Article

Dopamine-modified alpha-synuclein blocks chaperone-mediated autophagy. J Clin Invest

Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, Yeshiva University, New York, New York 10461, USA.
Journal of Clinical Investigation (Impact Factor: 13.77). 03/2008; 118(2):777-88. DOI: 10.1172/JCI32806
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ABSTRACT Altered degradation of alpha-synuclein (alpha-syn) has been implicated in the pathogenesis of Parkinson disease (PD). We have shown that alpha-syn can be degraded via chaperone-mediated autophagy (CMA), a selective lysosomal mechanism for degradation of cytosolic proteins. Pathogenic mutants of alpha-syn block lysosomal translocation, impairing their own degradation along with that of other CMA substrates. While pathogenic alpha-syn mutations are rare, alpha-syn undergoes posttranslational modifications, which may underlie its accumulation in cytosolic aggregates in most forms of PD. Using mouse ventral medial neuron cultures, SH-SY5Y cells in culture, and isolated mouse lysosomes, we have found that most of these posttranslational modifications of alpha-syn impair degradation of this protein by CMA but do not affect degradation of other substrates. Dopamine-modified alpha-syn, however, is not only poorly degraded by CMA but also blocks degradation of other substrates by this pathway. As blockage of CMA increases cellular vulnerability to stressors, we propose that dopamine-induced autophagic inhibition could explain the selective degeneration of PD dopaminergic neurons.

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    • "Clearance of WT and/or A53T α-synuclein aggregates has been shown to be mediated by both autophagy and the ubiquitin/proteasome pathway (Cuervo et al., 2004; Ebrahimi-Fakhari et al., 2011; Webb et al., 2003). Reciprocally, α-synuclein can interfere with autophagy (Martinez-Vicente et al., 2008; Winslow et al., 2010) and the ubiquitin/proteasome system (Chen et al., 2005; Lindersson et al., 2004; Martin-Clemente et al., 2004; Snyder et al., 2003; Tanaka et al., 2001; Zhang et al., 2008). For example, WT and A53T α-synuclein variants inhibit autophagy via impairment of the cytosolic translocation of the high mobility group box 1 (HMGB1), reducing HMGB1-beclin-1 binding , and increasing Beclin-1-Bcl-2 association (Song et al., 2014), as well as by a decrease in the activity of the transcriptional regulator of the autophagy-lysosome pathway, TFEB (transcriptional factor EB) (Decressac et al., 2013). "
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    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. Copyright © 2014. Published by Elsevier Inc.
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    • "Both mutant forms of a-synuclein as well as post-translationally modified forms of the wild type protein can be delivered to lysosomes by hsc70, where they bind with abnormally high affinity to LAMP-2A. For reasons yet unclear, these pathogenic proteins fail to translocate across the lysosomal membrane, but because they remain tightly bound to the CMA receptor, they compromise clearance of any other protein through this pathway (Cuervo et al. 2004; Martinez-Vicente et al. 2008). A similar CMA shut-down has been proposed to be induced by other PD mutant proteins, such as ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1; Kabuta et al. 2008), and even beyond PD, with the identification that specific mutant forms of tau – a protein linked to AD pathogenesis – also interact in an abnormal way with components of CMA at the lysosomal membrane and block the degradation of other substrates (Wang et al. 2009). "
    Protein quality control in neurodegenerative diseases, 2013 edited by Morimoto RI, Christen Y, 12/2012: chapter Selective autophagy in cellular quality control: pages 63-75; Springer., ISBN: 978-3642279270
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    • "Normal Asyn binds to the CMAspecific receptor LAMP-2A on the lysosomal membrane and is subsequently degraded by CMA. However, mutant forms of Asyn (A53T and A30P) and Asyn modified by dopamine tightly bind to the CMA receptors on the lysosomal membrane and inhibit both their own degradation and that of other CMA substrates [38] [41]. The dysfunction of CMA triggers neuronal dysfunction and increases vulnerability to stress. "
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