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Roles of ER in distal axon pathologies

ER 在远端轴突病理中的作用

基本信息

批准号：
MR/S011226/1
负责人：
Cahir O'Kane
金额：
$ 64.43万
依托单位：
University of Cambridge
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2019
资助国家：
英国
起止时间：
2019 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=MR%2FS011226%2F1
关键词：
Roles ER distal axon pathologies

项目摘要

Our movement depends on the ability of nerve cells to carry signals along narrow projections known as axons, which in humans can extend a metre from the centre of the cell, the cell body. The challenge of maintaining longer axons is shown by symptoms when they go wrong - axon degeneration, paralysis, or lack of sensation. These occurs in genetic conditions like Hereditary Spastic Paraplegia (HSP), in which degeneration of longer spinal cord motor axons selectively paralyses the lower body, or acquired conditions like diabetic or chemotherapy-induced neuropathy, in which peripheral neuron disease can cause pain or numbness of body extremities. However, the physiological processes that make distal axons vulnerable in these conditions are not known; our goal is to answer this question. We focus on genetic conditions, since genes give us clues about the affected mechanisms, and insights from genetics often apply to acquired conditions. We study a structure called endoplasmic reticulum (ER), consisting of hollow tubules that run lengthwise through the axon, and fuse and split from each other to form a network. Due to their length and continuity, and their potential to carry signals for long distances, they have been termed a "neuron within a neuron". Many HSP mutations that disrupt proteins that help model ER, for example by inserting in one face of the ER membrane and curving it to make tubules: this suggests an important role for the ER network in maintaining axon function and survival.Axonal ER is an underexplored structure and we have only recently developed tools to visualize and see defects in it. We see that removing some HSP membrane-curving proteins, in fruitfly mutants, disurupts the ER network in motor axons, e.g. altered levels of ER tubules, larger tubules, or interrupted continuity; loss of ER continuity is an attractive model for distal axon conditions, since the probability of a gap somewhere along the axon increases with distance from the cell body. It has been easier to make these advances in fruitflies than with human or mammalian neurons, and fruitflies also allow us to work with axons in an intact organism. ER tubules store calcium ions, and can either release calcium into the surrounding cytoplasm as a local transient signal, or remove excess calcium from there, thus maintaining low levels of calcium in cytoplasm. We therefore focus mainly on the consequences of ER structural changes in fly HSP mutants, for local and long-range signalling by calcium flows. We have four main aims, that together should uncover the consequences of altering the amount or presence of ER, its continuity, or its tubule diameter; by analysing mainly (not exclusively) distal axons or presynaptic terminals, we hope to learn more of the mechanisms that affect the regions furthest from the cell body. First we examine how mutations in the fly homolog of a commonly mutated HSP gene, atlastin, affect continuity of axonal ER. Second we examine the consequences of ER depletion for local calcium handling, synaptic transmission, and on lipid transfer between ER and plasma membrane, using another HSP mutant that lacks ER in some synaptic branches. This work will test whether these defects could be plausible factors in pathology. Third, we will test the consequences of ER loss or discontinuity on the properties of mitochondria - organelles that provide cells with usable energy, whose activity is controlled by release of calcium from ER, and which can be harmful if uncontrolled. Finally, we will test the consequences of ER abnormalities for the spread of calcium signals in axons, since longer axons could be more vulnerable to impaired spread of a signal than shorter ones. Together these analyses will provide models for the disease mechanisms of HSP, that can be tested in mammalian or human neurons as our previous fly findings were. They can underpin rational approaches to therapy of HSPs or other diseases of distal axons.

我们的运动依赖于神经细胞沿着被称为轴突的狭窄投射携带信号的能力，在人类中，轴突可以从细胞的中心--细胞体延伸一米。保持较长轴突的挑战表现为当它们出现错误时的症状-轴突退化、瘫痪或缺乏知觉。这些疾病发生在遗传性痉挛截瘫(HSP)等遗传性疾病中，其中较长的脊髓运动轴突变性选择性地瘫痪下半身，或者发生在获得性疾病中，如糖尿病或化疗引起的神经病变，在这种情况下，周围神经元疾病可导致身体四肢疼痛或麻木。然而，在这些情况下使远端轴突脆弱的生理过程尚不清楚；我们的目标是回答这个问题。我们把重点放在遗传条件上，因为基因为我们提供了关于影响机制的线索，而遗传学的见解通常适用于后天条件。我们研究了一种名为内质网(ER)的结构，它由纵向穿过轴突的中空小管组成，相互融合和分离形成一个网络。由于它们的长度和连续性，以及它们可以长距离携带信号的潜力，它们被称为“神经元内的神经元”。许多HSP突变破坏了帮助建模ER的蛋白质，例如通过插入ER膜的一个面并将其弯曲以形成小管：这表明ER网络在维持轴突功能和生存方面发挥了重要作用。轴性ER是一个未被探索的结构，我们最近才开发出工具来可视化和查看其中的缺陷。我们看到，在果蝇突变体中移除一些HSP膜弯曲蛋白，会扰乱运动轴突中的ER网络，例如ER管水平的变化、更大的管或中断的连续性；对于远端轴突条件，ER连续性的丧失是一个有吸引力的模型，因为沿着轴突某处出现间隙的可能性随着与细胞体的距离而增加。在果蝇身上取得这些进展比在人类或哺乳动物的神经元上更容易，而且果蝇还允许我们在一个完整的有机体中处理轴突。内质网小管储存钙离子，并可将钙作为局部瞬间信号释放到周围的细胞质中，或从那里清除多余的钙，从而维持细胞质中低水平的钙。因此，我们主要关注飞行HSP突变体中内质网结构变化的后果，以及钙流动对局部和远程信号的影响。我们有四个主要目标，这四个目标一起应该揭示改变ER的数量或存在、其连续性或其管径的后果；通过主要(而不是唯一地)分析远端轴突或突触前终末，我们希望了解更多影响距离细胞体最远的区域的机制。首先，我们研究了一种常见的HSP基因atlastin在果蝇中的同源突变是如何影响轴突ER的连续性的。其次，我们使用另一个在一些突触分支中缺乏ER的HSP突变体，研究了内质网枯竭对局部钙处理、突触传递以及内质网和质膜之间脂质转移的影响。这项工作将检验这些缺陷是否可能是病理学上的合理因素。第三，我们将测试内质网丢失或中断对线粒体细胞器特性的影响，线粒体细胞器为细胞提供可用能量，其活动受内质网释放钙的控制，如果不受控制，可能是有害的。最后，我们将测试内质网异常对钙信号在轴突中传播的影响，因为较长的轴突可能比较短的轴突更容易受到信号传播的损害。这些分析将为HSP的疾病机制提供模型，这些模型可以在哺乳动物或人类神经元中进行测试，就像我们之前的Fly发现一样。它们可以为热休克或其他远端轴突疾病的治疗提供合理的方法。