Methionine sulfoxide reductase A protects neuronal cells against brief hypoxia/reoxygenation

10-(6-Plastoquinonyl) decyltriphenylphosphonium imparts anti-colitogenic protection through recovery of mitochondrial dysfunction in ulcerated murine colon: Implications in ulcerative colitis

AIMS

To elucidate the impact of 10-(6-plastoquinonyl) decyltriphenylphosphonium (SkQ1) as an anti-colitogenic agent for maintenance of colon epithelial tract in ulcerated mice through recovery of mitochondrial dysfunction and mitochondrial stress by virtue of its free radical scavenging properties.

MAIN METHODS

DSS induced ulcerated BALB/c mice were treated with SkQ1 for 14 days @ 30 nmol/kg/body wt./day/mice. Post-treatment, isolated colonic mitochondria were utilized for spectrophotometric and spectrofluorometric biochemical analysis of various mitochondrial functional variables including individual mitochondrial respiratory enzyme complexes. Confocal microscopy was utilized for measuring mitochondrial membrane potential in vivo. ELISA technique was adapted for measuring colonic nitrite and 3-nitrotyrosine (3-NT) content. Finally in vitro cell line study was carried out to substantiate in vivo findings and elucidate the involvement of free radicals in UC using antioxidant/free radical scavenging regimen.

KEY FINDINGS

Treatment with SkQ1 in vivo reduced histopathological severity of colitis, induced recovery of mitochondrial respiratory complex activities and associated functional variables, improved oxidative stress indices and normalized mitochondrial cardiolipin content. Importantly, SkQ1 lowered nitrite concentration and 3-nitrotyrosine formation in vivo. In vitro SkQ1 restored mitochondrial functions wherein the efficacy of SkQ1 proved equal or better compared to SOD and DMSO indicating predominant involvement of O2- and OH in UC. However, NO and ONOO- also seemed to play a secondary role as MEG and L-NAME provided lesser protection as compared to SOD and DMSO.

SIGNIFICANCE

SkQ1 can be considered as a potent anti-colitogenic agent by virtue of its free radical scavenging properties in treating UC.

Integrated analysis of the association between methionine cycle and risk of moyamoya disease

OBJECTIVE

The role of methionine (Met) cycle in the pathogenesis and progression of cardiovascular and cerebrovascular diseases has been established, but its association with moyamoya disease (MMD) has rarely been studied. This study aimed to analyze the levels of Met cycle-related metabolites and constructed a risk model to explore its association with the risk of MMD.

METHODS

In this prospective study, a total of 302 adult MMD patients and 88 age-matched healthy individuals were consecutively recruited. The serum levels of Met cycle-related metabolites were quantified by liquid chromatography-mass spectrometry (LC-MS). Participants were randomly divided into training set and testing set at a ratio of 1:1. The training set was used to construct the risk score model by LASSO regression. The association between Met cycle-related risk score and the risk of MMD was analyzed using logistic regression and assessed by ROC curves. The testing set was used for validation.

RESULTS

The levels of methionine sulfoxide and homocysteine were significantly increased, while the levels of betaine and choline were significantly decreased in MMD and its subtypes compared to healthy controls (p < 0.05 for all). The training set was used to construct the risk model and the risk score of each participant has been calculated. After adjusting for potential confounders, the risk score was independently associated with the risk of MMD and its subtypes (p < 0.05 for all). We then divided the participants into low-risk and high-risk groups, the high-risk score was significantly associated with the risk of MMD and its subtypes (p < 0.05 for all). The risk scores were further assessed as tertiles, the highest tertile was significantly associated with a higher risk of MMD and its subtypes compared to the lowest (p < 0.05 for all). The results were validated in the testing set.

CONCLUSION

This study has constructed and validated a risk model based on Met cycle-related metabolites, which was independently associated with the risk of MMD and its subtypes. The findings provided a new perspective on the risk evaluation and prevention of MMD.

Short-term hypoxia triggers ROS and SAFB mediated nuclear matrix and mRNA splicing remodeling

The cellular response to hypoxia, in addition to HIF-dependent transcriptional reprogramming, also involves less characterized transcription-independent processes, such as alternative splicing of the VEGFA transcript leading to the production of the proangiogenic VEGF form. We now show that this event depends on reorganization of the splicing machinery, triggered after short-term hypoxia by ROS production and intranuclear redistribution of the nucleoskeletal proteins SAFB1/2. Exposure to low oxygen causes fast dissociation of SAFB1/2 from the nuclear matrix, which is reversible, inhibited by antioxidant treatment, and also observed under normoxia when the mitochondrial electron transport chain is blocked. This is accompanied by altered interactions between SAFB1/2 and the splicing machinery, translocation of kinase SRPK1 to the cytoplasm, and dephosphorylation of RS-splicing factors. Depletion of SAFB1/2 under normoxia phenocopies the hypoxic and ROS-mediated switch in VEGF mRNA splicing. These data suggest that ROS-dependent remodeling of the nuclear architecture can promote production of splicing variants that facilitate adaptation to hypoxia.

Methionine sulfoxide reductase B5 plays a key role in preserving seed vigor and longevity in rice (Oryza sativa)

Oxidation of methionine leads to the formation of methionine S-sulfoxide and methionine R-sulfoxide, which can be reverted by two types of methionine sulfoxide reductase (MSR): MSRA and MSRB. Though the role of MSR enzymes has been elucidated in various physiological processes, the regulation and role of MSR in seeds remains poorly understood. In this study, through molecular, biochemical, and genetic studies using seed-specific overexpression and RNAi lines of OsMSRB5 in Oryza sativa, we demonstrate the role of OsMSRB5 in maintaining seed vigor and longevity. We show that an age-induced reduction in the vigor and viability of seeds is correlated with reduced MSR activity and increased methionine sulfoxide (MetSO) formation. OsMSRB5 expression increases during seed maturation and is predominantly localized to the embryo. Further analyses on transgenic lines reveal the role of OsMSRB5 in modulating reactive oxygen species (ROS) homeostasis to preserve seed vigor and longevity. We show that ascorbate peroxidase and PROTEIN l-ISOASPARTYL METHYLTRANSFERASE undergo MetSO modification in seeds that affects their functional competence. OsMSRB5 physically interacts with these proteins and reverts this modification to facilitate their functions and preserve seed vigor and longevity. Our results thus illustrate the role of OsMSRB5 in preserving seed vigor and longevity by modulating ROS homeostasis in seeds.

