Upregulation Of Glucose Uptake Research Articles

Mildronate decreases carnitine availability and up-regulates glucose uptake and related gene expression in the mouse heart

Aims l-carnitine has been shown to play a central role in both fat and carbohydrate metabolisms. This study investigated whether acute and long-term treatments with an l-carnitine biosynthesis inhibitor, mildronate (3-(2,2,2-trimethylhydrazinium) propionate), modulate glucose uptake. Main methods The effects of acute and long-term administration of mildronate at a dose of 200 mg/kg (i.p. daily for 20 days) were tested in mouse blood plasma and heart. Key findings Acute administration of mildronate in vivo, or in vitro administration with perfusion buffer in isolated heart experiments, did not induce any effects on glucose blood concentration and uptake in the heart. Mildronate long-term treatment significantly decreased carnitine concentration in plasma and heart tissues, as well as increased the rate of insulin-stimulated glucose uptake by 35% and the expression of glucose transporter 4, hexokinase II, and insulin receptor proteins in mouse hearts. In addition, expression of both carnitine palmitoyltransferases IA and IB were significantly increased. Mildronate long-term treatment statistically significantly decreased fed state blood glucose from 6 ± 0.2 to 5 ± 0.1 mM, but did not affect plasma insulin and C-peptide levels. Significance Our experiments demonstrate for the first time that long-term mildronate treatment decreases carnitine content in the mouse heart and leads to increased glucose uptake and glucose metabolism-related gene expression.

Iron Depletion by Deferoxamine Up-Regulates Glucose Uptake and Insulin Signaling in Hepatoma Cells and in Rat Liver

Iron depletion improves insulin resistance in patients with nonalcoholic fatty liver disease and diabetes and also stabilizes the hypoxia-inducible factor (HIF)-1, resulting in increased glucose uptake in vitro. This study investigated the effect of iron depletion by deferoxamine on insulin signaling and glucose uptake in HepG2 hepatocytes and in rat liver. In HepG2 cells, deferoxamine stabilized HIF-1alpha and induced the constitutive glucose transporter Glut1 and the insulin receptor. Up-regulation of insulin receptor by deferoxamine was mimicked by the intracellular iron chelator deferasirox and the hypoxia inducer CoCl2 and required the HIF-1 obligate partner ARNT/HIF-1beta. Iron depletion increased insulin receptor activity, whereas iron supplementation had the opposite effect. Deferoxamine consistently increased the phosphorylation status of Akt/PKB and its targets FoxO1 and Gsk3beta, which mediate the effect of insulin on gluconeogenesis and glycogen synthesis, and up-regulated genes involved in glucose uptake and utilization. Iron depletion of Sprague-Dawley rats increased HIF-1alpha expression, improved glucose clearance, and was associated with up-regulation of insulin receptor and Akt/PKB levels and of glucose transport in hepatic tissue. Conversely, gluconeogenic genes were not affected. In rats with fatty liver because of a high-calorie and high-fat diet, glucose clearance was increased by iron depletion and decreased by iron supplementation. Thus, iron depletion by deferoxamine up-regulates glucose uptake, and increases insulin receptor activity and signaling in hepatocytes in vitro and in vivo.

Galectin-1 upregulates glucose transporter-1 expression level via protein kinase C, phosphoinositol-3 kinase, and mammalian target of rapamycin pathways in mouse embryonic stem cells

Although galectin-1 is expressed in various stem cells, our understanding of the functional roles of galectin-1 in embryonic stem (ES) cells is still fragmentary and incomplete. Thus, this study investigated the effect of galectin-1 on the 2-deoxyglucose (2-DG) uptake and its related signal cascades. Galectin-1 significantly increased 2-deoxyglucose uptake time- and dose-dependently. In addition, galectin-1-induced 2-deoxyglucose uptake was inhibited by glucose transporter-1 siRNA. Moreover, galectin-1 increased glucose transporter-1 mRNA and protein expression levels, which were inhibited by a disruption in transcription by actinomycin D and translation by the cycloheximide. Subsequently, the galectin-1-induced 2-deoxyglucose uptake was attenuated by these inhibitors. In investigation of signal transduction involved in this process, galectin-1 increased intracellular Ca 2+ concentration and the protein kinase C activation, which induced extracellular signal regulated kinase1/2 phosphorylation. On the other hand, phosphoinositol-3-kinase/Akt activated by galectin-1 was not involved in extracellular signal regulated kinase1/2 pathway. Moreover, mammalian target of rapamycin signal pathway was stimulated in response to galectin-1. Finally, galectin-1-induced increase of glucose transporter-1 expression and 2-deoxyglucose uptake were inhibited by blocking of Ca 2+/protein kinase C/extracellular signal regulated kinase1/2, phosphoinositol-3-kinase/Akt, and mammalian target of rapamycin pathways. In conclusion, galectin-1 upregulates glucose uptake through Ca 2+/protein kinase C/extracellular signal regulated kinase1/2, phosphoinositol-3-kinase/Akt, and mammalian target of rapamycin pathways in mouse ES cells.

