Microglia-Astrocyte Crosstalk Regulating SynapseRemodeling

项目摘要 这项提案的目标是确定小胶质细胞和星形胶质细胞如何沟通， 突触数以万亿计的突触在大脑中形成了高度精确的电路图。这些地图的形状和 由感官体验（视觉、触觉等）维持，包括消除不太活跃的突触和F 维持和加强其他突触。尽管经过50多年的研究， 活动决定去除某些突触而不是其他突触的机制仍然是一个悬而未决的问题。 我们初步发现，小胶质细胞，一种常驻中枢神经系统（CNS）的巨噬细胞，吞噬和 消除发育中的视网膜膝状体和桶状皮质回路中较不活跃的突触。在上一次融资中， 我们发现，去除新生儿鼻子一侧的胡须会导致小胶质细胞的吞噬 以及消除相应的桶皮质中的丘脑皮质（TC）突触。不像视网膜膝状体 电路，这是不受补体调节。相反，小胶质细胞未能吞噬和消除TC突触， 神经元Fractalkine（CX 3CL 1）-小胶质细胞Fractalkine受体（CX 3CR 1）信号传导缺陷的小鼠。这项工作 建立了不同的神经胶质机制调节活动依赖性突触重塑，并开辟了新的 问题：小胶质细胞重塑成人大脑中的突触吗？有证据表明星形胶质细胞也吞噬突触 在其他中枢神经系统回路中，星形胶质细胞是否也参与了桶状皮质突触重塑？如果是这样， 与小胶质细胞沟通来调节这个过程我们新的初步数据表明，星形胶质细胞不 新生儿去除胡须后，吞噬突触，但减少了与突触的接触 以CX 3CL 1依赖的方式。此外，小胶质细胞不再吞噬TC突触后，胡须去除， 年龄较大的动物，伴随着星形胶质细胞突触鞘的增加。细胞特异性RNAseq 去除胡须进一步揭示了典型的Wnt信号传导作为小胶质细胞信号传导的假定机制， 星形胶质细胞调节突触鞘。我们现在提出了一个新的模型，通过它小胶质细胞调节 星形胶质细胞以活性和CX 3CL 1-CX 3CR 1-Wnt依赖的方式鞘化突触。反过来， 小胶质细胞获得进入以吞噬和移除TC突触。我们现在将利用桶状皮层的力量 1）定义CX 3CL 1-CX 3CR 1的发育窗口， 依赖性小胶质细胞突触吞噬和星形胶质细胞突触鞘化（Aim 1）。2)确定是否 星形胶质细胞鞘化突触影响小胶质细胞依赖性突触重塑（Aim 2）。3)确定如何 小胶质细胞调节星形胶质细胞的突触鞘化（Aim 3）。答案将说明一些突触是如何 被神经胶质细胞消除，而其他细胞则完好无损-这是该领域的一个关键开放问题，对各种 神经发育障碍和神经退行性疾病与突触的潜在变化 连通性。

Project Summary The goal of this proposal is to determine how microglia and astrocytes communicate to remodel synapses. Trillions of synapses form highly precise circuit maps in the brain. These maps are shaped and maintained by sensory experience (vision, touch, etc.), including elimination of less active synapses and f maintenance and strengthening of other synapses. Despite over 50 years of research, the underlying mechanisms by which activity dictates removal of some synapses, but not others, remains an open question. We made the initial discovery that microglia, a resident central nervous system (CNS) macrophage, engulf and eliminate less active synapses in the developing retinogeniculate and barrel cortex circuits. In the last funding cycle, we showed that removal of whiskers on one side of the snout in neonates resulted in microglial engulfment and elimination of thalamocortical (TC) synapses in the corresponding barrel cortex. Unlike the retinogeniculate circuit, this was not regulated by complement. Instead, microglia failed to engulf and eliminate TC synapses in mice deficient in neuronal fractalkine (CX3CL1)-to microglial fractalkine receptor (CX3CR1) signaling. This work established that diverse glial mechanisms regulate activity-dependent synapse remodeling and opened up new questions: Do microglia remodel synapses in the adult brain? With evidence that astrocytes also engulf synapses in other CNS circuits, are astrocytes also involved in barrel cortex synapse remodeling? If so, do they communicate with microglia to regulate this process? Our new preliminary data show that astrocytes do not engulf synapses in response to whisker removal in neonates, but rather they reduce their contact with synapses in a CX3CL1-dependent manner. Also, microglia no longer engulf TC synapses following whisker removal in older animals, concomitant with elevated astrocyte synapse ensheathment. Cell-specific RNAseq following whisker removal further reveals canonical Wnt signaling as a putative mechanism by which microglia signal to astrocytes to regulate synapse ensheathment. We now propose a novel model by which microglia regulate astrocyte ensheathment of synapses in an activity and CX3CL1-CX3CR1-Wnt dependent manner. In turn, microglia gain access to engulf and remove TC synapses. We will now leverage the power of the barrel cortex circuit with cell-specific genetic approaches to: 1) Define the developmental window for CX3CL1-CX3CR1- dependent microglial synapse engulfment and astrocyte synapse ensheathment (Aim 1). 2) Determine if astrocyte ensheathment of synapses impacts microglia-dependent synapse remodeling (Aim 2). 3) Identify how microglia regulate astrocyte ensheathment of synapses (Aim 3). Answers will address how some synapses are eliminated by glia while others are left intact—a key open question in the field with implications for a variety of neurodevelopmental disorders and neurodegenerative diseases with underlying changes in synaptic connectivity.