1
|
Mick E, Titov DV, Skinner OS, Sharma R, Jourdain AA, Mootha VK. Distinct mitochondrial defects trigger the integrated stress response depending on the metabolic state of the cell. eLife 2020; 9:e49178. [PMID: 32463360 PMCID: PMC7255802 DOI: 10.7554/elife.49178] [Citation(s) in RCA: 118] [Impact Index Per Article: 29.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2019] [Accepted: 05/04/2020] [Indexed: 12/13/2022] Open
Abstract
Mitochondrial dysfunction is associated with activation of the integrated stress response (ISR) but the underlying triggers remain unclear. We systematically combined acute mitochondrial inhibitors with genetic tools for compartment-specific NADH oxidation to trace mechanisms linking different forms of mitochondrial dysfunction to the ISR in proliferating mouse myoblasts and in differentiated myotubes. In myoblasts, we find that impaired NADH oxidation upon electron transport chain (ETC) inhibition depletes asparagine, activating the ISR via the eIF2α kinase GCN2. In myotubes, however, impaired NADH oxidation following ETC inhibition neither depletes asparagine nor activates the ISR, reflecting an altered metabolic state. ATP synthase inhibition in myotubes triggers the ISR via a distinct mechanism related to mitochondrial inner-membrane hyperpolarization. Our work dispels the notion of a universal path linking mitochondrial dysfunction to the ISR, instead revealing multiple paths that depend both on the nature of the mitochondrial defect and on the metabolic state of the cell.
Collapse
Affiliation(s)
- Eran Mick
- Howard Hughes Medical Institute and Department of Molecular Biology, Massachusetts General HospitalBostonUnited States
- Broad InstituteCambridgeUnited States
- Department of Systems Biology, Harvard Medical SchoolBostonUnited States
| | - Denis V Titov
- Howard Hughes Medical Institute and Department of Molecular Biology, Massachusetts General HospitalBostonUnited States
- Broad InstituteCambridgeUnited States
- Department of Systems Biology, Harvard Medical SchoolBostonUnited States
| | - Owen S Skinner
- Howard Hughes Medical Institute and Department of Molecular Biology, Massachusetts General HospitalBostonUnited States
- Broad InstituteCambridgeUnited States
- Department of Systems Biology, Harvard Medical SchoolBostonUnited States
| | - Rohit Sharma
- Howard Hughes Medical Institute and Department of Molecular Biology, Massachusetts General HospitalBostonUnited States
- Broad InstituteCambridgeUnited States
- Department of Systems Biology, Harvard Medical SchoolBostonUnited States
| | - Alexis A Jourdain
- Howard Hughes Medical Institute and Department of Molecular Biology, Massachusetts General HospitalBostonUnited States
- Broad InstituteCambridgeUnited States
- Department of Systems Biology, Harvard Medical SchoolBostonUnited States
| | - Vamsi K Mootha
- Howard Hughes Medical Institute and Department of Molecular Biology, Massachusetts General HospitalBostonUnited States
- Broad InstituteCambridgeUnited States
- Department of Systems Biology, Harvard Medical SchoolBostonUnited States
| |
Collapse
|
2
|
Crossland H, Smith K, Atherton PJ, Wilkinson DJ. A novel stable isotope tracer method to simultaneously quantify skeletal muscle protein synthesis and breakdown. Metabol Open 2020; 5:100022. [PMID: 32494771 PMCID: PMC7259457 DOI: 10.1016/j.metop.2020.100022] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2019] [Revised: 12/11/2019] [Accepted: 01/01/2020] [Indexed: 01/08/2023] Open
Abstract
Background/aims Methodological challenges have been associated with the dynamic measurement of muscle protein breakdown (MPB), as have the measurement of both muscle protein synthesis (MPS) and MPB within the same experiment. Our aim was to use the transmethylation properties of methionine as proof-of-concept to measure rates of MPB via its methylation of histidine within skeletal muscle myofibrillar proteins, whilst simultaneously utilising methionine incorporation into bound protein to measure MPS. Results During the synthesis measurement period, incorporation of methyl[D3]-13C-methionine into cellular protein in C2C12 myotubes was observed (representative of MPS), alongside an increase in the appearance of methyl[D3]-methylhistidine into the media following methylation of histidine (representative of MPB). For further validation of this approach, fractional synthetic rates (FSR) of muscle protein were increased following treatment of the cells with the anabolic factors insulin-like growth factor-1 (IGF-1) and insulin, while dexamethasone expectedly reduced MPS. Conversely, rates of MPB were reduced with IGF-1 and insulin treatments, whereas dexamethasone accelerated MPB. Conclusions This is a novel stable isotope tracer approach that permits the dual assessment of muscle cellular protein synthesis and breakdown rates, through the provision of a single methionine amino acid tracer that could be utilised in a wide range of biological settings.
