Selective Regulation of MAPK Signaling Mediates RANKL-dependent Osteoclast Differentiation

Curcumin alleviates osteoarthritis in mice by suppressing osteoclastogenesis in subchondral bone via inhibiting NF-κB/JNK signaling pathway

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.

Ubiquitin C-terminal hydrolase L1 activation in periodontal ligament cells mediates orthodontic tooth movement via the MAPK signaling pathway

PURPOSE

Periodontal ligament cells (PDLCs) play a significant role in orthodontic force induced bone remodeling. However, the molecular mechanisms by which PDLCs respond to mechanical stimuli and influence osteoclastic activities remain unclear. This study aims to investigate the role of UCHL1, a key deubiquitinating enzyme involved in protein degradation and cellular responses, in force-treated PDLCs during orthodontic tooth movement (OTM).

MATERIALS AND METHODS

In this study, we conducted in vivo and in vitro experiments using human PDLCs and a rat model of OTM. Mechanical stress was applied to PDLCs, and UCHL1 expression was analyzed through quantitative real-time polymerase chain reaction (qPCR), Western blot, and immunofluorescence staining. UCHL1 knockdown was achieved using siRNA, and its effects on osteoclast differentiation were assessed. The role of the MAPK/ERK pathway was investigated using the MEK-specific inhibitor U0126. An animal model of OTM was established, and the impact of UCHL1 inhibitor-LDN57444 on OTM and osteoclastic activity was evaluated through micro-CT analysis, histological staining, and immunohistochemistry.

RESULTS

Mechanical force induced UCHL1 expression in PDLCs during OTM. UCHL1 knockdown downregulated the RANKL/OPG ratio in PDLCs, affecting osteoclast differentiation. LDN57444 inhibited OTM and osteoclastic activity. UCHL1 activation correlated with ERK1/2 phosphorylation in force-treated PDLCs.

CONCLUSIONS

Mechanical force mediated UCHL1 activation in PDLCs promotes osteoclast differentiation via the ERK1/2 signaling pathway during OTM.

Surface Pre-Reacted Glass-Ionomer Eluate Suppresses Osteoclastogenesis through Downregulation of the MAPK Signaling Pathway

Surface pre-reacted glass-ionomer (S-PRG) is a new bioactive filler utilized for the restoration of decayed teeth by its ability to release six bioactive ions that prevent the adhesion of dental plaque to the tooth surface. Since ionic liquids are reported to facilitate transepithelial penetration, we reasoned that S-PRG applied to root caries could impact the osteoclasts (OCs) in the proximal alveolar bone. Therefore, this study aimed to investigate the effect of S-PRG eluate solution on RANKL-induced OC-genesis and mineral dissolution in vitro. Using RAW264.7 cells as OC precursor cells (OPCs), TRAP staining and pit formation assays were conducted to monitor OC-genesis and mineral dissolution, respectively, while OC-genesis-associated gene expression was measured using quantitative real-time PCR (qPCR). Expression of NFATc1, a master regulator of OC differentiation, and the phosphorylation of MAPK signaling molecules were measured using Western blotting. S-PRG eluate dilutions at 1/200 and 1/400 showed no cytotoxicity to RAW264.7 cells but did significantly suppress both OC-genesis and mineral dissolution. The same concentrations of S-PRG eluate downregulated the RANKL-mediated induction of OCSTAMP and CATK mRNAs, as well as the expression of NFATc1 protein and the phosphorylation of ERK, JNK, and p38. These results demonstrate that S-PRG eluate can downregulate RANKL-induced OC-genesis and mineral dissolution, suggesting that its application to root caries might prevent alveolar bone resorption.

Comparative Transcriptomic Analyses of Peripheral Blood Mononuclear Cells of COVID-19 Patients without Pneumonia and with Severe Pneumonia in the First Year of Follow-Up

The multisystemic effects of COVID-19 may continue for a longer time period following the acute phase, depending on the severity of the disease. However, long-term systemic transcriptomic changes associated with COVID-19 disease and the impact of disease severity are not fully understood. We aimed to investigate the impact of COVID-19 and its severity on transcriptomic alterations in peripheral blood mononuclear cells (PBMCs) following 1 year of the disease. PBMCs were isolated from the peripheral blood of healthy control donors who did not have COVID-19 (C; n = 13), from COVID-19 patients without pneumonia (NP; n = 11), and from COVID-19 patients with severe pneumonia (SP; n = 10) after 1-year of follow-up. Following RNA isolation from PBMCs, high-quality RNAs were sequenced after creating a library. Differentially expressed genes (DEGs) and differentially expressed long non-coding RNAs (DElncRNAs) were identified using Benjamini-Hochberg correction and they were analysed for hierarchical clustering and principal component analysis (PCA). Intergroup comparisons (C vs. NP, C vs. SP, and NP vs. SP) of DEGs and DElncRNAs were performed and hub genes were determined. Functional enrichment analyses of DEGs and DElncRNAs were made using Metascape (v3.5.20240101) and the first version of NCPATH. The RNA sequencing analysis revealed 4843 DEGs and 1056 DElncRNAs in "C vs. NP", 1651 DEGs and 577 DElncRNAs in "C vs. SP", and 954 DEGs and 148 DElncRNAs in "NP vs. SP", with 291 DEGs and 70 DElncRNAs shared across all groups, respectively. We identified 14 hub genes from 291 DEGs, with functional enrichment analysis showing upregulated DEGs mainly linked to inflammation and osteoclast differentiation and downregulated DEGs to viral infections and immune responses. The analysis showed that 291 common and 14 hub genes were associated with pneumonia and that these genes could be regulated by the transcription factors JUN and NFκB1 carrying the NFκB binding site. We also revealed unique immune cell signatures across DEG categories indicating that the upregulated DEGs were associated with neutrophils and monocytes, while downregulated DEGs were associated with CD4 memory effector T cells. The comparative transcriptomic analysis of NP and SP groups with 52 gene signatures suggestive of IPF risk showed a lower risk of IPF in the SP group than the NP patients. Our findings suggest that COVID-19 may cause long term pathologies by modulating the expression of various DEGs, DeLncRNAs, and hub genes at the cellular level.

New insights into dairy management and the prevention and treatment of osteoporosis: The shift from single nutrient to dairy matrix effects-A review

Dairy is recognized as a good source of calcium, which is important for preventing osteoporosis. However, the relationship between milk and bone health is more complex than just calcium supplementation. It is unwise to focus solely on observing the effects of a single nutrient. Lactose, proteins, and vitamins in milk, as well as fatty acids, oligosaccharides, and exosomes, all work together with calcium to enhance its bioavailability and utilization efficiency through various mechanisms. We evaluate the roles of dairy nutrients and active ingredients in maintaining bone homeostasis from the perspective of the dairy matrix effects. Special attention is given to threshold effects, synergistic effects, and associations with the gut-bone axis. We also summarize the associations between probiotic/prebiotic milk, low-fat/high-fat milk, lactose-free milk, and fortified milk with a reduced risk of osteoporosis and discuss the potential benefits and controversies of these dairy products. Moreover, we examine the role of dairy products in increasing peak bone mass during adolescence and reducing bone loss in old age. It provides a theoretical reference for the use of dairy products in the accurate prevention and management of osteoporosis and related chronic diseases and offers personalized dietary recommendations for bone health in different populations.

Isobavachin attenuates osteoclastogenesis and periodontitis-induced bone loss by inhibiting cellular iron accumulation and mitochondrial biogenesis

As bone-resorbing cells rich in mitochondria, osteoclasts require high iron uptake to promote mitochondrial biogenesis and maintain a high-energy metabolic state for active bone resorption. Given that abnormal osteoclast formation and activation leads to imbalanced bone remodeling and osteolytic bone loss, osteoclasts may be crucial targets for treating osteolytic diseases such as periodontitis. Isobavachin (IBA), a natural flavonoid compound, has been confirmed to be an inhibitor of receptor activator of nuclear factor κB ligand (RANKL)-induced osteoclast differentiation from bone marrow-derived macrophages (BMMs). However, its effects on periodontitis-induced bone loss and the potential mechanism of its anti-osteoclastogenesis effect remain unclear. Our study demonstrated that IBA suppressed RANKL-induced osteoclastogenesis in BMMs and RAW264.7 cells and inhibited osteoclast-mediated bone resorption in vitro. Transcriptomic analysis indicated that iron homeostasis and reactive oxygen species (ROS) metabolic process were enriched among the differentially expressed genes following IBA treatment. IBA exerted its anti-osteoclastogenesis effect by inhibiting iron accumulation in osteoclasts. Mechanistically, IBA attenuated iron accumulation in RANKL-induced osteoclasts by inhibiting the mitogen-activated protein kinase (MAPK) pathway to upregulate ferroportin1 (Fpn1) expression and promote Fpn1-mediated intracellular iron efflux. We also found that IBA inhibited mitochondrial biogenesis and function, and reduced RANKL-induced ROS generation in osteoclasts. Furthermore, IBA attenuated periodontitis-induced bone loss by reducing osteoclastogenesis in vivo. Overall, these results suggest that IBA may serve as a promising therapeutic strategy for bone diseases characterized by osteoclastic bone resorption.

Quercetin in Osteoporosis Treatment: A Comprehensive Review of Its Mechanisms and Therapeutic Potential

PURPOSE OF REVIEW

This review aims to provide a theoretical basis and insights for quercetin's clinical application in the prevention and treatment of osteoporosis (OP), analyzing its roles in bone formation promotion, bone resorption inhibition, anti-inflammation, antioxidant effects, and potential mechanisms.

