Paraquat affects the homeostasis of dopaminergic system in PC12 cells

Abstract

The broad application of paraquat (PQ) has given rise to wide public concern over its potential to damage the nigrostriatal dopaminergic system because its chemical structure closely resembles that of the well-known dopaminergic neurotoxicant MPP+. However, little is known about the relevance of dopamine homeostasis changes in response to PQ exposure as the underlying mechanism of the neurotoxicity. We used the PC12 cell, a popular in vitro cell model system for characterizing the dopaminergic neuron to examine the effects of PQ on dopamine homeostasis. After 24h treatment with different concentrations of PQ (from 0 to 1000μmol/l), MTT tests showed that cell viability decreased with increasing PQ concentrations. Flow cytometry analysis also showed that PQ induced cell apoptosis in a dose-dependent manner. An enzyme-linked immunosorbent assay revealed that the intracellular dopamine content increased after PQ treatment. The mRNA expression of genes associated with dopamine synthesis (TH), storage (VMAT2), transportation (DAT and D2R) and degradation (MAO) was assessed using real-time PCR. Results showed that the expression of TH and COMT were unaffected while the expression of MAO was suppressed after PQ treatment. In addition, exposure to PQ reduced the expression of VMAT2 but up-regulated the expression of D2R. Moreover, the expression of DAT was up-regulated at a lower dose of PQ, and then decreased at a higher dose. These alterations of gene expression of MAO, D2R and DAT are consistent with an increase of intracellular dopamine content. Together, these findings suggest that PQ exposure can influence dopamine homeostasis, which may be partly related to the neurotoxicity of PQ.