Downregulation of let-7 by Electrical Acupuncture Increases Protein Synthesis in Mice

BackgroundOur previous study found that acupuncture with low frequency electrical stimulation (Acu/LFES) prevents muscle atrophy by attenuation of protein degradation in mice. The current study examines the impact of Acu/LFES on protein synthesis.MethodC57/BL6 mice received Acu/LFES treatment on hindlimb for 30 min once. Acu/LFES points were selected by WHO Standard Acupuncture Nomenclature and electric stimulation applied using an SDZ-II Electronic acupuncture instrument. Muscle protein synthesis was measured by the surface-sensing of translation (SUnSET) assay. Exosomes were isolated using serial centrifugation and concentration and size of the collected exosomes were measured using a NanoSight instrument. The mature microRNA library in serum exosomes was validated using a High Sensitivity DNA chip.ResultsProtein synthesis was enhanced in the both hindlimb and forelimb muscles. Blocking exosome secretion with GW4869 decreased the Acu/LFES-induced increases in protein synthesis. MicroRNA-deep sequencing demonstrated that four members of the Let-7 miRNA family were significantly decreased in serum exosomes. Real time qPCR further verified Acu/LFES-mediated decreases of let-7c-5p in serum exosomes and skeletal muscles. In cultured C2C12 myotubes, inhibition of let-7c not only increased protein synthesis, but also enhanced protein abundance of Igf1 and Igf1 receptors. Using a luciferase reporter assay, we demonstrated that let-7 directly inhibits Igf1.ConclusionAcu/LFES on hindlimb decreases let-7-5p leading to upregulation of the Igf1 signaling and increasing protein synthesis in both hindlimb and forelimb skeletal muscles. This provides a new understanding of how the electrical acupuncture treatment can positively influence muscle health.

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Electrical acupuncture increases protein synthesis through downregulation of let-7

10.21203/rs.2.20415/v1 ◽

2020 ◽

Author(s):

Zhen Su ◽

Manshu Yu ◽

Akihiro Kuma ◽

Faten Hassounah ◽

Fuying Ma ◽

...

Keyword(s):

Protein Synthesis ◽

Deep Sequencing ◽

Low Frequency ◽

High Sensitivity ◽

Luciferase Reporter ◽

C2c12 Myotubes ◽

Triceps Brachii ◽

Student’S T ◽

Igf1 Receptor ◽

Serum Exosomes

Abstract Background: Our previous study found that acupuncture with low frequency electrical stimulation (Acu/LFES) prevents muscle atrophy by attenuation of protein degradation in chronic kidney disease. However, it is not clear whether Acu/LFES can increase protein synthesis in skeletal muscle. Methods: Normal C57/BL6 mice were given Acu/LFES treatment, applied for 30 minutes once. Gastrocnemius and triceps brachii muscles were harvested at 0, 6, 24, 48 and 72 hours after treatment. Protein synthesis was measured by the surface sensing of translation (SUnSET) assay. Exosomes were harvested using serial centrifugations and subjected to microRNA deep sequencing. The mature microRNA library was validated using a High Sensitivity DNA chip. The Student’s t-test and ANOVA were used for statistics. Results: Protein synthesis was enhanced in the both hindlimb (gastrocnemius) and forelimb (triceps brachii) muscles. To identify how exosomes regulate protein synthesis, we performed microRNA deep sequencing in serum exosomes isolated from treated and untreated mice and found that the 34 microRNAs were altered by Acu/LFES. Specifically, five members of the let-7 miRNA family were significantly decreased in the Acu/LFES treated mice. Blocking exosome secretion using GW4869 before treatment decreased the Acu/LFES-induced increases in protein synthesis. This provided evidence that the increased protein synthesis in response to Acu/LFES is exosome mediated. In cultured C2C12 myotubes, overexpressing let-7c-5p resulted in decreased protein synthesis. Conversely, inhibition of let-7c not only increased protein synthesis, but also increased the expression of Igf1, Igf1 receptor, insulin receptor and Igf2 receptor mRNA. In addition, inhibiting let-7c resulted in enhanced protein abundance of Igf1, Igf1 receptor, mTOR and p70S6. In silico searching suggested that let-7 could target Igf1. Using a luciferase reporter assay, we demonstrated that let-7 directly inhibited Igf1. Conclusions: Acu/LFES increases protein synthesis through a mechanism related with exosome secretion. Acu/LFES on hindlimb decreases let-7-5p in serum exosomes leading to upregulation of the Igf1 signaling pathway and increasing protein synthesis in both hindlimb and forelimb skeletal muscles.

