Chen Kun-Lin, Wang Steven Sheng-Shih, Yang Yi-Yuan, Yuan Rey-Yue, Chen Ruei-Ming, Hu Chaur-Jong
Department of Neurology and The Topnotch Stroke Research Center, Taipei Medical University, 250 Wu-Hsing Street, Taipei 110, Taiwan.
Biochem Biophys Res Commun. 2009 Jan 2;378(1):57-61. doi: 10.1016/j.bbrc.2008.10.173. Epub 2008 Nov 11.
Amyloid-beta (Abeta) is the core component of senile plaques, which are the pathological markers for Alzheimer's disease and cerebral amyloid angiopathy. DNA methylation/demethylation plays a crucial role in gene regulation and could also be responsible for presentation of senescence. Oxidative stress, which may be induced by Abeta, is thought to be an important contributor of DNA hyper-methylation; however, contradicting this is the fact that global DNA hypo-methylation has been found in aging brains. It therefore remains largely unknown as to whether Abeta does in fact cause DNA methylation/demethylation. Neprilysin (NEP) is one of the enzymes responsible for Abeta degradation, with its expression decreasing in both Alzheimer and aging brains. Using high-performance liquid chromatography (HPLC), we explore whether Abeta is responsible for alteration of the global DNA methylation status on a murine cerebral endothelial cells model, and also use methylation-specific PCR (MSPCR) to examine whether DNA methylation status is altered on the NEP promoter region. We find that Abeta reduces global DNA methylation whilst increasing NEP DNA methylation and further suppressing the NEP expression in mRNA and protein levels. Our results support that Abeta induces epigenetic effects, implying that DNA methylation may be part of a vicious cycle involving the reduction in NEP expression along with a resultant increase in Abeta accumulation, and that Abeta may induce global DNA hypo-methylation.
β-淀粉样蛋白（Aβ）是老年斑的核心成分，而老年斑是阿尔茨海默病和脑淀粉样血管病的病理标志物。DNA甲基化/去甲基化在基因调控中起关键作用，也可能与衰老的表现有关。氧化应激可能由Aβ诱导，被认为是DNA高甲基化的重要促成因素；然而，与此相矛盾的是，在衰老大脑中发现了整体DNA低甲基化。因此，Aβ是否真的会导致DNA甲基化/去甲基化在很大程度上仍然未知。中性内肽酶（NEP）是负责Aβ降解的酶之一，其在阿尔茨海默病患者大脑和衰老大脑中的表达均降低。我们使用高效液相色谱（HPLC），在小鼠脑内皮细胞模型上探究Aβ是否导致整体DNA甲基化状态的改变，还使用甲基化特异性PCR（MSPCR）来检测NEP启动子区域的DNA甲基化状态是否改变。我们发现，Aβ降低了整体DNA甲基化，同时增加了NEP的DNA甲基化，并进一步抑制了NEP在mRNA和蛋白质水平的表达。我们的数据支持Aβ诱导表观遗传效应，这意味着DNA甲基化可能是一个恶性循环的一部分，该循环涉及NEP表达减少以及随之而来的Aβ积累增加，并且Aβ可能诱导整体DNA低甲基化。
