Proteomic analysis and protein carbonylation profile in trained and untrained rat muscles

Oxime blot: A novel method for reliable and sensitive detection of carbonylated proteins in diverse biological systems

Oxidative stress and oxidative protein damage occur in various biological processes and diseases. The carbonyl group on amino acid side chains is the most widely used protein oxidation biomarker. Carbonyl groups are commonly detected indirectly through their reaction with 2,4-dinitrophenylhydrazine (DNPH) and subsequent labeling with an anti-DNP antibody. However, the DNPH immunoblotting method lacks protocol standardization, exhibits technical bias, and has low reliability. To overcome these shortcomings, we have developed a new blotting method in which the carbonyl group reacts with the biotin-aminooxy probe to form a chemically stable oxime bond. The reaction speed and the extent of the carbonyl group derivatization are increased by adding a p-phenylenediamine (pPDA) catalyst under neutral pH conditions. These improvements are crucial since they ensure that the carbonyl derivatization reaction reaches a plateau within hours and increases the sensitivity and robustness of protein carbonyl detection. Furthermore, derivatization under pH-neutral conditions facilitates a good SDS-PAGE protein migration pattern, avoids protein loss by acidic precipitation, and is directly compatible with protein immunoprecipitation. This work describes the new Oxime blot method and demonstrates its use in detecting protein carbonylation in complex matrices from diverse biological samples.

Proteomic Signatures of Lifestyle Risk Factors for Cardiovascular Disease: A Cross-Sectional Analysis of the Plasma Proteome in the Framingham Heart Study

Background Proteomic biomarkers related to cardiovascular disease risk factors may offer insights into the pathogenesis of cardiovascular disease. We investigated whether modifiable lifestyle risk factors for cardiovascular disease are associated with distinctive proteomic signatures. Methods and Results We analyzed 1305 circulating plasma proteomic biomarkers (assayed using the SomaLogic platform) in 897 FHS (Framingham Heart Study) Generation 3 participants (mean age 46±8 years; 56% women; discovery sample) and 1121 FOS (Framingham Offspring Study) participants (mean age 52 years; 54% women; validation sample). Participants were free of hypertension, diabetes mellitus, and clinical cardiovascular disease. We used linear mixed effects models (adjusting for age, sex, body mass index, and family structure) to relate levels of each inverse-log transformed protein to 3 lifestyle factors (ie, smoking, alcohol consumption, and physical activity). A Bonferroni-adjusted P value indicated statistical significance (based on number of proteins and traits tested, P<4.2×10-6 in the discovery sample; P<6.85×10-4 in the validation sample). We observed statistically significant associations of 60 proteins with smoking (37/40 top proteins validated in FOS), 30 proteins with alcohol consumption (23/30 proteins validated), and 5 proteins with physical activity (2/3 proteins associated with the physical activity index validated). We assessed the associations of protein concentrations with previously identified genetic variants (protein quantitative trait loci) linked to lifestyle-related disease traits in the genome-wide-association study catalogue. The protein quantitative trait loci were associated with coronary artery disease, inflammation, and age-related mortality. Conclusions Our cross-sectional study from a community-based sample elucidated distinctive sets of proteins associated with 3 key lifestyle factors.

Characterization of Contractile Proteins from Skeletal Muscle Using Gel-Based Top-Down Proteomics

The mass spectrometric analysis of skeletal muscle proteins has used both peptide-centric and protein-focused approaches. The term 'top-down proteomics' is often used in relation to studying purified proteoforms and their post-translational modifications. Two-dimensional gel electrophoresis, in combination with peptide generation for the identification and characterization of intact proteoforms being present in two-dimensional spots, plays a critical role in specific applications of top-down proteomics. A decisive bioanalytical advantage of gel-based and top-down approaches is the initial bioanalytical focus on intact proteins, which usually enables the swift identification and detailed characterisation of specific proteoforms. In this review, we describe the usage of two-dimensional gel electrophoretic top-down proteomics and related approaches for the systematic analysis of key components of the contractile apparatus, with a special focus on myosin heavy and light chains and their associated regulatory proteins. The detailed biochemical analysis of proteins belonging to the thick and thin skeletal muscle filaments has decisively improved our biochemical understanding of structure-function relationships within the contractile apparatus. Gel-based and top-down proteomics has clearly established a variety of slow and fast isoforms of myosin, troponin and tropomyosin as excellent markers of fibre type specification and dynamic muscle transition processes.

