Humanin

This landmark study reported the identification of Humanin (HN), a novel 24-residue peptide isolated via functional expression screening of a cDNA library constructed from the occipital lobe of an Alzheimer's disease brain — a region noted to remain relatively intact in AD. In cultured neuronal cells, Humanin abolished cell death induced by overexpression of multiple familial Alzheimer's disease (FAD) genes (mutant APP, presenilin-1, and presenilin-2) as well as by exogenous amyloid-β (Aβ1–43 and Aβ1–42). The protective effect was observed in the nanomolar range and was sequence-specific: a Cys-to-Ser substitution at position 8 abolished activity, while a Ser-to-Gly substitution at position 14 (HNG) enhanced potency by approximately 1000-fold. The peptide did not protect against insults unrelated to FAD signaling, suggesting a mechanism specific to the AD-associated cell death pathway. This paper established the foundation for the mitochondrial-derived peptide (MDP) family.

Scientists were looking for natural factors in the brain that might protect neurons from the damage seen in Alzheimer's disease. They screened a library of genetic material from a brain region that tends to be spared in Alzheimer's patients, and identified a small 24-amino-acid peptide they named Humanin. In a laboratory dish, Humanin rescued nerve cells from death caused by mutant Alzheimer's-related genes and by amyloid-beta — the protein fragment that forms plaques in Alzheimer's brains. The protection was very specific: changing one amino acid eliminated the effect, while a different single-amino-acid swap made it about a thousand times more potent. This was the first description of what is now called the mitochondrial-derived peptide family.

Using yeast two-hybrid screening with Humanin as bait against a human testis cDNA library, the authors identified insulin-like growth factor binding protein 3 (IGFBP-3) as a direct Humanin-binding partner. The Humanin–IGFBP-3 interaction was confirmed by GST pull-down, surface plasmon resonance, and co-immunoprecipitation. Both proteins were shown to colocalize in human brain tissue. Functionally, Humanin and IGFBP-3 reciprocally modulated each other's effects on cell survival: Humanin attenuated IGFBP-3-induced apoptosis in glioblastoma cells, while IGFBP-3 blocked Humanin's rescue of neuronal cells from FAD-gene-induced death. The work linked the mitochondrial-derived peptide Humanin to the insulin/IGF signaling axis — an axis with well-characterized roles in cellular aging — and was a foundational paper from the Cohen laboratory framing Humanin as a metabolic-aging signal in addition to a cytoprotective factor.

Researchers wanted to find out what proteins Humanin physically interacts with inside cells. Using a screening method that pulls binding partners out of a library, they identified IGFBP-3, a protein already known to influence the IGF growth/aging pathway. The two proteins were shown to bind each other directly and to colocalize in human brain tissue. They also influenced each other's effects on cell survival in opposite directions. This study connected Humanin — originally discovered for its rescue of neurons — to the broader insulin and IGF signaling system that has been heavily studied in aging research, helping frame Humanin as both a stress-response peptide and a possible signal in metabolic aging.