Fundamental Patterns Underlying Neurotoxicity Revealed by DNA Microarray Expression Profiling

摘要

The selective neurotoxins l-methyl-4-phenylpyridinium (MPP+) and 6- hydroxydopamine (6-OHDA) have been widely used to generate animal models of Parkinson's disease (PD). To understand the genetic events associated with these neurotoxins, microarray technology served to monitor differences in gene expression patterns in normal versus pathological conditions. Microarray analysis of RNA isolated from toxin treated samples revealed that the stress- induced transcription factor CHOP was dramatically up regulated by both toxins. 6-OHDA also induced a large number of genes involved in endoplasmic reticulum (ER) stress and unfolded protein response (UPR) such as ER chaperones and elements of the ubiquitin-proteasome system. RT-PCR, Western blotting, and immunocytochemical approaches were used to quantify and temporally order the UPR pathways involved in neurotoxin-induced cell death. 6-OHDA, but not MPP+, significantly increased hallmarks of UPR such as BiP, c-jun, and processed xbp1 mRNA. Both toxins increased the phosphorylation of UPR proteins, PERK and eIF2a, but only 6-OHDA increased phosphorylation of c-jun. Thus, 6-OHDA triggers multiple pathways associated with UPR, whereas MPP+ exhibits a more restricted response. 6-OHDA induced similar responses in primary dopaminergic neurons. These experiments will help clarify the molecular mechanisms associated with 6- OHDA and MPP+ toxicity and might aid in developing novel therapeutic avenues relevant to PD.