Mitochondrial-Derived Peptides: Humanin, MOTS-c, SHLPs and the MDP Class

A hidden layer inside the mitochondrial genome

For decades, biology textbooks framed the mitochondrion as the cell's "powerhouse" and stopped there: an organelle with its own small circular genome coding for just 13 proteins, all of them parts of the energy-generating machinery. That tidy picture turned out to be incomplete. Tucked inside the same mitochondrial DNA is a second, far smaller class of proteins — the mitochondrial-derived peptides, or MDPs. Everything discussed here concerns material sold and studied for research use only, and nothing below is a recommendation for human or animal use.

If you're researching this family of compounds, the MDPs are one of the genuinely novel corners of cell-signaling and longevity science. This article walks through what the class is, its three named members — humanin, MOTS-c, and the six small humanin-like peptides (SHLPs) — what cell-culture and animal studies have observed, and the open questions that keep the field busy.

What mitochondrial-derived peptides are

Put simply: MDPs are tiny proteins written into mitochondrial DNA that seem to act as signaling molecules, not as parts of the energy machinery. They're encoded by small open reading frames (sORFs) — short stretches of code, roughly 9 to 40 amino acids long — that sit inside the mitochondrial ribosomal RNA genes, separate from the 13 canonical proteins of oxidative phosphorylation (Miller et al., genomic and therapeutic implications of small mitochondrial ORFs).

The characterized class currently stands at eight peptides: humanin, MOTS-c, and SHLP1 through SHLP6 (Kim et al., MDPs in aging and healthspan). Their genetic addresses differ in a useful way. MOTS-c is encoded within the 12S ribosomal RNA gene (MT-RNR1), while humanin and all six SHLPs come from the neighboring 16S ribosomal RNA gene (MT-RNR2) (PMC7778388).

What makes the class conceptually interesting is retrograde signaling — the idea that mitochondria talk back to the nucleus rather than only taking orders from it. Several MDPs appear to carry status messages out of the mitochondrion and into the wider cell, and in some cases into the nucleus itself (PMC9057581). Seen that way, the MDPs join a long list of endogenous signaling-peptide families the body already runs on — much like the natriuretic peptide family or the other endogenous peptide families — except these are written into the mitochondrial genome instead of the nuclear one.

Humanin: the first mitochondrial-derived peptide

Humanin was the discovery that opened the whole field. It's a 24-amino-acid peptide identified in the early 2000s by three independent research groups, originally from brain tissue in Alzheimer's disease research (PMC7778388). Its first-noticed property was cytoprotection. In neuronal cell-culture models, humanin blunted the toxicity of amyloid-beta, the protein fragment at the center of Alzheimer's pathology (PMC9057581).

Receptors and signaling

Humanin works through cell-surface receptors. In research models it binds a trimeric receptor built from gp130, WSX-1, and CNTFR, plus the FPRL1 receptor, switching on downstream STAT3 and ERK1/2 pathways that feed into cell-survival and mitochondrial-maintenance programs (PMC7778388). Those are the same broad channels many growth-factor and cytokine systems use — part of why humanin drew such early interest.

What research models show

The aging associations are striking on paper. Circulating humanin declines with age in both mice and human plasma, and researchers have measured notably higher levels in the offspring of centenarians than in age-matched peers without exceptional-longevity family histories (PMC9057581). In the worm C. elegans, overexpressing humanin lengthened lifespan in a way that hinged on the FOXO longevity pathway. The register matters here, though: these are observations in cell cultures and model organisms, not outcomes in people. Research-grade humanin is also not equivalent to any FDA-approved pharmaceutical product.

MOTS-c: the exercise-mimetic peptide

If humanin is the neuroprotection story, MOTS-c is the metabolism story. It's a shorter 16-amino-acid peptide encoded in the 12S rRNA gene, and the literature describes it as an "exercise mimetic" — a molecule that reproduces some of the cellular signals normally triggered by physical activity (PMC9057581). The mechanism has two nice hooks. MOTS-c activates AMPK, the cell's master fuel-sensing enzyme, and it can travel from the mitochondrion into the nucleus, where it binds transcription factors that regulate metabolism-related genes — retrograde signaling made literal (PMC7778388).

Metabolic findings in models

Animal studies have turned up broad metabolic effects. In mice on a high-fat diet, MOTS-c limited weight gain, improved insulin sensitivity, and increased exercise capacity in both obese and older animals (Merry et al., antidiabetic functions and evolutionary perspectives). In one model it improved insulin sensitivity by raising the glucose infusion rate roughly 30%, apparently by helping shuttle the GLUT4 glucose transporter to the cell membrane. Circulating MOTS-c also tracks metabolic health in the direction you'd hope: its levels correlate negatively with body-mass index, fasting insulin, and insulin-resistance scores (PMC9057581). That puts MOTS-c in the same research conversation as other metabolism-adjacent signaling families, including the growth hormone secretagogue class.

A telling natural variant

Genetics adds a sharp footnote. A naturally occurring MOTS-c variant called K14Q (from the SNP rs111033358) swaps a single amino acid — and that one swap leaves the peptide biologically inactive. In population studies, the inactive variant is associated with higher type 2 diabetes risk in Asian and specifically Japanese populations (PMC9057581). It reads like an elegant natural experiment: switch off the peptide's activity through evolution, and a metabolic-disease signal surfaces.

