c-Fos: a key regulator of osteoclast-macrophage lineage determination and bone remodeling

Xenoextracellular matrix-rosiglitazone complex-mediated immune evasion promotes xenogenic bioengineered root regeneration by altering M1/M2 macrophage polarization

Xenogenic extracellular matrix (xECM)-based organ transplantation will be a promising approach to address the problem of donor shortage for allotransplantation, which has achieved great success in organ regeneration. However, current approaches to utilize xECM-based organ have limited capacity to yield the host a biofriendly microenvironment for long-term immunity homeostasis, compromising the application of these xenografts for repairing and replacing damaged tissues. As the key innate immune cells, macrophages directly determine the prognosis of xenografts in long term. However, it has not been fully elucidated that how to modulate their biological behavior for microenvironment homeostasis in tissue reconstruction. In this study, we report a robust strategy to impart an immunosuppressive surface to naturally sponge-like porous xECM scaffolds by loading rosiglitazone (RSG) to activate peroxisome proliferators receptors-γ (PPAR-γ). The resultant xECM-RSG complex, enabling RSG to be delivered sequentially and continuously to cells without obvious systemic side effects, is recognized as "self" to escape immune monitoring in local immunoregulation by downregulating the expression of proinflammatory NOS2+ M1 macrophages and oxygen species (ROS) through suppressing NF-κB expression, greatly facilitating the regeneration of enthesis anchoring between the transplanted xenograft and host in both heterotopic and orthotopic models. The newly formed bio-root is morphologically and biomechanically equivalent to native tooth root with a significant expression of odontogenic differentiation-related critical proteins. Therefore, the PPAR-γ-NF-κB axis activated by the xECM-RSG complex enables the xenografts to converse towards M2 macrophages with a modest immunosuppressive capacity for facilitating in xECM-based tissue or organ regeneration.

RANKL-Induced Btn2a2 - A T Cell Immunomodulatory Molecule - During Osteoclast Differentiation Fine-Tunes Bone Resorption

Butyrophilins, which are members of the extended B7 family of immunoregulators structurally related to the B7 family, have diverse functions on immune cells as co-stimulatory and co-inhibitory molecules. Despite recent advances in the understanding on butyrophilins' role on adaptive immune cells during infectious or autoimmune diseases, nothing is known about their role in bone homeostasis. Here, we analyzed the role of one specific butyrophilin, namely Btn2a2, as we have recently shown that Btn2a2 is expressed on the monocyte/macrophage lineage that also gives rise to bone degrading osteoclasts. We found that expression of Btn2a2 on monocytes and pre-osteoclasts is upregulated by the receptor activator of nuclear factor κ-B ligand (RANKL), an essential protein required for osteoclast formation. Interestingly, in Btn2a2-deficient osteoclasts, typical osteoclast marker genes (Nfatc1, cathepsin K, TRAP, and RANK) were downregulated following RANKL stimulation. In vitro osteoclast assays resulted in decreased TRAP positive osteoclast numbers in Btn2a2-deficient cells. However, Btn2a2-deficient osteoclasts revealed abnormal fusion processes shown by their increased size. In vivo steady state µCT and histological analysis of bone architecture in complete Btn2a2-deficient mice showed differences in bone parameters further highlighting the fine-tuning effect of BTN2a2. Moreover, in rheumatoid arthritis patients and experimental arthritis, we detected significantly decreased serum levels of the secreted soluble Btn2a2 protein. Taken together, we identified the involvement of the immunomodulatory molecule Btn2a2 in osteoclast differentiation with potential future implications in basic and translational osteoimmunology.

Effects of Melandrium firmum Rohrbach on RANKL‑induced osteoclast differentiation and OVX rats

Osteoporosis is a systemic skeletal disease characterized by reduced bone mineral density (BMD), which results in an increased risk of fracture. Melandrium firmum (Siebold & Zucc.) Rohrbach (MFR), 'Wangbulryuhaeng' in Korean, is the dried aerial portion of Melandrii Herba Rohrbach, which is a member of the Caryophyllaceae family and has been used to treat several gynecological conditions as a traditional medicine. However, to the best of our knowledge, the effect of MFR on osteoclast differentiation and osteoporosis has not been assessed. To evaluate the effects of MFR on osteoclast differentiation, tartrate‑resistant acid phosphatase staining, actin ring formation and bone resorption assays were used. Additionally, receptor activator of nuclear factor‑κB ligand‑induced expression of nuclear factor of activated T cell, cytoplasmic 1 (NFATc1) and c‑Fos were measured using western blotting and reverse transcription‑PCR. The expression levels of osteoclast‑related genes were also examined. To further investigate the anti‑osteoporotic effects of MFR in vivo, an ovariectomized (OVX) rat model of menopausal osteoporosis was established. Subsequently, the femoral head was scanned using micro‑computed tomography. The results revealed that MFR suppressed osteoclast differentiation, formation and function. Specifically, MFR reduced the expression levels of osteoclast‑related genes by downregulating transcription factors, such as NFATc1 and c‑Fos. Consistent with the in vitro results, administration of MFR water extract to OVX rats reduced BMD loss, and reduced the expression levels of NFATc1 and cathepsin K in the femoral head. In conclusion, MFR may contribute to alleviate osteoporosis‑like symptoms. These results suggested that MFR may exhibit potential for the prevention and treatment of postmenopausal osteoporosis.

Fenugreek steroidal saponins hinder osteoclastogenic bone resorption by targeting CSF-1R which diminishes the RANKL/OPG ratio

Osteoporosis is skeletal fragility caused by the excessive bone resorption due to osteoclastogenesis. But current drugs are less bioavailable and possess higher toxicity. Our study was conducted to identify safe oral bioavailable drugs from Fenugreek steroidal saponins and to delineate underlying mechanism of them to lower the osteoclastogenic bone resorption. We observed higher molecular docked binding affinities in finally selected eight hit compounds within the range of -11.0 to -10.1 kcal/mol which was greater than currently used drugs. Molecular Dynamics simulation with Root Mean Square Deviation (RMSD), Root Mean Square Fluctuation (RMSF), Solvent Accessible Surface Area (SASA) and Gyration trajectory projection reinforced the stability of the protein-ligand complexes. Pharmacokinetics analysis confirmed bioavailability of seven compounds out of eight, and drug likeliness and bioavailability profile evaluation indicated that they all are eligible to be developed as a potent oral inhibitor of CSF-1R. By literature mining knowledge-driven analysis, RNAseq data and Molecular Dynamics Simulation, we proposed that, the hit derivatives block the CSF-1/CSF-1R induced phosphorylation signaling pathway in both osteoclast and osteoblast resulting in hindrance of RANK expression and formation of Reactive oxygen species (ROS) in osteoclast and osteoblast respectively, thus declines the RANKL/OPG ratio, lowering the osteoclast survival, proliferation and differentiation.

Hinokitiol inhibits RANKL-induced osteoclastogenesis in vitro and prevents ovariectomy-induced bone loss in vivo

Osteoporosis is a metabolic bone-loss disease characterized by abnormally excessive osteoclast formation and bone resorption. Identification of natural medicines that can inhibit osteoclastogenesis, bone resorption, and receptor activator of nuclear factor-κB ligand (RANKL)-induced signaling is necessary for improved treatment of osteoporosis. In this study, hinokitiol, a tropolone-related compound extracted from the heart wood of several cupressaceous plants, was found to inhibit RANKL-induced osteoclast formation and bone resorption in vitro. Hinokitiol inhibited early activation of the ERK, p38, and JNK-MAPK pathways, thereby suppressing the activity and expression of downstream factors (c-Jun, c-Fos, and NFATC1). Consistent with the above in vitro findings, hinokitiol treatment protected against ovariectomy-induced bone loss in vivo. Collectively, our results imply that hinokitiol can potentially serve as an effective agent for treating osteoclast-induced osteoporosis.

Flunarizine inhibits osteoclastogenesis by regulating calcium signaling and promotes osteogenesis

Many bone diseases such as osteoporosis and periodontitis are caused by hyperactivation of osteoclasts. Calcium (Ca²⁺ ) signals are crucial for osteoclast differentiation and function. Thus, the blockade of Ca²⁺ signaling may be a strategy for regulating osteoclast activity and has clinical implications. Flunarizine (FN) is a Ca²⁺ channel antagonist that has been used for reducing migraines. However, the role of FN in osteoclast differentiation and function remains unknown. Here, we investigated whether FN regulates osteoclastogenesis and elucidated the molecular mechanism. FN inhibited osteoclast differentiation along with decreased expression of nuclear factor of activated T cells, cytoplasmic 1 (NFATc1), and attenuated osteoclast maturation and bone resorption. FN inhibition of osteoclast differentiation was restored by ectopic expression of constitutively active NFATc1. FN reduced calcium oscillations and its inhibition of osteoclast differentiation and resorption function was reversed by ionomycin, an ionophore that binds Ca²⁺ . FN also inhibited Ca²⁺ /calmodulin-dependent protein kinase IV (CaMKIV) and calcineurin leading to a decrease in the cAMP-responsive element-binding protein-dependent cFos and peroxisome proliferator-activated receptor-γ coactivator 1β expression, and NFATc1 nuclear translocation. These results indicate that FN inhibits osteoclastogenesis via regulating CaMKIV and calcineurin as a Ca²⁺ channel blocker. In addition, FN-induced apoptosis in osteoclasts and promoted osteogenesis. Furthermore, FN protected lipopolysaccharide- and ovariectomy-induced bone destruction in mouse models, suggesting that it has therapeutic potential for treating inflammatory bone diseases and postmenopausal osteoporosis.

