Aging and calorie restriction modulate yeast redox state, oxidized protein removal, and the ubiquitin-proteasome system

Mitochondrial redox state, bioenergetics, and calcium transport in caloric restriction: A metabolic nexus

Mitochondria congregate central reactions in energy metabolism, many of which involve electron transfer. As such, they are expected to both respond to changes in nutrient supply and demand and also provide signals that integrate energy metabolism intracellularly. In this review, we discuss how mitochondrial bioenergetics and reactive oxygen species production is impacted by dietary interventions that change nutrient availability and impact on aging, such as calorie restriction. We also discuss how dietary interventions alter mitochondrial Ca2+ transport, regulating both mitochondrial and cytosolic processes modulated by this ion. Overall, a plethora of literature data support the idea that mitochondrial oxidants and calcium transport act as integrating signals coordinating the response to changes in nutritional supply and demand in cells, tissues, and animals.

Glucose restriction in Saccharomyces cerevisiae modulates the phosphorylation pattern of the 20S proteasome and increases its activity

Caloric restriction is known to extend the lifespan and/or improve diverse physiological parameters in a vast array of organisms. In the yeast Saccharomyces cerevisiae, caloric restriction is performed by reducing the glucose concentration in the culture medium, a condition previously associated with increased chronological lifespan and 20S proteasome activity in cell extracts, which was not due to increased proteasome amounts in restricted cells. Herein, we sought to investigate the mechanisms through which glucose restriction improved proteasome activity and whether these activity changes were associated with modifications in the particle conformation. We show that glucose restriction increases the ability of 20S proteasomes, isolated from Saccharomyces cerevisiae cells, to degrade model substrates and whole proteins. In addition, threonine 55 and/or serine 56 of the α5-subunit, were/was consistently found to be phosphorylated in proteasomes isolated from glucose restricted cells, which may be involved in the increased proteolysis capacity of proteasomes from restricted cells. We were not able to observe changes in the gate opening nor in the spatial conformation in 20S proteasome particles isolated from glucose restricted cells, suggesting that the changes in activity were not accompanied by large conformational alterations in the 20S proteasome but involved allosteric activation of proteasome catalytic site.

The Effect of Calorie Restriction on Protein Quality Control in Yeast

Initially, protein aggregates were regarded as a sign of a pathological state of the cell. Later, it was found that these assemblies are formed in response to stress, and that some of them serve as signalling mechanisms. This review has a particular focus on how intracellular protein aggregates are related to altered metabolism caused by different glucose concentrations in the extracellular environment. We summarise the current knowledge of the role of energy homeostasis signalling pathways in the consequent effect on intracellular protein aggregate accumulation and removal. This covers regulation at different levels, including elevated protein degradation and proteasome activity mediated by the Hxk2 protein, the enhanced ubiquitination of aberrant proteins through Torc1/Sch9 and Msn2/Whi2, and the activation of autophagy mediated through ATG genes. Finally, certain proteins form reversible biomolecular aggregates in response to stress and reduced glucose levels, which are used as a signalling mechanism in the cell, controlling major primary energy pathways related to glucose sensing.

Evaluation of the carbonylation of filamentous fungi proteins by dry immune dot blotting

The development of mycological gerontology requires effective methods for assessing the biological age of fungal cells. This assessment is based on the analysis of a complex of aging and oxidative stress markers. One of the most powerful such markers is the protein carbonylation. In this study, the already known method of dry immune dot blotting is adapted for mycological studies of the content of protein carbonyl groups. After testing the method on a number of filamentous fungi species, some features of the accumulation of carbonylated proteins in mycelium were established. Among these features: (i) a weak effect of exogenous oxidative stress on the accumulation of carbonyls in a number of fungi, (ii) reversibility of the carbonyl accumulation, (iii) possibility of arbitrary regulation of carbonyl content by fungus itself and (iv) the influence of hormesis. In addition, two polar strategies for the accumulation of carbonyl modification were revealed, named Id-strategy (Indifferent) and Cn-strategy (Concern). Thus, even the analysis of one marker allows making some preliminary general assumptions and conclusions. For example, the idea that fungi can freely regulate their biological age is confirmed. This feature makes fungi very flexible in terms of responding to environmental influences and promising objects for gerontology.

