Publications by authors named "Andrew Philp"

94 Publications

Diet-induced vitamin D deficiency reduces skeletal muscle mitochondrial respiration.

J Endocrinol 2021 May;249(2):113-124

Mitochondrial Metabolism and Ageing Laboratory, Garvan Institute of Medical Research, Sydney, New South Wales, Australia.

Vitamin D deficiency is associated with symptoms of skeletal muscle myopathy including muscle weakness and fatigue. Recently, vitamin D-related metabolites have been linked to the maintenance of mitochondrial function within skeletal muscle. However, current evidence is limited to in vitro models and the effects of diet-induced vitamin D deficiency upon skeletal muscle mitochondrial function in vivo have received little attention. In order to examine the role of vitamin D in the maintenance of mitochondrial function in vivo, we utilised an established model of diet-induced vitamin D deficiency in C57BL/6J mice. Mice were either fed a control diet (2200 IU/kg i.e. vitamin D replete) or a vitamin D-deplete (0 IU/kg) diet for periods of 1, 2 and 3 months. Gastrocnemius muscle mitochondrial function and ADP sensitivity were assessed via high-resolution respirometry and mitochondrial protein content via immunoblotting. As a result of 3 months of diet-induced vitamin D deficiency, respiration supported via complex I + II (CI + IIP) and the electron transport chain (ETC) were 35 and 37% lower when compared to vitamin D-replete mice (P < 0.05). Despite functional alterations, citrate synthase activity, AMPK phosphorylation, mitofilin, OPA1 and ETC subunit protein content remained unchanged in response to dietary intervention (P > 0.05). In conclusion, we report that 3 months of diet-induced vitamin D deficiency reduced skeletal muscle mitochondrial respiration in C57BL/6J mice. Our data, when combined with previous in vitro observations, suggest that vitamin D-mediated regulation of mitochondrial function may underlie the exacerbated muscle fatigue and performance deficits observed during vitamin D deficiency.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1530/JOE-20-0233DOI Listing
May 2021

Association between vitamin D deficiency and exercise capacity in patients with CKD, a cross-sectional analysis.

J Steroid Biochem Mol Biol 2021 Mar 3;210:105861. Epub 2021 Mar 3.

Department of Health Sciences, University of Leicester, United Kingdom.

Background: Evidence is growing for a role of vitamin D in regulating skeletal muscle mass, strength and functional capacity. Given the role the kidneys play in activating total vitamin D, and the high prevalence of vitamin D deficiency in Chronic Kidney Disease (CKD), it is possible that deficiency contributes to the low levels of physical function and muscle mass in these patients.

Methods: This is a secondary cross-sectional analysis of previously published interventional study, with in vitro follow up work. 34 CKD patients at stages G3b-5 (eGFR 25.5 ± 8.3 mL/min/1.73m2; age 61 ± 12 years) were recruited, with a sub-group (n = 20) also donating a muscle biopsy. Vitamin D and associated metabolites were analysed in plasma by liquid chromatography tandem-mass spectroscopy and correlated to a range of physiological tests of muscle size, function, exercise capacity and body composition. The effects of 1α,25(OH)2D3 supplementation on myogenesis and myotube size was investigated in primary skeletal muscle cells from vitamin D deficient donors.

Results: In vivo, there was no association between total or active vitamin D and muscle size or strength, but a significant correlation with V̇O was seen with total vitamin D (25OHD). in vitro, 1α,25(OH)D3 supplementation reduced IL-6 mRNA expression, but had no effect upon proliferation, differentiation or myotube diameter.

Conclusions: Vitamin D deficiency is not a prominent factor driving the loss of muscle mass in CKD, but may play a role in reduced exercise capacity.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.jsbmb.2021.105861DOI Listing
March 2021

Mitochondrial hydrogen sulfide supplementation improves health in the Duchenne muscular dystrophy model.

Proc Natl Acad Sci U S A 2021 Mar;118(9)

Medical Research Council (MRC) Versus Arthritis Centre for Musculoskeletal Ageing Research, Royal Derby Hospital, University of Nottingham, Derby DE22 3DT, United Kingdom;

Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder characterized by progressive muscle degeneration and weakness due to mutations in the dystrophin gene. The symptoms of DMD share similarities with those of accelerated aging. Recently, hydrogen sulfide (HS) supplementation has been suggested to modulate the effects of age-related decline in muscle function, and metabolic HS deficiencies have been implicated in affecting muscle mass in conditions such as phenylketonuria. We therefore evaluated the use of sodium GYY4137 (NaGYY), a HS-releasing molecule, as a possible approach for DMD treatment. Using the 33 DMD model, we found that NaGYY treatment (100 µM) improved movement, strength, gait, and muscle mitochondrial structure, similar to the gold-standard therapeutic treatment, prednisone (370 µM). The health improvements of either treatment required the action of the kinase JNK-1, the transcription factor SKN-1, and the NAD-dependent deacetylase SIR-2.1. The transcription factor DAF-16 was required for the health benefits of NaGYY treatment, but not prednisone treatment. AP39 (100 pM), a mitochondria-targeted HS compound, also improved movement and strength in the 33 model, further implying that these improvements are mitochondria-based. Additionally, we found a decline in total sulfide and HS-producing enzymes in dystrophin/utrophin knockout mice. Overall, our results suggest that HS deficit may contribute to DMD pathology, and rectifying/overcoming the deficit with HS delivery compounds has potential as a therapeutic approach to DMD treatment.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1073/pnas.2018342118DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7936346PMC
March 2021

Nicotinamide riboside supplementation does not alter whole-body or skeletal muscle metabolic responses to a single bout of endurance exercise.

J Physiol 2021 03 29;599(5):1513-1531. Epub 2021 Jan 29.

School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, UK.

Key Points: Acute nicotinamide riboside (NR) supplementation does not alter substrate metabolism at rest, during or in recovery from endurance exercise. NR does not alter NAD -sensitive signalling pathways in human skeletal muscle. NR supplementation and acute exercise influence the NAD metabolome.

Abstract: Oral supplementation of the NAD precursor nicotinamide riboside (NR) has been reported to alter metabolism alongside increasing sirtuin (SIRT) signalling and mitochondrial biogenesis in rodent skeletal muscle. However, whether NR supplementation can elicit a similar response in human skeletal muscle is unclear. This study assessed the effect of 7-day NR supplementation on whole-body metabolism and exercise-induced mitochondrial biogenic signalling in skeletal muscle. Eight male participants (age: 23 ± 4 years, 46.5 ± 4.4 ml kg  min ) received 1 week of NR or cellulose placebo (PLA) supplementation (1000 mg day ). Muscle biopsies were collected from the medial vastus lateralis prior to supplementation and pre-, immediately post- and 3 h post-exercise (1 h of 60% W cycling) performed following the supplementation period. There was no effect of NR supplementation on substrate utilisation at rest or during exercise or on skeletal muscle mitochondrial respiration. Global acetylation, auto-PARylation of poly ADP-ribose polymerase 1 (PARP1), acetylation of Tumour protein 53 (p53) and Manganese superoxide dismutase (MnSOD) were also unaffected by NR supplementation or exercise. NR supplementation did not increase skeletal muscle NAD concentration, but it did increase the concentration of deaminated NAD precursors nicotinic acid riboside (NAR) and nicotinic acid mononucleotide (NAM) and methylated nicotinamide breakdown products (Me2PY and Me4PY), demonstrating the skeletal muscle bioavailability of NR supplementation. In summary, 1 week of NR supplementation does not alter whole-body metabolism or skeletal muscle signal transduction pathways implicated in the mitochondrial adaptation to endurance exercise.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1113/JP280825DOI Listing
March 2021

The influence of aerobic exercise on mitochondrial quality control in skeletal muscle.