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.

L-Methionine Protects against Oxidative Stress and Mitochondrial Dysfunction in an In Vitro Model of Parkinson's Disease

Methionine is an aliphatic, sulfur-containing, essential amino acid that has been demonstrated to have crucial roles in metabolism, innate immunity, and activation of endogenous antioxidant enzymes, including methionine sulfoxide reductase A/B and the biosynthesis of glutathione to counteract oxidative stress. Still, methionine restriction avoids altered methionine/transmethylation metabolism, thus reducing DNA damage and possibly avoiding neurodegenerative processes. In this study, we wanted to study the preventive effects of methionine in counteracting 6-hydroxydopamine (6-OHDA)-induced injury. In particular, we analyzed the protective effects of the amino acid L-methionine in an in vitro model of Parkinson's disease and dissected the underlying mechanisms compared to the known antioxidant taurine to gain insights into the potential of methionine treatment in slowing the progression of the disease by maintaining mitochondrial functionality. In addition, to ascribe the effects of methionine on mitochondria and oxidative stress, methionine sulfoxide was used in place of methionine. The data obtained suggested that an L-methionine-enriched diet could be beneficial during aging to protect neurons from oxidative imbalance and mitochondrial dysfunction, thus preventing the progression of neurodegenerative processes.

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.

Substance P failed to reverse dextran sulfate sodium-induced murine colitis mediated by mitochondrial dysfunction: implications in ulcerative colitis

As controversy exists about the efficacy of substance P (SP) in treating ulcerative colitis (UC) with no previous study highlighting the impact of SP on mitochondrial dysfunction in this diseased condition, it became logical to perform the present study. C57BL/6 J mice were administered with DSS @ 3.5%/gm body weight for 3 cycles of 5 days each followed by i.v. dose of SP @ 5nmole per kg for consecutive 7 days. Histopathological features were noticed in the affected colon along with colonic mitochondrial dysfunction, alterations in mitochondrial stress variables and enhanced colonic cell death. Interestingly, SP failed to reverse colitic features and proved ineffective in inhibiting mitochondrial dysfunction. Unexpectedly SP alone seemed to impart detrimental effects on some of the mitochondrial functions, enhanced lipid peroxidation and increased staining intensities for caspases 3 and 9 in the normal colon. To substantiate in vivo findings and to assess free radical scavenging property of SP, Caco-2 cells were exposed to DSS with or without SP in the presence and absence of specific free radical scavengers and antioxidants. Interestingly, in vitro treatment with SP failed to restore mitochondrial functions and its efficacy proved below par compared to SOD and DMSO indicating involvement of O2 •- and •OH in the progression of UC. Besides, catalase, L-NAME and MEG proved ineffective indicating non-involvement of H2O2, NO and ONOO- in UC. Thus, SP may not be a potent anti-colitogenic agent targeting colonic mitochondrial dysfunction for maintenance of colon epithelial tract as it lacks free radical scavenging property.

The Antioxidant Role of One-Carbon Metabolism on Stroke

One-carbon (1C) metabolism is a metabolic network that is centered on folate, a B vitamin; it integrates nutritional signals with biosynthesis, redox homeostasis, and epigenetics. This metabolic pathway also reduces levels of homocysteine, a non-protein amino acid. High levels of homocysteine are linked to increased risk of hypoxic events, such as stroke. Several preclinical studies have suggested that 1C metabolism can impact stroke outcome, but the clinical data are unclear. The objective of this paper was to review preclinical and clinical research to determine whether 1C metabolism has an antioxidant role on stroke. To accomplish the objective, we searched for publications using the following medical subject headings (MeSH) keywords: antioxidants, hypoxia, stroke, homocysteine, one-carbon metabolism, folate, methionine, and dietary supplementation of one-carbon metabolism. Both pre-clinical and clinical studies were retrieved and reviewed. Our review of the literature suggests that deficiencies in 1C play an important role in the onset and outcome of stroke. Dietary supplementation of 1C provides beneficial effects on stroke outcome. For stroke-affected patients or individuals at high risk for stroke, the data suggest that nutritional modifications in addition to other therapies could be incorporated into a treatment plan.

MsrA Suppresses Inflammatory Activation of Microglia and Oxidative Stress to Prevent Demyelination via Inhibition of the NOX2-MAPKs/NF-κB Signaling Pathway

Introduction

Demyelination causes neurological deficits involving visual, motor, sensory symptoms. Deregulation of several enzymes has been identified in demyelination, which holds potential for the development of treatment strategies for demyelination. However, the specific effect of methionine sulfoxide reductase A (MsrA) on demyelination remains unclear. Hence, this study aims to explore the effect of MsrA on oxidative stress and inflammatory response of microglia in demyelination.

Methods

Initially, we established a mouse model with demyelination induced by cuprizone and a cell model provoked by lipopolysaccharide (LPS). The expression of MsrA in wild-type (WT) and MsrA-knockout (MsrA^-/-) mice were determined by RT-qPCR and Western blot analysis. In order to further explore the function of MsrA on inflammatory response, and oxidative stress in demyelination, we detected the expression of microglia marker Iba1, inflammatory factors TNF-α and IL-1β and intracellular reactive oxygen species (ROS), superoxide dismutase (SOD) activity, as well as expression of the NOX2-MAPKs/NF-κB signaling pathway-related genes in MsrA^-/- mice and LPS-induced microglia following different treatments.

Results

MsrA expression was downregulated in MsrA^-/- mice. MsrA silencing was shown to produce severely injured motor coordination, increased expressions of Iba1, TNF-α, IL-1β, ROS and NOX2, and extent of ERK, p38, IκBα, and p65 phosphorylation, but reduced SOD activity. Conjointly, our study suggests that Tat-MsrA fusion protein can prevent the cellular inflammatory response and subsequent demyelination through negative regulation of the NOX2-MAPKs/NF-κB signaling pathway.

Conclusion

Our data provide a profound insight on the role of endogenous antioxidative defense systems such as MsrA in controlling microglial function.

Genetic Signatures of Acute Asthma Exacerbation Related With Ineffective Response to Corticosteroid

Purpose

Acute exacerbation (AE) is an important domain of asthma management and may be related with ineffective response to corticosteroid. This study aimed to find mechanisms of AE using genome-wide gene expression profiles of blood cells from asthmatics and its perturbation by in vitro dexamethasone (Dex)-treatment.