Phenotypic Plasticity in Vertebrate Dentitions

Vertebrates interact directly with food items through their dentition, and these interactions with trophic resources could often feedback to influence tooth structure. Although dentitions are often considered to be a fixed phenotype, there is the potential for environmentally induced phenotypic plasticity in teeth to extensively influence their diversity. Here, we review the literature concerning phenotypic plasticity of vertebrate teeth. Even though only a few taxonomically disparate studies have focused on phenotypic plasticity in teeth, there are a number of ways teeth can change their size, shape, or patterns of replacement as a response to the environment. Elucidating the underlying physiological, developmental, and genetic mechanisms that generate phenotypic plasticity can clarify its potential role in the evolution of dental phenotypes.

Sesamolin Protects Mice From Ovariectomized Bone Loss by Inhibiting Osteoclastogenesis and RANKL-Mediated NF-κB and MAPK Signaling Pathways

This article was submitted to Experimental Pharmacology and Drug Discovery, a section of the journal Frontiers in Pharmacology. Postmenopausal osteoporosis (PMOP), which increases the risk of fracture, is the most common bone disease in women. PMOP not only increases the risk of death but also imposes a financial burden on countless families. At present, most of the drugs used to treat osteoporosis have significant side effects, so it is important to find effective anti-osteoporosis medications without major side effects. Sesamolin (Ses) is a kind of natural lignan extracted from sesame oil. Many researches have shown that Ses has anti-inflammatory, antioxidative, and anticancer effects, however it is still unknown whether it has any effect on osteoporosis. In this research, we explored the therapeutic effect of Ses in the process of osteoclast formation and bone resorption and found that Ses effectively inhibited osteoclast formation in vitro through TRAcP staining and hydroxyapatite resorption assays. Through Western blot analysis of the NF-κB pathway, MAPK pathway, c-Fos and NFATc1, it was found that Ses not only effectively inhibited the activation of NF-κB and MAPK signaling pathways induced by RANKL but also significantly reduced the protein expression of c-Fos and NFATc1. Several genes specifically expressed in osteoclasts were determined by qPCR, and Ses was also found to play a significant inhibitory role on the expression of these genes. Besides, an osteoporosis model induced in ovariectomized (OVX) mice was employed to verify that Ses could effectively reduce bone loss caused by estrogen deficiency in vivo. In conclusion, Ses showed promise as a new treatment for postmenopausal osteoporosis.

Celastrol Attenuates RANKL-Induced Osteoclastogenesis in vitro and Reduces Titanium Particle-Induced Osteolysis and Ovariectomy-Induced Bone Loss in vivo

Excessive bone resorption by osteoclasts contributes significantly to osteoclast-related diseases such as periprosthetic osteolysis and osteoporosis. Osteolysis in a titanium particle-induced calvarial model and bone loss in an ovariectomized mice model occurred similarly to those in humans; thus, these models can be used to evaluate potential therapies for aseptic prosthetic loosening and osteoporosis. Celastrol, which is extracted from the seeds of the genus Tripterygium, has been thoroughly investigated for its anti-inflammatory and anti-cancer pharmacological effects. However, the mechanisms involving bone metabolism by which celastrol inhibits osteoclastogenesis are not yet fully understood. We demonstrated that celastrol inhibited the receptor activator of nuclear factor κB ligand-induced osteoclastogenesis and the bone resorptive function of osteoclasts in vitro by inhibiting the activation of transforming growth factor β-activated kinase 1-mediated NF-κB and mitogen-activated protein kinase signaling pathways and downregulating osteoclastogenesis marker-related genes. Furthermore, celastrol was also shown to be beneficial in both the titanium particle-induced osteolysis calvarial and the murine ovariectomy-induced bone loss. Collectively, our results suggested that celastrol is promising for the prevention of aseptic prosthetic loosening and osteoporosis in the treatment of osteolytic diseases induced by disrupted osteoclast formation and function.

Celastrol Attenuates RANKL-Induced Osteoclastogenesis in vitro and Reduces Titanium Particle-Induced Osteolysis and Ovariectomy-Induced Bone Loss in vivo

Excessive bone resorption by osteoclasts contributes significantly to osteoclast-related diseases such as periprosthetic osteolysis and osteoporosis. Osteolysis in a titanium particle-induced calvarial model and bone loss in an ovariectomized mice model occurred similarly to those in humans; thus, these models can be used to evaluate potential therapies for aseptic prosthetic loosening and osteoporosis. Celastrol, which is extracted from the seeds of the genus Tripterygium, has been thoroughly investigated for its anti-inflammatory and anti-cancer pharmacological effects. However, the mechanisms involving bone metabolism by which celastrol inhibits osteoclastogenesis are not yet fully understood. We demonstrated that celastrol inhibited the receptor activator of nuclear factor κB ligand-induced osteoclastogenesis and the bone resorptive function of osteoclasts in vitro by inhibiting the activation of transforming growth factor β-activated kinase 1-mediated NF-κB and mitogen-activated protein kinase signaling pathways and downregulating osteoclastogenesis marker-related genes. Furthermore, celastrol was also shown to be beneficial in both the titanium particle-induced osteolysis calvarial and the murine ovariectomy-induced bone loss. Collectively, our results suggested that celastrol is promising for the prevention of aseptic prosthetic loosening and osteoporosis in the treatment of osteolytic diseases induced by disrupted osteoclast formation and function.

ZhiJingSan Inhibits Osteoclastogenesis via Regulating RANKL/NF-κB Signaling Pathway and Ameliorates Bone Erosion in Collagen-Induced Mouse Arthritis

Bone erosion is the most evident pathological condition of rheumatoid arthritis (RA), which is the main cause of joint deformities and disability in RA patients. At present, the conventional RA drugs have not achieved satisfactory effect in improving bone erosion. ZhiJingSan (ZJS), which is a traditional Chinese prescription composed of scolopendra (dried body of Scolopendra subspinipes mutilans L. Koch, scolopendridae) and scorpion (dried body of Buthus martensii Karsch, Buthus), exhibits anti-rheumatism, analgesic and joint deformities improvement effects. This study aimed to assess the therapeutic effect of ZJS on RA bone erosion and to elucidate the underlying mechanism. The effect of ZJS on RA bone erosion was investigated in a murine model of bovine collagen-induced arthritis (CIA), and the underlying mechanism was investigated in vitro in an osteoclast differentiation cell model. Administration of ZJS delayed the onset of arthritis, alleviated joint inflammation, and attenuated bone erosion in the CIA mice. Meanwhile, ZJS decreased the serum levels of TNF-α, IL-6, and anti-bovine collagen II-specific antibodies. Furthermore, ZJS treatment reduced the number of osteoclasts and the expression of cathepsin K in the ankle joints of CIA mice. ZJS also inhibited receptor activator of NF-κB ligand (RANKL)-induced osteoclast differentiation and the expression of MMP9 and cathepsin K in vitro. Mechanistically, ZJS blocked RANKL-induced p65 phosphorylation, nucleation, and inhibited the expression of downstream NFATc1 and c-Fos in bone marrow-derived macrophages (BMMs). Taken together, ZJS exerts a therapeutic effect on bone erosion in CIA mice by inhibiting RANKL/NF-κB-mediated osteoclast differentiation, which suggested that ZJS is a promising prescription for treating RA bone erosion.

The Role of AP-1 Transcription Factors in Plasma Cell Biology and Multiple Myeloma Pathophysiology

Multiple myeloma (MM) is an incurable hematologic malignancy characterized by the clonal expansion of malignant plasma cells within the bone marrow. Activator Protein-1 (AP-1) transcription factors (TFs), comprised of the JUN, FOS, ATF and MAF multigene families, are implicated in a plethora of physiologic processes and tumorigenesis including plasma cell differentiation and MM pathogenesis. Depending on the genetic background, the tumor stage, and cues of the tumor microenvironment, specific dimeric AP-1 complexes are formed. For example, AP-1 complexes containing Fra-1, Fra-2 and B-ATF play central roles in the transcriptional control of B cell development and plasma cell differentiation, while dysregulation of AP-1 family members c-Maf, c-Jun, and JunB is associated with MM cell proliferation, survival, drug resistance, bone marrow angiogenesis, and bone disease. The present review article summarizes our up-to-date knowledge on the role of AP-1 family members in plasma cell differentiation and MM pathophysiology. Moreover, it discusses novel, rationally derived approaches to therapeutically target AP-1 TFs, including protein-protein and protein-DNA binding inhibitors, epigenetic modifiers and natural products.

