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Hiroshi Takayanagi

Publications and source records attributed to Hiroshi Takayanagi.

At least 19 recordsLinked to original sources
PubMed2006

Regulation of osteoclast differentiation and function by the CaMK-CREB pathway.

Calcium (Ca(2+)) signaling is essential for a variety of cellular responses and higher biological functions. Ca(2+)/calmodulin-dependent kinases (CaMKs) and the phosphatase calcineurin activate distinct downstream pathways that are mediated by the transcription factors cAMP response element (CRE)-binding protein (CREB) and nuclear factor of activated T cells (NFAT), respectively. The importance of the calcineurin-NFAT pathway in bone metabolism has been demonstrated in osteoclasts, osteoblasts and chondrocytes. However, the contribution of the CaMK-CREB pathway is poorly understood, partly because of the difficulty of dissecting the functions of homologous family members. Here we show that the CaMKIV-CREB pathway is crucial for osteoclast differentiation and function. Pharmacological inhibition of CaMKs as well as the genetic ablation of Camk4 reduced CREB phosphorylation and downregulated the expression of c-Fos, which is required for the induction of NFATc1 (the master transcription factor for osteoclastogenesis) that is activated by receptor activator of NF-kappaB ligand (RANKL). Furthermore, CREB together with NFATc1 induced the expression of specific genes expressed by differentiated osteoclasts. Thus, the CaMK-CREB pathway biphasically functions to regulate the transcriptional program of osteoclastic bone resorption, by not only enhancing induction of NFATc1 but also facilitating NFATc1-dependent gene regulation once its expression is induced. This provides a molecular basis for a new therapeutic strategy for bone diseases.

Animals↗
PubMed2006

The molecular understanding of osteoclast differentiation.

Osteoclasts are multinucleated cells of monocyte/macrophage origin that degrade bone matrix. The differentiation of osteoclasts is dependent on a tumor necrosis factor (TNF) family cytokine, receptor activator of nuclear factor (NF)-kappaB ligand (RANKL), as well as macrophage colony-stimulating factor (M-CSF). Congenital lack of osteoclasts causes osteopetrosis, investigation of which has provided insights into the essential molecules for osteoclastogenesis, including TNF receptor-associated factor (TRAF) 6, NF-kappaB and c-Fos. In addition, genome-wide screening techniques have shed light on an additional set of gene products such as nuclear factor of activated T cells (NFAT) c1. Here we summarize the efforts to understand the sequential molecular events induced by RANKL during osteoclast differentiation. RANKL binds to its receptor RANK, which recruits adaptor molecules such as TRAF6. TRAF6 activates NF-kappaB, which is important for the initial induction of NFATc1. NFATc1 is activated by calcium signaling and binds to its own promoter, thus switching on an autoregulatory loop. An activator protein (AP)-1 complex containing c-Fos is required for the autoamplification of NFATc1, enabling the robust induction of NFATc1. Finally, NFATc1 cooperates with other transcriptional partners to activate osteoclast-specific genes. NFATc1 autoregulation is controlled by an epigenetic mechanism, which has profound implications for an understanding of the general mechanism of irreversible cell fate determination. From the clinical point of view, RANKL signaling pathway has promise as a strategy for suppressing the excessive osteoclast formation characteristic of a variety of bone diseases.

Animals↗
PubMed2006

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)-gamma 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-gamma 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.

Animals↗
PubMed2006

Evidence for licensing of IFN-gamma-induced IFN regulatory factor 1 transcription factor by MyD88 in Toll-like receptor-dependent gene induction program.

The recognition of microbial components by Toll-like receptors (TLRs) initiates signal transduction pathways, which trigger the expression of a series of target genes. It has been reported that TLR signaling is enhanced by cytokines such as IFN-gamma, but the mechanisms underlying this enhancement remain unclear. The MyD88 adaptor, which is essential for signaling by many TLRs, recruits members of the IFN regulatory factor (IRF) family of transcription factors, such as IRF5 and IRF7, to evoke the activation of TLR target genes. In this study we demonstrate that IRF1, which is induced by IFN-gamma, also interacts with and is activated by MyD88 upon TLR activation. We provide evidence that MyD88-associated IRF1 migrates into the nucleus more efficiently than non-MyD88-associated IRF1 and that this IRF1 selectively participates in the TLR-dependent gene induction program. The critical role of MyD88-dependent "IRF1 licensing" is underscored by the observation that the induction of a specific gene subset downstream of the TLR-MyD88 pathway, such as IFN-beta, inducible NO synthase, and IL-12p35, are impaired in Irf1-deficient cells. Thus, our present study places IRF1 as an additional member participating in MyD88 signaling and provides a mechanistic insight into the enhancement of the TLR-dependent gene induction program by IFN-gamma.

