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Veronique A Lacombe - One of the best experts on this subject based on the ideXlab platform.

  • The impact of prolonged hyperinsulinaemia on glucose transport in equine skeletal muscle and digital lamellae
    Science & Engineering Faculty, 2015
    Co-Authors: Melody A. De Laat, Chelsie Clement, Christopher C. Pollitt, Catherine M. Mcgowan, Martin N. Sillence, Veronique A Lacombe
    Abstract:

    REASONS FOR PERFORMING STUDY An increased incidence of metabolic disease in horses has led to heightened recognition of the pathological consequences of insulin resistance (IR). Laminitis, failure of the weight-bearing digital lamellae, is an important consequence. Altered trafficking of specialised glucose transporters (GLUTs) responsible for glucose uptake, are central to the dysregulation of glucose metabolism and may play a role in laminitis pathophysiology. OBJECTIVES We hypothesised that prolonged hyperinsulinaemia alters the regulation of glucose transport in insulin-sensitive tissue and digital lamellae. Our objectives were to compare the relative protein expression of major GLUT isoforms in striated muscle and digital lamellae in healthy horses and during hyperinsulinaemia. STUDY DESIGN Randomised, controlled study. METHODS Prolonged hyperinsulinaemia and lamellar damage were induced by a prolonged-euglycaemic hyperinsulinaemic clamp (p-EHC) or a prolonged-glucose infusion (p-GI) and results were compared to electrolyte-treated controls. GLUT protein expression was examined with immunoblotting. RESULTS Lamellar tissue contained more GLUT1 protein than skeletal muscle (p = 0.002) and less GLUT4 than the heart (p = 0.037). During marked hyperinsulinaemia and acute laminitis (induced by the p-EHC), GLUT1 protein expression was decreased in skeletal muscle (p = 0.029) but unchanged in the lamellae, while novel GLUTs (8; 12) were increased in the lamellae (p = 0.03), but not skeletal muscle. However, moderate hyperinsulinaemia and subclinical laminitis (induced by the p-GI) did not cause differential GLUT protein expression in the lamellae vs. control horses. CONCLUSIONS The results suggest that lamellar tissue functions independently of insulin and that IR may not be an essential component of laminitis aetiology. Marked differences in GLUT expression exist between insulin-sensitive and insulin-independent tissues during metabolic dysfunction in horses. The different expression profiles of novel GLUTs during acute and subclinical laminitis may be important to disease pathophysiology and require further investigation.

  • AICAR administration affects glucose metabolism by upregulating the novel glucose transporter, GLUT8, in equine skeletal muscle
    Science & Engineering Faculty, 2015
    Co-Authors: M. A. De Laat, Robinson, K.j. Gruntmeir, Y Liu, Lawrence R. Soma, Veronique A Lacombe
    Abstract:

    Equine metabolic syndrome is characterized by obesity and insulin resistance (IR). Currently, there is no effective pharmacological treatment for this insidious disease. Glucose uptake is mediated by a family of glucose transporters (GLUT), and is regulated by insulin-dependent and -independent pathways, including 5-AMP-activated protein kinase (AMPK). Importantly, the activation of AMPK, by 5-aminoimidazole- 4-carboxamide-1-D-ribofuranoside (AICAR) stimulates glucose uptake in both healthy and diabetic humans. However, whether AICAR promotes glucose uptake in horses has not been established. It is hypothesized that AICAR administration would enhance glucose transport in equine skeletal muscle through AMPK activation. In this study, the effect of an intravenous AICAR infusion on blood glucose and insulin concentrations, as well as on GLUT expression and AMPK activation in equine skeletal muscle (quantified by Western blotting) was examined. Upon administration, plasma AICAR rapidly reached peak concentration. Treatment with AICAR resulted in a decrease (P < 0.05) in blood glucose and an increase (P < 0.05) in insulin concentration without a change in lactate concentration. The ratio of phosphorylated to total AMPK was increased (P < 0.05) in skeletal muscle. While GLUT4 and GLUT1 protein expression remained unchanged, GLUT8 was increased (P < 0.05) following AICAR treatment. Up-regulation of GLUT8 protein expression by AICAR suggests that this novel GLUT isoform plays an important role in equine muscle glucose transport. In addition, the data suggest that AMPK activation enhances pancreatic insulin secretion. Collectively, the findings suggest that AICAR acutely promotes muscle glucose uptake in healthy horses and thus its therapeutic potential for managing IR requires investigation.

