RESUMEN
The phosphatidylinositol 3-kinase signaling pathway in vascular endothelial cells is important for systemic angiogenesis and glucose metabolism. In this study, we addressed the precise role of the 3-phosphoinositide-dependent protein kinase 1 (PDK1)-regulated signaling network in endothelial cells in vivo, using vascular endothelial PDK1 knockout (VEPDK1KO) mice. Surprisingly, VEPDK1KO mice manifested enhanced glucose tolerance and whole-body insulin sensitivity due to suppression of their hepatic glucose production with no change in either peripheral glucose disposal or even impaired vascular endothelial function at 6 months of age. When mice were fed a standard diet at 6 months of age and a high-fat diet at 3 months of age, hypertrophy of epididymal adipose tissues was inhibited, adiponectin mRNA was significantly increased, and mRNA of MCP1, leptin, and TNFα was decreased in the white adipose tissue of VEPDK1KO mice in comparison with controls. Consequently, both the circulating adiponectin levels and the activity of hepatic AMP-activated protein kinase were significantly increased, subsequently enhancing whole-body insulin sensitivity and energy expenditure with increased hepatic fatty acid oxidation in VEPDK1KO mice. These results provide the first in vivo evidence that lowered angiogenesis through the deletion of PDK1 signaling not only interferes with the growth of adipose tissue but also induces increased energy expenditure due to amelioration of the adipocytokine profile. This demonstrates an unexpected role of PDK1 signaling in endothelial cells on the maintenance of proper glucose homeostasis through the regulation of adipocyte development.
Asunto(s)
Células Endoteliales/metabolismo , Resistencia a la Insulina , Grasa Intraabdominal/metabolismo , Neovascularización Fisiológica , Proteínas Serina-Treonina Quinasas/genética , Proteínas Serina-Treonina Quinasas/metabolismo , Proteínas Quinasas Dependientes de 3-Fosfoinosítido , Adiponectina/biosíntesis , Adiponectina/sangre , Adiponectina/genética , Tejido Adiposo Blanco/metabolismo , Animales , Quimiocina CCL2/biosíntesis , Glucosa/metabolismo , Leptina/biosíntesis , Metabolismo de los Lípidos , Hígado/metabolismo , Masculino , Ratones , Ratones Noqueados , Obesidad/metabolismo , Fosfatidilinositol 3-Quinasa/metabolismo , Proteínas Serina-Treonina Quinasas/deficiencia , ARN Mensajero/genética , ARN Mensajero/metabolismo , Transducción de Señal , Factor de Necrosis Tumoral alfa/biosíntesisRESUMEN
Physical exercise ameliorates metabolic disorders such as type 2 diabetes mellitus and obesity, but the molecular basis of these effects remains elusive. In the present study, we found that exercise up-regulates heparin-binding epidermal growth factor-like growth factor (HB-EGF) in skeletal muscle. To address the metabolic consequences of such gain of HB-EGF function, we generated mice that overexpress this protein specifically in muscle. The transgenic animals exhibited a higher respiratory quotient than did wild-type mice during indirect calorimetry, indicative of their selective use of carbohydrate rather than fat as an energy substrate. They also showed substantial increases in glucose tolerance, insulin sensitivity, and glucose uptake by skeletal muscle. These changes were accompanied by increased kinase activity of Akt in skeletal muscle and consequent inhibition of Forkhead box O1-dependent expression of the pyruvate dehydrogenase kinase 4 gene. Furthermore, mice with a high level of transgene expression were largely protected from obesity, hepatic steatosis, and insulin resistance, even when maintained on a high-fat diet. Our results suggest that HB-EGF produced by contracting muscle acts as an insulin sensitizer that facilitates peripheral glucose disposal.
