Autophagy is essential to support skeletal muscle plasticity in response to endurance exercise

Physical exercise is a stress that can substantially modulate cellular signaling mechanisms to promote morphological and metabolic adaptations. Skeletal muscle protein and organelle turnover is dependent on two major cellular pathways: Forkhead box class O proteins (FOXO) transcription factors that regulate two main proteolytic systems, the ubiquitin-proteasome, and the autophagy-lysosome systems, including mitochondrial autophagy, and the MTORC1 signaling associated with protein translation and autophagy inhibition. In recent years, it has been well documented that both acute and chronic endurance exercise can affect the autophagy pathway. Importantly, substantial efforts have been made to better understand discrepancies in the literature on its modulation during exercise. A single bout of endurance exercise increases autophagic flux when the duration is long enough, and this response is dependent on nutritional status, since autophagic flux markers and mRNA coding for actors involved in mitophagy are more abundant in the fasted state. In contrast, strength and resistance exercises preferentially raise ubiquitin-proteasome system activity and involve several protein synthesis factors, such as the recently characterized DAGK for mechanistic target of rapamycin activation. In this review, we discuss recent progress on the impact of acute and chronic exercise on cell component turnover systems, with particular focus on autophagy, which until now has been relatively overlooked in skeletal muscle. We especially highlight the most recent studies on the factors that can impact its modulation, including the mode of exercise and the nutritional status, and also discuss the current limitations in the literature to encourage further works on this topic.

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Disruption of REDD1 gene ameliorates sepsis-induced decrease in mTORC1 signaling but has divergent effects on proteolytic signaling in skeletal muscle

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00264.2015 ◽

2015 ◽

Vol 309 (12) ◽

pp. E981-E994 ◽

Cited By ~ 16

Author(s):

Jennifer L. Steiner ◽

Kristen T. Crowell ◽

Scot R. Kimball ◽

Charles H. Lang

Keyword(s):

Skeletal Muscle ◽

Protein Synthesis ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Cecal Ligation ◽

Skeletal Muscle Atrophy ◽

Matched Pair ◽

Mtorc1 Signaling ◽

Ubiquitin Proteasome ◽

Lysosomal System

Sepsis-induced skeletal muscle atrophy and weakness are due in part to decreased mTORC1-mediated protein synthesis and increased proteolysis via the autophagy-lysosomal system and ubiquitin-proteasome pathway. The REDD1 (regulated in development and DNA damage-1) protein is increased in sepsis and can negatively regulate mTORC1 activity. However, the contribution of REDD1 to the sepsis-induced change in muscle protein synthesis and degradation has not been determined. Sepsis was produced by cecal ligation and puncture in female REDD1−/− or wild-type (WT) mice, and end points were assessed 24 h later in gastrocnemius; time-matched, pair-fed controls of each genotype were included. Sepsis increased REDD1 protein 300% in WT mice, whereas REDD1 was absent in REDD1−/− muscle. Sepsis decreased protein synthesis and phosphorylation of downstream targets of mTORC1 (S6K1 Thr389, rpS6 Ser240/244, 4E-BP1 Ser65) in WT but not REDD1−/− mice. However, Akt and PRAS40 phosphorylation was suppressed in both sham and septic muscle from REDD1−/− mice despite unaltered PDK1, PP2A, or TSC2 expression. Sepsis increased autophagy as indicated by decreased ULK1 Ser757 phosphorylation and p62 abundance and increased LC3B-II/I in WT mice, whereas these changes were absent in septic REDD1−/− mice. Conversely, REDD1 deletion did not prevent the sepsis-induced decrease in IGF-I mRNA or the concomitant increase in IL-6, TNFα, MuRF1, and atrogin1 mRNA expression. Lastly, 5-day survival in a separate set of septic mice did not differ between WT and REDD1−/− mice. These data highlight the central role of REDD1 in regulating both protein synthesis and autophagy in skeletal muscle during sepsis.

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IGF-I has no effect on postexercise suppression of the ubiquitin-proteasome system in rat skeletal muscle

Journal of Applied Physiology ◽

10.1152/japplphysiol.01030.2001 ◽

2002 ◽

Vol 92 (6) ◽

pp. 2277-2284 ◽

Cited By ~ 10

Author(s):

Anthony J. Kee ◽

Alan J. Taylor ◽

Anthony R. Carlsson ◽

Andre Sevette ◽

Ross C. Smith ◽

...