Collapse
Affiliation(s)
- Hannah Crossland
- MRC-ARUK Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Biomedical Research Centre (BRC), Clinical, Metabolic and Molecular Physiology, University of Nottingham, Royal Derby Hospital, Derby, UK
| | - Kenneth Smith
- MRC-ARUK Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Biomedical Research Centre (BRC), Clinical, Metabolic and Molecular Physiology, University of Nottingham, Royal Derby Hospital, Derby, UK
| | - Philip J Atherton
- MRC-ARUK Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Biomedical Research Centre (BRC), Clinical, Metabolic and Molecular Physiology, University of Nottingham, Royal Derby Hospital, Derby, UK
| | - Daniel J Wilkinson
- MRC-ARUK Centre for Musculoskeletal Ageing Research, National Institute for Health Research (NIHR) Biomedical Research Centre (BRC), Clinical, Metabolic and Molecular Physiology, University of Nottingham, Royal Derby Hospital, Derby, UK
| |
Collapse
|
3
|
Mao X, Ren M, Chen D, Yu B, Che L, He J, Luo J, Luo Y, Wang J, Sun H. Leucine modulates the IPEC-J2 cell proteome associated with cell proliferation, metabolism and phagocytosis. ACTA ACUST UNITED AC 2018; 4:316-321. [PMID: 30175261 PMCID: PMC6116325 DOI: 10.1016/j.aninu.2018.03.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2017] [Revised: 03/14/2018] [Accepted: 03/19/2018] [Indexed: 12/21/2022]
Abstract
Leucine can affect intestinal protein expressions, and improve mucosal immune function. However, little study has been conducted to determine the change of protein component by leucine treatment in intestine epithelial cells. The present study was to cover the key proteins and cell pathways that could be regulated by leucine treatment in porcine intestinal epithelial cell line (IPEC-J2) cells with the approach of proteome analysis. A total number of 3,211 proteins were identified in our approach by searching the database of Uniprot sus scrofa. Among identified proteins, there were 101 proteins expressed differently between control group and leucine group. Compared with the control group, there were 50 up-regulated proteins and 51 down-regulated proteins in leucine group. In these proteins, leucine treatment decreased the expression of some proteins including pyruvate kinase, glyceraldehyde-3-phosphate dehydrogenase, E3 ubiquitin ligase, cathepsin D, caspase 3 and caspase 6, and increased the levels of some proteins, such as some eukaryotic translation initiation factors, ubiquitin carboxyl-terminal hydrolase, DNA-related RNA polymerase II, urokinase plasminogen activator, cyclin-dependent kinase inhibitor 2b, MutL homolog 1, 5-methylcytosine binding domain 4, polymerase δ, α-tubulin, syntaxin 18, Ras homolog D, actin related protein 2/3 complex and cofilin. Via the analysis of Gene Ontology and pathways, these proteins in IPEC-J2 cells were related with some physiological functions, such as protein metabolism, glycolysis, cell proliferation, apoptosis and phagocytosis. Thus, these results suggest that leucine affects gut barrier function possibly via regulating cell proliferation and apoptosis, metabolism and phagocytosis.
Collapse
Affiliation(s)
- Xiangbing Mao
- Animal Nutrition Institute, Sichuan Agricultural University, Ya'an 625014, China
- Corresponding authors.
| | - Man Ren
- Animal Science Collage, Anhui Science and Technology University, Chuzhou 233100, China
| | - Daiwen Chen
- Animal Nutrition Institute, Sichuan Agricultural University, Ya'an 625014, China
| | - Bing Yu
- Animal Nutrition Institute, Sichuan Agricultural University, Ya'an 625014, China
| | - Lianqiang Che
- Animal Nutrition Institute, Sichuan Agricultural University, Ya'an 625014, China
- Corresponding authors.
| | - Jun He
- Animal Nutrition Institute, Sichuan Agricultural University, Ya'an 625014, China
| | - Junqiu Luo
- Animal Nutrition Institute, Sichuan Agricultural University, Ya'an 625014, China
| | - Yuheng Luo
- Animal Nutrition Institute, Sichuan Agricultural University, Ya'an 625014, China
| | - Jianping Wang
- Animal Nutrition Institute, Sichuan Agricultural University, Ya'an 625014, China
| | - Hui Sun
- College of Animal Science and Technology, Jilin Agricultural University, Changchun 130033, China
| |
Collapse
|
4
|
Chanon S, Chazarin B, Toubhans B, Durand C, Chery I, Robert M, Vieille-Marchiset A, Swenson JE, Zedrosser A, Evans AL, Brunberg S, Arnemo JM, Gauquelin-Koch G, Storey KB, Simon C, Blanc S, Bertile F, Lefai E. Proteolysis inhibition by hibernating bear serum leads to increased protein content in human muscle cells. Sci Rep 2018; 8:5525. [PMID: 29615761 PMCID: PMC5883044 DOI: 10.1038/s41598-018-23891-5] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2017] [Accepted: 03/21/2018] [Indexed: 12/29/2022] Open
Abstract
Muscle atrophy is one of the main characteristics of human ageing and physical inactivity, with resulting adverse health outcomes. To date, there are still no efficient therapeutic strategies for its prevention and/or treatment. However, during hibernation, bears exhibit a unique ability for preserving muscle in conditions where muscle atrophy would be expected in humans. Therefore, our objective was to determine whether there are components of bear serum which can control protein balance in human muscles. In this study, we exposed cultured human differentiated muscle cells to bear serum collected during winter and summer periods, and measured the impact on cell protein content and turnover. In addition, we explored the signalling pathways that control rates of protein synthesis and degradation. We show that the protein turnover of human myotubes is reduced when incubated with winter bear serum, with a dramatic inhibition of proteolysis involving both proteasomal and lysosomal systems, and resulting in an increase in muscle cell protein content. By modulating intracellular signalling pathways and inducing a protein sparing phenotype in human muscle cells, winter bear serum therefore holds potential for developing new tools to fight human muscle atrophy and related metabolic disorders.
