Yoon-Hee Cheon

Emodin regulates bone remodeling by inhibiting osteoclastogenesis and stimulating osteoblast formation.

Bone remodeling, a physiological process in which new bone is formed by osteoblasts and the preexisting bone matrix is resorbed by osteoclasts, is vital for the maintenance of healthy bone tissue in adult humans. Imbalances in this process can cause various pathological conditions, including osteoporosis. Emodin, a naturally occurring anthraquinone derivative found in Asian herbal medicines, has numerous beneficial pharmacologic effects, including anticancer and antidiabetic activities. However, the effect of emodin on the regulation of osteoblast and osteoclast activity has not yet been investigated. We show here that emodin is a potential target for osteoporosis therapeutics, as treatment with this agent enhances osteoblast differentiation and bone growth and suppresses osteoclast differentiation and bone resorption. In this study, emodin suppressed receptor activator of nuclear factor‐κB (NF‐κB) ligand (RANKL)‐induced osteoclast differentiation of bone marrow macrophages (BMMs) and the bone‐resorbing activity of mature osteoclasts by inhibiting RANKL‐induced NF‐κB, c‐Fos, and NFATc1 expression. Emodin also increased ALP, Alizarin Red‐mineralization activity, and the expression of osteoblastogenic gene markers, such as Runx2, osteocalcin (OCN), and ALP in mouse calvarial primary osteoblasts, as well as activated the p38‐Runx2 pathway, which enhanced osteoblast differentiation. Moreover, mice treated with emodin showed marked attenuation of lipopolysaccharide (LPS)‐induced bone erosion and increased bone‐forming activity in a mouse calvarial bone formation model based on micro‐computed tomography and histologic analysis of femurs. Our findings reveal a novel function for emodin in bone remodeling, and highlight its potential for use as a therapeutic agent in the treatment of osteoporosis that promotes bone anabolic activity and inhibits osteoclast differentiation.

Oleanolic acid acetate inhibits osteoclast differentiation by downregulating PLCγ2–Ca2 +-NFATc1 signaling, and suppresses bone loss in mice

Owing to their potential pharmacological activities in human disease, natural plant-derived compounds have recently become the focus of increased research interest. In this study, we first isolated oleanolic acid acetate (OAA), a triterpenoid compound, from Vigna angularis (azuki bean) to discover anti-bone resorptive agents. Many studies have identified and described the various medicinal effects of V. angularis extract. However, the pharmacological effect of OAA-derived V. angularis extract, particularly the effect on osteoclastogenesis, is not known. Therefore, we investigated the effect and mechanism of OAA in receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis. OAA inhibited RANKL-induced osteoclast differentiation in bone marrow macrophages (BMMs) without any evidence of cytotoxicity. Interestingly, OAA significantly inhibited Btk phosphorylation, phospholipase Cγ2 (PLCγ2) phosphorylation, calcium ion (Ca(2+)) oscillation, and nuclear factor of activated T cell c1 (NFATc1) expression in RANKL-stimulated BMMs, but did not affect RANKL-induced mitogen-activated protein kinase. OAA also inhibited the bone-resorbing activity of mature osteoclasts. Furthermore, mice treated with OAA demonstrated marked attenuation of lipopolysaccharide-induced bone erosion based on micro-computed tomography and histologic analysis of femurs. Taken together, the results suggested that OAA inhibited RANKL-mediated osteoclastogenesis via PLCγ2-Ca(2+)-NFATc1 signaling in vitro and suppressed inflammatory bone loss in vivo.

Parthenolide inhibits osteoclast differentiation and bone resorbing activity by down-regulation of NFATc1 induction and c-Fos stability, during RANKL-mediated osteoclastogenesis

Parthenolide, a natural product derived from Feverfew, prevents septic shock and inflammation. We aimed to identify the effects of parthenolide on the RANKL (receptor activator of NF-κB ligand)-induced differentiation and bone resorbing activity of osteoclasts. In this study, parthenolide dose-dependently inhibited RANKL-mediated osteoclast differentiation in BMMs, without any evidence of cytotoxicity and the phosphorylation of p38, ERK, and IκB, as well as IκB degradation by RANKL treatment. Parthenolide suppressed the expression of NFATc1, OSCAR, TRAP, DC-STAMP, and cathepsin K in RANKL-treated BMMs. Furthermore, parthenolide down-regulated the stability of c-Fos protein, but could not suppress the expression of c-Fos. Overexpression of NFATc1 and c-Fos in BMMs reversed the inhibitory effect of parthenolide on RANKL-mediated osteoclast differentiation. Parthenolide also inhibited the bone resorbing activity of mature osteoclasts. Parthenolide inhibits the differentiation and bone-resolving activity of osteoclast by RANKL, suggesting its potential therapeutic value for bone destructive disorders associated with osteoclast-mediated bone resorption. [BMB Reports 2014; 47(8): 451-456]

