51
|
Markofski MM, Dickinson JM, Drummond MJ, Fry CS, Fujita S, Gundermann DM, Glynn EL, Jennings K, Paddon-Jones D, Reidy PT, Sheffield-Moore M, Timmerman KL, Rasmussen BB, Volpi E. Effect of age on basal muscle protein synthesis and mTORC1 signaling in a large cohort of young and older men and women. Exp Gerontol 2015; 65:1-7. [PMID: 25735236 DOI: 10.1016/j.exger.2015.02.015] [Citation(s) in RCA: 106] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2014] [Revised: 02/25/2015] [Accepted: 02/27/2015] [Indexed: 12/21/2022]
Abstract
The rate of muscle loss with aging is higher in men than women. However, women have smaller muscles throughout the adult life. Protein content is a major determinant of skeletal muscle size. This study was designed to determine if age and sex differentially impact basal muscle protein synthesis and mammalian/mechanistic target of rapamycin complex 1 (mTORC1) signaling. We performed a secondary data analysis on a cohort of 215 healthy, non-obese (BMI<30kg·m(-2)) young (18-40y; 74 men, 52 women) and older (60-87y; 57 men, 32 women) adults. The database contained information on physical characteristics, basal muscle protein fractional synthetic rate (FSR; n=215; stable isotope methodology) and mTORC1 signaling (n=125, Western blotting). FSR and mTORC1 signaling were measured at rest and after an overnight fast. mTORC1 and S6K1 phosphorylation were higher (p<0.05) in older subjects with no sex differences. However, there were no age or sex differences or interaction for muscle FSR (p>0.05). Body mass index, fat free mass, or body fat was not a significant covariate and did not influence the results. We conclude that age and sex do not influence basal muscle protein synthesis. However, basal mTORC1 hyperphosphorylation in the elderly may contribute to insulin resistance and the age-related anabolic resistance of skeletal muscle protein metabolism to nutrition and exercise.
Collapse
Affiliation(s)
- Melissa M Markofski
- Sealy Center on Aging, University of Texas Medical Branch, 301 University Blvd., Galveston, TX, USA
| | - Jared M Dickinson
- Department of Nutrition and Metabolism, University of Texas Medical Branch, 301 University Blvd., Galveston, TX, USA; Division of Rehabilitation Sciences, University of Texas Medical Branch, 301 University Blvd., Galveston, TX, USA
| | - Micah J Drummond
- Division of Rehabilitation Sciences, University of Texas Medical Branch, 301 University Blvd., Galveston, TX, USA
| | - Christopher S Fry
- Sealy Center on Aging, University of Texas Medical Branch, 301 University Blvd., Galveston, TX, USA; Department of Nutrition and Metabolism, University of Texas Medical Branch, 301 University Blvd., Galveston, TX, USA; Division of Rehabilitation Sciences, University of Texas Medical Branch, 301 University Blvd., Galveston, TX, USA
| | - Satoshi Fujita
- Sealy Center on Aging, University of Texas Medical Branch, 301 University Blvd., Galveston, TX, USA; Division of Rehabilitation Sciences, University of Texas Medical Branch, 301 University Blvd., Galveston, TX, USA
| | - David M Gundermann
- Department of Nutrition and Metabolism, University of Texas Medical Branch, 301 University Blvd., Galveston, TX, USA; Division of Rehabilitation Sciences, University of Texas Medical Branch, 301 University Blvd., Galveston, TX, USA
| | - Erin L Glynn
- Division of Rehabilitation Sciences, University of Texas Medical Branch, 301 University Blvd., Galveston, TX, USA
| | - Kristofer Jennings
- Sealy Center on Aging, University of Texas Medical Branch, 301 University Blvd., Galveston, TX, USA; Department of Preventive Medicine and Community Health, University of Texas Medical Branch, 301 University Blvd., Galveston, TX, USA
| | - Douglas Paddon-Jones
- Sealy Center on Aging, University of Texas Medical Branch, 301 University Blvd., Galveston, TX, USA; Department of Nutrition and Metabolism, University of Texas Medical Branch, 301 University Blvd., Galveston, TX, USA; Division of Rehabilitation Sciences, University of Texas Medical Branch, 301 University Blvd., Galveston, TX, USA
| | - Paul T Reidy
- Division of Rehabilitation Sciences, University of Texas Medical Branch, 301 University Blvd., Galveston, TX, USA
| | - Melinda Sheffield-Moore
- Sealy Center on Aging, University of Texas Medical Branch, 301 University Blvd., Galveston, TX, USA; Department of Internal Medicine, University of Texas Medical Branch, 301 University Blvd., Galveston, TX, USA
| | - Kyle L Timmerman
- Sealy Center on Aging, University of Texas Medical Branch, 301 University Blvd., Galveston, TX, USA; Division of Rehabilitation Sciences, University of Texas Medical Branch, 301 University Blvd., Galveston, TX, USA
| | - Blake B Rasmussen
- Sealy Center on Aging, University of Texas Medical Branch, 301 University Blvd., Galveston, TX, USA; Department of Nutrition and Metabolism, University of Texas Medical Branch, 301 University Blvd., Galveston, TX, USA; Division of Rehabilitation Sciences, University of Texas Medical Branch, 301 University Blvd., Galveston, TX, USA
| | - Elena Volpi
- Sealy Center on Aging, University of Texas Medical Branch, 301 University Blvd., Galveston, TX, USA; Department of Internal Medicine, University of Texas Medical Branch, 301 University Blvd., Galveston, TX, USA.
| |
Collapse
|
52
|
Thrane S, Pedersen AM, Thomsen MBH, Kirkegaard T, Rasmussen BB, Duun-Henriksen AK, Lænkholm AV, Bak M, Lykkesfeldt AE, Yde CW. A kinase inhibitor screen identifies Mcl-1 and Aurora kinase A as novel treatment targets in antiestrogen-resistant breast cancer cells. Oncogene 2014; 34:4199-210. [DOI: 10.1038/onc.2014.351] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2013] [Revised: 09/15/2014] [Accepted: 09/23/2014] [Indexed: 02/07/2023]
|
53
|
Dickinson JM, Gundermann DM, Walker DK, Reidy PT, Borack MS, Drummond MJ, Arora M, Volpi E, Rasmussen BB. Leucine-enriched amino acid ingestion after resistance exercise prolongs myofibrillar protein synthesis and amino acid transporter expression in older men. J Nutr 2014; 144:1694-702. [PMID: 25332468 PMCID: PMC4195415 DOI: 10.3945/jn.114.198671] [Citation(s) in RCA: 76] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
BACKGROUND Postexercise protein or amino acid ingestion restores muscle protein synthesis in older adults and represents an important therapeutic strategy for aging muscle. However, the precise nutritional factors involved are unknown. OBJECTIVE The purpose of this study was to determine the role of increased postexercise Leu ingestion on skeletal muscle myofibrillar protein synthesis (MyoPS), mammalian/mechanistic target of rapamycin complex 1 signaling, and amino acid transporter (AAT) mRNA expression in older men over a 24-h post-resistance exercise (RE) time course. METHODS During a stable isotope infusion trial (l-[ring-(13)C6]Phe; l-[1-(13)C]Leu), older men performed RE and, at 1 h after exercise, ingested 10 g of essential amino acids (EAAs) containing either a Leu content similar to quality protein (control, 1.85 g of Leu, n = 7) or enriched Leu (LEU; 3.5 g of Leu, n = 8). Muscle biopsies (vastus lateralis) were obtained at rest and 2, 5, and 24 h after exercise. RESULTS p70 S6 kinase 1 phosphorylation was increased in each group at 2 h (P < 0.05), whereas 4E binding protein 1 phosphorylation increased only in the LEU group (P < 0.05). MyoPS was similarly increased (∼90%) above basal in each group at 5 h (P < 0.05) and remained elevated (∼90%) at 24 h only in the LEU group (P < 0.05). The mRNA expression of select AATs was increased at 2 and 5 h in each group (P < 0.05), but AAT expression was increased at 24 h only in the LEU group (P < 0.05). CONCLUSIONS Leu-enriched EAA ingestion after RE may prolong the anabolic response and sensitivity of skeletal muscle to amino acids in older adults. These data emphasize the potential importance of adequate postexercise Leu ingestion to enhance the response of aging muscle to preventive or therapeutic exercise-based rehabilitation programs. This trial was registered at clinicaltrials.gov as NCT00891696.
Collapse
Affiliation(s)
- Jared M. Dickinson
- Departments of Nutrition and Metabolism and,Division of Rehabilitation Sciences, and,Sealy Center on Aging, University of Texas Medical Branch, Galveston, TX; and,School of Nutrition and Health Promotion, Healthy Lifestyles Research Center, Exercise Science and Health Promotion, Arizona State University, Phoenix, AZ,To whom correspondence should be addressed. E-mail:
| | - David M. Gundermann
- Departments of Nutrition and Metabolism and,Division of Rehabilitation Sciences, and
| | | | - Paul T. Reidy
- Departments of Nutrition and Metabolism and,Division of Rehabilitation Sciences, and
| | - Michael S. Borack
- Departments of Nutrition and Metabolism and,Division of Rehabilitation Sciences, and
| | - Micah J. Drummond
- Departments of Nutrition and Metabolism and,Division of Rehabilitation Sciences, and,Sealy Center on Aging, University of Texas Medical Branch, Galveston, TX; and
| | - Mohit Arora
- Sealy Center on Aging, University of Texas Medical Branch, Galveston, TX; and
| | - Elena Volpi
- Internal Medicine–Geriatrics,Division of Rehabilitation Sciences, and,Sealy Center on Aging, University of Texas Medical Branch, Galveston, TX; and
| | - Blake B. Rasmussen
- Departments of Nutrition and Metabolism and,Division of Rehabilitation Sciences, and,Sealy Center on Aging, University of Texas Medical Branch, Galveston, TX; and
| |
Collapse
|
54
|
Timmerman KL, Amonette WE, Markofski MM, Ansinelli HA, Gleason EA, Rasmussen BB, Mossberg KA. Blunted IL-6 and IL-10 response to maximal aerobic exercise in patients with traumatic brain injury. Eur J Appl Physiol 2014; 115:111-8. [PMID: 25213007 DOI: 10.1007/s00421-014-2997-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2014] [Accepted: 09/03/2014] [Indexed: 12/18/2022]
Abstract
INTRODUCTION In healthy individuals, strenuous exercise typically results in a transient increase in the inflammatory cytokine, interleukin-6 (IL-6). This increase in IL-6 is reported to have pleiotropic effects including increased glucose uptake, increased fat oxidation, and anti-inflammatory actions. PURPOSE The purpose of this study was to determine if patients with a traumatic brain injury (TBI) have a differential cytokine response to exercise compared to healthy control subjects (CON). METHODS Eight patients with a TBI and eight age- and sex-matched controls completed an exercise test to volitional exhaustion. Metabolic data were collected continuously, and blood was collected at baseline, immediately post-exercise, and every 10 min for an hour post-exercise. Serum was analyzed for IL-6, tumor necrosis factor-alpha, interleukin-10 (IL-10), and cortisol. RESULTS Peak oxygen consumption (CON 33 ± 2 ml kg(-1) min(-1); TBI 29 ± 2 ml kg(-1) min(-1)) and respiratory exchange ratio during exercise were equivalent between groups. There were no baseline differences between groups for cytokine or cortisol concentrations. Exercise did not increase IL-6 in TBI, whereas IL-6 was elevated from baseline in CON at 0, 40, and 50 min post-exercise (p < 0.05). IL-10 and cortisol increased from baseline in CON at 40 min post-exercise (p < 0.05). CONCLUSIONS These data indicate that patients recovering from TBI have blunted IL-6, IL-10, and cortisol responses following a peak exercise test compared to non-TBI controls. This lack of an exercise response may represent impaired hypothalamic-pituitary-adrenal axis function.
