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Biomedical subjects

Toru Nakano

Publications and source records attributed to Toru Nakano.

At least 55 records · Page 3Linked to original sources
PubMed2003

Growth arrest-specific gene 6 is involved in glomerular hypertrophy in the early stage of diabetic nephropathy.

Nephropathy is one of the most common complications of diabetes mellitus. Glomerular hypertrophy is a hallmark in the early phase of the nephropathy. The mechanism of glomerular hypertrophy, however, remains incompletely understood. We have reported that Gas6 (growth arrest-specific gene 6) and its receptor, Axl, play a key role in the development of glomerulonephritis. Here we show the important role of Gas6/Axl in the pathogenesis of diabetic glomerular hypertrophy. In streptozotocin (STZ)-induced diabetic rats, mesangial and glomerular hypertrophy and an increase in the glomerular filtration rate (GFR) and albuminuria were observed after 12 weeks of STZ injection. The glomerular expression of Gas6 and Axl was increased in those rats. Administration of warfarin inhibited mesangial and glomerular hypertrophy and the increase in GFR and albuminuria in STZ rats. Moreover, we found less mesangial hypertrophy in STZ-treated Gas6 knockout mice than control mice. In vitro we found that stimulation of mesangial cells with Gas6 resulted in mesangial cell hypertrophy. Thus we have found a novel mechanism of glomerular hypertrophy through the Gas6/Axl-mediated pathway in the development of diabetic nephropathy. Inhibition of the Gas6/Axl pathway in diabetic patients might be beneficial to slow down the progression of diabetic nephropathy.

Albuminuria↗
PubMed2003

Critical roles of Pten in B cell homeostasis and immunoglobulin class switch recombination.

Pten is a tumor suppressor gene mutated in human cancers. We used the Cre-loxP system to generate a B cell-specific mutation of Pten in mice (bPten(flox/flox)mice). bPten(flox/flox) mice showed elevated numbers of B1a cells and increased serum autoantibodies. Among B2 cells in bPten(flox/flox) spleens, numbers of marginal zone B (MZB) cells were significantly increased while those of follicular B (FOB) cells were correspondingly decreased. Pten-deficient B cells hyperproliferated, were resistant to apoptotic stimuli, and showed enhanced migration. The survival kinase PKB/Akt was highly activated in Pten-deficient splenic B cells. In addition, immunoglobulin class switch recombination was defective and induction of activation-induced cytidine deaminase (AID) was impaired. Thus, Pten plays a role in developmental fate determination of B cells and is an indispensable regulator of B cell homeostasis.

Animals↗
PubMed2003

Keratinocyte-specific Pten deficiency results in epidermal hyperplasia, accelerated hair follicle morphogenesis and tumor formation.

PTEN is a tumor suppressor gene mutated in many human cancers. We used the Cre-loxP system to generate a keratinocyte-specific null mutation of Pten in mice (k5Pten(flox/flox) mice). k5Pten(flox/flox) mice exhibit wrinkled skin because of epidermal hyperplasia and hyperkeratosis and ruffled, shaggy, and curly hair. Histological examination revealed that skin morphogenesis is accelerated in k5Pten(flox/flox) mice. Within 3 weeks of birth, 90% of k5Pten(flox/flox) mice die of malnutrition possibly caused by hyperkeratosis of the esophagus. All k5Pten(flox/flox) mice develop spontaneous tumors within 8.5 months of birth, and chemical treatment accelerates the onset of tumors. k5Pten(flox/flox) keratinocytes are hyperproliferative and resistant to apoptosis and show increased activation of the Pten downstream signaling mediators Akt/protein kinase B (PKB) and extracellular signal-regulated kinase. Pten is thus an important regulator of normal development and oncogenesis in the skin.

Animals↗
PubMed2003

Hematopoietic stem cells: generation and manipulation.

Hematopoietic stem cells (HSCs) are at the forefront of both basic stem cell research and clinical applications. Regenerative medicine has recently become a viable form of therapy and can potentially cure several diseases. The generation of blood cells from embryonic stem cells and the manipulation of HSCs continue to provide insights into other stem cell systems. The importance of HSCs as a model of an ideal source for cell therapy is increasing.

Animals↗
PubMed2003

Mouse germ cell-less as an essential component for nuclear integrity.

