Biology of the RANKL-RANK-OPG System in Immunity, Bone, and Beyond

Matrine derivate MASM uncovers a novel function for ribosomal protein S5 in osteoclastogenesis and postmenopausal osteoporosis

Postmenopausal osteoporosis (POMP) is a public health problem characterized by decreased bone density and increased fracture risk. Over-activated osteoclastogenesis plays a vital role in POMP. Here we developed a novel bioactive compound MASM (M19) based on sophocarpine. Although it showed no significant effects on osteogenesis and adipogenesis for bone marrow-derived mesenchymal stem cells (BMSCs) in vitro, it could significantly inhibit RANKL/M-CSF induced osteoclastogenesis through suppressing NF-κB, MAPKs and PI3K/Akt pathways in vitro and ameliorate bone loss in ovariectomized mice in vivo. Ribosomal protein s5 (RPS5) has been identified as a target of M19 and regulates PI3K/Akt, NF-κB and MAPKs pathways in osteoclastogenesis. Overexpressions of RPS5 synergistically inhibited osteoclastogenesis with M19 while silencing RPS5 compromised M19 inhibitory effects on osteoclastogenesis in vitro. Among the three pathways, Akt plays a major role in M19 effects. The Akt activator SC₇₉ partially reversed the inhibitory effects on osteoclastogenesis by M19 and RPS5-knocking-down. It indicates that RPS5 serves as a potential candidate target for inhibiting osteoclastogenesis and osteoporosis therapy and M19 is a promising agent for POMP treatment.

Matrine prevents bone loss in ovariectomized mice by inhibiting RANKL-induced osteoclastogenesis

Osteoporosis is a metabolic bone disease characterized by decreased bone density and strength due to excessive loss of bone protein and mineral content. The imbalance between osteogenesis by osteoblasts and osteoclastogenesis by osteoclasts contributes to the pathogenesis of postmenopausal osteoporosis. Estrogen withdrawal leads to increased levels of proinflammatory cytokines. Overactivated osteoclasts by inflammation play a vital role in the imbalance. Matrine is an alkaloid found in plants from the Sophora genus with various pharmacological effects, including anti-inflammatory activity. Here we demonstrate that matrine significantly prevented ovariectomy-induced bone loss and inhibited osteoclastogenesis in vivo with decreased serum levels of TRAcp5b, TNF-α, and IL-6. In vitro matrine significantly inhibited osteoclast differentiation induced by receptor activator for NF-κB ligand (RANKL) and M-CSF in bone marrow monocytes and RAW264.7 cells as demonstrated by tartrate-resistant acid phosphatase (TRAP) staining and actin-ring formation as well as bone resorption through pit formation assays. For molecular mechanisms, matrine abrogated RANKL-induced activation of NF-κB, AKT, and MAPK pathways and suppressed osteoclastogenesis-related marker expression, including matrix metalloproteinase 9, NFATc1, TRAP, C-Src, and cathepsin K. Our study demonstrates that matrine inhibits osteoclastogenesis through modulation of multiple pathways and that matrine is a promising agent in the treatment of osteoclast-related diseases such as osteoporosis.-Chen, X., Zhi, X., Pan, P., Cui, J., Cao, L., Weng, W., Zhou, Q., Wang, L., Zhai, X. Zhao, Q., Hu, H., Huang, B., Su, J. Matrine prevents bone loss in ovariectomized mice by inhibiting RANKL-induced osteoclastogenesis.

CCL11, a novel mediator of inflammatory bone resorption

Normal bone homeostasis, which is regulated by bone-resorbing osteoclasts and bone-forming osteoblasts is perturbed by inflammation. In chronic inflammatory disease with disturbed bone remodelling, e.g. rheumatoid arthritis, patients show increased serum levels of the chemokine eotaxin-1 (CCL11). Herein, we demonstrate an inflammatory driven expression of CCL11 in bone tissue and a novel role of CCL11 in osteoclast migration and resorption. Using an inflammatory bone lesion model and primary cell cultures, we discovered that osteoblasts express CCL11 in vivo and in vitro and that expression increased during inflammatory conditions. Osteoclasts did not express CCL11, but the high affinity receptor CCR3 was significantly upregulated during osteoclast differentiation and found to colocalise with CCL11. Exogenous CCL11 was internalised in osteoclast and stimulated the migration of pre-osteoclast and concomitant increase in bone resorption. Our data pinpoints that the CCL11/CCR3 pathway could be a new target for treatment of inflammatory bone resorption.

TNF and Bone Remodeling

PURPOSE OF REVIEW

The mechanisms involved in the TNF-mediated deregulated bone remodeling are little appreciated. This review will discuss and summarize the impact of TNF, Notch, and RBP-J signaling on bone remodeling.

RECENT FINDINGS

The integrity of the adult skeleton undergoes constant and dynamic remodeling throughout life to maintain a proper bone homeostasis, which is achieved by the essential tight control of coupling between osteoclast-mediated bone resorption and osteoblast-mediated bone formation. The studies in this field include not only the differentiation and function of osteoblasts and osteoclasts, but also the mechanisms that simultaneously control both cell types during bone remodeling. Chronic inflammation is one of the most evident and common pathological settings that often leads to deregulated bone remodeling. The resounding success of TNF blockade therapy has demonstrated a key role for TNF in inflammation and the pathogenesis of inflammatory bone resorption associated with diseases such as rheumatoid arthritis and periodontitis. Recent studies have highlighted the function of Notch and RBP-J signaling in both physiological and TNF-mediated inflammatory bone remodeling.

Plasma levels of sRANKL and OPG are associated with atherogenic cytokines in patients with intermediate cardiovascular risk

Osteoprotegerin (OPG) and receptor activator of nuclear factor-κB ligand (RANKL) are regulators of bone remodeling, but are also considered to play important roles in coronary artery disease (CAD). This study evaluated potential associations of soluble (s) RANKL and OPG with atherosclerosis-relevant cytokines. Blood was collected from 414 individuals who presented to our hospital with intermediate likelihood for CAD for further examination. Plasma concentrations of total sRANKL, OPG, and 20 cytokines were measured using sandwich-type enzyme-linked immunoassays (ELISAs; OPG and sRANKL) and Luminex laser-based fluorescence analysis and correlated with each other. The plasma levels of interferon-γ (IFN-γ) and the T-helper cell 2 cytokines interleukin-4 (IL-4) and IL-13 showed a positive correlation with sRANKL. The association with sRANKL levels was negative for IFN-γ-induced protein-10 (IP-10) and monocyte chemotactic protein-1 (MCP-1). The strongest independent association with sRANKL in multivariable analyses was found for IFN-γ (positive) and IP-10 (negative), while IL-13 showed a positive and independent association with OPG plasma levels. OPG and sRANKL plasma levels correlate strongly and independently with specific circulating atherosclerosis-related cytokines in patients with intermediate cardiovascular risk.

Low-level laser therapy (780 nm) combined with collagen sponge scaffold promotes repair of rat cranial critical-size defects and increases TGF-β, FGF-2, OPG/RANK and osteocalcin expression

The aim of this study was to evaluate the effect of collagen sponge scaffold (CSS) implantation associated with low-level laser therapy (LLLT) on repairing bone defects. A single 5-mm cranial defect was surgically created in forty Wistar rats, which then received one of the following four interventions (n = 10 per group): no treatment (G0); bone defect implanted with collagen sponge scaffold (CSS) alone (G1); defect treated with low-level laser therapy (LLLT) (wavelength 780 nm; total energy density 120 J/cm² ; power 50 mW) alone (G2); and CSS associated with LLLT treatment (G3). After surgery, animals in each group were euthanized at 21 days and 30 days (n = 5 per euthanasia time group). Bone formation was monitored by X-ray imaging analysis. Biopsies were collected and processed for histological analysis and immunohistochemical evaluation of transforming growth factor-beta (TGF-β), fibroblast growth factor-2 (FGF-2), osteoprotegerin (OPG) and receptor activator of nuclear factor ƙ (RANK). Osteocalcin (OCN) was detected by immunofluorescence analysis. Compared to the G0 group, defects in the 30-day G3 group exhibited increased bone formation, both by increase in radiopaque areas (P < 0.01) and by histomorphometric analysis (P < 0.001). The histopathological analysis showed a decreased number of inflammatory cells (P < 0.001). The combined CCS + LLLT (G3) treatment also resulted in the most intense immunostaining for OPG, RANK, FGF-2 and TGF-β, and the most intense and diffuse OCN immunofluorescent labelling at 30 days postsurgery (G3 vs. G0 group, P < 0.05). Therefore, the use of CCS associated with LLLT could offer a synergistic advantage in improving the healing of bone fractures.

