Philip J. Atherton’s research while affiliated with University of Nottingham and other places

There is speculation that oral contraceptive pill (OCP) use affects skeletal muscle biology and protein turnover in response to resistance exercise; however, research in this area is scarce. We aimed to assess, using stable isotope tracers and skeletal muscle biopsies, how second-generation OCP phase affected muscle protein synthesis and whole-body proteolysis. Participants (n=12) completed two 6-day study phases in a randomized order: an active pill phase (Active; week two of a monthly active OCP cycle) and an inactive pill phase (Inactive; final week of a monthly OCP cycle). Participants performed unilateral resistance exercise in each study phase, exercising the contralateral leg in the opposite phase in a randomized, counterbalanced order. The Active phase myofibrillar protein synthesis (MPS) rates were 1.44 ± 0.14 %•d ⁻¹ in the control leg and 1.64 ± 0.15 %•d ⁻¹ in the exercise leg (p < 0.001). The Inactive phase MPS rates were 1.49 ± 0.12 %•d-1 %/d in the control leg and 1.71 ± 0.16 %•d ⁻¹ in the exercise leg (p < 0.001), with no interaction between phases (p = 0.63). There was no significant effect of OCP phase on whole-body myofibrillar proteolytic rate (active phase k = 0.018 ± 0.01; inactive phase k = 0.018 ± 0.006; p = 0.55). Skeletal muscle remains equally as responsive, in terms of stimulation of MPS, during Active and Inactive OCP phases; hence, our data does not support a pro-anabolic or catabolic, based on myofibrillar proteolysis, effect of OCP phase on skeletal muscle in females.

Background While decreased protein intake is associated with muscle mass loss, it is unclear whether a decrease in carbohydrate intake adversely affects muscle atrophy independently of protein intake. Herein, we examined whether a low‐carbohydrate (low‐CHO) diet exacerbates denervation‐induced muscle atrophy under conditions of identical protein intake. Methods On day one of the experiment, male Wistar rats underwent unilateral denervation. The contralateral leg was used as the control. After denervation, rats were divided into two dietary groups: high‐carbohydrate (high‐CHO) and low‐CHO. Each group was fed a high‐CHO (70% carbohydrate) or low‐CHO (20% carbohydrate) diet over 7 days. Total protein and energy intakes in both groups were matched by pair feeding. Rats were provided with deuterium oxide (D2O) tracer over the last 3 days of dietary intervention to quantify myofibrillar (muscle) protein synthesis (MPS). Results Denervation reduced wet weight of the gastrocnemius muscle compared to the contralateral control (p < 0.05). Reductions in gastrocnemius muscle weight were greater in the low‐CHO group (−34%) than the high‐CHO group (−28%) (p < 0.05). Although denervation decreased MPS compared to the contralateral control (p < 0.05), no dietary effect on MPS was observed. Denervation resulted in increased mRNA and protein expression of Atrogin‐1, a ubiquitin E3 ligase, compared to that in the contralateral control (p < 0.05). Increases in Atrogin‐1 gene and protein expression due to denervation were greater in the low‐CHO group than in the high‐CHO group (p < 0.05). Conclusions We conclude that a low‐CHO diet may exacerbate denervation‐induced atrophy in fast‐twitch‐dominant muscles compared to a high‐CHO diet, even when the same protein intake is maintained. Although blunted MPS contributed to muscle atrophy due to denervation, exacerbation of muscle atrophy by the low‐CHO diet was not accompanied by explanatory changes in MPS. The effect of the low‐CHO diet might be related to promotion of muscle‐specific ubiquitin E3 ligase gene expression.

Introduction Resistance exercise (RE) enhances functionality in older adults and has proven effective as a means of cross-education in scenarios of unilateral disuse. However, the extent to which older adults demonstrate cross-limb transfer at the motor unit (MU) level following a single bout of unilateral RE is unclear. Methods Thirteen healthy older adults (> 60 years; 5 females) underwent bilateral neuromuscular assessments pre- and post- a single bout of unilateral RE consisting of 3-4 sets of 8-12 repetitions of leg extension of the dominant (exercise) leg, at 75% of 1 repetition maximum, performed to failure. Maximum voluntary contraction (MVC) and force steadiness (FS) were measured. Central and peripheral features of individual MU were recorded using high-density surface electromyography and intramuscular electromyography (HDs/iEMG), during contractions normalised to 25% MVC. Results Following unilateral RE, MVC reduced in exercise (-14.8%, p < 0.001) and control (-6.9%, p = 0.003) legs, with reduced FS performance in the exercise leg compared to the control (p = 0.002). MU firing rate increased during contractions normalised to 25% baseline MVC in the exercised leg (p < 0.05), with no adaptation in the control leg (p > 0.05). All iEMG recorded measures of MU potentials remained unchanged in both legs (all p > 0.05). Conclusion Acute unilateral RE leads to bilateral MVC reduction in older males and females, demonstrating the cross-limb transfer effect. However, adaptation of MU features was only apparent in the exercised limb, and mechanisms underlying the force decline in the non-exercised limb remain uncertain.

