This study explored the mechanism of curcumin (CUR) suppressing osteoclastogenesis and evaluated its effects on osteoarthritis (OA) mouse. Bone marrow-derived macrophages were isolated as osteoclast precursors. In the presence or absence of CUR, cell proliferation was detected by CCK-8, osteoclastogenesis was detected by tartrate-resistant acid phosphatase (TRAP) staining, F-actin rings formation was detected by immunofluorescence, bone resorption was detected by bone slices, IκBα, nuclear factor kappa-B (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways were detected using western blot, osteoclastogenesis-related gens were measured using quantitative polymerase chain reaction. A knee OA mouse model was designed by destabilizing the medial meniscus (DMM). Thirty-six male mice were divided into sham+vehicle, OA+vehicle, and OA+CUR groups. Mice were administered with or without CUR at 25 mg/kg/d from the first post-operative day until sacrifice. After 4 and 8 weeks of OA induction, micro-computed tomography was performed to analyze microstructure changes in subchondral bone, hematoxylin and eosin staining was performed to calculate the thickness of the calcified and hyaline cartilage layers, toluidine blue O staining was performed to assess the degenerated cartilage, TRAP-stained osteoclasts were counted, and NF-κB, phosphorylated Jun N-terminal Kinases (p-JNK), and receptor activator of nuclear factor κB ligand (RANKL) were detected using immunohistochemistry. CUR suppressed osteoclastogenesis and bone resorption without cytotoxicity. CUR restrained RANKL-induced activation of NF-κB, p-JNK and up-regulation of osteoclastogenesis-related genes. CUR delayed cartilage degeneration by suppressing osteoclastogenesis and bone resorption in early OA. The mechanism of CUR inhibiting osteoclastogenesis might be associated with NF-κB/JNK signaling pathway, indicating a novel strategy for OA treatment.

Osteoporosis remains incurable. The most widely used antiresorptive agents, bisphosphonates (BPs), also inhibit bone formation, while the anabolic agent, teriparatide, does not inhibit bone resorption, and thus they have limited efficacy in preventing osteoporotic fractures and cause some side effects. Thus, there is an unmet need to develop dual antiresorptive and anabolic agents to prevent and treat osteoporosis. Hydroxychloroquine (HCQ), which is used to treat rheumatoid arthritis, prevents the lysosomal degradation of TNF receptor-associated factor 3 (TRAF3), an NF-κB adaptor protein that limits bone resorption and maintains bone formation. We attempted to covalently link HCQ to a hydroxyalklyl BP (HABP) with anticipated low antiresorptive activity, to target delivery of HCQ to bone to test if this targeting increases its efficacy to prevent TRAF3 degradation in the bone microenvironment and thus reduce bone resorption and increase bone formation, while reducing its systemic side effects. Unexpectedly, HABP-HCQ was found to exist as a salt in aqueous solution, composed of a protonated HCQ cation and a deprotonated HABP anion. Nevertheless, it inhibited osteoclastogenesis, stimulated osteoblast differentiation, and increased TRAF3 protein levels in vitro. HABP-HCQ significantly inhibited both osteoclast formation and bone marrow fibrosis in mice given multiple daily PTH injections. In contrast, HCQ inhibited marrow fibrosis, but not osteoclast formation, while the HABP alone inhibited osteoclast formation, but not fibrosis, in the mice. HABP-HCQ, but not HCQ, prevented trabecular bone loss following ovariectomy in mice and, importantly, increased bone volume in ovariectomized mice with established bone loss because HABP-HCQ increased bone formation and decreased bone resorption parameters simultaneously. In contrast, HCQ increased bone formation, but did not decrease bone resorption parameters, while HABP also restored the bone lost in ovariectomized mice, but it inhibited parameters of both bone resorption and formation. Our findings suggest that the combination of HABP and HCQ could have dual antiresorptive and anabolic effects to prevent and treat osteoporosis.