J Physiol 2020 Dec 28. Epub 2020 Dec 28.

Healthy Ageing Research Theme, Garvan Institute of Medical Research, 384 Victoria Street, Sydney, New South Wales, 2010, Australia.

Mitochondria are dynamic organelles, intricately designed to meet cellular energy requirements. To accommodate alterations in energy demand, mitochondria have a high degree of plasticity, changing in response to transient activation of numerous stress-related pathways. This adaptive response is particularly relevant in highly metabolic tissues such as skeletal muscle, where mitochondria support numerous biological processes related to metabolism, growth and regeneration. Aerobic exercise is a potent stimulus for skeletal muscle remodelling, leading to alterations in substrate utilisation, fibre-type composition and performance. Underlying these physiological responses is a change in mitochondrial quality control (MQC), a term encompassing the co-ordination of mitochondrial synthesis (biogenesis), remodelling (dynamics) and degradation (mitophagy) pathways. Understanding of MQC in skeletal muscle and the regulatory role of aerobic exercise of this process are rapidly advancing, as are the molecular techniques allowing the study of MQC in vivo. Given the emerging link between MQC and the onset of numerous non-communicable diseases, understanding the molecular regulation of MQC, and the role of aerobic exercise in this process, will have substantial future impact on therapeutic approaches to manipulate MQC and maintain mitochondrial function across health span.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1113/JP279411DOI Listing
December 2020

Metabolic remodeling of dystrophic skeletal muscle reveals biological roles for dystrophin and utrophin in adaptation and plasticity.

Mol Metab 2021 03 24;45:101157. Epub 2020 Dec 24.

Centre for Muscle Research, Department of Anatomy and Physiology, The University of Melbourne, Melbourne, Victoria, 3010, Australia. Electronic address:

Objectives: Preferential damage to fast, glycolytic myofibers is common in many muscle-wasting diseases, including Duchenne muscular dystrophy (DMD). Promoting an oxidative phenotype could protect muscles from damage and ameliorate the dystrophic pathology with therapeutic relevance, but developing efficacious strategies requires understanding currently unknown biological roles for dystrophin and utrophin in dystrophic muscle adaptation and plasticity.

Methods: Combining whole transcriptome RNA sequencing and mitochondrial proteomics with assessments of metabolic and contractile function, we investigated the roles of dystrophin and utrophin in fast-to-slow muscle remodeling with low-frequency electrical stimulation (LFS, 10 Hz, 12 h/d, 7 d/wk, 28 d) in mdx (dystrophin null) and dko (dystrophin/utrophin null) mice, two established preclinical models of DMD.

Results: Novel biological roles in adaptation were demonstrated by impaired transcriptional activation of estrogen-related receptor alpha-responsive genes supporting oxidative phosphorylation in dystrophic muscles. Further, utrophin expression in dystrophic muscles was required for LFS-induced remodeling of mitochondrial respiratory chain complexes, enhanced fiber respiration, and conferred protection from eccentric contraction-mediated damage.

Conclusions: These findings reveal novel roles for dystrophin and utrophin during LFS-induced metabolic remodeling of dystrophic muscle and highlight the therapeutic potential of LFS to ameliorate the dystrophic pathology and protect from contraction-induced injury with important implications for DMD and related muscle disorders.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.molmet.2020.101157DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7811171PMC
March 2021

The effect of short-term exercise prehabilitation on skeletal muscle protein synthesis and atrophy during bed rest in older men.

J Cachexia Sarcopenia Muscle 2021 Feb 21;12(1):52-69. Epub 2020 Dec 21.

School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, UK.

Background: Poor recovery from periods of disuse accelerates age-related muscle loss, predisposing individuals to the development of secondary adverse health outcomes. Exercise prior to disuse (prehabilitation) may prevent muscle deterioration during subsequent unloading. The present study aimed to investigate the effect of short-term resistance exercise training (RET) prehabilitation on muscle morphology and regulatory mechanisms during 5 days of bed rest in older men.

Methods: Ten healthy older men aged 65-80 years underwent four bouts of high-volume unilateral leg RET over 7 days prior to 5 days of inpatient bed rest. Physical activity and step-count were monitored over the course of RET prehabilitation and bed rest, whilst dietary intake was recorded throughout. Prior to and following bed rest, quadriceps cross-sectional area (CSA), and hormone/lipid profiles were determined. Serial muscle biopsies and dual-stable isotope tracers were used to determine integrated myofibrillar protein synthesis (iMyoPS) over RET prehabilitation and bed rest phases, and acute postabsorptive and postprandial myofibrillar protein synthesis (aMyoPS) rates at the end of bed rest.

Results: During bed rest, daily step-count and light and moderate physical activity time decreased, whilst sedentary time increased when compared with habitual levels (P < 0.001 for all). Dietary protein and fibre intake during bed rest were lower than habitual values (P < 0.01 for both). iMyoPS rates were significantly greater in the exercised leg (EX) compared with the non-exercised control leg (CTL) over prehabilitation (1.76 ± 0.37%/day vs. 1.36 ± 0.18%/day, respectively; P = 0.007). iMyoPS rates decreased similarly in EX and CTL during bed rest (CTL, 1.07 ± 0.22%/day; EX, 1.30 ± 0.38%/day; P = 0.037 and 0.002, respectively). Postprandial aMyoPS rates increased above postabsorptive values in EX only (P = 0.018), with no difference in delta postprandial aMyoPS stimulation between legs. Quadriceps CSA at 40%, 60%, and 80% of muscle length decreased significantly in EX and CTL over bed rest (0.69%, 3.5%, and 2.8%, respectively; P < 0.01 for all), with no differences between legs. No differences in fibre-type CSA were observed between legs or with bed rest. Plasma insulin and serum lipids did not change with bed rest.

Conclusions: Short-term resistance exercise prehabilitation augmented iMyoPS rates in older men but did not offset the relative decline in iMyoPS and muscle mass during bed rest.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/jcsm.12661DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7890266PMC
February 2021

The mechanisms of skeletal muscle atrophy in response to transient knockdown of the vitamin D receptor in vivo.

J Physiol 2021 02 24;599(3):963-979. Epub 2020 Dec 24.

MRC/ARUK Centre for Musculoskeletal Ageing Research and National Institute for Health Research (NIHR), Nottingham Biomedical Research Centre (BRC), School of Medicine, University of Nottingham, Nottingham, UK.

Key Points: Reduced vitamin D receptor (VDR) expression prompts skeletal muscle atrophy. Atrophy occurs through catabolic processes, namely the induction of autophagy, while anabolism remains unchanged. In response to VDR-knockdown mitochondrial function and related gene-set expression is impaired. In vitro VDR knockdown induces myogenic dysregulation occurring through impaired differentiation. These results highlight the autonomous role the VDR has within skeletal muscle mass regulation.

