The role of mechanistic target of rapamycin (mTOR) signalling in skeletal muscle ageing
Publication Date
October 15, 2025
Creator
Liu, Hui Tien
Abstract
The mechanistic target of rapamycin (mTOR) plays a crucial role in regulating essential cellular functions, including metabolism, survival, and growth. In skeletal muscle, the mTOR signalling pathway is fundamental for maintaining muscle protein homeostasis, with increased activity typically promoting skeletal muscle anabolic process under normal conditions. However, recent studies have identified dysregulated mTOR activity in aged rodent and human muscle, revealing an age-related increase in mTOR signalling that contributes to ageing related muscle loss (sarcopenia)—contrary to its traditionally recognized anabolic role. Notably, mTOR inhibition has been reported to improve muscle quality, enhancing muscle mass and cross-sectional area in aged muscle, highlighting its unanticipated potential as a therapeutic target for mitigating age-related muscle atrophy.
Given the dysregulation of mTOR with aging, we investigated mTOR signalling and its potential link to aging-induced muscle loss (sarcopenia) by analysing muscle biopsy samples from young and old rodents and humans. Our findings revealed an age-associated increase in mTOR pathway activity, including heightened AKT-mTOR-rps6 signalling in rat soleus muscle and an elevated phosphorylated protein amount and ratio (phosphorylated/Pan) of rps6 in human samples, demonstrating a positive correlation between mTOR activation and ageing. Additionally, we observed that mTOR pathway activation varied across muscle groups and sexes. Specifically, the rat soleus muscle exhibited greater mTOR signalling elevation than the tibialis anterior, whereas the latter showed a decline in AMPK-FoxO pathway activity. Furthermore, males exhibited a greater increase in rps6 and PI3K activity than females, while females showed a reduced TSC2-AKT ratio with ageing. These findings highlight sex- and muscle group-specific differences in mTOR signalling, providing a foundation for understanding its role in age-related muscle atrophy.
Our results indicate an elevation of mTOR with aging, highlighting mTOR inhibition as a potential treatment for age-related muscle loss (sarcopenia). Rapamycin, a potent mTOR inhibitor, emerges as a promising therapeutic target. To investigate its physiological effects, we conducted a C2C12 cell experiment to determine the minimum effective concentration required to inhibit the mTOR signalling pathway. We found that 10 nM rapamycin effectively suppressed mTOR signalling, as evidenced by decreased phosphorylated S6K1 and RPS6 levels. Additionally, rapamycin treatment reduced C2C12 cell numbers, suggesting an inhibition of key physiological functions such as proliferation and protein synthesis. Furthermore, we examined the impact of rapamycin in human primary myotube cells derived from young and old donors. We observed that rapamycin effectively inhibited mTOR signalling in both age groups, indicating no significant differences in response based on age or cell type. Notably, primary myotube cells from older donors exhibited lower mTOR signalling activation in response to high FBS stimulation compared to those from younger donors. This result suggests anabolic resistance in aged cells, reinforcing the notion that this resistance originates at the cellular level.
Since rapamycin alters cell metabolism, we conducted a metabolomics analysis to better understand its effects. Our findings revealed that both aging and rapamycin influence amino acid and fatty acid metabolism, as well as cellular energetics, leading to disruptions in protein and lipid homeostasis and energy balance—key factors associated with muscular aging. These metabolic shifts provide deeper insights into physiological changes such as anabolic resistance and rapamycin-induced cellular adaptations. These metabolic shifts provide deeper insights into the physiological changes observed, including anabolic resistance and rapamycin-induced cellular adaptations. Notably, in human primary myotube cells, rapamycin reduced metabolic variability associated with aging, particularly in metabolites related to essential amino acid and plasma membrane lipid metabolism. These metabolic alterations may offer a mechanistic explanation for rapamycin's anti-ageing effects at the cellular level from a metabolomics perspective.
In conclusion, our study reinforces the link between mTOR signal pathway increase and ageing, suggesting its potential contribution to ageing induced muscle loss (sarcopenia). We also provide insights into sex- and muscle group-specific differences, which may help explain variations in atrophy progression between sexes and different muscle groups. Furthermore, our metabolomics analysis highlights key metabolic pathways influenced by ageing and rapamycin, offering valuable insights for future research aimed at understanding and mitigating ageing induced muscle loss (sarcopenia).
Item Type
ethesis
Thesis Type
PhD
Subjects (LC)
Associated Schools / Departments
School of Medicine
eprints ID
81887
UoN Repository URI
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hui Tien Liu 20213243 PhD thesis final vision.pdf
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Full-text
Description
Examined. The thesis with correction from viva report
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8.03 MB
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