RECENT FINDINGS

OP, a prevalent bone disorder, is marked by reduced bone mineral density and impaired bone architecture, elevating the risk of fractures in patients. The primary approach to OP management is pharmacotherapy, with quercetin, a phytochemical compound, emerging as a focus of recent interest. This natural flavonoid exerts regulatory effects on bone marrow mesenchymal stem cells, osteoblasts, and osteoclasts and promotes bone health and metabolic equilibrium via anti-inflammatory and antioxidative pathways. Although quercetin has demonstrated significant potential in regulating bone metabolism, there is a need for further high-quality clinical studies focused on medicinal quercetin.

Natural Compounds for Bone Remodeling: A Computational and Experimental Approach Targeting Bone Metabolism-Related Proteins

Osteoporosis, characterized by reduced bone density and increased fracture risk, affects over 200 million people worldwide, predominantly older adults and postmenopausal women. The disruption of the balance between bone-forming osteoblasts and bone-resorbing osteoclasts underlies osteoporosis pathophysiology. Standard treatment includes lifestyle modifications, calcium and vitamin D supplementation and specific drugs that either inhibit osteoclasts or stimulate osteoblasts. However, these treatments have limitations, including side effects and compliance issues. Natural products have emerged as potential osteoporosis therapeutics, but their mechanisms of action remain poorly understood. In this study, we investigate the efficacy of natural compounds in modulating molecular targets relevant to osteoporosis, focusing on the Mitogen-Activated Protein Kinase (MAPK) pathway and the gut microbiome's influence on bone homeostasis. Using an in silico and in vitro methodology, we have identified quercetin as a promising candidate in modulating MAPK activity, offering a potential therapeutic perspective for osteoporosis treatment.

Local application of zoledronate inhibits early bone resorption and promotes bone formation

Nonunion resulting from early bone resorption is common after bone transplantation surgery. In these patients, instability or osteoporosis causes hyperactive catabolism relative to anabolism, leading to graft resorption instead of fusion. Systemic zoledronate administration inhibits osteoclastogenesis and is widely used to prevent osteoporosis; however, evidence on local zoledronate application is controversial due to osteoblast cytotoxicity, uncontrolled dosing regimens, and local release methods. We investigated the effects of zolendronate on osteoclastogenesis and osteogenesis and explored the corresponding signaling pathways. In vitro cytotoxicity and differentiation of MC3T3E1 cells, rat bone marrow stromal cells (BMSCs) and preosteoclasts (RAW264.7 cells) were evaluated with different zolendronate concentrations. In vivo bone regeneration ability was tested by transplanting different concentrations of zolendronate with β-tricalcium phosphate (TCP) bone substitute into rat femoral critical-sized bone defects. In vitro, zolendronate concentrations below 2.5 × 10-7 M did not compromise viability in the three cell lines and did not promote osteogenic differentiation in MC3T3E1 cells and BMSCs. In RAW264.7 cells, zoledronate inhibited extracellular regulated protein kinases and c-Jun n-terminal kinase signaling, downregulating c-Fos and NFATc1 expression, with reduced expression of fusion-related dendritic cell‑specific transmembrane protein and osteoclast-specific Ctsk and tartrate-resistant acid phosphatase (. In vivo, histological staining revealed increased osteoid formation and neovascularization and reduced fibrotic tissue with 500 μM and 2000 μM zolendronate. More osteoclasts were found in the normal saline group after 6 weeks, and sequential osteoclast formation occurred after zoledronate treatment, indicating inhibition of bone resorption during early callus formation without inhibition of late-stage bone remodeling. In vivo, soaking β-TCP artificial bone with 500 μM or 2000 μM zoledronate is a promising approach for bone regeneration, with potential applications in bone transplantation.

Research Progress on Anti-Inflammatory Effects and Related Mechanisms of Astragalin

Chronic inflammation is a significant contributor to the development of cancer, cardiovascular disease, diabetes, obesity, autoimmune disease, inflammatory bowel disease, and other illnesses. In the academic field, there is a constant demand for effective methods to alleviate inflammation. Astragalin (AST), a type of flavonoid glycoside that is the primary component in several widely used traditional Chinese anti-inflammatory medications in clinical practice, has garnered attention from numerous experts and scholars. This article focuses on the anti-inflammatory effects of AST and conducts research on relevant literature from 2003 to 2023. The findings indicate that AST demonstrates promising anti-inflammatory potential in various models of inflammatory diseases. Specifically, AST is believed to possess inhibitory effects on inflammation-related factors and protein levels in various in vitro cell models, such as macrophages, microglia, and epithelial cells. In vivo studies have shown that AST effectively alleviates neuroinflammation and brain damage while also exhibiting potential for treating moderate diseases such as depression and stroke; it also demonstrates significant anti-inflammatory effects on both large and small intestinal epithelial cells. Animal experiments have further demonstrated that AST exerts therapeutic effects on colitis mice. Molecular biology studies have revealed that AST regulates complex signaling networks, including NF-κB, MAPK, JAK/STAT pathways, etc. In conclusion, this review will provide insights and references for the development of AST as an anti-inflammatory agent as well as for related drug development.

Ethanol extract of Cyathulae Radix inhibits osteoclast differentiation and bone loss

Cyathulae Radix, a traditional Chinese medicine and a common vegetable, boasts a history spanning millennia. It enhances bone density, boosts metabolism, and effectively alleviates osteoporosis-induced pain. Despite its historical use, the molecular mechanisms behind Cyathulae Radix's impact on osteoporosis remain unexplored. In this study, we investigated the effects and mechanisms of Cyathulae Radix ethanol extract (CEE) in inhibiting osteoporosis and osteoclastogenesis. Eight-week-old female mice underwent ovariectomy and were treated with CEE for eight weeks. Micro-computed tomography (micro-CT) assessed histomorphometric parameters, bone tissue staining observed distal femur histomorphology, and three-point bending tests evaluated tibia mechanical properties. Enzyme-linked immunosorbent assay (ELISA) measured serum estradiol (E2), receptor activator for nuclear factor B ligand (RANKL), and osteoprotegerin (OPG) levels. Osteoclastogenesis-related markers were analyzed via Western blotting (WB) and quantitative real-time polymerase chain reaction (qRT-PCR). Additionally, CEE effects on RANKL-induced osteoclast formation and bone resorption were investigated in vitro using tartrate-resistant acid phosphatase (TRAP) staining, qRT-PCR, and WB assay. Compared with the ovariectomy (OVX) group, CEE treatment enhanced trabecular bone density, maximal load-bearing capacity, and various histomorphometric parameters. Serum E2 and OPG levels significantly increased, while Receptor activator of nuclear factor-κB (RANK) decreased in the CEE group. CEE downregulated matrix metallopeptidase 9 (MMP-9), Cathepsin K (CTSK), and TRAP gene and protein expression. In bone marrow macrophages (BMMs), CEE reduced mature osteoclasts, bone resorption pit areas, and MMP-9, CTSK, and TRAP expression during osteoclast differentiation. Compared with DMSO treatment, CEE markedly inhibited RANK, TNF receptor associated factor 6 (TRAF6), Proto-oncogene c-Fos (c-Fos), Nuclear factor of activated T-cells cytoplasmic 1 (NFATc1) expressions, and Extracellular regulated protein kinases (ERK), c-Jun N-terminal kinase (JNK), NF-kappa B-p65 (p65) phosphorylation in osteoclasts. In conclusion, CEE significantly inhibits OVX-induced osteoporosis and RANKL-induced osteoclastogenesis, potentially through modulating the Estrogen Receptor (ER)/RANK/NFATc1 signaling pathway.

Therapeutic potential of a prominent dihydroxyflavanone pinocembrin for osteolytic bone disease: In vitro and in vivo evidence

Background/objective

As the pivotal cellular mediators of bone resorption and pathological bone remodeling, osteoclasts have emerged as a prominent target for anti-resorptive interventions. Pinocembrin (PIN), a predominant flavonoid found in damiana, honey, fingerroot, and propolis, has been recognized for its potential therapeutic effects in osteolysis. The purpose of our project is to investigate the potential of PIN to prevent bone resorption in ovariectomized (OVX) mice by suppressing osteoclast production through its underlying mechanisms.

Methods

The study commenced by employing protein-ligand molecular docking to ascertain the specific interaction between PIN and nuclear factor-κB (NF-κB) ligand (RANKL). Subsequently, PIN was introduced to bone marrow macrophages (BMMs) under the stimulation of RANKL. The impact of PIN on osteoclastic activity was assessed through the utilization of a positive TRAcP staining kit and a hydroxyapatite resorption assay. Furthermore, the study investigated the generation of reactive oxygen species (ROS) in osteoclasts induced by RANKL using H2DCFDA. To delve deeper into the underlying mechanisms, molecular cascades triggered by RANKL, including NF-κB, ROS, calcium oscillations, and NFATc1-mediated signaling pathways, were explored using Luciferase gene report, western blot analysis, and quantitative real-time polymerase chain reaction. Moreover, an estrogen-deficient osteoporosis murine model was established to evaluate the therapeutic effects of PIN in vivo.

Results

In this study, we elucidated the profound inhibitory effects of PIN on osteoclastogenesis and bone resorption, achieved through repression of NF-κB and NFATc1-mediated signaling pathways. Notably, PIN also exhibited potent anti-oxidative properties by mitigating RANKL-induced ROS generation and augmenting activities of ROS-scavenging enzymes, ultimately leading to a reduction in intracellular ROS levels. Moreover, PIN effectively abrogated the expression of osteoclast-specific marker genes (Acp5, Cathepsin K, Atp6v0d2, Nfatc1, c-fos, and Mmp9), further underscoring its inhibitory impact on osteoclast differentiation and function. Additionally, employing an in vivo mouse model, we demonstrated that PIN effectively prevented osteoclast-induced bone loss resultant from estrogen deficiency.