Suppression of Osteoclastogenesis by Melatonin: A Melatonin Receptor-Independent Action

In vertebrates, melatonin is primarily secreted from the pineal gland but it affects various biological processes including the sleep-wake cycle, vasomotor control, immune system and bone homeostasis. Melatonin has been known to promote osteoblast differentiation and bone maturation, but a direct role of melatonin on osteoclast differentiation is still elusive. The present study investigated the effect of melatonin on the differentiation of macrophages to osteoclasts. The presence of melatonin significantly reduced receptor activator of nuclear factor κB ligand (RANKL)-induced osteoclastogenesis and the siRNA-mediated knockdown of the melatonin receptor failed to overcome the anti-osteoclastogenic effect of melatonin. Although melatonin treatment did not affect the phosphorylation of extracellular signal-regulated kinase (ERK), p38 and c-Jun N-terminal kinase (JNK), it markedly inhibited the activation of NF-κB and subsequent induction of nuclear factor of activated T cell cytoplasmic 1(NFATc1). Thus, our results suggest that melatonin could suppress osteoclast differentiation through downregulation of NF-κB pathway with concomitant decrease in the NFATc1 transcription factor induction. Furthermore, melatonin seems to have an anti-osteoclastogenic effect independent of plasma membrane melatonin receptors. In addition to previously reported properties of melatonin, our study proposes another aspect of melatonin and bone homeostasis.

Posttranscriptional Interaction Between miR-450a-5p and miR-28-5p and STAT1 mRNA Triggers Osteoblastic Differentiation of Human Mesenchymal Stem Cells

We demonstrate that the interaction between miR-450a-5p and miR-28-5p and signal transducer and activator of transcription 1 (STAT1) mRNA correlates with the osteoblastic differentiation of mesenchymal stem cells from human exfoliated deciduous teeth (shed cells). STAT1 negatively regulates runx-related transcription factor 2 (RUNX2), which is an essential transcription factor in this process. However, the elements that trigger osteoblastic differentiation and therefore pause the inhibitory effect of STAT1 need investigation. Usually, STAT1 can be posttranscriptionally regulated by miRNAs. To test this, we used an in vitro model system in which shed cells were chemically induced toward osteoblastic differentiation and temporally analyzed, comparing undifferentiated cells with their counterparts in the early (2 days) or late (7 or 21 days) periods of induction. The definition of the entire functional genome expression signature demonstrated that the transcriptional activity of a large set of mRNAs and miRNAs changes during this process. Interestingly, STAT1 and RUNX2 mRNAs feature contrasting expression levels during the course of differentiation. While undifferentiated or early differentiating cells express high levels of STAT1 mRNA, which was gradually downregulated, RUNX2 mRNA was upregulated toward differentiation. The reconstruction of miRNA-mRNA interaction networks allowed the identification of six miRNAs (miR-17-3p, miR-28-5p, miR-29b, miR-29c-5p, miR-145-3p, and miR-450a-5p), and we predicted their respective targets, from which we focused on miR-450a-5p and miR-28-5p STAT1 mRNA interactions, whose intracellular occurrence was validated through the luciferase assay. Transfections of undifferentiated shed cells with miR-450a-5p or miR-28-5p mimics or with miR-450a-5p or miR-28-5p antagonists demonstrated that these miRNAs might play a role as posttranscriptional controllers of STAT1 mRNA during osteoblastic differentiation. J. Cell. Biochem. 118: 4045-4062, 2017. © 2017 Wiley Periodicals, Inc.

Poor prognosis of patients with triple-negative breast cancer can be stratified by RANK and RANKL dual expression

PURPOSE

As clinical studies have correlated RANK expression levels with survival in breast cancer, and that RANK signaling is dependent on its cognate ligand RANKL, we hypothesized that dual protein expression further stratifies the poor outcome in TNBC.

METHODS

RANK mRNA and protein expression was evaluated in TNBC using genomic databases, cell lines and in a tissue microarray of curated primary tumor samples derived from 87 patients with TNBC. RANK expression was evaluated either by Mann-Whitney U test on log-normalized gene expression data or by Student's t test on FACS data. Analysis of RANK and RANKL immunostaining was calculated by H-score, and correlations to clinical factors performed using χ ² or Fisher's exact test. Associations with RFS and OS were assessed using univariate and multivariate Cox proportional hazard models. Survival estimates were generated using the Kaplan-Meier method.

RESULTS

In three distinct datasets spanning 684 samples, RANK mRNA expression was higher in primary tumors derived from TNBC patients than from those with other molecular subtypes (P < 0.01). Cell surface-localized RANK protein was consistently higher in TNBC cell lines (P = 0.037). In clinical samples, TNBC patients that expressed both RANK and RANKL proteins had significantly worse RFS (P = 0.0032) and OS (P = 0.004) than patients with RANK-positive, RANKL-negative tumors. RANKL was an independent, poor prognostic factor for RFS (P = 0.04) and OS (P = 0.01) in multivariate analysis in samples that expressed both RANK and RANKL.

CONCLUSIONS

RANK and RANKL co-expression is associated with poor RFS and OS in patients with TNBC.

Monogenic Autoinflammatory Diseases with Mendelian Inheritance: Genes, Mutations, and Genotype/Phenotype Correlations

Autoinflammatory diseases (AIDs) are a genetically heterogeneous group of diseases caused by mutations of genes encoding proteins, which play a pivotal role in the regulation of the inflammatory response. In the pathogenesis of AIDs, the role of the genetic background is triggered by environmental factors through the modulation of the innate immune system. Monogenic AIDs are characterized by Mendelian inheritance and are caused by highly penetrant genetic variants in single genes. During the last years, remarkable progress has been made in the identification of disease-associated genes by using new technologies, such as next-generation sequencing, which has allowed the genetic characterization in undiagnosed patients and in sporadic cases by means of targeted resequencing of a gene panel and whole exome sequencing. In this review, we delineate the genetics of the monogenic AIDs, report the role of the most common gene mutations, and describe the evidences of the most sound genotype/phenotype correlations in AID.

TRAF6 Mediates Suppression of Osteoclastogenesis and Prevention of Ovariectomy-Induced Bone Loss by a Novel Prenylflavonoid

Given the limitations of current therapeutic options for postmenopausal osteoporosis, there is a need for alternatives with minimal adverse effects. In this study, we evaluated the effects of icaritin (ICT), a natural prenylflavonoid, on osteoclastogenesis both in vitro and in an ovariectomized (OVX) rat model and investigated its underlying molecular mechanism(s) of action. ICT inhibited osteoclast formation in two osteoclast precursor models, RAW 264.7 mouse monocyte cell line and human PBMC. ICT also inhibited sealing zone and resorption pit formation in a dose-dependent manner. Mechanistically, ICT inhibited RANKL-induced NF-κB and MAPK/AP-1 pathways to suppress gene expression of nuclear factor of activated T cells (NFAT)c1, the master transcription regulator of osteoclast differentiation. ICT, by inhibiting the TRAF6/c-Src/PI3K pathway, suppressed NADPH oxidase-1 activation to attenuate intracellular ROS production and downregulate calcineurin phosphatase activity. As a result, NFATc1 nuclear translocation and activity was suppressed. Crucially, ICT promoted proteasomal degradation of TRAF6, the critical adaptor protein that transduces RANKL/RANK signaling, and the inhibitory effect of ICT on osteoclastogenesis was reversed by the proteasomal inhibitor MG 132. ICT administration inhibited OVX-induced bone loss and resorption by suppressing osteoclast formation and activity. Consistent with cellular studies, ICT downregulated TRAF6 and NFATc1 protein expression in CD11b⁺ /Gr-1^-/low osteoclast precursors isolated from OVX rats. Put together, we present novel findings that ICT, by downregulating TRAF6, coordinates inhibition of NF-κB, MAPK/AP-1, and ROS signaling pathways to reduce expression and activity of NFATc1. These results demonstrate the potential of ICT for treatment of postmenopausal osteoporosis and point to TRAF6 as a promising target for novel anti-osteoporotic drugs. © 2017 American Society for Bone and Mineral Research.

