Muscle Protein Synthesis Research Articles

Reconsidering the pre-eminence of dietary leucine and plasma leucinemia for predicting the stimulation of postprandial muscle protein synthesis rates

The regulation of postprandial muscle protein synthesis (MPS) with or without physical activity has been an intensely studied area within nutrition and physiology. The leucine content of dietary protein and the subsequent plasma leucinemia it elicits postingestion is often considered the primary drivers of the postprandial MPS response. This concept, generally known as the leucine “trigger” hypothesis, has also been adopted within more applied aspects of nutrition. Our view is that recent evidence is driving a more nuanced picture of the regulation of postprandial MPS by revealing a compelling dissociation between ingested leucine or plasma leucinemia and the magnitude of the postprandial MPS response. Much of this lack of coherence has arisen as experimental progress has demanded relevant studies move beyond reliance on isolated amino acids and proteins to use increasingly complex protein-rich meals, whole foods, and mixed meals. Our overreliance on the centrality of leucine in this field has been reflected in 2 recent systematic reviews. In this perspective, we propose a re-evaluation of the pre-eminent role of these leucine variables in the stimulation of postprandial MPS. We view the development of a more complex intellectual framework now a priority if we are to see continued progress concerning the mechanistic regulation of postprandial muscle protein turnover, but also consequential from an applied perspective when evaluating the value of novel dietary protein sources.

Gene structure, expression and function analysis of the MyoD gene in the Pacific white shrimp Litopenaeus vannamei

The Pacific white shrimp Litopenaeus vannamei is a representative species of decapod crustacean and an economically important marine aquaculture species worldwide. However, research on the genes involved in muscle growth and development in shrimp is still lacking. MyoD is recognized as a crucial regulator of myogenesis and plays an essential role in muscle growth and differentiation in various animals. Nonetheless, little information is available concerning the function of this gene among crustaceans. In this study, we identified a sequence of the MyoD gene (LvMyoD) with a conserved bHLH domain in the L. vannamei genome. Phylogenetic analysis revealed that both the overall protein sequence and specific functional sites of LvMyoD are highly conserved with those of other crustacean species and that they are evolutionarily closely related to vertebrate MyoD and Myf5. LvMyoD expression is initially high during early muscle development in shrimp and gradually decreases after 40 days post-larval development. In adults, the muscle-specific expression of LvMyoD was confirmed through RT–qPCR analysis. Knockdown of LvMyoD inhibited the growth of the shrimp in body length and weight. Histological observation and transcriptome sequencing of muscle samples after RNA interference (RNAi) revealed nuclear agglutination and looseness in muscle fibers. Additionally, we observed significant effects on the expression of genes involved in heat shock proteins, myosins, actins, protein synthesis, and glucose metabolism. These findings suggest that LvMyoD plays a critical role in regulating muscle protein synthesis and muscle cell differentiation. Overall, this study highlights the involvement of LvMyoD in myogenesis and muscle growth, suggesting that it is a potentially important regulatory target for shrimp breeding efforts.

NSAIDs do not influence exercise effects on muscle size in rats or muscle protein synthesis signaling in humans