Conclusion

Our findings highlight the potent inhibitory effects of PIN on osteoclastogenesis, bone resorption, and RANKL-induced signaling pathways, thereby establishing PIN as a promising therapeutic candidate for the prevention and management of osteolytic bone diseases.

The translational potential of this article

PIN serves as a promising therapeutic agent for the prevention and management of osteolytic bone diseases and holds promise for future clinical applications in addressing conditions characterized by excessive bone resorption. PIN is a natural compound found in various sources, including damiana, honey, fingerroot, and propolis. Its widespread availability and potential for therapeutic use make it an attractive candidate for further investigation and development as a clinical intervention.

Eosinophils preserve bone homeostasis by inhibiting excessive osteoclast formation and activity via eosinophil peroxidase

Eosinophils are involved in tissue homeostasis. Herein, we unveiled eosinophils as important regulators of bone homeostasis. Eosinophils are localized in proximity to bone-resorbing osteoclasts in the bone marrow. The absence of eosinophils in ΔdblGATA mice results in lower bone mass under steady-state conditions and amplified bone loss upon sex hormone deprivation and inflammatory arthritis. Conversely, increased numbers of eosinophils in IL-5 transgenic mice enhance bone mass under steady-state conditions and protect from hormone- and inflammation- mediated bone loss. Eosinophils strongly inhibit the differentiation and demineralization activity of osteoclasts and lead to profound changes in the transcriptional profile of osteoclasts. This osteoclast-suppressive effect of eosinophils is based on the release of eosinophil peroxidase causing impaired reactive oxygen species and mitogen-activated protein kinase induction in osteoclast precursors. In humans, the number and the activity of eosinophils correlates with bone mass in healthy participants and rheumatoid arthritis patients. Taken together, experimental and human data indicate a regulatory function of eosinophils on bone.

Ginsenoside Rb2 exhibits therapeutic value for male osteoporosis in orchiectomy mice by suppressing osteoclastogenesis and modulating NF-κB/MAPK signaling pathways

Osteoporosis (OP) is a systemic disorder characterized by decreased bone mass as well as deteriorated microarchitecture. Although OP in men is common, it has received much less attention than that in women. Ginseng, a famous traditional herb in Asia, is used to strengthen and repair bones by invigorating vital bioenergy and maintaining body homeostasis in dietary intake and clinical applications. However, there is currently no study investigating the impact of ginseng and its active compounds on male osteoporosis. In this study, RNA sequencing and bioinformatic analysis were conducted to reveal the influence of Ginsenoside-Rb2 on RAW264.7 cells and its underlying signaling pathways. The potential anti-osteoporosis effects of Rb2 as well as its molecular mechanisms were elucidated in RAW264.7 cells and BMMs by TRAP staining, F-actin belt staining, qRT-PCR and WB. Moreover, orchiectomy (ORX) was utilized to demonstrate the influence of Rb2 on bone mass loss in vivo by micro-CT scanning, and H&E, TRAP, and IHC staining. The results suggested that Rb2 suppressed osteoclastogenesis and mitigated bone loss in orchiectomy mice through NF-κB/MAPK signaling pathways. These findings indicate that ginseng as well as its active component Rb2 have potential therapeutic value in the management of osteoporosis in men.

Pharmacological and mechanistic aspects of quercetin in osteoporosis

Osteoporosis (OP) is a bone disease associated with increasing age. Currently, the most common medications used to treat OP are anabolic agents, anti-resorptive agents, and medications with other mechanisms of action. However, many of these medications have unfavorable adverse effects or are not intended for long-term use, potentially exerting a severe negative impact on a patient's life and career and placing a heavy burden on families and society. There is an urgent need to find new drugs that can replace these and have fewer adverse effects. Quercetin (Que) is a common flavonol in nature. Numerous studies have examined the therapeutic applications of Que. However, a comprehensive review of the anti-osteoporotic effects of Que has not yet been conducted. This review aimed to describe the recent studies on the anti-osteoporotic effects of Que, including its biological, pharmacological, pharmacokinetic, and toxicological properties. The outcomes demonstrated that Que could enhance OP by increasing osteoblast differentiation and activity and reducing osteoclast differentiation and activity via the pathways of Wnt/β-catenin, BMP/SMAD/RUNX2, OPG/RANKL/RANK, ERK/JNK, oxidative stress, apoptosis, and transcription factors. Thus, Que is a promising novel drug for the treatment of OP.

Oxyresveratrol attenuates bone resorption by inhibiting the mitogen-activated protein kinase pathway in ovariectomized rats

BACKGROUND

Bone is continuously produced by osteoblasts and resorbed by osteoclasts to maintain homeostasis. Impaired bone resorption by osteoclasts causes bone diseases such as osteoporosis and arthritis. Most pharmacological treatment of osteoporosis focuses on inhibiting osteoclast differentiation, often to restore osteoclast/osteoclast balance. However, recent osteoporosis treatments have various side effects. According to a recent study, resveratrol, known as a stilbenoid family, is known to increase bone density, and the osteoclast inhibitory effect was confirmed using oxyresveratrol, a stilbenoid family. Here, we investigated the effect of oxyresveratrol on osteoclast differentiation and an ovariectomized mouse model.

METHODS

Mouse leukemia monocyte/macrophage cell line RAW 264.7 was treated with oxyresveratrol, and cell cytotoxicity was confirmed by measuring MTT assay. Tartrate-resistant acid phosphatase (TRAP), an enzyme marker for osteoclasts, was confirmed by staining. In addition, osteoclast differentiation markers and MAPK-related markers were confirmed at the mRNA level and protein expression. The effect of oxyresveratrol was confirmed using ovariectomized mice. Deoxypyridinoline (DPD) was measured using mouse urine and TRAP activity was observed using serum. Bone mineral density was also measured using Micro-CT.

RESULTS

The polyphenol oxyresveratrol inhibited receptor activator of nuclear factor kappa-Β ligand (RANKL)-induced osteoclast differentiation of RAW 264.7 cells. Furthermore, oxyresveratrol inhibited TRAP activity and actin-ring formation. Moreover, oxyresveratrol suppressed the phosphorylation of the RANKL-induced mitogen-activated protein kinases (MAPKs) p38, JNK, and ERK and significantly reduced the expression of bone differentiation markers (NFATc1, cathepsin K, and TRAP).

CONCLUSION

Oxyresveratrol inhibits osteoclast differentiation via MAPK and increases bone density in ovariectomized rats, suggesting it has therapeutic potential for bone diseases such as osteoporosis. We confirmed the osteoporosis prevention effect of OR in Raw 264.7 cells, and future studies should confirm the effect of OR using rat bone marrow-derived cells.

Morusin Inhibits RANKL-induced Osteoclastogenesis and Ovariectomized Osteoporosis

BACKGROUND

Postmenopausal osteoporosis (PMOP) is a classic type of osteoporosis that has gradually become a significant health problem worldwide. There is an urgent need for a safe alternative therapeutic agent considering the poor therapeutic strategies currently available for this disease. The roots and bark of the Morus australis tree (Moraceae) are used to make a traditional Chinese medicine known as "Morusin", and accumulating evidence has demonstrated its multiple activities, such as anti-inflammatory and anti-tumor effects.

OBJECTIVE

In this study, we aim to explore the effect of Morusin on mouse osteoclasts and its mechanism.

METHODS

In this study, we explored the inhibitory effects of Morusin on murine osteoclasts in vitro and its mechanism, and the protective effect of Morusin on an ovariectomy (OVX)-induced osteoporosis model in vivo.

RESULTS

The results showed that Morusin prevented OVX-induced bone loss and dramatically decreased RANKL-induced osteoclastogenesis. Morusin interfered with RANKL-activated NF- κB, MAPK, and PI3K/AKT signaling pathways. The expression of three master factors that control osteoclast differentiation, c-Fos, NFATc1, and c-Jun, was reduced by Morusin treatment. Collectively, in vitro results indicated that Morusin has a protective effect on OVX-induced bone loss in a mouse model.

CONCLUSION

Our data provide encouraging evidence that Morusin may be an effective treatment for PMOP.

Highly cyto- and immune compatible new synthetic fluorapatite nanomaterials co-doped with rubidium(I) and europium(III) ions

In the present study, biocompatible luminescent of nanosized fluorapatite doped with rubidium(I) (Rb+ ion) and europium(III) (Eu3+ ion) ions were synthesized via hydrothermal method. It was investigated the influence of co-doped Rb+ and Eu3+ ions on the structural, and morphological characteristics of the obtained fluorapatite materials. The characterization techniques utilized included: X-ray powder diffraction (XRPD), infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM). Moreover, to establish the influence of the co-doped Rb+ and Eu3+ ions on the luminescence properties of the lanthanide ion, emission excitation, emission spectrum and luminescence decays were measured. This confirmed a distinct red emission originating from Eu3+ ions and an increased emission lifetime. To determine the biocompatibility of the obtained fluorapatite compounds, in vitro studies using normal dermal human fibroblasts were performed. The results of these studies clearly demonstrate the remarkable biocompatibility of our compounds. This discovery opens exciting prospects for the use of synthetic fluorapatites doped with Eu3+ and Rb+ ions in various biomedical contexts. In particular, these materials hold great promise for potential applications in regenerative engineering, but also serve as innovative and practical solutions as bone scaffolds and dental implants containing nano-fluorapatite. Further discussion of these properties can be found in this article, along with a discussion of their importance and potential in the field of biomedical applications. However, according to our pervious study and based on our current investigations but also based on available scientific records, it was proposed potential molecular mechanism of Rb+ ions in the process of osteoclastogenesis.

