INSERM, U872, Team 9, Paris, France.
Diabetes. 2011 Oct;60(10):2598-607. doi: 10.2337/db10-1740. Epub 2011 Aug 18.
In healthy rodents, intestinal sugar absorption in response to sugar-rich meals and insulin is regulated by GLUT2 in enterocyte plasma membranes. Loss of insulin action maintains apical GLUT2 location. In human enterocytes, apical GLUT2 location has not been reported but may be revealed under conditions of insulin resistance.
Subcellular location of GLUT2 in jejunal enterocytes was analyzed by confocal and electron microscopy imaging and Western blot in 62 well-phenotyped morbidly obese subjects and 7 lean human subjects. GLUT2 locations were assayed in ob/ob and ob/+ mice receiving oral metformin or in high-fat low-carbohydrate diet-fed C57Bl/6 mice. Glucose absorption and secretion were respectively estimated by oral glucose tolerance test and secretion of [U-(14)C]-3-O-methyl glucose into lumen.
In human enterocytes, GLUT2 was consistently located in basolateral membranes. Apical GLUT2 location was absent in lean subjects but was observed in 76% of obese subjects and correlated with insulin resistance and glycemia. In addition, intracellular accumulation of GLUT2 with early endosome antigen 1 (EEA1) was associated with reduced MGAT4a activity (glycosylation) in 39% of obese subjects on a low-carbohydrate/high-fat diet. Mice on a low-carbohydrate/high-fat diet for 12 months also exhibited endosomal GLUT2 accumulation and reduced glucose absorption. In ob/ob mice, metformin promoted apical GLUT2 and improved glucose homeostasis. Apical GLUT2 in fasting hyperglycemic ob/ob mice tripled glucose release into intestinal lumen.
In morbidly obese insulin-resistant subjects, GLUT2 was accumulated in apical and/or endosomal membranes of enterocytes. Functionally, apical GLUT2 favored and endosomal GLUT2 reduced glucose transepithelial exchanges. Thus, altered GLUT2 locations in enterocytes are a sign of intestinal adaptations to human metabolic pathology.
在健康的啮齿动物中，肠内对富含糖分的膳食和胰岛素的糖吸收受肠细胞浆膜上的 GLUT2 调节。胰岛素作用的丧失维持了顶端 GLUT2 的位置。在人类肠细胞中，尚未报道顶端 GLUT2 的位置，但在胰岛素抵抗的情况下可能会显现出来。
通过共聚焦和电子显微镜成像以及 Western blot 在 62 名表型良好的病态肥胖患者和 7 名瘦人患者中分析空肠肠细胞中 GLUT2 的亚细胞位置。在接受口服二甲双胍的 ob/ob 和 ob/+ 小鼠或高脂肪低碳水化合物饮食喂养的 C57Bl/6 小鼠中检测 GLUT2 位置。通过口服葡萄糖耐量试验分别估计葡萄糖吸收和分泌，并将 [U-(14)C]-3-O-甲基葡萄糖分泌到腔中。
在人类肠细胞中，GLUT2 始终位于基底外侧膜。在瘦人中，顶端 GLUT2 的位置不存在，但在 76%的肥胖患者中观察到，与胰岛素抵抗和血糖有关。此外，在低碳水化合物/高脂肪饮食的 39%肥胖患者中，与早期内体抗原 1 (EEA1) 的细胞内积累与 MGAT4a 活性（糖基化）降低相关。在接受低碳水化合物/高脂肪饮食 12 个月的小鼠中，也观察到内体 GLUT2 积累和葡萄糖吸收减少。在 ob/ob 小鼠中，二甲双胍促进顶端 GLUT2 并改善葡萄糖稳态。空腹高血糖 ob/ob 小鼠的顶端 GLUT2 增加了三倍葡萄糖释放到肠腔中。
在病态肥胖和胰岛素抵抗的患者中，GLUT2 在肠细胞的顶端和/或内体膜中积累。功能上，顶端 GLUT2 有利于内体 GLUT2 减少葡萄糖跨上皮交换。因此，肠细胞中 GLUT2 位置的改变是肠道适应人类代谢病理的标志。
