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Journal of animal science2020; 98(9); doi: 10.1093/jas/skaa268

Pathways regulating equine skeletal muscle protein synthesis respond in a dose-dependent manner to graded levels of protein intake.

Abstract: Activation of the mechanistic target of rapamycin (mTOR)-controlled anabolic signaling pathways in skeletal muscle of rodents and humans is responsive to the level of dietary protein supply, with maximal activation and rates of protein synthesis achieved with 0.2 to 0.4 g protein/kg body weight (BW). In horses, few data are available on the required level of dietary protein to maximize protein synthesis for maintenance and growth of skeletal muscle. To evaluate the effect of dietary protein level on muscle mTOR pathway activation, five mares received different amounts of a protein supplement that provided 0, 0.06, 0.125, 0.25, or 0.5 g of crude protein (CP)/kg BW per meal in a 5 × 5 Latin square design. On each sample day, horses were fasted overnight and were fed only their protein meal the following morning. A preprandial (0 min) and postprandial (90 min) blood sample was collected and a gluteus medius muscle sample was obtained 90 min after feeding the protein meal. Blood samples were analyzed for glucose, insulin, and amino acid concentrations. Activation of mTOR pathway components (mTOR and ribosomal protein S6 [rpS6]) in the muscle samples was measured by Western immunoblot analysis. Postprandial plasma glucose (P = 0.007) and insulin (P = 0.09) showed a quadratic increase, while total essential amino acid (P < 0.0001) concentrations increased linearly with the graded intake of the protein supplement. Activation of mTOR (P = 0.02) and its downstream target, rpS6 (P = 0.0008), increased quadratically and linearly in relation to the level of protein intake, respectively. Comparisons of individual doses showed no differences (P > 0.05) between the 0.25 and 0.5 g of protein intake for either mTOR or rpS6 activation, indicating that protein synthesis may have reached near maximal capacity around 0.25 g CP/kg BW. This is the first study to show that the activation of muscle protein synthetic pathways in horses is dose-dependent on the level of protein intake. Consumption of a moderate dose of high-quality protein resulted in near maximal muscle mTOR pathway activation in mature, sedentary horses.
© The Author(s) 2020. Published by Oxford University Press on behalf of the American Society of Animal Science. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.
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Publication Date: 2020-08-25 PubMed ID: 32835365PubMed Central: PMC7497812DOI: 10.1093/jas/skaa268Google Scholar: Lookup
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Summary

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The researchers explored the effect of different levels of protein consumption on muscle protein synthesis in horses, uncovering that muscle protein synthesis pathways are activated in a dose-dependent manner on the level of protein intake.

Study Design and Procedure

  • The research was conducted on five mature mares using a 5 × 5 Latin square design wherein each horse received varying amounts of protein supplement.
  • Five different levels of protein supplement were used in this study: 0, 0.06, 0.125, 0.25, or 0.5 g of crude protein per kg body weight (BW).
  • The horses were fasted overnight and were provided only their protein meals the next morning. Blood and muscle samples were then obtained for examination.
  • Blood samples were analyzed for glucose, insulin, and amino acid concentrations. Muscle samples were used to measure the activation of the mTOR pathway components through Western immunoblot analysis.

Findings and Implications

  • The research showed that with a graded intake of protein supplement, postprandial plasma glucose and insulin levels experienced a quadratic increase while total essential amino acid concentrations increase linearly.
  • Furthermore, the activation of the mTOR pathway and ribosomal protein S6 (rpS6), its downstream target, increased in relation to the level of protein intake; with mTOR activation increasing quadratically and rpS6 activation increasing linearly.
  • The study found no notable difference between the 0.25 g and the 0.5 g levels of protein intake concerning the activation of mTOR or rpS6, suggesting that protein synthesis could be nearing its maximal capacity around 0.25 g crude protein per kg body weight.
  • This research is the first to demonstrate that muscle protein synthetic pathways in horses are dose-dependent on the level of protein intake. It highlighted that consuming a moderate quantity of high-quality protein could lead to near-maximal muscle mTOR pathway activation in mature, sedentary horses.
  • These findings provide valuable insights for equine diet planning and indicate potential pathways for enhancing muscle protein synthesis.

Cite This Article

APA
Loos CMM, McLeod KR, Stratton SC, van Doorn DA, Kalmar ID, Vanzant ES, Urschel KL. (2020). Pathways regulating equine skeletal muscle protein synthesis respond in a dose-dependent manner to graded levels of protein intake. J Anim Sci, 98(9). https://doi.org/10.1093/jas/skaa268

Publication

Journal of animal science
ISSN: 1525-3163
NlmUniqueID: 8003002
Country: United States
Language: English
Volume: 98
Issue: 9

Researcher Affiliations

Loos, Caroline M M
  • Department of Animal and Food Sciences, University of Kentucky, Lexington, KY.
McLeod, Kyle R
  • Department of Animal and Food Sciences, University of Kentucky, Lexington, KY.
Stratton, Sophie C
  • Department of Animal and Food Sciences, University of Kentucky, Lexington, KY.
van Doorn, David A
  • Equivado Consultancy B.V., Utrecht, The Netherlands.
Kalmar, Isabelle D
  • Department of Nutrition, Genetics and Ethology, Ghent University, Gent, Belgium.
Vanzant, Eric S
  • Department of Animal and Food Sciences, University of Kentucky, Lexington, KY.
Urschel, Kristine L
  • Department of Animal and Food Sciences, University of Kentucky, Lexington, KY.

MeSH Terms

  • Animals
  • Blood Glucose / analysis
  • Diet / veterinary
  • Dietary Proteins / analysis
  • Dietary Supplements / analysis
  • Fasting
  • Female
  • Horses / physiology
  • Insulin / blood
  • Muscle Proteins / metabolism
  • Muscle, Skeletal / drug effects
  • Postprandial Period / drug effects
  • Protein Biosynthesis / drug effects
  • Random Allocation
  • Signal Transduction / drug effects
  • TOR Serine-Threonine Kinases / metabolism

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Citations

This article has been cited 2 times.
  1. Ferguson TD, Loos CMM, Vanzant ES, Urschel KL, Klotz JL, McLeod KR. Impact of ergot alkaloid and steroidal implant on whole-body protein turnover and expression of mTOR pathway proteins in muscle of cattle. Front Vet Sci 2023;10:1104361.
    doi: 10.3389/fvets.2023.1104361pubmed: 37143501google scholar: lookup
  2. Loos CMM, McLeod KR, Vanzant ES, Stratton SA, Bohannan AD, Coleman RJ, van Doorn DA, Urschel KL. Differential effect of two dietary protein sources on time course response of muscle anabolic signaling pathways in normal and insulin dysregulated horses. Front Vet Sci 2022;9:896220.
    doi: 10.3389/fvets.2022.896220pubmed: 35978710google scholar: lookup
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