Parkinsonian Mimetics Induce Aspects of Unfolded Protein Response in Death of Dopaminergic Neurons

Abstract

Genes associated with Parkinson's disease (PD) have suggested a role for ubiquitin-proteasome dysfunction and aberrant protein degradation in this disorder. Inasmuch as oxidative stress has also been implicated in PD, the present study examined transcriptional changes mediated by the Parkinsonism-inducing neurotoxins 6-hydroxydopamine (6-OHDA) and 1-methyl-4-phenylpyridinium (MPP ؉ ) in a dopaminergic cell line. Microarray analysis of RNA isolated from toxin treated samples revealed that the stress-induced transcription factor CHOP/Gadd153 was dramatically up-regulated by both 6-OHDA and MPP ؉ . Treatment with 6-OHDA also induced a large number of genes involved in endoplasmic reticulum stress and unfolded protein response (UPR) such as ER chaperones and elements of the ubiquitinproteasome system. Reverse transcription-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 eIF2␣, but only 6-OHDA increased phosphorylation of c-Jun. Thus, 6-OHDA is capable of triggering multiple pathways associated with UPR, whereas MPP ؉ exhibits a more restricted response. The involvement of UPR in these widely used neurotoxin models supports the role of ubiquitin-proteasome pathway dysfunction in PD.

Roles of CHOP/GADD153 in endoplasmic reticulum stress

“…Mutation of parkin, that is an E3 ubiquitin ligase, is one of the major causes of familial Parkinson's disease. 103 Parkin is induced by ER stress, and overexpression of parkin confers resistance to both ER stress and mutant a-synuclein-induced toxicity. 104,105 Furthermore, accumulation of polyglutamine-containing proteins was found to cause ER stress, presumably due to saturation of the cytosolic protein degradation system.…”

ER stress and neurodegenerative diseases

“…36,37 Compounds, such as 6-hydroxydopamine (6-OHDA) and N-methyl-4-phenyl-1, 2,3,6-tetrahydroyridine or its active derivative, MPP þ , induce oxidative stress and impair mitochondrial respiration and energy metabolism. Recent studies with cultured neuronal cells, including dopaminergic neurons, showed that these compounds trigger ER stress and induce a number of genes.…”

“…Recent studies with cultured neuronal cells, including dopaminergic neurons, showed that these compounds trigger ER stress and induce a number of genes. 36,37 Gene profiling revealed that both ER chaperones and other components of the UPR such as the transcription factor, CHOP/Gadd153 were upregulated in exposed cells, in addition to the phosphorylation of the ER stress kinases, IRE and PERK. 36,37 These changes were specific for the two PD mimetic and rotenone, a mitochondrial inhibitor that causes degeneration of dopaminergic neurons but not with other agents.…”

“…36,37 Gene profiling revealed that both ER chaperones and other components of the UPR such as the transcription factor, CHOP/Gadd153 were upregulated in exposed cells, in addition to the phosphorylation of the ER stress kinases, IRE and PERK. 36,37 These changes were specific for the two PD mimetic and rotenone, a mitochondrial inhibitor that causes degeneration of dopaminergic neurons but not with other agents. 37 There were some differences in the magnitude and pattern of gene responses induced by 6-OHDA and MPP þ , but both compounds clearly elicited an UPR in the neurons.…”

“…37 There were some differences in the magnitude and pattern of gene responses induced by 6-OHDA and MPP þ , but both compounds clearly elicited an UPR in the neurons. 36 Experiments carried out using neuronal cultures from Perk gene deleted mice revealed an increased sensitivity of the cells against treatment with 6-OHDA. 37 This suggests that neurons lacking Perk were unable to mount a proper UPR and are more vulnerable to 6-OHDA.…”