Peroxiredoxin 2 is required for the redox mediated adaptation to exercise

Exercise generates a site-specific increase in Reactive Oxygen Species (ROS) within muscle that promotes changes in gene transcription and mitochondrial biogenesis, required for the beneficial adaptive response. We demonstrate that Peroxiredoxin 2 (Prdx2), an abundant cytoplasmic 2-Cys peroxiredoxin, is required for the adaptive hormesis response to physiological levels of H₂O₂ in myoblasts and following exercise in C. elegans. A short bolus addition of H₂O₂ increases mitochondrial capacity and improves myogenesis of cultured myoblasts, this beneficial adaptive response was suppressed in myoblasts with decreased expression of cytoplasmic Prdxs. Moreover, a swimming exercise protocol in C. elegans increased mitochondrial content, fitness, survival and longevity in wild type (N2) worms. In contrast, prdx-2 mutant worms had decreased fitness, disrupted mitochondria, reduced survival and lifespan following exercise. Global proteomics following exercise identified distinct changes in the proteome of N2 and prdx-2 mutants. Furthermore, a redox proteomic approach to quantify reversible oxidation of specific Cysteine residues revealed a more reduced redox state in the non-exercised prdx-2 mutant strain that become oxidized following exercise. In contrast, specific Cys residues from regulatory proteins become more reduced in the N2 strain following exercise, establishing the key regulatory role of PRDX-2 in a redox signalling cascade following endogenous ROS generation. Our results demonstrate that conserved cytoplasmic 2-Cys Peroxiredoxins are required for the beneficial adaptive response to a physiological redox stress.

Extracellular Vesicles, Cell-Penetrating Peptides and miRNAs as Future Novel Therapeutic Interventions for Parkinson’s and Alzheimer’s Disease

Neurodegeneration is hallmarked by the progressive loss of dopaminergic neurons and/or a significant increase in protein aggregates in the brain. Neurodegenerative diseases are a leading cause of death worldwide with over 15 million people currently suffering from either Parkinson’s disease (PD) or Alzheimer’s disease (AD). PD is often characterized by both motor and non-motor symptoms, including muscle rigidity, tremors and bradykinesia, with AD displaying symptoms of confusion and dementia. The current mainstay of therapeutics includes pharmacological approaches such as levodopa to replace dopamine in PD patients, deep brain stimulation in affected regions of the brain and physical therapy. However, these treatments are typically not disease-modifying, though they do help at least for some time with symptom management. These treatments often also fail due to their inability to cross the blood–brain barrier. There is a need to develop new strategies to target neurodegeneration in an ever-ageing population. First, we review the current PD and AD treatments and their limitations. Second, we review the current use of extracellular vesicles (EVs), cell-penetrating peptides (CPPs) and miRNAs as neuroprotective agents. Finally, we discuss the possibility of exploiting these as a combinatory therapeutic, alongside some potential drawbacks.

MicroRNAs as the Sentinels of Redox and Hypertrophic Signalling

Oxidative stress and inflammation are associated with skeletal muscle function decline with ageing or disease or inadequate exercise and/or poor diet. Paradoxically, reactive oxygen species and inflammatory cytokines are key for mounting the muscular and systemic adaptive responses to endurance and resistance exercise. Both ageing and lifestyle-related metabolic dysfunction are strongly linked to exercise redox and hypertrophic insensitivity. The adaptive inability and consequent exercise intolerance may discourage people from physical training resulting in a vicious cycle of under-exercising, energy surplus, chronic mitochondrial stress, accelerated functional decline and increased susceptibility to serious diseases. Skeletal muscles are malleable and dynamic organs, rewiring their metabolism depending on the metabolic or mechanical stress resulting in a specific phenotype. Endogenous RNA silencing molecules, microRNAs, are regulators of these metabolic/phenotypic shifts in skeletal muscles. Skeletal muscle microRNA profiles at baseline and in response to exercise have been observed to differ between adult and older people, as well as trained vs. sedentary individuals. Likewise, the circulating microRNA blueprint varies based on age and training status. Therefore, microRNAs emerge as key regulators of metabolic health/capacity and hormetic adaptability. In this narrative review, we summarise the literature exploring the links between microRNAs and skeletal muscle, as well as systemic adaptation to exercise. We expand a mathematical model of microRNA burst during adaptation to exercise through supporting data from the literature. We describe a potential link between the microRNA-dependent regulation of redox-signalling sensitivity and the ability to mount a hypertrophic response to exercise or nutritional cues. We propose a hypothetical model of endurance exercise-induced microRNA "memory cloud" responsible for establishing a landscape conducive to aerobic as well as anabolic adaptation. We suggest that regular aerobic exercise, complimented by a healthy diet, in addition to promoting mitochondrial health and hypertrophic/insulin sensitivity, may also suppress the glycolytic phenotype and mTOR signalling through miRNAs which in turn promote systemic metabolic health.

Evidence of impaired mitochondrial cellular bioenergetics in ocular fibroblasts derived from glaucoma patients

Glaucoma is a progressive optic neuropathy characterized by the neurodegeneration of the retinal ganglion cells (RGCs) resulting in irreversible visual impairment and eventual blindness. RGCs are extremely susceptible to mitochondrial compromise due to their marked bioenergetic requirements and morphology. There is increasing interest in therapies targeting mitochondrial health as a method of preventing visual loss in managing glaucoma. The bioenergetic profile of Tenon's ocular fibroblasts from glaucoma patients and controls was investigated using the Seahorse XF24 analyser. Impaired mitochondrial cellular bioenergetics was detected in glaucomatous ocular fibroblasts including basal respiration, maximal respiration and spare capacity. Spare respiratory capacity levels reflect mitochondrial bio-energetic adaptability in response to pathophysiological stress. Basal oxidative stress was elevated in glaucomatous Tenon's ocular fibroblasts and hydrogen peroxide (H₂O₂) induced reactive oxygen species (ROS) simulated the glaucomatous condition in normal Tenon's ocular fibroblasts. This work supports the role of therapeutic interventions to target oxidative stress or provide mitochondrial energetic support in glaucoma.

Exercise stress leads to an acute loss of mitochondrial proteins and disruption of redox control in skeletal muscle of older subjects: An underlying decrease in resilience with aging?

Reactive oxygen species (ROS) are recognized as important signaling molecules in healthy skeletal muscle. Redox sensitive proteins can respond to intracellular changes in ROS by oxidation of reactive thiol groups on cysteine (Cys) residues. Exercise is known to induce the generation of superoxide and nitric oxide, resulting in the activation of several adaptive signaling pathways; however, it has been suggested that aging attenuates these redox-regulated adaptations to acute exercise. In the present study, we used redox proteomics to study the vastus lateralis muscles of Adult (n = 6 male, 6 female; 18-30 yrs) and Old (n = 6 male, 6 female; 64-79 yrs) adults. Participants completed a bout of high intensity cycling exercise consisting of five sets of 2-min intervals performed at 80% maximal aerobic power output (PPO), with 2 min recovery cycling at 40% PPO between sets. Muscle biopsies were collected prior to exercise, and immediately following the first, second, and fifth high intensity interval. Global proteomic analysis indicated differences in abundance of a number of individual proteins between skeletal muscles of Adult and Old subjects at rest with a significant exacerbation of these differences induced by the acute exercise. In particular, we observed an exercise-induced decrease in abundance of mitochondrial proteins in muscles from older subjects only. Redox proteome analysis revealed cysteines from five cytosolic proteins in older subjects with lower oxidation (i.e. greater reduction) than was seen in muscle from the young adults at rest. Redox homeostasis was well maintained in Adult subjects following exercise, but there was significant increase in oxidation of multiple mitochondrial and cytosolic protein cysteines in Old subjects. We also observed that oxidation of peroxiredoxin 3 occurred following exercise in both Adult and Old groups, supporting the possibility that this is a key effector protein for mitochondrial redox signaling. Thus, we show, for the first time that exercise reveals a lack of resilience in muscle of older human participants, that is apparent as a loss of mitochondrial proteins and oxidation of multiple protein cysteines that are not seen in younger subjects. The precise consequences of this redox disruption are unclear, but this likely play a role in the attenuation of multiple adaptations to exercise that are classically seen with aging. Such changes were only seen following the acute stress of exercise., highlighting the need to consider not only basal differences seen during aging but also the difference following physiological challenge.