  • Abstract 15940: Calcium and Insulin Regulate the Novel Glucose Transporter 8 (GLUT8) in the Healthy and Diabetic Myocardium
    Circulation, 2014
    Co-Authors: Emilie Martinez, Zahra Maria, Muthu Periasamy, Veronique A Lacombe
    Abstract:

    Diabetes, an epidemic disease, is associated with the development of diabetic cardiomyopathy. Glucose uptake from the bloodstream into the cell is the rate-limiting step in whole body glucose utilization and is regulated by a family of membrane proteins called the glucose transporters (GLUT). The translocation of GLUT4, the main isoform, to the cell surface is insulin and contraction/calcium dependent in striated muscle. Contraction is regulated by the sarcoplasmic reticulum calcium ATPase (SERCA) pump. We recently demonstrated that diabetes impairs cardiac GLUT4 trafficking due to alterations of insulin signaling pathway and SERCA pump activity. However, the role of other GLUTs in the heart is still not elucidated. Although GLUT8 is highly expressed in the heart and could play a key role in cardiac glucose transport, its function and regulation are unknown. We hypothesized that, as for GLUT4, insulin and calcium will regulate GLUT8 translocation to the myocardial cell surface, which will be impaired during diabetes. Active cell surface GLUT (4 & 8) content was quantified by a biotinylated photolabeled assay in both intact perfused myocardium and isolated ventricular myocytes. To our knowledge, we are the first to apply this technique to GLUT8. Total GLUT (4 & 8) protein expression was measured by Western blot. Diabetes was induced by streptozotocin injection in wild type (WT) and transgenic (TG) mice overexpressing the SERCA pump in the heart and compared to their respective healthy littermates (n=16/group). In healthy myocytes, GLUT8 was primarily located intracellularly under basal condition, as for GLUT4. Insulin, calcium and isoproterenol stimulation (a beta-adrenergic agonist) significantly increased the translocation of both GLUT-4 and -8 to the cell surface. In addition, total GLUT-4 and -8 protein content was increased by 30 and 40% (P

  • The impact of prolonged hyperinsulinaemia on glucose transport in equine skeletal muscle and digital lamellae
    Equine Veterinary Journal, 2014
    Co-Authors: Melody A. De Laat, C. K. Clement, Christopher C. Pollitt, Catherine M. Mcgowan, Martin N. Sillence, Veronique A Lacombe
    Abstract:

    An increased incidence of metabolic disease in horses has led to heightened recognition of the pathological consequences of insulin resistance. Laminitis, failure of the weightbearing digital lamellae, is an important consequence. Altered trafficking of specialised glucose transporters (GLUTs), responsible for glucose uptake, is central to the dysregulation of glucose metabolism and may play a role in the pathophysiology of laminitis. We hypothesised that prolonged hyperinsulinaemia alters the regulation of glucose transport in insulin-sensitive tissue and digital lamellae. Our objectives were to compare the relative protein expression of major GLUT isoforms in striated muscle and digital lamellae in healthy horses and during marked and moderate hyperinsulinaemia. Randomised, controlled study. Prolonged hyperinsulinaemia and lamellar damage were induced by a prolonged euglycaemic-hyperinsulinaemic clamp or a prolonged glucose infusion, and results were compared with those of electrolyte-treated control animals. Protein expression of GLUTs was examined with immunoblotting. Lamellar tissue contained more GLUT1 protein than skeletal muscle (P = 0.002) and less GLUT4 than the heart (P = 0.037). During marked hyperinsulinaemia and acute laminitis (induced by the prolonged euglycaemic-hyperinsulinaemic clamp), GLUT1 protein expression was decreased in skeletal muscle (P = 0.029) but unchanged in the lamellae, while novel GLUTs (8 and 12) were increased in the lamellae (P = 0.03) but not in skeletal muscle. However, moderate hyperinsulinaemia and subclinical laminitis (induced by the prolonged glucose infusion) did not cause differential GLUT protein expression in the lamellae compared with control horses. The results suggest that lamellar tissue functions independently of insulin and that insulin resistance may not be an essential component of the aetiology of laminitis. Marked differences in GLUT expression exist between insulin-sensitive and insulin-independent tissues during metabolic dysfunction in horses. The different expression profiles of novel GLUTs during acute and subclinical laminitis may be important to disease pathophysiology and require further investigation.