Methods

We utilized lymphoblastoid B cells from 107 childhood asthmatics and peripheral blood mononuclear cells from 29 adult asthmatics who were treated with inhaled corticosteroids. We searched for a preserved co-expression gene module significantly associated with the AE rate in both cohorts and measured expression changes of genes belong to this module after Dex-treatment.

Results

We identified a preserved module composed of 77 genes. Among them, expressions of 2 genes (EIF2AK2 and NOL11) decreased significantly after Dex-treatment in both cohorts. EIF2AK2, a key gene acting antiviral defense mechanism, showed significantly higher expressions in asthmatics with AE. The protein repair pathway was enriched significantly in 64 genes which belong to the preserved module but showed no expression differences after Dex-treatment in both cohorts. Among them, MSRA and MSRB2 may play key roles by controlling oxidative stress.

Conclusions

Many genes belong to the AE rate-associated and preserved module identified in blood cells from childhood and adults asthmatics showed no expression changes after in vitro Dex-treatment. These findings suggest that we may need alternative treatment options to corticosteroids to prevent AE. EIF2AK2, MSRA and MSRB2 expressions on blood cells may help us select AE-susceptible asthmatics and adjust treatments to prevent AE.

Loss of methionine sulfoxide reductases increases resistance to oxidative stress

Oxidation of methionine residues to methionine sulfoxide scavenges reactive species, thus protecting against oxidative stress. Reduction of the sulfoxide back to methionine by methionine sulfoxide reductases creates a cycle with catalytic efficiency. Protection by the methionine sulfoxide reductases is well documented in cultured cells, from microorganisms to mammals. However, knocking out one or two of the 4 mammalian reductases had little effect in mice that were not stressed. We hypothesized that the minimal effect is due to redundancy provided by the 4 reductases. We tested the hypothesis by creating a transgenic mouse line lacking all 4 reductases and predicted that this mouse would be exceptionally sensitive to oxidative stress. The mutant mice were phenotypically normal at birth, exhibited normal post-natal growth, and were fertile. Surprisingly, rather than being more sensitive to oxidative stress, they were more resistant to both cardiac ischemia-reperfusion injury and to parenteral paraquat, a redox-cycling agent. Resistance was not a result of hormetic induction of the antioxidant transcription factor Nrf2 nor activation of Akt. The mechanism of protection may be novel.

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.

Characterization of the cellular effects and mechanism of arsenic trioxide-induced hepatotoxicity in broiler chickens

To characterize the cellular effects and mechanism of arsenic trioxide (ATO)-induced hepatotoxicity in broiler chickens, increasing concentrations of ATO (0, 0.6, 1.2, 2.4, and 4.8 μM) were added to chicken hepatocyte cultures in vitro. The changes in hepatocyte morphology, oxidative stress and apoptosis were evaluated using fluorescence microscopy and flow cytometry. The effects of ATO on mRNA or protein expression of antioxidant enzymes, especially methionine sulfoxide reductase (Msr), were analyzed using qRT-PCR and western blotting assays. Increased apoptosis were concomitant with increased reactive oxygen species (ROS) accumulation and upregulation of antioxidant enzymes such as catalase (CAT) and superoxide dismutase (SOD) with increasing ATO concentrations. Moreover, G₁ phase arrest and dysregulation of the balance between antiapoptotic versus proapoptotic factors were noted. Furthermore, upregulation of HO-1, SOD-1, and TRX in the ATO groups were consistent with ATO-induced oxidative damage. High Msr, SOD-1, TRX, Bak1, Bax, and p53 protein levels in the ATO groups indicate that these proteins may have accumulated to counter ATO-induced oxidative stress. ROS scavenger N-acetyl-l-cysteine (NAC) could reverse ATO-induced oxidative damage and restore hepatocyte viability, even with compromised Msr function. Our findings suggest that Msr can protect broiler hepatocytes against ATO-induced oxidative stress. Furthermore, NAC-mediated reversal of oxidative damage may represent a strategy to mitigate potential economic losses associated with arsenic poisoning in the poultry industry.

Mitochondrial MsrB2 serves as a switch and transducer for mitophagy

Mitophagy can selectively remove damaged toxic mitochondria, protecting a cell from apoptosis. The molecular spatial-temporal mechanisms governing autophagosomal selection of reactive oxygen species (ROS)-damaged mitochondria, particularly in a platelet (no genomic DNA for transcriptional regulation), remain unclear. We now report that the mitochondrial matrix protein MsrB2 plays an important role in switching on mitophagy by reducing Parkin methionine oxidation (MetO), and transducing mitophagy through ubiquitination by Parkin and interacting with LC3. This biochemical signaling only occurs at damaged mitochondria where MsrB2 is released from the mitochondrial matrix. MsrB2 platelet-specific knockout and in vivo peptide inhibition of the MsrB2/LC3 interaction lead to reduced mitophagy and increased platelet apoptosis. Pathophysiological importance is highlighted in human subjects, where increased MsrB2 expression in diabetes mellitus leads to increased platelet mitophagy, and in platelets from Parkinson's disease patients, where reduced MsrB2 expression is associated with reduced mitophagy. Moreover, Parkin mutations at Met192 are associated with Parkinson's disease, highlighting the structural sensitivity at the Met192 position. Release of the enzyme MsrB2 from damaged mitochondria, initiating autophagosome formation, represents a novel regulatory mechanism for oxidative stress-induced mitophagy.

The presence of elevated circulating trimethylamine N-oxide exaggerates postoperative cognitive dysfunction in aged rats

Surgical trauma can cause brain oxidative stress and neuroinflammation, leading to postoperative cognitive dysfunction (POCD), especially in the elderly. Additionally, the pre-existing risk factors may enhance POCD. Gut microbiota-derived metabolite trimethylamine N-oxide (TMAO) has recently been shown to contribute to the pathogenesis of many diseases by increasing oxidative stress and inflammation in the peripheral tissues. Here we examined whether the presence of elevated circulating TMAO would influence surgery-induced cognitive decline. Aged rats were treated with vehicle or TMAO for 3 weeks. After two weeks of treatment, these rats underwent sham-operation or laparotomy. One week after surgery, rats underwent laparotomy exhibited hippocampal-dependent cognitive dysfunction as evidenced by reduced contextual freezing time, which was associated with elevated plasma proinflammatory cytokine levels, increased microglia-mediated neuroinflammation and reactive oxygen species (ROS) production in the hippocampus. Treatment with TMAO, which elevated plasma TMAO before and 1 week after surgery, further increased microglia-mediated neuroinflammation and ROS production in the hippocampus, resulting in exaggerated cognitive dysfunction in laparotomy group but not in sham-operation group. Moreover, TMAO treatment decreased expression of antioxidant enzyme methionine sulfoxide reductase (Msr) A in both groups. The results suggest that the presence of elevated circulating TMAO downregulates antioxidant enzyme MsrA in the hippocampus, which may increase the susceptibility to surgery-induced oxidative stress, contributing to exaggerations of neuroinflammation and cognitive decline in aged rats following surgery. Interventions to reduce circulating TMAO in the perioperative period may be a novel strategy to prevent the exaggeration of cognitive decline in elderly patients with high circulating TMAO.

