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A major breakthrough in cancer treatment occurred with the development of strategies that overcome T-cell tolerance toward tumor cells. These approaches enhance antitumor immunity by overcoming mechanisms that are normally in place to prevent autoimmunity but simultaneously prevent rejection of tumor cells. Although tolerance mechanisms that restrict antitumor immunity take place both in the thymus and periphery, only immunotherapies that target peripheral tolerance mechanisms occurring outside of the thymus are currently available. We review here recent gains in our understanding of how thymic tolerance mediated by the autoimmune regulator (Aire) impedes antitumor immunity. It is now clear that transient depletion of Aire-expressing cells in the thymus can be achieved with RANKL blockade. Finally, we discuss key findings that support the repurposing of anti-RANKL as a cancer immunotherapy with a unique mechanism of action.

BACKGROUND: Osteoclasts are the only known type of bone resorption cells, and its life activities are essential to the normal development of bones and the repair of bone damage. Osteoclasts show abnormal proliferation and differentiation and increased bone resorption activity in most bone diseases, while receptor activator of nuclear factor-kappa B (RANK) is a key signal pathway that regulates osteoclastogenesis. OBJECTIVE: To summarize the latest research progress on the downstream targets of osteoclast RANK signal and DNA transcription factors at home and abroad, and provide a basis for the research and treatment of related diseases. METHODS: A computer-based retrieval was conducted in CNKI, WanFang, VIP, PubMed, Embase and Web of Science databases. The search terms were “osteoclasts, osteoclast precursor cells, osteoporosis, bone metabolism, pathogenesis, epigenetics, signaling pathway, signal transduction, transcription factors, tissue engineering” in Chinese and English. The retrieval time was set to 2017-2021. Finally 52 articles were included according to the inclusion and exclusion criteria. RESULTS AND CONCLUSION: The special structure of RANK determines that its signal transduction needs to be combined with tumor necrosis factor receptorassociated factor 6 to recruit a variety of proteins, active enzymes and cytokines to form a RANK complex with intrinsic enzyme activity. This complex then activates nuclear factor-κB, mitogen-activated protein kinase and other signal pathways, ultimately regulating osteoclast differentiation, proliferation, and bone resorption. [ABSTRACT FROM AUTHOR]

BackgroundThe receptor activator of NF-κB ligand (RANKL), a member of the TNF ligand superfamily, is known to regulate bone metabolism. The expression of each component of the RANK/RANKL/osteoprotegerin (OPG) system in the intervertebral disc (IVD) has not been examined in detail. The purposes of this study were to examine the expression of the RANK/RANKL/OPG system and to evaluate the function of RANKL in the matrix metabolism of the rat IVD.MethodsSprague-Dawley, 12-week-old, male rats were used in this study. Anulus fibrosus (AF), nucleus pulposus (NP) and cartilaginous endplate (CEP) cells isolated from dissected thoracolumbar discs were monolayer-cultured. RANK/RANKL/OPG expression in rat IVDs was examined using real-time polymerase chain reaction (PCR) and immunohistochemical analysis (cultured cells and IVD tissues). To examine the effect of interleukin-1β (IL-1β) stimulation on the mRNA levels of RANK, RANKL and OPG, the cells were cultured with or without recombinant human IL-1β (rhIL-1β). To evaluate the effect of RANKL on the mRNA expression of catabolic factors (IL-1β, matrix metalloproteinase-3 (MMP-3) and MMP-13), the cells were cultured with RANKL in the presence or absence of rhIL-1β. The immunohistochemical expression of this system was also evaluated using human IVD tissues with different grades of degeneration.ResultsmRNA expression levels of RANK, RANKL, and OPG were clearly identified in AF, NP and CEP cells. Immunoreactivity to RANK, RANKL and OPG was distributed in the cell membranes and/or cytoplasm of the three types of cells. The mRNA level of RANKL was significantly upregulated by treatment with rhIL-1β of the three types of cells. Treatment with RANKL without rhIL-1β did not induce significant effects on the mRNA expression of catabolic factors by AF, NP and CEP cells. However, the expression was significantly upregulated by stimulation with RANKL in the presence of rhIL-1β. There was a general trend for more RANK/RANKL/OPG-positive cells in human IVD tissues in an advanced stage of degeneration compared to an early stage.ConclusionsOur study showed the possibility that the RANK/RANKL/OPG system may play a part in the process of intervertebral disc degeneration.

PurposeThe receptor activator of nuclear factor kappa B (RANK)/RANK ligand (RANKL)/osteoprotegerin (OPG) axis may contribute to the development of bone metastases (BM). We studied gene expression in this pathway in primary breast cancer (BC) to determine correlations with clinical characteristics and outcomes in the neoadjuvant I-SPY1 study.MethodsWe evaluated RANK/RANKL/OPG expression using expression microarrays in I-SPY1 (n = 149). Associations with clinical features were determined using t test and ANOVA. Associations between biomarker high versus low groups (dichotomized at an optimal cutpoint) and recurrence-free survival (RFS) were evaluated using the log-rank test and in a multivariate Cox proportional hazard model. A pooled external neoadjuvant cohort with gene expression data (GSE25066) (Hatzis et al. in JAMA 305(18):1873-1881, 30) (n = 425) was used for validation. Associations with site-specific relapse were evaluated using the t-test and multivariate logistic regression adjusting for hormone receptor (HR) status.ResultsRANK was significantly higher in HR negative versus HR positive (p = 0.027), in basal versus non-basal disease (p = 0.004), and in those achieving pathologic complete response (p = 0.038); the associations with HR negative and basal BC were also significant in GSE25066. In both datasets, higher RANK associated with significantly worse RFS (I-SPY1: p = 0.045, GSE25066: p = 0.044). However, this association did not remain significant after adjusting for HR status. In I-SPY1 patients with recurrence, higher RANK correlated with BM versus non-BM (p = 0.045), even after adjusting for HR status (p = 0.035).ConclusionsRANK is increased in HR negative and basal BC, and correlates with worse RFS and risk of BM. The RANK pathway is a potential therapeutic target in BC.