BACKGROUND: The aim of this project was to determine the impact of non-steroidal anti-inflammatory drugs (NSAIDs) on skeletal muscle adaptations to exercise. NSAIDs possess analgesic and anti‐inflammatory properties that occur by blocking cyclooxygenase (COX) enzymes, thereby inhibiting the production of prostaglandins. In the first study, we determined if low-dose chronic NSAID use affects muscle size in rodents exercising for six weeks. In the second study, we determined if a single high dose of NSAIDs effects the muscle protein synthetic signaling response to a bout of plyometric exercise. Our hypotheses were that NSAIDs would reduce both muscle size and muscle protein synthesis (MPS) signaling. METHODS: Study 1: 9-wk-old male Wistar rats (n=80) were randomized to placebo (PLA), naproxen (NAP), ibuprofen (IBU), or flurbiprofen (FLU) with or without exercise (EX) for six weeks. Exercise consisted of treadmill running at 25 m/min, for 30 minutes per day, five days per week. Soleus muscle was stained for myosin heavy chain (MHC) I or MHC IIA then analyzed for cross sectional area (CSA) and fiber type percentage. Rodent data were analyzed using a one-way ANOVA. Study 2: In a randomized, counter-balanced order, 12 participants (2 females, 10 males), performed four independent plyometric exercise bouts consisting of 10 sets of 10 plyometric jumps at 40% of their 1RM, separated by a minimum of one week. Prior to each session, participants consumed a single dose of celecoxib (CEL 200 mg), IBU (800 mg), FLU (100 mg) or PLA. Muscle biopsies were collected before (PRE) and 3-hours post (POST) exercise. Muscle was analyzed via immunoblot for the following: phospho(p)-AKT(S473), total AKT, p-mTOR (S448), total mTOR, p-S6 (S235/236), total S6, p-4EBP1, and total 4EBP1. Fold changes were calculated from PRE to POST. Data were analyzed using a repeated measures ANOVA. All data are presented as mean ± SD. RESULTS: Study 1: There was no significant difference (p<0.05) in muscle CSA (PLA: 4060±517; PLA+EX: 3965±605; IBU: 3720±804; IBU+EX:4129±477; FLU: 3743±671; FLU+EX: 3649±541; NAP: 4157±1011; NAP+EX: 4123±586) or MHC IIA percentage (PLA: 10±7; PLA+EX: 10±5; IBU: 7±5; IBU+EX:9±3; FLU: 11±4; FLU+EX: 11±6; NAP: 11±4; NAP+EX: 12±3) between groups. Study 2: There was no significant difference (p<0.05) in fold-change between groups for p-AKT/total AKT (PLA: 1.23±0.4; IBU: 1.13±0.3; CEL: 1.26±0.4; FLU: 1.31±0.4), p-mTOR/total mTOR (PLA: 1.21±0.2; IBU: 1.21±0.3; CEL:1.34±0.2; FLU: 1.49±0.3), p-S6/total S6 (PLA: 11.48±10.6; IBU: 10.9±6.8; CEL: 6.01±2.98; FLU: 25.25±19.38), or p-4EBP1/total 4EBP1 (PLA: 1.71± 1.35; IBU: 1.23±0.98; CEL: 1.07 ±0.64; FLU: 2.03±1.49). CONCLUSION: Chronic low-dose NSAID consumption does not influence muscle size or MHC in exercising rodents. Similarly, an acute high dose of an NSAID does not affect the MPS signaling response in exercising humans. Funding was provided by the Military Operational Medicine Research Program. The opinions or assertions contained herein are the private views of the author(s) and are not to be construed as offcial or as reflecting the views of the Army or the Department of Defense. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Investigating the Effect of Rapamycin on Impaired Proteostasis in Aged Skeletal Muscle After Disuse Atrophy

Older individuals undergo loss of muscle mass and strength, which can be compounded during bed rest and extended hospital stays. Adult and aged individuals lose muscle mass at similar rates during periods of disuse; however, only aged skeletal muscle fails to fully recover once activity resumes. Current efforts to facilitate skeletal muscle recovery are aimed at increasing myofibrillar protein synthesis by stimulating mTORC1(mammalian target of rapamycin complex 1), a major regulator of protein synthesis. However, we showed that skeletal muscle in aged rats already has higher rates of myofibrillar protein synthesis and mTORC1 activity than adult rats. We also showed that aged skeletal muscle has an accumulation of insoluble ubiquitinated proteins compared to adult muscle, indicating impaired proteostasis and possibly impaired autophagy degradation. We hypothesized that mTORC1 inhibition via rapamycin administration would reduce protein synthesis and the accumulation of p62 aggregates, facilitating recovery in aged skeletal muscle after disuse. Methods: Adult (10 months) and old (26 months) OKC HET rats were hindlimb unloaded (HU) for 14-days to induce atrophy, followed by subsequent 14 days of reloading (RE) through normal ambulation. Animals were fed either a control or rapamycin-supplemented (42 ppm) diet. To determine bulk protein synthesis, rats were labeled with deuterium oxide (D2O) during weight bearing (WB), HU, and RE, (n=4-6 per time point per group). Finally, to assess the presence of autophagy related protein aggregates we immuno stained for Sequestosome 1/p62, an autophagy cargo receptor protein. Results: Our data showed that myofibrillar protein synthesis rates were elevated in the old muscle compared to the adult ( k = 0.029 1/day ±0.002 vs. 0.039 1/day ±0.002, p<0.0001), and that protein synthesis rates were lower in the old rapamycin cohort (k = 1/day ±0.002 vs. 1/day ±0.003, p<0.0001). Furthermore, p62 puncta was three-fold more abundant (p<0.01) in aged skeletal muscle, compared to the adult muscle. Although the sample size is small, when comparing p62 puncta in the old rapamycin group to the old controls, there was no difference between the cohorts. Conclusion: We show that mTORC1 inhibition reduces protein synthesis in aged skeletal muscle. We also show that aged muscle has more p62 aggregates compared to adult skeletal muscle, indicating that autophagy related targets are not being degraded effciently with age. Further analyses will assess the effects of mTORC1 inhibition on other proteostatic mechanisms in atrophied skeletal muscle of aged rats. NIA Training Grant: 5T32AG052363-04VA I01 BX005592 APS SURF. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Analysis of the stimulative effect of arginine on translation initiation of protein synthesis in skeletal muscle

