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Lee MK, Ryu H, Van JY, Kim MJ, Jeong HH, Jung WK, Jun JY, Lee B. The Role of Macrophage Populations in Skeletal Muscle Insulin Sensitivity: Current Understanding and Implications. Int J Mol Sci 2023; 24:11467. [PMID: 37511225 PMCID: PMC10380189 DOI: 10.3390/ijms241411467] [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: 06/16/2023] [Revised: 07/07/2023] [Accepted: 07/13/2023] [Indexed: 07/30/2023] Open
Abstract
Insulin resistance is a crucial factor in the development of type 2 diabetes mellitus (T2DM) and other metabolic disorders. Skeletal muscle, the body's largest insulin-responsive tissue, plays a significant role in the pathogenesis of T2DM due to defects in insulin signaling. Recently, there has been growing evidence that macrophages, immune cells essential for tissue homeostasis and injury response, also contribute to the development of skeletal muscle insulin resistance. This review aims to summarize the current understanding of the role of macrophages in skeletal muscle insulin resistance. Firstly, it provides an overview of the different macrophage populations present in skeletal muscle and their specific functions in the development of insulin resistance. Secondly, it examines the underlying mechanisms by which macrophages promote or alleviate insulin resistance in skeletal muscle, including inflammation, oxidative stress, and altered metabolism. Lastly, the review discusses potential therapeutic strategies targeting macrophages to improve skeletal muscle insulin sensitivity and metabolic health.
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Affiliation(s)
- Min-Kyeong Lee
- Department of Food Science and Nutrition, Pukyong National University, Busan 48513, Republic of Korea; (M.-K.L.); (H.R.)
| | - Heeyeon Ryu
- Department of Food Science and Nutrition, Pukyong National University, Busan 48513, Republic of Korea; (M.-K.L.); (H.R.)
| | - Ji Yun Van
- Department of Smart Green Technology Engineering, Pukyong National University, Busan 48513, Republic of Korea; (J.Y.V.)
| | - Myeong-Jin Kim
- Department of Food Science and Nutrition, Pukyong National University, Busan 48513, Republic of Korea; (M.-K.L.); (H.R.)
| | - Hyeon Hak Jeong
- Department of Smart Green Technology Engineering, Pukyong National University, Busan 48513, Republic of Korea; (J.Y.V.)
| | - Won-Kyo Jung
- Division of Biomedical Engineering and Research Center for Marine Integrated Bionics Technology, Pukyong National University, Busan 48513, Republic of Korea;
| | - Joo Yun Jun
- Neuroscience and Cognitive Science Program, University of Maryland, College Park, MD 20742, USA;
| | - Bonggi Lee
- Department of Food Science and Nutrition, Pukyong National University, Busan 48513, Republic of Korea; (M.-K.L.); (H.R.)
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Sharp M, Wilson J, Stefan M, Gheith R, Lowery R, Ottinger C, Reber D, Orhan C, Sahin N, Tuzcu M, Durkee S, Saiyed Z, Sahin K. Marine phytoplankton improves recovery and sustains immune function in humans and lowers proinflammatory immunoregulatory cytokines in a rat model. Phys Act Nutr 2021; 25:42-55. [PMID: 33887828 PMCID: PMC8076584 DOI: 10.20463/pan.2021.0007] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2021] [Accepted: 03/30/2021] [Indexed: 11/22/2022] Open
Abstract
Purpose This study investigated the effects of marine phytoplankton supplementation (Oceanix®, Tetraselmis chuii) on 1) maximal isometric strength and immune function in healthy humans following a oneweek high-intensity resistance-training program and 2) the proinflammatory cytokine response to exercise in a rat model. Methods In the human trial, 22 healthy male and female participants were randomly divided into marine phytoplankton and placebo groups. Following baseline testing, participants underwent a 14-day supplement loading phase before completing five consecutive days of intense resistance training. In the rat model, rats were randomly divided into four groups (n=7 per condition): (i) control, (ii) exercise, (iii) exercise + marine phytoplankton (2.55 mg/kg/day), or (iv) exercise + marine phytoplankton (5.1 mg/kg/day). Rats in the exercising groups performed treadmill exercise 5 days per week for 6 weeks. Results In the human model, marine phytoplankton prevented significant declines in the isometric peak rate of force development compared to placebo. Additionally, salivary immunoglobulin A concentration was significantly lower following the resistance training protocol in the placebo group but not in the marine phytoplankton group. Marine phytoplankton in exercising rats decreased intramuscular levels and serum concentrations of tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β) and intramuscular concentrations of malondialdehyde. Conclusion Marine phytoplankton prevented decrements in indices of functional exercise recovery and immune function. Mechanistically, these outcomes could be prompted by modulating the oxidative stress and proinflammatory cytokine response to exercise.
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Affiliation(s)
- Matthew Sharp
- Research Division, Applied Science and Performance Institute, Florida, USA
| | - Jacob Wilson
- Research Division, Applied Science and Performance Institute, Florida, USA
| | - Matthew Stefan
- Research Division, Applied Science and Performance Institute, Florida, USA
| | - Raad Gheith
- Research Division, Applied Science and Performance Institute, Florida, USA
| | - Ryan Lowery
- Research Division, Applied Science and Performance Institute, Florida, USA
| | - Charlie Ottinger
- Research Division, Applied Science and Performance Institute, Florida, USA
| | - Dallen Reber
- Research Division, Applied Science and Performance Institute, Florida, USA
| | - Cemal Orhan
- Department of Animal Nutrition, Firat University, Elazig, Turkey
| | - Nurhan Sahin
- Department of Animal Nutrition, Firat University, Elazig, Turkey
| | - Mehmet Tuzcu
- Department of Biology, Firat University, Elazig, Turkey
| | - Shane Durkee
- Lonza Consumer Health Inc., Greenwood, South Carolina, USA
| | | | - Kazim Sahin
- Department of Animal Nutrition, Firat University, Elazig, Turkey
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BST Stimulation Induces Atrophy and Changes in Aerobic Energy Metabolism in Rat Skeletal Muscles-The Biphasic Action of Endogenous Glucocorticoids. Int J Mol Sci 2020; 21:ijms21082787. [PMID: 32316389 PMCID: PMC7216182 DOI: 10.3390/ijms21082787] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2020] [Revised: 04/12/2020] [Accepted: 04/15/2020] [Indexed: 12/14/2022] Open
Abstract
(1) The primary involvement in stress-induced disturbances in skeletal muscles is assigned to the release of glucocorticoids (GCs). The current study aims to investigate the impact of the biphasic action of the chronic stress response (CSR) induced by the electrical stimulation of the bed nucleus of the stria terminalis (BST) effects on muscle atrophy and aerobic energy metabolism in soleus (SOL) and extensor digitorum longus (EDL) muscles. (2) Male Wistar rats (n = 17) were used. The rats were divided randomly into three groups: the BST two weeks (ST2), four weeks (ST4), and the sham (SHM) electrically stimulated group. The plasma corticosterone (CORT) and irisin concentration were measured. Glucocorticoid and mineralocorticoid receptors (GR and MR), 11β-hydroxysteroid dehydrogenase type 1 and 2 (HSD11B1 and HSD11B2), atrogin-1, and insulin-like growth factor-1 (IGF-1) level were determined in SOL and EDL muscles. Citrate synthase (CS) activity was measured in both muscles. (3) We found elevated plasma concentration of CORT and irisin, raised the level of GR in SOL muscle, and the higher level of MR in both muscles in the ST4 group. The level of HSD11B1 was also higher in the ST4 group compared to the SHM group. Moreover, we observed increased activity of CS in SOL. (4) We suggest that biphasic action of the glucocorticoid induced by the CSR occurs and causes dysregulation of proteins involved in muscle atrophy and aerobic energy metabolism. Our findings potentially contribute to a better understanding of the mechanisms by which GCs and the CSR may regulate muscle atrophy and energy preservation of the red muscle.
