Axon degeneration and PGC1α-mediated protection in a vertebrate model of α-synuclein toxicity

• Published in: Disease models & mechanisms
• Main Authors: O'Donnell, Kelley C., Lulla, Aaron, Stahl, Mark C., Wheat, Nickolas D., Bronstein, Jeff M., Sagasti, Alvaro
• Format: Journal Article
• Language: English
• Published: 01.01.2014
• ISSN: 1754-8403; 1754-8411
• DOI: 10.1242/dmm.013185

Abstract α-Synuclein (aSyn) expression is implicated in neurodegenerative processes, including Parkinson disease (PD) and dementia with Lewy bodies (DLB). In animal models of these diseases, axon pathology often precedes cell death, raising the question of whether aSyn has compartment-specific toxic effects that may require early and/or independent therapeutic intervention. The relevance of axonal pathology to degeneration can only be addressed through longitudinal, in vivo monitoring of different neuronal compartments. With current imaging methods, dopaminergic neurons do not readily lend themselves to such a task in any vertebrate system. We therefore expressed human wild-type aSyn in zebrafish peripheral sensory neurons, which project elaborate superficial axons that can be continuously imaged in vivo. Axonal outgrowth was normal in these neurons, but by 2 days post-fertilization (dpf), many aSyn-expressing axons became dystrophic, with focal varicosities or diffuse beading. Approximately 20% of aSyn-expressing cells died by 3 dpf. Time-lapse imaging revealed that focal axonal swelling, but not overt fragmentation, usually preceded cell death. Co-expressing aSyn with a mitochondrial reporter revealed deficits in mitochondrial transport and morphology even when axons appeared overtly normal. The axon-protective protein Wallerian degeneration slow (WldS) delayed axon degeneration but not cell death caused by aSyn. By contrast, the transcriptional co-activator PGC-1α, which has roles in the regulation of mitochondrial biogenesis and reactive oxygen species detoxification, abrogated aSyn toxicity in both the axon and the cell body. The rapid onset of axonal pathology in this system, and the relatively moderate degree of cell death, provide a new model for the study of aSyn toxicity and protection. Moreover, the accessibility of peripheral sensory axons will allow effects of aSyn to be studied in different neuronal compartments, and may have utility in screening for novel disease-modifying compounds.