Neuronal identity defines a-synuclein and tau toxicity

Pathogenic a-synuclein and tau are critical drivers of neurodegeneration and their mutations cause neuronal loss in patients. Whether the underlying preferential neuronal vulnerability is a cell-type intrinsic property or a consequence of increased expression levels remains elusive. Here, we explore cell-type specific a-synuclein and tau expression in human brain datasets and use deep phenotyping as well as brain- wide single-cell RNA sequencing of >200 live neuron types in fruit flies to ask which cellular environments react most to a-synuclein or tau toxicity. We detect phenotypic and transcriptomic evidence of differential neuronal vulnerability independent of a-synuclein or tau expression levels. Comparing vulnerable with resilient neurons in Drosophila enabled us to predict numerous human neuron subtypes with increased intrinsic susceptibility to pathogenic a-synuclein or tau. By uncovering synapse and Ca2+ homeostasis related genes as tau toxicity modifiers our work paves the way to leverage neuronal identity to uncover modifiers of neurodegeneration-associated toxic proteins. Drosophila brains at 5, 25 and 45 days were dissected, dissociated and scRNAseq performed with 10x v3.1 chemistry; GFP+ C2_3 neurons were FAC-sorted and 400 cells/sample were processed with an adapted Smart-seq3 protocol.