Defining The Substrates of Acyl Protein Thioesterase-1: Their Role in Modulating Alpha-Synuclein Toxicity

The neuronal protein alpha-synuclein (αS) plays a key role in the group of neurodegenerative diseases known as synucleinopathies: Parkinson disease (PD), Parkinson disease dementia (PDD), and Dementia with Lewy bodies (DLB). The prevalence and associated societal and personal burdens of these disorders is increasing

rapidly, yet no disease modifying treatment exists. Thus, new therapeutic strategies are urgently needed. Prior work of the PI has shown that targeting palmitoylation may be such a strategy. Palmitoylation is the post- translational modification of proteins by fatty acids, usually palmitate. Palmitoylation plays a key role in protein

and vesicle trafficking. While αS itself is not palmitoylated, under pathologic conditions it disrupts trafficking. Thus, palmitoylation facilitates normal trafficking, while disease-associated αS disrupts it. In accord, the PI has found that enhancing palmitoylation by inhibiting the depalmitoylase acyl protein thioesterase-1 (APT1), which

increases palmitoylation of its unknown brain substrate(s), ameliorates multiple measures of αS cytopathology including toxicity and inclusions. Further, treating genetically modified PD/DLB model mice with a pharmacologic APT1 inhibitor, ML348, improves their motor and dementia-like symptoms on validated

measures such as the rotarod, pole climbing, Y-maze, and Morris water maze tests. While compelling, in the context of clinical translation these results are incomplete: the brain substrates of APT1 are unknown, and this is a major obstacle to developing palmitoylation-based treatments for PD/DLB. In particular, information on the

APT1 substrate(s) responsible for these benefits can 1) ensure specificity of any potential drug by targeting individual pathways and 2) uncover new palmitoylation-based therapeutic targets. Furthermore, it is not known how αS itself may alter palmitoylation profiles (the “palmitoylome”) in the brain. This information would provide

insight into whether APT1 inhibition corrects an underlying αS-dependent change in palmitoylation, or compensates via a separate pathway. Our Aims address each of these questions and together represent a crucial step in the pre-clinical assessment of palmitoylation as a therapeutic strategy for PD/DLB, using both

physiologic and cellular approaches. In Aim 1, we identify physiologic APT1 substrates by isolating the palmitoylome in rat and human iPSC derived neurons with and without APT1 inhibition. We then validate the effect of potential substrates on αS pathology by assessing for somatic and synaptic trafficking defects. In Aim

2, we compare the brain palmitoylomes of wild type versus mutant αS transgenic PD/DLB model mice to evaluate for potential αS-dependent changes in palmitoylation. As in Aim 1, we then validate the role of this second set of proteins in synucleinopathy trafficking defects. Together, our Aims address important questions

crucial to the development of palmitoylation-based therapeutics for PD/DLB while providing new leads for mechanistic insights into the intersection of palmitoylation and αS pathophysiology. To that end, they pursue research priorities pertaining to the Alzheimer’s disease related dementias (ADRD), specifically PDD and DLB.