Myostatin is a key mediator between energy metabolism and endurance capacity of skeletal muscle

Myostatin (Mstn) participates in the regulation of skeletal muscle size and has emerged as a regulator of muscle metabolism. Here, we hypothesized that lack of myostatin profoundly depresses oxidative phosphorylation-dependent muscle function. Toward this end, we explored Mstn/ mice as a model for the constitutive absence of myostatin and AAV-mediated overexpression of myostatin propeptide as a model of myostatin blockade in adult wild-type mice. We show that muscles from Mstn/ mice, although larger and stronger, fatigue extremely rapidly. Myostatin deficiency shifts muscle from aerobic toward anaerobic energy metabolism, as evidenced by decreased mitochondrial respiration, reduced expression of PPAR transcriptional regulators, increased enolase activity, and exercise-induced lactic acidosis. As a consequence, constitutively reduced myostatin signaling diminishes exercise capacity, while the hypermuscular state of Mstn/ mice increases oxygen consumption and the energy cost of running. We wondered whether these results are the mere consequence of the congenital fiber-type switch toward a glycolytic phenotype of constitutive Mstn/ mice. Hence, we overexpressed myostatin propeptide in adult mice, which did not affect fiber-type distribution, while nonetheless causing increased muscle fatigability, diminished exercise capacity, and decreased Pparb/d and Pgc1a expression. In conclusion, our results suggest that myostatin endows skeletal muscle with high oxidative capacity and low fatigability, thus regulating the delicate balance between muscle mass, muscle force, energy metabolism, and endurance capacity

Individualisation de l entraînement physique chez la souris (influence du fonds génétique sur l adaptation musculaire, applications aux maladies du motoneurone)

La remarquable plasticité du muscle squelettique permet d envisager de façon thérapeutique l exercice physique. Après avoir validé un modèle de mesure des capacités motrices (Vitesse Critique, VC) chez la souris saine, nous nous sommes basés sur cet index pour mettre en place un entraînement individualisé de courte durée. Les résultats ont montré des améliorations de la VC et de la capacité musculaire oxydative dépendantes du fonds génétique des animaux. Ces données nous ont cependant conforté dans l application de l exercice chez des modèles murins de pathologies du motoneurone. Après vérification de l adéquation de la VC à l évaluation des capacités motrices de modèles de paraplégie spastique héréditaire, d amyotrophie spinale et de sclérose latérale amyotrophique, nous avons pu mettre respectivement en évidence chez ces modèles des déclins moteurs tardif, précoce et modulable par l entraînement physique. Cette dernière observation ouvre d intéressantes perspectives thérapeutiques.The remarkable plasticity of skeletal muscle in response to physiological stress or diseases leads to consider physical exercise as a therapeutically approach. After validation of motor capacity model (Critical Speed, CS) in healthy mice, we used this index to define a short individualized training protocol. Surprisingly, the results showed improvements of CS and oxidative muscular capacity, both parameters being dependent on the genetic background. These data lead us to suggest that exercise could be regarded as a therapeutically approach in mouse models of neuromuscular disorders and in particular motor neuron diseases. After validating the CS as a reliable parameter to evaluate the motor capacities of mouse models of hereditary spastic paraplegia, spinal muscular atrophy and amyotrophic lateral sclerosis (ALS), we have shown that physical training was able to delay motor defect in a mouse model of ALS. This last observation opens exciting therapeutic prospects.EVRY-BU (912282101) / SudocSudocFranceF

Myostatin knockout mice increase oxidative muscle phenotype as an adaptive response to exercise

Myostatin-deficient mice (MSTN (-/-)) display excessive muscle mass and this is associated with a profound loss of oxidative metabolic properties. In this study we analysed the effect of two endurance-based exercise regimes, either a forced high-impact swim training or moderate intensity voluntary wheel running on the adaptive properties of the tibialis anterior and plantaris muscle from MSTN (-/-) mice. MSTN (-/-) and wild type (MSTN (+/+)) animals had comparable performances in the wheel running regime in terms of distance, average speed and time, but MSTN (-/-) mice showed a reduced ability to sustain a high-impact activity via swimming. Swim training elicited muscle specific adaptations on fibre type distribution in MSTN (-/-); the tibialis anterior displaying a partial transformation in contrast to the plantaris which showed no change. Conversely, wheel running induced similar changes in fibre type composition of both muscles, favouring transitions from IIB-to-IIA. Succinate dehydrogenase activity, an indicator of mitochondrial oxidative potential was increased in response to either exercise regime, with wheel running eliciting more robust changes in the MSTN (-/-) muscles. Examination of the cross sectional area of individual fibre types showed genotype-specific responses with MSTN (-/-) mice exhibiting an incapability of fibre enlargement following the wheel running regime, as opposed to MSTN (+/+) mice and a greater susceptibility to muscle fibre area loss following swimming. In conclusion, the muscle fibre hypertrophy, oxidative capacity and glycolytic phenotype of myostatin deficient muscle can be altered with endurance exercise regimes

