The accumulation of reactive oxygen species (ROS) within cells regulates the formation and function of osteoclasts, which is crucial therapeutic target for the treatment of osteoporosis. Ergothioneine (EGT) is a rare amino acid with strong antioxidant and anti-inflammatory properties. However, its application on osteoporosis has not been reported. In this study, we investigated the effects of EGT on osteoclastogenesis in vitro and in ovariectomized (OVX) mice. The results revealed that EGT could suppress RANKL-induced podosome belt formation and osteoclast development in vitro, while reducing intracellular ROS levels by upregulating key antioxidant enzymes, including HO-1 and Catalase. EGT was also found to downregulate the expression of critical osteoclast-specific proteins such as Trap, c-Fos, and Ctsk through attenuation of MAPK signaling. The potential of EGT to protect against trabecular bone loss in OVX mice was further demonstrated by micro-CT imaging, possibly by reducing osteoclast numbers shown by histological outcomes. These findings together highlighted the potential value of EGT as a novel tool for treating osteoporosis through its ability to suppress osteoclastogenesis and mitigate the accumulation of intracellular ROS.

Bone defects, caused by trauma, osteomyelitis, or osteoporosis, represent a significant global health challenge in orthopedics. However, current bone repair strategies often neglect the critical role of the immune microenvironment, which can impede effective bone regeneration. To address this gap, we developed a 3D-printed triple crosslinked hydrogel scaffold incorporating slow-release glycopyrrolate (GA) and epigallocatechin gallate (EGCG), that it could promote bone regeneration by modulating the immune response. We evaluated their immunomodulatory and bone-regenerative effects through in vitro cellular experiments and rat cranial defect models. Results demonstrated that these scaffolds effectively modulated the immune microenvironment, reducing inflammation while promoting osteoblast differentiation and proliferation, thereby significantly enhancing new bone formation and density. In conclusion, our novel 3D-printed hydrogel scaffold offers a promising approach to bone defect repair through its unique combination of mechanical strength, immunomodulation, and osteogenesis. This study provides valuable insights into leveraging immunomodulatory agents for enhanced bone regeneration, highlighting potential clinical applications.

Osteoclasts are multinucleated giant cells that are formed by the fusion of precursor cells. Cell-cell fusion is mediated by membrane protrusion driven by actin reorganization, but the role of membrane mechanics in this process is unknown. Utilizing live-cell imaging, optical tweezers, manipulation of membrane-to-cortex attachment (MCA), and genetic interference, we show that a decrease in plasma membrane (PM) tension is a mechanical prerequisite for osteoclast fusion. Upon RANKL-induced differentiation, ezrin expression in fusion progenitor cells is reduced, resulting in a decrease in MCA-dependent PM tension. A forced elevation of PM tension by reinforcing the MCA conversely suppresses cell-cell fusion. Mechanistically, reduced PM tension leads to membrane protrusive invadosome formation driven by membrane curvature-inducing/sensing BAR proteins, thereby promoting cell-cell fusion. These findings provide insights into the mechanism of cell-cell fusion under the control of membrane mechanics.

Peroxisomal biogenesis factor 5 (PEX5), a peroxisomal import receptor, is well recognized for its role in protein trafficking and oxidative stress regulation. However, its function in bone metabolism remains unclear. Given the established impact of oxidative stress on osteoclast differentiation, this study explores the previously uncharacterized role of PEX5 in osteoclastogenesis and bone resorption. Using bone marrow-derived macrophages, we examined the effects of PEX5 knockdown (siPEX5) and recombinant PEX5 protein (rpPEX5) on osteoclast differentiation. Osteoclast activity was evaluated through TRAP staining, F-actin ring formation, and bone resorption assays. qRT-PCR and Western blot analyses assessed gene and protein expression, while an lipopolysaccharide (LPS)-induced calvarial bone loss model provided in vivo validation. PEX5 expression declined during osteoclast differentiation, and its suppression promoted osteoclastogenesis by increasing c-Fos, NFATc1, and osteoclast-specific gene expression. Loss of PEX5 also enhanced receptor activator of nuclear factor kappa-Β ligand (RANKL)-induced activation of Akt, MAPK, IκB, and calcium-dependent pathways, accelerating osteoclast maturation. In contrast, rpPEX5 treatment effectively inhibited osteoclast differentiation and bone resorption by downregulating NFATc1 and dampening RANKL-mediated signaling. In vivo, rpPEX5 administration mitigated LPS-induced bone loss by preserving bone structure and reducing osteoclast activity. These findings reveal a novel function of PEX5 as a regulator of osteoclast differentiation, independent of its peroxisomal role. The extracellular activity of PEX5 suggests a broader regulatory mechanism in bone metabolism, with potential therapeutic implications for osteolytic diseases.

As a major substitute for the bisphenol A (BPA), the use of the bisphenol F (BPF) has increased dramatically in recent years. Growing evidence suggest that BPF shares numerous toxicological properties with BPA, raising the concerns about its potential impact on the health of organisms. However, the developmental toxicity of BPF remains poorly understood. In this study, we conducted a 5-day BPF exposure experiment on zebrafish (Danio rerio) from blastula stage at concentrations of 2, 20, 200, and 2000 µg/L. Our results demonstrated a significant increase in hatching rates across all treatment groups at 2 days post-fertilization (dpf). The esr1 was significantly upregulated at 2000 µg/L by 5 dpf, while no significant change was observed in ar. The frequency of operculum loss significantly increased at exposure concentrations of 20, 200, and 2000 µg/L, and a notable increase in notochord loss was observed at 2000 µg/L. To explore the underlying mechanisms, transcriptomic analysis was performed to identify differentially expressed genes (DEGs). GO and KEGG pathway enrichment analysis revealed that the toxic effects of BPF were closely associated with osteoclast differentiation, the FoxO signaling pathway, and the MAPK signaling pathway. These pathways influenced critical biological processes, including response to stimuli, animal organ morphogenesis, detoxification, and biomineralization. This study provides evidence that BPF exposure at environmentally relevant concentrations (2 µg/L) is harmful to hatching, concentrations above 20 µg/L exhibit estrogenic-disrupting activity and exert toxicological effects on the development of the head skeleton in zebrafish. These effects are particularly linked to disruptions in osteoclast differentiation.

Aging profoundly impacts mesenchymal and hematopoietic lineage cells, including their progenitors-the skeletal stem cells (SSCs) and hematopoietic stem cells (HSCs), respectively. SSCs are crucial for skeletal development, homeostasis, and regeneration, maintaining bone integrity by differentiating into osteoblasts, adipocytes, and other lineages that contribute to the bone marrow (BM) microenvironment. Meanwhile, HSCs sustain hematopoiesis and immune function. With aging, SSCs and HSCs undergo significant functional decline, partly driven by cellular senescence-a hallmark of aging characterized by irreversible growth arrest, secretion of pro-inflammatory factors (senescence associated secretory phenotype, SASP), and impaired regenerative potential. In SSCs, senescence skews lineage commitment toward adipogenesis at the expense of osteogenesis, contributing to increased bone marrow adiposity , reduced bone quality, and osteoporosis. Similarly, aged HSCs exhibit diminished self-renewal, biased differentiation, and heightened inflammation, compromising hematopoietic output and immune function. In this review, we examine the age-related cellular and molecular changes in SSCs and HSCs, their lineage decisions in the aging microenvironment, and the interplay between skeletal and hematopoietic compartments. We also discuss the role of senescence-driven alterations in BM homeostasis and how targeting cellular aging mechanisms may offer therapeutic strategies for mitigating age-related skeletal and hematopoietic decline.

