Humanin — Mitochondrial-Derived 24-Amino-Acid Peptide

Discovery

In 2001, Yoshiko Hashimoto and colleagues at Keio University in Tokyo published a landmark paper describing a previously unknown peptide recovered from neurons that had survived the neurodegeneration of Alzheimer's disease [PMID:11371638]. The researchers screened a cDNA library constructed from the surviving cells of postmortem Alzheimer's brains, searching for sequences capable of blocking the toxic effect of amyloid-beta on cultured neurons. One clone stood out: a reading frame buried inside the mitochondrial 16S ribosomal RNA gene that encoded a short, 24-amino-acid peptide they named Humanin.

The name itself reflected the discovery context — a human-specific rescue signal found only in cells that had, against the odds, survived a profoundly hostile environment. Subsequent sequencing confirmed that the open reading frame responsible sits within the mitochondrial genome, making Humanin the founding member of a family now called mitochondrial-derived peptides (MDPs). Contemporaneous work demonstrated that the peptide was not merely an artefact of the cDNA library: Humanin mRNA and protein could be detected in multiple human tissues, with particularly notable expression in brain, heart, and testis.

The discovery attracted immediate attention because it inverted a prevailing assumption — that mitochondrial DNA existed solely to encode components of the oxidative phosphorylation apparatus. Humanin established that the mitochondrial genome harbours biologically active signalling peptides capable of crossing cellular compartments and exerting systemic effects. This insight seeded an entire sub-field and eventually led to the identification of related peptides including MOTS-c, SHLP1-6, and others now grouped under the MDP umbrella.

Mechanism of Action

Humanin operates through at least three distinct but interacting pathways, which together explain its broad cytoprotective profile.

FPRL1/FPR3 receptor engagement. Humanin binds and activates formyl peptide receptor-like 1 (FPRL1, now redesignated FPR3 in revised nomenclature), a G-protein-coupled receptor expressed on neurons, monocytes, cardiomyocytes, and vascular endothelium. Receptor engagement initiates downstream ERK1/2 and Akt phosphorylation cascades that promote cell survival and suppress inflammatory cytokine release. The FPRL1 interaction is considered the primary extracellular signalling route and accounts for much of Humanin's neuroprotective activity in amyloid-beta-challenge models.

Bax suppression and mitochondrial apoptosis blockade. Intracellularly, Humanin physically associates with Bax, a pro-apoptotic Bcl-2 family member that normally oligomerises at the outer mitochondrial membrane to trigger cytochrome c release. By binding Bax and preventing its translocation, Humanin blocks the intrinsic apoptotic cascade at an early, reversible checkpoint. This mechanism is independent of FPRL1 and operates even in cells with surface receptor knockdown, confirming a direct intracellular role.

STAT3 and mitochondrial signalling. A third pathway involves mitochondrial STAT3 (mitoSTAT3), a transcription factor isoform that localises to the inner mitochondrial membrane and modulates electron transport chain activity. Humanin promotes STAT3 phosphorylation at Ser727, stabilising complex I and II activity, reducing reactive oxygen species leak, and maintaining membrane potential under hypoxic or metabolic stress. Separately, Humanin activates the mitochondrial unfolded protein response (UPRmt) through MUPR signalling, upregulating chaperones such as HSP60 and ClpP to restore proteostasis in stressed organelles.

Together these pathways confer a layered cytoprotective effect: extracellular receptor activation attenuates inflammatory signalling, intracellular Bax sequestration prevents committed cell death, and mitochondrial STAT3 and UPRmt engagement preserves bioenergetic capacity.

Researched Applications

Neurodegeneration and Alzheimer's models. The original discovery context has remained the most studied application. Multiple in vitro and rodent in vivo experiments confirm that Humanin and its more potent analogue HNG (Gly14-Humanin, with a serine-to-glycine substitution that increases potency approximately one-thousand-fold) suppress amyloid-beta-induced neuronal apoptosis, reduce tau hyperphosphorylation in tangle models, and improve spatial memory in transgenic Alzheimer's mice. Human observational data show that cerebrospinal fluid Humanin concentrations are lower in Alzheimer's patients than in age-matched cognitively intact controls, though causality remains unestablished.

Cardioprotection and ischaemia-reperfusion injury. Pre-treatment with Humanin before experimental myocardial ischaemia-reperfusion reduces infarct size, preserves left ventricular ejection fraction, and attenuates cardiomyocyte apoptosis in rodent models. The mechanism is attributed primarily to FPRL1 activation and mitoSTAT3-mediated preservation of electron transport chain integrity during the reperfusion phase, when reactive oxygen species generation peaks. These findings have prompted interest in peri-operative or acute-coronary applications, though no human clinical trials have been conducted.

Insulin sensitivity and metabolic regulation. Humanin acts as an endocrine-like signal with documented insulin-sensitising properties. Intraperitoneal Humanin reduces hepatic glucose output, improves peripheral glucose uptake in high-fat-diet mice, and synergises with insulin at the receptor level. The Lee laboratory has characterised a Humanin–MOTS-c axis in which the two mitochondrial peptides act cooperatively to regulate AMP-activated protein kinase (AMPK) activity and mitochondrial fatty-acid oxidation, suggesting that declining MDP levels with age may contribute to the deterioration of metabolic flexibility observed in older individuals [PMID:31747572].