A mouse homologue of the Drosophila melanogaster germ cell-less (mgcl-1) gene is expressed ubiquitously, and its gene product is localized to the nuclear envelope based on its binding to LAP2 beta (lamina-associated polypeptide 2 beta). To elucidate the role of mgcl-1, we analyzed two mutant mouse lines that lacked mgcl-1 gene expression. Abnormal nuclear morphologies that were probably due to impaired nuclear envelope integrity were observed in the liver, exocrine pancreas, and testis. In particular, functional abnormalities were observed in testis in which the highest expression of mgcl-1 was detected. Fertility was significantly impaired in mgcl-1-null male mice, probably as a result of severe morphological abnormalities in the sperm. Electron microscopic observations showed insufficient chromatin condensation and abnormal acrosome structures in mgcl-1-null sperm. In addition, the expression patterns of transition proteins and protamines, both of which are essential for chromatin remodeling during spermatogenesis, were aberrant. Considering that the first abnormality during the process of spermatogenesis was abnormal nuclear envelope structure in spermatocytes, the mgcl-1 gene product appears to be essential for appropriate nuclear-lamina organization, which in turn is essential for normal sperm morphogenesis and chromatin remodeling.

Animals↗
PubMed2003

Conditional loss of PTEN leads to testicular teratoma and enhances embryonic germ cell production.

The tumor suppressor gene PTEN, which is frequently mutated in human cancers, encodes a lipid phosphatase for phosphatidylinositol 3,4,5-triphosphate [PtdIns(3,4,5)P3] and antagonizes phosphatidylinositol 3 kinase. Primordial germ cells (PGCs), which are the embryonic precursors of gametes, are the source of testicular teratoma. To elucidate the intracellular signaling mechanisms that underlie germ cell differentiation and proliferation, we have generated mice with a PGC-specific deletion of the Pten gene. Male mice that lacked PTEN exhibited bilateral testicular teratoma, which resulted from impaired mitotic arrest and outgrowth of cells with immature characters. Experiments with PTEN-null PGCs in culture revealed that these cells had greater proliferative capacity and enhanced pluripotent embryonic germ (EG) cell colony formation. PTEN appears to be essential for germ cell differentiation and an important factor in testicular germ cell tumor formation.

Animals↗
PubMed2003

Physiological functions of Pten in mouse tissues.

PTEN is a tumor suppressor gene mutated in many human sporadic cancers and in hereditary cancer syndromes such as Cowden disease, Bannayan-Zonana syndrome and Lhermitte-Duclos disease. The major substrate of PTEN is PIP3, a second messenger molecule produced following PI3K activation induced by variety of stimuli. PIP3 activates the serine-threonine kinase PKB/Akt which is involved in anti-apoptosis, proliferation and oncogenesis. In mice, heterozygosity for a null mutation of Pten (Pten(+/-) mice) frequently leads to the development of a variety of cancers and autoimmune disease. Homozygosity for the null mutation (Pten (-/-) mice) results in early embryonic lethality, precluding the functional analysis of Pten in various organs. To investigate the physiological functions of Pten in viable mice, various tissue-specific Pten mutations have been generated using the Cre-loxP system. This review will summarize the phenotypes of conditional mutant mice lacking Pten function in specific tissues, and discuss how these phenotypes relate to the physiological roles of Pten in various organ systems.

Animals↗
PubMed2003

Differences between peripheral blood and cord blood in the kinetics of lineage-restricted hematopoietic cells: implications for delayed platelet recovery following cord blood transplantation.

Cord blood (CB) cells are a useful source of hematopoietic cells for transplantation. The hematopoietic activities of CB cells are different from those of bone marrow and peripheral blood (PB) cells. Platelet recovery is significantly slower after transplantation with CB cells than with cells from other sources. However, the cellular mechanisms underlying these differences have not been elucidated. We compared the surface marker expression profiles of PB and CB hematopoietic cells. We focused on two surface markers of hematopoietic cell immaturity, i.e., CD34 and AC133. In addition to differences in surface marker expression, the PB and CB cells showed nonidentical differentiation pathways from AC133(+)CD34(+) (immature) hematopoietic cells to terminally differentiated cells. The majority of the AC133(+)CD34(+) PB cells initially lost AC133 expression and eventually became AC133(-)CD34(-) cells. In contrast, the AC133(+)CD34(+) CB cells did not go through the intermediate AC133(-)CD34(+) stage and lost both markers simultaneously. Meanwhile, the vast majority of megakaryocyte progenitors were of the AC133(-)CD34(+) phenotype. We conclude that the delayed recovery of platelets after CB transplantation is due to both subpopulation distribution and the process of differentiation from AC133(+)CD34(+) cells.