Abstract: Vitamin D deficiency is estimated to affect ∼40% of the world's population and has been associated with impaired muscle maintenance. Vitamin D exerts its actions through the vitamin D receptor (VDR), the expression of which was recently confirmed in skeletal muscle, and its down-regulation is linked to reduced muscle mass and functional decline. To identify potential mechanisms underlying muscle atrophy, we studied the impact of VDR knockdown (KD) on mature skeletal muscle in vivo, and myogenic regulation in vitro in C2C12 cells. Male Wistar rats underwent in vivo electrotransfer (IVE) to knock down the VDR in hind-limb tibialis anterior (TA) muscle for 10 days. Comprehensive metabolic and physiological analysis was undertaken to define the influence loss of the VDR on muscle fibre composition, protein synthesis, anabolic and catabolic signalling, mitochondrial phenotype and gene expression. Finally, in vitro lentiviral transfection was used to induce sustained VDR-KD in C2C12 cells to analyse myogenic regulation. Muscle VDR-KD elicited atrophy through a reduction in total protein content, resulting in lower myofibre area. Activation of autophagic processes was observed, with no effect upon muscle protein synthesis or anabolic signalling. Furthermore, RNA-sequencing analysis identified systematic down-regulation of multiple mitochondrial respiration-related protein and genesets. Finally, in vitro VDR-knockdown impaired myogenesis (cell cycling, differentiation and myotube formation). Together, these data indicate a fundamental regulatory role of the VDR in the regulation of myogenesis and muscle mass, whereby it acts to maintain muscle mitochondrial function and limit autophagy.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1113/JP280652DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7986223PMC
February 2021

Editorial: Nutritional Strategies to Promote Muscle Mass and Function Across the Health Span.

Front Nutr 2020 2;7:569270. Epub 2020 Oct 2.

Health Ageing Division, Garvan Institute of Medical Research, Darlinghurst, NSW, Australia.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3389/fnut.2020.569270DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7561707PMC
October 2020

Influence of sex and fiber type on the satellite cell pool in human skeletal muscle.

Scand J Med Sci Sports 2021 Feb 20;31(2):303-312. Epub 2020 Oct 20.

Department of Physiology, Nutrition and Biomechanics, Åstrand Laboratory, Swedish School of Sport and Health Sciences, Stockholm, Sweden.

The repair, remodeling, and regeneration of myofibers are dependent on satellite cells (SCs), although, the distribution of SCs in different fiber types of human muscle remains inconclusive. There is also a paucity of research comparing muscle fiber characteristics in a sex-specific manner. Therefore, the aim of this study was to investigate fiber type-specific SC content in men and women. Muscle biopsies from vastus lateralis were collected from 64 young (mean age 27 ± 5), moderately trained men (n = 34) and women (n = 30). SCs were identified by Pax7-staining together with immunofluorescent analyses of fiber type composition, fiber size, and myonuclei content. In a mixed population, comparable number of SCs was associated to type I and type II fibers (0.07 ± 0.02 vs 0.07 ± 0.02 SCs per fiber, respectively). However, unlike men, women displayed a fiber type-specific distribution, with SC content being lower in type II than type I fibers (P = .041). Sex-based differences were found specifically for type II fibers, where women displayed lower SC content compared to men (P < .001). In addition, positive correlations (r-values between 0.36-0.56) were found between SC content and type I and type II fiber size in men (P = .03 and P < .01, respectively), whereas similar relationships could not be detected in women. Sex-based differences were also noted for fiber type composition and fiber size, but not for myonuclei content. We hereby provide evidence for sex-based differences present at the myocellular level, which may have important implications when studying exercise- and training-induced myogenic responses in skeletal muscle.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/sms.13848DOI Listing
February 2021

Protein-carbohydrate ingestion alters Vps34 cellular localization independent of changes in kinase activity in human skeletal muscle.

Exp Physiol 2020 12 17;105(12):2178-2189. Epub 2020 Oct 17.

School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, UK.

New Findings: What is the central question of the study? Is Vps34 a nutrient-sensitive activator of mTORC1 in human skeletal muscle? What is the main finding and its importance? We show that altering nutrient availability, via protein-carbohydrate feeding, does not increase Vps34 kinase activity in human skeletal muscle. Instead, feeding increased Vps34-mTORC1 co-localization in parallel to increased mTORC1 activity. These findings may have important implications in the understanding nutrient-induced mTORC1 activation in skeletal muscle via interaction with Vps34.

Abstract: The Class III PI3Kinase, Vps34, has recently been proposed as a nutrient sensor, essential for activation of the mechanistic target of rapamycin (mTOR) complex 1 (mTORC1). We therefore investigated the effects of increasing nutrient availability through protein-carbohydrate (PRO-CHO) feeding on Vps34 kinase activity and cellular localization in human skeletal muscle. Eight young, healthy males (21 ± 0.5 yrs, 77.7 ± 9.9 kg, 25.9 ± 2.7 kg/m , mean ± SD) ingested a PRO-CHO beverage containing 20/44/1 g PRO/CHO/FAT respectively, with skeletal muscle biopsies obtained at baseline and 1 h and 3 h post-feeding. PRO-CHO feeding did not alter Vps34 kinase activity, but did stimulate Vps34 translocation toward the cell periphery (PRE (mean ± SD) - 0.273 ± 0.040, 1 h - 0.348 ± 0.061, Pearson's Coefficient (r)) where it co-localized with mTOR (PRE - 0.312 ± 0.040, 1 h - 0.348 ± 0.069, Pearson's Coefficient (r)). These alterations occurred in parallel to an increase in S6K1 kinase activity (941 ± 466% of PRE at 1 h post-feeding). Subsequent in vitro experiments in C2C12 and human primary myotubes displayed no effect of the Vps34-specific inhibitor SAR405 on mTORC1 signalling responses to elevated nutrient availability. Therefore, in summary, PRO-CHO ingestion does not increase Vps34 activity in human skeletal muscle, whilst pharmacological inhibition of Vps34 does not prevent nutrient stimulation of mTORC1 in vitro. However, PRO-CHO ingestion promotes Vps34 translocation to the cell periphery, enabling Vps34 to associate with mTOR. Therefore, our data suggests that interaction between Vps34 and mTOR, rather than changes in Vps34 activity per se may be involved in PRO-CHO activation of mTORC1 in human skeletal muscle.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1113/EP088805DOI Listing
December 2020

High-dose leucine supplementation does not prevent muscle atrophy or strength loss over 7 days of immobilization in healthy young males.

Am J Clin Nutr 2020 11;112(5):1368-1381

School of Sport, Exercise, and Rehabilitation Sciences, University of Birmingham, Birmingham, United Kingdom.

Background: Unavoidable periods of disuse lead to muscle atrophy and functional decline. Preventing such declines can reduce the risk of re-injury and improve recovery of normal physiological functioning.

Objectives: We aimed to determine the effectiveness of high-dose leucine supplementation on muscle morphology and strength during 7 d of unilateral lower-limb immobilization, and the role of myofibrillar (MyoPS) and mitochondrial (MitoPS) protein synthesis in disuse atrophy.

