A DIGE approach for the assessment of rat soleus muscle changes during unloading: effect of acetyl-L-carnitine supplementation

l-carnitine: Nutrition, pathology, and health benefits

Carnitine is a medically needful nutrient that contributes in the production of energy and the metabolism of fatty acids. Bioavailability is higher in vegetarians than in people who eat meat. Deficits in carnitine transporters occur as a result of genetic mutations or in combination with other illnesses such like hepatic or renal disease. Carnitine deficit can arise in diseases such endocrine maladies, cardiomyopathy, diabetes, malnutrition, aging, sepsis, and cirrhosis due to abnormalities in carnitine regulation. The exogenously provided molecule is obviously useful in people with primary carnitine deficits, which can be life-threatening, and also some secondary deficiencies, including such organic acidurias: by eradicating hypotonia, muscle weakness, motor skills, and wasting are all improved l-carnitine (LC) have reported to improve myocardial functionality and metabolism in ischemic heart disease patients, as well as athletic performance in individuals with angina pectoris. Furthermore, although some intriguing data indicates that LC could be useful in a variety of conditions, including carnitine deficiency caused by long-term total parenteral supplementation or chronic hemodialysis, hyperlipidemias, and the prevention of anthracyclines and valproate-induced toxicity, such findings must be viewed with caution.

Comparative 3-Sample 2D-DIGE Analysis of Skeletal Muscles

The skeletal muscle proteome consists of a large number of diverse protein species with a broad and dynamic concentration range. Since mature skeletal muscles are characterized by a distinctive combination of contractile cells with differing physiological and biochemical properties, it is essential to determine specific differences in the protein composition of fast, slow, and hybrid fibers. Fluorescence two-dimensional difference gel electrophoresis (2D-DIGE) is a powerful comparative tool to analyze fiber type-specific differences between predominantly fast contracting versus slower twitching muscles. In this chapter, the application of the 2D-DIGE method for the comparative analysis of different subtypes of skeletal muscles is outlined in detail. A standardized proteomic workflow is described, involving sample preparation, protein extraction, differential fluorescence labeling using a 3-CyDye system, first-dimension isoelectric focusing, second-dimension slab gel electrophoresis, 2D-DIGE image analysis, protein digestion, and mass spectrometry.

Proteomic profiling of carbonic anhydrase CA3 in skeletal muscle

INTRODUCTION

Carbonic anhydrase (CA) is a key enzyme that mediates the reversible hydration of carbon dioxide. Skeletal muscles contain high levels of the cytosolic isoform CA3. This enzyme has antioxidative function and plays a crucial role in the maintenance of intracellular pH homeostasis.

AREAS COVERED

Since elevated levels of serum CA3, often in combination with other muscle-specific proteins, are routinely used as a marker of general muscle damage, it was of interest to examine recent analyses of this enzyme carried out by modern proteomics. This review summarizes the mass spectrometry-based identification and evaluation of CA3 in normal, adapting, dystrophic, and aging skeletal muscle tissues.

EXPERT OPINION

The mass spectrometric characterization of CA3 confirmed this enzyme as a highly useful marker of both physiological and pathophysiological alterations in skeletal muscles. Cytosolic CA3 is clearly enriched in slow-twitching type I fibers, which makes it an ideal marker for studying fiber type shifting and muscle adaptations. Importantly, neuromuscular diseases feature distinct alterations in CA3 in skeletal muscle tissues versus biofluids, such as serum. Characteristic changes of CA3 in age-related muscle wasting and dystrophinopathy established this enzyme as a suitable biomarker candidate for differential diagnosis and monitoring of disease progression and therapeutic impact.

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.