Epoxyeicosatrienoic acids (EETs), metabolites of arachidonic acid derived from the cytochrome P450 enzymes, are mainly metabolized by soluble epoxide hydrolase (sEH) to their corresponding diols. EETs but not their diols, have anti-inflammatory properties, and inhibition of sEH might provide protective effects against inflammatory bone loss. Thus, in the present study, we tested the selective sEH inhibitor, 1-trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl) urea (TPPU), in a mouse model of periodontitis induced by infection with Aggregatibacter actinomycetemcomitans Oral treatment of wild-type mice with TPPU and sEH knockout (KO) animals showed reduced bone loss induced by A. actinomycetemcomitans This was associated with decreased expression of key osteoclastogenic molecules, receptor activator of nuclear factor-κB/RANK ligand/osteoprotegerin, and the chemokine monocyte chemotactic protein 1 in the gingival tissue without affecting bacterial counts. In addition, downstream kinases p38 and c-Jun N-terminal kinase known to be activated in response to inflammatory signals were abrogated after TPPU treatment or in sEH KO mice. Moreover, endoplasmic reticulum stress was elevated in periodontal disease but was abrogated after TPPU treatment and in sEH knockout mice. Together, these results demonstrated that sEH pharmacological inhibition may be of therapeutic value in periodontitis.

AimTo evaluate the effects of metformin (Met) on inflammation, oxidative stress, and bone loss in a rat model of ligature-induced periodontitis.Materials & methodsMale albino Wistar rats were divided randomly into five groups of twenty-one rats each, and given the following treatments for 10 days: (1) no ligature + water, (2) ligature + water, (3) ligature + 50 mg/kg Met, (4) ligature + 100 mg/kg Met, and (5) ligature + 200 mg/kg Met. Water or Met was administered orally. Maxillae were fixed and scanned using Micro-computed Tomography (μCT) to quantitate linear and bone volume/tissue volume (BV/TV) volumetric bone loss. Histopathological characteristics were assessed through immunohistochemical staining for MMP-9, COX-2, the RANKL/RANK/OPG pathway, SOD-1, and GPx-1. Additionally, confocal microscopy was used to analyze osteocalcin fluorescence. UV-VIS analysis was used to examine the levels of malondialdehyde, glutathione, IL-1β and TNF-α from gingival tissues. Quantitative RT-PCR reaction was used to gene expression of AMPK, NF-κB (p65), and Hmgb1 from gingival tissues. Significance among groups were analysed using a one-way ANOVA. A p-value of p

AimTo evaluate the effects of metformin (Met) on inflammation, oxidative stress, and bone loss in a rat model of ligature-induced periodontitis.Materials & methodsMale albino Wistar rats were divided randomly into five groups of twenty-one rats each, and given the following treatments for 10 days: (1) no ligature + water, (2) ligature + water, (3) ligature + 50 mg/kg Met, (4) ligature + 100 mg/kg Met, and (5) ligature + 200 mg/kg Met. Water or Met was administered orally. Maxillae were fixed and scanned using Micro-computed Tomography (μCT) to quantitate linear and bone volume/tissue volume (BV/TV) volumetric bone loss. Histopathological characteristics were assessed through immunohistochemical staining for MMP-9, COX-2, the RANKL/RANK/OPG pathway, SOD-1, and GPx-1. Additionally, confocal microscopy was used to analyze osteocalcin fluorescence. UV-VIS analysis was used to examine the levels of malondialdehyde, glutathione, IL-1β and TNF-α from gingival tissues. Quantitative RT-PCR reaction was used to gene expression of AMPK, NF-κB (p65), and Hmgb1 from gingival tissues. Significance among groups were analysed using a one-way ANOVA. A p-value of p

Abstract Background The objective of this scoping review was to systematically explore the current knowledge of cellular and molecular processes that drive and control trauma-associated root resorption, to identify research gaps and to provide a basis for improved prevention and therapy. Methods Four major bibliographic databases were searched according to the research question up to February 2021 and supplemented manually. Reports on physiologic, histologic, anatomic and clinical aspects of root resorption following dental trauma were included. Duplicates were removed, the collected material was screened by title/abstract and assessed for eligibility based on the full text. Relevant aspects were extracted, organized and summarized. Results 846 papers were identified as relevant for a qualitative summary. Consideration of pathophysiological mechanisms concerning trauma-related root resorption in the literature is sparse. Whereas some forms of resorption have been explored thoroughly, the etiology of others, particularly invasive cervical resorption, is still under debate, resulting in inadequate diagnostics and heterogeneous clinical recommendations. Effective therapies for progressive replacement resorptions have not been established. Whereas the discovery of the RANKL/RANK/OPG system is essential to our understanding of resorptive processes, many questions regarding the functional regulation of osteo-/odontoclasts remain unanswered. Conclusions This scoping review provides an overview of existing evidence, but also identifies knowledge gaps that need to be addressed by continued laboratory and clinical research.

