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Background: The molecular mechanisms involved in the invasion of bone by oral squamous cell carcinomas (OSCC) are poorly understood, and little is known about the role of cancer-associated fibroblasts (CAF), the presence of which confers a poor prognosis. Methods: Clinicopathological data from 277 OSCC cases involving bone resections were reviewed, and 32 cases thoroughly analysed histologically. Immunohistochemistry was used to examine α SMA, RANKL and OPG. Western blotting and qPCR were used to assess myofibroblast (CAF-like) differentiation, RANKL and OPG expression in vitro , and RANKL secretion was analysed by ELISA. Osteoclastogenesis was examined using TRAP staining, multinucleation and pit forming assays. Results: Fibrous stroma intervened between tumour and bone in the majority of cases, with no direct contact between cancer cells and bone. RANKL and OPG, two proteins key to regulating bone resorption, were expressed in tumour cells as well as fibrous stroma adjacent to bone and α SMA-positive myofibroblastic CAF were consistently seen infiltrating into bone ahead of tumour cells. Human primary osteoblasts cultured with conditioned media from human OSCC-derived cells and human primary CAF showed a significant increase in RANKL and a decline in OPG mRNA expression. RANKL secretion was significantly increased in primary oral fibroblasts induced to differentiate into a CAF-like phenotype by transforming growth factor- β 1 (TGF- β 1) treatment and in primary CAF. Indirect co-culture of murine macrophages with conditioned media from CAF (experimentally derived and isolated from OSCCs) resulted in a marked increase in osteoclastogenesis (in excess of that provoked by cancer cells) determined by tartrate-resistant acid phosphatase activity, multinucleation and resorption pit formation. Conclusions: This study is the first to describe a functional role for CAFs in bone invasion and turnover, identifying a novel potential therapeutic target and diagnostic indicator in this difficult to treat bone invasive malignancy.

RANK ligand (RANKL) is a member of the tumor necrosis factor alpha superfamily of cytokines. It is the only known ligand binding to a membrane receptor named receptor activator of nuclear factor-kappa B (RANK), thereby triggering recruitment of tumor necrosis factor (TNF) receptor associated factor (TRAF) adaptor proteins and activation of downstream pathways. RANK/RANKL signaling is controlled by a decoy receptor called osteoprotegerin (OPG), but also has additional more complex levels of regulation. The existing literature on RANK/RANKL signaling in cervical cancer was reviewed, particularly focusing on the effects on the microenvironment. RANKL and RANK are frequently co-expressed in cervical cancer cells lines and in carcinoma of the uterine cervix. RANKL and OPG expression strongly increases during cervical cancer progression. RANKL is directly secreted by cervical cancer cells, which may be a mechanism they use to create an immune suppressive environment. RANKL induces expression of multiple activating cytokines by dendritic cells. High RANK mRNA levels and high immunohistochemical OPG expression are significantly correlated with high clinical stage, tumor grade, presence of lymph node metastases, and poor overall survival. Inhibition of RANKL signaling has a direct effect on tumor cell proliferation and behavior, but also alters the microenvironment. Abundant circumstantial evidence suggests that RANKL inhibition may (partially) reverse an immunosuppressive status. The use of denosumab, a monoclonal antibody directed to RANKL, as an immunomodulatory strategy is an attractive concept which should be further explored in combination with immune therapy in patients with cervical cancer.

