Comparison of the time courses of selective gene expression and dopaminergic depletion induced by MPP+ in MN9D cells

Parkinson's disease (PD) is a common neurodegenerative disease characterized by progressive loss of midbrain dopaminergic neurons with unknown etiology. MPP+ (1-methyl-4-phenylpyridinium ion) is the active metabolite of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which induces Parkinson's-like symptoms in humans and animals. MPTP/MPP+ produces selective dopaminergic neuronal degeneration, therefore, these agents are commonly used to study the pathogenesis of PD. However, the mechanisms of their toxicity have not been fully elucidated. Recently, we reported in a microarray study using a midbrain-derived dopaminergic neuronal cell line, MN9D, that MPP+ induced significant changes in a number of genes known to be associated with the dopaminergic system. In this study, we investigated the expression time courses of six genes using real-time RT-PCR, and compared them with the progressive dopaminergic depletion caused by MPP+. Our data showed that dopamine content was significantly decreased after 0.5 h of MPP+ (200 μM) exposure and was completely depleted after 40 h. The expression of Gpr37, which is closely related to the pathogenesis of autosomal recessive juvenile Parkinsonism, was up-regulated after 0.5 h, and stayed up-regulated up to 48 h. Txnip, which is critical to the adjustment of cellular redox status, was down-regulated after 1 h and stayed down-regulated up to 48 h. Ldh1 and Cdo1, which are also involved in oxidative stress, were down-regulated after 16 h and stayed down-regulated up to 48 h. Two pro-apoptotic genes, Egln3 and Bnip3, were down-regulated after 2 and 4 h, and stayed down-regulated up to 48 h. These findings suggested that the time course of expression for multiple genes correlated with the dopaminergic depletion; and MPP+-induced neurotoxicity in MN9D cells could be used as a model to further explore the roles of these and other genes in the pathogenesis and possible treatment of PD.