Effects of a 6-wk Sprint Interval Training Protocol at Different Altitudes on Circulating Extracellular Vesicles

PURPOSE

This study aimed to investigate the modulation of circulating exosome-like extracellular vesicles (ELVs) after 6 wk of sprint interval training (SIT) at sea level and at 2000, 3000, and 4000 m.

METHODS

Thirty trained endurance male athletes (18-35 yr) participated in a 6-wk SIT program (30-s all-out sprint, 4-min 30-s recovery; 4-9 repetitions, 2 sessions per week) at sea level ( n = 8), 2000 m (fraction of inspired oxygen (F io2 ) 0.167, n = 8), 3000 m (F io2 0.145, n = 7), or 4000 m (F io2 0.13, n = 7). Venous blood samples were taken before and after the training period. Plasma ELVs were isolated by size exclusion chromatography, counted by nanoparticle tracking analysis, and characterized according to international standards. Candidate ELV microRNAs (miRNAs) were quantified by real-time polymerase chain reaction.

RESULTS

When the three hypoxic groups were analyzed separately, only very minor differences could be detected in the levels of circulating particles, ELV markers, or miRNA. However, the levels of circulating particles increased (+262%) after training when the three hypoxic groups were pooled, and tended to increase at sea level (+65%), with no difference between these two groups. A trend to an increase was observed for the two ELV markers, TSG101 (+65%) and HSP60 (+441%), at sea level, but not in hypoxia. Training also seemed to decrease the abundance of miR-23a-3p and to increase the abundance of miR-21-5p in hypoxia but not at sea level.

CONCLUSIONS

A 6-wk SIT program tended to increase the basal levels of circulating ELVs when performed at sea level but not in hypoxia. In contrast, ELV miRNA cargo seemed to be modulated in hypoxic conditions only. Further research should explore the potential differences in the origin of ELVs between normoxic and local and systemic hypoxic conditions.

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.

Effects of Sprint Interval Training at Different Altitudes on Cycling Performance at Sea-Level

BACKGROUND

Benefits of sprint interval training performed in hypoxia (SIH) compared to normoxia (SIN) have been assessed by studies mostly conducted around 3000 m of simulated altitude. The present study aims to determine whether SIH at an altitude as high as 4000 m can elicit greater adaptations than the same training at 2000 m, 3000 m or sea-level.

METHODS

Thirty well-trained endurance male athletes (18-35 years old) participated in a six-week repeated sprint interval training program (30 s all-out sprint, 4 min 30 s recovery; 4-9 repetitions, 2 sessions/week) at sea-level (SL, n = 8), 2000 m (FiO2 16.7%, n = 8), 3000 m (FiO2 14.5%, n = 7) or 4000 m (FiO2 13.0%, n = 7). Aerobic and anaerobic exercise components were evaluated by an incremental exercise test, a 600 kJ time trial and a Wingate test before and after the training program.

RESULTS

After training, peak power output (PPO) during the incremental exercise test increased (~6%) without differences between groups. The lactate threshold assessed by Dmax increased at 2000 m (+14 ± 12 W) and 4000 m (+12 ± 11 W) but did not change at SL and 3000 m. Mean power during the Wingate test increased at SL, 2000 m and 4000 m, although peak power increased only at 4000 m (+38 ± 38 W).

CONCLUSIONS

The present study indicates that SIH using 30 s sprints is as efficient as SIN for improving aerobic and anaerobic qualities. Additional benefits such as lactate-related adaptations were found only in SIH and Wingate peak power only increased at 4000 m. This finding is of particular interest for disciplines requiring high power output, such as in very explosive sports.

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; β-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.

Does High Cardiorespiratory Fitness Confer Some Protection Against Proinflammatory Responses After Infection by SARS-CoV-2?

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) originated in China in late 2019 and has since spread rapidly to every continent in the world. This pandemic continues to cause widespread personal suffering, along with severe pressure on medical and health care providers. The symptoms of SARS-CoV-2 and the subsequent prognosis are worsened in individuals who have preexisting comorbidities prior to infection by the virus. Individuals with obesity or overweight, insulin resistance, and diabetes typically have chronic low-grade inflammation characterized by increased levels of several proinflammatory cytokines and the inflammasome; this state predisposes to greater risk for infection along with more adverse outcomes. Here, we consider whether a high level of cardiorespiratory fitness induced by prior exercise training may confer some innate immune protection against COVID-19 by attenuating the "cytokine storm syndrome" often experienced by "at risk" individuals.

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 (VO_2max ) is the gold standard to assess exercise tolerance in healthy subjects (HS). Among patients with MS, the accuracy of VO_2max 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 (PWC_75% ), 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 PWC_75% ). 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 VO_2peak , in both groups, without difference between groups. PWR-based prediction of VO_2peak showed a standard error of the estimate of 315 mL min^-1 in HS and 176 mL min^-1 in MS. PWC_75% did not correlate to VO_2peak 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 VO_2peak are usable to accurately assess exercise tolerance.

