What are the latest findings on the role of amino acids in muscle repair and growth?
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Introduction
Amino acids (AAs) play a crucial role in muscle repair and growth, acting as building blocks for proteins and influencing various metabolic and signaling pathways. Recent research has focused on understanding how different amino acids and their metabolites contribute to muscle protein synthesis (MPS), muscle growth, and overall muscle function.
Key Insights
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Amino Acids and mTORC1 Signaling:
- Essential amino acids (EAAs) and branched-chain amino acids (BCAAs) like leucine activate the mTORC1 signaling pathway, which is crucial for muscle protein synthesis and growth .
- Ingestion of EAAs or protein shortly after resistance exercise enhances MPS and mTORC1 signaling more than exercise or EAAs alone .
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Role of Specific Amino Acids:
- Leucine and its metabolite HMB (β-hydroxy-β-methylbutyrate) significantly increase protein synthesis through mTORC1 activation .
- Valine's metabolite BAIBA (β-aminoisobutyric acid) increases energy expenditure and has beneficial effects on muscle function.
- Lysine has a pronounced effect on muscle growth and quality, particularly in poultry, by modulating protein synthesis and muscle composition.
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Amino Acids and Muscle MicroRNAs:
- EAAs increase the expression of muscle-specific microRNAs (miR-499, -208b, -23a) and downregulate growth inhibitors like myostatin, promoting muscle growth.
- Amino acids also upregulate muscle differentiation and growth-related genes, enhancing muscle repair and development .
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Amino Acids in Aging and Muscle Wasting:
- Older adults show impaired muscle response to anabolic stimuli, but EAAs combined with resistance exercise can improve muscle repair and growth, counteracting sarcopenia.
- BFR (blood flow restriction) exercise combined with EAAs can overcome age-related impairments in muscle protein synthesis.
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Amino Acid Transporters:
- Amino acid transporters play a critical role in delivering amino acids to intracellular sensors, regulating protein metabolism and muscle adaptation.
- The expression of these transporters is dynamic and responsive to various stimuli, indicating their importance in muscle health.
Conclusion
Amino acids, particularly EAAs and BCAAs, are vital for muscle repair and growth by activating the mTORC1 signaling pathway and enhancing muscle protein synthesis. Specific amino acids like leucine and lysine have significant effects on muscle quality and growth. Additionally, amino acids influence muscle-specific microRNAs and gene expression, promoting muscle differentiation and repair. In older adults, combining EAAs with resistance exercise can effectively counteract muscle wasting. Understanding the role of amino acid transporters further highlights the importance of optimizing amino acid nutrition for muscle health.
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