Asunto(s)
Glucosa/metabolismo , Resistencia a la Insulina/fisiología , Insulina/metabolismo , Péptidos y Proteínas de Señalización Intercelular/metabolismo , Músculo Esquelético/metabolismo , Condicionamiento Físico Animal/fisiología , Animales , Modelos Animales de Enfermedad , Metabolismo Energético/fisiología , Hígado Graso/prevención & control , Proteína Forkhead Box O1 , Factores de Transcripción Forkhead/metabolismo , Regulación de la Expresión Génica , Factor de Crecimiento Similar a EGF de Unión a Heparina , Homeostasis/fisiología , Péptidos y Proteínas de Señalización Intercelular/genética , Masculino , Ratones , Ratones Transgénicos , Obesidad/prevención & control , Proteínas Quinasas/metabolismo , Proteínas Proto-Oncogénicas c-akt/metabolismoRESUMEN
OBJECTIVE: Extracellular nucleotides are important mediators of inflammatory responses and could also impact metabolic homeostasis. Type 2 purinergic (P2) receptors bind extracellular nucleotides and are expressed by major peripheral tissues responsible for glucose homeostasis. CD39/ENTPD1 is the dominant vascular and immune cell ectoenzyme that hydrolyzes extracellular nucleotides to regulate purinergic signaling. RESEARCH DESIGN AND METHODS: We have studied Cd39/Entpd1-null mice to determine whether any associated changes in extracellular nucleotide concentrations influence glucose homeostasis. RESULTS: Cd39/Entpd1-null mice have impaired glucose tolerance and decreased insulin sensitivity with significantly higher plasma insulin levels. Hyperinsulinemic-euglycemic clamp studies indicate altered hepatic glucose metabolism. These effects are mimicked in vivo by injection into wild-type mice of either exogenous ATP or an ecto-ATPase inhibitor, ARL-67156, and by exposure of hepatocytes to extracellular nucleotides in vitro. Increased serum interleukin-1beta, interleukin-6, interferon-gamma, and tumor necrosis factor-alpha levels are observed in Cd39/Entpd1-null mice in keeping with a proinflammatory phenotype. Impaired insulin sensitivity is accompanied by increased activation of hepatic c-Jun NH(2)-terminal kinase/stress-activated protein kinase in Cd39/Entpd1 mice after injection of ATP in vivo. This results in decreased tyrosine phosphorylation of insulin receptor substrate-2 with impeded insulin signaling. CONCLUSIONS: CD39/Entpd1 is a modulator of extracellular nucleotide signaling and also influences metabolism. Deletion of Cd39/Entpd1 both directly and indirectly impacts insulin regulation and hepatic glucose metabolism. Extracellular nucleotides serve as "metabolokines," indicating further links between inflammation and associated metabolic derangements.
Asunto(s)
Antígenos CD/genética , Antígenos CD/inmunología , Apirasa/genética , Apirasa/inmunología , Resistencia a la Insulina/inmunología , Hígado/metabolismo , Adenosina Trifosfato/metabolismo , Adenosina Trifosfato/farmacología , Tejido Adiposo Pardo/inmunología , Tejido Adiposo Pardo/metabolismo , Animales , Glucemia/metabolismo , Células Cultivadas , Citocinas/sangre , Metabolismo Energético/fisiología , Técnica de Clampeo de la Glucosa , Hepatocitos/citología , Hepatocitos/inmunología , Hepatocitos/metabolismo , Hiperinsulinismo/inmunología , Hiperinsulinismo/fisiopatología , Insulina/sangre , Proteínas Sustrato del Receptor de Insulina , Péptidos y Proteínas de Señalización Intracelular/metabolismo , Proteínas Quinasas JNK Activadas por Mitógenos/metabolismo , Hígado/citología , Hígado/inmunología , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Músculo Esquelético/inmunología , Músculo Esquelético/metabolismo , Consumo de Oxígeno/fisiología , Páncreas/inmunología , Páncreas/metabolismo , Fosfoproteínas/metabolismo , Fosforilación , Transducción de Señal/fisiologíaRESUMEN
Insulin receptor substrate (IRS)-1 and IRS-2 have dominant roles in the action of insulin, but other substrates of the insulin receptor kinase, such as Gab1, c-Cbl, SH2-B and APS, are also of physiological relevance. Although the protein downstream of tyrosine kinases-1 (Dok1) is known to function as a multisite adapter molecule in insulin signaling, its role in energy homeostasis has remained unclear. Here we show that Dok1 regulates adiposity. Expression of Dok1 in white adipose tissue was markedly increased in mice fed a high-fat diet, whereas adipocytes lacking this adapter were smaller and showed a reduced hypertrophic response to this dietary manipulation. Dok1-deficient mice were leaner and showed improved glucose tolerance and insulin sensitivity compared with wild-type mice. Embryonic fibroblasts from Dok1-deficient mice were impaired in adipogenic differentiation, and this defect was accompanied by an increased activity of the protein kinase ERK and a consequent increase in the phosphorylation of peroxisome proliferator-activated receptor (PPAR)-gamma on Ser112. Mutation of this negative regulatory site for the transactivation activity of PPAR-gamma blocked development of the lean phenotype caused by Dok1 ablation. These results indicate that Dok1 promotes adipocyte hypertrophy by counteracting the inhibitory effect of ERK on PPAR-gamma and may thus confer predisposition to diet-induced obesity.