Effect of pravastatin on the development of diabetes and adiponectin production

In the West of Scotland Coronary Prevention Study (WOSCOPS), treatment of hypercholesterolemic men with pravastatin, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, reduced their likelihood to progress to diabetes mellitus by 30%. However, the mechanism of this effect of pravastatin has not been investigated. In the current study, we examined the effect of pravastatin on the development of diabetes in obese diabetic mice, and on the insulin-induced glucose uptake and adiponectin production. Pravastatin treatment attenuated the development of diabetes in db/db and high fat/high sucrose diet-fed C57BL/6J mice. An in vivo glucose transport assay showed that pravastatin upregulated glucose uptake in adipose tissue. Insulin-stimulated glucose uptake was enhanced in primary adipocytes isolated from pravastatin-treated mice. Pravastatin treatment increased adiponectin production in 3T3-L1 adipocytes. Plasma adiponectin levels were significantly increased in pravastatin-treated mice. Analyses of plasma samples from the WOSCOPS biobank indicated a significant increase of plasma adiponectin levels with pravastatin treatment (placebo −0.28±0.34μg/ml versus pravastatin +1.47±0.33μg/ml, p=0.0003). Taken together, our findings suggest that pravastatin may have beneficial effects on adipose tissue, which may partly explain the reduction of the development of diabetes by pravastatin treatment.

Isoform-specific requirement for Akt1 in the developmental regulation of cellular metabolism during lactation

The metabolic demands and synthetic capacity of the lactating mammary gland exceed that of any other tissue, thereby providing a useful paradigm for understanding the developmental regulation of cellular metabolism. By evaluating mice bearing targeted deletions in Akt1 or Akt2, we demonstrate that Akt1 is specifically required for lactating mice to synthesize sufficient quantities of milk to support their offspring. Whereas cellular proliferation, differentiation, and apoptosis are unaffected, loss of Akt1 disrupts the coordinate regulation of metabolic pathways that normally occurs at the onset of lactation. This results in a failure to upregulate glucose uptake, Glut1 surface localization, lipid synthesis, and multiple lipogenic enzymes, as well as a failure to downregulate lipid catabolic enzymes. These findings demonstrate that Akt1 is required in an isoform-specific manner for orchestrating many of the developmental changes in cellular metabolism that occur at the onset of lactation and establish a role for Akt1 in glucose metabolism.

The Novel Roles of Liver for Compensation of Insulin Resistance in Human Growth Hormone Transgenic Rats

Chronic excess of GH is known to cause hyperinsulinemia and insulin resistance. We developed human GH transgenic (TG) rats, which were characterized by high plasma levels of human GH and IGF-I. These TG rats showed higher levels of plasma insulin, compared with control littermates, whereas plasma glucose concentrations were normal. Insulin-dependent glucose uptake into adipocytes and muscle was impaired, suggesting that these rats developed insulin resistance. In contrast, insulin-independent glucose uptake into hepatocytes from TG rats was significantly increased, and glycogen and lipid levels in livers of TG rats were remarkably high. Because the role of liver in GH-induced insulin resistance is poorly understood, we studied insulin signaling at early stages and insulin action in liver and primary cultures of hepatocytes prepared from TG rats. There was no difference in insulin receptor kinase activity induced by insulin between TG and control rats; however, insulin-dependent insulin receptor substrate-2 tyrosine phosphorylation, glycogen synthase activation, and expression of enzymes that induce lipid synthesis were potentiated in hepatocytes of TG rats. These results suggest that impairment of insulin-dependent glucose uptake by GH excess in adipose tissue and muscle is compensated by up-regulation of glucose uptake in liver and that potentiation of insulin signaling through insulin receptor substrate-2 in liver experiencing GH excess causes an increase in glycogen and lipid synthesis from incorporated glucose, resulting in accumulation of glycogen and lipids in liver. This novel mechanism explains normalization of plasma glucose levels at least in part in a GH excess model.

