Regulation of osteoclast differentiation

Single-cell profiling of bone metastasis ecosystems from multiple cancer types reveals convergent and divergent mechanisms of bone colonization

Bone is a common site for metastasis of solid cancers. The diversity of histological and molecular characteristics of bone metastases (BMs) remains poorly studied. Here, we performed single-cell RNA sequencing on 42 BMs from eight cancer types, identifying three distinct ecosystem archetypes, each characterized by an enrichment of specific immune cells: macrophages/osteoclasts, regulatory/exhausted T cells, or monocytes. We validated these archetypes by immunostaining on tissue sections and bioinformatic analysis of bulk RNA sequencing/microarray data from 158 BMs across more than 10 cancer types. Interestingly, we found only a modest correlation between the BM archetypes and the tissues of origin; BMs from the same cancer type often fell into different archetypes, while BMs from different cancer types sometimes converged on the same archetype. Additional analyses revealed parallel immunosuppression and bone remodeling mechanisms, some of which were experimentally validated. Overall, we discovered unappreciated heterogeneity of BMs across different cancers.

Discovery of a lignan alkaloid, vitedoamine A, as an IKKβ inhibitor for suppressing NF-κB mediated inflammatory responses and osteoclastogenesis in rheumatoid arthritis

Phenylnaphthalene-type lignans have been recognized as the major anti-inflammatory constituents in V. negundo seeds, among which vitedoamine A (VA) was the first discovered lignan alkaloid bearing a γ-lactam. However, the protective effects and specific target of VA against rheumatoid arthritis (RA) have not been explored yet. Herein, our study revealed that VA could inhibit the transcriptional activity of NF-κB, and suppress the production of NO and reduce the expressions of inflammatory cytokines (IL-1β, IL-6, and TNF-α) in several inflammatory cell models, mainly via inhibiting the phosphorylation of IKKα/β and p65, and prevented the degradation of IκBα, thus restraining NF-κB activation. Meanwhile, VA considerably down-regulated the phosphorylation of IKKα/β and p65, and inhibited the degradation of IκBα in RANKL-induced osteoclasts formation and differentiation, suggesting that VA may impede osteoclastogenesis and relieve joint damage in RA. Furthermore, VA interfered IKK/IκBα/NF-κB pathway and decreased the expressions of inflammatory cytokines in IL-1β stimulated fibroblast-like synoviocytes (FLSs), suggesting that VA possessed promising in vitro anti-RA capacity, probably by direct targeting IKKβ and inhibiting its activity (IC50 value: 39 μM). In addition, molecular docking displayed that VA could bind with residues Cys99 and Asp103 in IKKβ via hydrogen bonds, thus preventing ATP from binding with IKKβ to inhibit the activity of IKKβ. Taken together, VA directly targets IKKβ and significantly inhibits the IKK/IκBα/NF-κB pathway, thus inhibiting inflammatory responses in FLSs and mitigating joint damage related to osteoclastogenesis, displaying great potential in treating RA.

Fraxin inhibits ovariectomized-induced bone loss and osteoclastogenesis by suppressing ROS activity

Osteoporosis is characterized by increased osteoclast activity, which is strongly associated with increased levels of reactive oxygen species (ROS). Fraxin, a natural coumarin glycoside, has shown anti-inflammatory and antioxidant properties, but its effects on bone homeostasis are obscure. The effects of fraxin on osteoclast formation and activation were measured via an in vitro osteoclastogenesis assay. Mitochondrial and total ROS production were evaluated with the aid of MitoSOX Red and DCFH-DA, respectively. Osteoclast-related gene expression analysis was performed via qPCR. Key proteins related to osteoclast formation, ROS scavenging, and ROS-regulated signaling, such as mitogen-activated protein kinases (MAPKs), NF-κB pathways, and nuclear factor of activated T cells 1 (NFATc1) signaling, were detected via western blotting. An ovariectomized mouse model was used to evaluate the therapeutic effects of fraxin in vivo. Fraxin inhibited osteoclastogenesis and osteoclast-related gene expression. Mechanistically, fraxin restored the levels of ROS-scavenging enzymes to inhibit ROS accumulation, eventually downregulating ROS-regulated signaling. The measurement of Micro-CT and histological analyses revealed that fraxin treatment significantly reduced OVX-induced bone loss by decreasing the number of osteoclasts. Fraxin shows promise as a novel therapeutic agent for osteoclast-related bone diseases, especially osteoporosis.

Roles of Toll-like Receptor Signaling in Inflammatory Bone Resorption

Toll-like receptors (TLRs) are pattern recognition receptors expressed in immune cells, including neutrophils, macrophages, and dendritic cells. Microbe-associated molecular patterns, including bacterial components, membranes, nucleic acids, and flagella are recognized by TLRs in inflammatory immune responses. Periodontal disease is an inflammatory disease known to cause local infections associated with gingival inflammation, subsequently leading to alveolar bone resorption. Prostaglandin E2 (PGE2) is a key mediator of TLR-induced inflammatory bone resorption. We previously reported that membrane-bound PGE synthase (mPGES-1)-deficient mice failed to induce bone resorption by lipopolysaccharide (LPS), a major pathogenic factor involved in periodontal bone resorption. Further experiments exploring specific pathogen-promoting osteoclast differentiation revealed that various TLR ligands induced osteoclast differentiation in a co-culture model. The ligands for TLR2/1, TLR2/6, TLR3, and TLR5, as well as TLR4, induce osteoclast differentiation associated with the production of PGE2 and the receptor activator of nuclear factor-kappa B ligand (RANKL), an inevitable inducer of osteoclast differentiation in osteoblasts. In vivo, local injection of TLR ligands, including TLR2/1, TLR2/6, and TLR3, resulted in severe alveolar bone resorption. This review summarizes the latest findings on TLR-mediated osteoclast differentiation and bone resorption in inflammatory diseases, such as periodontal diseases.

Effects of IL-34 and anti-IL-34 neutralizing mAb on alveolar bone loss in a ligature-induced model of periodontitis

Macrophage colony-stimulating factor (M-CSF) and interleukin-34 (IL-34) are ligands for the colony-stimulating factor-1  receptor (CSF-1r) expressed on the surface of monocyte/macrophage lineage cells. The importance of coordinated signaling between M-CSF/receptor activator of the nuclear factor kappa-Β ligand (RANKL) in physiological and pathological bone remodeling and alveolar bone loss in response to oral bacterial colonization is well established. However, our knowledge about the IL-34/RANKL signaling in periodontal bone loss remains limited. Recently published cohort studies have demonstrated that the expression patterns of IL-34 are dramatically elevated in gingival crevicular fluid collected from patients with periodontitis. Therefore, the present study aims to evaluate the effects of IL-34 on osteoclastogenesis in vitro and in experimental ligature-mediated model of periodontitis using male mice. Our initial in vitro study demonstrated increased RANKL-induced osteoclastogenesis of IL-34-primed osteoclast precursors (OCPs) compared to M-CSF-primed OCPs. Using an experimental model of ligature-mediated periodontitis, we further demonstrated elevated expression of IL-34 in periodontal lesions. In contrast, M-CSF levels were dramatically reduced in these periodontal lesions. Furthermore, local injections of mouse recombinant IL-34 protein significantly elevated cathepsin K activity, increased the number of tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts and promoted alveolar bone loss in periodontitis lesions. In contrast, anti-IL-34 neutralizing monoclonal antibody significantly reduced the level of alveolar bone loss and the number of TRAP-positive osteoclasts in periodontitis lesions. No beneficial effects of locally injected anti-M-CSF neutralizing antibody were observed in periodontal lesions. This study illustrates the role of IL-34 in promoting alveolar bone loss in periodontal lesions and proposes the potential of anti-IL34 monoclonal antibody (mAb)-based therapeutic regimens to suppress alveolar bone loss in periodontitis lesions.

