Methionine sulfoxide reductase A expression is regulated by the DAF-16/FOXO pathway in Caenorhabditis elegans

Early-adult methionine restriction reduces methionine sulfoxide and extends lifespan in Drosophila

Methionine restriction (MetR) extends lifespan in various organisms, but its mechanistic understanding remains incomplete. Whether MetR during a specific period of adulthood increases lifespan is not known. In Drosophila, MetR is reported to extend lifespan only when amino acid levels are low. Here, by using an exome-matched holidic medium, we show that decreasing Met levels to 10% extends Drosophila lifespan with or without decreasing total amino acid levels. MetR during the first four weeks of adult life only robustly extends lifespan. MetR in young flies induces the expression of many longevity-related genes, including Methionine sulfoxide reductase A (MsrA), which reduces oxidatively-damaged Met. MsrA induction is foxo-dependent and persists for two weeks after cessation of the MetR diet. Loss of MsrA attenuates lifespan extension by early-adulthood MetR. Our study highlights the age-dependency of the organismal response to specific nutrients and suggests that nutrient restriction during a particular period of life is sufficient for healthspan extension.

CaMKII, 'jack of all trades' in inflammation during cardiac ischemia/reperfusion injury

Myocardial infarction and revascularization cause cardiac ischemia/reperfusion (I/R) injury featuring cardiomyocyte death and inflammation. The Ca2+/calmodulin dependent protein kinase II (CaMKII) family are serine/ threonine protein kinases that are involved in I/R injury. CaMKII exists in four different isoforms, α, β, γ, and δ. In the heart, CaMKII-δ is the predominant isoform，with multiple splicing variants, such as δB, δC and δ9. During I/R, elevated intracellular Ca2+ concentrations and reactive oxygen species activate CaMKII. In this review, we summarized the regulation and function of CaMKII in multiple cell types including cardiomyocytes, endothelial cells, and macrophages during I/R. We conclude that CaMKII mediates inflammation in the microenvironment of the myocardium, resulting in cell dysfunction, elevated inflammation, and cell death. However, different CaMKII-δ variants exhibit distinct or even opposite functions. Therefore, reagents/approaches that selectively target specific CaMKII isoforms and variants are needed for evaluating and counteracting the exact role of CaMKII in I/R injury and developing effective treatments against I/R injury.

Oxidative Stress and Natural Antioxidants: Back and Forth in the Neurological Mechanisms of Alzheimer's Disease

Alzheimer's disease (AD) is characterized by the progressive degeneration of neuronal cells. With the increase in aged population, there is a prevalence of irreversible neurodegenerative changes, causing a significant mental, social, and economic burden globally. The factors contributing to AD are multidimensional, highly complex, and not completely understood. However, it is widely known that aging, neuroinflammation, and excessive production of reactive oxygen species (ROS), along with other free radicals, substantially contribute to oxidative stress and cell death, which are inextricably linked. While oxidative stress is undeniably important in AD, limiting free radicals and ROS levels is an intriguing and potential strategy for deferring the process of neurodegeneration and alleviating associated symptoms. Therapeutic compounds from natural sources have recently become increasingly accepted and have been effectively studied for AD treatment. These phytocompounds are widely available and a multitude of holistic therapeutic efficiencies for treating AD owing to their antioxidant, anti-inflammatory, and biological activities. Some of these compounds also function by stimulating cholinergic neurotransmission, facilitating the suppression of beta-site amyloid precursor protein-cleaving enzyme 1, α-synuclein, and monoamine oxidase proteins, and deterring the occurrence of AD. Additionally, various phenolic, flavonoid, and terpenoid phytocompounds have been extensively described as potential palliative agents for AD progression. Preclinical studies have shown their involvement in modulating the cellular redox balance and minimizing ROS formation, displaying them as antioxidant agents with neuroprotective abilities. This review emphasizes the mechanistic role of natural products in the treatment of AD and discusses the various pathological hypotheses proposed for AD.

Recombinant Humanized IgG1 Antibody Protects against oxLDL-Induced Oxidative Stress and Apoptosis in Human Monocyte/Macrophage THP-1 Cells by Upregulation of MSRA via Sirt1-FOXO1 Axis

Oxidized low-density lipoprotein (oxLDL)-induced oxidative stress and apoptosis are considered as critical contributors to cardiovascular diseases. Methionine sulfoxide reductase A (MSRA) is a potent intracellular oxidoreductase and serves as an essential factor that protects cells against oxidative damage. Here, we firstly provide evidence that recombinant humanized IgG1 antibody treatment upregulated the expression of MSRA in THP-1 cells to defend against oxLDL-induced oxidative stress and apoptosis. It was also observed that the upregulation of MSRA is regulated by the forkhead box O transcription factor (FOXO1), and the acetylation of FOXO1 increased when exposed to oxLDL but declined when treated with recombinant humanized IgG1 antibody. In addition, we identified that silent information regulator 1 (SIRT1) suppresses FOXO1 acetylation. Importantly, SIRT1 or FOXO1 deficiency impaired the anti-oxidative stress and anti-apoptotic effect of recombinant humanized IgG1 antibody. Together, our results suggest that recombinant humanized IgG1 antibody exerts its anti-oxidative stress and anti-apoptotic function by upregulation of MSRA via the Sirt1-FOXO1 axis.

Assessment of the effects of organic vs. inorganic arsenic and mercury in Caenorhabditis elegans

Exposures to mercury and arsenic are known to pose significant threats to human health. Effects specific to organic vs. inorganic forms of these toxic elements are less understood however, especially for organic dimethylarsinic acid (DMA), which has recently been detected in pups of rodent dams orally exposed to inorganic sodium (meta)arsenite (NaAsO2). Caenorhabditis elegans is a small animal alternative toxicity model. To fill data gaps on the effects of DMA relative to NaAsO2, C. elegans were exposed to these two compounds alongside more thoroughly researched inorganic mercury chloride (HgCl2) and organic methylmercury chloride (meHgCl). For timing of developmental milestone acquisition in C. elegans, meHgCl was 2 to 4-fold more toxic than HgCl2, and NaAsO2 was 20-fold more toxic than DMA, ranking the four compounds meHgCl > HgCl2 > NaAsO2 ≫ DMA for developmental toxicity. Methylmercury induced significant decreases in population locomotor activity levels in developing C. elegans. DMA was also associated with developmental hypoactivity, but at >100-fold higher concentrations than meHgCl. Transcriptional alterations in native genes were observed in wild type C. elegans adults exposed to concentrations equitoxic for developmental delay in juveniles. Both forms of arsenic induced genes involved in immune defense and oxidative stress response, while the two mercury species induced proportionally more genes involved in transcriptional regulation. A transgenic bioreporter for activation of conserved proteosome specific unfolded protein response was strongly activated by NaAsO2, but not DMA at tested concentrations. HgCl2 and meHgCl had opposite effects on a bioreporter for unfolded protein response in the endoplasmic reticulum. Presented experiments indicating low toxicity for DMA in C. elegans are consistent with human epidemiologic data correlating higher arsenic methylation capacity with resistance to arsenic toxicity. This work contributes to the understanding of the accuracy and fit-for-use categories for C. elegans toxicity screening and its usefulness to prioritize compounds of concern for further testing.

