Stimulation of osteoclastogenesis by enhanced levels of MIP-1alpha in BALB/c mice in vitro

Regulation of osteoclast-mediated bone resorption by lipids

Hyperactivation of osteoclasts has been identified as a significant etiological factor in several bone resorption-related disorders, including osteoporosis, periodontitis, arthritis, and bone metastasis of tumors. It has been demonstrated that the severity of these diseases is influenced by lipids that regulate osteoclast differentiation and activity through specific signaling pathways and cytokine levels. The regulatory mechanisms of different types of lipids on osteoclastogenesis vary across diverse disease contexts in bone resorption regulated by osteoclasts. This review presents an overview of the mechanisms underlying osteoclast formation and summarizes the pathways through which various lipids regulate osteoclastogenesis in different pathological contexts. We also discuss effective therapeutic strategies for osteolytic diseases based on modulation of lipid metabolism.

The role of E3 ubiquitin ligases in bone homeostasis and related diseases

The ubiquitin-proteasome system (UPS) dedicates to degrade intracellular proteins to modulate demic homeostasis and functions of organisms. These enzymatic cascades mark and modifies target proteins diversly through covalently binding ubiquitin molecules. In the UPS, E3 ubiquitin ligases are the crucial constituents by the advantage of recognizing and presenting proteins to proteasomes for proteolysis. As the major regulators of protein homeostasis, E3 ligases are indispensable to proper cell manners in diverse systems, and they are well described in physiological bone growth and bone metabolism. Pathologically, classic bone-related diseases such as metabolic bone diseases, arthritis, bone neoplasms and bone metastasis of the tumor, etc., were also depicted in a UPS-dependent manner. Therefore, skeletal system is versatilely regulated by UPS and it is worthy to summarize the underlying mechanism. Furthermore, based on the current status of treatment, normal or pathological osteogenesis and tumorigenesis elaborated in this review highlight the clinical significance of UPS research. As a strategy possibly remedies the limitations of UPS treatment, emerging PROTAC was described comprehensively to illustrate its potential in clinical application. Altogether, the purpose of this review aims to provide more evidence for exploiting novel therapeutic strategies based on UPS for bone associated diseases.

CCL3 in the bone marrow microenvironment causes bone loss and bone marrow adiposity in aged mice

The central physiological role of the bone marrow renders bone marrow stromal cells (BMSCs) particularly sensitive to aging. With bone aging, BMSCs acquire a differentiation potential bias in favor of adipogenesis over osteogenesis, and the underlying molecular mechanisms remain unclear. Herein, we investigated the factors underlying age-related changes in the bone marrow and their roles in BMSCs' differentiation. Antibody array revealed that CC chemokine ligand 3 (CCL3) accumulation occurred in the serum of naturally aged mice along with bone aging phenotypes, including bone loss, bone marrow adiposity, and imbalanced BMSC differentiation. In vivo Ccl3 deletion could rescue these phenotypes in aged mice. CCL3 improved the adipogenic differentiation potential of BMSCs, with a positive feedback loop between CCL3 and C/EBPα. CCL3 activated C/EBPα expression via STAT3, while C/EBPα activated CCL3 expression through direct promoter binding, facilitated by DNA hypomethylation. Moreover, CCL3 inhibited BMSCs' osteogenic differentiation potential by blocking β-catenin activity mediated by ERK-activated Dickkopf-related protein 1 upregulation. Blocking CCL3 in vivo via neutralizing antibodies ameliorated trabecular bone loss and bone marrow adiposity in aged mice. This study provides insights regarding age-related bone loss and bone marrow adiposity pathogenesis and lays a foundation for the identification of new targets for senile osteoporosis treatment.

Curcumin inhibits the migration of osteoclast precursors and osteoclastogenesis by repressing CCL3 production

BACKGROUND

Curcumin can inhibit the osteoclastogenesis and the migration of several cells including macrophages. Osteoclast precursors (OCPs) are known to exist as bone marrow-derived macrophages (BMMs). This study aims to explore whether curcumin can prevent the fusion and differentiation of OCPs to mature osteoclasts by inhibiting OCP migration.

