GLUT4 Glucose Transporter Protein Research Articles

Dietary management and access to treatment for patients with glucose deficiency syndrome type 1: an overview review with focus on the European regulatory framework.

Glut-1 deficiency Syndrome (GLUT-1 DS) is a rare disease caused by a mutation in the SLC2A1 gene that codes for the glucose transporter protein GLUT-1 DS. Currently, there is no indicated drug therapy for this condition and ketogenic diet (KD) is the most effective remedy to treat it. The objective of this study was to review the published literature that evaluated the effectiveness of KD in the dietary management of GLUT-1 DS syndrome, describing the state-of-the-art the treatment pathway for patients with GLUT-1 DS syndrome in light of the current European regulatory framework within the National Health Services. The literature search was carried out on September 10, 2023, and all studies conducted in humans diagnosed with GLUT-1 deficiency syndrome and treated with KD were included. A total of 156 scientific papers have been extracted. Applying the exclusion criteria, 38 articles have been considered eligible. In 29 out of 38 studies, the main outcome for determining the efficacy of KD was the measurement of the number of epileptic seizures, demonstrating that patients treated with KD experienced improvements with a clear reduction in the number of epileptic attacks. Currently, in the European Union, only one country provides full reimbursement by the national health system for KD. Although they are crucial for the treatment of GLUT-1 DS, according with current food regulations, KD are not evaluated on the basis of an unambiguous efficacy result, but only on the basis of safety. As a result, it is desirable to carry out clinical studies in the coming years based on the determination of efficacy in target populations, also in view of the marketing of these products on the European market.

AS160 expression, but not AS160 Serine-588, Threonine-642, and Serine-704 phosphorylation, is essential for elevated insulin-stimulated glucose uptake by skeletal muscle from female rats after acute exercise.

One exercise session can increase subsequent insulin-stimulated glucose uptake (ISGU) by skeletal muscle in both sexes. We recently found that muscle expression and phosphorylation of key sites of Akt substrate of 160 kDa (AS160; also called TBC1D4) are essential for the full-exercise effect on postexercise-ISGU (PEX-ISGU) in male rats. In striking contrast, AS160's role in increased PEX-ISGU has not been rigorously tested in females. Our rationale was to address this major knowledge gap. Wild-type (WT) and AS160-knockout (KO) rats were either sedentary or acutely exercised. Adeno-associated virus (AAV) vectors were engineered to express either WT-AS160 or AS160 mutated on key serine and threonine residues (Ser588, Thr642, and Ser704) to alanine to prevent their phosphorylation. AAV vectors were delivered to the muscle of AS160-KO rats to determine if WT-AS160 or phosphorylation-inactivated AS160 would influence PEX-ISGU. AS160-KO rats have lower skeletal muscle abundance of the GLUT4 glucose transporter protein. This GLUT4 deficit was rescued using AAV delivery of GLUT4 to determine if eliminating muscle GLUT4 deficiency would normalize PEX-ISGU. The novel results were as follows: (1) AS160 expression was required for greater PEX-ISGU; (2) rescuing muscle AS160 expression in AS160-KO rats restored elevated PEX-ISGU; (3) AS160's essential role for the postexercise increase in ISGU was not attributable to reduced muscle GLUT4 content; and (4) AS160 phosphorylation on Ser588, Thr642, and Ser704 was not essential for greater PEX-ISGU. In conclusion, these novel findings revealed that three phosphosites widely proposed to influence PEX-ISGU are not required for this important outcome in female rats.

Akt substrate of 160kDa is essential for the calorie restriction-induced increase in insulin-stimulated glucose uptake by skeletal muscle of female rats.