Signaling pathways of dietary energy restriction and metabolism on brain physiology and in age-related neurodegenerative diseases

Several laboratory animal models have shown that dietary energy restriction (ER) can promote longevity and improve various health aspects in old age. However, whether the entire spectrum of ER-induced short- and long-term physiological and metabolic adaptions is translatable to humans remains to be determined. In this review article, we present recent evidence towards the elucidation of the impact of ER on brain physiology and in age-related neurodegenerative diseases. We also discuss modulatory influences of ER on metabolism and overall on human health, limitations of current experimental designs as well as future perspectives for ER trials in humans. Finally, we summarize signaling pathways and processes known to be affected by both aging and ER with a special emphasis on the link between ER and cellular proteostasis.

Expression of human HSP27 in yeast extends replicative lifespan and uncovers a hormetic response

Human HSP27 is a small heat shock protein that modulates the ability of cells to respond to heat shock and oxidative stress, and also functions as a chaperone independent of ATP, participating in the proteasomal degradation of proteins. The expression of HSP27 is associated with survival in mammalian cells. In cancer cells, it confers resistance to chemotherapy; in neurons, HSP27 has a positive effect on neuronal viability in models of Alzheimer's and Parkinson's diseases. To better understand the mechanism by which HSP27 expression contributes to cell survival, we expressed human HSP27 in the budding yeast Saccharomyces cerevisiae under control of different mutant TEF promoters, that conferred nine levels of graded basal expression, and showed that replicative lifespan and proteasomal activity increase as well as the resistance to oxidative and thermal stresses. The profile of these phenotypes display a dose-response effect characteristic of hormesis, an adaptive phenomenon that is observed when cells are exposed to increasing amounts of stress or toxic substances. The hormetic response correlates with changes in expression levels of HSP27 and also with its oligomeric states when correlated to survival assays. Our results indicate that fine tuning of HSP27 concentration could be used as a strategy for cancer therapy, and also for improving neuronal survival in neurodegenerative diseases.

Caloric restriction rescues yeast cells from alpha-synuclein toxicity through autophagic control of proteostasis

α-Synuclein (SNCA) is a presynaptic protein that is associated with the pathophysiology of synucleinopathies, including Parkinson's disease. SNCA is a naturally aggregation-prone protein, which may be degraded by the ubiquitin-proteasome system (UPS) and by lysosomal degradation pathways. Besides being a target of the proteolytic systems, SNCA can also alter the function of these pathways further, contributing to the progression of neurodegeneration. Deterioration of UPS and autophagy activities with aging further aggravates this toxic cycle. Caloric restriction (CR) is still the most effective non-genetic intervention promoting lifespan extension. It is known that CR-mediated lifespan extension is linked to the regulation of proteolytic systems, but the mechanisms underlying CR rescue of SNCA toxicity remain poorly understood. This study shows that CR balances UPS and autophagy activities during aging. CR enhances UPS activity, reversing the decline of the UPS activity promoted by SNCA, and keeps autophagy at homeostatic levels. Maintenance of autophagy at homeostatic levels appears to be relevant for UPS activity and for the mechanism underlying rescue of cells from SNCA-mediated toxicity by CR.

The TORC1-Sch9 pathway as a crucial mediator of chronological lifespan in the yeast Saccharomyces cerevisiae

The concept of ageing is one that has intrigued mankind since the beginning of time and is now more important than ever as the incidence of age-related disorders is increasing in our ageing population. Over the past decades, extensive research has been performed using various model organisms. As such, it has become apparent that many fundamental aspects of biological ageing are highly conserved across large evolutionary distances. In this review, we illustrate that the unicellular eukaryotic organism Saccharomyces cerevisiae has proven to be a valuable tool to gain fundamental insights into the molecular mechanisms of cellular ageing in multicellular eukaryotes. In addition, we outline the current knowledge on how downregulation of nutrient signaling through the target of rapamycin (TOR)-Sch9 pathway or reducing calorie intake attenuates many detrimental effects associated with ageing and leads to the extension of yeast chronological lifespan. Given that both TOR Complex 1 (TORC1) and Sch9 have mammalian orthologues that have been implicated in various age-related disorders, unraveling the connections of TORC1 and Sch9 with yeast ageing may provide additional clues on how their mammalian orthologues contribute to the mechanisms underpinning human ageing and health.

