Chronic clenbuterol treatment compromises force production without directly altering skeletal muscle contractile machinery.

Clenbuterol is a ß2 -adrenergic receptor agonist known to induce skeletal muscle hypertrophy and a slow-to-fast phenotypic shift. The aim of the present study was to test the effects of chronic clenbuterol treatment on contractile efficiency and explore the underlying mechanisms, i.e. the muscle contractile machinery and calcium-handling ability. Forty-three 6-week-old male Wistar rats were randomly allocated to one of six groups that were treated with either subcutaneous equimolar doses of clenbuterol (4 mg kg(-1) day(-1) ) or saline solution for 9, 14 or 21 days. In addition to the muscle hypertrophy, although an 89% increase in absolute maximal tetanic force (Po ) was noted, specific maximal tetanic force (sPo) was unchanged or even depressed in the slow twitch muscle of the clenbuterol-treated rats (P < 0.05). The fit of muscle contraction and relaxation force kinetics indicated that clenbuterol treatment significantly reduced the rate constant of force development and the slow and fast rate constants of relaxation in extensor digitorum longus muscle (P < 0.05), and only the fast rate constant of relaxation in soleus muscle (P < 0.05). Myofibrillar ATPase activity increased in both relaxed and activated conditions in soleus (P < 0.001), suggesting that the depressed specific tension was not due to the myosin head alteration itself. Moreover, action potential-elicited Ca(2+) transients in flexor digitorum brevis fibres (fast twitch fibres) from clenbuterol-treated animals demonstrated decreased amplitude after 14 days (-19%, P < 0.01) and 21 days (-25%, P < 0.01). In conclusion, we showed that chronic clenbuterol treatment reduces contractile efficiency, with altered contraction and relaxation kinetics, but without directly altering the contractile machinery. Lower Ca(2+) release during contraction could partially explain these deleterious effects.

Effect of muscle unloading, reloading and exercise on inflammation during a head-down bed rest.

Muscles are affected by unloading during head-down bed rests and by reloading through normal reambulation. This study investigated the effects of a 60 days head-down long-term bed rest with or without predefined exercise countermeasures on the development of an inflammatory reaction.Blood samples were taken before, during and after bed rest in control and exercise groups of women. They were assayed for soluble ICAM-1, VCAM-1, E- and L-selectin, IL1ß, IL6, TNFα and CRP as markers of inflammation with ELISA.Head-down long-term bed rest induced plasma volume variations which had an impact on the concentrations of the inflammatory factors and led to data corrections for a reliable analysis of the results. None of the marker of inflammation, except IL6 in control group, showed a significant change from baseline during bed rest. The main results were obtained during recovery. VCAM-1 increased in all groups, ICAM-1, in the control group, and L-selectin, in the exercise group. Peaks of IL6 and CRP were observed on day 59 of bed rest for IL6 and on day 2 of recovery for CRP in the control group. Exercise during bed rest prevented the augmentation of IL6, CRP and ICAM-1. These results might suggest a shift towards pro-inflammatory conditions, prevented in part by exercises.

Negative impact of disuse and unloading on tendon enthesis structure and function.

Exposure to chronic skeletal muscle disuse and unloading that astronauts experience results in muscle deconditioning and bone remodeling. Tendons involved in the transmission of force from muscles to skeleton are also affected. Understanding the changes that occur in muscle, tendon, and bone is an essential step toward limiting or preventing the deleterious effects of chronic reduction in mechanical load. Numerous reviews have reported the effects of this reduction on both muscle and bone, and to a lesser extent on the tendon. However, none focused on the tendon enthesis, the tendon-to-bone attachment site. While the enthesis structure appears to be determined by mechanical stress, little is known about enthesis plasticity. Our review first looks at the relationship between entheses and mechanical stress, exploring how tensile and compressive loads determine and influence enthesis structure and composition. The second part of this review addresses the deleterious effects of skeletal muscle disuse and unloading on enthesis structure, composition, and function. We discuss the possibility that spaceflight-induced enthesis remodeling could impact both the capacity of the enthesis to withstand compressive stress and its potential weakness. Finally, we point out how altered compressive strength at entheses could expose astronauts to the risk of developing enthesopathies.

