Latrophilin Function in Synapse Formation

神经回路是由突触构成的，突触将神经元连接成巨大的网络。尽管已经确定了许多神经回路的特征，但构建其突触结构的分子和细胞机制在很大程度上仍不清楚。在建立神经回路突触结构的突触形成过程中，通过跨突触黏附分子的双向信号被认为控制突触的组装。值得注意的是，跨突触黏附分子的遗传变化往往容易导致神经精神障碍，这表明神经回路突触结构的功能障碍导致神经精神障碍，尽管这些损害的性质尚不清楚。我们的初步数据显示，在海马神经元中，兴奋性突触亚群的形成需要拉特罗菲林(Lphns)，这是一个由三个突触后黏附-GPCRs组成的家族。不同的Lphns介导不同突触的建立，即使在相同的神经元中，这表明它们不仅参与构建突触，而且还参与决定它们的特异性。Lphns如何介导突触形成，以及它们的突触形成功能在多大程度上涉及GPCR信号或黏附相互作用，目前尚不清楚。此外，人类Lphn3基因(ADGRL3)中的SNPs强烈下调Lphn3的表达。本申请旨在研究介导Lphn依赖突触形成的信号机制，探索Lphns如何决定突触的特异性，并研究Lphn3表达的变化如何改变突触功能。具体地说，拟议的实验将检验以下总体假设：(1)Lphns通过涉及局部受限信号的GPCR介导的机制控制突触的形成和维持，(2)不同的Lphn亚型通过蛋白质相互作用和GPCR功能的序列特异性差异控制不同突触的形成，以及(3)Lphn3表达的变化损害特定突触子集的形成。三个特定的目标将检验这些假说，从而瞄准与理解神经回路是如何连接以及神经回路受损如何改变认知最相关的关键问题。该项目将使用小鼠和人类神经元作为模型系统，在小鼠和人类神经元中寻求广泛的跨学科方法，范围从配体-受体复合体的生物物理研究到细胞内信号的细胞生物学研究，再到探索认知变化的行为研究。因此，这一应用将为深入了解Lphns如何驱动小鼠突触形成，以及Lphn3表达减少如何导致人类神经元的突触变化提供深入的了解。解决这些问题是基础神经科学和翻译神经科学最感兴趣的问题，因为处理大脑信息的神经回路是由突触形成构成的，神经回路中突触交流的功能障碍或失衡可能是神经精神障碍的发病基础。

Neural circuits are constructed by synapses that connect neurons into vast networks. Although many neural circuits have been characterized, the molecular and cellular mechanisms that build their synaptic architecture remain largely unknown. During synapse formation that establishes the synaptic architecture of neural circuits, bi-directional signaling via trans-synaptic adhesion molecules is thought to control assembly of synapses. Strikingly, genetic changes in trans-synaptic adhesion molecules often predispose to neuropsychiatric disorders, suggesting that dysfunction of the synaptic architecture of neural circuits contributes to neuropsychiatric disorders, although the nature of these impairments is poorly understood. Our preliminary data show that in hippocampal neurons, formation of subsets of excitatory synapses requires latrophilins (Lphns), a family of three postsynaptic adhesion-GPCRs. Different Lphns mediate establishment of distinct synapses even in the same neuron, suggesting that they are involved not only in constructing synapses, but also in determining their specificity. How Lphns mediate synapse formation, and to what extent their synapse-formation function involves GPCR signaling or adhesive interactions, remains unknown. Moreover, SNPs in the human Lphn3 gene (ADGRL3) downregulate Lphn3 expression robustly. The present application proposes to examine the signaling mechanisms that mediate Lphn-dependent synapse formation, to explore how Lphns determine synapse specificity, and to investigate how changes in Lphn3 expression change synaptic function. Specifically, the proposed experiments will test the overall hypotheses that (1) Lphns control synapse formation and maintenance by a GPCR-mediated mechanism involving locally restricted signaling, that (2) different Lphn isoforms control formation of distinct synapses via sequence-specific differences in their protein interactions and GPCR function, and that (3) changes in Lphn3 expression impair formation of a specific subset of synapses. Three Specific Aims will test these hypotheses, thus targeting key questions that are most relevant for understanding how neural circuits are wired and how impairment of neural circuits alter cognition. Using both mouse and human neurons as a model system, the project will pursue broadly interdisciplinary approaches in both mice and human neurons that range from biophysical studies of ligand-receptor complexes to cell-biological investigations of intracellular signaling to behavioral studies probing for cognitive changes. Thereby, this application will provide insight into how Lphns drive synapse formation in mice, and how decreased expression of Lphn3 predisposes to synaptic changes in human neurons. Addressing these questions is of paramount interest in basic and translational neuroscience because neural circuits that process the brain’s information are constructed by synapse formation, and dysfunction or imbalance of synaptic communication in neural circuits likely underlies the pathogenesis of neuropsychiatric disorders.