NF-κB signaling participates in both RANKL- and IL-4-induced macrophage fusion: receptor cross-talk leads to alterations in NF-κB pathways

Formation and biological activities of foreign body giant cells in response to biomaterials

The integration of biomaterials in medical applications triggers the foreign body response (FBR), a multi-stage immune reaction characterized by the formation of foreign body giant cells (FBGCs). Originating from the fusion of monocyte/macrophage lineage cells, FBGCs are pivotal participants during tissue-material interactions. This review provides an in-depth examination of the molecular processes during FBGC formation, highlighting signaling pathways and fusion mediators in response to both exogenous and endogenous stimuli. Moreover, a wide range of material-specific characteristics, such as surface chemical and physical properties, has been proven to influence the fusion of macrophages into FBGCs. Multifaceted biological activities of FBGCs are also explored, with emphasis on their phagocytic capabilities and extracellular secretory functions, which profoundly affect the vascularization, degradation, and encapsulation of the biomaterials. This review further elucidates the heterogeneity of FBGCs and their diverse roles during FBR, as demonstrated by their distinct behaviors in response to different materials. By presenting a comprehensive understanding of FBGCs, this review intends to provide strategies and insights into optimizing biocompatibility and the therapeutic potential of biomaterials for enhanced stability and efficacy in clinical applications. STATEMENT OF SIGNIFICANCE: As a hallmark of the foreign body response (FBR), foreign body giant cells (FBGCs) significantly impact the success of implantable biomaterials, potentially leading to complications such as chronic inflammation, fibrosis, and device failure. Understanding the role of FBGCs and modulating their responses are vital for successful material applications. This review provides a comprehensive overview of the molecules and signaling pathways guiding macrophage fusion into FBGCs. By elucidating the physical and chemical properties of materials inducing distinct levels of FBGCs, potential strategies of materials in modulating FBGC formation are investigated. Additionally, the biological activities of FBGCs and their heterogeneity in responses to different material categories in vivo are highlighted in this review, offering crucial insights for improving the biocompatibility and efficacy of biomaterials.

Balancing the Scales: The Dual Role of Interleukins in Bone Metastatic Microenvironments

Bone metastases, a common and debilitating consequence of advanced cancers, involve a complex interplay between malignant cells and the bone microenvironment. Central to this interaction are interleukins (ILs), a group of cytokines with critical roles in immune modulation and inflammation. This review explores the dualistic nature of pro-inflammatory and anti-inflammatory interleukins in bone metastases, emphasizing their molecular mechanisms, pathological impacts, and therapeutic potential. Pro-inflammatory interleukins, such as IL-1, IL-6, and IL-8, have been identified as key drivers in promoting osteoclastogenesis, tumor proliferation, and angiogenesis. These cytokines create a favorable environment for cancer cell survival and bone degradation, contributing to the progression of metastatic lesions. Conversely, anti-inflammatory interleukins, including IL-4, IL-10, and IL-13, exhibit protective roles by modulating immune responses and inhibiting osteoclast activity. Understanding these opposing effects is crucial for developing targeted therapies aimed at disrupting the pathological processes in bone metastases. Key signaling pathways, including NF-κB, JAK/STAT, and MAPK, mediate the actions of these interleukins, influencing tumor cell survival, immune cell recruitment, and bone remodeling. Targeting these pathways presents promising therapeutic avenues. Current treatment strategies, such as the use of denosumab, tocilizumab, and emerging agents like bimekizumab and ANV419, highlight the potential of interleukin-targeted therapies in mitigating bone metastases. However, challenges such as therapeutic resistance, side effects, and long-term efficacy remain significant hurdles. This review also addresses the potential of interleukins as diagnostic and prognostic biomarkers, offering insights into patient stratification and personalized treatment approaches. Interleukins have multifaceted roles that depend on the context, including the environment, cell types, and cellular interactions. Despite substantial progress, gaps in research persist, particularly regarding the precise mechanisms by which interleukins influence the bone metastatic niche and their broader clinical implications. While not exhaustive, this overview underscores the critical roles of interleukins in bone metastases and highlights the need for continued research to fully elucidate their complex interactions and therapeutic potential. Addressing these gaps will be essential for advancing our understanding and treatment of bone metastases in cancer patients.

Exercise and osteoimmunology in bone remodeling

Bones can form the scaffolding of the body, support the organism, coordinate somatic movements, and control mineral homeostasis and hematopoiesis. The immune system plays immune supervisory, defensive, and regulatory roles in the organism, which mainly consists of immune organs (spleen, bone marrow, tonsils, lymph nodes, etc.), immune cells (granulocytes, platelets, lymphocytes, etc.), and immune molecules (immune factors, interferons, interleukins, tumor necrosis factors, etc.). Bone and the immune system have long been considered two distinct fields of study, and the bone marrow, as a shared microenvironment between the bone and the immune system, closely links the two. Osteoimmunology organically combines bone and the immune system, elucidates the role of the immune system in bone, and creatively emphasizes its interdisciplinary characteristics and the function of immune cells and factors in maintaining bone homeostasis, providing new perspectives for skeletal-related field research. In recent years, bone immunology has gradually become a hot spot in the study of bone-related diseases. As a new branch of immunology, bone immunology emphasizes that the immune system can directly or indirectly affect bones through the RANKL/RANK/OPG signaling pathway, IL family, TNF-α, TGF-β, and IFN-γ. These effects are of great significance for understanding inflammatory bone loss caused by various autoimmune or infectious diseases. In addition, as an external environment that plays an important role in immunity and bone, this study pays attention to the role of exercise-mediated bone immunity in bone reconstruction.

Unraveling the potential of 3D bioprinted immunomodulatory materials for regulating macrophage polarization: State-of-the-art in bone and associated tissue regeneration

Macrophage-assisted immunomodulation is an alternative strategy in tissue engineering, wherein the interplay between pro-inflammatory and anti-inflammatory macrophage cells and body cells determines the fate of healing or inflammation. Although several reports have demonstrated that tissue regeneration depends on spatial and temporal regulation of the biophysical or biochemical microenvironment of the biomaterial, the underlying molecular mechanism behind immunomodulation is still under consideration for developing immunomodulatory scaffolds. Currently, most fabricated immunomodulatory platforms reported in the literature show regenerative capabilities of a particular tissue, for example, endogenous tissue (e.g., bone, muscle, heart, kidney, and lungs) or exogenous tissue (e.g., skin and eye). In this review, we briefly introduced the necessity of the 3D immunomodulatory scaffolds and nanomaterials, focusing on material properties and their interaction with macrophages for general readers. This review also provides a comprehensive summary of macrophage origin and taxonomy, their diverse functions, and various signal transduction pathways during biomaterial-macrophage interaction, which is particularly helpful for material scientists and clinicians for developing next-generation immunomodulatory scaffolds. From a clinical standpoint, we briefly discussed the role of 3D biomaterial scaffolds and/or nanomaterial composites for macrophage-assisted tissue engineering with a special focus on bone and associated tissues. Finally, a summary with expert opinion is presented to address the challenges and future necessity of 3D bioprinted immunomodulatory materials for tissue engineering.

NIK inhibitor impairs chronic periodontitis via suppressing non-canonical NF-κB and osteoclastogenesis

Periodontitis is an inflammatory disease that causes damages to periodontium and alveolar bone. Overactivation and formation of osteoclasts can cause bone destruction, which contributes to periodontitis development. Receptor activator of nuclear factor κB ligand (RANKL)-mediated NF-κB signaling plays an essential role in osteoclasts differentiation. We aimed to study the effects of NIK-SMI1, an NF-κB-inducing kinase (NIK) inhibitor, on the osteoclastogenesis in vitro and periodontitis progression in vivo. A ligature-induced mice model of periodontitis was incorporated to test the potential therapeutic effect of NIK-SMI1 on periodontitis. The target protein and mRNA expression levels were determined by Western blot assay and real-time PCR assay, respectively. We found that the administration of NIK-SMI1 strongly inhibited the RANKL-stimulated non-canonical NF-κB signaling as demonstrated by decreased nuclear p52 expression and activity. Blocking NIK activity also resulted in reduced osteoclasts specific genes expression and enhanced IFN-β expression. NIK-SMI1 treatment resulted in attenuated periodontitis progression and pro-inflammatory cytokines expression in vivo. Our study suggested that NIK-SMI1 exerts beneficial effects on the mitigation of osteoclastogenesis in vitro and periodontitis progression in vivo. Application of NIK-SMI1 may serve as a potential therapeutic approach for periodontitis.

