LRP AND APP PROCESSING IN NEURODEGENERATION

描述（由申请人提供）：淀粉样β肽（AB）在大脑中的积累和毒性是阿尔茨海默病（AD）发病机制的中心事件。低密度脂蛋白受体相关蛋白（LRP）与β -淀粉样蛋白前体蛋白（APP）相互作用，并调节其内吞运输和AB的加工。LRP也是脑内载脂蛋白E （apoE）的主要受体，其调节AB的清除，胆固醇代谢和细胞信号传导。以往的研究在外周细胞中检测到大量的功能性可溶性LRP (sLRP)，我们的初步工作在人脑和脑脊液（CSF）中检测到sLRP。分子和细胞研究已经定义了基质金属蛋白酶（MMP）和b-和g-分泌酶对LRP的Notch/ app样顺序加工。我们的长期目标是了解LRP蛋白水解在大脑中如何被调节，在AD中如何失调，以及这些蛋白水解事件和加工产物如何影响其在apoE代谢和信号传导中的功能，以及APP的运输和AB的加工。我们的初步研究表明，g分泌酶切割产物APP胞内结构域（AICD）通过直接结合LRP启动子来调节LRP的表达和功能。我们的研究还发现了一种新的接头蛋白，分类连接蛋白17 (SNX17)，它调节LRP和APP的内噬运输和加工。我们的中心假设是，LRP和APP的蛋白水解加工在AD中因病理性配体和运输事件而失调，这反过来又损害了LRP在apoE代谢和大脑信号传导中的表达和功能。我们提出了四个具体目标来验证我们的假设：1)鉴定LRP脱落酶，并检查LRP脱落改变对载脂蛋白e代谢和信号传导的功能影响；2)研究LRP的表达、脱落和蛋白水解在阿尔茨海默病小鼠模型中以及在衰老和人类阿尔茨海默病中是如何改变的；3)研究APP加工产物及其他g-分泌酶裂解事件对LRP表达和功能的调控作用；4)分析神经元接头蛋白对LRP和APP的内吞运输改变对其蛋白水解加工、载脂蛋白e代谢和AB产生的影响。总之，这些研究将使我们能够明确衰老和AD期间大脑中LRP的表达、加工和功能的机制和调控。我们提出的研究也可能为阿尔茨海默病的诊断和治疗确定新的靶点。公共卫生相关性：我们建议的主要目的是了解apoE受体LRP如何经历蛋白水解加工以及这些细胞事件如何在大脑中被调节。因为载脂蛋白e是阿尔茨海默病的主要危险因素，阿尔茨海默病是老年人痴呆的主要原因，我们的研究结果可能为阿尔茨海默病的诊断和/或治疗提供知识。

DESCRIPTION (provided by applicant): Amyloid beta-peptide (AB) accumulation and toxicity in the brain are central events in the pathogenesis of Alzheimer's disease (AD). The low-density lipoprotein receptor-related protein (LRP) interacts with beta-amyloid-precursor protein (APP) and regulates its endocytic trafficking and processing to AB. LRP is also a major receptor in the brain for apolipoprotein E (apoE), which modulates AB clearance, cholesterol metabolism, and cellular signaling. Previous studies have detected abundant functional soluble LRP (sLRP) in peripheral and our preliminary work has detected sLRP in human brain and cerebral spinal fluid (CSF). Molecular and cellular studies have defined Notch/APP-like sequential processing of LRP by matrix metalloprotease (MMP) and by b- and g-secretases. Our long-term goal is to understand how LRP proteolysis is regulated in the brain and dysregulated in AD, and how these proteolytic events and processing products impact its function in apoE metabolism and signaling, as well as APP trafficking and processing to AB. Our preliminary studies have shown that a g-secretase cleavage product, APP intracellular domain (AICD), regulates LRP expression and function by directly binding to LRP promoter. Our studies also identified a novel adaptor protein, sorting nexin 17 (SNX17), that modulates endocytic trafficking and processing of both LRP and APP. Our central hypothesis is that LRP and APP proteolytic processing is dysregulated in AD by pathological ligands and trafficking events, and that this in turn impairs LRP expression and function in apoE metabolism and signaling in the brain. We propose four specific aims to test our hypothesis: 1) to identify LRP shedding enzymes and examine the functional impact of altered LRP shedding on apoE metabolism and signaling; 2) to examine how LRP expression, shedding, and proteolysis are altered in AD mouse models and during aging and AD in humans; 3) to study how APP processing products and other g-secretase cleavage events regulate LRP expression and function; and 4) to analyze how altered endocytic trafficking of LRP and APP by neuronal adaptor proteins influences their proteolytic processing, apoE metabolism and AB production. Together, these studies should allow us to define the mechanism and regulation of LRP expression, processing and function in the brain during aging and AD. Our proposed studies may also identify novel targets for AD diagnosis and therapy. PUBLIC HEALTH RELEVANCE: The major objective of our proposal is to understand how an apoE receptor LRP undergoes proteolytic processing and how these cellular events are regulated in the brain. Because apoE is a major risk factor for Alzheimer's disease, a leading cause of dementia in elderly, our results may provide knowledge for diagnosis and/or therapy for Alzheimer's disease.