Disturbed MEK/ERK signaling increases osteoclast activity via the Hedgehog-Gli pathway in postmenopausal osteoporosis

Estrogenic post-menopausal anti-osteoporotic mechanism of Achyranthes aspera L.: Phytochemicals and network pharmacology approaches

Hormone replacement therapy is used to treat postmenopausal syndrome caused by estrogen deficiency, but it has been linked to an increased risk of breast cancer. In India, Achyranthes aspera L. is traditionally used to treat menstrual problems; however, there is a lack of mechanistic evidence of its phytoestrogenicity. Therefore, this study investigated the estrogenic activity of A. aspera on estrogen-responsive MCF-7 breast cancer cells. In a cell proliferation assay, the MeOH fraction (100 μg/mL) exhibited the highest proliferation effect (PE) of 138 % (p < 0.001) and relative proliferation effect (RPE) of 96.5 %, compared to 17β-estradiol (0.01 μM: 143 % PE, p < 0.001; 100 % RPE). The MeOH fraction was shown to upregulate the oestrogen marker genes trefoil factor 1 and progesterone receptor by 20.14-23.94 folds and 10.83-14.83 folds, respectively. Twelve phenolics were identified by LC-MS/MS in the active MeOH fraction, i.e. quinic acid, kaempferol hexoside, kaempferol 3-O-(2″-O-galloyl)-glucoside)-β-D-glucoside, geniposide, 3-O-(6'-O-(9Z,12Z-octadecadienoyl)-β-D-glucopyranosyl)-stigmast-5,22E-dien-3β-ol, kaempferol-3-O-glucoside (astragalin), 3,30-di-O-methylellagic acid isomer, procyanidin, naringin, propapyriogenin A2, (3β,22E,24R)-23-methylergosta-5,7,22-trien-3-ol and 6-prenylapigenin. Through network pharmacology, the potential effects, and mechanisms of these compounds in osteoporosis were revealed. About 55 target genes were linked to osteoporosis. GO and KEGG enrichment suggest regulation of female reproductive hormone related signaling pathways, which are also associated with estrogen dependent osteoporosis. Molecular docking analysis of the compounds revealed potential interactions with hERα receptor for 3-O-(6'-O-(9Z,12Z-octadecadienoyl)-β-D-glucopyranosyl)-stigmast-5,22E-dien-3β-ol and kaempferol-3-O-glucoside (astragalin) (docking scores of -9.3 and -10.1 kcal/mol, respectively) as compared to 17β-estradiol (-9.3 kcal/mol). These results suggest the estrogenicity of A. aspera via an ERα-associated mechanism and support its traditional usage in the management of menopausal-related problems.

Comprehensive analysis of epigenetics mechanisms in osteoporosis

Epigenetic modification pertains to the alteration of genetic-expression, which could be transferred to the next generations, without any alteration in the fundamental DNA sequence. Epigenetic modification could include various processes such as DNA methylation, histone alteration, non-coding RNAs (ncRNAs), and chromatin adjustment are among its primary operations. Osteoporosis is a metabolic disorder that bones become more fragile due to the decrease in mineral density, which could result in a higher risk of fracturing. Recently, as the investigation of the causal pathology of osteoporosis has been progressed, remarkable improvement has been made in epigenetic research. Recent literatures have illustrated that epigenetics is estimated to be one of the most contributing factors to the emergence and progression of osteoporosis. This dissertation primarily focuses on indicating the research progresses of epigenetic mechanisms and also the regulation of bone metabolism and the pathogenesis of osteoporosis in light of the significance of epigenetic mechanisms. In addition, it aims to provide new intelligence for the treatment of diseases related to bone metabolism.