The down-regulation of melanogenesis via MITF and FOXO1 signaling pathways in SIRT1 knockout cells using CRISPR/Cas9 system

Hair graying is processed by the inactivation of tyrosinase caused by the accumulation of oxidative stress and a decrease in the number of melanocytes. Therefore, the purpose of this study was to investigate the effect of SIRT1 gene knockout using the CRISPR/Cas9 system on the protein and gene expressions related to melanogenesis. In this study, the mutation in the SIRT1 knockout(KO) gene was verified by T7EI assay and Sanger DNA sequencing. Furthermore, the expression levels of SIRT1 protein and gene in KO cells were remarkably decreased compared with normal cells. Therefore, the SIRT1 gene KO cell line was successfully established for further study. The KO cells also increased SA-β-galactosidase and decreased melanin production and the scavenging activity of hydrogen peroxide. In particular, the down-regulation of p38 and c-kit as well as the up-regulation of ERK resulted in the inactivation of MITF in the KO cells. Thus, KO cells reduced the expressions of Tyrosinase, Tyrosine hydroxylase, TRP-1 and TRP-2 through the negative modulation of MITF. Furthermore, SIRT1 gene KO cells negatively modulated antioxidant proteins such as Catalase, MnSOD, MsrA and MsrB3 through FOXO1 and Keap1. Therefore, it is suggested that SIRT1 could play a positive role in melanogenesis via MITF and FOXO1.

Hypoxia Tolerance Declines with Age in the Absence of Methionine Sulfoxide Reductase (MSR) in Drosophila melanogaster

Unlike the mammalian brain, Drosophila melanogaster can tolerate several hours of hypoxia without any tissue injury by entering a protective coma known as spreading depression. However, when oxygen is reintroduced, there is an increased production of reactive oxygen species (ROS) that causes oxidative damage. Methionine sulfoxide reductase (MSR) acts to restore functionality to oxidized methionine residues. In the present study, we have characterized in vivo effects of MSR deficiency on hypoxia tolerance throughout the lifespan of Drosophila. Flies subjected to sudden hypoxia that lacked MSR activity exhibited a longer recovery time and a reduced ability to survive hypoxic/re-oxygenation stress as they approached senescence. However, when hypoxia was induced slowly, MSR deficient flies recovered significantly quicker throughout their entire adult lifespan. In addition, the wildtype and MSR deficient flies had nearly 100% survival rates throughout their lifespan. Neuroprotective signaling mediated by decreased apoptotic pathway activation, as well as gene reprogramming and metabolic downregulation are possible reasons for why MSR deficient flies have faster recovery time and a higher survival rate upon slow induction of spreading depression. Our data are the first to suggest important roles of MSR and longevity pathways in hypoxia tolerance exhibited by Drosophila.

Differential Responses of Methionine Sulfoxide Reductases A and B to Anoxia and Oxidative Stress in the Freshwater Turtle Trachemys scripta

Oxidative stress has been acknowledged as a major factor in aging, senescence and neurodegenerative conditions. Mammalian models are susceptible to these stresses following the restoration of oxygen after anoxia; however, some organisms including the freshwater turtle Trachemys scripta can withstand repeated anoxia and reoxygenation without apparent pathology. T. scripta thus provides us with an alternate vertebrate model to investigate physiological mechanisms of neuroprotection. The objective of this study was to investigate the antioxidant methionine sulfoxide reductase system (Msr) in turtle neuronal tissue. We examined brain transcript and protein levels of MsrA and MsrB and examined the potential for the transcription factor FOXO3a to regulate the oxygen-responsive changes in Msr in vitro. We found that Msr mRNA and protein levels are differentially upregulated during anoxia and reoxygenation, and when cells were exposed to chemical oxidative stress. However, while MsrA and MsrB3 levels increased when cell cultures were exposed to chemical oxidative stress, this induction was not enhanced by treatment with epigallocatechin gallate (EGCG), which has previously been shown to enhance FOXO3a levels in the turtle. These results suggest that FOXO3a and Msr protect the cells from oxidative stress through different molecular pathways, and that both the Msr pathway and EGCG may be therapeutic targets to treat diseases related to oxidative damage.

Methionine sulfoxide and the methionine sulfoxide reductase system as modulators of signal transduction pathways: a review

Methionine oxidation and reduction is a common phenomenon occurring in biological systems under both physiological and oxidative-stress conditions. The levels of methionine sulfoxide (MetO) are dependent on the redox status in the cell or organ, and they are usually elevated under oxidative-stress conditions, aging, inflammation, and oxidative-stress related diseases. MetO modification of proteins may alter their function or cause the accumulation of toxic proteins in the cell/organ. Accordingly, the regulation of the level of MetO is mediated through the ubiquitous and evolutionary conserved methionine sulfoxide reductase (Msr) system and its associated redox molecules. Recent published research has provided new evidence for the involvement of free MetO or protein-bound MetO of specific proteins in several signal transduction pathways that are important for cellular function. In the current review, we will focus on the role of MetO in specific signal transduction pathways of various organisms, with relation to their physiological contexts, and discuss the contribution of the Msr system to the regulation of the observed MetO effect.

20-hydroxyecdysone regulates expression of methioninesulfoxide reductases through transcription factor FOXO in the red flour beetle, Tribolium castaneum

The oxidation of methionine (Met) by reactive oxygen species (ROS) causes detrimental effects on the protein functions. Methionine sulfoxide reductase (Msr) is the secondary antioxidant enzyme involved in protein repair, and is divided into two distinct classes, MsrA and MsrB, although the mechanisms underlying the transcriptional regulation of Msrs remain largely unknown. In this study, the full-length cDNAs encoding MsrA and three alternatively spliced isoforms of MsrB were isolated from the red flour beetle, Tribolium castaneum. Exposure of female adults to oxidative, heat and cold stresses induced expressions of both MsrA and MsrB. RNAi-mediated knockdown of MsrA and MsrB resulted in increased sensitivity of T. castaneum to paraquat-induced oxidative stress. Treatment with 20-hydroxyecdysone (20E) increased expression levels of both MsrA and MsrB. Knockdown of transcription factor forkhead box O (FOXO) decreased both MsrA and MsrB mRNA levels and abolished the induction of MsrA and MsrB by paraquat. Luciferase reporter assays revealed that FOXO directly activates the promoters of both MsrA and MsrB. Moreover, paraquat treatment induced expression of two ecdysone biosynthesis genes, Shade and Phantom, 20E upregulated exoression of FOXO, promoted FOXO nuclear translocation，and knockdown of FOXO abolished induction of MsrA and MsrB expression by 20E, suggesting that regulation of MsrA and MsrB by 20E was mediated by FOXO. Overall, these results provide important insights into the transcriptional regulation of insect Msrs.

Methionine sulfoxide reductase (Msr) dysfunction in human brain disease

Extensive research has shown that oxidative stress is strongly associated with aging, senescence and several diseases, including neurodegenerative and psychiatric disorders. Oxidative stress is caused by the overproduction of reactive oxygen species (ROS) that can be counteracted by both enzymatic and nonenzymatic antioxidants. One of these antioxidant mechanisms is the widely studied methionine sulfoxide reductase system (Msr). Methionine is one of the most easily oxidized amino acids and Msr can reverse this oxidation and restore protein function, with MsrA and MsrB reducing different stereoisomers. This article focuses on experimental and genetic research performed on Msr and its link to brain diseases. Studies on several model systems as well as genome-wide association studies are compiled to highlight the role of MSRA in schizophrenia, Alzheimer's disease, and Parkinson's disease. Genetic variation of MSRA may also contribute to the risk of psychosis, personality traits, and metabolic factors.

