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Biomedical subjects

Y Terauchi

Publications and source records attributed to Y Terauchi.

At least 37 records · Page 2Linked to original sources
PubMed1999

NADH shuttle system regulates K(ATP) channel-dependent pathway and steps distal to cytosolic Ca(2+) concentration elevation in glucose-induced insulin secretion.

The NADH shuttle system is composed of the glycerol phosphate and malate-aspartate shuttles. We generated mice that lack mitochondrial glycerol-3-phosphate dehydrogenase (mGPDH), a rate-limiting enzyme of the glycerol phosphate shuttle. Application of aminooxyacetate, an inhibitor of the malate-aspartate shuttle, to mGPDH-deficient islets demonstrated that the NADH shuttle system was essential for coupling glycolysis with activation of mitochondrial ATP generation to trigger glucose-induced insulin secretion. The present study revealed that blocking the NADH shuttle system severely suppressed closure of the ATP-sensitive potassium (K(ATP)) channel and depolarization of the plasma membrane in response to glucose in beta cells, although properties of the K(ATP) channel on the excised beta cell membrane were unaffected. In mGPDH-deficient islets treated with aminooxyacetate, Ca(2+) influx through the plasma membrane induced by a depolarizing concentration of KCl in the presence of the K(ATP) channel opener diazoxide restored insulin secretion. However, the level of the secretion was only approximately 40% of wild-type controls. Thus, glucose metabolism through the NADH shuttle system leading to efficient ATP generation is pivotal to activation of both the K(ATP) channel-dependent pathway and steps distal to an elevation of cytosolic Ca(2+) concentration in glucose-induced insulin secretion.

Animals↗
PubMed1999

Role of NADH shuttle system in glucose-induced activation of mitochondrial metabolism and insulin secretion.

Glucose metabolism in glycolysis and in mitochondria is pivotal to glucose-induced insulin secretion from pancreatic beta cells. One or more factors derived from glycolysis other than pyruvate appear to be required for the generation of mitochondrial signals that lead to insulin secretion. The electrons of the glycolysis-derived reduced form of nicotinamide adenine dinucleotide (NADH) are transferred to mitochondria through the NADH shuttle system. By abolishing the NADH shuttle function, glucose-induced increases in NADH autofluorescence, mitochondrial membrane potential, and adenosine triphosphate content were reduced and glucose-induced insulin secretion was abrogated. The NADH shuttle evidently couples glycolysis with activation of mitochondrial energy metabolism to trigger insulin secretion.

Adenosine Triphosphate↗
PubMed1999

Xid-like immunodeficiency in mice with disruption of the p85alpha subunit of phosphoinositide 3-kinase.

Mice with a targeted gene disruption of p85alpha, a regulatory subunit of phosphoinositide 3-kinase, had impaired B cell development at the pro-B cell stage, reduced numbers of mature B cells and peritoneal CD5+ Ly-1 B cells, reduced B cell proliferative responses, and no T cell-independent antibody production. These phenotypes are nearly identical to those of Btk-/- or xid (X-linked immunodeficiency) mice. These results provide evidence that p85alpha is functionally linked to the Btk pathway in antigen receptor-mediated signal transduction and is pivotal in B cell development and functions.

Agammaglobulinaemia Tyrosine Kinase↗
PubMed1999

PPAR gamma mediates high-fat diet-induced adipocyte hypertrophy and insulin resistance.

Agonist-induced activation of peroxisome proliferator-activated receptor gamma (PPAR gamma) is known to cause adipocyte differentiation and insulin sensitivity. The biological role of PPAR gamma was investigated by gene targeting. Homozygous PPAR gamma-deficient embryos died at 10.5-11.5 dpc due to placental dysfunction. Quite unexpectedly, heterozygous PPAR gamma-deficient mice were protected from the development of insulin resistance due to adipocyte hypertrophy under a high-fat diet. These phenotypes were abrogated by PPAR gamma agonist treatment. Heterozygous PPAR gamma-deficient mice showed overexpression and hypersecretion of leptin despite the smaller size of adipocytes and decreased fat mass, which may explain these phenotypes at least in part. This study reveals a hitherto unpredicted role for PPAR gamma in high-fat diet-induced obesity due to adipocyte hypertrophy and insulin resistance, which requires both alleles of PPAR gamma.