Arecoline suppresses RANKL-induced osteoclast differentiation in vitro and attenuates LPS-induced bone loss in vivo

BACKGROUND

Areca nut has anti-inflammatory, antiparasitic, antihypertensive, and antidepressant properties. The pathological hallmarks of inflammatory joint diseases are an increased number of osteoclasts and impaired differentiation of osteoblasts, which may disrupt the bone remodeling balance and eventually lead to bone loss.

PURPOSE

The present study assessed the effects of arecoline, the main alkaloid found in areca nut, on osteoclast and osteoblast differentiation and function.

METHOD

M-CSF/RANKL-stimulated murine bone marrow-derived macrophages (BMMs) were incubated with several concentrations of arecoline, and TRAP staining and pit formation were assessed to monitor osteoclast formation. Quantitative real-time RT-PCR and western blot analyses were used to analyze the expression of osteoclast-associated genes and signaling pathways. The effects of arecoline on bone were investigated in an in vivo mouse model of lipopolysaccharide (LPS)-induced trabecular bone loss after oral administration of arecoline. Alizarin red S staining and assays to measure ALP activity and the transcription level of osteoblast-related genes were used to evaluate the effects of arecoline on osteoblast differentiation and bone mineralization.

RESULTS

In a dose-dependent manner, arecoline at concentrations of 50-100 μM reduced both the development of TRAP-positive multinucleated osteoclasts and the formation of resorption pits in M-CSF/RANKL-stimulated BMMs. In M-CSF/RANKL-stimulated BMMs, arecoline also suppressed the expression and translocation of c-Fos and NFATcl, and osteoclast differentiated-related genes via interference with the AKT, MAPK, and NF-kB activation pathways. Femur bone loss and microcomputed tomography parameters were recovered by oral administration of arecoline in the mouse LPS-induced bone loss model. Lastly, arecoline increased ALP activity, bone mineralization, and the expression of osteoblast differentiation-related genes, such as ALP and Runx2, in MC3T3-E1 cells.

CONCLUSION

Our data suggest that arecoline may attenuate or prevent bone loss by suppressing osteoclastogenesis and promoting osteoblastogenesis. These findings provide evidence supporting arecoline's use as a potential therapeutic agent in bone-loss disorders and 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.

Mineralized collagen-modified PMMA cement enhances bone integration and reduces fibrous encapsulation in the treatment of lumbar degenerative disc disease

As a minimally invasive surgery, percutaneous cement discoplasty (PCD) is now contemplated to treat lumbar disc degeneration disease in elder population. Here, we investigated whether the osteogenic mineralized collagen (MC) modified polymethylmethacrylate (PMMA) cement could be a suitable material in PCD surgery. Injectability, hydrophilicity and mechanical properties of the MC-modified PMMA (PMMA-MC) was characterized. The introduction of MC did not change the application and setting time of PMMA and was easy to be handled in minimally invasive operation. Hydrophilicity of PMMA-MC was greatly improved and its elastic modulus was tailored to complement mechanical performance of bone under dynamic stress. Then, PCD surgery in a goat model with induced disc degeneration was performed with implantation of PMMA-MC or PMMA. Three months after implantation, micro-computed tomography analysis revealed a 36.4% higher circumferential contact index between PMMA-MC and bone, as compared to PMMA alone. Histological staining confirmed that the surface of PMMA-MC was in direct contact with new bone, while the PMMA was covered by fibrous tissue. The observed gathering of macrophages around the implant was suspected to be the cause of fibrous encapsulation. Therefore, the interactions of PMMA and PMMA-MC with macrophages were investigated in vitro. We discovered that the addition of MC could hinder the proliferation and fusion of the macrophages. Moreover, expressions of fibroblast-stimulating growth factors, insulin-like growth factor, basic fibroblast growth factor and tumor necrosis factor-β were significantly down-regulated in the macrophages cocultured with PMMA-MC. Together, the promoted osteointegration and reduced fibrous tissue formation observed with PMMA-MC material makes it a promising candidate for PCD surgery.

Factors influencing multinucleated giant cell formation in vitro

Macrophages fuse together to form multinucleated giant cells (MGC) in granulomas associated with various pathological conditions. Improved in vitro methods are required to better enable investigations of MGC biology and potential contribution to disease. There is a need for standardization of MGC quantification, purification of MGC populations, and characterization of how cell culture variables influence MGC formation. This study examined solutions to address these needs while providing context with other current and alternative methods. Primary mouse bone marrow-derived macrophages were treated with interleukin-4, a cytokine known to induce fusion into MGC. This model was used to systematically assess the influence of cell stimulant timing, cell seeding density, colony stimulating factors, and culture vessel type. Results indicated that MGC formation is greatly impacted by alterations in certain culture variables. An assessment of previously published research showed that these culture conditions varied widely between different laboratories, which may explain inconsistencies in the literature. A particularly novel and unexpected observation was that MGC formation appears to be greatly increased by silicone, which is a component of a chamber slide system commonly used for MGC studies. The most successful quantification method was fluorescent staining with semi-automated morphological evaluation. The most successful enrichment method was microfiltration. Overall, this study takes steps toward standardizing in vitro methods, enhancing replicability, and guiding investigators attempting to culture, quantify, and enrich MGC.

Mesenchymal stem cell-based bioengineered constructs: foreign body response, cross-talk with macrophages and impact of biomaterial design strategies for pelvic floor disorders

An excessive foreign body response (FBR) has contributed to the adverse events associated with polypropylene mesh usage for augmenting pelvic organ prolapse surgery. Consequently, current biomaterial research considers the critical role of the FBR and now focuses on developing better biocompatible biomaterials rather than using inert implants to improve the clinical outcomes of their use. Tissue engineering approaches using mesenchymal stem cells (MSCs) have improved outcomes over traditional implants in other biological systems through their interaction with macrophages, the main cellular player in the FBR. The unique angiogenic, immunomodulatory and regenerative properties of MSCs have a direct impact on the FBR following biomaterial implantation. In this review, we focus on key aspects of the FBR to tissue-engineered MSC-based implants for supporting pelvic organs and beyond. We also discuss the immunomodulatory effects of the recently discovered endometrial MSCs on the macrophage response to new biomaterials designed for use in pelvic floor reconstructive surgery. We conclude with a focus on considerations in biomaterial design that take into account the FBR and will likely influence the development of the next generation of biomaterials for gynaecological applications.

Fructose 1,6-bisphosphate inhibits osteoclastogenesis by attenuating RANKL-induced NF-κB/NFATc-1

BACKGROUND

Although some glycolytic intermediates have been shown to modulate several cell type formation and activation, the functional role of fructose 1,6-bisphosphate (FBP) on osteoclastogenesis is still unknown.

METHODS

Osteoclastogenesis was evaluated on bone marrow preosteoclasts cultured with M-CSF - 30 ng/ml, RANKL - 10 ng/ml, and two concentrations of FBP (100 and 300 µM). TRAP-positive stained cells were counted, and osteoclastogenic marker genes expression were evaluated by qPCR. Osteoclasts resorption capacity was evaluated by the expression of specific enzymes and capacity to resorb a mineralized matrix. The NF-κB activation was detected using RAW 264.7, stably expressing luciferase on the NF-κB responsive promoter.

RESULTS

We show that FBP, the product of the first stage of glycolysis, inhibited RANKL-induced osteoclasts differentiation and TRAP activity. The treatment of preosteoclasts with FBP attenuated osteoclast fusion and formation, without affecting cell viability. Moreover, the inhibition of several osteoclastogenic marker genes expression (TRAP, OSCAR, DC-STAMP, Integrin αv, NFATc1) by FBP correlates with a reduction of mineralized matrix resorption capacity. The mechanism underlying FBP-inhibition of osteoclastogenesis involves NF-κB/NFATc1 signaling pathway inhibition.

CONCLUSION

Altogether these data show a protective role of a natural glycolytic intermediate in bone homeostasis that may have therapeutic benefit for osteolytic diseases.

