The inhibitory effect of interleukin-10 on mouse osteoclast formation involves novel tyrosine-phosphorylated proteins

Megakaryocyte Secreted Factors Regulate Bone Marrow Niche Cells During Skeletal Homeostasis, Aging, and Disease

The bone marrow microenvironment contains a diverse array of cell types under extensive regulatory control and provides for a novel and complex mechanism for bone regulation. Megakaryocytes (MKs) are one such cell type that potentially acts as a master regulator of the bone marrow microenvironment due to its effects on hematopoiesis, osteoblastogenesis, and osteoclastogenesis. While several of these processes are induced/inhibited through MK secreted factors, others are primarily regulated by direct cell-cell contact. Notably, the regulatory effects that MKs exert on these different cell populations has been found to change with aging and disease states. Overall, MKs are a critical component of the bone marrow that should be considered when examining regulation of the skeletal microenvironment. An increased understanding of the role of MKs in these physiological processes may provide insight into novel therapies that can be used to target specific pathways important in hematopoietic and skeletal disorders.

Regulation of differentiation and generation of osteoclasts in rheumatoid arthritis

INTRODUCTION

Rheumatoid arthritis (RA), which affects nearly 1% of the world's population, is a debilitating autoimmune disease. Bone erosion caused by periarticular osteopenia and synovial pannus formation is the most destructive pathological changes of RA, also leads to joint deformity and loss of function,and ultimately affects the quality of life of patients. Osteoclasts (OCs) are the only known bone resorption cells and their abnormal differentiation and production play an important role in the occurrence and development of RA bone destruction; this remains the main culprit behind RA.

METHOD

Based on the latest published literature and research progress at home and abroad, this paper reviews the abnormal regulation mechanism of OC generation and differentiation in RA and the possible targeted therapy.

RESULT

OC-mediated bone destruction is achieved through the regulation of a variety of cytokines and cell-to-cell interactions, including gene transcription, epigenetics and environmental factors. At present, most methods for the treatment of RA are based on the regulation of inflammation, the inhibition of bone injury and joint deformities remains unexplored.

DISCUSSION

This article will review the mechanism of abnormal differentiation of OC in RA, and summarise the current treatment oftargeting cytokines in the process of OC generation and differentiation to reduce bone destruction in patients with RA, which isexpected to become a valuable treatment choice to inhibit bone destruction in RA.

Cytokine-mediated immunomodulation of osteoclastogenesis

Cytokines are an important set of proteins regulating bone homeostasis. In inflammation induced bone resorption, cytokines, such as RANKL, TNF-α, M-CSF, are indispensable for the differentiation and activation of resorption-driving osteoclasts, the process we know as osteoclastogenesis. On the other hand, immune system produces a number of regulatory cytokines, including IL-4, IL-10 and IFNs, and limits excessive activation of osteoclastogenesis and bone loss during inflammation. These unique properties make cytokines powerful targets as rheostat to maintain bone homeostasis and for potential immunotherapies of inflammatory bone diseases. In this review, we summarize recent advances in cytokine-mediated regulation of osteoclastogenesis and provide insights of potential translational impact of bench-side research into clinical treatment of bone disease.

Liquefied Microcapsules Compartmentalizing Macrophages and Umbilical Cord-Derived Cells for Bone Tissue Engineering

Extraordinary capabilities underlie the potential use of immune cells, particularly macrophages, in bone tissue engineering. Indeed, the depletion of macrophages during bone repair often culminates in disease scenarios. Inspired by the native dynamics between immune and skeletal systems, this work proposes a straightforward in vitro method to bioengineer biomimetic bone niches using biological waste. For that, liquefied and semipermeable reservoirs generated by electrohydrodynamic atomization and layer-by-layer techniques are developed to coculture umbilical cord-derived human cells, namely monocyte-derived macrophages, mesenchymal-derived stromal cells (MSCs), and human umbilical vein endothelial cells (HUVECs). Poly(ε-caprolactone) microparticles are also added to the liquefied core to act as cell carriers. The fabricated microcapsules grant the successful development of viable microtissues, ensuring the high diffusion of bioactive factors. Interestingly, macrophages within the bioengineered microcapsules increase the release of osteocalcin, osteoprotegerin, and vascular endothelial growth factor. The cytokines profile variation indicates macrophages' polarization into a prohealing phenotype. Altogether, the incorporation of macrophages within the fabricated microcapsules allows to recreate an appropriate bone microenvironment for developing new bone mineralized microtissues. The proposed bioencapsulation protocol is a powerful self-regulated system, which might find great applicability in bone tissue engineering based on bottom-up approaches or disease modeling.

Effect of TNF-α and IL-6 on Compact Bone-Derived Cells

BACKGROUND

Although bone tissue engineering has already been applied clinically, its regeneration efficacy is not always sufficient. Local inflammatory cytokines are considered as the major factors that induce apoptosis of transplanted cells, thus leading to insufficient new bone formation. In this study, we focused on the effects of interleukin (IL)-6 and tumor necrosis factor-alpha (TNF-α) on differentiation and apoptosis of compact bone-derived cells (CBDCs).

METHODS

CBDCs were obtained from mouse legs and cultured. The effects of TNF-α and/or IL-6 on the osteogenic differentiation and apoptosis of CBDCs were analyzed in vitro. To confirm the expression of local inflammatory cytokines in vivo, CBDCs were transplanted to the back of immunocompetent mice.

RESULTS

IL-6 exerted inconsistent effects on the expression of the different osteogenic markers tested, while significantly upregulating Fas. By contrast, the addition of TNF-α dramatically reduced the expression of all tested osteogenic markers and increased Fas expression. The highest dose of IL-6 could partially reverse the repressive effect of TNF-α, while the addition of IL-6 further increased Fas expression in CBDCs compared to TNF-α alone. The results from in vivo experiments showed the presence of transplants with and without new bone formation. The transplants without bone formation were characterized by higher IL-6 and lower IL-10 expression than those with bone formation, while the expression of TNF-α did not show notable difference.

CONCLUSION

The results of this study suggest an important role for IL-6 in modulating the efficacy of bone tissue engineering, which can affect osteogenic cells both positively and negatively.

Potency of Bone Marrow-Derived Mesenchymal Stem Cells and Indomethacin in Complete Freund's Adjuvant-Induced Arthritic Rats: Roles of TNF-α, IL-10, iNOS, MMP-9, and TGF-β1

Rheumatoid arthritis (RA) is an autoimmune syndrome affecting joint spaces, leading to the disabled state. Currently, there is no optimal therapy for RA except for systemic immunosuppressants that have variable undesirable effects after long-term use. Hence, the need for other treatment modalities has emerged in an attempt to develop a treating agent that is effective but without bad effects. Bone marrow-derived mesenchymal stem cells (BM-MSCs) may be an alternative medicine since they may differentiate into a variety of mesenchymal tissues including bone and cartilage. Indomethacin (IMC) could be suggested as an analgesic, anti-inflammatory, and antirheumatic potential agent against the course of RA since it possesses significant palliative effects and antipyretic properties. Therefore, our target of this study was to explore and compare the effect of BM-MSCs (1 × 10⁶ cells/rat at the 1^st, 6^th, 12^th, and 18^th days) and IMC (2 mg/kg b.w./day for 3 weeks) either alone or in combination on arthritic rats. The model of rheumatoid arthritis in rats was induced by subcutaneous injection of 0.1 mL/rat CFA into the footpad of the right hind paw. The BM-MSC intravenous injection and IMC oral administration significantly reduced the elevated right hind leg paw diameter and circumference, serum anti-CCP, and ankle joint articular tissue expressions of TNF-α, iNOS, MMP-9, and TGF-β1 while they significantly increased the lowered articular IL-10 expression in CFA-induced arthritic rats. The combinatory effect of the two treatments was the most potent. In conclusion, the treatment of RA with BM-MSCs and IMC together is more effective than the treatment with either BM-MSCs or IMC. The Th1 cytokine (TNF-α), Th2 cytokine (IL-10), iNOS, MMP-9, and TGF-β1 are important targets for mediating the antiarthritic effects of BM-MSCs and IMC in CFA-induced arthritis in rats.

