Humanin

What Is Humanin?

Humanin is a 24-amino-acid peptide encoded within mitochondrial DNA and the first mitochondrial-derived peptide (MDP) to be described. It was first reported in the early 2000s as a neuroprotective and cytoprotective factor that rescued neuronal cells from death caused by various Alzheimer’s disease-associated insults^[1].

Humanin is encoded in the 16S rRNA region of the mitochondrial genome, alongside the small humanin-like peptides SHLP1-6^[2]. Its discovery as a signaling peptide from a short open reading frame in mitochondrial DNA prompted searches for others, leading to the identification of MOTS-c in 2015^[3].

Reviews describe humanin as acting inside the cell or being released to act as an autocrine, paracrine or endocrine cytoprotective factor in the cellular stress response^[4]. Because it circulates in blood, it has also been studied as a biomarker^[4]. Most mechanistic work is preclinical, in cultured cells, worms and rodents.

Chemical Structure and Molecular Identity

Humanin is a linear 24-residue peptide with the sequence MAPRGFSCLLLLTSEIDLPVKRRA and the molecular formula C119H204N34O32S2. PubChem lists a molecular weight of 2687.2 g/mol under CID 16131438, CAS number 330936-69-1, and InChIKey DPEUWKZJZIPZKE-OFANTOPUSA-N.

The PubChem record describes the peptide with free termini (H-MAPRGFSCLLLLTSEIDLPVKRRA-OH). The two sulfur atoms in the formula come from methionine at position 1 and a single cysteine at position 8. The sequence has a distinctive run of four leucines (positions 9-12) and a basic C-terminal stretch of lysine and two arginines.

• Length: 24 amino acids, all standard L-residues
• Hydrophobic core: Leu9-Leu12, plus Leu18 and Ile16
• Charged residues: Arg4, Glu15, Asp17, Lys21, Arg22, Arg23
• Single cysteine: position 8, with a free thiol

Much of the published research uses synthetic analogs rather than native humanin. The most common is HNG, in which serine 14 is replaced by glycine; studies describe it as a potent humanin analog^[5] and a synthetic humanin agonist^[6]. A 2023 review covers a range of mainly synthetic humanin analogs studied for neuroprotection^[1].

Research History and Development

Humanin research began in neuroprotection and expanded into metabolism, cardiovascular disease, fertility and aging as the mitochondrial-derived peptide field grew. After its identification as a protective factor against Alzheimer’s disease-associated insults, it was tested in models of other conditions including age-related macular degeneration, cardiovascular disease and diabetes^[1].

The 2015 discovery of MOTS-c was explicitly motivated by humanin, as evidence that mitochondrial DNA might contain additional signaling-peptide open reading frames^[3]. The family now includes humanin, SHLP1-6, MOTS-c and SHMOOSE^[2].

A 2020 study in Aging was the first to link humanin directly to lifespan and healthspan, combining worm, mouse, naked mole-rat and human data^[5]. More recent reviews place humanin among mitokines, signaling molecules that communicate local mitochondrial stress to distant cells and tissues, together with FGF21 and GDF15^[7].

Exercise physiology added another thread. A 2021 review proposed that mitochondrial-derived peptides, including humanin, form a newly recognized branch of retrograde signaling from mitochondria that may help coordinate the adaptive response to regular exercise^[8].

Mechanisms Studied in Research

Humanin is studied mainly as an anti-apoptotic, cytoprotective peptide that acts through several protein interactions and signaling pathways. Reviews report protective effects in leukocytes, germ cells and neurons against cellular stress and apoptosis, through mechanisms including the JAK/STAT pathway and interaction with BCL-2 family proteins^[9].

Reported targets and pathways

Stress-responsive signaling

As a mitokine, humanin responds to mitochondrial stress, including stress in skeletal muscle during exercise^[7]. A 2020 review notes that mitochondrial-derived peptides can translocate to the nucleus and interact with DNA as part of a transcriptional stress response^[10].

Key Findings From Published Studies

Published findings come mostly from cell, worm and rodent models, with human data limited to observational measurements of circulating humanin. No controlled trial of administered humanin in people appears in the literature summarized here.

Lifespan and healthspan (animal)

In C. elegans, humanin overexpression was sufficient to increase lifespan. Humanin transgenic mice showed increased protection against toxic insults, and treating middle-aged mice with HNG improved metabolic healthspan parameters and reduced inflammatory markers^[5].

Circulating levels in humans (observational)

• Aging: humanin levels generally declined with age across species but were stable in the naked mole-rat; children of centenarians had much higher circulating humanin than age-matched controls; levels were lower in Alzheimer’s disease and MELAS^[5].
• Polycystic ovary syndrome: in 40 women with PCOS and 40 matched controls, median serum humanin was lower with PCOS (474.9 vs 672.3 pg/mL, p < 0.001), while skeletal muscle humanin did not differ; serum levels correlated negatively with testosterone, 2-hour insulin and lipids^[11].
• Exercise: acute high-intensity exercise in humans increased humanin and MOTS-c concentrations in skeletal muscle and plasma; evidence on chronic training effects was conflicting^[8].

Tissue protection (animal and in vitro)

In rodent testes, HNG protected male germ cells against apoptosis induced by hormonal deprivation, testicular hyperthermia and chemotherapeutic agents^[6]. A review of in-vitro and in-vivo studies reported that humanin suppressed apoptosis in models of osteoporosis, cardiovascular disease, diabetes and neurodegenerative disease^[9]. Humanin analogs and peptide mimetics have shown promising results in preclinical models of degenerative disease^[4].

Because humanin contains a free cysteine and a leucine-rich stretch, researchers verify sequence, purity and oxidation state with HPLC and mass-spectrometry certificates of analysis.

Because humanin contains a free cysteine and a leucine-rich stretch, researchers verify sequence, purity and oxidation state with HPLC and mass-spectrometry certificates of analysis.

Regulatory and Research Status

Humanin is not an FDA-approved drug and remains a preclinical research peptide. The evidence base consists of in-vitro work, animal studies, observational human biomarker data and narrative reviews.

Reviews flag unresolved questions. A 2019 review stated that controversy over humanin’s role in cancer progression and chemoresistance should be addressed before therapeutic approaches are translated^[4]. A 2023 review of mitokines cautioned that excessive mitokine concentrations can be harmful and are associated with conditions such as cancer and heart failure, and that it remains unproven whether age-related changes in mitokines drive aging or act as rescue factors^[7].

Other proposed directions remain at the hypothesis stage, including use of humanin as a marker of mitochondrial function in cardiovascular disease^[10] and local gene therapy vectors that raise or silence endogenous humanin^[4].

Exercise researchers have also called for studies to determine whether mitochondrial-derived peptides other than MOTS-c, humanin among them, have exercise mimetic properties, and how training mode, intensity and participant characteristics affect their levels^[8].