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Role of insulin and IGF-I in activation of muscle protein synthesis after oral feeding

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1996.270.4.e614 ◽

1996 ◽

Vol 270 (4) ◽

pp. E614-E620 ◽

Cited By ~ 16

Author(s):

E. Svanberg ◽

H. Zachrisson ◽

C. Ohlsson ◽

B. M. Iresjo ◽

K. G. Lundholm

Keyword(s):

Protein Synthesis ◽

Skeletal Muscles ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Oral Feeding ◽

Myofibrillar Proteins ◽

Diabetic Mice ◽

Igf I ◽

Stimulation Of

The aim was to evaluate the role of insulin and insulin-like growth factor I (IGF-I) in activation of muscle protein synthesis after oral feeding. Synthesis rate of globular and myofibrillar proteins in muscle tissue was quantified by a flooding dose of radioactive phenylalanine. Muscle tissue expression of IGF-I mRNA was measured. Normal (C57 Bl) and diabetic mice (type I and type II) were subjected to an overnight fast (18 h) with subsequent refeeding procedures for 3 h with either oral chow intake or provision of insulin, IGF-I, glucose, and amino acids. Anti-insulin and anti-IGF-I were provided intraperitoneally before oral refeeding in some experiments. An overnight fast reduced synthesis of both globular (38 +/- 3%) and myofibrillar proteins (54 +/- 3%) in skeletal muscles, which was reversed by oral refeeding. Muscle protein synthesis, after starvation/ refeeding, was proportional and similar to changes in skeletal muscle IGF-I mRNA expression. Diabetic mice responded quantitatively similarly to starvation/refeeding in muscle protein synthesis compared with normal mice (C57 Bl). Both anti-insulin and anti-IGF-I attenuated significantly the stimulation of muscle protein synthesis in response to oral feeding, whereas exogenous provision of either insulin or IGF-I to overnight-starved and freely fed mice did not clearly stimulate protein synthesis in skeletal muscles. Our results support the suggestion that insulin and IGF-I either induce or facilitate the protein synthesis machinery in skeletal muscles rather than exerting a true stimulation of the biosynthetic process during feeding.

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Proteasome- and Calpain-Mediated Proteolysis, but Not Autophagy, Is Required for Leucine-Induced Protein Synthesis in C2C12 Myotubes

Physiologia ◽

10.3390/physiologia1010005 ◽

2021 ◽

Vol 1 (1) ◽

pp. 22-33

Author(s):

Shelby C. Osburn ◽

Christopher G. Vann ◽

David D. Church ◽

Arny A. Ferrando ◽

Michael D. Roberts

Keyword(s):

Protein Synthesis ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Muscle Growth ◽

Proteasome Inhibition ◽

Coupled Processes ◽

C2c12 Myotubes ◽

Calpain Inhibitor ◽

Tightly Coupled

Muscle protein synthesis and proteolysis are tightly coupled processes. Given that muscle growth is promoted by increases in net protein balance, it stands to reason that bolstering protein synthesis through amino acids while reducing or inhibiting proteolysis could be a synergistic strategy in enhancing anabolism. However, there is contradictory evidence suggesting that the proper functioning of proteolytic systems in muscle is required for homeostasis. To add clarity to this issue, we sought to determine if inhibiting different proteolytic systems in C2C12 myotubes in conjunction with acute and chronic leucine treatments affected markers of anabolism. In Experiment 1, myotubes underwent 1-h, 6-h, and 24-h treatments with serum and leucine-free DMEM containing the following compounds (n = 6 wells per treatment): (i) DMSO vehicle (CTL), (ii) 2 mM leucine + vehicle (Leu-only), (iii) 2 mM leucine + 40 μM MG132 (20S proteasome inhibitor) (Leu + MG132), (iv) 2 mM leucine + 50 μM calpeptin (calpain inhibitor) (Leu + CALP), and (v) 2 mM leucine + 1 μM 3-methyladenine (autophagy inhibitor) (Leu + 3MA). Protein synthesis levels significantly increased (p < 0.05) in the Leu-only and Leu + 3MA 6-h treatments compared to CTL, and levels were significantly lower in Leu + MG132 and Leu + CALP versus Leu-only and CTL. With 24-h treatments, total protein yield was significantly lower in Leu + MG132 cells versus other treatments. Additionally, the intracellular essential amino acid (EAA) pool was significantly greater in 24-h Leu + MG132 treatments versus other treatments. In a follow-up experiment, myotubes were treated for 48 h with CTL, Leu-only, and Leu + MG132 for morphological assessments. Results indicated Leu + MG132 yielded significantly smaller myotubes compared to CTL and Leu-only. Our data are limited in scope due to the utilization of select proteolysis inhibitors. However, this is the first evidence to suggest proteasome and calpain inhibition with MG132 and CALP, respectively, abrogate leucine-induced protein synthesis in myotubes. Additionally, longer-term Leu + MG132 treatments translated to an atrophy phenotype. Whether or not proteasome inhibition in vivo reduces leucine- or EAA-induced anabolism remains to be determined.

