclastogenic genes. Multiplex in situ hybridization and artificial intelligence-assisted analysis depicted Ots with senescence-associated satellite distension, telomere dysfunction, and p16Ink4a expression in mice and patients with breast cancer bone metastasis. Breast cancer cells promoted Ot senescence and enhanced their osteoclastogenic potential in in vitro and ex vivo organ cultures. Clearance of senescent cells with senolytics suppressed bone resorption and preserved bone mass in mice with breast cancer bone metastasis. These results demonstrate that Ots undergo pathological reprogramming by breast cancer cells and identify Ot senescence as an initiating event triggering lytic bone disease in breast cancer metastases. Significance: Breast cancer cells remodel the bone microenvironment by promoting premature cellular senescence and SASP in osteocytes, which can be targeted with senolytics to alleviate bone loss induced by metastatic breast cancer. See related commentary by Frieling and Lynch, p. 3917., (©2024 American Association for Cancer Research.)

Cancer-induced bone disease greatly diminishes the quality of life for patients with bone metastatic breast cancer, resulting in painful skeletal-related events including bone loss and fracture. Improved understanding of the roles of osteoblasts and osteoclasts, and how tumors alter their biology, has led to blockbuster therapies that significantly reduce skeletal-related events, but the disease remains incurable. However, emerging technologies and tools for studying the role of other stromal and immune components in controlling tumor-host interactions have begun to reveal new insights that may yield tractable therapeutic targets to further mitigate the painful effects of bone metastases. In this issue of Cancer Research, Kaur and colleagues study osteocytes, which are terminally differentiated osteoblasts and entombed within the bone matrix, from established bone metastatic breast cancer and report how the disease ages them as characterized by a senescence-associated secretory phenotype. This premature development of osteocyte senescence in turn enhances bone destruction and osteoclastogenic potential. Targeting senescent cells using senolytics suppressed bone resorption and preserved bone mass. Collectively, these findings underscore osteocyte involvement in the "vicious cycle" of bone metastasis, and targeting senescent osteocytes represents a new avenue for managing cancer-induced bone disease. See related article by Kaur et al., p. 3936., (©2024 American Association for Cancer Research.)

A 76-year-old man presented with a pancreatic cystic lesion on magnetic resonance imaging before surgery for bladder cancer. Endoscopic ultrasound(EUS)suggested a malignant tumor such as a neuroendocrine neoplasm, but EUS-fine-needle aspiration was not performed. In addition, a single tumor 10 mm in size was found in the liver(S5), and liver metastasis was suspected. We judged that surgery would be useful for treating the neuroendocrine neoplasm and liver metastasis, so we performed distal pancreatectomy, splenectomy, and partial hepatectomy. Histopathological examination revealed anaplastic carcinoma with osteoclast-like giant cells and liver metastasis. Four courses of modified FOLFIRINOX and 3 courses of liposomal irinotecan plus 5-fluorouracil/Leucovorin were administered as chemotherapy, but it was discontinued due to adverse events. Thereafter, S-1 monotherapy was performed for 7 months, and the patient was alive without recurrence as of 1 year and 8 months postoperatively. Anaplastic carcinoma of the pancreas often recurs early after surgery; thus, long-term survival is difficult to achieve, even after R0 resection. Here, we report this case of anaplastic carcinoma with osteoclast-like giant cells of the pancreas and synchronous liver metastasis that was successfully treated with surgery and chemotherapy.

Impaired callus remodeling significantly contributes to the delayed healing of osteoporotic fractures; however, the underlying mechanisms remain unclear. Sensory neuronal signaling plays a crucial role in bone repair. In this study, we aimed to investigate the pathological mechanisms hindering bone remodeling in osteoporotic fractures, particularly focusing on the role of sensory neuronal signaling. We demonstrate that in ovariectomized (OVX) mice, the loss of CGRP + TrkA + sensory neuronal signaling during callus remodeling correlates with increased Cx3cr1 + iOCs expression within the bone callus. Conditional knockout of Cx3cr1 + iOCs restored CGRP + TrkA + sensory neuronal, enabling normal callus remodeling progression. Mechanistically, we further demonstrate that Cx3cr1 + iOCs secrete Sema3A in the osteoporotic fracture repair microenvironment, inhibiting CGRP + TrkA + sensory neurons' axonal regeneration and suppressing nerve-bone signaling exchange, thus hindering bone remodeling. Lastly, in human samples, we observed an association between the loss of CGRP + TrkA + sensory neuronal signaling and increased expression of Cx3cr1 + iOCs. In conclusion, enhancing CGRP + TrkA + sensory nerve signaling by inhibiting Cx3cr1 + iOCs activity presents a potential strategy for treating delayed healing in osteoporotic fractures. Inhibition of inflammatory osteoclasts enhances CGRP + TrkA + signaling and accelerates callus remodeling in osteoporotic fractures., Competing Interests: Competing interests: The authors declare no competing interests. Ethics approval and consent to participate: All animal experiments were approved by the Ethics Committee of Tongren Hospital, affiliated with Shanghai Jiao Tong University School of Medicine (ethical approval number A2023-057-01), and conducted in accordance with the guidelines of Experimental Animal Science at Shanghai Jiao Tong University School of Medicine. Human sample collection was also approved by the Ethics Committee of Tongren Hospital (ethical approval number 2023-054-01). Informed consent was obtained in writing from all participants or their legal guardians., (© 2024. The Author(s).)

Bone metastasis (BM) is a common complication of cancer and contributes to a higher mortality rate in patients with cancer. The treatment of BM remains a significant challenge for oncologists worldwide. The colony‑stimulating factor (CSF) has an important effect on the metastasis of multiple cancers. In vitro studies have shown that CSF acts as a cytokine, promoting the colony formation of hematopoietic cells by activating granulocytes and macrophages. Other studies have shown that CSF not only promotes cancer aggressiveness but also correlates with the development and prognosis of various types of cancer. In recent years, the effect of CSF on BM has been primarily investigated using cellular and animal models, with limited clinical studies available. The present review discussed the composition and function of CSF, as well as its role in the progression of BM across various types of cancer. The mechanisms by which osteoclast‑ and osteoblast‑mediated BM occur are comprehensively described. In addition, the mechanisms of action of emerging therapeutic agents are explored for their potential clinical applications. However, further clinical studies are required to validate these findings.

Tay-Sachs Disease is a rare lysosomal storage disorder caused by mutations in the HEXA gene, responsible for the degradation of ganglioside GM2. In addition to progressive neurodegeneration, Tay-Sachs patients display bone anomalies, including kyphosis. Tay-Sachs disease mouse model (Hexa-/-Neu3-/-) shows both neuropathological and clinical abnormalities of the infantile-onset disease phenotype. In this study, we investigated the effects of GM2 accumulation on bone remodeling activity. Here, we evaluated the bone phenotype of 5-month-old Hexa-/-Neu3-/- mice with age-matched control groups using gene expression analysis, bone plasma biomarker analysis, and micro-computed tomography. We demonstrated lower plasma alkaline phosphatase activity and calcium levels with increased tartrate-resistant acid phosphatase levels, indicating reduced bone remodeling activity in mice. Consistently, gene expression analysis confirmed osteoblast reduction and osteoclast induction in the femur of mice. Micro-computed tomography and analysis show reduced trabecular bone volume, mineral density, number, and thickness in Hexa-/-Neu3-/- mice. In conclusion, we demonstrated that abnormal GM2 ganglioside accumulation significantly triggers skeletal abnormality in Tay-Sachs mice. We suggest that further investigation of the molecular basis of bone structure anomalies is necessary to elucidate new therapeutic targets that prevent the progression of bone symptoms and improve the life standards of Tay-Sachs patients. KEY MESSAGES: We detected the markers of bone loss-associated disorders such as osteopenia and osteoporosis in the Tay-Sachs disease mice model Hexa-/-Neu3-/-. We also demonstrated for the first time there is an increase in trabecular spacing and a reduction in trabecular thickness and number indicating skeletal abnormalities in mice model using micro-CT analysis., Competing Interests: Declarations. Ethics approval: The animal study was reviewed and approved by IYTEHADYEK. Conflict of interest: The authors declare that the research was conducted without any commercial or financial relationships that could be construed as a potential conflict of interest., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Background: Prostate cancer (PCa) is a serious malignancy. The main causes of PCa aggravation and death are unexplained resistance to chemotherapy and bone metastases., Objective: This study aimed to investigate the molecular mechanisms associated with the dynamic processes of progression, bone metastasis, and chemoresistance in PCa., Methods: Through comprehensive analysis of single-cell RNA sequencing (scRNA-seq) data, Gene Expression Omnibus (GEO) tumor progression and metastasis-related genes were identified. These genes were subjected to lasso regression modeling using the Cancer Genome Atlas (TCGA) database. Tartrate-resistant acid phosphatase (TRAP) staining and real-time quantitative PCR (RT-qPCR) were used to evaluate osteoclast differentiation. CellMiner was used to confirm the effect of LDHA on chemoresistance. Finally, the relationship between LDHA and chemoresistance was verified using doxorubicin-resistant PCa cell lines., Results: 7928 genes were identified as genes related to tumor progression and metastasis. Of these, 7 genes were found to be associated with PCa prognosis. The scRNA-seq and TCGA data showed that the expression of LDHA was higher in tumors and associated with poor prognosis of PCa. In addition, upregulation of LDHA in PCa cells induces osteoclast differentiation. Additionally, high LDHA expression was associated with resistance to Epirubicin, Elliptinium acetate, and doxorubicin. Cellular experiments demonstrated that LDHA knockdown inhibited doxorubicin resistance in PCa cells., Conclusions: LDHA may play a potential contributory role in PCa initiation and development, bone metastasis, and chemoresistance. LDHA is a key target for the treatment of PCa., Competing Interests: Declarations. Ethics approval: Not application. Consent for publication: Not applicable. Competing interests: All authors declare that they have no conflict of interest., (© 2024. The Author(s) under exclusive licence to The Genetics Society of Korea.)