Collapse
|
55
|
Porter C, Herndon DN, Børsheim E, Chao T, Reidy PT, Borack MS, Rasmussen BB, Chondronikola M, Saraf MK, Sidossis LS. Uncoupled skeletal muscle mitochondria contribute to hypermetabolism in severely burned adults. Am J Physiol Endocrinol Metab 2014; 307:E462-7. [PMID: 25074988 PMCID: PMC4154069 DOI: 10.1152/ajpendo.00206.2014] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Elevated metabolic rate is a hallmark of the stress response to severe burn injury. This response is mediated in part by adrenergic stress and is responsive to changes in ambient temperature. We hypothesize that uncoupling of oxidative phosphorylation in skeletal muscle mitochondria contributes to increased metabolic rate in burn survivors. Here, we determined skeletal muscle mitochondrial function in healthy and severely burned adults. Indirect calorimetry was used to estimate metabolic rate in burn patients. Quadriceps muscle biopsies were collected on two separate occasions (11 ± 5 and 21 ± 8 days postinjury) from six severely burned adults (68 ± 19% of total body surface area burned) and 12 healthy adults. Leak, coupled, and uncoupled mitochondrial respiration was determined in permeabilized myofiber bundles. Metabolic rate was significantly greater than predicted values for burn patients at both time points (P < 0.05). Skeletal muscle oxidative capacity, citrate synthase activity, a marker of mitochondrial abundance, and mitochondrial sensitivity to oligomycin were all lower in burn patients vs. controls at both time points (P < 0.05). A greater proportion of maximal mitochondrial respiration was linked to thermogenesis in burn patients compared with controls (P < 0.05). Increased metabolic rate in severely burned adults is accompanied by derangements in skeletal muscle mitochondrial function. Skeletal muscle mitochondria from burn victims are more uncoupled, indicating greater heat production within skeletal muscle. Our findings suggest that skeletal muscle mitochondrial dysfunction contributes to increased metabolic rate in burn victims.
Collapse
Affiliation(s)
- Craig Porter
- Metabolism Unit, Shriners Hospitals for Children, Galveston, Texas; Department of Surgery, University of Texas Medical Branch, Galveston, Texas;
| | - David N Herndon
- Metabolism Unit, Shriners Hospitals for Children, Galveston, Texas; Department of Surgery, University of Texas Medical Branch, Galveston, Texas
| | - Elisabet Børsheim
- Arkansas Children's Nutrition Center and Arkansas Children's Hospital Research Institute, Little Rock, Arkansas; Department of Pediatrics, University of Arkansas for Medical Sciences, Little Rock, Arkansas
| | - Tony Chao
- Metabolism Unit, Shriners Hospitals for Children, Galveston, Texas; Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, Texas
| | - Paul T Reidy
- Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, Texas
| | - Michael S Borack
- Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, Texas
| | - Blake B Rasmussen
- Department of Nutrition and Metabolism, University of Texas Medical Branch, Galveston, Texas; and
| | - Maria Chondronikola
- Metabolism Unit, Shriners Hospitals for Children, Galveston, Texas; Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, Texas
| | - Manish K Saraf
- Metabolism Unit, Shriners Hospitals for Children, Galveston, Texas; Department of Surgery, University of Texas Medical Branch, Galveston, Texas
| | - Labros S Sidossis
- Metabolism Unit, Shriners Hospitals for Children, Galveston, Texas; Department of Surgery, University of Texas Medical Branch, Galveston, Texas; Department of Internal Medicine, University of Texas Medical Branch, Galveston, Texas
| |
Collapse
|
56
|
Gundermann DM, Walker DK, Reidy PT, Borack MS, Dickinson JM, Volpi E, Rasmussen BB. Activation of mTORC1 signaling and protein synthesis in human muscle following blood flow restriction exercise is inhibited by rapamycin. Am J Physiol Endocrinol Metab 2014; 306:E1198-204. [PMID: 24691032 PMCID: PMC4116405 DOI: 10.1152/ajpendo.00600.2013] [Citation(s) in RCA: 80] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Restriction of blood flow to a contracting muscle during low-intensity resistance exercise (BFR exercise) stimulates mTORC1 signaling and protein synthesis in human muscle within 3 h postexercise. However, there is a lack of mechanistic data to provide a direct link between mTORC1 activation and protein synthesis in human skeletal muscle following BFR exercise. Therefore, the primary purpose of this study was to determine whether mTORC1 signaling is necessary for stimulating muscle protein synthesis after BFR exercise. A secondary aim was to describe the 24-h time course response in muscle protein synthesis and breakdown following BFR exercise. Sixteen healthy young men were randomized to one of two groups. Both the control (CON) and rapamycin (RAP) groups completed BFR exercise; however, RAP was administered 16 mg of the mTOR inhibitor rapamycin 1 h prior to BFR exercise. BFR exercise consisted of four sets of leg extension exercise at 20% of 1 RM. Muscle biopsies were collected from the vastus lateralis before exercise and at 3, 6, and 24 h after BFR exercise. Mixed-muscle protein fractional synthetic rate increased by 42% at 3 h postexercise and 69% at 24 h postexercise in CON, whereas this increase was inhibited in the RAP group. Phosphorylation of mTOR (Ser(2448)) and S6K1 (Thr(389)) was also increased in CON but inhibited in RAP. Mixed-muscle protein breakdown was not significantly different across time or groups. We conclude that activation of mTORC1 signaling and protein synthesis in human muscle following BFR exercise is inhibited in the presence of rapamycin.
Collapse
Affiliation(s)
- David M Gundermann
- Department of Nutrition and Metabolism, Division of Rehabilitation Sciences
| | - Dillon K Walker
- Department of Nutrition and Metabolism, Division of Rehabilitation Sciences
| | - Paul T Reidy
- Department of Nutrition and Metabolism, Division of Rehabilitation Sciences
| | - Michael S Borack
- Department of Nutrition and Metabolism, Division of Rehabilitation Sciences
| | - Jared M Dickinson
- Department of Nutrition and Metabolism, Division of Rehabilitation Sciences, Sealy Center on Aging, and
| | - Elena Volpi
- Division of Rehabilitation Sciences, Sealy Center on Aging, and Department of Internal Medicine-Geriatrics, University of Texas Medical Branch, Galveston, Texas
| | - Blake B Rasmussen
- Department of Nutrition and Metabolism, Division of Rehabilitation Sciences, Sealy Center on Aging, and
| |
Collapse
|
57
|
Dickinson JM, Gundermann DM, Walker DK, Reidy PT, Borack MS, Drummond MJ, Volpi E, Rasmussen BB. Markers Of Muscle Protein Breakdown Are Unaffected By Excess Postexercise Leucine Ingestion In Older Men. Med Sci Sports Exerc 2014. [DOI: 10.1249/01.mss.0000493249.99603.ce] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
58
|
Markofski MM, Jennings K, Fisher SR, Rasmussen BB, Volpi E. Supervised Walking 3 Times/week Increases The Weekly Step Activity In Low Active Older Adults. Med Sci Sports Exerc 2014. [DOI: 10.1249/01.mss.0000493540.30559.ee] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
59
|
Reidy PT, Walker DK, Dickinson JM, Gundermann DM, Drummond MJ, Timmerman KL, Cope MB, Mukherjea R, Jennings K, Volpi E, Rasmussen BB. Soy-dairy protein blend and whey protein ingestion after resistance exercise increases amino acid transport and transporter expression in human skeletal muscle. J Appl Physiol (1985) 2014; 116:1353-64. [PMID: 24699854 DOI: 10.1152/japplphysiol.01093.2013] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Increasing amino acid availability (via infusion or ingestion) at rest or postexercise enhances amino acid transport into human skeletal muscle. It is unknown whether alterations in amino acid availability, from ingesting different dietary proteins, can enhance amino acid transport rates and amino acid transporter (AAT) mRNA expression. We hypothesized that the prolonged hyperaminoacidemia from ingesting a blend of proteins with different digestion rates postexercise would enhance amino acid transport into muscle and AAT expression compared with the ingestion of a rapidly digested protein. In a double-blind, randomized clinical trial, we studied 16 young adults at rest and after acute resistance exercise coupled with postexercise (1 h) ingestion of either a (soy-dairy) protein blend or whey protein. Phenylalanine net balance and transport rate into skeletal muscle were measured using stable isotopic methods in combination with femoral arteriovenous blood sampling and muscle biopsies obtained at rest and 3 and 5 h postexercise. Phenylalanine transport into muscle and mRNA expression of select AATs [system L amino acid transporter 1/solute-linked carrier (SLC) 7A5, CD98/SLC3A2, system A amino acid transporter 2/SLC38A2, proton-assisted amino acid transporter 1/SLC36A1, cationic amino acid transporter 1/SLC7A1] increased to a similar extent in both groups (P < 0.05). However, the ingestion of the protein blend resulted in a prolonged and positive net phenylalanine balance during postexercise recovery compared with whey protein (P < 0.05). Postexercise myofibrillar protein synthesis increased similarly between groups. We conclude that, while both protein sources enhanced postexercise AAT expression, transport into muscle, and myofibrillar protein synthesis, postexercise ingestion of a protein blend results in a slightly prolonged net amino acid balance across the leg compared with whey protein.