Linking cellular proteostasis to yeast longevity

Proteostasis is a cellular housekeeping process that refers to the healthy maintenance of the cellular proteome that governs the fate of proteins from synthesis to degradation. Perturbations of proteostasis might result in protein dysfunction with consequent deleterious effects that can culminate in cell death. To deal with the loss of proteostasis, cells are supplied with a highly sophisticated and interconnected network that integrates as major players the molecular chaperones and the protein degradation pathways. It is well recognized that the ability of cells to maintain proteostasis declines during ageing, although the precise mechanisms are still elusive. Indeed, genetic or pharmacological enhancement of the proteostasis network has been shown to extend lifespan in a variety of ageing models. Therefore, an improved understanding of the interventions/mechanisms that contribute to cellular protein quality control will have a huge impact on the ageing field. This mini-review centers on the current knowledge about the major pathways that contribute for the maintenance of Saccharomyces cerevisiae proteostasis, with particular emphasis on the developments that highlight the multidimensional nature of the proteostasis network in the maintenance of proteostasis, as well as the age-dependent changes on this network.

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

Ageing is a complex and multifactorial process driven by genetic, environmental and stochastic factors that lead to the progressive decline of biological systems. Mechanisms of ageing have been extensively investigated in various model organisms and systems generating fundamental advances. Notably, studies on yeast ageing models have made numerous and relevant contributions to the progress in the field. Different longevity factors and pathways identified in yeast have then been shown to regulate molecular ageing in invertebrate and mammalian models. Currently the best candidates for anti-ageing drugs such as spermidine and resveratrol or anti-ageing interventions such as caloric restriction were first identified and explored in yeast. Yeasts have also been instrumental as models to study the cellular and molecular effects of proteins associated with age-related diseases such as Parkinson's, Huntington's or Alzheimer's diseases. In this chapter, a review of the advances on ageing and age-related diseases research in yeast models will be made. Particular focus will be placed on key longevity factors, ageing hallmarks and interventions that slow ageing, both yeast-specific and those that seem to be conserved in multicellular organisms. Their impact on the pathogenesis of age-related diseases will be also discussed.

Heterologous expression of mitochondrial nicotinamide adenine dinucleotide transporter (Ndt1) from Aspergillus fumigatus rescues impaired growth in Δndt1Δndt2 Saccharomyces cerevisiae strain

Our understanding of nicotinamide adenine dinucleotide mitochondrial transporter 1 (Ndt1A) in Aspergillus fumigatus remains poor. Thus, we investigated whether Ndt1A could alter fungi survival. To this end, we engineered the expression of an Ndt1A-encoding region in a Δndt1Δndt2 yeast strain. The resulting cloned Ndt1A protein promoted the mitochondrial uptake of nicotinamide adenine dinucleotide (NAD⁺), generating a large mitochondrial membrane potential. The NAD⁺ carrier utilized the electrochemical proton gradient to drive NAD⁺ entrance into mitochondria when the mitochondrial membrane potential was sustained by succinate. Its uptake has no impact on oxidative stress, and Ndt1A expression improved growth and survival of the Δndt1Δndt2 Saccharomyces cerevisiae strain.

