Molecular analysis of RANKL-independent cell fusion of osteoclast-like cells induced by TNF-alpha, lipopolysaccharide, or peptidoglycan

A Synthetic Small Molecule, LGM2605: A Promising Modulator of Increased Pro-Inflammatory Cytokine and Osteoclast Differentiation by Aggregatibacter actinomycetemcomitans Cytolethal Distending Toxin

Our research explores the interplay between Aggregatibacter actinomycetemcomitans (Aa) cytolethal distending toxin (Cdt) and the host's inflammatory response in molar/incisor pattern periodontitis (MIPP). Cdt disrupts phosphatidylinositol-3,4,5-triphosphate (PIP3) signaling, influencing cytokine expression through canonical and non-canonical inflammasome activation as well as nuclear factor-κB (NF-κB) activation, leading to inflammation in MIPP. THP-1 differentiated macrophages (TDMs) exposed to Cdt exhibited an upregulation of pro-inflammatory genes and subsequent cytokine release. We analyzed the ability of a small molecule therapeutic, LGM2605, known for its anti-inflammatory properties, to reduce pro-inflammatory gene expression and cytokine release in Cdt-exposed and Aa-inoculated TDMs. LGM2605's mechanism of action involves inhibiting NF-κB while activating the Nrf2-transcription factor and antioxidants. Herein, we show that this small molecule therapeutic mitigates Cdt-induced pro-inflammatory cytokine expression and secretion. Our study also further defines Cdt's impact on osteoclast differentiation and maturation in MIPP. Cdt promotes increased TRAP+ cells, indicating heightened osteoclast differentiation, specific to Cdt's phosphatase activity. Cathepsin K levels rise during this process, reflecting changes in TRAP distribution between control and Cdt-treated cells. Exploring LGM2605's effect on Cdt-induced osteoclast differentiation and maturation, we found TRAP+ cells significantly reduced with LGM2605 treatment compared to Cdt alone. Upon LGM2605 treatment, immunocytochemistry revealed a decreased TRAP intensity and number of multinucleated cells. Moreover, immunoblotting showed reduced TRAP and cathepsin K levels, suggesting LGM2605's potential to curb osteoclast differentiation and maturation by modulating inflammatory cytokines, possibly involving Nrf2 activation. In summary, our research reveals the intricate connections between Cdt, pro-inflammatory cytokines, and osteoclast differentiation, offering novel therapeutic possibilities for managing these conditions.

How Much Do You Fuse? A Comparison of Cell Fusion Assays in a Breast Cancer Model

Cell fusion is a biological process that is crucial for the development and homeostasis of different tissues, but it is also pathophysiologically associated with tumor progression and malignancy. The investigation of cell fusion processes is difficult because there is no standardized marker. Many studies therefore use different systems to observe and quantify cell fusion in vitro and in vivo. The comparability of the results must be critically questioned, because both the experimental procedure and the assays differ between studies. The comparability of the fluorescence-based fluorescence double reporter (FDR) and dual split protein (DSP) assay was investigated as part of this study, in which general conditions were kept largely constant. In order to be able to induce both a high and a low cell fusion rate, M13SV1 breast epithelial cells were modified with regard to the expression level of the fusogenic protein Syncytin-1 and its receptor ASCT2 and were co-cultivated for 72 h with different breast cancer cell lines. A high number of fused cells was found in co-cultures with Syncytin-1-overexpressing M13SV1 cells, but differences between the assays were also observed. This shows that the quantification of cell fusion events in particular is highly dependent on the assay selected, but the influence of fusogenic proteins can be visualized very well.

Artemisinic acid attenuates osteoclast formation and titanium particle-induced osteolysis via inhibition of RANKL-induced ROS accumulation and MAPK and NF-κB signaling pathways

Periprosthetic osteolysis (PPO) is the most common cause of joint arthroplasty failure. Its progression involves both biological and mechanical factors. Osteoclastogenesis induced by wear from debris-cell interactions, ultimately leading to excessive bone erosion, is considered the primary cause of PPO; therefore, targeting osteoclasts is a promising treatment approach. Currently available drugs have various side effects and limitations. Artemisinic acid (ArA) is a sesquiterpene isolated from the traditional herb Artemisia annua L. that has various pharmacological effects, such as antimalarial, anti-inflammatory, and antioxidant activities. Therefore, this study was aimed at investigating the effect of ArA on osteoclast formation and bone resorption function in vitro, as well as wear particle-induced osteolysis in vivo, and to explore its molecular mechanism of action. Here, we report that ArA inhibits RANKL-stimulated osteoclast formation and function. Mechanistically, ArA suppresses intracellular reactive oxygen species levels by activating the antioxidant response via nuclear factor erythroid-2-related factor 2 (Nrf2) pathway upregulation. It also inhibits the mitogen-activated kinases (MAPK) and nuclear factor-κB (NF-κB) pathways, as well as the transcription and expression of NFATc1 and c-Fos. In vivo experiments demonstrated that ArA reduces osteoclast formation and alleviates titanium particle-induced calvarial osteolysis. Collectively, our study highlights that ArA, with its osteoprotective and antioxidant effects, is a promising therapeutic agent for preventing and treating PPO and other osteoclast-mediated osteolytic diseases.

Microbiota metabolites in bone: Shaping health and Confronting disease

The intricate interplay between the gut microbiota and bone health has become increasingly recognized as a fundamental determinant of skeletal well-being. Microbiota-derived metabolites play a crucial role in dynamic interaction, specifically in bone homeostasis. In this sense, short-chain fatty acids (SCFAs), including acetate, propionate, and butyrate, indirectly promote bone formation by regulating insulin-like growth factor-1 (IGF-1). Trimethylamine N-oxide (TMAO) has been found to increase the expression of osteoblast genes, such as Runt-related transcription factor 2 (RUNX2) and bone morphogenetic protein-2 (BMP2), thus enhancing osteogenic differentiation and bone quality through BMP/SMADs and Wnt signaling pathways. Remarkably, in the context of bone infections, the role of microbiota metabolites in immune modulation and host defense mechanisms potentially affects susceptibility to infections such as osteomyelitis. Furthermore, ongoing research elucidates the precise mechanisms through which microbiota-derived metabolites influence bone cells, such as osteoblasts and osteoclasts. Understanding the multifaceted influence of microbiota metabolites on bone, from regulating homeostasis to modulating susceptibility to infections, has the potential to revolutionize our approach to bone health and disease management. This review offers a comprehensive exploration of this evolving field, providing a holistic perspective on the impact of microbiota metabolites on bone health and diseases.

Long noncoding RNA Malat1 protects against osteoporosis and bone metastasis

MALAT1, one of the few highly conserved nuclear long noncoding RNAs (lncRNAs), is abundantly expressed in normal tissues. Previously, targeted inactivation and genetic rescue experiments identified MALAT1 as a suppressor of breast cancer lung metastasis. On the other hand, Malat1-knockout mice are viable and develop normally. On a quest to discover the fundamental roles of MALAT1 in physiological and pathological processes, we find that this lncRNA is downregulated during osteoclastogenesis in humans and mice. Remarkably, Malat1 deficiency in mice promotes osteoporosis and bone metastasis of melanoma and mammary tumor cells, which can be rescued by genetic add-back of Malat1. Mechanistically, Malat1 binds to Tead3 protein, a macrophage-osteoclast-specific Tead family member, blocking Tead3 from binding and activating Nfatc1, a master regulator of osteoclastogenesis, which results in the inhibition of Nfatc1-mediated gene transcription and osteoclast differentiation. Notably, single-cell transcriptome analysis of clinical bone samples reveals that reduced MALAT1 expression in pre-osteoclasts and osteoclasts is associated with osteoporosis and metastatic bone lesions. Altogether, these findings identify Malat1 as a lncRNA that protects against osteoporosis and bone metastasis.

The role of autophagy in SIM mediated anti-inflammatory osteoclastogenesis through NLRP3 signaling pathway

BACKGROUND

Inflammatory bone resorption is a prominent risk factor for implantation failure. Simvastatin (SIM) has anti-inflammatory effects independent of cholesterol lowering and reduces osteoclastogenesis by decreasing both the number and activity of osteoclasts. However, the specific mechanism of inflammatory bone loss alleviation by SIM remains to be elucidated. We hypothesized that SIM relieves inflammatory bone loss by modulating autophagy and suppressing the NOD-like receptor family pyrin domain-containing protein 3 (NLRP3) signaling pathway.