Introduction: Amino acids are not only important precursors for the synthesis of proteins, but also participate in the regulation of major metabolic pathways. Specific amino acids stimulate protein synthesis. Previous studies have shown that arginine (Arg) stimulates protein synthesis at the level of translation initiation through the activation of the mechanistic target of rapamycin complex 1 (mTORC1) in cell culture system; however, little is known about the effect of Arg on protein synthesis in vivo. Here, we evaluated whether Arg stimulates protein synthesis at the level of translation initiation and compared the effects of Arg on translation initiation with those of leucine (Leu), which is well-studied the detail of its stimulative mechanism, in mouse skeletal muscle. Methods: Eighteen hour-fasted mice were intraperitoneally injected with saline or 4.6 mmol/ kg/ body weight of Arg or Leu and subsequently sacrificed and excised gastrocnemius muscles at 1 h after injection. In addition, we used mouse-derived C2C12 myotubes treated with Arg to examine the mechanism by which Arg stimulates translation initiation in mouse skeletal muscle. The cells were preincubated with several kinds of inhibitors for appropriate time and then treated with Arg or Leu. Using homogenate of skeletal muscle and cell lysate, the phosphorylation states of eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) and ribosomal protein S6 kinase 1 (S6K1), key regulatory factors involved in the translation initiation were measured by immunoblotting as indicators of translation initiation activity. Results: Intraperitoneal injection of either Arg or Leu significantly increased S6K1 phosphorylation compared to the saline-injection, but the increase in 4E-BP1 phosphorylation was observed in Leu-injected mice not in Arg-injected mice. These results suggest that Arg can stimulate translation initiation in skeletal muscle of fasted mice. In C2C12 myotubes, as with Leu, Arg increased both 4E-BP1 and S6K phosphorylation, and these increases were abolished by the treatment of rapamycin, a mTORC1 inhibitor. These data indicate that Arg directly activates mTORC1 pathway as well as Leu. In addition, the treatment of a phosphoinositide 3-kinase (PI3K) inhibitor and a AKT inhibitor completely cancelled Arg-dependent 4E-BP1 and S6K1 phosphorylation; however, the inhibition of Leu-induced 4E-BP1 and S6K1 phosphorylation by these inhibitors were in partial. Furthermore, the inhibitor of the G protein‐coupled receptor family C, group 6, subtype A (GPRC6a), which has been shown to associate with regulation of PI3K/AKT pathway and mTORC1 activation, completely suppressed the increases of 4E-BP1 and S6K1 phosphorylation by Arg. Conclusion:Our data indicate that Arg has the ability to activate translation initiation in mouse skeletal muscle. In addition, the results of our experiments using skeletal muscle cells support the idea that Arg stimulates translation initiation via GPRC6a/PI3K/AKT/mTORC1 pathway in mouse skeletal muscle. Unlike the effects of Arg, it is likely that besides the PI3K/AKT pathway, Leu activates another signaling pathways upstream of mTORC1 to stimulate translation initiation in skeletal muscle. This research was funded by JSPS KAKENHI, grant number 18K05501. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Skeletal muscle ULK1 and ULK2 modulate protein synthesis impacting fiber size

Maintenance of skeletal muscle homeostasis is largely influenced by the processes of protein synthesis and degradation. However, the regulation of these processes remains incompletely understood particularly in a tissue or cell type-specific manner. We have previously demonstrated that Unc-51 like autophagy activating kinases 1 and 2 (Ulk1/2) are among the top 5 mostly enriched putative autophagy genes in skeletal muscle when compared to >90 other mouse tissues and cell lines (Fuqua et al., FASEB J, 2019). However, because protein kinases commonly have several downstream targets, here we hypothesized that skeletal muscle ULK1 and ULK2 redundantly modulate other important cellular processes. To begin to address this question, we generated mice with skeletal muscle-specific knockout of ULK1 and ULK2 (i.e., ULK1/2 skmDKO) and studied those at different ages. Muscle basal autophagy flux was impaired in ULK1/2 skmDKO mice. However, contrary to other models of autophagy impairment, which commonly leads to muscle atrophy, adult ULK1/2 skmDKO mice had increased muscle size (15-25%, P≤0.01). Hypertrophy occurred in all fiber types (6-20% increase in fiber diameter, P≤0.05) and in response to an acute (4-week) deficiency of ULK1/2 (via electroporations of plasmids encoding ULK1/2miR), where TA fiber diameter increased by 9% (p<0.05). Further studies using D2O labeling and cellular fractionation revealed that ULK1/2 skmDKO mice have increased myofibrillar protein synthesis rates (~5%/day, p<0.05). Examination of the molecular mechanisms involved suggests that ULK1/2 skmDKO mice have enhanced mTORC1-dependent signaling, particularly in the fed state. Altogether, our findings reveal for the first time that ULK1 and ULK2 collectively stimulate protein degradation and inhibit protein synthesis in skeletal muscle potentially impacting muscle mass and function in conditions of muscle atrophy and hypertrophy. Supported by the University of Iowa Fraternal Order of Eagles Diabetes Research Center (UIowa FOEDRC). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Bed-rest and exercise remobilisation: concurrent adaptations in muscle glucose and protein metabolism