A mini review: Proteomics approaches to understand disused vs. exercised human skeletal muscle

Immobilization, bed rest, or denervation leads to muscle disuse and subsequent skeletal muscle atrophy. Muscle atrophy can also occur as a component of various chronic diseases such as cancer, AIDS, sepsis, diabetes, and chronic heart failure or as a direct result of genetic muscle disorders. In addition to this atrophic loss of muscle mass, metabolic deregulation of muscle also occurs. In contrast, physical exercise plays a beneficial role in counteracting disuse-induced atrophy by increasing muscle mass and strength. Along with this, exercise can also reduce mitochondrial dysfunction and metabolic deregulation. Still, while exercise causes valuable metabolic and functional adaptations in skeletal muscle, the mechanisms and effectors that lead to these changes such as increased mitochondria content or enhanced protein synthesis are not fully understood. Therefore, mechanistic insights may ultimately provide novel ways to treat disuse induced atrophy and metabolic deregulation. Mass spectrometry (MS)-based proteomics offers enormous promise for investigating the molecular mechanisms underlying disuse and exercise-induced changes in skeletal muscle. This review will focus on initial findings uncovered by using proteomics approaches with human skeletal muscle specimens and discuss their potential for the future study.

Comparative 3-Sample DIGE Analysis of Skeletal Muscles

The skeletal muscle proteome consists of a large number of diverse protein species with a broad and dynamic concentration range. Since mature skeletal muscles are characterized by a specific combination of contractile cells with differing physiological and biochemical properties, it is essential to determine specific differences in the protein composition of fast, slow, and hybrid fibers. Fluorescence two-dimensional gel electrophoresis (DIGE) is a powerful comparative tool to analyze fiber type-specific differences between fast and slow muscles. In this chapter, the application of the DIGE method for the comparative analysis of different subtypes of skeletal muscles is outlined in detail. A standardized proteomic workflow is described, involving sample preparation, protein extraction, differential fluorescence labeling using a 3-dye system, first-dimension isoelectric focusing, second-dimension slab gel electrophoresis, DIGE image analysis, protein digestion, and mass spectrometry.

Mapping the human skeletal muscle proteome: progress and potential

INTRODUCTION

Human skeletal muscle represents 40% of our body mass and deciphering its proteome composition to further understand mechanisms regulating muscle function under physiological and pathological conditions has proved a challenge. The inter-individual variability, the presence of structurally and functionally different muscle types and the high protein dynamic range require carefully selected methodologies for the assessment of the muscle proteome. Furthermore, physiological studies are understandingly hampered by ethical issues related to biopsies on healthy subjects, making it difficult to recruit matched controls essential for comparative studies. Areas covered: This review critically analyses studies performed on muscle to date and identifies what still remains unknown or poorly investigated in physiological and pathological states, such as training, aging, metabolic disorders and muscular dystrophies. Expert commentary: Efforts should be made on biological fluid analyses targeting low abundant/low molecular weight fragments generated from muscle cell disruption to improve diagnosis and clinical monitoring. From a methodological point of view, particular attention should be paid to improve the characterization of intact proteins and unknown post translational modifications to better understand the molecular mechanisms of muscle disorders.

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 Sick and the Weak: Neuropathies/Myopathies in the Critically Ill

Critical illness polyneuropathies (CIP) and myopathies (CIM) are common complications of critical illness. Several weakness syndromes are summarized under the term intensive care unit-acquired weakness (ICUAW). We propose a classification of different ICUAW forms (CIM, CIP, sepsis-induced, steroid-denervation myopathy) and pathophysiological mechanisms from clinical and animal model data. Triggers include sepsis, mechanical ventilation, muscle unloading, steroid treatment, or denervation. Some ICUAW forms require stringent diagnostic features; CIM is marked by membrane hypoexcitability, severe atrophy, preferential myosin loss, ultrastructural alterations, and inadequate autophagy activation while myopathies in pure sepsis do not reproduce marked myosin loss. Reduced membrane excitability results from depolarization and ion channel dysfunction. Mitochondrial dysfunction contributes to energy-dependent processes. Ubiquitin proteasome and calpain activation trigger muscle proteolysis and atrophy while protein synthesis is impaired. Myosin loss is more pronounced than actin loss in CIM. Protein quality control is altered by inadequate autophagy. Ca(2+) dysregulation is present through altered Ca(2+) homeostasis. We highlight clinical hallmarks, trigger factors, and potential mechanisms from human studies and animal models that allow separation of risk factors that may trigger distinct mechanisms contributing to weakness. During critical illness, altered inflammatory (cytokines) and metabolic pathways deteriorate muscle function. ICUAW prevention/treatment is limited, e.g., tight glycemic control, delaying nutrition, and early mobilization. Future challenges include identification of primary/secondary events during the time course of critical illness, the interplay between membrane excitability, bioenergetic failure and differential proteolysis, and finding new therapeutic targets by help of tailored animal models.