Excessive osteoclastogenesis is a key driver of inflammatory bone loss. Suppressing osteoclastogenesis has always been considered essential for the treatment of inflammatory bone loss. N-acetyltransferase 10 (NAT10) is the sole enzyme responsible for N4-acetylcytidine (ac4C) modification of mRNA, and is involved in cell development. However, its role in osteoclastogenesis and inflammatory bone loss remained elusive.

We aimed to clarify the regulatory mechanism of NAT10 and ac4C modification in osteoclastogenesis and inflammatory bone loss.

NAT10 expression and ac4C modification during osteoclastogenesis were determined by quantitative real-time PCR (qPCR), western blotting, dot blot and immunofluorescent staining, and the effect of NAT10 inhibition on osteoclast differentiation in vitro was measured by the tartrate-resistant acid phosphatase staining, podosome belts staining assay and bone resorption pit assay. Then, acRIP-qPCR and NAT10RIP-qPCR, ac4C site prediction, mRNA decay assay and luciferase reporter assay were performed to further study the underlying mechanisms. At last, mice models of inflammatory bone loss were applied to verify the therapeutic effect of NAT10 inhibition in vivo.

NAT10 expression was upregulated during osteoclast differentiation and highly expressed in alveolar bone osteoclasts from periodontitis mice. Inhibition of NAT10 notably reduced osteoclast differentiation in vitro, as indicated by great reduction of tartrated resistant acid phosphatse positive multinuclear cells, osteoclast-specific gene expression, F-actin ring formation and bone resorption capacity. Mechanistically, NAT10 catalyzed ac4C modification of Fos (encoding AP-1 component c-Fos) mRNA and maintained its stabilization. Besides, NAT10 promoted MAPK signaling pathway and thereby activated AP-1 (c-Fos/c-Jun) transcription for osteoclastogenesis. Therapeutically, administration of Remodelin, the specific inhibitor of NAT10, remarkably impeded the ligature-induced alveolar bone loss and lipopolysaccharide-induced inflammatory calvarial osteolysis.

Our study demonstrated that NAT10-mediated ac4C modification is an important epigenetic regulation of osteoclast differentiation and proposed a promising therapeutic target for inflammatory bone loss.

Osteoporosis following stroke is a significant impediment to patient recovery. Decreased mechanical loading and locomotion following the onset of paralysis in stroke patients, especially those who are non-ambulatory, contributes greatly to bone loss. Sclerostin, a protein encoded by the SOST gene, accumulates as a result of reduced mechanical loading and inhibits bone formation. This study explores the relationship between mechanical unloading, sclerostin levels, and bone mineral density (BMD) in stroke patients, utilizing three cohorts. Analysis of Cohort 1, consisting of patients with available sclerostin level measurements, found significantly elevated sclerostin levels in non-ambulatory patients compared to ambulatory patients, indicating the influence of ambulatory status on sclerostin regulation. Cohort 2, consisting of patients with BMD measurements, demonstrated that prolonged mechanical unloading in non-ambulatory patients resulted in a greater decline in BMD over time. Analysis in Cohort 3 patients, who had bilateral BMD measurements available, revealed that hemiplegic sides subjected to reduced mechanical loading exhibited lower BMD compared to non-hemiplegic sides. These findings collectively confirm the hypothesis that reduced mechanical loading elevates sclerostin levels and accelerates bone loss. By integrating data across the three cohorts, this study underscores the critical impact of mechanical unloading on bone health, particularly in chronic stroke patients with limited mobility. Our study provides clinical insights for treatments integrating ambulatory status, sclerostin levels, and BMD in chronic stroke patients and highlights an increased need for therapeutics targeting mechanical loading pathways and sclerostin accumulation which can be administered to treat chronic osteoporosis following stroke.

1,25(OH)2D3 is well known for its role in maintaining normal serum calcium levels. Through its receptor, 1,25(OH)2D3 enhances intestinal calcium absorption and renal calcium reabsorption, thereby ensuring serum calcium levels are within physiological range, which is in turn important for normal bone development and mineralization. The vitamin D receptor (VDR) achieves this via transcriptional induction of genes important in calcium transport. When intestinal and renal calcium (re)absorption is impaired, VDR-mediated signaling will stimulate bone resorption and inhibit mineralization in order to maintain normal serum calcium levels, as evidenced in mice with a systemic or intestine-specific deletion of the VDR. However, VDR signaling in bone is also reported to have anabolic effects. In this review we will discuss the effects of 1,25(OH)2D3-mediated VDR signaling on bone homeostasis and provide an overview of the in vitro experiments and various transgenic mice models that have been generated to unravel the role of VDR signaling in different bone cell types such as chondrocytes, (pre)osteoblasts, osteocytes, and (pre)osteoclasts.

Bone remodeling is essential for maintaining bone homeostasis throughout life by replacing old bone with new tissue. This dynamic process occurs continuously within basic multicellular unit (BMU) through well-coordinated interactions among osteocytes, osteoblasts, and osteoclasts. However, a precise in vitro model that accurately replicates this mechanism has not yet been developed. In this study, we created a human in vitro BMU-modeling chip platform by tri-culturing cells within a chip unit integrated into a tissue culture well plate, enabling high-throughput three-dimensional (3D) cell culture. To establish the tri-culture, human osteoblasts were isolated from human surgical bone samples and differentiated into osteocytes within collagen gel inside the chip unit. Subsequently, osteoblasts and peripheral blood mononuclear cells (PBMCs) containing osteoclast precursors were added to the chip unit. To simulate each phase of the bone remodeling cycle, we optimized the tri-culture process by adjusting the timing and using two types of osteoblasts at different stages of differentiation. The completed tri-culture model successfully mimicked the bone formation phase. When receptor activators of nuclear factor kappa-Β (RANKL) and macrophage colony-stimulating factor (M-CSF) were introduced, the cells exhibited characteristics of the reversal phase, where osteogenic and osteoclastogenic environments coexist. Additionally, using more differentiated osteoblasts within the tri-culture platform induced osteoclast differentiation, resembling the bone resorption phase. Overall, our model effectively replicates each phase of the bone remodeling cycle in BMUs, both spatially and temporally. This advancement not only facilitates the study of the intricate mechanisms of bone remodeling and cellular function but also aids drug development by providing a robust bone model for testing target drugs.