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Human Muscle Protein Synthesis Rates after Intake of Hydrolyzed Porcine-Derived and Cows’ Milk Whey Proteins—A Randomized Controlled Trial

Nutrients ◽

10.3390/nu11050989 ◽

2019 ◽

Vol 11 (5) ◽

pp. 989 ◽

Cited By ~ 3

Author(s):

Bendtsen ◽

Thorning ◽

Reitelseder ◽

Ritz ◽

Hansen ◽

...

Keyword(s):

Protein Synthesis ◽

G Protein ◽

Whey Protein ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Synthesis Rate ◽

Protein Synthesis Rate ◽

Muscle Proteins ◽

Mixed Meal ◽

The Impact

Abstract: Background: Whey protein has been shown to be one of the best proteins to stimulate muscle protein synthesis rate (MPS), but other high quality proteins, e.g., animal/porcine-derived, could have similar effects. Objective: To investigate the effects of hydrolyzed porcine proteins from blood (HPB) and muscle (HPM), in comparison to hydrolyzed whey protein (HW), on MPS after intake of 15 g alone or 30 g protein as part of a mixed meal. We hypothesized that the postprandial MPS would be similar for porcine proteins and whey protein. Design: Eighteen men (mean ± SD age: 24 ± 1 year; BMI: 21.7 ± 0.4 kg/m2) participated in the randomized, double-blind, three-way cross-over study. Subjects consumed the three test products (HPB, HPM and HW) in a random order in two servings at each test day. Serving 1 consisted of a drink with 15 g protein and serving 2 of a drink with 30 g protein together with a mixed meal. A flood-primed continuous infusion of (ring-13C6) phenylalanine was performed and muscle biopsies, blood and urine samples were collected for determination of MPS, muscle free leucine, plasma amino acid concentrations and urea excretion. Results: There were no statistical differences between the MPS measured after consuming 15 g protein alone or 30 g with a mixed meal (p = 0.53) of HPB (0.048 ± 0.007 vs. 0.049 ± 0.008%/h, resp.), HPM (0.063 ± 0.011 vs. 0.062 ± 0.011 %/h, resp.) and HW (0.058 ± 0.007 vs. 0.071 ± 0.013%/h, resp.). However, the impact of protein type on MPS reached statistical tendency (HPB vs. HPM (p = 0.093) and HPB vs. HW (p = 0.067)) with no difference between HPM and HW (p = 0.88). Plasma leucine, branched-chain, essential and total amino acids were generally higher for HPB and HW than HPM (p < 0.01), which reflected their content in the proteins. Muscle-free leucine was higher for HPB than HW and HPM (p < 0.05). Conclusion: Hydrolyzed porcine proteins from blood and muscle resulted in an MPS similar to that of HW, although with a trend for porcine blood proteins to be inferior to muscle proteins and whey. Consequently, these porcine-derived muscle proteins can be used similarly to whey protein to support maintenance of skeletal muscle as part of supplements and ingredients in foods.

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Daily resistance-type exercise stimulates muscle protein synthesis in vivo in young men

Journal of Applied Physiology ◽

10.1152/japplphysiol.00610.2017 ◽

2018 ◽

Vol 124 (1) ◽

pp. 66-75 ◽

Cited By ~ 14

Author(s):

Andrew M. Holwerda ◽

Kevin J. M. Paulussen ◽

Maarten Overkamp ◽

Joey S. J. Smeets ◽

Annemie P. Gijsen ◽

...