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Kemp PR, Griffiths M, Polkey MI. Muscle wasting in the presence of disease, why is it so variable? Biol Rev Camb Philos Soc 2018; 94:1038-1055. [PMID: 30588725 DOI: 10.1111/brv.12489] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2018] [Revised: 11/22/2018] [Accepted: 11/27/2018] [Indexed: 12/16/2022]
Abstract
Skeletal muscle wasting is a common clinical feature of many chronic diseases and also occurs in response to single acute events. The accompanying loss of strength can lead to significant disability, increased care needs and have profound negative effects on quality of life. As muscle is the most abundant source of amino acids in the body, it appears to function as a buffer for fuel and substrates that can be used to repair damage elsewhere and to feed the immune system. In essence, the fundamentals of muscle wasting are simple: less muscle is made than is broken down. However, although well-described mechanisms modulate muscle protein turnover, significant individual differences in the amount of muscle lost in the presence of a given severity of disease complicate the understanding of underlying mechanisms and suggest that individuals have different sensitivities to signals for muscle loss. Furthermore, the rate at which muscle protein is turned over under normal conditions means that clinically significant muscle loss can occur with changes in the rate of protein synthesis and/or breakdown that are too small to be measurable. Consequently, the changes in expression of factors regulating muscle turnover required to cause a decline in muscle mass are small and, except in cases of rapid wasting, there is no consistent pattern of change in the expression of factors that regulate muscle mass. MicroRNAs are fine tuners of cell phenotype and are therefore ideally suited to cause the subtle changes in proteome required to tilt the balance between synthesis and degradation in a way that causes clinically significant wasting. Herein we present a model in which muscle loss as a consequence of disease in non-muscle tissue is modulated by a set of microRNAs, the muscle expression of which is associated with severity of disease in the non-muscle tissue. These microRNAs alter fundamental biological processes including the synthesis of ribosomes and mitochondria leading to reduced protein synthesis and increased protein breakdown, thereby freeing amino acids from the muscle. We argue that the variability in muscle loss observed in the human population arises from at least two sources. The first is from pre-existing or disease-induced variation in the expression of microRNAs controlling the sensitivity of muscle to the atrophic signal and the second is from the expression of microRNAs from imprinted loci (i.e. only expressed from the maternally or paternally inherited allele) and may control the rate of myonuclear recruitment. In the absence of disease, these factors do not correlate with muscle mass, since there is no challenge to the established balance. However, in the presence of such a challenge, these microRNAs determine the rate of decline for a given disease severity. Together these mechanisms provide novel insight into the loss of muscle mass and its variation in the human population. The involvement of imprinted loci also suggests that genes that regulate early development also contribute to the ability of individuals to resist muscle loss in response to disease.
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Affiliation(s)
- Paul R Kemp
- National Heart & Lung Institute, Imperial College London, South Kensington Campus, London, SW7 2AZ, U.K
| | - Mark Griffiths
- National Heart & Lung Institute, Imperial College London, South Kensington Campus, London, SW7 2AZ, U.K
| | - Michael I Polkey
- National Institute for Health Research Respiratory Biomedical Research Unit, Royal Brompton and Harefield NHS Foundation Trust and Imperial College London, Sydney Street, London SW3 6NP, U.K
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S-allyl cysteine inhibits TNFα-induced skeletal muscle wasting through suppressing proteolysis and expression of inflammatory molecules. Biochim Biophys Acta Gen Subj 2018; 1862:895-906. [DOI: 10.1016/j.bbagen.2017.12.015] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2017] [Revised: 12/15/2017] [Accepted: 12/26/2017] [Indexed: 12/20/2022]
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Brioche T, Pagano AF, Py G, Chopard A. Muscle wasting and aging: Experimental models, fatty infiltrations, and prevention. Mol Aspects Med 2016; 50:56-87. [PMID: 27106402 DOI: 10.1016/j.mam.2016.04.006] [Citation(s) in RCA: 67] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2015] [Revised: 04/13/2016] [Accepted: 04/13/2016] [Indexed: 12/21/2022]
Abstract
Identification of cost-effective interventions to maintain muscle mass, muscle strength, and physical performance during muscle wasting and aging is an important public health challenge. It requires understanding of the cellular and molecular mechanisms involved. Muscle-deconditioning processes have been deciphered by means of several experimental models, bringing together the opportunities to devise comprehensive analysis of muscle wasting. Studies have increasingly recognized the importance of fatty infiltrations or intermuscular adipose tissue for the age-mediated loss of skeletal-muscle function and emphasized that this new important factor is closely linked to inactivity. The present review aims to address three main points. We first mainly focus on available experimental models involving cell, animal, or human experiments on muscle wasting. We next point out the role of intermuscular adipose tissue in muscle wasting and aging and try to highlight new findings concerning aging and muscle-resident mesenchymal stem cells called fibro/adipogenic progenitors by linking some cellular players implicated in both FAP fate modulation and advancing age. In the last part, we review the main data on the efficiency and molecular and cellular mechanisms by which exercise, replacement hormone therapies, and β-hydroxy-β-methylbutyrate prevent muscle wasting and sarcopenia. Finally, we will discuss a potential therapeutic target of sarcopenia: glucose 6-phosphate dehydrogenase.
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Affiliation(s)
- Thomas Brioche
- Université de Montpellier, INRA, UMR 866 Dynamique Musculaire et Métabolisme, Montpellier F-34060, France.
| | - Allan F Pagano
- Université de Montpellier, INRA, UMR 866 Dynamique Musculaire et Métabolisme, Montpellier F-34060, France
| | - Guillaume Py
- Université de Montpellier, INRA, UMR 866 Dynamique Musculaire et Métabolisme, Montpellier F-34060, France
| | - Angèle Chopard
- Université de Montpellier, INRA, UMR 866 Dynamique Musculaire et Métabolisme, Montpellier F-34060, France
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Passey SL, Bozinovski S, Vlahos R, Anderson GP, Hansen MJ. Serum Amyloid A Induces Toll-Like Receptor 2-Dependent Inflammatory Cytokine Expression and Atrophy in C2C12 Skeletal Muscle Myotubes. PLoS One 2016; 11:e0146882. [PMID: 26784349 PMCID: PMC4718684 DOI: 10.1371/journal.pone.0146882] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2015] [Accepted: 12/24/2015] [Indexed: 12/20/2022] Open
Abstract
BACKGROUND Skeletal muscle wasting is an important comorbidity of Chronic Obstructive Pulmonary Disease (COPD) and is strongly correlated with morbidity and mortality. Patients who experience frequent acute exacerbations of COPD (AECOPD) have more severe muscle wasting and reduced recovery of muscle mass and function after each exacerbation. Serum levels of the pro-inflammatory acute phase protein Serum Amyloid A (SAA) can rise more than 1000-fold in AECOPD and are predictively correlated with exacerbation severity. The direct effects of SAA on skeletal muscle are poorly understood. Here we have examined SAA effects on pro-inflammatory cachectic cytokine expression (IL-6 and TNFα) and atrophy in C2C12 myotubes. RESULTS SAA increased IL-6 (31-fold) and TNFα (6.5-fold) mRNA levels compared to control untreated cells after 3h of SAA treatment, and increased secreted IL-6 protein at 24h. OxPAPC, a dual TLR2 and TLR4 inhibitor, reduced the response to SAA by approximately 84% compared to SAA alone, and the TLR2 neutralising antibody T2.5 abolished SAA-induced expression of IL-6, indicating that SAA signalling in C2C12 myotubes is primarily via TLR2. SAA also reduced myotube width by 10-13% and induced a 2.5-fold increase in the expression of the muscle atrophy gene Atrogin-1, suggesting direct effects of SAA on muscle wasting. Blocking of TLR2 inhibited the SAA-induced decrease in myotube width and Atrogin-1 gene expression, indicating that SAA induces atrophy through TLR2. CONCLUSIONS These data demonstrate that SAA stimulates a robust pro-inflammatory response in skeletal muscle myotubes via the TLR2-dependent release of IL-6 and TNFα. Furthermore, the observed atrophy effects indicate that SAA could also be directly contributing to the wasting and poor recovery of muscle mass. Therapeutic strategies targeting this SAA-TLR2 axis may therefore ameliorate muscle wasting in AECOPD and a range of other inflammatory conditions associated with loss of muscle mass.
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Affiliation(s)
- Samantha L. Passey
- Lung Health Research Centre, Department of Pharmacology and Therapeutics, University of Melbourne, Parkville, Melbourne, Victoria, Australia
- School of Health and Biomedical Sciences, RMIT University, Bundoora, Melbourne, Victoria, Australia
| | - Steven Bozinovski
- Lung Health Research Centre, Department of Pharmacology and Therapeutics, University of Melbourne, Parkville, Melbourne, Victoria, Australia
- School of Health and Biomedical Sciences, RMIT University, Bundoora, Melbourne, Victoria, Australia
| | - Ross Vlahos
- Lung Health Research Centre, Department of Pharmacology and Therapeutics, University of Melbourne, Parkville, Melbourne, Victoria, Australia
- School of Health and Biomedical Sciences, RMIT University, Bundoora, Melbourne, Victoria, Australia
| | - Gary P. Anderson
- Lung Health Research Centre, Department of Pharmacology and Therapeutics, University of Melbourne, Parkville, Melbourne, Victoria, Australia
| | - Michelle J. Hansen
- Lung Health Research Centre, Department of Pharmacology and Therapeutics, University of Melbourne, Parkville, Melbourne, Victoria, Australia
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Litwiniuk A, Pijet B, Pijet-Kucicka M, Gajewska M, Pająk B, Orzechowski A. FOXO1 and GSK-3β Are Main Targets of Insulin-Mediated Myogenesis in C2C12 Muscle Cells. PLoS One 2016; 11:e0146726. [PMID: 26785133 PMCID: PMC4718532 DOI: 10.1371/journal.pone.0146726] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2015] [Accepted: 12/20/2015] [Indexed: 11/18/2022] Open
Abstract
Myogenesis and muscle hypertrophy account for muscle growth and adaptation to work overload, respectively. In adults, insulin and insulin-like growth factor 1 stimulate muscle growth, although their links with cellular energy homeostasis are not fully explained. Insulin plays critical role in the control of mitochondrial activity in skeletal muscle cells, and mitochondria are essential for insulin action. The aim of this study was to elucidate molecular mechanism(s) involved in mitochondrial control of insulin-dependent myogenesis. The effects of several metabolic inhibitors (LY294002, PD98059, SB216763, LiCl, rotenone, oligomycin) on the differentiation of C2C12 myoblasts in culture were examined in the short-term (hours) and long-term (days) experiments. Muscle cell viability and mitogenicity were monitored and confronted with the activities of selected genes and proteins expression. These indices focus on the roles of insulin, glycogen synthase kinase 3 beta (GSK-3β) and forkhead box protein O1 (FOXO1) on myogenesis using a combination of treatments and inhibitors. Long-term insulin (10 nM) treatment in “normoglycemic” conditions led to increased myogenin expression and accelerated myogenesis in C2C12 cells. Insulin-dependent myogenesis was accompanied by the rise of mtTFA, MtSSB, Mfn2, and mitochondrially encoded Cox-1 gene expressions and elevated levels of proteins which control functions of mitochondria (kinase—PKB/AKT, mitofusin 2 protein—Mfn-2). Insulin, via the phosphatidylinositol 3-kinase (PI3-K)/AKT-dependent pathway reduced transcription factor FOXO1 activity and altered GSK-3β phosphorylation status. Once FOXO1 and GSK-3β activities were inhibited the rise in Cox-1 gene action and nuclear encoded cytochrome c oxidase subunit IV (COX IV) expressions were observed, even though some mRNA and protein results varied. In contrast to SB216763, LiCl markedly elevated Mfn2 and COX IV protein expression levels when given together with insulin. Thus, inhibition of GSK-3β activity by insulin alone or together with LiCl raised the expression of genes and some proteins central to the metabolic activity of mitochondria resulting in higher ATP synthesis and accelerated myogenesis. The results of this study indicate that there are at least two main targets in insulin-mediated myogenesis: notably FOXO1 and GSK-3β both playing apparent negative role in muscle fiber formation.
