Humanin, a tiny protein fragment, can turn on a cell‑survival pathway that raises levels of a protein called Apollon/Bruce, which helps protect brain cells from dying in an Alzheimer’s‑related model. This shows another way Humanin might support brain health, but the study is still at the cell‑culture stage and doesn’t give dosing or real‑world usage tips.

Humanin, a short bioactive peptide, inhibits a variety of cell deaths. Humanin-mediated inhibition of neuronal cell death, caused by an Alzheimer's disease (AD)-linked mutant gene occurs via binding of Humanin to its heterotrimeric Humanin receptor (htHNR), which results in the activation of the Janus-associated kinases (JAKs) and signal transducer and activator and transcription 3 (STAT3) signaling pathway. A previous study demonstrated that the Humanin-induced activation of the htHNR/JAK2/STAT3 signaling pathway leads to increased expression of SH3 domain-binding protein 5 (SH3BP5), which is an essential effector of Humanin's anti-cell death activity in some cultured neuronal cells. However, it remains unknown whether SH3BP5 is the sole effector of the Humanin signaling pathway via htHNR/JAKs/STAT3. Here we show that the Humanin signaling pathway via htHNR/JAKs/STAT3 increased the expression levels of mRNA and protein of Apollon/Bruce, an unusual member of the inhibitors of apoptosis proteins, and that overexpression of Apollon/Bruce inhibits neuronal death, caused by a London-type familial AD-linked mutant (V642I) of amyloid β precursor protein. Overall, the results indicate that expression of Apollon/Bruce is upregulated by Humanin, and Apollon/Bruce could be an effector of Humanin in a context-dependent manner.