Collapse
Affiliation(s)
- P T Reidy
- Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, Texas; Department of Nutrition & Metabolism, University of Texas Medical Branch, Galveston, Texas
| | - D K Walker
- Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, Texas; Department of Nutrition & Metabolism, University of Texas Medical Branch, Galveston, Texas
| | - J M Dickinson
- Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, Texas; Department of Nutrition & Metabolism, University of Texas Medical Branch, Galveston, Texas; Sealy Center on Aging, University of Texas Medical Branch, Galveston, Texas
| | - D M Gundermann
- Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, Texas; Department of Nutrition & Metabolism, University of Texas Medical Branch, Galveston, Texas
| | - M J Drummond
- Department of Nutrition & Metabolism, University of Texas Medical Branch, Galveston, Texas; Sealy Center on Aging, University of Texas Medical Branch, Galveston, Texas
| | - K L Timmerman
- Department of Nutrition & Metabolism, University of Texas Medical Branch, Galveston, Texas
| | - M B Cope
- DuPont Nutrition & Health, St. Louis, Missouri
| | - R Mukherjea
- DuPont Nutrition & Health, St. Louis, Missouri
| | - K Jennings
- Department of Preventive Medicine and Community Health, University of Texas Medical Branch, Galveston, Texas; and
| | - E Volpi
- Department of Internal Medicine/Geriatrics, University of Texas Medical Branch, Galveston, Texas; Sealy Center on Aging, University of Texas Medical Branch, Galveston, Texas
| | - B B Rasmussen
- Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, Texas; Department of Nutrition & Metabolism, University of Texas Medical Branch, Galveston, Texas; Sealy Center on Aging, University of Texas Medical Branch, Galveston, Texas;
| |
Collapse
|
60
|
Walker DK, Drummond MJ, Dickinson JM, Borack MS, Jennings K, Volpi E, Rasmussen BB. Insulin increases mRNA abundance of the amino acid transporter SLC7A5/LAT1 via an mTORC1-dependent mechanism in skeletal muscle cells. Physiol Rep 2014; 2:e00238. [PMID: 24760501 PMCID: PMC4002227 DOI: 10.1002/phy2.238] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Abstract Amino acid transporters (AATs) provide a link between amino acid availability and mammalian/mechanistic target of rapamycin complex 1 (mTORC1) activation although the direct relationship remains unclear. Previous studies in various cell types have used high insulin concentrations to determine the role of insulin on mTORC1 signaling and AAT mRNA abundance. However, this approach may limit applicability to human physiology. Therefore, we sought to determine the effect of insulin on mTORC1 signaling and whether lower insulin concentrations stimulate AAT mRNA abundance in muscle cells. We hypothesized that lower insulin concentrations would increase mRNA abundance of select AAT via an mTORC1-dependent mechanism in C2C12 myotubes. Insulin (0.5 nmol/L) significantly increased phosphorylation of the mTORC1 downstream effectors p70 ribosomal protein S6 kinase 1 (S6K1) and ribosomal protein S6 (S6). A low rapamycin dose (2.5 nmol/L) significantly reduced the insulin-(0.5 nmol/L) stimulated S6K1 and S6 phosphorylation. A high rapamycin dose (50 nmol/L) further reduced the insulin-(0.5 nmol/L) stimulated phosphorylation of S6K1 and S6. Insulin (0.5 nmol/L) increased mRNA abundance of SLC38A2/SNAT2 (P ≤ 0.043) and SLC7A5/LAT1 (P ≤ 0.021) at 240 min and SLC36A1/PAT1 (P = 0.039) at 30 min. High rapamycin prevented an increase in SLC38A2/SNAT2 (P = 0.075) and SLC36A1/PAT1 (P ≥ 0.06) mRNA abundance whereas both rapamycin doses prevented an increase in SLC7A5/LAT1 (P ≥ 0.902) mRNA abundance. We conclude that a low insulin concentration increases SLC7A5/LAT1 mRNA abundance in an mTORC1-dependent manner in skeletal muscle cells.
Collapse
Affiliation(s)
- Dillon K Walker
- Department of Nutrition and Metabolism, University of Texas Medical Branch, Galveston, Texas
| | | | | | | | | | | | | |
Collapse
|
61
|
Abstract
PURPOSE OF REVIEW To highlight recent research on amino acid sensing and signaling and the role of amino acid transporters in the regulation of human skeletal muscle protein metabolism. RECENT FINDINGS The mechanisms that sense amino acid availability and activate mechanistic target of rapamycin complex 1 signaling and protein synthesis are emerging, with multiple new proteins and intracellular amino acid sensors recently identified. Amino acid transporters have a role in the delivery of amino acids to these intracellular sensors and new findings provide further support for amino acid transporters as possible extracellular amino acid sensors. There is growing evidence in human skeletal muscle that amino acid transporter expression is dynamic and responsive to various stimuli, indicating amino acid transporters may have a unique role in the regulation of human skeletal muscle adaptation. SUMMARY There is a clear need to further examine the role of amino acid transporters in human skeletal muscle and their link to cellular amino acid sensing and signaling in the control of protein metabolism. A better understanding of amino acid transport and transporters will allow us to optimize nutritional strategies to accelerate muscle health and improve outcomes for clinical populations.
Collapse
Affiliation(s)
- Jared M Dickinson
- Department of Nutrition and Metabolism, University of Texas Medical Branch, Galveston, Texas, USA
| | | |
Collapse
|
62
|
Ryding J, Hjertberg E, Rasmussen BB. Comparison of two direct neutralizing assay formats using recombinant follicle-stimulating hormone as agonist. J Immunol Methods 2013; 400-401:87-96. [PMID: 24184184 DOI: 10.1016/j.jim.2013.10.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2013] [Revised: 10/22/2013] [Accepted: 10/22/2013] [Indexed: 11/28/2022]
Abstract
Characterizing anti-drug antibodies for neutralizing activity is commonly part of the immunogenicity testing package for most therapeutic proteins. Cell-based neutralization assays can generally be categorized as direct- or indirect assays depending on whether they are associated with therapeutics with agonistic- or antagonistic properties. This paper's aim is a comparison of the two direct neutralization assay formats; the variable- and fixed concentration assay format, using recombinant follicle-stimulating hormone as drug agonist. Essential validation- and performance parameters, such as sample through-put, cut-point, precision, sensitivity and drug tolerance, were compared. The fixed concentration assay format offers superior sample through-put (40 versus 6 samples), precision (coefficient of variation of ≤14% versus 34%) and almost 6 times better sensitivity and is generally recommended as the better option particularly for quasi-quantitative assessments of neutralizing antibodies.
Collapse
Affiliation(s)
- J Ryding
- Ferring Pharmaceuticals A/S, Kaj Fiskers Plads 11, DK-2300 Copenhagen, Denmark.
| | | | | |
Collapse
|
63
|
Szczesny B, Olah G, Walker DK, Volpi E, Rasmussen BB, Szabo C, Mitra S. Deficiency in repair of the mitochondrial genome sensitizes proliferating myoblasts to oxidative damage. PLoS One 2013; 8:e75201. [PMID: 24066171 PMCID: PMC3774773 DOI: 10.1371/journal.pone.0075201] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2013] [Accepted: 08/12/2013] [Indexed: 11/18/2022] Open
Abstract
Reactive oxygen species (ROS), generated as a by-product of mitochondrial oxidative phosphorylation, are particularly damaging to the genome of skeletal muscle because of their high oxygen consumption. Proliferating myoblasts play a key role during muscle regeneration by undergoing myogenic differentiation to fuse and restore damaged muscle. This process is severely impaired during aging and in muscular dystrophies. In this study, we investigated the role of oxidatively damaged DNA and its repair in the mitochondrial genome of proliferating skeletal muscle progenitor myoblasts cells and their terminally differentiated product, myotubes. Using the C2C12 cell line as a well-established model for skeletal muscle differentiation, we show that myoblasts are highly sensitive to ROS-mediated DNA damage, particularly in the mitochondrial genome, due to deficiency in 5’ end processing at the DNA strand breaks. Ectopic expression of the mitochondrial-specific 5’ exonuclease, EXOG, a key DNA base excision/single strand break repair (BER/SSBR) enzyme, in myoblasts but not in myotubes, improves the cell’s resistance to oxidative challenge. We linked loss of myoblast viability by activation of apoptosis with deficiency in the repair of the mitochondrial genome. Moreover, the process of myoblast differentiation increases mitochondrial biogenesis and the level of total glutathione. We speculate that our data may provide a mechanistic explanation for depletion of proliferating muscle precursor cells during the development of sarcopenia, and skeletal muscle dystrophies.
Collapse
Affiliation(s)
- Bartosz Szczesny
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, Texas, United States of America
- * E-mail:
| | - Gabor Olah
- Department of Anesthesiology, University of Texas Medical Branch, Galveston, Texas, United States of America
| | - Dillon K. Walker
- Department of Nutrition and Metabolism, University of Texas Medical Branch, Galveston, Texas, United States of America
| | - Elena Volpi
- Department of Internal Medicine, University of Texas Medical Branch, Galveston, Texas, United States of America
| | - Blake B. Rasmussen
- Department of Nutrition and Metabolism, University of Texas Medical Branch, Galveston, Texas, United States of America
| | - Csaba Szabo
- Department of Anesthesiology, University of Texas Medical Branch, Galveston, Texas, United States of America
| | - Sankar Mitra
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, Texas, United States of America
| |
Collapse
|
64
|
Drummond MJ, Timmerman KL, Markofski MM, Walker DK, Dickinson JM, Jamaluddin M, Brasier AR, Rasmussen BB, Volpi E. Short-term bed rest increases TLR4 and IL-6 expression in skeletal muscle of older adults. Am J Physiol Regul Integr Comp Physiol 2013; 305:R216-23. [PMID: 23761639 DOI: 10.1152/ajpregu.00072.2013] [Citation(s) in RCA: 77] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Bed rest induces significant loss of leg lean mass in older adults. Systemic and tissue inflammation also accelerates skeletal muscle loss, but it is unknown whether inflammation is associated to inactivity-induced muscle atrophy in healthy older adults. We determined if short-term bed rest increases toll-like receptor 4 (TLR4) signaling and pro-inflammatory markers in older adult skeletal muscle biopsy samples. Six healthy, older adults underwent seven consecutive days of bed rest. Muscle biopsies (vastus lateralis) were taken after an overnight fast before and at the end of bed rest. Serum cytokine expression was measured before and during bed rest. TLR4 signaling and cytokine mRNAs associated with pro- and anti-inflammation and anabolism were measured in muscle biopsy samples using Western blot analysis and qPCR. Participants lost ∼4% leg lean mass with bed rest. We found that after bed rest, muscle levels of TLR4 protein expression and interleukin-6 (IL-6), nuclear factor-κB1, interleukin-10, and 15 mRNA expression were increased after bed rest (P < 0.05). Additionally, the cytokines interferon-γ, and macrophage inflammatory protein-1β, were elevated in serum samples following bed rest (P < 0.05). We conclude that short-term bed rest in older adults modestly increased some pro- and anti-inflammatory cytokines in muscle samples while systemic changes in pro-inflammatory cytokines were mostly absent. Upregulation of TLR4 protein content suggests that bed rest in older adults increases the capacity to mount an exaggerated, and perhaps unnecessary, inflammatory response in the presence of specific TLR4 ligands, e.g., during acute illness.
Collapse
Affiliation(s)
- Micah J Drummond
- Univ. of Utah, 520 Wakara Way, Salt Lake City, UT 84108-1213, USA.
| | | | | | | | | | | | | | | | | |
Collapse
|
65
|
Reidy PT, Walker DK, Dickinson JM, Gundermann DM, Drummond MJ, Timmerman KL, Fry CS, Borack MS, Cope MB, Mukherjea R, Jennings K, Volpi E, Rasmussen BB. Protein blend ingestion following resistance exercise promotes human muscle protein synthesis. J Nutr 2013; 143:410-6. [PMID: 23343671 PMCID: PMC3738242 DOI: 10.3945/jn.112.168021] [Citation(s) in RCA: 119] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
High-quality proteins such as soy, whey, and casein are all capable of promoting muscle protein synthesis postexercise by activating the mammalian target of rapamycin (mTORC1) signaling pathway. We hypothesized that a protein blend of soy and dairy proteins would capitalize on the unique properties of each individual protein and allow for optimal delivery of amino acids to prolong the fractional synthetic rate (FSR) following resistance exercise (RE). In this double-blind, randomized, clinical trial, 19 young adults were studied before and after ingestion of ∼19 g of protein blend (PB) or ∼18 g whey protein (WP) consumed 1 h after high-intensity leg RE. We examined mixed-muscle protein FSR by stable isotopic methods and mTORC1 signaling with western blotting. Muscle biopsies from the vastus lateralis were collected at rest (before RE) and at 3 postexercise time points during an early (0-2 h) and late (2-4 h) postingestion period. WP ingestion resulted in higher and earlier amplitude of blood branched-chain amino acid (BCAA) concentrations. PB ingestion created a lower initial rise in blood BCAA but sustained elevated levels of blood amino acids later into recovery (P < 0.05). Postexercise FSR increased equivalently in both groups during the early period (WP, 0.078 ± 0.009%; PB, 0.088 ± 0.007%); however, FSR remained elevated only in the PB group during the late period (WP, 0.074 ± 0.010%; PB, 0.087 ± 0.003%) (P < 0.05). mTORC1 signaling similarly increased between groups, except for no increase in S6K1 phosphorylation in the WP group at 5 h postexercise (P < 0.05). We conclude that a soy-dairy PB ingested following exercise is capable of prolonging blood aminoacidemia, mTORC1 signaling, and protein synthesis in human skeletal muscle and is an effective postexercise nutritional supplement.
