Higher strength gain after hypoxic vs normoxic resistance training despite no changes in muscle thickness and fractional protein synthetic rate.

Acute hypoxia has previously been suggested to potentiate resistance training-induced hypertrophy by activating satellite cell-dependent myogenesis rather than an improvement in protein balance in human. Here, we tested this hypothesis after a 4-week hypoxic vs normoxic resistance training protocol. For that purpose, 19 physically active male subjects were recruited to perform 6 sets of 10 repetitions of a one-leg knee extension exercise at 80% 1-RM 3 times/week for 4 weeks in normoxia (FiO2 : 0.21; n = 9) or in hypoxia (FiO2 : 0.135, n = 10). Blood and skeletal muscle samples were taken before and after the training period. Muscle fractional protein synthetic rate was measured over the whole period by deuterium incorporation into the protein pool and muscle thickness by ultrasound. At the end of the training protocol, the strength gain was higher in the hypoxic vs the normoxic group despite no changes in muscle thickness and in the fractional protein synthetic rate. Only early myogenesis, as assessed by higher MyoD and Myf5 mRNA levels, appeared to be enhanced by hypoxia compared to normoxia. No effects were found on myosin heavy chain expression, markers of oxidative metabolism and lactate transport in the skeletal muscle. Though the present study failed to unravel clearly the mechanisms by which hypoxic resistance training is particularly potent to increase muscle strength, it is important message to keep in mind that this training strategy could be effective for all athletes looking at developing and optimizing their maximal muscle strength.

Regulation of satellite cells by exercise in hypoxic conditions: a narrative review.

PURPOSE: To investigate in vivo the adaptations of satellite cell induced by exercise performed in acute or chronic hypoxic conditions and their contribution to muscle remodeling and hypertrophy. METHODS: Search terms related to exercise, hypoxia and satellite cells were entered on Embase, PubMed and Scopus. Studies were selected for their relevance in terms of regulation of satellite cells by in vivo exercise and muscle contraction in hypoxic conditions. RESULTS: Satellite cell activation and proliferation seem to be enabled after acute hypoxic exercise via regulations induced by myogenic regulatory factors. Several studies reported also a role of the inflammatory pathway nuclear factor-kappa B and angiogenic factors such as vascular endothelial growth factor, both known to upregulate myogenesis. By stimulating angiogenesis, repeated exercise performed in acute hypoxia might contribute to satellite cell activation. Contrary to such exercise conditions, chronic exposure to hypoxia downregulates myogenesis despite the maintenance of physical activity. This impaired myogenesis might be induced by excessive oxidative stress and proteolysis. CONCLUSION: In vivo studies suggest that, in comparison to exercise or hypoxia alone, exercise performed in a hypoxic environment, may improve or impair muscle remodeling induced by contractile activity depending upon the duration of hypoxia. Satellite cells seem to be major actors in these dichotomous adaptations. Further research on the role of angiogenesis, types of contraction and autophagy is needed for a better understanding of their respective role in hypoxic exercise-induced modulations of satellite cell activity in human.

Muscle structural, energetic and functional benefits of endurance exercise training in sickle cell disease.

Sickle cell disease (SCD) patients display skeletal muscle hypotrophy, altered oxidative capacity, exercise intolerance and poor quality of life. We previously demonstrated that moderate-intensity endurance training is beneficial for improving muscle function and quality of life of patients. The present study evaluated the effects of this moderate-intensity endurance training program on skeletal muscle structural and metabolic properties. Of the 40 randomized SCD patients, complete data sets were obtained from 33. The training group (n = 15) followed a personalized moderate-intensity endurance training program, while the non-training (n = 18) group maintained a normal lifestyle. Biopsies of the vastus lateralis muscle and submaximal incremental cycling tests were performed before and after the training program. Endurance training increased type I muscle fiber surface area (P = .038), oxidative enzyme activity [citrate synthase, P < .001; ß-hydroxyacyl-CoA dehydrogenase, P = .009; type-I fiber cytochrome c oxidase, P = .042; respiratory chain complex IV, P = .017] and contents of respiratory chain complexes I (P = .049), III (P = .005), IV (P = .003) and V (P = .002). Respiratory frequency, respiratory exchange ratio, blood lactate concentration and rating of perceived exertion were all lower at a given submaximal power output after training vs non-training group (all P < .05). The muscle content of proteins involved in glucose transport and pH regulation were unchanged in the training group relative to the non-training group. The moderate-intensity endurance exercise program improved exercise capacity and muscle structural and oxidative properties. This trial was registered at www.clinicaltrials.gov as #NCT02571088.

