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.
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
Increased intracellular levels of dopamine enhance the association of modified α-syn to lysosomes and block CMA.