Methionine (Met) can activate the mechanistic target of rapamycin (mTOR) to promote milk synthesis in mammary epithelial cells. However, it is largely unknown which G protein-coupled receptor can mediate the stimulation of Met on mTOR activation. In this study, we employed transcriptome sequencing to analyse which G protein-coupled receptors were associated with the role of Met and further used gene function study approaches to explore the role of G protein-coupled receptor 183 (GPR183) in Met stimulation on mTOR activation in HC11 cells. We identified nine G protein-coupled receptors including GPR183 whose expression levels were upregulated by Met treatment through RNA sequencing and subsequent quantitative real-time PCR analysis. Using GPR183 knockdown and overexpression technology, we demonstrate that GPR183 is a positive regulator of milk protein and fat synthesis and proliferation of HC11 cells. Met affected GPR183 expression in a dose-dependent manner, and GPR183 mediated the stimulation of Met (0·6 mM) on milk protein and fat synthesis, cell proliferation and mTOR phosphorylation and mRNA expression. The inhibition of phosphoinositide 3-kinase blocked the phosphorylation of mTOR and AKT stimulated by GPR183 activation. In summary, through RNA sequencing and gene function study, we uncover that GPR183 is a key mediator for Met to activate the phosphoinositide 3-kinase-mTOR signalling and milk synthesis in mouse mammary epithelial cells.

Branched-chain amino acids (BCAA: leucine, isoleucine and valine) are three of the nine indispensable amino acids, and are frequently consumed as a dietary supplement by athletes and recreationally active individuals alike. The popularity of BCAA supplements is largely predicated on the notion that they can stimulate rates of muscle protein synthesis (MPS) and suppress rates of muscle protein breakdown (MPB), the combination of which promotes a net anabolic response in skeletal muscle. To date, several studies have shown that BCAA (particularly leucine) increase the phosphorylation status of key proteins within the mechanistic target of rapamycin (mTOR) signalling pathway involved in the regulation of translation initiation in human muscle. Early research in humans demonstrated that BCAA provision reduced indices of whole-body protein breakdown and MPB; however, there was no stimulatory effect of BCAA on MPS. In contrast, recent work has demonstrated that BCAA intake can stimulate postprandial MPS rates at rest and can further increase MPS rates during recovery after a bout of resistance exercise. The purpose of this evidence-based narrative review is to critically appraise the available research pertaining to studies examining the effects of BCAA on MPS, MPB and associated molecular signalling responses in humans. Overall, BCAA can activate molecular pathways that regulate translation initiation, reduce indices of whole-body and MPB, and transiently stimulate MPS rates. However, the stimulatory effect of BCAA on MPS rates is less than the response observed following ingestion of a complete protein source providing the full complement of indispensable amino acids.

The G protein-coupled receptors (GPCR) sensing nutritional signals (amino acids, fatty acids, glucose, etc.) are not fully understood. In this research, we used transcriptome sequencing to analyse differentially expressed genes (DEG) in mouse mammary gland tissues at puberty, lactation and involution stages, in which eight GPCR were selected out and verified by qRT-PCR assay. It was further identified the role of GPR110-mediating nutrients including palmitic acid (PA) and methionine (Met) to improve milk synthesis using mouse mammary epithelial cell line HC11. PA but not Met affected GPR110 expression in a dose-dependent manner. GPR110 knockdown decreased milk protein and fat synthesis and cell proliferation and blocked the stimulation of PA on mechanistic target of rapamycin (mTOR) phosphorylation and sterol-regulatory element binding protein 1c (SREBP-1c) expression. In summary, these experimental results disclose DEG related to lactation and reveal that GPR110 mediates PA to activate the mTOR and SREBP-1c pathways to promote milk protein and fat synthesis.

