Pharmacological inhibition of myostatin improves skeletal muscle mass and function in a mouse model of stroke.

In stroke patients, loss of skeletal muscle mass leads to prolonged weakness and less efficient rehabilitation. We previously showed that expression of myostatin, a master negative regulator of skeletal muscle mass, was strongly increased in skeletal muscle in a mouse model of stroke. We therefore tested the hypothesis that myostatin inhibition would improve recovery of skeletal muscle mass and function after cerebral ischemia. Cerebral ischemia (45 minutes) was induced by intraluminal right middle cerebral artery occlusion (MCAO). Swiss male mice were randomly assigned to Sham-operated mice (n = 10), MCAO mice receiving the vehicle (n = 15) and MCAO mice receiving an anti-myostatin PINTA745 (n = 12; subcutaneous injection of 7.5 mg.kg-1 PINTA745 immediately after surgery, 3, 7 and 10 days after MCAO). PINTA745 reduced body weight loss and improved body weight recovery after cerebral ischemia, as well as muscle strength and motor function. PINTA745 also increased muscle weight recovery 15 days after cerebral ischemia. Mechanistically, the better recovery of skeletal muscle mass in PINTA745-MCAO mice involved an increased expression of genes encoding myofibrillar proteins. Therefore, an anti-myostatin strategy can improve skeletal muscle recovery after cerebral ischemia and may thus represent an interesting strategy to combat skeletal muscle loss and weakness in stroke patients.

Molecular mechanisms of skeletal muscle atrophy in a mouse model of cerebral ischemia.

BACKGROUND AND PURPOSE: Loss of muscle mass and function is a severe complication in patients with stroke that contributes to promoting physical inactivity and disability. The deleterious consequences of skeletal muscle mass loss underline the necessity to identity the molecular mechanisms involved in skeletal muscle atrophy after cerebral ischemia. METHODS: Transient focal cerebral ischemia (60 minutes) was induced by occlusion of the right middle cerebral artery in C57BL/6J male mice. Skeletal muscles were removed 3 days later and analyzed for the regulation of critical determinants of muscle mass homeostasis (Akt/mammalian target of rapamycin pathway, myostatin-Smad2/3 and bone morphogenetic protein-Smad1/5/8 signaling pathways, ubiquitin-proteasome and autophagy-lysosome proteolytic pathways). RESULTS: Cerebral ischemia induced severe sensorimotor deficits associated with muscle mass loss of the paretic limbs. Mechanistically, cerebral ischemia repressed Akt/mammalian target of rapamycin pathway and increased expression of key players of ubiquitin-proteasome pathway (MuRF1 [muscle RING finger-1], MAFbx [muscle atrophy F-box], Musa1 [muscle ubiquitin ligase of SCF complex in atrophy-1]), together with a marked increase in myostatin expression, in both paretic and nonparetic skeletal muscles. The Smad1/5/8 pathway was also activated. CONCLUSIONS: Our data fit with a model in which a repression of Akt/mammalian target of rapamycin pathway and an increase in the expression of key players of ubiquitin-proteasome pathway are critically involved in skeletal muscle atrophy after cerebral ischemia. Cerebral ischemia also caused an activation of bone morphogenetic protein-Smad1/5/8 signaling pathway, suggesting that compensatory mechanisms are also concomitantly activated to limit the extent of skeletal muscle atrophy.

Post-transcriptional regulation of autophagy in C2C12 myotubes following starvation and nutrient restoration.

In skeletal muscle, autophagy is activated in multiple physiological and pathological conditions, notably through the transcriptional regulation of autophagy-related genes by FoxO3. However, recent evidence suggests that autophagy could also be regulated by post-transcriptional mechanisms. The purpose of the study was therefore to determine the temporal regulation of transcriptional and post-transcriptional events involved in the control of autophagy during starvation (4h) and nutrient restoration (4h) in C2C12 myotubes. Starvation was associated with an activation of autophagy (decrease in mTOR activity, increase in AMPK activity and Ulk1 phosphorylation on Ser467), an increase in autophagy flux (increased LC3B-II/LC3B-I ratio, LC3B-II level and LC3B-positive punctate), and an increase in the content of autophagy-related proteins (Ulk1, Atg13, Vps34, and Atg5-Atg12 conjugate). Our data also indicated that the content of autophagy-related proteins was essentially maintained when nutrient sufficiency was restored. By contrast, mRNA level of Ulk1, Atg5, Bnip3, LC3B and Gabarapl1 did not increase in response to starvation. Accordingly, binding of FoxO3 transcription factor on LC3B promoter was only increased at the end of the starvation period, whereas mRNA levels of Atrogin1/MAFbx and MuRF1, two transcriptional targets of FoxO involved in ubiquitin-proteasome pathway, were markedly increased at this time. Together, these data provide evidence that target genes of FoxO3 are differentially regulated during starvation and that starvation of C2C12 myotubes is associated with a post-transcriptional regulation of autophagy.