Purslane Suppresses Osteoclast Differentiation and Bone Resorbing Activity via Inhibition of Akt/GSK3β-c-Fos-NFATc1 Signaling in Vitro and Prevents Lipopolysaccharide-Induced Bone Loss in Vivo

Purslane (Portulaca oleracea L.) is popular as a potherb in many areas of Europe, Asia, and the Mediterranean region and is widely distributed around the globe. It has a wide range of pharmacological effects, such as antibacterial, anti-aging, anti-inflammatory, and anti-oxidative properties. Although the extract of purslane has numerous beneficial pharmacological effects, its effect on osteoclasts remains unknown. We aimed to investigate the anti-osteoclastogenic activity in vitro and in vivo and to elucidate the underlying mechanism. The effect of purslane on the differentiation and function of bone marrow-derived macrophages (BMMs) into osteoclasts was examined using a phenotype assay such as tartrate-resistant acid phosphatase (TRAP) staining, F-actin staining, and pit assay and followed by confirmation by real-time reverse transcription polymerase chain reaction (RT-PCR) and Western blot analysis. To address the effect of purslane in vivo, the inflammatory, lipopolysaccharide (LPS)-induced osteolysis mouse model was chosen. Bone volume and bone microarchitecture were evaluated by microcomputed tomography and histologic analysis. Purslane inhibited receptor activator of nuclear factor-kappa B ligand (RANKL)-stimulated osteoclast differentiation accompanied by inhibition of Akt/glycogen synthase kinase 3β (GSK3β) signaling, which could underlie purslane-induced downregulation of c-Fos and nuclear factor of activated T cells 1 (NFATc1) expression levels, transcription factors that regulate osteoclast-specific genes, as well as osteoclast fusion and resorption-related molecules. Moreover, in vivo studies further verified the bone protection activity of purslane in the LPS-induced osteolysis animal model. Purslane could exhibit its anti-osteoclastogenic activity by inhibiting Akt/GSK3β-c-Fos-NFATc1 signaling cascades. Therefore, purslane is a potential natural medicine for the treatment of osteoclast-related diseases.

9-Hydroxy-6,7-dimethoxydalbergiquinol inhibits osteoclast differentiation through down-regulation of Akt, c-Fos and NFATc1

Recently, natural plant-derived products have been recognized as one of the main sources for drug discovery and development in human disease. 9-Hydroxy-6,7-dimethoxydalbergiquinol (HDDQ) isolated from the heart wood of Dalbergia odorifera is widely used in oriental medicine, however, the pharmacological effect of HDDQ in osteoclast-associated diseases remains unknown. In this study, HDDQ dose-dependently inhibited the early stage of RANKL-mediated osteoclast differentiation in bone marrow macrophages (BMMs) without cytotoxicity. HDDQ strongly inhibited Akt phosphorylation in RANKL-stimulated BMMs and did not show any effects on p38, JNK, and IκB phosphorylation and IκB degradation. Interestingly, we found that HDDQ down-regulated the induction by RANKL of c-Fos protein by suppressing its translation. Also, ectopic overexpression of c-Fos and NFATc1 rescued the inhibition of osteoclast differentiation by HDDQ. Furthermore, the Akt/c-Fos/NFATc1-regulated expression of genes required for osteoclastogenesis, such as OSCAR and TRAP, was inhibited by HDDQ. These findings suggest that HDDQ prevents osteoclast differentiation via down-regulation of Akt, c-Fos, and NFATc1 signaling molecules, suggesting a potential therapeutic value of HDDQ for bone disorders associated with increased bone resorption.

Esculetin attenuates receptor activator of nuclear factor kappa-B ligand-mediated osteoclast differentiation through c-Fos/nuclear factor of activated T-cells c1 signaling pathway.