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Affiliation(s)
- Anna Litwiniuk
- Department of Neuroendocrinology, Centre of Postgraduate Medical Education, Marymoncka 99/103, 01-813, Warsaw, Poland
| | - Barbara Pijet
- Department of Molecular and Cellular Neurobiology, Laboratory of Neurobiology, Nencki Institute of Experimental Biology PAS, Pasteura 3, 02-093, Warsaw, Poland
| | - Maja Pijet-Kucicka
- Department of Dermatology, Medical University of Warsaw, Koszykowa 82A, 02-008, Warsaw, Poland
| | - Małgorzata Gajewska
- Department of Physiological Sciences, Warsaw University of Life Sciences-SGGW, Nowoursynowska 159, 02-776, Warsaw, Poland
| | - Beata Pająk
- Department of Physiological Sciences, Warsaw University of Life Sciences-SGGW, Nowoursynowska 159, 02-776, Warsaw, Poland.,Electron Microscopy Platform, Mossakowski Medical Research Centre PAS, Pawińskiego 5, 02-106, Warsaw, Poland
| | - Arkadiusz Orzechowski
- Department of Physiological Sciences, Warsaw University of Life Sciences-SGGW, Nowoursynowska 159, 02-776, Warsaw, Poland.,Electron Microscopy Platform, Mossakowski Medical Research Centre PAS, Pawińskiego 5, 02-106, Warsaw, Poland
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Gao S, Carson JA. Lewis lung carcinoma regulation of mechanical stretch-induced protein synthesis in cultured myotubes. Am J Physiol Cell Physiol 2015; 310:C66-79. [PMID: 26491045 DOI: 10.1152/ajpcell.00052.2015] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2015] [Accepted: 10/19/2015] [Indexed: 11/22/2022]
Abstract
Mechanical stretch can activate muscle and myotube protein synthesis through mammalian target of rapamycin complex 1 (mTORC1) signaling. While it has been established that tumor-derived cachectic factors can induce myotube wasting, the effect of this catabolic environment on myotube mechanical signaling has not been determined. We investigated whether media containing cachectic factors derived from Lewis lung carcinoma (LLC) can regulate the stretch induction of myotube protein synthesis. C2C12 myotubes preincubated in control or LLC-derived media were chronically stretched. Protein synthesis regulation by anabolic and catabolic signaling was then examined. In the control condition, stretch increased mTORC1 activity and protein synthesis. The LLC treatment decreased basal mTORC1 activity and protein synthesis and attenuated the stretch induction of protein synthesis. LLC media increased STAT3 and AMP-activated protein kinase phosphorylation in myotubes, independent of stretch. Both stretch and LLC independently increased ERK1/2, p38, and NF-κB phosphorylation. In LLC-treated myotubes, the inhibition of ERK1/2 and p38 rescued the stretch induction of protein synthesis. Interestingly, either leukemia inhibitory factor or glycoprotein 130 antibody administration caused further inhibition of mTORC1 signaling and protein synthesis in stretched myotubes. AMP-activated protein kinase inhibition increased basal mTORC1 signaling activity and protein synthesis in LLC-treated myotubes, but did not restore the stretch induction of protein synthesis. These results demonstrate that LLC-derived cachectic factors can dissociate stretch-induced signaling from protein synthesis through ERK1/2 and p38 signaling, and that glycoprotein 130 signaling is associated with the basal stretch response in myotubes.
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Affiliation(s)
- Song Gao
- Integrative Muscle Biology Laboratory, Department of Exercise Science, University of South Carolina, Columbia, South Carolina; and
| | - James A Carson
- Integrative Muscle Biology Laboratory, Department of Exercise Science, University of South Carolina, Columbia, South Carolina; and Center for Colon Cancer Research, University of South Carolina, Columbia, South Carolina
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Kraemer WJ, Hatfield DL, Comstock BA, Fragala MS, Davitt PM, Cortis C, Wilson JM, Lee EC, Newton RU, Dunn-Lewis C, Häkkinen K, Szivak TK, Hooper DR, Flanagan SD, Looney DP, White MT, Volek JS, Maresh CM. Influence of HMB Supplementation and Resistance Training on Cytokine Responses to Resistance Exercise. J Am Coll Nutr 2014; 33:247-55. [DOI: 10.1080/07315724.2014.911669] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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11
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Joshi R, Kadeer N, Sheriff S, Friend LA, James JH, Balasubramaniam A. Phosphodiesterase (PDE) inhibitor torbafylline (HWA 448) attenuates burn-induced rat skeletal muscle proteolysis through the PDE4/cAMP/EPAC/PI3K/Akt pathway. Mol Cell Endocrinol 2014; 393:152-63. [PMID: 24973766 DOI: 10.1016/j.mce.2014.06.012] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/10/2014] [Revised: 06/02/2014] [Accepted: 06/16/2014] [Indexed: 10/25/2022]
Abstract
Treatment of rats after burn-injury with the cyclic AMP phosphodiesterase (PDE) inhibitor, torbafylline (also known as HWA 448) significantly reversed changes in rat skeletal muscle proteolysis, PDE4 activity, cAMP concentrations and mRNA expression of TNFα, IL-6, ubiquitin and E3 ligases. Torbafylline also attenuated muscle proteolysis during in vitro incubation, and this effect was blocked by the inhibitor Rp-cAMPS. Moreover, torbafylline significantly increased phospho-Akt levels, and normalized downregulated phospho-FOXO1 and phospho-4E-BP1 in muscle of burn rats. Similarly, torbafylline also normalized phosphorylation levels of Akt and its downstream elements in TNFα+IFNγ treated C2C12 myotubes. Torbafylline enhanced protein levels of exchange protein directly activated by cAMP (Epac) both in skeletal muscle of burn rats and in TNFα+IFNγ treated C2C12 myotubes. Pretreatment with a specific antagonist of PI3K or Epac significantly reversed the inhibitory effects of torbafylline on TNFα+IFNγ-induced MAFbx mRNA expression and protein breakdown in C2C12 myotubes. Torbafylline inhibits burn-induced muscle proteolysis by activating multiple pathways through PDE4/cAMP/Epac/PI3K/Akt.
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Affiliation(s)
- Rashika Joshi
- Department of Surgery, University of Cincinnati College of Medicine, 231 Albert Sabin Way, Cincinnati, OH 45267, USA; Shriners Hospital for Children, 3229 Burnet Avenue, Cincinnati, OH 45229, USA
| | - Nijiati Kadeer
- Shriners Hospital for Children, 3229 Burnet Avenue, Cincinnati, OH 45229, USA
| | - Sulaiman Sheriff
- Department of Surgery, University of Cincinnati College of Medicine, 231 Albert Sabin Way, Cincinnati, OH 45267, USA
| | - Lou Ann Friend
- Department of Surgery, University of Cincinnati College of Medicine, 231 Albert Sabin Way, Cincinnati, OH 45267, USA; Shriners Hospital for Children, 3229 Burnet Avenue, Cincinnati, OH 45229, USA
| | - J Howard James
- Department of Surgery, University of Cincinnati College of Medicine, 231 Albert Sabin Way, Cincinnati, OH 45267, USA; Shriners Hospital for Children, 3229 Burnet Avenue, Cincinnati, OH 45229, USA
| | - Ambikaipakan Balasubramaniam
- Department of Surgery, University of Cincinnati College of Medicine, 231 Albert Sabin Way, Cincinnati, OH 45267, USA; Shriners Hospital for Children, 3229 Burnet Avenue, Cincinnati, OH 45229, USA; Cincinnati Veterans Affairs Medical Center, 3200 Vine Street, Cincinnati, OH 45220, USA.