Collapse
Affiliation(s)
- Stéphanie Chanon
- CarMeN Laboratory, INSERM, INRA, University of Lyon, Pierre-Benite, France
| | - Blandine Chazarin
- Université de Strasbourg, CNRS, IPHC UMR 7178, F-67000, Strasbourg, France
- Laboratoire de Spectrométrie de Masse Bio-Organique, 25 rue Becquerel, F-67087, Strasbourg, France
- Centre National d'Etudes Spatiales, CNES, 75039, Paris, France
| | - Benoit Toubhans
- CarMeN Laboratory, INSERM, INRA, University of Lyon, Pierre-Benite, France
| | - Christine Durand
- CarMeN Laboratory, INSERM, INRA, University of Lyon, Pierre-Benite, France
| | - Isabelle Chery
- Université de Strasbourg, CNRS, IPHC UMR 7178, F-67000, Strasbourg, France
- Département Ecologie, Physiologie et Ethologie, 23 rue Becquerel, F-67087, Strasbourg, France
| | - Maud Robert
- CarMeN Laboratory, INSERM, INRA, University of Lyon, Pierre-Benite, France
- Department of digestive and bariatric surgery, Obesity Integrated Center, University Hospital of Edouard Herriot, Hospices Civils de Lyon, Lyon 1 University, Lyon, France
| | | | - Jon E Swenson
- Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, 1432, Ås, Norway
- Norwegian Institute for Nature Research, 7485, Trondheim, Norway
| | - Andreas Zedrosser
- Department of Natural Sciences and Environmental Health, University College of Southeast Norway, N3800 Bø in Telemark, Bø, Norway
- Institute of Wildlife Biology and Game Management, University of Natural Resources and Life Sciences, Vienna, Gregor Mendel Str. 33, A-1180, Vienna, Austria
| | - Alina L Evans
- Department of Forestry and Wildlife Management, Inland Norway University of Applied Sciences, NO-2480, Koppang, Norway
| | - Sven Brunberg
- Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, 1432, Ås, Norway
| | - Jon M Arnemo
- Department of Forestry and Wildlife Management, Inland Norway University of Applied Sciences, NO-2480, Koppang, Norway
- Department of Wildlife, Fish, and Environmental Studies, Swedish University of Agricultural Sciences, SE-901 83, Umeå, Sweden
| | | | - Kenneth B Storey
- Institute of Biochemistry and Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6, Canada
| | - Chantal Simon
- CarMeN Laboratory, INSERM, INRA, University of Lyon, Pierre-Benite, France
| | - Stéphane Blanc
- Université de Strasbourg, CNRS, IPHC UMR 7178, F-67000, Strasbourg, France
- Département Ecologie, Physiologie et Ethologie, 23 rue Becquerel, F-67087, Strasbourg, France
| | - Fabrice Bertile
- Université de Strasbourg, CNRS, IPHC UMR 7178, F-67000, Strasbourg, France
- Laboratoire de Spectrométrie de Masse Bio-Organique, 25 rue Becquerel, F-67087, Strasbourg, France
| | - Etienne Lefai
- CarMeN Laboratory, INSERM, INRA, University of Lyon, Pierre-Benite, France.
| |
Collapse
|
5
|
Duan Y, Li F, Guo Q, Wang W, Zhang L, Wen C, Chen X, Yin Y. β-Hydroxy-β-methyl Butyrate Is More Potent Than Leucine in Inhibiting Starvation-Induced Protein Degradation in C2C12 Myotubes. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2018; 66:170-176. [PMID: 29227681 DOI: 10.1021/acs.jafc.7b04841] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Leucine (Leu) and its metabolites α-ketoisocaproate (KIC) and β-hydroxy-β-methyl butyrate (HMB) are potent regulators of protein turnover. The aim of this study was to compare the inhibitory effects of Leu, KIC, and HMB on protein degradation and to investigate the mechanisms involved. The results showed that the inhibitory effect of HMB (0.38 ± 0.04) was more potent than that of Leu (0.76 ± 0.04) and KIC (0.56 ± 0.04, P < 0.01), and was significantly abolished in the presence of LY294002 (1.48 ± 0.02) and rapamycin (1.96 ± 0.02, P < 0.01). In the presence of insulin, the inhibitory effect of HMB (0.34 ± 0.03) was still more effective than that of Leu (0.60 ± 0.04) and KIC (0.57 ± 0.08, P < 0.05). Interestingly, LY294002 treatment markedly attenuated the effect of HMB, while rapamycin treatment failed to exert the same effect. Thus, HMB appears to be more potent than Leu and KIC in inhibiting protein degradation in the absence or presence of insulin, and this inhibitory effect may be dependent on PI3K/Akt signaling pathway regardless of insulin, and mTOR signaling was only involved in this effect of HMB in the absence of insulin.
Collapse
Affiliation(s)
- Yehui Duan
- Laboratory of Animal Nutritional Physiology and Metabolic Process, Institute of Subtropical Agriculture Chinese Academy of Sciences; Key Laboratory of Agro-ecological Processes in Subtropical Region; Hunan Provincial Engineering Research Center for Healthy Livestock and Poultry Production; Scientific Observing and Experimental Station of Animal Nutrition and Feed Science in South-Central, Ministry of Agriculture , Changsha 410125, China
- University of Chinese Academy of Sciences, Beijing 100039, China
| | - Fengna Li
- Laboratory of Animal Nutritional Physiology and Metabolic Process, Institute of Subtropical Agriculture Chinese Academy of Sciences; Key Laboratory of Agro-ecological Processes in Subtropical Region; Hunan Provincial Engineering Research Center for Healthy Livestock and Poultry Production; Scientific Observing and Experimental Station of Animal Nutrition and Feed Science in South-Central, Ministry of Agriculture , Changsha 410125, China
- Hunan Co-Innovation Center of Animal Production Safety, CICAPS; Hunan Collaborative Innovation Center for Utilization of Botanical Functional Ingredients, Changsha, Hunan 410128, China
| | - Qiuping Guo
- Laboratory of Animal Nutritional Physiology and Metabolic Process, Institute of Subtropical Agriculture Chinese Academy of Sciences; Key Laboratory of Agro-ecological Processes in Subtropical Region; Hunan Provincial Engineering Research Center for Healthy Livestock and Poultry Production; Scientific Observing and Experimental Station of Animal Nutrition and Feed Science in South-Central, Ministry of Agriculture , Changsha 410125, China
- University of Chinese Academy of Sciences, Beijing 100039, China
| | - Wenlong Wang
- Laboratory of Animal Nutrition and Human Health, School of Biology, Hunan Normal University , Changsha, Hunan 410018, China
| | - Lingyu Zhang
- Laboratory of Animal Nutritional Physiology and Metabolic Process, Institute of Subtropical Agriculture Chinese Academy of Sciences; Key Laboratory of Agro-ecological Processes in Subtropical Region; Hunan Provincial Engineering Research Center for Healthy Livestock and Poultry Production; Scientific Observing and Experimental Station of Animal Nutrition and Feed Science in South-Central, Ministry of Agriculture , Changsha 410125, China
- University of Chinese Academy of Sciences, Beijing 100039, China
| | - Chaoyue Wen
- Laboratory of Animal Nutrition and Human Health, School of Biology, Hunan Normal University , Changsha, Hunan 410018, China
| | - Xiao'an Chen
- Hunan Shengshi Fenghua Biological Technology Co., Ltd., Longhui 422200, China
| | - Yulong Yin