Oridonin ameliorates inflammation-induced bone loss in mice via suppressing DC-STAMP expression

Currently, dendritic cell-specific transmembrane protein (DC-STAMP), a multipass transmembrane protein, is considered as the master regulator of cell-cell fusion, which underlies the formation of functional multinucleated osteoclasts. Thus, DC-STAMP has become a promising target for osteoclast-associated osteolytic diseases. In this study, we investigated the effects of oridonin (ORI), a natural tetracyclic diterpenoid compound isolated from the traditional Chinese herb Rabdosia  rubescens, on osteoclastogenesis in vivo and ex vivo. ICR mice were injected with LPS (5 mg/kg, ip, on day 0 and day 4) to induce inflammatory bone destruction. Administration of ORI (2, 10 mg·kg^-1·d^-1, ig, for 8 days) dose dependently ameliorated inflammatory bone destruction and dramatically decreased DC-STAMP protein expression in BMMs isolated from LPS-treated mice. Treatment of preosteoclast RAW264.7 cells with ORI (0.78-3.125 μM) dose dependently inhibited both mRNA and protein levels of DC-STAMP, and suppressed the following activation of NFATc1 during osteoclastogenesis. Knockdown of DC-STAMP in RAW264.7 cells abolished the inhibitory effects of ORI on RANKL-induced NFATc1 activity and osteoclast formation. In conclusion, we show for the first time that ORI effectively attenuates inflammation-induced bone loss by suppressing DC-STAMP expression, suggesting that ORI is a potential agent against inflammatory bone diseases.

A novel RANKL-targeted flavonoid glycoside prevents osteoporosis through inhibiting NFATc1 and reactive oxygen species

BACKGROUND AND PURPOSE

Osteoporosis is characterized by excessive bone resorption due to enhanced osteoclast activation. Stimulation of nuclear factor of activated T cells 1 (NFATc1) and accumulation of reactive oxygen species (ROS) are important mechanisms underlying osteoclastogenesis. Robinin (Rob) is a flavonoid glycoside that has shown anti-inflammatory and antioxidative effects in previous studies, but little is known about its effects on bone homeostasis. The purpose of our research was to investigate whether Rob could prevent bone resorption in ovariectomized (OVX) mice by suppressing osteoclast production through its underlying mechanisms.

METHODS

The docking pose of Rob and RANKL was identified by protein-ligand molecular docking. Rob was added to bone marrow macrophages (BMMs) stimulated by nuclear factor-κB (NF-κB) ligand (RANKL). The effects of Rob on osteoclastic activity were evaluated by positive tartrate resistant acid phosphatase (TRAcP) staining kit and hydroxyapatite resorption assay. RANKL-induced ROS generation in osteoclasts was detected by H2 DCFDA and MitoSox Red staining. The classic molecular cascades triggered by RANKL, such as NF-κB, ROS, calcium oscillations, and NFATc1-mediated signaling pathways, were investigated using Fluo4 staining, western blot, and quantitative real-time polymerase chain reaction. In addition, an OVX mouse model mimicking estrogen-deficient osteoporosis was created to evaluate the therapeutic effects of Rob in vivo.

RESULTS

Computational docking results showed that Rob could bind specifically to RANKL's predicted binding sites. In vitro, Rob inhibited RANKL-mediated osteoclastogenesis dose-dependently without obvious cytotoxicity at low concentrations. We also found that Rob attenuated RANKL-induced mitochondrial ROS production or enhanced activities of ROS-scavenging enzymes, and ultimately reduced intracellular ROS levels. Rob abrogated the RANKL-induced mitogen-activated protein kinase (MAPK) and NF-κB signaling pathways, and subsequently blocked NFATc1 signaling and TRAcP expression. In addition, Rob inhibited osteoclast proliferation by downregulating the expression of osteoclast target genes (Acp5, Cathepsin K, Atp6v0d2, Nfact1, c-Fos, and Mmp9) and reducing Ca2+ oscillations. Our in vivo results showed that Rob reduced bone resorption in OVX animal model by repressing osteoclast activity and function.

CONCLUSIONS

Rob inhibits the activation of osteoclasts by targeting RANKL and is therefore a potential osteoporosis drug.

Reprogrammed intestinal functions in Astragalus polysaccharide-alleviated osteoporosis: combined analysis of transcriptomics and DNA methylomics demonstrates the significance of the gut-bone axis in treating osteoporosis

Researchers have noted that organ-organ communication between bone and intestine has significant effects on bone health and its related diseases. In this study, we collected colonic epithelial tissue from dexamethasone-induced osteoporotic rats and Astragalus polysaccharide (APS)-alleviated osteoporotic rats and employed transcriptome sequencing to investigate the functional changes that occurred in the intestine. Principal component analysis showed that both dexamethasone (inducer of osteoporosis) and APS reprogrammed the gene expression profile of the intestine. Further analysis identified 496 and 291 differentially expressed genes (DEGs) in osteoporotic and APS-treated osteoporotic rats, respectively. KEGG enrichment analysis of these DEGs demonstrated osteoporosis-induced intestinal dysfunctions that were further modified by APS treatment. Further analysis demonstrated that APS could restore intestinal functions by reversing the expression of 53 DEGs in osteoporotic rats. Recovery of osteoclast differentiation and the calcium signalling pathway might contribute to the improvement of osteoporosis. Moreover, utilizing methylC-capture sequencing (MCC-Seq), we studied the changes in DNA methylation and performed epigenetic analysis of dexamethasone- and APS-induced gene expression changes. In this study, osteoporosis was observed to cause intestinal dysfunction, which is a complication of this disease. More importantly, APS was determined to reprogram intestinal functions to alleviate osteoporosis via the gut-bone axis. Our results support the existence of a gut-bone axis and suggest new therapeutic opportunities for the treatment of osteoporosis via the gut-bone axis.

Selenoprotein W ensures physiological bone remodeling by preventing hyperactivity of osteoclasts

Selenoproteins containing selenium in the form of selenocysteine are critical for bone remodeling. However, their underlying mechanism of action is not fully understood. Herein, we report the identification of selenoprotein W (SELENOW) through large-scale mRNA profiling of receptor activator of nuclear factor (NF)-κΒ ligand (RANKL)-induced osteoclast differentiation, as a protein that is downregulated via RANKL/RANK/tumour necrosis factor receptor-associated factor 6/p38 signaling. RNA-sequencing analysis revealed that SELENOW regulates osteoclastogenic genes. SELENOW overexpression enhances osteoclastogenesis in vitro via nuclear translocation of NF-κB and nuclear factor of activated T-cells cytoplasmic 1 mediated by 14-3-3γ, whereas its deficiency suppresses osteoclast formation. SELENOW-deficient and SELENOW-overexpressing mice exhibit high bone mass phenotype and osteoporosis, respectively. Ectopic SELENOW expression stimulates cell-cell fusion critical for osteoclast maturation as well as bone resorption. Thus, RANKL-dependent repression of SELENOW regulates osteoclast differentiation and blocks osteoporosis caused by overactive osteoclasts. These findings demonstrate a biological link between selenium and bone metabolism.

Selenoproteins containing selenium have a variety of physiological functions including redox homeostasis and thyroid hormone metabolism. Here, the authors show that RANKL-dependent repression of selenoprotein W regulates cell fusion during osteoclast differentiation and bone remodelling in mice.

Do We Use Methylation of NFATC1 and FOS Genes As a Biomarker for Postmenopausal Osteoporosis?

Genetic and epigenetic factors have an important role during the development of osteoporosis. Receptor activator of nuclear factor-κ B (NF-κB) (RANK)/receptor activator of NF-κB ligand (RANKL) pathway is important for the bone remodeling, and NFATC1 and FOS are the downtargets of this pathway. Here, we report methylation status of NFATC1 and FOS genes in post- and premenopausal women. In this study, 30 premenopausal and 35 postmenopausal women were included. Methylation sensitive-high resolution melting (MS-HRM) analysis was used for identification of NFATC1 and FOS genes methylation. The NFATC1 gene was methylated in 11 of the 35 postmenopausal women, and the FOS gene was methylated in six of the postmenopausal women (p >0.005). Here, we found statistically significant association between unmethylation of the NFATC1 gene and postmenopausal status. This result explains the epigenetic regulation of osteoclasts during the menopausal transition, and for the first time, our results can be used for epigenetic explanation of postmenopausal osteoporosis in the literature. However, the limited number of studies in this field makes our results crucial. Our results showed great value of epigenetic profiles of postmenopausal women.

The Macrophage-Osteoclast Axis in Osteoimmunity and Osteo-Related Diseases

Osteoimmunity is involved in regulating the balance of bone remodeling and resorption, and is essential for maintaining normal bone morphology. The interaction between immune cells and osteoclasts in the bone marrow or joint cavity is the basis of osteoimmunity, in which the macrophage-osteoclast axis plays a vital role. Monocytes or tissue-specific macrophages (macrophages resident in tissues) are an important origin of osteoclasts in inflammatory and immune environment. Although there are many reports on macrophages and osteoclasts, there is still a lack of systematic reviews on the macrophage-osteoclast axis in osteoimmunity. Elucidating the role of the macrophage-osteoclast axis in osteoimmunity is of great significance for the research or treatment of bone damage caused by inflammation and immune diseases. In this article, we introduced in detail the concept of osteoimmunity and the mechanism and regulators of the differentiation of macrophages into osteoclasts. Furthermore, we described the role of the macrophage-osteoclast axis in typical bone damage caused by inflammation and immune diseases. These provide a clear knowledge framework for studying macrophages and osteoclasts in inflammatory and immune environments. And targeting the macrophage-osteoclast axis may be an effective strategy to treat bone damage caused by inflammation and immune diseases.