miR-24 and its target gene Prdx6 regulate viability and senescence of myogenic progenitors during aging

Satellite cell-dependent skeletal muscle regeneration declines during aging. Disruptions within the satellite cells and their niche, together with alterations in the myofibrillar environment, contribute to age-related dysfunction and defective muscle regeneration. In this study, we demonstrated an age-related decline in satellite cell viability and myogenic potential and an increase in ROS and cellular senescence. We detected a transient upregulation of miR-24 in regenerating muscle from adult mice and downregulation of miR-24 during muscle regeneration in old mice. FACS-sorted satellite cells were characterized by decreased levels of miR-24 and a concomitant increase in expression of its target: Prdx6. Using GFP reporter constructs, we demonstrated that miR-24 directly binds to its predicted site within Prdx6 mRNA. Subtle changes in Prdx6 levels following changes in miR-24 expression indicate miR-24 plays a role in fine-tuning Prdx6 expression. Changes in miR-24 and Prdx6 levels were associated with altered mitochondrial ROS generation, increase in the DNA damage marker: phosphorylated-H2Ax and changes in viability, senescence, and myogenic potential of myogenic progenitors from mice and humans. The effects of miR-24 were more pronounced in myogenic progenitors from old mice, suggesting a context-dependent role of miR-24 in these cells, with miR-24 downregulation likely a part of a compensatory response to declining satellite cell function during aging. We propose that downregulation of miR-24 and subsequent upregulation of Prdx6 in muscle of old mice following injury are an adaptive response to aging, to maintain satellite cell viability and myogenic potential through regulation of mitochondrial ROS and DNA damage pathways.

Multiomics analysis of the mdx/mTR mouse model of Duchenne muscular dystrophy

PURPOSE/AIM

Duchenne muscular dystrophy (DMD) is a progressive neuromuscular disease characterized by extensive muscle weakness. Patients with DMD lack a functional dystrophin protein, which transmits force and organizes the cytoskeleton of skeletal muscle. Multiomic studies have been proposed as a way to obtain novel insight about disease processes from preclinical models, and we used this approach to study pathological changes in dystrophic muscles.

MATERIALS AND METHODS

We evaluated hindlimb muscles of male mdx/mTR mice, which lack a functional dystrophin protein and have deficits in satellite cell abundance and proliferative capacity. Wild type (WT) C57BL/6 J mice served as controls. Muscle fiber contractility was measured, along with changes in the transcriptome using RNA sequencing, and in the proteome, metabolome, and lipidome using mass spectrometry.

RESULTS

While mdx/mTR mice displayed gross pathological changes and continued cycles of degeneration and regeneration, we found no differences in permeabilized fiber contractility between strains. However, there were numerous changes in the transcriptome and proteome related to protein balance, contractile elements, extracellular matrix, and metabolism. There was only a 53% agreement in fold-change data between the proteome and transcriptome. Numerous changes in markers of skeletal muscle metabolism were observed, with dystrophic muscles exhibiting elevated glycolytic metabolites such as 6-phosphoglycerate, fructose-6-phosphate and glucose-6-phosphate, fructose bisphosphate, phosphorylated hexoses, and phosphoenolpyruvate.

CONCLUSIONS

These findings highlight the utility of multiomics in studying muscle disease, and provide additional insight into the pathological changes in dystrophic muscles that might help to indirectly guide evidence-based nutritional or exercise prescription in DMD patients.

2-Cys peroxiredoxin oxidation in response to hydrogen peroxide and contractile activity in skeletal muscle: A novel insight into exercise-induced redox signalling?

Skeletal muscle generates superoxide during contractions which is rapidly converted to H2O2. This molecule has been proposed to activate signalling pathways and transcription factors that regulate key adaptive responses to exercise but the concentration of H2O2 required to oxidise and activate key signalling proteins in vitro is much higher than the intracellular concentration in muscle fibers following exercise. We hypothesised that Peroxiredoxins (Prx), which reacts with H2O2 at the low intracellular concentrations found in muscle, would be rapidly oxidised in contracting muscle and hence potentially transmit oxidising equivalents to downstream signalling proteins as a method for their oxidation and activation. The aim of this study was to characterise the effects of muscle contractile activity on the oxidation of Prx1, 2 and 3 and determine if these were affected by aging. Prx1, 2 and 3 were all rapidly and reversibly oxidised following treatment with low micromolar concentrations of H2O2 in C2C12 myotubes and also in isolated mature flexor digitalis brevis fibers from adult mice following a protocol of repeated isometric contractions. Significant oxidation of Prx2 was seen within 1 min (i.e. after 12 contractions), whereas significant oxidation was seen after 2 min for Prx1 and 3. In muscle fibers from old mice, Prx2 oxidation was significantly attenuated following contractile activity. Thus we show for the first time that Prx are rapidly and reversibly oxidised in response to contractile activity in skeletal muscle and hypothesise that these proteins act as effectors of muscle redox signalling pathways which are key to adaptations to exercise that are attenuated during aging.

MicroRNAs as potential therapeutic targets for muscle wasting during cancer cachexia

PURPOSE OF REVIEW

Muscle wasting in cancer cachexia remains an unmet clinical need due to lack of effective therapies associated with the complexity of the disease. Here, we discuss microRNAs, robust regulators of the expression of multiple genes, only recently characterized in cancer cachexia in humans and their therapeutic potential for muscle wasting.

RECENT FINDINGS

Changes in microRNAs in muscle of cancer patients have been demonstrated for the first time and these are associated with dysregulated signalling networks during muscle wasting. These data, together with studies in animal models, indicate that microRNAs are attractive therapeutic candidates for maintaining muscle mass, both during and following cancer treatment ultimately improving patient outcomes.

SUMMARY

Cancer cachexia is a complex metabolic condition associated with muscle wasting. Maintenance of muscle mass in cancer patients can improve their response to therapy and prognosis. microRNAs, which can act as oncogenes or tumour suppressors, are also dysregulated in muscle of cachexia patients. Studies in animal models of muscle wasting have demonstrated that microRNAs regulate muscle mass and strength. With more microRNA-based therapeutics in clinical trials and first RNA drugs approved, microRNAs present an attractive novel therapeutic avenue for maintaining muscle homeostasis in cachexia patients to improve their prognosis.