Several amino acids can stimulate milk synthesis in mammary epithelial cells (MEC); however, the regulatory role of isoleucine (Ile) and underlying molecular mechanism remain poorly understood. In this study, we aimed to evaluate the regulatory effects of Ile on milk protein and fat synthesis in MEC and reveal the mediation mechanism of Brahma-related gene 1 (BRG1) on this regulation. Ile dose dependently affected milk protein and fat synthesis, mechanistic target of rapamycin (mTOR) phosphorylation, sterol regulatory element binding protein 1c (SREBP-1c) expression and maturation, and BRG1 protein expression in bovine MEC. Phosphatidylinositol 3 kinase (PI3K) inhibition by LY294002 treatment blocked the stimulation of Ile on BRG1 expression. BRG1 knockdown and gene activation experiments showed that it mediated the stimulation of Ile on milk protein and fat synthesis, mTOR phosphorylation, and SREBP-1c expression and maturation in MEC. ChIP-PCR analysis detected that BRG1 bound to the promoters of mTOR and SREBP-1c, and ChIP-qPCR further detected that these bindings were increased by Ile stimulation. In addition, BRG1 positively regulated the binding of H3K27ac to these two promoters, while it negatively affected the binding of H3K27me3 to these promoters. BRG1 knockdown blocked the stimulation of Ile on these two gene expressions. The expression of BRG1 was higher in mouse mammary gland in the lactating period, compared with that in the puberty or dry period. Taken together, these experimental data reveal that Ile stimulates milk protein and fat synthesis in MEC via the PI3K-BRG1-mTOR/SREBP-1c pathway.

Obesity remains a serious relevant public health concern throughout the world despite related countermeasures being well understood (i.e. mainly physical activity and an adjusted diet). Among different nutritional approaches, there is a growing interest in ketogenic diets (KD) to manipulate body mass (BM) and to enhance fat mass loss. KD reduce the daily amount of carbohydrate intake drastically. This results in increased fatty acid utilisation, leading to an increase in blood ketone bodies (acetoacetate, 3-β-hydroxybutyrate and acetone) and therefore metabolic ketosis. For many years, nutritional intervention studies have focused on reducing dietary fat with little or conflicting positive results over the long term. Moreover, current nutritional guidelines for athletes propose carbohydrate-based diets to augment muscular adaptations. This review discusses the physiological basis of KD and their effects on BM reduction and body composition improvements in sedentary individuals combined with different types of exercise (resistance training or endurance training) in individuals with obesity and athletes. Ultimately, we discuss the strengths and the weaknesses of these nutritional interventions together with precautionary measures that should be observed in both individuals with obesity and athletic populations. A literature search from 1921 to April 2021 using Medline, Google Scholar, PubMed, Web of Science, Scopus and Sportdiscus Databases was used to identify relevant studies. In summary, based on the current evidence, KD are an efficient method to reduce BM and body fat in both individuals with obesity and athletes. However, these positive impacts are mainly because of the appetite suppressive effects of KD, which can decrease daily energy intake. Therefore, KD do not have any superior benefits to non-KD in BM and body fat loss in individuals with obesity and athletic populations in an isoenergetic situation. In sedentary individuals with obesity, it seems that fat-free mass (FFM) changes appear to be as great, if not greater, than decreases following a low-fat diet. In terms of lean mass, it seems that following a KD can cause FFM loss in resistance-trained individuals. In contrast, the FFM-preserving effects of KD are more efficient in endurance-trained compared with resistance-trained individuals.

Skeletal muscle atrophy causes decreased physical activity and increased risk of metabolic diseases. We investigated the effects of oleamide (cis-9,10-octadecanamide) treatment on skeletal muscle health. The plasma concentration of endogenous oleamide was approximately 30 nm in male ddY mice under normal physiological conditions. When the stable isotope-labelled oleamide was orally administered to male ddY mice (50 mg/kg), the plasma concentration of exogenous oleamide reached approximately 170 nm after 1 h. Male ddY mice were housed in small cages (one-sixth of normal size) to enforce sedentary behaviour and orally administered oleamide (50 mg/kg per d) for 4 weeks. Housing in small cages decreased tibialis anterior (TA) muscle mass and the cross-sectional area of the myofibres in TA muscle. Dietary oleamide alleviated the decreases in TA muscle and resulted in plasma oleamide concentration of approximately 120 nm in mice housed in small cages. Housing in small cages had no influence on the phosphorylation levels of Akt serine/threonine kinase (Akt), mechanistic target of rapamycin (mTOR) and ribosomal protein S6 kinase (p70S6K) in TA muscle; nevertheless, oleamide increased the phosphorylation levels of the proteins. Housing in small cages increased the expression of microtubule-associated protein 1 light chain 3 (LC3)-II and sequestosome 1 (p62), but not LC3-I, in TA muscle, and oleamide reduced LC3-I, LC3-II and p62 expression levels. In C2C12 myotubes, oleamide increased myotube diameter at ≥100 nm. Furthermore, the mTOR inhibitor, Torin 1, suppressed oleamide-induced increases in myotube diameter and protein synthesis. These results indicate that dietary oleamide rescued TA muscle atrophy in mice housed in small cages, possibly by activating the phosphoinositide 3-kinase/Akt/mTOR signalling pathway and restoring autophagy flux.