Elevated pre-activation basal level of nuclear NF-κB in native macrophages accelerates LPS-induced translocation of cytosolic NF-κB into the cell nucleus

Signaling via Toll-like receptor 4 (TLR4) in macrophages constitutes an essential part of the innate immune response to bacterial infections. Detailed and quantified descriptions of TLR4 signal transduction would help to understand and exploit the first-line response of innate immune defense. To date, most mathematical modelling studies were performed on transformed cell lines. However, properties of primary macrophages differ significantly. We therefore studied TLR4-dependent activation of NF-κB transcription factor in bone marrow-derived and peritoneal primary macrophages. We demonstrate that the kinetics of NF-κB phosphorylation and nuclear translocation induced by a wide range of bacterial lipopolysaccharide (LPS) concentrations in primary macrophages is much faster than previously reported for macrophage cell lines. We used a comprehensive combination of experiments and mathematical modeling to understand the mechanisms of this rapid response. We found that elevated basal NF-κB in the nuclei of primary macrophages is a mechanism increasing native macrophage sensitivity and response speed to the infection. Such pre-activated state of macrophages accelerates the NF-κB translocation kinetics in response to low agonist concentrations. These findings enabled us to refine and construct a new model combining both NF-κB phosphorylation and translocation processes and predict the existence of a negative feedback loop inactivating phosphorylated NF-κB.

Naringenin mitigates titanium dioxide (TiO2)-induced chronic arthritis in mice: role of oxidative stress, cytokines, and NFκB

OBJECTIVE

To evaluate the effect and mechanisms of naringenin in TiO₂-induced chronic arthritis in mice, a model resembling prosthesis and implant inflammation.

TREATMENT

Flavonoids are antioxidant and anti-inflammatory molecules with important anti-inflammatory effect. Mice were daily treated with the flavonoid naringenin (16.7-150 mg/kg, orally) for 30 days starting 24 h after intra-articular knee injection of 3 mg of TiO₂.

METHODS

TiO₂-induced arthritis resembles cases of aseptic inflammation induced by prosthesis and/or implants. Mice were stimulated with 3 mg of TiO₂ and after 24 h mice started to be treated with naringenin. The disease phenotype, treatment toxicity, histopathological damage, oxidative stress, cytokine expression and NFκB were evaluated after 30 days of treatment.

RESULTS

Naringenin inhibited TiO₂-induced mechanical hyperalgesia (96%), edema (77%) and leukocyte recruitment (74%) without inducing toxicity. Naringenin inhibited histopathological index (HE, 49%), cartilage damage (Toluidine blue tibial staining 49%, and proteoglycan 98%), and bone resorption (TRAP-stained 73%). These effects were accompanied by inhibition of oxidative stress (gp91^phox 93%, NBT 83%, and TBARS 41%) cytokine mRNA expression (IL-33 82%, TNFα 76%, pro-IL-1β 100%, and IL-6 61%), and NFκB activation (100%).

CONCLUSION

Naringenin ameliorates TiO₂-induced chronic arthritis inducing analgesic and anti-inflammatory responses with improvement in the histopathological index, cartilage damage, and bone resorption.

Effects of Lectin (ScLL) on osteoclast-like multinucleated giant cells' maturation-A preliminary in vitro study

BACKGROUND/AIM

Lectin (ScLL) has been recently evaluated in the oral cavity due to its anti-inflammatory activities. ScLL could be a promising agent for blocking osteoclast activity and preventing root resorption. The aim of this study was to evaluate the effect of ScLL on the viability of the RAW 264.7 macrophage lineage, osteoclast-like maturation and the release of TNF-α and nitric oxide (NO).

MATERIALS AND METHODS

The viability of RAW 264.7 cells was determined by MTT and Alamar Blue assays after ScLL treatment for 24 hours. ScLL effects on RANKL-induced osteoclast-like maturation were assessed by tartrate-resistant acid phosphatase (TRAP) staining and F-actin ring formation. The supernatant was collected to detect the release of TNF-α using ELISA and NO using a nitrite assay.

RESULTS

ScLL suppressed osteoclast-like maturation by decreasing TRAP activity as well as F-actin ring formation. ScLL at 10 μg/mL showed the highest values of NO release compared with all other groups (P < .05). Lower levels of TNF-α were found for the negative control.

CONCLUSIONS

ScLL at 5 μg/mL suppressed osteoclast-like maturation in vitro and had no cytotoxic effect on RAW cell cultures.

Activation of the non-canonical NF-κB/p52 pathway in vascular endothelial cells by RANKL elicits pro-calcific signalling in co-cultured smooth muscle cells

BACKGROUND

The intimal endothelium is known to condition the underlying medial smooth muscle cell (SMC) layer of the vessel wall, and is highly responsive to receptor-activator of nuclear factor-κB ligand (RANKL) and tumour necrosis factor-related apoptosis-inducing ligand (TRAIL), pro-calcific and anti-calcific agents, respectively. In this paper, we tested the hypothesis that RANKL-induced activation of endothelial NF-κB signalling is essential for pro-calcific activation of the underlying SMCs.

METHODS

For these studies, human aortic endothelial and smooth muscle cell mono-cultures (HAECs, HASMCs) were treated with RANKL (0-25 ng/ml ± 5 ng/ml TRAIL) for 72 h. Non-contact transwell HAEC:HASMC co-cultures were also employed in which the luminal HAECs were treated with RANKL (± 5 ng/ml TRAIL), followed by analysis of pro-calcific markers in the underlying subluminal HASMCs.

RESULTS

Treatment of either HAECs or HASMCs with RANKL activated the non-canonical NF-κB/p52 and canonical NF-κB/p65 pathways in both cell types. In RANKL ± TRAIL-treated HAECs, recombinant TRAIL, previously demonstrated by our group to strongly attenuate the pro-calcific signalling effects of RANKL, was shown to specifically block the RANKL-mediated activation of non-canonical NF-κB/p52, clearly pointing to the mechanistic relevance of this specific pathway to RANKL function within endothelial cells. In a final series of HAEC:HASMC transwell co-culture experiments, RANKL treatment of HAECs that had been genetically silenced (via siRNA) for the NF-κB2 gene (the molecular forerunner to NF-κB/p52 generation) exhibited strongly attenuated pro-calcific activation of underlying HASMCs relative to scrambled siRNA controls.

SUMMARY

These in vitro observations provide valuable mechanistic insights into how RANKL may potentially act upon endothelial cells through activation of the alternative NF-κB pathway to alter endothelial paracrine signalling and elicit pro-calcific responses within underlying vascular smooth muscle cells.

The immunopathogenic and immunomodulatory effects of interleukin-12 in periodontal disease

Interleukin 12 (IL-12) is an inflammatory cytokine that promotes the response of the immune system. This cytokine has been implicated as a potent stimulator of several diseases characterized by inflammatory-induced bone destruction, such as rheumatoid arthritis and periodontitis. Yet, the exact role of IL-12 in the development and progress of periodontitis has not been clarified. Several studies have demonstrated a positive correlation between the level of IL-12 and the severity of periodontal destruction. Deletion of IL-12 in mice with periodontitis significantly suppressed the level of bone destruction. Interestingly, next to a role in modulating the pathogenesis, IL-12 also has immunological-regulatory properties. This cytokine induces expression of immunosuppressive molecules, such as indoleamine-pyrrole 2,3-dioxygenase (IDO). Thus, these findings suggest both negative and positive influences of IL-12 in periodontal disease. It is currently proposed that the diversity of action of cytokines is a molecular key which regulates biological development and homeostasis. Accordingly, the actions of IL-12 might be one of the mechanisms that regulate homeostasis of periodontal tissue during and following inflammation. Therefore, this article aims to review both destructive and protective functionalities of IL-12 with an emphasis on periodontal disease.

Dual-specificity tyrosine phosphorylation-regulated kinase 2 regulates osteoclast fusion in a cell heterotypic manner

Monocyte fusion into osteoclasts, bone resorbing cells, plays a key role in bone remodeling and homeostasis; therefore, aberrant cell fusion may be involved in a variety of debilitating bone diseases. Research in the last decade has led to the discovery of genes that regulate osteoclast fusion, but the basic molecular and cellular regulatory mechanisms underlying the fusion process are not completely understood. Here, we reveal a role for Dyrk2 in osteoclast fusion. We demonstrate that Dyrk2 down regulation promotes osteoclast fusion, whereas its overexpression inhibits fusion. Moreover, Dyrk2 also promotes the fusion of foreign-body giant cells, indicating that Dyrk2 plays a more general role in cell fusion. In an earlier study, we showed that fusion is a cell heterotypic process initiated by fusion-founder cells that fuse to fusion-follower cells, the latter of which are unable to initiate fusion. Here, we show that Dyrk2 limits the expansion of multinucleated founder cells through the suppression of the fusion competency of follower cells.