Methods: Sixteen healthy males (mean ± SEM age: 23 ± 1 y) underwent 7 d of unilateral lower-limb immobilization, with thrice-daily leucine (LEU; n = 8) or placebo (PLA; n = 8) supplementation (15 g/d). Before and after immobilization, muscle strength and compartmental tissue composition were assessed. A primed continuous infusion of l-[ring-13C6]-phenylalanine with serial muscle biopsies was used to determine postabsorptive and postprandial (20 g milk protein) MyoPS and MitoPS, fiber morphology, markers of protein turnover, and mitochondrial function between the control leg (CTL) and the immobilized leg (IMB).

Results: Leg fat-free mass was reduced in IMB (mean ± SEM: -3.6% ± 0.5%; P = 0.030) but not CTL with no difference between supplementation groups. Isometric knee extensor strength declined to a greater extent in IMB (-27.9% ± 4.4%) than in CTL (-14.3% ± 4.4%; P = 0.043) with no difference between groups. In response to 20 g milk protein, postprandial MyoPS rates were significantly lower in IMB than in CTL (-22% ± 4%; P < 0.01) in both LEU and PLA. Postabsorptive MyoPS rates did not differ between legs or groups. Postabsorptive MitoPS rates were significantly lower in IMB than in CTL (-14% ± 5%; P < 0.01) and postprandial MitoPS rates significantly declined in response to 20 g milk protein ingestion (CTL: -10% ± 8%; IMB: -15% ± 10%; P = 0.039), with no differences between legs or groups. There were no significant differences in measures of mitochondrial respiration between legs, but peroxisome proliferator-activated receptor γ coactivator 1-α and oxidative phosphorylation complex II and III were significantly lower in IMB than in CTL (P < 0.05), with no differences between groups.

Conclusions: High-dose leucine supplementation (15 g/d) does not appear to attenuate any functional declines associated with 7 d of limb immobilization in young, healthy males.This trial was registered at clinicaltrials.gov as NCT03762278.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1093/ajcn/nqaa229DOI Listing
November 2020

Achieving energy balance with a high-fat meal does not enhance skeletal muscle adaptation and impairs glycaemic response in a sleep-low training model.

Exp Physiol 2020 10 7;105(10):1778-1791. Epub 2020 Sep 7.

Department of Physical Performance, Norwegian School of Sport Sciences, Oslo, Norway.

New Findings: What is the central question of this study? Does achieving energy balance mainly with ingested fat in a 'sleep-low' model of training with low muscle glycogen affect the early training adaptive response during recovery? What is the main finding and its importance? Replenishing the energy expended during exercise mainly from ingested fat to achieve energy balance in a 'sleep-low' model does not enhance the response of skeletal muscle markers of early adaptation to training and impairs glycaemic control the morning after compared to training with low energy availability. These findings are important for optimizing post-training dietary recommendations in relation to energy balance and macronutrient intake.

Abstract: Training with low carbohydrate availability (LCHO) has been shown to acutely enhance endurance training skeletal muscle response, but the concomitant energy deficit (ED) in LCHO interventions has represented a confounding factor in past research. This study aimed at determining if achieving energy balance with high fat (EB-HF) acutely enhances the adaptive response in LCHO compared to ED with low fat (ED-LF). In a crossover design, nine well-trained males completed a 'sleep-low' protocol: on day 1 they cycled to deplete muscle glycogen while reaching a set energy expenditure (30 kcal (kg of fat free mass (FFM)) ). Post-exercise, low carbohydrate, protein-matched meals completely (EB-HF, 30 kcal (kg FFM) ) or partially (ED-LF, 9 kcal (kg FFM) ) replaced the energy expended, with the majority of energy derived from fat in EB-HF. In the morning of day 2, participants exercised fasted, and skeletal muscle and blood samples were collected and a carbohydrate-protein drink was ingested at 0.5 h recovery. Muscle glycogen showed no treatment effect (P < 0.001) and decreased from 350 ± 98 to 192 ± 94 mmol (kg dry mass) between rest and 0.5 h recovery. Phosphorylation status of the mechanistic target of rapamycin and AMP-activated protein kinase pathway proteins showed only time effects. mRNA expression of p53 increased after exercise (P = 0.005) and was higher in ED-LF at 3.5 h compared to EB-HF (P = 0.027). Plasma glucose and insulin area under the curve (P < 0.04) and peak values (P ≤ 0.05) were higher in EB-HF after the recovery drink. Achieving energy balance with a high-fat meal in a 'train-low' ('sleep-low') model did not enhance markers of skeletal muscle adaptation and impaired glycaemia in response to a recovery drink following training in the morning.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1113/EP088795DOI Listing
October 2020

Overexpression of the vitamin D receptor (VDR) induces skeletal muscle hypertrophy.

Mol Metab 2020 12 7;42:101059. Epub 2020 Aug 7.

MRC/ARUK Centre for Musculoskeletal Ageing Research and National Institute for Health Research (NIHR), Nottingham Biomedical Research Centre (BRC), School of Medicine, University of Nottingham, DE22 3DT, UK. Electronic address:

Objective: The Vitamin D receptor (VDR) has been positively associated with skeletal muscle mass, function and regeneration. Mechanistic studies have focused on the loss of the receptor, with in vivo whole-body knockout models demonstrating reduced myofibre size and function and impaired muscle development. To understand the mechanistic role upregulation of the VDR elicits in muscle mass/health, we studied the impact of VDR over-expression (OE) in vivo before exploring the importance of VDR expression upon muscle hypertrophy in humans.

Methods: Wistar rats underwent in vivo electrotransfer (IVE) to overexpress the VDR in the Tibialis anterior (TA) muscle for 10 days, before comprehensive physiological and metabolic profiling to characterise the influence of VDR-OE on muscle protein synthesis (MPS), anabolic signalling and satellite cell activity. Stable isotope tracer (DO) techniques were used to assess sub-fraction protein synthesis, alongside RNA-Seq analysis. Finally, human participants underwent 20 wks of resistance exercise training, with body composition and transcriptomic analysis.

Results: Muscle VDR-OE yielded total protein and RNA accretion, manifesting in increased myofibre area, i.e., hypertrophy. The observed increases in MPS were associated with enhanced anabolic signalling, reflecting translational efficiency (e.g., mammalian target of rapamycin (mTOR-signalling), with no effects upon protein breakdown markers being observed. Additionally, RNA-Seq illustrated marked extracellular matrix (ECM) remodelling, while satellite cell content, markers of proliferation and associated cell-cycled related gene-sets were upregulated. Finally, induction of VDR mRNA correlated with muscle hypertrophy in humans following long-term resistance exercise type training.

Conclusion: VDR-OE stimulates muscle hypertrophy ostensibly via heightened protein synthesis, translational efficiency, ribosomal expansion and upregulation of ECM remodelling-related gene-sets. Furthermore, VDR expression is a robust marker of the hypertrophic response to resistance exercise in humans. The VDR is a viable target of muscle maintenance through testable Vitamin D molecules, as active molecules and analogues.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.molmet.2020.101059DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7475200PMC
December 2020

Mitochondrial uncoupler BAM15 reverses diet-induced obesity and insulin resistance in mice.

Nat Commun 2020 05 14;11(1):2397. Epub 2020 May 14.

School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW, 2052, Australia.

