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Insulin Internalizes GLUT2 in the Enterocytes of Healthy but Not Insulin-Resistant Mice

¹ Université Pierre et Marie Curie-Paris 6, Unité Mixte de Recherche S 872, Paris, France
² Institut National de la Santé et de la Recherche Médicale, Unité Mixte de Recherche S 872, Paris, France
³ Université Paris Descartes-Paris 5, Unité Mixte de Recherche S 872, Paris, France
⁴ Université Paris 7, Centre National de la Recherche Scientifique, Paris, France
⁵ Laboratory of Experimental Pathology and Drug Targeting, University of Salamanca, CIBERehd, Spain
⁶ IFR58, Centre de Recherche des Cordeliers, Paris, France
⁷ Institut de Génétique et Microbiologie, Centre Scientifique d'Orsay, Université Paris 11-Orsay, Orsay, France

Address correspondence and reprint requests to Edith Brot-Laroche, CRC, Team 9, 15 rue de l'Ecole de Médecine, 75006 Paris, France. E-mail: edith.brot-laroche{at}crc.jussieu.fr

Abbreviations: BBM, brush border membrane; BLM, basolateral membrane; Caco-2/TC7, colon carcinoma TC7 subclone; GIR, glucose infusion rate; 3-OMG, [³H]-3-O-methyl-glucose; PepT1, peptide transporter-1; PiP₃, phosphatidylinositol (3,4,5)-trisphosphate; SGLT1, sodium-dependent glucose cotransporter

OBJECTIVES—A physiological adaptation to a sugar-rich meal is achieved by increased sugar uptake to match dietary load, resulting from a rapid transient translocation of the fructose/glucose GLUT2 transporter to the brush border membrane (BBM) of enterocytes. The aim of this study was to define the contributors and physiological mechanisms controlling intestinal sugar absorption, focusing on the action of insulin and the contribution of GLUT2-mediated transport.

RESEARCH DESIGN AND METHODS—The studies were performed in the human enterocytic colon carcinoma TC7 subclone (Caco-2/TC7) cells and in vivo during hyperinsulinemic-euglycemic clamp experiments in conscious mice. Chronic high-fructose or high-fat diets were used to induce glucose intolerance and insulin resistance in mice.

RESULTS AND CONCLUSIONS—In Caco-2/TC7 cells, insulin action diminished the transepithelial transfer of sugar and reduced BBM and basolateral membrane (BLM) GLUT2 levels, demonstrating that insulin can target sugar absorption by controlling the membrane localization of GLUT2 in enterocytes. Similarly, in hyperinsulinemic-euglycemic clamp experiments in sensitive mice, insulin abolished GLUT2 (i.e., the cytochalasin B-sensitive component of fructose absorption), decreased BBM GLUT2, and concomitantly increased intracellular GLUT2. Acute insulin treatment before sugar intake prevented the insertion of GLUT2 into the BBM. Insulin resistance in mice provoked a loss of GLUT2 trafficking, and GLUT2 levels remained permanently high in the BBM and low in the BLM. We propose that, in addition to its peripheral effects, insulin inhibits intestinal sugar absorption to prevent excessive blood glucose excursion after a sugar meal. This protective mechanism is lost in the insulin-resistant state induced by high-fat or high-fructose feeding.

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