Keyword(s):

Skeletal Muscle ◽

Endurance Exercise ◽

Protein Turnover ◽

Muscle Protein ◽

Male Rats ◽

Ubiquitin Proteasome Pathway ◽

Muscle Protein Turnover ◽

Igf I ◽

Ubiquitin Proteasome ◽

Proteasome Pathway

Both exercise and insulin-like growth factor I (IGF-I) are known to have major hypertrophic effects in skeletal muscle; however, the interactive effect of exogenous IGF-I and exercise on muscle protein turnover or the ubiquitin-proteasome pathway has not been reported. In the present study, we have examined the interaction between endurance exercise training and IGF-I treatment on muscle protein turnover and the ubiquitin-proteasome pathway in the postexercise period. Adult male rats (270–280 g) were randomized to receive 5 consecutive days of progressive treadmill exercise and/or IGF-I treatment (1 mg · kg body wt−1 · day−1). Twenty-four hours after the last bout of exercise, the rate of protein breakdown in incubated muscles was significantly reduced compared with that in unexercised rats. This was associated with a significant reduction in the chymotrypsin-like activity of the proteasome and the rate of ubiquitin-proteasome-dependent casein hydrolysis in muscle extracts from exercised compared with unexercised rats. In contrast, the muscle expression of the 20S proteasome subunit β-1, ubiquitin, and the 14-kDa E2 ubiquitin-conjugating enzyme was not altered by exercise or IGF-I treatment 24 h postexercise. Exercise had no effect on the rates of total mixed muscle protein synthesis in incubated muscles 24 h postexercise. IGF-I treatment had no effect on muscle weights or the rates of protein turnover 24 h after endurance exercise. These results suggest that a suppression of the ubiquitin-proteasome proteolytic pathway after endurance exercise may contribute to the acute postexercise net protein gain.

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The impact of postexercise essential amino acid ingestion on the ubiquitin proteasome and autophagosomal-lysosomal systems in skeletal muscle of older men

Journal of Applied Physiology ◽

10.1152/japplphysiol.00632.2016 ◽

2017 ◽

Vol 122 (3) ◽

pp. 620-630 ◽

Cited By ~ 12

Author(s):

Jared M. Dickinson ◽

Paul T. Reidy ◽

David M. Gundermann ◽

Michael S. Borack ◽

Dillon K. Walker ◽

...

Keyword(s):

Older Adults ◽

Skeletal Muscle ◽

Essential Amino Acid ◽

Muscle Protein ◽

Ubiquitin Proteasome System ◽

Older Men ◽

Intact Proteins ◽

Ubiquitin Proteasome ◽

Muscle Breakdown ◽

The Impact

Essential amino acid (EAA) ingestion enhances postexercise muscle protein synthesis, and, in particular, the anabolic response of older adults appears sensitive to the quantity of ingested leucine. The effect of leucine ingestion on muscle breakdown following resistance exercise (RE) is less understood. The purpose of this study was to identify the impact of postexercise leucine ingestion on the ubiquitin proteasome and autophagosomal-lysosomal systems following acute RE in older men. Subjects (72 ± 2 yr) performed RE and 1 h postexercise ingested 10 g of EAA containing a leucine quantity similar to quality protein (control, 1.8 g leucine, n = 7) or enriched in leucine (leucine, 3.5 g leucine, n = 8). Stable isotope infusion and muscle biopsies (vastus lateralis) obtained at rest and 2, 5, and 24 h postexercise were used to examine protein content (Western blot), mRNA expression (RT-quantitative PCR), and muscle protein fractional breakdown rate (FBR). Muscle-specific RING finger 1 mRNA increased in both groups at 2 and 5 h ( P < 0.05). LC3 mRNA increased, and the LC3BII-to-LC3BI ratio decreased at all postexercise time points in control ( P < 0.05). Conversely, LC3 mRNA only increased at 2 h, and the LC3BII-to-LC3BI ratio only decreased at 2 and 5 h in leucine ( P < 0.05). Tumor necrosis factor receptor-associated factor-6 mRNA increased ( P < 0.05) in control at 5 h. FBR was not statistically different between groups or from basal 24 h postexercise ( P > 0.05). These data indicate that ingesting a larger quantity of leucine following RE may further reduce postexercise skeletal muscle autophagy in older men; however, it does not appear to influence the acute postexercise elevation in markers of the ubiquitin proteasome system or the breakdown of intact proteins. NEW & NOTEWORTHY The impact of postexercise leucine ingestion on processes of skeletal muscle breakdown in older adults is not well understood. Additional postexercise leucine ingestion appears to further reduce autophagy, but it does not interfere with the increase in ubiquitin proteasome system markers or the breakdown of intact proteins in skeletal muscle of older men. Postexercise leucine ingestion may promote a healthier protein pool and favorable muscle adaptations in older adults through greater accretion of myofibrillar proteins.

