Environmental Toxicology Graduate Program, Clemson University, Clemson, South Carolina, USA.
US Environmental Protection Agency, Durham, North Carolina, USA.
J Appl Toxicol. 2021 Jul;41(7):1089-1102. doi: 10.1002/jat.4095. Epub 2020 Oct 30.
Arsenic is a contaminant found in many foods and drinking water. Exposure to arsenic during development can cause improper neuronal progenitor cell development, differentiation, and function, while in vitro studies have determined that acute arsenic exposure to stem and progenitor cells reduced their ability to differentiate. In the current study, P19 mouse embryonal stem cells were exposed continuously to 0.1-μM (7.5 ppb) arsenic for 32 weeks. A cell lineage array examining messenger RNA (mRNA) changes after 8 and 32 weeks of exposure showed that genes involved in pluripotency were increased, whereas those involved in differentiation were reduced. Therefore, temporal changes of select pluripotency and neuronal differentiation markers throughout the 32-week chronic arsenic exposure were investigated. Sox2 and Oct4 mRNA expression were increased by 1.9- to 2.5-fold in the arsenic-exposed cells, beginning at Week 12. Sox2 protein expression was similarly increased starting at Week 16 and remained elevated by 1.5-fold to sixfold. One target of Sox2 is N-cadherin, whose expression is a hallmark of epithelial-mesenchymal transitions (EMTs). Exposure to arsenic significantly increased N-cadherin protein levels beginning at Week 20, concurrent with increased grouping of N-cadherin positive cells at the perimeter of the embryoid body. Expression of Zeb1, which helps increase the expression of Sox2, was also increased started at Week 16. In contrast, Gdf3 mRNA expression was reduced by 3.4- to 7.2-fold beginning at Week 16, and expression of its target protein, phospho-Smad2/3, was also reduced. These results suggest that chronic, low-level arsenic exposure may delay neuronal differentiation and maintain pluripotency.
砷是许多食物和饮用水中的污染物。在发育过程中接触砷会导致神经元祖细胞发育、分化和功能异常，而体外研究已经确定急性砷暴露会降低干细胞和祖细胞的分化能力。在本研究中，P19 小鼠胚胎干细胞连续暴露于 0.1-μM（7.5 ppb）砷 32 周。细胞谱系分析检测暴露 8 周和 32 周后的信使 RNA（mRNA）变化表明，与多能性相关的基因增加，而与分化相关的基因减少。因此，研究了整个 32 周慢性砷暴露过程中选择的多能性和神经元分化标志物的时间变化。Sox2 和 Oct4 的 mRNA 表达在暴露于砷的细胞中增加了 1.9-2.5 倍，从第 12 周开始。Sox2 蛋白表达也从第 16 周开始增加，并持续增加 1.5 到 6 倍。Sox2 的一个靶标是 N-钙黏蛋白，其表达是上皮-间充质转化（EMT）的标志。从第 20 周开始，砷暴露显著增加了 N-钙黏蛋白蛋白水平，同时在胚胎体的外围，N-钙黏蛋白阳性细胞的聚集增加。Zeb1 的表达也从第 16 周开始增加，Zeb1 有助于增加 Sox2 的表达。相比之下，Gdf3 的 mRNA 表达从第 16 周开始减少了 3.4-7.2 倍，其靶蛋白磷酸化 Smad2/3 的表达也减少了。这些结果表明，慢性低水平砷暴露可能会延迟神经元分化并维持多能性。
