Acute response of primary glial cells to methylmercury exposure

Abstract

Mercury accumulates in fish-eating populations. Glial cells have diverse functions including providing nutrition[1], maintaining CNS homeostasis, removing pathogens, inducing neuronal differentiation and mediating CNS immune responsiveness. Dysfunction of glial cells is contributed to MeHg-induced brain damage. We hypothesized that 1) the cellular responses to MeHg are cell-type specific; 2) differences exist in the uptake of MeHg between astrocytes and microglia, leading to differential temporal cellular responses. I tested the unique response of primary glial cells to MeHg exposure at physiologically relevant concentration. The results are presented in this dissertation.

Firstly, I established the methodology to separate a large amount of rat primary microglial cells with high purity (>95%) from mixed glial cell culture. Secondly, I investigated the toxic effects of MeHg on primary glial cells as well as their cellular response to acute MeHg exposure at environmentally relevant concentrations (0.1µM~ 5µM). The results showed MeHg treatment caused a concentration- and time- dependent microglial cell death, intracellular ROS generation and GSH depletion. I analyzed the dynamic changes of nuclear factor erythroid- derived 2- like 2 (NFE2L2) in both cytosolic fraction and nuclear fraction. My results suggested that the increase in Nrf2 protein level and the subsequent nuclear translocation are regulated by ROS in both glial cell types. However, Nrf2 changes in astrocytes occurred on a protracted time scale. Thirdly, the effects of Nrf2 on its downstream gene expression and cell viability post MeHg exposure were further studied, using short hairpin RNA (shRNA) approach. Finally the responses of rat primary microglial cells post MeHg treatment were compared with those of rat primary astrocytes. In conclusion, our study has demonstrated that microglial cells are more sensitive than astrocytes to MeHg. Their regulation kinetics differ, therefore allowing astrocytes and microglial cells to play different roles in mediating MeHg toxicity.