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TNF- α and IFN-s-dependent muscle decay is linked to NF-κB- and STAT-1α-stimulated Atrogin1 and MuRF1 genes in C2C12 myotubes. Mediators Inflamm 2013; 2013:171437. [PMID: 24453411 PMCID: PMC3877628 DOI: 10.1155/2013/171437] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2013] [Revised: 09/09/2013] [Accepted: 10/04/2013] [Indexed: 01/05/2023] Open
Abstract
TNF-α was shown to stimulate mitogenicity in C2C12 myoblasts. Selected cytokines TNF-α, IFNα, or IFNγ reduced the expression of myosin heavy chain (MyHC IIa) when given together. Molecular mechanisms of cytokine activities were controlled by NF-κB and JAK/STAT signaling pathways, as metabolic inhibitors, curcumin and AG490, inhibited some of TNF-α and IFNα/IFNγ effects. Insulin was hardly antagonistic to TNF-α- and IFNα/IFNγ-dependent decrease in MyHC IIa protein expression. Cytokines used individually or together also repressed myogenesis of C2C12 cells. Moreover, TNF-α- and IFNα/IFNγ-dependent effects on C2C12 myotubes were associated with increased activity of Atrogin1 and MuRF1 genes, which code ubiquitin ligases. MyHC IIa gene activity was unaltered by cytokines. Inhibition of NF-κB or JAK/STAT with specific metabolic inhibitors decreased activity of Atrogin1 and MuRF1 but not MyHC IIa gene. Overall, these results suggest cooperation between cytokines in the reduction of MyHC IIa protein expression level via NF-κB/JAK/STAT signaling pathways and activation of Atrogin1 and MuRF1 genes as their molecular targets. Insulin cotreatment or pretreatment does not protect against muscle decay induced by examined proinflammatory cytokines.
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Pooley NJ, Tacchi L, Secombes CJ, Martin SAM. Inflammatory responses in primary muscle cell cultures in Atlantic salmon (Salmo salar). BMC Genomics 2013; 14:747. [PMID: 24180744 PMCID: PMC3819742 DOI: 10.1186/1471-2164-14-747] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2013] [Accepted: 10/26/2013] [Indexed: 11/22/2022] Open
Abstract
BACKGROUND The relationship between fish health and muscle growth is critical for continued expansion of the aquaculture industry. The effect of immune stimulation on the expression of genes related to the energy balance of fish is poorly understood. In mammals immune stimulation results in major transcriptional changes in muscle, potentially to allow a reallocation of amino acids for use in the immune response and energy homeostasis. The aim of this study was to investigate the effects of immune stimulation on fish muscle gene expression. RESULTS Atlantic salmon (Salmo salar) primary muscle cell cultures were stimulated with recombinant (r)IL-1β, a major proinflammatory cytokine, for 24 h in order to simulate an acute immune response. The transcriptomic response was determined by RNA hybridization to a 4 × 44 K Agilent Atlantic salmon microarray platform. The rIL-1β stimulation induced the expression of genes related to both the innate and adaptive immune systems. In addition there were highly significant changes in the expression of genes related to regulation of the cell cycle, growth/structural proteins, proteolysis and lipid metabolism. Of interest were a number of IGF binding proteins that were differentially expressed, which may demonstrate cross talk between the growth and immune systems. CONCLUSION We show rIL-1β modulates the expression of not only immune related genes, but also that of genes involved in processes related to growth and metabolism. Co-stimulation of muscle cells with both rIGF-I and rIL-1β demonstrates cross talk between these pathways providing potential avenues for further research. This study highlights the potential negative effects of inflammation on muscle protein deposition and growth in fish and extends our understanding of energy allocation in ectothermic animals.
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Affiliation(s)
- Nicholas J Pooley
- Institute of Biological and Environmental Sciences, University of Aberdeen, Tillydrone Avenue, Aberdeen AB24 2TZ, UK
| | - Luca Tacchi
- Institute of Biological and Environmental Sciences, University of Aberdeen, Tillydrone Avenue, Aberdeen AB24 2TZ, UK
- Current address: Centre for Evolutionary and Theoretical Immunology, University of New Mexico, Albuquerque, NM 87131-0001, USA
| | - Christopher J Secombes
- Institute of Biological and Environmental Sciences, University of Aberdeen, Tillydrone Avenue, Aberdeen AB24 2TZ, UK
| | - Samuel AM Martin
- Institute of Biological and Environmental Sciences, University of Aberdeen, Tillydrone Avenue, Aberdeen AB24 2TZ, UK
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Ramirez SH, Fan S, Dykstra H, Rom S, Mercer A, Reichenbach NL, Gofman L, Persidsky Y. Inhibition of glycogen synthase kinase 3β promotes tight junction stability in brain endothelial cells by half-life extension of occludin and claudin-5. PLoS One 2013; 8:e55972. [PMID: 23418486 PMCID: PMC3572160 DOI: 10.1371/journal.pone.0055972] [Citation(s) in RCA: 81] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2012] [Accepted: 01/04/2013] [Indexed: 12/26/2022] Open
Abstract
Neuroinflammatory conditions often involve dysfunction of the Blood-Brain Barrier (BBB). Therefore, identifying molecular targets that can maintain barrier fidelity is of clinical importance. We have previously reported on the anti-inflammatory effects that glycogen synthase kinase 3β (GSK3β) inhibition has on primary human brain endothelial cells. Here we show that GSK3β inhibitors also promote barrier tightness by affecting tight junction (TJ) protein stability. Transendothelial electrical resistance (TEER) was used to evaluate barrier integrity with both pharmacological inhibitors and mutants of GSK3β. Inhibition of GSK3β produced a gradual and sustained increase in TEER (as much as 22% over baseline). Analysis of subcellular membrane fractions revealed an increase in the amount of essential tight junction proteins, occludin and claudin-5, but not claudin-3. This phenomenon was attributed to a decrease in TJ protein turnover and not transcriptional regulation. Using a novel cell-based assay, inactivation of GSK3β significantly increased the half-life of occludin and claudin-5 by 32% and 43%, respectively. A correlation was also established between the enhanced association of β-catenin with ZO-1 as a function of GSK3β inhibition. Collectively, our findings suggest the possibility of using GSK3β inhibitors as a means to extend the half-life of key tight junction proteins to promote re-sealing of the BBB during neuroinflammation.
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Affiliation(s)
- Servio H Ramirez
- Department of Pathology and Laboratory Medicine, Temple University School of Medicine, Philadelphia, Pennsylvania, United States of America.
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Colombo E, Romaggi S, Blasevich F, Mora M, Falcone C, Lochmüller H, Morandi L, Farina C. The neurotrophin receptor p75NTR is induced on mature myofibres in inflammatory myopathies and promotes myotube survival to inflammatory stress. Neuropathol Appl Neurobiol 2012; 38:367-78. [PMID: 21851375 DOI: 10.1111/j.1365-2990.2011.01212.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
AIMS Recent studies propose the neurotrophin receptor p75NTR as a marker for muscle satellite cells and a key regulator of regenerative processes after injury. Here, we investigated the contribution of cellular compartments other than satellite cells and regenerating myofibres to p75NTR signal in diseased skeletal muscle. METHODS We checked regulation of p75NTR expression in muscle biopsies from patients with inflammatory myopathies (polymyositis, dermatomyositis and inclusion body myositis), or Becker muscular dystrophy, and in nonmyopathic tissues. Quantitative PCR, immunohistochemistry, immunofluorescence or electron microscopy were used. RNA interference approaches were applied to myotubes to explore p75NTR function. RESULTS We found p75NTR transcript and protein upregulation in all inflammatory myopathies but not in dystrophic muscle, suggesting a role for inflammatory mediators in induction of p75NTR expression. In inflamed muscle p75NTR was localized on distinct cell types, including immune cells and mature myofibres. In vitro assays on human myotubes confirmed that inflammatory factors such as IL-1 could induce p75NTR. Finally, RNA interference experiments in differentiated cells showed that, in the absence of p75NTR, myotubes were more susceptible to apoptosis when exposed to inflammatory stimuli. CONCLUSIONS Our observations that p75NTR is upregulated on skeletal myofibres in inflammatory myopathies in vivo and promotes resistance to inflammatory mediators in vitro suggest that neurotrophin signalling through p75NTR may mediate a tissue-protective response to inflammation in skeletal myofibres.
