Iseki Takamoto

The University of Tokyo, 白山, Tōkyō, Japan

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Publications (27)242.02 Total impact

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    ABSTRACT: SGLT2 inhibitors have attracted attention as they exert anti-diabetic and anti-obesity effects. In this study, we investigated the effects of tofogliflozin on glucose homeostasis and its metabolic consequences and clarified the underlying molecular mechanisms. C57BL/6 mice were fed normal chow (NC) containing tofogliflozin (0.005%) for 20 weeks or a high-fat diet (HFD) containing tofogliflozin (0.005%) for 8 weeks ad libitum. In addition, the animals were pair-fed in relation to controls to exclude the influence of increased food intake. Tofogliflozin reduced the body weight gain, mainly because of fat mass reduction associated with a diminished adipocyte size. Glucose tolerance and insulin sensitivity were ameliorated. The serum levels of non-esterified fatty acid (NEFA) and ketone bodies were increased and the respiratory quotient (RQ) was decreased in the tofogliflozin-treated mice, suggesting the acceleration of lipolysis in the white adipose tissue (WAT) and hepatic β-oxidation. In fact, the phosphorylation of hormone-sensitive lipase (HSL) and the adipose triglyceride lipase (ATGL) protein levels in the WAT as well as the gene expressions related to β-oxidation, such as Cpt1α in the liver, were significantly increased. The hepatic triglyceride contents and the expression levels of lipogenic genes were decreased. Pair-fed mice exhibited almost the same results as mice fed an HFD ad libitum. Moreover, a hyperinsulinemic-euglycemic clamp revealed that tofogliflozin improved insulin resistance by increasing glucose uptake, especially in the skeletal muscle, in pair-fed mice. Taken together, these results suggest tofogliflozin ameliorates insulin resistance and obesity by increasing glucose uptake in skeletal muscle and lipolysis in adipose tissue.
    No preview · Article · Dec 2015 · Endocrinology
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    ABSTRACT: Background: Insulin allergy, one of insulin's adverse effects, is rare, especially in patients with Type 2 diabetes, but management is difficult and no effective strategy has yet been established. We experienced an insulin allergy case successfully managed with a novel combination of insulins. Case report: A 38-year-old woman started insulin therapy when diabetes was diagnosed at age 19 years. Despite poorly controlled diabetes because of poor adherence, she hoped to conceive a child and continuous subcutaneous insulin infusion was introduced using insulin aspart at age 32 years. One month thereafter, she developed skin reactions at the subcutaneous insulin infusion catheter insertion site. The patient was then tested for all rapid-acting insulin formulations, all of which triggered local reactions. She decided to continue the continuous subcutaneous infusion of human regular insulin, accompanied by oral cetirizine hydrochloride and betamethasone valerate ointment. The patient was admitted to our hospital at age 38 years with high HbA1c levels. She was tested for all long-acting insulin analogues. All results, except for insulin degludec, were positive. She discontinued continuous subcutaneous insulin infusion and switched to insulin degludec combined with liraglutide. The allergic reactions had completely disappeared and her blood glucose was well controlled by the time of discharge. Conclusion: Our patient was allergic to all insulin formulations except insulin degludec. Her allergic reactions completely disappeared after switching to insulin degludec. The crystallized structure of this insulin might mask its skin allergen antigenicity. Furthermore, her postprandial hyperglycaemia was successfully controlled with liraglutide. We propose multihexamer-forming ultra-long-acting insulin plus glucagon-like peptide-1 analogues as a therapeutic option for patients with insulin allergy. This article is protected by copyright. All rights reserved.