Crataegus pinnatifida Bunge Inhibits RANKL-Induced Osteoclast Differentiation in RAW 264.7 Cells and Prevents Bone Loss in an Ovariectomized Rat Model

Osteoporosis is characterized by a decrease in bone microarchitecture with an increased risk of fracture. Long-term use of primary treatments, such as bisphosphonates and selective estrogen receptor modulators, results in various side effects. Therefore, it is necessary to develop alternative therapeutics derived from natural products. Crataegus pinnatifida Bunge (CPB) is a dried fruit used to treat diet-induced indigestion, loss of appetite, and diarrhea. However, research into the effects of CPB on osteoclast differentiation and osteoporosis is still limited. In vitro experiments were conducted to examine the effects of CPB on RANKL-induced osteoclast differentiation in RAW 264.7 cells. Moreover, we investigated the effects of CPB on bone loss in the femoral head in an ovariectomized rat model using microcomputed tomography. In vitro, tartrate-resistant acid phosphatase (TRAP) staining results showed the number of TRAP-positive cells, and TRAP activity significantly decreased following CPB treatment. CPB also significantly decreased pit formation. Furthermore, CPB inhibited osteoclast differentiation by suppressing NFATc1, and c-Fos expression. Moreover, CPB treatment inhibited osteoclast-related genes, such as Nfatc1, Ca2, Acp5, mmp9, CtsK, Oscar, and Atp6v0d2. In vivo, bone mineral density and structure model index were improved by administration of CPB. In conclusion, CPB prevented osteoclast differentiation in vitro and prevented bone loss in vivo. Therefore, CPB could be a potential alternative medicine for bone diseases, such as osteoporosis.

Genome-Wide Association Identifies Risk Pathways for SAPHO Syndrome

SAPHO syndrome is a rare chronic inflammatory disease which is characterized by the comprehensive manifestations of bone, joint, and skin. However, little is known about the pathogenesis of SAPHO syndrome. A genome-wide association study (GWAS) of 49 patients and 121 control subjects have primarily focused on identification of common genetic variants associated with SAPHO, the data were analyzed by classical multiple logistic regression. Later, GWAS findings were further validated using whole exome sequencing (WES) in 16 patients and 15 controls to identify potentially functional pathways involved in SAPHO pathogenesis. In general, 40588 SNPs in genomic regions were associated with P < 0.05 after filter process, only 9 SNPs meet the expected cut-off P-value, however, none of them had association with SAPHO syndrome based on published literatures. And then, 15 pathways were found involved in SAPHO pathogenesis, of them, 6 pathways including osteoclast differentiation, bacterial invasion of epithelial cells, et al., had strong association with skin, osteoarticular manifestations of SAPHO or inflammatory reaction based published research. This study identified aberrant osteoclast differentiation and other pathways were involved in SAPHO syndrome. This finding may give insight into the understanding of pathogenic genes of SAPHO and provide the basis for SAPHO research and treatment.

The effect of the WKYMVm peptide on promoting mBMSC secretion of exosomes to induce M2 macrophage polarization through the FPR2 pathway

Background

When multicystic vesicles (precursors of exosomes) are formed in cells, there are two results. One is decomposition by lysosomes, and the other is the generation of exosomes that are transported out through the transmembrane. On the other hand, M2 macrophages promote the formation of local vascularization and provide necessary support for the repair of bone defects. To provide a new idea for the treatment of bone defects, the purpose of our study was to investigate the effect of WKYMVm (Trp-Lys-Tyr-Met-Val-D-Met-NH2) peptide on the secretion of exosomes from murine bone marrow-derived MSCs (mBMSCs) and the effect of exosomes on the polarization of M2 macrophages.

Methods

The WKYMVm peptide was used to activate the formyl peptide receptor 2 (FPR2) pathway in mBMSCs. First, we used Cell Counting Kit-8 (CCK-8) to detect the cytotoxic effect of WKYMVm peptide on mBMSCs. Second, we used western blotting (WB) and quantitative real-time polymerase chain reaction (qRT-PCR) to detect the expression of interferon stimulated gene 15 (ISG15) and transcription factor EB (TFEB) in mBMSCs. Then, we detected lysosomal activity using a lysozyme activity assay kit. Third, we used an exosome extraction kit and western blotting to detect the content of exosomes secreted by mBMSCs. Fourth, we used immunofluorescence and western blotting to count the number of polarized M2 macrophages. Finally, we used an inhibitor to block miRNA-146 in exosomes secreted by mBMSCs and counted the number of polarized M2 macrophages.

Results

We first found that the WKYMVm peptide had no toxic effect on mBMSCs at a concentration of 1 μmol/L. Second, we found that when the FPR2 pathway was activated by the WKYMVm peptide in mBMSCs, ISG15 and TFEB expression was decreased, leading to increased secretion of exosomes. We also found that lysosomal activity was decreased when the FPR2 pathway was activated by the WKYMVm peptide in mBMSCs. Third, we demonstrated that exosomes secreted by mBMSCs promote the polarization of M2 macrophages. Moreover, all these effects can be blocked by the WRWWWW (WRW4, H-Trp-Arg-Trp-Trp-Trp-Trp-OH) peptide, an inhibitor of the FPR2 pathway. Finally, we confirmed the effect of miRNA-146 in exosomes secreted by mBMSCs on promoting the polarization of M2 macrophages.

Conclusion

Our findings demonstrated the potential value of the WKYMVm peptide in promoting the secretion of exosomes by mBMSCs and eventually leading to M2 macrophage polarization. We believe that our study could provide a research basis for the clinical treatment of bone defects.

Selective deletion of the receptor for CSF1, c-fms, in osteoclasts results in a high bone mass phenotype, smaller osteoclasts in vivo and an impaired response to an anabolic PTH regimen

The receptor for Colony Stimulating Factor 1 (CSF1), c-fms, is highly expressed on mature osteoclasts suggesting a role for this cytokine in regulating the function of these cells. Consistent with this idea, in vitro studies have documented a variety of effects of CSF1 in mature osteoclasts. To better define the role of CSF1 in these cells, we conditionally deleted c-fms in osteoclasts (c-fms-OC^-/-) by crossing c-fms^flox/flox mice with mice expressing Cre under the control of the cathepsin K promoter. The c-fms-OC^-/- mice were of normal weight and had normal tooth eruption. However, when quantified by DXA, bone mass was significantly higher in the spine and femur of female knock out mice and in the femurs of male knock out mice. MicroCT analyses of femurs showed that female c-fms-OC^-/- mice had significantly increased trabecular bone mass with a similar trend in males and both sexes demonstrated significantly increased trabecular number and reduced trabecular spacing. Histomorphometric analysis of the femoral trabecular bone compartment demonstrated a trend towards increased numbers of osteoclasts, +26% in Noc/BPm and +22% in OcS/BS in the k/o animals but this change was not significant. However, when the cellular volume of osteoclasts was quantified, the c-fms-OC^-/- cells were found to be significantly smaller than controls. Mature osteoclasts show a marked spreading response when exposed to CSF1 in a non-gradient fashion. However, osteoclasts freshly isolated from c-fms-OC^-/- mice had a near complete abrogation of this response. C-fms-OC^-/- mice treated with (1–34)hPTH 80 ng/kg/d in single daily subcutaneous doses for 29 days showed an attenuated anabolic response in trabecular bone compared to wild-type animals. Taken together, these data indicate an important non-redundant role for c-fms in regulating mature osteoclast function in vivo.

The role of miR-29 family in disease

MicroRNAs are small noncoding RNAs that can bind to the target sites in the 3’‐untranslated region of messenger RNA to regulate posttranscriptional gene expression. Increasing evidence has identified the miR‐29 family, consisting of miR‐29a, miR‐29b‐1, miR‐29b‐2, and miR‐29c, as key regulators of a number of biological processes. Moreover, their abnormal expression contributes to the etiology of numerous diseases. In the current review, we aimed to summarize the differential expression patterns and functional roles of the miR‐29 family in the etiology of diseases including osteoarthritis, osteoporosis, cardiorenal, and immune disease. Furthermore, we highlight the therapeutic potential of targeting members of miR‐29 family in these diseases. We present miR‐29s as promoters of osteoblast differentiation and apoptosis but suppressors of chondrogenic and osteoclast differentiation, fibrosis, and T cell differentiation, with clear avenues for therapeutic manipulation. Further research will be crucial to identify the precise mechanism of miR‐29 family in these diseases and their full potential in therapeutics.