Metabolic Biomarkers in Aging and Anti-Aging Research

Although human life expectancy has increased significantly over the last two centuries, this has not been paralleled by a similar rise in healthy life expectancy. Thus, an important goal of anti-aging research has been to reduce the impact of age-associated diseases as a way of extending the human healthspan. This review will explore some of the potential avenues which have emerged from this research as the most promising strategies and drug targets for therapeutic interventions to promote healthy aging.

Cytoplasmic and Mitochondrial NADPH-Coupled Redox Systems in the Regulation of Aging

The reduced form of nicotinamide adenine dinucleotide phosphate (NADPH) protects against redox stress by providing reducing equivalents to antioxidants such as glutathione and thioredoxin. NADPH levels decline with aging in several tissues, but whether this is a major driving force for the aging process has not been well established. Global or neural overexpression of several cytoplasmic enzymes that synthesize NADPH have been shown to extend lifespan in model organisms such as Drosophila suggesting a positive relationship between cytoplasmic NADPH levels and longevity. Mitochondrial NADPH plays an important role in the protection against redox stress and cell death and mitochondrial NADPH-utilizing thioredoxin reductase 2 levels correlate with species longevity in cells from rodents and primates. Mitochondrial NADPH shuttles allow for some NADPH flux between the cytoplasm and mitochondria. Since a decline of nicotinamide adenine dinucleotide (NAD⁺) is linked with aging and because NADP⁺ is exclusively synthesized from NAD⁺ by cytoplasmic and mitochondrial NAD⁺ kinases, a decline in the cytoplasmic or mitochondrial NADPH pool may also contribute to the aging process. Therefore pro-longevity therapies should aim to maintain the levels of both NAD⁺ and NADPH in aging tissues.

Temporal pattern of neuronal insulin release during Caenorhabditis elegans aging: Role of redox homeostasis

The insulin‐IGF‐1/DAF‐2 pathway has a central role in the determination of aging and longevity in Caenorhabditis elegans and other organisms. In this paper, we measured neuronal insulin secretion (using INS‐22::Venus) during C. elegans lifespan and monitored how this secretion is modified by redox homeostasis. We showed that INS‐22::Venus secretion fluctuates during the organism lifetime reaching maximum levels in the active reproductive stage. We also demonstrate that long‐lived daf‐2 insulin receptor mutants show remarkable low levels of INS‐22::Venus secretion. In contrast, we found that short‐lived mutant worms that lack the oxidation repair enzyme MSRA‐1 show increased levels of INS‐22::Venus secretion, specifically during the reproductive stage. MSRA‐1 is a target of the insulin‐IGF‐1/DAF‐2 pathway, and the expression of this antioxidant enzyme exclusively in the nervous system rescues the mutant insulin release phenotype and longevity. The msra‐1 mutant phenotype can also be reverted by antioxidant treatment during the active reproductive stage. We showed for the first time that there is a pattern of neuronal insulin release with a noticeable increment during the peak of reproduction. Our results suggest that redox homeostasis can modulate longevity through the regulation of insulin secretion, and that the insulin‐IGF‐1/DAF‐2 pathway could be regulated, at least in part, by a feedback loop. These findings highlight the importance of timing for therapeutic interventions aimed at improving health span.

Metabolic Biomarkers in Nematode C. elegans During Aging

Changes in energy metabolism occur not only in diseases such as cancer but also in the normal development and aging processes of various organisms. These metabolic changes result to lead to imbalances in energy metabolism related to cellular and tissue homeostasis. In the model organism C. elegans, which is used to study aging, an imbalance in age-related energy metabolism exists between mitochondrial oxidative phosphorylation and aerobic glycolysis. Cellular lactate and pyruvate are key intermediates in intracellular energy metabolic pathways and can indicate age-related imbalances in energy metabolism. Thus, the cellular lactate/pyruvate ratio can be monitored as a biomarker during aging. Moreover, recent studies have proposed a candidate novel biomarker for aging and age-related declines in the nematode C. elegans.

The Oxidized Protein Repair Enzymes Methionine Sulfoxide Reductases and Their Roles in Protecting against Oxidative Stress, in Ageing and in Regulating Protein Function

Cysteine and methionine residues are the amino acids most sensitive to oxidation by reactive oxygen species. However, in contrast to other amino acids, certain cysteine and methionine oxidation products can be reduced within proteins by dedicated enzymatic repair systems. Oxidation of cysteine first results in either the formation of a disulfide bridge or a sulfenic acid. Sulfenic acid can be converted to disulfide or sulfenamide or further oxidized to sulfinic acid. Disulfide can be easily reversed by different enzymatic systems such as the thioredoxin/thioredoxin reductase and the glutaredoxin/glutathione/glutathione reductase systems. Methionine side chains can also be oxidized by reactive oxygen species. Methionine oxidation, by the addition of an extra oxygen atom, leads to the generation of methionine sulfoxide. Enzymatically catalyzed reduction of methionine sulfoxide is achieved by either methionine sulfoxide reductase A or methionine sulfoxide reductase B, also referred as to the methionine sulfoxide reductases system. This oxidized protein repair system is further described in this review article in terms of its discovery and biologically relevant characteristics, and its important physiological roles in protecting against oxidative stress, in ageing and in regulating protein function.

Genetic regulation of longevity and age-associated diseases through the methionine sulfoxide reductase system

Methionine sulfoxide reductase enzymes are a protective system against biological oxidative stress in aerobic organisms. Modifications to this antioxidant system have been shown to impact the lifespan of several model system organisms. In humans, methionine oxidation of critical proteins and deficiencies in the methionine sulfoxide reductase system have been linked to age-related diseases, including cancer and neurodegenerative disease. Substrates for methionine sulfoxide reductases have been reviewed multiple times, and are still an active area of discovery. In contrast, less is known about the genetic regulation of methionine sulfoxide reductases. In this review, we discuss studies on the genetic regulation of the methionine sulfoxide reductase system with relevance to longevity and age-related diseases. A better understanding of genetic regulation for methionine sulfoxide reductases may lead to new therapeutic approaches for age-related diseases in the future.

The AAA ATPase Afg1 preserves mitochondrial fidelity and cellular health by maintaining mitochondrial matrix proteostasis

Mitochondrial functions are critical for cellular physiology; therefore, several conserved mechanisms are in place to maintain the functional integrity of mitochondria. However, many of the molecular details and components involved in ensuring mitochondrial fidelity remain obscure. Here, we identify a novel role for the conserved mitochondrial AAA ATPase Afg1 in mediating mitochondrial protein homeostasis during aging and in response to various cellular challenges. Saccharomyces cerevisiae cells lacking functional Afg1 are hypersensitive to oxidative insults, unable to tolerate protein misfolding in the matrix compartment and exhibit progressive mitochondrial failure as they age. Loss of the Afg1 ortholog LACE-1 in Caenorhabditis elegans is associated with reduced lifespan, impeded oxidative stress tolerance, impaired mitochondrial proteostasis in the motor neuron circuitry and altered behavioral plasticity. Our results indicate that Afg1 is a novel protein quality control factor, which plays an important evolutionarily conserved role in mitochondrial surveillance, and cellular and organismal health.