METHODS AND RESULTS

RAW264.7 cells were stimulated by lipopolysaccharide (LPS) after being pretreated with various concentrations of SIM. Osteoclast (OC) differentiation, formation and activity were evaluated by tartrate-resistant acid phosphatase staining, F-actin ring staining and bone resorption pit assays, respectively. We observed autophagosomes by transmission electron microscopy. Then NLRP3 inhibitor MCC950 was used to further explore the corresponding molecular mechanism underlying anti-inflammatory bone resorption, the expression of autophagy-related proteins and NLRP3 signaling pathway factors in pre-OCs were evaluated by western blot analysis, and the expression of OC-specific molecules was analyzed using reverse transcription-quantitative polymerase chain reaction. The results showed that SIM decreased the expression of tumor necrosis factor-α, whereas increased Interleukin-10. In addition, SIM inhibited LPS-induced OC differentiation, formation, bone resorption activity, the level of autophagosomes, and OC-specific markers. Furthermore, SIM significantly suppressed autophagy by downregulating LC3II, Beclin1, ATG7, and NLRP3-related proteins expression while upregulating P62 under inflammatory conditions.

CONCLUSIONS

SIM may reduce autophagy secretion to attenuate LPS-induced osteoclastogenesis and the NLRP3 signaling pathway participates in this process, thus providing theoretical basis for the application of this drug in peri-implantitis.

Cell Fusion and Syncytia Formation in Cancer

The natural phenomenon of cell-cell fusion does not only take place in physiological processes, such as placentation, myogenesis, or osteoclastogenesis, but also in pathophysiological processes, such as cancer. More than a century ago postulated, today the hypothesis that the fusion of cancer cells with normal cells leads to the formation of cancer hybrid cells with altered properties is in scientific consensus. Some studies that have investigated the mechanisms and conditions for the fusion of cancer cells with other cells, as well as studies that have characterized the resulting cancer hybrid cells, are presented in this review. Hypoxia and the cytokine TNFα, for example, have been found to promote cell fusion. In addition, it has been found that both the protein Syncytin-1, which normally plays a role in placentation, and phosphatidylserine signaling on the cell membrane are involved in the fusion of cancer cells with other cells. In human cancer, cancer hybrid cells were detected not only in the primary tumor, but also in the circulation of patients as so-called circulating hybrid cells, where they often correlated with a worse outcome. Although some data are available, the questions of how and especially why cancer cells fuse with other cells are still not fully answered.

Ageing and Inflammation: What Happens in Periodontium?

Periodontitis is a chronic inflammatory disease with a high incidence and severity in the elderly population, making it a significant public health concern. Ageing is a primary risk factor for the development of periodontitis, exacerbating alveolar bone loss and leading to tooth loss in the geriatric population. Despite extensive research, the precise molecular mechanisms underlying the relationship between ageing and periodontitis remain elusive. Understanding the intricate mechanisms that connect ageing and inflammation may help reveal new therapeutic targets and provide valuable options to tackle the challenges encountered by the rapidly expanding global ageing population. In this review, we highlight the latest scientific breakthroughs in the pathways by which inflammaging mediates the decline in periodontal function and triggers the onset of periodontitis. We also provide a comprehensive overview of the latest findings and discuss potential avenues for future research in this critical area of investigation.

Gingival Mesenchymal Stem Cells Metabolite Decreasing TRAP, NFATc1, and Sclerostin Expression in LPS-Associated Inflammatory Osteolysis In Vivo

OBJECTIVE

 Bone is a dynamic tissue that undergoes remodeling. During bone remodeling, there are transcription factors such as nuclear factor-activated T cells-1 (NFATc1), sclerostin, and tartrate-resistant acid phosphatase (TRAP) that are released for bone resorption. Metabolite from gingival mesenchymal stem cells (GMSCs) has the ability to activate proliferation, migration, immunomodulation, and tissue regeneration of bone cells and tissues. Furthermore, the aim of this study is to investigate the metabolite of GMSCs' effect on expression of NFATc1, TRAP, and sclerostin in calvaria bone resorption of Wistar rats.

MATERIALS AND METHODS

 Twenty male healthy Wistar rats (Rattus norvegicus), 1 to 2 months old, 250 to 300 g body were divided into four groups, namely group 1 (G1): 100 µg phosphate-buffered saline day 1 to 7; group 2 (G2): 100 μg lipopolysaccharide (LPS) day 1 to 7; group 3 (G3): 100 μg LPS + 100 μg GMSCs metabolite day 1 to 7; and group 4 (G4): 100 μg GMSCs metabolite day 1 to 7. Escherichia coli LPS was used to induce inflammatory osteolysis on the calvaria with subcutaneous injection. GMSCs metabolite was collected after passage 4 to 5, then injected subcutaneously on the calvaria. All samples were sacrificed on the day 8 through cervical dislocation. The expression of TRAP, NFATc1, and sclerostin of osteoclast in the calvaria was observed with 1,000× magnification.

STATISTICAL ANALYSIS

 One-way analysis of variance and Tukey honest significant different were conducted to analyze differences between groups (p < 0.05).

RESULTS

 The administration of GMSCs metabolite can significantly decrease TRAP, NFATc1, and sclerostin expression (p < 0.05) in LPS-associated inflammatory osteolysis calvaria in Wistar rats (R. norvegicus). There were significantly different TRAP, NFATc1, and sclerostin expressions between groups (p < 0.05).

CONCLUSION

 GMSCs metabolite decrease TRAP, NFATc1, and sclerostin expression in LPS-associated osteolysis calvaria in Wistar rats (R. norvegicus) as documented immunohistochemically.

Therapeutic Effects of Curcumin Liposomes and Nanocrystals on Inflammatory Osteolysis: In Vitro and In Vivo Comparative Study

Curcumin could inhibit periprosthetic osteolysis induced by wear debris and adherent endotoxin, which commonly cause prosthesis loosening and negatively influence the long-term survival of joint arthroplasty. However, its limited water solubility and poor stability pose challenges for its further clinical application. To address these issues, we developed curcumin liposomes for intraarticular injection, as liposomes possess good lubricant capacity and pharmacological synergy with curcumin. Additionally, a nanocrystal dosage form was prepared to enable comparison with the liposomes based on their ability to disperse curcumin effectively. A microfluidic method was used for its controllability, repeatability, and scalability. The Box-Behnken Design was employed to screen the formulations and flow parameters, while computational fluid dynamics was used to simulate the mixing process and predict the formation of liposomes. The optimized curcumin liposomes (Cur-LPs) had a size of 132.9nm and an encapsulation efficiency of 97.1%, whereas the curcumin nanocrystals (Cur-NCs) had a size of 172.3nm. Both Cur-LPs and Cur-NCs inhibited LPS-induced pro-inflammatory polarization of macrophages and reduced the expression and secretion of inflammatory factors. The mouse air pouch model further demonstrated that both dosage forms attenuated inflammatory cell infiltration and inflammatory fibrosis in subcutaneous tissues. Interestingly, the anti-inflammatory effect of Cur-LPs was more potent than that of Cur-NCs, both in vitro and in vivo, although the cellular uptake of Cur-NCs was quicker. In conclusion, the results demonstrate that Cur-LPs have great potential for the clinical treatment of inflammatory osteolysis and that the therapeutic effect is closely related to the liposomal dosage form.

Molecular Basis beyond Interrelated Bone Resorption/Regeneration in Periodontal Diseases: A Concise Review

Periodontitis is the sixth most common chronic inflammatory disease, destroying the tissues supporting the teeth. There are three distinct stages in periodontitis: infection, inflammation, and tissue destruction, where each stage has its own characteristics and hence its line of treatment. Illuminating the underlying mechanisms of alveolar bone loss is vital in the treatment of periodontitis to allow for subsequent reconstruction of the periodontium. Bone cells, including osteoclasts, osteoblasts, and bone marrow stromal cells, classically were thought to control bone destruction in periodontitis. Lately, osteocytes were found to assist in inflammation-related bone remodeling besides being able to initiate physiological bone remodeling. Furthermore, mesenchymal stem cells (MSCs) either transplanted or homed exhibit highly immunosuppressive properties, such as preventing monocytes/hematopoietic precursor differentiation and downregulating excessive release of inflammatory cytokines. In the early stages of bone regeneration, an acute inflammatory response is critical for the recruitment of MSCs, controlling their migration, and their differentiation. Later during bone remodeling, the interaction and balance between proinflammatory and anti-inflammatory cytokines could regulate MSC properties, resulting in either bone formation or bone resorption. This narrative review elaborates on the important interactions between inflammatory stimuli during periodontal diseases, bone cells, MSCs, and subsequent bone regeneration or bone resorption. Understanding these concepts will open up new possibilities for promoting bone regeneration and hindering bone loss caused by periodontal diseases.

