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Pumar OYT, Zanotelli MR, Lin MCJ, Schmitt RR, Green KS, Rojas KS, Hwang IY, Cerione RA, Wilson KF. A multiprotein signaling complex sustains AKT and mTOR/S6K activity necessary for the survival of cancer cells undergoing stress. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.01.03.522657. [PMID: 36711811 PMCID: PMC9881951 DOI: 10.1101/2023.01.03.522657] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Cancer cells encounter stresses during tumor progression and metastatic spread, however, how they survive these challenges is not fully understood. We now identify a mechanism for cancer cell survival through the discovery of a multiprotein signaling complex that includes the GTPase Cdc42, the Cdc42 GEF/effector protein Dock7, AKT, mTOR and the mTORC1 regulatory partners TSC1, TSC2, and Rheb. This pro-survival signaling complex sustains the activated state of AKT by preventing its dephosphorylation at Ser473 during serum starvation, resulting in a low but critical activation of a Raptor-independent mTOR/S6K activity. We demonstrate that the Dock7 DHR1 domain, previously of unknown function, is responsible for preserving AKT phosphorylation through an interaction requiring its C2-like motif. Collectively, these findings help address long-standing questions of how Cdc42 signals mTOR activation by elucidating the unique functions of its signaling partner Dock7 as an AKT regulator necessary for resistance to anoikis and apoptosis in cancer cells.
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Affiliation(s)
| | | | - Miao-chong Joy Lin
- Department of Molecular Medicine, Cornell University, Ithaca, NY 14853, USA
| | - Rebecca R. Schmitt
- Department of Molecular Medicine, Cornell University, Ithaca, NY 14853, USA
| | - Kai Su Green
- Department of Molecular Medicine, Cornell University, Ithaca, NY 14853, USA
| | - Katherine S. Rojas
- Department of Molecular Medicine, Cornell University, Ithaca, NY 14853, USA
| | - Irene Y. Hwang
- Department of Molecular Medicine, Cornell University, Ithaca, NY 14853, USA
| | - Richard A. Cerione
- Department of Molecular Medicine, Cornell University, Ithaca, NY 14853, USA
- Department of Chemistry, Cornell University, Ithaca, NY 14853, USA
| | - Kristin F. Wilson
- Department of Molecular Medicine, Cornell University, Ithaca, NY 14853, USA
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Domma AJ, Henderson LA, Goodrum FD, Moorman NJ, Kamil JP. Human cytomegalovirus attenuates AKT activity by destabilizing insulin receptor substrate proteins. J Virol 2023; 97:e0056323. [PMID: 37754763 PMCID: PMC10617551 DOI: 10.1128/jvi.00563-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2023] [Accepted: 08/09/2023] [Indexed: 09/28/2023] Open
Abstract
IMPORTANCE Human cytomegalovirus (HCMV) requires inactivation of AKT to efficiently replicate, yet how AKT is shut off during HCMV infection has remained unclear. We show that UL38, an HCMV protein that activates mTORC1, is necessary and sufficient to destabilize insulin receptor substrate 1 (IRS1), a model insulin receptor substrate (IRS) protein. Degradation of IRS proteins in settings of excessive mTORC1 activity is an important mechanism for insulin resistance. When IRS proteins are destabilized, PI3K cannot be recruited to growth factor receptor complexes, and hence, AKT membrane recruitment, a rate limiting step in its activation, fails to occur. Despite its penchant for remodeling host cell signaling pathways, our results reveal that HCMV relies upon a cell-intrinsic negative regulatory feedback loop to inactivate AKT. Given that pharmacological inhibition of PI3K/AKT potently induces HCMV reactivation from latency, our findings also imply that the expression of UL38 activity must be tightly regulated within latently infected cells to avoid spontaneous reactivation.
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Affiliation(s)
- Anthony J. Domma
- Department of Microbiology and Immunology, Louisiana State University Health Sciences Center Shreveport, Shreveport, Louisiana, USA
| | - Lauren A. Henderson
- Department of Microbiology and Immunology, Louisiana State University Health Sciences Center Shreveport, Shreveport, Louisiana, USA
| | - Felicia D. Goodrum
- Department of Immunobiology, University of Arizona, Tucson, Arizona, USA
- Bio5 Institute, University of Arizona, Tucson, Arizona, USA
| | - Nathaniel J. Moorman
- Department of Microbiology and Immunology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - Jeremy P. Kamil
- Department of Microbiology and Immunology, Louisiana State University Health Sciences Center Shreveport, Shreveport, Louisiana, USA
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3
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Shekoohi N, Naik AS, Amigo-Benavent M, Harnedy-Rothwell PA, Carson BP, FitzGerald RJ. Physicochemical, technofunctional, in vitro antioxidant, and in situ muscle protein synthesis properties of a sprat ( Sprattus sprattus) protein hydrolysate. Front Nutr 2023; 10:1197274. [PMID: 37426190 PMCID: PMC10328741 DOI: 10.3389/fnut.2023.1197274] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2023] [Accepted: 06/01/2023] [Indexed: 07/11/2023] Open
Abstract
Introduction Sprat (Sprattus sprattus) is an underutilized fish species that may act as an economic and sustainable alternative source of protein due to its good amino acid (AA) profile along with its potential to act as a source of multiple bioactive peptide sequences. Method and results This study characterized the physicochemical, technofunctional, and in vitro antioxidant properties along with the AA profile and score of a sprat protein enzymatic hydrolysate (SPH). Furthermore, the impact of the SPH on the growth, proliferation, and muscle protein synthesis (MPS) in skeletal muscle (C2C12) myotubes was examined. The SPH displayed good solubility and emulsion stabilization properties containing all essential and non-essential AAs. Limited additional hydrolysis was observed following in vitro-simulated gastrointestinal digestion (SGID) of the SPH. The SGID-treated SPH (SPH-SGID) displayed in vitro oxygen radical antioxidant capacity (ORAC) activity (549.42 μmol TE/g sample) and the ability to reduce (68%) reactive oxygen species (ROS) production in C2C12 myotubes. Muscle growth and myotube thickness were analyzed using an xCELLigence™ platform in C2C12 myotubes treated with 1 mg protein equivalent.mL-1 of SPH-SGID for 4 h. Anabolic signaling (phosphorylation of mTOR, rpS6, and 4E-BP1) and MPS (measured by puromycin incorporation) were assessed using immunoblotting. SPH-SGID significantly increased myotube thickness (p < 0.0001) compared to the negative control (cells grown in AA and serum-free medium). MPS was also significantly higher after incubation with SPH-SGID compared with the negative control (p < 0.05). Conclusions These preliminary in situ results indicate that SPH may have the ability to promote muscle enhancement. In vivo human studies are required to verify these findings.
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Affiliation(s)
- Niloofar Shekoohi
- Department of Biological Sciences, University of Limerick, Limerick, Ireland
| | - Azza Silotry Naik
- Department of Biological Sciences, University of Limerick, Limerick, Ireland
| | - Miryam Amigo-Benavent
- Department of Biological Sciences, University of Limerick, Limerick, Ireland
- Health Research Institute, University of Limerick, Limerick, Ireland
| | - Pádraigín A. Harnedy-Rothwell
- Department of Biological Sciences, University of Limerick, Limerick, Ireland
- Health Research Institute, University of Limerick, Limerick, Ireland
| | - Brian P. Carson
- Health Research Institute, University of Limerick, Limerick, Ireland
- Department of Physical Education and Sport Sciences, Faculty of Education and Health Sciences, University of Limerick, Limerick, Ireland
| | - Richard J. FitzGerald
- Department of Biological Sciences, University of Limerick, Limerick, Ireland
- Health Research Institute, University of Limerick, Limerick, Ireland
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4
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Warrier S, Srinivasan S, Chedere A, Rangarajan A. Inhibition of protein translation under matrix-deprivation stress in breast cancer cells. Front Med (Lausanne) 2023; 10:1124514. [PMID: 37425300 PMCID: PMC10324034 DOI: 10.3389/fmed.2023.1124514] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2022] [Accepted: 05/25/2023] [Indexed: 07/11/2023] Open
Abstract
Matrix-deprivation stress leads to cell-death by anoikis, whereas overcoming anoikis is critical for cancer metastasis. Work from our lab and others has identified a crucial role for the cellular energy sensor AMPK in anoikis-resistance, highlighting a key role for metabolic reprogramming in stress survival. Protein synthesis is a major energy-consuming process that is tightly regulated under stress. Although an increase in protein synthesis in AMPK-depleted experimentally-transformed MEFs has been associated with anoikis, the status and regulation of protein translation in epithelial-origin cancer cells facing matrix-detachment remains largely unknown. Our study shows that protein translation is mechanistically abrogated at both initiation and elongation stages by the activation of the unfolded protein response (UPR) pathway and inactivation of elongation factor eEF2, respectively. Additionally, we show inhibition of the mTORC1 pathway known for regulation of canonical protein synthesis. We further functionally assay this inhibition using SUnSET assay, which demonstrates repression of global protein synthesis in MDA-MB-231 and MCF7 breast cancer cells when subjected to matrix-deprivation. In order to gauge the translational status of matrix-deprived cancer cells, we undertook polysome profiling. Our data revealed reduced but continuous mRNA translation under matrix-deprivation stress. An integrated analysis of transcriptomic and proteomic data further identifies novel targets that may aid cellular adaptations to matrix-deprivation stress and can be explored for therapeutic intervention.
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5
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Domma AJ, Goodrum FD, Moorman NJ, Kamil JP. Human cytomegalovirus attenuates AKT activity by destabilizing insulin receptor substrate proteins. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.04.17.537203. [PMID: 37131605 PMCID: PMC10153195 DOI: 10.1101/2023.04.17.537203] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
The phosphoinositide 3-kinase (PI3K)/AKT pathway plays crucial roles in cell viability and protein synthesis and is frequently co-opted by viruses to support their replication. Although many viruses maintain high levels of AKT activity during infection, other viruses, such as vesicular stomatitis virus and human cytomegalovirus (HCMV), cause AKT to accumulate in an inactive state. To efficiently replicate, HCMV requires FoxO transcription factors to localize to the infected cell nucleus (Zhang et. al. mBio 2022), a process directly antagonized by AKT. Therefore, we sought to investigate how HCMV inactivates AKT to achieve this. Subcellular fractionation and live cell imaging studies indicated that AKT failed to recruit to membranes upon serum-stimulation of infected cells. However, UV-inactivated virions were unable to render AKT non-responsive to serum, indicating a requirement for de novo viral gene expression. Interestingly, we were able to identify that UL38 (pUL38), a viral activator of mTORC1, is required to diminish AKT responsiveness to serum. mTORC1 contributes to insulin resistance by causing proteasomal degradation of insulin receptor substrate (IRS) proteins, such as IRS1, which are necessary for the recruitment of PI3K to growth factor receptors. In cells infected with a recombinant HCMV disrupted for UL38 , AKT responsiveness to serum is retained and IRS1 is not degraded. Furthermore, ectopic expression of UL38 in uninfected cells induces IRS1 degradation, inactivating AKT. These effects of UL38 were reversed by the mTORC1 inhibitor, rapamycin. Collectively, our results demonstrate that HCMV relies upon a cell-intrinsic negative feedback loop to render AKT inactive during productive infection.
