The role of TREM2 in human microglial function and Alzheimer disease pathogenesis

描述（由申请人提供）：阿尔茨海默病（AD）是年龄相关性痴呆的主要原因，仅在美国就影响了500多万人。不幸的是，目前的治疗方法在很大程度上是姑息性的，几种有前途的候选药物在后期临床试验中失败了。因此，迫切需要提高我们对晚发型AD发展的基本机制的理解。最近的遗传学研究发现了一些影响AD风险的基因。虽然这些基因中的许多赋予AD风险的小幅增加，但最近发现的一种基因，触发髓样细胞表达受体2（TREM 2），使AD风险增加约3倍。然而，TREM 2在脑中的功能及其在AD发病机制中的作用在很大程度上仍然未知。在这里，我们将进行一些研究，以检验TREM 2突变损害小胶质细胞介导的β-淀粉样蛋白（Aβ）清除，加剧tau病理的促炎诱导，并改变神经元健康的假设。为了实现这些目标，我们将从携带TREM 2中R47 H突变的AD患者中产生诱导多能干细胞（iPSC）。然后使用TALEN介导的基因编辑技术修复这种突变，以创建同基因突变体和对照iPSC。由于小胶质细胞是大脑中表达TREM 2的主要细胞类型，我们将使iPSC分化为小胶质细胞，并检查TREM 2突变对小胶质细胞功能的影响。首先，使用体外方法，我们将量化TREM 2 R47 H突变对小胶质细胞迁移和激活状态、Aβ吞噬作用和神经元活力的影响。由于小胶质细胞是固有的可塑性细胞，它们的功能和激活状态受到大脑中其他细胞类型的显著影响。因此，我们还将通过将iPSC衍生的小胶质细胞移植到两种新的异种移植相容的AD转基因小鼠模型中来研究TREM 2突变在体内的影响。对这些小鼠的检查将使我们能够确定TREM 2突变是否改变Aβ的降解或调节体内tau病理学的进展。使用荧光激活细胞分选方法，我们还将确定AD病理对小胶质细胞基因表达和激活状态的影响。总之，这些研究希望破译TREM 2突变影响AD的机制，并对小胶质细胞和炎症过程在AD发病机制中的作用提供更广泛的理解。

DESCRIPTION (provided by applicant): Alzheimer disease (AD) is the leading cause of age-related dementia, affecting over 5 million people in the United States alone. Unfortunately, current therapies are largely palliative and several promising drug candidates have failed in late-stage clinical trials. Hence, there is urgent need to improve our understanding of the basic mechanisms that drive the development of late-onset AD. Recent genetic studies have uncovered a number of genes that influence the risk of developing AD. While many of these gene confer small increases in the risk of AD, one recently discovered gene, triggering receptor expressed on myeloid cells 2 (TREM2), increases AD risk by about 3-fold. Yet the function of TREM2 in the brain and its role in AD pathogenesis remains largely unknown. Here, we will perform a number of studies to test the hypothesis that mutations in TREM2 impair microglial-mediated clearance of beta-amyloid (Aβ), exacerbate the pro-inflammatory induction of tau pathology, and alter neuronal health. To achieve these goals, we will generate induced pluripotent stem cells (iPSCs) from AD patients carrying the R47H mutation in TREM2. This mutation will then be repaired using TALEN-mediated gene editing technology to create isogenic mutant and control iPSCs. As microglia are the primary cell type within the brain that express TREM2, we will differentiate iPSCs into microglia and examine the effects of TREM2 mutations on microglia function. First, using in vitro approaches, we will quantify the effects of TREM2 R47H mutations on microglia migration and activation state, Aβ phagocytosis, and neuronal viability. As microglia are inherently plastic cells, their function and activation state s dramatically influenced by other cell types within the brain. We will therefore also study the effects of TREM2 mutations in vivo by transplanting iPSC-derived microglia into two novel xenotransplantation-compatible transgenic mouse models of AD. Examination of these mice will allow us to determine whether TREM2 mutations alter the degradation of Aβ or modulate the progression of tau pathology in vivo. Using fluorescence activated cell sorting approaches we will also determine the impact of AD pathology on microglia gene expression and activation state. Together, these studies hope to decipher the mechanisms by which TREM2 mutations influence AD and provide a broader understanding of the role of microglia and inflammatory processes in AD pathogenesis.