Extracellular Events Involved in Cancer Cell-Cell Fusion

Fusion among different cell populations represents a rare process that is mediated by both intrinsic and extracellular events. Cellular hybrid formation is relayed by orchestrating tightly regulated signaling pathways that can involve both normal and neoplastic cells. Certain important cell merger processes are often required during distinct organismal and tissue development, including placenta and skeletal muscle. In a neoplastic environment, however, cancer cell fusion can generate new cancer hybrid cells. Following survival during a subsequent post-hybrid selection process (PHSP), the new cancer hybrid cells express different tumorigenic properties. These can include elevated proliferative capacity, increased metastatic potential, resistance to certain therapeutic compounds, and formation of cancer stem-like cells, all of which characterize significantly enhanced tumor plasticity. However, many parts within this multi-step cascade are still poorly understood. Aside from intrinsic factors, cell fusion is particularly affected by extracellular conditions, including an inflammatory microenvironment, viruses, pH and ionic stress, hypoxia, and exosome signaling. Accordingly, the present review article will primarily highlight the influence of extracellular events that contribute to cell fusion in normal and tumorigenic tissues.

Generation of Cancer Stem/Initiating Cells by Cell-Cell Fusion

CS/ICs have raised great expectations in cancer research and therapy, as eradication of this key cancer cell type is expected to lead to a complete cure. Unfortunately, the biology of CS/ICs is rather complex, since no common CS/IC marker has yet been identified. Certain surface markers or ALDH1 expression can be used for detection, but some studies indicated that cancer cells exhibit a certain plasticity, so CS/ICs can also arise from non-CS/ICs. Another problem is intratumoral heterogeneity, from which it can be inferred that different CS/IC subclones must be present in the tumor. Cell–cell fusion between cancer cells and normal cells, such as macrophages and stem cells, has been associated with the generation of tumor hybrids that can exhibit novel properties, such as an enhanced metastatic capacity and even CS/IC properties. Moreover, cell–cell fusion is a complex process in which parental chromosomes are mixed and randomly distributed among daughter cells, resulting in multiple, unique tumor hybrids. These, if they have CS/IC properties, may contribute to the heterogeneity of the CS/IC pool. In this review, we will discuss whether cell–cell fusion could also lead to the origin of different CS/ICs that may expand the overall CS/IC pool in a primary tumor.

Developmental programming of macrophages by early life adversity

Macrophages are central elements of all organs, where they have a multitude of physiological and pathological functions. The first macrophages are produced during fetal development, and most adult organs retain populations of fetal-derived macrophages that self-maintain without major input of hematopoietic stem cell-derived monocytes. Their developmental origins make macrophages highly susceptible to environmental perturbations experienced in early life, in particular the fetal period. It is now well recognized that such adverse developmental conditions contribute to a wide range of diseases later in life. This chapter explores the notion that macrophages are key targets of environmental adversities during development, and mediators of their long-term impact on health and disease. We first briefly summarize our current understanding of macrophage ontogeny and their biology in tissues and consider potential mechanisms by which environmental stressors may mediate fetal programming. We then review evidence for programming of macrophages by adversities ranging from maternal immune activation and diet to environmental pollutants and toxins, which have disease relevance for different organ systems. Throughout this chapter, we contemplate appropriate experimental strategies to study macrophage programming. We conclude by discussing how our current knowledge of macrophage programming could be conceptualized, and finally highlight open questions in the field and approaches to address them.

Extracellular pyruvate kinase M2 promotes osteoclastogenesis and is associated with radiographic progression in early rheumatoid arthritis

Extracellular PKM2 (exPKM2) levels have been reported to be increased in several cancers and inflammatory diseases, including rheumatoid arthritis (RA). This study aimed to investigate the association of circulating exPKM2 levels with radiographic progression in RA patients and the effect of exPKM2 on osteoclastogenesis. Plasma and synovial fluid exPKM2 levels were significantly elevated in RA patients. Plasma exPKM2 levels were correlated with RA disease activity and were an independent predictor for radiographic progression in RA patients with a disease duration of ≤ 12 months. CD14⁺ monocytes but not RA fibroblast-like synoviocytes secreted PKM2 upon stimulation with inflammatory mediators. Recombinant PKM2 (rPKM2) increased the formation of tartrate-resistant acid phosphatase (TRAP)-positive multinuclear cells and resorption pit in osteoclast precursors, dose-dependently, even in the absence of receptor activator of nuclear factor-kappa B ligand (RANKL). rPKM2 treatment upregulated the expression of dendrocyte-expressed seven transmembrane protein (DC-STAMP) and MMP-9 via the ERK pathway. Although rPKM2 did not directly bind to RAW264.7 cells, extracellular application of pyruvate, the end-product of PKM2, showed effects similar to those seen in rPKM2-induced osteoclastogenesis. These results suggest that exPKM2 is a potential regulator of RA-related joint damage and a novel biomarker for subsequent radiographic progression in patients with early-stage RA.

The gut microbiota can be a potential regulator and treatment target of bone metastasis

The gut microbiota, an often forgotten organ, have a tremendous impact on human health. It has long been known that the gut microbiota are implicated in cancer development, and more recently, the gut microbiota have been shown to influence cancer metastasis to distant organs. Although one of the most common sites of distant metastasis is the bone, and the skeletal system has been shown to be a subject of interactions with the gut microbiota to regulate bone homeostasis, little research has been done regarding how the gut microbiota control the development of bone metastasis. This review will discuss the mechanisms through which the gut microbiota and derived microbial compounds (i) regulate gastrointestinal cancer disease progression and metastasis, (ii) influence skeletal remodeling and potentially modulate bone metastasis, and (iii) affect and potentially enhance immunotherapeutic treatments for bone metastasis.

Marein Prevented LPS-Induced Osteoclastogenesis by Regulating the NF-κB Pathway In Vitro

Many bone diseases such as osteolysis, osteomyelitis, and septic arthritis are caused by gram-negative bacterial infection, and lipopolysaccharide (LPS), a bacterial product, plays an essential role in this process. Drugs that inhibit LPS-induced osteoclastogenesis are urgently needed to prevent bone destruction in infective bone diseases. Marein, a major bioactive compound of Coreopsis tinctoria, possesses anti-oxidative, anti-inflammatory, anti-hypertensive, anti-hyperlipidemic, and anti-diabetic effects. In this study, we measured the effect of marein on RAW264.7 cells by CCK-8 assay and used TRAP staining to determine osteoclastogenesis. The levels of osteoclast-related genes and NF-κB-related proteins were then analyzed by western blot, and the levels of pro-inflammatory cytokines were quantified by ELISA. Our results showed that marein inhibited LPS-induced osteoclast formation by osteoclast precursor RAW264.7 cells. The effect of marein was related to its inhibitory function on expressions of pro-inflammatory cytokines and osteoclast-related genes containing RANK, TRAF6, MMP-9, CK, and CAII. Additionally, marein leads to markedly inhibited NF-κB signaling pathway activation in LPS-induced RAW264.7 cells. Concurrently, when the NF-κB signaling pathway was inhibited, osteoclast formation and pro-inflammatory cytokine expression were decreased. Collectively, marein could inhibit LPS-induced osteoclast formation in RAW264.7 cells via regulating the NF-κB signaling pathway. Our data demonstrate that marein might be a potential drug for bacteria-induced bone destruction disease. Our findings provide new insights into LPS-induced bone disease.

