Role of Insulin-like Signaling in Glial Responses to Axon Degeneration

描述(由申请人提供)：神经胶质细胞通过在形态、基因表达、迁移和吞噬活性方面表现出明显的变化，对神经元损伤和神经退行性疾病做出强有力的反应。功能失调的反应会导致阿尔茨海默病和帕金森氏病等破坏性神经疾病的进展，也会促进一些自身免疫性疾病的发生。尽管胶质细胞在保护大脑健康方面很重要，但人们对神经元损伤反应的分子基础知之甚少。一个重要的长期目标是了解成人大脑中如何触发基本的神经胶质免疫反应，以应对受损和死亡的神经元。核心细胞事件(如神经胶质细胞向损伤部位的迁移和吞噬细胞的清除 神经元碎片)在物种间高度保守，最近的研究也揭示了惊人的分子保守。这项建议使用在果蝇身上建立的成熟的成体轴突切断实验来研究神经胶质反应的分子特征；果蝇提供了一个易于处理的遗传系统，以在体内以精致的细胞和时间精度操纵基因的表达和功能。我们的初步工作确定了进化上保守的胰岛素/胰岛素样生长因子(IGF)样信号通路(ILS)在协调神经胶质细胞对轴突损伤的反应中扮演的新角色。根据我们的发现，我们假设ILS通过两种基本方式调节神经胶质细胞的免疫反应：(1)成年胶质细胞中ILS的基础活性确保神经胶质细胞表达检测和执行轴突损伤反应所需的关键基因(即Draper受体和适配器Ced-6)；(2)ILS通路在损伤部位的急性激活触发局部胶质细胞的快速反应，以确保受损神经元从中枢神经系统清除。这项提议将使用强大的遗传分子工具来研究ILS途径如何促进神经轴突切断诱导的神经胶质细胞功能。我们将：(目标1)确定胰岛素样受体(INR)活性在神经胶质细胞对轴突切断反应的每个步骤中的作用，包括基因表达的改变、损伤部位的胶质细胞募集和胶质细胞的吞噬活性；(目标2)确定如何 胰岛素样多肽(ILP)是INR的配体，影响Draper和Ced-6的基础表达，以及局部胶质细胞损伤反应的每一步；(目的3)定义INR下游与这些重要的胶质反应相偶联的分子信号级联。这项工作将提供关键的机制洞察受损的神经元如何与神经胶质细胞沟通，以引发反应，并阐明控制这些基本神经胶质功能的内在分子途径。我们的发现还将为探索ILS成分作为治疗中枢神经系统损伤和慢性神经退行性疾病的治疗靶点提供一个新的框架。

DESCRIPTION (provided by applicant): Glial cells respond potently to neuronal damage, as well as neurodegenerative disease, by displaying overt changes in morphology, gene expression, migration, and phagocytic activity. Dysfunctional responses contribute to the progression of devastating neurological diseases, such as Alzheimer's disease and Parkinson's disease, and can also promote the onset of some autoimmune disorders. Despite the importance of glia in defending brain health, remarkably little is known about the molecular underpinnings of responses to neuronal damage. A vital long-term goal is to understand how basic glial immune reactions are triggered in the adult brain in response to damaged and dying neurons. The core cellular events (e.g. glial migration to injury sites and phagocytic clearance of neuronal debris) are highly conserved across species and recent work is revealing striking molecular conservation, as well. This proposal uses a well- established adult axotomy assay in Drosophila to investigate the molecular features of glial reactions; the fly offers a tractable genetic system to manipulate gene expression and function with exquisite cellular and temporal precision in vivo. Our preliminary work has identified a novel role for the evolutionarily conserved Insulin/insulin-like growth factor (IGF)-Like Signaling (ILS) pathway in orchestrating glial reactions to axon injury. Based on our findings, we hypothesize that ILS regulates glial immune responses in two fundamental ways: (1) Basal ILS activity in adult glia ensures that glia express key genes (i.e. the Draper receptor and adaptor Ced-6) required to detect and carry out responses to axon damage, and (2) Acute activation of the ILS pathway at injury sites triggers rapid responses in local glia to ensure that damaged neurons are cleared from the CNS. This proposal will employ powerful genetic-molecular tools to investigate how the ILS pathway contributes to axotomy-induced functions in glia. We will: (Aim 1) define the role of Insulin-like Receptor (InR) activity in each step of the glial response to axotomy, including altered gene expression, glial recruitment to injury sites, and glial phagocytic activity; (Aim 2) determine how insulin-like peptides (ilps), the InR ligands, influence basal expression of Draper and Ced-6, as well as each step of the injury response in local glia; and (Aim 3) define the molecular signaling cascades downstream of InR that are coupled to these important glial responses. This work will provide critical mechanistic insight into how damaged neurons communicate with glia to elicit responses and elucidate intrinsic molecular pathways that control these essential glial functions. Our findings will also offer a novel framework for exploring ILS components as therapeutic targets to treat CNS injury, as well as chronic neurodegenerative conditions.