    No preview · Article · Oct 2015 · Diabetic Medicine
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    ABSTRACT: Increase in the concentration of plasma l-cysteine is closely associated with defective insulin secretion from pancreatic β-cells, which results in type 2 diabetes (T2D). In this study, we investigated the effects of prolonged l-cysteine treatment on glucose-stimulated insulin secretion (GSIS) from mouse insulinoma 6 (MIN6) cells and from mouse pancreatic islets, and found that the treatment reversibly inhibited glucose-induced ATP production and resulting GSIS without affecting proinsulin and insulin synthesis. Comprehensive metabolic analyses using capillary electrophoresis time-of-flight mass spectrometry showed that prolonged l-cysteine treatment decreased the levels of pyruvate and its downstream metabolites. In addition, methyl pyruvate, a membrane-permeable form of pyruvate, rescued l-cysteine-induced inhibition of GSIS. Based on these results, we found that both in vitro and in MIN6 cells, l-cysteine specifically inhibited the activity of pyruvate kinase muscle isoform 2 (PKM2), an isoform of pyruvate kinases that catalyze the conversion of phosphoenolpyruvate to pyruvate. l-cysteine also induced PKM2 subunit dissociation (tetramers to dimers/monomers) in cells, which resulted in impaired glucose-induced ATP production for GSIS. DASA-10 (NCGC00181061, a substituted N,N'-diarylsulfonamide), a specific activator for PKM2, restored the tetramer formation and the activity of PKM2, glucose-induced ATP production, and biphasic insulin secretion in l-cysteine-treated cells. Collectively, our results demonstrate that impaired insulin secretion due to exposure to l-cysteine resulted from its direct binding and inactivation of PKM2 and suggest that PKM2 is a potential therapeutic target for T2D.
    Preview · Article · Feb 2015 · Proceedings of the National Academy of Sciences
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    ABSTRACT: Endothelial cells are considered to be essential for normal pancreatic β-cell function. The present study attempted to demonstrate the role of Irs2 in endothelial cells with regard to insulin secretion. Endothelial cell-specific insulin receptor substrate-2 knockout (ETIrs2KO) mice exhibited impaired glucose-induced, arginine-induced, and glucagon-induced insulin secretion and showed glucose intolerance. In batch incubation and perifusion experiments using isolated islets, glucose-induced insulin secretion was not significantly different between the control and the ETIrs2KO mice. In contrast, in perfusion experiments, glucose-induced insulin secretion was significantly impaired in the ETIrs2KO mice. The islet blood flow was significantly impaired in the ETIrs2KO mice. Following the treatment of these knockout mice with enalapril maleate, which improved the islet blood flow, glucose-stimulated insulin secretion was almost completely restored to levels equal to those in the control mice. These data suggest that Irs2 deletion in endothelial cells leads to a decreased islet blood flow, which may cause impaired glucose-induced insulin secretion. Thus, Irs2 in endothelial cells may serve as a novel therapeutic target for preventing and ameliorating type 2 diabetes and metabolic syndrome.
    No preview · Article · Oct 2014 · Diabetes
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    ABSTRACT: Beraprost sodium (BPS) is an orally active prostacyclin analog that is widely used in the treatment of atherosclerotic peripheral arterial disease (PAD). The aim of this study was to evaluate the effects of BPS on the insulin resistance in type 2 diabetic patients with PAD. A euglycemic-hyperinsulinemic clamp study was performed to determine the insulin sensitivity (based on the M/I ratio) before and after 12 weeks’ BPS treatment in 14 patients (12 men; mean age, 68.7 ± 5.5 years) with type 2 diabetes and PAD. While there was no significant change of the BMI or waist circumference, a tendency towards improvement of the M/I ratio and decrease of the HbA1c and serum triglyceride level was observed. Subgroup analyses revealed that the improvement of the M/I ratio was more pronounced in the subgroups with a higher serum triglyceride level and lower value of the M/I ratio at the baseline. Our findings suggest that BPS may improve the insulin resistance in diabetic patients, especially in those with greater degrees of insulin resistance.
