GLUT4 distribution in the plasma membrane: from single molecules to whole muscles

胰岛素通过将GLUT 4从胰岛素敏感的细胞内储存转移到质膜（PM）来促进葡萄糖转运。最近的研究表明，除了促进GLUT 4向PM的运输外，胰岛素还刺激GLUT 4在PM内的分散。在不存在胰岛素的情况下，GLUT 4的簇保留在递送部位并迅速重新内化。胰岛素促进GLUT 4从融合位点分散的速率增加60倍;这被认为是葡萄糖转运功能激活的重要步骤，因此代表了胰岛素作用的新范例。造成这种分散的机制仍然没有得到解决。目前尚不清楚胰岛素是否刺激心肌细胞或人骨骼肌细胞中的分散，运动如何影响这种现象，或者这种分散是否在糖尿病中被调节。在转基因模型中，GLUT 4用GFP标记，并且可以使用显微镜在完整组织中成像。我们将把这个机会与mesolens的成像能力结合起来，mesolens提供了一个无与伦比的组织结构分析水平。我们将利用这个系统的力量来探测GLUT 4在整个组织中的分布，特别是心脏和肌肉。肌肉中的GLUT 4易位了解甚少，部分原因是分离肌细胞的困难以及研究肌细胞中标记的GLUT 4分子的行为的困难，肌细胞的长度可能超过常规显微镜的几mm。我们将使用这个系统来研究GLUT 4在完整心脏和肌肉细胞中的分布，并比较胰岛素和运动对GLUT 4分布的作用。GLUT 4是否以相同的方式运输到肌膜以响应不同的刺激？它们是添加剂吗？每个肌原纤维看起来都一样吗？这些是使用现有技术无法回答的问题的例子。本研究将解决的关键未回答的问题是：（i）胰岛素是否促进心肌细胞或肌肉细胞中的GLUT 4分散？(ii)T2 DM或肥胖患者的这种分散受损吗？(iii)胰岛素如何调节完整组织中GLUT 4的分布-所有细胞的行为都相似吗？若否，原因为何？以及（iv）我们能否研究疾病进展过程中的变化？

Insulin promotes glucose transport by moving GLUT4 from insulin-sensitive intracellular stores to the plasma membrane (PM). Recent work has revealed that in addition to promotingGLUT4 traffic to the PM, insulin also stimulates the dispersal of GLUT4 within the PM. In the absence of insulin, clusters of GLUT4 are retained at the site of delivery and are rapidly re-internalised. Insulin promotes a 60-fold increase in the rate of dispersal of GLUT4 away from the fusion site; this is thought to be an essential step in the activation of the glucose transport function and thus represents a new paradigm for insulin action. The mechanism(s) which underpin this dispersal remain unresolved. At present it is unclear whether insulin stimulates dispersal in either cardiomyocytes or human skeletal muscle cells, how exercise impacts on this phenomenon, or whether this dispersal is modulated in diabetes. In the transgenic model GLUT4 is tagged with GFP and can be imaged in intact tissues using microscopy. We shall marry this opportunity with the imaging capability of the mesolens which offers a level of unparalleled structural analysis of tissues over a significant scale. We will use the power of this system to probe the distribution of GLUT4 in whole tissues, notably heart and muscle. GLUT4 translocation in muscle is poorly understood in part because of difficulties in isolating muscle cells and by difficulties in studying behaviour of tagged-GLUT4 molecules in muscle cells which may cover several mm in length - way beyond conventional microscopy. We will use this system to study GLUT4 distribution in intact hearts and muscle cells and compare the actions of insulin and exercise on GLUT4 distribution. Does GLUT4 traffic to the sarcolemma in the same way in response to different stimuli? Are they additive? Does each myofibril look the same? These are examples of questions which cannot be answered using existing technology.The key unanswered questions which this studentship will address are:(i) Does insulin promote GLUT4 dispersal in cardiomyocytes or muscle cells?(ii) Is this dispersal impaired in T2DM or obesity?(iii) How is the distribution of GLUT4 modulated by insulin in intact tissues - do all cells behave similarly? If not, why not? and(iv) Can we study changes in this during disease progression?