Effects of Probiotic Culture Supernatant on Cariogenic Biofilm Formation and RANKL-Induced Osteoclastogenesis in RAW 264.7 Macrophages

Postbiotics are a promising functional ingredient that can overcome the limitations of viability and storage stability that challenge the production of probiotics. To evaluate the effects of postbiotics on oral health, eight spent culture supernatants (SCSs) of probiotics were prepared, and the effects of SCSs on Streptococcus mutans-induced cariogenic biofilm formation and the receptor activator of the nuclear factor κB ligand (RANKL)-induced osteoclastogenesis were evaluated in RAW 264.7 macrophages. SCS of Lactobacillus salivarius MG4265 reduced S. mutans-induced biofilm formation by 73% and significantly inhibited tartrate-resistant acid phosphatase (TRAP) activity, which is a biomarker of mature osteoclasts in RAW 264.7 macrophages. The suppression of RANKL-induced activation of mitogen activated the protein kinases (c-Jun N-terminal kinase, extracellular signal-regulated kinase, and p38) and nuclear factor κB pathways, as well as the upregulation of heme oxygenase-1 expression. The suppression of RANK-L-induced activation of mitogen also inhibited the expression of transcriptional factors (c-fos and nuclear factor of activated T cells cytoplasmic 1) and, subsequently, osteoclastogenesis-related gene expression (tartrate-resistant acid phosphatase-positive (TRAP), cathepsin K, and matrix metalloproteinase-9).Therefore, SCS of L. salivarius MG4265 has great potential as a multifunctional oral health ingredient that inhibits biofilm formation and suppresses the alveolar bone loss that is associated with periodontitis.

Deletion of phospholipase D1 decreases bone mass and increases fat mass via modulation of Runx2, β-catenin-osteoprotegerin, PPAR-γ and C/EBPα signaling axis

In osteoporosis, mesenchymal stem cells (MSCs) prefer to differentiate into adipocytes at the expense of osteoblasts. Although the balance between adipogenesis and osteogenesis has been closely examined, the mechanism of commitment determination switch is unknown. Here we demonstrate that phospholipase D1 (PLD1) plays a key switch in determining the balance between bone and fat mass. Ablation of Pld1 reduced bone mass but increased fat in mice. Mechanistically, Pld1^/- MSCs inhibited osteoblast differentiaion with diminished Runx2 expression, while osteoclast differentiation was accelerated in Pld1^-/- bone marrow-derived macrophages. Pld1^-/- osteoblasts showed decreased expression of osteogenic makers. Increased number and resorption activity of osteoclasts in Pld1^-/- mice were corroborated with upregulation of osteoclastogenic markers. Moreover, Pld1^-/- osteoblasts reduced β-catenin mediated-osteoprotegerin (OPG) with increased RANKL/OPG ratio which resulted in accelerated osteoclast differentiation. Thus, low bone mass with upregulated osteoclasts could be due to the contribution of both osteoblasts and osteoclasts during bone remodeling. Moreover, ablation of Pld1 further increased bone loss in ovariectomized mice, suggesting that PLD1 is a negative regulator of osteoclastogenesis. Furthermore, loss of PLD1 increased adipogenesis, body fat mass, and hepatic steatosis along with upregulation of PPAR-γ and C/EBPα. Interestingly, adipocyte-specific Pld1 transgenic mice rescued the compromised phenotypes of fat mass and adipogenesis in Pld1 knockout mice. Collectively, PLD1 regulated the bifurcating pathways of mesenchymal cell lineage into increased osteogenesis and decreased adipogenesis, which uncovered a previously unrecognized role of PLD1 in homeostasis between bone and fat mass.

Osteoclast fusion and bone loss are restricted by interferon inducible guanylate binding proteins

Chronic inflammation during many diseases is associated with bone loss. While interferons (IFNs) are often inhibitory to osteoclast formation, the complex role that IFN and interferon-stimulated genes (ISGs) play in osteoimmunology during inflammatory diseases is still poorly understood. We show that mice deficient in IFN signaling components including IFN alpha and beta receptor 1 (IFNAR1), interferon regulatory factor 1 (IRF1), IRF9, and STAT1 each have reduced bone density and increased osteoclastogenesis compared to wild type mice. The IFN-inducible guanylate-binding proteins (GBPs) on mouse chromosome 3 (GBP1, GBP2, GBP3, GBP5, GBP7) are required to negatively regulate age-associated bone loss and osteoclastogenesis. Mechanistically, GBP2 and GBP5 both negatively regulate in vitro osteoclast differentiation, and loss of GBP5, but not GBP2, results in greater age-associated bone loss in mice. Moreover, mice deficient in GBP5 or chromosome 3 GBPs have greater LPS-mediated inflammatory bone loss compared to wild type mice. Overall, we find that GBP5 contributes to restricting age-associated and inflammation-induced bone loss by negatively regulating osteoclastogenesis.

Inhibition of zoledronic acid derivatives with extended methylene linkers on osteoclastogenesis involve downregulation of JNK and Akt pathways

Bisphosphonates (BPs), especially zoledronic acid (ZOL), are clinically used to treat osteolytic bone lesions. However, serious side-effects may be also induced during the therapeutic process. To improve the BPs drugs, here, we investigated the effects of a series of ZOL derivatives with increasing number of methylene linker between the imidazole ring and the P-C-P backbone named IPrDP, IBDP, IPeDP, and IHDP on cell viability and receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast differentiation, function and apoptosis induction in mouse bone marrow-derived macrophages (BMMs). Our results suggested that IPeDP and IHDP, which contains 4 and 5 methylene linkers, respectively, exerted lower toxicity on BMMs compared with ZOL, IPrDP, and IBDP, which contains 1, 2, and 3 methylene linkers respectively. At concentrations below cytotoxicity threshold, IPeDP and IHDP possessed strong abilities of antiosteoclast formation, antibone absorption, and inducing osteoclast apoptosis, which were similar to ZOL and more powerful than IPrDP and IBDP. The mechanism behind these effects of IPeDP and IHDP might involve the interference of small GTPases prenylation through suppression of mevalonate pathway. The downregulation of JNK and Akt phosphorylation and subsequent inhibition of the expression of c-Fos and NFATc1 might also be involved. Our results supported the potential usage of IPeDP and IHDP to treat bone-related disorders involving increased osteoclastogenesis. Our attempt to extend the methylene linker between the imidazole ring and the P-C-P backbone of ZOL also reveals some regularities between the structure and properties of the BPs drugs.

MEF2C regulates osteoclastogenesis and pathologic bone resorption via c-FOS

Osteoporosis is a metabolic bone disease with dysregulated coupling between bone resorption and bone formation, which results in decreased bone mineral density. The MEF2C locus, which encodes the transcription factor MADS box transcription enhancer factor 2, polypeptide C (MEF2C), is strongly associated with adult osteoporosis and osteoporotic fractures. Although the role of MEF2C in bone and cartilage formation by osteoblasts, osteocytes, and chondrocytes has been studied, the role of MEF2C in osteoclasts, which mediate bone resorption, remains unclear. In this study, we identified MEF2C as a positive regulator of human and mouse osteoclast differentiation. While decreased MEF2C expression resulted in diminished osteoclastogenesis, ectopic expression of MEF2C enhanced osteoclast generation. Using transcriptomic and bioinformatic approaches, we found that MEF2C promotes the RANKL-mediated induction of the transcription factors c-FOS and NFATc1, which play a key role in osteoclastogenesis. Mechanistically, MEF2C binds to FOS regulatory regions to induce c-FOS expression, leading to the activation of NFATC1 and downstream osteoclastogenesis. Inducible deletion of Mef2c in mice resulted in increased bone mass under physiological conditions and protected mice from bone erosion by diminishing osteoclast formation in K/BxN serum induced arthritis, a murine model of inflammatory arthritis. Our findings reveal direct regulation of osteoclasts by MEF2C, thus adding osteoclasts as a cell type in which altered MEF2C expression or function can contribute to pathological bone remodeling.

Hispolon inhibits RANKL induced osteoclast differentiation in vitro

Hispolon (HISP) is a bioactive compound isolated from Phellinu linteus. It has various pharmacological activities, including antioxidant, anti-inflammatory, and anti-cancer. However, its anti-osteoclastogenic activity has not yet been reported. Hence, in the current study, we have explored the anti-osteoclastogenic activity of HISP and elucidated the molecular mechanisms. HISP inhibited the RANKL induced differentiation of RAW 264.7 cells into osteoclasts in a dose-dependent manner. Mechanistic studies showed that HISP inhibited RANKL-mediated activation of NF-κB and MAPK signaling pathways in osteoclast precursors RAW 264.7 cells. In addition, Hispolon also downregulated the expression of master transcriptional factors essential for osteoclast differentiation, such as NFATc1 and c-FOS. In conclusion, these findings establish molecular mechanisms behind the anti-osteoclastogenic activity of HISP.

Dehydrocostus lactone inhibits NFATc1 via regulation of IKK, JNK, and Nrf2, thereby attenuating osteoclastogenesis

Excessive and hyperactive osteoclast activity causes bone diseases such as osteoporosis and periodontitis. Thus, the regulation of osteoclast differentiation has clinical implications. We recently reported that dehydrocostus lactone (DL) inhibits osteoclast differentiation by regulating a nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1), but the underlying mechanism remains to be elucidated. Here we demonstrated that DL inhibits NFATc1 by regulating nuclear factor-κB (NF-κB), activator protein-1 (AP-1), and nuclear factor-erythroid 2-related factor 2 (Nrf2). DL attenuated IκBα phosphorylation and p65 nuclear translocation as well as decreased the expression of NF-κB target genes and c-Fos. It also inhibited c-Jun N-terminal kinase (JNK) but not p38 or extracellular signal-regulated kinase. The reporter assay revealed that DL inhibits NF-κB and AP-1 activation. In addition, DL reduced reactive oxygen species either by scavenging them or by activating Nrf2. The DL inhibition of NFATc1 expression and osteoclast differentiation was less effective in Nrf2-deficient cells. Collectively, these results suggest that DL regulates NFATc1 by inhibiting NF-κB and AP-1 via down-regulation of IκB kinase and JNK as well as by activating Nrf2, and thereby attenuates osteoclast differentiation.