Bone metastasis is the second most common site of distant metastatic spread in renal cell carcinoma (RCC) patients, significantly contributing to cancer-related mortality. The metastatic process is driven by both intrinsic tumor cell properties, such as cancer stem cell-like characteristics, and the bone microenvironment. Understanding the complex interactions between cancer cells and their niche is crucial for identifying therapeutic targets to eliminate metastasis-initiating cells and prevent overt metastasis. In this study, a murine bone metastasis model is developed using renal cancer cells derived from fibrin gel-induced 3D tumor spheres, which exhibit stem-like phenotypes. It is found that a stable form of vitamin C, L-ascorbic acid 2-phosphate sesquimagnesium (APM), significantly inhibits the growth of renal cancer stem-like cells in vitro and the progression of RCC bone metastasis in vivo. Single-cell RNA sequencing revealed that APM induces cell cycle arrest and reduces the metastatic potential of cancer cells. Furthermore, APM remodels the tumor microenvironment by suppressing osteoclast differentiation and neutrophil recruitment. Combining APM with a CXCR2 antagonist, SB225002, further inhibits bone metastasis progression. This study provides a high-resolution profile of vitamin C's antitumor effects in the bone metastatic microenvironment and supports the rationale for clinical trials of vitamin C in bone metastatic RCC.

Oral cellular aging plays a critical role in the pathogenesis of chronic periodontitis and alveolar bone resorption. Although activating transcription factor 3 (ATF3) has been implicated as a senescence-associated factor, its specific role in periodontal ligament cell (PDLC) senescence remains unclear. Human PDLCs were exposed to lipopolysaccharide (LPS, 1 μg/mL) and nicotine (5 mM) for 3 days to induce senescence. ATF3 expression was silenced using siRNA. The expression of senescence-associated secretory phenotype (SASP) factors (IFNγ, IL6, IL8, TNFα, and IL1β) and the secretion of nitric oxide (NO) and prostaglandin E2 (PGE2) were assessed by RT-PCR and immunoassay. Conditioned media (CM) from these cells were applied to mouse bone marrow macrophages (BMMs) to evaluate osteoclast differentiation and bone resorption. In addition, key signaling pathways, including STAT3, ERK, NF-κB (p65), and AP-1, were investigated by Western blotting and immunofluorescence. ATF3 knockdown markedly reduced the LPS/nicotine-induced expression of SASP factors and decreased NO and PGE2 levels. CM from ATF3-silenced PDLCs markedly inhibited osteoclast differentiation, as evidenced by reduced tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells and diminished bone resorption. Moreover, ATF3 inhibition led to a decreased RANKL/OPG ratio and attenuated the phosphorylation of STAT3 and ERK, along with the reduced nuclear translocation of p65 and AP-1 components. These findings suggest that ATF3 plays a critical role in mediating cellular senescence and osteoclastogenesis in PDLCs. Targeting ATF3 may represent a novel therapeutic strategy for managing age-related oral diseases, such as chronic periodontitis.

Osteoporosis is a chronic metabolic bone disorder characterized by excessive bone resorption. The NuanXin Formula (NX) is a classical traditional Chinese medicine formula that can warm and tonify kidney Yang, as well as replenish Qi and blood, which are essential for maintaining bone health and regulating bone metabolism. Nevertheless, the functions and mechanisms of NX in osteoporosis therapy remain unclear.

This study aims to evaluate the effects and mechanisms of NX on osteoclastogenesis and to investigate its potential in combating osteoporosis.

The inhibitory effects of NX on RANKL-induced osteoclastogenesis were evaluated using Western blotting, quantitative PCR (Q-PCR), TRAP staining, and pit-formation assays. Bone mass and structure were assessed through micro-CT, biomechanical testing, TRAP staining, IHC staining, and H&E staining. The mechanism of action of NX on osteoclasts was investigated using RNA sequencing, ROS staining, ATP measurement, and mitochondrial membrane potential assays.

The in vitro findings demonstrated that NX treatment significantly inhibited osteoclast differentiation and bone resorption activity. Q-PCR and WB analyses indicated that NX substantially downregulates the expression levels of key osteoclast markers, including Nfatc1, Ctsk, Mmp9, and Trap. In vivo experiments revealed that intragastric administration of NX effectively suppressed bone loss and bone resorption, while enhancing the biomechanical properties of bone in ovariectomized (OVX) mice. Mechanistically, NX inhibits oxidative phosphorylation (OXPHOS), decreases mitochondrial membrane potential, and reduces ATP production and reactive oxygen species generation, thereby impeding osteoclast differentiation and activity.

NX mitigates osteoporosis by modulating OXPHOS to inhibit osteoclast differentiation and activity, thus offering a potential therapeutic approach for osteoporosis management. However, the study has limitations that require further investigation. NX did not show a clear dose-dependent effect in animal tests, suggesting a need for improved dosing designs. Although we emphasize NX's therapeutic potential, more research is necessary to clarify its mechanism. Variability in plant materials and ingredient ratios might influence NX's pharmacological effects, with specific bioactive components potentially playing a major role. Future research should integrate network pharmacology with experimental validation for a more thorough understanding.

Estrogen levels are the core factor influencing postmenopausal osteoporosis (PMOP). Estrogen can affect the progression of PMOP by regulating bone metabolism, influencing major signaling pathways related to bone metabolism, and modulating immune responses. When estrogen levels decline, the activity of Sirtuins (SIRTs) is reduced. SIRTs are enzymes that function as NAD+-dependent deacetylases. SIRTs can modulate osteocyte function, sustain mitochondrial homeostasis, and modulate relevant signaling pathways, thereby improving bone metabolic imbalances, reducing bone resorption, and promoting bone formation. In PMOP, SIRT1, SIRT3, and SIRT6 are primarily affected. Oxidative stress (OS) is a crucial factor in PMOP, as it generates excessive reactive oxygen species (ROS) that exacerbate PMOP. There is a certain interplay between SIRTs and OS. The reduced activity of SIRTs leads to intensified OS and the excessive accumulation of ROS. In return, ROS suppresses the AMPK signaling pathway and the synthesis of NAD+, which consequently diminishes the function of SIRTs. Natural SIRT activators and natural antioxidants, which are characterized by high safety, convenience, and minimal side effects, represent a potential therapeutic strategy for PMOP. This study aims to investigate the mechanisms of SIRTs and OS in PMOP and summarize potential therapeutic strategies to assist in the improvement of PMOP.

Bone metastases are a common and severe complication in advanced breast cancer, affecting approximately 65% to 70% of patients and significantly reducing survival time. Osteolytic bone metastases, in particular, are challenging to manage due to their association with skeletal-related events (SREs) that accelerate disease progression and diminish the quality of life. These metastases are driven by a complex interaction between breast cancer cells and the bone microenvironment, leading to increased osteoclast activity and bone destruction. Current treatments, such as bisphosphonates, primarily aim to inhibit osteoclast function but are associated with serious side effects, underscoring the need for alternative therapies. Triptolide (TP), a bioactive compound derived from the traditional Chinese medicinal herb Tripterygium wilfordii Hook F. (TwHF), has demonstrated potent anti-tumor and anti-inflammatory properties, especially in abnormal bone remodeling disorders. This study aims to investigate the therapeutic potential of TP in treating breast cancer-induced bone metastases by examining its effects on osteoclastogenesis and tumor-bone microenvironment interactions.

