Abstract
The etiology of Parkinson’s disease (PD) converges on a common pathogenic pathway of mitochondrial defects in which α-Synuclein (αSyn) is thought to play a role. However, the mechanisms by which αSyn and its disease-associated allelic variants cause mitochondrial dysfunction remain unknown. Here, we analyzed mitochondrial axonal transport and morphology in human-derived neurons overexpressing wild-type (WT) αSyn or the mutated variants A30P or A53T, which are known to have differential lipid affinities. A53T αSyn was enriched in mitochondrial fractions, inducing significant mitochondrial transport defects and fragmentation, while milder defects were elicited by WT and A30P. We found that αSyn-mediated mitochondrial fragmentation was linked to expression levels in WT and A53T variants. Targeted delivery of WT and A53T αSyn to the outer mitochondrial membrane further increased fragmentation, whereas A30P did not. Genomic editing to disrupt the N-terminal domain of αSyn, which is important for membrane association, resulted in mitochondrial elongation without changes in fusion-fission protein levels, suggesting that αSyn plays a direct physiological role in mitochondrial size maintenance. Thus, we demonstrate that the association of αSyn with the mitochondria, which is modulated by protein mutation and dosage, influences mitochondrial transport and morphology, highlighting its relevance in a common pathway impaired in PD.
Highlights
The etiology of Parkinson’s disease (PD) converges on a common pathogenic pathway of mitochondrial defects in which α-Synuclein is thought to play a role
To study the physiological and pathological roles of αSyn in mitochondrial dynamics within the context of human PD, we obtained enriched, polarized, and functional human neurons derived from human neurons derived from embryonic stem cells (hESC) according to a previously described protocol (Figs 1A–F, S1A)[32]
To distinguish transfected αSyn from endogenous protein, neurons co-transfected with vectors encoding EGFP and WT, A30P, or A53T αSyn were analyzed by immunofluorescence (Fig. 1I)
Summary
The etiology of Parkinson’s disease (PD) converges on a common pathogenic pathway of mitochondrial defects in which α-Synuclein (αSyn) is thought to play a role. Genomic editing to disrupt the N-terminal domain of αSyn, which is important for membrane association, resulted in mitochondrial elongation without changes in fusion-fission protein levels, suggesting that αSyn plays a direct physiological role in mitochondrial size maintenance. Mitochondrial-related proteins govern both fusion-fission rates and transport, leading to a direct effect on mitochondrial size and homeostasis. Impairments in these processes have been associated with many neurodegenerative diseases[11]. In addition to the aggregation properties of αSyn, in vitro membrane-binding studies suggest that αSyn adopts an α-helix conformation at the N-terminal domain when interacting with lipids[21] Disruption of this conformation via the A30P αSyn mutation leads to a reduced affinity for lipids, whereas the A53T αSyn mutation produces the opposite effect[22]. It is unclear how these two distinct mutations, which have opposing effects on membrane affinity, result in mitochondrial defects
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