Obesity is a health problem affecting more than 40% of US adults and 13% of the global population. Anti-obesity treatments including diet, exercise, surgery and pharmacotherapies have so far failed to reverse obesity incidence. Herein, we target obesity with a pharmacotherapeutic approach that decreases caloric efficiency by mitochondrial uncoupling. We show that a recently identified mitochondrial uncoupler BAM15 is orally bioavailable, increases nutrient oxidation, and decreases body fat mass without altering food intake, lean body mass, body temperature, or biochemical and haematological markers of toxicity. BAM15 decreases hepatic fat, decreases inflammatory lipids, and has strong antioxidant effects. Hyperinsulinemic-euglycemic clamp studies show that BAM15 improves insulin sensitivity in multiple tissue types. Collectively, these data demonstrate that pharmacologic mitochondrial uncoupling with BAM15 has powerful anti-obesity and insulin sensitizing effects without compromising lean mass or affecting food intake.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41467-020-16298-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7224297PMC
May 2020

Immobilization Leads to Alterations in Intracellular Phosphagen and Creatine Transporter Content in Human Skeletal Muscle.

Am J Physiol Cell Physiol 2020 May 6. Epub 2020 May 6.

School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, UK; MRC-ARUK Centre for Musculoskeletal Ageing Research, University of Birmingham, UK.

The role of dysregulated intracellular creatine metabolism in disuse atrophy is unknown. In this study, skeletal muscle biopsy samples were obtained after 7-days of unilateral leg immobilization (IMMOB) and the non-immobilized control limb (CTRL) of 15 healthy males (23.1 ± 3.5 yrs). Samples were analyzed for fibre-type cross-sectional area (CSA) and creatine transporter (CreaT) at the cell membrane periphery (MEM) or intracellular (INT) areas, via immunoflouresence microscopy. Creatine kinase (CK) and AMP-activated protein kinase (AMPK) were determined via immunoblot. PCr, Cr and ATP were measured via enzymatic analysis. Body composition and maximal isometric knee extensor strength were assessed before and after disuse. Leg strength and fat-free mass were reduced in IMMOB (~32% and 4%, respectively; P<0.01 for both). Type II fibre CSA was smaller (~12%; P=0.028) and intramuscular PCr lower (~13%; P=0.015) in IMMOB vs. CTRL. CreaT protein was greater in Type I fibres in both limbs (P<0.01). CreaT was greater in IMMOB vs. CTRL (P < 0.01) and inversely associated with PCr concentration in both limbs (P < 0.05). MEM CreaT was greater than the INT CreaT in Type I and II fibres of both limbs (~14% for both; P<0.01 for both). Type I fibre CreaT tended to be greater in IMMOB vs. CTRL (P=0.074). CK was greater, and phospho-to-total AMPK tended to be greater in IMMOB vs. CTRL (P=0.013 and 0.051, respectively). These findings suggest that modulation of intracellular creatine metabolism is an adaptive response to immobilisation in young healthy skeletal muscle.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1152/ajpcell.00072.2020DOI Listing
May 2020

Fine wine or sour grapes? A systematic review and meta-analysis of the impact of red wine polyphenols on vascular health.

Eur J Nutr 2021 Feb 17;60(1):1-28. Epub 2020 Apr 17.

School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, B15 2TT, UK.

Purpose: Red wine polyphenols (RWP) are plant-based molecules that have been extensively studied in relation to their protective effects on vascular health in both animals and humans. The aim of this review was to quantify and compare the efficacy of RWP and pure resveratrol on outcomes measures of vascular health and function in both animals and humans.

Methods: Comprehensive database searches were carried out through PubMed, Web of Science and OVID for randomised, placebo-controlled studies in both animals and humans. Meta-analyses were carried out on acute and chronic studies of RWP in humans, alongside sub-group analysis where possible. Risk-of-bias assessment was carried out for all included studies based on randomisation, allocation, blinding, outcome data reporting, and other biases.

Results: 48 animal and 37 human studies were included in data extraction following screening. Significant improvements in measures of blood pressure and vascular function following RWP were seen in 84% and 100% of animal studies, respectively. Human studies indicated significant improvements in systolic blood pressure overall (- 2.6 mmHg, 95% CI: [- 4.8, - 0.4]), with a greater improvement in pure-resveratrol studies alone (- 3.7 mmHg, 95% CI: [- 7.3, - 0.0]). No significant effects of RWP were seen in diastolic blood pressure or flow-mediated dilation (FMD) of the brachial artery.

Conclusion: RWP have the potential to improve vascular health in at risk human populations, particularly in regard to lowering systolic blood pressure; however, such benefits are not as prevalent as those observed in animal models.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s00394-020-02247-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7867547PMC
February 2021

AMPK activation induces mitophagy and promotes mitochondrial fission while activating TBK1 in a PINK1-Parkin independent manner.

FASEB J 2020 05 22;34(5):6284-6301. Epub 2020 Mar 22.

School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, UK.

Mitophagy is a key process regulating mitochondrial quality control. Several mechanisms have been proposed to regulate mitophagy, but these have mostly been studied using stably expressed non-native proteins in immortalized cell lines. In skeletal muscle, mitophagy and its molecular mechanisms require more thorough investigation. To measure mitophagy directly, we generated a stable skeletal muscle C2C12 cell line, expressing a mitophagy reporter construct (mCherry-green fluorescence protein-mtFIS1 ). Here, we report that both carbonyl cyanide m-chlorophenyl hydrazone (CCCP) treatment and adenosine monophosphate activated protein kinase (AMPK) activation by 991 promote mitochondrial fission via phosphorylation of MFF and induce mitophagy by ~20%. Upon CCCP treatment, but not 991, ubiquitin phosphorylation, a read-out of PTEN-induced kinase 1 (PINK1) activity, and Parkin E3 ligase activity toward CDGSH iron sulfur domain 1 (CISD1) were increased. Although the PINK1-Parkin signaling pathway is active in response to CCCP treatment, we observed no change in markers of mitochondrial protein content. Interestingly, our data shows that TANK-binding kinase 1 (TBK1) phosphorylation is increased after both CCCP and 991 treatments, suggesting TBK1 activation to be independent of both PINK1 and Parkin. Finally, we confirmed in non-muscle cell lines that TBK1 phosphorylation occurs in the absence of PINK1 and is regulated by AMPK-dependent signaling. Thus, AMPK activation promotes mitophagy by enhancing mitochondrial fission (via MFF phosphorylation) and autophagosomal engulfment (via TBK1 activation) in a PINK1-Parkin independent manner.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1096/fj.201903051RDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7212019PMC
May 2020

High Levels of Physical Activity in Later Life Are Associated With Enhanced Markers of Mitochondrial Metabolism.

J Gerontol A Biol Sci Med Sci 2020 07;75(8):1481-1487

School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, UK.