Cistanche Deserticola for Regulation of Bone Metabolism: Therapeutic Potential and Molecular Mechanisms on Postmenopausal Osteoporosis

Osteoporosis is a generalized disease of bone that leads to a loss of bone density and bone mass, destruction of bone microstructure, increased brittleness and therefore fracture. At present, the main treatment of Western medicine is drug therapy such as bisphosphonates, calcitriol, vitamin D, etc. However, long-term use of these drugs may bring some adverse reactions. Chinese herbal medicine Cistanche deserticola could regulate bone metabolism by promoting osteoblast activity and inhibiting osteoclast activity with low toxicity and adverse reactions. Therefore, Cistanche deserticola has attracted increasing attention for its efficacy in the prevention and treatment of osteoporosis in recent years. Here we present a literature review of the molecular pathways involved in osteoporosis and the effects of Cistanche deserticola on bone metabolism. Our objective is to clarify the mechanism of Cistanche deserticola in the treatment of osteoporosis.

Research on the Mechanism of Liuwei Dihuang Decoction for Osteoporosis Based on Systematic Biological Strategies

Background

Osteoporosis is an important health problem worldwide. Liuwei Dihuang Decoction (LDD) and its main ingredients may have a good clinical effect on osteoporosis. Meanwhile, its mechanism for treating osteoporosis needs to be further revealed in order to provide a basis for future drug development.

Methods

A systematic biological methodology was utilized to construct and analyze the LDD-osteoporosis network. After that, the human transcription data of LDD intervention in patients with osteoporosis and protein arrays data of LDD intervention in osteoporosis rats were collected. The human transcription data analysis, protein arrays data analysis, and molecular docking were performed to validate the findings of the prediction network (LDD-osteoporosis PPI network). Finally, animal experiments were conducted to verify the prediction results of systematic pharmacology.

Results

(1) LDD-osteoporosis PPI network shows the potential compounds, potential targets (such as ALB, IGF1, SRC, and ESR1), clusters, biological processes (such as positive regulation of calmodulin 1-monooxygenase activity, estrogen metabolism, and endothelial cell proliferation), and signaling and Reactome pathways (such as JAK-STAT signaling pathway, osteoclast differentiation, and degradation of the extracellular matrix) of LDD intervention in osteoporosis. (2) Human transcriptomics data and protein arrays data validated the findings of the LDD-osteoporosis PPI network. (3) The animal experiments showed that LDD can improve bone mineral density (BMD), increase serum estradiol (E2) and alkaline phosphatase (ALP) levels, and upregulate Wnt3a and β-catenin mRNA expression (P < 0.05). (4) Molecular docking results showed that alisol A, dioscin, loganin, oleanolic acid, pachymic acid, and ursolic acid may stably bind to JAK2, ESR1, and CTNNB1.

Conclusion

LDD may have a therapeutic effect on osteoporosis through regulating the targets (such as ALB, IGF1, SRC, and ESR1), biological processes (such as positive regulation of calmodulin 1-monooxygenase activity, estrogen metabolism, and endothelial cell proliferation), and pathways (such as JAK-STAT signaling pathway, osteoclast differentiation, and degradation of the extracellular matrix) found in this research.

New Function of Cholesterol Oxidation Products Involved in Osteoporosis Pathogenesis

Osteoporosis (OP) is a systemic bone disease characterized by decreased bone strength, microarchitectural changes in bone tissues, and increased risk of fracture. Its occurrence is closely related to various factors such as aging, genetic factors, living habits, and nutritional deficiencies as well as the disturbance of bone homeostasis. The dysregulation of bone metabolism is regarded as one of the key influencing factors causing OP. Cholesterol oxidation products (COPs) are important compounds in the maintenance of bone metabolic homeostasis by participating in several important biological processes such as the differentiation of mesenchymal stem cells, bone formation in osteoblasts, and bone resorption in osteoclasts. The effects of specific COPs on mesenchymal stem cells are mainly manifested by promoting osteoblast genesis and inhibiting adipocyte genesis. This review aims to elucidate the biological roles of COPs in OP development, starting from the molecular mechanisms of OP, pointing out opportunities and challenges in current research, and providing new ideas and perspectives for further studies of OP pathogenesis.