Introduction : Periodontitis and apical periodontitis are multifactorial inflammatory diseases involving microbial activity and host responses that lead to tissue destruction. Biomarkers such as receptor activator of nuclear factor-kappa B (RANK), its ligand (RANKL), and the osteoprotegerin (OPG) system in gingival crevicular fluid (GCF) have been investigated for their diagnostic and prognostic roles in these conditions. Aim : This study evaluates these biomarkers’ levels to differentiate between stage I and stage III periodontitis, and healthy controls. Materials and methods : This cross-sectional study included 90 participants divided into three groups: stage I periodontitis, stage III periodontitis, and healthy control. GCF samples were collected from all participants in this study to measure the immunomarkers using ELISA. Results : The result revealed significantly higher levels of RANKL and OPG in stage I periodontitis compared to stage III periodontitis and controls. Additionally, we observed a significant difference between the study groups in the RANK/OPG and RANKL/OPG ratios, with stage I periodontitis showing the highest ratios. Conclusion : This study demonstrated that the levels of receptor activator of nuclear factor-kappa B (RANK), its ligand (RANKL), and osteoprotegerin (OPG) in the gingival crevicular fluid (GCF) can serve as valuable biomarkers for distinguishing between stage I and stage III periodontitis. The results showed a significant increase in RANKL and OPG levels in stage I periodontitis compared to stage III and control groups. Moreover, the RANK/OPG and RANKL/OPG ratios were significantly higher in stage I periodontitis, indicating their potential as diagnostic indicators.

Objective Extracellular vesicles (EVs) are subcellular signalosomes. Although characteristic EV production is associated with numerous physiological and pathological conditions, the effect of blood-derived EVs on bone homeostasis is unknown. Herein we evaluated the role of circulating EVs on human osteoclastogenesis. Methods Blood samples from healthy volunteers, rheumatoid arthritis (RA) and psoriatic arthritis (PsA) patients were collected. Size-based EV sub-fractions were isolated by gravity-driven filtration and differential centrifugation. To investigate the properties of EV samples, resistive pulse sensing technique, transmission electron microscopy, flow cytometry and western blot were performed. CD14 + monocytes were separated from PBMCs, and stimulated with recombinant human M-CSF, RANKL and blood-derived EV sub-fractions. After 7 days, the cells were fixed and stained for tartrate-resistant acid phosphatase and counted. Results EVs isolated by size-based sub-fractions were characterized as either microvesicles or exosomes (EXO). Healthy ( n  = 11) and RA-derived ( n  = 12) EXOs profoundly inhibited osteoclast differentiation (70%, p  < 0.01; 65%, p  < 0.01, respectively). In contrast, PsA-derived ( n  = 10) EXOs had a stimulatory effect (75%, p  < 0.05). In cross-treatment experiments where EXOs and CD14 + cells were interchanged between the three groups, only healthy ( n  = 5) and RA ( n  = 5)-derived EXOs inhibited ( p  < 0.01, respectively) the generation of osteoclasts in all groups, whereas PsA ( n  = 7)-derived EXOs were unable to mediate this effect. Conclusions Our data suggest that blood-derived EXOs are novel regulators of the human osteoclastogenesis and may offer discrete effector function in distinct inflammatory arthropathies.

Macrophage colony-stimulating factor (M-CSF) is essential for differentiation from hematopoietic precursor cells into osteoclasts. M-CSF transiently increased the intracellular level of reactive oxygen species (ROS) through an NADPH oxidase (Nox) and induced the expression of receptor for activation of nuclear factor-κB (RANK) in early-stage osteoclast precursor cells (c-fms+RANK−). Blocking of the activity of Nox with diphenylene iodonium inhibited ROS production, activation of extracellular signal-regulated kinase (ERK), and the expression of RANK, PU.1 and MITF. The suppression of Nox2, but not Nox1, expression by RNA interference inhibited ROS production and RANK expression. These results suggested that ROS produced in response to M-CSF via a process mediated by Nox2 acted as an intracellular signaling mediator for RANK expression through the activation of ERK and the expression of PU.1 and MITF in early-stage osteoclast precursor cells.

Nitric oxide (NO) derived from inducible nitric oxide synthase (iNOS) plays an important role in host defense, as well as in inflammation-induced tissue lesions. Here we evaluated the role of NO in bone loss in bacterial infection-induced apical periodontitis by using iNOS-deficient mice (iNOS−/−). The iNOS−/− mice developed greater inflammatory cell recruitment and osteolytic lesions than WT mice. Moreover, tartrate-resistant acid-phosphatase-positive (TRAP+) osteoclasts were significantly more numerous in iNOS−/− mice. Furthermore, the increased bone resorption in iNOS−/− mice also correlated with the increased expression of receptor activator NF-kappaB (RANK), stromal-cell-derived factor-1α (SDF-1α/CXCL12), and reduced expression of osteoprotegerin (OPG). These results show that NO deficiency was associated with an imbalance of bone-resorption-modulating factors, leading to severe infection-stimulated bone loss.

