Yeast at the Forefront of Research on Ageing and Age-Related Diseases

Unraveling the Anti-Aging Properties of Phycocyanin from the Cyanobacterium Spirulina (Arthrospira platensis)

In recent years, marine natural products have become one of the most important resources of novel lead compounds for critical diseases associated with age. Spirulina, a dietary supplement made from blue-green algae (cyanobacteria: scientific name Arthrospira platensis), is particularly rich in phycocyanin, a phycobiliprotein, which accounts for up to 20% of this cyanobacterium's dry weight and is considered responsible for its anti-cancer, anti-inflammatory and antioxidant activities. Although the anti-aging activity of phycocyanin has been investigated, how exactly this compound works against aging remains elusive. The aim of our research is to use the yeast Saccharomyces cerevisiae as a model organism to investigate the anti-aging properties of phycocyanin from A. platensis. Our results show that phycocyanin has a powerful anti-aging effect, greatly extending the chronological life span of yeast cells in a dose-dependent way, as the effect was also pronounced when cells were grown in SD medium under calorie restriction conditions (0.2% glucose). Both ROS and accumulation of dead cells were followed by staining chronologically aged cells with dihydrorhodamine 123 (DHR123) and propidium iodide (PI). Interestingly, we found that most of the aged phycocyanin-treated cells, which were unable to form colonies, were actually ROS+/PI-. Finally, we show that the moment in which phycocyanin is added to the culture does not substantially influence its effectiveness in counteracting chronological aging.

Multiple tethers of organelle contact sites are involved in α-synuclein toxicity in yeast

The protein α-synuclein (α-syn) is one of the major factors linked to Parkinson's disease, yet how its misfolding and deposition contribute to the pathology remains largely elusive. Recently, contact sites among organelles were implicated in the development of this disease. Here, we used the budding yeast Saccharomyces cerevisiae, in which organelle contact sites have been characterized extensively, as a model to investigate their role in α-syn cytotoxicity. We observed that lack of specific tethers that anchor the endoplasmic reticulum to the plasma membrane resulted in cells with increased resistance to α-syn expression. Additionally, we found that strains lacking two dual-function proteins involved in contact sites, Mdm10 and Vps39, were resistant to the expression of α-syn. In the case of Mdm10, we found that this is related to its function in mitochondrial protein biogenesis and not to its role as a contact site tether. In contrast, both functions of Vps39, in vesicular transport and as a tether of the vacuole-mitochondria contact site, were required to support α-syn toxicity. Overall, our findings support that interorganelle communication through membrane contact sites is highly relevant for α-syn-mediated toxicity.

Oxidation of biological molecules with age and induced oxidative stress in different growth phases of Saccharomyces cerevisiae

One of the mechanistic approaches for explaining ageing is the oxidative stress theory of ageing. Saccharomyces cerevisiae has been used as a model to study ageing due to many factors. We have attempted to investigate if the differential ability to withstand oxidative stress can be correlated with their lifespans. In all the four strains studied (AP22, 699, 8C, and SP4), there was no age-associated increases in lipid peroxidation levels measured as thiobarbituric acid reactive substances (TBARS). Under induced oxidative stress conditions, there was an increased TBARS level in both the ages assessed with a quantum-fold increase in the stationary phase cells of AP22. In contrast, the late stationary phase cells of 8C exhibited the least susceptibility to induced oxidative stress. The level of TBARS in both exponential and late stationary phase cells of 699 was overall more than that in the other three strains. Protein carbonylation increased with age in 8C and 699. Induced stress increased carbonylation in the exponential cells of SP4 and 699 and the stationary phase cells of all four strains. Protein carbonylation data indicate that the AP22 cells exhibit decreased protein carbonylation vis-à-vis the other strains. Induced stress data showed that while the exponential cells of 699 are susceptible, the late stationary phase cells of 699 are most resistant. Western blotting analysis using anti-HNE antibodies showed two proteins of molecular mass ~ 56 and ~ 84 kDa that were selectively modified with age in all the strains. Under induced stress conditions, an additional protein of ~ 69 kDa was oxidized. Our investigation shows that the difference in lifespan between the four strains of S. cerevisiae may be regulated by oxidative stress. Knowledge of the identity of the oxidized proteins will significantly facilitate a better understanding of the effect of oxidative stress conditions on the cells of S. cerevisiae.

