Toxicity mechanisms of Aβ42 and Tau in aged cells

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ABSTRACT Alzheimer's disease (AD) is characterized by a progressive loss of neuronal structures and functions that underlie cognitive defects and dementia. The neuronal damage has been linked to the aggregation of Aβ peptides and hyperphosphorylated Tau proteins. However, clinical results of reducing these neurotoxic proteins have been disappointing. These failures suggest that AD is a multifactorial process and that many cellular defects were left uncorrected after removing the Aβ/Tau depositions. Finding these resistant cellular defects is a critical step towards the successful intervention of AD. Studies in humans have shown that aging is the biggest risk factor for AD. However, most cellular mechanisms of Aβ/Tau toxicity are generated by research in young cells. As aged cells have different proteomes and physiology than young cells, studying the cellular toxicity of Aβ42/Tau in aged cells is a better model for their toxicity in older AD patients and is required to reveal the resistant cellular defects that are induced by Aβ42/Tau during aging. The goal of this proposal is to determine how Aβ/Tau, together with aging, changes the cellular compartmentalization and whether rejuvenating some of these defects can protect cells from the toxicity of Aβ/Tau. Identifying these age-specific Aβ/Tau sensitive targets will reveal novel mechanisms of Aβ/Tau toxicity and enable strategies to rescue cellular defects that are left uncorrected after removing the Aβ/Tau depositions. We propose to use Saccharomyces cerevisiae (yeast) and Drosophila melanogaster (fly) for this pilot project as these two model organisms are widely used to study molecular mechanisms of aging and AD. Yeast and fly share many biological processes with humans and develop age- related cellular dysfunctions similar to human aging. The yeast model of AD has been used to reveal conserved mechanisms of amyloid aggregation and the cellular toxicity of Aβ and Tau, as well as the genetic and chemical toxicity modifiers. However, these studies looked at the young yeast cells expressing the human Aβ/Tau proteins. Therefore, we want to combine the strength of aging and AD research in yeast to screen for the defects of protein expression and localization caused by Aβ42/Tau in aged cells. Our strategy is to use aged yeast to screen for hits and test the conserved ones in fly models of AD. We intend to accomplish our goal by 1) determining how Aβ and Tau proteins interfere with protein expression and localization in replicatively old yeast cells, and 2) evaluating the beneficial effect of newly identified longevity factors in fly models of AD. The yeast screen will be accomplished by using a new high-throughput microscopic screening method developed in our lab for aged cells. The insights gained from the yeast screen will also be tested in the fly models of AD. This work will advance our understanding of the interactions between aging and AD-related proteins that together cause the age-related neurodegenerative diseases.