Regular aerobic exercise-ameliorated troponin I carbonylation to mitigate aged rat soleus muscle functional recession

NEW FINDINGS

What is the central question of this study? What is the biological role of carbonylation in muscle age-related functional decline and how might exercise affect the carbonylation process differently compared to habitual sedentary behaviour? What is the main finding and its importance? The carbonylation of troponin I (TNNI1), tropomyosin α-1 chain and α-actinin-1 demonstrated a relationship with muscle age-related functional decline. Exercise attenuated the decline by slowing the rate of carbonylation and promoting antioxidant reactions within the muscle. As exercise demonstrated the greatest effect on TNNI1, quantification of protein carbonyls in TNNI1 may be used as a potential biomarker of muscle age-related functional decline.

ABSTRACT

This study investigated the biological role of carbonylation in muscle age-related functional decline and how regular aerobic exercise may affect the carbonylation process differently from habitual sedentary behaviour. Twenty-four healthy male Sprague-Dawley (SD) rats (mean age: 23 months) were randomly divided into an old-aged sedentary control group (O-SED) and an old-aged aerobic exercise group (O-EX). The O-EX group participated in regular aerobic exercise - treadmill running - with exercise intensity increased gradually from 50-55% to 65-70% of maximum oxygen consumption ( V ̇ O 2 max ) over 10 weeks. Rats' body weight, exercise behaviour index, morphology and oxidative stress were monitored. Avidin magnetic beads and electrospray ionization quadrupole time-of-flight mass spectrometry were used for gathering and separating carbonylated proteins while western blot tested for molecular targets. O-SED and O-EX rats both had 19 oxidative modification sites for protein carbonylation. In the O-SED group, 16 specific carbonylated proteins were identified, while 16 additional specific species were also found in the O-EX group, with all 28 species demonstrating oxidative modifications. The carbonylated proteins included troponin I (TNNI1; slow skeletal muscle), tropomyosin α1 and α-actinin 1. In particular, TNNI1 carbonylation modifications were found only in sedentary rats. Aerobic exercise increased TNNI1 and Ca²⁺ /calmodulin-dependent protein kinase IIα expression significantly. Observations suggested that quantification of TNNI1 carbonylation may be a potential biomarker of muscle age-related functional decline. Importantly, regular aerobic exercise appeared to have antioxidant effects in the muscle that reduced TNNI1 slow carbonylation and promoted Ca²⁺ /calmodulin-dependent protein kinase IIα (CAMK2) and TNNI1 expression for skeletal muscle contraction regulation, thus attenuating possible age-related skeletal muscle functional decline.

Irreversible plasma and muscle protein oxidation and physical exercise

The imbalance between the reactive oxygen (ROS) and nitrogen (RNS) species production and their handling by the antioxidant machinery (low molecular weight antioxidant molecules and antioxidant enzymes), also known as oxidative stress, is a condition caused by physiological and pathological processes. Moreover, oxidative stress may be due to an overproduction of free radicals during physical exercise. Excess of radical species leads to the modification of molecules, such as proteins - the most susceptible to oxidative modification - lipids and DNA. With regard to the oxidation of proteins, carbonylation is an oxidative modification that has been widely described. Several studies have detected changes in the total amount of protein carbonyls following different types of physical exercise, but only few of these identified the specific amino acidic residues targets of such oxidation. In this respect, proteomic approaches allow to identify the proteins susceptible to carbonylation and in many cases, it is also possible to identify the specific protein carbonylation sites. This review focuses on the role of protein oxidation, and specifically carbonyl formation, for plasma and skeletal muscle proteins, following different types of physical exercise performed at different intensities. Furthermore, we focused on the proteomic strategies used to identify the specific protein targets of carbonylation. Overall, our analysis suggests that regular physical activity promotes a protection against protein carbonylation, due to the activation of the antioxidant defence or of the turnover of protein carbonyls. However, we can conclude that from the comprehensive bibliography analysed, there is no clearly defined specific physiological role about this post-translational modification of proteins.