Role of HSP90α in osteoclast formation and osteoporosis development

Osteoporosis (OP) is a systemic metabolic bone disease that occurs most frequently in the elderly. The main pathogenesis of OP is excessive proliferation and differentiation of osteoclasts, in which the peroxisome proliferator-activated receptor γ (PPARγ) pathway has a pivotal role. Recently, heat shock protein (HSP)90α has been identified as an important molecular chaperone with PPARγ, which regulates the effect of the PPARγ pathway. The aim of the present study was to investigate the role of HSP90α involved in the regulation of osteoclast formation and the process of osteoporosis. Firstly, the expression of HSP90α in osteoclast differentiation was detected by western blotting in vitro, then the effect of HSP90α inhibition on the formation and differentiation of osteoclasts was examined. Furthermore, the nuclear import of PPARγ was also assessed to confirm the synergistic effect of HSP90α. Finally, the inhibitory effect of HSP90α in vivo was explored, using a mouse model of osteoporosis. As a result, in the process of osteoclast differentiation and proliferation, the expression of HSP90α was upregulated. Inhibition of HSP90α could block the formation and differentiation of osteoclasts, and remit osteoporosis in mice. Regarding the underlying mechanism, inhibition of HSP90α could block the nuclear import of PPARγ to inhibit osteoclast differentiation and proliferation. In conclusion, these data indicated that the inhibition of HSP90α could block osteoclast formation and remit osteoporosis by reducing the nuclear import of PPARγ.

Cell-free culture supernatant of Lactobacillus curvatus Wikim38 inhibits RANKL-induced osteoclast differentiation and ameliorates bone loss in ovariectomized mice

This study was conducted to investigate the inhibitory effects of the cell-free culture supernatant of Lactobacillus curvatus Wikim 38 (LC38-CS) on RANKL-induced osteoclast differentiation and bone loss in a mice model of ovariectomy-induced post-menopausal osteoporosis. LC38-CS inhibited the RANKL-induced differentiation of bone marrow-derived macrophages (BMDMs) into osteoclasts in a dose-dependent manner. F-actin ring formation and bone resorption were also reduced by LC38-CS treatment of RANKL-treated BMDMs. In addition, LC38-CS decreased the RANKL-induced activation of the TRAF6/NF-κB/MAPKs axis at the early stage and the expression of osteoclastogenesis-related genes in BMDMs treated with RANKL. PRMT1 and ADMA levels, new biomarkers for osteoclastogenesis, were decreased by LC38-CS treatment. The administration of LC38-CS increased bone volume and bone mineral density in ovariectomized mice in μ-CT analysis. These findings suggest that LC38-CS inhibited RANKL-induced osteoclast differentiation by the downregulation of molecular mechanisms and exerted anti-osteoporotic effects.

Expression of Neurokinin B Receptor in the Gingival Squamous Cell Carcinoma Bone Microenvironment

Gingival squamous cell carcinoma (SCC) frequently invades the maxillary or mandibular bone, and bone destruction is known as a key prognostic factor in gingival SCCs. Recently, Neurokinin 3 receptor (NK-3R), the receptor ligand for NK-3, which is a member of the tachykinin family expressed in the central nervous system, was identified through pathway analysis as a molecule expressed in osteoclasts induced by the hedgehog signal. Although the expression of NK-3R has been detected in osteoclast and SCC cells at the bone invasion front, the relationship between NK-3R expression and the prognosis of gingival SCC patients remains unclear. In the present study, we retrospectively reviewed 27 patients with gingival SCC who had undergone surgery with curative intent. Significantly higher NK-3R expression in tumor cells was found in a case of jawbone invasion than in a case of exophytic poor jawbone invasion. On the other hand, no significant association was observed between NK-3R tumor-positive cases and tumor size, TNM stage, or tumor differentiation. The survival rate tended to be lower in NK-3R tumor-positive cases, but not significantly. However, the disease-specific survival rate was significantly lower in patients with a large number of NK-3R-positive osteoclasts than in those with a small number of them at the tumor bone invasion front. Our results suggest that NK-3R signaling in the gingival SCC bone microenvironment plays an important role in tumor bone destruction and should be considered a potential therapeutic target in advanced gingival SCC with bone destruction.

Exploration of the Molecular Mechanism of Polygonati Rhizoma in the Treatment of Osteoporosis Based on Network Pharmacology and Molecular Docking

OBJECTIVE

To explore the effective components and mechanism of Polygonati Rhizoma (PR) in the treatment of osteoporosis (OP) based on network pharmacology and molecular docking methods.

