Humanin

Overview

Humanin is a small peptide made directly by the mitochondria, the energy centres of our cells. It is encoded in the mitochondrial DNA, inside the 16S ribosomal RNA gene (MT-RNR2). The discovery was unexpected: mitochondrial DNA had long been assumed to encode only the building blocks of energy production. Humanin showed that mitochondria also produce signalling molecules that talk to the rest of the cell. It was the first known mitochondria-derived peptide (MDP).

Humanin exists in two natural forms. Translated inside the mitochondria, it is 21 amino acids long; translated in the cytoplasm, it is 24. Both are biologically active. The form most commonly used in research, and the one described here, is the 24-amino-acid variant.

In preclinical research, Humanin has been studied primarily in the context of cell survival under stress, neuronal protection, and metabolic regulation. It appears to act through several receptor systems, including FPRL1 and a receptor complex that engages the JAK2/STAT3 pathway, a signalling route tied to cell survival and immune regulation.

One distinction matters in particular for this peptide, and this page applies it strictly. A large share of the literature does not use Humanin itself but a more potent engineered analogue: HNG (also called S14G-Humanin). Findings from analogue studies cannot be transferred to Humanin without qualification. When reading any publication, check carefully which variant was actually studied.

Mechanism of action

Humanin protects cells primarily by inhibiting programmed cell death (apoptosis) and by activating the JAK2/STAT3 pathway through a tripartite receptor complex. The mechanisms below have been established in cell and animal models.

Inhibition of cell death

• Binds IGFBP-3 and BAX, blocking initiation of the apoptosis cascade. BAX is a protein that triggers cell death.
• Reduces cytochrome c release from mitochondria under stress. Cytochrome c is a signalling molecule that, once released, sets off cell death.
• Interacts with FPRL1, a receptor that regulates inflammatory signals.

JAK2/STAT3 signalling

• Activates a receptor complex composed of CNTFR, WSX-1, and gp130.
• This switches on JAK2 and the downstream phosphorylation of STAT3. Phosphorylation is the activation of a protein by attaching a phosphate group.
• Activated STAT3 is linked to cell survival and to the expression of metabolic genes.

Metabolic and insulin signalling

• Preclinical data indicate interaction with insulin signalling pathways.
• Improved insulin sensitivity has been observed in metabolic-stress models.
• The relationship with the metabolic effects of MOTS-c, another mitochondrial peptide in this database, is under active investigation.

Research findings

• In vitro studies show that Humanin inhibits amyloid-beta-induced neuronal apoptosis
• In rodent models, Humanin is associated with improved insulin sensitivity and reduced hepatic fat accumulation
• Cross-sectional studies in humans show a decline in circulating Humanin levels with age, but causality is not established
• Analogues of Humanin, particularly HNG with a glycine substitution, show substantially higher potency in preclinical models
• Children of centenarians have measurably higher circulating Humanin levels than age-matched controls

Cell models (in vitro)

• Inhibition of amyloid-beta-induced neuronal cell death.
• Protection against oxidative-stress-induced cell death in multiple cell lines. Oxidative stress is damage caused by reactive oxygen species.
• Modulation of inflammatory cytokines in macrophage models. Macrophages are immune cells.
• Activation of the ERK1/2, AKT, and STAT3 pathways via the gp130 receptor complex.

Animal models

• Improved insulin sensitivity in mouse models of diet-induced obesity.
• Reduced loss of neurons in Alzheimer mouse models.
• Extended lifespan in the roundworm C. elegans.
• An age-dependent hippocampal effect: in aged mice, but not young, Humanin enhanced signalling in a brain region central to memory formation.

Human data

• Observational: cross-sectional studies show that circulating Humanin levels decline with age.
• Observational: children of centenarians carry higher Humanin levels than peers.
• Observational: lower Humanin levels in Alzheimer and MELAS patients.
• In two randomised trials in humans, Humanin levels rose after an exercise programme: in muscle tissue in prediabetics, and in neuronal extracellular vesicles in Alzheimer patients. In both cases exercise was the intervention and Humanin the measured outcome.
• To date, no human study has administered Humanin itself.

Research context

Humanin sits at an early-to-intermediate stage of the research pipeline. The mechanistic basis is reasonably well characterised in cell and animal models, but translation to human physiology is largely unestablished.

