shRNA targeting α-synuclein prevents neurodegeneration in a Parkinson’s disease model
Alevtina D. Zharikov, … , J. Timothy Greenamyre, Edward A. Burton
Alevtina D. Zharikov, … , J. Timothy Greenamyre, Edward A. Burton
Published June 15, 2015
Citation Information: J Clin Invest. 2015;125(7):2721-2735. https://doi.org/10.1172/JCI64502.
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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 5

Preserved nigrostriatal morphology and TH expression, but reduced striatal dopamine content, following α-synuclein knockdown.

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Preserved nigrostriatal morphology and TH expression, but reduced striat...
Animals from cohorts 2 (A–E) and 3 (F and G) were analyzed for changes in the nigrostriatal system following unilateral α-synuclein knockdown. Measurements from the nontransduced (white triangles), AAV-sh[control]–transduced (gray circles), and AAV-sh[SNCA]–transduced (black squares) sides of each brain are shown. In A, C, and E–G, small markers show data points from each individual animal (the two sides of each brain are connected by a line); large markers show the group mean ± SEM. (A) Unbiased stereology was employed to quantify the number of nigral dopaminergic neurons on each side of the brain. (B and C) TH expression was measured in nigral dopaminergic neurons by confocal microscopy. In B, measurements for individual neurons are shown normalized to nontransduced cells in the same sections (small markers). Large markers show mean ± SEM for each animal. (D and E) Striatal TH expression was measured using quantitative near-infrared immunofluorescence. In D, measurements in individual sections are shown normalized to the nontransduced side of the same section (small markers). Large markers show mean ± SEM for each animal. (F and G) HPLC was employed to quantify dopamine levels (F) and the ratio of dopamine metabolites to dopamine (G) as an index of dopamine turnover. Data were analyzed using 2-tailed paired t tests comparing the vector-transduced and control sides of each brain; *P < 0.05.