WORDS-c : the mitochondrial peptide that mimics exercise
MOTS-c (Mitochondrial Open Reading Frame of the 12S rRNA type-c) is a 16-amino-acid micropeptide encoded by mitochondrial DNA—a major 2015 discovery that revolutionized our understanding of mitochondrial signaling. It activates the AMPK pathway, enhances insulin sensitivity, and produces exercise-like effects in preclinical models.
An unexpected discovery: a peptide encoded by mtDNA
Until 2015, the human mitochondrial genome (mtDNA, 16,569 bp) was thought to code for only 13 proteins, 22 tRNAs, and 2 rRNAs. Lee's discovery of MOTS-c et al. (Cell Metabolism, 2015) showed that the 12S rRNA region of mtDNA contains a functional ORF (Open Reading Frame) producing a bioactive micropeptide of 16 amino acids.
The MOTS-c gene is located in the 12S rRNA region of mitochondrial DNA. Sequence: MRWQEMGYIFYPRKLR. Molecular weight: 2,174 Da. Encoded by reading frames 1337–1390 of human mtDNA. Ubiquitously expressed, with high levels in the liver, skeletal muscle, and stem cells.
What makes MOTS-c particularly interesting is its dual localization: produced in mitochondria, it can be secreted into the bloodstream where it acts like a hormone — a concept now referred to by the term "mitokine"It can also translocalize to the cell nucleus and directly modulate gene expression.
Activation of the AMPK pathway: the metabolic crossroads
AMPK, guardian of cellular energy
AMPK (AMP-activated protein kinase) is the main sensor kinase of cellular energy status. It is activated when the AMP/ATP ratio increases (energy stress) and orchestrates a catabolic response: stimulation of glycolysis, β-oxidation of fatty acids, autophagy and mitochondrial biogenesis, while inhibiting ATP-intensive anabolic pathways (protein synthesis via mTOR, lipogenesis).
How to activate AMPK on MOTS-c
MOTS-c disrupts the methionine pathway via inhibition of AICAR transformylase in the folate cycle—leading to an accumulation of AICAR (5-Aminoimidazole-4-carboxamide ribonucleotide), a potent endogenous activator of AMPK. This indirect mechanism is distinct from that of metformin (mitochondrial complex I inhibition) but produces convergent effects on glucose metabolism.
Both activate AMPK, but through distinct mechanisms. Metformin inhibits complex I of the mitochondrial respiratory chain, leading to increased AMP/ATP levels and AMPK activation. MOTS-c acts via the accumulation of AICAR (an intermediate in the folate cycle), directly activating AMPK. Their combination is being studied as potentially synergistic.
Insulin sensitivity and type 2 diabetes
The seminal study (Lee et al., 2015) showed that injecting MOTS-c into mice on a high-fat diet prevents the development of obesity and insulin resistance. In models of established type 2 diabetes, MOTS-c significantly improves glucose homeostasis.
- Increased muscle absorption of glucose (GLUT4 translocation)
- Reduction of hepatic glucose production (gluconeogenesis)
- Enhancement of insulin receptor signaling (IRS-1/PI3K/Akt)
- Reduction of low-grade chronic inflammation in adipose tissue (IL-6, TNF-α)
| Study | Model | Observed effect |
|---|---|---|
| Lee et al. 2015 Cell Metabolism |
HFD (obese) mice, aged mice | Obesity prevention, improved insulin sensitivity, ↓ body fat |
| Ming et al. 2016 Sci Rep |
db/db mouse (T2D) | ↓ fasting blood glucose, ↑ glucose tolerance, ↓ HbA1c |
| Kim et al. 2018 Cell Metab |
HFD mouse + exercise | MOTS-c secreted during exercise, mediates muscle metabolic adaptation |
| Reynolds et al. 2021 Nat Aging |
Old male mice | Increased physical resistance, decreased frailty index, increased insulin sensitivity in senescent individuals |
| Lu et al. 2023 Aging Cell |
elderly macaque monkeys | Increased glucose tolerance, increased muscle IGF-1, improved metabolic markers |
MOTS-c as in "exercise mimetic"
One of the most striking findings (Kim et al., Cell Metabolism, 2018) is that endogenous MOTS-c is released by skeletal muscles during exercise and that its circulating levels increase proportionally to the intensity of the effort. MOTS-c thus contributes to the full range of beneficial metabolic adaptations of exercise:
Activation of PGC-1α via AMPK → increased number and density of muscle mitochondria.
Stimulation of β-oxidation in muscle and liver → preferential mobilization of lipids as an energy source.
Translocation of GLUT4 to the plasma membrane of myocytes independently of insulin → post-exercise carbohydrate uptake.
Protection of cardiomyocytes against oxidative stress and ischemia-reperfusion via AMPK/Nrf2.
WORDS and longevity
Decline with age
The circulating levels of MOTS-c decrease significantly with age — a pattern consistent with the decline in mitochondrial function and insulin sensitivity observed in aging. Human epidemiological studies (Japanese centenarian cohorts, CALERIE studies) show associations between variants of the MOTS-c gene and longevity.
Longevity models
In 26-month-old mice (an advanced age equivalent to ~80 human years), MOTS-c injection improves exercise capacity, reduces markers of systemic inflammation, improves insulin sensitivity, and preserves muscle density—phenotypes directly linked to the "healthspan" rather than the maximum lifespan.
A 2019 study (Zempo et al., J Gerontol) identified several polymorphisms of the MOTS-c gene associated with longevity in Japanese cohorts. The K14Q variant (c.40A>C) is 3× more frequent in centenarians than in the general population, suggesting a functional role for MOTS-c in the biology of human aging.
c-words in the nucleus: transcriptomic regulation
A recent discovery (Kim et al., 2018) shows that MOTS-c can translocalize to the cell nucleus in response to metabolic or oxidative stress, where it interacts directly with transcription factors to regulate genes involved in the antioxidant response (Nrf2), metabolism (ARE-genes), and cell survival. This ability to act simultaneously in mitochondria, cytoplasm, and the nucleus makes it a unique "multi-compartment" metabolic regulator.
Peptide size
Genomic origin
Primary target
Muscle secretion
Human data and clinical perspectives
Preclinical data in mice and non-human primates are promising, but human clinical trials are still in their early stages. The first phase 1 studies evaluating the pharmacokinetics and tolerability of exogenous MOTS-c in humans are underway (2024). Human pharmacokinetic parameters have not yet been published.
MOTS-c has no approved clinical indication. All efficacy data are derived from preclinical studies (rodents, non-human primates) and genetic epidemiological studies. Extrapolation to humans should be made with caution. Randomized clinical trials are still lacking.
Technical specifications
| Setting | Value |
|---|---|
| Sequence | MRWQEMGYIFYPRKLR |
| Length | 16 amino acids |
| Molecular weight | 2,174.6 Da |
| Formula | C₁₀₀H₁₅₈N₂₈O₂₆S |
| Origin | human mitochondrial DNA (12S rRNA region) |
| Reconstitution solvent | Sterile water or bacteriostatic water |
| Molecular targets | AMPK, AICAR pathway, Nrf2, PGC-1α |
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📚 Scientific reference:
Lee C et al. “The mitochondrial-derived peptide MOTS-c promotes metabolic homeostasis. » Cell Metab. 2015.
PubMed PMID:25738459 →