METHODS

In this study, we investigated the role of curcumin in regulating the production of several chemokines (CCL2, CCL3 and CX3CL1) and the migration of OCPs by ELISA, Western blotting and Transwell assays. Furthermore, we explored the role of curcumin in the chemokines-related osteoclastogenesis using pharmacological intervention and virus infection, and used ovariectomized (OVX) mice (osteoporosis model) to explore the effect of curcumin on the production of specific chemokine in vivo.

RESULTS

The results showed that curcumin significantly reduced the production of CCL3 in OCPs. Moreover, curcumin-inhibited the migration of OCPs was not affected by CCR1 (Receptor of CCL3) overexpression. Remarkably, curcumin-reduced osteoclastogenesis was significantly reversed by CCL3 addition, while CCR1 overexpression did not increase the osteoclastogenesis in the presence of curcumin. Furthermore, in vivo assays also showed that curcumin significantly reduced the production of CCL3 in OCPs in the trabecular bone of OVX mice.

CONCLUSIONS

In conclusion, curcumin prevents the migration of OCPs by reducing CCL3 production, ultimately inhibiting the formation of mature osteoclasts. Therefore, our study provides the clues for improving the clinical strategies of osteoporosis, dental implantation or orthodontic treatment.

New 8-C-p-Hydroxylbenzylflavonol Glycosides from Pumpkin (Cucurbita moschata Duch.) Tendril and Their Osteoclast Differentiation Inhibitory Activities

Six new 8-C-p-hydroxybenzylflavonol glycosides were isolated from a hot water extract of pumpkin (Cucurbita moschata Duch.) tendril and elucidated as 8-C-p-hydroxybenzylquercetin 3-O-rutinoside, 8-C-p-hydroxybenzoylquercetin 3-O-β-D-glucopyranoside, 8-C-p-hydroxybenzylkaempferol 3-O-(α-L-rhamnopyranosyl(1→6)-β-D-galactopyranoside, 8-C-p-hydroxybenzoylkaempferol 3-O-rutinoside, 8-C-p-hydroxybenzylisorhamnetin 3-O-rutinoside, and 8-C-p-hydroxybenzylisorhamnetin 3-O-(α-L-rhamnopyranosyl(1→6)-β-D-galactopyranoside. Their chemical structures were determined using nuclear magnetic resonance (NMR) and electrospray ionization-mass spectrometer (ESIMS) analyses. The 8-C-p-hydroxybenzylflavonol glycosides were found to inhibit the receptor activator of nuclear factor-κB (RANKL)-induced osteoclast differentiation of bone marrow derived macrophage (BMDM), an osteoclast progenitor. Additionally, 8-C-p-hydroxybenzylflavonol glycosides effectively reduced the expression of osteoclast-related genes, such as tartrate-resistant acid phosphatase, cathepsin K, nuclear factor activated T-cell cytoplasmic 1, and dendritic cell specific transmembrane protein in RANKL-treated BMDMs. These results indicate that the 8-C-p-hydroxybenzylflavonol glycosides may be the main components responsible for the osteoclast differentiation inhibitory effect of pumpkin tendril.

Water extract of tendril of Cucurbita Moschata Duch. suppresses RANKL-induced osteoclastogenesis by down-regulating p38 and ERK signaling

