Mechanisms of activity-dependent microglia-neuron interactions in development and disease

摘要 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控 但在疾病模型中，它在脆弱的大脑区域的激活表明，疾病和 发育具有共同的调控机制和修剪机制。突触的细化是一种活动- 优先修剪弱突触的依赖过程。我们假设神经活动是一个关键 小胶质细胞介导的修剪在发育和疾病中的上游激活物和调节器。为了支持这一点 假设，我们和其他人证明了小胶质细胞吞噬突触元素并能够 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， 小胶质细胞如何决定吞噬和避免哪些突触，以及上游神经元的身份 检测神经活动并将信息传递给小胶质细胞的信号尚不清楚。 在免疫系统中，吞噬作用受到吞噬细胞、“吞噬我”和抗吞噬细胞的小心控制。 吞噬细胞，“不要吃我”的分子。在大脑中，我们发现了神经元CD47，一个“不要吃我”的信号保护 不恰当的移除导致的突触。我们进一步发现，暴露的磷脂酰丝氨酸(PS)，一种“吃我的信号” 推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， PYK2和JAK2作为神经元信号，在不活跃的突触被激活，是消除 这些输入。最后，我们发现阿尔茨海默病患者早期海马区PS暴露水平升高 (Ad)小鼠模型。基于这些和其他数据，我们建议检验依赖于活动的假设 神经元内的信号，如PYK2和JAK2，动态调节“吃我”和“不吃我”的信号 突触驱动非活动突触的适当的小胶质细胞吞噬。我们进一步假设这一反常现象 在阿尔茨海默氏症等神经退行性疾病中，这些信号的激活会导致异常突触丢失 疾病(AD)。具体地说，我们的目标是测试以下几个方面：目的1)研究活性调节PS的机制 暴露和发育突触的功能；目标2：确定活动依赖的神经元信号转导 调节小胶质细胞吞噬的“吃我”和“不吃我”信号；目标3：研究其机制 阿尔茨海默病相关的早期突触功能障碍和小胶质突触靶向。我们将使用跨学科 体内和体外分子/细胞生物学、组织学、小鼠遗传学、成像和 电生理技术和各种新开发的系统来解决我们的目标。我们的研究可以 也为治疗干预提供了新的目标，如恢复保护和消除的平衡 在阿尔茨海默病和其他疾病的早期，信号可以防止突触丢失。

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.