AC133 Antigen↗
PubMed2003

[Establishment, maintenance and differentiation induction of embryonic stem cells].

Embryonic stem(ES) cells are the cell lines derived from the inner cell mass of early preimplantation embryos at blastocyst stage. Mouse ES cells are pluripotent since the cells can be differentiated into all lineages of the cells once re-introduced into blastocysts. Human ES cells have been established from the inner cell mass of blastocysts which are developed from surplus embryos obtained by in vitro fertilization. ES cells are considered valuable resource of regeneration medicine because of their vigorous proliferative activity and broad differentiation capacity. Establishment, maintenance and in vitro differentiation of the cells are key points for the utilization of ES cells in regeneration medicine.

Animals↗
PubMed2002

Megakaryocytes derived from embryonic stem cells implicate CalDAG-GEFI in integrin signaling.

Fibrinogen binding to integrin alphaIIbbeta3 mediates platelet aggregation and requires agonist-induced "inside-out" signals that increase alphaIIbbeta3 affinity. Agonist regulation of alphaIIbbeta3 also takes place in megakaryocytes, the bone marrow cells from which platelets are derived. To facilitate mechanistic studies of inside-out signaling, we describe here the generation of megakaryocytes in quantity from murine embryonic stem (ES) cells. Coculture of ES cells for 8-12 days with OP9 stromal cells in the presence of thrombopoietin, IL-6, and IL-11 resulted in the development of large, polyploid megakaryocytes that produced proplatelets. These cells expressed alphaIIbbeta3 and platelet glycoprotein Ibalpha but were devoid of hematopoietic stem cell, erythrocyte, and leukocyte markers. Mature megakaryocytes, but not megakaryocyte progenitors, specifically bound fibrinogen by way of alphaIIbbeta3 in response to platelet agonists. Retrovirus-mediated expression of the reporter gene, green fluorescent protein, in ES cell-derived megakaryocytes did not affect viability or alphaIIbbeta3 function. On the other hand, retroviral expression of CalDAG-GEFI, a Rap1 exchange factor identified by megakaryocyte gene profiling as a candidate integrin regulator, enhanced agonist-induced activation of Rap1b and fibrinogen binding to alphaIIbbeta3 (P < 0.01). These results establish that ES cells are a ready source of mature megakaryocytes for integrin studies and other biological applications, and they implicate CalDAG-GEFI in inside-out signaling to alphaIIbbeta3.

Animals↗
PubMed2002

GATA-2 and GATA-2/ER display opposing activities in the development and differentiation of blood progenitors.

GATA-2 is a zinc finger transcription factor essential for the development of hematopoiesis. While GATA-2 is generally considered to play an important role in the biology of hematopoietic stem and progenitor cells, its function within these compartments is not well understood. Here we have employed both conditional expression of GATA-2 and conditional activation of a GATA-2/estrogen receptor (ER) chimera to examine the effect of enforced GATA-2 expression in the development and differentiation of hematopoietic progenitors from murine embryonic stem cells. Consistent with the phenotype of GATA-2 null animals, conditional expression of GATA-2 from a tetracycline-inducible promoter enhanced the production of hematopoietic progenitors. Conditional activation of a GATA-2/ER chimera produced essentially opposite effects to those observed with conditional GATA-2 expression. GATA-2 and GATA-2/ER differ in their binding activities and transcriptional interactions from other hematopoietic-associated transcription factors such as c-Myb and PU.1. While we have exploited these differences in activity to explore the transcriptional networks underlying hematopoietic cell fate determination, our results suggest that care should be taken in interpreting results obtained using only chimeric proteins.

Animals↗
PubMed2002

Orderly and nonstochastic acquisition of CD94/NKG2 receptors by developing NK cells derived from embryonic stem cells in vitro.