Background: Pumpkin (Curcubita sp.) is a natural product that is commonly used in folk medicine. However, the inhibitory effect and molecular mechanisms of tendril of Cucurbita Moschata Duch. (TCMD) on osteoclast differentiation have yet to be clearly elucidated. Thus, the present study aimed to investigate the effect and underlying mechanism of water extract of TCMD on osteoclast differentiation. Methods: Bone marrow-derived macrophages (BMDMs), osteoclast precursors, were cultured with macrophage colony stimulating factor (M-CSF) 30 ng/ml and receptor activator of nuclear factor-kappa B ligand (RANKL) 100 ng/ml for four days. We investigated the effect of TCMD on RANKL-induced osteoclast differentiation, tartrate-resistant acid phosphatase (TRAP) staining, F-actin ring formation, and bone resorption assay. RANKL signaling pathways were determined through Western blotting, and osteoclast differentiation marker genes were confirmed by Real-time PCR. Results: TCMD inhibited the RANKL-induced osteoclast differentiation in a dose-dependent manner without cytotoxicity. Further, F-actin ring formation and bone resorption were reduced by TCMD in RANKL-treated BMDMs. In addition, TCMD decreased the phosphorylation of p38 and ERK as well as the expression of osteoclast-related genes in BMDMs treated with RANKL. Conclusion: These findings suggest that TCMD may have preventive and therapeutic effects for destructive bone diseases.

Chemokines in Physiological and Pathological Bone Remodeling

The bone matrix is constantly remodeled by bone-resorbing osteoclasts and bone-forming osteoblasts. These two cell types are fundamentally different in terms of progenitor cells, mode of action and regulation by specific molecules, acting either systemically or locally. Importantly, there is increasing evidence for an impact of cell types or molecules of the adaptive and innate immune system on bone remodeling. Understanding these influences is the major goal of a novel research area termed osteoimmunology, which is of key relevance in the context of inflammation-induced bone loss, skeletal metastases, and diseases of impaired bone remodeling, such as osteoporosis. This review article aims at summarizing the current knowledge on one particular aspect of osteoimmunology, namely the impact of chemokines on skeletal cells in order to regulate bone remodeling under physiological and pathological conditions. Chemokines have key roles in the adaptive immune system by controlling migration, localization, and function of immune cells during inflammation. The vast majority of chemokines are divided into two subgroups based on the pattern of cysteine residues. More specifically, there are 27 known C-C-chemokines, binding to 10 different C-C receptors, and 17 known C-X-C-chemokines binding to seven different C-X-C receptors. Three additional chemokines do not fall into this category, and only one of them, i.e., CX3CL1, has been shown to influence bone remodeling cell types. There is a large amount of published studies demonstrating specific effects of certain chemokines on differentiation and function of osteoclasts and/or osteoblasts. Chemokine signaling by skeletal cells or by other cells of the bone marrow niche regulates bone formation and resorption through autocrine and paracrine mechanisms. In vivo evidence from mouse deficiency models strongly supports the role of certain chemokine signaling pathways in bone remodeling. We will summarize these data in the present review with a special focus on the most established subsets of chemokines. In combination with the other review articles of this issue, the knowledge presented here confirms that there is a physiologically relevant crosstalk between the innate immune system and bone remodeling cell types, whose molecular understanding is of high clinical relevance.

MicroRNA-183 increases osteoclastogenesis by repressing heme oxygenase-1

Emerging evidence suggests that microRNAs (miRs) influence skeletal structure by modulating osteoclastogenesis and bone resorption. We have demonstrated previously that the up-regulation of heme oxygenase-1 (HO-1) attenuated osteoclastogenesis in bone marrow-derived macrophages (BMMs). RANKL-induced osteoclastogenesis elevates microRNA-183 (miR-183) in BMM. We show here that HO-1 is a target gene of miR-183 and that this miRNA binds to the 3'-UTR of HO-1. We find that a synthetic inhibitor that binds to miR-183 decreases osteoclast (OC) differentiation and increases the expression of HO-1, while a mimic of endogenous mature miR-183 has the opposite effect. Moreover, the HO-1 inducers, resveratrol and piceatannol decrease the expression of miR-183, resulting in attenuated osteoclastogenesis. Our findings reveal how miR-183 affects OC formation.

Cilostazol attenuates ovariectomy-induced bone loss by inhibiting osteoclastogenesis

Background

Cilostazol has been reported to alleviate the metabolic syndrome induced by increased intracellular adenosine 3’,5’-cyclic monophosphate (cAMP) levels, which is also associated with osteoclast (OC) differentiation. We hypothesized that bone loss might be attenuated via an action on OC by cilostazol.

