Loureirin B suppresses RANKL-induced osteoclastogenesis and ovariectomized osteoporosis via attenuating NFATc1 and ROS activities

3D-printed manganese dioxide incorporated scaffold promotes osteogenic-angiogenic coupling for refractory bone defect by remodeling osteo-regenerative microenvironment

The treatment of refractory bone defects is a major clinical challenge, especially in steroid-associated osteonecrosis (SAON), which is characterized by insufficient osteogenesis and angiogenesis. Herin, a microenvironment responsiveness scaffold composed of poly-L-lactide (PLLA), and manganese dioxide (MnO2) nanoparticles is designed to enhance bone regeneration by scavenging endogenous reactive oxygen species (ROS) and modulating immune microenvironment in situ. A catalase-like catalytic reaction between MnO2 and endogenous hydrogen peroxide (H2O2) generated at the bone defect area, which typically becomes acidic and ROS-rich, triggers on-demand release of oxygen and Mn2+, significantly ameliorating inflammatory response by promoting M2-type polarization of macrophages, reprograming osteoimmune microenvironment conducive to angiogenesis and osteogenesis. Furthermore, the fundamental mechanisms were explored through transcriptome sequencing analysis, revealing that PLLA/MnO2 scaffolds (PMns) promote osteogenic differentiation by upregulating the TGF-β/Smad signaling pathway in human bone marrow mesenchymal stem cells (hBMSCs). Overall, the PMns exhibit superior immunomodulatory, excellent osteogenic-angiogenic properties and promising candidates as bone graft substitutes for therapy clinical refractory bone defects.

Isoginkgetin Inhibits RANKL-induced Osteoclastogenesis and Alleviates Bone Loss

Osteoporosis is characterized by excessive osteoclast activity leading to bone loss, decreased bone mineral density, and increased susceptibility to fractures. Through in vivo/vitro experiments, along with network pharmacology analysis, we aimed to explore the underlying mechanisms of Isoginkgetin (IGG) in inhibiting osteoclastogenesis, providing valuable insights for further research in the future. Firstly, we ascertained the safe concentration of IGG stimulation on BMMs, followed by a systematic exploration of the concentration gradient at which IGG inhibited osteoclastogenesis using TRAP analysis. An osteoporosis model was established to further validate the in vitro experimental findings by combining Micro-CT and immunohistochemical analysis. The results show that IGG did not exhibit cytotoxicity or proliferative effects on BMMs at concentrations equal to or less than 10 μM. Additionally, IGG inhibited the activity of osteoclastogenesis and bone resorption function at lower concentrations. RT-PCR and Western Blot results demonstrated that IGG could downregulate genes and proteins associated with osteoclastogenesis. The Western Blot results also showed that IGG inhibited the phosphorylation expression of P38, ERK, and P65 in the MAPK and NF-κB pathways. At the same time, it rescued the degradation of IκB-α at 15 and 60 min. IGG can also impact the relative expression levels of oxidative proteins such as SOD-1, HO-1, and catalase, thereby influencing cellular equilibrium and stress levels, ultimately inhibiting the formation of mature OC. In vivo experiments demonstrated that IGG alleviated bone loss caused by osteoclasts and improved relevant parameters of trabecular bone. So, IGG effectively attenuated osteoclastogenesis, and improved bone density, thereby portraying its role in osteoporosis management.

4-Hydroxyphenylacetic Acid, a microbial-derived metabolite of Polyphenols, inhibits osteoclastogenesis by inhibiting ROS production

Intracellular reactive oxygen species (ROS) accumulation is key to osteoclast differentiation. Plant-derived polyphenols that have reduced ROS production have been widely studied for the treatment of osteoporosis. However, these compounds are rarely absorbed in the small intestine and are instead converted to phenolic acids by the microbiota in the colon. These large quantities of low-molecular-weight phenolic acids can then be absorbed by the body. 4-Hydroxyphenylacetic acid (4-HPA) is an important metabolite of these polyphenols that is generated by the human intestinal microbiota. However, its potential mechanism is not fully understood. In this study, we aimed to elucidate the role of 4-HPA on osteoclastogenesis and treating osteoporosis. Our study showed that 4-HPA inhibited osteoclast differentiation and function and downregulated osteoclast-specific genes, including NFATc1, Atp6v0d2, MMP9, CTSK, Acp5, and c-Fos. As for further mechanism exploration, 4-HPA reduced ROS accumulation by regulating nuclear factor erythroid 2-related factor (Nrf2) and subsequently inhibited the nuclear factor kappa B (NF-κB) and mitogen-activated protein kinase (MAPK) pathways. To evaluate the effect of 4-HPA on postmenopausal osteoporosis, an ovariectomized (OVX) mouse model was used. The Micro-CT and histomorphometry analyses showed that 4-HPA effectively prevents bone loss. Encouragingly, 4-HPA demonstrated efficacy in treating osteoporosis induced by OVX. In conclusion, our study revealed that 4-HPA, a polyphenol metabolite produced by intestinal microorganisms, also inhibits osteoclast formation and treats osteoporosis, which provides a new experimental basis and candidate drug for the treatment of osteoporosis.

Mechanisms of Nrf2 suppression and Camkk1 upregulation in Echinococcus granulosus-induced bone loss

Osteoclast differentiation is essential for maintaining bone metabolism, and its dysregulation, particularly in the context of Echinococcus granulosus (CE) infection, can lead to severe bone loss. This study explores a novel mechanism by which CE protoscolices (PSC) drive osteoclast differentiation through the inhibition of Nrf2, followed by the upregulation of Camkk1. Transcriptome sequencing revealed a significant down-regulation of Nrf2 in cells treated with PSC. This was confirmed by Western blot and Q-PCR assays showing reduced Nrf2 protein and gene levels. In vivo studies with Nrf2 knockout mice demonstrated that the absence of Nrf2 exacerbates bone loss induced by PSC in both the spine and lower limbs, as observed through Micro-CT imaging and TRAP staining.Further investigations identified Camkk1 as a key downstream target of Nrf2. Using high-throughput sequencing and CO-IP experiments, we established that Nrf2 directly interacts with and regulates Camkk1. Functional assays indicated that PSC-induced upregulation of Camkk1 is significantly enhanced by Nrf2 knockdown, while silencing Camkk1 alone inhibits osteoclast differentiation.The therapeutic potential of this pathway was evaluated by screening small molecule inhibitors of Camkk1, with Crenolani emerging as a potent compound. In vivo administration of Crenolani in PSC-treated mice significantly alleviated bone loss in a dose-dependent manner.These findings elucidate a crucial molecular mechanism in osteoclast differentiation driven by CE infection and propose a promising therapeutic strategy for combating CE-induced bone destruction. This study advances our understanding of bone.

A natural agent, 5-deoxycajanin, mitigates estrogen-deficiency bone loss via modulating osteoclast-osteoblast homeostasis

Hyperactive osteoclasts and hypoactive osteoblasts usually result in osteolytic conditions such as estrogen-deficiency bone loss. Few natural compounds that both attenuating bone resorption and enhancing bone formation could exert effects on this imbalance. 5-Deoxycajanin (5-D), an isoflavonoid extracted from Cajan leaf with estrogen-like properties, were found to have beneficial pharmacological effects on rebalancing the activities of osteoclasts and osteoblasts. This study revealed that 5-D at the same concentration could inhibit osteoclastogenesis of BMMs and promoted osteoblast differentiation of BMSCs. 5-D not only attenuated the fluorescent formation of RANKL-induced F-actin belts and NFATc1, but also activated ALP and RUNX2 expressions. As to downstream factor expressions, 5-D could block osteoclast-specific genes and proteins including NFATc1 and CTSK, while increased osteogenic genes and proteins including OPG and OCN, as confirmed by Real-time PCR and Western Blotting. Additionally, the network pharmacology and molecular docking identified the involvement of 5-D in the MIF and MAPK signaling pathways and the stable binding between 5-D and MAPK2K1. Further Western blot studies showed that 5-D decreased the phosphorylation of p38 and ERK in osteoclasts, but promoted these phosphorylations in osteoblasts. In a female C57BL/6J mouse model of estrogen deficiency-induced bone loss, 5-D demonstrated efficacy in enhancing BMD through attenuating osteoclast activities and promoting osteogenesis. These results underscore the potential application of 5-D on treating osteolysis resulting from hyperactive osteoclasts and hypoactive osteoblasts, shedding light on modulating osteoclast-osteoblast homeostasis.

The Effects and Mechanisms of Chrysosplenetin in Targeting RANKL-Induced NF-κB Signaling and NFATc1 Activation to Protect Bone Density in Osteolytic Diseases

Chrysosplenetin (CHR), an O-methylated flavonol from Chamomilla recutita and Laggera pterodonta, has previously demonstrated efficacy in enhancing osteoblast differentiation for treating postmenopausal osteoporosis. This study aims to evaluate CHR's potential to inhibit osteoclastogenesis and prevent bone deterioration in both in vitro and in vivo models. Using tartaric acid-resistant acid phosphatase staining and hydroxyapatite resorption assays, we examined the impact of CHR on RANKL-induced osteoclasts derived from mouse bone marrow monocytes. Additionally, Western blot analysis and qRT-PCR were utilized to assess the protein and gene expressions within the MAPK and NF-κB signaling pathways, as well as the NFATc1 pathway. In vivo, CHR's effects were validated using micro-CT and histomorphometry in an ovariectomized mouse model, showing significant reduction in osteoclast activity and bone loss. The study confirms CHR's inhibition of osteoclastogenesis through interference with RANKL-mediated signaling pathways, suggesting its potential as a novel therapeutic agent for osteolytic conditions related to osteoclast-osteoblast dysregulation.