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Affiliation(s)
- Anthony J. Domma
- Department of Microbiology and Immunology, LSU Health Sciences Center Shreveport, Shreveport Louisiana, USA
| | - Felicia D. Goodrum
- Department of Immunobiology, University of Arizona, Tucson, AZ, USA
- Bio5 Institute, University of Arizona, Tucson, AZ, USA
| | - Nathaniel J. Moorman
- Department of Microbiology and Immunology, UNC Chapel Hill, Chapel Hill, NC, USA
| | - Jeremy P. Kamil
- Department of Microbiology and Immunology, LSU Health Sciences Center Shreveport, Shreveport Louisiana, USA
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6
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Shekoohi N, Amigo-Benavent M, Wesley Peixoto da Fonseca G, Harnedy-Rothwell PA, FitzGerald RJ, Carson BP. A Cell-Based Assessment of the Muscle Anabolic Potential of Blue Whiting ( Micromesistius poutassou) Protein Hydrolysates. Int J Mol Sci 2023; 24:ijms24032001. [PMID: 36768324 PMCID: PMC9916327 DOI: 10.3390/ijms24032001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2022] [Revised: 01/14/2023] [Accepted: 01/17/2023] [Indexed: 01/21/2023] Open
Abstract
Blue whiting (BW) represents an underutilised fish species containing a high-quality protein and amino acid (AA) profile with numerous potentially bioactive peptide sequences, making BW an economic and sustainable alternative source of protein. This study investigated the impact of three different BW protein hydrolysates (BWPH-X, Y and Z) on growth, proliferation and muscle protein synthesis (MPS) in skeletal muscle (C2C12) myotubes. BWPHs were hydrolysed using different enzymatic and heat exposures and underwent simulated gastrointestinal digestion (SGID), each resulting in a high degree of hydrolysis (33.41-37.29%) and high quantities of low molecular mass peptides (86.17-97.12% <1 kDa). C2C12 myotubes were treated with 1 mg protein equivalent/mL of SGID-BWPHs for 4 h. Muscle growth and myotube thickness were analysed using an xCelligence™ platform. Anabolic signalling (phosphorylation of mTOR, rpS6 and 4E-BP1) and MPS measured by puromycin incorporation were assessed using immunoblotting. BWPH-X significantly increased muscle growth (p < 0.01) and myotube thickness (p < 0.0001) compared to the negative control (amino acid and serum free media). Muscle protein synthesis (MPS), as measured by puromycin incorporation, was significantly higher after incubation with BWPH-X compared with the negative control, but did not significantly change in response to BWPH-Y and Z treatments. Taken together, these preliminary findings demonstrate the anabolic potential of some but not all BWPHs on muscle enhancement, thus providing justification for human dietary intervention studies to confirm and translate the results of such investigations to dietary recommendations and practices.
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Affiliation(s)
- Niloofar Shekoohi
- Department of Biological Sciences, University of Limerick, V94 T9PX Limerick, Ireland
| | - Miryam Amigo-Benavent
- Department of Biological Sciences, University of Limerick, V94 T9PX Limerick, Ireland
- Health Research Institute, University of Limerick, V94 T9PX Limerick, Ireland
| | - Guilherme Wesley Peixoto da Fonseca
- Heart Institute (InCor), University of São Paulo Medical School, São Paulo 01246-903, Brazil
- Department of Physical Education and Sport Sciences, Faculty of Education and Health Sciences, University of Limerick, V94 T9PX Limerick, Ireland
| | - Pádraigín A. Harnedy-Rothwell
- Department of Biological Sciences, University of Limerick, V94 T9PX Limerick, Ireland
- Health Research Institute, University of Limerick, V94 T9PX Limerick, Ireland
| | - Richard J. FitzGerald
- Department of Biological Sciences, University of Limerick, V94 T9PX Limerick, Ireland
- Health Research Institute, University of Limerick, V94 T9PX Limerick, Ireland
| | - Brian P. Carson
- Health Research Institute, University of Limerick, V94 T9PX Limerick, Ireland
- Department of Physical Education and Sport Sciences, Faculty of Education and Health Sciences, University of Limerick, V94 T9PX Limerick, Ireland
- Correspondence:
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7
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Tinline-Goodfellow CT, Lees MJ, Hodson N. The skeletal muscle fiber periphery: A nexus of mTOR-related anabolism. SPORTS MEDICINE AND HEALTH SCIENCE 2022; 5:10-19. [PMID: 36994172 PMCID: PMC10040390 DOI: 10.1016/j.smhs.2022.11.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2022] [Revised: 11/16/2022] [Accepted: 11/23/2022] [Indexed: 12/02/2022] Open
Abstract
Skeletal muscle anabolism is driven by numerous stimuli such as growth factors, nutrients (i.e., amino acids, glucose), and mechanical stress. These stimuli are integrated by the mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) signal transduction cascade. In recent years, work from our laboratory and elsewhere has sought to unravel the molecular mechanisms underpinning the mTOR-related activation of muscle protein synthesis (MPS), as well as the spatial regulation of these mechanisms within the skeletal muscle cell. These studies have suggested that the skeletal muscle fiber periphery is a region of central importance in anabolism (i.e., growth/MPS). Indeed, the fiber periphery is replete with the substrates, molecular machinery, and translational apparatus necessary to facilitate MPS. This review provides a summary of the mechanisms underpinning the mTOR-associated activation of MPS from cell, rodent, and human studies. It also presents an overview of the spatial regulation of mTORC1 in response to anabolic stimuli and outlines the factors that distinguish the periphery of the cell as a highly notable region of skeletal muscle for the induction of MPS. Future research should seek to further explore the nutrient-induced activation of mTORC1 at the periphery of skeletal muscle fibers.
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Affiliation(s)
| | - Matthew J. Lees
- Faculty of Kinesiology and Physical Education, University of Toronto, Canada
| | - Nathan Hodson
- Faculty of Kinesiology and Physical Education, University of Toronto, Canada
- Institute of Sport, Manchester Metropolitan University, Manchester, United Kingdom
- Department of Sport and Exercise Sciences, Manchester Metropolitan University, Manchester, United Kingdom
- Corresponding author. Faculty of Kinesiology and Physical Education, University of Toronto, Canada.
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8
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Palmitate Inhibits Mouse Macrophage Efferocytosis by Activating an mTORC1-Regulated Rho Kinase 1 Pathway: Therapeutic Implications for the Treatment of Obesity. Cells 2022; 11:cells11213502. [PMID: 36359898 PMCID: PMC9657837 DOI: 10.3390/cells11213502] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2022] [Revised: 10/24/2022] [Accepted: 11/03/2022] [Indexed: 11/09/2022] Open
Abstract
Every day, billions of our cells die and get cleared without inducing inflammation. When, clearance is improper, uncleared cells undergo secondary necrosis and trigger inflammation. In addition, proper efferocytosis would be required for inducing resolution of inflammation, thus clearance deficiencies in the long term lead to development of various chronic inflammatory diseases. Increasing evidence indicates that obesity, itself being a low-grade inflammatory disease, predisposes to a variety of other chronic inflammatory diseases. Previous studies indicated that this later might be partially related to an impaired efferocytosis induced by increased uptake of circulating saturated fatty acids by macrophages in obese people. Here, we show that palmitate inhibits efferocytosis by bone marrow-derived macrophages in a dose-dependent manner. Palmitate triggers autophagy but also activates an energy-sensing mTORC1/ROCK1 signaling pathway, which interferes with the autophagosome–lysosome fusion, resulting in accumulation of the cellular membranes in autophagosomes. We propose that lack of sufficient plasma membrane supply attenuates efferocytosis of palmitate-exposed macrophages. AMP-activated protein kinase activators lead to mTORC1 inhibition and, consequently, released the palmitate-induced efferocytosis block in macrophages. Thus, they might be useful in the treatment of obesity not only by affecting metabolism thought so far. ROCK1 inhibitors could also be considered.
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9
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Wang Q, Mao Z, Liu Z, Xu M, Huang S, Wang Y, Xu Y, Qi L, Liu M, Liu Y. Akt/mTOR integrate energy metabolism with Wnt signal to influence wound epithelium growth in Gekko Japonicus. Commun Biol 2022; 5:1018. [PMID: 36167813 PMCID: PMC9515156 DOI: 10.1038/s42003-022-04004-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2022] [Accepted: 09/15/2022] [Indexed: 11/25/2022] Open
Abstract
The formation of wound epithelium initiates regeneration of amputated tail in Gekko japonicus. Energy metabolism is indispensable for the growth of living creatures and typically influenced by temperature. In this study, we reveal that low temperature lowers energy metabolism level and inhibits the regeneration of amputated tails of Gekko japonicus. We further find that low temperature attenuates the activation of protein kinase B (Akt) and mammalian target of rapamycin (mTOR) in regenerated tissues upon injury signals, and the inhibition of Akt hinders proliferation of the wound epithelium. Additionally, wingless/integrated (Wnt) inhibition suppresses epithelium proliferation and formation by inhibiting Akt activation. Finally, low temperature elevates the activity of adenylate-activated kinase (AMPK) pathway and in turn attenuates wound epithelium formation. Meanwhile, either mTOR downregulation or AMPK upregulation is associated with worse wound epithelium formation. Summarily, low temperature restricts wound epithelium formation by influencing energy sensory pathways including Akt/mTOR and AMPK signaling, which is also modulated by injury induced Wnt signal. Our results provide a mechanism that incorporates the injury signals with metabolic pathway to facilitate regeneration. Low temperature inhibits the regeneration of amputated tails of Gekko japonicus by influencing the energy sensory Akt/mTOR pathway, which is also modulated by injury-induced Wnt signal.
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Affiliation(s)
- Qinghua Wang
- Key Laboratory of Neuroregeneration of Jiangsu Province and Ministry of Education, Co-innovation Center of Neuroregeneration, Nantong University, Nantong, 226001, China.,Comparative Medicine Research Institution, Nantong University, Nantong, 226001, China
| | - Zuming Mao
- Key Laboratory of Neuroregeneration of Jiangsu Province and Ministry of Education, Co-innovation Center of Neuroregeneration, Nantong University, Nantong, 226001, China
| | - Zhuang Liu
- Key Laboratory of Neuroregeneration of Jiangsu Province and Ministry of Education, Co-innovation Center of Neuroregeneration, Nantong University, Nantong, 226001, China
| | - Man Xu
- Key Laboratory of Neuroregeneration of Jiangsu Province and Ministry of Education, Co-innovation Center of Neuroregeneration, Nantong University, Nantong, 226001, China
| | - Shuai Huang
- Key Laboratory of Neuroregeneration of Jiangsu Province and Ministry of Education, Co-innovation Center of Neuroregeneration, Nantong University, Nantong, 226001, China
| | - Yin Wang
- Key Laboratory of Neuroregeneration of Jiangsu Province and Ministry of Education, Co-innovation Center of Neuroregeneration, Nantong University, Nantong, 226001, China
| | - Yanran Xu
- Key Laboratory of Neuroregeneration of Jiangsu Province and Ministry of Education, Co-innovation Center of Neuroregeneration, Nantong University, Nantong, 226001, China
| | - Longju Qi
- Affiliated Nantong Hospital 3 of Nantong University, Nantong University, Nantong, 226001, China
| | - Mei Liu
- Key Laboratory of Neuroregeneration of Jiangsu Province and Ministry of Education, Co-innovation Center of Neuroregeneration, Nantong University, Nantong, 226001, China
| | - Yan Liu
- Key Laboratory of Neuroregeneration of Jiangsu Province and Ministry of Education, Co-innovation Center of Neuroregeneration, Nantong University, Nantong, 226001, China.
