Laboratory of Molecular Physiology, Faculty of Health and Life Sciences, Universitat Pompeu Fabra, Barcelona, Spain.
Cell Signaling Laboratory, Centro UC de Envejecimiento y Regeneración (CARE), Department of Cellular and Molecular Biology, Biological Sciences Faculty, Pontificia Universidad Católica de Chile, Santiago, Chile.
Oxid Med Cell Longev. 2020 Sep 19;2020:2739459. doi: 10.1155/2020/2739459. eCollection 2020.
Alzheimer's disease (AD) is tightly linked to oxidative stress since amyloid beta-peptide (A) aggregates generate free radicals. Moreover, the aggregation of A is increased by oxidative stress, and the neurotoxicity induced by the oligomers and fibrils is in part mediated by free radicals. Interestingly, it has been reported that oxidative stress can also induce BACE1 transcription and expression. BACE1 is the key enzyme in the cleavage of the amyloid precursor protein to produce A, and the expression of this enzyme has been previously shown to be enhanced in the brains of Alzheimer's patients. Here, we have found that BACE1 expression is increased in the hippocampi from AD patients at both the early (Braak stage II) and late (Braak stage VI) stages of the disease as studied by immunohistochemistry and western blot. To address the role of A and oxidative stress in the regulation of BACE1 expression, we have analyzed the effect of subtoxic concentrations of A oligomers (0.25 M) and HO (10 mM) on a human neuroblastoma cell line. Firstly, our results show that A oligomers and HO induce an increase of mRNA as we studied by qPCR. Regarding BACE1 translation, it is dependent on the phosphorylation of the eukaryotic initiation factor 2 (eIF2), since mRNA bears a 5'UTR that avoids its translation under basal conditions. BACE1 5'UTR contains four upstream initiating codons (uAUGs), and its translation is activated when eIF2 is phosphorylated. Consistently, we have obtained that A oligomers and HO increase the levels of BACE1 and p-eIF2 assayed by western blot and confocal microscopy. Our results suggest that A oligomers increase BACE1 translation by phosphorylating eIF2 in a process that involves oxidative stress and conforms a pathophysiological loop, where the A once aggregated favors its own production continuously by the increase in BACE1 expression as observed in AD patients.
阿尔茨海默病（AD）与氧化应激密切相关，因为淀粉样β肽（A）聚集体会产生自由基。此外，氧化应激会增加 A 的聚集，寡聚物和原纤维诱导的神经毒性部分是由自由基介导的。有趣的是，据报道氧化应激也可以诱导 BACE1 转录和表达。BACE1 是切割淀粉样前体蛋白产生 A 的关键酶，先前的研究表明，这种酶在阿尔茨海默病患者的大脑中表达增强。在这里，我们通过免疫组织化学和 Western blot 发现，在 AD 患者的海马体中，BACE1 的表达在疾病的早期（Braak 阶段 II）和晚期（Braak 阶段 VI）均增加。为了研究 A 和氧化应激在调节 BACE1 表达中的作用，我们分析了亚毒性浓度的 A 寡聚物（0.25 μM）和 HO（10 mM）对人神经母细胞瘤细胞系的影响。首先，我们的结果表明，正如我们通过 qPCR 研究的那样，A 寡聚物和 HO 诱导 mRNA 的增加。关于 BACE1 的翻译，它依赖于真核起始因子 2（eIF2）的磷酸化，因为 mRNA 带有一个 5'UTR，在基础条件下会避免其翻译。BACE1 5'UTR 包含四个上游起始密码子（uAUGs），当 eIF2 磷酸化时，其翻译被激活。一致地，我们通过 Western blot 和共聚焦显微镜获得了 A 寡聚物和 HO 增加 BACE1 和 p-eIF2 水平的结果。我们的结果表明，A 寡聚物通过磷酸化 eIF2 增加 BACE1 的翻译，这一过程涉及氧化应激，并构成了一个病理生理循环，其中一旦聚集的 A 通过增加 BACE1 的表达来不断促进自身的产生，就像在 AD 患者中观察到的那样。
