Search

The mechanistic/mammalian target of rapamycin (mTOR) is a well-known serine/threonine kinase that activates muscle protein synthesis in response to anabolic conditions after exercise or nutrition intake. Rapamycin, a canonical inhibitor of mTOR complex 1 (mTORC1), induces mitochondrial dysfunction in addition to attenuating the muscle protein synthesis response. These findings suggest that mTORC1 contributes to mitochondrial homeostasis; however, the involvement of mTOR complex 2 (mTORC2) and the relationship between mTORC1 and mTORC2 are unclear. Therefore, this study was conducted to determine the role of the mTOR complex in mitochondrial function in skeletal muscle cells using rapamycin and AZD8055, as an ATP-competitive mTOR kinase inhibitor that inhibits both mTORC1 and mTORC2. AZD8055 treatment more significantly reduced the expression of proteins associated with mitochondrial oxidative phosphorylation, fusion, and fission, and decreased the respiratory capacity than rapamycin treatment. In conclusion, mTORC1 and mTORC2 cooperatively regulate mitochondrial protein expressions and respiratory function in skeletal muscle cells. [ABSTRACT FROM AUTHOR]

For many ball games, both resistance and endurance training are necessary to improve muscle strength and endurance capacity. Endurance training has been reported to inhibit muscle strength and hypertrophy, but some studies have reported that endurance exercise (EE) does not inhibit the effects of resistance exercise. Here, we examined the effect of short‐ or long‐duration EE on mouse skeletal muscle hypertrophy induced by functional overload (OL) at the molecular level. Plantaris muscle hypertrophy was induced by OL with synergist ablation in mice. Body mass was reduced with endurance training, but EE duration (30 or 90 min) had no effect. The ratio of plantaris muscle weight to body weight was higher in the OL and EE for 30 min (OL+EE30) and OL and EE for 90 min (OL+EE90) groups compared with the OL group. Expression of mechanistic target of rapamycin signaling proteins, which is related to protein synthesis and hypertrophy, was increased in the OL+EE30 group. Expression of Forkhead box‐containing protein O1, which is related to protein breakdown and atrophy, remained unchanged. However, microtubule‐associated protein 1 light chain 3, a known marker of autophagy, and MAFbx, which is related to protein breakdown, were significantly increased in the OL+EE90 group. Furthermore, markers of oxidative stress, ubiquitin and 4‐hydroxynonenal were also significantly increased in the OL+EE90 group compared with other groups. In conclusion, EE duration did not affect body mass and plantaris mass and did not interfere with mechanistic target of rapamycin signaling, but it did increase ubiquitinated proteins and oxidative stress. It is therefore necessary to consider training durations for EE when combining endurance and resistance training. [ABSTRACT FROM AUTHOR]

The enhanced rate of protein synthesis in skeletal muscle cells results in a net increase in total protein content that leads to skeletal muscle growth/hypertrophy. The mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK)-dependent regulation of the activity of mechanistic target of rapamycin (mTOR) and subsequent protein synthesis has been suggested as a regulatory mechanism; however, the exact molecular processes underlying such a regulation are poorly defined. The purpose of this study was to investigate regulatory mechanisms involved in the MEK/ERK-dependent pathway leading to mTORC1 activation in skeletal muscle cells. Treatment with phorbol-12-myristate-13-acetate (PMA), a potent agonist of protein kinase C (PKC) and its downstream effector in the MEK/ERK-dependent pathway, resulted in the activation of mTORC1 signaling and phosphorylation of the upstream regulator tuberous sclerosis 2 (TSC2) in C2C12 myoblasts. PMA-induced activation of mTORC1 signaling was partially prevented by treatment with U0126 (a selective inhibitor of MEK1/2) or BIX-02189 (a selective inhibitor of MEK5) and completely blocked with BIM-I (a selective inhibitor of upstream PKC). TSC2 phosphorylation at Ser664 (an ERK-dependent phosphorylation site) was prevented with U0126, and BIM-I treatment blocked PMA-induced phosphorylation of TSC2 at multiple residues (Ser664, Ser939, and Thr1462). Overexpression of Ras homolog enriched in brain (Rheb), a downstream target of TSC2, and an mTORC1 activator, was sufficient to activate mTORC1 signaling. We also identified that PMA-induced activation of mTORC1 signaling was significantly inhibited in the absence of Rheb with siRNA knockdown. These observations demonstrate that the PKC/MEK/ERK-dependent activation of mTORC1 is mediated through TSC2 phosphorylation and its downstream target Rheb in C2C12 myoblasts. [ABSTRACT FROM AUTHOR]