The SHLP family and what cell-culture studies show

Rounding out the class are the six small humanin-like peptides, SHLP1 through SHLP6 — all encoded in the 16S rRNA gene, all sharing structural features with humanin. Their effects look tissue-specific rather than uniform. SHLP2 and SHLP3 are the standouts in cell and animal work: applying them promoted mitochondrial biogenesis, raised oxygen consumption and ATP output, and lowered both reactive oxygen species and oxidative damage to mitochondrial DNA (PMC9057581). SHLP2 also behaves like a molecular chaperone, and lower circulating SHLP2 has been linked with elevated prostate-cancer risk; like humanin, it declines with age in mice (PMC7778388).

A concrete in-vitro example

A 2025 study on human skeletal-muscle cells makes the observed-in-research framing concrete. Researchers grew myotubes from young donors' tissue, exposed them to dexamethasone — a glucocorticoid that drives muscle-wasting — at a 10 µM concentration in the culture medium, then tested MOTS-c and a stabilized humanin analog (S14G-humanin) alongside it (Gatti et al., MDPs and dexamethasone-induced atrophy in human muscle cells). MOTS-c fully preserved myotube size and fusion capacity, blunting the atrophy gene MURF1, damping STAT3 activation, and raising phosphorylated Akt — a combination the authors read as both anti-catabolic and pro-anabolic. The humanin analog gave partial protection for cell size, working mainly through STAT3. One detail stood out: the human cells behaved differently from rodent models on a key marker, a reminder of why human-cell studies matter and why animal findings don't transfer automatically.

Evolution and genetic variation across the class

Not every named MDP looks equally "real" under evolutionary scrutiny — and that's a useful filter. Researchers examined synonymous codon bias, a statistical fingerprint of natural selection, across vertebrate species. Humanin and SHLP6 came out strongly conserved: humanin with p-values below 0.001 across vertebrate alignments, and SHLP6 with invariant start and stop codons — both hallmarks of a sequence evolution has worked to keep (Miller et al., natural selection in humanin and SHLP6). SHLP1, SHLP2, SHLP3, and SHLP5, by contrast, showed poor conservation and no codon-bias signal, hinting they may be more recent or less essential.

There's an important caveat baked into the genetics. Because these peptides are nested inside ribosomal RNA genes, apparent conservation could reflect the importance of the peptide or simply the importance of the underlying rRNA — the two are hard to separate (PMC10465549). The same analysis flagged a previously unrecognized peptide, tentatively SHLP2b, sitting upstream of SHLP2 with strong codon bias, plus a highly conserved five-residue stretch (MGYIF) inside MOTS-c (PMC10838678). The map of this class is clearly still being drawn.

The metabolic and aging research picture

Step back, and a theme snaps into focus: the best-studied MDPs sit right at the intersection of mitochondrial status and whole-body metabolism. In research models, MOTS-c, humanin, and SHLP2 each improved insulin sensitivity and glucose handling through overlapping routes — AMPK activation, better GLUT4 trafficking, signaling that reaches the central nervous system — and their circulating levels fall in obesity, insulin resistance, and type 2 diabetes (PMC10838678).

That's why longevity and metabolism researchers treat the MDPs as a candidate regulatory layer: molecules that report on mitochondrial health and, in the process, help tune metabolism across tissues. It sets them alongside better-known metabolic-peptide research, such as the incretin peptide class, even though the MDPs come from an entirely different part of the genome. The honest summary: the associations are consistent and mechanistically plausible, while the human evidence is still early.

Frequently Asked Questions

What are mitochondrial-derived peptides?

Mitochondrial-derived peptides (MDPs) are small bioactive microproteins encoded by short open reading frames inside mitochondrial DNA, separate from the 13 large proteins the mitochondrion makes for oxidative phosphorylation. The characterized class includes humanin, MOTS-c, and the six small humanin-like peptides (SHLP1-6).

How many mitochondrial-derived peptides are there?

Eight MDPs have been characterized so far: humanin, MOTS-c, and SHLP1 through SHLP6. MOTS-c is encoded within the 12S rRNA gene, while humanin and the SHLPs are encoded within the 16S rRNA gene. Researchers believe many more putative MDPs remain uncharacterized in the mitochondrial genome.

What is the difference between humanin and MOTS-c?

Humanin is a 24-amino-acid peptide first studied for cytoprotection against Alzheimer's-related neurotoxicity, and it signals through the gp130/WSX-1/CNTFR receptors. MOTS-c is a shorter 16-amino-acid peptide studied as an exercise mimetic that activates AMPK and moves to the nucleus to influence metabolism-related gene expression.

Are mitochondrial-derived peptides approved for human use?

No. Humanin, MOTS-c, and the SHLPs are studied in cell-culture and animal models and are not FDA-approved for any use. Research-grade material is sold for laboratory research only and is not equivalent to any approved pharmaceutical product.

The bottom line

The mitochondrial-derived peptides are a real, still-expanding signaling layer hidden in the mitochondrial genome. Humanin and MOTS-c are the best-characterized members — one rooted in neuroprotection research, the other in metabolism — while SHLP6 looks like the most evolutionarily conserved of the six SHLPs. Most of what we know comes from cell-culture and animal studies, with human data only beginning to accumulate. And with hundreds of putative MDPs still uncharacterized in the mitochondrial genome, the most interesting members of this class may not have been described yet. For readers following peptide science, the MDPs are a frontier worth watching — and a good reason to keep exploring the related class explainers linked throughout this article.

For research use only. Not for human or animal consumption of any kind. The information in this article is for educational purposes only and is not intended to diagnose, treat, cure, or prevent any disease. The statements made have not been evaluated by the U.S. Food and Drug Administration. These products are NOT FDA APPROVED. Please consult with a licensed healthcare professional before making any decisions regarding your health or research.

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