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

胰岛素通过将GLUT4从对胰岛素敏感的细胞内储存物转移到质膜(PM)来促进葡萄糖的运输。最近的研究表明，除了促进GLUT4交通到PM外，胰岛素还刺激GLUT4在PM内的扩散在没有胰岛素的情况下，GLUT4簇保留在释放部位，并迅速重新内化。胰岛素促进GLUT4从融合部位分散的速度增加60倍；这被认为是激活葡萄糖运输功能的关键步骤，因此代表了胰岛素作用的新范例。支撑这种扩散的机制(S)仍然没有解决。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扩散，运动对这一现象有何影响，或者这种扩散是否在糖尿病中受到调节。在转基因模型中，GLUT4被GFP标记，并可以在显微镜下在完整的组织中成像。我们将把这一机会与中胚层的成像能力结合起来，它提供了在大范围内对组织进行无与伦比的结构分析的水平。我们将利用这个系统的力量来探索GLUT4在整个组织中的分布，特别是心脏和肌肉。对GLUT4在肌肉中的移位知之甚少，部分原因是分离肌肉细胞的困难，以及研究标记的GLUT4分子在肌肉细胞中的行为的困难，这些分子的长度可能比传统显微镜长几毫米。我们将利用这个系统来研究GLUT4在完整的心脏和肌肉细胞中的分布，并比较胰岛素和运动对GLUT4分布的影响。对于不同的刺激，GLUT4是否以相同的方式进入肌膜？它们是相加的吗？每个肌原纤维看起来都一样吗？这些都是使用现有技术无法回答的问题的例子。本课程将解决的关键未回答问题是：(I)胰岛素是否促进GLUT4在心肌细胞或肌肉细胞中的扩散？(Ii)这种扩散在T2 DM或肥胖症中是否受到损害？(Iii)GLUT4在完整组织中的分布是如何被胰岛素调节的--所有细胞的行为都相似吗？若否，原因为何？以及(Iv)我们能研究疾病发展过程中这种变化吗？

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?