title: Impairment of Atg5-dependent autophagic flux promotes paraquat- and MPP⁺-induced apoptosis but not rotenone or 6-hydroxydopamine toxicity.
abstract: Controversial reports on the role of autophagy as a survival or cell death mechanism in dopaminergic cell death induced by parkinsonian toxins exist. We investigated the alterations in autophagic flux and the role of autophagy protein 5 (Atg5)-dependent autophagy in dopaminergic cell death induced by parkinsonian toxins. Dopaminergic cell death induced by the mitochondrial complex I inhibitors 1-methyl-4-phenylpyridinium (MPP⁺) and rotenone, the pesticide paraquat, and the dopamine analog 6-hydroxydopamine (6-OHDA) was paralleled by increased autophagosome accumulation. However, when compared with basal autophagy levels using chloroquine, autophagosome accumulation was a result of impaired autophagic flux. Only 6-OHDA induced an increase in autophagosome formation. Overexpression of a dominant negative form of Atg5 increased paraquat- and MPP⁺-induced cell death. Stimulation of mammalian target of rapamycin (mTOR)-dependent signaling protected against cell death induced by paraquat, whereas MPP⁺-induced toxicity was enhanced by wortmannin, a phosphoinositide 3-kinase class III inhibitor, rapamycin, and trehalose, an mTOR-independent autophagy activator. Modulation of autophagy by either pharmacological or genetic approaches had no effect on rotenone or 6-OHDA toxicity. Cell death induced by parkinsonian neurotoxins was inhibited by the pan caspase inhibitor (Z-VAD), but only caspase-3 inhibition was able to decrease MPP⁺-induced cell death. Finally, inhibition of the lysosomal hydrolases, cathepsins, increased the toxicity by paraquat and MPP⁺, supporting a protective role of Atg5-dependent autophagy and lysosomes degradation pathways on dopaminegic cell death. These results demonstrate that in dopaminergic cells, Atg5-dependent autophagy acts as a protective mechanism during apoptotic cell death induced by paraquat and MPP⁺ but not during rotenone or 6-OHDA toxicity.
authors.affiliation: * Redox Biology Center.
authors.forename: Aracely
authors.initials: A
authors.lastname: Garcia-Garcia
authors.forename: Annandurai
authors.initials: A
authors.lastname: Anandhan
authors.forename: Michaela
authors.initials: M
authors.lastname: Burns
authors.forename: Han
authors.initials: H
authors.lastname: Chen
authors.forename: You
authors.initials: Y
authors.lastname: Zhou
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Franco
mesh_terms: D015655:1-Methyl-4-phenylpyridinium / Q000633:toxicity*; D017209:Apoptosis / Q000187:drug effects*; D000071187:Autophagy-Related Protein 5; D053148:Caspase 3 / Q000378:metabolism; D061945:Caspase Inhibitors / Q000494:pharmacology; D002403:Cathepsins / Q000037:antagonists & inhibitors / Q000378:metabolism; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D020536:Enzyme Activators / Q000494:pharmacology; D006801:Humans; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D016627:Oxidopamine / Q000633:toxicity*; D010269:Paraquat / Q000633:toxicity*; D058539:Phosphatidylinositol 3-Kinase / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D012402:Rotenone / Q000633:toxicity*; D015398:Signal Transduction / Q000187:drug effects; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism; D014162:Transfection
chemical_list: C502778:ATG5 protein, human; D000071187:Autophagy-Related Protein 5; D061945:Caspase Inhibitors; D020536:Enzyme Activators; D008869:Microtubule-Associated Proteins; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors; D012402:Rotenone; D016627:Oxidopamine; C546842:MTOR protein, human; D058539:Phosphatidylinositol 3-Kinase; D058570:TOR Serine-Threonine Kinases; D002403:Cathepsins; C505407:CASP3 protein, human; D053148:Caspase 3; D010269:Paraquat; D015655:1-Methyl-4-phenylpyridinium
keywords: 6-hydroxydopamine; Atg5; MPP+; Parkinson’s disease.; apoptosis; autophagy; cathepsins; neurodegeneration; paraquat; rotenone