Mechanisms of APP and APLP2 function at synapses

 描述（由申请人提供）：阿尔茨海默病（AD）是世界上年龄依赖性痴呆的最常见原因，与大脑淀粉样斑块相关，主要由Aβ肽组成。这些肽是由淀粉样前体蛋白（APP）的双重切割产生的。BACE 1裂解产生C-末端片段β-CTF，然后通过γ-分泌酶加工成几种Aβ亚型。遗传数据表明，APP加工的调节有助于AD。此外，APP的多态性减少BACE 1对APP的加工，可防止散发性AD和正常的衰老依赖性认知衰退。因此，人类遗传学证据表明APP和APP加工对正常认知功能很重要。为了深入了解APP在中枢神经系统中的功能，我们表征了APP细胞内结构域的脑相互作用组。我们分离了几种蛋白质，包括调节突触囊泡胞吐作用的蛋白质（我们统称为APP突触前相互作用体或Appresyome）和组成E3连接酶CRL 4CRBN的多分子复合物。有趣的是，CRL 4CRBN的组成部分之一，即CRBN，是由与智力残疾相关的基因编码的。我们的初步研究表明，APP调节的概率释放的突触囊泡，这一功能是由APP的BACE 1加工调节。我们还发现，CRL 4CRBN介导Snap 25，Vamp 2和Stxbp 1的泛素化，这三种蛋白质调节突触囊泡胞吐作用，也是Appresyome的一部分。值得注意的是，CRL 4CRBN和近似体结合APP胞内结构域的两个不同区域。最后，我们发现APP蛋白家族的成员APLP 2具有许多这些APP功能。在本研究中，我们将分析APP和APLP 2在突触传递中的作用及其分子机制，并研究APP（和APLP 2）加工如何调节突触传递。最后，我们将分析CRL 4CRBN和CRL 4CRBN/APP-CRL 4CRBN/APLP 2复合物的功能。我们的研究将有助于我们了解APP，BACE 1和CRBN的突触功能，并可能揭示AD中可能改变的信号通路。因此，这项研究可能揭示AD的发病机制，以及揭示疾病修饰AD药物的新靶点。

 DESCRIPTION (provided by applicant): Alzheimer's Disease (AD) is the most common cause of ageing-dependent dementia in the world and is associated with cerebral amyloid plaques, mostly composed of Aβ peptides. These peptides are produced by a double cleavage of the amyloid precursor protein (APP). BACE1 cleavage produces the C-terminal fragment, β-CTF, which is then processed into several Aβ isoforms by γ-secretase. Genetic data suggest that regulation of APP processing contributes to AD. In addition, a polymorphism of APP that reduces processing of APP by BACE1 protects from sporadic AD and from normal aging-dependent cognitive decline. Thus, the human genetic evidence indicates that APP and APP processing are important for normal cognitive functions. To gain insights into the function of APP in the central nervous system, we have characterized the brain interactome of the APP intracellular domain. We isolated several proteins including proteins that regulate synaptic vesicles exocytosis (which we collectively refer to as the APP presynaptic interactome or Appresyome) and a multimolecular complex composing the E3 ligase CRL4CRBN. Interestingly, one of the components of CRL4CRBN, i.e. CRBN, is coded by a gene linked to intellectual disability. Our preliminary studies suggest that APP regulates the probability of release of glutamatergic synaptic vesicles and that this function is regulated by APP processing by BACE1. We also found that CRL4CRBN mediates ubiquitination of Snap25, Vamp2 and Stxbp1, three proteins that regulate synaptic vesicles exocytosis and that are also part of the Appresyome. Of note, CRL4CRBN and the Appresyome bind two distinct regions of the APP intracellular domain. Finally, we found that APLP2, a member of the APP protein family, shares many of these APP functions. In this study we will analyze the role of APP and APLP2 in synaptic transmission as well as the molecular mechanisms underlying it. We will also study how processing of APP (and APLP2) regulates synaptic transmission. Lastly, we will analyze the function of CRL4CRBN and of the CRL4CRBN/APP-CRL4CRBN/APLP2 complexes. Our studies will contribute to our understanding of the synaptic function of APP, BACE1 and CRBN and, perhaps, uncover signaling pathways that may be altered in AD. Thus, this study may shed light on the pathogenesis of AD, as well as unveil novel targets for disease-modifying AD drugs.