We evaluated effects of calorie restriction (CR; consuming 65% of ad libitum (AL) intake) for 8 weeks on female wildtype (WT) and Akt substrate of 160kDa knockout (AS160-KO) rats. Insulin-stimulated glucose uptake (ISGU) was determined in isolated epitrochlearis muscles incubated with 0, 50, 100, or 500 µU/mL insulin. Phosphorylation of key insulin signaling proteins that control ISGU (Akt and AS160) was assessed by immunoblotting (Akt phosphorylation on Threonine-308, pAktThr308 and Serine-473, pAktSer473; AS160 phosphorylation on Serine-588, pAS160Ser588, and Threonine-642, pAS160Thr642). Abundance of proteins that regulate ISGU (GLUT4 glucose transporter protein and hexokinase II) was also determined by immunoblotting. The major results were as follows: (i) WT-CR versus WT-AL rats had greater ISGU with 100 and 500 µU/mL insulin; (ii) CR versus WT-AL rats had greater GLUT4 protein abundance; (iii) WT-CR versus WT-AL rats had greater pAktThr308 with 500 µU/mL insulin; (iv) WT-CR versus WT-AL rats did not differ for pAktSer473, pAS160Ser588, or pAS160Thr642 at any insulin concentration; (v) AS160-KO versus WT rats with each diet had lower ISGU at each insulin concentration, but not lower pAkt on either phosphosite; (vi) AS160-KO versus WT rats had lower muscle GLUT4 abundance regardless of diet; and (vii) AS160-KO-CR versus AS160-KO-AL rats did not differ for ISGU, GLUT4 abundance, pAkt on either phosphosite, or pAS160 on either phosphosite. These novel results demonstrated that AS160 expression, but not greater pAS160 on key phosphosites, was essential for the CR-induced increases in muscle ISGU and GLUT4 abundance of female rats.

First person – Hannah Black and Rachel Livingstone

ABSTRACT First Person is a series of interviews with the first authors of a selection of papers published in Journal of Cell Science, helping early-career researchers promote themselves alongside their papers. Hannah Black and Rachel Livingstone are co-first authors on ‘ Knockout of syntaxin-4 in 3T3-L1 adipocytes reveals new insight into GLUT4 trafficking and adiponectin secretion’, published in JCS. Hannah conducted the research described in this article while a PhD student in Professor Nia Bryant and Professor Gwyn Gould's lab at the Henry Wellcome Laboratory for Cell Biology, University of Glasgow, UK. She is now a postdoc in the lab of Professor Nia Bryant at the Department of Biology, University of York, UK, investigating membrane trafficking of the glucose transporter protein GLUT4. Rachel is a PhD student in the lab of Professor Gwyn Gould at the Henry Wellcome Laboratory for Cell Biology, University of Glasgow, UK, where she is also investigating membrane trafficking of GLUT4.

Differential Expression of Glucose Transporter Proteins GLUT-1, GLUT-3, GLUT-8 and GLUT-12 in the Placenta of Macrosomic, Small-for-Gestational-Age and Growth-Restricted Foetuses.

Placental transfer of glucose constitutes one of the major determinants of the intrauterine foetal growth. The objective of the present study was to evaluate the expression of glucose transporter proteins GLUT-1, GLUT-3, GLUT-8 and GLUT-12 in the placenta of macrosomic, small-for-gestational-age (SGA) and growth-restricted foetuses (FGR). A total of 70 placental tissue samples were collected from women who delivered macrosomic ≥4000 g (n = 26), SGA (n = 11), growth-restricted (n = 13) and healthy control neonates (n = 20). Computer-assisted quantitative morphometry of stained placental sections was performed to determine the expression of selected GLUT proteins. Immunohistochemical staining identified the presence of all glucose transporters in the placental tissue. Quantitative morphometric analysis performed for the vascular density-matched placental samples revealed a significant decrease in GLUT-1 and increase in GLUT-3 protein expression in pregnancies complicated by FGR as compared to other groups (p < 0.05). In addition, expression of GLUT-8 was significantly decreased among SGA foetuses (p < 0.05). No significant differences in GLUTs expression were observed in women delivering macrosomic neonates. In the SGA group foetal birth weight (FBW) was negatively correlated with GLUT-3 (rho = −0.59, p < 0.05) and positively with GLUT-12 (rho = 0.616, p < 0.05) placental expression. In addition, a positive correlation between FBW and GLUT-12 expression in the control group (rho = 0.536, p < 0.05) was noted. In placentas derived from FGR-complicated pregnancies the expression of two major glucose transporters GLUT-1 and GLUT-3 is altered. On the contrary, idiopathic foetal macrosomia is not associated with changes in the placental expression of GLUT-1, GLUT-3, GLUT-8 and GLUT-12 proteins.