BackgroundPatent ductus arteriosus (PDA) in the newborn is the most common congenital heart anomaly and is significantly more common in preterm infants. Contemporary pharmacological treatment is effective in only 70-80% of the cases. Moreover, indomethacin or ibuprofen, which are used to close a PDA may be accompanied by serious side effects in premature infants. To explore the novel molecular pathways, which may be involved in the maturation and closure of the ductus arteriosus (DA), we used fetal and neonatal sheep to test the hypothesis that maturational development of DA is associated with significant alterations in specific mRNA expression.MethodsWe conducted oligonucleotide microarray experiments on the isolated mRNA from DA and ascending aorta from three study groups (premature fetus-97 ± 0 d, near-term fetus-136 ± 0.8 d, and newborn lamb-12 ± 0 h). We compared the alterations in mRNA expression in DA and aorta to identify genes specifically involved in DA maturation.ResultsResults demonstrate significant changes in wingless-integrin1, thrombospondin 1, receptor activator of nuclear factor-kappa B, nitric oxide synthase, and retinoic acid receptor activation signaling pathways.ConclusionWe conclude that these pathways may play an important role during both development and postnatal DA closure and warrant further investigation.

Osteoclasts require coordinated co-stimulation by several signaling pathways to initiate and regulate their cellular differentiation. Receptor activator for NF-κB ligand (RANKL or TNFSF11), a tumor necrosis factor (TNF) superfamily member, is the master cytokine required for osteoclastogenesis with essential co-stimulatory signals mediated by immunoreceptor tyrosine-based activation motif (ITAM)-signaling adaptors, DNAX-associated protein 12 kDa size (DAP12) and FcεRI gamma chain (FcRγ). The ITAM-signaling adaptors do not have an extracellular ligand-binding domain and, therefore, must pair with ligand-binding immunoreceptors to interact with their extracellular environment. DAP12 pairs with a number of different immunoreceptors including triggering receptor expressed on myeloid cells 2 (TREM2), myeloid DAP12-associated lectin (MDL-1), and sialic acid-binding immunoglobulin-type lectin 15 (Siglec-15); while FcRγ pairs with a different set of receptors including osteoclast-specific activating receptor (OSCAR), paired immunoglobulin receptor A (PIR-A), and Fc receptors. The ligands for many of these receptors in the bone microenvironment remain unknown. Here, we will review immunoreceptors known to pair with either DAP12 or FcRγ that have been shown to regulate osteoclastogenesis. Co-stimulation and the effects of ITAM-signaling have turned out to be complex, and now include paradoxical findings that ITAM-signaling adaptor-associated receptors can inhibit osteoclastogenesis and immunoreceptor tyrosine-based inhibitory motif (ITIM) receptors can promote osteoclastogenesis. Thus, co-stimulation of osteoclastogenesis continues to reveal additional complexities that are important in the regulatory mechanisms that seek to maintain bone homeostasis.

Breast cancer is the most common female cancer, affecting approximately one in eight women during their life-time. Besides environmental triggers and hormones, inherited mutations in the breast cancer 1 (BRCA1) or BRCA2 genes markedly increase the risk for the development of breast cancer. Here, using two different mouse models, we show that genetic inactivation of the key osteoclast differentiation factor RANK in the mammary epithelium markedly delayed onset, reduced incidence, and attenuated progression of Brca1;p53 mutation-driven mammary cancer. Long-term pharmacological inhibition of the RANK ligand RANKL in mice abolished the occurrence of Brca1 mutation-driven pre-neoplastic lesions. Mechanistically, genetic inactivation of Rank or RANKL/RANK blockade impaired proliferation and expansion of both murine Brca1;p53 mutant mammary stem cells and mammary progenitors from human BRCA1 mutation carriers. In addition, genome variations within the RANK locus were significantly associated with risk of developing breast cancer in women with BRCA1 mutations. Thus, RANKL/RANK control progenitor cell expansion and tumorigenesis in inherited breast cancer. These results present a viable strategy for the possible prevention of breast cancer in BRCA1 mutant patients.

Background:The aim of this study was to investigate levels of bone morphogenetic protein-2 (BMP-2), BMP-7, soluble receptor activator of nuclear factor-kB ligand (sRANKL) and osteoprotegerin (OPG) in the peri-implant crevicular fluid (PICF) of implants placed in both maxilla and mandible during the osseointegration period.Methods:Thirty-three patients (17 females and 16 males; mean age 47.03±11.23 years) were included in this study. A total of 33 implants were placed in both of maxilla (Group 1/n=18) and mandible (group 2/n=15). Peri-implant crevicular fluid (PICF) samples, modified plaque index (MPI), gingival index (GI) and probing depth (PD) measurements were obtained at 1 and 3 months after surgery. PICF levels of BMP-2/-7, sRANKL and OPG were analyzed by ELISA.Results:No complications were observed during the healing period. No significant differences were observed in the PICF levels of sRANKL, OPG, BMP-2 and BMP-7 and evaluated clinical parameters between groups at any time point (p>0.05). While PICF volume of group 2 was greater than group 1 at first month, PICF volume of group 1 was greater than group 2 at 3 months (p