CGK733 alleviates ovariectomy-induced bone loss through blocking RANKL-mediated Ca2+ oscillations and NF-κB/MAPK signaling pathways

Osteoporosis is a prevalent systemic metabolic disease in modern society, in which patients often suffer from bone loss due to over-activation of osteoclasts. Currently, amelioration of bone loss through modulation of osteoclast activity is a major therapeutic strategy. Ataxia telangiectasia mutated (ATM) inhibitor CGK733 (CG) was reported to have a sensitizing impact in treating malignancies. However, its effect on osteoporosis remains unclear. In this study, we investigated the effects of CG on osteoclast differentiation and function, as well as the therapeutic effects of CG on osteoporosis. Our study found that CG inhibits osteoclast differentiation and function. We further found that CG inhibits the activation of NFATc1 and ultimately osteoclast formation by inhibiting RANKL-mediated Ca2+ oscillation and the NF-κB/MAPK signaling pathway. Next, we constructed an ovariectomized mouse model and demonstrated that CG improved bone loss in ovariectomized mice. Therefore, CG may be a potential drug for the prevention and treatment of osteoporosis.

Extracellular Signal-Regulated Kinases Play Essential but Contrasting Roles in Osteoclast Differentiation

Bone homeostasis is regulated by the balanced actions of osteoblasts that form the bone and osteoclasts (OCs) that resorb the bone. Bone-resorbing OCs are differentiated from hematopoietic monocyte/macrophage lineage cells, whereas osteoblasts are derived from mesenchymal progenitors. OC differentiation is induced by two key cytokines, macrophage colony-stimulating factor (M-CSF), a factor essential for the proliferation and survival of the OCs, and receptor activator of nuclear factor kappa-B ligand (RANKL), a factor for responsible for the differentiation of the OCs. Mitogen-activated protein kinases (MAPKs), including extracellular signal-regulated kinases (ERKs), p38, and c-Jun N-terminal kinases, play an essential role in regulating the proliferation, differentiation, and function of OCs. ERKs have been known to play a critical role in the differentiation and activation of OCs. In most cases, ERKs positively regulate OC differentiation and function. However, several reports present conflicting conclusions. Interestingly, the inhibition of OC differentiation by ERK1/2 is observed only in OCs differentiated from RAW 264.7 cells. Therefore, in this review, we summarize the current understanding of the conflicting actions of ERK1/2 in OC differentiation.

Gleditsiae fructus regulates osteoclastogenesis by inhibiting the c‑Fos/NFATc1 pathway and alleviating bone loss in an ovariectomy model

Medical and economic developments have allowed the human lifespan to extend and, as a result, the elderly population has increased worldwide. Osteoporosis is a common geriatric disease that has no symptoms and even a small impact can cause fractures in patients, leading to a serious deterioration in the quality of life. Osteoporosis treatment typically involves bisphosphonates and selective estrogen receptor modulators. However, these treatments are known to cause severe side effects, such as mandibular osteonecrosis and breast cancer, if used for an extended period of time. Therefore, it is essential to develop therapeutic agents from natural products that have fewer side effects. Gleditsiae fructus (GF) is a dried or immature fruit of Gleditsia sinensis Lam. and is composed of various triterpenoid saponins. The anti‑inflammatory effect of GF has been confirmed in various diseases, and since the anti‑inflammatory effect plays a major role in inhibiting osteoclast differentiation, GF was expected to be effective in osteoclast differentiation and menopausal osteoporosis; however, to the best of our knowledge, it has not yet been studied. Therefore, the present study was designed to examine the effect of GF on osteoclastogenesis and to investigate the mechanism underlying inhibition of osteoclast differentiation. The effects of GF on osteoclastogenesis were determined in vitro by tartrate‑resistant acid phosphatase (TRAP) staining, pit formation assays, filamentous actin (F‑actin) ring formation assays, western blotting and reverse transcription‑quantitative PCR analyses. Furthermore, the administration of GF to an animal model exhibiting menopausal osteoporosis allowed for the analysis of alterations in the bone microstructure of the femur using micro‑CT. Additionally, assessments of femoral tissue and serum were conducted. The present study revealed that the administration of GF resulted in a reduction in osteoclast levels, F‑actin rings, TRAP activity and pit area. Furthermore, GF showed a dose‑dependent suppression of nuclear factor of activated T‑cells cytoplasmic, c‑Fos and other osteoclastogenesis‑related markers.

Isobavachalcone inhibits RANKL-induced osteoclastogenesis via miR-193-3p/NF-κB/NFATc1 signaling pathway in BMMs cells

Inhibition of extensive osteoclastogenesis and bone resorption is considered a potential therapeutic target for the treatment of osteoporosis. Isobavachalcone (IBC) is derived from the traditional Chinese herb Psoralea corylifolia Linn. We showed that IBC dose-dependently suppressed receptor activator of nuclear factor kappa B ligand (RANKL)-induced osteoclastogenesis in bone marrow monocyte/macrophage (BMMs) and osteoclastic bone-resorption function without cytotoxicity at a dose of no more than 8 µmin vitro. Mechanistically, the results of western blot and quantitative real-time polymerase chain reaction (qRT-PCR) indicated that IBC inhibited the RANKL-induced degradation of IκBα and phosphorylation of nuclear factor kappa B (NF-κB) in BMMs, and subsequently downregulated the expression of osteoclastic-specific genes and osteoclastogenesis-related proteins. TRAP staining and qRT-PCR showed that IBC can inhibit osteoclast differentiation by down-regulating the expression of miR-193-3p on osteoclast differentiation. Overall, our findings suggest that IBC may serve as a promising compound for the treatment of osteoporosis and other metabolic bone diseases.

Iris Koreana NAKAI Inhibits Osteoclast Formation via p38-Mediated Nuclear Factor of Activated T Cells 1 Signaling Pathway

BACKGROUND

Iris Koreana NAKAI (IKN) is a flowering perennial plant that belongs to the Iridaceae family. In this study, we aimed to demonstrate the effects of IKN on osteoclast differentiation in vitro and in vivo. We also sought to verify the molecular mechanisms underlying its anti-osteoclastogenic effects.

METHODS

Osteoclasts were formed by culturing mouse bone marrow macrophage (BMM) cells with macrophage colony-stimulating factor and receptor activator of nuclear factor-κB ligand (RANKL). Bone resorption assays were performed on dentin slices. mRNA expression levels were analyzed by quantitative polymerase chain reaction. Western blotting was performed to detect protein expression or activation. Lipopolysaccharide (LPS)-induced osteoclast formation was performed using a mouse calvarial model.

RESULTS

In BMM cultures, an ethanol extract of the root part of IKN suppressed RANKL-induced osteoclast formation and bone resorptive activity. In contrast, an ethanol extract of the aerial parts of IKN had a minor effect on RANKL-induced osteoclast formation. Mechanistically, the root part of IKN suppressed RANKL-induced p38 mitogen-activated protein kinase (MAPK) activation, effectively abrogating the induction of c-Fos and nuclear factor of activated T cells 1 (NFATc1) expression. IKN administration decreased LPS-induced osteoclast formation in a calvarial osteolysis model in vivo.

CONCLUSIONS

Our study suggested that the ethanol extract of the root part of IKN suppressed osteoclast differentiation and function partly by downregulating the p38 MAPK/c-Fos/NFATc1 signaling pathways. Thus, the root part.

Protaetia brevitarsis Extract Attenuates RANKL-Induced Osteoclastogenesis by Inhibiting the JNK/NF-κB/PLCγ2 Signaling Pathway

Protaetia brevitarsis (PB)-derived bioactive substances have been used as food and medicine in many Asian countries because of their antioxidant, antidiabetic, anti-cancer, and hepatoprotective properties. However, the effect of PB extracts (PBE) on osteoclast differentiation is unclear. In this study, we investigated the effect of PBE on RANKL-induced osteoclastogenesis in mouse bone marrow-derived macrophages (BMMs). To investigate the cytotoxicity of PBE, the viability of BMMs was confirmed via MTT assay. Tartrate-resistant acid phosphatase (TRAP) staining and pit assays were performed to confirm the inhibitory effect of PBE on osteoclast differentiation and bone resorption. The expression levels of osteoclast differentiation-related genes and proteins were evaluated using quantitative real-time PCR and Western blotting. PBE attenuated osteoclastogenesis in BMMs in TRAP and pit assays without cytotoxicity. The expression levels of osteoclast marker genes and proteins induced by RANKL were decreased after PBE treatment. PBE suppressed osteoclastogenesis by inhibiting the RANKL-induced activated JNK/NF-κB/PLCγ2 signaling pathway and the expression of NFATc1 and c-Fos. Collectively, these results suggest that PBE could be a potential therapeutic strategy or functional product for osteoclast-related bone disease.

The Molecular Mechanisms Study of Engeletin Suppresses RANKL-Induced Osteoclastogenesis and Inhibits Ovariectomized Murine Model Bone Loss

Objective

Osteoclastogenesis, the process of osteoclast differentiation, plays a critical role in bone homeostasis. Overexpression of osteoclastogenesis can lead to pathological conditions, such as osteoporosis and osteolysis. This study aims to investigate the role of Engelitin in the process of RAW264.7 cell differentiation into osteoclasts induced by RANKL, as well as in a mouse model of bone loss following ovariectomy.