Anthony Carruthers - One of the best experts on this subject based on the ideXlab platform.

  • red wine and green tea flavonoids are cis allosteric activators and competitive inhibitors of glucose transporter 1 glut1 mediated sugar uptake
    Journal of Biological Chemistry, 2018
    Co-Authors: Ogooluwa A Ojelabi, Julie K De Zutter, Kenneth P Lloyd, Anthony Carruthers
    Abstract:

    : The antioxidant- and flavonoid-rich contents of red wine and green tea are reported to offer protection against cancer, cardiovascular disease, and diabetes. Some studies, however, show that flavonoids inhibit GLUT1-mediated, facilitative glucose transport, raising the possibility that their interaction with GLUT1 and subsequent downstream effects on carbohydrate metabolism may also impact health. The present study explores the structure-function relationships of flavonoid-GLUT1 interactions. We find that low concentrations of flavonoids act as cis-allosteric activators of sugar uptake, whereas higher concentrations competitively inhibit sugar uptake and noncompetitively inhibit sugar exit. Studies with heterologously expressed human GLUT1, -3, or -4 reveal that quercetin-GLUT1 and -GLUT4 interactions are stronger than quercetin-GLUT3 interactions, that epicatechin gallate (ECG) is more selective for GLUT1, and that epigallocatechin gallate (EGCG) is less GLUT isoform-selective. Docking studies suggest that only one flavonoid can bind to GLUT1 at any instant, but sugar transport and ligand-binding studies indicate that human erythrocyte GLUT1 can bind at least two flavonoid molecules simultaneously. Quercetin and EGCG are each characterized by positive, cooperative binding, whereas ECG shows negative cooperative binding. These findings support recent studies suggesting that GLUT1 forms an oligomeric complex of interacting, allosteric, alternating access transporters. We discuss how modulation of facilitative glucose transporters could contribute to the protective actions of the flavonoids against diabetes and Alzheimer's disease.

  • wzb117 2 fluoro 6 m hydroxybenzoyloxy phenyl m hydroxybenzoate inhibits glut1 mediated sugar transport by binding reversibly at the exofacial sugar binding site
    Journal of Biological Chemistry, 2016
    Co-Authors: Ogooluwa A Ojelabi, Julie K De Zutter, Kenneth P Lloyd, Andrew H Simon, Anthony Carruthers
    Abstract:

    Abstract WZB117 (2-fluoro-6-(m-hydroxybenzoyloxy) phenyl m-hydroxybenzoate) inhibits passive sugar transport in human erythrocytes and cancer cell lines and, by limiting glycolysis, inhibits tumor growth in mice. This study explores how WZB117 inhibits the erythrocyte sugar transporter glucose transport protein 1 (GLUT1) and examines the transporter isoform specificity of inhibition. WZB117 reversibly and competitively inhibits erythrocyte 3-O-methylglucose (3MG) uptake with Ki(app) = 6 μm but is a noncompetitive inhibitor of sugar exit. Cytochalasin B (CB) is a reversible, noncompetitive inhibitor of 3MG uptake with Ki(app) = 0.3 μm but is a competitive inhibitor of sugar exit indicating that WZB117 and CB bind at exofacial and endofacial sugar binding sites, respectively. WZB117 inhibition of GLUTs expressed in HEK293 cells follows the order of potency: insulin-regulated GLUT4 ≫ GLUT1 ≈ neuronal GLUT3. This may explain WZB117-induced murine lipodystrophy. Molecular docking suggests the following. 1) The WZB117 binding envelopes of exofacial GLUT1 and GLUT4 conformers differ significantly. 2) GLUT1 and GLUT4 exofacial conformers present multiple, adjacent glucose binding sites that overlap with WZB117 binding envelopes. 3) The GLUT1 exofacial conformer lacks a CB binding site. 4) The inward GLUT1 conformer presents overlapping endofacial WZB117, d-glucose, and CB binding envelopes. Interrogating the GLUT1 mechanism using WZB117 reveals that subsaturating WZB117 and CB stimulate erythrocyte 3MG uptake. Extracellular WZB117 does not affect CB binding to GLUT1, but intracellular WZB117 inhibits CB binding. These findings are incompatible with the alternating conformer carrier for glucose transport but are consistent with either a multisubunit, allosteric transporter, or a transporter in which each subunit presents multiple, interacting ligand binding sites.

