A novel role for astrocyte-secreted synaptogenic factor Hevin/SPARCL1 in microglia-mediated synaptic pruning in response to visual experience

星形胶质细胞分泌的突触因子 Hevin/SPARCL1 在小胶质细胞介导的视觉体验突触修剪中的新作用

• 批准号: 10388491
• 负责人: Juan Jose Ramirez
• 金额: $ 3.89万
• 依托单位: DUKE UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-04-01 至 2024-02-29
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/10388491
• 关键词: Acute; Address; Animals; Antibodies; Astrocytes; Axon; Behavior; Binding; Biological Models; Brain; C-terminal; Cell Adhesion Molecules; Cells; Co-Immunoprecipitations; Cognition; Communication; Data; Defect; Development; Equilibrium; Event; Evoked Potentials; Extracellular Space; Eye; Eyelid structure; Immune; Immune response; Immunohistochemistry; Impairment; In Situ Hybridization; In Vitro; Knock-in; Knockout Mice; Length; Life; Link; Maintenance; Mediating; Messenger RNA; Microglia; Molecular; Mus; N-terminal; Neuroglia; Ocular Dominance; Pathology; Phagocytes; Phagocytosis; Play; Population; Process; Proteins; Reporter; Role; Sensory; Signal Pathway; Signal Transduction; Synapses; System; TLR2 gene; TLR4 gene; Testing; Thalamic structure; Time; Transgenic Organisms; Up-Regulation; Virus; Vision; Visual; Visual Cortex; Visual impairment; Western Blotting; Work; base; cell type; critical developmental period; critical period; density; experience; hevin; in vivo; mutant; nervous system disorder; neural circuit; neuronal circuitry; novel; postnatal; receptor; response; synaptic function; synaptic pruning; synaptogenesis; viral rescue

ABSTRACT Synaptic circuits underlie behavior and cognition in higher animals. Proper establishment and maintenance of these circuits requires a balance in the number of connections formed and removed early in life. Increasing evidence suggests that impaired synapse formation and elimination contribute to the synaptic pathologies found in many neurological disorders. Rigorous in vitro and in vivo work from our lab and others have demonstrated the critical role for astrocytes and microglia in mediating synapse formation and elimination, respectively. Further work in the field has begun to describe how these two glial cell types may communicate to balance synapse formation and elimination. However, a detailed molecular understanding of the signals that mediate this communication and the role of such communication in circuit development have not been fully addressed. In my preliminary studies, I have identified the astrocyte-derived synaptogenic factor, Hevin/Sparcl1, as a direct signal to microglia. Hevin is proteolytically cleaved just after eye opening which coincides with a period of net decrease in thalamocortical synapse density. Additionally, Hevin’s C-terminal binds and activates TLR4 leading to an increase in the expression of microglia TLR2. Using a recently developed TLR2 knock in reporter line, I further show that TLR2 expression is restricted to microglia in the developing cortex and can be used to identify two populations of microglia, TLR2-low vs. TLR2-high. Intriguingly, I found that TLR2-high microglia have a high lysosomal compartment suggesting they represent a more phagocytic population of microglia. Based on these findings, this proposal will test the hypothesis that astrocyte secreted Hevin is cleaved in a sensory experience dependent manner to produce a C- terminal fragment that is required for synapse development. I further propose that Hevin signals locally through microglia expressed TLR4 to prime a subpopulation of the surrounding microglia to be more phagocytic marking them with an increased expression of TLR2. This hypothesis will be tested in two aims. Aim 1 will elucidate the role of Hevin proteolytic cleavage in synapse development and plasticity and link this event to sensory experience. Aim 2 will define a molecular mechanism that links processing of an astrocyte-derived synaptogenic factor with heightened microglia mediated synapse elimination. The findings from this study will for the first time identify a molecular signaling pathway from astrocytes to microglia that coordinates astrocyte and microglia function in response to sensory experience.

抽象的 突触回路是高等动物行为和认知的基础。正确建立和维护 这些电路需要在生命早期形成和移除的连接数量上达到平衡。增加 有证据表明，突触形成和消除受损会导致突触病理学 发现于许多神经系统疾病中。我们的实验室和其他实验室进行了严格的体外和体内工作 证明了星形胶质细胞和小胶质细胞在介导突触形成和消除中的关键作用， 分别。该领域的进一步工作已经开始描述这两种神经胶质细胞类型如何进行交流 平衡突触的形成和消除。然而，对信号的详细分子理解 调解这种沟通以及这种沟通在电路开发中的作用尚未得到充分的了解 已解决。在我的初步研究中，我已经确定了星形胶质细胞衍生的突触因子， Hevin/Sparcl1，作为小胶质细胞的直接信号。 Hevin 在睁眼后立即被蛋白水解裂解 与丘脑皮质突触密度净减少的时期一致。此外，Hevin 的 C 端 结合并激活 TLR4，导致小胶质细胞 TLR2 表达增加。最近使用 在报告系中开发了 TLR2 敲除，我进一步表明 TLR2 表达仅限于小胶质细胞 发育中的皮层，可用于识别两个小胶质细胞群体：TLR2 低和 TLR2 高。 有趣的是，我发现 TLR2 高的小胶质细胞具有高溶酶体区室，表明它们代表了 更多的小胶质细胞吞噬细胞群。根据这些发现，该提案将检验假设 星形胶质细胞分泌的 Hevin 以依赖感觉体验的方式裂解，产生 C- 突触发育所需的末端片段。我进一步建议赫文在本地发出信号 通过小胶质细胞表达 TLR4 来启动周围小胶质细胞的亚群 吞噬细胞用 TLR2 表达增加来标记它们。该假设将分两部分进行检验 目标。目标 1 将阐明 Hevin 蛋白水解裂解在突触发育和可塑性中的作用 将这一事件与感官体验联系起来。目标 2 将定义一种分子机制，将 星形胶质细胞衍生的突触发生因子具有增强的小胶质细胞介导的突触消除。研究结果 这项研究将首次确定从星形胶质细胞到小胶质细胞的分子信号传导途径 协调星形胶质细胞和小胶质细胞的功能以响应感官体验。