No abstract

Irisin is mainly released from skeletal muscle (myocytes) and promotes thermogenesis by browning of the white adipose tissue. Although exercise has been shown to increase irisin concentration in blood and myocytes via up-regulation peroxisome proliferator receptor γ coactivator-1α (PGC-1α) expression, the influence of exercise intensity on irisin secretion remains unclear. Therefore, we determined circulating irisin responses following a single bout of running at different intensities. Six sedentary males underwent treadmill running under two different conditions: a low-intensity (40% of V 4 O 2max ) exercise trial (LIE) or a high-intensity (80% of V 4 O 2max ) exercise trial (HIE). The exercises in LIE and HIE were lasted for 20 and 40 min, respectively. All subjects underwent the two trials on separate days, and a randomized cross-over design was used. Blood samples were collected before (Pre) and immediately after exercise, at 3, 6, and 19 h after exercise. Energy consumption during exercise did not significantly differ between the two trials. HIE significantly increased blood lactate and serum lactate dehydrogenase levels (P < 0.05). Compared with pre-exercise levels, the irisin concentrations were elevated at 6 h (18% increase) and 19 h (23% increase) after HIE, but significantly decreased after LIE. The relative irisin concentrations (compared with pre-exercise levels) were significantly greater in HIE than in LIE immediately after exercise, and at 6 and 19 h after exercise (P < 0.05). These findings suggest that irisin secretion after acute running exercise is affected by exercise intensity, independent of energy consumption.

Satellite cells, the muscle tissue stem cells, express three Notch receptors (Notch1-3). The function of Notch1 and Notch2 in satellite cells has to date not been fully evaluated. We investigated the role of Notch1 and Notch2 in myogenic progression in adult skeletal muscle using tamoxifen-inducible satellite cell-specific conditional knockout mice for Notch1 (N1-scKO), Notch2 (N2-scKO), and Notch1/Notch2 (scDKO). In the quiescent state, the number of satellite cells was slightly reduced in N2-scKO, but not significantly in N1-scKO, and almost completely depleted in scDKO mice. N1-scKO and N2-scKO mice both exhibited a defect in muscle regeneration induced by cardiotoxin injection, while muscle regeneration was severely compromised with marked fibrosis in scDKO mice. In the activated state, ablation of either Notch1 or Notch2 alone in satellite cells prevented population expansion and self-renewal but induced premature myogenesis. Therefore, our results indicate that Notch1 and Notch2 coordinately maintain the stem-cell pool in the quiescent state by preventing activation and regulate stem-cell-fate decision in the activated state, governing adult muscle regeneration. Stem Cells 2018;36:278-285.

The present study examined the effects of wearing a lower-body compression garment (CG) after endurance exercise on recovery of physiological function. 18 males were divided into 2 experiments, the downhill running (n=10, DHR) experiments and the level running (n=8, LR) experiments. Subjects performed 30 min of DHR (gradient: - 10%) or LR (gradient: 0%) at 70% of  ˙VO2max with either wearing a CG (CG trial) or normal garment (CON trial) for 24 h after running. Changes in jump performance (counter movement jump; CMJ, rebound jump; RJ, drop jump; DJ), subjective feelings, circumferences of leg, and blood variables (creatine kinase, myoglobin, interleukin-6, high-sensitivity C-reactive protein) were evaluated before exercise, immediately after exercise, 1, 3 and 24 h following exercise. Running economy was evaluated at 24 h following exercise. CMJ height and RJ index were significantly higher in the CG trial than in the CON trial 24 h after running (P<0.05). Although changes in muscle soreness and blood variables were significantly greater in the DHR experiment than in the LR experiment, there was no significant difference between the trials in either experiment. Wearing a CG following endurance exercise facilitated recovery of jump performance under situations with severe exercise-induced muscle damage.