1.
Use of Optogenetic Amyloid-β to Monitor Protein Aggregation in Drosophila melanogaster, Danio rerio and Caenorhabditis elegans.
Abstract:
Alzheimer's Disease (AD) has long been associated with accumulation of extracellular amyloid plaques (Aβ) originating from the Amyloid Precursor Protein. Plaques have, however, been discovered in healthy individuals and not all AD brains show plaques, suggesting that extracellular Aβ aggregates may play a smaller role than anticipated. One limitation to studying Aβ peptide in vivo during disease progression is the inability to induce aggregation in a controlled manner. We developed an optogenetic method to induce Aβ aggregation and tested its biological influence in three model organisms-D. melanogaster, C. elegans and D. rerio. We generated a fluorescently labeled, optogenetic Aβ peptide that oligomerizes rapidly in vivo in the presence of blue light in all organisms. Here, we detail the procedures for expressing this fusion protein in animal models, investigating the effects on the nervous system using time lapse light-sheet microscopy, and performing metabolic assays to measure changes due to intracellular Aβ aggregation. This method, employing optogenetics to study the pathology of AD, allows spatial and temporal control in vivo that cannot be achieved by any other method at present.
2.
Application of optogenetic Amyloid-β distinguishes between metabolic and physical damage in neurodegeneration.
Abstract:
The brains of Alzheimer's Disease patients show a decrease in brain mass and a preponderance of extracellular Amyloid-β plaques. These plaques are formed by aggregation of polypeptides that are derived from the Amyloid Precursor Protein (APP). Amyloid-β plaques are thought to play either a direct or an indirect role in disease progression, however the exact role of aggregation and plaque formation in the aetiology of Alzheimer's Disease is subject to debate as the biological effects of soluble and aggregated Amyloid-β peptides are difficult to separate in vivo. To investigate the consequences of formation of Amyloid-β oligomers in living tissues, we developed a fluorescently tagged, optogenetic Amyloid-β peptide that oligomerizes rapidly in the presence of blue light. We applied this system to the crucial question of how intracellular Amyloid-β oligomers underlie the pathologies of Alzheimer's Disease. We use Drosophila, C. elegans and D. rerio to show that, although both expression and induced oligomerization of Amyloid-β were detrimental to lifespan and healthspan, we were able to separate the metabolic and physical damage caused by light-induced Amyloid-β oligomerization from Amyloid-β expression alone. The physical damage caused by Amyloid-β oligomers also recapitulated the catastrophic tissue loss that is a hallmark of late AD. We show that the lifespan deficit induced by Amyloid-β oligomers was reduced with Li+ treatment. Our results present the first model to separate different aspects of disease progression.