Redox modulation of muscle mass and function.

Muscle mass and strength are very important for exercise performance. Training-induced musculoskeletal injuries usually require periods of complete immobilization to prevent any muscle contraction of the affected muscle groups. Disuse muscle wasting will likely affect every sport practitioner in his or her lifetime. Even short periods of disuse results in significant declines in muscle size, fiber cross sectional area, and strength. To understand the molecular signaling pathways involved in disuse muscle atrophy is of the utmost importance to develop more effective countermeasures in sport science research. We have divided our review in four different sections. In the first one we discuss the molecular mechanisms involved in muscle atrophy including the main protein synthesis and protein breakdown signaling pathways. In the second section of the review we deal with the main cellular, animal, and human atrophy models. The sources of reactive oxygen species in disuse muscle atrophy and the mechanism through which they regulate protein synthesis and proteolysis are reviewed in the third section of this review. The last section is devoted to the potential interventions to prevent muscle disuse atrophy with especial consideration to studies on which the levels of endogenous antioxidants enzymes or dietary antioxidants have been tested.

Large-scale mRNA analysis of female skeletal muscles during 60 days of bed rest with and without exercise or dietary protein supplementation as countermeasures.

Microgravity has a dramatic impact on human physiology, illustrated in particular, with skeletal muscle impairment. A thorough understanding of the mechanisms leading to loss of muscle mass and structural disorders is necessary for defining efficient clinical and spaceflight countermeasures. We investigated the effects of long-term bed rest on the transcriptome of soleus (SOL) and vastus lateralis (VL) muscles in healthy women (BRC group, n = 8), and the potential beneficial impact of protein supplementation (BRN group, n = 8) and of a combined resistance and aerobic training (BRE group, n = 8). Gene expression profiles were obtained using a customized microarray containing 6,681 muscles-relevant genes. A two-class statistical analysis was applied on 2,103 genes with consolidated expression in BRC, BRN, and BRE groups. We identified 472 and 207 mRNAs whose expression was modified in SOL and VL from BRC group, respectively. Further clustering analysis, identifying relevant biological mechanisms and pathways, reported five main subclusters. Three are composed of upregulated mRNAs involved mainly in nucleic acid and protein metabolism, and two made up of downregulated transcripts encoding components involved in energy metabolism. Exercise countermeasure demonstrated drastic compensatory effects, decreasing the number of differentially expressed mRNAs by 89 and 96% in SOL and VL, respectively. In contrast, nutrition countermeasure had moderate effects and decreased the number of differentially-expressed transcripts by 40 and 25% in SOL and VL. Together, these data present a systematic, global and comprehensive view of the adaptive response of female muscle to long-term atrophy.

Changes in dysferlin, proteins from dystrophin glycoprotein complex, costameres, and cytoskeleton in human soleus and vastus lateralis muscles after a long-term bedrest with or without exercise.

This study was designed to evaluate the effects of hypokinesia and hypodynamia on cytoskeletal and related protein contents in human skeletal muscles. Twelve proteins: dystrophin and its associated proteins (DGC), dysferlin, talin, vinculin and meta-vinculin, alpha-actinin, desmin, actin, and myosin, were quantitatively analyzed during an 84-day long-term bedrest (LTBR). The preventive or compensatory effects of maximal resistance exercise (MRE) as a countermeasure were evaluated. Most of these proteins are involved in several myopathies, and they play an important role in muscle structure, fiber cohesion, cell integrity maintenance, and force transmission. This is the first comparison of the cytoskeletal protein contents between slow postural soleus (SOL) and mixed poly-functional vastus lateralis (VL) human muscles. Protein contents were higher in VL than in SOL (from 12 to 94%). These differences could be mainly explained by the differential mechanical constraints imposed on the muscles, i.e., cytoskeletal protein contents increase with mechanical constraints. After LTBR, proteins belonging to the DGC, dysferlin, and proteins of the costamere exhibited large increases, higher in SOL (from 67 to 216%) than in VL (from 32 to 142%). Plasma membrane remodeling during muscle atrophy is probably one of the key points for interpreting these modifications, and mechanisms other than those involved in the resistance of the cytoskeleton to mechanical constraints may be implicated (membrane repair). MRE compensates the cytoskeletal changes induced by LTBR in SOL, except for gamma-sarcoglycan (+70%) and dysferlin (+108%). The exercise only partly compensated the DGC changes induced in VL, and, as for SOL, dysferlin remained largely increased (+132%). Moreover, vinculin and metavinculin, which exhibited no significant change in VL after LTBR, were increased with MRE during LTBR, reinforcing the pre-LTBR differences between SOL and VL. This knowledge will contribute to the development of efficient space flight countermeasures and rehabilitation methods in clinical situations where musculoskeletal unloading is a component.

Characterization of adipocytes derived from fibro/adipogenic progenitors resident in human skeletal muscle.

A population of fibro/adipogenic but non-myogenic progenitors located between skeletal muscle fibers was recently discovered. The aim of this study was to determine the extent to which these progenitors differentiate into fully functional adipocytes. The characterization of muscle progenitor-derived adipocytes is a central issue in understanding muscle homeostasis. They are considered as being the cellular origin of intermuscular adipose tissue that develops in several pathophysiological situations. Here fibro/adipogenic progenitors were isolated from a panel of 15 human muscle biopsies on the basis of the specific cell-surface immunophenotype CD15+/PDGFRα+CD56-. This allowed investigations of their differentiation into adipocytes and the cellular functions of terminally differentiated adipocytes. Adipogenic differentiation was found to be regulated by the same effectors as those regulating differentiation of progenitors derived from white subcutaneous adipose tissue. Similarly, basic adipocyte functions, such as triglyceride synthesis and lipolysis occurred at levels similar to those observed with subcutaneous adipose tissue progenitor-derived adipocytes. However, muscle progenitor-derived adipocytes were found to be insensitive to insulin-induced glucose uptake, in association with the impairment of phosphorylation of key insulin-signaling effectors. Our findings indicate that muscle adipogenic progenitors give rise to bona fide white adipocytes that have the unexpected feature of being insulin-resistant.

Does antioxidant system adaptive response alleviate related oxidative damage with long term bed rest?

OBJECTIVES: The aim of the study was to evidence oxidative damage and erythrocyte antioxidant enzyme activities during long term bed rest (LTBR) and recovery, while verifying the prophylactic effects of resistance exercise on LTBR-induced oxidative damage. DESIGN AND METHODS: 11 healthy male participated in the study. Nutrient intakes were monitored. Assessments occurred during LTBR (60th and 90th day) and 90 days after the end. RESULTS: LTBR induced only a slight decrease in total thiol protein (SH) group concentrations. Glutathione peroxidase (GPx) activity was upregulated during LTBR and down regulated after recovery suggesting that hypokinesia induces an oxidative stress. These effects where not correlated to antioxidant intake as nutritional density is preserved. Lipoperoxidative markers stay unchanged. CONCLUSIONS: Exercise alleviates hypokinesia outcomes by preserving glutathione reductase activity with minor effect on hypokinesia-induced antioxidant response and oxidative stress which both exhibit a high magnitude inter-individual variability. Return to initial physical activity allows biomarkers to return to initial values marking the end of the stress. Hypokinetic situations should be considered as an oxidative stressful situation requiring exercise and nutritional strategies.

Structural organization of the perimysium in bovine skeletal muscle: Junctional plates and associated intracellular subdomains.

We analyzed the structural features of the perimysium collagen network in bovine Flexor carpi radialis muscle using various sample preparation methods and microscopy techniques. We first observed by scanning electron microscopy that perimysium formed a regular network of collagen fibers with three hierarchical levels including (i) a loose lattice of large interwoven fibers ramified in (ii) numerous collagen plexi attaching together adjacent myofibers at the level of (iii) specific structures that we call perimysial junctional plates. Second, we looked more closely at the intracellular organization underneath each plate using transmission electron microscopy, immunohistochemistry, and a three-dimensional reconstruction from serial sections. We observed the accumulation of myonuclei arranged in clusters surrounded by a high density of subsarcolemmal mitochondria and the proximity of capillary branches. Third, we analyzed the distribution of these perimysial junctional plates, subsarcolemmal mitochondria, and myonuclei clusters along the myofibers using a statistical analysis of the distances between these structures. This revealed a global colocalization and the existence of adhesion domains between endomysium and perimysium. Taken together, our observations give a better description of the perimysium organization in skeletal muscle, and provide evidence that perimysial junctional plates with associated intracellular subdomains may participate in the lateral transmission of contractile forces as well as mechanosensing.

