Dietary arginine supplementation increases mTOR signaling activity in skeletal muscle of neonatal pigs

Molecular cloning, characterization and expression analysis of Frizzled 6 in the small intestine of pigs (Sus scrofa)

Frizzled 6 (FZD6) encodes an integral membrane protein that functions in multiple signal transduction pathways, for example, as a receptor in Wnt/planar cell polarity (PCP) signaling pathway for polarized cell migration and organ morphogenesis. Mutations in FZD6 have been identified in a variety of tumors. In this study, the full-length cDNA of Sus scrofa FZD6 (Sfz6) was cloned and characterized. Nucleotide sequence analysis demonstrates that the Sfz6 gene encodes the 712 amino-acid (aa) protein with seven transmembrane domain. Tissue distribution analysis showed that Sfz6 mRNA is ubiquitously expressed in various tissues, being highest in kidney, moderate in jejunum, ileum, colon, liver, and spleen. However, FZD6 protein is highly expressed in the heart and there was no significant difference in other tissues. The relative abundance and localization of FZD6 protein in jejunum along the crypt-villus axis was determined by Western blot and immunohistochemical localization. The results show that in the jejunum, FZD6 protein is highly expressed in the villus and less in the crypt cells. Cellular proliferation and viability assays indicate that knockdown of FZD6 with small interfering RNAs (siRNA) significantly reduced the cell viability of the intestinal porcine enterocyte cells (IPEC-J2). Furthermore, qPCR and Western blot analysis revealed that expressions of ras-related C3 botulinum toxin substrate 1 (Rac1); ras homolog gene family member A (RhoA) and c-Jun N-terminal kinase 1 (JNK1), some components of PCP signaling pathway were upregulated (P < 0.05) by knockdown of FZD6 in IPEC-J2 cells. In conclusion, these results showed that FZD6 abundance in the villus was higher than that in crypt cells and knockdown of FZD6 induces PCP signal pathway components expression in IPEC-J2 cells. Our findings provide the foundation for further investigation into porcine FZD6 gene.

Intravenous maternal -arginine administration to twin-bearing ewes, during late pregnancy, is associated with increased fetal muscle mTOR abundance and postnatal growth in twin female lambs

The aims of this study were to determine whether parenteral Arg administered to well-fed twin-bearing ewes from 100 to 140 d of pregnancy influences fetal skeletal muscle growth, the abundance and activation of mechanistic target of rapamycin (mTOR) protein, and postnatal muscle growth of the offspring. Ewes fed 100% of NRC-recommended nutrient requirements for twin-bearing ewes were administered an intravenous bolus of either 345 μmol Arg HCl/kg BW or saline solution (Control) 3 times per day. At 140 d of pregnancy (P140), a group of 11 Control and 9 Arg-treated ewes were euthanized and hind leg muscles and longissimus dorsi (LD) were excised and weighed. A sample of LD was snap frozen in liquid nitrogen for later analysis of free AA (FAA) concentration, mTOR abundance and phosphorylation, and biochemical indices (DNA, RNA, and protein content). For the remaining 25 ewes (Arg, = 13, and Control, = 12), Arg administration was continued until the initiation of parturition and ewes were allowed to lamb. Lambs were weaned at postnatal Day 82 and grazed on pasture until postnatal day 153 (PN153), when a subset of 20 lambs ( = 10 per group) was euthanized. At P140, only the psoas major was heavier in the Arg-administered group compared with the Control group. Female lambs from ewes supplemented with Arg (Arg-F) had increased abundance of total mTOR, RNA concentration, and RNA:DNA ratio in LD compared with female lambs from Control ewes (Con-F), whereas males did not differ. At PN153, Arg-F were heavier than Con-F and had heavier LD and plantaris and a trend for heavier psoas major muscles compared with Con-F. In contrast, BW and individual muscle weights did not differ in male lambs. Lambs from Arg-treated ewes had heavier semimembranosus and tended to have heavier biceps femoris compared with Control lambs. The RNA concentration in LD was greater in Arg-F compared with Con-F, and DNA concentration was greater in the Arg group compared with the Control group. In conclusion, Arg administration to the ewe during gestation increases female lamb weight and muscle weight after birth and these changes are associated with altered mTOR protein abundance and have potential implications for sheep production.

Fetal and neonatal programming of postnatal growth and feed efficiency in swine

Maternal undernutrition or overnutrition during pregnancy alters organ structure, impairs prenatal and neonatal growth and development, and reduces feed efficiency for lean tissue gains in pigs. These adverse effects may be carried over to the next generation or beyond. This phenomenon of the transgenerational impacts is known as fetal programming, which is mediated by stable and heritable alterations of gene expression through covalent modifications of DNA and histones without changes in DNA sequences (namely, epigenetics). The mechanisms responsible for the epigenetic regulation of protein expression and functions include chromatin remodeling; DNA methylation (occurring at the 5´-position of cytosine residues within CpG dinucleotides); and histone modifications (acetylation, methylation, phosphorylation, and ubiquitination). Like maternal malnutrition, undernutrition during the neonatal period also reduces growth performance and feed efficiency (weight gain:feed intake; also known as weight-gain efficiency) in postweaning pigs by 5-10%, thereby increasing the days necessary to reach the market body-weight. Supplementing functional amino acids (e.g., arginine and glutamine) and vitamins (e.g., folate) play a key role in activating the mammalian target of rapamycin signaling and regulating the provision of methyl donors for DNA and protein methylation. Therefore, these nutrients are beneficial for the dietary treatment of metabolic disorders in offspring with intrauterine growth restriction or neonatal malnutrition. The mechanism-based strategies hold great promise for the improvement of the efficiency of pork production and the sustainability of the global swine industry.

A Systems Biology Approach Using Transcriptomic Data Reveals Genes and Pathways in Porcine Skeletal Muscle Affected by Dietary Lysine

Nine crossbred finishing barrows (body weight 94.4 ± 6.7 kg) randomly assigned to three dietary treatments were used to investigate the effects of dietary lysine on muscle growth related metabolic and signaling pathways. Muscle samples were collected from the longissimus dorsi of individual pigs after feeding the lysine-deficient (4.30 g/kg), lysine-adequate (7.10 g/kg), or lysine-excess (9.80 g/kg) diet for five weeks, and the total RNA was extracted afterwards. Affymetrix Porcine Gene 1.0 ST Array was used to quantify the expression levels of 19,211 genes. Statistical ANOVA analysis of the microarray data showed that 674 transcripts were differentially expressed (at p ≤ 0.05 level); 60 out of 131 transcripts (at p ≤ 0.01 level) were annotated in the NetAffx database. Ingenuity pathway analysis showed that dietary lysine deficiency may lead to: (1) increased muscle protein degradation via the ubiquitination pathway as indicated by the up-regulated DNAJA1, HSP90AB1 and UBE2B mRNA; (2) reduced muscle protein synthesis via the up-regulated RND3 and ZIC1 mRNA; (3) increased serine and glycine synthesis via the up-regulated PHGDH and PSPH mRNA; and (4) increased lipid accumulation via the up-regulated ME1, SCD, and CIDEC mRNA. Dietary lysine excess may lead to: (1) decreased muscle protein degradation via the down-regulated DNAJA1, HSP90AA1, HSPH1, and UBE2D3 mRNA; and (2) reduced lipid biosynthesis via the down-regulated CFD and ME1 mRNA. Collectively, dietary lysine may function as a signaling molecule to regulate protein turnover and lipid metabolism in the skeletal muscle of finishing pigs.

Neonatal Citrulline Supplementation and Later Exposure to a High Fructose Diet in Rats Born with a Low Birth Weight: A Preliminary Report

A low birth weight (LBW) leads to a higher risk of metabolic syndrome in adulthood. Literature suggests that citrulline supplementation in adulthood prevents the effect of a high fructose diet on energy metabolism. Whether neonatal citrulline supplementation would alter early growth or energy metabolism in the long-term in rats with LBW is unknown. LBW pups born from dams fed a low (4%) protein diet, were nursed by normally-fed dams and received isonitrogenous supplements of either l-citrulline or l-alanine by gavage from the sixth day of life until weaning, and were subsequently exposed to 10%-fructose in drinking water from weaning to 90 days of age. The oral glucose tolerance was tested (OGTT) at 70 days of age, and rats were sacrificed at 90 days of age. Pre-weaning citrulline supplementation failed to alter the growth trajectory, OGTT, plasma triglycerides, or fat mass accretion in adulthood; yet, it was associated with increased liver triglycerides, decreased liver total cholesterol, and a distinct liver lipidomic profile that may result in a predisposition to liver disease. We conclude that pre-weaning supplementation with citrulline does not impact early growth, but might impact liver fat metabolism in adulthood upon exposure to a high fructose diet.