Aim: This study aimed to reveal the unique microenvironment of peri-implantitis through single-cell analysis., Materials and Methods: Herein, we performed single-cell RNA sequencing (scRNA-seq) of biopsies from patients with peri-implantitis (PI) and compared the results with healthy individuals (H) and patients with periodontitis (PD)., Results: Decreased numbers of stromal cells and increased immune cells were found in the PI group, which implies a severe inflammatory infiltration. The fibroblasts were found to be heterogeneous and the specific pro-inflammatory CXCL13 + sub-cluster was more represented in the PI group, in contrast to the PD and H groups. Furthermore, more neutrophil infiltration was detected in the PI group than in the PD group, and cell-cell communication and ligand-receptor pairs revealed most neutrophils were recruited by CXCL13 + fibroblasts through CXCL8/CXCL6-CXCR2/CXCR1. Notably, our study demonstrated that the unique microenvironment of the PI group promoted the differentiation of monocyte/macrophage lineage cells into osteoclasts, which might explain the faster and more severe bone resorption in the progression of PI than PD., Conclusions: Collectively, this study suggests a unique immune microenvironment of PI, which may explain the differences between PI and PD in the clinic. These outcomes will aid in finding new specific and effective treatments for PI., (© 2024 The Authors. Journal of Clinical Periodontology published by John Wiley & Sons Ltd.)

