REGULATION OF HUMAN GLUCOSE HOMEOSTASIS BY THE NOVEL CHC22 CLATHRIN ISOFORM

2型糖尿病（T2D）和胰岛素抵抗（IR）导致过高的血糖（葡萄糖），产生重大的健康问题，影响全球3.82亿人，约占英国人口的6%，给现代社会造成了巨大的经济负担。开发有效的治疗方法势在必行，需要基础研究来确定新的治疗靶点，并提高我们对人体葡萄糖代谢的理解。这项研究资助的重点是CHC22网格蛋白，一种新的人类葡萄糖运输调节剂，有可能影响t2dm和IR患者的健康和福祉。蛋白质是细胞内的分子机器，像任何机器一样，蛋白质必须在正确的时间处于正确的位置才能正常发挥其功能。网格蛋白是一种负责将其他蛋白质从细胞的一部分运送到另一部分的蛋白质，这一过程被称为细胞内运输。这项拟议的研究调查了一种叫做CHC22的网格蛋白，我们发现它在调节血糖水平的GLUT4葡萄糖转运蛋白的细胞内运输中起作用。饭后，胰腺分泌胰岛素。作为反应，葡萄糖通过GLUT4从血液中输入到肌肉和脂肪中，GLUT4是葡萄糖可以通过的通道。在禁食期间，GLUT4被保存在GLUT4储存室（GSC）的细胞内。在进食后产生胰岛素的作用下，GLUT4从GSC释放到细胞表面，使葡萄糖被吸收并从血液中清除。在胰岛素作用下，组织停止释放GLUT4并输入葡萄糖，最终胰腺停止分泌胰岛素（T2D）。我们观察到，在T2D患者的肌肉中，当GLUT4在胰岛素刺激后没有到达表面时，GLUT4与过量的我们感兴趣的蛋白质CHC22网格蛋白一起被困在GSC中。我们假设CHC22在非功能性GSC的存在有助于IR。网格蛋白最常见的作用是将蛋白质从细胞表面转移到细胞内部，即胞吞作用。网格蛋白的多个分子聚集在细胞的内表面形成一层涂层。外衣把膜拉到里面，最终膜脱离，形成一个被包裹的结构，携带细胞表面的蛋白质，并将这些货物运送到细胞内的特定位置。在人类中，有两种网格蛋白。与常见的CHC17形式不同，CHC22不参与内吞作用，但在将GLUT4运送到GSC中起特殊作用。我们将通过分析CHC22的分子和细胞特性以及其功能如何受到其他蛋白质的控制来表征这一作用。拟议的实验将确定细胞中CHC22网格蛋白外壳的形成是如何以及在何处受到调节的，并描述CHC22在胰岛素和IR下的行为变化。我们还将探讨在人类中发现的两种形式的CHC22蛋白之间的差异，这些差异可能会影响IR的发展。总之，这些研究将揭示CHC22在人体葡萄糖调节中的分子控制功能。研究GLUT4的科学家尚未完全定义人类GSC的特性和调控，我们的实验将阐明人类营养的这一基本方面。我们还将开发新的工具，供其他研究人员用于研究IR和T2D。我们的研究将进一步澄清网格蛋白生物学领域，该领域主要集中在CHC17的作用上。

Type 2 Diabetes (T2D) and Insulin Resistance (IR), which result in excessively high blood sugar (glucose), generate major health problems affecting 382 million people worldwide and ~6% of the UK population, creating an enormous economic burden on modern society. Development of effective therapies is imperative, and requires fundamental research to identify new therapeutic targets and improve our understanding of human glucose metabolism. This research grant focuses on CHC22 clathrin, a novel regulator of human glucose transport, with potential to influence the health and wellbeing of people living with T2D and IR.Proteins are molecular machines inside cells, and like any machine, a protein must be at the right place at the right time to perform its function properly. Clathrins are proteins responsible for transporting other proteins from one part of the cell to another, a process known as intracellular trafficking. The proposed research investigates a form of clathrin called CHC22 that we have found plays a role in intracellular trafficking of the GLUT4 glucose transporter protein, which regulates blood glucose levels.After a meal, insulin is secreted from the pancreas. In response, glucose is imported from the blood into muscle and fat by GLUT4, a channel through which glucose can pass. During fasting, GLUT4 is held inside cells in the GLUT4 storage compartment (GSC). GLUT4 is released from the GSC to the cell surface in response to insulin produced after feeding, allowing glucose uptake and clearance from blood. In IR, tissues stop releasing GLUT4 and importing glucose in response to insulin, and eventually the pancreas stops secreting insulin (T2D). We have observed that, in muscle from T2D patients, when GLUT4 does not get to the surface after insulin stimulation, GLUT4 is trapped in the GSC together with excessive amounts of our protein of interest, CHC22 clathrin. We hypothesize that the presence of CHC22 at the non-functional GSC contributes to IR.The most familiar role of clathrin is to move proteins from the cell surface to the inside of the cell, known as endocytosis. Multiple molecules of clathrin assemble to form a coat on the inside surface of the cell. The coat pulls the membrane to the inside and eventually the membrane breaks away, forming a coated structure that takes cell-surface proteins with it and carries this cargo to specific intracellular locations. In humans, there are two types of clathrin. Unlike the common CHC17 form, CHC22 is not involved in endocytosis, but has a specialized role in transporting GLUT4 to the GSC. We will characterize this role by analyzing the molecular and cellular properties of CHC22 and how its function is controlled by other proteins. Proposed experiments will define how and where formation of the CHC22 clathrin coat is regulated in cells and characterise CHC22 behaviour changes in response to insulin and and IR. We will also explore the differences between two forms of CHC22 proteins found in humans - differences that may influence the development of IR. Together, these studies will reveal the molecular control of CHC22 function in human glucose regulation.Scientists studying GLUT4 have not yet fully defined properties and regulation of the human GSC, and our experiments will shed light on this fundamental aspect of human nutrition. We will also develop new tools that can be used by other researchers studying IR and T2D. Our studies will further clarify the field of clathrin biology, which has been primarily focused on the roles of CHC17.