The age-associated reduction in muscle mass is well characterized; however, less is known regarding the mechanisms responsible for the decline in oxidative capacity also observed with advancing age. The purpose of the current study was therefore to compare mitochondrial gene expression and protein content between young and old recreationally active, and older highly active individuals. Muscle biopsies were obtained from the vastus lateralis of young males (YG: 22 ± 3 years) and older (OG: 67 ± 2 years) males not previously engaged in formal exercise and older male master cyclists (OT: 65 ± 5 years) who had undertaken cycling exercise for 32 ± 17 years. Comparison of gene expression between YG, OG, and OT groups revealed greater expression of mitochondrial-related genes, namely, electron transport chain (ETC) complexes II, III, and IV (p < .05) in OT compared with YG and OG. Gene expression of mitofusion (MFN)-1/2, mitochondrial fusion genes, was greater in OT compared with OG (p < .05). Similarly, protein content of ETC complexes I, II, and IV was significantly greater in OT compared with both YG and OG (p < .001). Protein content of peroxisome proliferator-activated receptor gamma, coactivator 1 α (PGC-1α), was greater in OT compared with YG and OG (p < .001). Our results suggest that the aging process per se is not associated with a decline in gene expression and protein content of ETC complexes. Mitochondrial-related gene expression and protein content are substantially greater in OT, suggesting that exercise-mediated increases in mitochondrial content can be maintained into later life.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1093/gerona/glaa005DOI Listing
July 2020

The vitamin D receptor regulates mitochondrial function in C2C12 myoblasts.

Am J Physiol Cell Physiol 2020 03 15;318(3):C536-C541. Epub 2020 Jan 15.

School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, United Kingdom.

Vitamin D deficiency has been linked to a reduction in skeletal muscle function and oxidative capacity; however, the mechanistic bases of these impairments are poorly understood. The biological actions of vitamin D are carried out via the binding of 1α,25-dihydroxyvitamin D (1α,25(OH)D) to the vitamin D receptor (VDR). Recent evidence has linked 1α,25(OH)D to the regulation of skeletal muscle mitochondrial function in vitro; however, little is known with regard to the role of the VDR in this process. To examine the regulatory role of the VDR in skeletal muscle mitochondrial function, we used lentivirus-mediated shRNA silencing of the VDR in C2C12 myoblasts (VDR-KD) and examined mitochondrial respiration and protein content compared with an shRNA scrambled control. VDR protein content was reduced by ~95% in myoblasts and myotubes ( < 0.001). VDR-KD myoblasts displayed a 30%, 30%, and 36% reduction in basal, coupled, and maximal respiration, respectively ( < 0.05). This phenotype was maintained in VDR-KD myotubes, displaying a 34%, 33%, and 48% reduction in basal, coupled, and maximal respiration ( < 0.05). Furthermore, ATP production derived from oxidative phosphorylation (ATP) was reduced by 20%, suggesting intrinsic impairments within the mitochondria following VDR-KD. However, despite the observed functional decrements, mitochondrial protein content, as well as markers of mitochondrial fission were unchanged. In summary, we highlight a direct role for the VDR in regulating skeletal muscle mitochondrial respiration in vitro, providing a potential mechanism as to how vitamin D deficiency might impact upon skeletal muscle oxidative capacity.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1152/ajpcell.00568.2019DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7099523PMC
March 2020

Reductions in skeletal muscle mitochondrial mass are not restored following exercise training in patients with chronic kidney disease.

FASEB J 2020 01 6;34(1):1755-1767. Epub 2019 Dec 6.

Department of Health Sciences, University of Leicester, Leicester, UK.

Patients with chronic kidney disease (CKD) exhibit reduced exercise capacity, poor physical function and symptoms of fatigue. The mechanisms that contribute to this are not clearly defined but may involve reductions in mitochondrial function, mass and biogenesis. Here we report on the effect of non-dialysis dependent CKD (NDD-CKD) on mitochondrial mass and basal expression of transcription factors involved in mitochondrial biogenesis compared to a healthy control cohort (HC). In addition, we sought to investigate the effect of a 12-week exercise-training programme on these aspects of mitochondrial dysfunction in a NDD-CKD cohort.For the comparison between NDD-CKD and HC populations, skeletal muscle biopsies were collected from the vastus lateralis (VL) of n=16 non-dialysis dependent CKD patient's stage 3b-5 (NDD-CKD) and n=16 healthy controls matched for age, gender and physical activity (HC). To investigate the effect of exercise training, VL biopsies were collected from n=17 NDD-CKD patients before and after a 12-week exercise intervention that was comprised of aerobic exercise (AE) or a combination of aerobic exercise and resistance training (CE). Mitochondrial mass was analysed by citrate synthase activity and mitochondrial protein content by Porin expression, whilst the expression of transcription factors involved in mitochondrial biogenesis were quantified by real-time qPCR. NDD-CKD patients exhibited a significant reduction in mitochondrial mass when compared to HC, coupled to a reduction in PGC-1α, NRF-1, Nrf2, TFam, mfn2 and SOD1/2 gene expression. 12-weeks of exercise training resulted in a significant increase in PGC-1α expression in both groups, with no further changes seen across indicators of mitochondrial biogenesis. No significant changes in mitochondrial mass were observed in response to either exercise programme. NDD-CKD patients exhibit reduced skeletal muscle mitochondrial mass and gene expression of transcription factors involved in mitochondrial biogenesis compared to HC. These reductions were not restored following 12-weeks of exercise training implying exercise resistance in this cohort. The reasons for this lack of improvement are currently unknown and require further investigation, as reversing the dysregulation of these processes in NDD-CKD may provide a therapeutic opportunity to improve muscle fatigue and dysfunction in this population.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1096/fj.201901936RRDOI Listing
January 2020

p300 and cAMP response element-binding protein-binding protein in skeletal muscle homeostasis, contractile function, and survival.

J Cachexia Sarcopenia Muscle 2020 04 3;11(2):464-477. Epub 2020 Jan 3.

Department of Orthopaedic Surgery, University of California San Diego, La Jolla, CA, USA.

Background: Reversible ε-amino acetylation of lysine residues regulates transcription as well as metabolic flux; however, roles for specific lysine acetyltransferases in skeletal muscle physiology and function are unknown. In this study, we investigated the role of the related acetyltransferases p300 and cAMP response element-binding protein-binding protein (CBP) in skeletal muscle transcriptional homeostasis and physiology in adult mice.

Methods: Mice with skeletal muscle-specific and inducible knockout of p300 and CBP (PCKO) were generated by crossing mice with a tamoxifen-inducible Cre recombinase expressed under the human α-skeletal actin promoter with mice having LoxP sites flanking exon 9 of the Ep300 and Crebbp genes. Knockout of PCKO was induced at 13-15 weeks of age via oral gavage of tamoxifen for 5 days to both PCKO and littermate control [wildtype (WT)] mice. Body composition, food intake, and muscle function were assessed on day 0 (D0) through 5 (D5). Microarray and tandem mass tag mass spectrometry analyses were performed to assess global RNA and protein levels in skeletal muscle of PCKO and WT mice.

Results: At D5 after initiating tamoxifen treatment, there was a reduction in body weight (-15%), food intake (-78%), stride length (-46%), and grip strength (-45%) in PCKO compared with WT mice. Additionally, ex vivo contractile function [tetanic tension (kPa)] was severely impaired in PCKO vs. WT mice at D3 (~70-80% lower) and D5 (~80-95% lower) and resulted in lethality within 1 week-a phenotype that is reversed by the presence of a single allele of either p300 or CBP. The impaired muscle function in PCKO mice was paralleled by substantial transcriptional alterations (3310 genes; false discovery rate < 0.1), especially in gene networks central to muscle contraction and structural integrity. This transcriptional uncoupling was accompanied by changes in protein expression patterns indicative of impaired muscle function, albeit to a smaller magnitude (446 proteins; fold-change > 1.25; false discovery rate < 0.1).

