Study the Underlying Mechanisms of an Alzheimer’s-Disease-Protective ApoE Mutation

项目摘要 阿尔茨海默病(AD)是最常见的痴呆症，目前影响着美国10%的人口 65岁以上的人。AD的最大遗传风险因素是载脂蛋白(Apo)E4的存在，这一发现 在50-75%的AD病例中。ApoE4加剧了阿尔茨海默病的经典分子病理学： 细胞外淀粉样β蛋白(Aβ)斑块和神经元内神经纤维缠结的积聚 过度磷酸化的tau(p-tau)。越来越多的证据将apoE4毒性与增强tau病理联系起来。 尽管阿尔茨海默病在患者中普遍存在，并且对阿尔茨海默病的分子发病机制进行了数十年的研究，但 载脂蛋白E4‘S的致病机制尚不完全清楚。 然而，最近的一项发现进一步强调了载脂蛋白E在AD的tau发病机制中的重要作用。 一名患有PSEN1-E280A的患者，是早发性阿尔茨海默病的一种强穿透性因果突变， 被发现被保护了20多年不受其临床影响。值得注意的是，她表现出轻微的tau病变。 尽管有非常高的Aβ负担。对临床效果的抵抗归因于一种罕见的 ApoE的变种，apoE3-R136S。保护AD的apoE3-R136S变体的一个显著功能特征是 减少与硫酸肝素蛋白多糖(HSPGs)的结合，HSPG是tau内化所必需的关键受体。这 这并不令人惊讶，因为对HSPG亲和力降低的罕见载脂蛋白E变体，如APOE2，似乎也提供了 增加对患阿尔茨海默氏症风险的保护。 了解R136S突变的保护机制将解决一个基本的未知问题： R136S突变是否对影响大多数阿尔茨海默病患者的apoE4的毒性效应具有保护作用 疾病患者。越来越多的证据证实载脂蛋白E受体在病理性tau摄取和扩散中的作用。 因此，研究载脂蛋白E受体结合区的R136S突变是如何 通过限制病理性tau负荷水平挽救apoE4亚型的毒性和功能障碍 神经元。这一建议的中心假设是载脂蛋白E受体结合中的R136S突变 区域通过调节tau磷酸化和/或对apoE4驱动的tau病理具有保护作用 神经元通过特定的载脂蛋白E受体途径摄取P-tau。目标1中提出的实验将确定 如果apoE4-R136S在转录和蛋白质水平上改变了激酶和磷酸酶的平衡， 在人类诱导多能干细胞(HiPSC)来源的神经元中，tau的磷酸化状态负责， 如果是这样，以细胞自主或非细胞自主的方式。AIM 2将调查R136S 突变通过特定的apoE受体调节HiPSC来源神经元对p-tau的摄取。这次会议的结果 拟议的研究将揭示R136S突变如何在晚期赋予apoE4对tau病理的抵抗力。 发病阿尔茨海默病，并潜在地确定具有治疗意义的阿尔茨海默病的细胞靶点。

Project Summary Alzheimer's disease (AD) is the most common dementia, currently affecting 10% of the US population over age of 65. The strongest genetic risk factor for AD is the presence of apolipoprotein (apo) E4, which is found in 50–75% of AD cases. ApoE4 exacerbates the classic molecular pathologies of Alzheimer's disease: accumulation of extracellular amyloid-beta (Aβ) plaques and intraneuronal neurofibrillary tangles composed of hyperphosphorylated tau (p-tau). Increasing evidence connects apoE4 toxicity to enhancing tau pathology. Despite its prevalence in patients and decades of research on the molecular pathogenesis of AD, the mechanisms of apoE4's detrimental effects remain incompletely understood. However, a recent discovery further highlights the important role apoE plays in tau pathogenesis in AD. A patient with PSEN1-E280A, a strongly penetrant causal mutation for early onset Alzheimer's disease, was found to be protected from its clinical effects for over 20 years. Significantly, she displayed minimal tau pathology in spite of having very high Aβ burden. The resistance to clinical effects were attributed to the presence of a rare variant of apoE, apoE3-R136S. One notable functional feature of the AD-protective apoE3-R136S variant is a reduced binding to heparin sulfate proteoglycans (HSPGs), a key receptor necessary for tau internalization. This is unsurprising as rare apoE variants with decreasing affinity for HSPGs, such as apoE2, also appear to confer increasing protection against this risk of developing Alzheimer's disease. Understanding the protective mechanisms of the R136S mutation will address a fundamental unknown: whether the R136S mutation protects against the toxic effects of apoE4, which affect the majority of Alzheimer's disease patients. Growing evidence confirms the role of apoE receptors in pathological tau uptake and spread. Therefore, it is important to investigate how this R136S mutation in the receptor-binding region of apoE can rescue the toxicity and dysfunction of the apoE4 isoform by limiting the level of pathological tau burden in neurons. The central hypothesis of this proposal is that the R136S mutation in the apoE receptor-binding region is protective against apoE4-driven tau pathology through modulating tau phosphorylation and/or p-tau uptake by neurons via specific apoE receptor pathways. Experiments proposed in Aim 1 will determine if apoE4-R136S alters the balance of kinases and phosphatases, at the transcriptomic and protein levels, responsible for the phosphorylation state of tau in human induced pluripotent stem cell (hiPSC)-derived neurons, and if so, in a cell-autonomous or non-cell-autonomous manner. Aim 2 will investigate whether the R136S mutation modulates p-tau uptake by hiPSC-derived neurons via specific apoE receptors. The outcomes of the proposed studies will reveal how the R136S mutation confers the resistance of apoE4 to tau pathology in late- onset AD and potentially identify cellular targets with therapeutic implications for Alzheimer's disease.