TRANCE (tumor necrosis factor [TNF]-related activation-induced cytokine), a new TNF family member predominantly expressed in T cells, is a dendritic cell-specific survival factor

Possible mechanisms of the crosstalk between Langerhans cells and regulatory T cells in extramammary Paget disease by receptor activator of nuclear factor kappa B (RANK) ligand/RANK pathways

BACKGROUND

Extramammary Paget disease (EMPD) is a skin adenocarcinoma of apocrine gland origin, in which Paget cells express receptor activator of nuclear factor kappa B (RANK) ligand (RANKL) and matrix metalloproteinase (MMP)-7, and release soluble (s)RANKL into the tumour microenvironment. We previously reported that about 60% of the RANK⁺ cells among the stromal cells are M2 macrophages, but the identity of the remaining population of RANK⁺ cells is still unknown.

OBJECTIVES

To investigate the unknown subpopulation of RANK-expressing cells in EMPD.

METHODS

The main population of RANK-expressing cells in the epidermis was composed of epidermal Langerhans cells (LCs). To explore the effects of RANKL on LCs, we stimulated LCs generated from human CD34⁺ hematopoietic progenitor cells with graded concentrations of sRANKL. To further examine the correlation between LCs and regulatory T cells (Tregs) in EMPD, we employed immunohistochemical staining.

RESULTS

sRANKL stimulation was shown to augment the production of C-C motif chemokine ligand 17 (CCL17) from LCs. We additionally demonstrated CCL17 expression by CD1a⁺ LCs in EMPD in an immunofluorescence study. Spearman's rank correlation test confirmed a correlation between the number of LCs and the number of Foxp3⁺ Tregs in the lesional skin of invasive EMPD. In addition, the numbers of Foxp3⁺ Tregs in the sentinel lymph nodes of metastatic EMPD were significantly higher than those of metastatic melanoma, which did not express RANKL.

CONCLUSIONS

The findings suggest that the RANKL/RANK pathway in EMPD might contribute to the recruitment of Tregs and to maintenance of the tumour microenvironment.

Dendritic Cell KLF2 Expression Regulates T Cell Activation and Proatherogenic Immune Responses

Dendritic cells (DCs) have been implicated as important regulators of innate and adaptive inflammation in many diseases, including atherosclerosis. However, the molecular mechanisms by which DCs mitigate or promote inflammatory pathogenesis are only partially understood. Previous studies have shown an important anti-inflammatory role for the transcription factor Krüppel-like factor 2 (KLF2) in regulating activation of various cell types that participate in atherosclerotic lesion development, including endothelial cells, macrophages, and T cells. We used a pan-DC, CD11c-specific cre-lox gene knockout mouse model to assess the role of KLF2 in DC activation, function, and control of inflammation in the context of hypercholesterolemia and atherosclerosis. We found that KLF2 deficiency enhanced surface expression of costimulatory molecules CD40 and CD86 in DCs and promoted increased T cell proliferation and apoptosis. Transplant of bone marrow from mice with KLF2-deficient DCs into Ldlr-/- mice aggravated atherosclerosis compared with control mice, most likely due to heightened vascular inflammation evidenced by increased DC presence within lesions, enhanced T cell activation and cytokine production, and increased cell death in atherosclerotic lesions. Taken together, these data indicate that KLF2 governs the degree of DC activation and hence the intensity of proatherogenic T cell responses.

Protective and Destructive Immunity in the Periodontium: Part 2—T-cell-mediated Immunity in the Periodontium

Based on the results of recent research in the field and Part 1 of this article (in this issue), the present paper will discuss the protective and destructive aspects of the T-cell-mediated adaptive immunity associated with the bacterial virulent factors or antigenic determinants during periodontal pathogenesis. Attention will be focused on: (i) osteoimmunology and periodontal disease; (ii) some molecular techniques developed and applied to identify critical microbial virulence factors or antigens associated with host immunity (with Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis as the model species); and (iii) summarizing the identified virulence factors/antigens associated with periodontal immunity. Thus, further understanding of the molecular mechanisms of the host’s T-cell-mediated immune responses and the critical microbial antigens related to disease pathogenesis will facilitate the development of novel therapeutics or protocols for future periodontal treatments. Abbreviations used in the paper are as follows: A. actinomycetemcomitans ( Aa), Actinobacillus actinomycetemcomitans; Ab, antibody; DC, dendritic cells; mAb, monoclonal antibody; pAb, polyclonal antibody; OC, osteoclast; PAMP, pathogen-associated molecular patterns; P. gingivalis ( Pg), Porphyromonas gingivalis; RANK, receptor activator of NF-κB; RANKL, receptor activator of NF-κB ligand; OPG, osteoprotegerin; TCR, T-cell-receptors; TLR, Toll-like receptors.

Increase in RANKL: OPG Ratio in Synovia of Patients with Temporomandibular Joint Disorder

Although a recent study suggested the involvement of RANKL and osteoprotegerin (OPG) in the pathogenesis of bone-destructive disease, no study has focused on the RANKL:OPG ratio in the synovial fluid of patients with temporomandibular joint (TMJ) disorder. This communication reports on the concentrations of RANKL and OPG in synovial fluid from TMJ patients and healthy control individuals. In contrast to an unchanged concentration of RANKL, a strong decrease in the concentration of OPG was detected in the synovial fluid from patients with TMJ internal derangement. Treatment with the synovial fluid of osteoarthritis (OA) patients resulted in the high production of osteoclast-like cells from blood mononuclear cells in vitro, as well as in pit formation in dentin slices. The addition of anti-RANKL IgG or OPG attenuated OA-synovial fluid-induced osteoclast formation, suggesting that the increase in the RANKL:OPG ratio in the microenvironment of the joint has the potential to induce osteoclastogenesis in TMJ osteoarthritis.

It May Seem Inflammatory, but Some T Cells Are Innately Healing to the Bone

Among the most significant developments to have taken place in osteology over the last few decades is an evolution from treating and viewing bone disorders primarily through an endocrine lens to instead seeing them as metabolic disorders that interface at the molecular and cellular level with the immune system. Osteoimmunology was officially born in response to accumulating evidence that the immune system is integrally involved in bone remodeling, but much of the early work focused on the role of conventional αβ T cells in driving bone loss. There is, however, emerging data indicating that innate lymphocytes, in particular γδ T cells, may in fact be important for bone regeneration. We first observed that bisphosphonate-associated osteonecrosis of the jaw (ONJ), a rare but serious adverse drug effect characterized by nonhealing necrotic bone tissue of the mandible or maxilla, was linked to a deficiency in a subset of γδ T cells found in human peripheral blood. Patients who developed ONJ while on bisphosphonate therapy not only lacked the main subset of circulating γδ T cells, but they also all had underlying conditions that compromised their immune integrity. A number of recent studies have unraveled the role of γδ T cells (and lymphocytes sharing their characteristics) in bone regeneration-particularly for fracture healing. These findings seem to contradict the prevailing view of such "inflammatory" T cells as being bone degenerative rather than restorative. This viewpoint melds together the emerging evidence of these so-called inflammatory T cells in bone remodeling and healing-showing that they are not in fact "all bad to the bone." © 2016 American Society for Bone and Mineral Research.

