Receptor activator of nuclear factor-kappaB ligand-induced nuclear factor of activated T cells (C1) autoregulates its own expression in osteoclasts and mediates the up-regulation of tartrate-resistant acid phosphatase

Long noncoding RNA Malat1 protects against osteoporosis and bone metastasis

MALAT1, one of the few highly conserved nuclear long noncoding RNAs (lncRNAs), is abundantly expressed in normal tissues. Previously, targeted inactivation and genetic rescue experiments identified MALAT1 as a suppressor of breast cancer lung metastasis. On the other hand, Malat1-knockout mice are viable and develop normally. On a quest to discover the fundamental roles of MALAT1 in physiological and pathological processes, we find that this lncRNA is downregulated during osteoclastogenesis in humans and mice. Remarkably, Malat1 deficiency in mice promotes osteoporosis and bone metastasis of melanoma and mammary tumor cells, which can be rescued by genetic add-back of Malat1. Mechanistically, Malat1 binds to Tead3 protein, a macrophage-osteoclast-specific Tead family member, blocking Tead3 from binding and activating Nfatc1, a master regulator of osteoclastogenesis, which results in the inhibition of Nfatc1-mediated gene transcription and osteoclast differentiation. Notably, single-cell transcriptome analysis of clinical bone samples reveals that reduced MALAT1 expression in pre-osteoclasts and osteoclasts is associated with osteoporosis and metastatic bone lesions. Altogether, these findings identify Malat1 as a lncRNA that protects against osteoporosis and bone metastasis.

Periplogenin attenuates LPS-mediated inflammatory osteolysis through the suppression of osteoclastogenesis via reducing the NF-κB and MAPK signaling pathways

The key target for treating inflammatory osteolysis is osteoclasts. In an inflammatory environment, osteoclast differentiation increases, and bone resorption is enhanced. Periplogenin (Ppg) is a traditional Chinese medicine. It has anti-inflammatory and antitumor effects, but its impact on inflammatory osteolysis is unknown. This study found that Ppg prevented LPS-induced skull osteolysis by inhibiting the expression of inflammatory cytokines and osteoclast production. In vitro, Ppg blocked the RANKL-induced generation of osteoclasts, the development of pseudopodia bands, and bone resorption. Ppg also attenuated the expression of NFATc1, c-Fos, CTSK, and Atp6v0d2 proteins by inhibiting the NFATc1 signaling pathway. In addition, Ppg inhibited the expression of osteoclast-specific genes, including NFATc1, c-Fos, CTSK, Atp6v0d2, and Mmp9. Moreover, Ppg also inhibited NF-κB and MAPK pathways. In vivo, Ppg reduced the number of osteoclasts on the surface of the bone and suppressed LPS-induced osteolysis of the skull. These outcomes suggest that Ppg can serve as a new alternative therapy for treating inflammatory osteolysis by inhibiting inflammation and osteoclasts.

Rab34 plays a critical role as a bidirectional regulator of osteoclastogenesis

Accumulating evidence suggests that Rab GTPases representing the largest branch of Ras superfamily have recently emerged as the core factors for the regulation of osteoclastogenesis through modulating vesicular transport amongst specific subcellular compartments. Among these, Rab34 GTPase has been identified to be important for the post-Golgi secretory pathway and for phagocytosis; nevertheless, its specific role in osteoclastogenesis has been completely obscure. Here, upon the in vitro model of osteoclast formation derived from murine macrophages like RAW-D cells or bone marrow-derived macrophages, we reveal that Rab34 regulates osteoclastogenesis bidirectionally. More specifically, Rab34 serves as a negative regulator of osteoclast differentiation by promoting the lysosome-induced proteolysis of two osteoclastogenic surface receptors, c-fms and RANK, via the axis of early endosomes-late endosomes-lysosomes, leading to alleviate the transcriptional activity of two of the master regulator of osteoclast differentiation, c-fos and NFATc-1, eventually attenuating osteoclast differentiation and bone resorption. Besides, Rab34 plays a crucial role in modulating the secretory network of lysosome-related proteases including matrix metalloprotease 9 and Cathepsin K across the ruffled borders of osteoclasts, contributing to the regulation of bone resorption.