BACKGROUND: Mechanical unloading-induced bone loss threatens prolonged spaceflight and human health. Recent studies have confirmed that osteoporosis is associated with a significant reduction in bone microvessels, but the relationship between them and the underlying mechanism under mechanical unloading are still unclear.
METHODS: We established a 2D clinostat and hindlimb-unloaded (HLU) mouse model to simulate unloading in vitro and in vivo. Micro-CT scanning was performed to assess changes in the bone microstructure and mass of the tibia. The levels of CD31, Endomucin (EMCN) and histone deacetylase 6 (HDAC6) in tibial microvessels were detected by immunofluorescence (IF) staining. In addition, we established a coculture system of microvascular endothelial cells (MVECs) and osteoblasts, and qRT‒PCR or western blotting was used to detect RNA and protein expression; cell proliferation was detected by CCK‒8 and EdU assays. ChIP was used to detect whether HDAC6 binds to the miRNA promoter region.
RESULTS: Bone mass and bone microvessels were simultaneously significantly reduced in HLU mice. Furthermore, MVECs effectively promoted the proliferation and differentiation of osteoblasts under coculture conditions in vitro. Mechanistically, we found that the HDAC6 content was significantly reduced in the bone microvessels of HLU mice and that HDAC6 inhibited the expression of miR-375-3p by reducing histone acetylation in the miR-375 promoter region in MVECs. miR-375-3p was upregulated under unloading and it could inhibit MVEC proliferation by directly targeting low-density lipoprotein-related receptor 5 (LRP5) expression. In addition, silencing HDAC6 promoted the miR-375-3p/LRP5 pathway to suppress MVEC proliferation under mechanical unloading, and regulation of HDAC6/miR-375-3p axis in MVECs could affect osteoblast proliferation under coculture conditions.
CONCLUSIONS: Our study revealed that disuse-induced bone loss may be closely related to a reduction in the number of bone microvessels and that the modulation of MVEC function could improve bone loss induced by unloading. Mechanistically, the HDAC6/miR-375-3p/LRP5 pathway in MVECs might be a promising strategy for the clinical treatment of unloading-induced bone loss.

Neuromuscular inhibitors have been quickly advanced from being used only for aesthetic purposes to being used as a treatment for musculoskeletal pain and muscle spasticity. This phenomenon stems from the diminished force exerted by muscles, which are essential for bone remodeling. In this context, it is hypothesized that botulinum toxin (BTX) might exert a direct influence on bone resorption. Although such treatments have the potential to provide patients with significant relief, bone loss occurring due to elective muscle paralysis has yet to be examined in clinical trials. The disuse model resulting from spinal cord injury, characterized by the absence of ground reaction and muscle forces, provides an ideal context for exploring the skeletal ramifications of intramuscular BTX injection. This approach enables an investigation into the intricate interplay between muscle and bone, encompassing the impact of spasticity on bone preservation, the potential positive and negative outcomes of BTX on bone metabolism, and the involvement of the autonomic nervous system in bone remodeling regulation. This paper presents a narrative review of research findings on the disturbance of the typical balance between muscles and bones caused by acute muscle paralysis from BTX, resulting in osteopenia and bone resorption.

BACKGROUND: Bone loss caused by microgravity exposure presents a serious threat to the health of astronauts, but existing treatment strategies have specific restrictions. This research aimed to investigate whether salidroside (SAL) can mitigate microgravity-induced bone loss and its underlying mechanism.
METHODS: In this research, we used hindlimb unloading (HLU) and the Rotary Cell Culture System (RCCS) to imitate microgravity in vivo and in vitro.
RESULTS: The results showed that salidroside primarily enhances bone density, microstructure, and biomechanical properties by stimulating bone formation and suppressing bone resorption, thereby preserving bone mass in HLU rats. In MC3T3-E1 cells cultured under simulated microgravity in rotary wall vessel bioreactors, the expression of osteogenic genes significantly increased after salidroside administration, indicating that salidroside can promote osteoblast differentiation under microgravity conditions. Furthermore, the Nrf2 inhibitor ML385 diminished the therapeutic impact of salidroside on microgravity-induced bone loss. Overall, this research provides the first evidence that salidroside can mitigate bone loss induced by microgravity exposure through stimulating the Nrf2/HO-1 pathway.
CONCLUSIONS: These findings indicate that salidroside has great potential for treating space-related bone loss in astronauts and suggest that Nrf2/HO-1 is a viable target for counteracting microgravity-induced bone damage.

