Abstract
Evolving concepts on Parkinson’s disease (PD) pathology suggest that α-synuclein (aSYN) promote dopaminergic neuron dysfunction and death through accumulating in the mitochondria. However, the consequence of mitochondrial aSYN localisation on mitochondrial structure and bioenergetic functions in neuronal cells are poorly understood. Therefore, we investigated deleterious effects of mitochondria-targeted aSYN in differentiated human dopaminergic neurons in comparison with wild-type (WT) aSYN overexpression and corresponding EGFP (enhanced green fluorescent protein)-expressing controls. Mitochondria-targeted aSYN enhanced mitochondrial reactive oxygen species (ROS) formation, reduced ATP levels and showed severely disrupted structure and function of the dendritic neural network, preceding neuronal death. Transmission electron microscopy illustrated distorted cristae and many fragmented mitochondria in response to WT-aSYN overexpression, and a complete loss of cristae structure and massively swollen mitochondria in neurons expressing mitochondria-targeted aSYN. Further, the analysis of mitochondrial bioenergetics in differentiated dopaminergic neurons, expressing WT or mitochondria-targeted aSYN, elicited a pronounced impairment of mitochondrial respiration. In a pharmacological compound screening, we found that the pan-caspase inhibitors QVD and zVAD-FMK, and a specific caspase-1 inhibitor significantly prevented aSYN-induced cell death. In addition, the caspase inhibitor QVD preserved mitochondrial function and neuronal network activity in the human dopaminergic neurons overexpressing aSYN. Overall, our findings indicated therapeutic effects by caspase-1 inhibition despite aSYN-mediated alterations in mitochondrial morphology and function.
Highlights
Parkinson’s disease (PD) is a neurodegenerative movement disorder characterised by the progressive dopaminergic neurodegeneration in the substantia nigra pars compacta
Western blots showed that the formation of oligomers by aSYN occurs predominantly in the cytoplasm and the assembly patterns differ from the mito-aSYN
With our new AAV system for expression of mitochondrial localisation sequence (MLS)-tagged aSYN or WT-aSYN, we investigated the effects of aSYN on the ultrastructural integrity of mitochondria in human dopaminergic neurons by electron microscopy
Summary
Parkinson’s disease (PD) is a neurodegenerative movement disorder characterised by the progressive dopaminergic neurodegeneration in the substantia nigra pars compacta. Aggregation of aSYN into Lewy bodies (LBs) is a hallmark of PD, dementia with LBs, and neurodegenerative synucleinopathies like multiple systems atrophy or pure autonomic failure[1]. Duplication, triplication or A30P, A53T, A53E, G51D, or E46K point mutations in PD and cellular overexpressing aSYN revealed mitochondrial localisation of aSYN may accelerate aSYN toxicity in dopaminergic neurons[4,5,6]. Familial forms of PD-like mutations in PTEN-induced putative kinase-1, aSYN, leucine-rich repeat kinase-2, parkin or DJ-1 have been associated with dysfunctional mitochondria[7,8]. Variety of cell death mechanisms were linked to the pathogenesis of PD, such as extrinsic and intrinsic apoptosis, (regulated) necrosis and autophagy[9].
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