Intricate effects of primary motor neuronopathy on contractile proteins and metabolic muscle enzymes as revealed by label-free mass spectrometry

While the long-term physiological adaptation of the neuromuscular system to changed functional demands is usually reflected by unilateral skeletal muscle transitions, the progressive degeneration of distinct motor neuron populations is often associated with more complex changes in the abundance and/or isoform expression pattern of contractile proteins and metabolic enzymes. In order to evaluate these intricate effects of primary motor neuronopathy on the skeletal muscle proteome, label-free MS was employed to study global alterations in the WR (wobbler) mouse model of progressive neurodegeneration. In motor neuron disease, fibre-type specification and the metabolic weighting of bioenergetic pathways appear to be strongly influenced by both a differing degree of a subtype-specific vulnerability of neuromuscular synapses and compensatory mechanisms of fibre-type shifting. Proteomic profiling confirmed this pathobiochemical complexity of disease-induced changes and showed distinct alterations in 72 protein species, including a variety of fibre-type-specific isoforms of contractile proteins, metabolic enzymes, metabolite transporters and ion-regulatory proteins, as well as changes in molecular chaperones and various structural proteins. Increases in slow myosin light chains and the troponin complex and a decrease in fast MBP (myosin-binding protein) probably reflect the initial preferential loss of the fast type of neuromuscular synapses in motor neuron disease.

The systematic biochemical analysis of muscle from the wobbler mouse model of motor neuron disease suggests that the loss of neuromuscular synapses causes complex changes in the protein profile of contractile tissues, affecting especially the contractile apparatus and energy metabolism.

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.

L-carnitine pretreatment protects slow-twitch skeletal muscles in a rat model of ischemia-reperfusion injury

Ischemia-reperfusion (I/R) injury negatively affects the outcome of surgical interventions for amputated or severely traumatized extremities. This study aimed to evaluate the protective role of l-carnitine on the contractile properties of fast-twitch (extensor digitorum longus [EDL]) and slow-twitch (soleus [SOL]) skeletal muscles following I/R-induced injury in a rat model. Rats were divided into 4 groups (1) saline pretreatment, (2) l-carnitine pretreatment, (3) saline pretreatment and I/R, and (4) l-carnitine pretreatment and I/R. Twitch and tetanic contractions in the EDL and SOL muscles in each group were recorded. Additionally, a fatigue protocol was performed in these muscles. Twitch and tetanic contraction amplitudes were lower in the EDL and SOL muscles in which I/R was induced (P < .01). l-Carnitine pretreatment significantly increased tetanic contraction amplitude in the SOL muscles following I/R (P < .01) but not in the EDL muscles. l-Carnitine pretreatment did not alter the fatigue response in any of the muscles.

Carnitine supplementation to obese Zucker rats prevents obesity-induced type II to type I muscle fiber transition and favors an oxidative phenotype of skeletal muscle

BACKGROUND

In the present study, we tested the hypothesis that carnitine supplementation counteracts obesity-induced muscle fiber transition from type I to type II.

METHODS

24 obese Zucker rats were randomly divided into two groups of 12 rats each (obese control, obese carnitine) and 12 lean Zucker rats were selected for lean control group. A control diet was given to both control groups and a carnitine supplemented diet (3 g/kg diet) was given to obese carnitine group for 4 wk. Components of the muscle fiber transformation in skeletal muscle were examined.

RESULTS

The plasma level of carnitine were lower in the obese control group compared to the lean control group and higher in the obese carnitine group than in the other groups (P < 0.05). Plasma concentrations of triglycerides and non-esterified fatty acids were increased in obese animals compared to lean animals and the obese carnitine group had lower level compared to the obese control group (P < 0.05). The obese carnitine group had an increased number of type I muscle fibers and higher mRNA levels of type I fiber-specific myosin heavy chain, regulators of muscle fiber transition and of genes involved in carnitine uptake, fatty acid transport, β-oxidation, angiogenesis, tricarboxylic acid cycle and thermo genesis in M. rectus femoris compared to the other groups (P < 0.05).