Water Extract of Fritillariae thunbergii Bulbus Inhibits RANKL-Mediated Osteoclastogenesis and Ovariectomy-Induced Trabecular Bone Loss

Fritillariae thunbergii bulbus has been widely used to treat symptoms of coughs and airway congestion in the chest due to pathological colds and damp phlegm in traditional Chinese medicine. Despite its long history of traditional use, its pharmacological activities on osteoclastogenesis and osteoporosis have not been evaluated. This study investigated the effects of the water extract of Fritillariae thunbergii bulbus (WEFT) on osteoclast differentiation in bone marrow-derived macrophage cells and on ovariectomy (OVX)-induced osteoporosis in mice. We found that WEFT significantly inhibited osteoclastogenesis by downregulating the receptor activator of the NF-κB ligand (RANKL) signaling-induced nuclear factor of activated T-cells cytoplasmic 1 (NFATc1) expression. In an OVX-induced osteoporosis model, WEFT significantly prevented the OVX-induced trabecular loss of femurs, accompanied by a reduction in fat accumulation in the bone marrow and liver. In addition, WEFT significantly prevented weight gain and gonadal fat gain without recovering uterine atrophy. Using ultrahigh-performance liquid chromatography-tandem mass spectrometry, seven alkaloids (peimisine glucoside, yibeissine, peiminoside, sipeimine-glucoside, peimisine, peimine, and peiminine) were identified in WEFT. The results of this study suggest that WEFT can be a potential pharmacological candidate to reduce menopausal osteoporosis and menopause-related symptoms, such as fat accumulation.

Comparing Antibiotic Pastes with Electrospun Nanofibers as Modern Drug Delivery Systems for Regenerative Endodontics

Nanomaterials have various features that make these types of materials able to be applied in different biomedical applications like, diagnosis, treatment, and drug delivery. Using such materials in endodontic filed both to face the challenges that occur during treatment processes and to make these materials have an antibacterial effect without showing any harm on the host cells. The approach of nanofibers loaded with various antibacterial drugs offers a potential treatment method to enhance the elimination procedure of intracanal biofilms. Clinically, many models of bacterial biofilms have been prepared under in vitro conditions for different aims. The process of drug delivery from polymeric nanofibers is based on the principle that the releasing ratio of drug molecules increases due to the increase in the surface area of the hosted structure. In our review, we discuss diverse approaches of loading/releasing drugs on/from nanofibers and we summarized many studies about electrospun nanofibers loaded various drugs applied in the endodontic field. Moreover, we argued both the advantages and the limitations of these modern endodontic treatment materials comparing them with the traditional ones.

Oral Osteomicrobiology: The Role of Oral Microbiota in Alveolar Bone Homeostasis

Osteomicrobiology is a new research field in which the aim is to explore the role of microbiota in bone homeostasis. The alveolar bone is that part of the maxilla and mandible that supports the teeth. It is now evident that naturally occurring alveolar bone loss is considerably stunted in germ-free mice compared with specific-pathogen-free mice. Recently, the roles of oral microbiota in modulating host defense systems and alveolar bone homeostasis have attracted increasing attention. Moreover, the mechanistic understanding of oral microbiota in mediating alveolar bone remodeling processes is undergoing rapid progress due to the advancement in technology. In this review, to provide insight into the role of oral microbiota in alveolar bone homeostasis, we introduced the term “oral osteomicrobiology.” We discussed regulation of alveolar bone development and bone loss by oral microbiota under physiological and pathological conditions. We also focused on the signaling pathways involved in oral osteomicrobiology and discussed the bridging role of osteoimmunity and influencing factors in this process. Finally, the critical techniques for osteomicrobiological investigations were introduced.

Macrophage-biomimetic porous Se@SiO2 nanocomposites for dual modal immunotherapy against inflammatory osteolysis

Background

Inflammatory osteolysis, a major complication of total joint replacement surgery, can cause prosthesis failure and necessitate revision surgery. Macrophages are key effector immune cells in inflammatory responses, but excessive M1-polarization of dysfunctional macrophages leads to the secretion of proinflammatory cytokines and severe loss of bone tissue. Here, we report the development of macrophage-biomimetic porous SiO₂-coated ultrasmall Se particles (porous Se@SiO₂ nanospheres) to manage inflammatory osteolysis.

Results

Macrophage membrane-coated porous Se@SiO₂ nanospheres(M-Se@SiO₂) attenuated lipopolysaccharide (LPS)-induced inflammatory osteolysis via a dual-immunomodulatory effect. As macrophage membrane decoys, these nanoparticles reduced endotoxin levels and neutralized proinflammatory cytokines. Moreover, the release of Se could induce macrophage polarization toward the anti-inflammatory M2-phenotype. These effects were mediated via the inhibition of p65, p38, and extracellular signal-regulated kinase (ERK) signaling. Additionally, the immune environment created by M-Se@SiO₂ reduced the inhibition of osteogenic differentiation caused by proinflammation cytokines, as confirmed through in vitro and in vivo experiments.

Conclusion

Our findings suggest that M-Se@SiO₂ have an immunomodulatory role in LPS-induced inflammation and bone remodeling, which demonstrates that M-Se@SiO₂ are a promising engineered nanoplatform for the treatment of osteolysis occurring after arthroplasty.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-01128-4.

Hairy and enhancer of split 1 is a primary effector of NOTCH2 signaling and induces osteoclast differentiation and function

Notch2^tm1.1Ecan mice, which harbor a mutation replicating that found in Hajdu–Cheney syndrome, exhibit marked osteopenia because of increased osteoclast number and bone resorption. Hairy and enhancer of split 1 (HES1) is a Notch target gene and a transcriptional modulator that determines osteoclast cell fate decisions. Transcript levels of Hes1 increase in Notch2^tm1.1Ecan bone marrow–derived macrophages (BMMs) as they mature into osteoclasts, suggesting a role in osteoclastogenesis. To determine whether HES1 is responsible for the phenotype of Notch2^tm1.1Ecan mice and the skeletal manifestations of Hajdu–Cheney syndrome, Hes1 was inactivated in Ctsk-expressing cells from Notch2^tm1.1Ecan mice. Ctsk encodes the protease cathepsin K, which is expressed preferentially by osteoclasts. We found that the osteopenia of Notch2^tm1.1Ecan mice was ameliorated, and the enhanced osteoclastogenesis was reversed in the context of the Hes1 inactivation. Microcomputed tomography revealed that the downregulation of Hes1 in Ctsk-expressing cells led to increased bone volume/total volume in female mice. In addition, cultures of BMMs from Ctsk^Cre/WT;Hes1^Δ/Δ mice displayed a decrease in osteoclast number and size and decreased bone-resorbing capacity. Moreover, activation of HES1 in Ctsk-expressing cells led to osteopenia and enhanced osteoclast number, size, and bone resorptive capacity in BMM cultures. Osteoclast phenotypes and RNA-Seq of cells in which HES1 was activated revealed that HES1 modulates cell–cell fusion and bone-resorbing capacity by supporting sealing zone formation. In conclusion, we demonstrate that HES1 is mechanistically relevant to the skeletal manifestation of Notch2^tm1.1Ecan mice and is a novel determinant of osteoclast differentiation and function.

Mechanism of alveolar bone destruction in periodontitis - Periodontal bacteria and inflammation

Periodontal disease is an inflammatory disease caused by periodontopathogenic bacteria, which eventually leads to bone tissue (alveolar bone) destruction as inflammation persists. Periodontal tissues have an immune system against the invasion of these bacteria, however, due to the persistent infection by periodontopathogenic bacteria, the host innate and acquired immunity is impaired, and tissue destruction, including bone tissue destruction, occurs. Osteoclasts are essential for bone destruction. Osteoclast progenitor cells derived from hematopoietic stem cells differentiate into osteoclasts. In addition, bone loss occurs when bone resorption by osteoclasts exceeds bone formation by osteoblasts. In inflammatory bone disease, inflammatory cytokines act on osteoblasts and receptor activator of nuclear factor-κB ligand (RANKL)-producing cells, resulting in osteoclast differentiation and activation. In addition to this mechanism, pathogenic factors of periodontal bacteria and mechanical stress activate osteoclasts and destruct alveolar bone in periodontitis. In this review, we focused on the mechanism of osteoclast activation in periodontitis and provide an overview based on the latest findings.

