Cellular pathologies in SNCA mutant neurons: Implications for Parkinson’s disease
Parkinson’s disease (PD) is associated with oxidative stress, a genetic susceptibility to agrochemical exposure, and impaired proteostasis which primarily affect dopaminergic neurons that populate the substantia nigra pars compacta, the region of the PD brain that most prominently degenerates. The discovery that mutations in alpha-synuclein (aSyn) causes inherited forms of PD has dramatically improved our understanding of PD at a cellular level. Herein, we use human stem-cell derived-dopaminergic neurons harboring the A53T or E46K aSyn mutation and isogenic controls to assess PD-related pathologies. We show that early accumulation of aSyn in PDneurons results in impairments to the antioxidant response and mitochondrial dynamics. We determined that these impairments can be attributed to mutant aSyn’s inability to associate with PKC, resulting in decreased Nrf2 phosphorylation and activation, consequently reducing the antioxidant response. We demonstrate that forced activation of Nrf2 by pharmaceutical modulation with dimethyl fumarate (DMF) rescues antioxidant enzyme expression in PD neurons. Further, our findings highlight the importance of genetic vulnerability to toxin exposure, including the agrochemicals paraquat, maneb and rotenone. Using these toxins below the reported EPAlowest observable effects levels we demonstrate that anterograde mitochondrial transport was impaired in mutant aSyn neurons, but not in control neurons. We determined that this was due to the nitration of alpha-tubulin which inhibited the association of aSyn and kinesin 5B with microtubules. We showed that we could rescue mitochondrial anterograde trafficking by using the nitric oxide synthetase inhibitor L-NAME. In addition, we demonstrate that aSyn accumulates on multi-vesicular bodies and lysosomes in PD neurons. As such, aSyn is secreted by exosomes which promotes the spread of disease from cell-to-cell. We demonstrate that constitutive expression of LC3B reduces the accumulation of aSyn (PS129) as well as the amount of secreted aSyn in exosomes. Since transmission of aSyn is coincident with mitochondrial pathology and oxidative stress in previously healthy cells, our findings suggest that targeting aSyn or exosomes might slow disease progression. Altogether this research offers mechanistic insight as to the development and spread of PD-pathology.
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