The Parkinson's disease-associated A53E mutation decreases alpha-synuclein aggregation and phosphorylation in vivo

Abnormal α-synuclein aggregation is the defining feature of Parkinson's disease (PD) and related synucleinopathies. Rare disease-causing alpha-synuclein mutations either accelerate or slow fibrillization in vitro, however their effects in vivo are less well understood. Interestingly, the A53E mutation slows fibrillization in vitro but causes a more virulent form of PD. We use an in vivo model to examine the aggregation dynamics of disease-causing A53E and E46K alpha-synuclein mutations. Fluorescence recovery after photobleaching within presynaptic terminals shows that A53E-alpha-synuclein is significantly more mobile than E46K- or wild-type (WT)-alpha-synuclein. Longitudinal analysis in vivo reveals that E46K- and WT-alpha-synuclein become progressively less mobile over days, while A53E maintains high mobility, suggesting delayed progression toward aggregated states. We also find that A53E-alpha-synuclein lacks detectable disease-relevant phosphorylation at serine-129, unlike E46K-and WT-alpha-synuclein. To mechanistically test whether this unique lack of phosphorylation drives its high mobility, we genetically modified A53E-alpha-synuclein to mimic S129 phosphorylation, and show that this manipulation indeed decreases its mobility, directly implicating the phosphorylation status of this residue in mobility.