Ubiquitin targeting of rat muscle proteins during short periods of unloading.

AIM: The ubiquitin-proteasome system is known to be involved in many situations leading to skeletal muscle atrophy. However, the cellular mechanisms triggering the atrophic process initiation are still poorly understood. For short periods of rat hindlimb unloading, we assessed the specific ubiquitin targeting of sarcoplasmic or myofibrillar proteins in slow and fast rat muscle types. METHODS: Adult Sprague Dawley rats were randomly assigned to three groups: control, hindlimb-unloaded for 4 days (HU4) and hindlimb-unloaded for 8 days (HU8). In fractionated extracts from soleus (SOL) and Extensor Digitorum Longus (EDL) muscles, the relative contents of free and conjugated ubiquitin were quantified by immunoblotting. RESULTS: Hindlimb unloading of short durations resulted in a preferential atrophy of slow-twitch fibres and bound ubiquitin levels were increased by 37 and 68% in the soleus myofibrillar fraction after respectively 4 and 8 days. The ubiquitin conjugation was shown to principally affect the high molecular weight proteins. Free and conjugated ubiquitin levels remained unchanged in sarcoplasmic fraction from SOL muscle after 8 days HU. For the fast muscle (EDL), ubiquitin contents were approximately twofold lower in control conditions, and did not significantly change during the hindlimb unloading periods considered. CONCLUSION: The postural SOL muscle was shown to contain higher constitutive sarcoplasmic ubiquitin levels than the phasic EDL. The high response to unloading of the slow twitch fibres rich SOL muscle was accompanied by a specific conjugation of its myofibrillar proteins that may participate in the initiation of skeletal muscle remodelling consequent to disuse.

Cytoskeletal protein contents before and after hindlimb suspension in a fast and slow rat skeletal muscle.

Transversal cytoskeletal organization of muscle fibers is well described, although very few data are available concerning protein content. Measurements of desmin, alpha-actinin, and actin contents in soleus and extensor digitorum longus (EDL) rat skeletal muscles, taken with the results previously reported for several dystrophin-glycoprotein complex (DGC) components, indicate that the contents of most cytoskeletal proteins are higher in slow-type fibers than in fast ones. The effects of hypokinesia and unloading on the cytoskeleton were also investigated, using hindlimb suspension. First, this resulted in a decrease in contractile protein contents, only after 6 wk, in the soleus. Dystrophin and associated proteins were shown to be reduced for soleus at 3 wk, whereas only the dystrophin-associated proteins were found to increase after 6 wk. On the other hand, the contents of DGC components were increased for EDL for the two durations. Desmin and alpha-actinin levels were unchanged in the same conditions. Consequently, it can be concluded that the cytoskeletal protein expression levels could largely contribute to muscle fiber adaptation induced by modified functional demands.

Quantitative analysis of relative protein contents by Western blotting: comparison of three members of the dystrophin-glycoprotein complex in slow and fast rat skeletal muscle.

We have developed a method for accurate quantitative analysis and statistical comparison of the relative contents of the dystrophin-glycoprotein complex (DGC) in skeletal muscle. This method was applied to compare DGC contents in slow (soleus) and in fast (extensor digitorum longus, EDL) rat skeletal muscles. The quantitative analysis combines a modified bicinchoninic acid (BCA) assay with Western blotting and enhanced chemiluminescence (ECL). This combination allows the use of high levels of detergents and reducing reagents essential for extracting DGC. In addition, the evaluation of the total amount of proteins in each sample makes it possible to have a reference and to accurately compare relative protein levels without using a specific standard. With a large gradient gel, we could concomitantly compare two groups (n = 9) and quantify all protein contents differing highly in their molecular masses (from 35 kDa to 427 kDa). Each experiment was triplicated and normalized; the two muscles were compared using the Mann-Whitney test (P<0.001) to establish their protein content. The DGC relative levels for the slow muscle soleus and the fast muscle EDL differed significantly: dystrophin, beta-dystroglycan, and gamma-sarcoglycan levels were 130%, 110% and 120% higher in the soleus, respectively. The differences observed in the expression level of cytoskeletal associated protein (dystrophin) and transmembranous anchorage components may correspond to a physiological response of the muscle fibers to duration, magnitude, and frequency of the imposed mechanical loading.