  • sequence determinants of glut1 oligomerization analysis by homology scanning mutagenesis
    Journal of Biological Chemistry, 2013
    Co-Authors: Julie K De Zutter, Kara B Levine, Di Deng, Anthony Carruthers
    Abstract:

    Abstract The human blood-brain barrier glucose transport protein (GLUT1) forms homodimers and homotetramers in detergent micelles and in cell membranes, where the GLUT1 oligomeric state determines GLUT1 transport behavior. GLUT1 and the neuronal glucose transporter GLUT3 do not form heterocomplexes in human embryonic kidney 293 (HEK293) cells as judged by co-immunoprecipitation assays. Using homology-scanning mutagenesis in which GLUT1 domains are substituted with equivalent GLUT3 domains and vice versa, we show that GLUT1 transmembrane helix 9 (TM9) is necessary for optimal association of GLUT1-GLUT3 chimeras with parental GLUT1 in HEK cells. GLUT1 TMs 2, 5, 8, and 11 also contribute to a less abundant heterocomplex. Cell surface GLUT1 and GLUT3 containing GLUT1 TM9 are 4-fold more catalytically active than GLUT3 and GLUT1 containing GLUT3 TM9. GLUT1 and GLUT3 display allosteric transport behavior. Size exclusion chromatography of detergent solubilized, purified GLUT1 resolves GLUT1/lipid/detergent micelles as 6- and 10-nm Stokes radius particles, which correspond to GLUT1 dimers and tetramers, respectively. Studies with GLUTs expressed in and solubilized from HEK cells show that HEK cell GLUT1 resolves as 6- and 10-nm Stokes radius particles, whereas GLUT3 resolves as a 6-nm particle. Substitution of GLUT3 TM9 with GLUT1 TM9 causes chimeric GLUT3 to resolve as 6- and 10-nm Stokes radius particles. Substitution of GLUT1 TM9 with GLUT3 TM9 causes chimeric GLUT1 to resolve as a mixture of 6- and 4-nm particles. We discuss these findings in the context of determinants of GLUT oligomeric structure and transport function.

  • role of monosaccharide transport proteins in carbohydrate assimilation distribution metabolism and homeostasis
    Comprehensive Physiology, 2012
    Co-Authors: Anthony J Cura, Anthony Carruthers
    Abstract:

    The facilitated diffusion of glucose, galactose, fructose, urate, myoinositol, and dehydroascorbic acid in mammals is catalyzed by a family of 14 monosaccharide transport proteins called GLUTs. These transporters may be divided into three classes according to sequence similarity and function/substrate specificity. GLUT1 appears to be highly expressed in glycolytically active cells and has been coopted in vitamin C auxotrophs to maintain the redox state of the blood through transport of dehydroascorbate. Several GLUTs are definitive glucose/galactose transporters, GLUT2 and GLUT5 are physiologically important fructose transporters, GLUT9 appears to be a urate transporter while GLUT13 is a proton/myoinositol cotransporter. The physiologic substrates of some GLUTs remain to be established. The GLUTs are expressed in a tissue specific manner where affinity, specificity, and capacity for substrate transport are paramount for tissue function. Although great strides have been made in characterizing GLUT-catalyzed monosaccharide transport and mapping GLUT membrane topography and determinants of substrate specificity, a unifying model for GLUT structure and function remains elusive. The GLUTs play a major role in carbohydrate homeostasis and the redistribution of sugar-derived carbons among the various organ systems. This is accomplished through a multiplicity of GLUT-dependent glucose sensing and effector mechanisms that regulate monosaccharide ingestion, absorption, distribution, cellular transport and metabolism, and recovery/retention. Glucose transport and metabolism have coevolved in mammals to support cerebral glucose utilization. © 2012 American Physiological Society. Compr Physiol 2:863-914, 2012.

