Humanin

A 24-amino-acid peptide your own mitochondria make (encoded inside the 16S rRNA gene MT-RNR2) — the first-discovered "mitochondrial-derived peptide" and the older sibling of MOTS-c. Hashimoto and Nishimoto identified it in 2001 by screening cDNA from the surviving neurons of an Alzheimer's brain that resisted Aβ toxicity. Mechanism is genuinely impressive on paper: anti-apoptotic via FPR2/CNTFR/gp130 → STAT3, direct Bax/tBid antagonism at the outer mitochondrial membrane, IGFBP-3 modulation, and convergent positive signals across Alzheimer's, ischemia, atherosclerosis, type 2 diabetes, and aging rodent models. Human evidence: zero RCTs, zero Phase 1 trials in any registry as of May 2026. Cohen lab at USC continues mechanistic work; analogs HNG (Gly14-humanin, ~1000× more potent than wild-type in Aβ-protection assays) and colivelin exist but have not advanced to humans. For Dylan: WATCH-LIST, not actionable. The mitochondrial-peptide family (Humanin + MOTS-c + SS-31 + the SHLP series) is collectively interesting longevity-protocol material; Humanin specifically is the most preclinical-only of the bunch and the least vendor-served. Track Cohen lab publications and ClinicalTrials.gov annually; revisit verdict when any human trial opens.

Humanin (HN) is a 24-amino-acid peptide with sequence MAPRGFSCLLLLTSEIDLPVKRRA (also written MAPRGFSCLLLLTSEIDLPVKRR-COOH for the canonical 24-mer; some sources cite a 21-residue version from alternative ORF reading). Molecular weight ~2687 g/mol. It is encoded inside the mitochondrial 16S rRNA gene (MT-RNR2) as a small open reading frame nested within the rRNA sequence. The peptide is translated and exported from the mitochondrion; it acts both intracellularly and as a circulating extracellular signaling peptide.

Discovery (2001): Identified by Yuichi Hashimoto and Ikuo Nishimoto at Keio University, published in PNAS 2001 (PMID 11371646: "A rescue factor abolishing neuronal cell death by a wide spectrum of familial Alzheimer's disease genes and Aβ"). The discovery method is part of why Humanin is interesting: the team screened a cDNA library from the occipital lobe of an Alzheimer's patient specifically because the occipital lobe is one of the brain regions that resists Aβ accumulation and neuronal death in AD. They were looking for "rescue factor(s)" — endogenously produced molecules that protect the surviving neurons. Humanin emerged as a hit: a small peptide whose presence rescued neurons from death induced by Aβ and by familial-AD-linked mutant genes (V642I-APP, M146L-PS1, N141I-PS2). This origin story is mechanistically anchored — the peptide was discovered specifically as an anti-AD-cytotoxicity factor, not as a mitochondrial peptide first. The mitochondrial-encoding finding came later.

Plain English origin: Imagine a brain region that should die from Alzheimer's damage but doesn't. Hashimoto and Nishimoto asked "what's keeping these neurons alive?" — and found Humanin. It's an endogenous neuroprotection mechanism your mitochondria already deploy. Exogenous administration in animals adds more of what the body's own surviving neurons are using.

Pathway 1 — Heterotrimeric receptor / STAT3 anti-apoptotic signaling (the main extracellular axis):

1. Humanin binds an extracellular heterotrimeric receptor complex consisting of:
   • FPR2 / FPRL1 (formyl peptide receptor 2 — a G-protein-coupled receptor on neurons, immune cells, and endothelium)
   • CNTFR (ciliary neurotrophic factor receptor)
   • WSX-1
   • gp130 (the shared signal transducer of the IL-6 cytokine family)
2. Receptor engagement activates the JAK2 → STAT3 signaling cascade.
3. Activated STAT3 translocates to the nucleus and upregulates anti-apoptotic genes (Bcl-2 family pro-survival members), suppresses pro-apoptotic transcription, and broadly tilts the cell toward survival under stress.
4. This is the main extracellular pathway by which Humanin protects neurons from Aβ-induced apoptosis, ischemia-reperfusion injury, and other stress-induced cell death.

Pathway 2 — Direct Bax / tBid / BimEL antagonism at the mitochondrial outer membrane (the intracellular axis):

1. Humanin physically binds Bax (Bcl-2-associated X protein) — the key pro-apoptotic effector that, when activated, oligomerizes at the mitochondrial outer membrane and triggers cytochrome c release.
2. Humanin blocks Bax oligomerization and translocation, preventing mitochondrial outer membrane permeabilization (MOMP) — the point-of-no-return in intrinsic apoptosis.
3. Humanin similarly antagonizes tBid (truncated Bid, a pro-apoptotic BH3-only protein activated by extrinsic apoptotic signaling that crosses to the intrinsic pathway) and BimEL.
4. Net effect: directly stabilizes mitochondria against apoptotic triggers, independent of upstream STAT3 signaling.
5. This dual-pathway architecture (extracellular receptor + direct intracellular Bax-block) is unusual among cytoprotective peptides and explains why Humanin shows broad-spectrum cytoprotection across many stress models.

