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Methylmercury induces acute oxidative stress, altering Nrf2 protein level in primary microglial cells
Mingwei Ni1, Xin Li, Zhaobao Yin
1Department of Pharmacology, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA.
Abstract:
The neurotoxicity of methylmercury (MeHg) is well documented in both humans and animals. MeHg causes acute and chronic damage to multiple organs, most profoundly the central nervous system (CNS). Microglial cells are derived from macrophage cell lineage, making up approximately 12% of cells in the CNS, yet their role in MeHg-induced neurotoxicity is not well defined. The purpose of the present study was to characterize microglial vulnerability to MeHg and their potential adaptive response to acute MeHg exposure. We examined the effects of MeHg on microglial viability, reactive oxygen species (ROS) generation, glutathione (GSH) level, redox homeostasis, and Nrf2 protein expression. Our data showed that MeHg (1-5 microM) treatment caused a rapid (within 1 min) concentration- and time-dependent increase in ROS generation, accompanied by a statistically significant decrease in the ratio of GSH and its oxidized form glutathione disulfide (GSSG) (GSH:GSSG ratio). MeHg increased the cytosolic Nrf2 protein level within 1 min of exposure, followed by its nuclear translocation after 10 min of treatment. Consistent with the nuclear translocation of Nrf2, quantitative real-time PCR revealed a concentration-dependent increase in the messenger RNA level of Ho-1, Nqo1, and xCT 30 min post MeHg exposure, whereas Nrf2 knockdown greatly reduced the upregulation of these genes. Furthermore, we observed increased microglial death upon Nrf2 knockdown by the small hairpin RNA approach. Taken together, our study has demonstrated that microglial cells are exquisitely sensitive to MeHg and respond rapidly to MeHg by upregulating the Nrf2-mediated antioxidant response.
Insights
Microglial cells are highly sensitive to methylmercury (MeHg) neurotoxicity. They rapidly activate the Nrf2 antioxidant pathway to counteract MeHg-induced oxidative stress and cell death.
Area of Science:
- Neuroscience
- Toxicology
- Cell Biology
Background:
- Methylmercury (MeHg) is a potent neurotoxin affecting multiple organs, particularly the central nervous system (CNS).
- The specific role of microglial cells, the resident immune cells of the CNS, in MeHg neurotoxicity remains unclear.
Purpose of the Study:
- To investigate microglial cell vulnerability to MeHg.
- To characterize the adaptive responses of microglia following acute MeHg exposure.
Main Methods:
- Assessed microglial viability, reactive oxygen species (ROS) generation, and glutathione (GSH) levels.
- Measured Nrf2 protein expression, translocation, and downstream gene targets (Ho-1, Nqo1, xCT) via qPCR.
- Utilized Nrf2 knockdown using small hairpin RNA (shRNA) to evaluate its role.
Main Results:
- MeHg exposure rapidly increased ROS generation and decreased the GSH:GSSG ratio in microglia.
- MeHg induced a rapid increase in cytosolic Nrf2, followed by nuclear translocation.
- Upregulation of antioxidant genes (Ho-1, Nqo1, xCT) was observed, dependent on Nrf2.
- Nrf2 knockdown exacerbated MeHg-induced microglial death.
Conclusions:
- Microglial cells are highly sensitive to MeHg.
- Microglia mount a rapid Nrf2-mediated antioxidant response to MeHg exposure.
- This Nrf2 pathway is crucial for microglial survival against MeHg toxicity.