Bicarbonate Increases Ischemia-Reperfusion Damage by Inhibiting Mitophagy

During an ischemic event, bicarbonate and CO2 concentration increase as a consequence of O2 consumption and lack of blood flow. This event is important as bicarbonate/CO2 is determinant for several redox and enzymatic reactions, in addition to pH regulation. Until now, most work done on the role of bicarbonate in ischemia-reperfusion injury focused on pH changes; although reperfusion solutions have a fixed pH, cardiac resuscitation protocols commonly employ bicarbonate to correct the profound acidosis associated with respiratory arrest. However, we previously showed that bicarbonate can increase tissue damage and protein oxidative damage independent of pH. Here we show the molecular basis of bicarbonate-induced reperfusion damage: the presence of bicarbonate selectively impairs mitophagy, with no detectable effect on autophagy, proteasome activity, reactive oxygen species production or protein oxidation. We also show that inhibition of autophagy reproduces the effects of bicarbonate in reperfusion injury, providing additional evidence in support of this mechanism. This phenomenon is especially important because bicarbonate is widely used in resuscitation protocols after cardiac arrest, and while effective as a buffer, may also contribute to myocardial injury.

UPS Activation in the Battle Against Aging and Aggregation-Related Diseases: An Extended Review

Aging is a biological process accompanied by gradual increase of damage in all cellular macromolecules, i.e., nucleic acids, lipids, and proteins. When the proteostasis network (chaperones and proteolytic systems) cannot reverse the damage load due to its excess as compared to cellular repair/regeneration capacity, failure of homeostasis is established. This failure is a major hallmark of aging and/or aggregation-related diseases. Dysfunction of the major cellular proteolytic machineries, namely the proteasome and the lysosome, has been reported during the progression of aging and aggregation-prone diseases. Therefore, activation of these pathways is considered as a possible preventive or therapeutic approach against the progression of these processes. This chapter focuses on UPS activation studies in cellular and organismal models and the effects of such activation on aging, longevity and disease prevention or reversal.

Inhibition of Protein Ubiquitination by Paraquat and 1-Methyl-4-Phenylpyridinium Impairs Ubiquitin-Dependent Protein Degradation Pathways

Intracytoplasmic inclusions of protein aggregates in dopaminergic cells (Lewy bodies) are the pathological hallmark of Parkinson's disease (PD). Ubiquitin (Ub), alpha (α)-synuclein, p62/sequestosome 1, and oxidized proteins are the major components of Lewy bodies. However, the mechanisms involved in the impairment of misfolded/oxidized protein degradation pathways in PD are still unclear. PD is linked to mitochondrial dysfunction and environmental pesticide exposure. In this work, we evaluated the effects of the pesticide paraquat (PQ) and the mitochondrial toxin 1-methyl-4-phenylpyridinium (MPP(+)) on Ub-dependent protein degradation pathways. No increase in the accumulation of Ub-bound proteins or aggregates was observed in dopaminergic cells (SK-N-SH) treated with PQ or MPP(+), or in mice chronically exposed to PQ. PQ decreased Ub protein content, but not its mRNA transcription. Protein synthesis inhibition with cycloheximide depleted Ub levels and potentiated PQ-induced cell death. The inhibition of proteasomal activity by PQ was found to be a late event in cell death progression and had neither effect on the toxicity of either MPP(+) or PQ, nor on the accumulation of oxidized sulfenylated, sulfonylated (DJ-1/PARK7 and peroxiredoxins), and carbonylated proteins induced by PQ. PQ- and MPP(+)-induced Ub protein depletion prompted the dimerization/inactivation of the Ub-binding protein p62 that regulates the clearance of ubiquitinated proteins by autophagy. We confirmed that PQ and MPP(+) impaired autophagy flux and that the blockage of autophagy by the overexpression of a dominant-negative form of the autophagy protein 5 (dnAtg5) stimulated their toxicity, but there was no additional effect upon inhibition of the proteasome. PQ induced an increase in the accumulation of α-synuclein in dopaminergic cells and membrane-associated foci in yeast cells. Our results demonstrate that the inhibition of protein ubiquitination by PQ and MPP(+) is involved in the dysfunction of Ub-dependent protein degradation pathways.