Esculetin exerts various biological effects on anti-oxidation, anti-tumors, and anti-inflammation. However, the involvement of esculetin in the bone metabolism process, particularly osteoclast differentiation has not yet been investigated. In the present study, we first confirmed the inhibitory effect of esculetin on receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast formation. We then revealed the relationship between esculetin and the expression of osteoclast-specific molecules to elucidate its underlying mechanisms. Esculetin interfered with the expression of c-Fos and nuclear factor of activated T cell c1 (NFATc1) both at the mRNA and protein level with no involvement in osteoclast-associated early signaling pathways, suppressing the expression of various transcription factors exclusively expressed in osteoclasts such as tartrate-resistant acid phosphatase (Trap), osteoclast-associated receptor (Oscar), dendritic cell-specific transmembrane protein (Dcstamp), osteoclast stimulatory transmembrane protein (Ocstamp), cathepsin K, αvβ3 integrin, and calcitonin receptor (Ctr). Additionally, esculetin inhibited the formation of filamentous actin (F-actin) ring-positive osteoclasts during osteoclast differentiation. However, the development of F-actin structures and subsequent bone resorbing activity of mature osteoclasts, which are observed in osteoclast/osteoblast co-culture systems were not affected by esculetin. Taken together, our results indicate for the first time that esculetin inhibits RANKL-mediated osteoclastogenesis via direct suppression of c-Fos and NFATc1 expression and exerts an inhibitory effect on actin ring formation during osteoclastogenesis.

Costunolide inhibits osteoclast differentiation by suppressing c-Fos transcriptional activity.

Costunolide, a sesquiterpene lactone, exhibits anti‐inflammatory and anti‐oxidant properties and mediates apoptosis. However, its effects and mechanism of action in osteoclasts remain unknown. Herein, we found that costunolide significantly inhibited RANKL‐induced BMM differentiation into osteoclasts in a dose‐dependent manner without affecting cytotoxicity. Costunolide did not regulate the early signaling pathways of RANKL, including the mitogen‐activated protein kinase and NF‐κB pathways. However, costunolide suppressed nuclear factor of activated T‐cells, cytoplasmic 1 (NFATc1) expression via inhibition of c‐Fos transcriptional activity without affecting RANKL‐induced c‐Fos expression. The inhibitory effects of costunolide were rescued by overexpression of constitutively active (CA)‐NFATc1. Taken together, our results suggest that costunolide inhibited RANKL‐induced osteoclast differentiation by suppressing RANKL‐mediated c‐Fos transcriptional activity. Copyright

Protocatechuic Acid Attenuates Osteoclastogenesis by Downregulating JNK/c-Fos/NFATc1 Signaling and Prevents Inflammatory Bone Loss in Mice

Protocatechuic acid (PCA) plays a critical role in nutritional metabolism; it is a major metabolite of anthocyanins, which are flavonoids with a range of health benefits. PCA has a variety of biological activities including anti‐oxidant, antiinflammatory, anti‐apoptosis, and anti‐microbial activities. However, the pharmacological effect of PCA, especially on osteoclastogenesis, remains unknown. We examined the effect of PCA on receptor activator of NF‐κB ligand (RANKL)‐induced osteoclast differentiation and bone resorption. PCA dose‐dependently inhibited RANKL‐induced osteoclast differentiation in mouse bone marrow macrophages (BMMs) and suppressed the bone‐resorbing activity of mature osteoclasts. At the molecular level, PCA suppressed RANKL‐induced phosphorylation of JNK among MAPKs only, without significantly affecting the early signaling pathway. PCA also suppressed RANKL‐stimulated expression of c‐Fos and nuclear factor of activated T cells c1 (NFATc1) at the mRNA and protein levels, without altering c‐Fos mRNA expression. Additionally, PCA down‐regulated the expression of downstream osteoclastogenesis‐related genes including β3‐integrin, DC‐STAMP, OC‐STAMP, Atp6v0d2, CTR, and CtsK. Mice treated with PCA efficiently recovered from lipopolysaccharide‐induced bone loss in vivo. Thus, PCA inhibits RANKL‐induced osteoclast differentiation and function by suppressing JNK signaling, c‐Fos stability, and expression of osteoclastic marker genes. These results suggest that PCA could be useful in treatment of inflammatory bone disorders. Copyright

