APOE4 Causes Widespread Molecular and Cellular Alterations Associated with Alzheimer's Disease Phenotypes in Human iPSC-Derived Brain Cell Types

The apolipoprotein E4 (APOE4) variant is the single greatest genetic risk factor for sporadic Alzheimer's disease (sAD). However, the cell-type-specific functions of APOE4 in relation to AD pathology remain understudied. Here, we utilize CRISPR/Cas9 and induced pluripotent stem cells (iPSCs) to examine APOE4 effects on human brain cell types. Transcriptional profiling identified hundreds of differentially expressed genes in each cell type, with the most affected involving synaptic function (neurons), lipid metabolism (astrocytes), and immune response (microglia-like cells). APOE4 neurons exhibited increased synapse number and elevated Ab42 secretion relative to isogenic APOE3 cells while APOE4 astrocytes displayed impaired Ab uptake and cholesterol accumulation. Notably, APOE4 microglia-like cells exhibited altered morphologies, which correlated with reduced Ab phagocytosis. Consistently, converting APOE4 to APOE3 in brain cell types from sAD iPSCs was sufficient to attenuate multiple AD-related pathologies. Our study establishes a reference for human cell-type-specific changes associated with the APOE4 variant. We used CRISPR/Cas9 to create isogenic APOE3 and APOE4 human iPSC lines that enable us to carry out comprehensive analysis of biochemical, cellular, and transcriptional changes by APOE variants in multiple iPSC-derived brain cell types

载脂蛋白E4（apolipoprotein E4, APOE4）变异体是散发性阿尔茨海默病（sporadic Alzheimer's disease, sAD）最主要的单一遗传风险因子。然而，APOE4在细胞类型特异性层面与AD病理相关的功能仍未得到充分研究。本研究借助CRISPR/Cas9技术与诱导多能干细胞（induced pluripotent stem cells, iPSCs），探究APOE4对人类脑细胞类型的影响。转录组分析（transcriptional profiling）在每种细胞类型中均鉴定出数百个差异表达基因，其中受影响最为显著的功能模块涉及突触功能（神经元）、脂质代谢（星形胶质细胞）以及免疫应答（小胶质样细胞）。与同基因型的APOE3细胞相比，APOE4神经元的突触数量增多且Ab42分泌水平升高；而APOE4星形胶质细胞则表现出Ab摄取受损与胆固醇蓄积。值得注意的是，APOE4小胶质样细胞的形态发生异常，这与Ab吞噬能力降低密切相关。一致的是，在源自sAD iPSCs的脑细胞类型中将APOE4转化为APOE3，足以缓解多种AD相关病理特征。本研究为与APOE4变异体相关的人类细胞类型特异性分子变化建立了参考数据集。我们通过CRISPR/Cas9技术构建了同基因型的APOE3与APOE4人类iPSC细胞系，借此可全面分析多种iPSC源性脑细胞类型中APOE变异体介导的生化、细胞及转录组变化。