Non-essential and branched-chain amino acids differentially regulate insulin-like growth factor binding protein-1 production and phosphorylation in HepG2 cells

Deprivation of branched-chain amino acids (BCAAs) induces insulin-like growth factor binding protein-1 (IGFBP-1) production in HepG2 cells, while the role of non-essential amino acids (NEAAs) remains unknown. We investigated changes in IGFBP-1 production and phosphorylation induced by NEAAs and also examined its significance on IGF-I activity in HepG2 cells. We demonstrated that decreased BCAAs and increased NEAAs stimulated phosphorylated IGFBP-1 secretion. We also revealed that decreased BCAA-to-NEAA ratios enhanced phosphorylated IGFBP-1 secretion, while changes in the total amount of amino acids (AAs) had no effect. Phosphorylation of IGF-I receptor β-subunits mediated by exogenous IGF-I in HepG2 cells was inhibited by decreased BCAAs, increased NEAAs, and decreased BCAA-to-NEAA ratios, while the total amount of AAs had no effect. In addition to BCAAs, NEAAs are also responsible for the regulation of IGFBP-1 secretion and phosphorylation in HepG2 cells. Moreover, the balance of BCAAs and NEAAs regulated IGFBP-1 secretion and phosphorylation.

Low-level arginine supplementation (0.1%) of wheat-based diets in pregnancy increases the total and live-born litter sizes in gilts

The present study was conducted to test the effects of l-arginine supplementation of wheat-based diets on the pregnancy outcome of gilts. Pregnant gilts (Yorkshire × Landrace, n = 113) were assigned randomly into two groups representing dietary supplementation with 0.1% l-arginine as l-arginine-HCl or 0.17% l-alanine (isonitrogenous control) between Days 30 and 110 of pregnancy. Blood samples were obtained from the ear vein on Days 30, 70 and 90 of pregnancy. Compared with the control, arginine supplementation increased the total number of piglets born by 1.10 per litter and the number of live-born piglets by 1.10 per litter (P < 0.05). Plasma concentration of spermine was higher in gilts fed arginine diets than in those fed control diets at Day 90 of pregnancy (P < 0.05). Dietary arginine supplementation increased plasma concentration of IGF-I of gilts at Day 90 of pregnancy (P < 0.01) and plasma concentrations of arginine, proline and ornithine at Days 70 and 90 of pregnancy (P < 0.05). These results indicated that low-level supplementation (0.1%) of l-arginine–HCl of wheat-based diets beneficially enhances the reproductive performance of gilts and is feasible for use in commercial production.

Changes in the metabolome of rats after exposure to arginine and N-carbamylglutamate in combination with diquat, a compound that causes oxidative stress, assessed by 1H NMR spectroscopy

Numerous factors can induce oxidative stress in animal production and lead to growth retardation, disease, and even death. Arginine and N-carbamylglutamate can alleviate the effects of oxidative stress. However, the systematic changes in metabolic biochemistry linked to oxidative stress and arginine and N-carbamylglutamate treatment remain largely unknown. This study aims to examine the effects of arginine and N-carbamylglutamate on rat metabolism under oxidative stress. Thirty rats were randomly divided into three dietary groups (n = 10 each). The rats were fed a basal diet supplemented with 0 (control), 1% arginine, or 0.1% N-carbamylglutamate for 30 days. On day 28, the rats in each treatment were intraperitoneally injected with diquat at 12 mg per kg body weight or sterile solution. Urine and plasma samples were analyzed by metabolomics. Compared with the diquat group, the arginine + diquat group had significantly lower levels of acetamide, alanine, lysine, pyruvate, tyrosine, α-glucose, and β-glucose in plasma; N-carbamylglutamate + diquat had higher levels of 3-hydroxybutyrate, 3-methylhistidine, acetone, allantoin, asparagine, citrate, phenylalanine, trimethylamine-N-oxide, and tyrosine, and lower levels of low density lipoprotein, lipid, lysine, threonine, unsaturated lipid, urea, and very low density lipoprotein (P < 0.05) in plasma. Compared with the diquat group, the arginine + diquat group had significantly higher levels of citrate, creatinine, homogentisate, and α-ketoglutarate while lower levels of acetamide, citrulline, ethanol, glycine, isobutyrate, lactate, malonate, methymalonate, N-acetylglutamate, N-methylnicotinamide, propionate, and β-glucose (P < 0.05) in urine. Compared with the diquat group, the N-carbamylglutamate + diquat group had significantly higher levels of allantoin, citrate, homogentisate, phenylacetylglycine, α-ketoglutarate, and β-glucose while lower levels of acetamide, acetate, acetone, benzoate, citrulline, ethanol, hippurate, lactate, N-acetylglutamate, nicotinamide, ornithine, and trigonelline (P < 0.05) in urine. Overall, these results suggest that arginine and N-carbamylglutamate can alter the metabolome associated with energy metabolism, amino acid metabolism, and gut microbiota metabolism under oxidative stress.

Recent Advances in Understanding Amino Acid Sensing Mechanisms that Regulate mTORC1

The mammalian target of rapamycin (mTOR) is the central regulator of mammalian cell growth, and is essential for the formation of two structurally and functionally distinct complexes: mTORC1 and mTORC2. mTORC1 can sense multiple cues such as nutrients, energy status, growth factors and hormones to control cell growth and proliferation, angiogenesis, autophagy, and metabolism. As one of the key environmental stimuli, amino acids (AAs), especially leucine, glutamine and arginine, play a crucial role in mTORC1 activation, but where and how AAs are sensed and signal to mTORC1 are not fully understood. Classically, AAs activate mTORC1 by Rag GTPases which recruit mTORC1 to lysosomes, where AA signaling initiates. Plasma membrane transceptor L amino acid transporter 1 (LAT1)-4F2hc has dual transporter-receptor function that can sense extracellular AA availability upstream of mTORC1. The lysosomal AA sensors (PAT1 and SLC38A9) and cytoplasmic AA sensors (LRS, Sestrin2 and CASTOR1) also participate in regulating mTORC1 activation. Importantly, AAs can be sensed by plasma membrane receptors, like G protein-coupled receptor (GPCR) T1R1/T1R3, and regulate mTORC1 without being transported into the cells. Furthermore, AA-dependent mTORC1 activation also initiates within Golgi, which is regulated by Golgi-localized AA transporter PAT4. This review provides an overview of the research progress of the AA sensing mechanisms that regulate mTORC1 activity.

Structural insight into the arginine-binding specificity of CASTOR1 in amino acid-dependent mTORC1 signaling

The mechanistic Target Of Rapamycin Complex 1 (mTORC1) is central to the cellular response to changes in nutrient signals such as amino acids. CASTOR1 is shown to be an arginine sensor, which plays an important role in the activation of the mTORC1 pathway. In the deficiency of arginine, CASTOR1 interacts with GATOR2, which together with GATOR1 and Rag GTPases controls the relocalization of mTORC1 to lysosomes. The binding of arginine to CASTOR1 disrupts its association with GATOR2 and hence activates the mTORC1 signaling. Here, we report the crystal structure of CASTOR1 in complex with arginine at 2.5 Å resolution. CASTOR1 comprises of four tandem ACT domains with an architecture resembling the C-terminal allosteric domains of aspartate kinases. ACT1 and ACT3 adopt the typical βαββαβ topology and function in dimerization via the conserved residues from helices α1 of ACT1 and α5 of ACT3; whereas ACT 2 and ACT4, both comprising of two non-sequential regions, assume the unusual ββαββα topology and contribute an arginine-binding pocket at the interface. The bound arginine makes a number of hydrogen-bonding interactions and extensive hydrophobic contacts with the surrounding residues of the binding pocket. The functional roles of the key residues are validated by mutagenesis and biochemical assays. Our structural and functional data together reveal the molecular basis for the arginine-binding specificity of CASTOR1 in the arginine-dependent activation of the mTORC1 signaling.