Keyword(s):

Protein Synthesis ◽

Exercise Training ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Living Conditions ◽

Deuterated Water ◽

Free Living ◽

The Impact ◽

Free Living Conditions

Resistance-type exercise increases muscle protein synthesis rates during acute postexercise recovery. The impact of resistance-type exercise training on (local) muscle protein synthesis rates under free-living conditions on a day-to-day basis remains unclear. We determined the impact of daily unilateral resistance-type exercise on local myofibrillar protein synthesis rates during a 3-day period. Twelve healthy young men (22 ± 1 yr) were recruited to participate in this study where they performed daily, unilateral resistance-type exercise during a 3-day intervention period. Two days before the exercise training subjects ingested 400 ml deuterated water (2H2O). Additional 50-ml doses of deuterated water were ingested daily during the training period. Saliva and blood samples were collected daily to assess body water and amino acid precursor deuterium enrichments, respectively. Muscle tissue biopsies were collected before and after the 3 days of unilateral resistance-type exercise training from both the exercised and the nonexercised, control leg for the assessment of muscle protein synthesis rates. Deuterated water dosing resulted in a steady-state body water enrichment of 0.70 ± 0.03%. Intramuscular free [2H]alanine enrichment increased up to 1.84 ± 0.06 mole percent excess (MPE) before the exercise training and did not change in both the exercised and control leg during the 3 subsequent exercise training days (2.11 ± 0.11 and 2.19 ± 0.12 MPE, respectively; P > 0.05). Muscle protein synthesis rates averaged 1.984 ± 0.118 and 1.642 ± 0.089%/day in the exercised vs. nonexercised, control leg when assessed over the entire 3-day period ( P < 0.05). Daily resistance-type exercise stimulates (local) muscle protein synthesis in vivo in humans. NEW & NOTEWORTHY This study demonstrates that daily resistance-type exercise stimulates muscle protein synthesis rates in vivo in humans over multiple days. Whereas acute studies have shown that resistance-type exercise increases muscle protein synthesis rates by 50–100%, we observed a lower impact of resistance-type exercise under free-living conditions. We also compared precursor tracer selection for the calculation of muscle protein synthesis rates and observed that saliva deuterium enrichment serves as an appropriate and practical choice of precursor.

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Post-exercise whey protein hydrolysate supplementation induces a greater increase in muscle protein synthesis than its constituent amino acid content

British Journal Of Nutrition ◽

10.1017/s0007114512006174 ◽

2013 ◽

Vol 110 (6) ◽

pp. 981-987 ◽

Cited By ~ 29

Author(s):

Atsushi Kanda ◽

Kyosuke Nakayama ◽

Tomoyuki Fukasawa ◽

Jinichiro Koga ◽

Minoru Kanegae ◽

...

Keyword(s):

Amino Acids ◽

Protein Synthesis ◽

Amino Acid ◽

Whey Protein ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Acid Mixture ◽

Post Exercise ◽

The Impact ◽

Mtor Signalling

It is well known that ingestion of a protein source is effective in stimulating muscle protein synthesis after exercise. In addition, there are numerous reports on the impact of leucine and leucine-rich whey protein on muscle protein synthesis and mammalian target of rapamycin (mTOR) signalling. However, there is only limited information on the effects of whey protein hydrolysates (WPH) on muscle protein synthesis and mTOR signalling. The aim of the present study was to compare the effects of WPH and amino acids on muscle protein synthesis and the initiation of translation in skeletal muscle during the post-exercise phase. Male Sprague–Dawley rats swam for 2 h to depress muscle protein synthesis. Immediately after exercise, the animals were administered either carbohydrate (CHO), CHO plus an amino acid mixture (AA) or CHO plus WPH. At 1 h after exercise, the supplements containing whey-based protein (AA and WPH) caused a significant increase in the fractional rate of protein synthesis (FSR) compared with CHO. WPH also caused a significant increase in FSR compared with AA. Post-exercise ingestion of WPH caused a significant increase in the phosphorylation of mTOR levels compared with AA or CHO. In addition, WPH caused greater phosphorylation of ribosomal protein S6 kinase and eukaryotic initiation factor 4E-binding protein 1 than AA and CHO. In contrast, there was no difference in plasma amino acid levels following supplementation with either AA or WPH. These results indicate that WPH may include active components that are superior to amino acids for stimulating muscle protein synthesis and initiating translation.

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A randomized controlled trial of the impact of protein supplementation on leg lean mass and integrated muscle protein synthesis during inactivity and energy restriction in older persons

American Journal of Clinical Nutrition ◽

10.1093/ajcn/nqy193 ◽

2018 ◽

Vol 108 (5) ◽

pp. 1060-1068 ◽

Cited By ~ 17

Author(s):

Sara Y Oikawa ◽

Chris McGlory ◽

Lisa K D'Souza ◽

Adrienne K Morgan ◽

Nelson I Saddler ◽

...

