Biomedical subjects

Nacksung Kim

Publications and source records attributed to Nacksung Kim.

At least 19 recordsLinked to original sources

PubMed2007

Osteoblasts support B-lymphocyte commitment and differentiation from hematopoietic stem cells.

Early B lymphopoiesis in mammals is induced within the bone marrow (BM) microenvironment, but which cells constitute this niche is not known. Previous studies had shown that osteoblasts (OBs) support hematopoietic stem cell (HSC) proliferation and myeloid differentiation. We now find that purified primary murine OBs also support the differentiation of primitive hematopoietic stem cells through lymphoid commitment and subsequent differentiation to all stages of B-cell precursors and mature B cells. Lin(-)Sca-1(+)Rag-2(-) BM cell differentiation to B cells requires their attachment to OBs in vitro, and this developmental process is mediated via VCAM-1, SDF-1, and IL-7 signaling induced by parathyroid hormone (PTH). Addition of cytokines produced by nonosteoblastic stromal cells (c-Kit ligand, IL-6, and IL-3) shifted the cultures toward myelopoiesis. Confirming the role of OBs in B lymphopoiesis, we found that selective elimination of osteoblasts in Col2.3Delta-TK transgenic mice severely depleted pre-pro-B and pro-B cells from BM, preceding any decline in HSCs. Taken together, these results demonstrate that osteoblasts are both necessary and sufficient for murine B-cell commitment and maturation, and thereby constitute the cellular homolog of the avian bursa of Fabricius.

Animals↗

PubMed2006

Enhancer of polycomb1, a novel homeodomain only protein-binding partner, induces skeletal muscle differentiation.

Homeodomain only protein, Hop, is an unusual small protein that modulates target gene transcription without direct binding to DNA. Here we show that Hop interacts with Enhancer of Polycomb1 (Epc1), a homolog of a Drosophila polycomb group gene product that regulates transcription, to induce the skeletal muscle differentiation. Yeast two-hybrid assay with the human adult heart cDNA library revealed that Hop can associate with Epc1. The amino-terminal domain of Epc1 as well as full Epc1 physically interacted with Hop in mammalian cells and in yeast. Epc1 is highly expressed in the embryonic heart and adult skeletal muscles. Serum deprivation induced differentiation of H9c2, a myoblast cell line, into skeletal myocytes, and Epc1 was up-regulated. Differentiation of H9c2 was induced by Epc1 overexpression, although it was severely impaired in Epc1-knockdown cells. Co-transfection of Hop potentiated Epc1-induced transactivation of myogenin and myotube formation. Hop knock-out mice elicited a decrease in myosin heavy chain and myogenin expressions in skeletal muscle and showed delay in hamstring muscle healing after injury. Differentiation was impaired in skeletal myoblasts from Hop knock-out mice. These results suggest that Epc1 plays a role in the initiation of skeletal muscle differentiation, and its interaction with Hop is required for the full activity.

Animals↗

PubMed2006

MafB negatively regulates RANKL-mediated osteoclast differentiation.

Receptor activator of nuclear factor kappaB ligand (RANKL) induces osteoclast formation from hematopoietic cells via regulation of various transcription factors. Here, we show that MafB negatively regulates RANKL-induced osteoclast differentiation. Expression levels of MafB are significantly reduced by RANKL during osteoclastogenesis. Overexpression of MafB in bone marrow-derived monocyte/macrophage lineage cells (BMMs) inhibits the formation of TRAP(+) multinuclear osteoclasts, but phagocytic activity of BMMs is retained. Furthermore, overexpression of MafB in BMMs attenuates the gene induction of NFATc1 and osteoclast-associated receptor (OSCAR) during RANKL-mediated osteoclastogenesis. In addition, MafB proteins interfere with the DNA-binding ability of c-Fos, Mitf, and NFATc1, inhibiting their transactivation of NFATc1 and OSCAR. Furthermore, reduced expression of MafB by RNAi enhances osteoclastogenesis and increases expression of NFATc1 and OSCAR. Taken together, our results suggest that MafB can act as an important modulator of RANKL-mediated osteoclastogenesis.