Proteasome activation: An innovative promising approach for delaying aging and retarding age-related diseases

Aging is a natural process accompanied by a progressive accumulation of damage in all constituent macromolecules (nucleic acids, lipids and proteins). Accumulation of damage in proteins leads to failure of proteostasis (or vice versa) due to increased levels of unfolded, misfolded or aggregated proteins and, in turn, to aging and/or age-related diseases. The major cellular proteolytic machineries, namely the proteasome and the lysosome, have been shown to dysfunction during aging and age-related diseases. Regarding the proteasome, it is well established that it can be activated either through genetic manipulation or through treatment with natural or chemical compounds that eventually result to extension of lifespan or deceleration of the progression of age-related diseases. This review article focuses on proteasome activation studies in several species and cellular models and their effects on aging and longevity. Moreover, it summarizes findings regarding proteasome activation in the major age-related diseases as well as in progeroid syndromes.

Sch9 regulates intracellular protein ubiquitination by controlling stress responses

Protein ubiquitination and the subsequent degradation are important means by which aberrant proteins are removed from cells, a key requirement for long-term survival. In this study, we found that the overall level of ubiquitinated proteins dramatically decreased as yeast cell grew from log to stationary phase. Deletion of SCH9, a gene encoding a key protein kinase for longevity control, decreased the level of ubiquitinated proteins in log phase and this effect could be reversed by restoring Sch9 function. We demonstrate here that the decrease of ubiquitinated proteins in sch9Δ cells in log phase is not caused by changes in ubiquitin expression, proteasome activity, or autophagy, but by enhanced expression of stress response factors and a decreased level of oxidative stress. Our results revealed for the first time how Sch9 regulates the level of ubiquitinated proteins and provides new insight into how Sch9 controls longevity.

The controversial world of sirtuins

The controversy around sirtuins and their functions in aging has drawn in the past few years as much attention, if not more, from the scientific community and the public as they did when first proposed as the key conserved aging regulators in eukaryotes. With some of the basic observations on sirtuin longevity promoting functions being questioned in popular model systems, researchers are wondering if this family of conserved enzymes still holds strong potential as therapeutic targets. This review examines the several controversial issues around sirtuins and their functions in aging, calorie restriction, as well as age-related diseases in light of recent studies in mammalian systems and discusses whether modulators of sirtuins still hold the secret of life.:

Cross-talk between redox regulation and the ubiquitin-proteasome system in mammalian cell differentiation

BACKGROUND

Embryogenesis and stem cell differentiation are complex and orchestrated signaling processes. Reactive oxygen species (ROS) act as essential signal transducers in cellular differentiation, as has been shown through recent discoveries. On the other hand, the ubiquitin-proteasome system (UPS) has long been known to play an important role in all cellular regulated processes, including differentiation.

SCOPE OF REVIEW

In the present review, we focus on findings that highlight the interplay between redox signaling and the UPS regarding cell differentiation. Through systems biology analyses, we highlight major routes during cardiomyocyte differentiation based on redox signaling and UPS modulation.

MAJOR CONCLUSION

Oxygen availability and redox signaling are fundamental regulators of cell fate upon differentiation. The UPS plays an important role in the maintenance of pluripotency and the triggering of differentiation.

GENERAL SIGNIFICANCE

Cellular differentiation has been a matter of intense investigation mainly because of its potential therapeutic applications. Understanding regulatory mechanisms underlying cell differentiation is an important issue. Correspondingly, the role of UPS and regulation of redox processes have been emerged as essential factors to control the fate of cells upon differentiation. This article is part of a Special Issue entitled Redox regulation of differentiation and de-differentiation.

Proteasome activation delays aging in vitro and in vivo

Aging is a natural biological process that is characterized by a progressive accumulation of macromolecular damage. In the proteome, aging is accompanied by decreased protein homeostasis and function of the major cellular proteolytic systems, leading to the accumulation of unfolded, misfolded, or aggregated proteins. In particular, the proteasome is responsible for the removal of normal as well as damaged or misfolded proteins. Extensive work during the past several years has clearly demonstrated that proteasome activation by either genetic means or use of compounds significantly retards aging. Importantly, this represents a common feature across evolution, thereby suggesting proteasome activation to be an evolutionarily conserved mechanism of aging and longevity regulation. This review article reports on the means of function of these proteasome activators and how they regulate aging in various species.

