Interleukin 18 inhibits osteoclast formation via T cell production of granulocyte macrophage colony-stimulating factor

Granulocyte macrophage colony-stimulating factor may modulate the post-transcription pathway of interleukin-6 expression in prostate carcinoma cells

Interleukin-6 (IL-6) can stimulate a variety of tumors including prostatic carcinoma. Research has recently shown that IL-6 may act to stimulate the progression of prostatic cancer. To date, little research has been performed to better understand the nature of granulocyte macrophage colony-stimulating factor (GM-CSF) and the expression of IL-6. The aim of this study was to evaluate the effects of GM-CSF on the expression of IL-6 in prostate cancer-3 (PC-3) cells. The bone-derived PC-3 cell line was used in this study. Reverse transcription polymerase chain reaction (RT-PCR) and real- time PCR were performed to detect IL-6 mRNA expression. The IL-6 protein was measured by enzyme-linked immunosorbent assay (ELISA) after treatment with hGM-CSF. Our data indicated that IL-6 mRNA expression did not increase after treatment with hGM-CSF in comparison to the control group. However, the expression of IL-6 protein was increased compared to the control group. GM-CSF may modulate the post-transcription pathway of IL-6 expression in prostate carcinoma cells. Our data suggest that GM-CSF may have a role in IL-6-mediated development of prostate cancer.

Interleukin-18 is regulated by parathyroid hormone and is required for its bone anabolic actions

Interleukin-18 (IL-18) can regulate osteoblast and osteoclast function. We have identified, using cDNA microarray technology, that IL-18 expression is increased in UMR 106-01 rat osteoblastic cells in response to parathyroid hormone (PTH) treatment. Confirmation of these data using real-time reverse transcription-PCR showed that steady-state levels of IL-18 mRNA increased by 2 h (3-fold), peaked by 4 h (10-fold), and had diminished after 12 h (4.4-fold) and that this regulation was via the protein kinase A signaling pathway and did not involve activation of the PKC signal cascade. PTH regulation of IL-18 was confirmed at the protein level, and analysis of differentiating primary rat calvarial osteoblasts verified that both IL-18 mRNA and protein are regulated by PTH in primary rat osteoblasts. Promoter reporter assays revealed that PTH regulated the upstream IL-18 promoter and induced the exon 1 containing 1.1-kb IL-18 mRNA transcript in primary osteoblast cells. The in vivo physiological role of IL-18 in the anabolic actions of PTH on bone was then assessed using IL-18 knock-out mice. Female IL-18 null mice and wild-type littermate controls were injected with vehicle or 8 microg/100 g of human 1-38 PTH for 4 weeks. In IL-18 knock-out animals the anabolic effect of PTH (determined by bone mineral density changes in the proximal tibia) was abolished in trabecular bone but not in the cortical component. These data characterize the PTH regulation of IL-18 expression in osteoblastic cells and suggest that this cytokine is involved in the anabolic actions of PTH.

Roles of specific cytokines in bone remodeling and hematopoiesis in Gaucher disease

BACKGROUND

Gaucher disease type 1 and type 3 are characterized by bone disease and hematological symptoms. It is known that monocyte/macrophage lineage is activated in Gaucher disease, and accordingly certain cytokines are elevated in blood. The aim of the present study was to explore the possible relationships between cytokines and bone remodeling and hematological abnormalities in this disease.

METHODS

The concentrations of seven cytokines and two related proteins were measured in patients with Gaucher disease type 1 and type 3 (n= 8; age range, 2-50 years) who had received enzyme replacement therapy.

RESULTS

Concentrations of interleukin-18 and transforming growth factor-beta1 were elevated in patients of all clinical types. Elevation of these cytokines in Gaucher disease has not been previously reported. Analysis of correlation among cytokines and bone-turnover markers showed that interleukin-18 concentration was correlated with each of two bone formation markers of bone-specific alkaline phosphatase activity and osteocalcin concentration, whereas macrophage colony-stimulating factor concentration correlated with the bone absorption marker of N-telopeptide to helix in urine. Concentrations of macrophage colony-stimulating factor and tumor necrosis factor-alpha were inversely correlated with hemoglobin concentration.

CONCLUSIONS

Interleukin-18 and monocyte macrophage colony-stimulating factor are cytokines mainly involved in the mechanism of bone disease, while macrophage colony-stimulating factor and tumor necrosis factor-alpha may play a role in the development of hematological abnormalities in Gaucher disease.

APC-derived cytokines and T cell polarization in autoimmune inflammation

T cell-mediated autoimmune diseases such as multiple sclerosis and rheumatoid arthritis are driven by autoaggressive Th cells. The pathogenicity of such Th cells has, in the past, been considered to be dictated by their cytokine polarization profile. The polarization of such effector T cells relies critically upon the actions of cytokines secreted by APCs. While Th1 polarization has long been associated with the pathogenesis of autoimmune diseases, recent data obtained in gene-targeted mice and the discovery of Th17 cell involvement in autoimmunity conflict with this hypothesis. In light of these recent developments, we discuss in this review the actions of APC-derived cytokines and their emerging roles in T cell polarization in the context of autoimmune inflammatory responses.

Cellular targets of interleukin-18 in rheumatoid arthritis

Recent data are presented which indicate a critical role for interleukin (IL)-18 in rheumatoid arthritis (RA). The T cells and macrophages invading the synovium or in the synovial fluid are the chief cellular targets of IL-18 in RA. Neutrophils, dendritic cells and endothelial cells may also be cellular mediators of IL-18. The direct effect of IL-18 on fibroblast-like synoviocytes or chondrocytes may not be essential or important. In RA, IL-18, which is mainly produced by macrophages, activates T cells and macrophages to produce proinflammatory cytokines, chemokines, adhesion molecules and RANKL which, in turn, perpetuate chronic inflammation and induce bone and cartilage destruction.

Fcgamma receptors directly mediate cartilage, but not bone, destruction in murine antigen-induced arthritis: uncoupling of cartilage damage from bone erosion and joint inflammation

OBJECTIVE

To determine the relationship between synovial inflammation and the concomitant occurrence of cartilage and bone erosion during conditions of variable inflammation using various Fcgamma receptor knockout (FcgammaR(-/-)) mice.

METHODS

Antigen-induced arthritis (AIA) was introduced in the knee joints of various FcgammaR(-/-) mice and wild-type controls. Joint inflammation and cartilage and bone destruction levels were determined by histologic analysis. Cathepsin K, RANKL, and osteoprotegerin (OPG) levels were detected by immunolocalization.

RESULTS

In FcgammaRIIb(-/-) mice, which lack the inhibiting Fcgamma receptor IIb, levels of joint inflammation and cartilage and bone destruction were significantly higher (infiltrate 93%, exudate 200%, cartilage 100%, bone 156%). AIA in mice lacking activating FcgammaR types I, III, and IV, but not FcgammaRIIb (FcR gamma-chain(-/-) mice), prevented cartilage destruction completely. In contrast, levels of bone erosion and joint inflammation were comparable with their wild-type controls. Of great interest, in arthritic mice lacking activating FcgammaR types I, II, and III, but not IV (FcgammaRI/II/III(-/-) mice), levels of joint inflammation were highly elevated (infiltrate and exudate, 100% and 188%, respectively). Cartilage destruction levels were decreased by 92%, whereas bone erosion was increased by 200%. Cathepsin K, a crucial mediator of osteoclasts, showed a strong correlation with the amount of inflammation but not with the amount of activating FcgammaR, which was low in osteoclasts. RANKL, but not OPG, levels were higher in the inflammatory cells of arthritic knee joints of FcgammaRI/II/III(-/-) mice versus wild-type mice.

CONCLUSION

Activating FcgammaR are crucial in mediating cartilage destruction independently of joint inflammation. In contrast, FcgammaR are not directly involved in bone erosion. Indirectly, FcgammaR drive bone destruction by regulating joint inflammation.

