Methylmercury exposure downregulates the expression of Racl and leads to neuritic degeneration and ultimately apoptosis in cerebrocortical neurons
Methylmercury exposure downregulates the expression of Racl and leads to neuritic degeneration and ultimately apoptosis in cerebrocortical neurons
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DOI：
10.1016/j.neuro.2008.10.002
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发表时间：
2009-01-01
期刊：
影响因子：
3.4
通讯作者：
Takashima, Akihiko
中科院分区：
文献类型：
--
作者：
Fujimura, Masatake;Usuki, Fusako;Takashima, Akihiko
甲基汞（MeHg）被认为是一种神经毒物，作用于包括小脑和大脑皮层在内的中枢神经系统。甲基汞的一些分子靶点已被确定使用小脑神经元细胞，但鲜为人知的是，在大脑皮层神经元细胞。在这项研究中，潜在的甲基汞诱导的细胞死亡的大脑皮层神经元的分子机制进行了研究，使用胚胎大鼠皮层神经元细胞的原代培养。暴露于100 nM的甲基汞后3天，培养的细胞表现出凋亡，这表明参与半胱天冬酶依赖的凋亡途径。我们第一次证明了神经炎变性之前，甲基汞诱导的神经元细胞凋亡暴露于100 nM甲基汞。神经突特异性蛋白，即tau和MAP 2的免疫细胞化学和ELISA分析表明，首先诱导损伤tau阳性轴突，然后损伤树突和细胞体。为了进一步研究导致神经元死亡的因素，我们研究了Rho家族蛋白（Rack Cdc42和RhoA）的表达水平，这些蛋白调节神经元中的神经炎功能和凋亡。Western blot分析表明，甲基汞对RhoA无影响，但可下调Rac1和Cdc42的表达水平。暴露浓度和时间过程研究证实，Rac1是在甲基汞诱导的细胞毒性的早期阶段的目标。结果表明，神经炎性变性，特别是轴突变性引发的Rac 1表达下调，有助于甲基汞诱导的细胞凋亡的细胞死亡在培养的皮质神经元。(C)2008年爱思唯尔公司All rights reserved.
Methylmercury (MeHg) has been recognized as a neurotoxicant targeted on the central nervous system including cerebellum and cerebral cortex. Some molecular targets of MeHg have been identified using cerebellar neuronal cells, but little is known in the cerebrocortical neuronal cells. In this study, the molecular mechanism underlying MeHg-induced cell death in cerebrocortical neurons was investigated using a primary culture of embryonic rat cortical neuronal cells. The cultured cells exhibited apoptosis 3 days after exposure to 100 nM MeHg, suggesting the involvement of caspase-dependent apoptotic pathways. We demonstrated for the first time that neuritic degeneration precedes MeHg-induced apoptotic death in neurons exposed to 100 nM MeHg. Immunocytochemical and ELISA analyses for neurite-specific proteins namely, tau and MAP2, showed that injury to tau-positive axons was first induced followed by damage to the dendrites and cellular bodies. To further investigate the factors responsible for neuronal death, we investigated the expression levels of Rho-family proteins (Rack Cdc42, and RhoA), which regulate neuritic functions and apoptosis in neurons. Western blot analysis demonstrated that MeHg downregulated the expression levels of Rac1 and Cdc42 but did not affect RhoA. The exposure concentration and time course studies confirmed that Rac1 is targeted during an early stage of MeHg-induced cytotoxicity. The results indicate that neuritic degeneration, in particular axonal degeneration triggered by the downregulation of Rac1 expression, contributes to MeHg-induced apoptotic cell death in cultured cerebrocortical neurons. (C) 2008 Elsevier Inc. All rights reserved.