Overexpression of c-Fos reverses osteoprotegerin-mediated suppression of osteoclastogenesis by increasing the Beclin1-induced autophagy

Osteoclastogenesis requires the involvement of transcription factors and degrading enzymes, and is regulated by upstream and downstream signalling. However, c-Fos how regulates osteoclastogenesis through autophagy remain unclear. This study aimed to explore the role of c-Fos during osteoprotegerin (OPG)-mediated suppression of osteoclastogenesis. We found that the number of osteoclasts and the expression of c-Fos, MMP-9, CAⅡ, Src and p62 were decreased after treated with OPG, including attenuation the PI3K/Akt and the TAK1/S6 signalling pathways, but the expression of Beclin1 and LC3Ⅱ were increased. Knockdown of Beclin1 could reverse the expression of c-Fos and MMP-9 by activating the PI3K/Akt signalling pathway, but inhibiting the autophagy and the TAK1/S6 signalling pathway. In addition, inhibition of autophagy using the PI3K inhibitor LY294002 did not rescues OPG-mediated suppression of osteoclastogenesis, but caused reduction of the expression of c-Fos and CAⅡ by attenuating the autophagy, as well as the PI3K/Akt and the TAK1/S6 signalling pathways. Furthermore, continuous activation of c-Fos could reverse OPG-mediated suppression of osteoclastogenesis by activating the autophagy and the PI3K/Akt and the TAK1/S6 signalling pathways. Thus, overexpression of c-Fos could reverse OPG-mediated suppression of osteoclastogenesis via activation of Beclin1-induced autophagy, indicating c-Fos might serve as a new candidate for bone-related basic studies.

6'-O-Galloylpaeoniflorin Attenuates Osteoclasto-genesis and Relieves Ovariectomy-Induced Osteoporosis by Inhibiting Reactive Oxygen Species and MAPKs/c-Fos/NFATc1 Signaling Pathway

Emerging evidence suggests bright prospects of some natural antioxidants in the treatment of osteoporosis. 6'-O-Galloylpaeoniflorin (GPF), an antioxidant isolated from peony roots (one of very widely used Oriental medicines, with various anti-inflammatory, antitumor, and antioxidant activities), shows a series of potential clinical applications. However, its effects on osteoporosis remain poorly investigated. The current study aimed to explore whether GPF can attenuate osteoclastogenesis and relieve ovariectomy-induced osteoporosis via attenuating reactive oxygen species (ROS), and investigate the possible mechanism. After the culture of primary murine bone marrow-derived macrophages/monocytes were induced by the use of macrophage colony-stimulating factor (M-CSF) and the receptor activator of NF-κB ligand (RANKL) and then treated with GPF. Cell proliferation and viability were assessed by Cell Counting Kit-8 (CCK-8) assay. Thereafter, the role of GPF in the production of osteoclasts and the osteogenic resorption of mature osteoclasts were evaluated by tartrate-resistant acid phosphatase (TRAP) staining, podosome belt formation, and resorption pit assay. Western blotting and qRT-PCR examination were performed to evaluate proteins' generation and osteoclast-specific gene levels, respectively. The ROS generation in cells was measured in vitro by 2',7'-Dichlorodi-hydrofluorescein diacetate (DCFH-DA). Ovariectomy-induced osteoporosis mouse administered with GPF or vehicle was performed to explore the in vivo potential of GPF, then a micro-CT scan was performed in combination with histological examination for further analysis. GPF suppressed the formation of osteoclasts and podosome belts, as well as bone resorption when induced by RANKL through affecting intracellular ROS activity, MAPKs signaling pathway, and subsequent NFATc1 translocation and expression, as well as osteoclast-specific gene expression in vitro. In vivo study suggested that exposure to GPF prevented osteoporosis-related bone loss in the ovariectomized mice. These findings indicate that GPF attenuates osteoclastogenesis and relieves ovariectomy-induced osteoporosis by inhibiting ROS and MAPKs/c-Fos/NFATc1 signaling pathway. This suggested that GPF may be potentially used to treat bone diseases like periodontitis, rheumatoid arthritis, and osteoporosis associated with osteoclasts.

Dectin-1-mediated suppression of RANKL-induced osteoclastogenesis by glucan from baker's yeast

Immunoreceptors expressed on osteoclast precursor cells modify osteoclast differentiation and bone resorption activity. Dectin-1 is a lectin receptor of β-glucan and is specifically expressed in osteoclast precursor cells. In this study, we evaluated the bioactivity of β-glucan on receptor activator of nuclear factor-kappa B ligand (RANKL)-induced osteoclastogenesis and observed that glucan from baker's yeast inhibited this process in mouse bone marrow cells and dectin-1-overexpressing RAW264.7 (d-RAW) cells. In conjunction, RANKL-induced nuclear factor of activated T cell c1 expression was suppressed, subsequently downregulating TRAP and Oc-stamp. Additionally, nuclear factor-kappa B activation and the expression of c-fos and Blimp1 were reduced in d-RAW cells. Furthermore, glucan from baker's yeast induced the degradation of Syk protein, essential factor for osteoclastogenesis. These results suggest that glucan from baker's yeast suppresses RANKL-induced osteoclastogenesis and can be applied as a new treatment strategy for bone-related diseases.

Mini-review: Functions and Action Mechanisms of PQQ in Osteoporosis and Neuro Injury

Pyrroloquinoline Quinone (PQQ) is the third coenzyme found after niacinamide and flavone nucleotides and is widely present in microorganisms, plants, animals, and humans. PQQ can stimulate the growth of organisms and is very important for the growth, development and reproduction of animals. Owing to the inherent properties of PQQ as an antioxidant and redox modulator in various systems. In recent years, the role of PQQ in the field of osteoporosis and neuro injury has become a research hotspot. This article mainly discusses the derivatives, distribution of PQQ, in vitro models of osteoporosis and neuro injury, and the research progress of its mechanism of action. It provides new ideas in the study of osteoporosis and neuro injury.

Dynamin-related protein 1 positively regulates osteoclast differentiation and bone loss

Dynamin-related protein 1 (DRP1) is a mitochondrial membrane GTPase and regulates mitochondrial fission. In this study, we found that the cytokine RANKL increased the expression of DRP1 and its receptor proteins, Fis1, Mid49, and Mid 51, during osteoclast formation in mouse bone marrow-derived macrophages. Inactivation of the kinase GSK3β appeared to induce DRP1 expression. DRP1 knockdown or the DRP1 inhibitor Mdivi1 suppressed osteoclast differentiation via downregulation of c-Fos and NFATc1, the key transcription factor for osteoclast formation. Finally, the DRP1 inhibitor suppressed lipopolysaccharide-induced osteoclast formation in a calvarial model and ovariectomy-induced bone loss in vivo. Taken together, our data demonstrate that DRP1 positively contributes to RANKL-induced osteoclast differentiation by regulating the c-Fos-NFATc1 axis, suggesting the importance of mitochondrial DRP1 in osteoclastogenesis.

Kynurenine Promotes RANKL-Induced Osteoclastogenesis In Vitro by Activating the Aryl Hydrocarbon Receptor Pathway

There is increasing evidence of the involvement of the tryptophan metabolite kynurenine (KYN) in disrupting osteogenesis and contributing to aging-related bone loss. Here, we show that KYN has an effect on bone resorption by increasing osteoclastogenesis. We have previously reported that in vivo treatment with KYN significantly increased osteoclast number lining bone surfaces. Here, we report the direct effect of KYN on receptor activator of nuclear factor kappa-B ligand (RANKL)-induced osteoclastogenesis in Raw 264.7 macrophage cells, and we propose a potential mechanism for these KYN-mediated effects. We show that KYN/RANKL treatment results in enhancement of RANKL-induced osteoclast differentiation. KYN drives upregulation and activation of the key osteoclast transcription factors, c-fos and NFATc1 resulting in an increase in the number of multinucleated TRAP+ osteoclasts, and in hydroxyapatite bone resorptive activity. Mechanistically, the KYN receptor, aryl hydrocarbon receptor (AhR), plays an important role in the induction of osteoclastogenesis. We show that blocking AhR signaling using an AhR antagonist, or AhR siRNA, downregulates the KYN/RANKL-mediated increase in c-fos and NFATc1 and inhibits the formation of multinucleated TRAP + osteoclasts. Altogether, this work highlights that the novelty of the KYN and AhR pathways might have a potential role in helping to regulate osteoclast function with age and supports pursuing additional research to determine if they are potential therapeutic targets for the prevention or treatment of osteoporosis.