Genetic ablation of acetylcholinesterase alters muscle function in mice.

Although acetylcholinesterase (AChE) knockout mice survive, they have abnormal neuromuscular function. We analysed further the effects of the mutation on hind limb muscle contractile properties. Tibialis anterior muscle from AChE KO mice is unable to maintain tension during a short period of repetitive nerve stimulation (tetanic fade) and has an increased twitch tension in response to a single nerve electric stimulation. In response to direct muscle stimulation, we found that maximal velocity of shortening of soleus muscle is increased and maximum tetanic force is decreased in AchE KO mice versus control animals. As the contractile properties of the soleus muscle were altered by AChE ablation, our results suggest cellular and molecular changes in AChE ablated muscle containing both fast and slow muscle fibres

Partial inhibition of hormone-sensitive lipase improves insulin sensitivity by induction of de novo lipogenesis and elongase ELOVL6 in human adipocytes

International audienc

Surplus fat rapidly increases fat oxidation and insulin resistance in lipodystrophic mice.

OBJECTIVE: Surplus dietary fat cannot be converted into other macronutrient forms or excreted, so has to be stored or oxidized. Healthy mammals store excess energy in the form of triacylgycerol (TAG) in lipid droplets within adipocytes rather than oxidizing it, and thus ultimately gain weight. The 'overflow hypothesis' posits that the capacity to increase the size and number of adipocytes is finite and that when this limit is exceeded, fat accumulates in ectopic sites and leads to metabolic disease. METHODS: Here we studied the energetic and biochemical consequences of short-term (2-day) excess fat ingestion in a lipodystrophic (A-ZIP/F-1) mouse model in which adipose capacity is severely restricted. RESULTS: In wildtype littermates, this acute exposure to high fat diets resulted in excess energy intake and weight gain without any significant changes in macronutrient oxidation rates, glucose, TAG, or insulin levels. In contrast, hyperphagic lipodystrophic mice failed to gain weight; rather, they significantly increased hepatic steatosis and fat oxidation. This response was associated with a significant increase in hyperglycemia, hyperinsulinemia, glucosuria, hypertriglyceridemia, and worsening insulin tolerance. CONCLUSIONS: These data suggest that when adipose storage reserves are saturated, excess fat intake necessarily increases fat oxidation and induces oxidative substrate competition which exacerbates insulin resistance resolving any residual energy surplus through excretion of glucose

Exercise training attenuates the hypermuscular phenotype and restores skeletal muscle function in the myostatin null mouse

Myostatin regulates both muscle mass and muscle metabolism. The myostatin null (MSTN -/- ) mouse has a hypermuscular phenotype owing to both hypertrophy and hyperplasia of the myofibres. The enlarged muscles display a reliance on glycolysis for energy production; however, enlarged muscles that develop in the absence of myostatin have compromised force-generating capacity. Recent evidence has suggested that endurance exercise training increases the oxidative properties of muscle. Here, we aimed to identify key changes in the muscle phenotype of MSTN -/- mice that can be induced by training. To this end, we subjected MSTN -/- mice to two different forms of training, namely voluntary wheel running and swimming, and compared the response at the morphological, myocellular and molecular levels. We found that both regimes normalized changes of myostatin deficiency and restored muscle function. We showed that both exercise training regimes increased muscle capillary density and the expression of Ucp3, Cpt1α, Pdk4 and Errγ, key markers for oxidative metabolism. Cross-sectional area of hypertrophic myofibres from MSTN -/- mice decreased towards wild-type values in response to exercise and, in this context, Bnip3, a key autophagy-related gene, was upregulated. This reduction in myofibre size caused an increase of the nuclear-to-cytoplasmic ratio towards wild-type values. Importantly, both training regimes increased muscle force in MSTN -/- mice. We conclude that impaired skeletal muscle function in myostatin-deficient mice can be improved through endurance exercise-mediated remodelling of muscle fibre size and metabolic profile. © 2011 The Authors. Experimental Physiology © 2012 The Physiological Society