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Affiliation(s)
- E Colombo
- Neuroimmunology and Neuromuscular Disorders, Foundation IRCCS Neurological Institute Carlo Besta, Milan, Italy
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Fanzani A, Conraads VM, Penna F, Martinet W. Molecular and cellular mechanisms of skeletal muscle atrophy: an update. J Cachexia Sarcopenia Muscle 2012; 3:163-79. [PMID: 22673968 PMCID: PMC3424188 DOI: 10.1007/s13539-012-0074-6] [Citation(s) in RCA: 234] [Impact Index Per Article: 19.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/09/2012] [Accepted: 05/13/2012] [Indexed: 02/06/2023] Open
Abstract
Skeletal muscle atrophy is defined as a decrease in muscle mass and it occurs when protein degradation exceeds protein synthesis. Potential triggers of muscle wasting are long-term immobilization, malnutrition, severe burns, aging as well as various serious and often chronic diseases, such as chronic heart failure, obstructive lung disease, renal failure, AIDS, sepsis, immune disorders, cancer, and dystrophies. Interestingly, a cooperation between several pathophysiological factors, including inappropriately adapted anabolic (e.g., growth hormone, insulin-like growth factor 1) and catabolic proteins (e.g., tumor necrosis factor alpha, myostatin), may tip the balance towards muscle-specific protein degradation through activation of the proteasomal and autophagic systems or the apoptotic pathway. Based on the current literature, we present an overview of the molecular and cellular mechanisms that contribute to muscle wasting. We also focus on the multifacetted therapeutic approach that is currently employed to prevent the development of muscle wasting and to counteract its progression. This approach includes adequate nutritional support, implementation of exercise training, and possible pharmacological compounds.
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Affiliation(s)
- Alessandro Fanzani
- Department of Biomedical Sciences and Biotechnologies and Interuniversitary Institute of Myology (IIM), University of Brescia, viale Europa 11, 25123, Brescia, Italy,
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Sheriff S, Kadeer N, Joshi R, Friend LA, James JH, Balasubramaniam A. Des-acyl ghrelin exhibits pro-anabolic and anti-catabolic effects on C2C12 myotubes exposed to cytokines and reduces burn-induced muscle proteolysis in rats. Mol Cell Endocrinol 2012; 351:286-95. [PMID: 22266196 DOI: 10.1016/j.mce.2011.12.021] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/08/2011] [Revised: 12/16/2011] [Accepted: 12/30/2011] [Indexed: 01/22/2023]
Abstract
Although ghrelin and GHRP-2 have been shown to inhibit skeletal muscle proteolysis in rats with burn injury, the effects of des-acyl ghrelin (DAG) have not been reported. In this paper, we demonstrate that continuous 24h administration of DAG attenuated burn-induced EDL muscle proteolysis, and normalized elevated TNFα mRNA. Combined treatment of cultured C2C12 myotubes with TNFα and IFN-γ (TNF+IFN) inhibited protein synthesis and increased protein breakdown; DAG abolished both effects. PI3 kinase inhibition by LY294002 and mTOR inhibition by rapamycin blocked the reversal of the anti-anabolic effects of TNF+IFN-treated myotubes by DAG. DAG also reversed or attenuated the TNF+IFN-induced reduction in phosphorylation of Akt, FOXO1, 4E-BP-1, and GSK-3β in myotubes. Furthermore, DAG attenuated the atrophy signal, phospho-NF-κB, and the mRNA expression of MAFbx and MuRF1, upregulated by TNF+IFN in C2C12 myotubes. We conclude that DAG reduces muscle cachexia produced by injury and proinflammatory cytokines, and that DAG or DAG-based compounds may be useful in treating wasting disorders.
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Affiliation(s)
- Sulaiman Sheriff
- Department of Surgery, University of Cincinnati College of Medicine, Cincinnati, OH, USA
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Does Branched-Chain Amino Acids Supplementation Modulate Skeletal Muscle Remodeling through Inflammation Modulation? Possible Mechanisms of Action. J Nutr Metab 2012; 2012:136937. [PMID: 22536489 PMCID: PMC3321450 DOI: 10.1155/2012/136937] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2011] [Revised: 12/01/2011] [Accepted: 01/12/2012] [Indexed: 12/22/2022] Open
Abstract
Skeletal muscle protein turnover is modulated by intracellular signaling pathways involved in protein synthesis, degradation, and inflammation. The proinflammatory status of muscle cells, observed in pathological conditions such as cancer, aging, and sepsis, can directly modulate protein translation initiation and muscle proteolysis, contributing to negative protein turnover. In this context, branched-chain amino acids (BCAAs), especially leucine, have been described as a strong nutritional stimulus able to enhance protein translation initiation and attenuate proteolysis. Furthermore, under inflammatory conditions, BCAA can be transaminated to glutamate in order to increase glutamine synthesis, which is a substrate highly consumed by inflammatory cells such as macrophages. The present paper describes the role of inflammation on muscle remodeling and the possible metabolic and cellular effects of BCAA supplementation in the modulation of inflammatory status of skeletal muscle and the consequences on protein synthesis and degradation.
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TNF-α- and tumor-induced skeletal muscle atrophy involves sphingolipid metabolism. Skelet Muscle 2012; 2:2. [PMID: 22257771 PMCID: PMC3344678 DOI: 10.1186/2044-5040-2-2] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2011] [Accepted: 01/18/2012] [Indexed: 11/11/2022] Open
Abstract
Background Muscle atrophy associated with various pathophysiological conditions represents a major health problem, because of its contribution to the deterioration of patient status and its effect on mortality. Although the involvement of pro-inflammatory cytokines in this process is well recognized, the role of sphingolipid metabolism alterations induced by the cytokines has received little attention. Results We addressed this question both in vitro using differentiated myotubes treated with TNF-α, and in vivo in a murine model of tumor-induced cachexia. Myotube atrophy induced by TNF-α was accompanied by a substantial increase in cell ceramide levels, and could be mimicked by the addition of exogenous ceramides. It could be prevented by the addition of ceramide-synthesis inhibitors that targeted either the de novo pathway (myriocin), or the sphingomyelinases (GW4869 and 3-O-methylsphingomyelin). In the presence of TNF-α, ceramide-synthesis inhibitors significantly increased protein synthesis and decreased proteolysis. In parallel, they lowered the expression of both the Atrogin-1 and LC3b genes, involved in muscle protein degradation by proteasome and in autophagic proteolysis, respectively, and increased the proportion of inactive, phosphorylated Foxo3 transcription factor. Furthermore, these inhibitors increased the expression and/or phosphorylation levels of key factors regulating protein metabolism, including phospholipase D, an activator of mammalian target of rapamycin (mTOR), and the mTOR substrates S6K1 and Akt. In vivo, C26 carcinoma implantation induced a substantial increase in muscle ceramide, together with drastic muscle atrophy. Treatment of the animals with myriocin reduced the expression of the atrogenes Foxo3 and Atrogin-1, and partially protected muscle tissue from atrophy. Conclusions Ceramide accumulation induced by TNF-α or tumor development participates in the mechanism of muscle-cell atrophy, and sphingolipid metabolism is a logical target for pharmacological or nutritional interventions aiming at preserving muscle mass in pathological situations.
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Jespersen JG, Nedergaard A, Reitelseder S, Mikkelsen UR, Dideriksen KJ, Agergaard J, Kreiner F, Pott FC, Schjerling P, Kjaer M. Activated protein synthesis and suppressed protein breakdown signaling in skeletal muscle of critically ill patients. PLoS One 2011; 6:e18090. [PMID: 21483870 PMCID: PMC3069050 DOI: 10.1371/journal.pone.0018090] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2010] [Accepted: 02/20/2011] [Indexed: 12/25/2022] Open
Abstract
Background Skeletal muscle mass is controlled by myostatin and Akt-dependent signaling on mammalian target of rapamycin (mTOR), glycogen synthase kinase 3β (GSK3β) and forkhead box O (FoxO) pathways, but it is unknown how these pathways are regulated in critically ill human muscle. To describe factors involved in muscle mass regulation, we investigated the phosphorylation and expression of key factors in these protein synthesis and breakdown signaling pathways in thigh skeletal muscle of critically ill intensive care unit (ICU) patients compared with healthy controls. Methodology/Principal Findings ICU patients were systemically inflamed, moderately hyperglycemic, received insulin therapy, and showed a tendency to lower plasma branched chain amino acids compared with controls. Using Western blotting we measured Akt, GSK3β, mTOR, ribosomal protein S6 kinase (S6k), eukaryotic translation initiation factor 4E binding protein 1 (4E-BP1), and muscle ring finger protein 1 (MuRF1); and by RT-PCR we determined mRNA expression of, among others, insulin-like growth factor 1 (IGF-1), FoxO 1, 3 and 4, atrogin1, MuRF1, interleukin-6 (IL-6), tumor necrosis factor α (TNF-α) and myostatin. Unexpectedly, in critically ill ICU patients Akt-mTOR-S6k signaling was substantially higher compared with controls. FoxO1 mRNA was higher in patients, whereas FoxO3, atrogin1 and myostatin mRNAs and MuRF1 protein were lower compared with controls. A moderate correlation (r2 = 0.36, p<0.05) between insulin infusion dose and phosphorylated Akt was demonstrated. Conclusions/Significance We present for the first time muscle protein turnover signaling in critically ill ICU patients, and we show signaling pathway activity towards a stimulation of muscle protein synthesis and a somewhat inhibited proteolysis.
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Affiliation(s)
- Jakob G Jespersen
- Department of Orthopedic Surgery M, Institute of Sports Medicine Copenhagen, Bispebjerg Hospital and Center for Healthy Aging, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark.