Understanding the turnover of proteins in tissues gives information as to how external stimuli result in phenotypic change. Nowhere is such phenotypic change more conspicuous than skeletal muscle, which can be effectively remodelled by increased loading, ageing and unloading (disuse), all of which are subject to modification by nutrition and other environmental stimuli. The understanding of muscle proteome remodelling has undergone a renaissance recently with the reintroduction of deuterated water (D2O) and its ingestion to label amino acids and measure their incorporation into proteins. However, there is confusion around the use of the deuterated water methodology and the interpretation of the data it provides. Here, we provide a short review of some of the more salient features of the method and clarify some of the confusion around the method of deuterated water methods and its use in humans and how the interpretation of the data is in contrast to that of rodents.

It has been hypothesised that skeletal muscle protein turnover is affected by menstrual cycle phase with a more anabolic environment during the follicular vs. the luteal phase. We assessed the influence of menstrual cycle phase on muscle protein synthesis and myofibrillar protein breakdown in response to 6 days of controlled resistance exercise in young females during peak oestrogen and peak progesterone, using stable isotopes, unbiased metabolomics and muscle biopsies. We used comprehensive menstrual cycle phase‐detection methods, including cycle tracking, blood samples and urinary test kits, to classify menstrual phases. Participants (n = 12) completed two 6 day study phases in a randomised order: late follicular phase and mid‐luteal phase. Participants performed unilateral resistance exercise in each menstrual cycle phase, exercising the contralateral leg in each phase in a counterbalanced manner. Follicular phase myofibrillar protein synthesis (MPS) rates were 1.33 ± 0.27% d⁻¹ in the control leg and 1.52 ± 0.27% d⁻¹ in the exercise leg. Luteal phase MPS was 1.28 ± 0.27% d⁻¹ in the control leg and 1.46 ± 0.25% d⁻¹ in the exercise leg. We observed a significant effect of exercise (P < 0.001) but no effect of cycle phase or interaction. There was no significant effect of menstrual cycle phase on whole‐body myofibrillar protein breakdown (P = 0.24). Using unbiased metabolomics, we observed no notable phase‐specific changes in circulating blood metabolites associated with any particular menstrual cycle phase. Fluctuations in endogenous ovarian hormones influenced neither MPS, nor MPB in response to resistance exercise. Skeletal muscle is not more anabolically responsive to resistance exercise in a particular menstrual cycle phase. image Key points It has been hypothesised that the follicular (peak oestrogen) vs. the luteal (peak progesterone) phase of the menstrual cycle is more advantageous for skeletal muscle anabolism in response to resistance exercise. Using best practice methods to assess menstrual cycle status, we measured integrated (over 6 days) muscle protein synthesis (MPS) and myofibrillar protein breakdown (MPB) following resistance exercise in females (n = 12) in their follicular and luteal phases. We observed the expected differences in oestrogen and progesterone concentrations that confirmed our participants’ menstrual cycle phase; however, there were no notable metabolic pathway differences, as measured using metabolomics, between cycle phases. We observed that resistance exercise stimulated MPS, but there was no effect of menstrual cycle phase on either resting or exercise‐stimulated MPS or MPB. Our data show no greater anabolic effect of resistance exercise in the follicular vs. the luteal phase of the menstrual cycle.

Background/Objectives: The acute phase of stroke is marked by inflammation and mobility changes that can compromise nutritional status. This study was a randomized, double-blind, placebo-controlled trial evaluating the effectiveness of creatine supplementation for older people during seven days of hospitalization for stroke compared to usual care. Method: The primary outcome measures were changes in functional capacity, strength, muscle mass, and muscle degradation. The secondary outcomes were changes in serum biomarkers related to inflammation, fibrosis, anabolism, and muscle synthesis. In addition, a follow-up 90 days after the stroke verified functional capacity, strength, quality of life, and mortality. Following admission for an acute stroke, participants received either creatine (10 g) or a visually identical placebo (10 g) orally twice daily. Both groups received supplementation with protein to achieve the goal of 1.5 g of protein/kg of body weight/day and underwent daily mobility training during seven days of hospitalization. Results: Thirty older people were included in two similar groups concerning baseline attributes (15—treatment/15—placebo). Conclusions: Creatine supplementation did not influence functional capacity, strength, or muscle mass during the first 7 days or outcomes 90 days after stroke. There were no serious adverse events associated with creatine supplementation. However, it decreased progranulin levels, raising a new possibility of creatine action. This finding needs further exploration to understand the biological significance of creatine–progranulin interaction.