In Vivo Effects of Methionine Sulfoxide Reductase Deficiency in Drosophila melanogaster

The deleterious alteration of protein structure and function due to the oxidation of methionine residues has been studied extensively in age-associated neurodegenerative disorders such as Alzheimer's and Parkinson's Disease. Methionine sulfoxide reductases (MSR) have three well-characterized biological functions. The most commonly studied function is the reduction of oxidized methionine residues back into functional methionine thus, often restoring biological function to proteins. Previous studies have successfully overexpressed and silenced MSR activity in numerous model organisms correlating its activity to longevity and oxidative stress. In the present study, we have characterized in vivo effects of MSR deficiency in Drosophila. Interestingly, we found no significant phenotype in animals lacking either methionine sulfoxide reductase A (MSRA) or methionine sulfoxide reductase B (MSRB). However, Drosophila lacking any known MSR activity exhibited a prolonged larval third instar development and a shortened lifespan. These data suggest an essential role of MSR in key biological processes.

The Functions of the Mammalian Methionine Sulfoxide Reductase System and Related Diseases

This review article describes and discusses the current knowledge on the general role of the methionine sulfoxide reductase (MSR) system and the particular role of MSR type A (MSRA) in mammals. A powerful tool to investigate the contribution of MSRA to molecular processes within a mammalian system/organism is the MSRA knockout. The deficiency of MSRA in this mouse model provides hints and evidence for this enzyme function in health and disease. Accordingly, the potential involvement of MSRA in the processes leading to neurodegenerative diseases, neurological disorders, cystic fibrosis, cancer, and hearing loss will be deliberated and evaluated.

Dysregulation of DAF-16/FOXO3A-mediated stress responses accelerates oxidative DNA damage induced aging

DNA damage is presumed to be one type of stochastic macromolecular damage that contributes to aging, yet little is known about the precise mechanism by which DNA damage drives aging. Here, we attempt to address this gap in knowledge using DNA repair-deficient C. elegans and mice. ERCC1-XPF is a nuclear endonuclease required for genomic stability and loss of ERCC1 in humans and mice accelerates the incidence of age-related pathologies. Like mice, ercc-1 worms are UV sensitive, shorter lived, display premature functional decline and they accumulate spontaneous oxidative DNA lesions (cyclopurines) more rapidly than wild-type worms. We found that ercc-1 worms displayed early activation of DAF-16 relative to wild-type worms, which conferred resistance to multiple stressors and was important for maximal longevity of the mutant worms. However, DAF-16 activity was not maintained over the lifespan of ercc-1 animals and this decline in DAF-16 activation corresponded with a loss of stress resistance, a rise in oxidant levels and increased morbidity, all of which were cep-1/ p53 dependent. A similar early activation of FOXO3A (the mammalian homolog of DAF-16), with increased resistance to oxidative stress, followed by a decline in FOXO3A activity and an increase in oxidant abundance was observed in Ercc1^-/- primary mouse embryonic fibroblasts. Likewise, in vivo, ERCC1-deficient mice had transient activation of FOXO3A in early adulthood as did middle-aged wild-type mice, followed by a late life decline. The healthspan and mean lifespan of ERCC1 deficient mice was rescued by inactivation of p53. These data indicate that activation of DAF-16/FOXO3A is a highly conserved response to genotoxic stress that is important for suppressing consequent oxidative stress. Correspondingly, dysregulation of DAF-16/FOXO3A appears to underpin shortened healthspan and lifespan, rather than the increased DNA damage burden itself.

Sulfoxidation Regulation of Musa acuminata Calmodulin (MaCaM) Influences the Functions of MaCaM-Binding Proteins

Sulfoxidation of methionine in proteins by reactive oxygen species can cause conformational alteration or functional impairment, and can be reversed by methionine sulfoxide reductase (Msr). Currently, only a few potential Msr substrates have been confirmed in higher plants. Here, we investigated Msr-mediated sulfoxidation regulation of calmodulin (CaM) and its underlying biological significance in relation to banana fruit ripening and senescence. Expression of MaCaM1 and MaMsrA7 was up-regulated with increased ripening and senescence. We verified that MaCaM1 interacts with MaMsrA7 in vitro and in vivo, and sulfoxidated MaCaM1 could be partly repaired by MaMsrA7 (MaMsrA7 reduces oxidized residues Met77 and Met110 in MaCaM1). Furthermore, we investigated two known CaM-binding proteins, catalase (MaCAT1) and MaHY5-1. MaHY5-1 acts as a transcriptional repressor of carotenoid biosynthesis-related genes (MaPSY1, MaPSY2 and MaPSY3) in banana fruit. MaCaM1 could enhance the catalytic activity of MaCAT1 and the transcriptional repression activity of MaHY5-1 toward MaPSY2. Mimicked sulfoxidation in MaCaM1 did not affect the physical interactions of the protein with MaHY5-1 and MaCAT1, but reduced the catalytic activity of MaCAT1 and the transcriptional repression activity of MaHY5-1. Our data suggest that sulfoxidation modification in MaCaM1 by MaMsrA7 regulates antioxidant response and gene transcription, thereby being involved in regulation of ripening and senescence of banana fruit.

Defective protein repair under methionine sulfoxide A deletion drives autophagy and ARE-dependent gene transcription

OBJECTIVE

Reduction of oxidized methionines is emerging as a major protein repair pathway. The lack of methionine sulfoxide reductase A (MsrA) exacerbates cardiovascular disease phenotypes driven by increased oxidative stress. However, the role of MsrA on maintaining cellular homeostasis in the absence of excessive oxidative stress is less well understood.

METHODS AND RESULTS

Constitutive genetic deletion of MsrA increased formation of p62-containing protein aggregates, activated autophagy, and decreased a marker of apoptosis in vascular smooth muscle cells (VSMC). The association of Keap1 with p62 was augmented in MsrA-/- VSMC. Keap1 targets the transcription factor Nrf2, which regulates antioxidant genes, for proteasomal degradation. However, in MsrA-/- VSMC, the association of Nrf2 with Keap1 was diminished. Whereas Nrf2 mRNA levels were not decreased in MsrA-/- VSMC, we detected decreased ubiquitination of Nrf2 and a corresponding increase in total Nrf2 protein in the absence of biochemical markers of oxidative stress. Moreover, nuclear-localized Nrf2 was increased under MsrA deficiency, resulting in upregulation of Nrf2-dependent transcriptional activity. Consequently, transcription, protein levels and enzymatic activity of glutamate-cysteine ligase and glutathione reductase were greatly augmented in MsrA-/- VSMC.

SUMMARY

Our findings demonstrate that reversal of methionine oxidation is required for maintenance of cellular homeostasis in the absence of increased oxidative stress. These data provide the first link between autophagy and activation of Nrf2 in the setting of MsrA deletion.