Subchondral osteoclasts and osteoarthritis: new insights and potential therapeutic avenues

Osteoarthritis (OA) is the most common joint disease, and good therapeutic results are often difficult to obtain due to its complex pathogenesis and diverse causative factors. After decades of research and exploration of OA, it has been progressively found that subchondral bone is essential for its pathogenesis, and pathological changes in subchondral bone can be observed even before cartilage lesions develop. Osteoclasts, the main cells regulating bone resorption, play a crucial role in the pathogenesis of subchondral bone. Subchondral osteoclasts regulate the homeostasis of subchondral bone through the secretion of degradative enzymes, immunomodulation, and cell signaling pathways. In OA, osteoclasts are overactivated by autophagy, ncRNAs, and Rankl/Rank/OPG signaling pathways. Excessive bone resorption disrupts the balance of bone remodeling, leading to increased subchondral bone loss, decreased bone mineral density and consequent structural damage to articular cartilage and joint pain. With increased understanding of bone biology and targeted therapies, researchers have found that the activity and function of subchondral osteoclasts are affected by multiple pathways. In this review, we summarize the roles and mechanisms of subchondral osteoclasts in OA, enumerate the latest advances in subchondral osteoclast-targeted therapy for OA, and look forward to the future trends of subchondral osteoclast-targeted therapies in clinical applications to fill the gaps in the current knowledge of OA treatment and to develop new therapeutic strategies.

Consequences of Aging on Bone

With the aging of the global population, the incidence of musculoskeletal diseases has been increasing, seriously affecting people's health. As people age, the microenvironment within skeleton favors bone resorption and inhibits bone formation, accompanied by bone marrow fat accumulation and multiple cellular senescence. Specifically, skeletal stem/stromal cells (SSCs) during aging tend to undergo adipogenesis rather than osteogenesis. Meanwhile, osteoblasts, as well as osteocytes, showed increased apoptosis, decreased quantity, and multiple functional limitations including impaired mechanical sensing, intercellular modulation, and exosome secretion. Also, the bone resorption function of macrophage-lineage cells (including osteoclasts and preosteoclasts) was significantly enhanced, as well as impaired vascularization and innervation. In this study, we systematically reviewed the effect of aging on bone and the within microenvironment (including skeletal cells as well as their intracellular structure variations, vascular structures, innervation, marrow fat distribution, and lymphatic system) caused by aging, and mechanisms of osteoimmune regulation of the bone environment in the aging state, and the causal relationship with multiple musculoskeletal diseases in addition with their potential therapeutic strategy.

A comprehensive review on environmental pollutants and osteoporosis: Insights into molecular pathways

A significant problem that has an impact on community wellbeing is environmental pollution. Environmental pollution due to air, water, or soil pollutants might pose a severe risk to global health, necessitating intense scientific effort. Osteoporosis is a common chronic condition with substantial clinical implications on mortality, morbidity, and quality of life. It is closely linked to bone fractures. Worldwide, osteoporosis affects around 200 million people, and every year, there are almost 9 million fractures. There is evidence that certain environmental factors may increase the risk of osteoporosis in addition to traditional risk factors. It is crucial to understand the molecular mechanisms at play because there is a connection between osteoporosis and exposure to environmental pollutants such as heavy metals, air pollutants, endocrine disruptors, metal ions and trace elements. Hence, in this scoping review, we explore potential explanations for the link between pollutants and bone deterioration through deep insights into molecular pathways. Understanding and recognizing these pollutants as modifiable risk factors for osteoporosis would possibly help to enhance environmental policy thereby aiding in the improvement of bone health and improving patient quality of life.

Treating bone metastases with local therapy in a breast cancer patient resulted in decreased pain and prevented fracture

Lytic lesions from bone metastases from breast, lung and prostate carcinomas, are associated with a poor prognosis and significant morbidities that include fracture and debilitating pain. Chemotherapeutics, palliative radiation therapy and surgical intervention are routinely used to treat these lesions. The ZetaMet™ Bone Graft is a novel antitumorigenic and osteoinductive graft that offers a potential alternative treatment option. ZetaMet is composed of calcium phosphate salts, type-I collagen and the small molecule N-allyl noroxymorphone dihydrate. Here, we report the case of a stage IV breast cancer patient with multiple lytic metastatic lesions to the spine that were successfully treated, which led to a significant reduction in pain and increased quality of life. This outcome demonstrates that a locally administered therapeutic intervention may represent an important alternative for patients with bone metastases that warrants further study.

CircFam190a: a critical positive regulator of osteoclast differentiation via enhancement of the AKT1/HSP90β complex

The identification of key regulatory factors that control osteoclastogenesis is important. Accumulating evidence indicates that circular RNAs (circRNAs) are discrete functional entities. However, the complexities of circRNA expression as well as the extent of their regulatory functions during osteoclastogenesis have yet to be revealed. Here, based on circular RNA sequencing data, we identified a circular RNA, circFam190a, as a critical regulator of osteoclast differentiation and function. During osteoclastogenesis, circFam190a is significantly upregulated. In vitro, circFam190a enhanced osteoclast formation and function. In vivo, overexpression of circFam190a induced significant bone loss, while knockdown of circFam190a prevented pathological bone loss in an ovariectomized (OVX) mouse osteoporosis model. Mechanistically, our data suggest that circFam90a enhances the binding of AKT1 and HSP90β, promoting AKT1 stability. Altogether, our findings highlight the critical role of circFam190a as a positive regulator of osteoclastogenesis, and targeting circFam190a might be a promising therapeutic strategy for treating pathological bone loss.

Exosomes derived from mesenchymal stem cells: Heralding a new treatment for periodontitis?

Periodontitis, as a complex inflammatory disorder, is characterized by continuous destruction of the teeth-supporting components, like alveolar bone and periodontal ligament, and affects a great percentage of individuals over the world. Also, this oral disease is linked with multiple serious illnesses, e.g., cardiovascular disorders, diabetes, and oral cancer; thus, exerting efficient therapy for periodontitis is necessary. Unfortunately, the current therapies for the disease (e.g., surgical and nonsurgical methods) have not reflected enough effectiveness against periodontitis. At present, mesenchymal stem cell (MSC)-based remedy has created new hope for curating different diseases; however, MSCs have no capability to engraft into the chosen tissue, and the tumorigenic influences of MSCs are still the main concern. Interestingly, documents have revealed that MSC-derived mediators, like exosomes, which their exploitation is more feasible than intact MSCs, can be an effective therapeutic candidate for periodontitis. Therefore, in this study, we will review evidence in conjunction with their possible curative impacts on periodontitis cases.

EVI2B Is a Prognostic Biomarker and Is Correlated with Monocyte and Macrophage Infiltration in Osteosarcoma Based on an Integrative Analysis

Osteosarcoma (OS) is the most common malignant bone tumor. However, treatment strategies have not changed over the past 30 years. The relationship between OS and the immune microenvironment may provide a basis for the establishment of novel therapeutic targets. In this study, a large-scale gene expression dataset (GSE42352) was used to identify key genes in OS. A Target-OS dataset from the Cancer Genome Atlas was used as a validation set. Ecotropic viral integration site 2B (EVI2B) was significantly upregulated in OS tumor samples. Differentially expressed genes (DEGs) were identified between samples with high and low EVI2B expression in both the test and validation cohorts. The top three functions of DEGs determined by a gene set enrichment analysis (GSEA) were chemokine signaling, cytokine-cytokine receptor interaction, and Human T-cell leukemia virus 1 infection. A prognostic prediction model including EVI2B, DOCK2, and CD33 was constructed by a Cox regression analysis. This model indicated that EVI2B is an independent protective prognostic marker in OS. An analysis of immune infiltration further showed that high EVI2B expression levels were correlated with high levels of macrophage infiltration. Protein expression data derived from the Human Protein Atlas suggested EVI2B to be highly expressed in monocytes. Finally, we validated the elevated expression of EVI2B in OS cell lines and OS tissue samples; these results were consistent with those of the analyses of the GSE42352 and Target-OS datasets. Our integrative bioinformatics analysis and experimental results provide clear evidence for the prognostic value of EVI2B in OS and its close relationship with monocyte and macrophage infiltration.