Nicorandil Inhibits Osteoclast Formation Base on NF-κB and p-38 MAPK Signaling Pathways and Relieves Ovariectomy-Induced Bone Loss

Osteolytic bone disorders are characterized by an overall reduction in bone mineral density which enhances bone ductility and vulnerability to fractures. This disorder is primarily associated with superabundant osteoclast formation and bone resorption activity. Nicorandil (NIC) is a vasodilatory anti-anginal drug with ATP-dependent potassium (KATP) channel openings. However, NIC is adopted to manage adverse cardiovascular and coronary events. Recent research has demonstrated that NIC also possesses anti-inflammatory peculiarity through the regulation of p38 MAPK and NF-κB signaling pathways. Both MAPK and NF-κB signaling pathways play pivotal roles in RANKL-induced osteoclast formation and bone resorption function. Herein, we hypothesized that NIC may exert potential biological effects against osteoclasts, and revealed that NIC dose-dependently suppressed bone marrow macrophage (BMM) precursors to differentiate into TRAP + multinucleated osteoclasts in vitro. Furthermore, osteoclast resorption assays demonstrated anti-resorptive effects exhibited by NIC. NIC had no impact on osteoblast differentiation or mineralization function. Based on Biochemical analyses, NIC relieved RANKL-induced ERK, NF-κB and p38 MAPK signaling without noticeable effects on JNK MAPK activation. However, the attenuation of NF-κB and p38 MAPK activation was sufficient to hamper the downstream induction of c-Fos and NFATc1 expression. Meanwhile, NIC administration markedly protected mice from ovariectomy (OVX)-induced bone loss through in vivo inhibition of osteoclast formation and bone resorption activity. Collectively, this work demonstrated the potential of NIC in the management of osteolytic bone disorders mediated by osteoclasts.

Inhibition of NFAM1 suppresses phospho-SAPK/JNK signaling during osteoclast differentiation and bone resorption

We have recently demonstrated NFAT activating protein with ITAM motif 1 (NFAM1) signaling increases osteoclast (OCL) formation/bone resorption associated with the Paget's disease of bone, however, the underlying molecular mechanisms of the NFAM1 regulation of OCL differentiation and bone resorption remains unclear. Here, we showed that RANK ligand stimulation enhances NFAM1 expression in preosteoclast cells. Conditioned media collected from RANKL stimulated RAW264.7 NFAM1 knockdown (KD) stable cells showed inhibition of interleukin-6 (2.5-fold), tumour necrosis factor-α (2.2-fold) and CXCL-5 (3-fold) levels compared to wild-type (WT) cells. Further, RANKL stimulation significantly increased p-STAT6 expression (5.5-fold) in WT cells, but no significant effect was observed in NFAM1-KD cells. However, no changes were detected in signal transducer and activator of transcription 3 levels in either of cell groups. Interestingly, NFAM1-KD suppressed the RANKL stimulated c-fos, p-c-Jun and c-Jun N-terminal kinase (JNK) activity in preosteoclasts. We further showed that the suppression of JNK activity is through inhibition of p-SAPK/JNK in these cells. In addition, NFATc1 expression, a critical transcription factor associated with osteoclastogenesis is significantly inhibited in NFAM1-KD preosteoclast cells. Interestingly, NFAM1 inhibition suppressed the OCL differentiation and bone resorption capacity in mouse bone marrow cell cultures. We also demonstrated inhibition of tartrate-resistant acid phosphatase expression in RANKL stimulated NFAM1-KD preosteoclast cells. Thus, our results suggest that NFAM1 control SAPK/JNK signaling to modulate osteoclast differentiation and bone resorption.

Inhibition Effect of Zoledronate on the Osteoclast Differentiation of RAW264.7 Induced by Titanium Particles

OBJECTIVE

This study is aimed at studying the effect of zoledronate (ZOL) on the differentiation of osteoclast precursor RAW264.7 cells induced by titanium (Ti) particles and explores the possibility of preventing and treating periprosthetic osteoporosis using ZOL.