Effects of 14-day spaceflight on myosin heavy chain expression in biceps and triceps muscles of the rhesus monkey.

In rats, changes in myosin expression are induced by the chronic elimination of weight-bearing activity, particularly in the postural muscles. This occurs during spaceflight and hindlimb suspension. Myosin heavy chain (MHC) changes affect fast and slow fiber types differently depending on muscle function. An increase in co-expression of different MHC within the same fiber will signal early changes in muscle fibers. In the rat soleus muscles, the spaceflight-induced increase in fast MHC expression appears to be essentially due to the enhanced or de novo synthesis of IID or IIX MHC. In response to microgravity, the expression of slow-type myosin decreases, while that of fast-type increases. There is scarce information concerning the effect of microgravity on rhesus monkeys (Macaca mulatta), especially on their upper limbs. We investigated the expression of MHC using an immunocytochemical approach to determine the nature and magnitude of the changes in biceps and triceps muscles of rhesus monkeys during the Bion 11 14-day mission.

[XY pure gonadal dysgenesis. Two cases report (author's transl)]. / Dysgénésie gonadique pure XY. A propos de deux observations.

Two cases of XY dysgenesis are reported. In one case, that of a 13 year-old girl presenting with impuberism, a gonadoblastoma was detected by histologic examination of the streak. In the second case, that of a 6 month-old girl, short stature and dysplasia of the nails suggested the diagnosis.

Effect of a 14-day spaceflight on dystrophin associated proteins complex in rat soleus muscle.

One of the most obvious effects of hypokinesia and hypodynamia is muscular atrophy. Changes in myosin expression are induced by the chronic elimination of the weight-bearing activity, particularly in the postural muscles, which occur during spaceflight and hindlimb suspension. Other morphological changes, such as the remodeling of myotendinous junction, are also induced by this reduction in mechanical stress. Moreover, the transversal interface between the cytoskeleton and the extracellular matrix of the muscle fiber can also be modified by the functional demand imposed on muscle. Dystrophin and its associated proteins appear to be essential for the stability of this interface and the deletion of one of these proteins results in a pathological phenotype. Changes in their expression appears to be induced by muscle disuse. We have quantified the changes in the expression of dystrophin and associated proteins induced by a 14-day spaceflight.

[Septo-optic dysplasia with antidiuretic hormone deficiency and central adrenocortical insufficiency. Three cases report in infants (author's transl)]. / La dysplasie septo-optique avec déficit en hormone antidiurétique et insuffisance surrénale centrale. Trois nouvelles observations chez le nourrisson.

Three cases of septo-optic dysplasia are related in infants. A neurogenic diabetes insipidus and an central adrenocortical insufficiency is proved. An growth hormone deficiency is founded in one case. The other anterior pituitary functions are normal. The pneumo-encephalography with congenital absence of septum lucidum and the ophtalmologic anomalies are typical. The treatment is envisaged. In one case an autopsy sustains the radiologic aspect.

[Combined test for assessment of anterior pituitary function using glucagon-propranolol, TRH and LHRH (author's transl)]. / Test combiné d'exploration fonctionnelle anté-hypophysaire utilisant le glucagon-propranolol, la TRH et la LHRH.

Combined Glucagon-Propranolol test used for study of growth hormone is advantages. The combined administration of TRH and LHRH is possible. In 53 children, the hormone responses (GH, TSH, FSH, LH and prolactin) were studied. This combined test allows the rapid assessment of anterior pituitary function.