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10
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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.
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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
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11
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Gourmaud S, Shou H, Irwin DJ, Sansalone K, Jacobs LM, Lucas TH, Marsh ED, Davis KA, Jensen FE, Talos DM. Alzheimer-like amyloid and tau alterations associated with cognitive deficit in temporal lobe epilepsy. Brain 2020; 143:191-209. [PMID: 31834353 DOI: 10.1093/brain/awz381] [Citation(s) in RCA: 66] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2019] [Revised: 10/08/2019] [Accepted: 10/17/2019] [Indexed: 01/27/2023] Open
Abstract
Temporal lobe epilepsy represents a major cause of drug-resistant epilepsy. Cognitive impairment is a frequent comorbidity, but the mechanisms are not fully elucidated. We hypothesized that the cognitive impairment in drug-resistant temporal lobe epilepsy could be due to perturbations of amyloid and tau signalling pathways related to activation of stress kinases, similar to those observed in Alzheimer's disease. We examined these pathways, as well as amyloid-β and tau pathologies in the hippocampus and temporal lobe cortex of drug-resistant temporal lobe epilepsy patients who underwent temporal lobe resection (n = 19), in comparison with age- and region-matched samples from neurologically normal autopsy cases (n = 22). Post-mortem temporal cortex samples from Alzheimer's disease patients (n = 9) were used as positive controls to validate many of the neurodegeneration-related antibodies. Western blot and immunohistochemical analysis of tissue from temporal lobe epilepsy cases revealed increased phosphorylation of full-length amyloid precursor protein and its associated neurotoxic cleavage product amyloid-β*56. Pathological phosphorylation of two distinct tau species was also increased in both regions, but increases in amyloid-β1-42 peptide, the main component of amyloid plaques, were restricted to the hippocampus. Furthermore, several major stress kinases involved in the development of Alzheimer's disease pathology were significantly activated in temporal lobe epilepsy brain samples, including the c-Jun N-terminal kinase and the protein kinase R-like endoplasmic reticulum kinase. In temporal lobe epilepsy cases, hippocampal levels of phosphorylated amyloid precursor protein, its pro-amyloidogenic processing enzyme beta-site amyloid precursor protein cleaving enzyme 1, and both total and hyperphosphorylated tau expression, correlated with impaired preoperative executive function. Our study suggests that neurodegenerative and stress-related processes common to those observed in Alzheimer's disease may contribute to cognitive impairment in drug-resistant temporal lobe epilepsy. In particular, we identified several stress pathways that may represent potential novel therapeutic targets.
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Affiliation(s)
- Sarah Gourmaud
- Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Haochang Shou
- Department of Biostatistics, Epidemiology and Informatics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - David J Irwin
- Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.,Penn Frontotemporal Degeneration Center, University of Pennsylvania, Philadelphia, PA, USA
| | - Kimberly Sansalone
- Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Leah M Jacobs
- Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Timothy H Lucas
- Department of Neurosurgery, University of Pennsylvania, Perelman School of Medicine, Philadelphia, PA, USA
| | - Eric D Marsh
- Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.,Division of Child Neurology, Children's Hospital of Philadelphia, Philadelphia, PA, USA
| | - Kathryn A Davis
- Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Frances E Jensen
- Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Delia M Talos
- Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
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12
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Kim Y, Kim HS, Sohn J, Ji JD. 1,25-Dihydroxyvitamin D 3 induces human myeloid cell differentiation via the mTOR signaling pathway. Biochem Biophys Res Commun 2019; 519:909-915. [PMID: 31563324 DOI: 10.1016/j.bbrc.2019.09.100] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2019] [Accepted: 09/23/2019] [Indexed: 11/17/2022]
Abstract
1,25-Dihydroxyvitamin D3 or 1,25(OH)2D3 is known to play an important role in the differentiation of human myeloid cells. However, the molecular mechanism underlying the 1,25(OH)2D3-mediated differentiation of human myeloid cells is incompletely understood. Here, we report that 1,25(OH)2D3 induces differentiation of human myeloid cell lines such as U937 and THP-1 cells via the mammalian target of rapamycin (mTOR) signaling pathway. Both the expression of the differentiation marker CD14 and activation of the mTOR signaling pathway were induced by 1,25(OH)2D3 in phorbol 12-myristate 13-acetate (PMA)-differentiated U937 and THP-1 cells. The 1,25(OH)2D3-induced expression of CD14 in PMA-differentiated U937 and THP-1 cells was prevented by mTOR inhibitors, PP242 and Torin1. The 1,25(OH)2D3-induced morphological changes as characteristics of differentiated myeloid cells were also reversed after PP242 and Torin1 treatment. Silencing of either regulatory-associated protein of mTOR (Raptor) or rapamycin-insensitive companion of mTOR (Rictor) in PMA-differentiated THP-1 cells with small-interfering RNA resulted in the inhibition of CD14 expression and morphological changes induced by 1,25(OH)2D3, indicating that both mTORC1 and mTORC2 were important for the differentiation of myeloid THP-1 cells. Previous studies have shown that phosphatidic acid (PA) maintains the stability of the mTOR complex. Here we found that the attenuation of PA production with 1-butanol or a PLD inhibitor prevented the 1,25(OH)2D3-induced upregulation of CD14. Taken together, our results show that 1,25(OH)2D3 enhances the differentiation of human myeloid cells through the mTOR signaling pathway.
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Affiliation(s)
- Yongjin Kim
- Department of Biochemistry, College of Medicine, Korea University, Seoul, South Korea
| | - Hee Suk Kim
- Department of Biochemistry, College of Medicine, Korea University, Seoul, South Korea
| | - Jeongwon Sohn
- Department of Biochemistry, College of Medicine, Korea University, Seoul, South Korea.
| | - Jong Dae Ji
- Rheumatology, College of Medicine, Korea University, Seoul, South Korea.
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13
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Loh J, Chuang MC, Lin SS, Joseph J, Su YA, Hsieh TL, Chang YC, Liu AP, Liu YW. An acute decrease in plasma membrane tension induces macropinocytosis via PLD2 activation. J Cell Sci 2019; 132:jcs.232579. [PMID: 31391241 DOI: 10.1242/jcs.232579] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2019] [Accepted: 07/29/2019] [Indexed: 12/13/2022] Open
Abstract
Internalization of macromolecules and membrane into cells through endocytosis is critical for cellular growth, signaling and plasma membrane (PM) tension homeostasis. Although endocytosis is responsive to both biochemical and physical stimuli, how physical cues modulate endocytic pathways is less understood. Contrary to the accumulating discoveries on the effects of increased PM tension on endocytosis, less is known about how a decrease of PM tension impacts on membrane trafficking. Here, we reveal that an acute decrease of PM tension results in phosphatidic acid (PA) production, F-actin and phosphatidylinositol (4,5)-bisphosphate [PI(4,5)P2]-enriched dorsal membrane ruffling and subsequent macropinocytosis in myoblasts. The PA production induced by decreased PM tension depends on phospholipase D2 (PLD2) activation via PLD2 nanodomain disintegration. Furthermore, the 'decreased PM tension-PLD2-macropinocytosis' pathway is prominent in myotubes, reflecting a potential mechanism of PM tension homeostasis upon intensive muscle stretching and relaxation. Together, we identify a new mechanotransduction pathway that converts an acute decrease in PM tension into PA production and then initiates macropinocytosis via actin and PI(4,5)P2-mediated processes.
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Affiliation(s)
- Julie Loh
- Institute of Molecular Medicine, College of Medicine, National Taiwan University, Taipei 10002, Taiwan
| | - Mei-Chun Chuang
- Institute of Molecular Medicine, College of Medicine, National Taiwan University, Taipei 10002, Taiwan
| | - Shan-Shan Lin
- Institute of Molecular Medicine, College of Medicine, National Taiwan University, Taipei 10002, Taiwan
| | - Jophin Joseph
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109, USA
| | - You-An Su
- Institute of Molecular Medicine, College of Medicine, National Taiwan University, Taipei 10002, Taiwan
| | - Tsung-Lin Hsieh
- Institute of Molecular Medicine, College of Medicine, National Taiwan University, Taipei 10002, Taiwan
| | - Yu-Chen Chang
- Institute of Molecular Medicine, College of Medicine, National Taiwan University, Taipei 10002, Taiwan
| | - Allen P Liu
- Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109, USA
| | - Ya-Wen Liu
- Institute of Molecular Medicine, College of Medicine, National Taiwan University, Taipei 10002, Taiwan .,Center of Precision Medicine, College of Medicine, National Taiwan University, Taipei 10002, Taiwan
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14
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Edman S, Söderlund K, Moberg M, Apró W, Blomstrand E. mTORC1 Signaling in Individual Human Muscle Fibers Following Resistance Exercise in Combination With Intake of Essential Amino Acids. Front Nutr 2019; 6:96. [PMID: 31294029 PMCID: PMC6603157 DOI: 10.3389/fnut.2019.00096] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2019] [Accepted: 06/10/2019] [Indexed: 11/13/2022] Open
Abstract
Human muscles contain a mixture of type I and type II fibers with different contractile and metabolic properties. Little is presently known about the effect of anabolic stimuli, in particular nutrition, on the molecular responses of these different fiber types. Here, we examine the effect of resistance exercise in combination with intake of essential amino acids (EAA) on mTORC1 signaling in individual type I and type II human muscle fibers. Five strength-trained men performed two sessions of heavy leg press exercise. During exercise and recovery, the subjects ingested an aqueous solution of EAA (290 mg/kg) or flavored water (placebo). Muscle biopsies were taken from the vastus lateralis before and 90 min after exercise. The biopsies were freeze-dried and single fibers dissected out and weighed (range 0.95-8.1 μg). The fibers were homogenized individually and identified as type I or II by incubation with antibodies against the different isoforms of myosin. They were also analyzed for both the levels of protein as well as phosphorylation of proteins in the mTORC1 pathway using Western blotting. The levels of the S6K1 and eEF2 proteins were ~50% higher in type II than in type I fibers (P < 0.05), but no difference was found between fiber types with respect to the level of mTOR protein. Resistance exercise led to non-significant increases (2-3-fold) in mTOR and S6K1 phosphorylation as well as a 50% decrease (P < 0.05) in eEF2 phosphorylation in both fiber types. Intake of EAA caused a 2 and 6-fold higher (P < 0.05) elevation of mTOR and S6K1 phosphorylation, respectively, in both type I and type II fibers compared to placebo, with no effect on phosphorylation of eEF2. In conclusion, protein levels of S6K1 and eEF2 were significantly higher in type II than type I fibers suggesting higher capacity of the mTOR pathway in type II fibers. Ingestion of EAA enhanced the effect of resistance exercise on phosphorylation of mTOR and S6K1 in both fiber types, but with considerable variation between single fibers of both types.