AMPK, a hub for the microenvironmental regulation of bone homeostasis and diseases

AMP-activated protein kinase (AMPK), a crucial regulatory kinase, monitors energy levels, conserving ATP and boosting synthesis in low-nutrition, low-energy states. Its sensitivity links microenvironmental changes to cellular responses. As the primary support structure and endocrine organ, the maintenance, and repair of bones are closely associated with the microenvironment. While a series of studies have explored the effects of specific microenvironments on bone, there is lack of angles to comprehensively evaluate the interactions between microenvironment and bone cells, especially for bone marrow mesenchymal stem cells (BMMSCs) which mediate the differentiation of osteogenic lineage. It is noteworthy that accumulating evidence has indicated that AMPK may serve as a hub between BMMSCs and microenvironment factors, thus providing a new perspective for us to understand the biology and pathophysiology of stem cells and bone. In this review, we emphasize AMPK's pivotal role in bone microenvironment modulation via ATP, inflammation, reactive oxygen species (ROS), calcium, and glucose, particularly in BMMSCs. We further explore the use of AMPK-activating drugs in the context of osteoarthritis and osteoporosis. Moreover, building upon the foundation of AMPK, we elucidate a viewpoint that facilitates a comprehensive understanding of the dynamic relationship between the microenvironment and bone homeostasis, offering valuable insights for prospective investigations into stem cell biology and the treatment of bone diseases.

Bilobalide ameliorates osteoporosis by influencing the SIRT3/NF-κB axis in osteoclasts and promoting M2 polarization in macrophages

Osteoporosis is a systemic disease with complex etiology and high prevalence, resulting in a huge economic burden. For a long time, the search for new therapeutic pharmaceuticals has never stopped. Bone loss is related to the imbalance between bone resorption by osteoclasts and bone formation by osteoblasts. In recent years, the role of immunity and inflammation in the development of osteoporosis has studied well. For example, various cytokines, chemokines and endocrine factors regulate osteoclastogenesis via activating different macrophage subtypes, including pro-inflammatory M1 and anti-inflammatory M2. Bilobalide (Bil), an active Ginkgo biloba ingredient, has garnered great interest because of its anti-oxidant and anti-inflammatory activities. In this study, we found that Bil can attenuate osteoclast generation induced by receptor activator of nuclear factor- kappa B ligand (RANKL) through upregulating the sirtuin 3 (SIRT3) and negatively regulating NF-κB signaling. Furthermore, Bil promotes M2 polarization of macrophages in a dose-dependent manner. In vivo studies provided evidence that Bil improves bone density in osteoporosis mice models. Based on the above results, we have reason to believe that Bil has potential therapeutic value in osteoclast-mediated bone loss and offers an effective option for long-term osteoporosis management.

Loureirin B improves H/R-induced hepatic ischemia-reperfusion injury by downregulating ALOX5 to regulate mitochondrial homeostasis

This study was conceived to explore the role and the mechanism of Loureirin B (LB) in hepatic IRI. The viability of LB-treated AML-12 cells was assessed using CCK-8 assay and inflammatory cytokines were detected using ELISA. The activities of ROS and oxidative stress markers MDA, SOD, and GSH-Px were detected using DCFH-DA and corresponding assay kits. The cell apoptosis and caspase3 activity were estimated with flow cytometry and caspase3 assay kits. The expressions of arachidonate 5-lipoxygenase (ALOX5) and apoptosis- and mitochondrial dynamics-related proteins were detected using western blot. The interaction between LB and ALOX5 was analyzed with molecular docking. The transfection efficacy of oe-ALOX5 was examined with RT-qPCR and western blot. Mitochondrial membrane potential was detected with JC-1 staining and immunofluorescence (IF) assay was employed to estimate mitochondrial fusion and fission. The present work found that LB revived the viability, inhibited inflammatory response, suppressed oxidative stress, repressed the apoptosis, and maintained mitochondrial homeostasis in H/R-induced AML-12 cells, which were all reversed by ALOX5 overexpression. Collectively, LB regulated mitochondrial homeostasis by downregulating ALOX5, thereby improving hepatic IRI.

Trifolirhizin reduces osteoclast formation and prevents inflammatory osteolysis by inhibiting RANKL-induced activation of NF-κB and MAPK signaling pathways and ROS

Inflammatory osteolysis is often caused by the excessive activation of osteoclasts stimulated by bacterial products such as lipopolysaccharide. The natural flavonoid trifolirhizin (TRI) has anti-inflammatory properties; however, its function in inflammatory bone lysis remains unclear. This study aimed to elucidate the potential regulatory mechanisms of TRI in osteoclasts.Tartrate-resistant acid phosphatase (TRAP) staining, acid secretion assays, podosomal actin belt fluorescence staining, and bone resorption assays were used to investigate the effects of TRI on osteoclast differentiation and bone resorption. A reactive oxygen species (ROS) measurement kit was used to detect the effect of TRI on ROS levels in osteoclasts. The effects of TRI on genes and signaling pathways related to osteoclast differentiation were determined by quantitative polymerase chain reaction (qPCR) and western blotting. A mouse model of lipopolysaccharide-mediated inflammatory osteolysis was established, and the effects of TRI treatment on bone mass were observed using micro-CT and histological examination. Mechanistically, TRI reduced ROS production by inhibiting receptor activator of nuclear factor-κB ligand (RANKL)-induced activation of the nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways, and by upregulating the expression levels of the anti-ROS enzymes heme oxygenase-1 (HO-1) and catalase (CAT), which contributed to the degradation of ROS, ultimately leading to a decrease in osteoclastogenesis. TRI inhibited osteoclast formation and ameliorated lipopolysaccharide (LPS)-mediated inflammatory osteolysis. Thus, TRI may be a candidate agent for anti-inflammatory osteolysis.

Rapid Selenoprotein Activation by Selenium Nanoparticles to Suppresses Osteoclastogenesis and Pathological Bone Loss

Osteoclast hyperactivation stands as a significant pathological factor contributing to the emergence of bone disorders driven by heightened oxidative stress levels. The modulation of the redox balance to scavenge reactive oxygen species emerges as a viable approach to addressing this concern. Selenoproteins, characterized by selenocysteine (SeCys2) as the active center, are crucial for selenium-based antioxidative stress therapy for inflammatory diseases. This study reveals that surface-active elemental selenium (Se) nanoparticles, particularly lentinan-Se (LNT-Se), exhibit enhanced cellular accumulation and accelerated metabolism to SeCys2, the primary active Se form in biological systems. Consequently, LNT-Se demonstrates significant inhibition of osteoclastogenesis. Furthermore, in vivo studies underscore the superior therapeutic efficacy of LNT-Se over SeCys2, potentially attributable to the enhanced stability and safety profile of LNT-Se. Specifically, LNT-Se effectively modulates the expression of the selenoprotein GPx1, thereby exerting regulatory control over osteoclastogenesis inhibition, and the prevention of osteolysis. In summary, these results suggest that the prompt activation of selenoproteins by Se nanoparticles serves to suppress osteoclastogenesis and pathological bone loss by upregulating GPx1. Moreover, the utilization of bioactive Se species presents a promising avenue for effectively managing bone disorders.

Osteoporotic osseointegration: therapeutic hallmarks and engineering strategies

Osteoporosis is a systemic skeletal disease caused by an imbalance between bone resorption and formation. Current treatments primarily involve systemic medication and hormone therapy. However, these systemic treatments lack directionality and are often ineffective for locally severe osteoporosis, with the potential for complex adverse reactions. Consequently, treatment strategies using bioactive materials or external interventions have emerged as the most promising approaches. This review proposes twelve microenvironmental treatment targets for osteoporosis-related pathological changes, including local accumulation of inflammatory factors and reactive oxygen species (ROS), imbalance of mitochondrial dynamics, insulin resistance, disruption of bone cell autophagy, imbalance of bone cell apoptosis, changes in neural secretions, aging of bone cells, increased local bone tissue vascular destruction, and decreased regeneration. Additionally, this review examines the current research status of effective or potential biophysical and biochemical stimuli based on these microenvironmental treatment targets and summarizes the advantages and optimal parameters of different bioengineering stimuli to support preclinical and clinical research on osteoporosis treatment and bone regeneration. Finally, the review addresses ongoing challenges and future research prospects.

An injectable magnesium-loaded hydrogel releases hydrogen to promote osteoporotic bone repair via ROS scavenging and immunomodulation

Background: The repair of osteoporotic bone defects remains challenging due to excessive reactive oxygen species (ROS), persistent inflammation, and an imbalance between osteogenesis and osteoclastogenesis. Methods: Here, an injectable H2-releasing hydrogel (magnesium@polyethylene glycol-poly(lactic-co-glycolic acid), Mg@PEG-PLGA) was developed to remodel the challenging bone environment and accelerate the repair of osteoporotic bone defects. Results: This Mg@PEG-PLGA gel shows excellent injectability, shape adaptability, and phase-transition ability, can fill irregular bone defect areas via minimally invasive injection, and can transform into a porous scaffold in situ to provide mechanical support. With the appropriate release of H2 and magnesium ions, the 2Mg@PEG-PLGA gel (loaded with 2 mg of Mg) displayed significant immunomodulatory effects through reducing intracellular ROS, guiding macrophage polarization toward the M2 phenotype, and inhibiting the IκB/NF-κB signaling pathway. Moreover, in vitro experiments showed that the 2Mg@PEG-PLGA gel inhibited osteoclastogenesis while promoting osteogenesis. Most notably, in animal experiments, the 2Mg@PEG-PLGA gel significantly promoted the repair of osteoporotic bone defects in vivo by scavenging ROS and inhibiting inflammation and osteoclastogenesis. Conclusions: Overall, our study provides critical insight into the design and development of H2-releasing magnesium-based hydrogels as potential implants for repairing osteoporotic bone defects.