Methodology and Principal Findings

To test this idea, we investigated the effect of cilostazol on ovariectomy (OVX)-induced bone loss in mice and on OC differentiation in vitro, using μCT and tartrate-resistant acid phosphatase staining, respectively. Cilostazol prevented from OVX-induced bone loss and decreased oxidative stress in vivo. It also decreased the number and activity of OC in vitro. The effect of cilostazol on reactive oxygen species (ROS) occurred via protein kinase A (PKA) and cAMP-regulated guanine nucleotide exchange factor 1, two major effectors of cAMP. Knockdown of NADPH oxidase using siRNA of p47^phox attenuated the inhibitory effect of cilostazol on OC formation, suggesting that decreased OC formation by cilostazol was partly due to impaired ROS generation. Cilostazol enhanced phosphorylation of nuclear factor of activated T cells, cytoplasmic 1 (NFAT2) at PKA phosphorylation sites, preventing its nuclear translocation to result in reduced receptor activator of nuclear factor-κB ligand-induced NFAT2 expression and decreased binding of nuclear factor-κB-DNA, finally leading to reduced levels of two transcription factors required for OC differentiation.

Conclusions/Significance

Our data highlight the therapeutic potential of cilostazol for attenuating bone loss and oxidative stress caused by loss of ovarian function.

Reactive oxygen species induce the association of SHP-1 with c-Src and the oxidation of both to enhance osteoclast survival

Loss of ovarian function causes oxidative stress as well as bone loss. We hypothesized that reactive oxygen species (ROS) induced by the failure of ovarian function are responsible for the bone loss by increasing the number of osteoclasts (OC). We found that ROS enhanced OC survival via Src homology 2 domain-containing phosphatase-1 (SHP-1), c-Src, Akt, and ERK. ROS induced the association of SHP-1 with c-Src as well as the oxidation of c-Src and SHP-1. This resulted in inactivation of SHP-1 and activation of c-Src via phosphorylation of Tyr(416). Knockdown of c-Src or SHP-1 abolished the effect of ROS on OC survival. Moreover, downregulation of SHP-1 upregulated activation of c-Src, Akt, and ERK in the absence of any stimulus, suggesting that inactivation of SHP-1 is required for OC survival. We demonstrated that the association and oxidation of c-Src and SHP-1 by ROS are key steps in enhancing OC survival, which are responsible for increased bone loss when ovarian function ceases.

Protection against ovariectomy-induced bone loss by tranilast

Background

Tranilast (N-(3′,4′-dimethoxycinnamonyl) anthranilic acid) has been shown to be therapeutically effective, exerting anti-inflammatory and anti-oxidative effects via acting on macrophage. We hypothesized that Tranilast may protect against oxidative stress-induced bone loss via action in osteoclasts (OCs) that shares precursors with macrophage.

Methodology and Principal Findings

To elucidate the role of Tranilast, ovariectomy (OVX)-induced bone loss in vivo and OC differentiation in vitro were evaluated by µCT and tartrate-resistant acid phosphatase staining, respectively. Oral administration of Tranilast protected against OVX-induced bone loss with decreased serum level of reactive oxygen species (ROS) in mice. Tranilast inhibited OC formation in vitro. Decreased osteoclastogenesis by Tranilast was due to a defect of receptor activator of nuclear factor-κB ligand (RANKL) signaling, at least partly via decreased activation of nuclear factor-κB and reduced induction and nuclear translocation of nuclear factor of activated T cells, cytoplasmic 1 (or NFAT2). Tranilast also decreased RANKL-induced a long lasting ROS level as well as TGF-β to inhibit osteoclastogenesis. Reduced ROS caused by Tranilast was due to the induction of ROS scavenging enzymes (peroxiredoxin 1, heme oxygenase-1, and glutathione peroxidase 1) as well as impaired ROS generation.

Conclusions/Significance

Our data suggests the therapeutic potential of Tranilast for amelioration of bone loss and oxidative stress due to loss of ovarian function.