Mouse bone marrow cells, RAW264.7 pre-osteoclasts and MC3T3-E1 pre-osteoblasts were cultured with MDA-MB-231 breast cancer cells or their conditioned medium to replicate the tumor microenvironment. Osteoclast formation was assessed via TRAP staining. Translational and transcriptional expression of key signaling molecules and related markers were determined using western blot and RT-PCR. Binding interactions between TP and parathyroid hormone-related protein (PTHrP) were analyzed using microscale thermophoresis and molecular docking.

TP treatment significantly reduced osteoclastogenesis in both co-culture and conditioned medium systems. Our findings suggest that TP inhibits NF-κB and ERK signaling pathways, reduces breast cancer-induced osteoclastogenesis, and decreases NFATc1, CTSK, and RANKL expression. Molecular assays revealed a direct binding affinity between TP and PTHrP, suggesting TP interferes with PTHrP-mediated signaling that promotes osteoclast activity.

This study demonstrates that Triptolide effectively inhibits breast cancer-induced osteolytic bone metastasis by suppressing key osteoclastogenic signaling pathways and modulating the tumor-bone microenvironment. We provide the first evidence of a direct interaction between TP and PTHrP, suggesting a novel mechanism through which TP may disrupt PTHrP-mediated osteoclast activation. These findings position TP as a promising alternative to current anti-resorptive therapies for managing breast cancer-associated bone metastases.

Osteoporosis is the most common metabolic skeletal disorder of the skeleton, stemming from a cellular imbalance between bone formation by osteoblasts and bone resorption by osteoclasts. This imbalance causes bones to become weak and brittle, thus increasing the risk of fractures. The prevalence of osteoporosis escalates with advancing age, thereby presenting a considerable public health challenge that has elicited substantial public concern. Existing anti-osteoporotic drugs typically act by inhibiting bone resorption, promoting bone formation, and exerting a dual effect. Yet, most of these pharmaceuticals have fundamental limitations, such as targeting only one specific site and a tendency to cause side effects. With advancements in anti-osteoporotic medications, numerous new small-molecule drugs have been developed and synthesized. These novel active compounds exhibit good anti-osteoporotic activity both in vitro and in vivo by enhancing osteoblast differentiation and mineralization, as well as inhibiting osteoclast resorption. The present study seeks to review the development and current status of new compounds exhibiting anti-osteoporotic activity, to establish a solid foundation for preventing and treating osteoporosis, promoting pharmacological research, and aiding in developing new medications.

Bisphosphonates (BPs) are drugs used to cure metabolic diseases like osteoporosis and oncological conditions, such as multiple myeloma and bone metastases. The pharmacological activity of these compounds is mediated by their capacity to induce a systemic osteoclast depletion, finally resulting in reduced bone resorption. In spite of their efficacy, the clinical application of BPs is sometimes associated with a frightening side effect known as osteonecrosis of the jaw (ONJ). In principle, a therapeutic approach able to elicit the local re-activation of osteoclast production could counteract the onset of ONJ and promote the healing of its lesions. Using a vitamin D3-dependent model of osteoclast differentiation, it has been previously demonstrated that when used at supra-physiological concentrations, magnesium strongly favors the process under consideration, and its effect is furtherly enhanced by the presence of a BP called zoledronate. Here, we show that similar results can be obtained in a RANKL-dependent model of osteoclast differentiation, suggesting that a topical therapy based on magnesium may be also suitable for ONJ determined by denosumab in light of the ability of this monoclonal antibody to target RANKL.

A large number of studies have shown that osteoporosis is closely related to bone immunology. The purpose of this study is to conduct bibliometrics and visual analysis of the fields related to osteoimmunology and osteoporosis from 2013 to 2022 and to summarize the research hotspots and trends in this field.

We searched the Web of Science core collection database for articles on osteoimmunology and osteoporosis published between 2013 and 2022. Vosviewer 1.6.18 and CiteSpace.6.2. R4 were used to analyze the retrieved data.

A total of 3218 articles on osteoimmunology and osteoporosis were included in this study. A total of 76 countries, 347 institutions, and 502 authors were included in the articles examined in this study. The main research countries were China, the United States, and South Korea. Shanghai Jiaotong University, Harvard University, and the University of California system were the main research institutions. The author who published the most papers was Xu, Jiake.

This study is the first to summarize the global research trends in the field of osteoimmunology and osteoporosis from 2013 to 2022. That helps researchers quickly understand the research hotspots and directions in this field.

Bone destruction in rheumatoid arthritis (RA) leads to significant disability, yet effective treatments are limited. Sinomenine (Sino) demonstrates anti-arthritic and bone-protective effects but requires high doses. In this study, we developed a Sino derivative, SINX, and evaluated its efficacy in RA. Safety assessments in mice confirmed its suitability for further study. In vitro, SINX inhibited osteoclast differentiation by reducing TRAP-positive cells, disrupting F-actin ring formation, and suppressing bone resorption pits, alongside downregulating osteoclast-specific genes. It also showed strong anti-inflammatory properties by reducing inflammatory cytokine levels. In vivo, using a collagen-induced arthritis (CIA) mouse model, SINX improved bone integrity by reducing joint inflammation, maintaining trabecular bone density, and preventing erosion. Histological and micro-CT analyses confirmed its effects, including suppressed osteoclast activity and reduced bone resorption-related gene expression. Mechanistically, SINX ameliorated mitochondrial dysfunction, decreased ROS levels, and activated the NRF2/HO-1/NQO1 pathway, enhancing antioxidant defenses. Compared to Sino, SINX achieved similar results at lower doses. These findings highlight the potential of SINX as a safe, effective treatment for RA-related bone destruction.