Plant-derived flavonoids are a potential source of drugs for the treatment of liver fibrosis

Liver fibrosis is a dynamic pathological process that can be triggered by any chronic liver injury. If left unaddressed, it will inevitably progress to the severe outcomes of liver cirrhosis or even hepatocellular carcinoma. In the past few years, the prevalence and fatality of hepatic fibrosis have been steadily rising on a global scale. As a result of its intricate pathogenesis, the quest for pharmacological interventions targeting liver fibrosis has remained a formidable challenge. Currently, no pharmaceuticals are exhibiting substantial clinical efficacy in the management of hepatic fibrosis. Hence, it is of utmost importance to expedite the development of novel therapeutics for the treatment of this condition. Various research studies have revealed the ability of different natural flavonoid compounds to alleviate or reverse hepatic fibrosis through a range of mechanisms, which are related to the regulation of liver inflammation, oxidative stress, synthesis and secretion of fibrosis-related factors, hepatic stellate cells activation, and proliferation, and extracellular matrix synthesis and degradation by these compounds. This review summarizes the progress of research on different sources of natural flavonoids with inhibitory effects on liver fibrosis over the last decades. The anti-fibrotic effects of natural flavonoids have been increasingly studied, making them a potential source of drugs for the treatment of liver fibrosis due to their good efficacy and biosafety.

Metal-Phenolic Networks-Reinforced Extracellular Matrix Scaffold for Bone Regeneration via Combining Radical-Scavenging and Photo-Responsive Regulation of Microenvironment

The limited regulation strategies of the regeneration microenvironment significantly hinder bone defect repair effectiveness. One potential solution is using biomaterials capable of releasing bioactive ions and biomolecules. However, most existing biomaterials lack real-time control features, failing to meet high regulation requirements. Herein, a new Strontium (Sr) and epigallocatechin-3-gallate (EGCG) based metal-phenolic network with polydopamine (PMPNs) modification is prepared. This material reinforces a biomimetic scaffold made of extracellular matrix (ECM) and hydroxyapatite nanowires (nHAW). The PMPNs@ECM/nHAW scaffold demonstrates exceptional scavenging of free radicals and reactive oxygen species (ROS), promoting HUVECs cell migration and angiogenesis, inducing stem cell osteogenic differentiation, and displaying high biocompatibility. Additionally, the PMPNs exhibit excellent photothermal properties, further enhancing the scaffold's bioactivities. In vivo studies confirm that PMPNs@ECM/nHAW with near-infrared (NIR) stimulation significantly promotes angiogenesis and osteogenesis, effectively regulating the microenvironment and facilitating bone tissue repair. This research not only provides a biomimetic scaffold for bone regeneration but also introduces a novel strategy for designing advanced biomaterials. The combination of real-time photothermal intervention and long-term chemical intervention, achieved through the release of bioactive molecules/ions, represents a promising direction for future biomaterial development.

Loureirin B ameliorates cholestatic liver fibrosis via AKT/mTOR/ATG7-mediated autophagy of hepatic stellate cells

AIM OF THE STUDY

Chronic cholestasis leads to liver fibrosis, which lacks effective treatment. In this study, we investigated the role and mechanisms of action of loureirin B (LB) in cholestatic liver fibrosis.

MATERIALS AND METHODS

Bile duct ligation (BDL)-induced hepatic fibrosis mice were used as in vivo models. Transforming growth factor-β1 (TGF-β1)-pretreated HSC-T6 cells were used to explore the mechanism by which LB attenuates liver fibrosis in vitro. RNA sequencing, quantitative PCR (qPCR), western blotting, immunohistochemistry and immunofluorescence were performed to detect the fibrosis markers and measure autophagy levels. Flow cytometry, cell counting kit-8 (CCK-8) assay, and 5'-ethynyl-2'-deoxyuridine (EdU) assay were conducted to detect cell proliferation and viability. GFP-RFP-LC3 adenovirus, autophagy-related protein 7 (ATG7) siRNA, and bafilomycin A1 (BafA1) were used to verify autophagic flux.

RESULTS

Our results showed that LB ameliorates liver injury, inhibits collagen deposition, and decreases the expressions of fibrosis-related markers in BDL-induced mouse livers. In vitro, we found that LB inhibited proliferation and migration, promoted apoptosis, and inhibited the activation of HSC-T6 cells pretreated with TGF-β1. RNA sequencing analysis of HSC-T6 cells showed that LB treatment predominantly targeted autophagy-related pathways. Further protein analysis indicated that LB downregulated the expression of phosphorylated AKT (p-AKT) and phosphorylated mTOR (p-mTOR), and upregulated LC3-II, p62, and ATG7 both in vivo and in vitro. Intriguingly, ATG7 inactivation reversed the antifibrotic effects of LB on HSC-T6 cells.

CONCLUSIONS

LB can improve BDL-induced liver fibrosis by inhibiting the activation and proliferation of HSCs and is expected to be a promising antifibrotic drug.

Ziyuglycoside II attenuated OVX mice bone loss via inflammatory responses and regulation of gut microbiota and SCFAs

BACKGROUND AND PURPOSE

Osteoporosis (OP) is a frequent clinical problem for the elderly. Traditional Chinese Medicine (TCM) has achieved beneficial results in the treatment of OP. Ziyuglycoside II (ZGS II) is a major active compound of Sanguisorba officinalis L. that has shown anti-inflammation and antioxidation properties, but little information concerning its anti-OP potential is available. Our research aims to investigate the mechanism of ZGS II in ameliorating bone loss by inflammatory responses and regulation of gut microbiota and short chain fatty acids (SCFAs) in ovariectomized (OVX) mice.

METHODS

We predicted the mode of ZGS II action on OP through network pharmacology and molecular docking, and an OVX mouse model was employed to validate its anti-OP efficacy. Then we analyzed its impact on bone microstructure, the levels of inflammatory cytokines and pain mediators in serum, inflammation in colon, intestinal barrier, gut microbiota composition and SCFAs in feces.

RESULTS

Network pharmacology identified 55 intersecting targets of ZGS II related to OP. Of these, we predicted IGF1 may be the core target, which was successfully docked with ZGS II and showed excellent binding ability. Our in vivo results showed that ZGS II alleviated bone loss in OVX mice, attenuated systemic inflammation, enhanced intestinal barrier, reduced the pain threshold, modulated the abundance of gut microbiota involving norank_f__Muribaculaceae and Dubosiella, and increased the content of acetic acid and propanoic acid in SCFAs.

CONCLUSIONS

Our data indicated that ZGS II attenuated bone loss in OVX mice by relieving inflammation and regulating gut microbiota and SCFAs.

Lactobacillus plantarum 45 activates SHP2 through inhibition of oxidative stress to regulate osteoblast and osteoclast differentiation

BACKGROUND

The purpose of this study is to observe LP45 (Lactobacillus plantarum 45) to investigate the mechanism by which LP45 attenuates oxidative stress-induced damage and regulates the osteoblast-osteoclast balance.

MATERIALS AND METHODS

The oxidative stress level and osteoblast- and osteoclast-related proteins were detected by immunofluorescence staining, Western blotting, ROS fluorescent probe and ELISA. Osteoblast cell proliferation capacity was determined by the CCK-8 assay. X-ray observation and HE staining were used to detect the effect of LP45 on osteoporosis.

RESULTS

The expression level of SHP2 and Src was significantly increased, and the expression levels of NOX4, P22, P47, IL-1β, NLRP3, IRF3, RANK, β-catenin and INF-β were inhibited in LP45 group and LPS + LP45 group as compared to those in LPS group. Compared with that in LPS group, the concentration of SOD was increased and the concentration of MDA was decreased in LPS + LP45 group. The protein expressions of OPG, RANKL, RUNX3, RANK and β-catenin in LP45 group and LPS + LP45 group increased. The protein expressions of NF-κB, CREB and AP-1 in LP45 group and LPS + LP45 group decreased significantly. The results were also confirmed by immunofluorescence staining and ROS fluorescent probe. X-ray observation and HE staining showed that LP45 could inhibit the progression of osteoporosis.

CONCLUSION

LP45 can exert its antioxidant effect by inhibiting the production of oxidative stress to activate the SHP2 signaling pathway, thus promoting osteoblast differentiation and repressing osteoclast formation to maintain bone homeostasis and improve bone metabolism.

Cichoric acid targets RANKL to inhibit osteoclastogenesis and prevent ovariectomy-induced bone loss

BACKGROUND AND AIM

Osteoporosis, a systemic metabolic bone disease, is characterized by the decline of bone mass and quality due to excessive osteoclast activity. Currently, drug-targeting osteoclasts show promising therapy for osteoporosis. In this study, we investigated the effect of cichoric acid (CA) on receptor activator of nuclear kappa-B ligand (RANKL)-induced osteoclastogenesis and the bone loss induced by ovariectomy in mice.

EXPERIMENTAL PROCEDURE

Molecular docking technologies were employed to examine the interaction between CA and RANKL. CCK8 assay was used to evaluate the cell viability under CA treatment. TRAcP staining, podosome belt staining, and bone resorption assays were used to test the effect of CA on osteoclastogenesis and osteoclast function. Further, an OVX-induced osteoporosis mice model was employed to identify the effect of CA on bone loss using micro-CT scanning and histological examination. To investigate underlying mechanisms, network pharmacology was applied to predict the downstream signaling pathways, which were verified by Western blot and immunofluorescence staining.

KEY RESULTS

The molecular docking analysis revealed that CA exhibited a specific binding affinity to RANKL, engaging multiple binding sites. CA inhibited RANKL-induced osteoclastogenesis and bone resorption without cytotoxic effects. Mechanistically, CA suppressed RANKL-induced intracellular reactive oxygen species, nuclear factor-kappa B, and mitogen-activated protein kinase pathways, followed by abrogated nuclear factor activated T-cells 1 activity. Consistent with this finding, CA attenuated post-ovariectomy-induced osteoporosis by ameliorating osteoclastogenesis.