Myoferlin Is a Yet Unknown Interactor of the Mitochondrial Dynamics' Machinery in Pancreas Cancer Cells

Pancreas ductal adenocarcinoma is one of the deadliest cancers where surgery remains the main survival factor. Mitochondria were described to be involved in tumor aggressiveness in several cancer types including pancreas cancer. We have previously reported that myoferlin controls mitochondrial structure and function, and demonstrated that myoferlin depletion disturbs the mitochondrial dynamics culminating in a mitochondrial fission. In order to unravel the mechanism underlying this observation, we explored the myoferlin localization in pancreatic cancer cells and showed a colocalization with the mitochondrial dynamic machinery element: mitofusin. This colocalization was confirmed in several pancreas cancer cell lines and in normal cell lines as well. Moreover, in pancreas cancer cell lines, it appeared that myoferlin interacted with mitofusin. These discoveries open-up new research avenues aiming at modulating mitofusin function in pancreas cancer.

Regular Endurance Exercise Promotes Fission, Mitophagy, and Oxidative Phosphorylation in Human Skeletal Muscle Independently of Age

This study investigated whether regular endurance exercise maintains basal mitophagy and mitochondrial function during aging. Mitochondrial proteins and total mRNA were isolated from vastus lateralis biopsies (n = 33) of young sedentary (YS), old sedentary (OS), young active (YA), and old active (OA) men. Markers for mitophagy, fission, fusion, mitogenesis, and mitochondrial metabolism were assessed using qRT-PCR, Western blot, and immunofluorescence staining. Independently of age, fission protein Fis1 was higher in active vs. sedentary subjects (+80%; P < 0.05). Mitophagy protein PARKIN was more elevated in OA than in OS (+145%; P = 0.0026). mRNA expression of Beclin1 and Gabarap, involved in autophagosomes synthesis, were lower in OS compared to YS and OA (P < 0.05). Fusion and oxidative phosphorylation proteins were globally more elevated in the active groups (P < 0.05), while COx activity was only higher in OA than in OS (P = 0.032). Transcriptional regulation of mitogenesis did not vary with age or exercise. In conclusion, physically active lifestyle seems to participate in the maintenance of lifelong mitochondrial quality control by increasing fission and mitophagy.

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.

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 (NN_SL); 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.

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.

Electronic supplementary material

The online version of this article (10.1186/s12915-018-0525-4) contains supplementary material, which is available to authorized users.

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.

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.

Activating transcription factor 3 regulates chemokine expression in contracting C2C12 myotubes and in mouse skeletal muscle after eccentric exercise

Activating transcription factor (ATF) 3 regulates chemokine expression in various cell types and tissues. Herein, we studied this regulation in contracting muscle cells in vitro, and in skeletal muscle after muscle-damaging exercise in vivo. C₂C₁₂ myotubes with normal or low ATF3 levels (atf3_siRNA) were electrically stimulated (EPS). Also, ATF3-knockout (ATF3-KO) and control mice ran downhill until exhaustion, and muscles were analyzed post-exercise. EPS increased ATF3 levels in myotubes (P < 0.01). Chemokine C-C motif ligand (ccl) 2 mRNA increased post-EPS, but atf3_siRNA attenuated the response (P < 0.05). Atf3_siRNA up-regulated ccl6 basal mRNA, and down-regulated ccl9 and chemokine C-X-C motif ligand (cxcl) 1 basal mRNAs. Post-exercise, ATF3-KO mice showed exacerbated mRNA levels of ccl6 and ccl9 in soleus (P < 0.05), and similar trends were observed for ccl2 and interleukin (il) 1β (P < 0.09). In quadriceps, il6 mRNA level increased only in ATF3-KO (P < 0.05), and cxcl1 mRNA showed a similar trend (P = 0.082). Cluster of differentiation-68 (cd68) mRNA, a macrophage marker, increased in quadriceps and soleus independently of genotype (P < 0.001). Our data demonstrate that ATF3 regulates chemokine expression in muscle cells in vitro and skeletal muscle in vivo, but the regulation differs in each model. Cells other than myofibers may thus participate in the response observed in skeletal muscle. Our results also indicate that ATF3-independent mechanisms would regulate macrophage infiltration upon muscle-damaging exercise. The implications of chemokine regulation in skeletal muscle remain to be determined.

Urolithin B, a newly identified regulator of skeletal muscle mass

BACKGROUND

The control of muscle size is an essential feature of health. Indeed, skeletal muscle atrophy leads to reduced strength, poor quality of life, and metabolic disturbances. Consequently, strategies aiming to attenuate muscle wasting and to promote muscle growth during various (pathological) physiological states like sarcopenia, immobilization, malnutrition, or cachexia are needed to address this extensive health issue. In this study, we tested the effects of urolithin B, an ellagitannin-derived metabolite, on skeletal muscle growth.