Current guidelines recommend weight loss in obese cancer survivors. Weight loss, however, has adverse effects on bone health in obese individuals without cancer but this has not been evaluated in breast cancer survivors. We investigated the associations of intentional weight loss with bone mineral density (BMD) and bone turn-over markers in overweight/obese postmenopausal breast cancer survivors. Participants were overweight/obese breast cancer survivors (N = 81) with stage I, II or IIIA disease enrolled in the St. Louis site of a multi-site Exercise and Nutrition to Enhance Recovery and Good health for You (ENERGY) study; a randomized-controlled clinical trial designed to achieve a sustained ≥7 % loss in body weight at 2 years. Weight loss was achieved through dietary modification with the addition of physical activity. Generalized estimating equations were used to assess differences in mean values between follow-up and baseline. Mean weight decreased by 3 and 2.3 % between baseline and 6-month follow-up, and 12-month follow-up, respectively. There were decreases in osteocalcin (10.6 %, p value < 0.001), PINP (14.5 %, p value < 0.001), NTx (19.2 % p value < 0.001), and RANK (48.5 %, p value < 0.001), but not BALP and CTX-1 levels between baseline and 12-month follow-up. No significant changes occurred in mean T-scores, pelvis and lumbar spine BMD between baseline and 12-month follow-up. A 2.3 % weight loss over 12 months among overweight/obese women with early-stage breast cancer does not appear to have deleterious effect on bone health, and might even have beneficial effect. These findings warrant confirmation, particularly among breast cancer survivors with a larger magnitude of weight loss.

ObjectiveTo identify genetic associations with severity of radiographic damage in ankylosing spondylitis (AS).MethodWe studied 1537 AS cases of European descent; all fulfilled the modified New York Criteria. Radiographic severity was assessed from digitised lateral radiographs of the cervical and lumbar spine using the modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS). A two-phase genotyping design was used. In phase 1, 498 single nucleotide polymorphisms (SNPs) were genotyped in 688 cases; these were selected to capture >90% of the common haplotypic variation in the exons, exon-intron boundaries, and 5 kb flanking DNA in the 5' and 3' UTR of 74 genes involved in anabolic or catabolic bone pathways. In phase 2, 15 SNPs exhibiting p

Purpose: The aim of this prospective controlled study was to evaluate the influence of osteopenia on the levels of osteoclastogenesis-related factors in the peri-implant crevicular fluid (PICF) and on the clinical parameters of immediately loaded implants. Materials and Methods: This study included 24 patients who received at least two implants in the mandible, with restorations delivered 48 hours after implant placement. Patients were divided into control (n = 11) and osteopenia (n = 13) groups. Seven days after implant placement (baseline) and 4 months after implant placement, PICF samples were obtained, and clinical parameters (Plaque Index, Gingival Index, bleeding on probing, suppuration, probing depths, clinical attachment levels) were measured. A commercially available enzyme-linked immunosorbent assay was used to analyze PICF samples for levels of soluble receptor activator of nuclear factor of κB ligand (sRANKL) and osteoprotegerin (OPG). At the 4-month follow-up visit, the implant-supported restorations were removed and periapical radiographs were acquired to evaluate bone loss around the implants. Results: Eighty-eight immediately loaded implants were included in this study (38 in the control group, 50 in the osteopenia group). The RANKL and OPG levels, the RANKL/OPG ratio, and the clinical parameters were similar between the groups at both time points. However, the levels of these factors in PICF differed significantly between baseline and 4 months after surgery. Conclusion: Within the limitations of this short-term study, it can be concluded that osteopenia does not influence the PICF levels of osteoclastogenesis-related factors in immediately loaded implants after 4 months of loading. [ABSTRACT FROM AUTHOR]

Osteoprotegerin (OPG), receptor activator of nuclear factor-kappa B (RANK) and receptor activator of nuclear factor-kappa B ligand (RANKL), the members of the tumor necrosis factor (TNF) family, have multiple effects on bone metabolism, endocrine functions and, as an inflammatory pathway, in the immune system. This study tried to determine the association of the OPG/RANKL/RANK axis with the severity of unstable angina (UA) as an inflammatory condition. Our study involved 50 patients with UA and 50 healthy people. Serum and peripheral blood mononuclear cells were isolated from all participants. Serum levels and gene expression of OPG, RANKL, and RANK in mononuclear cells were measured by enzyme-linked immunosorbent assay (ELISA) and real-time polymerase chain reaction (RT-PCR), respectively. For each patient with UA, the thrombolysis in myocardial infarction (TIMI) and the global registry of acute coronary events (GRACE) scores were determined to evaluate the severity of the disease. Then we analyzed the relation of OPG, RANKL, and RANK levels with TIMI and GRACE scores in patients with UA. Discriminate analysis was used to predict the combinational models of such factors on the prediction of UA. Serum levels of OPG and RANKL (p

Osteoprotegerin (OPG), receptor activator of nuclear factor-kappa B (RANK) and receptor activator of nuclear factor-kappa B ligand (RANKL), the members of the tumor necrosis factor (TNF) family, have multiple effects on bone metabolism, endocrine functions and, as an inflammatory pathway, in the immune system. This study tried to determine the association of the OPG/RANKL/RANK axis with the severity of unstable angina (UA) as an inflammatory condition. Our study involved 50 patients with UA and 50 healthy people. Serum and peripheral blood mononuclear cells were isolated from all participants. Serum levels and gene expression of OPG, RANKL, and RANK in mononuclear cells were measured by enzyme-linked immunosorbent assay (ELISA) and real-time polymerase chain reaction (RT-PCR), respectively. For each patient with UA, the thrombolysis in myocardial infarction (TIMI) and the global registry of acute coronary events (GRACE) scores were determined to evaluate the severity of the disease. Then we analyzed the relation of OPG, RANKL, and RANK levels with TIMI and GRACE scores in patients with UA. Discriminate analysis was used to predict the combinational models of such factors on the prediction of UA. Serum levels of OPG and RANKL (p<0.001) and gene expression of RANKL (p<0.001) were significantly more in patients than those in healthy ones. No relation was seen between the OPG/RANKL/RANK axis and the severity of UA according to TIMI and GRACE scores. Our study shows that serum level, as well as gene expression of OPG/RANKL/RANK axis neither, predicts the occurrence of UA nor shows any relationship with its severity. [ABSTRACT FROM AUTHOR]