Simplified indices of exercise tolerance in patients with multiple sclerosis and healthy subjects: A case-control study.

Among patients with multiple sclerosis (MS), the impairment of exercise tolerance is closely related to disability. Maximal oxygen uptake (VO2max ) is the gold standard to assess exercise tolerance in healthy subjects (HS). Among patients with MS, the accuracy of VO2max measurement is often impaired because the patients are unable to reach the maximal exercise intensity due to interdependent factors linked to the disease (such as pathological fatigue, pain, lack of exercise habit, and lack of mobility). This study assesses the accuracy of simplified indices for assessing exercise tolerance, which are more suitable in patients with MS. They are simple in the way they are either measurable during submaximal exercise (oxygen uptake efficiency slopes (OUES), physical working capacity at 75% of maximal heart rate (PWC75% ), oxygen consumption at a respiratory exchange ratio of 1 (VO2 @RER1)) or not based on gas exchange analysis (peak work rate (PWR)-based predictive equation and PWC75% ). All indices were significantly lower in the MS group compared to the HS group (P < .001). OUES appeared highly correlated (r > .70, P < .001) with VO2peak , in both groups, without difference between groups. PWR-based prediction of VO2peak showed a standard error of the estimate of 315 mL min-1 in HS and 176 mL min-1 in MS. PWC75% did not correlate to VO2peak in neither group. These findings suggest an impairment of exercise tolerance functions in mildly disabled persons with MS, independently from other factors. Submaximal indices involving gas exchange analysis or peakWR-based estimation of VO2peak are usable to accurately assess exercise tolerance.

Exercise and the control of muscle mass in human.

During the course of life, muscle mass undergoes many changes in terms of quantity and quality. Skeletal muscle is a dynamic tissue able to hypertrophy or atrophy according to growth, ageing, physical activity, nutrition and health state. The purpose of the present review is to present the mechanisms by which exercise can induce changes in human skeletal muscle mass by modulating protein balance and regulating the fate of satellite cells. Exercise is known to exert transcriptional, translational and post-translational regulations as well as to induce epigenetic modifications and to control messenger RNA stability, which all contribute to the regulation of protein synthesis. Exercise also regulates the autophagy-lysosomal and the ubiquitin-proteasome pathways, the two main proteolytic systems in skeletal muscle, indicating that exercise participates to the regulation of the quality control mechanisms of cellular components and, therefore, to muscle health. Finally, activation, proliferation and differentiation of satellite cells can be enhanced by exercise to induce muscle remodelling and hypertrophy. Each of these mechanisms can potentially impact skeletal muscle mass, depending on the intensity, duration and frequency with which the signal appears.

Environmental hypoxia favors myoblast differentiation and fast phenotype but blunts activation of protein synthesis after resistance exercise in human skeletal muscle.

