Abstract TMP50: Suppression of α-synuclein Mitigates Secondary Ischemic Brain Damage

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α-synuclein (α-syn) is one of the most abundant proteins in mammalian brain that is known to be a major player in the neurodegeneration observed in chronic conditions like Parkinson’s disease (PD). Several mechanisms were proposed for α-syn-induced neuronal death in PD including inflammation, oxidative stress, mitochondrial fission, and autophagy. Interestingly, all these pathophysiologic mechanisms also mediate neuronal death after acute CNS insults like stroke. Therefore, we examined whether α-syn contributes to post-stroke neuronal death and neurological dysfunction. Rodents were subjected to transient middle cerebral artery occlusion (tMCAO) and α-syn induction was silenced with a cocktail of α-syn-specific siRNAs. The levels of α-syn were estimated with qPCR and Western Blots. Post-ischemic motor deficit was evaluated with rotarod, beam walk and adhesive removal test 1 to 7 days after ischemia, and infarct volume was measured on cresyl violet stained brain sections. Cellular changes after ischemia were examined using immunofluorescence staining. Following tMCAO, α-syn levels were significantly up-regulated and phosphorylated at serine-129 in ischemic penumbra. Interestingly, in the ischemic brain non-phosphorylated and phosphorylated α-syn species translocated into the neuronal nuclei. We also observed that silencing α-syn by α-syn siRNA cocktail before tMCAO significantly decreased the infarction and improved the motor function. The neuroprotective effects were still observed when α-syn siRNAs were administered 30 min after the tMCAO. We found that the rate of survival at 7 days after a 90 min tMCAO was significantly higher in α-syn KO mice compared to wild-type control mice. Furthermore, α-syn suppression significantly mitigated the post-ischemic oxidative stress (8-OHdG and 3-NT), apoptosis (cleaved Caspase-3) and mitochondrial dysfunction (phospho-Drp1). Thus, we show that α-syn plays a critical role in neuronal death following stroke. Furthermore, phospho-S129 α-syn in the neuronal nuclei might be a potential mediator of the induction of ischemic brain damage. Preventing α-syn expression is a potential therapeutic target to minimize post-stroke brain damage.

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