shRNA targeting α-synuclein prevents neurodegeneration in a Parkinson’s disease model
Alevtina D. Zharikov, Jason R. Cannon, Victor Tapias, Qing Bai, Max P. Horowitz, Vipul Shah, Amina El Ayadi, Teresa G. Hastings, J. Timothy Greenamyre, Edward A. Burton
Alevtina D. Zharikov, Jason R. Cannon, Victor Tapias, Qing Bai, Max P. Horowitz, Vipul Shah, Amina El Ayadi, Teresa G. Hastings, J. Timothy Greenamyre, Edward A. Burton
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Research Article Neuroscience

shRNA targeting α-synuclein prevents neurodegeneration in a Parkinson’s disease model

Abstract

Multiple convergent lines of evidence implicate both α-synuclein (encoded by SCNA) and mitochondrial dysfunction in the pathogenesis of sporadic Parkinson’s disease (PD). Occupational exposure to the mitochondrial complex I inhibitor rotenone increases PD risk; rotenone-exposed rats show systemic mitochondrial defects but develop specific neuropathology, including α-synuclein aggregation and degeneration of substantia nigra dopaminergic neurons. Here, we inhibited expression of endogenous α-synuclein in the adult rat substantia nigra by adeno-associated virus–mediated delivery of a short hairpin RNA (shRNA) targeting the endogenous rat Snca transcript. Knockdown of α-synuclein by ~35% did not affect motor function or cause degeneration of nigral dopaminergic neurons in control rats. However, in rotenone-exposed rats, progressive motor deficits were substantially attenuated contralateral to α-synuclein knockdown. Correspondingly, rotenone-induced degeneration of nigral dopaminergic neurons, their dendrites, and their striatal terminals was decreased ipsilateral to α-synuclein knockdown. These data show that α-synuclein knockdown is neuroprotective in the rotenone model of PD and indicate that endogenous α-synuclein contributes to the specific vulnerability of dopaminergic neurons to systemic mitochondrial inhibition. Our findings are consistent with a model in which genetic variants influencing α-synuclein expression modulate cellular susceptibility to environmental exposures in PD patients. shRNA targeting the SNCA transcript should be further evaluated as a possible neuroprotective therapy in PD.

Authors

Alevtina D. Zharikov, Jason R. Cannon, Victor Tapias, Qing Bai, Max P. Horowitz, Vipul Shah, Amina El Ayadi, Teresa G. Hastings, J. Timothy Greenamyre, Edward A. Burton

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Figure 10

Rescue of dopaminergic function precedes degeneration of striatal terminals.

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Rescue of dopaminergic function precedes degeneration of striatal termin...
Animals from cohort 6 received either AAV-sh[SNCA] (black squares) or AAV-sh[control] (gray circles) unilaterally in the substantia nigra or no vector (white triangles). Starting at 21 days after transduction, rats were administered rotenone 2.8 mg/kg/d via intraperitoneal injection for 6 days, after which brains were harvested for analysis. (A) A postural instability test was used to evaluate forelimb motor function during rotenone administration. Mean ± SEM distance to trigger a compensatory forelimb movement is shown for the right forepaw (controlled by nontransduced side of brain; left graph) and left forepaw (controlled by vector-transduced side of brain; right graph). ***P < 0.001, ****P < 0.0000001, left forepaw of AAV-sh[SNCA] group versus left forepaw of AAV-sh[control] or non-vector groups, one-way ANOVA. (B and C) Once motor asymmetry was clearly established in the AAV-sh[SNCA] group after 6 days of rotenone exposure, brains were analyzed for striatal dopaminergic terminal integrity. Quantitative near-infrared immunofluorescence was used to measure dorsolateral striatal TH expression on each side of 5–6 sections per animal. Small markers show the mean for each animal (+, vector side; –, nontransduced control side; lines join the means for the two sides of each brain); large markers show mean ± SEM for all eight animals in each group.