alpha-Synuclein budding yeast model: toxicity enhanced by impaired proteasome and oxidative stress

Parkinson's disease (PD) is a common neurodegenerative disorder that results from the selective loss of midbrain dopaminergic neurons. Misfolding and aggregation of the protein alpha-synuclein, oxidative damage, and proteasomal impairment are all hypotheses for the molecular cause of this selective neurotoxicity. Here, we describe a Saccharomyces cerevisiae model to evaluate the misfolding, aggregation, and toxicity-inducing ability of wild-type alpha-synuclein and three mutants (A30P, A53T, and A30P/A53T), and we compare regulation of these properties by dysfunctional proteasomes and by oxidative stress. We found prominent localization of wild-type and A53T alpha-synuclein near the plasma membrane, supporting known in vitro lipid-binding ability. In contrast, A30P was mostly cytoplasmic, whereas A30P/A53T displayed both types of fluorescence. Surprisingly, alpha-synuclein was not toxic to several yeast strains tested. When yeast mutants for the proteasomal barrel (doa3-1) were evaluated, delayed alpha-synuclein synthesis and membrane association were observed; yeast mutant for the proteasomal cap (sen3-1) exhibited increased accumulation and aggregation of alpha-synuclein. Both sen3-1and doa3-1 mutants exhibited synthetic lethality with alpha-synuclein. When yeasts were challenged with an oxidant (hydrogen peroxide), alpha-synuclein was extremely lethal to cells that lacked manganese superoxide dismutase Mn-SOD (sod2Delta) but not to cells that lacked copper, zinc superoxide dismutase Cu,Zn-SOD (sod1Delta). Despite the toxicity, sod2Delta cells never displayed intracellular aggregates of alpha-synuclein. We suggest that the toxic alpha-synuclein species in yeast are smaller than the visible aggregates, and toxicity might involve alpha-synuclein membrane association. Thus, yeasts have emerged effective organisms for characterizing factors and mechanisms that regulate alpha-synuclein toxicity.