Suppression of -synuclein toxicity and vesicle trafficking defects by phosphorylation at S129 in yeast depends on genetic context

The aggregation of -synuclein (Syn) is a neuropathologic hallmark of Parkinsons disease and other synucleinopathies. In Lewy bodies, Syn is extensively phosphorylated, predominantly at serine 129 (S129). Recent studies in yeast have shown that, at toxic levels, Syn disrupts Rab homeostasis, causing an initial endoplasmic reticulum-to-Golgi block that precedes a generalized trafficking collapse. However, whether Syn phosphorylation modulates trafficking defects has not been evaluated. Here, we show that constitutive expression of Syn in yeast impairs late-exocytic, early-endocytic and/or recycling trafficking. Although members of the casein kinase I (CKI) family phosphorylate Syn at S129, they attenuate Syn toxicity and trafficking defects by an S129 phosphorylation-independent mechanism. Surprisingly, phosphorylation of S129 modulates Syn toxicity and trafficking defects in a manner strictly determined by genetic background. Abnormal endosome morphology, increased levels of the endosome marker Rab5 and co-localization of mammalian CKI with Syn aggregates are observed in brain sections from Syn-overexpressing mice and human synucleinopathies. Our results contribute to evidence that suggests Syn-induced defects in endocytosis, exocytosis and/or recycling of vesicles involved in these cellular processes might contribute to the pathogenesis of synucleinopathies.