In vivo Proximity & Spatial Proteomics with CRISPR Screening Identify STXBP1 as a Protective Modifier of α-synuclein Toxicity in Dopamine Neurons.

Parkinson's disease (PD) is a disease of adults involving the loss of dopaminergic neurons after a long, asymptomatic, prodromal period. α-synuclein, LRRK2, and VPS35 are linked to familial PD, however, how these mutations predispose dopamine neurons to death during the early prodromal phases remains unclear. Here, we used in vivo native proximity proteomics (iBioID) and dopaminergic neuron-specific subcellular proteomics across multiple PD models to uncover early alterations preceding neuronal loss. Our analyses identified convergent disruptions in synaptic protein abundance, indicating that presynaptic trafficking defects are early events in PD pathogenesis. Using a targeted CRISPR-based genetic screen in dopamine neurons, we demonstrated that mimicking this misregulation of STXBP1 amplifies vulnerability to α-synuclein, implicating it as a previously underappreciated toxicity buffering factor. These findings highlight convergent mechanisms that sensitize dopamine neuronal degeneration and that presynaptic vesicle SNARE-complex proteins could serve as key targets for disease-modifying therapies in PD and related neurodegenerative disorders.