Osteopontin inhibits osteoblast responsiveness through the down-regulation of focal adhesion kinase mediated by the induction of low-molecular weight protein tyrosine phosphatase

Osteopontin (OPN), a major marker of osteogenic differentiation, suppresses osteoblast responses to mechanical stress and cytokines, including HGF and PDGF. These OPN-induced effects are mediated through focal adhesion kinase inactivation by the induction of low–molecular weight protein tyrosine phosphatase.

Osteopontin (OPN) is an osteogenic marker protein. Osteoblast functions are affected by inflammatory cytokines and pathological conditions. OPN is highly expressed in bone lesions such as those in rheumatoid arthritis. However, local regulatory effects of OPN on osteoblasts remain ambiguous. Here we examined how OPN influences osteoblast responses to mechanical stress and growth factors. Expression of NO synthase 1 (Nos1) and Nos2 was increased by low-intensity pulsed ultrasound (LIPUS) in MC3T3-E1 cells and primary osteoblasts. The increase of Nos1/2 expression was abrogated by both exogenous OPN overexpression and recombinant OPN treatment, whereas it was promoted by OPN-specific siRNA and OPN antibody. Moreover, LIPUS-induced phosphorylation of focal adhesion kinase (FAK), a crucial regulator of mechanoresponses, was down-regulated by OPN treatments. OPN also attenuated hepatocyte growth factor–induced vitamin D receptor (Vdr) expression and platelet-derived growth factor–induced cell mobility through the repression of FAK activity. Of note, the expression of low–molecular weight protein tyrosine phosphatase (LMW-PTP), a FAK phosphatase, was increased in both OPN-treated and differentiated osteoblasts. CD44 was a specific OPN receptor for LWW-PTP induction. Consistently, the suppressive influence of OPN on osteoblast responsiveness was abrogated by LMW-PTP knockdown. Taken together, these results reveal novel functions of OPN in osteoblast physiology.

Effect of 15-Deoxy-Δ12,14-prostaglandin J2Nanocapsules on Inflammation and Bone Regeneration in a Rat Bone Defect Model

BACKGROUND

15-Deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2), one of the major metabolites from prostaglandin D2 in arachidonic acid metabolic pathway, has potential anti-inflammatory properties. The objective of this study was to explore the effects of 15d-PGJ2-loaded poly(D,L-lactide-co-glycolide) nanocapsules (15d-PGJ2-NC) on inflammatory responses and bone regeneration in local bone defect.

METHODS

The study was conducted on 96 Wistar rats from June 2014 to March 2016. Saline, unloaded nanoparticles, free 15d-PGJ2or 15d-PGJ2-NC, were delivered through a collagen vehicle inside surgically created transcortical defects in rat femurs. Interleukin-6 (IL-6), interleukin-1 beta (IL-1β), and tumor necrosis factor-alpha (TNF-α) levels in the surrounding soft tissue were analyzed by Western blot and in the defect by quantitative real-time polymerase chain reaction over 14 days. Simultaneously, bone morphogenetic protein-6 (BMP-6) and platelet-derived growth factor-B (PDGF-B) messenger RNA (mRNA) in the defect were examined. New bone formation and EphrinB2 and osteoprotegerin (OPG) protein expression in the cortical defect were observed by Masson's Trichrome staining and immunohistochemistry over 28 days. Data were analyzed by one-way analysis of variance. Least-significant difference and Dunnett's T3 methods were used with a bilateral P< 0.05.

RESULTS

Application of l5d-PGJ2-NC (100 μg/ml) in the local bone defect significantly decreased IL-6, IL-1β, and TNF-α mRNA and protein, compared with saline-treated controls (P < 0.05). l5d-PGJ2-NC upregulated BMP-6 and PDGF-B mRNA (P < 0.05). New bone formation was observed in the cortical defect in l5d-PGJ2-NC-treated animals from 7th day onward (P < 0.001). Expression of EphrinB2 and OPG presented early on day 3 and persisted through day 28 in 15d-PGJ2-NC group (P < 0.05).

CONCLUSION

Stable l5d-PGJ2-NC complexes were prepared that could attenuate IL-6, IL-1β, and TNF-α expression, while increasing new bone formation and growth factors related to bone regeneration.

Recessive coding and regulatory mutations in FBLIM1 underlie the pathogenesis of chronic recurrent multifocal osteomyelitis (CRMO)

Chronic recurrent multifocal osteomyelitis (CRMO) is a rare, pediatric, autoinflammatory disease characterized by bone pain due to sterile osteomyelitis, and is often accompanied by psoriasis or inflammatory bowel disease. There are two syndromic forms of CRMO, Majeed syndrome and DIRA, for which the genetic cause is known. However, for the majority of cases of CRMO, the genetic basis is unknown. Via whole-exome sequencing, we detected a homozygous mutation in the filamin-binding domain of FBLIM1 in an affected child with consanguineous parents. Microarray analysis of bone marrow macrophages from the CRMO murine model (cmo) determined that the Fblim1 ortholog is the most differentially expressed gene, downregulated over 20-fold in the cmo mouse. We sequenced FBLIM1 in 96 CRMO subjects and found a second proband with a novel frameshift mutation in exon 6 and a rare regulatory variant. In SaOS2 cells, overexpressing the regulatory mutation showed the flanking region acts as an enhancer, and the mutation ablates enhancer activity. Our data implicate FBLIM1 in the pathogenesis of sterile bone inflammation and our findings suggest CRMO is a disorder of chronic inflammation and imbalanced bone remodeling.

Immune mediators in the tumor microenvironment of prostate cancer

Prostate cancer tissue is composed of both cancer cells and host cells. The milieu of host components that compose the tumor is termed the tumor microenvironment (TME). Host cells can be those derived from the tissue in which the tumor originates (e.g., fibroblasts and endothelial cells) or those recruited, through chemotactic or other factors, to the tumor (e.g., circulating immune cells). Some immune cells are key players in the TME and represent a large proportion of non-tumor cells found within the tumor. Immune cells can have both anti-tumor and pro-tumor activity. In addition, crosstalk between prostate cancer cells and immune cells affects immune cell functions. In this review, we focus on immune cells and cytokines that contribute to tumor progression. We discuss T-regulatory and T helper 17 cells and macrophages as key modulators in prostate cancer progression. In addition, we discuss the roles of interleukin-6 and receptor activator of nuclear factor kappa-B ligand in modulating prostate cancer progression. This review highlights the concept that immune cells and cytokines offer a potentially promising target for prostate cancer therapy.

Beyond TNF: TNF superfamily cytokines as targets for the treatment of rheumatic diseases

TNF blockers are highly efficacious at dampening inflammation and reducing symptoms in rheumatic diseases such as rheumatoid arthritis, psoriatic arthritis and ankylosing spondylitis, and also in nonrheumatic syndromes such as inflammatory bowel disease. As TNF belongs to a superfamily of 19 structurally related proteins that have both proinflammatory and anti-inflammatory activity, reagents that disrupt the interaction between proinflammatory TNF family cytokines and their receptors, or agonize the anti-inflammatory receptors, are being considered for the treatment of rheumatic diseases. Biologic agents that block B cell activating factor (BAFF) and receptor activator of nuclear factor-κB ligand (RANKL) have been approved for the treatment of systemic lupus erythematosus and osteoporosis, respectively. In this Review, we focus on additional members of the TNF superfamily that could be relevant for the pathogenesis of rheumatic disease, including those that can strongly promote activity of immune cells or increase activity of tissue cells, as well as those that promote death pathways and might limit inflammation. We examine preclinical mouse and human data linking these molecules to the control of damage in the joints, muscle, bone or other tissues, and discuss their potential as targets for future therapy of rheumatic diseases.