Background: Knee osteoarthritis (KOA) is the most common type of joint disease in elderly people and is characterized by pain and dysfunction. Although the monoiodoacetate (MIA)-induced model is widely used as a rodent KOA model, it is important to acknowledge the inherent limitations of this model, as the MIA model develops complex pathological phases on a daily basis. An accurate understanding of this model and the selection of an appropriate time point according to the target for drug candidates can lead to the development of clinically effective drugs., Methods: Changes in the pathological state of the MIA model were assessed via histopathological evaluation. Clodronate, a bisphosphonate, and diclofenac, a nonsteroidal anti-inflammatory drug (NSAID), were selected as models of clinically effective drugs due to their different mechanisms of action. The analgesic effects of both drugs on the MIA model were evaluated. The long-term effect of clodronate on subchondral bone osteoclasts was also evaluated., Results: Histopathological evaluation revealed that MIA-induced symptomatic behavior occurred in the early and late phases and was accompanied by synovial inflammation and osteoclast-related joint degeneration, respectively. Although clodronate inhibited symptomatic behavior and prevented cartilage degeneration from the early to late phases, diclofenac inhibited symptomatic behavior only in the early phase. Clodronate acted locally and inhibited the activation of subchondral osteoclasts., Conclusions: Pathological changes, such as synovial changes in the early phase and knee joint degeneration in the late phase, in the MIA model are similar to those in human KOA. Our results indicate that the early phase in the MIA model is appropriate for evaluating the effects of anti-inflammatory agents such as NSAIDs and corticosteroids. The late phase in the MIA model is appropriate for evaluating the effects of drugs that act on cartilage and subchondral bone., Competing Interests: Declarations. Ethics approval and consent to participate: All animal studies were reviewed and approved by the Institutional Animal Care and Use Committee of Seikagaku Corporation and were performed under an animal husbandry/management system in an appropriate environment with animal protection and welfare (Approval number: 70–101, 72–15, 73–187, and 75–119). Clinical trial number: not applicable. Consent for publication: Not applicable. Competing interests: The authors declare no competing interests., (© 2024. The Author(s).)

Background: Epithelial stromal interaction 1 (EPSTI1) plays an important role in M1 macrophages, which induce osteoclastogenesis. One recent genome-wide association study (GWAS) involving 426,824 individuals has shown that EPSTI1 is strongly associated with osteoporosis (P < 5E-8). Therefore, we speculate that EPSTI1 participates in the modulation of osteoporosis through osteoclastogenesis. The roles of EPSTI1 in osteoclastogenesis and bone resorption remain unclear., Methods: Femur specimens were collected from osteoporotic patients and control patients. Immunofluorescence staining was used to detect the expression of EPSTI1 and signaling pathways. The osteoclastic potential of RAW264.7 cells with Sh-EPSTI1 lentivirus infection was tested using tartrate-resistant acid phosphatase (TRAP) staining, western blotting, and quantitative reverse transcription polymerase chain reaction (qRT-PCR). Western blotting was also used to examine signaling pathways., Results: In this study, EPSTI1 was found to be significantly increased in tartrate-resistant acid phosphatase positive (ACP5 + ) osteoclasts of bone sections from osteoporotic patients. Next, we identified EPSTI1 as a positive regulator of osteoclastogenesis and osteoclast differentiation capability. Diminished EPSTI1 expression resulted in reduced osteoclastic resorption. Mechanistically, EPSTI1-driven osteoclastogenesis was regulated by NF-κB pathway, which was mediated by the phosphorylation of protein kinase R (p-PKR). Furthermore, EPSTI1 participating in the modulation of osteoporosis via PKR/NF-κB pathway was also verified in the bone samples of osteoporotic patients., Conclusions: Collectively, our findings suggest that EPSTI1 may regulate osteoclast differentiation and bone resorption through PKR/NF-κB pathway and in vivo experiments are needed to further verify EPSTI1 as the therapy target for osteoporosis., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

New insights into cellular interactions and key biomolecules involved in lung cancer (LC) bone metastasis could offer remarkable therapeutic benefits. Using a panel of four LC cells, we investigated LC-bone interaction by exposing differentiating osteoclasts (OCs) to LC cells (LC-OC interaction) directly in a co-culture setting or indirectly via treatment with LC secretomes (conditioned media or exosomes). LC-OC interaction facilitated the production of large-sized OCs (nuclei > 10) coupled with extensive bone resorption pits. Proteomic analysis of LC exosomes identified galectin-3-binding protein (Gal3bp) as a potential biomarker which was released primarily by most of LC-derived exosomes. The facilitation of OC differentiation and function by LC-exosomal Gal3bp was supported by the application of recombinant Gal3bp and anti-Gal3bp in OC treatment. Further, our results exhibited a dysregulation of crucial OC markers (TRAF6, p-SAPK/JNK, p-44/42 MAPK, NFAT2 and CD9) during LC-OC interaction that possibly contributed to the facilitation of osteoclastogenesis. Simulation of bone metastasis via intratibial injection of LC cells revealed Gal3bp's possible roles in enhancing OC activation leading to osseous tissue resorption. Overall, this work implicated LC-exosomal Gal3bp in osteolytic metastasis of LC which warrants further studies to assess its potential prognostic and therapeutic relevance., (© 2024. The Author(s).)

