1
|
Thorley J, Thomas C, Bailey SJ, Martin NRW, Bishop NC, Clifford T. Mechanically demanding eccentric exercise increases nuclear factor erythroid 2-related factor 2 activity in human peripheral blood mononuclear cells. J Sports Sci 2023; 41:1231-1239. [PMID: 37756518 DOI: 10.1080/02640414.2023.2263713] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2023] [Accepted: 09/20/2023] [Indexed: 09/29/2023]
Abstract
PRE-REGISTRATION NUMBER osf.io/kz37g.
Collapse
Affiliation(s)
- Josh Thorley
- School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, UK
| | - Craig Thomas
- School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, UK
| | - Stephen J Bailey
- School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, UK
| | - Neil R W Martin
- School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, UK
| | - Nicolette C Bishop
- School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, UK
| | - Tom Clifford
- School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, UK
| |
Collapse
|
2
|
Davids CJ, Næss TC, Moen M, Cumming KT, Horwath O, Psilander N, Ekblom B, Coombes JS, Peake JM, Raastad T, Roberts LA. Acute cellular and molecular responses and chronic adaptations to low-load blood flow restriction and high-load resistance exercise in trained individuals. J Appl Physiol (1985) 2021; 131:1731-1749. [PMID: 34554017 DOI: 10.1152/japplphysiol.00464.2021] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Blood flow restriction (BFR) with low-load resistance exercise (RE) is often used as a surrogate to traditional high-load RE to stimulate muscular adaptations, such as hypertrophy and strength. However, it is not clear whether such adaptations are achieved through similar cellular and molecular processes. We compared changes in muscle function, morphology and signaling pathways between these differing training protocols. Twenty-one males and females (mean ± SD: 24.3 ± 3.1 years) experienced with resistance training (4.9 ± 2.6 years) performed nine weeks of resistance training (three times per week) with either high-loads (75-80% 1RM; HL-RT), or low-loads with BFR (30-40% 1RM; LL-BFR). Before and after the training intervention, resting muscle biopsies were collected, and quadricep cross-sectional area (CSA), muscular strength and power were measured. Approximately 5 days following the intervention, the same individuals performed an additional 'acute' exercise session under the same conditions, and serial muscle biopsies were collected to assess hypertrophic- and ribosomal-based signaling stimuli. Quadricep CSA increased with both LL-BFR (7.4±4.3%) and HL-RT (4.6±2.9%), with no significant differences between training groups (p=0.37). Muscular strength also increased in both training groups, but with superior gains in squat 1RM occurring with HL-RT (p<0.01). Acute phosphorylation of several key proteins involved in hypertrophy signaling pathways, and expression of ribosomal RNA transcription factors occurred to a similar degree with LL-BFR and HL-RT (all p>0.05 for between-group comparisons). Together, these findings validate low-load resistance training with continuous BFR as an effective alternative to traditional high-load resistance training for increasing muscle hypertrophy in trained individuals.
Collapse
Affiliation(s)
- Charlie J Davids
- School of Human Movement and Nutrition Sciences, University of Queensland, Brisbane, Australia.,Queensland Academy of Sport, Nathan, Australia
| | - Tore C Næss
- Department of Physical Performance, Norwegian School of Sport Science, Oslo, Norway
| | - Maria Moen
- Department of Physical Performance, Norwegian School of Sport Science, Oslo, Norway
| | | | - Oscar Horwath
- Åstrand Laboratory, Department of Physiology, Nutrition and Biomechanics, Swedish School of Sport and Health Sciences, Stockholm, Sweden
| | - Niklas Psilander
- Åstrand Laboratory, Department of Physiology, Nutrition and Biomechanics, Swedish School of Sport and Health Sciences, Stockholm, Sweden
| | - Björn Ekblom
- Åstrand Laboratory, Department of Physiology, Nutrition and Biomechanics, Swedish School of Sport and Health Sciences, Stockholm, Sweden
| | - Jeff S Coombes
- School of Human Movement and Nutrition Sciences, University of Queensland, Brisbane, Australia
| | - Jonathan M Peake
- Queensland Academy of Sport, Nathan, Australia.,Queensland University of Technology, School of Biomedical Science, Brisbane, Australia
| | - Truls Raastad
