Elodie Ponsot

Effect of interval versus continuous training on cardiorespiratory and mitochondrial functions: relationship to aerobic performance improvements in sedentary subjects

The goal of the study was to determine the effects of continuous (CT) vs. intermittent (IT) training yielding identical mechanical work and training duration on skeletal muscle and cardiorespiratory adaptations in sedentary subjects. Eleven subjects (6 men and 5 women, 45 +/- 3 years) were randomly assigned to either of the two 8-wk training programs in a cross-over design, separated by 12 wk of detraining. Maximal oxygen uptake (Vo2max) increased after both trainings (9% with CT vs. 15% with IT), whereas only IT was associated with faster Vo2 kinetics (tau: 68.0 +/- 1.6 vs. 54.9 +/- 0.7 s, P < 0.05) measured during a test to exhaustion (TTE) and with improvements in maximal cardiac output (Qmax, from 18.1 +/- 1.1 to 20.1 +/- 1.2 l/min; P < 0.01). Skeletal muscle mitochondrial oxidative capacities (Vmax) were only increased after IT (3.3 +/- 0.4 before and 4.5 +/- 0.6 micromol O2 x min(-1) x g dw(-1) after training; P < 0.05), whereas capillary density increased after both trainings, with a two-fold higher enhancement after CT (+21 +/- 1% for IT and +40 +/- 3% after CT, P < 0.05). The gain of Vmax was correlated with the gain of TTE and the gain of Vo2max with IT. The gain of Qmax was also correlated with the gain of VO2max. These results suggest that fluctuations of workload and oxygen uptake during training sessions, rather than exercise duration or global energy expenditure, are key factors in improving muscle oxidative capacities. In an integrative view, IT seems optimal in maximizing both peripheral muscle and central cardiorespiratory adaptations, permitting significant functional improvement. These data support the symmorphosis concept in sedentary subjects.

The biology of satellite cells and telomeres in human skeletal muscle: effects of aging and physical activity.

The decline in the neuromuscular function affects the physical performance and is a threat for independent living in later life. The age‐related decrease in muscle satellite cells observed by the age of 70 can be specific to type II fibers in some muscles. Several studies have shown that different forms of exercise induce the expansion of satellite cell pool in human skeletal muscle of young and elderly. Exercise is a powerful non‐pharmacological tool inducing the renewal of the satellite cell pool in skeletal muscles. Skeletal muscle is not a stable tissue as satellite cells are constantly recruited during normal daily activities. Satellite cells and the length of telomeres are important in the context of muscle regeneration. It is likely that the regulation of telomeres in vitro cannot fully mimic the behavior of telomeres in human tissues. New insights suggest that telomeres in skeletal muscle are dynamic structures under the influence of their environment. When satellite cells are heavily recruited for regenerative events as in the skeletal muscle of athletes, telomere length has been found to be either dramatically shortened or maintained and even longer than in non‐trained individuals. This suggests the existence of mechanisms allowing the control of telomere length in vivo.

Mitochondrial tissue specificity of substrates utilization in rat cardiac and skeletal muscles.

As energetic metabolism is crucial for muscles, they develop different adaptations to respond to fluctuating demand among muscle types. Whereas quantitative characteristics are known, no study described simultaneously quantitative and qualitative differences among muscle types in terms of substrates utilization patterns. This study thus defined the pattern of substrates preferential utilization by mitochondria from glycolytic gastrocnemius (GAS) and oxidative soleus (SOL) skeletal muscles and from heart left ventrical (LV) in rats. We measured in situ, ADP (2 mM)‐stimulated, mitochondrial respiration rates from skinned fibers in presence of increasing concentrations of pyruvate (Pyr) + malate (Mal), palmitoyl‐carnitine (Palm‐C) + Mal, glutamate (Glut) + Mal, glycerol‐3‐phosphate (G3‐P), lactate (Lact) + Mal. Because the fibers oxygen uptake (Vs) followed Michaelis–Menten kinetics in function of substrates level we determined the Vs and Km, representing maximal oxidative capacity and the mitochondrial sensibility for each substrate, respectively. Vs were in the order GAS < SOL < LV for Pyr, Glu, and Palm‐C substrates, whereas in the order SOL = LV < GAS with G3‐P. Moreover, the relative capacity to oxidize Palm‐C is extremely higher in LV than in SOL. Vs was not stimulated by the Lact substrate. The Km was equal for Pyr among muscles, but much lower for G3‐P in GAS and lower for Palm‐C in LV. These results demonstrate qualitative mitochondrial tissue specificity for metabolic pathways. Mitochondria of glycolytic muscle fibers are well adapted to play a central role for maintaining a satisfactory cytosolic redox state in these fibers, whereas mitochondria of LV developed important capacities to use fatty acids.