Voluntary Physical Activity Protects from Susceptibility to Skeletal Muscle Contraction-Induced Injury But Worsens Heart Function in mdx Mice

International audienceIt is well known that inactivity/activity influences skeletal muscle physiological characteristics. However, the effects of inactivity/activity on muscle weakness and increased susceptibility to muscle contraction-induced injury have not been extensively studied in mdx mice, a murine model of Duchenne muscular dystrophy with dystrophin deficiency. In the present study, we demonstrate that inactivity (ie, leg immobilization) worsened the muscle weakness and the susceptibility to contraction-induced injury in mdx mice. Inactivity also mimicked these two dystrophic features in wild-type mice. In contrast, we demonstrate that these parameters can be improved by activity (ie, voluntary wheel running) in mdx mice. Biochemical analyses indicate that the changes induced by inactivity/activity were not related to fiber-type transition but were associated with altered expression of different genes involved in fiber growth (GDF8), structure (Actg1), and calcium homeostasis (Stim1 and Jph1). However, activity reduced left ventricular function (ie, ejection and shortening fractions) in mdx, but not C57, mice. Altogether, our study suggests that muscle weakness and susceptibility to contraction-induced injury in dystrophic muscle could be attributable, at least in part, to inactivity. It also suggests that activity exerts a beneficial effect on dystrophic skeletal muscle but not on the heart

A mutation of spastin is responsible for swellings and impairment of transport in a region of axon characterized by changes in microtubule composition.

International audienceMutations of the spastin gene (Sp) are responsible for the most frequent autosomal dominant form of spastic paraplegia, a disease characterized by the degeneration of corticospinal tracts. We show that a deletion in the mouse Sp gene, generating a premature stop codon, is responsible for progressive axonal degeneration, restricted to the central nervous system, leading to a late and mild motor defect. The degenerative process is characterized by focal axonal swellings, associated with abnormal accumulation of organelles and cytoskeletal components. In culture, mutant cortical neurons showed normal viability and neurite density. However, they develop neurite swellings associated with focal impairment of retrograde transport. These defects occur near the growth cone, in a region characterized by the transition between stable microtubules rich in detyrosinated alpha-tubulin and dynamic microtubules composed almost exclusively of tyrosinated alpha-tubulin. Here, we show that the Sp mutation has a major impact on neurite maintenance and transport both in vivo and in vitro. These results highlight the link between spastin and microtubule dynamics in axons, but not in other neuronal compartments. In addition, it is the first description of a human neurodegenerative disease which involves this specialized region of the axon

Perilipin 5 fine-tunes lipid oxidation to metabolic demand and protects against lipotoxicity in skeletal muscle

Lipid droplets (LD) play a central role in lipid homeostasis by controlling transient fatty acid (FA) storage and release from triacylglycerols stores, while preventing high levels of cellular toxic lipids. This crucial function in oxidative tissues is altered in obesity and type 2 diabetes. Perilipin 5 (PLIN5) is a LD protein whose mechanistic and causal link with lipotoxicity and insulin resistance has raised controversies. We investigated here the physiological role of PLIN5 in skeletal muscle upon various metabolic challenges. We show that PLIN5 protein is elevated in endurance-trained (ET) subjects and correlates with muscle oxidative capacity and whole-body insulin sensitivity. When overexpressed in human skeletal muscle cells to recapitulate the ET phenotype, PLIN5 diminishes lipolysis and FA oxidation under basal condition, but paradoxically enhances FA oxidation during forskolin-and contraction-mediated lipolysis. Moreover, PLIN5 partly protects muscle cells against lipid-induced lipotoxicity. In addition, we demonstrate that down-regulation of PLIN5 in skeletal muscle inhibits insulin-mediated glucose uptake under normal chow feeding condition, while paradoxically improving insulin sensitivity upon high-fat feeding. These data highlight a key role of PLIN5 in LD function, first by finely adjusting LD FA supply to mitochondrial oxidation, and second acting as a protective factor against lipotoxicity in skeletal muscle