The development and maintenance of body composition and functions require an adequate protein intake with a continuous supply of amino acids (AA) to tissues. Body pool and AA cellular concentrations are tightly controlled and maintained through AA supply (dietary intake, recycled from proteolysis and de novo synthesis), AA disposal (protein synthesis and other AA-derived molecules) and AA losses (deamination and oxidation). Different molecular regulatory pathways are involved in the control of AA sufficiency including the mechanistic target of rapamycin complex 1, the general control non-derepressible 2/activating transcription factor 4 system or the fibroblast growth factor 21. There is a tight control of protein intake, and human subjects and animals appear capable of detecting and adapting food and protein intake and metabolism in face of foods or diets with different protein contents. A severely protein deficient diet induces lean body mass losses and ingestion of sufficient dietary energy and protein is a prerequisite for body protein synthesis and maintenance of muscle, bone and other lean tissues and functions. Maintaining adequate protein intake with age may help preserve muscle mass and strength but there is an ongoing debate as to the optimal protein intake in older adults. The protein synthesis response to protein intake can also be enhanced by prior completion of resistance exercise but this effect could be somewhat reduced in older compared to young individuals and gain in muscle mass and function due to exercise require regular training over an extended period.

Eggs are considered a high-quality protein source for their complete amino acid profile and digestibility. Therefore, this study aimed to compare the effects of whole egg (WE) v. egg white (EW) ingestion during 12 weeks of resistance training (RT) on the skeletal muscle regulatory markers and body composition in resistance-trained men. Thirty resistance-trained men (mean age 24·6 (sd 2·7) years) were randomly assigned into the WE + RT (WER, n 15) or EW + RT (EWR, n 15) group. The WER group ingested three WE, while the EWR group ingested an isonitrogenous quantity of six EW per d immediately after the RT session. Serum concentrations of regulatory markers and body composition were measured at baseline and after 12 weeks. Significant main effects of time were observed for body weight (WER 1·7, EWR 1·8 kg), skeletal muscle mass (WER 2·9, EWR 2·7 kg), fibroblast growth factor-2 (WER 116·1, EWR 83·2 pg/ml) and follistatin (WER 0·05, EWR 0·04 ng/ml), which significantly increased (P < 0·05), and for fat mass (WER –1·9, EWR –1·1 kg), transforming growth factor-β1 (WER –0·5, EWR −0·1 ng/ml), activin A (WER –6·2, EWR –4·5 pg/ml) and myostatin (WER –0·1, EWR –0·06 ng/ml), which significantly decreased (P < 0·05) in both WER and EWR groups. The consumption of eggs absent of yolk during chronic RT resulted in similar body composition and functional outcomes as WE of equal protein value. EW or WE may be used interchangeably for the dietary support of RT-induced muscular hypertrophy when protein intake is maintained.