Delay in the growth of skeletal muscle resulting from physical inactivity during the juvenile period may affect the subsequent quality of life. Therefore, it is important to clarify whether recovery of this muscle growth delay can be achieved by physical training thereafter. In the present study, mice were subjected to hindlimb suspension from 5 to 8 weeks of age to induce a delay of muscle growth and reloading from 8 weeks of age to recovery of muscle. Growth of the plantaris muscle, which is composed of fast-twitch fibers, was monitored at 5, 8, 11 and 14 weeks of age. This revealed that the growth of the plantaris had completely recovered from this delay by 11 weeks of age. Moreover, the recovery was accompanied by a significant increase of RNA content relative to control muscle. Since ribosomal RNA accounts for the majority of total RNA, it was thought that the machinery for protein synthesis had become activated in the recovering muscle. In addition, phosphorylated ribosomal protein S6, which is an important factor for efficient translation, was increased at the same time. These results suggested that protein synthesis was enhanced in recovering muscle. In addition, the recovering muscle showed activation of the Erk pathway, one of the pathways controlling the expression of ribosomal RNA. These results suggest that loss of skeletal muscle due to unloading during the juvenile period can be completely recovered by reloading, and that this recovery might require an increase of RNA content mediated by the Erk pathway. [ABSTRACT FROM AUTHOR]

TAKEMASA, T., ABE, Y., KUMAGAI, C. and KIYOSAWA, H. Possible Involvement of MicroRNA-21 in Skeletal Muscle Hypertrophy. Adv. Exerc. Sports Physiol., Vol.18, No.1 pp.5-15, 2012. In order to elucidate the function of microRNAs (miRNAs) in the plasticity of skeletal muscle, we analyzed global changes in miRNA expression using the microarray technique during muscle hypertrophy induced by compensatory overload following bilateral Achilles tenotomy in mice. The most prominent change observed by microarray analysis was that of miR-21 expression. The expression of myogenic genes, myogenin and MEF2D was increased, and that of MyoD and MHCIIb was decreased in overloaded muscle. We also investigated the changes in expression of PDCD4, PTEN, and SPRY2, which are potential targets of miR- 21, and reduction in the expression of all three genes was observed in hypertrophic muscle We next investigated the expression of miR-21 and its prospective target genes using an in vitro differentiation system with C2C12 cultured myocytes through overexpressed or suppressed miR-21 by introducing the miR-21 precursor or inhibitor. When the miR-21 precursor was transfected, miR-21 expression was significantly increased, but the genes controlling muscle differentiation (MyoD, myogenin, MHCIIb, MEF2D) and possible miR-21 target genes (PDCD4, PTEN, and SPRY2) were not significantly changed in myoblasts. Similary, when we applied the miR-12 inhibitor to C2C12, the expression of myogenic genes was not significantly changed, although possible miR-21 target genes (PDCD4, PTEN, and SPRY2) tended to be up-regulated. These results raise the possibility that microRNA may regulate muscle plasticity during exercise and training [ABSTRACT FROM AUTHOR]

