Search

Summary: Skeletal muscle is the largest organ of the human body and plays a pivotal role in whole-body homeostasis through the maintenance of physical and metabolic health. Establishing strategies aimed at increasing the amount, and minimising loss, of muscle mass are of upmost importance. Muscle mass is primarily dictated by the meal-to-meal fluctuations in muscle protein synthesis (MPS) and muscle protein breakdown (MPB), each of which can be quantified through the use of stable isotopically labelled tracers. Importantly, both MPS and MPB can be influenced by external factors such as nutritional manipulation, specifically protein ingestion, and changes in loading via exercise. To date, research involving stable isotopic tracers has focused on determining the optimal dose, timing surrounding bouts of exercise, distribution and composition of protein to maximally stimulate MPS and inhibit MPB, both at rest and following exercise. In this review we focus on the use of these stable isotopically-labeled tracers to unravel the intricacies of skeletal muscle protein turnover in response to specific nutritional interventions.

Purpose This is the first study to examine whether age impacts the response of single muscle fibers to high/low frequency and high/low volume electrical pulse stimulation. We performed in vitro experiments to evaluate the effect of low-frequency high-volume electrical pulse stimulation (EPS) on mechanistic target of rapamycin (mTOR), mitogen-activated protein kinase (MAPK) signaling pathway, and satellite cell activation in singles fibers of young and aged muscles. Methods Isolated single fibers from gastocnemius in 12-wk (n=21) and 72-wk (n=21) old male C57BL/6 mice were divided into four groups: 1) control (Con) received no EPS, 2) low-frequency low-volume EPS (LL), 3) low-frequency high-volume EPS (LH), and 4) high-frequency low-volume EPS (HL) were made to contract using independent EPS protocols. Satellite cell activation and anabolic pathway (mTOR and MAPK signaling) were measured before and after EPS. Results The number of quiescent (Pax7+/Ki67-) and active (Pax7+/Ki67+) satellite cells, myonuclear content and the phosphorylation of 4E-BP1 and ERK were higher in young when compared with old. However, regardless of age, LH and HL EPS significantly increased the number of activate satellite cells (142%, both) and phosphorylation of mTOR (129% and 133%, respectively), p70S6K (133% and 136%, respectively) and 4E-BP1 (140% and 129%, respectively) compared with Con. The protein expression of ERK phosphorylation only increased by LH EPS in both the young and old groups (123% and 125%, respectively). Conclusion Low-frequency high-volume EPS stimulated satellite cell activation and the mTOR signaling pathway in older similar to young muscle.

PURPOSE: Previous studies have reported that low-load high-repetition (LLHR) resistance exercise can induce muscle hypertrophy to a similar extent as high-load low-repetition (HLLR). However, it is unclear which mechanical stress, such as exercise intensity, contraction number, and/or total work volume and which molecular mechanisms underpin the greater relative muscle hypertrophy after LLHR exercise.METHODS: Sprague-Dawley rats (12 weeks, N=35) were randomly allocated into control (Con, n=7), low-load low-repetition (LLLR, n=7), low-load medium-repetition (LLMR, n=7), LLHR (n=7), and HLLR (n=7) resistance exercise groups. They performed a ladder climbing exercise to evaluate the effect of exercise intensity, contraction number and work volume on the activation of satellite cells and protein synthesis signaling pathway.RESULTS: The number of active satellite cells and the phosphorylation of mTOR, p70S6K, ERK, and p38 were increased after LLHR and HLLR exercise (pp

PURPOSE This study was performed to investigate the effect of maternal exercise on cardiac and skeletal muscle telomere length and telomere repeat binding factor 2 (TRF2) in rat offspring. METHODS Sprague-Dawley rats (10 wk, N=21) were randomly assigned into control (CON), exercise during pregnancy (ExD), and exercise before and during pregnancy (ExBD) groups. Maternal training was performed on a rodent treadmill for 1 hour at 60-75% VO2max for 3 weeks (5 d/w) before and during pregnancy respectively. The offspring were sacrificed at birth and telomere length and TRF2 expression were measured with cardiac and skeletal muscle samples. RESULTS CON group had significantly longer telomere length (p=.011, p=.049) and higher TRF2 expression (p=.011, p=.002) than other two groups in skeletal muscle of offspring. In the cardiac muscle, CON group showed longer telomere length compared with ExD group in offspring (p=.001). CONCLUSIONS Intense maternal exercise before or during pregnancy may negatively affect their new offspring’s cardiac and skeletal muscle telomere length and TRF2 expression.

