Oxidative stress and programmed cell death in yeast

Yeasts, such as Saccharomyces cerevisiae, have long served as useful models for the study of oxidative stress, an event associated with cell death and severe human pathologies.This reviewwill discuss oxidative stress in yeast, in terms of sources of reactive oxygen species (ROS), their molecular targets, and the metabolic responses elicited by cellular ROS accumulation. Responses of yeast to accumulated ROS include upregulation of antioxidants mediated by complex transcriptional changes, activation of pro-survival pathways such as mitophagy, and programmed cell death (PCD) which, apart from apoptosis, includes pathways such as autophagy and necrosis, a form of cell death long considered accidental and uncoordinated. The role of ROS in yeast aging will also be discussed.Work in the authors’ laboratory is partly funded by the Malta Government Scholarship Scheme (MGSS) award, fund number ME 367/07/8, to Gianluca Farrugia and partly by Research Fund grants to Rena Balzan from the University of Malta.peer-reviewe

Stem Cell Repair for Cardiac Muscle Regeneration: A Review of the Literature

The notion that the human adult heart is a quiescent organ incapable of self-regeneration has been successfully challenged. It is now evident that the heart possesses a significant ability for repair and regeneration. Stem cells of endogenous cardiac origin are currently considered to possess the greatest ability to differentiate into cardiomyocytes. The major types of cardiac stem cells that show a promising potential to replace damaged cardiomyocytes include C-KIT positive (C-KIT+) cardiac progenitor cells, cardiosphere-derived progenitor cells, islet-1 (Isl1+) cardiac progenitor cells, side-population cardiac progenitor cells, epicardium-derived progenitor cells and stem cell antigen-1 (SCA1+) cardiac progenitor cells. Moreover, stem cells of extra-cardiac origin are also thought to restore contractility and vascularization of the myocardium. These include skeletal myoblasts, bone marrow mononuclear cells, mesenchymal stem cells, endothelial progenitor cells as well as embryonic stem cells. The need for further investigation on cardiac stem cell therapeutic strategies still remains

Dinja t’għasfur ċkejken

Din il-poeżija bl-isem `Dinja t’għasfur ċkejken’ ta’ Rena Balzan dehret fil-ġurnal Il-Malti : Rivista tal-Akkademja tal-Malti ħarġa letterarja, 93.peer-reviewe

Aspirin commits yeast cells to apoptosis depending on carbon source

The effect of aspirin on the growth of a wild-type Saccharomyces cerevisiae strain (EG103), containing both copper,zinc superoxide dismutase (CuZnSOD) and manganese superoxide dismutase (MnSOD), a strain deficient in MnSOD (EG110) and a strain deficient in CuZnSOD (EG118) was measured in media containing different carbon sources. Aspirin inhibited the fermentative growth of all three strains in glucose medium. It inhibited the non-fermentative growth of the MnSOD-deficient strain very drastically in ethanol medium and had no effect on this strain in glycerol or acetate medium. The non-fermentative growth of the other two strains was not affected by aspirin. The growth inhibition of strain EG110 was associated with early necrosis in glucose medium and late apoptosis in ethanol medium. The apoptosis was preceded by a pronounced loss of cell viability. The growth inhibitory effect of aspirin was not reversed by the antioxidants N-acetylcysteine and vitamin E. Furthermore, aspirin itself appeared to act as an antioxidant until the onset of overt apoptosis, when a moderate increase in the intracellular oxidation level occurred. This suggested that reactive oxygen species probably do not play a primary role in the apoptosis of cells exposed to aspirin.peer-reviewe

Aspirin-induced apoptosis of yeast cells is associated with mitochondrial superoxide radical accumulation and NAD(P)H oxidation

In previous studies, we observed that aspirin, a promising cancer-preventive agent, induces apoptosis in mitochondrial manganese superoxide dismutase(MnSOD)-deficient Saccharomyces cerevisiae cells grown aerobically in ethanol medium. In this study, we show that aspirin-induced apoptosis is associated with a significant increase in mitochondrial and cytosolic O2 and oxidation of mitochondrial NAD(P)H. A concomitant rise in the level of cytosolic CuZn-SOD activity failed to compensate for mitochondrial MnSOD deficiency. However, an observed increase in activity of Escherichia coli FeSOD targeted to the mitochondrial matrix of the MnSOD-deficient yeast cells, markedly decreased aspirin-induced accumulation of mitochondrial O 2 , significantly increased the mitochondrial NAD(P)H level and rescued the apoptotic phenotype. Indeed, recombinant yeast cells expressing E. coli FeSOD behaved in a similar manner to the parent wild-type yeast cells with native mitochondrial MnSOD activity. Wild-type cells consistently showed a decrease in mitochondrial O 2 and an increase in mitochondrial NAD(P)H levels in the presence of aspirin in ethanol medium. In fact, in wild-type cells, our studies supported an antioxidant action of aspirin. Taken together, our results indicate that a pro-oxidant effect of aspirin occurring predominantly in cells with compromised mitochondrial redox balance may be enough to overcome antioxidant defences resulting in apoptosis, as observed in MnSOD-deficient yeast cells.peer-reviewe

Prokaryotic iron superoxide dismutase replaces cytosolic copper, zinc superoxide dismutase in protecting yeast cells against oxidative stress