- Department of Physical Performance, Norwegian School of Sport Science, Oslo, Norway
| | - Llion Arwyn Roberts
- School of Human Movement and Nutrition Sciences, University of Queensland, Brisbane, Australia.,Queensland Academy of Sport, Nathan, Australia.,Griffith Sports Science, School of Health Sciences and Social Work, Griffith University, Gold Coast, Australia
| |
Collapse
|
3
|
Skeletal muscle hypertrophy: molecular and applied aspects of exercise physiology. GERMAN JOURNAL OF EXERCISE AND SPORT RESEARCH 2020. [DOI: 10.1007/s12662-020-00652-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
|
4
|
Ato S, Tsushima D, Isono Y, Suginohara T, Maruyama Y, Nakazato K, Ogasawara R. The Effect of Changing the Contraction Mode During Resistance Training on mTORC1 Signaling and Muscle Protein Synthesis. Front Physiol 2019; 10:406. [PMID: 31057416 PMCID: PMC6482468 DOI: 10.3389/fphys.2019.00406] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2018] [Accepted: 03/22/2019] [Indexed: 12/16/2022] Open
Abstract
Acute resistance exercise (RE) increases muscle protein synthesis (MPS) via activation of mechanistic target of rapamycin complex (mTORC), and chronic resistance exercise training (RT) results in skeletal muscle hypertrophy. Although MPS in response to RE is blunted over time during RT, no effective restorative strategy has been identified. Since eccentric muscle contraction (EC) has the potential to strongly stimulate mTORC1 activation and MPS, changing the muscle contraction mode to EC might maintain the MPS response to RE during chronic RT. Male rats were randomly divided into RE (1 bout of RE) and RT (13 bouts of RE) groups. Additionally, each group was subdivided into isometric contraction (IC) and EC subgroups. The RE groups performed acute, unilateral RE using IC or EC. The RT groups performed 12 bouts of unilateral RE using IC. For bout 13, the RT-IC subgroup performed a further IC bout, while the RT-EC subgroup changed to EC. All muscle contractions were induced by percutaneous electrical stimulation. Muscle samples were obtained at 6 h post exercise in all groups. After the 1st RE bout, the EC group showed significantly higher p70S6K Thr389 phosphorylation than the IC group. However, the phosphorylation of other mTORC1-associated proteins (4E-BP1 and ribosomal protein S6) and the MPS response did not differ between the contraction modes. After the 13th bout of RE, mTORC1 activation and the MPS response were significantly blunted as compared with the 1st bout of RE. Changing from IC to EC did not improve these responses. In conclusion, changing the contraction mode to EC does not reinvigorate the blunted mTORC1 activation and MPS in response to RE during chronic RT.
Collapse
Affiliation(s)
- Satoru Ato
- Department of Life Science and Applied Chemistry, Nagoya Institute of Technology, Nagoya, Japan
| | - Daisuke Tsushima
- Department of Life Sciences, The University of Tokyo, Tokyo, Japan
| | - Yurie Isono
- Department of Life Science and Applied Chemistry, Nagoya Institute of Technology, Nagoya, Japan
| | - Takeshi Suginohara
- Department of Life Science and Applied Chemistry, Nagoya Institute of Technology, Nagoya, Japan
| | - Yuki Maruyama
- Department of Life Science and Applied Chemistry, Nagoya Institute of Technology, Nagoya, Japan
| | - Koichi Nakazato
- Department of Exercise Physiology, Nippon Sport Science University, Tokyo, Japan
| | - Riki Ogasawara
- Department of Life Science and Applied Chemistry, Nagoya Institute of Technology, Nagoya, Japan
| |
Collapse
|
5
|
Ashida Y, Himori K, Tatebayashi D, Yamada R, Ogasawara R, Yamada T. Effects of contraction mode and stimulation frequency on electrical stimulation-induced skeletal muscle hypertrophy. J Appl Physiol (1985) 2018; 124:341-348. [DOI: 10.1152/japplphysiol.00708.2017] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