The lifetime of the oxygen-evolving complex subunit PSBO depends on light intensity and carbon availability in Chlamydomonas

PSBO is essential for the assembly of the oxygen-evolving complex in plants and green algae. Despite its importance, we lack essential information on its lifetime and how it depends on the environmental conditions. We have generated nitrate-inducible PSBO amiRNA lines in the green alga Chlamydomonas reinhardtii. Transgenic strains grew normally under non-inducing conditions, and their photosynthetic performance was comparable to the control strain. Upon induction of the PSBO amiRNA constructs, cell division halted. In acetate-containing medium, cellular PSBO protein levels decreased by 60% within 24 h in the dark, by 75% in moderate light, and in high light, the protein completely degraded. Consequently, the photosynthetic apparatus became strongly damaged, probably due to 'donor-side-induced photoinhibition', and cellular ultrastructure was also severely affected. However, in the absence of acetate during induction, PSBO was remarkably stable at all light intensities and less substantial changes occurred in photosynthesis. Our results demonstrate that the lifetime of PSBO strongly depends on the light intensity and carbon availability, and thus, on the metabolic status of the cells. We also confirm that PSBO is required for photosystem II stability in C. reinhardtii and demonstrate that its specific loss also entails substantial changes in cell morphology and cell cycle.

The First Yarrowia lipolytica Yeast Models Expressing Hepatitis B Virus X Protein: Changes in Mitochondrial Morphology and Functions

Chronic hepatitis B virus infection is the dominant cause of hepatocellular carcinoma, the main cause of cancer death. HBx protein, a multifunctional protein, is essential for pathogenesis development; however, the underlying mechanisms are not fully understood. The complexity of the system itself, and the intricate interplay of many factors make it difficult to advance in understanding the mechanisms underlying these processes. The most obvious solution is to use simpler systems by reducing the number of interacting factors. Yeast cells are particularly suitable for studying the relationships between oxidative stress, mitochondrial dynamics (mitochondrial fusion and fragmentation), and mitochondrial dysfunction involved in HBx-mediated pathogenesis. For the first time, genetically modified yeast, Y. lipolytica, was created, expressing the hepatitis B virus core protein HBx, as well as a variant fused with eGFP at the C-end. It was found that cells expressing HBx experienced stronger oxidative stress than the control cells. Oxidative stress was alleviated by preincubation with the mitochondria-targeted antioxidant SkQThy. Consistent with these data, in contrast to the control cells (pZ-0) containing numerous mitochondrial forming a mitochondrial reticulum, in cells expressing HBx protein, mitochondria were fragmented, and preincubation with SkQThy partially restored the mitochondrial reticulum. Expression of HBx had a significant influence on the bioenergetic function of mitochondria, making them loosely coupled with decreased respiratory rate and reduced ATP formation. In sum, the first highly promising yeast model for studying the impact of HBx on bioenergy, redox-state, and dynamics of mitochondria in the cell and cross-talk between these parameters was offered. This fairly simple model can be used as a platform for rapid screening of potential therapeutic agents, mitigating the harmful effects of HBx.

Yeast as a Model to Find New Drugs and Drug Targets for VPS13-Dependent Neurodegenerative Diseases

Mutations in human VPS13A-D genes result in rare neurological diseases, including chorea-acanthocytosis. The pathogenesis of these diseases is poorly understood, and no effective treatment is available. As VPS13 genes are evolutionarily conserved, the effects of the pathogenic mutations could be studied in model organisms, including yeast, where one VPS13 gene is present. In this review, we summarize advancements obtained using yeast. In recent studies, vps13Δ and vps13-I2749 yeast mutants, which are models of chorea-acanthocytosis, were used to screen for multicopy and chemical suppressors. Two of the suppressors, a fragment of the MYO3 and RCN2 genes, act by downregulating calcineurin activity. In addition, vps13Δ suppression was achieved by using calcineurin inhibitors. The other group of multicopy suppressors were genes: FET4, encoding iron transporter, and CTR1, CTR3 and CCC2, encoding copper transporters. Mechanisms of their suppression rely on causing an increase in the intracellular iron content. Moreover, among the identified chemical suppressors were copper ionophores, which require a functional iron uptake system for activity, and flavonoids, which bind iron. These findings point at areas for further investigation in a higher eukaryotic model of VPS13-related diseases and to new therapeutic targets: calcium signalling and copper and iron homeostasis. Furthermore, the identified drugs are interesting candidates for drug repurposing for these diseases.