Animals↗
PubMed2006

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.

Arthritis, Rheumatoid↗
PubMed2005

Autoamplification of NFATc1 expression determines its essential role in bone homeostasis.

NFATc1 and NFATc2 are functionally redundant in the immune system, but it was suggested that NFATc1 is required exclusively for differentiation of osteoclasts in the skeletal system. Here we provide genetic evidence that NFATc1 is essential for osteoclast differentiation in vivo by adoptive transfer of NFATc1(-/-) hematopoietic stem cells to osteoclast-deficient Fos(-/-) mice, and by Fos(-/-) blastocyst complementation, thus avoiding the embryonic lethality of NFATc1(-/-) mice. However, in vitro osteoclastogenesis in NFATc1-deficient cells was rescued by ectopic expression of NFATc2. The discrepancy between the in vivo essential role of NFATc1 and the in vitro effect of NFATc2 was attributed to selective autoregulation of the NFATc1 gene by NFAT through its promoter region. This suggested that an epigenetic mechanism contributes to the essential function of NFATc1 in cell lineage commitment. Thus, this study establishes that NFATc1 represents a potential therapeutic target for bone disease and reveals a mechanism that underlies the essential role of NFATc1 in bone homeostasis.

Animals↗
PubMed2005

Contribution of nuclear factor of activated T cells c1 to the transcriptional control of immunoreceptor osteoclast-associated receptor but not triggering receptor expressed by myeloid cells-2 during osteoclastogenesis.

Bone homeostasis depends on the coordination of osteoclastic bone resorption and osteoblastic bone formation. Receptor activator of NF-kappaB ligand (RANKL) induces osteoclast differentiation through activating a transcriptional program mediated by the key transcription factor nuclear factor of activated T cells (NFAT) c1. Immunoreceptors, including osteoclast-associated receptor (OSCAR) and triggering receptor expressed by myeloid cells (TREM)-2, constitute the co-stimulatory signals required for RANKL-mediated activation of calcium signaling, which leads to the activation of NFATc1. However, it remains unknown whether the expression of immunoreceptors are under the control of NFATc1. Here we demonstrate that the expression of OSCAR, but not that of TREM-2, is up-regulated during osteoclastogenesis and markedly suppressed by the calcineurin inhibitor FK506, suggesting that OSCAR is transcriptionally regulated by NFATc1. NFATc1 expression results in the activation of the OSCAR promoter, which was found to be further enhanced by co-expression of PU.1 and microphthalmia-associated transcription factor (MITF). We further provide evidence that NFATc1 specifically regulates OSCAR by chromatin immunoprecipitation assay and quantification of OSCAR and TREM-2 mRNA in NFATc1-/- cells. Thus, OSCAR but not TREM-2 is involved in the positive feedback loop of the immunoreceptor-NFATc1 pathway during osteoclastogenesis. Although several immunoreceptors have been identified as co-stimulatory molecules for RANKL, the expression and function are differentially regulated. These mechanisms, possibly together with the delicate regulation of their ligands on osteoblasts, may provide the exquisite machinery for the modulation of osteoclastogenesis in the maintenance of bone homeostasis.

Animals↗
PubMed2005

NFAT and Osterix cooperatively regulate bone formation.

