LRP AND APP PROCESSING IN NEURODEGENERATION

描述（由申请人提供）：淀粉样β-肽（AB）在脑中的蓄积和毒性是阿尔茨海默病（AD）发病机制中的中心事件。低密度脂蛋白受体相关蛋白（LRP）与β-淀粉样前体蛋白（APP）相互作用，并调节其内吞运输和加工成AB。LRP也是脑中载脂蛋白E（apoE）的主要受体，其调节AB清除、胆固醇代谢和细胞信号传导。以往的研究已经在外周血中检测到了丰富的功能性可溶性LRP（sLRP），我们的初步工作已经在人脑和脑脊液（CSF）中检测到了sLRP。分子和细胞研究已经定义了Notch/APP样的基质金属蛋白酶（MMP）和B-和G-分泌酶的LRP的顺序加工。我们的长期目标是了解LRP蛋白水解如何在大脑中调节和在AD中失调，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运输和加工到AB。我们的初步研究表明，G-分泌酶裂解产物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。我们的研究还确定了一种新的衔接蛋白，分选连接蛋白17（SNX 17），调节内吞贩运和加工的LRP和APP。我们的中心假设是，LRP和APP的蛋白水解加工失调，在AD的病理配体和贩运事件，这反过来又损害LRP的表达和功能的apoE代谢和信号在大脑中。我们提出了四个具体的目标来验证我们的假设：1）鉴定LRP脱落酶并检查改变的LRP脱落对apoE代谢和信号传导的功能影响; 2）检查LRP表达、脱落和蛋白水解在AD小鼠模型中以及在人类衰老和AD期间如何改变; 3）研究APP加工产物和其他g-分泌酶切割事件如何调节LRP表达和功能;分析神经元衔接蛋白对LRP和APP的内吞转运的改变如何影响它们的蛋白水解加工、apoE代谢和AB产生。总之，这些研究应该使我们能够定义在衰老和AD过程中LRP在大脑中的表达、加工和功能的机制和调节。我们提出的研究也可能为AD诊断和治疗确定新的靶点。公共卫生相关性：我们的建议的主要目标是了解载脂蛋白E受体LRP如何进行蛋白水解处理，以及这些细胞事件是如何在大脑中进行调节。由于apoE是阿尔茨海默病的主要危险因素，阿尔茨海默病是老年痴呆症的主要原因，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.