Targeting innate immunity for neurodegenerative disorders of the central nervous system

Neuroinflammation is critically involved in numerous neurodegenerative diseases, and key signaling steps of innate immune activation hence represent promising therapeutic targets. This mini review series originated from the 4th Venusberg Meeting on Neuroinflammation held in Bonn, Germany, 7-9th May 2015, presenting updates on innate immunity in acute brain injury and chronic neurodegenerative disorders, such as traumatic brain injury and Alzheimer disease, on the role of astrocytes and microglia, as well as technical developments that may help elucidate neuroinflammatory mechanisms and establish clinical relevance. In this meeting report, a brief overview of physiological and pathological microglia morphology is followed by a synopsis on PGE2 receptors, insights into the role of arginine metabolism and further relevant aspects of neuroinflammation in various clinical settings, and concluded by a presentation of technical challenges and solutions when working with microglia and astrocyte cultures. Microglial ontogeny and induced pluripotent stem cell-derived microglia, advances of TREM2 signaling, and the cytokine paradox in Alzheimer's disease are further contributions to this article. Neuroinflammation is critically involved in numerous neurodegenerative diseases, and key signaling steps of innate immune activation hence represent promising therapeutic targets. This mini review series originated from the 4th Venusberg Meeting on Neuroinflammation held in Bonn, Germany, 7-9th May 2015, presenting updates on innate immunity in acute brain injury and chronic neurodegenerative disorders, such as traumatic brain injury and Alzheimer's disease, on the role of astrocytes and microglia, as well as technical developments that may help elucidate neuroinflammatory mechanisms and establish clinical relevance. In this meeting report, a brief overview on physiological and pathological microglia morphology is followed by a synopsis on PGE2 receptors, insights into the role of arginine metabolism and further relevant aspects of neuroinflammation in various clinical settings, and concluded by a presentation of technical challenges and solutions when working with microglia cultures. Microglial ontogeny and induced pluripotent stem cell-derived microglia, advances of TREM2 signaling, and the cytokine paradox in Alzheimer's disease are further contributions to this article.

Amino Acids Regulate mTORC1 by an Obligate Two-step Mechanism

The mechanistic target of rapamycin complex 1 (mTORC1) coordinates cell growth with its nutritional, hormonal, energy, and stress status. Amino acids are critical regulators of mTORC1 that permit other inputs to mTORC1 activity. However, the roles of individual amino acids and their interactions in mTORC1 activation are not well understood. Here we demonstrate that activation of mTORC1 by amino acids includes two discrete and separable steps: priming and activation. Sensitizing mTORC1 activation by priming amino acids is a prerequisite for subsequent stimulation of mTORC1 by activating amino acids. Priming is achieved by a group of amino acids that includes l-asparagine, l-glutamine, l-threonine, l-arginine, l-glycine, l-proline, l-serine, l-alanine, and l-glutamic acid. The group of activating amino acids is dominated by l-leucine but also includes l-methionine, l-isoleucine, and l-valine. l-Cysteine predominantly inhibits priming but not the activating step. Priming and activating steps differ in their requirements for amino acid concentration and duration of treatment. Priming and activating amino acids use mechanisms that are distinct both from each other and from growth factor signaling. Neither step requires intact tuberous sclerosis complex of proteins to activate mTORC1. Concerted action of priming and activating amino acids is required to localize mTORC1 to lysosomes and achieve its activation.

Arginine: New Insights into Growth Performance and Urinary Metabolomic Profiles of Rats

Arginine regulates growth performance, nutrient metabolism and health effects, but the underlying mechanism remains unknown. This study aims to investigate the effect of dietary arginine supplementation on rat growth performance and urinary metabolome through ¹H-NMR spectroscopy. Twenty rats were randomly assigned to two groups supplemented with 0% or 1.0% l-arginine for 4 weeks. Urine samples were analyzed through NMR-based metabolomics. Arginine supplementation significantly increased the urine levels of 4-aminohippurate, acetate, creatine, creatinine, ethanolamine, formate, hippurate, homogentisate, indoxyl sulfate, and phenylacetyglycine. Conversely, arginine decreased the urine levels of acetamide, β-glucose, cirtulline, ethanol, glycine, isobutyrate, lactate, malonate, methymalonate, N-acetylglutamate, N-methylnicotinamide, and propionate. Results suggested that arginine can alter common systemic metabolic processes, including energy metabolism, amino acid metabolism, and gut microbiota metabolism. Moreover, the results also imply a possible physiological role of the metabolism in mediating the arginine supplementation-supported growth of rats.

Mechanism of arginine sensing by CASTOR1 upstream of mTORC1

The mechanistic Target of Rapamycin Complex 1 (mTORC1) is a major regulator of eukaryotic growth that coordinates anabolic and catabolic cellular processes with inputs such as growth factors and nutrients, including amino acids. In mammals arginine is particularly important, promoting diverse physiological effects such as immune cell activation, insulin secretion, and muscle growth, largely mediated through activation of mTORC1 (refs 4, 5, 6, 7). Arginine activates mTORC1 upstream of the Rag family of GTPases, through either the lysosomal amino acid transporter SLC38A9 or the GATOR2-interacting Cellular Arginine Sensor for mTORC1 (CASTOR1). However, the mechanism by which the mTORC1 pathway detects and transmits this arginine signal has been elusive. Here, we present the 1.8 Å crystal structure of arginine-bound CASTOR1. Homodimeric CASTOR1 binds arginine at the interface of two Aspartate kinase, Chorismate mutase, TyrA (ACT) domains, enabling allosteric control of the adjacent GATOR2-binding site to trigger dissociation from GATOR2 and downstream activation of mTORC1. Our data reveal that CASTOR1 shares substantial structural homology with the lysine-binding regulatory domain of prokaryotic aspartate kinases, suggesting that the mTORC1 pathway exploited an ancient, amino-acid-dependent allosteric mechanism to acquire arginine sensitivity. Together, these results establish a structural basis for arginine sensing by the mTORC1 pathway and provide insights into the evolution of a mammalian nutrient sensor.

Dietary Supplementation with α-Ketoglutarate Activates mTOR Signaling and Enhances Energy Status in Skeletal Muscle of Lipopolysaccharide-Challenged Piglets

BACKGROUND

Skeletal muscle undergoes rapid loss in response to inflammation. α-Ketoglutarate (AKG) has been reported to enhance muscle growth in piglets, but the underlying mechanisms are largely unknown.

OBJECTIVES

This study tested the hypothesis that dietary AKG supplementation activates mechanistic target of rapamycin (mTOR) signaling and improves skeletal muscle energy metabolism in lipopolysaccharide (LPS)-challenged piglets.

METHODS

Forty-eight male piglets (Duroc × Landrace × Yorkshire) were weaned at 21 d of age to a corn- and soybean meal-based diet. After a 3-d period of adaptation, piglets with a mean weight of 7.21 kg were randomly assigned to control, LPS (intraperitoneal administration of 80 μg LPS/kg body weight on days 10, 12, 14, and 16), or LPS plus 1% dietary AKG (LPS+AKG) groups. On day 16, blood samples were collected from 8 piglets/group 3 h after LPS administration. On day 17, piglets were killed to obtain gastrocnemius muscle from 8 piglets/group for biochemical analysis.

RESULTS

Compared with the control group, LPS administration increased (P < 0.05) plasma concentrations of globulin (by 14%) and tumor necrosis factor α (by 59%) and the intramuscular ratio of AMP to ATP (by 93%) and abundance of phosphorylated acetyl-coenzyme A carboxylase (ACC) β protein (by 64%). Compared with the control group, LPS administration reduced (P < 0.05) weight gain (by 15%); plasma concentrations of glutamine (by 20%), glucose (by 23%), insulin, insulin-like growth factor I, and epidermal growth factor; intramuscular concentrations of glutamine (by 27%), ATP (by 12%), ADP (by 22%), and total adenine nucleotides; and intramuscular ratios of phosphorylated mTOR to total mTOR (by 38%) and of phosphorylated 70-kDa ribosomal protein S6 kinase (p70S6K) to total p70S6K (by 39%). These adverse effects of LPS were ameliorated (P < 0.05) by AKG supplementation.

CONCLUSIONS

Dietary AKG supplementation activated mTOR signaling, inhibited ACC-β, and improved energy status in skeletal muscle of LPS-challenged piglets. These results provide a biochemical basis for the use of AKG to enhance piglet growth under inflammatory or practical postweaning conditions.

N-carbamylglutamate and L-arginine improved maternal and placental development in underfed ewes

The objectives of this study were to determine how dietary supplementation ofN-carbamylglutamate (NCG) and rumen-protected L-arginine (RP-Arg) in nutrient-restricted pregnant Hu sheep would affect (1) maternal endocrine status; (2) maternal, fetal, and placental antioxidation capability; and (3) placental development. From day 35 to day 110 of gestation, 32 Hu ewes carrying twin fetuses were allocated randomly into four groups: 100% of NRC-recommended nutrient requirements, 50% of NRC recommendations, 50% of NRC recommendations supplemented with 20g/day RP-Arg, and 50% of NRC recommendations supplemented with 5g/day NCG product. The results showed that in maternal and fetal plasma and placentomes, the activities of total antioxidant capacity and superoxide dismutase were increased (P<0.05); however, the activity of glutathione peroxidase and the concentration of maleic dialdehyde were decreased (P<0.05) in both NCG- and RP-Arg-treated underfed ewes. The mRNA expression of vascular endothelial growth factor and Fms-like tyrosine kinase 1 was increased (P<0.05) in 50% NRC ewes than in 100% NRC ewes, and had no effect (P>0.05) in both NCG- and RP-Arg-treated underfed ewes. A supplement of RP-Arg and NCG reduced (P<0.05) the concentrations of progesterone, cortisol, and estradiol-17β; had no effect on T4/T3; and improved (P<0.05) the concentrations of leptin, insulin-like growth factor 1, tri-iodothyronine (T3), and thyroxine (T4) in serum from underfed ewes. These results indicate that dietary supplementation of NCG and RP-Arg in underfed ewes could influence maternal endocrine status, improve the maternal–fetal–placental antioxidation capability, and promote fetal and placental development during early-to-late gestation.