Murine Rankl-/- Mesenchymal Stromal Cells Display an Osteogenic Differentiation Defect Improved by a RANKL-Expressing Lentiviral Vector

Autosomal recessive osteopetrosis (ARO) is a severe bone disease characterized by increased bone density due to impairment in osteoclast resorptive function or differentiation. Hematopoietic stem cell transplantation is the only available treatment; however, this therapy is not effective in RANKL-dependent ARO, since in bone this gene is mainly expressed by cells of mesenchymal origin. Of note, whether lack of RANKL production might cause a defect also in the bone marrow (BM) stromal compartment, possibly contributing to the pathology, is unknown. To verify this possibility, we generated and characterized BM mesenchymal stromal cell (BM-MSC) lines from wild type and Rankl^-/- mice, and found that Rankl^-/- BM-MSCs displayed reduced clonogenicity and osteogenic capacity. The differentiation defect was significantly improved by lentiviral transduction of Rankl^-/- BM-MSCs with a vector stably expressing human soluble RANKL (hsRANKL). Expression of Rankl receptor, Rank, on the cytoplasmic membrane of BM-MSCs pointed to the existence of an autocrine loop possibly activated by the secreted cytokine. Based on the close resemblance of RANKL-defective osteopetrosis in humans and mice, we expect that our results are also relevant for RANKL-dependent ARO patients. Data obtained in vitro after transduction with a lentiviral vector expressing hsRANKL would suggest that restoration of RANKL production might not only rescue the defective osteoclastogenesis of this ARO form, but also improve a less obvious defect in the osteoblast lineage, thus possibly achieving higher benefit for the patients, when the approach is translated to clinics. Stem Cells 2017;35:1365-1377.

Does the OPG/RANKL system contribute to the bone-vascular axis in chronic kidney disease? A systematic review

Vascular calcification (VC) is highly prevalent in patients with chronic kidney disease (CKD) and is strongly associated with cardiovascular mortality and morbidity. Accumulating evidence over the past decade has challenged the hypothesis of close interaction between bone and VC what raises the possibility of a common underlying pathophysiological mechanism. Lately, bone regulatory proteins such as: osteoprotegerin (OPG) and Receptor Activator for Nuclear Factor κB Ligand (RANKL) has attracted attention of researchers as a possible key mediators of bone-vascular calcification imbalance. The literature search was carried out using the MEDLINE/PubMed database and a combination of keywords and MeSH terms, and only papers published since January 2005 to July 2016 were selected. The search resulted in 562 potential articles. After selection according to the eligibility criteria, 107 studies fulfilled were included (102 full texts and 5 was case reports). OPG and RANKL plays essential role in the regulation of bone metabolism and may be regarded as a possible link between VC, bone and mineral metabolism in CKD patients. Further studies are required to determine the diagnostic significance of these proteins in evaluation of progression and severity of VC process in CKD patients. Finally, the efficacy and safety, especially in regard to VC, of anti-RANKL therapy in CKD patients requires well-designed prospective, randomized trials.

Role of odanacatib in reducing bone loss due to endodontic disease: An overview

Aims and Objectives:

Through a comprehensive literature review, this article provides an overview of the potential role of odanacatib (ODN) in reducing bone loss due to endodontic disease.

Materials and Methods:

A literature review was performed in PubMed Central, MEDLINE, Cochrane Library, and EBSCO databases. The articles identified included those published between 2002 and 2016. Based on the predetermined inclusion and exclusion criteria, out of 237 articles found, 50 were selected for this review.

Results:

Cathepsin K (CstK), which is indispensible to the immune system, also plays an important role in osteoclastic bone resorption. ODN, which is an orally active, selective, and effective inhibitor of CstK, decreases bone resorption by selectively inhibiting proteolysis of matrix proteins by CstK, without affecting other osteoclastic activity or osteoblast viability.

Conclusion:

The goal of endodontic treatment is to achieve a clinically asymptomatic state along with formation of reparative bone. This process could take 6 months or longer, hence, an earlier reversal of the resorption process could lead to faster healing and resolution of the periapical lesion. Use of ODN can be of help in achieving this goal.

Macrophage Polarization and Bone Formation: A review

The contribution of inflammation to bone loss is well documented in arthritis and other diseases with an emphasis on how inflammatory cytokines promote osteoclastogenesis. Macrophages are the major producers of cytokines in inflammation, and the factors they produce depend upon their activation state or polarization. In recent years, it has become apparent that macrophages are also capable of interacting with osteoblasts and their mesenchymal precursors. This interaction provides growth and differentiation factors from one cell that act on the other and visa versa-a concept akin to the requirement for a feeder layer to grow hemopoietic cells or the coupling that occurs between osteoblasts and osteoclasts to maintain bone homeostasis. Alternatively, activated macrophages are the most likely candidates to promote bone formation and have also been implicated in the tissue repair process in other tissues. In bone, a number of factors, including oncostatin M, have been shown to promote osteoblast formation both in vitro and in vivo. This review discusses the different cell types involved, cellular mediators, and how this can be used to direct new bone anabolic approaches.

Denosumab: targeting the RANKL pathway to treat rheumatoid arthritis

INTRODUCTION

Rheumatoid arthritis (RA) is a chronic inflammatory disorder characterized by focal pathologic bone resorption due to excessive activity of osteoclasts (OC). Receptor activator of nuclear factor kappa B ligand (RANKL) is essential for the proliferation, differentiation, and survival of OC. Denosumab (DMab) is a humanized monoclonal antibody that binds to RANKL with high affinity and blocks its subsequent association with its receptor RANK on the surface of OC precursors. Area covered: The authors review the molecular and cellular mechanisms underlying therapeutic applications of DMab, provide recent highlights on pharmacology, efficacy and safety of DMab, and discuss the potential of DMab as a novel therapeutic option for the treatment of rheumatoid arthritis. Expert opinion: Clinical results suggest that DMab is efficient both in systemic and articular bone loss in RA with limited side effects. Diminished bone erosion activity was also noted in RA patients on corticosteroids and bisphosphonates. Combination of DMab with an anti-TNF agent was not associated with increased infection rates. Collectively, these data indicate that DMab, in combination with methotrexate and possibly other conventional synthetic Disease Modifying Anti-Rheumatic Drugs (csDMARDs), is an effective, safe and cost-effective option for the treatment of RA.

Enhancing the osteogenic capacity of MG63 cells through N-isopropylacrylamide-modified polyethylenimine-mediated oligodeoxynucleotide MT01 delivery

The delivery of MT01 into MG63 cells was successfully achieved using the PEN derivative.

Effects of Osteogenic-Conditioned Medium from Human Periosteum-Derived Cells on Osteoclast Differentiation

Stem/progenitor cell-based regenerative medicine using the osteoblast differentiation of mesenchymal stem cells (MSCs) is regarded as a promising approach for the therapeutic treatment of various bone defects. The effects of the osteogenic differentiation of stem/progenitor cells on osteoclast differentiation may have important implications for use in therapy. However, there is little data regarding the expression of osteoclastogenic proteins during osteoblastic differentiation of human periosteum-derived cells (hPDCs) and whether factors expressed during this process can modulate osteoclastogenesis. In the present study, we measured expression of RANKL in hPDCs undergoing osteoblastic differentiation and found that expression of RANKL mRNA was markedly increased in these cells in a time-dependent manner. RANKL protein expression was also significantly enhanced in osteogenic-conditioned media from hPDCs undergoing osteoblastic differentiation. We then isolated and cultured CD34+ hematopoietic stem cells (HSCs) from umbilical cord blood (UCB) mononuclear cells (MNCs) and found that these cells were well differentiated into several hematopoietic lineages. Finally, we co-cultured human trabecular bone osteoblasts (hOBs) with CD34+ HSCs and used the conditioned medium, collected from hPDCs during osteoblastic differentiation, to investigate whether factors produced during osteoblast maturation can affect osteoclast differentiation. Specifically, we measured the effect of this osteogenic-conditioned media on expression of osteoclastogenic markers and osteoclast cell number. We found that osteoclastic marker gene expression was highest in co-cultures incubated with the conditioned medium collected from hPDCs with the greatest level of osteogenic maturation. Although further study will be needed to clarify the precise mechanisms that underlie osteogenic-conditioned medium-regulated osteoclastogenesis, our results suggest that the osteogenic maturation of hPDCs could promote osteoclastic potential.

