Department of Neurosciences, University of New Mexico School of Medicine, United States.
Neurotoxicol Teratol. 2011 Sep-Oct;33(5):530-7. doi: 10.1016/j.ntt.2011.07.003. Epub 2011 Jul 19.
Changes within the glucocorticoid receptor (GR) cellular signaling pathway were evaluated in adolescent mice exposed to 50 ppb arsenic during gestation. Previously, we reported increased basal plasma corticosterone levels, decreased hippocampal GR levels and deficits in learning and memory performance in perinatal arsenic-exposed mice. The biosynthesis of members of the mitogen-activated protein kinase (MAPK) signaling pathway, known to be involved in learning and memory, is modulated by the binding of GR to glucocorticoid response elements (GREs) in the gene promoters. Two genes of the MAPK pathway, Ras and Raf, contain GREs which are activated upon binding of GRs. We evaluated the activity of GRs at Ras and Raf promoters using chromatin immunoprecipitation and real-time PCR and report decreased binding of the GR at these promoters. An ELISA-based GR binding assay was used to explore whether this decreased binding was restricted to in vivo promoters and revealed no differences in binding of native GR to synthetic GREs. The decreased in vivo GR binding coincides with significantly decreased mRNA levels and slight reductions of protein of both H-Ras and Raf-1 in perinatally arsenic-exposed mice. Nuclear activated extracellular-signal regulated kinase (ERK), a downstream target of Ras and Raf, whose transcriptional targets also play an important role in learning and memory, was decreased in the hippocampus of arsenic-exposed animals when compared to controls. GR-mediated transcriptional deficits in the MAPK/ERK pathway could be an underlying cause of previously reported learning deficits and provide the link to arsenic-induced deficiencies in cognitive development.
研究人员评估了发育期暴露于 50ppb 砷环境中的青春期小鼠的糖皮质激素受体（GR）细胞信号通路变化。此前，我们曾报道过围产期砷暴露的小鼠基础血浆皮质酮水平升高、海马 GR 水平降低以及学习和记忆表现受损。已知参与学习和记忆的丝裂原活化蛋白激酶（MAPK）信号通路的成员的生物合成，受 GR 与基因启动子中糖皮质激素反应元件（GREs）结合的调节。MAPK 通路中的两个基因，Ras 和 Raf，含有 GREs，当与 GR 结合时会被激活。我们使用染色质免疫沉淀和实时 PCR 评估 Ras 和 Raf 启动子上的 GR 活性，并报告这些启动子上 GR 的结合减少。基于 ELISA 的 GR 结合测定法用于研究这种结合减少是否仅限于体内启动子，并揭示了天然 GR 与合成 GREs 结合没有差异。体内 GR 结合的减少与 Ras 和 Raf 中明显减少的 mRNA 水平和 H-Ras 和 Raf-1 的蛋白水平相吻合-1 在围产期砷暴露的小鼠中。核激活细胞外信号调节激酶（ERK）是 Ras 和 Raf 的下游靶点，其转录靶标也在学习和记忆中发挥重要作用，与对照组相比，砷暴露动物的海马中ERK 减少。MAPK/ERK 通路中 GR 介导的转录缺陷可能是先前报道的学习缺陷的潜在原因，并为砷诱导的认知发育缺陷提供了联系。