    No preview · Article · Mar 2014 · Diabetology International
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    ABSTRACT: Common genetic variations of the transcription factor 7-like 2 gene (encoded by TCF7L2), one of the T cell factor/lymphoid enhancer-binding factor transcription factors for the converging wingless-type MMTV integration site family (Wnt)/β-catenin signalling pathway, are known to be associated with type 2 diabetes. Individuals with at-risk alleles of TCF7L2 exhibit impaired insulin secretion. Although previous studies using animal models have revealed the existence of a relationship between the Wnt/β-catenin signalling pathway and glucose homeostasis, it remains unclear whether TCF7L2 in the pancreatic beta cells might be causally involved in insulin secretion in vivo. In this study, we investigated the role of TCF7L2 expressed in the pancreatic beta cells in glucose homeostasis. Three independent groups of genetically engineered mice (DN mice) were generated, in which expression of the dominant-negative form of Tcf7l2 was driven under a rat insulin promoter. Phenotypes of both adult and newborn mice were evaluated. The levels of genes and proteins expressed in isolated islets were determined by reverse transcription-quantitative PCR and western blot analysis, respectively. Adult DN mice showed impaired glucose tolerance and decreased insulin secretion in both oral and intraperitoneal glucose tolerance tests. Marked reduction of the beta cell area and whole-pancreas insulin content was observed in both the adult and newborn DN mice. Islets from the DN mice showed decreased gene expressions of Ccnd1, Ccnd2, Irs1, Irs2, Ins1, Ins2 and Mafa, consistent with the deleterious effects of the dominant-negative form of Tcf7l2 on beta cell proliferation and insulin production. TCF7L2 expressed in the pancreatic beta cells plays a crucial role in glucose metabolism through regulation of the beta cell mass.
    Full-text · Article · Dec 2013 · Diabetologia
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    ABSTRACT: Type 2 diabetes is a chronic metabolic disorder characterized by hyperglycemia with insulin resistance and impaired insulin secretion. DPP-4 inhibitors have attracted attention as a new class of anti-diabetic agents for the treatment of type 2 diabetes. We investigated the effects of anagliptin, a highly selective DPP-4 inhibitor, on insulin secretion and insulin resistance in high-fat diet-fed mice with haploinsufficiency of glucokinase (GckKO) as animal models of type 2 diabetes. Wild-type and GckKO mice were administered two doses of anagliptin by dietary admixture (0.05% and 0.3%) for 10weeks. Both doses of anagliptin significantly inhibited the plasma DPP-4 activity and increased the plasma active GLP-1 levels in both the wild-type and GckKO mice to a similar degree. After 10weeks of treatment with 0.3% anagliptin, body weight gain and food intake were significantly suppressed in both wild-type and GckKO mice. In addition, 0.3% anagliptin ameliorated insulin resistance and glucose intolerance in both genotypes of mice. On the other hand, treatment with 0.05% anagliptin was not associated with any significant change of the body weight, food intake or insulin sensitivity in either genotype of mice, but it did improve the glucose tolerance by enhancing insulin secretion and increasing the β-cell mass in both genotypes of mice. High-dose anagliptin treatment improved glucose tolerance by suppression of body weight gain and amelioration of insulin resistance, whereas low-dose anagliptin treatment improved glucose tolerance by enhancing insulin secretion.
    No preview · Article · Jul 2013 · Metabolism: clinical and experimental
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    ABSTRACT: Aims/hypothesis: Insufficient insulin secretion and reduced pancreatic beta cell mass are hallmarks of type 2 diabetes. Here, we focused on a family of serine-threonine kinases known as homeodomain-interacting protein kinases (HIPKs). HIPKs are implicated in the modulation of Wnt signalling, which plays a crucial role in transcriptional activity, and in pancreas development and maintenance. The aim of the present study was to characterise the role of HIPKs in glucose metabolism. Methods: We used RNA interference to characterise the role of HIPKs in regulating insulin secretion and transcription activity. We conducted RT-PCR and western blot analyses to analyse the expression and abundance of HIPK genes and proteins in the islets of high-fat diet-fed mice. Glucose-induced insulin secretion and beta cell proliferation were measured in islets from Hipk3 ( -/- ) mice, which have impaired glucose tolerance owing to an insulin secretion deficiency. The abundance of pancreatic duodenal homeobox (PDX)-1 and glycogen synthase kinase (GSK)-3β phosphorylation in Hipk3 ( -/- ) islets was determined by immunohistology and western blot analyses. Results: We found that HIPKs regulate insulin secretion and transcription activity. Hipk3 expression was most significantly increased in the islets of high-fat diet-fed mice. Furthermore, glucose-induced insulin secretion and beta cell proliferation were decreased in the islets of Hipk3 ( -/- ) mice. Levels of PDX1 and GSK-3β phosphorylation were significantly decreased in Hipk3 ( -/- ) islets. Conclusions/interpretation: Depletion of HIPK3 impairs insulin secretion and glucose tolerance. Decreased levels of HIPK3 may play a substantial role in the pathogenesis of type 2 diabetes.
