Liu Jui Tung, Bain Lisa J
Environmental Toxicology Program, Clemson University, 132 Long Hall, Clemson, SC 29634, USA.
Environmental Toxicology Program, Clemson University, 132 Long Hall, Clemson, SC 29634, USA; Department of Biological Sciences, Clemson University, 132 Long Hall, Clemson, SC 29634, USA.
Toxicol Appl Pharmacol. 2014 Dec 15;281(3):243-53. doi: 10.1016/j.taap.2014.10.007. Epub 2014 Oct 30.
Arsenic is a toxicant found in ground water around the world, and human exposure mainly comes from drinking water or from crops grown in areas containing arsenic in soils or water. Epidemiological studies have shown that arsenic exposure during development decreased intellectual function, reduced birth weight, and altered locomotor activity, while in vitro studies have shown that arsenite decreased muscle and neuronal cell differentiation. The sonic hedgehog (Shh) signaling pathway plays an important role during the differentiation of both neurons and skeletal muscle. The purpose of this study was to investigate whether arsenic can disrupt Shh signaling in P19 mouse embryonic stem cells, leading to changes muscle and neuronal cell differentiation. P19 embryonic stem cells were exposed to 0, 0.25, or 0.5 μM of sodium arsenite for up to 9 days during cell differentiation. We found that arsenite exposure significantly reduced transcript levels of genes in the Shh pathway in both a time and dose-dependent manner. This included the Shh ligand, which was decreased 2- to 3-fold, the Gli2 transcription factor, which was decreased 2- to 3-fold, and its downstream target gene Ascl1, which was decreased 5-fold. GLI2 protein levels and transcriptional activity were also reduced. However, arsenic did not alter GLI2 primary cilium accumulation or nuclear translocation. Moreover, additional extracellular SHH rescued the inhibitory effects of arsenic on cellular differentiation due to an increase in GLI binding activity. Taken together, we conclude that arsenic exposure affected Shh signaling, ultimately decreasing the expression of the Gli2 transcription factor. These results suggest a mechanism by which arsenic disrupts cell differentiation.
砷是一种在世界各地地下水中发现的有毒物质，人类接触主要来自饮用水或生长在土壤或水中含砷地区的农作物。流行病学研究表明，发育过程中接触砷会降低智力功能、减少出生体重并改变运动活动，而体外研究表明亚砷酸盐会降低肌肉和神经元细胞分化。音猬因子（Shh）信号通路在神经元和骨骼肌的分化过程中起重要作用。本研究的目的是调查砷是否会破坏P19小鼠胚胎干细胞中的Shh信号，导致肌肉和神经元细胞分化发生变化。在细胞分化过程中，将P19胚胎干细胞暴露于0、0.25或0.5 μM的亚砷酸钠中长达9天。我们发现，亚砷酸盐暴露以时间和剂量依赖性方式显著降低了Shh通路中基因的转录水平。这包括Shh配体，其降低了2至3倍；Gli2转录因子，其降低了2至3倍；以及其下游靶基因Ascl1，其降低了5倍。GLI2蛋白水平和转录活性也降低了。然而，砷并未改变GLI2在初级纤毛中的积累或核转位。此外，额外的细胞外SHH由于GLI结合活性的增加而挽救了砷对细胞分化的抑制作用。综上所述，我们得出结论，砷暴露影响了Shh信号，最终降低了Gli2转录因子的表达。这些结果提示了一种砷破坏细胞分化的机制。