Collapse
Affiliation(s)
- Paul T. Reidy
- Division of Rehabilitation Sciences,Department of Nutrition and Metabolism
| | - Dillon K. Walker
- Division of Rehabilitation Sciences,Department of Nutrition and Metabolism
| | - Jared M. Dickinson
- Division of Rehabilitation Sciences,Department of Nutrition and Metabolism
| | | | | | | | | | - Michael S. Borack
- Division of Rehabilitation Sciences,Department of Nutrition and Metabolism
| | | | | | - Kristofer Jennings
- Department of Preventative Medicine and Community Health, University of Texas Medical Branch, Galveston, TX; and
| | - Elena Volpi
- Department of Internal Medicine/Geriatrics,Sealy Center on Aging, and
| | - Blake B. Rasmussen
- Division of Rehabilitation Sciences,Department of Nutrition and Metabolism,Sealy Center on Aging, and,To whom correspondence should be addressed. E-mail:
| |
Collapse
|
66
|
Dickinson JM, Gundermann DM, Walker DK, Reidy PT, Borack M, Drummond MJ, Arora M, Volpi E, Rasmussen BB. Excess postexercise leucine ingestion enhances muscle protein synthesis in skeletal muscle of older men. FASEB J 2013. [DOI: 10.1096/fasebj.27.1_supplement.350.2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Jared M Dickinson
- Nutrition and MetabolismUniversity of Texas Medical BranchGalvestonTX
- Sealy Center on AgingUniversity of Texas Medical BranchGalvestonTX
| | | | - Dillon K Walker
- Nutrition and MetabolismUniversity of Texas Medical BranchGalvestonTX
| | - Paul T Reidy
- Nutrition and MetabolismUniversity of Texas Medical BranchGalvestonTX
| | - Michael Borack
- Nutrition and MetabolismUniversity of Texas Medical BranchGalvestonTX
| | - Micah J Drummond
- Nutrition and MetabolismUniversity of Texas Medical BranchGalvestonTX
- Sealy Center on AgingUniversity of Texas Medical BranchGalvestonTX
| | - Mohit Arora
- Sealy Center on AgingUniversity of Texas Medical BranchGalvestonTX
| | - Elena Volpi
- Sealy Center on AgingUniversity of Texas Medical BranchGalvestonTX
- Internal MedicineUniversity of Texas Medical BranchGalvestonTX
| | - Blake B Rasmussen
- Nutrition and MetabolismUniversity of Texas Medical BranchGalvestonTX
- Sealy Center on AgingUniversity of Texas Medical BranchGalvestonTX
| |
Collapse
|
67
|
Markofski MM, Timmerman KL, Dickinson JM, Reidy PT, Borack M, Rasmussen BB, Volpi E. The acute aerobic exercise‐induced increase in amino acid transporter expression adapts to exercise training in older adults. FASEB J 2013. [DOI: 10.1096/fasebj.27.1_supplement.350.3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | | | | | - Paul T Reidy
- Rehabilitaiton SciencesUniv. of Texas Medical BranchGalvestonTX
| | - Michael Borack
- Rehabilitaiton SciencesUniv. of Texas Medical BranchGalvestonTX
| | | | - Elena Volpi
- Sealy Center on AgingUniv. of Texas Medical BranchGalvestonTX
- Dept. of Internal Medicine‐Division of GeriatricsUniv. of Texas Medical BranchGalvestonTX
| |
Collapse
|
68
|
Glynn EL, Fry CS, Timmerman KL, Drummond MJ, Volpi E, Rasmussen BB. Addition of carbohydrate or alanine to an essential amino acid mixture does not enhance human skeletal muscle protein anabolism. J Nutr 2013; 143:307-14. [PMID: 23343676 PMCID: PMC3713020 DOI: 10.3945/jn.112.168203] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
In humans, essential amino acids (EAAs) stimulate muscle protein synthesis (MPS) with no effect on muscle protein breakdown (MPB). Insulin can stimulate MPS, and carbohydrates (CHOs) and insulin decrease MPB. Net protein balance (NB; indicator of overall anabolism) is greatest when MPS is maximized and MPB is minimized. To determine whether adding CHO or a gluconeogenic amino acid to EAAs would improve NB compared with EAA alone, young men and women (n = 21) ingested 10 g EAA alone, with 30 g sucrose (EAA+CHO), or with 30 g alanine (EAA+ALA). The fractional synthetic rate and phenylalanine kinetics (MPS, MPB, NB) were assessed by stable isotopic methods on muscle biopsies at baseline and 60 and 180 min following nutrient ingestion. Insulin increased 30 min postingestion in all groups and remained elevated in the EAA+CHO and EAA+ALA groups for 60 and 120 min, respectively. The fractional synthetic rate increased from baseline at 60 min in all groups (P < 0.05; EAA = 0.053 ± 0.018 to 0.090 ± 0.039% · h(-1); EAA+ALA = 0.051 ± 0.005 to 0.087 ± 0.015% · h(-1); EAA+CHO = 0.049 ± 0.006 to 0.115 ± 0.024% · h(-1)). MPS and NB peaked at 30 min in the EAA and EAA+CHO groups but at 60 min in the EAA+ALA group and NB was elevated above baseline longer in the EAA+ALA group than in the EAA group (P < 0.05). Although responses were more robust in the EAA+CHO group and prolonged in the EAA+ALA group, AUCs were similar among all groups for fractional synthetic rate, MPS, MPB, and NB. Because the overall muscle protein anabolic response was not improved in either the EAA+ALA or EAA+CHO group compared with EAA, we conclude that protein nutritional interventions to enhance muscle protein anabolism do not require such additional energy.
Collapse
Affiliation(s)
| | | | | | - Micah J. Drummond
- Department of Nutrition and Metabolism,Division of Rehabilitation Sciences,Sealy Center on Aging, University of Texas Medical Branch, Galveston, TX
| | - Elena Volpi
- Department of Internal Medicine,Division of Geriatrics, and,Sealy Center on Aging, University of Texas Medical Branch, Galveston, TX
| | - Blake B. Rasmussen
- Department of Nutrition and Metabolism,Division of Rehabilitation Sciences,Sealy Center on Aging, University of Texas Medical Branch, Galveston, TX,To whom correspondence should be addressed. E-mail:
| |
Collapse
|
69
|
Dickinson JM, Drummond MJ, Fry CS, Gundermann DM, Walker DK, Timmerman KL, Volpi E, Rasmussen BB. Rapamycin does not affect post-absorptive protein metabolism in human skeletal muscle. Metabolism 2013; 62:144-51. [PMID: 22959478 PMCID: PMC3680880 DOI: 10.1016/j.metabol.2012.07.003] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/23/2012] [Revised: 06/22/2012] [Accepted: 07/11/2012] [Indexed: 10/27/2022]
Abstract
UNLABELLED Administration of the mTORC1 inhibitor, rapamycin, to humans blocks the increase in skeletal muscle protein synthesis in response to resistance exercise or amino acid ingestion. OBJECTIVE To determine whether rapamycin administration influences basal post-absorptive protein synthesis or breakdown in human skeletal muscle. MATERIALS/METHODS Six young (26±2 years) subjects were studied during two separate trials, in which each trial was divided into two consecutive 2 h basal periods. The trials were identical except during one trial a single oral dose (16 mg) of rapamycin was administered immediately prior to the second basal period. Muscle biopsies were obtained from the vastus lateralis at 0, 2, and 4 h to examine protein synthesis, mTORC1 signaling, and markers of autophagy (LC3B-I and LC3B-II protein) associated with each 2 h basal period. RESULTS During the Control trial, muscle protein synthesis, whole body protein breakdown (phenylalanine Ra), mTORC1 signaling, and markers of autophagy were similar between both basal periods (p>0.05). During the Rapamycin trial, these variables were similar to the Control trial (p>0.05) and were unaltered by rapamycin administration (p>0.05). Thus, post-absorptive muscle protein metabolism and mTORC1 signaling were not affected by rapamycin administration. CONCLUSIONS Short-term rapamycin administration may only impair protein synthesis in human skeletal muscle when combined with a stimulus such as resistance exercise or increased amino acid availability.
Collapse
Affiliation(s)
- Jared M. Dickinson
- Department of Nutrition and Metabolism, University of Texas Medical Branch, Galveston, TX 77555, USA
- Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, TX 77555, USA
| | - Micah J. Drummond
- Department of Nutrition and Metabolism, University of Texas Medical Branch, Galveston, TX 77555, USA
- Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, TX 77555, USA
- Sealy Center on Aging, University of Texas Medical Branch, Galveston, TX 77555, USA
| | - Christopher S. Fry
- Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, TX 77555, USA
| | - David M. Gundermann
- Department of Nutrition and Metabolism, University of Texas Medical Branch, Galveston, TX 77555, USA
- Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, TX 77555, USA
| | - Dillon K. Walker
- Department of Nutrition and Metabolism, University of Texas Medical Branch, Galveston, TX 77555, USA
- Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, TX 77555, USA
| | - Kyle L. Timmerman
- Department of Nutrition and Metabolism, University of Texas Medical Branch, Galveston, TX 77555, USA
- Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, TX 77555, USA
- Sealy Center on Aging, University of Texas Medical Branch, Galveston, TX 77555, USA
| | - Elena Volpi
- Sealy Center on Aging, University of Texas Medical Branch, Galveston, TX 77555, USA
- Department of Internal Medicine-Geriatrics, University of Texas Medical Branch, Galveston, TX 77555, USA
| | - Blake B. Rasmussen
- Department of Nutrition and Metabolism, University of Texas Medical Branch, Galveston, TX 77555, USA
- Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, TX 77555, USA
- Sealy Center on Aging, University of Texas Medical Branch, Galveston, TX 77555, USA
- Corresponding author. University of Texas Medical Branch, Department of Nutrition and Metabolism, Division of Rehabilitation Sciences, Sealy Center on Aging, 301 University Blvd., Galveston, TX 77555-1124, USA. Tel.: +1 409 747 1619; fax: +1 409 747 1613. (B.B. Rasmussen)
| |
Collapse
|
70
|
Abstract
INTRODUCTION Paraplegia results in significant skeletal muscle atrophy through increases in skeletal muscle protein breakdown. Recent work has identified a novel SIRT1-p53 pathway that is capable of regulating autophagy and protein breakdown. METHODS Soleus muscle was collected from 6 male Sprague-Dawley rats 10 weeks after complete T4-5 spinal cord transection (paraplegia group) and 6 male sham-operated rats (control group). We utilized immunoblotting methods to measure intracellular proteins and quantitative real-time polymerase chain reaction to measure the expression of skeletal muscle microRNAs. RESULTS SIRT1 protein expression was 37% lower, and p53 acetylation (LYS379) was increased in the paraplegic rats (P < 0.05). Atg7 and Beclin-1, markers of autophagy induction, were elevated in the paraplegia group compared with controls (P < 0.05). CONCLUSIONS Severe muscle atrophy resulting from chronic paraplegia appears to increase skeletal muscle autophagy independent of SIRT1 signaling. We conclude that chronic paraplegia may cause an increase in autophagic cell death and negatively impact skeletal muscle protein balance.
