Muscle protein synthesis and gene expression during recovery from aerobic exercise in the fasted and fed states

The effects of temperature and seasons on subcutaneous white adipose tissue in humans: evidence for thermogenic gene induction

CONTEXT

Although brown adipose tissue (BAT) activity is increased by a cold environment, little is known of the response of human white adipose tissue (WAT) to the cold.

DESIGN

We examined both abdominal and thigh subcutaneous (SC) WAT from 71 subjects who were biopsied in the summer or winter, and adipose expression was assessed after an acute cold stimulus applied to the thigh of physically active young subjects.

RESULTS

In winter, UCP1 and PGC1α mRNA were increased 4 to 10-fold (p < 0.05) and 1.5 to 2-fold, respectively, along with beige adipose markers, and UCP1 protein was 3-fold higher in the winter. The seasonal increase in abdominal SC WAT UCP1 mRNA was considerably diminished in subjects with a BMI > 30 kg/m(2), suggesting that dysfunctional WAT in obesity inhibits adipose thermogenesis. After applying an acute cold stimulus to the thigh of subjects for 30 min, PGC1α and UCP1 mRNA was stimulated 2.7-fold (p < 0.05) and 1.9-fold (p = 0.07), respectively. Acute cold also induced a 2 to 3-fold increase in PGC1α and UCP1 mRNA in human adipocytes in vitro, which was inhibited by macrophage-conditioned medium and by the addition of TNFα.

CONCLUSION

Human SC WAT increases thermogenic genes seasonally and acutely in response to a cold stimulus and this response is inhibited by obesity and inflammation.

Post-Exercise Protein Trial: Interactions between Diet and Exercise (PEPTIDE): study protocol for randomized controlled trial

BACKGROUND

Performing regular exercise is known to manifest a number of health benefits that mainly relate to cardiovascular and muscular adaptations to allow for greater oxygen extraction and utilization. There is increasing evidence that nutrient intake can affect the adaptive response to a single exercise bout, and that protein feeding is important to facilitate this process. Thus, the exercise-nutrient interaction may potentially lead to a greater response to training. The role of post-exercise protein ingestion in enhancing the effects of running-based endurance exercise training relative to energy-matched carbohydrate intervention remains to be established. Additionally, the influence of immediate versus overnight protein ingestion in mediating these training effects is currently unknown. The current protocol aims to establish whether post-exercise nutrient intake and timing would influence the magnitude of improvements during a prescribed endurance training program.

METHODS/DESIGN

The project involves two phases with each involving two treatment arms applied in a randomized investigator-participant double-blind parallel group design. For each treatment, participants will be required to undergo six weeks of running-based endurance training. Immediately post-exercise, participants will be prescribed solutions providing 0.4 grams per kilogram of body mass (g · kg(-1)) of whey protein hydrolysate plus 0.4 g · kg(-1) sucrose, relative to an isocaloric sucrose control (0.8 g · kg(-1); Phase I). In Phase II, identical protein supplements will be provided (0.4 + 0.4 g · kg(-1) · h(-1) of whey protein hydrolysate and sucrose, respectively), with the timing of ingestion manipulated to compare immediate versus overnight recovery feedings. Anthropometric, expired gas, venous blood and muscle biopsy samples will be obtained at baseline and following the six-week training period.

DISCUSSION

By investigating the role of nutrition in enhancing the effects of endurance exercise training, we will provide novel insight regarding nutrient-exercise interactions and the potential to help and develop effective methods to maximize health or performance outcomes in response to regular exercise.

TRIAL REGISTRATION

Current Controlled Trials registration number: ISRCTN27312291 (date assigned: 4 December 2013). The first participant was randomized on 11 December 2013.

Skeletal muscle hypertrophy after aerobic exercise training

Current dogma suggests that aerobic exercise training has minimal effects on skeletal muscle size. We and others have demonstrated that aerobic exercise acutely and chronically alters protein metabolism and induces skeletal muscle hypertrophy. These findings promote an antithesis to the status quo by providing novel perspective on skeletal muscle mass regulation and insight into exercise countermeasures for populations prone to muscle loss.

Single muscle fiber gene expression with run taper

This study evaluated gene expression changes in gastrocnemius slow-twitch myosin heavy chain I (MHC I) and fast-twitch (MHC IIa) muscle fibers of collegiate cross-country runners (n = 6, 20±1 y, VO_2max = 70±1 ml•kg⁻¹•min⁻¹) during two distinct training phases. In a controlled environment, runners performed identical 8 kilometer runs (30∶18±0∶30 min:s, 89±1% HR_max) while in heavy training (∼72 km/wk) and following a 3 wk taper. Training volume during the taper leading into peak competition was reduced ∼50% which resulted in improved race times and greater cross-section and improved function of MHC IIa fibers. Single muscle fibers were isolated from pre and 4 hour post run biopsies in heavily trained and tapered states to examine the dynamic acute exercise response of the growth-related genes Fibroblast growth factor-inducible 14 (FN14), Myostatin (MSTN), Heat shock protein 72 (HSP72), Muscle ring-finger protein-1 (MURF1), Myogenic factor 6 (MRF4), and Insulin-like growth factor 1 (IGF1) via qPCR. FN14 increased 4.3-fold in MHC IIa fibers with exercise in the tapered state (P<0.05). MSTN was suppressed with exercise in both fiber types and training states (P<0.05) while MURF1 and HSP72 responded to running in MHC IIa and I fibers, respectively, regardless of training state (P<0.05). Robust induction of FN14 (previously shown to strongly correlate with hypertrophy) and greater overall transcriptional flexibility with exercise in the tapered state provides an initial molecular basis for fast-twitch muscle fiber performance gains previously observed after taper in competitive endurance athletes.