- Laboratory of Animal Nutritional Physiology and Metabolic Process, Institute of Subtropical Agriculture Chinese Academy of Sciences; Key Laboratory of Agro-ecological Processes in Subtropical Region; Hunan Provincial Engineering Research Center for Healthy Livestock and Poultry Production; Scientific Observing and Experimental Station of Animal Nutrition and Feed Science in South-Central, Ministry of Agriculture , Changsha 410125, China
- Laboratory of Animal Nutrition and Human Health, School of Biology, Hunan Normal University , Changsha, Hunan 410018, China
| |
Collapse
|
6
|
Proteolytic systems' expression during myogenesis and transcriptional regulation by amino acids in gilthead sea bream cultured muscle cells. PLoS One 2017; 12:e0187339. [PMID: 29261652 PMCID: PMC5737955 DOI: 10.1371/journal.pone.0187339] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2017] [Accepted: 10/18/2017] [Indexed: 12/30/2022] Open
Abstract
Proteolytic systems exert an important role in vertebrate muscle controlling protein turnover, recycling of amino acids (AA) or its use for energy production, as well as other functions like myogenesis. In fish, proteolytic systems are crucial for the relatively high muscle somatic index they possess, and because protein is the most important dietary component. Thus in this study, the molecular profile of proteolytic markers (calpains, cathepsins and ubiquitin-proteasome system (UbP) members) were analyzed during gilthead sea bream (Sparus aurata) myogenesis in vitro and under different AA treatments. The gene expression of calpains (capn1, capn3 and capns1b) decreased progressively during myogenesis together with the proteasome member n3; whereas capn2, capns1a, capns1b and ubiquitin (ub) remained stable. Contrarily, the cathepsin D (ctsd) paralogs and E3 ubiquitin ligases mafbx and murf1, showed a significant peak in gene expression at day 8 of culture that slightly decreased afterwards. Moreover, the protein expression analyzed for selected molecules presented in general the same profile of the mRNA levels, which was confirmed by correlation analysis. These data suggest that calpains seem to be more important during proliferation, while cathepsins and the UbP system appear to be required for myogenic differentiation. Concerning the transcriptional regulation by AA, the recovery of their levels after a short starvation period did not show effects on cathepsins expression, whereas it down-regulated the expression of capn3, capns1b, mafbx, murf1 and up-regulated n3. With regards to AA deficiencies, the major changes occurred at day 2, when leucine limitation suppressed ctsb and ctsl expression. Besides at the same time, both leucine and lysine deficiencies increased the expression of mafbx and murf1 and decreased that of n3. Overall, the opposite nutritional regulation observed, especially for the UbP members, points out an efficient and complementary role of these factors that could be useful in gilthead sea bream diets optimization.
Collapse
|
7
|
Carbohydrate intake and resistance-based exercise: are current recommendations reflective of actual need? Br J Nutr 2016; 116:2053-2065. [PMID: 27993175 DOI: 10.1017/s0007114516003949] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Substantial research has been completed examining the impact of carbohydrate (CHO) intake on endurance exercise, whereas its role in resistance-based exercise performance, adaptation and cell signalling has yet to be fully characterised. This empirical shortcoming has precluded the ability to establish specific CHO recommendations for resistance exercise. This results in recommendations largely stemming from findings based on endurance exercise and/or anecdotal evidence despite the distinct energetic demands and molecular responses mediating adaptation from endurance- and resistance-based exercise. Moreover, the topic of CHO and exercise has become one of polarising nature with divergent views - some substantiated, others lacking evidence. Current literature suggests a moderately high daily CHO intake (3-7 g/kg per d) for resistance training, which is thought to prevent glycogen depletion and facilitate performance and adaptation. However, contemporary investigation, along with an emerging understanding of the molecular underpinnings of resistance exercise adaptation, may suggest that such an intake may not be necessary. In addition to the low likelihood of true glycogen depletion occurring in response to resistance exercise, a diet restrictive in CHO may not be detrimental to acute resistance exercise performance or the cellular signalling activity responsible for adaptation, even when muscle glycogen stores are reduced. Current evidence suggests that signalling of the mammalian target of rapamycin complex 1, the key regulatory kinase for gene translation (protein synthesis), is unaffected by CHO restriction or low muscular glycogen concentrations. Such findings may call into question the current view and subsequent recommendations of CHO intake with regard to resistance-based exercise.
Collapse
|
8
|
Leucine-induced anabolic-catabolism: two sides of the same coin. Amino Acids 2015; 48:321-36. [DOI: 10.1007/s00726-015-2109-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2015] [Accepted: 09/28/2015] [Indexed: 10/22/2022]
|
9
|
Polge C, Attaix D, Taillandier D. Role of E2-Ub-conjugating enzymes during skeletal muscle atrophy. Front Physiol 2015; 6:59. [PMID: 25805999 PMCID: PMC4354305 DOI: 10.3389/fphys.2015.00059] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2014] [Accepted: 02/14/2015] [Indexed: 01/05/2023] Open
Abstract
The Ubiquitin Proteasome System (UPS) is a major actor of muscle wasting during various physio-pathological situations. In the past 15 years, increasing amounts of data have depicted a picture, although incomplete, of the mechanisms implicated in myofibrillar protein degradation, from the discovery of muscle-specific E3 ligases to the identification of the signaling pathways involved. The targeting specificity of the UPS relies on the capacity of the system to first recognize and then label the proteins to be degraded with a poly-ubiquitin (Ub) chain. It is fairly assumed that the recognition of the substrate is accomplished by the numerous E3 ligases present in mammalian cells. However, most E3s do not possess any catalytic activity and E2 enzymes may be more than simple Ub-providers for E3s since they are probably important actors in the ubiquitination machinery. Surprisingly, most authors have tried to characterize E3 substrates, but the exact role of E2s in muscle protein degradation is largely unknown. A very limited number of the 35 E2s described in humans have been studied in muscle protein breakdown experiments and the vast majority of studies were only descriptive. We review here the role of E2 enzymes in skeletal muscle and the difficulties linked to their study and provide future directions for the identification of muscle E2s responsible for the ubiquitination of contractile proteins.
