**3. Humanin**

Humanin was the first MDP discovered within the mammalian mitochondrial genome and is encoded from the 16S rRNA coding region of the mtDNA. Humanin cDNA was first discovered in 2001 by functional expression screening of a cDNA library preparation from the occipital cortex of an Alzheimer's disease patient brain [21]. The study identified clones that protected against neuronal cell death induced by neurotoxic amyloid-β peptides and by mutants of FAD (Familial Alzheimer's Disease) genes, namely *APP* (Amyloid Precursor Protein), *PS1* (Presenilin 1), and *PS2* (Presenilin 2). A 75 bp open reading frame that codes for a 24-residue peptide was identified and its sequence was found to be similar to that of a human cDNA and 99% identical to the mtDNA sequence; it was therefore named Humanin. Humanin antagonized the cytotoxicity caused by *APP* (Amyloid Precursor Protein (APP), *PS1* (Presenilin 1), and *PS2* (Presenilin 2) mutants, by suppressing amyloid-β1-42-triggered neurotoxicity and attenuating neuronal cell death.
