Parkinson’s disease is characterized by a progressive degeneration of substantia nigra (SN) dopaminergic neurons with age. We previously found that a single systemic lipopolysaccharide (LPS, 5 mg/kg, i.p.) injection caused a slow progressive loss of tyrosine hydroxylase immunoreactive (THþIR) neurons in SN associated with increasing motor dysfunction. In this study, we investigated the role of NADPH oxidase (NOX) in inflammation-mediated SN neurotoxicity. A comparison of control (NOX2þ/þ) mice with NOX subunit gp91phox-deficient (NOX2/) mice 10 months after LPS administration (5 mg/kg, i.p.) resulted in a 39% (P < 0.01) loss of THþIR neurons in NOX2þ/þ mice, whereas NOX2/ mice did not show a significant decrease. Microglia (Iba1þIR) showed morphological activation in NOX2þ/þ mice, but not in NOX2/ mice at 1 hr.
Treatment of NOX2þ/þ mice with LPS resulted in a 12-fold increase in NOX2 mRNA in midbrain and 5.5–6.5-fold increases in NOX2 protein (þIR) in SN compared with the saline controls. Brain reactive oxygen species (ROS), determined using diphenyliodonium histochemistry, was increased by LPS in SN between 1 hr and 20 months. Diphenyliodonium (DPI), an NOX inhibitor, blocked LPS-induced activation of microglia and production of ROS, TNFa, IL-1b, and MCP-1. Although LPS increased microglial activation and ROS at all ages studied, saline control NOX2þ/þ mice showed age-related increases in microglial activation, NOX, and ROS levels at 12 and 22 months of
Together, these results suggest that NOX contributes to persistent microglial activation, ROS production, and dopaminergic neurodegeneration that persist and continue to increase with age.