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: 13.22). 03/2008; 118(2):777-88. DOI: 10.1172/JCI32806
Source: PubMed


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.
    Neurobiology of Disease 12/2014; DOI:10.1016/j.nbd.2014.11.018 · 5.08 Impact Factor
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    • "Once forming insoluble inclusions, they are much more resistant to CMA-mediated degradation. These aggregates may often exert a “clogging or blockage effect” at the lysosomal membrane, thus becoming toxic by inhibiting the CMA-mediated degradation of other cytosolic substrate proteins [51,55]. Although it is not clear whether CMA dysfunction may contribute to the initial formation of insoluble inclusions, it is quite possible that the “blockage effect” on CMA may exacerbate the formation of inclusion bodies by increasing misfolded protein concentrations in the cytoplasm. "
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    ABSTRACT: Chaperone-mediated autophagy (CMA) selectively delivers cytosolic proteins with an exposed CMA-targeting motif to lysosomes for degradation and plays an important role in protein quality control and cellular homeostasis. A growing body of evidence supports the hypothesis that CMA dysfunction may be involved in the pathogenic process of neurodegenerative diseases. Both down-regulation and compensatory up-regulation in CMA activities have been observed in association with neurodegenerative conditions. Recent studies have revealed several new mechanisms by which CMA function may be involved in the regulation of factors critical for neuronal viability and homeostasis. Here, we summarize these recent advances in the understanding of the relationship between CMA dysfunction and neurodegeneration and discuss the therapeutic potential of targeting CMA in the treatment of neurodegenerative diseases.
    Translational Neurodegeneration 09/2014; 3(1):20. DOI:10.1186/2047-9158-3-20
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    • "Interestingly, both CMA and proteasome can degrade the two proteins associated with autosomal dominant inheritance of PD, i.e., α-syn (PARK1/PARK4 locus) and Leucine-rich repeat kinase 2 (LRRK2–PARK8 locus) (Webb et al., 2003; Cuervo et al., 2004; Orenstein et al., 2013). However, PD-linked α-syn mutants (as well as post-translationally dopamine-modified wild-type α-syn) and mutant forms of LRRK2 block CMA activity, resulting in insufficient clearance and subsequent accumulation and aggregation of α-syn (Cuervo et al., 2004; Martinez-Vicente et al., 2008; Mak et al., 2010; Orenstein et al., 2013). Notably, two other genes encoding for lysosomal proteins have been linked to PD: the lysosomal type 5 P-type ATPase (ATP13A2—PARK9 locus) (Ramirez et al., 2006) and the enzyme glucocerebrosidase (GBA; Aharon-Peretz et al., 2004; Di Fonzo et al., 2007; Sidransky et al., 2009). "
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    ABSTRACT: Neurodegenerative diseases are (i) characterized by a selective neuronal vulnerability to degeneration in specific brain regions; and (ii) likely to be caused by disease-specific protein misfolding. Parkinson's disease (PD) is characterized by the presence of intraneuronal proteinacious cytoplasmic inclusions, called Lewy Bodies (LB). α-Synuclein, an aggregation prone protein, has been identified as a major protein component of LB and the causative for autosomal dominant PD. Lysosomes are responsible for the clearance of long-lived proteins, such as α-synuclein, and for the removal of old or damaged organelles, such as mitochondria. Interestingly, PD-linked α-synuclein mutants and dopamine-modified wild-type α-synuclein block its own degradation, which result in insufficient clearance, leading to its aggregation and cell toxicity. Moreover, both lysosomes and lysosomal proteases have been found to be involved in the activation of certain cell death pathways. Interestingly, lysosomal alterations are observed in the brains of patients suffering from sporadic PD and also in toxic and genetic rodent models of PD-related neurodegeneration. All these events have unraveled a causal link between lysosomal impairment, α-synuclein accumulation, and neurotoxicity. In this review, we emphasize the pathophysiological mechanisms connecting α-synuclein and lysosomal dysfunction in neuronal cell death.
    Frontiers in Neuroanatomy 08/2014; 8(83). DOI:10.3389/fnana.2014.00083 · 3.54 Impact Factor
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