    No preview · Article · Sep 2012 · Diabetologia
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    ABSTRACT: Insulin resistance is often associated with impeded insulin signaling due either to decreased concentrations or functional modifications of crucial signaling molecules including insulin receptor substrates (IRS) in the liver. Many actions of adiponectin, a well-recognized antidiabetic adipokine, are currently attributed to the activation of two critical molecules downstream of AdipoR1 and R2: AMP-activated kinase (AMPK) and peroxisome proliferator-activated receptor α (PPARα). However, the direct effects of adiponectin on insulin signaling molecules remain poorly understood. We show here that adiponectin upregulates IRS-2 through activation of signal transducer and activator of transcription-3 (STAT3). Surprisingly, this activation is associated with IL-6 production from macrophages induced by adiponectin through NFκB activation independent of its authentic receptors, AdipoR1 and AdipoR2. These data have unraveled an insulin-sensitizing action initiated by adiponectin leading to upregulation of hepatic IRS-2 via an IL-6 dependent pathway through a still unidentified adiponectin receptor.
    Full-text · Article · Apr 2011 · Cell metabolism
  • Iseki Takamoto · Takashi Kadowaki
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    ABSTRACT: As the number of type 2 diabetes patients is still increasing in Japan, careful management and appropriate treatment of diabetes with oral hypoglycemic agents are required for all general physicians. Ultimate aim of treatment should be maintenance of a quality of life not different from that of persons without diabetes. Recently various new oral hypoglycemic agents have been developed and six different classes of agents are available now: sulfonylureas, biguanides, alpha-glucosidase inhibitors, glinides, thiazolidinediones, and dipeptidyl peptidase-4 inhibitors. In this article we describe the specific mechanisms of actions, side effects, and important points in clinical usage. Every drug therapy should be supported by lifestyle changes and the agents to be used should be selected after consideration of patient's patho-physiological state of diabetes, the presence of any complications, age, functional disorders of the liver, kidney, heart and lung, and the risk for hypoglycemia.
    No preview · Article · Mar 2011 · Nippon rinsho. Japanese journal of clinical medicine
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    ABSTRACT: In obese patients with type 2 diabetes, insulin delivery to and insulin-dependent glucose uptake by skeletal muscle are delayed and impaired. The mechanisms underlying the delay and impairment are unclear. We demonstrate that impaired insulin signaling in endothelial cells, due to reduced Irs2 expression and insulin-induced eNOS phosphorylation, causes attenuation of insulin-induced capillary recruitment and insulin delivery, which in turn reduces glucose uptake by skeletal muscle. Moreover, restoration of insulin-induced eNOS phosphorylation in endothelial cells completely reverses the reduction in capillary recruitment and insulin delivery in tissue-specific knockout mice lacking Irs2 in endothelial cells and fed a high-fat diet. As a result, glucose uptake by skeletal muscle is restored in these mice. Taken together, our results show that insulin signaling in endothelial cells plays a pivotal role in the regulation of glucose uptake by skeletal muscle. Furthermore, improving endothelial insulin signaling may serve as a therapeutic strategy for ameliorating skeletal muscle insulin resistance.
