Sclerostin blockade promotes bone metastases of Wnt-responsive breast cancer cells.

The secreted protein sclerostin is primarily produced by osteocytes and suppresses osteoblast differentiation and function by inhibiting the canonical Wnt signaling pathway. Genetic and pharmacological inhibition of sclerostin has been shown to increase bone formation and an anti-sclerostin antibody has been clinically approved for the treatment of osteoporosis. Canonical Wnt signaling is also involved in the progression of several types of cancers including breast cancer. Here, we studied the effects of sclerostin inhibition on the development of bone metastases of breast cancer using mouse models. TOPFLASH assay and real-time PCR analysis of AXIN2, a target of canonical Wnt signaling, revealed that, among four cell lines tested, MDA-MB-231 human breast cancer cells responded highly to the canonical Wnt ligand Wnt3a, whereas other cell lines exhibited marginal responses. Consistent with these results, treatment with an anti-sclerostin antibody significantly increased the bone metastases of MDA-MB-231 but not those of other breast cancer cells. Immunohistochemical studies demonstrated that an anti-sclerostin antibody induced intracellular accumulation of ß-catenin in bone-colonized MDA-MB-231 cells. Suspension culture assays showed that Wnt3a accelerated the tumorsphere formation of MDA-MB-231 cells, whereas monolayer cell proliferation and migration were not affected. Furthermore, the numbers of osteoclasts and their precursor cells in bone metastases of MDA-MB-231 were significantly increased in mice treated with an anti-sclerostin antibody. These results collectively suggest that sclerostin blockade activates canonical Wnt signaling in ligand-responsive breast cancer cells metastasized to bone, thereby increasing bone metastases, likely to have been mediated at least in part by enhancing stem cell-like properties of cancer cells and osteoclastogenesis.

Angiotensin II Induces Aortic Rupture and Dissection in Osteoprotegerin-Deficient Mice.

Background The biological mechanism of action for osteoprotegerin, a soluble decoy receptor for the receptor activator of nuclear factor-kappa B ligand in the vascular structure, has not been elucidated. The study aim was to determine if osteoprotegerin affects aortic structural integrity in angiotensin II (Ang II)-induced hypertension. Methods and Results Mortality was higher (P<0.0001 by log-rank test) in 8-week-old male homozygotes of osteoprotegerin gene-knockout mice given subcutaneous administration of Ang II for 28 days, with an incidence of 21% fatal aortic rupture and 23% aortic dissection, than in age-matched wild-type mice. Ang II-infused aorta of wild-type mice showed that osteoprotegerin immunoreactivity was present with proteoglycan. The absence of osteoprotegerin was associated with decreased medial and adventitial thickness and increased numbers of elastin breaks as well as with increased periostin expression and soluble receptor activator of nuclear factor-kappa B ligand concentrations. PEGylated human recombinant osteoprotegerin administration decreased all-cause mortality (P<0.001 by log-rank test), the incidence of fatal aortic rupture (P=0.08), and aortic dissection (P<0.001) with decreasing numbers of elastin breaks, periostin expressions, and soluble receptor activator of nuclear factor-kappa B ligand concentrations in Ang II-infused osteoprotegerin gene-knockout mice. Conclusions These data suggest that osteoprotegerin protects against aortic rupture and dissection in Ang II-induced hypertension by inhibiting receptor activator of nuclear factor-kappa B ligand activity and periostin expression.

Inhibitor of protein kinase N3 suppresses excessive bone resorption in ovariectomized mice.