The iron superoxide dismutase (FeSOD) gene of Escherichia coli was cloned in Saccharomyces cerevisiae cells deficient in copper,zinc superoxide dismutase (Cu,ZnSOD). FeSOD replaced Cu,ZnSOD in protecting the yeast cells against oxidative stress. In the recombinant strains the FeSOD gene, which was under the transcriptional control of the yeast phosphoglycerate kinase gene promoter, was functionally expressed at two different levels on episomal and centromeric plasmids. Despite suppression of methionine and lysine auxotrophy, the higher level of FeSOD activity was more beneficial to growth of the mutant yeast cells only when these were exposed to higher levels of oxidative stress induced by paraquat or 100% oxygen. In the presence of paraquat, there was a novel stimulation of FeSOD activity. This was associated with a marked increase in catalase activity, and a decrease in glutathione reductase activity.peer-reviewe

Cloned prokaryotic iron superoxide dismutase protects yeast cells against oxidative stress depending on mitochondrial location

Superoxide dismutase (SOD) is considered to be the first line of defense against oxygen toxicity. It exists as a family of three metalloproteins with copper,zinc (Cu,ZnSOD), manganese (MnSOD), and iron (FeSOD) forms. In this work, we have targetedEscherichia coliFeSOD to the mitochondrial intermembrane space (IMS) of yeast cells deficient in mitochondrial MnSOD. Our results show that FeSOD in the IMS increases the growth rate of the cells growing in minimal medium in air but does not protect the MnSOD-deficient yeast cells when exposed to induced oxidative stress. Cloned FeSOD must be targeted to the mitochondrial matrix to protect the cells from both physiological and induced oxidative stress. This confirms that the superoxide radical is mainly generated on the matrix side of the inner mitochondrial membrane of yeast cells, without excluding its potential appearance in the mitochondrial IMS where its elimination by SOD is beneficial to the cells.peer-reviewe

Stimulation of yeast 3-phosphoglycerate kinase gene promoter by paraquat

Yeast cells exposed to adverse conditions employ a number of defense mechanisms in order to respond effectively to the stress and sustain a high proliferation rate. It has been shown that several glycolytic enzymes are induced upon heat treatment of yeast. In this work, we used a reporter plasmid construct to study the effects of oxidative stress, induced by the O•−2-generating compound paraquat (PQ), on the yeast 3-phosphoglycerate kinase gene (PGK) promoter. Our results show that (i) moderate, as opposed to excessive, doses of PQ induce increased stimulation of the PGK promoter, at midlogarithmic phase of growth; and (ii) the thiol antioxidant N-acetylcysteine cancels this stimulatory effect. These observations may represent one aspect of a more general role for glycolysis in maintaining the energy pools of yeast cells under stress.peer-reviewe

Superoxide dismutases : recent advances and clinical applications

The Escherichia coli iron superoxide dismutase (FeSOD) gene was expressed, at two different levels (using episomal and centromeric plasmid systems), in Saccharomyces cerevisiae cells deficient in copper, zinc superoxide dismutase. Levels of antioxidant enzymes were studied in the recombinant strains in the presence and absence of 1 mM paraquat in minimal medium. Exposure to paraquat resulted in: (1) increase in the levels of total SOD, FeSOD, and catalase activities in both yeast strains expressing the FeSOD gene, and (2) decrease in the levels of glutathione reductase in yeast cells expressing the cloned FeSOD gene on the episomal, but not on the centromeric, plasmid The increase in FeSOD activity suggested that there is stimulation of the yeast 3-phosphoglycerate kinase gene (PGK) promoter controlling the cloned FeSOD gene in the presence of paraquat This could be either due to the oxidative stress induced by paraquat, or as a result of an inherent effect of paraquat itself. This hypothesis, that is, induction of the PGK promoter in S. cerevisiae under oxidative stress, is presently being studied in our laboratory. If confirmed, this finding would complement previous observations that transcription of S. cerevisiae PGK increases on heat-shock (Piper et al. (1986) Eur. 1. Bioc/zem., 161,525-531). Thus the PGK gene could be implicated as being one of the genes that are induced as part of the general stress response of S. cerevisiae.peer-reviewe

Aspirin impairs acetyl-coenzyme A metabolism in redox-compromised yeast cells

Aspirin is a widely used anti-inflammatory and antithrombotic drug also known in recent years for its promising chemopreventive antineoplastic properties, thought to be mediated in part by its ability to induce apoptotic cell death. However, the full range of mechanisms underlying aspirin’s cancer-preventive properties is still elusive. In this study, we observed that aspirin impaired both the synthesis and transport of acetyl-coenzyme A (acetyl-CoA) into the mitochondria of manganese superoxide dismutase (MnSOD)-deficient Saccharomyces cerevisiae EG110 yeast cells, but not of the wild-type cells, grown aerobically in ethanol medium. This occurred at both the gene level, as indicated by microarray and qRT-PCR analyses, and at the protein level as indicated by enzyme assays. These results show that in redox-compromised MnSOD-deficient yeast cells, but not in wild-type cells, aspirin starves the mitochondria of acetyl-CoA and likely causes energy failure linked to mitochondrial damage, resulting in cell death. Since acetyl-CoA is one of the least-studied targets of aspirin in terms of the latter’s propensity to prevent cancer, this work may provide further mechanistic insight into aspirin’s chemopreventive behavior with respect to early stage cancer cells, which tend to have downregulated MnSOD and are also redox-compromised.Austrian Science Fund, Malta Council for Science and Technology and Bundesministerium für Wissenschaft, Forschung und Wirtschaft.peer-reviewe