Mechanisms of Activity-dependent Microglia-neuron Interactions in Development and Disease

总结 小胶质细胞介导的突触修剪在突触发育关键期受到高度调节 但它在疾病模型中脆弱的大脑区域的激活表明，疾病和 发展共享共同的监管机构和修剪机制。突触优化是一种活动- 弱突触优先被修剪的依赖过程。我们假设神经活动是 在发育和疾病中小胶质细胞介导的修剪的上游激活剂和调节剂。为支持这一 假设，我们和其他人证明，小胶质细胞吞噬突触元件，并能够 感知和响应与活动相关的信号，因为它们优先吞噬不太活跃的突触。然而，在这方面， 小胶质细胞如何决定吞噬哪些突触，避免哪些突触，以及上游神经元的身份 检测神经活动并将该信息传递给小胶质细胞的信号是未知的。 在免疫系统中，吞噬作用是由吞噬细胞，“吃我”和抗- 吞噬细胞的“别吃我”分子在大脑中，我们发现了神经元CD 47，一个“不要吃我”的信号可以保护 不适当的切除造成的神经突触损伤我们进一步发现，暴露的磷脂酰丝氨酸（PS），一个“吃我的信号”， 驱动小胶质细胞识别突触以进行吞噬。此外，我们还鉴定了酪氨酸激酶， Pyk 2和JAK 2作为神经元信号，在非活性突触处被激活，并且是消除神经元信号所必需的。 这些投入。最后，我们发现PS暴露在阿尔茨海默病的海马早期升高 (AD)小鼠模型基于这些和其他数据，我们建议测试的假设，活动依赖 神经元内的信号，如Pyk 2和JAK 2，动态调节“吃我”和“不吃我”的信号。 突触驱动适当的小胶质细胞吞噬不活跃的突触。我们进一步假设， 这些信号的激活导致神经退行性疾病（如阿尔茨海默氏病）中的异常突触丧失 疾病（AD）。具体而言，我们的目标是测试以下内容：目的1）研究活性调节PS的机制 目的2：确定活动依赖性神经元信号传导， 调节小胶质细胞吞噬的“吃我”和“不吃我”信号;目标3：研究机制 与AD相关的早期突触功能障碍和小胶质细胞突触靶向。我们将使用跨学科的 采用分子/细胞生物学、组织学、小鼠遗传学、成像和 电生理技术与各种新开发的系统，以满足我们的目标。我们的研究可以 也为治疗干预提供了新的目标，因为恢复了保护和消除的平衡， 信号可以在AD和其他疾病的早期阶段防止突触丢失。

Summary Microglia-mediated synaptic pruning is highly regulated during developmental critical periods of synaptic refinement, but its activation in vulnerable brain regions in disease models suggests that disease and development share common regulators and mechanisms of pruning. Synaptic refinement is an activity- dependent process where weak synapses are preferentially pruned. We hypothesize that neural activity is a key upstream activator and regulator of microglia-mediated pruning in development and disease. In support of this hypothesis, we and others demonstrated that microglia phagocytose synaptic elements and are capable of sensing and responding to activity-related signals as they preferentially engulf less active synapses. However, how microglia determine which synapses to engulf and which to avoid, and the identity of the upstream neuronal signals that detect neural activity and transmit this information to microglia are not known. In the immune system, phagocytosis is carefully governed by both phagocytic, “eat me” and anti- phagocytic, “don’t eat me” molecules. In the brain, we identified neuronal CD47, a “don’t eat me” signal protects synapses from inappropriate removal. We further found that exposed phosphatidylserine (PS), an “eat me signal” drives microglial recognition of synapses for engulfment. Furthermore, we have identified the tyrosine kinases, Pyk2 and JAK2 as neuronal signals that are activated at inactive synapses and necessary for the elimination of these inputs. Finally, we found that PS exposure is elevated early in the hippocampus in an Alzheimer's disease (AD) mouse model. Based on these and other data, we propose to test the hypothesis that activity-dependent signals within neurons, such as Pyk2 and JAK2, dynamically regulate "eat me" and "don't eat me" signals on synapses to drive proper microglial phagocytosis of inactive synapses. We further hypothesize that aberrant activation of such signals lead to abnormal synapse loss in neurodegenerative diseases, such as Alzheimer’s Disease (AD). Specifically we aim to test the following: Aim 1) Investigate mechanisms of activity-regulated PS exposure and function at developing synapses; Aim 2: Determine activity-dependent neuronal signaling that regulates "eat me" and "don't eat me" signals for microglial engulfment; and Aim 3: Investigate the mechanisms of early synaptic dysfunction and microglial synaptic targeting associated with AD. We will use interdisciplinary in vivo and in vitro approaches with molecular/cell biological, histological, mouse genetic, imaging, and electrophysiological techniques with various newly developed systems to address our aims. Our studies could also provide new targets for therapeutic intervention, as restoring the balance of protective and elimination signals could protect against synapse loss in early stages of AD and other diseases.