INTRODUCTION: The long-term inhibition of bone resorption suppresses new bone formation because these processes are coupled during physiological bone remodeling. The development of anti-bone-resorbing agents that do not suppress bone formation is urgently needed. We previously demonstrated that Wnt5a-Ror2 signaling in mature osteoclasts promoted bone-resorbing activity through protein kinase N3 (Pkn3). The p38 MAPK inhibitor SB202190 reportedly inhibited Pkn3 with a low Ki value (0.004 µM). We herein examined the effects of SB202190 on osteoclast differentiation and function in vitro and in vivo. MATERIALS AND METHODS: Bone marrow cells were cultured in the presence of M-csf and GST-Rankl to differentiate into multinucleated osteoclasts. Osteoclasts were treated with increasing concentrations of SB202190. For in vivo study, 10-week-old female mice were subjected to ovariectomy (OVX). OVX mice were intraperitoneally administered with a Pkn3 inhibitor at 2 mg/kg or vehicle for 4 weeks, and bone mass was analyzed by micro-CT. RESULTS: SB202190 suppressed the auto-phosphorylation of Pkn3 in osteoclast cultures. SB202190 significantly inhibited the formation of resorption pits in osteoclast cultures by suppressing actin ring formation. SB202190 reduced c-Src activity in osteoclast cultures without affecting the interaction between Pkn3 and c-Src. A treatment with SB202190 attenuated OVX-induced bone loss without affecting the number of osteoclasts or bone formation by osteoblasts. CONCLUSIONS: Our results showed that Pkn3 has potential as a therapeutic target for bone loss due to increased bone resorption. SB202190 is promising as a lead compound for the development of novel anti-bone-resorbing agents.

Osteoclast differentiation by RANKL and OPG signaling pathways.

INTRODUCTION: In bone tissue, bone resorption by osteoclasts and bone formation by osteoblasts are repeated continuously. Osteoclasts are multinucleated cells that derive from monocyte-/macrophage-lineage cells and resorb bone. In contrast, osteoblasts mediate osteoclastogenesis by expressing receptor activator of nuclear factor-kappa B ligand (RANKL), which is expressed as a membrane-associated cytokine. Osteoprotegerin (OPG) is a soluble RANKL decoy receptor that is predominantly produced by osteoblasts and which prevents osteoclast formation and osteoclastic bone resorption by inhibiting the RANKL-RANKL receptor interaction. MATERIALS AND METHODS: In this review, we would like to summarize our experimental results on signal transduction that regulates the expression of RANKL and OPG. RESULTS: Using OPG gene-deficient mice, we have demonstrated that OPG and sclerostin produced by osteocytes play an important role in the maintenance of cortical and alveolar bone. In addition, it was shown that osteoclast-derived leukemia inhibitory factor (LIF) reduces the expression of sclerostin in osteocytes and promotes bone formation. WP9QY (W9) is a peptide that was designed to be structurally similar to one of the cysteine-rich TNF-receptortype-I domains. Addition of the W9 peptide to bone marrow culture simultaneously inhibited osteoclast differentiation and stimulated osteoblastic cell proliferation. An anti-sialic acid-binding immunoglobulin-like lectin 15 (Siglec-15) antibody inhibited multinucleated osteoclast formation induced by RANKL and macrophage colony-stimulating factor (M-CSF). Pit-forming activity of osteoclasts was also inhibited by the anti-Siglec-15 antibody. In addition, anti-Siglec-15 antibody treatment stimulated the appearance of osteoblasts in cultures of mouse bone marrow cells in the presence of RANKL and M-CSF. CONCLUSIONS: Bone mass loss depends on the RANK-RANKL-OPG system, which is a major regulatory system of osteoclast differentiation induction, activation, and survival.

Sclerostin expression in trabecular bone is downregulated by osteoclasts.

