Lysine restriction and realimentation affected growth, blood profiles and expression of genes related to protein and fat metabolism in weaned pigs

Lysine stimulates the development of the murine mammary gland at puberty via PI3K/AKT/mTOR signalling axis

Lysine is one of the essential amino acids. The effect of lysine on milk protein and milk fat anabolism has been reported, but the effect on mammary glands development has not been studied in detail. The normal development of the mammary glands at puberty is crucial to lactation of mammals. In this study, to explore the effect of lysine on mammary glands development, we fed different concentrations of lysine (0.025%, 0.05%, 0.1%) to pubertal mice and found that the addition of 0.1% lysine to drinking water significantly promoted mammary glands development. Furthermore, we treated mMECs (mouse mammary epithelial cells) with different concentrations of lysine (0, 0.2, 0.4, 0.6, 0.8 and 1 mM) to explore the underlying mechanism, and found that lysine promoted the proliferation of mMECs and development of mammary glands through PI3K/AKT/mTOR signalling pathway in pubertal mice. Overall, the results of this study revealed that lysine activated the PI3K/AKT/mTOR signal axis, elevated protein concentrations of cell proliferation markers, such as PCNA, Cyclin D1 and D3, and enhanced the proliferation of mMECs, finally promoted the murine mammary glands development at puberty.

mTORC1-Mediated Satellite Cell Differentiation Is Required for Lysine-Induced Skeletal Muscle Growth

Skeletal muscle is the primary source of protein for humans. However, the mechanisms of skeletal muscle growth, such as nutrition control, remain unknown. Moreover, the function of lysine (Lys) in controling skeletal muscle growth has gradually demonstrated that Lys is not only substantial for protein synthesis but also a signaling molecule for satellite cell (SC) activation. In the current work, the number of differentiated SCs in the longissimus thoracis muscle and the fusion index of SCs were both governed by Lys supplementation. Meanwhile, the myogenic regulatory factors and the mammalian target of rapamycin complex 1 (mTORC1) pathway showed the same tendencies of changes as the differentiation of SCs. After Lys was resupplemented with rapamycin, the mTORC1 pathway was inhibited and the differentiation ability of SCs was suppressed. Collectively, the results showed that the mTORC1-pathway-mediated SC differentiation was required for Lys-promoted skeletal muscle growth.

Dietary lysine affects amino acid metabolism and growth performance, which may not involve the GH/IGF-1 axis, in young growing pigs1

Lysine is the first limiting amino acid (AA) in typical swine diets. Our previous research showed that dietary lysine restriction compromised the growth performance of late-stage finishing pigs, which was associated with the changes in plasma concentrations of nutrient metabolites and hormone insulin-like growth factor 1 (IGF-1). This study was conducted to investigate how dietary lysine restriction affects the plasma concentrations of selected metabolites and three anabolic hormones in growing pigs. Twelve individually penned young barrows (Yorkshire × Landrace; 22.6 ± 2.04 kg) were randomly assigned to two dietary treatments (n = 6). Two corn and soybean meal based diets were formulated to contain 0.65% and 0.98% standardized ileal digestible lysine as a lysine-deficient (LDD) and a lysine-adequate (LAD) diets, respectively. During the 8-week feeding trial, pigs had ad libitum access to water and their respective diets, and the growth performance parameters including average daily gain (ADG), average daily feed intake (ADFI), and gain-to-feed ratio (G:F) were determined. At the end of the trial, jugular vein blood was collected for plasma preparation. The plasma concentrations of free AA and six metabolites were analyzed with the established chemical methods, and the hormone concentrations were analyzed with the commercial ELISA kits. Data were analyzed with Student's t-test. The ADG of LDD pigs was lower (P < 0.01) than that of LAD pigs, and so was the G:F (P < 0.05) since there was no difference in the ADFI between the two groups of pigs. In terms of free AA, the plasma concentrations of lysine, methionine, leucine, and tyrosine were lower (P < 0.05), while that of β-alanine was higher (P < 0.01), in the LDD pigs. The total plasma protein concentration was lower (P < 0.02) in the LDD pigs, whereas no differences were observed for the other metabolites between the two groups. No differences were observed in the plasma concentrations of growth hormone (GF), insulin, and IGF-1 between the two groups as well. These results indicate that the lack of lysine as a protein building block must be the primary reason for a reduced body protein synthesis and, consequently, the compromised G:F ratio and ADG. The changes in the plasma concentrations of total protein and four AA suggest that the compromised growth performance might be associated with some cell signaling and metabolic pathways that may not involve the GH/IGF-1 axis.

mTORC1 Mediates Lysine-Induced Satellite Cell Activation to Promote Skeletal Muscle Growth

As the first limiting amino acid, lysine (Lys) has been thought to promote muscle fiber hypertrophy by increasing protein synthesis. However, the functions of Lys seem far more complex than that. Despite the fact that satellite cells (SCs) play an important role in skeletal muscle growth, the communication between Lys and SCs remains unclear. In this study, we investigated whether SCs participate directly in Lys-induced skeletal muscle growth and whether the mammalian target of rapamycin complex 1 (mTORC1) pathway was activated both in vivo and in vitro to mediate SC functions in response to Lys supplementation. Subsequently, the skeletal muscle growth of piglets was controlled by dietary Lys supplementation. Isobaric tag for relative and absolute quantitation (iTRAQ) analysis showed activated SCs were required for longissimus dorsi muscle growth, and this effect was accompanied by mTORC1 pathway upregulation. Furthermore, SC proliferation was governed by medium Lys concentrations, and the mTORC1 pathway was significantly enhanced in vitro. After verifying that rapamycin inhibits the mTORC1 pathway and suppresses SC proliferation, we conclude that Lys is not only a molecular building block for protein synthesis but also a signal that activates SCs to manipulate muscle growth via the mTORC1 pathway.

