Functions of Heparan Sulfate Proteoglycans in Axon Guidance and Degeneration.

项目摘要/摘要 神经元连接的精确组织对于处理信息至关重要。一项重大挑战是 神经科学就是要了解这些连接是如何正确建立的，以及这种连接中的错误是如何建立的 这一过程可能会导致自闭症或精神分裂症等精神障碍。在发育过程中，神经元延伸 通过吸引和排斥的线索引导轴突沿着确定的路径到达它们的大脑目标。在……里面 除了这一引导过程，涉及修剪或退化的机制纠正了具有 偏离了正确的路径，从而确保了电路形成的准确性。几种因素对轴突的调节 指导，但它们提供的组合信息不足以塑造整个神经元网络。 硫酸乙酰肝素蛋白多糖(HSPGs)是一种结合了肝素的细胞表面和细胞外核心蛋白 硫酸盐(HS)糖链在轴突寻路中发挥关键作用，并对触发 被误导的轴突选择性变性。然而，HSPG如何控制这些不同的过程仍然是一个 神秘感。HS链经历了许多修饰，特别是硫酸盐，这赋予了它们独特的多样性 和结构的复杂性。这些修改被提议用来生成一个复杂的“糖码” 通过调节大脑连接所必需的大多数因素来协调轴突连接的形成。而当 吸引人的是，这种“糖码”假设仍然是理论上的，还没有在脊椎动物身上进行测试。此外， 携带这些特定HS模式的核心蛋白的贡献尚不清楚。用斑马鱼 视网膜顶盖系统作为活体模型，我发现了三个不同的HSPG(SDC2、GPC1a和 GPC1b)调节视网膜轴突引导的不同步骤。在这个项目中，我打算剖析这些 核心蛋白和HS链修饰通过体内独特的组合调节轴突导航 方法、遗传学和HS生物化学。这项提案的第一个目标将确认 SDC2、GPC1a和GPC1b，并在细胞和分子水平上研究它们的作用模式。会的 确定它们的缺失如何影响轴突行为并导致指导错误，它们在哪里起作用，它们的 HS链是其功能所必需的，它们与哪些因素相互作用。这样做的第二个目的是 该项目将确定特定的HS结构基序对轴突寻径和退变的贡献。它 将测试6-O和3-O磺基转移酶在特定情况下用硫酸盐修饰HS链的作用 位置，并研究具有定义的硫化基序和大小的合成HS寡糖如何调节 视网膜轴突导航，无论是在体外培养系统中还是在体内发育的胚胎中。通过研究 核心蛋白和HS精细结构的作用，拟议的研究提供了一个独特的机会来测试 在发育过程中，糖码是否协调大脑连接。它还可能提供新的研究思路 在神经性疾病的背景下，未来治疗和再生策略的发展。

Project Summary/Abstract Precise organization of neuronal connections is crucial for processing information. A major challenge in neuroscience is to understand how these connections are properly established, and how errors in this wiring process can lead to psychiatric disorders like autism or schizophrenia. During development, neurons extend axons that are guided along defined paths by attractive and repulsive cues to reach their brain target. In addition to this guidance process, mechanisms involving pruning or degeneration correct axons that have deviated from the right path, thereby ensuring accuracy of circuit formation. Several factors regulate axon guidance, but the combined information they provide is not sufficient to sculpt the entire neuronal network. Heparan sulfate proteoglycans (HSPGs) are cell-surface and extracellular core proteins with attached heparan sulfate (HS) sugar chains that play crucial roles in axon pathfinding, and are essential for triggering the selective degeneration of misguided axons. How HSPGs control these different processes remains however a mystery. HS chains undergo many modifications, especially sulfations, that confer on them a unique diversity and structural complexity. These modifications have been proposed to generate a complex “sugar code” orchestrating the formation of axonal connections by regulating most factors essential for brain wiring. While appealing, this “sugar code” hypothesis is still theoretical and has not been tested in vertebrates. Moreover, the contribution of the core proteins carrying these specific HS patterns is not known. Using the zebrafish retinotectal system as an in vivo model, I have discovered that three distinct HSPGs (SDC2, GPC1a and GPC1b) regulate different steps of retinal axon guidance. In this project, I propose to dissect out how these core proteins and HS chain modifications regulate axon navigation using a unique combination of in vivo approaches, genetics and HS biochemistry. The first aim of this proposal will confirm the novel functions of SDC2, GPC1a and GPC1b, and investigate their mode of action at a cellular and molecular level. It will determine how their absence affects axon behavior and leads to guidance errors, where they act, whether their HS chains are required for their function, and what are the factors they interact with. The second aim of this project will determine the contribution of specific HS structural motifs for axon pathfinding and degeneration. It will test the roles of the 6-O and 3-O sulfotransferases that modify HS chains with sulfations at specific positions, and examine how synthetic HS oligosaccharides with defined sulfation motifs and sizes regulate retinal axon navigation, both in vitro in culture systems and in vivo in the developing embryo. By studying the roles of both core proteins and HS fine structure, the proposed studies give a unique opportunity to test whether a sugar code orchestrates brain wiring during development. It might also provide new lines of research for future development of therapeutic and regenerative strategies in the context of neurological disorders.