The redox environment and mitochondrial dysfunction in age-related skeletal muscle atrophy

Medical advancements have extended human life expectancy, which is not always accompanied by an improved quality of life or healthspan. A decline in muscle mass and function is a consequence of ageing and can result in a loss of independence in elderly individuals while increasing their risk of falls. Multiple cellular pathways have been implicated in age-related muscle atrophy, including the contribution of reactive oxygen species (ROS) and disrupted redox signalling. Aberrant levels of ROS disrupts the redox environment in older muscle, potentially disrupting cellular signalling and in some cases blunting the adaptive response to exercise. Age-related muscle atrophy is associated with disrupted mitochondrial content and function, one of the hallmarks of age-related diseases. There is a critical link between abnormal ROS generation and dysfunctional mitochondrial dynamics including mitochondrial biogenesis, fusion and fission. In order to develop effective treatments or preventative strategies, it is important to gain a comprehensive understanding of the mechanistic pathways implicated in age associated loss of muscle.

miR-181a regulates p62/SQSTM1, parkin, and protein DJ-1 promoting mitochondrial dynamics in skeletal muscle aging

One of the key mechanisms underlying skeletal muscle functional deterioration during aging is disrupted mitochondrial dynamics. Regulation of mitochondrial dynamics is essential to maintain a healthy mitochondrial population and prevent the accumulation of damaged mitochondria; however, the regulatory mechanisms are poorly understood. We demonstrated loss of mitochondrial content and disrupted mitochondrial dynamics in muscle during aging concomitant with dysregulation of miR‐181a target interactions. Using functional approaches and mito‐QC assay, we have established that miR‐181a is an endogenous regulator of mitochondrial dynamics through concerted regulation of Park2, p62/SQSTM1, and DJ‐1 in vitro. Downregulation of miR‐181a with age was associated with an accumulation of autophagy‐related proteins and abnormal mitochondria. Restoring miR‐181a levels in old mice prevented accumulation of p62, DJ‐1, and PARK2, and improved mitochondrial quality and muscle function. These results provide physiological evidence for the potential of microRNA‐based interventions for age‐related muscle atrophy and of wider significance for diseases with disrupted mitochondrial dynamics.

The clinical potential of thiol redox proteomics

Introduction: Protein thiols are susceptible to oxidation in health and disease. Redox proteomics methods facilitate the identification, quantification, and rationalization of oxidation processes including those involving protein thiols. These residues are crucial to understanding redox homeostasis underpinning normal cell functioning and regulation as well as novel biomarkers of pathology and promising novel drug targets.Areas covered: This article reviews redox proteomic approaches to study of protein thiols in some important human pathologies and assesses the clinical potential of individual Cys residues as novel biomarkers for disease detection and as targets for novel treatments.Expert commentary: Although protein thiols are not as routinely used as redox biomarkers as some other lesions such as carbonylation, there has been growing recent interest in their potential. Driven largely by developments in high-resolution mass spectrometry it is possible now to identify proteins that are redox modified at thiol groups or that interact with regulatory oxidoreductases. Thiols that are specifically susceptible to modification by reactive oxygen species can be routinely identified now and quantitative MS can be used to quantify the proportion of a protein that is redox modified.

Peroxiredoxin 6 Down-Regulation Induces Metabolic Remodeling and Cell Cycle Arrest in HepG2 Cells

Peroxiredoxin 6 (Prdx6) is the only member of 1-Cys subfamily of peroxiredoxins in human cells. It is the only Prdx acting on phospholipid hydroperoxides possessing two additional sites with phospholipase A2 (PLA2) and lysophosphatidylcholine-acyl transferase (LPCAT) activities. There are contrasting reports on the roles and mechanisms of multifunctional Prdx6 in several pathologies and on its sensitivity to, and influence on, the redox environment. We have down-regulated Prdx6 with specific siRNA in hepatoblastoma HepG2 cells to study its role in cell proliferation, redox homeostasis, and metabolic programming. Cell proliferation and cell number decreased while cell volume increased; import of glucose and nucleotide biosynthesis also diminished while polyamines, phospholipids, and most glycolipids increased. A proteomic quantitative analysis suggested changes in membrane arrangement and vesicle trafficking as well as redox changes in enzymes of carbon and glutathione metabolism, pentose-phosphate pathway, citrate cycle, fatty acid metabolism, biosynthesis of aminoacids, and Glycolysis/Gluconeogenesis. Specific redox changes in Hexokinase-2 (HK2), Prdx6, intracellular chloride ion channel-1 (CLIC1), PEP-carboxykinase-2 (PCK2), and 3-phosphoglycerate dehydrogenase (PHGDH) are compatible with the metabolic remodeling toward a predominant gluconeogenic flow from aminoacids with diversion at 3-phospohglycerate toward serine and other biosynthetic pathways thereon and with cell cycle arrest at G1/S transition.

Translational regulation contributes to the secretory response of chondrocytic cells following exposure to interleukin-1β

Osteoarthritis is a chronic disease characterized by the loss of articular cartilage in synovial joints through a process of extracellular matrix destruction that is strongly associated with inflammatory stimuli. Chondrocytes undergo changes to their protein translational capacity during osteoarthritis, but a study of how disease-relevant signals affect chondrocyte protein translation at the transcriptomic level has not previously been performed. In this study, we describe how the inflammatory cytokine interleukin 1-β (IL-1β) rapidly affects protein translation in the chondrocytic cell line SW1353. Using ribosome profiling we demonstrate that IL-1β induced altered translation of inflammatory-associated transcripts such as NFKB1, TNFAIP2, MMP13, CCL2, and CCL7, as well as a number of ribosome-associated transcripts, through differential translation and the use of multiple open reading frames. Proteomic analysis of the cellular layer and the conditioned media of these cells identified changes in a number of the proteins that were differentially translated. Translationally regulated secreted proteins included a number of chemokines and cytokines, underlining the rapid, translationally mediated inflammatory cascade that is initiated by IL-1β. Although fewer cellular proteins were found to be regulated in both ribosome profiling and proteomic data sets, we did find increased levels of SOD2, indicative of redox changes within SW1353 cells being modulated at the translational level. In conclusion, we have produced combined ribosome profiling and proteomic data sets that provide a valuable resource in understanding the processes that occur during cytokine stimulation of chondrocytic cells.

Reduced mitochondrial lipid oxidation leads to fat accumulation in myosteatosis

Myosteatosis is the pathologic accumulation of lipid that can occur in conjunction with atrophy and fibrosis following skeletal muscle injury. Little is known about the mechanisms by which lipid accumulates in myosteatosis, but many clinical studies have demonstrated that the degree of lipid infiltration negatively correlates with muscle function and regeneration. Our objective was to determine the pathologic changes that result in lipid accumulation in injured muscle fibers. We used a rat model of rotator cuff injury in this study because the rotator cuff muscle group is particularly prone to the development of myosteatosis after injury. Muscles were collected from uninjured controls or 10, 30, or 60 d after injury and analyzed using a combination of muscle fiber contractility assessments, RNA sequencing, and undirected metabolomics, lipidomics, and proteomics, along with bioinformatics techniques to identify potential pathways and cellular processes that are dysregulated after rotator cuff tear. Bioinformatics analyses indicated that mitochondrial function was likely disrupted after injury. Based on these findings and given the role that mitochondria play in lipid metabolism, we then performed targeted biochemical and imaging studies and determined that mitochondrial dysfunction and reduced fatty acid oxidation likely leads to the accumulation of lipid in myosteatosis.-Gumucio, J. P., Qasawa, A. H., Ferrara, P. J., Malik, A. N., Funai, K., McDonagh, B., Mendias, C. L. Reduced mitochondrial lipid oxidation leads to fat accumulation in myosteatosis.