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Affiliation(s)
- Sebastian Edman
- The Åstrand Laboratory, the Swedish School of Sport and Health Sciences, Stockholm, Sweden
| | - Karin Söderlund
- The Åstrand Laboratory, the Swedish School of Sport and Health Sciences, Stockholm, Sweden
| | - Marcus Moberg
- The Åstrand Laboratory, the Swedish School of Sport and Health Sciences, Stockholm, Sweden
| | - William Apró
- The Åstrand Laboratory, the Swedish School of Sport and Health Sciences, Stockholm, Sweden
| | - Eva Blomstrand
- The Åstrand Laboratory, the Swedish School of Sport and Health Sciences, Stockholm, Sweden.,Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden
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15
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Lin SS, Liu YW. Mechanical Stretch Induces mTOR Recruitment and Activation at the Phosphatidic Acid-Enriched Macropinosome in Muscle Cell. Front Cell Dev Biol 2019; 7:78. [PMID: 31139627 PMCID: PMC6518962 DOI: 10.3389/fcell.2019.00078] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2019] [Accepted: 04/24/2019] [Indexed: 12/22/2022] Open
Abstract
The mammalian target of rapamycin (mTOR) is an evolutionarily conserved kinase which assembles a signaling network that integrates diverse biochemical and mechanical cues to coordinate cell growth and proliferation. Mechanical load has been well-appreciated to induce mTOR activation that leads to skeletal muscle growth through phospholipase D (PLD) activity and phosphatidic acid (PA) production. While PA produced by PLD1 is critical for mTOR activation upon mitogenic stimulation at the lysosome, it is unclear where PA is produced upon mechanical stimulation in skeletal muscle. Here we report that membrane tension fluctuation induces the formation of PA-enriched macropinosome in mouse C2C12-derived myotube by either mechanical stretch or osmotic shock. The tension oscillation-induced PA is accumulated at the membrane of macropinosome, not the lysosome. Furthermore, mTOR is recruited to the PA-enriched macropinosome, and its downstream signaling is activated. Our findings reveal the underpinning of mechanical activation of mTOR signaling, and more importantly, the stretch-induced PA-macropinosome as a new platform for mTOR activation.
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Affiliation(s)
- Shan-Shan Lin
- Institute of Molecular Medicine, College of Medicine, National Taiwan University, Taipei, Taiwan
| | - Ya-Wen Liu
- Institute of Molecular Medicine, College of Medicine, National Taiwan University, Taipei, Taiwan.,Center of Precision Medicine, College of Medicine, National Taiwan University, Taipei, Taiwan
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16
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Hall DT, Griss T, Ma JF, Sanchez BJ, Sadek J, Tremblay AMK, Mubaid S, Omer A, Ford RJ, Bedard N, Pause A, Wing SS, Di Marco S, Steinberg GR, Jones RG, Gallouzi IE. The AMPK agonist 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR), but not metformin, prevents inflammation-associated cachectic muscle wasting. EMBO Mol Med 2019; 10:emmm.201708307. [PMID: 29844217 PMCID: PMC6034131 DOI: 10.15252/emmm.201708307] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Activation of AMPK has been associated with pro-atrophic signaling in muscle. However, AMPK also has anti-inflammatory effects, suggesting that in cachexia, a syndrome of inflammatory-driven muscle wasting, AMPK activation could be beneficial. Here we show that the AMPK agonist AICAR suppresses IFNγ/TNFα-induced atrophy, while the mitochondrial inhibitor metformin does not. IFNγ/TNFα impair mitochondrial oxidative respiration in myotubes and promote a metabolic shift to aerobic glycolysis, similarly to metformin. In contrast, AICAR partially restored metabolic function. The effects of AICAR were prevented by the AMPK inhibitor Compound C and were reproduced with A-769662, a specific AMPK activator. AICAR and A-769662 co-treatment was found to be synergistic, suggesting that the anti-cachectic effects of these drugs are mediated through AMPK activation. AICAR spared muscle mass in mouse models of cancer and LPS induced atrophy. Together, our findings suggest a dual function for AMPK during inflammation-driven atrophy, wherein it can play a protective role when activated exogenously early in disease progression, but may contribute to anabolic suppression and atrophy when activated later through mitochondrial dysfunction and subsequent metabolic stress.
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Affiliation(s)
- Derek T Hall
- Department of Biochemistry, McGill University, Montreal, QC, Canada.,Rosalind and Morris Goodman Cancer Centre, Montreal, QC, Canada
| | - Takla Griss
- Rosalind and Morris Goodman Cancer Centre, Montreal, QC, Canada.,Department of Physiology, McGill University, Montreal, QC, Canada
| | - Jennifer F Ma
- Department of Biochemistry, McGill University, Montreal, QC, Canada.,Rosalind and Morris Goodman Cancer Centre, Montreal, QC, Canada
| | - Brenda Janice Sanchez
- Department of Biochemistry, McGill University, Montreal, QC, Canada.,Rosalind and Morris Goodman Cancer Centre, Montreal, QC, Canada
| | - Jason Sadek
- Department of Biochemistry, McGill University, Montreal, QC, Canada.,Rosalind and Morris Goodman Cancer Centre, Montreal, QC, Canada
| | - Anne Marie K Tremblay
- Department of Biochemistry, McGill University, Montreal, QC, Canada.,Rosalind and Morris Goodman Cancer Centre, Montreal, QC, Canada
| | - Souad Mubaid
- Department of Biochemistry, McGill University, Montreal, QC, Canada.,Rosalind and Morris Goodman Cancer Centre, Montreal, QC, Canada
| | - Amr Omer
- Department of Biochemistry, McGill University, Montreal, QC, Canada.,Rosalind and Morris Goodman Cancer Centre, Montreal, QC, Canada
| | - Rebecca J Ford
- Division of Endocrinology and Metabolism, Department of Medicine, McMaster University, Hamilton, ON, Canada
| | - Nathalie Bedard
- Department of Medicine, McGill University and the Research Institute of the McGill University Health Centre, Montreal, QC, Canada
| | - Arnim Pause
- Department of Biochemistry, McGill University, Montreal, QC, Canada.,Rosalind and Morris Goodman Cancer Centre, Montreal, QC, Canada
| | - Simon S Wing
- Department of Medicine, McGill University and the Research Institute of the McGill University Health Centre, Montreal, QC, Canada
| | - Sergio Di Marco
- Department of Biochemistry, McGill University, Montreal, QC, Canada.,Rosalind and Morris Goodman Cancer Centre, Montreal, QC, Canada
| | - Gregory R Steinberg
- Division of Endocrinology and Metabolism, Department of Medicine, McMaster University, Hamilton, ON, Canada
| | - Russell G Jones
- Rosalind and Morris Goodman Cancer Centre, Montreal, QC, Canada.,Department of Physiology, McGill University, Montreal, QC, Canada
| | - Imed-Eddine Gallouzi
- Department of Biochemistry, McGill University, Montreal, QC, Canada .,Rosalind and Morris Goodman Cancer Centre, Montreal, QC, Canada.,Life Sciences Division, College of Sciences and Engineering, Hamad Bin Khalifa University (HBKU), Doha, Qatar
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17
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Roeseler DA, McGraw NJ, Butteiger DN, Shah N, Hall-Porter J, Mukherjea R, Krul ES. Muscle Protein Signaling in C2C12 Cells Is Stimulated to Similar Degrees by Diverse Commercial Food Protein Sources and Experimental Soy Protein Hydrolysates. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2017; 65:2956-2964. [PMID: 28339214 DOI: 10.1021/acs.jafc.6b05460] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Dietary protein stimulates muscle protein synthesis and is essential for muscle health. We developed a screening assay using C2C12 mouse muscle cells to assess the relative abilities of diverse commercial protein sources and experimental soy protein hydrolysates (ESH), after simulated gut digestion (SGD), to activate the mechanistic target of rapamycin complex I (mTORC1) muscle protein synthesis signaling pathway (p70S6K(Thr389) phosphorylation). Activation of mTORC1 was expressed as a percentage of a maximal insulin response. The bioactivities of proteins grouped by source including fish (81.3 ± 10.6%), soy (66.2 ± 4.7%), dairy (61.8 ± 4.3%), beef (53.7 ± 8.6%), egg (52.3 ± 10.6%), soy whey (43.4 ± 8.6%), and pea (31.4 ± 10.6%) were not significantly different from each other. Bioactivity for ESH ranged from 28.0 ± 7.5 to 98.2 ± 6.6%. The results indicate that both the protein source and processing conditions are key determinants for mTORC1 activation. Regression analyses demonstrated that neither leucine nor total branched-chain amino acid content of proteins is the sole predictor of mTORC1 activity and that additional factors are necessary.
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Affiliation(s)
- David A Roeseler
- DuPont Nutrition & Health , St. Louis, Missouri 63110, United States
| | - Nancy J McGraw
- DuPont Nutrition & Health , St. Louis, Missouri 63110, United States
| | | | - Naina Shah
- DuPont Nutrition & Health , St. Louis, Missouri 63110, United States
| | | | - Ratna Mukherjea
- DuPont Nutrition & Health , St. Louis, Missouri 63110, United States
| | - Elaine S Krul
- DuPont Nutrition & Health , St. Louis, Missouri 63110, United States
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18
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Rindom E, Vissing K. Mechanosensitive Molecular Networks Involved in Transducing Resistance Exercise-Signals into Muscle Protein Accretion. Front Physiol 2016; 7:547. [PMID: 27909410 PMCID: PMC5112233 DOI: 10.3389/fphys.2016.00547] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2016] [Accepted: 10/31/2016] [Indexed: 02/05/2023] Open
Abstract
Loss of skeletal muscle myofibrillar protein with disease and/or inactivity can severely deteriorate muscle strength and function. Strategies to counteract wasting of muscle myofibrillar protein are therefore desirable and invite for considerations on the potential superiority of specific modes of resistance exercise and/or the adequacy of low load resistance exercise regimens as well as underlying mechanisms. In this regard, delineation of the potentially mechanosensitive molecular mechanisms underlying muscle protein synthesis (MPS), may contribute to an understanding on how differentiated resistance exercise can transduce a mechanical signal into stimulation of muscle accretion. Recent findings suggest specific upstream exercise-induced mechano-sensitive myocellular signaling pathways to converge on mammalian target of rapamycin complex 1 (mTORC1), to influence MPS. This may e.g. implicate mechanical activation of signaling through a diacylglycerol kinase (DGKζ)-phosphatidic acid (PA) axis or implicate integrin deformation to signal through a Focal adhesion kinase (FAK)-Tuberous Sclerosis Complex 2 (TSC2)-Ras homolog enriched in brain (Rheb) axis. Moreover, since initiation of translation is reliant on mRNA, it is also relevant to consider potentially mechanosensitive signaling pathways involved in muscle myofibrillar gene transcription and whether some of these pathways converge with those affecting mTORC1 activation for MPS. In this regard, recent findings suggest how mechanical stress may implicate integrin deformation and/or actin dynamics to signal through a Ras homolog gene family member A protein (RhoA)-striated muscle activator of Rho signaling (STARS) axis or implicate deformation of Notch to affect Bone Morphogenetic Protein (BMP) signaling through a small mother of decapentaplegic (Smad) axis.