Collapse
Affiliation(s)
- Cecile Polge
- UMR 1019 Nutrition Humaine, Institut National de la Recherche Agronomique Saint Genès Champanelle, France
| | - Didier Attaix
- UMR 1019 Nutrition Humaine, Institut National de la Recherche Agronomique Saint Genès Champanelle, France
| | - Daniel Taillandier
- UMR 1019 Nutrition Humaine, Institut National de la Recherche Agronomique Saint Genès Champanelle, France
| |
Collapse
|
10
|
Seiliez I, Dias K, Cleveland BM. Contribution of the autophagy-lysosomal and ubiquitin-proteasomal proteolytic systems to total proteolysis in rainbow trout (Oncorhynchus mykiss) myotubes. Am J Physiol Regul Integr Comp Physiol 2014; 307:R1330-7. [PMID: 25274907 DOI: 10.1152/ajpregu.00370.2014] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The ubiquitin-proteasome system (UPS) is recognized as the major contributor to total proteolysis in mammalian skeletal muscle, responsible for 50% or more of total protein degradation in skeletal muscle, whereas the autophagic-lysosome system (ALS) plays a more minor role. While the relative contribution of these systems to muscle loss is well documented in mammals, little is known in fish species. The current study uses myotubes derived from rainbow trout myogenic precursor cells as an in vitro model of white muscle tissue. Cells were incubated in complete or serum-deprived media or media supplemented with insulin-like growth factor-1 (IGF-1) and exposed to selective proteolytic inhibitors to determine the relative contribution of the ALS and UPS to total protein degradation in myotubes in different culture conditions. Results indicate that the ALS is responsible for 30-34% and 50% of total protein degradation in myotubes in complete and serum-deprived media, respectively. The UPS appears to contribute much less to total protein degradation at almost 4% in cells in complete media to nearly 17% in serum-deprived cells. IGF-1 decreases activity of both systems, as it inhibited the upregulation of both proteolytic systems induced by serum deprivation. The combined inhibition of both the ALS and UPS reduced degradation by a maximum of 55% in serum-deprived cells, suggesting an important contribution of other proteolytic systems to total protein degradation. Collectively, these data identify the ALS as a potential target for strategies aimed at improving muscle protein retention and fillet yield through reductions in protein degradation.
Collapse
Affiliation(s)
- Iban Seiliez
- Institut National de la Recherche Agronomique, Nutrition Métabolisme Aquaculture, St-Pée-sur-Nivelle, France; and
| | - Karine Dias
- Institut National de la Recherche Agronomique, Nutrition Métabolisme Aquaculture, St-Pée-sur-Nivelle, France; and
| | - Beth M Cleveland
- National Center for Cool and Cold Water Aquaculture, Agricultural Research Service/United States Department of Agriculture, Kearneysville, West Virginia
| |
Collapse
|
11
|
Amitani M, Asakawa A, Amitani H, Inui A. Control of food intake and muscle wasting in cachexia. Int J Biochem Cell Biol 2013; 45:2179-85. [DOI: 10.1016/j.biocel.2013.07.016] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2013] [Revised: 07/16/2013] [Accepted: 07/16/2013] [Indexed: 12/14/2022]
|
12
|
Saturated fatty acid palmitate-induced insulin resistance is accompanied with myotube loss and the impaired expression of health benefit myokine genes in C2C12 myotubes. Lipids Health Dis 2013; 12:104. [PMID: 23866690 PMCID: PMC3723881 DOI: 10.1186/1476-511x-12-104] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2013] [Accepted: 07/02/2013] [Indexed: 02/05/2023] Open
Abstract
Background Excessive circular fatty acid, particlarly saturated fatty acid, can result in insulin resistance in skeletal muscle, but other adverse effects of fatty acid accumulation in myocytes remain unclear. Methods Differentiated C2C12 myotubes were used. The effects of palmitate on cell viability, glucose uptake, gene expression and myotube loss were evaluated by MTT assay, 2NBDG uptake, qRT-PCR, Western Blot and crystal staining-based myotube counting, respectively. In some expreiments, oleate was administrated, or the inhibitors of signaling pathways were applied. Results Palmitate-induced cellular insulin resistance was clarified by the reduced Akt phosphorylation, glucose uptake and Glut4 expression. Palmitate-caused myotube loss was clearly observed under microscope and proved by myotube counting and expression analysis of myotube marker genes. Moreover, palmitate-induced transcriptional suppression of three health benefit myokine genes (FNDC5, CTRP15 and FGF21) was found, and the different involvement of p38 and PI3K in the transcription of these genes was noticed. Conclusions Palmitate-induced insulin resistance accompanys myotube loss and the impaired expression of FNDC5, CTRP15 and FGF21genes in C2C12 myotubes. These results provide novel evidence indicating the negative role of high concentration of palmitate in myotubes.