Asunto(s)
Adipocitos/patología , Proteínas de Unión al ADN/metabolismo , Dieta , Ácidos Grasos/farmacología , Obesidad/patología , PPAR gamma/metabolismo , Fosfoproteínas/metabolismo , Proteínas de Unión al ARN/metabolismo , Adipocitos/efectos de los fármacos , Adipogénesis/efectos de los fármacos , Tejido Adiposo Blanco/efectos de los fármacos , Tejido Adiposo Blanco/patología , Adiposidad/efectos de los fármacos , Animales , Proteínas de Unión al ADN/deficiencia , Proteínas de Unión al ADN/genética , Quinasas MAP Reguladas por Señal Extracelular/metabolismo , Fibroblastos/efectos de los fármacos , Fibroblastos/enzimología , Glucosa/metabolismo , Hipertrofia , Insulina/metabolismo , Ratones , Fosfoproteínas/deficiencia , Fosfoproteínas/genética , Fosforilación/efectos de los fármacos , Fosfoserina/metabolismo , Proteínas de Unión al ARN/genética , Regulación hacia Arriba/efectos de los fármacosRESUMEN
A necessary condition of advocated criteria to determine the metabolic syndrome (MetS) in Japan is waist circumference (WC), which varies among races. In this study, we measured WC and visceral fat area (VFA) in subjects with type 2 diabetes (T2DM) and assessed the propriety of new criteria of MetS in Japan. Four hundred and nineteen patients (M/F: 258/161, age: 60.4+/-0.7 years, BMI: 24.4+/-0.2 kg/m(2)) who received abdominal CT examination were analyzed, and 178 (M/F: 111/67) subjects sufficed the criteria of MetS. Average VFA was significantly larger in subjects with MetS (162+/-3 cm(2) versus 82+/-3 cm(2), p<0.01). The WC and VFA were correlated significantly in both male (r=0.78, p<0.001) and female (r=0.82, p<0.001), and corresponding VFA at 85 cm of WC in male and at 90 cm in female were 125 cm(2) and 120 cm(2). Incidence of cardio- and cerebro-vascular diseases (CVD) was not different between subjects with and without MetS. The present cross-sectional study strongly suggests that the recommended WC is not suitable to define the current criteria of MetS (VFA, > or =100 cm(2)) and its criteria is not appropriate to segregate a risk of CVD in Japanese T2DM subjects. Further prospective analysis should be required to validate the criteria and clinical significance of MetS in T2DM.
Asunto(s)
Tamaño Corporal , Diabetes Mellitus Tipo 2/fisiopatología , Síndrome Metabólico/diagnóstico , Abdomen , Tejido Adiposo/anatomía & histología , Anciano , Diabetes Mellitus Tipo 2/diagnóstico por imagen , Diagnóstico Diferencial , Femenino , Humanos , Japón , Masculino , Síndrome Metabólico/diagnóstico por imagen , Persona de Mediana Edad , Tomografía Computarizada por Rayos X , VíscerasRESUMEN
Adipocytes secrete a variety of bioactive molecules that affect the insulin sensitivity of other tissues. We now show that the abundance of monocyte chemoattractant protein-1 (MCP-1) mRNA in adipose tissue and the plasma concentration of MCP-1 were increased both in genetically obese diabetic (db/db) mice and in WT mice with obesity induced by a high-fat diet. Mice engineered to express an MCP-1 transgene in adipose tissue under the control of the aP2 gene promoter exhibited insulin resistance, macrophage infiltration into adipose tissue, and increased hepatic triglyceride content. Furthermore, insulin resistance, hepatic steatosis, and macrophage accumulation in adipose tissue induced by a high-fat diet were reduced extensively in MCP-1 homozygous KO mice compared with WT animals. Finally, acute expression of a dominant-negative mutant of MCP-1 ameliorated insulin resistance in db/db mice and in WT mice fed a high-fat diet. These findings suggest that an increase in MCP-1 expression in adipose tissue contributes to the macrophage infiltration into this tissue, insulin resistance, and hepatic steatosis associated with obesity in mice.