METHODS

C2C12 myotubes were treated with 15 μM of urolithin B for 24 h. For in vivo experiments, mice were implanted with mini-osmotic pumps delivering continuously 10 μg/day of urolithin B during 28 days. Muscle atrophy was studied in mice with a sciatic nerve denervation receiving urolithin B by the same way.

RESULTS

Our experiments reveal that urolithin B enhances the growth and differentiation of C2C12 myotubes by increasing protein synthesis and repressing the ubiquitin-proteasome pathway. Genetic and pharmacological arguments support an implication of the androgen receptor. Signalling analyses suggest a crosstalk between the androgen receptor and the mTORC1 pathway, possibly via AMPK. In vivo experiments confirm that urolithin B induces muscle hypertrophy in mice and reduces muscle atrophy after the sciatic nerve section.

CONCLUSIONS

This study highlights the potential usefulness of urolithin B for the treatment of muscle mass loss associated with various (pathological) physiological states.

Hippo Pathway and Skeletal Muscle Mass Regulation in Mammals: A Controversial Relationship

Skeletal muscle mass reflects a dynamic turnover between net protein synthesis and degradation. In addition, satellite cell inclusion may contribute to increase muscle mass while fiber loss results in a reduction of muscle mass. Since 2010, a few studies looked at the involvement of the newly discovered Hippo pathway in the regulation of muscle mass. In line with its roles in other organs, it has been hypothesized that the Hippo pathway could play a role in different regulatory mechanisms in skeletal muscle as well, namely proliferation and renewal of satellite cells, differentiation, death, and growth of myogenic cells. While the Hippo components have been identified in skeletal muscle, their role in muscle mass regulation has been less investigated and conflicting results have been reported. Indeed, the first studies described both atrophic and hypertrophic roles of the Hippo pathway and its effectors Yap/Taz using different biochemical approaches. Further, investigation is therefore warranted to determine the role of the Hippo pathway in the regulation of skeletal muscle mass. New components of the pathway will probably emerge and unsuspected roles will likely be discovered due to its numerous interactions with different cellular processes. This mini-review aims to summarize the current literature concerning the roles of the Hippo pathway in the regulation of muscle mass and to develop the hypothesis that this pathway could contribute to muscle mass adaptation after exercise.

Pomegranate extract prevents skeletal muscle of mice against wasting induced by acute TNF-α injection

SCOPE

We investigated whether punicalagin-rich pomegranate extract (PE) protects skeletal muscle of mice against inflammation induced by an acute injection of TNF-α.

RESULTS

Mice fed with PE or standard chow during 6 wk were injected with TNF-α (100 ng/g) or vehicle and sacrificed 6 h later. Prior supplementation with PE prevented the loss of tibialis anterior mass induced by TNF-α. In skeletal muscle, the activation of the NF-κB signaling and the induction of cytokines mRNA were reduced in mice having received PE. In those mice, the activity of the Akt/mTORC1 pathway and the protein synthesis were maintained after TNF-α injection whereas markers involved in the ubiquitin proteasome pathway were less activated. As urolithin A was the only punicalagin metabolite detectable in plasma of mice supplemented with PE, we performed in vitro experiments using a murine cell line (C2C12) to provide evidence that urolithin A is likely the active compound protecting skeletal muscle against TNF-α-induced inflammation.

CONCLUSION (FOCUS ON NUTRITIONAL RELEVANCE)

These results suggest that supplementation with a punicalagin-rich PE may protect skeletal muscle against an acute inflammation.

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, il1β, 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.

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.

Nuclear respiratory factor 1 and endurance exercise promote human telomere transcription

DNA breaks activate the DNA damage response and, if left unrepaired, trigger cellular senescence. Telomeres are specialized nucleoprotein structures that protect chromosome ends from persistent DNA damage response activation. Whether protection can be enhanced to counteract the age-dependent decline in telomere integrity is a challenging question. Telomeric repeat-containing RNA (TERRA), which is transcribed from telomeres, emerged as important player in telomere integrity. However, how human telomere transcription is regulated is still largely unknown. We identify nuclear respiratory factor 1 and peroxisome proliferator-activated receptor γ coactivator 1α as regulators of human telomere transcription. In agreement with an upstream regulation of these factors by adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK), pharmacological activation of AMPK in cancer cell lines or in normal nonproliferating myotubes up-regulated TERRA, thereby linking metabolism to telomere fitness. Cycling endurance exercise, which is associated with AMPK activation, increased TERRA levels in skeletal muscle biopsies obtained from 10 healthy young volunteers. The data support the idea that exercise may protect against aging.