We hypothesized that a single session of resistance exercise performed in moderate hypoxic (FiO2: 14%) environmental conditions would potentiate the anabolic response during the recovery period spent in normoxia. Twenty subjects performed a 1-leg knee extension session in normoxic or hypoxic conditions. Muscle biopsies were taken 15 min and 4 h after exercise in the vastus lateralis of the exercised and the nonexercised legs. Blood and saliva samples were taken at regular intervals before, during, and after the exercise session. The muscle fractional-protein synthetic rate was determined by deuterium incorporation into proteins, and the protein-degradation rate was determined by methylhistidine release from skeletal muscle. We found that: 1) hypoxia blunted the activation of protein synthesis after resistance exercise; 2) hypoxia down-regulated the transcriptional program of autophagy; 3) hypoxia regulated the expression of genes involved in glucose metabolism at rest and the genes involved in myoblast differentiation and fusion and in muscle contraction machinery after exercise; and 4) the hypoxia-inducible factor-1α pathway was not activated at the time points studied. Contrary to our hypothesis, environmental hypoxia did not potentiate the short-term anabolic response after resistance exercise, but it initiated transcriptional regulations that could potentially translate into satellite cell incorporation and higher force production in the long term.-Gnimassou, O., Fernández-Verdejo, R., Brook, M., Naslain, D., Balan, E., Sayda, M., Cegielski, J., Nielens, H., Decottignies, A., Demoulin, J.-B., Smith, K., Atherton, P. J., Fancaux, M., Deldicque, L. Environmental hypoxia favors myoblast differentiation and fast phenotype but blunts activation of protein synthesis after resistance exercise in human skeletal muscle.

Glucocorticoid-dependent REDD1 expression reduces muscle metabolism to enable adaptation under energetic stress.

BACKGROUND: Skeletal muscle atrophy is a common feature of numerous chronic pathologies and is correlated with patient mortality. The REDD1 protein is currently recognized as a negative regulator of muscle mass through inhibition of the Akt/mTORC1 signaling pathway. REDD1 expression is notably induced following glucocorticoid secretion, which is a component of energy stress responses. RESULTS: Unexpectedly, we show here that REDD1 instead limits muscle loss during energetic stresses such as hypoxia and fasting by reducing glycogen depletion and AMPK activation. Indeed, we demonstrate that REDD1 is required to decrease O2 and ATP consumption in skeletal muscle via reduction of the extent of mitochondrial-associated endoplasmic reticulum membranes (MAMs), a central hub connecting energy production by mitochondria and anabolic processes. In fact, REDD1 inhibits ATP-demanding processes such as glycogen storage and protein synthesis through disruption of the Akt/Hexokinase II and PRAS40/mTORC1 signaling pathways in MAMs. Our results uncover a new REDD1-dependent mechanism coupling mitochondrial respiration and anabolic processes during hypoxia, fasting, and exercise. CONCLUSIONS: Therefore, REDD1 is a crucial negative regulator of energy expenditure that is necessary for muscle adaptation during energetic stresses. This present study could shed new light on the role of REDD1 in several pathologies associated with energetic metabolism alteration, such as cancer, diabetes, and Parkinson's disease.

Effect of environmental feedbacks on pacing strategy and affective load during a self-paced 30 min cycling time trial.

The purpose of this study was to analyze the pacing strategy and its affective consequences during self-paced cycling time trials (TT) performed at different severity of hypoxia. Eight competitive cyclists performed five 30 min self-paced TTs at their best performance in the following conditions: 1) normobaric normoxia (NNSL); 2) normobaric hypoxia under two simulated altitudes: 2000 m (NH2000) and 3500 m (NH3500) and 3) normobaric hypoxia but the cyclists were deceived and thought to be at sea level for 2000 m (DecNH2000) and 3500 m (DecNH3500). Power Output (PO), oxygen uptake (VO2), and blood lactate concentration ([La]) were recorded to assess exercise intensity and physiological adaptations. The rate of perceived exertion (RPE) and pleasure were measured with a CR10 Borg scale to evaluate the affective load (AL). PO and VO2 decreased with the severity of hypoxia but no significantly difference on performance was measured between deceived and real conditions, except for pacing strategy. The started intensity depends on the exercise expectations, but PO was rapidly adjusted with the physiological constraints and the rate of increase of RPE. Finally, AL did not reach maximal values so that the athletes sustained a physiological and emotional reserve to perform a final spurt.