Collapse
Affiliation(s)
- Christopher S Fry
- Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, Texas 77555-1144, USA
| | | | | | | | | |
Collapse
|
71
|
Fry CS, Drummond MJ, Glynn EL, Dickinson JM, Gundermann DM, Timmerman KL, Walker DK, Volpi E, Rasmussen BB. Skeletal muscle autophagy and protein breakdown following resistance exercise are similar in younger and older adults. J Gerontol A Biol Sci Med Sci 2012; 68:599-607. [PMID: 23089333 DOI: 10.1093/gerona/gls209] [Citation(s) in RCA: 120] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
BACKGROUND The loss of skeletal muscle mass and strength during aging, sarcopenia, increases the risk for falls and dependency. Resistance exercise (RE) training is effective at improving muscle mass and strength in older adults; however, aging is associated with reduced training-induced hypertrophy. Recent research has illustrated an impaired muscle protein synthetic response following an acute bout of RE in older adults but much less is known regarding the effect of acute RE on muscle protein breakdown (MPB). We hypothesize that the ubiquitin proteasome system and the autophagosomal-lysosomal system may regulate the overall rate of MPB during postexercise recovery. METHODS Muscle biopsies of the vastus lateralis were sampled from 16 older (age = 70±2 years) and 16 younger (age = 27±2 years) participants at baseline and at 3, 6, and 24 hours following an acute bout of RE. In conjunction with stable isotopic techniques to measure MPB, we utilized immunoblotting and RT-PCR to examine protein and mRNA expression for key signaling molecules in both the ubiquitin proteasome system and the autophagosomal-lysosomal system. RESULTS MuRF1 mRNA expression increased, whereas GABARAP mRNA decreased after RE in both younger and older adults (p < .05). The LC3B-II/LC3B-I protein ratio decreased in both groups after RE (p < .05), but MPB was not different 24 hour post-RE in either group (p > .05). CONCLUSIONS Aging does not influence skeletal MPB, autophagy, or the ubiquitin proteasome system following an acute bout of RE. Therefore, targeting the muscle protein synthesis response to exercise may hold more promise in the prevention of sarcopenia.
Collapse
Affiliation(s)
- Christopher S Fry
- Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, Texas 77555-1144, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
72
|
Butteiger DN, Cope M, Liu P, Mukherjea R, Volpi E, Rasmussen BB, Krul ES. A soy, whey and caseinate blend extends postprandial skeletal muscle protein synthesis in rats. Clin Nutr 2012; 32:585-91. [PMID: 23127543 DOI: 10.1016/j.clnu.2012.10.001] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2012] [Revised: 09/25/2012] [Accepted: 10/01/2012] [Indexed: 10/27/2022]
Abstract
BACKGROUND & AIMS Blends of dairy and soy protein are used in commercial sports nutrition products; however, no studies have systematically compared blends to isolated protein sources and their effects on muscle protein synthesis (MPS). Dairy whey protein (WP), soy protein isolate (SP), and two blends (Blend 1 and Blend 2) consisting of ratios of 50:25:25 and 25:50:25 for whey:caseinate:soy, respectively, were evaluated for their ability to affect MPS. METHODS Male Sprague-Dawley rats were trained to eat 3 meals/day: a 4 g meal at 0700-0720 hours followed by ad lib feeding at 1300-1400 hours and 1800-1900 hours. After ~5 days of training, fasted rats were administered their respective 4 g meal at 0700-0720 hours and an intravenous flooding dose of (2)H5-phenylalanine 10 min prior to euthanasia. Individual rats were euthanized at designated postprandial time points. Blood and gastrocnemius samples were collected and the latter was used to measure mixed muscle protein fractional synthetic rates (FSR). RESULTS Plasma leucine concentrations peaked in all groups at 90 min and were still above baseline at 300 min post-meal. FSR tended to increase in all groups post-meal but initial peaks of FSR were different times (45, 90 and 135 min for WP or SP, Blend 1 and Blend 2, respectively). Blend 2 had a significantly higher FSR compared to WP alone at 135 min (P < 0.05). CONCLUSIONS Single source proteins and protein blends all enhance skeletal MPS after a meal, however, Blend 2 had a delayed FSR peak which was significantly higher than whey protein at 135 min.
Collapse
Affiliation(s)
- D N Butteiger
- Solae, LLC, Global Nutrition, 4300 Duncan Ave, St Louis, MO 63110, USA.
| | | | | | | | | | | | | |
Collapse
|
73
|
Dickinson JM, Drummond MJ, Coben JR, Volpi E, Rasmussen BB. Aging differentially affects human skeletal muscle amino acid transporter expression when essential amino acids are ingested after exercise. Clin Nutr 2012; 32:273-80. [PMID: 22889597 DOI: 10.1016/j.clnu.2012.07.009] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2012] [Revised: 07/13/2012] [Accepted: 07/24/2012] [Indexed: 01/17/2023]
Abstract
BACKGROUND & AIMS Amino acid transporters have been proposed as regulators of protein synthesis. The primary aim of this study was to determine whether amino acid transporter expression is increased in human muscle following resistance exercise (RE) coupled with essential amino acid (EAA) ingestion, and whether a differential response occurs with aging. Secondly, we aimed to compare this response to a previous study examining RE alone. METHODS Young (n = 7, 30 ± 2 yr) and older men (n = 6, 70 ± 2 yr) ingested EAA 1 h after RE. Muscle biopsies were obtained at rest and 3 and 6 h post exercise to examine amino acid transporter mRNA and protein expression. RESULTS In both age groups, RE + EAA increased mRNA of L-type amino acid transporter 1 (LAT1)/solute linked carrier (SLC)7A5, sodium-coupled neutral amino acid transporter 2 (SNAT2)/SLC38A2, and cationic amino acid transporter 1/SLC7A1 (p < 0.05). SNAT2 protein increased in young at 3 and 6 h (p < 0.05), whereas old maintained higher LAT1 protein (p < 0.05). Compared to RE alone, RE + EAA enhanced amino acid transporter expression only in young (p < 0.05). CONCLUSIONS RE increases muscle amino acid transporter expression in young and older adults, however, post exercise EAA ingestion enhances amino acid transporter expression only in young indicating that aging may influence the function of specific amino acid transporters.
Collapse
Affiliation(s)
- Jared M Dickinson
- Department of Nutrition and Metabolism, University of Texas Medical Branch, Galveston, TX 77555, United States.
| | | | | | | | | |
Collapse
|
74
|
Timmerman KL, Dhanani S, Glynn EL, Fry CS, Drummond MJ, Jennings K, Rasmussen BB, Volpi E. A moderate acute increase in physical activity enhances nutritive flow and the muscle protein anabolic response to mixed nutrient intake in older adults. Am J Clin Nutr 2012; 95:1403-12. [PMID: 22572647 PMCID: PMC3349455 DOI: 10.3945/ajcn.111.020800] [Citation(s) in RCA: 103] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
BACKGROUND Nutrient stimulation of muscle protein anabolism is blunted with aging and may contribute to the development and progression of sarcopenia in older adults. This is likely due to insulin resistance of protein metabolism and/or endothelial dysfunction with a reduction in nutritive flow, both of which can be improved by aerobic exercise. OBJECTIVE Our objective was to determine whether increasing physical activity can enhance the muscle protein anabolic effect of essential amino acid (EAA) + sucrose intake in older subjects by improving nutritive flow and/or insulin signaling. DESIGN Using a randomized crossover design, we measured in older subjects [n = 6, 70 ± 3 y of age, BMI (in kg/m2) of 25 ± 1] the acute effects of increasing physical activity with aerobic exercise, as compared with normal sedentary lifestyle, on the response of blood flow, microvascular perfusion, insulin signaling, and muscle protein kinetics to EAA+sucrose intake. RESULTS No differences between treatment groups were found in the basal state. The change from the basal state in blood flow, muscle perfusion, phenylalanine delivery, net balance, and muscle protein synthesis during the consumption of EAA+sucrose was significantly higher after the exercise than after the control treatment (P < 0.05). Insulin signaling increased during EAA+sucrose ingestion in both groups (P < 0.05). CONCLUSIONS Our data indicate that a prior bout of aerobic exercise increases the anabolic effect of nutrient intake in older adults. This effect appears to be mediated by an exercise-induced improvement in nutrient-stimulated vasodilation and nutrient delivery to muscle rather than to improved insulin signaling. This trial was registered at clinicaltrials.gov as NCT00690534.
Collapse
Affiliation(s)
- Kyle L Timmerman
- Department of Nutrition & Metabolism, University of Texas Medical Branch, Galveston, TX, USA
| | | | | | | | | | | | | | | |
Collapse
|
75
|
Walker DK, Fry CS, Drummond MJ, Dickinson JM, Timmerman KL, Gundermann DM, Jennings K, Volpi E, Rasmussen BB. PAX7+ satellite cells in young and older adults following resistance exercise. Muscle Nerve 2012; 46:51-9. [PMID: 22644638 DOI: 10.1002/mus.23266] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/29/2011] [Indexed: 01/23/2023]
Abstract
INTRODUCTION Resistance exercise (RE) stimulates a muscle protein anabolic response partially through enhanced satellite cell (SC) activity, however, age- and gender-related changes in SC content over a 24-h time course are not known. METHODS Ten young (27 ± 2 years) men and women and 11 older (70 ± 2 years) men and women performed an acute bout of RE. Myofiber and SC characteristics were determined from muscle biopsies of the vastus lateralis using immunohistochemistry. Immunoblotting was used to determine phosphorylation of cyclin-dependent kinase-2 and protein expression of p27(Kip1) and cyclin D1. RESULTS Pax7+ SC were significantly increased in young men 24 h following RE. Percent SC were significantly increased in older women at 6 and 24 h following RE. Aging decreased myonuclear domain and increased protein expression of p27(Kip1) . CONCLUSIONS An acute bout of RE increases SC content in young men at 24 h and older women at 6 and 24 h.