Physiological and pathophysiological bone turnover - role of the immune system

Osteoporosis develops when the rate of osteoclastic bone breakdown (resorption) exceeds that of osteoblastic bone formation, which leads to loss of BMD and deterioration of bone structure and strength. Osteoporosis increases the risk of fragility fractures, a cause of substantial morbidity and mortality, especially in elderly patients. This imbalance between bone formation and bone resorption is brought about by natural ageing processes, but is frequently exacerbated by a number of pathological conditions. Of importance to the aetiology of osteoporosis are findings over the past two decades attesting to a deep integration of the skeletal system with the immune system (the immuno-skeletal interface (ISI)). Although protective of the skeleton under physiological conditions, the ISI might contribute to bone destruction in a growing number of pathophysiological states. Although numerous research groups have investigated how the immune system affects basal and pathological osteoclastic bone resorption, recent findings suggest that the reach of the adaptive immune response extends to the regulation of osteoblastic bone formation. This Review examines the evolution of the field of osteoimmunology and how advances in our understanding of the ISI might lead to novel approaches to prevent and treat bone loss, and avert fractures.

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.

T helper 17 and T helper 1 cells are increased but regulatory T cells are decreased in subchondral bone marrow microenvironment of patients with rheumatoid arthritis

OBJECTIVES

The present study is to investigate the profiles of Th17, Th1 and Treg cells in bone marrow of patients with rheumatoid arthritis (RA).

METHODS

Flow cytometry was used to analyze the frequencies of Th17, Th1 and Treg cells in paired peripheral blood and bone marrow of 26 RA patients and 11 osteoarthritis (OA) patients, as well as 10 healthy controls. In addition, the disease activity was analyzed by the 28-joint disease activity score (DAS28).

RESULTS

The frequencies of Th17 and Th1 cells were significantly elevated in bone marrow of RA patients. Importantly, Th17 and Th1 cells were significantly elevated in bone marrow compared with the matched peripheral blood from RA patients. However, Treg cells were significantly decreased in bone marrow of RA patients compared with the matched peripheral blood of RA patients and bone marrow of osteoarthritis patients and healthy controls. Moreover, the frequencies of tumor necrosis factor-α-producing T cells were significantly elevated in bone marrow from RA patients. Additionally, Th17 and Th1 cells in bone marrow were positively correlated with DAS28, while Treg cells were negatively correlated with DAS28.

CONCLUSIONS

The present study demonstrates that Th17 and Th1 cells are markedly increased in bone marrow from RA patients. By contrast, Treg cells are significantly decreased in bone marrow from RA patients. These results suggest that local abnormality of Th17, Th1 and Treg cells in bone marrow of RA patients may contribute to bone destruction in skeletal system.

Innate immunity and atherogenesis

Atherosclerosis is recognized as the pathological basis of cardiovascular disease (CVD) and recent advances in basic science have shown that it should be considered as a chronic inflammatory process. Both elements of the innate and the adaptive immunity appear to be actively involved in atherogenesis. In fact, the potential role played by pattern-recognition receptors (Toll-like receptors and scavenger receptors), cytokines (such as IL-1, IL-6, TNFa), chemokines and pentraxines (such as CRP and PTX3) represents an emerging field of investigation in atherogenesis. In the near future we expect a better definition of the real biological and clinical impact on CVD of these mediators. On one side, they could become useful to complement traditional risk factors, in order to identify new categories of subjects prone to CVD development. On the other, they could become an additional potential target for therapeutic strategies.

Tumor necrosis factor receptor- associated factor 6 (TRAF6) regulation of development, function, and homeostasis of the immune system

Tumor necrosis factor receptor (TNFR)-associated factor 6 (TRAF6) is an adapter protein that mediates a wide array of protein-protein interactions via its TRAF domain and a RING finger domain that possesses non-conventional E3 ubiquitin ligase activity. First identified nearly two decades ago as a mediator of interleukin-1 receptor (IL-1R)-mediated activation of NFκB, TRAF6 has since been identified as an actor downstream of multiple receptor families with immunoregulatory functions, including members of the TNFR superfamily, the Toll-like receptor (TLR) family, tumor growth factor-β receptors (TGFβR), and T-cell receptor (TCR). In addition to NFκB, TRAF6 may also direct activation of mitogen-activated protein kinase (MAPK), phosphoinositide 3-kinase (PI3K), and interferon regulatory factor pathways. In the context of the immune system, TRAF6-mediated signals have proven critical for the development, homeostasis, and/or activation of B cells, T cells, and myeloid cells, including macrophages, dendritic cells, and osteoclasts, as well as for organogenesis of thymic and secondary lymphoid tissues. In multiple cellular contexts, TRAF6 function is essential not only for proper activation of the immune system but also for maintaining immune tolerance, and more recent work has begun to identify mechanisms of contextual specificity for TRAF6, involving both regulatory protein interactions, and messenger RNA regulation by microRNAs.

Dendritic-cell-derived osteoclasts: a new game changer in bone-resorption-associated diseases

Bone-resorbing cells, osteoclasts (OCs), and antigen-presenting cells, dendritic cells (DCs), share several features. They are derived from a common hematopoietic precursor, exhibit phagocytic activities and their functions are dependent upon receptor activator of nuclear factor κB ligand (RANKL). Upon inflammatory conditions, DCs can transdifferentiate toward functional OCs in the presence of RANKL. It has then been assumed that the increase in proinflammatory cytokines could provide a supportive environment for this transdifferentiation. In this review, we emphasize the molecular mechanisms underlying the potential for DCs to give rise to resorbing OCs in the context of bone-destruction-associated diseases upon inflammatory conditions. Whether these mechanisms reveal new strategies for the discovery of therapeutic targets and drugs is discussed extensively.

Effects of electromagnetic radiation exposure on bone mineral density, thyroid, and oxidative stress index in electrical workers

Background

In the literature, some articles report that the incidence of numerous diseases increases among the individuals who live around high-voltage electric transmission lines (HVETL) or are exposed vocationally. However, it was not investigated whether HVETL affect bone metabolism, oxidative stress, and the prevalence of thyroid nodule.

Methods

Dual-energy X-ray absorptiometry (DEXA) bone density measurements, serum free triiodothyronine (FT3), free thyroxine (FT4), RANK, RANKL, osteoprotegerin (OPG), alkaline phosphatase (ALP), phosphor, total antioxidant status (TAS), total oxidant status (TOS), and oxidative stress index (OSI) levels were analyzed to investigate this effect.