Osteoclasts are multinucleated bone-resorbing cells, and their formation is tightly regulated to prevent excessive bone loss. However, the mechanisms by which osteoclast formation is restricted remain incompletely determined. Here, we found that sterol regulatory element binding protein 2 (SREBP2) functions as a negative regulator of osteoclast formation and inflammatory bone loss. Cholesterols and SREBP2, a key transcription factor for cholesterol biosynthesis, increased in the late phase of osteoclastogenesis. The ablation of SREBP2 in myeloid cells resulted in increased in vivo and in vitro osteoclastogenesis, leading to low bone mass. Moreover, deletion of SREBP2 accelerated inflammatory bone destruction in murine inflammatory osteolysis and arthritis models. SREBP2-mediated regulation of osteoclastogenesis is independent of its canonical function in cholesterol biosynthesis but is mediated, in part, by its downstream target, interferon regulatory factor 7 (IRF7). Taken together, our study highlights a previously undescribed role of the SREBP2-IRF7 regulatory circuit as a negative feedback loop in osteoclast differentiation and represents a novel mechanism to restrain pathological bone destruction.

UNASSIGNED: Proper nutrition is a crucial factor in preventing osteoporosis, a significant pathological cause linked to skeletal weakness; this study investigated the relationship between dietary diversity score and food group diversity score with osteoporosis in postmenopausal women.
UNASSIGNED: This case-control study was conducted on 378 menopausal women aged 45-85 in Tehran, Iran. The age-matching method to control the confounding effect of age was used. The method of dual-energy X-ray absorptiometry (DXA) was used for assessing the bone mineral density of lumbar vertebrae and femoral neck. The bone mass status was evaluated with WHO criteria. All subjects were divided into the osteoporosis group and the non-osteoporosis group according to their T-score. A convenience sampling method was utilized to select the participants, which included two groups: case (n = 189) and control (n = 189). Data was collected using demographic and anthropometric information questionnaires, a valid 147 item food frequency questionnaire, and a physical activity questionnaire. Statistical analyses were conducted using SPSS-26, and p-values less than 0.05 were deemed to be statistically significant.
UNASSIGNED: The results indicated significant differences in weight, body mass index, physical activity, smoking, and alcohol use between the two groups. The mean ± standard deviation of dietary diversity score (DDS) was lower in participants with osteoporosis (case) (3.31 ± 1.26) than in control (4.64 ± 1.33) (p < 0.001). The mean ± standard deviation of diversity score of cereals, fruits, and vegetables in the osteoporosis group (respectively: 0.71 ± 0.21, 0.94 ± 0.76, and 0.45 ± 0.44) was less than the control group (respectively: 0.80 ± 0.21, 1.64 ± 0.55 and 0.87 ± 0.42) (p < 0.001). After adjusting the confounding variables, the risk of osteoporosis had an inverse relationship with the diversity score of vegetable (OR = 0.16; 95%CI: 0.07-0.35), bread and cereal (OR = 0.21; 95% CI: 0.05-0.87) and fruit (OR = 0.35; 95%CI: 0.22-0.56) (p < 0.05). Nevertheless, no discernible correlation was seen between the tertiles of DDS, dairy and meat diversity score, and osteoporosis.
UNASSIGNED: We found a correlation between the diversity score of fruits, vegetables, and grains and osteoporosis. However, there is no significant correlation between the DDS triads and the diversity score of dairy products and meats with osteoporosis.

