Uphues I, Kolter T, Goud B, Eckel J
Laboratory of Molecular Cardiology, Diabetes Research Institute, Düsseldorf, Germany.
Biochem J. 1995 Oct 1;311 ( Pt 1)(Pt 1):161-6. doi: 10.1042/bj3110161.
Cardiac ventricular tissue of lean and genetically obese (fa/fa) Zucker rats was used to study the expression, subcellular distribution and insulin-induced recruitment of the glucose transporter GLUT4 and to elucidate possible molecular alterations of the translocation process. Hearts were removed from basal and insulin-treated (20 min) lean and obese Zucker rats, and processed for subcellular fractionation and Western blotting of proteins. In obese rats, the total GLUT4 content in a crude membrane fraction was reduced to 75 +/- 8% (P = 0.019) of lean controls. In contrast, GLUT4 abundance in plasma membranes was not significantly different between lean and obese rats with a concomitant decrease (47 +/- 3%) in the microsomal fraction of obese animals. In plasma membranes of lean animals insulin was found to increase the GLUT4 abundance to 294 +/- 43% of control with a significantly (P = 0.009) reduced effect in the obese group (139 +/- 10% of control). In these animals insulin failed to recruit GLUT4 from the microsomal fraction, whereas the hormone induced a significant decrease (41 +/- 4%) of microsomal GLUT4 in lean controls. In GLUT4-enriched membrane vesicles, obtained from cardiac microsomes of lean rats, a 24 kDa GTP-binding protein could be detected, whereas no significant labelling of this species was observed in GLUT4 vesicles prepared from obese animals. In addition to the translocation of GLUT4, insulin was found to promote the movement of the small GTP-binding protein rab4A from the cytosol (decrease to 61 +/- 13% of control) to the plasma membrane (increase to 177 +/- 19% of control) in lean rats with no effect of the hormone on rab4A redistribution in the obese group. In conclusion, cardiac glucose uptake of insulin-resistant obese Zucker rats is subject to multiple cellular abnormalities involving a reduced expression, altered redistribution and defective recruitment of GLUT4. We show here an association of the latter defect with alterations at the level of small GTP-binding proteins possibly leading to an impaired trafficking of GLUT4 in the insulin-resistant state.
利用瘦型和遗传性肥胖（fa/fa） Zucker大鼠的心室组织，研究葡萄糖转运蛋白GLUT4的表达、亚细胞分布以及胰岛素诱导的募集情况，并阐明转运过程中可能存在的分子改变。从基础状态和经胰岛素处理（20分钟）的瘦型和肥胖Zucker大鼠中取出心脏，进行亚细胞分级分离和蛋白质的Western印迹分析。在肥胖大鼠中，粗膜部分的总GLUT4含量降至瘦型对照的75±8%（P = 0.019）。相比之下，瘦型和肥胖大鼠质膜中GLUT4的丰度无显著差异，同时肥胖动物微粒体部分的GLUT4丰度下降（47±3%）。在瘦型动物的质膜中，胰岛素可使GLUT4丰度增加至对照的294±43%，而在肥胖组中该效应显著降低（P = 0.009，为对照的139±10%）。在这些动物中，胰岛素未能促使GLUT4从微粒体部分募集，而在瘦型对照中该激素可使微粒体GLUT4显著减少（41±4%）。在从瘦型大鼠心脏微粒体获得的富含GLUT4的膜囊泡中，可检测到一种24 kDa的GTP结合蛋白，而在从肥胖动物制备的GLUT4囊泡中未观察到该蛋白的显著标记。除了GLUT4的转位，还发现胰岛素可促使小GTP结合蛋白rab4A在瘦型大鼠中从胞质溶胶（降至对照的61±13%）转运至质膜（增至对照的177±19%），而该激素对肥胖组中rab4A的重新分布无影响。总之，胰岛素抵抗的肥胖Zucker大鼠的心脏葡萄糖摄取存在多种细胞异常，包括GLUT4表达降低、重新分布改变以及募集缺陷。我们在此展示了后一种缺陷与小GTP结合蛋白水平改变之间的关联，这可能导致胰岛素抵抗状态下GLUT4的转运受损。