Pulsatile delivery of a leucine supplement during long-term continuous enteral feeding enhances lean growth in term neonatal pigs

Neonatal pigs are used as a model to study and optimize the clinical treatment of infants who are unable to maintain oral feeding. Using this model, we have shown previously that pulsatile administration of leucine during continuous feeding over 24 h via orogastric tube enhanced protein synthesis in skeletal muscle compared with continuous feeding alone. To determine the long-term effects of leucine pulses, neonatal piglets (n = 11-12/group) were continuously fed formula via orogastric tube for 21 days, with an additional parenteral infusion of either leucine (CON + LEU; 800 μmol·kg^-1·h^-1) or alanine (CON + ALA) for 1 h every 4 h. The results show that body and muscle weights and lean gain were ∼25% greater, and fat gain was 48% lower in CON + LEU than CON + ALA; weights of other tissues were unaffected by treatment. Fractional protein synthesis rates in longissimus dorsi, gastrocnemius, and soleus muscles were ∼30% higher in CON + LEU compared with CON + ALA and were associated with decreased Deptor abundance and increased mTORC1, mTORC2, 4E-BP1, and S6K1 phosphorylation, SNAT2 abundance, and association of eIF4E with eIF4G and RagC with mTOR. There were no treatment effects on PKB, eIF2α, eEF2, or PRAS40 phosphorylation, Rheb, SLC38A9, v-ATPase, LAMTOR1, LAMTOR2, RagA, RagC, and LAT1 abundance, the proportion of polysomes to nonpolysomes, or the proportion of mRNAs encoding rpS4 or rpS8 associated with polysomes. Our results demonstrate that pulsatile delivery of a leucine supplement during 21 days of continuous enteral feeding enhances lean growth by stimulating the mTORC1-dependent translation initiation pathway, leading to protein synthesis in skeletal muscle of neonates.

The CASTOR Proteins Are Arginine Sensors for the mTORC1 Pathway

Amino acids signal to the mTOR complex I (mTORC1) growth pathway through the Rag GTPases. Multiple distinct complexes regulate the Rags, including GATOR1, a GTPase activating protein (GAP), and GATOR2, a positive regulator of unknown molecular function. Arginine stimulation of cells activates mTORC1, but how it is sensed is not well understood. Recently, SLC38A9 was identified as a putative lysosomal arginine sensor required for arginine to activate mTORC1 but how arginine deprivation represses mTORC1 is unknown. Here, we show that CASTOR1, a previously uncharacterized protein, interacts with GATOR2 and is required for arginine deprivation to inhibit mTORC1. CASTOR1 homodimerizes and can also heterodimerize with the related protein, CASTOR2. Arginine disrupts the CASTOR1-GATOR2 complex by binding to CASTOR1 with a dissociation constant of ~30 μM, and its arginine-binding capacity is required for arginine to activate mTORC1 in cells. Collectively, these results establish CASTOR1 as an arginine sensor for the mTORC1 pathway.

Endogenous Synthesis of Amino Acids Limits Growth, Lactation, and Reproduction in Animals

Amino acids (AAs) are building blocks of protein. Eight AAs (Ala, Asn, Asp, Glu, Gln, Gly, Pro, and Ser) are formed by all animals, whereas de novo synthesis of Arg occurs in a species-specific manner in most mammals (e.g., humans, pigs, and rats). Synthesizable AAs were traditionally classified as nutritionally nonessential for animals, because they were thought to be formed in sufficient amounts. However, this assumption is not supported by evidence showing that 1) rats grow slowly when their diets do not contain Arg, Glu, or Gln despite adequate provision of all other proteinogenous AAs; 2) pigs cannot achieve maximum growth, lactation, or reproduction performance when fed corn- and soybean meal-based diets meeting National Research Council-recommended requirements of protein and AAs without supplemental Arg, Glu, Gln, Gly, or Pro; 3) chickens exhibit increases in lean tissue gain and feed efficiency when their diets are supplemented with Glu, Gln, Gly, and Pro; 4) lactating cows cannot obtain maximum milk protein production without a postruminal supply of Gln or Pro; 5) fish cannot achieve maximum growth when diets do not contain Gln or Pro; and 6) men fail to sustain spermatogenesis when fed an Arg-deficient diet. Quantitative analysis of nitrogen metabolism showed that AA synthesis in animals is constrained by both precursor availability and enzyme activity. Taken together, these findings support the conclusion that the endogenous synthesis of AAs limits growth, lactation, and reproduction in animals. This new knowledge can guide the optimization of human nutrition for improving health and well-being.

Conserved regulators of Rag GTPases orchestrate amino acid-dependent TORC1 signaling

The highly conserved target of rapamycin complex 1 (TORC1) is the central component of a signaling network that couples a vast range of internal and external stimuli to cell growth, proliferation and metabolism. TORC1 deregulation is associated with a number of human pathologies, including many cancers and metabolic disorders, underscoring its importance in cellular and organismal growth control. The activity of TORC1 is modulated by multiple inputs; however, the presence of amino acids is a stimulus that is essential for its activation. Amino acid sufficiency is communicated to TORC1 via the highly conserved family of Rag GTPases, which assemble as heterodimeric complexes on lysosomal/vacuolar membranes and are regulated by their guanine nucleotide loading status. Studies in yeast, fly and mammalian model systems have revealed a multitude of conserved Rag GTPase modulators, which have greatly expanded our understanding of amino acid sensing by TORC1. Here we review the major known modulators of the Rag GTPases, focusing on recent mechanistic insights that highlight the evolutionary conservation and divergence of amino acid signaling to TORC1.

Molecular cloning, characterization and expression of the energy homeostasis-associated gene in piglet

The energy homeostasis-associated (Enho) gene encodes a secreted protein, adropin, which regulates the expression of hepatic lipogenic genes and adipose tissue peroxisome proliferator-activated receptor γ, a major regulator of lipogenesis. In the present study, the porcine (Sus scrofa) homologue of the Enho gene, which was named pEnho, was amplified by reverse transcriptase polymerase chain reaction (RT-PCR) using oligonucleotide primers derived from in silico sequences. The gene sequence was submitted into the GenBank of NCBI, and the access number is GQ414763. The pEnho encodes a protein of 76 amino acids which shows 75% similarity to Homo sapiens adropin. The expression profile of pEnho in tissues (liver, muscle, anterior jejunum, posterior jejunum, and ileum) was determined by quantitative real-time RT-PCR. pEnho was localized on porcine chromosome 10 and no introns were found. In conclusion, pEnho was cloned and analysed with the aim of increasing knowledge about glucose and lipid metabolism in piglets and helping to promote the health and growth of piglets through adropin regulation.

Supplementation of pre-weaning diet with l-arginine has carry-over effect to improve intestinal development in young piglets

This study tested the hypothesis that pre-weaning supplemental arginine may have a carry-over effect on intestinal growth and development of piglets immediately after weaning. Fifty-four [Duroc × (Landrace × Yorkshire)] piglets were fed a milk replacer diet supplemented with 0 (control), 4, or 8 g kg−1 of l-arginine from d 4 to 21 of age (6 replicate pens of 3 piglets per group). Piglets were then weaned to a common corn–soybean meal diet and fed for another 21 d. On day 42, 6 pigs per treatment were randomly selected for blood and tissue sampling. Arginine supplementation improved body weight of the piglets on d 42, average daily gain during d 22–31 (P < 0.05). Supplementation of 8 g kg−1 arginine decreased feed:gain (F:G) ratio in piglets during d 22–31 (P = 0.010). Compared with controls, 8 g kg−1 arginine improved villous height in duodenum, jejunum, and ileum; villous area in duodenum and jejunum; relative intestine weight; and plasma contents of insulin at d 42 (P < 0.05). Arginine supplementation increased mucosal protein content in all 3 segments of the small intestine (P < 0.05). These novel results clearly demonstrate a carry-over effect of pre-weaning supplementation with arginine on enhanced intestinal growth and development in the early post-weaning period.

L-Citrulline Supplementation Enhances Fetal Growth and Protein Synthesis in Rats with Intrauterine Growth Restriction

BACKGROUND

Intrauterine growth restriction (IUGR) results from either maternal undernutrition or impaired placental blood flow, exposing offspring to increased perinatal mortality and a higher risk of metabolic syndrome and cardiovascular disease during adulthood. l-Citrulline is a precursor of l-arginine and nitric oxide (NO), which regulates placental blood flow. Moreover, l-citrulline stimulates protein synthesis in other models of undernutrition.