CONCLUSIONS AND IMPLICATIONS

CA inhibited osteoclast activity and bone loss by targeting RANKL. CA might represent a promising candidate for treating osteoclast-related diseases, such as osteoporosis.

Icariin ameliorates osteoporosis in ovariectomized rats by targeting Cullin 3/Nrf2/OH pathway for osteoclast inhibition

Osteoporosis, characterized by low bone mass and bone microarchitecture breakdown, has become a growing public health problem. The increase in oxidative stress could lead to an imbalance between osteoblasts-mediated osteogenesis and osteoclast-mediated bone resorption, which gives rise to osteoporosis. Nrf2 is a master transcription factor that regulates oxidative stress and has recently been reported to take part in the development of osteoporosis. Icariin, a leading active flavonoid in herbal Epimedium pubescens, has significant antioxidant activity in and is widely applied for treating bone diseases. In this study, we aimed to explore the effect of icariin on osteoclastogenesis and its potential mechanism from the perspective of oxidative stress inhibition, using ovariectomized (OVX) rats and RANKL-induced RAW264.7 cells. Our results demonstrated that icariin-treated OVX rats exhibited higher bone density, fewer tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts, and lower ROS levels in bone tissues than vehicle-treated OVX rats. Also, icariin suppressed osteoclast differentiation and inhibited the expression of osteoclastogenesis-related genes, such as NFATc1, Ctsk, Trap, and c-Fos, in RANKL-induced RAW264.7 cells. Icariin also reduced intracellular ROS levels by increasing the expression of nuclear Nrf2 and HO-1. Further mechanistic studies showed icariin inhibited Cullin 3 expression and could delay Nrf2 degradation by reducing the ubiquitination of endogenous Nrf2 in RANKL-stimulated RAW264.7 cells, and these effects were markedly reversed by cullin three overexpression. These findings suggest icariin alleviated osteoporosis by suppressing osteoclastogenesis via targeting the Cullin 3/Nrf2/OH signaling pathway. Our study implied that icariin may be a potential candidate to treat osteoporosis.

Inhibition of PPP1R15A alleviates osteoporosis via suppressing RANKL-induced osteoclastogenesis

Osteoporosis results from overactivation of osteoclasts. There are currently few drug options for treatment of this disease. Since the successful development of allosteric inhibitors, phosphatases have become attractive therapeutic targets. Protein phosphatase 1, regulatory subunit 15 A (PPP1R15A), is a stress-responsive protein, which promotes the UPR (unfolded protein response) and restores protein homeostasis. In this study we investigated the role of PPP1R15A in osteoporosis and osteoclastogenesis. Ovariectomy (OVX)-induced osteoporosis mouse model was established, osteoporosis was evaluated in the left femurs using micro-CT. RANKL-stimulated osteoclastogenesis was used as in vitro models. We showed that PPP1R15A expression was markedly increased in BMMs derived from OVX mice and during RANKL-induced osteoclastogenesis in vitro. Knockdown of PPP1R15A or application of Sephin1 (a PPP1R15A allosteric inhibitor in a phase II clinical trial) significantly inhibited osteoclastogenesis in vitro. Sephin1 (0.78, 3.125 and 12.5 μM) dose-dependently mitigated the changes in NF-κB, MAPK, and c-FOS and the subsequent nuclear factor of activated T cells 1 (NFATc1) translocation in RANKL-stimulated BMMs. Both Sephin1 and PPP1R15A knockdown increased the phosphorylated form of eukaryotic initiation factor 2α (eIF2α); knockdown of eIF2α reduced the inhibitory effects of Sephin1 on NFATc1-luc transcription and osteoclast formation. Furthermore, Sephin1 or PPP1R15A knockdown suppressed osteoclastogenesis in CD14+ monocytes from osteoporosis patients. In OVX mice, injection of Sephin1 (4, 8 mg/kg, i.p.) every two days for 6 weeks significantly inhibited bone loss, and restored bone destruction and decreased TRAP-positive cells. This study has identified PPP1R15A as a novel target for osteoclast differentiation, and genetic inhibition or allosteric inhibitors of PPP1R15A, such as Sephin1, can be used to treat osteoporosis. This study revealed that PPP1R15A expression was increased in osteoporosis in both human and mice. Inhibition of PPP1R15A by specific knockdown or an allosteric inhibitor Sephin1 mitigated murine osteoclast formation in vitro and attenuated ovariectomy-induced osteoporosis in vivo. PPP1R15A inhibition also suppressed pathogenic osteoclastogenesis in CD14+ monocytes from osteoporosis patients. These results identify PPP1R15A as a novel regulator of osteoclastogenesis and a valuable therapeutic target for osteoporosis.

Biological Activities of Deer Antler-Derived Peptides on Human Chondrocyte and Bone Metabolism

Orally administered "tortoiseshell and deer antler gelatin" is a common traditional medicine for patients with osteoporosis or osteoarthritis. From the pepsin-digested gelatin, we previously isolated and identified the osteoblast-stimulating pentapeptide, TSKYR. Its trypsin digestion products include the dipeptide YR, enhancing calcium ion uptake, and tripeptide TSK, resulting in remarkable 30- and 50-fold increases in mineralized nodule area and density in human osteoblast cells. These peptides were chemically synthesized in this study. The composition of deer antler preparations comprises not only proteins and peptides but also a significant quantity of metal ion salts. By analyzing osteoblast growth in the presence of peptide YR and various metal ions, we observed a synergistic effect of calcium and strontium on the effects of YR. Those peptides could also stimulate the growth of C2C12 skeletal muscle cells and human chondrocytes, increasing collagen and glycosaminoglycan content in a three-dimensional environment. The maintenance of bone homeostasis relies on a balance between osteoclasts and osteoblasts. Deer antler peptides were observed to inhibit osteoclast differentiation, as evidenced by ROS generation, tartrate-resistant acid phosphatase (TRACP) activity assays, and gene expression in RAW264.7 cells. In summary, our findings provide a deep understanding of the efficacy of this folk medicine.

Bioactives and Biomaterial Construction for Modulating Osteoclast Activities

Bone tissue constitutes 15-20% of human body weight and plays a crucial role in supporting the body, coordinating movement, regulating mineral homeostasis, and hematopoiesis. The maintenance of bone homeostasis relies on a delicate balance between osteoblasts and osteoclasts. Osteoclasts, as the exclusive "bone resorbers" in the human skeletal system, are of paramount significance yet often receive inadequate attention. When osteoclast activity becomes excessive, it frequently leads to various bone metabolic disorders, subsequently resulting in secondary bone injuries, such as fractures. This not only reduces life quality of patients, but also imposes a significant economic burden on society. In response to the pressing need for biomaterials in the treatment of osteoclast dysregulation, there is a surge of research and investigations aimed at osteoclast regulation. Promising progress is achieved in this domain. This review seeks to provide a comprehensive understanding of how to modulate osteoclast activities. It summarizes bioactive substances that influence osteoclasts and elucidates strategies for constructing related biomaterial systems. It offers practical insights and ideas for the development and application of biomaterials and tissue engineering, with the hope of guiding the clinical treatment of osteoclast-related bone diseases using biomaterials in the future.

Unveiling the potential of Butylphthalide: inhibiting osteoclastogenesis and preventing bone loss

Osteoporosis, resulting from overactive osteoclasts and leading to elevated fracture risk, has emerged as a global public health concern due to the aging population. Therefore, inhibiting osteoclastogenesis and bone resorption function represents a crucial approach for preventing and treating osteoporosis. The purpose of this study was to examine the effects and molecular mechanisms of Butylphthalide (NBP) on the differentiation and function of osteoclasts induced by RANKL. Osteoclastogenesis was assessed through TRAP staining and bone slice assay. An animal model that underwent ovariectomy, simulating postmenopausal women's physiological characteristics, was established to investigate the impact of Butylphthalide on ovariectomy-induced bone loss. To delve deeper into the specific mechanisms, we employed Western blot, PCR, immunofluorescence, and immunohistochemical staining to detect the expression of proteins that are associated with the osteoclast signaling pathway. In this study, we found that Butylphthalide not only suppressed osteoclastogenesis and bone resorption in vitro but also significantly decreased TRAcP-positive osteoclasts and prevented bone loss in vivo. Further mechanistic experiments revealed that Butylphthalide reduces intracellular ROS in osteoclasts, inhibits the MAPK and NFATc1 signaling pathways, and downregulates the key genes and proteins of osteoclasts. This inhibits osteoclast formation and function. The reduction in ROS in osteoclasts is intricately linked to the activity of Butylphthalide-modulated antioxidant enzymes. Overall, NBP may offer a alternative treatment option with fewer side effects for skeletal diseases such as osteoporosis.

Exploring the therapeutic potential of isoorientin in the treatment of osteoporosis: a study using network pharmacology and experimental validation

BACKGROUND

Isoorientin (ISO) is a glycosylated flavonoid with antitumor, anti-inflammatory, and antioxidant properties. However, its effects on bone metabolism remain largely unknown.

METHODS

In this study, we aimed to investigate the effects of ISO on receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast formation in vitro and bone loss in post-ovariectomy (OVX) rats, as well as to elucidate the underlying mechanism. First, network pharmacology analysis indicated that MAPK1 and AKT1 may be potential therapeutic targets of ISO and that ISO has potential regulatory effects on the mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) pathways, as well as oxidative stress. ISO was added to RAW264.7 cells stimulated by RANKL, and its effects on osteoclast differentiation were evaluated using tartrate-resistant acid phosphatase (TRAP) staining, TRAP activity measurement, and F-actin ring analysis. Reactive oxygen species (ROS) production in osteoclasts was detected using a ROS assay kit. The effects of ISO on RANKL-triggered molecular cascade response were further investigated by Western blotting, quantitative real-time polymerase chain reaction, and immunofluorescence staining. In addition, the therapeutic effects of ISO were evaluated in vivo.