Collapse
|
13
|
Nilsson MI, Dobson JP, Greene NP, Wiggs MP, Shimkus KL, Wudeck EV, Davis AR, Laureano ML, Fluckey JD. Abnormal protein turnover and anabolic resistance to exercise in sarcopenic obesity. FASEB J 2013; 27:3905-16. [PMID: 23804240 DOI: 10.1096/fj.12-224006] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Obesity may impair protein synthesis rates and cause anabolic resistance to growth factors, hormones, and exercise, ultimately affecting skeletal muscle mass and function. To better understand muscle wasting and anabolic resistance with obesity, we assessed protein 24-h fractional synthesis rates (24-h FSRs) in selected hind-limb muscles of sedentary and resistance-exercised lean and obese Zucker rats. Despite atrophied hind-limb muscles (-28% vs. lean rats), 24-h FSRs of mixed proteins were significantly higher in quadriceps (+18%) and red or white gastrocnemius (+22 or +38%, respectively) of obese animals when compared to lean littermates. Basal synthesis rates of myofibrillar (+8%) and mitochondrial proteins (-1%) in quadriceps were not different between phenotypes, while manufacture of cytosolic proteins (+12%) was moderately elevated in obese cohorts. Western blot analyses revealed a robust activation of p70S6k (+178%) and a lower expression of the endogenous mTOR inhibitor DEPTOR (-28%) in obese rats, collectively suggesting that there is an obesity-induced increase in net protein turnover favoring degradation. Lastly, the protein synthetic response to exercise of mixed (-7%), myofibrillar (+6%), and cytosolic (+7%) quadriceps subfractions was blunted compared to the lean phenotype (+34, +40, and +17%, respectively), indicating a muscle- and subfraction-specific desensitization to the anabolic stimulus of exercise in obese animals.
Collapse
Affiliation(s)
- Mats I Nilsson
- 1Department of Health and Kinesiology, Texas A&M University, College Station, TX 77843-4243.
| | | | | | | | | | | | | | | | | |
Collapse
|
14
|
|
15
|
Quy PN, Kuma A, Pierre P, Mizushima N. Proteasome-dependent activation of mammalian target of rapamycin complex 1 (mTORC1) is essential for autophagy suppression and muscle remodeling following denervation. J Biol Chem 2012; 288:1125-34. [PMID: 23209294 DOI: 10.1074/jbc.m112.399949] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Drastic protein degradation occurs during muscle atrophy induced by denervation, fasting, immobility, and various systemic diseases. Although the ubiquitin-proteasome system is highly up-regulated in denervated muscles, the involvement of autophagy and protein synthesis has been controversial. Here, we report that autophagy is rather suppressed in denervated muscles even under autophagy-inducible starvation conditions. This is due to a constitutive activation of mammalian target of rapamycin complex 1 (mTORC1). We further reveal that denervation-induced mTORC1 activation is dependent on the proteasome, which is likely mediated by amino acids generated from proteasomal degradation. Protein synthesis and ribosome biogenesis are paradoxically increased in denervated muscles in an mTORC1-dependent manner, and mTORC1 activation plays an anabolic role against denervation-induced muscle atrophy. These results suggest that denervation induces not only muscle degradation but also adaptive muscle response in a proteasome- and mTORC1-dependent manner.
Collapse
Affiliation(s)
- Pham Nguyen Quy
- Department of Physiology and Cell Biology, Tokyo Medical and Dental University, Tokyo 113-8519, Japan
| | | | | | | |
Collapse
|
16
|
Carbone JW, McClung JP, Pasiakos SM. Skeletal muscle responses to negative energy balance: effects of dietary protein. Adv Nutr 2012; 3:119-26. [PMID: 22516719 PMCID: PMC3648712 DOI: 10.3945/an.111.001792] [Citation(s) in RCA: 82] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Sustained periods of negative energy balance decrease body mass due to losses of both fat and skeletal muscle mass. Decreases in skeletal muscle mass are associated with a myriad of negative consequences, including suppressed basal metabolic rate, decreased protein turnover, decreased physical performance, and increased risk of injury. Decreases in skeletal muscle mass in response to negative energy balance are due to imbalanced rates of muscle protein synthesis and degradation. However, the underlying physiological mechanisms contributing to the loss of skeletal muscle during energy deprivation are not well described. Recent studies have demonstrated that consuming dietary protein at levels above the current recommended dietary allowance (0.8 g · kg(-1) · d(-1)) may attenuate the loss of skeletal muscle mass by affecting the intracellular regulation of muscle anabolism and proteolysis. However, the specific mechanism by which increased dietary protein spares skeletal muscle through enhanced molecular control of muscle protein metabolism has not been elucidated. This article reviews the available literature related to the effects of negative energy balance on skeletal muscle mass, highlighting investigations that assessed the influence of varying levels of dietary protein on skeletal muscle protein metabolism. Further, the molecular mechanisms that may contribute to the regulation of skeletal muscle mass in response to negative energy balance and alterations in dietary protein level are described.
Collapse
Affiliation(s)
- John W. Carbone
- School of Health Sciences, Eastern Michigan University, Ypsilanti, MI; and
| | - James P. McClung
- Military Nutrition Division, United States Army Research Institute of Environmental Medicine, Natick, MA
| | - Stefan M. Pasiakos
- Military Nutrition Division, United States Army Research Institute of Environmental Medicine, Natick, MA,To whom correspondence should be addressed: E-mail:
| |
Collapse
|
17
|
Chen Q, Li N, Zhu W, Li W, Tang S, Yu W, Gao T, Zhang J, Li J. Insulin alleviates degradation of skeletal muscle protein by inhibiting the ubiquitin-proteasome system in septic rats. JOURNAL OF INFLAMMATION-LONDON 2011; 8:13. [PMID: 21639905 PMCID: PMC3120636 DOI: 10.1186/1476-9255-8-13] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/30/2010] [Accepted: 06/03/2011] [Indexed: 01/03/2023]
Abstract
Hypercatabolism is common under septic conditions. Skeletal muscle is the main target organ for hypercatabolism, and this phenomenon is a vital factor in the deterioration of recovery in septic patients. In skeletal muscle, activation of the ubiquitin-proteasome system plays an important role in hypercatabolism under septic status. Insulin is a vital anticatabolic hormone and previous evidence suggests that insulin administration inhibits various steps in the ubiquitin-proteasome system. However, whether insulin can alleviate the degradation of skeletal muscle protein by inhibiting the ubiquitin-proteasome system under septic condition is unclear. This paper confirmed that mRNA and protein levels of the ubiquitin-proteasome system were upregulated and molecular markers of skeletal muscle proteolysis (tyrosine and 3-methylhistidine) simultaneously increased in the skeletal muscle of septic rats. Septic rats were infused with insulin at a constant rate of 2.4 mU.kg-1.min-1 for 8 hours. Concentrations of mRNA and proteins of the ubiquitin-proteasome system and molecular markers of skeletal muscle proteolysis were mildly affected. When the insulin infusion dose increased to 4.8 mU.kg-1.min-1, mRNA for ubiquitin, E2-14 KDa, and the C2 subunit were all sharply downregulated. At the same time, the levels of ubiquitinated proteins, E2-14KDa, and the C2 subunit protein were significantly reduced. Tyrosine and 3-methylhistidine decreased significantly. We concluded that the ubiquitin-proteasome system is important skeletal muscle hypercatabolism in septic rats. Infusion of insulin can reverse the detrimental metabolism of skeletal muscle by inhibiting the ubiquitin-proteasome system, and the effect is proportional to the insulin infusion dose.