Keyword(s):

Protein Synthesis ◽

Lean Mass ◽

Older Persons ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Controlled Trial ◽

Protein Supplementation ◽

Energy Restriction ◽

Habitual Activity ◽

The Impact

ABSTRACT Background In older persons, muscle loss is accelerated during physical inactivity and hypoenergetic states, both of which are features of hospitalization. Protein supplementation may represent a strategy to offset the loss of muscle during inactivity, and enhance recovery on resumption of activity. Objective We aimed to determine if protein supplementation, with proteins of substantially different quality, would alleviate the loss of lean mass by augmenting muscle protein synthesis (MPS) while inactive during a hypoenergetic state. Design Participants (16 men, mean ± SD age: 69 ± 3 y; 15 women, mean ± SD age: 68 ± 4 y) consumed a diet containing 1.6 g protein · kg–1 · d–1, with 55% ± 9% of protein from foods and 45% ± 9% from supplements, namely, whey protein (WP) or collagen peptides (CP): 30 g each, consumed 2 times/d. Participants were in energy balance (EB) for 1 wk, then began a period of energy restriction (ER; –500 kcal/d) for 1 wk, followed by ER with step reduction (ER + SR; <750 steps/d) for 2 wk, before a return to habitual activity in recovery (RC) for 1 wk. Results There were significant reductions in leg lean mass (LLM) from EB to ER, and from ER to ER + SR in both groups (P < 0.001) with no differences between WP and CP or when comparing the change from phase to phase. During RC, LLM increased from ER + SR, but in the WP group only. Rates of integrated muscle protein synthesis decreased during ER and ER + SR in both groups (P < 0.01), but increased during RC only in the WP group (P = 0.05). Conclusions Protein supplementation did not confer a benefit in protecting LLM, but only supplemental WP augmented LLM and muscle protein synthesis during recovery from inactivity and a hypoenergetic state. This trial was registered at http://www.clinicaltrials.gov as NCT03285737.

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The use of doubly labeled milk protein to measure postprandial muscle protein synthesis rates in vivo in humans

Journal of Applied Physiology ◽

10.1152/japplphysiol.00411.2014 ◽

2014 ◽

Vol 117 (11) ◽

pp. 1363-1370 ◽

Cited By ~ 23

Author(s):

Nicholas A. Burd ◽

Naomi M. Cermak ◽

Imre W. K. Kouw ◽

Stefan H. Gorissen ◽

Annemie P. Gijsen ◽

...

Keyword(s):

Protein Synthesis ◽

Continuous Infusion ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Constant Infusion ◽

Synthesis Rate ◽

Mole Percent ◽

Precursor Pool ◽

The Impact

We aimed to determine the impact of precursor pool dilution on the assessment of postprandial myofibrillar protein synthesis rates (MPS). A Holstein dairy cow was infused with large amounts of L-[1-13C]phenylalanine and L-[1-13C]leucine, and the milk was collected and fractionated. The enrichment levels in the casein were 38.7 and 9.3 mole percent excess, respectively. In a subsequent human experiment, 11 older men (age: 71 ± 1 y, body mass index: 26 ± 0.1 kg·m−2) received a primed constant infusion of L-[ring-2H5]phenylalanine and L-[1-13C]leucine. Blood and muscle samples were collected before and after the ingestion of 20-g doubly labeled casein to assess postprandial MPS based on the 1) constant tracer infusion of L-[ ring-2H5]phenylalanine, 2) ingestion of intrinsically L-[1-13C]phenylalanine-labeled casein, and 3) constant infusion of L-[1-13C]leucine in combination with the ingestion of intrinsically L-[1-13C]leucine-labeled casein. Postprandial MPS was increased ( P < 0.05) after protein ingestion (∼70% above postabsorptive values) based on the L-[1-13C]leucine tracer. There was no significant stimulation of postprandial MPS (∼27% above postabsorptive values) when the calculated fractional synthesis rate was based on the L-[ring-2H5]phenylalanine ( P = 0.2). Comparisons of postprandial MPS based on the primed continuous infusion of L-[1-13C]leucine or the ingestion of intrinsically L-[1-13C]phenylalanine-labeled casein protein demonstrated differences compared with the primed continuous infusion of L-[ ring-2H5]phenylalanine ( P > 0.05). Our findings confirm that the postprandial MPS assessed using the primed continuous tracer infusion approach may differ if tracer steady-state conditions in the precursor pools are perturbed. The use of intrinsically doubly labeled protein provides a method to study the metabolic fate of the ingested protein and the subsequent postprandial MPS response.