Our aim was to examine the impact of TLR5 ligation in rheumatoid arthritis (RA) and experimental arthritis pathology. Studies were conducted to investigate the role of TLR5 ligation on RA and mouse myeloid cell chemotaxis or osteoclast formation, and in addition, to uncover the significance of TNF-α function in TLR5-mediated pathogenesis. Next, the in vivo mechanism of action was determined in collagen-induced arthritis (CIA) and local joint TLR5 ligation models. Last, to evaluate the importance of TLR5 function in RA, we used anti-TLR5 Ab therapy in CIA mice. We show that TLR5 agonist, flagellin, can promote monocyte infiltration and osteoclast maturation directly through myeloid TLR5 ligation and indirectly via TNF-α production from RA and mouse cells. These two identified TLR5 functions are potentiated by TNF-α, because inhibition of both pathways can more strongly impair RA synovial fluid-driven monocyte migration and osteoclast differentiation compared with each factor alone. In preclinical studies, flagellin postonset treatment in CIA and local TLR5 ligation in vivo provoke homing and osteoclastic development of myeloid cells, which are associated with the TNF-α cascade. Conversely, CIA joint inflammation and bone erosion are alleviated when TLR5 function is blocked. We found that TLR5 and TNF-α pathways are interconnected, because TNF-α is produced by TLR5 ligation in RA myeloid cells, and anti-TNF-α therapy can markedly suppress TLR5 expression in RA monocytes. Our novel findings demonstrate that a direct and an indirect mechanism are involved in TLR5-driven RA inflammation and bone destruction.

Precise regulation of bone resorption is critical for skeletal homeostasis. We report a 32-year-old man with a panostotic expansile bone disease and a massive hemorrhagic mandibular tumor. Originally from Mexico, he was deaf at birth and became bow-legged during childhood. There was no family history of skeletal disease. Puberty occurred normally, but during adolescence he experienced difficulty straightening his limbs, sustained multiple fractures, and developed a bony tumor on his chin. By age 18 years, all limbs were misshapen. The mandibular mass grew and protruded from the oral cavity, extending to the level of the lower ribs. Other bony defects included a similar maxillary mass and serpentine limbs. Upon referral at age 27 years, biochemical studies showed serum alkaline phosphatase of 1760 U/L (Nl: 29-111) and other elevated bone turnover markers. Radiography of the limbs showed medullary expansion and cortical thinning with severe bowing. Although the jaw tumors were initially deemed inoperable, mandibular mass excision and staged partial maxillectomy were eventually performed. Tumor histopathology showed curvilinear trabeculae of woven bone on a background of hypocellular fibrous tissue. Fibrous dysplasia of bone was suspected, but there was no mutation in codon 201 of GNAS in samples from blood or tumor. His clinical and radiographic findings, elevated serum markers, and disorganized bone morphology suggested amplified receptor activator of NF-κB (RANK) signaling, even though his disorder differed from conditions with known constitutive activation of RANK signaling (eg, familial expansile osteolysis). We found a unique 12-base pair duplication in the signal peptide of TNFRSF11A, the gene that encodes RANK. No exon or splice site mutations were found in the genes encoding RANK ligand or osteoprotegerin. Alendronate followed by pamidronate therapies substantially decreased his serum alkaline phosphatase activity. This unique patient expands the phenotypes and genetic basis of the mendelian disorders of RANK signaling activation.

The role of the receptor activator of nuclear factor-κB ligand (RANKL)/RANK system is well characterized within bone, where RANKL/RANK signaling mediates osteoclastogenesis and bone resorption. However, this system has also been shown to influence biologic processes beyond the skeletal system, including in the immune system and in cancer. RANKL/RANK signaling is important in lymph-node development, lymphocyte differentiation, dendritic cell survival, T-cell activation, and tolerance induction. The RANKL/RANK axis may also have direct, osteoclast-independent effects on tumor cells. Indeed, activity of the RANKL/RANK pathway in cancer cells has been correlated with tumor progression and advanced disease. Denosumab, a fully human monoclonal antibody against RANKL, inhibits osteoclastogenesis and is widely used not just for the treatment of osteoporosis, but for the prevention of skeletal-related events from bone metastases in solid malignancies such as breast and prostate cancer. The potential effects of denosumab on the immune system have been largely ignored. Nevertheless, with the emergence of immunotherapies for cancer, denosumab may impact the effectiveness of these therapies, especially if they are given in combination. In this article, we review the role of RANKL/RANK in bone, immunity, and cancer. Examining the potential effects of routine treatment with denosumab beyond the bone represents an important area of investigation.