A proteomics approach to identify targets of the ubiquitin-like molecule Urm1 in Drosophila melanogaster

By covalently conjugating to target proteins, ubiquitin-like modifiers (UBLs) act as important regulators of target protein localization and activity, thereby playing a critical role in the orchestration of cellular biology. The most ancient and one of the least studied UBLs is Urm1, a dual-function protein that in parallel to performing similar functions as its prokaryotic ancestors in tRNA modification, also has adopted the capacity to conjugate to cellular proteins analogous to ubiquitin and other UBL modifiers. In order to increase the understanding of Urm1 and its role in multicellular organisms, we have used affinity purification followed by mass spectrometry to identify putative targets of Urm1 conjugation (urmylation) at three developmental stages of the Drosophila melanogaster lifecycle. Altogether we have recovered 79 Urm1-interacting proteins in Drosophila, which include the already established Urm1 binding partners Prx5 and Uba4, together with 77 candidate urmylation targets that are completely novel in the fly. Among these, the majority was exclusively identified during either embryogenesis, larval stages or in adult flies. We further present biochemical evidence that four of these proteins are covalently conjugated by Urm1, whereas the fifth verified Urm1-binding protein appears to interact with Urm1 via non-covalent means. Besides recapitulating the previously established roles of Urm1 in tRNA modification and during oxidative stress, functional clustering of the newly identified Urm1-associated proteins further positions Urm1 in protein networks that control other types of cellular stress, such as immunological threats and DNA damage. In addition, the functional characteristics of several of the candidate targets strongly match the phenotypes displayed by Urm1n123 null animals, including embryonic lethality, reduced fertility and shortened lifespan. In conclusion, this identification of candidate targets of urmylation significantly increases the knowledge of Urm1 and presents an excellent starting point for unravelling the role of Urm1 in the context of a complex living organism.

Dimethyl sulfide protects against oxidative stress and extends lifespan via a methionine sulfoxide reductase A-dependent catalytic mechanism

Methionine (Met) sulfoxide reductase A (MsrA) is a key endogenous antioxidative enzyme with longevity benefits in animals. Only very few approaches have been reported to enhance MsrA function. Recent reports have indicated that the antioxidant capability of MsrA may involve a Met oxidase activity that facilities the reaction of Met with reactive oxygen species (ROS). Herein, we used a homology modeling approach to search the substrates for the oxidase activity of MsrA. We found that dimethyl sulfide (DMS), a main metabolite that produced by marine algae, emerged as a good substrate for MsrA‐catalytic antioxidation. MsrA bounds to DMS and promoted its antioxidant capacity via facilitating the reaction of DMS with ROS through a sulfonium intermediate at residues Cys72, Tyr103, and Glu115, followed by the release of dimethyl sulfoxide (DMSO). DMS reduced the antimycin A‐induced ROS generation in cultured PC12 cells and alleviated oxidative stress. Supplement of DMS exhibited cytoprotection and extended longevity in both Caenorhabditis elegans and Drosophila. MsrA knockdown abolished the cytoprotective effect and the longevity benefits of DMS. Furthermore, we found that the level of physiologic DMS was at the low micromolar range in different tissues of mammals and its level decreased after aging. This study opened a new window to elucidate the biological role of DMS and other low‐molecular sulfides in the cytoprotection and aging.

Feeding recombinant E. coli with GST-mBmKTX fusion protein increases the fecundity and lifespan of Caenorhabditis elegans

Scorpion venom could be a useful treatment for a variety of diseases, such as cancer, epilepsy and analgesia. BmKTX is a polypeptide extracts from scorpion venom (PESV), which have attracted much attention from researchers in recent years. mBmKTX is a mutant polypeptide according to the amino acid sequence of BmKTX. We expressed it with the vector pGEX-4T-1 in Escherichia coli, and Caenorhabditis elegans were used as the animal model and fed with the strains. In this study, the expression of pGEX-mBmKTX was analyzed by SDS-PAGE, and GST-mBmKTX purified from pGEX-mBmKTX as a glutathione S-transferase (GST)-tagged fusion protein is approximately 30kDa. The secondary structure prediction shows that mBmKTX is mainly composed of approximately 13% β-sheet and 86% loop. A food clearance assay and brood size assay indicated that the worms fed pGEX-mBmKTX ate more and had greater fecundity than those fed the empty vector. A lifespan analysis demonstrated that mBmKTX could significantly prolong the lifespan of C. elegans, with an increase of 22.5% compared with the control. Behavioral assays confirmed that mBmKTX had no influence on the locomotion of C. elegans. In addition, microarray analysis and quantitative real-time PCR demonstrated that there are 320 differentially expressed genes, 182 of which are related to reproduction, growth and lifespan. In conclusion, the data suggested that mBmKTX has potential utility for increasing fecundity and animal survival.

Redox regulation of methionine in calmodulin affects the activity levels of senescence-related transcription factors in litchi

Reactive oxygen species (ROS) play a role in aging and senescence in organisms. The oxidation of methionine (Met) residues in proteins to Met sulfoxide by ROS can cause conformational alteration and functional impairments. Met oxidation is reversed by Met sulfoxide reductase (Msr) A and B. Currently, the repair of oxidized proteins by Msr and Msr-mediated physiological functions are not well understood, especially in higher plants. The down-regulated expression of LcMsrA1/B1 may be involved in the senescence of litchi (Litchi chinensis) fruit. We verified that LcCaM1 is a substrate of LcMsrA1 and LcMsrB1 in vitro and in vivo, and oxidized LcCaM1 could be repaired by LcMsrA1 in combination with LcMsrB1. Moreover, LcMsrA1 and LcMsrB1 play important roles in repairing oxidized Met110 and Met125 residues, respectively, in LcCaM1. Furthermore, the Met oxidation in LcCaM1 did not affect its physical interactions with two LcCaM1-binding senescence-related transcription factors LcNAC13 and LcWRKY1, but enhanced their DNA-binding activities. Therefore, we hypothesized that the down-regulated expression of LcMsrA1/B1 results in the accelerated oxidation of LcCaM1, which enhanced the DNA-binding activities of LcNAC13 and LcWRKY1, thereby activating or repressing the expression of senescence-related genes.

Is cancer a severe delayed hypersensitivity reaction and histamine a blueprint?