Cell-Cell Fusion Mediated by Viruses and HERV-Derived Fusogens in Cancer Initiation and Progression

Cell fusion is a well-known, but still scarcely understood biological phenomenon, which might play a role in cancer initiation, progression and formation of metastases. Although the merging of two (cancer) cells appears simple, the entire process is highly complex, energy-dependent and tightly regulated. Among cell fusion-inducing and -regulating factors, so-called fusogens have been identified as a specific type of proteins that are indispensable for overcoming fusion-associated energetic barriers and final merging of plasma membranes. About 8% of the human genome is of retroviral origin and some well-known fusogens, such as syncytin-1, are expressed by human (cancer) cells. Likewise, enveloped viruses can enable and facilitate cell fusion due to evolutionarily optimized fusogens, and are also capable to induce bi- and multinucleation underlining their fusion capacity. Moreover, multinucleated giant cancer cells have been found in tumors derived from oncogenic viruses. Accordingly, a potential correlation between viruses and fusogens of human endogenous retroviral origin in cancer cell fusion will be summarized in this review.

Hybrid Formation and Fusion of Cancer Cells In Vitro and In Vivo

Simple Summary

Cell fusion as a fundamental biological process is required for various physiological processes, including fertilization, placentation, myogenesis, osteoclastogenesis, and wound healing/tissue regeneration. However, cell fusion is also observed during pathophysiological processes like tumor development. Mesenchymal stroma/stem-like cells (MSC) which play an important role within the tumor microenvironment like other cell types such as macrophages can closely interact and hybridize with cancer cells. The formation of cancer hybrid cells can involve various different mechanisms whereby the genomic parts of the hybrid cells require rearrangement to form a new functional hybrid cell. The fusion of cancer cells with neighboring cell types may represent an important mechanism during tumor development since cancer hybrid cells are detectable in various tumor tissues. During this rare event with resulting genomic instability the cancer hybrid cells undergo a post-hybrid selection process (PHSP) to reorganize chromosomes of the two parental nuclei whereby the majority of the hybrid population undergoes cell death. The remaining cancer hybrid cells survive by displaying altered properties within the tumor tissue.

Abstract

The generation of cancer hybrid cells by intra-tumoral cell fusion opens new avenues for tumor plasticity to develop cancer stem cells with altered properties, to escape from immune surveillance, to change metastatic behavior, and to broaden drug responsiveness/resistance. Genomic instability and chromosomal rearrangements in bi- or multinucleated aneuploid cancer hybrid cells contribute to these new functions. However, the significance of cell fusion in tumorigenesis is controversial with respect to the low frequency of cancer cell fusion events and a clonal advantage of surviving cancer hybrid cells following a post-hybrid selection process. This review highlights alternative processes of cancer hybrid cell development such as entosis, emperipolesis, cannibalism, therapy-induced polyploidization/endoreduplication, horizontal or lateral gene transfer, and focusses on the predominant mechanisms of cell fusion. Based upon new properties of cancer hybrid cells the arising clinical consequences of the subsequent tumor heterogeneity after cancer cell fusion represent a major therapeutic challenge.

Cell-Cell Fusion and the Roads to Novel Properties of Tumor Hybrid Cells

The phenomenon of cancer cell–cell fusion is commonly associated with the origin of more malignant tumor cells exhibiting novel properties, such as increased drug resistance or an enhanced metastatic capacity. However, the whole process of cell–cell fusion is still not well understood and seems to be rather inefficient since only a certain number of (cancer) cells are capable of fusing and only a rather small population of fused tumor hybrids will survive at all. The low survivability of tumor hybrids is attributed to post-fusion processes, which are characterized by the random segregation of mixed parental chromosomes, the induction of aneuploidy and further random chromosomal aberrations and genetic/epigenetic alterations in daughter cells. As post-fusion processes also run in a unique manner in surviving tumor hybrids, the occurrence of novel properties could thus also be a random event, whereby it might be speculated that the tumor microenvironment and its spatial habitats could direct evolving tumor hybrids towards a specific phenotype.

The role of fibroblasts in the modulation of dental pulp inflammation

BACKGROUND/PURPOSE

Dental pulp fibroblasts can protect dental pulp from microbial invasion. However, little is known about the interaction between pulp fibroblasts and the immune cells. In this study, the production of proinflammatory cytokines related to inflammatory cell recruitment was evaluated in tumor necrosis factor (TNF)-α-stimulated human dental pulp fibroblasts (HDPFs). The role of TNF-α-stimulated HDPFs in the cell fusion under inflammatory process was determined with the cell co-culture with peripheral blood mononuclear cells (PBMCs).

METHODS

HDPFs were stimulated with various concentrations of TNF-α, and the secretion of interleukin (IL)-6, IL-8 and monocyte chemoattractant protein (MCP)-1 was analyzed by the enzyme-linked immunosorbent assay. The mRNA expression levels of intercellular adhesion molecule-1 (ICAM-1), macrophage colony-stimulating factor (M-CSF), receptor activator of nuclear factor κB ligand (RANKL) and osteoprotegerin (OPG) were determined by real-time quantitative polymerase chain reaction. TNF-α-treated HDPFs were co-cultured with PBMCs for 21 days, and characteristics of cell differentiation were assessed.

RESULTS

TNF-α induced IL-6, IL-8 and MCP-1 production in HDPFs. Moreover, mRNA expression levels of ICAM-1, M-CSF and OPG were significantly increased in TNF-α-treated HDPFs. Co-culture of TNF-α-treated HDPFs and PBMCs stimulated formation of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells, and the F-actin rings were observed in these multinucleated cells.

CONCLUSION

Our results indicate that under the stimulation of TNF-α, HDPFs may amplify inflammatory response by cytokines production, which in turn can modulate the differentiation of immune cells.

Alcoholism and Osteoimmunology

BACKGROUND

Chronic consumption of alcohol has an adverse effect on the skeletal system, which may lead to osteoporosis, delayed fracture healing and osteonecrosis of the femoral head. Currently, the treatment is limited, therefore, there is an urgent need to determine the underline mechanism and develop a new treatment. It is well-known that normal bone remodeling relies on the balance between osteoclast-mediated bone resorption and - mediated bone formation. Various factors can destroy the balance, including the dysfunction of the immune system. In this review, we summarized the relevant research in the alcoholic osteopenia with a focus on the abnormal osteoimmunology signals. We provided a new theoretical basis for the prevention and treatment of the alcoholic bone.

METHODS

We searched PubMed for publications from 1 January 1980 to 1 February 2020 to identify relevant and recent literature, summarizing evaluation and the prospect of alcoholic osteopenia. Detailed search terms were 'alcohol', 'alcoholic osteoporosis', 'alcoholic osteopenia' 'immune', 'osteoimmunology', 'bone remodeling', 'osteoporosis treatment' and 'osteoporosis therapy'.

RESULTS

A total of 135 papers are included in the review. About 60 papers described the mechanisms of alcohol involved in bone remodeling. Some papers were focused on the pathogenesis of alcohol on bone through osteoimmune mechanisms.

CONCLUSION

There is a complex network of signals between alcohol and bone remodeling and intercellular communication of osteoimmune may be a potential mechanism for alcoholic bone. Studying the osteoimmune mechanism is critical for drug development specific to the alcoholic bone disorder.

Fucoxanthin Suppresses Osteoclastogenesis via Modulation of MAP Kinase and Nrf2 Signaling

Fucoxanthin (FX), a natural carotenoid present in edible brown seaweed, is known for its therapeutic potential in various diseases, including bone disease. However, its underlying regulatory mechanisms in osteoclastogenesis remain unclear. In this study, we investigated the effect of FX on osteoclast differentiation and its regulatory signaling pathway. In vitro studies were performed using osteoclast-like RAW264.7 cells stimulated with the soluble receptor activator of nuclear factor-κB ligand or tumor necrosis factor-alpha/interleukin-6. FX treatment significantly inhibited osteoclast differentiation and bone resorption ability, and downregulated the expression of osteoclast-specific markers such as nuclear factor of activated T cells 1, dendritic cell-specific seven transmembrane protein, and matrix metallopeptidase 9. Intracellular signaling pathway analysis revealed that FX specifically decreased the activation of the extracellular signal-regulated kinase and p38 kinase, and increased the nuclear translocation of phosphonuclear factor erythroid 2-related factor 2 (Nrf2). Our results suggest that FX regulates the expression of mitogen-activated protein kinases and Nrf2. Therefore, FX is a potential therapeutic agent for osteoclast-related skeletal disorders including osteoporosis and rheumatoid arthritis.