Inverse Association Between Serum Osteoprotegerin and Bone Mineral Density in Renal Transplant Recipients

BACKGROUND

Osteoprotegerin (OPG) has pleiotropic effects on bone metabolism as well as endocrine function. Our aim was to evaluate the relationship between bone mineral density (BMD) and serum OPG concentration in renal transplant recipients.

METHODS

Fasting blood samples were obtained from 69 renal transplant recipients. BMD was measured in lumbar vertebrae (L2-L4) by dual-energy X-ray absorptiometry. Eight patients (11.6%) had BMD values indicative of osteoporosis, 28 patients (40.6%) had BMD values indicative of osteopenia, and 33 patients had normal BMD values. Increased serum OPG levels (P < .001), decreased body mass index (BMI) (P = .033), and decreased body weight (P = .010) were significantly correlated with low lumbar T-score cut-off points between groups (normal, osteopenia, and osteoporosis).

RESULTS

Women had significantly lower lumbar BMD values than men (P = .013). Menopause (P = .005), use of tacrolimus (P = .020), and use of cyclosporine (P = .046) were associated with lower lumbar BMD in renal transplant recipients. Univariate linear regression analysis revealed that lumbar BMD was positively correlated with height (P = .016), body weight (P = .001), and BMI (P = .015) and negatively correlated with age (P = .039) and log-OPG (P = .001). Multivariate linear regression analysis revealed that log-OPG (β: -0.275, R(2) change = 0.154, P = .014), body weight (β: 0.334, R(2) change = 0.073, P = .004), and age (β: -0.285, R(2) change = 0.079, P = .008) were independent predictors of lumbar BMD values in renal transplant recipients.

CONCLUSIONS

Serum OPG concentration correlated negatively with lumbar BMD values in renal transplant recipients.

Senescence: novel insight into DLX3 mutations leading to enhanced bone formation in Tricho-Dento-Osseous syndrome

The homeodomain transcription factor distal-less homeobox 3 gene (DLX3) is required for hair, tooth and skeletal development. DLX3 mutations have been found to be responsible for Tricho-Dento-Osseous (TDO) syndrome, characterized by kinky hair, thin-pitted enamel and increased bone density. Here we show that the DLX3 mutation (c.533 A>G; Q178R) attenuates osteogenic potential and senescence of bone mesenchymal stem cells (BMSCs) isolated from a TDO patient, providing a molecular explanation for abnormal increased bone density. Both DLX3 mutations (c.533 A>G and c.571_574delGGGG) delayed cellular senescence when they were introduced into pre-osteoblastic cells MC3T3-E1. Furthermore, the attenuated skeletal aging and bone loss in DLX3 (Q178R) transgenic mice not only reconfirmed that DLX3 mutation (Q178R) delayed cellular senescence, but also prevented aging-mediated bone loss. Taken together, these results indicate that DLX3 mutations act as a loss of function in senescence. The delayed senescence of BMSCs leads to increased bone formation by compensating decreased osteogenic potentials with more generations and extended functional lifespan. Our findings in the rare human genetic disease unravel a novel mechanism of DLX3 involving the senescence regulation of bone formation.

Activation of dimeric glucocorticoid receptors in osteoclast progenitors potentiates RANKL induced mature osteoclast bone resorbing activity

Glucocorticoid (GC) therapy is the greatest risk factor for secondary osteoporosis. Pathogenic mechanisms involve an initial increase in bone resorption followed by decreased bone formation. To gain a better understanding of the resorptive activity of GCs, we have used mouse bone marrow macrophages (BMM) to determine if GCs can directly modulate RANKL stimulated osteoclast formation and/or activity. In agreement with previous studies, experiments performed in plastic wells showed that GCs (dexamethasone, hydrocortisone, and prednisolone) inhibited osteoclast number and size during the initial phases of RANKL stimulated osteoclastogenesis; however, in prolonged cultures, decreased apoptosis was observed and escape from GC induced inhibition occurred with an enhanced number of osteoclasts formed, many with an increased area. When BMM cells were seeded on bone slices, GCs robustly enhanced RANKL stimulated formation of resorption pits and release of CTX without affecting the number or size of osteoclasts formed and with no effect on apoptosis. Stimulation of pit formation was not associated with increased life span of osteoclasts or an effect on mRNA expression of several osteoclastic or osteoclastogenic genes. The potentiation of RANKL induced CTX release by dexamethasone was significantly less in BMM cells from mice with conditional knockout of the osteoclastic glucocorticoid receptor and completely absent in cells from GR^dim mice, which carry a point mutation in one dimerizing interface of the GC receptor. These data suggest that: 1. Plastic is a poor medium to use for studying direct effects of GCs on osteoclasts 2. GCs can enhance bone resorption without decreasing apoptosis, and 3. A direct enhancement of RANKL mediated resorption is stimulated by the dimeric GC-receptor.

The inhibitory effect of beta-lapachone on RANKL-induced osteoclastogenesis

β-lapachone (β-L) is a substrate of reduced nicotinamide adenine dinucleotide (NADH): quinone oxidoreductase 1 (NQO1). NQO1 reduces quinones to hydroquinones using NADH as an electron donor and consequently increases the intracellular NAD+/NADH ratio. The activation of NQO1 by β-L has beneficial effects on several metabolic syndromes, such as obesity, hypertension, and renal injury. However, the effect of β-L on bone metabolism remains unclear. Here, we show that β-L might be a potent inhibitor of receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis. β-L inhibited osteoclast formation in a dose-dependent manner and also reduced the expression of osteoclast differentiation marker genes, such as tartrate-resistant acid phosphatase (Acp5 or TRAP), cathepsin K (CtsK), the d2 isoform of vacuolar ATPase V0 domain (Atp6v0d2), osteoclast-associated receptor (Oscar), and dendritic cell-specific transmembrane protein (Dc-stamp). β-L treatment of RANKL-induced osteoclastogenesis significantly increased the cellular NAD+/NADH ratio and resulted in the activation of 5' AMP-activated protein kinase (AMPK), a negative regulator of osteoclast differentiation. In addition, β-L treatment led to significant suppression of the expression of peroxisome proliferator-activated receptor gamma (PPARγ) and peroxisome proliferator-activated receptor gamma coactivator 1β (PGC1β), which can stimulate osteoclastogenesis. β-L treatment downregulated c-Fos and nuclear factor of activated T-cells 1 (NFATc1), which are master transcription factors for osteoclastogenesis. Taken together, the results demonstrated that β-L inhibits RANKL-induced osteoclastogenesis and could be considered a potent inhibitor of RANKL-mediated bone diseases, such as postmenopausal osteoporosis, rheumatoid arthritis, and periodontitis.