Erythromyeloid progenitors give rise to a population of osteoclasts that contribute to bone homeostasis and repair

Osteoclasts are multinucleated cells of the monocyte/macrophage lineage that degrade bone. Here, we used lineage tracing studies-labelling cells expressing Cx3cr1, Csf1r or Flt3-to identify the precursors of osteoclasts in mice. We identified an erythromyeloid progenitor (EMP)-derived osteoclast precursor population. Yolk-sac macrophages of EMP origin produced neonatal osteoclasts that can create a space for postnatal bone marrow haematopoiesis. Furthermore, EMPs gave rise to long-lasting osteoclast precursors that contributed to postnatal bone remodelling in both physiological and pathological settings. Our single-cell RNA-sequencing data showed that EMP-derived osteoclast precursors arose independently of the haematopoietic stem cell (HSC) lineage and the data from fate tracking of EMP and HSC lineages indicated the possibility of cell-cell fusion between these two lineages. Cx3cr1⁺ yolk-sac macrophage descendants resided in the adult spleen, and parabiosis experiments showed that these cells migrated through the bloodstream to the remodelled bone after injury.

Cytokines and Bone: Osteoimmunology

Cytokines and hematopoietic growth factors have traditionally been thought of as regulators of the development and function of immune and blood cells. However, an ever-expanding number of these factors have been discovered to have major effects on bone cells and the development of the skeleton in health and disease (Table 1). In addition, several cytokines have been directly linked to the development of osteoporosis in both animal models and in patients. In order to understand the mechanisms regulating bone cells and how this may be dysregulated in disease states, it is necessary to appreciate the diverse effects that cytokines and inflammation have on osteoblasts, osteoclasts, and bone mass. This chapter provides a broad overview of this topic with extensive references so that, if desired, readers can access specific references to delve into individual topics in greater detail.

Beneficial effects of Lactobacillus reuteri 6475 on bone density in male mice is dependent on lymphocytes

Oral treatment with probiotic bacteria has been shown to prevent bone loss in multiple models of osteoporosis. In previous studies we demonstrated that oral administration of Lactobacillus reuteri in healthy male mice increases bone density. The host and bacterial mechanisms of these effects however are not well understood. The objective of this study was to understand the role of lymphocytes in mediating the beneficial effects of L. reuteri on bone health in male mice. We administered L. reuteri in drinking water for 4 weeks to wild type or Rag knockout (lack mature T and B lymphocytes) male mice. While L. reuteri treatment increased bone density in wild type, no significant increases were seen in Rag knockout mice, suggesting that lymphocytes are critical for mediating the beneficial effects of L. reuteri on bone density. To understand the effect of L. reuteri on lymphocytes in the intestinal tissues, we isolated mesenteric lymph node (MLN) from naïve wild type mice. In ex vivo studies using whole mesenteric lymph node (MLN) as well as CD3+ T-cells, we demonstrate that live L. reuteri and its secreted factors have concentration-dependent effects on the expression of cytokines, including anti-inflammatory cytokine IL-10. Fractionation studies identified that the active component of L. reuteri is likely water soluble and small in size (<3 kDa) and its effects on lymphocytes are negatively regulated by a RIP2 inhibitor, suggesting a role for NOD signaling. Finally, we show that T-cells from MLNs treated with L. reuteri supernatants, secrete factors that enhance osterix (transcription factor involved in osteoblast differentiation) expression in MC3T3-E1 osteoblasts. Together, these data suggest that L. reuteri secreted factors regulate T-lymphocytes which play an important role in mediating the beneficial effects of L. reuteri on bone density.

Loss of interleukin-10 exacerbates early Type-1 diabetes-induced bone loss

Type-1 diabetes (T1D) increases systemic inflammation, bone loss, and risk for bone fractures. Levels of the anti-inflammatory cytokine interleukin-10 (IL-10) are decreased in T1D, however their role in T1D-induced osteoporosis is unknown. To address this, diabetes was induced in male IL-10 knockout (KO) and wild-type (WT) mice. Analyses of femur and vertebral trabecular bone volume fraction identified bone loss in T1D-WT mice at 4 and 12 weeks, which in T1D-IL-10-KO mice was further reduced at 4 weeks but not 12 weeks. IL-10 deficiency also increased the negative effects of T1D on cortical bone. Osteoblast marker osterix was decreased, while osteoclast markers were unchanged, suggesting that IL-10 promotes anabolic processes. MC3T3-E1 osteoblasts cultured under high glucose conditions displayed a decrease in osterix which was prevented by addition of IL-10. Taken together, our results suggest that IL-10 is important for promoting osteoblast maturation and reducing bone loss during early stages of T1D.

Notch3 promotes prostate cancer-induced bone lesion development via MMP-3

Prostate cancer metastases primarily localize in the bone where they induce a unique osteoblastic response. Elevated Notch activity is associated with high-grade disease and metastasis. To address how Notch affects prostate cancer bone lesions, we manipulated Notch expression in mouse tibia xenografts and monitored tumor growth, lesion phenotype, and the bone microenvironment. Prostate cancer cell lines that induce mixed osteoblastic lesions in bone expressed 5–6 times more Notch3, than tumor cells that produce osteolytic lesions. Expression of active Notch3 (NICD3) in osteolytic tumors reduced osteolytic lesion area and enhanced osteoblastogenesis, while loss of Notch3 in osteoblastic tumors enhanced osteolytic lesion area and decreased osteoblastogensis. This was accompanied by a respective decrease and increase in the number of active osteoclasts and osteoblasts at the tumor-bone interface, without any effect on tumor proliferation. Conditioned medium from NICD3-expressing cells enhanced osteoblast differentiation and proliferation in vitro, while simultaneously inhibiting osteoclastogenesis. MMP-3 was specifically elevated and secreted by NICD3-expressing tumors, and inhibition of MMP-3 rescued the NICD3-induced osteoblastic phenotypes. Clinical osteoblastic bone metastasis samples had higher levels of Notch3 and MMP-3 compared to patient matched visceral metastases or osteolytic metastasis samples. We identified a Notch3-MMP-3 axis in human prostate cancer bone metastases that contributes to osteoblastic lesion formation by blocking osteoclast differentiation, while also contributing to osteoblastogenesis. These studies define a new role for Notch3 in manipulating the tumor microenvironment in bone metastases.

Immune Function and Diversity of Osteoclasts in Normal and Pathological Conditions

Osteoclasts (OCLs) are key players in controlling bone remodeling. Modifications in their differentiation or bone resorbing activity are associated with a number of pathologies ranging from osteopetrosis to osteoporosis, chronic inflammation and cancer, that are all characterized by immunological alterations. Therefore, the 2000s were marked by the emergence of osteoimmunology and by a growing number of studies focused on the control of OCL differentiation and function by the immune system. At the same time, it was discovered that OCLs are much more than bone resorbing cells. As monocytic lineage-derived cells, they belong to a family of cells that displays a wide heterogeneity and plasticity and that is involved in phagocytosis and innate immune responses. However, while OCLs have been extensively studied for their bone resorption capacity, their implication as immune cells was neglected for a long time. In recent years, new evidence pointed out that OCLs play important roles in the modulation of immune responses toward immune suppression or inflammation. They unlocked their capacity to modulate T cell activation, to efficiently process and present antigens as well as their ability to activate T cell responses in an antigen-dependent manner. Moreover, similar to other monocytic lineage cells such as macrophages, monocytes and dendritic cells, OCLs display a phenotypic and functional plasticity participating to their anti-inflammatory or pro-inflammatory effect depending on their cell origin and environment. This review will address this novel vision of the OCL, not only as a phagocyte specialized in bone resorption, but also as innate immune cell participating in the control of immune responses.

Systemic and local effects of radiotherapy: an experimental study on implants placed in rats

OBJECTIVES

Evaluate the modulating effect of ionizing radiation, blood cytokine levels, and bone remodeling of the interface around the implant to understand the radiation mechanisms which can impair the implants receptor site.