Objectives To examine the effect of the NAD⁺ precursor, nicotinic acid (NA), for improving skeletal muscle status in sedentary older people. Methods In a double-blind, randomised, placebo-controlled design, 18 sedentary yet otherwise healthy older (65–75 y) males were assigned to 2-weeks of NA (acipimox; 250 mg × 3 daily, n=8) or placebo (PLA, n=10) supplementation. At baseline, and after week 1 and week 2 of supplementation, a battery of functional, metabolic, and molecular readouts were measured. Results Resting and submaximal respiratory exchange ratio was lower (p<0.05) after 2 weeks in the NA group only, but maximal aerobic and anaerobic function and glucose handling were unchanged (p>0.05). Bayesian statistical modelling identified that leak, maximal coupled and maximal uncoupled mitochondrial respiratory states, increased over the 2-week supplemental period in the NA group (probability for a positive change (pd) 85.2, 90.8 and 95.9 %, respectively) but not in PLA. Citrate synthase and protein content of complex II (SDHB) and V (ATP5A) electron transport chain (ETC) components increased over the 2-week period in the NA group only (pd 95.1, 74.5 and 82.3 %, respectively). Mitochondrial and myofibrillar protein synthetic rates remained unchanged in both groups. NA intake altered the muscle transcriptome by increasing the expression of gene pathways related to cell adhesion/cytoskeleton organisation and inflammation/immunity and decreasing pathway expression of ETC and aerobic respiration processes. NAD⁺-specific pathways (e.g., de novo NAD⁺ biosynthetic processes) and genes (e.g., NADSYN1) were uniquely regulated by NA. Conclusions NA might be an effective strategy for improving ageing muscle mitochondrial health.

Insulin Resistance (IR) is a component of the pathogenesis of type 2 diabetes mellitus (T2DM), and risk factor for cardiovascular and neurodegenerative diseases. Amino acid and lipid metabolomic IR diagnostics associate with future T2DM risk in epidemiological cohorts. Whether these assays can accurately detect altered IR following treatment has not been established. In the present study we evaluated the ability of metabolomic diagnostics to predict altered IR following exercise treatment. We evaluated the performance of two distinct insulin assays and built combined clinical and metabolomic IR diagnostics. These were utilised to stratify IR status in the pre intervention fasting samples in three independent cohorts (META PREDICT (MP, n=179), STRRIDE AT/RT (S2, n=116) and STRRIDE PD (SPD, n=149)). Linear and Bayesian projective prediction strategies were used to evaluate biomarkers for fasting insulin and HOMA2IR and change in fasting insulin with treatment. Both insulin assays accurately quantified international standard insulin (R2>0.99), yet agreement for fasting insulin was less congruent (R2=0.65). Only the high-sensitivity ELISA assay could identify the mean effect of treatment on fasting insulin. Clinical metabolomic models were statistically related to fasting insulin (R2 0.33 0.39) but had modest capacity to classify HOMA2IR at a clinically relevant threshold. Furthermore, no model predicted treatment responses in any cohort. Thus, we demonstrate that the choice of insulin assay is critical when quantifying the influence of lifestyle on fasting insulin, while none of the clinical metabolomic biomarkers, validated in cross sectional data, are suitable for monitoring longitudinally changes in IR status

Theta-gamma transcranial alternating current stimulation (TG tACS) over primary motor cortex (M1) can improve motor skill acquisition in young adults, but the effect on older adults is unknown. This study investigated the effects of TG tACS on motor skill acquisition and M1 excitability in 18 young and 18 older adults. High-definition TG tACS (6 Hz theta, 75 Hz gamma) or sham tACS was applied over right M1 for 20 minutes during a ballistic left-thumb abduction motor training task performed in two experimental sessions. Motor skill acquisition was quantified as changes in movement acceleration during and up to 60 minutes after training. Transcranial magnetic stimulation (TMS) was used to assess changes in M1 excitability with motor-evoked potentials (MEP) and short-interval intracortical inhibition (SICI) before and after training. We found that TG tACS increased motor skill acquisition compared with sham tACS in young and older adults ( P < 0.001), with greater effects for young adults ( P = 0.01). The improved motor performance with TG tACS lasted at least 60 minutes after training in both age groups. Motor training was accompanied by greater MEP amplitudes with TG tACS compared to sham tACS in young and older adults ( P < 0.001), but SICI did not vary between tACS sessions ( P = 0.40). These findings indicate that TG tACS over M1 improves motor skill acquisition and alters training-induced changes in M1 excitability in healthy young and older adults. TG tACS may therefore be beneficial to alleviate motor deficits in the ageing population. Key Points Summary Theta-gamma transcranial alternating current stimulation (TG tACS) can improve motor function in healthy young adults, but the effect on older adults is unknown. We found that TG tACS improved motor skill acquisition with long-lasting effects in healthy young and older adults, but effects were stronger in young adults. Transcranial magnetic stimulation showed that TG tACS altered the training-induced changes in motor cortex excitability, but there was no effect of TG tACS on intracortical inhibition in young or older adults. Our data suggest that TG tACS represents a promising approach to improve motor skill acquisition throughout the lifespan, and may be beneficial in older patient populations that experience motor or cognitive deficits.