Effect of Caloric Restriction on Aging: Fixing the Problems of Nutrient Sensing in Postmitotic Cells?

The review discusses the role of metabolic disorders (in particular, insulin resistance) in the development of age-related diseases and normal aging with special emphasis on the changes in postmitotic cells of higher organisms. Caloric restriction helps to prevent such metabolic disorders, which could probably explain its ability to prolong the lifespan of laboratory animals. Maintaining metabolic homeostasis is especially important for the highly differentiated long-lived body cells, whose lifespan is comparable to the lifespan of the organism itself. Normal functioning of these cells can be ensured only upon correct functioning of the cytoplasm clean-up system and availability of all required nutrients and energy sources. One of the central problems in gerontology is the age-related disruption of glucose metabolism leading to obesity, diabetes, metabolic syndrome, and other related pathologies. Along with the adipose tissue, skeletal muscles are the main consumers of insulin; hence the physical activity of muscles, which supports their energy metabolism, delays the onset of insulin resistance. Insulin resistance disrupts the metabolism of cardiomyocytes, so that they fail to utilize the nutrients to perform their functions even being surrounded by a nutrient-rich environment, which contributes to the development of age-related cardiovascular diseases. Metabolic pathologies also alter the nutrient sensitivity of neurons, thus disrupting the action of insulin in the central nervous system. In addition, there is evidence that neurons can develop insulin resistance as well. It has been suggested that affecting nutritional sensors (e.g., AMPK) in postmitotic cells might improve the state of the entire multicellular organism, slow down its aging, and increase the lifespan.

Aging of the Retina: Molecular and Metabolic Turbulences and Potential Interventions

Multifaceted and divergent manifestations across tissues and cell types have curtailed advances in deciphering the cellular events that accompany advanced age and contribute to morbidities and mortalities. Increase in human lifespan during the past century has heightened awareness of the need to prevent age-associated frailty of neuronal and sensory systems to allow a healthy and productive life. In this review, we discuss molecular and physiological attributes of aging of the retina, with a goal of understanding age-related impairment of visual function. We highlight the epigenome-metabolism nexus and proteostasis as key contributors to retinal aging and discuss lifestyle changes as potential modulators of retinal function. Finally, we deliberate promising intervention strategies for promoting healthy aging of the retina for improved vision.

A New Geniposidic Acid Derivative Exerts Antiaging Effects through Antioxidative Stress and Autophagy Induction

Two compounds that can prolong the replicative lifespan of yeast, geniposidic acid (Compound 1) and geniposide (Compound 2), were isolated from Gardenia jasminoides Ellis. Compared with Compound 1, Compound 2 was different at C11 and showed better bioactivity. On this basis, seven new geniposidic derivatives (3-9) were synthesized. Geniposidic 4-isoamyl ester (8, GENI), which remarkably prolonged the replicative and chronological lifespans of K6001 yeast at 1 µM, was used as the lead compound. Autophagy and antioxidative stress were examined to clarify the antiaging mechanism of GENI. GENI increased the enzymes activities and gene expression levels of superoxide dismutase (SOD) and reduced the contents of reactive oxygen species (ROS) and malondialdehyde (MDA) to improve the survival rate of yeast under oxidative stress. In addition, GENI did not extend the replicative lifespan of ∆sod1, ∆sod2, ∆uth1, ∆skn7, ∆cat, and ∆gpx mutants with K6001 background. The free green fluorescent protein (GFP) signal from the cleavage of GFP-Atg8 was increased by GENI. The protein level of free GFP showed a considerable increase and was time-dependent. Furthermore, GENI failed to extend the replicative lifespans of ∆atg32 and ∆atg2 yeast mutants. These results indicated that antioxidative stress and autophagy induction were involved in the antiaging effect of GENI.