Proteome analysis in dystrophic mdx mouse muscle reveals a drastic alteration of key metabolic and contractile proteins after chronic exercise and the potential modulation by anti-oxidant compounds

Weakness and fatigability are typical features of Duchenne muscular dystrophy patients and are aggravated in dystrophic mdx mice by chronic treadmill exercise. In the present study, we describe, the pattern of differentially abundant spots that is associated to the worsening of dystrophy phenotype induced by chronic exercise. Our proteomic analysis pointed out 34 protein spots with different abundance between sedentary and exercised mdx mice. These proteins belong mostly to glucose metabolism, energy production and sarcomere structure categories. Interestingly exercise induced an increase of typical fast twitch fiber proteins (Troponin T fast skeletal muscle, Troponin I fast skeletal muscle and Myozenin-1) combined with an increase of several glycolytic enzymes. Concerning energy transfer, Adenylate kinase, showed a marked decrease when compared with non-exercised mdx. The decline of this enzyme correlates with increased Creatin kinase enzyme, suggesting that a compensatory energy metabolism mechanism could be activated in mdx mouse skeletal muscle following exercise. In addition, we analysed muscles from exercised mdx mice treated with two natural anti-oxidant compounds, apocynin and taurine, that in our previous study, were proved to be beneficial on some pathology related parameters, and we showed that these compounds can counteract exercise-induced changes in the abundance of several proteins.

SIGNIFICANCE

Mdx mouse model of Duchenne muscular dystrophy shows a phenotype of the disorder milder than in human sufferers. This phenotype can be worsened by a different protocols of chronic exercise. These protocols can mimic the muscle progressive damage observed in humans, can allow studying the effects of inadequate training on dystrophic muscles and have been largely used to assess the ability of a drug to reduce the damage induced by exercise. In this study, we describe for the first time, the pattern of protein variation associated with the worsening of dystrophy phenotype induced by chronic exercise. Our proteomic analysis pointed out 34 protein spots with different amount between sedentary and exercised mdx mice. These proteins belong mostly to glucose metabolism, energy production and sarcomere structure categories and their variation indicates that mdx exercised muscle are not able to carry out the metabolic changes associated to fast-to-slow transition typically observed in aerobically trained muscle.

Global Proteome Changes in the Rat Diaphragm Induced by Endurance Exercise Training

Mechanical ventilation (MV) is a life-saving intervention for many critically ill patients. Unfortunately, prolonged MV results in the rapid development of diaphragmatic atrophy and weakness. Importantly, endurance exercise training results in a diaphragmatic phenotype that is protected against ventilator-induced diaphragmatic atrophy and weakness. The mechanisms responsible for this exercise-induced protection against ventilator-induced diaphragmatic atrophy remain unknown. Therefore, to investigate exercise-induced changes in diaphragm muscle proteins, we compared the diaphragmatic proteome from sedentary and exercise-trained rats. Specifically, using label-free liquid chromatography-mass spectrometry, we performed a proteomics analysis of both soluble proteins and mitochondrial proteins isolated from diaphragm muscle. The total number of diaphragm proteins profiled in the soluble protein fraction and mitochondrial protein fraction were 813 and 732, respectively. Endurance exercise training significantly (P<0.05, FDR <10%) altered the abundance of 70 proteins in the soluble diaphragm proteome and 25 proteins of the mitochondrial proteome. In particular, key cytoprotective proteins that increased in relative abundance following exercise training included mitochondrial fission process 1 (Mtfp1; MTP18), 3-mercaptopyruvate sulfurtransferase (3MPST), microsomal glutathione S-transferase 3 (Mgst3; GST-III), and heat shock protein 70 kDa protein 1A/1B (HSP70). While these proteins are known to be cytoprotective in several cell types, the cyto-protective roles of these proteins have yet to be fully elucidated in diaphragm muscle fibers. Based upon these important findings, future experiments can now determine which of these diaphragmatic proteins are sufficient and/or required to promote exercise-induced protection against inactivity-induced muscle atrophy.

