Garvey W T, Maianu L, Zhu J H, Brechtel-Hook G, Wallace P, Baron A D
Department of Medicine, Medical University of South Carolina and Ralph H. Johnson Veterans Affairs Medical Center, Charleston, South Carolina 29425, USA.
J Clin Invest. 1998 Jun 1;101(11):2377-86. doi: 10.1172/JCI1557.
Insulin resistance is instrumental in the pathogenesis of type 2 diabetes mellitus and the Insulin Resistance Syndrome. While insulin resistance involves decreased glucose transport activity in skeletal muscle, its molecular basis is unknown. Since muscle GLUT4 glucose transporter levels are normal in type 2 diabetes, we have tested the hypothesis that insulin resistance is due to impaired translocation of intracellular GLUT4 to sarcolemma. Both insulin-sensitive and insulin-resistant nondiabetic subgroups were studied, in addition to type 2 diabetic patients. Biopsies were obtained from basal and insulin-stimulated muscle, and membranes were subfractionated on discontinuous sucrose density gradients to equilibrium or under nonequilibrium conditions after a shortened centrifugation time. In equilibrium fractions from basal muscle, GLUT4 was decreased by 25-29% in both 25 and 28% sucrose density fractions and increased twofold in both the 32% sucrose fraction and bottom pellet in diabetics compared with insulin-sensitive controls, without any differences in membrane markers (phospholemman, phosphalamban, dihydropyridine-binding complex alpha-1 subunit). Thus, insulin resistance was associated with redistribution of GLUT4 to denser membrane vesicles. No effects of insulin stimulation on GLUT4 localization were observed. In non-equilibrium fractions, insulin led to small GLUT4 decrements in the 25 and 28% sucrose fractions and increased GLUT4 in the 32% sucrose fraction by 2.8-fold over basal in insulin-sensitive but only by 1.5-fold in both insulin-resistant and diabetic subgroups. The GLUT4 increments in the 32% sucrose fraction were correlated with maximal in vivo glucose disposal rates (r = +0.51, P = 0.026), and, therefore, represented GLUT4 recruitment to sarcolemma or a quantitative marker for this process. Similar to GLUT4, the insulin-regulated aminopeptidase (vp165) was redistributed to a dense membrane compartment and did not translocate in response to insulin in insulin-resistant subgroups. In conclusion, insulin alters the subcellular localization of GLUT4 vesicles in human muscle, and this effect is impaired equally in insulin-resistant subjects with and without diabetes. This translocation defect is associated with abnormal accumulation of GLUT4 in a dense membrane compartment demonstrable in basal muscle. We have previously observed a similar pattern of defects causing insulin resistance in human adipocytes. Based on these data, we propose that human insulin resistance involves a defect in GLUT4 traffic and targeting leading to accumulation in a dense membrane compartment from which insulin is unable to recruit GLUT4 to the cell surface.
胰岛素抵抗在2型糖尿病和胰岛素抵抗综合征的发病机制中起重要作用。虽然胰岛素抵抗涉及骨骼肌中葡萄糖转运活性降低，但其分子基础尚不清楚。由于2型糖尿病患者肌肉中的GLUT4葡萄糖转运蛋白水平正常，我们检验了胰岛素抵抗是由于细胞内GLUT4向肌膜转位受损这一假说。除2型糖尿病患者外，还研究了胰岛素敏感和胰岛素抵抗的非糖尿病亚组。从基础状态和胰岛素刺激后的肌肉获取活检样本，在缩短离心时间后，将膜在不连续蔗糖密度梯度上进行分级分离至平衡或非平衡状态。在基础肌肉的平衡级分中，与胰岛素敏感对照组相比，糖尿病患者在25%和28%蔗糖密度级分中的GLUT4减少了25 - 29%，而在32%蔗糖级分和底部沉淀中增加了两倍，膜标记物（磷膜蛋白、受磷蛋白、二氢吡啶结合复合物α-1亚基）无任何差异。因此，胰岛素抵抗与GLUT4重新分布到密度更高的膜囊泡有关。未观察到胰岛素刺激对GLUT4定位有影响。在非平衡级分中，胰岛素使25%和28%蔗糖级分中的GLUT4略有减少，并使32%蔗糖级分中的GLUT4在胰岛素敏感组中比基础水平增加2.8倍，但在胰岛素抵抗组和糖尿病亚组中仅增加1.5倍。32%蔗糖级分中GLUT4的增加与最大体内葡萄糖处置率相关（r = +0.51，P = 0.026），因此代表GLUT4募集到肌膜或该过程的定量标志物。与GLUT4相似，胰岛素调节的氨肽酶（vp165）在胰岛素抵抗亚组中重新分布到致密膜区室，且不响应胰岛素转位。总之，胰岛素改变了人肌肉中GLUT4囊泡的亚细胞定位，这种效应在有糖尿病和无糖尿病的胰岛素抵抗受试者中同样受损。这种转位缺陷与基础肌肉中可证实的GLUT4在致密膜区室中的异常积累有关。我们之前在人脂肪细胞中观察到了类似的导致胰岛素抵抗的缺陷模式。基于这些数据，我们提出人胰岛素抵抗涉及GLUT4运输和靶向缺陷，导致其在致密膜区室中积累，胰岛素无法从该区域将GLUT4募集到细胞表面。
