Aging: the sins of the parents

Effects of an unusual poison identify a lifespan role for Topoisomerase 2 in Saccharomyces cerevisiae

A progressive loss of genome maintenance has been implicated as both a cause and consequence of aging. Here we present evidence supporting the hypothesis that an age-associated decay in genome maintenance promotes aging in Saccharomyces cerevisiae (yeast) due to an inability to sense or repair DNA damage by topoisomerase 2 (yTop2). We describe the characterization of LS1, identified in a high throughput screen for small molecules that shorten the replicative lifespan of yeast. LS1 accelerates aging without affecting proliferative growth or viability. Genetic and biochemical criteria reveal LS1 to be a weak Top2 poison. Top2 poisons induce the accumulation of covalent Top2-linked DNA double strand breaks that, if left unrepaired, lead to genome instability and death. LS1 is toxic to cells deficient in homologous recombination, suggesting that the damage it induces is normally mitigated by genome maintenance systems. The essential roles of yTop2 in proliferating cells may come with a fitness trade-off in older cells that are less able to sense or repair yTop2-mediated DNA damage. Consistent with this idea, cells live longer when yTop2 expression levels are reduced. These results identify intrinsic yTop2-mediated DNA damage as a potentially manageable cause of aging.

Protein deacetylation by sirtuins: delineating a post-translational regulatory program responsive to nutrient and redox stressors

Lysine acetylation/deacetylation is increasingly being recognized as common post-translational modification that appears to be broadly operational throughout the cell. The functional roles of these modifications, outside of the nucleus, have not been extensively studied. Moreover, as acetyl-CoA donates the acetyl group for acetylation, nutrient availability and energetic status may be pivotal in this modification. Similarly, nutrient limitation is associated with the deacetylation reaction. This modification is orchestrated by a novel family of sirtuin deacetylases that function in a nutrient and redox dependent manner and targets non-histone protein deacetylation. In compartment-specific locations, candidate target proteins undergoing lysine-residue deacetylation are being identified. Through these investigations, the functional role of this post-translational modification is being delineated. We review the sirtuin family proteins, discuss their functional effects on target proteins, and postulate on potential biological programs and disease processes that may be modified by sirtuin-mediated deacetylation of target proteins.

Accumulation of oxidative damage during replicative aging of the yeast Saccharomyces cerevisiae

Comparison of senescent yeast obtained by the "baby machine" technique with 2-day-old stationary phase cells revealed decreased activities of glutathione reductase, glutathione S-transferase, glutathione peroxidase and alcohol dehydrogenase, reduction of total antioxidant capacity, protein glycation and accumulation of products of oxidative damage: protein carbonyls and DNA damage assessed by augmented content of 8-oxoguanine and increased tail momentum of cellular DNA in the comet assay. These results are consistent with a role for oxidative damage during replicative senescence of Saccharomyces cerevisiae.