Results

Bone mineral density levels of L1–L4 vertebrae and femur were observed significantly lower in the electrical workers. ALP, phosphor, RANK, RANKL, TOS, OSI, and anteroposterior diameter of the left thyroid lobe levels were significantly higher, and OPG, TAS, and FT4 levels were detected significantly lower in the study group when compared with the control group.

Conclusion

Consequently, it was observed that the balance between construction and destruction in the bone metabolism of the electrical workers who were employed in HVETL replaced toward destruction and led to a decrease in OPG levels and an increase in RANK and RANKL levels. In line with the previous studies, long-term exposure to an electromagnetic field causes disorders in many organs and systems. Thus, it is considered that long-term exposure to an electromagnetic field affects bone and thyroid metabolism and also increases OSI by increasing the TOS and decreasing the antioxidant status.

Usefulness of ceruloplasmin testing as a screening methodology for geriatric patients with osteoporosis

[Purpose] To evaluate serum ceruloplasmin levels in geriatric patients with osteoporosis. [Subjects and Methods] Seventy geriatric patients over 65 years of age were recruited. Patients were divided into two groups: group 1 ('OP', n=35) consisted of patients with osteoporosis, and group 2 (n=35) consisted of patients without osteoporosis. Dual-energy X-ray absorptiometry scanning was used in the measurement of bone mineral density in all cases. Inflammatory parameters, including C-reactive protein, sedimentation rate, and serum ceruloplasmin levels were analyzed in blood samples. [Results] No statistical differences in inflammatory parameters were observed between the two groups, however, serum ceruloplasmin levels were significantly higher in group 1 than in group 2. In Pearson analysis, serum ceruloplasmin levels were not found to be correlated with any biochemical parameters. Receiver operator characteristic curve analysis revealed that serum ceruloplasmin levels were predictive of osteoporosis with 85.7% sensitivity and 85.7% specificity over the level of 830.15. [Conclusion] Our study demonstrated that measurement of serum ceruloplasmin levels may have potential as a screening methodology for geriatric patients with osteoporosis.

RANK as a therapeutic target in cancer

The RANK signaling pathway has emerged as a new target in breast cancer as receptor activator of nuclear factor κB ligand (RANKL) and its receptor RANK mediate the pro-tumorigenic role of progesterone in the mammary gland. Thousands of cancer patients worldwide are already taking RANKL inhibitors for the management of bone metastasis, given the relevance of this pathway in osteoclastogenesis and bone resorption. RANK signaling also has multiple divergent effects in immunity and inflammation, both in the generation of active immune responses and in the induction of tolerance: it is required for lymph node organogenesis, thymic medullary epithelial development and self-tolerance, and regulates activation of several immune cells and inflammatory processes. The RANK pathway interferes with mammary epithelial differentiation and mediates the major proliferative response of mammary epithelium to progesterone and progesterone-driven expansion of mammary stem cells; it also controls hair follicle and epidermal stem cell homeostasis, pointing to RANK as a key regulator of epithelial stemness. Here we revisit the main functions of RANK signaling in bone remodeling, immune cells and epithelial differentiation. We also discuss the mechanistic evidence that supports its pleiotropic effects on cancer: from bone metastasis to immune and cancer-cell-dependent effects.

Role of the RANK/RANKL pathway in breast cancer

The discovery of the OPG/RANK/RANKL pathway two decades ago has initiated novel insights into regulation of bone formation. More recently this pathway has been found to be also relevant in osteoclastic-independent mechanisms, mainly in mammary physiology and breast cancer. RANKL/RANK function is essential for epithelial cell proliferation and cellular survival as well as lobulo-alveolar development. The endogenous OPG functions as a soluble decoy receptor, binding the cytokine RANKL to prevent RANKL from activating its receptor RANK. The regulatory function of RANKL is one of the key factors in progesterone-induced proliferation of the breast. Progesterone has a direct action of progesterone on progesterone-receptor (PR) expressing cells but PR-negative cells are affected indirectly through RANKL-induced paracrine actions leading to proliferation of mammary epithelial PR-negative cells. RANK induces epithelial-mesenchymal transition and stemness in human mammary epithelial cells and promotes tumorigenesis and metastasis. Inhibition of the RANK/RANKL pathway using the monoclonal antibody denosumab can neutralize RANKL and inhibiting its interaction with its receptor RANK. Denosumab is currently used to treat osteoporosis and in prevention of skeletal related events in patients suffering from bone metastases due to solid tumors. As preclinical experiments suggest the RANKL/RANK pathway plays an important role in primary breast cancer development. The interference with the RANK/RANKL system could therefore serve as a potential target for prevention and treatment of breast cancer.

Characterization and application of two RANK-specific antibodies with different biological activities

Antibodies play an important role in therapy and investigative biomedical research. The TNF-family member Receptor Activator of NF-κB (RANK) is known for its role in bone homeostasis and is increasingly recognized as a central player in immune regulation and epithelial cell activation. However, the study of RANK biology has been hampered by missing or insufficient characterization of high affinity tools that recognize RANK. Here, we present a careful description and comparison of two antibodies, RANK-02 obtained by phage display (Newa, 2014 [1]) and R12-31 generated by immunization (Kamijo, 2006 [2]). We found that both antibodies recognized mouse RANK with high affinity, while RANK-02 and R12-31 recognized human RANK with high and lower affinities, respectively. Using a cell apoptosis assay based on stimulation of a RANK:Fas fusion protein, and a cellular NF-κB signaling assay, we showed that R12-31 was agonist for both species. R12-31 interfered little or not at all with the binding of RANKL to RANK, in contrast to RANK-02 that efficiently prevented this interaction. Depending on the assay and species, RANK-02 was either a weak agonist or a partial antagonist of RANK. Both antibodies recognized human Langerhans cells, previously shown to express RANK, while dermal dendritic cells were poorly labeled. In vivo R12-31 agonist activity was demonstrated by its ability to induce the formation of intestinal villous microfold cells in mice. This characterization of two monoclonal antibodies should now allow better evaluation of their application as therapeutic reagents and investigative tools.

Expression of the receptor activator of nuclear factor-kB ligand in peripheral blood mononuclear cells in patients with acute Charcot neuroarthropathy

Introduction. The receptor activator of nuclear factor-kB (RANK), ligand (RANK-L) and osteoprotegerin (OPG) are implicated in the pathogenesis of acute Charcot neuroarthropathy (CN). Materials and Methods. This study aimed to investigate the expression of RANK-L and OPG in peripheral blood mononuclear cells (PBMC) from patients with acute CN. Results. We found that the expression of RANK-L was lower in patients with acute CN as compared with diabetic control subjects and healthy control participants; whereas OPG expression was not detected in patients and in both control groups. RANK-L expression at the onset of disease was inversely correlated with the index of polyunsaturation (PUI), a bone marrow MRS-derived measurable index that allows evaluation of disease activity in acute CN, and recovery time. Finally, the expression of RANK-L increased at the time of healing compared with the values found during the acute phase. Conclusions. In conclusion, our preliminary data provide a first step in applying analysis of RANK-L expression in peripheral blood cells to the diagnosis of acute CN. Based on our data we also suggest that analysis of RANK-L expression could be a complementary tool that can be employed to obtain quantitative parameters that may help clinicians to monitor disease activity in patients with acute CN.

