Autophagy Dysfunction in Parkinson’s Disease and Related Synucleinopathies

Pitcairn, Caleb

doi:https://doi.org/10.21985/n2-n18c-fv83

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Autophagy Dysfunction in Parkinson’s Disease and Related Synucleinopathies

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Genetic studies have found variants in the protein-degrading autophagy-lysosomal pathway (ALP) to be among the most common risk factors for developing Parkinson’s disease (PD). Macroautophagy (MA) is the arm of this pathway which delivers cytosolic components to lysosomes for degradation and is essential for neuronal health. The defining pathological protein of PD, alpha-synuclein (a-syn), has been shown to inhibit MA in cell lines and animal models, but the mechanism of inhibition is not well understood. We previously found that a-syn adversely associates with SNARE protein ykt6 and inhibits its hydrolase trafficking activity (Cuddy et al., 2019). Because ykt6 is regulated by farnesylation, this activity could be rescued by activating ykt6 with farnesyltransferase inhibitor (FTI) treatment. Ykt6 is also required for several steps in MA, and we hypothesized that a similar mechanism may explain a-syn’s inhibition of autophagy. We therefore investigated autophagy phenotypes in PD patient-derived human iPSC-derived dopaminergic neurons (iPSn) carrying an endogenous multiplication in the gene encoding a-syn. Mature a-syn-overexpressing iPSn exhibited reduced MA flux and dysfunctional autophagosome-lysosome fusion when compared to CRISPR-corrected isogenic controls. This was accompanied by reduced association of ykt6 with its fusion SNARE binding partner SNAP-29 and increased farnesyltransferase enzyme. Treatment with small molecule FTI LNK-754 restored autophagy to control levels, and this rescue was found to depend on ykt6 activity. Continuing towards clinical translation, we investigated treatment with FDA-approved FTI lonafarnib and found the same effects. Methods were also optimized to explore the use of ykt6 as a treatment biomarker in human erythrocytes. Overall, this work reveals a novel mechanism for a-syn-mediated autophagy inhibition in human neurons and identifies a novel druggable target capable of accelerating the clearance of pathological protein.

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