Conclusions: These data reveal that p300 and CBP are required for the control and maintenance of contractile function and transcriptional homeostasis in skeletal muscle and, ultimately, organism survival. By extension, modulating p300/CBP function may hold promise for the treatment of disorders characterized by impaired contractile function in humans.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/jcsm.12522DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7113519PMC
April 2020

Lipid Metabolism Links Nutrient-Exercise Timing to Insulin Sensitivity in Men Classified as Overweight or Obese.

J Clin Endocrinol Metab 2020 03;105(3)

Department for Health, University of Bath, Bath, United Kingdom.

Context: Pre-exercise nutrient availability alters acute metabolic responses to exercise, which could modulate training responsiveness.

Objective: To assess acute and chronic effects of exercise performed before versus after nutrient ingestion on whole-body and intramuscular lipid utilization and postprandial glucose metabolism.

Design: (1) Acute, randomized, crossover design (Acute Study); (2) 6-week, randomized, controlled design (Training Study).

Setting: General community.

Participants: Men with overweight/obesity (mean ± standard deviation, body mass index: 30.2 ± 3.5 kg⋅m-2 for Acute Study, 30.9 ± 4.5 kg⋅m-2 for Training Study).

Interventions: Moderate-intensity cycling performed before versus after mixed-macronutrient breakfast (Acute Study) or carbohydrate (Training Study) ingestion.

Results: Acute Study-exercise before versus after breakfast consumption increased net intramuscular lipid utilization in type I (net change: -3.44 ± 2.63% versus 1.44 ± 4.18% area lipid staining, P < 0.01) and type II fibers (-1.89 ± 2.48% versus 1.83 ± 1.92% area lipid staining, P < 0.05). Training Study-postprandial glycemia was not differentially affected by 6 weeks of exercise training performed before versus after carbohydrate intake (P > 0.05). However, postprandial insulinemia was reduced with exercise training performed before but not after carbohydrate ingestion (P = 0.03). This resulted in increased oral glucose insulin sensitivity (25 ± 38 vs -21 ± 32 mL⋅min-1⋅m-2; P = 0.01), associated with increased lipid utilization during exercise (r = 0.50, P = 0.02). Regular exercise before nutrient provision also augmented remodeling of skeletal muscle phospholipids and protein content of the glucose transport protein GLUT4 (P < 0.05).

Conclusions: Experiments investigating exercise training and metabolic health should consider nutrient-exercise timing, and exercise performed before versus after nutrient intake (ie, in the fasted state) may exert beneficial effects on lipid utilization and reduce postprandial insulinemia.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1210/clinem/dgz104DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7112968PMC
March 2020

Molecular regulation of human skeletal muscle protein synthesis in response to exercise and nutrients: a compass for overcoming age-related anabolic resistance.

Am J Physiol Cell Physiol 2019 12 28;317(6):C1061-C1078. Epub 2019 Aug 28.

Faculty of Kinesiology and Physical Education, University of Toronto, Toronto, Ontario, Canada.

Skeletal muscle mass, a strong predictor of longevity and health in humans, is determined by the balance of two cellular processes, muscle protein synthesis (MPS) and muscle protein breakdown. MPS seems to be particularly sensitive to changes in mechanical load and/or nutritional status; therefore, much research has focused on understanding the molecular mechanisms that underpin this cellular process. Furthermore, older individuals display an attenuated MPS response to anabolic stimuli, termed anabolic resistance, which has a negative impact on muscle mass and function, as well as quality of life. Therefore, an understanding of which, if any, molecular mechanisms contribute to anabolic resistance of MPS is of vital importance in formulation of therapeutic interventions for such populations. This review summarizes the current knowledge of the mechanisms that underpin MPS, which are broadly divided into mechanistic target of rapamycin complex 1 (mTORC1)-dependent, mTORC1-independent, and ribosomal biogenesis-related, and describes the evidence that shows how they are regulated by anabolic stimuli (exercise and/or nutrition) in healthy human skeletal muscle. This review also summarizes evidence regarding which of these mechanisms may be implicated in age-related skeletal muscle anabolic resistance and provides recommendations for future avenues of research that can expand our knowledge of this area.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1152/ajpcell.00209.2019DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6962519PMC
December 2019

Nicotinamide Riboside Augments the Aged Human Skeletal Muscle NAD Metabolome and Induces Transcriptomic and Anti-inflammatory Signatures.

Cell Rep 2019 08;28(7):1717-1728.e6

Institute of Metabolism and Systems Research, University of Birmingham, Birmingham, UK; Centre for Endocrinology, Diabetes and Metabolism, Birmingham Health Partners, Birmingham, UK; MRC-Arthritis Research UK Centre for Musculoskeletal Ageing Research, Institute of Inflammation and Ageing, University of Birmingham, Birmingham, UK. Electronic address:

Nicotinamide adenine dinucleotide (NAD) is modulated by conditions of metabolic stress and has been reported to decline with aging in preclinical models, but human data are sparse. Nicotinamide riboside (NR) supplementation ameliorates metabolic dysfunction in rodents. We aimed to establish whether oral NR supplementation in aged participants can increase the skeletal muscle NAD metabolome and if it can alter muscle mitochondrial bioenergetics. We supplemented 12 aged men with 1 g NR per day for 21 days in a placebo-controlled, randomized, double-blind, crossover trial. Targeted metabolomics showed that NR elevated the muscle NAD metabolome, evident by increased nicotinic acid adenine dinucleotide and nicotinamide clearance products. Muscle RNA sequencing revealed NR-mediated downregulation of energy metabolism and mitochondria pathways, without altering mitochondrial bioenergetics. NR also depressed levels of circulating inflammatory cytokines. Our data establish that oral NR is available to aged human muscle and identify anti-inflammatory effects of NR.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.celrep.2019.07.043DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6702140PMC
August 2019

One Week of Step Reduction Lowers Myofibrillar Protein Synthesis Rates in Young Men.

Med Sci Sports Exerc 2019 10;51(10):2125-2134

School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, UNITED KINGDOM.

Purpose: Across the lifespan, physical activity levels decrease and time spent sedentary typically increases. However, little is known about the impact that these behavioral changes have on skeletal muscle mass regulation. The primary aim of this study was to use a step reduction model to determine the impact of reduced physical activity and increased sedentary time on daily myofibrillar protein synthesis rates in healthy young men.

Methods: Eleven men (22 ± 2 yr) completed 7 d of habitual physical activity (HPA) followed by 7 d of step reduction (SR). Myofibrillar protein synthesis rates were determined during HPA and SR using the deuterated water (H2O) method combined with the collection of skeletal muscle biopsies and daily saliva samples. Gene expression of selected proteins related to muscle mass regulation and oxidative metabolism were determined via real time reverse transcription-quantitative polymerase chain reaction (RT-qPCR).

Results: Daily step count was reduced by approximately 91% during SR (from 13,054 ± 2763 steps per day to 1192 ± 330 steps per day; P < 0.001) and this led to an increased contribution of sedentary time to daily activity (73% ± 6% to 90% ± 3%; P < 0.001). Daily myofibrillar protein synthesis decreased by approximately 27% from 1.39 ± 0.32%·d during HPA to 1.01 ± 0.38%·d during SR (P < 0.05). Muscle atrophy F-box and myostatin mRNA expression were upregulated, whereas mechanistic target of rapamycin, p53, and PDK4 mRNA expression were downregulated after SR (P < 0.05).