In mice there are two families of MHC class I-specific receptors, namely the Ly49 and CD94/NKG2 receptors. The latter receptors recognize the nonclassical MHC class I Qa-1(b) and are thought to be responsible for the recognition of missing-self and the maintenance of self-tolerance of fetal and neonatal NK cells that do not express Ly49. Currently, how NK cells acquire individual CD94/NKG2 receptors during their development is not known. In this study, we have established a multistep culture method to induce differentiation of embryonic stem (ES) cells into the NK cell lineage and examined the acquisition of CD94/NKG2 by NK cells as they differentiate from ES cells in vitro. ES-derived NK (ES-NK) cells express NK cell-associated proteins and they kill certain tumor cell lines as well as MHC class I-deficient lymphoblasts. They express CD94/NKG2 heterodimers, but not Ly49 molecules, and their cytotoxicity is inhibited by Qa-1(b) on target cells. Using RT-PCR analysis, we also report that the acquisition of these individual receptor gene expressions during different stages of differentiation from ES cells to NK cells follows a predetermined order, with their order of acquisition being first CD94; subsequently NKG2D, NKG2A, and NKG2E; and finally, NKG2C. Single-cell RT-PCR showed coexpression of CD94 and NKG2 genes in most ES-NK cells, and flow cytometric analysis also detected CD94/NKG2 on most ES-NK cells, suggesting that the acquisition of these receptors by ES-NK cells in vitro is nonstochastic, orderly, and cumulative.

Animals↗
PubMed2002

Notch-RBP-J signaling is involved in cell fate determination of marginal zone B cells.

RBP-J is a key mediator of Notch signaling that regulates cell fate determination in various lineages. To investigate the function of Notch-RBP-J in mature B cell differentiation, we generated mice that selectively lacked B cell RBP-J expression using conditional mutagenesis. Absence of RBP-J led to the loss of marginal zone B (MZB) cells with a concomitant increase in follicular B cells; in contrast, B1 cells in the peritoneal cavity were unaffected. Lack of RBP-J caused no defects in B cells maintenance, survival, plasma cell differentiation or activation. It is therefore likely that Notch-RBP-J signaling regulates the lineage commitment of mature B cells into follicular versus MZB cells. In addition, in mice with RBP-J-deficient B cells, had no obvious changes in immunoglobulin production in response to Ficoll, lipopolysaccharide or chicken gammaglobulin. In contrast, these mice exhibited increased mortality rates after blood-borne bacterial infection, which indicates that MZB cells play pivotal roles in the clearance of these bacteria.

Animals↗
PubMed2002

Identification of Gas6, a putative ligand for Sky and Axl receptor tyrosine kinases, as a novel neurotrophic factor for hippocampal neurons.

Sky (also known as "Tyro3" and "Rse") is a member of the Axl/Sky/Mer receptor tyrosine kinase family and has two immunoglobulin-like repeats and two fibronectin type III-like repeats in the extracellular domain. Gas6 is a ligand for all members of the Axl family, each of which (Axl, Sky, and c-Mer) has different affinities to Gas6. Physiological functions of Sky and Gas6 in the nervous system are not well understood, despite their importance, which is suggested by Sky structural features and its predominant expression in the brain. We found in the RNase protection assays that gas6 and sky mRNAs are expressed in the adult rat hippocampus and are similarly regulated during development. Expression levels were low during embryonic stages but gradually increased during development and reached the highest level in adulthood. Sky, but not Axl, immunoreactivity was observed in the adult hippocampus. Recombinant rat Gas6 attenuated hippocampal neuronal cell death that was caused by serum starvation in vitro, indicating that Gas6 is a novel neurotrophic factor for hippocampal neurons. Gas6 showed regulated expression in the sciatic nerve after nerve transection. Therefore, Sky and Gas6 have neurotrophic roles in the nervous system.

Amino Acid Sequence↗
PubMed2002

Identification of PGC7, a new gene expressed specifically in preimplantation embryos and germ cells.

The gene expression patterns of primordial germ cells (PGCs) and embryonic stem cells were analyzed by a modified serial analysis of gene expression. During the process, we cloned a novel gene, PGC7, which was preferentially expressed in PGCs. Immunohistochemical analysis revealed that PGC7 was specifically expressed in early pre-implantation embryos, PGCs and oocytes. These results suggest that PGC7 might play an important role in the development of PGCs and oocytes.

Amino Acid Sequence↗