Elucidating the Function of Class 4 Semaphorins in GABAergic Synapse Formation.

 描述(申请人提供)：神经元网络中兴奋和抑制之间的平衡(E/I平衡)调节整个网络功能；这种平衡的破坏被认为是导致神经发育障碍的基础，如自闭症、谱系障碍和癫痫。为了了解E/I平衡是如何建立和调节的，首先需要定义指导神经元之间兴奋性和抑制性突触连接的基因和信号通路。在上一个资金周期中，我们发现了一对新的配体-受体对，Sema4D和PlexinB1，它在前所未有的快速时间尺度上双向调节GABA能突触的形成。我们还发现Sema4D可以用来在器官型海马片培养中快速(2小时内)驱动抑制和抑制神经元的过度活动。有趣的是，我们的初步数据还表明，在体内应用Sema4D可以降低癫痫小鼠模型的癫痫发作严重程度，这与这些动物神经系统中Sema4D依赖的抑制增加一致。此外，初步研究表明，Sema4D治疗的相对较短的时间窗口(例如2小时)促进了功能性GABA能突触的形成，该突触可持续数天。这一建议的总体目标是阐明Sema4D依赖的信号通路如何通过促进GABA能、抑制性突触的发育来重置神经元回路中的E/I平衡。特别是，我们提出了一系列实验，以了解Sema4D和PlexinB1如何结合分子生物学、生物化学、电生理学和尖端的时移显微镜在体外和体内介导GABA能突触的快速形成。此外，这种依赖Sema4D的快速形成的GABA能突触使我们假设，从长远来看，利用Sema4D/PlexinB1信号的突触生成潜力可以转化为对E/I平衡被破坏为显著特征的神经系统疾病的有效治疗。

 DESCRIPTION (provided by applicant): The balance between excitation and inhibition in neuronal networks (E/I balance) regulates overall network function; disruptions to this balance are thought to underlie neurodevelopmental disorders such as Autism Spectrum Disorders and epilepsy. To understand how E/I balance is established and regulated, it is first necessary to define the genes and signaling pathways that instruct excitatory and inhibitory synaptic connections between neurons. During the last funding cycle, we identified a novel ligand-receptor pair, Sema4D and PlexinB1, which bi-directionally regulates GABAergic synapse formation on an unprecedentedly fast time-scale. We also discovered that Sema4D could be used to rapidly (within 2 hrs) drive inhibition and suppress neuronal hyperactivity in organotypic hippocampal slice cultures. Intriguingly, our preliminary data also demonstrate that in vivo application of Sema4D can reduce seizure severity in a mouse model of epilepsy, consistent with a Sema4D-dependent increase in inhibition in the nervous system of these animals. In addition, preliminary studies indicate that a relatively short time window of Sema4D treatment (e.g. 2 hrs) promotes the formation of functional GABAergic synapses that persist for days. The overall goal of this proposal is to elucidate how the Sema4D-dependent signaling pathway acts to re-set E/I balance in neuronal circuits through the promotion of GABAergic, inhibitory synapse development. In particular, we propose a set of experiments to understand how Sema4D and PlexinB1 mediate the rapid formation of GABAergic synapses using a combination of molecular biology, biochemistry, electrophysiology, and cutting-edge, time-lapse microscopy both in vitro and in vivo. Further, this Sema4D-dependent, rapid formation of GABAergic synapses leads us to hypothesize that, in the long term, harnessing the synaptogenic potential of Sema4D/PlexinB1 signaling could translate into an effective therapeutic for neurological conditions in which disruptions to the E/I balance is a salient feature.