Collapse
Affiliation(s)
- Dillon K Walker
- Department of Nutrition & Metabolism, University of Texas Medical Branch, 301 University Boulevard, Galveston, Texas 77555, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
76
|
Drummond MJ, Dickinson JM, Fry CS, Walker DK, Gundermann DM, Reidy PT, Timmerman KL, Markofski MM, Paddon-Jones D, Rasmussen BB, Volpi E. Bed rest impairs skeletal muscle amino acid transporter expression, mTORC1 signaling, and protein synthesis in response to essential amino acids in older adults. Am J Physiol Endocrinol Metab 2012; 302:E1113-22. [PMID: 22338078 PMCID: PMC3361979 DOI: 10.1152/ajpendo.00603.2011] [Citation(s) in RCA: 157] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Skeletal muscle atrophy during bed rest is attributed, at least in part, to slower basal muscle protein synthesis (MPS). Essential amino acids (EAA) stimulate mammalian target of rapamycin (mTORC1) signaling, amino acid transporter expression, and MPS and are necessary for muscle mass maintenance, but there are no data on the effect of inactivity on this anabolic mechanism. We hypothesized that bed rest decreases muscle mass in older adults by blunting the EAA stimulation of MPS through reduced mTORC1 signaling and amino acid transporter expression in older adults. Six healthy older adults (67 ± 2 yr) participated in a 7-day bed rest study. We used stable isotope tracers, Western blotting, and real-time qPCR to determine the effect of bed rest on MPS, muscle mTORC1 signaling, and amino acid transporter expression and content in the postabsorptive state and after acute EAA ingestion. Bed rest decreased leg lean mass by ∼4% (P < 0.05) and increased postabsorptive mTOR protein (P < 0.05) levels while postabsorptive MPS was unchanged (P > 0.05). Before bed rest acute EAA ingestion increased MPS, mTOR (Ser(2448)), S6 kinase 1 (Thr(389), Thr(421)/Ser(424)), and ribosomal protein S6 (Ser(240/244)) phosphorylation, activating transcription factor 4, L-type amino acid transporter 1 and sodium-coupled amino acid transporter 2 protein content (P < 0.05). However, bed rest blunted the EAA-induced increase in MPS, mTORC1 signaling, and amino acid transporter protein content. We conclude that bed rest in older adults significantly attenuated the EAA-induced increase in MPS with a mechanism involving reduced mTORC1 signaling and amino acid transporter protein content. Together, our data suggest that a blunted EAA stimulation of MPS may contribute to muscle loss with inactivity in older persons.
Collapse
Affiliation(s)
- Micah J Drummond
- Department of Nutrition and Metabolism, University of Texas Medical Branch, Galveston, USA.
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
77
|
Ejlertsen B, Aldridge J, Nielsen KV, Regan MM, Henriksen KL, Lykkesfeldt AE, Müller S, Gelber RD, Price KN, Rasmussen BB, Viale G, Mouridsen H. Prognostic and predictive role of ESR1 status for postmenopausal patients with endocrine-responsive early breast cancer in the Danish cohort of the BIG 1-98 trial. Ann Oncol 2012; 23:1138-1144. [PMID: 21986093 PMCID: PMC3335246 DOI: 10.1093/annonc/mdr438] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2011] [Revised: 08/10/2011] [Accepted: 08/19/2011] [Indexed: 11/12/2022] Open
Abstract
BACKGROUND Estrogen Receptor 1 (ESR1) aberrations may be associated with expression of estrogen receptor (ER) or progesterone receptor (PgR), human epidermal growth factor receptor-2 (HER2) or Ki-67 labeling index and prognosis. PATIENTS AND METHODS ESR1 was assessed in 1129 (81%) of 1396 postmenopausal Danish women with early breast cancer randomly assigned to receive 5 years of letrozole, tamoxifen or a sequence of these agents in the Breast International Group 1-98 trial and who had ER ≥ 1% after central review. RESULTS By FISH, 13.6% of patients had an ESR1-to-Centromere-6 (CEN-6) ratio ≥ 2 (amplified), and 4.2% had ESR1-to-CEN-6 ratio <0.8 (deleted). Deletion of ESR1 was associated with significantly lower levels of ER (P < 0.0001) and PgR (P = 0.02) and more frequent HER2 amplification. ESR1 deletion or amplification was associated with higher-Ki-67 than ESR1-normal tumors. Overall, there was no evidence of heterogeneity of disease-free survival (DFS) or in treatment effect according to ESR1 status. However, significant differences in DFS were observed for subsets based on a combination of ESR1 and HER2 status (P = 0.02). CONCLUSIONS ESR1 aberrations were associated with HER2 status, Ki-67 labeling index and ER and PgR levels. When combined with HER2, ESR1 may be prognostic but should not be used for endocrine treatment selection in postmenopausal women with endocrine-responsive early breast cancer.
Collapse
Affiliation(s)
- B Ejlertsen
- Danish Breast Cancer Cooperative Group Statistical Center; Department of Oncology, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark.
| | - J Aldridge
- International Breast Cancer Study Group Statistical Center, Department of Biostatistics and Computational Biology, Dana-Farber Cancer Institute, Boston, USA
| | | | - M M Regan
- International Breast Cancer Study Group Statistical Center, Department of Biostatistics and Computational Biology, Dana-Farber Cancer Institute, Boston, USA; Department of Biostatistics, Harvard School of Public Health; Department of Medicine, Harvard Medical School, Boston, USA
| | - K L Henriksen
- Department of Breast Cancer Research, Institute of Cancer Biology, Danish Cancer Society, Copenhagen, Denmark
| | - A E Lykkesfeldt
- Department of Breast Cancer Research, Institute of Cancer Biology, Danish Cancer Society, Copenhagen, Denmark
| | | | - R D Gelber
- International Breast Cancer Study Group Statistical Center, Department of Biostatistics and Computational Biology, Dana-Farber Cancer Institute, Boston, USA; Department of Biostatistics, Harvard School of Public Health; Department of Medicine, Harvard Medical School, Boston, USA; International Breast Cancer Study Group Statistical Center, Frontier Science and Technology Research Foundation, Boston, USA
| | - K N Price
- International Breast Cancer Study Group Statistical Center, Department of Biostatistics and Computational Biology, Dana-Farber Cancer Institute, Boston, USA; International Breast Cancer Study Group Statistical Center, Frontier Science and Technology Research Foundation, Boston, USA
| | - B B Rasmussen
- Department of Pathology, Herlev Hospital, Copenhagen University Hospital, Herlev, Denmark
| | - G Viale
- Division of Pathology and Laboratory Medicine, International Breast Cancer Study Group Pathology Review Office, European Institute of Oncology, University of Milan, Milan, Italy
| | - H Mouridsen
- Danish Breast Cancer Cooperative Group Statistical Center; Department of Oncology, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark
| |
Collapse
|
78
|
Timmerman KL, West JN, Markofski MM, Dhanani S, Rasmussen BB, Ckoksi KB, Barbagelata NA, Volpi E. Chronic Heart Failure is Associated with Elevated Skeletal Muscle Inflammation and Toll‐Like Receptor 4 Signaling. FASEB J 2012. [DOI: 10.1096/fasebj.26.1_supplement.835.12] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Kyle L Timmerman
- Nutrition and MetabolismUniversity of Texas Medical BranchGalvestonTX
| | - Jeremiah N West
- Nutrition and MetabolismUniversity of Texas Medical BranchGalvestonTX
| | | | - Shaheen Dhanani
- Sealy Center on AgingUniversity of Texas Medical BranchGalvestonTX
| | - Blake B Rasmussen
- Nutrition and MetabolismUniversity of Texas Medical BranchGalvestonTX
| | | | | | - Elena Volpi
- Internal MedicineUniversity of Texas Medical BranchGalvestonTX
| |
Collapse
|
79
|
Drummond MJ, Timmerman KL, Markofski MM, Walker DK, Dickinson JM, Jamaluddin M, Rasmussen BB, Volpi E. Short‐term bed rest increases inflammation as evidenced by elevated TLR4, NFκB1 and IL6 expression in skeletal muscle of older adults. FASEB J 2012. [DOI: 10.1096/fasebj.26.1_supplement.715.2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | - Kyle L Timmerman
- Nutrition & MetabolismUniversity of Texas Medical BranchGalvestonTX
| | | | - Dillon K Walker
- Rehabilitation SciencesUniversity of Texas Medical BranchGalvestonTX
| | - Jared M Dickinson
- Rehabilitation SciencesUniversity of Texas Medical BranchGalvestonTX
| | - Mohammad Jamaluddin
- Institute for Translational SciencesUniversity of Texas Medical BranchGalvestonTX
| | | | - Elena Volpi
- Internal MedicineUniversity of Texas Medical BranchGalvestonTX
| |
Collapse
|
80
|
Dickinson JM, Drummond MJ, Fry CS, Gundermann DM, Walker DK, Volpi E, Rasmussen BB. Rapamycin administration does not impair basal protein metabolism in human skeletal muscle. FASEB J 2012. [DOI: 10.1096/fasebj.26.1_supplement.1075.3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | | | | | | | | | - Elena Volpi
- University of Texas Medical BranchGalvestonTX
| | | |
Collapse
|
81
|
Reidy P, Walker DK, Dickinson JM, Gundermann DM, Drummond MJ, Timmerman KL, Fry CS, Cope M, Mukherkea R, Volpi E, Rasmussen BB. Effect of protein blend vs whey protein ingestion on muscle protein synthesis following resistance exercise. FASEB J 2012. [DOI: 10.1096/fasebj.26.1_supplement.1013.9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Paul Reidy
- Nutrition and MetabolismUniversity of Texas Medical BranchGalvestonTX
| | - Dillon K Walker
- Nutrition and MetabolismUniversity of Texas Medical BranchGalvestonTX
| | - Jared M Dickinson
- Nutrition and MetabolismUniversity of Texas Medical BranchGalvestonTX
| | | | - Micah J Drummond
- Nutrition and MetabolismUniversity of Texas Medical BranchGalvestonTX
| | - Kyle L Timmerman
- Nutrition and MetabolismUniversity of Texas Medical BranchGalvestonTX
| | - Chris S Fry
- Nutrition and MetabolismUniversity of Texas Medical BranchGalvestonTX
| | | | | | - Elena Volpi
- Internal MedicineUniversity of Texas Medical BranchGalvestonTX
| | - Blake B Rasmussen
- Nutrition and MetabolismUniversity of Texas Medical BranchGalvestonTX
| |
Collapse
|
82
|
Dickinson JM, Gundermann DM, Walker DK, Reidy PT, Drummond MJ, Arora M, Volpi E, Rasmussen BB. Influence of excess postexercise leucine ingestion on mTORC1 signaling and gene expression in skeletal muscle of older men: a 24 hr time‐course. FASEB J 2012. [DOI: 10.1096/fasebj.26.1_supplement.42.8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | | | | | | | | | - Mohit Arora
- University of Texas Medical BranchGalvestonTX
| | - Elena Volpi
- University of Texas Medical BranchGalvestonTX
| | | |
Collapse
|
83
|
Gundermann DM, Dickinson JM, Fry CS, Walker DK, Volpi E, Rasmussen BB. Inhibition of Glycolysis and mTORC1 activation in Human Skeletal Muscle with Blood Flow Restriction Exercise. FASEB J 2012. [DOI: 10.1096/fasebj.26.1_supplement.1076.3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | - Jared M Dickinson
- Nutrition and MetabolismUniversity of Texas Medicdal BranchGalvestonTX
| | - Christopher S Fry
