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Longevity University / Lesson 1

mTOR and AMPK: the cell's nutrient sensors

Two signaling hubs decide whether a cell builds or conserves. Food, protein, exercise, rapamycin and metformin all push on them.

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Human fibroblasts, fluorescence: mitochondria in red, nuclei in blue, nanoparticles in green
Human fibroblasts, fluorescence: mitochondria in red, nuclei in blue, nanoparticles in green. Image: Matteo Battaglini, CC BY 4.0

Education only, not medical advice. Talk to your clinician before changing medication or if you have a condition.

mTOR and AMPKProtein, insulin and amino acids activate mTOR (growth). Exercise and low energy activate AMPK, which restrains mTOR and favors autophagy. Rapamycin inhibits mTOR; metformin acts partly via AMPK.Plenty signalsprotein · amino acids · insulinScarcity signalsexercise · fasting · low energymTORbuildAMPKsave energyAMPK restrains mTORprotein synthesis, muscleless autophagyfuel burningmore autophagyrapamycin inhibits mTORmetformin: partly AMPK
mTOR and AMPK. Protein, insulin and amino acids activate mTOR (growth). Exercise and low energy activate AMPK, which restrains mTOR and favors autophagy. Rapamycin inhibits mTOR; metformin acts partly via AMPK.

Two switches

mTOR (mechanistic target of rapamycin) is a protein kinase that integrates signals from amino acids, insulin and growth factors and, when active, drives protein synthesis and cell growth while suppressing autophagy, the cell's recycling program [1].

AMPK is the energy sensor: it switches on when the ratio of AMP to ATP rises, as during exercise or low energy, and it turns on energy-producing pathways while turning off energy-consuming ones, including mTOR signaling [2].

Why aging researchers care

Deregulated nutrient sensing is one of the recognized hallmarks of aging [3]. Rapamycin, which inhibits mTOR, extended lifespan in mice even when started late in life [4]. Whether that translates to people is unproven: the 48-week PEARL trial of low-dose rapamycin did not change its primary endpoint [5].

Metformin is often described as acting partly through AMPK and is proposed for testing against aging in the TAME trial, which has not yet run [6].

Not an on-off morality tale

mTOR is not simply bad. Its activation after protein intake and resistance exercise is how muscle is built, and muscle strength is linked to longer survival [1][7]. The practical takeaway is balance: train, eat enough protein, and let exercise and the overnight fast provide natural AMPK periods.

Check your understanding

1. What tends to switch AMPK on?
  1. A large protein meal
  2. Low cellular energy, as during exercise
  3. Rapamycin
Tap to reveal the answer

Answer: b. AMPK senses a rising AMP to ATP ratio [2].

2. Has rapamycin been shown to extend human lifespan?
  1. Yes
  2. No, only mice so far
Tap to reveal the answer

Answer: b. Lifespan data are from mice [4]; the PEARL human trial missed its primary endpoint [5].

Sources

  1. Saxton & Sabatini 2017, Cell. doi.org/10.1016/j.cell.2017.02.004
  2. Hardie et al. 2012, Nat Rev Mol Cell Biol. doi.org/10.1038/nrm3311
  3. López-Otín et al. 2023, Cell. doi.org/10.1016/j.cell.2022.11.001
  4. Harrison et al. 2009, Nature. doi.org/10.1038/nature08221
  5. Moel et al. 2025, Aging (PEARL). doi.org/10.18632/aging.206235
  6. Barzilai et al. 2016, Cell Metab. doi.org/10.1016/j.cmet.2016.05.011
  7. Leong et al. 2015, Lancet (PURE). doi.org/10.1016/S0140-6736(14)62000-6

DOIs verified against Crossref on 2026-10-15.

Next: Cellular senescence and senolytics