Asunto(s)
Tejido Adiposo/metabolismo , Quimiocina CCL2/sangre , Hígado Graso , Resistencia a la Insulina , Macrófagos/metabolismo , Obesidad/fisiopatología , Células 3T3 , Tejido Adiposo/citología , Animales , Quimiocina CCL2/genética , Grasas de la Dieta , Glucosa/metabolismo , Humanos , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Ratones Obesos , Ratones Transgénicos , Análisis de Secuencia por Matrices de Oligonucleótidos , ARN Mensajero/metabolismo , Triglicéridos/metabolismoRESUMEN
Mice with muscle-specific knockout of the Glut4 glucose transporter (muscle-G4KO) are insulin resistant and mildly diabetic. Here we show that despite markedly reduced glucose transport in muscle, muscle glycogen content in the fasted state is increased. We sought to determine the mechanism(s). Basal glycogen synthase activity is increased by 34% and glycogen phosphorylase activity is decreased by 17% (P < 0.05) in muscle of muscle-G4KO mice. Contraction-induced glycogen breakdown is normal. The increased glycogen synthase activity occurs in spite of decreased signaling through the insulin receptor substrate 1 (IRS-1)-phosphoinositide (PI) 3-kinase-Akt pathway and increased glycogen synthase kinase 3beta (GSK3beta) activity in the basal state. Hexokinase II is increased, leading to an approximately twofold increase in glucose-6-phosphate levels. In addition, the levels of two scaffolding proteins that are glycogen-targeting subunits of protein phosphatase 1 (PP1), the muscle-specific regulatory subunit (RGL) and the protein targeting to glycogen (PTG), are strikingly increased by 3.2- to 4.2-fold in muscle of muscle-G4KO mice compared to wild-type mice. The catalytic activity of PP1, which dephosphorylates and activates glycogen synthase, is also increased. This dominates over the GSK3 effects, since glycogen synthase phosphorylation on the GSK3-regulated site is decreased. Thus, the markedly reduced glucose transport in muscle results in increased glycogen synthase activity due to increased hexokinase II, glucose-6-phosphate, and RGL and PTG levels and enhanced PP1 activity. This, combined with decreased glycogen phosphorylase activity, results in increased glycogen content in muscle in the fasted state when glucose transport is reduced.
Asunto(s)
Transportador de Glucosa de Tipo 4/fisiología , Glucógeno/metabolismo , Músculo Esquelético/metabolismo , Animales , Ayuno/metabolismo , Femenino , Transportador de Glucosa de Tipo 4/genética , Glucosa-6-Fosfato/metabolismo , Glucógeno Fosforilasa/metabolismo , Glucógeno Sintasa/metabolismo , Glucógeno Sintasa Quinasa 3/metabolismo , Hexoquinasa/metabolismo , Técnicas In Vitro , Péptidos y Proteínas de Señalización Intracelular/metabolismo , Glucógeno Hepático/metabolismo , Masculino , Ratones , Ratones Noqueados , Fosfatidilinositol 3-Quinasas/metabolismo , Fosfoproteínas Fosfatasas/metabolismo , Fosforilación , Proteína Fosfatasa 1 , Proteínas Proto-Oncogénicas c-akt/metabolismoRESUMEN
The frequency of cardiovascular disease associated with metabolic disorder is increasing rapidly worldwide. The metabolic syndrome, a concurrence of glucose intolerance, obesity, dyslipidemia, and hypertension that are risk factors for atherosclerosis, accounts for a large proportion of cardiovascular morbidity and mortality. Exceeding energy intake coupled with high fat diet, sedentary lifestyle, and multiple genetic factors interact to produce the metabolic syndrome, and insulin resistance and visceral adiposity have been suggested to be the common pathophysiological basis of the metabolic syndrome. Adiposity is correlated with altered production of so-called adipocytokines that play a role on the atherosclerotic angiopathy. At the cellular level, excess insulin is involved in VLDL-triglycerides production, decreased HDL, and various elements of atherogenesis. Detecting the metabolic syndrome and implementing preventive lifestyle interventions--diet education, physical activity, and weight control--is a high clinical priority.