Progestogens and risk of breast cancer: a link between bone and breast?

This article reviews the data supporting the role of receptor activator of the nuclear factor kappa (RANK) and its ligand, RANKL, in progestogen-induced breast cancer. Both experimental and clinical studies have been included. The expression of both RANK and RANKL has been described in epithelial cells of both mice and humans. Experiments of gain and loss of function in mice have shown that RANK/RANKL mediate alveologenesis during pregnancy or the estrous cycle. Moreover, the participation of the RANK/RANKL has been detected in models of breast carcinogenesis associated with progestogens-like medroxyprogesterone acetate. Recent clinical studies have found that the expression of RANK is associated with parameters of aggressiveness of the tumor.

The Modulatory Effects of Mesenchymal Stem Cells on Osteoclastogenesis

The effect of mesenchymal stem cells (MSCs) on bone formation has been extensively demonstrated through several in vitro and in vivo studies. However, few studies addressed the effect of MSCs on osteoclastogenesis and bone resorption. Under physiological conditions, MSCs support osteoclastogenesis through producing the main osteoclastogenic cytokines, RANKL and M-CSF. However, during inflammation, MSCs suppress osteoclast formation and activity, partly via secretion of the key anti-osteoclastogenic factor, osteoprotegerin (OPG). In vitro, co-culture of MSCs with osteoclasts in the presence of high concentrations of osteoclast-inducing factors might reflect the in vivo inflammatory pathology and prompt MSCs to exert an osteoclastogenic suppressive effect. MSCs thus seem to have a dual effect, by stimulating or inhibiting osteoclastogenesis, depending on the inflammatory milieu. This effect of MSCs on osteoclast formation seems to mirror the effect of MSCs on other immune cells, and may be exploited for the therapeutic potential of MSCs in bone loss associated inflammatory diseases.

Ginsenoside metabolite compound K exerts joint-protective effect by interfering with synoviocyte function mediated by TNF-α and Tumor necrosis factor receptor type 2

Ginsenoside metabolite compound K (CK), metabolite of the ginsenoside, is considered to exert numerous pharmacological efficacies of ginsenoside, including anti-inflammation and immunoregulatory effects. Rheumatoid arthritis (RA) is a multi-systemic autoimmune disease characterized by hyperplastic synovial membrane and systemic inflammation, which ultimately lead to progressive destructive inflammatory arthropathy. To evaluate the potential joint-protective effects of CK and the underlying mechanism, adjuvant arthritis (AA) was induced by complete Freund's adjuvant in rats. After the onset of arthritis, The effect of CK on AA rats was evaluated by histopathology of the joint. The proliferation of fibroblast-like synoviocyte(FLS) was assayed by the Cell Counting Kit-8.The migration of FLS was assayed by transwell migration assay. Cytokines in the supernatant from FLS were measured by ELISA kit. Expression of Tumor Necrosis Factor Receptor Type 1(TNFR1) and Tumor Necrosis Factor Receptor Type 2(TNFR2) were detected by immunostaining analysis and western blot analysis. CK (80mg/kg) significantly ameliorated the histopathological change of joint in AA rats, balanced the RANKL/OPG ratio and attenuated the proliferation and migration of AA-FLS. CK suppressed the secretion of proinflammatory cytokines TNF-α and downregulated the expression of TNFR2 on AA-FLS. In vitro CK also significantly suppressed proliferation, migration and secretion of AA-FLS mediated by TNF-α. Further studies showed that the effects of CK on AA-FLS were reversed by using glucocorticoid receptor (GR) antagonist (mifepristone). Our data suggest that CK exerts joint-protective effect by interfering with synoviocyte function mediated by TNF-α and TNFR2, and this effect may be mediated by GR.

Inhibition of the TNF Family Cytokine RANKL Prevents Autoimmune Inflammation in the Central Nervous System

The central nervous system (CNS) is an immunologically privileged site protected from uncontrolled access of T cells by the blood-brain barrier (BBB), which is breached upon autoimmune inflammation. Here we have shown that receptor activator of nuclear factor-κB (NF-κB) ligand (RANKL) on T cells regulates C-C type chemokine ligand 20 (CCL20) production by astrocytes and T cell localization in the CNS. Importantly, mice specifically lacking RANKL in T cells were resistant to experimental autoimmune encephalomyelitis (EAE) due to altered T cell trafficking. Pharmacological inhibition of RANKL prevented the development of EAE without affecting the peripheral immune response, indicating that RANKL is a potential therapeutic target for treating autoimmune diseases in the CNS.

Vaccination Produces CD4 T Cells with a Novel CD154-CD40-Dependent Cytolytic Mechanism

The discovery of new vaccines against infectious diseases and cancer requires the development of novel adjuvants with well-defined activities. The TLR4 agonist adjuvant GLA-SE elicits robust Th1 responses to a variety of vaccine Ags and is in clinical development for both infectious diseases and cancer. We demonstrate that immunization with a recombinant protein Ag and GLA-SE also induces granzyme A expression in CD4 T cells and produces cytolytic cells that can be detected in vivo. Surprisingly, these in vivo CTLs were CD4 T cells, not CD8 T cells, and this cytolytic activity was not dependent on granzyme A/B or perforin. Unlike previously reported CD4 CTLs, the transcription factors Tbet and Eomes were not necessary for their development. CTL activity was also independent of the Fas ligand-Fas, TRAIL-DR5, and canonical death pathways, indicating a novel mechanism of CTL activity. Rather, the in vivo CD4 CTL activity induced by vaccination required T cell expression of CD154 (CD40L) and target cell expression of CD40. Thus, vaccination with a TLR4 agonist adjuvant induces CD4 CTLs, which kill through a previously unknown CD154-dependent mechanism.

Transcriptional regulation of the human TNFSF11 gene in T cells via a cell type-selective set of distal enhancers

In addition to osteoblast lineage cells, the TNF-like factor receptor activator of NF-κB ligand (RANKL) is expressed in both B and T cells and may play a role in bone resorption. Rankl gene (Tnfsf11) expression in mouse T cells is mediated through multiple distal elements marked by increased transcription factor occupancy, histone tail acetylation, and RNA polymerase II recruitment. Little is known, however, of the regulation of human TNFSF11 in T cells. Accordingly, we examined the consequence of T cell activation on the expression of this factor both in Jurkat cells and in primary human T cells. We then explored the mechanism of this regulation by scanning over 400 kb of DNA surrounding the TNFSF11 locus for regulatory enhancers using ChIP-chip analysis. Histone H3/H4 acetylation enrichment identified putative regulatory regions located between -170 and -220 kb upstream of the human TNFSF11 TSS that we designated the human T cell control region (hTCCR). This region showed high sequence conservation with the mouse TCCR. Inhibition of MEK1/2 by U0126 resulted in decreased RANKL expression suggesting that stimulation through MEK1/2 was a prerequisite. ChIP-chip analysis also revealed that c-FOS was recruited to the hTCCR as well. Importantly, both the human TNFSF11 D5a/b (RLD5a/b) enhancer and segments of the hTCCR mediated robust inducible reporter activity following TCR activation. Finally, SNPs implicated in diseases characterized by dysregulated BMD co-localized to the hTCCR region. We conclude that the hTCCR region contains a cell-selective set of enhancers that plays an integral role in the transcriptional regulation of the TNFSF11 gene in human T cells.