Hyponatremia elicits gene expression changes driving osteoclast differentiation and functions

Growing evidence indicates that chronic hyponatremia represents a significant risk for bone loss, osteoporosis, and fractures in our aging population. Our prior studies on a rat model of the syndrome of inappropriate antidiuretic hormone secretion indicated that chronic hyponatremia causes osteoporosis by increasing osteoclastic bone resorption, thereby liberating stored sodium from bone. Moreover, studies in RAW264.7 pre-osteoclastic cells showed increased osteoclast formation and resorptive activity in response to low extracellular fluid sodium ion concentration (low [Na+]). These studies implicated a direct stimulatory effect of low [Na+] rather than the low osmolality on cultured osteoclastic cells. In the present cellular studies, we explored gene expression changes triggered by low [Na+] using RNA sequencing and gene ontology analysis. Results were confirmed by mouse whole genome microarray, and quantitative RT-PCR. Findings confirmed gene expression changes supporting osteoclast growth and differentiation through stimulation of receptor activator of nuclear factor kappa-B ligand (RANKL), and PI3K/Akt pathways, and revealed additional pathways. New findings on low [Na+]-induced upregulation of lysosomal genes, mitochondrial energy production, MMP-9 expression, and osteoclast motility have supported the significance of osteoclast transcriptomic responses. Functional assays demonstrated that RANL and low [Na+] independently enhance osteoclast functions. Understanding the molecular mechanisms of hyponatremia-induced osteoporosis provides the basis for future studies identifying sodium-sensing mechanisms in osteoclasts, and potentially other bone cells, and developing strategies for treatment of bone fragility in the vulnerable aging population most affected by both chronic hyponatremia and osteoporosis. ISSUE SECTIONS: Signaling Pathways; Parathyroid, Bone, and Mineral Metabolism.

The Effects of Crocin on Bone and Cartilage Diseases

Crocin, the main biologically active carotenoid of saffron, generally is derived from the dried trifid stigma of Crocus sativus L. Many studies have demonstrated that crocin has several therapeutic effects on biological systems through its anti-oxidant and anti-inflammatory properties. The wide range of crocin activities is believed to be because of its ability to anchor to many proteins, triggering some cellular pathways responsible for cell proliferation and differentiation. It also has therapeutic potentials in arthritis, osteoarthritis, rheumatoid arthritis, and articular pain probably due to its anti-inflammatory properties. Anti-apoptotic effects, as well as osteoclast inhibition effects of crocin, have suggested it as a natural substance to treat osteoporosis and degenerative disease of bone and cartilage. Different mechanisms underlying crocin effects on bone and cartilage repair have been investigated, but remain to be fully elucidated. The present review aims to undertake current knowledge on the effects of crocin on bone and cartilage degenerative diseases with an emphasis on its proliferative and differentiative properties in mesenchymal stem cells.

Effect of Non-surgical Periodontal Treatment on Salivary and Serum Biomarkers in Stage III Grade B and C Periodontitis

BACKGROUND

This study aimed to evaluate the levels of total matrix metalloproteinase-8 (MMP-8), macrophage-activating factors (MAF), macrophage inflammatory protein (MIP)-1α, macrophage colony-stimulating factor (M-CSF), interleukin (IL)-34 in saliva and serum of periodontally healthy, periodontitis stage III grade B (P-III-B) and grade C (P-III-C) participants and to compare the changes after non-surgical periodontal treatment (NSPT).

METHODS

A total of non-smoker and systemically healthy 65 participants, 20 periodontally healthy, 20 P-III-B, and 25 P-III-C were recruited for the study. The periodontal parameters were recorded, saliva and serum samples were obtained from all participants at baseline. In periodontitis groups, the periodontal parameters were reevaluated, and the samples were recollected at 1 and 3 months following the NSPT. MMP-8, MAF, MIP-1α, M-CSF, and IL34 levels were measured by ELISA. Receiver operating characteristics curve was performed for estimating the area under the curve (AUC).

RESULTS

All periodontal parameters were improved in periodontitis groups after NSPT (p<0.05). Among tested molecules, salivary MMP-8 and MAF were higher in both periodontitis groups compared to healthy controls (p<0.05) at baseline and significantly decreased after NSPT (p<0.05) to healthy levels or below. Salivary MMP-8 had the highest diagnostic ability both for P-III-B (AUC:0.78 sensitivity: 80%; specificity: 80%) and P-III-C (AUC:0.88 sensitivity: 88%; specificity: 80%). Moreover, after adjusting for age, periodontitis groups were associated with salivary MMP-8 and MAF levels (p<0.05).

CONCLUSION

The present study showed that high salivary MMP-8 and MAF levels were associated with non-smoker, systemically healthy P-III-B and P-III-C. Moreover, NSPT was remarkably reduced their levels. This article is protected by copyright. All rights reserved.

Expression of Receptor Activator of Nuclear – Kappa β Ligand in Patients with Metastatic Bone Disease

BACKGROUND: Bone metastasis is a complication that often occurs due to cancer in solid organs, and more often compared to primary bone tumors. Bone metastasis is associated with excessive osteolytic processes. AIM: This study was conducted to reveal the correlation between Receptor Activator of Nuclear factor kβ Ligand (RANKL) expression, lactate dehydrogenase (LDH), and neutrophil-lymphocyte ratio (NLR) level in patients with bone metastatic lesions. METHODS: This cross-sectional study was conducted in 15 subjects with bone metastatic lesions. The specimens were fresh bone tissues obtained by open biopsy. Expression of RANKL in mRNA level was detected quantitatively using reverse transcription-polymerase chain reaction. LDH and NLR were analyzed from the peripheral blood analysis. The correlation of RANKL expression with LDH and NLR was statistically analyzed. RESULTS: This study enrolled 15 subjects with bone metastasis disease based on the clinical, radiological, and histopathological results. The means of LDH, NLR, and RANKL expression were not significantly different. There was no significant association between the characteristics of metastatic lesion and RANKL expression. The correlation between LDH levels with RANKL expression was positive (p < 0.05), while the correlation between NLR and RANKL expression was negative (p < 0.05). CONCLUSION: RANKL expression was positively correlated with LDH and negatively correlated with the NLR. Both LDH and NLR can be used as predictive factors of RANKL expression in bone metastasis.

Macrophage-Osteoclast Associations: Origin, Polarization, and Subgroups

Cellular associations in the bone microenvironment are involved in modulating the balance between bone remodeling and resorption, which is necessary for maintaining a normal bone morphology. Macrophages and osteoclasts are both vital components of the bone marrow. Macrophages can interact with osteoclasts and regulate bone metabolism by secreting a variety of cytokines, which make a significant contribution to the associations. Although, recent studies have fully explored either macrophages or osteoclasts, indicating the significance of these two types of cells. However, it is of high importance to report the latest discoveries on the relationships between these two myeloid-derived cells in the field of osteoimmunology. Therefore, this paper reviews this topic from three novel aspects of the origin, polarization, and subgroups based on the previous work, to provide a reference for future research and treatment of bone-related diseases.

The Role of Post-Translational Modifications of Chemokines by CD26 in Cancer

Chemokines are a large family of small chemotactic cytokines that fulfill a central function in cancer. Both tumor-promoting and -impeding roles have been ascribed to chemokines, which they exert in a direct or indirect manner. An important post-translational modification that regulates chemokine activity is the NH₂-terminal truncation by peptidases. CD26 is a dipeptidyl peptidase (DPPIV), which typically clips a NH₂-terminal dipeptide from the chemokine. With a certain degree of selectivity in terms of chemokine substrate, CD26 only recognizes chemokines with a penultimate proline or alanine. Chemokines can be protected against CD26 recognition by specific amino acid residues within the chemokine structure, by oligomerization or by binding to cellular glycosaminoglycans (GAGs). Upon truncation, the binding affinity for receptors and GAGs is altered, which influences chemokine function. The consequences of CD26-mediated clipping vary, as unchanged, enhanced, and reduced activities are reported. In tumors, CD26 most likely has the most profound effect on CXCL12 and the interferon (IFN)-inducible CXCR3 ligands, which are converted into receptor antagonists upon truncation. Depending on the tumor type, expression of CD26 is upregulated or downregulated and often results in the preferential generation of the chemokine isoform most favorable for tumor progression. Considering the tight relationship between chemokine sequence and chemokine binding specificity, molecules with the appropriate characteristics can be chemically engineered to provide innovative therapeutic strategies in a cancer setting.