RESULTS

ISO inhibited osteoclastogenesis in a time- and concentration-dependent manner. Mechanistically, ISO downregulated the expression of the main transcription factor for osteoclast differentiation by inhibiting MAPK and PI3K/AKT1 signaling pathways. Moreover, ISO exhibited protective effects in OVX-induced bone loss rats. This was consistent with the results derived from network pharmacology.

CONCLUSION

Our findings suggest a potential therapeutic utility of ISO in the management of osteoclast-associated bone diseases, including osteoporosis.

Redox signaling and antioxidant defense in osteoclasts

Bone remodeling is essential for the repair and replacement of damaged or aging bones. Continuous remodeling is necessary to prevent the accumulation of bone damage and to maintain bone strength and calcium balance. As bones age, the coupling mechanism between bone formation and absorption becomes dysregulated, and bone loss becomes dominant. Bone development and repair rely on interaction and communication between osteoclasts and surrounding cells. Osteoclasts are specialized cells that are accountable for bone resorption and degradation, and any abnormalities in their activity can result in notable alterations in bone structure and worsen disease symptoms. Recent findings from transgenic mouse models and bone analysis have greatly enhanced our understanding of the origin, differentiation pathway, and activation stages of osteoclasts. In this review, we explore osteoclasts and discuss the cellular and molecular events that drive their generation, focusing on intracellular oxidative and antioxidant signaling. This knowledge can help develop targeted therapies for diseases associated with osteoclast activation.

Piperlongumine, a Piper longum-derived amide alkaloid, protects mice from ovariectomy-induced osteoporosis by inhibiting osteoclastogenesis via suppression of p38 and JNK signaling

Postmenopausal osteoporosis (PMOP) is a metabolic bone disease that results from overproduction and hyperactivation of osteoclasts caused by insufficient estrogen in women after menopause. Current therapeutic strategies are mainly focused on treating PMOP patients who have already developed severe bone loss or even osteoporotic fractures. Obviously, a better strategy is to prevent PMOP from occurring in the first place. However, such reagents are largely lacking. Piperlongumine (PLM), an amide alkaloid extracted from long pepper Piper longum, exhibits the anti-osteoclastogenic effect in normal bone marrow macrophages (BMMs) and the protective effect against osteolysis induced by titanium particles in mice. This study examined the preventive effect of PLM on PMOP and explored the potential mechanism of this effect using both ovariectomized mice and their primary cells. The result showed that PLM (5 and 10 mg kg-1) administered daily for 6 weeks ameliorated ovariectomy-induced bone loss and osteoclast formation in mice. Further cell experiments showed that PLM directly suppressed osteoclast formation, F-actin ring formation, and osteoclastic resorption pit formation in BMMs derived from osteoporotic mice, but did not obviously affect osteogenic differentiation of bone marrow stromal cells (BMSCs) from these mice. Western blot analysis revealed that PLM attenuated maximal activation of p38 and JNK pathways by RANKL stimulation without affecting acute activation of NF-κB, AKT, and ERK signaling. Furthermore, PLM inhibited expression of key osteoclastogenic transcription factors NFATc1/c-Fos and their target genes (Dcstamp, Atp6v0d2, Acp5, and Oscar). Taken together, our findings suggest that PLM inhibits osteoclast formation and function by suppressing RANKL-induced activation of the p38/JNK-cFos/NFATc1 signaling cascade, thereby preventing ovariectomy-induced osteoporosis in mice. Thus, PLM can potentially be used as an anti-resorption drug or dietary supplement for the prevention of PMOP.

Biomimetic Therapeutics for Bone Regeneration: A Perspective on Antiaging Strategies

Advances in modern medicine and the significant reduction in infant mortality have steadily increased the population's lifespan. As more and more people in the world grow older, incidence of chronic, noncommunicable disease is anticipated to drastically increase. Recent studies have shown that improving the health of the aging population is anticipated to provide the most cost-effective and impactful improvement in quality of life during aging-driven disease. In bone, aging is tightly linked to increased risk of fracture, and markedly decreased regenerative potential, deeming it critical to develop therapeutics to improve aging-driven bone regeneration. Biomimetics offer a cost-effective method in regenerative therapeutics for bone, where there are numerous innovations improving outcomes in young models, but adapting biomimetics to aged models is still a challenge. Chronic inflammation, accumulation of reactive oxygen species, and cellular senescence are among three of the more unique challenges facing aging-induced defect repair. This review dissects many of the innovative biomimetic approaches research groups have taken to tackle these challenges, and discusses the further uncertainties that need to be addressed to push the field further. Through these research innovations, it can be noted that biomimetic therapeutics hold great potential for the future of aging-complicated defect repair.

Corylifol A suppresses osteoclastogenesis and alleviates ovariectomy-induced bone loss via attenuating ROS production and impairing mitochondrial function

Osteoporosis is a systemic disease characterized by an imbalance in bone homeostasis, where osteoblasts fail to fully compensate for the bone resorption induced by osteoclasts. Corylifol A, a flavonoid extracted from Fructus psoraleae, has been identified as a potential treatment for this condition. Predictions from network pharmacology and molecular docking studies suggest that Corylifol A exhibits strong binding affinity with NFATc1, Nrf2, PI3K, and AKT1. Empirical evidence from in vivo experiments indicates that Corylifol A significantly mitigates systemic bone loss induced by ovariectomy by suppressing both the generation and activation of osteoclasts. In vitro studies further showed that Corylifol A inhibited the activation of PI3K-AKT and MAPK pathways and calcium channels induced by RANKL in a time gradient manner, and specifically inhibited the phosphorylation of PI3K, AKT, GSK3 β, ERK, CaMKII, CaMKIV, and Calmodulin. It also diminishes ROS production through Nrf2 activation, leading to a decrease in the expression of key regulators such as NFATcl, C-Fos, Acp5, Mmp9, and CTSK that are involved in osteoclastogenesis. Notably, our RNA-seq analysis suggests that Corylifol A primarily impacts mitochondrial energy metabolism by suppressing oxidative phosphorylation. Collectively, these findings demonstrate that Corylifol A is a novel inhibitor of osteoclastogenesis, offering potential therapeutic applications for diseases associated with excessive bone resorption.

Tanshinone I attenuates estrogen-deficiency bone loss via inhibiting RANKL-induced MAPK and NF-κB signaling pathways

AIM OF THE STUDY

This study aims to reveal the role of Tanshinone I (TI) in inhibiting osteoclast activity and bone loss in vitro and in vivo, as well as elucidate its underlying molecular mechanism.

MATERIALS AND METHODS

A mouse model of estrogen deficiency was used to assess the inhibitory effect of TI on osteoclast activity and subsequent bone loss. To validate the impact of TI on osteoclast formation, TRAcP staining and pseudopodia belt staining were conducted. The expressions of osteoclast-specific genes and proteins were evaluated using RT-PCR and Western Blot analyses. Additionally, immunofluorescence staining was employed to examine the effect of TI on p65 nuclear translocation and the expression level of reactive oxygen species (ROS).

RESULTS

TI demonstrated significant efficacy in alleviating bone mass loss and suppressing osteoclast activity and function in ovariectomized mice. This outcome was predominantly ascribed to a decrease in ROS levels, thereby impeding the NF-κB signaling pathway and the translocation of p65 to the nucleus. Additionally, TI hindered the RANKL-induced phosphorylation of the MAPK signaling pathway. Moreover, TI played a role in the reduction of osteoclast-specific genes and proteins.

CONCLUSIONS

To summarize, this study sheds light on TI's capacity to modulate various signaling pathways triggered by RANKL, effectively impeding osteoclast formation and mitigating bone loss resulting from estrogen deficiency. Consequently, TI emerges as a promising therapeutic option for estrogen-deficiency bone loss.

Bone-targeting engineered small extracellular vesicles carrying anti-miR-6359-CGGGAGC prevent valproic acid-induced bone loss

The clinical role and underlying mechanisms of valproic acid (VPA) on bone homeostasis remain controversial. Herein, we confirmed that VPA treatment was associated with decreased bone mass and bone mineral density (BMD) in both patients and mice. This effect was attributed to VPA-induced elevation in osteoclast formation and activity. Through RNA-sequencing, we observed a significant rise in precursor miR-6359 expression in VPA-treated osteoclast precursors in vitro, and further, a marked upregulation of mature miR-6359 (miR-6359) in vivo was demonstrated using quantitative real-time PCR (qRT-PCR) and miR-6359 fluorescent in situ hybridization (miR-6359-FISH). Specifically, the miR-6359 was predominantly increased in osteoclast precursors and macrophages but not in neutrophils, T lymphocytes, monocytes and bone marrow-derived mesenchymal stem cells (BMSCs) following VPA stimulation, which influenced osteoclast differentiation and bone-resorptive activity. Additionally, VPA-induced miR-6359 enrichment in osteoclast precursors enhanced reactive oxygen species (ROS) production by silencing the SIRT3 protein expression, followed by activation of the MAPK signaling pathway, which enhanced osteoclast formation and activity, thereby accelerating bone loss. Currently, there are no medications that can effectively treat VPA-induced bone loss. Therefore, we constructed engineered small extracellular vesicles (E-sEVs) targeting osteoclast precursors in bone and naturally carrying anti-miR-6359 by introducing of EXOmotif (CGGGAGC) in the 3'-end of the anti-miR-6359 sequence. We confirmed that the E-sEVs exhibited decent bone/osteoclast precursor targeting and exerted protective therapeutic effects on VPA-induced bone loss, but not on ovariectomy (OVX) and glucocorticoid-induced osteoporotic models, deepening our understanding of the underlying mechanism and treatment strategies for VPA-induced bone loss.