METHODS

RAW264.7 cells were cultured in vitro. Ti particles were prepared. The cell proliferation curve of RAW264.7 cells was plotted using the MTT assay to find the best concentration of ZOL for intervention. The cells were divided into three groups: control, Ti particles, and Ti particles+ZOL. The cell morphology was observed using tartaric acid-resistant acid phosphatase (TRAP) staining, and the activity of TRAP in cell supernatant was determined using the biochemical method. The number of bone resorption lacunae was detected using toluidine blue staining. The mRNA expression of RANK, NFATcl, CAII, and MMP-9 was detected using real-time polymerase chain reaction. The protein expression of RANK, NFATcl, and MMP-9 was detected using Western blot analysis.

RESULTS

Ti particles stimulated the differentiation of RAW264.7 cells into osteoclasts. They also increased the activity of TRAP, number of bone resorption lacunae, and mRNA and protein expression of RANK, NFATcl, and MMP-9. However, ZOL could suppress the effect of TI particles on the osteoclast differentiation of RAW264.7 cells.

CONCLUSIONS

ZOL could effectively inhibit the differentiation of RAW264.7 cells into osteoclasts induced by Ti particles, decrease the activity of TRAP, reduce the number of bone resorption lacunae, and decrease the mRNA and protein expression of RANK, NFATcl, and MMP-9. Hence, it may be a promising candidate for preventing and treating periprosthetic osteoporosis after the artificial joint operation.

Pristimerin Protects Against OVX-Mediated Bone Loss by Attenuating Osteoclast Formation and Activity via Inhibition of RANKL-Mediated Activation of NF-κB and ERK Signaling Pathways

Introduction

Osteoporosis is an osteolytic bone condition characterized by decreased bone strength and increased bone fragility. It is the result of elevated formation or activity of bone-resorbing osteoclasts. Although current therapeutic agents are efficacious against osteoclast-mediated bone loss, detrimental side effects preclude the long-term use of these agents. Pristimerin (PRI) is a naturally occurring quinone-methide triterpenoid that has been revealed to exert anti-inflammatory and anti-tumor effects via regulating various signaling cascades including NF-κB and MAPK activation.

Methods

The bone marrow macrophages were used to confirm the anti-osteoclastic and anti-resorptive functions of PRI in vitro. An in vivo ovariectomy (OVX) model was applied to verify the function of PRI protecting bone loss.

Results

PRI abolished the early activation of NF-κB and ERK MAPK signal cascades thereby thwarting the downstream expression of c-Fos and NFATc1, which prevented the production of mature osteoclasts. In vivo, PRI protects mice against ovariectomy (OVX)-mediated bone loss by diminishing osteoclast formation and bone resorptive activity.

Conclusion

Our study shows that PRI demonstrates therapeutic potential in the effective treatment against osteoclast-induced osteolytic diseases like osteoporosis.

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.

The role of small leucine zipper protein in osteoclastogenesis and its involvement in bone remodeling

Bone remodeling is critical to maintain the quality of bone tissues and to heal bone tissue injury. Osteoclasts and osteoblasts are special types of cells involved in this event. In particular, the resorption activity of mature osteoclasts is required for the formation of new bones. Human small leucine zipper protein (sLZIP) is known to induce the osteoblast differentiation of mesenchymal stem cells. However, the roles of sLZIP in osteoclast differentiation and bone remodeling have not been explored. In this study, we investigated the roles of sLZIP in regulating osteoclast formation and in the bone remodeling process using sLZIP transgenic (TG) mice. Tibiae from sLZIP TG mice contained more osteoclasts than those from wild type (WT) mice. Bone marrow-derived macrophages (BMM) from sLZIP TG mice showed increased differentiation into osteoclasts compared with BMM from WT mice. sLZIP bound to the promotor and induced the expression of nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1) and its target osteoclastogenic genes. To understand the role of sLZIP in bone remodeling, a bone-defect model was generated. Results of micro-CT scanning and histologic analysis demonstrated that sLZIP TG mice have faster bone formation during healing compared with WT mice. Notably, the soft callus around the defect area was replaced faster by hard callus in sLZIP TG mice than in WT mice. These findings suggest that sLZIP promotes osteoclast differentiation and plays an important role in bone remodeling.

