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化的关键特征。PSEN基因常染色体显性突变导致家族性早发性AD。早老素(PS)形成了伽马分泌酶的催化中心，伽马分泌酶是一种负责产生β淀粉样多肽的酶，积累在AD患者的大脑中。除了APP的膜内切割外，Notch配体/Notch受体和几种细胞黏附分子(CAM)，包括钙粘素、原钙粘素、DCC、ErbB4、EPhin/Eph受体、Nectin-1α和Syndecan，也被伽马分泌酶处理。值得注意的是，这些蛋白中的每一种都促进了胚胎发育过程中不同的神经元功能，如轴突引导、神经元突起和突触形成。最近，我们报道了培养神经元中PS表达或功能的丧失增强了谷氨酸能突触传递、突触形成和激活cAMP依赖的信号级联反应。有趣的是，使用PS1 M146V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依赖的信号，并导致海马CA1区脊椎密度增加。对DCC(网织蛋白受体)处理的分析表明，缺乏伽马分泌酶的切割会增加轴突生长和cAMP依赖的信号转导，这说明了PS的一种新功能，即伽玛分泌酶的切割终止了与某些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CaM的伽马分泌酶处理调节在突触形成、突触传递和可塑性中发挥关键作用的信号级联。我们还假设，FAD连锁的PS1变体通过影响Aβ的产生以及对突触功能至关重要的某些CAM的蛋白分解来促进AD的发病。这项研究的具体目的是检测依赖PS的CAMS蛋白分解对细胞功能的影响，2)对突触形成的影响，3)对记忆的细胞底物的影响。利用PS1缺失的胚胎、PS1 M146V基因敲除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，以探讨依赖PS的CaM蛋白分解如何影响突触功能。特别是，我们将重点研究APP、DCC和N-钙粘素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、突触形成和与突触功能相关的信号通路有关。我们非常相信，我们在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械性见解。

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.