Bed rest (BR) of only a few days duration reduces muscle protein synthesis and induces skeletal muscle atrophy and insulin resistance, but the scale and juxtaposition of these events has not been investigated concurrently in the same individuals. Moreover, the impact of short-term exercise-supplemented remobilisation (ESR) on muscle volume, protein turnover and leg glucose uptake (LGU) in humans is unknown. Ten healthy males (24±1 years, body mass index (BMI) 22.7±0.6) underwent 3 days of BR, followed immediately by 3 days of ESR consisting of 5x30 maximal voluntary single leg isokinetic knee-extensions at 90o/sec each day. An isoenergetic diet was maintained throughout the study (30% fat,15% protein, 55% carbohydrate). Resting LGU was calculated from arteriovenous-venous difference across the leg and leg blood flow during the steady-state of a 3 hr hyperinsulinaemic euglycaemic clamp (60 mU/m2/min) measured pre BR, post BR and after remobilisation. Glycogen content was measured in Vastus Lateralis muscle biopsy samples obtained before and after each clamp. Leg muscle volume (LMV) was measured using magnetic resonance imaging pre BR, post BR and after remobilisation. Cumulative myofibrillar protein fractional synthesis rate (FSR), and whole-body muscle protein breakdown (MPB) were measured over the course of BR and remobilisation using deuterium oxide and 3-methylhistidine stable isotope tracers that were administered orally. Compared with pre BR, there was a 45% decline in insulin-stimulated LGU (p<0.05) after BR, which was paralleled by a reduction in insulin stimulated leg blood flow (p<0.01) and removal of insulin stimulated muscle glycogen storage. These events were accompanied by a 43% reduction in myofibrillar protein FSR (p<0.05) and a 2.5% decrease in LMV (p<0.01) during BR, along with a 30% decline in whole-body muscle myofibrillar protein breakdown after 2 days BR (p<0.05). Myofibrillar protein FSR and LMV were restored by 3 days of ERS (p<0.01, p<0.01; respectively), but not by ambulation alone. However, insulin stimulated LGU and muscle glycogen storage were not restored by ESR. Three days of BR caused concurrent reductions in LMV, myofibrillar protein FSR, myofibrillar protein breakdown and insulin stimulated LGU, leg blood flow and muscle glycogen storage in healthy, young volunteers. Resistance ESR restored LMV and myofibrillar protein FSR, but LGU and muscle glycogen storage remained depressed, highlighting divergences in muscle fuel and protein metabolism. Furthermore, ambulation alone did not restore LMV and myofibrillar protein FSR in the non-exercised contralateral limb, emphasising the importance of exercise rehabilitation following even short-term BR. This study was supported by the Biotechnology and Biological Sciences Research Council (BB/P005004/1), the Centre for Sport, Exercise and Osteoarthritis Research Versus Arthritis (grant no. 21595), and the National Institute of Health Research (NIHR) Nottingham Biomedical Research Centre. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

A Patented Dietary Supplement (Hydroxy-Methyl-Butyrate, Carnosine, Magnesium, Butyrate, Lactoferrin) Is a Promising Therapeutic Target for Age-Related Sarcopenia through the Regulation of Gut Permeability: A Randomized Controlled Trial.

Adequate diet, physical activity, and dietary supplementation with muscle-targeted food for special medical purposes (FSMP) or dietary supplement (DS) are currently considered fundamental pillars in sarcopenia treatment. The aim of this study is to evaluate the effectiveness of a DS (containing hydroxy-methyl-butyrate, carnosine, and magnesium, for its action on muscle function and protein synthesis and butyrate and lactoferrin for their contribution to the regulation of gut permeability and antioxidant/anti-inflammation activity) on muscle mass (assessed by dual X-ray absorptiometry (DXA)), muscle function (by handgrip test, chair test, short physical performance battery (SPPB) test, and walking speed test), inflammation (tumor necrosis factor-alpha (TNF-a), C-reactive protein (CRP), and visceral adipose tissue (VAT)) and gut axis (by zonulin). A total of 59 participants (age 79.7 ± 4.8 years, body mass index 20.99 ± 2.12 kg/m2) were enrolled and randomly assigned to intervention (n = 30) or placebo (n = 28). The skeletal muscle index (SMI) significantly improved in the supplemented group compared to the placebo one, +1.02 (CI 95%: -0.77; 1.26), p = 0.001; a significant reduction in VAT was observed in the intervention group, -70.91 g (-13.13; -4.70), p = 0.036. Regarding muscle function, all the tests significantly improved (p = 0.001) in the supplemented group compared to the placebo one. CRP, zonulin, and TNF-alpha significantly decreased (p = 0.001) in intervention, compared to placebo, -0.74 mg/dL (CI 95%: -1.30; -0.18), -0.30 ng/mL (CI 95%: -0.37; -0.23), -6.45 pg/mL (CI 95%: -8.71; -4.18), respectively. This DS improves muscle mass and function, and the gut muscle has emerged as a new intervention target for sarcopenia.