Longevity and accumulation of multiple context-dependent signaling pathways of long-standing inflammation (antigen-load or oxidative stress) are the results of decreased/altered regulation of immunity and loss of control switch mechanisms that we defined as Yin and Yang of acute inflammation or immune surveillance. Chronic inflammation is initiated by immune disruptors-induced progressive changes in physiology and function of susceptible host tissues that lead to increased immune suppression and multistep disease processes including carcinogenesis. The interrelated multiple hypotheses that are presented for the first time in this article are extension of author's earlier series of 'accidental' discoveries on the role of inflammation in developmental stages of immune dysfunction toward tumorigenesis and angiogenesis. Detailed analyses of data on chronic diseases suggest that nearly all age-associated illnesses, generally categorized as 'mild' (e.g., increased allergies), 'moderate' (e.g., hypertension, colitis, gastritis, pancreatitis, emphysema) or 'severe' (e.g., accelerated neurodegenerative and autoimmune diseases or site-specific cancers and metastasis) are variations of hypersensitivity responses of tissues that are manifested as different diseases in immune-responsive or immune-privileged tissues. Continuous release/presence of low level histamine (subclinical) in circulation could contribute to sustained oxidative stress and induction of 'mild' or 'moderate' or 'severe' (immune tsunami) immune disorders in susceptible tissues. Site-specific cancers are proposed to be 'severe' (irreversible) forms of cumulative delayed hypersensitivity responses that would induce immunological chaos in favor of tissue growth in target tissues. Shared or special features of growth from fetus development into adulthood and aging processes and carcinogenesis are briefly compared with regard to energy requirements of highly complex function of Yin and Yang. Features of Yang (growth-promoting) arm of acute inflammation during fetus and cancer growth will be compared for consuming low energy from glycolysis (Warburg effect). Growth of fetus and cancer cells under hypoxic conditions and impaired mitochondrial energy requirements of tissues including metabolism of essential branched amino acids (e.g., val, leu, isoleu) will be compared for proposing a working model for future systematic research on cancer biology, prevention and therapy. Presentation of a working model provides insightful clues into bioenergetics that are required for fetus growth (absence of external threat and lack of high energy-demands of Yin events and parasite-like survival in host), normal growth in adulthood (balance in Yin and Yang processes) or disease processes and carcinogenesis (loss of balance in Yin-Yang). Future studies require focusing on dynamics and promotion of natural/inherent balance between Yin (tumoricidal) and Yang (tumorigenic) of effective immunity that develop after birth. Lawless growth of cancerous cells and loss of cell contact inhibition could partially be due to impaired mitochondria (mitophagy) that influence metabolism of branched chain amino acids for biosynthesis of structural proteins. The author invites interested scientists with diverse expertise to provide comments, confirm, dispute and question and/or expand and collaborate on many components of the proposed working model with the goal to better understand cancer biology for future designs of cost-effective research and clinical trials and prevention of cancer. Initial events during oxidative stress-induced damages to DNA/RNA repair mechanisms and inappropriate expression of inflammatory mediators are potentially correctable, preventable or druggable, if future studies were to focus on systematic understanding of early altered immune response dynamics toward multistep chronic diseases and carcinogenesis.

Effects of transgenic methionine sulfoxide reductase A (MsrA) expression on lifespan and age-dependent changes in metabolic function in mice

Mechanisms that preserve and maintain the cellular proteome are associated with long life and healthy aging. Oxidative damage is a significant contributor to perturbation of proteostasis and is dealt with by the cell through regulation of antioxidants, protein degradation, and repair of oxidized amino acids. Methionine sulfoxide reductase A (MsrA) repairs oxidation of free- and protein-bound methionine residues through enzymatic reduction and is found in both the cytosol and the mitochondria. Previous studies in Drosophila have shown that increasing expression of MsrA can extend longevity. Here we test the effects of increasing MsrA on longevity and healthy aging in two transgenic mouse models. We show that elevated expression of MsrA targeted specifically to the cytosol reduces the rate of age-related death in female mice when assessed by Gompertz analysis. However, neither cytosolic nor mitochondrial MsrA overexpression extends lifespan when measured by log-rank analysis. In mice with MsrA overexpression targeted to the mitochondria, we see evidence for improved insulin sensitivity in aged female mice. With these and our previous data, we conclude that the increasing MsrA expression in mice has differential effects on aging and healthy aging that are dependent on the target of its subcellular localization.

Oxidation of ion channels in the aging nervous system

Ion channels are integral membrane proteins that allow passive diffusion of ions across membranes. In neurons and in other excitable cells, the harmonious coordination between the numerous types of ion channels shape and propagate electrical signals. Increased accumulation of reactive oxidative species (ROS), and subsequent oxidation of proteins, including ion channels, is a hallmark feature of aging and may contribute to cell failure as a result. In this review we discuss the effects of ROS on three major types of ion channels of the central nervous system, namely the potassium (K(+)), calcium (Ca(2+)) and sodium (Na(+)) channels. We examine two general mechanisms through which ROS affect ion channels: via direct oxidation of specific residues and via indirect interference of pathways that regulate the channels. The overall status of the present studies indicates that the interaction of ion channels with ROS is multimodal and pervasive in the central nervous system and likely constitutes a general mechanism of aging susceptibility.

Identification of activators of methionine sulfoxide reductases A and B

The methionine sulfoxide reductase (Msr) family of enzymes has been shown to protect cells against oxidative damage. The two major Msr enzymes, MsrA and MsrB, can repair oxidative damage to proteins due to reactive oxygen species, by reducing the methionine sulfoxide in proteins back to methionine. A role of MsrA in animal aging was first demonstrated in Drosophila melanogaster where transgenic flies over-expressing recombinant bovine MsrA had a markedly extended life span. Subsequently, MsrA was also shown to be involved in the life span extension in Caenorhabditis elegans. These results supported other studies that indicated up-regulation, or activation, of the normal cellular protective mechanisms that cells use to defend against oxidative damage could be an approach to treat age related diseases and slow the aging process. In this study we have identified, for the first time, compounds structurally related to the natural products fusaricidins that markedly activate recombinant bovine and human MsrA and human MsrB.

Resveratrol prevents cigarette smoke-induced keratinocytes damage

The plant polyphenol, resveratrol (Resv, 3,4,5-trihydroxystilbene), naturally occurring in a number of fruits and other food products, has been extensively studied over the last two decades for its beneficial properties. Recently, its possible topical use in ameliorating skin conditions has also been proposed; however, its role in preventing cigarette smoke (CS)-induced keratinocyte damage has not been investigated yet. Because of its peculiar location, cutaneous tissue is constantly exposed to several environmental stressors, such as CS. Many compounds presented in CS, have been shown to induce, directly or indirectly, cellular oxidative stress (OS) and inflammation via the production of ROS and lipid peroxidation compounds, among which 4HNE has been shown to be one of the most reactive. In this study, we have shown that resveratrol (at a dose of 10 μM) can decrease CS-induced ROS and carbonyl formation in human keratinocytes. In addition, pre-treatment with resveratrol prevented the induction of TRPA1 expression (mRNA and protein levels), a known receptor involved in cellular differentiation and inflammation, which has been recently shown to be activated by 4HNE. Finally, in keratinocytes, resveratrol could increase the expression of MsrA, enzyme involved in cell defence against oxidative protein damage. The present study further confirms the idea that the topical use of resveratrol can provide a good defence against CS-induced skin damage.

The protein oxidation repair enzyme methionine sulfoxide reductase a modulates Aβ aggregation and toxicity in vivo

AIMS

To examine the role of the enzyme methionine sulfoxide reductase A-1 (MSRA-1) in amyloid-β peptide (Aβ)-peptide aggregation and toxicity in vivo, using a Caenorhabditis elegans model of the human amyloidogenic disease inclusion body myositis.

RESULTS

MSRA-1 specifically reduces oxidized methionines in proteins. Therefore, a deletion of the msra-1 gene was introduced into transgenic C. elegans worms that express the Aβ-peptide in muscle cells to prevent the reduction of oxidized methionines in proteins. In a constitutive transgenic Aβ strain that lacks MSRA-1, the number of amyloid aggregates decreases while the number of oligomeric Aβ species increases. These results correlate with enhanced synaptic dysfunction and mislocalization of the nicotinic acetylcholine receptor ACR-16 at the neuromuscular junction (NMJ).