Redox proteomic identification of carbonylated proteins in autism plasma: insight into oxidative stress and its related biomarkers in autism

BACKGROUND

Autism is a severe childhood neurological disorder with poorly understood etiology and pathology. Currently, there is no authentic laboratory test to confirm the diagnosis of autism. Oxidative damage may play a central role in the pathogenesis of autism. Present study is an effort to search for possible biomarkers of autism and further clarify the molecular changes associated with oxidative stress that occurs in the plasma of autistic children.

METHODS

We performed redox proteomics analysis to compare carbonylated proteins in the plasma of autistic subjects and healthy controls. Immunoprecipitation and Western blot analysis were used to validate carbonylated proteins identified by the redox proteomics.

RESULTS

Protein carbonylation levels in two proteins, complement component C8 alpha chain and Ig kappa chain C were found to be significantly increased in autistic patients compared with controls. These two proteins were successfully validated via immunoprecipitation and Western blot analysis.

CONCLUSIONS

The results further highlight the role of oxidative stress in the pathogenesis of autism and provide some information for the diagnosis and/or monitoring of autism.

Uncovering the exercise-related proteome signature in skeletal muscle

Exercise training has been recommended as a nonpharmacological strategy for the prevention and attenuation of skeletal muscle atrophy in distinct pathophysiological conditions. Despite the well-established phenotypic alterations, the molecular mechanisms underlying exercise-induced skeletal muscle remodeling are poorly characterized. Proteomics based on mass spectrometry have been successfully applied for the characterization of skeletal muscle proteome, representing a pivotal approach for the wide characterization of the molecular networks that lead to skeletal muscle remodeling. Nevertheless, few studies were performed to characterize the exercise-induced proteome remodeling of skeletal muscle, with only six research papers focused on the cross-talk between exercise and pathophysiological conditions. In order to add new insights on the impact of distinct exercise programs on skeletal muscle proteome, molecular network analysis was performed with bioinformatics tools. This analysis highlighted an exercise-related proteome signature characterized by the up-regulation of the capacity for ATP generation, oxygen delivery, antioxidant capacity and regulation of mitochondrial protein synthesis. Chronic endurance training up-regulates the tricarboxylic acid cycle and oxidative phosphorylation system, whereas the release of calcium ion into cytosol and amino acid metabolism are the biological processes up-regulated by a single bout of exercise. Other issues as exercise intensity, load, mode and regimen as well as muscle type also influence the exercise-induced proteome signature. The comprehensive analysis of the molecular networks modulated by exercise training in health and disease, taking in consideration all these variables, might not only support the therapeutic effect of exercise but also highlight novel targets for the development of enhanced pharmacological strategies.

Profiling Carbonylated Proteins in Heart and Skeletal Muscle Mitochondria from Trained and Untrained Mice

Understanding the relationship between physical exercise, reactive oxygen species, and skeletal muscle modification is important in order to better identify the benefits or the damages that appropriate or inappropriate exercise can induce. Heart and skeletal muscles have a high density of mitochondria with robust energetic demands, and mitochondria plasticity has an important role in both the cardiovascular system and skeletal muscle responses. The aim of this study was to investigate the influence of regular physical activity on the oxidation profiles of mitochondrial proteins from heart and tibialis anterior muscles. To this end, we used the mouse as animal model. Mice were divided into two groups: untrained and regularly trained. The carbonylated protein pattern was studied by two-dimensional gel electrophoresis followed by Western blot with anti-dinitrophenyl hydrazone antibodies. Mass spectrometry analysis allowed the identification of several different protein oxidation sites, including methionine, cysteine, proline, and leucine residues. A large number of oxidized proteins were found in both untrained and trained animals. Moreover, mitochondria from skeletal muscles and heart showed almost the same carbonylation pattern. Interestingly, exercise training seems to increase the carbonylation level mainly of mitochondrial proteins from skeletal muscle.