CONCLUSION

The results demonstrate that carnitine supplementation to obese Zucker a rat counteracts the obesity-induced muscle fiber transition and restores the muscle oxidative metabolic phenotype. Carnitine supplementation is supposed to be beneficial for the treatment of elevated levels of plasma lipids during obesity or diabetes.

Pathobiochemical changes in diabetic skeletal muscle as revealed by mass-spectrometry-based proteomics

Insulin resistance in skeletal muscle tissues and diabetes-related muscle weakness are serious pathophysiological problems of increasing medical importance. In order to determine global changes in the protein complement of contractile tissues due to diabetes mellitus, mass-spectrometry-based proteomics has been applied to the investigation of diabetic muscle. This review summarizes the findings from recent proteomic surveys of muscle preparations from patients and established animal models of type 2 diabetes. The potential impact of novel biomarkers of diabetes, such as metabolic enzymes and molecular chaperones, is critically examined. Disease-specific signature molecules may be useful for increasing our understanding of the molecular and cellular mechanisms of insulin resistance and possibly identify new therapeutic options that counteract diabetic abnormalities in peripheral organ systems. Importantly, the biomedical establishment of biomarkers promises to accelerate the development of improved diagnostic procedures for characterizing individual stages of diabetic disease progression, including the early detection of prediabetic complications.

Proteomic analysis of skeletal muscle tissue using SELDI-TOF MS: application to disuse atrophy

Skeletal muscle atrophy in response to disuse/unloading is a complex adaptation that involves many components of the muscle tissue. The underlying mechanisms that initiate and control the loss of muscle tissue during this response, especially contractile proteins located within the myofibers, are as yet unclear. One approach capable of distinguishing protein changes specifically associated with disuse/unloading-induced skeletal muscle atrophy is to compare the proteomic profiles of similar muscles between control, unloaded/atrophied, and unloaded/"atrophy-protected" experimental conditions. By utilizing a subtractive proteomic analysis approach, those proteins specifically modulated during the atrophic response can be identified and discriminated from those associated with disuse in general. We here describe the use of SELDI-TOF MS coupled with micro-scale preparative ion-exchange chromatography to detect proteins potentially specifically associated with the atrophic response in rat skeletal muscle.

Proteomic responses of skeletal and cardiac muscle to exercise

Regular exercise is effective in the prevention of chronic diseases and confers a lower risk of death in individuals displaying risk factors such as hypertension and dyslipidemia. Thus, knowledge of the molecular responses to exercise provides a valuable contrast for interpreting investigations of disease and can highlight novel therapeutic targets. While exercise is an everyday experience and can be conceptualized in simple terms, it is also a complex physiological phenomenon and investigation of exercise responses requires sophisticated analytical techniques and careful standardization of the exercise stimulus. Proteomic investigation of exercise is in its infancy but the ability to link changes in function with comprehensive changes in protein expression and post-translational modification holds great promise for advancing physiology. This article highlights recent pioneering work investigating the effects of exercise in skeletal and cardiac muscle that has uncovered novel mechanisms underlying the benefits of physical activity.

Protein modulation in mouse heart under acute and chronic hypoxia

Exploring cellular mechanisms underlying beneficial and detrimental responses to hypoxia represents the object of the present study. Signaling molecules controlling adaptation to hypoxia (HIF-1α), energy balance (AMPK), mitochondrial biogenesis (PGC-1α), autophagic/apoptotic processes regulation and proteomic dysregulation were assessed. Responses to acute hypoxia (AH) and chronic hypoxia (CH) in mouse heart proteome were detected by 2-D DIGE, mass spectrometry and antigen-antibody reactions. Both in AH and CH, the results indicated a deregulation of proteins related to sarcomere stabilization and muscle contraction. Neither in AH nor in CH the HIF-1α stabilization was observed. In AH, the metabolic adaptation to lack of oxygen was controlled by AMPK activation and sustained by an up-regulation of adenosylhomocysteinase and acetyl-CoA synthetase. AH was characterized by the mitophagic protein Bnip 3 increment. PGC-1α, a master regulator of mitochondrial biogenesis, was down-regulated. CH was characterized by the up-regulation of enzymes involved in antioxidant defense, in aldehyde bio-product detoxification and in misfolded protein degradation. In addition, a general down-regulation of enzymes controlling anaerobic metabolism was observed. After 10 days of hypoxia, cardioprotective molecules were substantially decreased whereas pro-apoptotic molecules increased accompained by down-regulation of specific target proteins.