Asunto(s)
Resistencia a la Insulina , Síndrome Metabólico/etiología , Adiponectina , Tejido Adiposo/metabolismo , Arteriosclerosis/etiología , Arteriosclerosis/prevención & control , Enfermedades Cardiovasculares/etiología , Enfermedades Cardiovasculares/prevención & control , HDL-Colesterol/deficiencia , Complicaciones de la Diabetes , Ingestión de Energía , Humanos , Hiperglucemia/complicaciones , Hiperinsulinismo/complicaciones , Péptidos y Proteínas de Señalización Intercelular/fisiología , Estilo de Vida , Lipoproteínas VLDL/metabolismo , Síndrome Metabólico/fisiopatología , Factores de Riesgo , Triglicéridos/metabolismo , Vísceras/metabolismoRESUMEN
In obesity and type 2 diabetes, expression of the GLUT4 glucose transporter is decreased selectively in adipocytes. Adipose-specific Glut4 (also known as Slc2a4) knockout (adipose-Glut4(-/-)) mice show insulin resistance secondarily in muscle and liver. Here we show, using DNA arrays, that expression of retinol binding protein-4 (RBP4) is elevated in adipose tissue of adipose-Glut4(-/-) mice. We show that serum RBP4 levels are elevated in insulin-resistant mice and humans with obesity and type 2 diabetes. RBP4 levels are normalized by rosiglitazone, an insulin-sensitizing drug. Transgenic overexpression of human RBP4 or injection of recombinant RBP4 in normal mice causes insulin resistance. Conversely, genetic deletion of Rbp4 enhances insulin sensitivity. Fenretinide, a synthetic retinoid that increases urinary excretion of RBP4, normalizes serum RBP4 levels and improves insulin resistance and glucose intolerance in mice with obesity induced by a high-fat diet. Increasing serum RBP4 induces hepatic expression of the gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PEPCK) and impairs insulin signalling in muscle. Thus, RBP4 is an adipocyte-derived 'signal' that may contribute to the pathogenesis of type 2 diabetes. Lowering RBP4 could be a new strategy for treating type 2 diabetes.
Asunto(s)
Diabetes Mellitus Tipo 2/sangre , Resistencia a la Insulina/fisiología , Obesidad/sangre , Proteínas de Unión al Retinol/metabolismo , Tejido Adiposo/efectos de los fármacos , Tejido Adiposo/metabolismo , Animales , Diabetes Mellitus Tipo 2/metabolismo , Modelos Animales de Enfermedad , Regulación de la Expresión Génica , Transportador de Glucosa de Tipo 4 , Hepatocitos/efectos de los fármacos , Hepatocitos/enzimología , Hepatocitos/metabolismo , Insulina/farmacología , Hígado/citología , Hígado/efectos de los fármacos , Hígado/enzimología , Ratones , Ratones Noqueados , Proteínas de Transporte de Monosacáridos/deficiencia , Proteínas de Transporte de Monosacáridos/genética , Proteínas de Transporte de Monosacáridos/metabolismo , Proteínas Musculares/deficiencia , Proteínas Musculares/genética , Proteínas Musculares/metabolismo , Músculos/efectos de los fármacos , Músculos/metabolismo , Obesidad/metabolismo , Análisis de Secuencia por Matrices de Oligonucleótidos , Fosfoenolpiruvato Carboxiquinasa (GTP)/metabolismo , Proteínas de Unión al Retinol/genética , Proteínas Plasmáticas de Unión al Retinol , Rosiglitazona , Transducción de Señal/efectos de los fármacos , Tiazolidinedionas/farmacologíaRESUMEN
Adipose tissue plays an important role in glucose homeostasis and affects insulin sensitivity in other tissues. In obesity and type 2 diabetes, glucose transporter 4 (GLUT4) is downregulated in adipose tissue, and glucose transport is also impaired in muscle. To determine whether overexpression of GLUT4 selectively in adipose tissue could prevent insulin resistance when glucose transport is impaired in muscle, we bred muscle GLUT4 knockout (MG4KO) mice to mice overexpressing GLUT4 in adipose tissue (AG4Tg). Overexpression of GLUT4 in fat not only normalized the fasting hyperglycemia and glucose intolerance in MG4KO mice, but it reduced these parameters to below normal levels. Glucose infusion rate during a euglycemic clamp study was reduced 46% in MG4KO compared with controls and was restored to control levels in AG4Tg-MG4KO. Similarly, insulin action to suppress hepatic glucose production was impaired in MG4KO mice and was restored to control levels in AG4Tg-MG4KO. 2-deoxyglucose uptake during the clamp was increased approximately twofold in white adipose tissue but remained reduced in skeletal muscle of AG4Tg-MG4KO mice. AG4Tg and AG4Tg-MG4KO mice have a slight increase in fat mass, a twofold elevation in serum free fatty acids, an approximately 50% increase in serum leptin, and a 50% decrease in serum adiponectin. In MG4KO mice, serum resistin is increased 34% and GLUT4 overexpression in fat reverses this. Overexpression of GLUT4 in fat also reverses the enhanced clearance of an oral lipid load in MG4KO mice. Thus overexpression of GLUT4 in fat reverses whole body insulin resistance in MG4KO mice without restoring glucose transport in muscle. This effect occurs even though AG4Tg-MG4KO mice have increased fat mass and low adiponectin and is associated with normalization of elevated resistin levels.