We compared the skeletal muscle hypertrophy resulting from isometric (Iso) or eccentric (Ecc) electrical stimulation (ES) training with different stimulation frequencies. Male Wistar rats were assigned to the Iso and Ecc groups. These were divided into three further subgroups that were stimulated at 10 Hz (Iso-10 and Ecc-10), 30 Hz (Iso-30 and Ecc-30), or 100 Hz (Iso-100 and Ecc-100). In experiment 1, the left plantarflexor muscles were stimulated every other day for 3 wk. In experiment 2, mammalian target of rapamycin complex 1 (mTORC1) signaling was investigated 6 h after one bout of ES. The contralateral right muscle served as a control (non-ES). Ecc contractions comprised forced dorsiflexion combined with ES. The peak torque and torque-time integral during ES were higher in the Ecc group than that in the Iso group in all stimulation frequencies examined. The gastrocnemius muscle weight normalized to body weight in ES side was increased compared with the non-ES side by 6, 7, and 17% in the Ecc-30, Iso-100, and Ecc-100 groups, respectively, with a greater gain in Ecc-100 than the Ecc-30 and Iso-100 groups. The p70S6K (Thr389) phosphorylation level was higher in the Ecc-30 and -100 than in the Iso-30 and -100 groups, respectively. The peak torque and torque-time integral were highly correlated with the magnitude of increase in muscle mass and the phosphorylation of p70S6K. These data suggest that ES-induced muscle hypertrophy and mTORC1 activity are determined by loading intensity and volume during muscle contraction independent of the contraction mode.NEW & NOTEWORTHY Eccentric contraction and high-frequency stimulation (HFS) are regarded as an effective way to increase muscle mass by electrical stimulation (ES) training. However, little is known about whether muscle hypertrophy is affected by contraction mode and stimulation frequency in ES training. Here, we provide the evidence that muscle hypertrophy and mammalian target of rapamycin complex 1 activity are determined by mechanical loading during contraction but not on the contraction mode itself, with a greater gain at HFS.
Collapse
Affiliation(s)
- Yuki Ashida
- Graduate School of Health Sciences, Sapporo Medical University, Sapporo, Japan
| | - Koichi Himori
- Graduate School of Health Sciences, Sapporo Medical University, Sapporo, Japan
| | - Daisuke Tatebayashi
- Graduate School of Health Sciences, Sapporo Medical University, Sapporo, Japan
| | - Ryotaro Yamada
- Graduate School of Health Sciences, Sapporo Medical University, Sapporo, Japan
| | - Riki Ogasawara
- Department of Life Science and Applied Chemistry, Nagoya Institute of Technology, Nagoya, Japan
| | - Takashi Yamada
- Graduate School of Health Sciences, Sapporo Medical University, Sapporo, Japan
| |
Collapse
|
6
|
Ato S, Makanae Y, Kido K, Fujita S. Contraction mode itself does not determine the level of mTORC1 activity in rat skeletal muscle. Physiol Rep 2017; 4:4/19/e12976. [PMID: 27688433 PMCID: PMC5064134 DOI: 10.14814/phy2.12976] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2016] [Accepted: 08/19/2016] [Indexed: 11/24/2022] Open
Abstract
Resistance training with eccentric contraction has been shown to augment muscle hypertrophy more than other contraction modes do (i.e., concentric and isometric contraction). However, the molecular mechanisms involved remain unclear. The purpose of this study was to investigate the effect of muscle contraction mode on mammalian target of rapamycin complex 1 (mTORC1) signaling using a standardized force‐time integral (load (weight) × contraction time). Male Sprague–Dawley rats were randomly assigned to three groups: eccentric contraction, concentric contraction, and isometric contraction. The right gastrocnemius muscle was exercised via percutaneous electrical stimulation‐induced maximal contraction. In experiment 1, different modes of muscle contraction were exerted using the same number of reps in all groups, while in experiment 2, muscle contractions were exerted using a standardized force‐time integral. Muscle samples were obtained immediately and 3 h after exercise. Phosphorylation of molecules associated with mTORC1 activity was assessed using western blot analysis. In experiment 1, the force‐time integral was significantly different among contraction modes with a higher force‐time integral for eccentric contraction compared to that for other contraction modes (P < 0.05). In addition, the force‐time integral was higher for concentric contraction compared to that for isometric contraction (P < 0.05). Similarly, p70S6K phosphorylation level was higher for eccentric contraction than for other modes of contraction (P < 0.05), and concentric contraction was higher than isometric contraction (P < 0.05) 3 h after exercise. In experiment 2, under the same force‐time integral, p70S6K (Thr389) and 4E‐BP1 phosphorylation levels were similar among contraction modes 3 h after exercise. Our results suggest that mTORC1 activity is not determined by differences in muscle contraction mode itself. Instead, mTORC1 activity is determined by differences in the force‐time integral during muscle contraction.