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Affiliation(s)
- Emil Rindom
- Section of Sport Science, Department of Public Health, Aarhus UniversityAarhus, Denmark; Department of Biomedicine, Aarhus UniversityAarhus, Denmark
| | - Kristian Vissing
- Section of Sport Science, Department of Public Health, Aarhus University Aarhus, Denmark
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19
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Corpeno Kalamgi R, Salah H, Gastaldello S, Martinez-Redondo V, Ruas JL, Fury W, Bai Y, Gromada J, Sartori R, Guttridge DC, Sandri M, Larsson L. Mechano-signalling pathways in an experimental intensive critical illness myopathy model. J Physiol 2016; 594:4371-88. [PMID: 26990577 DOI: 10.1113/jp271973] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2015] [Accepted: 03/11/2016] [Indexed: 01/07/2023] Open
Abstract
KEY POINTS Using an experimental rat intensive care unit (ICU) model, not limited by early mortality, we have previously shown that passive mechanical loading attenuates the loss of muscle mass and force-generation capacity associated with the ICU intervention. Mitochondrial dynamics have recently been shown to play a more important role in muscle atrophy than previously recognized. In this study we demonstrate that mitochondrial dynamics, as well as mitophagy, is affected by mechanosensing at the transcriptional level, and muscle changes induced by unloading are counteracted by passive mechanical loading. The recently discovered ubiquitin ligases Fbxo31 and SMART are induced by mechanical silencing, an induction that similarly is prevented by passive mechanical loading. ABSTRACT The complete loss of mechanical stimuli of skeletal muscles, i.e. loss of external strain related to weight bearing and internal strain related to activation of contractile proteins, in mechanically ventilated, deeply sedated and/or pharmacologically paralysed intensive care unit (ICU) patients is an important factor triggering the critical illness myopathy (CIM). Using a unique experimental ICU rat model, mimicking basic ICU conditions, we have recently shown that mechanical silencing is a dominant factor triggering the preferential loss of myosin, muscle atrophy and decreased specific force in fast- and slow-twitch muscles and muscle fibres. The aim of this study is to gain improved understanding of the gene signature and molecular pathways regulating the process of mechanical activation of skeletal muscle that are affected by the ICU condition. We have focused on pathways controlling myofibrillar protein synthesis and degradation, mitochondrial homeostasis and apoptosis. We demonstrate that genes regulating mitochondrial dynamics, as well as mitophagy are induced by mechanical silencing and that these effects are counteracted by passive mechanical loading. In addition, the recently identified ubiquitin ligases Fbxo31 and SMART are induced by mechanical silencing, an induction that is reversed by passive mechanical loading. Thus, mechano-cell signalling events are identified which may play an important role for the improved clinical outcomes reported in response to the early mobilization and physical therapy in immobilized ICU patients.
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Affiliation(s)
- Rebeca Corpeno Kalamgi
- Department of Physiology and Pharmacology, Karolinska Institutet, SE-171 77, Stockholm, Sweden
| | - Heba Salah
- Department of Physiology and Pharmacology, Karolinska Institutet, SE-171 77, Stockholm, Sweden
| | - Stefano Gastaldello
- Department of Physiology and Pharmacology, Karolinska Institutet, SE-171 77, Stockholm, Sweden
| | | | - Jorge L Ruas
- Department of Physiology and Pharmacology, Karolinska Institutet, SE-171 77, Stockholm, Sweden
| | - Wen Fury
- Regeneron Pharmaceuticals, Tarrytown, 10591, NY, USA
| | - Yu Bai
- Regeneron Pharmaceuticals, Tarrytown, 10591, NY, USA
| | | | - Roberta Sartori
- Venetian Institute of Molecular Medicine, 35131, Padova, Italy.,Department of Biomedical Sciences, University of Padova, 35131, Padova, Italy
| | - Denis C Guttridge
- Department of Molecular Virology, Immunology and Medical Genetics, The Ohio State University Medical Centre, Columbus, 43210, OH, USA
| | - Marco Sandri
- Venetian Institute of Molecular Medicine, 35131, Padova, Italy.,Department of Biomedical Sciences, University of Padova, 35131, Padova, Italy
| | - Lars Larsson
- Department of Physiology and Pharmacology, Karolinska Institutet, SE-171 77, Stockholm, Sweden.,Department of Clinical Neuroscience, Clinical Neurophysiology, Karolinska Institutet, SE-171 77, Stockholm, Sweden.,Department of Biobehavioral Health, The Pennsylvania State University, University Park, PA, USA
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20
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Kalamgi RC, Larsson L. Mechanical Signaling in the Pathophysiology of Critical Illness Myopathy. Front Physiol 2016; 7:23. [PMID: 26869939 PMCID: PMC4740381 DOI: 10.3389/fphys.2016.00023] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2015] [Accepted: 01/18/2016] [Indexed: 12/14/2022] Open
Abstract
The complete loss of mechanical stimuli of skeletal muscles, i.e., the loss of external strain, related to weight bearing, and internal strain, related to the contraction of muscle cells, is uniquely observed in pharmacologically paralyzed or deeply sedated mechanically ventilated intensive care unit (ICU) patients. The preferential loss of myosin and myosin associated proteins in limb and trunk muscles is a significant characteristic of critical illness myopathy (CIM) which separates CIM from other types of acquired muscle weaknesses in ICU patients. Mechanical silencing is an important factor triggering CIM. Microgravity or ground based microgravity models form the basis of research on the effect of muscle unloading-reloading, but the mechanisms and effects may differ from the ICU conditions. In order to understand how mechanical tension regulates muscle mass, it is critical to know how muscles sense mechanical information and convert stimulus to intracellular biochemical actions and changes in gene expression, a process called cellular mechanotransduction. In adult skeletal muscles and muscle fibers, this process may differ, the same stimulus can cause divergent response and the same fiber type may undergo opposite changes in different muscles. Skeletal muscle contains multiple types of mechano-sensors and numerous structures that can be affected differently and hence respond differently in distinct muscles.
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Affiliation(s)
- Rebeca C Kalamgi
- Basic and Clinical Muscle Biology, Department of Physiology and Pharmacology, Karolinska Institutet Stockholm, Sweden
| | - Lars Larsson
- Basic and Clinical Muscle Biology, Department of Physiology and Pharmacology, Karolinska InstitutetStockholm, Sweden; Department of Clinical Neuroscience, Clinical Neurophysiology, Karolinska InstitutetStockholm, Sweden
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21
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Lee HJ, Ryu JM, Jung YH, Oh SY, Lee SJ, Han HJ. Novel Pathway for Hypoxia-Induced Proliferation and Migration in Human Mesenchymal Stem Cells: Involvement of HIF-1α, FASN, and mTORC1. Stem Cells 2015; 33:2182-95. [DOI: 10.1002/stem.2020] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2014] [Accepted: 02/28/2015] [Indexed: 12/24/2022]
Affiliation(s)
- Hyun Jik Lee
- BK21 PLUS Creative Veterinary Research Center; Seoul National University; Seoul Korea
| | - Jung Min Ryu
- Department of Veterinary Physiology, College of Veterinary Medicine; Research Institute for Veterinary Science, Seoul National University; Seoul Korea
| | - Young Hyun Jung
- BK21 PLUS Creative Veterinary Research Center; Seoul National University; Seoul Korea
| | - Sang Yub Oh
- BK21 PLUS Creative Veterinary Research Center; Seoul National University; Seoul Korea
| | - Sei-Jung Lee
- BK21 PLUS Creative Veterinary Research Center; Seoul National University; Seoul Korea
| | - Ho Jae Han
- BK21 PLUS Creative Veterinary Research Center; Seoul National University; Seoul Korea
- Department of Veterinary Physiology, College of Veterinary Medicine; Research Institute for Veterinary Science, Seoul National University; Seoul Korea
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22
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Yano H, Choudhury ME, Islam A, Kobayashi K, Tanaka J. Cellular mechanotransduction of physical force and organ response to exercise-induced mechanical stimuli. THE JOURNAL OF PHYSICAL FITNESS AND SPORTS MEDICINE 2015. [DOI: 10.7600/jpfsm.4.83] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/08/2023]
Affiliation(s)
- Hajime Yano
- Department of Molecular and Cellular Physiology, Ehime University Graduate School of Medicine
| | - Mohammed E Choudhury
- Department of Molecular and Cellular Physiology, Ehime University Graduate School of Medicine
| | - Afsana Islam
- Department of Molecular and Cellular Physiology, Ehime University Graduate School of Medicine
| | - Kana Kobayashi
- Department of Molecular and Cellular Physiology, Ehime University Graduate School of Medicine
| | - Junya Tanaka
- Department of Molecular and Cellular Physiology, Ehime University Graduate School of Medicine
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23
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Houédé N, Pourquier P. Targeting the genetic alterations of the PI3K-AKT-mTOR pathway: its potential use in the treatment of bladder cancers. Pharmacol Ther 2014; 145:1-18. [PMID: 24929024 DOI: 10.1016/j.pharmthera.2014.06.004] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2014] [Accepted: 06/06/2014] [Indexed: 02/07/2023]
Abstract
Urothelial carcinoma of the bladder is the most frequent tumor of the urinary tract and represents the fifth cause of death by cancer worldwide. The current first line chemotherapy is a combination of cisplatin and gemcitabine with median survival not exceeding 15months. Vinflunine is the only drug approved by EMEA as second-line treatment and few progresses have been made for the past 20years to increase the survival of metastatic patients, especially those who are not eligible for cisplatin-based regimen. The recent studies characterizing the genetic background of urothelial cancers of the bladder, revealed chromosomal alterations that are not seen at the same level in other types of cancers. This is especially the case for mutations of genes involved in the PI3K/AKT/mTOR signaling pathway that occupies a major place in the etiology of these tumors. Here, we describe the mutations leading to constitutive activation of the PI3K/AKT/mTOR pathway and discuss the potential use of the different classes of PI3K/AKT/mTOR inhibitors in the treatment of urothelial bladder cancers. Despite the recent pivotal study evidencing specific mutations of TSC1 in bladder cancer patients responding to everolimus and the encouraging results obtained with other derivatives than rapalogs, few clinical trials are ongoing in bladder cancers. Because of the genetic complexity of these tumors, the cross-talks of the PI3K/AKT/mTOR pathway with other pathways, and the small number of eligible patients, it will be of utmost importance to carefully choose the drugs or drug combinations to be further tested in the clinic.