Macrophage lineage phenotypes and osteoclastogenesis--complexity in the control by GM-CSF and TGF-beta

Bone-resorbing osteoclasts (OCs) derive from macrophage lineage precursors under the potential control of many factors. Addition of macrophage-colony stimulating factor (M-CSF or CSF-1) to murine bone marrow cells gives rise to so-called bone marrow-derived macrophages (BMM); this adherent population can then be quantitatively converted into OC lineage cells when receptor activator of NFkappaB ligand (RANKL) is included. The effect of another CSF, granulocyte macrophage-CSF (GM-CSF), on OC differentiation in vitro is quite complex with both enhancing and suppressive actions being described. We report here that GM-CSF can generate a population of adherent macrophage lineage cells from murine bone marrow precursors (GM-BMM) which is also capable of giving rise to OC lineage cells in the presence of M-CSF and RANKL as effectively as BMM. The degree of this differentiation was surprising considering that GM-BMM are often referred to as immature dendritic cells and that, for both BMM and the GM-BMM, GM-CSF suppressed subsequent OC differentiation governed by M-CSF and RANKL. Unlike for BMM, this GM-CSF-mediated suppression for GM-BMM appeared to be independent of c-fos expression. The effects on bone of another cytokine, transforming growth factor-beta (TGF-beta), are also quite complex although usually found to be stimulatory for OC differentiation. Unexpectedly, we observed that TGF-beta1 also potently suppressed M-CSF+RANKL-driven OC differentiation from both BMM and GM-BMM. Using cells from gene-deficient mice, this inhibition of OC differentiation by both GM-CSF and TGF-beta1 appeared to be independent of endogenous interferon alpha/beta production. It appears therefore that the influence of GM-CSF and TGF-beta on osteoclastogenesis depends on the presence or otherwise of other stimuli such as RANKL and possibly upon the maturation state of the OC precursors. It is proposed that the findings have particular relevance for the control of bone resorption in pathology, for example, in inflammatory lesions.

Activated T lymphocytes suppress osteoclastogenesis by diverting early monocyte/macrophage progenitor lineage commitment towards dendritic cell differentiation through down-regulation of receptor activator of nuclear factor-kappaB and c-Fos

Activated T lymphocytes either stimulate or inhibit osteoclastogenesis from haematopoietic progenitors in different experimental models. To address this controversy, we used several modes of T lymphocyte activation in osteoclast differentiation--mitogen-pulse, anti-CD3/CD28 stimulation and in vivo and in vitro alloactivation. Osteoclast-like cells were generated from non-adherent immature haematopoietic monocyte/macrophage progenitors in murine bone-marrow in the presence of receptor activator of nuclear factor (NF)-kappaB ligand (RANKL) and monocyte-macrophage colony-stimulating factor (M-CSF). All modes of in vivo and in vitro T lymphocyte activation and both CD4(+) and CD8(+) subpopulations produced similar inhibitory effects on osteoclastogenesis paralleled by enhanced dendritic cell (DC) differentiation. Osteoclast-inhibitory effect was associated with T lymphocyte activation and not proliferation, and could be replaced by their culture supernatants. The stage of osteoclast differentiation was crucial for the inhibitory action of activated T lymphocytes on osteoclastogenesis, because the suppressive effect was visible only on early osteoclast progenitors but not on committed osteoclasts. Inhibition was associated specifically with increased granulocyte-macrophage colony-stimulating factor (GM-CSF) expression by the mechanism of progenitor commitment toward lineages other than osteoclast because activated T lymphocytes down-regulated RANK, CD115, c-Fos and calcitonin receptor expression, and increased differentiation towards CD11c-positive DC. An activated T lymphocyte inhibitory role in osteoclastogenesis, confirmed in vitro and in vivo, mediated through GM-CSF release, may be used to counteract activated bone resorption mediated by T lymphocyte-derived cytokines in inflammatory and immune disorders. We also demonstrated the importance of alloactivation in osteoclast differentiation and the ability of cyclosporin A to abrogate T lymphocyte inhibition of osteoclastogenesis, thereby confirming the functional link between alloreaction and bone metabolism.

Changes in serum cytokine concentrations during the menopausal transition

OBJECTIVE

The purpose of the present study was to clarify the changes in serum concentrations of 17 cytokines in healthy women during the menopausal transition by using a multiplexed cytokine assay and to clarify the associations of these cytokines with serum estradiol concentration.

METHODS

Sixteen premenopausal, 54 perimenopausal and 52 postmenopausal women were enrolled in this study. Seventeen cytokines in serum samples were measured simultaneously using a Bio-Plex human cytokine 17-Plex assay.

RESULTS

Serum IL-6 concentration showed a weak positive correlation with age (r=0.196, p<0.05). Postmenopausal women for whom less than 5 years had passed since menopause showed significant (p<0.05) increase in serum concentrations of IL-2, GM-CSF and G-CSF, while serum IL-4 concentration was significantly (p<0.05) increased in postmenopausal women for whom more than 5 years had passed since menopause. Serum estradiol concentration showed a significant negative correlation with serum IL-6 concentration and weak negative correlations with serum concentrations of IL-2, IL-8 and GM-CSF.

CONCLUSION

We were able to simultaneously measure the levels of 17 cytokines using a highly sensitive cytokine assay, and we found that the changes in serum cytokine concentrations during the menopausal transition differed. We also found that serum IL-6 concentration during the menopausal transition was negatively correlated with serum estradiol concentration.

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.

Megakaryocyte-mediated inhibition of osteoclast development

A growing body of evidence indicates that megakaryocytes (MK) or their growth factors play a role in skeletal homeostasis. We previously identified a novel regulatory pathway that controls bone formation, which is mediated by MK. In vivo megakaryocytosis resulted in massive bone formation. The co-culture of MK with osteoblasts (OB) resulted in increased OB proliferation in vitro, by a mechanism that required direct cell-to-cell contact. Here, we examined a second MK-mediated pathway that regulates osteoclast (OC) development. We have begun examining the unique inhibitory effect of MK on OC development. Spleen or bone marrow (BM) cells from C57BL/6 mice, as a source of OC precursors, were cultured with M-CSF and RANKL to induce OC development. MK were prepared by culturing fetal liver cells with thrombopoietin and separating cells into MK and non-MK populations. MK were titrated into spleen cell cultures and OC were identified as tartrate-resistant acid phosphatase-positive giant cells with >3 nuclei. There was a significant, P < 0.001, up to 10-fold reduction in OC formed when MK were added to the spleen cell cultures. We determined that 30% (vol:vol) MK conditioned media (CM) were able to completely block OC development from precursors, whereas 3% MK CM resulted in up to a 10-fold reduction in OC development, P < 0.001. These data indicate that a soluble factor(s) was responsible, at least in part, for the inhibition. We examined MK CM for known inhibitors of OC formation, using ELISAs. IL-4 was undetectable in MK CM, whereas IL-10 and IFN-gamma levels were similar in MK and non-MK CM. TGFbeta-1 levels were increased 2-fold in MK CM compared to control CM but were not responsible for the inhibition in OC development. Although, we found a significant increase in the levels of osteoprotegerin (OPG) in MK CM, antibody neutralization studies, MK derived from OPG-deficient mice, and tandem mass spectrophotometry, all confirm that OPG was not responsible for the MK-mediated inhibition of OC development. Overall, these data suggest that an unidentified factor(s) is present in MK CM that inhibits OC development. These studies indicate that MK can play a dual role in skeletal homeostasis by stimulating OB proliferation and simultaneously inhibiting OC development.

Immunomodulatory effects of statins and autoimmune rheumatic diseases: novel intracellular mechanism involved

Inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, known as statins, are the most commonly prescribed agents for the treatment of hypercholesterolemia. However, the effects of statins may extend beyond their influences on serum cholesterol levels resulting in cholesterol-independent or pleiotropic effects. Clinical, animal and in vitro studies suggest that statins have additional clinical uses because of their anti-inflammatory and immunomodulatory effects, in part due to their capacity to interfere with the mevalonate pathway and inhibit prenylation of Rho family GTPases. This review focuses on the molecular mechanisms of the anti-inflammatory and immunomodulatory effects of statins. In base to all these information, we suggest that statins could have similar inhibitory effects on MAPKs pathways in cells from RA patients, including osteoclasts and fibroblasts.