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21
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Haren MT, Siddiqui AM, Armbrecht HJ, Kevorkian RT, Kim MJ, Haas MJ, Mazza A, Kumar VB, Green M, Banks WA, Morley JE. Testosterone modulates gene expression pathways regulating nutrient accumulation, glucose metabolism and protein turnover in mouse skeletal muscle. ACTA ACUST UNITED AC 2011; 34:55-68. [DOI: 10.1111/j.1365-2605.2010.01061.x] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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22
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Frost RA, Huber D, Pruznak A, Lang CH. Regulation of REDD1 by insulin-like growth factor-I in skeletal muscle and myotubes. J Cell Biochem 2010; 108:1192-202. [PMID: 19795384 DOI: 10.1002/jcb.22349] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Insulin-like growth factor-I (IGF-I) is a major anabolic hormone for skeletal muscle and a potent stimulus for protein synthesis and translation initiation. Recent studies suggest that translation can be inhibited by over expression of the mammalian target of rapamycin (mTOR) repressor REDD1. The purpose of the present study was to determine whether IGF-I alters the expression of REDD1 and whether this is associated with a concomitant change in protein synthesis in vitro. Subcutaneous injection of IGF-I or intravenous delivery of insulin for 3-4 h increased REDD1 mRNA in skeletal muscle 7-10-fold. A threefold increase in REDD1 was observed when C2C12 myotubes were treated with IGF-I. REDD1 protein continued to be expressed for up to 24 h after addition of IGF-I to cells. Withdrawal of IGF-I from myotubes lead to a rapid loss of REDD1 protein content. IGF-I-induced REDD1 mRNA and protein expression were prevented by inhibitors of transcription and translation. IGF-I had an additive effect with dexamethasone (Dex) on REDD1 protein content in myotubes. The PI3K inhibitor LY294002 blocked IGF-I but not Dex induced REDD1. IGF-I also stimulated REDD1 promoter activity. Although REDD1 protein was elevated 5-6 h after addition of IGF-I to myotubes, protein synthesis measured during this 1 h window was paradoxically greater in myotubes expressing more REDD1. In contrast to the IGF-I induced increase in REDD1 mRNA, REDD2 mRNA was decreased by IGF-I. We conclude that IGF-I stimulates REDD1 expression in skeletal muscle and myotubes but under these conditions the REDD1 response is not sufficient to repress protein synthesis.
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Affiliation(s)
- Robert A Frost
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA.
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Peake J, Della Gatta P, Cameron-Smith D. Aging and its effects on inflammation in skeletal muscle at rest and following exercise-induced muscle injury. Am J Physiol Regul Integr Comp Physiol 2010; 298:R1485-95. [PMID: 20393160 DOI: 10.1152/ajpregu.00467.2009] [Citation(s) in RCA: 131] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The world's elderly population is expanding rapidly, and we are now faced with the significant challenge of maintaining or improving physical activity, independence, and quality of life in the elderly. Counteracting the progressive loss of muscle mass that occurs in the elderly, known as sarcopenia, represents a major hurdle in achieving these goals. Indirect evidence for a role of inflammation in sarcopenia is that markers of systemic inflammation correlate with the loss of muscle mass and strength in the elderly. More direct evidence is that compared with skeletal muscle of young people, the number of macrophages is lower, the gene expression of several cytokines is higher, and stress signaling proteins are activated in skeletal muscle of elderly people at rest. Sarcopenia may also result from inadequate repair and chronic maladaptation following muscle injury in the elderly. Macrophage infiltration and the gene expression of certain cytokines are reduced in skeletal muscle of elderly people compared with young people following exercise-induced muscle injury. Further research is required to identify the cause(s) of inflammation in skeletal muscle of elderly people. Additional work is also needed to expand our understanding of the cells, proteins, and transcription factors that regulate inflammation in the skeletal muscle of elderly people at rest and after exercise. This knowledge is critical for devising strategies to restrict sarcopenia, and improve the health of today's elderly population.
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Affiliation(s)
- Jonathan Peake
- The University of Queensland, School of Human Movement Studies, Brisbane, Australia.
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Dumont N, Frenette J. Macrophages protect against muscle atrophy and promote muscle recovery in vivo and in vitro: a mechanism partly dependent on the insulin-like growth factor-1 signaling molecule. THE AMERICAN JOURNAL OF PATHOLOGY 2010; 176:2228-35. [PMID: 20304951 DOI: 10.2353/ajpath.2010.090884] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Hindlimb unloading and reloading are characterized by a major loss of muscle force and are associated with classic leukocyte infiltration during recovery from muscle atrophy. Macrophages act as a cellular cornerstone by playing both pro- and anti-inflammatory roles during muscle recovery from atrophy. In the present study, we investigated the role of macrophages in muscle atrophy and regrowth using in vivo and in vitro models. Mice depleted in monocytes/macrophages and submitted to a hindlimb unloading and reloading protocol experienced a significant delay in muscle force recovery compared with matched placebo mice at 7 and 14 days after reloading. Furthermore, an in vitro myotube/macrophage coculture showed that anti-inflammatory macrophages, which contain apoptotic neutrophils and express low levels of cyclooxygenase-2, completely prevented the loss of protein content and the myotube atrophy observed after 2 days in low serum medium. The presence of macrophages also protected against the decrease in myosin heavy chain content in myotubes exposed to low serum medium for 1 day. Interestingly, the addition of an anti-IGF-1 antibody to the coculture significantly decreased the ability of macrophages to protect against myotube atrophy and myosin heavy chain loss after 2 days in low serum medium. These results clearly indicate that macrophages and, more precisely, the release of IGF-1 by macrophages, play an important role in recovery from muscle atrophy.
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Affiliation(s)
- Nicolas Dumont
- Centre Hospitalier Universitaire de Québec-Centre de Recherche du Centre Hospitalier de l'Université Laval, Faculté de Médecine, Université Laval, Quebec City, Quebec, Canada
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Modulation of caspase activity regulates skeletal muscle regeneration and function in response to vasopressin and tumor necrosis factor. PLoS One 2009; 4:e5570. [PMID: 19440308 PMCID: PMC2680623 DOI: 10.1371/journal.pone.0005570] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2009] [Accepted: 04/20/2009] [Indexed: 11/19/2022] Open
Abstract
Muscle homeostasis involves de novo myogenesis, as observed in conditions of acute or chronic muscle damage. Tumor Necrosis Factor (TNF) triggers skeletal muscle wasting in several pathological conditions and inhibits muscle regeneration. We show that intramuscular treatment with the myogenic factor Arg8-vasopressin (AVP) enhanced skeletal muscle regeneration and rescued the inhibitory effects of TNF on muscle regeneration. The functional analysis of regenerating muscle performance following TNF or AVP treatments revealed that these factors exerted opposite effects on muscle function. Principal component analysis showed that TNF and AVP mainly affect muscle tetanic force and fatigue. Importantly, AVP counteracted the effects of TNF on muscle function when delivered in combination with the latter. Muscle regeneration is, at least in part, regulated by caspase activation, and AVP abrogated TNF-dependent caspase activation. The contrasting effects of AVP and TNF in vivo are recapitulated in myogenic cell cultures, which express both PW1, a caspase activator, and Hsp70, a caspase inhibitor. We identified PW1 as a potential Hsp70 partner by screening for proteins interacting with PW1. Hsp70 and PW1 co-immunoprecipitated and co-localized in muscle cells. In vivo Hsp70 protein level was upregulated by AVP, and Hsp70 overexpression counteracted the TNF block of muscle regeneration. Our results show that AVP counteracts the effects of TNF through cross-talk at the Hsp70 level. Therefore, muscle regeneration, both in the absence and in the presence of cytokines may be enhanced by increasing Hsp70 expression.
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Sylvester FA, Leopold S, Lincoln M, Hyams JS, Griffiths AM, Lerer T. A two-year longitudinal study of persistent lean tissue deficits in children with Crohn's disease. Clin Gastroenterol Hepatol 2009; 7:452-5. [PMID: 19249399 DOI: 10.1016/j.cgh.2008.12.017] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/06/2008] [Revised: 09/24/2008] [Accepted: 12/13/2008] [Indexed: 01/03/2023]
Abstract
BACKGROUND & AIMS Deficits in lean body mass have been reported in cross-sectional studies of children with Crohn's disease, but no longitudinal data exist from diagnosis. We observed the effects of Crohn's disease on body composition and bone mineral content (BMC), beginning at diagnosis and followed prospectively for 2 years. METHODS The study was conducted at 2 tertiary care centers for pediatric inflammatory bowel diseases. At diagnosis we recorded age, weight, height, levels of serum interleukin-6 and insulin-like growth factor-1, sexual maturation stage, disease activity, z scores for body mass index (BMI), fat-free mass (FFM), and bone mineral content (BMC). z Scores were adjusted for height and age, when appropriate. Measurements were made yearly in patients with Crohn's disease (n = 42) but only at the start of the study in controls (n = 81). RESULTS BMI and FFM z scores were significantly reduced at the time of diagnosis in children with Crohn's disease, compared with controls. During the 2-year study period, the BMI z scores normalized in patients with Crohn's disease, but the FFM z scores did not increase significantly. The BMC z scores increased significantly, but they were still lower than control values after 2 years. Changes in BMC during a period of 2 years were associated with increases in FFM (R(2) = 0.318, P < .01). CONCLUSIONS The correction of BMI that is associated with clinical improvement in children with Crohn's disease 2 years after diagnosis results from gains in fat mass. Significant FFM deficits might hamper normal acquisition of bone mass in children with Crohn's disease because of a lack of mechanical strain.