Animals↗

PubMed2006

v-ATPase V0 subunit d2-deficient mice exhibit impaired osteoclast fusion and increased bone formation.

Matrix-producing osteoblasts and bone-resorbing osteoclasts maintain bone homeostasis. Osteoclasts are multinucleated, giant cells of hematopoietic origin formed by the fusion of mononuclear pre-osteoclasts derived from myeloid cells. Fusion-mediated giant cell formation is critical for osteoclast maturation; without it, bone resorption is inefficient. To understand how osteoclasts differ from other myeloid lineage cells, we previously compared global mRNA expression patterns in these cells and identified genes of unknown function predominantly expressed in osteoclasts, one of which is the d2 isoform of vacuolar (H(+)) ATPase (v-ATPase) V(0) domain (Atp6v0d2). Here we show that inactivation of Atp6v0d2 in mice results in markedly increased bone mass due to defective osteoclasts and enhanced bone formation. Atp6v0d2 deficiency did not affect differentiation or the v-ATPase activity of osteoclasts. Rather, Atp6v0d2 was required for efficient pre-osteoclast fusion. Increased bone formation was probably due to osteoblast-extrinsic factors, as Atp6v02 was not expressed in osteoblasts and their differentiation ex vivo was not altered in the absence of Atp6v02. Our results identify Atp6v0d2 as a regulator of osteoclast fusion and bone formation, and provide genetic data showing that it is possible to simultaneously inhibit osteoclast maturation and stimulate bone formation by therapeutically targeting the function of a single gene.

Animals↗

PubMed2006

Ribavirin enhances osteoclast formation through osteoblasts via up-regulation of TRANCE/RANKL.

Hepatitis C combination therapy comprising ribavirin and interferon-alpha causes dramatic improvement with the sustained virological response; however, this treatment may result in the loss of bone mineral density. To investigate the effects of ribavirin on bone cells, we examined osteoblast differentiation as well as the formation of osteoclasts from their precursors. Ribavirin enhances osteoclast formation through osteoblasts by up-regulation of TRANCE/RANKL gene expression, whereas it has no significant effect on either osteoblast differentiation or on bone formation. Understanding ribavirin's underlying mechanism of action on bone cells will enable the improved management of bone loss in chronic hepatitis C patients.

Alkaline Phosphatase↗

PubMed2006

Protective effect of the DNA vaccine encoding the major house dust mite allergens on allergic inflammation in the murine model of house dust mite allergy.

BACKGROUND: Vaccination with naked DNA encoding antigen induces cellular and humoral immunity characterized by the activation of specific Th1 cells. OBJECTIVE: To evaluate the effects of vaccination with mixed naked DNA plasmids encoding Der p 1, Der p 2, Der p 3, Der f 1, Der f 2, and Der f 3, the major house dust mite allergens on the allergic inflammation to the whole house dust mites (HDM) crude extract. METHODS: Three hundred micrograms of these gene mixtures were injected into muscle of BALB/c mice. Control mice were injected with the pcDNA 3.1 blank vector. After 3 weeks, the mice were actively sensitized and inhaled with the whole house dust mite extract intranasally. RESULTS: The vaccinated mice showed a significantly decreased synthesis of total and HDM-specific IgE compared with controls. Analysis of the cytokine profile of lymphocytes after challenge with HDM crude extract revealed that mRNA expression of interferon-gamma was higher in the vaccinated mice than in the controls. Reduced infiltration of inflammatory cells and the prominent infiltration of CD8+ T cells were observed in histology of lung tissue from the vaccinated mice. CONCLUSION: Vaccination with DNA encoding the major house dust mite allergens provides a promising approach for treating allergic responses to whole house dust mite allergens.

Journal Article↗

PubMed2006

Osteoimmunology: interplay between the immune system and bone metabolism.