Immunosuppressants are crucial in the prevention of detrimental immune reactions associated with allogenic organ transplantation, but they often cause adverse effects in a number of biological systems, including the skeletal system. Calcineurin inhibitors FK506 and cyclosporin A inhibit nuclear factor of activated T cells (NFAT) activity and induce strong immunosuppression. Among NFAT proteins, NFATc1 is crucial for the differentiation of bone-resorbing osteoclasts. Here we show FK506 administration induces the reduction of bone mass despite a blockade of osteoclast differentiation. This reduction is caused by severe impairment of bone formation, suggesting that NFAT transcription factors also have an important role in the transcriptional program of osteoblasts. In fact, bone formation is inhibited in Nfatc1- and Nfatc2-deficient cells as well as in FK506-treated osteoblasts. Overexpression of NFATc1 stimulates Osterix-dependent activation of the Col1a1 (encoding type I collagen) promoter, but not Runx2-dependent activation of the Bglap1 (encoding osteocalcin) promoter. NFAT and Osterix form a complex that binds to DNA, and this interaction is important for the transcriptional activity of Osterix. Thus, NFAT and Osterix cooperatively control osteoblastic bone formation. These results may provide important insight into the management of post-transplantation osteoporosis as well as a new strategy for promoting bone regeneration in osteopenic disease.

Animals↗
PubMed2005

mu-Calpain regulates receptor activator of NF-kappaB ligand (RANKL)-supported osteoclastogenesis via NF-kappaB activation in RAW 264.7 cells.

To clarify the role of calpain in the receptor activator of NF-kappaB ligand (RANKL)-supported osteoclastogenesis, RANKL-induced calpain activation was examined by using murine RAW 264.7 cells and bone marrow-derived monocyte/macrophage progenitors. We found that calpain activity increased in response to RANKL in both cell types based on alpha-spectrinolysis and that mu-calpain, rather than m-calpain, was activated during RANKL-supported osteoclastogenesis in RAW 264.7 cells. Overexpression of mu-calpain clearly augmented RANKL-supported osteoclastogenesis in RAW 264.7 cells, thereby implicating its pivotal role in this process. Cell-permeable calpain inhibitors, including calpastatin and calpeptin, were sufficient to suppress RANKL-supported osteoclastogenesis based on decreased expression of the osteoclastogenic marker, matrix metalloproteinase 9, and the generation of tartrate-resistant acid phosphatase-positive multinucleated cells in both cell types. Calpain inhibitors suppressed NF-kappaB activation via inhibition of the cleavage of inhibitor of NF-kappaB(IkappaBalpha)in RAW 264.7 cells. Taken together, our findings suggest that mu-calpain is essential to the regulation of RANKL-supported osteoclastogenesis via NF-kappaB activation.

Animals↗
PubMed2005

Stat1-mediated cytoplasmic attenuation in osteoimmunology.

Signal transducer and activator of transcription 1 (Stat1) is a critical mediator of gene transcription in type I interferon (IFN-alpha/beta) signaling that is essential for host defense against viruses. In the skeletal system, type I IFNs (IFN-alpha/beta) also play an important physiological role in the inhibition of receptor activator of NF-kappaB ligand (RANKL)-induced osteoclast differentiation and bone resorption: mice deficient in IFN signaling exhibit decreased bone mass accompanied by the activation of osteoclastogenesis. On the other hand, an unexpected increase in bone mass was observed in Stat1-deficient mice, indicating that Stat1 has a hitherto unknown function in the regulation of bone formation. Indeed, Stat1 was found to have a unique, non-canonical function as a cytoplasmic attenuator of Runx2, a key transcription factor for osteoblast differentiation. Thus, the loss of Stat1 results in excessive activation of Runx2 and osteoblast differentiation, thereby tipping the balance in favor of bone formation over bone resorption. This is an interesting example in which a latent transcription factor attenuates the activity of another transcription factor in the cytoplasm, and reveals a novel regulatory mechanism of bone remodeling by immunomodulatory molecules. Here, we summarize recent advances in the study of Stat1 and IFNs in the context of osteoimmunology, including latest reports that question whether the inhibitory function of Stat1 in chondrocytes is responsible for dwarfism in achondroplasia.

Animals↗
PubMed2005

RANK-mediated amplification of TRAF6 signaling leads to NFATc1 induction during osteoclastogenesis.

