L-Arginine Enhances Protein Synthesis by Phosphorylating mTOR (Thr 2446) in a Nitric Oxide-Dependent Manner in C2C12 Cells

Muscle atrophy may arise from many factors such as inactivity, malnutrition, and inflammation. In the present study, we investigated the stimulatory effect of nitric oxide (NO) on muscle protein synthesis. Primarily, C2C12 cells were supplied with extra L-arginine (L-Arg) in the culture media. L-Arg supplementation increased the activity of inducible nitric oxide synthase (iNOS), the rate of protein synthesis, and the phosphorylation of mTOR (Thr 2446) and p70S6K (Thr 389). L-NAME, an NOS inhibitor, decreased NO concentrations within cells and abolished the stimulatory effect of L-Arg on protein synthesis and the phosphorylation of mTOR and p70S6K. In contrast, SNP (sodium nitroprusside), an NO donor, increased NO concentrations, enhanced protein synthesis, and upregulated mTOR and p70S6K phosphorylation, regardless of L-NAME treatment. Blocking mTOR with rapamycin abolished the stimulatory effect of both L-Arg and SNP on protein synthesis and p70S6K phosphorylation. These results indicate that L-Arg stimulates protein synthesis via the activation of the mTOR (Thr 2446)/p70S6K signaling pathway in an NO-dependent manner.

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.

Invited review: impact of specific nutrient interventions during mid-to-late gestation on physiological traits important for survival of multiple-born lambs

To improve production efficiency, the sheep meat industry has increased flock prolificacy. However, multiple-born lambs have lower birth weights, increased mortality and reduced growth rate compared with single-born lambs. Lamb mortality is a major issue for livestock farming globally and solutions are required to increase survival to realise the value of increased flock fecundity. Nutrition during gestation can influence maternal-foetal placental nutrient transfer and thus foetal growth and organ/tissue development, as well as improve postnatal productivity. This review covers the challenges and opportunities associated with increased prolificacy, highlights gaps in our knowledge and identifies some opportunities for how targeted intervention with specific nutrients during mid-to-late pregnancy may influence lamb survival and productivity with a specific focus on pasture-based systems. This time frame was selected as intervention strategies in short-time windows post-pregnancy scanning and before lambing to improve lamb survival in high-risk groups (e.g. triplets) are likely to be the most practical and economically feasible options for pasture-based extensive farming systems.

Maternal Low Quality Protein Diet Alters Plasma Amino Acid Concentrations of Weaning Rats

Several studies have indicated the influence of a maternal low protein diet on the fetus. However, the effect of a maternal low quality protein diet on fetal growth and development is largely unknown. Wistar rats (11 weeks old) were mated and maintained on either a chow diet with 20% casein (n = 6) as the control group (C), or a low quality protein diet with 20% wheat gluten (n = 7) as the experimental group (WG) through gestation and lactation. Maternal body weights were similar in both groups throughout the study. Birth weights were not influenced by maternal diet and offspring body weights during lactation were similar between the groups. Offspring’s plasma amino acid profiles showed that plasma methionine, glutamine and lysine were significantly lower and aspartic acid, ornithine and glycine-proline were significantly higher in the WG. Plant based protein comprises an important part of protein intake in developing countries. It is well-known that these diets can be inadequate in terms of essential amino acids. The current study shows differential effects of a maternal low quality protein diet on the offspring’s plasma amino acids. Future studies will examine further aspects of the influence of maternal low quality protein diets on fetal growth and development.