Proteomic strategies to unravel age-related redox signalling defects in skeletal muscle

Increased oxidative damage and disrupted redox signalling are consistently associated with age-related loss of skeletal muscle mass and function. Redox signalling can directly regulate biogenesis and degradation pathways and indirectly via activation of key transcription factors. Contracting skeletal muscle fibres endogenously generate free radicals (e.g. superoxide) and non-radical derivatives (e.g. hydrogen peroxide). Exercise induced redox signalling can promote beneficial adaptive responses that are disrupted by age-related redox changes. Identifying and quantifying the redox signalling pathways responsible for successful adaptation to exercise makes skeletal muscle an attractive physiological model for redox proteomic approaches. Site specific identification of the redox modification and quantification of site occupancy in the context of protein abundance remains a crucial concept for redox proteomics approaches. Notwithstanding, the technical limitations associated with skeletal muscle for proteomic analysis, we discuss current approaches for the identification and quantification of transient and stable redox modifications that have been employed to date in ageing research. We also discuss recent developments in proteomic approaches in skeletal muscle and potential implications and opportunities for investigating disrupted redox signalling in skeletal muscle ageing.

Thioredoxin and glutaredoxin regulate metabolism through different multiplex thiol switches

The aim of the present study was to define the role of Trx and Grx on metabolic thiol redox regulation and identify their protein and metabolite targets. The hepatocarcinoma-derived HepG2 cell line under both normal and oxidative/nitrosative conditions by overexpression of NO synthase (NOS3) was used as experimental model. Grx1 or Trx1 silencing caused conspicuous changes in the redox proteome reflected by significant changes in the reduced/oxidized ratios of specific Cys's including several glycolytic enzymes. Cys⁹¹ of peroxiredoxin-6 (PRDX6) and Cys¹⁵³ of phosphoglycerate mutase-1 (PGAM1), that are known to be involved in progression of tumor growth, are reported here for the first time as specific targets of Grx1. A group of proteins increased their Cys_RED/Cys_OX ratio upon Trx1 and/or Grx1 silencing, including caspase-3 Cys¹⁶³, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) Cys²⁴⁷ and triose-phosphate isomerase (TPI) Cys²⁵⁵ likely by enhancement of NOS3 auto-oxidation. The activities of several glycolytic enzymes were also significantly affected. Glycolysis metabolic flux increased upon Trx1 silencing, whereas silencing of Grx1 had the opposite effect. Diversion of metabolic fluxes toward synthesis of fatty acids and phospholipids was observed in siRNA-Grx1 treated cells, while siRNA-Trx1 treated cells showed elevated levels of various sphingomyelins and ceramides and signs of increased protein degradation. Glutathione synthesis was stimulated by both treatments. These data indicate that Trx and Grx have both, common and specific protein Cys redox targets and that down regulation of either redoxin has markedly different metabolic outcomes. They reflect the delicate sensitivity of redox equilibrium to changes in any of the elements involved and the difficulty of forecasting metabolic responses to redox environmental changes.

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Trx1 and Grx1 Cys redox targets are abundant among Glycolytic enzymes.

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PRDX6-Cys⁹¹ and PGAM-Cys¹⁵³ are specific targets of Grx1.

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Down regulation of thioredoxin and glutaredoxin have different metabolic outcomes.

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Glutathione synthesis and membrane lipid composition are sensitive to Trx1 and Grx1 down regulation.

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Redoxins down regulation also induce target Cys reductive changes under NOS3 overexpression.

Redox responses are preserved across muscle fibres with differential susceptibility to aging

Age-related loss of muscle mass and function is associated with increased frailty and loss of independence. The mechanisms underlying the susceptibility of different muscle types to age-related atrophy are not fully understood. Reactive oxygen species (ROS) are recognised as important signalling molecules in healthy muscle and redox sensitive proteins can respond to intracellular changes in ROS concentrations modifying reactive thiol groups on Cysteine (Cys) residues. Conserved Cys residues tend to occur in functionally important locations and can have a direct impact on protein function through modifications at the active site or determining protein conformation. The aim of this work was to determine age-related changes in the redox proteome of two metabolically distinct murine skeletal muscles, the quadriceps a predominantly glycolytic muscle and the soleus which contains a higher proportion of mitochondria. To examine the effects of aging on the global proteome and the oxidation state of individual redox sensitive Cys residues, we employed a label free proteomics approach including a differential labelling of reduced and reversibly oxidised Cys residues. Our results indicate the proteomic response to aging is dependent on muscle type but redox changes that occur primarily in metabolic and cytoskeletal proteins are generally preserved between metabolically distinct tissues.

BIOLOGICAL SIGNIFICANCE

Skeletal muscle containing fast twitch glycolytic fibres are more susceptible to age related atrophy compared to muscles with higher proportions of oxidative slow twitch fibres. Contracting skeletal muscle generates reactive oxygen species that are required for correct signalling and adaptation to exercise and it is also known that the intracellular redox environment changes with age. To identify potential mechanisms for the distinct response to age, this article combines a global proteomic approach and a differential labelling of reduced and reversibly oxidised Cysteine residues in two metabolically distinct skeletal muscles, quadriceps and soleus, from adult and old mice. Our results indicate that the global proteomic changes with age in skeletal muscles are dependent on fibre type. However, redox specific changes are preserved across muscle types and accompanied with a reduction in the number of redox sensitive Cysteine residues.

Comparison of Whole Body SOD1 Knockout with Muscle-Specific SOD1 Knockout Mice Reveals a Role for Nerve Redox Signaling in Regulation of Degenerative Pathways in Skeletal Muscle

AIMS

Lack of Cu,Zn-superoxide dismutase (CuZnSOD) in homozygous knockout mice (Sod1^-/-) leads to accelerated age-related muscle loss and weakness, but specific deletion of CuZnSOD in skeletal muscle (mSod1KO mice) or neurons (nSod1KO mice) resulted in only mild muscle functional deficits and failed to recapitulate the loss of mass and function observed in Sod1^-/- mice. To dissect any underlying cross-talk between motor neurons and skeletal muscle in the degeneration in Sod1^-/- mice, we characterized neuromuscular changes in the Sod1^-/- model compared with mSod1KO mice and examined degenerative molecular mechanisms and pathways in peripheral nerve and skeletal muscle.

RESULTS

In contrast to mSod1KO mice, myofiber atrophy in Sod1^-/- mice was associated with increased muscle oxidative damage, neuromuscular junction degeneration, denervation, nerve demyelination, and upregulation of proteins involved in maintenance of myelin sheaths. Proteomic analyses confirmed increased proteasomal activity and adaptive stress responses in muscle of Sod1^-/- mice that were absent in mSod1KO mice. Peripheral nerve from neither Sod1^-/- nor mSod1KO mice showed increased oxidative damage or molecular responses to increased oxidation compared with wild type mice. Differential cysteine (Cys) labeling revealed a specific redox shift in the catalytic Cys residue of peroxiredoxin 6 (Cys47) in the peripheral nerve from Sod1^-/- mice. Innovation and Conclusion: These findings demonstrate that neuromuscular integrity, redox mechanisms, and pathways are differentially altered in nerve and muscle of Sod1^-/- and mSod1KO mice. Results support the concept that impaired redox signaling, rather than oxidative damage, in peripheral nerve plays a key role in muscle loss in Sod1^-/- mice and potentially sarcopenia during aging. Antioxid. Redox Signal. 28, 275-295.