METHODS

The effective components and predicted targets of PR were obtained through the Traditional Chinese Medicine Systems Pharmacology and Analysis Platform (TCMSP) database. The disease database was used to screen the disease targets of OP. The obtained key targets were uploaded to the Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) database for protein-protein interaction (PPI) network analysis. The Database for Annotation, Visualization, and Integrated Discovery (DAVID) was used for Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses of key targets. Analysis and docking verification of chemical effective drug components and key targets were performed with IGEMDOCK software.

RESULTS

A total of 12 chemically active components, 84 drug target proteins and 84 common targets related to drugs and OP were obtained. Key targets such as JUN, TP53, AKT1, ESR1, MAPK14, AR and CASP3 were identified through PPI network analysis. The results of enrichment analysis showed that the potential core drug components regulate the HIF-1 signaling pathway, PI3K-Akt signaling pathway, estrogen signaling pathway and other pathways by intervening in biological processes such as cell proliferation and apoptosis and estrogen response regulation, with an anti-OP pharmacological role. The results of molecular docking showed that the key targets in the regulatory network have high binding activity to related active components.

CONCLUSIONS

PR may regulate OP by regulating core target genes, such as JUN, TP53, AKT1, ESR1, AR and CASP3, and acting on multiple key pathways, such as the HIF-1 signaling pathway, PI3K-Akt signaling pathway, and estrogen signaling pathway.

Systemic osteoprotective effects of Epimedii Folium and Ligustri Lucidi Fructus in senile osteoporosis rats by promoting the osteoblastogenesis and osteoclastogenesis based on MLP-ANN model

Background

Senile osteoporosis (SOP), which is caused by unbalanced bone remodeling, leads to significant economic and societal burdens globally. The combination of Epimedii Folium (EF) and Ligustri Lucidi Fructus (LLF) serves as a commonly-used prescription for SOP in Traditional Chinese Medicine (TCM). This study aimed to evaluate the osteoprotective effects of EF and LLF in combination on SOP rats based on the constructed multilayer perception (MLP)-artificial neural network (ANN) model.

Methods

15 month old male Sprague-Dawley rats were administrated with EF, LLF or the combination of EF and LLF (EF&LLF) for 2 months, while 17 month old rats were used as the aging control group. All the rats were anesthetized with 25% ethyl carbamate, then their serum liver and bone tissues were taken. We detected bone mass, bone mineral density (BMD), biomechanics and the microstructure of bone trabecula by micro-CT and H&E staining to evaluate the degree of osteoporosis. Blood lipids and serum alanine aminotransferase (ALT), aspartate aminotransferase (AST) and γ-glutamyl transferase (GGT) and liver pathology were use to assess the side effects of drugs. Levels of alkaline phosphatase (ALP) and Tartrate-resistant acid phosphatase (TRACP) and the ratio of ALP to TRACP both in serum and bone were measured for the evaluation of bone turnover rate. The bone mRNA and protein expression of osteoprotegerin (OPG), nuclear factor-kappa B ligand (RANKL), macrophage colony-stimulating factor (M-CSF), d2 isoform of vacuolar (H⁺) ATPase (ATP6V0d2), insulin-like growth factor (IGF-1), bone morphogenetic protein-2 (BMP2), M-CSF, Wnt5a, transforming growth factor-β1 (TGF-β1) were detected for evaluating bone metabolism.

Results

The results showed that EF&LLF improved bone mass and bone quality by preventing bone loss, increasing maximal load as well as protecting the micro-structural retrogressive change of trabecular bone in SOP rats; ameliorated the steatosis in the liver and decreased blood lipids and serum ALT, AST and GGT; enhanced bone remodeling by stimulating the expression of ALP and TRACP. At the molecular levels, EF&LLF stimulated the osteoclastogenesis by upregulating the protein and mRNA expression of OPG, RANKL, M-CSF and ATP6V0d2; meanwhile, EF&LLF stimulated osteoblastogenesis by enhancing the expression of TGF-β1, BMP2, Wnt5a and IGF-1. According to our established MLP model, EF&LLF has a better effect on osteoclastogenesis or steoblastogenesis in SOP rats than EF or LLF.