Bone tissues have trabecular bone with a high bone turnover and cortical bone with a low turnover. The mechanisms by which the turnover rate of these bone tissues is determined remain unclear. Osteocytes secrete sclerostin, a Wnt/ß-catenin signaling antagonist, and inhibit bone formation. We found that sclerostin expression in cortical bone is more marked than in trabecular bone in Sost reporter mice. Leukemia inhibitory factor (LIF) secreted from osteoclasts reportedly suppressed sclerostin expression and promoted bone formation. Here, we report that osteoclasts downregulate sclerostin expression in trabecular bone and promote bone turnover. Treatment of C57BL/6 mice with an anti-RANKL antibody eliminated the number of osteoclasts and LIF-positive cells in trabecular bone. The number of sclerostin-positive cells was increased in trabecular bone, while the number of ß-catenin-positive cells and bone formation were decreased in trabecular bone. Besides, Tnfsf11 heterozygous (Rankl+/-) mice exhibited a decreased number of LIF-positive cells and increased number of sclerostin-positive cells in trabecular bone. Rankl+/- mice exhibited a decreased number of ß-catenin-positive cells and reduced bone formation in trabecular bone. Furthermore, in cultured osteoclasts, RANKL stimulation increased Lif mRNA expression, suggesting that RANKL signal increased LIF expression. In conclusion, osteoclasts downregulate sclerostin expression and promote trabecular bone turnover.

The Regulation of Bone Metabolism and Disorders by Wnt Signaling.

Wnt, a secreted glycoprotein, has an approximate molecular weight of 40 kDa, and it is a cytokine involved in various biological phenomena including ontogeny, morphogenesis, carcinogenesis, and maintenance of stem cells. The Wnt signaling pathway can be classified into two main pathways: canonical and non-canonical. Of these, the canonical Wnt signaling pathway promotes osteogenesis. Sclerostin produced by osteocytes is an inhibitor of this pathway, thereby inhibiting osteogenesis. Recently, osteoporosis treatment using an anti-sclerostin therapy has been introduced. In this review, the basics of Wnt signaling, its role in bone metabolism and its involvement in skeletal disorders have been covered. Furthermore, the clinical significance and future scopes of Wnt signaling in osteoporosis, osteoarthritis, rheumatoid arthritis and neoplasia are discussed.

Blockade of the angiotensin II type 1 receptor increases bone mineral density and left ventricular contractility in a mouse model of juvenile Paget disease.

Juvenile Paget disease (JPD1), an autosomal-recessive disorder, is characterized by extremely rapid bone turnover due to osteoprotegerin deficiency. Its extra-skeletal manifestations, such as hypertension and heart failure, suggest a pathogenesis with shared skeletal and cardiovascular system components. In spite of this, the effects of anti-hypertensive drugs on bone morphometry remain unknown. We administered an angiotensin II type 1 receptor blocker, olmesartan (5 mg/kg/day) to 8-week-old male mice lacking the osteoprotegerin gene, with and without 1 µg/kg/min of angiotensin II infusion for 14 days. Olmesartan treatment decreased systolic blood pressure, and echocardiography showed increased left ventricular systolic contractility. Three-dimensional micro-computed tomography scans demonstrated that olmesartan treatment increased trabecular bone volume (sham, +176%; angiotensin II infusion, +335%), mineral density (sham, +150%; angiotensin II infusion, +313%), and trabecular number (sham, +407%; angiotensin II infusion, +622%) in the tibia. Olmesartan increased cortical mineral density (sham, +19%; angiotensin II infusion, +24%), decreased the cortical bone section area (sham, -16%; angiotensin II infusion, -18%), decreased thickness (sham, -18%; angiotensin II infusion, -31%), and decreased the lacunar area (sham, -41%; angiotensin II infusion, -27%) in the tibia. Similar trend was observed in the femur. Moreover, olmesartan decreased angiotensin II-induced increases in tartrate-resistant acid phosphatase concentrations in plasma, but it affected neither type I procollagen N-terminal propeptides, nor the receptor activator of nuclear factor kappa-B ligand. Our data suggest that blockade of the angiotensin II type 1 receptor improves bone vulnerability, and helps to maintain the heart's structural integrity in osteoprotegerin-deficient mice.

Treatment of OPG-deficient mice with WP9QY, a RANKL-binding peptide, recovers alveolar bone loss by suppressing osteoclastogenesis and enhancing osteoblastogenesis.