Impact of pre-exercise feeding status on metabolic adaptations to endurance-type exercise training.

Nutrition and exercise metabolism are vibrant physiological fields, yet at times it feels as if greater progress could be made by better integrating these disciplines. Exercise is advocated for improving metabolic health, in part by increasing peripheral insulin sensitivity and glycaemic control. However, when a modest-to-high carbohydrate load is consumed before and/or during each exercise bout within a training programme, increases in oral glucose insulin sensitivity can be blunted in both men of a healthy weight and those with overweight/obesity. Exercise training-induced adaptation in the energy sensing AMP-activated protein kinase (AMPK) and the insulin-sensitive glucose transporter GLUT4 protein levels are sensitive to pre-exercise feeding status in both healthy individuals and individuals classified as overweight or obese. Increased lipid oxidation may, in part, explain the enhanced adaptive responses to exercise training performed before (i.e. fasted-state exercise) versus after nutrient ingestion. Evidence in individuals with type 2 diabetes currently shows no effect of altering nutrient-exercise timing for measured markers of metabolic health, or greater reductions in glycated haemoglobin (HbA1c) concentrations with exercise performed after versus before nutrient provision. Since the metabolic inflexibility associated with type 2 diabetes diminishes differences in lipid oxidation between the fasted and fed states, it is plausible that pre-exercise feeding status does not alter adaptations to exercise when metabolic flexibility is already compromised. Current evidence suggests restricting carbohydrate intake before and during exercise can enhance some health benefits of exercise, but in order to establish clinical guidelines, further research is needed with hard outcomes and different populations.

In This Issue

In This Issue

Muscle Fibers Utilize its Glucose Uptake Machinery to Reseal Sarcolemma Disruptions &amp; Stimulating Affiliated Rab G Proteins Improves Repair Capacity in Muscle Dystrophic Mice

The glucose uptake machinery in cells and muscle fibers is a robust and highly regulated system used to import extracellular glucose for intracellular metabolic processing. The majority of glucose uptake in skeletal muscle is done through stimulated exocytosis and fusion of vesicles to the plasma membrane to enrich the cellular exterior with glucose transporter protein GLUT4. In our investigation, we found evidence that GLUT4 containing vesicles (GSV) and the glucose uptake regulators AS160, rab8A, and rab10 serve an additional role in the plasma membrane repair response. Through the use of mutant plasmids and live cell imaging, we observed that GSVs, as well as affiliated rabs, translocate to injury sites in C2C12 myoblasts and isolated mouse muscle fibers under different modes of damage. We observed that AS160 phosphorylation from the phosphoinositide‐3 kinase (PI3K)/Akt1 signaling axis regulates membrane repair in cultured muscle cells. In addition, we screened GSV associating rab G proteins and saw that knocking down rab8A and rab10 expression reduced the repair capacity of the cells. Importantly, through the electroporation of overexpression or constitutively active rab10 mutant constructs in skeletal muscle of Duchenne muscular dystrophy mdx mice, there was a significant improvement in membrane resealing in vivo. Overall, our findings suggest that the glucose uptake vesicles commonly thought of as important for metabolic homeostasis, serve an additional function in repairing membrane wounds in some cell lines and mouse muscle fibers. Targeting glucose uptake regulators could lead to the development of new therapies for muscle disease and injury.

Lipid Metabolism Links Nutrient-Exercise Timing to Insulin Sensitivity in Men Classified as Overweight or Obese.

