BACKGROUND The apolipoprotein E (APOE) gene is the strongest genetic risk factor for late-onset Alzheimer disease (AD). ApoE is produced by both astrocytes and microglia in the brain, whereas hepatocytes produce the majority of apoE found in the periphery. Studies using APOE knock-in and transgenic mice have demonstrated a strong isoform-dependent effect of apoE on the accumulation of amyloid-β (Aβ) deposition in the brain in the form of both Aβ-containing amyloid plaques and cerebral amyloid angiopathy. However, the specific contributions of different apoE pools to AD pathogenesis remain unknown. METHODS We have begun to address these questions by generating new lines of APOE knock-in (APOE-KI) mice (ε2/ε2, ε3/ε3, and ε4/ε4) where the exons in the coding region of APOE are flanked by loxP sites, allowing for cell type-specific manipulation of gene expression. We assessed these mice both alone and after crossing them with mice with amyloid deposition in the brain. Using biochemical and histological methods. We also investigated how removal of APOE expression from hepatocytes affected cerebral amyloid deposition. RESULTS As in other APOE knock-in mice, apoE protein was present predominantly in astrocytes in the brain under basal conditions and was also detected in reactive microglia surrounding amyloid plaques. Primary cultured astrocytes and microglia from the APOE-KI mice secreted apoE in lipoprotein particles of distinct size distribution upon native gel analysis with microglial particles being substantially smaller than the HDL-like particles secreted by astrocytes. Crossing of APP/PS1 transgenic mice to the different APOE-KI mice recapitulated the previously described isoform-specific effect (ε4 > ε3) on amyloid plaque and Aβ accumulation. Deletion of APOE in hepatocytes did not alter brain apoE levels but did lead to a marked decrease in plasma apoE levels and changes in plasma lipid profile. Despite these changes in peripheral apoE and on plasma lipids, cerebral accumulation of amyloid plaques in APP/PS1 mice was not affected. CONCLUSIONS Altogether, these new knock-in strains offer a novel and dynamic tool to study the role of APOE in AD pathogenesis in a spatially and temporally controlled manner.

中文翻译：

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缺乏肝apoE不会影响早期Aβ沉积：来自新的APOE敲入模型的观察结果。

背景载脂蛋白E（APOE）基因是迟发性阿尔茨海默病（AD）的最强遗传危险因素。ApoE由大脑中的星形胶质细胞和小胶质细胞共同产生，而肝细胞则产生在外周发现的大部分apoE。使用APOE敲入和转基因小鼠的研究表明apoE对脑中淀粉样β（Aβ）沉积具有强烈的同种型依赖性，其形式为含Aβ的淀粉样斑块和脑淀粉样血管病。但是，不同的apoE库对AD发病机制的具体贡献仍然未知。方法我们已经开始通过生成新的APOE敲入（APOE-KI）小鼠系（ε2/ε2，ε3/ε3和ε4/ε4）来解决这些问题，其中APOE编码区中的外显子侧翼为loxP网站，允许对细胞类型进行基因表达的特异性操作。我们单独评估了这些小鼠，并将它们与具有淀粉样蛋白沉积在大脑中的小鼠杂交后进行了评估。使用生化和组织学方法。我们还调查了如何从肝细胞中去除APOE表达影响脑淀粉样蛋白沉积。结果与其他APOE敲入小鼠一样，apoE蛋白主要存在于基础条件下的大脑星形胶质细胞中，并且在淀粉样蛋白斑块周围的反应性小胶质细胞中也检测到。在天然凝胶分析中，来自APOE-KI小鼠的原代培养的星形胶质细胞和小胶质细胞在大小不同的脂蛋白颗粒中分泌apoE，其中小胶质颗粒明显小于星形胶质细胞分泌的HDL样颗粒。将APP / PS1转基因小鼠与不同的APOE-KI小鼠杂交后，可以概括上述同种型对淀粉样斑块和Aβ积累的特异效应（ε4>ε3）。肝细胞中APOE的删除不会改变脑apoE的水平，但会导致血浆apoE的水平显着下降和血浆脂质谱的变化。尽管外围apoE和血浆脂质发生了这些变化，但APP / PS1小鼠的淀粉样蛋白斑块在大脑中的蓄积并未受到影响。结论总的来说，这些新的敲入菌株为以空间和时间控制的方式研究APOE在AD发病机理中的作用提供了一种新颖而动态的工具。肝细胞中APOE的删除不会改变脑apoE的水平，但会导致血浆apoE的水平显着下降和血浆脂质谱的变化。尽管外围apoE和血浆脂质发生了这些变化，但APP / PS1小鼠的淀粉样蛋白斑块在大脑中的蓄积并未受到影响。结论总的来说，这些新的敲入菌株为以空间和时间控制的方式研究APOE在AD发病机理中的作用提供了一种新颖而动态的工具。肝细胞中APOE的删除不会改变脑apoE的水平，但会导致血浆apoE的水平显着下降和血浆脂质谱的变化。尽管外围apoE和血浆脂质发生了这些变化，但APP / PS1小鼠的淀粉样蛋白斑块在大脑中的蓄积并未受到影响。结论总的来说，这些新的敲入菌株为以空间和时间控制的方式研究APOE在AD发病机理中的作用提供了一种新颖而动态的工具。