Influence of aerobic exercise intensity on myofibrillar and mitochondrial protein synthesis in young men during early and late postexercise recovery

Aerobic exercise is typically associated with expansion of the mitochondrial protein pool and improvements in muscle oxidative capacity. The impact of aerobic exercise intensity on the synthesis of specific skeletal muscle protein subfractions is not known. We aimed to study the effect of aerobic exercise intensity on rates of myofibrillar (MyoPS) and mitochondrial (MitoPS) protein synthesis over an early (0.5-4.5 h) and late (24-28 h) period during postexercise recovery. Using a within-subject crossover design, eight males (21 ± 1 yr, Vo2peak 46.7 ± 2.0 ml·kg(-1)·min(-1)) performed two work-matched cycle ergometry exercise trials (LOW: 60 min at 30% Wmax; HIGH: 30 min at 60% Wmax) in the fasted state while undergoing a primed constant infusion of l-[ring-(13)C6]phenylalanine. Muscle biopsies were obtained at rest and 0.5, 4.5, 24, and 28 h postexercise to determine both the "early" and "late" response of MyoPS and MitoPS and the phosphorylation status of selected proteins within both the Akt/mTOR and MAPK pathways. Over 24-28 h postexercise, MitoPS was significantly greater after the HIGH vs. LOW exercise trial (P < 0.05). Rates of MyoPS were increased equivalently over 0.5-4.5 h postexercise recovery (P < 0.05) but remained elevated at 24-28 h postexercise only following the HIGH trial. In conclusion, an acute bout of high- but not low-intensity aerobic exercise in the fasted state resulted in a sustained elevation of both MitoPS and MyoPS at 24-28 h postexercise recovery.

Soy-dairy protein blend and whey protein ingestion after resistance exercise increases amino acid transport and transporter expression in human skeletal muscle

Increasing amino acid availability (via infusion or ingestion) at rest or postexercise enhances amino acid transport into human skeletal muscle. It is unknown whether alterations in amino acid availability, from ingesting different dietary proteins, can enhance amino acid transport rates and amino acid transporter (AAT) mRNA expression. We hypothesized that the prolonged hyperaminoacidemia from ingesting a blend of proteins with different digestion rates postexercise would enhance amino acid transport into muscle and AAT expression compared with the ingestion of a rapidly digested protein. In a double-blind, randomized clinical trial, we studied 16 young adults at rest and after acute resistance exercise coupled with postexercise (1 h) ingestion of either a (soy-dairy) protein blend or whey protein. Phenylalanine net balance and transport rate into skeletal muscle were measured using stable isotopic methods in combination with femoral arteriovenous blood sampling and muscle biopsies obtained at rest and 3 and 5 h postexercise. Phenylalanine transport into muscle and mRNA expression of select AATs [system L amino acid transporter 1/solute-linked carrier (SLC) 7A5, CD98/SLC3A2, system A amino acid transporter 2/SLC38A2, proton-assisted amino acid transporter 1/SLC36A1, cationic amino acid transporter 1/SLC7A1] increased to a similar extent in both groups (P < 0.05). However, the ingestion of the protein blend resulted in a prolonged and positive net phenylalanine balance during postexercise recovery compared with whey protein (P < 0.05). Postexercise myofibrillar protein synthesis increased similarly between groups. We conclude that, while both protein sources enhanced postexercise AAT expression, transport into muscle, and myofibrillar protein synthesis, postexercise ingestion of a protein blend results in a slightly prolonged net amino acid balance across the leg compared with whey protein.

Alterations in human muscle protein metabolism with aging: Protein and exercise as countermeasures to offset sarcopenia

Aging is associated with a reduction in skeletal muscle mass-sarcopenia-the etiology of which is multifactorial. One mechanism is that aging has, as one of its hallmarks, a reduced sensitivity of skeletal muscle to the normally potent anabolic effects of protein feeding and resistance exercise, and to the anticatabolic effects of insulin, the combination of which has been termed "anabolic resistance." However, this reduced sensitivity of skeletal muscle to anabolic stimuli may, in some cases, be overcome by providing a greater quantity of the nutrition and/or exercise stimulus. Daily habitual physical activity appears to be a primary determinant of anabolic resistance as we have recently shown that as little as 14 days of reduced ambulatory activity was sufficient to induce anabolic resistance in the elderly by attenuating the postprandial increase in muscle protein synthesis (MPS). The etiology of anabolic resistance is complex and may include alterations in amino acid uptake/utilization, cell signaling status, muscle blood flow, and microvascular perfusion (impacting amino acid delivery and availability). Further, there appears to be sexual dimorphism with advancing age in the response of MPS to amino acid/insulin provision. Maintenance of physical activity during aging is of fundamental importance for skeletal muscle to allow it to appropriately respond to the anabolic effects of nutrition.

