Research libraryMitochondrial peptides and NAD+
MOTS-c: A Mitochondrial-Derived Peptide Encoded in the 12S rRNA
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MOTS-c is a 16 amino acid peptide encoded inside the mitochondrial genome rather than the nuclear one, which is still an odd thing to write. Nearly every peptide a lab works with comes from nuclear DNA. MOTS-c comes from a short open reading frame tucked inside the 12S rRNA gene of mitochondrial DNA, and it was only described in 2015. This article pulls together what the primary papers report about its origin, its sequence, what it binds, and how it behaves in plasma, with the vaguer claims from older write ups cut out.
Key findings
- MOTS-c stands for mitochondrial open reading frame of the 12S rRNA-c. Lee and colleagues reported the peptide in 2015 [1].
- Its described cellular action was inhibition of the folate cycle and the de novo purine biosynthesis tethered to it, leading to AMPK activation [1].
- A 2024 paper identified casein kinase 2 as a direct binding partner, with MOTS-c activating CK2 in cell free systems [2].
- Under cellular stress the peptide moves into the nucleus and regulates nuclear gene expression, which is bi-genomic signalling in the unusual direction [3].
- Circulating MOTS-c fell with age in healthy men, while skeletal muscle expression was about 1.5 fold higher in older and middle aged men than in young men [4].
- The m.1382A>C polymorphism sits in the MOTS-c coding region and is specific to Northeast Asian populations [5].
A peptide with the wrong return address
Humanin came first. Once a short open reading frame in mitochondrial DNA had been shown to encode a signalling peptide, it was reasonable to go looking for others, and that search is exactly how MOTS-c turned up [1]. The sequence sits within the 12S rRNA region, which means the peptide is read from a gene that is better known for making a structural RNA. Mitochondrial DNA is small, circular and inherited maternally, and until recently nobody expected it to be sending peptide messages anywhere.
The sequence is well conserved across mammals, and plenty of the published work runs in mouse models with the human peptide. That conservation is the usual justification for cross species work here, though it is worth saying out loud that conservation is an argument, not a result.
Folate cycle, purines, AMPK
The mechanism Lee’s group described in 2015 is more specific than the shorthand usually passed around. MOTS-c did not simply switch on AMPK. It inhibited the folate cycle, and with it the de novo purine biosynthesis pathway that depends on folate derived one carbon units [1]. AICAR, an intermediate in that pathway, accumulates when the cycle is blocked, and AICAR is a known AMPK activator. So AMPK activation came downstream of a metabolite shift rather than from direct enzyme contact. Skeletal muscle appeared to be the primary target tissue in those experiments.
The 2024 CK2 work added a second and more direct mechanism [2]. MOTS-c bound casein kinase 2 and activated it without any cellular machinery in between. The tissue specificity in that paper is the interesting part: systemically delivered MOTS-c bound CK2 in both fat and muscle, yet stimulated CK2 activity in muscle while suppressing it in fat, apparently by modifying different CK2 interacting proteins in each tissue. The same paper reported a naturally occurring variant, K14Q MOTS-c, that binds CK2 poorly and fails to activate it, and that variant did not produce the usual effects.
Into the nucleus
Lee’s follow up work described MOTS-c translocating to the nucleus under cellular stress and regulating nuclear gene expression directly [3]. Mitochondria have always been understood as recipients of nuclear instructions, since the proteins that run them are nuclear encoded. A mitochondrially encoded peptide that walks into the nucleus and changes transcription inverts that relationship. Whether this turns out to be a general mechanism or a one off is still open.
What was measured, and in what
Here are the specific endpoints from the main papers, in past tense, with the model attached. Treat anything that is not in this shape with suspicion.
| Study | Model | Measured endpoint |
|---|---|---|
| Lee 2015 [1] | Mice | Measured insulin sensitivity and body mass in aged mice and mice on a high fat diet |
| Reynolds 2021 [6] | Mice at 2, 12 and 22 months | Measured physical capacity at all three ages; exposure in the late-life arm began at 23.5 months, 3 times weekly |
| Reynolds 2021 [6] | Humans | Exercise induced endogenous MOTS-c expression in skeletal muscle and in circulation |
| von Walden 2021 [7] | 30 adults, randomized | MOTS-c showed a trend to rise after 45 minutes of cycling; resistance exercise did not move it |
| D’Souza 2020 [4] | Healthy men, 18 to 81 years | Plasma MOTS-c fell with age; muscle expression about 1.5 fold higher in older groups |
| Kumagai 2024 [2] | Mice plus human cohort | Prevented skeletal muscle atrophy and enhanced muscle glucose uptake, both blunted when CK2 was suppressed |
The von Walden result is the one we would flag to anyone building on this. Plasma levels of mitochondrial derived peptides were not correlated with maximal oxygen uptake, leg press strength or muscle mitochondrial measures [7]. Humanin responded more clearly than MOTS-c did. If you are treating circulating MOTS-c as a tidy readout of mitochondrial condition, that paper argues against it.