OBJECTIVE

The aim of the study was to determine whether l-citrulline supplementation would enhance fetal growth in a model of IUGR induced by maternal dietary protein restriction.

METHODS

Pregnant rats were fed either a control (20% protein) or a low-protein (LP; 4% protein) diet. LP dams were randomly allocated to drink tap water either as such or supplemented with l-citrulline (2 g · kg(-1) · d(-1)), an isonitrogenous amount of l-arginine, or nonessential l-amino acids (NEAAs). On day 21 of gestation, dams received a 2-h infusion of l-[1-(13)C]-valine until fetuses were extracted by cesarean delivery. Isotope enrichments were measured in free amino acids and fetal muscle, liver, and placenta protein by GC-mass spectrometry.

RESULTS

Fetal weight was ∼29% lower in the LP group (3.82 ± 0.06 g) than in the control group (5.41 ± 0.10 g) (P < 0.001). Regardless of supplementation, fetal weight remained below that of control fetuses. Yet, compared with the LP group, l-citrulline and l-arginine equally increased fetal weight to 4.15 ± 0.08 g (P < 0.05) and 4.13 ± 0.1 g (P < 0.05 compared with LP), respectively, whereas NEAA did not (4.05 ± 0.05 g; P = 0.07). Fetal muscle protein fractional synthesis rate was 35% lower in the LP fetuses (41% ± 11%/d) than in the control (61% ± 13%/d) fetuses (P < 0.001) and was normalized by l-citrulline (56% ± 4%/d; P < 0.05 compared with LP, NS compared with control) and not by other supplements. Urinary nitrite and nitrate excretion was lower in the LP group (6.4 ± 0.8 μmol/d) than in the control group (17.9 ± 1.1 μmol/d; P < 0.001) and increased in response to l-citrulline or l-arginine (12.1 ± 2.2 and 10.6 ± 0.9 μmol/d; P < 0.05), whereas they did not in the LP + NEAA group.

CONCLUSION

l-Citrulline increases fetal growth in a model of IUGR, and the effect may be mediated by enhanced fetal muscle protein synthesis and/or increased NO production.

Suppression of mTOR Signaling Pathways in Skeletal Muscle of Finishing Pigs by Increasing the Ratios of Ether Extract and Neutral Detergent Fiber at the Expense of Starch in Iso-energetic Diets

Three iso-energetic and iso-nitrogenous diets were fed to finishing pigs for 28 days to investigate the mammalian target of rapamycin (mTOR) and ubiquitin-proteasome signaling pathways of skeletal muscle by altering compositions of dietary energy sources. Diet A, diet B, and diet C contained 44.1%, 37.6%, and 30.9% starch; 5.9%, 9.5%, and 14.3% ether extract (EE); and 12.6%, 15.4%, and 17.8% neutral detergent fiber (NDF), respectively. An increase of mRNA expression of MuRF1 (1.09 ± 0.10 vs 1.00 ± 0.08) and MAFbx (1.10 ± 0.06 vs 1.00 ± 0.11) and a decrease of concentrations of plasma insulin (8.2 ± 0.8 vs 10.8 ± 1.2) and glucose (5.76 ± 0.12 vs 6.43 ± 0.33) together with mRNA expression of IRS (0.78 ± 0.19 vs 1.01 ± 0.05) and Akt (0.92 ± 0.01 vs 1.00 ± 0.05) were observed in pigs fed diet C compared with diet A. Protein levels of total and phosphorylated mTOR (0.31 ± 0.04 vs 0.48 ± 0.03 and 0.39 ± 0.01 vs 0.56 ± 0.02), 4EBP1 (0.66 ± 0.06 vs 0.90 ± 0.09 and 0.60 ± 0.12 vs 0.84 ± 0.09), and S6K1 (0.66 ± 0.01 vs 0.89 ± 0.01 and 0.48 ± 0.03 vs 0.79 ± 0.02) were decreased; however, total and phosphorylated AMPK (0.96 ± 0.06 vs 0.64 ± 0.04 and 0.97 ± 0.09 vs 0.61 ± 0.09) were increased in pigs fed diet C compared with diet A. In conclusion, diet C suppressed the mTOR pathway and accelerated the ubiquitin-proteasome pathway in skeletal muscle of finishing pigs.

Sustained Arginase 1 Expression Modulates Pathological Tau Deposits in a Mouse Model of Tauopathy

Tau accumulation remains one of the closest correlates of neuronal loss in Alzheimer's disease. In addition, tau associates with several other neurodegenerative diseases, collectively known as tauopathies, in which clinical phenotypes manifest as cognitive impairment, behavioral disturbances, and motor impairment. Polyamines act as bivalent regulators of cellular function and are involved in numerous biological processes. The regulation of the polyamines system can become dysfunctional during disease states. Arginase 1 (Arg1) and nitric oxide synthases compete for l-arginine to produce either polyamines or nitric oxide, respectively. Herein, we show that overexpression of Arg1 using adeno-associated virus (AAV) in the CNS of rTg4510 tau transgenic mice significantly reduced phospho-tau species and tangle pathology. Sustained Arg1 overexpression decreased several kinases capable of phosphorylating tau, decreased inflammation, and modulated changes in the mammalian target of rapamycin and related proteins, suggesting activation of autophagy. Arg1 overexpression also mitigated hippocampal atrophy in tau transgenic mice. Conversely, conditional deletion of Arg1 in myeloid cells resulted in increased tau accumulation relative to Arg1-sufficient mice after transduction with a recombinant AAV-tau construct. These data suggest that Arg1 and the polyamine pathway may offer novel therapeutic targets for tauopathies.

Supplemental arginine above the requirement during suckling causes obesity and insulin resistance in rats

Nutrition in early life is important in determining susceptibility to adult obesity, and arginine may promote growth acceleration in infants. We hypothesized that maternal arginine supplementation may promote growth in their pups and contribute to obesity and alteration of the metabolic system in later life. Dams and pups of Wistar rats were given a normal diet (15% protein) as a control (CN) or a normal diet with 2% arginine (ARG). Altered profiles of free amino acids in breast milk were observed in that the concentrations of threonine and glycine were lower in the ARG dams compared with the CN dams. The offspring of the CN and ARG dams were further subdivided into normal-diet (CN-CN and ARG-CN) groups and a high fat-diet groups (CN-HF and ARG-HF). In response to the high fat-diet feeding, the visceral fat deposits were significantly increased in the ARG-HF group (although not compared with the CN-HF group); no difference was observed between the CN-CN and ARG-CN groups. The blood glucose and insulin levels after glucose loading were significantly higher in the ARG-HF group compared with the CN-HF group. The results suggest that the offspring of dams supplemented with arginine during lactation acquired increased susceptibility to a high-fat diet, resulting in visceral obesity and insulin resistance. The lower supply of threonine and glycine to pups may be one of the contributing causes to the programming of lifelong obesity risk in offspring. Our findings also indicated that maternal arginine supplementation during suckling causes obesity and insulin resistance in rats.

Identification of (-)-epigallocatechin-3-gallate as a potential agent for blocking infection by grass carp reovirus

Grass carp reovirus (GCRV), the representative strain of the species Aquareovirus C, serves as a model for studying the pathogenesis of aquareoviruses. Previously, epigallocatechin gallate (EGCG) was shown to inhibit orthoreovirus infection. The aim of this study was to test its potential in blocking infection by GCRV. We show that adhesion to the CIK (Ctenopharyngodon idellus kidney) cell surface by GCRV particles is inhibited in a dose-dependent manner by EGCG, as well as by a crude extract of green tea. We also evaluated the safety of EGCG and green tea extract using CIK cells, and the results suggest that EGCG is a promising compound that may be developed as a plant-derived small molecular therapeutic agent against grass carp hemorrhagic disease caused by GCRV infection. As the ligand for the 37/67-kDa laminin receptor (LamR), EGCG's blocking effect on GCRV attachment was associated with the binding potential of GCRV particles to LamR, which was inferred from a VOPBA assay.