- Nutrition and MetabolismUniversity of Texas Medicdal BranchGalvestonTX
| | - Dillon K Walker
- Nutrition and MetabolismUniversity of Texas Medicdal BranchGalvestonTX
| | - Elena Volpi
- Internal MedicineUniversity of Texas Medicdal BranchGalvestonTX
| | - Blake B Rasmussen
- Nutrition and MetabolismUniversity of Texas Medicdal BranchGalvestonTX
| |
Collapse
|
84
|
Markofski MM, Timmerman KL, Reidy PT, Dickinson JM, Walker DK, Timmerman JZ, Rasmussen BB, Volpi E. Acute aerobic exercise increases AdipoR1 and RAGE proteins and decreases HSP60 protein in skeletal muscle of physically inactive older adults. FASEB J 2012. [DOI: 10.1096/fasebj.26.1_supplement.1142.5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | - Kyle L Timmerman
- Nutrition and MetabolismUniversity of Texas Medical BranchGalvestonTX
| | - Paul T Reidy
- Rehabilitation SciencesUniversity of Texas Medical BranchGalvestonTX
| | - Jared M Dickinson
- Rehabilitation SciencesUniversity of Texas Medical BranchGalvestonTX
| | - Dillon K Walker
- Rehabilitation SciencesUniversity of Texas Medical BranchGalvestonTX
| | | | - Blake B Rasmussen
- Nutrition and MetabolismUniversity of Texas Medical BranchGalvestonTX
| | - Elena Volpi
- Sealy Center on AgingUniversity of Texas Medical BranchGalvestonTX
- Internal MedicineUniversity of Texas Medical BranchGalvestonTX
| |
Collapse
|
85
|
Markofski MM, Timmerman KL, Fujita S, Fry CS, Glynn EL, Drummond MJ, Dickinson JM, Reidy PT, Gundermann DM, Rasmussen BB, Volpi E. Basal muscle protein synthesis is unaffected by sex in young and older adults. FASEB J 2012. [DOI: 10.1096/fasebj.26.1_supplement.42.6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | | | | | | | | | | | | | | | | | | | - Elena Volpi
- University of Texas Medical BranchGalvestonTX
| |
Collapse
|
86
|
Walker DK, Dickinson JM, Timmerman KL, Drummond MJ, Reidy PT, Fry CS, Gundermann DM, Rasmussen BB. Exercise, amino acids, and aging in the control of human muscle protein synthesis. Med Sci Sports Exerc 2012; 43:2249-58. [PMID: 21606874 DOI: 10.1249/mss.0b013e318223b037] [Citation(s) in RCA: 97] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
In this review, we discuss recent research in the field of human skeletal muscle protein metabolism characterizing the acute regulation of mammalian target of rapamycin complex (mTORC) 1 signaling and muscle protein synthesis (MPS) by exercise, amino acid nutrition, and aging. Resistance exercise performed in the fasted state stimulates mixed MPS within 1 h after exercise, which can remain elevated for 48 h. We demonstrate that the activation of mTORC1 signaling (and subsequently enhanced translation initiation) is required for the contraction-induced increase in MPS. In comparison, low-intensity blood flow restriction (BFR) exercise stimulates MPS and mTORC1 signaling to an extent similar to traditional, high-intensity resistance exercise. We also show that mTORC1 signaling is required for the essential amino acid (EAA)-induced increase in MPS. Ingestion of EAAs (or protein) shortly after resistance exercise enhances MPS and mTORC1 signaling compared with resistance exercise or EAAs alone. In older adults, the ability of the skeletal muscle to respond to anabolic stimuli is impaired. For example, in response to an acute bout of resistance exercise, older adults are less able to activate mTORC1 or increase MPS during the first 24 h of postexercise recovery. However, BFR exercise can overcome this impairment. Aging is not associated with a reduced response to EAAs provided the EAA content is sufficient. Therefore, we propose that exercise combined with EAA should be effective not only in improving muscle repair and growth in response to training in athletes, but that strategies such as EAA combined with resistance exercise (or BFR exercise) may be very useful as a countermeasure for sarcopenia and other clinical conditions associated with muscle wasting.
Collapse
Affiliation(s)
- Dillon K Walker
- Department of Nutrition & Metabolism, University of Texas Medical Branch, Galveston, TX 77555-1144, USA
| | | | | | | | | | | | | | | |
Collapse
|
87
|
Gundermann DM, Fry CS, Dickinson JM, Walker DK, Timmerman KL, Drummond MJ, Volpi E, Rasmussen BB. Reactive hyperemia is not responsible for stimulating muscle protein synthesis following blood flow restriction exercise. J Appl Physiol (1985) 2012; 112:1520-8. [PMID: 22362401 DOI: 10.1152/japplphysiol.01267.2011] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Blood flow restriction (BFR) to contracting skeletal muscle during low-intensity resistance exercise training increases muscle strength and size in humans. However, the mechanism(s) underlying these effects are largely unknown. We have previously shown that mammalian target of rapamycin complex 1 (mTORC1) signaling and muscle protein synthesis (MPS) are stimulated following an acute bout of BFR exercise. The purpose of this study was to test the hypothesis that reactive hyperemia is the mechanism responsible for stimulating mTORC1 signaling and MPS following BFR exercise. Six young men (24 ± 2 yr) were used in a randomized crossover study consisting of two exercise trials: low-intensity resistance exercise with BFR (BFR trial) and low-intensity resistance exercise with sodium nitroprusside (SNP), a pharmacological vasodilator infusion into the femoral artery immediately after exercise to simulate the reactive hyperemia response after BFR exercise (SNP trial). Postexercise mixed-muscle fractional synthetic rate from the vastus lateralis increased by 49% in the BFR trial (P < 0.05) with no change in the SNP trial (P > 0.05). BFR exercise increased the phosphorylation of mTOR, S6 kinase 1, ribosomal protein S6, ERK1/2, and Mnk1-interacting kinase 1 (P < 0.05) with no changes in mTORC1 signaling in the SNP trial (P > 0.05). We conclude that reactive hyperemia is not a primary mechanism for BFR exercise-induced mTORC1 signaling and MPS. Further research is necessary to elucidate the cellular mechanism(s) responsible for the increase in mTOR signaling, MPS, and hypertrophy following acute and chronic BFR exercise.
Collapse
Affiliation(s)
- David M Gundermann
- The Univ. of Texas Medical Branch, Dept. of Nutrition and Metabolism, Division of Rehabilitation Sciences, 301 Univ. Blvd., Galveston, TX 77555-1124, USA
| | | | | | | | | | | | | | | |
Collapse
|
88
|
Abstract
The loss of lean muscle mass occurring with advancing age is termed sarcopenia. This condition often leads to a concomitant loss of strength, increased frailty and risk of falls and an overall loss of functional independence in the elderly. Muscle protein metabolism is a dynamic process characterized by the balance between the synthesis and breakdown of muscle proteins. A disturbance of this equilibrium can lead to the loss of muscle mass, and a perturbation of muscle protein turnover with aging has been proposed to play a role in the development of sarcopenia. However, basal muscle protein synthesis and breakdown rates do not differ between young and old adults, which has led to the hypothesis that older adults are resistant to anabolic stimuli. In support of this hypothesis, older adults have either no response or a blunted response to nutrients, insulin and resistance exercise, and this anabolic resistance is likely a key factor in the loss of skeletal muscle mass with aging. Recent studies have investigated potential interventions to overcome this anabolic resistance. In particular, combining resistance exercise with essential amino acid supplementation restores the muscle protein anabolic response in older men. The novel rehabilitation technique of performing light resistance exercise during blood flow restriction was also successful in overcoming the anabolic resistance to exercise. Future research is needed to determine whether these novel interventions will be successful in preventing sarcopenia and improving muscle strength and function in older adults.
Collapse
Affiliation(s)
- Christopher S. Fry
- Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, Texas, U.S.A
| | - Blake B. Rasmussen
- Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, Texas, U.S.A
- Department of Physical Therapy, University of Texas Medical Branch, Galveston, Texas, U.S.A
- Sealy Center on Aging, University of Texas Medical Branch, Galveston, Texas, U.S.A
| |
Collapse
|
89
|
Affiliation(s)
- Blake B Rasmussen
- Department of Physical Therapy, Division of Rehabilitation Sciences, and the Sealy Centre on Aging, University ofTexas Medical Branch, Galveston, TX, USA.
| |
Collapse
|
90
|
Dickinson JM, Fry CS, Drummond MJ, Gundermann DM, Walker DK, Glynn EL, Timmerman KL, Dhanani S, Volpi E, Rasmussen BB. Mammalian target of rapamycin complex 1 activation is required for the stimulation of human skeletal muscle protein synthesis by essential amino acids. J Nutr 2011; 141:856-62. [PMID: 21430254 PMCID: PMC3077888 DOI: 10.3945/jn.111.139485] [Citation(s) in RCA: 190] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
The relationship between mammalian target of rapamycin complex 1 (mTORC1) signaling and muscle protein synthesis during instances of amino acid surplus in humans is based solely on correlational data. Therefore, the goal of this study was to use a mechanistic approach specifically designed to determine whether increased mTORC1 activation is requisite for the stimulation of muscle protein synthesis following L-essential amino acid (EAA) ingestion in humans. Examination of muscle protein synthesis and signaling were performed on vastus lateralis muscle biopsies obtained from 8 young (25 ± 2 y) individuals who were studied prior to and following ingestion of 10 g of EAA during 2 separate trials in a randomized, counterbalanced design. The trials were identical except during 1 trial, participants were administered a single oral dose of a potent mTORC1 inhibitor (rapamycin) prior to EAA ingestion. In response to EAA ingestion, an ~60% increase in muscle protein synthesis was observed during the control trial, concomitant with increased phosphorylation of mTOR (Ser(2448)), ribosomal S6 kinase 1 (Thr(389)), and eukaryotic initiation factor 4E binding protein 1 (Thr(37/46)). In contrast, prior administration of rapamycin completely blocked the increase in muscle protein synthesis and blocked or attenuated activation of mTORC1-signaling proteins. The inhibition of muscle protein synthesis and signaling was not due to differences in either extracellular or intracellular amino acid availability, because these variables were similar between trials. These data support a fundamental role for mTORC1 activation as a key regulator of human muscle protein synthesis in response to increased EAA availability. This information will be useful in the development of evidence-based nutritional therapies targeting mTORC1 to counteract muscle wasting associated with numerous clinical conditions.
