Key Insights
- The protein complex and mTORC1 is critical for muscle growth. But it must be kept in balance where either underactivation or overactivation can lead to muscle loss (sarcopenia).
- In aging muscles, mTORC1 complex gets overactivated, leading to mucle fiber damage and muscle loss
- Researchers have now shown that in mice, exercise suppresses a protein that control mTORC1 expression and restores its balance in aging muscles
- The result: exercise reversed muscle aging!
How muscles grow and why we lose muscle with age
An ancient group of proteins called the mechanistic target of rapamycin complex 1 (mTORC1) is at the heart of how muscles grow. When we eat a high protein meal, amino acids, the building blocks of proteins and muscle, become available. In response, muscle cells activate the mTORC1 protein complex, the cells synthesize proteins and slow down cellular recycling (autophagy). Higher protein synthesis and suppressed recycling, both of which are controlled by mTORC1, are crucial for muscle growth.
But mTORC1 has to be maintained in a tight balance and too much or too little of its activity are both bad for muscle health. This is precisely what happens to aging muscles. Chronic overactivation of mTORC1 in aging muscles leads to damaged mitochondria, disruption of protein quality control (proteostasis), suppressed protein recycling (autophagy), muscle cell aging (senescence) producing muscle fiber damage and gradual loss of muscle mass.
How to restore muscle protein balance during aging
Researchers from Singapore (Duke-NUS) wanted to explore why mTOR is overactivated in aging muscles and ways to restore balance in mTORC1 activation. Testing first in fruit flies and then in mice, they identified a protein called DEAF1 that controls mTORC1 overactivation in aging muscles.
The study found that:
- DEAF1 levels rise in aged muscle, directly increasing mTORC1 activity and disrupting muscle protein balance. Reducing DEAF1 in aging flies preserved climbing ability and muscle structure.
- Exercise activates FOXO proteins, which suppress DEAF1, normalize mTORC1, and restore muscle protein balance.
- In mice, activating FOXO or knocking down DEAF1 improved autophagy, reduced cellular senescence markers (p16, p21), and lowered age-related protein aggregates in muscle.
- These effects are evolutionarily conserved from flies to mammals, suggesting a common fundamental mechanism for muscle maintenance.
Exercise as a molecular reset for aging muscle cells
The study shows that exercise is a powerful way to flip a molecular switch in aging muscles. When we exercise, mTORC1 activity is lowered to a healthy normal level. This restores protein balance, boosts muscle cleanup processes, and reduces markers of cellular aging. In other words, exercise doesn’t just make muscles stronger, it tunes the molecular machinery that keeps muscles youthful.
Han, X., Goh, K. Y., Lee, W. X., Choy, S. M., & Tang, H. W. (2022, December 24). The Importance of mTORC1-Autophagy Axis for Skeletal Muscle Diseases. International Journal of Molecular Sciences. https://doi.org/10.3390/ijms24010297
Tang, H., Inoki, K., Brooks, S. V., Okazawa, H., Lee, M., Wang, J., Kim, M., Kennedy, C. L., Macpherson, P. C. D., Ji, X., Van Roekel, S., Fraga, D. A., Wang, K., Zhu, J., Wang, Y., Sharp, Z. D., Miller, R. A., Rando, T. A., Goldman, D., Guan, K.-L., & Shrager, J. B. (2019, June). mTORC1 underlies age-related muscle fiber damage and loss by inducing oxidative stress and catabolism. Aging Cell. https://doi.org/10.1111/acel.12943
Nacarelli, T., Azar, A., & Sell, C. (2016, June). Mitochondrial stress induces cellular senescence in an mTORC1-dependent manner. Free Radical Biology and Medicine. https://doi.org/10.1016/j.freeradbiomed.2016.03.008
Choy, S. M., Goh, K. Y., Lee, W. X., Jiang, W., Gou, Q., Gopal Krishnan, P. D., Ong, S. C., Chua, K., Harmston, N., & Tang, H. W. (2025, November 24). Exercise suppresses DEAF1 to normalize mTORC1 activity and reverse muscle aging. Proceedings of the National Academy of Sciences. https://doi.org/10.1073/pnas.2508893122