Setup for human sera MALDI profiling: the case of rhEPO treatment

The implementation of high-throughput technologies based on qualitative and quantitative methodologies for the characterization of complex protein mixtures is increasingly required in clinical laboratories. MALDI profiling is a robust and sensitive technology although the serum high dynamic range imposes a major limitation hampering the identification of less abundant species decreasing the quality of MALDI profiling. A setup to improve these parameters has been performed for recombinant human erythropoietin (rhEPO) monitoring in serum, analyzing the effects of two commercially available columns (MARS Hu7 and Hu14) for immunodepletion, and two matrices (α-cyano-4-hydroxycinnamic acid and 2',4'-dihydroxyacetophenone) for peak quality improvement. The immunodepletion capability of both columns was determined by 2-D DIGE, which precisely revealed the efficacy of Hu14 in protein removal and the serum dynamic range decrement. In addition, the type of matrix, the sample dilution, and the efficacy of optimized parameters were used for serum profiling of ten healthy subjects before and after rhEPO treatment. The principal component analysis indicates that a combination of Hu14 column and 2',4'-dihydroxyacetophenone matrix increases data quality allowing the discrimination between treated and untreated samples, making serum MALDI profiling suitable for clinical monitoring of rhEPO.

Diversity of human skeletal muscle in health and disease: contribution of proteomics

Muscle represents a large fraction of the human body mass. It is an extremely heterogeneous tissue featuring in its contractile structure various proportions of heavy- and light-chain slow type 1 and fast types 2A and 2X myosins, actins, tropomyosins, and troponin complexes as well as metabolic proteins (enzymes and most of the players of the so-called excitation-transcription coupling). Muscle is characterized by wide plasticity, i.e. capacity to adjust size and functional properties in response to endogenous and exogenous influences. Over the last decade, proteomics has become a crucial technique for the assessment of muscle at the molecular level and the investigation of its functional changes. Advantages and shortcomings of recent techniques for muscle proteome analysis are discussed. Data from differential proteomics applied to healthy individuals in normal and unusual environments (hypoxia and cold), in exercise, immobilization, aging and to patients with neuromuscular hereditary disorders (NMDs), inclusion body myositis and insulin resistance are summarized, critically discussed and, when required, compared with homologous data from pertinent animal models. The advantages as well as the limits of proteomics in view of the identification of new biomarkers are evaluated.

Skeletal muscle proteomics: current approaches, technical challenges and emerging techniques

Background

Skeletal muscle fibres represent one of the most abundant cell types in mammals. Their highly specialised contractile and metabolic functions depend on a large number of membrane-associated proteins with very high molecular masses, proteins with extensive posttranslational modifications and components that exist in highly complex supramolecular structures. This makes it extremely difficult to perform conventional biochemical studies of potential changes in protein clusters during physiological adaptations or pathological processes.

Results

Skeletal muscle proteomics attempts to establish the global identification and biochemical characterisation of all members of the muscle-associated protein complement. A considerable number of proteomic studies have employed large-scale separation techniques, such as high-resolution two-dimensional gel electrophoresis or liquid chromatography, and combined them with mass spectrometry as the method of choice for high-throughput protein identification. Muscle proteomics has been applied to the comprehensive biochemical profiling of developing, maturing and aging muscle, as well as the analysis of contractile tissues undergoing physiological adaptations seen in disuse atrophy, physical exercise and chronic muscle transformation. Biomedical investigations into proteome-wide alterations in skeletal muscle tissues were also used to establish novel biomarker signatures of neuromuscular disorders. Importantly, mass spectrometric studies have confirmed the enormous complexity of posttranslational modifications in skeletal muscle proteins.

