ABSTRACT
The aggregation of α-synuclein (Syn or S) to form insoluble fibrils is important in the pathogenesis of Parkinson's disease, but key risk factors remain ill-defined. We have developed Fluorescence Resonance Energy Transfer (FRET)-based assays for α-synuclein aggregation, using Green Fluorescent Protein variants Cerulean (C) or Venus (V), fused to each other (CV, VC) or to human synuclein (SC, SV etc). Bacterially expressed proteins were purified to homogeneity, and C-terminal fusions SC and SV largely retained their ability to aggregate in vitro. FRET signals from mixtures of SC and SV were used to monitor aggregation. These fusion genes were linked to the C. elegans unc-54 myosin promoter to generate integrated transgenic strains. Increased FRET signals, indicative of S aggregation, were observed following treatment of unc-54::SC + unc-54::SV double transgenic worms with low concentrations of mercury or chlorpyrifos, or with RNAi against hsp-70 and hip-1. Opposite changes in Yellow Fluorescent Protein (YFP) fluorescence in an unc-54::SV strain (NL5901) are likely to reflect FRET from Yellow Fluorescent Protein to aggregates of Syn fusion protein. This could provide the basis for a high throughput screening assay, which could be used for studying the effects of toxic chemicals and environmental pollutants on the aggregation of proteins such as Syn in vivo.
Subject(s)
Fluorescence Resonance Energy Transfer/methods , Parkinsonian Disorders/metabolism , alpha-Synuclein/metabolism , Animals , Animals, Genetically Modified , Bacterial Proteins/genetics , Bacterial Proteins/metabolism , Blotting, Western , Caenorhabditis elegans , Circular Dichroism , Escherichia coli , Green Fluorescent Proteins/genetics , Green Fluorescent Proteins/metabolism , HSP70 Heat-Shock Proteins/antagonists & inhibitors , HSP70 Heat-Shock Proteins/genetics , HSP70 Heat-Shock Proteins/metabolism , Humans , Luminescent Proteins/genetics , Luminescent Proteins/metabolism , Microscopy, Confocal , Microscopy, Electron, Transmission , Protein Aggregates/physiology , Protein Aggregation, Pathological/metabolism , RNA Interference , alpha-Synuclein/genetics , alpha-Synuclein/isolation & purificationABSTRACT
The neural protein α-synuclein aggregates both in vivo and in vitro to form insoluble fibrils that are involved in Parkinson's disease pathogenesis. We have generated α-synuclein/fluorescent-protein fusion constructs overexpressed in muscle cells of the nematode, Caenorhabdtis elegans. Green Fluorescent Protein (GFP) variants, Cerulean (C) or Venus (V), were fused to the C-terminus of human α-synuclein (S); the resultant fusion genes were designated SV and SC, plus a CV fusion as well as S, C and V singly. The aggregation behavior of the purified fusion proteins (expressed in E. coli) will be described elsewhere. These constructs were fused to a C. elegans unc-54 myosin promoter, and integrated transgenic lines generated by microinjection, λ-irradiation, and outcrossing of fluorescent progeny. All transgenic lines expressing α- synuclein showed significant reductions (p <0.05) in lifespan, motility and pharyngeal pumping, as compared to wildtype worms or lines expressing CFP and/or YFP only. We showed that CFP and YFP labels colocalised in granular inclusions throughout the body wall in transgenic lines expressing both SC and SV fusions (SC+SV), whereas SV+C worms displayed YFP-labelled inclusions on a diffuse CFP background. These findings implied that the α-synuclein moieties of these fusion proteins still aggregated together in vivo, whereas CFP or YFP moieties alone did not. This in turn suggested that Foerster Resonanace Energy Transfer (FRET) between CFP and YFP labels in α-synuclein aggregates could allow the extent of aggregation to be quantified. Accordingly, we also showed that net FRET signals increased 2- fold between L4 and adult SC+SV worms.