Systemic immunity shapes the oral microbiome and susceptibility to bisphosphonate-associated osteonecrosis of the jaw

Background

Osteonecrosis of the jaw (ONJ) is a rare but serious adverse drug effect linked to long-term and/or high-dose exposure to nitrogen-bisphosphonates (N-BP), the standard of care for the treatment of bone fragility disorders. The mechanism leading to bisphosphonate-associated ONJ (BAONJ) is unclear and optimal treatment strategies are lacking. Recent evidence suggests that BAONJ may be linked to drug-induced immune dysfunction, possibly associated with increased susceptibility to infections in the oral cavity. The objective of this investigation was to comprehensively assess the relationship linking immune function, N-BP exposure, the oral microbiome and ONJ susceptibility.

Methods

Leukocyte gene expression of factors important for immunity, wound healing and barrier function were assessed by real-time quantitative PCR and the oral microbiome was characterized by 454 pyrosequencing of the 16S rRNA gene in 93 subjects stratified by N-BP exposure and a history of ONJ.

Results

There were marked differences in the systemic expression of genes regulating immune and barrier functions including RANK (p = 0.007), aryl hydrocarbon receptor (AHR, p < 0.001), and FGF9 (p < 0.001), which were collectively up-regulated in individuals exposed to N-BP without ONJ relative to treatment controls. In contrast, the expression levels of these same genes were significantly down-regulated in those who had experienced BAONJ. Surprisingly, the oral microbiome composition was not directly linked to either BAONJ or N-BP exposure, rather the systemic leukocyte expression levels of RANK, TNFA and AHR each explained 9% (p = 0.04), 12% (p = 0.01), and 7% (p = 0.03) of the oral bacterial beta diversity.

Conclusions

The oral microbiome is unlikely causative of ONJ, rather individuals with BAONJ lacked immune resiliency which impaired their capacity to respond adequately to the immunological stress of N-BP treatment. This may be the common factor linking N-BP and anti-RANK agents to ONJ in at-risk individuals. Preventive and/or therapeutic strategies should target the wound healing deficits present in those with ONJ.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0568-z) contains supplementary material, which is available to authorized users.

The functions of the avian receptor activator of NF-κB ligand (RANKL) and its receptors, RANK and osteoprotegerin, are evolutionarily conserved

A new member of the chicken TNF superfamily has recently been identified, namely receptor activator of NF-κB ligand (RANKL), as have its signalling receptor, RANK, and its decoy receptor, osteoprotegerin (OPG). In mammals, RANKL and RANK are transmembrane proteins expressed on the surface of Th1 cells and dendritic cells (DC) respectively, whereas OPG is expressed as a soluble protein from osteoblasts and DC. Recombinant soluble chicken RANKL (chRANKL) forms homotrimers whereas chicken OPG (chOPG) forms homodimers, characteristic of these molecules in mammals. ChRANKL, chRANK and chOPG are expressed at the mRNA level in most tissues and organs. ChRANKL is transcriptionally regulated by Ca(2+) mobilisation and enhances the mRNA expression levels of pro-inflammatory cytokines in bone marrow-derived DC (BMDC); this is inhibited by both chOPG-Fc and soluble chRANK-Fc. However, chRANKL does not enhance the expression of cell surface markers in either BMDC or BM-derived macrophages (BMM). Furthermore, chRANKL enhances the survival of APC similar to its mammalian orthologue.

Protein kinase C inhibitor, GF109203X attenuates osteoclastogenesis, bone resorption and RANKL-induced NF-κB and NFAT activity

Osteolytic bone diseases are characterized by excessive osteoclast formation and activation. Protein kinase C (PKC)-dependent pathways regulate cell growth, differentiation and apoptosis in many cellular systems, and have been implicated in cancer development and osteoclast formation. A number of PKC inhibitors with anti-cancer properties have been developed, but whether they might also influence osteolysis (a common complication of bone invading cancers) is unclear. We studied the effects of the PKC inhibitor compound, GF109203X on osteoclast formation and activity, processes driven by receptor activator of NFκB ligand (RANKL). We found that GF109203X strongly and dose dependently suppresses osteoclastogenesis and osteoclast activity in RANKL-treated primary mouse bone marrow cells. Consistent with this GF109203X reduced expression of key osteoclastic genes, including cathepsin K, calcitonin receptor, tartrate resistant acid phosphatase (TRAP) and the proton pump subunit V-ATPase-d2 in RANKL-treated primary mouse bone marrow cells. Expression of these proteins is dependent upon RANKL-induced NF-κB and NFAT transcription factor actions; both were reduced in osteoclast progenitor populations by GF109203X treatment, notably NFATc1 levels. Furthermore, we showed that GF109203X inhibits RANKL-induced calcium oscillation. Together, this study shows GF109203X may block osteoclast functions, suggesting that pharmacological blockade of PKC-dependent pathways has therapeutic potential in osteolytic diseases.

The Impact of Immune System in Regulating Bone Metastasis Formation by Osteotropic Tumors

Bone metastases are frequent and debilitating consequence for many tumors, such as breast, lung, prostate, and kidney cancer. Many studies report the importance of the immune system in the pathogenesis of bone metastasis. Indeed, bone and immune system are strictly linked to each other because bone regulates the hematopoietic stem cells from which all cells of the immune system derive, and many immunoregulatory cytokines influence the fate of bone cells. Furthermore, both cytokines and factors produced by immune and bone cells promote the growth of tumor cells in bone, contributing to supporting the vicious cycle of bone metastasis. This review summarizes the current knowledge on the interactions among bone, immune, and tumor cells aiming to provide an overview of the osteoimmunology field in bone metastasis from solid tumors.

