what is MOTS-c?

For decades the mitochondrial genome was taught as a small, austere thing. About 16.5 kilobases, circular, 37 genes: 13 protein-coding genes for the electron transport chain, 22 transfer RNAs, and 2 ribosomal RNAs (called 12S and 16S). The 2 rRNAs sit inside the mitochondrial ribosome; their job is structural and catalytic, not informational. They are not supposed to code for protein.

In 2015 Changhan Lee and colleagues looked at the 12S rRNA gene, called MT-RNR1, and noticed something other people had ignored: nested inside the rRNA sequence was a short open reading frame -- a stretch of nucleotides that could in principle be read as a protein. They synthesized the predicted peptide, injected it into mice, raised antibodies against it, and showed it was real, circulating, and biologically active. They named it MOTS-c, for mitochondrial open reading frame of the 12S rRNA type-c (Lee 2015).

The 16-residue peptide turned out to do something striking. In high-fat-diet mice, MOTS-c treatment improved insulin sensitivity and metabolic flexibility. The mechanistic chain Lee proposed ran through one-carbon metabolism: MOTS-c perturbed folate-cycle flux, accumulated an intermediate called AICAR, and AICAR turned on the master cellular energy sensor AMPK. This is the same general direction metformin works -- but driven by a peptide that the mitochondrial genome itself encodes.

Before 2001, the textbook count of bioactive molecules coming out of the mitochondrial genome was zero. The genome was understood to encode 13 inner-membrane proteins that build the cellular power plant, plus the RNA hardware (22 tRNAs, 2 rRNAs) needed to translate those 13. Nothing exported. Nothing hormonal. Nothing that talks to other cells.

That count is now at least eight. Three discoveries built the field, each one expanding the role the mitochondrial genome plays in cell-to-cell communication.

The point is no longer "look at this oddity." The point is that the mitochondrial ribosomal RNA genes are now known peptide-coding genes too, on top of their original day jobs as ribosome hardware.

For most of the history of cell biology, mitochondria were treated as energy converters: power plants that burn fuel, make ATP, throw off some reactive oxygen species as a side effect, and trigger apoptosis when they fail. MOTS-c made that picture too small.

That single fact reshapes downstream thinking. If the mitochondrial genome encodes peptide signals, then mitochondrial state -- how stressed your mitochondria are, what fuel they are burning, whether they are healthy or damaged -- becomes a signal the rest of the cell can read. That is a different model of metabolism than the one in most undergraduate textbooks, and it is the model the next nine units of this course are built on.

Section S4.5.2 is WADA's bucket for metabolic modulators and AMPK activators. It already captured AICAR, GW1516, and SR9009 -- compounds from earlier doping cases. The 2026 update adds MOTS-c by name. The category is banned at all times under WADA-aligned testing programs, in-competition and out, with no therapeutic-use exemption pathway for AMPK activators of this class.

The reason MOTS-c made the list is the mechanism this course is about: it activates AMPK. AMPK activation is the cellular signature exercise produces, so any compound that flips that switch on its own is treated by sport-regulatory bodies as a potential performance enhancer. The Reynolds 2021 Nature Communications paper -- treated old mice running farther on a treadmill -- is exactly the kind of data that triggers the listing logic (Reynolds 2021).

In the United States, the FDA places MOTS-c in Category 2 bulk drug substances under its compounding policy, meaning it has been flagged as raising significant safety concerns for compounding evaluation. This is not an approval and not a ban; it is a regulatory signal that the agency does not consider it appropriate to compound from bulk material without further evaluation. Together the WADA listing and the FDA compounding category form the real regulatory boundary any honest course on MOTS-c has to surface.

The next nine units take this unit's overview and go much deeper -- each one earning the "mastery" label by a different kind of depth.

By the end you will be able to read a paper, a Reddit post, or a vendor page about MOTS-c and immediately tell which claims have evidence behind them, which are extrapolated from rodent studies, and which are pure marketing.