Fifteen days of 3,200 m simulated hypoxia marginally regulates markers for protein synthesis and degradation in human skeletal muscle

Chronic hypoxia leads to muscle atrophy. The molecular mechanisms responsible for this phenomenon are not well defined in vivo. We sought to determine how chronic hypoxia regulates molecular markers of protein synthesis and degradation in human skeletal muscle and whether these regulations were related to the regulation of the hypoxia-inducible factor (HIF) pathway. Eight young male subjects lived in a normobaric hypoxic hotel (FiO₂ 14.1%, 3,200 m) for 15 days in well-controlled conditions for nutrition and physical activity. Skeletal muscle biopsies were obtained in the musculus vastus lateralis before (PRE) and immediately after (POST) hypoxic exposure. Intramuscular hypoxia-inducible factor-1 alpha (HIF-1α) protein expression decreased (-49%, P=0.03), whereas hypoxia-inducible factor-2 alpha (HIF-2α) remained unaffected from PRE to POST hypoxic exposure. Also, downstream HIF-1α target genes VEGF-A (-66%, P=0.006) and BNIP3 (-24%, P=0.002) were downregulated, and a tendency was measured for neural precursor cell expressed, developmentally Nedd4 (-47%, P=0.07), suggesting lowered HIF-1α transcriptional activity after 15 days of exposure to environmental hypoxia. No difference was found on microtubule-associated protein 1 light chain 3 type II/I (LC3b-II/I) ratio, and P62 protein expression tended to increase (+45%, P=0.07) compared to PRE exposure levels, suggesting that autophagy was not modulated after chronic hypoxia. The mammalian target of rapamycin complex 1 pathway was not altered as Akt, mammalian target of rapamycin, S6 kinase 1, and 4E-binding protein 1 phosphorylation did not change between PRE and POST. Finally, myofiber cross-sectional area was unchanged between PRE and POST. In summary, our data indicate that moderate chronic hypoxia differentially regulates HIF-1α and HIF-2α, marginally affects markers of protein degradation, and does not modify markers of protein synthesis or myofiber cross-sectional area in human skeletal muscle.

Aging Reduces the Activation of the mTORC1 Pathway after Resistance Exercise and Protein Intake in Human Skeletal Muscle: Potential Role of REDD1 and Impaired Anabolic Sensitivity

This study was designed to better understand the molecular mechanisms involved in the anabolic resistance observed in elderly people. Nine young (22 ± 0.1 years) and 10 older (69 ± 1.7 years) volunteers performed a one-leg extension exercise consisting of 10 × 10 repetitions at 70% of their 3-RM, immediately after which they ingested 30 g of whey protein. Muscle biopsies were taken from the vastus lateralis at rest in the fasted state and 30 min after protein ingestion in the non-exercised (Pro) and exercised (Pro+ex) legs. Plasma insulin levels were determined at the same time points. No age difference was measured in fasting insulin levels but the older subjects had a 50% higher concentration than the young subjects in the fed state (p < 0.05). While no difference was observed in the fasted state, in response to exercise and protein ingestion, the phosphorylation state of PKB (p < 0.05 in Pro and Pro+ex) and S6K1 (p = 0.059 in Pro; p = 0.066 in Pro+ex) was lower in the older subjects compared with the young subjects. After Pro+ex, REDD1 expression tended to be higher (p = 0.087) in the older group while AMPK phosphorylation was not modified by any condition. In conclusion, we show that the activation of the mTORC1 pathway is reduced in skeletal muscle of older subjects after resistance exercise and protein ingestion compared with young subjects, which could be partially due to an increased expression of REDD1 and an impaired anabolic sensitivity.

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.

Recommendations for Healthy Nutrition in Female Endurance Runners: An Update

The purpose of this review is to present the basic principles of a healthy nutrition in female endurance runner enriched by the latest scientific recommendations. Female endurance runners are a specific population of athletes who need to take specifically care of daily nutrition due to the high load of training and the necessity to keep a rather low body mass. This paradoxical situation can create some nutritional imbalances and deficiencies. Female endurance athletes should pay attention to their total energy intake, which is often lower than their energy requirement. The minimal energy requirement has been set to 45 kcal/kg fat free mass/day plus the amount of energy needed for physical activity. The usual recommended amount of 1.2–1.4 g protein/kg/day has recently been questioned by new findings suggesting that 1.6 g/kg/day would be more appropriate for female athletes. Although a bit less sensitive to carbohydrate loading than their male counterparts, female athletes can benefit from this nutritional strategy before a race if the amount of carbohydrates reaches 8 g/kg/day and if their daily total energy intake is sufficient. A poor iron status is a common issue in female endurance runners but iron-enriched food as well as iron supplementation may help to counterbalance this poor status. Finally, they should also be aware that they may be at risk for low calcium and vitamin D levels.