RANK and CD40 activate NF-kappaB and MAPKs to similar levels via TRAF6. Even though overexpression of TRAF6 results in osteoclast formation, RANK but not CD40 promotes osteoclastogenesis. To understand the molecular basis for RANK-specific activity in osteoclastogenesis, we created an osteoclast formation system driven by anti-human CD40 antibody-mediated stimulation of a chimeric receptor, h40/mRK, which consists of the extracellular domain of human CD40 and the transmembrane and cytoplasmic domains of mouse RANK. By introducing mutations into three TRAF6-binding sites of RANK, we found that h40/mRK with a single TRAF6-binding site efficiently induced Ca2+ oscillation and expression of NFATc1, a master switch in osteoclastogenesis, whereas CD40 carrying a single TRAF6-binding site did not. However, expression of CD40 that was approximately 100 times greater than that of h40/mRK resulted in osteoclast formation, indicating that the RANK-TRAF6 signal is more potent than the CD40-TRAF6 signal in terms of NFATc1 activation and osteoclastogenesis. These results suggest that RANK may harbor a specific domain that amplifies TRAF6 signaling.

Animals↗
PubMed2005

Mechanistic insight into osteoclast differentiation in osteoimmunology.

Recently a close relationship between the immune and skeletal systems or the interdisciplinary field called osteoimmunology has attracted much attention due to the observations that bone destruction is caused by an abnormal activation of the immune system in rheumatoid arthritis, and that mice lacking immunomodulatory molecules often exhibit an unexpected bone phenotype. Osteoclasts are cells of monocyte/macrophage origin that degrade the bone matrix. They are among the key players in the control of bone metabolism in health and disease. Receptor activator of NF-kappaB ligand (RANKL), a tumor necrosis factor (TNF) family cytokine, induces the differentiation of osteoclasts in the presence of macrophage-colony stimulating factor. RANKL activates TRAF6, c-Fos, and calcium signaling pathways, all of which are indispensable for the induction and activation of nuclear factor of activated T cells (NFAT) c1, the master transcription factor for osteoclastogenesis. The autoamplification of NFATc1 gene results in the efficient induction of osteoclast-specific genes. An AP-1 transcription factor complex containing c-Fos plays a crucial role in these processes, although results in conditional knockout mice show that Jun family members have a redundant role. The immunoreceptor tyrosine-based activation motif (ITAM) is an important signaling component for a number of receptors in the immune system including T-cell, B-cell, NK-cell, and Fc receptors, but its contribution to the skeletal system remains unclarified. In search for the calcium-mobilizing mechanism during osteoclastogenesis we determined that multiple immunoglobulinlike receptors associated with ITAM-harboring adaptors, Fc receptor common gamma chain (FcRgamma), and DNAX-activating protein (DAP) 12, are essential for osteoclastogenesis. In osteoclast precursor cells FcRgamma-associated receptors include osteoclast-associated receptor and paired immunoglobulinlike receptor A, while triggering receptor expressed in myeloid cells 2 and signal-regulatory protein beta1 preferentially associate with DAP12. In cooperation with RANKL these receptors activate phospholipase Cgamma and calcium signaling essential for the induction of NFATc1 through ITAM phosphorylation. Thus we have established the importance of the ITAM-mediated costimulatory signals in RANKL-induced osteoclast differentiation, which is analogous to the role of costimulatory signals in the immune system. Here we summarize recent advances in the study of signaling mechanism of osteoclast differentiation in the context of osteoimmunology.

Animals↗
PubMed2005

Osteoimmunological insight into bone damage in rheumatoid arthritis.

Research into the bone destruction associated with rheumatoid arthritis has highlighted the importance of the interplay of the immune and skeletal systems. Arthritic bone destruction is attributable to the defective control of osteoclastogenesis by T cells. We revealed that excessive expression of receptor activator of NF-kappaB ligand (RANKL) and a paucity of interferon-gamma underlie the enhanced osteoclastogenesis in arthritis. The interdisciplinary research field called osteoimmunology has attracted further attention after identification of a number of unexpected bone phenotypes in mice lacking immunomodulatory molecules. Accumulating evidence suggests that the immune and skeletal systems share not only cytokines but also various signaling molecules, transcription factors, and membrane receptors. Thus, bone turns out to be a dynamic tissue that is constantly renewed, where the immune system participates to a hitherto unexpected extent. This emerging field will be of great importance for a better understanding and treatment of rheumatic diseases.