Conclusions

This review critically examines the scientific impact of modern muscle proteomics and discusses its successful application for a better understanding of muscle biology, but also outlines its technical limitations and emerging techniques to establish new biomarker candidates.

Oxidative stress in the denervated muscle

Following experimental hind limb denervation in rats, this study demonstrates that oxidative stress occurs and advances an hypothesis about its origin. In fact: (i) ROS are formed; (ii) membrane lipids are oxidized; (iii) oxidized ion channels and pumps may lead to increased [Ca(2+)](i); all the above mentioned events increase with denervation time. In the denervated muscle, (iv) mRNA abundance of cytoprotective and anti-oxidant proteins (Hsp70, Hsp27, Sod1, Catalase, Gpx1, Gpx4, Gstm1), as well as (v) SOD1 enzymatic activity and HSP70i protein increase; (vi) an unbalance in mitochondrial OXPHOS enzymes occurs, presumably leading to excess mitochondrial ROS production; (vii) increased cPLA2alpha expression (mRNA) and activation (increased [Ca(2+)](i)) may lead to increased hydroperoxides release. Since anti-oxidant defences appear inadequate to counterbalance increased ROS production with increased denervation time, an anti-oxidant therapeutic strategy seems to be advisable in the many medical conditions where the nerve-muscle connection is impaired.

Proteomics of skeletal muscle differentiation, neuromuscular disorders and fiber aging

Skeletal muscle fibers are the most abundant cellular structure in the human body. Altered neuromuscular activity, traumatic injury or genetic abnormalities have profound effects on muscle integrity, tissue mass, fiber type distribution, metabolic integration and contractile function. The recent application of mass spectrometry-based proteomics has decisively advanced our molecular understanding of numerous physiological adaptations in healthy muscle and pathophysiological mechanisms associated with major muscle diseases. Skeletal muscle proteomics promises to play a major role in the establishment of a disease-specific biomarker signature for the major classes of neuromuscular disorders. New muscle markers will be crucial for the development of improved diagnostics, the monitoring of disease progression, evaluation of drug action and the identification of novel therapeutic targets.

Muscle unloading potentiates the effects of acetyl-L-carnitine on the slow oxidative muscle phenotype

The effect of acetyl-L-carnitine (ALCAR) supplementation to 3-month-old rats in normal-loading and unloading conditions has been here investigated by a combined morphological, biochemical and transcriptional approach to test whether ALCAR might cause a remodeling of the metabolic/contractile phenotype of soleus muscle. Morphological assessment demonstrated an increase of type I oxidative fiber content and cross-sectional area in ALCAR-treated animals both in normal-loading and in unloading conditions. ALCAR prevented loss of mitochondrial mass in unloaded animals whereas no ALCAR-dependent increase of mitochondrial mass occurred in normal-loaded muscle. Validated microarray analysis delineated an ALCAR-induced maintenance of a slow-oxidative expression program only in unloaded soleus muscle. Indeed, the muscle adjustment of the expression profile of factors underlying mitochondrial oxidative metabolism, protein turnover, fiber type differentiation and an adaptation of voltage-gated ion channel expression was distinguishable with respect to the loading status. This selectivity may suggest a key role of muscle loading status in the manifestation of ALCAR effects. The results extend to a broader level of biological informations the previous notion on ALCAR positive effect in rat soleus muscle during unloading and point to a role of ALCAR for the maintenance of its slow-oxidative fiber character.

Mitochondria in the elderly: Is acetylcarnitine a rejuvenator?

Endogenous acetylcarnitine is an indicator of acetyl-CoA synthesized by multiple metabolic pathways involving carbohydrates, amino acids, fatty acids, sterols, and ketone bodies, and utilized mainly by the tricarboxylic acid cycle. Acetylcarnitine supplementation has beneficial effects in elderly animals and humans, including restoration of mitochondrial content and function. These effects appear to be dose-dependent and occur even after short-term therapy. In order to set the stage for understanding the mechanism of action of acetylcarnitine, we review the metabolism and role of this compound. We suggest that acetylation of mitochondrial proteins leads to a specific increase in mitochondrial gene expression and mitochondrial protein synthesis. In the aged rat heart, this effect is translated to increased cytochrome b content, restoration of complex III activity, and oxidative phosphorylation, resulting in amelioration of the age-related mitochondrial defect.