Effects of exercise and training in hypoxia on antioxidant/pro-oxidant balance

Objective:The aim was to investigate the effects of acute exercise under hypoxic condition and the repetition of such exercise in a ‘living low-training high’ training on the antioxidant/prooxidant balance.Design:Randomized, repeated measures design.Setting:Faculté de Médecine, Clermont-Ferrand, France.Subjects:Fourteen runners were randomly divided into two groups. A 6-week endurance training protocol integrated two running sessions per week at the second ventilatory threshold into the usual training.Intervention:A 6-week endurance training protocol integrated two running sessions per week at the second ventilatory threshold into the usual training. The first hypoxic group (HG, n=8) carried out these sessions under hypoxia (3000 m simulated altitude) and the second normoxic group (NG, n=6) in normoxia. In control period, the runners were submitted to two incremental cycling tests performed in normoxia and under hypoxia (simulated altitude of 3000 m). Plasma levels of advanced oxidation protein products (AOPP), malondialdehydes (MDA) and lipid oxidizability, ferric-reducing antioxidant power (FRAP), lipid-soluble antioxidants (α-tocopherol and β-carotene) normalized for triacyglycerols and cholesterol were measured before and after the two incremental tests and at rest before and after training.Results:No significant changes of MDA and AOPP level were observed after normoxic exercise, whereas hypoxic exercise induced a 56% rise of MDA and a 44% rise of AOPP. Plasma level of MDA and arterial oxygen hemoglobin desaturations after the acute both exercises were highly correlated (r=0.73). α-Tocopherol normalized for cholesterol and triacyglycerols increased only after hypoxic exercise (10–12%, P<0.01). After training, FRAP resting values (−21%, P<0.05) and α-tocopherol/triacyglycerols ratio (−24%, P<0.05) were diminished for HG, whereas NG values remained unchanged.Conclusions:Intense exercise and hypoxia exposure may have a cumulative effect on oxidative stress. As a consequence, the repetition of such exercise characterizing the ‘living low-training high’ model has weakened the antioxidant capacities of the athletes.Sponsorship:International Olympic Committee and the Direction Régionale de la Jeunesse et des Sports de la Région Auvergne.

Muscular mitochondrial function in amyotrophic lateral sclerosis is progressively altered as the disease develops : A temporal study in man

We performed repeated analysis of mitochondrial respiratory function in skeletal muscle (SM) of patients with early-stage sporadic amyotrophic lateral sclerosis (SALS) to determine whether mitochondrial function was altered as the disease advanced. SM biopsies were obtained from 7 patients with newly diagnosed SALS, the same 7 patients 3 months later, and 7 sedentary controls. Muscle fibers were permeabilized with saponin, then skinned and placed in an oxygraphic chamber to measure basal and maximal adenosine diphosphate (ADP)-stimulated respiration rates and to assess mitochondrial regulation by ADP. We found that the maximal oxidative phosphorylation capacity of muscular mitochondria significantly increased, and muscular mitochondrial respiratory complex IV activity significantly decreased as the disease advanced. This temporal study demonstrates for the first time that mitochondrial function in SM in human SALS is progressively altered as the disease develops.

SKELETAL MUSCLE TELOMERE LENGTH IS NOT IMPAIRED IN HEALTHY PHYSICALLY ACTIVE OLD WOMEN AND MEN

We have previously shown that the number of satellite cells is lower in old than young men and women. The aim of this study was to further explore the effects of aging on the regenerative potential of skeletal muscle in 16 young and 26 old men and women with comparable physical activity level (young, 25 ± 4 years; old, 75 ± 4 years). Mean and minimum telomere lengths were determined using Southern blot analyses on biopsies obtained from the tibialis anterior muscle. There were no significant age or gender effects on mean and minimal telomeric lengths, suggesting that the replicative potential in the remaining satellite cells in the tibialis anterior muscle is not impaired with increasing age and the existence of in vivo regulatory mechanisms allowing the maintenance of telomere length. These results imply that moderate physical activity regularly performed by old subjects is not associated with accelerated telomere loss. Muscle Nerve, 2008

Evaluation of quantitative and qualitative aspects of mitochondrial function in human skeletal and cardiac muscles

Techniques and protocols of assessment of mitochondrial properties are of physiological and physiopathological important significance. A precise knowledge of the advantages and limitations of the different protocols used to investigate the mitochondrial function, is therefore necessary. This report presents examples of how the skinned (or permeabilized) fibers technique could be applied for the polarographic determination of the actual quantitative and qualitative aspects of mitochondrial function in human muscle samples. We described and compared the main available respiration protocols in order to sort out which protocol seems more appropriate for the characterization of mitochondrial properties according to the questions under consideration: quantitative determination of oxidative capacities of a given muscle, characterization of the pattern of control of mitochondrial respiration, or assessment of a mitochondrial defect at the level of the respiratory chain complexes. We showed that while protocol A, using only two levels of the phosphate acceptor adenosine diphosphate (ADP) concentration and the adjunction of creatine, could be used for the determination of quantitative changes in very small amount of muscle samples, the ADP sensitivity of mitochondrial respiration was underestimated by this protocol in muscles with high oxidative capacities. The actual apparent Km for ADP and the role of functional activation of miCK in ATP production and energy transfer in oxidative muscles, are well-assessed by protocol B (in the absence of creatine) together with protocol C (in the presence of creatine) that use increasing concentrations of ADP ranging from 2.5–2000 μM. Protocol D is well-adapted to investigate the potential changes at different levels of the respiratory chain, by the use of specific substrates and inhibitors. As can be seen from the present data and the current review of previous reports in the literature, a standardization of the respiration protocols is needed for useful comparisons between studies.