Beyond muscle hypertrophy: why dietary protein is important for endurance athletes

Recovery from the demands of daily training is an essential element of a scientifically based periodized program whose twin goals are to maximize training adaptation and enhance performance. Prolonged endurance training sessions induce substantial metabolic perturbations in skeletal muscle, including the depletion of endogenous fuels and damage/disruption to muscle and body proteins. Therefore, increasing nutrient availability (i.e., carbohydrate and protein) in the post-training recovery period is important to replenish substrate stores and facilitate repair and remodelling of skeletal muscle. It is well accepted that protein ingestion following resistance-based exercise increases rates of skeletal muscle protein synthesis and potentiates gains in muscle mass and strength. To date, however, little attention has focused on the ability of dietary protein to enhance skeletal muscle remodelling and stimulate adaptations that promote an endurance phenotype. The purpose of this review is to critically discuss the results of recent studies that have examined the role of dietary protein for the endurance athlete. Our primary aim is to consider the results from contemporary investigations that have advanced our knowledge of how the manipulation of dietary protein (i.e., amount, type, and timing of ingestion) can facilitate muscle remodelling by promoting muscle protein synthesis. We focus on the role of protein in facilitating optimal recovery from, and promoting adaptations to strenuous endurance-based training.

Acute molecular responses in untrained and trained muscle subjected to aerobic and resistance exercise training versus resistance training alone

AIM

This study assessed and compared acute muscle molecular responses before and after 5-week training, employing either aerobic (AE) and resistance exercise (RE) or RE only.

METHODS

Ten men performed one-legged RE, while the contralateral limb performed AE followed by RE 6 h later (AE+RE). Before (untrained) and after (trained) the intervention, acute bouts of RE were performed with or without preceding AE. Biopsies were obtained from m. vastus lateralis of each leg pre- and 3 h post-RE to determine mRNA levels of VEGF, PGC-1α, MuRF-1, atrogin-1, myostatin and phosphorylation of mTOR, p70S6K, rpS6 and eEF2.

RESULTS

PGC-1α and VEGF expression increased (P < 0.05) after acute RE in the untrained, but not the trained state. These markers showed greater response after AE+RE than RE in either condition. Myostatin was lower after AE+RE than RE, both before and after training. AE+RE showed higher MuRF-1 and atrogin-1 expression than RE in the untrained, not the trained state. Exercise increased (P < 0.05) p70S6K phosphorylation both before and after training, yet this increase tended to be more prominent for AE+RE than RE before training. Phosphorylation of p70S6K was greater in trained muscle. Changes in these markers did not correlate with exercise-induced alterations in strength or muscle size.

CONCLUSION

Concurrent exercise in untrained skeletal muscle prompts global molecular responses consistent with resulting whole muscle adaptations. Yet, training blunts the more robust anabolic response shown after AE+RE compared with RE. This study challenges the concept that single molecular markers could predict training-induced changes in muscle size or strength.

Mitochondrial and skeletal muscle health with advancing age

With increasing age there is a temporal relationship between the decline of mitochondrial and skeletal muscle volume, quality and function (i.e., health). Reduced mitochondrial mRNA expression, protein abundance, and protein synthesis rates appear to promote the decline of mitochondrial protein quality and function. Decreased mitochondrial function is suspected to impede energy demanding processes such as skeletal muscle protein turnover, which is critical for maintaining protein quality and thus skeletal muscle health with advancing age. The focus of this review was to discuss promising human physiological systems underpinning the decline of mitochondrial and skeletal muscle health with advancing age while highlighting therapeutic strategies such as aerobic exercise and caloric restriction for combating age-related functional impairments.

Protein blend ingestion following resistance exercise promotes human muscle protein synthesis

High-quality proteins such as soy, whey, and casein are all capable of promoting muscle protein synthesis postexercise by activating the mammalian target of rapamycin (mTORC1) signaling pathway. We hypothesized that a protein blend of soy and dairy proteins would capitalize on the unique properties of each individual protein and allow for optimal delivery of amino acids to prolong the fractional synthetic rate (FSR) following resistance exercise (RE). In this double-blind, randomized, clinical trial, 19 young adults were studied before and after ingestion of ∼19 g of protein blend (PB) or ∼18 g whey protein (WP) consumed 1 h after high-intensity leg RE. We examined mixed-muscle protein FSR by stable isotopic methods and mTORC1 signaling with western blotting. Muscle biopsies from the vastus lateralis were collected at rest (before RE) and at 3 postexercise time points during an early (0-2 h) and late (2-4 h) postingestion period. WP ingestion resulted in higher and earlier amplitude of blood branched-chain amino acid (BCAA) concentrations. PB ingestion created a lower initial rise in blood BCAA but sustained elevated levels of blood amino acids later into recovery (P < 0.05). Postexercise FSR increased equivalently in both groups during the early period (WP, 0.078 ± 0.009%; PB, 0.088 ± 0.007%); however, FSR remained elevated only in the PB group during the late period (WP, 0.074 ± 0.010%; PB, 0.087 ± 0.003%) (P < 0.05). mTORC1 signaling similarly increased between groups, except for no increase in S6K1 phosphorylation in the WP group at 5 h postexercise (P < 0.05). We conclude that a soy-dairy PB ingested following exercise is capable of prolonging blood aminoacidemia, mTORC1 signaling, and protein synthesis in human skeletal muscle and is an effective postexercise nutritional supplement.