Asunto(s)
Tejido Adiposo/metabolismo , Glucemia/análisis , Diabetes Mellitus/metabolismo , Resistencia a la Insulina , Insulina/metabolismo , Proteínas de Transporte de Monosacáridos/metabolismo , Proteínas Musculares/metabolismo , Músculo Esquelético/metabolismo , Animales , Femenino , Regulación de la Expresión Génica , Prueba de Tolerancia a la Glucosa , Transportador de Glucosa de Tipo 4 , Masculino , Ratones , Ratones Noqueados , Ratones Transgénicos , Proteínas de Transporte de Monosacáridos/deficiencia , Proteínas de Transporte de Monosacáridos/genética , Proteínas Musculares/deficiencia , Proteínas Musculares/genética , Proteínas Recombinantes/metabolismoRESUMEN
The protein p27(Kip1) regulates cell cycle progression in mammals by inhibiting the activity of cyclin-dependent kinases (CDKs). Here we show that p27(Kip1) progressively accumulates in the nucleus of pancreatic beta cells in mice that lack either insulin receptor substrate 2 (Irs2(-/-)) or the long form of the leptin receptor (Lepr(-/-) or db/db). Deletion of the gene encoding p27(Kip1) (Cdkn1b) ameliorated hyperglycemia in these animal models of type 2 diabetes mellitus by increasing islet mass and maintaining compensatory hyperinsulinemia, effects that were attributable predominantly to stimulation of pancreatic beta-cell proliferation. Thus, p27(Kip1) contributes to beta-cell failure during the development of type 2 diabetes in Irs2(-/-) and Lepr(-/-) mice and represents a potential new target for the treatment of this condition.
Asunto(s)
Proteínas de Ciclo Celular/metabolismo , Diabetes Mellitus Tipo 2/metabolismo , Inhibidores Enzimáticos/metabolismo , Hiperinsulinismo/metabolismo , Proteínas Supresoras de Tumor/metabolismo , Animales , Proteínas de Ciclo Celular/genética , Núcleo Celular/metabolismo , Inhibidor p27 de las Quinasas Dependientes de la Ciclina , Modelos Animales de Enfermedad , Hiperglucemia/metabolismo , Proteínas Sustrato del Receptor de Insulina , Factor I del Crecimiento Similar a la Insulina/metabolismo , Péptidos y Proteínas de Señalización Intracelular , Islotes Pancreáticos/citología , Islotes Pancreáticos/metabolismo , Leptina/genética , Leptina/metabolismo , Ratones , Ratones Noqueados , Fosfoproteínas/genética , Fosfoproteínas/metabolismo , Proteínas Serina-Treonina Quinasas/metabolismo , Proteínas Proto-Oncogénicas/metabolismo , Proteínas Proto-Oncogénicas c-akt , Receptores de Superficie Celular/genética , Receptores de Superficie Celular/metabolismo , Receptores de Leptina , Transducción de Señal/fisiología , Proteínas Supresoras de Tumor/genéticaRESUMEN
A critical defect in type 2 diabetes is impaired insulin-stimulated glucose transport and metabolism in muscle and adipocytes. To understand the metabolic adaptations this elicits, we generated mice with targeted disruption of the GLUT4 glucose transporter in both adipocytes and muscle (AMG4KO). In contrast to total body GLUT4-null mice, AMG4KO mice exhibit normal growth, development, adipose mass, and longevity. They develop fasting hyperglycemia and glucose intolerance and are at risk for greater insulin resistance than mice lacking GLUT4 in only one tissue. Hyperinsulinemic-euglycemic clamp studies showed a 75% decrease in glucose infusion rate and markedly reduced 2-deoxyglucose uptake into skeletal muscle (85-90%) and white adipose tissue (65%). However, AMG4KO mice adapt by preferentially utilizing lipid fuels, as evidenced by a lower respiratory quotient and