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 β1, β2 and β5 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 β5 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.

Higher activation of autophagy in skeletal muscle of mice during endurance exercise in the fasted state

Activation of autophagy in skeletal muscle has been reported in response to endurance exercise and food deprivation independently. The purpose of this study was to evaluate whether autophagy was more activated when both stimuli were combined, namely when endurance exercise was performed in a fasted rather than a fed state. Mice performed a low-intensity running exercise (10 m/min for 90min) in both dietary states after which the gastrocnemius muscles were removed. LC3b-II, a marker of autophagosome presence, increased in both conditions, but the increase was higher in the fasted state. Other protein markers of autophagy, like Gabarapl1-II and Atg12 conjugated form as well as mRNA of Lc3b, Gabarapl1, and p62/Sqstm1 were increased only when exercise was performed in a fasted state. The larger activation of autophagy by exercise in a fasted state was associated with a larger decrease in plasma insulin and phosphorylation of Akt(Ser473), Akt(Thr308), FoxO3a(Thr32), and ULK1(Ser757). AMPKα(Thr172), ULK1(Ser317), and ULK1(Ser555) remained unchanged in both conditions, whereas p38(Thr180/Tyr182) increased during exercise to a similar extent in the fasted and fed conditions. The marker of mitochondrial fission DRP1(Ser616) was increased by exercise independently of the nutritional status. Changes in mitophagy markers BNIP3 and Parkin suggest that mitophagy was increased during exercise in the fasted state. In conclusion, our results highlight a major implication of the insulin-Akt-mTOR pathway and its downstream targets FoxO3a and ULK1 in the larger activation of autophagy observed when exercise is performed in a fasted state compared with a fed state.

Effect of acute environmental hypoxia on protein metabolism in human skeletal muscle

Hypoxia-induced muscle wasting has been observed in several environmental and pathological conditions. However, the molecular mechanisms behind this loss of muscle mass are far from being completely elucidated, certainly in vivo. When studying the regulation of muscle mass by environmental hypoxia, many confounding factors have to be taken into account, such as decreased protein ingestion, sleep deprivation or reduced physical activity, which make difficult to know whether hypoxia per se causes a reduction in muscle mass.

AIM

We hypothesized that acute exposure to normobaric hypoxia (11% O2 ) would repress the activation of the mTOR pathway usually observed after a meal and would activate the proteolytic pathways in skeletal muscle.

METHODS

Fifteen subjects were exposed passively for 4 h to normoxic and hypoxic conditions in a random order after consumption of a light breakfast. A muscle biopsy and a blood sample were taken before, after 1 and 4 h of exposure.

RESULTS

After 4 h, plasma insulin concentration and the phosphorylation state of PKB and S6K1 in skeletal muscle were higher in hypoxia than in normoxia (P < 0.05). At the same time, Redd1 mRNA level was upregulated (P < 0.05), whilst MAFbx mRNA decreased (P < 0.05) in hypoxia compared with normoxia. Proteasome, cathepsin L and calpain activities were not altered by environmental hypoxia.

CONCLUSION

Contrary to our hypothesis and despite an increase in the mRNA level of Redd1, an inhibitor of the mTORC1 pathway, short-term acute environmental hypoxia induced a higher response of PKB and S6K1 to a meal, which may be due to increased plasma insulin concentration.

TLR2 and TLR4 activate p38 MAPK and JNK during endurance exercise in skeletal muscle

PURPOSE

Toll-like receptors 2 and 4 (TLR2, TLR4) are found in the membrane of skeletal muscle cells. A variety of molecular components can activate TLR2 and TLR4, among others, long-chain fatty acids. The subsequent downstream signaling triggers the mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB) pathways. Therefore, the purpose of this study was to test whether an elevation of extracellular nonesterified fatty acids (NEFA) observed during endurance exercise may activate the MAPK and NF-κB pathways via TLR2 and TLR4.

METHODS

tlr2 and tlr4 mice and wild-type C57BL/6J animals (WT) were submitted to a standardized endurance exercise.

RESULTS

Immediately after exercise, the phosphorylation state of p38 MAPK, c-Jun NH2-terminal kinase (JNK), and c-Jun was increased in the tibialis anterior (TA) and soleus (SOL) muscles of WT (P < 0.05). The phosphorylation state of extracellular signal-regulated kinases 1 and 2 (ERK1/2) and IκB kinase α/β and the DNA-binding of NF-κB remained unchanged. The activation of p38 MAPK, JNK, and c-Jun was completely blunted in TA of tlr2 and tlr4 mice, whereas in SOL, it represented only 25% of the increase observed in WT mice. The causal relationship between NEFA concentration and MAPK activation was evaluated by injecting mice with heparin. A similar increase in plasma NEFA was observed after heparin injection than after endurance exercise. JNK and p38 MAPK were activated under heparin in TA and SOL of WT (P < 0.05) but not in muscles of tlr2 and tlr4 mice.