Breast cancer-associated gene 3 interacts with Rac1 and augments NF-κB signaling in vitro, but has no effect on RANKL-induced bone resorption in vivo

Breast cancer-associated gene 3 (BCA3) is a recently identified adaptor protein whose functions are still being defined. BCA3 has been reported to be an important regulator of nuclear factor-κB (NF-κB) signaling. It has also been reported to interact with the small GTPase, Rac1. Consistent with that observation, in the present study, BCA3 was found to interact with nuclear Rac1 in 293 cells and influence NF-κB signaling. Additional experiments revealed that depending on cell type, BCA3 augmented, attenuated or had no effect on NF-κB signaling in vitro. Since canonical NF-κB signaling is a critical downstream target from activated receptor activator of nuclear factor κB (RANK) that is required for mature osteoclast formation and function, BCA3 was selectively overexpressed in osteoclasts in vivo using the cathepsin K promoter and the response to exogenous receptor activator of nuclear factor κB ligand (RANKL) administration was examined. Despite its ability to augment NF-κB signaling in other cells, transgenic animals injected with high-dose RANKL had the same hypercalcemic response as their wild-type littermates. Furthermore, the degree of bone loss induced by a 2-week infusion of low-dose RANKL was the same in both groups. Combined with earlier studies, the data from our study data indicate that BCA3 can affect NF-κB signaling and that BCA3 plays a cell-type dependent role in this process. The significance of the BCA3/NF-κB interaction in vivo in bone remains to be determined.

The purinergic receptor P2X5 regulates inflammasome activity and hyper-multinucleation of murine osteoclasts

Excessive bone resorption by osteoclasts (OCs) can result in serious clinical outcomes, including bone loss that may weaken skeletal or periodontal strength. Proper bone homeostasis and skeletal strength are maintained by balancing OC function with the bone-forming function of osteoblasts. Unfortunately, current treatments that broadly inhibit OC differentiation or function may also interfere with coupled bone formation. We therefore identified a factor, the purinergic receptor P2X5 that is highly expressed during the OC maturation phase, and which we show here plays no apparent role in early bone development and homeostasis, but which is required for osteoclast-mediated inflammatory bone loss and hyper-multinucleation of OCs. We further demonstrate that P2X5 is required for ATP-mediated inflammasome activation and IL-1β production by OCs, and that P2X5-deficient OC maturation is rescued in vitro by addition of exogenous IL-1β. These findings identify a mechanism by which OCs react to inflammatory stimuli, and may identify purinergic signaling as a therapeutic target for bone loss-related inflammatory conditions.

Interleukin-12 Induces Receptor Activator of Nuclear Factor-Kappa B Ligand Expression by Human Periodontal Ligament Cells

BACKGROUND

Increased level of proinflammatory cytokine interleukin (IL)-12 correlates with the severity of periodontitis. Yet, a possible role of IL-12 in periodontal disease has not been clarified. The aim of this study is to investigate whether IL-12 affects expression of receptor activator of nuclear factor-kappa B (NF-κB) ligand (RANKL), a potent osteoclast-stimulating factor, by human periodontal ligament (hPDL) cells.

METHODS

To determine the effect of IL-12, hPDL cells were incubated with recombinant human IL-12 (p70) in a dose- (0 to 10 ng/mL) and time-dependent manner. Expression of RANKL was evaluated at mRNA and protein levels. Underlying signaling pathways of IL-12 were determined by using specific inhibitors.

RESULTS

Under the influence of IL-12, hPDL cells expressed significantly higher levels of RANKL. Expression was mediated by signal transducer and activator of transcription 4 and NF-κB signaling pathways. Conditioned medium of IL-12-incubated cells proved to contain molecule(s) that induced RANKL expression. Addition of suramin (G protein-coupled receptor inhibitor) and ethylene glycol tetraacetic acid (calcium chelator) suggested existence of intermediate molecule(s) that could activate heterotrimeric G protein signaling in a calcium-dependent pathway.

CONCLUSIONS

Expression of RANKL by hPDL cells significantly increased after IL-12 treatment. Therefore, this study supports a close interrelationship between immune and skeletal systems and suggests an osteolytic role of IL-12 in pathogenesis of periodontal disease.

The Simultaneous Inhibitory Effect of Niclosamide on RANKL-Induced Osteoclast Formation and Osteoblast Differentiation

The bone destruction disease including osteoporosis and rheumatoid arthritis are caused by the imbalance between osteoblastogenesis and osteoclastogenesis. Inhibition of the NF-κB pathway was responsible for decreased osteoclastogenesis. Recently many studies indicated that niclosamide, the FDA approved an antihelminth drug, inhibits prostate and breast cancer cells growth by targeting NF-κB signaling pathways. This study evaluated the effects of niclosamide on osteoclast and osteoblast differentiation and function in vitro. In RANKL-induced murine osteoclast precursor cell RAW264.7 and M-CSF/RANKL-stimulated primary murine bone marrow-derived macrophages (BMM), niclosamide dose-dependently inhibited the formation of TRAP-positive multinucleated osteoclasts and resorption pits formation between 0.5uM and 1uM. In addition, niclosamide suppressed the expression of nuclear factor of activated T cells c1 (NFATc1) and osteoclast differentiated-related genes in M-CSF/ RANKL-stimulated BMM by interference with TRAF-6, Erk1/2, JNK and NF-κB activation pathways. However, the cytotoxic effects of niclosamide obviously appeared at the effective concentrations for inhibiting osteoclastogenesis (0.5-1uM) with increase of apoptosis through caspase-3 activation in osteoblast precursor cell line, MC3T3-E1. Niclosamide also inhibited ALP activity, bone mineralization and osteoblast differentiation-related genes expression in MC3T3-E1. Therefore, our findings suggest the new standpoint that niclosamide's effects on bones must be considered before applying it in any therapeutic treatment.

IL-4 induces the formation of multinucleated giant cells and expression of β5 integrin in central giant cell lesion

Background

It is now well established that IL-4 has a central role in the development of monocytes to multinucleated giant cells (MGCs) by inducing the expression of integrins on the surface of monocytes. The aim of this study was to investigate the potential role of IL-4 in induction of β5 integrin expression in the peripheral blood samples of patients with giant cell granuloma.

Material and Methods

Monocytes were isolated from peripheral blood samples of patients with central giant cell granuloma (CGCG) and healthy controls using human Monocyte Isolation Kit II. Isolated monocytes were then cultured in the absence or presence of IL-4 (10 and 20 ng/mL), and following RNA extraction and cDNA synthesis, Real-time PCR was performed to determine the level of β5 integrin expression. The formation of CGCGs and morphological analyses were done under light microscopy. For confirmation of CGCGs, immunocytochemistry technique was also carried out by anti-RANK (receptor-activator of NF-κB ligand) antibody.

Results

In both patient and control groups, β5 levels were significantly enhanced by increasing the IL-4 dose from 10 to 20 ng/mL. In addition, these differences were significant between patient and control groups without IL-4 treatment. On the other hand, the number of cells which expressed RANK and therefore the number of giant cells were significantly higher in the patient group in comparison to controls, as assessed by immunohistochemistry evaluations.

Conclusions

In this study, we showed an elevation in the expression levels of β5 integrin when stimulated by IL-4. It is strongly indicated that this integrin acts as an important mediator during macrophage to macrophage fusion and development of giant cells.

Key words:β5 integrin, giant cell, Il-4, monocyte, rank.

Low‑molecular weight fucoidan inhibits the differentiation of osteoclasts and reduces osteoporosis in ovariectomized rats

Fucoidan is a type of sulfated polysaccharide isolated from seaweed. The present study used ovariectomized Sprague‑Dawley rats, which were treated with fucoidan. The effects of fucoidan on bone metabolism, density and microarchitecture were assessed using micro‑computed tomography (CT), histomorphometric analysis, biochemical markers of bone metabolism (Serum procollagen type I N propeptide and C‑terminal telopeptide‑1) and tests of mechanical competence of the femur. In addition, the effects of low‑molecular weight fucoidan (LMWF) on in vitro cultured osteoclasts were examined, in order to determine the mechanisms underlying LMWF‑induced osteoclastic inhibition. In ovariectomized rats, LMWF increased femoral bone density. Micro‑CT scan also revealed that LMWF prevented microarchitectural deterioration and histomorphometric analysis determined that LMWF increased trabecular bone number and reduced the surface of bone resorption. In addition, LMWF reduced the high bone turnover rate, and improved the mechanical properties of the femur in ovariectomized rats. In vitro experiments revealed that LMWF inhibited the receptor activator of nuclear factor κB ligand (RANKL) and macrophage colony‑stimulating factor‑induced differentiation of RAW264.7 cells into tartrate‑resistant acid phosphatase (TRAP)‑positive osteoclasts, and reduced the bone resorption surface of the osteoclasts. Reverse transcription‑quantitative polymerase chain reaction demonstrated that LMWF inhibited mRNA expression of TRAP, matrix metallopeptidase‑9, nuclear activator of activated T‑cells 1, and osteoclast‑associated immunoglobulin‑like receptor, which are components of the signaling pathway for osteoclast differentiation. LMWF had no effect on RANK mRNA expression. In conclusion, the present study confirmed that LMWF inhibited osteoclast differentiation and bone resorption, and may be a potential treatment for osteoporosis in ovariectomized rats.

Low-level laser therapy stimulates bone metabolism and inhibits root resorption during tooth movement in a rodent model

This study evaluated the biological effects of low-level laser therapy (LLLT) on bone remodeling, tooth displacement and root resorption, occurred during the orthodontic tooth movement. Upper first molars of a total of sixty-eight male rats were subjected to orthodontic tooth movement and euthanized on days 3, 6, 9, 14 and 21 days and divided as negative control, control and LLLT group. Tooth displacement and histomorphometric analysis were performed in all animals; scanning electron microscopy analysis was done on days 3, 6 and 9, as well as the immunohistochemistry analysis of RANKL/OPG and TRAP markers. Volumetric changes in alveolar bone were analyzed using MicroCT images on days 14 and 21. LLLT influenced bone resorption by increasing the number of TRAP-positive osteoclasts and the RANKL expression at the compression side. This resulted in less alveolar bone and hyalinization areas on days 6, 9 and 14. LLLT also induced less bone volume and density, facilitating significant acceleration of tooth movement and potential reduction in root resorption besides stimulating bone formation at the tension side by enhancing OPG expression, increasing trabecular thickness and bone volume on day 21. Taken together, our results indicate that LLLT can stimulate bone remodeling reducing root resorption in a rat model. LLLT improves tooth movement via bone formation and bone resorption in a rat model.

Stiffened Extracellular Matrix and Signaling from Stromal Fibroblasts via Osteoprotegerin Regulate Tumor Cell Invasion in a 3-D Tumor in Situ Model

Several changes have been described in the stroma surrounding a tumor, including changes in cellular composition, altered extracellular matrix composition and organization, and increases in stiffness. Tumor cells are influenced by the composition, organization, and mechanical properties of the microenvironment, and by signals from stromal cells. Here we sought to test whether signaling from stromal fibroblasts and/or the small change in stiffness observed in vivo surrounding epithelial tumors regulates tumor cell invasion from a model of a tumor in situ. We generated a novel tumor in situ model system in which a tumor spheroid is encased within a collagen-IV containing membrane and further encased within a collagen-I matrix of in vivo stiffness with or without fibroblasts. Effects of the matrix, fibroblasts or fibroblast signals were determined by observing the invasion of tumor cells into the matrix. Effects of reciprocal tumor cell signaling upon fibroblasts were determined by observing markers of fibroblast activation. We found that a stiffened matrix led to increased dissemination of MDA-MB-231 cells from tumor spheroids when no fibroblasts were present and that MCF10A cells maintained a more normal organization with a stiffened matrix. The presence of fibroblasts, or fibroblast conditioned media, attenuated the effect upon MDA-MB-231 cells. We also observed an attenuation of fibroblast activation associated gene expression in the presence of MDA-MB-231 cells, with a paradoxical increase in activation associated contractile activity. Furthermore, we identified osteoprotegerin as a soluble factor released by fibroblasts in the stiffened environment that is key to the inhibition of cell invasion.

RANKL blockade prevents and treats aggressive osteosarcomas

Osteosarcoma (OS) is the most common primary bone cancer, which occurs primarily in children and adolescents, severely affecting survivors' quality of life. Despite its chemosensitivity and treatment advances, long-term survival rates for OS patients have stagnated over the last 20 years. Thus, it is necessary to develop new molecularly targeted therapies for this metastatic bone cancer. Mutations in TP53 and RB are linked to OS predisposition and to the evolution of spontaneous OS. We established receptor activator of nuclear factor κB ligand (RANKL) as a therapeutic target for suppression and prevention of OS. Combined conditional osteoblast-specific deletions of Rb, p53, and the protein kinase A (PKA) regulatory subunit Prkar1α genes in genetically engineered mouse models (GEMMs) generate aggressive osteosarcomas, characterized by PKA, RANKL, and osteoclast hyperactivity. Whole-body Rankl deletion completely abrogates tumorigenesis. Although osteoblastic Rank deletion has little effect, osteoclastic Rank deletion delays tumorigenesis and prolongs life span. The latter is associated with inactivation of osteoclastogenesis and up-regulation of the tumor suppressor phosphatase and tensin homolog (PTEN). Further, we use these GEMMs as preclinical platforms to show that RANKL blockade with RANK-Fc arrests tumor progression and improves survival and also inhibits lung metastasis. Moreover, preemptive administration of RANK-Fc completely prevents tumorigenesis in mice highly predisposed to this aggressive cancer. Denosumab, a fully human monoclonal antibody against RANKL, is currently used to treat patients with osteoporosis or bone metastases. Our studies provide a strong rationale to consider RANKL blockade for the treatment and prevention of aggressive RANKL-overexpressing OS in humans.

The adaptor protein insulin receptor substrate 2 inhibits alternative macrophage activation and allergic lung inflammation

Insulin receptor substrate 2 (IRS2) is an adaptor protein that becomes tyrosine-phosphorylated in response to the cytokines interleukin-4 (IL-4) and IL-13, which results in activation of the phosphoinositide 3-kinase (PI3K)-Akt pathway. IL-4 and IL-13 contribute to allergic lung inflammation. To examine the role of IRS2 in allergic disease, we evaluated the responses of IRS2-deficient (IRS2(-/-)) mice. Unexpectedly, loss of IRS2 resulted in a substantial increase in the expression of a subset of genes associated with the generation of alternatively activated macrophages (AAMs) in response to IL-4 or IL-13 in vitro. AAMs secrete factors that enhance allergic responses and promote airway remodeling. Moreover, compared to IRS2(+/+) mice, IRS2(+/-) and IRS2(-/-) mice developed enhanced pulmonary inflammation, accumulated eosinophils and AAMs, and exhibited airway and vascular remodeling upon allergen stimulation, responses that partially depended on macrophage-intrinsic IRS2 signaling. Both in unstimulated and IL-4-stimulated macrophages, lack of IRS2 enhanced phosphorylation of Akt and ribosomal S6 protein. Thus, we identified a critical inhibitory loop downstream of IRS2, demonstrating an unanticipated and previously unrecognized role for IRS2 in suppressing allergic lung inflammation and remodeling.

Plasmid DNA-coding p62 as a bone effective anti-inflammatory/anabolic agent

We recently reported that a DNA plasmid coding p62-SQSTM1 acts as an effective anti tumor vaccine against both transplantable mouse tumors and canine spontaneous mammary neoplasms. Here we report the unexpected finding that intramuscular delivery of p62 DNA exerts a powerful anti-osteoporotic activity in a mouse model of inflammatory bone loss (i.e, ovariectomy) by combining bone-sparing and osteo-synthetic effects. Notably, the suppression of osteoporosis by p62DNA was associated with a sharp down-regulation of master inflammatory cytokines, and up-regulation of endogenous p62 protein by bone-marrow stromal cells. The present data provide a solid rational to apply p62 DNA vaccine as a safe, new therapeutic for treatment of inflammatory related bone loss diseases.