Collapse
Affiliation(s)
- Satoru Ato
- Faculty of Sport and Health Science, Ritsumeikan University, Kusatsu, Japan
| | - Yuhei Makanae
- Faculty of Sport and Health Science, Ritsumeikan University, Kusatsu, Japan
| | - Kohei Kido
- Faculty of Sport and Health Science, Ritsumeikan University, Kusatsu, Japan
| | - Satoshi Fujita
- Faculty of Sport and Health Science, Ritsumeikan University, Kusatsu, Japan
| |
Collapse
|
7
|
Chen G, Jiang H, Tian X, Tang J, Bai X, Zhang Z, Wang L. Mechanical loading modulates heterotopic ossification in calcific tendinopathy through the mTORC1 signaling pathway. Mol Med Rep 2017; 16:5901-5907. [PMID: 28901376 PMCID: PMC5865767 DOI: 10.3892/mmr.2017.7380] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2016] [Accepted: 03/20/2017] [Indexed: 01/05/2023] Open
Abstract
Excessive mechanical loading is a major factor affecting heterotopic ossification (HO), which is a major pathological alteration in calcific tendinopathy. However, physical therapies with mechanical loading as the functional element have exhibited promising results in the treatment of calcific tendinopathy. The dual effects that mechanical loading may have on the pathogenesis and rehabilitation of calcified tendinopathy remain unclear. The present study was designed to investigate the effects of mechanical loading on HO in calcific tendinopathy. In the present study, a tendon cell in vitro stretch model and an Achilles tenotomy rat model were used to simulate different elongation mechanical loading scenarios in order to investigate the effects of mechanical loading on HO of the tendon. In addition, rapamycin, a selective mammalian target of rapamycin complex-1 (mTORC1) signaling pathway inhibitor, was employed to determine whether mechanical loading modulates heterotopic ossification in calcific tendinopathy through the mTORC1 signaling pathway. The data indicate that mechanical loading modulated HO of the tendon through the mTORC1 signaling pathway, and that low elongation mechanical loading attenuated HO, while high elongation mechanical loading accelerated HO in vivo. This study may improve the understanding of the effect of physical therapies used to treat calcific tendinopathy, so as to guide clinical treatment more effectively. Furthermore, rapamycin may be a potential drug for the treatment of calcific tendinopathy.
Collapse
Affiliation(s)
- Guorong Chen
- Department of Orthopedics, The Third Affiliated Hospital of Southern Medical University, Guangzhou, Guangdong 510630, P.R. China
| | - Huaji Jiang
- Department of Orthopedics, The Third Affiliated Hospital of Southern Medical University, Guangzhou, Guangdong 510630, P.R. China
| | - Xinggui Tian
- Department of Orthopedics, The Third Affiliated Hospital of Southern Medical University, Guangzhou, Guangdong 510630, P.R. China
| | - Jiajun Tang
- Department of Orthopedics, The Third Affiliated Hospital of Southern Medical University, Guangzhou, Guangdong 510630, P.R. China
| | - Xiaochun Bai
- Department of Orthopedics, The Third Affiliated Hospital of Southern Medical University, Guangzhou, Guangdong 510630, P.R. China
| | - Zhongmin Zhang
- Department of Orthopedics, The Third Affiliated Hospital of Southern Medical University, Guangzhou, Guangdong 510630, P.R. China
| | - Liang Wang
- Department of Orthopedics, The Third Affiliated Hospital of Southern Medical University, Guangzhou, Guangdong 510630, P.R. China
| |
Collapse
|
8
|
Mirzoev TM, Tyganov SA, Petrova IO, Shenkman BS. The realization of a mechanical signal during gravitational unloading: The response of mTORC1 targets to eccentric contractions. Biophysics (Nagoya-shi) 2016. [DOI: 10.1134/s0006350916050213] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
|
9
|
Baumann CW, Rogers RG, Otis JS, Ingalls CP. Recovery of strength is dependent on mTORC1 signaling after eccentric muscle injury. Muscle Nerve 2016; 54:914-924. [PMID: 27015597 DOI: 10.1002/mus.25121] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/22/2016] [Indexed: 01/14/2023]
