Effects of methylmercury on the secretion of pro-inflammatory cytokines from primary microglial cells and astrocytes

Glial cells, including oligodendrocytes, astrocytes and microglia are important to proper central nervous system (CNS) function. Deregulation or changes to CNS populations of astrocytes and microglia in particular are expected to play a role in many neurodegenerative diseases, including Parkinson's disease, amyotrophic lateral sclerosis (ALS) and Alzheimer's disease (AD). Previous studies have reported methylmercury (MeHg) induced changes in glial cell function; however, the effects of MeHg on these cells remains poorly understood. This study aims to examine the effect of MeHg on the secretion of pro-inflammatory cytokines from microglia and astrocytes. The impact of the microglia/astrocyte ratio on cytokine secretion was also examined. Microglia and astrocytes were cultured from the brains of neo-natal BALB/C mice and dosed with MeHg (0–1 μM) and stimulated with PAM(3)CSK(4) (PAM(3)), a toll-like receptor (TLR) ligand. After this, the secretion of interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α) and interleukin-1-beta (IL-1β) was measured by ELISA. MeHg reduced the secretion of IL-6 in a dose dependant manner but did not effect the secretion of TNF-α. No change in IL-1β was observed in any treatments, indicating that PAM(3) cannot induce the secretion of this cytokine from glial cells. Additionally, the ratio of microglia/astrocyte had an effect on the secretion of IL-6 but not TNF-α. These results indicate that MeHg can modify the response of glial cells and the interactions with astrocytes can affect the response of the microglia cells in culture. These results are significant in understanding the potential relationship with MeHg and neurodegenerative diseases and for the interpretation of results of future in vitro studies using monoculture.

► Impact of methylmercury on cytokine secretion from astrocytes and microglia was assessed.
► Impact of microglia/astrocyte ratio on cytokine secretion was examined.
► Both cell ratio and methylmercury were observed to affect the secretion of select cytokines.
► Glial cell ratio should be considered when using primary glial cells as an experimental model.