Endurance exercise training pro- motes angiogenesis in skeletal muscle. In order to elucidate the mechanisms of exercise-induced angiogenesis in skeletal muscle, many researchers have focused on gene expression in skeletal muscle during and after an exercise, and it is well understood that acute endurance exercise induces temporarily increasing VEGF mRNA in skeletal muscle and secreting VEGF from active muscle. Because of these results, exercise-induced VEGF expression from skeletal muscle has been believed to be an early step of exercise-induced skeletal muscle angiogenesis. Recently it was revealed that inflammatory cells including macrophage secreted pro-angiogenesis cytokine including VEGF, which had an ability to facilitate angiogenesis in vivo. However the relationship between exercise-induced skeletal muscle angiogenesis and these inflammatory cells is not revealed. Therefore we had hypothesized that exercise-induced angiogenesis in skeletal muscle is facilitated by inflammatory cells secreting VEGF. To explore this hypothesis, we subjected ICR mice (male, 8 week-old) to acute endurance exercise (90 min, 20 m/min, 10° incline), sacrificed these mice by cervical dislocation at pre-exercise, 6 hour, 1 day, 2 day and 3 day after exercise, and harvested both gastrocnemius and plantaris muscle as hind-limb muscle. And, we used immunohistochemical method and observed significant increase of macrophage in hind-limb muscle at 1 day after exercise compared with pre exercise. Subsequently we observed that increment of percent- age of VEGF-secreting macrophage. These results suggest that migrating macrophages have a positive role in exercise-induced angiogenesis in skeletal muscle. [ABSTRACT FROM AUTHOR]

It has long been known that acute cold stress suppresses immune responses, and that swimming training increases tolerance to cold. The aim of the current study was to investigate whether the improved cold tolerance occasioned by swimming training prevented the suppression of immune responses as a result of acute cold stress, focusing in particular on the generation of suppressor macrophages and glucocorticoid hormones. This is because acute cold stress induces the generation of suppressor macrophages that express large numbers of receptors to the Fc portion of immunoglobulin G (MAC-1+Fc γ RII/IIIbright cells), leading to the suppression of splenocyte mitogenesis; moreover, the generation of MAC-1+Fc γγ RII/IIIbright cells is partly mediated by increased glucocorticoid levels during acute cold stress. The trained mice underwent a 6-week endurance swimming training (5 times/week) in water at 30γ for 90min. The swimming training remarkably increased brown adipose tissue mass, suggesting an improved cold tolerance. Indeed, when the swimming-trained mice were exposed to 5γ for 3h (acute cold stress), the rectal temperature was not substantially decreased, unlike the case for control mice. The proportion of MAC-1+Fc γ RII/IIIbright cells in peritoneal exudate cell population from the trained mice was unaffected by the acute cold stress. The swimming training significantly attenuated the increases in serum corticosterone levels in response to acute cold stress. Taken together, the results obtained suggegst that swimming training not only improves cold tolerance but also inhibits the generation of suppressor macrophages under acute cold stress. [ABSTRACT FROM AUTHOR]

Oligonol is a new lychee fruit-derived polyphenol converted into a low-molecular-form, which has improved absorption and strong antioxidative activity. The aim of the current study was to investigate the effects of Oligonol supplementation on perceived subjective mood states in addition to oxidative stress in 47 undergraduate athletes during 52 days of track-and-field training. This was a prospective single blind crossover study. The ratings of perceived exertion (RPE) responses were significantly (P<0.05) lower following Oligonol supplementation, suggesting that Oligonol intake caused the subjects to feel less fatigued during regular training. The results of our own questionnaire on fatigue and pain were as follows: Oligonol supplementation significantly (P<0.05)improved all the fatigue scores and tended to attenuate the feeling of three kinds of pains(muscular/anticular pain, lumbago, and menstrual pain), followed by a change fot the worse after the discontinuance of Oligonol intake. Unexpectedly, however, there were no definite changes in the Profile of Moods States (POMS) scores or oxidative stress markers (8-hydroxy-2'-deoxyguanosine and hexanoyllysine) in urine after Oligonol supplementation. The results obtained suggest that Oligonol supplementation in young athletes shows significant subjective positive effect particularly on the feeling of fatigue during regular track and-field training, possibly contributing to the maintenance of good conditioning. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to elucidate the effect of early onset of exercise on muscle injury. Methods: Mice were divided into 3 groups, control group, injury group and exercise group. For injury group and exercise group, we forced micc to get muscle injury (eccentric-stimulation induced muscle injury). Then, for only exercise group, we let mice exercise (60 minutes swimming for 3 in every 4 days) after 7 days of muscle injury. All groups were sacrificed 21 days after muscle injury. Result and Discussion: we observed that the cross sectional area of the regenerating myofibers in exercise group was larger than that in injury group and the level of fibrosis in the exercise group was lower than that in injury group. Then, we measured mRNA level of collagenlα2 and collagen5α3, which are known to be fibrosis structural component. Collagen1α2 mRNA level are almost the same among 3 groups. On the other hand, in collagen5α3 mRNA level, exercise group showed less collagen5α3 mRNA level than injury group. Then, in order to reveal how exercise inhibits fibrosis, we measured mRNA level of TGF-β 1, which is a cytokine for promoting fibrosis. We observed that TGF-β 1 mRNA level of exercise group was less than that of injury group. Taken together, our data suggests that exercise improves healing process and exercise inhibit fibrosis via TGF-β 1 down regulation. [ABSTRACT FROM AUTHOR]