This study explored the interaction effects of dietary Vitamin A (VA) and Vitamin D3 (VD3) on growth performance, jejunal function, and tibia development in goslings, aiming to identify any synergistic outcomes that may reshape nutritional strategies for geese production. A total of 540 one-day-old male Jiangnan White goslings with similar body weight (82 ± 5 g) were randomly assigned into 9 treatments with five replicate pens per treatment and 12 birds per pen. The bird trial employed a 3 × 3, two-factorial treatment with three levels of VA (5000, 7000, and 9000 IU/kg) and three levels of VD3 (1000, 1500, and 2000 IU/kg) from one to 28 days of age. Main effects analysis indicated that birds fed 7000 IU/kg VA exhibited the highest ADG, BW, jejunal maltase activity and IL-10 content (P < 0.05), while 9000 IU/kg VA had the highest SOD activity and content of IL-6 and TNF-α in jejunal mucosa (P < 0.05). Both 7000 IU/kg or 9000 IU/kg VA increased the jejunal IL-1β content, relative expression of tight junction protein 1 (TJP1) mRNA, tibia defatted weight and ash weight (P < 0.05). Birds fed 2000 IU/kg VD3 exhibited the highest ADFI, while both 1500 or 2000 IU/kg VD3 increased jejunal maltase activity, and tibia ash content (P < 0.05). An interaction between VA and VD3 on ADFI, F/G, jejunal maltase activity, mucosal immune factors (IL-1β, IL-6, IL-10, TNF-α), tibia ash content, and bone morphogenetic protein-2 (BMP-2) expression. A simple effects analysis revealed that at a 5000 IU/kg VA, adding 1000 IU/kg VD3 decreased IL-1β, IL-6, TNF-α (P < 0.05). At a 7000 IU/kg VA, adding 1500 or 2000 IU/kg VD3 decreased TNF-α, and increased jejunal maltase activity(P < 0.05). At a 9000 IU/kg VA, adding 1000 IU/kg VD3 decreased ADFI, F/G, jejunal maltase activity, tibia ash, and BMP-2, while IL-1β, IL-6, and TNF-α increased (P < 0.05). At a 9000 IU/kg VA, adding 2000 IU/kg VD3 increased IL-10 (P < 0.05). At a 1000 IU/kg VD3, adding 5000 IU/kg VA increased F/G, jejunal maltase activity and IL-10, while decreased IL-1β, IL-6, TNF-α (P < 0.05), and adding 9000 IU/kg VA decreased tibia ash and BMP-2 (P < 0.05). At 1500 or 2000 IU/kg VD3, adding 7000 IU/kg VA increased jejunal maltase activity, IL-10 (P < 0.05). At a 2000 IU/kg VD3, adding 9000 IU/kg VA increased IL-6, and TNF-α (P < 0.05). In summary, a dietary level of 7000 IU/kg of VA and 2000 IU/kg of VD3 can be a balanced combination to optimize feed intake and conversion, jejunal function, and tibia mineralization, consequently enhancing growth performance in goslings.

Breast cancer is the leading cause of death in the female population. Hormone receptor-positive cancers are usually treated with surgery in combination with endocrine therapy. The latter is known to lower estrogen levels, contributing, therefore, to loss of bone density (BMD) and higher risk of fracture. Bone-modifying agents (BMAs) can regulate the bone-related adverse effects of cancer treatment. In premenopausal women, intravenous zoledronate effectively prevents bone loss. However, the evidence regarding its ability to reduce disease recurrence remains inconclusive. In postmenopausal women, denosumab demonstrates the most substantial evidence for fracture prevention, supported by one well-powered randomized controlled trial, but has not been shown to confer anticancer benefits. While bisphosphonates effectively prevent and reduce clinical vertebra fractures, their impact on overall fracture risk is unclear. In clinical practice, management of bone health in this group of patients starts with stratification for the risk of fracture. This can be done using the FRAX algorithm; measurements of bone mineral density can help to optimize stratification for individuals at higher fracture risk. Caution is advised when interpreting the results, as the FRAX algorithm has been considered to underestimate the true fracture risk in this population, given that the algorithm has not been adjusted for the effect of anti-cancer agents. Nowadays, clodronate, ibandronate, and zoledronic acid are recommended for bone protection in this group of patients, while denosumab is not. Further research is required to highlight the optimal BMA according to patient characteristics.

As people age, degenerative bone and joint diseases (DBJDs) become more prevalent. When middle-aged and elderly people are diagnosed with one or more disorders such as osteoporosis (OP), osteoarthritis (OA), and intervertebral disc degeneration (IVDD), it often signals the onset of prolonged pain and reduced functionality. Chronic inflammation has been identified as the underlying cause of various degenerative diseases, including DBJDs. Recently, excessive activation of pyroptosis, a form of programed cell death (PCD) mediated by inflammasomes, has emerged as a primary driver of harmful chronic inflammation. Consequently, pyroptosis has become a potential target for preventing and treating DBJDs.

This review explored the physiological and pathological roles of the pyroptosis pathway in bone and joint development and its relation to DBJDs. Meanwhile, it elaborated the molecular mechanisms of pyroptosis within individual cell types in the bone marrow and joints, as well as the interplay among different cell types in the context of DBJDs. Furthermore, this review presented the latest compelling evidence supporting the idea of regulating the pyroptosis pathway for DBJDs treatment, and discussed the potential, limitations, and challenges of various therapeutic strategies involving pyroptosis regulation.

In summary, an interesting identity for the unregulated pyroptosis pathway in the context of DBJDs was proposed in this review, which was undertaken as a spoiler of peaceful coexistence between cells in a degenerative environment. Over the extended course of DBJDs, pyroptosis pathway perpetuated its activity through crosstalk among pyroptosis cascades in different cell types, thus exacerbating the inflammatory environment throughout the entire bone marrow and joint degeneration environment. Correspondingly, pyroptosis regulation therapy emerged as a promising option for clinical treatment of DBJDs.

Natural compounds have shown promising application prospects in preventing or treating various diseases, including osteoporosis on account of their abundant sources, low price, multi-targeting and multiple biological effects. As a bioactive natural product, quercetin (Que) has previously demonstrated to ameliorate osteoporosis (OP), however, its poor bioavailability resulting from low water solubility, poor stability and lack of bone-targeting largely restricted its efficacy and clinical applications. Inspired by the bone-targeting capability of phosphate compounds, we reported a one-step procedure for synthesis of phosphorylated Que (p-Que) by direct phosphorylating phenol groups of Que for the first time. The phosphate groups on p-Que could not only improve the water dispersibility of Que, but also endow p-Que desirable bioavailability and bone-targeting feature. The results from biological assays suggested that p-Que could inhibit osteoclastogenesis and bone resorption and alleviate trabeculae loss in osteoporotic mice. In conclusion, this work demonstrated that phosphorylation strategy can effectively solve low water solubility, lack of bone-targeting capability and poor bioavailability of natural compounds, providing a novel and efficient approach for development of OP nanomedicines.

The inflammatory response in bone tissue often triggered by LPS is a complex process. Since LPS through TLR4 and in presence of IFNγ activates osteoclast differentiation and bone resorption, therefore, suppression of osteoclastogenesis through inhibition of TLR4 vs IFNγ mediated inflammation could be a reasonable strategy for the treatment of inflammatory bone loss. Administration of anti-TLR4 (30 mg/kg) and anti-IFNγ antibodies (6.6 mg/kg) were utilized before LPS (5 mg/kg) challenge and subsequently mice were treated with mouse IL-10 (0.02 mg/kg). Then RBMCs were isolated from different groups of mice and stimulated (in vitro) with M-CSF (10 ng/ml) and RANKL (10 ng/ml) to induce bone marrow cell differentiation in presence of LPS (100 ng/ml). The involvement of RANKL and M-CSF in the regulation of bone inflammation underlines the intricate signaling pathways. Furthermore, the study sheds light on the potential therapeutic effects of exogenous IL-10 possibly through STAT3 signaling in the RBMCs. The use of antibodies against TLR4 and IFNγ, in conjugation with IL-10in LPS bone damage model, appears to downregulate the activation of NF-κB, and reduction of many pro-inflammatory cytokines regulating the inflammatory cascade in RBMC. This suggests a promising avenue for the development of treatments aimed at mitigating bone inflammation associated with bacterial infections. Therefore, inhibition of TLR4 and IFNγ could be explored as potential therapeutic agents against LPS induced bone loss.