Studies of bone and the immune system have converged in recent years under the banner of osteoimmunology. The immune system is spawned in the bone marrow reservoir, and investigators now recognize that important niches also exist there for memory lymphocytes. At the same time, various factors produced during immune responses are capable of profoundly affecting regulation of bone. Mechanisms have evolved to prevent excessive interference by the immune system with bone homeostasis, yet pathologic bone loss is a common sequela associated with autoimmunity and cancer. There are also developmental links, or parallels, between bone and the immune system. Cells that regulate bone turnover share a common precursor with inflammatory immune cells and may restrict themselves anatomically, in part by utilizing a signaling network analogous to lymphocyte costimulation. Efforts are currently under way to further characterize how these two organ systems overlap and to develop therapeutic strategies that benefit from this understanding.

Animals↗

PubMed2005

Inhibition of histone deacetylation blocks cardiac hypertrophy induced by angiotensin II infusion and aortic banding.

BACKGROUND: A number of distinct stress signaling pathways in myocardium cause cardiac hypertrophy and heart failure. Class II histone deacetylases (HDACs) antagonize several stress-induced pathways and hypertrophy. However, cardiac hypertrophy induced by transgenic overexpression of the homeodomain only protein, HOP, can be prevented by the nonspecific HDAC inhibitors trichostatin A and valproic acid, suggesting that alternate targets that oppose class II HDAC function might exist in myocardium. We tested the effects of several HDAC inhibitors, including a class I HDAC-selective inhibitor, SK-7041, on cardiac hypertrophy induced by angiotensin II (Ang II) treatment or aortic banding (AB). METHODS AND RESULTS: Cardiac hypertrophy was induced by chronic infusion of Ang II or by AB in mice or rats and evaluated by determining the ratio of heart weight to body weight or to tibia length, cross-sectional area, or echocardiogram. Cardiac hypertrophy induced by Ang II or AB for 2 weeks was significantly reduced by simultaneous administration of trichostatin A, valproic acid, or SK-7041. Echocardiogram revealed that exaggerated left ventricular systolic dimensions were relieved by HDAC inhibitors. HDAC inhibitors partially reversed preestablished cardiac hypertrophy and improved survival of AB mice. The expressions of atrial natriuretic factor, alpha-tubulin, beta-myosin heavy chain, and interstitial fibrosis were reduced by HDAC inhibition. CONCLUSIONS: These results suggest that the predominant effect of HDAC inhibition, mainly mediated by class I HDACs, is to prevent cardiac hypertrophy in response to a broad range of agonist and stretch stimuli.

Angiotensin II↗

PubMed2005

Id helix-loop-helix proteins negatively regulate TRANCE-mediated osteoclast differentiation.

Tumor necrosis factor (TNF)-related activation-induced cytokine (TRANCE) induces osteoclast formation from monocyte/macrophage lineage cells via various transcription factors, including the Mi transcription factor (Mitf). Here, we show that inhibitors of differentiation/DNA binding (Ids), helix-loop-helix (HLH) transcription factors, negatively regulate TRANCE-induced osteoclast differentiation. Expression levels of Id1, Id2, and Id3 genes are significantly reduced by TRANCE during osteoclastogenesis. Interestingly, overexpression of the 3 Id genes in bone marrow-derived monocyte/macrophage lineage cells (BMMs) inhibits the formation of tartrate-resistant acid phosphatase (TRAP)-positive multinuclear osteoclasts, but it does not alter the ability of BMMs to either phagocytose or differentiate into dendritic cells (DCs). Overexpression of Id2 in BMMs attenuates the gene induction of nuclear factor of activated T cells c1 (NFATc1) and osteoclast-associated receptor (OSCAR) during TRANCE-mediated osteoclastogenesis. Furthermore, Id proteins interact with Mitf, a basic HLH (bHLH) transcription factor, and inhibit its transactivation of OSCAR, which is a costimulatory receptor expressed by osteoclast precursors, by attenuating the DNA binding ability of Mitf to the E-box site of the OSCAR promoter. Taken together, our results reveal both a new facet of negative regulation, mediated by Id proteins, as well as the mechanism whereby TRANCE signaling overcomes it, allowing osteoclastogenesis to proceed.

Animals↗

PubMed2005

Osteoclast differentiation independent of the TRANCE-RANK-TRAF6 axis.