Pantoprazole (PPZ) Inhibits RANKL-Induced Osteoclast Formation and Function In Vitro and Prevents Lipopolysaccharide- (LPS-) Induced Inflammatory Calvarial Bone Loss In Vivo

Bone remodeling is a process delicately balanced between osteoclastic bone resorption and osteoblastic bone formation. Osteoclasts (OCs) are multinucleated giant cells formed through the fusion of monocytic precursors of the hematopoietic stem cells lineage. OCs are the exclusive cells responsible for the resorption and degradation of the mineralized bone matrix. Pantoprazole (PPZ), a proton pump inhibitor (PPI), is commonly prescribed to reduce excess gastric acid production for conditions such as gastroesophageal reflux disease and peptic ulcer disease. Studies have found contradictory effects of PPI therapy on bone metabolism due to the lack of understanding of the exact underlying mechanism. In this study, we found that PPZ inhibits receptor activator of nuclear factor-κB (NF-κB) ligand- (RANKL-) induced osteoclastogenesis from bone marrow monocytic/macrophage (BMMs) precursors and the bone-resorbing activity of mature OCs. Correspondingly, the expression of OC marker genes was also attenuated. At the molecular level, PPZ treatment was associated with reduced activation of the ERK MAPK signaling pathways crucial to OC differentiation. Additionally, the in vivo administration of PPZ protected mice against lipopolysaccharide- (LPS-) induced inflammatory calvarial bone erosion, as a result of the reduced number and activity of OCs on the calvarial bone surface. Although PPI use is associated with increased risk of osteoporosis and bone fractures, our study provides evidence for the direct inhibitory effect of PPZ on OC formation and bone resorption in vitro and in vivo, suggesting a potential therapeutic use of PPZ in the treatment of osteolytic disease with localized bone destruction.

ASP2-1, a polysaccharide from Acorus tatarinowii Schott, inhibits osteoclastogenesis via modulation of NFATc1 and attenuates LPS-induced bone loss in mice

Spectroscopic analysis of HPLC-purified 7.3-kD Acorus tatarinowii Schott root polysaccharide ASP2-1 (FT-IR, NMR) revealed respective monosaccharide proportions of glucose: galactose: arabinose: xylose: galacturonic acid: mannose: rhamnose: glucuronic acid:fucose of 49.1:16.0:11.6:10.2:5.3:2.9:2.2:1.7:0.8. In vitro, ASP2-1 inhibited osteoclastogenesis-associated bone resorption, RANKL-induced osteoclastogenesis and F-actin ring formation and suppressed osteoclastogenesis-associated gene expression (e.g., TRAP, OSCAR, Atp6v0d2, αV, β3, MMP9 and CtsK) as shown via RT-PCR. ASP2-1-treated RANKL-stimulated bone marrow-derived macrophages exhibited decreased levels of NFATc1 and c-Fos mRNAs and corresponding transcription factor proteins, elevated expression of negative NFATc1 regulators (Mafb, IRF8, Bcl6) and reduced their upstream negative regulator (Blimp1) expression. ASP2-1 inhibition of NFATc1 expression involved PLCγ2-Ca²⁺ oscillation-calcineurin axis suppression, reflecting suppression of RANKL-induced PLCγ2 activation (and associated Ca²⁺ oscillation) and calcineurin catalytic subunit PP2BAα expression without inhibiting NF-κB and MAPKs activation or phosphorylation. Staining (H&E, TRAP) and micro-CT assays revealed ASP2-1 attenuated bone destruction and osteoclast over-activation and improved tibia micro-architecture in a murine LPS-induced bone loss model. Thus, ASP2-1 may alleviate inflammatory bone loss-associated diseases.

Delineating role of NF-κB and interacting cytokines during prostate cancer-induced osteoclastogenesis

Prostate cancer (PCa) frequently metastasizes to the bone leading to devastating complications such as severe pain and fracture. However, the mechanisms by which PCa cells cause bone loss remain less understood. We investigated the role and mechanisms by which PCa cells induce osteoclastogenesis using cultured monocytic osteoclast precursors. Treatment of RAW264.7 cells with PCa cell lines: DU145, LNCaP, PC-3, or their conditioned media led to the formation of distinct multinucleated, TRAP⁺ osteoclasts. This phenomenon was associated with the increased activation of transcription factor nuclear factor-kB (NF-κB). High transcript level of receptor activator of nuclear factor-kB ligand (RANKL), tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6) were detected in PCa cells. TNF-α and LT-α augmented, whereas IL-6 reduced the RANKL-induced osteoclast formation in RAW264.7 cultures. Our results also demonstrated that PCa cells-induced osteoclastogenesis involved the activation of the TRAF6-IKK-p65-NF-κB signaling cascade. Together, our study demonstrates that PCa cells produce RANKL and several other pro-inflammatory cytokines known to influence osteoclastogenesis, by targeting the NF-κB signaling pathway.

Macrolactin A protects against LPS-induced bone loss by regulation of bone remodeling

An imbalance between bone resorption and bone formation leads to several kinds of bone diseases such as rheumatoid arthritis, osteoporosis and Paget's disease. The imbalance between bone formations relative to bone resorption is responsible in bone remodeling. Several studies have suggested that macrolactin A (MA) has potent anti-inflammatory, anti-cancer and anti-angiogenic effects in various cell types. We investigate whether macrolactin A (MA) could inhibit bone loss and enhance bone formation. We used bone marrow monocytes/macrophages (BMMs) cells to study osteoclast activity and MC3T3-E1 cells to study osteoblast activity. MA suppressed tartrate resistant acid phosphatase (TRAP) positive multinucleated cells in a concentration-dependent manner, as well as at a specific time point. MA markedly reduced bone resorption activity and F-actin ring formation. Moreover, MA markedly suppressed receptor activator of nuclear factor k-B ligand (RANKL)-induced osteoclastogenic marker genes and transcription factors in-vitro. MA repressed osteoclast differentiation via activation of the phosphoinositide kinase-3/Akt, extracellular signal-regulated kinase 1/2 (ERK 1/2), c-Jun N-terminal kinase (JNK), nuclear factor of activated T cells, cytoplasmic 1 (NFATc1) and c-Fos signaling pathways. MA enhanced pre-osteoblast cell differentiation on mineralization activity, alkaline phosphatase (ALP) activity, and the expression of osteoblastogenic markers including osterix, RUNX-2, SMAD4, BMP-2, and ALP. Importantly, MA repressed lipopolysaccharide (LPS)-induced inflammatory bone loss in mice as shown by TRAP staining of femurs and μCT analysis. Therefore, MA could be a promising candidate for the inhibition and management of osteoporosis, arthritis, and bone lytic diseases.

Cell Fusion-Mediated Tissue Regeneration as an Inducer of Polyploidy and Aneuploidy

The biological phenomenon of cell fusion plays a crucial role in several physiological processes, including wound healing and tissue regeneration. Here, it is assumed that bone marrow-derived stem cells (BMSCs) could adopt the specific properties of a different organ by cell fusion, thereby restoring organ function. Cell fusion first results in the production of bi- or multinucleated hybrid cells, which either remain as heterokaryons or undergo ploidy reduction/heterokaryon-to-synkaryon transition (HST), thereby giving rise to mononucleated daughter cells. This process is characterized by a merging of the chromosomes from the previously discrete nuclei and their subsequent random segregation into daughter cells. Due to extra centrosomes concomitant with multipolar spindles, the ploidy reduction/HST could also be associated with chromosome missegregation and, hence, induction of aneuploidy, genomic instability, and even putative chromothripsis. However, while the majority of such hybrids die or become senescent, aneuploidy and genomic instability appear to be tolerated in hepatocytes, possibly for stress-related adaption processes. Likewise, cell fusion-induced aneuploidy and genomic instability could also lead to a malignant conversion of hybrid cells. This can occur during tissue regeneration mediated by BMSC fusion in chronically inflamed tissue, which is a cell fusion-friendly environment, but is also enriched for mutagenic reactive oxygen and nitrogen species.

