The mitochondrial derived peptide humanin is a regulator of lifespan and healthspan

Abstract

Humanin is a member of a new family of peptides that are encoded by short open reading frames within the mitochondrial genome. It is conserved in animals and is both neuroprotective and cytoprotective. Here we report that in C. elegans the overexpression of humanin is sufficient to increase lifespan, dependent on daf-16/Foxo. Humanin transgenic mice have many phenotypes that overlap with the worm phenotypes and, similar to exogenous humanin treatment, have increased protection against toxic insults. Treating middle-aged mice twice weekly with the potent humanin analogue HNG, humanin improves metabolic healthspan parameters and reduces inflammatory markers. In multiple species, humanin levels generally decline with age, but here we show that levels are surprisingly stable in the naked mole-rat, a model of negligible senescence. Furthermore, in children of centenarians, who are more likely to become centenarians themselves, circulating humanin levels are much greater than age-matched control subjects. Further linking humanin to healthspan, we observe that humanin levels are decreased in human diseases such as Alzheimer's disease and MELAS (Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like episodes). Together, these studies are the first to demonstrate that humanin is linked to improved healthspan and increased lifespan.

Keywords: aging; humanin; mitochondria; peptides.

Figure 1

Humanin overexpression is sufficient to increase lifespan in C. elegans. HN overexpression significantly increased lifespan in worms (average lifespan of 19.0 days) compared to wild-type/N2 (average lifespan 17.7 days) (A). This increase in lifespan was dependent on daf-16 as daf-16(mu86) mutants did not have any increase in lifespan when crossed with the humanin-tg strain (average lifespan 15.5 days vs 16.1 days respectively) (p < 0.2) (B). Hn-tg worms also had a significant decrease in body length, body fat, and reproductive output (C–E). *indicates p<.05.

Figure 2

HN-tg mice phenocopy the transgenic worms and are protected from toxic insult. Humanin transgenic mice have a significant decrease in body length by 12% at 28 days of age (n= 5 for control and n=3 for the hn-tg mice) (A). Body weight at the same age was also decreased by 10.4% (n=26 and n=16 for control and hn-tg mice respectively) (B), while litter size decreased by 46.5% (n=10 and n=15 for control and hn-tg mice respectively) (C). When administered cyclophosphamide, mice have a decreased lymphocyte count and transgenic mice are protected from this toxin (n=6 or 7 per group) (D). Similarly, when examining germ cell apoptosis organized by spermatogenic stages in the same cyclophosphamide treated mice, humanin transgenic mice are significantly protected from CP induced apoptosis (E). * indicates p<.05.

Figure 3

Midlife humanin treatment improves metabolic health in mice. Twice weekly treatment with HNG in midlife improves weight (A) without changing food intake (B). There were also improvements in body composition with a decreased values in visceral fat (C), an increase in lean body mass (D), and no change in subcutaneous fat (E). Although there was no significant difference in lifespan with this low of a dose of humanin (F), there was a significant decrease in circulating IGF-I (G) and a trend (p<.1) for leptin (H). *indicates p<.05 +indicates p<.10.

Figure 4

Humanin levels are related to human mitochondrial health. Low mtDNA copy number is associated with lower levels of humanin (A). Increased mtDNA mutation or absence of mtDNA (rho0 cells) is associated with decreased levels of humanin (B). Humanin levels are also decreased in the CSF of Alzheimer’s diseases patients (n=4) compared to control (n=3) (C) *indicates p<.05.

Figure 5

Humanin levels are correlated with longevity. HN levels decline with age in monkeys between 19 and 25 years of age but not between 25 and 35 years of age (n=40, 25, and 21 for 19, 25, and 35 years of age respectively) (A). In two rodents, the short-lived mouse (n=29) has a decline in humanin levels over the first 16 months of life, while the long-lived naked mole rat (NMR) (n=10) maintains levels over 2 decades (B). