Inducible over‐expression of wild type α‐synuclein in human neuronal cells leads to caspase‐dependent non‐apoptotic death

Alpha‐synuclein (ASYN) is central in Parkinson’s disease pathogenesis. Converging pieces of evidence suggest that the levels of ASYN expression play a critical role in both familial and sporadic Parkinson’s disease. To elucidate the mechanism underlying wild type (WT) ASYN‐mediated neurotoxicity, we have generated a novel Tet‐Off SHSY‐5Y cell line, conditionally expressing WT ASYN. Induction of human WT ASYN in retinoic acid‐differentiated SHSY‐5Y cells leads to accumulation of soluble ASYN oligomers, in the absence of inclusions, and to gradual cellular degeneration. Morphologically, the death observed is non‐apoptotic. Caspases other than caspase 3, including caspase 9, are activated and caspase inhibition diminishes death by acting at a point upstream of cytochrome c release. Application of Scyllo‐inositol, an oligomer‐stabilizing compound, prevents neuronal death in this model. These findings are consistent with a model in which oligomeric ASYN triggers the initial activation of the apoptotic pathway, which is however blocked downstream of the mitochondrial checkpoint, thus leading to a death combining in a unique fashion both apoptotic and non‐apoptotic features. This novel inducible cell model system may prove valuable in the deciphering of WT ASYN‐induced pathogenic effects and in the assessment and screening of potential therapeutic strategies.