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Barker T, Leonard SW, Trawick RH, Martins TB, Kjeldsberg CR, Hill HR, Traber MG. Modulation of inflammation by vitamin E and C supplementation prior to anterior cruciate ligament surgery. Free Radic Biol Med 2009; 46:599-606. [PMID: 19111610 DOI: 10.1016/j.freeradbiomed.2008.11.006] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/22/2008] [Revised: 10/17/2008] [Accepted: 11/15/2008] [Indexed: 01/01/2023]
Abstract
Muscle atrophy commonly follows anterior cruciate ligament (ACL) injury and surgery. Proinflammatory cytokines can induce and exacerbate oxidative stress, potentiating muscle atrophy. The purpose of this study was to evaluate the influence of prior antioxidant (AO) supplementation on circulating cytokines following ACL surgery. A randomized, double-blind, placebo-controlled trial was conducted in men undergoing ACL surgery, who were randomly assigned to either: (1) AO (200 IU of vitamin E (50% d-alpha-tocopheryl acetate and 50% d-alpha-tocopherol) and 500 mg ascorbic acid), or (2) matching placebos (PL). Subjects took supplements twice daily for 2 weeks prior to and up to 12 weeks after surgery. Each subject provided five blood samples: (1) baseline (Bsl, prior to supplementation and approximately 2 weeks prior to surgery), (2) presurgery (Pre), (3) 90 min, (4) 72 h, and (5) 7 days postsurgery. Following surgery, inflammation and muscle damage increased in both groups, as assessed by increased circulating IL-6, C-reactive protein, and creatine kinase. During AO supplementation, plasma alpha-T and AA increased while gamma-T concentrations decreased significantly (P< 0.05). At 90 min the AO group displayed a significant decrease in AA, an inverse correlation between AA and (interleukin) IL-8 (r(2)= 0.50, P< 0.05), and a significantly lower IL-10 response than that of the PL group. IL-10 was significantly elevated at 90 min and 72 h in the PL group. In summary, our findings show that circulating inflammatory cytokines increase and AO supplementation attenuated the increase in IL-10 in patients post-ACL surgery.
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Affiliation(s)
- Tyler Barker
- The Orthopedic Specialty Hospital, Murray, UT 84107, USA
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Balasubramaniam A, Joshi R, Su C, Friend LA, Sheriff S, Kagan RJ, James JH. Ghrelin inhibits skeletal muscle protein breakdown in rats with thermal injury through normalizing elevated expression of E3 ubiquitin ligases MuRF1 and MAFbx. Am J Physiol Regul Integr Comp Physiol 2009; 296:R893-901. [PMID: 19211729 DOI: 10.1152/ajpregu.00015.2008] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
We previously determined that ghrelin synthesis was downregulated after burn injury and that exogenous ghrelin retained its ability both to stimulate food intake and to restore plasma growth hormone levels in burned rats. These observations and the finding that anabolic hormones can attenuate skeletal muscle catabolism led us to investigate whether ghrelin could attenuate burn-induced skeletal muscle protein breakdown in rats. These studies were performed in young rats (50-60 g) 24 h after approximately 30% total body surface area burn injury. Burn injury increased total and myofibrillar protein breakdown in extensor digitorum longus (EDL) muscles assessed by in vitro tyrosine and 3-methyl-histidine release, respectively. Continuous 24-h administration of ghrelin (0.2 mg.kg(-1).h(-1)) significantly inhibited both total and myofibrillar protein breakdown in burned rats. Ghrelin significantly attenuated burn-induced changes in mRNA expression of IGFBP-1 and IGFBP-3 in liver. In EDL, ghrelin attenuated the increases in mRNA expression of the binding proteins, but had no significant effect on reduced expression of IGF-I. Ghrelin markedly reduced the elevated mRNA expression of TNF-alpha and IL-6 in EDL muscle that occurred after burn. Moreover, ghrelin normalized plasma glucocorticoid levels, which were elevated after burn. Expression of the muscle-specific ubiquitin-ligating enzyme (E3) ubiquitin ligases MuRF1 and MAFbx were markedly elevated in both EDL and gastrocnemius and were normalized by ghrelin. These results suggest that ghrelin is a powerful anticatabolic compound that reduces skeletal muscle protein breakdown through attenuating multiple burn-induced abnormalities.
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Affiliation(s)
- Ambikaipakan Balasubramaniam
- Department of Surgery, University of Cincinnati College of Medicine, 231 Albert Sabin Way, Cincinnati, OH 45267-0558.
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Telgmann R, Dördelmann C, Brand E, Nicaud V, Hagedorn C, Pavenstädt H, Cambien F, Tiret L, Paul M, Brand‐Herrmann S. Molecular genetic analysis of a human insulin‐like growth factor 1 promoter P1 variation. FASEB J 2008; 23:1303-13. [DOI: 10.1096/fj.08-116863] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Ralph Telgmann
- Department of Molecular Genetics of Cardiovascular DiseaseLeibniz‐Institute for Arteriosclerosis ResearchUniversity of MünsterMünsterGermany
| | - Corinna Dördelmann
- Department of Molecular Genetics of Cardiovascular DiseaseLeibniz‐Institute for Arteriosclerosis ResearchUniversity of MünsterMünsterGermany
| | - Eva Brand
- University Hospital MünsterInternal Medicine and Nephrology DMünsterGermany
| | | | - Claudia Hagedorn
- Department of Molecular Genetics of Cardiovascular DiseaseLeibniz‐Institute for Arteriosclerosis ResearchUniversity of MünsterMünsterGermany
| | - Hermann Pavenstädt
- University Hospital MünsterInternal Medicine and Nephrology DMünsterGermany
| | | | | | - Martin Paul
- Faculty of Health Medicine and Life ScienceMaastricht UniversityMaastrichtThe Netherlands
| | - Stefan‐Martin Brand‐Herrmann
- Department of Molecular Genetics of Cardiovascular DiseaseLeibniz‐Institute for Arteriosclerosis ResearchUniversity of MünsterMünsterGermany
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Murton A, Constantin D, Greenhaff P. The involvement of the ubiquitin proteasome system in human skeletal muscle remodelling and atrophy. Biochim Biophys Acta Mol Basis Dis 2008; 1782:730-43. [DOI: 10.1016/j.bbadis.2008.10.011] [Citation(s) in RCA: 190] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2008] [Revised: 10/23/2008] [Accepted: 10/24/2008] [Indexed: 12/14/2022]
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Kim J, Wende AR, Sena S, Theobald HA, Soto J, Sloan C, Wayment BE, Litwin SE, Holzenberger M, LeRoith D, Abel ED. Insulin-like growth factor I receptor signaling is required for exercise-induced cardiac hypertrophy. Mol Endocrinol 2008; 22:2531-43. [PMID: 18801929 DOI: 10.1210/me.2008-0265] [Citation(s) in RCA: 154] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The receptors for IGF-I (IGF-IR) and insulin (IR) have been implicated in physiological cardiac growth, but it is unknown whether IGF-IR or IR signaling are critically required. We generated mice with cardiomyocyte-specific knockout of IGF-IR (CIGF1RKO) and compared them with cardiomyocyte-specific insulin receptor knockout (CIRKO) mice in response to 5 wk exercise swim training. Cardiac development was normal in CIGF1RKO mice, but the hypertrophic response to exercise was prevented. In contrast, despite reduced baseline heart size, the hypertrophic response of CIRKO hearts to exercise was preserved. Exercise increased IGF-IR content in control and CIRKO hearts. Akt phosphorylation increased in exercise-trained control and CIRKO hearts and, surprisingly, in CIGF1RKO hearts as well. In exercise-trained control and CIRKO mice, expression of peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha) and glycogen content were both increased but were unchanged in trained CIGF1RKO mice. Activation of AMP-activated protein kinase (AMPK) and its downstream target eukaryotic elongation factor-2 was increased in exercise-trained CIGF1RKO but not in CIRKO or control hearts. In cultured neonatal rat cardiomyocytes, activation of AMPK with 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR) prevented IGF-I/insulin-induced cardiomyocyte hypertrophy. These studies identify an essential role for IGF-IR in mediating physiological cardiomyocyte hypertrophy. IGF-IR deficiency promotes energetic stress in response to exercise, thereby activating AMPK, which leads to phosphorylation of eukaryotic elongation factor-2. These signaling events antagonize Akt signaling, which although necessary for mediating physiological cardiac hypertrophy, is insufficient to promote cardiac hypertrophy in the absence of myocardial IGF-I signaling.