Redox Homeostasis in Age-Related Muscle Atrophy

Muscle atrophy and weakness, characterized by loss of lean muscle mass and function, has a significant effect on the independence and quality of life of older people. The cellular mechanisms that drive the age-related decline in neuromuscular integrity and function are multifactorial. Quiescent and contracting skeletal muscle can endogenously generate reactive oxygen and nitrogen species (RONS) from various cellular sites. Excessive RONS can potentially cause oxidative damage and disruption of cellular signaling pathways contributing to the initiation and progression of age-related muscle atrophy. Altered redox homeostasis and modulation of intracellular signal transduction processes have been proposed as an underlying mechanism of sarcopenia. This chapter summarizes the current evidence that has associated disrupted redox homeostasis and muscle atrophy as a result of skeletal muscle inactivity and aging.

Advanced aging causes diaphragm functional abnormalities, global proteome remodeling, and loss of mitochondrial cysteine redox flexibility in mice

AIM

Inspiratory muscle (diaphragm) function declines with age, contributing to exercise intolerance and impaired airway clearance. Studies of diaphragm dysfunction in rodents have focused on moderate aging (~24months); thus, the impact of advanced age on the diaphragm and potential mechanisms of dysfunction are less clear. Therefore, we aimed to define the effects of advanced age on the mechanics, morphology, and global and redox proteome of the diaphragm.

METHODS

We studied diaphragm from young (6months) and very old male mice (30months). Diaphragm function was evaluated using isolated muscle bundles. Proteome analyses followed LC-MS/MS processing of diaphragm muscle.

RESULTS

Advanced aging decreased diaphragm peak power by ~35% and maximal isometric specific force by ~15%, and prolonged time to peak twitch tension by ~30% (P<0.05). These changes in contractile properties were accompanied, and might be caused by, decreases in abundance of calsequestrin, sarcoplasmic reticulum C^a2+-ATPase, sarcalumenin, and parvalbumin that were revealed by our label-free proteomics data. Advanced aging also increased passive stiffness (P<0.05), which might be a consequence of an upregulation of cytoskeletal and extracellular matrix proteins identified by proteomics. Analyses of cysteine redox state indicated that the main diaphragm abnormalities with advanced aging are in metabolic enzymes and mitochondrial proteins.

CONCLUSION

Our novel findings are that the most pronounced impact of advanced aging on the diaphragm is loss of peak power and disrupted cysteine redox homeostasis in metabolic enzymes and mitochondrial proteins.

Redox homeostasis and age-related deficits in neuromuscular integrity and function

Skeletal muscle is a major site of metabolic activity and is the most abundant tissue in the human body. Age-related muscle atrophy (sarcopenia) and weakness, characterized by progressive loss of lean muscle mass and function, is a major contributor to morbidity and has a profound effect on the quality of life of older people. With a continuously growing older population (estimated 2 billion of people aged >60 by 2050), demand for medical and social care due to functional deficits, associated with neuromuscular ageing, will inevitably increase. Despite the importance of this 'epidemic' problem, the primary biochemical and molecular mechanisms underlying age-related deficits in neuromuscular integrity and function have not been fully determined. Skeletal muscle generates reactive oxygen and nitrogen species (RONS) from a variety of subcellular sources, and age-associated oxidative damage has been suggested to be a major factor contributing to the initiation and progression of muscle atrophy inherent with ageing. RONS can modulate a variety of intracellular signal transduction processes, and disruption of these events over time due to altered redox control has been proposed as an underlying mechanism of ageing. The role of oxidants in ageing has been extensively examined in different model organisms that have undergone genetic manipulations with inconsistent findings. Transgenic and knockout rodent studies have provided insight into the function of RONS regulatory systems in neuromuscular ageing. This review summarizes almost 30 years of research in the field of redox homeostasis and muscle ageing, providing a detailed discussion of the experimental approaches that have been undertaken in murine models to examine the role of redox regulation in age-related muscle atrophy and weakness.

Detection of ROS Induced Proteomic Signatures by Mass Spectrometry

Reversible and irreversible post-translational modifications (PTMs) induced by endogenously generated reactive oxygen species (ROS) in regulatory enzymes and proteins plays an essential role in cellular signaling. Almost all cellular processes including metabolism, transcription, translation and degradation have been identified as containing redox regulated proteins. Specific redox modifications of key amino acids generated by ROS offers a dynamic and versatile means to rapidly alter the activity or functional structure of proteins in response to biochemical, environmental, genetic and pathological perturbations. How the proteome responds to these stimuli is of critical importance in oxidant physiology, as it can regulate the cell stress response by reversible and irreversible PTMs, affecting protein activity and protein-protein interactions. Due to the highly labile nature of many ROS species, applying redox proteomics can provide a signature footprint of the ROS species generated. Ideally redox proteomic approaches would allow; (1) the identification of the specific PTM, (2) identification of the amino acid residue that is modified and (3) the percentage of the protein containing the PTM. New developments in MS offer the opportunity of a more sensitive targeted proteomic approach and retrospective data analysis. Subsequent bioinformatics analysis can provide an insight into the biochemical and physiological pathways or cell signaling cascades that are affected by ROS generation. This mini-review will detail current redox proteomic approaches to identify and quantify ROS induced PTMs and the subsequent effects on cellular signaling.

Restless legs syndrome in patients with chronic venous disorders: an untold story

Objectives: To prospectively study the profile of restless leg syndrome (RLS) in patients presenting to a phlebology practice.

Methods: The study uses prospective questionnaire and clinical observation study. In all, 174 consecutive patients and 174 matched controls were evaluated in detail. The diagnosis of restless legs syndrome (RLS) was established by the International RLS study group (IRLSSG) criteria. Detailed clinical, systemic and Duplex ultrasound evaluations were done to establish the presence of chronic venous disorders (CVD) (reflux > 0.5s on augmentation manoeuvers and revised clinical, aetiological, anatomical and pathological [CEAP] criteria).

Results: Of the 174 consecutive subjects studied (22M: 152F), 63 (36%) had evidence of RLS compared with only 34 of 174 of the controls (19%, P <0.05). Sixty-two (98%) of these RLS-positive study subjects were subsequently diagnosed with CVD. In comparison, 31 (91%) of the RLS-positive control subjects ( n = 34) were found to have CVD. This prevalence of CVD was comparable with RLS-positive study subjects, but was significantly higher than the prevalence in CVD in RLS-negative controls ( P <0.01). Only three (9%) of the controls had RLS without CVD. RLS-positive subjects were typically women above the age of 40 years ( P <0.01 vs. men, P <0.01 vs. below 40 years). A significant difference in clinical presentation in the study subjects was the high prevalence of leg cramps in the RLS-positive subjects ( P <0.01). None of the patients with RLS in this series gave history of anaemia, chronic renal failure or an established psychiatric or neurological disease as found pathognomic for RLS by others.

Conclusions: RLS appears to be a common overlapping clinical syndrome in patients with CVD. Prospective blinded therapeutic trials are planned to study the influence of definitive treatments for CVD on sequential RLS scores.

Clinical spectrum of recurrent postoperative varicose veins and efficacy of sclerotherapy management using the compass technique

Objectives: Tostudy the clinical spectrum of recurrent varices after surgery (REVAS) and the efficacy of sclerotherapy under the comprehensive objective mapping, precise image-guided injection, antireflux positioning and sequential sclerotherapy (COMPASS) technique in their management.

