Role of the Mitochondrial Peptide Humanin in Regulating Aging and Healthspan Diet and the GH/IGF axis are central to aging and longevity. We identified a key role for the novel mitochondrial- derived peptide (MDP), humanin, which is encoded from a small open reading frame (sORF) within the mitochondrial genome (16S rRNA gene) in this regard. Dietary manipulations, administration of H2S-donors, and IGF-I reduction lead to increases in humanin levels, while humanin itself mimics dietary restriction (DR) in multiple ways including suppressing IGF-I, increasing IGFBP-1, improving insulin sensitivity, and reducing weight. Humanin levels fall with age and correlate with lifespan, and humanin overexpression or administration to various organisms leads to healthspan and lifespan extension. Similarly to dietary interventions and H2S, humanin protects from a variety of insults, and its administration prevents the development of diseases of aging. Our collaborative studies with Projects 1 & 3 indicate that humanin is a central connecting link between dietary restriction, IGF reduction, and H2S expression, integrating stress resistance and fitness during aging. Our central hypotheses are (1) humanin is a mitochondrial hormone whose expression is directly regulated by aging-modulating interventions such as dietary manipulations, H2S, and IGF-reduction, (2) Humanin regulates circulating IGF-I (mimicking DR) by direct activity on the hypothalamus leading to a central-hepatic effect that inhibits IGF-I production in liver (3) humanin administration can act similarly to DR and fasting mimicking diets or protein restriction cycles, H2S, and GH/IGF-blockade, to promote healthspan and possibly longevity. We will study the mechanisms by which diet, IGF-I, and H2S regulate humanin expression; and study the transcriptional and post-transcriptional regulation of the humanin-sORF. We will decipher the mechanisms involved in the DR-mimetic effects of humanin action through hypothalamic-mediated suppression of hepatic IGF-I; as well as through direct protective effects on target tissues. We will characterize the effects of humanin on healthspan and identify the mechanisms involved, using novel humanin-transgenic mouse models, GP130- inhibitors, and IGF-add-back experiments. Together, this project will demonstrate the physiological significance of humanin as a mediator and regulator of healthspan and longevity pathways including those related to diet, IGF-I, and H2S. We hope to demonstrate that HN is necessary and sufficient for healthspan/lifespan enhancement.