Osteoblasts express two key molecules for osteoclast differentiation, receptor activator of NF-κB ligand (RANKL) and osteoprotegerin (OPG), a soluble decoy receptor for RANKL. RANKL induces osteoclastogenesis, while OPG inhibits it by blocking the binding of RANKL to RANK, a cellular receptor of RANKL. OPG-deficient (OPG-/-) mice exhibit severe alveolar bone loss with enhanced bone resorption. WP9QY (W9) peptide binds to RANKL and blocks RANKL-induced osteoclastogenesis. W9 is also reported to stimulate bone formation in vivo. Here, we show that treatment with W9 restores alveolar bone loss in OPG-/-mice by suppressing osteoclastogenesis and enhancing osteoblastogenesis. Administration of W9 or risedronate, a bisphosphonate, to OPG-/-mice significantly decreased the osteoclast number in the alveolar bone. Interestingly, treatment with W9, but not risedronate, enhanced Wnt/ß-catenin signaling and induced alveolar bone formation in OPG-/-mice. Expression of sclerostin, an inhibitor of Wnt/ß-catenin signaling, was significantly lower in tibiae of OPG-/-mice than in wild-type mice. Treatment with risedronate recovered sclerostin expression in OPG-/-mice, while W9 treatment further suppressed sclerostin expression. Histomorphometric analysis confirmed that bone formation-related parameters in OPG-/-mice, such as osteoblast number, osteoblast surface and osteoid surface, were increased by W9 administration but not by risedronate administration. These results suggest that treatment of OPG-/-mice with W9 suppressed osteoclastogenesis by inhibiting RANKL signaling and enhanced osteoblastogenesis by attenuating sclerostin expression in the alveolar bone. Taken together, W9 may be a useful drug to prevent alveolar bone loss in periodontitis.

A Jak1/2 inhibitor, baricitinib, inhibits osteoclastogenesis by suppressing RANKL expression in osteoblasts in vitro.

The Janus kinases (Jaks) are hubs in the signaling process of more than 50 cytokine or hormone receptors. However, the function of Jak in bone metabolism remains to be elucidated. Here, we showed that the inhibition of Jak1 and/or Jak2 in osteoblast-lineage cells led to impaired osteoclastogenesis due to the reduced expression of receptor activator of nuclear factor-κB ligand (RANKL). Murine calvaria-derived osteoblasts induced differentiation of bone marrow cells into osteoclasts in the presence of 1,25-dihydroxyvitamin D3 (1,25D3) and prostaglandin E2 (PGE2) in vitro. However, treatment with the Jak1/2 inhibitor, baricitinib, markedly inhibited osteoclastogenesis in the co-culture. On the other hand, baricitinib did not inhibit RANKL-induced osteoclast differentiation of bone marrow macrophages. These results indicated that baricitinib acted on osteoblasts, but not on bone marrow macrophages. Baricitinib suppressed 1,25D3 and PGE2-induced up-regulation of RANKL in osteoblasts, but not macrophage colony-stimulating factor expression. Moreover, the addition of recombinant RANKL to co-cultures completely rescued baricitinib-induced impairment of osteoclastogenesis. shRNA-mediated knockdown of Jak1 or Jak2 also suppressed RANKL expression in osteoblasts and inhibited osteoclastogenesis. Finally, cytokine array revealed that 1,25D3 and PGE2 stimulated secretion of interleukin-6 (IL-6), IL-11, and leukemia inhibitory factor in the co-culture. Hence, Jak1 and Jak2 represent novel therapeutic targets for osteoporosis as well as inflammatory bone diseases including rheumatoid arthritis.

Bone Formation Is Coupled to Resorption Via Suppression of Sclerostin Expression by Osteoclasts.

