A1 astrocytes activated by 2-Chloroethanol via the ROS-induced p38 MAPK/NF-κB and AP-1 pathways modulate microglia polarization

Background: 1,2-Dichloroethane (1,2-DCE) is a synthetic organic chemical that causes brain edema under subacute poisoning. Our previous studies indicated that the neuroinflammation could be induced due to activation of both astrocytes and microglia during the course of brain edema in 1,2-DCE intoxicated mice. However, the crosstalk between the two glial cells in 1,2-DCE-induced neuroinflammation is unclear. In the current studies, we hypothesized that astrocytes are the first responder to the effects of 1,2-DCE in the brain, as they adhere to the cerebral capillaries, and they are an essential component of the blood-brain barrier (BBB). Methods: We used primary cultured rat astrocytes and microglia, as well as a highly aggressively proliferating immortalized (HAPI) microglia cell line to study the effects of astrocytes on microglia polarization following exposure to 2-CE. Results: Findings from the present studies demonstrated that treatment of primary rat astrocytes with 2-chloroethanol (2-CE), the intermediate metabolite of 1,2-DCE in vivo , can stimulate the activation of A1 reactive astrocytes (A1s) through p38 mitogen-activated protein kinase (p38 MAPK)/ nuclear factor-κB (NF-κB) and activator protein-1 (AP-1) signaling pathways by the reactive oxygen species (ROS) produced during 2-CE metabolism. A1s activated by 2-CE can upregulate the expression of interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and inducible nitric oxide synthase (iNOS), and stimulate the M1 polarization of microglia through IL-1β and TNF-α released by 2-CE activated A1s. Microglia are less sensitive to 2-CE than astrocytes, since treatment of primary rat microglia with 30 mM 2-CE alone failed to activate them, though this dose of 2-CE can activate A1s and in turn stimulate M1 polarization of microglia through the factors released by A1s. Conclusion: The neuroinflammation induced by 1,2-DCE in the brain of mice is most probably triggered by the activation of astrocytes. The understanding of the multidimensional roles of reactive astrocytes may further the development of new treatment strategies in reducing neuroinflammation and brain edema following 1,2-DCE-induced toxic encephalopathy.