MATERIAL AND METHODS

Sixty rats were submitted to grade V titanium implants in the femurs and were divided into the following groups: no-irradiation (N-Ir): control group with implant only; early-irradiation (E-Ir): implant + irradiation after 24 h; late-irradiation (L-Ir): implant + irradiation after 4 weeks; and previous-irradiation (P-Ir): irradiation + implant after 4 weeks. The animals in the E-Ir, L-Ir, and P-Ir groups were irradiated in two fractional stages of 15 Gy. At 3 days, 2 weeks, and 7 weeks after the final procedure, five animals were randomly euthanized per group. Serum levels of TNF-ɑ, IL-1β, TGF-β, IL-6, M-CSF, and IL-10 were measured from blood collected prior to euthanasia using the ELISA test. The pieces containing the implants were subjected to immunohistochemical labeling using the tartrate acid resistant to phosphatase, osteocalcin, and caspase-3 markers and mCT. The ANOVA test was used for statistical analysis, and the Tukey multiple comparison test (p < 0.05) was applied.

RESULTS

The results indicated that ionizing radiation modifies the production of pro- and anti-inflammatory serum cytokines, the expression of proteins involved in bone remodeling and cellular apoptosis, as well as changes in bone formation.

CONCLUSIONS

The results suggests that a longer period between radiotherapy and implant placement surgery when irradiation occurs prior to implant installation would allow the recovery and renewal of bone cells and avoid future failures in osseointegration.

CLINICAL RELEVANCE

The search for modifications caused by ionizing irradiation in bone tissue can indicate the ideal period for implant placement without affecting the osseointegration process.

The relationship between T-helper cell polarization and the RANKL/OPG ratio in gingival tissues from chronic periodontitis patients

This study aimed to investigate the relationship between inflammation‐related T‐helper cell polarization and the receptor activator for nuclear factor‐κB ligand (RANKL)/osteoprotegerin (OPG) ratio, which is associated with bone resorption or remodeling of chronic periodontitis patients. Gingival crevicular fluid (GCF) and gingival tissues were obtained from periodontally healthy individuals (PH group) and chronic periodontitis patients (CP group). The GCF levels of IFN‐γ, IL‐4, IL‐17, and IL‐10 linked to T‐helper cell polarization toward the Th1, Th2, Th17, and Treg phenotypes, respectively, were determined by ELISA. The expression levels of these cytokines and the polarized T‐helper cells in gingival tissues were assessed through immunohistochemical and immunofluorescence assays. In addition, the RANKL and OPG expression levels in gingival tissues were detected by immunohistochemical assays, and linear regression analysis was used to identify the potential relationship between T‐helper cell polarization and the RANKL/OPG ratio. In total, 22 individuals and 35 patients were enrolled in the present study. In both GCF and gingival tissues, increased levels of IL‐17 and the decreased levels of IL‐4 and IL‐10 were observed in the CP group. When polarized T‐helper cells were identified in gingival tissues, more Th1 and Th17 cells were found in the CP group, whereas more Th2 and Treg cells were found in the PH group. Although there was no significant difference in OPG expression between the two groups, the RANKL/OPG ratio in the CP group was higher than that in the PH group. The linear regression analysis showed that the presence of more Th1 and Th17 cells correlated with a higher RANKL/OPG ratio, whereas the presence of more Th2 cells correlated with a lower RANKL/OPG ratio. Th1 and Th17 cells are positively correlated and Th2 cells are negatively correlated with the RANKL/OPG ratio. Our data suggest that T‐helper cell polarization is closely linked to the RANKL/OPG ratio in gingival tissues from chronic periodontitis patients.

Interferon-Gamma-Mediated Osteoimmunology

Osteoimmunology is the interdiscipline that focuses on the relationship between the skeletal and immune systems. They are interconnected by shared signal pathways and cytokines. Interferon-gamma (IFN-γ) plays important roles in immune responses and bone metabolism. IFN-γ enhances macrophage activation and antigen presentation. It regulates antiviral and antibacterial immunity as well as signal transduction. IFN-γ can promote osteoblast differentiation and inhibit bone marrow adipocyte formation. IFN-γ plays dual role in osteoclasts depending on its stage. Furthermore, IFN-γ is an important pathogenetic factor in some immune-mediated bone diseases including rheumatoid arthritis, postmenopausal osteoporosis, and acquired immunodeficiency syndrome. This review will discuss the contradictory findings of IFN-γ in osteoimmunology and its clinical application potential.

The enigmatic role of IL-38 in inflammatory diseases

IL-38 is the most recently discovered cytokine of the IL-1 family and is considered a potential inhibitor of the IL-1 and Toll-like receptor families. IL-38 exerts anti-inflammatory properties, especially on macrophages, by inhibiting secretion of pro-inflammatory cytokines, leading to reduced T-lymphocyte TH17 maturation. IL-38 has been studied most extensively in the context of chronic inflammatory diseases, particularly arthritis, where it is considered an attractive new drug candidate. IL-38 research has entered a new phase, with the realization that IL-38 is important in the pathophysiology of TH17 dependent-diseases (psoriasis, psoriatic arthritis and ankylosing spondylitis). In this review, we provide a critical evaluation of several controversial issues concerning IL-38 function and regulation. There is effectively contrasting data regarding IL-38: it is produced in conditions such as apoptosis, necrosis or inflammation, but data is lacking regarding IL-38 processing and biological function. Furthermore, the receptor for IL-38 has yet to be identified, although three candidate receptors - IL-1R1, IL-36R and IL-1RAPL1-have been proposed. Future studies will hopefully uncover new aspects of this enigmatic cytokine.

Nanotopography-based strategy for the precise manipulation of osteoimmunomodulation in bone regeneration

Immune cells play vital roles in regulating bone dynamics. Successful bone regeneration requires a favourable osteo-immune environment. The high plasticity and diversity of immune cells make it possible to manipulate the osteo-immune response of immune cells, thus modulating the osteoimmune environment and regulating bone regeneration. With the advancement in nanotechnology, nanotopographies with different controlled surface properties can be fabricated. On tuning the surface properties, the osteo-immune response can be precisely modulated. This highly tunable characteristic and immunomodulatory effects make nanotopography a promising strategy to precisely manipulate osteoimmunomdulation for bone tissue engineering applications. This review first summarises the effects of the immune response during bone healing to show the importance of regulating the immune response for the bone response. The plasticity of immune cells is then reviewed to provide rationales for manipulation of the osteoimmune response. Subsequently, we highlight the current types of nanotopographies applied in bone biomaterials and their fabrication techniques, and explain how these nanotopographies modulate the immune response and the possible underlying mechanisms. The effects of immune cells on nanotopography-mediated osteogenesis are emphasized, and we propose the concept of "nano-osteoimmunomodulation" to provide a valuable strategy for the development of nanotopographies with osteoimmunomodulatory properties that can precisely regulate bone dynamics.

IL-38 overexpression induces anti-inflammatory effects in mice arthritis models and in human macrophages in vitro

OBJECTIVES

Interleukin (IL)-38 is a newly characterised cytokine that belongs to the IL-1 family. This cytokine is expressed in the rheumatoid arthritis (RA) synovial tissue and IL-38 deficient mice have exacerbated arthritis. Here, we analysed the effect of IL-38 overexpression in the joints of arthritic mice, in human macrophages and synovial fibroblasts in vitro.

METHODS

Articular injections of an adeno-associated virus (AAV) 2/8 encoding IL-38 were performed in collagen-induced arthritis (CIA), K/BxN serum transfer-induced arthritis (STIA) and antigen-induced arthritis (AIA) in mice. The effect of IL-38 overexpression was evaluated through clinical scores, immunohistochemistry, microCT, Luminex and RT-qPCR analysis. THP-1 macrophages were transduced with a lentiviral vector to overexpress IL-38.

RESULTS

Clinical inflammatory scores were significantly decreased after AAV IL-38 injection in joints of mice with CIA and STIA, but not AIA. This decrease was accompanied by reduced macrophage infiltration and a decreased expression of Th17 cytokines (IL-17, IL-23, IL-22) and TNFα. However, IL-38 overexpression had no effect on cartilage or bone destruction. In vitro, the THP-1 monocytic cell line expressed less IL-6, TNFα and IL-23 after IL-38 overexpression. Conditioned media from these cells, containing released IL-38, also exert an anti-inflammatory effect on human primary macrophages and synovial fibroblasts from patients with RA.

CONCLUSIONS

This study shows for the first time that IL-38 overexpression attenuates the severity of experimental arthritis. IL-38 may exert its anti-inflammatory effects by decreasing the production of proinflammatory cytokines by macrophages and synovial fibroblasts. This effect can lead to the development of novel treatment strategies in arthritis.