Patients with HIV‑1 infection often develop multiple complications and comorbidities, including osteoporosis and atherosclerosis. The receptor activator of nuclear factor kappa-B/receptor activator of nuclear factor kappa-B ligand/osteoprotegerin axis has been identified as a possible common link between osteoporosis and vascular diseases. Since the discovery of this axis, much has been learned about its role in controlling skeletal biology and less about its role in the context of vascular biology. However, the exact role of the receptor activator of nuclear factor kappa-B ligand/osteoprotegerin axis in HIV infection is not completely understood. In this review we examine the mechanisms by which inflammation and immune dysregulation in HIV‑1 infection may impact bone turnover and atherogenesis through perturbations in the receptor activator of nuclear factor kappa-B/receptor activator of nuclear factor kappa-B ligand/osteoprotegerin axis.

Background: The objective of this scoping review was to systematically explore the current knowledge of cellular and molecular processes that drive and control trauma-associated root resorption, to identify research gaps and to provide a basis for improved prevention and therapy. Methods: Four major bibliographic databases were searched according to the research question up to February 2021 and supplemented manually. Reports on physiologic, histologic, anatomic and clinical aspects of root resorption following dental trauma were included. Duplicates were removed, the collected material was screened by title/abstract and assessed for eligibility based on the full text. Relevant aspects were extracted, organized and summarized. Results: 846 papers were identified as relevant for a qualitative summary. Consideration of pathophysiological mechanisms concerning trauma-related root resorption in the literature is sparse. Whereas some forms of resorption have been explored thoroughly, the etiology of others, particularly invasive cervical resorption, is still under debate, resulting in inadequate diagnostics and heterogeneous clinical recommendations. Effective therapies for progressive replacement resorptions have not been established. Whereas the discovery of the RANKL/RANK/OPG system is essential to our understanding of resorptive processes, many questions regarding the functional regulation of osteo-/odontoclasts remain unanswered. Conclusions: This scoping review provides an overview of existing evidence, but also identifies knowledge gaps that need to be addressed by continued laboratory and clinical research. [ABSTRACT FROM AUTHOR]

Aim: This study compared the quality and quantity of newly formed bone in rabbits' critical-sized calvarial defects filled with enamel matrix derivative (EMD) combined with freeze-dried bone allograft (FDBA) vs FDBA alone., Materials and Methods: A total of 24 adult male white New Zealand rabbits were included. In each rabbit, three bone defects with a diameter of 8 mm were created on the calvarium bone; the first defect was left untreated, while the second was filled with FDBA, and the third was filled with EMD + FDBA. Twelve rabbits were randomly euthanized after a month, and the remaining 2 month postsurgery. Bone sections were histologically evaluated by hematoxylin and eosin and vascular endothelial growth factor (VEGF), alkaline phosphatase (ALP), osteoprotegerin (OPG), and receptor activator of NF-kappaB (RANK) immune-histochemical staining., Results: An improvement in the newly formed bone percentage was found in the defects filled with EMD + FDBA in comparison with FDBA and control defects at 1 month and 2 months postsurgery. Additionally, the expression of VEGF, ALP, OPG, and RANK showed highly significant differences in the defects filled with EMD + FDBA compared to the FDBA and control ones at 1 month postsurgery ( p = 0.001). Meanwhile, VEGF and ALP expression showed a significant decrease in defects filled with EMD + FDBA compared to the FDBA and control ones ( p = 0.001), while OPG and RANK expression showed non-significant differences between treated groups at 2 months postsurgery., Conclusion: Enamel matrix derivative combined with FDBA has a synergistic effect on bone formation and graft substitution. This combination accelerates the expression of VEGF, ALP, OPG, and RANK., Clinical Significance: The combination of EMD and FDBA accelerates and ameliorates the quality of newly formed bone, aiding in maxillofacial reconstruction. How to cite this article: Zakri RN, Grawish ME, Mowafey B, et al. Impact of Freeze-dried Corticocancellous Bone Allograft Combined with Enamel Matrix Derivative in the Treatment of Critical-sized Calvarial Bone Defects: An Animal Study. J Contemp Dent Pract 2024;25(5):424-431.

In cancer, multiple factors converge upon receptor activator of nuclear factor κB (RANK) and its ligand (RANKL) signaling to promote the development of bone metastases; agents that inhibit RANKL signaling reduce skeletal-related events (SRE) in patients with cancer. In addition, RANKL signaling is important in augmenting the ability of dendritic cells (DC) to stimulate both naïve T-cell proliferation and the survival of RANK+ T cells. In this issue, Chang and colleagues using high-dimensional cytometry to evaluate immunomodulatory effects of denosumab in patients with advanced solid, observe early on treatment changes in multiple compartments, and greater effects in patients receiving concurrent chemotherapy or steroids. See related article by Chang et al., p. 453 (4)., (©2024 American Association for Cancer Research.)

Purpose: The OPG/RANKL (osteoprotegerin/receptor activator of nuclear factor kappa-B) system, which plays a crucial role in bone metabolism, is also associated with vascular calcification. Acromegaly is characterized by excessive secretion of growth hormone and insulin-like growth factor, and studies have demonstrated an elevated risk of cardiovascular disease in individuals with acromegaly. In this study, our objective was to investigate the relationship between OPG/RANKL and various cardiovascular risk scoring systems., Methods: We recruited 44 consecutive acromegaly patients and 41 healthy controls with a similar age and gender distribution for this study., Results: While RANKL levels were significantly higher in the acromegaly group compared to the controls, OPG levels were not found to be significantly different between the two groups. Furthermore, within the acromegaly group, RANKL levels were significantly higher in patients with active acromegaly compared to those with controlled acromegaly. Osteoprotegerin levels showed a positive correlation with the Framingham risk score (FRS) in the acromegaly group. Linear regression analysis revealed an association of OPG with FRS (adjusted R 2 value of 21.7%)., Conclusion: OPG and RANKL may serve as potential markers for assessment of cardiovascular calcification and prediction of the cardiovascular risk status in acromegalic patients., (© 2023. The Author(s), under exclusive licence to Hellenic Endocrine Society.)

