Direct Modulation of the Mitochondrial Permeability Transition Pore by Oligomeric Alpha-Synuclein Causes Toxicity in PD

Alpha-synuclein aggregation and mitochondrial dysfunction are central to the pathogenesis of Parkinson's disease (PD). This study investigates the structure specific effects of α-synuclein on mitochondrial function and demonstrates the mechanism by which oligomerisation of the protein results in a toxic gain of function within mitochondria.We have previously shown that monomeric α-synuclein enters mitochondria where it interacts with ATP synthase, and aids its efficiency. Employing a proximity ligation assay, we show an interaction between oligomers and ATP synthase, a proposed key component of the mPTP. We demonstrate that beta sheet rich α-synuclein oligomers uniquely induce opening of the mitochondrial permeability transition pore (mPTP) in whole cells and isolated mitochondria. We report that oligomers, but not monomers, generate reactive oxygen species and mitochondrial membrane lipid peroxidation, and these trigger mPTP opening. This oligomer-induced effects lead to neuronal cell death, which could be abrogated by preincubation of the cells with the mPTP inhibitor Cyclosporin A.We validated our findings in an iPS derived neuronal model with an α-synuclein triplication in which increased levels of aggregated α-synuclein cause early onset PD. In this model we report that oligomers also have a strong interaction with the ATP synthase. Furthermore, we demonstrate a low threshold for mPTP opening on exposure to high laser and calcium. mPTP opening in this model led to cell death which could again be prevented by mPTP inhibition. We were thus able to conclude that the mitochondrial abnormalities seen in the iPS cells with high levels of α-synuclein were likely to be mediated by the beta-sheet oligomeric form of the protein.This study provides evidence of a direct effect of oligomers on mitochondria and is the first to specifically link oligomeric α-synuclein to ATP synthase leading to neuronal death.