Response of Bone Turnover Markers and Cytokines to High-Intensity Low-Impact Exercise

INTRODUCTION

Low-impact, high-intensity interval exercise (HIE) was used to investigate the postexercise response in bone turnover markers and cytokines.

METHODS

Twenty-three recreationally active males (21.8 ± 2.4 yr) performed one HIE bout on a cycle ergometer at 90% maximum workload. The total duration of the exercise was 12 min and included six 1-min high-intensity exercise intervals separated by 1-min rest intervals. Blood samples were collected before exercise, 5 min, 1 h, and 24 h after exercise and were analyzed for serum levels of anti- and pro-inflammatory cytokines (interleukin 10 [IL-10], interleukin 6 [IL-6], interleukin 1-alpha [IL-1α], interleukin 1-beta [IL-1β], and tumor necrosis factor alpha [TNF-α]) and markers of bone formation (bone alkaline phosphatase [BAP], osteoprotegerin [OPG]) and resorption (amino-terminal cross-linking propeptide [NTX], receptor activator of NF-κB ligand [RANKL]).

RESULTS

There was a significant (P < 0.05) time effect for all bone turnover markers. Post hoc analysis showed that BAP, OPG, and RANKL significantly increased from baseline to 5 min after exercise (10.9%, 13.5%, and 34.2%, P < 0.05). At 1 h after exercise, only BAP was significantly higher than baseline (9.5%, P = 0.010) and remained higher than baseline at 24 h (10.9%, P = 0.001). NTX was significantly lower than baseline 24 h after exercise (-14.6%, P = 0.046). Significant (P < 0.05) time effects were also observed for IL-1α, IL-1β, IL-6, and TNF-α, with all four significantly increasing 5 min after exercise and returning to baseline levels 1 h after exercise. The postexercise changes in bone formation markers correlated positively with the anti-inflammatory cytokine (IL-10) and negatively with the pro-inflammatory cytokines while NTX correlated positively with a pro-inflammatory cytokine, TNF-α (P < 0.05).

CONCLUSIONS

These results suggest that HIE stimulates a response in bone turnover markers and cytokines and that a correlation exists between immune and skeletal responses to this form of exercise. This type of exercise may benefit individuals for whom high-impact exercise might be contraindicated.

Host response mechanisms in periodontal diseases

Periodontal diseases usually refer to common inflammatory disorders known as gingivitis and periodontitis, which are caused by a pathogenic microbiota in the subgingival biofilm, including Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, Tannerella forsythia and Treponema denticola that trigger innate, inflammatory, and adaptive immune responses. These processes result in the destruction of the tissues surrounding and supporting the teeth, and eventually in tissue, bone and finally, tooth loss. The innate immune response constitutes a homeostatic system, which is the first line of defense, and is able to recognize invading microorganisms as non-self, triggering immune responses to eliminate them. In addition to the innate immunity, adaptive immunity cells and characteristic cytokines have been described as important players in the periodontal disease pathogenesis scenario, with a special attention to CD4⁺ T-cells (T-helper cells). Interestingly, the T cell-mediated adaptive immunity development is highly dependent on innate immunity-associated antigen presenting cells, which after antigen capture undergo into a maturation process and migrate towards the lymph nodes, where they produce distinct patterns of cytokines that will contribute to the subsequent polarization and activation of specific T CD4+ lymphocytes. Skeletal homeostasis depends on a dynamic balance between the activities of the bone-forming osteoblasts (OBLs) and bone-resorbing osteoclasts (OCLs). This balance is tightly controlled by various regulatory systems, such as the endocrine system, and is influenced by the immune system, an osteoimmunological regulation depending on lymphocyte- and macrophage-derived cytokines. All these cytokines and inflammatory mediators are capable of acting alone or in concert, to stimulate periodontal breakdown and collagen destruction via tissue-derived matrix metalloproteinases, a characterization of the progression of periodontitis as a stage that presents a significantly host immune and inflammatory response to the microbial challenge that determine of susceptibility to develop the destructive/progressive periodontitis under the influence of multiple behavioral, environmental and genetic factors.

Role of inflammation in the aging bones

Chronic inflammation in aging is characterized by increased inflammatory cytokines, bone loss, decreased adaptation, and defective tissue repair in response to injury. Aging leads to inherent changes in mesenchymal stem cell (MSC) differentiation, resulting in impaired osteoblastogenesis. Also, the pro-inflammatory cytokines increase with aging, leading to enhanced myelopoiesis and osteoclastogenesis. Bone marrow macrophages (BMMs) play pivotal roles in osteoblast differentiation, the maintenance of hematopoietic stem cells (HSCs), and subsequent bone repair. However, during aging, little is known about the role of macrophages in the differentiation and function of MSC and HSC. Aged mammals have higher circulating pro-inflammatory cytokines than young adults, supporting the hypothesis of increased inflammation with aging. This review will aid in the understanding of the potential role(s) of pro-inflammatory (M1) and anti-inflammatory (M2) macrophages in differentiation and function of osteoblasts and osteoclasts in relation to aging.

Osteoimmunology in orthodontic tooth movement

The skeletal and immune systems share a multitude of regulatory molecules, including cytokines, receptors, signaling molecules, and signaling transducers, thereby mutually influencing each other. In recent years, several novel insights have been attained that have enhanced our current understanding of the detailed mechanisms of osteoimmunology. In orthodontic tooth movement, immune responses mediated by periodontal tissue under mechanical force induce the generation of inflammatory responses with consequent alveolar bone resorption, and many regulators are involved in this process. In this review, we take a closer look at the cellular/molecular mechanisms and signaling involved in osteoimmunology and at relevant research progress in the context of the field of orthodontic tooth movement.

MKP-1 signaling events are required for early osteoclastogenesis in lineage defined progenitor populations by disrupting RANKL-induced NFATc1 nuclear translocation

Cytokine-directed osteoclastogenesis is initiated in response to macrophage colony stimulating factor (M-CSF) and receptor activator of NF-κB ligand (RANKL) to drive formation of osteoclasts (OC), large bone resorptive cells of hematopoietic origin. RANKL-induced signaling activates the MAPK pathways, which initiates nuclear translocation of the master regulator of osteoclast formation, transcription factor NFATc1. Proper control over these signaling events is essential to normal OC formation response to stimuli. MAPK phosphatase 1 (MKP-1), a serine and tyrosine phosphatase encoded by the gene Dusp1, functions to dephosphorylate and subsequently inactivate MAPK (p38 and JNK) signaling essential in osteoclastogenesis. Here, we explored the role of MKP-1 during RANKL-driven osteoclastogenesis from defined (B220/CD45(-)GR1(-)CD11b(lo/-)CD115(+)) OC progenitor (dOCP) populations using WT and Dusp1(-/-) global knockout mice. Sorted cells were driven to OC by M-CSF pre-treatment followed by RANKL stimulation for 3days. OC formation and qPCR products were analyzed for maturation. Results indicate that Dusp1(-/-) dOCP form less numerous, significantly smaller and less functional OC compared to WT controls. These data were corroborated by mRNA expression of the key OC genes, Nfatc1 and Tm7sf4 (DC-STAMP), which were significantly reduced in early osteoclastogenesis in OC progenitor from Dusp1(-/-) mice. Intriguingly, our data reveals that MKP-1 may positively control OC formation in response to RANKL by regulating NFATc1 nuclear translocation. Collectively, this report supports the idea that MKP-1 signaling is essential in early osteoclastogenesis in response to RANKL-induced signaling.

