ABSTRACT
Yeast chronological aging is regarded as a model for aging of mammalian post-mitotic cells. It refers to changes occurring in stationary phase cells over a relatively long period of time. How long these cells can survive in such a non-dividing state defines the chronological lifespan. Several factors influence cell survival including two well known normal by-products of yeast glucose fermentation such as ethanol and acetic acid. In fact, the presence in the growth medium of these C2 compounds has been shown to limit the chronological lifespan. In the chronological aging paradigm, a pro-aging role has also emerged for the deacetylase Sir2, the founding member of the Sirtuin family, whose loss of function increases the depletion of extracellular ethanol by an unknown mechanism. Here, we show that lack of Sir2 strongly influences carbon metabolism. In particular, we point out a more efficient acetate utilization which in turn may have a stimulatory effect on ethanol catabolism. This correlates with an enhanced glyoxylate/gluconeogenic flux which is fuelled by the acetyl-CoA produced from the acetate activation. Thus, when growth relies on a respiratory metabolism such as that on ethanol or acetate, SIR2 inactivation favors growth. Moreover, in the chronological aging paradigm, the increase in the acetate metabolism implies that sir2Δ cells avoid acetic acid accumulation in the medium and deplete ethanol faster; consequently pro-aging extracellular signals are reduced. In addition, an enhanced gluconeogenesis allows replenishment of intracellular glucose stores which may be useful for better long-term cell survival.