Artesunate attenuates LPS-induced osteoclastogenesis by suppressing TLR4/TRAF6 and PLCγ1-Ca2+-NFATc1 signaling pathway

In chronic infectious diseases caused by gram-negative bacteria, such as osteomyelitis, septic arthritis, and periodontitis, osteoclastic activity is enhanced with elevated inflammation, which disturbs the bone homeostasis and results in osteolysis. Lipopolysaccharide (LPS), as a bacteria product, plays an important role in this process. Recent evidence shows that an antimalarial drug artesunate attenuates LPS-induced osteolysis independent of RANKL. In this study we evaluated the effects of artesunate on LPS-induced osteoclastogenesis in vitro and femur osteolysis in vivo, and explored the mechanisms underlying the effects of artesunate on LPS-induced osteoclast differentiation independent of RANKL. In preosteoclastic RAW264.7 cells, we found that artesunate (1.56-12.5 μM) dose dependently inhibited LPS-induced osteoclast formation accompanied by suppressing LPS-stimulated osteoclast-related gene expression (Fra-2, TRAP, Cathepsin K, β3-integrin, DC-STAMP, and Atp6v0d2). We showed that artesunate (3.125-12.5 µM) inhibited LPS-stimulated nuclear factor of activated T cells c1 (NFATc1) but not NF-κB transcriptional activity; artesunate (6.25, 12.5 μM) significantly inhibited LPS-stimulated NFATc1 protein expression. Furthermore, artesunate treatment markedly suppressed LPS-induced Ca2+ influx, and decreased the expression of PP2B-Aα (calcineurin) and pPLCγ1 in the cells. In addition, artesunate treatment significantly decreased the expression of upstream signals TLR4 and TRAF6 during LPS-induced osteoclastogenesis. Administration of artesunate (10 mg/kg, ip) for 8 days effectively inhibited serum TNF-α levels and ameliorated LPS (5 mg/kg, ip)-induced inflammatory bone loss in vivo. Taken together, artesunate attenuates LPS-induced inflammatory osteoclastogenesis by inhibiting the expression of TLR4/TRAF6 and the downstream PLCγ1-Ca2+-NFATc1 signaling pathway. Artesunate is a valuable choice to treat bone loss induced by gram-negative bacteria infection or inflammation in RANKL-independent pathway.

Experimental arthritis and Porphyromonas gingivalis administration synergistically decrease bone regeneration in femoral cortical defects

Porphyromonas gingivalis infection can lead to periodontitis and dysbiosis, which are known risk factors for rheumatoid arthritis (RA). We investigated whether P. gingivalis administration affected bone regeneration in mice with or without arthritis. We administered P. gingivalis to male DBA/1 J mice that were or were not sensitised to type II collagen-induced arthritis (CIA). All mice underwent drilling of bilateral femurs. We histologically evaluated new bone regeneration (bone volume of the defect [BVd]/tissue volume of the defect [TVd]) using micro-computed tomography (micro-CT), osteoclast number/bone area, and active osteoblast surface/bone surface (Ob.S/BS). We measured serum cytokine levels and bone mineral density of the proximal tibia using micro-CT. CIA resulted in significantly reduced bone regeneration (BVd/TVd) at all time-points, whereas P. gingivalis administration showed similar effects at 2 weeks postoperatively. CIA resulted in higher osteoclast number/bone area and lower Ob.S/BS at 2 and 3 weeks postoperatively, respectively. However, P. gingivalis administration resulted in lower Ob.S/BS only at 2 weeks postoperatively. During later-stage bone regeneration, CIA and P. gingivalis administration synergistically decreased BVd/TVd, increased serum tumour necrosis factor-α, and resulted in the lowest bone mineral density. Therefore, RA and dysbiosis could be risk factors for prolonged fracture healing.

Phillyrin Attenuates Osteoclast Formation and Function and Prevents LPS-Induced Osteolysis in Mice

As the sole cell type responsible for bone resorption, osteoclasts play a pivotal role in a variety of lytic bone diseases. Suppression of osteoclast formation and activation has been proposed as an effective protective therapy for new bone. In this study, we reported for the first time that phillyrin (Phil), an active ingredient extracted from forsythia, significantly inhibited RANKL-induced osteoclastogenesis and bone resorption in vitro and protected against lipopolysaccharide-induced osteolysis in vivo. Further molecular investigations demonstrated that Phil effectively blocked RANKL-induced activations of c-Jun N-terminal kinase and extracellular signal-regulated kinase, which suppressed the expression of c-Fos and nuclear factor of activated T-cells cytoplasmic 1. Taken together, these data suggested that Phil might be a potential antiosteoclastogenesis agent for treating osteoclast-related bone lytic diseases.

Coordination of Fusion and Trafficking of Pre-osteoclasts at the Marrow-Bone Interface

Fusion is the final osteoclast differentiation step leading to bone resorption. In healthy trabecular bone, osteoclast fusion is restricted to bone surfaces undergoing resorption, and necessarily requires site-specific recruitment of mononucleated pre-osteoclasts originating from the bone marrow. However, the spatiotemporal mechanism coordinating recruitment and fusion is poorly investigated. Herein we identify a collagen/vascular network as a likely structure supporting this mechanism. We therefore used multiplex immunohistochemistry and electron microscopy on human iliac crest bone samples, in combination with functional assays performed in vitro with osteoclasts generated from healthy blood donors. First, we found that putative pre-osteoclasts are in close vicinity of a network of collagen fibers associated with vessels and bone remodeling compartment canopies. Based on 3D-reconstructions of serial sections, we propose that this network may serve as roads leading pre-osteoclasts to resorption sites, as reported for cell migration in other tissues. Importantly, almost all these bone marrow pre-osteoclasts, but only some osteoclasts, express the collagen receptor OSCAR, which is reported to induce fusion competence. Furthermore, differentiating osteoclasts cultured on collagen compared to mineral show higher fusion rates, higher expression of fusogenic cytokines, and a CD47 plasma membrane distribution pattern reported to be typical of a pre-fusion state-thus collectively supporting collagen-induced fusion competence. Finally, these in vitro assays show that collagen induces high cell mobility. The present data lead to a model where collagen fibers/vasculature support the coordination between traffic and fusion of pre-osteoclasts, by serving as a physical road and inducing fusion competence as well as cell mobility.

Puerarin Exerts Protective Effects on Wear Particle-Induced Inflammatory Osteolysis

Wear particle-stimulated inflammatory bone destruction and the consequent aseptic loosening remain major postoperative problems for artificial joints. Studies have indicated that puerarin promotes osteogenesis and alleviates lipopolysaccharide-induced osteoclastogenesis in vitro. However, the underlying molecular mechanism by which puerarin interacts with receptor activator of nuclear factor kappa-B ligand (RANKL)-mediated osteoclast formation in vitro and wear particle-stimulated osteolysis in vivo has not been reported. In this work, the protective effects exerted by puerarin on titanium particle-stimulated bone destruction in vivo and on RANKL-induced osteoclast activation in osteoclastic precursor cells in vitro were investigated. As expected, puerarin significantly inhibited wear particle-mediated bone resorption and proinflammatory cytokine productions in a calvarial resorption model. Additionally, puerarin inhibited RANKL-induced osteoclast activation, bone resorption ability, and F-actin ring formation in vitro as puerarin concentration increased. Furthermore, mechanistic investigation indicated that reduced RANKL-stimulated MEK/ERK/NFATc1 signaling cascades might regulate the protective effect of puerarin. Conclusively, these results indicate that puerarin, a type of polyphenol, might serve as a protective agent to prevent osteoclast-related osteolytic diseases.

Reversine inhibits MMP-3, IL-6 and IL-8 expression through suppression of ROS and JNK/AP-1 activation in interleukin-1β-stimulated human gingival fibroblasts

OBJECTIVE

Periodontitis is an inflammatory disease of the supporting tissue around teeth commonly caused by gram-negative bacterial infections. Interleukin (IL)-1β, a cytokine involved in host immune and inflammatory responses, is known to induce the activation of various intracellular signaling pathways. One of these signaling mechanisms involves the regulation of gene expression by activation of transcription factors (AP-1 and NF-κB). These transcription factors are controlled by mitogen-activated protein kinases (MAPKs), which increase cytokine and matrix metalloproteinase (MMP) expression. We examined the preventive effects of reversine, a 2,6-disubstituted purine derivative, on cytokine and MMP-3 expression in human gingival fibroblasts (HGFs) stimulated with IL-lβ.

