Excitatory and inhibitory synaptogenesis by FGFs and their role in epilepsy

描述（申请人提供）：突触的精确组装是大脑正常运作的关键。突触的异常形成或突触的缺失导致了许多神经系统疾病的进展。本文提出的研究目标是了解大脑中突触形成的分子机制，然后利用这些信息开发由突触功能障碍引起的疾病的新疗法。突触是由突触前细胞和突触后细胞之间的信号传导形成的。突触后细胞衍生的“突触前组织者”促进突触前轴突局部分化为突触接触部位的功能性神经末梢。我们对这些突触前组织者进行了无偏差的搜索，并确定成纤维细胞生长因子22 （FGF22）及其近亲FGF7和FGF10是促进突触前神经末梢分化的分子。在大脑中，两种主要类型的突触，兴奋性和抑制性，需要在适当的位置形成。兴奋性突触和抑制性突触之间的不平衡被认为是导致各种神经系统疾病的原因，包括自闭症、精神分裂症、图雷特综合征和癫痫。我们最近发现FGF22和FGF7分别促进兴奋性和抑制性突触前末梢的组织，作为海马中靶源性突触前组织者。在缺乏FGF22或FGF7的突变体中，兴奋性或抑制性神经末梢的分化特别受损。正如兴奋/抑制平衡改变所预期的那样，FGF22敲除（KO）小鼠具有抗性，而FGF7KO小鼠容易发生癫痫发作。这些结果表明，了解fgf介导的兴奋性和抑制性突触形成的确切机制将导致新的癫痫治疗策略。在这里，我们将探讨(1)FGF22和FGF7对兴奋性和抑制性突触前分化的差异作用的机制，(2)介导FGF作用的信号传导机制，(3)体内FGF缺乏的生理后果，以及(4)FGF在癫痫发生中的作用。对于这些研究，我们提出以下目标。目的1：确定FGF22和FGF7在体内的定位及其在不同突触后部位的动态分布。目的2：研究FGF22和FGF7是否通过不同的FGF受体和信号通路进行信号传导，从而产生不同的突触前效应。目的3：描述脑发育过程中FGF失活的功能后果。目的4：确定fgf是否在发育期间或脑损伤后参与癫痫回路的形成。我们将使用分子遗传学，细胞生物学，生物化学，电生理和成像技术的综合组合来解决这些目标。预计这项研究将揭示特定突触形成的新机制，并为治疗脑疾病（如癫痫）提供新的策略，这些疾病是由突触形成不当引起的。

DESCRIPTION (provided by applicant): Precise assembly of synapses is critical for proper functioning of the brain. Abnormal synapse formation or synaptic loss contributes to the progression of many neurological disorders. The goals of the research proposed here are to understand the molecular mechanisms underlying synapse formation in the brain and then use this information to develop new treatments for diseases resulting from synaptic malfunction. Synapses are formed by signaling between presynaptic and postsynaptic cells. Postsynaptic cell-derived "presynaptic organizers" promote local differentiation of presynaptic axons into functional nerve terminals at sites of synaptic contact. We performed an unbiased search for such presynaptic organizers and identified fibroblast growth factor 22 (FGF22), and its close relatives FGF7 and FGF10 as molecules that promote differentiation of presynaptic nerve terminals. In the brain, two major types of synapses, excitatory and inhibitory, need to be formed at their appropriate sites. An imbalance between excitatory and inhibitory synapses has been proposed to contribute to various neurological disorders including autism, schizophrenia, Tourette syndrome and epilepsy. We have recently found that FGF22 and FGF7 promote the organization of excitatory and inhibitory presynaptic terminals, respectively, as target-derived presynaptic organizers in the hippocampus. The differentiation of excitatory or inhibitory nerve terminals is specifically impaired in mutants lacking FGF22 or FGF7. As expected from the alterations in excitatory/inhibitory balance, FGF22 knockout (KO) mice are resistant and FGF7KO mice are prone to epileptic seizures. These results indicate that understanding the precise mechanisms of FGF-mediated excitatory and inhibitory synapse formation will lead to novel treatment strategies for epilepsy. Here we address (1) the mechanisms underlying the differential effects by FGF22 and FGF7 on excitatory and inhibitory presynaptic differentiation, (2) the signaling mechanisms that mediate the effects of FGFs, (3) physiological consequences of FGF deficiency in vivo, and (4) the role of FGFs in epileptogenesis. For these studies, we propose the following aims. Aim 1: Determine the in vivo localization of FGF22 and FGF7 and their dynamic distribution to distinct postsynaptic sites. Aim 2: Examine whether FGF22 and FGF7 signal through different FGF receptors and signaling pathways for their differential presynaptic effects. Aim 3: Delineate the functional consequences of FGF inactivation during brain development. Aim 4: Determine whether FGFs are involved in epileptic circuit formation during development or after brain insults. We will use an integrated combination of molecular genetic, cellular biological, biochemical, electrophysiological and imaging techniques to address these aims. It is anticipated that this study will reveal novel mechanisms underlying specific synapse formation and suggest novel strategies for treating brain disorders, such as epilepsy, that result from improper synapse formation.