Single-Cell Transcriptomics Reveals the Complexity of the Tumor Microenvironment of Treatment-Naive Osteosarcoma

Osteosarcoma (OS), which occurs most commonly in adolescents, is associated with a high degree of malignancy and poor prognosis. In order to develop an accurate treatment for OS, a deeper understanding of its complex tumor microenvironment (TME) is required. In the present study, tissues were isolated from six patients with OS, and then subjected to single-cell RNA sequencing (scRNA-seq) using a 10× Genomics platform. Multiplex immunofluorescence staining was subsequently used to validate the subsets identified by scRNA-seq. ScRNA-seq of six patients with OS was performed prior to neoadjuvant chemotherapy, and data were obtained on 29,278 cells. A total of nine major cell types were identified, and the single-cell transcriptional map of OS was subsequently revealed. Identified osteoblastic OS cells were divided into five subsets, and the subsets of those osteoblastic OS cells with significant prognostic correlation were determined using a deconvolution algorithm. Thereby, different transcription patterns in the cellular subtypes of osteoblastic OS cells were reported, and key transcription factors associated with survival prognosis were identified. Furthermore, the regulation of osteolysis by osteoblastic OS cells via receptor activator of nuclear factor kappa-B ligand was revealed. Furthermore, the role of osteoblastic OS cells in regulating angiogenesis through vascular endothelial growth factor-A was revealed. C3_TXNIP⁺ macrophages and C5_IFIT1⁺ macrophages were found to regulate regulatory T cells and participate in CD8⁺ T cell exhaustion, illustrating the possibility of immunotherapy that could target CD8⁺ T cells and macrophages. Our findings here show that the role of C1_osteoblastic OS cells in OS is to promote osteolysis and angiogenesis, and this is associated with survival prognosis. In addition, T cell depletion is an important feature of OS. More importantly, the present study provided a valuable resource for the in-depth study of the heterogeneity of the OS TME.

Doxycycline-Doped Polymeric Membranes Induced Growth, Differentiation and Expression of Antigenic Phenotype Markers of Osteoblasts

Polymeric membranes are employed in guided bone regeneration (GBR) as physical barriers to facilitate bone in-growth. A bioactive and biomimetic membrane with the ability to participate in the healing and regeneration of the bone is necessary. The aim of the present study was to analyze how novel silicon dioxide composite membranes functionalized with zinc or doxycycline can modulate the osteoblasts' proliferation, differentiation, and expression of selected antigenic markers related to immunomodulation. Nanostructured acrylate-based membranes were developed, blended with silica, and functionalized with zinc or doxycycline. They were subjected to MG63 osteoblast-like cells culturing. Proliferation was assessed by MTT-assay, differentiation by evaluating the alkaline phosphatase activity by a spectrophotometric method and antigenic phenotype was assessed by flow cytometry for selected markers. Mean comparisons were conducted by one-way ANOVA and Tukey tests (p < 0.05). The blending of silica nanoparticles in the tested non-resorbable polymeric scaffold improved the proliferation and differentiation of osteoblasts, but doxycycline doped scaffolds attained the best results. Osteoblasts cultured on doxycycline functionalized membranes presented higher expression of CD54, CD80, CD86, and HLA-DR, indicating a beneficial immunomodulation activity. Doxycycline doped membranes may be a potential candidate for use in GBR procedures in several challenging pathologies, including periodontal disease.

Dental pulp-derived stem cells inhibit osteoclast differentiation by secreting osteoprotegerin and deactivating AKT signalling in myeloid cells

Osteoclasts (OCs) differentiate from the monocyte/macrophage lineage, critically regulate bone resorption and remodelling in both homeostasis and pathology. Various immune and non‐immune cells help initiating activation of myeloid cells for differentiation, whereas hyper‐activation leads to pathogenesis, and mechanisms are yet to be completely understood. Herein, we show the efficacy of dental pulp–derived stem cells (DPSCs) in limiting RAW 264.7 cell differentiation and underlying molecular mechanism, which has the potential for future therapeutic application in bone‐related disorders. We found that DPSCs inhibit induced OC differentiation of RAW 264.7 cells when co‐cultured in a contact‐free system. DPSCs reduced expression of key OC markers, such as NFATc1, cathepsin K, TRAP, RANK and MMP‐9 assessed by quantitative RT‐PCR, Western blotting and immunofluorescence detection methods. Furthermore, quantitative RT‐PCR analysis revealed that DPSCs mediated M2 polarization of RAW 264.7 cells. To define molecular mechanisms, we found that osteoprotegerin (OPG), an OC inhibitory factor, was up‐regulated in RAW 264.7 cells in the presence of DPSCs. Moreover, DPSCs also constitutively secrete OPG that contributed in limiting OC differentiation. Finally, the addition of recombinant OPG inhibited OC differentiation in a dose‐dependent manner by reducing the expression of OC differentiation markers, NFATc1, cathepsin K, TRAP, RANK and MMP9 in RAW 264.7 cells. RNAKL and M‐CSF phosphorylate AKT and activate PI3K‐AKT signalling pathway during osteoclast differentiation. We further confirmed that OPG‐mediated inhibition of the downstream activation of PI3K‐AKT signalling pathway was similar to the DPSC co‐culture–mediated inhibition of OC differentiation. This study provides novel evidence of DPSC‐mediated inhibition of osteoclastogenesis mechanisms.

Grape Seed Proanthocyanidin Extract Prevents Bone Loss via Regulation of Osteoclast Differentiation, Apoptosis, and Proliferation

Dietary procyanidin has been shown to be an important bioactive component that regulates various pharmacological activities to maintain metabolic homeostasis. In particular, grape seed proanthocyanidin extract (GSPE) is a commercially available medicine for the treatment of venous and lymphatic dysfunction. This study aimed to investigate whether GSPE protects against lipopolysaccharide (LPS)-induced bone loss in vivo and the related mechanism of action in vitro. The administration of GSPE restored the inflammatory bone loss phenotype stimulated by acute systemic injection of LPS in vivo. GSPE strongly suppressed receptor activator of nuclear factor kappa-B ligand (RANKL)-induced osteoclast differentiation and bone resorption activity of mature osteoclasts by decreasing the RANKL-induced nuclear factor-κB transcription activity. GSPE mediates this effect through decreased phosphorylation and degradation of NF-κB inhibitor (IκB) by IκB kinaseβ, subsequently inhibiting proto-oncogene cellular Fos and nuclear factor of activated T cells. Additionally, GSPE promotes osteoclast proliferation by increasing the phosphorylation of components of the Akt and mitogen-activated protein kinase signaling pathways and it also inhibits apoptosis by decreasing the activity of caspase-8, caspase-9, and caspase-3, as corroborated by a decrease in the Terminal deoxynucleotidyl transferase dUTP nick end labeling -positive cells. Our study suggests a direct effect of GSPE on the proliferation, differentiation, and apoptosis of osteoclasts and reveals the mechanism responsible for the therapeutic potential of GSPE in osteoclast-associated bone metabolism disease.

Rev-erbα Negatively Regulates Osteoclast and Osteoblast Differentiation through p38 MAPK Signaling Pathway

The circadian clock regulates various physiological processes, including bone metabolism. The nuclear receptors Reverbs, comprising Rev-erbα and Rev-erbβ, play a key role as transcriptional regulators of the circadian clock. In this study, we demonstrate that Rev-erbs negatively regulate differentiation of osteoclasts and osteoblasts. The knockdown of Rev-erbα in osteoclast precursor cells enhanced receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast formation, as well as expression of nuclear factor of activated T cells 1 (NFATc1), osteoclast-associated receptor (OSCAR), and tartrate-resistant acid phosphatase (TRAP). The overexpression of Rev-erbα leads to attenuation of the NFATc1 expression via inhibition of recruitment of c-Fos to the NFATc1 promoter. The overexpression of Rev-erbα in osteoblast precursors attenuated the expression of osteoblast marker genes including Runx2, alkaline phosphatase (ALP), bone sialoprotein (BSP), and osteocalcin (OC). Rev-erbα interfered with the recruitment of Runx2 to the promoter region of the target genes. Conversely, knockdown of Reverbα in the osteoblast precursors enhanced the osteoblast differentiation and function. In addition, Rev-erbα negatively regulated osteoclast and osteoblast differentiation by suppressing the p38 MAPK pathway. Furthermore, intraperitoneal administration of GSK4112, a Rev-erb agonist, protects RANKL-induced bone loss via inhibition of osteoclast differentiation in vivo . Taken together, our results demonstrate a molecular mechanism of Rev-erbs in the bone remodeling, and provide a molecular basis for a potential therapeutic target for treatment of bone disease characterized by excessive bone resorption.