Progranulin and a Five Transmembrane Domain-Containing Receptor-like Gene Are the Key Components in Receptor Activator of Nuclear Factor κB (RANK)-dependent Formation of Multinucleated Osteoclasts

Background: Molecular mechanisms of RANKL/RANK-mediated formation of multinucleated osteoclasts are not fully understood. Results: PIRO (progranulin (PGRN)-induced receptor-like gene during osteoclastogenesis) is a direct target for the formation of multinucleated osteoclasts by PGRN upon RANK activation. Conclusion: Progranulin/PIRO axis is a new regulatory axis in osteoclastogenesis. Significance: This noble regulatory axis offers new avenues for the development of effective therapeutic strategies for osteoporosis. Homeostatic bone remodeling is vital to maintain healthy bone tissue. Although the receptor activator of nuclear factor κB ligand (RANKL)/RANK axis is considered the master regulator of osteoclastogenesis, the underlying mechanisms including cell fusion remain incompletely defined. Here, we introduce a new axis in the formation of multinucleated cells via RANK signaling: the progranulin (PGRN)/PIRO (PGRN-induced receptor-like gene during osteoclastogenesis) axis. When mouse bone marrow-derived macrophages were stimulated with PGRN in the presence of RANKL, explosive OC formation was observed. PGRN knockdown experiments suggested that endogenous PGRN is an essential component of the RANKL/RANK axis. Our efforts for identifying genes that are induced by PGRN unveiled a remarkably induced (20-fold) gene named PIRO. Substantial PGRN and PIRO expression was detected after 2 and 3 days, respectively, suggesting that their sequential induction. PIRO was predicted to be a five transmembrane domain-containing receptor-like molecule. The tissue distribution of PGRN and PIRO mRNA expression suggested that bone marrow cells are the most suitable niche. Mouse and human PIRO are part of a multigene family. Knockdown experiments suggested that PIRO is a direct target for the formation of multinucleated cells by PGRN. PGRN levels were also substantially higher in ovariectomized mice than in sham control mice. These observations suggest that PGRN and PIRO form a new regulatory axis in osteoclastogenesis that is included in RANK signaling in cell fusion and OC resorption of osteoclastogenesis, which may offer a novel therapeutic modality for osteoporosis and other bone-associated diseases.

Stauntonia hexaphylla (Lardizabalaceae) leaf methanol extract inhibits osteoclastogenesis and bone resorption activity via proteasome-mediated degradation of c-Fos protein and suppression of NFATc1 expression

BackgroundNatural plants, including common vegetables and fruits, have been recognized as essential sources for drug discovery and the development of new, safe, and economical medicaments. Stauntonia hexaphylla (Lardizabalaceae) is widely distributed in Korea, Japan, and China, and is a popular herbal supplement in Korean and Chinese folk medicine owing to its analgesic, sedative, and diuretic properties. However, the exact pharmacological effects of S. hexaphylla extract, particularly its effect on osteoclastogenesis, are not known.MethodsOsteoclast differentiation and function were identified with tartrate-resistant acid phosphatase (TRAP) staining and bone resorption assay, and the underling mechanisms were determined by real-time RT-PCR and western blot analysis.ResultsS. hexaphylla was found to inhibit early-stage receptor activator of nuclear factor-κB (NF-κB) ligand (RANKL)-mediated osteoclast differentiation in bone marrow macrophages (BMMs) without cytotoxicity and bone-resorbing activity in mature osteoclasts in a dose-dependent manner. This S. hexaphylla-mediated blockade of osteoclastogenesis involved abrogation of the NF-κB, ERK, and c-Src-Btk-PLCγ2 calcium signal pathways. Interestingly, we found that S. hexaphylla down-regulated RANKL-associated c-Fos protein induction by suppressing its translation. Furthermore, ectopic overexpression of c-Fos and NFATc1 rescued the inhibition of osteoclast differentiation by S. hexaphylla. Furthermore, S. hexaphylla inhibited the c-Fos- and NFATc1-regulated expression of genes required for osteoclastogenesis, such as TRAP, OSCAR, β3-integrin, ATP6v0d2, and CtsK.ConclusionsThese findings suggest that S. hexaphylla might be useful for the development of new anti-osteoporosis agents.