Comparative Skeletal Muscle Proteomics Using Two-Dimensional Gel Electrophoresis

The pioneering work by Patrick H. O’Farrell established two-dimensional gel electrophoresis as one of the most important high-resolution protein separation techniques of modern biochemistry (Journal of Biological Chemistry1975, 250, 4007–4021). The application of two-dimensional gel electrophoresis has played a key role in the systematic identification and detailed characterization of the protein constituents of skeletal muscles. Protein changes during myogenesis, muscle maturation, fibre type specification, physiological muscle adaptations and natural muscle aging were studied in depth by the original O’Farrell method or slightly modified gel electrophoretic techniques. Over the last 40 years, the combined usage of isoelectric focusing in the first dimension and sodium dodecyl sulfate polyacrylamide slab gel electrophoresis in the second dimension has been successfully employed in several hundred published studies on gel-based skeletal muscle biochemistry. This review focuses on normal and physiologically challenged skeletal muscle tissues and outlines key findings from mass spectrometry-based muscle proteomics, which was instrumental in the identification of several thousand individual protein isoforms following gel electrophoretic separation. These muscle-associated protein species belong to the diverse group of regulatory and contractile proteins of the acto-myosin apparatus that forms the sarcomere, cytoskeletal proteins, metabolic enzymes and transporters, signaling proteins, ion-handling proteins, molecular chaperones and extracellular matrix proteins.

The Effects of Acute and Chronic Exercise on Skeletal Muscle Proteome

Skeletal muscle plasticity and its adaptation to exercise is a topic that is widely discussed and investigated due to its primary role in the field of exercise performance and health promotion. Repetitive muscle contraction through exercise stimuli leads to improved cardiovascular output and the regulation of endothelial dysfunction and metabolic disorders such as insulin resistance and obesity. Considerable improvements in proteomic tools and data analysis have broth some new perspectives in the study of the molecular mechanisms underlying skeletal muscle adaptation in response to physical activity. In this sense, this review updates the main relevant studies concerning muscle proteome adaptation to acute and chronic exercise, from aerobic to resistance training, as well as the proteomic profile of natural inbred high running capacity animal models. Also, some promising prospects in the muscle secretome field are presented, in order to better understand the role of physical activity in the release of extracellular microvesicles and myokines activity. Thus, the present review aims to update the fast-growing exercise-proteomic scenario, leading to some new perspectives about the molecular events under skeletal muscle plasticity in response to physical activity. J. Cell. Physiol. 232: 257-269, 2017. © 2016 Wiley Periodicals, Inc.

Redox Proteomic Profiling of Specifically Carbonylated Proteins in the Serum of Triple Transgenic Alzheimer's Disease Mice

Oxidative stress is a key event in the onset and progression of neurodegenerative diseases, including Alzheimer’s disease (AD). To investigate the role of oxidative stress in AD and to search for potential biomarkers in peripheral blood, serums were collected in this study from the 3-, 6-, and 12-month-old triple transgenic AD mice (3×Tg-AD mice) and the age- and sex-matched non-transgenic (non-Tg) littermates. The serum oxidized proteins were quantified by slot-blot analysis and enzyme-linked immunosorbent assay (ELISA) to investigate the total levels of serum protein carbonyl groups. Western blotting, in conjunction with two-dimensional gel electrophoresis (2D-Oxyblot), was employed to identify and quantify the specifically-carbonylated proteins in the serum of 3×Tg-AD mice. The results showed that the levels of serum protein carbonyls were increased in the three month old 3×Tg-AD mice compared with the non-Tg control mice, whereas no significant differences were observed in the six and 12 months old AD mice, suggesting that oxidative stress is an early event in AD progression. With the application of 2D-Oxyblot analysis, (immunoglobin) Ig gamma-2B chain C region (IGH-3), Ig lambda-2 chain C region (IGLC2), Ig kappa chain C region (IGKC), and Ig kappa chain V-V region HP R16.7 were identified as significantly oxidized proteins compared with the control. Among them IGH-3 and IGKC were validated via immunoprecipitation and Western blot analysis. Identification of oxidized proteins in the serums of 3×Tg-AD mice can not only reveal potential roles of those proteins in the pathogenesis of AD but also provide potential biomarkers of AD at the early stage.

