Effects of advanced age on whole-body protein synthesis and skeletal muscle mechanistic target of rapamycin signaling in horses.

The research investigates the impact of aging on protein production throughout the horse body and in muscle tissues, focusing on a specific pathway related to this process, known as the mechanistic target of rapamycin or mTOR signaling. The study found that while overall protein synthesis was not impacted, protein generation in muscles was reduced, indicated by reduced mTOR pathway activity.

Research Methodology

• The researchers used a sample of twelve horses, split into two groups based on age – one group comprised of aged horses between 22 to 26 years, and the other of mature horses between 7 to 14 years.
• Whole-body protein synthesis in these horses was measured using a process involving a primed constant infusion of (13)C sodium bicarbonate, followed by a further 4-hour infusion of 1-(13)C phenylalanine.
• A tissue biopsy was taken from a gluteus medius muscle in each horse post the infusions. Through this specimen, activation of protein kinase B (Akt), p70 riboprotein S6 kinase (S6K1), riboprotein S6 (rpS6), and eukaryotic initiation factor 4E binding protein 1 (4EBP1) was determined, using western immunoblot analysis.
• Additionally, expression of inflammatory cytokine in muscle and blood samples from all horses was quantified using real-time PCR analysis.

Findings of the Research

• Advanced age did not have a noticeable impact on whole-body protein synthesis in the horses. The phosphorylation or energy exchange-related activities of Akt, rpS6, and 4EBP1 were also not affected.
• However, muscle tissues of aged horses showed 42% lower activation of p70 riboprotein S6 kinase (S6K1) compared to those of mature horses. Lower S6K1 activation is generally associated with lower rates of muscle protein synthesis.
• The expression of inflammatory cytokines, markers of internal inflammation, were found to be similar in both aged and mature horses.

Conclusion and Implications

• The observed lower S6K1 activation in aged horses suggests that their muscle protein synthesis rates might be lower than in mature horses, but no other evidence supporting this was found.
• Based on these findings, the study concludes that the impact of age on whole-body protein synthesis and muscle inflammation may be limited, suggesting that healthy mature and aged horses may not have different protein metabolism and requirements.