ContextPre-exercise nutrient availability alters acute metabolic responses to exercise, which could modulate training responsiveness.ObjectiveTo assess acute and chronic effects of exercise performed before versus after nutrient ingestion on whole-body and intramuscular lipid utilization and postprandial glucose metabolism.Design(1) Acute, randomized, crossover design (Acute Study); (2) 6-week, randomized, controlled design (Training Study).SettingGeneral community.ParticipantsMen with overweight/obesity (mean ± standard deviation, body mass index: 30.2 ± 3.5 kg⋅m-2 for Acute Study, 30.9 ± 4.5 kg⋅m-2 for Training Study).InterventionsModerate-intensity cycling performed before versus after mixed-macronutrient breakfast (Acute Study) or carbohydrate (Training Study) ingestion.ResultsAcute Study—exercise before versus after breakfast consumption increased net intramuscular lipid utilization in type I (net change: –3.44 ± 2.63% versus 1.44 ± 4.18% area lipid staining, P < 0.01) and type II fibers (–1.89 ± 2.48% versus 1.83 ± 1.92% area lipid staining, P < 0.05). Training Study—postprandial glycemia was not differentially affected by 6 weeks of exercise training performed before versus after carbohydrate intake (P > 0.05). However, postprandial insulinemia was reduced with exercise training performed before but not after carbohydrate ingestion (P = 0.03). This resulted in increased oral glucose insulin sensitivity (25 ± 38 vs –21 ± 32 mL⋅min-1⋅m-2; P = 0.01), associated with increased lipid utilization during exercise (r = 0.50, P = 0.02). Regular exercise before nutrient provision also augmented remodeling of skeletal muscle phospholipids and protein content of the glucose transport protein GLUT4 (P < 0.05).ConclusionsExperiments investigating exercise training and metabolic health should consider nutrient-exercise timing, and exercise performed before versus after nutrient intake (ie, in the fasted state) may exert beneficial effects on lipid utilization and reduce postprandial insulinemia.

The exocyst complex regulates insulin-stimulated glucose uptake of skeletal muscle cells.

Skeletal muscle handles ~80-90% of the insulin-induced glucose uptake. In skeletal muscle, insulin binding to its cell surface receptor triggers redistribution of intracellular glucose transporter GLUT4 protein to the cell surface, enabling facilitated glucose uptake. In adipocytes, the eight-protein exocyst complex is an indispensable constituent in insulin-induced glucose uptake, as it is responsible for the targeted trafficking and plasma membrane-delivery of GLUT4. However, the role of the exocyst in skeletal muscle glucose uptake has never been investigated. Here we demonstrate that the exocyst is a necessary factor in insulin-induced glucose uptake in skeletal muscle cells as well. The exocyst complex colocalizes with GLUT4 storage vesicles in L6-GLUT4myc myoblasts at a basal state and associates with these vesicles during their translocation to the plasma membrane after insulin signaling. Moreover, we show that the exocyst inhibitor endosidin-2 and a heterozygous knockout of Exoc5 in skeletal myoblast cells both lead to impaired GLUT4 trafficking to the plasma membrane and hinder glucose uptake in response to an insulin stimulus. Our research is the first to establish that the exocyst complex regulates insulin-induced GLUT4 exocytosis and glucose metabolism in muscle cells. A deeper knowledge of the role of the exocyst complex in skeletal muscle tissue may help our understanding of insulin resistance in type 2 diabetes.

Key Facilitator Proteins that Mediate Sarcolemma Membrane Repair have Potential as Therapeutics for Muscle Disease and Injury

