Abstract
Aβ metabolism plays a pivotal role in Alzheimer’s disease. Here, we used a yeast model to monitor Aβ42 toxicity when entering the secretory pathway and demonstrate that processing in, and exit from the endoplasmic reticulum (ER) is required to unleash the full Aβ42 toxic potential. Consistent with previously reported data, our data suggests that Aβ42 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 Aβ42 toxicity, based on screening of the yeast knockout collection. This revealed a reduced Aβ42 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 Aβ42 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 Aβ42 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 Aβ42. Combined, our studies once more validated the use of yeast as a model to investigate fundamental mechanisms underlying the etiology of neurodegenerative disorders.
Highlights
Amyloid β1−42 is an intensively investigated peptide involved in Alzheimer’s disease (AD) but beyond its role as a possibly malignant factor, the physiological functions of Aβ42 are still speculative
We used a yeast model transformed with plasmids carrying the galactose-inducible GAL10 promoter to control expression of wild-type or mutant Aβ42 that is N-terminally fused to the α-prepro sequence and C-terminally to a linker and GFP (D’Angelo et al, 2013; Vignaud et al, 2013)
Supplementary Figure S1A), both spot assays and growth analysis in liquid medium confirmed that wild-type or mutant αAβ42 instigated a significantly higher level of toxicity that was similar in the BY4741 and the BY4742 strains (Figures 1B,C and Supplementary Figure S1)
Summary
Amyloid β1−42 (referred to as Aβ42) is an intensively investigated peptide involved in Alzheimer’s disease (AD) but beyond its role as a possibly malignant factor, the physiological functions of Aβ42 are still speculative. It has been shown that it has a role in activity dependent synaptic vesicle release and there is evidence that it might act as an antimicrobial agent in the brain, but besides that, not much is known about its physiological function The membrane bound amyloid precursor protein, APP, is processed in two possible ways: it can enter the nonamyloidogenic pathway or it might be cleaved by β- and γ-secretases in the amyloidogenic pathway producing Aβ peptides of lengths between 37 and 43 amino acids (LaFerla et al, 2007). Strong evidence was found for that Aβ42 perturbs proper function of mitochondria through blocking respiration at complex IV, resulting in cells producing more reactive oxygen species (ROS) and eventually apoptotic cell death (Wang et al, 2010; Ittner and Gotz, 2011; Benilova et al, 2012; Jackrel et al, 2014; Alexandrov et al, 2016; Vicente Miranda et al, 2016)
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