Drosophila methionine sulfoxide reductase A (MSRA) lacks methionine oxidase activity

Mouse, human, and E. coli methionine sulfoxide reductase A (MSRA) stereospecifically catalyze both the reduction of S-methionine sulfoxide to methionine and the oxidation of methionine to S-methionine sulfoxide. Calmodulin has 9 methionine residues, but only Met77 is oxidized by MSRA, and this is completely reversed when MSRA operates in the reductase direction. Given the powerful genetic tools available for Drosophila, we selected this model organism to identify the in vivo calmodulin targets regulated by redox modulation of Met77. The active site sequences of mammalian and Drosophila MSRA are identical, and both contain two cysteine residues in their carboxy terminal domains. We produced recombinant Drosophila MSRA and studied its biochemical and biophysical properties. The enzyme is active as a methionine sulfoxide reductase, but it cannot function as a methionine oxidase. The first step in the mammalian oxidase reaction is formation of a sulfenic acid at the active site, and the second step is the reaction of the sulfenic acid with a carboxy terminal domain cysteine to form a disulfide bond. The third step regenerates the active site through a disulfide exchange reaction with a second carboxy terminal domain cysteine. Drosophila MSRA carries out the first and second steps, but it cannot regenerate the active site in the third step. Thus, unlike the E. coli and mammalian enzymes, Drosophila MSRA catalyzes only the reduction of methionine sulfoxide and not the oxidation of methionine.

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.

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.

Myristoylated methionine sulfoxide reductase A is a late endosomal protein

Methionine residues in proteins provide antioxidant defense by reacting with oxidizing species, which oxidize methionine to methionine sulfoxide. Reduction of the sulfoxide back to methionine is catalyzed by methionine sulfoxide reductases, essential for protection against oxidative stress. The nonmyristoylated form of methionine sulfoxide reductase A (MSRA) is present in mitochondria, whereas the myristoylated form has been previously reported to be cytosolic. Despite the importance of MSRA in antioxidant defense, its in vivo binding partners and substrates have not been identified. Starting with a protein array, and followed by immunoprecipitation experiments, colocalization studies, and subcellular fractionation, we identified the late endosomal protein, StAR-related lipid transfer domain-containing 3 (STARD3), as a binding partner of myristoylated MSRA, but not of nonmyristoylated MSRA. STARD3 is known to have both membrane-binding and cytosolic domains that are important in STARD3-mediated transport of cholesterol from the endoplasmic reticulum to the endosome. We found that the STARD3 cytosolic domain localizes MSRA to the late endosome. We propose that the previous conclusion that myristoylated MSRA is strictly a cytosolic protein is artifactual and likely due to vigorous overexpression of MSRA. We conclude that myristoylated MSRA is a late endosomal protein that may play a role in lipid metabolism or may protect endosomal proteins from oxidative damage.

Methionine in Proteins: It's Not Just for Protein Initiation Anymore

Methionine in proteins is often thought to be a generic hydrophobic residue, functionally replaceable with another hydrophobic residue such as valine or leucine. This is not the case, and the reason is that methionine contains sulfur that confers special properties on methionine. The sulfur can be oxidized, converting methionine to methionine sulfoxide, and ubiquitous methionine sulfoxide reductases can reduce the sulfoxide back to methionine. This redox cycle enables methionine residues to provide a catalytically efficient antioxidant defense by reacting with oxidizing species. The cycle also constitutes a reversible post-translational covalent modification analogous to phosphorylation. As with phosphorylation, enzymatically-mediated oxidation and reduction of specific methionine residues functions as a regulatory process in the cell. Methionine residues also form bonds with aromatic residues that contribute significantly to protein stability. Given these important functions, alteration of the methionine-methionine sulfoxide balance in proteins has been correlated with disease processes, including cardiovascular and neurodegenerative diseases. Methionine isn't just for protein initiation.

Oxidation Resistance of the Sulfur Amino Acids: Methionine and Cysteine

Sulfur amino acids are a kind of amino acids which contain sulfhydryl, and they play a crucial role in protein structure, metabolism, immunity, and oxidation. Our review demonstrates the oxidation resistance effect of methionine and cysteine, two of the most representative sulfur amino acids, and their metabolites. Methionine and cysteine are extremely sensitive to almost all forms of reactive oxygen species, which makes them antioxidative. Moreover, methionine and cysteine are precursors of S-adenosylmethionine, hydrogen sulfide, taurine, and glutathione. These products are reported to alleviate oxidant stress induced by various oxidants and protect the tissue from the damage. However, the deficiency and excess of methionine and cysteine in diet affect the normal growth of animals; thereby a new study about defining adequate levels of methionine and cysteine intake is important.

Methionine Sulfoxide Reductase A Deficiency Exacerbates Cisplatin-Induced Nephrotoxicity via Increased Mitochondrial Damage and Renal Cell Death

AIMS

Methionine sulfoxide reductase A (MsrA), which is abundantly localized in the mitochondria, reduces methionine-S-sulfoxide, scavenging reactive oxygen species (ROS). Cisplatin, an anticancer drug, accumulates at high levels in the mitochondria of renal cells, causing mitochondrial impairment that ultimately leads to nephrotoxicity. Here, we investigated the role of MsrA in cisplatin-induced mitochondrial damage and kidney cell death using MsrA gene-deleted (MsrA^-/-) mice.