Rheumatic diseases: the effects of inflammation on bone

Rheumatoid arthritis, juvenile idiopathic arthritis, the seronegative spondyloarthropathies including psoriatic arthritis, and systemic lupus erythematosus are all examples of rheumatic diseases in which inflammation is associated with skeletal pathology. Although some of the mechanisms of skeletal remodeling are shared among these diseases, each disease has a unique impact on articular bone or on the axial or appendicular skeleton. Studies in human disease and in animal models of arthritis have identified the osteoclast as the predominant cell type mediating bone loss in arthritis. Many of the cytokines and growth factors implicated in the inflammatory processes in rheumatic diseases have also been demonstrated to impact osteoclast differentiation and function either directly, by acting on cells of the osteoclast-lineage, or indirectly, by acting on other cell types to modulate expression of the key osteoclastogenic factor receptor activator of nuclear factor (NF) kappaB ligand (RANKL) and/or its inhibitor osteoprotegerin (OPG). Further elucidation of the mechanisms responsible for inflammation-induced bone loss will potentially lead to the identification of novel therapeutic strategies for the prevention of bone loss in these diseases. In this review, we provide an overview of the cell types, inflammatory mediators, and mechanisms that are implicated in bone loss and new bone formation in inflammatory joint diseases.

Targeting cytokines beyond tumor necrosis factor-α and interleukin-1 in rheumatoid arthritis

Targeting tumor necrosis factor-a has proven of considerable value in treatment for rheumatoid arthritis, with substantial benefits achieved in a proportion of treated patients. However, a significant number of patients do not achieve sufficient improvement and as a result there remains considerable unmet clinical need. A number of cytokines have recently been described with proinflammatory activity in rheumatoid arthritis synovitis, including interleukin (IL)-6, IL-12, IL-15, and IL-18. We review recent data that support the notion that some or all of these moieties offer therapeutic potential. The possibility that some may be useful in partial responders to tumor necrosis factor blocking agents or in synergy with the latter is discussed.

Association between IL-18 gene promoter polymorphisms and inflammatory bowel disease in a Japanese population

BACKGROUND

Interleukin-18 (IL-18) is a pleiotropic cytokine that induces the production of interferon (IFN)-gamma and also to regulate Th2 cytokines. Recently, association studies between IL-18 gene promoter polymorphisms and several Th1- or Th2-mediated inflammatory diseases were reported. In inflammatory bowel diseases (IBD), including ulcerative colitis (UC) and Crohn's disease (CD), recent evidence suggests that IL-18 is involved in the pathogenesis.

METHODS

Using DNA direct sequencing, we investigated IL-18 gene promoter polymorphisms at -607C/A and -137G/C. Allele, genotype, and haplotype frequencies were determined in 210 Japanese patients with UC, 205 patients with CD, and 212 controls.

RESULTS

In UC, the -137C allele frequency was significantly higher in the proctitis-type patients than in controls (Pc = 0.0068). The -137 genotype frequency was also significantly different in the proctitis-type patients than in controls (Pc = 0.032). No other allele and genotype frequencies were significantly associated with UC after Bonferroni correction. Furthermore, the frequency of haplotype 2 (-607A, -137C), which had a lower promoter activity and IFN-gamma mRNA level than the other haplotypes as previously reported, was significantly higher in the proctitis-type patients than in controls (Pc = 0.01). In CD, we could not find any significant differences.

CONCLUSIONS

IL-18 gene promoter polymorphisms may not be associated with disease susceptibility but related to the extent of disease in UC.

Dysregulation of Expression of Immunoregulatory and Cytokine Genes and Its Association with the Immaturity in Neonatal Phagocytic and Cellular Immunity

BACKGROUND

Innate and adaptive immunity is comprised of cellular and humoral factors that provide rapid protection against microbial invasion. However, immaturity of innate and adaptive immune responses in the perinatal period predisposes the neonate to increased infectious morbidity and mortality from a variety of organisms.

OBJECTIVES

To elucidate dysregulation of expression of various immunoregulatory and cytokine genes and its association with the immaturity in neonatal phagocytic cellular immunity.

METHODS

Comparison of protein production and mRNA of granulocyte macrophage colony-stimulating factor (GM-CSF), macrophage colony-stimulating factor (M-CSF), granulocyte colony-stimulating factor (G-CSF), interleukin (IL)-12, IL-15 and IL-18 in adult peripheral blood (APB) mononuclear cells (MNC) and cord blood (CB) MNC was studied. Effects of hematopoietic growth factors (HGFs, GM-CSF, M-CSF, G-CSF, IL-11) were studied in vivo in rats as well as randomized controlled studies conducted in neonates. Oligonucleotide microarrays were used to study gene expression patterns of activated CB and APB monocytes and dendritic cells.

RESULTS AND CONCLUSIONS

We demonstrated dysregulation of various immunoregulatory and cytokine genes in CB MNC. This dysregulation may in part explain the immaturity of neonatal cell-mediated immunity. There are probably various dysregulated cytokines yet to be discovered. Biological agents such as IL-2, IL-12, IL-11 and/or IL-18 alone or in combination with HGFs should be considered for future studies to identify new approaches to enhance neonatal host defense, and thereby decrease the incidence of neonatal sepsis and the consequent high risk of morbidity and mortality.

Immaturity of IL-18 gene expression and protein production in cord blood (CB) versus peripheral blood (PB) mononuclear cells and differential effects in natural killer (NK) cell development and function

We have previously demonstrated dysregulation of IL-12 and IL-15 gene and protein expression between activated cord blood (CB) versus peripheral blood (PB) mononuclear cells (MNCs). In the present study, we compared IL-18 gene expression and protein production and IL-18 mRNA half-life in basal versus activated CB versus PB MNCs, the effects of IL-18 +/- IL-12 on MNCs IFN-gamma protein production and ex vivo expansion and activation of CB with IL-12 + IL-2 + anti-CD3 +/- IL-18. Basal and activated levels of IL-18 were significantly higher in PB versus CB MNCs (P < 0.05). IL-18 mRNA was coincidental with protein levels and significantly lower in CB (P < 0.05) and its half-life significantly shorter in CB versus PB MNCs (P < 0.05). IL-18 synergistically with IL-12 induced IFN-gamma production from PB greater than CB MNCs (P < 0.05). NK cells expansion (P < 0.001) and cytotoxicity (P < 0.01) was significantly increased with IL-12 + IL-2 + anti-CD3 and IL-18. In summary IL-18 gene expression and protein production are significantly decreased in activated CB versus PB MNCs, in part secondary to increased degradation of CB IL-18 mRNA. These results may have implications for the mechanism(s) in part responsible for the immaturity of CB T-cell immunity.

Osteoblast responses to bacterial pathogens: a previously unappreciated role for bone-forming cells in host defense and disease progression

Although the primary roles of osteoblasts are to synthesize the components of bone matrix and to regulate the activity of bone resorbing osteoclasts, there is growing realization that osteoblasts have an additional function during bone diseases, such as osteomyelitis. Based on our recent studies, we propose a novel role for osteoblasts during bacterial infections of bone, namely, the initiation and maintenance of inflammatory immune responses. In this article, we describe how these nonleukocytic cells can perceive bacterial pathogens of bone to initiate the production of an array of immune regulatory molecules. This pattern of expression is one that could promote the recruitment of leukocytes to sites of bacterial challenge, initiate antigen-specific activation of infiltrating cells, and facilitate the development of cell-mediated host responses to intracellular pathogens of bone tissue, thereby identifying this cell type as a previously unappreciated component in host responses.