Osteoclasts are derived from myeloid lineage cells, and their differentiation is supported by various osteotropic factors, including the tumor necrosis factor (TNF) family member TNF-related activation-induced cytokine (TRANCE). Genetic deletion of TRANCE or its receptor, receptor activator of nuclear factor kappaB (RANK), results in severely osteopetrotic mice with no osteoclasts in their bones. TNF receptor-associated factor (TRAF) 6 is a key signaling adaptor for RANK, and its deficiency leads to similar osteopetrosis. Hence, the current paradigm holds that TRANCE-RANK interaction and subsequent signaling via TRAF6 are essential for the generation of functional osteoclasts. Surprisingly, we show that hematopoietic precursors from TRANCE-, RANK-, or TRAF6-null mice can become osteoclasts in vitro when they are stimulated with TNF-alpha in the presence of cofactors such as TGF-beta. We provide direct evidence against the current paradigm that the TRANCE-RANK-TRAF6 pathway is essential for osteoclast differentiation and suggest the potential existence of alternative routes for osteoclast differentiation.

Animals↗

PubMed2005

Selenite-induced apoptosis of osteoclasts mediated by the mitochondrial pathway.

The possible effects of sodium selenite on mature osteoclasts were investigated. Incubation of osteoclast-like cells differentiated from RAW 264.7 cells with sodium selenite induced apoptosis as revealed by morphological changes, internucleosomal DNA fragmentation, and activation of caspase-3. Selenite also induced generation of the superoxide anion and reduced the number of free thiol groups in the osteoclast-like cells, suggestive of a shift to a more oxidizing intracellular environment. In addition, selenite induced protein aggregation by thiol cross-linking, loss of the mitochondrial membrane potential, and cytochrome c release in mitochondria isolated from the osteoclast-like cells. Finally, selenite-induced DNA fragmentation in osteoclasts was inhibited both by cyclosporin A, a blocker of the mitochondrial permeability transition pore, and by DEVD-CHO, a cell-permeable inhibitor of caspase-3. These results thus suggest that selenite induces apoptosis mediated by the mitochondrial pathway in mature osteoclasts.

Animals↗

PubMed2005

Nuclear factor of activated T cells c1 induces osteoclast-associated receptor gene expression during tumor necrosis factor-related activation-induced cytokine-mediated osteoclastogenesis.

Osteoclast differentiation from hematopoietic precursors is controlled by the tumor necrosis factor family member tumor necrosis factor-related activation-induced cytokine (TRANCE) via induction of various transcription factors, including nuclear factor of activated T cells (NFAT) c1. During osteoclast differentiation, NFATc1 is further activated via calcium signaling when costimulatory receptors expressed on osteoclast precursors, such as osteoclast-associated receptor (OSCAR), are stimulated. Here we show that NFATc1 expression precedes that of OSCAR during TRANCE-mediated osteoclastogenesis and that inhibition of NFATc1 by cyclosporin A abolishes TRANCE-induced OSCAR expression and subsequent osteoclast differentiation. Moreover, we show that the 1.0-kb promoter region of the OSCAR gene contains three potential NFATc1-binding sites. Induction of an OSCAR promoter-luciferase reporter is significantly increased when transiently transfected into 293T cells in combination with NFATc1 expression plasmid. Deletion and site-directed mutant constructs confirmed that NFATc1-binding sites are both functional and NFATc1-specific. Furthermore, NFATc1 synergistically activates an OSCAR reporter construct together with microphthalmia transcription factor and PU.1, transcription factors previously shown to be critical for osteoclast differentiation. In addition, a plasmid expressing constitutively active MAP kinase kinase 6 enhances the transactivation activity of NFATc1/microphthalmia transcription factor/PU.1 on the OSCAR promoter. Taken together, our results indicate that NFATc1 is an important transcription factor in the induction of OSCAR during osteoclastogenesis. Elucidation of NFATc1 as a transcription factor for OSCAR expression implies the presence of a positive feedback circuit of TRANCE-induced activation of NFATc1, involving NFATc1-mediated OSCAR expression and its subsequent activation of NFATc1, necessary for efficient differentiation of osteoclasts.