Stress and ageing in yeast

There has long been speculation about the role of various stresses in ageing. Some stresses have beneficial effects on ageing-dependent on duration and severity of the stress, others have negative effects and the question arises whether these negative effects are causative of ageing or the result of the ageing process. Cellular responses to many stresses are highly coordinated in a concerted way and hence there is a great deal of cross-talk between different stresses. Here the relevant aspects of the coordination of stress responses and the roles of different stresses on yeast cell ageing are discussed, together with the various functions that are involved. The cellular processes that are involved in alleviating the effects of stress on ageing are considered, together with the possible role of early stress events on subsequent ageing of cells.

Membrane-Interacting Antifungal Peptides

The incidence of invasive fungal infections is increasing worldwide, resulting in more than 1.6 million deaths every year. Due to growing antifungal drug resistance and the limited number of currently used antimycotics, there is a clear need for novel antifungal strategies. In this context, great potential is attributed to antimicrobial peptides (AMPs) that are part of the innate immune system of organisms. These peptides are known for their broad-spectrum activity that can be directed toward bacteria, fungi, viruses, and/or even cancer cells. Some AMPs act via rapid physical disruption of microbial cell membranes at high concentrations causing cell leakage and cell death. However, more complex mechanisms are also observed, such as interaction with specific lipids, production of reactive oxygen species, programmed cell death, and autophagy. This review summarizes the structure and mode of action of antifungal AMPs, thereby focusing on their interaction with fungal membranes.

Propagation of Mitochondria-Derived Reactive Oxygen Species within the Dipodascus magnusii Cells

Mitochondria are considered to be the main source of reactive oxygen species (ROS) in the cell. It was shown that in cardiac myocytes exposed to excessive oxidative stress, ROS-induced ROS release is triggered. However, cardiac myocytes have a network of densely packed organelles that do not move, which is not typical for the majority of eukaryotic cells. The purpose of this study was to trace the spatiotemporal development (propagation) of prooxidant-induced oxidative stress and its interplay with mitochondrial dynamics. We used Dipodascus magnusii yeast cells as a model, as they have advantages over other models, including a uniquely large size, mitochondria that are easy to visualize and freely moving, an ability to vigorously grow on well-defined low-cost substrates, and high responsibility. It was shown that prooxidant-induced oxidative stress was initiated in mitochondria, far preceding the appearance of generalized oxidative stress in the whole cell. For yeasts, these findings were obtained for the first time. Preincubation of yeast cells with SkQ1, a mitochondria-addressed antioxidant, substantially diminished production of mitochondrial ROS, while only slightly alleviating the generalized oxidative stress. This was expected, but had not yet been shown. Importantly, mitochondrial fragmentation was found to be primarily induced by mitochondrial ROS preceding the generalized oxidative stress development.

In S. cerevisiae hydroxycitric acid antagonizes chronological aging and apoptosis regardless of citrate lyase

Caloric restriction mimetics (CRMs) are promising molecules to prevent age-related diseases as they activate pathways driven by a true caloric restriction. Hydroxycitric acid (HCA) is considered a bona fide CRM since it depletes acetyl-CoA pools by acting as a competitive inhibitor of ATP citrate lyase (ACLY), ultimately repressing protein acetylation and promoting autophagy. Importantly, it can reduce inflammation and tumour development. In order to identify phenotypically relevant new HCA targets we have investigated HCA effects in Saccharomyces cerevisiae, where ACLY is lacking. Strikingly, the drug revealed a powerful anti-aging effect, another property proposed to mark bona fide CRMs. Chronological life span (CLS) extension but also resistance to acetic acid of HCA treated cells were associated to repression of cell apoptosis and necrosis. HCA also largely prevented cell deaths caused by a severe oxidative stress. The molecule could act widely by negatively modulating cell metabolism, similarly to citrate. Indeed, it inhibited both growth reactivation and the oxygen consumption rate of yeast cells in stationary phase. Genetic analyses on yeast CLS mutants indicated that part of the HCA effects can be sensed by Sch9 and Ras2, two conserved key regulators of nutritional and stress signal pathways of primary importance. Our data together with published biochemical analyses indicate that HCA may act with multiple mechanisms together with ACLY repression and allowed us to propose an integrated mechanistic model as a basis for future investigations.