Is oxidative stress a cause or consequence of disuse muscle atrophy in mice? A proteomic approach in hindlimb-unloaded mice

Two-dimensional proteomic maps of soleus (Sol), a slow oxidative muscle, and gastrocnemius (Gas), a fast glycolytic muscle of control mice (CTRL), of mice hindlimb unloaded for 14 days (HU mice) and of HU mice treated with trolox (HU-TRO), a selective and potent antioxidant, were compared. The proteomic analysis identified a large number of differentially expressed proteins in a pool of approximately 800 proteins in both muscles. The protein pattern of Sol and Gas adapted very differently to hindlimb unloading. The most interesting adaptations related to the cellular defense systems against oxidative stress and energy metabolism. In HU Sol, the antioxidant defense systems and heat shock proteins were downregulated, and protein oxidation index and lipid peroxidation were higher compared with CTRL Sol. In contrast, in HU Gas the antioxidant defense systems were upregulated, and protein oxidation index and lipid peroxidation were normal. Notably, both Sol and Gas muscles and their muscle fibres were atrophic. Antioxidant administration prevented the impairment of the antioxidant defense systems in Sol and further enhanced them in Gas. Accordingly, it restored normal levels of protein oxidation and lipid peroxidation in Sol. However, muscle and muscle fibre atrophy was not prevented either in Sol or in Gas. A general downsizing of all energy production systems in Sol and a shift towards glycolytic metabolism in Gas were observed. Trolox administration did not prevent metabolic adaptations in either Sol or Gas. The present findings suggest that oxidative stress is not a major determinant of muscle atrophy in HU mice.

Comparative proteomic profile of rat sciatic nerve and gastrocnemius muscle tissues in ageing by 2-D DIGE

Ageing induces a progressive morphological change and functional decline in muscles and in nerves. Light and electron microscopy, 2-D DIGE and MS, were applied to profile the qualitative and quantitative differences in the proteome and morphology of rat gastrocnemius muscle and sciatic nerve, in healthy 22-month-old rats. At muscle level, morphological changes are associated to fibre atrophy accompanied by myofibrillar loss and degeneration, disappearance of sarcomeres and sarcoplasmic reticulum dilatation, internal migration of nuclei, longitudinal fibre splitting, increment of subsarcolemmal mitochondria aggregates and increment of lipofuscin granules. Sciatic nerve shows myelin abnormalities like enfoldings, invaginations, onion bulbs, breakdowns and side axonal atrophy. Proteomic analysis identified changes correlated to morphological abnormalities in metabolic, contractile and cytoskeletal proteins, deregulation of iron homeostasis, change of Ca(2+) balance and stress response proteins, accompanied by a deregulation of myelin membrane adhesion protein and proteins regulating the neuronal caliber. By comparing proteomic results from the two tissues, 16 protein isoforms showed the same up and down regulation trend suggesting that there are changes implying a general process which may act as a signal event of degeneration. Only beta enolase and tropomyosin 1alpha were differentially expressed in the tissues.

Accumulation of overoxidized Peroxiredoxin III in aged rat liver mitochondria

Overoxidation and subsequent inactivation of Peroxiredoxin III (PrxIII), a mitochondrial H(2)O(2) scavenging enzyme, have been reported in oxidative stress conditions. No data are available in the literature about the presence of overoxidized forms of PrxIII in aged tissues. Liver mitochondria from 12-month-old rats and 28-month-old rats were here analyzed by two-dimensional gel electrophoresis. A spot corresponding to the native form of PrxIII was present in adult and old rats with the same volume, whereas an additional, more acidic spot, of the same molecular weight of the native form, accumulated only in old rats. The acidic spot was identified, by MALDI-MS analysis, as a form of PrxIII bearing the cysteine of the catalytic site overoxidized to sulphonic acid. This modified PrxIII form corresponds to the irreversibly inactivated enzyme, here reported, for the first time, in aging. Three groups of 28-month-old rats treated with acetyl-l-carnitine were also examined. Reduced accumulation of the overoxidized PrxIII form was found in all ALCAR-treated groups.