Mitochondrial dysfunction, proteasome inhibition, and α‐synuclein aggregation are thought to play important roles in the pathogenesis of Parkinson’s disease (PD). Rare cases of early‐onset PD have been linked to mutations in the gene encoding DJ‐1, a protein with antioxidant and chaperone functions. In this study, we examined whether DJ‐1 protects against various stresses involved in PD, and we investigated the underlying mechanisms. Expression of wild‐type DJ‐1 rescued primary dopaminergic neurons from toxicity elicited by rotenone, proteasome inhibitors, and mutant α‐synuclein. Neurons with reduced levels of endogenous DJ‐1 were sensitized to each of these insults, and DJ‐1 mutants involved in familial PD exhibited decreased neuroprotective activity. DJ‐1 alleviated rotenone toxicity by up‐regulating total intracellular glutathione. In contrast, inhibition of α‐synuclein toxicity by DJ‐1 correlated with up‐regulation of the stress‐inducible form of Hsp70. RNA interference studies revealed that this increase in Hsp70 levels was necessary for DJ‐1‐mediated suppression of α‐synuclein aggregation, but not toxicity. Our findings suggest that DJ‐1 acts as a versatile pro‐survival factor in dopaminergic neurons, activating different protective mechanisms in response to a diverse range of PD‐related insults.

Parkinson's disease (PD) is a neurologic disorder characterized by dopaminergic cell death in the substantia nigra. PD pathogenesis involves mitochondrial dysfunction, proteasome impairment, and α-synuclein aggregation, insults that may be especially toxic to oxidatively stressed cells including dopaminergic neurons. The enzyme methionine sulfoxide reductase A (MsrA) plays a critical role in the antioxidant response by repairing methionine-oxidized proteins and by participating in cycles of methionine oxidation and reduction that have the net effect of consuming reactive oxygen species. Here, we show that MsrA suppresses dopaminergic cell death and protein aggregation induced by the complex I inhibitor rotenone or mutant α-synuclein, but not by the proteasome inhibitor MG132. By comparing the effects of MsrA and the small-molecule antioxidants N-acetyl-cysteine and vitamin E, we provide evidence that MsrA protects against PD-related stresses primarily via methionine sulfoxide repair rather than by scavenging reactive oxygen species. We also demonstrate that MsrA efficiently reduces oxidized methionine residues in recombinant α-synuclein. These findings suggest that enhancing MsrA function may be a reasonable therapeutic strategy in PD. Keywords aggresome; dopamine; glutathione; heat shock protein; methionine sulfoxide reductase; neurodegeneration; oxidative stress; Parkinson's disease; proteasome; protofibril; rotenone; synuclein Parkinson's disease (PD) is a neurologic disorder that involves a selective loss of dopaminergic neurons from the substantia nigra [1,2]. The postmortem brains of PD patients are characterized by reduced activity of mitochondrial complex I, an enzyme of the mitochondrial electron transport chain [3,4]. In turn, this defect may cause a 'leakage' of electrons from mitochondria, leading to the accumulation of reactive oxygen species (ROS) that damage *Corresponding author. Address: Jean-Christophe Rochet, Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, 575 Stadium Mall Drive, RHPH 410A, West Lafayette, Indiana, 47907-209147907- . Fax: 765-494-1414. E-mail: rochet@pharmacy.purdue.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access Author ManuscriptFree Radic Biol Med. Author manuscript; available in PMC 2009 August 1. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript proteins, lipids, and nucleic acids [3,5]. The brains of PD patients also show evidence of impaired proteasomal function [6], a defect that results in increased oxidative stress and decreased elimination...