Mechanisms of APP and APLP2 function at synapses

 描述(申请人提供)：阿尔茨海默病(AD)是世界上最常见的衰老依赖型痴呆的原因，与大脑淀粉样斑块有关，主要由Aβ多肽组成。这些多肽是由淀粉样前体蛋白(APP)的双裂解产生的。BACE1裂解产生C-末端片段β-CTF，由β-分泌酶将其加工成几种A-γ亚型。遗传数据表明，APP处理的调节与AD有关。此外，APP的一种多态可以减少BACE1对APP的处理，从而防止散发性AD和正常的依赖衰老的认知能力下降。因此，人类遗传证据表明，APP和APP处理对正常认知功能非常重要。为了深入了解APP在中枢神经系统中的功能，我们对APP细胞内域的大脑相互作用组进行了表征。我们分离了几种蛋白质，包括调节突触小泡胞吐的蛋白质(我们统称为APP突触前相互作用体或Appresyome)和组成E3连接酶CRL4CRBN的多分子复合体。有趣的是，CRL4CRBN的一个组成部分，即CRBN，是由一个与智力残疾有关的基因编码的。我们的初步研究表明，APP调节谷氨酸能突触小泡的释放，这一功能是由BACE1通过APP处理来调节的。我们还发现CRL4CRBN介导Snap25、Vamp2和STXBP1的泛素化，这三种蛋白质调节突触小泡的胞吐，也是Appresyome的一部分。值得注意的是，CRL4CRBN和Appresyome结合了APP胞内域的两个不同区域。最后，我们发现APLP2，APP蛋白家族的成员，分享了许多APP功能。在本研究中，我们将分析APP和APLP2在突触传递中的作用及其分子机制。我们还将研究APP(和APLP2)的处理如何调节突触传递。最后，我们将分析CRL4CRBN和CRL4CRBN/APP-CRL4CRBN/APLP2复合体的功能。我们的研究将有助于我们理解APP、BACE1和CRBN的突触功能，并可能揭示AD可能改变的信号通路。因此，这项研究可能有助于揭示AD的发病机制，并为治疗AD的药物提供新的靶点。

 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.