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AMP-Activated Protein Kinase as a Key Trigger for the Disuse-Induced Skeletal Muscle Remodeling

International Journal of Molecular Sciences ◽

10.3390/ijms19113558 ◽

2018 ◽

Vol 19 (11) ◽

pp. 3558 ◽

Cited By ~ 13

Author(s):

Natalia Vilchinskaya ◽

Igor Krivoi ◽

Boris Shenkman

Keyword(s):

Skeletal Muscle ◽

Protein Kinase ◽

Histone Deacetylases ◽

Molecular Mechanisms ◽

Weight Bearing ◽

Mammalian Target Of Rapamycin ◽

Adenosine Monophosphate ◽

Chain Gene ◽

Mtorc1 Signaling ◽

The Impact

Molecular mechanisms that trigger disuse-induced postural muscle atrophy as well as myosin phenotype transformations are poorly studied. This review will summarize the impact of 5′ adenosine monophosphate -activated protein kinase (AMPK) activity on mammalian target of rapamycin complex 1 (mTORC1)-signaling, nuclear-cytoplasmic traffic of class IIa histone deacetylases (HDAC), and myosin heavy chain gene expression in mammalian postural muscles (mainly, soleus muscle) under disuse conditions, i.e., withdrawal of weight-bearing from ankle extensors. Based on the current literature and the authors’ own experimental data, the present review points out that AMPK plays a key role in the regulation of signaling pathways that determine metabolic, structural, and functional alternations in skeletal muscle fibers under disuse.

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Mechanisms Underlying Muscle Protein Imbalance Induced by Alcohol

Annual Review of Nutrition ◽

10.1146/annurev-nutr-071816-064642 ◽

2018 ◽

Vol 38 (1) ◽

pp. 197-217 ◽

Cited By ~ 9

Author(s):

Scot R. Kimball ◽

Charles H. Lang

Keyword(s):

Skeletal Muscle ◽

Protein Synthesis ◽

Muscle Protein ◽

Cardiac Contractility ◽

Metabolic Phenotype ◽

Alcoholic Myopathy ◽

Ubiquitin Proteasome ◽

Proteasome Pathway ◽

Induced Changes ◽

Skeletal Muscle Strength

Both acute intoxication and longer-term cumulative ingestion of alcohol negatively impact the metabolic phenotype of both skeletal and cardiac muscle, independent of overt protein calorie malnutrition, resulting in loss of skeletal muscle strength and cardiac contractility. In large part, these alcohol-induced changes are mediated by a decrease in protein synthesis that in turn is governed by impaired activity of a protein kinase, the mechanistic target of rapamycin (mTOR). Herein, we summarize recent advances in understanding mTOR signal transduction, similarities and differences between the effects of alcohol on this central metabolic controller in skeletal muscle and in the heart, and the effects of acute versus chronic alcohol intake. While alcohol-induced alterations in global proteolysis via activation of the ubiquitin-proteasome pathway are equivocal, emerging data suggest alcohol increases autophagy in muscle. Further studies are necessary to define the relative contributions of these bidirectional changes in protein synthesis and autophagy in the etiology of alcoholic myopathy in skeletal muscle and the heart.

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Changes in skeletal muscle protein synthesis in trained adults during recovery from endurance exercise

The FASEB Journal ◽

10.1096/fasebj.22.1_supplement.312.8 ◽

2008 ◽

Vol 22 (S1) ◽

Author(s):

Lisa Vislocky ◽

P. Courtney Gaine ◽

Matthew Pikosky ◽

Douglas Bolster ◽

Arny Ferrando ◽

...

Keyword(s):

Skeletal Muscle ◽

Protein Synthesis ◽

Endurance Exercise ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Skeletal Muscle Protein ◽

Skeletal Muscle Protein Synthesis

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Knockdown of the E3 ubiquitin ligase UBR5 and its role in skeletal muscle anabolism

AJP Cell Physiology ◽

10.1152/ajpcell.00432.2020 ◽

2021 ◽

Vol 320 (1) ◽

pp. C45-C56

Author(s):

David C. Hughes ◽

Daniel C. Turner ◽

Leslie M. Baehr ◽

Robert A. Seaborne ◽

Mark Viggars ◽

...