CONCLUSIONS

The present study supports the idea that during endurance exercise, TLR2 and TLR4 mediate a signal linking the elevated plasma NEFA concentration to the activation of p38 MAPK and JNK.

Role of alpha-actinin-3 in contractile properties of human single muscle fibers: a case series study in paraplegics

A common nonsense polymorphism in the ACTN3 gene results in the absence of α-actinin-3 in XX individuals. The wild type allele has been associated with power athlete status and an increased force output in numeral studies, though the mechanisms by which these effects occur are unclear. Recent findings in the Actn3(-/-) (KO) mouse suggest a shift towards 'slow' metabolic and contractile characteristics of fast muscle fibers lacking α-actinin-3. Skinned single fibers from the quadriceps muscle of three men with spinal cord injury (SCI) were tested regarding peak force, unloaded shortening velocity, force-velocity relationship, passive tension and calcium sensitivity. The SCI condition induces an 'equal environment condition' what makes these subjects ideal to study the role of α-actinin-3 on fiber type expression and single muscle fiber contractile properties. Genotyping for ACTN3 revealed that the three subjects were XX, RX and RR carriers, respectively. The XX carrier's biopsy was the only one that presented type I fibers with a complete lack of type II(x) fibers. Properties of hybrid type II(a)/II(x) fibers were compared between the three subjects. Absence of α-actinin-3 resulted in less stiff type II(a)/II(x) fibers. The heterozygote (RX) exhibited the highest fiber diameter (0.121±0.005 mm) and CSA (0.012±0.001 mm(2)) and, as a consequence, the highest peak force (2.11±0.14 mN). Normalized peak force was similar in all three subjects (P = 0.75). Unloaded shortening velocity was highest in R-allele carriers (P<0.001). No difference was found in calcium sensitivity. The preservation of type I fibers and the absence of type II(x) fibers in the XX individual indicate a restricted transformation of the muscle fiber composition to type II fibers in response to long-term muscle disuse. Lack of α-actinin-3 may decrease unloaded shortening velocity and increase fiber elasticity.

Endurance training in mice increases the unfolded protein response induced by a high-fat diet

Certain conditions, such as several weeks of high-fat diet, disrupt endoplasmic reticulum (ER) homeostasis and activate an adaptive pathway referred as the unfolded protein response. When the unfolded protein response fails, the result is the development of inflammation and insulin resistance. These two pathological states are known to be improved by regular exercise training but the mechanisms remain largely undetermined. As it has recently been shown that the unfolded protein response is regulated by exercise, we hypothesised that concomitant treadmill exercise training (HFD+ex) prevents ER homeostasis disruption and its downstream consequences induced by a 6-week high-fat diet (HFD) in mice by activating the protective unfolded protein response. Several well-documented markers of the unfolded protein response were measured in the soleus and tibialis anterior muscles as well as in the liver and pancreas. In HFD mice, an increase in these markers was observed (from 2- to 15-fold, P < 0.05) in all tissues studied. The combination of HFD+ex increased the expression of several markers further, up to 100 % compared to HFD alone (P < 0.05). HFD increased inflammatory markers both in the plasma (IL-6 protein, 2.5 ± 0.52-fold; MIP-1α protein, 1.3 ± 0.13-fold; P < 0.05) and in the tissues studied, and treadmill exercise attenuated the inflammatory state induced by HFD (P < 0.05). However, treadmill exercise could not reverse HFD-induced whole body glucose intolerance, assessed by OGTT (AUC, 1.8 ± 0.29-fold, P < 0.05). In conclusion, our results show that a HFD activated the unfolded protein response in mouse tissues in vivo, and that endurance training promoted this response. We speculate that the potentiation of the unfolded protein response by endurance training may represent a positive adaptation protecting against further cellular stress.

Modulation of autophagy and ubiquitin-proteasome pathways during ultra-endurance running