Bone formation is coupled to bone resorption throughout life. However, the coupling mechanisms are not fully elucidated. Using Tnfrsf11b-deficient (OPG-/- ) mice, in which bone formation is clearly coupled to bone resorption, we found here that osteoclasts suppress the expression of sclerostin, a Wnt antagonist, thereby promoting bone formation. Wnt/ß-catenin signals were higher in OPG-/- and RANKL-transgenic mice with a low level of sclerostin. Conditioned medium from osteoclast cultures (Ocl-CM) suppressed sclerostin expression in UMR106 cells and osteocyte cultures. In vitro experiments revealed that osteoclasts secreted leukemia inhibitory factor (LIF) and inhibited sclerostin expression. Anti-RANKL antibodies, antiresorptive agents, suppressed LIF expression and increased sclerostin expression, thereby reducing bone formation in OPG-/- mice. Taken together, osteoclast-derived LIF regulates bone turnover through sclerostin expression. Thus, LIF represents a target for improving the prolonged suppression of bone turnover by antiresorptive agents. © 2017 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals Inc.

Dendritic cell-based immunotherapy targeting Wilms' tumor 1 in patients with recurrent malignant glioma.

OBJECT: Dendritic cell (DC)-based vaccination is considered a potentially effective therapy against advanced cancer. The authors conducted a Phase I study to investigate the safety and immunomonitoring of Wilms' tumor 1 (WT1)-pulsed DC vaccination therapy for patients with relapsed malignant glioma. METHODS: WT1-pulsed and/or autologous tumor lysate-pulsed DC vaccination therapy was performed in patients with relapsed malignant gliomas. Approximately 1 × 10(7) to 2 × 10(7) pulsed DCs loaded with WT1 peptide antigen and/or tumor lysate were intradermally injected into the axillary areas with OK-432, a streptococcal preparation, at 2-week intervals for at least 5-7 sessions (1 course) during an individual chemotherapy regimen. RESULTS: Ten patients (3 men, 7 women; age range 24-64 years [median 39 years]) with the following tumors were enrolled: glioblastoma (6), anaplastic astrocytoma (2), anaplastic oligoastrocytoma (1), and anaplastic oligodendroglioma (1). Modified WT1 peptide-pulsed DC vaccine was administered to 7 patients, tumor lysate-pulsed DC vaccine to 2 patients, and both tumor lysate-pulsed and WT1-pulsed DC vaccine to 1 patient. The clinical response was stable disease in 5 patients with WT1-pulsed DC vaccination. In 2 of 5 patients with stable disease, neurological findings improved, and MR images showed tumor shrinkage. No serious adverse events occurred except Grade 1-2 erythema at the injection sites. WT1 tetramer analysis detected WT1-reactive cytotoxic T cells after vaccination in patients treated with WT1-pulsed therapy. Positivity for skin reaction at the injection sites was 80% (8 of 10 patients) after the first session, and positivity remained for these 8 patients after the final session. CONCLUSIONS: This study of WT1-pulsed DC vaccination therapy demonstrated safety, immunogenicity, and feasibility in the management of relapsed malignant gliomas.

The regulation of osteoclast differentiation by Wnt signals.

Wnt ligands activate ß-catenin-dependent canonical and -independent noncanonical signaling pathways. Wnt regulates many physiological events such as the development of organs and bone metabolism. In contrast, failed signaling leads to pathological conditions including cancer and osteoporosis. Analyses of loss-of-function mutations in the low-density lipoprotein receptor-related protein (Lrp) 5 gene revealed that Lrp5 acted as a co-receptor of Wnt/ß-catenin signals and positively regulated bone mass in humans and mice. Many players in Wnt signals including sclerostin, an osteocyte-derived Wnt antagonist, also have since been found to influence bone mass. Bone mass is regulated by the activities of bone-forming osteoblasts, -resorbing osteoclasts and matrix-embedded osteocytes. The roles of Wnt/ß-catenin signals in osteoblastogenesis and osteoclastogenesis have been established by the findings of a large number of in vitro and in vivo studies. In contrast, the roles of noncanonical Wnt signals in bone metabolism are only now being examined. In this review, we introduced and discussed recent information on the roles of Wnt signals in bone resorption.

Wnt16 regulates osteoclast differentiation in conjunction with Wnt5a.