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Affiliation(s)
- Nadine Houédé
- Service d'Oncologie Médicale, Centre Hospitalier Universitaire de Nîmes, France; INSERM U896, Institut de Recherche en Cancérologie de Montpellier & Université de Montpellier 1, France.
| | - Philippe Pourquier
- Service d'Oncologie Médicale, Centre Hospitalier Universitaire de Nîmes, France; INSERM U896, Institut de Recherche en Cancérologie de Montpellier & Université de Montpellier 1, France
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Jacobs BL, Goodman CA, Hornberger TA. The mechanical activation of mTOR signaling: an emerging role for late endosome/lysosomal targeting. J Muscle Res Cell Motil 2014; 35:11-21. [PMID: 24162376 PMCID: PMC3981920 DOI: 10.1007/s10974-013-9367-4] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2013] [Accepted: 10/18/2013] [Indexed: 01/03/2023]
Abstract
It is well recognized that mechanical signals play a critical role in the regulation of skeletal muscle mass, and the maintenance of muscle mass is essential for mobility, disease prevention and quality of life. Furthermore, over the last 15 years it has become established that signaling through a protein kinase called the mammalian (or mechanistic) target of rapamycin (mTOR) is essential for mechanically-induced changes in protein synthesis and muscle mass, however, the mechanism(s) via which mechanical stimuli regulate mTOR signaling have not been defined. Nonetheless, advancements are being made, and an emerging body of evidence suggests that the late endosome/lysosomal (LEL) system might play a key role in this process. Therefore, the purpose of this review is to summarize this body of evidence. Specifically, we will first explain why the Ras homologue enriched in brain (Rheb) and phosphatidic acid (PA) are considered to be direct activators of mTOR signaling. We will then describe the process of endocytosis and its involvement in the formation of LEL structures, as well as the evidence which indicates that mTOR and its direct activators (Rheb and PA) are all enriched at the LEL. Finally, we will summarize the evidence that has implicated the LEL in the regulation of mTOR by various growth regulatory inputs such as amino acids, growth factors and mechanical stimuli.
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Affiliation(s)
- Brittany L Jacobs
- Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin-Madison, 2015 Linden Drive, Madison, WI, 53706, USA
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Adams GR, Bamman MM. Characterization and regulation of mechanical loading-induced compensatory muscle hypertrophy. Compr Physiol 2013; 2:2829-70. [PMID: 23720267 DOI: 10.1002/cphy.c110066] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
In mammalian systems, skeletal muscle exists in a dynamic state that monitors and regulates the physiological investment in muscle size to meet the current level of functional demand. This review attempts to consolidate current knowledge concerning development of the compensatory hypertrophy that occurs in response to a sustained increase in the mechanical loading of skeletal muscle. Topics covered include: defining and measuring compensatory hypertrophy, experimental models, loading stimulus parameters, acute responses to increased loading, hyperplasia, myofiber-type adaptations, the involvement of satellite cells, mRNA translational control, mechanotransduction, and endocrinology. The authors conclude with their impressions of current knowledge gaps in the field that are ripe for future study.
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Affiliation(s)
- Gregory R Adams
- Department of Physiology and Biophysics, University of California Irvine, Irvine, California, USA.
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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
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27
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Cariaga-Martinez AE, López-Ruiz P, Nombela-Blanco MP, Motiño O, González-Corpas A, Rodriguez-Ubreva J, Lobo MV, Cortés MA, Colás B. Distinct and specific roles of AKT1 and AKT2 in androgen-sensitive and androgen-independent prostate cancer cells. Cell Signal 2013; 25:1586-97. [DOI: 10.1016/j.cellsig.2013.03.019] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2012] [Revised: 03/23/2013] [Accepted: 03/28/2013] [Indexed: 11/16/2022]
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Martelli AM, Chiarini F, Evangelisti C, Ognibene A, Bressanin D, Billi AM, Manzoli L, Cappellini A, McCubrey JA. Targeting the liver kinase B1/AMP-activated protein kinase pathway as a therapeutic strategy for hematological malignancies. Expert Opin Ther Targets 2012; 16:729-42. [PMID: 22686561 DOI: 10.1517/14728222.2012.694869] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
INTRODUCTION Despite considerable advances, several hematological malignancies remain incurable with standard treatments. Therefore, there is a need for novel targeted and less toxic therapies, particularly for patients who develop resistance to traditional chemotherapeutic drugs. The liver kinase B1 (LKB1)/AMP-activated protein kinase (AMPK) signaling pathway has recently emerged as a tumor suppressor axis. A critical point is that the LKB1/AMPK network remains functional in a wide range of cancers and could be stimulated by drugs, such as N,N-dimethylimidodicarbonimidic diamide (metformin) or 5-aminoimidazole-4-carboxamide 1-β-D-ribofuranoside (AICAR). AREAS COVERED The literature data show that drugs activating LKB1/AMPK signaling induced cell cycle arrest, caspase-dependent apoptosis or autophagy in hematopoietic tumors. Moreover, metformin effectively inhibited mammalian target of rapamycin complex 1 (mTORC1)-controlled oncogenetic protein translation, which does not occur with allosteric mTORC1 inhibitors, such as rapamycin and its derivatives. Metformin was also capable of targeting leukemic stem cells, the most relevant target for leukemia eradication. EXPERT OPINION Data emerging from preclinical settings suggest that the LKB1/AMPK pathway is critically involved in regulating proliferation and survival of malignant hematopoietic cells. Thus, it is proposed that drugs activating the LKB1/AMPK axis may offer a novel and less toxic treatment option for some types of hematological malignancies.
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Affiliation(s)
- Alberto M Martelli
- University of Bologna, Human Anatomy, via Irnerio 48, Bologna, 40126, Italy.
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29
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Weigl LG. Lost in translation: regulation of skeletal muscle protein synthesis. Curr Opin Pharmacol 2012; 12:377-82. [PMID: 22445545 DOI: 10.1016/j.coph.2012.02.017] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2011] [Revised: 02/17/2012] [Accepted: 02/24/2012] [Indexed: 10/28/2022]
Abstract
Skeletal muscle accounts for about 50% of the body's mass in higher vertebrates. Besides its obvious role in motor activity, it also can serve as a reservoir for amino acids during times of starvation, or even as a metabolic water supply for migratory birds' during long flights. An imbalance between anabolic and catabolic processes can lead to the loss of muscle mass and life-threatening cachexia or sarcopenia. This review summarizes the current state of knowledge about the regulation of protein translation in skeletal muscle; it also discusses the role of the mTOR pathway, as well as new findings about the influence of specific miRNAs on protein expression in skeletal muscle.
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Affiliation(s)
- Lukas G Weigl
- Medical University Vienna, Department of Special Anesthesia and Paintherapy, Währinger Gürtel 18 - 20, A-1090 Vienna, Austria.
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Understanding selenoprotein function and regulation through the use of rodent models. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2012; 1823:1633-42. [PMID: 22440326 DOI: 10.1016/j.bbamcr.2012.02.018] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/06/2012] [Revised: 02/27/2012] [Accepted: 02/29/2012] [Indexed: 01/18/2023]
Abstract
Selenium (Se) is an essential micronutrient. Its biological functions are associated with selenoproteins, which contain this trace element in the form of the 21st amino acid, selenocysteine. Genetic defects in selenocysteine insertion into proteins are associated with severe health issues. The consequences of selenoprotein deficiency are more variable, with several selenoproteins being essential, and several showing no clear phenotypes. Much of these functional studies benefited from the use of rodent models and diets employing variable levels of Se. This review summarizes the data obtained with these models, focusing on mouse models with targeted expression of individual selenoproteins and removal of individual, subsets or all selenoproteins in a systemic or organ-specific manner. This article is part of a Special Issue entitled: Cell Biology of Metals.
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Goodman CA, Frey JW, Mabrey DM, Jacobs BL, Lincoln HC, You JS, Hornberger TA. The role of skeletal muscle mTOR in the regulation of mechanical load-induced growth. J Physiol 2011; 589:5485-501. [PMID: 21946849 DOI: 10.1113/jphysiol.2011.218255] [Citation(s) in RCA: 213] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Chronic mechanical loading (CML) of skeletal muscle induces compensatory growth and the drug rapamycin has been reported to block this effect. Since rapamycin is considered to be a highly specific inhibitor of the mammalian target of rapamycin (mTOR), many have concluded that mTOR plays a key role in CML-induced growth regulatory events. However, rapamycin can exert mTOR-independent actions and systemic administration of rapamycin will inhibit mTOR signalling in all cells throughout the body. Thus, it is not clear if the growth inhibitory effects of rapamycin are actually due to the inhibition of mTOR signalling, and more specifically, the inhibition of mTOR signalling in skeletal muscle cells. To address this issue, transgenic mice with muscle specific expression of various rapamycin-resistant mutants of mTOR were employed. These mice enabled us to demonstrate that mTOR, within skeletal muscle cells, is the rapamycin-sensitive element that confers CML-induced hypertrophy, and mTOR kinase activity is necessary for this event. Surprisingly, CML also induced hyperplasia, but this occurred through a rapamycin-insensitive mechanism. Furthermore, CML was found to induce an increase in FoxO1 expression and PKB phosphorylation through a mechanism that was at least partially regulated by an mTOR kinase-dependent mechanism. Finally, CML stimulated ribosomal RNA accumulation and rapamycin partially inhibited this effect; however, the effect of rapamycin was exerted through a mechanism that was independent of mTOR in skeletal muscle cells. Overall, these results demonstrate that CML activates several growth regulatory events, but only a few (e.g. hypertrophy) are fully dependent on mTOR signalling within the skeletal muscle cells.
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Affiliation(s)
- Craig A Goodman
- Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, 2015 Linden Drive, Madison, WI 53706, USA
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Hornberger TA. Mechanotransduction and the regulation of mTORC1 signaling in skeletal muscle. Int J Biochem Cell Biol 2011; 43:1267-76. [PMID: 21621634 PMCID: PMC3146557 DOI: 10.1016/j.biocel.2011.05.007] [Citation(s) in RCA: 108] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2011] [Revised: 05/11/2011] [Accepted: 05/12/2011] [Indexed: 12/20/2022]
Abstract
Mechanical stimuli play a major role in the regulation of skeletal muscle mass, and the maintenance of muscle mass contributes significantly to disease prevention and issues associated with the quality of life. Although the link between mechanical signals and the regulation of muscle mass has been recognized for decades, the mechanisms involved in converting mechanical information into the molecular events that control this process remain poorly defined. Nevertheless, our knowledge of these mechanisms is advancing and recent studies have revealed that signaling through a protein kinase called the mammalian target of rapamycin (mTOR) plays a central role in this event. In this review we will, (1) discuss the evidence which implicates mTOR in the mechanical regulation of skeletal muscle mass, (2) provide an overview of the mechanisms through which signaling by mTOR can be regulated, and (3) summarize our current knowledge of the potential mechanisms involved in the mechanical activation of mTOR signaling.