Uncovering the secreted signals and transcription factors regulating the development of mammalian middle ear ossicles

The mammalian middle ear comprises a chain of ossicles, the malleus, incus, and stapes that act as an impedance matching device during the transmission of sound from the tympanic membrane to the inner ear. These ossicles are derived from cranial neural crest cells that undergo endochondral ossification and subsequently differentiate into their final functional forms. Defects that occur during middle ear development can result in conductive hearing loss. In this review, we summarize studies describing the crucial roles played by signaling molecules such as sonic hedgehog, bone morphogenetic proteins, fibroblast growth factors, notch ligands, and chemokines during the differentiation of neural crest into the middle ear ossicles. In addition to these cell-extrinsic signals, we also discuss studies on the function of transcription factor genes such as Foxi3, Tbx1, Bapx1, Pou3f4, and Gsc in regulating the development and morphology of the middle ear ossicles.

PERK controls bone homeostasis through the regulation of osteoclast differentiation and function

Osteoclasts are multinucleated giant cells with the ability to degrade bone tissue, and are closely related to abnormal bone metabolic diseases. Endoplasmic reticulum (ER) is an organelle responsible for protein modification, quality control, and transportation. The accumulation of unfolded or misfolded proteins in ER cavity induces ER stress. Double-stranded RNA-dependent protein kinase-like ER kinase (PERK) is an ER stress-sensing protein, which is ubiquitous in eukaryotic cells. Systemic PERK knockout mice show severe bone loss, suggesting that PERK is of great significance for maintaining the normal growth and development of bone tissue, but the role of PERK in osteoclastogenesis is still unclear. In this study, we found that PERK was significantly activated during RANKL-induced osteoclast differentiation; knockdown of PERK by siRNA and inhibition of PERK by GSK2606414, respectively, had significant negative regulatory effects on the formation and bone resorption of osteoclasts. PERK inhibitor GSK2606414 down-regulated the mRNA levels and protein expression of osteoclast differentiation marker genes, and inhibited RANKL-induced activation of Mitogen-activated protein kinase (MAPK) and nuclear factor κB (NF-κB) pathways. Treatment with PERK inhibitor GSK2606414 in ovariectomized mouse model significantly suppressed bone loss and osteoclast formation. Thapsigargin activated ER stress to enhance autophagy, while GSK2606414 had a significant inhibitory effect on autophagy flux and autophagosome formation. Antioxidant N-acetylcysteine (NAC) could inhibit the expression of PERK phosphorylation, osteoclast-related proteins and autophagy-related proteins, but the use of PERK activator CCT020312 can reverse inhibition effect of NAC. Our findings demonstrate a key role for PERK in osteoclast differentiation and suggest its therapeutic potential.

Sarsasapogenin Suppresses RANKL-Induced Osteoclastogenesis in vitro and Prevents Lipopolysaccharide-Induced Bone Loss in vivo

INTRODUCTION

Osteoclasts are giant polynuclear cells; their main function is bone resorption. An increased number of osteoclasts and enhanced bone resorption exert significant effects on osteoclast-related bone-lytic diseases, including osteoporosis. Given the limitations of current therapies for osteolytic diseases, it is urgently required to develop safer and more effective alternatives. Sarsasapogenin, a major sapogenin from Anemarrhena asphodeloides Bunge, possesses potent antitumor effects and inhibits NF-κB and MAPK signaling. However, the manner in which it affects osteoclasts is unclear.

METHODS

We investigated the effects of anti-osteoclastogenic and anti-resorptive of sarsasapogenin on bone marrow-derived osteoclasts.

RESULTS

Sarsasapogenin inhibited multiple RANKL-induced signaling cascades, thereby inhibiting the induction of key osteoclast transcription factor NFATc1. The in vivo and in vitro results were consistent: sarsasapogenin treatment protected against bone loss in a mouse osteolysis model induced by lipopolysaccharide.

CONCLUSION

Our research confirms that sarsasapogenin can be used as a new treatment for osteoclast-related osteolytic diseases.

Role of c-Fos in orthodontic tooth movement: an in vivo study using transgenic mice

Objectives

The transcription factor c-Fos controls the differentiation of osteoclasts and is expressed in periodontal ligament cells after mechanical stimulation in vitro. However, it is unclear how c-Fos regulates orthodontic tooth movement (OTM) in vivo. The aim of this study was therefore to analyse OTM in transgenic mice with overexpression of c-Fos.

Materials and methods

We employed c-Fos transgenic mice (c-Fos tg) and wild-type littermates (WT) in a model of OTM induced by Nitinol tension springs that were bonded between the left first maxillary molars and the upper incisors. The unstimulated contralateral side served as an internal control. Mice were analysed by contact radiography, micro-computed tomography, decalcified histology and histochemistry.

Results

Our analysis of the unstimulated side revealed that alveolar bone and root morphology were similar between c-Fos tg and control mice. However, we observed more osteoclasts in the alveolar bone of c-Fos tg mice as tartrate-resistant acid phosphatase (TRAP)-positive cells were increased by 40%. After 12 days of OTM, c-Fos tg mice exhibited 62% increased tooth movement as compared with WT mice. Despite the faster tooth movement, c-Fos tg and WT mice displayed the same amount of root resorption. Importantly, we did not observe orthodontically induced tissue necrosis (i.e. hyalinization) in c-Fos tg mice, while this was a common finding in WT mice.

Conclusion

Overexpression of c-Fos accelerates tooth movement without causing more root resorption.

Clinical relevance

Accelerated tooth movement must not result in more root resorption as higher tissue turnover may decrease the amount of mechanically induced tissue necrosis.

Electronic supplementary material

The online version of this article (10.1007/s00784-020-03503-1) contains supplementary material, which is available to authorized users.

3-Hydroxyolean-12-en-27-oic Acids Inhibit RANKL-Induced Osteoclastogenesis in Vitro and Inflammation-Induced Bone Loss in Vivo

Olean-12-en-27-oic acids possess a variety of pharmacological effects. However, their effects and underlying mechanisms on osteoclastogenesis remain unclear. This study aimed to investigate the anti-osteoclastogenic effects of five olean-12-en-27-oic acid derivatives including 3α,23-isopropylidenedioxyolean-12-en-27-oic acid (AR-1), 3-oxoolean-12-en-27-oic acid (AR-2), 3α-hydroxyolean-12-en-27-oic acid (AR-3), 23-hydroxy-3-oxoolean-12-en-27-oic acid (AR-4), and aceriphyllic acid A (AR-5). Among the five olean-12-en-27-oic acid derivatives, 3-hydroxyolean-12-en-27-oic acid derivatives, AR-3 and AR-5, significantly inhibited receptor activator of nuclear factor-κB ligand (RANKL)-induced mature osteoclast formation by reducing the number of tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts, F-actin ring formation, and mineral resorption activity. AR-3 and AR-5 decreased RANKL-induced expression levels of osteoclast-specific marker genes such as c-Src, TRAP, and cathepsin K (CtsK) as well as c-Fos and nuclear factor of activated T cells cytoplasmic 1 (NFATc1). Mice treated with either AR-3 or AR-5 showed significant protection of the mice from lipopolysaccharide (LPS)-induced bone destruction and osteoclast formation. In particular, AR-5 suppressed RANKL-induced phosphorylation of JNK and ERK mitogen-activated protein kinases (MAPKs). The results suggest that AR-3 and AR-5 attenuate osteoclast formation in vitro and in vivo by suppressing RANKL-mediated MAPKs and NFATc1 signaling pathways and could potentially be lead compounds for the prevention or treatment of osteolytic bone diseases.

Abeliophyllum distichum Nakai alleviates postmenopausal osteoporosis in ovariectomized rats and prevents RANKL-induced osteoclastogenesis in vitro

ETHNOPHARMACOLOGICAL RELEVANCE

Abeliophyllum distichum Nakai (AD), called Miseon, is one of Korea's monotypic endemic species. As a folk remedy, the AD has been used to treat inflammatory disease, stomachaches, diarrhea, and gynecologic disease in Korea. Some researchers have reported that the AD has anti-cancer, anti-inflammatory, and anti-oxidant effects. But the protective effect of AD leaf for osteoporosis has not been reported yet.

AIM OF THE STUDY

This study aimed to analyze the effects and mechanism of AD-ethyl acetate fraction (EA) extract on the osteoporosis, one of the gynecologic disease.

MATERIALS AND METHODS

The RAW 264.7 cells were used as a model for RANKL-induced osteoclastogenesis. We measured the TRAcP activity, expressions of NFATc1, c-fos, and MAPK to investigate the effect of AD-EA. OVX-induced osteoporosis rat model was used as menopausal osteoporosis. After both ovaries were removed through a surgical procedure, and AD-EA or 17b-estradiol was orally administered for 8 weeks. BMD of femurs was measured as well as the bone morphometric parameter, such as BV/TV, trabecular thickness, number and surface using a micro CT.

RESULTS

AD-EA significantly inhibited TRAcP activity, actin ring formation, pit formation and the expressions of osteoclast-related genes in a dose-dependent manner through the inhibition of the MAPK and c-fos/NFATc1 pathway. In addition, low dose administration of AD-EA improved the deterioration of trabecular bone microarchitecture caused by OVX through the inhibition of bone resorption by TRAcP and CTK.

CONCLUSIONS

These results suggest that AD-EA may contribute to the therapy of osteoporosis caused by menopause in women.