Modulation of Astroglial Energy Metabolism by Nitric Oxide

Activated astroglial cells produce large amounts of nitric oxide (NO) which, through the binding to soluble guanylyl cyclase, rapidly increases cyclic GMP concentrations. In addition, through the binding with the a-a (3) binuclear center of cytochrome c oxidase, NO rapidly decreases the affinity of this complex for O(2), hence reversibly inhibiting the mitochondrial electron flux and ATP synthesis. Despite promoting a profound degree of mitochondrial inhibition, astrocytes show remarkable resistance to NO and peroxynitrite, whereas neurons are highly vulnerable. Recent evidence suggests that the inhibition of mitochondrial respiration by these nitrogen-derived reactive species leads to the modulation of key regulatory steps of glucose metabolism. Thus, upregulation of glucose uptake, the stimulation of glycolysis and the activation of pentose-phosphate pathway appear to be important sites of action. The stimulation of these glucose-metabolizing pathways by NO would represent a transient attempt by the glial cells to compensate for energy impairment and oxidative stress, and thus to emerge from an otherwise pathological outcome.

Adipocytes with increased hexosamine flux exhibit insulin resistance, increased glucose uptake, and increased synthesis and storage of lipid

The hexosamine signaling pathway has been shown to serve a nutrient-sensing function. We have previously shown that overexpression of the rate-limiting enzyme for hexosamine synthesis (glutamine-fructose-6-phosphate amidotransferase) in adipose tissue of transgenic mice results in skeletal muscle insulin resistance and altered regulation of leptin and adiponectin. To dissect the pathways by which the hexosamine pathway affects fuel storage and energy homeostasis, we have examined the characteristics of adipocytes from these animals. After 3 mo of age, epididymal fat pads from adult transgenic animals are 42% heavier (P = 0.003) and individual adipocytes are 23% larger in diameter (P < 0.05) than those from littermate wild-type controls. Isolated adipocytes from transgenic mice are insulin resistant, with a 2.5-fold increase in the ED50 for stimulation of 2-deoxy-D-glucose uptake. However, maximal insulin-stimulated glucose uptake is increased in transgenic adipocytes by 39% (P < 0.05). This upregulation of glucose uptake was associated with a 41% increase in the expression of GLUT4 mRNA and a 28% increase in GLUT4 protein in transgenics compared with controls (P < 0.05). GLUT1 mRNA and protein did not significantly differ between fasted control and transgenics. Total lipid synthesis was also increased in epididymal adipocytes from transgenic animals by 206% compared with controls (P < 0.05). Fatty acid oxidation was increased 1.6-fold in the transgenic adipocytes (P < 0.05). We conclude that the hexosamine signaling pathway upregulates fat storage in adipocytes in states of carbohydrate excess, in part by increasing GLUT4 and glucose uptake and by augmenting fatty acid synthesis.

Up-regulation of Sodium-dependent Glucose Transporter by Interaction with Heat Shock Protein 70

Heat shock stress induces some heat shock proteins, including Hsp70, and activates sodium-dependent glucose transport in porcine renal LLC-PK(1) cells, but its mechanisms have not been described in detail. We investigated whether sodium-dependent glucose transporter (SGLT1) interacts with Hsp70 to increase SGLT1 activity. Heat shock stress increased SGLT1 activity without changing SGLT1 expression. The increase of SGLT1 activity was completely inhibited by an anti-transforming growth factor-beta1 (TGF-beta1) antibody. Instead of heat shock stress, TGF-beta1 increased SGLT1 activity dose- and time-dependently without changing SGLT1 expression. We found that the amount of Hsp70 immunoprecipitated from TGF-beta1-treated cells with an anti-SGLT1 antibody was higher than that of the control cells. Transfection of an anti-Hsp70 antibody into the cells inhibited the increase of SGLT1 activity. With confocal laser microscopy, both SGLT1 and Hsp70 was localized near the apical membrane in the TGF-beta1-treated cells, and an anti-Hsp70 antibody disturbed this localization. Furthermore, we clarified that an anti-Hsp70 antibody inhibited interaction of SGLT1 with Hsp70 in vitro. These results suggest that Hsp70 forms a complex with SGLT1 and increases the expression level of SGLT1 in the apical membrane, resulting in up-regulation of glucose uptake.

