Structural and Morphological Characterization of Aggregated Species of α-Synuclein Induced by Docosahexaenoic Acid

The interaction of brain lipids with alpha-synuclein may play an important role in the pathogenesis of Parkinson disease (PD). Docosahexaenoic acid (DHA) is an abundant fatty acid of neuronal membranes, and it is presents at high levels in brain areas with alpha-synuclein inclusions of patients with PD. In animal models, an increase of DHA content in the brain induces alpha-synuclein oligomer formation in vivo. However, it is not clear whether these oligomeric species are the precursors of the larger aggregates found in Lewy bodies of post-mortem PD brains. To characterize these species and to define the role of fatty acids in amyloid formation, we investigated the aggregation process of alpha-synuclein in the presence of DHA. We found that DHA readily promotes alpha-synuclein aggregation and that the morphology of these aggregates is dependent on the ratio between the protein and DHA. In the presence of a molar ratio protein/DHA of 1:10, amyloid-like fibrils are formed. These fibrils are morphologically different from those formed by alpha-synuclein alone and have a less packed structure. At a protein/DHA molar ratio of 1:50, we observe the formation of stable oligomers. Moreover, chemical modifications, methionine oxidations, and protein-lipid adduct formations are induced by increasing concentrations of DHA. The extent of these modifications defines the structure and the stability of aggregates. We also show that alpha-synuclein oligomers are more toxic if generated in the presence of DHA in dopaminergic neuronal cell lines, suggesting that these species might be important in the neurodegenerative process associated with PD.