Sumoylated α-skeletal muscle actin in the skeletal muscle of adult rats

Skeletal muscles are composed of two major muscle fiber types: slow-twitch oxidative fibers and fast-twitch glycolytic fibers. The proteins in these muscle fibers are known to differ in their expression, relative abundance, and post-translational modifications. In this study, we report a previously unreported post-translational modification of α-skeletal muscle actin in the skeletal muscles of adult male F344 rats in vivo. Using two-dimensional electrophoresis (2D-PAGE), we first examined the differences in the protein expression profiles between the soleus and plantaris muscles. We found higher intensity protein spots at approximately 60 kDa and pH 9 on 2D-PAGE for the soleus muscle compared with the plantaris muscle. These spots were identified as α-skeletal muscle actin by liquid chromatography-nanoelectrospray ionization-tandem mass spectrometry and western blot analyses. In addition, we found that the 60 kDa α-skeletal muscle actin is modified by small ubiquitin-like modifier (SUMO) 1, using 2D-PAGE and western blot analyses. Furthermore, we found that α-skeletal muscle actin with larger molecular weight was localized in the nuclear and cytosol of the skeletal muscle, but not in the myofibrillar fraction by the combination of subcellular fractionation and western blot analyses. These results suggest that α-skeletal muscle actin is modified by SUMO-1 in the skeletal muscles, localized in nuclear and cytosolic fractions, and the extent of this modification is much higher in the slow muscles than in the fast muscles. This is the first study to show the presence of SUMOylated actin in animal tissues.

Low intensity training of mdx mice reduces carbonylation and increases expression levels of proteins involved in energy metabolism and muscle contraction

High intensity training induces muscle damage in dystrophin-deficient mdx mice, an animal model for Duchenne muscular dystrophy. However, low intensity training (LIT) rescues the mdx phenotype and even reduces the level of protein carbonylation, a marker of oxidative damage. Until now, beneficial effects of LIT were mainly assessed at the physiological level. We investigated the effects of LIT at the molecular level on 8-week-old wild-type and mdx muscle using 2D Western blot and protein-protein interaction analysis. We found that the fast isoforms of troponin T and myosin binding protein C as well as glycogen phosphorylase were overcarbonylated and downregulated in mdx muscle. Some of the mitochondrial enzymes of the citric acid cycle were overcarbonylated, whereas some proteins of the respiratory chain were downregulated. Of functional importance, ATP synthase was only partially assembled, as revealed by Blue Native PAGE analysis. LIT decreased the carbonylation level and increased the expression of fast isoforms of troponin T and of myosin binding protein C, and glycogen phosphorylase. In addition, it increased the expression of aconitate hydratase and NADH dehydrogenase, and fully restored the ATP synthase complex. Our study demonstrates that the benefits of LIT are associated with lowered oxidative damage as revealed by carbonylation and higher expression of proteins involved in energy metabolism and muscle contraction. Potentially, these results will help to design therapies for DMD based on exercise mimicking drugs.

Basal and exercise induced label-free quantitative protein profiling of m. vastus lateralis in trained and untrained individuals

Morphological and metabolic adaptations of the human skeletal muscle to exercise are crucial to improve performance and prevent chronic diseases and metabolic disorders. In this study we investigated human skeletal muscle protein composition in endurance trained (ET) versus untrained individuals (UT) and its modulation by an acute bout of endurance exercise. Participants were recruited based on their VO2max and subjected to a bicycle exercise test. M. vastus lateralis biopsies were taken before and three hours after exercise. Muscle lysates were analyzed using off-gel LC-MS/MS. Relative protein abundances were compared between ET and UT at rest and after exercise. Comparing UT and ET, we identified 92 significantly changed proteins under resting conditions. Specifically, fiber-type-specific and proteins of the oxidative phosphorylation and tricarboxylic acid cycle were increased in ET. In response to acute exercise, 71 proteins in ET and 44 in UT were altered. Here, a decrease of proteins involved in energy metabolism accompanied with alterations of heat shock and proteasomal proteins could be observed. In summary, long-term endurance training increased the basal level of structural and mitochondrial proteins in skeletal muscle. In contrast, acute exercise resulted in a depletion of proteins related to substrate utilization, especially in trained athletes.