  • role of monosaccharide transport proteins in carbohydrate assimilation distribution metabolism and homeostasis
    Comprehensive Physiology, 2012
    Co-Authors: Anthony J Cura, Anthony Carruthers
    Abstract:

    The facilitated diffusion of glucose, galactose, fructose, urate, myoinositol, and dehydroascorbicacid in mammals is catalyzed by a family of 14 monosaccharide transport proteins called GLUTs. These transporters may be divided into three classes according to sequence similarity and function/substrate specificity. GLUT1 appears to be highly expressed in glycolytically active cells and has been coopted in vitamin C auxotrophs to maintain the redox state of the blood through transport of dehydroascorbate. Several GLUTs are definitive glucose/galactose transporters, GLUT2 and GLUT5 are physiologically important fructose transporters, GLUT9 appears to be a urate transporter while GLUT13 is a proton/myoinositol cotransporter. The physiologic substrates of some GLUTs remain to be established. The GLUTs are expressed in a tissue specific manner where affinity, specificity, and capacity for substrate transport are paramount for tissue function. Although great strides have been made in characterizing GLUT-catalyzed monosaccharide transport and mapping GLUT membrane topography and determinants of substrate specificity, a unifying model for GLUT structure and function remains elusive. The GLUTs play a major role in carbohydrate homeostasis and the redistribution of sugar-derived carbons among the various organ systems. This is accomplished through a multiplicity of GLUT-dependent glucose sensing and effector mechanisms that regulate monosaccharide ingestion, absorption,distribution, cellular transport and metabolism, and recovery/retention. Glucose transport and metabolism have coevolved in mammals to support cerebral glucose utilization.

Tu Lin - One of the best experts on this subject based on the ideXlab platform.

  • Expression and regulation of glucose transporter 8 in rat Leydig cells.
    The Journal of endocrinology, 2003
    Co-Authors: Y Chen, Madan L. Nagpal, Tu Lin
    Abstract:

    Basal and LH/human chorionic gonadotropin (hCG)stimulated testosterone formation by Leydig cells is dependent on ambient glucose levels. Inhibition of glucose uptake is associated with decreased testosterone formation. Recently, glucose transporter 8 (GLUT8) has been shown to be highly expressed in the testis. In the present study, we have investigated the expression and regulation of the GLUT8 gene in rat Leydig cells. Primers were designed by using sequences that are not conserved in GLUT1 to GLUT5 and that contain the glycosylation region of GLUT8. This yielded an amplicon of 186 bp. The tissue-specific expression experiments in adult rat (55- to 65-day-old) tissues revealed that GLUT8 is expressed predominantly in the testis, in smaller amounts in heart and kidney, and in negligible amounts in liver and spleen. Furthermore, GLUT8 mRNA was found to be highly expressed in crude interstitial cells, Leydig cells and testicular and epididymal germ cells. In prepubertal rat (20-day-old) tissues, GLUT8 expression was comparatively much lower than in the adult rat tissues. By comparative RT-PCR, hCG caused dose- and timedependent increases of GLUT8 mRNA levels. hCG and IGF-I had synergistic effects on GLUT8 mRNA and protein expression. GLUT1 and GLUT3 were also found to be expressed in Leydig cells. However, neither GLUT1 nor GLUT3 were affected by treatments with hCG, IGF-I or hCG and IGF-I combined. The addition of murine interleukin-1 (mIL-1; 10 ng/ml), murine tumor necrosis factor- (mTNF-; 10 ng/ml), murine interferon(mIFN-; 500 U/ml) separately or in combination decreased hCG-induced GLUT8 mRNA levels significantly. In conclusion, GLUT8 mRNA in Leydig cells was positively regulated by hCG and IGF-I and downregulated by cytokines, mIL-1, mTNF- and mIFN-. These results indicate that hCG, growth factors and cytokines affect Leydig cell steroidogenesis by modulating GLUT8 expression.