Rheumatoid arthritis (RA) is a chronic autoimmune disease. Its pathological features include synovial inflammation, bone erosion, and joint structural damage. Our previous studies have shown that interleukin (IL)-35 is involved in the pathogenesis of bone loss in RA patients. In this study, we are further evaluating the efficacy of IL-35 on collagen-induced arthritis (CIA) in the mouse model. Male DBA/1J mice (n = 10) were initially immunized, 2 μg/mouse IL-35 was injected intraperitoneally every week for 3 weeks after the establishment of the CIA model. Clinical arthritis, histopathological analysis, and three-dimensional micro‑computed tomography (3D micro‑CT) were determined after the mice were anesthetized on the 42th day. In vitro, RANKL/M-CSF induced mouse preosteoclasts (RAW264.7 cells line) was subjected to antiarthritis mechanism study in the presence of IL-35. The results of clinical arthritis, histopathological analysis, and 3D micro‑CT, the expression of RANK/RANKL/OPG axis, inflammatory cytokines, and osteoclastogenesis-related makers demonstrated decreasing severity of synovitis and bone destruction in the ankle joints after IL-35 treatment. Furthermore, IL-35 attenuated inflammatory cytokine production and the expression of osteoclastogenesis-related makers in a mouse preosteoclasts cell line RAW264.7. The osteoclastogenesis-related makers were significantly reduced in IL-35 treated RAW264.7 cells line after blockage with the JAK/STAT1 signaling pathway. These results demonstrated that IL-35 protein could inhibits osteoclastogenesis and attenuates CIA in mice. We concluded that IL-35 can exhibit anti-osteoclastogenesis effects by reducing the expression of inflammatory cytokines and osteoclastogenesis-related makers, thus alleviating bone destruction in the ankle joint and could be a potential therapeutic target for RA., (© 2024 Wiley Periodicals LLC.)

The regulatory mechanisms underlying bone metastasis in lung adenocarcinoma (LUAD) are not yet fully understood despite the frequent occurrence of bone involvement. This study aimed to examine the involvement and mechanism of integrin subunit beta 3 (ITGB3) in the process of LUAD bone metastasis. Our findings indicate that ITGB3 facilitates the migration and invasion of LUAD cells in vitro and metastasis to the bone in vivo. Furthermore, ITGB3 stimulates osteoclast production and activation, thereby expediting osteolytic lesion progression. Extracellular vesicles (EVs) isolated from the conditioned medium (CM) of LUAD cells overexpressing ITGB3 determined that ITGB3 facilitates osteoclastogenesis and enhances osteoclast activity by utilizing EVs-mediated transport to RAW264.7 cells. Our in vivo findings demonstrated that ITGB3-EVs augmented the population of osteoclasts, thereby establishing an osteoclastic pre-metastatic niche (PMN) conducive to the colonization and subsequent growth of LUAD cells in the bone. ITGB3 is enriched in serum EVs of patients diagnosed with LUAD bone metastasis, potentially facilitating osteoclast differentiation and activation in vitro. Our research illustrates that ITGB3-EVs derived from LUAD cells facilitate osteoclast differentiation and activation by modulating the phosphorylation level of p38 MAPK. This process ultimately leads to the generation of osteolytic PMN and accelerates the progression of bone metastasis., (© 2024 Wiley Periodicals LLC.)

Background: Zoledronic acid (ZOL) is a type of bisphosphonate with good therapeutic effects on orthopaedic diseases. However, the pharmacological functions of ZOL on steroid-induced avascular necrosis of femoral head (SANFH) and the underlying mechanism remain unclear, which deserve further research., Methods: SANFH models both in vivo and in vitro were established by dexamethasone (Dex) stimulation. Osteoclastogenesis was examined by TRAP staining. Immunofluorescence was employed to examine autophagy marker (LC3) level. Cell apoptosis was analyzed by TUNEL staining. The interaction between Foxhead box D3 protein (FOXD3) and Annexin A2 (ANXA2) promoter was analyzed using ChIP and dual luciferase reporter gene assays., Results: Dex aggravated osteoclastogenesis and induced osteoclast differentiation and autophagy in vitro, which was abrogated by ZOL treatment. PI3K inhibitor LY294002 abolished the inhibitory effect of ZOL on Dex-induced osteoclast differentiation and autophagy. FOXD3 overexpression neutralized the downregulation effects of ZOL on Dex-induced osteoclasts by transcriptionally activating ANXA2. ANXA2 knockdown reversed the effect of FOXD3 overexpression on ZOL-mediated biological effects in Dex-treated osteoclasts. In addition, ZOL improved SANFH symptoms in rats., Conclusion: ZOL alleviated SANFH through regulating FOXD3 mediated ANXA2 transcriptional activity and then promoting PI3K/AKT/mTOR pathway, revealing that FOXD3 might be a target for ZOL in SANFH treatment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Inc.)