BIOLOGICAL SIGNIFICANCE

The investigation of the human skeletal muscle proteome in response to exercise may provide novel insights into the process of muscular plasticity. It is of importance in the development of exercise-based strategies in the prevention and therapy of many chronic inflammatory and degenerative diseases which are often accompanied by muscular deconditioning. Up to date, proteomic investigations of the human muscle proteome in adaptation to exercise are mainly focused on untrained individuals and often restricted to animal studies. In the present study we compare the protein composition in endurance trained athletes and untrained individuals in the resting muscle and its modulation in response to acute exercise. To our knowledge, we present the first comprehensive analysis of skeletal muscle proteome alterations in response to acute and long-term exercise intervention.

Protein carbonylation as a major hallmark of oxidative damage: update of analytical strategies

Protein carbonylation, one of the most harmful irreversible oxidative protein modifications, is considered as a major hallmark of oxidative stress-related disorders. Protein carbonyl measurements are often performed to assess the extent of oxidative stress in the context of cellular damage, aging and several age-related disorders. A wide variety of analytical techniques are available to detect and quantify protein-bound carbonyls generated by metal-catalyzed oxidation, lipid peroxidation or glycation/glycoxidation. Here we review current analytical approaches for protein carbonyl detection with a special focus on mass spectrometry-based techniques. The utility of several carbonyl-derivatization reagents, enrichment protocols and especially advanced mass spectrometry techniques are compared and discussed in detail. Furthermore, the mechanisms and biology of protein carbonylation are summarized based on recent high-throughput proteomics data.

Effect of IR laser on myoblasts: a proteomic study

Laser therapy is used in physical medicine and rehabilitation to accelerate muscle recovery and in sports medicine to prevent damages produced by metabolic disturbances and inflammatory reactions after heavy exercise. The aim of this research was to get insight into possible benefits deriving from the application of an advanced IR laser system to counteract deficits of muscle energy metabolism and stimulate the recovery of hypotrophic tissue. We studied the effect of IR laser treatment on proliferation, differentiation, cytoskeleton organization and global protein expression in C2C12 myoblasts. We found that laser treatment induced a decrease in the cell proliferation rate without affecting cell viability, while leading to cytoskeletal rearrangement and expression of the early differentiation marker MyoD. The differential proteome analysis revealed the up-regulation and/or modulation of many proteins known to be involved in cell cycle regulation, cytoskeleton organization and differentiation.

Potential role of oxidative protein modification in energy metabolism in exercise

Exercise leads to the production of reactive oxygen species (ROS) via several sources in the skeletal muscle. In particular, the mitochondrial electron transport chain in the muscle cells produces ROS along with an elevation in the oxygen consumption during exercise. Such ROS generated during exercise can cause oxidative modification of proteins and affect their functionality. Many evidences have been suggested that some muscle proteins, i.e., myofiber proteins, metabolic signaling proteins, and sarcoplasmic reticulum proteins can be a targets modified by ROS generated due to exercise. We detected the modification of carnitine palmitoyltransferase I (CPT I) by Nε-(hexanoyl)lysine (HEL), one of the lipid peroxides, in exercised muscles, while the antioxidant astaxanthin reduced this oxidative stress-induced modification. Exercise-induced ROS may diminish CPT I activity caused by HEL modification, leading to a partly limited lipid utilization in the mitochondria. This oxidative protein modification may be useful as a potential biomarker to examine the oxidative stress levels, antioxidant compounds, and their possible benefits in exercise.

Proteomic identification of biomarkers of skeletal muscle disorders

Disease-specific biomarkers play a central diagnostic and therapeutic role in muscle pathology. Serum levels of a variety of muscle-derived enzymes are routinely used for the detection of muscle damage in diagnostic procedures, as well as for the monitoring of physical training status in sports medicine. Over the last few years, the systematic application of mass spectrometry-based proteomics for studying skeletal muscle degeneration has greatly expanded the range of muscle biomarkers, including new fiber-associated proteins involved in muscle transformation, muscular atrophy, muscular dystrophy, motor neuron disease, inclusion body myositis, myotonia, hypoxia, diabetes, obesity and sarcopenia of old age. These mass spectrometric studies have clearly established skeletal muscle proteomics as a reliable method for the identification of novel indicators of neuromuscular diseases.