Collapse
Affiliation(s)
- Qiyi Chen
- Department of General Surgery, Jinling Hospital, Medical College of Nanjing University, Nanjing 210002, Jiangsu Province, China.
| | | | | | | | | | | | | | | | | |
Collapse
|
18
|
Kim J, Saidel GM, Kalhan SC. Regulation of Adipose Tissue Metabolism in Humans: Analysis of Responses to the Hyperinsulinemic-Euglycemic Clamp Experiment. Cell Mol Bioeng 2011; 4:281-301. [PMID: 23646067 DOI: 10.1007/s12195-011-0162-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The suppression of lipolysis is one of the key metabolic responses of the adipose tissue during hyperinsulinemia. The failure to respond and resulting increase in plasma fatty acids could contribute to the development of insulin resistance and perturbations in the fuel homeostasis in the whole body. In this study, a mechanistic, computational model of adipose tissue metabolism in vivo has been enhanced to simulate the physiological responses during hyperinsulinemic-euglycemic clamp experiment in humans. The model incorporates metabolic intermediates and pathways that are important in the fed state. In addition, it takes into account the heterogeneity of triose phosphate pools (glycolytic vs. glyceroneogenic), within the adipose tissue. The model can simulate not only steady-state responses at different insulin levels, but also concentration dynamics of major metabolites in the adipose tissue venous blood in accord with the in vivo data. Simulations indicate that (1) regulation of lipoprotein lipase (LPL) reaction is important when the intracellular lipolysis is suppressed by insulin; (2) intracellular diglyceride levels can affect the regulatory mechanisms; and (3) glyceroneogenesis is the dominant pathway for glycerol-3-phosphate synthesis even in the presence of increased glucose uptake by the adipose tissue. Reduced redox and increased phosphorylation states provide a favorable milieu for glyceroneogenesis in response to insulin. A parameter sensitivity analysis predicts that insulin-stimulated glucose uptake would be more severely affected by impairment of GLUT4 translocation and glycolysis than by impairment of glycogen synthesis and pyruvate oxidation. Finally, simulations predict metabolic responses to altered expression of phosphoenolpyruvate carboxykinase (PEP-CK). Specifically, the increase in the rate of re-esterification of fatty acids observed experimentally with the overexpression of PEPCK in the adipose tissue would be accompanied by the up-regulation of acyl Co-A synthase.
Collapse
Affiliation(s)
- Jaeyeon Kim
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH 44106, USA ; Center for Modeling Integrated Metabolic Systems, Case Western Reserve University, Cleveland, OH 44106, USA ; Department of Pathobiology, Lerner Research Institute, NE4-203, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195, USA
| | | | | |
Collapse
|
19
|
Op den Kamp CM, Langen RC, Haegens A, Schols AM. Muscle atrophy in cachexia: can dietary protein tip the balance? Curr Opin Clin Nutr Metab Care 2009; 12:611-6. [PMID: 19741519 DOI: 10.1097/mco.0b013e3283319399] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
PURPOSE OF REVIEW To review the efficacy of dietary protein supplementation in attenuating muscle atrophy in cachexia. RECENT FINDINGS Only very few recent randomized controlled trials have studied the effects of protein supplementation in clinical cachexia. It appears that supplementation of dietary protein (>1.5 g/kg per day) alone or in combination with other anabolic stimuli such as exercise training maintains or even improves muscle mass, but results on muscle function are controversial and no clinical studies have yet directly linked alterations in cellular signaling or metabolic signatures of protein intake-induced muscle anabolism to muscle weight gain. SUMMARY To elucidate the role of dietary protein supplementation in attenuating muscle atrophy in cachectic patients, randomized clinical trials are needed in adequately phenotyped patients using sensitive measures of muscle mass and function.
Collapse
Affiliation(s)
- Céline M Op den Kamp
- Department of Respiratory Medicine, NUTRIM School for Nutrition, Toxicology & Metabolism, Maastricht University Medical Centre +, NL-6202 AZ Maastricht, The Netherlands
| | | | | | | |
Collapse
|
20
|
Knecht E, Aguado C, Cárcel J, Esteban I, Esteve JM, Ghislat G, Moruno JF, Vidal JM, Sáez R. Intracellular protein degradation in mammalian cells: recent developments. Cell Mol Life Sci 2009; 66:2427-43. [PMID: 19399586 PMCID: PMC11115841 DOI: 10.1007/s00018-009-0030-6] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2009] [Accepted: 04/02/2009] [Indexed: 12/16/2022]
Abstract
In higher organisms, dietary proteins are broken down into amino acids within the digestive tract but outside the cells, which incorporate the resulting amino acids into their metabolism. However, under certain conditions, an organism loses more nitrogen than is assimilated in the diet. This additional loss was found in the past century to come from intracellular proteins and started an intensive research that produced an enormous expansion of the field and a dispersed literature. Therefore, our purpose is to provide an updated summary of the current knowledge on the proteolytic machinery involved in intracellular protein degradation and its physiological and pathological relevance, especially addressed to newcomers in the field who may find further details in more specialized reviews. However, even providing a general overview, this is an extremely wide field and, therefore, we mainly focus on mammalian cells, while other cells will be mentioned only for comparison purposes.