OBJECTIVE: Progressive bone resorption and destruction is one of the most critical clinical features of middle ear cholesteatoma, potentially leading to various intracranial and extracranial complications. However, the mechanisms underlying bone destruction in middle ear cholesteatoma remain unclear. This study aims to explore the role of parathyroid hormone-related protein (PTHrP) in bone destruction associated with middle ear cholesteatoma.
METHODS: A total of 25 cholesteatoma specimens and 13 normal external auditory canal skin specimens were collected from patients with acquired middle ear cholesteatoma. Immunohistochemical staining was used to detect the expressions of PTHrP, receptor activator for nuclear factor-kappa B ligand (RANKL), and osteoprotegerin (OPG) in cholesteatoma and normal tissues. Tartrate-resistant acid phosphatase (TRAP) staining was used to detect the presence of TRAP positive multi-nucleated macrophages in cholesteatoma and normal tissues. Mono-nuclear macrophage RAW264.7 cells were subjected to interventions, divided into a RANKL intervention group and a PTHrP+ RANKL co-intervention group. TRAP staining was used to detect osteoclast formation in the 2 groups. The mRNA expression levels of osteoclast-related genes, including TRAP, cathepsin K (CTSK), and nuclear factor of activated T cell cytoplasmic 1 (NFATc1), were measured using real-time polymerase chain reaction (real-time PCR) after the interventions. Bone resorption function of osteoclasts was assessed using a bone resorption pit analysis.
RESULTS: Immunohistochemical staining showed significantly increased expression of PTHrP and RANKL and decreased expression of OPG in cholesteatoma tissues (all P<0.05). PTHrP expression was significantly positively correlated with RANKL, the RANKL/OPG ratio, and negatively correlated with OPG expression (r=0.385, r=0.417, r=-0.316, all P<0.05). Additionally, the expression levels of PTHrP and RANKL were significantly positively correlated with the degree of bone destruction in cholesteatoma (r=0.413, r=0.505, both P<0.05). TRAP staining revealed a large number of TRAP-positive cells, including multi-nucleated osteoclasts with three or more nuclei, in the stroma surrounding the cholesteatoma epithelium. After 5 days of RANKL or PTHrP+RANKL co-intervention, the number of osteoclasts was significantly greater in the PTHrP+RANKL co-intervention group than that in the RANKL group (P<0.05), with increased mRNA expression levels of TRAP, CTSK, and NFATc1 (all P<0.05). Scanning electron microscopy of bone resorption pits showed that the number (P<0.05) and size of bone resorption pits on bone slices were significantly greater in the PTHrP+RANKL co-intervention group compared with the RANKL group.
CONCLUSIONS: PTHrP may promote the differentiation of macrophages in the surrounding stroma of cholesteatoma into osteoclasts through RANKL induction, contributing to bone destruction in middle ear cholesteatoma.
目的: 骨质进行性吸收破坏是中耳胆脂瘤最重要的临床特征之一，可导致一系列颅内外并发症，而目前中耳胆脂瘤骨破坏的机制尚未明确。本研究旨在探究甲状旁腺激素相关蛋白(parathyroid hormone-related protein，PTHrP)参与中耳胆脂瘤骨破坏的机制。方法: 收集后天性中耳胆脂瘤患者的25例胆脂瘤标本和13例外耳道正常皮肤组织标本。采用免疫组织化学染色方法检测PTHrP、核因子κB受体活化因子配体(receptor activator for nuclear factor-kappa B ligand，RANKL)和骨保护素(osteoprotegerin，OPG)在中耳胆脂瘤和外耳道正常皮肤组织中的表达，抗酒石酸酸性磷酸酶(tartrate-resistant acid phosphatase，TRAP)染色法检测中耳胆脂瘤和外耳道正常皮肤组织中是否存在TRAP阳性多核巨噬细胞。选取小鼠单核巨噬细胞RAW264.7细胞进行干预，分为RANKL干预组和PTHrP+RANKL共同干预组，采用TRAP染色法检测2组破骨细胞的生成情况，实时聚合酶链反应(real-time polymerase chain reaction，real-time PCR)检测干预后2组破骨细胞相关基因TRAP、组织蛋白酶K(cathepsin K，CTSK)和活化T细胞核因子1(nuclear factor of activated T cell cytoplasmic 1，NFATc1)的mRNA表达水平，骨吸收陷窝实验检测2组破骨细胞的骨吸收功能。结果: 免疫组织化学染色结果显示，PTHrP和RANKL在中耳胆脂瘤组织中的表达均显著增高，OPG表达降低(均P<0.05)，且PTHrP的表达与RANKL、RANKL/OPG比值均呈显著正相关，与OPG表达呈显著负相关(分别r=0.385、r=0.417、r=-0.316，均P<0.05)。同时，PTHrP、RANKL的表达水平与中耳胆脂瘤的骨破坏程度均呈显著正相关(分别r=0.413、r=0.505，均P<0.05)。TRAP染色结果显示中耳胆脂瘤上皮周围基质中有大量TRAP阳性细胞，并存在细胞核数量为3个或3个以上的TRAP阳性破骨细胞。RANKL或PTHrP+RANKL联合干预5 d后，与RANKL干预组相比，PTHrP+RANKL联合干预组的破骨细胞数量显著增加(P<0.05)，且破骨细胞相关基因TRAP、CTSK和NFATc1的mRNA表达水平均升高(均P<0.05)。骨吸收陷窝扫描电镜结果显示RANKL干预组、PTHrP+RANKL联合干预组的骨片表面均形成骨吸收陷窝；与RANKL干预组相比，PTHrP+RANKL联合干预组的骨片表面骨吸收陷窝数量显著增加(P<0.05)，面积也更大。结论: PTHrP可能通过促进RANKL诱导胆脂瘤组织周围基质中的巨噬细胞分化为破骨细胞，参与中耳胆脂瘤骨破坏。.