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Affiliation(s)
- Jaetaek Kim
- Program in Human Molecular Biology and Genetics, University of Utah, Salt Lake City, Utah 84112, USA
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Moylan JS, Smith JD, Chambers MA, McLoughlin TJ, Reid MB. TNF induction of atrogin-1/MAFbx mRNA depends on Foxo4 expression but not AKT-Foxo1/3 signaling. Am J Physiol Cell Physiol 2008; 295:C986-93. [PMID: 18701653 DOI: 10.1152/ajpcell.00041.2008] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Murine models of starvation-induced muscle atrophy demonstrate that reduced protein kinase B (AKT) function upregulates the atrophy-related gene atrogin-1/MAFbx (atrogin). The mechanism involves release of inhibition of Forkhead transcription factors, namely Foxo1 and Foxo3. Elevated atrogin mRNA also corresponds with elevated TNF in inflammatory catabolic states, including cancer and chronic heart failure. Exogenous tumor necrosis factor (TNF) increases atrogin mRNA in vivo and in vitro. We used TNF-treated C2C12 myotubes to test the hypothesis that AKT-Foxo1/3 signaling mediates TNF regulation of atrogin mRNA. Here we confirm that exposure to TNF increases atrogin mRNA (+125%). We also confirm that canonical AKT-mediated regulation of atrogin is active in C2C12 myotubes. Inhibition of phosphoinositol-3 kinase (PI3K)/AKT signaling with wortmannin reduces AKT phosphorylation (-87%) and increases atrogin mRNA (+340%). Activation with insulin-like growth factor (IGF) increases AKT phosphorylation (+126%) and reduces atrogin mRNA (-15%). Although AKT regulation is intact, our data suggest it does not mediate TNF effects on atrogin. TNF increases AKT phosphorylation (+50%) and stimulation of AKT with IGF does not prevent TNF induction of atrogin mRNA. Nor does TNF appear to signal through Foxo1/3 proteins. TNF has no effect on Foxo1/3 mRNA or Foxo1/3 nuclear localization. Instead, TNF increases nuclear Foxo4 protein (+55%). Small interfering RNA oligos targeted to two distinct regions of Foxo4 mRNA reduce the TNF-induced increase in atrogin mRNA (-34% and -32%). We conclude that TNF increases atrogin mRNA independent of AKT via Foxo4. These results suggest a mechanism by which inflammatory catabolic states may persist in the presence of adequate growth factors and nutrition.
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Affiliation(s)
- Jennifer S Moylan
- Department of Physiology, University of Kentucky, Lexington, Kentucky 40536-0298, USA.
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Senf SM, Dodd SL, McClung JM, Judge AR. Hsp70 overexpression inhibits NF-kappaB and Foxo3a transcriptional activities and prevents skeletal muscle atrophy. FASEB J 2008; 22:3836-45. [PMID: 18644837 DOI: 10.1096/fj.08-110163] [Citation(s) in RCA: 215] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Heat shock protein 70 (Hsp70) is a highly conserved and ubiquitous protein that is reported to provide cytoprotection in various cell types and tissues. However, the importance of Hsp70 expression during skeletal muscle atrophy, when Hsp70 levels are significantly decreased, is not known. The current study aimed to determine whether plasmid-mediated overexpression of Hsp70, in the soleus muscle of rats, was sufficient to regulate specific atrophy signaling pathways and attenuate skeletal muscle disuse atrophy. We found that Hsp70 overexpression prevented disuse muscle fiber atrophy and inhibited the increased promoter activities of atrogin-1 and MuRF1. Importantly, the transcriptional activities of Foxo3a and NF-kappaB, which are implicated in the regulation of atrogin-1 and MuRF1, were abolished by Hsp70. These data suggest that Hsp70 may regulate key atrophy genes through inhibiting Foxo3a and NF-kappaB activities during disuse. Indeed, we show that specific inhibition of Foxo3a prevented the increases in both atrogin-1 and MuRF1 promoter activities during disuse. However, inhibition of NF-kappaB did not affect the activation of either promoter, suggesting its requirement for disuse atrophy is through its regulation of other atrophy genes. We conclude that overexpression of Hsp70 is sufficient to inhibit key atrophy signaling pathways and prevent skeletal muscle atrophy.
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Affiliation(s)
- Sarah M Senf
- Department of Applied Physiology and Kinesiology, 25 Stadium Rd., University of Florida, Gainesville, FL 32611, USA
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Quinn LS, Anderson BG, Plymate SR. Muscle-specific overexpression of the type 1 IGF receptor results in myoblast-independent muscle hypertrophy via PI3K, and not calcineurin, signaling. Am J Physiol Endocrinol Metab 2007; 293:E1538-51. [PMID: 17940216 DOI: 10.1152/ajpendo.00160.2007] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The insulin-like growth factors (IGF-I and IGF-II), working through the type 1 IGF receptor (IGF-1R), are key mediators of skeletal muscle fiber growth and hypertrophy. These processes are largely dependent on stimulation of proliferation and differentiation of muscle precursor cells, termed myoblasts. It has not been rigorously determined whether the IGFs can also mediate skeletal muscle hypertrophy in a myoblast-independent fashion. Similarly, although the phosphatidylinositol 3-kinase (PI3K) and calcineurin signaling pathways have been implicated in skeletal muscle hypertrophy, these pathways are also involved in skeletal myoblast differentiation. To determine whether the IGFs can stimulate skeletal muscle hypertrophy in a myoblast-independent fashion, we developed and validated a retroviral expression vector that mediated overexpression of the human IGF-1R in rat L6 skeletal myotubes (immature muscle fibers), but not in myoblasts. L6 myotubes transduced with this vector accumulated significantly higher amounts of myofibrillar proteins, in a ligand- and receptor-dependent manner, than controls and demonstrated significantly increased rates of protein synthesis. Stimulation of myotube hypertrophy was independent of myoblast contributions, inasmuch as these cultures did not exhibit increased levels of myoblast proliferation or differentiation. Experiments with PI3K and calcineurin inhibitors indicated that myoblast-independent myotube hypertrophy was mediated by PI3K, but not calcineurin, signaling. This study demonstrates that IGF can mediate skeletal muscle hypertrophy in a myoblast-independent fashion and suggests that muscle-specific overexpression of the IGF-1R or stimulation of its signaling pathways could be used to develop strategies to ameliorate muscle wasting without stimulating proliferative pathways leading to carcinogenesis or other pathological sequelae.
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Affiliation(s)
- Lebris S Quinn
- Department of Gerontology, University of Washington, Seattle, WA 98493, USA.
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Strasser EM, Wessner B, Roth E. [Cellular regulation of anabolism and catabolism in skeletal muscle during immobilisation, aging and critical illness]. Wien Klin Wochenschr 2007; 119:337-48. [PMID: 17634890 DOI: 10.1007/s00508-007-0817-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2007] [Accepted: 05/16/2007] [Indexed: 12/13/2022]
Abstract
Skeletal muscle atrophy is associated with situations of acute and chronical illness, such as sepsis, surgery, trauma and immobility. Additionally, it is a common problem during the physiological process of aging. The myofibrillar proteins myosin and actin, which are essential for muscle contraction, are the major targets during the process of protein degradation. This leads to a general loss of muscle mass, muscle strength and to increased muscle fatigue. In critically ill or immobile patients skeletal muscle atrophy is accompanied by enhanced inflammation, reduced wound healing, weaning complications and difficulties in mobilisation. During aging it results in falls, fractures, physical injuries and loss of mobility. Relating to the primary stimulators - hormones, muscle lengthening, stress, inflammation, neuronal activity - research is now focusing on the investigation of the signal transduction pathways, which influence protein synthesis and protein degradation during skeletal muscle atrophy.
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Affiliation(s)
- Eva-Maria Strasser
- Chirurgische Forschungslaboratorien, Medizinische Universität Wien, Wien, Austria
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Frost RA, Lang CH. Protein kinase B/Akt: a nexus of growth factor and cytokine signaling in determining muscle mass. J Appl Physiol (1985) 2007; 103:378-87. [PMID: 17332274 DOI: 10.1152/japplphysiol.00089.2007] [Citation(s) in RCA: 138] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Although the boundaries of skeletal muscle size are fundamentally determined by genetics, this dynamic tissue also demonstrates great plasticity in response to environmental and hormonal factors. Recent work indicates that contractile activity, nutrients, growth factors, and cytokines all contribute to determining muscle mass. Muscle responds not only to endocrine hormones but also to the autocrine production of growth factors and cytokines. Skeletal muscle synthesizes anabolic growth factors such as insulin-like growth factor (IGF)-I and potentially inhibitory cytokines such as interleukin (IL)-6, tumor necrosis factor (TNF)-alpha, and myostatin. These self-regulating inputs in turn influence muscle metabolism, including the use of nutrients such as glucose and amino acids. These changes are principally achieved by altering the activity of the protein kinase known as protein kinase B or Akt. Akt plays a central role in integrating anabolic and catabolic responses by transducing growth factor and cytokine signals via changes in the phosphorylation of its numerous substrates. Activation of Akt stimulates muscle hypertrophy and antagonizes the loss of muscle protein. Here we review the many signals that funnel through Akt to alter muscle mass.
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Affiliation(s)
- Robert A Frost
- Department of Cellular and Molecular Physiology, The Penn State University College of Medicine, Hershey, PA 17033, USA.
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