Osteoporosis is a common bone disease that has become a serious public health problem with the aging of population. Osteoclasts are the only cells in body that can resorb bone, whose dysfunction is closely related to osteoporosis. Pyruvate kinase M2 (PKM2) is one of the essential rate-limiting enzymes in the process of glycolysis. This study aimed to elucidate the role of PKM2 in osteoclastogenesis and bone resorption. Bone marrow-derived macrophages were transfected with adenovirus to knock down the expression of PKM2 gene or treated with the PKM2 activators, DASA-58 and TEPP-46. Osteoclast formation was detected by tartrate-resistant acid phosphatase staining, osteoclast-specific gene and protein expression was detected by RT-quantitative PCR and Western blotting, and the effect of DASA-58 on osteoclast gene expression at the transcriptional level was examined by RNA sequencing. The results showed that knockdown of PKM2 by adenoviral transfection or treatment with PKM2 activators, DASA-58 and TEPP-46, inhibited osteoclast differentiation and suppressed the expression of osteoclast-associated genes in bone marrow-derived macrophages. Furthermore, PKM2 activators, DASA-58 and TEPP-46, could inhibit several signaling pathways in osteoclasts; knockdown of PKM2 or treatment with PKM2 activators, DASA-58 and TEPP-46, both affected osteoclast precursor cell fusion by inhibiting the expression of osteoclast stimulatory transmembrane protein (OC-STAMP) and dendritic cell-specific transmembrane protein (DC-STAMP). Therefore, PKM2 is closely related to osteoclast differentiation and formation, and the development of new therapeutic strategies targeting the PKM2 gene in osteoclasts may be feasible for the prevention and treatment of osteoporosis.

To determine the association between obstructive sleep apnea syndrome (OSAS) and predicted bone mineral density (BMD) in adults presenting for orthodontic treatment.

This retrospective cross-sectional study included 38 adults divided into OSAS and non-OSAS groups. Using pre-treatment CBCT images, radiographic density (RD) of left and right lateral regions of the 1st cervical vertebrae and dens of the 2nd cervical vertebrae were measured as an indicator for BMD.

When controlling for age, sex, and BMI, the mean RD was significantly lower in the OSAS group compared to the non-OSAS group (left CV1: 36.69 ± 84.50 vs. 81.67 ± 93.25 Hounsfield Units [HU], respectively, p = 0.031; right CV1: 30.59 ± 81.18 vs. 74.26 ± 91.81 HU, p = 0.045; dens: 159.25 ± 115.96 vs. 223.94 ± 106.09 HU, p = 0.038).

Adults with OSAS have lower values for predicted BMD than those without OSAS.

This study aims to prepare collagen peptides from bovine bone meal using a combination of heat pretreatment and enzymatic digestion, and to chelate them with calcium chloride to form peptide-calcium chelates. The effects of both on the proliferation and differentiation of osteoclasts were investigated using cellular experiments (RAW 264.7 cells).

Both bovine collagen peptides and their calcium chelates (BPs, HBPs, BPs-Ca, and HBPs-Ca) can significantly inhibit the RANKL-induced differentiation of RAW 264.7 cells into osteoclasts. The preheating treatment before enzymatic hydrolysis of bone materials has an improving effect on the inhibition of RAW 264.7 differentiation into osteoblasts by collagen peptides and their peptide calcium chelates. HBP and HBPs-Ca could significantly activate the NF-κB signaling pathway, among which HBPs-Ca was the most effective, which could significantly downregulate the mRNA expression of genes related to osteoclast differentiation, such as AP-1, c-Fos, TRAP, and NFATc1. Additionally, the expression of NF-κB p65, c-Fos, IKK and IκBα were also significantly inhibited after treatment with HBPs-Ca, with IKK being the most significantly downregulated, with an 8.2-fold reduction compared to the control group.

HBPs and HBPs-Ca demonstrated stronger activity in inhibiting osteoclast formation compared to BPs and BPs-Ca. This enhanced activity is likely due to structural changes in the peptides caused by heat treatment, which increase their antioxidant properties and antagonistic effects on RANKL. These findings indicate that bovine collagen peptides and their calcium chelates can inhibit the formation of osteoclasts by activating the NF-κB pathway, thereby influencing bone metabolism and providing a theoretical basis for the treatment of osteoporosis. © 2025 Society of Chemical Industry.

Estrogen deficiency following menopause increases receptor activator of nuclear factor-kappa B ligand (RANKL) expression in osteoblasts, thereby promoting osteoclast differentiation, and enhances T cell-derived tumor necrosis factor-alpha (TNFα) production, which induces sclerostin expression in osteocytes, thereby inhibiting bone formation. This study aimed to develop a novel uncoupling therapeutic agent for osteoporosis.

We developed microglial healing peptide 1 with N-terminal acetylation and C-terminal amidation (MHP1-AcN), a modified RANKL peptide with N-terminal acetylation and C-terminal amidation lacking the osteoclast activating CD loop. Given the structural similarities of RANK and TNF receptor 1 (TNFR1), we hypothesized that MHP1-AcN could inhibit both the RANKL-RANK and TNFα-TNFR1 pathways to address the pathophysiology of osteoporosis, as evaluated in vitro and in vivo using an ovariectomized mouse model.

In ovariectomized mice, MHP1-AcN inhibited osteoclastogenesis, reduced osteocytic sclerostin expression, prevented bone loss, and improved the femoral cancellous and cortical bone microarchitecture. Unlike anti-RANKL antibody, MHP1-AcN considerably preserved bone formation by osteoblasts and enhanced bone strength, as evidenced by increases in energy absorption capacity. In vitro, MHP1-AcN bound to both RANK and TNFR1, suppressing osteoclast activity via the RANKL-RANK pathway and reducing sclerostin expression through the TNFα-TNFR1-nuclear factor-kappa B pathway. MHP1-AcN did not affect osteoblast proliferation and differentiation or RANKL expression.

MHP1-AcN effectively inhibits osteoclastogenesis and sclerostin-mediated suppression of bone formation while considerably preserving osteoblast function. These findings suggest that MHP1-AcN, which targets dual pathways critical for bone homeostasis, is a promising uncoupling therapeutic agent for osteoporosis.

Osteoarthritis (OA) is a degenerative joint disease that remains challenging to treat due to lack of complete understanding of its pathogenesis. Previous studies have identified RO5126766 (RO) as a small molecule compound that inhibited RAF/MEK-ERK pathway and garnered much interest for its anti-cancer properties. But its role in the treatment of OA remains unclear.