RESULTS

Cisplatin injection resulted in increases of ROS production, methionine oxidation, and oxidative damage in the kidneys. This oxidative stress was greater in MsrA^-/- mouse kidneys than in wild-type (MsrA^+/+) mouse kidneys. MsrA gene deletion exacerbated cisplatin-induced reductions in the expression and activity of MsrA and MsrBs, and the expression of thioredoxin 1, glutathione peroxidase 1 and 4, mitochondrial superoxide dismutase, cystathionine-β-synthase, and cystathionine-γ-lyase. Cisplatin induced swelling, cristae loss, and fragmentation of mitochondria with increased lipid peroxidation, more so in MsrA^-/- than in MsrA^+/+ kidneys. The ratio of mitochondrial fission regulator (Fis1) to fusion regulator (Opa1) was higher in MsrA^-/- than MsrA^+/+ mice. MsrA deletion exacerbated cisplatin-induced increases in Bax to Bcl-2 ratio, cleaved caspase-3 level, and apoptosis, whereas MsrA overexpression attenuated cisplatin-induced oxidative stress and apoptosis.

INNOVATION

MsrA gene deletion in mice exacerbates cisplatin-induced renal injury through increases of mitochondrial susceptibility, whereas MsrA overexpression protects cells against cisplatin.

CONCLUSION

This study demonstrates that MsrA protects kidney cells against cisplatin-induced methionine oxidation, oxidative stress, mitochondrial damage, and apoptosis, suggesting that MsrA could be a useful target protein for the treatment of cisplatin-induced nephrotoxicity. Antioxid. Redox Signal. 27, 727-741.

Methionine 35 sulphoxide reduces toxicity of Aβ in red blood cell

BACKGROUND

The oxidation of methionine residue in position 35 of Ab to sulphoxide (Ab-sulphoxide) has the ability to deeply modify wild-type Ab 1-42 (Ab) neurotoxic action. Our previous studies suggest that in nucleated cells, lower toxicity of Ab-sulphoxide might result not from structural alteration, but from elevation of methionine sulphoxide reductase A (MsrA) activity and mRNA levels.

DESIGN

On this basis, we hypothesised that red blood cell (RBC), a cell devoid almost completely of MsrA activity, shares with nucleated cells an antioxidant system induced by methionine 35 sulphoxide, responsible for the lower toxicity of Ab-sulphoxide in RBC. (Results) Supporting this hypothesis, we found that the low toxicity of Ab-sulphoxide in RBC correlated with pentose phosphate pathway (PPP) flux increase, and this event was associated with a low level of methionine oxidation in total proteins. None of these effects were observed when cells were exposed to Ab native.

DISCUSSION

These results outline the importance of the redox state of methionine 35 in the modulation of Ab-mediated events and suggest an important protective role for PPP in RBC of patients affected by Alzheimer's disease.

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.

A specific fluorescent probe reveals compromised activity of methionine sulfoxide reductases in Parkinson's disease

A general strategy for designing probes of methionine sulfoxide reductases was reported and a first turn on probe was disclosed.

Oxidation of methionine residues to methionine sulfoxide (MetSO) may cause changes in protein structure and function, and may eventually lead to cell damage. Methionine sulfoxide reductases (Msrs) are the only known enzymes that catalyze the reduction of MetSO back to methionine by taking reducing equivalents from the thioredoxin system, and thus protect cells from oxidative damage. Nonetheless, a lack of convenient assays for the enzymes hampers the exploration of their functions. We report the discovery of Msr-blue, the first turn-on fluorescent probe for Msr with a >100-fold fluorescence increment from screening a rationally-designed small library. Intensive studies demonstrated the specific reduction of Msr-blue by the enzymes. Msr-blue is ready to determine Msr activity in biological samples and live cells. Importantly, we disclosed a decline of Msr activity in a Parkinson's model, thus providing a mechanistic linkage between the loss of function of Msrs and the development of neurodegeneration. The strategy for the discovery of Msr-blue would also provide guidance for developing novel probes with longer excitation/emission wavelengths and specific probes for Msr isoforms.

Neuroprotective Efficacy of Mitochondrial Antioxidant MitoQ in Suppressing Peroxynitrite-Mediated Mitochondrial Dysfunction Inflicted by Lead Toxicity in the Rat Brain

Lead (Pb) is one of the most pollutant metals that accumulate in the brain mitochondria disrupting mitochondrial structure and function. Though oxidative stress mediated by reactive oxygen species remains the most accepted mechanism of Pb neurotoxicity, some reports suggest the involvement of nitric oxide (^•NO) and reactive nitrogen species in Pb-induced neurotoxicity. But the impact of Pb neurotoxicity on mitochondrial respiratory enzyme complexes remains unknown with no relevant report highlighting the involvement of peroxynitrite (ONOO^-) in it. Herein, we investigated these effects in in vivo rat model by oral application of MitoQ, a known mitochondria-specific antioxidant with ONOO^- scavenging activity. Interestingly, MitoQ efficiently alleviated ONOO^--mediated mitochondrial complexes II, III and IV inhibition, increased mitochondrial ATP production and restored mitochondrial membrane potential. MitoQ lowered enhanced caspases 3 and 9 activities upon Pb exposure and also suppressed synaptosomal lipid peroxidation and protein oxidation accompanied by diminution of nitrite production and protein-bound 3-nitrotyrosine. To ascertain our in vivo findings on mitochondrial dysfunction, we carried out similar experiments in the presence of different antioxidants and free radical scavengers in the in vitro SHSY5Y cell line model. MitoQ provided better protection compared to mercaptoethylguanidine, N-nitro-L-arginine methyl ester and superoxide dismutase suggesting the predominant involvement of ONOO^- compared to ^•NO and O₂^•-. However, dimethylsulphoxide and catalase failed to provide protection signifying the noninvolvement of ^•OH and H₂O₂ in the process. The better protection provided by MitoQ in SHSY5Y cells can be attributed to the fact that MitoQ targets mitochondria whereas mercaptoethylguanidine, N-nitro-L-arginine methyl ester and superoxide dismutase are known to target mainly cytoplasm and not mitochondria. Taken together the results from the present study clearly brings out the potential of MitoQ against ONOO^--induced toxicity upon Pb exposure indicating its therapeutic potential in metal toxicity.