The canonical Wnt/ß-catenin signaling pathway in osteoblast-lineage cells inhibits osteoclastogenesis through the expression of osteoprotegerin (Opg), a decoy receptor of receptor activator of Nf-κb (Rank) ligands. Wnt5a, a typical non-canonical Wnt ligand, enhances the expression of Rank in osteoclast precursors, which, in turn, promotes the Rank ligand (Rankl)-induced formation of osteoclasts. In contrast, Wnt16 and Wnt4 have been shown to inhibit the Rankl-induced formation of osteoclasts through non-canonical Wnt signals. However, the relationships among these Wnt ligands in osteoclastogenesis remained to be elucidated. We herein showed that Wnt16, but not Wnt4, inhibited the Rankl-induced osteoclastogenesis in bone marrow-derived macrophage (BMM) cultures. Wnt3a and Wnt4 inhibited the 1α,25-dihydroxy vitamin D3 (1,25D3)-induced osteoclastogenesis in co-cultures prepared from wild-type mice, but not in those from Opg(-/-) nice. Wnt16 inhibited the 1,25D3-induced formation of osteoclasts in both wild-type and Opg(-/-) co-cultures. Wnt16, Wnt4, and Wnt3a failed to inhibit the pit-forming activity of osteoclasts. Wnt16 failed to inhibit the Wnt5a-induced expression of Rank in osteoclast precursors. In contrast, Wnt5a abrogated the inhibitory effects of Wnt16 on Rankl-induced osteoclastogenesis. These results suggested that Wnt16 inhibited osteoclastogenesis, but not the function of osteoclasts and that Wnt16, an inhibitory Wnt ligand for osteoclastogenesis, regulates bone resorption in conjunction with Wnt5a.

Roles of cathelicidin-related antimicrobial peptide in murine osteoclastogenesis.

Cathelicidin-related antimicrobial peptide (CRAMP) not only kills bacteria but also binds to lipopolysaccharide (LPS) to neutralize its activity. CRAMP is highly expressed in bone marrow and its expression is reported to be up-regulated by inflammatory and infectious stimuli. Here, we examined the role of CRAMP in murine osteoclastogenesis. Osteoclasts were formed in co-cultures of osteoblasts and bone marrow cells in response to 1α,25-dihydroxyvitamin D3 [1α,25(OH)2 D3 ], prostaglandin E2 (PGE2 ), and Toll-like receptor (TLR) ligands such as LPS and flagellin through the induction of receptor activator of nuclear factor-κB ligand (RANKL) expression in osteoblasts. CRAMP inhibited the osteoclastogenesis in co-cultures treated with LPS and flagellin, but not in those treated with 1α,25(OH)2 D3 or PGE2 . Although bone marrow macrophages (BMMs) highly expressed formyl peptide receptor 2 (a receptor of CRAMP), CRAMP showed no inhibitory effect on osteoclastogenesis in BMM cultures treated with RANKL. CRAMP suppressed both LPS- and flagellin-induced RANKL expression in osteoblasts and tumour necrosis factor-α (TNF-α) expression in BMMs, suggesting that CRAMP neutralizes the actions of LPS and flagellin. LPS and flagellin enhanced the expression of CRAMP mRNA in osteoblasts. Extracellularly added CRAMP suppressed LPS- and flagellin-induced CRAMP expression. These results suggest that the production of CRAMP promoted by LPS and flagellin is inhibited by CRAMP released by osteoblasts through a feedback regulation. Even though CRAMP itself has no effect on osteoclastogenesis in mice, we propose that CRAMP is an osteoblast-derived protector in bacterial infection-induced osteoclastic bone resorption.

Osteoprotegerin-deficient male mice as a model for severe alveolar bone loss: comparison with RANKL-overexpressing transgenic male mice.

