Methylmercury Induces Acute Oxidative Stress, Altering Nrf2 Protein Level in Primary Microglial Cells

Toxicol Sci. 2010 Aug;116(2):590-603. doi: 10.1093/toxsci/kfq126. Epub 2010 Apr 26.

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.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Amino Acid Transport System y+ / genetics
  • Amino Acid Transport Systems, Acidic
  • Animals
  • Cells, Cultured
  • Glutathione / metabolism
  • Heme Oxygenase (Decyclizing) / genetics
  • Interleukin-6 / biosynthesis
  • Methylmercury Compounds / toxicity*
  • Microglia / drug effects*
  • Microglia / metabolism
  • NAD(P)H Dehydrogenase (Quinone) / genetics
  • NF-E2-Related Factor 2 / analysis*
  • NF-E2-Related Factor 2 / metabolism
  • Oxidative Stress / drug effects*
  • Protein Transport / drug effects
  • Rats
  • Rats, Sprague-Dawley

Substances

  • Amino Acid Transport System y+
  • Amino Acid Transport Systems, Acidic
  • Interleukin-6
  • Methylmercury Compounds
  • NF-E2-Related Factor 2
  • Nfe2l2 protein, rat
  • xCT protein, rat
  • Heme Oxygenase (Decyclizing)
  • Hmox1 protein, rat
  • NAD(P)H Dehydrogenase (Quinone)
  • NQO1 protein, rat
  • Glutathione