Upregulation of Cellular Palmitoylation Mitigates α-Synuclein Accumulation and Neurotoxicity

Background Synucleinopathies, including Parkinson's disease (PD), are characterized by alpha-synuclein (alpha S) cytoplasmic inclusions. alpha S-dependent vesicle-trafficking defects are important in PD pathogenesis, but their mechanisms are not well understood. Protein palmitoylation, post-translational addition of the fatty acid palmitate to cysteines, promotes trafficking by anchoring specific proteins to the vesicle membrane. alpha S itself cannot be palmitoylated as it lacks cysteines, but it binds to membranes, where palmitoylation occurs, via an amphipathic helix. We hypothesized that abnormal alpha S membrane-binding impairs trafficking by disrupting palmitoylation. Accordingly, we investigated the therapeutic potential of increasing cellular palmitoylation. Objectives We asked whether upregulating palmitoylation by inhibiting the depalmitoylase acyl-protein-thioesterase-1 (APT1) ameliorates pathologic alpha S-mediated cellular phenotypes and sought to identify the mechanism. Methods Using human neuroblastoma cells, rat neurons, and iPSC-derived PD patient neurons, we examined the effects of pharmacologic and genetic downregulation of APT1 on alpha S-associated phenotypes. Results APT1 inhibition or knockdown decreased alpha S cytoplasmic inclusions, reduced alpha S serine-129 phosphorylation (a PD neuropathological marker), and protected against alpha S-dependent neurotoxicity. We identified the APT1 substrate microtubule-associated-protein-6 (MAP6), which binds to vesicles in a palmitoylation-dependent manner, as a key mediator of these effects. Mechanistically, we found that pathologic alpha S accelerated palmitate turnover on MAP6, suggesting that APT1 inhibition corrects a pathological alpha S-dependent palmitoylation deficit. We confirmed the disease relevance of this mechanism by demonstrating decreased MAP6 palmitoylation in neurons from alpha S gene triplication patients. Conclusions Our findings demonstrate a novel link between the fundamental process of palmitoylation and alpha S pathophysiology. Upregulating palmitoylation represents an unexplored therapeutic strategy for synucleinopathies. (c) 2020 International Parkinson and Movement Disorder Society

Automated summary

The study demonstrated that inhibiting depalmitoylase acyl-protein-thioesterase-1 (APT1) can reduce alpha-synuclein (αS) cytoplasmic inclusions and alpha S-dependent neurotoxicity, while maintaining the palmitoylation level of the protein MAP6. This reveals a novel link between palmitoylation and αS pathophysiology, suggesting upregulating palmitoylation as a potential therapeutic strategy for synucleinopathies.