Microglial activation and dopaminergic cell injury: An in vitro model relevant to Parkinson's disease

Microglial activation and oxidative stress are significant components of the pathology of Parkinson's disease (PD), but their exact contributions to disease pathogenesis are unclear. We have developed an in vitro model of nigral injury, in which lipopolysaccharide-induced microglial activation leads to injury of a dopaminergic cell line (MES 23.5 cells) and dopaminergic neurons in primary mesencephalic cell cultures. The microglia are also activated by PD IgGs in the presence of low-dose dopa-quinone- or H₂O₂-modified dopaminergic cell membranes but not cholinergic cell membranes. The activation requires the microglial FcγR receptor as demonstrated by the lack of activation with PD IgG Fab fragments or microglia from FcγR-/- mice. Although microglial activation results in the release of several cytokines and reactive oxygen species, only nitric oxide and H₂O₂ appear to mediate the microglia-induced dopaminergic cell injury. These studies suggest a significant role for microglia in dopaminergic cell injury and provide a mechanism whereby immune/inflammatory reactions in PD could target oxidative injury relatively specifically to dopaminergic cells.