Variation in lipid mediator and cytokine levels during mouse femur fracture healing

Fracture healing is regulated by a variety of inflammatory mediators and growth factors which act over time to regenerate the injured tissue. This study used a mouse femur fracture model to quantify the temporal expression pattern of lipid mediators, cytokines, and related mRNAs during healing. Cyclooxygenase (COX-1 and COX-2) and 5-lipoxygenase (5-LO) derived lipid mediators, cytokines, and mRNA levels were quantified using mass spectrometry (LC-MS/MS), bead-based multiplex assays (xMAP), and quantitative PCR of cDNA (RTqPCR), respectively. Our analysis found that, the early inflammatory response (between 0 and 4 days after fracture) in the mouse femur fracture model coincided with elevated levels of COX-derived lipid mediators and inflammatory cytokines but with decreased levels of 5-LO-derived lipid mediators. Further, the COX-derived lipid mediators remained elevated for at least 7 days after fracture, suggesting that the COX-derived lipid mediators have additional functions during later phases of the fracture healing response. Differences were also found between mRNA levels and corresponding cytokines and lipid mediator levels, supporting a role for post-transcriptional regulation of gene expression. The temporal changes in fracture callus lipid mediator levels and inflammatory cytokines support a general positive role for inflammatory cytokines and COX-derived lipid mediators on fracture healing and a general negative role for 5-lipoxygenase derived lipid mediators during the initial stages of repair. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1883-1893, 2016.

Increased chemotaxis and activity of circulatory myeloid progenitor cells may contribute to enhanced osteoclastogenesis and bone loss in the C57BL/6 mouse model of collagen-induced arthritis

Our study aimed to determine the functional activity of different osteoclast progenitor (OCP) subpopulations and signals important for their migration to bone lesions, causing local and systemic bone resorption during the course of collagen-induced arthritis in C57BL/6 mice. Arthritis was induced with chicken type II collagen (CII), and assessed by clinical scoring and detection of anti-CII antibodies. We observed decreased trabecular bone volume of axial and appendicular skeleton by histomorphometry and micro-computed tomography as well as decreased bone formation and increased bone resorption rate in arthritic mice in vivo. In the affected joints, bone loss was accompanied with severe osteitis and bone marrow hypercellularity, coinciding with the areas of active osteoclasts and bone erosions. Flow cytometry analysis showed increased frequency of putative OCP cells (CD3^- B220^- NK1.1^- CD11b^-/lo CD117⁺ CD115⁺ for bone marrow and CD3^- B220^- NK1.1^- CD11b⁺ CD115⁺ Gr-1⁺ for peripheral haematopoietic tissues), which exhibited enhanced differentiation potential in vitro. Moreover, the total CD11b⁺ population was expanded in arthritic mice as well as CD11b⁺ F4/80⁺ macrophage, CD11b⁺ NK1.1⁺ natural killer cell and CD11b⁺ CD11c⁺ myeloid dendritic cell populations in both bone marrow and peripheral blood. In addition, arthritic mice had increased expression of tumour necrosis factor-α, interleukin-6, CC chemokine ligand-2 (Ccl2) and Ccl5, with increased migration and differentiation of circulatory OCPs in response to CCL2 and, particularly, CCL5 signals. Our study characterized the frequency and functional properties of OCPs under inflammatory conditions associated with arthritis, which may help to clarify crucial molecular signals provided by immune cells to mediate systemically enhanced osteoresorption.

Of skin and bone: did Langerhans cells and osteoclasts evolve from a common ancestor?

Skin Langerhans cells are antigen-presenting cells of the interfollicular epidermis and the upper part of the hair follicle, whereas osteoclasts are specialized bone-resorbing macrophages. Although at first view these two cell types appear to have little in common, a closer analysis reveals shared features, and when taking into account their surrounding environment, a hypothesis can be developed that Langerhans cells and osteoclasts have evolved from a common ancestral cell type. In this mini-review, we have compared the ontogenetic features of Langerhans cells and osteoclasts from a genetic and a functional point of view, an issue that so far has been overlooked. The gene programs that control cell differentiation, and the body parts where they reside, present surprising similarities. Whereas the function of osteoclasts in bone degradation has been established since the first vertebrates, Langerhans cells may have undergone a stepwise adaptation from aquatic to terrestrial life. Their cell function co-evolved with the imperatives of the skin to protect against physical impact, heat, water loss and pathogens, which implied the capacity of Langerhans cells to associate with skin appendages and to develop immunostimulatory functions. For the highly versatile and efficient immune system of modern vertebrates, Langerhans cells may be a memory of the past.

Association between RANK, RANKL and OPG polymorphisms with ACPA and erosions in rheumatoid arthritis: results from a meta-analysis involving three French cohorts

OBJECTIVES

The RANK/RANKL/osteoprotegerin (OPG) system plays a central role in the pathogenesis of bone erosions in rheumatoid arthritis (RA). The aim of this study was to test the association between 11 single-nucleotide polymorphisms (SNPs) located on RANK, RANKL and OPG genes and anticitrullinated peptide antibody (ACPA) presence or erosions in RA.

METHODS

PATIENTS

This work was performed on three independent samples of French patients with RA: the Etude de Suivi des PolyArthrites Indifférenciées Récentes (ESPOIR) (n=632), Rangueil Midi-Pyrénées (RMP) (n=249) and French Rheumatoid Arthritis Genetic Consortium (FRAGC) (n=590) cohorts. Genotyping: the genotyping of 11 SNPs located on RANK, RANKL and OPG were performed by PCR.

STATISTICAL ANALYSES

The association between the genotypes with ACPA or erosions was first tested in the ESPOIR cohort using a χ(2) test and, in the case of significant association, replicated in the RMP and FRACG cohorts. A meta-analysis on the three cohorts was performed using the Mantel-Haenszel method.

RESULTS

One SNP on RANK (rs8086340) and three SNPs on RANKL (rs7984870, rs7325635, rs1054016) were significantly associated with ACPA presence, while one SNP on OPG (rs2073618) and one SNP on RANKL (rs7325635) were significantly associated with erosions in the ESPOIR cohort. Following meta-analysis performed on the three samples, the SNP on RANK and the GGG haplotype of the three SNPs located on RANKL were both significantly associated with ACPA presence, while only the SNP on OPG remained significantly associated with erosions.

CONCLUSIONS

This study identified one SNP located on RANK, one haplotype on RANKL associated with ACPA presence, and one SNP located on OPG associated with erosions in three different samples of French patients with RA.

Effects of low-frequency ultrasound treatment of titanium surface roughness on osteoblast phenotype and maturation

OBJECTIVE

Low-frequency ultrasound is widely used in the treatment of chronically infected wounds. To investigate its feasibility as a method for in situ restoration of metal implant surfaces in cases of peri-implantitis, we evaluated how low-frequency ultrasound affected surface properties of and response of human osteoblast-like MG63 cells to titanium (Ti).

MATERIAL AND METHODS

Three Ti surfaces [hydrophobic/smooth (pretreatment, PT); hydrophobic/rough (sandblasted/acid-etched, SLA); and hydrophilic/rough (SLA processed and stored hydrophilicity, mSLA)] were subjected to 25 kHz ultrasound for 10 min/cm² . Substrate roughness, chemical composition, and wettability were analyzed before and after ultrasound application. Osteoblastic maturation of cells on sonicated disks was compared to cells on untreated disks.

RESULTS

Ultrasound treatment altered the topography of all surfaces. Contact angles were reduced, and chemical compositions were altered by ultrasound on PT and SLA surfaces. Cell response to sonicated PT was comparable to untreated PT. Alkaline phosphatase was increased on sonicated SLA compared to untreated SLA, whereas DNA, osteocalcin, BMP2, osteoprotegerin, and VEGF-A were unchanged. Cells produced less osteocalcin and BMP2 on sonicated mSLA than on untreated mSLA, but no other parameters were affected.

CONCLUSIONS

These results show that low-frequency ultrasound altered Ti surface properties. Osteoblasts were sensitive to the changes induced by ultrasound treatment. The data suggest that the effect is to delay differentiation, but it is unclear whether this delay will prevent osseointegration. These results suggest that low-frequency ultrasound may be useful for treating implant surfaces in situ leading to successful re-osseointegration of implants affected by peri-implantitis.

