101
|
Timmerman KL, Volpi E. Endothelial function and the regulation of muscle protein anabolism in older adults. Nutr Metab Cardiovasc Dis 2013; 23 Suppl 1:S44-S50. [PMID: 22902187 PMCID: PMC3597759 DOI: 10.1016/j.numecd.2012.03.013] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/01/2011] [Revised: 03/21/2012] [Accepted: 03/26/2012] [Indexed: 12/19/2022]
Abstract
Sarcopenia, the loss of skeletal muscle mass and function with aging, is a major contributor to frailty and morbidity in older adults. Recent evidence has emerged suggesting that endothelial dysfunction and insulin resistance of muscle protein metabolism may significantly contribute to the development of sarcopenia. In this article we review: 1) recent studies and theories on the regulation of skeletal muscle protein balance in older adults; 2) the link between insulin resistance of muscle protein synthesis and endothelial dysfunction in aging; 3) mechanisms for impaired endothelial responsiveness in aging; and 4) potential treatments that may restore the endothelial responsiveness and muscle protein anabolic sensitivity in older adults.
Collapse
|
102
|
Bednar T, Heyde CE, Bednar G, Nguyen D, Volpi E, Przkora R. Kyphoplasty for vertebral augmentation in the elderly with osteoporotic vertebral compression fractures: scenarios and review of recent studies. Clin Ther 2013; 35:1721-7. [PMID: 24139093 DOI: 10.1016/j.clinthera.2013.09.016] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2013] [Revised: 09/19/2013] [Accepted: 09/20/2013] [Indexed: 11/25/2022]
Abstract
BACKGROUND Vertebral compression fractures caused by osteoporosis are among the most common fractures in the elderly. The treatment focuses on pain control, maintenance of independence, and management of the osteoporosis. Elderly patients often encounter adverse effects to pain medications, do not tolerate bed rest, and are not ideal candidates for invasive spinal reconstructive surgery. Percutaneous vertebral augmentation (vertebroplasty or kyphoplasty) has become popular as a less-invasive alternative. However, studies have questioned the effectiveness of these procedures. METHODS The authors conducted a MEDLINE search using relevant search terms including osteoporosis, osteoporotic vertebral compression fracture, elderly, kyphoplasty and vertebroplasty. CASE SUMMARY/RESULTS Two elderly patients presented with a fracture of their third and first lumbar vertebral body, respectively. One patient progressed well with conservative treatment, whereas the other patient was hospitalized secondary to pain after conservative measures failed to offer improvement. The hospitalized patient subsequently opted for a kyphoplasty and was able to resume his normal daily activities after the procedure. CONCLUSIONS Selecting patients on an individual case-by-case basis can optimize the effectiveness and outcomes of a vertebral augmentation. This process includes the documentation of an osteoporotic vertebral compression fracture with the aide of imaging studies, including the acuity of the fracture as well as the correlation with the physical examination findings. Patients who are functional and improving under a conservative regimen are not candidates for kyphoplasty. However, if the conservative management is not successful after 4 to 6 weeks and the patient is at risk to become bedridden, an augmentation should be considered. A kyphoplasty procedure may be preferred over vertebroplasty, given the lower risk profile and better outcomes regarding spinal alignment.
Collapse
|
103
|
Dickinson JM, Volpi E, Rasmussen BB. Exercise and nutrition to target protein synthesis impairments in aging skeletal muscle. Exerc Sport Sci Rev 2013; 41:216-23. [PMID: 23873131 PMCID: PMC3790587 DOI: 10.1097/jes.0b013e3182a4e699] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The loss of skeletal muscle size and function with aging and sarcopenia may be related, in part, to an age-related muscle protein synthesis impairment. In this review, we discuss to what extent aging affects skeletal muscle protein synthesis and how nutrition and exercise can be used strategically to overcome age-related protein synthesis impairments and slow the progression of sarcopenia.
Collapse
|
104
|
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] [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
|
105
|
Bauer J, Biolo G, Cederholm T, Cesari M, Cruz-Jentoft AJ, Morley JE, Phillips S, Sieber C, Stehle P, Teta D, Visvanathan R, Volpi E, Boirie Y. Evidence-Based Recommendations for Optimal Dietary Protein Intake in Older People: A Position Paper From the PROT-AGE Study Group. J Am Med Dir Assoc 2013; 14:542-59. [DOI: 10.1016/j.jamda.2013.05.021] [Citation(s) in RCA: 1068] [Impact Index Per Article: 97.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2013] [Accepted: 05/29/2013] [Indexed: 12/20/2022]
|
106
|
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] [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
|
107
|
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] [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
|
108
|
Chondronikola M, Hurren NM, Porter G, Annamalai P, Volpi E, Borsheim E, Sidossis L. Effect of prolonged, mild cold exposure on metabolic regulation in insulin resistant overweight and obese men. FASEB J 2013. [DOI: 10.1096/fasebj.27.1_supplement.1154.20] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
|
109
|
Hurren NM, Porter C, Chondronikola M, Yfanti C, Volpi E, Belalcazar LM, Kinsky M, Sidossis L, Børsheim E. Acute oral amino acid intake increases both secretion and breakdown of very low density lipoprotein‐triacylglycerol. FASEB J 2013. [DOI: 10.1096/fasebj.27.1_supplement.1192.25] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
|
110
|
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] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
|
111
|
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] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
|
112
|
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] [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
|
113
|
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] [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
|
114
|
Volpi E, Campbell WW, Dwyer JT, Johnson MA, Jensen GL, Morley JE, Wolfe RR. Is the optimal level of protein intake for older adults greater than the recommended dietary allowance? J Gerontol A Biol Sci Med Sci 2012. [PMID: 23183903 DOI: 10.1093/gerona/gls229] [Citation(s) in RCA: 244] [Impact Index Per Article: 20.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
BACKGROUND Protein is a macronutrient essential for growth, muscle function, immunity and overall tissue homeostasis. Suboptimal protein intake can significantly impact physical function and overall health in older adults. METHODS This article reviews the literature on the recommendations for protein intake in older adults in light of the new evidence linking protein intake with sarcopenia and physical function. Challenges and opportunities for optimal protein nutrition in older persons are discussed. RESULTS Recent metabolic and epidemiological studies suggest that the current recommendations of protein intake may not be adequate for maintenance of physical function and optimal health in older adults. Methodological limitations and novel concepts in protein nutrition are also discussed. CONCLUSION We conclude that new research and novel research methodologies are necessary to establish the protein needs and optimal patterns of protein intake for older persons.
