Quercetin protects Saccharomyces cerevisiae against oxidative stress by inducing trehalose biosynthesis and the cell wall integrity pathway.

BACKGROUND: Quercetin is a naturally occurring flavonol with antioxidant, anticancer and anti-ageing properties. In this study we aimed to identify genes differentially expressed in yeast cells treated with quercetin and its role in oxidative stress protection. METHODS: A microarray analysis was performed to characterize changes in the transcriptome and the expression of selected genes was validated by RT-qPCR. Biological processes significantly affected were identified by using the FUNSPEC software and their relevance in H(2)O(2) resistance induced by quercetin was assessed. RESULTS: Genes associated with RNA metabolism and ribosome biogenesis were down regulated in cells treated with quercetin, whereas genes associated with carbohydrate metabolism, endocytosis and vacuolar proteolysis were up regulated. The induction of genes related to the metabolism of energy reserves, leading to the accumulation of the stress protectant disaccharide trehalose, and the activation of the cell wall integrity pathway play a key role in oxidative stress resistance induced by quercetin. CONCLUSIONS: These results suggest that quercetin may act as a modulator of cell signaling pathways related to carbohydrate metabolism and cell integrity to exert its protective effects against oxidative stress.

Activation of the Hog1p kinase in Isc1p-deficient yeast cells is associated with mitochondrial dysfunction, oxidative stress sensitivity and premature aging.

The Saccharomyces cerevisiae Isc1p, an orthologue of mammalian neutral sphingomyelinase 2, plays a key role in mitochondrial function, oxidative stress resistance and chronological lifespan. Isc1p functions upstream of the ceramide-activated protein phosphatase Sit4p through the modulation of ceramide levels. Here, we show that both ceramide and loss of Isc1p lead to the activation of Hog1p, the MAPK of the high osmolarity glycerol (HOG) pathway that is functionally related to mammalian p38 and JNK. The hydrogen peroxide sensitivity and premature aging of isc1Δ cells was partially suppressed by HOG1 deletion. Notably, Hog1p activation mediated the mitochondrial dysfunction and catalase A deficiency associated with oxidative stress sensitivity and premature aging of isc1Δ cells. Downstream of Hog1p, Isc1p deficiency activated the cell wall integrity (CWI) pathway. Deletion of the SLT2 gene, which encodes for the MAPK of the CWI pathway, was lethal in isc1Δ cells and this mutant strain was hypersensitive to cell wall stress. However, the phenotypes of isc1Δ cells were not associated with cell wall defects. Our findings support a role for Hog1p in the regulation of mitochondrial function and suggest that constitutive activation of Hog1p is deleterious for isc1Δ cells under oxidative stress conditions and during chronological aging.

Role for Sit4p-dependent mitochondrial dysfunction in mediating the shortened chronological lifespan and oxidative stress sensitivity of Isc1p-deficient cells.

Saccharomyces cerevisiae cells lacking Isc1p, an orthologue of mammalian neutral sphingomyelinase 2, display a shortened lifespan and an increased sensitivity to oxidative stress. A lipidomic analysis revealed specific changes in sphingolipids that accompanied the premature ageing of Isc1p-deficient cells under severe calorie restriction conditions, including a decrease of dihydrosphingosine levels and an increase of dihydro-C(26) -ceramide and phyto-C(26) -ceramide levels, the latter raising the possibility of activation of ceramide-dependent protein phosphatases. Consequently, deletion of the SIT4 gene, which encodes for the catalytic subunit of type 2A ceramide-activated protein phosphatase in yeast, abolished the premature ageing and hydrogen peroxide sensitivity of isc1Δ cells. SIT4 deletion also abolished the respiratory defects and catalase A deficiency exhibited by isc1Δ mutants. These results are consistent with catabolic derepression associated with the loss of Sit4p. The overall results show that Isc1p is an upstream regulator of Sit4p and implicate Sit4p activation in mitochondrial dysfunction leading to the shortened chronological lifespan and oxidative stress sensitivity of isc1Δ mutants.

Quercetin increases oxidative stress resistance and longevity in Saccharomyces cerevisiae.

Quercetin, the major flavonol found in several fruits and vegetables, is a natural antioxidant with potential anticancer and antiaging activities. In this paper, the effect of quercetin in Sacharomyces cerevisiae cells submitted to oxidative stress was studied. Hydrogen peroxide resistance increased in cells pretreated with quercetin. Cellular protection was correlated with a decrease in oxidative stress markers, namely, levels of reactive oxygen species, glutathione oxidation, protein carbonylation, and lipid peroxidation. The acquisition of H2O2 resistance was not associated with the induction of antioxidant defenses or with iron chelation. Oxidative stress is a limiting factor for longevity. In agreement, quercetin also increased 60% chronological life span. These results support the utilization of yeast as a useful model to screen in vivo for natural antioxidants with putative health beneficial effects.

Hydrogen peroxide-induced carbonylation of key metabolic enzymes in Saccharomyces cerevisiae: the involvement of the oxidative stress response regulators Yap1 and Skn7.

H(2)O(2) induces a specific protein oxidation in yeast cells, and the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (Tdh) is a major target. Using a 2D-gel system to study protein carbonylation, it is shown in this work that both Tdh2p and Tdh3p isozymes were oxidized during exposure to H(2)O(2). In addition, we identified two other proteins carbonylated and inactivated: Cu,Zn-superoxide dismutase and phosphoglycerate mutase. The oxidative inactivation of Cu,Zn-superoxide dismutase decreases the antioxidant capacity of yeast cells and probably contributes to H(2)O(2)-induced cell death. Cyclophilin 1 was also carbonylated, but CPH1 gene disruption did not affect peroxide stress sensitivity. The correlation between H(2)O(2) sensitivity and the accumulation of oxidized proteins was evaluated by assaying protein carbonyls in mutants deficient in the stress response regulators Yap1p and Skn7p. The results show that the high sensitivity of yap1delta and skn7delta mutants to H(2)O(2) was correlated with an increased induction of protein carbonylation. In wild-type cells, the acquisition of stress resistance by pre-exposure to a sublethal H(2)O(2) stress was associated with a lower accumulation of oxidized proteins. However, pre-exposure of yap1delta and skn7delta cells to 0.4 mM H(2)O(2) decreased protein carbonylation induced by 1.5 mM H(2)O(2), indicating that the adaptive mechanism involved in the protection of proteins from carbonylation is Yap1p- and Skn7p-independent.