Abstract
INTRODUCTION Eccentric contractions may cause immediate and long-term reductions in muscle strength that can be recovered through increased protein synthesis rates. The purpose of this study was to determine whether the mechanistic target-of-rapamycin complex 1 (mTORC1), a vital controller of protein synthesis rates, is required for return of muscle strength after injury. METHODS Isometric muscle strength was assessed before, immediately after, and then 3, 7, and 14 days after a single bout of 150 eccentric contractions in mice that received daily injections of saline or rapamycin. RESULTS The bout of eccentric contractions increased the phosphorylation of mTORC1 (1.8-fold) and p70s6k1 (13.8-fold), mTORC1's downstream effector, 3 days post-injury. Rapamycin blocked mTORC1 and p70s6k1 phosphorylation and attenuated recovery of muscle strength (∼20%) at 7 and 14 days. CONCLUSION mTORC1 signaling is instrumental in the return of muscle strength after a single bout of eccentric contractions in mice. Muscle Nerve 54: 914-924, 2016.
Collapse
Affiliation(s)
- Cory Walter Baumann
- Muscle Biology Laboratory, Department of Kinesiology and Health, Georgia State University, Atlanta, Georgia, 30302-3975, USA
| | - Russell George Rogers
- Muscle Biology Laboratory, Department of Kinesiology and Health, Georgia State University, Atlanta, Georgia, 30302-3975, USA
| | - Jeffrey Scott Otis
- Muscle Biology Laboratory, Department of Kinesiology and Health, Georgia State University, Atlanta, Georgia, 30302-3975, USA
| | - Christopher Paul Ingalls
- Muscle Biology Laboratory, Department of Kinesiology and Health, Georgia State University, Atlanta, Georgia, 30302-3975, USA.
| |
Collapse
|
10
|
Van Dyke JM, Bain JL, Riley DA. Stretch-activated signaling is modulated by stretch magnitude and contraction. Muscle Nerve 2013; 49:98-107. [DOI: 10.1002/mus.23880] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/10/2013] [Indexed: 11/08/2022]
Affiliation(s)
- Jonathan M. Van Dyke
- Department of Cell Biology; Neurobiology & Anatomy, Medical College of Wisconsin; 8701 Watertown Plank Road Milwaukee Wisconsin 53226 USA
| | - James L.W. Bain
- Department of Cell Biology; Neurobiology & Anatomy, Medical College of Wisconsin; 8701 Watertown Plank Road Milwaukee Wisconsin 53226 USA
| | - Danny A. Riley
- Department of Cell Biology; Neurobiology & Anatomy, Medical College of Wisconsin; 8701 Watertown Plank Road Milwaukee Wisconsin 53226 USA
| |
Collapse
|
11
|
The role of mTORC1 in regulating protein synthesis and skeletal muscle mass in response to various mechanical stimuli. Rev Physiol Biochem Pharmacol 2013; 166:43-95. [PMID: 24442322 DOI: 10.1007/112_2013_17] [Citation(s) in RCA: 91] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Skeletal muscle plays a fundamental role in mobility, disease prevention, and quality of life. Skeletal muscle mass is, in part, determined by the rates of protein synthesis, and mechanical loading is a major regulator of protein synthesis and skeletal muscle mass. The mammalian/mechanistic target of rapamycin (mTOR), found in the multi-protein complex, mTORC1, is proposed to play an essential role in the regulation of protein synthesis and skeletal muscle mass. The purpose of this review is to examine the function of mTORC1 in relation to protein synthesis and cell growth, the current evidence from rodent and human studies for the activation of mTORC1 signaling by different types of mechanical stimuli, whether mTORC1 signaling is necessary for changes in protein synthesis and skeletal muscle mass that occur in response to different types of mechanical stimuli, and the proposed molecular signaling mechanisms that may be responsible for the mechanical activation of mTORC1 signaling.