Animals↗

PubMed2005

A crucial role for reactive oxygen species in RANKL-induced osteoclast differentiation.

Signaling by receptor activator of NF-kappaB (nuclear factor-kappaB) ligand (RANKL) is essential for differentiation of bone marrow monocyte-macrophage lineage (BMM) cells into osteoclasts. Here, we show RANKL stimulation of BMM cells transiently increased the intracellular level of reactive oxygen species (ROS) through a signaling cascade involving TNF (tumor necrosis factor) receptor-associated factor (TRAF) 6, Rac1, and NADPH (nicotinamide adenine dinucleotide phosphate) oxidase (Nox) 1. A deficiency in TRAF6 or expression of a dominant-interfering mutant of TRAF6 blocks RANKL-mediated ROS production. Application of N-acetylcysteine (NAC) or blocking the activity of Nox, a protein leading to the formation of ROS, with diphenylene iodonium (DPI) inhibits the responses of BMM cells to RANKL, including ROS production, activation of c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein (MAP) kinase, and extracellular signal-regulated kinase (ERK), and osteoclast differentiation. Moreover, both RANKL-mediated ROS production and osteoclast differentiation were completely blocked in precursors depleted of Nox1 activity by RNA interference or by expressing a dominant-negative mutant of Rac1. Together, these results indicate that ROSs act as an intracellular signal mediator for osteoclast differentiation.

Animals↗

PubMed2005

Strength of TRAF6 signalling determines osteoclastogenesis.

TRANCE/TRAF6 signalling governs osteoclastogenesis in vivo. Only the TRANCE receptor (TRANCE-R) has been shown to induce osteoclastogenesis, even though other immune receptors, including CD40 and IL-1R/Toll-like receptor, use TRAF6 to activate overlapping signalling cascades. These observations led us to question whether qualitative or quantitative differences exist between the TRAF6-mediated signals induced by TRANCE and by other ligand-receptor pairs. Here we show that stimulation by overexpressed wild-type CD40 can induce osteoclastogenesis. Stimulation through modified CD40 containing increased numbers of TRAF6-binding sites in the cytoplasmic tails showed a dose-dependent increase in the activation of p38 kinase and more pronounced osteoclastogenesis. Moreover, precursors overexpressing TRAF6 differentiate into osteoclasts in the absence of additional signals from TRANCE. Our results suggest that differences in the osteoclastogenesis-inducing capacity of TRANCE-R versus other TRAF6-associated receptors may in part stem from a quantitative difference in the TRAF6-mediated signals.

Animals↗

PubMed2003

TRANCE-RANK costimulation is required for IL-12 production and the initiation of a Th1-type response to Leishmania major infection in CD40L-deficient mice.

Blockade of TNF-related activation-induced cytokine (TRANCE)-receptor activator of NF-kappaB (RANK) interaction reverses healing in CD40L(-/-) mice infected with Leishmania major. Although previous studies demonstrated a requirement for CD40-CD40L interaction in production of IL-12 and the development of resistance to Leishmania infection, we recently showed that CD40L(-/-) mice control infection when inoculated with low numbers of parasites and that cells from these mice produce IL-12. Here, we show that in vivo treatment with a TRANCE receptor fusion protein results in a decrease in numbers of IL-12 producing cells as well as a shift from a dominant Th1 to Th2 type response in infected mice. These results demonstrate that CD40L(-/-) mice use the TRANCE-RANK costimulatory pathway to promote IL-12 production and the activation of a protective Th1 type response.

Animals↗

PubMed2003

Microphthalmia transcription factor and PU.1 synergistically induce the leukocyte receptor osteoclast-associated receptor gene expression.