Methods: Design: prospective open study with 1.5-5.7-year follow up. Patients: 253 legs of 168 consecutive patients who had received previous surgery for primary varicosity.

Main outcome measures: obliteration, recanalization, residual reflux, neovascularization, venous dysfunction score and cumulative obliteration.

Results: REVAS presents as a symptomatic chronic venous disease of women in their fifties, a decade later than primary varicosities are reported. Almost 75% of REVAS occurred at the groin, mostly with features of chronic venous disease. The COMPASS technique achieved sustained obliteration in 97% of the groin varices and in 100% of the thigh and isolated refluxes around the popliteal fossa. The cumulative obliteration rate was sustained at >90% and obliteration of perforator reflux was sustained. There was a significant decrease in the venous dysfunction score. In the mean 3.1±1.7 years of follow up, only 3% possible neovascularization was seen. There were no serious adverse experiences reported.

Conclusions: REVAS is a symptomatic chronic venous disease requiring skilled medical attention. The COMPASS technique appears to be more efficacious than the presently available surgical approaches to its long-term management.

Management of venous malformations in Klippel–Trenaunay syndrome with ultrasound-guided foam sclerotherapy

Objective: To study the clinical profile of Klippel–Trenaunay syndrome (KTS) and the management of venous malformations (VMs) with ultrasound-guided foam sclerotherapy using the compass technique.

Methods: In this open prospective series, 11 consecutive patients with KTS seeking therapy at a phlebology group practice were included. Seven (64%) of them were post-surgical recurrences.

Results: Pain was the commonest presenting complaint (100%), accompanied with VMs/ varicose veins in all except one (91%). Chronic venous insufficiency (CVI) was seen in seven (64%). Soft tissue and bone deformity was present in all (100%). Limb lengthening was frequent and detected in eight (73%), thickening in six (54%); unusually, one patient (9%) presented with severe thinning and shortening of the leg. Venous malformation was the primary vascular problem in nine patients (82%), with capillary malformation (CM)/port wine stain in seven (64%) and isolated lymphatic malformation (LM) in two (18%). The lateral embryonic/Klippel–Trenaunay (KT) vein was detected in 10 patients (91%). Deep vein deformity was not detected in any of them. All the deformities were of the lower limb (100%), while two (18%) had deformities of the thorax and one (9%) had gastrointestinal (GI) malformation. None of the patients gave family history of KTS, while five (45%) had history of varicosities in the family. Eight patients (73%) completed the therapeutic plan with a mean follow-up of 5±3.9 years. An excellent to good type result could be documented in six of the eight cases (75%). These patients had an event-free, good quality of life. Follow-up duplex studies revealed the evolving refluxing tracts requiring sequential therapies.

Conclusions: The results in this series demonstrate the utility of foam sclerotherapy using the compass technique in the management of KTS. Chronicity of the VMs in KTS necessitates strict clinical monitoring and sequential therapies.

Efficacy of the Comprehensive Objective Mapping, Precise Image Guided Injection, Anti-Reflux Positioning and Sequential Sclerotherapy (COMPASS) Technique in the Management of Greater Saphenous Varicosities with Saphenofemoral Incompetence

Objective:

To evaluate the efficacy of the COMPASS technique in the management of greater saphenous varicosities with saphenofemoral incompetence.

Design:

Prospective open trial (2-6 year follow-up).

Patients:

One hundred and eighty-six limbs with refluxing greater saphenous vein (5.4–25.4 mm) and incompetent saphenofemoral junction (6.1–31.3 mm).

Main outcome measure:

Obliteration, recanalisation, residual veins, neovascularisation, venous dysfunction score.

Results:

Greater saphenous varicosity is commonly a disease of individuals in their forties, with morbid clinical presentations. Three stages of the COMPASS technique achieved 100% and 98% obliteration of the saphenofemoral junction and greater saphenous vein respectively. There was significant improvement in the venous dysfunction score. Residual refluxing veins were easily managed by sequential treatment. The results are sustained in the 3.4 SD 1.7 year follow up. There was no serious adverse experience reported.

Conclusion:

The COMPASS technique is safe and highly efficacious in the management of extensive large vein varicose disease.

Ageing in relation to skeletal muscle dysfunction: redox homoeostasis to regulation of gene expression

Ageing is associated with a progressive loss of skeletal muscle mass, quality and function—sarcopenia, associated with reduced independence and quality of life in older generations. A better understanding of the mechanisms, both genetic and epigenetic, underlying this process would help develop therapeutic interventions to prevent, slow down or reverse muscle wasting associated with ageing. Currently, exercise is the only known effective intervention to delay the progression of sarcopenia. The cellular responses that occur in muscle fibres following exercise provide valuable clues to the molecular mechanisms regulating muscle homoeostasis and potentially the progression of sarcopenia. Redox signalling, as a result of endogenous generation of ROS/RNS in response to muscle contractions, has been identified as a crucial regulator for the adaptive responses to exercise, highlighting the redox environment as a potentially core therapeutic approach to maintain muscle homoeostasis during ageing. Further novel and attractive candidates include the manipulation of microRNA expression. MicroRNAs are potent gene regulators involved in the control of healthy and disease-associated biological processes and their therapeutic potential has been researched in the context of various disorders, including ageing-associated muscle wasting. Finally, we discuss the impact of the circadian clock on the regulation of gene expression in skeletal muscle and whether disruption of the peripheral muscle clock affects sarcopenia and altered responses to exercise. Interventions that include modifying altered redox signalling with age and incorporating genetic mechanisms such as circadian- and microRNA-based gene regulation, may offer potential effective treatments against age-associated sarcopenia.

Ageing-induced changes in the redox status of peripheral motor nerves imply an effect on redox signalling rather than oxidative damage

Ageing is associated with loss of skeletal muscle fibres, atrophy of the remaining fibres and weakness. These changes in muscle are accompanied by disruption of motor neurons and neuromuscular junctions although the direct relationship between the nerve and muscle degeneration is not understood. Oxidative changes have been implicated in the mechanisms leading to age-related loss of muscle mass and in degeneration of the central nervous system, but little is known about age-related changes in oxidation in specific peripheral nerves that supply muscles that are affected by ageing. We have therefore examined the sciatic nerve of old mice at an age when loss of tibialis anterior muscle mass and function is apparent. Sciatic nerve from old mice did not show a gross increase in oxidative damage, but electron paramagnetic resonance (EPR) studies indicated an increase in the activity of superoxide and/or peroxynitrite in the nerves of old mice at rest that was further exacerbated by electrical stimulation of the nerve to activate muscle contractions. Proteomic analyses indicated that specific redox-sensitive proteins are increased in content in the nerves of old mice that may reflect an adaptation to regulate the increased superoxide/peroxynitrite and maintain redox homoeostasis. Analysis of redox active cysteines showed some increase in reversible oxidation in specific proteins in nerves of old mice, but this was not universally seen across all redox-active cysteines. Detailed analysis of the redox-active cysteine in one protein in the nerve of old mice that is key to redox signalling (Peroxiredoxin 6, Cys 47) showed a minor increase in reversible oxidation that would be compatible with a change in its redox signalling function. In conclusion, the data presented indicate that sciatic nerve from old mice does not show a gross increase in oxidative damage similar to that seen in the TA and other muscles that it innervates. Our results indicate an adaptation to increased oxidation with minor changes in the oxidation of key cysteines that may contribute to defective redox signalling in the nerve.

