Upregulation of Cellular Palmitoylation Mitigates α‐Synuclein Accumulation and Neurotoxicity

Abstract

Background Synucleinopathies, including Parkinson's disease (PD), are characterized by α‐synuclein (αS) cytoplasmic inclusions. αS‐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. αS itself cannot be palmitoylated as it lacks cysteines, but it binds to membranes, where palmitoylation occurs, via an amphipathic helix. We hypothesized that abnormal αS 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 αS‐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 αS‐associated phenotypes. Results APT1 inhibition or knockdown decreased αS cytoplasmic inclusions, reduced αS serine‐129 phosphorylation (a PD neuropathological marker), and protected against αS‐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 αS accelerated palmitate turnover on MAP6, suggesting that APT1 inhibition corrects a pathological αS‐dependent palmitoylation deficit. We confirmed the disease relevance of this mechanism by demonstrating decreased MAP6 palmitoylation in neurons from αS gene triplication patients. Conclusions Our findings demonstrate a novel link between the fundamental process of palmitoylation and αS pathophysiology. Upregulating palmitoylation represents an unexplored therapeutic strategy for synucleinopathies. © 2020 International Parkinson and Movement Disorder Society

Modulation of the Interactions Between α-Synuclein and Lipid Membranes by Post-translational Modifications

“…For example, palmitoylation, which is the post-translational addition of the fatty acid palmitate to cysteine residues, mediates the interactions of SNARE proteins with lipid membranes. Thus, although α-synuclein is not known to be palmitoylated, its interactions with lipid membranes can be affected indirectly by this post-translational modification (219).…”

Parkinson's disease risk genes act in glia to control neuronal α-synuclein toxicity

“…Our finding that the other glial modifiers increase α-synuclein oligomers without seemingly impairing neuronal autophagy suggests that different modifiers can exert their effects on proteostasis through different upstream mechanisms. Beyond macro-autophagy, there are numerous other cellular processes that affect α-synuclein toxicity, including proteosome function, interactions with chaperones( Burmann et al, 2020 ) that prevent misfolding or induce chaperone-mediated autophagy, phosphorylation( Zhao et al, 2020 ; Pinho et al, 2019 ) and other( Ho et al, 2021 ) post-translational modifications of α-synuclein, and subcellular localization( Pinho et al, 2019 ) of α-synuclein. Whether glia can indirectly affect these processes is unknown.…”

A sticky situation: regulation and function of protein palmitoylation with a spotlight on the axon and axon initial segment

“…In a recently published study, Ho et al showed that palmitoylation may play a role in PD for the first time. Inhibiting depalmitoylation reduces α-synuclein inclusions and phosphorylation at Ser 129 (a PD neuropathological marker) as well as decreases neurotoxicity in human neuroblastoma cells, rat neurons, and induced pluripotent stem cell-derived PD patient neurons [ 128 ]. These protective effects are proposed to be due to restoring palmitoylation of microtubule-associated protein 6 (MAP6) [ 128 ].…”

“…Inhibiting depalmitoylation reduces α-synuclein inclusions and phosphorylation at Ser 129 (a PD neuropathological marker) as well as decreases neurotoxicity in human neuroblastoma cells, rat neurons, and induced pluripotent stem cell-derived PD patient neurons [ 128 ]. These protective effects are proposed to be due to restoring palmitoylation of microtubule-associated protein 6 (MAP6) [ 128 ]. It will be interesting to see the results of depalmitoylation inhibitor treatment in a longer term preclinical study in animal models of PD, such as was recently done in HD [ 125 ].…”