Investigating the mechanisms of Arc-dependent synaptic plasticity

项目摘要 目前的学习和记忆模型集中在突触强度的细胞自主调节， 长时程增强和抑制（LTP/LTD）。学习和经验诱导了一组特定的基因 介导突触强度的持久维持、染色质的表观遗传改变和神经元的 体内平衡一个关键的活性依赖性基因Arc是持久突触可塑性的关键介质， 记忆最近，我们发现了一种由Arc介导的新型细胞间通讯， 它的功能。我们意外地观察到纯化的Arc蛋白自发地形成病毒样衣壳， 确定Arc基因起源于一个古老的逆转录转座子家族。我们假设如果Arc形成 衣壳，也许逆转录病毒的其他功能方面也被保留。我们发现纯化的Arc 衣壳包裹RNA，包括Arc mRNA。脑内的内源性Arc也与自身的mRNA结合 并从原代培养的神经元释放到细胞外囊泡（EV）中。引人注目的是，含电弧的电动汽车可以 将Arc mRNA转移到Arc敲除神经元中。因此，Arc保留了祖先的生化功能， 逆转录病毒Gag蛋白。这些发现提出了依赖ARC的细胞间通讯可能 是它在学习和记忆中功能的基础。Arc EV在邻近神经元中的摄取可能导致Arc- 介导的AMPAR内吞作用和突触弱化。Arc参与了AMPAR的移除 来自同一树突上的弱突触，以异突触抑制的形式。然而，Arc mRNA或 突触之间的蛋白质转移可以在回路水平介导异突触可塑性， 通过削弱在学习过程中不活跃的周围神经元来稳定记忆回路。主要 本研究的目的是探讨Arc是否介导细胞间突触可塑性及其机制 细胞间信号我们已经将BAR结构域蛋白IRSp53鉴定为Arc相互作用蛋白， 在LTP诱导后介导Arc从细胞的释放。在初步数据中，我们发现Arc EV诱导了 受体细胞表面AMPA受体的丧失。 基于这些数据，我们将使用实时成像和电生理技术测试以下模型：LTP 增加树突中的Arc蛋白表达，树突组装成寡聚病毒样衣壳。LTP也 增加树突中的IRSp53表达，在树突中它与Arc相互作用以促进EV中的Arc释放。一旦 释放后，Arc EV被邻近的神经元吸收，诱导AMPAR内吞作用，导致非细胞 突触强度的自主减弱。这项研究将有助于揭示一种新的细胞间 突触可塑性，这可能对记忆和认知很重要。弧依赖塑性的破坏是 与各种神经发育和精神疾病有关-因此，我们的工作将有助于进一步阐明 这些疾病的潜在机制。

PROJECT SUMMARY Current models of learning and memory have focused on cell-autonomous regulation of synaptic strength such as long-term potentiation and depression (LTP/LTD). Learning and experience induces a specific set of genes that mediate long-lasting maintenance of synaptic strength, epigenetic alterations of chromatin, and neuronal homeostasis. One key activity-dependent gene, Arc, is a critical mediator of long-lasting synaptic plasticity and memory. Recently, we identified a new type of intercellular communication mediated by Arc that could be central to its function. We unexpectedly observed that purified Arc protein spontaneously forms virus-like capsids and determined that the Arc gene originated from an ancient family of retrotransposons. We posited that if Arc forms capsids, perhaps other functional aspects of retroviruses have also been retained. We found that purified Arc capsids encapsulate RNA, including Arc mRNA. Endogenous Arc from brain also associates with its own mRNA and is released in extracellular vesicles (EVs) from primary cultured neurons. Strikingly, Arc-containing EVs can transfer Arc mRNA into Arc knock-out neurons. Thus, Arc has retained biochemical functions of the ancestral retrovirus Gag protein. These findings raise the possibility that Arc-dependent intercellular communication might underlie its function in learning and memory. Uptake of Arc EVs in neighboring neurons could result in Arc- mediated AMPAR endocytosis and synapse weakening. Arc has been implicated in the removal of AMPARs from weak synapses on the same dendrite in a form of heterosynaptic depression. However, Arc mRNA or protein transfer between synapses could mediate heterosynaptic plasticity at the circuit level, facilitating the stabilization of memory circuits by weaking surrounding neurons that were not active during learning. The main aim of this proposal is to test whether Arc mediates intercellular synaptic plasticity and mechanisms of Arc intercellular signaling. We have identified the BAR domain protein IRSp53 as an Arc interacting protein that mediates the release of Arc from cells after LTP induction. In preliminary data, we found that Arc EVs induce a loss of surface AMPA receptors in recipient cells. Based on these data, we will test the following model using live-imaging and electrophysiology techniques: LTP increases Arc protein expression in dendrites, which assembles into oligomeric virus-like capsids. LTP also increases IRSp53 expression in dendrites, where it interacts with Arc to facilitate Arc release in EVs. Once released, Arc EVs are taken up by neighboring neurons, inducing AMPAR endocytosis that results in non-cell autonomous weakening of synapse strength. The proposed studies will help uncover a new form of intercellular synaptic plasticity that may be important for memory and cognition. Disruption of Arc-dependent plasticity is implicated in various neurodevelopmental and psychiatric disorders – thus our work will help further clarify mechanisms underlying these disorders.