Lysosomes serve as catabolic centers and signaling hubs in cells, regulating a multitude of cellular processes such as intracellular environment homeostasis, macromolecule degradation, intracellular vesicle trafficking and autophagy. Alterations in lysosomal level and function are crucial for cellular adaptation to external stimuli, with lysosome dysfunction being implicated in the pathogenesis of numerous diseases. Osteoclasts (OCs), as multinucleated cells responsible for bone resorption and maintaining bone homeostasis, have a complex relationship with lysosomes that is not fully understood. Dysregulated function of OCs can disrupt bone homeostasis leading to the development of various bone disorders. The regulation of OC differentiation and bone resorption for the treatment of bone disease have received considerable attention in recent years, yet the role and regulation of lysosomes in OCs, as well as the potential therapeutic implications of intervening in lysosomal biologic behavior for the treatment of bone diseases, remain relatively understudied. This review aims to elucidate the mechanisms involved in lysosomal biogenesis and to discuss the functions of lysosomes in OCs, specifically in relation to differentiation, bone resorption, and autophagy. Finally, we explore the potential therapeutic implication of targeting lysosomes in the treatment of bone metabolic disorders.

Osteoporosis, a systemic skeletal disorder marked by diminished bone mass and compromised bone microarchitecture, is becoming increasingly prevalent due to an aging population. The underlying pathophysiology of osteoporosis is attributed to an imbalance between osteoclast-mediated bone resorption and osteoblast-mediated bone formation. Osteoclasts play a crucial role in the development of osteoporosis through various molecular pathways, including the RANK/RANKL/OPG signaling axis, cytokines, and integrins. Notably, the calcium signaling pathway is pivotal in regulating osteoclast activation and function, influencing bone resorption activity. Disruption in calcium signaling can lead to increased osteoclast-mediated bone resorption, contributing to the progression of osteoporosis. Emerging research indicates that calcium-permeable channels on the cellular membrane play a critical role in bone metabolism by modulating these intracellular calcium pathways. Here, we provide an overview of current literature on the regulation of plasma membrane calcium channels in relation to bone metabolism with particular emphasis on their dysregulation during the progression of osteoporosis. Targeting these calcium channels may represent a potential therapeutic strategy for treating osteoporosis.