INNOVATION

This approach aims at modulating the oxidation of Aβ in vivo indirectly by dismantling the methionine sulfoxide repair system. The evidence presented here shows that the absence of MSRA-1 influences Aβ aggregation and aggravates locomotor behavior and NMJ dysfunction. The results suggest that therapies which boost the activity of the Msr system could have a beneficial effect in managing amyloidogenic pathologies.

CONCLUSION

The absence of MSRA-1 modulates Aβ-peptide aggregation and increments its deleterious effects in vivo.

Guanine nucleotide exchange factor OSG-1 confers functional aging via dysregulated Rho signaling in Caenorhabditis elegans neurons

Rho signaling regulates a variety of biological processes, but whether it is implicated in aging remains an open question. Here we show that a guanine nucleotide exchange factor of the Dbl family, OSG-1, confers functional aging by dysregulating Rho GTPases activities in C. elegans. Thus, gene reporter analysis revealed widespread OSG-1 expression in muscle and neurons. Loss of OSG-1 gene function was not associated with developmental defects. In contrast, suppression of OSG-1 lessened loss of function (chemotaxis) in ASE sensory neurons subjected to conditions of oxidative stress generated during natural aging, by oxidative challenges, or by genetic mutations. RNAi analysis showed that OSG-1 was specific toward activation of RHO-1 GTPase signaling. RNAi further implicated actin-binding proteins ARX-3 and ARX-5, thus the actin cytoskeleton, as one of the targets of OSG-1/RHO-1 signaling. Taken together these data suggest that OSG-1 is recruited under conditions of oxidative stress, a hallmark of aging, and contributes to promote loss of neuronal function by affecting the actin cytoskeleton via altered RHO-1 activity.

Proteome alteration in oxidative stress-sensitive methionine sulfoxide reductase-silenced HEK293 cells

Methionine sulfoxide reductases (Msr's) are key enzymes proficient in catalyzing the reduction of oxidized methionines. This reductive trait is essential to maintaining cellular redox homeostasis from bacteria to mammals and is also regarded as a potential mechanism to regulate protein activities and signaling pathways, considering the inactivating effects that can be induced by methionine oxidation. In this study, we have generated stable human embryonic kidney HEK293 clones with an altered Msr system by silencing the expression of the main Msr elements-MsrA, MsrB1, or MsrB2. The isolated clones--the single mutants MsrA, MsrB1, and MsrB2 and double mutant MsrA/B1-show a reduced Msr activity and an exacerbated sensitivity toward oxidative stress. A two-dimensional difference in-gel electrophoresis analysis was performed on the Msr-silenced cells grown under basal conditions or submitted to oxidative stress. This proteomic analysis revealed that the disruption of the Msr system mainly affects proteins with redox, cytoskeletal or protein synthesis, and maintenance roles. Interestingly, most of the proteins found altered in the Msr mutants were also identified as potential Msr substrates and have been associated with redox or aging processes in previous studies. This study, through an extensive analysis of Msr-inhibited mutants, offers valuable input on the cellular network of a crucial maintenance system such as methionine sulfoxide reductases.

Methionine sulphoxide reductases revisited: free methionine as a primary target of H₂O₂stress in auxotrophic fission yeast

Amino acid methionine can suffer reversible oxidation to sulphoxide and further irreversible over-oxidation to methionine sulphone. As part of the cellular antioxidant scavenging activities are the methionine sulphoxide reductases (Msrs), with a reported role in methionine sulphoxide reduction, both free and in proteins. Three families of Msrs have been described, but the fission yeast genome only includes one representative for two of these families: MsrA/Mxr1 and MsrB/Mxr2. We have investigated their role in methionine reduction and H2 O2 sensitivity. We show here that MsrA/Mxr1 is able to reduce free oxidized methionine. Cells lacking each one of the genes are not significantly sensitive to different types of oxidative stresses, neither display altered life span. However, only when deletion of msrA/mxr1 is combined with deletion of met6, which confers methionine auxotrophy, the survival upon H2 O2 stress decreases by 100-fold. In fact, cells lacking only Met6, and which therefore require addition of methionine to the growth media, are extremely sensitive to H2 O2 stress. These and other evidences suggest that oxidation of free methionine is a primary target of peroxide toxicity in cells devoid of methionine biosynthetic capacity, and that an important role of Msrs is to recycle this oxidized free amino acid.

The methionine sulfoxide reduction system: selenium utilization and methionine sulfoxide reductase enzymes and their functions

SIGNIFICANCE

Selenium is utilized in the methionine sulfoxide reduction system that occurs in most organisms. Methionine sulfoxide reductases (Msrs), MsrA and MsrB, are the enzymes responsible for this system. Msrs repair oxidatively damaged proteins, protect against oxidative stress, and regulate protein function, and have also been implicated in the aging process. Selenoprotein forms of Msrs containing selenocysteine (Sec) at the catalytic site are found in bacteria, algae, and animals.

RECENT ADVANCES

A selenoprotein MsrB1 knockout mouse has been developed. Significant progress in the biochemistry of Msrs has been made, which includes findings of a novel reducing system for Msrs and of an interesting reason for the use of Sec in the Msr system. The effects of mammalian MsrBs, including selenoprotein MsrB1 on fruit fly aging, have been investigated. Furthermore, it is evident that Msrs are involved in methionine metabolism and regulation of the trans-sulfuration pathway.

CRITICAL ISSUES

This article presents recent progress in the Msr field while focusing on the physiological roles of mammalian Msrs, functions of selenoprotein forms of Msrs, and their biochemistry.

FUTURE DIRECTIONS

A deeper understanding of the roles of Msrs in redox signaling, the aging process, and metabolism will be achieved. The identity of selenoproteome of Msrs will be sought along with characterization of the identified selenoprotein forms. Exploring new cellular targets and new functions of Msrs is also warranted.

The mysterious case of the C. elegans gut granule: death fluorescence, anthranilic acid and the kynurenine pathway

Gut granules are lysosome-like organelles with acidic interiors that are found in large numbers within the intestine of the nematode Caenorhabditis elegans. They are particularly prominent when viewed under ultraviolet light, which causes them to emit intense blue fluorescence. Yet the function of these large and abundant organelles in this heavily-studied model organism remains unclear. One possibility is that they serve as storage organelles, for example of zinc. A new clue to gut granule function is the identification of the blue fluorescent material that they contain as a glycosylated form of anthranilic acid, which is derived from tryptophan by action of the kynurenine pathway. This compound can also serve a surprising role as a natural, endogenous marker of organismal death.

Recharging oxidative protein repair: catalysis by methionine sulfoxide reductases towards their amino acid, protein, and model substrates

The sulfur-containing amino acid methionine (Met) in its free and amino acid residue forms can be readily oxidized to the R and S diastereomers of methionine sulfoxide (MetO). Methionine sulfoxide reductases A (MSRA) and B (MSRB) reduce MetO back to Met in a stereospecific manner, acting on the S and R forms, respectively. A third MSR type, fRMSR, reduces the R form of free MetO. MSRA and MSRB are spread across the three domains of life, whereas fRMSR is restricted to bacteria and unicellular eukaryotes. These enzymes protect against abiotic and biotic stresses and regulate lifespan. MSRs are thiol oxidoreductases containing catalytic redox-active cysteine or selenocysteine residues, which become oxidized by the substrate, requiring regeneration for the next catalytic cycle. These enzymes can be classified according to the number of redox-active cysteines (selenocysteines) and the strategies to regenerate their active forms by thioredoxin and glutaredoxin systems. For each MSR type, we review catalytic parameters for the reduction of free MetO, low molecular weight MetO-containing compounds, and oxidized proteins. Analysis of these data reinforces the concept that MSRAs reduce various types of MetO-containing substrates with similar efficiency, whereas MSRBs are specialized for the reduction of MetO in proteins.