Adipocytes↗
PubMed1999

Increased insulin sensitivity and hypoglycaemia in mice lacking the p85 alpha subunit of phosphoinositide 3-kinase.

The hallmark of type 2 diabetes, the most common metabolic disorder, is a defect in insulin-stimulated glucose transport in peripheral tissues. Although a role for phosphoinositide-3-kinase (PI3K) activity in insulin-stimulated glucose transport and glucose transporter isoform 4 (Glut4) translocation has been suggested in vitro, its role in vivo and the molecular link between activation of PI3K and translocation has not yet been elucidated. To determine the role of PI3K in glucose homeostasis, we generated mice with a targeted disruption of the gene encoding the p85alpha regulatory subunit of PI3K (Pik3r1; refs 3-5). Pik3r1-/- mice showed increased insulin sensitivity and hypoglycaemia due to increased glucose transport in skeletal muscle and adipocytes. Insulin-stimulated PI3K activity associated with insulin receptor substrates (IRSs) was mediated via full-length p85 alpha in wild-type mice, but via the p50 alpha alternative splicing isoform of the same gene in Pik3r1-/- mice. This isoform switch was associated with an increase in insulin-induced generation of phosphatidylinositol(3,4,5)triphosphate (PtdIns(3,4,5)P3) in Pik3r1-/- adipocytes and facilitation of Glut4 translocation from the low-density microsome (LDM) fraction to the plasma membrane (PM). This mechanism seems to be responsible for the phenotype of Pik3r1-/- mice, namely increased glucose transport and hypoglycaemia. Our work provides the first direct evidence that PI3K and its regulatory subunit have a role in glucose homeostasis in vivo.

Animals↗
PubMed1998

Ethidium bromide-induced inhibition of mitochondrial gene transcription suppresses glucose-stimulated insulin release in the mouse pancreatic beta-cell line betaHC9.

Recently, a mitochondrial mutation was found to be associated with maternally inherited diabetes mellitus (Kadowaki, T., Kadowaki, H., Mori, Y., Tobe, K., Sakuta, R., Suzuki, Y., Tanabe, Y, Sakura, H., Awata, T., Goto, Y., Hayakawa, T., Matsuoka, K., Kawamori, R., Kamada, T., Horai, S., Nonaka, I., Hagura, R., Akanuma, Y., and Yazaki, Y. (1994) N. Engl. J. Med. 330, 962-968). In order to elucidate its etiology, we have investigated the involvement of mitochondrial function in insulin secretion. Culture of the pancreatic beta-cell line, betaHC9, with low dose ethidium bromide (EB) (0.4 microg/ml) for 2-6 days resulted in a substantial decrease in the transcription level of mitochondrial DNA (to 10-20% of the control cells) without changing its copy number, whereas the transcription of nuclear genes was grossly unaffected. Electron microscopic analysis revealed that treatment by EB caused morphological changes only in mitochondria and not in other organelles such as nuclei, endoplasmic reticula, Golgi bodies, or secretory granules. When the cells were treated with EB for 6 days, glucose (20 mM) could no longer stimulate insulin secretion, while glibenclamide (1 microM) still did. When EB was removed after 3- or 6-day treatment, mitochondrial gene transcription recovered within 2 days, and the profiles of insulin secretion returned to normal within 7 days. Studies with fura-2 indicated that in EB-treated cells, glucose (20 mM) failed to increase intracellular Ca2+, while the effect of glibenclamide (1 microM) was maintained. Our system provides a unique way to investigate the relationship between mitochondrial function and insulin secretion.

Animals↗
PubMed1998

Involvement of p85 in p53-dependent apoptotic response to oxidative stress.

Reactive oxygen species have damaging effects on cellular components and so trigger defensive responses by the cell and even programmed cell death, although the mechanisms by which mammalian cells transmit signals in response to oxidative damage are unknown. We report here that the protein p85, a regulator of the signalling protein phosphatidyl-3-OH kinase (PI(3)K), participates in the cell death process that is induced in response to oxidative stress and that this role of p85 in apoptosis does not involve PI(3)K. We show that disruption of p85 by homologous recombination impairs the cellular apoptotic response to oxidative stress. Because the protein p53 is required for cell death induced by oxidative damage, we examined the relation between p85 and p53. Using a chimaeric p53 fusion protein with the oestrogen receptor (p53ER) to supply p53 (p53 is induced upon binding of p53ER to oestradiol) in a p53-deficient cell line, we found that p85 is upregulated by p53 and that its involvement in p53-mediated apoptosis is independent of PI(3)K. We propose that p85 acts as a signal transducer in the cellular response to oxidative stress, mediating cell death regulated by p53.