A common aspect of many diseases and traumatic injuries affecting skeletal muscle is the necrotic death of muscle fibers. Necrotic death of muscle fibers involves the breakdown of the sarcolemmal membrane that can be exacerbated by increased fragility of the membrane or by compromised endogenous sarcolemmal membrane repair processes. Increasing these repair mechanisms could act as a therapeutic approach for a number of muscle diseases and injuries. Duchenne muscular dystrophy (DMD) is a fatal X‐linked inherited neuromuscular disorder caused by mutations in the dystrophin gene that provides a model for muscle injury and the effects of membrane repair. The dystrophin protein normally serves as a shock absorber for mechanical stress and as a signaling platform protein in muscle fibers. When dystrophin is lacking, patients experience an accumulation of membrane damage that muscle fibers cannot adequately repair. As a result, there is an increase in fiber necrosis that exceeds the regenerative capacity of the muscle. This causes DMD patients to develop striated muscle deterioration that leads to eventual death in the third decade of life. There is currently no cure for DMD and treatments that stimulate the membrane repair process in muscle fibers have been greatly overlooked and underutilized as a potential therapeutic approach. This project investigates a novel membrane repair signaling cascade in skeletal muscle that utilizes glucose storage vesicles (GSVs) and their key regulators Akt Substrate 160 kDa (AS160) and rab G proteins as a means to close membrane wounds. Based on our preliminary data, we hypothesize that AS160 phosphorylation and activation of associating rab G proteins facilitate the translocation of intracellular GSVs to disruption sites in the sarcolemma membrane for wound closure. Thus, modulating the function of these proteins may stimulate repair and have therapeutic benefits for DMD. Through the use of mutant plasmids and live cell imaging, we have observed that GSVs containing the glucose transport protein GLUT4, as well as affiliated rabs, translocate to injury cites in C2C12 myoblasts and isolated mouse muscle fibers. We have also identified that AS160 phosphorylation from the phosphoinositide‐3 kinase (PI3K)/Akt1 signaling axis regulates membrane repair in cultured muscle cells. Importantly, we have screened GSV associating rab G proteins and have found that specific rab proteins are involved in sarcolemma membrane repair in vivo, and that activating rab10 significantly improves membrane resealing in vivo in the muscle of a Duchenne muscular dystrophy mouse model (MDX). This project explores a novel signaling cascade controlling membrane repair that could be leveraged to develop new therapies for muscle disease and injury.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

A Potential Role for GSK3β in Glucose-Driven Intrauterine Catch-Up Growth in Maternal Obesity.

Obesity and unhealthy nutrition are increasing and affect women of childbearing age and hence during pregnancy. Despite normal or even high birth weight, the offspring suffers from long-term metabolic risks. We hypothesized that fetal growth is disturbed during different intrauterine phases. Underlying molecular events remain elusive. Female mice were fed either a standard diet (SD) or a high-fat diet (HFD) after weaning until mating and during pregnancy. Pregnant mice were euthanized at gestational day (G)15.5 and G18.5, and fetuses and placentas were removed for analysis. HFD fetuses displayed intrauterine growth restriction (IUGR) at G15.5, which disappeared until G18.5, indicating intrauterine catch-up growth during that time period. Main placental findings indicate decreased canonical Wnt-GSK3β signaling and lower proliferation rates at G18.5, which goes along with a smaller placental transfer zone. On the other hand, glucose depots (glycogen cluster) in HFD placentas decreased more strongly between G15.5 and G18.5 compared with placentas from SD mothers, and the glucose transporter protein GLUT-1 was increased at G18.5 in the HFD group. Maternal diet-induced obesity causes an IUGR phenotype at the beginning of the third week (G15.5) in our mouse model. This phenotype is reversed by the end of the third week (G18.5) despite a smaller placental transfer zone, probably based on GSK3β-mediated increased glucose mobilization in the placenta and hence an increased glucose supply to the fetus.

Transmembrane Exchange of Fluorosugars: Characterization of Red Cell GLUT1 Kinetics Using 19F NMR

