Abstract
While mutations in the SNCA gene (α-synuclein [α-syn]) are causal in rare familial forms of Parkinson's disease (PD), the prevalence of α-syn aggregates in the cortices of sporadic disease cases emphasizes the need to understand the link between α-syn accumulation and disease pathogenesis. By employing a combination of human pluripotent stem cells (hPSCs) that harbor the SNCA-A53T mutation contrasted against isogenic controls, we evaluated the consequences of α-syn accumulation in human A9-type dopaminergic (DA) neurons (hNs). We show that the early accumulation of α-syn in SNCA-A53T hNs results in changes in gene expression consistent with the expression profile of the substantia nigra (SN) from PD patients, analyzed post mortem. Differentially expressed genes from both PD patient SN and SNCA-A53T hNs were associated with regulatory motifs transcriptionally activated by the antioxidant response pathway, particularly Nrf2 gene targets. Differentially expressed gene targets were also enriched for gene ontologies related to microtubule binding processes. We thus assessed the relationship between Nrf2-mediated gene expression and neuritic pathology in SNCA-A53T hNs. We show that SNCA-mutant hNs have deficits in neuritic length and complexity relative to isogenic controls as well as contorted axons with Tau-positive varicosities. Furthermore, we show that mutant α-syn fails to complex with protein kinase C (PKC), which, in turn, results in impaired activation of Nrf2. These neuritic defects result from impaired Nrf2 activity on antioxidant response elements (AREs) localized to a microtubule-associated protein (Map1b) gene enhancer and are rescued by forced expression of Map1b as well as by both Nrf2 overexpression and pharmaceutical activation in PD neurons.