Methods

We used RANKL-stimulated RAW264.7 cells as an in vitro osteoclast differentiation model. The effects of Eng on morphological changes during osteoclast differentiation were evaluated using TRAP and F-actin staining. The effects of Eng on the molecular level of osteoclast differentiation were evaluated using Western blot and q-PCR. The level of reactive oxygen species was evaluated using the DCFH-DA staining method. We then used ovariectomized mice as a bone loss animal model. The effects of Eng on changes in bone loss in vivo were evaluated using micro-CT and histological analysis staining.

Results

In the in vitro experiments, Eng exhibited dose-dependent inhibition of osteoclast formation and F-actin formation. At the molecular level, Eng dose-dependently suppressed the expression of specific RNAs (NFATc1, c-Fos, TRAP, Cathepsin K, MMP-9) involved in osteoclast differentiation, and inhibited the phosphorylation of proteins such as IκBα, P65, ERK, JNK, and P38. Additionally, Eng dose-dependently suppressed ROS levels and promoted the expression of antioxidant enzymes such as Nrf2, HO-1, and NQO1. In the in vivo experiments, Eng improved bone loss in ovariectomized mice.

Conclusion

Our study found that Eng inhibited RANKL-induced osteoclast differentiation through multiple signaling pathways, including MAPKs, NF-κB, and ROS aggregation. Furthermore, Eng improved bone loss in ovariectomized mice.

Revisiting Resveratrol as an Osteoprotective Agent: Molecular Evidence from In Vivo and In Vitro Studies

Resveratrol (RSV) (3,5,4'-trihydroxystilbene) is a stilbene found in abundance in berry fruits, peanuts, and some medicinal plants. It has a diverse range of pharmacological activities, underlining the significance of illness prevention and health promotion. The purpose of this review was to delve deeper into RSV's bone-protective properties as well as its molecular mechanisms. Several in vivo studies have found the bone-protective effects of RSV in postmenopausal, senile, and disuse osteoporosis rat models. RSV has been shown to inhibit NF-κB and RANKL-mediated osteoclastogenesis, oxidative stress, and inflammation while increasing osteogenesis and boosting differentiation of mesenchymal stem cells to osteoblasts. Wnt/β-catenin, MAPKs/JNK/ERK, PI3K/AKT, FoxOs, microRNAs, and BMP2 are among the possible kinases and proteins involved in the underlying mechanisms. RSV has also been shown to be the most potent SIRT1 activator to cause stimulatory effects on osteoblasts and inhibitory effects on osteoclasts. RSV may, thus, represent a novel therapeutic strategy for increasing bone growth and reducing bone loss in the elderly and postmenopausal population.

Ras family signaling pathway in immunopathogenesis of inflammatory rheumatic diseases

The Ras (rat sarcoma virus) is a GTP-binding protein that is considered one of the important members of the Ras-GTPase superfamily. The Ras involves several pathways in the cell that include proliferation, migration, survival, differentiation, and fibrosis. Abnormalities in the expression level and activation of the Ras family signaling pathway and its downstream kinases such as Raf/MEK/ERK1-2 contribute to the pathogenic mechanisms of rheumatic diseases including immune system dysregulation, inflammation, and fibrosis in systemic sclerosis (SSc); destruction and inflammation of synovial tissue in rheumatoid arthritis (RA); and autoantibody production and immune complexes formation in systemic lupus erythematosus (SLE); and enhance osteoblast differentiation and ossification during skeletal formation in ankylosing spondylitis (AS). In this review, the basic biology, signaling of Ras, and abnormalities in this pathway in rheumatic diseases including SSc, RA, AS, and SLE will be discussed.

Fine-tuning osteoclastogenesis: An insight into the cellular and molecular regulation of osteoclastogenesis

Osteoclasts, the bone-resorbing cells, are essential for the bone remodeling process and are involved in the pathophysiology of several bone-related diseases. The extensive corpus of in vitro research and crucial mouse model studies in the 1990s demonstrated the key roles of monocyte/macrophage colony-stimulating factor, receptor activator of nuclear factor kappa B ligand (RANKL) and integrin αvβ3 in osteoclast biology. Our knowledge of the molecular mechanisms by which these variables control osteoclast differentiation and function has significantly advanced in the first decade of this century. Recent developments have revealed a number of novel insights into the fundamental mechanisms governing the differentiation and functional activity of osteoclasts; however, these mechanisms have not yet been adequately documented. Thus, in the present review, we discuss various regulatory factors including local and hormonal factors, innate as well as adaptive immune cells, noncoding RNAs (ncRNAs), etc., in the molecular regulation of the intricate and tightly regulated process of osteoclastogenesis. ncRNAs have a critical role as epigenetic controllers of osteoclast physiologic activities, including differentiation and bone resorption. The primary ncRNAs, which include micro-RNAs, circular RNAs, and long noncoding RNAs, form a complex network that affects gene transcription activities associated with osteoclast biological activity. Greater knowledge of the involvement of ncRNAs in osteoclast biological activities will contribute to the treatment and management of several skeletal diseases such as osteoporosis, osteoarthritis, rheumatoid arthritis, etc. Moreover, we further outline potential therapies targeting these regulatory pathways of osteoclastogenesis in distinct bone pathologies.

Annexin A3 accelerates osteoclast differentiation by promoting the level of RANK and TRAF6

Annexin A3 (ANXA3), a member of Annexin family, is reported to mediate membrane transport and cancer development. However, the effect of ANXA3 on osteoclast formation and bone metabolism is still unclear. In this study, we found that knockdown of ANXA3 can significantly inhibit receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast formation through NF-κB signaling. ANXA3 downregulation abrogated the expression of osteoclast-specific genes, including Acp5, Mmp9 and Ctsk in osteoclast precursors. Moreover, lentiviral of shRNA against ANXA3 reversed the bone loss in osteoporosis using ovariectomized mice model. Mechanistically, we found that ANXA3 directly bound to RANK and TRAF6 to accelerate osteoclast differentiation by promoting their transcription and limiting degradation. In conclusion, we propose a fundamentally novel RANK-ANXA3-TRAF6 complex to effectively modulate the formation and differentiation of osteoclast to manipulate bone metabolism. The ANXA3-targeted therapeutic strategy may provide new insight for bone degrading-related diseases prevention and treatment.

Cedrol, a Ginger-derived sesquiterpineol, suppresses estrogen-deficient osteoporosis by intervening NFATc1 and reactive oxygen species

Osteoporosis is a prevalent bone metabolic disease in menopause, and long-term medication is accompanied by serious side effects. Ginger, a food spice and traditional medicine with ancient history, exhibits the potential to alleviate osteoporosis in preclinical experiments, whereas its complex composition leads to ambiguous pharmacological mechanisms. The purpose of this study was to investigate the effect and mechanism of Ced in estrogen-deficient osteoporosis, a sesquiterpene alcohol recently discovered from Ginger with multiple pharmacological properties. RANKL was stimulated BMM (bone marrow macrophages) differentiation into osteoclasts in vitro. And the osteoclast activity and number were assessed by TRAcP and SEM. We found that Ced mitigated RANKL-induced osteoclastogenesis by descending the ROS content and obstructing NFATc1, NF-κB, and MAPK signaling. Also, Ced-mediated anti-osteolytic property was found in ovariectomized mice by Micro-CT scanning and histological staining. Summarily, our works demonstrated the anti-osteoporotic potential of Cedrol in Ginger for the first time, which also offered more pharmacological evidence for Ginger as food or medicine used for bone metabolic disease.

Pilose antler (Cervus elaphus Linnaeus) polysaccharide and polypeptide extract inhibits bone resorption in high turnover type osteoporosis by stimulating the MAKP and MMP-9 signaling pathways

ETHNOPHARMACOLOGICAL RELEVANCE

Pilose antler is a traditional Chinese medicine used to improve kidney function, strengthen tendons and bones, and prolong life, among other uses. It is widely employed in the treatment of osteoporosis. However, the molecular mechanisms underlying the treatment of high turnover osteoporosis are not fully understood.

AIM OF THE STUDY

The present study aimed to investigate the molecular mechanism underlying pilose antler polysaccharide and polypeptide extracts in inhibiting bone resorption in high turnover osteoporosis, and compare the effects of the two components alone and in combination to explore whether they could produce synergistic enhancement effects.

MATERIALS AND METHODS

The quantitative and qualitative characteristics of pilose antler polysaccharide and polypeptide extracts were detected by UV-visible spectrophotometry and high-performance liquid chromatography. A rat model of retinoic acid-induced osteoporosis was used to evaluate the inhibitory effect of the extracts on bone resorption. Enzyme-linked immunosorbent assay (ELISA) was used to detect the activity of factors related to high turnover type osteoporosis in rat serum. Western blotting was used to detect the expression of proteins related to the MAKP and MMP-9 signaling pathways in rat femurs. Fluorescence quantitative PCR was used to detect the transcription levels of genes related to the MAKP and MMP-9 signaling pathways in rat femur tissues. Hematoxylin and eosin staining were used to observe the osteoprotective effects of pilose antler polysaccharides and polypeptides.