Impact of Very Early Physical Therapy During Septic Shock on Skeletal Muscle: A Randomized Controlled Trial.

OBJECTIVES: As the catabolic state induced by septic shock together with the physical inactivity of patients lead to the rapid loss of muscle mass and impaired function, the purpose of this study was to test whether an early physical therapy during the onset of septic shock regulates catabolic signals and preserves skeletal muscle mass. DESIGN: Randomized controlled trial. SETTING: Tertiary mixed ICU. PATIENTS: Adult patients admitted for septic shock within the first 72 hours. INTERVENTIONS: Patients were assigned randomly into two groups. The control group benefited from manual mobilization once a day. The intervention group had twice daily sessions of both manual mobilization and 30-minute passive/active cycling therapy. MEASUREMENTS AND MAIN RESULTS: Skeletal muscle biopsies and electrophysiology testing were performed at day 1 and day 7. Muscle biopsies were analyzed for histology and molecular components of signaling pathways regulating protein synthesis and degradation as well as inflammation markers. Hemodynamic values and patient perception were collected during each session. Twenty-one patients were included. Three died before the second muscle biopsy. Ten patients in the control and eight in the intervention group were analyzed. Markers of the catabolic ubiquitin-proteasome pathway, muscle atrophy F-box and muscle ring finger-1 messenger RNA, were reduced at day 7 only in the intervention group, but without difference between groups (muscle atrophy F-box: -7.3% ± 138.4% in control vs -56.4% ± 37.4% in intervention group; p = 0.23 and muscle ring finger-1: -30.8% ± 66.9% in control vs -62.7% ± 45.5% in intervention group; p = 0.15). Muscle fiber cross-sectional area (µm) was preserved by exercise (-25.8% ± 21.6% in control vs 12.4% ± 22.5% in intervention group; p = 0.005). Molecular regulations suggest that the excessive activation of autophagy due to septic shock was lower in the intervention group, without being suppressed. Markers of anabolism and inflammation were not modified by the intervention, which was well tolerated by the patients. CONCLUSIONS: Early physical therapy during the first week of septic shock is safe and preserves muscle fiber cross-sectional area.

Using polyphenol derivatives to prevent muscle wasting.

PURPOSE OF REVIEW: To highlight recent evidence for the ability of polyphenols and their derivatives to reduce muscle wasting in different pathological states. RECENT FINDINGS: From January 2016 to August 2017, four articles dealt with the effects of polyphenols on muscle wasting, which were all carried out in mice. The four studies found that polyphenols reduced muscle mass loss associated with cancer cachexia, acute inflammation or sciatic nerve section. One study even showed that muscle mass was totally preserved when rutin was added to the diet of mice undergoing cancer cachexia. The beneficial effects of polyphenols on muscle wasting were mainly due to a reduction in the activation of the nuclear factor-kappa B pathway, a lower oxidative stress level and a better mitochondrial function. In addition, urolithin B was found to have a testosterone-like effect and to favorably regulate muscle protein balance. SUMMARY: During the last 20 months, additional data have been collected about the beneficial effects of rutin, curcumin, quercetin, ellagitanins and urolithin B to limit the loss of muscle mass associated with several pathological states. However, currently, scientific evidence lacks for their use as nutraceuticals in human.

Activating transcription factor 3 attenuates chemokine and cytokine expression in mouse skeletal muscle after exercise and facilitates molecular adaptation to endurance training.