Annette Schürmann - One of the best experts on this subject based on the ideXlab platform.

  • the glucose transporter families sglt and glut molecular basis of normal and aberrant function
    Journal of Parenteral and Enteral Nutrition, 2004
    Co-Authors: Andrea Scheepers, Hansgeorg Joost, Annette Schürmann
    Abstract:

    Glucose enters eucaryotic cells via 2 different types of membrane associated carrier proteins, the Na+-coupled glucose transporters (SGLT) and glucose transporter facilitators (GLUT). Three members of the SGLT family function as sugar transporters (SGLT1 and SGLT2) or sensors (SGLT3). The human GLUT family consists of 14 members, of which 11 have been shown to catalyze sugar transport. The individual isotypes exhibit different substrate specificity, kinetic characteristics, and expression profiles, thereby allowing a tissue-specific adaptation of glucose uptake through regulation of their gene expression. Furthermore, some transporters (eg, GLUT4 and GLUT8) are regulated by their subcellular distribution. In addition to catalyzing glucose entry into cells, some isotypes (eg, GLUT2) seem to be involved in the mechanisms of glucosensing of pancreatic beta-cells, neuronal, or other cells, thereby playing a major role in the hormonal and neural control. Targeted disruption in mice has helped to elucidate the physiologic function of some isotypes (GLUT1, GLUT2, GLUT4). Furthermore, several congenital defects of sugar metabolism are caused by aberrant transporter genes (eg, the glucose-galactose malabsorption syndrome, SGLT1; the glucose transporter 1 deficiency syndrome; and the Fanconi-Bickel syndrome, GLUT2). In addition, a malfunction of glucose transporter expression or regulation (GLUT4) appears to contribute to the insulin resistance syndrome.

  • GLUT11, but not GLUT8 or GLUT12, is expressed in human skeletal muscle in a fibre type-specific pattern.
    Pflugers Archiv : European journal of physiology, 2003
    Co-Authors: Michael Gaster, H G Joost, Annette Schürmann, Aase Handberg, Henning Beck-nielsen, Henrik Daa Schrøder
    Abstract:

    Nine novel sugar transporter-like proteins have been discovered in the past 5 years. The mRNA for three of these, the glucose transporters (GLUT) GLUT8, GLUT11 and GLUT12, have been detected in human skeletal muscle. In the present study, we examined the pattern of expression and localization of the GLUT isoforms 8, 11 and 12 in human skeletal muscle using an immunohistochemical approach. Biopsies of human skeletal muscle from sedentary or trained healthy adults, from fetal muscle (24 weeks of gestation), from obese type-2 diabetic subjects, and from patients suffering from polymyositis or amyotrophic lateral sclerosis (ALS) were studied. GLUT8 and 12 immunoreactivity was below detection level in both developing and adult muscle fibres. GLUT11 immunoreactivity, however, was present in slow-twitch muscle fibres, but not in fast twitch fibres. Since, in contrast, GLUT4 was expressed in all investigated muscle fibres, the pattern of expression of GLUT11 differs from that of GLUT4, suggesting a specialized function for GLUT11 with a regulation independent from that of GLUT4. Obesity, type-2 diabetes, training, conditions of de- and reinnervation (ALS) and regeneration (polymyositis) failed to induce GLUT8 or -12 expression. Likewise, the fibre type-dependent pattern of GLUT11 immunoreactivity was unaltered. However, some slow muscle fibres lose their GLUT11 immunoreactivity under regeneration. Our results indicate that GLUT11 immunoreactivity, in contrast to that of GLUT4, is expressed exclusively in slow-twitch muscle fibres and is unaffected by physiological and pathophysiological conditions except in primary myopathy. GLUT8 and GLUT12 do not appear to be of importance in human muscle under physiological and pathophysiological conditions.