Proteomic and carbonylation profile analysis of rat skeletal muscles following acute swimming exercise

Previous studies by us and other groups characterized protein expression variation following long-term moderate training, whereas the effects of single bursts of exercise are less known. Making use of a proteomic approach, we investigated the effects of acute swimming exercise (ASE) on protein expression and carbonylation patterns in two hind limb muscles: the Extensor Digitorum Longus (EDL) and the Soleus, mostly composed of fast-twitch and slow-twitch fibres, respectively. Carbonylation is one of the most common oxidative modifications of proteins and a marker of oxidative stress. In fact, several studies suggest that physical activity and the consequent increase in oxygen consumption can lead to increase in reactive oxygen and nitrogen species (RONS) production, hence the interest in examining the impact of RONS on skeletal muscle proteins following ASE. Results indicate that protein expression is unaffected by ASE in both muscle types. Unexpectedly, the protein carbonylation level was reduced following ASE. In particular, the analysis found 31 and 5 spots, in Soleus and EDL muscles respectively, whose carbonylation is reduced after ASE. Lipid peroxidation levels in Soleus were markedly reduced as well. Most of the decarbonylated proteins are involved either in the regulation of muscle contractions or in the regulation of energy metabolism. A number of hypotheses may be advanced to account for such results, which will be addressed in future studies.

Serological muscle loss biomarkers: an overview of current concepts and future possibilities

BACKGROUND

The skeletal muscle mass is the largest organ in the healthy body, comprising 30-40 % of the body weight of an adult man. It confers protection from trauma, locomotion, ventilation, and it represents a "sink" in glucose metabolism and a reservoir of amino acids to other tissues such as the brain and blood cells. Naturally, loss of muscle has dire consequences for health as well as functionality. Muscle loss is a natural consequence of especially aging, inactivity, and their associated metabolic dysfunction, but it is strongly accelerated in critical illness such as organ failure, sepsis, or cancer. Whether this muscle loss is considered a primary or secondary condition, it is known that muscle loss is a symptom that predicts morbidity and mortality and one that is known to impact quality of life and independence. Therefore, monitoring of muscle mass is relevant in a number of pathologies as well as in clinical trials as measures of efficacy as well as safety.

METHODS AND RESULTS

Existing biomarkers of muscle mass or muscle loss have shown to be either too unreliable or too impractical in relation to the perceived clinical benefit to reach regular clinical research or use. We suggest serological neoepitope biomarkers as a possible technology to address some of these problems. Blood biomarkers of this kind have previously been shown to respond with high sensitivity and shorter time to minimum significant change than available biomarkers of muscle mass. We provide brief reviews of existing muscle mass or function biomarker technologies, muscle protein biology, and existing neoepitope biomarkers and proceed to present tentative recommendations on how to select and detect neoepitope biomarkers.

CONCLUSION

We suggest that serological peptide biomarkers whose tissue and pathology specificity are derived from post-translational modification of proteins in tissues of interest, presenting so-called neoepitopes, represents an exciting candidate technology to fill out an empty niche in biomarker technology.

Brain activation patterns at exhaustion in rats that differ in inherent exercise capacity

In order to further understand the genetic basis for variation in inherent (untrained) exercise capacity, we examined the brains of 32 male rats selectively bred for high or low running capacity (HCR and LCR, respectively). The aim was to characterize the activation patterns of brain regions potentially involved in differences in inherent running capacity between HCR and LCR. Using quantitative in situ hybridization techniques, we measured messenger ribonuclease (mRNA) levels of c-Fos, a marker of neuronal activation, in the brains of HCR and LCR rats after a single bout of acute treadmill running (7.5-15 minutes, 15° slope, 10 m/min) or after treadmill running to exhaustion (15-51 minutes, 15° slope, initial velocity 10 m/min). During verification of trait differences, HCR rats ran six times farther and three times longer prior to exhaustion than LCR rats. Running to exhaustion significantly increased c-Fos mRNA activation of several brain areas in HCR, but LCR failed to show significant elevations of c-Fos mRNA at exhaustion in the majority of areas examined compared to acutely run controls. Results from these studies suggest that there are differences in central c-Fos mRNA expression, and potential brain activation patterns, between HCR and LCR rats during treadmill running to exhaustion and these differences could be involved in the variation in inherent running capacity between lines.