Abl interactor 1: A novel biomarker for osteoporosis in Chinese elderly men

Low bone mineral density (BMD) is a high-risk factor of osteoporosis (OP) and osteoporotic fracture (OF). Peripheral blood monocytes (PBM) can give birth to osteoclasts to resorb bone. Herein, we attempted to identify OP susceptible proteins in human PBM and characterize their functions in bone. Employing the label-free quantitative proteomics methodology (Easy-nLC1000 and Q-exactive) and traditional Western Blotting (WB), we discovered and validated that a key protein, i.e. Abl Interactor 1(ABI1), was significantly down-regulated in PBM in Chinese elderly men with extremely low vs. high BMD (n = 18, p < .05), as well as in OF patients vs. non-fractured (NF) subjects (n = 36, p < .05). The above down-regulation tendency was also observed in Chinese elderly women (n = 51, P < .05). For translational purpose, plasma ABI1 protein was assessed by ELISA in Chinese elderly men, which was found significantly down-regulated in OF (n = 20) vs. NF (n = 64) subjects (Mean: 0.41 vs. 1.03 ng/ml, FC = 0.39, p = .039), as well as in low (n = 32) vs. high (n = 32) BMD subjects (Mean: 0.5 vs. 1.57 ng/ml, FC = 0.32,p = .0012). ROC analyses in another independent study sample (n = 75) showed that the plasma ABI1 protein has superior performance in discriminating osteopenia and healthy subjects (AUC = 0.755, 95% CI: 0.632-0.877, p = .001). Follow-up cellular functional studies revealed that ABI1 protein significantly promoted osteoblast growth (optimal concentration 2.0 ng/ml), osteoblastic gene expression (OPN, ALP, COL1A1, p < .05) and osteoblast differentiation.ABI1 protein also significantly attenuated monocyte trans-endothelial migration and osteoclast differentiation and activity. In conclusion, ABI1 is a novel protein biomarker for OP in Chinese elderly. ABI1 protein, via promoting osteoblast growth, differentiation and activity, and attenuating monocyte trans-endothelial migration and osteoclast differentiation, influences BMD variation and fracture risk in humans. SIGNIFICANCE: Previous plentiful studies indicated that protein ABI1 played an essential role in the progression of several malignancies, including hepatoma, colon cancer and epithelial ovarian cancer. However, there was relatively limited understandings regarding its molecular and cellular functions relevant to bone phenotypes. Employing the label-free quantitative proteomics methodology (Easy-nLC1000 and Q-exactive) and traditional Western Blotting (WB), we discovered and validated that ABI1 was significantly down-regulated in PBM in Chinese elderly men with extremely low BMD as well as in OF patients. The down-regulation trend was consistent in plasma samples in Chinese elderly men. Follow-up cellular functional studies revealed that, on the one hand, ABI1 protein significantly promoted osteoblast growth, osteoblastic gene expression and osteoblast differentiation; on the other hand, it also significantly attenuated monocyte trans-endothelial migration and osteoclast differentiation and activity. It suggested that ABI1 is a promising biomarker with translational value.

Role of ANTXR1 in the regulation of RANKL-induced osteoclast differentiation and function

Anthrax toxin receptor 1 (ANTXR1) is a transmembrane protein with an extracellular domain which is deeply associated with the process of bone formation and plays an important role in angiogenesis. However, there have been no reports investigating the effects of ANTXR1 on bone metabolism mediated by the two types of bone cells, osteoclasts, and osteoblasts. The aim of this study is to reveal the role of ANTXR1 in the differentiation and function of osteoclasts and osteoblasts. We found that ANTXR1 positively regulated the receptor activator of nuclear factor kappa B ligand (RANKL)-induced osteoclast differentiation and bone resorption with no effects on osteoblast differentiation by performing gain- and loss-of-function studies. During ANTXR1-mediated regulation of osteoclastogenesis, phosphorylation of early signal transducers such as c-Jun N-terminal kinase (JNK), Akt, inhibitor of kappa B (IκB), and phospholipase C gamma 2 (PLCγ2) was affected, which in turn altered the mRNA and protein levels of c-Fos and nuclear factor of activated T cells cytoplasmic 1 (NFATc1). In addition, genetic manipulation of ANTXR1 in bone marrow macrophages (BMMs) modulated the capillary-like tube formation in HUVECs via secretion of two angiogenic factors, matrix metalloproteinase-9 (MMP-9) and vascular endothelial growth factor-A (VEGF-A). These results elucidated the importance of ANTXR1 in osteoclast differentiation and functional activity, as well as, osteoclast-mediated angiogenesis of endothelial cells. Taken together, we propose that ANTXR1 might be a promising candidate for gene therapy for bone metabolic diseases and further, might potentially serve as an important biomarker in the field of bone metastasis associated with vascularization.

Loss of ENT1 increases cell proliferation in the annulus fibrosus of the intervertebral disc

Mice lacking equilibrative nucleoside transporter 1 (ENT1 ^-/- ) demonstrate progressive calcification of spinal tissues including the annulus fibrosus (AF) of the intervertebral disc (IVD). We previously established ENT1 as the primary nucleoside transporter in the AF and demonstrated dysregulation of biomineralization pathways. To identify cellular pathways altered by loss of ENT1, we conducted microarray analysis of AF tissue from wild-type (WT) and ENT1 ^-/- mice before calcification (2 months of age) and associated with calcification (6 months of age). Bioinformatic analyses identified cell cycle dysregulation in ENT1 ^-/- AF tissues and implicated the E2f family of transcription factors as potential effectors. Quantitative polymerase chain reaction analysis confirmed increased expression of multiple E2f transcription factors and E2f interacting proteins ( Rb1 and Cdk2) in ENT1 ^-/- AF cells compared with WT at 6 months of age. At this time point, ENT1 ^-/- AF tissues showed increased JNK MAPK pathway activation, CDK1, minichromosome maintenance complex component 5 (Mcm5), and proliferating cell nuclear antigen (PCNA) protein expression, and PCNA-positive proliferating cells compared with WT controls. The current study demonstrates that loss of ENT1-mediated adenosine transport leads to increased cell proliferation in the AF of the IVD.

Nox2 Activity Is Required in Obesity-Mediated Alteration of Bone Remodeling

Despite increasing evidence suggesting a role for NADPH oxidases (Nox) in bone pathophysiology, whether Nox enzymes contribute to obesity-mediated bone remodeling remains to be clearly elucidated. Nox2 is one of the predominant Nox enzymes expressed in the bone marrow microenvironment and is a major source of ROS generation during inflammatory processes. It is also well recognized that a high-fat diet (HFD) induces obesity, which negatively impacts bone remodeling. In this work, we investigated the effect of Nox2 loss of function on obesity-mediated alteration of bone remodeling using wild-type (WT) and Nox2-knockout (KO) mice fed with a standard lab chow diet (SD) as a control or a HFD as an obesity model. Bone mineral density (BMD) of mice was assessed at the beginning and after 3 months of feeding with SD or HFD. Our results show that HFD increased bone mineral density to a greater extent in KO mice than in WT mice without affecting the total body weight and fat mass. HFD also significantly increased the number of adipocytes in the bone marrow microenvironment of WT mice as compared to KO mice. The bone levels of proinflammatory cytokines and proosteoclastogenic factors were also significantly elevated in WT-HFD mice as compared to KO-HFD mice. Furthermore, the in vitro differentiation of bone marrow cells into osteoclasts was significantly increased when using bone marrow cells from WT-HFD mice as compared to KO-HFD mice. Our data collectively suggest that Nox2 is implicated in HFD-induced deleterious bone remodeling by enhancing bone marrow adipogenesis and osteoclastogenesis.

Clastic cells are absent around the root surface in pulp-exposed periapical periodontitis lesions in mice

INTRODUCTION

Clastic cells, originating from the monocyte-macrophage lineage, resorb mineralized tissues. In periapical periodontitis, alveolar bone around the tooth apex becomes resorbed; however, the roots of the teeth are often left intact by yet unknown mechanisms. Here, we examined the status of clastic cells in a periapical periodontitis model in mice.

METHODS

Periapical periodontitis was induced by performing pulp exposure on the maxillary first molar. The contralateral maxillary first molar was used as a control. The maxillae were harvested, fixed, and subjected to μCT scanning and three-dimensional volumetric analysis. TRAP staining was performed, and osteoclasts were quantified. Immunohistochemical staining was performed for RANKL, OPG, and F4/80, a marker for macrophages.

RESULTS

At the apex of the tooth, pulp exposure resulted in periapical radiolucency with mineralized tissues at the surrounding bone surfaces but not on the root surfaces. Histologically, clastic cells were present on the bone surfaces but absent around the root surfaces. Expression of F4/80 and RANKL was not found at close proximity to the root surfaces, but OPG was globally expressed.