Journal Article↗
PubMed2005

Interplay between interferon and other cytokine systems in bone metabolism.

Interferons (IFNs) play crucial roles in the regulation of a wide variety of innate and adaptive immune responses. Type I interferons (IFN-alpha/beta) are central to the host defense against pathogens such as viruses, whereas type II interferon (IFN-gamma) mainly contributes to the T-cell-mediated regulation of the immune responses. Studies of bone destruction associated with rheumatoid arthritis have highlighted the importance of the interaction between the immune and skeletal systems. Recently, a new research area, termed osteoimmunology, has been spawned by a series of studies focusing on the signaling networks between IFN and other cytokines in bone metabolisms. It has been revealed that IFN-gamma interferes with the osteoclast differentiation induced by receptor activator of nuclear factor-kappaB ligand (RANKL), and this mechanism is critical for the suppression of pathological bone resorption associated with inflammation. In addition, RANKL induces the IFN-beta gene in osteoclast precursor cells, and this induction constitutes a critical aspect of the negative feedback regulation mechanisms of RANKL signaling to suppress excessive osteoclastogenesis. Furthermore, a novel function of signal transducer and activator of transcription 1 (Stat1), the essential transcription factor for both type I and type II IFN responses, was revealed in the regulation of osteoblast differentiation. Collectively, these studies unveil novel aspects of the IFN system and indicate the operation of the intricate signaling network among IFN and other cytokine systems in bone remodeling, which might offer a molecular basis for the treatment of bone diseases.

Animals↗
PubMed2005

Inflammatory bone destruction and osteoimmunology.

OBJECTIVES: The metabolism of hard tissue is influenced by the immune system. Research into the bone destruction associated with inflammatory diseases such as periodontal disease and rheumatoid arthritis has highlighted the importance of the interplay of the immune and skeletal systems. This interdisciplinary research field, called 'osteoimmunology', has become increasingly important for each system by itself as well as the biology linking them. The history and recent progress of this field are reviewed. MATERIAL AND METHODS: 'Osteoimmunology' was coined to describe the pioneering work on the T-cell regulation of osteoclastogenesis by the receptor activator of nuclear factor-kappaB ligand (RANKL) and interferon (IFN)-gamma. Accumulating evidence suggests that the immune and skeletal systems share not only cytokines but also various signaling molecules, transcription factors and membrane receptors. The contribution of T cells to the pathogenesis of inflammatory bone destruction is discussed, and our recent findings are summarized to illustrate how the osteoimmunological network functions. RESULTS: RANKL is an osteoclastogenic cytokine that links bone and the immune system. Immunomodulatory cytokines such as IFNs also participate in the regulation of RANKL signaling and inflammatory bone loss. The transcription factor nuclear factor of activated T cells c1 (NFATc1) has been identified as a master switch regulator of osteoclastogenesis. In addition, immunoglobulin-like receptors are critically involved in bone homeostasis. CONCLUSION: Bone turns out to be a dynamic tissue that is constantly renewed, where the immune system participates to a hitherto unexpected extent. This emerging field will be of great importance to a better understanding and treatment of diseases of the skeletal and immune systems, as well as to the fundamental biology underpinning both.

Animals↗
PubMed2005

[GeneChip analysis for osteoimmunology].

The interdisciplinary field called osteoimmunology has attracted much attention, due to the observations that bone destruction is caused by an abnormal activation of the immune system in rheumatoid arthritis, and mice lacking immunomodulatory molecules often exhibit an unexpected bone phenotype. Osteoclasts are cells of monocyte/macrophage origin that degrade the bone matrix in health and disease. Receptor activator of NF-kappaB ligand (RANKL), a tumor necrosis factor (TNF) family cytokine, is an essential osteoclastogenic factor linking the bone and the immune system. In the genomewide screening of RANKL-inducible genes using GeneChip, we identified nuclear factor of activated T cells c1 (NFATc1) as the master transcription factor for osteoclastogenesis. We also applied the GeneChip method to the analysis of osteoimmunological regulation: analysis of costimulatory signal for RANKL and the target genes of antirheumatic drugs. Here we summarize our recent findings in the field of osteoimmunology obtained by GeneChip.

Animals↗