The effect of the physical characteristics of hydroxyapatite particles on human monocytes IL-18 production in vitro

Hydroxyapatite (HA) is widely used to coat the metal parts of prosthetic implants in order to improve their biocompatibility and as a bone defect filling material. HA has been demonstrated to produce particles at the prosthetic interface that lead to an activation of phagocytic cells that induce a cascade reaction leading to bone resorption and aseptic loosening. Monocytes/macrophages are commonly observed in the interface tissue, and are among the first cells to colonize the inflammatory site where they play a key role in the immune response. IL-18 is a pro-inflammatory cytokine. Monocytes/macrophages were described as IL-18 producing cells. IL-18 works antagonistically to IL-6, which activates osteoclastogenesis. In the present study, we investigated the ability of HA particles to induce the production of active IL-18 by human monocytes according to particle characteristics (size, sintering temperature and shape). Our study demonstrates, for the first time, that HA particles are capable of stimulating the production of the proinflammatory cytokine IL-18 in human monocytes according to their particle characteristics. The expression and the production of IL-18 was modified by the parameter studied. The difference observed between the expression and the production could be explain by the production of ICE. The needle shaped particles induced the larger production of IL-18.

Modulation of osteoclast formation

Osteoclasts are derived following the fusion of precursors of hematopoietic and myelomonocytic origin after appropriate stimulus, such as that afforded by RANKL and M-CSF. Thus the osteoclast can be considered as a specialized type of macrophage, and several of the factors that affect osteoclast formation also have affects upon macrophage differentiation. Inhibitors of osteoclast formation may perturb RANKL or M-CSF signalling or affect other signalling pathways. Several of these inhibitors are discussed with the view of their capacity to influence osteoclast differentiation, but not necessarily their activity.

Interleukin-3 and granulocyte-macrophage colony-stimulating factor inhibits tumor necrosis factor (TNF)-alpha-induced osteoclast differentiation by down-regulation of expression of TNF receptors 1 and 2

Osteoclasts, the multinucleated cells that resorb bone, differentiate from hemopoietic precursors of monocyte/macrophage lineage, which also give rise to macrophages or dendritic cells. In this study we investigated the mechanism by which interleukin-3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GM-CSF) inhibit tumor necrosis factor (TNF)-alpha-induced osteoclast differentiation in mouse osteoclast precursors. We show here that both IL-3 and GM-CSF potently inhibits TNF-alpha-induced osteoclast differentiation by direct action on osteoclast precursors. The inhibitory effect of IL-3 and GM-CSF on osteoclast differentiation was completely neutralized by anti-IL-3 and anti-GM-CSF antibodies, respectively. In addition, the inhibitory effect of IL-3 and GM-CSF on TNF-alpha-induced osteoclast differentiation was irreversible. In osteoclast precursors, IL-3 and GM-CSF inhibited c-Fms expression post-transcriptionally. Interestingly, IL-3 and GM-CSF down-regulated both mRNA and surface expression of TNF receptor 1 (TNFR1) and TNFR2. Furthermore, cells in the presence of IL-3 and GM-CSF showed high expression of macrophage antigen CD11b, and low expression of dendritic cells antigen CD11c and prolong exposure of osteoclast precursors to GM-CSF increased the CD11c expression compare with IL-3. In summary, we provide the first evidence that IL-3 and GM-CSF block TNF-alpha-induced osteoclast differentiation by down-regulation of mRNA and surface expression of TNFR1 and TNFR2.

Interleukin-18: a therapeutic target in rheumatoid arthritis?

Interleukin 18 (IL-18), a member of the IL-1 superfamily of cytokines has been demonstrated to be an important mediator of both innate and adaptive immune responses. Several reports have implicated its role in the pathogenesis of rheumatoid arthritis (RA). Although biologic therapy is firmly established in the treatment of a number of inflammatory diseases including RA, partial and non-responder patients constitute residual unmet clinical need. The aim of this article is to briefly review the biology of, and experimental approaches to IL-18 neutralisation, together with speculation as to the relative merits of IL-18 as an alternative to existing targets.

Interleukin (IL) 18 stimulates osteoclast formation through synovial T cells in rheumatoid arthritis: comparison with IL1 beta and tumour necrosis factor alpha

OBJECTIVE

To determine whether IL18 has any indirect effects on osteoclastogenesis mediated by T cells in RA synovium, and compare its effects with those of IL1 beta and TNF alpha.

METHODS

Resting T cells were isolated from peripheral blood of healthy donors, and stimulated with 2 microg/ml phytohaemagglutinin (PHA) and 0.5 ng/ml IL2 for 24 hours. Synovial T cells were isolated from RA synovial tissue. The levels of soluble receptor activator of the NF-kappa B ligand (RANKL), osteoprotegerin (OPG), IFN gamma, M-CSF, and GM-CSF were determined by ELISA. Membrane bound RANKL expression was analysed by flow cytometry. Commercially available human osteoclast precursors were cocultured with T cells to induce osteoclast formation, which was determined with tartrate resistant acid phosphatase staining and pit formation assay.

RESULTS

In PHA prestimulated T cells or RA synovial T cells, IL18, IL1 beta, or TNFalpha increased soluble RANKL production and membrane bound RANKL expression in a dose dependent manner. IL18, IL1 beta, and TNF alpha did not induce M-CSF, GM-CSF, IFN gamma, or OPG production in PHA prestimulated T cells or RA synovial T cells. IL18 increased the number of osteoclasts and bone resorption area on dentine slices in the coculture of human osteoclast precursors with PHA prestimulated T cells or RA synovial T cells; its ability was equivalent to that of IL1 beta, but less potent than that of TNF alpha. In the coculture system, OPG completely blocked osteoclast induction by IL18 or IL1 beta, and greatly inhibited induction by TNF alpha.

CONCLUSION

IL18, IL1 beta, or TNF alpha can indirectly stimulate osteoclast formation through up regulation of RANKL production from T cells in RA synovitis; IL18 is as effective as IL1 beta, but less potent than TNF alpha.

Secreted frizzled-related protein-1 inhibits RANKL-dependent osteoclast formation

We determined that sFRP-1 mRNA was differentially expressed by osteoblast/stromal cell lines and that sFRP-1 neutralizing antibodies and siRNA complementary to sFRP-1 coding sequence enhanced, while recombinant sFRP-1 inhibited, osteoclast formation. In studying the mechanism of action for sFRP-1, we found that sFRP-1 could bind recombinant RANKL. These results suggest potential cross-talk between Wnt and RANKL pathways.

INTRODUCTION

Osteoclast formation in normal bone remodeling requires the presence of osteoblast lineage cells that express RANKL and macrophage-colony-stimulating factor (M-CSF), which interact with their cognate receptors on the osteoclast precursor. We identified secreted Frizzled-related protein-1 (sFRP-1), which is known to bind to Wnt and inhibit the Wnt signaling pathway, as an osteoblast-derived factor that impinges on osteoclast formation and activity.

MATERIALS AND METHODS

Differential display of mRNA from osteoblast lineage cell lines established sFRP-1 to be highly expressed in an osteoclast supporting cell line. sFRP-1 expression in bone was determined by in situ hybridization, and the effects of sFRP-1 on osteoclast formation were determined using a neutralizing antibody, siRNA, for sFRP-1 and recombinant protein.

RESULTS

In situ hybridization revealed sFRP-1 mRNA expression in osteoblasts and chondrocytes in murine bone. sFRP-1 mRNA expression could be elevated in calvarial primary osteoblasts in response to prostaglandin E2 (PGE2) or interleukin (IL)-11, whereas many other osteotropic agents (e.g., IL-1, IL-6, calcitrol, parathyroid hormone) were without any effect. In vitro assays of osteoclast formation established sFRP-1 to be an inhibitor of osteoclast formation. Neutralizing antibodies against sFRP-1 enhanced TRACP+ mononuclear and multinuclear osteoclast formation (3- and 2-fold, respectively) in co-cultures of murine osteoblasts with spleen cells, whereas siRNA complementary to sFRP-1 coding sequence significantly enhanced osteoclast formation in co-cultures of KUSA O (osteoblast/stromal cell line) and bone marrow cells, cultured in the presence of PGE2 and 1,25(OH)2 vitamin D3. Recombinant sFRP-1 dose-dependently inhibited osteoclast formation in osteoblast/spleen co-cultures, RANKL + M-CSF-treated splenic cultures, and RANKL-treated RAW264.7 cell cultures, indicating a direct action of sFRP-1 on hematopoietic cells. Consistent with this, sFRP-1 was found to bind to RANKL in ELISAs.