We have developed a new approach, to our knowledge, to quantify the equilibrium exchange kinetics of carrier-mediated transmembrane transport of fluorinated substrates. The method is based on adapted kinetic theory that describes the concentration dependence of the transmembrane exchange rates of two competing, simultaneously transported species. Using the new approach, we quantified the kinetics of membrane transport of both anomers of three monofluorinated glucose analogs in human erythrocytes (red blood cells) using 19F NMR exchange spectroscopy. An inosine-based glucose-free medium was shown to promote survival and stable metabolism of red blood cells over the duration of the experiments (several hours). Earlier NMR studies only yielded the apparent rate constants and transmembrane fluxes of the anomeric species, whereas we could categorize the two anomers in terms of the catalytic activity (specificity constants) of the glucose transport protein GLUT1 toward them. Differences in the membrane permeability of the three glucose analogs were qualitatively interpreted in terms of local perturbations in the bonding of substrates to key amino acid residues in the active site of GLUT1. The methodology of this work will be applicable to studies of other carrier-mediated membrane transport processes, especially those with competition between simultaneously transported species. The GLUT1-specific results can be applied to the design of probes of glucose transport or inhibitors of glucose metabolism in cells, including those exhibiting the Warburg effect.

Estrogen Receptor 1 (ESR1) Enhances Slc2a4/GLUT4 Expression by a SP1 Cooperative Mechanism.

Background: Estrogens are involved in glycemic regulation, playing an important role in the development and/or progression of insulin resistance. For that, estrogens regulate the expression of the glucose transporter protein GLUT4 (codified by the solute carrier family 2 member 4 gene, Slc2a4), thus modulating adipose and muscle glucose disposal. This regulation is a balance between ESR1-mediated enhancer effect and ESR2-mediated repressor effect on Slc2a4 gene. However, molecular mechanisms involved in these effects are poorly understood. Since the specificity protein 1 (SP1) participates in several ESR-mediated genomic regulations, the aim of the present study is to investigate the participation of SP1 in the ESR1/2-mediated regulation of Slc2a4 gene.Methods: Differentiated 3T3-L1 adipocytes were 24-hour challenged with 10 nM estradiol (E2) and 10 nM ESR1 agonist (PPT) or 100 nM ESR2 agonist (DPN), added or not with E2. Slc2a4 and Sp1 mRNAs (RT-qPCR), total GLUT4 and nuclear ESR1, ESR2 and SP1 proteins (Western blotting), SP1 binding activity into Slc2a4 promoter (EMSA), and nuclear complexation of SP1/ESR1 (immunoprecipitation) were analyzed.Results: E2 and PPT increased (25-50%) whereas DPN reduced (20-45%) Slc2a4 and GLUT4 expression. Nuclear content of ESR1 and ESR2 remained unchanged. Nuclear content of SP1 increased (50 to 90%) by PPT and DPN added or not with E2; the highest effect observed with PPT alone. PPT also increased the nuclear content of SP1/ESR1 complex and the SP1 binding into the Slc2a4 promoter.Conclusions: ESR1 activation in adipocytes increased the nuclear content of SP1 protein, the SP1/ESR1 interaction and SP1 binding into the Slc2a4 gene promoter, culminating with increased Slc2a4/GLUT4 expression. No involvement of SP1 seems to occur in ESR2-mediated repressor effect on Slc2a4. We expect that this ESR1/SP1 cooperative effect can contribute to the development of new approaches for prevention or treatment of insulin resistance and diabetes mellitus.

Placental Expression of Glucose Transporter Proteins in Pregnancies Complicated by Gestational and Pregestational Diabetes Mellitus.

Gestational diabetes mellitus and pregestational diabetes mellitus constitute carbohydrate metabolism disorders, which, if not diagnosed and adequately treated, lead to serious and often life-threatening pregnancy complications. According to a recently formulated hypothesis, some diabetes-related complications, such as fetal macrosomia, may be the result of disturbances in the transplacental transport of nutrients-in particular, excessive maternal-fetal glucose transfer. Throughout pregnancy, glucose flux across the placenta is mediated by the group of facilitative glucose transporters (GLUT), the expression of which in different placental compartments is the precondition for effective glucose uptake from maternal blood and its subsequent transfer to the fetal circulation. In diabetes-complicated pregnancies, the location, expression and activity of glucose transporters are modified to an extent that results in alterations in the maternal-fetal glucose exchange, potentially leading to an excessive supply of energy substrates to the fetus. This paper reviews the literature on the expression and activity of glucose transporter proteins-GLUT-1, GLUT-3, GLUT-4, GLUT-8, GLUT-9 and GLUT-12-in the human placenta, with a special focus on diabetes-complicated pregnancy. The characteristics of transporters in conditions of maternal normoglycemia and modifications occurring in the diabetic placenta are summarized, and the factors responsible for the regulation of the expression of selected isoforms are described. Finally, the impact of alterations in the placental expression of the aforementioned members of the GLUT family on intrauterine fetal development in pregnancies complicated by diabetes mellitus is discussed.

