LAUSR

a-Synuclein (asyn) is the primary component of proteinaceous aggregates that pathologically define a category of diseases termed synucleinopathies, which includes Parkinson’s disease (PD) and dementia with Lewy bodies. Elucidating the native function and pathway involvement of asyn may provide insight into its pathogenic mechanism in neurodegeneration. Two recent articles published in conjunction in Cell Systems point to key cellular pathways involved in asyn toxicity that may ultimately enhance our understanding of asyn native function and assist in the discovery of targets for therapeutic intervention. aSyn has previously been shown to interact with proteins involved in vesicle trafficking, mitochondrial transport, and cytoskeletal function. However, traditional methods for determining protein-protein interactions, such as coimmunoprecipitation assays, rely on cell lysis, which can disturb normal compartmental localization. To determine more biologically relevant interactions based on native cellular localization, Chung et al used a novel approach combining ascorbate peroxidase (APEX) labeling with mass spectrometry to identify proteins that are spatially linked to asyn in living neurons. This novel technology has the unique advantage of labeling transient protein interactions in a live neuron with intact membranes and organelles. Using this methodology, they identified 225 potential asyn-interacting partners, including proteins found in the endocytic and retrograde trafficking pathways, proteins involved in mRNA metabolism and translation, and proteins encoded by genes known to be causal for Parkinson’s disease such as PARKIN and VPS35. Further validation of these targets by immunoprecipitation and membrane-2-hybrid methods confirmed a selection of direct physical asyn interactors. A limitation of the APEX-based approach is that potential interactions were investigated in normal neurons, and may not necessarily reflect interactions in disease. In addition, asyn is a small protein, and the C-terminal tag used for APEX labeling could impact normal protein-protein interactions. Khurana et al published an accompanying article from the same group in Cell Systems describing a yeast-based genetic screen to identify genes that modulate asyn toxicity. Yeast genes that impacted asyn toxicity were used to build networks of human gene interactions using TransposeNet, a novel computational approach, by redefining yeast gene homology to more broadly include known molecular interactions and protein structure. They found complementary results linking known PD genes involved in endocytic and retrograde trafficking such as VPS35 and RAB7L1. Through two very different and independent experimental approaches, they linked the same cellular pathways to asyn pathogenesis and found that known causal and risk factor genes for PD were functionally linked to asyn. The convergence of their spatial and genetic interaction data on the same protein networks emphasizes the importance of mRNA metabolism and the endocytic trafficking pathways in asyn pathogenesis and provides insight into how seemingly disparate genes and proteins may interconnect to cause neurodegeneration.