N-acetylglucosamine-1-Phosphate Transferase Suppresses Lysosomal Hydrolases in Dysfunctional Osteoclasts: A Potential Mechanism for Vascular Calcification

In addition to increased differentiation of vascular smooth muscle cells into osteoblast-like phenotypes, the limited accumulation of osteoclasts in atherosclerotic plaques or their dysfunction may participate in potential mechanisms for vascular calcification. N-acetylglucosamine-1-phosphate transferase containing alpha and beta subunits (GNPTAB) is a transmembrane enzyme complex that mediates the vesicular transport of lysosomal hydrolases. GNPTAB may also regulate the biogenesis of lysosomal hydrolases from bone-marrow derived osteoclasts. In this study, the areas surrounding calcification in human atherosclerotic plaques contained high levels of GNPTAB and low levels of lysosomal hydrolases such as cathepsin K (CTSK) and tartrate-resistant acid phosphatase (TRAP), as demonstrated by immunohistochemistry and laser-capture microdissection-assisted mRNA expression analysis. We therefore hypothesized that GNPTAB secretion may suppress the release of CTSK and TRAP by vascular osteoclast-like cells, thus causing their dysfunction and reducing the resorption of calcification. We used human primary macrophages derived from peripheral blood mononuclear cells, an established osteoclast differentiation model. GNPTAB siRNA silencing accelerated the formation of functional osteoclasts as detected by increased secretion of CTSK and TRAP and increased their bone resorption activity as gauged by resorption pits assay. We concluded that high levels of GNPTAB inhibit secretion of lysosomal hydrolases in dysfunctional osteoclasts, thereby affecting their resorption potential in cardiovascular calcification.

Obatoclax regulates the proliferation and fusion of osteoclast precursors through the inhibition of ERK activation by RANKL

Obatoclax, a pan-Bcl2 inhibitor, shows antitumor activities in various solid malignancies. Bcl2-deficient mice have shown the importance of Bcl2 in osteoclasts, as the bone mass of the mice was increased by the induced apoptosis of osteoclasts. Despite the importance of Bcl2, the effects of obatoclax on the proliferation and differentiation of osteoclast precursors have not been studied extensively. Here, we describe the anti-proliferative effects of obatoclax on osteoclast precursors and its negative role on fusion of the cells. Stimulation with low doses of obatoclax significantly suppressed the proliferation of osteoclast precursors in a dose-dependent manner while the apoptosis was markedly increased. Its stimulation was sufficient to block the activation of ERK MAP kinase by RANKL. The same was true when PD98059, an ERK inhibitor, was administered to osteoclast precursors. The activation of JNK1/2 and p38 MAP kinase, necessary for osteoclast differentiation, by RANKL was not affected by obatoclax. Interestingly, whereas the number of TRAP-positive mononuclear cells was increased by both obatoclax and PD98059, fused, multinucleated cells larger than 100 μm in diameter containing more than 20 nuclei were completely reduced. Consistently, obatoclax failed to regulate the expression of osteoclast marker genes, including c-Fos, TRAP, RANK and CtsK. Instead, the expression of DC-STAMP and Atp6v0d2, genes that regulate osteoclast fusion, by RANKL was significantly abrogated by both obatoclax and PD98059. Taken together, these results suggest that obatoclax down-regulates the proliferation and fusion of osteoclast precursors through the inhibition of the ERK1/2 MAP kinase pathway.

Biotechnological approach for systemic delivery of membrane Receptor Activator of NF-κB Ligand (RANKL) active domain into the circulation

Deficiency of Receptor Activator of NF-κB Ligand (RANKL) prevents osteoclast formation causing osteopetrosis. RANKL is a membrane-bound protein cleaved into active soluble (s)RANKL by metalloproteinase 14 (MMP14). We created a bio-device that harbors primary osteoblasts, cultured on 3D hydroxyapatite scaffolds carrying immobilized MMP14 catalytic domain. Scaffolds were sealed in diffusion chambers and implanted in RANKL-deficient mice. Mice received 1 or 2 diffusion chambers, once or twice and were sacrificed after 1 or 2 months from implants. A progressive increase of body weight was observed in the implanted groups. Histological sections of tibias of non-implanted mice were negative for the osteoclast marker Tartrate-Resistant Acid Phosphatase (TRAcP), consistent with the lack of osteoclasts. In contrast, tibias excised from implanted mice showed TRAcP-positive cells in the bone marrow and on the bone surface, these latter morphologically similar to mature osteoclasts. In mice implanted with 4 diffusion chambers total, we noted the highest number and size of TRAcP-positive cells, with quantifiable eroded bone surface and significant reduction of trabecular bone volume. These data demonstrate that our bio-device delivers effective sRANKL, inducing osteoclastogenesis in RANKL-deficient mice, supporting the feasibility of an innovative experimental strategy to treat systemic cytokine deficiencies.

Mycobacterium indicus pranii induces dendritic cell activation, survival, and Th1/Th17 polarization potential in a TLR-dependent manner

MIP is a nonpathogenic, soil-borne predecessor of Mycobacterium avium. It has been reported previously that MIP possesses strong immunomodulatory properties and confers protection against experimental TB and tumor. DCs, by virtue of their unmatched antigen-presentation potential, play a critical role in activation of antitumor and antimycobacterial immune response. The effect of MIP on the behavior of DCs and the underlying mechanisms, however, have not been investigated so far. In the present study, we showed that MIP induces significant secretion of IL-6, IL-12p40, IL-10, and TNF-α by DCs and up-regulates the expression of costimulatory molecules CD40, CD80, and CD86. MIP(L) induced a significantly higher response compared with MIP(K). PI and Annexin V staining showed that MIP increases DC survival by inhibiting apoptosis. Consistently, higher expression of antiapoptotic proteins Bcl-2 and Bcl-xl was observed in MIP-stimulated DCs. Cytokines, produced by naïve T cells, cocultured with MIP-stimulated DCs, showed that MIP promotes Th1/Th17 polarization potential in DCs. Response to MIP was lost in MyD88(-/-)DCs, underscoring the critical role of TLRs in MIP-induced DC activation. Further studies revealed that TLR2 and TLR9 are involved in DC activation by MIP(L), whereas MIP(K) activates the DCs through TLR2. Our findings establish the DC activation by MIP, define the behavior of MIP-stimulated DCs, and highlight the role of TLRs in MIP-induced DC activation.

Receptor activator of nuclear factor-κB ligand (RANKL)/RANK/osteoprotegerin system in bone and other tissues (review)

The receptor activator of nuclear factor‑κB ligand (RANKL)/RANK/osteoprotegerin (OPG) system was identified in the late 1990s, ending the search for the specific factors expressed by osteoblasts and stromal cells in order to regulate osteoclastogenesis. The identification of the RANKL/RANK/OPG system was a breakthrough in bone biology; however, the system not only works as a dominant mediator in osteoclast activation, formation and survival, but also functions in other tissues, including the mammary glands, brain and lymph nodes. Evidence has indicated that the existence of the RANKL/RANK/OPG system in these tissues suggests that it may have specific functions beyond those in bone. Disorders of the RANKL/RANK/OPG system are associated with certain human diseases, including postmenopausal osteoporosis, rheumatoid arthritis (RA), bone tumors and certain bone metastatic tumors. Genetic studies have indicated that the RANKL/RANK/OPG system may be a key regulator in the formation of lymph nodes and in the autoimmune disease RA, which further suggests that the immune system may interact with the RANKL/RANK/OPG system. The present review aimed to provide an overview of the role of the RANKL/RANK/OPG system in osteoclastogenesis, bone disease and tissues beyond bone.