CONCLUSION

sFRP-1 is expressed by osteoblasts and inhibits osteoclast formation. While sFRP-1 activity might involve the blocking of endogenous Wnt signaling, our results suggest that, alternatively, it could be because of direct binding to RANKL. This study describes a new mechanism whereby osteoblasts regulate osteoclastogenesis through the expression and release of sFRP-1.

Targeting cytokines beyond tumor necrosis factor-α and interleukin-1 in rheumatoid arthritis

Targeting tumor necrosis factor-a has proven of considerable value in treatment for rheumatoid arthritis, with substantial benefits achieved in a proportion of treated patients. However, a significant number of patients do not achieve sufficient improvement and as a result there remains considerable unmet clinical need. A number of cytokines have recently been described with proinflammatory activity in rheumatoid arthritis synovitis, including interleukin (IL) -6, IL-12, IL-15, and IL-18. We review recent data that support the notion that some or all of these moieties offer therapeutic potential. The possibility that some may be useful in partial responders to tumor necrosis factor blocking agents or in synergy with the latter is discussed.

Imbalance of osteoclastogenesis-regulating factors in patients with celiac disease

Celiac disease is an autoimmune disorder characterized by atrophy of the intestine villi triggered by ingestion of gluten in genetically susceptible individuals. The association between celiac disease and low BMD has been recognized, but the mechanisms of disturbance are poorly understood. We show imbalance of cytokines relevant to bone metabolism in celiac patients' sera and the direct effect of these sera on in vitro bone cell activity.

INTRODUCTION

Celiac disease is associated with mineral metabolism derangement and low BMD. We investigated whether imbalance of serum factors in celiac patients could affect human bone cell activity in vitro.

MATERIALS AND METHODS

We studied two groups of celiac patients--one on a gluten-free diet and another before the diet--both with decreased bone mass. Patients were investigated for bone turnover markers, and their sera were used for culturing bone cells from healthy donors and evaluate changes in cell activity.

RESULTS

The N-terminal telopeptide of procollagen type I and interleukin (IL)-6 were higher than normal in patients not on the gluten-free diet. IL-1beta and TNF-alpha/beta were normal in all patients. IL-12 was reduced in all patients, whereas IL-18 was reduced only in patients on the diet. The RANKL/osteoprotegerin (OPG) ratio was increased in patients not on the gluten-free diet. Persistently increased osteoclast numbers were obtained from peripheral blood mononuclear cells of healthy donors on incubation with sera of patients not on the gluten-free diet versus control sera and sera from patients on the diet. In human osteoblasts from healthy individuals, IL-18 was reduced on incubation with sera from all patients, whereas OPG expression was lower when sera from patients not on the diet were used. Proliferation, alkaline phosphatase, and nodule mineralization were increased in osteoblast cultures containing sera from all celiac patients, either on or not on the gluten-free diet.

CONCLUSIONS

We conclude that bone loss in celiac disease might also be caused by a cytokine imbalance directly affecting osteoclastogenesis and osteoblast activity.

Gamma interferon (IFN-gamma) and IFN-gamma-inducing cytokines interleukin-12 (IL-12) and IL-18 do not augment infection-stimulated bone resorption in vivo

Periapical granulomas are induced by bacterial infection of the dental pulp and result in destruction of the surrounding alveolar bone. In previous studies we have reported that the bone resorption in this model is primarily mediated by macrophage-expressed interleukin-1 (IL-1). The expression and activity of IL-1 is in turn modulated by a network of Th1 and Th2 regulatory cytokines. In the present study, the functional roles of the Th1 cytokine gamma interferon (IFN-gamma) and IFN-gamma-inducing cytokines IL-12 and IL-18 were determined in a murine model of periapical bone destruction. IL-12-/-, IL-18-/-, and IFN-gamma-/- mice were subjected to surgical pulp exposure and infection with a mixture of four endodontic pathogens, and bone destruction was determined by microcomputed tomography on day 21. The results indicated that all IL-12-/-, IL-18-/-, and IFN-gamma-/- mice had similar infection-stimulated bone resorption in vivo as wild-type control mice. Mice infused with recombinant IL-12 also had resorption similar to controls. IFN-gamma-/- mice exhibited significant elevations in IL-6, IL-10, IL-12, and tumor necrosis factor alpha in lesions compared to wild-type mice, but these modulations had no net effect on IL-1alpha levels. Recombinant IL-12, IL-18, and IFN-gamma individually failed to consistently modulate macrophage IL-1alpha production in vitro. We conclude that, at least individually, endogenous IL-12, IL-18, and IFN-gamma do not have a significant effect on the pathogenesis of infection-stimulated bone resorption in vivo, suggesting possible functional redundancy in proinflammatory pathways.

Osteoclastic potential of human CFU-GM: biphasic effect of GM-CSF

Human osteoclasts can be efficiently generated in vitro from cord blood mononuclear cells and derived CFU-GM colonies. However, CFU-M colonies are poorly osteoclastogenic. Short-term (2-48 h) treatment with GM-CSF stimulates osteoclast formation by proliferating precursors, whereas longer exposure favors dendritic cell formation.

INTRODUCTION

Osteoclasts (OC) differentiate from cells of the myelomonocytic lineage under the influence of macrophage-colony stimulating factor (M-CSF) and RANKL. However, cells of this lineage can also differentiate to macrophages and dendritic cells (DC) depending on the cytokine environment. The aims of this study were to develop an efficient human osteoclastogenesis model and to investigate the roles of granulocyte macrophage-colony stimulating factor (GM-CSF) and M-CSF in human OC differentiation.

MATERIALS AND METHODS

A human osteoclastogenesis model, using as precursors colony forming unit-granulocyte macrophage (CFU-GM) colonies generated from umbilical cord mononuclear cells cultured in methylcellulose with GM-CSF, interleukin (IL)-3 and stem cell factor (SCF), has been developed. CFU-GM, colony forming unit-macrophage (CFU-M), or mixed colonies were cultured on dentine with soluble RANKL (sRANKL) and human M-CSF with and without GM-CSF. Major endpoints were OC number, dentine resorption, and CD1a+ DC clusters.

RESULTS

Osteoclast generation from CFU-GM and mixed colonies treated with M-CSF and sRANKL for 7-14 days was highly efficient, but CFU-M colonies were poorly osteoclastogenic under these conditions. Pretreatment of precursors with M-CSF for 7 or 14 days maintained the precursor pool, but OCs were smaller and resorption was reduced. The effect of GM-CSF treatment was biphasic, depending on the timing and duration of exposure. Short-term treatment (2-48 h) at the beginning of the culture stimulated cell proliferation and enhanced OC formation up to 100%, independent of sRANKL. Longer-term GM-CSF treatment in the presence of sRANKL, however, inhibited OC generation with the formation of extensive CD1a+ DC clusters, accompanied by downregulation of c-Fos mRNA. Delaying the addition of GM-CSF resulted in progressively less inhibition of osteoclastogenesis.

CONCLUSIONS

Human CFU-GM, but not CFU-M, progenitors have high osteoclastogenic potential. GM-CSF plays an important role in osteoclastogenesis and has a biphasic effect: Short-term treatment potentiates OC differentiation by proliferating precursors, but persistent exposure favors DC formation.

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.

