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Aβ metabolism plays a pivotal role in Alzheimer's disease. Here, we used a yeast model to monitor Aβ 42 toxicity when entering the secretory pathway and demonstrate that processing in, and exit from the endoplasmic reticulum (ER) is required to unleash the full Aβ 42 toxic potential. Consistent with previously reported data, our data suggests that Aβ 42 interacts with mitochondria, thereby enhancing formation of reactive oxygen species and eventually leading to cell demise. We used our model to search for genes that modulate this deleterious effect, either by reducing or enhancing Aβ 42 toxicity, based on screening of the yeast knockout collection. This revealed a reduced Aβ 42 toxicity not only in strains hampered in ER-Golgi traffic and mitochondrial functioning but also in strains lacking genes connected to the cell cycle and the DNA replication stress response. On the other hand, increased Aβ 42 toxicity was observed in strains affected in the actin cytoskeleton organization, endocytosis and the formation of multivesicular bodies, including key factors of the ESCRT machinery. Since the latter was shown to be required for the repair of membrane lesions in mammalian systems, we studied this aspect in more detail in our yeast model. Our data demonstrated that Aβ 42 heavily disturbed the plasma membrane integrity in a strain lacking the ESCRT-III accessory factor Bro1, a phenotype that came along with a severe growth defect and enhanced loading of lipid droplets. Thus, it appears that also in yeast ESCRT is required for membrane repair, thereby counteracting one of the deleterious effects induced by the expression of Aβ 42 . Combined, our studies once more validated the use of yeast as a model to investigate fundamental mechanisms underlying the etiology of neurodegenerative disorders.

The yeast Saccharomyces cerevisiae, a unicellular eukaryotic model, has enabled major breakthroughs in our understanding of a plethora of cellular and molecular processes. Today, a 're-invention' of its use in fundamental and applied research is paving the way for a better understanding of the mechanisms causing neurodegeneration. The increasing emergence of neurodegenerative disorders is becoming more and more problematic in our ageing society. Most prevalent is Alzheimer's disease (AD), affecting more than 35 million people worldwide (Abbott, Nature 475, S2-S4, 2011) and causing an enormous burden on a personal and communal level. The disease is characterized by two major pathological hallmarks: extracellular amyloid plaques consisting mainly of deposits of amyloid β (Aβ) peptides, and intracellular neurofibrillary tangles (NFTs), consisting mainly of aggregates of hyperphosphorylated tau protein. Despite the huge importance of thoroughly understanding the underlying molecular mechanisms of neurodegeneration, progress has been slow. However, multiple complementary research methods are proving their value, particularly with the work done with S. cerevisiae, which combines well-established, fast genetic and molecular techniques with the ability to faithfully capture key molecular aspects of neurodegeneration. In this review chapter, we focus on the considerable progress made using S. cerevisiae as a model system for Alzheimer's disease.

Hyperphosphorylated and aggregated human protein tau constitutes a hallmark of a multitude of neurodegenerative diseases called tauopathies, exemplified by Alzheimer's disease. In spite of an enormous amount of research performed on tau biology, several crucial questions concerning the mechanisms of tau toxicity remain unanswered. In this paper we will highlight some of the processes involved in tau biology and pathology, focusing on tau phosphorylation and the interplay with oxidative stress. In addition, we will introduce the development of a human tau-expressing yeast model, and discuss some crucial results obtained in this model, highlighting its potential in the elucidation of cellular processes leading to tau toxicity.