Glutathione Is the Resolving Thiol for Thioredoxin Peroxidase Activity of 1-Cys Peroxiredoxin Without Being Consumed During the Catalytic Cycle

AIMS

A three-step catalytic cycle is common to all peroxiredoxins (Prxs), despite structural and kinetic differences. The second step in 1-Cys type Prxs is a matter of debate since they lack an additional cysteine to play the resolving role, as happens with the 2-Cys Prxs. The aim of this study was to elucidate the role of glutathione (GSH) in the thioredoxin-dependent peroxidase activity of Saccharomyces cerevisiae mitochondrial Prx1p, a 1-Cys type Prx.

RESULTS

The peroxidatic Cys91 residue of two Prx1p peptides can be linked by a disulfide, which can be reduced by thioredoxin and by GSH (Km=6.1 μM). GSH forms a mixed disulfide with the peroxidatic cysteine spontaneously in vitro and in vivo. Mitochondrial Trx3p deglutathionylates Prx1p without formation of GSSG so that GSH is not consumed in the process. The structural unit of native Prx1p is a dimer whose subunits are not covalently linked, but a hexameric assembly of three disulfide-bound dimers can also be formed.

INNOVATION

GSH is presented as a protective cofactor of Prx1p, which is not consumed during the peroxidase reaction, but provides a robust mechanism as the resolving cysteine and efficiently prevents Prx1p overoxidation. GSH exerts these roles at concentrations well below those commonly considered necessary for its antioxidant and redox buffering functions.

CONCLUSION

A 1-Cys peroxide scavenging mechanism operates in yeast mitochondria involving an autonomous glutathione molecule and the thioredoxin system, which could have universal validity. Prx1p is fairly well protected from overoxidation, questioning its role in a floodgate mechanism for H2O2 signaling.

Redox proteomic analysis of the gastrocnemius muscle from adult and old mice

The data provides information in support of the research article, "Differential Cysteine Labeling and Global Label-Free Proteomics Reveals an Altered Metabolic State in Skeletal Muscle Aging", Journal of Proteome Research, 2014, 13 (11), 2008-21 [1]. Raw data is available from ProteomeXchange [2] with identifier PDX001054. The proteome of gastrocnemius muscle from adult and old mice was analyzed by global label-free proteomics and the relative quantification of specific reduced and reversibly oxidized Cysteine (Cys) residues was performed using Skyline [3]. Briefly, reduced Cysteine (Cys) containing peptides was alkylated using N-ethylmalemide (d0-NEM). Samples were desalted and reversibly oxidized Cys residues were reduced using tris(2-carboxyethyl)phosphine (TCEP) and the newly formed reduced Cys residues were labeled with heavy NEM( d5-NEM). Label-free analysis of the global proteome of adult (n=5) and old (n=4) gastrocnemius muscles was performed using Peaks7™ mass spectrometry data analysis software [4]. Relative quantification of Cys containing peptides that were identified as reduced (d(0) NEM labeled) and reversibly oxidized d(5)-NEM labeled was performed using the intensity of their precursor ions in Skyline. Results indicate that muscles from old mice show reduced redox flexibility particularly in proteins involved in the generation of precursor metabolites and energy metabolism, indicating a loss in the flexibility of the redox energy response.

Differential cysteine labeling and global label-free proteomics reveals an altered metabolic state in skeletal muscle aging

The molecular mechanisms underlying skeletal muscle aging and associated sarcopenia have been linked to an altered oxidative status of redox-sensitive proteins. Reactive oxygen and reactive nitrogen species (ROS/RNS) generated by contracting skeletal muscle are necessary for optimal protein function, signaling, and adaptation. To investigate the redox proteome of aging gastrocnemius muscles from adult and old male mice, we developed a label-free quantitative proteomic approach that includes a differential cysteine labeling step. The approach allows simultaneous identification of up- and downregulated proteins between samples in addition to the identification and relative quantification of the reversible oxidation state of susceptible redox cysteine residues. Results from muscles of adult and old mice indicate significant changes in the content of chaperone, glucose metabolism, and cytoskeletal regulatory proteins, including Protein DJ-1, cAMP-dependent protein kinase type II, 78 kDa glucose regulated protein, and a reduction in the number of redox-responsive proteins identified in muscle of old mice. Results demonstrate skeletal muscle aging causes a reduction in redox-sensitive proteins involved in the generation of precursor metabolites and energy metabolism, indicating a loss in the flexibility of the redox energy response. Data is available via ProteomeXchange with identifier PXD001054.

Redox proteomics in study of kidney-associated hypertension: new insights to old diseases

SIGNIFICANCE

The kidney helps to maintain low blood pressure in the human body, and impaired kidney function is a common attribute of aging that is often associated with high blood pressure (hypertension). Kidney-related pathologies are important contributors (either directly or indirectly) to overall human mortality. In comparison with other organs, kidney has an unusually wide range of oxidative status, ranging from the well-perfused cortex to near-anoxic medulla.

RECENT ADVANCES

Oxidative stress has been implicated in many kidney pathologies, especially chronic kidney disease, and there is considerable research interest in oxidative stress biomarkers for earlier prediction of disease onset. Proteomics approaches have been taken to study of human kidney tissue, serum/plasma, urine, and animal models of hypertension.

CRITICAL ISSUES

Redox proteomics, in which oxidative post-translational modifications can be identified in protein targets of oxidative or nitrosative stress, has not been very extensively pursued in this set of pathologies.

FUTURE DIRECTIONS

Proteomics studies of kidney and related tissues have relevance to chronic kidney disease, and redox proteomics, in particular, represents an under-exploited toolkit for identification of novel biomarkers in this commonly occurring pathology.

Nitrogen starvation induces extensive changes in the redox proteome of Prochlorococcus sp. strain SS120

Very low nitrogen concentration is a critical limitation in the oligotrophic oceans inhabited by the cyanobacterium Prochlorococccus, one of the main primary producers on Earth. It is well known that nitrogen starvation affects redox homeostasis in cells. We have studied the effect of nitrogen starvation on the thiol redox proteome in the Prochlorococcus sp. SS120 strain, by using shotgun proteomic techniques to map the cysteine modified in each case and to quantify the ratio of reversibly oxidized/reduced species. We identified a number of proteins showing modified cysteines only under either control or N-starvation, including isocitrate dehydrogenase and ribulose phosphate 3-epimerase. We detected other key enzymes, such as glutamine synthetase, transporters and transaminases, showing that nitrogen-related pathways were deeply affected by nitrogen starvation. Reversibly oxidized cysteines were also detected in proteins of other important metabolic pathways, such as photosynthesis, phosphorus metabolism, ATP synthesis and nucleic acids metabolism. Our results demonstrate a wide effect of nitrogen limitation on the redox status of the Prochlorococcus proteome, suggesting that besides previously reported transcriptional changes, this cyanobacterium responds with post-translational redox changes to the lack of nitrogen in its environment.

Diagonal electrophoresis for the detection of protein disulfides

Cysteines are one of the most rarely used amino acids in proteins, therefore when conserved in proteins they usually play critical roles in structure, function, or regulation of the protein. These cysteines or thiols can be reversibly oxidised to sulfenic acid (-SOH), thiyl radicals (-S) or nitrosothiols (-SNO) or form both inter-and intra-disulfide bridges (PSSP). The protein thiol groups PSSPs, represent a larger active redox pool than glutathione and are likely to be directly involved in cellular defence against oxidative stress. Diagonal electrophoresis is a relatively simple technique to analyze the formation of protein disulfides by sequential non-reducing/reducing electrophoresis. Proteins that do not form disulfides, electrophorese identically in both dimensions and form a diagonal after the second dimension, proteins that contained intra-chain disulfides lie above this diagonal, while those that formed inter-disulfides fall below the diagonal. This technique therefore allows for the detection and identification of protein disulfides.

