Molecular Logic Sculpting Cell-Specific Contributions of Neurexin-1 at the Tripartite Synapse

摘要 大量证据表明编码神经毒素-1（Nrxn 1）的基因的拷贝数变异（CNVs）， 突触细胞粘附分子在自闭症谱系障碍、精神分裂症和抽动秽语症病因学中的作用 综合征然而，关于Nrxn 1在发育和成年时的功能和调节知之甚少 突触，了解这一点可以提高我们对大脑疾病的认识，并揭示新的治疗方法。 目标的我的初步数据显示，Nrxn 1不仅在神经元中表达，而且在星形胶质细胞中表达， 挑战了Nrxn 1完全是突触前的经典观点。在这里，我提出星形胶质细胞Nrxn 1 介导星形胶质细胞和突触之间的一种重要的通讯形式， 兴奋性突触的发育和功能。我的初步发现表明星形胶质细胞和神经元Nrxn 1 在主要同种型表达、选择性剪接和硫酸乙酰肝素（HS）修饰方面有根本不同。 星形胶质细胞Nrxn 1的选择性丢失导致AMPA受体（AMPAR）的显著和选择性减少。 介导的突触传递，而不影响海马体中的突触数量，海马体是一个重要的大脑区域， 用于将信息从短期记忆巩固到长期记忆和空间记忆。如何 突触后膜，其含有许多neurexin配体（例如LRRTM、神经配素等）， 区分突触前和星形胶质细胞的Nrxn 1，以允许在三部分内的隔室特异性信号传导 synapse？为了更好地理解星形胶质细胞Nrxn 1用于指导细胞凋亡的分子机制， 突触发育我将在Nrxn 1星形胶质细胞条件性敲除（acKO）小鼠中进行拯救实验 使用AAV递送在主要同种型同一性、可变剪接、HS修饰和 胞内信号传导记录自发和诱发兴奋性突触反应， 在CA 1锥体神经元上进行以测量拯救功效。接下来，我将扩展我们对 通过研究星形胶质细胞Nrxn 1是否是基础和/或 活动诱导的树突棘形态和密度的变化，以及三维密度 功能性AMPAR。最后，在星形胶质细胞Nrxn 1缺失后观察到的突触缺陷可能是一种神经元损伤。 星形胶质细胞功能受损的下游后果。因此，我将测量星形胶质细胞的几个方面， 星形胶质细胞中Nrxn 1缺失后的功能，包括生理学（即膜特性和通道特性） 电流）、形态学（即领域、间隙连接耦合以及与突触的关联）和电路相关 (i.e.钙动力学）性质。预计拟议的研究将提供关键的见解， Nrxn 1 CNVs如何引起神经发育障碍的分子和细胞基础， 一种新的分子程序支持神经元和星形胶质细胞间室的通讯 三重突触的。

ABSTRACT Substantial evidence implicates copy number variations (CNVs) of the gene encoding Neurexin-1 (Nrxn1), a synaptic cell adhesion molecule, in the pathoetiology of Autism spectrum disorder, schizophrenia, and Tourette syndrome. However, very little is known regarding the function and regulation of Nrxn1 at developing and adult synapses, an understanding of which may improve our knowledge of brain disorders and reveal novel therapeutic targets. My preliminary data show that Nrxn1 is not only expressed by neurons, but also by astrocytes, challenging the classical view of Nrxn1 as being exclusively presynaptic. Here, I propose that astrocytic Nrxn1 mediates an important form of communication between astrocytes and synapses that is required for normal excitatory synapse development and function. My preliminary findings show that astrocytic and neuronal Nrxn1 fundamentally differ in major isoform expression, alternative splicing, and heparan sulfate (HS) modification. Selective loss of astrocytic Nrxn1 leads to a significant and selective reduction in AMPA receptor (AMPAR)- mediated synaptic transmission without affecting synapse number in the hippocampus, a brain region important for consolidation of information from short-term memory to long-term memory and spatial memory. How does the postsynaptic membrane, which contains numerous neurexin ligands (e.g. LRRTMs, neuroligins, etc.), distinguish between presynaptic and astrocytic Nrxn1 to allow compartment-specific signaling within the tripartite synapse? In order to better understand the molecular mechanisms utilized by astrocytic Nrxn1 to instruct synapse development I will perform rescue experiments in Nrxn1 astrocyte conditional knockout (acKO) mice using AAVs to deliver Nrxn1 variants differing in major isoform identity, alternative splicing, HS modification, and intracellular signaling. Recordings of both spontaneous and evoked excitatory synaptic responses will be performed on CA1 pyramidal neurons to measure rescue efficacy. Next, I will extend our understanding of the functional consequences of Nrxn1 deletion through studying whether astrocytic Nrxn1 is required for basal and/or activity-induced changes in dendritic spine morphology and density, as well as the three-dimensional density of functional AMPARs. Finally, the synaptic deficits observed following deletion of astrocytic Nrxn1 may be a downstream consequence of impaired astrocyte function. Thus, I will measure several aspects of astrocyte function following Nrxn1 deletion in astrocytes, including physiological (i.e. membrane properties and channel currents), morphological (i.e. territory, gap-junction coupling, and association with synapses), and circuit-related (i.e. calcium dynamics) properties. It is anticipated that the proposed research will provide critical insights into the molecular and cellular basis of how Nrxn1 CNVs give rise to neurodevelopmental disorders and will shed light on a novel molecular program underpinning communication between neuronal and astrocytic compartments of the tripartite synapse.