Novel factors modulating human β-cell proliferation

β-Cell dysfunction in type 1 and type 2 diabetes is accompanied by a progressive loss of β-cells, and an understanding of the cellular mechanism(s) that regulate β-cell mass will enable approaches to enhance hormone secretion. It is becoming increasingly recognized that enhancement of human β-cell proliferation is one potential approach to restore β-cell mass to prevent and/or cure type 1 and type 2 diabetes. While several reports describe the factor(s) that enhance β-cell replication in animal models or cell lines, promoting effective human β-cell proliferation continues to be a challenge in the field. In this review, we discuss recent studies reporting successful human β-cell proliferation including WS6, an IkB kinase and EBP1 inhibitor; harmine and 5-IT, both DYRK1A inhibitors; GNF7156 and GNF4877, GSK-3β and DYRK1A inhibitors; osteoprotegrin and Denosmab, receptor activator of NF-kB (RANK) inhibitors; and SerpinB1, a protease inhibitor. These studies provide important examples of proteins and pathways that may prove useful for designing therapeutic strategies to counter the different forms of human diabetes.

Increased receptor activator of nuclear factor κβ ligand/osteoprotegerin ratio exacerbates cartilage destruction in osteoarthritis in vitro

Osteoarthritis (OA) is a degenerative joint disease characterized by progressive cartilage destruction, matrix degradation and bony changes. Subchondral bone alterations in osteoarthritis are associated with cartilage destruction. It has previously been demonstrated that osteoprotegerin (OPG) and receptor activator of nuclear factor κβ ligand (RANKL) mediate this process. The RANKL/OPG ratio is altered in OA chondrocytes compared with normal chondrocytes. In the pathogenesis of OA, abnormal expression levels of matrix metalloproteinase-13 (MMP-13) are secreted by chondrocytes has a vital role in the progression of cartilage erosion. In the present study, the effect of various RANKL/OPG ratios on MMP-13 expression levels was investigated in interleukin-1β-stimulated SW1353 human chondrosarcoma cells. Cell viability was assessed by MTT assay and MMP-13 mRNA and protein expression levels were analyzed by quantitative reverse-transcription-quantitative polymerase chain reaction, ELISA and western blot analyses, respectively. The results demonstrated that an increase in MMP-13 mRNA and protein expression levels was observed with increasing RANKL/OPG ratio. These findings suggest that this mechanism may be used as a novel therapeutic strategy against OA.

Denosumab Related Osteonecrosis of the Jaw with Spontaneous Necrosis of the Soft Palate: Report of a Life Threatening Case

Bisphosphonates have been used for years in the treatment of patients with distant bony metastasis and in the prevention of osteoporosis. One of main side effects of these medications is the development of bisphosphonate related osteonecrosis of the jaw (BRONJ) in a small subset of patients. A new class of medications with a shorter half-life, known as receptor activator of nuclear factor kappa-B ligand (RANKL) inhibitors, was introduced with the hopes of avoiding this side effect. However, reports of osteonecrosis of the jaw after the use of RANKL inhibitors have also been documented. We report on a patient who developed a life threatening osteonecrosis of the jaw with sepsis shortly after switching from a bisphosphonate to a RANKL inhibitor for osteoporosis treatment. This patient developed several soft tissue defects including spontaneous necrosis of the soft palate. To our knowledge this is the first time this presentation has been described.

RANK-RANKL signalling in cancer

Oncogenic events combined with a favourable environment are the two main factors in the oncological process. The tumour microenvironment is composed of a complex, interconnected network of protagonists, including soluble factors such as cytokines, extracellular matrix components, interacting with fibroblasts, endothelial cells, immune cells and various specific cell types depending on the location of the cancer cells (e.g. pulmonary epithelium, osteoblasts). This diversity defines specific "niches" (e.g. vascular, immune, bone niches) involved in tumour growth and the metastatic process. These actors communicate together by direct intercellular communications and/or in an autocrine/paracrine/endocrine manner involving cytokines and growth factors. Among these glycoproteins, RANKL (receptor activator nuclear factor-κB ligand) and its receptor RANK (receptor activator nuclear factor), members of the TNF and TNFR superfamilies, have stimulated the interest of the scientific community. RANK is frequently expressed by cancer cells in contrast with RANKL which is frequently detected in the tumour microenvironment and together they participate in every step in cancer development. Their activities are markedly regulated by osteoprotegerin (OPG, a soluble decoy receptor) and its ligands, and by LGR4, a membrane receptor able to bind RANKL. The aim of the present review is to provide an overview of the functional implication of the RANK/RANKL system in cancer development, and to underline the most recent clinical studies.

Serum CX3CL1/fractalkine concentrations are positively associated with disease severity in postmenopausal osteoporotic patients

BACKGROUND

The chemokine (C-X3-C motif) ligand 1 (CX3CL1), also called fractalkine (FKN), has recently been reported to be involved in osteoclastogenic process and pathological bone destruction.

OBJECTIVE

This study aimed to investigate the link between serum CX3CL1/FKN levels with disease progression of postmenopausal osteoporotic patients.

METHODS

A total of 53 women with postmenopausal osteoporosis (PMOP group), 51 postmenopausal non-osteoporotic female patients (PMNOP group) and 50 premenopausal non-osteoporotic healthy women of childbearing age (control group) were enrolled in the study. The bone mineral density (BMD) for all subjects was determined via dual-energy X-ray absorptiometry of the lumbar spine, femoral neck, internal trochanter, total hip, greater trochanter and Ward's triangle. The levels of FKN in the serum were examined using the enzyme-linked immunosorbent assay method. The serum bone resorption markers TRACP-5b, NTX levels, inflammation markers IL-1β and IL-6 as well as oestrogen-2(E2) were also detected in all participants. The visual analogue scores (VAS) and Oswestry Disability Index (ODI) for low back pain were recorded in PMOP females for evaluation of osteoporotic pain and function.

RESULTS

FKN levels were significantly higher in postmenopausal osteoporotic patients compared with postmenopausal non-osteoporotic females (139.8 ± 44.3 pg/mL VS 116.5 ± 23.1 pg/mL, p < 0.05) and healthy controls (139.8 ± 44.3 pg/mL VS 109.7 ± 19.4 pg/mL, p < 0.05). Serum FKN concentrations were negatively associated with BMD at femoral neck (r = -0.394, p = 0.004), total hip(r = -0.374, p = 0.006), internal trochanter(r = -0.340, p = 0.013), greater trochanter(r = -0.376, p = 0.006), Ward's triangle(r = -0.343, p = 0.012), L1-L4 lumbar spine(r = -0.339, p = 0.013) and positively associated with VAS (r = 0.321, p = 0.019) and ODI (r = 0.377, p = 0.005) scores, bone turnover makers (TRACP-5b:r = 0.341, p = 0.012; NTX:r = 0.364, p = 0.007)as well as inflammation markers (IL-1β: r = 0.396, p = 0.003; IL-6:r = 0.355, p = 0.009) in postmenopausal osteoporotic patients.

CONCLUSIONS

Serum FKN may serve as a novel biomarker for assessing disease progression and a new potential therapeutic target for anti-resorptive treatment in osteoporosis patients.

Ellagic acid inhibits RANKL-induced osteoclast differentiation by suppressing the p38 MAP kinase pathway

Bone undergoes continuous remodeling by a coupled action between osteoblasts and osteoclasts. During osteoporosis, osteoclast activity is often elevated leading to increased bone destruction. Hence, osteoclasts are deemed as potential therapeutic targets to alleviate bone loss. Ellagic acid (EA) is a polyphenol reported to possess anticancer, antioxidant and anti-inflammatory properties. However, its effects on osteoclast formation and function have not yet been examined. Here, we explored the effects of EA on RANKL-induced osteoclast differentiation in RAW264.7 murine macrophages (in vitro) and human CD14⁺monocytes (ex vivo). EA dose-dependently attenuated RANKL-induced TRAP⁺ osteoclast formation in osteoclast progenitors with maximal inhibition seen at 1 µM concentration without cytotoxicity. Moreover, owing to perturbed osteoclastogenesis, EA disrupted actin ring formation and bone resorptive function of osteoclasts. Analysis of the underlying molecular mechanisms revealed that EA suppressed the phosphorylation and activation of the p38 MAP kinase pathway which subsequently impaired the RANKL-induced differentiation of osteoclast progenitors. Taken together, these novel results indicate that EA alleviates osteoclastogenesis by suppressing the p38 signaling pathway downstream of RANKL and exerts inhibitory effects on bone resorption and actin ring formation.