Sotrastaurin, a PKC inhibitor, attenuates RANKL-induced bone resorption and attenuates osteochondral pathologies associated with the development of OA

Osteoarthritis (OA) is a common degenerative disease that affects the musculoskeletal structure of the whole joint, which is characterized by progressive destruction of both articular cartilage and subchondral bone. Treatment of the bone pathologies, particularly osteoclast‐mediated subchondral bone loss in the early stages of OA, could prevent subsequent cartilage degeneration and progression of OA. In the present study, the PKC inhibitor, Sotrastaurin, was found to inhibit RANKL‐induced osteoclast formation in vitro in a dose‐ and time‐dependent manner. In particular, SO exerted its anti‐osteoclastic effect predominantly at the early stages of RANKL stimulation, suggesting inhibitory effects on precursor cell fusion. Using mature osteoclasts cultured on bovine bone discs, we showed that SO also exerts anti‐resorptive effects on mature osteoclasts bone resorptive function. Mechanistically, SO attenuates the early activation of the p38, ERK and JNK signalling pathways, leeding to impaired induction of crucial osteoclast transcription factors c‐Jun, c‐Fos and NFATc1. We also showed that SO treatment significantly inhibited the phosphorylation of PKCδ and MARCKS, an upstream regulator of cathepsin K secretion. Finally, in animal studies, SO significantly alleviates the osteochondral pathologies of subchondral bone destruction as well as articular cartilage degeneration following DMM‐induced OA, markedly improving OARSI scores. The reduced subchondral bone loss was associated with marked reductions in TRAP(+) osteoclasts in the subchondral bone tissue. Collectively, our data provide evidence for the protective effects of SO against OA by preventing aberrant subchondral bone and articular cartilage changes. Thus, SO demonstrates potential for further development as an alternative therapeutic option against OA.

Early B Cell Factor 1 (EBF1) Regulates Glomerular Development by Controlling Mesangial Maturation and Consequently COX-2 Expression

BACKGROUND

We recently showed the transcription factor Early B cell factor 1 (EBF1) is essential for the last stages of metanephric development, and that mice globally deficient in EBF1 display impaired maturation of peripheral glomeruli. EBF1 is present within multiple glomerular cell types, including the glomerular mesangium and podocytes.

METHODS

To identify which cell type is driving the glomerular developmental defects in the global EBF1 knockout mice, we deleted EBF1 from the mesangium/pericytes (Foxd1-cre) or podocytes (Podocin-cre) in mice.

RESULTS

Deletion of EBF1 from Foxd1 lineage cells resulted in hypoplastic kidneys, poorly differentiated peripheral glomeruli, and decreased proximal tubular mass in the outer cortex. Renal insufficiency was apparent at P21 when proteinuria presents, fibrosis of both the glomeruli and interstitium rapidly progresses, microthrombi appear, and hematuria develops. Approximately half of the Foxd1⁺, Ebf1 ^fl/fl mice die before they are 3 months old. Mice with podocyte-targeted deletion of EBF1 exhibited no developmental abnormalities. Mice with Ebf1 deficiency in Foxd1 lineage cells shared characteristics with Ptgs2/COX-2-insufficient models, and mechanistic investigation revealed impaired calcineurin/NFATc1 activation and decreased COX-2 expression. Deletion of COX-2 from the interstitial/mesangial lineage displayed a less severe phenotype than EBF1 deficiency in mice. Overexpressing COX-2 in the EBF1-deficient mice, however, partially restored glomerular development.

CONCLUSIONS

The results suggest that EBF1 regulates metanephric development at the last stages of glomerular maturation through its actions in the stromal progenitor (Foxd1⁺) lineage where it mediates proper regulation of calcineurin/NFAT signaling and COX-2 expression.

Roles of SP600125 in expression of JNK, RANKL and OPG in cultured dental follicle cells

OBJECTIVE

To investigate the expression of C-JNK, RANKL and OPG after SP600125 administration in cultured dental follicle cells (DFCs).

METHODS

TRAP staining and electron microscope were carried out on day 7 and 9 after coculture of BMMs and DFCs with a ratio of 5:1 in different groups. To determine the effects of SP600125 on the expression of C-JNK, RANKL and OPG mRNA and protein, cultured DFCs were divided into control group, DMSO group and SP600125 groups. Real-time PCR and Western blot analysis were performed to investigate the expression of the mRNA and protein, respectively.

