Targeting Endosomal dysfunction as a new source of biomarkers for Alzheimer's disease

内体功能障碍是阿尔茨海默病（AD）公认的细胞生物学特征。然而，在这方面， 仍然缺乏反映内体运输缺陷的生物标志物。当前成像和脑脊液（CSF） AD生物标志物主要集中在疾病的组织病理学上-即，与AD相关的生物标志物。 神经纤维缠结和淀粉样斑块。这项建议旨在扩大这一重点，以发展 AD的“细胞生物学”的生物标志物。这些生物标志物可能会加速药物发现， 目前正在开发靶向AD中的内体运输缺陷的治疗干预。 遗传和细胞生物学研究先前已经将内体运输组装体Retromer与 AD病理学最值得注意的是retromer核心蛋白VPS 35的缺陷和罕见突变， retromer受体SORL 1。VPS 35或SORL 1的耗尽模拟AD中的核心细胞病理学，放大 神经元中的内体，伴随着内体货物的错误运输。 为了描述由retromer功能障碍引起的内吞途径的缺陷，我们最近 完成了VPS 35敲除（KO）小鼠和对照同窝出生仔的CSF的蛋白质组学筛选。在VPS 35 KO小鼠CSF中发现升高的蛋白质中，有公认的β-分泌酶BACE 1底物，包括APP（淀粉样前体蛋白）、APLP 1/2（淀粉样β前体样蛋白1和2）和CHL 1（神经细胞粘附分子L1样蛋白）。这些蛋白质中的两种-APLP 1和CHL 1-在小鼠CSF和来自认知健康参与者和前驱AD患者的人CSF中得到进一步验证。总的来说，我们的研究表明BACE 1底物作为逆转录酶依赖性内体功能障碍的潜在生物标志物。 然而，由于VPS 35涉及其他神经退行性疾病，包括帕金森病（PD）， 这些新的生物标志物可能不是AD特异性的。因此，依靠这些令人兴奋的发现， 旨在开发一组反映内体运输缺陷的生物标志物， AD，我们将检查SORL 1小鼠模型和人多能干细胞（hPSC）SORL 1衍生的神经元 作为内体运输生物标志物的新来源。我们还将研究外泌体， 内体缺陷生物标志物的来源。最后，由于Sorl 1蛋白水平在AD和CSF中发生改变， 对于AD患者，我们将检查SORL 1 CSF水平作为AD的潜在生物标志物。完成本研究将 提供了SORL 1依赖性内体运输是AD生物标志物新来源的证据。 此外，我们预测，这里提出的广泛研究将确定一个独特的和具体的 AD的“细胞生物学”的内体生物标志物。

Endosomal dysfunction is a well-accepted cell biological feature in Alzheimer’s disease (AD). However, biomarkers reflecting endosomal traffic defects are still lacking. Current imaging and cerebrospinal fluid (CSF) AD biomarkers focus primarily on the histopathology of the disease—that is, biomarkers that are linked to neurofibrillary tangles and amyloid plaques. This proposal is designed to expand this focus to develop biomarkers of the ‘cell biology’ of AD. Such biomarkers could potentially accelerate drug discovery, as therapeutic interventions are currently being developed that target endosomal trafficking defects in AD. Genetic and cell biology studies have previously linked the endosomal trafficking assembly Retromer to AD pathology. Most notable are deficiencies and rare mutations in retromer’s core protein, VPS35, and retromer’s receptor, SORL1. Depletion of either VPS35 or SORL1 mimics the core cytopathology in AD, enlarged endosomes in neurons, with concomitant mis-trafficking of endosomal cargoes. In an effort to characterize defects in the endocytic pathway resulting from retromer dysfunction, we recently completed a proteomic screen of CSF of VPS35 knock-out (KO) mice and control littermates. Among the proteins found elevated in the CSF of VPS35 KO mice were well established β-secretase BACE1 substrates, includingAPP (Amyloid Precursor Protein); APLP1/2 (Amyloid Beta Precursor Like Proteins 1 and 2); and CHL1 (Neuralcell adhesion molecule L1-like protein). Two of these proteins --APLP1 and CHL1-- were further validated inmouse CSF, and human CSF from cognitively healthy participants and prodromal AD patients. Collectively, our studies suggest BACE1 substrates as potential biomarkers of retromer-dependent endosomal dysfunction. However, since VPS35 is implicated in other neurodegenerative disorders, including Parkinson’s disease (PD), these new biomarkers may not be specific to AD. Therefore, relying on these exciting findings, but moving towards the development of a panel of biomarkers reflecting endosomal trafficking defects that are specific to AD, we will examine SORL1 mouse models and human pluripotent stem cell (hPSC) SORL1-derived neurons as a new source of biomarkers of endosomal trafficking. We will also investigate exosomes as an additional source of biomarkers of endosomal defects. Lastly, since Sorl1 protein levels are altered in AD and CSF from AD patients, we will examine SORL1 CSF levels as a potential biomarker for AD. Completion of this study will provide evidence that SORL1-dependent endosomal trafficking is a new source of biomarkers for AD. Moreover, we predict that the extensive studies here proposed will identify a unique and specific endosomal biomarker of the “cell biology” of AD.