MOTS-c: A Mitochondrially Encoded Peptide, Its AMPK Route and Its Oxidation Risk

Rather than the nuclear genome, it is mitochondrial DNA — specifically the 12S ribosomal RNA region — that encodes MOTS-c, a peptide of 16 amino acids belonging to the small family known as mitochondrial-derived peptides. The name, mitochondrial open reading frame of the twelve S rRNA type-c, simply records where the reading frame is located. Since its description in 2015 it has been studied as a signalling molecule that exits the mitochondrion, acts upon cytosolic metabolic pathways and, when the cell is under metabolic stress, reportedly enters the nucleus and shapes transcription. That final property is what marks it out: a peptide from the organelle's own genome, signalling backward to the cell that contains it.

We supply MOTS-c as lyophilized powder in 10 mg, 20 mg and 40 mg vials, within the mitochondrial peptides range.

Defining MOTS-c

At roughly 16.5 kilobases, the circular human mitochondrial genome was long thought to encode just 13 respiratory chain proteins along with the RNA machinery needed to produce them. Mitochondrial-derived peptides come from short open reading frames sitting inside the ribosomal RNA genes of that circle, and this one was the first found in the 12S rRNA region. The sequence reads Met-Arg-Trp-Gln-Glu-Met-Gly-Tyr-Ile-Phe-Tyr-Pro-Arg-Lys-Leu-Arg; its CAS number is 1627580-64-6, its formula C101H152N28O22S2 and its molecular weight 2,174.55 g/mol.

Before any experiment, note two chemical characteristics. The chain includes two methionine residues, whose side chains oxidise more readily than anything else in peptide chemistry, and a tryptophan that is sensitive to light. Both matter directly for storage and for interpreting a certificate that falls out of specification.

Origin and structure

A University of Southern California group described MOTS-c in 2015, extending the same team's earlier work on the peptide humanin. Their approach was computational to begin with: scan mitochondrial rRNA genes for open reading frames, then verify that the predicted peptides really are produced and can be detected in tissue and in plasma.

A mitochondrial reading frame means translation can occur on mitochondrial ribosomes, which read a genetic code slightly different from the cytosolic one. The peptide itself is short, unstructured and markedly basic — three arginines plus a lysine among sixteen residues — and that distribution of charge is believed to help it traverse membranes and bind nucleic acid.

One genetic finding has sustained interest. Within the MOTS-c reading frame, the variant m.1382A>C replaces lysine 14 with glutamine; it was reported to occur more often in long-lived Japanese cohorts, and cell assays show the variant peptide behaving unlike the reference sequence. That is population genetics plus work in cell systems, not causal proof.

The proposed mechanism

As first reported, the mechanism operates through the folate–methionine one-carbon pathway. The peptide was described as inhibiting steps in that pathway so that the intermediate known as AICAR accumulates; AICAR activates AMPK endogenously, AMPK being the cell's main sensor of low energy. Literature associates AMPK activation with greater glucose uptake, more fatty-acid oxidation and suppressed anabolic pathways, and most metabolic observations reported for this peptide align with that route.

A second arm, described later, is nuclear. Under metabolic stress — glucose restriction or oxidative challenge in the models reported — the peptide has been described moving out of the cytosol into the nucleus, where it associates with stress-response transcription factors and regulates genes carrying antioxidant response elements. That casts it as a retrograde signal conveying mitochondrial status to the nuclear genome, a mechanistically separate claim from AMPK activation and supported by a thinner evidence base.

No cell-surface receptor has been definitively identified, which is the outstanding question about its mechanism and a departure from the growth-factor and secretagogue families, where receptor identity is long settled.

What has been studied

Metabolic and insulin-sensitivity models

In the founding rodent study, giving the peptide to mice on a high-fat diet was reported to limit diet-induced weight gain and to improve insulin sensitivity as assessed by clamp and tolerance testing. Later rodent studies examining glucose handling in liver and skeletal muscle have pointed broadly the same way. All of it is preclinical animal work.

Exercise physiology

Human work here observes rather than intervenes: circulating MOTS-c has been reported to increase in skeletal muscle and plasma after acute exercise, and to differ between trained and untrained participants. Such data describe the endogenous peptide as a biomarker; they are not studies of peptide given to people.

Ageing and cellular stress

Cell models and aged rodents have been used to examine how well mitochondria function, markers of oxidative stress and measures of physical performance, and the longevity-cohort genetics mentioned above belong to this strand.

Bone, immune and other tissue models

Smaller literatures cover osteoblast differentiation, inflammatory signalling and endothelial function, largely exploratory and mostly from single groups.

What remains unestablished

No controlled human trial of administered MOTS-c has been completed, and no product is approved. MOTS-c vs the tetrapeptide SS-31 lays out the comparison with the other well-studied mitochondrial peptides, and the mitochondrial peptide renaissance gives the wider context.

Presentations available

Three sizes exist because the quantity a cell-culture series needs differs greatly from what an animal study consumes. There is also an oral capsule presentation, MOTS-c Oral Capsules, for research settings where an injectable format does not suit the design. Sourcing checks appear in our MOTS-c buying guide.

Reconstitution and storage at the bench

The peptide goes into bacteriostatic or plain sterile water and into aqueous buffers without trouble, its basic residues making solubility easy. Direct the solvent down the vial wall onto the cake and swirl the vial instead of shaking it.

Here is the laboratory arithmetic: 2 mL of diluent added to a 10 mg vial produces 5 mg/mL, that is 5,000 mcg/mL, so 0.1 mL — ten units on a U-100 syringe — holds 500 mcg. Using 5 mL instead yields 2 mg/mL from the same vial, or 200 mcg per 0.1 mL. In molar terms, at 2,174.55 g/mol, 1 mg is roughly 0.46 µmol. Our reconstitution guide gives the method.

Because of those two methionines and the tryptophan, storage warrants more care than an average peptide needs. Keep lyophilized vials sealed at −20 °C, away from light and moisture; hold reconstituted material at 2–8 °C through the study window, aliquot and freeze it for longer programmes, and keep it dark throughout. Oxidised peptide still presents as a clear solution, so looking at the vial tells you nothing. Broader guidance is in how to store peptides.

Purity, the COA and how to read it

Identity is confirmed by a mass spectrometric measurement agreeing with 2,174.55 g/mol. For this particular sequence, the numbers to watch are +16 Da and +32 Da: each marks an oxygen added at a methionine, and their appearance signals oxidation during synthesis, purification or storage rather than a failed synthesis. A properly handled lot shows a clean parent mass with no such satellites. Oxidised peptide usually elutes slightly ahead of the parent on the HPLC trace, so an early shoulder on an otherwise tidy chromatogram says the same thing. Purity percentage, counter-ion and lot number round out the document; the rest is covered in our guide to reading a peptide certificate of analysis.

Regulatory position

Nowhere does MOTS-c hold a marketing authorisation as a medicine; there is no reference-listed product, no approved labelling, and it is not a dietary supplement. In no form does an approved use exist for it.

Related peptides and further reading

Two other molecules in this space are well characterised: Humanin, a 24-residue mitochondrial-derived peptide from the 16S rRNA region, and SS-31 (Elamipretide), which is not mitochondrially encoded at all but a synthetic tetrapeptide built to concentrate at the inner membrane.