The discovery of methionine sulfoxide reductase enzymes: An historical account and future perspectives

L-Methionine (L-Met) is the only sulphur-containing proteinogenic amino acid together with cysteine. Its importance is highlighted by it being the initiator amino acid for protein synthesis in all known living organisms. L-Met, free or inserted into proteins, is sensitive to oxidation of its sulfide moiety, with formation of L-Met sulfoxide. The sulfoxide could not be inserted into proteins, and the oxidation of L-Met in proteins often leads to the loss of biological activity of the affected molecule. Key discoveries revealed the existence, in rats, of a metabolic pathway for the reduction of free L-Met sulfoxide and, later, in Escherichia coli, of the enzymatic reduction of L-Met sulfoxide inserted in proteins. Upon oxidation, the sulphur atom becomes a new stereogenic center, and two stable diastereoisomers of L-Met sulfoxide exist. A fundamental discovery revealed the existence of two unrelated families of enzymes, MsrA and MsrB, whose members display opposite stereospecificity of reduction for the two sulfoxides. The importance of Msrs is additionally emphasized by the discovery that one of the only 25 selenoproteins expressed in humans is a Msr. The milestones on the road that led to the discovery and characterization of this group of antioxidant enzymes are recounted in this review.

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.

Methionine sulfoxide reductase A negatively controls microglia-mediated neuroinflammation via inhibiting ROS/MAPKs/NF-κB signaling pathways through a catalytic antioxidant function

AIMS

Oxidative burst is one of the earliest biochemical events in the inflammatory activation of microglia. Here, we investigated the potential role of methionine sulfoxide reductase A (MsrA), a key antioxidant enzyme, in the control of microglia-mediated neuroinflammation.

RESULTS

MsrA was detected in rat microglia and its expression was upregulated on microglial activation. Silencing of MsrA exacerbated lipopolysaccharide (LPS)-induced activation of microglia and the production of inflammatory markers, indicating that MsrA may function as an endogenous protective mechanism for limiting uncontrolled neuroinflammation. Application of exogenous MsrA by transducing Tat-rMsrA fusion protein into microglia attenuated LPS-induced neuroinflammatory events, which was indicated by an increased Iba1 (a specific microglial marker) expression and the secretion of pro-inflammatory cytokines, and this attenuation was accompanied by inhibiting multiple signaling pathways such as p38 and ERK mitogen-activated protein kinases (MAPKs) and nuclear factor kappaB (NF-κB). These effects were due to MsrA-mediated reactive oxygen species (ROS) elimination, which may be derived from a catalytic effect of MsrA on the reaction of methionine with ROS. Furthermore, the transduction of Tat-rMsrA fusion protein suppressed the activation of microglia and the expression of pro-inflammatory factors in a rat model of neuroinflammation in vivo.

INNOVATION

This study provides the first direct evidence for the biological significance of MsrA in microglia-mediated neuroinflammation.

CONCLUSION

Our data provide a profound insight into the role of endogenous antioxidative defense systems such as MsrA in the control of microglial function.

Corynebacterium glutamicum methionine sulfoxide reductase A uses both mycoredoxin and thioredoxin for regeneration and oxidative stress resistance

Oxidation of methionine leads to the formation of the S and R diastereomers of methionine sulfoxide (MetO), which can be reversed by the actions of two structurally unrelated classes of methionine sulfoxide reductase (Msr), MsrA and MsrB, respectively. Although MsrAs have long been demonstrated in numerous bacteria, their physiological and biochemical functions remain largely unknown in Actinomycetes. Here, we report that a Corynebacterium glutamicum methionine sulfoxide reductase A (CgMsrA) that belongs to the 3-Cys family of MsrAs plays important roles in oxidative stress resistance. Deletion of the msrA gene in C. glutamicum resulted in decrease of cell viability, increase of ROS production, and increase of protein carbonylation levels under various stress conditions. The physiological roles of CgMsrA in resistance to oxidative stresses were corroborated by its induced expression under various stresses, regulated directly by the stress-responsive extracytoplasmic-function (ECF) sigma factor SigH. Activity assays performed with various regeneration pathways showed that CgMsrA can reduce MetO via both the thioredoxin/thioredoxin reductase (Trx/TrxR) and mycoredoxin 1/mycothione reductase/mycothiol (Mrx1/Mtr/MSH) pathways. Site-directed mutagenesis confirmed that Cys56 is the peroxidatic cysteine that is oxidized to sulfenic acid, while Cys204 and Cys213 are the resolving Cys residues that form an intramolecular disulfide bond. Mrx1 reduces the sulfenic acid intermediate via the formation of an S-mycothiolated MsrA intermediate (MsrA-SSM) which is then recycled by mycoredoxin and the second molecule of mycothiol, similarly to the glutathione/glutaredoxin/glutathione reductase (GSH/Grx/GR) system. However, Trx reduces the Cys204-Cys213 disulfide bond in CgMsrA produced during MetO reduction via the formation of a transient intermolecular disulfide bond between Trx and CgMsrA. While both the Trx/TrxR and Mrx1/Mtr/MSH pathways are operative in reducing CgMsrA under stress conditions in vivo, the Trx/TrxR pathway alone is sufficient to reduce CgMsrA under normal conditions. Based on these results, a catalytic model for the reduction of CgMsrA by Mrx1 and Trx is proposed.

Arrest defective 1 regulates the oxidative stress response in human cells and mice by acetylating methionine sulfoxide reductase A

Methionine sulfoxide reductase A (MSRA) protects proteins from oxidation, and also helps remove reactive oxygen species (ROS) by recovering antioxidant enzymes inactivated by oxidation. Although its functions have been investigated extensively, little is known about the mechanism by which MSRA is regulated. Arrest defective 1 (ARD1) is an enzyme that catalyzes not only N-terminal acetylation as a cotranslational modification but also lysine acetylation as a posttranslational modification. ARD1, which is expressed in most cell types, is believed to participate in diverse biological processes, but its roles are poorly understood. Given that MSRA was hunted in a yeast two-hybrid screen with ARD1 as the bait, we here investigated whether ARD1 is a novel regulator of MSRA. ARD1 was shown to interact with and acetylate MSRA in both cells and test tubes. It specifically acetylated the K49 residue of MSRA, and by doing so repressed the enzymatic function of MSRA. ARD1 increased cellular levels of ROS, carbonylated proteins and DNA breaks under oxidative stress. Moreover, it promoted cell death induced by pro-oxidants, which was attenuated in MSRA-deficient cells. When mice were exposed to hyperoxic conditions for 2 days, their livers and kidneys were injured and protein carbonylation was increased. The oxidative tissue injury was more severe in ARD1 transgenic mice than in their wild-type littermates. In conclusion, ARD1 has a crucial role in the cellular response to oxidative stress as a bona fide regulator of MSRA. ARD1 is a potential target for ameliorating oxidative injury or for potentiating ROS-producing anticancer agents.