RESULTS

TRAP assay indicated that the number of multinucleated osteoclasts in the SP600125 group showed significant decrease compared with that of control (P < 0.05). The expression of JNK protein in the SP600125 groups showed significant decline compared with that of the control group and blank control (P < 0.05). Significant decrease was noticed in the RANKL protein expression with the elevation of SP600125.

CONCLUSIONS

SP600125 could inhibit the formation of osteoclast in the coculture system of DFCs and BMMs. After SP600125 treatment, the expression of RANKL and JNK showed a trend of decrease, and the expression of OPG showed gradual increase followed by gradual decrease.

AP-1 and Mitf interact with NFATc1 to stimulate cathepsin K promoter activity in osteoclast precursors

Cathepsin K (CTSK) is a secreted protease that plays an essential role in osteoclastic bone resorption and osteoporotic bone loss. We have previously shown that activator protein 1 (AP-1) stimulates CTSK promoter activity and that proximal nuclear factor of activated T cells cytoplasmic 1 (NFATc1)-binding sites play a major role in the stimulation of CTSK gene expression by receptor activator of NFκB ligand (RANKL). In the present study, we have extended these observations and further dissected the effects of transcription factors involved in the regulation of CTSK gene expression. Our aim was to investigate the cooperative interplay among transcription factors AP-1, microphthalmia-associated transcription factor (Mitf), and NFATc1, and the consequent regulatory effects on CTSK transcription. Experiments were carried out in RAW 264.7 cells, which can be readily differentiated to osteoclasts upon RANKL stimulation. Our data show that AP-1, Mitf, and NFATc1 are capable of independently stimulating CTSK promoter activity. A combination of any two factors further enhances CTSK promoter activity, with the combination of AP-1 (c-fos/c-jun) and NFATc1 inducing the largest increase. We further identify a synergistic effect when all three factors cooperate intimately at the proximal promoter region, yielding maximal transcriptional upregulation of the CTSK promoter. RANKL induces temporal localization of AP-1 and NFATc1 to the CTSK promoter. These results suggest that the interaction of multiple transcription factors mediate a maximal response to RANKL-induced CTSK gene expression.

Vitexin suppresses RANKL-induced osteoclastogenesis and prevents lipopolysaccharide (LPS)-induced osteolysis

Osteolytic diseases are characterized by an increase in the number and/or activity of bone-resorbing osteoclasts. Identification of natural compounds that can suppress osteoclast formation and function is crucial for the prevention and treatment of osteolytic diseases. Vitexin, a naturally-derived flavonoid extracted from various medicinal plant species, demonstrates a broad range of pharmacological properties including anticancer and anti-inflammatory effects. Here in this study, we showed that vitexin exerts antiosteoclastogenic effects by directly inhibiting receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast formation and bone resorption in vitro and protected against lipopolysaccharide (LPS)-induced inflammatory osteolysis in vivo. Vitexin suppressed the early activation of ERK and p38 MAPK pathways in response to RANKL thereby attenuating the downstream induction of c-Fos and NFATc1, and abrogating the expression of osteoclast marker genes. Collectively, these results provide evidence for the therapeutic application of vitexin in the treatment of osteoclast-mediated bone lytic diseases.

Rosiglitazone suppresses RANKL-induced NFATc1 autoamplification by disrupting the physical interaction between NFATc1 and PPARγ

Receptor activator of nuclear factor-κB ligand (RANKL) is required for initiation of osteoclastogenesis, with the signaling pathway including the NF-kB, c-Fos, and nuclear factor of activated T cells, cytoplasmic 1 (NFATc1) transcription factors. Because NFATc1 expression is autoamplified, we investigated the molecular mechanism by which peroxisome proliferator-activated receptor gamma (PPARγ) activation by the thiazolidinedione drug rosiglitazone decreases NFATc1 expression during RANKL stimulation. Western blotting demonstrated that rosiglitazone attenuated the increase in NFATc1 protein level induced by RANKL without affecting that of PPARγ. Immunofluorescence data indicated that rosiglitazone tended to suppress RANKL-induced NFATc1 nuclear translocation, partly by reducing calcineurin activity, as reflected by the observed decrease in nuclear NFATc1 abundance. On coimmunoprecipitation, the intensity of the physical interaction between NFATc1 and PPARγ was unexpectedly higher in the RANKL-stimulated group than in the control, but rosiglitazone reduced this to basal levels. Furthermore, RANKL failed to elevate mRNA expression of NFATc1 after PPARγ knockdown. ChIP assay indicated that rosiglitazone significantly reduced the binding of NFATc1 to its own promoter despite RANKL stimulation. These findings suggest that PPARγ activation by rosiglitazone blocks NFATc1 from binding to its own promoter, thereby reducing RANKL-induced NFATc1 autoamplification.