Age-related decline in melatonin contributes to enhanced osteoclastogenesis via disruption of redox homeostasis

BACKGROUND

Increased oxidative stress contributes to enhanced osteoclastogenesis and age-related bone loss. Melatonin (MT) is an endogenous antioxidant and declines with aging. However, it was unclear whether the decline of MT was involved in the enhanced osteoclastogenesis during the aging process.

METHODS

The plasma level of MT, oxidative stress status, bone mass, the number of bone marrow-derived monocytes (BMMs) and its osteoclastogenesis were analyzed in young (3-month old) and old (18-month old) mice (n = 6 per group). In vitro, BMMs isolated from aged mice were treated with or without MT, followed by detecting the change of osteoclastogenesis and intracellular reactive oxygen species (ROS) level. Furthermore, old mice were treated with MT for 2 months to investigate the therapeutic effect.

RESULTS

The plasma level of MT was markedly lower in aged mice compared with young mice. Age-related decline in MT was accompanied by enhanced oxidative stress, osteoclastogenic potential and bone loss. MT intervention significantly suppressed the receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis, decreased intracellular ROS and enhanced antioxidant capacity of BMMs from aged mice. MT supplementation significantly attenuated oxidative stress, osteoclastogenesis, bone loss and deterioration of bone microstructure in aged mice.

CONCLUSIONS

These results suggest that age-related decline of MT enhanced osteoclastogenesis via disruption of redox homeostasis. MT may serve as a key regulator in osteoclastogenesis and bone homeostasis, thereby highlighting its potential as a preventive agent for age-related bone loss.

IKK/NF-κB and ROS signal axes are involved in Tenacissoside H mediated inhibitory effects on LPS-induced inflammatory osteolysis

Periodontal disease and arthroplasty prosthesis loosening and destabilization are both associated with osteolysis, which is predominantly caused by abnormal bone resorption triggered by pro-inflammatory cytokines. Osteoclasts (OCs) are critical players in the process. Concerns regarding the long-term efficacy and side effects of current frontline therapies, however, remain. Alternative therapies are still required. The aim of this work was to investigate the involvement of Tenacissoside H (TDH) in RANKL-mediated OC differentiation, as well as inflammatory osteolysis and associated processes. In vitro, bone marrow-derived macrophages (BMMs) cultured with RANKL and M-CSF were used to detect TDH in the differentiation and function of OCs. Real-time quantitative PCR was used to measure the expression of specific genes and inflammatory factors in OCs. Western blot was used to identify NFATc1, IKK, NF-κB, MAPK pathway, and oxidative stress-related components. Finally, an LPS-mediated calvarial osteolysis mouse model was employed to explore TDH's role in inflammatory osteolysis. The results showed that in vivo TDH inhibited the differentiation and resorption functions of OCs and down-regulated the transcription of osteoclast-specific genes, as well as Il-1β, Il-6 and Tnf-α. In addition, TDH inhibited the IKK and NF-κB signalling pathways and down-regulated the level of ROS. In vivo studies revealed that TDH improves the bone loss caused by LPS. TDH may be a new candidate or treatment for osteoclast-associated inflammatory osteolytic disease.

CB2 regulates oxidative stress and osteoclastogenesis through NOX1-dependent signaling pathway in titanium particle-induced osteolysis

Periprosthetic osteolysis (PPO) induced by wear particles at the interface between the prosthesis and bone is a crucial issue of periprosthetic bone loss and implant failure. After wear and tear, granular material accumulates around the joint prosthesis, causing a chronic inflammatory response, progressive osteoclast activation and eventual loosening of the prosthesis. Although many studies have been conducted to address bone loss after joint replacement surgeries, they have not fully addressed these issues. Focusing on osteoclast activation induced by particles has important theoretical implications. Cannabinoid type II receptor (CB2) is a seven-transmembrane receptor that is predominantly distributed in the human immune system and has been revealed to be highly expressed in bone-associated cells. Previous studies have shown that modulation of CB2 has a positive effect on bone metabolism. However, the exact mechanism has not yet been elucidated. In our experiments, we found that NOX1-mediated ROS accumulation was involved in titanium particle-stimulated osteoclast differentiation. Furthermore, we confirmed that CB2 blockade alleviated titanium particle-stimulated osteoclast activation by inhibiting the NOX1-mediated oxidative stress pathway. In animal experiments, downregulation of CB2 alleviated the occurrence of titanium particle-induced cranial osteolysis by inhibiting osteoclasts and scavenging intracellular ROS. Collectively, our results suggest that CB2 blockade may be an attractive and promising therapeutic scheme for particle-stimulated osteoclast differentiation and preventing PPO.

Tussilagone inhibits osteoclastogenesis by modulating mitochondrial function and ROS production involved Nrf2 activation

Reactive Oxygen Species (ROS) play an essential role in the pathogenesis of osteoporosis mainly characterized by excessive osteoclasts (OCs) activity. OCs are rich in mitochondria for energy support, which is a major source of total ROS. Tussilagone (TSG), a natural Sesquiterpenes from the flower of Tussilago farfara, has plentiful beneficial pharmacological characteristics with anti-inflammatory and anti-oxidative activity, but its effects and mechanism in osteopathology are still unclear. In our study, we investigated the regulation of ROS generated from the mitochondria in OCs. We found that TSG inhibited OCs differentiation and bone resorption without any cytotoxicity. Mechanistically, TSG reduced RANKL-mediated total ROS level by down-regulating intracellular ROS production and mitochondrial function, leading to the suppression of NFATc1 transcription. We also found that nuclear factor erythroid 2-related factor 2 (Nrf2) could enhance ROS scavenging enzymes in response to RANKL-induced oxidative stress. Furthermore, TSG up-regulated the expression of Nrf2 by inhibiting its proteosomal degradation. Interestingly, Nrf2 deficiency reversed the suppressive effect of TSG on mitochondrial activity and ROS signaling in OCs. Consistent with this finding, TSG attenuated post-ovariectomy (OVX)- and lipopolysaccharide (LPS) induced bone loss by ameliorating osteoclastogenesis. Taken together, TSG has an anti-bone resorptive effect by modulating mitochondrial function and ROS production involved Nrf2 activation.

Myrislignan targets extracellular signal-regulated kinase (ERK) and modulates mitochondrial function to dampen osteoclastogenesis and ovariectomy-induced osteoporosis

BACKGROUND

Activated osteoclasts cause excessive bone resorption, and disrupt bone homeostasis, leading to osteoporosis. The extracellular signal-regulated kinase (ERK) signaling is the classical pathway related to osteoclast differentiation, and mitochondrial reactive oxygen species are closely associated with the differentiation of osteoclasts. Myrislignan (MRL), a natural product derived from nutmeg, has multiple pharmacological activities; however, its therapeutic effect on osteoporosis is unclear. Here, we investigated whether MRL could inhibit osteoclastogenesis and bone mass loss in an ovariectomy mouse model by suppressing mitochondrial function and ERK signaling.

METHODS

Tartrate-resistant and phosphatase (TRAP) and bone resorption assays were performed to observe the effect of MRL on osteoclastogenesis of bone marrow macrophages. MitoSOX RED and tetramethyl rhodamine methyl ester (TMRM) staining was performed to evaluate the inhibitory effect of MRL on mitochondria. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) assay was performed to detect whether MRL suppressed the expression of osteoclast-specific genes. The impact of MRL on the protein involved in the mitogen-activated protein kinase (MAPK) and nuclear factor-κB pathways was evaluated using western blotting. In addition, a specific ERK agonist LM22B-10, was used to revalidate the inhibitory effect of MRL on ERK. Finally, we established an ovariectomy mouse model to assess the therapeutic effect of MRL on osteoporosis in vivo.

RESULTS

MRL inhibited osteoclast differentiation and the associated bone resorption, by significantly decreasing osteoclastic gene expression. Mechanistically, MRL inhibited the phosphorylation of ERK by suppressing the mitochondrial function, thereby downregulating the nuclear factor of activated T cells 1 (NFATc1) signaling. LM22B-10 treatment further verified the targeted inhibition effect of MRL on ERK. Microscopic computed tomographic and histologic analyses of the tibial tissue sections indicated that ovariectomized mice had lower bone mass and higher expression of ERK compared with normal controls. However, MRL treatment significantly reversed these effects, indicating the anti-osteoporosis effect of MRL.

CONCLUSION

We report for the first time that MRL inhibits ERK signaling by suppressing mitochondrial function, thereby ameliorating ovariectomy-induced osteoporosis. Our findings can provide a basis for the development of a novel therapeutic strategy for osteoporosis.

[Oridonin suppresses the effect of thioacetamide for promoting osteoclast differentiation of RAW264.7 cells and inhibiting osteoblast differentiation of bone mesenchymal stem cells]

OBJECTIVE

To explore the effect of oridonin (ORI) for suppressing thioacetamide (TAA)-induced osteoclast differentiation of RAW264.7 cells and antagonizing the inhibitory effect of TAA on osteogenic differentiation of bone mesenchymal stem cells (BMSCs).

METHODS

The effects of TAA and ORI on the proliferation of RAW264.7 cells and SD rat BMSCs were examined using CCK-8 assay. TRAP staining and immunofluorescence staining were used to observe the effects of TAA and ORI on osteoclast differentiation in RAW264.7 cells. The expressions of osteoclast-specific proteins in the treated cells were detected using Western blotting, and p65 nuclear translocation and reactive oxygen species (ROS) production in the cells were assessed with immunofluorescence assay and flow cytometry. Alkaline phosphatase (ALP) staining and alizarin red staining were used to examine the effects of TAA and ORI on osteogenic differentiation of BMSCs, and the expressions of osteogenic and apoptosis-related proteins in the cells were detected with Western blotting.

