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

Although a-synucleinis 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) .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.Transcriptomic analysis and isogenic correction of a-synuclein triplication revealed that intraneuronal a-synuclein levels solely and sufficiently explained vulnerability to cell death. Overall design: RNASeq experiment to compare the SNCA triplication iPSC lines (n=3 or 3 clones) or healthy control lines (n=3) at baseline and after induction of alpha-synuclein aggregation for 2 weeks. This was to investigate whether there are consistent changes upon synuclein aggregation in Triplication lines (clone 1, clone 3, clone 5) or healthy control lines (AH017, OX3, SFC840) when compared to their corresponding baseline (NSC) using the three different aggregation conditions (WTPFF, PDamp, MSAamp). A total of 24 different human iPSC samples were sequenced on the Novaseq 6000 platform.