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Minimal whey protein with carbohydrate stimulates muscle protein synthesis following resistance exercise in trained young men

Applied Physiology Nutrition and Metabolism ◽

10.1139/h07-076 ◽

2007 ◽

Vol 32 (6) ◽

pp. 1132-1138 ◽

Cited By ~ 73

Author(s):

Jason E. Tang ◽

Joshua J. Manolakos ◽

Greg W. Kujbida ◽

Paul J. Lysecki ◽

Daniel R. Moore ◽

...

Keyword(s):

Protein Synthesis ◽

Resistance Exercise ◽

Whey Protein ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Young Men ◽

Skeletal Muscle Protein ◽

Double Blind ◽

Exercise Period ◽

The Impact

Whey protein is a supplemental protein source often used by athletes, particularly those aiming to gain muscle mass; however, direct evidence for its efficacy in stimulating muscle protein synthesis (MPS) is lacking. We aimed to determine the impact of consuming whey protein on skeletal muscle protein turnover in the post-exercise period. Eight healthy resistance-trained young men (age = 21 ± 1 .0 years; BMI = 26.8 ± 0.9 kg/m2 (means ± SE)) participated in a double-blind randomized crossover trial in which they performed a unilateral leg resistance exercise workout (EX: 4 sets of knee extensions and 4 sets of leg press; 8–10 repetitions/set; 80% of maximal), such that one leg was not exercised and acted as a rested (RE) comparator. After exercise, subjects consumed either an isoenergetic whey protein plus carbohydrate beverage (WHEY: 10 g protein and 21 g fructose) or a carbohydrate-only beverage (CHO: 21 g fructose and 10 g maltodextran). Subjects received pulse-tracer injections of l-[ring-2H5]phenylalanine and l-[15N]phenylalanine to measure MPS. Exercise stimulated a rise in MPS in the WHEY-EX and CHO-EX legs, which were greater than MPS in the WHEY-RE leg and the CHO-RE leg (all p < 0.05), respectively. The rate of MPS in the WHEY-EX leg was greater than in the CHO-EX leg (p < 0.001). We conclude that a small dose (10 g) of whey protein with carbohydrate (21 g) can stimulate a rise in MPS after resistance exercise in trained young men that would be supportive of a positive net protein balance, which, over time, would lead to hypertrophy.

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Mechanistic Links Underlying the Impact of C-Reactive Protein on Muscle Mass in Elderly

Cellular Physiology and Biochemistry ◽

10.1159/000484679 ◽

2017 ◽

Vol 44 (1) ◽

pp. 267-278 ◽

Cited By ~ 17

Author(s):

Britta Wåhlin-Larsson ◽

Daniel J. Wilkinson ◽

Emelie Strandberg ◽

Adrian Hosford-Donovan ◽

Philip J. Atherton ◽

...

Keyword(s):

Protein Synthesis ◽

Muscle Mass ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Inflammatory Marker ◽

Immunofluorescent Staining ◽

Age Related ◽

Human Myotubes ◽

The Impact ◽

The Relationship

Background/Aims: Mechanisms underlying the relationship between systemic inflammation and age-related decline in muscle mass are poorly defined. The purpose of this work was to investigate the relationship between the systemic inflammatory marker CRP and muscle mass in elderly and to identify mechanisms by which CRP mediates its effects on skeletal muscle, in-vitro. Methods: Muscle mass and serum CRP level were determined in a cohort of 118 older women (67±1.7 years). Human muscle cells were differentiated into myotubes and were exposed to CRP. The size of myotubes was determined after immunofluorescent staining using troponin. Muscle protein synthesis was assessed using stable isotope tracers and key signalling pathways controlling protein synthesis were determined using western-blotting. Results: We observed an inverse relationship between circulating CRP level and muscle mass (β= -0.646 (95% CI: -0.888, -0.405) p<0.05) and demonstrated a reduction (p < 0.05) in the size of human myotubes exposed to CRP for 72 h. We next showed that this morphological change was accompanied by a CRP-mediated reduction (p < 0.05) in muscle protein fractional synthetic rate of human myotubes exposed to CRP for 24 h. We also identified a CRP-mediated increased phosphorylation (p<0.05) of regulators of cellular energy stress including AMPK and downstream targets, raptor and ACC-β, together with decreased phosphorylation of Akt and rpS6, which are important factors controlling protein synthesis. Conclusion: This work established for the first time mechanistic links by which chronic elevation of CRP can contribute to age-related decline in muscle function.

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