CONCLUSION

The absence of clastic cells around the root surface of pulp-exposed teeth, in part, is associated with the lack of macrophages and RANKL expression.

Brief Review on Metabolic Bone Disease

Metabolic bone disease (MBD) is a broad term that describes a clinically heterogeneous group of diseases that are only united by a common denominator of an aberrant bone chemical milieu leading to a defective skeleton and bone abnormalities. From a forensic pathologist's perspective, MBDs create a challenging diagnostic dilemma in differentiating them from child abuse, particularly when the victim is an infant. Through this brief narrative review on MBD, bone pathophysiology and two relatively challenging pediatric MBDs will be discussed.

TRIM38 regulates NF-κB activation through TAB2 degradation in osteoclast and osteoblast differentiation

The tripartite motif protein 38 (TRIM38), a member of the TRIM family, is involved in various cellular processes such as cell proliferation, differentiation, apoptosis, and antiviral defense. However, the role of TRIM38 in osteoclast and osteoblast differentiation is not yet known. In this study, we report the involvement of TRIM38 in osteoclast and osteoblast differentiation. Overexpression of TRIM38, in osteoclast precursor cells, attenuated receptor activator of nuclear factor kappa B ligand (RANKL)-induced osteoclast formation, RANKL-triggered NF-κB activation, and expression of osteoclast marker genes, such as NFATc1, osteoclast-associated receptor (OSCAR), and tartrate-resistant acid phosphatase (TRAP); and down-regulation of TRIM38 expression showed the opposite effects. Ectopic expression of TRIM38 in osteoblast precursors induced increased osteoblast differentiation and function. Elevated expression of alkaline phosphatase (ALP), bone sialoprotein (BSP), and osteocalcin was also observed due to blockade of NF-κB activation. Conversely, knockdown of TRIM38 showed the opposite effects. TRIM38 also induced degradation of lysosome-dependent transforming growth factor beta-activated kinase 1 and MAP3K7-binding protein 2 (TAB2), further blocking NF-κB activation. Taken together, our data suggest that TRIM38 plays a critical role in bone remodeling as a negative regulator of NF-κB in both osteoclast and osteoblast differentiation.

Crocin inhibits RANKL‑induced osteoclastogenesis by regulating JNK and NF‑κB signaling pathways

Receptor activator of nuclear factor‑κB ligand (RANKL), a member of the tumor necrosis factor receptor-ligand family, is a crucial factor involved in osteoclast differentiation. Crocin, a pharmacologically active component of Crocus sativus L., has been reported to attenuate ovariectomy‑induced osteoporosis in rats. However, the molecular mechanism underlying the effect of crocin on osteoclast formation remains to be determined. The present study aimed to investigate the effect of crocin on RANKL‑induced osteoclastogenesis and its underlying molecular mechanism. Results demonstrated that crocin decreased osteoclastogenesis in bone marrow‑derived macrophages (BMMs). In addition, the expression levels of osteoclast marker proteins were downregulated by crocin. Mechanistically, crocin inhibited RANKL‑induced activation of nuclear factor‑κB (NF‑κB) by suppressing inhibitor of κBα degradation and preventing NF‑κB p65 subunit nuclear translocation, and by activating c‑Jun N‑terminal kinase (JNK) in BMMs. In summary, the results of the present study suggested that crocin downregulates osteoclast differentiation via inhibition of JNK and NF‑κB signaling pathways. Thus, crocin may be a potential therapeutic agent for the treatment of osteoclast‑associated diseases, including osteoporosis.

Anxa2 attenuates osteoblast growth and is associated with hip BMD and osteoporotic fracture in Chinese elderly

Low bone mineral density (BMD) is a risk factor of osteoporotic fracture (OF). Peripheral blood monocytes (PBM) can differentiate into osteoclasts to resorb bone. It was known that PBM-expressed Anxa2 protein is associated with BMD, and extracellular Anxa2 protein promotes osteoclastogenesis. This study aimed to test 1) whether Anxa2 protein level in PBM differs significantly between subjects with OF and without fracture history (NF); 2) whether Anxa2 level in plasma is associated with BMD; 3) how Anxa2 protein at various concentrations would affect osteoblastic activity in vitro. All the study subjects were Chinese Han elderly. Firstly, Anxa2 protein in PBM was identified and quantitated by LC-MS/MS and compared between 45 OF cases and 42 healthy controls. Secondly, plasma Anxa2 protein level was quantitated by ELISA and compared between unrelated subjects with extremely low vs. high hip BMD (0.63±0.10 vs. 1.05±0.10 g/cm², n = 75). Furthermore, in vitro functional assay was utilized to test the effects of extracellular Anxa2 protein on osteoblastic growth. We found that Anxa2 protein expression in PBM was significantly up-regulated in OF vs. NF subjects (fold change [FC)] = 1.16, P<0.05). Plasma Anxa2 protein concentration (range: 31.69–227.35ng/ml) was significantly elevated in low vs. high BMD subjects (84.85 vs. 66.15ng/ml, FC = 1.28, P<0.05). Cellular dynamical monitoring demonstrated that the general shape of dose-response relationship is the inverse U-shaped curve. Specifically, lower dose of Anxa2 protein may promote osteoblast growth and the optimal concentration for osteoblastic growth was around 50ng/ml, but even higher concentration could attenuate hFOB1.19 osteoprogenitor cell growth. We concluded that Anxa2 protein could attenuate osteoblast growth and be associated with hip BMD and OF in Chinese elderly.

Study of bone metabolism and angiogenesis in patients undergoing high-dose chemotherapy/autologous hematopoietic stem cell transplantation

OBJECTIVES

As the interaction between hematopoietic stem cells (HSCs) and endosteal and endothelial niches in HSCs homing is essential, we aimed to study bone turnover and angiogenesis in 29 patients with lymphoma/multiple myeloma undergoing hematopoietic stem cell transplantation (HSCT).

METHODS

Serum samples were collected before high-dose chemotherapy (HDT), at the end of HDT, after HSC infusion, at the nadir of myelotoxicity, and at engraftment. Bone metabolism (CTX, TRACP-5b, bALP, OC, DKK1, RANKL, OPG), and angiogenesis (Ang1, Ang2) markers were measured. These markers were also measured in 21 control patients before and after conventional chemotherapy.

RESULTS AND CONCLUSIONS

Bone resorption declined during HSCT (decrease in TRACP-5b [P < .001] and CTX [P = .006]). Bone formation declined as well (decrease in bALP and OC [P < .001 for both]). RANKL/OPG ratio, an indicator of osteoclastic activation, did not change significantly (P = .5). Ang1/Ang2 ratio, a vessel equilibrium marker, decreased significantly (P < .001) suggesting endothelial destabilization. The changes observed in the control group were similar except of bALP and RANKL/OPG ratio. Moreover, Ang1/Ang2 ratio on the day after HSC infusion strongly correlated with time to neutrophil and platelet engraftment (P < .001 for both). Conclusively, bone turnover and vessel destabilization represent important events during HSCT probably reflecting the effect of chemotherapy.

Mesenchymal stem cells inhibit RANK-RANKL interactions between osteoclasts and Th17 cells via osteoprotegerin activity

Th17 cells play a critical role in several autoimmune diseases, including psoriasis and psoriatic arthritis (PsA). Psoriasis is a chronic inflammatory skin disease associated with systemic inflammation and comorbidities, such as PsA. PsA develops in nearly 70% of patients with psoriasis, and osteoclasts associated bone erosion is a hallmark of the disease. Thus far, the effect of Th17 cells on osteoclastogenesis via direct cell-to-cell interactions is less understood. In this study, we observed that Th17 cells directly promote osteoclast differentiation and maturation via expression of receptor activator of nuclear factor-κ β ligand (RANKL) in vitro. We investigated the impact of conditioned medium obtained from human palatine tonsil-derived mesenchymal stem cells (T-CM) on the interactions between osteoclasts and Th17 cells. T-CM effectively blunted the RANK-RANKL interaction between the osteoclast precursor cell line RAW 264.7 and Th17 cells via osteoprotegerin (OPG) activity. The frequency of tartrate-resistant acid phosphatase (TRAP)-positive cells in the bone marrow of an imiquimod (IMQ)-induced psoriasis mouse model was decreased following T-CM injection. Therefore, our data provide novel insight into the therapeutic potential of tonsil-derived mesenchymal stem cell-mediated therapy (via OPG production) for the treatment of pathophysiologic processes induced by osteoclasts under chronic inflammatory conditions such as psoriasis.