Mesenchymal stem cells markedly suppress inflammatory bone destruction in rats with adjuvant-induced arthritis

Mesenchymal stem cells (MSCs) have potential to differentiate into multiple cell lineages. Recently, it was shown that MSCs also have anti-inflammatory and immunomodulatory functions. In this report, we investigated the regulatory function of MSCs in the development of inflammatory bone destruction in rats with adjuvant-induced arthritis (AA rats). MSCs were isolated from rat bone marrow tissues, expanded in the presence of basic FGF, and intraperitoneally injected into AA rats. MSC administration significantly suppressed inflammatory parameters: swelling score, swelling width, and thickness of hind paw. Radiographic evaluation indicated that MSC significantly suppressed bone destruction. Histological analysis showed that administration of MSCs markedly suppressed osteoclastogenesis in AA rats. To further delineate their effects on osteoclastogenesis, MSCs were added to in vitro bone marrow cultures undergoing osteoclastogenesis. MSCs significantly suppressed osteoclastogenesis in this system. Chemokine receptor expression in MSCs was assessed by RT-PCR, and a chemotactic assay was performed using a transwell culture system. MSCs showed significant chemotaxis to MIP-1α (CCL3) and SDF-1α (CXCL12), chemokines preferentially expressed in the area of inflammatory bone destruction. Furthermore, MSCs expressed IL-10 and osteoprotegerin, cytokines that suppress osteoclastogenesis. These data suggest that recruitment of MSC to the area of bone destruction in AA rats could suppress inflammatory bone destruction and raise the possibility that MSCs may have potential for the treatment of inflammatory bone destruction in arthritis.

Interleukin-10 inhibits bone resorption: a potential therapeutic strategy in periodontitis and other bone loss diseases

Periodontitis and other bone loss diseases, decreasing bone volume and strength, have a significant impact on millions of people with the risk of tooth loss and bone fracture. The integrity and strength of bone are maintained through the balance between bone resorption and bone formation by osteoclasts and osteoblasts, respectively, so the loss of bone results from the disruption of such balance due to increased resorption or/and decreased formation of bone. The goal of therapies for diseases of bone loss is to reduce bone loss, improve bone formation, and then keep healthy bone density. Current therapies have mostly relied on long-term medication, exercise, anti-inflammatory therapies, and changing of the life style. However there are some limitations for some patients in the effective treatments for bone loss diseases because of the complexity of bone loss. Interleukin-10 (IL-10) is a potent anti-inflammatory cytokine, and recent studies have indicated that IL-10 can contribute to the maintenance of bone mass through inhibition of osteoclastic bone resorption and regulation of osteoblastic bone formation. This paper will provide a brief overview of the role of IL-10 in bone loss diseases and discuss the possibility of IL-10 adoption in therapy of bone loss diseases therapy.

KMUP-1 suppresses RANKL-induced osteoclastogenesis and prevents ovariectomy-induced bone loss: roles of MAPKs, Akt, NF-κB and calcium/calcineurin/NFATc1 pathways

Background

KMUP-1 is a xanthine derivative with inhibitory activities on the phosphodiesterase (PDE) 3,4 and 5 isoenzymes to suppress the degradation of cyclic AMP and cyclic GMP. However, the effects of KMUP-1 on osteoclast differentiation are still unclear. In this study, we investigated whether KMUP-1 inhibits osteoclastogenesis induced by RANKL in RAW 264.7 cells and bone loss induced by ovariectomy in mice, and the underlying mechanisms.

Principal Findings

In vitro, KMUP-1 inhibited RANKL-induced TRAP activity, the formation of multinucleated osteoclasts and resorption-pit formation. It also inhibited key mediators of osteoclastogenesis including IL-1β, IL-6, TNF-α and HMGB1. In addition, KMUP-1 inhibited RANKL-induced activation of signaling molecules (Akt, MAPKs, calcium and NF-κB), mRNA expression of osteoclastogensis-associated genes (TRAP, MMP-9, Fra-1, and cathepsin K) and transcription factors (c-Fos and NFATc1). Furthermore, most inhibitory effects of KMUP-1 on RANKL-mediated signal activations were reversed by a protein kinase A inhibitor (H89) and a protein kinase G inhibitor (KT5823). In vivo, KMUP-1 prevented loss of bone mineral content, preserved serum alkaline phosphate and reduced serum osteocalcin in ovariectomized mice.

Conclusions

KMUP-1 inhibits RANKL-induced osteoclastogenesis in vitro and protects against ovariectomy-induced bone loss in vivo. These effects are mediated, at least in part, by cAMP and cGMP pathways. Therefore, KMUP-1 may have a role in pharmacologic therapy of osteoporosis.

Estradiol ameliorates arthritis and protects against systemic bone loss in Staphylococcus aureus infection in mice

INTRODUCTION

Staphylococcus aureus is a common cause of bacterial arthritis, which is associated with progressive bone loss in affected joints. We recently showed that S. aureus infection also induces a significant systemic bone loss in mice. This study was performed to assess the effect of estradiol treatment on the clinical course and outcome of S. aureus arthritis and on infection-induced bone loss in experimental S. aureus infection.

METHODS

Mice were ovariectomized, treated with estradiol or placebo, and S. aureus infection was established by intravenous inoculation of bacteria.

RESULTS

Estradiol treatment was found to decrease significantly the frequency and clinical severity of S. aureus arthritis, a finding that was accompanied with significantly higher serum levels of interleukin-10 in estradiol-treated mice. Estradiol was also highly protective against S. aureus-induced systemic trabecular, and cortical bone loss. Lack of endogenous estrogens and S. aureus infection had additive effects on trabecular bone loss. The S. aureus-infected, ovariectomized mice lost as much as 76% of their trabecular bone mass.

CONCLUSIONS

Treatment with estradiol ameliorates S. aureus arthritis and is protective against infection-induced systemic bone loss in experimental S. aureus infection.

Cross talk between the bone and immune systems: osteoclasts function as antigen-presenting cells and activate CD4+ and CD8+ T cells

The bone and immune systems are closely related through cellular and molecular interactions. Because bone-resorbing osteoclasts (OCs) are derived from the monocyte/macrophage lineage, similar to dendritic cells (DCs), we hypothesized that OCs could serve as antigen-presenting cells (APCs) to activate T cells. In this study, OCs were generated from human monocytes with stimulation by receptor activator of nuclear factor kappaB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF). Results showed that, similar to DCs, OCs express major histocompatibility complex (MHC) classes I and II, and CD80, CD86, and CD40; and uptake soluble antigens. OCs secrete interleukin-10 (IL-10), transforming growth factor-beta (TGF-beta), IL-6, and tumor necrosis factor-alpha (TNF-alpha), but not IL-12p70. OCs present allogeneic antigens and activate both CD4+ and CD8+ alloreactive T cells in an MHC-restricted fashion. OCs also present soluble protein tetanus toxoid to activate autologous CD4+ T cells. These findings indicate that OCs can function as APCs and activate both CD4+ and CD8+ T cells. Thus, our study provides new insight into the effect of OCs on the immune system and may help develop novel strategies for treating diseases such as rheumatoid arthritis and multiple myeloma, which affect both the bone and immune systems.

MRI for assessing erosion and joint space narrowing in inflammatory arthropathies

The superior soft tissue contrast and multiplanar capability of magnetic resonance imaging has contributed to earlier diagnosis and implementation of effective treatment for a variety of arthropathies. Owing to overlapping clinical signs and symptoms, MRI plays a role in delineating the features and stages of these conditions. With the advent of disease-modifying therapies, it is important to diagnose inflammatory arthropathy as early as possible. In this chapter, we discuss the pathophysiology of bone erosion and joint space narrowing, as well as the role of MRI in the imaging of the seropositive and seronegative inflammatory arthropathies.

Cytokine-controlled RANKL and osteoprotegerin expression by human and mouse synovial fibroblasts: fibroblast-mediated pathologic bone resorption

OBJECTIVE

To determine whether proinflammatory cytokine treatment or the complete absence of select cytokines modulates the expression of RANKL and osteoprotegerin (OPG) in synovial fibroblasts.

METHODS

Fibroblasts were isolated from normal and rheumatoid human synovium and from normal or arthritic joints of wild-type and cytokine gene-deficient (interleukin-4-knockout [IL-4 (-/-)] and interferon-gamma-knockout [IFNgamma (-/-)]) mice. Fibroblasts were stimulated with proinflammatory cytokines (tumor necrosis factor alpha [TNFalpha], IL-1beta, and IL-17) or antiosteoclastogenic cytokines (IL-4 and IFNgamma), alone or in combination, and the expression of RANKL and OPG was measured.

RESULTS

Proinflammatory cytokine-stimulated fibroblasts from rheumatoid and arthritic mouse joints expressed higher levels of RANKL and OPG than those from normal joints. IL-4 suppressed RANKL expression and increased OPG expression, IFNgamma reduced the production of both RANKL and OPG, and IL-17 had only a modest effect on the expression of RANKL or OPG. Additive effects of combination treatment (TNFalpha/IL-17 or IL-1beta/IL-17) were observed only in the human system. Extensive destruction was observed in the arthritic joints of IL-4 (-/-) mice, with a corresponding upward shift of the RANKL:OPG ratios. However, an IL-17 deficiency did not attenuate arthritis or reduce bone resorption.