STUDY DESIGN

Western blot analyses were performed to verify the activities of MAPK, p65, p50, and c-Jun and the expression of MMPs in IL-1β-stimulated HGFs. Cytokine and MMP-3 expression in IL-1β-stimulated HGFs was measured by real-time quantitative polymerase chain reaction.

RESULTS

Reversine decreased the IL-1β-induced expression of proinflammatory cytokines (IL-6 and IL-8) and MMP-3 in HGFs. Furthermore, the mechanism underlying the effects of reversine involved the suppression of IL-1β-stimulated MAPK activation and AP-1 activation.

CONCLUSION

Reversine inhibits IL-1β-induced MMP and cytokine expression via inhibition of MAPK/AP-1 activation and ROS generation. Therefore, we suggest that reversine may be an effective therapeutic candidate for preventing periodontitis.

Diosmetin inhibits osteoclast formation and differentiation and prevents LPS-induced osteolysis in mice

Osteolytic bone diseases are closely linked to the over-activation of osteoclasts and enhancement of bone resorption. It has become a major health issue in orthopedic practice worldwide. Inhibition of osteoclasts is proposed to be the main treatment for osteolytic disorders. Diosmetin (DIO) is a natural flavonoid with properties of antioxidant, anti-infection, and antishock. The effect of DIO on osteoclast differentiation is poorly understood. In this study project, we found that DIO could inhibit osteoclastic formation induced by receptor activator of nuclear factor kappa-B ligand (RANKL) in a dose-dependent manner. The expression of the osteoclast differentiation marker genes, cathepsin K, nuclear factor of activated T-cells 1 (NFATc1), Acp5, Ctr, Atp6v0d2, and Mmp9 were also decreased by the treatment of DIO. In addition, DIO attenuated the formation of actin ring and the ability of bone resorption. Further, the western blotting showed that DIO inhibits the phosphorylation of the mitogen-activated protein kinases signaling pathway induced by RANKL, accompanied by the downregulation of NFATc1 and c-Fos expression. We also found that DIO could reduce the accumulation of reactive oxygen species (ROS) induced by RANKL. In vivo, the study revealed that DIO can significantly reduce LPS-induced osteolysis in mice. Collectively, our study shows that DIO can inhibit osteoclast formation and activation, and could serve as a potential therapeutic drug for osteolytic bone diseases.

Cellular study of the LPS-induced osteoclastic multinucleated cell formation from RAW264.7 cells

Despite the response to the receptor activator of nuclear factor κ-Β ligand (RANKL), a study has reported that lipopolysaccharide (LPS) could induce RAW264.7 linage osteoclastic differentiation. However, on the contrary, another study recently showed that the LPS-induced multinuclear cells from RAW264.7 did not express osteoclastic functions. Interestingly, in our previous study, we found that RAW264.7 cells pretreated with 10 ng LPS plus macrophage-colony stimulating factor did not show any effects for enhancing RANKL-induced osteoclastic cell differentiation. Therefore, in our current study, we aim to investigate the oteoclastogesis induction ability and efficacy of LPS in the RAW264.7 cell line and relevant molecular signaling. The osteoclastogenic activity of LPS-treated RAW264.7 linage was studied by bone resorption pits and fibrous actin study. Besides that, through polymerase chain reaction and western blot, we showed that the transcriptional factor c-Fos and Nfatc1 might be associated with LPS-induced osteoclastogenesis. Overall, the results of our current study showed positive proof for osteoclast generation from LPS-independent treatment, as well as established an optimal and efficient method for this process.

Dehydrocostus lactone attenuates osteoclastogenesis and osteoclast-induced bone loss by modulating NF-κB signalling pathway

Osteolysis is characterized by overactivated osteoclast formation and potent bone resorption. It is enhanced in many osteoclast‐related diseases including osteoporosis and periprosthetic osteolysis. The shortage of effective treatments for these pathological processes emphasizes the importance of screening and identifying potential regimens that could attenuate the formation and function of osteoclasts. Dehydrocostus lactone (DHE) is a natural sesquiterpene lactone containing anti‐inflammatory properties. Here, we showed that DHE suppressed receptor activator of nuclear factor‐κB ligand (RANKL)‐induced osteoclast formation and osteoclast marker gene expression. It also inhibited F‐actin ring formation and bone resorption in a dose‐dependent manner in vitro. Moreover, DHE inhibited the RANKL‐induced phosphorylation of NF‐κB, mitigated bone erosion in vivo in lipopolysaccharide‐induced inflammatory bone loss model and particle‐induced calvarial osteolysis model. Together, these results suggest that DHE reduces osteoclast‐related bone loss via the modulation of NF‐κB activation during osteoclastogenesis indicating that it might be a useful treatment for osteoclast‐related skeletal disorders.

Cancer cell fusion: a potential target to tackle drug-resistant and metastatic cancer cells

Cell fusion is an integral, established phenomenon underlying various physiological processes in the cell cycle. Although research in cancer metastasis has hypothesised numerous molecular mechanisms and signalling pathways responsible for invasion and metastasis, the origin and progression of metastatic cells within primary tumours remains unclear. Recently, the role of cancer cell fusion in cancer metastasis and development of multidrug resistance (MDR) in tumours has gained prominence. However, evidence remains lacking to justify the role of cell fusion in cancer metastasis and drug resistance. Here, we highlight plausible mechanisms governing cell fusion with different cell types in the tumour microenvironment (TME), the clinical relevance of cancer cell fusion, its potential as a target for overcoming MDR and inhibiting metastasis, and putative modes of treatment.

An Overview of the Derivation and Function of Multinucleated Giant Cells and Their Role in Pathologic Processes

Monocyte lineage cells play important roles in health and disease. Their differentiation into macrophages is crucial for a broad array of immunologic processes that regulate inflammation, neoplasia, and infection. In certain pathologic conditions, such as foreign body reactions and peripheral inflammatory lesions, monocytes fuse to form large, multinucleated giant cells (MGCs). Currently, our knowledge of the fusion mechanisms of monocytes and the regulation of MGC formation and function in discrete pathologies is limited. Herein, we consider the types and function of MGCs in disease and assess the mechanisms by which monocyte fusion contributes to the formation of MGCs. An improved understanding of the cellular origins and metabolic functions of MGCs will facilitate their identification and ultimately the treatment of diseases and disorders that involve MGCs.

Overview of RAW264.7 for osteoclastogensis study: Phenotype and stimuli

Bone homeostasis is preserved by the balance of maintaining between the activity of osteogenesis and osteoclastogenesis. However, investigations for the osteoclastogenesis were hampered by considerable difficulties associated with isolating and culturing osteoclast in vivo. As the alternative, stimuli‐induced osteoclasts formation from RAW264.7 cells (RAW‐OCs) have gain its importance for extensively osteoclastogenic study of bone diseases, such as rheumatoid arthritis, osteoporosis, osteolysis and periodontitis. However, considering the RAW‐OCs have not yet been well‐characterized and RAW264.7 cells are polymorphic because of a diverse phenotype of the individual cells comprising this cell linage, and different fate associated with various stimuli contributions. Thus, in present study, we provide an overview for current knowledge of the phenotype of RAW264.7 cells, as well as the current understanding of the complicated interactions between various stimuli and RAW‐OCs in the light of the recent progress.

Cell Fusion in Human Cancer: The Dark Matter Hypothesis

Current strategies to determine tumor × normal (TN)-hybrid cells among human cancer cells include the detection of hematopoietic markers and other mesodermal markers on tumor cells or the presence of donor DNA in cancer samples from patients who had previously received an allogenic bone marrow transplant. By doing so, several studies have demonstrated that TN-hybrid cells could be found in human cancers. However, a prerequisite of this cell fusion search strategy is that such markers are stably expressed by TN-hybrid cells over time. However, cell fusion is a potent inducer of genomic instability, and TN-hybrid cells may lose these cell fusion markers, thereby becoming indistinguishable from nonfused tumor cells. In addition, hybrid cells can evolve from homotypic fusion events between tumor cells or from heterotypic fusion events between tumor cells and normal cells possessing similar markers, which would also be indistinguishable from nonfused tumor cells. Such indistinguishable or invisible hybrid cells will be referred to as dark matter hybrids, which cannot as yet be detected and quantified, but which contribute to tumor growth and progression.