Activating transcription factor (ATF)3 regulates the expression of inflammation-related genes in several tissues under pathological contexts. In skeletal muscle, atf3 expression increases after exercise, but its target genes remain unknown. We aimed to identify those genes and to determine the influence of ATF3 on muscle adaptation to training. Skeletal muscles of ATF3-knockout (ATF3-KO) and control mice were analyzed at rest, after exercise, and after training. In resting muscles, there was no difference between genotypes in enzymatic activities or fiber type. After exercise, a microarray analysis in quadriceps revealed ATF3 affects genes modulating chemotaxis and chemokine/cytokine activity. Quantitative PCR showed that the mRNA levels of chemokine C-C motif ligand (ccl)8 and chemokine C-X-C motif ligand (cxcl)13 were higher in quadriceps of ATF3-KO mice than in control mice. The same was observed for ccl9 and cxcl13 in soleus. Also in soleus, ccl2, interleukin (il)6, il1ß, and cluster of differentiation (cd)68 mRNA levels increased after exercise only in ATF3-KO mice. Endurance training increased the basal mRNA level of hexokinase-2, hormone sensitive lipase, glutathione peroxidase-1, and myosin heavy chain IIa in quadriceps of control mice but not in ATF3-KO mice. In summary, ATF3 attenuates the expression of inflammation-related genes after exercise and thus facilitates molecular adaptation to training.-Fernández-Verdejo, R., Vanwynsberghe, A. M., Essaghir, A., Demoulin, J.-B., Hai, T., Deldicque, L., Francaux, M. Activating transcription factor 3 attenuates chemokine and cytokine expression in mouse skeletal muscle after exercise and facilitates molecular adaptation to endurance training.

Toll like receptor expression induced by exercise in obesity and metabolic syndrome: A systematic review.

BACKGROUND: Obesity and metabolic syndrome are disorders that correlate with the activation of pro-inflammatory pathways and cytokine production, to which Toll like receptors (TLR) contribute. Exercise may act as an anti-inflammatory modulator, but there is no consensus about the role of the TLR in this tuning. The present styudy aims to systematically review the current evidence on exercise-induced TLR regulation in animals and humans suffering from obesity and metabolic syndrome. METHODS: Pubmed and Scopus databases were searched for publications from 1990 to September 2015. Search terms included: "Toll like Receptor", "TLR", "exercise", "obesity", "diabetes", and "metabolic syndrome". Elegibility criteria comprised: randomized control trials, cross-sectional and cohort studies; human or animal models with metabolic syndrome; any type of exercise; TLR expression measurement in any tissue by a clearly reported technique. The quality of selected studies was assessed using a modified version of the Downs and Black Quality Assessment Checklist. Data of study design; population; exercise type, timing and training elements; measurement technique, tissue analyzed and main outcome were extracted and categorized to facilitate data synthesis. RESULTS: 17 studies were included, of which 11 publications obtained a high, 5 a moderate and 1 a low score for quality assessment. A total of 8 human studies were analyzed: 6 studies used endurance continuous or interval training protocols, 1 study resistance training and the remaining study was performed following a marathon race. Blood cells were analyzed in seven studies, of which four studies sampled peripheral blood mononuclear cells (PBMC), three analyzed whole blood and one study sampled skeletal muscle. Nine animal studies were included: 8 used endurance training and 1 acute aerobic exercise. A variety of tissues samples were explored such as PBMC, skeletal muscle, adipose, vascular and nervous tissue. Globally, the animal studies showed a marked tendency towards a down-regulation of TLR2 and 4 expression accompagnied with, a reduced activation of nuclear factorkappaB (NF-κB) signaling and cytokine production, and an improvement in insulin sensitivity and body composition. CONCLUSION: While animal studies showed a marked tendency towards TLR2 and 4 down-regulation after chronic endurance exercise, the current evidence in human is not sufficiently robust to conclude any role of TLR in the anti-inflammatory properties of exercise.

Potential harmful effects of dietary supplements in sports medicine.