Discovery of fifteen new geroprotective plant extracts and identification of cellular processes they affect to prolong the chronological lifespan of budding yeast

In a quest for previously unknown geroprotective natural chemicals, we used a robust cell viability assay to search for commercially available plant extracts that can substantially prolong the chronological lifespan of budding yeast. Many of these plant extracts have been used in traditional Chinese and other herbal medicines or the Mediterranean and other customary diets. Our search led to a discovery of fifteen plant extracts that significantly extend the longevity of chronologically aging yeast not limited in calorie supply. We show that each of these longevity-extending plant extracts is a geroprotector that decreases the rate of yeast chronological aging and promotes a hormetic stress response. We also show that each of the fifteen geroprotective plant extracts mimics the longevity-extending, stress-protecting, metabolic and physiological effects of a caloric restriction diet but if added to yeast cultured under non-caloric restriction conditions. We provide evidence that the fifteen geroprotective plant extracts exhibit partially overlapping effects on a distinct set of longevity-defining cellular processes. These effects include a rise in coupled mitochondrial respiration, an altered age-related chronology of changes in reactive oxygen species abundance, protection of cellular macromolecules from oxidative damage, and an age-related increase in the resistance to long-term oxidative and thermal stresses.

The antifungal plant defensin HsAFP1 induces autophagy, vacuolar dysfunction and cell cycle impairment in yeast

The plant defensin HsAFP1 is characterized by broad-spectrum antifungal activity and induces apoptosis in Candida albicans. In this study, we performed a transcriptome analysis on C. albicans cultures treated with HsAFP1 to gain further insight in the antifungal mode of action of HsAFP1. Various genes coding for cell surface proteins, like glycosylphosphatidylinositol (GPI)-anchored proteins, and proteins involved in cation homeostasis, autophagy and in cell cycle were differentially expressed upon HsAFP1 treatment. The biological validation of these findings was performed in the model yeast Saccharomyces cerevisiae. To discriminate between events linked to HsAFP1's antifungal activity and those that are not, we additionally used an inactive HsAFP1 mutant. We demonstrated that (i) HsAFP1-resistent S. cerevisiae mutants that are characterized by a defect in processing GPI-anchors are unable to internalize HsAFP1, and (ii) moderate doses (FC50, fungicidal concentration resulting in 50% killing) of HsAFP1 induce autophagy in S. cerevisiae, while high HsAFP1 doses result in vacuolar dysfunction. Vacuolar function is an important determinant of replicative lifespan (RLS) under dietary restriction (DR). In line, HsAFP1 specifically reduces RLS under DR. Lastly, (iii) HsAFP1 affects S. cerevisiae cell cycle in the G2/M phase. However, the latter HsAFP1-induced event is not linked to its antifungal activity, as the inactive HsAFP1 mutant also impairs the G2/M phase. In conclusion, we demonstrated that GPI-anchored proteins are involved in HsAFP1's internalization, and that HsAFP1 induces autophagy, vacuolar dysfunction and impairment of the cell cycle. Collectively, all these data provide novel insights in the mode of action of HsAFP1 as well as in S. cerevisiae tolerance mechanisms against this peptide.

PCK1 Deficiency Shortens the Replicative Lifespan of Saccharomyces cerevisiae through Upregulation of PFK1