Increased osteoclastic bone resorption leads to periarticular erosions and systemic osteoporosis in RA patients. Although a great deal is known about how osteoclasts differentiate from precursors and resorb bone, the identity of an osteoclast precursor (OCP) population in vivo and its regulatory role in RA remains elusive. Here, we report the identification of a CD11b(-/lo)Ly6C(hi) BM population with OCP activity in vitro and in vivo. These cells, which can be distinguished from previously characterized precursors in the myeloid lineage, display features of both M1 and M2 monocytes and expand in inflammatory arthritis models. Surprisingly, in one mouse model of RA (adoptive transfer of SKG arthritis), cotransfer of OCP with SKG CD4+ T cells diminished inflammatory arthritis. Similar to monocytic myeloid-derived suppressor cells (M-MDSCs), OCPs suppressed CD4+ and CD8+ T cell proliferation in vitro through the production of NO. This study identifies a BM myeloid precursor population with osteoclastic and T cell-suppressive activity that is expanded in inflammatory arthritis. Therapeutic strategies that prevent the development of OCPs into mature bone-resorbing cells could simultaneously prevent bone resorption and generate an antiinflammatory milieu in the RA joint.

This review focuses on the mechanisms by which PTH stimulates both osteoblast and osteoclast function, emphasizing the critical role that IGF-I plays in these processes. After reviewing the current literature on the skeletal actions of PTH and the modulation of IGF action on bone by the different IGF-binding proteins, the review then examines studies from mouse models in which IGF-I or its receptor have been selectively deleted in different cells of the skeletal system, in particular osteoprogenitors, mature osteoblasts, and osteoclasts. Mice in which IGF-I production has been deleted from all cells are deficient in both bone formation and bone resorption with few osteoblasts or osteoclasts in bone in vivo, reduced osteoblast colony forming units, and an inability of either the osteoblasts or osteoclast precursors to support osteoclastogenesis in vitro. Mice in which the IGF-I receptor is specifically deleted in mature osteoblasts have a mineralization defect in vivo, and bone marrow stromal cells from these mice fail to mineralize in vitro. Mice in which the IGF-I receptor is deleted in osteoprogenitor cells have a marked reduction in osteoblast proliferation and differentiation leading to osteopenia. Finally mice lacking the IGF-I receptor in their osteoclasts have increased bone and decreased osteoclast formation. PTH fails to stimulate bone formation in the mice lacking IGF-I or its receptor in osteoblasts or enhance the signaling between osteoblasts and osteoclasts through RANKL/RANK and Ephrin B2/Eph B4, emphasizing the role IGF-I signaling plays in cell-communication per se and as stimulated by PTH.

Abstract Background Radix Paeoniae Rubra (RPR), a traditional Chinese herb, has anti-inflammatory and immuno-regulatory properties. This study explored the effects of RPR on stimulation of osteoclast differentiation in RAW264.7 cells and peripheral blood mononuclear cells (PBMC)s. Methods The mature osteoclasts were measured by bone resorption assays and TRAP staining. JNK, ERK, p38 and NF-κB inhibitors were used applied in order to verify their contribution in RPR-induced osteoclast differentiation. The NF-κB and MAPK pathways were evaluated by western blotting, RT-PCR and luciferase assay. Results RPR induced osteoclast differentiation in a dose-dependent manner and induced the resorption activity of osteoclasts differentiation of RAW264.7 cells and PBMCs. Western blotting showed that RPR treatment induced phosphorylation of JNK, ERK, and p38 in RAW 264.7 cells. Treatment of JNK, ERK, and p38 MAP kinase inhibitors verified the contribution of JNK, ERK and p38. RPR treatment induced c-Fos and NFATc1 protein expression; NF-κB inhibitor treatment and luciferase assay verified the contribution of the NF-κB pathway. Conclusions This study demonstrated the interesting effect, in which RPR stimulated osteoclast differentiation in murine RAW264.7 cells and human monocytes.

Inflammatory arthritides are commonly characterized by localized and generalized bone loss. Localized bone loss in the form of joint erosions and periarticular osteopenia is a hallmark of rheumatoid arthritis, the prototype of inflammatory arthritis. Recent studies have highlighted the importance of receptor activator of nuclear factor-kappa B ligand (RANKL)-dependent osteoclast activation by inflammatory cells and subsequent bone loss. In this article, we review the pathogenesis of inflammatory bone loss and explore the possible therapeutic interventions to prevent it.

