Neuroprotective signaling and transcriptional pathways in microglia associated with Alzheimer's disease

功能基因组学研究已确定活跃的阿尔茨海默病(AD)风险变异的丰富 人类髓系细胞增强剂。这些数据，以及几个AD风险基因的髓系特异性表达， 这些细胞与阿尔茨海默病的病因密切相关。触发受体的部分功能丧失突变 在髓样细胞2(TREM2)上的表达与AD风险增加有关，表明TREM2具有保护作用 抗神经退行性变。众所周知，小胶质细胞在大脑中发挥着许多有益的功能，包括 清除死亡细胞以及细胞碎片，并协调对组织压力或损伤的复杂反应。 然而，小胶质细胞的慢性激活可导致中毒性神经炎和动态平衡受损。 功能。更好地理解小胶质细胞神经保护功能的潜在机制是 对于确定预防或延迟AD发病的治疗靶点至关重要。使用精细测绘方法，我们有 在许多AD基因座中发现了可能的致病基因。在一个基因座上，编码胚胎外胚层的基因 发育(EED)是一种强有力的候选致病基因，也是一种髓系细胞增强剂的潜在靶点，包括 与AD相关的功能变体。EED是多梳抑制的一个重要的非催化成分 复合体2(PRC2)，其功能是维持抑制性组蛋白标记H3K27me3。调制方式 H3K27me3在炎症刺激后的表观遗传重塑中起关键作用，并已被卷入 小胶质细胞对凋亡细胞的清除。细胞质PrC2(CPRC2)也显示出直接的信号活性， 控制受体驱动的ERK激活以及免疫细胞、细胞过程中的肌动蛋白聚合 与我们的AD遗传学研究有关。此外，我们的初步数据显示，小胶质细胞在 5XFAD背景表型为TREM2-/-。基于这些遗传和生化观察，我们 假设EED和PRC2作为TREM2信号通路的主调节因子 控制PRC2表达水平和活性的基因决定了TREM2驱动的神经保护性小胶质细胞状态。至 验证这一假设，我们提出了4个目标，以检查Eed/PRC2对人和小鼠小胶质细胞的影响 体内外的功能和TREM2信号转导。我们将确定EED/PRC2功能丧失在 小胶质细胞功能和TREM2信号转导系统的体外和体内研究 5XFAD小鼠(目标2)。在目标3中，我们将研究细胞质PRC2对小胶质细胞功能和TREM2的影响 在体外和体内发出信号。在目标4中，我们将使用人类遗传数据来测试AD风险等位基因的丰富程度 在TREM2信号通路基因内和在Eed调控网络中确定SELECT的影响 小胶质细胞功能和TREM2信号转导的等位基因。最后，我们将通过检查以下项的影响来测试上位性 EED+/-对5XFAD小鼠体内TREM2单倍体不足和体外hPSC来源的小胶质细胞的影响。

Functional genomics studies have identified an enrichment for Alzheimer’s disease (AD) risk variants in active enhancers of human myeloid cells. These data, along with myeloid-specific expression of several AD risk genes, strongly implicate these cells in the etiology of AD. Partial loss-of-function mutations in Triggering Receptor Expressed on Myeloid cells 2 (TREM2), linked to increased risk for AD, point to a protective role for TREM2 against neurodegeneration. Microglia are known to play numerous beneficial functions in the brain, including clearance of dying cells as well as cellular debris and orchestrate complex responses to tissue stress or damage. However, chronic activation of microglia can lead to toxic neuroinflammation and impairment of homeostatic functions. A better understanding of the mechanisms underlying the neuroprotective functions of microglia is critical to identifying therapeutic targets to prevent or delay AD onset. Using fine mapping approaches, we have identified likely causal genes within many AD GWAS loci. In one locus, the gene encoding embryonic ectoderm development (EED) is a strong candidate causal gene and a putative target of a myeloid cell enhancer containing an AD-associated functional variant. EED is an essential, non-catalytic component of the polycomb repressive complex 2 (PRC2), which functions to maintain the repressive histone mark H3K27me3. Modulation of H3K27me3 is critical for epigenetic remodeling following inflammatory stimuli and has been implicated in microglial clearance of apoptotic cells. Cytoplasmic PRC2 (cPRC2), also exhibits direct signaling activity, controlling receptor-driven activation of Erk as well as actin polymerization in immune cells, cellular processes implicated by our AD genetics studies. Furthermore, our preliminary data show that microglial Eed-/- on the 5XFAD background phenocopies TREM2-/-. Based on these genetic and biochemical observations we hypothesize that EED and PRC2 operate as a master regulator of the TREM2 signaling pathway and that factors that control PRC2 expression levels and activity define the TREM2 driven neuroprotective microglial state. To test this hypothesis, we propose 4 aims to examine the impact of Eed/PRC2 on both human and mouse microglial function and Trem2 signaling in vitro and in vivo. We will determine the role of EED/PRC2 loss of function on microglial function and TREM2 signaling using both mouse and human microglia in vitro (aim 1) and in vivo in 5XFAD mice (aim 2). In aim 3 we will examine the impact of cytoplasmic PRC2 on microglial function and Trem2 signaling in vitro and in vivo. In aim 4 we will use human genetic data to test for enrichment of AD risk alleles within the Trem2 signaling pathway genes and in the Eed regulatory network and determine the impact of select alleles on microglial function and Trem2 signaling. Finally, we will test for epistasis by examining the impact of Eed+/- on Trem2 haploinsufficiency in 5XFAD mice in vivo and in hiPSC-derived microglia in vitro.