We have recently reported the identification of a novel member of the leukocyte receptor family, osteoclast-associated receptor (OSCAR), which has two Ig-like domains and functions as a bone-specific regulator of osteoclast differentiation. Here, we have cloned the OSCAR promoter region to examine its regulation by transcription factors. The 1.7-kb promoter region of the mouse OSCAR gene contains two potential E-box elements for microphthalmia transcription factor (MITF) and three putative PU.1 sites. MITF or PU.1 alone activates the OSCAR reporter construct 5-6-fold, and the combination of MITF and PU.1 synergistically activates the OSCAR reporter activity up to 110-fold. The mRNA expression patterns of MITF, PU.1, and OSCAR in TRANCE-treated (RAW 264.7) or TRANCE/M-CSF-treated cells (primary osteoclasts) reveal that MITF mRNA expression is induced at a much earlier time point than OSCAR gene expression. In contrast to MITF, PU.1 mRNA levels remain relatively constant at all time points, suggesting that TRANCE-induced MITF, not PU.1 expression, is one of the critical regulatory mechanisms for optimal OSCAR expression during osteoclastogenesis. In addition, we have shown that the combination of MITF and constitutively active MKK6-expressing plasmids synergistically activates OSCAR reporter activity. Taken together, our results strongly suggest that PU.1 and MITF transcription factors synergistically activate OSCAR gene expression. Moreover, the activation of OSCAR gene expression by PU.1/MITF is further enhanced by the TRANCE-induced MKK6/p38 signaling cascade.

Animals↗

PubMed2003

The role of RANKL (TRANCE/TNFSF11), a tumor necrosis factor family member, in skeletal development: effects of gene knockout and transgenic rescue.

We report the skeletal manifestations of restoring RANKL (TNFSF11/TRANCE; see foot note on nomenclature) expression in null mice using a lymphocyte-specific promoter. RANKL was discovered independently by immunologists and bone researchers by virtue of its essential roles in lymph node organogenesis, normal cellular immunity, and osteoclastogenesis. "Rescue" of RANKL knockout mice by a T- and B-cell expressed transgene reversed many immunological manifestations of the knockout, while it had highly selective effects on the skeletal pathology. RANKL-null mice exhibit severe osteopetrosis, no tooth eruption, markedly reduced skeletal growth, and growth plate chondrodystrophy. The transgene induced tartrate-resistant acid phosphatase (TRAP) positive cells in long bones as early as 3 days postpartum, restored marrow spaces in long bones, produced lamellar bone in the diaphyses, and restored osteoclasts at many endosteal sites, but not in periosteum nor the jaws. It did not improve the chondrodystrophy, chondroosseous junction defects, or tooth eruption. The ends of limb and axial skeletal elements remained highly sclerotic while diaphyses became osteopenic, and growth retardation persisted. Together, these results demonstrate the importance of local delivery of RANKL for many skeletal processes.

Animals↗

PubMed2002

Stimulation by toll-like receptors inhibits osteoclast differentiation.

Osteoclasts, the cells capable of resorbing bone, are derived from hemopoietic precursor cells of monocyte-macrophage lineage. The same precursor cells can also give rise to macrophages and dendritic cells, which are essential for proper immune responses to various pathogens. Immune responses to microbial pathogens are often triggered because various microbial components induce the maturation and activation of immunoregulatory cells such as macrophages or dendritic cells by stimulating Toll-like receptors (TLRs). Since osteoclasts arise from the same precursors as macrophages, we tested whether TLRs play any role during osteoclast differentiation. We showed here that osteoclast precursors prepared from mouse bone marrow cells expressed all known murine TLRs (TLR1-TLR9). Moreover, various TLR ligands (e.g., peptidoglycan, poly(I:C) dsRNA, LPS, and CpG motif of unmethylated DNA, which act as ligands for TLR2, 3, 4, and 9, respectively) induced NF-kappa B activation and up-regulated TNF-alpha production in osteoclast precursor cells. Unexpectedly, however, TLR stimulation of osteoclast precursors by these microbial products strongly inhibited their differentiation into multinucleated, mature osteoclasts induced by TNF-related activation-induced cytokine. Rather, TLR stimulation maintained the phagocytic activity of osteoclast precursors in the presence of osteoclastogenic stimuli M-CSF and TNF-related activation-induced cytokine. Taken together, these results suggest that TLR stimulation of osteoclast precursors inhibits their differentiation into noninflammatory mature osteoclasts during microbial infection. This process favors immune responses and may be critical to prevent pathogenic effects of microbial invasion on bone.

Animals↗