Cytoplasmic hnRNPK interacts with GSK3β and is essential for the osteoclast differentiation

Osteoclast differentiation is a complex and finely regulated physiological process that involves a variety of signaling pathways and factors. Recent studies suggested that the Ser9 phosphorylation of Glycogen synthase kinase-3β (GSK3β) is required for the osteoclast differentiation. However, the precise underlying mechanism remains unclear. We have previously identified the heterogeneous nuclear ribonucleoprotein K (hnRNPK) as a putative GSK3β interactor. In the present study, we demonstrate that, during the RANKL-induced osteoclast differentiation, the PI3K/Akt-mediated Ser9 phosphorylation of GSK3β provokes the nuclear-cytoplasmic translocation of hnRNPK in an ERK-dependent manner, enhancing the cytoplasmic co-localization and interaction of GSK3β and hnRNPK. We show that hnRNPK is essential for the osteoclast differentiation, and is involved in several reported functions of GSK3β, including the activation of NF-κB, the expression of NFATc1, and the acetylation of tubulin, all known to be critical for osteoclast differentiation and functions. We find that hnRNPK is localized in the actin belt, and is important for the mature osteoclast formation. Taken together, we demonstrate here the critical role of hnRNPK in osteoclast differentiation, and depict a model in which the cytoplasmic hnRNPK interacts with GSK3β and regulates its function.

Pressuromodulation at the cell membrane as the basis for small molecule hormone and peptide regulation of cellular and nuclear function

Building on recent knowledge that the specificity of the biological interactions of small molecule hydrophiles and lipophiles across microvascular and epithelial barriers, and with cells, can be predicted on the basis of their conserved biophysical properties, and the knowledge that biological peptides are cell membrane impermeant, it has been further discussed herein that cellular, and thus, nuclear function, are primarily regulated by small molecule hormone and peptide/factor interactions at the cell membrane (CM) receptors. The means of regulating cellular, and thus, nuclear function, are the various forms of CM Pressuromodulation that exist, which include Direct CM Receptor-Mediated Stabilizing Pressuromodulation, sub-classified as Direct CM Receptor-Mediated Stabilizing Shift Pressuromodulation (Single, Dual or Tri) or Direct CM Receptor-Mediated Stabilizing Shift Pressuromodulation (Single, Dual or Tri) cum External Cationomodulation (≥3+ → 1+); which are with respect to acute CM receptor-stabilizing effects of small biomolecule hormones, growth factors or cytokines, and also include Indirect CM- or CM Receptor-Mediated Pressuromodulation, sub-classified as Indirect 1ary CM-Mediated Shift Pressuromodulation (Perturbomodulation), Indirect 2ary CM Receptor-Mediated Shift Pressuromodulation (Tri or Quad Receptor Internal Pseudo-Cationomodulation: SS 1+), Indirect 3ary CM Receptor-Mediated Shift Pressuromodulation (Single or Dual Receptor Endocytic External Cationomodulation: 2+) or Indirect (Pseudo) 3ary CM Receptor-Mediated Shift Pressuromodulation (Receptor Endocytic Hydroxylocarbonyloetheroylomodulation: 0), which are with respect to sub-acute CM receptor-stabilizing effects of small biomolecules, growth factors or cytokines. As a generalization, all forms of CM pressuromodulation decrease CM and nuclear membrane (NM) compliance (whole cell compliance), due to pressuromodulation of the intracellular microtubule network and increases the exocytosis of pre-synthesized vesicular endogolgi peptides and small molecules as well as nuclear-to-rough endoplasmic reticulum membrane proteins to the CM, with the potential to simultaneously increase the NM-associated chromatin DNA transcription of higher molecular weight protein forms, secretory and CM-destined, mitochondrial and nuclear, including the highest molecular weight nuclear proteins, Ki67 (359 kDa) and Separase (230 kDa), with the latter leading to mitogenesis and cell division; while, in the case of growth factors or cytokines with external cationomodulation capability, CM Receptor External Cationomodulation of CM receptors (≥3+ → 1+) results in cationic extracellular interaction (≥3+) with extracellular matrix heparan sulfates (≥3+ → 1+) concomitant with lamellopodesis and cell migration. It can be surmised that the modulation of cellular, and nuclear, function is mostly a reactive process, governed, primarily, by small molecule hormone and peptide interactions at the cell membrane, with CM receptors and the CM itself. These insights taken together, provide valuable translationally applicable knowledge.

Quantification of cell fusion events human breast cancer cells and breast epithelial cells using a Cre-LoxP-based double fluorescence reporter system

The biological phenomenon of cell fusion plays an important role in several physiological processes, like fertilization, placentation, or wound healing/tissue regeneration, as well as pathophysiological processes, such as cancer. Despite this fact, considerably less is still known about the factors and conditions that will induce the merging of two plasma membranes. Inflammation and proliferation has been suggested as a positive trigger for cell fusion, but it remains unclear, which of the factor(s) of the inflamed microenvironment are being involved. To clarify this we developed a reliable assay to quantify the in vitro fusion frequency of cells using a fluorescence double reporter vector (pFDR) containing a LoxP-flanked HcRed/DsRed expression cassette followed by an EGFP expression cassette. Because cell fusion has been implicated in cancer progression four human breast cancer cell lines were stably transfected with a pFDR vector and were co-cultured with the stably Cre-expressing human breast epithelial cell line. Cell fusion is associated with a Cre-mediated recombination resulting in induction of EGFP expression in hybrid cells, which can be quantified by flow cytometry. By testing a panel of different cytokines, chemokines, growth factors and other compounds, including exosomes, under normoxic and hypoxic conditions our data indicate that the proinflammatory cytokine TNF-α together with hypoxia is a strong inducer of cell fusion in human MDA-MB-435 and MDA-MB-231 breast cancer cells.

Loss of monocyte chemoattractant protein-1 alters macrophage polarization and reduces NFκB activation in the foreign body response

Implantation of biomaterials elicits a foreign body response characterized by fusion of macrophages to form foreign body giant cells and fibrotic encapsulation. Studies of the macrophage polarization involved in this response have suggested that alternative (M2) activation is associated with more favorable outcomes. Here we investigated this process in vivo by implanting mixed cellulose ester filters or polydimethylsiloxane disks in the peritoneal cavity of wild-type (WT) and monocyte chemoattractant protein-1 (MCP-1) knockout mice. We analyzed classical (M1) and alternative (M2) gene expression via quantitative polymerase chain reaction, immunohistochemistry and enzyme-linked immunosorbent assay in both non-adherent cells isolated by lavage and implant-adherent cells. Our results show that macrophages undergo unique activation that displays features of both M1 and M2 polarization including induction of tumor necrosis factor α (TNF), which induces the expression and nuclear translocation of p50 and RelA determined by immunofluorescence and Western blot. Both processes were compromised in fusion-deficient MCP-1 KO macrophages in vitro and in vivo. Furthermore, inclusion of BAY 11-7028, an inhibitor of NFκB activation, reduced nuclear translocation of RelA and fusion in WT macrophages. Our studies suggest that peritoneal implants elicit a unique macrophage polarization phenotype leading to induction of TNF and activation of the NFκB pathway.

Molecular Characterization of Macrophage-Biomaterial Interactions

Implantation of biomaterials in vascularized tissues elicits the sequential engagement of molecular and cellular elements that constitute the foreign body response. Initial events include the non-specific adsorption of proteins to the biomaterial surface that render it adhesive for cells such as neutrophils and macrophages. The latter undergo unique activation and in some cases undergo cell-cell fusion to form foreign body giant cells that contribute to implant damage and fibrotic encapsulation. In this review, we discuss the molecular events that contribute to macrophage activation and fusion with a focus on the role of the inflammasome, signaling pathways such as JAK/STAT and NF-κB, and the putative involvement of micro RNAs in the regulation of these processes.