CONCLUSION

Proinflammatory cytokines induce the expression of RANKL and OPG in both human and murine synovial fibroblasts. The RANKL:OPG ratios are shifted in favor of bone protection by IL-4 treatment, and, to a lesser extent, by IFNgamma treatment. Unexpectedly, an IL-17 deficiency alone does not induce reduced inflammatory bone destruction. Our results suggest that synovial fibroblasts may significantly contribute to bone resorption through modulation of RANKL and OPG production in a cytokine-rich milieu of inflamed joints.

Osteoimmunology: cytokines and the skeletal system

It has become clear that complex interactions underlie the relationship between the skeletal and immune systems. This is particularly true for the development of immune cells in the bone marrow as well as the functions of bone cells in skeletal homeostasis and pathologies. Because these two disciplines developed independently, investigators with an interest in either often do not fully appreciate the influence of the other system on the functions of the tissue that they are studying. With these issues in mind, this review will focus on several key areas that are mediated by crosstalk between the bone and immune systems. A more complete appreciation of the interactions between immune and bone cells should lead to better therapeutic strategies for diseases that affect either or both systems.

Osteoimmunology: interactions of the bone and immune system

Bone and the immune system are both complex tissues that respectively regulate the skeleton and the body's response to invading pathogens. It has now become clear that these organ systems often interact in their function. This is particularly true for the development of immune cells in the bone marrow and for the function of bone cells in health and disease. Because these two disciplines developed independently, investigators in each don't always fully appreciate the significance that the other system has on the function of the tissue they are studying. This review is meant to provide a broad overview of the many ways that bone and immune cells interact so that a better understanding of the role that each plays in the development and function of the other can develop. It is hoped that an appreciation of the interactions of these two organ systems will lead to better therapeutics for diseases that affect either or both.

Interleukin-10 inhibits RANKL-mediated expression of NFATc1 in part via suppression of c-Fos and c-Jun in RAW264.7 cells and mouse bone marrow cells

Interleukin-10 (IL-10), an anti-inflammatory cytokine, has been shown to inhibit osteoclast formation and bone resorption in rat and mouse systems. However, the precise intracellular mechanism(s) of this action remains unclear. The aim of this study was to clarify the role of IL-10 in the regulation of critical transcription factors involved in osteoclastogenesis. A RAW264.7 macrophage cell line, which constitutively expressed IL-10 receptor, was differentiated to osteoclasts with stimulation of receptor activator of nuclear factor kappaB ligand (RANKL). IL-10 inhibited the RANKL-induced osteoclastogenesis. IL-10 potently reduced the RANKL-induced expression of NFATc1, c-Jun and c-Fos, which are known to be essential for osteoclastogenesis, in time- and dose-dependent manners. The IL-10-induced inhibition of these transcription factors was observed in the system of mouse bone marrow precursors. Besides these transcription factors, IL-10 also decreased the RANKL-induced expression of NF-kappaB p50 and phosphorylation of JNK. To determine which signaling was critical for the IL-10 effect, we examined the effect of overexpression of NFATc1, c-Fos, and c-Jun on the IL-10-induced inhibition of osteoclastogenesis. As expected, overexpression of NFATc1 abrogated the IL-10-induced inhibition of osteoclastogenesis. Interestingly, overexpression of either c-Fos or c-Jun partially rescued the reduction of RANKL-induced expression of NFATc1 and osteoclastogenesis by IL-10. These data suggest that IL-10 may down-regulate osteoclastogenesis mainly through inhibition of the expression of NFATc1, c-Fos and c-Jun. These findings provide new insight into the inhibitory action of IL-10 on RANKL-mediated osteoclastogenesis.

Type II collagen autoimmunity in a mouse model of human rheumatoid arthritis

Type II collagen (CII) is expressed exclusively in the joint articular. Although the relationship between anti-CII immunity and human rheumatoid arthritis (RA) has been studied for a long time, definitive conclusions have not been reached. CII, as an autoantigen, has been studied extensively in small animal models, such as mice, and the collagen-induced arthritis (CIA) model has increased our understanding of the pathogenesis of human RA. In the present report, we summarize the available information on anti-CII immunity and discuss recent updates regarding pathogenesis in the CIA model, including the role of Th17 cells.

Interleukin-10 inhibits osteoclastogenesis by reducing NFATc1 expression and preventing its translocation to the nucleus

Background

IL-10 has a potent inhibitory effect on osteoclastogenesis. In vitro and in vivo studies confirm the importance of this cytokine in bone metabolism, for instance IL-10-deficient mice develop the hallmarks of osteoporosis. Although it is known that IL-10 directly inhibits osteoclastogenesis at an early stage, preventing differentiation of osteoclast progenitors to preosteoclasts, the precise mechanism of its action is not yet clear. Several major pathways regulate osteoclastogenesis, with key signalling genes such as p38, TRAF6, NF-κB and NFATc1 well established as playing vital roles. We have looked at gene expression in eleven of these genes using real-time quantitative PCR on RNA extracted from RANKL-treated RAW264.7 monocytes.

Results

There was no downregulation by IL-10 of DAP12, FcγRIIB, c-jun, RANK, TRAF6, p38, NF-κB, Gab2, Pim-1, or c-Fos at the mRNA level. However, we found that IL-10 significantly reduces RANKL-induced NFATc1 expression. NFATc1 is transcribed from two alternative promoters in Mus musculus and, interestingly, only the variant transcribed from promoter P1 and beginning with exon 1 was downregulated by IL-10 (isoform 1). In addition, immunofluorescence studies showed that IL-10 reduces NFATc1 levels in RANKL-treated precursors and suppresses nuclear translocation. The inhibitory effect of IL-10 on tartrate-resistant acid phosphatase-positive cell number and NFATc1 mRNA expression was reversed by the protein kinase C agonist phorbol myristate acetate, providing evidence that interleukin-10 disrupts NFATc1 activity through its effect on Ca²⁺ mobilisation.

Conclusion

IL-10 acts directly on mononuclear precursors to inhibit NFATc1 expression and nuclear translocation, and we provide evidence that the mechanism may involve disruption of Ca²⁺ mobilisation. We detected downregulation only of the NFATc1 isoform 1 transcribed from promoter P1. This is the first report indicating that one of the ways in which IL-10 directly inhibits osteoclastogenesis is by suppressing NFATc1 activity.

Cytokines regulating osteoclast formation and function

PURPOSE OF REVIEW

The osteoclast is the principal bone-resorbing cell. Because of its unique ability to efficiently remove both the mineral and the organic matrix of bone, the osteoclast is an important element of the homeostatic mechanisms that maintain skeletal integrity and serum calcium levels. Over the past 30 years, a number of immune cell modulators have been shown to have effects on osteoclast formation and function. This review will briefly summarize the roles that cytokines have in osteoclast regulation.

RECENT FINDINGS

A large number of cytokines have been shown to regulate osteoclast formation and function. In addition, a number of additional cytokines are now known to have a major influence on the ability of osteoclasts to resorb bone. Interactions of the immune system with bone, which has been recently labeled 'osteoimmunology', appear to be mediated mainly by cytokine signals. Cytokines are known to regulate many of the responses of bone to inflammatory conditions; however, they also may regulate physiologic responses of bone.

SUMMARY

In the future it is hoped that therapies that target cytokine actions may be used to reduce the effects of inflammatory diseases on bone, as well as to regulate normal bone physiology.

Osteoclasts, rheumatoid arthritis, and osteoimmunology

PURPOSE OF REVIEW

Osteoclasts are terminally differentiated cells of the monocyte/macrophage lineage that resorb bone matrix. Bone destruction in rheumatoid arthritis is mainly attributable to the abnormal activation of osteoclasts, and studies on activation of osteoclasts by the immune system have led to the new research field called osteoimmunology. This interdisciplinary field is very important to biologic research and to the treatment of diseases associated with the bone and immune systems.