    Full-text · Article · Mar 2011 · Cell metabolism
  • Iseki Takamoto · Takashi Kadowaki

    No preview · Article · Nov 2010 · Nippon rinsho. Japanese journal of clinical medicine
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    ABSTRACT: Adiponectin is an anti-diabetic adipokine. Its receptors possess a seven-transmembrane topology with the amino terminus located intracellularly, which is the opposite of G-protein-coupled receptors. Here we provide evidence that adiponectin induces extracellular Ca(2+) influx by adiponectin receptor 1 (AdipoR1), which was necessary for subsequent activation of Ca(2+)/calmodulin-dependent protein kinase kinase beta (CaMKKbeta), AMPK and SIRT1, increased expression and decreased acetylation of peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha), and increased mitochondria in myocytes. Moreover, muscle-specific disruption of AdipoR1 suppressed the adiponectin-mediated increase in intracellular Ca(2+) concentration, and decreased the activation of CaMKK, AMPK and SIRT1 by adiponectin. Suppression of AdipoR1 also resulted in decreased PGC-1alpha expression and deacetylation, decreased mitochondrial content and enzymes, decreased oxidative type I myofibres, and decreased oxidative stress-detoxifying enzymes in skeletal muscle, which were associated with insulin resistance and decreased exercise endurance. Decreased levels of adiponectin and AdipoR1 in obesity may have causal roles in mitochondrial dysfunction and insulin resistance seen in diabetes.
    Full-text · Article · Mar 2010 · Nature
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    ABSTRACT: Phosphoinositide 3-kinase (PI3K) p85alpha-deficient mice exhibit hypoglycemia as a result of increased insulin sensitivity and glucose uptake in peripheral tissues. Although PI3K is central to the metabolic actions of insulin, its mechanism of action in liver is not well understood. In the present study, we investigated hepatic insulin signaling and glucose homeostasis in p85alpha-deficient and wild-type mice. In the livers of p85alpha-deficient mice, p50alpha played a compensatory role in insulin-stimulated PI3K activation by binding to insulin receptor substrate (IRS)-1/2. In p85alpha-deficient mice, the ratio of p50alpha over p110 catalytic subunit of PI3K in the liver was higher than in the muscles. PI3K activity associated with IRS-1/2 was not affected by the lack of p85alpha in the liver. Insulin-stimulated Akt and phosphatase and tensin homologue deleted on chromosome 10 (PTEN) activities in the liver were similar in p85alpha-deficient and wild-type mice. A hyperinsulinemic-euglycemic clamp study revealed that the glucose infusion rate and the rate of disappearance were higher in p85alpha-deficient mice than in wild-type mice but that endogenous glucose production tended to be higher in p85alpha-deficient mice than in wild-type mice. Consistent with this finding, the expression of glucose-6-phosphatase and phosphoenolpyruvate carboxykinase in livers after fasting was higher in p85alpha-deficient mice than in wild-type mice. After mice were fasted, the intrahepatic glucose-6-phosphate level was almost completely depleted in p85alpha-deficient mice. The glycogen content fell to nearly zero as a result of glycogenolysis shortly after the initiation of fasting in p85alpha-deficient mice. The absence of an increase in insulin-stimulated PI3K activation in the liver of p85alpha-deficient mice, unlike the muscles, may be associated with the molecular balance between the regulatory subunit and the catalytic subunit of PI3K. Gluconeogenesis was rather elevated in p85alpha-deficient mice, compared with in wild-type mice, and the liver seemed to partially compensate for the increase in glucose uptake in peripheral tissues.