The role of mTORC1 in regulating protein synthesis and skeletal muscle mass in response to various mechanical stimuli

Skeletal muscle plays a fundamental role in mobility, disease prevention, and quality of life. Skeletal muscle mass is, in part, determined by the rates of protein synthesis, and mechanical loading is a major regulator of protein synthesis and skeletal muscle mass. The mammalian/mechanistic target of rapamycin (mTOR), found in the multi-protein complex, mTORC1, is proposed to play an essential role in the regulation of protein synthesis and skeletal muscle mass. The purpose of this review is to examine the function of mTORC1 in relation to protein synthesis and cell growth, the current evidence from rodent and human studies for the activation of mTORC1 signaling by different types of mechanical stimuli, whether mTORC1 signaling is necessary for changes in protein synthesis and skeletal muscle mass that occur in response to different types of mechanical stimuli, and the proposed molecular signaling mechanisms that may be responsible for the mechanical activation of mTORC1 signaling.

'Sarcobesity': a metabolic conundrum

Two independent but inter-related conditions that have a growing impact on healthy life expectancy and health care costs in developed nations are an age-related loss of muscle mass (i.e., sarcopenia) and obesity. Sarcopenia is commonly exacerbated in overweight and obese individuals. Progression towards obesity promotes an increase in fat mass and a concomitant decrease in muscle mass, producing an unfavourable ratio of fat to muscle. The coexistence of diminished muscle mass and increased fat mass (so-called 'sarcobesity') is ultimately manifested by impaired mobility and/or development of life-style-related diseases. Accordingly, the critical health issue for a large proportion of adults in developed nations is how to lose fat mass while preserving muscle mass. Lifestyle interventions to prevent or treat sarcobesity include energy-restricted diets and exercise. The optimal energy deficit to reduce body mass is controversial. While energy restriction in isolation is an effective short-term strategy for rapid and substantial weight loss, it results in a reduction of both fat and muscle mass and therefore ultimately predisposes one to an unfavourable body composition. Aerobic exercise promotes beneficial changes in whole-body metabolism and reduces fat mass, while resistance exercise preserves lean (muscle) mass. Current evidence strongly supports the inclusion of resistance and aerobic exercise to complement mild energy-restricted high-protein diets for healthy weight loss as a primary intervention for sarcobesity.

Aerobic exercise training induces skeletal muscle hypertrophy and age-dependent adaptations in myofiber function in young and older men

To examine potential age-specific adaptations in skeletal muscle size and myofiber contractile physiology in response to aerobic exercise, seven young (YM; 20 ± 1 yr) and six older men (OM; 74 ± 3 yr) performed 12 wk of cycle ergometer training. Muscle biopsies were obtained from the vastus lateralis to determine size and contractile properties of isolated slow [myosin heavy chain (MHC) I] and fast (MHC IIa) myofibers, MHC composition, and muscle protein concentration. Aerobic capacity was higher (P < 0.05) after training in both YM (16 ± 2%) and OM (13 ± 3%). Quadriceps muscle volume, determined via MRI, was 5 ± 1 and 6 ± 1% greater (P < 0.05) after training for YM and OM, respectively, which was associated with an increase in MHC I myofiber cross-sectional area (CSA), independent of age. MHC I peak power was higher (P < 0.05) after training for both YM and OM, while MHC IIa peak power was increased (P < 0.05) with training in OM only. MHC I and MHC IIa myofiber peak and normalized (peak force/CSA) force were preserved with training in OM, while MHC I peak force/CSA and MHC IIa peak force were lower (P < 0.05) after training in YM. The age-dependent adaptations in myofiber function were not due to changes in protein content, as total muscle protein and myofibrillar protein concentration were unchanged (P > 0.05) with training. Training reduced (P < 0.05) the proportion of MHC IIx isoform, independent of age, whereas no other changes in MHC composition were observed. These data suggest relative improvements in muscle size and aerobic capacity are similar between YM and OM, while adaptations in myofiber contractile function showed a general improvement in OM. Training-related increases in MHC I and MHC IIa peak power reveal that skeletal muscle of OM is responsive to aerobic exercise training and further support the use of aerobic exercise for improving cardiovascular and skeletal muscle health in older individuals.

Exercise and amino acid anabolic cell signaling and the regulation of skeletal muscle mass

A series of complex intracellular networks influence the regulation of skeletal muscle protein turnover. In recent years, studies have examined how cellular regulators of muscle protein turnover modulate metabolic mechanisms contributing to the loss, gain, or conservation of skeletal muscle mass. Exercise and amino acids both stimulate anabolic signaling potentially through several intracellular pathways including the mammalian target of rapamycin complex 1 and the mitogen activated protein kinase cell signaling cascades. As novel molecular regulators of muscle integrity continue to be explored, a contemporary analysis of the literature is required to understand the metabolic mechanisms by which contractile forces and amino acids affect cellular process that contribute to long-term adaptations and preservation of muscle mass. This article reviews the literature related to how exercise and amino acid availability affect cellular regulators of skeletal muscle mass, especially highlighting recent investigations that have identified mechanisms by which contractile forces and amino acids modulate muscle health. Furthermore, this review will explore integrated exercise and nutrition strategies that promote the maintenance of muscle health by optimizing exercise, and amino acid-induced cell signaling in aging adults susceptible to muscle loss.