Proteasome inhibitor MG132 inhibits the proliferation and promotes the cisplatin-induced apoptosis of human esophageal squamous cell carcinoma cells

Comprehensive treatment based on chemotherapy is regarded as the first-line treatment for patients with unresectable or metastatic esophageal squamous cell carcinoma (ESCC). However, chemoresistance is common among patients with ESCC. Therefore, there is a need to explore new therapeutic strategies or adjuvant drugs. One promising possibility is to use dietary agents that can increase tumor cell sensitivity to drugs. In this study, we initially investigated the antitumor activity of proteasome inhibitor MG132 in vitro and in vivo. Effects of MG132 on the enhancment of the anticancer functions of cisplatin were then investigated in human esophageal cancer EC9706 cells in relation to apoptosis and cell signaling events. Exposure of cells to MG132 resulted in a marked decrease in cell viability in a dose- and time-dependent manner. Administration of MG132 markedly inhibited tumor growth in the EC9706 xenograft model. MG132 significantly enhanced cisplatin-induced apoptosis in association with the activation of caspase-3 and -8. These events were accompanied by the downregulation of NF-κB, which plays a key role in cell apoptosis. Taken together, these findings demonstrate a novel mechanism by which proteasome inhibitor MG132 potentiates cisplatin-induced apoptosis in human ESCC and inhibitory activity of tumor growth of the EC9706 xenograft model.

Redox regulation of the proteasome via S-glutathionylation

The proteasome is a multimeric and multicatalytic intracellular protease responsible for the degradation of proteins involved in cell cycle control, various signaling processes, antigen presentation, and control of protein synthesis. The central catalytic complex of the proteasome is called the 20S core particle. The majority of these are flanked on one or both sides by regulatory units. Most common among these units is the 19S regulatory unit. When coupled to the 19S unit, the complex is termed the asymmetric or symmetric 26S proteasome depending on whether one or both sides are coupled to the 19S unit, respectively. The 26S proteasome recognizes poly-ubiquitinylated substrates targeted for proteolysis. Targeted proteins interact with the 19S unit where they are deubiquitinylated, unfolded, and translocated to the 20S catalytic chamber for degradation. The 26S proteasome is responsible for the degradation of major proteins involved in the regulation of the cellular cycle, antigen presentation and control of protein synthesis. Alternatively, the proteasome is also active when dissociated from regulatory units. This free pool of 20S proteasome is described in yeast to mammalian cells. The free 20S proteasome degrades proteins by a process independent of poly-ubiquitinylation and ATP consumption. Oxidatively modified proteins and other substrates are degraded in this manner. The 20S proteasome comprises two central heptamers (β-rings) where the catalytic sites are located and two external heptamers (α-rings) that are responsible for proteasomal gating. Because the 20S proteasome lacks regulatory units, it is unclear what mechanisms regulate the gating of α-rings between open and closed forms. In the present review, we discuss 20S proteasomal gating modulation through a redox mechanism, namely, S-glutathionylation of cysteine residues located in the α-rings, and the consequence of this post-translational modification on 20S proteasomal function.

Maintenance of cellular ATP level by caloric restriction correlates chronological survival of budding yeast

The free radical theory of aging emphasizes cumulative oxidative damage in the genome and intracellular proteins due to reactive oxygen species (ROS), which is a major cause for aging. Caloric restriction (CR) has been known as a representative treatment that prevents aging; however, its mechanism of action remains elusive. Here, we show that CR extends the chronological lifespan (CLS) of budding yeast by maintaining cellular energy levels. CR reduced the generation of total ROS and mitochondrial superoxide; however, CR did not reduce the oxidative damage in proteins and DNA. Subsequently, calorie-restricted yeast had higher mitochondrial membrane potential (MMP), and it sustained consistent ATP levels during the process of chronological aging. Our results suggest that CR extends the survival of the chronologically aged cells by improving the efficiency of energy metabolism for the maintenance of the ATP level rather than reducing the global oxidative damage of proteins and DNA.