Concomitant lysine and phosphorus addition to a wheat gluten protein diet highly amplified growth measures of rats

OBJECTIVE

In humans, the effects of lysine-fortified wheat on growth measures was much lower than that of animal experimentations that used phosphorus-containing mineral mix. It is known that wheat contains a limited amount of available phosphorus, which is believed to support growth. The aim of this study was to determine the involvement of phosphorus in growth measures of rats maintained on a lysine-supplemented wheat gluten diet.

METHODS

Forty male Sprague-Dawley (6 wk old) rats were randomly divided into four equal groups and fed wheat gluten protein (10%)-based diets with added lysine (0.6%), phosphorus (0.3%), or both (0.6% lysine and 0.3% phosphorus), ad libitum for 9 wk. Rats were monitored for changes in food intake, body weight, body and liver compositions, plasma urea nitrogen, and albumin.

RESULTS

The addition of lysine or phosphorus to wheat gluten-based diets increased energy intake modestly (∼15%), whereas their combination caused a higher increase (∼45%). Similarly, the magnitude of improvement in weight gain and energy efficiency by the addition of lysine or phosphorus (∼1g/d and 2.7g/MJ, respectively) was much lower than that of the combination (∼4g/d and 8.7g/MJ). In the phosphorus-containing groups, plasma urea nitrogen was significantly reduced and this was associated with higher body protein (%) and hepatic fat (%); whereas plasma albumin was significantly increased in the lysine-containing groups.

CONCLUSION

When using gluten protein, concomitant lysine and phosphorus availability is required to support growth measures, although phosphorus seems to have an independent effect on protein metabolism. Thus, human interventions should consider the improvement of the amino acid profile and phosphorus availability.

Perspective: The Potential Role of Essential Amino Acids and the Mechanistic Target of Rapamycin Complex 1 (mTORC1) Pathway in the Pathogenesis of Child Stunting

Stunting is the best summary measure of chronic malnutrition in children. Approximately one-quarter of children under age 5 worldwide are stunted. Lipid-based or micronutrient supplementation has little to no impact in reducing stunting, which suggests that other critical dietary nutrients are missing. A dietary pattern of poor-quality protein is associated with stunting. Stunted children have significantly lower circulating essential amino acids than do nonstunted children. Inadequate dietary intakes of essential amino acids could adversely affect growth, because amino acids are required for synthesis of proteins. The master growth regulation pathway, the mechanistic target of rapamycin complex 1 (mTORC1) pathway, is exquisitely sensitive to amino acid availability. mTORC1 integrates cues such as nutrients, growth factors, oxygen, and energy to regulate growth of bone, skeletal muscle, nervous system, gastrointestinal tract, hematopoietic cells, immune effector cells, organ size, and whole-body energy balance. mTORC1 represses protein and lipid synthesis and cell and organismal growth when amino acids are deficient. Over the past 4 decades, the main paradigm for child nutrition in developing countries has been micronutrient malnutrition, with relatively less attention paid to protein. In this Perspective, we present the view that essential amino acids and the mTORC1 pathway play a key role in child growth. The current assumption that total dietary protein intake is adequate for growth among most children in developing countries needs re-evaluation.

Severe dietary lysine restriction affects growth and body composition and hepatic gene expression for nitrogen metabolism in growing rats

Dietary lysine restriction may differentially affect body growth and lipid and nitrogen metabolism, depending on the degree of lysine restriction. This study was conducted to examine the effect of dietary lysine restriction on growth and lipid and nitrogen metabolism with two different degree of lysine restriction. Isocaloric amino acid-defined diets containing 1.4% lysine (adequate), 0.70% lysine (50% moderate lysine restriction) and 0.35% lysine (75% severe lysine restriction) were fed from the age of 52 to 77 days for 25 days in male Sprague-Dawley rats. The 75% severe lysine restriction increased (p < 0.05) food intake, but retarded (p < 0.05) growth, increased (p < 0.05) liver and muscle lipid contents and abdominal fat accumulation, increased (p < 0.05) blood urea nitrogen levels and mRNA levels of the serine-synthesizing 3-phosphoglycerate dehydrogenase gene, but decreased (p < 0.05) urea cycle arginase gene mRNA levels. In contrast, the 50% lysine restriction did not significantly (p > 0.05) affect body growth and lipid and nitrogen metabolism. Our results demonstrate that severe 75% lysine restriction has detrimental effects on body growth and deregulate lipid and nitrogen metabolism.

Nitrogen balance during compensatory growth when changing the levels of dietary lysine from deficiency to sufficiency in growing pigs

Two experiments were conducted to elucidate the nitrogen (N) balance of pigs exhibiting compensatory growth when changing the dietary lysine levels from deficiency to sufficiency. Experiment 1 elucidated whether pigs exhibited compensatory growth with dietary lysine sufficiency. Twenty 6-week-old males were assigned to one of two treatments: control and LC (lysine and control). Control pigs were fed a control diet throughout the 24-day experimental period, whereas LC pigs were fed a low lysine diet until day 21 of the experiment, followed by the control diet until the end of experiment. The dietary lysine sufficiency treatment induced an 80% increase in the growth rate of LC pigs (P < 0.05). Experiment 2 focused on the N balance of pigs that exhibited compensatory growth with dietary lysine sufficiency. Eighteen 6-week-old males were assigned to one of three treatments: control, LC, and LL (low lysine). LL pigs were fed a low lysine diet throughout the 24-day experimental period. Pigs that exhibited compensatory growth with dietary lysine sufficiency tended to retain a higher amount of N than control pigs (P = 0.10). These finding suggest that the compensatory growth induced in pigs by dietary lysine sufficiency was partly attributable to a higher level of N retention.