increased clearance of lipids from serum after oral lipid gavage. While insulin action on hepatic glucose production and gluconeogenic enzymes is impaired, hepatic glucokinase expression, incorporation of 14C-glucose into lipids, and hepatic VLDL-triglyceride release are increased. The lipogenic activity may be mediated by increased hepatic expression of SREBP-1c and acetyl-CoA carboxylase. Thus, inter-tissue communication results in adaptations to impaired glucose transport in muscle and adipocytes that involve increased hepatic glucose uptake and lipid synthesis, while muscle adapts by preferentially utilizing lipid fuels. Genetic determinants limiting this "metabolic flexibility" may contribute to insulin resistance and type 2 diabetes in humans.
Asunto(s)
Tejido Adiposo/fisiología , Metabolismo de los Lípidos , Hígado/metabolismo , Proteínas de Transporte de Monosacáridos/metabolismo , Proteínas Musculares/metabolismo , Músculos/fisiología , Tejido Adiposo/citología , Animales , Peso Corporal/fisiología , Diabetes Mellitus Tipo 2/metabolismo , Metabolismo Energético , Femenino , Glucosa/metabolismo , Intolerancia a la Glucosa/genética , Prueba de Tolerancia a la Glucosa , Transportador de Glucosa de Tipo 1 , Transportador de Glucosa de Tipo 4 , Humanos , Insulina/metabolismo , Resistencia a la Insulina/genética , Lipoproteínas VLDL/metabolismo , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Proteínas de Transporte de Monosacáridos/genética , Proteínas Musculares/genética , Fenotipo , Triglicéridos/metabolismoRESUMEN
In humans with obesity or type 2 diabetes, insulin target tissues are resistant to many actions of insulin. The atypical protein kinase C (PKC) isoforms lambda and zeta are downstream of phosphatidylinositol-3 kinase (PI3K) and are required for maximal insulin stimulation of glucose uptake. Phosphoinositide-dependent protein kinase-1 (PDK-1), also downstream of PI3K, mediates activation of atypical PKC isoforms and Akt. To determine whether impaired PKClambda/zeta or PDK-1 activation plays a role in the pathogenesis of insulin resistance, we measured the activities of PKClambda/zeta and PDK-1 in vastus lateralis muscle of lean, obese, and obese/type 2 diabetic humans. Biopsies were taken after an overnight fast and after a 3-h hyperinsulinemic-euglycemic clamp. Obese subjects were also studied after weight loss on a very-low-calorie diet. Insulin-stimulated glucose disposal rate is reduced 26% in obese subjects and 62% in diabetic subjects (both comparisons P < 0.001). Insulin-stimulated insulin receptor substrate (IRS)-1 tyrosine phosphorylation and PI3K activity are impaired 40-50% in diabetic subjects compared with lean or obese subjects. Insulin stimulates PKClambda/zeta activity approximately 2.3-fold in lean subjects; the increment above basal is reduced 57% in obese and 65% in diabetic subjects. PKClambda/zeta protein amount is decreased 46% in diabetic subjects but is normal in obese nondiabetic subjects, indicating impaired insulin action on PKClambda/zeta. Importantly, weight loss in obese subjects normalizes PKClambda/zeta activation and increases IRS-1 phosphorylation and PI3K activity. Insulin also stimulates PDK-1 activity approximately twofold with no impairment in obese or diabetic subjects. In contrast to our previous data on Akt, reduced insulin-stimulated PKClambda/zeta activity could play a role in the pathogenesis of insulin resistance in muscle of obese and type 2 diabetic subjects.