Probing SORL1 Risk Factors with Human Induced Pluripotent Stem Cell Technology

项目1：摘要。 理解并最终治疗阿尔茨海默病(AD)的一个关键问题是我们的不完整 了解遗传危险因素在晚发性散发性阿尔茨海默病(SAD)中的作用。虽然没有明确的 导致SAD的单个遗传损伤，观察到的高遗传率表明个体遗传 背景在其中扮演着重要的角色。在这里，我们提出了人类诱导多能性的独特应用 干细胞(HiPSC)技术剖析个体遗传背景和识别的风险因素 易感人类神经元的SAD生化表型，并将该信息与临床数据联系起来 对个别患者和身体进行病理检查。我们的工作是基于我们最近的发现，使用 验证R单倍型导致SORL1普遍减少的假设的HiPSC技术 表达导致淀粉样β蛋白(A？)多肽增加和由此导致的SAD[3，7- 10]。利用HiPSC技术，我们发现R单倍型削弱了SORL1基因的信号输入。 具体地说，P单倍型通过诱导SORL1表达来响应BDNF，而R单倍型不能。 基础表达水平与R或P单倍型无相关性。因此，SORL1的遗传贡献 SAD可能是由活体人类神经元中复杂的调节变异引起的。我们现在建议测试一下 我们的工作模型是关于SORL1单倍型如何影响SAD神经元表型，从而导致SAD风险 人体在体外，在人体内也有病人。我们建议检验：1)BDNF诱导的假设 SORL1表达调控APP及其下游SAD相关淀粉样蛋白的形成 生化变化；2)假设SORL1单倍型对神经细胞表型的影响。 体外实验反映了SAD患者的临床数据，特别是BDNF和SORL1的相对数量 脑脊液蛋白质和死后神经病理表型。在一个相关的目标中，我们 将调查从我们收集的患者HiPSC系中获得的纯化神经元是否与 个别患者的临床行为。目前，我们只有太少的HiPSC系，无法确定 关联度严格，但考虑到线路的存在，我们将开始收集比较 将数据作为促进未来研究的一种方式。总而言之，这些实验将提供关于 SORL1变异对人类不同基因神经元SAD表型的影响细节 背景和可能导致药物发现和临床试验分层的新途径 基于遗传背景。我们的具体目标是：1.检验简化的BDNF 具有SORL1风险变异单倍型的纯化人神经元的诱导反应增强SORL1- 依赖下游生化SAD表型。2.检验这样一种假设，即 SORL1基因座的患者对脑脊液或脑脊液中的临床表型标记物有显著影响 是死后病理造成的。

PROJECT 1: ABSTRACT. A key problem in understanding and eventually treating Alzheimer's disease (AD) is our incomplete understanding of the role of genetic risk factors in late-onset, sporadic AD (SAD). While there is no clear single genetic lesion that causes SAD, the observed high heritability suggests that individual genetic background plays a significant role. Here we propose unique applications of human induced pluripotent stem cell (hIPSC) technology to dissect how individual genetic background and identified risk factors predispose to SAD biochemical phenotypes in human neurons and to link that information to clinical data on individual patients and to post-mortem pathology. We are basing our work on our recent finding using hIPSC technology that tested the hypothesis that R haplotypes cause general reduction of SORL1 expression leading to increased amyloid beta (Aß) peptides and consequent risk of developing SAD [3, 7- 10]. Using hIPSC technology we found that R haplotypes impair a signaling input to the SORL1 gene. Specifically, P haplotypes respond to BDNF by inducing SORL1 expression, while R haplotypes do not. Basal expression levels show no correlation with R or P haplotypes. Thus, the SORL1 genetic contribution to SAD may be caused by complex regulatory variation in living human neurons. We now propose to test our working model for how SORL1 haplotypes contribute to SAD neuronal phenotypes and thus SAD risk in humans in vitro, and in vivo in human patients. We propose to test: 1) the hypothesis that BDNF-induced SORL1 expression modulates amyloidogenic processing of APP and downstream SAD-associated biochemical changes; and 2) the hypothesis that effects of SORL1 haplotype on neuronal phenotypes in vitro are mirrored in clinical data on SAD patients, specifically the relative amounts of BDNF and SORL1 proteins in cerebrospinal fluid (CSF) and post-mortem neuropathological phenotypes. In a related goal, we will investigate whether purified neurons made from our collection of patient hIPSC lines correlates with clinical behavior of individual patients. At present, we have too few hIPSC lines to definitively establish the degree of correlation rigorously, but given the existence of the lines, we will begin to collect comparative data as a way of contributing to future studies. Together, these experiments will provide new data about the details of SORL1 variant contributions to SAD phenotypes in human neurons with differing genetic backgrounds and potentially lead to new pathways for drug discovery and stratification of clinical trials based on genetic background. Our specific aims are to: 1. Test the hypothesis that the reduced BDNF induction response of purified human neurons with SORL1 risk variant haplotypes enhances SORL1- dependent downstream biochemical SAD phenotypes. 2. To test the hypothesis that the genetic status of patients at the SORL1 locus has a significant influence on clinical phenotypic markers measured in CSF or by post-mortem pathology.