Pathway 3 — IGF-1 / IGFBP-3 axis modulation:

1. Humanin binds IGFBP-3 (insulin-like growth factor binding protein 3) with high affinity.
2. IGFBP-3 has dual roles: it normally binds and sequesters IGF-1 (regulating its bioavailability), AND it has IGF-1-independent pro-apoptotic actions in many cell types (this is the IGFBP-3 "death receptor" effect).
3. By binding IGFBP-3, Humanin:
   • Suppresses IGFBP-3-induced apoptosis (cytoprotection)
   • Modulates free IGF-1 availability (with downstream effects on growth, metabolism, glucose handling, and longevity)
4. The plasma Humanin / IGF-1 / IGFBP-3 axis has been characterized in human cohorts — Humanin levels track inversely with age and positively with longevity in centenarian cohorts, paralleling some of the IGF-1-axis longevity findings.

Pathway 4 — Aβ neutralization and AD-specific neuroprotection:

1. Humanin (and especially the HNG / Gly14-humanin analog) directly binds soluble Aβ oligomers in some assays, blocking Aβ-induced membrane disruption and neurotoxicity.
2. Humanin protects cultured neurons from a wide range of AD-linked insults: V642I-APP, M146L-PS1, N141I-PS2 mutations, Aβ1-42 and Aβ25-35 peptide exposure.
3. In transgenic AD mouse models (3xTg-AD, APP/PS1), intracerebroventricular or intranasal Humanin administration reduces Aβ load, improves spatial memory (Morris water maze), and reduces neuronal loss.
4. HNG (Gly14-humanin, S14G-humanin) — the substitution of serine-14 with glycine — produces a peptide ~1000× more potent than wild-type Humanin in Aβ-protection assays. HNG is the most-studied analog and the version most peptide-vendor catalogs list when they list a "Humanin analog."

Pathway 5 — Metabolic / insulin sensitivity (smaller axis vs MOTS-c):

• Humanin administration in obese, insulin-resistant, and type-2-diabetic rodent models improves insulin sensitivity (~20–30% improvement in glucose infusion rate during clamp studies, more modest than MOTS-c).
• Mechanism: partly via IGFBP-3 axis modulation, partly via hypothalamic Humanin signaling affecting peripheral glucose handling.
• This is the secondary Humanin axis. MOTS-c is the dominant metabolic MDP; Humanin is the dominant cytoprotective/neuroprotective MDP. They are sister peptides with substantially divergent primary functions.

Pathway 6 — Atherosclerosis / vascular protection:

• Humanin reduces oxidized-LDL-induced endothelial apoptosis, foam-cell formation, and atherosclerotic plaque burden in ApoE-knockout mouse models.
• Endothelial Humanin signaling improves nitric oxide bioavailability and reduces inflammatory cytokine signaling in vascular tissue.

Pathway 7 — Aging and longevity correlation:

• Plasma Humanin declines with age in humans — multiple cross-sectional cohorts show a substantial drop from young adulthood to old age (estimates vary but commonly ~30–50% lower in 70+ vs 20s).
• Centenarian cohorts show preserved or elevated plasma Humanin relative to age-matched non-centenarian controls.
• Long-lived growth hormone receptor knockout (Ghr-KO) mice ("Laron mice") — which live ~40% longer than wild-type — have elevated plasma Humanin. This is the most-cited animal-longevity correlation for Humanin.
• These are correlational data, not interventional. The "humanin = longevity peptide" framing in vendor marketing significantly outpaces the interventional evidence.

Plain English mechanism summary: Humanin is a peptide your mitochondria make to keep cells from dying when they're under stress. It works two ways at once: from outside the cell, it tells survival pathways to turn on; from inside the cell, it physically blocks the proteins that trigger apoptosis at the mitochondrial membrane. It's particularly notable for protecting neurons from Alzheimer's-type damage and was specifically discovered as an anti-AD factor. Sister peptide MOTS-c does metabolic signaling (exercise mimetic); Humanin does cytoprotection and anti-apoptosis. The mechanism is genuinely interesting and well-characterized in cell and animal models — but no human has ever been dosed with Humanin in a registered clinical trial.