Phenotypic manifestation of alpha-synuclein strains derived from Parkinson's disease and multiple system atrophy in human dopaminergic neurons

Although?a-synuclein is implicated in the pathogenesis of Parkinson's disease and related disorders, it remains unclear whether specific conformations or levels of?a-synuclein assemblies are toxic and how they cause progressive loss of human dopaminergic neurons. To address this issue, we used iPSC-derived dopaminergic neurons with a-synuclein triplication or controls where endogenous a-synuclein was imprinted into synthetic or disease-relevant conformations. We used a-synuclein fibrils generated de novo or amplified from homogenates of brains affected with Parkinson's disease (n=3) or multiple system atrophy (n=5). We found that a 2.5-fold increase in a-synuclein levels in a-synuclein gene triplication neurons promoted seeded aggregation in a dose and time-dependent fashion, which was associated with a further increase in a-synuclein gene expression.? Progressive neuronal loss was observed only in a-synuclein triplication neurons seeded with brain-amplified fibrils. Transcriptomic analysis and isogenic correction of a-synuclein triplication revealed that intraneuronal?alpha-synuclein levels solely and sufficiently explained vulnerability to neuronal death Overall design: RNASeq experiment to compare the SNCA triplication iPSC line (n=3 biological replicates per condition) at baseline and after induction of alpha-synuclein aggregation for 1 and 2 weeks. This was done to investigate whether there are transcriptomic changes upon alpha-synuclein aggregation within neurons using SNCA Triplication line (SFC831-03-03) when compared to their corresponding baseline Non-seeded controls (NSC) using three different types of fibrils: de novo generated fibrils (FIB), MSA amplified Fibrils (MSA) or PD amlpified Fibrils (PD) at 1 microM. A total of 24 different human iPSC samples were sequenced on the Novaseq 6000 platform.