RESULTS

The yield of pilose antler polysaccharides was 8.3%, and was mainly composed of mannose, glucosamine hydrochloride, glucuronic acid, Galacturonic acid, Galactose hydrochloride, glucose, and galactose. The yield of the polypeptides was 26.2%, and eighty percent of the molecular weight of the antler polypeptides was 1.6 kDa-7kD, among which, the molecular weight of 7kD peptide accounted for 52% of the total. Both polysaccharides and peptides could reduce the activities of TRACP, OCN, ERK1, JNK, and MMP-9 in rat serum and reduce both the protein expression and gene transcription levels of ERK1, JNK, and MMP-9 in rat femur tissue with significant differences compared with the model group. Both extracts exerted significant protective effects on rat femur tissue. The effect of pilose antler polypeptides alone was better than that of polysaccharides either alone or in combination.

CONCLUSIONS

Pilose antler polysaccharides, polypeptides, and their mixtures could inhibit the occurrence of bone resorption of high turnover osteoporosis by stimulating the MAKP and MMP-9 signaling pathways to reduce the expression of the ERK1, JNK, and MMP-9 genes and proteins, and could help alleviate bone loss caused by retinoic acid. Pilose antler polypeptides had a stronger effect on inhibiting bone resorption. The combination of the two components did not show synergistic enhancement effect, and the polysaccharide tended to moderate the inhibitory enhancement effect of the polypeptide.

Moringa oleifera leaf attenuate osteoporosis in ovariectomized rats by modulating gut microbiota composition and MAPK signaling pathway

Moringa oleifera leaf (MLP) contains abundant complex nutrients with anti-osteoporosis potential. However, its efficacy and mechanisms against osteoporosis remain unknown. The purpose of this research is to investigate MLP's anti-osteoporotic effects and mechanisms. Animal experiments were used in this work to validate MLP's anti-osteoporotic efficacy. We investigated the mode of action of MLP, analyzed its impact on the gut microbiota, and predicted and validated its anti-osteoporosis-related molecular targets and pathways through network pharmacology, molecular docking, and western blotting. In an ovariectomized osteoporosis rat model, MLP significantly increased bone mineral density and improved bone metabolism-related indicators, bone microstructure, and lipid profile. Moreover, it improved gut microbiota composition and increased the expression of Occludin and Claudin-1 protein in the duodenum. Network pharmacology identified a total of 97 active ingredients and 478 core anti-osteoporosis targets. Of these, MAPK1 (also known as ERK2), MAPK3 (also known as ERK1), and MAPK8 (also known as JNK) were successfully docked with the active constituents of MLP. Interestingly, MLP increased ERK and VAV3 protein expression and decreased p-ERK and JNK protein expression in the femur. These findings confirm MLP's anti-osteoporotic efficacy, which could be mediated via regulation of gut microbiota and MAPK signaling.

Facile synthesis of curcumin-containing poly(amidoamine) dendrimers as pH-responsive delivery system for osteoporosis treatment

Osteoporosis is an age-related metabolic disease of bone, resulting in bone pain and even bone fragility and brittle fracture. Inhibiting overactive osteoclasts while promoting osteoblast activity is an ideal way to treat osteoporosis. Previous studies have demonstrated that natural compounds, such as curcumin (Cur) have dual roles both in promoting bone formation and inhibiting bone resorption, making them promising candidates for osteoporosis treatment. However, their poor water solubility, high dosage of curative effect and significant toxicity to other organs have largely limited their clinical translations. In this study, a novel method was reported to conjugate Cur and poly(amidoamine) dendrimers (PAD) using hexachlorocyclotriphosphazene (HCCP) as the linkage through a one-pot reaction, forming stable and uniform Cur loaded nanospheres (HCCP-Cur-PAD, HCP NPs). Owing to the hydrophilicity of PAD and hydrophobicity of Cur, HCP NPs can self-assemble into nanoparticles with particle size of 138.8 ± 78.7 nm and display excellent water dispersity. The loading capacity of Cur can reach 27.2% and it can be released from HCP NPs with pH-responsiveness. In vitro experimental results demonstrated that the HCP NPs entered lysosomes by endocytosis and proved dual anti-osteoporosis effects of inhibiting osteoclasts and promoting osteoblasts.

Isopsoralen suppresses receptor activator of nuclear factor kappa-β ligand-induced osteoclastogenesis by inhibiting the NF-κB signaling

Osteoporosis is a serious systemic metabolic bone system disease.This study aimed to identify the target genes of isopsoralen and the signaling pathways involved in the differential expression of the genes involved in osteoclast differentiation. We hypothesized that isopsoralen may inhibit osteoclast differentiation by blocking the nuclear factor kappa-B (NF-κB) signaling pathway and verified our hypothesis through basic experiments. The 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay was used to detect the effect of isopsoralen on the proliferation and viability of primary mouse bone marrow monocytes (BMMCs). The effect of isopsoralen on receptor activator of nuclear factor kappa-B ligand (RANKL)-induced osteoclast differentiation was determined by using tartrate-resistant acid phosphatase (TRAP) staining. Quantitative real-time PCR (qRT-PCR) and Western blot were used to detect the expression of the related genes and proteins. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway of isopsoralen target genes were obtained through comprehensive analysis using the STITCH database, Cytoscape 3.8.2, and R-Studio software. Differentially expressed genes (DEGs) were found in osteoclasts induced by RANKL before and after 3 days using R-Studio, following which KEGG analysis was performed. Next, enrichment analysis was performed on the KEGG pathway shared by the target genes of isopsoralen and the differentially expressed genes during osteoclast differentiation to predict the signaling pathway underlying the inhibition of osteoclast differentiation by isopsoralen. Finally, Western blot was used to detect the effect of isopsoralen on the activation of signaling pathways to verify the results of our bioinformatics analysis. Based on the enrichment analysis of isopsoralen target genes and differentially expressed genes during osteoclastogenesis, we believe that isopsoralen can inhibit RANKL-induced osteoclastogenesis by inhibiting the NF-κB signaling pathway.

RANKL interferes with osteoclastogenesis in PEG-fused U937 cells through LGR4

INTRODUCTION

RANKL plays an important role in the differentiation and maturation process of preosteoclast cells. The osteoclast is a multinucleated cell that can have various sizes and a variable number of nuclei. However, there are no models that allow us to understand how successive cell fusions have a limit, or how cell fusion is regulated.

METHODOLOGY

The present investigation was aimed to determine whether fusing U937 cells with PEG to generate osteoclast-like cells expresses LGR4 and whether applying RANKL to these cells modifies osteoclastic activity compared to non-PEG-fused and RANKL-treated cells.

RESULTS

By fusing U937 cells with PEG, it was found that the LGR4 receptor expression was promoted as early as 24 hours of culture. Applying RANKL before or after fusion inhibits osteoclastic activity. Interfering RANKL interaction with LGR4 in PEG-treated cells recovers and increases cell fusion and osteoclastic activity. PEG-fused U937 cells show osteoclast markers similar to those observed in the classical RANKL-stimulated cell model.

CONCLUSION

Our model allows us to understand that RANKL has fusogenic activity during the first days of culture and in fused cells modulates fusion, contributing to differentiate the role of RANKL before and after fusion through LGR4.

Evaluation of culture conditions for osteoclastogenesis in RAW264.7 cells

Osteoclasts are the only multinucleated cells in vivo responsible for bone resorption and are vital for regulating bone remodeling and maintaining bone mass. The RAW264.7 cell line is widely used to study osteoclastic differentiation and biological molecular mechanism. However, protocols for inducing osteoclast formation in RAW264.7 cells vary considerably between laboratories, hindering the replication of results. Therefore, we tested the influence of culture conditions on osteoclast differentiation, including cell density and receptor activator of nuclear factor kappa-B ligand (RANKL) concentrations with or without macrophage colony-stimulating factors (M-CSF). Tartrate-resistant acid phosphatase (TRAP) staining was used to detect the morphology of osteoclasts. qPCR was used to detect gene expression of osteoclast-specific gene marker cathepsin K (CTSK), osteoclast transcription factors c-Fos and nuclear factor of activated T cells, cytoplasmic 1 (NFATc1). The bone resorption function was evaluated by a scanning electron microscope (SEM). RANKL treatment increased multinucleated osteoclasts formation and increased CTSK, c-Fos and NFATc1 gene expression. Compared with RANKL treatment, M-CSF significantly decreased multinucleated osteoclasts formation, reduced CTSK gene expression and had little effect on c-Fos and NFATc1 gene expression. Concerning bone resorption activity, RANKL treatment increased bone resorption pits on bovine bone slices. Significantly higher levels of osteoclastogenesis were observed with RAW264.7-cell density of 2×104 cells/well in 24-well plates. Our results suggest that the addition of 50 ng/ml M-CSF has no positive effect on osteoclastogenesis. RANKL treatment and cell density contribute to osteoclast formation, and the optimal conditions are beneficial when exploring osteoclast function and mechanism.

Receptor activator of nuclear factor-κB ligand-mediated osteoclastogenesis signaling pathway and related therapeutic natural compounds

Osteoclast is a hematopoietic precursor cell derived from the mononuclear macrophage cell line, which is the only cell with bone resorption function. Its abnormal activation can cause serious osteolysis related diseases such as rheumatoid arthritis, Paget's disease and osteoporosis. In recent years, the adverse effects caused by anabolic anti-osteolytic drugs have increased the interest of researchers in the potential therapeutic and preventive effects of natural plant derivatives and natural compounds against osteolytic diseases caused by osteoclasts. Natural plant derivatives and natural compounds have become major research hotspots for the treatment of osteolysis-related diseases due to their good safety profile and ability to improve bone. This paper provides an overview of recent advances in the molecular mechanisms of RANKL and downstream signaling pathways in osteoclast differentiation, and briefly outlines potential natural compounds with antiosteoclast activity and molecular mechanisms.

