Saccharomyces cerevisiae, baker's yeast, is an established model organism of ageing research. There are many different pathologies associated with the ageing of yeast, ranging from phenotypic to global transcriptome changes. We have followed changes of several ageing markers and alteration of the global transcriptome under different dietary conditions and introduced genetic modifications to be able to uncover cellular and molecular mechanisms that play a role in the process of replicative ageing.

We used imaging flow cytometry to monitor parameters and fluorescence levels of different markers of ageing and bulk RNA-sequencing to follow transcriptome changes in yeast cells during ageing. One particular focus of our research was the change in mitochondrial Tom70-GFP intensity, which has recently been found to undergo a dramatic accumulation throughout ageing, especially when the cell enters into senescence. We have tested the effects of different dietary environments on this and other markers of ageing, by growing cells on glucose (GLU), where the fermentation process is preferred, or an alternative carbon source galactose (GAL), where cells utilise both fermentation and respiration. Interestingly, ageing on GAL resulted in significantly lower Tom70-GFP marker accumulation than ageing on GLU, while cells had similar replicative age on both sugar sources. Furthermore, we have shown that the first 24 hours of growth is the primary determinant of the level of Tom70-GFP fluoresce intensity, even if the cells are shifted to a different carbon source. Differences in the global transcriptome revealed an overall more “young-like” transcriptome of GAL aged cells compared to GLU grown cells of the same timepoint.

We demonstrated that increased respiration during ageing on GLU is sufficient to lower the Tom70-GFP marker aggregation phenotype. This was achieved by overexpression of the HAP4 gene, a transcriptional activator of mitochondrial biogenesis, and also overexpression of the SAK1 gene, which is a key regulator of the Snf1/AMPK pathway. On the other hand, we found that hindering respiration on GAL with a cox9Δ gal80Δ double mutation results in higher Tom70-GFP marker intensity after 48 hours of ageing. Forced reduction of the Snf1 pathway activity via deletion of the SNF4 gene in a GAL environment also resulted in increased ageing marker. These changes are also reflected in the extent of global transcriptional de-repression.

In this thesis work we have shown that dietary change without restriction can also protect against phenotypic and transcriptome changes associated with ageing in yeast cells. Furthermore, we have demonstrated that early life respiration and the Snf1/AMPK pathway activity is important in the control of yeast ageing pathology. We can also conclude that global transcriptome changes are at least partly influenced by the respiration process. Therefore, our work has revealed potential signalling pathway targets for the improvement of yeast ageing process. Due to the conserved nature of these pathways it can also further our understanding of improved ageing health in higher organisms too.