Cyanidin Chloride inhibits ovariectomy-induced osteoporosis by suppressing RANKL-mediated osteoclastogenesis and associated signaling pathways

Over-production and activation of osteoclasts is a common feature of osteolytic conditions such as osteoporosis, tumor-associated osteolysis, and inflammatory bone erosion. Cyanidin Chloride, a subclass of anthocyanin, displays antioxidant and anti-carcinogenesis properties, but its role in osteoclastic bone resorption and osteoporosis is not well understood. In this study, we showed that Cyanidin Chloride inhibits osteoclast formation, hydroxyapatite resorption, and receptor activator of NF-κB ligand (RANKL)-induced osteoclast marker gene expression; including ctr, ctsk, and trap. Further investigation revealed that Cyanidin Chloride inhibits RANKL-induced NF-κB activation, suppresses the degradation of IκB-α and attenuates the phosphorylation of extracellular signal-regulated kinases (ERK). In addition, Cyanidin Chloride abrogated RANKL-induced calcium oscillations, the activation of nuclear factor of activated T cells calcineurin-dependent 1 (NFATc1), and the expression of c-Fos. Further, we showed that Cyanidin Chloride protects against ovariectomy-induced bone loss in vivo. Together our findings suggest that Cyanidin Chloride is capable of inhibiting osteoclast formation, hydroxyapatite resorption and RANKL-induced signal pathways in vitro and OVX-induced bone loss in vivo, and thus might have therapeutic potential for osteolytic diseases.

Ampelopsis brevipedunculata extract prevents bone loss by inhibiting osteoclastogenesis in vitro and in vivo

Osteoclasts play a critical role in bone resorbing disorders such as osteoporosis, periodontitis, and rheumatoid arthritis. Therefore, discovery of agents capable of suppressing osteoclast differentiation may aid the development of a therapeutic access for the treatment of pathological bone loss. Ampelopsis brevipedunculata has been used as herbal folk medicine to treat liver diseases and inflammation in Asia. However, its effects on osteoclast differentiation are unknown. We were aimed to investigate the anti-osteoclastogenic activity in vitro and in vivo and to elucidate the underlying mechanism of Ampelopsis brevipedunculata extract (ABE). In this study, ABE inhibited receptor activator of NF-κB ligand (RANKL)-induced osteoclast differentiation, the formation of filamentous actin rings and the bone resorbing activity of mature osteoclasts. ABE inhibited RANKL-induced p38 and IκB phosphorylation and IκB degradation. Also, ABE suppressed the mRNA and protein expression of nuclear factor of activated T cells c1 (NFATc1) and c-Fos, and the mRNA expression of genes required for cell fusion and bone resorption, such as osteoclast-associatedreceptor (OSCAR), tartrate resistant acid phosphatase (TRAP), cathepsinK, dendritic cell-specific transmembrane protein(DC-STAMP), β3-integrin and osteoclast stimulatory transmembrane protein(OC-STAMP). Furthermore, results of micro-CT and histologic analysis indicated that ABE remarkably prevented lipopolysaccharide (LPS)-induced bone erosion. These results demonstrate that ABE prevents LPS-induced bone erosion through inhibition of osteoclast differentiation and function, suggesting the promise of ABE as a potential cure for various osteoclast-associated bone diseases.