RESULTS

Compared with RAW264.7 cells treated with TAA alone, the cells with the combined treatment with TAA and ORI showed decreased osteoclast differentiation (P < 0.01) and significant inhibition of the MAPK/NF-κB pathway (P < 0.01) with reduced p65 nuclear translocation and intracellular ROS production (P < 0.01). In rat BMSCs, treatment with TAA alone significantly inhibited ALP activity and formation of calcified nodules (P < 0.01) and induced obvious cell apoptosis. Compared with TAA-treated BMSCs, the cells treated with both TAA and ORI showed upregulated expressions of the BMP-2/RUNX2 pathway with enhanced ALP activity (P < 0.01) and calcium deposition (P < 0.01) and a lowered cell apoptosis level.

CONCLUSION

ORI inhibits TAA-induced osteoclast differentiation via regulating the MAPK/NF-κB pathway and antagonizes TAA-induced inhibition of bone formation by regulating the BMP-2/RUNX2 pathway.

Ginsenoside compound-K attenuates OVX-induced osteoporosis via the suppression of RANKL-induced osteoclastogenesis and oxidative stress

Osteoporosis (OP), a systemic and chronic bone disease, is distinguished by low bone mass and destruction of bone microarchitecture. Ginsenoside Compound-K (CK), one of the metabolites of ginsenoside Rb1, has anti-aging, anti-inflammatory, anti-cancer, and hypolipidemic activities. We have demonstrated CK could promote osteogenesis and fracture healing in our previous study. However, the contribution of CK to osteoporosis has not been examined. In the present study, we investigated the effect of CK on osteoclastogenesis and ovariectomy (OVX)-induced osteoporosis. The results showed that CK inhibited receptor activator for nuclear factor-κB ligand (RANKL)-mediated osteoclast differentiation and reactive oxygen species (ROS) activity by inhibiting the phosphorylation of NF-κB p65 and oxidative stress in RAW264.7 cells. In addition, we also demonstrated that CK could inhibit bone resorption using bone marrow-derived macrophages. Furthermore, we demonstrated that CK attenuated bone loss by suppressing the activity of osteoclast and alleviating oxidative stress in vivo. Taken together, these results showed CK could inhibit osteoclastogenesis and prevent OVX-induced bone loss by inhibiting NF-κB signaling pathway.

Icariin inhibits prostate cancer bone metastasis and destruction via suppressing TAM/CCL5-mediated osteoclastogenesis

BACKGROUND

Bone metastasis occurs in nearly 70% of patients with metastatic prostate cancer (PCa), and represents the leading cause of death in patients with PCa. Emerging evidence has demonstrated the potential activities of icariin in modulating bone metabolism and remodelling the tumor microenvironment (TME). However, whether icariin could inhibit PCa bone metastasis and destruction by modulating the TME as well as the underlying mechanisms remains unclear.

PURPOSE

This study investigated whether icariin could inhibit PCa bone metastasis and destruction by modulating the bone TME as well as the underlying mechanisms.

METHODS

Osteoclasts were induced from mouse bone marrow-derived macrophages (BMMs) or Raw264.7 cells. PCa cells were cultured in the conditional medium (CM) of macrophages in vitro or co-injected with macrophages in vivo to simulate their coexistence in the TME. Multiple molecular biology experiments and the mouse RM1-Luc PCa bone metastasis model were used to explore the inhibitory activity and mechanism of icariin on PCa metastasis and bone destruction.

RESULTS

Icariin treatment significantly suppressed PCa growth, bone metastasis and destruction as well as osteoclastogenesis in vivo. Furthermore, icariin remarkably inhibited osteoclast differentiation, even in the presence of the CM of tumor-associated macrophages (TAMs), while exhibiting no obvious effect on osteoblasts. Moreover, icariin suppressed the M2 phenotype polarization of Raw264.7-derived TAMs and transcriptionally attenuated their CC motif chemokine ligand 5 (CCL5) expression and secretion via inhibiting SPI1. Additionally, CCL5 induced the differentiation and chemotaxis of osteoclast precursor cells by binding with its receptor CCR5. The clinicopathological analysis further verified the positive correlation between the TAM/CCL5/CCR5 axis and osteoclastogenesis within the TME of PCa patients. More importantly, icariin remarkably suppressed PCa metastasis-induced bone destruction in vivo by inhibiting osteoclastogenesis via downregulating the TAM/CCL5 pathway.

CONCLUSION

Altogether, these results not only implicate icariin as a promising candidate immunomodulator for PCa bone metastasis and destruction but also shed novel insight into targeting TAM/CCL5-mediated osteoclastogenesis as a potential treatment strategy for osteolytic bone metastasis. This study helps to advance the understanding of the crosstalk between bone TME and bone homeostasis.

FHL2 regulates microglia M1/M2 polarization after spinal cord injury via PARP14-depended STAT1/6 pathway

Neuronal apoptosis and inflammation exacerbate the secondary injury after spinal cord injury (SCI). Four and a half domains 2 (FHL2) is a multifunctional scaffold protein with tissue- and cell-type specific effects on the regulation of inflammation, but its role in SCI remains unclear. The T10 mouse spinal cord contusion model was established, and the mice were immediately injected with lentiviruses carrying FHL2 shRNA after SCI. The results showed that FHL2 expression was increased following SCI, and then gradually decreased. Moreover, FHL2 depletion aggravated functional impairment, neuronal necrosis, and enlarged lesion cavity areas in the injured spinal cord. FHL2 deficiency facilitated neuronal apoptosis by elevating cleaved caspase 3/9 expression, neuroinflammation by regulating microglia polarization, and bone loss. Indeed, FHL2 deficiency increased the secretion of TNF-α and IL-6, M1 microglia polarization, and the activation of STAT1 pathway but decreased the secretion of IL-10 and IL-4, M2 microglia polarization, and the activation of the STAT6 pathway in the spinal cord. In vitro, FHL2 silencing promoted LPS + IFN-γ-induced microglia M1 polarization through activating the STAT1 pathway and alleviated IL-4-induced microglia M2 polarization via inhibiting the STAT6 pathway. FHL2 positively regulated the expression of poly (ADP-ribose) polymerase family member 14 (PARP14) by promoting its transcription. PARP14 overexpression inhibited FHL2 silencing-induced microglia M1 polarization and relieved the inhibitory effect of FHL2 silencing on microglia M2 polarization. Collectively, the study suggests that FHL2 reduces the microglia M1/M2 polarization-mediated inflammation via PARP14-dependent STAT1/6 pathway and thereby improves functional recovery after SCI.

Combined Molybdenum Gelatine Methacrylate Injectable Nano-Hydrogel Effective Against Diabetic Bone Regeneration

Introduction

Bone defects in diabetes mellitus (DM) remain a major challenge for clinical treatment. Fluctuating glucose levels in DM patients lead to excessive production of reactive oxygen species (ROS), which disrupt bone repair homeostasis. Bone filler materials have been widely used in the clinical treatment of DM-related bone defects, but overall they lack efficacy in improving the bone microenvironment and inducing osteogenesis. We utilized a gelatine methacrylate (GelMA) hydrogel with excellent biological properties in combination with molybdenum (Mo)-based polyoxometalate nanoclusters (POM) to scavenge ROS and promote osteoblast proliferation and osteogenic differentiation through the slow-release effect of POM, providing a feasible strategy for the application of biologically useful bone fillers in bone regeneration.

Methods

We synthesized an injectable hydrogel by gelatine methacrylate (GelMA) and POM. The antioxidant capacity and biological properties of the synthesized GelMA/POM hydrogel were tested.

Results

In vitro, studies showed that hydrogels can inhibit excessive reactive oxygen species (ROS) and reduce oxidative stress in cells through the beneficial effects of pH-sensitive POM. Osteogenic differentiation assays showed that GelMA/POM had good osteogenic properties with upregulated expression of osteogenic genes (BMP2, RUNX2, Osterix, ALP). Furthermore, RNA-sequencing revealed that activation of the PI3K/Akt signalling pathway in MC3T3-E1 cells with GelMA/POM may be a potential mechanism to promote osteogenesis. In an in vivo study, radiological and histological analyses showed enhanced bone regeneration in diabetic mice, after the application of GelMA/POM.

Conclusion

In summary, GelMA/POM hydrogels can enhance bone regeneration by directly scavenging ROS and activating the PI3K/Akt signalling pathway.

Immunoglobulin G inhibits glucocorticoid-induced osteoporosis through occupation of FcγRI

Glucocorticoid-induced osteoporosis (GIOP) is a severe and common complication of long-term usage of glucocorticoids (GCs) and lacks of efficient therapy. Here, we investigated the mechanism of anti-inflammation effect and osteoclastogenesis side effect of GCs and immunoglobulin G (IgG) treatment against GIOP. GCs inhibited SLE IgG-induced inflammation, while IgG inhibited GCs-induced osteoclastogenesis. FcγRI and glucocorticoid receptor (GR) were found directly interacted with each other. GCs and IgG could reduce the expression of FcγRI on macrophages. The deficiency of FcγRI affected osteoclastogenesis by GCs and systemic lupus erythematosus (SLE) IgG-induced inflammation. Also, IgG efficiently reduced GIOP in mice. These data showed that GCs could induce osteoporosis and inhibit IgG-induced inflammation through FcγRI while IgG efficiently suppressed osteoporosis induced by GCs through FcγRI. Hence, our findings may help in developing a feasible therapeutic strategy against osteoporosis, such as GIOP.

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.