This study employed the anterior cruciate ligament transection (ACLT) procedure to create an OA model in mice. The effects of RO on pathological changes in articular cartilage and subchondral bone were assessed using micro-CT and histological staining. Mice received peritoneal injections of RO at 1 mg/kg and 5 mg/kg biweekly for 4 weeks after ACLT, while control mice received saline. In vitro, bone marrow-derived macrophages were cultured to examine the effects of RO on osteoclast activation using immunofluorescence, TRAP staining, and bone resorption assays. The inflammatory degeneration of chondrocytes and gene expression levels were evaluated using staining and RT-qPCR. Western blot and immunohistochemistry were used to analyze MAPK signaling and autophagy-related protein expression, investigating RO's molecular mechanism in OA treatment. Human single-cell data were also analyzed to identify genes and pathways upregulated in OA tissues.

Our findings showed that RO protects subchondral bone by inhibiting osteoclast formation in the ACLT mouse model of OA. In vitro, RO was shown to inhibit osteoclast differentiation and reduce inflammatory degeneration of chondrocytes. Mechanistically, RO counteracted subchondral osteoclast hyperactivation by suppressing the ERK/c-fos/NFATc1 signaling pathway. Additionally, RO inhibited LPS-induced inflammatory degeneration of chondrocytes and enhanced autophagy via the ERK pathway. Single-cell analysis further confirmed significant upregulation of the ERK signaling pathway in human OA tissues.

Overall, our findings suggested that RO inhibited osteoclast differentiation and protected articular cartilage, suggesting its potential as a novel treatment for OA.

In this study, we have, for the first time, substantiated the therapeutic potential of RO in the treatment of OA. By demonstrating its ability to inhibit osteoclast differentiation and protect articular cartilage, RO could offer a new avenue for disease-modifying treatments in OA. Thus, this paper provides valuable insights into understanding the molecular mechanisms and treatment of OA.

To date, cell-based approaches to stimulate bone formation have primarily focused on mesenchymal stromal cells (MSCs) for their supposed osteogenic potential, but despite some pre-clinical successes, clinical outcomes have remained unsatisfactory. Emerging data suggest that osteoclasts play crucial roles in stimulating bone formation beyond their catabolic function in bone resorption. Interestingly, osteoclastic activity precedes osteoblastic bone formation in the physiological bone remodeling cycle. To explore the role of osteoclasts in bone formation further, we prepared osteoclast-based constructs and implanted them (i) ectopically to evaluate their potential to induce bone formation, and (ii) orthotopically to evaluate effects on bone regeneration. Remarkably, constructs containing primary mouse osteoclasts showed consistent and robust de novo bone formation, which presented comparable osteogenic efficacy to BMP-2 treatment. Additionally, we observed de novo bone marrow formation upon ectopic implantation of osteoclast-based constructs (incidence 73 %) and BMP-2 loaded controls (incidence 91 %). Importantly, constructs containing macrophages (MФs) or scaffold only (negative control) showed neither bone nor bone marrow formation. Further, a mouse cranial defect model confirmed the stimulatory bone regeneration capabilities of Osteoclast-based constructs, evidenced by 2.5-fold increased bone formation compared to scaffold only. These findings demonstrate the osteoinduction and osteogenesis capacity of osteoclasts, reshaping our understanding of their role in bone formation and opening new avenues for the design and development of cell-based constructs for bone repair.

Research on the role of macrophages in musculoskeletal (MSK) diseases has significantly increased in recent years. However, a thorough evaluation of the developmental trajectory of this field, including the contributions of prominent authors and primary research themes, remains insufficient. Furthermore, the identification of emerging research hotspots requires more detailed exploration. This study collated articles and reviews addressing "macrophages in MSK diseases" published between 2004 and 2023, with all data extracted from the Web of Science database. The collected data were analyzed using a variety of bibliometric and visualization tools, such as VOSviewer, CiteSpace, GraphPad Prism, and R packages. Results indicate that China and the United States are the leading contributors in this research domain. Among the many academic institutions involved, Shanghai Jiao Tong University and the University of California stand out as the most productive. The journal "Frontiers in Immunology" had the highest publication output on this topic. The five most frequently explored research domains include Immunology, Rheumatology, Pharmacology and Pharmacy, Cell Biology, and Biochemistry and Molecular Biology. These results offer a comprehensive overview of the current state of research in this field and provide meaningful insights for guiding future studies.

ROS produced under oxidative stress are crucial for osteoclast differentiation. Metallothionein (MT) is a ROS-scavenging molecule. As a member of MT family, MT2 can clear ROS in osteoclast precursors (OCPs) and contributes to osteoclast differentiation. RANKL can promote OCP autophagy. Given the molecular-degrading effect of autophagy, the relationship between RANKL-dependent autophagy, MT2 and ROS during osteoclast differentiation is worth exploring. We depended in vitro RANKL administration and RANKL-overexpressing (Tg-RANKL) mice to observe the effects of RANKL on ROS production, MT2 protein expression, Beclin1 expression and autophagic activity in OCPs. Spautin1 was used to investigate the relationship between Beclin1-dependent autophagy and RANKL-regulated MT2 expression. Osteoclast-targeting MT2-cDNA-AAVs were applied to assess the therapeutic effect of MT2 on Tg-RANKL-related bone loss. The results showed that RANKL promoted ROS production but reduced MT2 protein expression in OCPs. RANKL also enhanced Beclin1 expression and LC3-puncta abundance. Decreased Beclin1 expression with spautin1 blocked RANKL-increased ROS production and osteoclast differentiation and recovered RANKL-decreased MT2 expression. MT2 selective overexpression with CD11b-promoter-MT2-cDNA-AAVs attenuated ROS production and osteoclastogenesis in Tg-RANKL mice and improved bone loss. Overall, RANKL can reduce MT2 protein expression through Beclin1-dependent autophagy, thereby promoting ROS production and osteoclast differentiation; this suggests that MT2-overexpressing small molecule drugs have the potential to treat RANKL-related bone loss.

Tripartite motif-containing 27 (TRIM27) is highly expressed in the mouse thymus, spleen, and hematopoietic compartment cells and regulates cell proliferation, apoptosis, and innate immune responses. However, the role of TRIM27 in bone remodeling remains unknown. This study aimed to investigate the role of TRIM27 in the differentiation of osteoclasts and osteoblasts.

We measured the effects of overexpression or knockdown of TRIM27 in osteoclasts and osteoblasts using real-time PCR and Western blot analysis to quantify the mRNA and protein levels of marker genes. Additionally, we performed an in vivo analysis of TRIM27 knockout mice through bone mineral density analysis and histological analysis.

TRIM27 deficiency decreased bone mineral density by enhancing osteoclast differentiation and inhibiting osteoblast differentiation. Overexpression of TRIM27 in osteoclast precursors suppressed osteoclast formation and resorption activity, and ectopic expression of TRIM27 in osteoblast precursors induced osteoblast differentiation and mineralization. Additionally, we found that TRIM27 attenuated NF-κB activation in both osteoclasts and osteoblasts by interacting with TAB2 and promoting TAB2 degradation through lysosomal-dependent pathways, thereby inhibiting NF-κB signaling.

