Microglial remodeling of the extracellular matrix in memory circuits

项目总结 突触和回路的结构重塑对于经验依赖性可塑性是必不可少的，就像在 将学到的经验巩固成长期记忆。免疫功能障碍被认为与 许多认知障碍，包括精神分裂症和神经退行性疾病，导致越来越多的 对脑内巨噬细胞的功能感兴趣，小胶质细胞是主要的免疫细胞 在脑实质中。我们之前发表了IL-1家族细胞因子IL-33，它是由 星形胶质细胞在发育过程中，信号通过其专有受体IL1RL1在小胶质细胞上表达，促进 小胶质细胞活化和吞噬功能。在构成这一提议基础的初步数据中，我们发现 一组新的IL-33在两个成年大脑区域表达的神经元：海马区和额叶皮质。在……里面 对海马区的详细结构分析，我们发现神经元特异性的IL-33或小胶质细胞的缺失- IL-33R的特异性缺失会导致树突棘减少，脊柱可塑性的标志物减少 头部丝状突起，神经发生受损。此外，这一信号通路的缺失会导致细胞内 情境恐惧条件作用：小鼠能够正常学习识别恐惧情境，但有一种渐进的 在15-30天后，他们区分恐惧背景和中性背景的能力下降 训练。从机制上讲，我们发现细胞外基质蛋白(硫酸软骨素蛋白多糖 和聚集素)在IL-33缺乏的动物的海马区积聚。我们发现小胶质细胞吞噬了aggrecan， 而IL-33信号的丧失可以减少这种吞噬。我们还开发了一种神经元功能增益 构建能够结构性分泌IL-33的细胞。我们发现这足以增加海马棘的数量， 吞噬小胶质细胞外基质，清除树突棘周围的细胞外基质。根据这些初步数据，这 该提案将检验神经元来源的IL-33推动ECM小胶质细胞重塑的中心假设 促进电路可塑性，支持记忆巩固。目的一探讨细胞因子的分子调控机制。 IL-33从神经元释放及其活性依赖关系，并测试两种介导小胶质细胞的候选蛋白 对IL-33反应的重塑。目标二将测试这种神经元-小胶质细胞信号对细胞外基质的影响 额叶皮质的组成，重点放在神经周网络上，并确定其对大脑皮质连接的影响 大脑皮层微电路。目标3将在背景恐惧条件反射任务中使用钙成像来测试神经元如何 在从近期记忆到远程记忆的过渡过程中，活动模式发生了变化，解决了以下关键问题 记忆巩固背后的结构性变化。总之，这些研究将系统地剖析 在健康大脑中调节可塑性的新细胞回路的作用。这项工作的成果是 了解与小胶质细胞和免疫相关的多种疾病的认知功能障碍的意义 系统，包括精神分裂症和神经退行性疾病，如阿尔茨海默病。

PROJECT SUMMARY Structural remodeling of synapses and circuits is essential to experience-dependent plasticity, as occurs during the consolidation of learned experiences into long-term memory. Immune dysfunction has been implicated in numerous cognitive disorders, including schizophrenia and neurodegenerative diseases, leading to increasing interest in the function of brain-resident macrophages known as microglia, which are the dominant immune cell in the brain parenchyma. We previously published that the IL-1 family cytokine Interleukin-33, which is made by astrocytes during development, signals to its obligate receptor IL1RL1 expressed on microglia to promote microglial activation and phagocytic function. In preliminary data that forms the basis for this proposal, we identify a novel population of IL-33 expressing neurons in two adult brain regions: hippocampus and frontal cortex. In detailed structural analyses in the hippocampus, we find that neuron-specific deletion of IL-33 or microglial- specific deletion of IL-33 R leads to fewer dendritic spines, diminished markers of spine plasticity known as spine head filopodia, and impaired neurogenesis. Furthermore, loss of this signaling pathway leads to deficits in contextual fear conditioning: mice are able to normally learn to recognize a fear context but have a progressive decrease in their ability to discriminate the fear context from a neutral context emerging at 15-30 days post training. Mechanistically, we find that extracellular matrix proteins (the chondroitin sulfate proteoglycans brevican and aggrecan) accumulate in the hippocampus of IL-33 deficient animals. We find that microglia engulf aggrecan, and that loss of IL-33 signaling diminishes this engulfment. We also developed a neuronal gain of function construct that constitutively secretes IL-33. We find this is sufficient to increase hippocampal spine numbers, microglial ECM engulfment, and to clear ECM around dendritic spines. Based on these preliminary data, this proposal will test the central hypothesis that neuron-derived IL-33 drives microglial remodeling of ECM to promote circuit plasticity in support of memory consolidation. Aim One will explore the molecular regulation of IL-33 release from neurons and its activity dependence, and test two candidate proteases mediating microglial remodeling in response to IL-33. Aim Two will test the impact of this neuron-microglia signaling on the ECM composition of the frontal cortex with a focus on perineuronal nets and determine its impact on connectivity of the cortical microcircuit. Aim 3 will use calcium imaging in a contextual fear conditioning task to test how neuronal activity patterns shift during the transition from recent to remote memories, addressing key questions regarding the structural changes that underlie memory consolidation. Together, these studies will systematically dissect the role of a novel cellular circuit regulating plasticity in the healthy brain. The outcome of this work has implications for understanding cognitive dysfunction in numerous diseases linked to microglia and the immune system , including schizophrenia and neurodegenerative conditions such as Alzheimer's Disease.