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Affiliation(s)
- Troy A Hornberger
- Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, 2015 Linden Drive, Madison, WI 53706, USA.
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Wu M, Fannin J, Rice KM, Wang B, Blough ER. Effect of aging on cellular mechanotransduction. Ageing Res Rev 2011; 10:1-15. [PMID: 19932197 DOI: 10.1016/j.arr.2009.11.002] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2009] [Revised: 11/11/2009] [Accepted: 11/16/2009] [Indexed: 12/27/2022]
Abstract
Aging is becoming a critical heath care issue and a burgeoning economic burden on society. Mechanotransduction is the ability of the cell to sense, process, and respond to mechanical stimuli and is an important regulator of physiologic function that has been found to play a role in regulating gene expression, protein synthesis, cell differentiation, tissue growth, and most recently, the pathophysiology of disease. Here we will review some of the recent findings of this field and attempt, where possible, to present changes in mechanotransduction that are associated with the aging process in several selected physiological systems, including musculoskeletal, cardiovascular, neuronal, respiratory systems and skin.
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Nakai N, Kawano F, Oke Y, Nomura S, Ohira T, Fujita R, Ohira Y. Mechanical stretch activates signaling events for protein translation initiation and elongation in C2C12 myoblasts. Mol Cells 2010; 30:513-8. [PMID: 20957453 DOI: 10.1007/s10059-010-0147-3] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2010] [Revised: 09/01/2010] [Accepted: 09/02/2010] [Indexed: 01/02/2023] Open
Abstract
It has been proposed that mechanically induced tension is the critical factor in the induction of muscle hypertrophy. However, the molecular mechanisms involved in this process are still under investigation. In the present study, the effect of mechanical stretch on intracellular signaling for protein translation initiation and elongation was studied in C2C12 myoblasts. Cells were grown on a silicone elastomer chamber and subjected to 30-min of 5 or 15% constant static or cyclic (60 cycles/min) uniaxial stretch. Western blot analyses revealed that p70 S6 kinase (p70S6K) and eukaryotic elongation factor 2 (eEF2), which are the markers for translation initiation and peptide chain elongation, respectively, were activated by both static and cyclic stretch. The magnitude of activation was greater in response to the 15% cyclic stretch. Cyclic stretch also increased the phosphorylation of MAP kinases (p38 MAPK, ERK1/2 and JNK). However, the pharmacological inhibition of MAP kinases did not block the stretch-induced activation of p70S6K and eEF2. An inhibitor of the mammalian target of rapamycin (mTOR) blocked the stretch-induced phosphorylation of p70S6K but did not affect the eEF2 activation. A broad-range tyrosine kinase inhibitor, genistein, blocked the stretch-induced activation of p70S6K and eEF2, whereas Src tyrosine kinase and Janus kinase (JAK) inhibitors did not. These results suggest that the stretch-induced activation of protein translation initiation and elongation in mouse myoblast cell lines is mediated by tyrosine kinase(s), except for Src kinase or JAK.
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Affiliation(s)
- Naoya Nakai
- Section of Applied Physiology, Department of Health and Sports Sciences, Graduate School of Medicine, Osaka University, Osaka 560-0043, Japan.
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van Wessel T, de Haan A, van der Laarse WJ, Jaspers RT. The muscle fiber type-fiber size paradox: hypertrophy or oxidative metabolism? Eur J Appl Physiol 2010; 110:665-94. [PMID: 20602111 PMCID: PMC2957584 DOI: 10.1007/s00421-010-1545-0] [Citation(s) in RCA: 180] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/11/2010] [Indexed: 12/11/2022]
Abstract
An inverse relationship exists between striated muscle fiber size and its oxidative capacity. This relationship implies that muscle fibers, which are triggered to simultaneously increase their mass/strength (hypertrophy) and fatigue resistance (oxidative capacity), increase these properties (strength or fatigue resistance) to a lesser extent compared to fibers increasing either of these alone. Muscle fiber size and oxidative capacity are determined by the balance between myofibrillar protein synthesis, mitochondrial biosynthesis and degradation. New experimental data and an inventory of critical stimuli and state of activation of the signaling pathways involved in regulating contractile and metabolic protein turnover reveal: (1) higher capacity for protein synthesis in high compared to low oxidative fibers; (2) competition between signaling pathways for synthesis of myofibrillar proteins and proteins associated with oxidative metabolism; i.e., increased mitochondrial biogenesis via AMP-activated protein kinase attenuates the rate of protein synthesis; (3) relatively higher expression levels of E3-ligases and proteasome-mediated protein degradation in high oxidative fibers. These observations could explain the fiber type-fiber size paradox that despite the high capacity for protein synthesis in high oxidative fibers, these fibers remain relatively small. However, it remains challenging to understand the mechanisms by which contractile activity, mechanical loading, cellular energy status and cellular oxygen tension affect regulation of fiber size. Therefore, one needs to know the relative contribution of the signaling pathways to protein turnover in high and low oxidative fibers. The outcome and ideas presented are relevant to optimizing treatment and training in the fields of sports, cardiology, oncology, pulmonology and rehabilitation medicine.
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Affiliation(s)
- T. van Wessel
- Research Institute MOVE, Faculty of Human Movement Sciences, VU University Amsterdam, Van der Boechorststraat 9, 1081 BT Amsterdam, The Netherlands
| | - A. de Haan
- Research Institute MOVE, Faculty of Human Movement Sciences, VU University Amsterdam, Van der Boechorststraat 9, 1081 BT Amsterdam, The Netherlands
- Institute for Biomedical Research into Human Movement and Health, Manchester Metropolitan University, Manchester, UK
| | - W. J. van der Laarse
- Department of Physiology, Institute for Cardiovascular Research, VU University Medical Centre, Amsterdam, The Netherlands
| | - R. T. Jaspers
- Research Institute MOVE, Faculty of Human Movement Sciences, VU University Amsterdam, Van der Boechorststraat 9, 1081 BT Amsterdam, The Netherlands
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Goncalves MD, Pistilli EE, Balduzzi A, Birnbaum MJ, Lachey J, Khurana TS, Ahima RS. Akt deficiency attenuates muscle size and function but not the response to ActRIIB inhibition. PLoS One 2010; 5:e12707. [PMID: 20856813 PMCID: PMC2939888 DOI: 10.1371/journal.pone.0012707] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2010] [Accepted: 08/23/2010] [Indexed: 11/19/2022] Open
Abstract
Background Akt is a critical mediator of developmental skeletal muscle growth. Treatment with a soluble ActRIIB fusion protein (ActRIIB-mFc) increases skeletal muscle mass and strength by inhibiting myostatin and related peptides. Recent in vitro studies have suggested that Akt signaling is necessary for the ability of ActRIIB inhibition to induce muscle hypertrophy. Thus, we hypothesized that mice deficient in either Akt1 or Akt2 would not respond to in vivo inhibition of ActRIIB with ActRIIB-mFc treatment. Methodology and Principal Findings We analyzed body composition and muscle parameters in wild-type C57BL/6J and Akt1 and Akt2 knockout mice, and compared the responses to blockade of ActRIIB signaling via ActRIIB-mFc treatment. Mice lacking Akt1 or Akt2 had reduced muscle mass, grip strength and contractile force. However, deficiency of Akt1 or Akt2 did not prevent the ability of ActRIIB-mFc treatment to induce muscle hypertrophy, or increase grip strength and contractile force. Akt1 and Akt2 deficient mice responded similarly as wild type mice to ActRIIB-mFc treatment by increasing fiber size. Conclusions and Significance Akt1 and Akt2 are important for the regulation of skeletal muscle mass and function. However, these Akt isoforms are not essential for the ability of ActRIIB inhibition to regulate muscle size, fiber type, strength or contractile force.
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Affiliation(s)
- Marcus D. Goncalves
- Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, United States of America
- Institute for Diabetes, Obesity and Metabolism, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, United States of America
| | - Emidio E. Pistilli
- Department of Physiology and Pennsylvania Muscle Institute, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, United States of America
| | - Anthony Balduzzi
- Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, United States of America
| | - Morris J. Birnbaum
- Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, United States of America
- Institute for Diabetes, Obesity and Metabolism, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, United States of America
| | - Jennifer Lachey
- Acceleron Pharma, Cambridge, Massachusetts, United States of America
| | - Tejvir S. Khurana
- Department of Physiology and Pennsylvania Muscle Institute, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, United States of America
| | - Rexford S. Ahima
- Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, United States of America
- Institute for Diabetes, Obesity and Metabolism, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, United States of America
- * E-mail:
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Goodman CA, Miu MH, Frey JW, Mabrey DM, Lincoln HC, Ge Y, Chen J, Hornberger TA. A phosphatidylinositol 3-kinase/protein kinase B-independent activation of mammalian target of rapamycin signaling is sufficient to induce skeletal muscle hypertrophy. Mol Biol Cell 2010; 21:3258-68. [PMID: 20668162 PMCID: PMC2938390 DOI: 10.1091/mbc.e10-05-0454] [Citation(s) in RCA: 95] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Overexpression of Rheb activates mTOR signaling via a PI3K/PKB-independent mechanism and is sufficient to induce skeletal muscle hypertrophy. The hypertrophic effects of Rheb are driven through a rapamycin-sensitive (RS) mechanism, mTOR is the RS element that confers the hypertrophy and the kinase activity of mTOR is necessary for this event. It has been widely proposed that signaling by mammalian target of rapamycin (mTOR) is both necessary and sufficient for the induction of skeletal muscle hypertrophy. Evidence for this hypothesis is largely based on studies that used stimuli that activate mTOR via a phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB)-dependent mechanism. However, the stimulation of signaling by PI3K/PKB also can activate several mTOR-independent growth-promoting events; thus, it is not clear whether signaling by mTOR is permissive, or sufficient, for the induction of hypertrophy. Furthermore, the presumed role of mTOR in hypertrophy is derived from studies that used rapamycin to inhibit mTOR; yet, there is very little direct evidence that mTOR is the rapamycin-sensitive element that confers the hypertrophic response. In this study, we determined that, in skeletal muscle, overexpression of Rheb stimulates a PI3K/PKB-independent activation of mTOR signaling, and this is sufficient for the induction of a rapamycin-sensitive hypertrophic response. Transgenic mice with muscle specific expression of various mTOR mutants also were used to demonstrate that mTOR is the rapamycin-sensitive element that conferred the hypertrophic response and that the kinase activity of mTOR is necessary for this event. Combined, these results provide direct genetic evidence that a PI3K/PKB-independent activation of mTOR signaling is sufficient to induce hypertrophy. In summary, overexpression of Rheb activates mTOR signaling via a PI3K/PKB-independent mechanism and is sufficient to induce skeletal muscle hypertrophy. The hypertrophic effects of Rheb are driven through a rapamycin-sensitive (RS) mechanism, mTOR is the RS element that confers the hypertrophy, and the kinase activity of mTOR is necessary for this event.