Purpose: Gorham-Stout disease is a very rare disorder characterized by progressive bone erosion and angiomatous proliferation; its etiopathogenesis is still unknown, and diagnosis is still performed by exclusion criteria. The alteration of bone remodeling activity has been reported in patients; in this study, we characterized circulating osteoclast and osteogenic precursors that could be important to better understand the osteolysis observed in patients., Methods: Flow cytometry analysis of PBMC (Peripheral Blood Mononuclear Cells) was performed to characterize circulating osteoclast and osteogenic precursors in GSD patients (n = 9) compared to healthy donors (n = 55). Moreover, ELISA assays were assessed to evaluate serum levels of bone markers including RANK-L (Receptor activator of NF-κB ligand), OPG (Osteoprotegerin), BALP (Bone Alkaline Phosphatase) and OCN (Osteocalcin)., Results: We found an increase of CD16 - /CD14 + CD11b + and CD115 + /CD14 + CD11b + osteoclast precursors in GSD patients, with high levels of serum RANK-L that could reflect the increase of bone resorption activity observed in patients. Moreover, no significant alterations were found regarding osteogenic precursors and serum levels of BALP and OCN., Conclusion: The analysis of circulating bone cell precursors, as well as of RANK-L, could be relevant as an additional diagnostic tool for these patients and could be exploited for therapeutic purposes., (© 2024. The Author(s), under exclusive licence to Italian Society of Endocrinology (SIE).)

Rufy4, a protein belonging to the RUN and FYVE domain-containing protein family, participates in various cellular processes such as autophagy and intracellular trafficking. However, its role in osteoclast-mediated bone resorption remains uncertain. In this study, we investigated the expression and role of the Rufy4 gene in osteoclasts using small interfering RNA (siRNA) transfection and gene overexpression systems. Our findings revealed a significant increase in Rufy4 expression during osteoclast differentiation. Silencing Rufy4 enhanced osteoclast differentiation, intracellular cathepsin K levels, and formation of axial protrusive structures but suppressed bone resorption. Conversely, overexpressing wild-type Rufy4 in osteoclasts hindered differentiation while promoting podosome formation and bone resorption. Similarly, overexpression of a Rufy4 variant lacking the RUN domain mimics the effects of Rufy4 knockdown, significantly increasing intracellular cathepsin K levels, promoting osteoclastogenesis, and elongated axial protrusions formation, yet inhibiting bone resorption. These findings indicate that Rufy4 plays a critical role in osteoclast differentiation and bone resorption by regulating the cytoskeletal organization through its RUN domain. Our study provides new insights into the molecular mechanisms governing osteoclast activity and underscores Rufy4's potential as a novel therapeutic target for bone disorders characterized by excessive bone resorption.