Comparative proteomic analyses provide new insights into low phosphorus stress responses in maize leaves

Phosphorus deficiency limits plant growth and development. To better understand the mechanisms behind how maize responds to phosphate stress, we compared the proteome analysis results of two groups of maize leaves that were treated separately with 1,000 µM (control, +P) and 5 µM of KH2PO4 (intervention group, -P) for 25 days. In total, 1,342 protein spots were detected on 2-DE maps and 15.43% had changed (P<0.05; ≥1.5-fold) significantly in quantity between the +P and -P groups. These proteins are involved in several major metabolic pathways, including photosynthesis, carbohydrate metabolism, energy metabolism, secondary metabolism, signal transduction, protein synthesis, cell rescue and cell defense and virulence. The results showed that the reduction in photosynthesis under low phosphorus treatment was due to the down-regulation of the proteins involved in CO2 enrichment, the Calvin cycle and the electron transport system. Electron transport and photosynthesis restrictions resulted in a large accumulation of peroxides. Maize has developed many different reactive oxygen species (ROS) scavenging mechanisms to cope with low phosphorus stress, including up-regulating its antioxidant content and antioxidase activity. After being subjected to phosphorus stress over a long period, maize may increase its internal phosphorus utilization efficiency by altering photorespiration, starch synthesis and lipid composition. These results provide important information about how maize responds to low phosphorus stress.

Non-essential amino acids attenuate apoptosis of gastric cancer cells induced by glucose starvation

Energy and nutrition are essential requirements for all living cells, including cancer cells. In the initiating stage of cancer in organs, cancer cells grow fast and have inadequate supplies of glucose, oxygen and other nutrients due to deficient angiogenesis. Anaerobic conditions cause cancer cells to rely on glycolysis, which produces pyruvate and ATP that can be used by cancer cells to survive. However, glucose starvation may result in apoptosis or necrosis of cancer cells. It has been reported that autophagy is a consequence of glucose starvation and that amino acids are products of autophagy. The present study investigated whether amino acids may represent an alternative energy source for cancer cells undergoing glucose starvation. With non-essential amino acids, growth inhibition and apoptosis of gastric cancer cells induced by glucose starvation were attenuated compared with that of cells undergoing glucose starvation without amino acids, as measured by cell viability, apoptosis rates, membrane potential of mitochondria, and apoptosis-related genes. Meanwhile, both mitochondrial DNA copy number and amino acid transporter genes were increased compared with those in control cells. Non-essential amino acids prevented gastric cancer cells from glucose starvation-induced apoptosis.

Protein redox modification as a cellular defense mechanism against tissue ischemic injury

Protein oxidative or redox modifications induced by reactive oxygen species (ROS) or reactive nitrogen species (RNS) not only can impair protein function, but also can regulate and expand protein function under a variety of stressful conditions. Protein oxidative modifications can generally be classified into two categories: irreversible oxidation and reversible oxidation. While irreversible oxidation usually leads to protein aggregation and degradation, reversible oxidation that usually occurs on protein cysteine residues can often serve as an “on and off” switch that regulates protein function and redox signaling pathways upon stress challenges. In the context of ischemic tolerance, including preconditioning and postconditioning, increasing evidence has indicated that reversible cysteine redox modifications such as S-sulfonation, S-nitrosylation, S-glutathionylation, and disulfide bond formation can serve as a cellular defense mechanism against tissue ischemic injury. In this review, I highlight evidence of cysteine redox modifications as protective measures in ischemic injury, demonstrating that protein redox modifications can serve as a therapeutic target for attenuating tissue ischemic injury. Prospectively, more oxidatively modified proteins will need to be identified that can play protective roles in tissue ischemic injury, in particular, when the oxidative modifications of such identified proteins can be enhanced by pharmacological agents or drugs that are available or to be developed.

Dopamine Cytotoxicity Involves Both Oxidative and Nonoxidative Pathways in SH-SY5Y Cells: Potential Role of Alpha-Synuclein Overexpression and Proteasomal Inhibition in the Etiopathogenesis of Parkinson's Disease

Background. The cytotoxic effects of dopamine (DA) on several catecholaminergic cell lines involve DA oxidation products like reactive oxygen species (ROS) and toxic quinones and have implications in the pathogenesis of sporadic Parkinson's disease (PD). However, many molecular details are yet to be elucidated, and the possible nonoxidative mechanism of dopamine cytotoxicity has not been studied in great detail. Results. Cultured SH-SY5Y cells treated with DA (up to 400 μM) or lactacystin (5 μM) or DA (400 μM) plus N-acetylcysteine (NAC, 2.5 mM) for 24 h are processed accordingly to observe the cell viability, mitochondrial dysfunctions, oxidative stress parameters, proteasomal activity, expression of alpha-synuclein gene, and intracellular accumulation of the protein. DA causes mitochondrial dysfunction and extensive loss of cell viability partially inhibited by NAC, potent inhibition of proteasomal activity marginally prevented by NAC, and overexpression with accumulation of intracellular alpha-synuclein partially preventable by NAC. Under similar conditions of incubation, NAC completely prevents enhanced production of ROS and increased formation of quinoprotein adducts in DA-treated SH-SY5Y cells. Separately, proteasomal inhibitor lactacystin causes accumulation of alpha-synuclein as well as mitochondrial dysfunction and cell death. Conclusions. DA cytotoxicity includes both oxidative and nonoxidative modes and may involve overexpression and accumulation of alpha-synuclein as well as proteasomal inhibition.

Methionine oxidation and reduction in proteins

BACKGROUND

Cysteine and methionine are the two sulfur containing amino acids in proteins. While the roles of protein-bound cysteinyl residues as endogenous antioxidants are well appreciated, those of methionine remain largely unexplored.

SCOPE

We summarize the key roles of methionine residues in proteins.

MAJOR CONCLUSION

Recent studies establish that cysteine and methionine have remarkably similar functions.

GENERAL SIGNIFICANCE

Both cysteine and methionine serve as important cellular antioxidants, stabilize the structure of proteins, and can act as regulatory switches through reversible oxidation and reduction. This article is part of a Special Issue entitled Current methods to study reactive oxygen species - pros and cons and biophysics of membrane proteins. Guest Editor: Christine Winterbourn.