Purpose: Ammonia, one of the factors inducing fatigue, is transported by Rh b glycoprotein (Rhbg) and Rh c glycoprotein (Rhcg) in liver, kidney and other organs. The purpose of this study is examination of expression of Rhbg and Rhcg in skeletal muscle. Methods: Skeletal muscle samples (Soleus: Sol, Plantaris: Pia, Gastrocremius: Gas) were dissected from ICR mice (male, 8weeks old). Rhbg and Rhcg protein contents were analyzed by Western blot. Localization of Rhbg and Rhcg were analyzed by immunofluorescent microscopy. Myosin Heavy Chain (MHC) type composition of each muscles were measured by SDS-PAGE. Results: Rhbg and Rhcg protein much expressed in Sol than Pia and Gas. A positive correlation was found between MHC type I + II a/ II b and Rhbg/Rhcg expression. Immnofluorescent microscopy identified that Rhbg was colocalized with dystrophin, plasma membrane protein marker. On the other hand, staining for Rhcg showed colocalization with CD31 (vascular endothelial cell marker). Discussion: Ammonia transporters, both Rhbg and Rhcg, were rich in slow type fiber predominance muscle. Ammonia transporters may contribute in slow fiber than fast fiber. Rhbg and Rhcg localizations were different in types ofskeletal muscle. This result indicates that Rhbg and Rhbg have different role in skeletal muscle. [ABSTRACT FROM AUTHOR]

Purpose: We investigated the effects of exercise on adult satellite cell conversion focusing at Wnt signaling, which plays important roles in lineage control during embryonic myogenesis and postnatal development. Methods: Male C57BL/6J mice ages 8 weeks (adult) and 24 months (aged) were used and divided into control group and runner group. Runner group mice were housed individually in cages equipped with a running wheel and performed voluntary wheel running for 4 weeks. After 4 weeks of exercise, mice were sacrificed and the gastrocnemius muscles were dissected out quickly from each mouse. Results: We demonstrated that voluntary wheel running exercise, which was a low-stress exercise, converted satellite cells to activated state due to accelerated Wnt signaling. Our analyses showed that upregulated canonical Wnt/b-catenin signaling directly modulated chromatin structures of both MyoD and Myf5 genes, resulting in increases in the mRNA expression of Myf5 and MyoD and the number of proliferative Pax7(+)Myf5(+) and Pax7(+)MyoD(+) cells in skeletal muscle. The effect of Wnt signaling on the activation of satellite cells, rather than Wnt-mediated fibrosis, was observed in both adult and aged mice. Discussion: These results indicate that exercise-stimulated extracellular Wnts play a critical role in the regulation of satellite cells in adult and aged skeletal muscle. [ABSTRACT FROM AUTHOR]