RECENT FINDINGS

The T-cell-mediated regulation of osteoclast differentiation is dependent on cytokines and membrane-bound factors expressed by T cells. The cross-talk between receptor activator of nuclear factor-kappaB ligand and interferon-gamma has been shown to be crucial for the regulation of osteoclast formation in arthritic joints. Recent studies indicate that an increasing number of immunomodulatory factors are associated with the regulation of bone metabolism: nuclear factor of activated T cells c1 has been shown to be the key transcription factor for osteoclastogenesis, the activation of which requires calcium signaling induced by the immunoglobulin-like receptors.

SUMMARY

New findings in osteoimmunology will be instrumental in the development of strategies for research into the treatment of various diseases afflicting the skeletal and immune systems.

Th17 functions as an osteoclastogenic helper T cell subset that links T cell activation and bone destruction

In autoimmune arthritis, traditionally classified as a T helper (Th) type 1 disease, the activation of T cells results in bone destruction mediated by osteoclasts, but how T cells enhance osteoclastogenesis despite the anti-osteoclastogenic effect of interferon (IFN)-γ remains to be elucidated. Here, we examine the effect of various Th cell subsets on osteoclastogenesis and identify Th17, a specialized inflammatory subset, as an osteoclastogenic Th cell subset that links T cell activation and bone resorption. The interleukin (IL)-23–IL-17 axis, rather than the IL-12–IFN-γ axis, is critical not only for the onset phase, but also for the bone destruction phase of autoimmune arthritis. Thus, Th17 is a powerful therapeutic target for the bone destruction associated with T cell activation.

The hemoglobin receptor protein of porphyromonas gingivalis inhibits receptor activator NF-kappaB ligand-induced osteoclastogenesis from bone marrow macrophages

Extracellular proteinaceous factors of Porphyromonas gingivalis, a periodontal pathogen, that influence receptor activator of nuclear factor-kappaB (NF-kappaB) ligand (RANKL)-induced osteoclastogenesis from bone marrow macrophages were investigated. The culture supernatant of P. gingivalis had the ability to inhibit RANKL-induced in vitro osteoclastogenesis. A major protein of the culture supernatant, hemoglobin receptor protein (HbR), suppressed RANKL-induced osteoclastogenesis in a dose-dependent fashion. HbR markedly inhibited RANKL-induced osteoclastogenesis when present in the culture for the first 24 h after addition of RANKL, whereas no significant inhibition was observed when HbR was added after 24 h or later, implying that HbR might interfere with only the initial stage of RANKL-mediated differentiation. HbR tightly bound to bone marrow macrophages and had the ability to induce phosphorylation of ERK, p38, NF-kappaB, and Akt. RANKL-induced phosphorylation of ERK, p38, and NF-kappaB was not suppressed by HbR, but that of Akt was markedly suppressed. HbR inhibited RANKL-mediated induction of c-Fos and NFATc1. HbR could induce beta interferon (IFN-beta) from bone marrow macrophages, but the induction level of IFN-beta might not be sufficient to suppress RANKL-mediated osteoclastogenesis, implying presence of an IFN-beta-independent pathway in HbR-mediated inhibition of osteoclastogenesis. Since rapid and extensive destruction of the alveolar bone causes tooth loss, resulting in loss of the gingival crevice that is an anatomical niche for periodontal pathogens such as P. gingivalis, the suppressive effect of HbR on osteoclastogenesis may help the microorganism exist long in the niche.

Effect of interleukin-10 on gene expression of osteoclastogenic regulatory molecules in the rat dental follicle

The aim of this study was to determine the effect of interleukin-10 (IL-10) on the gene expression of osteoclastogenic regulatory molecules in rat dental follicle cells. Interleukin-10 is an anti-inflammatory cytokine that inhibits alveolar bone resorption, but the molecular basis for this is unknown. Alveolar bone resorption is required for tooth eruption and the dental follicle functions to regulate the osteoclastogenesis needed for eruption. It does this by regulating its expression of receptor activator of nuclear factor-kappa B ligand (RANKL), colony-stimulating factor-1 (CSF-1), and osteoprotegerin (OPG). In this study, dental follicle cells were treated with IL-10, and the effect on gene expression of CSF-1, RANKL, and OPG was measured by reverse transcription-polymerase chain reaction (RT-PCR). Interleukin-10 enhanced the expression of OPG and down-regulated the expression of RANKL and CSF-1. Laser capture microdissection was carried out to detect IL-10 gene expression in the dental follicle. Knockdown of the IL-10 gene expression in the follicle cells was accomplished using a short interfering RNA (siRNA) targeting IL-10 mRNA. In these knockdowns, RANKL expression was increased and OPG expression was decreased. All of these results suggest that IL-10 inhibits bone resorption by up-regulating OPG expression while down-regulating expression of RANKL and CSF-1.

The role of the immune system in the pathophysiology of osteoporosis

The role of the immune system in the development of senile osteoporosis, which arises primarily through the effects of estrogen deficiency and secondary hyperparathyroidism, is slowly being unraveled. This review focuses on our current understanding of how the components of this complex-interlinked system are regulated and how these fit with previous models of senile and postmenopausal osteoporosis. There is certainly substantial evidence that bone remodeling is a tightly regulated, finely balanced process influenced by subtle changes in proinflammatory and inhibitory cytokines as well as hormones and cellular components that act primarily but not exclusively through the receptor activator of nuclear factor-kappaB (RANK)/RANK ligand/osteoprotegerin system. In addition, an acute or chronic imbalance in the system due to infection or inflammation could contribute to systemic (or local) bone loss and increase the risk of fracture. Although significant progress has been made, there remains much to be done in unraveling this complex interaction between the immune system and bone.

Prostaglandin E2Is a Main Mediator in Receptor Activator of Nuclear Factor-κB Ligand-Dependent Osteoclastogenesis Induced byPorphyromonas gingivalis, Treponema denticola, andTreponema socranskii

BACKGROUND

Periodontitis is an inflammatory disease that often leads to destruction of alveolar bone; a number of bacteria in subgingival plaque are associated with bone destruction in periodontitis. To understand the mechanism of how periodontopathogens induce osteoclastogenesis, we determined which mediators are involved in the osteoclastogenesis.

METHODS

We investigated effects of sonicates from three periodontopathic bacteria, Porphyromonas gingivalis, Treponema denticola, and Treponema socranskii, on osteoclast formation in a co-culture system of mouse calvaria-derived osteoblasts and bone marrow cells. The osteoclast formation was determined by tartrate resistant acid phosphatase (TRAP) staining. The expression of the receptor activator of nuclear factor-kappa B ligand (RANKL), prostaglandin E(2) (PGE(2)) and osteoprotegerin (OPG) in mouse calvaria-derived osteoblasts was determined by immunoassay.

RESULTS

Each bacterial sonicate induced the osteoclast formation in the co-culture system. These bacterial sonicates increased the expression of RANKL and PGE(2), and decreased the expression of OPG in osteoblasts. The addition of OPG, an inhibitor of RANKL, in the co-culture completely suppressed the osteoclastogenesis that was stimulated by each bacterial sonicate. Indomethacin, which is an inhibitor of PGE(2) synthesis, reduced more than 88% of the osteoclast formation induced by each bacterial sonicate. Indomethacin inhibited more than 80% of RANKL expression in osteoblasts induced by T. denticola and T. socranskii, and 59% by P. gingivalis. Indomethacin completely recovered the depression of OPG expression in osteoblasts by T. denticola and T. socranskii to the level of the untreated osteoblasts. Indomethacin recovered the reduction of OPG expression by P. gingivalis to 67%.

CONCLUSION

These findings suggest that the osteoclastogenesis by P. gingivalis, T. denticola, and T. socranskii is mediated by a RANKL-dependent pathway and that PGE(2) is a main factor in the pathway by the enhancing of RANKL expression and the depression of osteoprotegerin, a RANKL inhibitor.