Age effect on myocellular remodeling: response to exercise and nutrition in humans

Aging is associated with decline in muscle mass and muscle functions. Muscle strength declines disproportionate to the decline in muscle mass indicating that muscle quality or protein quality also declines with age. Human studies have shown a progressive decline in muscle protein synthesis including proteins in the contractile apparatus and mitochondria with age. However, the decline in muscle protein synthesis is disproportionate to the decline in muscle mass that occurs with age prompting to hypothesize that muscle protein degradation also declines with age. A decline in mitochondrial capacity to synthesize ATP is likely a limiting factor of both synthesis and degradation, which are ATP dependent processes. In support of the above hypothesis, several studies have shown a decline in whole body protein turnover (synthesis and degradation). The timely and efficient degradation of irreversibly damaged or modified proteins is critical to maintain the quality of protein. It is proposed that a failure to degrade the damaged proteins and replacing them with newly synthesized proteins contribute to age related decline in muscle mass and quality of muscle proteins. The underlying molecular mechanism of these age related changes in human muscle needs further investigation.

Dietary protein for athletes: from requirements to optimum adaptation

Opinion on the role of protein in promoting athletic performance is divided along the lines of how much aerobic-based versus resistance-based activity the athlete undertakes. Athletes seeking to gain muscle mass and strength are likely to consume higher amounts of dietary protein than their endurance-trained counterparts. The main belief behind the large quantities of dietary protein consumption in resistance-trained athletes is that it is needed to generate more muscle protein. Athletes may require protein for more than just alleviation of the risk for deficiency, inherent in the dietary guidelines, but also to aid in an elevated level of functioning and possibly adaptation to the exercise stimulus. It does appear, however, that there is a good rationale for recommending to athletes protein intakes that are higher than the RDA. Our consensus opinion is that leucine, and possibly the other branched-chain amino acids, occupy a position of prominence in stimulating muscle protein synthesis; that protein intakes in the range of 1.3-1.8 g · kg(-1) · day(-1) consumed as 3-4 isonitrogenous meals will maximize muscle protein synthesis. These recommendations may also be dependent on training status: experienced athletes would require less, while more protein should be consumed during periods of high frequency/intensity training. Elevated protein consumption, as high as 1.8-2.0 g · kg(-1) · day(-1) depending on the caloric deficit, may be advantageous in preventing lean mass losses during periods of energy restriction to promote fat loss.

Exercise, amino acids, and aging in the control of human muscle protein synthesis

In this review, we discuss recent research in the field of human skeletal muscle protein metabolism characterizing the acute regulation of mammalian target of rapamycin complex (mTORC) 1 signaling and muscle protein synthesis (MPS) by exercise, amino acid nutrition, and aging. Resistance exercise performed in the fasted state stimulates mixed MPS within 1 h after exercise, which can remain elevated for 48 h. We demonstrate that the activation of mTORC1 signaling (and subsequently enhanced translation initiation) is required for the contraction-induced increase in MPS. In comparison, low-intensity blood flow restriction (BFR) exercise stimulates MPS and mTORC1 signaling to an extent similar to traditional, high-intensity resistance exercise. We also show that mTORC1 signaling is required for the essential amino acid (EAA)-induced increase in MPS. Ingestion of EAAs (or protein) shortly after resistance exercise enhances MPS and mTORC1 signaling compared with resistance exercise or EAAs alone. In older adults, the ability of the skeletal muscle to respond to anabolic stimuli is impaired. For example, in response to an acute bout of resistance exercise, older adults are less able to activate mTORC1 or increase MPS during the first 24 h of postexercise recovery. However, BFR exercise can overcome this impairment. Aging is not associated with a reduced response to EAAs provided the EAA content is sufficient. Therefore, we propose that exercise combined with EAA should be effective not only in improving muscle repair and growth in response to training in athletes, but that strategies such as EAA combined with resistance exercise (or BFR exercise) may be very useful as a countermeasure for sarcopenia and other clinical conditions associated with muscle wasting.

Late evening snack: exploiting a period of anabolic opportunity in cirrhosis

BACKGROUND AND AIM

Cirrhosis is a state of accelerated starvation with impaired protein synthesis. Increased rate of gluconeogenesis and alterations in skeletal muscle signaling pathways result in anabolic resistance and consequent loss of muscle mass or sarcopenia in cirrhosis. Late evening snack (LES) is an intervention to reduce the postabsorptive (fasting) phase with the potential to improve substrate utilization and reverse sarcopenia. Published reports were evaluated to examine the effect of LES on regulation of substrate utilization (short-term studies) and nutritional outcomes (long-term studies).

