Differential effects of overexpression of wild-type and mutant human α-synuclein on MPP+-induced neurotoxicity in PC12 cells

The genetic background and the pathogenesis of familial Parkinson's disease (PD) have not been fully elucidated. Two missense mutations in the α-synuclein gene, A30P and A53T, have been linked to familial PD. Increasing evidence suggests the involvement of α-synuclein, the dopamine transporter (DAT), and neurotoxins in the pathogenesis of PD, but their relationships to the death of nigral cells remains poorly understood. In the present study, we used the PC12 cell line, a well recognized model of the nigral cell, to investigate the effects of overexpression of wild-type (WT) and mutant human α-synuclein on MPP+-induced neurotoxicity. We found that overexpression of mutant α-synuclein enhanced the toxicity of MPP+ to PC12 cells and elevated intracellular reactive oxygen species (ROS) levels, whereas overexpression of WT α-synuclein protected PC12 cells against MPP+ toxicity and lowered ROS levels. Furthermore, assays of 131I-FP-β-CIT binding with DAT membrane fractions showed that WT and mutant α-synuclein had different effects on the expression of DAT on the cell membrane following exposure to MPP+. WT α-synuclein reduced the toxic effect of MPP+ by facilitating DAT internalization, while both A30P and A53T α-synuclein aggravated the toxic effect of MPP+ by reducing DAT internalization. These data indicate that α-synuclein regulates ROS levels and DAT surface expression in dopaminergic neurons, and thus changes the response of these cells to MPP+.