Periodontitis, an inflammatory disease of periodontal tissues, is characterized by excessive alveolar bone resorption. An increase in the receptor activator of nuclear factor-κB ligand (RANKL) to osteoprotegerin (OPG) ratio is thought to reflect the severity of periodontitis. Here, we examined alveolar bone loss in OPG-deficient (OPG(-/-)) mice and RANKL-overexpressing transgenic (RANKL-Tg) mice. Alveolar bone loss in OPG(-/-) mice at 12 weeks was significantly higher than that in RANKL-Tg mice. OPG(-/-) but not RANKL-Tg mice exhibited severe bone resorption especially in cortical areas of the alveolar bone. An increased number of osteoclasts was observed in the cortical areas in OPG(-/-) but not in RANKL-Tg mice. Immunohistochemical analyses showed many OPG-positive signals in osteocytes but not osteoblasts. OPG-positive osteocytes in the cortical area of alveolar bones and long bones were abundant in both wild-type and RANKL-Tg mice. This suggests the resorption in cortical bone areas to be prevented by OPG produced locally. To test the usefulness of OPG(-/-) mice as an animal model for screening drugs to prevent alveolar bone loss, we administered an antimouse RANKL antibody or risedronate, a bisphosphonate, to OPG(-/-) mice. They suppressed alveolar bone resorption effectively. OPG(-/-) mice are useful for screening therapeutic agents against alveolar bone loss.

Tetracyclines convert the osteoclastic-differentiation pathway of progenitor cells to produce dendritic cell-like cells.

Tetracyclines, such as doxycycline and minocycline, are used to suppress the growth of bacteria in patients with inflammatory diseases. Tetracyclines have been shown to prevent bone loss, but the mechanism involved is unknown. Osteoclasts and dendritic cells (DCs) are derived from common progenitors, such as bone marrow-derived macrophages (BMMs). In this article, we show that tetracyclines convert the differentiation pathway, resulting in DC-like cells not osteoclasts. Doxycycline and minocycline inhibited the receptor activator of NF-κB ligand (RANKL)-induced osteoclastogenesis of BMMs, but they had no effects on cell growth and phagocytic activity. They influenced neither the proliferation nor the differentiation of bone-forming osteoblasts. Surprisingly, doxycycline and minocycline induced the expression of DC markers, CD11c and CD86, in BMMs in the presence of RANKL. STAT5 is involved in DC differentiation induced by GM-CSF. Midostaurin, a STAT5-signaling inhibitor, and an anti-GM-CSF-neutralizing Ab suppressed the differentiation induced by GM-CSF but not by tetracyclines. In vivo, the injection of tetracyclines into RANKL-injected mice and RANKL-transgenic mice suppressed RANKL-induced osteoclastogenesis and promoted the concomitant appearance of CD11c(+) cells. These results suggested that tetracyclines prevent bone loss induced by local inflammation, including rheumatoid arthritis and periodontitis, through osteoclast-DC-like cell conversion.

Evaluation of pharmaceuticals with a novel 50-hour animal model of bone loss.

Osteoporosis remains a major public health problem through its associated fragility fractures. Several animal models for the study of osteoporotic bone loss, such as ovariectomy (OVX) and denervation, require surgical skills and several weeks to establish. Osteoclast differentiation and activation is mediated by RANKL. Here we report the establishment of a novel and rapid bone loss model by the administration of soluble RANKL (sRANKL) to mice. Mice were injected intraperitoneally with sRANKL and used to evaluate existing anti-osteoporosis drugs. sRANKL decreased BMD within 50 h in a dose-dependent manner. The marked decrease in femoral trabecular BMD shown by pQCT and the 3D images obtained by microCT were indistinguishable from those observed in the OVX model. Histomorphometry showed that osteoclastic activity was significantly increased in the sRANKL-injected mice. In addition, serum biochemical markers of bone turnover such as Ca, C-telopeptide of type 1 collagen (CTX), and TRACP5b were also significantly increased in the sRANKL-injected mice in a dose-dependent manner. Bisphosphonates (BPs), selective estrogen receptor modulators (SERMs), and PTH are commonly used for the treatment of osteoporosis. We successfully evaluated the effects of anti-bone-resorbing agents such as BPs, a SERM, and anti-RANKL-neutralizing antibody on bone resorption in a couple of weeks. We also evaluated the effects of PTH on bone formation in 2 wk. A combination of sRANKL injections and OVX made it possible to evaluate a SERM. The sRANKL model is the simplest, fastest, and easiest of all osteoporosis models and could be useful in the evaluation of drug candidates for osteoporosis.