Bicarbonate modulates oxidative and functional damage in ischemia-reperfusion

The carbon dioxide/bicarbonate (CO(2)/HCO(3)(-)) pair is the main biological pH buffer. However, its influence on biological processes, and in particular redox processes, is still poorly explored. Here we study the effect of CO(2)/HCO(3)(-) on ischemic injury in three distinct models (cardiac HL-1 cells, perfused rat heart, and Caenorhabditis elegans). We found that, although various concentrations of CO(2)/HCO(3)(-) do not affect function under basal conditions, ischemia-reperfusion or similar insults in the presence of higher CO(2)/HCO(3)(-) resulted in greater functional loss associated with higher oxidative damage in all models. Because the effect of CO(2)/HCO(3)(-) was observed in all models tested, we believe this buffer is an important determinant of oxidative damage after ischemia-reperfusion.

Exercise training restores cardiac protein quality control in heart failure

Exercise training is a well-known coadjuvant in heart failure treatment; however, the molecular mechanisms underlying its beneficial effects remain elusive. Despite the primary cause, heart failure is often preceded by two distinct phenomena: mitochondria dysfunction and cytosolic protein quality control disruption. The objective of the study was to determine the contribution of exercise training in regulating cardiac mitochondria metabolism and cytosolic protein quality control in a post-myocardial infarction-induced heart failure (MI-HF) animal model. Our data demonstrated that isolated cardiac mitochondria from MI-HF rats displayed decreased oxygen consumption, reduced maximum calcium uptake and elevated H₂O₂ release. These changes were accompanied by exacerbated cardiac oxidative stress and proteasomal insufficiency. Declined proteasomal activity contributes to cardiac protein quality control disruption in our MI-HF model. Using cultured neonatal cardiomyocytes, we showed that either antimycin A or H₂O₂ resulted in inactivation of proteasomal peptidase activity, accumulation of oxidized proteins and cell death, recapitulating our in vivo model. Of interest, eight weeks of exercise training improved cardiac function, peak oxygen uptake and exercise tolerance in MI-HF rats. Moreover, exercise training restored mitochondrial oxygen consumption, increased Ca²⁺-induced permeability transition and reduced H₂O₂ release in MI-HF rats. These changes were followed by reduced oxidative stress and better cardiac protein quality control. Taken together, our findings uncover the potential contribution of mitochondrial dysfunction and cytosolic protein quality control disruption to heart failure and highlight the positive effects of exercise training in re-establishing cardiac mitochondrial physiology and protein quality control, reinforcing the importance of this intervention as a non-pharmacological tool for heart failure therapy.

Protein carbonylation and metabolic control systems

Oxidative stress is linked to the production of reactive lipid aldehydes that non-enzymatically alkylate cysteine, histidine, or lysine residues in a reaction termed protein carbonylation. Reactive lipid aldehydes and their derivatives are detoxified via a variety of phase I and phase II systems, and when antioxidant defenses are compromised or oxidative conditions are increased, protein carbonylation is increased. The resulting modification has been implicated as causative in a variety of metabolic states including neurodegeneration, muscle wasting, insulin resistance, and aging. Although such modifications usually result in loss of protein function, protein carbonylation may be regulatory and activate signaling pathways involved in antioxidant biology and cellular homeostasis.

Age-related and sex-specific differences in proteasome activity in individual Drosophila flies from wild type, longevity-selected and stress resistant strains

We have measured the caspase-like proteasome activity in individual male and female Drosophila flies by using a non-denaturing lysing technique that consistently extracts total protein. The mean proteasome activity in control C1 females was more than two times higher as compared with that in C1 males. However, in longevity-selected LS1 flies the proteasome activity was significantly lower compared to C1 flies, but the sex differences were maintained to some extent. Five other stress resistant lines also had significantly reduced proteasome activity in both sexes. During ageing, there was a progressive decrease in proteasome activity in C1 females, but not in C1 males. This age-related decline in proteasome activity observed in C1 females was not observed in LS1 flies. We conclude that the proteasome activity in control male and female flies is significantly different from each other and that increased lifespan and stress resistance lead to a reduction in proteasome activity and recession of the age-related decline observed in control females.