Dihydrotanshinone I attenuates estrogen-deficiency bone loss through RANKL-stimulated NF-κB, ERK and NFATc1 signaling pathways

Postmenopausal osteoporosis, a chronic condition that predominantly affects postmenopausal women, presents a significant impediment to their overall well-being. The condition arises from estrogen deficiency, leading to enhanced osteoclast activity. Salvia miltiorrhiza, a well-established Chinese herbal medicine with a history of clinical use for osteoporosis treatment, contains diverse active constituents that have shown inhibitory effects on osteoclast formation and bone loss. Dihydrotanshinone I (DTI), a phenanthrenonequinone compound derived from the root of Salvia miltiorrhiza, has been identified as a potential therapeutic agent, although its mechanism of action on osteoclasts remains elusive. In this study, we aimed to elucidate the inhibitory potential of DTI on RANKL-induced osteoclastogenesis. We observed the ability of DTI to effectively impede the expression of key osteoclast-specific genes and proteins, as assessed by Real-time PCR and Western Blotting analyses. Mechanistically, DTI exerted its inhibitory effects on osteoclast formation by modulating critical signaling pathways including NF-κB, ERK, and calcium ion signaling. Notably, DTI intervention disrupted the nuclear translocation and subsequent transcriptional activity of the NFATc1, thus providing mechanistic insights into its inhibitory role in osteoclastogenesis. To further assess the therapeutic potential of DTI, we employed an ovariectomized osteoporosis animal model to examine its impact on bone loss. Encouragingly, DTI demonstrated efficacy in mitigating bone loss induced by estrogen deficiency. In conclusion, our investigation elucidates the ability of DTI to regulate multiple signaling pathways activated by RANKL, leading to the inhibition of osteoclast formation and prevention of estrogen-deficiency osteoporosis. Consequently, DTI emerges as a promising candidate for the treatment of osteoporosis.

MT2 INHIBITS OSTEOCLASTOGENESIS BY SCAVENGING ROS

Context and objective

Reactive oxygen species (ROS) produced under oxidative stress is important for osteoclastogenesis. As a major member of the metallothionein (MT) family, metallothionein2 (MT2) can scavenge ROS in osteoblasts. However, the role of MT2 in osteoclastogenesis and ROS production in osteoclast precursors (OCPs) is unknown.

Material and methods

In this study, we first investigated MT2 expression level in osteoporotic model mice. Next, we explored the roles of MT2 in osteoclastic differentiation and ROS production in OCPs. Ultimately, via rescue assays based on hydrogen peroxide (H2O2), the significance of ROS in MT-2-regulated osteoclastic differentiation was further elucidated.

Results

Compared with sham operated (Sham) mice, ovariectomized (OVX) mice displayed bone marrow primary OCPs (Ly6C+CD11b-) having higher ROS levels and lower MT2 expression. MT2 overexpression inhibited the formation of mature osteoclasts, while MT2 knockdown was contrary. Moreover, MT2 overexpression inhibited ROS production in OCPs, while MT2 knockdown exhibited the opposite effects. Notably, the inhibitory effect of MT2 overexpression on osteoclastogenesis and ROS production was blocked by the addition of H2O2.

Conclusion

MT2 inhibits osteoclastogenesis through repressing ROS production in OCPs, which indicates that the strategy of upregulating MT2 in OCPs may be applied to the clinical treatment of osteoclastic bone loss.

Pteryxin suppresses osteoclastogenesis and prevents bone loss via inhibiting the MAPK/Ca2+ signaling pathways mediated by ROS

Osteoporosis, as a severe public health problem worldwide, causes systemic damage to bone mass, strength, and microstructure with an increased propensity for fragility fractures. Given the inherent adverse effects associated with long-term use of current prescription medications for osteoporosis treatment, identifying natural alternatives to existing treatment methods is imperative. Pteryxin (PTX), a natural coumarin, is isolated from the Peucedanum species belonging to the family Apiaceae. PTX has been reported to have antioxidant, anti-inflammatory and anti-obesity properties. However, its effect on osteoporosis has not been clarified. Our study confirmed that PTX could attenuate the formation of osteoclasts and bone resorption on a dose-dependent basis in vitro. Consistently, in vivo ovariectomy (OVX)-induced osteoporosis models simulating the physiological characteristics of postmenopausal women showed that PTX could partially reverse the bone loss caused by OVX. Further study of its mechanism revealed that PTX might block the MAPK and Ca2+-calcineurin-NFATc1 signaling pathways by decreasing the reactive oxygen species (ROS) level in osteoclasts to dampen the expression of critical transcriptional NFATc1 and downstream osteoclast-specific genes. Overall, PTX may present a new or alternative treatment option for osteoporosis.

Dragon blood resin ameliorates steroid-induced osteonecrosis of femoral head through osteoclastic pathways

Objective: Dragon's Blood resin (DBR) is a traditional medicinal substance renowned for its diverse pharmacological effects, which consists of potent anti-inflammatory, antioxidant and angiogenic properties. This study aimed to elucidate its therapeutic mechanism in alleviating steroid-induced osteonecrosis of the femoral head (SIONFH). Methods: Techniques such as SPR and LC-MS were employed to identify and analyze the target proteins of DBR in bone marrow macrophages (BMMs). In vitro, BMMs were treated with RANKL and DBR, and TRAcP staining and actin belt staining were utilized to assess osteoclast activity. The inhibitory effects and underlying mechanisms of DBR on osteoclastogenesis and reactive oxygen species (ROS) generation were determined using real-time PCR, western blotting and immunofluorescence staining. An in vivo SIONFH rat model was set up to assess the curative impacts of DBR using micro-CT scanning and pathological staining. Results: Bioinformatic tools revealed a pivotal role of osteoclast differentiation in SIONFH. Proteomic analysis identified 164 proteins binding in BMMs. In vitro assessments demonstrated that DBR hindered osteoclastogenesis by modulating the expression of specific genes and proteins, along with antioxidant proteins including TRX1 and Glutathione Reductase. Notably, the resin effectively inhibited the expression of crucial proteins, such as the phosphorylation of JNK and the nuclear localization of p65 within the TRAF6/JNK and NFκB signaling pathways. In vivo experiments further confirmed that DBR mitigated the onset of SIONFH in rats by curbing osteoclast and ROS activities. Conclusion: These findings underscore the potential of Dragon's Blood as an effective administration for early-stage SIONFH, shedding light on its therapeutic influence on ROS-mediated osteoclastic signaling pathways.

CUL4A-mediated ZEB1/microRNA-340-5p/HMGB1 axis promotes the development of osteoporosis

Understanding the molecular mechanisms underlying osteoclast differentiation provides insights into bone loss and even osteoporosis. The specific mechanistic actions of cullin 4A (CUL4A) in osteoclast differentiation and resultant osteoporosis is poorly explored. We developed a mouse model of osteoporosis using bilateral ovariectomy (OVX) and examined CUL4A expression. It was noted that CUL4A expression was increased in the bone marrow of OVX mice. Overexpression of CUL4A promoted osteoclast differentiation, and knockdown of CUL4A alleviated osteoporosis symptoms of OVX mice. Bioinformatic analyses were applied to identify the downstream target genes of microRNA-340-5p (miR-340-5p), followed by interaction analysis. The bone marrow macrophages (BMMs) were isolated from femur of OVX mice, which were transfected with different plasmids to alter the expression of CUL4A, Zinc finer E-box binding homeobox 1 (ZEB1), miR-340-5p, and Toll-like receptor 4 (TLR4). ChIP assay was performed to detect enrichment of ZEB1 promoter by H3K4me3 antibody in BMMs. ZEB1 was overexpressed in the bone marrow of OVX mice. Overexpression of CUL4A mediated H3K4me3 methylation to increase ZEB1 expression, thus promoting osteoclast differentiation. Meanwhile, ZEB1 could inhibit miR-340-5p expression and upregulate HMGB1 to induce osteoclast differentiation. Overexpressed ZEB1 activated the TLR4 pathway by regulating the miR-340-5p/HMGB1 axis to induce osteoclast differentiation, thus promoting the development of osteoporosis. Overall, E3 ubiquitin ligase CUL4A can upregulate ZEB1 to repress miR-340-5p expression, leading to HMGB1 upregulation and the TLR4 pathway activation, which promotes osteoclast differentiation and the development of osteoporosis.

ER Stress, the Unfolded Protein Response and Osteoclastogenesis: A Review

Endoplasmic reticulum (ER) stress and its adaptive mechanism, the unfolded protein response (UPR), are triggered by the accumulation of unfolded and misfolded proteins. During osteoclastogenesis, a large number of active proteins are synthesized. When an imbalance in the protein folding process occurs, it causes osteoclasts to trigger the UPR. This close association has led to the role of the UPR in osteoclastogenesis being increasingly explored. In recent years, several studies have reported the role of ER stress and UPR in osteoclastogenesis and bone resorption. Here, we reviewed the relevant literature and discussed the UPR signaling cascade response, osteoclastogenesis-related signaling pathways, and the role of UPR in osteoclastogenesis and bone resorption in detail. It was found that the UPR signal (PERK, CHOP, and IRE1-XBP1) promoted the expression of the receptor activator of the nuclear factor-kappa B ligand (RANKL) in osteoblasts and indirectly enhanced osteoclastogenesis. IRE1 promoted osteoclastogenesis via promoting NF-κB, MAPK signaling, or the release of pro-inflammatory factors (IL-6, IL-1β, and TNFα). CREBH promoted osteoclast differentiation by promoting NFATc1 expression. The PERK signaling pathway also promoted osteoclastogenesis through NF-κB and MAPK signaling pathways, autophagy, and RANKL secretion from osteoblasts. However, salubrinal (an inhibitor of eIF2α dephosphorylation that upregulated p-eIF2α expression) directly inhibited osteoclastogenesis by suppressing NFATc1 expression and indirectly promoted osteoclastogenesis by promoting RANKL secretion from osteoblasts. Therefore, the specific effects and mechanisms of p-PERK and its downstream signaling on osteoclastogenesis still need further experiments to confirm. In addition, the exact role of ATF6 and BiP in osteoclastogenesis also required further exploration. In conclusion, our detailed and systematic review provides some references for the next step to fully elucidate the relationship between UPR and osteoclastogenesis, intending to provide new insights for the treatment of diseases caused by osteoclast over-differentiation, such as osteoporosis.