Lower-load (LL), higher-repetition resistance exercise training (RET) can increase muscle mass in a similar degree as higher-load (HL), lower-repetition RET. However, little is known about how LL and HL RET modulate other aspects of the RET phenotype such as satellite cells, myonuclei, and mitochondrial proteins. We aimed to investigate changes in muscle mass, muscle strength, satellite cell activity, myonuclear addition, and mitochondrial protein content after prolonged RET with LL and HL RET.We recruited 21 young men and randomly assigned them to perform 10 wk RET (leg press, leg extension, and leg curl) three times per week with the following conditions: 80FAIL (80% one-repetition maximum [1RM] performed to volitional fatigue), 30WM (30%1RM with volume matched to 80FAIL), and 30FAIL (30%1RM to volitional fatigue). Skeletal muscle biopsies were taken from the vastus lateralis pre- and post-RET intervention.After 10 wk of RET, only 30FAIL and 80FAIL showed an increase in peak torque and type I fiber cross-sectional area (P0.05). Moreover, only 30FAIL resulted in a significant decrease in the myonuclear domain of type II muscle fibers and an increase in mitochondrial proteins related to autophagy, fission, and fusion (all P0.05).We discovered that LL RET was effective at increasing the content of several mitochondrial proteins. Similar to previous research, we found that changes in muscle mass and strength were independent of load when repetitions were performed to volitional fatigue.

Exercise training causes epigenetic changes in skeletal muscle, although it is unclear how resistance exercise (RE) affects histone modifications. The present study was carried out to investigate the effects of acute RE and RE training on gene expression profiles and histone modifications in human skeletal muscle. Healthy male adults were assigned to acute RE (n = 9, age = 20.5±4.3yr, BMI = 28.0±6.8kg/m2) or RE training (n = 21, age = 23.7±2.5yr, BMI = 24.2±2.7kg/m2) groups. Biopsy samples were obtained from the vastus lateralis muscle before and three hours after a single bout of acute RE, or 3-days after 10 weeks of RE training. RNA sequencing analysis revealed that 153 genes with GO terms including muscle development, stress response, metabolism, cell death, and transcription factor were significantly up-regulated (+291% vs. pre-acute RE) upon acute RE. Expressions of these genes were also greater (+9.6% vs. pre-RE training, p

Objective Environmental and maternal exercise experienced even during the very earliest stages of life has the potential to cause developmental changes.The growing evidence demonstrated that diverse environmental stressors affect offspring in variousaspects in early stage of lifeand can be transmitted directly or indirectly by both parental lines.The purpose of the present study was to investigate the effect of across generations maternal exercise training under the hypoxic environment on mitochondrial biogenesis and angiogenesis related protein expressions of skeletal muscle in offspring ofmultiple generations. Methods The experimental groups were divided into four groups as NCON (control in normoxia), NEXE (exercise in normoxia), HCON (control under hypoxia), HEXE (exercise under hypoxia), and studied for three generations. Exercise groups were run on animal treadmill at 60%-75% VO2maxfor one hour per day, five times per week for 10 weeks (seven weeks before conception and during conception for three weeks). Animals were sacrificed at a given time table and assayed mitochondrial biogenesis and angiogenesis related protein expressions using western blotting. Results The major findings from the present study were firstly, maternal exercise training before and during conception under hypoxic environment increase in mitochondrial biogenesis and angiogenesis related proteins expressions in both maternal and offspring skeletal muscles, secondly, long term of exposure to hypoxic environment without exercise training increase in mitochondrial biogenesis and angiogenesis related proteins expressions in offspring skeletal muscles, and further increased when exercise training performed at hypoxic environment, lastly, there was no cumulative benefit by consecutively exposure for three generations under hypoxic environment, which is indicating world winning runners from high altitude dwellers may not relay on the duration of sojourn under hypoxic environment, but rather selection and training related factors. Conclusions In summary, maternal exercise training before and during conception under hypoxic environment increase in mitochondrial biogenesis(PGC-1α, COX-Ⅳ, NRF-1, mtTFA) and angiogenesis(HIF-1α, VEGFtotal) related proteins expressions in both maternal and offspring skeletal muscles, especially exercise training stimulated the protein expressions under hypoxic environment than normoxic condition. Therefore, exercise capacity may be endowed by both hypoxic environment and exercise training at hypoxic environment.

New monoclonal antibodies (mAbs) against microcystin (MC), a cyclic peptide toxin of the freshwater cyanobacterium Microcystis aeruginosa, were prepared from cloned hybridoma cell lines. Using these mAbs, an immunochromatographic assay system was designed for the detection of cyanobacterial hepatotoxins, MCs in water. The immunochromatographic assay system is composed of anti‐MCs‐mAb, fluorescence conjugates in detection solution, an immunochromatographic assay strip, and a laser fluorescence scanner. The performance of the immunochromatographic assay system was compared with high performance liquid chromatography (HPLC) detection. As the detection limit of HPLC is several orders of magnitude higher than with immunochromatographic assay systems, attention was also given to preconcentration of samples with solid phase extraction cartridges.