Keyword(s):

Skeletal Muscle ◽

Muscle Mass ◽

Ubiquitin Ligase ◽

Fluorescent Protein ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Tibialis Anterior Muscle ◽

E3 Ubiquitin Ligase ◽

Skeletal Muscle Atrophy ◽

The Impact

UBR5 is an E3 ubiquitin ligase positively associated with anabolism, hypertrophy, and recovery from atrophy in skeletal muscle. The precise mechanisms underpinning UBR5’s role in the regulation of skeletal muscle mass remain unknown. The present study aimed to elucidate these mechanisms by silencing the UBR5 gene in vivo. To achieve this aim, we electroporated a UBR5-RNAi plasmid into mouse tibialis anterior muscle to investigate the impact of reduced UBR5 on anabolic signaling MEK/ERK/p90RSK and Akt/GSK3β/p70S6K/4E-BP1/rpS6 pathways. Seven days after UBR5 RNAi electroporation, although reductions in overall muscle mass were not detected, the mean cross-sectional area (CSA) of green fluorescent protein (GFP)-positive fibers were reduced (−9.5%) and the number of large fibers were lower versus the control. Importantly, UBR5-RNAi significantly reduced total RNA, muscle protein synthesis, ERK1/2, Akt, and GSK3β activity. Although p90RSK phosphorylation significantly increased, total p90RSK protein levels demonstrated a 45% reduction with UBR5-RNAi. Finally, these early events after 7 days of UBR5 knockdown culminated in significant reductions in muscle mass (−4.6%) and larger reductions in fiber CSA (−18.5%) after 30 days. This was associated with increased levels of phosphatase PP2Ac and inappropriate chronic elevation of p70S6K and rpS6 between 7 and 30 days, as well as corresponding reductions in eIF4e. This study demonstrates that UBR5 plays an important role in anabolism/hypertrophy, whereby knockdown of UBR5 culminates in skeletal muscle atrophy.

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Insulin Stimulates Human Skeletal Muscle Protein Synthesis via an Indirect Mechanism Involving Endothelial-Dependent Vasodilation and Mammalian Target of Rapamycin Complex 1 Signaling

Molecular Endocrinology ◽

10.1210/mend.24.6.9996 ◽

2010 ◽

Vol 24 (6) ◽

pp. 1306-1306

Author(s):

Kyle L. Timmerman ◽

Jessica L. Lee ◽

Hans C. Dreyer ◽

Shaheen Dhanani ◽

Erin L. Glynn ◽

...

Keyword(s):

Skeletal Muscle ◽

Protein Synthesis ◽

Muscle Protein ◽

Muscle Protein Synthesis ◽

Mammalian Target Of Rapamycin ◽

Skeletal Muscle Protein ◽

Capillary Recruitment ◽

Isotope Tracers ◽

Skeletal Muscle Protein Synthesis ◽

Mtorc1 Signaling

Abstract Objective: Our objective was to determine whether endothelial-dependent vasodilation is an essential mechanism by which insulin stimulates human skeletal muscle protein synthesis and anabolism. Subjects: Subjects were healthy young adults (n = 14) aged 31 ± 2 yr. Design: Subjects were studied at baseline and during local leg infusion of insulin alone (control, n = 7) or insulin plus the nitric oxide synthase inhibitor NG-monomethyl-l-arginine (L-NMMA, n = 7) to prevent insulin-induced vasodilation. Methods: We measured skeletal muscle protein metabolism with stable isotope tracers, blood flow with indocyanine green, capillary recruitment with contrast enhanced ultrasound, glucose metabolism with stable isotope tracers, and phosphorylation of proteins associated with insulin (Akt) and amino acid-induced mammalian target of rapamycin(mTOR) complex 1 (mTORC1) signaling (mTOR, S6 kinase 1, and eukaryotic initiation factor 4Ebinding protein 1) with Western blot analysis. Results: No basal differences between groups were detected. During insulin infusion, blood flow and capillary recruitment increased in the control (P < 0.05) group only; Akt phosphorylation and glucose uptake increased in both groups (P < 0.05), with no group differences; and mTORC1 signaling increased more in control (P < 0.05) than in l-NMMA. Phenylalanine net balance increased (P < 0.05) in both groups, but with opposite mechanisms: increased protein synthesis (basal, 0.051 ± 0.006%/h; insulin, 0.077 ± 0.008%/h; P < 0.05) with no change in proteolysis in control and decreased proteolysis (P < 0.05) with no change in synthesis (basal, 0.061 ± 0.004%/h; insulin, 0.050 ± 0.006%/h; P value not significant) in l-NMMA. Conclusions: Endothelial-dependent vasodilation and the consequent increase in nutritive flow and mTORC1 signaling, rather than Akt signaling, are fundamental mechanisms by which insulin stimulates muscle protein synthesis in humans. Additionally, these data underscore that insulin modulates skeletal muscle proteolysis according to its effects on nutritive flow.

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