Biosynthetic and iron metabolism is regulated by thiol proteome changes dependent on glutaredoxin-2 and mitochondrial peroxiredoxin-1 in Saccharomyces cerevisiae

Redoxins are involved in maintenance of thiol redox homeostasis, but their exact sites of action are only partly known. We have applied a combined redox proteomics and transcriptomics experimental strategy to discover specific functions of two interacting redoxins: dually localized glutaredoxin 2 (Grx2p) and mitochondrial peroxiredoxin 1 (Prx1p). We have identified 139 proteins showing differential postranslational thiol redox modifications when the cells do not express Grx2p, Prx1p, or both and have mapped the precise cysteines involved in each case. Some of these modifications constitute functional switches that affect metabolic and signaling pathways as the primary effect, leading to gene transcription remodeling as the secondary adaptive effect as demonstrated by a parallel high throughput gene expression analysis. The results suggest that in the absence of Grx2p, the metabolic flow toward nucleotide and aromatic amino acid biosynthesis is slowed down by redox modification of the key enzymes Rpe1p (D-ribulose-5-phosphate 3-epimerase), Tkl1p (transketolase) and Aro4p (3-deoxy-D-arabino-heptulosonate-7-phosphate synthase). The glycolytic mainstream is then diverted toward carbohydrate storage by induction of trehalose and glycogen biosynthesis genes. Porphyrin biosynthesis may also be compromised by inactivation of the redox-sensitive cytosolic enzymes Hem12p (uroporphyrinogen decarboxylase) and Sam1p (S-adenosyl methionine synthetase) and a battery of respiratory genes sensitive to low heme levels are induced. Genes of the Aft1p-dependent iron regulon were induced specifically in the absence of Prx1p despite optimal mitochondrial Fe-S biogenesis, suggesting dysfunction of the mitochondria to the cytosol signaling pathway. Strikingly, requirement of Grx2p for these events places dithiolic Grx2 in the framework of iron metabolism.

Proteomics in investigation of protein nitration in kidney disease: technical challenges and perspectives from the spontaneously hypertensive rat

Kidneys are the mammalian organs with widest range of oxidative status ranging from the well-perfused cortex to the relatively anoxic medulla. This organ is of key interest from the perspective of hypertension, an important contributor to human mortality, and there has been growing use of the spontaneously hypertensive rat (SHR) as a model to explore oxidative stress in hypertensive kidney. Nitrosative stress is often associated with oxidative stress and, like oxidative stress, can lead to covalent modification of protein side-chains. It is especially relevant to kidney because of high levels of both nitrite/nitrate and nitric oxide synthase in medulla. Because of their relatively low abundance and their well-known role in signal transduction, nitration of tyrosines to 3-nitrotyrosines (3NT) is of particular interest in this regard. This modification has the potential to contribute to changes in regulation, in protein activity and may provide a means of specific targeting of key proteins. Mass spectrometry (MS) offers a promising route to detecting this modification. This review surveys protein nitration in kidney disease and highlights opportunities for MS detection of nitrated residues in the SHR.

Ubiquitination and carbonylation of proteins in the clam Ruditapes decussatus, exposed to nonylphenol using redox proteomics

Ubiquitination and carbonylation of proteins were investigated in the gill and digestive gland of Ruditapes decussatus exposed to NP (nonylphenol) (100 μgL(-1)) using redox proteomics. After 21 d of exposure, clams were dissected and cytosolic proteins of both tissues separated by 2DE SDS-PAGE. Protein expression profiles were tissue-dependent and differently affected by NP exposure. Ubiquitination and carbonylation were also tissue-specific. NP exposure induced significantly more ubiquitinated proteins in gills than in digestive glands, compared to controls. Digestive gland showed a significant higher number of carbonylated proteins than gills after NP exposure. Protein ubiquitination and carbonylation are therefore independent processes. Results showed that NP exposure generated ROS in gill and digestive gland of R. decussatus that significantly altered the proteome. Results also highlighted the advantage of using redox proteomics in the assessment of protein ubiquitination and carbonylation, which may be markers of oxidative stress in R. decussatus.

Glutaredoxin participates in the reduction of peroxides by the mitochondrial 1-CYS peroxiredoxin in Saccharomyces cerevisiae

The mechanism for regeneration of the active-site "peroxidatic" cysteine in 1-Cys peroxiredoxins is a matter of debate. Saccharomyces cerevisiae Prx1 is a mitochondrial enzyme belonging to the 1-Cys Prx, whereas Grx2 is involved in antioxidant defense and localizes at the mitochondria, so we hypothesized that it could be a perfect candidate to resolve the sulfenate in Prx1 with GSH. In vitro experiments with purified Prx1p and Grx2p demonstrate that Grx2p, at concentrations <1 microM, coupled to GSH, is a very efficient thiolic intermediary for the reduction of the peroxidatic Cys in Prx1p. Prx1p forms oligomeric aggregates natively, but depolymerizes down to a dimeric state after treatment with GSH. The catalytic cycle involves glutathionylation of dimeric Prx1p and deglutathionylation by Grx2p. Dihydrolipoamide, a genuine mitochondrial dithiol, can efficiently substitute for GSH. The activity is highest at alkaline pH, consistent with the conditions of active respiring mitochondria, and the process is highly specific for 1-Cys Prx because Grx2p is totally inactive with human PRX1, a typical 2-Cys Prx, as opposed to the promiscuity of Trx. Our results suggest that although Trx is the reductant involved in the reduction of peroxides by 2-Cys-Prx, Grx might be the natural resolving partner of 1-Cys Prx through a monothiolic mechanism.

Structure and function of yeast glutaredoxin 2 depend on postranslational processing and are related to subcellular distribution

We have previously shown that glutaredoxin 2 (Grx2) from Saccharomyces cerevisiae localizes at 3 different subcellular compartments, cytosol, mitochondrial matrix and outer membrane, as the result of different postranslational processing of one single gene. Having set the mechanism responsible for this remarkable phenomenon, we have now aimed at defining whether this diversity of subcellular localizations correlates with differences in structure and function of the Grx2 isoforms. We have determined the N-terminal sequence of the soluble mitochondrial matrix Grx2 by mass spectrometry and have determined the exact cleavage site by Mitochondrial Processing Peptidase (MPP). As a consequence of this cleavage, the mitochondrial matrix Grx2 isoform possesses a basic tetrapeptide extension at the N-terminus compared to the cytosolic form. A functional relationship to this structural difference is that mitochondrial Grx2 displays a markedly higher activity in the catalysis of GSSG reduction by the mitochondrial dithiol dihydrolipoamide. We have prepared Grx2 mutants affected on key residues inside the presequence to direct the protein to one single cellular compartment; either the cytosol, the mitochondrial membrane or the matrix and have analyzed their functional phenotypes. Strains expressing Grx2 only in the cytosol are equally sensitive to H(2)O(2) as strains lacking the gene, whereas those expressing Grx2 exclusively in the mitochondrial matrix are more resistant. Mutations on key basic residues drastically affect the cellular fate of the protein, showing that evolutionary diversification of Grx2 structural and functional properties are strictly dependent on the sequence of the targeting signal peptide.