PURPOSE OF REVIEW: The purpose of this article is to collect the most recent data regarding the safety of well-known or emerging dietary supplements used by athletes. RECENT FINDINGS: From January 2014 to April 2016, about 30 articles have been published in the field. New data show that 90% of sports supplements contain trace of estrogenic endocrine disruptors, with 25% of them having a higher estrogenic activity than acceptable. About 50% of the supplements are contaminated by melamine, a source of nonprotein nitrogen. Additional data accumulate toward the safety of nitrate ingestion. In the last 2 years, the safety of emerging supplements such as higenamine, potentially interesting to lose weight, creatine nitrate and guanidinoacetic acid has been evaluated but still needs further investigation. SUMMARY: The consumption of over-the-counter supplements is very popular in athletes. Although most supplements may be considered as safe when taking at the recommended doses, athletes should be aware of the potential risks linked to the consumption of supplements. In addition to the risks linked to overdosage and cross-effects when combining different supplements at the same time, inadvertent or deliberate contamination with stimulants, estrogenic compounds, diuretics or anabolic agents may occur.

Activation of autophagy in human skeletal muscle is dependent on exercise intensity and AMPK activation.

In humans, nutrient deprivation and extreme endurance exercise both activate autophagy. We hypothesized that cumulating fasting and cycling exercise would potentiate activation of autophagy in skeletal muscle. Well-trained athletes were divided into control (n = 8), low-intensity (LI, n = 8), and high-intensity (HI, n = 7) exercise groups and submitted to fed and fasting sessions. Muscle biopsy samples were obtained from the vastus lateralis before, at the end, and 1 h after a 2 h LI or HI bout of exercise. Phosphorylation of ULK1(Ser317) was higher after exercise (P < 0.001). In both the fed and the fasted states, LC3bII protein level and LC3bII/I were decreased after LI and HI (P < 0.05), while p62/SQSTM1 was decreased only 1 h after HI (P < 0.05), indicating an increased autophagic flux after HI. The autophagic transcriptional program was also activated, as evidenced by the increased level of LC3b, p62/SQSTM1, GabarapL1, and Cathepsin L mRNAs observed after HI but not after LI. The increased autophagic flux after HI exercise could be due to increased AMP-activated protein kinase α (AMPKα) activity, as both AMPKα(Thr172) and ACC(Ser79) had a higher phosphorylation state after HI (P < 0.001). In summary, the most effective strategy to activate autophagy in human skeletal muscle seems to rely on exercise intensity more than diet.

IRE1α and TRB3 do not contribute to the disruption of proximal insulin signaling caused by palmitate in C2C12 myotubes.

Endoplasmic reticulum (ER) stress is a central actor in the physiopathology of insulin resistance (IR) in various tissues. The subsequent unfolded protein response (UPR) interacts with insulin signaling through inositol-requiring 1α (IRE1α) activation and tribbles homolog 3 (TRB3) expressions. IRE1α impairs insulin actions through the activation of c-Jun N-terminal kinase (JNK), and TRB3 is a pseudokinase inhibiting Akt. In muscle cells, the link between ER stress and IR has only been demonstrated by using chemical ER stress inducers or overexpression techniques. However, the involvement of ER stress in lipid-induced muscle IR remains controversial. The aim of the study is to test whether palmitate-induced IRE1α signaling and TRB3 expression disturb insulin signaling in myogenic cells. C2C12 myotubes were exposed to palmitate and then stimulated with insulin. siRNA transfection was used to downregulate TRB3 and IRE1α. Palmitate increased TRB3 expression, activated IRE1α signaling, and reduced the insulin-dependent Akt phosphorylation. Knocking down TRB3 or IRE1α did not prevent the inhibitory effect of palmitate on Akt phosphorylation. Our results support the idea that ER stress is not responsible for lipid-induced IR in C2C12 myotubes.

Aging related ER stress is not responsible for anabolic resistance in mouse skeletal muscle.