Platinum nanoparticles reduce ovariectomy-induced bone loss by decreasing osteoclastogenesis

Platinum nanoparticles (PtNP) exhibit remarkable antioxidant activity. There is growing evidence concerning a positive relationship between oxidative stress and bone loss, suggesting that PtNP could protect against bone loss by modulating oxidative stress. Intragastric administration of PtNP reduced ovariectomy (OVX)-induced bone loss with a decreased level of activity and number of osteoclast (OC) in vivo. PtNP inhibited OC formation by impairing the receptor activator of nuclear factor-κB ligand (RANKL) signaling. This impairment was due to a decreased activation of nuclear factor-κB and a reduced level of nuclear factor in activated T-cells, cytoplasmic 1 (NFAT2). PtNP lowered RANKL-induced long lasting reactive oxygen species as well as intracellular concentrations of Ca²⁺ oscillation. Our data clearly highlight the potential of PtNP for the amelioration of bone loss after estrogen deficiency by attenuated OC formation.

Overexpression of developmentally regulated GTP-binding protein-2 increases bone loss

The developmentally regulated GTP-binding protein-2 (DRG2) is a novel subclass of GTP-binding proteins. Many functional characteristics of osteoclasts (OC) are associated with small GTPases. We hypothesized that DRG2 affects bone mass via modulating OC activity. Using DRG2 transgenic mice, we investigated the role of DRG2 in bone remodeling. DRG2 overexpression caused a decrease in bone mass and an increase in the number and activity of OC in vivo. DRG2 overexpression increased fusion, spreading, survival, and resorption activity of OC in vitro. Downregulation of DRG2 by siRNA decreased fusion, spreading, and survival of OC, supporting the observations found in DRG2 transgenic OC. Transgenic mature OCs were larger, with actin rings and higher ERK, Akt, Rac1 and Rho activities than wild-type OCs. Inhibition of these proteins abolished the effects of DRG2 on formation of large OCs with actin rings, implying that DRG2 affects cytoskeleton reorganization in a Rac1/Rho/ERK/Akt-dependent manner. In summary, DRG2 is associated with survival and cytoskeleton organization of OC under influence of macrophage colony-stimulating factor, and its overexpression leads to elevated bone resorptive activity of OC, resulting in bone loss.

Absence of herpes virus entry mediator (HVEM) increases bone mass by attenuating receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis

Herpes virus entry mediator (HVEM), which is constitutively expressed at a high level on myeloid lineage cells, is also expressed on bone marrow-derived macrophages, suggesting that it may play a role in bone metabolism by affecting osteoclasts (OC) derived from bone marrow-derived macrophages. To address this question, we evaluated bone mass by micro-computed tomography and the number and activity of OC by tartrate-resistant acid phosphatase (TRAP) and pit formation on dentine slices, comparing HVEM-knockout mice with wild-type mice. The absence of HVEM led to a higher bone mass and to decreased levels of serum collagen type I fragments and serum TRACP5b in vivo. In vitro HVEM deficiency resulted in a reduced number and activity of OC and an impaired receptor activator of nuclear factor-κB ligand signaling through reduced activation of nuclear factor-κB and of nuclear factor of activated T-cells cytoplasmic 1. Exogenous soluble HVEM decreased expression of TRAP, whereas soluble LIGHT (a ligand of HVEM) increased it, indicating the occurrence of a positive signaling through HVEM during osteoclastogenesis. Our findings indicate that HVEM regulates bone remodeling via action on OC. The higher bone mass in the femurs of HVEM-knockout mice could be, at least in part, due to attenuated osteoclastogenesis and bone resorption resulting from decreased receptor activator of nuclear factor-κB ligand signaling in the OC.

Saturated fatty acids enhance osteoclast survival

Hyperlipidemia and marrow fat are associated with lowering bone density in vivo, suggesting that lipid contributes to bone loss. Using bone marrow-derived macrophages, we investigated the effect of saturated fatty acids (SFA) on osteoclastogenesis. The level of free fatty acids and adiposity in bone marrow was significantly elevated in obese mice. SFA increased osteoclast (OC) survival by preventing apoptosis. SFA caused the production of MIP-1alpha and led to activation of nuclear factor (NF)-kappaB in the OC. The absence of Toll-like receptor 4 (TLR4) or myeloid differentiation factor 88 (MyD88) abolished the survival effect of SFA on OC.

