Abstract
The alpha-synuclein protein is associated with several neurodegenarative diseases, including Parkinson's disease (PD). In humans, only mutated forms of alpha-synuclein are linked to PD; however, panneural expression of human wild-type (WT) alpha-synuclein induces Parkinson's like-symptoms in Drosophila. Here, we report a quantitative proteomic analysis of WT alpha-synuclein transgenic flies with age-matched controls at the presymptomatic stage utilizing a global isotopic labeling strategy combined with multidimensional liquid chromatographies and tandem mass spectrometry. The analysis includes two biological replicates, in which samples are isotopically labeled in forward and reverse directions. In total, 229 proteins were quantified from assignments of at least two peptide sequences. Of these, 188 (82%) proteins were detected in both forward and reverse labeling measurements. Twelve proteins were found to be differentially expressed in response to the expression of human WT alpha-synuclein; down-regulations of larval serum protein 2 and fat body protein 1 levels were confirmed by Western blot analysis. Gene Ontology analysis indicates that the dysregulated proteins are primarily associated with cellular metabolism and signaling, suggesting potential contributions of perturbed metabolic and signaling pathways to PD. An increased level of the iron (III)-binding protein, ferritin, typically found in the brains of PD patients, is also observed in presymptomatic WT alpha-synuclein expressing animals. The observed alterations in both pathology-associated and novel proteins may shed light on the pathological roles of alpha-synuclein that may lead to the development of diagnostic strategies at the presymptomatic stage.