Extensive inflammatory cell infiltration in human skeletal muscle in response to an ultraendurance exercise bout in experienced athletes

The impact of a 24-h ultraendurance exercise bout on systemic and local muscle inflammatory reactions was investigated in nine experienced athletes. Blood and muscle biopsies were collected before (Pre), immediately after the exercise bout (Post), and after 28 h of recovery (Post28). Circulating blood levels of leukocytes, creatine kinase (CK), C-reactive protein (CRP), and selected inflammatory cytokines were assessed together with the evaluation of the occurrence of inflammatory cells (CD3(+), CD8(+), CD68(+)) and the expression of major histocompatibility complex class I (MHC class I) in skeletal muscle. An extensive inflammatory cell infiltration occurred in all athletes, and the number of CD3(+), CD8(+), and CD68(+) cells were two- to threefold higher at Post28 compared with Pre (P < 0.05). The inflammatory cell infiltration was associated with a significant increase in the expression of MHC class I in muscle fibers. There was a significant increase in blood leukocyte count, IL-6, IL-8, CRP, and CK at Post. At Post28, total leukocytes, IL-6, and CK had declined, whereas IL-8 and CRP continued to increase. Increases in IL-1β and TNF-α were not significant. There were no significant associations between the magnitude of the systemic and local muscle inflammatory reactions. Signs of muscle degenerative and regenerative events were observed in all athletes with various degrees of severity and were not affected by the 24-h ultraendurance exercise bout. In conclusion, a low-intensity but very prolonged single-endurance exercise bout can generate a strong inflammatory cell infiltration in skeletal muscle of well-trained experienced ultraendurance athletes, and the amplitude of the local reaction is not proportional to the systemic inflammatory response.

Activation of satellite cells and the regeneration of human skeletal muscle are expedited by ingestion of nonsteroidal anti-inflammatory medication

With this study we investigated the role of nonsteroidal anti‐inflammatory drugs (NSAIDs) in human skeletal muscle regeneration. Young men ingested NSAID [1200 mg/d ibuprofen (IBU)] or placebo (PLA) daily for 2 wk before and 4 wk after an electrical stimulation‐induced injury to the leg extensor muscles of one leg. Muscle biopsies were collected from the vastus lateralis muscles before and after stimulation (2.5 h and 2,7, and 30 d) and were assessed for satellite cells and regeneration by immunohistochemistry and real‐time RT‐PCR, and we also measured telomere length. After injury, and compared with PLA, IBU was found to augment the proportion of ActiveNotch1+ satellite cells at 2 d [IBU, 29 ± 3% vs. PLA, 19 ± 2% (means ± sem)], satellite cell content at 7 d [IBU, 0.16 ± 0.01 vs. PLA, 0.12 ± 0.01 (Pax7+ cells/fiber)], and to expedite muscle repair at 30 d. The PLA group displayed a greater proportion of embryonic myosin+ fibers and a residual ~2‐fold increase in mRNA levels of matrix proteins (all P< 0.05). Endomysial collagen was also elevated with PLA at 30 d. Minimum telomere length shortening was not observed. In conclusion, ingestion of NSAID has a potentiating effect on Notch activation of satellite cells and muscle remodeling during large‐scale regeneration of injured human skeletal muscle.—Mackey, A. L., Rasmussen, L. K., Kadi, F., Schjerling, P., Helmark, I. C., Ponsot, E., Aagaard, P., Durigan, J. L. Q., Kjaer, M. Activation of satellite cells and the regeneration of human skeletal muscle are expedited by ingestion of nonsteroidal anti‐inflammatory medication. FASEB J. 30, 2266–2281 (2016). www.fasebj.org

Regenerative capacity of human satellite cells: the mitotic clock in cell transplantation.

Abstract In this communication, we will review the problems caused by cell-mediated gene therapy, taking skeletal muscle as a physiological model. In particular we have utilised vectors transferring telomerase under the control of retroviral promoters into human satellite cells. The set of results presented here has several implications regarding gene therapy trials. Nevertheless, more experiments will be required to fully validate this cellular model and to use telomerase to safely extend the lifespan of putative gene therapy vectors.