Strain Dependent Effects of Alpha-Synuclein Mutations on Mitochondrial Dysfunction

Abstract

Presence of α-synuclein aggregates in the brain is one of the major pathological hallmarks of Parkinson's disease (PD) and a point mutation in the gene encoding a-synuclein has been reported in familial PD cases. Previously, we have shown that for wild-type α-synuclein aggregation into oligomeric status is required for mitochondrial regulated cell toxicity. However, there is little understanding of how variant strains (monomers, oligomers, fibrils) of the α-synuclein mutations implicate neuronal vulnerability associated with PD. Here using various α-synuclein strains, monomers, oligomers and fibrils, carrying A30P, A53T or E46K point mutation, we examined the effect of these different forms of the mutants on neuronal survival following 24 hours incubation and the immediate effect on mitochondrial membrane potential as well as reactive oxygen spices (ROS) production using live cell imaging. We also measured the cellular redox state following exposure to the mutants using NADH autofluorescence. Our results show that unlike wild-type α-synuclein, all three mutant forms of α-synuclein induce cell toxicity and loss of mitochondrial membrane potential in their unfolded monomeric forms, prior to their aggregation into oligomeric species. Importantly, the different mutations A30P and A53T lead to an increase in cellular ROS production through different mechanisms. This work suggests that point mutations in α-synuclein, in addition to misfolding and aggregation of α-synuclein, are sufficient to cause neuronal vulnerability including cell death through oxidative stress related to mitochondrial dysfunction and excessive ROS.