Collapse
|
12
|
Khodabukus A, Baar K. Defined Electrical Stimulation Emphasizing Excitability for the Development and Testing of Engineered Skeletal Muscle. Tissue Eng Part C Methods 2012; 18:349-57. [DOI: 10.1089/ten.tec.2011.0364] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Affiliation(s)
- Alastair Khodabukus
- Division of Neurobiology, Physiology and Behavior, University of California Davis, Davis, California
| | - Keith Baar
- Division of Neurobiology, Physiology and Behavior, University of California Davis, Davis, California
| |
Collapse
|
13
|
Spangenburg EE. Changes in muscle mass with mechanical load: possible cellular mechanismsThis paper is one of a selection of papers published in this Special Issue, entitled 14th International Biochemistry of Exercise Conference – Muscles as Molecular and Metabolic Machines, and has undergone the Journal’s usual peer review process. Appl Physiol Nutr Metab 2009; 34:328-35. [DOI: 10.1139/h09-010] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Understanding the mechanisms that regulate skeletal muscle mass has remained a focus of numerous researchers for many years. Recent investigations have begun to elucidate cellular signaling mechanisms that regulate skeletal muscle hypertrophy, with significant effort being focused on the Akt/mammalian target of rapamycin (mTOR) signaling pathway. The Akt/mTOR pathway plays a major role in regulating the initiation of protein synthesis after the onset of mechanical loading of skeletal muscle. Although a number of downstream substrates for Akt/mTOR have been elucidated, very little is known about the upstream mechanisms that mechanical load employs to activate the Akt/mTOR signaling pathway. Thus, the purpose of this review is to discuss potential mechanisms that may contribute to the activation of the Akt/mTOR signaling mechanism in mechanically loaded skeletal muscle.
Collapse
Affiliation(s)
- Espen E. Spangenburg
- University of Maryland, School of Public Health, Department of Kinesiology, College Park, MD 20742, USA (e-mail: )
| |
Collapse
|
14
|
O'Neil TK, Duffy LR, Frey JW, Hornberger TA. The role of phosphoinositide 3-kinase and phosphatidic acid in the regulation of mammalian target of rapamycin following eccentric contractions. J Physiol 2009; 587:3691-701. [PMID: 19470781 DOI: 10.1113/jphysiol.2009.173609] [Citation(s) in RCA: 161] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Resistance exercise induces a hypertrophic response in skeletal muscle and recent studies have begun to shed light on the molecular mechanisms involved in this process. For example, several studies indicate that signalling by the mammalian target of rapamycin (mTOR) is necessary for a hypertrophic response. Furthermore, resistance exercise has been proposed to activate mTOR signalling through an upstream pathway involving the phosphoinositide 3-kinase (PI3K) and protein kinase B (PKB); however, this hypothesis has not been thoroughly tested. To test this hypothesis, we first evaluated the temporal pattern of signalling through PI3K-PKB and mTOR following a bout of resistance exercise with eccentric contractions (EC). Our results indicated that the activation of signalling through PI3K-PKB is a transient event (<15 min), while the activation of mTOR is sustained for a long duration (>12 h). Furthermore, inhibition of PI3K-PKB activity did not prevent the activation of mTOR signalling by ECs, indicating that PI3K-PKB is not part of the upstream regulatory pathway. These observations led us to investigate an alternative pathway for the activation of mTOR signalling involving the synthesis of phosphatidic acid (PA) by phospholipase D (PLD). Our results demonstrate that ECs induce a sustained elevation in [PA] and inhibiting the synthesis of PA by PLD prevented the activation of mTOR. Furthermore, we determined that similar to ECs, PA activates mTOR signalling through a PI3K-PKB-independent mechanism. Combined, the results of this study indicate that the activation of mTOR following eccentric contractions occurs through a PI3K-PKB-independent mechanism that requires PLD and PA.