Methionine is a limiting amino acid (AA) in fish diets, particularly in those containing high levels of plant protein (PP), and is key in the immune system. Accordingly, outcome on the fish immune mechanisms of methionine-deficient and methionine-supplemented diets within the context of 0 % fishmeal formulation, after a short and prolonged feeding period, was studied in European seabass (Dicentrarchus labrax). For this, seabass juveniles were fed a (i) fishmeal-free diet, meeting AA requirements, but deficient in methionine (MET0·65); (ii) as control, the MET0·65 supplemented with l-methionine at 0·22 % of feed weight (CTRL); (iii) two diets, identical to MET0·65 but supplemented at 0·63 and 0·88 % of feed weight of l-methionine (MET1·25 and MET1·5, respectively); and (iv) a fishmeal-based diet (FM), as positive control. After 2 and 12 weeks of feeding, blood and plasma were sampled for leucocyte counting and humoral parameter assays and head-kidney collected for gene expression. After 2 weeks of feeding, a fishmeal-free diet supplemented with methionine led to changes in the expression of methionine- and leucocyte-related genes. A methionine immune-enhancer role was more evident after 12 weeks with an increased neutrophil percentage and a decreased expression of apoptotic genes, possibly indicating an enhancement of fish immunity by methionine dietary supplementation. Furthermore, even though CTRL and FM present similar methionine content, CTRL presented a reduced expression of several immune-related genes indicating that in a practical PP-based diet scenario, the requirement level of methionine for an optimal immune status could be higher.

Leucine plays an important role in promoting muscle protein synthesis and muscle remodelling. However, what percentage of leucine is appropriate in creep feed and what proteome profile alterations are caused by dietary leucine in the skeletal muscle of piglets remain elusive. In this case, we applied isobaric tags for relative and absolute quantitation to analyse the proteome profile of the longissimus dorsi muscles of weanling piglets fed a normal leucine diet (NL; 1·66 % leucine) and a high-leucine diet (HL; 2·1 % leucine). We identified 157 differentially expressed proteins between these two groups. Bioinformatics analysis of these proteins exhibited the suppression of oxidative phosphorylation and fatty acid β-oxidation, as well as the activation of glycolysis, in the HL group. For further confirmation, we identified that SDHB, ATP5F1, ACADM and HADHB were significantly down-regulated (P<0·01, except ATP5F1, P<0·05), whereas the glycolytic enzyme pyruvate kinase was significantly up-regulated (P<0·05) in the HL group. We also show that enhanced muscle protein synthesis and the transition from slow-to-fast fibres are altered by leucine. Together, these results indicate that leucine may alter energy metabolism and promote slow-to-fast transitions in the skeletal muscle of weanling piglets.

The present study investigated the effects of dietary arginine (Arg) supplementation on intestinal structure and functionality in broiler chickens subjected to coccidial challenge. The present study was a randomised complete block design employing a 3 × 2 factorial arrangement (n 8) with three dietary concentrations of Arg (11·1, 13·3 and 20·2 g/kg) with or without coccidial vaccine challenge (unchallenged and coccidial challenge). On day 14, birds were orally administered with coccidial vaccine or saline. On day 21, birds were killed to obtain jejunal tissue and mucosal samples for histological, gene expression and mucosal immunity measurements. Within 7 d of the challenge, there was a decrease in body-weight gain and feed intake, and an increase in the feed:gain ratio (P< 0·05). Jejunal inflammation was evidenced by villus damage, crypt dilation and goblet cell depletion. Coccidial challenge increased mucosal secretory IgA concentration and inflammatory gene (iNOS, IL-1β, IL-8 and MyD88) mRNA expression levels (P< 0·05), as well as reduced jejunal Mucin-2, IgA and IL-1RI mRNA expression levels (P< 0·05). Increasing Arg concentration (1) increased jejunal villus height (P< 0·05) and linearly increased jejunal crypt depth (P< 0·05); (2) quadratically increased mucosal maltase activity (P< 0·05) and linearly decreased mucosal secretory IgG concentration (P< 0·05) within the coccidiosis-challenged groups; and (3) linearly decreased jejunal Toll-like receptor 4 (TLR4) mRNA expression level (P< 0·05) within the coccidiosis-challenged groups. The mRNA expression of mechanistic target of rapamycin (mTOR) complex 1 pathway genes (mTOR and RPS6KB1) and the anti-apoptosis gene Bcl-2 quadratically responded to increasing dietary Arg supplementation (P< 0·05). These results indicate that dietary Arg supplementation attenuates intestinal mucosal disruption in coccidiosis-challenged chickens probably through suppressing TLR4 and activating mTOR complex 1 pathways.