Androstadienes↗
PubMed1998

Glucose modulation of ATP-sensitive K-currents in wild-type, homozygous and heterozygous glucokinase knock-out mice.

One type of maturity-onset diabetes of the young (MODY2) is caused by mutations in the glucokinase gene, a key glycolytic enzyme in the beta cell and liver. Glucose fails to stimulate insulin secretion in mice in which the glucokinase gene has been selectively knocked out in the beta cell. We tested the hypothesis that this effect results from defective metabolic regulation of beta cell ATP-sensitive potassium (K(ATP)) channels. Glucose had little effect on K(ATP) currents in homozygous (-/-) mice but inhibited K(ATP) currents in wild-type (+/+) and heterozygous (+/-) mice with EC50 of 3.2 mM and 5.5 mM, respectively, in newborn animals, and of 4.7 mM and 9.9 mM, respectively, in 1.5-year-old mice. Glucose (20 mmol/l) did not affect the resting membrane potential of -/- beta cells but depolarised wild-type and + /- beta cells and induced electrical activity. In contrast, 20 mmol/l ketoisocaproic acid or 0.5 mmol/ l tolbutamide depolarised all three types of beta-cell. These results support the idea that defective glycolytic metabolism, produced by a loss (-/- mice) or reduction (+/- mice) of glucokinase activity, leads to defective K(ATP) channel regulation and thereby to the selective loss, or reduction, of glucose-induced insulin secretion.

Adenosine Triphosphate↗
PubMed1998

N-Dealkylation and hydroxylation of ebastine by human liver cytochrome P450.

Ebastine [4'-tert-butyl-4-[4-(diphenylmethoxy)piperidino]butyro phe- none] is a new-generation, nonsedative, H1 antihistamine. The present study was performed to characterize the cytochrome P450 (CYP) isoforms responsible for ebastine N-dealkylation and hydroxylation. Human liver microsomes metabolized ebastine to two major metabolites, i.e. a desbutyrophenone metabolite (des-BP) and hydroxyebastine (M-OH), and the ratio of Vmax values was 3:1. N-Dealkylation yielded des-BP, whereas M-OH, an hydroxylation product, could be further oxidized to the pharmacologically active carebastine. In a panel of 14 human liver microsomal preparations, the rate of dealkylation showed a highly significant correlation with CYP3A-mediated testosterone 6beta-hydroxylation but not with reactions of seven other CYP isoforms. However, there was no correlation between the two pathways for ebastine (dealkylation and hydroxylation). Differential chemical inhibition in liver microsomes, in which dealkylation was more sensitive than hydroxylation, was demonstrated with ketoconazole, troleandomycin, cyclosporin A, and midazolam. Anti-CYP3A antibodies markedly reduced the dealkylation rate (>95%) in liver microsomes but exhibited insignificant effects on hydroxylation (<5%). Among 12 cDNA-expressed human CYP isoforms, which account for up to 70% of the total CYP enzyme content in human liver, CYP3A4 alone metabolized ebastine; the ratio of des-BP to M-OH formation was 12:1. This ratio for metabolism by the pure enzyme was much larger than the ratio (3:1) observed for the microsomal reaction mixture. This change in ratio, which is attributed to a decrease in M-OH formation, indicates that, although ebastine is metabolized to two major metabolites, N-dealkylation to des-BP is mediated by CYP3A, whereas hydroxylation to M-OH appears to be mediated mainly by unidentified enzymes other than CYP3A.

Butyrophenones↗
PubMed1997

Development of non-insulin-dependent diabetes mellitus in the double knockout mice with disruption of insulin receptor substrate-1 and beta cell glucokinase genes. Genetic reconstitution of diabetes as a polygenic disease.