The distinction between types of human evidence matters most here. Human data does exist, and part of it even comes from randomised trials, but in none of those trials was Humanin administered. The observational data show that Humanin levels fall with age; the randomised data show that levels rise after exercise. Both are informative, but neither tells us what happens when Humanin is given as an intervention. That final, decisive step has not yet been taken in humans.

The observational finding, declining Humanin with age, is also not conclusive on its own. Whether that decline is a cause or a consequence of ageing cannot be settled by a cross-sectional study. This distinction is important when interpreting the research.

The evidence base is further review- and biomarker-heavy: a substantial share of the literature consists of review articles and of studies that measure Humanin as a level, rather than of direct intervention work. A critical counterweight has also been published: at least one review describes mitochondria-derived peptides, including Humanin, as potentially exacerbating senescence phenotypes under certain conditions, rather than mitigating them. That is an important corrective to a one-sided positive reading.

Open questions

Humanin research is advancing but remains largely preclinical. The gap between promising animal data and established human evidence, particularly the absence of any human study administering Humanin itself, should be kept in mind when interpreting any findings.

• No human study to date has administered Humanin. For research groups, this is the most direct next step: a first-in-human safety and pharmacokinetic study.
• Optimal dosing, route of administration, and human pharmacokinetics are unknown.
• The long-term safety profile is not established.
• Whether the age-related decline in endogenous Humanin is cause or consequence remains unresolved.
• Differences between Humanin itself and its analogues (HNG, HNGF6A) are not fully characterised, while much of the strongest evidence rests on those very analogues.
• Interactions with MOTS-c and other mitochondria-derived peptides have not been studied in humans.

Research outlook

First-in-human studies with Humanin or its analogues are anticipated as the MDP field matures.

Combined research across multiple mitochondria-derived peptides (Humanin with MOTS-c) may expose synergistic mechanisms.

The biomarker potential (Humanin as an indicator of ageing or metabolic health) is under investigation.

Analogue development (HNG and variants) continues to refine potency and selectivity.

Scientific interest

Mitochondria-derived peptide signalling

Cytoprotection and apoptosis inhibition

Metabolic regulation and insulin sensitivity

Ageing biology and longevity research

Specifications

References

1. The mitochondrial-derived peptide humanin activates the ERK1/2, AKT, and STAT3 signaling pathways. · Kim SJ, Guerrero N, Wassef G, et al. · Oncotarget · 2016
2. Humanin skeletal muscle protein levels increase after resistance training in men with impaired glucose metabolism. · Gidlund EK, von Walden F, Venojärvi M, et al. · Physiological Reports · 2016
3. Humanin: Functional Interfaces with IGF-I. · Xiao J, Kim SJ, Cohen P, Yen K. · Growth Hormone & IGF Research · 2016
4. Mitochondrial-Derived Peptides Exacerbate Senescence. · Mendelsohn AR, Larrick JW. · Rejuvenation Research · 2018
5. Humanin, a Mitochondrial-Derived Peptide Released by Astrocytes, Prevents Synapse Loss in Hippocampal Neurons. · Zárate SC, Traetta ME, Codagnone MG, et al. · Frontiers in Aging Neuroscience · 2019
6. The mitochondrial derived peptide humanin is a regulator of lifespan and healthspan. · Yen K, Mehta HH, Kim SJ, et al. · Aging (Albany NY) · 2020
7. Cardio-protective role of Humanin in myocardial ischemia-reperfusion. · Gong Z, Goetzman E, Muzumdar RH. · Biochimica et Biophysica Acta — General Subjects · 2022
8. Roles of humanin and derivatives on the pathology of neurodegenerative diseases and cognition. · Thiankhaw K, Chattipakorn K, Chattipakorn SC, Chattipakorn N. · Biochimica et Biophysica Acta — General Subjects · 2022
9. Effect of Humanin G (HNG) on inflammation in age-related macular degeneration. · Nashine S, Cohen P, Wan J, Kenney MC. · Aging (Albany NY) · 2022
10. Neuron-derived extracellular vesicles in blood reveal effects of exercise in Alzheimer's disease. · Delgado-Peraza F, Nogueras-Ortiz C, Simonsen AH, et al. · Alzheimer's Research & Therapy · 2023

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