The Influence of Stress and Binge-Patterned Alcohol Drinking on Mouse Skeletal Muscle Protein Synthesis and Degradation Pathways.

Adverse experiences (e.g., acute stress) and alcohol misuse can both impair skeletal muscle homeostasis, resulting in reduced protein synthesis and greater protein breakdown. Exposure to acute stress is a significant risk factor for engaging in alcohol misuse. However, little is known about how these factors together might further affect skeletal muscle health. To that end, this study investigated the effects of acute stress exposure followed by a period of binge-patterned alcohol drinking on signaling factors along mouse skeletal muscle protein synthesis (MPS) and degradation (MPD) pathways. Young adult male C57BL/6J mice participated in the Drinking in the Dark paradigm, where they received 2-4 h of access to 20% ethanol (alcohol group) or water (control group) for four days to establish baseline drinking levels. Three days later, half of the mice in each group were either exposed to a single episode of uncontrollable tail shocks (acute stress) or remained undisturbed in their home cages (no stress). Three days after stress exposure, mice received 4 h of access to 20% ethanol (alcohol) to model binge-patterned alcohol drinking or water for ten consecutive days. Immediately following the final episode of alcohol access, mouse gastrocnemius muscle was extracted to measure changes in relative protein levels along the Akt-mTOR MPS, as well as the ubiquitin-proteasome pathway (UPP) and autophagy MPD pathways via Western blotting. A single exposure to acute stress impaired Akt singling and reduced rates of MPS, independent of alcohol access. This observation was concurrent with a potent increase in heat shock protein seventy expression in the muscle of stressed mice. Alcohol drinking did not exacerbate stress-induced alterations in the MPS and MPD signaling pathways. Instead, changes in the MPS and MPD signaling factors due to alcohol access were primarily observed in non-stressed mice. Taken together, these data suggest that exposure to a stressor of sufficient intensity may cause prolonged disruptions to signaling factors that impact skeletal muscle health and function beyond what could be further induced by periods of alcohol misuse.

Effectiveness of Exercise Interventions on Body Composition, Exercise Capacity, Fatigue, and Quality of Life in Patients with Liver Cirrhosis: A Meta-Analysis of Randomized Controlled Trials.

Diminished muscle protein synthesis in cirrhosis leads to reduced strength and mass, impacting daily activities and overall quality of life. This study aimed to examine the effectiveness of exercise intervention in body composition, exercise capacity, fatigue, and quality of life in patients with liver cirrhosis. A systematic search of medical databases, including PubMed, Embase, Cochrane, and CINAHL, was executed from their inception to November 2022. The inclusion criteria were randomized controlled trials comparing exercise interventions with a control group that did not receive exercise interventions. From the initially identified 2,565 articles, eight studies with a total of 220 patients were eligible for inclusion in this meta-analysis. According to the meta-analysis, exercise significantly improved the six-minute walk distance (6MWD) by 68.93m (95% CI 14.29-123.57) compared to the control group. Furthermore, the subgroup analysis revealed that combing exercise with amino acid supplementation had a greater positive effect on the 6MWD (MD = 144.72, 95% CI 87.44-202.01). Exercise also significantly increased thigh circumference (MD = 1.26, 95% CI 0.12-2.39) and the thigh ultrasound average compression index (MD = 0.07, 95% CI 0.00-0.14). Moreover, exercise significantly decreased fatigue levels by 0.7 points in patients with liver cirrhosis (95% CI 0.38-1.03). However, no significant effects were observed on body mass index (BMI), fat mass, fat-free mass, and quality of life. Exercise can improve exercise capacity, thigh muscle thickness, and fatigue in patients with cirrhosis, but it does not have a significant impact on fat mass, BMI, or quality of life.

Not Only Protein: Dietary Supplements to Optimize the Skeletal Muscle Growth Response to Resistance Training: The Current State of Knowledge

Regarding skeletal muscle hypertrophy, resistance training and nutrition, the most often discussed and proposed supplements include proteins. Although, the correct amount, quality, and daily distribution of proteins is of paramount importance for skeletal muscle hypertrophy, there are many other nutritional supplements that can help and support the physiological response of skeletal muscle to resistance training in terms of muscle hypertrophy. A healthy muscle environment and a correct whole muscle metabolism response to the stress of training is a prerequisite for the increase in muscle protein synthesis and, therefore, muscle hypertrophy. In this review, we discuss the role of different nutritional supplements such as carbohydrates, vitamins, minerals, creatine, omega-3, polyphenols, and probiotics as a support and complementary factors to the main supplement i.e., protein. The different mechanisms are discussed in the light of recent evidence.

Targeting Molecular Mechanisms of Obesity- and Type 2 Diabetes Mellitus-Induced Skeletal Muscle Atrophy with Nerve Growth Factor.