Our results identify TRIM27 as a novel negative regulator of NF-κB in bone remodeling, suggesting that regulating TRIM27 may be useful in developing treatments for musculoskeletal diseases, such as osteoporosis.

Osteoarthritis, a progressive and degenerative joint disease, disrupts the integrity of the entire joint structure, underscoring the urgency of identifying more effective therapeutic strategies and innovative targets. Among these, exercise therapy is considered a key component in the early management of osteoarthritis, functioning by stimulating the secretion of myokines from the skeletal muscle system. Irisin, a myokine predominantly secreted by skeletal muscle during exercise and encoded by the FNDC5 gene, has garnered attention for its regulatory effects on bone health. Emerging evidence suggests that irisin may play a protective role in osteoarthritis by promoting tissue homeostasis, enhancing subchondral bone density and microstructure, and inhibiting chondrocyte apoptosis. By improving chondrocyte viability, preserving extracellular matrix integrity, and maintaining homeostasis in osteoblasts, osteoclasts, and osteocytes, irisin emerges as a promising therapeutic target for osteoarthritis. This review delves into the role of irisin in osteoarthritis pathogenesis, highlighting its influence on cartilage and bone metabolism as well as its dynamic relationship with exercise. Additionally, this review suggests that further exploration on its specific molecular mechanisms, optimization of drug delivery systems, and strategic utilization of exercise-induced benefits will be pivotal in unlocking the full potential of irisin as a novel intervention for osteoarthritis.

Osteoporosis, a condition marked by reduced bone mass and structural deterioration, continues to be a major public health concern, especially as global populations age. Excessive osteoclast formation is a hallmark of osteoporosis. The transcription factor nuclear factor of activated T-cells cytoplasmic 1 (NFATc1) is indispensable for the early differentiation of osteoclasts, orchestrating the expression of essential genes, while at the later stages, cathepsin K (CTSK) is essential for bone resorption activities of mature osteoclasts. Here, we fabricated ultrasound-responsive microdroplets (MDs) by modulating both the early stages of osteoclast differentiation and the functions of mature osteoclasts via targeting the NFATc1 and CTSK. The internalization of these dual MDs was evaluated in human bone marrow-derived mesenchymal stromal cells (hBMSCs) and murine RAW 264.7 macrophages, alongside the biocompatibility assay. Their effects on osteogenesis and osteoclastogenesis were further investigated in vitro, followed by in vivo analysis in osteoporotic rat models. The dual MDs exhibited a well-defined core-shell structure and demonstrated efficient cellular uptake with minimal cytotoxicity. Furthermore, dual MDs showed a minimal effect on the osteogenic differentiation of the hBMSCs. In in vitro osteoclastogenesis assays, dual MDs effectively suppressed both osteoclast differentiation and formation through a synergistic inhibitory effect. In vivo studies demonstrated that osteoporotic rats receiving dual MDs showed significant protection against bone loss induced by ovariectomy. These results highlight the potential of dual MDs as a sophisticated, targeted therapeutic approach to osteoporosis treatment.

Overactivation of osteoclasts disrupt the delicate balance between bone-resorbing osteoclasts and bone-forming osteoblasts, resulting in development of osteoporosis and various inflammatory disorders, including rheumatoid arthritis, spondyloarthropathies, and psoriatic arthritis. While inhibiting osteoclastogenesis represents a promising therapeutic strategy, current treatments targeting the RANKL pathway (such as bisphosphonates and denosumab) are associated with severe side effects, necessitating the development of safer alternatives. We hypothesize that the compound (4E)-7-(4-hydroxy-3-methoxyphenyl)-1-phenylhept-4-en-3-one (DPHB), derived from Alpinia officinarum Hance, can effectively inhibit RANKL-induced osteoclastic activity while maintaining a favorable safety profile. Through tartrate-resistant acid phosphatase (TRAP) staining and bone resorption pit assays, we demonstrate that DPHB inhibits osteoclast formation and function. Mechanistically, DPHB suppresses both NF-κB and MAPK signaling pathways while inhibiting NFATc1 activation and nuclear translocation, as evidenced by immunofluorescence staining, real-time PCR, and western blotting assays. In a LPS-induced inflammatory osteolysis mouse model, intraperitoneal administration of DPHB significantly alleviated bone destruction, confirmed through Micro-CT scanning, histological staining, and enzyme-linked immunosorbent assay (ELISA). Our findings establish DPHB as a promising osteoclast inhibitor for treating bone loss disorders through its dual suppression of osteoclastogenesis via NF-κB and MAPK signaling pathways and amelioration of inflammatory bone destruction.

During orthodontic tooth movement, sterile inflammatory processes and alveolar bone resorption occur in the periodontal ligament, involving myeloid cells such as macrophages and osteoclasts. The myeloid p38α/MAPK (mitogen-activated protein kinase) not only regulates the inflammatory response of macrophages and osteoclast differentiation but also the activation of the osmoprotective transcription factor NFAT5 (nuclear factor of activated T cells 5) under high-salt conditions. Therefore, this study aims to investigate the relative role of myeloid p38α/MAPK in orthodontic tooth movement as a function of extracellular salt content.

Macrophages and osteoclasts were differentiated from the bone marrow of mice lacking p38α/MAPK expression in myeloid cells (p38α Δmyel) and controls for RNA analysis and calcium phosphate resorption assay. Controls and p38α Δmyel mice were fed a low or a high salt diet for a total of two weeks. One week after the start of the diet, an elastic band was inserted between the first and second molar to induce orthodontic tooth movement. Atomic absorption spectrometry was used to assess the sodium balance of the jaw bone tissue. RNA was isolated from the periodontium of the first molar, osteoclast numbers and extent of orthodontic tooth movement were assessed.

Nfat5 mRNA was increased in macrophages and osteoclasts in vitro and in the periodontium in vivo after high salt treatment in control mice but not in p38α Δmyel mice. While there was no salt effect on interleukin-6 (Il6) gene expression, prostaglandin endoperoxide synthase-2 (Ptgs2) mRNA was upregulated in control but not in p38α Δmyel mice in vitro and in vivo. p38α/MAPK deletion increased osteoclast numbers after low and high salt diet. Of note, deletion of p38α/MAPK elevated osteoclast activity under control salt conditions but reduced osteoclast activity under high salt conditions. High-salt diet resulted in increased sodium ion deposition in the jaw of both genotypes, while tooth movement was only increased in control mice. In p38α Δmyel mice, high salt diet reduced the extent of orthodontic tooth movement, which could be explained by the reduced bone resorption of osteoclasts.

We conclude that myeloid p38α/MAPK promotes macrophage Ptgs2 expression and osteoclast activity in response to extracellular salt levels, thereby supporting orthodontic tooth movement.