T cell costimulation molecules CD80/86 inhibit osteoclast differentiation by inducing the IDO/tryptophan pathway

Bone resorption is seminal for the physiological remodeling of bone during life. However, this process needs to be strictly controlled; excessive bone resorption results in pathologic bone loss, osteoporosis, and fracture. We describe a control mechanism of bone resorption by the adaptive immune system. CD80/86, a pair of molecules expressed by antigen-presenting cells and involved in T cell costimulation, act as negative regulator for the generation of bone-resorbing osteoclasts. CD80/86-deficient mice were osteopenic because of increased osteoclast differentiation. CD80/86-deficient osteoclasts escaped physiological inhibition by CTLA-4 or regulatory T cells. Mechanistically, engagement of CD80/86 by CTLA-4 induced activation of the enzyme indoleamine 2,3-dioxygenase (IDO) in osteoclast precursors, which degraded tryptophan and promoted apoptosis. Concordantly, IDO-deficient mice also showed an osteopenic bone phenotype with higher numbers of osteoclast precursors and osteoclasts. Also, IDO-deficient mononuclear cells escaped the anti-osteoclastogenic effect of CTLA-4. This molecular mechanism was also present in humans because targeting CD80/86 by abatacept, a CTLA-4-immunoglobulin fusion protein, reduced, whereas blockade of CTLA-4 by ipilimumab antibody enhanced, the frequency of peripheral osteoclast precursors and osteoclastogenesis. In summary, these data show an important role of the adaptive immune system, in particular T cell CD80/86 costimulation molecules, in the physiological regulation of bone resorption and preservation of bone mass, as well as affect the understanding of the function of current and future drugs fostering or blocking the effects of CTLA-4 in humans.

Dendritic cell vaccines containing lymphocytes produce improved immunogenicity in patients with cancer

BACKGROUND

Dendritic cells are currently under investigation for their ability to generate anti-cancer immune responses. No consensus has been reached as to the optimal method of dendritic cell vaccine preparation and is a barrier to success in the field.

METHODS

Over a course of three separate dendritic cell vaccine studies to treat cancer, we tested two different methods for preparing dendritic cells from peripheral blood mononuclear cells: adherence and antibody-selected CD14+ cells.

RESULTS

Surprisingly, we found that patients who received dendritic cell vaccines generated by the adherence method mounted increased T cell proliferation in response to vaccination. This difference could not be accounted for by dendritic cell vaccine dose, cell surface phenotype or dendritic cell function in vitro. One notable difference between the two vaccine preparation methods was that the dendritic cell vaccine cultures generated by the adherence method contained up to 10% lymphocytes, and these lymphocytes were proliferating and producing IFNγ in response to antigen in vitro at the time of administration.

CONCLUSIONS

Enhanced immunogenicity of adherence dendritic cell vaccinations may be due to the presence of lymphocytes during dendritic cell culture.

TRIAL REGISTRATION

Clinicaltrials.gov identifiers: NCT00289341, NCT00345293, and NCT00893945.

Are OPG and RANKL involved in human fracture healing?

Human fracture healing is a complex interaction of several cytokines that regulate osteoblast and osteoclast activity. By monitoring OPG (osteoprotegerin) and sRANKL we aimed to possibly predict normal or impaired fracture healing. In 64 patients with a fracture of a long bone serum level of sRANKL and OPG were evaluated with respect to bony union (n=57) or pseudarthrosis (n=7). Measurements were carried out at admission and at 1, 2, 4, 6, 8, 12, 24, and 48 weeks after the injury. Patients' serum levels were compared to 33 healthy controls. Fracture hematoma contained significantly higher sRANKL and OPG concentrations compared to patients serum (p=0.005, p=0.028). OPG level in fracture hematoma was higher compared to the unions serum level (p=0.028). sRANKL was decreased in unions during the observation period. In non-unions sRANKL and OPG levels showed a variable course, with no statistical significance. This is the first study to document the course of OPG and sRANKL in normal and delayed human fracture healing emphasizing its local and systemic involvement. We provide evidence of strongly enhanced OPG levels in patients with a long bone fracture compared to healthy controls. Further, levels of free sRANKL were decreased during regular fracture repair.

In human basophils, IL-3 selectively induces RANKL expression that is modulated by IgER-dependent and IgER-independent stimuli

BACKGROUND

Receptor activator of NF-κB ligand (RANKL) is expressed as either surface (hRANKL1, hRANKL2) or soluble (hRANKL3) form. RANKL is involved in multifaceted processes of immunoregulation and bone resorption such as they occur in rheumatoid arthritis (RA). Interestingly, activated basophils, which are effector cells in allergic inflammation, contribute to the progress of collagen-induced arthritis (CIA), a mouse model for RA. Here, we investigate under which conditions human basophils express RANKL.

METHODS

Among other stimuli, basophils were cultured with IL-3 alone. Alternatively, as a secondary stimulus, IgER-dependent or IgER-independent agents were added simultaneously either with IL-3 or after prolonged IL-3 culturing. Expression of RANKL protein and mRNA was analyzed by flow cytometry, ELISA, and real-time PCR. A coculture system was applied to investigate biological activity of basophil-derived RANKL.

RESULTS

We show that in human basophils, IL-3 but no other stimulus induces de novo expression of soluble and surface RANKL, of which the latter enhances survival of MoDC. Upon simultaneous stimulation, IgER cross-linking reduces surface RANKL expression, while IgER-independent stimuli have no effect. This is in contrast to consecutive stimulation, as triggering with both IgER-dependent and IgER-independent stimuli enhances RANKL expression, particularly in its soluble form. Real-time PCR analysis shows that RANKL expression is mainly regulated at the mRNA level.

CONCLUSION

This study identifies IL-3 as a potent inducer of RANKL expression in human basophils, suggesting them to interact with bone physiology and activation of immune cells. IgER-dependent and IgER-independent stimuli modulate the IL-3-mediated RANKL expression in a time- and stimulus-dependent fashion.

Management of postmenopausal osteoporosis

A hallmark of menopause, which follows the decline in the ovarian production of estrogen, is the aggressive and persistent loss of bone mineral and structural elements leading to loss of bone strength and increased fracture risk. This review focuses on newer methods of diagnosing osteoporosis and assessing fracture risk, as well as on novel management strategies for prevention and treatment. Fracture-risk prediction has been significantly enhanced by the development of methods such as the trabecular bone score, which helps assess bone microarchitecture and adds value to standard bone densitometry, and the Fracture Risk Assessment Tool (FRAX) algorithm techniques. The treatment of osteoporosis, which has the goals of fracture prevention and risk reduction, is moving beyond traditional monotherapies with antiresorptives and anabolic agents into new combination regimens.