Signaling Pathways Related to Protein Synthesis and Amino Acid Concentration in Pig Skeletal Muscles Depend on the Dietary Protein Level, Genotype and Developmental Stages

Muscle growth is regulated by the homeostatic balance of the biosynthesis and degradation of muscle proteins. To elucidate the molecular interactions among diet, pig genotype, and physiological stage, we examined the effect of dietary protein concentration, pig genotype, and physiological stages on amino acid (AA) pools, protein deposition, and related signaling pathways in different types of skeletal muscles. The study used 48 Landrace pigs and 48 pure-bred Bama mini-pigs assigned to each of 2 dietary treatments: lower/GB (Chinese conventional diet)- or higher/NRC (National Research Council)-protein diet. Diets were fed from 5 weeks of age to respective market weights of each genotype. Samples of biceps femoris muscle (BFM, type I) and longissimus dorsi muscle (LDM, type II) were collected at nursery, growing, and finishing phases according to the physiological stage of each genotype, to determine the AA concentrations, mRNA levels for growth-related genes in muscles, and protein abundances of mechanistic target of rapamycin (mTOR) signaling pathway. Our data showed that the concentrations of most AAs in LDM and BFM of pigs increased (P<0.05) gradually with increasing age. Bama mini-pigs had generally higher (P<0.05) muscle concentrations of flavor-related AA, including Met, Phe, Tyr, Pro, and Ser, compared with Landrace pigs. The mRNA levels for myogenic determining factor, myogenin, myocyte-specific enhancer binding factor 2 A, and myostatin of Bama mini-pigs were higher (P<0.05) than those of Landrace pigs, while total and phosphorylated protein levels for protein kinase B, mTOR, and p70 ribosomal protein S6 kinases (p70S6K), and ratios of p-mTOR/mTOR, p-AKT/AKT, and p-p70S6K/p70S6K were lower (P<0.05). There was a significant pig genotype-dependent effect of dietary protein on the levels for mTOR and p70S6K. When compared with the higher protein-NRC diet, the lower protein-GB diet increased (P<0.05) the levels for mTOR and p70S6K in Bama mini-pigs, but repressed (P<0.05) the level for p70S6K in Landrace pigs. The higher protein-NRC diet increased ratio of p-mTOR/mTOR in Landrace pigs. These findings indicated that the dynamic consequences of AA profile and protein deposition in muscle tissues are the concerted effort of distinctive genotype, nutrient status, age, and muscle type. Our results provide valuable information for animal feeding strategy.

Differential expression of proteins involved in energy production along the crypt-villus axis in early-weaning pig small intestine

Weaning of piglets reflects intestinal dysfunction and atrophy and affected the physiological state of enterocytes. However, few studies have defined physiological state of enterocytes along the crypt-villus axis in early-weaning piglets. A total of 16 piglets from 8 litters were used in the experiment. One group of piglets was nursed by sows until age 21 days, and another group was weaned at age 14 days and then fed creep feed instead of breast milk for 7 days. Piglets were killed at 21 days, and the jejunum segments were dissected. After sequential isolation of jejunum epithelial cells along the crypt-villus axis, their proteins were analyzed through the isobaric tags for relative and absolute quantification, and proteins involved in the mammalian target of rapamycin signaling pathway and proliferating cell nuclear antigen abundances in jejunal epithelial cells of weaning or suckling group were determined by Western blotting. The differential proteins in three cell fractions were identified and analyzed. The results showed that proteins involved in the tricarboxylic acid cycle, β-oxidation, and the glycolysis pathway were significantly downregulated in the upper and middle villus of the early-weaned group. However, proteins involved in glycolysis were significantly upregulated in crypt cells. In addition, Western blot analysis showed that the expression of mammalian target of rapamycin pathway-related proteins was decreased (P < 0.05) in the early-weaned group. The present results showed that early-weaning differentially affect the expression of proteins involved in energy production of enterocytes along the jejunal crypt-villus axis.

Genome-wide association study of body weight in Australian Merino sheep reveals an orthologous region on OAR6 to human and bovine genomic regions affecting height and weight

Background

Body weight (BW) is an important trait for meat production in sheep. Although over the past few years, numerous quantitative trait loci (QTL) have been detected for production traits in cattle, few QTL studies have been reported for sheep, with even fewer on meat production traits. Our objective was to perform a genome-wide association study (GWAS) with the medium-density Illumina Ovine SNP50 BeadChip to identify genomic regions and corresponding haplotypes associated with BW in Australian Merino sheep.

Methods

A total of 1781 Australian Merino sheep were genotyped using the medium-density Illumina Ovine SNP50 BeadChip. Among the 53 862 single nucleotide polymorphisms (SNPs) on this array, 48 640 were used to perform a GWAS using a linear mixed model approach. Genotypes were phased with hsphase; to estimate SNP haplotype effects, linkage disequilibrium blocks were identified in the detected QTL region.

Results

Thirty-nine SNPs were associated with BW at a Bonferroni-corrected genome-wide significance threshold of 1 %. One region on sheep (Ovis aries) chromosome 6 (OAR6) between 36.15 and 38.56 Mb, included 13 significant SNPs that were associated with BW; the most significant SNP was OAR6_41936490.1 (P = 2.37 × 10⁻¹⁶) at 37.69 Mb with an allele substitution effect of 2.12 kg, which corresponds to 0.248 phenotypic standard deviations for BW. The region that surrounds this association signal on OAR6 contains three genes: leucine aminopeptidase 3 (LAP3), which is involved in the processing of the oxytocin precursor; NCAPG non-SMC condensin I complex, subunit G (NCAPG), which is associated with foetal growth and carcass size in cattle; and ligand dependent nuclear receptor corepressor-like (LCORL), which is associated with height in humans and cattle.

Conclusions

The GWAS analysis detected 39 SNPs associated with BW in sheep and a major QTL region was identified on OAR6. In several other mammalian species, regions that are syntenic with this region have been found to be associated with body size traits, which may reflect that the underlying biological mechanisms share a common ancestry. These findings should facilitate the discovery of causative variants for BW and contribute to marker-assisted selection.

Electronic supplementary material

The online version of this article (doi:10.1186/s12711-015-0142-4) contains supplementary material, which is available to authorized users.

Co-dependence of genotype and dietary protein intake to affect expression on amino acid/peptide transporters in porcine skeletal muscle

A total of 96 barrows (48 pure-bred Bama mini-pigs representing fatty genotype, and 48 Landrace pigs representing lean genotype) were randomly assigned to either a low- or adequate-protein treatment diet. The experimental period commenced at 5 weeks of age and extended to the finishing period. After euthanasia, blood and skeletal muscle samples were collected from pigs at the nursery, growing, and finishing phases. Our results indicate that the concentrations of free AAs in the plasma and muscle decreased as the age of the pigs increased. In addition, a strain × growth phase interaction (P < 0.05) was observed for the free AA pool in the plasma and muscle. The low-protein diet upregulated (P < 0.05) the mRNA levels for T1R1/T1R3 involved in glutamate binding, but downregulated (P < 0.05) the mRNA levels for PAT1, PAT2, and ASCT2, which transport neutral AAs into muscles. Bama mini-pigs had higher (P < 0.05) mRNA levels for LAT1, SNAT2, and EAAC1, but a lower (P < 0.05) mRNA level for PepT1, compared with Landrace pigs. Collectively, our findings indicate that adequate provision of dietary protein plays an important role in regulating profiles of free AA pools and expression of key AA/peptide transporters/transceptors in a genotype- and tissue-specific manner.

Administration of Exogenous Growth Hormone Is Associated with Changes in Plasma and Intracellular Mammary Amino Acid Profiles and Abundance of the Mammary Gland Amino Acid Transporter SLC3A2 in Mid-Lactation Dairy Cows

The objectives of this study were to (1) identify changes in plasma and mammary intracellular amino acid (AA) profiles in dairy cows treated with growth hormone (GH), and (2) evaluate the expression of mammary gland genes involved in the transport of AA identified in (1). Eight non-pregnant (n = 4 per group) lactating dairy cows were treated with a single subcutaneous injection of either a slow-release formulation of commercially available GH (Lactotropin 500 mg) or physiological saline solution. Six days after treatment, cows were milked and blood collected from the jugular vein for the analysis of free AA in the plasma. Cows were euthanized and mammary tissue harvested. Treatment with GH increased milk, protein, fat and lactose yields, with no effect on dry matter intake. Plasma concentrations of lysine and group I AA decreased significantly, and arginine, methionine, tyrosine and arginine-family AA tended to decrease in GH-treated cows. Concentrations of intracellular glycine, serine and glutamate increased significantly, with a trend for decreased arginine observed in the mammary gland of GH-treated cows. A trend for increased concentrations of intracellular total AA, NEAA and arginine-family AA were observed in the mammary gland of GH-treated cows. Variance in the concentration of plasma methionine, tyrosine, valine, alanine, ornithine, BCAA, EAA was significantly different between treatments. Variance in the concentration of intracellular lysine, valine, glutamine, EAA and group II was significantly different between treatments. AA changes were associated with increased mRNA abundance of the mammary gland AA transporter SLC3A2. We propose that these changes occur to support increased milk protein and fatty acid production in the mammary gland of GH-treated cows via potential mTOR pathway signaling.