MKP-1 signaling events are required for early osteoclastogenesis in lineage defined progenitor populations by disrupting RANKL-induced NFATc1 nuclear translocation

Cytokine-directed osteoclastogenesis is initiated in response to macrophage colony stimulating factor (M-CSF) and receptor activator of NF-κB ligand (RANKL) to drive formation of osteoclasts (OC), large bone resorptive cells of hematopoietic origin. RANKL-induced signaling activates the MAPK pathways, which initiates nuclear translocation of the master regulator of osteoclast formation, transcription factor NFATc1. Proper control over these signaling events is essential to normal OC formation response to stimuli. MAPK phosphatase 1 (MKP-1), a serine and tyrosine phosphatase encoded by the gene Dusp1, functions to dephosphorylate and subsequently inactivate MAPK (p38 and JNK) signaling essential in osteoclastogenesis. Here, we explored the role of MKP-1 during RANKL-driven osteoclastogenesis from defined (B220/CD45(-)GR1(-)CD11b(lo/-)CD115(+)) OC progenitor (dOCP) populations using WT and Dusp1(-/-) global knockout mice. Sorted cells were driven to OC by M-CSF pre-treatment followed by RANKL stimulation for 3days. OC formation and qPCR products were analyzed for maturation. Results indicate that Dusp1(-/-) dOCP form less numerous, significantly smaller and less functional OC compared to WT controls. These data were corroborated by mRNA expression of the key OC genes, Nfatc1 and Tm7sf4 (DC-STAMP), which were significantly reduced in early osteoclastogenesis in OC progenitor from Dusp1(-/-) mice. Intriguingly, our data reveals that MKP-1 may positively control OC formation in response to RANKL by regulating NFATc1 nuclear translocation. Collectively, this report supports the idea that MKP-1 signaling is essential in early osteoclastogenesis in response to RANKL-induced signaling.

(+)-Vitisin A inhibits osteoclast differentiation by preventing TRAF6 ubiquitination and TRAF6-TAK1 formation to suppress NFATc1 activation

We recently reported that oral administration of a (+)-vitisin A-enriched product prepared from Vitis thunbergii obviously ameliorated bone loss in ovariectomized mice and (+)-vitisin A was able to inhibit receptor activator of NF-κB ligand (RANKL)-induced osteoclast differentiation in RAW264.7 cells. Here we further clarified the mechanism(s) by which (+)-vitisin A targets osteoclastic differentiation and activity. Osteoclast-characteristic enzyme activity was determined using gel zymography or spectroflurometric-based assay. Expression of signal molecules was analyzed via Western blot or immunoprecipitation. Results showed that (+)-vitisin A suppressed RANKL-induced multinuclear cells (MNCs) formation and bone resorption which was accompanied with reduction in β3 integrin, osteoclast stimulatory transmembrane protein (OC-STAMP), matrix metalloproteinase-9 (MMP-9) and cathepsin K proteins expression. (+)-Vitisin A also down-regulated the proteolytic activities of MMP-9 and cathepsin K via targeting at the late stage function. (+)-Vitisin A prominently abrogated RANKL-triggered nuclear translocations of NF-κB, AP-1 (c-Fos/c-Jun dimer) and associated induction and nuclear accumulation of nuclear factor of activated T cells c1 (NFATc1). The upstream IκB degradation as well as ERK and JNK phosphorylation were also substantially repressed. Transfection with siRNA targeting tumor necrosis factor receptor associated factor 6 (TRAF6) clearly restrained RANKL-induced MNCs formation and NFATc1 induction. Interesting, RANKL triggered poly-ubiquitination of TRAF6 and associated TRAF6-TAK1 (transforming growth factor β-activated kinase 1) complex formation was prominently attenuated by (+)-vitisin A. Furthermore, the interaction between c-src tyrosine kinase (c-Src) and β3 was markedly induced by RANKL stimulation. (+)-Vitisin A significantly attenuated this interaction when concomitant treated with RANKL in RAW264.7 cells, but failed to affect c-Src/β3 complex formation when post-cultured with MNCs. Taken together, (+)-vitisin A suppressed bone resorption possibly via interruption of RANKL-induced TRAF6 ubiquitination and associated downstream signaling pathways. Furthermore, action through negative regulation of the proteolytic activity of MMP-9 and cathepsin K might also contribute to the anti-resorption effect of (+)-vitisin A.