The cytosolic isozyme of phosphoenolpyruvate carboxykinase (PCK1) was the first rate-limiting enzyme in the gluconeogenesis pathway, which exerted a critical role in maintaining the blood glucose levels. PCK1 has been established to be involved in various physiological and pathological processes, including glucose metabolism, lipid metabolism, diabetes, and tumorigenesis. Nonetheless, the association of PCK1 with aging process and the detailed underlying mechanisms of PCK1 on aging are still far to be elucidated. Hence, we herein constructed the PCK1-deficient (pck1Δ) and PCK1 overexpression (PCK1 OE) Saccharomyces cerevisiae. The results unveiled that PCK1 deficiency significantly shortened the replicative lifespan (RLS) in the S. cerevisiae, while overexpression of PCK1 prolonged the RLS. Additionally, we noted that the ROS level was significantly enhanced in PCK1-deficient strain and decreased in PCK1 OE strain. Then, a high throughput analysis by deep sequencing was performed in the pck1Δ and wild-type strains, in an attempt to shed light on the effect of PCK1 on the lifespan of aging process. The data showed that the most downregulated mRNAs were enriched in the regulatory pathways of glucose metabolism. Fascinatingly, among the differentially expressed mRNAs, PFK1 was one of the most upregulated genes, which was involved in the glycolysis process and ROS generation. Thus, we further constructed the pfk1Δpck1Δ strain by deletion of PFK1 in the PCK1-deficient strain. The results unraveled that pfk1Δpck1Δ strain significantly suppressed the ROS level and restored the RLS of pck1Δ strain. Taken together, our data suggested that PCK1 deficiency enhanced the ROS level and shortened the RLS of S. cerevisiae via PFK1.

Mitochondrial Dysfunctions May Be One of the Major Causative Factors Underlying Detrimental Effects of Benzalkonium Chloride

Benzalkonium chloride (BAC) is currently the most commonly used antimicrobial preservative in ophthalmic solutions, nasal sprays, and cosmetics. However, a large number of clinical and experimental investigations showed that the topical administration of BAC-containing eye drops could cause a variety of ocular surface changes, from ocular discomfort to potential risk for future glaucoma surgery. BAC-containing albuterol may increase the risk of albuterol-related systemic adverse effects. BAC, commonly present in personal care products, in cosmetic products can induce irritation and dose-dependent changes in the cell morphology. The cationic nature of BAC (it is a quaternary ammonium) suggests that one of the major targets of BAC in the cell may be mitochondria, the only intracellular compartment charged negatively. However, the influence of BAC on mitochondria has not been clearly understood. Here, the effects of BAC on energy parameters of rat liver mitochondria as well as on yeast cells were examined. BAC, being a "weaker" uncoupler, potently inhibited respiration in state 3, diminished the mitochondrial membrane potential, caused opening of the Ca2+/Pi-dependent pore, blocked ATP synthesis, and promoted H₂O₂ production by mitochondria. BAC triggered oxidative stress and mitochondrial fragmentation in yeast cells. BAC-induced oxidative stress in mitochondria and yeast cells was almost totally prevented by the mitochondria-targeted antioxidant SkQ1; the protective effect of SkQ1 on mitochondrial fragmentation was only partial. Collectively, these data showed that BAC acts adversely on cell bioenergetics (especially on ATP synthesis) and mitochondrial dynamics and that its prooxidant effect can be partially prevented by the mitochondria-targeted antioxidant SkQ1.

Life-span extension by pigmented rice bran in the model yeast Saccharomyces cerevisiae

Benefits of whole grains as dietary supplements and active ingredients in health products have been promoted. Despite being neglected as an agricultural byproduct of polished rice, pigmented rice bran has emerged as a promising source of natural anti-aging compounds. Indeed, the extract of red rice bran Hom Dang cultivar contained rich phenolic acids and flavonoids. It displayed high antioxidant activities in vitro and in vivo assays. Using yeast model, extract and bioactive compounds, quercetin and protocatechuic acid found in the rice bran pericarp, effectively reduced levels of intracellular reactive oxygen species (ROS), restored plasma membrane damages and prolonged life-span of pre-treated wild-yeast cells. Importantly, these molecules modulated life span-extension through a mechanism of ROS reduction that resembles to that operated under the highly conserved Tor1- and Sir2-dependent signaling pathways, with the human homologs TORC1 and SIRT1, respectively. The key longevity factors Sch9 and Rim15 kinases, Msn2/4 regulators and a novel transcription factor Asg1, the antioxidant enzymes superoxide dismutases and glutathione peroxidases played important role in mediating longevity. Yeast clearly provides an instrumental platform for rapid screening of compounds with anti-aging efficacies and advances knowledge in the molecular study of ageing.