Bain Lisa J, Liu Jui-Tung, League Ryan E
Environmental Toxicology Graduate Program, Clemson University, 132 Long Hall, Clemson, SC 29634, USA; Department of Biological Sciences, Clemson University, 132 Long Hall, Clemson, SC 23964, USA.
Environmental Toxicology Graduate Program, Clemson University, 132 Long Hall, Clemson, SC 29634, USA.
Toxicol Rep. 2016;3:405-413. doi: 10.1016/j.toxrep.2016.03.011.
Millions of people are exposed to arsenic through their drinking water and food, but the mechanisms by which it impacts embryonic development are not well understood. Arsenic exposure during embryogenesis is associated with neurodevelopmental effects, reduced weight gain, and altered locomotor activity, and data indicates that arsenic exposure inhibits stem cell differentiation. This study investigated whether arsenic disrupted the Wnt3a signaling pathway, critical in the formation of myotubes and neurons, during the differentiation in P19 mouse embryonic stem cells. Cells were exposed to 0, 0.1, or 0.5 μM arsenite, with or without exogenous Wnt3a, for up to 9 days of differentiation. Arsenic exposure alone inhibits the differentiation of stem cells into neurons and skeletal myotubes, and reduces the expression of both β-catenin and GSK3β mRNA to ~55% of control levels. Co-culture of the arsenic-exposed cells with exogenous Wnt3a rescues the morphological phenotype, but does not alter transcript, protein, or phosphorylation status of GSK3β or β-catenin. However, arsenic exposure maintains high levels of Hes5 and decreases the expression of MASH1 by 2.2-fold, which are anti- and pro-myogenic and neurogenic genes, respectively, in the Notch signaling pathway. While rescue with exogenous Wnt3a reduced Hes5 levels, MASH1 levels stay repressed. Thus, while Wnt3a can partially rescue the inhibition of differentiation from arsenic, it does so by also modulating Notch target genes rather than only working through the canonical Wnt signaling pathway. These results indicate that arsenic alters the interplay between multiple signaling pathways, leading to reduced stem cell differentiation.
数以百万计的人通过饮用水和食物接触到砷，但人们对其影响胚胎发育的机制尚不完全了解。胚胎发生过程中接触砷与神经发育效应、体重增加减少和运动活动改变有关，并且数据表明砷暴露会抑制干细胞分化。本研究调查了在P19小鼠胚胎干细胞分化过程中，砷是否会破坏对肌管和神经元形成至关重要的Wnt3a信号通路。将细胞暴露于0、0.1或0.5μM亚砷酸盐中，添加或不添加外源性Wnt3a，进行长达9天的分化。单独暴露于砷会抑制干细胞向神经元和骨骼肌管的分化，并将β-连环蛋白和GSK3β mRNA的表达降低至对照水平的约55%。将暴露于砷的细胞与外源性Wnt3a共培养可挽救形态学表型，但不会改变GSK3β或β-连环蛋白的转录、蛋白质或磷酸化状态。然而，砷暴露会维持高水平的Hes5，并使MASH1的表达降低2.2倍，它们分别是Notch信号通路中的抗成肌和促成肌及神经源性基因。虽然用外源性Wnt3a挽救可降低Hes5水平，但MASH1水平仍受到抑制。因此，虽然Wnt3a可以部分挽救砷对分化的抑制作用，但它是通过调节Notch靶基因来实现的，而不是仅通过经典的Wnt信号通路起作用。这些结果表明，砷改变了多种信号通路之间的相互作用，导致干细胞分化减少。