The genetics angle
Fuku and colleagues pointed out that the m.1382A>C polymorphism falls inside the MOTS-c coding sequence and is found specifically in Northeast Asian populations, and they raised it as a candidate contributor to the high life expectancy recorded in Japan [5]. That was framed as a hypothesis in a two page paper, not a demonstration, and we would read it that way. The K14Q variant from the CK2 paper is on firmer ground mechanistically, since the authors tied reduced CK2 binding to absent downstream effects in the same study [2].
Measuring and handling the peptide
MOTS-c is short, 16 residues, and made by standard solid phase synthesis, so identity and purity work is routine: reversed phase HPLC for purity, mass spectrometry to confirm the molecular mass matches the expected sequence. Reference standard practice for synthetic peptides leans on exactly this combination, with chromatography assigning content and impurity levels and mass spectrometry plus NMR confirming identity [8]. The thing to watch with any lyophilized peptide this small is not the headline purity figure but what the remaining percentage consists of, residual solvent, counterion and deletion sequences are not equivalent problems. Pull the certificate of analysis and look at the actual chromatogram, and our notes on third party tested material explain what a usable report contains.
Assay choice matters too. Plasma MOTS-c measurements in the literature come from immunoassays with their own cross reactivity caveats, and D’Souza’s group found plasma and muscle levels correlated only in the young group [4]. Two labs reporting different absolute concentrations are probably using different antibodies rather than studying different biology.
Reading the MOTS-c literature without getting burned
Three practical cautions, learned by reading these papers next to each other rather than one at a time.
First, cell free results and whole animal results are doing different jobs. CK2 activation was shown in a cell free system, which is strong evidence of a direct interaction and says nothing about what concentration reaches a tissue [2]. The folate cycle work was cellular [1]. Mixing the two levels into one tidy mechanism statement is how inaccurate summaries get written.
Second, almost every major paper on this peptide comes from a small number of connected groups, several with declared commercial interests in MOTS-c. That is normal for a young field and it is also a reason to want independent replication before treating any single number as settled.
Third, the human data is mostly observational. Age associations, polymorphism frequencies and exercise responses are correlations measured in modest sample sizes, the von Walden study randomized 30 people in total [7]. They are a reasonable starting point for designing an experiment and a poor basis for any firm conclusion.
Frequently asked questions
Is MOTS-c a hormone?
Some authors describe mitochondrial derived peptides that way because MOTS-c is detectable in circulation and acts on tissues other than the one that made it. It does not have a dedicated receptor on the record; the clearest direct target published so far is CK2 [2].
Why is MOTS-c measured in both plasma and muscle?
Because the two do not track each other. In healthy aging men, circulating levels fell with age while skeletal muscle expression rose, and the two compartments correlated only in young subjects [4].
How many mitochondrial derived peptides are known?
Humanin was first, MOTS-c followed, and the SHLP family has also been described. MOTS-c is the one with the most mechanistic work behind it so far [1][3].
References
- Lee C, Zeng J, Drew BG, et al. The mitochondrial-derived peptide MOTS-c […]. Cell Metab. 2015. PMID 25738459
- Kumagai H, Kim SJ, Miller B, et al. MOTS-c modulates skeletal muscle function by directly binding and activating CK2. iScience. 2024. PMID 39559755
- Lee C. Nuclear transcriptional regulation by mitochondrial-encoded MOTS-c. Mol Cell Oncol. 2019. PMID 31131297
- D’Souza RF, Woodhead JST, Hedges CP, et al. Increased expression of the mitochondrial derived peptide, MOTS-c, in skeletal muscle of healthy aging men is associated with myofiber composition. Aging (Albany NY). 2020. PMID 32182209
- Fuku N, Pareja-Galeano H, Zempo H, et al. The mitochondrial-derived peptide MOTS-c: a player in exceptional longevity? Aging Cell. 2015. PMID 26289118
- Reynolds JC, Lai RW, Woodhead JST, et al. MOTS-c is an exercise-induced mitochondrial-encoded regulator of age-dependent physical decline and muscle homeostasis. Nat Commun. 2021. PMID 33473109
- von Walden F, Fernandez-Gonzalo R, Norrbom J, et al. Acute endurance exercise stimulates circulating levels of mitochondrial-derived peptides in humans. J Appl Physiol. 2021. PMID 34351816
- McCarthy D, Han Y, Carrick K, et al. Reference Standards to Support Quality of Synthetic Peptide Therapeutics. Pharm Res. 2023. PMID 36949371
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