Diphenylhydantoin inhibits osteoclast differentiation and function through suppression of NFATc1 signaling.

Diphenylhydantoin (DPH) is widely used as an anticonvulsant drug. We examined the effects of DPH on osteoclast differentiation and function using in vivo and in vitro assay systems. Transgenic mice overexpressing a soluble form of RANKL (RANKL Tg) exhibited increased osteoclastic bone resorption. Injection of DPH into the subcutaneous tissue overlying calvaria of RANKL Tg mice suppressed the enhanced resorption in the calvaria. In co-cultures of mouse osteoblasts and bone marrow cells, DPH inhibited lipopolysaccharide (LPS)-induced osteoclast formation. DPH affected neither the mRNA expression of RANKL and osteoprotegerin nor the growth of mouse osteoblasts in culture. On the other hand, DPH inhibited the RANKL-induced formation of osteoclasts in cultures of mouse bone marrow-derived macrophages (BMMphis) and of human peripheral blood-derived CD14(+) cells. DPH concealed LPS-induced bone resorption in mouse calvarial organ cultures and inhibited the pit-forming activity of mouse osteoclasts cultured on dentine slices. DPH suppressed the RANKL-induced calcium oscillation and expression of nuclear factor of activated T cells c1 (NFATc1) and c-fos in BMMphis. Moreover, DPH inhibited the RANKL-induced nuclear localization and auto-amplification of NFATc1 in mature osteoclasts. Both BMMphis and osteoclasts expressed mRNA of a T-type calcium channel, Cav3.2, a target of DPH. Blocking the expression of Cav3.2 by short hairpin RNAs significantly suppressed RANKL-induced osteoclast differentiation. These results suggest that DPH inhibits osteoclast differentiation and function through suppression of NFATc1 signaling. The topical application of DPH may be a therapeutic treatment to prevent bone loss induced by local inflammation such as periodontitis.

Lipopolysaccharide-mediated enhancement of bone metabolism in estrogen-deficient mice.

BACKGROUND: Osteoporosis may be a risk factor in periodontal disease. However, biologic mechanisms explaining the apparent interaction between these two diseases have not been defined. It is well known that lipopolysaccharide (LPS) increases the resorption of alveolar bone. We hypothesized that LPS and estrogen deficiency have synergistic effects on bone metabolism and may lead to enhanced bone resorption. METHODS: Eighty 8-week-old female ddY mice were divided into two groups and underwent a sham operation or bilateral ovariectomy. They were maintained for 4 weeks to assess estrogen-deficient bone loss. Osteoblasts and bone marrow cells (BMCs) were collected from ovariectomized (OVX) and sham-operated mice. Osteoclast differentiation in a coculture of osteoblasts and BMCs was investigated by tartrate-resistant acid phosphatase staining. Receptor activator of nuclear factor-kappa B ligand (RANKL) mRNA expression in LPS-treated osteoblasts was investigated using real-time polymerase chain reaction. Interferon-gamma (IFN-gamma) and interleukin (IL)-6 and -10 levels in the culture supernatants were evaluated by enzyme-linked immunosorbent assay. Group means were compared by analysis of variance followed by Tukey's honestly significant difference. RESULTS: There was a significant increase in the number of osteoclasts in LPS-treated cocultures from OVX mice compared to sham controls (P <0.05). RANKL mRNA expression in LPS-treated osteoblasts from OVX mice was greater than in sham mice (P <0.05). In contrast, the production of IFN-gamma in LPS-treated coculture from OVX mice was significantly lower than in sham mice (P <0.05). CONCLUSION: LPS-bearing Gram-negative organisms are abundant in periodontal disease, and the results supported the hypothesis that bone resorption is increased in estrogen-deficient patients.