Dehydromiltirone inhibits osteoclast differentiation in RAW264.7 and bone marrow macrophages by modulating MAPK and NF-κB activity

Background: Osteoporosis is a type of systematic metabolic bone disease caused by the decrease in osteogenic activity or excessive resorption of bone with the relative enhancement of osteoclast function. As osteoporosis seriously affects the quality of patients’ life, effective drugs are needed to treat this disease. Based on the combination of network pharmacology and cellular studies, this study aimed to investigate the probable mechanism of Dehydromiltirone (DHT) in the treatment of osteoporosis.

Method: The targets of DHT in osteoporosis were searched using the PharmGKB, OMIM, and Genecard platforms. The PPI core targets, and the GO and KEGG enrichment analysis results were obtained using Cytoscape software, and the David and Metascape databases, respectively. The network pharmacology results were also verified via in vitro cellular experiments.

Results: Through network pharmacology and docking analysis, we found DHT was involved in peptide tyrosine phosphorylation, cell surface receptor tyrosine kinase signaling pathways, and MAPK signaling pathways. According to the molecular docking results, the binding of DHT to MAPK14 was more stable than other proteins, which suggests that DHT may affect osteoclast formation through the MAPK signaling pathway. Moreover, DHT was found to inhibit the expression of osteoclast-associated genes, including NFATc1, CTSK, c-Fos, Acp5, and MMP9; as well as the phosphorylation of P38, ERK, and JNK of the MAPK signaling pathway; and the degradation of IκB-α of NF-κB signaling pathway.

Conclusion: DHT exhibited an anti-osteoclastogenesis effect by reducing the expression of related genes, ultimately inhibiting bone resorption in vitro.

GSK 650394 Inhibits Osteoclasts Differentiation and Prevents Bone Loss via Promoting the Activities of Antioxidant Enzymes In Vitro and In Vivo

Osteoporosis (OP) is one of the most common bone disorders among the elderly, characterized by abnormally elevated bone resorption caused by formation and activation of osteoblast (OC). Excessive reactive oxygen species (ROS) accumulation might contribute to the formation process of OC as an essential role. Although accumulated advanced treatment target on OP have been proposed in recent years, clinical outcomes remain unexcellence attributed to severe side effects. The purpose of present study was to explore the underlying mechanisms of GSK 650394 (GSK) on inhibiting formation and activation of OC and bone resorption in vitro and in vivo. GSK could inhibit receptor activator of nuclear-κB ligand (RANKL-)-mediated Oc formation via suppressing the activation of NF-κB and MAPK signaling pathways, regulating intracellular redox status, and downregulate the expression of nuclear factor of activated T cells c1 (NFATc1). In addition, quantitative RT-PCR results show that GSK could suppress the expression of OC marker gene and antioxidant enzyme genes. Consistent with in vitro cellular results, GSK treatment improved bone density in the mouse with ovariectomized-induced bone loss according to the results of CT parameters, HE staining, and Trap staining. Furthermore, GSK treatment could enhance the capacity of antioxidant enzymes in vivo. In conclusion, this study suggested that GSK could suppress the activation of osteoclasts and therefore maybe a potential therapeutic reagent for osteoclast activation-related osteoporosis.

Network pharmacology analysis of molecular targets and related mechanisms of Guizhi decoction in treating of menopausal syndrome

Compared with hormone therapy, TCM had the advantages of overall adjustment and less side effects in the treatment of menopausal syndrome. But due to the complex pharmacodynamic composition of Guizhi decoction (GZD), the mechanism of TCM treating diseases was not clear. Network pharmacology could analyze drug action pathways through multi-pathway and multi-target, which provide a new direction for TCM mechanism research. The common targets of GZD and menopausal syndrome (MPS) were obtained by TCMSP and DisGeNET databases. And for the common targets, protein-protein interaction networks were established using the STRING database and analyzed by Gene Ontology and the Kyoto Encyclopedia of Genes and Genomes. (Our research does not require ethical approval). One hundred forty-six active ingredients with 283 targets were obtained from GZD by network pharmacological analysis. Besides, 230 target genes were found to have interactions with MPS, 52 of which were common targets between MPS and GZD and were predicted to be potential targets for MPS treatment of GZD. GO enrichment analysis revealed that GZD could affect 51 biological processes, 15 cellular components, and 13 molecular functions. Kyoto Encyclopedia of Genes and Genomes enrichment analysis yielded a total of 223. The pathways that are closely related to the pathogenesis of MPS are MAPK, PI3K-Akt. In this study, the relevant targets and mechanisms of GZD in the treatment of MPS were discussed from the perspective of network pharmacological analysis, reflecting the characteristics of multi-component, multi-target and multiple pathways, and it provides a good theoretical basis for the clinical application of GZD.

Monascin abrogates RANKL-mediated osteoclastogenesis in RAW264.7 cells via regulating MAPKs signaling pathways

Osteoclasts (OCs) are multinucleated cells that play a major role in osteolytic diseases such as osteoporosis. Monascin (Ms) is one of the active substances in the traditional Chinese medicine red yeast rice. Studies have found that red yeast rice can maintain bone health. In this study, the anti-osteoclastogenesis effects of Ms on RANKL-induced RAW264.7 cells were assessed, and the underlying mechanism was investigated. Ms exhibited inhibitory effects on OC differentiation and formation in a dose-dependent manner and suppressed the bone-resorbing activity of mature OCs. Ms blocked OCs-typical genes (c-Fos, NFATc1, CSTK, MMP-9, TRAP, ITG-β3, OSCAR and DC-STAMP). Furthermore, Ms treatment considerably inhibited the activation of MAPKs, JNK and p38. Taken together, Ms suppresses RANKL-induced osteoclastogenesis of RAW264.7 cells by restraining MAPKs signaling pathways and is a potential therapeutic option as a novel OC inhibitor to mitigate bone erosion.

Genkwanin Prevents Lipopolysaccharide-Induced Inflammatory Bone Destruction and Ovariectomy-Induced Bone Loss

Objectives

The first objective of this study was to probe the effects of genkwanin (GKA) on osteoclast. The second goal of this study was to study whether GKA can protect lipopolysaccharide (LPS) and ovariectomized (OVX) induced bone loss.

Materials and Methods

Various concentrations of GKA (1 and 10 mg/kg) were injected into mice. Different concentrations of GKA (1 and 5 μM) were used to detect the effects of GKA on osteoclast and osteoblast.

Key Findings

GKA attenuated the osteoclast differentiation promoted by RANKL and expression of marker genes containing c-fos, ctsk as well as bone resorption related gene Trap and to the suppression of MAPK signaling pathway. In addition, GKA induced BMMs cell apoptosis in vitro. Moreover, GKA prevented LPS-induced and ovariectomized-induced bone loss in mice.

Conclusion

Our research revealed that GKA had a potential to be an effective therapeutic agent for osteoclast-mediated osteoporosis.

A vitronectin-derived dimeric peptide suppresses osteoclastogenesis by binding to c-Fms and inhibiting M-CSF signaling

Vitronectin is an abundant multifunctional glycoprotein found in serum, the extracellular matrix, and bone, and is involved in diverse physiological processes. Here, we developed a new bioactive dimeric peptide (VnP-8-DN1 dimer) from a human vitronectin-derived motif (IDAAFTRINCQG; residues 206-217; VnP-8) via removal of an isoleucine residue at the N-terminus of VnP-8 and spontaneous air oxidation. The VnP-8-DN1 dimer potently enhanced cell attachment activity, and this activity was mediated by binding to cellular heparan sulfate proteoglycan receptors. Moreover, the VnP-8-DN1 dimer suppressed osteoclast differentiation by blocking the early stage of osteoclastogenesis induced by macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor-κB ligand (RANKL). Furthermore, the VnP-8-DN1 dimer decreased the bone-resorbing activity of osteoclasts and increased the survival of osteoclast precursor cells by decreasing the cellular level of c-Fms and reducing RANK expression. Taken together, these results demonstrate that the VnP-8-DN1 dimer inhibits the early stages of M-CSF- and RANK-induced osteoclast differentiation by binding to c-Fms and inhibiting M-CSF signaling.

miR-134-5p inhibits osteoclastogenesis through a novel miR-134-5p/Itgb1/MAPK pathway

Osteoporosis affects approximately 200 million people and severely affects quality of life, but the exact pathological mechanisms behind this disease remain unclear. Various miRNAs have been shown to play a predominant role in the regulation of osteoclast formation. In this study, we explored the role of miR-134-5p in osteoclastogenesis both in vivo and in vitro. We constructed an ovariectomized (OVX) mouse model and performed microarray analysis using bone tissue from OVX mice and their control counterparts. Quantitative RT-PCR data from bone tissue and bone marrow macrophages (BMMs) confirmed the decreased expression of miR-134-5p in OVX mice observed in microarray analysis. In addition, a decrease in miR-134-5p was also observed during induced osteoclastogenesis of BMMs collected from C57BL/6N mice. Through transfection with miR-134-5p agomirs and antagomirs, we found that miR-134-5p knockdown significantly accelerated osteoclast formation and cell proliferation and inhibited apoptosis. Furthermore, a luciferase reporter assay showed that miR-134-5p directly targets the integrin surface receptor gene Itgb1. Cotransfection with Itgb1 siRNA reversed the effect of the miR-134-5p antagomir in promoting osteoclastogenesis. Moreover, the abundance levels of MAPK pathway proteins phosphorylated-p38 (p-p38) and phosphorylated-ERK (p-ERK) were significantly increased after transfection with the miR-134-5p antagomir but decreased after transfection with the miR-134-5p agomir or Itgb1 siRNA, which indicated a potential relationship between the miR-134-5p/Itgb1 axis and the MAPK pathway. Collectively, these results revealed that miR-134-5p inhibits osteoclast differentiation of BMMs both in vivo and in vitro and that the miR-134-5p/Itgb1/MAPK pathway might be a potential target for osteoporosis therapy.