METHODS

PubMed, EMBASE, Google scholar and OVID databases were searched. All studies published on LES in cirrhosis were included. Studies that included few (n < 3) subjects and patients with hepatocellular carcinoma were excluded.

RESULTS

Late evening snack decreased lipid oxidation and improved nitrogen balance, irrespective of the composition or type of formulation used. Daytime isocaloric isonitrogenous snacks did not have the metabolic or clinical benefit of LES. LES decreased skeletal muscle proteolysis. No studies have examined its effect on muscle protein synthesis. There was inconsistent translation into an increase in lean body or skeletal muscle mass. Improved quality of life occurs but decreased mortality or need for transplantation has not been reported. The optimal composition of LES has not been defined, but based on mechanistic considerations, a branched chain supplemented LES holds most promise.

CONCLUSIONS

Late evening snack holds the most promise as an intervention to reverse anabolic resistance and sarcopenia of cirrhosis with improved quality of life in patients with cirrhosis. Long term benefit and improved survival need critical evaluation.

Modulation of autophagy and ubiquitin-proteasome pathways during ultra-endurance running

In this study, the coordinated activation of ubiquitin-proteasome pathway (UPP), autophagy-lysosomal pathway (ALP), and mitochondrial remodeling including mitophagy was assessed by measuring protein markers during ultra-endurance running exercise in human skeletal muscle. Eleven male, experienced ultra-endurance athletes ran for 24 h on a treadmill. Muscle biopsy samples were taken from the vastus lateralis muscle 2 h before starting and immediately after finishing exercise. Athletes ran 149.8 ± 16.3 km with an effective running time of 18 h 42 min ( ± 41 min). The phosphorylation state of Akt (-74 ± 5%; P < 0.001), FOXO3a (-49 ± 9%; P < 0.001), mTOR Ser2448 (-32 ± 14%; P = 0.028), and 4E-BP1 (-34 ± 7%; P < 0.001) was decreased, whereas AMPK phosphorylation state increased by 247 ± 170% (P = 0.042). Proteasome β2 subunit activity increased by 95 ± 44% (P = 0.028), whereas the activities associated with the β1 and β5 subunits remained unchanged. MuRF1 protein level increased by 55 ± 26% (P = 0.034), whereas MAFbx protein and ubiquitin-conjugated protein levels did not change. LC3bII increased by 554 ± 256% (P = 0.005), and the form of ATG12 conjugated to ATG5 increased by 36 ± 17% (P = 0.042). The mitochondrial fission marker phospho-DRP1 increased by 110 ± 47% (P = 0.003), whereas the fusion marker Mfn1 and the mitophagy markers Parkin and PINK1 remained unchanged. These results fit well with a coordinated regulation of ALP and UPP triggered by FOXO3 and AMPK during ultra-endurance exercise.

Muscle protein synthesis in response to nutrition and exercise

Muscle protein synthesis (MPS) is the driving force behind adaptive responses to exercise and represents a widely adopted proxy for gauging chronic efficacy of acute interventions, (i.e. exercise/nutrition). Recent findings in this arena have been progressive. Nutrient-driven increases in MPS are of finite duration (∼1.5 h), switching off thereafter despite sustained amino acid availability and intramuscular anabolic signalling. Intriguingly, this 'muscle-full set-point' is delayed by resistance exercise (RE) (i.e. the feeding × exercise combination is 'more anabolic' than nutrition alone) even 24 h beyond a single exercise bout, casting doubt on the importance of nutrient timing vs. sufficiency per se. Studies manipulating exercise intensity/workload have shown that increases in MPS are negligible with RE at 20-40% but maximal at 70-90% of one-repetition maximum when workload is matched (according to load × repetition number). However, low-intensity exercise performed to failure equalises this response. Analysing distinct subcellular fractions (e.g. myofibrillar, sarcoplasmic, mitochondrial) may provide a readout of chronic exercise efficacy in addition to effect size in MPS per se, i.e. while 'mixed' MPS increases similarly with endurance and RE, increases in myofibrillar MPS are specific to RE, prophetic of adaptation (i.e. hypertrophy). Finally, the molecular regulation of MPS by exercise and its regulation via 'anabolic' hormones (e.g. IGF-1) has been questioned, leading to discovery of alternative mechanosensing-signalling to MPS.

Leucine-enriched essential amino acid supplementation during moderate steady state exercise enhances postexercise muscle protein synthesis

BACKGROUND

The effects of essential amino acid (EAA) supplementation during moderate steady state (ie, endurance) exercise on postexercise skeletal muscle metabolism are not well described, and the potential role of supplemental leucine on muscle protein synthesis (MPS) and associated molecular responses remains to be elucidated.

OBJECTIVE

This randomized crossover study examined whether EAA supplementation with 2 different concentrations of leucine affected post-steady state exercise MPS, whole-body protein turnover, and mammalian target of rapamycin 1 (mTORC1) intracellular signaling.

DESIGN

Eight adults completed 2 separate bouts of cycle ergometry [60 min, 60% VO(2)peak (peak oxygen uptake)]. Isonitrogenous (10 g EAA) drinks with different leucine contents [leucine-enriched (l)-EAA, 3.5 g leucine; EAA, 1.87 g leucine] were consumed during exercise. MPS and whole-body protein turnover were determined by using primed continuous infusions of [(2)H(5)]phenylalanine and [1-(13)C]leucine. Multiplex and immunoblot analyses were used to quantify mTORC1 signaling.