Digitoxin induces apoptosis in cancer cells by inhibiting nuclear factor of activated T-cells-driven c-MYC expression

Background:

Cardiac glycosides such as digitoxin have been shown to directly cause apoptotic death of cancer cells both in vitro, and in vivo. However, the mechanism connecting cardiac glycoside action to apoptosis is not known. It has been reported that compounds resembling digitoxin are able to reduce c-MYC expression. Furthermore, it has been previously shown that the transcription of c-MYC depends on nuclear factor of activated T-cells (NFAT) binding sites in the c-MYC promoter. We have therefore hypothesized that NFAT might mediate digitoxin effects on c-MYC mRNA message.

Materials and Methods:

We have chosen to study this process in HeLa cells where structurally intact c-MYC genes in 8q24 co-localize with human papilloma virus 18 at all integration sites.

Results:

Here we show that within the 1^st h following treatment with digitoxin, a significant reduction in c-MYC mRNA occurs. This is followed by a precipitous loss of c-MYC protein, activation of caspase 3, and subsequent apoptotic cell death. To test the NFAT-dependence mechanism, we analyzed the effects of digitoxin on NFAT isoform-dependent auto-activation of a NFAT-luciferase expression system. Drug dependent effects on expression varied according to each of the four canonical NFAT isoforms (1, 2, 3 or 4). The most digitoxin-sensitive NFAT isoform was NFAT1. Using c-MYC chromatin immune precipitation, we find that digitoxin inhibits interaction of NFAT1 with the proximal c-MYC promoter.

Conclusions:

These results suggest that the carcinotoxic activity of digitoxin includes suppression of NFAT-driven c-MYC expression.

Dried plum polyphenols inhibit osteoclastogenesis by downregulating NFATc1 and inflammatory mediators

Dried plums and their polyphenols have been shown to suppress bone resorption by downregulating receptor activator NF-kappaB ligand (RANKL). Due to the anti-inflammatory and antioxidant properties of these compounds, this study was designed to investigate whether dried plum polyphenols exert additional, more direct effects on osteoclasts and their precursors. RAW 264.7 macrophages were used as a model to study osteoclast precursors and osteoclast differentiation and activity. Under inflammatory conditions induced by lipopolysaccharide (LPS), polyphenols extracted from dried plum (10, 20, and 30 microg/mL) downregulated osteoclast precursor cyclooxygenase expression and nitric oxide (NO) by inhibiting inducible NO synthase. NO and tumor necrosis factor (TNF)-alpha were also suppressed in the presence of RANKL during osteoclastogenesis by the polyphenols. Increased TNF-alpha production in response to oxidative stress, but not LPS, was decreased over time. As expected, LPS and H2O2 significantly increased the number of tartrate-resistant acid phosphatase-positive cells by 127% and 30%, respectively. Dried plum polyphenols decreased osteoclast differentiation under normal as well as inflammatory and oxidative stress conditions, coincident with the suppression of the transcription factor, nuclear factor for activated T cells (NFATcl). These inhibitory effects on osteoclastogenesis were confirmed in primary bone marrow cultures. Resorption pit formation was decreased to a similar extent as osteoclast differentiation, suggesting that dried plum polyphenols primarily affect osteoclast differentiation as opposed to activity. Our data demonstrate that dried plum polyphenols directly inhibit osteoclastogenesis, leading to a decrease in osteoclast activity, by downregulating NFATc1 and inflammatory mediators.

Functions of RANKL/RANK/OPG in bone modeling and remodeling

The discovery of the RANKL/RANK/OPG system in the mid 1990s for the regulation of bone resorption has led to major advances in our understanding of how bone modeling and remodeling are regulated. It had been known for many years before this discovery that osteoblastic stromal cells regulated osteoclast formation, but it had not been anticipated that they would do this through expression of members of the TNF superfamily: receptor activator of NF-kappaB ligand (RANKL) and osteoprotegerin (OPG), or that these cytokines and signaling through receptor activator of NF-kappaB (RANK) would have extensive functions beyond regulation of bone remodeling. RANKL/RANK signaling regulates osteoclast formation, activation and survival in normal bone modeling and remodeling and in a variety of pathologic conditions characterized by increased bone turnover. OPG protects bone from excessive resorption by binding to RANKL and preventing it from binding to RANK. Thus, the relative concentration of RANKL and OPG in bone is a major determinant of bone mass and strength. Here, we review our current understanding of the role of the RANKL/RANK/OPG system in bone modeling and remodeling.