Presenilins and Cell Adhesion Molecules

描述（由申请人提供）：突触功能障碍是与阿尔茨海默病（AD）相关的认知下降和神经变性的关键特征。PSEN基因常染色体显性突变导致家族性早发性AD早老素（PS）形成γ-分泌酶的催化中心，γ-分泌酶是一种负责产生β淀粉样肽的酶，β淀粉样肽在AD患者的大脑中积累。除了APP的膜内切割外，Notch配体/Notch受体和几种细胞粘附分子（CAM）（包括钙粘蛋白、原钙粘蛋白、DCC、ErbB 4、ephrin/Eph受体、nectin-1 α和syndecan）也被γ-分泌酶加工。值得注意的是，这些蛋白质中的每一种在胚胎发育期间促进不同的神经元功能，例如轴突引导、神经元生长和突触发生。最近，我们报道了培养的神经元中PS表达或功能的丧失增强了突触能突触传递、突触形成和cAMP依赖性信号级联的激活。有趣的是，使用PS1 M146 V敲入小鼠，我们发现FAD连锁突变体的表达也提高了培养神经元中cAMP依赖性信号传导，并导致海马CA 1区棘密度增加。DCC（netrin受体）加工的分析揭示，缺乏γ-分泌酶切割增加神经突生长和cAMP依赖性信号传导，说明PS的新功能，其中γ-分泌酶的切割终止与某些CAM底物相关的细胞内信号传导级联。综上所述，我们推测，γ-分泌酶处理某些CAM调节信号级联发挥关键作用，突触形成，突触传递和可塑性。我们还假设FAD相关的PS1变体通过影响Abeta的产生以及对突触功能重要的某些CAM的蛋白水解来促进AD的发病机制。本研究的具体目的是检查PS依赖的CAM蛋白水解的影响：1）对细胞功能，2）对突触形成，和3）对记忆的细胞基质。使用PS1空胚胎，PS1 M146 V敲入小鼠，和培养的细胞系统，我们建议进行电生理，生化和成像研究，以探讨如何PS依赖的CAM蛋白水解影响突触功能。特别是，我们将集中我们的研究在正常和病理条件下的APP，DCC和N-cadherin的突触影响，因为他们已知的关联与AD的发病机制，突触形成和突触功能相关的信号通路。我们非常有信心，我们在提案中概述的补充方法将为PS在健康和疾病中的作用提供重要的机制见解。

DESCRIPTION (provided by applicant): Synaptic dysfunction is a critical feature of cognitive decline and neurodegeneration associated with Alzheimer's disease (AD). Autosomal dominant mutations in PSEN genes cause familial early-onset AD. Presenilins (PS) form the catalytic center of gamma-secretase, an enzyme responsible for the generation of beta amyloid peptides, which accumulate in the brains of individuals with AD. In addition to intramembranous cleavage of APP, Notch ligands/Notch receptor, and several cell adhesion molecules (CAMs) including cadherins, protocadherins, DCC, ErbB4, ephrin/Eph receptors, nectin-1alpha and syndecan, are also processed by gamma-secretase. Notably, each of these proteins facilitates diverse neuronal functions during embryonic development such as axon guidance, neuronal outgrowth and synaptogenesis. Recently, we reported that loss of PS expression or function in cultured neurons enhances glutamatergic synaptic transmission, synapse formation, and activation of cAMP-dependent signaling cascades. Interestingly, using PS1 M146V knock-in mice we find that expression of FAD-linked mutant also elevates cAMP-dependent signaling in cultured neurons, and leads to increased spine density in CA1 area of hippocampus. Analysis of DCC (the netrin receptor) processing revealed that lack of gamma-secretase cleavage increases neurite outgrowth and cAMP-dependent signaling, illustrating a novel function for PS wherein cleavage by gamma-secretase terminates intracellular signaling cascades associated with certain CAM substrates. Taken together, we hypothesize that gamma-secretase processing of certain CAMs regulates signaling cascades that play pivotal roles in synapse formation, synaptic transmission and plasticity. We also hypothesize that FAD-linked PS1 variants promote AD pathogenesis by influencing Abeta generation as well as proteolysis of certain CAMs that are important for synaptic function. The specific aims of this investigation are to examine the influence of PS-dependent proteolysis of CAMs: 1) on cellular function, 2) on synapse formation, and 3) on cellular substrates of memory. Using PS1 null embryos, PS1 M146V knock-in mice, and cultured cell systems we propose to perform electrophysiological, biochemical and imaging studies to investigate how PS-dependent proteolysis of CAMs influences synaptic functions. In particular, we will focus our studies on the synaptic influence of APP, DCC and N-cadherin in normal and pathological conditions because of their known association with the pathogenesis of AD, synapse formation and signaling pathways related to synaptic functions. We are extremely confident that our complementary approaches outlined in our proposal will provide important mechanistic insights into the role of PS in health and disease.