The impact of exosome-mediated crosstalk between multiple myeloma (MM) cells and osteoclasts (OCs) on bone lesions remains to be investigated. Here, we identified NSUN2 and YBX1-mediated m5C modifications upregulated LncRNA MALAT1 expression in MM cells, which could be transported to OCs via exosomes and promote bone lesions. Methodologically, RNA-seq was carried out to detect the cargoes of exosomes. TRAP staining and WB were used to evaluate osteoclastogenesis in vitro. Micro-CT and bone histomorphometric analyses were performed to identify bone destruction in vivo. RNA pull-down, RIP, MeRIP, and luciferase reporter assays were used to test the interactions between molecules. The clinical features of MALAT1, NSUN2 and YBX1 were verified through public datasets and clinicopathological data analyses. Mechanistically, MALAT1 was the highest expressed lncRNA in U266 exosomes and could be transported to RAW264.7 cells. MALAT1 could enhance the differentiation of RAW264.7 cells into OCs by stimulating RANKL expression and its downstream AKT and MAPKs signaling pathways via a ceRNA mechanism. Additionally, MALAT1 could be modified by NSUN2, an m5C methyltransferase, which in turn stabilized MALAT1 through the "reader" YBX1. Clinical studies indicated a notable positive correlation between MALAT1, NSUN2, YBX1 levels and bone destruction features, as well as with RANKL expression., (© 2024. The Author(s).)

Staphylococcus aureus osteomyelitis leads to extensive bone destruction. Osteoclasts are bone resorbing cells that are often increased in bone infected with S. aureus. The cytokine RANKL is essential for osteoclast formation under physiological conditions but in vitro evidence suggests that inflammatory cytokines may by-pass the requirement for RANKL. The goal of this study was to determine whether RANKL-dependent osteoclast formation is essential for the bone loss that occurs in a murine model of S. aureus osteomyelitis. To this end, humanized-RANKL mice were infected by direct inoculation of S. aureus into a unicortical defect in the femur. Mice were treated with vehicle or denosumab, a human monoclonal antibody that inhibits RANKL, both before and during a 14-day infection period. The severe cortical bone destruction caused by infection was completely prevented by denosumab administration even though the bacterial burden in the femur was not affected. Osteoclasts were abundant near the inoculation site in vehicle-treated mice but absent in denosumab-treated mice. In situ hybridization demonstrated that S. aureus infection potently stimulated RANKL expression in bone marrow stromal cells. The extensive reactive bone formation that occurs in this osteomyelitis model was also reduced by denosumab administration. Lastly, there was a notable lack of osteoblasts near the infection site suggesting that the normal coupling of bone formation to bone resorption was disrupted by S. aureus infection. These results demonstrate that RANKL-mediated osteoclast formation is required for the bone loss that occurs in S. aureus infection and suggest that disruption of the coupling of bone formation to bone resorption may also contribute to bone loss in this condition., Competing Interests: Declaration of competing interest The authors declare that they have no competing interests., (Published by Elsevier Inc.)

Osteoporosis (OP) is a systemic metabolic bone disease resulting in reduced bone strength and increased susceptibility to fractures, making it a significant public health and economic problem worldwide. The clinical use of anti-osteoporosis agents is limited because of their serious side effects or the high cost of long-term use. The Xianlinggubao (XLGB) formula is an effective traditional Chinese herbal medicine commonly used in orthopedics to treat osteoporosis; however, its mechanism of action remains unclear. In this study, we screened 40 small RNAs derived from XLGB capsules and found that XLGB28-sRNA targeting TNFSF11 exerted a significant anti-osteoporosis effect in vitro and in vivo by simultaneously promoting osteogenesis and inhibiting osteoclastogenesis. Oral administration of bencaosome [16:0 Lyso PA+XLGB28-sRNA] effectively improved bone mineral density and reduced the damage to the bone microstructure in mice. These results suggest that XLGB28-sRNA may be a novel oligonucleotide drug that promotes osteogenesis and inhibits osteoclastogenesis in mice., (© 2024 International Union of Biochemistry and Molecular Biology.)

