Doerenkamp-Zbinden Chair of in-vitro Toxicology and Biomedicine, Department of Biology, University of Konstanz, D-78457 Konstanz, Germany.
Toxicol Sci. 2011 Jun;121(2):357-67. doi: 10.1093/toxsci/kfr054. Epub 2011 Mar 7.
Perinatal exposure to low doses of methylmercury (MeHg) can cause adult neurological symptoms. Rather than leading to a net cell loss, the toxicant is assumed to alter the differentiation and neuronal functions such as catecholaminergic transmission. We used neuronally differentiating murine embryonic stem cells (mESC) to explore such subtle toxicity. The mixed neuronal cultures that formed within 20 days contained a small subpopulation of tyrosine hydroxylase (TH)-positive neurons with specific dopaminergic functions such as dopamine transport (DAT) activity. The last 6 days of differentiation were associated with the functional maturation of already preformed neuronal precursors. Exposure to MeHg during this period downregulated several neuronal transcripts, without affecting housekeeping genes or causing measurable cell loss. Profiling of mRNAs relevant for neurotransmitter systems showed that dopamine receptors were coordinately downregulated, whereas known counterregulatory systems such as galanin receptor 2 were upregulated. The chronic (6 days) exposure to MeHg, but not shorter incubation periods, attenuated the expression levels of endogenous neurotrophic factors required for the maturation of TH cells. Accordingly, the size of this cell population was diminished, and DAT activity as its signature function was lost. When mixed lineage kinase activity was blocked during MeHg exposure, DAT activity was restored, and the reduction of TH levels was prevented. Thus, transcriptional profiling in differentiating mESC identified a subpopulation of neurons affected by MeHg, and a pharmacological intervention was identified that specifically protected these cells.
围产期暴露于低剂量的甲基汞（MeHg）可导致成人神经症状。这种有毒物质不是导致净细胞丢失，而是被认为改变了分化和神经元功能，如儿茶酚胺能传递。我们使用神经分化的鼠胚胎干细胞（mESC）来探索这种微妙的毒性。在 20 天内形成的混合神经元培养物中含有一小部分酪氨酸羟化酶（TH）阳性神经元，具有特定的多巴胺能功能，如多巴胺转运（DAT）活性。分化的最后 6 天与已经预先形成的神经元前体的功能成熟有关。在此期间，MeHg 的暴露下调了几种神经元转录物，而不影响管家基因或导致可测量的细胞丢失。对与神经递质系统相关的 mRNAs 的分析表明，多巴胺受体被协调地下调，而众所周知的拮抗调节系统，如甘丙肽受体 2，则被上调。慢性（6 天）暴露于 MeHg，但不是较短的孵育时间，会减弱成熟 TH 细胞所需的内源性神经营养因子的表达水平。因此，该细胞群体的大小减小，其特征功能 DAT 活性丧失。当在 MeHg 暴露期间阻断多谱系激酶活性时，DAT 活性得到恢复，并且 TH 水平的降低得到预防。因此，分化的 mESC 的转录谱鉴定出受 MeHg 影响的神经元亚群，并确定了一种药理学干预措施，该措施可特异性保护这些细胞。