Progestins and breast cancer Progestins, used in contraceptives and hormone replacement therapy, have been linked to breast cancer. Two teams working independently have now found a mechanistic basis for this association. Schramek et al . show in a mouse model that synthetic progestins can promote mammary tumour formation by inducing the osteoclast differentiation factor RANKL, which acts on mammary epithelial cells through the RANKL receptor RANK. Gonzalez-Suarez et al . find that inhibition of RANKL reduces tumorigenesis in hormone-induced as well as in other mouse mammary gland tumour models, suggesting a new therapeutic approach. One RANKL inhibitor (denosumab) is in clinical trials as a treatment for bone loss in post-menopausal osteoporosis and for the treatment of skeletal-related symptoms in metastatic bone disease. Progestins, used in contraceptives and hormone replacement therapy, have been linked to breast cancer. These authors provide a mechanistic basis for this association. They show in a mouse model that synthetic progestins can promote mammary tumour formation by inducing RANKL (receptor activator of NF-KB ligand), which acts on mammary epithelial cells through the RANKL receptor RANK. Breast cancer is one of the most common cancers in humans and will on average affect up to one in eight women in their lifetime in the United States and Europe 1 . The Women’s Health Initiative and the Million Women Study have shown that hormone replacement therapy is associated with an increased risk of incident and fatal breast cancer 2 , 3 . In particular, synthetic progesterone derivatives (progestins) such as medroxyprogesterone acetate (MPA), used in millions of women for hormone replacement therapy and contraceptives, markedly increase the risk of developing breast cancer. Here we show that the in vivo administration of MPA triggers massive induction of the key osteoclast differentiation factor RANKL (receptor activator of NF-κB ligand) in mammary-gland epithelial cells. Genetic inactivation of the RANKL receptor RANK in mammary-gland epithelial cells prevents MPA-induced epithelial proliferation, impairs expansion of the CD49f hi stem-cell-enriched population, and sensitizes these cells to DNA-damage-induced cell death. Deletion of RANK from the mammary epithelium results in a markedly decreased incidence and delayed onset of MPA-driven mammary cancer. These data show that the RANKL/RANK system controls the incidence and onset of progestin-driven breast cancer.

High serum levels of osteoprotegerin (OPG) are found in patients with obesity, type 2 diabetes, sepsis, or septic shock and are associated with a high mortality rate in stroke. The primary known function of OPG is to bind to the receptor activator of NF-κB ligand (RANKL), and by doing so, it inhibits the binding between RANKL and its receptor (RANK). TLR4 signaling in macrophages involves TRAF6 recruitment and contributes to low-grade chronic inflammation in adipose tissue. LPS is a classical activator of the TLR4 pathway and induces the expression of inflammatory cytokines in macrophages. We have previously observed that in the presence of RANKL, there is no LPS-induced activation of TLR4 in macrophages. In this study, we investigated the crosstalk between RANK and TLR4 pathways in macrophages stimulated with both RANKL and LPS to unveil the role of OPG in inflammatory processes. We found that RANKL inhibits TLR4 activation by binding to RANK, promoting the binding between TRAF6 and RANK, lowering TLR4 activation and the expression of proinflammatory mediators. Furthermore, high OPG levels aggravate inflammation by inhibiting RANKL. Our findings elect RANKL as a candidate for drug development as a way to mitigate the impact of obesity-induced inflammation in patients.

