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）相关的认知能力下降和神经退行性变的关键特征。PSEN基因的常染色体显性突变导致家族性早发性AD。早老素（PS）是-分泌酶的催化中心，-分泌酶是一种负责产生-淀粉样肽的酶，在AD患者的大脑中积累。除了APP的膜内切割外，Notch配体/Notch受体以及包括cadherins、原cadherins、DCC、ErbB4、ephrin/Eph受体、nectin-1alpha和syndecan在内的几种细胞粘附分子（CAMs）也被γ -分泌酶加工。值得注意的是，在胚胎发育过程中，这些蛋白质中的每一种都促进了不同的神经元功能，如轴突引导、神经元生长和突触发生。最近，我们报道了培养神经元中PS表达或功能的丧失会增强谷氨酸能突触传递、突触形成和camp依赖性信号级联的激活。有趣的是，使用PS1 M146V敲入小鼠，我们发现fad相关突变体的表达也提高了培养神经元中camp依赖的信号，并导致海马CA1区脊柱密度增加。对DCC （netrin受体）加工过程的分析表明，缺乏-分泌酶裂解会增加神经突的生长和camp依赖的信号传导，这说明了PS的一种新功能，即-分泌酶的裂解终止了与某些CAM底物相关的细胞内信号级联反应。综上所述，我们假设某些CAMs的γ分泌酶加工调节了在突触形成、突触传递和可塑性中起关键作用的信号级联反应。我们还假设fad相关的PS1变异体通过影响β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研究ps依赖性CAMs蛋白水解的影响：1)对细胞功能的影响，2)对突触形成的影响，以及3)对细胞记忆底物的影响。利用PS1缺失胚胎、PS1 M146V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，以研究CAMs的ps依赖性蛋白水解如何影响突触功能。特别是，我们将重点研究APP、DCC和N-cadherin在正常和病理条件下对突触的影响，因为它们与AD的发病机制、突触形成和突触功能相关的信号通路有关。我们非常有信心，我们提案中概述的互补方法将为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.