Redox control of 20S proteasome gating

The proteasome is the primary contributor in intracellular proteolysis. Oxidized or unstructured proteins can be degraded via a ubiquitin- and ATP-independent process by the free 20S proteasome (20SPT). The mechanism by which these proteins enter the catalytic chamber is not understood thus far, although the 20SPT gating conformation is considered to be an important barrier to allowing proteins free entrance. We have previously shown that S-glutathiolation of the 20SPT is a post-translational modification affecting the proteasomal activities.

AIMS

The goal of this work was to investigate the mechanism that regulates 20SPT activity, which includes the identification of the Cys residues prone to S-glutathiolation.

RESULTS

Modulation of 20SPT activity by proteasome gating is at least partially due to the S-glutathiolation of specific Cys residues. The gate was open when the 20SPT was S-glutathiolated, whereas following treatment with high concentrations of dithiothreitol, the gate was closed. S-glutathiolated 20SPT was more effective at degrading both oxidized and partially unfolded proteins than its reduced form. Only 2 out of 28 Cys were observed to be S-glutathiolated in the proteasomal α5 subunit of yeast cells grown to the stationary phase in glucose-containing medium.

INNOVATION

We demonstrate a redox post-translational regulatory mechanism controlling 20SPT activity.

CONCLUSION

S-glutathiolation is a post-translational modification that triggers gate opening and thereby activates the proteolytic activities of free 20SPT. This process appears to be an important regulatory mechanism to intensify the removal of oxidized or unstructured proteins in stressful situations by a process independent of ubiquitination and ATP consumption. Antioxid. Redox Signal. 16, 1183-1194.

Caloric restriction and redox state: does this diet increase or decrease oxidant production?

Calorie restriction (CR) is well established to enhance the lifespan of a wide variety of organisms, although the mechanisms are still being uncovered. Recently, some authors have suggested that CR acts through hormesis, enhancing the production of reactive oxygen species (ROS), activating stress response pathways, and increasing lifespan. Here, we review the literature on the effects of CR and redox state. We find that there is no evidence in rodent models of CR that an increase in ROS production occurs. Furthermore, results in Caenorhabditis elegans and Saccharomyces cerevisiae suggesting that CR increases intracellular ROS are questionable, and probably cannot be resolved until adequate, artifact free, tools for real-time, quantitative, and selective measurements of intracellular ROS are developed. Overall, the largest body of work indicates that CR improves redox state, although it seems improbable that a global improvement in redox state is the mechanism through which CR enhances lifespan.

Physiological and pathological role of the ubiquitin-proteasome system in the vascular smooth muscle cell

Vascular smooth muscle cell (VSMC) plasticity implies a capacity for rapid change and adaptability through processes requiring protein turnover. The ubiquitin-proteasome system (UPS) is at the core of protein turnover as the main pathway for the degradation of proteins related to cell-cycle regulation, signalling, apoptosis, and differentiation. This review briefly addresses some structural UPS aspects under the perspective of VSMC (patho)biology. The UPS loss-of-function promotes direct cell effects and many indirect effects related to the adaptation to apoptosis/survival signalling, oxidative stress, and endoplasmic reticulum stress. The UPS regulates redox homeostasis and is redox-regulated. Also, the UPS closely interacts with endoplasmic reticulum (ER) homeostasis as the effector of un/misfolded protein degradation, and ER stress is strongly involved in atherosclerosis. Inhibition of cell cycle-controlling ubiquitin ligases or the proteasome reduces VSMC proliferation and prevents modulation of their synthetic phenotype. Proteasome inhibition also strongly promotes VSMC apoptosis and reduces neointima. In atherosclerosis models, proteasome inhibitors display vasculoprotective effects and reduce inflammation. However, worsening of atherosclerosis or vascular dysfunction has also been reported. Proteasome inhibitors sensitize VSMC to increased ER stress-mediated cell death and suppress unfolded protein response signalling. Taken together, these observations show that the UPS has powerful effects in the control of VSMC phenotype and survival signalling. However, more profound knowledge of mechanisms is needed in order to render the UPS an operational therapeutic target.