Overexpression of alpha-synuclein at non-toxic levels increases dopaminergic cell death induced by copper exposure via modulation of protein degradation pathways

Authors

Annadurai Anandhan, University of Nebraska-Lincoln
Humberto Rodriguez-Rocha, University of Nebraska-Lincoln
Iryna Bohovych, University of Nebraska-LincolnFollow
Amy M. Griggs, Purdue University
Laura Zavala-Flores, University of Nebraska-Lincoln
Elsa M. Reyes-Reyes, University of Arizona
Javier Seravalli, University of Nebraska-LincolnFollow
Lia A. Stanciu, Purdue University
Jaekwon Lee, University of Nebraska-LincolnFollow
Jean-Christophe Rochet, Purdue University
Oleh Khalimonchuk, University of Nebraska-LincolnFollow
Rodrigo Franco, University of Nebraska-LincolnFollow

Date of this Version

2015

Citation

Neurobiol Dis. 2015 September ; 81: 76–92.

Comments

Copyright © 2014 Elsevier Inc. Used by permission.

Abstract

Gene multiplications or point mutations in alpha (α)-synuclein are associated with familial and sporadic Parkinson’s disease (PD). An increase in copper (Cu) levels has been reported in the cerebrospinal fluid and blood of PD patients, while occupational exposure to Cu has been suggested to augment the risk to develop PD. We aimed to elucidate the mechanisms by which α-synuclein and Cu regulate dopaminergic cell death. Short-term overexpression of WT or A53T α-synuclein had no toxic effect in human dopaminergic cells and primary midbrain cultures, but it exerted a synergistic effect on Cu-induced cell death. Cell death induced by Cu was potentiated by overexpression of the Cu transporter protein 1 (Ctr1) and depletion of intracellular glutathione (GSH) indicating that the toxic effects of Cu are linked to alterations in its intracellular homeostasis. Using the redox sensor roGFP, we demonstrated that Cu-induced oxidative stress was primarily localized in the cytosol and not in the mitochondria. However, α-synuclein overexpression had no effect on Cu-induced oxidative stress. WT or A53T α-synuclein overexpression exacerbated Cu toxicity in dopaminergic cells and yeast in the absence of α-synuclein aggregation. Cu increased autophagic flux and protein ubiquitination. Impairment of autophagy by overexpression of a dominant negative Atg5 form or inhibition of the ubiquitin/proteasome system (UPS) with MG132 enhanced Cu-induced cell death. However, only inhibition of the UPS stimulated the synergistic toxic effects of Cu and α-synuclein overexpression. Our results demonstrate that α-synuclein stimulates Cu toxicity in dopaminergic cells independent from its aggregation via modulation of protein degradation pathways.