In vitro and in silico analysis of an inhibitory mechanism of osteoclastogenesis by salubrinal and guanabenz

Inactivating bone-resorbing osteoclasts is a prime therapeutic strategy for the prevention of bone loss in patients with osteopenia and osteoporosis. Synthetic agents such as salubrinal and guanabenz, which attenuate stress to the endoplasmic reticulum, are reported to inhibit development of osteoclasts. However, the mechanism of their inhibitory action on osteoclasts is largely unknown. Using genome-wide expression profiles, we predicted key transcription factors that downregulated nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1), a master transcription factor for osteoclastogenesis. Principal component analysis (PCA) predicted a list of transcription factors that were potentially responsible for reversing receptor activator of nuclear factor kappa-B ligand (RANKL)-driven stimulation of osteoclastogenesis. A partial silencing of NFATc1 allowed a selection of transcription factors that were likely to be located upstream of NFATc1. We validated the predicted transcription factors by focusing on two AP-1 transcription factors (c-Fos and JunB) using RAW264.7 pre-osteoclasts as well as primary bone marrow cells. As predicted, their mRNA and protein levels were elevated by RANKL, and the elevation was suppressed by salubrinal and guanabenz. A partial silencing of c-Fos or JunB by RNA interference decreased NFATc1 as well as tartrate-resistant acid phosphatase (TRAP) mRNA. Collectively, a systems-biology approach allows the prediction of a RANKL-salubrinal/guanabenz-NFATc1 regulatory axis, and in vitro assays validate an involvement of AP-1 transcription factors in suppression of osteoclastogenesis.

Saliva Suppresses Osteoclastogenesis in Murine Bone Marrow Cultures

Saliva can reach mineralized surfaces in the oral cavity; however, the relationship between saliva and bone resorption is unclear. Herein, we examined whether saliva affects the process of osteoclastogenesis in vitro. We used murine bone marrow cultures to study osteoclast formation. The addition of fresh sterile saliva eliminated the formation of multinucleated cells that stained positive for tartrate-resistant acid phosphatase (TRAP). In line with the histochemical staining, saliva substantially reduced gene expression of cathepsin K, calcitonin receptor, and TRAP. Addition of saliva led to considerably decreased gene expression of receptor activator of nuclear factor kappa-B (RANK) and, to a lesser extent, that of c-fms. The respective master regulators of osteoclastogenesis (c-fos and NFATc1) and the downstream cell fusion genes (DC-STAMP and Atp6v0d2) showed decreased expression after the addition of saliva. Among the costimulatory molecules for osteoclastogenesis, only OSCAR showed decreased expression. In contrast, CD40, CD80, and CD86—all costimulatory molecules of phagocytic cells—were increasingly expressed with saliva. The phagocytic capacity of the cells was confirmed by latex bead ingestion. Based on these in vitro results, it can be concluded that saliva suppresses osteoclastogenesis and leads to the development of a phagocytic cell phenotype.

Activation of EPAC1/2 is essential for osteoclast formation by modulating NFκB nuclear translocation and actin cytoskeleton rearrangements

Bisphosphonates inhibit osteoclast differentiation/function via inhibition of Rap1A isoprenylation. As Rap1 is the effector of exchange protein directly activated by cAMP (EPAC) proteins, we determined the role of EPAC in osteoclast differentiation. We examined osteoclast differentiation as the number of primary murine/human bone-marrow precursors that differentiated into multinucleated TRAP-positive cells in the presence of EPAC-selective stimulus (8-pCTP-2'-O-Me-cAMP, 100 μM; 8-pCTP-2'-O-Me-cAMP-AM, 1 μM) or inhibitor brefeldin A (BFA), ESI-05, and ESI-09 (10 μM each). Rap1 activity was assessed, and signaling events, as well as differentiation in EPAC1/2-knockdown RAW264.7 cells, were studied. Direct EPAC1/2 stimulation significantly increased osteoclast differentiation, whereas EPAC1/2 inhibition diminished differentiation (113 ± 6%, P < 0.05, and 42 ± 10%, P < 0.001, of basal, respectively). Rap1 activation was maximal 15 min after RANKL stimulation (147 ± 9% of basal, P < 0.001), whereas silencing of EPAC1/2 diminished activated Rap1 (43 ± 13 and 20 ± 15% of control, P < 0.001) and NFkB nuclear translocation. TRAP-staining revealed no osteoclast differentiation in EPAC1/2-KO cells. Cathepsin K, NFATc1, and osteopontin mRNA expression decreased in EPAC1/2-KO cells when compared to control. RhoA, cdc42, Rac1, and FAK were activated in an EPAC1/2-dependent manner, and there was diminished cytoskeletal assembly in EPAC1/2-KO cells. In summary, EPAC1 and EPAC2 are critical signaling intermediates in osteoclast differentiation that permit RANKL-stimulated NFkB nuclear translocation and actin rearrangements. Targeting this signaling intermediate may diminish bone destruction in inflammatory arthritis.

A high-content imaging assay for the quantification of the Burkholderia pseudomallei induced multinucleated giant cell (MNGC) phenotype in murine macrophages

BACKGROUND

Burkholderia pseudomallei (Bp), a Gram-negative, motile, facultative intracellular bacterium is the causative agent of melioidosis in humans and animals. The Bp genome encodes a repertoire of virulence factors, including the cluster 3 type III secretion system (T3SS-3), the cluster 1 type VI secretion system (T6SS-1), and the intracellular motility protein BimA, that enable the pathogen to invade both phagocytic and non-phagocytic cells. A unique hallmark of Bp infection both in vitro and in vivo is its ability to induce cell-to-cell fusion of macrophages to form multinucleated giant cells (MNGCs), which to date are semi-quantitatively reported following visual inspection.

RESULTS

In this study we report the development of an automated high-content image acquisition and analysis assay to quantitate the Bp induced MNGC phenotype. Validation of the assay was performed using T6SS-1 (∆hcp1) and T3SS-3 (∆bsaZ) mutants of Bp that have been previously reported to exhibit defects in their ability to induce MNGCs. Finally, screening of a focused small molecule library identified several Histone Deacetylase (HDAC) inhibitors that inhibited Bp-induced MNGC formation of macrophages.

CONCLUSIONS

We have successfully developed an automated HCI assay to quantitate MNGCs induced by Bp in macrophages. This assay was then used to characterize the phenotype of the Bp mutants for their ability to induce MNGC formation and identify small molecules that interfere with this process. Successful application of chemical genetics and functional reverse genetics siRNA approaches in the MNGC assay will help gain a better understanding of the molecular targets and cellular mechanisms responsible for the MNGC phenotype induced by Bp, by other bacteria such as Mycobacterium tuberculosis, or by exogenously added cytokines.

Mechanosignaling in bone health, trauma and inflammation

SIGNIFICANCE

Mechanosignaling is vital for maintaining the structural integrity of bone under physiologic conditions. These signals activate and suppress multiple signaling cascades regulating bone formation and resorption. Understanding these pathways is of prime importance to exploit their therapeutic potential in disorders associated with bone loss due to disuse, trauma, or disruption of homeostatic mechanisms.

RECENT ADVANCES

In the case of cells of the bone, an impressive amount of data has been generated that provides evidence of a complex mechanism by which mechanical signals can maintain or disrupt cellular homeostasis by driving transcriptional regulation of growth factors, matrix proteins and inflammatory mediators in health and inflammation. Mechanical signals act on cells in a magnitude dependent manner to induce bone deposition or resorption. During health, physiological levels of these signals are essential for maintaining bone strength and architecture, whereas during inflammation, similar signals can curb inflammation by suppressing the nuclear factor kappa B (NF-κB) signaling cascade, while upregulating matrix synthesis via mothers against decapentaplegic homolog and/or Wnt signaling cascades. Contrarily, excessive mechanical forces can induce inflammation via activation of the NF-κB signaling cascade.

CRITICAL ISSUES

Given the osteogenic potential of mechanical signals, it is imperative to exploit their therapeutic efficacy for the treatment of bone disorders. Here we review select signaling pathways and mediators stimulated by mechanical signals to modulate the strength and integrity of the bone.

FUTURE DIRECTIONS

Understanding the mechanisms of mechanotransduction and its effects on bone lay the groundwork for development of nonpharmacologic mechanostimulatory approaches for osteodegenerative diseases and optimal bone health.