Spontaneous osteoclastogenesis: Hypothesis for gender-unrelated osteoporosis screening and diagnosis

Women are at greater risk of developing osteoporosis (OP). However, in the past few years it has become more widely recognized that OP is a significant problem also in men although OP is frequently under-diagnosed and, consequently, under treated in men. Most guidelines, screening and fracture risk evaluation methods as well as pharmacologic agents have been developed for women and then adapted to men. Bone Mineral Density (BMD) measurement by Dual X-ray Absorptiometry (DEXA) is reported as T score and the capability of DEXA to diagnose OP and predict fracture risk is still debated. In addition, the use of female T score references for the diagnosis of OP in men is incorrect for the following reasons: 1) DXA definition was developed just for Caucasian women, 2) men and women display structural differences in terms of bone growth, catabolism and size; 3) aging men have more periosteal apposition, less cortical porosity and endocortical resorption than aging women; and 4) T scores results, both in man and in women, can be affected by the presence of co-morbidities and it is known that in men OP is often secondary. From a biological point of view, OP is mainly due to increased osteoclastic activity leading to an imbalance in bone remodeling that favors resorption. However, some evidence suggests a more complex identity for osteoclasts (OCs) over and above their simple role of 'bone eaters'. In our laboratory, we observed spontaneous OCs formation in vitro in peripheral blood mononuclear cells (PBMC) from OP patients (n.12 female patients and n.6 male patients; DXA T score-2.5 or less). Some researchers demonstrated OCs gender differences in bone resorption activity of female-derived versus male-derived OCs. Indeed, further data from our laboratory also showed gender differences in number of spontaneously differentiated OCs and differentiation time. Therefore, we hypothesized that it would be possible to perform OP screening and diagnosis observing and measuring PBMCs different ability to differentiate spontaneously into OCs in male and female patients. If this hypothesis will be confirmed, it will result in an effective and efficient strategy for OP screening, diagnosis, monitoring and fracture prevention, targeting health service resources on selected patients. However, our hypothesis must be tested in a properly designed clinical trial and several key issues still need to be addressed.

The potential of mangosteen (Garcinia mangostana) peel extract, combined with demineralized freeze-dried bovine bone xenograft, to reduce ridge resorption and alveolar bone regeneration in preserving the tooth extraction socket

BACKGROUND

Following the extraction of a tooth, bone resorption can cause significant problems for a subsequent denture implant and restorative dentistry. Thus, the tooth extraction socket needs to be maintained to reduce the chance of any alveolar ridge bone resorption.

OBJECTIVE

The objective of this study is to determine whether the administration of mangosteen peel extracts (MPEs), combined with demineralized freeze-dried bovine bone xenograft (DFBBX) materials for tooth extraction socket preservation, could potentially reduce inflammation by decreased the expression of nuclear factor κβ (NfKb) and receptor activator of nuclear factor-κβ ligand (RANKL), to inhibit alveolar bone resorption, and increased of bone morphogenetic protein-2 (BMP2) expressions to accelerate alveolar bone regeneration.

MATERIALS AND METHODS

This study consists of several stages. First, a dosage of MPE combined with graft materials was applied to a preserved tooth extraction socket of a Cavia cobaya. Second, the C. cobaya was examined using immune histochemical expression of NfKb, RANKL, BMP2, as well as histology of osteoblasts and osteoclasts. The research was statistically analyzed, using an analysis of variance test and Tukey honest significant difference test.

RESULTS

The results of this research were that it was determined that MPEs combined with graft materials on a preserved tooth extraction socket can reduce NfKb, RANK, and osteoclasts also increase of BMP2 and osteoblast.

CONCLUSION

The induction of MPEs and DFBBX is effective in reducing inflammation, lowering osteoclasts, decreasing alveolar bone resorption, and also increasing BMP2 expression and alveolar bone regeneration.

Methyl Gallate Inhibits Osteoclast Formation and Function by Suppressing Akt and Btk-PLCγ2-Ca2+ Signaling and Prevents Lipopolysaccharide-Induced Bone Loss

In the field of bone research, various natural derivatives have emerged as candidates for osteoporosis treatment by targeting abnormally elevated osteoclastic activity. Methyl gallate, a plant-derived phenolic compound, is known to have numerous pharmacological effects against inflammation, oxidation, and cancer. Our purpose was to explore the relation between methyl gallate and bone metabolism. Herein, we performed screening using methyl gallate by tartrate resistant acid phosphatase (TRAP) staining and revealed intracellular mechanisms responsible for methyl gallate-mediated regulation of osteoclastogenesis by Western blotting and quantitative reverse transcription polymerase chain reaction (RT-PCR). Furthermore, we assessed the effects of methyl gallate on the characteristics of mature osteoclasts. We found that methyl gallate significantly suppressed osteoclast formation through Akt and Btk-PLCγ2-Ca²⁺ signaling. The blockade of these pathways was confirmed through transduction of cells with a CA-Akt retrovirus and evaluation of Ca²⁺ influx intensity (staining with Fluo-3/AM). Indeed, methyl gallate downregulated the formation of actin ring-positive osteoclasts and resorption pit areas. In agreement with in vitro results, we found that administration of methyl gallate restored osteoporotic phenotype stimulated by acute systemic injection of lipopolysaccharide in vivo according to micro-computed tomography and histological analysis. Our data strongly indicate that methyl gallate may be useful for the development of a plant-based antiosteoporotic agent.

Combination of IL-6 and sIL-6R differentially regulate varying levels of RANKL-induced osteoclastogenesis through NF-κB, ERK and JNK signaling pathways

Interleukin (IL)-6 is known to indirectly enhance osteoclast formation by promoting receptor activator of nuclear factor kappa-B ligand (RANKL) production by osteoblastic/stromal cells. However, little is known about the direct effect of IL-6 on osteoclastogenesis. Here, we determined the direct effects of IL-6 and its soluble receptor (sIL-6R) on RANKL-induced osteoclast formation by osteoclast precursors in vitro. We found IL-6/sIL-6R significantly promoted and suppressed osteoclast differentiation induced by low- (10 ng/ml) and high-level (50 ng/ml) RANKL, respectively. Using a bone resorption pit formation assay, expression of osteoclastic marker genes and transcription factors confirmed differential regulation of RANKL-induced osteoclastogenesis by IL-6/sIL-6R. Intracellular signaling transduction analysis revealed IL-6/sIL-6R specifically upregulated and downregulated the phosphorylation of NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells), ERK (extracellular signal-regulated kinase) and JNK (c-Jun N-terminal kinase) induced by low- and high level RANKL, respectively. Taken together, our findings demonstrate that IL-6/sIL-6R differentially regulate RANKL-induced osteoclast differentiation and activity through modulation of NF-κB, ERK and JNK signaling pathways. Thus, IL-6 likely plays a dual role in osteoclastogenesis either as a pro-resorption factor or as a protector of bone, depending on the level of RANKL within the local microenvironment.

Bone metabolism and RANKL/RANK/OPG trail in periodontal disease

Periodontal disease is an inflammatory disease of multifactorial etiology. In order for it to appear there must come to an imbalance between the effects of pathogens and host defense mechanisms. As a result of its course the destruction of structures supporting the teeth appears (periodontium, cement, bone), and consequently leads to teeth loosening and loss. In recent years, the participation of RANKL/RANK/OPG in bone remodeling process was highligted.

At the molecular level the bone resorption is regulated through the interaction of the ligand receptor activator of nuclear NF-kappa B (RANKL) and osteoprotegerin (OPG), which is a system of two proteins belonging to the protein tumor necrosis factor (TNF). Recent findings about the RANKL protein and OPG have shed new light on the previously unexplained phenomenon of the basis of bone resorption.

Research has shown that both protein OPG and RANKL can be detected in gingival crevicular fluid, which has become a window of opportunity in the analysis of non-invasive markers of periodontal tissues, confirming elevated levels of RANKL protein in periodontal disease, and decreased levels of OPG protein. Bone resorption is initiated by the binding of the RANKL protein to receptors RANK present on the surface of mature osteoclasts, and their precursors, which leads to the differentiation and activation of osteoclasts. OPG, being RANKL’s inhibitor, has, in turn, opposite characteristics to RANKL, resulting in the reduction of osteoclastogenesis process. Despite all this, the exact mechanism of bone resorption has not yet been elucidated.