Betulinic Acid Protects From Bone Loss in Ovariectomized Mice and Suppresses RANKL-Associated Osteoclastogenesis by Inhibiting the MAPK and NFATc1 Pathways

Osteoclasts with elevated bone resorption are commonly present in postmenopausal osteoporosis, and other osteolytic pathologies. Therefore, suppressing osteoclast generation and function has been the main focus of osteoporosis treatment. Betulinic acid (BA) represents a triterpenoid mainly purified from the bark of Betulaceae. BA shows multiple biological activities, including antitumor and anti-HIV properties, but its effect on osteolytic conditions is unknown. Here, BA suppressed receptor activator of nuclear factor‐κB ligand (RANKL)‐associated osteoclastogenesis and bone resorptive function, as assessed by tartrate‐resistant acid phosphatase (TRAP) staining, fibrous actin ring generation, and hydroxyapatite resorption assays. Mechanistically, BA downregulated the expression of osteoclastic-specific genes. Western blot analysis revealed that BA significantly interrupted ERK, JNK and p38 MAPK activation as well as intracellular reactive oxygen species (ROS) production, thus altering c-Fos and NFATc1 activation. Corroborating the above findings in cell-based assays, BA prevented ovariectomy-associated bone loss in an animal model. In conclusion, these findings suggest that BA can inhibit osteoclast generation and function as well as the RANKL signaling pathway, and might be used for treating osteoclast-related osteoporosis.

Poncirin Inhibits Osteoclast Differentiation and Bone Loss through Down-Regulation of NFATc1 In Vitro and In Vivo

Activation of osteoclast and inactivation of osteoblast result in loss of bone mass with bone resorption, leading to the pathological progression of osteoporosis. The receptor activator of NF-κB ligand (RANKL) is a member of the TNF superfamily, and is a key mediator of osteoclast differentiation. A flavanone glycoside isolated from the fruit of Poncirus trifoliata, poncirin has anti-allergic, hypocholesterolemic, anti-inflammatory and anti-platelet activities. The present study investigates the effect of poncirin on osteoclast differentiation of RANKL-stimulated RAW264.7 cells. We observed reduced formation of RANKL-stimulated TRAP-positive multinucleated cells (a morphological feature of osteoclasts) after poncirin exposure. Real-time qPCR analysis showed suppression of the RANKL-mediated induction of key osteoclastogenic molecules such as NFATc1, TRAP, c-Fos, MMP9 and cathepsin K after poncirin treatment. Poncirin also inhibited the RANKL-mediated activation of NF-κB and, notably, JNK, without changes in ERK and p38 expression in RAW264.7 cells. Furthermore, we assessed the in vivo efficacy of poncirin in the lipopolysaccharide (LPS)-induced bone erosion model. Evaluating the micro-CT of femurs revealed that bone erosion in poncirin treated mice was markedly attenuated. Our results indicate that poncirin exerts anti-osteoclastic effects in vitro and in vivo by suppressing osteoclast differentiation. We believe that poncirin is a promising candidate for inflammatory bone loss therapeutics.

Role of PTH1R Signaling in Prx1+ Mesenchymal Progenitors during Eruption

Tooth eruption is a complex process requiring precise interaction between teeth and adjacent tissues. Molecular analysis demonstrates that bone remodeling plays an essential role during eruption, suggesting that a parathyroid hormone 1 receptor (PTH1R) gene mutation is associated with disturbances in bone remodeling and results in primary failure of eruption (PFE). Recent research reveals the function of PTH1R signaling in mesenchymal progenitors, whereas the function of PTH1R in mesenchymal stem cells during tooth eruption remains incompletely understood. We investigated the specific role of PTH1R in Prx1⁺ progenitor expression during eruption. We found that Prx1⁺-progenitors occur in mesenchymal stem cells residing in alveolar bone marrow surrounding incisors, at the base of molars and in the dental follicle and pulp of incisors. Mice with conditional deletion of PTH1R using the Prx1 promoter exhibited arrested mandibular incisor eruption and delayed molar eruption. Micro-computed tomography, histomorphometry, and molecular analyses revealed that mutant mice had significantly reduced alveolar bone formation concomitant with downregulated gene expression of key regulators of osteogenesis in PTH1R-deficient cells. Moreover, culturing orofacial bone-marrow-derived mesenchymal stem cells (OMSCs) from Prx1Cre;PTH1R^fl/fl mice or from transfecting Cre recombinase adenovirus in OMSCs from PTH1R^fl/fl mice suggested that lack of Pth1r expression inhibited osteogenic differentiation in vitro. However, bone resorption was not affected by PTH1R ablation, indicating the observed reduced alveolar bone volume was mainly due to impaired bone formation. Furthermore, we found irregular periodontal ligaments and reduced Periostin expression in mutant incisors, implying loss of PTH1R results in aberrant differentiation of periodontal ligament cells. Collectively, these data suggest that PTH1R signaling in Prx1⁺ progenitors plays a critical role in alveolar bone formation and periodontal ligament development during eruption. These findings have implications for our understanding of the physiologic and pathologic function of PTH1R signaling in tooth eruption and the progression of PFE.

The extract of Trachelospermum jasminoides (Lindl.) Lem. vines inhibits osteoclast differentiation through the NF-κB, MAPK and AKT signaling pathways

Osteoclasts are the only cells in the body with a bone-resorption function. The identification of anti-osteoclastogenic agents is important in managing bone loss diseases. The dried vines of Trachelospermum jasminoides (Lindl.) Lem. have been used as a herbal medicine to treat musculoskeletal soreness in East Asia for hundreds of years. In the present study, we focused on the effect of Trachelospermum jasminoides (Lindl.) Lem. extract (TJE) on osteoclast differentiation. As indicated by tartrate-resistant acid phosphatase (TRAP) staining, TJE inhibited osteoclastogenesis induced by receptor activator of nuclear factor-κB ligand from bone marrow-derived monocytes/macrophages without showing any cytotoxicity. In addition, TJE effectively suppressed F-actin ring formation and the bone-resorption function of osteoclasts. The subsequent studies such as network pharmacology and molecular investigation, revealed that TJE inhibited osteoclastogenesis-related genes in a dose- and time-dependent manner through NF-κB, MAPK and AKT-mediated mechanism followed by the nuclear factor of activated T cells, cytoplasmic 1 (NFATc1)/c-Fos pathway. Our study could potentially explain the underlying molecular pharmacology of TJE in osteoclast-related diseases. What's more, it suggested that network pharmacology could help the modernization of traditional Chinese medicine.

DAPT inhibits titanium particle-induced osteolysis by suppressing the RANKL/Notch2 signaling pathway

Artificial prosthesis is wildly used in clinical medicine for degenerative disease such as osteoclast-related diseases. However, the material wear particles released from the surface of prostheses cause prosthetic loosening as a result of aseptic osteolysis in long-term use. Therefore, it is important to find an agent that inhibits the formation and function of osteoclast for therapeutic use. Notch signaling pathway plays a lot of roles in cell proliferation, differentiation, and apoptosis. However, the role of Notch signaling pathway in osteoclastogenesis remains unclear. The aim of this study is to assess the effects of γ-secretase inhibitor DAPT on osteoclastogenesis via Notch signaling pathway in vitro and titanium particle-induced osteolysis in vivo. In animal experiments, the inhibitory effect of DAPT on titanium particle-induced osteolysis in a mouse calvaria model was demonstrated. Interestingly, few resorption pits were observed following administration of DAPT and almost no osteoclasts formed at high concentration of DAPT. in vitro experiments revealed the mechanism of the effects of DAPT on osteoclastogenesis. DAPT inhibited the formation and function of osteoclast by blocking RANKL-induced Notch2-NF-κB complex signaling pathway. In conclusion, these results indicated that DAPT could prevent and cure titanium particle-induced prosthetic loosening and other osteoclast-related diseases.

Concentration and Duration of Indoxyl Sulfate Exposure Affects Osteoclastogenesis by Regulating NFATc1 via Aryl Hydrocarbon Receptor

Indoxyl sulfate (IS) is a chronic kidney disease (CKD)-specific renal osteodystrophy metabolite that affects the nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1), a transcription factor promoting osteoclastogenesis. However, the mechanisms underlying the regulation of NFATc1 by IS remain unknown. It is intriguing that the Aryl hydrocarbon receptor (AhR) plays a key role in osteoclastogenesis, since IS is an endogenous AhR agonist. This study investigates the relationship between IS concentration and osteoclast differentiation in Raw 264.7 cells, and examines the effects of different IS concentrations on NFATc1 expression through AhR signaling. Our data suggest that both osteoclastogenesis and NFATc1 are affected by IS through AhR signaling in both dose- and time-dependent manners. Osteoclast differentiation increases with short-term, low-dose IS exposure and decreases with long-term, high-dose IS exposure. Different IS levels switch the role of AhR from that of a ligand-activated transcription factor to that of an E3 ubiquitin ligase. We found that the AhR nuclear translocator may play an important role in the regulation of these dual functions of AhR under IS treatment. Altogether, this study demonstrates that the IS/AhR/NFATc1 signaling axis plays a critical role in osteoclastogenesis, indicating a potential role of AhR in the pathology and abnormality of bone turnover in CKD patients.