Protein damage, repair and proteolysis

Proteins are continuously affected by various intrinsic and extrinsic factors. Damaged proteins influence several intracellular pathways and result in different disorders and diseases. Aggregation of damaged proteins depends on the balance between their generation and their reversal or elimination by protein repair systems and degradation, respectively. With regard to protein repair, only few repair mechanisms have been evidenced including the reduction of methionine sulfoxide residues by the methionine sulfoxide reductases, the conversion of isoaspartyl residues to L-aspartate by L-isoaspartate methyl transferase and deglycation by phosphorylation of protein-bound fructosamine by fructosamine-3-kinase. Protein degradation is orchestrated by two major proteolytic systems, namely the lysosome and the proteasome. Alteration of the function for both systems has been involved in all aspects of cellular metabolic networks linked to either normal or pathological processes. Given the importance of protein repair and degradation, great effort has recently been made regarding the modulation of these systems in various physiological conditions such as aging, as well as in diseases. Genetic modulation has produced promising results in the area of protein repair enzymes but there are not yet any identified potent inhibitors, and, to our knowledge, only one activating compound has been reported so far. In contrast, different drugs as well as natural compounds that interfere with proteolysis have been identified and/or developed resulting in homeostatic maintenance and/or the delay of disease progression.

Resveratrol preconditioning increases methionine sulfoxide reductases A expression and enhances resistance of human neuroblastoma cells to neurotoxins

Methionine sulfoxide reductases A (MsrA) has been postulated to act as a catalytic antioxidant system involved in the protection of oxidative stress-induced cell injury. Recently, attention has turned to MsrA in coupling with the pathology of Parkinson's disease, which is closely related to neurotoxins that cause dopaminergic neuron degeneration. Here, we firstly provided evidence that pretreatment with a natural polyphenol resveratrol (RSV) up-regulated the expression of MsrA in human neuroblastoma SH-SY5Y cells. It was also observed that the expression and nuclear translocation of forkhead box group O 3a (FOXO3a), a transcription factor that activates the human MsrA promoter, increased after RSV pretreatment. Nicotinamide , an inhibitor of silent information regulator 1 (SIRT1), prevented RSV-induced elevation of FOXO3a and MsrA expression, indicating that the effect of RSV was mediated by a SIRT1-dependent pathway. RSV preconditioning increased methionine sulfoxide(MetO)-reducing activity in SH-SY5Y cells and enhanced their resistance to neurotoxins, including chloramine-T and 1-methyl-4-phenyl-pyridinium. In addition, the enhancement of cell resistance to neurotoxins caused by RSV preconditioning can be largely prevented by MsrA inhibitor dimethyl sulfoxide. Our findings suggest that treatment with polyphenols such as RSV can be used as a potential regulatory strategy for MsrA expression and function.

ROS in aging Caenorhabditis elegans: damage or signaling?

Many insights into the mechanisms and signaling pathways underlying aging have resulted from research on the nematode Caenorhabditis elegans. In this paper, we discuss the recent findings that emerged using this model organism concerning the role of reactive oxygen species (ROS) in the aging process. The accrual of oxidative stress and damage has been the predominant mechanistic explanation for the process of aging for many years, but reviewing the recent studies in C. elegans calls this theory into question. Thus, it becomes more and more evident that ROS are not merely toxic byproducts of the oxidative metabolism. Rather it seems more likely that tightly controlled concentrations of ROS and fluctuations in redox potential are important mediators of signaling processes. We therefore discuss some theories that explain how redox signaling may be involved in aging and provide some examples of ROS functions and signaling in C. elegans metabolism. To understand the role of ROS and the redox status in physiology, stress response, development, and aging, there is a rising need for accurate and reversible in vivo detection. Therefore, we comment on some methods of ROS and redox detection with emphasis on the implementation of genetically encoded biosensors in C. elegans.

Calmodulin-dependent protein kinase II: linking heart failure and arrhythmias

Understanding relationships between heart failure and arrhythmias, important causes of suffering and sudden death, remains an unmet goal for biomedical researchers and physicians. Evidence assembled over the past decade supports a view that activation of the multifunctional Ca(2+) and calmodulin-dependent protein kinase II (CaMKII) favors myocardial dysfunction and cell membrane electrical instability. CaMKII activation follows increases in intracellular Ca(2+) or oxidation, upstream signals with the capacity to transition CaMKII into a Ca(2+) and calmodulin-independent constitutively active enzyme. Constitutively active CaMKII appears poised to participate in disease pathways by catalyzing the phosphorylation of classes of protein targets important for excitation-contraction coupling and cell survival, including ion channels and Ca(2+) homeostatic proteins, and transcription factors that drive hypertrophic and inflammatory gene expression. This rich diversity of downstream targets helps to explain the potential for CaMKII to simultaneously affect mechanical and electrical properties of heart muscle cells. Proof-of-concept studies from a growing number of investigators show that CaMKII inhibition is beneficial for improving myocardial performance and for reducing arrhythmias. We review the molecular physiology of CaMKII and discuss CaMKII actions at key cellular targets and results of animal models of myocardial hypertrophy, dysfunction, and arrhythmias that suggest CaMKII inhibition may benefit myocardial function while reducing arrhythmias.

Methionine sulfoxide reductases preferentially reduce unfolded oxidized proteins and protect cells from oxidative protein unfolding

Reduction of methionine sulfoxide (MetO) residues in proteins is catalyzed by methionine sulfoxide reductases A (MSRA) and B (MSRB), which act in a stereospecific manner. Catalytic properties of these enzymes were previously established mostly using low molecular weight MetO-containing compounds, whereas little is known about the catalysis of MetO reduction in proteins, the physiological substrates of MSRA and MSRB. In this work we exploited an NADPH-dependent thioredoxin system and determined the kinetic parameters of yeast MSRA and MSRB using three different MetO-containing proteins. Both enzymes showed Michaelis-Menten kinetics with the K(m) lower for protein than for small MetO-containing substrates. MSRA reduced both oxidized proteins and low molecular weight MetO-containing compounds with similar catalytic efficiencies, whereas MSRB was specialized for the reduction of MetO in proteins. Using oxidized glutathione S-transferase as a model substrate, we showed that both MSR types were more efficient in reducing MetO in unfolded than in folded proteins and that their activities increased with the unfolding state. Biochemical quantification and identification of MetO reduced in the substrates by mass spectrometry revealed that the increased activity was due to better access to oxidized MetO in unfolded proteins; it also showed that MSRA was intrinsically more active with unfolded proteins regardless of MetO availability. Moreover, MSRs most efficiently protected cells from oxidative stress that was accompanied by protein unfolding. Overall, this study indicates that MSRs serve a critical function in the folding process by repairing oxidatively damaged nascent polypeptides and unfolded proteins.