Relationship between A163G osteoprotegerin gene polymorphism and other osteoporosis parameters in Roma and non-Roma postmenopausal women in eastern Slovakia

BACKGROUND

The study was focused on evaluating the possible correlation between biochemical, anthropometric, and genetic indicators of osteoporosis in postmenopausal women. The frequency of genotypes and differences in measured parameters were evaluated within two ethnically different groups of women in Slovakia.

METHODS

The study included 310 postmenopausal women divided into non-Roma and Roma groups. Based on results of densitometry, they were divided into control groups and women with osteoporosis and osteopenia. In all women, a genetic analysis of polymorphism of osteoprotegerin gene promotor region (A163G) was provided along with measurement of indicators of bone tissue metabolism.

RESULTS

There is a particularly low incidence of osteoporosis in Roma women. We found a correlation between bone mineral density (BMD), body mass index, and waist and hip circumference in women with osteoporosis and in Roma women with osteopenia. The frequency of the AG genotype was higher in non-Roma women with osteoporosis, but reached only 10.7% in Roma women with osteopenia. While the presence of the G allele in the non-Roma population was accompanied by higher BMD and markers of osteoformation, it was accompanied by significantly higher concentrations of parathyroid hormone in the Roma population.

CONCLUSION

The presence of the AG genotype has a different effect on bone metabolism in two ethnically diverse populations of women in Slovakia. In the general population, the presence of the G allele exhibited protective effects consistent with other studies, but in Roma population this appears to be the allele A. However, this requires a further study for confirmation and more detailed characterization of the differences between populations that have this work indicated.

Functional osteoclastogenesis: the baseline variability in blood donor precursors is not associated with age and gender

Mononuclear osteoclast precursors circulate in the monocyte fraction of peripheral blood and form multinuclear cells with all osteoclastic phenotypic characteristics when cultured in the presence of macrophage colony stimulating factor (M-CSF) and receptor activator of nuclear factor kB ligand (RANKL). The method to obtain osteoclast precursors from peripheral blood is simple but the number of recovered osteoclasts is often largely insufficient for functional analyses. The original aim of this study was to develop a rapid and efficient method that could overcome the donor variability and enrich the osteoclast precursors from a small volume of peripheral blood as a basis for future clinical studies to correlate the differentiation potential of circulating osteoclast precursors with bone lesions in cancer patients. We improved the efficiency of osteoclastogenesis by reducing isolation and purification times and overcame the use of flow cytometry and immunomagnetic purification procedures. In our culture system the osteoclast number was increased several-fold and the precursors were able to reach a full differentiation within seven days of culture. Both age as well as gender differences in osteoclastogenesis efficiency were no longer evident by processing limited volume blood samples with this simple and rapid method.

Quantitative proteomics and integrative network analysis identified novel genes and pathways related to osteoporosis

Osteoporosis is mainly characterized by low bone mineral density (BMD), and can be attributed to excessive bone resorption by osteoclasts. Migration of circulating monocytes from blood to bone is important for subsequent osteoclast differentiation and bone resorption. Identification of those genes and pathways related to osteoclastogenesis and BMD will contribute to a better understanding of the pathophysiological mechanisms of osteoporosis. In this study, we applied the LC-nano-ESI-MS(E) (Liquid Chromatograph-nano-Electrospray Ionization-Mass Spectrometry) for quantitative proteomic profiling in 33 female Caucasians with discordant BMD levels, with 16 high vs. 17 low BMD subjects. Protein quantitation was accomplished by label-free measurement of total ion currents collected from MS(E) data. Comparison of protein expression in high vs. low BMD subjects showed that ITGA2B (p=0.0063) and GSN (p=0.019) were up-regulated in the high BMD group. Additionally, our protein-RNA integrative analysis showed that RHOA (p=0.00062) differentially expressed between high vs. low BMD groups. Network analysis based on multiple tools revealed two pathways: "regulation of actin cytoskeleton" (p=1.13E-5, FDR=3.34E-4) and "leukocyte transendothelial migration" (p=2.76E-4, FDR=4.71E-3) that are functionally relevant to osteoporosis. Consistently, ITGA2B, GSN and RHOA played crucial roles in these two pathways respectively. All together, our study strongly supported the contribution of the genes ITGA2B, GSN and RHOA and the two pathways to osteoporosis risk.

BIOLOGICAL SIGNIFICANCE

Mass spectrometry based quantitative proteomics study integrated with network analysis identified novel genes and pathways related to osteoporosis. The results were further verified in multiple level studies including protein-RNA integrative analysis and genome wide association studies.

The Alternative Faces of Macrophage Generate Osteoclasts

The understanding of how osteoclasts are generated and whether they can be altered by inflammatory stimuli is a topic of particular interest for osteoclastogenesis. It is known that the monocyte/macrophage lineage gives rise to osteoclasts (OCs) by the action of macrophage colony stimulating factor (M-CSF) and receptor activator of nuclear factor-kB ligand (RANKL), which induce cell differentiation through their receptors, c-fms and RANK, respectively. The multinucleated giant cells (MGCs) generated by the engagement of RANK/RANKL are typical OCs. Nevertheless, very few studies have addressed the question of which subset of macrophages generates OCs. Indeed, two main subsets of macrophages are postulated, the inflammatory or classically activated type (M1) and the anti-inflammatory or alternatively activated type (M2). It has been proposed that macrophages can be polarized in vitro towards a predominantly M1 or M2 phenotype with the addition of granulocyte macrophage- (GM-) CSF or M-CSF, respectively. Various inflammatory stimuli known to induce macrophage polarization, such as LPS or TNF-α, can alter the type of MGC obtained from RANKL-induced differentiation. This review aims to highlight the role of immune-related stimuli and factors in inducing macrophages towards the osteoclastogenesis choice.

Inhibition of osteoclastogenesis through siRNA delivery with tunable mesoporous bioactive nanocarriers

Gene silencing through siRNA delivery has shown great promise for treating diseases and repairing damaged tissues, including bone. This report is the first to develop siRNA delivery system in the inhibition of osteoclastic functions which in turn can help turn-over bone mass increase in the diseases like osteoporosis. For this reason, biocompatible and degradable nanocarriers that can effectively load and deliver genetic molecules to target cells and tissues are being actively sought by researchers. In this study, mesoporous bioactive glass nanospheres (MBG), a novel unique biocompatible degradable inorganic nanocarrier, is introduced. Furthermore, siRNA was designed to function by inhibiting the expression of the receptor activator of nuclear factor kappa B (RANK) in order to suppress osteoclastogenesis. Amine-functionalized MBG were synthesized with tunable mesoporosities, showing a strong complexation with siRNA. An in vitro release profile indicated that the siRNA from the MBG was able to achieve a highly sustainable liberation for up to 4 days, confirming a temporary delivery system can be designed to function for that period of time. The intracellular uptake capacity of the complex siRNA(RANK)-MBG was recorded to be around 70%. Furthermore, the RANK-expressing cell population declined down to 29% due to the delivery of siRNA(RANK)-MBG (vs. 86% in control). The expression of osteoclastogenesis-related genes, including c-fos, cathepsin-K, tartrate-resistant acid phosphatase (TRAP), and nuclear factor of activated T-cells cytoplasmic 1 (NFATc1), was substantially down-regulated by the siRNA delivery system. This study reports for the first time on the use of a novel MBG delivery system for siRNA that aims to suppress osteoclastic actions. MBGs may be a potential gene delivery platform for hard tissue repair and disease treatment due to the collective results which indicate a high loading capacity, temporary release kinetics, high intracellular uptake rate, and sufficient gene silencing effects, together with the intrinsic beneficial properties like bone-bioactivity and degradability.

STATEMENT OF SIGNIFICANCE

This report is the first to develop siRNA delivery system of biocompatible and degradable nanocarriers made from a unique composition, i.e., mesoporous bioactive glass that can effectively load and deliver genetic molecules to osteoclastic cells. We proved through a series of studies that the biocompatible nanocarriers are effective for the delivery of siRNA in the inhibition of osteoclastic functions which thus might be considered as a nanocarrier platform to help turn-over bone mass increase in the diseases like osteoporosis.

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.