Apical and basolateral localisation of GLUT2 transporters in human lung epithelial cells

Glucose concentrations of normal human airway surface liquid are ~12.5 times lower than blood glucose concentrations indicating that glucose uptake by epithelial cells may play a role in maintaining lung glucose homeostasis. We have therefore investigated potential glucose uptake mechanisms in non-polarised and polarised H441 human airway epithelial cells and bronchial biopsies. We detected mRNA and protein for glucose transporter type 2 (GLUT2) and glucose transporter type 4 (GLUT4) in non-polarised cells but GLUT4 was not detected in the plasma membrane. In polarised cells, GLUT2 protein was detected in both apical and basolateral membranes. Furthermore, GLUT2 protein was localised to epithelial cells of human bronchial mucosa biopsies. In non-polarised H441 cells, uptake of d-glucose and deoxyglucose was similar. Uptake of both was inhibited by phloretin indicating that glucose uptake was via GLUT-mediated transport. Phloretin-sensitive transport remained the predominant route for glucose uptake across apical and basolateral membranes of polarised cells and was maximal at 5–10 mM glucose. We could not conclusively demonstrate sodium/glucose transporter-mediated transport in non-polarised or polarised cells. Our study provides the first evidence that glucose transport in human airway epithelial cells in vitro and in vivo utilises GLUT2 transporters. We speculate that these transporters could contribute to glucose uptake/homeostasis in the human airway

Loss of Sugar Detection by GLUT2 Affects Glucose Homeostasis in Mice

International audienceBACKGROUND: Mammals must sense the amount of sugar available to them and respond appropriately. For many years attention has focused on intracellular glucose sensing derived from glucose metabolism. Here, we studied the detection of extracellular glucose concentrations in vivo by invalidating the transduction pathway downstream from the transporter-detector GLUT2 and measured the physiological impact of this pathway. METHODOLOGY/PRINCIPAL FINDINGS: We produced mice that ubiquitously express the largest cytoplasmic loop of GLUT2, blocking glucose-mediated gene expression in vitro without affecting glucose metabolism. Impairment of GLUT2-mediated sugar detection transiently protected transgenic mice against starvation and streptozotocin-induced diabetes, suggesting that both low- and high-glucose concentrations were not detected. Transgenic mice favored lipid oxidation, and oral glucose was slowly cleared from blood due to low insulin production, despite massive urinary glucose excretion. Kidney adaptation was characterized by a lower rate of glucose reabsorption, whereas pancreatic adaptation was associated with a larger number of small islets. CONCLUSIONS/SIGNIFICANCE: Molecular invalidation of sugar sensing in GLUT2-loop transgenic mice changed multiple aspects of glucose homeostasis, highlighting by a top-down approach, the role of membrane glucose receptors as potential therapeutic targets

Rôle du transporteur-détecteur GLUT2 dans l'adaptation de l'intestin à un régime riche en sucre

L augmentation de la consommation de fructose dans les pays industrialisés participe à la survenue de maladies nutritionnelles. L intestin adapte sa capacité d absorption rapidement lors d un repas et à long terme en fonction du régime alimentaire. Le transporteur GLUT2 est au cœur de ces processus d adaptation. En effet, il détecte les concentrations de sucre environnant et modifie la transcription de gènes dans l entérocyte. Après un repas sucré, il est recruté à la membrane apicale des entérocytes et augmente rapidement la capacité de transport de sucre. La présence apicale de GLUT2 est transitoire et dépendrait d une balance entre le signal sucre luminal et un signal insuline basolatéral qui induit l endocytose de GLUT2 et freine l absorption. Un apport chronique de fructose induit une intolérance au glucose et une résistance à l insuline et inhibe le trafic apical de GLUT2 chez la souris. L apport prolongé en fructose maintient alors l entérocyte dans une configuration d absorption maximale des sucres.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Altérations fonctionnelle et immunitaire de l intestin humain dans l obésité