Effects of compression stockings during exercise and recovery on blood lactate kinetics.

This study aimed to investigate if wearing compression stockings (CS) during exercise and recovery could affect lactate profile in sportsmen. Eight young healthy trained male subjects performed two maximal exercise tests on a cycle ergometer on two different occasions performed randomly: CS during both exercise and recovery, and no CS. Blood lactate concentration was taken during exercise and at 0, 3, 5, 10, 15, 30 and 60 min post-exercise. The individual blood lactate recovery curves were fitted to a biexponential time function: La(t) = La(0) + A1(1 - e(-gamma1t)) + A2(1 - e(-gamma2t)), where gamma(1) and gamma(2) denote the abilities to exchange lactate between the previously active muscles and the blood and to remove lactate from the organism, respectively. A significantly higher blood lactate value at the end of the maximal exercise was found (12.1 +/- 0.5 vs. 10.8 +/- 0.5 mmol l(-1)) wearing CS as compared to no CS (P < 0.05). Lower gamma(1) and higher gamma(2) values were observed with CS during recovery, as compared to no CS. It was concluded that CS during graded exercise leads to a significant higher blood lactate value at exhaustion. Since lactate exchanges were expected to be decreased during exercise due to CS, this result was likely attributable to a higher lactate accumulation related to a greater overall contribution of anaerobic glycolysis. Although the lactate removal ability was significantly improved when wearing CS during recovery, its efficacy in promoting blood lactate clearance after high-intensity exercise is limited.

Effects of graduated compression stockings on cardiovascular and metabolic responses to exercise and exercise recovery in persons with spinal cord injury.

OBJECTIVE: To investigate whether reporting blood redistribution by means of graduated elastic stockings affects exercise and postexercise responses in people with spinal cord injury (SCI). DESIGN: Crossover trial. SETTING: Physical medicine and rehabilitation department in France. PARTICIPANTS: Fourteen men with traumatic SCI, grouped according to their level of injury. INTERVENTIONS: Subjects performed 2 maximal wheelchair exercise tests 1 week apart, in random order and under a counter-balanced design. One test was done with and the other without graduated elastic stockings (21 mmHg). MAIN OUTCOME MEASURES: Blood lactate, blood pressure, heart rate, maximal power output, and oxygen consumption (Vo2). RESULTS: Postexercise venous lactate concentration was reduced in SCI subjects with lesion levels below T6 while wearing graduated elastic stockings during both exercise and recovery (10.9+/-3.9 mmol/L vs 12.5+/-4.6 mmol/L, P<.05). There were no significant differences in submaximal and maximal values (heart rate, Vo2, power output) between subjects tested with and without graduated elastic stockings. CONCLUSIONS: Wearing elastic stockings affects postexercise responses by decreasing lactate concentration in well-trained, low-level paraplegic patients after a maximal exercise. The relatively low pressure generated by the stockings may not, however, influence the venous system enough to produce improved performance and cardiovascular responses.

Validity and reliability of the Huet questionnaire to assess maximal oxygen uptake.

The usual fitness tests available to assess maximal oxygen uptake (VO2max), a key fitness component, are not particularly useful for epidemiological studies. Questionnaires to assess VO2max, however, are simple, easy to use, and inexpensive. In 1986, Huet developed such a French general questionnaire, which now also has an English version. Its simplicity is interesting as it could be used to survey large populations. The purpose of this study was to assess the validity and reliability of this Huet questionnaire in a sample of healthy French volunteers. A total of 108 subjects were included in this study, 88 males and 20 females. The validity of the questionnaire was checked using correlation coefficients and a Bland-Altman plot between questionnaire estimations and measures of VO2max obtained with a stress test on a cycle ergometer. An intraclass correlation coefficient (ICC) was also calculated to determine the reliability of the questionnaire. Significant correlation was obtained with the Huet questionnaire and measured VO2max (r2 = 0.77, p = 0.0001, SEE = 5.97 ml x kg (-1 ) x min- (1), n = 108). The ICC showed very high reliability (ICC= 0.988, n = 21). The Huet questionnaire is an easy, rapidly administered tool that correlated highly with VO2 max in this sample population.