Mechanical deformation inhibits IL-10 and stimulates IL-12 production by mouse calvarial osteoblasts in vitro

The skeleton is continuously remodelled throughout life, a process that is orchestrated by cells of the osteoblast lineage. Remodelling involves a complex network of cell-cell signalling involving systemic hormones, locally produced cytokines, growth factors and the mechanical environment of the cells. Here, we report on the effect of mechanically-induced strain on the synthesis by mouse calvarial osteoblasts in monolayer culture of IL-10 and IL-12, two cytokines that inhibit osteoclast formation in bone marrow cultures; IL-10 also suppresses osteoblast differentiation suggesting a role for both cytokines in bone physiology. A tensile strain was applied to the cells intermittently for 6s, every 90s, for 2-96h. After 2-h culture, supernatants from deformed cells contained significantly less IL-10 than control cultures. In contrast, mechanical deformation had a stimulatory effect on IL-12 synthesis; however, by 48h both had returned to control levels. These data suggest that IL-10 and IL-12 can be added to the growing list of mechanical stress-responsive genes. The down-regulation of IL-10 and stimulation of IL-12 further suggests that the initial response of the cells to mechanical deformation was an osteogenic one.

Suppressors of Cytokine Signaling-1 and -3 Regulate Osteoclastogenesis in the Presence of Inflammatory Cytokines

Bone metabolism and the immune system have a correlative relationship, and both are controlled by various common cytokines, such as IFNs and ILs, produced in the bone microenvironments. The suppressor of cytokine signaling-1 (SOCS1) and SOCS3 are negative regulators of such cytokines. Although SOCSs are shown to be induced during osteoclast differentiation, their physiological roles in osteoclast differentiation and function have not been clarified. Thus, we examined the roles of SOCS1 and SOCS3 in osteoclastogenesis using SOCS1- and SOCS3-deficient mice. IFN-gamma-mediated inhibition of osteoclast differentiation from bone marrow-derived monocytes (BMMs) was strongly enhanced in SOCS1-deficient BMMs, but was diminished in SOCS1-overexpressing BMMs. Moreover, LPS-induced osteoclastogenesis and bone destruction in vivo were suppressed in SOCS1(+/-) mice compared with those in wild-type mice, suggesting that SOCS1 antagonizes the inhibitory effect of IFN-gamma on osteoclastogenesis. SOCS3 did not alter the inhibitory effect of IFNs in osteoclastogenesis in both gain and loss of functional assays; however, the suppressive effect of IL-6 on osteoclast differentiation was greater in SOCS3-deficient BMMs than in wild-type BMMs in vitro. In addition, IL-6 significantly prevented LPS-induced bone destruction in SOCS3-deficient mice, although it failed in wild-type mice in vivo. In SOCS3-deficient BMMs, expression levels of TNF-receptor-associated factor-6 and IkappaB were drastically reduced and receptor activator of the NF-kappaB ligand-induced IkappaB phosphorylation was severely impaired in the presence of IL-6. These data suggest that both SOCS1 and SOCS3 regulate osteoclastogenesis by blocking the inhibitory effect of inflammatory cytokines on receptor activator of the NF-kappaB ligand-mediated osteoclast differentiation signals. Selective suppression of SOCS1 and SOCS3 in osteoclast precursors may be a possible therapeutic strategy for inflammatory bone destruction.

Interleukin 10-deficient mice develop osteopenia, decreased bone formation, and mechanical fragility of long bones

BACKGROUND & AIMS

Bone loss is a common complication of human inflammatory bowel disease (IBD), but its mechanisms are not understood completely. We investigated bone metabolism in interleukin-10-deficient ( IL-10-/- ) mice, an animal model with IBD features.

METHODS

IL-10-/- male mice (8- and 12-weeks-old) and their age-matched wild-type counterparts (C57BL/6J) were studied. Bone mass of the femur was determined by ashing. Tibial cancellous and cortical bone mass and formation was measured by static and dynamic histomorphometry. Biomechanical strength of the femur was tested. Primary bone marrow stromal cell cultures were used to assess osteoblast generation. Serum levels of 25-OH vitamin D 3, insulin-like growth factor-1 (IGF-1), parathyroid hormone, osteocalcin, and deoxy-pyridinoline cross-links were measured. The presence of colitis was determined histologically, and by IL-12 and interferon-gamma (IFN-gamma) secretion from cultured colonic explants.

RESULTS

Eight- and 12-week-old IL-10-/- mice developed osteopenia of both cancellous and cortical bone, evidenced by lower femoral ash weight, cancellous bone area and surface, trabecular number, and decreased cortical bone area and width. Osteopenia was associated with mechanical fragility, manifested by decreased stiffness and mechanical load at fracture, and was caused by suppressed bone formation, indicated by decreased cancellous double-labeled surface, mineralizing surface, serum osteocalcin level, and mineralized nodule number in bone marrow stromal cell cultures. IL-10-/- mice with colitis had significantly less bone mass compared with IL-10-/- mice without colitis.

CONCLUSIONS

IL-10-/- mice develop the hallmarks of osteoporosis, that is, reduced bone mass, increased mechanical fragility, and suppressed bone formation. The presence of colitis is an important contributor to osteoporosis in IL-10-/- mice.

The effect of age and gender on cytokine production by human peripheral blood mononuclear cells and markers of bone metabolism

BACKGROUND

Aging has been associated with various alterations of immune functions, the musculoskeletal system and a decline of sex hormone levels. Estradiol has a central role in the regulation of bone turnover and also modulates the production of cytokines such as interleukin-1 and -6 and tumor necrosis factor-alpha. We therefore studied the effect of age and gender on cytokine production by mononuclear cells and markers of bone metabolism.

METHODS

Peripheral blood mononuclear cells were isolated from young and elderly subjects; intracellular detection of cytokine production after stimulation with ionomycine and PMA (T cells) or LPS (monocytes) was performed by four color flow cytometry. Sex hormone levels and markers of bone metabolism were measured by RIA or ELISA:

RESULTS

When we compared elderly to young women we found an increased proportion of T cells that were positive for interferon-gamma, interleukin-2, -4, -10 and -13. Also the percentage of cells producing interleukin-4 or interferon-gamma within the CD8(+) population was higher in the group of elderly women. In contrast, proportionally fewer monocytes of elderly women were positive for tumor necrosis factor-alpha or interleukin-6 than those of young women. In elderly men a higher percentage of T cells produced interleukin-2, -4 and -13. In the group of aged men we found a higher frequency of cells that produced interleukin-4 within the CD4(+) or CD8(+) population. Moreover, within monocytes of elderly men we found an increased percentage of cells positive for both interleukin-1beta and tumor necrosis factor-alpha. The data on markers of bone metabolism indicated an increase of bone turnover in old age.

CONCLUSION

Our data demonstrate that aging is associated with significant alterations of bone metabolism and cytokine production by T cells and monocytes. For particular cytokines (interferon-gamma and interleukin-10 in T cells, interleukin-6 and tumor necrosis factor-alpha in monocytes) these changes are gender specific.

A rapid multiparameter approach to study factors that regulate osteoclastogenesis: demonstration of the combinatorial dominant effects of TNF-alpha and TGF-ss in RANKL-mediated osteoclastogenesis

Macrophages differentiate into osteoclasts in response to the critical cytokine RANKL. However, the efficiency of RANKL-mediated osteoclastogenesis can be profoundly influenced by various cytokines. While studies describing the isolated effects of particular cytokines on osteoclastogenesis have been performed, combinatorial effects of cytokines have not been addressed routinely due to the absence of an efficient assay system. To study the effects of cytokine combinations on osteoclast formation, we performed in vitro assays using either the RAW293 cell line or primary murine splenic macrophages as osteoclast precursors. Using a multiparameter cytokine plating method, we analyzed osteoclastogenesis in response to multiple combinations of the following inflammation-related cytokines: RANKL, IFN-gamma, TNF-alpha, IL-1beta, IL-6, IL-10. We further investigated the role of T-cell-related cytokine combinations on osteoclastogenesis by measuring osteoclast area in response to RANKL with IFN-gamma, IL-2, IL-4, IL-6, TGF-ss, and TNF-alpha. Treatments with RANKL, TNF-alpha, and TGF-ss induced maximal osteoclast formation, suggesting a role for these cytokines in the most aggressive forms of inflammatory bone loss. TNF-alpha alone, however, was unable to induce osteoclast formation in the absence of RANKL despite co-administration of other proinflammatory cytokines. IFN-gamma was a potent inhibitor under all conditions, implicating T cells and NK cells in osteoclast inhibition. These studies demonstrate a rapid screening approach for identifying the potential collective effects of multiple factors on osteoclastic bone resorption.