Increased fat due to estrogen deficiency induces bone loss by elevating monocyte chemoattractant protein-1 (MCP-1) production

Ovariectomy (OVX)-induced estrogen withdrawal resulted in both bone loss and an increase in fat. We observed elevated osteoclast (OC) formation by bone marrow-derived macrophages treated with medium conditioned by fats from OVX mice, but not from sham-operated mice. Fats from OVX mice expressed and secreted higher levels of monocyte chemoattractant protein-1 (MCP-1) than those from sham-operated mice. Increased fat resulting from estrogen deficiency is thus responsible for bone loss due to enhanced OC formation, which is, at least partly, a consequence of elevated MCP-1 production.

CCR5 down-regulates osteoclast function in orthodontic tooth movement

During orthodontic tooth movement, there is local production of chemokines and an influx of leukocytes into the periodontium. CCL5 plays an important role in osteoclast recruitment and activation. This study aimed to investigate whether the CCR5-receptor influences these events and, consequently, orthodontic tooth movement. An orthodontic appliance was placed in wild-type mice (WT) and CCR5-deficient mice (CCR5(-/-)). The expression of mediators involved in bone remodeling was evaluated in periodontal tissues by Real-time PCR. The number of TRAP-positive osteoclasts and the expression of cathepsin K, RANKL, and MMP13 were significantly higher in CCR5(-/-). Meanwhile, the expression of two osteoblastic differentiation markers, RUNX2 and osteocalcin, and that of bone resorption regulators, IL-10 and OPG, were lower in CCR5(-/-). Analysis of the data also showed that CCR5(-/-) exhibited a greater amount of tooth movement after 7 days of mechanical loading. The results suggested that CCR5 might be a down-regulator of alveolar bone resorption during orthodontic movement.

Lipopolysaccharide-induced osteoclastogenesis from mononuclear precursors: a mechanism for osteolysis in chronic otitis

Osteoclasts are the only cells capable of carrying out bone resorption and therefore are responsible for the osteolysis seen in infectious diseases such as chronic otitis media and infected cholesteatoma. Pseudomonas aeruginosa is the most common organism isolated from these infectious middle ear diseases. In this study, we examined the mechanisms by which P. aeruginosa lipopolysaccharide (LPS) stimulates osteoclastogenesis directly from mononuclear osteoclast precursor cells. Osteoclast precursors demonstrated robust, bone-resorbing osteoclast formation when stimulated by P. aeruginosa LPS only if previously primed with permissive, sub-osteoclastogenic doses of receptor activator of NF-kappaB ligand (RANKL), suggesting that LPS is osteoclastogenic only during a specific developmental window. Numerous LPS-elicited cytokines were found to be released by osteoclast precursors undergoing P. aeruginosa LPS-mediated osteoclast formation. Two lines of evidence suggest that several cytokines promote Oc formation in an autocrine/paracrine manner. First, inhibition of several cytokine pathways including TNF-alpha, IL-1, and IL-6 block the osteoclastogenesis induced by LPS. Secondly, increased expression of the receptors for TNF-alpha and IL-1 was demonstrated by real-time quantitative polymerase chain reaction. Such a mechanism has not previously been established and demonstrates the ability of osteoclast precursors to autonomously facilitate bone destruction.

Rutin inhibits osteoclast formation by decreasing reactive oxygen species and TNF-alpha by inhibiting activation of NF-kappaB

Rutin, a glycoside of flavonol, inhibits osteoclast formation induced by receptor activator of NF-kappaB ligand (RANKL) in bone marrow-derived macrophages. It reduces reactive oxygen species produced by RANKL and its inhibitory effect results from reduced levels of TNF-alpha. Rutin also lowers NF-kappaB activation in response to RANKL.