    Full-text · Article · Feb 2009 · AJP Endocrinology and Metabolism
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    ABSTRACT: Rimonabant has been shown to not only decrease the food intake and body weight but also to increase serum adiponectin levels. This increase of the serum adiponectin levels has been hypothesized to be related to the rimonabant-induced amelioration of insulin resistance linked to obesity, although experimental evidence to support this hypothesis is lacking. To test this hypothesis experimentally, we generated adiponectin knock-out (adipo(-/-))ob/ob mice. After 21 days of 30 mg/kg rimonabant, the body weight and food intake decreased to similar degrees in the ob/ob and adipo(-/-)ob/ob mice. Significant improvement of insulin resistance was observed in the ob/ob mice following rimonabant treatment, associated with significant up-regulation of the plasma adiponectin levels, in particular, of high molecular weight adiponectin. Amelioration of insulin resistance in the ob/ob mice was attributed to the decrease of glucose production and activation of AMP-activated protein kinase (AMPK) in the liver induced by rimonabant but not to increased glucose uptake by the skeletal muscle. Interestingly, the rimonabant-treated adipo(-/-)ob/ob mice also exhibited significant amelioration of insulin resistance, although the degree of improvement was significantly lower as compared with that in the ob/ob mice. The effects of rimonabant on the liver metabolism, namely decrease of glucose production and activation of AMPK, were also less pronounced in the adipo(-/-)ob/ob mice. Thus, it was concluded that rimonabant ameliorates insulin resistance via both adiponectin-dependent and adiponectin-independent pathways.
    Full-text · Article · Dec 2008 · Journal of Biological Chemistry
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    ABSTRACT: We investigated the effect of glucokinase activator (GKA) on glucose metabolism and beta-cell mass. We analyzed four mouse groups: wild-type mice and beta-cell-specific haploinsufficiency of glucokinase gene (Gck(+/-)) mice on a high-fat (HF) diet. Each genotype was also treated with GKA mixed in the HF diet. Rodent insulinoma cells and isolated islets were used to evaluate beta-cell proliferation by GKA. After 20 wk on the above diets, there were no differences in body weight, lipid profiles, and liver triglyceride content among the four groups. Glucose tolerance was improved shortly after the GKA treatment in both genotypes of mice. beta-Cell mass increased in wild-type mice compared with Gck(+/-) mice, but a further increase was not observed after the administration of GKA in both genotypes. Interestingly, GKA was able to up-regulate insulin receptor substrate-2 (Irs-2) expression in insulinoma cells and isolated islets. The administration of GKA increased 5-bromo-2-deoxyuridine (BrdU) incorporation in insulinoma cells, and 3 d administration of GKA markedly increased BrdU incorporation in mice treated with GKA in both genotypes, compared with those without GKA. In conclusion, GKA was able to chronically improve glucose metabolism for mice on the HF diet. Although chronic GKA administration failed to cause a further increase in beta-cell mass in vivo, GKA was able to increase beta cell proliferation in vitro and with a 3-d administration in vivo. This apparent discrepancy can be explained by a chronic reduction in ambient blood glucose levels by GKA treatment.
    No preview · Article · Dec 2008 · Endocrinology
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    I Takamoto · Y Terauchi · N Kubota · M Ohsugi · K Ueki · T Kadowaki
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    ABSTRACT: In type 2 diabetes, there is a defect in the regulation of functional beta-cell mass to overcome high-fat (HF) diet-induced insulin resistance. Many signals and pathways have been implicated in beta-cell function, proliferation and apoptosis. The co-ordinated regulation of functional beta-cell mass by insulin signalling and glucose metabolism under HF diet-induced insulin-resistant conditions is discussed in this article. Insulin receptor substrate (IRS)-2 is one of the two major substrates for the insulin signalling. Interestingly, IRS-2 is involved in the regulation of beta-cell proliferation, as has been demonstrated using knockout mice models. On the other hand, in an animal model for human type 2 diabetes with impaired insulin secretion because of insufficiency of glucose metabolism, decreased beta-cell proliferation was observed in mice with beta-cell-specific glucokinase haploinsufficiency (Gck(+/) (-)) fed a HF diet without upregulation of IRS-2 in beta-cells, which was reversed by overexpression of IRS-2 in beta-cells. As to the mechanism underlying the upregulation of IRS-2 in beta-cells, glucose metabolism plays an important role independently of insulin, and phosphorylation of cAMP response element-binding protein triggered by calcium-dependent signalling is the critical pathway. Downstream from insulin signalling via IRS-2 in beta-cells, a reduction in FoxO1 nuclear exclusion contributes to the insufficient proliferative response of beta-cells to insulin resistance. These findings suggest that IRS-2 is critical for beta-cell hyperplasia in response to HF diet-induced insulin resistance.