Age-related decline. Circulating Humanin concentrations decrease progressively across the human lifespan. Cross-sectional studies in centenarian offspring — individuals with exceptional parental longevity — show significantly higher plasma Humanin compared to age-matched controls without a family longevity history, raising the hypothesis that sustained Humanin production may be one mechanism through which exceptional longevity is inherited. Conversely, conditions associated with accelerated ageing such as HIV treatment with nucleoside-analogue reverse transcriptase inhibitors also suppress Humanin levels, consistent with mitochondrial toxicity as a driver of premature MDP decline.

Dosing (Research Context Only)

Published small-scale protocols and research-grade exploratory use have employed doses in the range of five to ten micrograms per kilogram of bodyweight administered subcutaneously every other day, which for a seventy-kilogram individual corresponds to approximately 350 to 700 micrograms per injection. Some protocols extend to a twelve-week cycle before a four-to-six-week washout. The more potent synthetic analogue HNG is typically used at substantially lower absolute doses due to its markedly greater receptor affinity.

No consensus dosing exists. All quantities above are drawn from preclinical literature and informal research reports, not from controlled human trials. Any practical application is the sole responsibility of the supervising investigator and their ethics oversight body.

Safety and Tolerability

No formal human safety trials have been conducted. Animal studies at doses relevant to preclinical efficacy have not identified acute organ toxicity or haematological abnormalities. Given that Humanin appears to inhibit Bax-mediated apoptosis, a theoretical concern exists around whether sustained administration could impair normal apoptotic clearance of damaged or pre-malignant cells; this has not been observed in reported animal studies but cannot be ruled out in longer-duration human exposure. Local injection-site reactions (erythema, transient nodule formation) are the most commonly reported adverse events in informal research settings. Humanin should not be co-administered with agents that already maximally suppress apoptosis without careful monitoring of cellular proliferation markers.

UK Regulatory Status

Humanin is not approved by the Medicines and Healthcare products Regulatory Agency (MHRA) for any therapeutic indication. It is not listed as a controlled substance under the Misuse of Drugs Act 1971 or its subsequent amendments. However, because it exerts pharmacological effects, any preparation supplied for administration to humans would constitute an unlicensed medicinal product under the Human Medicines Regulations 2012 (SI 2012/1916). Supply or administration outside a licensed clinical trial framework would therefore carry regulatory risk. Possession of research-grade material for in vitro or animal research is not subject to the same restrictions, provided it is not sold or supplied for human use.

Reconstitution

Lyophilised Humanin powder is typically supplied in quantities of one to five milligrams per vial. Reconstitution should be performed under aseptic conditions using bacteriostatic water for injection or sterile normal saline. Add diluent slowly against the vial wall — do not vortex. A common working concentration is 0.5 mg/mL, achieved by adding one millilitre of diluent to a 0.5 mg vial. Once reconstituted, store at two to eight degrees Celsius and use within fourteen days; do not freeze reconstituted peptide as freeze-thaw cycles degrade the cysteine-containing backbone. Protect from light. Filter through a 0.22-micron syringe filter before injection.

Frequently Asked Questions

Is Humanin the same as HNG? No. HNG (Gly14-Humanin) is a synthetic analogue with a single amino-acid substitution (Ser14→Gly) that confers approximately one-thousand-fold greater bioactivity in Bax-suppression assays. Most recent in vivo preclinical work uses HNG rather than native Humanin because effective doses are correspondingly smaller.

How is Humanin different from MOTS-c? Both are mitochondrial-derived peptides encoded in the mitochondrial genome, but they act through different receptors and tissues. MOTS-c is a 16-amino-acid peptide that translocates to the nucleus under metabolic stress to regulate AMPK and nuclear gene expression, with particular effects on skeletal muscle glucose uptake. Humanin acts primarily at FPRL1 and intracellularly at Bax and mitoSTAT3, with stronger neuroprotective and cardioprotective profiles. The two peptides are increasingly studied together as part of an integrated mitochondrial signalling axis.

Why do plasma levels fall with age? The precise mechanism is not fully understood. Current hypotheses centre on age-related accumulation of mitochondrial DNA mutations and deletion events that progressively impair transcription of the 16S rRNA reading frame, combined with reduced mitochondrial biogenesis signalling as SIRT1 and PGC-1alpha activity decline. Caloric restriction and exercise, both of which stimulate mitochondrial biogenesis, have been associated with attenuation of age-related Humanin decline in animal models.

Is there any human trial data? As of mid-2026, no peer-reviewed randomised controlled trial in humans has been published. Small open-label observational reports exist in the grey literature. Several preclinical programmes have reached IND-enabling studies, but no Phase I result has entered the public domain.

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Related stacks:

• Epitalon + Humanin + MOTS-c Longevity Stack
• SS-31 + Humanin Mitochondrial Stack

Source research-grade Humanin

Humanin — Mitochondrial-Derived 24-Amino-Acid Peptide is sold for laboratory and in vitro research use only. UK regulatory status: Unapproved research compound globally. Laboratory and in vitro use only..

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