Copper supplementation increases yeast life span under conditions requiring respiratory metabolism

Abstract

To further exploit yeast as a model for cellular aging we have modified the replicative life span assay to force respiration, by replacing glucose with the non-fermentable carbon source glycerol. The growth rates of several different strains varied greatly, with doubling times ranging from 2.7 to 7 hours. Life spans of all strains were lower on media containing glycerol than on media containing glucose. However, supplementation of glycerol-containing media with copper resulted in increases in life span of between 17 and 72%; life spans equivalent to or beyond those obtained on glucose media. Addition of copper to glucose medium had no effect on life span. Microarray analysis showed that genes responsible for high affinity import of copper display reduced expression upon addition of copper, while most genes showed no change in expression. No differences in growth rate, oxygen uptake, or the levels of subunit II of the copper-containing cytochrome c oxidase were found between cultures of yeast grown with or without copper supplementation. Copper supplementation greatly extended the life span of sod1 and sod2 strains, suggesting that addition of copper may reduce the generation of superoxide. Forcing yeast to respire places an emphasis on mitochondrial function and may aid in the identification of factors involved in aging in other respiratory-dependent organisms.

Replicative Aging in Yeast: The Means to the End

“…Yeast, being facultative anaerobes, generate energy primarily from fermentation when glucose is available and switch to a primarily respiratory growth state either when glucose is depleted or when they are grown on a non-fermentable carbon source such as glycerol (Gancedo & Serrano 1989). Kirchman & Botta (2007) have argued that yeast aging assays testing the importance of mitochondrial function should be performed on a glycerol medium because this pushes metabolic pathways generating energy into a mode more similar to that of mammalian cells. Under these conditions, copper supplementation is associated with life span extension, possibly through the upregulation of oxygen-radical defense mechanisms.…”

Increased iron supplied through Fet3p results in replicative life span extension of Saccharomyces cerevisiae under conditions requiring respiratory metabolism

“…To examine the possibility that the increased iron reduces oxidative stress to extend life span we analyzed the effect of iron supplementation on the life spans of SOD1 (Cu/Zn SOD) and SOD2 (MnSOD) mutants. Previous research has shown that copper supplementation partially restores life span in these mutants (Kirchman & Botta, 2007). If copper’s effect was in fact due to increased iron uptake by the cells, then iron supplementation should have similar results.…”

“…We previously determined that copper’s influence on yeast longevity was not through the copper containing enzyme Cu/Zn SOD (Kirchman & Botta, 2007). This lead us to hypothesize that copper was acting indirectly to influence longevity.…”

“…We have previously shown that the extension of life span by copper supplementation only occurs on media requiring respiratory growth (Kirchman & Botta, 2007). Since copper supplementation extends life span by providing increased iron import through Fet3p, life span extension by iron supplementation should also be limited to respiratory growth.…”

“…We have previously shown that copper supplementation increases replicative life span of yeast grown on media requiring respiratory metabolism (Kirchman & Botta, 2007). We now show that copper’s influence on life span is through its involvement in iron import by Fet3p/Ftr1p.…”