    Full-text · Article · Nov 2008 · Diabetes Obesity and Metabolism
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    ABSTRACT: Adiponectin has been proposed to act as an antidiabetic adipokine, suppressing gluconeogenesis and stimulating fatty acid oxidation in the liver and skeletal muscle. Although adiponectin-knockout (adipo(-/-)) mice are known to exhibit insulin resistance, the degrees of insulin resistance and glucose intolerance are unexpectedly only moderate. In this study, the adipo(-/-) mice showed hepatic, but not muscle, insulin resistance. insulin-stimulated phosphorylation of IRS-1 and IRS-2 was impaired, the IRS-2 protein level was decreased, and insulin-stimulated phosphorylation of Akt was decreased in the liver of the adipo(-/-) mice. However, the triglyceride content in the liver was not increased in these mice, despite the decrease in the PPARalpha expression involved in lipid combustion, since the expressions of lipogenic genes such as SREBP-1 and SCD-1 were decreased in association with the increased leptin sensitivity. Consistent with this, the down-regulation SREBP-1 and SCD-1 observed in the adipo(-/-) mice was no longer observed, and the hepatic triglyceride content was significantly increased in the adiponectin leptin double-knockout (adipo(-/-)ob/ob) mice. On the other hand, the triglyceride content in the skeletal muscle was significantly decreased in the adipo(-/-) mice, probably due to up-regulated AMPK activity associated with the increased leptin sensitivity. In fact, these phenotypes in the skeletal muscle of these mice were no longer observed in the adipo(-/-)ob/ob mice. In conclusion, adipo(-/-) mice showed impaired insulin signaling in the liver to cause hepatic insulin resistance, however, no increase in the triglyceride content was observed in either the liver or the skeletal muscle, presumably on account of the increased leptin sensitivity.
    No preview · Article · Aug 2008 · Endocrine Journal
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    ABSTRACT: Insulin receptor substrate (Irs) mediates metabolic actions of insulin. Here, we show that hepatic Irs1 and Irs2 function in a distinct manner in the regulation of glucose homeostasis. The PI3K activity associated with Irs2 began to increase during fasting, reached its peak immediately after refeeding, and decreased rapidly thereafter. By contrast, the PI3K activity associated with Irs1 began to increase a few hours after refeeding and reached its peak thereafter. The data indicate that Irs2 mainly functions during fasting and immediately after refeeding, and Irs1 functions primarily after refeeding. In fact, liver-specific Irs1-knockout mice failed to exhibit insulin resistance during fasting, but showed insulin resistance after refeeding; conversely, liver-specific Irs2-knockout mice displayed insulin resistance during fasting but not after refeeding. We propose the concept of the existence of a dynamic relay between Irs1 and Irs2 in hepatic insulin signaling during fasting and feeding.
    Full-text · Article · Aug 2008 · Cell metabolism
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    ABSTRACT: Adiponectin has been shown to stimulate fatty acid oxidation and enhance insulin sensitivity through the activation of AMP-activated protein kinase (AMPK) in the peripheral tissues. The effects of adiponectin in the central nervous system, however, are still poorly understood. Here, we show that adiponectin enhances AMPK activity in the arcuate hypothalamus (ARH) via its receptor AdipoR1 to stimulate food intake; this stimulation of food intake by adiponectin was attenuated by dominant-negative AMPK expression in the ARH. Moreover, adiponectin also decreased energy expenditure. Adiponectin-deficient mice showed decreased AMPK phosphorylation in the ARH, decreased food intake, and increased energy expenditure, exhibiting resistance to high-fat-diet-induced obesity. Serum and cerebrospinal fluid levels of adiponectin and expression of AdipoR1 in the ARH were increased during fasting and decreased after refeeding. We conclude that adiponectin stimulates food intake and decreases energy expenditure during fasting through its effects in the central nervous system.
    Full-text · Article · Aug 2007 · Cell Metabolism