RESULTS

MPS was 33% greater (P < 0.05) after consumption of L-EAA (0.08 ± 0.01%/h) than after consumption of EAA (0.06 ± 0.01%/h). Whole-body protein breakdown and synthesis were lower (P < 0.05) and oxidation was greater (P < 0.05) after consumption of L-EAA than after consumption of EAA. Regardless of dietary treatment, multiplex analysis indicated that Akt and mammalian target of rapamycin phosphorylation were increased (P < 0.05) 30 min after exercise. Immunoblot analysis indicated that phosphorylation of ribosomal protein S6 and extracellular-signal regulated protein kinase increased (P < 0.05) and phosphorylation of eukaryotic elongation factor 2 decreased (P < 0.05) after exercise but was not affected by dietary treatment.

CONCLUSION

These findings suggest that increasing the concentration of leucine in an EAA supplement consumed during steady state exercise elicits a greater MPS response during recovery. This trial is registered at clinicaltrials.gov as NCT01366924.

The influence of carbohydrate-protein co-ingestion following endurance exercise on myofibrillar and mitochondrial protein synthesis

The aim of the present study was to determine mitochondrial and myofibrillar muscle protein synthesis (MPS) when carbohydrate (CHO) or carbohydrate plus protein (C+P) beverages were ingested following prolonged cycling exercise. The intracellular mechanisms thought to regulate MPS were also investigated. In a single-blind, cross-over study, 10 trained cyclists (age 29 ± 6 years, VO2max 66.5 ± 5.1 ml kg(−1) min(−1)) completed two trials in a randomized order. Subjects cycled for 90 min at 77 ± 1% VO2max before ingesting a CHO (25 g of carbohydrate) or C+P (25 g carbohydrate + 10 g whey protein) beverage immediately and 30 min post-exercise. A primed constant infusion of L-[ring-(13)C6]phenylalanine began 1.5 h prior to exercise and continued until 4 h post-exercise. Muscle biopsy samples were obtained to determine myofibrillar and mitochondrial MPS and the phosphorylation of intracellular signalling proteins. Arterialized blood samples were obtained throughout the protocol. Plasma amino acid and urea concentrations increased following ingestion of C+P only. Serum insulin concentration increased more for C+P than CHO. Myofibrillar MPS was ∼35% greater for C+P compared with CHO (0.087 ± 0.007 and 0.057 ± 0.006% h(−1), respectively; P = 0.025). Mitochondrial MPS rates were similar for C+P and CHO (0.082 ± 0.011 and 0.086 ± 0.018% h(−1), respectively). mTOR(Ser2448) phosphorylation was greater for C+P compared with CHO at 4 h post-exercise (P < 0.05). p70S6K(Thr389) phosphorylation increased at 4 h post-exercise for C+P (P < 0.05), whilst eEF2(Thr56) phosphorylation increased by ∼40% at 4 h post-exercise for CHO only (P < 0.01). The present study demonstrates that the ingestion of protein in addition to carbohydrate stimulates an increase in myofibrillar, but not mitochondrial, MPS following prolonged cycling. These data indicate that the increase in myofibrillar MPS for C+P could, potentially, be mediated through p70S6K, downstream of mTOR, which in turn may suppress the rise in eEF2 on translation elongation.

β-Adrenergic receptor blockade blunts postexercise skeletal muscle mitochondrial protein synthesis rates in humans

β-Adrenergic receptor (AR) signaling is a regulator of skeletal muscle protein synthesis and mitochondrial biogenesis in mice. We hypothesized that β-AR blockade blunts postexercise skeletal muscle mitochondrial protein synthesis rates in adult humans. Six healthy men (mean ± SD: 26 ± 6 yr old, 39.9 ± 4.9 ml·kg(-1)·min(-1) peak O(2) uptake, 26.7 ± 2.0 kg/m(2) body mass index) performed 1 h of stationary cycle ergometer exercise (60% peak O(2) uptake) during 1) β-AR blockade (intravenous propranolol) and 2) administration of saline (control). Skeletal muscle mitochondrial, myofibrillar, and sarcoplasmic protein synthesis rates were assessed using [(2)H(5)]phenylalanine incorporation into skeletal muscle proteins after exercise. The mRNA content of signals for mitochondrial biogenesis was determined using real-time PCR. β-AR blockade decreased mitochondrial (from 0.217 ± 0.076 to 0.135 ± 0.031%/h, P < 0.05), but not myofibrillar or sarcoplasmic, protein synthesis rates. Peroxisome proliferator-activated receptor-γ coactivator-1α mRNA was increased ∼2.5-fold (P < 0.05) at 5 h compared with 1 h postexercise but was not influenced by β-AR blockade. We conclude that decreased β-AR signaling during cycling can blunt the postexercise increase in mitochondrial protein synthesis rates without affecting mRNA content.