REDOX REGULATION OF CYTOKINE-INDUCED GLUCOSE UPTAKE IN SKELETAL MUSCLE

1523 Cytokines mediate the effects of infection on glucose metabolism causing transient increase in glucose uptake and insulin resistance. This study shows that in L6 skeletal myotubes, cytokine-induced up-regulation of glucose uptake is redox-regulated. In support of this it was observed that such effect of interferon (IFN) - γ or lipopolysaccharides (LPS), and a combination of LPS, IFN-γ and tumor necrosis factor (TNF) -α is: i) inhibited by treatment of cells with the antioxidant pyrrilodinedithiocarbamate and ii) potentiated in GSH deficient cells having impaired antioxidant defenses. Also, the stimulatory effect of LPS and IFN-γ individually, and a combination of LPS, IFN-γ and TNF-α on glucose uptake in L6 myotubes was associated with increased level of intracellular peroxides and loss of intracellular GSH. A recent report suggested that a combination of LPS, IFN-γ and TNF-α up-regulates glucose uptake in L6 myotubes by a nitric oxide dependent mechanism. Results obtained from experiments studying the individual effect of LPS, IFN-γ and TNF-α as well as a combination of the three activators provide evidence against a role of nitric oxide in mediating the stimulatory effect of the abovementioned agents on glucose uptake. We also sought to test whether the insulin-mimetic redox-active drug α-lipoic acid (LA) would increase skeletal muscle glucose uptake in cytokine- treated cells that are insulin-resistant. Treatment with a combination of LPS, IFN-γ and TNF-α did not compromise the sensitivity of skeletal muscle glucose uptake to LA suggesting that under conditions of acute infection LA may have therapeutic implications in restoring glucose availability in insulin-resistant tissues such as the skeletal muscle.

Effects of tumor necrosis factor-alpha on glucose metabolism in cultured human muscle cells from nondiabetic and type 2 diabetic subjects.

The effects of tumor necrosis factor-alpha (TNF alpha) on glucose uptake and glycogen synthase (GS) activity were studied in human skeletal muscle cell cultures from nondiabetic and type 2 diabetic subjects. In nondiabetic muscle cells, acute (90-min) exposure to TNF alpha (5 ng/ml) stimulated glucose uptake (73 +/- 14% increase) to a greater extent than insulin (37 +/- 4%; P < 0.02). The acute uptake response to TNF alpha in diabetic cells (51 +/- 6% increase) was also greater than that to insulin (31 +/- 3%; P < 0.05). Prolonged (24-h) exposure of nondiabetic muscle cells to TNF alpha resulted in a further stimulation of uptake (152 +/- 31%; P < 0.05), whereas the increase in cells from type 2 diabetics was not significant compared with that in cells receiving acute treatment. After TNF alpha treatment, the level of glucose transporter-1 protein was elevated in nondiabetic (4.6-fold increase) and type 2 (1.7-fold) cells. Acute TNF alpha treatment had no effect on the fractional velocity of GS in either nondiabetic or type 2 cells. Prolonged exposure reduced the GS fractional velocity in both nondiabetic and diabetic cells. In summary, both acute and prolonged treatment with TNF alpha up-regulate glucose uptake activity in cultured human muscle cells, but reduce GS activity. Increased skeletal muscle glucose uptake in conditions of TNF alpha excess may serve as a compensatory mechanism in the insulin resistance of type 2 diabetes.

Effects of Tumor Necrosis Factor- on Glucose Metabolism in Cultured Human Muscle Cells from Nondiabetic and Type 2 Diabetic Subjects

The effects of tumor necrosis factor-α (TNFα) on glucose uptake and glycogen synthase (GS) activity were studied in human skeletal muscle cell cultures from nondiabetic and type 2 diabetic subjects. In nondiabetic muscle cells, acute (90-min) exposure to TNFα (5 ng/ml) stimulated glucose uptake (73 ± 14% increase) to a greater extent than insulin (37 ± 4%; P < 0.02). The acute uptake response to TNFα in diabetic cells (51 ± 6% increase) was also greater than that to insulin (31 ± 3%; P < 0.05). Prolonged (24-h) exposure of nondiabetic muscle cells to TNFα resulted in a further stimulation of uptake (152 ± 31%; P < 0.05), whereas the increase in cells from type 2 diabetics was not significant compared with that in cells receiving acute treatment. After TNFα treatment, the level of glucose transporter-1 protein was elevated in nondiabetic (4.6-fold increase) and type 2 (1.7-fold) cells. Acute TNFα treatment had no effect on the fractional velocity of GS in either nondiabetic or type 2 cells. Prolonged exposure reduced the GS fractional velocity in both nondiabetic and diabetic cells. In summary, both acute and prolonged treatment with TNFα up-regulate glucose uptake activity in cultured human muscle cells, but reduce GS activity. Increased skeletal muscle glucose uptake in conditions of TNFα excess may serve as a compensatory mechanism in the insulin resistance of type 2 diabetes.