Impaired Autophagic-Lysosomal Fusion in Parkinson's Patient Midbrain Neurons Occurs through Loss of ykt6 and Is Rescued by Farnesyltransferase Inhibition

Abstract

Macroautophagy is a catabolic process that coordinates with lysosomes to degrade aggregation-prone proteins and damaged organelles. Loss of macroautophagy preferentially affects neuron viability and is associated with age-related neurodegeneration. We previously found that a-synuclein (a-syn) inhibits lysosomal function by blocking ykt6, a farnesyl-regulated SNARE protein that is essential for hydrolase trafficking in midbrain neurons. Using Parkinson’s disease (PD) patient iPSC-derived midbrain cultures, we find that chronic, endogenous accumulation of a-syn directly inhibits autophagosome-lysosome fusion by impairing ykt6-SNAP-29 complexes. In wild-type cultures, ykt6 depletion caused a near-complete block of autophagic flux, highlighting its critical role for autophagy in human iPSC-derived neurons. In PD, macroautophagy impairment was associated with increased farnesyltransferase (FTase) activity, and FTase inhibitors restored macroautophagic flux through promoting active forms of ykt6 in human cultures, and male and female mice. Our findings indicate that ykt6 mediates cellular clearance by coordinating autophagic-lysosomal fusion and hydrolase trafficking, and that macroautophagy impairment in PD can be rescued by FTase inhibitors.Significance Statement:The pathogenic mechanisms that lead to the death of neurons in Parkinson’s disease (PD) and Dementia with Lewy bodies (LBD) is currently unknown. Furthermore, disease modifying treatments for these diseases do not exist. Our study indicates that a cellular clearance pathway termed autophagy is impaired in patient-derived culture models of PD andin vivo. We identified a novel druggable target, a SNARE protein called ykt6, that rescues autophagyin vitroandin vivoupon blocking its farnesylation. Our work suggests that farnesyltransferase inhibitors may be useful therapies for PD and DLB through enhancing autophagic-lysosomal clearance of aggregated proteins.

Reciprocal effects of alpha-synuclein aggregation and lysosomal homeostasis in synucleinopathy models

“…5 e). FTI has been demonstrated to enhance a lysosomal stress response pathway by activating the small SNARE protein ykt6, boosting lysosomal enzyme trafficking and lysosomal function [ 36 , 37 ]. Enhancing the transport of hydrolases towards the lysosome by FTI decreased αSyn protein levels and pathology-associated αSyn conformers (insoluble and positive for LB509 αSyn antibody) in our cell models (Figs.…”

The hexosamine biosynthetic pathway rescues lysosomal dysfunction in Parkinson’s disease patient iPSC derived midbrain neurons

“…1D, ANOVA with Šídák's multiple comparisons test was used. Sample sizes were chosen based preliminary studies as well as on the expected variability between culture sets and assays based on our previous publications 10,14,20,59 . Samples used to measure metabolites in Fig.…”