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Affiliation(s)
- Craig A Goodman
- Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, Madison, WI 53706, USA
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Paturi S, Gutta AK, Katta A, Kakarla SK, Arvapalli RK, Gadde MK, Nalabotu SK, Rice KM, Wu M, Blough E. Effects of aging and gender on muscle mass and regulation of Akt-mTOR-p70s6k related signaling in the F344BN rat model. Mech Ageing Dev 2010; 131:202-9. [PMID: 20153766 DOI: 10.1016/j.mad.2010.01.008] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2009] [Revised: 12/17/2009] [Accepted: 01/27/2010] [Indexed: 02/05/2023]
Abstract
Sarcopenia is the loss of muscle mass and strength which occurs with aging. Whether the molecular basis of sarcopenia differs with muscle type and across sex is not well understood. Here we examine how aging affects the regulation of protein kinase B (Akt), the mammalian target of rapamycin (mTOR), AMP activated kinase (AMPK), p70 ribosomal S6 kinase (p70s6k), S6 ribosomal protein (rps6) and calcineurin (CaN) in the slow soleus and fast extensor digitorum longus (EDL) muscles of 6- (adult), 30- (aged), and 36-month (very aged) male and 6- (adult), 26- (aged), and 30-month (very aged) female Fischer 344xBrown Norway (F344BN) rats. In male animals, soleus and EDL muscle to body weight ratios decreased steadily with age while in the females, losses remained unchanged after 26 months. These age-related changes in the degree of muscle atrophy across sex were associated with differences in the regulation of Akt, mTOR, and p70s6k in the slow-twitch soleus and the regulation of AMPK, 4EBP1, p70s6k and rpS6 in the fast-twitch EDL. Irrespective of muscle type, aging in both the genders was associated with increased calcineurin expression. Taken together, these data suggest that indices of protein synthesis and muscle adaptation are regulated differently with aging in different muscle types and sex.
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Coffey VG, Jemiolo B, Edge J, Garnham AP, Trappe SW, Hawley JA. Effect of consecutive repeated sprint and resistance exercise bouts on acute adaptive responses in human skeletal muscle. Am J Physiol Regul Integr Comp Physiol 2009; 297:R1441-51. [DOI: 10.1152/ajpregu.00351.2009] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We examined acute molecular responses in skeletal muscle to repeated sprint and resistance exercise bouts. Six men [age, 24.7 ± 6.3 yr; body mass, 81.6 ± 7.3 kg; peak oxygen uptake, 47 ± 9.9 ml·kg−1·min−1; one repetition maximum (1-RM) leg extension 92.2 ± 12.5 kg; means ± SD] were randomly assigned to trials consisting of either resistance exercise (8 × 5 leg extension, 80% 1-RM) followed by repeated sprints (10 × 6 s, 0.75 N·m torque·kg−1) or vice-versa. Muscle biopsies from vastus lateralis were obtained at rest, 15 min after each exercise bout, and following 3-h recovery to determine early signaling and mRNA responses. There was divergent exercise order-dependent phosphorylation of p70 S6K (S6K). Specifically, initial resistance exercise increased S6K phosphorylation (∼75% P < 0.05), but there was no effect when resistance exercise was undertaken after sprints. Exercise decreased IGF-I mRNA following 3-h recovery (∼50%, P = 0.06) independent of order, while muscle RING finger mRNA was elevated with a moderate exercise order effect ( P < 0.01). When resistance exercise was followed by repeated sprints PGC-1α mRNA was increased (REX1-SPR2; P = 0.02) with a modest distinction between exercise orders. Repeated sprints may promote acute interference on resistance exercise responses by attenuating translation initiation signaling and exacerbating ubiquitin ligase expression. Indeed, repeated sprints appear to generate the overriding acute exercise-induced response when undertaking concurrent repeated sprint and resistance exercise. Accordingly, we suggest that sprint-activities are isolated from resistance training and that adequate recovery time is considered within periodized training plans that incorporate these divergent exercise modes.
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Affiliation(s)
- Vernon G. Coffey
- Exercise Metabolism Group, School of Medical Science, RMIT, Melbourne, Australia
| | - Bozena Jemiolo
- Human Performance Laboratory, Ball State University, Indiana
| | - Johann Edge
- Sport and Exercise Science Division, Institute of Food, Nutrition and Human Health, Massey University, New Zealand
- Department of Sport and Exercise, University of Auckland, New Zealand; and
| | - Andrew P. Garnham
- School of Exercise and Nutrition Sciences, Deakin University, Melbourne, Australia
| | - Scott W. Trappe
- Human Performance Laboratory, Ball State University, Indiana
| | - John A. Hawley
- Exercise Metabolism Group, School of Medical Science, RMIT, Melbourne, Australia
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Frey JW, Farley EE, O'Neil TK, Burkholder TJ, Hornberger TA. Evidence that mechanosensors with distinct biomechanical properties allow for specificity in mechanotransduction. Biophys J 2009; 97:347-56. [PMID: 19580773 DOI: 10.1016/j.bpj.2009.04.025] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2008] [Revised: 03/19/2009] [Accepted: 04/14/2009] [Indexed: 12/01/2022] Open
Abstract
Various cell types can sense and convert mechanical forces into biochemical signaling events through a process called mechanotransduction, and this process is often highly specific to the types of mechanical forces applied. However, the mechanism(s) that allow for specificity in mechanotransduction remain undefined. Thus, the goal of this study was to gain insight into how cells distinguish among specific types of mechanical information. To accomplish this goal, we determined if skeletal myoblasts can distinguish among differences in strain, strain rate, and strain-time integral (STI). Our results demonstrate that mechanically induced signaling through the c-jun N-terminal kinase 2 [JNK2] is elicited via a mechanism that depends on an interaction between the magnitude of strain and strain rate and is independent of STI. In contrast to JNK2, mechanically induced signaling through the ribosomal S6 kinase [p70(389)] is not strain rate sensitive, but instead involves a magnitude of strain and STI dependent mechanisms. Mathematical modeling also indicated that mechanically induced signaling through JNK2 and p70(389) can be isolated to separate viscous and elastic mechanosensory elements, respectively. Based on these results, we propose that skeletal myoblasts contain multiple mechanosensory elements with distinct biomechanical properties and that these distinct biomechanical properties provide a mechanism for specificity in mechanotransduction.
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Affiliation(s)
- J W Frey
- Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, Madison, Wisconsin 53706, USA
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Rivas DA, Lessard SJ, Coffey VG. mTOR function in skeletal muscle: a focal point for overnutrition and exercise. Appl Physiol Nutr Metab 2009; 34:807-16. [DOI: 10.1139/h09-073] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The mammalian target of rapamycin (mTOR) is a highly conserved atypical serine–threonine kinase that controls numerous functions essential for cell homeostasis and adaptation in mammalian cells via 2 distinct protein complex formations. Moreover, mTOR is a key regulatory protein in the insulin signalling cascade and has also been characterized as an insulin-independent nutrient sensor that may represent a critical mediator in obesity-related impairments of insulin action in skeletal muscle. Exercise characterizes a remedial modality that enhances mTOR activity and subsequently promotes beneficial metabolic adaptation in skeletal muscle. Thus, the metabolic effects of nutrients and exercise have the capacity to converge at the mTOR protein complexes and subsequently modify mTOR function. Accordingly, the aim of the present review is to highlight the role of mTOR in the regulation of insulin action in response to overnutrition and the capacity for exercise to enhance mTOR activity in skeletal muscle.
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Affiliation(s)
- Donato A. Rivas
- Exercise Metabolism Group, School of Medical Sciences, RMIT University, Bundoora, Victoria 3083, Australia
- The Research Division, Joslin Diabetes Center and Department of Medicine, Harvard Medical School, Boston, MA 02215, USA
| | - Sarah J. Lessard
- Exercise Metabolism Group, School of Medical Sciences, RMIT University, Bundoora, Victoria 3083, Australia
- The Research Division, Joslin Diabetes Center and Department of Medicine, Harvard Medical School, Boston, MA 02215, USA
| | - Vernon G. Coffey
- Exercise Metabolism Group, School of Medical Sciences, RMIT University, Bundoora, Victoria 3083, Australia
- The Research Division, Joslin Diabetes Center and Department of Medicine, Harvard Medical School, Boston, MA 02215, USA
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Mayhew DL, Kim JS, Cross JM, Ferrando AA, Bamman MM. Translational signaling responses preceding resistance training-mediated myofiber hypertrophy in young and old humans. J Appl Physiol (1985) 2009; 107:1655-62. [PMID: 19589955 DOI: 10.1152/japplphysiol.91234.2008] [Citation(s) in RCA: 157] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
While skeletal muscle protein accretion during resistance training (RT)-mediated myofiber hypertrophy is thought to result from upregulated translation initiation signaling, this concept is based on responses to a single bout of unaccustomed resistance exercise (RE) with no measure of hypertrophy across RT. Further, aging appears to affect acute responses to RE, but whether age differences in responsiveness persist during RT leading to impaired RT adaptation is unclear. We therefore tested whether muscle protein fractional synthesis rate (FSR) and Akt/mammalian target of rapamycin (mTOR) signaling in response to unaccustomed RE differed in old vs. young adults, and whether age differences in acute responsiveness were associated with differences in muscle hypertrophy after 16 wk of RT. Fifteen old and 21 young adult subjects completed the 16-wk study. The phosphorylation states of Akt, S6K1, ribosomal protein S6 (RPS6), eukaryotic initiation factor 4E (eIF4E) binding protein (4EBP1), eIF4E, and eIF4G were all elevated (23-199%) 24 h after a bout of unaccustomed RE. A concomitant 62% increase in FSR was found in a subset (6 old, 8 young). Age x time interaction was found only for RPS6 phosphorylation (+335% in old subjects only), while there was an interaction trend (P = 0.084) for FSR (+96% in young subjects only). After 16 wk of RT, gains in muscle mass, type II myofiber size, and voluntary strength were similar in young and old subjects. In conclusion, at the level of translational signaling, we found no evidence of impaired responsiveness among older adults, and for the first time, we show that changes in translational signaling after unaccustomed RE were associated with substantial muscle protein accretion (hypertrophy) during continued RT.
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Affiliation(s)
- David L Mayhew
- UAB Dept. of Physiology, 966 McCallum Basic Health Sciences Bldg., 1530 3rd Ave. South, Birmingham, AL 35294-0005, USA
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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.
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Affiliation(s)
- Espen E. Spangenburg
- University of Maryland, School of Public Health, Department of Kinesiology, College Park, MD 20742, USA (e-mail: )
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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.
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Affiliation(s)
- T K O'Neil
- Department of Comparative Biosciences, chool of Veterinary Medicine, University of Wisconsin, 2015 Linden Drive, Madison, WI 53706, USA
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Li RX, Yu XZ, Fu M, Zong M, Liu RL, Xie ZP. Frequency modulation of synchronized Ca2+ spikes in cultured hippocampal networks through mTOR. Neurosci Lett 2008; 441:50-5. [DOI: 10.1016/j.neulet.2008.06.006] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2008] [Revised: 05/14/2008] [Accepted: 06/03/2008] [Indexed: 11/28/2022]
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