  • Targeting of GLUT6 (formerly GLUT9) and GLUT8 in rat adipose cells.
    Biochemical Journal, 2001
    Co-Authors: Ivonne Lisinski, Hansgeorg Joost, Annette Schürmann, Samuel W. Cushman, Hadi Al-hasani
    Abstract:

    The subcellular targeting of the two recently cloned novel mammalian glucose transporters, GLUT6 {previously referred to as GLUT9 [Doege, Bocianski, Joost and Schurmann (2000) Biochem. J. 350 , 771–776]} and GLUT8, was analysed by expression of haemagglutinin (HA)-epitope-tagged GLUTs in transiently transfected primary rat adipose cells. Similar to HA-GLUT4, both transporters, HA-GLUT6 and HA-GLUT8, were retained in intracellular compartments in non-stimulated cells. In contrast, mutation of the N-terminal dileucine motifs in both constructs led to constitutive expression of the proteins on the plasma membrane. Likewise, when endocytosis was blocked by co-expression of a dominant-negative mutant of the dynamin GTPase, wild-type HA-GLUT6 and HA-GLUT8 accumulated on the cell surface. However, in contrast with HA-GLUT4, no translocation of HA-GLUT6 and HA-GLUT8 to the plasma membrane was observed when the cells were stimulated with insulin, phorbol ester or hyperosmolarity. Thus GLUT6 and GLUT8 appear to recycle in a dynamin-dependent manner between internal membranes and the plasma membrane in rat adipose cells, but are unresponsive to stimuli that induce translocation of GLUT4.

Emmanuele A. Jannini - One of the best experts on this subject based on the ideXlab platform.

  • Ontogenetic profile and thyroid hormone regulation of type-1 and type-8 glucose transporters in rat Sertoli cells.
    International journal of andrology, 2005
    Co-Authors: Eleonora Carosa, Carla Radico, Nadia Giansante, Simona Rossi, Fabio D'adamo, Savino M. Di Stasi, Andrea Lenzi, Emmanuele A. Jannini
    Abstract:

    The glucose transporters (GLUTs) gene encode glycoproteins responsible for facilitating transfer of glucose across plasma membrane. In testis, different members of this family are present. In particular the main GLUT mRNA expression within the adult testis is the type 8, while type 1 is more expressed in prepubertal testis. Thyroid hormone, which receptors and function have been characterized in the testis, plays a crucial role in the cellular energetic metabolism. In fact, in the immature Sertoli cells, GLUT1 is up regulated by l-triiodothyronine (T(3)). The aim of this paper is to investigate the expression profile of GLUT1 and GLUT8 in the testis during development and in adulthood and analyse the role of T(3) on their expression. To analyse the expression of GLUT8 and GLUT1 we performed Northern blot and RT-PCR experiments in the whole testis and in Sertoli cells from rats of different ages. Treatments in vivo and in vitro with T(3) were used to study the effect of thyroid hormones on GLUT1 and GLUT8 expression. The activity of the rat GLUT1 promoter and its regulation by T(3) was studied with transient transfections in gonadal and non-gonadal cell lines and in primary Sertoli cell cultures. GLUT8 is expressed at a low level in the prepubertal testis and Sertoli cells and does not appear to be under T(3) control. GLUT1 is the predominant form in immature Sertoli cells. The effect of T(3) on its mRNA accumulation was quantified and confirmed by RT-PCR (control: 0.65 +/- 0.17; T(3): 1.23 +/- 0.04, arbitrary units, p < 0.05). However, transfection experiments showed that T(3) does not directly regulate GLUT1 promoter in any cell line tested. This is confirmed by the evidence that, upon extensive analysis, the rat GLUT1 promoter and the first intron sequence do not shows any thyroid responsive elements. Our data demonstrate that GLUT1 and GLUT8 are both expressed in prepubertal testis, but only GLUT1 is regulated by T(3). In addition, we found that the effect of T(3) cannot be attributed to its action on GLUT1 promoter.