Long-term synthesis rates of skeletal muscle DNA and protein are higher during aerobic training in older humans than in sedentary young subjects but are not altered by protein supplementation

Consuming protein following exercise has been shown to stimulate protein synthesis acutely in skeletal muscle and has been recommended to prevent sarcopenia. It is not known, however, whether acute stimulation persists long term or includes muscle cell division. We asked here whether consuming protein following exercise during aerobic training increases long-term protein and DNA synthesis rates in skeletal muscle of adult humans. Sixteen previously untrained participants (50 ± 8 yr) consumed either a carbohydrate or carbohydrate and protein drink following each session during 6 wk of treadmill training. A younger untrained group provided a nonexercising comparison. Participants were administered heavy water (²H₂O; deuterium oxide) continuously for 6 wk to isotopically label newly synthesized skeletal muscle proteins and DNA. Muscle biopsies were performed after 6 wk of training. Contrary to acute studies, consuming protein after exercise did not increase skeletal muscle protein synthesis rates. In contrast, muscle protein synthesis, DNA, and phospholipid synthesis were significantly higher in the older exercise groups than the younger sedentary group. The higher DNA replication rate could not be attributed to mitochondrial DNA and may be due to satellite cell activation. We conclude that postexercise protein supplementation does not increase rates of mixed protein synthesis over 6 wk and that aerobic exercise may stimulate long-term cell division (DNA synthesis) in skeletal muscle of humans. Measurements of long-term synthesis rates provide important insights into aging and exercise adaptations.

Mammalian target of rapamycin complex 1 activation is required for the stimulation of human skeletal muscle protein synthesis by essential amino acids

The relationship between mammalian target of rapamycin complex 1 (mTORC1) signaling and muscle protein synthesis during instances of amino acid surplus in humans is based solely on correlational data. Therefore, the goal of this study was to use a mechanistic approach specifically designed to determine whether increased mTORC1 activation is requisite for the stimulation of muscle protein synthesis following L-essential amino acid (EAA) ingestion in humans. Examination of muscle protein synthesis and signaling were performed on vastus lateralis muscle biopsies obtained from 8 young (25 ± 2 y) individuals who were studied prior to and following ingestion of 10 g of EAA during 2 separate trials in a randomized, counterbalanced design. The trials were identical except during 1 trial, participants were administered a single oral dose of a potent mTORC1 inhibitor (rapamycin) prior to EAA ingestion. In response to EAA ingestion, an ~60% increase in muscle protein synthesis was observed during the control trial, concomitant with increased phosphorylation of mTOR (Ser(2448)), ribosomal S6 kinase 1 (Thr(389)), and eukaryotic initiation factor 4E binding protein 1 (Thr(37/46)). In contrast, prior administration of rapamycin completely blocked the increase in muscle protein synthesis and blocked or attenuated activation of mTORC1-signaling proteins. The inhibition of muscle protein synthesis and signaling was not due to differences in either extracellular or intracellular amino acid availability, because these variables were similar between trials. These data support a fundamental role for mTORC1 activation as a key regulator of human muscle protein synthesis in response to increased EAA availability. This information will be useful in the development of evidence-based nutritional therapies targeting mTORC1 to counteract muscle wasting associated with numerous clinical conditions.

Validation of a single biopsy approach and bolus protein feeding to determine myofibrillar protein synthesis in stable isotope tracer studies in humans

Background

Minimizing the number of muscle biopsies has important methodological implications and minimizes subject discomfort during a stable isotope amino acid infusion. We aimed to determine the reliability of obtaining a single muscle biopsy for the calculation of muscle protein fractional synthetic rate (FSR) as well as the amount of incorporation time necessary to obtain that biopsy after initiating a stable isotope infusion (Study 1). The calculation of muscle protein FSR requires tracer steady-state during the stable isotope infusion. Therefore, a second aim was to examine if steady-state conditions are compromised in the precursor pools (plasma free or muscle intracellular [IC]) after ingestion of a tracer enriched protein drink and after resistance exercise (Study 2).

Methods

Sixteen men (23 ± 3 years; BMI = 23.8 ± 2.2 kg/m², means ± SD) were randomized to perform Study 1 or Study 2 (n = 8, per study). Subjects received a primed, constant infusion of L-[ring-¹³C₆]phenylalanine coupled with muscle biopsies of the vastus lateralis to measure rates of myofibrillar protein synthesis (MPS). Subjects in Study 2 were fed 25 g of whey protein immediately after an acute bout of unilateral resistance exercise.

Results

There was no difference (P = 0.3) in rates of MPS determined using the steady-state precursor-product equation and determination of tracer incorporation between sequential biopsies 150 min apart or using plasma protein as the baseline enrichment, provided the infusion length was sufficient (230 ± 0.3 min). We also found that adding a modest amount of tracer (4% enriched), calculated based on the measured phenylalanine content of the protein (3.5%) in the drink, did not compromise steady-state conditions (slope of the enrichment curve not different from zero) in the plasma free or, more importantly, the IC pool (both P > 0.05).

Conclusions

These data demonstrate that the single biopsy approach yields comparable rates of muscle protein synthesis, provided a longer incorporation time is utilized, to that seen with a traditional two biopsy approach. In addition, we demonstrate that enriching protein-containing drinks with tracer does not disturb isotopic steady-state and thus both are reliable techniques to determine rates of MPS in humans.