Detection of novel intracellular α-synuclein oligomeric species by fluorescence lifetime imaging

Oligomerization and aggregation of α-synuclein molecules are believed to play a major role in neuronal dysfunction and loss in Parkinson's disease (PD) and dementia with Lewy bodies. However, α-synuclein oligomerization and aggregation have been detected only indirectly in cells using detergent extraction methods. Here, we show for the first time intracellular α-synuclein oligomerization using fluorescence lifetime imaging (FLIM). Two forms of α-synuclein homomeric interactions were detected: an antiparallel amino terminus-carboxyl terminus interaction between α-synuclein molecules, and a close amino terminus-carboxy terminus interaction within single α-synuclein molecules. Coexpression of the chaperone protein Hsp70, which can block α-synuclein toxicity in several systems, causes α-synuclein to adopt a different, open conformation, but Hsp70 does not alter α-synuclein-α-synuclein interactions. Thus, the neuroprotective effect of Hsp70 can be explained by its chaperone activity on α-synuclein molecules, rather than alteration of α-synuclein- α-synuclein interactions.