Skeletal muscle plays a critical role in metabolic diseases, such as obesity and type 2 diabetes mellitus (T2DM). Muscle atrophy, characterized by a decrease in muscle mass and function, occurs due to an imbalance between the rates of muscle protein synthesis and degradation. This study aimed to investigate the molecular mechanisms that lead to muscle atrophy in obese and T2DM mouse models. Additionally, the effect of nerve growth factor (NGF) on the protein synthesis and degradation pathways was examined. Male mice were divided into three groups: a control group that was fed a standard chow diet, and two experimental groups that were fed a Western diet. After 8 weeks, the diabetic group was injected with streptozotocin to induce T2DM. Each group was then further divided into NGF-treated or non-treated control group. In the gastrocnemius muscles of the Western diet group, increased expressions of myostatin, autophagy markers, and ubiquitin ligases were observed. Skeletal muscle tissue morphology indicated signs of muscle atrophy in both obese and diabetic mice. The NGF-treated group showed a prominent decrease in the protein levels of myostatin and autophagy markers. Furthermore, the NGF-treated group showed an increased Cyclin D1 level. Western diet-induced obesity and T2DM may be linked to muscle atrophy through upregulation of myostatin and subsequent increase in the ubiquitin and autophagy systems. Moreover, NGF treatment may improve muscle protein synthesis and cell cycling.

Post-prandial tracer studies of protein and amino acid utilisation: what can they tell us about human amino acid and protein requirements?

Nitrogen balance (NB), the principal methodology used to derive recommendations for human protein and amino acid requirements, has been widely criticised, and calls for increased protein and amino acid requirement recommendations have been made, often on the basis of post-prandial amino acid tracer kinetic studies of muscle protein synthesis, or of amino acid oxidation. This narrative review considers our knowledge of the homeostatic regulation of the FFM throughout the diurnal cycle of feeding and fasting and what can and has been learnt from post-prandial amino acid tracer studies, about amino acid and protein requirements. Within the FFM, muscle mass in well fed weight-stable adults with healthy lifestyles appears fixed at a phenotypic level within a wide range of habitual protein intakes. However homoeostatic regulation occurs in response to variation in habitual protein intake, with adaptive changes in amino acid oxidation which influence the magnitude of diurnal losses and gains of body protein. Post-prandial indicator amino acid oxidation (IAAO) studies have been introduced as an alternative to NB and to the logistically complex 24 h [13C-1] amino acid balance studies, for assessment of protein and amino acid requirements. However, a detailed examination of IAAO studies shows both a lack of concern for homeostatic regulation of amino acid oxidation and major flaws in their design and analytical interpretation, which seriously constrain their ability to provide reliable values. New ideas and a much more critical approach to existing work is needed if real progress is to be made in the area.

Hypoxia treatment and resistance training alters microRNA profiling in rats skeletal muscle

MicroRNAs (miRNAs) may play a crucial regulatory role in the process of muscle atrophy induced by high-altitude hypoxia and its amelioration through resistance training. However, research in this aspect is still lacking. Therefore, this study aimed to employ miRNA microarray analysis to investigate the expression profile of miRNAs in skeletal muscle from an animal model of hypoxia-induced muscle atrophy and resistance training aimed at mitigating muscle atrophy. The study utilized a simulated hypoxic environment (oxygen concentration at 11.2%) to induce muscle atrophy and established a rat model of resistance training using ladder climbing, with a total intervention period of 4 weeks. The miRNA expression profile revealed 9 differentially expressed miRNAs influenced by hypoxia (e.g., miR-341, miR-32-5p, miR-465-5p) and 14 differentially expressed miRNAs influenced by resistance training under hypoxic conditions (e.g., miR-338-5p, miR-203a-3p, miR-92b-3p) (∣log2(FC)∣ ≥ 1.5, p < 0.05). The differentially expressed miRNAs were found to target genes involved in muscle protein synthesis and degradation (such as Utrn, mdm2, eIF4E), biological processes (such as negative regulation of transcription from RNA polymerase II promoter, regulation of transcription, DNA-dependent), and signaling pathways (such as Wnt signaling pathway, MAPK signaling pathway, ubiquitin-mediated proteolysis, mTOR signaling pathway). This study provides a foundation for understanding and further exploring the molecular mechanisms underlying hypoxia-induced rats muscle atrophy and the mitigation of atrophy through resistance training.

Completely Plant-Based Diets That Meet Energy Requirements for Resistance Training Can Supply Enough Protein and Leucine to Maximize Hypertrophy and Strength in Male Bodybuilders: A Modeling Study.

