Comparative study on the response of rat primary astrocytes and microglia to methylmercury toxicity

Abstract

As the two major glial cell types in the brain, astrocytes and microglia play pivotal but different roles in maintaining optimal brain function. Although both cell types have been implicated as major targets of methylmercury (MeHg), their sensitivities and adaptive responses to this metal can vary given their distinctive properties and physiological functions. This study was carried out to compare the responses of astrocytes and microglia following MeHg treatment, specifically addressing the effects of MeHg on cell viability, reactive oxygen species (ROS) generation and glutathione (GSH) levels, as well as mercury (Hg) uptake and the expression of NF-E2-related factor 2 (Nrf2). Results showed that microglia are more sensitive to MeHg than astrocytes, a finding that is consistent with their higher Hg uptake and lower basal GSH levels. Microglia also demonstrated higher ROS generation compared to astrocytes. Nrf2 and its downstream genes were upregulated in both cell types, but with different kinetics (much faster in microglia). In summary, microglia and astrocytes each exhibit a distinct sensitivity to MeHg, resulting in their differential temporal adaptive responses. These unique sensitivities appear to be dependent on the cellular thiol status of the particular cell type.

Suppression of methylmercury-induced IL-6 and MCP-1 expressions by N-acetylcysteine in U-87MG human astrocytoma cells

“…On the other hand, a previous study reported a significant increase of intracellular mercury level in 10 min exposure to 5 μM MeHg in primary astrocytes isolated from neonatal rats [28].…”

Methylmercury Alters the Activities of Hsp90 Client Proteins, Prostaglandin E Synthase/p23 (PGES/23) and nNOS

“…After 2 weeks in culture, when cells reached ∼95% confluence, microglia and astrocytes were separated by gentle shaking for 20 min at room temperature. Using this protocol, our lab has achieved ≥95% purity of the isolated astrocytes, as verified by immunostaining for glial fibrillary acidic protein (GFAP) [29], [30]. Equal densities of astrocytes were plated in poly-L-lysine coated plates (BD Biocoat, San Jose, CA).…”

Glia and Methylmercury Neurotoxicity

“…Astrocytes are characterized by their star shape and expression of glial fibrillary acidic protein (GFAP) (Ni et al 2011). Astrocytes carry out many critical functions in the normal brain, including formation of BBB (Walz 1989) and expression of transporters for neurotransmitters, such as glutamate and γ-aminobutyric acid (GABA) (Santello and Volterra 2009).…”

“…Previous studies addressed intracellular Hg levels in astrocytes and microglia with 14 C-MeHg (Ni et al 2011). Direct evidence for MeHg uptake in microglial cells is still lacking (but likely reflects analogous functional transporters to those described in other cells, such as astrocytes).…”

“…Ni et al (2011) showed that MeHg produced increased intracellular reactive oxygen species (ROS) generation in both cell types, as detected in a lipophilic dichlorodihydrofluorescein diacetate acetylester (H 2 DCFDA) based assay. The intracellular ROS are detoxified by the reduced form of glutathione (GSH) to the oxidative form of GSH, GSSG.…”