Dietary essentiality of "nutritionally non-essential amino acids" for animals and humans

Based on growth or nitrogen balance, amino acids (AA) had traditionally been classified as nutritionally essential (indispensable) or non-essential (dispensable) for animals and humans. Nutritionally essential AA (EAA) are defined as either those AA whose carbon skeletons cannot be synthesized de novo in animal cells or those that normally are insufficiently synthesized de novo by the animal organism relative to its needs for maintenance, growth, development, and health and which must be provided in the diet to meet requirements. In contrast, nutritionally non-essential AA (NEAA) are those AA which can be synthesized de novo in adequate amounts by the animal organism to meet requirements for maintenance, growth, development, and health and, therefore, need not be provided in the diet. Although EAA and NEAA had been described for over a century, there are no compelling data to substantiate the assumption that NEAA are synthesized sufficiently in animals and humans to meet the needs for maximal growth and optimal health. NEAA play important roles in regulating gene expression, cell signaling pathways, digestion and absorption of dietary nutrients, DNA and protein synthesis, proteolysis, metabolism of glucose and lipids, endocrine status, men and women fertility, acid-base balance, antioxidative responses, detoxification of xenobiotics and endogenous metabolites, neurotransmission, and immunity. Emerging evidence indicates dietary essentiality of "nutritionally non-essential amino acids" for animals and humans to achieve their full genetic potential for growth, development, reproduction, lactation, and resistance to metabolic and infectious diseases. This concept represents a new paradigm shift in protein nutrition to guide the feeding of mammals (including livestock), poultry, and fish.

Effect of dietary glutamine on growth performance, non-specific immunity, expression of cytokine genes, phosphorylation of target of rapamycin (TOR), and anti-oxidative system in spleen and head kidney of Jian carp (Cyprinus carpio var. Jian)

This study was designed to investigate the effects of dietary glutamine on the growth performance, cytokines, target of rapamycin (TOR), and antioxidant-related parameters in the spleen and head kidney of juvenile Jian carp (Cyprinus carpio var. Jian). Fish were fed the basal (control) and glutamine-supplemented (12.0 g glutamine kg(-1) diet) diets for 6 weeks. Results indicated that the dietary glutamine supplementation improved the growth performance, spleen protein content, serum complement 3 content, and lysozyme activity in fish. In the spleen, glutamine down-regulated the expression of the interleukin 1 and interleukin 10 genes, and increased the level of phosphorylation of TOR protein. In the head kidney, glutamine down-regulated the tumor necrosis factor α and interleukin 10 gene expressions, phosphorylated and total TOR protein levels, while up-regulated the transforming growth factor β2 gene expression. Furthermore, the protein carbonyl content was decreased in the spleen of fish fed glutamine-supplemented diet; conversely, the anti-hydroxyl radical capacity and glutathione content in the spleen were increased by glutamine. However, diet supplemented with glutamine did not affect the lipid peroxidation, anti-superoxide anion capacity, and antioxidant enzyme activities in the spleen. Moreover, all of these antioxidant parameters in the head kidney were not affected by glutamine. Results from the present experiment showed the importance of dietary supplementation of glutamine in benefaction of the growth performance and several components of the innate immune system, and the deferential role in cytokine gene expression, TOR kinase activity, and antioxidant status between the spleen and head kidney of juvenile Jian carp.

Safety of long-term dietary supplementation with L-arginine in rats

This study was conducted with rats to determine the safety of long-term dietary supplementation with L-arginine. Beginning at 6 weeks of age, male and female rats were fed a casein-based semi-purified diet containing 0.61 % L-arginine and received drinking water containing L-arginine-HCl (0, 1.8, or 3.6 g L-arginine/kg body-weight/day; n = 10/group). These supplemental doses of L-arginine were equivalent to 0, 286, and 573 mg L-arginine/kg body-weight/day, respectively, in humans. After a 13-week supplementation period, blood samples were obtained from rats for biochemical analyses. Supplementation with L-arginine increased plasma concentrations of arginine, ornithine, proline, homoarginine, urea, and nitric oxide metabolites without affecting those for lysine, histidine, or methylarginines, while reducing plasma concentrations of ammonia, glutamine, free fatty acids, and triglycerides. L-Arginine supplementation enhanced protein gain and reduced white-fat deposition in the body. Based on general appearance, feeding behavior, and physiological parameters, all animals showed good health during the entire experimental period; Plasma concentrations of all measured hormones (except leptin) did not differ between control and arginine-supplemented rats. L-Arginine supplementation reduced plasma levels of leptin. Additionally, L-arginine supplementation increased L-arginine:glycine amidinotransferase activity in kidneys but not in the liver or small intestine, suggesting tissue-specific regulation of enzyme expression by L-arginine. Collectively, these results indicate that dietary supplementation with L-arginine (e.g., 3.6 g/kg body-weight/day) is safe in rats for at least 91 days. This dose is equivalent to 40 g L-arginine/kg body-weight/day for a 70-kg person. Our findings help guide clinical studies to determine the safety of long-term oral administration of L-arginine to humans.

Arginine depletion by arginine deiminase does not affect whole protein metabolism or muscle fractional protein synthesis rate in mice

Due to the absolute need for arginine that certain cancer cells have, arginine depletion is a therapy in clinical trials to treat several types of cancers. Arginine is an amino acids utilized not only as a precursor for other important molecules, but also for protein synthesis. Because arginine depletion can potentially exacerbate the progressive loss of body weight, and especially lean body mass, in cancer patients we determined the effect of arginine depletion by pegylated arginine deiminase (ADI-PEG 20) on whole body protein synthesis and fractional protein synthesis rate in multiple tissues of mice. ADI-PEG 20 successfully depleted circulating arginine (<1 μmol/L), and increased citrulline concentration more than tenfold. Body weight and body composition, however, were not affected by ADI-PEG 20. Despite the depletion of arginine, whole body protein synthesis and breakdown were maintained in the ADI-PEG 20 treated mice. The fractional protein synthesis rate of muscle was also not affected by arginine depletion. Most tissues (liver, kidney, spleen, heart, lungs, stomach, small and large intestine, pancreas) were able to maintain their fractional protein synthesis rate; however, the fractional protein synthesis rate of brain, thymus and testicles was reduced due to the ADI-PEG 20 treatment. Furthermore, these results were confirmed by the incorporation of ureido [14C]citrulline, which indicate the local conversion into arginine, into protein. In conclusion, the intracellular recycling pathway of citrulline is able to provide enough arginine to maintain protein synthesis rate and prevent the loss of lean body mass and body weight.

L-arginine upregulates the gene expression of target of rapamycin signaling pathway and stimulates protein synthesis in chicken intestinal epithelial cells

L-arginine (Arg) is an indispensable amino acid in avians and is required for growth. The aim of this study was to investigate the effects of L-Arg on protein synthesis and genes expression involved in target of rapamycin (TOR) signaling pathway in chicken enterocytes. Cells were cultured for 4 days in L-Arg-free Dulbecco's modified Eagle's medium containing 10, 100, 200, 400, or 600 μM L-Arg. Cell growth, cell cycle, protein synthesis, and protein degradation as well as mRNA expression levels of TOR, ribosomal protein S6 kinase 1 (S6K1), and eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) were determined. The results showed that cell viability was enhanced by L-Arg with a maximal response at 10 to 400 μM. Increasing extracellular concentrations of L-Arg from 10 to 400 μM increased the cells in S and G2/M phase to a significant extent and decreased cell numbers in G0/G1 phase. Further more, addition of 100, 200, or 400 μM L-Arg to culture medium increased protein synthesis and reduced protein degradation in chicken intestinal epithelial cells. Consistent with the data on cell growth and protein turnover, supplementation of 100, 200, or 400 μM L-Arg increased the mRNA abundances of TOR, 4E-BP1, and S6K1. It was concluded the action of L-Arg involves in upregulating the genes expression of TOR cell signaling pathway which increases protein synthesis and reduces protein degradation.

The impact of host diet on Wolbachia titer in Drosophila

While a number of studies have identified host factors that influence endosymbiont titer, little is known concerning environmental influences on titer. Here we examined nutrient impact on maternally transmitted Wolbachia endosymbionts in Drosophila. We demonstrate that Drosophila reared on sucrose- and yeast-enriched diets exhibit increased and reduced Wolbachia titers in oogenesis, respectively. The yeast-induced Wolbachia depletion is mediated in large part by the somatic TOR and insulin signaling pathways. Disrupting TORC1 with the small molecule rapamycin dramatically increases oocyte Wolbachia titer, whereas hyper-activating somatic TORC1 suppresses oocyte titer. Furthermore, genetic ablation of insulin-producing cells located in the Drosophila brain abolished the yeast impact on oocyte titer. Exposure to yeast-enriched diets altered Wolbachia nucleoid morphology in oogenesis. Furthermore, dietary yeast increased somatic Wolbachia titer overall, though not in the central nervous system. These findings highlight the interactions between Wolbachia and germline cells as strongly nutrient-sensitive, and implicate conserved host signaling pathways by which nutrients influence Wolbachia titer.

