Nicastrin and Presenilin-dependent gamma-secretase

描述(申请人提供)：阿尔茨海默病(AD)是一种进行性的老年人神经退行性疾病，其特征是贝塔淀粉样蛋白(ABeta)沉积和海马区和大脑皮层的神经原纤维缠结。分泌酶对淀粉样前体蛋白(APP)的内切蛋白降解导致ABeta多肽的产生，据信ABeta多肽具有神经毒性。早老素(PS1和PS2)，当突变时会导致家族性阿尔茨海默病，对于包括APP和Notch1在内的几种蛋白质的膜内蛋白分解是重要的。早老素是含有伽马分泌酶的高分子量复合体的一部分。对这个Gamma7-分泌酶复合体至关重要的是另一种I型跨膜糖蛋白，称为Nicastin，它与APP和Notch1结合，是GLP-1/Notch信号转导所必需的。最近在尼古丁缺乏的果蝇中的研究表明，尼古丁的丢失取消了依赖于早老素的Notch的膜内蛋白分解。因此，我们假设在哺乳动物中，尼卡斯特素是Notch1蛋白降解处理和信号传递所必需的。我们计划首先确定尼古丁水平降低是否通过产生尼古丁缺乏小鼠来影响哺乳动物早老素介导的Notch信号转导，并表征尼古丁水平降低的表型后果。其次，由于研究表明尼古丁在APP的加工过程中起着重要作用，我们将利用尼古丁基因敲除细胞来检测尼古丁在早老素介导的APP伽马分泌酶裂解中的作用。此外，我们还将确定尼卡泌素影响早老素促进Notch和APP跨膜切割的机制。最后，为了检验尼古丁在成人大脑中的体内作用，我们将产生并鉴定尼古丁条件性基因敲除小鼠。综上所述，这些努力的结果将对我们理解尼古丁影响早老素促进包括Notch和APP在内的几个关键途径上的早老素依赖的伽马分泌酶活性的机制以及尼卡泌素作为阿尔茨海默病潜在治疗靶点的机制具有重要意义。

DESCRIPTION (provided by applicant): Alzheimer's disease (AD), a progressive neurodegenerative disorder of the elderly, is characterized by the deposition of Beta-amyloid (ABeta) and neurofibrillary tangles in the hippocampus and cerebral cortex. Endoproteolytic cleavages of amyloid precursor protein (APP) by secretases result in the generation of ABeta peptides that are believed to be neurotoxic. The presenilins (PS1 and PS2), which when mutated cause familial Alzheimer's disease, are important for the intramembraneous proteolysis of several proteins, including APP and Notch1. The presenilins is part of a high molecular weight complex that contains the gamma-secretase. Critical to this gamma7-secretase complex is another type I transmembrane glycoprotein, termed nicastrin that binds to both APP and Notch1 and is required for glp-1/notch signaling. Recent studies in nicastrin-deficient Drosophila demonstrate that the loss of nicastrin abolishes the presenilin-dependent intramembraneous proteolysis of Notch. Thus, we hypothesize that nicastrin is required for proteolytic processing and signaling of Notch1 in mammals. We plan first to determine whether reduced levels of nicastrin impact on presenilin-mediated Notch signaling in mammals by generating nicastrin-deficient mice and characterize the phenotypic consequences of reduction in nicastrin. Secondly, because studies indicated that nicastion plays an important role in APP processing, we will test the role of nicastrin in presenilin-mediated gamma-secretase cleavage of APP using nicastrin knockout cells. In addition, we will determine the mechanism whereby nicastrin influences presenilins to facilitate transmembrane cleavage of Notch and APP. Finally, to examine the in vivo role of nicastrin in adult brain, we will generate and characterize nicastrin conditional knockout mice. Taken together, outcomes from these efforts will have important implications toward our understanding of the mechanism whereby nicastrin influences presenilins in facilitating the presenilin-dependent gamma-secretase activities on several critical pathways, including Notch and APP, as well as for nicastrin as a potential therapeutic target in Alzheimer's disease.