Collapse
|
115
|
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] [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
|
116
|
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] [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
|
117
|
Matveyenko AV, Liuwantara D, Gurlo T, Kirakossian D, Dalla Man C, Cobelli C, White MF, Copps KD, Volpi E, Fujita S, Butler PC. Pulsatile portal vein insulin delivery enhances hepatic insulin action and signaling. Diabetes 2012; 61:2269-79. [PMID: 22688333 PMCID: PMC3425431 DOI: 10.2337/db11-1462] [Citation(s) in RCA: 117] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Insulin is secreted as discrete insulin secretory bursts at ~5-min intervals into the hepatic portal vein, these pulses being attenuated early in the development of type 1 and type 2 diabetes mellitus (T2DM). Intraportal insulin infusions (pulsatile, constant, or reproducing that in T2DM) indicated that the pattern of pulsatile insulin secretion delivered via the portal vein is important for hepatic insulin action and, therefore, presumably for hepatic insulin signaling. To test this, we examined hepatic insulin signaling in rat livers exposed to the same three patterns of portal vein insulin delivery by use of sequential liver biopsies in anesthetized rats. Intraportal delivery of insulin in a constant versus pulsatile pattern led to delayed and impaired activation of hepatic insulin receptor substrate (IRS)-1 and IRS-2 signaling, impaired activation of downstream insulin signaling effector molecules AKT and Foxo1, and decreased expression of glucokinase (Gck). We further established that hepatic Gck expression is decreased in the HIP rat model of T2DM, a defect that correlated with a progressive defect of pulsatile insulin secretion. We conclude that the physiological pulsatile pattern of insulin delivery is important in hepatic insulin signaling and glycemic control. Hepatic insulin resistance in diabetes is likely in part due to impaired pulsatile insulin secretion.
Collapse
|
118
|
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] [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
|
119
|
Sommer J, Effenberger T, Volpi E, Waetzig GH, Bernhardt M, Suthaus J, Garbers C, Rose-John S, Floss DM, Scheller J. Constitutively active mutant gp130 receptor protein from inflammatory hepatocellular adenoma is inhibited by an anti-gp130 antibody that specifically neutralizes interleukin 11 signaling. J Biol Chem 2012; 287:13743-51. [PMID: 22523320 DOI: 10.1074/jbc.m111.349167] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Ligand-independent constitutively active gp130 mutants were described to be responsible for the development of inflammatory hepatocellular adenomas (IHCAs). These variants had gain-of-function somatic mutations within the extracellular domain 2 (D2) of the gp130 receptor chain. Cytokine-dependent Ba/F3 cells were transduced with the constitutively active variant of gp130 featuring a deletion in the domain 2 from Tyr-186 to Tyr-190 (gp130ΔYY). These cells showed constitutive phosphorylation of signal transducer and activator of transcription-3 (STAT3) and cytokine-independent proliferation. Deletion of the Ig-like domain 1 (D1) of gp130, but not anti-gp130 mAbs directed against D1, abolished constitutive activation of gp130ΔYY, highlighting that this domain is involved in ligand-independent activation of gp130ΔYY. Moreover, soluble variants of gp130 were not able to inhibit the constitutive activation of gp130ΔYY. However, the inhibition of constitutive activation of gp130ΔYY was achieved by the anti-gp130 mAb B-P4, which specifically inhibits gp130 signaling by IL-11 but not by other IL-6 type cytokines. IL-11 but not IL-6 levels were found previously to be up-regulated in IHCAs, suggesting that mutations in gp130 are leading to IL-11-like signaling. The mAb B-P4 might be a valuable tool to inhibit the constitutive activation of naturally occurring gp130 mutants in IHCAs and rare cases of gp130-associated hepatocellular carcinoma.
Collapse
|
120
|
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] [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
|
121
|
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] [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
|
122
|
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] [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
|
123
|
Mamerow MM, Mettler JA, English KL, Layman DK, Volpi E, Paddon-Jones D. Protein Distribution Effect on Indices of Satiety. FASEB J 2012. [DOI: 10.1096/fasebj.26.1_supplement.1013.5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
|
124
|
Mamerow MM, Mettler JA, English KL, Layman DK, Volpi E, Paddon-Jones D. Muscle protein synthesis is suboptimal following a typical carbohydrate‐rich breakfast. FASEB J 2012. [DOI: 10.1096/fasebj.26.1_supplement.1013.7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
|
125
|
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] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
|