Commentary: Systemic, Local, and Imaging Biomarkers of Brain Injury: More Needed, and Better Use of Those Already Established?

Commentary: Systemic, Local, and Imaging Biomarkers of Brain Injury: More Needed, and Better Use of Those Already Established?

Reduced Slc2a4/GLUT4 expression in subcutaneous adipose tissue of monosodium glutamate obese mice is recovered after atorvastatin treatment.

BackgroundDecreased expression of glucose transporter protein GLUT4, encoded by the solute carrier 2A4 (Slc2a4) gene, is involved in obesity-induced insulin resistance. Local tissue inflammation, by nuclear factor-κB (NFκB)-mediated pathway, has been related to Slc2a4 repression; a mechanism that could be modulated by statins. Using a model of obesity with insulin resistance, this study investigated whether (1) inflammatory markers and Slc2a4 expression are altered; (2) atorvastatin has beneficial effects on inflammation and Slc2a4 expression; and (3) inhibitor of NFκB (IKK)/NFκB pathway is involved in subcutaneous adipose tissue (SAT).FindingsObese mice showed insulin resistance, decreased expression of Slc2a4 mRNA (66%, P < 0.01) and GLUT4 protein (30%, P < 0.05), and increased expression of interleukin 6 (Il6) mRNA (44%, P < 0.05) in SAT. Obese mice treated with atorvastatin had enhanced in vivo insulin sensitivity, besides increased Slc2a4/GLUT4 expression and reduced Il6 expression in SAT. No alterations of tumor necrosis factor-α, interleukin 1β and adiponectin expression or IKKα/β activity in SAT of obese mice or obese mice treated with atorvastatin were observed.ConclusionsAtorvastatin has beneficial effect upon glycemic homeostasis, which may be related to its positive impact on Il6 and Slc2a4/GLUT4 expression in SAT.

Roles of facilitative glucose transporter GLUT1 in [18F]FDG positron emission tomography (PET) imaging of human diseases

The facilitative glucose transport protein GLUT1 has important roles in positron emission tomography (PET) imaging of human diseases. GLUT1 has widespread expression and catalyses the energyindependent facilitated diffusion of glucose down its concentration gradient across red blood cell membranes, blood-brain and blood-tissue barriers and membranes of some oragnelles. Import is usually the prevailing direction of transport for providing metabolic fuel, especially in proliferating cells. PET imaging using 2-deoxy-2-[ 18 F]fluoro-D-glucose ([ 18 F]FDG) measures the uptake of [ 18 F]FDG into cells and tissues as a marker of glucose transport and glycolytic activity. Diseases can alter glycolytic activity in localised regions of tissues or organs, which can be visualised using [ 18 F]FDG PET. Expression and/or activity levels of GLUT1 contribute to the pattern and intensity of [ 18 F]FDG. [ 18 F]FDG PET imaging is used in diagnosing and monitoring a range of human diseases and in analysing their response to treatments. Proliferating cancer cells display overexpression of GLUT1 and a vastly higher rate of glycolysis for satisfying their increased nutrient demands. Tumours therefore have significantly enhanced [ 18 F]FDG uptake compared with normal cells, so [ 18 F]FDG PET is routinely used in diagnosing and monitoring cancers. [ 18 F]FDG PET imaging of the brain allows identification of distinct patterns of hypometabolism and/or hypermetabolism associated with neurological disorders including Alzheimer’s disease, Parkinson’s disease, epilespsy,