Resting T cells negatively regulate osteoclast generation from peripheral blood monocytes

There is accumulating evidence that T cells may be involved in osteoclastogenesis in a variety of murine systems. However, the precise role of human T cells in the regulation of osteoclast generation is still unclear. To address this issue, we investigated the effect of resting peripheral T cells on receptor activator of NF-kappaB ligand (RANKL)-induced osteoclast generation from human peripheral monocytes. Although osteoclasts were not generated in the culture of human peripheral blood mononuclear cells (PBMC) in the presence of RANKL and macrophage colony-stimulating factor (M-CSF), the addition of cyclosporine A (CsA), a potent inhibitor of T-cell function, resulted in the formation of an increasing number of lacunae resorption on dentine, suggesting T cells may inhibit osteoclast formation. In a coculture of T cells and monocytes, which were isolated from PBMC, T cells inhibited the osteoclast generation from monocytes, as determined by tartrate-resistant acid phosphatase (TRAP) staining and a pit assay using dentine. This inhibition of osteoclast generation by T cells was also observed in a culture of the parathyroid hormone-stimulated SaOS4/3 osteoblast cell line and monocytes. The culture in Transwell plates revealed that the cell-to-cell interaction was not required for the inhibition, suggesting that T-cell cytokines may be responsible for the inhibition. Among inhibitory T-cell cytokines on osteoclastogenesis, granulocyte-macrophage colony-stimulating factor (GM-CSF) and interferon-gamma (IFN-gamma) were actively produced by CD4 T cells but not CD8 T cells in the coculture of T cells with monocytes, and the neutralizing antibodies to these cytokines partially rescued the T-cell-induced inhibition of osteoclast formation. Although CsA did not affect RANKL-induced osteoclast generation in the culture of monocytes alone, it completely rescued the T-cell-induced inhibition of osteoclast formation and strongly inhibited the production of GM-CSF and IFN-gamma. Thus, we demonstrate that resting T cells negatively regulate the osteoclast generation via production of GM-CSF and IFN-gamma by CD4 T cells and that CsA stimulates the osteoclast generation through the inhibition of the production of these cytokines. These findings provide new insight into therapeutic strategies for immunosuppression-induced bone loss in transplant and other diseases.

Inhibition of RANKL-induced osteoclast formation in mouse bone marrow cells by IL-12: involvement of IFN-gamma possibly induced from non-T cell population

IL-12 was shown to have the potential to inhibit osteoclast formation in mouse bone marrow cells treated with macrophage colony-stimulating factor (M-CSF) and receptor activator of NF-kappaB ligand (RANKL). When bone marrow macrophages (BMM) were used as osteoclast precursors, IL-12 failed to inhibit M-CSF/RANKL-induced osteoclast formation from BMM. In coculture experiments using transwells, IL-12 did inhibit osteoclast formation from BMM cocultured with whole bone marrow cells. These results indicated that IL-12 indirectly affected M-CSF/RANKL-induced osteoclastogenesis in bone marrow cells and that the inhibition of IL-12 on osteoclast formation was caused by a humoral factor from bone marrow cells treated with IL-12. Experiments with anti-interferon (IFN)-gamma antibody and bone marrow cells from IFN-gamma receptor knockout mice revealed that IFN-gamma might be involved in the inhibition of osteoclast formation in this system. The expression of osteoprotegerin mRNA in bone marrow cells was not affected by treatment with IL-12. The inhibitory effect of IL-12 on osteoclast formation was also seen in the T cell-depleted bone marrow cells of normal mice and the whole bone marrow cells of athymic nude mice, while the inhibitory effect of IL-12 was partially suppressed in the B cell-depleted bone marrow cells. The inhibitory effect of IL-12 on M-CSF/RANKL-induced osteoclastogenesis was not accompanied with cell death, in contrast with our previous finding that the inhibitory effect of IL-12 on M-CSF/TNF-alpha-induced osteoclastogenesis is attributable to Fas and FasL-mediated apoptosis.

Genetic regulation of osteoclast development and function

Osteoclasts are the principal, if not exclusive, bone-resorbing cells, and their activity has a profound impact on skeletal health. So, disorders of skeletal insufficiency, such as osteoporosis, typically represent enhanced osteoclastic bone resorption relative to bone formation. Prevention of pathological bone loss therefore depends on an appreciation of the mechanisms by which osteoclasts differentiate from their precursors and degrade the skeleton. The past five years have witnessed important insights into osteoclast formation and function. Many of these discoveries have been made through genetic experiments that involved the rare hereditary disorder osteopetrosis.

IL-3 acts directly on osteoclast precursors and irreversibly inhibits receptor activator of NF-kappa B ligand-induced osteoclast differentiation by diverting the cells to macrophage lineage

Osteoclasts, the multinucleated cells that resorb bone, differentiate from hemopoietic precursors of the monocyte/macrophage lineage in the presence of M-CSF and receptor activator of NF-kappaB ligand (RANKL). In this study we investigated the role of IL-3 in osteoclast differentiation. We show here that IL-3, a cytokine secreted by activated T lymphocytes, inhibits RANKL-induced osteoclast differentiation by a direct action on early osteoclast precursors. Anti-IL-3 Ab neutralized the inhibitory effect of IL-3 on osteoclast differentiation. In addition, IL-3 inhibits TNF-alpha-induced osteoclast differentiation in bone marrow-derived macrophages. However, IL-3 has no inhibitory effect on mature osteoclasts. In osteoclast precursors, IL-3 prevents RANKL-induced nuclear translocation of NF-kappaB by inhibiting the phosphorylation and degradation of IkappaB. RT-PCR analysis revealed that IL-3 down-regulated c-Fos transcription. Interestingly, the osteoclast precursors in the presence of IL-3 showed strong expression of macrophage markers such as Mac-1, MOMA-2, and F4/80. Furthermore, the inhibitory effect of IL-3 on osteoclast differentiation was irreversible, and the osteoclast precursors preincubated in IL-3 were resistant to RANKL action. Thus, our results reveal for the first time that IL-3 acts directly on early osteoclast precursors and irreversibly blocks RANKL-induced osteoclast differentiation by diverting the cells to macrophage lineage.

Bone malformations in interleukin-18 transgenic mice

The in vivo effects of IL-18 on bone metabolism were investigated by histopathology in IL-18 transgenic mice. Deformed cortical bone and decreased turnover rate of lumbar trabecular bone are consistent with increased expression of IFN-gamma and IL-18 in the bone marrow. Interleukin (IL)-18 has been demonstrated to inhibit osteoclastogenesis in an in vitro co-culture system. We investigated the effects of IL-18 overexpression on bone metabolism by comparing bone characteristics in male IL-18 transgenic (TG) mice, which secrete mature murine IL-18 from their B- and T-cells, and their wildtype littermates (WT). Histopathological analysis revealed that the cortical bone of the femur was thinner and more deformed in IL-18 TG mice. Bone histomorphometry showed that the cortical bone area of the mid-diaphysis of the femur and the trabecular bone volume of the lumbar vertebrae were significantly reduced in IL-18 TG mice. IL-18 TG mice also exhibited significantly fewer osteoclasts and a reduced bone formation rate in the trabecular bones of their lumbar vertebrae. Real-time reverse transcriptase-polymerase chain reaction amplification of bone marrow cell mRNA revealed that interferon (IFN)-gamma mRNA expression was significantly increased, whereas IL-4 mRNA expression was significantly reduced, in IL-18 TG mice. However, the expression ratio of receptor activator of NFkappaB ligand and osteoprotegerin mRNA was not significantly altered. Thus, deformed cortical bone and a decreased turnover rate of lumbar trabecular bone are characteristic of IL-18 TG mice, and these features might be associated with the increased expression of IFN-gamma and IL-18 in the bone marrow.