Objective: The pathological mechanism of osteoporosis (OP) involves increased bone resorption mediated by osteoclasts and decreased bone formation mediated by osteoblasts, leading to an imbalance in bone homeostasis. Identifying key molecules in osteoclast-mediated OP progression is crucial for the prevention and treatment of OP., Methods: Differential expression analysis and weighted gene co-expression network analysis (WGCNA) were performed on the OP patient datasets from the GEO database. The results were intersected with the differential expression results from the osteoclast differentiation dataset to identify key genes. These key genes were then subjected to disease relevance analysis, and consensus clustering was performed on OP patient samples based on their expression profiles. The subgroups were analyzed for differences, followed by GO, KEGG, GSEA, and GSVA analyses, and immune infiltration. Finally, osteoclast differentiation model was constructed. After validating the success of the model using TRAP and F-actin staining, the differential expression of key genes was validated in vitro via Western blot., Results: CTRL, ARHGEF5, PPAP2C, VSIG2, and PBLD were identified as key genes. These genes exhibited strong disease relevance (AUC > 0.9). Functional enrichment results also indicated their close association with OP and osteoclast differentiation. In vitro differential expression validation showed that during osteoclast differentiation, CTRL was downregulated, while ARHGEF5, PPAP2C, VSIG2, and PBLD were upregulated, with all differences being statistically significant ( P  < 0.05)., Discussion: Currently, there are no studies on the effects of these five genes on osteoclast differentiation. Therefore, it is meaningful to design in vivo and in vitro perturbation experiments to observe the impact of each gene on osteoclast differentiation and OP progression., Conclusion: CTRL, ARHGEF5, PPAP2C, VSIG2, and PBLD show high potential as molecular targets for basic and clinical research in osteoclast-mediated OP., Competing Interests: Declaration of conflicting interestsThe authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Abnormalities in osteoclastic generation or activity disrupt bone homeostasis and are highly involved in many pathologic bone-related diseases, including rheumatoid arthritis, osteopetrosis, and osteoporosis. Control of osteoclast-mediated bone resorption is crucial for treating these bone diseases. However, the mechanisms of control of osteoclastogenesis are incompletely understood. In this study, we identified that inosine 5'-monophosphate dehydrogenase type II (Impdh2) positively regulates bone resorption. By histomorphometric analysis, Impdh2 deletion in mouse myeloid lineage cells (Impdh2 LysM-/- mice) showed a high bone mass due to the reduced osteoclast number. qPCR and western blotting results demonstrated that the expression of osteoclast marker genes, including Nfatc1, Ctsk, Calcr, Acp5, Dcstamp, and Atp6v0d2, was significantly decreased in the Impdh2 LysM-/- mice. Furthermore, the Impdh inhibitor MPA treatment inhibited osteoclast differentiation and induced Impdh2-cytoophidia formation. The ability of osteoclast differentiation was recovered after MPA deprivation. Interestingly, genome-wide analysis revealed that the osteoclastic mitochondrial biogenesis and functions, such as oxidative phosphorylation, were impaired in the Impdh2 LysM-/- mice. Moreover, the deletion of Impdh2 alleviated ovariectomy-induced bone loss. In conclusion, our findings revealed a previously unrecognized function of Impdh2, suggesting that Impdh2-mediated mechanisms represent therapeutic targets for osteolytic diseases., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Purpose: Chordomas are malignant tumors that destroy bones, compress surrounding nerve tissues and exhibit phenotypes that recapitulate notochordal differentiation in the axial skeleton. Chordomas recur frequently, as they resist radio-chemotherapy and are difficult to completely resect, leading to repeated bone destruction and local expansion via unknown mechanisms. Here, using chordoma specimens and JHC7 chordoma cells, we asked whether chordoma cells possess bone-dissolving activity., Methods: CT imaging and histological analysis were performed to evaluate the structure and mineral density of chordoma-invaded bone and osteolytic marker expression. JHC7 cells were subjected to immunocytochemistry, imaging of cell fusion, calcium dynamics and acidic vacuoles, and bone lysis assays., Results: In patients, we found that the skull base invaded by chordoma was highly porous, showed low mineral density and contained brachyury-positive chordoma cells and conventional osteoclasts both expressing the osteolytic markers tartrate-resistant acid phosphatase (TRAP) and collagenases. JHC7 cells expressed TRAP and cathepsin K, became multinucleated via cell-cell fusion, showed spontaneous calcium oscillation, and were partly responsive to the osteoclastogenic cytokine RANKL. JHC7 cells exhibited large acidic vacuoles, and nonregulatory bone degradation without forming actin rings. Finally, bone-derived factors, calcium ions, TGF-β1, and IGF-1 enhanced JHC7 cell proliferation., Conclusion: In chordoma, we propose that in addition to conventional bone resorption by osteoclasts, chordoma cells possess bone-dissolving activity at the tumor-bone boundary. Furthermore, bone destruction and tumor expansion may occur in a positive feedback loop., (© 2024. The Author(s).)