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Influence of supplementation with branched-chain amino acids in combination with resistance exercise on p70S6 kinase phosphorylation in resting and exercising human skeletal muscle.
Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Eva Blomstrand's research group.ORCID iD: 0000-0003-1942-2919
Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Eva Blomstrand's research group.ORCID iD: 0000-0002-6537-042X
2010 (English)In: Acta Physiologica, ISSN 1748-1708, E-ISSN 1748-1716, Vol. 200, no 3, 237-48 p.Article in journal (Refereed) Published
Abstract [en]

AIM: Skeletal muscle growth is thought to be regulated by the mammalian target of rapamycin (mTOR) pathway, which can be activated by resistance exercise and branched-chain amino acids (BCAA). The major aim of the present study was to distinguish between the influence of resistance exercise and BCAA on key enzymes considered to be involved in the regulation of protein synthesis, including p70(S6) kinase (p70(S6k)). METHODS: Nine healthy subjects (four men and five women) performed unilateral resistance exercise on two occasions separated by 1 month. Subjects were randomly supplied either a mixture of BCAA or flavoured water. Muscle biopsies were taken from both resting and exercising muscle before, after and 1 h after exercise. RESULTS: Phosphorylation of Akt was unaltered by either resistance exercise and/or BCAA supplementation whereas mTOR phosphorylation was enhanced (P<0.05) to a similar extent in both exercising and resting muscle following exercise in the absence (70-90%) and presence of BCAA supplementation (80-130%). Phosphorylation of p70(S6k) was unaffected by resistance exercise alone; however, BCAA intake increased (P<0.05) this phosphorylation in both legs following exercise. In resting muscle, a 5- and 16-fold increase in p70(S6k) was observed immediately after and 1 h after exercise, respectively, as compared to 11- and 30-fold increases in the exercising muscle. Phosphorylation of eukaryotic elongation factor 2 was attenuated 1 h after exercise (P<0.05) in both resting (10-40%) and exercising muscle (30-50%) under both conditions. CONCLUSION: The present findings indicate that resistance exercise and BCAA exert both separate and combined effects on the p70(S6k) phosphorylation in an Akt-independent manner.

Place, publisher, year, edition, pages
2010. Vol. 200, no 3, 237-48 p.
National Category
Physiology
Research subject
Medicine/Technology
Identifiers
URN: urn:nbn:se:gih:diva-1480DOI: 10.1111/j.1748-1708.2010.02151.xPubMedID: 20528801OAI: oai:DiVA.org:gih-1480DiVA: diva2:369356
Available from: 2010-11-10 Created: 2010-11-10 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Regulation of protein synthesis in human skeletal muscle: separate and combined effects of exercise and amino acids
Open this publication in new window or tab >>Regulation of protein synthesis in human skeletal muscle: separate and combined effects of exercise and amino acids
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Skeletal muscle is a highly plastic tissue which has the ability to adapt to various forms of external stimuli such as diverse modes of contractile activity. Thus, performance of endurance exercise over several of weeks results in increased oxidative capacity. In contrast, prolonged performance of resistance exercise ultimately results in increased muscle mass. These adaptations are brought about by transient alterations in gene expression and mRNA translation which result in altered protein turnover, i.e. the balance between protein synthesis and protein breakdown. Protein synthesis is the major determinant of muscle growth, which at the molecular level, is regulated by the mTORC1 pathway. This pathway is potently activated by resistance exercise and amino acids, but the stimulatory role of individual amino acids in human skeletal muscle is unclear. Muscle adaptations in response to endurance exercise are largely dependent on the PGC-1 α pathway, which regulates mitochondrial biogenesis. Given the different training adaptations after resistance and endurance exercise, it has been suggested that these exercise modalities may be incompatible when combined. Such potential interference could be exerted at the molecular level between the pathways responsible for each adaptive response. AMPK, an enzyme usually activated by endurance exercise and, when pharmacologically activated in cell culture and rodent models, has been shown to inhibit mTORC1 and protein synthesis. However, it is not known if activation of AMPK by endurance exercise inhibits resistance exercise induced signaling through the mTORC1 pathway in human skeletal muscle.

Thus, the main objective of this thesis was to examine the molecular mechanisms regulating protein synthesis in response to amino acids and various modes of exercise in human skeletal muscle.

In study I, the role of BCAAs in stimulating the mTORC1 pathway was examined in both resting and exercising muscle. BCAA increased mTORC1 activity, as assessed by S6K1 phosphorylation, in both resting and exercising muscle, but more so when exercise and BCAA were combined. In study II, the effect of leucine was compared to that of essential amino acids with or without leucine. It was found that when leucine was combined with the remaining essential amino acids, S6K1 phosphorylation was more pronounced than when leucine was provided alone. Furthermore, when leucine was removed from the essential amino acids, the effect was equal to that of placebo. In study III, the impact of endurance exercise on resistance exercise induced mTORC1 signaling was examined. When performed after resistance exercise, endurance exercise did not inhibit S6K1 phosphorylation compared to when single mode resistance exercise was performed. In study IV, performance of high intensity endurance exercise prior to resistance exercise did not inhibit S6K1 phosphorylation compared to single mode resistance exercise, despite prior activation of AMPK.

In conclusion, amino acids and resistance exercise activate mTORC1 signaling, as assessed by S6K1 phosphorylation, in a synergistic manner. Leucine is crucial in mediating the amino acid response, however, additional amino acids appear to be required to induce a maximal response downstream of mTORC1. Activation of the mTORC1 pathway in response to heavy resistance exercise is robust and this activation does not appear to be inhibited by prior or by subsequent endurance exercise. As such, these results do not lend support to the existence of molecular interference when resistance and endurance exercise are combined acutely.

Place, publisher, year, edition, pages
Karolinska Institutet, 2014
National Category
Medical and Health Sciences
Research subject
Medicine/Technology
Identifiers
urn:nbn:se:gih:diva-3323 (URN)978-91-7549-513-2 (ISBN)
Public defence
2014-06-13, Aulan, Gymnastik- och idrottshögskolan, Lidingövägen 1, Stockholm, 10:00 (English)
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Supervisors
Available from: 2014-05-28 Created: 2014-05-28 Last updated: 2016-06-20Bibliographically approved

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