Collapse
Affiliation(s)
- Erwin Knecht
- Centro de Investigación Príncipe Felipe, Valencia, Spain.
| | | | | | | | | | | | | | | | | |
Collapse
|
21
|
Sadiq F, Crompton LA, Scaife JR, Lomax MA. Effect of prolonged intravenous glucose and essential amino acid infusion on nitrogen balance, muscle protein degradation and ubiquitin-conjugating enzyme gene expression in calves. Nutr Metab (Lond) 2008; 5:5. [PMID: 18269762 PMCID: PMC2263059 DOI: 10.1186/1743-7075-5-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2008] [Accepted: 02/12/2008] [Indexed: 12/02/2022] Open
Abstract
Background Intravenous infusions of glucose and amino acids increase both nitrogen balance and muscle accretion. We hypothesised that co-infusion of glucose (to stimulate insulin) and essential amino acids (EAA) would act additively to improve nitrogen balance by decreasing muscle protein degradation in association with alterations in muscle expression of components of the ubiquitin-proteasome proteolytic pathway. Methods We examined the effect of a 5 day intravenous infusions of saline, glucose, EAA and glucose + EAA, on urinary nitrogen excretion and muscle protein degradation. We carried out the study in 6 restrained calves since ruminants offer the advantage that muscle protein degradation can be assessed by excretion of 3 methyl-histidine and multiple muscle biopsies can be taken from the same animal. On the final day of infusion blood samples were taken for hormone and metabolite measurement and muscle biopsies for expression of ubiquitin, the 14-kDa E2 ubiquitin conjugating enzyme, and proteasome sub-units C2 and C8. Results On day 5 of glucose infusion, plasma glucose, insulin and IGF-1 concentrations were increased while urea nitrogen excretion and myofibrillar protein degradation was decreased. Co-infusion of glucose + EAA prevented the loss of urinary nitrogen observed with EAA infusions alone and enhanced the increase in plasma IGF-1 concentration but there was no synergistic effect of glucose + EAA on the decrease in myofibrillar protein degradation. Muscle mRNA expression of the ubiquitin conjugating enzyme, 14-kDa E2 and proteasome sub-unit C2 were significantly decreased, after glucose but not amino acid infusions, and there was no further response to the combined infusions of glucose + EAA. Conclusion Prolonged glucose infusion decreases myofibrillar protein degradation, prevents the excretion of infused EAA, and acts additively with EAA to increase plasma IGF-1 and improve net nitrogen balance. There was no evidence of synergistic effects between glucose + EAA infusion on muscle protein degradation or expression of components of the ubiquitin-proteasome proteolytic pathway.
Collapse
Affiliation(s)
- Fouzia Sadiq
- Division of Nutritional Sciences, University of Nottingham, Sutton Bonington Campus, LE12 5RD, UK.
| | | | | | | |
Collapse
|
22
|
Abstract
Continual synthesis and breakdown or remodeling of proteins (also called protein turnover) is a principal characteristic of protein metabolism. During animal production, the net differences between synthesis and breakdown represent the actual marketable muscle foods. Because protein synthesis is a highly end-ergonic and protein breakdown is metabolic energy dependent, efficiency of production can be markedly enhanced by lower muscle protein breakdown rates. Herein, various methodological approaches to studying protein breakdown, with particular emphasis toward food-producing animals, are presented. These include whole-animal tracer AA infusions in vivo, quantifying marker AA release from muscle proteins, and in vitro AA release-based methodologies. From such methods, protein synthesis rates and protein breakdown rates (mass units/time) may be obtained. The applications of such methods and innovations based on traditional methods are discussed. Whole-animal in vivo approaches are resource intensive and often not easily applied to high-throughput metabolic screening. Over the last 25 yr, biochemical mechanisms and molecular regulation of protein biosynthesis and protein breakdown have been extensively documented. Proteolysis is dependent in part on the extent of expression of genes for components of cellular proteolytic machinery during skeletal muscle atrophy. It is proposed that high-throughput methods, based on emerging understanding about protein breakdown, may be useful in enhancing production efficiency.
Collapse
Affiliation(s)
- W G Bergen
- Program in Cellular and Molecular Biosciences, Department of Animal Sciences, Auburn University, Auburn, TX 36849-5415, USA.
| |
Collapse
|
23
|
Esteban I, Aguado C, Sánchez M, Knecht E. Regulation of various proteolytic pathways by insulin and amino acids in human fibroblasts. FEBS Lett 2007; 581:3415-21. [PMID: 17610878 DOI: 10.1016/j.febslet.2007.06.043] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2007] [Revised: 06/15/2007] [Accepted: 06/18/2007] [Indexed: 02/08/2023]
Abstract
Intracellular protein degradation is a regulated process with several proteolytic pathways. Although regulation of macroautophagy has been investigated in some detail in hepatocytes and in few other cells, less is known on this regulation in other cells and proteolytic pathways. We show that in human fibroblasts insulin and amino acids reduce protein degradation by different signalling pathways and that this inhibition proceeds in part via the mammalian target of rapamycin, especially with amino acids, which probably increase lysosomal pH. Moreover, the regulatory amino acids (Phe, Arg, Met, Tyr, Trp and Cys) are partially different from other cells. Finally, and in addition to macroautophagy, insulin and amino acids modify, to different extents and sometimes in opposite directions, the activities of other proteolytic pathways.
Collapse
Affiliation(s)
- Inmaculada Esteban
- Laboratorio de Biología Celular, Centro de Investigación Príncipe Felipe, Avda. Autopista del Saler 16, 46013-Valencia, Spain
| | | | | | | |
Collapse
|