T-cells mediate an inhibitory effect of interleukin-4 on osteoclastogenesis

IL-4 is an important cytokine that can influence bone. We identified two distinct actions of IL-4 to inhibit osteoclast formation: one direct on osteoclast progenitors and the second through the production of a novel T-cell surface-associated molecule(s). These data show a new link between the immune system and bone. The Th2 cytokine interleukin (IL)-4 inhibits osteoclast formation in vitro but also acts on other cell types found in bone, including T-cells and macrophages. Because some osteoclastogenesis inhibitors (e.g., IL-12) act indirectly through T-cells, we investigated IL-4 action on osteoclastogenesis in the presence of T-cells. Osteoclast formation from murine spleen cells treated with RANKL and macrophage colony-stimulating factor (M-CSF) was blocked by IL-4 even when spleen cells were depleted of T-cells (Thy 1.2+) and/or B-cells (B220+). Also, IL-4 inhibited osteoclastogenesis in RANKL/M-CSF-stimulated adherent spleen cells, Rag1 -/- (lymphocyte-deficient) spleen cells, and bone marrow macrophages, indicating an action on myelomonocytic cells to block osteoclastogenesis. In contrast, IL-4 did not inhibit osteoclastogenesis in cells from IL-4 receptor null mice (IL-4R -/-). However, when wildtype T-cells were added to IL-4R -/- spleen cell cultures, IL-4 inhibited osteoclast formation, indicating a T-cell-dependent action. Osteoclast formation in RANKL-stimulated RAW 264.7 cells was not inhibited by IL-4 unless T-cells were added to the culture. Separation of RAW 264.7 cells and T-cells by semipermeable membrane ablated this action of IL-4, suggesting the induction of a membrane-associated osteoclastogenesis inhibitor. However, membrane-bound inhibitors thymic shared antigen-1 (TSA-1) and osteoclast inhibitory lectin (OCIL) were not regulated by IL-4. In summary, at least two mechanisms of IL-4 -mediated osteoclastogenesis inhibition exist, including a direct action on myelomonocytic progenitors (from which osteoclasts derive) and an indirect action through T-cells that may involve novel anti-osteoclastic factors.

Gene expression profiles and transcription factors involved in parathyroid hormone signaling in osteoblasts revealed by microarray and bioinformatics

Parathyroid hormone (PTH) binds to its receptor PTH1R (parathyroid hormone 1 receptor) in osteoblastic cells to regulate bone remodeling and calcium homeostasis. While prolonged exposure to PTH causes increased bone resorption, intermittent injections of PTH have an anabolic effect on bone. The molecular mechanisms regulating these processes are still largely unknown. Here, we present our results on gene expression profile changes in the PTH-treated osteoblastic cell line, UMR 106-01, using DNA microarray analysis. A total of 125 known genes and 30 unknown expressed sequence tags (ESTs) were found to have at least 2-fold expression changes after PTH treatment at 4, 12, and 24 h. 14 genes were previously known to be PTH-regulated but many were unknown to be regulated by PTH prior to our experiments. Real-time reverse transcriptase-PCR confirmed that 90 and 50% of the genes are regulated more than 2-fold by PTH in UMR 106-01 and rat primary osteoblastic cells, respectively. Most genes belong to the following protein families: hormones, growth factors, and receptors; signal transduction pathway proteins; transcription factors; proteases; metabolic enzymes; structural and matrix proteins; transporters; etc. These results provide a comprehensive and deeper knowledge about PTH regulation of osteoblastic gene expression. Next, we designed a computational method to extract information about transcription factors likely involved in regulating these genes. These factors include those previously known to be involved in PTH signaling (AP-1 and the cAMP response element-binding protein), those that were identified by microarray data (C/EBP), and some novel transcription factors (AP-2, AP-4, SP1, FoxD3, etc.). Our results suggest that a reliable bioinformatics approach can be easily applied for other systems.

[Pathogenesis of osteoporosis in rheumatoid arthritis]

Osteoporosis is a major clinical problem in rheumatoid arthritis. Patients with rheumatoid arthritis frequently not only present with juxta articular osteopenia and bone erosions but also with generalized axial and appendicular osteoporosis at sites distant from inflamed joints. The pathogenesis of bone loss in rheumatoid arthritis is multifactorial; disease activity certainly is a major determinant of bone mass. Further pathogenetic factors include effects of anti-inflammatory therapies (in particular glucocorticoids), reduced mobility, estrogen and/or androgen deficiency. Recently, receptor activator of nuclear factor kappa B ligand (RANKL) and osteoprotegerin (OPG), a decoy receptor for receptor activator of nuclear factor kappa B ligand, were identified as central regulators of osteoclast recruitment and activation. Osteoprotegerin and receptor activator of nuclear factor kappa B ligand production is modulated by several cytokines, growth factors and hormones. In rheumatoid synovium both fibroblasts and activated T cells express receptor activator of nuclear factor kappa B ligand and thereby promote osteoclast recruitment and activation. Thus, osteoprotegerin and receptor activator of nuclear factor kappa B ligand appear to represent important molecular links between the immune system and bone metabolism in rheumatoid arthritis.

Interleukin-18 is a novel mitogen of osteogenic and chondrogenic cells

IL-18 was identified due to its ability to induce interferon-gamma (IFNgamma) production by T cells. It is a pleiotropic factor that shares structural features with IL-1 and functional activities with IL-12. IL-18 has a role in T cell development, where it has been demonstrated to act cooperatively with IL-12 to regulate IFNgamma. In bone, IL-18 is mainly produced by macrophages, but is also expressed by osteoblasts and inhibits osteoclast formation through granulocyte-macrophage colony-stimulating factor (GM-CSF) and not IFNgamma production by T cells. We have investigated the effects of IL-18 on mature osteoclast activity and for potential actions on osteoblasts or chondrocytes. The effects of IL-18 on mature osteoclast activity were determined using two assays: isolated mature osteoclast cell culture and neonatal murine calvarial organ culture. IL-18 did not affect bone resorption in either assay system. The actions of IL-18 on osteogenic cells (primary cell cultures of fetal rat and neonatal mouse osteoblasts, as well as neonatal mouse calvarial organ culture) and primary chondrocytes (canine) were assessed by proliferation assays (quantification of cell numbers and thymidine incorporation). In each assay system, IL-18 acted as a mitogen to the osteogenic and chondrogenic cells. Since IL-18 signal transduction may involve IFNgamma or GM-CSF, we assessed their involvement in the IL-18 response. IL-18 did not induce IFNgamma production by primary osteoblasts, but, of greater significance, IFNgamma had the opposing action to IL-18 in that it inhibited the primary osteoblast cell proliferation. Although IL-18 rapidly induced GM-CSF production by primary osteoblasts, IL-18 was still mitogenic in osteoblast preparations established from GM-CSF-deficient mice. Combined, these studies indicate that IL-18 may have an autocrine/paracrine mitogen role for both osteogenic and chondrogenic cells, independent of the production of IFNgamma or GM-CSF.

Porphyromonas gingivalis antigen preferentially stimulates T cells to express IL-17 but not receptor activator of NF-kappaB ligand in vitro

Although T cells have been implicated in the pathogenesis and are considered to be central to both their progression and control of chronic inflammatory periodontal diseases, the precise contribution of T cells to tissue destruction has not been fully clarified. Recently, interleukin (IL)-17 and receptor activator of Nuclear factor kappaB NF-kappaB ligand (RANKL) have received much attention as a result of their proinflammatory and bone metabolic roles, respectively. We therefore investigated the effect of outer membrane protein (OMP) from Porphyromonas gingivalis (P. gingivalis) on the expression of IL-17 and RANKL in peripheral blood mononuclear cells (PBMCs) and compared these between gingivitis and periodontitis, which are representative of stable and progressive lesions, respectively. The in situ expression of these molecules was also examined. P. gingivalis OMP stimulated PBMCs to express IL-17 at both the mRNA and protein level. Although the mean expression of mRNA was not different between the two groups, the mean level of IL-17 in the culture supernatants was higher in gingivitis patients than in periodontitis patients. However, the frequency of IL-17-positive samples was higher in the periodontitis patients. This stimulatory effect was not evident for RANKL expression in either periodontitis or gingivitis patients. In gingival tissue samples, IL-17 mRNA was detected in gingivitis more frequently than in periodontitis. The expression of RANKL mRNA was much lower than that of IL-17 in terms of both level and frequency. These results suggest that IL-17 but not RANKL may be involved in the pathogenesis of periodontal diseases. However, there may be negative regulatory mechanisms for IL-17 in gingivitis.

