Mitochondria are usually introduced in school as "the powerhouse of the cell" and then forgotten. In the last decade they have become one of the busiest areas in biology, and a small group of peptides sits right at the centre of that research. This guide covers what mitochondria do, why their condition matters so much to scientists, and which peptides are studied in the field.
The short answer
Mitochondria turn food and oxygen into the energy every cell runs on. When they work well, cells have the power they need. When they wear down, cells struggle, and that decline is linked to ageing and to a range of inherited diseases. A few peptides are studied because they interact with mitochondria directly, and one of them became an approved drug in 2025.
What mitochondria are
Almost every cell in the human body contains mitochondria, from a handful to several thousand depending on how much energy the cell needs. Heart and muscle cells are packed with them.
Think of each cell as a small town and the mitochondria as its power plants. They take in fuel (broken-down sugars and fats) and oxygen, and they produce a molecule called ATP, the cell's spendable energy. Nearly everything a cell does, from contracting a muscle to firing a nerve, is paid for in ATP.
Two details make mitochondria unusual.
They have their own DNA. Mitochondria are thought to descend from free-living bacteria that were absorbed by larger cells some two billion years ago. They still carry a small genome of their own, separate from the DNA in the cell's nucleus. That detail turns out to matter for one of the peptides below.
They are more than power plants. Mitochondria also act as sensors and messengers. They help decide when a damaged cell should self-destruct, they influence inflammation, and they send signals back to the nucleus about the cell's energy state.
Why their condition matters
A power plant produces exhaust. When mitochondria make energy, a small fraction of the process leaks out as reactive molecules, often called free radicals or reactive oxygen species. In small amounts these act as useful signals. In larger amounts they damage nearby structures, including the mitochondria themselves.
Over time, in many research models, mitochondria tend to become less efficient: they produce less ATP, leak more, and are cleared and replaced less effectively. That pattern shows up in studies of ageing tissue, and it is why mitochondrial function is one of the recognised "hallmarks of ageing" in the scientific literature.
Mitochondrial problems are also the direct cause of a group of rare inherited conditions, known as primary mitochondrial diseases, where a genetic fault disrupts how the power plants are built or run. These conditions have driven much of the serious drug development in the field.
The peptides studied in mitochondrial research
Three peptides come up most often. They are very different from each other, and their evidence ranges from an approved drug to early laboratory work.
SS-31 (elamipretide)
What it is: a synthetic peptide of just four amino acids, designed in the early 2000s by researchers Hazel Szeto and Peter Schiller (the "SS" in its name). Two of its four building blocks are modified forms that do not occur in ordinary proteins.
What it does in research: SS-31 travels to the inner membrane of mitochondria and binds to cardiolipin, a fat molecule that acts like scaffolding for the energy-producing machinery. By binding there, it helps hold that machinery in its working shape.
Evidence: in September 2025 the FDA granted accelerated approval to elamipretide, sold as FORZINITY, for Barth syndrome, a very rare inherited disease in which cardiolipin is abnormal. It was the first FDA approval for that condition. Trials in other mitochondrial diseases continue, and some earlier trials did not meet their main goals. Evidence tier: A for the approved indication.
MOTS-c
What it is: a natural peptide of sixteen amino acids, discovered in 2015 at the University of Southern California. Unusually, its code is stored in the mitochondria's own DNA rather than in the nucleus. It is one of a small family called mitochondrial-derived peptides.
What it does in research: MOTS-c acts as a messenger. In cell and animal studies it activates AMPK, a sensor that works like the cell's fuel gauge, and under stress it can travel into the nucleus and influence which genes are switched on.
Evidence: mostly cell and animal studies. In people, observational research has found circulating levels rise during exercise. Controlled human trials have not been published. Evidence tier: D.
Humanin
What it is: the first mitochondrial-derived peptide ever identified, discovered in 2001. Like MOTS-c, its code sits in the mitochondrial genome.
What it does in research: humanin has been studied mainly for its protective role, helping cells resist signals that would otherwise trigger self-destruction. Measured levels in human blood tend to be lower in older age groups.
Evidence: cell and animal studies, plus observational human data. Evidence tier: D.
A note on NAD+
NAD+ is often mentioned in the same breath as mitochondrial peptides. It is not a peptide. It is a small helper molecule that mitochondria use in energy production. It belongs in the conversation about mitochondria, but it works differently from any compound above.
The takeaway
Mitochondria sit underneath almost everything a cell does, which is why their condition is central to research on ageing and inherited disease. The peptides studied in the field are not interchangeable. SS-31 is a designed molecule that reinforces the power plant's structure and has become an approved drug for one rare disease. MOTS-c and humanin are the body's own messengers, still in the early, fascinating stage of research. For a closer comparison of the two most discussed, see MOTS-c vs SS-31.
Frequently asked questions
Why is mitochondrial health important?
Mitochondria produce ATP, the energy almost every cell runs on, and they also help regulate cell survival and inflammation. Declining mitochondrial function is a recognised hallmark of ageing in research, and genetic mitochondrial faults cause a group of rare inherited diseases.
What are mitochondrial peptides?
The term covers two groups: peptides encoded by the mitochondria's own DNA, such as MOTS-c and humanin, and peptides designed to act on mitochondria, such as SS-31.
Is SS-31 FDA approved?
Yes, for one condition. In September 2025 the FDA granted accelerated approval to elamipretide (FORZINITY) for Barth syndrome, a rare inherited mitochondrial disease. It is not approved for any other use.
Do mitochondria have their own DNA?
Yes. Mitochondria carry a small genome separate from the DNA in the cell nucleus, inherited from the bacteria they are thought to have descended from. MOTS-c and humanin are both encoded there.
Is NAD+ a peptide?
No. NAD+ is a small helper molecule (a coenzyme) used in energy production. It is often discussed alongside mitochondrial peptides but is a different kind of compound.