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10%的美国人口 超过65岁。AD最强的遗传风险因素是载脂蛋白（apo）E4的存在， 在50-75%的AD病例中。ApoE 4加剧了阿尔茨海默病的经典分子病理学： 细胞外淀粉样蛋白β（Aβ）斑块和神经元内神经元缠结的积累， 过度磷酸化的tau（p-tau）。越来越多的证据将apoE 4毒性与增强tau病理学联系起来。 尽管其在患者中的流行以及数十年来对AD分子发病机制的研究， apoE 4有害作用的机制仍不完全清楚。 然而，最近的发现进一步强调了apoE在AD中tau发病机制中的重要作用。 一名携带PSEN 1-E280 A（一种早发性阿尔茨海默病的强外显因果突变）的患者， 被发现在20多年的临床效果中得到保护。值得注意的是， 尽管Aβ负荷很高。对临床效果的抵抗归因于一种罕见的 apoE的变体，apoE 3-R136 S。AD保护性apoE 3-R136 S变体的一个显著功能特征是 与硫酸肝素蛋白聚糖（HSPG）的结合减少，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apoE变体，如apoE 2，似乎也赋予了 增加对阿尔茨海默病风险的保护。 了解R136 S突变的保护机制将解决一个基本的未知问题： R136 S突变是否可以保护apoE 4的毒性作用，apoE 4影响大多数阿尔茨海默氏症患者， 疾病患者。越来越多的证据证实了apoE受体在病理性tau摄取和扩散中的作用。 因此，研究apoE受体结合区的R136 S突变如何影响apoE的表达具有重要意义。 通过限制apoE 4同种型中病理性tau负荷的水平来挽救apoE 4同种型的毒性和功能障碍， 神经元该建议的中心假设是apoE受体结合蛋白中的R136 S突变， 区域通过调节tau磷酸化来保护免受apoE 4驱动的tau病理，和/或 神经元通过特定的apoE受体途径吸收p-tau。目标1中提出的实验将确定 如果apoE 4-R136 S在转录组和蛋白质水平上改变激酶和磷酸酶的平衡， 负责人诱导多能干细胞（hiPSC）衍生的神经元中tau的磷酸化状态， 并且如果是，则以小区自主或非小区自主的方式。Aim 2将调查R136 S是否 突变通过特异性apoE受体调节hiPSC衍生的神经元对p-tau的摄取。的成果 拟议的研究将揭示R136 S突变如何赋予apoE 4对晚期tau病变的抗性， 并可能鉴定出对阿尔茨海默病具有治疗意义的细胞靶点。

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.