The intestinal epithelium has a determinant role in glucose homeostasis ensuring food digestion, nutrient absorption and gut-hormone release in response to dietary compounds. GLUT2, a high-capacity sugar transporter, is transiently recruited into the apical membrane of enterocytes in response to a sugar-rich meal. The consequent raise of serum insulin triggers GLUT2 internalization into the enterocytes, a mechanism that is lost in diabetic- or diet-induced insulin-resistant rodents. I could demonstrate an pathologic permanent apical GLUT2 location in the jejunum of morbidly obese subjects, who exhibit insulin resistance and type-2 diabetes. This apical GLUT2 location favors a bidirectional glucose transepithelial exchange. GLUT2 can also accumulate in enterocyte endosomes of obese subjects consuming a high-fat low-carbohydrate diet. Altered GLUT2 locations in enterocytes sign intestinal adaptations in human obesity (Diabetes J 2011). Obesity is a low-grade inflammatory disease, affecting the insulin sensitivity of many organs. Little is known about intestinal immunity in human obesity. I contributed to show that in obesity the intestinal mucosa is hypertrophic and contains an increased number of innate and adaptive immune cells. These modifications are associated to altered bioclinical parameters. The phenotype of jejunal T cell was determined in the epithelium and lamina propria by flow cytometry and by gene expression. The activity of T cell from obese, but not lean subjects impairs insulin sensitivity of Caco-2/TC7 enterocytes (2 manuscripts in preparation).Results show that immune adaptations of the small intestine lead to impaired insulin sensitivity of enterocytes and thereby may initiate the loss of GLUT2 trafficking, altering intestinal absorptive function in obesity.L'épithélium intestinal contribue à l'homéostasie glucidique assurant la digestion des aliments, l'absorption des nutriments et la sécrétion des entero-hormones apr s un repas. GLUT2, un transporteur de sucre à haute capacité, est transitoirement recruté dans la membrane apicale des entérocytes en réponse à un repas riche en sucre. L'augmentation de l'insulinémie provoquée par l'hyperglycémie postabsorptive déclenche l'internalisation de GLUT2 dans l'entérocyte, mécanisme qui est perdu chez les rongeurs diabétiques ou rendus résistants à l'insuline par le régime. Dans le jéjunum de sujets ob èses morbides résistants à l'insuline et/ou diabétiques de type 2, j'ai montré une localisation anormalement permanente, de GLUT2 dans la membrane apicale des entérocytes. La localisation apicale de GLUT2 favorise un échange bidirectionnel transépithélial de glucose. GLUT2 peut aussi s'accumuler dans les endosomes des sujets dont l'alimentation est riche en graisse et plus pauvre en hydrate de carbone. Ces localisations anormales de GLUT2 dans les entérocytes sont un signe d'adaptation pathologique de l'intestin à l'obésité humaine (Diabetes J 2011). L'obésité est une maladie inflammatoire à bas grade, affectant la sensibilité à l'insuline de plusieurs organes. L'immunité intestinale est peu étudiée dans l'obésité humaine. J'ai montré que la muqueuse intestinale des sujets obè ses est hypertrophique et associée à un accroissement du nombre de cellules de l'immunité innée et adaptative. Ces modifications sont en lien avec les changements biocliniques mesurés chez les sujets obè ses. Le phénotype des lymphocytes T du jéjunum a été établi en cytométrie de flux et par l'expression de gè nes. L'activité des lymphocytes T de sujets ob èses, pas celle des sujets minces, dégrade la sensibilité à l'insuline des entérocytes Caco2/TC7 (2 manuscripts en préparation). Nos résultats suggè rent que l'adaptation de l'immunité intestinale dans l'obésité affecte la sensibilité à l'insuline des entérocytes modifiant la fonction d'absorption des sucres dans l'intestin.PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Asymptomatic Giardia Intestinalis infection and Roux-Y-Gastric Bypass

International audienceGiardiasis is one of the most common parasitic infections of the human intestine worldwide, and ranges from 3-7% in western countries to 100% in some populations [1]. Giardia Intestinalis (i.e Duodenalis or Lamblia) is a flagellated, binucleated protozoan parasite that infects the upper intestinal tract in many mammalian hosts. Giardiasis can present with a broad range of clinical manifestations, from being asymptomatic to acute or chronic nonspecific gastro-intestinal symptoms associated with malnutrition [2]. However little is known regarding Giardiasis in human obesity. [...