Role of apoE structure and metabolism in neurodegeneration

描述(申请人提供)：载脂蛋白(Apo)E在血浆和中枢神经系统的脂代谢和运输中起关键作用。ApoE是人类三种主要载脂蛋白E亚型之一，apoE4是阿尔茨海默病的主要风险因素，其机制尚不清楚。我们的长期目标是采用结构-功能方法来建立这些机制，目的是确定潜在的治疗干预措施。这项建议侧重于与这一目标相关的两个主要领域。首先，我们将扩展我们的x射线衍射和小角x射线散射模型的分辨率，比较apoE4和apoE3与磷脂结合的结构。其次，我们将继续我们的研究，在我们的研究中，我们将结构域相互作用的apoE4结构属性与神经退行性变以及功能和认知缺陷联系起来。人apoE亚型敲打小鼠和我们的Arg-61 apoE小鼠模型引入结构域相互作用后，apoE4和Arg-61小鼠apoE的水平分别低于apoE3和小鼠野生型apoE。较低的水平是由于星形胶质细胞分泌减少，其中Arg-61 apoE被选择性降解，诱导未折叠的蛋白质应激反应。在这些研究的基础上，我们假设结构域相互作用通过对星形胶质细胞的两种影响促进神经退行性变。1)结构域相互作用被认为是一种异常折叠的蛋白质，导致内质网应激反应，从而导致支持神经元完整性的关键生化途径的下游效应。2)apoE4分泌减少导致支持突触形成和神经元维持的胆固醇水平降低。这一假设代表了一种新的范式，在这种范式中，apoE4结构域的相互作用有助于神经退化和功能和认知缺陷，在没有额外应激源的情况下涉及星形胶质细胞。我们认为，这些影响是载脂蛋白E4携带者的早期事件，并为添加脑应激源(例如，年龄、缺血或A2毒性)而产生更戏剧性的反应奠定了基础。这一范例将载脂蛋白E结构与神经退行性变和功能后果联系起来，并表明干扰结构域相互作用是一种可行的治疗方法。这些研究有可能确定apoE4与阿尔茨海默病和其他形式的神经退行性变的高风险相关的机制，并确定降低这种风险的治疗方法。公共卫生相关性：载脂蛋白E4(ApoE4)是一种大脑蛋白质，是阿尔茨海默病的主要遗传风险因素，尽管这种联系的基础尚不清楚。基于我们的apoE4结构研究，我们提出了一种涉及星形胶质细胞的新机制，星形胶质细胞是大脑中支持和维持神经细胞的细胞。这些研究有可能找到新的治疗方法来逆转载脂蛋白E4对阿尔茨海默病的影响。

DESCRIPTION (provided by applicant): Apolipoprotein (apo) E plays a key role in lipid metabolism and transport in plasma and the central nervous system. One of the three major human apoE isoforms, apoE4, is a major risk factor for Alzheimer's disease by as yet undefined mechanisms. Our long-range objective is to employ a structure-function approach to establish these mechanisms with the goal of identifying potential therapeutic interventions. This proposal focuses on two major areas related to this goal. First, we will extend the resolution of our x-ray diffraction and small-angle x- ray scattering model of apoE4 bound to phospholipids and compare the structures of apoE4 and apoE3 bound to lipid. Secondly, we will continue our studies in which we link the apoE4 structural property of domain interaction to neurodegeneration and functional and cognitive deficits. The brains of human apoE isoform knock in mice and our Arg-61 apoE mouse model in which domain interaction was introduced, contain lower levels of apoE4 and Arg-61 mouse apoE compared to apoE3 and mouse wild-type apoE, respectively. The lower levels were due to decreased secretion by astrocytes, in which the Arg-61 apoE was selectively degraded, inducing an unfolded protein stress response. Based on these studies, we hypothesize that domain interaction contributes to neurodegeneration through two effects on astrocytes. 1) Domain interaction is recognized as an abnormally folded protein, resulting in an endoplasmic reticulum stress response that leads to downstream effects on key biochemical pathways supporting neuronal integrity. 2) Decreased secretion of apoE4 results in lower levels of cholesterol to support synapse formation and neuronal maintenance. This hypothesis represents a novel paradigm in which apoE4 domain interaction contributes to neurodegeneration and functional and cognitive deficits, involving astrocytes in the absence of additional stressors. We believe that these effects are early events in apoE4 carriers and set the stage for more dramatic responses with the addition of brain stressors (e.g. age, ischemia or A2 toxicity). This paradigm links apoE structure with neurodegeneration and functional consequences and suggests that interference with domain interaction is a viable therapeutic approach. These studies hold the potential to determine the mechanisms by which apoE4 is associated with a high risk for Alzheimer's disease and other forms of neurodegeneration and for identifying therapeutic approaches to reduce this risk. PUBLIC HEALTH RELEVANCE: Apolipoprotein E4 (apoE4) a brain protein, is the major genetic risk factor for Alzheimer's disease although the basis for this association is unknown. Based on our apoE4 structure studies, we propose a new mechanism for this association involving astrocytes, which are cells in the brain that support and maintain nerve cells. These studies hold the potential to identify new therapeutic approaches to reverse the effects of apoE4 on Alzheimer's disease.