Conclusions

These findings demonstrate that the systemic bone protective effects of EF&LLF by promoting bone remodeling in aging rats might be a substitute medicine for the treatment of SOP.

3D Bioprinted Osteogenic Tissue Models for In Vitro Drug Screening

Metabolic bone disease affects hundreds of millions of people worldwide, and as a result, in vitro models of bone tissue have become essential tools to help analyze bone pathogenesis, develop drug screening, and test potential therapeutic strategies. Drugs that either promote or impair bone formation are in high demand for the treatment of metabolic bone diseases. These drugs work by targeting numerous signaling pathways responsible for regulating osteogenesis such as Hedgehog, Wnt/β-catenin, and PI3K-AKT. In this study, differentiated bone marrow-derived mesenchymal stem cell (BM-MSC) scaffold-free 3D bioprinted constructs and 2D monolayer cultures were utilized to screen four drugs predicted to either promote (Icariin and Purmorphamine) or impair osteogenesis (PD98059 and U0126). Osteogenic differentiation capacity was analyzed over a four week culture period by evaluating mineralization, alkaline phosphatase (ALP) activity, and osteogenesis related gene expression. Responses to drug treatment were observed in both 3D differentiated constructs and 2D monolayer cultures. After four weeks in culture, 3D differentiated constructs and 2D monolayer cultures treated with Icariin or Purmorphamine showed increased mineralization, ALP activity, and the gene expression of bone formation markers (BGLAP, SSP1, and COL1A1), signaling molecules (MAPK1, WNT1, and AKT1), and transcription factors (RUNX2 and GLI1) that regulate osteogenic differentiation relative to untreated. 3D differentiated constructs and 2D monolayer cultures treated with PD98059 or U0126 showed decreased mineralization, ALP activity, and the expression of the aforementioned genes BGLAP, SPP1, COL1A1, MAPK1, AKT1, RUNX2, and GLI1 relative to untreated. Differences in ALP activity and osteogenesis related gene expression relative to untreated cells cultured in a 2D monolayer were greater in 3D constructs compared to 2D monolayer cultures. These findings suggest that our bioprinted bone model system offers a more sensitive, biologically relevant drug screening platform than traditional 2D monolayer in vitro testing platforms.

Genetic and pharmacological activation of Hedgehog signaling inhibits osteoclastogenesis and attenuates titanium particle-induced osteolysis partly through suppressing the JNK/c-Fos-NFATc1 cascade

Rationale: Wear particle-induced periprosthetic osteolysis (PPO) is a common long-term complication of total joint arthroplasty, and represents the major cause of aseptic loosening and subsequent implant failure. Previous studies have identified the central role of osteoclast-mediated bone resorption in the pathogenesis of PPO. Thus, therapeutic approaches of inhibiting osteoclast formation and activity are considered to be of great potential to prevent and treat this osteolytic disease. Hedgehog (Hh) signaling has been shown to play an important role in promoting osteoblast differentiation and bone formation. While Hh signaling is also implicated in regulating osteoclastogenesis, whether it can directly inhibit osteoclast differentiation and bone resorption remains controversial. Moreover, its potential therapeutic effects on PPO have never been assessed. In this study, we explored the cell-autonomous role of Hh signaling in regulating osteoclastogenesis and its therapeutic potential in preventing wear particle-induced osteolysis. Methods: Hh signaling was activated in macrophages by genetically ablating Sufu in these cells using LysM-Cre or by treating them with purmorphamine (PM), a pharmacological activator of Smoothened (Smo). In vitro cell-autonomous effects of Hh pathway activation on RANKL-induced osteoclast differentiation and activity were evaluated by TRAP staining, phalloidin staining, qPCR analyses, and bone resorption assays. In vivo evaluation of its therapeutic efficacy against PPO was performed in a murine calvarial model of titanium particle-induced osteolysis by μCT and histological analyses. Mechanistic details were explored in RANKL-treated macrophages through Western blot analyses. Results: We found that Sufu deletion or PM treatment potently activated Hh signaling in macrophages, and strongly inhibited RANKL-induced TRAP+ osteoclast production, F-actin ring formation, osteoclast-specific gene expression, and osteoclast activity in vitro. Furthermore, we found that Sufu deletion or PM administration significantly attenuated titanium particle-induced osteoclast formation and bone loss in vivo. Our mechanistic study revealed that activation of Hh signaling suppressed RANKL-induced activation of JNK pathway and downregulated protein levels of two key osteoclastic transcriptional factors, c-Fos and its downstream target NFATc1. Conclusions: Both genetic and pharmacological activation of Hh signaling can cell-autonomously inhibit RANKL-induced osteoclast differentiation and activity in vitro and protect against titanium particle-induced osteolysis in vivo. Mechanistically, Hh signaling hinders osteoclastogenesis partly through suppressing the JNK/c-Fos-NFATc1 cascade. Thus, Hh signaling may serve as a promising therapeutic target for the prevention and treatment of PPO and other osteolytic diseases.

