Rohn Troy T, Beck James D, Galla Stephanie J, Isho Noail F, Pollock Tanner B, Suresh Tarun, Kulkarni Arni, Sanghal Tanya, Hayden Eric J
Department of Biological Sciences, Boise State University, USA.
University of Washington School of Medicine, University of Washington, USA.
Int J Neurodegener Dis. 2021;4(1). doi: 10.23937/2643-4539/1710020. Epub 2021 Sep 10.
The apolipoprotein E4 () allele represents the single greatest risk factor for late-onset Alzheimer's disease (AD) and accumulating evidence suggests that fragmentation with a toxic-gain of function may be a key molecular step associated with this risk. Recently, we demonstrated strong immunoreactivity of a 151 amino-terminal fragment of apoE4 (E4-fragment) within the nucleus of microglia in the human AD brain. In vitro, this fragment led to toxicity and activation of inflammatory processes in BV2 microglia cells. Additionally, a transcriptome analysis following exogenous treatment of BV2 microglia cells with this E4 fragment led to a > 2-fold up regulation of 1,608 genes, with many genes playing a role in inflammation and microglia activation. To extend these findings, we here report a similar transcriptome analysis in BV2 microglia cells following treatment with full-length ApoE4 (FL-ApoE4). The results indicated that full-length ApoE4 had a very small effect on gene expression compared to the fragment. Only 48 differentially expressed genes (DEGs) were identified (p < 0.05, and greater than 2-fold change). A gene ontology analysis of these DEGs indicated that they are not involved in inflammatory and activation processes, in contrast to the genes up regulated by the E4-fragment. In addition, genes that showed a negative fold-change upon FL-E4 treatment typically showed a strong positive fold-change upon treatment with the fragment (Pearson's r = -0.7). Taken together, these results support the hypothesis that a key step in the conversion of microglia to an activated phenotype is proteolytic cleavage of FL-ApoE4. Therefore, the neutralization of this amino-terminal fragment of ApoE4, specifically, may serve as an important therapeutic strategy in the treatment of AD.
载脂蛋白E4（）等位基因是晚发性阿尔茨海默病（AD）的单一最大风险因素，越来越多的证据表明，功能获得性毒性片段化可能是与该风险相关的关键分子步骤。最近，我们证明了载脂蛋白E4的151个氨基末端片段（E4片段）在人类AD脑小胶质细胞核内具有强免疫反应性。在体外，该片段导致BV2小胶质细胞毒性和炎症过程激活。此外，用该E4片段对外源处理BV2小胶质细胞后的转录组分析导致1608个基因上调超过2倍，许多基因在炎症和小胶质细胞激活中起作用。为扩展这些发现，我们在此报告用全长载脂蛋白E4（FL-ApoE4）处理BV2小胶质细胞后的类似转录组分析。结果表明，与片段相比，全长载脂蛋白E4对基因表达的影响非常小。仅鉴定出48个差异表达基因（DEG）（p<0.05，且变化大于2倍）。对这些DEG的基因本体分析表明，与E4片段上调的基因不同，它们不参与炎症和激活过程。此外，FL-E4处理后显示负倍数变化的基因在用片段处理时通常显示强正倍数变化（Pearson相关系数r=-0.7）。综上所述，这些结果支持以下假设：小胶质细胞向活化表型转化的关键步骤是FL-ApoE4的蛋白水解切割。因此，特异性中和ApoE4的这个氨基末端片段可能是治疗AD的重要治疗策略。