Collapse
Affiliation(s)
- T K O'Neil
- Department of Comparative Biosciences, chool of Veterinary Medicine, University of Wisconsin, 2015 Linden Drive, Madison, WI 53706, USA
| | | | | | | |
Collapse
|
15
|
Mechano-transduction to muscle protein synthesis is modulated by FAK. Eur J Appl Physiol 2009; 106:389-98. [PMID: 19294408 DOI: 10.1007/s00421-009-1032-7] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/02/2009] [Indexed: 01/27/2023]
Abstract
We examined the involvement of focal adhesion kinase (FAK) in mechano-regulated signalling to protein synthesis by combining muscle-targeted transgenesis with a physiological model for un- and reloading of hindlimbs. Transfections of mouse tibialis anterior muscle with a FAK expression construct increased FAK protein 1.6-fold versus empty transfection in the contralateral leg and elevated FAK concentration at the sarcolemma. Altered activation status of phosphotransfer enzymes and downstream translation factors showed that FAK overexpression was functionally important. FAK auto-phosphorylation on Y397 was enhanced between 1 and 6 h of reloading and preceded the activation of p70S6K after 24 h of reloading. Akt and translation initiation factors 4E-BP1 and 2A, which reside up- or downstream of p70S6K, respectively, showed no FAK-modulated regulation. The findings identify FAK as an upstream element of the mechano-sensory pathway of p70S6K activation whose Akt-independent regulation intervenes in control of muscle mass by mechanical stimuli in humans.
Collapse
|
16
|
McClung JM, Whidden MA, Kavazis AN, Falk DJ, Deruisseau KC, Powers SK. Redox regulation of diaphragm proteolysis during mechanical ventilation. Am J Physiol Regul Integr Comp Physiol 2008; 294:R1608-17. [PMID: 18321950 DOI: 10.1152/ajpregu.00044.2008] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Prevention of oxidative stress via antioxidants attenuates diaphragm myofiber atrophy associated with mechanical ventilation (MV). However, the specific redox-sensitive mechanisms responsible for this remain unknown. We tested the hypothesis that regulation of skeletal muscle proteolytic activity is a critical site of redox action during MV. Sprague-Dawley rats were assigned to five experimental groups: 1) control, 2) 6 h of MV, 3) 6 h of MV with infusion of the antioxidant Trolox, 4) 18 h of MV, and 5) 18 h of MV with Trolox. Trolox did not attenuate MV-induced increases in diaphragmatic levels of ubiquitin-protein conjugation, polyubiquitin mRNA, and gene expression of proteasomal subunits (20S proteasome alpha-subunit 7, 14-kDa E2, and proteasome-activating complex PA28). However, Trolox reduced both chymotrypsin-like and peptidylglutamyl peptide hydrolyzing (PGPH)-like 20S proteasome activities in the diaphragm after 18 h of MV. In addition, Trolox rescued diaphragm myofilament protein concentration (mug/mg muscle) and the percentage of easily releasable myofilament protein independent of alterations in ribosomal capacity for protein synthesis. In summary, these data are consistent with the notion that the protective effect of antioxidants on the diaphragm during MV is due, at least in part, to decreasing myofilament protein substrate availability to the proteasome.
Collapse
Affiliation(s)
- J M McClung
- Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL 32611, USA.
| | | | | | | | | | | |
Collapse
|
17
|
Hornberger TA, Sukhija KB, Wang XR, Chien S. mTOR is the rapamycin-sensitive kinase that confers mechanically-induced phosphorylation of the hydrophobic motif site Thr(389) in p70(S6k). FEBS Lett 2007; 581:4562-6. [PMID: 17825298 PMCID: PMC2084087 DOI: 10.1016/j.febslet.2007.08.045] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2007] [Revised: 08/09/2007] [Accepted: 08/23/2007] [Indexed: 10/22/2022]
Abstract
Mechanical stretch induces phosphorylation of the hydrophobic motif site Thr(389) in p70(S6k) through a rapamycin-sensitive (RS) pathway that involves a unique PI3K-independent mechanism. Rapamycin is considered to be a highly specific inhibitor of the protein kinase mTOR; however, mTOR is also considered to be a PI3K-dependent signaling molecule. Thus, questions remain as to whether mTOR is the RS element that confers mechanically-induced signaling to p70(S6k)(389). In this study, rapamycin-resistant mutants of mTOR along with mechanical stretch were used to address this question. The results indicate that mTOR is the RS element and reveal that mTOR signaling can be activated through a PI3K-independent mechanism.
Collapse
Affiliation(s)
- Troy Alan Hornberger
- Department of Bioengineering, University of California San Diego, 9500 Gilman Drive., La Jolla, CA 92093-0412, USA.
| | | | | | | |
Collapse
|