In this study, the coordinated activation of ubiquitin-proteasome pathway (UPP), autophagy-lysosomal pathway (ALP), and mitochondrial remodeling including mitophagy was assessed by measuring protein markers during ultra-endurance running exercise in human skeletal muscle. Eleven male, experienced ultra-endurance athletes ran for 24 h on a treadmill. Muscle biopsy samples were taken from the vastus lateralis muscle 2 h before starting and immediately after finishing exercise. Athletes ran 149.8 ± 16.3 km with an effective running time of 18 h 42 min ( ± 41 min). The phosphorylation state of Akt (-74 ± 5%; P < 0.001), FOXO3a (-49 ± 9%; P < 0.001), mTOR Ser2448 (-32 ± 14%; P = 0.028), and 4E-BP1 (-34 ± 7%; P < 0.001) was decreased, whereas AMPK phosphorylation state increased by 247 ± 170% (P = 0.042). Proteasome β2 subunit activity increased by 95 ± 44% (P = 0.028), whereas the activities associated with the β1 and β5 subunits remained unchanged. MuRF1 protein level increased by 55 ± 26% (P = 0.034), whereas MAFbx protein and ubiquitin-conjugated protein levels did not change. LC3bII increased by 554 ± 256% (P = 0.005), and the form of ATG12 conjugated to ATG5 increased by 36 ± 17% (P = 0.042). The mitochondrial fission marker phospho-DRP1 increased by 110 ± 47% (P = 0.003), whereas the fusion marker Mfn1 and the mitophagy markers Parkin and PINK1 remained unchanged. These results fit well with a coordinated regulation of ALP and UPP triggered by FOXO3 and AMPK during ultra-endurance exercise.

Autophagy-related and autophagy-regulatory genes are induced in human muscle after ultraendurance exercise

The purpose of this study was to evaluate whether ultra endurance exercise changes the mRNA levels of the autophagy-related and autophagy-regulatory genes. Eight men (44 ± 1 years, range: 38-50 years) took part in a 200-km running race. The average running time was 28 h 03 min ± 2 h 01 min (range: 22 h 15 min-35 h 04 min). A muscle sample was taken from the vastus lateralis 2 weeks prior to the race and 3 h after arrival. Gene expression was assessed by RT-qPCR. Transcript levels of autophagy-related genes were increased by 49% for ATG4b (P = 0.025), 57% for ATG12 (P = 0.013), 286% for Gabarapl1 (P = 0.008) and 103% for LC3b (P = 0.011). The lysosomal enzyme cathepsin L mRNA was upregulated by 123% (P = 0.003). Similarly, transcript levels of the autophagy-regulatory genes BNIP3 and BNIP3l were both increased by 113% (P = 0.031 and P = 0.007, respectively). Since upregulation of these genes has been related with an increased autophagic flux in various models, our results strongly suggest that autophagy is activated in response to ultra endurance exercise.

Hepatic n-3 polyunsaturated fatty acid depletion promotes steatosis and insulin resistance in mice: genomic analysis of cellular targets

Patients with non-alcoholic fatty liver disease are characterised by a decreased n-3/n-6 polyunsaturated fatty acid (PUFA) ratio in hepatic phospholipids. The metabolic consequences of n-3 PUFA depletion in the liver are poorly understood. We have reproduced a drastic drop in n-3 PUFA among hepatic phospholipids by feeding C57Bl/6J mice for 3 months with an n-3 PUFA depleted diet (DEF) versus a control diet (CT), which only differed in the PUFA content. DEF mice exhibited hepatic insulin resistance (assessed by euglycemic-hyperinsulinemic clamp) and steatosis that was associated with a decrease in fatty acid oxidation and occurred despite a higher capacity for triglyceride secretion. Microarray and qPCR analysis of the liver tissue revealed higher expression of all the enzymes involved in lipogenesis in DEF mice compared to CT mice, as well as increased expression and activation of sterol regulatory element binding protein-1c (SREBP-1c). Our data suggest that the activation of the liver X receptor pathway is involved in the overexpression of SREBP-1c, and this phenomenon cannot be attributed to insulin or to endoplasmic reticulum stress responses. In conclusion, n-3 PUFA depletion in liver phospholipids leads to activation of SREBP-1c and lipogenesis, which contributes to hepatic steatosis.

Endoplasmic reticulum stress markers and ubiquitin–proteasome pathway activity in response to a 200-km run

PURPOSE

This study investigated whether a 200-km run modulates signaling pathways implicated in cellular stress in skeletal muscle, with special attention paid to the endoplasmic reticulum (ER) stress and to the activation of the ubiquitin-proteasome pathway.

METHODS

Eight men ran 200 km (28 h 03 min ± 2 h 01 min). Two muscle biopsies were obtained from the vastus lateralis muscle 2 wk before and 3 h after the race. Mitogen-activated protein kinase, ubiquitin-proteasome pathway, ER stress, inflammation, and oxidative stress markers were assayed by Western blot analysis or by quantitative real-time polymerase chain reaction. Chymotrypsin-like activity of the proteasome was measured by a fluorimetric assay.