Interleukin-18

Interleukin-18 (IL-18), a recently described member of the IL-1 cytokine superfamily, is now recognized as an important regulator of innate and acquired immune responses. IL-18 is expressed at sites of chronic inflammation, in autoimmune diseases, in a variety of cancers, and in the context of numerous infectious diseases. This short review will describe the basic biology of IL-18 and thereafter address its potential effector and regulatory role in several human disease states including autoimmunity and infection. IL-18, previously known as interferon-gamma (IFN-gamma)-inducing factor, was identified as an endotoxin-induced serum factor that stimulated IFN-gamma production by murine splenocytes [(1) ]. IL-18 was cloned from a murine liver cell cDNA library generated from animals primed with heat-killed Propionibacterium acnes and subsequently challenged with lipopolysaccharide [(2) ]. Nucleotide sequencing of murine IL-18 predicted a precursor polypeptide of 192 amino acids lacking a conventional signal peptide and a mature protein of 157 amino acids. Subsequent cloning of human IL-18 cDNA revealed 65% homology with murine IL-18 [(3) ] and showed that both contain an unusual leader sequence consisting of 35 amino acids at their N terminus.

Osteoclast inhibitory lectin, a family of new osteoclast inhibitors

We have identified two novel type II membrane-bound C-lectins, designated mOCILrP1 and mOCILrP2, of 218 and 217 amino acids, respectively, that share substantial identity with the murine osteoclast inhibitory lectin (OCIL). The extracellular domains of mOCILrP1 and mOCILrP2 share 83 and 75% identity, respectively, with the extracellular domain of mOCIL. When the extracellular domains were expressed as recombinant proteins, each inhibited osteoclast formation in murine bone marrow cultures treated with M-CSF and RANKL with similar potencies to mOCIL (IC(50) of 0.2 ng/ml). Distinct but highly related genes encoded the three OCIL family members, with mOCIL and mOCILrP2 controlled by an inverted TATA promoter, and mOCILrP1 by a TTAAAA promoter. However only mOCIL was robustly regulated by calciotropic agents, while mOCILrP1 was not expressed, and mOCILrP2 was constitutively expressed in osteoblasts. Immunohistochemistry using antipeptide antibodies to the intracellular domain of mOCILrP1/mOCILrP2 and to mOCIL demonstrated that mOCIL and mOCILrP1/mOCILrP2 were concordantly expressed in osteoblasts, chondrocytes, and in extraskeletal tissues. Further, their cellular distribution was identical to that of RANKL. The identification of three distinct genes that were functionally related implies redundancy for OCIL, and their concordant expression with that of RANKL suggests that the RANKL:OPG axis may be further influenced by OCIL family members.

Effect of IL-12 on TNF-alpha-mediated osteoclast formation in bone marrow cells: apoptosis mediated by Fas/Fas ligand interaction

Recently, it has been found that differentiation into osteoclasts is induced by TNF-alpha. In this study, we investigated the effect of IL-12 on TNF-alpha-mediated osteoclastogenesis. When mouse bone marrow cells were cultured with TNF-alpha, osteoclast-like cells were formed. When they were cultured with both TNF-alpha and IL-12, the number of adherent cells in the bone marrow cells decreased in an IL-12 dose-dependent manner. A combination of IL-12 and TNF-alpha was necessary to induce death of the adherent cells in this culture system. Apoptotic alterations, which were indicated by morphological changes such as cellular atrophy, nuclear and cellular fragmentation, and biochemical changes such as DNA fragmentation, were observed in the adherent cells. Apoptosis of the adherent cells was markedly inhibited by anti-Fas ligand (FasL) Ab. RT-PCR and FACS analyses revealed that TNF-alpha up-regulated Fas transcription to lead to Fas expression on the surfaces of the adherent cells, whereas IL-12 could not induce Fas on the cells. In contrast, IL-12 induced FasL transcription to lead to FasL expression on the surfaces of nonadherent bone marrow cells, whereas TNF-alpha could not induce FasL on the cells. These results implied that apoptosis of the adherent cells in bone marrow cells might be caused by interaction between TNF-alpha-induced Fas on the adherent cells and IL-12-induced FasL on the nonadherent cells.

Interleukin-18 and interleukin-12 synergistically inhibit osteoclastic bone-resorbing activity

The effect of interleukin (IL)-18 on osteoclastic bone-resorbing activity was investigated in vitro. Osteoclast-enriched cells, about 70% of which were tartrate-resistant acid phosphatase (TRAP)-positive, were cultured on dentine slices, and then the total volume of resorption pits on each dentine slice was measured as bone-resorbing activity. When the effects of IL-18 alone at 1, 10, 100, and 1000 ng/mL were examined, bone-resorbing activity was significantly reduced only at 1000 ng/mL, by about 50%. However, IL-18 plus IL-12 (10 ng/mL each) reduced bone-resorbing activity by about 70%, whereas IL-12 alone had no significant effect. When the concentration of interferon (IFN)-gamma in the medium was measured, IL-18 or IL-12 was found to increase it slightly, and the combination of these two cytokines synergistically increased it. The inhibitory effect of the combination of the two cytokines was completely abolished by the addition of an anti-IFN-gamma neutralizing antibody to the medium, but IFN-gamma by itself did not inhibit osteoclastic bone resorption. IL-18 alone or in combination with IL-12 did not affect the number of TRAP-positive cells in culture of osteoclast-enriched cells. Osteoclasts prepared from osteoclast-enriched cells expressed mRNAs of IL-18 receptor, MyD88, and cathepsin K. Furthermore, IL-18 receptor protein was detected on the cell surface of osteoclasts. The present results indicate that the combination of IL-18 and IL-12 synergistically inhibits osteoclastic bone-resorbing activity, suggesting that IFN-gamma participates in the mechanism underlying this inhibition.

Cytokines in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic disease characterized by synovial inflammation that leads to the destruction of cartilage and bone. In the last decade, there was a lot of successful research in the field of cytokine expression and regulation. It has become clear that pro- and anti-inflammatory cytokines, derived predominantely from cells of macrophage lineage, play a major role in the initiation and perpetuation of the chronic inflammatory process in the RA synovial membrane. Monokines are abundant in rheumatoid synovial tissue, whereas low amounts of lymphokines are found. The involvement of pro-inflammatory cytokines, particularly interleukin (IL)-1 and tumor necrosis factor-alpha, in the pathogenesis of RA is well accepted. Recent data provide evidence that the pro-inflammatory cytokine IL-18 plays a crucial role in the development and sustenance of inflammatory joint diseases. There also appears to be a compensatory anti-inflammatory response in RA synovial membrane. It has become clear in the last few years that T cell-derived cytokines expressed preferentially by Th1 cells contribute to joint destruction and inflammation in RA. However, products from Th2 cells may be protective.

Interleukin-18 inhibits osteolytic bone metastasis by human lung cancer cells possibly through suppression of osteoclastic bone-resorption in nude mice

Interleukin (IL)-18 exhibits antitumor as well as antiosteoclastogenic activities. These findings suggest that IL-18 is a potential tool for the treatment of cancers with associated osteolytic bone metastasis. We have previously shown that systemic daily administration of recombinant (r) IL-18 inhibits the development of osteolytic bone metastasis by human breast cancer cells. Here we demonstrate that systemic daily administration of rIL-18 (1 microg/mouse/d) for 21 days significantly inhibited the number and the total area of osteolytic bone metastasis by RWGT2 human lung cancer cells in nude mice. No severe adverse effects were observed. Natural killer (NK) cells did not increase in splenocytes from rIL-18-treated mice, and the in vitro NK activity of splenocytes against RWGT2 cells was only weakly enhanced in the presence of IL-18. The administration of rIL-18 made no difference in the growth of subcutaneous tumors, histologic indices (mitotic index, apoptotic index, and Ki-67-labeling index) of subcutaneous tumors or metastatic bone foci, or in the number of osteoclasts along the bone surface adjacent to tumors. Moreover, serum levels of cytokines including interferon-gamma, IL-1alpha, IL-6, tumor necrosis factor-alpha, and granulocyte/macrophage colony-stimulating factor, which regulate bone-resorbing activity of osteoclasts, were evaluated. Among them, IL-6 was remarkably downregulated in rIL-18-treated mice. These findings suggest that IL-18 inhibits osteolytic bone metastasis possibly through suppression of osteoclastic bone-resorption mediated in part by IL-6.