MicroRNA-874 targeting SUFU involves in osteoblast proliferation and differentiation in osteoporosis rats through the Hedgehog signaling pathway

Osteoporosis is widely viewed as a major public health concern, but the exact magnitude of the problem is uncertain. MicroRNAs play a key role in maintaining bone development and metabolism. This study aims to investigate the effects that microRNA-874 (miR-874) has on osteoblast proliferation and differentiation in osteoporosis rats by targeting SUFU through the Hedgehog signaling pathway. Twenty Wistar female rats were selected for following experiment, and another 20 rats were served as the normal group. Their osteogenic tissues were obtained and the positive expression of SUFU in tissues was determined. Rat osteoblasts were isolated and. The targeting relationship between SUFU and miR-874 was verified and the expression of miR-874, SUFU, Sonic Hedgehog (Shh), Ptch, Smoothened (Smo), bone morphogenetic protein (BMP2), Runx2, proliferating cell nuclear antigen (PCNA) and Bcl-2 associated X protein (Bax) were identified. Besides, cell viability apoptosis, and differentiation were confirmed respectively. Moreover, calcium nodules were observed. Overexpression of SUFU and Bax but lower expression of miR-874, Shh, Ptch, Smo, BMP2, Runx2, and PCNA were found in osteoporosis mice. Besides, elevated expression of miR-874, Shh, Ptch, Smo, BMP2, Runx2 and PCNA, as well as increased cell viability, ALP activity and calcium nodules but decreased expression of SUFU and Bax, and reduced cell apoptosis were confirmed when treated with miR-874 mimic. And it is reciprocal when miR-874 was inhibited. Our study demonstrated that through targeted inhibition of SUFU and activation of Hedgehog signaling pathway, miR-874 could promote the proliferation and differentiation of osteoblasts in osteoporosis rats.

Roles of Mitogen-Activated Protein Kinases in Osteoclast Biology

Bone undergoes continuous remodeling, which is homeostatically regulated by concerted communication between bone-forming osteoblasts and bone-degrading osteoclasts. Multinucleated giant osteoclasts are the only specialized cells that degrade or resorb the organic and inorganic bone components. They secrete proteases (e.g., cathepsin K) that degrade the organic collagenous matrix and establish localized acidosis at the bone-resorbing site through proton-pumping to facilitate the dissolution of inorganic mineral. Osteoporosis, the most common bone disease, is caused by excessive bone resorption, highlighting the crucial role of osteoclasts in intact bone remodeling. Signaling mediated by mitogen-activated protein kinases (MAPKs), including extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38, has been recognized to be critical for normal osteoclast differentiation and activation. Various exogenous (e.g., toll-like receptor agonists) and endogenous (e.g., growth factors and inflammatory cytokines) stimuli contribute to determining whether MAPKs positively or negatively regulate osteoclast adhesion, migration, fusion and survival, and osteoclastic bone resorption. In this review, we delineate the unique roles of MAPKs in osteoclast metabolism and provide an overview of the upstream regulators that activate or inhibit MAPKs and their downstream targets. Furthermore, we discuss the current knowledge about the differential kinetics of ERK, JNK, and p38, and the crosstalk between MAPKs in osteoclast metabolism.