Toll-Like Receptor 2 Stimulation of Osteoblasts Mediates Staphylococcus Aureus Induced Bone Resorption and Osteoclastogenesis through Enhanced RANKL

Severe Staphylococcus aureus (S. aureus) infections pose an immense threat to population health and constitute a great burden for the health care worldwide. Inter alia, S. aureus septic arthritis is a disease with high mortality and morbidity caused by destruction of the infected joints and systemic bone loss, osteoporosis. Toll-Like receptors (TLRs) are innate immune cell receptors recognizing a variety of microbial molecules and structures. S. aureus recognition via TLR2 initiates a signaling cascade resulting in production of various cytokines, but the mechanisms by which S. aureus causes rapid and excessive bone loss are still unclear. We, therefore, investigated how S. aureus regulates periosteal/endosteal osteoclast formation and bone resorption. S. aureus stimulation of neonatal mouse parietal bone induced ex vivo bone resorption and osteoclastic gene expression. This effect was associated with increased mRNA and protein expression of receptor activator of NF-kB ligand (RANKL) without significant change in osteoprotegerin (OPG) expression. Bone resorption induced by S. aureus was abolished by OPG. S. aureus increased the expression of osteoclastogenic cytokines and prostaglandins in the parietal bones but the stimulatory effect of S. aureus on bone resorption and Tnfsf11 mRNA expression was independent of these cytokines and prostaglandins. Stimulation of isolated periosteal osteoblasts with S. aureus also resulted in increased expression of Tnfsf11 mRNA, an effect lost in osteoblasts from Tlr2 knockout mice. S. aureus stimulated osteoclastogenesis in isolated periosteal cells without affecting RANKL-stimulated resorption. In contrast, S. aureus inhibited RANKL-induced osteoclast formation in bone marrow macrophages. These data show that S. aureus enhances bone resorption and periosteal osteoclast formation by increasing osteoblast RANKL production through TLR2. Our study indicates the importance of using different in vitro approaches for studies of how S. aureus regulates osteoclastogenesis to obtain better understanding of the complex mechanisms of S. aureus induced bone destruction in vivo.

Development of a High-Throughput Screening Strategy for Upregulators of the OPG/RANKL Ratio with the Potential for Antiosteoporosis Effects

The ratio between osteoprotegerin (OPG) and the receptor activator of NF-κB ligand (RANKL) in the bone microenvironment indicates the level of osteoclastogenesis, and upregulation of this ratio would improve osteoporosis. In this study, we established a novel high-throughput screening (HTS) system using two stably transfected monoclonal cell lines that either express firefly luciferase under the OPG promoter control or concurrently express firefly and renilla luciferases under control of the OPG and RANKL promoters, respectively. With this system, we can conveniently and rapidly detect the effects of compounds on the expression of OPG and RANKL through changes in firefly and renilla luciferase activities. A total of 8160 compounds were screened using this system, yielding five compounds without previously reported activity. The compound with greatest potential is E05657 with high activity and low effective concentration in the HTS system. It increases the OPG/RANKL ratio and OPG secretion, decreases the NFATc1 expression, and reduces osteoclastogenesis in vitro. These results indicate that this novel HTS system can be used to identify small molecules with potential antiosteoporosis effects, and E05657 is a promising lead compound as a novel antiosteoporosis drug.

Sphingosine-1-Phosphate Receptor 2 Regulates Proinflammatory Cytokine Production and Osteoclastogenesis

Sphingosine-1-phosphate receptor 2 (S1PR2) couples with the Gi, Gq, and G_12/13 group of proteins, which modulate an array of cellular signaling pathways and affect immune responses to multiple stimuli. In this study, we demonstrated that knockdown of S1PR2 by a specific S1PR2 shRNA lentiviral vector significantly inhibited IL-1β, IL-6, and TNF-α protein levels induced by oral pathogen Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans) in murine bone marrow-derived monocytes and macrophages (BMMs) compared with controls. In addition, knockdown of S1PR2 by the S1PR2 shRNA lentiviral vector suppressed p-PI3K, p-ERK, p-JNK, p-p38, and p-NF-κBp65 protein expressions induced by A. actinomycetemcomitans. Furthermore, bone marrow cells treated with the S1PR2 shRNA lentiviral vector inhibited osteoclastogenesis induced by RANKL compared with controls. The S1PR2 shRNA suppressed the mRNA levels of six osteoclastogenic factors including nuclear factor of activated T-cells cytoplasmic calcineurin-dependent 1 (NFATc1), cathepsin K (Ctsk), acid phosphatase 5 (Acp5), osteoclast-associated receptor (Oscar), dendritic cells specific transmembrane protein (Dcstamp), and osteoclast stimulatory transmembrane protein (Ocstamp) in bone marrow cells. We conclude that S1PR2 plays an essential role in modulating proinflammatory cytokine production and osteoclastogenesis. Blocking S1PR2 signaling might be a novel therapeutic strategy to treat inflammatory bone loss diseases.

Muscle RANK is a key regulator of Ca2+ storage, SERCA activity, and function of fast-twitch skeletal muscles

Receptor-activator of nuclear factor-κB (RANK), its ligand RANKL, and the soluble decoy receptor osteoprotegerin are the key regulators of osteoclast differentiation and bone remodeling. Here we show that RANK is also expressed in fully differentiated myotubes and skeletal muscle. Muscle RANK deletion has inotropic effects in denervated, but not in sham, extensor digitorum longus (EDL) muscles preventing the loss of maximum specific force while promoting muscle atrophy, fatigability, and increased proportion of fast-twitch fibers. In denervated EDL muscles, RANK deletion markedly increased stromal interaction molecule 1 content, a Ca(2+)sensor, and altered activity of the sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) modulating Ca(2+)storage. Muscle RANK deletion had no significant effects on the sham or denervated slow-twitch soleus muscles. These data identify a novel role for RANK as a key regulator of Ca(2+)storage and SERCA activity, ultimately affecting denervated skeletal muscle function.

Interleukin-35 upregulates OPG and inhibits RANKL in mice with collagen-induced arthritis and fibroblast-like synoviocytes

IL-35 is a novel anti-inflammatory cytokine, but the exact role of IL-35 in the progression of RA remains unclear, especially associated with osteoporosis and bone erosion. The present research has not been reported. Our purpose is to study how IL-35 affects RA bone destruction.

INTRODUCTION

This study investigated the effect of interleukin-35 (IL-35) on OPG and RANKL expression in collagen-induced arthritis (CIA) in rats and in cultured fibroblast-like synoviocytes (FLS).

METHODS

Thirty DBA/1J mice were randomly assigned to three groups (n = 10 per group): the control group, the CIA group, and the CIA + IL-35 group. Collagen-induced arthritis was induced by immunization with collagen. IL-35 was intraperitoneally injected daily for 10 days, starting from the 24(th) day after immunization. FLS cells were isolated and cultured from CIA. The expression of IL-17, RANKL, and OPG was determined by RT-PCR and Western blot. Each experiment was repeated three times.

RESULTS

CIA mice exhibited arthritis symptoms on day 24, followed by a rapid progression of arthritis. The expression of IL-17 and RANKL was increased and the expression of OPG was decreased in CIA mice compared with control mice. IL-35 treatment inhibited the development of arthritis in CIA mice, accompanied by a decrease in the expression of IL-17 and RANKL and an increase in the expression of OPG. Furthermore, IL-35 dose-dependently inhibited the expression of RANKL and increased the expression of OPG in cultured FLS cells.

CONCLUSION

IL-35 inhibits RANKL expression and increases OPG expression in CIA mice. IL-35 may be used for treating rheumatoid arthritis.