Anabolic resistance reflects the inability of skeletal muscle to maintain protein mass by appropriate stimulation of protein synthesis. We hypothesized that endoplasmic reticulum (ER) stress contributes to anabolic resistance in skeletal muscle with aging. Muscles were isolated from adult (8 mo) and old (26 mo) mice and weighed. ER stress markers in each muscle were quantified, and the anabolic response to leucine was assessed by measuring the phosphorylation state of S6K1 in soleus and EDL using an ex vivo muscle model. Aging reduced the muscle-to-body weight ratio in soleus, gastrocnemius, and plantaris, but not in EDL and tibialis anterior. Compared to adult mice, the expression of ER stress markers BiP and IRE1α was higher in EDL, and phospho-eIF2α was higher in soleus and EDL of old mice. S6K1 response to leucine was impaired in soleus, but not in EDL, suggesting that anabolic resistance contributes to soleus weight loss in old mice. Pre-incubation with ER stress inducer tunicamycin before leucine stimulation increased S6K1 phosphorylation beyond the level reached by leucine alone. Since tunicamycin did not impair leucine-induced S6K1 response, and based on the different ER stress marker regulation patterns, ER stress is probably not involved in anabolic resistance in skeletal muscle with aging.

Pomegranate and green tea extracts protect against ER stress induced by a high-fat diet in skeletal muscle of mice.

PURPOSE: We tested the hypothesis that polyphenol-rich extracts can reduce endoplasmic reticulum (ER) stress induced by a high-fat diet (HFD) in skeletal muscle of mice. METHODS: Mice were randomly assigned to four groups receiving during 20 weeks either a standard chow control (CTRL), or a HFD supplemented, or not, with pomegranate (HFD + P) or green tea (HFD + GT) extracts. After the nutritional intervention, mice were killed and gastrocnemius muscles were taken. Proteins and mRNA were measured by Western blot and RT-qPCR, respectively. RESULTS: Body weight gain and visceral fat were higher in HFD, HFD + P and HFD + GT than in CTRL. The markers of the unfolded protein response BiP, XBP1u, XBP1s and ATF4 were higher only in HFD. In HFD + P and HFD + GT, this increase was not observed except for CHOP, which was elevated in all HFD groups. HFD increased also markers of ubiquitin-proteasome pathway, autophagy and oxidative stress, which were kept low in HFD + P and HFD + GT groups. CONCLUSION: Our data provide evidence for a protective effect of pomegranate and green tea extracts against ER stress, oxidative stress and protein degradation induced by HFD in skeletal muscle. They give arguments for a usefulness of these natural nutritional compounds to fight against cellular dysfunctions related to fat excess.

Activation of ER stress by hydrogen peroxide in C2C12 myotubes.

The purpose of this study was to examine the link between oxidative stress and endoplasmic reticulum (ER) stress in myogenic cells. C2C12 myotubes were incubated with hydrogen peroxide (H2O2, 200 µM) and harvested 4h or 17 h after the induction of this oxidative stress. A massive upregulation of binding immunoglobulin protein (BiP) was found, indicating the presence of ER stress. Nevertheless, the three branches of the unfolded protein response (UPR) were not activated to the same extent. The double-stranded RNA-dependent protein kinase (PKR)-like ER kinase (PERK) branch was the most activated as shown by the increase of phospho-eukaryotic translation-initiation factor 2α (eIF2α, Ser51) and the mRNA levels of activating transcription factor 4 (ATF4), C/EBP homologous (CHOP) and tribbles homolog 3 (TRB3). The slight increase in the spliced form of X-box binding protein 1 (XBP1s) together with the decrease of the unspliced form (XBP1u) indicated a higher endoribonuclease activity of inositol-requiring 1α (IRE1α). The transcriptional activity of activating transcription factor 6 (ATF6) remained unchanged after incubation with H2O2. The mechanisms by which the three branches of UPR can be specifically regulated by oxidative stress are currently unresolved and need further investigations.

