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

Implication de la karyopherine alpha 2 dans la transduction du signal glucose dans les cellules hépatiques

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Invalidation de la détection des sucres par le transporteur-détecteur GLUT2 (impacts sur les homéostasies glucidique et énergétique)

La détection des sucres est le mécanisme par lequel les concentrations de sucres sont converties en signaux intracellulaires permettant aux cellules d adapter leur équipement protéique et leurs fonctions. Nous étudions les mécanismes de détection des sucres par GLUT2. Par sa fonction de transporteur de glucose à l intérieur de la cellule, GLUT2 participe à la voie métabolique de détection des sucres intracellulaires. De plus, GLUT2 est impliqué dans la détection et la transmission du signal issu du glucose extracellulaire. Nous avons évalué l importance de la détection extracellulaire in vivo par une approche de souris Tg chez lesquelles seule la fonction de détection de GLUT2 a été invalidée. L homéostasie glucidique de ces souris est altérée, elles présentent une réduction des dépôts adipeux, un défaut de sécrétion d insuline et sont intolérantes au glucose. Néanmoins, ces souris sont protégées contre l excès de glucose par une fuite massive de glucose dans les urines. L homéostasie énergétique est également modifiée. La prise alimentaire des souris transgéniques est plus importante et n est plus régulée en présence ou en absence de glucose. De plus, la régulation des neuropeptides orexigéniques et anorexigéniques est altérée tout comme la sécrétion d hormones adipocytaires. Un détecteur des sucres extracellulaires, comme GLUT2, par sa localisation membranaire est accessible aux drogues offrant ainsi de nouvelles possibilités thérapeutiques pour les pathologies associées à la dérégulation de la prise alimentaire et également pour les pathologies associées à une malabsorption du glucoseWe are investigating the mechanisms by which cells sense and adapt their functions to their nutritional environment, focusing on glucose detection. Glucose is not only a substrate for most cells but it also generates a signal to the nucleus that regulates gene transcription. In culture cells, we can block the stimulation of glucose sensitive gene transcription by inhibiting glucose metabolism or by expressing a GLUT2 loop domain that leaves unaffected glucose metabolism. Thus the detection of extracellular glucose triggered by GLUT2 can be studied independently of intracellular glucose metabolism. To evaluate in vivo, the importance of this detection pathway, we produced transgenic mice that expressed ubiquitously the GLUT2 loop domain. Transgenic mice displayed increased daily food intake and perturbed hypothalamic expression of orexigenic and anorexigenic peptides. Interestingly, meal consumptions were neither reduced after a glucose injection nor increased after 2-deoxyglucose injection, suggesting a poor detection of glucose abundance or glucopenia. We recorded by indirect calorimetry that mice favoured lipid over glucose oxidation in accordance with their low fat mass. During an oral glucose challenge, we underlined a significantly reduced plasma insulin response. Together pancreatic and hypothalamic failures to detect glucose could contribute to the growth retardation of transgenic mice. Nevertheless, insulin tolerance tests were unchanged suggesting that peripheral tissues, that are not expressing GLUT2, were unaffected in these mice. Taken together, these data suggest that the detection of extracellular sugar mediated by GLUT2 in pancreas and brain, without affecting their basal functions, controls multiple aspects of food intake, satiety and glucose homeostasis. The sugar detector GLUT2 might constitute a new therapeutic target for the benefit of patients suffering from food intake disorders.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

The nucleo-junctional interplay of the cellular prion protein: A new partner in cancer-related signaling pathways?

International audienceThe cellular prion protein PrPc plays important roles in proliferation, cell death and survival, differentiation and adhesion. The participation of PrPc in tumor growth and metastasis was pointed out, but the underlying mechanisms were not deciphered completely. In the constantly renewing intestinal epithelium, our group demonstrated a dual localization of PrPc, which is targeted to cell-cell junctions in interaction with Src kinase and desmosomal proteins in differentiated enterocytes, but is predominantly nuclear in dividing cells. While the role of PrPc in the dynamics of intercellular junctions was confirmed in other biological systems, we unraveled its function in the nucleus only recently. We identified several nuclear PrPc partners, which comprise γ-catenin, one of its desmosomal partners, β-catenin and TCF7L2, the main effectors of the canonical Wnt pathway, and YAP, one effector of the Hippo pathway. PrPc up-regulates the activity of the β-catenin/TCF7L2 complex and its invalidation impairs the proliferation of intestinal progenitors. We discuss how PrPc could participate to oncogenic processes through its interaction with Wnt and Hippo pathway effectors, which are controlled by cell-cell junctions and Src family kinases and dysregulated during tumorigenesis. This highlights new potential mechanisms that connect PrPc expression and subcellular redistribution to cancer

Kinase cascades in the regulation of glucose homeostasis

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Characteristics and functions of lipid droplets and associated proteins in enterocytes

International audienceCytosolic lipid droplets (LDs) are observed in enterocytes of jejunum during lipid absorption. One important function of the intestine is to secrete chylomicrons, which provide dietary lipids throughout the body, from digested lipids in meals. The current hypothesis is that cytosolic LDs in enterocytes constitute a transient pool of stored lipids that provides lipids during interprandial period while lowering chylomicron production during the post-prandial phase. This smoothens the magnitude of peaks of hypertriglyceridemia. Here, we review the composition and functions of lipids and associated proteins of enterocyte LDs, the known physiological functions of LDs as well as the role of LDs in pathological processes in the context of the intestine

A method for quantifying insulin sensitivity in vivo in the anesthetized rat : the euglycemic insulin clamp technique coupled with isotopic measurement of glucose turnover

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