Inhibition of Membrane-Induced Alpha-Synuclein (aSyn) Aggregation: A Strategy to Interfere with aSyn Neurotoxicity in Parkinson's Disease (PD)

Oligomerization of the presynaptic protein aSyn is thought to play a key role in the pathogenesis of PD. aSyn exists in a number of conformations, including a membrane‐bound state likely involved in regulating synaptic vesicle trafficking. aSyn interacts with anionic phospholipid vesicles by forming an amphipathic α‐helix of various lengths. We hypothesize that disruption of interactions between aSyn and phospholipid membranes leads to a shift to a short‐helix, lipid‐bound form, which is more susceptible to forming toxic aSyn oligomers due to exposure of the protein's central hydrophobic region. Therefore, stabilization of the long‐helix form of lipid‐bound aSyn should prevent membrane‐induced aggregation and alleviate aSyn neurotoxicity. To address this hypothesis, endosulfine alpha (ENSA), a protein that interacts selectively with membrane‐bound aSyn, and a series of peptides identified as interactors of lipid‐bound aSyn via phage display screening were characterized in terms of their effects on membrane‐induced aSyn aggregation, aSyn‐mediated membrane permeabilization, and aSyn neurotoxicity in primary midbrain cultures. We found that A30P and G51D, two aSyn variants with disrupted membrane interactions, had an increased ability to form SDS‐resistant aggregates at the membrane surface and to elicit neurotoxicity than wild type (WT) aSyn, and both triggered the disruption of dye‐loaded vesicles under conditions identical to those that promoted membrane‐induced aggregation. WT ENSA (but not the non‐aSyn‐binding S109E variant) and a subset of phage display peptides attenuated aSyn self‐assembly at the membrane, vesicle disruption, and aSyn neurotoxicity. Intriguingly, ENSA was found to be down‐regulated in the brains of patients with dementia with Lewy bodies or PD versus non‐diseased individuals. Current efforts are focused on characterizing the aggregation of aSyn variants in biological membranes and monitoring aSyn‐mediated vesicle permeabilization in neuronal cells, with the ultimate aim of elucidating neuroprotective mechanisms of ENSA and aSyn‐binding peptides in cellular models relevant to PD. Our findings strongly support the idea that membrane‐induced aSyn aggregation plays a critical role in aSyn neurotoxicity, and they suggest that targeting this process is a viable therapeutic strategy for PD. Support or Funding Information Branfman Family Foundation, Indiana CTSI Core Pilot Grant, Indiana CTSI Collaboration in Translational Research Grant, Richard F. Borch Research Enhancement Award