Liu Wei, Xu Zhaofa, Yang Tianyao, Deng Yu, Xu Bin, Feng Shu
Department of Environmental Health, School of Public Health, China Medical University, Shenyang, 110122, Liaoning province, China.
Mol Neurobiol. 2016 Jul;53(5):2995-3009. doi: 10.1007/s12035-015-9161-y. Epub 2015 May 8.
Methylmercury (MeHg) is an extremely dangerous environmental contaminant, accumulating preferentially in CNS and causing a series of cytotoxic effects. However, the precise mechanisms are still incompletely understood. The current study explored the mechanisms that contribute to MeHg-induced cell injury focusing on the oxidative stress and Glu uptake/metabolism disorders in rat primary cultured astrocytes. Moreover, the neuroprotective effects of tea polyphenols (TP), a natural antioxidant, against MeHg cytotoxicity were also investigated. Astrocytes were exposed to 0, 2.5, 5, 10, and 20 μM MeHgCl for 6-30 h, or pretreated with 50, 100, 200, and 400 μM TP for 1-12 h; cell viability and LDH release were then determined. For further experiments, 50, 100, and 200 μM of TP pretreatment for 6 h followed by 10 μM MeHgCl for 24 h were performed for the examination of the responses of astrocytes, specifically addressing NPSH levels, ROS generation, ATPase activity, the expressions of Nrf2 pathway as well as Glu metabolism enzyme GS and Glu transporters (GLAST and GLT-1). Exposure of MeHg resulted in damages of astrocytes, which were shown by a loss of cell viability, and supported by high levels of LDH release, morphological changes, apoptosis rates, and NPSH depletion. In addition, astrocytes were sensitive to MeHg-mediated oxidative stress, a finding that is consistent with ROS overproduction; Nrf2 as well as its downstream genes HO-1 and γ-GCSh were markedly upregulated. Moreover, MeHg significantly inhibited GS activity, as well as expressions of GS, GLAST, and GLT-1. On the contrary, pretreatment with TP presented a concentration-dependent prevention against MeHg-mediated cytotoxic effects of astrocytes. In conclusion, the findings clearly indicated that MeHg aggravated oxidative stress and Glu uptake/metabolism dysfunction in astrocytes. TP possesses some abilities to prevent MeHg cytotoxicity through its antioxidative properties.
甲基汞（MeHg）是一种极其危险的环境污染物，优先在中枢神经系统中蓄积并引发一系列细胞毒性作用。然而，其确切机制仍未完全明确。本研究探讨了大鼠原代培养星形胶质细胞中，导致MeHg诱导细胞损伤的机制，重点关注氧化应激和谷氨酸摄取/代谢紊乱。此外，还研究了天然抗氧化剂茶多酚（TP）对MeHg细胞毒性的神经保护作用。将星形胶质细胞暴露于0、2.5、5、10和20 μM的氯化甲基汞中6 - 30小时，或用50、100、200和400 μM的TP预处理1 - 12小时；然后测定细胞活力和乳酸脱氢酶（LDH）释放量。为进行进一步实验，进行50、100和200 μM的TP预处理6小时，随后用10 μM的氯化甲基汞处理24小时，以检测星形胶质细胞的反应，具体包括非蛋白巯基（NPSH）水平、活性氧（ROS）生成、ATP酶活性、核因子E2相关因子2（Nrf2）信号通路的表达以及谷氨酸代谢酶谷氨酰胺合成酶（GS）和谷氨酸转运体（谷氨酸天冬氨酸转运体（GLAST）和谷氨酸转运体-1（GLT-1））。MeHg暴露导致星形胶质细胞受损，表现为细胞活力丧失，并伴有高水平的LDH释放、形态变化、凋亡率增加和NPSH耗竭。此外，星形胶质细胞对MeHg介导的氧化应激敏感，这一发现与ROS过量产生一致；Nrf2及其下游基因血红素加氧酶-1（HO-1）和γ-谷氨酰半胱氨酸合成酶（γ-GCSh）明显上调。此外，MeHg显著抑制GS活性以及GS、GLAST和GLT-1的表达。相反，TP预处理对MeHg介导的星形胶质细胞细胞毒性作用具有浓度依赖性的预防作用。总之，研究结果清楚地表明，MeHg加剧了星形胶质细胞中的氧化应激和谷氨酸摄取/代谢功能障碍。TP通过其抗氧化特性具有一定预防MeHg细胞毒性的能力。