Conclusions: One week of reduced physical activity and increased sedentary time substantially lowers daily myofibrillar protein synthesis rates in healthy young men.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1249/MSS.0000000000002034DOI Listing
October 2019

Graded reductions in preexercise muscle glycogen impair exercise capacity but do not augment skeletal muscle cell signaling: implications for CHO periodization.

J Appl Physiol (1985) 2019 06 2;126(6):1587-1597. Epub 2019 May 2.

Research Institute for Sport and Exercise Sciences, Liverpool John Moores University , Liverpool , United Kingdom.

We examined the effects of graded muscle glycogen on exercise capacity and modulation of skeletal muscle signaling pathways associated with the regulation of mitochondrial biogenesis. In a repeated-measures design, eight men completed a sleep-low, train-low model comprising an evening glycogen-depleting cycling protocol followed by an exhaustive exercise capacity test [8 × 3 min at 80% peak power output (PPO), followed by 1-min efforts at 80% PPO until exhaustion] the subsequent morning. After glycogen-depleting exercise, subjects ingested a total of 0 g/kg (L-CHO), 3.6 g/kg (M-CHO), or 7.6 g/kg (H-CHO) of carbohydrate (CHO) during a 6-h period before sleeping, such that exercise was commenced the next morning with graded ( < 0.05) muscle glycogen concentrations (means ± SD: L-CHO: 88 ± 43, M-CHO: 185 ± 62, H-CHO: 278 ± 47 mmol/kg dry wt). Despite differences ( < 0.05) in exercise capacity at 80% PPO between trials (L-CHO: 18 ± 7, M-CHO: 36 ± 3, H-CHO: 44 ± 9 min), exercise induced comparable AMPK phosphorylation (~4-fold) and PGC-1α mRNA expression (~5-fold) after exercise and 3 h after exercise, respectively. In contrast, neither exercise nor CHO availability affected the phosphorylation of p38MAPK or CaMKII or mRNA expression of p53, Tfam, CPT-1, CD36, or PDK4. Data demonstrate that when exercise is commenced with muscle glycogen < 300 mmol/kg dry wt, further graded reductions of 100 mmol/kg dry weight impair exercise capacity but do not augment skeletal muscle cell signaling. We provide novel data demonstrating that when exercise is commenced with muscle glycogen below 300 mmol/kg dry wt (as achieved with the sleep-low, train-low model) further graded reductions in preexercise muscle glycogen of 100 mmol/kg dry wt reduce exercise capacity at 80% peak power output by 20-50% but do not augment skeletal muscle cell signaling.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1152/japplphysiol.00913.2018DOI Listing
June 2019

Differential responses of myoblasts and myotubes to photobiomodulation are associated with mitochondrial number.

J Biophotonics 2019 06 20;12(6):e201800411. Epub 2019 Feb 20.

School of Dentistry, College of Medical and Dental Sciences, Institute of Clinical Sciences, University of Birmingham, Birmingham, UK.

Objective: Photobiomodulation (PBM) is the application of light to promote tissue healing. Current indications suggest PBM induces its beneficial effects in vivo through upregulation of mitochondrial activity. However, how mitochondrial content influences such PBM responses have yet to be evaluated. Hence, the current study assessed the biological response of cells to PBM with varying mitochondrial contents.

Methods: DNA was isolated from myoblasts and myotubes (differentiated myoblasts), and mitochondrial DNA (mtDNA) was amplified and quantified using a microplate assay. Cells were seeded in 96-wellplates, incubated overnight and subsequently irradiated using a light-emitting diode array (400, 450, 525, 660, 740, 810, 830 and white light, 24 mW/cm , 30-240 seconds, 0.72-5.76J/cm ). The effects of PBM on markers of mitochondrial activity including reactive-oxygen-species and real-time mitochondrial respiration (Seahorse XFe96) assays were assessed 8 hours post-irradiation. Datasets were analysed using general linear model followed by one-way analysis of variance (and post hoc-Tukey tests); P = 0.05).

Results: Myotubes exhibited mtDNA levels 86% greater than myoblasts (P < 0.001). Irradiation of myotubes at 400, 450 or 810 nm induced 53%, 29% and 47% increases (relative to non-irradiated control) in maximal respiratory rates, respectively (P < 0.001). Conversely, irradiation of myoblasts at 400 or 450 nm had no significant effect on maximal respiratory rates.

Conclusion: This study suggests that mitochondrial content may influence cellular responses to PBM and as such explain the variability of PBM responses seen in the literature.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/jbio.201800411DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065641PMC
June 2019

Postexercise skeletal muscle signaling responses to moderate- to high-intensity steady-state exercise in the fed or fasted state.

Am J Physiol Endocrinol Metab 2019 02 4;316(2):E230-E238. Epub 2018 Dec 4.

School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham , Birmingham , United Kingdom.

Exercise performed in the fasted state acutely increases fatty acid availability and utilization. Furthermore, activation of energy-sensing pathways and fatty acid metabolic genes can be augmented by fasting and fasted exercise. However, whether a similar effect occurs at higher exercise intensities remains poorly understood. This study aimed to assess the effect of fed and fasted exercise upon postexercise signaling and mRNA responses during moderate- to high-intensity steady-state exercise. Eight male participants [age: 25 (SD 2) yr, V̇o: 47.9 (SD 3.8) ml·kg·min] performed 1 h of cycling at 70% W in the fasted (FAST) state or 2 h following ingestion of a carbohydrate-rich mixed-macronutrient breakfast (FED). Muscle biopsies were collected pre-, immediately, and 3 h postexercise from the medial vastus lateralis, while venous blood samples were collected throughout the trial. Plasma, nonesterified fatty acid, and glycerol concentrations were elevated during FAST compared with FED, although substrate utilization during exercise was similar. AMPK phosphorylation was ~2.5-fold elevated postexercise in both trials and was significantly augmented by ~30% during FAST. CREB phosphorylation was elevated approximately twofold during FAST, although CREB phosphorylation acutely decreased by ~50% immediately postexercise. mRNA expression of PDK4 was approximately three- to fourfold augmented by exercise and approximately twofold elevated throughout FAST, while expression of PPARGC1A mRNA was similarly activated (~10-fold) by exercise in both FED and FAST. In summary, performing moderate- to high-intensity steady-state exercise in the fasted state increases systemic lipid availability, elevates phosphorylation of AMPK and CREB, and augments PDK4 mRNA expression without corresponding increases in whole body fat oxidation and the mRNA expression of PPARGC1A.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1152/ajpendo.00311.2018DOI Listing
February 2019

The Importance of mTOR Trafficking for Human Skeletal Muscle Translational Control.

Exerc Sport Sci Rev 2019 01;47(1):46-53

School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, UK.

The mechanistic target of rapamycin (mTOR) is a central regulator of muscle protein synthesis, and its activation has long been attributed to its translocation to the lysosome. Here, we present a novel model of mTOR activation in skeletal muscle where the translocation of mTOR and the lysosome toward the cell membrane is a key process in mTOR activation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1249/JES.0000000000000173DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6310455PMC
January 2019