Background The expression of the receptor activator of nuclear factor kappa B (RANK) /RANK ligand (RANKL) /osteoprotegerin (OPG) system and its association with the progression of intervertebral disc (IVD) degeneration has recently been reported in a human IVD. However, the effect of the RANK/RANKL/OPG system on the matrix metabolism of human IVD cells, especially on the expression of catabolic factors relevant to IVD degeneration, remains unknown. The purpose of this study was to examine the expression of the RANK/RANKL/OPG system, and then to evaluate the effect of this system on the expression of catabolic factors by human IVD cells. Methods Annulus fibrosus (AF) and nucleus pulposus (NP) cells isolated by sequential enzyme digestion from human IVD tissues obtained during spine surgeries were monolayer cultured. The expression of the RANK/RANKL/OPG system was determined using immunohistochemical methods and real-time polymerase chain reaction (PCR). To evaluate the influence of interleukin-1 beta (IL-1β) stimulation on the mRNA expression of RANK, RANKL, and OPG, recombinant human IL-1β (rhIL-1β) was administered in the culture media of IVD cells. To examine the influence of RANKL signaling on the expression of matrix metalloprotease-3 (MMP-3), MMP-13, and IL-1β, the cells were cultured with exogenous recombinant human RANKL (rhRANKL), recombinant human OPG (rhOPG) or anti-human RANKL mouse monoclonal antibody (ahRANKL-mAB) with or without rhIL-1β. Results Immunoreactivity to RANK/RANKL/OPG and the mRNA expression of the three genes were obviously identified in both AF and NP cells. rhIL-1β stimulation significantly upregulated the mRNA expression level of RANK/RANKL/OPG. The mRNA expression of catabolic factors was significantly upregulated by stimulation of rhRANKL in the presence of rhIL-1β. On the other hand, the administration of either rhOPG or ahRANKL-mAB significantly suppressed the mRNA expression of catabolic factors that had been upregulated by rhIL-1β stimulation. The suppressive effect of ahRANKL-mAB against rhIL-1β stimulation was also confirmed by the protein expression of MMP-3. Conclusions The present study showed that the RANK/RANKL/OPG system may be involved in the progression of IVD degeneration. This study also suggested the potential use of anti-RANKL monoclonal antibody and OPG as therapeutic agents to suppress the progression of IVD degeneration.

Introduction RANKL is important in mammary gland development during pregnancy and mediates the initiation and progression of progesterone-induced breast cancer. No clinical data are available on the effect of pregnancy on RANK/RANKL expression in young breast cancer patients. Methods We used our previously published dataset of 65 pregnant and 130 matched young breast cancer patients with full clinical, pathological, and survival information. 85% of patients had available transcriptomic data as well. RANK/RANKL expression by immunohistochemistry using H-score on the primary tumor and adjacent normal tissue was performed. We examined the difference in expression of RANK/RANKL between pregnant and non-pregnant patients and their association with clinicopathological features and prognosis. We also evaluated genes and pathways associated with RANK/RANKL expression on primary tumors. Results RANKL but not RANK expression was more prevalent in the pregnant group, both on the tumor and adjacent normal tissue, independent of other clinicopathological factors (both P <0.001). 18.7% of pregnant and 5.3% of non-pregnant patients had tumors showing ≥10% of cells with 3+ RANKL expression. RANKL expression was significantly higher in progesterone receptor-positive, and luminal A-like tumors, with negative correlation with Ki-67 (all P <0.001). On the contrary, RANK expression was higher in triple negative tumors ( P <0.001). Using false discovery rate <0.05, 151 and 1,207 genes were significantly correlated with tumor-expressed RANKL and RANK expression by immunohistochemistry, respectively. High RANKL expression within primary tumor was associated with pathways related to mammary gland development, bone resorption, T-cell proliferation and regulation of chemotaxis, while RANK expression was associated with immune response and proliferation pathways. At a median follow-up of 65 months, neither RANK nor RANKL expression within tumor was associated with disease free survival in pregnant or non-pregnant group. Conclusions Pregnancy increases RANKL expression both in normal breast and primary tumors. These results could guide further development of RANKL-targeted therapy.