Purpose: A number of studies have shown that changes in muscle contractile activity regulate the expression of monocarboxylate transporters (MCTs) in the skeletal muscle. The aim of this study was to investigate the effect offunctionaloverload on MCTI and MCT4 protein expression. Method: Plantaris muscles. from male ICR mice (8-week-old) were functionally overloaded for 15 days by ablation of the synergistic muscles. Blood samples are collected for measurirrg plasma testosterone and lactate·middot; ·middot;concentration MCT1, MCT4 ·middot;and AMPK protein expression was determined by Western blotting. Results and Discussion: The body weight was not altered thorough the experimental period. The ptanmris muscle weight increased after 1 day of overload (p<0.05). MCTl and MCT4 protein expression increased after 12 days after·middot; functional overload (p<0.05}. AMP-activated protein kinase (AMPK) phosphorylation status [phospho-AMPK (Thr172) tota TMPK] was elevated after 3-9 days of' functional overload (p<0.05). Plasma testosterone concentration was elevated after 12 days of functional overload (p<0.0-5), while lactate concentration was not altered. Thus, the current study demonstrated that heavy mechanical loading induces increase in MCTl and MCT4 protein expression in the muscles with increase in AMPK phosphorylation status and plasma testosterone concentration. [ABSTRACT FROM AUTHOR]

Purpose: Ibuprofen is a non-steroidal antiinflammatory drug that is often used as an analgesic, but its effect on skeletal muscle adaptation during endurance training is unclear Methods: In the present study, we administered ibuprofen to mice during running wheel exercise for four weeks, and examined its effects on the increase in the I and Ua myofibre and the C/F in skeletal muscle. Results and Discussion: We observed a significant increase of the I and Ila myofibre and C/F even in the presence of ibuprofen. Moreover, in untreated mice, there was a significant positive and strong correlation between these parameters and running distance. These results indicate that the increase in the I and lla myofibre and the C/F in skeletal muscle usually depend on running distance. Interestingly, we observed no significant correlation between these parameters and running distance in ibuprofen-administered mice. Moreover, we found no significant increase of these parameters when the running distance was significantly increased, in comparison with untreated mice. These results indicate that ibuprofen administration during endurance training cancels running-distance-dependent adaptations in skeletal muscle. This suggests that even if ibuprofen administration facilitates longer-distance running, no further effects of training on skeletal muscle can be expected. [ABSTRACT FROM AUTHOR]

Purpose: Muscle damage is occurred by excessive exercise training. Recently, it has been suggested that anti-oxidants and/or anti-inflammatory agents supplementation are effective for suppressing muscle damage and inducing muscle hypertrophy. The purpose of this study was to examine the effect of EMR supplementation on muscular hypertrophy model mice. Methods: Male ICR mice underwent ablation of the gastrocnemius and the soleus muscle to induce compensatory hypertrophy of the plantaris muscle. EMR and EMR-mixed whey protein were administered to half of each group for 3weeks, after which the cross-sectional area and minimum fiber diameter of the plantaris muscle fiber were measured Results: The muscle cross-sectional area and minimum fiber diameter of the EMR group and the EMR-mixed whey protein group significantly increased compared to their respective control groups. Discussion: EMR and EMR-mixed whey protein were effective for muscle hypertrophy in compensatory overload. [ABSTRACT FROM AUTHOR]

An abstract of the article "Expression of monocarboxylate transporter (MCT)1 and MCT4 in overloaded mouse plantaris muscle," by Yu Kitaoka and colleagues is presented.

An abstract of the article "Ribosome biogenesis is reduced under activated mTOR-pathway condition in denervated atrophying muscle," by Masanao Machida and colleagues is presented.

An abstract of the article "Assumption of influential molecular events for skeletal muscle hypertrophy from analysis of global gene expression during tenotomy-induced hypertrophy," by Masanao Machida and Tohru Takemasa is presented.

An abstract of the study "Expression of miRNA-21 during overload induced skeletal muscle hypertrophy," by Chiaki Kumagai and Tohru Takemasa is presented.

An abstract of the article "Effects of High-molecular-weight Polyphenol "MAF" on Gene Expression Are Comparable to That of Exercise in Skeletal Muscle Cells," by Chiaki Kumagai and Tohru Takemasa is presented.