Regulation of ubiquitin-proteasome and autophagy pathways after acute LPS and epoxomicin administration in mice.

BACKGROUND: The ubiquitin-proteasome pathway (UPP) is a major protein degradation pathway that is activated during sepsis and has been proposed as a therapeutic target for preventing skeletal muscle loss due to cachexia. Although several studies have investigated the modulation of proteasome activity in response to LPS administration, none have characterized the overall UPP response to LPS administration in the fate of proteasome inhibition. METHODS: Here, we determined the modulation pattern of the main key components of the UPP in the gastrocnemius (GAS) of mice during the acute phase of lipopolysaccharide (LPS)-mediated endotoxemia (7.5 mg/kg - 8 h) by measuring all three ß1, ß2 and ß5 activites of the 20S and 26S proteasomes, the levels of steady state polyubiquitinated proteins, mRNA levels of muscle ligases, as well as signaling pathways regulating the UPP. Another goal was to assess the effects of administration of a specific proteasome inhibitor (epoxomicin, 0.5 mg/kg) on UPP response to sepsis. RESULTS: The acute phase of LPS-induced endotoxemia lowered GAS/body weight ratio and increased MuRF1 and MAFbx mRNA concomitantly to an activation of the pathways known to regulate their expression. Unexpectedly, we observed a decrease in all 20S and 26S proteasome activities measured in GAS, which might be related to oxidative stress, as oxidized proteins (carbonyl levels) increase with LPS. While significantly inhibiting 20S and 26S proteasome ß5 activities in heart and liver, epoxomicin did not lower proteasome activity in GAS. However, the increase in mRNA expression of the muscle ligases MuRF1 and MAFbx were partially rescued without affecting the other investigated signaling pathways. LPS also strongly activated autophagy, which could explain the observed GAS atrophy with LPS-induced reduction of proteasome activity. CONCLUSIONS: Our results highlight an opposite regulation of UPP in the early hours of LPS-induced muscle atrophy by showing reduced proteasome activities and increased mRNA expression of muscle specific ligases. Furthermore, our data do not support any preventive effect of epoxomicin in muscle atrophy due to acute cachexia since proteasome activities are not further repressed.

Repeated Sprint Training in Hypoxia Improves Repeated Sprint Ability to Exhaustion Similarly in Active Males and Females.

PURPOSE: The aim of this study was to compare the physiological adaptations of males and females to repeated sprint training in hypoxia. METHODS: Active males and females completed 7 weeks of repeated sprint training in normoxia (RSN, FiO2 = 0.209, males: n = 11, females: n = 8) or hypoxia (RSH, FiO2 = 0.146, males: n = 12, females: n = 10). Before (Pre-) and after (Post-) training, a repeated sprint ability test (RSA) was performed (10 s cycle sprints with 20 s recovery between sprints, until exhaustion), and aerobic and anaerobic qualities were evaluated in normoxia. RESULTS: The number of sprints during RSA increased after training in HYP from 11 to 21 in males and from 8 to 14 in females (p < 0.001, CI = [5, 11]), without significant changes after RSN (10 vs 14 and 8 vs 10 in males and females, respectively). No improvements in mean or peak power output were found in either group. Total work during RSA improved after training in all groups (+9 ± 2 kJ, p < 0.001). Tissue saturation index (TSI) during the repeated sprints was higher in females than males (+10 ± 2 %, p < 0.001). The difference in TSI between the recovery and sprint phases remained unchanged after training. VO2peak during an incremental exercise test increased in all groups (+3 ± 1 ml·kg-1·min-1, p = 0.039). Mean power output during a Wingate test also increased in both males and females in RSN and RSH (+0.38 ± 0.18 W·kg-1, p = 0.036). No changes were observed in hematological parameters after training. CONCLUSIONS: Seven weeks of RSH further increased the number of repeated sprints performed to exhaustion compared to RSN in females, in the same order of magnitude as in males.