Despite increasing awareness of plant-based diets for health and athletic performance, athletes are cautioned that careful dietary monitoring is necessary. Whether commonly consumed plant-based diets are nutritionally adequate for maximal muscular hypertrophy remains unknown. This modeling study assessed the nutrient composition of completely plant-based diets scaled to the caloric demands of maximal muscle mass and strength development in adult male bodybuilders. To model calorie requirements, anthropometric data from bodybuilders were input into the Tinsley resting metabolic rate prediction equation, and an appropriate physical activity factor and calorie surplus were applied. Dietary data from a large cohort following completely plant-based diets were then scaled to meet these needs. Modeled intakes for nutrients of interest were calculated as 1.8 g/kg/day of protein and 2.75 g/meal of leucine, which surpass mean requirements for maximal increases in muscle mass and strength and muscle protein synthesis, respectively. Daily levels for all micronutrients, except vitamin D, also exceeded requirements. Saturated fat levels were aligned with dietary guidelines, although sodium levels exceeded recommended limits. Consumption of larger portions of commonplace plant-based diets, scaled to meet the energy demands of maximal accrual of muscle mass and strength, satisfied protein and leucine requirements without the need for additional planning.

The role of TGF-β signaling in muscle atrophy, sarcopenia and cancer cachexia

Skeletal muscle, comprising a significant proportion (40 to 50 percent) of total body weight in humans, plays a critical role in maintaining normal physiological conditions. Muscle atrophy occurs when the rate of protein degradation exceeds protein synthesis. Sarcopenia refers to age-related muscle atrophy, while cachexia represents a more complex form of muscle wasting associated with various diseases such as cancer, heart failure, and AIDS. Recent research has highlighted the involvement of signaling pathways, including IGF1-Akt-mTOR, MuRF1-MAFbx, and FOXO, in regulating the delicate balance between muscle protein synthesis and breakdown. Myostatin, a member of the TGF-β superfamily, negatively regulates muscle growth and promotes muscle atrophy by activating Smad2 and Smad3. It also interacts with other signaling pathways in cachexia and sarcopenia. Inhibition of myostatin has emerged as a promising therapeutic approach for sarcopenia and cachexia. Additionally, other TGF-β family members, such as TGF-β1, activin A, and GDF11, have been implicated in the regulation of skeletal muscle mass. Furthermore, myostatin cooperates with these family members to impair muscle differentiation and contribute to muscle loss. This review provides an overview of the significance of myostatin and other TGF-β signaling pathway members in muscular dystrophy, sarcopenia, and cachexia. It also discusses potential novel therapeutic strategies targeting myostatin and TGF-β signaling for the treatment of muscle atrophy.

Effects of supplementing coated methionine in a high plant-protein diet on growth, antioxidant capacity, digestive enzymes activity and expression of TOR signaling pathway associated genes in gibel carp, Carassius auratus gibelio.

This study explored the impacts of supplementation of different levels of coated methionine (Met) in a high-plant protein diet on growth, blood biochemistry, antioxidant capacity, digestive enzymes activity and expression of genes related to TOR signaling pathway in gibel carp (Carassius auratus gibeilo). A high-plant protein diet was formulated and used as a basal diet and supplemented with five different levels of coated Met at 0.15, 0.30, 0.45, 0.60 and 0.75%, corresponding to final analyzed Met levels of 0.34, 0.49, 0.64, 0.76, 0.92 and 1.06%. Three replicate groups of fish (initial mean weight, 11.37 ± 0.02g) (20 fish per replicate) were fed the test diets over a 10-week feeding period. The results indicated that with the increase of coated Met level, the final weight, weight gain (WG) and specific growth rate initially boosted and then suppressed, peaking at 0.76% Met level (P< 0.05). Increasing dietary Met level led to significantly increased muscle crude protein content (P< 0.05) and reduced serum alanine aminotransferase activity (P< 0.05). Using appropriate dietary Met level led to reduced malondialdehyde concentration in hepatopancreas (P< 0.05), improved superoxide dismutase activity (P< 0.05), and enhanced intestinal amylase and protease activities (P< 0.05). The expression levels of genes associated with muscle protein synthesis such as insulin-like growth factor-1, protein kinase B, target of rapamycin and eukaryotic initiation factor 4E binding protein-1 mRNA were significantly regulated, peaking at Met level of 0.76% (P< 0.05). In conclusion, supplementing optimal level of coated Met improved on fish growth, antioxidant capacity, and the expression of TOR pathway related genes in muscle. The optimal dietary Met level was determined to be 0.71% of the diet based on quadratic regression analysis of WG.

Lactobacillus gasseri BNR17 Ameliorates Dexamethasone-Induced Muscle Loss in BALB/c Mice and C2C12 Myotubes.