PRMT1 mediates RANKL-induced osteoclastogenesis and contributes to bone loss in ovariectomized mice

Protein arginine methylation is a novel form of posttranslational modification mediated by protein arginine methyltransferase (PRMTs). PRMT1, a major isoform of the PRMT family, is responsible for various biological functions, including cellular differentiation. Although the important function that PRMT1 plays in various tissues is being increasingly recognized, its role in receptor activation of NF-κB ligand (RANKL)-induced osteoclastogenesis or osteoporosis has not yet been described. Here, we show that PRMT1 is essential for RANKL-induced osteoclastogenesis in vitro and for bone loss in vivo. RANKL treatment increased the expression of PRMT1 and its nuclear localization in bone marrow-derived macrophages (BMDMs) in a c-Jun N-terminal kinase (JNK)-dependent manner. Silencing PRMT1 attenuated RANKL-induced osteoclastogenesis by decreasing tartrate-resistant acid phosphatase (TRAP)-positive cells and inhibiting F-actin ring formation and bone resorption, which was confirmed in a separate experiment using haploinsufficient cells from PRMT1^+/- mice. Our results also revealed that PRMT1 regulates the transcription activity of NF-κB by directly interacting with it in RANKL-treated BMDMs. An in vivo study showed that the haploinsufficiency of PRMT1 reduced the enzyme activity of TRAP and increased the bone mineral density in the metaphysis of ovariectomized (OVX) mice. Finally, treatment with estrogen (E2) downregulated the RANKL-induced expression of PRMT1, suggesting that estrogen may exert an inhibitory effect on osteoclastogenesis by suppressing PRMT1 expression. Our results suggest that PRMT1 plays an important role in the progression of osteoporosis and that it might be a good therapeutic target for postmenopausal osteoporosis.

A protein that helps trigger bone loss in postmenopausal osteoporosis could be a potential therapeutic target. After the menopause, decreases in estrogen hormone levels can lead to bone diseases including osteoporosis. Osteoporosis occurs when the bone remodeling process breaks down, and bone resorption by cells called osteoclasts outweighs bone formation. In a mouse model of postmenopausal osteoporosis, Jong-Hwan Park at Chonnam National University, Gwangju, South Korea and co-workers identified key players in the progression of the disease. The team focused on factors influencing the RANKL protein, a known controller of bone remodeling. They found that RANKL triggers the formation of osteoclasts via interaction with another protein, PRMT1. Suppression of PRMT1 by estrogen appears to inhibit excessive osteoclast formation, suggesting it could be a potential therapeutic target for treating osteoporosis.

Effects of interleukin-7/interleukin-7 receptor on RANKL-mediated osteoclast differentiation and ovariectomy-induced bone loss by regulating c-Fos/c-Jun pathway

To explore the effects of IL-7/IL-7R on the RANKL-mediated osteoclast differentiation in vitro and OVX-induced bone loss in vivo. BMMs and RAW264.7 were transfected with IL-7, IL-7R siRNA, c-Fos siRNA, and c-jun siRNA and later stimulated by RANKL. TRAP and toluidine blue staining were used to observe osteoclast formation and bone resorption, respectively. HE and TRAP staining were used to detect trabecular bone microstructure and osteoclasts of mice, respectively. qRT-PCR and Western blot analysis were used to examine expression. IL-7 unregulated the expression of CTSK, NFATc1, MMP9, and the phosphorylation of p38 and Akt by activating the c-Fos/c-Jun pathway, which increased osteoclast numbers and bone resorption in RANKL-stimulated macrophages. While IL-7R siRNA and c-Fos siRNA decreased the expression, as well as and the phosphorylation of p38 and Akt.IL-7 decreased the BMD and OPG expression in OVX-induced mice and increased the TRAP positive cells, the mRNA expression of c-fos, c-jun, and RANKL, which was contradictory to IL-7R siRNA, and c-Fos siRNA. Furthermore, IL-7R siRNA and c-Fos siRNA caused thicker trabeculae, increased trabecular number, and decreased osteolysis in OVX mice. IL-7/IL-7R can promote RANKL-mediated osteoclast formation and bone resorption by activating the c-Fos/c-Jun pathway, as well as inducing bone loss in OVX mice.