Mitochondrial dysfunction has been previously identified in neurodegenerative diseases such as Alzheimer disease, Huntington disease, and Parkinson disease. Chemical inhibition of the mitochondrial electron transport chain (ETC) was shown to trigger symptoms in animal models similar to those observed in human neurodegenerative diseases. In order to understand the effect of mitochondrial dysfunction on the proteome level, LC-MSE based bottom-up, label-free differential proteomics expression analysis was used to monitor protein level changes in SH-SY5Y neuroblastoma cells induced by ETC-specific inhibitors (MPTP, 3-NP, sodium azide, antimycin A, and oligomycin). A total of 379 proteins were identified across the sample set and 75 of them were found to be differentially expressed (>30% fold change). Complex-specific inhibition of the five ETS complexes were expected to result in the aberrant regulation of different molecular pathways, but the bioinformatics analysis of the LC-MSMS data showed that the differentially expressed proteins were mostly involved in similar metabolic processes. The findings suggest that the complex-specific alterations may not be directly linked to neurodegenerative pathways, but could be considered contributors. Moreover, the proteins that showed the highest protein expression difference (>60% fold change) are involved in pathways regarding protein-folding and response to unfolded proteins. The results indicate that protein misfolding pathways might have a central role in the genesis and progression of neurodegenerative diseases and that label-free LC-MSMS proteomics analysis is an invaluable approach for studying of molecular pathways in neurodegeneration.

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