The physiological role of reversible methionine oxidation

Sulfur-containing amino acids such as cysteine and methionine are particularly vulnerable to oxidation. Oxidation of cysteine and methionine in their free amino acid form renders them unavailable for metabolic processes while their oxidation in the protein-bound state is a common post-translational modification in all organisms and usually alters the function of the protein. In the majority of cases, oxidation causes inactivation of proteins. Yet, an increasing number of examples have been described where reversible cysteine oxidation is part of a sophisticated mechanism to control protein function based on the redox state of the protein. While for methionine the dogma is still that its oxidation inhibits protein function, reversible methionine oxidation is now being recognized as a powerful means of triggering protein activity. This mode of regulation involves oxidation of methionine to methionine sulfoxide leading to activated protein function, and inactivation is accomplished by reduction of methionine sulfoxide back to methionine catalyzed by methionine sulfoxide reductases. Given the similarity to thiol-based redox-regulation of protein function, methionine oxidation is now established as a novel mode of redox-regulation of protein function. This article is part of a Special Issue entitled: Thiol-Based Redox Processes.

Thymosin β4-sulfoxide attenuates inflammatory cell infiltration and promotes cardiac wound healing

The downstream consequences of inflammation in the adult mammalian heart are formation of a non-functional scar, pathological remodelling and heart failure. In zebrafish, hydrogen peroxide (H₂O₂) released from a wound is the initial instructive chemotactic cue for the infiltration of inflammatory cells, however, the identity of a subsequent resolution signal(s), to attenuate chronic inflammation, remains unknown. Here we reveal that Thymosin β4-Sulfoxide inhibits interferon-γ, and increases monocyte dispersal and cell death, lies downstream of H₂O₂ in the wounded fish and triggers depletion of inflammatory macrophages at the injury site. This function is conserved in the mouse and observed after cardiac injury, where it promotes wound healing and reduced scarring. In human T cell/CD14+ monocyte co-cultures, Tβ4-SO inhibits IFN-γ and increases monocyte dispersal and cell death, likely by stimulating superoxide production. Thus, Tβ4-SO is a putative target for therapeutic modulation of the immune response, resolution of fibrosis and cardiac repair.

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.

Independent roles of methionine sulfoxide reductase A in mitochondrial ATP synthesis and as antioxidant in retinal pigment epithelial cells

The antioxidant enzyme methionine sulfoxide reductase A (MsrA) is highly expressed in the retinal pigment epithelium (RPE), a support tissue for neighboring photoreceptors. MsrA protein levels correlate with sensitivity of RPE in culture to experimental oxidative stress. To investigate whether and how MsrA affects RPE functionality regardless of oxidative stress, we tested the effects of acute silencing or overexpression of MsrA on the phagocytosis of photoreceptor outer segment fragments (POS), a demanding, daily function of the RPE that is essential for vision. Endogenous MsrA localized to mitochondria and cytosol of rat RPE in culture. RPE cells manipulated to express higher or lower levels of MsrA than control cells showed no signs of cell death but increased or decreased, respectively, POS binding as well as engulfment. These effects of altered MsrA protein concentration on phagocytosis were independent of the levels of oxidative stress. However, altering MsrA expression had no effect on phagocytosis when mitochondrial respiration was inhibited. Furthermore, ATP content directly correlated with MsrA protein levels in RPE cells that used mitochondrial oxidative phosphorylation for ATP synthesis but not in RPE cells that relied on glycolysis alone. Overexpressing MsrA was sufficient to increase specifically the activity of complex IV of the respiratory chain, whereas activity of complex II and mitochondrial content were unaffected. Thus, MsrA probably enhances ATP synthesis by increasing complex IV activity. Such contribution of MsrA to energy metabolism is independent of its function in protection from elevated oxidative stress but contributes to routine but vital photoreceptor support by RPE cells.

Stereospecific oxidation of calmodulin by methionine sulfoxide reductase A

Methionine sulfoxide reductase A has long been known to reduce S-methionine sulfoxide, both as a free amino acid and within proteins. Recently the enzyme was shown to be bidirectional, capable of oxidizing free methionine and methionine in proteins to S-methionine sulfoxide. A feasible mechanism for controlling the directionality has been proposed, raising the possibility that reversible oxidation and reduction of methionine residues within proteins is a redox-based mechanism for cellular regulation. We undertook studies aimed at identifying proteins that are subject to site-specific, stereospecific oxidation and reduction of methionine residues. We found that calmodulin, which has nine methionine residues, is such a substrate for methionine sulfoxide reductase A. When calmodulin is in its calcium-bound form, Met77 is oxidized to S-methionine sulfoxide by methionine sulfoxide reductase A. When methionine sulfoxide reductase A operates in the reducing direction, the oxidized calmodulin is fully reduced back to its native form. We conclude that reversible covalent modification of Met77 may regulate the interaction of calmodulin with one or more of its many targets.

Oxidative and nitrative alpha-synuclein modifications and proteostatic stress: implications for disease mechanisms and interventions in synucleinopathies

Alpha-synuclein (ASYN) is a major constituent of the typical protein aggregates observed in several neurodegenerative diseases that are collectively referred to as synucleinopathies. A causal involvement of ASYN in the initiation and progression of neurological diseases is suggested by observations indicating that single-point (e.g., A30P, A53T) or multiplication mutations of the gene encoding for ASYN cause early onset forms of Parkinson's disease (PD). The relative regional specificity of ASYN pathology is still a riddle that cannot be simply explained by its expression pattern. Also, transgenic over-expression of ASYN in mice does not recapitulate the typical dopaminergic neuronal death observed in PD. Thus, additional factors must contribute to ASYN-related toxicity. For instance, synucleinopathies are usually associated with inflammation and elevated levels of oxidative stress in affected brain areas. In turn, these conditions favor oxidative modifications of ASYN. Among these modifications, nitration of tyrosine residues, formation of covalent ASYN dimers, as well as methionine sulfoxidations are prominent examples that are observed in post-mortem PD brain sections. Oxidative modifications can affect ASYN aggregation, as well as its binding to biological membranes. This would affect neurotransmitter recycling, mitochondrial function and dynamics (fission/fusion), ASYN's degradation within a cell and, possibly, the transfer of modified ASYN to adjacent cells. Here, we propose a model on how covalent modifications of ASYN link energy stress, altered proteostasis, and oxidative stress, three major pathogenic processes involved in PD progression. Moreover, we hypothesize that ASYN may act physiologically as a catalytically regenerated scavenger of oxidants in healthy cells, thus performing an important protective role prior to the onset of disease or during aging.