A "vicious cycle" of NK-cell immune evasion in acute myeloid leukemia mediated by RANKL?

Receptor activator of NFκB ligand (RANKL) is mainly known for its role in bone metabolism, constituting a target for therapeutic interventions. Increasing evidence suggests that RANKL is also involved in oncogenesis and tumor progression, including a prominent role in host-tumor interaction. Our data suggest that targeting RANKL may reinforce natural killer (NK) cell-mediated antitumor responses in patients affected by hematological malignancies.

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

Discovery and characterization of the cytokine receptor-cytokine-decoy receptor triad formed by receptor activator of nuclear factor kappa-B ligand (RANKL)–receptor activator of NF-κB (RANK)–osteoprotegerin (OPG) have led not only to immense advances in understanding the biology of bone homeostasis, but have also crystalized appreciation of the critical regulatory relationship that exists between bone and immunity, resulting in the emergence of the burgeoning field of osteoimmunology. RANKL–RANK–OPG are members of the tumor necrosis factor (TNF) and TNF receptor superfamilies, and share signaling characteristics common to many members of each. Developmentally regulated and cell-type specific expression patterns of each of these factors have revealed key regulatory functions for RANKL–RANK–OPG in bone homeostasis, organogenesis, immune tolerance, and cancer. Successful efforts at designing and developing therapeutic agents targeting RANKL–RANK–OPG have been undertaken for osteoporosis, and additional efforts are underway for other conditions. In this review, we will summarize the basic biology of the RANKL–RANK–OPG system, relate its cell-type specific functions to system-wide mechanisms of development and homeostasis, and highlight emerging areas of interest for this cytokine group.

RANKL promotes migration and invasion of hepatocellular carcinoma cells via NF-κB-mediated epithelial-mesenchymal transition

Background

Metastasis accounts for the most deaths in patients with hepatocellular carcinoma (HCC). Receptor activator of nuclear factor kappa B ligand (RANKL) is associated with cancer metastasis, while its role in HCC remains largely unknown.

Methods

Immunohistochemistry was performed to determine the expression of RANK in HCC tissue (n = 398). Quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot were used to examine the expression of RANK, E-cadherin, N-cadherin, vimentin, Snail, Slug, Twist and MMPs in HCC cells. Wound healing and Transwell assays were used to evaluate cell migration and invasion ability.

Results

We found that expression of RANK, the receptor of RANKL, was significantly higher in HCC tumor tissues than in peritumor liver tissues (p<0.001). Constitutive expression of RANK was detected in HCC cell lines, which can be up-regulated when HCC cells were stimulated with RANKL. Notably, in vitro experiments showed that activation of RANKL-RANK axis significantly promoted migration and invasion ability of HCC cells. In addition, RANKL stimulation increased the expression levels of N-cadherin, Snail, and Twist, while decreased the expression of E-cadherin, with concomitant activation of NF-κB signaling pathway. Moreover, administration of the NF-κB inhibitor attenuated RANKL-induced migration, invasion and epithelial-mesenchymal transition of HCC cells.

Conclusions

RANKL could potentiate migration and invasion ability of RANK-positive HCC cells through NF-κB pathway-mediated epithelial-mesenchymal transition, which means that RANKL-RANK axis could be a potential target for HCC therapy.

Osteoprotegerin, pericytes and bone-like vascular calcification are associated with carotid plaque stability

BACKGROUND AND PURPOSE

Vascular calcification, recapitulating bone formation, has a profound impact on plaque stability. The aim of the present study was to determine the influence of bone-like vascular calcification (named osteoid metaplasia = OM) and of osteoprotegerin on plaque stability.

METHODS

Tissue from carotid endarterectomies were analysed for the presence of calcification and signs of vulnerability according to AHA grading system. Osteoprotegerin (OPG), pericytes and endothelial cells were sought using immuno-histochemistry. Symptoms and preoperative imaging findings (CT-scan, MRI and Doppler-scan) were analyzed. Human pericytes were cultured to evaluate their ability to secrete OPG and to influence mineralization in the plaque.

RESULTS

Seventy-three carotid plaques (49 asymptomatic and 24 symptomatic) were harvested. A significantly higher presence of OM (18.4% vs 0%, p<0.01), OPG (10.2% of ROI vs 3.4% of ROI, p<0.05) and pericytes (19% of ROI vs 3.8% of ROI, p<0.05) were noted in asymptomatic compared to symptomatic plaques. Consistently, circulating OPG levels were higher in the plasma of asymptomatic patients (3.2 ng/mL vs 2.5 ng/mL, p = 0.05). In vitro, human vascular pericytes secreted considerable amounts of OPG and underwent osteoblastic differentiation. Pericytes also inhibited the osteoclastic differentiation of CD14+ cells through their secretion of OPG.

CONCLUSIONS

OPG (intraplaque an plasmatic) and OM are associated with carotid plaque stability. Pericytes may be involved in the secretion of intraplaque OPG and in the formation of OM.

Molecular and cellular basis of bone resorption

Osteoclast research has an exciting history and a challenging future. More than 3 decades ago, it became evident that bone-resorbing osteoclasts are of hematopoietic origin and are ultimately linked to the "basic multicellular unit," where they team up with the other cell types, including bone-forming osteoblasts. Since 2 decades, we have learned about the signaling pathways controlling genes relevant for osteoclastogenesis and bone resorption. It took another decade until the hypothesized "osteoclast differentiation" factor was discovered and was translated into an approved pharmacologic strategy. Here, the focus is on another molecular target, cathepsin K, a cysteine protease being released by the osteoclast into the resorption compartment. Genetic deletion and pharmacological blocking of cathepsin K reduces bone resorption but with ongoing bone formation. This observation not only holds great promise to become a new pharmacologic strategy, but it also provides new insights into the coordinated work of cells in the "basic multicellular unit" and thus, bridges the history and future of osteoclast research. This article is a short primer on osteoclast biology for readers of the special issue on odanacatib, a cathepsin K inhibitor.

Generation and culture of osteoclasts

Osteoclasts are highly specialized cells of haematopoietic lineage that are uniquely responsible for bone resorption. In the past, osteoclasts were isolated as mature cells from chicken long bones, or were generated using osteoblasts or stromal cells to induce osteoclast formation in total bone marrow from mice or rabbits. The Copernican revolution in osteoclast biology began with the identification of macrophage-colony stimulating factor (M-CSF) and receptor activator NFκB-ligand (RANKL ) as the key regulators of osteoclast formation, fusion and function. The availability of recombinant human and mouse M-CSF and RANKL has enabled researchers to reliably generate osteoclasts from primary monocyte/macrophage cells as well as from cell lines such as RAW 264.7. This article summarizes the most commonly used procedures for the isolation, generation and characterization of human, rodent and chicken osteoclasts in vitro. Lists of further reading and recommendations are included to facilitate a successful application by the reader.