This study aimed to investigate the effects and mechanism of Lactobacillus gasseri BNR17, a probiotic strain isolated from human breast milk, on dexamethasone-induced muscle loss in mice and cultured myotubes. BALB/c mice were intraperitoneally injected with dexamethasone, and orally administered L. gasseri BNR17 for 21 days. L. gasseri BNR17 treatment ameliorated dexamethasone-induced decline in muscle function, as evidenced by an increase in forelimb grip strength, treadmill running time, and rotarod retention time in both female and male mice. In addition, L. gasseri BNR17 treatment significantly increased the mass of the gastrocnemius and quadriceps muscles. Dual-energy X-ray absorptiometry showed a significant increase in lean body mass and a decrease in fat mass in both whole body and hind limb after treatment with L. gasseri BNR17. It was found that L. gasseri BNR17 treatment downregulated serum myostatin level and the protein degradation pathway composed of muscle-specific ubiquitin E3 ligases, MuRF1 and MAFbx, and their transcription factor FoxO3. In contrast, L. gasseri BNR17 treatment upregulated serum insulin-like growth factor-1 level and Akt-mTOR-p70S6K signaling pathway involved in protein synthesis in muscle. As a result, L. gasseri BNR17 treatment significantly increased the levels of major muscular proteins such as myosin heavy chain and myoblast determination protein 1. Consistent with in vivo results, L. gasseri BNR17 culture supernatant significantly ameliorated dexamethasone-induced C2C12 myotube atrophy in vitro. In conclusion, L. gasseri BNR17 ameliorates muscle loss by downregulating the protein degradation pathway and upregulating the protein synthesis pathway.

440 Muscle Protein Synthesis and Whole-Body Protein Balance Following Ingestion of Beef or a Soy Protein Based Meat Alternative

OBJECTIVES/GOALS: We endeavor to investigated the hypothesis that muscle protein synthesis (MPS) is stimulated more after consumption of a 4-ounce beef patty as compared to 4- and 8-ounces of a soy protein based meat alternative (SPBMA) and if a greater stimulation is related to differences in the responses of plasma essential amino acid (EAA) concentrations. METHODS/STUDY POPULATION: Participants were aged 18 to 40 years of age with a BMI between 20 and 32 kg/m2. Written informed consent was obtained from all participants, and approved by UAMS IRB. Participants were assigned to one of three intervention groups via a single-blinded permuted block randomization, stratified for sex: 4 oz beef patty; 4 oz SPBMA; 2 x 4 oz (8oz) SPBMA. The impossible burgerTM was selected as it is primarily soy protein, a high-quality plant protein, and specifically designed to mimic a beef burger. Stable isotope were infused to assess protein metabolism. Appropriate muscle and blood samples were obtained. Enrichment and plasma EAA concentrations were measured with mass spectrometry. ANOVA’s on the change from basal to postprandial were used to identify group difference, significance was accepted at p &lt; 0.05. RESULTS/ANTICIPATED RESULTS: The MPS increase from basal to postprandial indicated a significant main effect of group (p = 0.026), with the beef group (0.020 ± 0.016%/hour) being significantly greater than the 4oz SPBMA (0.003 ± 0.010%/hour; p = 0.021) but not the 8oz PBMA group (0.013 ± 0.016%/hour; p = 0.454). Similar results were observed for whole-body protein synthesis, where the beef group (p = 0.042) and 8oz SPBMA (p = 0.033) were significantly greater than the 4oz SPBMA (p = 0.021). Whole-body protein balance was significantly greater in the 8oz SPBMA as compared to 4oz of beef and SPBMA. Lastly, we observed a significantly relationship (p = 0.046; r = 0.411) between the maximal plasma EAA concentration and change in MPS, indicating the greater rate of MPS following 4oz of beef is mediated by an higher increase in plasma EAA concentrations. DISCUSSION/SIGNIFICANCE: In conclusion, 4oz of beef stimulates muscle protein FSR more than 4oz of a SPBMA. A common SPBMA can stimulate increase in protein metabolism, however, greater amounts are required as compared to beef protein. Further, the change in the muscle protein FSR response was significantly correlated with the maximal EAA concentration.

Intramuscular injection of mesenchymal stem cells augments basal muscle protein synthesis after bouts of resistance exercise in male mice.

Skeletal muscle mass is critical for activities of daily living. Resistance training maintains or increases muscle mass, and various strategies maximize the training adaptation. Mesenchymal stem cells (MSCs) are multipotent cells with differential potency in skeletal muscle cells and the capacity to secrete growth factors. However, little is known regarding the effect of intramuscular injection of MSCs on basal muscle protein synthesis and catabolic systems after resistance training. Here, we measured changes in basal muscle protein synthesis, the ubiquitin-proteasome system, and autophagy-lysosome system-related factors after bouts of resistance exercise by intramuscular injection of MSCs. Mice performed three bouts of resistance exercise (each consisting of 50 maximal isometric contractions elicited by electrical stimulation) on the right gastrocnemius muscle every 48 h, and immediately after the first bout, mice were intramuscularly injected with either MSCs (2.0 × 106 cells) labeled with green fluorescence protein (GFP) or vehicle only placebo. Seventy-two hours after the third exercise bout, GFP was detected only in the muscle injected with MSCs with concomitant elevation of muscle protein synthesis. The injection of MSCs also increased protein ubiquitination. These results suggest that the intramuscular injection of MSCs augmented muscle protein turnover at the basal state after consecutive resistance exercise.