Department of Biomedical & Pharmaceutical Sciences, Interdisciplinary Neuroscience Program, University of Rhode Island, Kingston, RI 02881, USA.
Curr Alzheimer Res. 2012 Jun;9(5):555-62. doi: 10.2174/156720512800617964.
Late onset Alzheimer's disease (LOAD) is typical of the majority of Alzheimer's disease (AD) cases (~90%), and has no clear genetic association. Previous studies from our lab suggest that an epigenetic component could be involved. Developmental exposure of primates and rodents to lead (Pb) predetermined the expression of AD-related genes, such as the amyloid-β precursor protein (AβPP), later in life. In addition to AβPP, the preponderance of genes that were reprogrammed was rich in CpG dinucleotides implicating DNA methylation and chromatin restructuring in their regulation. To examine the involvement of epigenetic intermediates in Pb-induced alterations in gene expression, differentiated SH-SY5Y cells were exposed to a series of Pb concentrations (5-100 μM) for 48 h and were analyzed for the protein expression of AβPP, β-site amyloid precursor protein cleaving enzyme 1 (BACE1), specificity protein 1 and 3 (Sp1, Sp3) and epigenetic intermediates like DNA methyltransferase 1, 3a (Dnmt1, Dnmt3a) and methyl CpG binding protein 2 (MeCP2) involved in DNA methylation six days after the exposure had ceased. Western blot analysis indicated a significant latent elevation in AD biomarkers as well as the transcription factors Sp1 and Sp3, accompanied by a significant reduction in the protein levels of DNA methylating enzymes. RT-PCR analysis of Dnmt1, Dnmt3a and MeCP2 indicated a significant down-regulation of the mRNA levels. These data suggest that Pb interferes with DNA methylating capacity in these cells, thus altering the expression of AD-related genes.
迟发性阿尔茨海默病（LOAD）是大多数阿尔茨海默病（AD）病例的典型表现（~90%），且与明确的遗传关联无关。我们实验室的先前研究表明，可能存在表观遗传成分。灵长类动物和啮齿动物在发育过程中接触铅（Pb），会预先决定 AD 相关基因的表达，例如淀粉样前体蛋白（AβPP），而这些基因的表达会在以后的生活中出现。除了 AβPP 之外，重编程的大多数基因富含 CpG 二核苷酸，表明 DNA 甲基化和染色质重构在其调控中发挥作用。为了研究表观遗传中间产物在 Pb 诱导的基因表达改变中的作用，用一系列 Pb 浓度（5-100 μM）处理分化的 SH-SY5Y 细胞 48 小时，然后分析 AβPP、β-位淀粉样前体蛋白切割酶 1（BACE1）、特异性蛋白 1 和 3（Sp1、Sp3）以及表观遗传中间产物的蛋白表达，这些中间产物如参与 DNA 甲基化的 DNA 甲基转移酶 1、3a（Dnmt1、Dnmt3a）和甲基 CpG 结合蛋白 2（MeCP2），在暴露停止六天后进行分析。Western blot 分析表明，AD 生物标志物以及转录因子 Sp1 和 Sp3 显著升高，同时 DNA 甲基转移酶的蛋白水平显著降低。Dnmt1、Dnmt3a 和 MeCP2 的 RT-PCR 分析表明，mRNA 水平显著下调。这些数据表明，Pb 会干扰这些细胞的 DNA 甲基化能力，从而改变 AD 相关基因的表达。
