Excitatory and inhibitory synaptogenesis by FGFs and their role in epilepsy

描述(申请人提供)：突触的精确组装对大脑的正常运作至关重要。突触形成异常或突触丢失会导致许多神经疾病的进展。这项研究的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新的治疗突触功能障碍引起的疾病的方法。突触是由突触前细胞和突触后细胞之间的信号形成的。突触后细胞衍生的“突触前组织者”促进突触前轴突在突触接触部位的局部分化为功能性神经末梢。我们对这种突触前组织者进行了无偏见的搜索，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--兴奋性突触和抑制性突触--需要在其适当的位置形成。兴奋性和抑制性突触之间的失衡被认为是导致各种神经疾病的原因，包括自闭症、精神分裂症、多发性抽动症和癫痫。我们最近发现，FGF22和FGF7分别促进兴奋性和抑制性突触前终末在海马区作为靶源性突触前组织者的组织。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尤其受损。正如从兴奋性/抑制性平衡的改变所预期的那样，FGF22基因敲除(KO)小鼠具有抵抗力，而FGF7KO小鼠容易发生癫痫发作。这些结果表明，了解成纤维细胞生长因子介导的兴奋性和抑制性突触形成的确切机制将为癫痫的治疗提供新的策略。在这里，我们讨论了(1)FGF22和FGF7对兴奋性和抑制性突触前分化的不同作用的机制，(2)介导FGFs作用的信号机制，(3)体内成纤维细胞生长因子缺乏的生理后果，(4)FGFs在癫痫发生中的作用。对于这些研究，我们提出了以下目标。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：研究FGF22和Fgf7是否通过不同的成纤维细胞生长因子受体和信号通路传递不同的突触前效应。目的3：描述成纤维细胞生长因子失活在脑发育过程中的功能后果。目的4：确定FGFs在发育过程中或脑损伤后是否参与癫痫环路的形成。我们将使用分子遗传学、细胞生物学、生化、电生理学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，并提出治疗因突触形成不当而导致的大脑疾病(如癫痫)的新策略。 与公共健康相关：这项拟议的研究旨在了解大脑中特定突触形成的分子和细胞机制。特定突触的形成对神经系统的正常运作至关重要。协调的研究集中在成纤维细胞生长因子(FGFs)的突触生成作用以及它们对海马区兴奋性和抑制性突触形成的不同影响。我们将具体确定FGFs在癫痫发病机制中的作用，癫痫是一种海马区突触连接不当的疾病。这项工作将使我们能够确定FGFs在特定突触形成中的确切功能和潜在机制，并有助于设计适当的治疗和预防癫痫的策略。

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. PUBLIC HEALTH RELEVANCE: The proposed research is aimed at understanding the molecular and cellular mechanisms of specific synapse formation in the brain. Specific synapse formation is critical for the proper functioning of the nervous system. The coordinated studies focus on the synaptogenic role of fibroblast growth factors (FGFs) and their differential effects on excitatory and inhibitory synapse formation in the hippocampus. We will specifically determine the role of FGFs in the pathogenesis of epilepsy, a disease with improper synaptic connections in the hippocampus. This body of work will allow us to determine the precise function and underlying mechanisms for FGFs in specific synapse formation, and help design appropriate strategies for the treatment and prevention of epilepsy.