Osteoporosis (OP) is a common metabolic bone disease. Excessive osteoclastic activity significantly contributes to the development of OP. Icariin (ICA) is a flavonol glycoside derived from herbal plants and possesses curative effects on postmenopausal OP and bone fracture. This study aimed to investigate the effects of ICA on osteoclast differentiation induced by receptor activator of nuclear factor kappa B (RANK) ligand (RANKL) and the involvement of estrogen receptor α (ER α ) and RANK signaling cascade in this process. RANKL was used to induce the differentiation of RAW264.7 cells to into osteoclasts. Small interfering RNA technique was used to knockdown ER α in cells. Cell counting kit-8 assay was performed to determine the cytotoxicity of ICA. The number of tartrate-resistant acid phosphatase (TRAP)-positive cells was quantified by TRAP staining. RANKL induced the differentiation of RAW264.7 cells into osteoclasts, while ICA abolished the pro-osteoporotic effect of RANKL. Moreover, ER α knockdown abolished the effects of ICA on RANKL-induced osteoclastogenesis. Further exploration revealed that ICA inhibited the phosphorylation of c -Src in osteoclasts via regulating ER α , while inactivation of c -Src reversed ER α knockdown-promoted osteoclastogenesis. Lastly, ICA inhibited the activation of the mitogen-activated protein kinase signaling pathway and downregulated the expressions of target osteoclastogenic proteins in RANKL-treated RAW 264.7 cells, while ER α knockdown almost completely diminished the effects of ICA. ICA inhibited RANKL-induced osteoclast differentiation via regulating the ER α / c -Src/RANK signaling. These findings elucidated a novel mechanism by which ICA exerts an anti-osteoporotic effect., (© 2024 IOP Publishing Ltd.)

Objective: Receptor activator of nuclear factor-kappa B ligand (RANKL) appears to be an osteoclast-activating factor, bearing an important role in the pathogenesis of multiple myeloma. Some studies demonstrated that U-266 myeloma cell line and primary myeloma cells expressed RANK and RANKL. It had been reported that the expression of myeloid and monocytoid markers was increased by co-culturing myeloma cells with hematopoietic stem cells (HSCs). This study also attempted to show the molecular mechanism of RANK and RANKL on differentiation capability of human cord blood HSC to osteoclast, as well as expression of calcitonin receptor (CTR) on cord blood HSC surface. Materials and Methods: In this experimental study, CD133+ hematopoietic stem cells were isolated from umbilical cord blood and cultured in the presence of macrophage colony-stimulating factor (M-CSF) and RANKL. Osteoclast differentiation was characterized by using tartrate-resistant acid phosphatase (TRAP) staining, giemsa staining, immunophenotyping, and reverse transcription-polymerase chain reaction (RT-PCR) assay for specific genes. Results: Hematopoietic stem cells expressed RANK before and after differentiation into osteoclast. Compared to control group, flow cytometric results showed an increased expression of RANK after differentiation. Expression of CTR mRNA showed TRAP reaction was positive in some differentiated cells, including osteoclast cells. Conclusion: Presence of RANKL and M-CSF in bone marrow could induce HSCs differentiation into osteoclast.

Recent multiple studies have shown that the long-term consequences of atopic dermatitis (AD) include an increased risk of osteoporosis and fracture, especially an increase in hip, pelvic, spinal and wrist fractures. AD is very common worldwide, and some kinds of fractures, such as hip fractures, are associated with increased mortality, which has a substantial socioeconomic impact; however, the precise mechanisms for this remain unclear. Receptor activator of nuclear factor kappa-Β (RANK) ligand (RANKL) and osteoprotegerin (OPG) are members of the tumour necrosis factor ligand and receptor family, members of which also are known as bone biomarkers. Alterations in the RANKL/RANK/OPG system and the balance among these factors (represented by the RANKL/OPG ratio) are central to the pathogenesis of bone loss from osteoporosis, and it is postulated that there is a potential association between the serum levels of RANKL and OPG, and bone density or fracture. Recently, our research group demonstrated that the serum RANKL/OPG ratio positively correlated with AD severity and suggests fracture risk in older women with AD. This review summarizes and discusses the risk and mechanisms of osteoporotic fracture in AD. RANKL may be involved in the pathogenesis of AD, regarding not only bone abnormality but also inflammation. Although further investigation will be needed to verify the hypotheses, recent findings may provide new insights into the pathogenesis of AD and therapeutic targets., Competing Interests: Conflicts of interest The author declares no conflicts of interest., (© The Author(s) 2022. Published by Oxford University Press on behalf of British Association of Dermatologists.)

Type 2 diabetes mellitus (T2DM) related bone fracture. The effects of glucagon-like peptide-1 receptor analogs for the treatment of T2DM on bone are controversial in human studies. This study aimed to compare the effects of GLP-1 receptor analogs exenatide and insulin glargine treatment on bone turnover marker levels and bone mineral density (BMD) in postmenopausal female patients with T2DM. Thirty female patients with T2DM who were naive to insulin and incretin-based treatments, with spontaneous postmenopause, were randomized to exenatide or insulin glargine arms and were followed up for 24 weeks. BMD was evaluated using dual-energy X-ray absorptiometry and bone turnover markers by serum enzyme-linked immunosorbent assay. The body mass index significantly decreased in the exenatide group compared to the glargine group (P < .001). Receptor activator of nuclear factor kappa-B (RANK) and RANK ligand (RANKL) levels were significantly decreased with exenatide treatment (P = .009 and P = .015, respectively). Osteoprotegerin (OPG) level significantly increased with exenatide treatment (P = .02). OPG, RANK, RANKL levels did not change with insulin glargine treatment. No statistically significant difference was found between the pre- and posttreatment BMD, alkaline phosphatase, bone-specific alkaline phosphatase, and type 1 crosslinked N-telopeptide levels in both treatment arms. Despite significant weight loss with exenatide treatment, BMD did not decrease, OPG increased, and the resorption markers of RANK and RANKL decreased, which may reflect early antiresorptive effects of exenatide via the OPG/RANK/RANKL pathway., Competing Interests: The authors have no conflicts of interest to disclose., (Copyright © 2023 the Author(s). Published by Wolters Kluwer Health, Inc.)