Collapse
Affiliation(s)
- Jared M. Dickinson
- Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, TX 77555
| | - Christopher S. Fry
- Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, TX 77555
| | - Micah J. Drummond
- Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, TX 77555,Sealy Center on Aging, University of Texas Medical Branch, Galveston, TX 77555
| | - David M. Gundermann
- Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, TX 77555
| | - Dillon K. Walker
- Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, TX 77555
| | - Erin L. Glynn
- Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, TX 77555
| | - Kyle L. Timmerman
- Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, TX 77555,Sealy Center on Aging, University of Texas Medical Branch, Galveston, TX 77555
| | - Shaheen Dhanani
- Sealy Center on Aging, University of Texas Medical Branch, Galveston, TX 77555
| | - Elena Volpi
- Department of Internal Medicine, and University of Texas Medical Branch, Galveston, TX 77555,Sealy Center on Aging, University of Texas Medical Branch, Galveston, TX 77555
| | - Blake B. Rasmussen
- Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, TX 77555,Sealy Center on Aging, University of Texas Medical Branch, Galveston, TX 77555,To whom correspondence should be addressed. E-mail:
| |
Collapse
|
91
|
Drummond MJ, Fry CS, Glynn EL, Timmerman KL, Dickinson JM, Walker DK, Gundermann DM, Volpi E, Rasmussen BB. Skeletal muscle amino acid transporter expression is increased in young and older adults following resistance exercise. J Appl Physiol (1985) 2011; 111:135-42. [PMID: 21527663 DOI: 10.1152/japplphysiol.01408.2010] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Amino acid transporters and mammalian target of rapamycin complex 1 (mTORC1) signaling are important contributors to muscle protein anabolism. Aging is associated with reduced mTORC1 signaling following resistance exercise, but the role of amino acid transporters is unknown. Young (n = 13; 28 ± 2 yr) and older (n = 13; 68 ± 2 yr) subjects performed a bout of resistance exercise. Skeletal muscle biopsies (vastus lateralis) were obtained at basal and 3, 6, and 24 h postexercise and were analyzed for amino acid transporter mRNA and protein expression and regulators of amino acid transporter transcription utilizing real-time PCR and Western blotting. We found that basal amino acid transporter expression was similar in young and older adults (P > 0.05). Exercise increased L-type amino acid transporter 1/solute-linked carrier (SLC) 7A5, CD98/SLC3A2, sodium-coupled neutral amino acid transporter 2/SLC38A2, proton-assisted amino acid transporter 1/SLC36A1, and cationic amino acid transporter 1/SLC7A1 mRNA expression in both young and older adults (P < 0.05). L-type amino acid transporter 1 and CD98 protein increased only in younger adults (P < 0.05). eukaryotic initiation factor 2 α-subunit (S52) increased similarly in young and older adults postexercise (P < 0.05). Ribosomal protein S6 (S240/244) and activating transcription factor 4 nuclear protein expression tended to be higher in the young, while nuclear signal transducer and activator of transcription 3 (STAT3) (Y705) was higher in the older subjects postexercise (P < 0.05). These results suggest that the rapid upregulation of amino acid transporter expression following resistance exercise may be regulated differently between the age groups, but involves a combination of mTORC1, activating transcription factor 4, eukaryotic initiation factor 2 α-subunit, and STAT3. We propose an increase in amino acid transporter expression may contribute to enhanced amino acid sensitivity following exercise in young and older adults. In older adults, the increased nuclear STAT3 phosphorylation may be indicative of an exercise-induced stress response, perhaps to export amino acids from muscle cells.
Collapse
Affiliation(s)
- Micah J Drummond
- University of Texas Medical Branch, Department of Nutrition and Metabolism, Division of Rehabilitation Sciences, Sealy Center on Aging, 301 Univ. Blvd., Galveston, TX 77555-1144, USA.
| | | | | | | | | | | | | | | | | |
Collapse
|
92
|
Markofski MM, Timmerman KL, Fry CS, Dickinson JM, Walker DK, Rasmussen BB, Volpi E. Nutritional predictors of muscle protein metabolism and function in older adults. FASEB J 2011. [DOI: 10.1096/fasebj.25.1_supplement.983.18] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | | | | | | | | | | | - Elena Volpi
- Internal MedicineUniversity of Texas Medical BranchGalvestonTX
- Sealy Center on Aging
| |
Collapse
|
93
|
Dickinson JM, Drummond MJ, Fry CS, Glynn EL, Gundermann DM, Walker DK, Timmerman KL, Volpi E, Rasmussen BB. High levels of leucine are required for the upregulation of amino acid transporters in human skeletal muscle following essential amino acid ingestion. FASEB J 2011. [DOI: 10.1096/fasebj.25.1_supplement.233.6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | | | | | | | | | | | | | - Elena Volpi
- Sealy Center on AgingUniversity of Texas Medical BranchGalvestonTX
| | | |
Collapse
|
94
|
Gundermann DM, Walker DK, Fry CS, Dickinson JM, Drummond MJ, Volpi E, Rasmussen BB. BFR Exercise Increases S6K1 Phosphorylation in Type‐I and Type‐II Skeletal Muscle Fibers. FASEB J 2011. [DOI: 10.1096/fasebj.25.1_supplement.1064.6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | | | | | | | - Micah J Drummond
- Division of Rehabilitation Sciences
- Department of Physical Therapy
| | - Elena Volpi
- Sealy Center on AgingUniversity of Texas Medical BranchGalvestonTX
| | | |
Collapse
|
95
|
Butteiger DN, Cope M, Liu P, Volpi E, Rasmussen BB, Krul ES. Effects of dietary soy, whey and caseinate blends versus whey or soy alone on skeletal muscle protein synthesis in rats. FASEB J 2011. [DOI: 10.1096/fasebj.25.1_supplement.217.6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | | | - Peter Liu
- Technology & Innovation, Solae, LLcSt. LouisMO
| | - Elena Volpi
- Sealy Center on AgingUniversity of Texas Medical BranchGalvestonTX
| | | | | |
Collapse
|
96
|
Timmerman KL, Markofski MM, Dhanani S, Fry CS, Dickinson JM, Walker DK, Gundermann DM, Rasmussen BB, Volpi E. Isolated pharmacological vasodilation does not stimulate skeletal muscle protein synthesis in healthy older adults. FASEB J 2011. [DOI: 10.1096/fasebj.25.1_supplement.233.7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | | | | | | | | | | | | | - Blake B Rasmussen
- Rehabilitation Sciences
- Physical TherapyUniversity of Texas Medical BranchGalvestonTX
| | | |
Collapse
|
97
|
Walker DK, Fry CS, Drummond MJ, Dickinson JM, Gundermann DM, Timmerman KL, Volpi E, Rasmussen BB. Skeletal muscle satellite cell content following acute resistance exercise with or without essential amino acid ingestion in young adults. FASEB J 2011. [DOI: 10.1096/fasebj.25.1_supplement.983.16] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | | | | | | | | | | | - Elena Volpi
- Sealy Center on AgingUniversity of Texas Medical BranchGalvestonTX
| | | |
Collapse
|
98
|
Fry CS, Drummond MJ, Glynn EL, Dickinson JM, Gundermann DM, Timmerman KL, Walker DK, Dhanani S, Volpi E, Rasmussen BB. Aging impairs contraction-induced human skeletal muscle mTORC1 signaling and protein synthesis. Skelet Muscle 2011; 1:11. [PMID: 21798089 PMCID: PMC3156634 DOI: 10.1186/2044-5040-1-11] [Citation(s) in RCA: 251] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2010] [Accepted: 03/02/2011] [Indexed: 12/19/2022] Open
Abstract
Background Sarcopenia, the loss of skeletal muscle mass during aging, increases the risk for falls and dependency. Resistance exercise (RE) training is an effective treatment to improve muscle mass and strength in older adults, but aging is associated with a smaller amount of training-induced hypertrophy. This may be due in part to an inability to stimulate muscle-protein synthesis (MPS) after an acute bout of RE. We hypothesized that older adults would have impaired mammalian target of rapamycin complex (mTORC)1 signaling and MPS response compared with young adults after acute RE. Methods We measured intracellular signaling and MPS in 16 older (mean 70 ± 2 years) and 16 younger (27 ± 2 years) subjects. Muscle biopsies were sampled at baseline and at 3, 6 and 24 hr after exercise. Phosphorylation of regulatory signaling proteins and MPS were determined on successive muscle biopsies by immunoblotting and stable isotopic tracer techniques, respectively. Results Increased phosphorylation was seen only in the younger group (P< 0.05) for several key signaling proteins after exercise, including mammalian target of rapamycin (mTOR), ribosomal S6 kinase (S6K)1, eukaryotic initiation factor 4E-binding protein (4E-BP)1 and extracellular signal-regulated kinase (ERK)1/2, with no changes seen in the older group (P >0.05). After exercise, MPS increased from baseline only in the younger group (P< 0.05), with MPS being significantly greater than that in the older group (P <0.05). Conclusions We conclude that aging impairs contraction-induced human skeletal muscle mTORC1 signaling and protein synthesis. These age-related differences may contribute to the blunted hypertrophic response seen after resistance-exercise training in older adults, and highlight the mTORC1 pathway as a key therapeutic target to prevent sarcopenia.
Collapse
Affiliation(s)
- Christopher S Fry
- Division of Rehabilitation Sciences, University of Texas Medical Branch, Galveston, Texas, 77550 USA.
| | | | | | | | | | | | | | | | | | | |
Collapse
|
99
|
Viale G, Regan MM, Dell'Orto P, Mastropasqua MG, Maiorano E, Rasmussen BB, MacGrogan G, Forbes JF, Paridaens RJ, Colleoni M, Láng I, Thürlimann B, Mouridsen H, Mauriac L, Gelber RD, Price KN, Goldhirsch A, Gusterson BA, Coates AS. Which patients benefit most from adjuvant aromatase inhibitors? Results using a composite measure of prognostic risk in the BIG 1-98 randomized trial. Ann Oncol 2011; 22:2201-7. [PMID: 21335417 DOI: 10.1093/annonc/mdq738] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
BACKGROUND On average, aromatase inhibitors are better than tamoxifen when used as initial or sequential therapy for postmenopausal women with endocrine-responsive early breast cancer. Because there may be contraindications to their use based on side-effects or cost, we investigated subgroups in which aromatase inhibitors may be more or less important. PATIENTS AND METHODS Breast International Group 1-98 trial randomized 6182 women among four groups comparing letrozole and tamoxifen with sequences of each agent; 5177 (84%) had centrally confirmed estrogen receptor (ER) positivity. We assessed whether centrally determined ER, progesterone receptor (PgR), human epidermal growth factor receptor 2, and Ki-67 labeling index, alone or in combination with other prognostic features, predicted the magnitude of letrozole effectiveness compared with either sequence or tamoxifen monotherapy. RESULTS Individually, none of the markers significantly predicted differential treatment effects. Subpopulation treatment effect pattern plot analysis of a composite measure of prognostic risk revealed three patterns. Estimated 5-year disease-free survival for letrozole monotherapy, letrozole→tamoxifen, tamoxifen→letrozole, and tamoxifen monotherapy were 96%, 94%, 93%, and 94%, respectively, for patients at lowest risk; 90%, 91%, 93%, and 86%, respectively, for patients at intermediate risk; and 80%, 76%, 74%, and 69%, respectively, for patients at highest risk. CONCLUSION A composite measure of risk informs treatment selection better than individual biomarkers and supports the choice of 5 years of letrozole for patients at highest risk for recurrence.
Collapse
Affiliation(s)
- G Viale
- International Breast Cancer Study Group Central Pathology Office, Division of Pathology and Laboratory Medicine, European Institute of Oncology, University of Milan, Milan, Italy.
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
100
|
Timmerman KL, Rasmussen BB. Does a reduction in anabolic signaling contribute to muscle wasting in chronic heart failure? J Appl Physiol (1985) 2011; 110:869-70. [PMID: 21270349 DOI: 10.1152/japplphysiol.00072.2011] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
|