Metabolism. Lysosomal amino acid transporter SLC38A9 signals arginine sufficiency to mTORC1

The mechanistic target of rapamycin complex 1 (mTORC1) protein kinase is a master growth regulator that responds to multiple environmental cues. Amino acids stimulate, in a Rag-, Ragulator-, and vacuolar adenosine triphosphatase-dependent fashion, the translocation of mTORC1 to the lysosomal surface, where it interacts with its activator Rheb. Here, we identify SLC38A9, an uncharacterized protein with sequence similarity to amino acid transporters, as a lysosomal transmembrane protein that interacts with the Rag guanosine triphosphatases (GTPases) and Ragulator in an amino acid-sensitive fashion. SLC38A9 transports arginine with a high Michaelis constant, and loss of SLC38A9 represses mTORC1 activation by amino acids, particularly arginine. Overexpression of SLC38A9 or just its Ragulator-binding domain makes mTORC1 signaling insensitive to amino acid starvation but not to Rag activity. Thus, SLC38A9 functions upstream of the Rag GTPases and is an excellent candidate for being an arginine sensor for the mTORC1 pathway.

Glucocorticoids retard skeletal muscle development and myoblast protein synthesis through a mechanistic target of rapamycin (mTOR)-signaling pathway in broilers (Gallus gallus domesticus)

Glucocorticoids exert a well-known catabolic protein action on skeletal muscle. The mechanistic target of rapamycin (mTOR) signaling pathway acts as a central regulator of protein metabolism. Whether glucocorticoids regulate protein synthesis through the mTOR pathway in skeletal muscle of chickens remains unknown. This study was performed to characterize the effect of glucocorticoids on the mTOR pathway in skeletal muscle development in chickens, and on protein synthesis in cultured embryonic myoblasts. Male 29-d-old chickens were given a dexamethasone injection (2 mg/kg) twice per day for 4 d (n = 16). Chicken embryonic myoblasts were exposed to dexamethasone for 24 h (100 µmol/L, n = 4 cultures). The interaction between dexamethasone and leucine was also investigated. ANOVA and Duncan's multiple test were used to analyze the effects of the dexamethasone and leucine treatments. The results showed that dexamethasone decreased body weight gain, body weight, and feed efficiency. Protein synthesis was inhibited by in vitro dexamethasone exposure. Phosphorylation of mTOR and ribosomal protein S6 protein kinase (p70S6K) were inhibited by dexamethasone, suggesting the mTOR pathway may be involved in dexamethasone-regulated muscle protein synthesis. Phosphorylation of AMP-activated protein kinase (AMPK) was not altered in vitro but was reduced in vivo by dexamethasone. These results imply that the mTOR and AMPK pathways are both involved in retarding muscle development and protein synthesis by glucocorticoids, but the mTOR pathway is a critical point linking glucocorticoid and protein synthesis. Leucine, at least partially, inhibited the effects of dexamethasone on protein synthesis via the mTOR pathway.

Dietary glutamate supplementation ameliorates mycotoxin-induced abnormalities in the intestinal structure and expression of amino acid transporters in young pigs

The purpose of this study was to investigate the hypothesis that dietary supplementation with glutamic acid has beneficial effects on growth performance, antioxidant system, intestinal morphology, serum amino acid profile and the gene expression of intestinal amino acid transporters in growing swine fed mold-contaminated feed. Fifteen pigs (Landrace×Large White) with a mean body weight (BW) of 55 kg were randomly divided into control group (basal feed), mycotoxin group (contaminated feed) and glutamate group (2% glutamate+contaminated feed). Compared with control group, mold-contaminated feed decreased average daily gain (ADG) and increased feed conversion rate (FCR). Meanwhile, fed mold-contaminated feed impaired anti-oxidative system and intestinal morphology, as well as modified the serum amino acid profile in growing pigs. However, supplementation with glutamate exhibited potential positive effects on growth performance of pigs fed mold-contaminated feed, ameliorated the imbalance antioxidant system and abnormalities of intestinal structure caused by mycotoxins. In addition, dietary glutamate supplementation to some extent restored changed serum amino acid profile caused by mold-contaminated feed. In conclusion, glutamic acid may be act as a nutritional regulating factor to ameliorate the adverse effects induced by mycotoxins.

Effects of intrauterine growth retardation and postnatal high-fat diet on hepatic inflammatory response in pigs

The objective of this study was to investigate the glucose and insulin response of pigs with intrauterine growth retardation (IUGR) to a high-fat (HF) feeding regimen and to observe the underlying toll-like receptor-4 (TLR4) signalling pathway. Weaned piglets with IUGR or normal birthweight (NBW) (n = 20 each) received during the whole fattening period control diets (0% lard) or HF diets (HF, 10% lard). At about 110 kg body weight, pigs were euthanised to collect hepatic samples. Compared with NBW pigs, IUGR pigs had lower daily gain and feed intake. Growth rate of pigs was increased by HF feeding. Pigs fed HF diets had lower peak concentrations of glucose and insulin, which decreased more slowly than in pigs that received the control diets. The mRNA expression abundances of peroxisome proliferator-activated receptor coactivator-1α (PGC-1α), TLR4, myeloid differentiation factor 88 (MyD88), tumour necrosis factor-α (TNF-α), interleukin 6 (IL-6) and IL-1 receptor antagonist (IL-1Rn) were significantly affected by HF feeding, and IL-6 and IL-1Rn mRNA expressions were up-regulated in IUGR pigs compared with NBW pigs. Western blot analysis indicated that HF feeding elevated the protein expressions of TLR4 signalling pathway, as TLR4, MyD88, IκB kinase β and nuclear factor-κB, and insulin signalling-related proteins, as phosphorylated insulin receptor substrate-1 and phosphorylated protein kinase B. In summary, hepatic TLR4 signalling pathway and inflammatory response induced by HF feeding played an important role in the aggravated development of insulin resistance in pigs.

Effect of L-lysine on expression of selected genes, serum concentration of amino acids, muscle growth and performance of growing pigs

Lysine (Lys) is the first limiting amino acid (AA) in most feed formulations for pigs and most abundant, along with leucine, in muscle proteins. An experiment was conducted with 17 pigs (17.7 ± 0.05 kg initial BW) to identify a role of dietary Lys in the control of protein synthesis in pigs. Fourteen pigs were randomly assigned to one of the two wheat-based dietary treatments: Lys-deficient, 3.0 g/kg (DEF) and Lys-adequate, 10.8 g/kg (ADE). Samples from jejunum mucosa, liver, Longissumus and Semitendinosus muscles, and blood were collected. The other three pigs were sacrificed at the beginning of the trial to measure basal carcass composition. Weight gain, gain:feed ratio, Lys intake and loin eye area were greater in ADE than in DEF pigs (p < 0.01). Muscle-related carcass characteristics were better, and myosin heavy chain IIb expression (MyHC IIb) in Semitendinosus was higher in ADE than in DEF pigs. Expression of AA transporters CAT-1 was lower (p < 0.05), serum Lys was higher and serum Val was lower in pigs fed the ADE diet. The higher muscularity, MyHC IIb expression in Semitendinosus muscle and Lys serum of pigs fed the ADE diet suggest that Lys increases growth rate not only by functioning as protein construction unit but also as potential control of the protein synthesis process.

Regulation of skeletal muscle protein degradation and synthesis by oral administration of lysine in rats

Several catabolic diseases and unloading induce muscle mass wasting, which causes severe pathological progression in various diseases and aging. Leucine is known to attenuate muscle loss via stimulation of protein synthesis and suppression of protein degradation in skeletal muscle. The aim of this study was to investigate the effects of lysine intake on protein degradation and synthesis in skeletal muscle. Fasted rats were administered 22.8-570 mg Lys/100 g body weight and the rates of myofibrillar protein degradation were assessed for 0-6 h after Lys administration. The rates of myofibrillar protein degradation evaluated by MeHis release from the isolated muscles were markedly suppressed after administration of 114 mg Lys/100 g body weight and of 570 mg Lys/100 g body weight. LC3-II, a marker of the autophagic-lysosomal pathway, tended to decrease (p=0.05, 0.08) after Lys intake (114 mg/100 g body weight). However, expression of ubiquitin ligase E3 atrogin-1 mRNA and levels of ubiquitinated proteins were not suppressed by Lys intake. Phosphorylation levels of mTOR, S6K1 and 4E-BP1 in the gastrocnemius muscle were not altered after Lys intake. These results suggest that Lys is able to suppress myofibrillar protein degradation at least partially through the autophagic-lysosomal pathway, not the ubiquitin-proteasomal pathway, whereas Lys might be unable to stimulate protein synthesis within this time frame.