Insulin acutely triggers transcription of Slc2a4 gene: Participation of the AT-rich, E-box and NFKB-binding sites

AimsThe insulin-sensitive glucose transporter protein GLUT4 (solute carrier family 2 member 4 (Slc2a4) gene) plays a key role in glycemic homeostasis. Decreased GLUT4 expression is a current feature in insulin resistant conditions such as diabetes, and the restoration of GLUT4 content improves glycemic control. This study investigated the effect of insulin upon Slc2a4/GLUT4 expression, focusing on the AT-rich element, E-box and nuclear factor NF-kappa-B (NFKB) site. Main methodsRat soleus muscles were incubated during 180min with insulin, added or not with wortmannin (phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit gamma isoform (PI3K)-inhibitor), ML9 (serine/threonine protein kinase (AKT) inhibitor) and tumor necrosis factor (TNF, GLUT4 repressor), and processed for analysis of GLUT4 protein (Western blotting); Slc2a4, myocyte enhancer factor 2a/d (Mef2a/d), hypoxia inducible factor 1a (Hif1a), myogenic differentiation 1 (Myod1) and nuclear factor of kappa light polypeptide gene enhancer in B-cells 1 (Nfkb1) messenger ribonucleic acids (mRNAs) (polymerase chain reaction (PCR)); and AT-rich- (myocyte-specific enhancer factor 2 (MEF2)-binding site), E-box- (hypoxia inducible factor 1 alpha (HIF1A)- and myoblast determination protein 1 (MYOD1)-binding site), and NFKB-binding activity (electrophoretic mobility assay). Key findingsInsulin increased Slc2a4 mRNA expression (140%) and nuclear proteins binding to AT-rich and E-box elements (~90%), all effects were prevented by wortmannin and ML9. Insulin also increased Mef2a/d and Myod1 mRNA expression, suggesting the participation of these transcriptional factors in the Slc2a4 enhancing effect. Conversely, insulin decreased Nfkb1 mRNA expression and protein binding to the NFKB-site (~50%). Furthermore, TNF-induced inhibition of GLUT4 expression (~40%) was prevented by insulin in an NFKB-binding repressing mechanism. GLUT4 protein paralleled the Slc2a4 mRNA regulations. SignificanceInsulin enhances the Slc2a4/GLUT4 expression in the skeletal muscle by activating AT-rich and E-box elements, in a PI3K/AKT-dependent mechanism, and repressing NFKB-site activity as well. These results unravel how post-prandial increase of insulin may guarantee GLUT4 expression, and how the insulin signaling impairment can participate in insulin resistance-induced repression of GLUT4.

A novel method for simulating insulin mediated GLUT4 translocation.

Glucose transport in humans is a vital process which is tightly regulated by the endocrine system. Specifically, the insulin hormone triggers a cascade of intracellular signals in target cells mediating the uptake of glucose. Insulin signaling triggers cellular relocalization of the glucose transporter protein GLUT4 to the cell surface, which is primarily responsible for regulated glucose import. Pathology associated with the disruption of this pathway can lead to metabolic disorders, such as type II diabetes mellitus, characterized by the failure of cells to appropriately uptake glucose from the blood. We describe a novel simulation tool of the insulin intracellular response, incorporating the latest findings regarding As160 and GEF interactions. The simulation tool differs from previous computational approaches which employ algebraic or differential equations; instead, the tool incorporates statistical variations of kinetic constants and initial molecular concentrations which more accurately mimic the intracellular environment. Using this approach, we successfully recapitulate observed in vitro insulin responses, plus the effects of Wortmannin-like inhibition of the pathway. The developed tool provides insight into transient changes in molecule concentrations throughout the insulin signaling pathway, and may be employed to identify or evaluate potentially critical components of this pathway, including those associated with insulin resistance. In the future, this highly tractable platform may be useful for simulating other complex cell signaling pathways. Biotechnol. Bioeng. 2014;111: 2454-2465. © 2014 Wiley Periodicals, Inc.