Sec-O-Glucosylhamaudol Inhibits RANKL-Induced Osteoclastogenesis by Repressing 5-LO and AKT/GSK3β Signaling

Sec-O-glucosylhamaudol (SOG), an active flavonoid compound derived from the root of Saposhnikovia divaricata (Turcz. ex Ledeb.) Schischk., exhibits analgesic, anti-inflammatory, and high 5-lipoxygenase (5-LO) inhibitory effects. However, its effect on osteoclastogenesis was unclear. We demonstrated that SOG markedly attenuated RANKL-induced osteoclast formation, F-actin ring formation, and mineral resorption by reducing the induction of key transcription factors NFATc1, c-Fos, and their target genes such as TRAP, CTSK, and DC-STAMP during osteoclastogenesis. Western blotting showed that SOG significantly inhibited the phosphorylation of AKT and GSK3β at the middle–late stage of osteoclastogenesis without altering calcineurin catalytic subunit protein phosphatase-2β-Aα expression. Moreover, GSK3β inhibitor SB415286 partially reversed SOG-induced inhibition of osteoclastogenesis, suggesting that SOG inhibits RANKL-induced osteoclastogenesis by activating GSK3β, at least in part. 5-LO gene silencing by small interfering RNA in mouse bone marrow macrophages markedly reduced RANKL-induced osteoclastogenesis by inhibiting NFATc1. However, it did not affect the phosphorylation of AKT or GSK3β, indicating that SOG exerts its inhibitory effects on osteoclastogenesis by suppressing both the independent 5-LO pathway and AKT-mediated GSK3β inactivation. In support of this, SOG significantly improved bone destruction in a lipopolysaccharide-induced mouse model of bone loss. Taken together, these results suggest a potential therapeutic effect for SOG on osteoclast-related bone lysis disease.

Network pharmacology explores the mechanisms of Eucommia ulmoides cortex against postmenopausal osteoporosis

Postmenopausal osteoporosis (PMOP) has become one of most frequent chronic disease worldwide with aging population. Eucommia ulmoides cortex (EU), a traditional Chinese medicine, has long since been used to treat PMOP. The aim of this study is to explore pharmacological mechanisms of EU against PMOP through using network pharmacology approach.The active ingredients of EU were obtained from Traditional Chinese Medicine System Pharmacology database, and target fishing was performed on these ingredients in UniProt database for identification of their relative targets. Then, we screened the targets of PMOP using GeneCards database and DisGeNET database. The overlapping genes between PMOP and EU were obtained to performed protein-protein interaction, Gene Ontology analysis, Kyoto encyclopedia of genes, and genomes analysis.Twenty-eight active ingredients were identified in EU, and corresponded to 207 targets. Also, 292 targets were closely associated with PMOP, and 50 of them matched with the targets of EU were considered as therapeutically relevant. Gene ontology enrichment analysis suggested that EU exerted anti-PMOP effects via modulating multiple biological processes including cell proliferation, angiogenesis, and inflammatory response. Kyoto encyclopedia of genes and genomes enrichment analysis revealed several pathways, such as PI3K-AKT pathway, mitogen-activated protein kinase pathway, hypoxia-inducible factors-1 pathway, tumor necrosis factor pathway, and interleukin-17 pathway that might be involved in regulating the above biological processes.Through the method of network pharmacology, we systematically investigated the mechanisms of EU against PMOP. The multi-targets and multi-pathways identified here could provide new insights for further determination of more exact mechanisms of EU.

Vesicle Induced Receptor Sequestration: Mechanisms behind Extracellular Vesicle-Based Protein Signaling

Extracellular vesicles (EVs) are fundamental for proper physiological functioning of multicellular organisms. By shuttling nucleic acids and proteins between cells, EVs regulate a plethora of cellular processes, especially those involved in immune signalling. However, the mechanistic understanding concerning the biophysical principles underlying EV-based communication is still incomplete. Towards holistic understanding, particular mechanisms explaining why and when cells apply EV-based communication and how protein-based signalling is promoted by EV surfaces are sought. Here, the authors study vesicle-induced receptor sequestration (VIRS) as a universal mechanism augmenting the signalling potency of proteins presented on EV-membranes. By bottom-up reconstitution of synthetic EVs, the authors show that immobilization of the receptor ligands FasL and RANK on EV-like vesicles, increases their signalling potential by more than 100-fold compared to their soluble forms. Moreover, the authors perform diffusion simulations within immunological synapses to compare receptor activation between soluble and EV-presented proteins. By this the authors propose vesicle-triggered local clustering of membrane receptors as the principle structural mechanism underlying EV-based protein presentation. The authors conclude that EVs act as extracellular templates promoting the local aggregation of membrane receptors at the EV contact site, thereby fostering inter-protein interactions. The results uncover a potentially universal mechanism explaining the unique structural profit of EV-based intercellular signalling.

A Nitrobenzoyl Sesquiterpenoid Insulicolide A Prevents Osteoclast Formation via Suppressing c-Fos-NFATc1 Signaling Pathway

It is a viable strategy to inhibit osteoclast differentiation for the treatment of osteolytic diseases such as osteoporosis, rheumatoid arthritis and tumor bone metastases. Here we assessed the effects of insulicolide A, a natural nitrobenzoyl sesquiterpenoid derived from marine fungus, on receptor activator of nuclear factor-κB ligand (RANKL)-stimulated osteoclastogenesis in vitro and its protective effects on LPS-induced osteolysis mice model in vivo. The results demonstrated that insulicolide A inhibited osteoclastogenesis from 1 μM in vitro. Insulicolide A could prevent c-Fos and nuclear factor of activated T-cell cytoplasmic 1 (NFATc1) nuclear translocation and attenuate the expression levels of osteoclast-related genes and DC-STAMP during RANKL-stimulated osteoclastogenesis but have no effects on NF-κB and MAPKs. Insulicolide A can also protect the mice from LPS-induced osteolysis. Our research provides the first evidence that insulicolide A may inhibit osteoclastogenesis both in vitro and in vivo, and indicates that it may have potential for the treatment of osteoclast-related diseases.

Cycloastragenol Attenuates Osteoclastogenesis and Bone Loss by Targeting RANKL-Induced Nrf2/Keap1/ARE, NF-κB, Calcium, and NFATc1 Pathways

Osteoporosis, which typically affects postmenopausal women, is an osteolytic disease due to over-activation of osteoclasts. However, current drugs targeting osteoclast inhibition face various side effects, making natural compounds with great interest as alternative treatment options. Cycloastragenol (CAG) is a triterpenoid with multiple biological activities. Previously, CAG's activity against aging-related osteoporosis was reported, but the mechanisms of actions for the activities were not understood. This study demonstrated that CAG dose-dependently inhibited osteoclast formation in receptor activator of nuclear factor-κB ligand (RANKL)-stimulated bone marrow macrophage (BMMs). Mechanism studies showed that CAG inhibited NF-κB, calcium, and nuclear factor of activated T cells 1 (NFATc1) pathways. Additionally, CAG also promoted the nuclear factor-erythroid 2-related factor 2 (Nrf2)/Kelch-like ECH-associated protein 1 (Keap1)/anti-oxidative response element (ARE) pathway that scavenges reactive oxygen species (ROS). Furthermore, CAG was also found to prevent bone loss of postmenopausal osteoporosis (PMO) in a preclinical model of ovariectomized (OVX) mice. Collectively, our research confirms that CAG inhibits the formation and function of osteoclasts by regulating RANKL-induced intracellular signaling pathways, which may represent a promising alternative for the therapy of osteoclast-related disease.

Bushen huoxue decoction inhibits RANKL-stimulated osteoclastogenesis and glucocorticoid-induced bone loss by modulating the NF-κB, ERK, and JNK signaling pathways

Glucocorticoid-induced osteoporosis (GIOP) is the most common form of secondary osteoporosis, which is caused by a disorder in bone metabolism due to excessive activation of osteoclasts. Bushen Huoxue decoction (BHD) is an herbal formula with multiple pharmacological effects, including anti-inflammatory, antioxidant activity and stem cell migration promotion. However, the effect of BHD on osteoclastogenesis has not been reported. In this study, we aimed to elucidate the effect of BHD on RANKL-stimulated osteoclastogenesis and explored its underlying mechanisms of action in vitro. Our results show that BHD had no effect on BMMs and RAW264.7 cells viability, but inhibited RANKL-induced osteoclast formation in vitro. Furthermore, BHD attenuated RANKL-induced NF-κB, ERK, and JNK signaling. The attenuation of NF-κB, ERK, and JNK activation were enough to impede downstream expression of c-fos and NFATc1 and related specific genes. Meanwhile, we investigated the therapeutic effect of BHD on glucocorticoid-induced osteoporosis (GIOP) mice. The result indicated that BHD prevents glucocorticoid-induced osteoporosis and preserves bone volume by repressing osteoclast activity. Collectively, BHD shows significant osteoclast inhibition and holds great promise in the treatment of osteoporosis.