The impact of anti-inflammatory cytokines on the pancreatic β-cell

Considerable efforts have been invested to understand the mechanisms by which pro-inflammatory cytokines mediate the demise of β-cells in type 1 diabetes but much less attention has been paid to the role of anti-inflammatory cytokines as potential cytoprotective agents in these cells. Despite this, there is increasing evidence that anti-inflammatory molecules such as interleukin (IL)-4, IL-10 and IL-13 can exert a direct influence of β-cell function and viability and that the circulating levels of these cytokines may be reduced in type 1 diabetes. Thus, it seems possible that targeting of anti-inflammatory pathways might offer therapeutic potential in this disease. In the present review, we consider the evidence implicating IL-4, IL-10 and IL-13 as cytoprotective agents in the β-cell and discuss the receptor components and downstream signaling pathways that mediate these effects.

Friend or foe: emerging role of nuclear factor kappa-light-chain-enhancer of activated B cells in cell senescence

The nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) proteins are a family of ubiquitously expressed transcription factors that regulate the response to cellular stress. They mediate innate and adaptive immunity through the initiation of an inflammatory response to pro-inflammatory signals. The role of persistent inflammation in aiding tumor development has led to the NF-κB family of transcription factors being strongly implicated in promoting cancer. However, recent studies have now revealed that NF-κB can also function as a tumor suppressor through the induction of cellular senescence. Cellular senescence is a stable cell cycle arrest that normal cells undergo in response to a variety of intrinsic and extrinsic stimuli including: progressive telomere shortening, changes in telomeric structure, or other forms of genotoxic stress. Senescence can compromise tissue repair and regeneration, contributing to tissue and organismal aging via the accumulation of senescent cells, depletion of stem/progenitor cells and secretion of an array of inflammatory cytokines, chemokines, and matrix metalloproteinases. Senescence can also lead to the removal of potentially cancerous cells, thereby acting as a potent tumor suppressor mechanism. Herein, we review the evidence indicating a role for NF-κB in tumor suppression via cellular senescence and suggest that depending upon the subunit expressed, the biological context, and the type and intensity of the signal, NF-κB can indeed promote senescence growth arrest.

Genetic basis of cell-cell fusion mechanisms

Cell-cell fusion in sexually reproducing organisms is a mechanism to merge gamete genomes and, in multicellular organisms, it is a strategy to sculpt organs, such as muscle, bone, and placenta. Moreover, this mechanism has been implicated in pathological conditions, such as infection and cancer. Studies of genetic model organisms have uncovered a unifying principle: cell fusion is a genetically programmed process. This process can be divided in three stages: competence (cell induction and differentiation); commitment (cell determination, migration, and adhesion); and cell fusion (membrane merging and cytoplasmic mixing). Recent work has led to the discovery of fusogens, which are cell fusion proteins that are necessary and sufficient to fuse cell membranes. Two unrelated families of fusogens have been discovered, one in mouse placenta and one in Caenorhabditis elegans (syncytins and F proteins, respectively). Current research aims to identify new fusogens and determine the mechanisms by which they merge membranes.

Genetic programs expressed in resting and IL-4 alternatively activated mouse and human macrophages: similarities and differences

The molecular repertoire of macrophages in health and disease can provide novel biomarkers for diagnosis, prognosis, and treatment. Th2-IL-4–activated macrophages (M2) have been associated with important diseases in mice, yet no specific markers are available for their detection in human tissues. Although mouse models are widely used for macrophage research, translation to the human can be problematic and the human macrophage system remains poorly described. In the present study, we analyzed and compared the transcriptome and proteome of human and murine macrophages under resting conditions (M0) and after IL-4 activation (M2). We provide a resource for tools enabling macrophage detection in human tissues by identifying a set of 87 macrophage-related genes. Furthermore, we extend current understanding of M2 activation in different species and identify Transglutaminase 2 as a conserved M2 marker that is highly expressed by human macrophages and monocytes in the prototypic Th2 pathology asthma.

Interleukin-4-induced β-catenin regulates the conversion of macrophages to multinucleated giant cells

The cytokine interleukin-4 (IL-4) exerts pleiotropic effects on macrophages as it plays a key role in the immune response to infectious agents, allergens, and vaccines. Macrophages exposed to IL-4 drastically change their gene expression and metabolic state to adjust to new functional requirements. IL-4 also induces macrophages to fuse together and form multinucleated giant cells (MGCs). MGC formation is associated with chronic inflammation resulting from persistence of pathogenic microorganisms or foreign materials in tissues. Very little is known, however, about the mechanisms regulating IL-4-induced macrophage-to-MGC conversion. We observed a dramatic increase in β-catenin protein but not mRNA amount in mouse macrophages following exposure to IL-4. To investigate the role of β-catenin in macrophages, we generated mice with a myeloid cell-specific deletion of the β-catenin gene. Ablation of β-catenin expression did not affect the viability of macrophages or impair expression of known IL-4-inducible genes. Intriguingly, β-catenin-deficient macrophages incubated with IL-4 formed MGCs with markedly greater efficiency than wild-type macrophages. Similar increases in multinucleated cell formation were detected in the peritoneal cavity of myeloid cell-specific β-catenin knockout mice injected with chitin, which is known to induce endogenous IL-4 production. Our findings reveal β-catenin as a novel regulator of macrophage responses to IL-4, and suggest that therapeutic modulation of its expression or function may help enhance the effectiveness or ameliorate the pathology of IL-4-driven immune responses.

Osteoclast fusion and regulation by RANKL-dependent and independent factors

Osteoclasts are the bone resorbing cells essential for bone remodeling. Osteoclasts are formed from hematopoietic progenitors in the monocyte/macrophage lineage. Osteoclastogenesis is composed of several steps including progenitor survival, differentiation to mono-nuclear pre-osteoclasts, fusion to multi-nuclear mature osteoclasts, and activation to bone resorbing osteoclasts. The regulation of osteoclastogenesis has been extensively studied, in which the receptor activator of NF-κB ligand (RANKL)-mediated signaling pathway and downstream transcription factors play essential roles. However, less is known about osteoclast fusion, which is a property of mature osteoclasts and is required for osteoclasts to resorb bone. Several proteins that affect cell fusion have been identified. Among them, dendritic cell-specific transmembrane protein (DC-STAMP) is directly associated to osteoclast fusion in vivo. Cytokines and factors influence osteoclast fusion through regulation of DC-STAMP. Here we review the recently discovered new factors that regulate osteoclast fusion with specific focus on DC-STAMP. A better understanding of the mechanistic basis of osteoclast fusion will lead to the development of a new therapeutic strategy for bone disorders due to elevated osteoclast bone resorption. Cell-cell fusion is essential for a variety of cellular biological processes. In mammals, there is a limited number of cell types that fuse to form multinucleated cells, such as the fusion of myoblasts for the formation of skeletal muscle and the fusion of cells of the monocyte/macrophage lineage for the formation of multinucleated osteoclasts and giant cells. In most cases, cell-cell fusion is beneficial for cells by enhancing function. Myoblast fusion increases myofiber size and diameter and thereby increases contractile strength. Multinucleated osteoclasts have far more bone resorbing activity than their mono-nuclear counterparts. Multinucleated giant cells are much more efficient in the removal of implanted materials and bacteria due to chronic infection than macrophages. Therefore, they are also called foreign-body giant cells. Cell fusion is a complicated process involving cell migration, chemotaxis, cell-cell recognition and attachment, as well as changes into a fusion-competent status. All of these steps are regulated by multiple factors. In this review, we will discuss osteoclast fusion and regulation.

Pathways for bone loss in inflammatory disease

Chronic inflammation including autoimmune disease is an important risk factor for the development of osteoporosis. Receptor activator of nuclear factor-κB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF) play a central role in osteoclast differentiation and function, and the molecular pathways by which M-CSF and RANKL induce osteoclast differentiation have been analyzed in detail. Proinflammatory cytokines directly or indirectly regulate osteoclastogenesis and bone resorption providing a link between inflammation and osteoporosis. Tumor necrosis factor-α, interleukin (IL)-1, IL-6, and IL-17 are the most important proinflammatory cytokines triggering inflammatory bone loss. Inhibition of these cytokines has provided potent therapeutic effects in the treatment of diseases such as rheumatoid arthritis. Further investigation is needed to understand the pathophysiology and to develop new strategies to treat inflammatory bone loss. This review summarizes new data on inflammatory bone loss obtained in 2011.