Dopamine-modified α-synuclein blocks chaperone-mediated autophagy
Marta Martinez-Vicente, … , David Sulzer, Ana Maria Cuervo
Marta Martinez-Vicente, … , David Sulzer, Ana Maria Cuervo
Published January 2, 2008
Citation Information: J Clin Invest. 2008;118(2):777-788. https://doi.org/10.1172/JCI32806.
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Research Article Neuroscience

Dopamine-modified α-synuclein blocks chaperone-mediated autophagy

Abstract

Altered degradation of α-synuclein (α-syn) has been implicated in the pathogenesis of Parkinson disease (PD). We have shown that α-syn can be degraded via chaperone-mediated autophagy (CMA), a selective lysosomal mechanism for degradation of cytosolic proteins. Pathogenic mutants of α-syn block lysosomal translocation, impairing their own degradation along with that of other CMA substrates. While pathogenic α-syn mutations are rare, α-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 α-syn impair degradation of this protein by CMA but do not affect degradation of other substrates. Dopamine-modified α-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.

Authors

Marta Martinez-Vicente, Zsolt Talloczy, Susmita Kaushik, Ashish C. Massey, Joseph Mazzulli, Eugene V. Mosharov, Roberto Hodara, Ross Fredenburg, Du-Chu Wu, Antonia Follenzi, William Dauer, Serge Przedborski, Harry Ischiropoulos, Peter T. Lansbury, David Sulzer, Ana Maria Cuervo

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Figure 1

Effect of oxidation and phosphorylation of α-syn on its degradation in lysosomes by CMA.

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Effect of oxidation and phosphorylation of α-syn on its degradation in l...
(A) Association of unmodified and oxidized α-syn and of the S129E mutant of α-syn with isolated lysosomes untreated (binding [Bind]) or previously treated with proteinase inhibitors (association: binding + uptake [Assoc]). Lane 1 shows one-tenth of the amount of protein added to the incubation (Input). (B) Percentage of each protein bound and translocated (uptake = association – binding) inside lysosomes calculated from the densitometric quantification of 11–13 immunoblots such as the representative immunoblots shown in A. The right-hand bars show the percentage of α-syn bound to the lysosomal membrane that was translocated into lysosomes. (C) Effect of a 2-molar excess of GAPDH or ovalbumin (Ovalb) on the association of unmodified, oxidized, and S129E mutant α-syn with lysosomes. Left panel: representative immunoblot. Right panel: percentage of inhibition of the lysosomal association of each form of α-syn calculated from the densitometric quantification of 4–6 immunoblots such as those shown here. (D) Effect of adding these 3 forms of α-syn in equimolar ratio with [14C]GAPDH on the degradation of [14C]GAPDH by intact lysosomes. Values are expressed as percentage of inhibition of GAPDH degradation and are mean + SEM of 4–5 experiments with triplicate samples. *P < 0.05; **P < 0.01.