Lipid Peroxidation Products HNE and ONE Promote and Stabilize Alpha-Synuclein Oligomers by Chemical Modifications

The aggregation of alpha-synuclein (alpha SN) and increased oxidative stress leading to lipid peroxidation are pathological characteristics of Parkinson's disease (PD). Here, we report that aggregation of alpha SN in the presence of lipid peroxidation products 4-hydroxy-2-nonenal (HNE) and 4-oxo-2-nonenal (ONE) increases the stability and the yield of alpha SN oligomers (alpha SO). Further, we show that ONE is more efficient than HNE at inducing alpha SO. In addition, we demonstrate that the two alpha SO differ in both size and shape. ONE-alpha SO are smaller in size than HNE-alpha SO, except when they are formed at a high molar excess of aldehyde. In both monomeric and oligomeric alpha SN, HisSO is the main target of HNE modification, and HNE-induced oligomerization is severely retarded in the mutant HisSOAla alpha SN. In contrast, ONE-induced aggregation of HisSOAla alpha SN occurs readily, demonstrating the different pathways for inducing alpha SN aggregation by HNE and ONE. Our results show different morphologies of the HNE-treated and ONE-treated alpha SO and different roles of HisSO in their modification of alpha SN, but we also observe structural similarities between these alpha SO and the non-treated alpha SO, e.g., flexible C-terminus, a folded core composed of the N-terminal and NAC region. Furthermore, HNE-alpha SO show a similar deuterium uptake as a previously characterized oligomer formed by non-treated alpha SO, suggesting that the backbone conformational dynamics of their folded cores resemble one another.