Non-insulin-dependent diabetes mellitus (NIDDM) is considered a polygenic disorder in which insulin resistance and insulin secretory defect are the major etiologic factors. Homozygous mice with insulin receptor substrate-1 (IRS-1) gene knockout showed normal glucose tolerance associated with insulin resistance and compensatory hyperinsulinemia. Heterozygous mice with beta cell glucokinase (GK) gene knockout showed impaired glucose tolerance due to decreased insulin secretion to glucose. To elucidate the interplay between insulin resistance and insulin secretory defect for the development of NIDDM, we generated double knockout mice with disruption of IRS-1 and beta cell GK genes by crossing the mice with each of the single gene knockout. The double knockout mice developed overt diabetes. Blood glucose levels 120 min after intraperitoneal glucose load (1.5 mg/g body wt) were 108 +/- 24 (wild type), 95 +/- 26 (IRS-1 knockout), 159 +/- 68 (GK knockout), and 210 +/- 38 (double knockout) mg/dl (mean +/- SD) (double versus wild type, IRS-1, or GK; P < 0.01). The double knockout mice showed fasting hyperinsulinemia and selective hyperplasia of the beta cells as the IRS-1 knockout mice (fasting insulin levels: 0.38 +/- 0.30 [double knockout], 0.35 +/- 0.27 [IRS-1 knockout] versus 0.25 +/- 0.12 [wild type] ng/ml) (proportion of areas of insulin-positive cells to the pancreas: 1.18 +/- 0.68%; P < 0.01 [double knockout], 1.20 +/- 0.93%; P < 0.05 [IRS-1 knockout] versus 0.54 +/- 0.26% [wild type]), but impaired insulin secretion to glucose (the ratio of increment of insulin to that of glucose during the first 30 min after load: 31 [double knockout] versus 163 [wild type] or 183 [IRS-1 knockout] ng insulin/mg glucose x 10(3)). In conclusion, the genetic abnormalities, each of which is nondiabetogenic by itself, cause overt diabetes if they coexist. This report provides the first genetic reconstitution of NIDDM as a polygenic disorder in mice.

Animals↗
PubMed1997

Germ-line contribution of embryonic stem cells in chimeric mice: influence of karyotype and in vitro differentiation ability.

The effect of the karyotype and the ability to differentiate in vitro upon germ-line transmission by A3-1 embryonic stem (ES) cells in chimeric mice were examined. Germ-line transmission was confirmed in ES cells exhibiting 38% and more of the normal karyotype, but no chimeric mice and/or germ-line transmitters were observed regardless of the karyotype when the cystic embryoid body (CEB) was formed on day 8 and later in the suspension culture. Germ-line transmission of the ES cells was not significantly influenced by formation of the simple embryoid body (SEB). Germ-line transmitters were preferentially observed in chimeras when the ES cell contribution to coat color was markedly increased, but this contribution to coat color varied regardless of the karyotype or in vitro differentiation ability. These results suggest that A3-1 ES cells which exhibit CEB at 7 days after suspension culture and approximately 40% of normal karyotype are capable of germ-line transmission in chimeric mice.

Animals↗
PubMed1996

Analysis of the pancreatic beta cell in the mouse with targeted disruption of the pancreatic beta cell-specific glucokinase gene.

This is the first systematic study on the pancreatic beta cell function in the heterozygous mouse with targeted disruption of the beta cell glucokinase gene. The heterozygotes' beta cell displayed the following characteristics: (1) impaired glucose sensitivity with normal glucose responsiveness, (2) poor discrimination of alpha and beta glucose anomers, and (3) normal response to glucose in the presence of 25 mM K+ and 150 microM diazoxide. Both the first and the second phases of glucose-stimulated insulin release were depressed. Although the heterozygotes were mildly hyperglycemic, insulin treatment further suppressed beta cell function, implying the beta cell glucose toxicity is not the cause of impaired glucose sensitivity. The data are compatible with the glucokinase glucose sensor concept inasmuch as glucose sensitivity is reduced in the heterozygotes' beta cell. The anomeric malaise and preservation of the ATP-sensitive K+ channel-independent glucose action were considered due to chronic hyperglycemia.

Animals↗
PubMed1996

Chloride-selective electrode based on molecular oriented membrane.

In order to improve durability of chloride ion selective electrode based on molecular oriented membrane (MO2), a novel polymer system (MO4) was developed. In the polymer, ion sensitive sites are immobilized by covalent bonds to prevent dissolution of membrane components to sample solution. And molecular orientation was observed in the new system by X-ray measurement. MO4 system showed the same selectivity profile as the previous system with improved durability.

Chlorides↗