RESULTS

Phosphorylation states of extracellular signal-related kinase 1/2 (+401% ± 173.8%, P = 0.027) and c-Jun N-terminal (+149% ± 61.9%, P = 0.023) increased after the race, whereas p38 phosphorylation remained unchanged. Increases in BiP (+235% ± 94.7%, P = 0.021) and in the messenger RNA level of total (+138% ± 31.2%, P = 0.002) and spliced X-box binding protein 1 (+241% ± 53.3%, P = 0.001) indicated the presence of ER stress. Transcripts of inflammatory markers interleukin-6 (+403% ± 96.1%, P = 0.002) and tumor necrosis factor-α (+233% ± 58.4%, P = 0.003) as well as oxidative stress markers metallothionein 1F (+519% ± 258.3%, P = 0.042), metallothionein 1H (+666% ± 157.5%, P = 0.002), and nicotinamide adenine dinucleotide phosphate-oxidase (NADPH oxidase) (+162% ± 60.5%, P = 0.016) were increased. The messenger RNA level of the ubiquitin ligases muscle-specific RING finger 1 (+583% ± 244.3%, P = 0.024) and muscle atrophy F-box (+249% ± 83.8%, P = 0.011) and the C2 proteasome subunit (+116% ± 40.6%, P = 0.012) also increased. Surprisingly, the amount of ubiquitin-conjugated proteins and the chymotrypsin-like activity of the proteasome were decreased by 20% ± 8.3% (P = 0.025) and 21% ± 4.4% (P = 0.001), respectively. The expression of ubiquitin-specific protease 28 deubiquitinase was increased (+81% ± 37.9%, P = 0.034).

CONCLUSIONS

In the skeletal muscle, a 200-km run activates the expression of ubiquitin ligases muscle-specific RING finger 1 and muscle atrophy F-box as well as various cellular stresses, among which are ER stress, oxidative stress, and inflammation. Meanwhile, compensatory mechanisms seem also triggered: the unfolded protein response is up-regulated, and the chymotrypsin-like activity of the proteasome is repressed.

ER stress induces anabolic resistance in muscle cells through PKB-induced blockade of mTORC1

Background

Anabolic resistance is the inability to increase protein synthesis in response to an increase in amino acids following a meal. One potential mediator of anabolic resistance is endoplasmic reticulum (ER) stress. The purpose of the present study was to test whether ER stress impairs the response to growth factors and leucine in muscle cells.

Methods

Muscle cells were incubated overnight with tunicamycin or thapsigargin to induce ER stress and the activation of the unfolded protein response, mTORC1 activity at baseline and following insulin and amino acids, as well as amino acid transport were determined.

Results

ER stress decreased basal phosphorylation of PKB and S6K1 in a dose-dependent manner. In spite of the decrease in basal PKB phosphorylation, insulin (10–50 nM) could still activate both PKB and S6K1. The leucine (2.5–5 mM)-induced phosphorylation of S6K1 on the other hand was repressed by low concentrations of both tunicamycin and thapsigargin. To determine the mechanism underlying this anabolic resistance, several inhibitors of mTORC1 activation were measured. Tunicamycin and thapsigargin did not change the phosphorylation or content of either AMPK or JNK, both increased TRB3 mRNA expression and thapsigargin increased REDD1 mRNA. Tunicamycin and thapsigargin both decreased the basal phosphorylation state of PRAS40. Neither tunicamycin nor thapsigargin prevented phosphorylation of PRAS40 by insulin. However, since PKB is not activated by amino acids, PRAS40 phosphorylation remained low following the addition of leucine. Blocking PKB using a specific inhibitor had the same effect on both PRAS40 and leucine-induced phosphorylation of S6K1.

Conclusion

ER stress induces anabolic resistance in muscle cells through a PKB/PRAS40-induced blockade of mTORC1.

Prevention of muscle disuse atrophy by MG132 proteasome inhibitor

INTRODUCTION

Our goal was to determine whether in vivo administration of the proteasome inhibitor MG132 can prevent muscle atrophy caused by hindlimb unloading (HU).

METHODS

Twenty-seven NMRI mice were assigned to a weight-bearing control, a 6-day HU, or a HU+MG132 (1 mg/kg/48 h) treatment group.

RESULTS

Gastrocnemius wasting was significantly less in HU+MG132 mice (-6.7 ± 2.0%) compared with HU animals (-12.6 ± 1.1%, P = 0.011). HU was also associated with an increased expression of MuRF-1 (P = 0.006), MAFbx (P = 0.001), and USP28 (P = 0.027) mRNA, whereas Nedd4, E3α, USP19, and UBP45 mRNA did not change significantly. Increases in MuRF-1, MAFbx, and USP28 mRNA were largely repressed after MG132 administration. β5 proteasome activity tended to increase in HU (+16.7 ± 6.1%, P = 0.086). Neither β1 and β2 proteasome activities nor ubiquitin-conjugated proteins were changed by HU.

CONCLUSIONS

Our results indicate that in vivo administration of MG132 partially prevents muscle atrophy associated with disuse and highlight an unexpected regulation of MG132 proteasome inhibitor on ubiquitin-ligases.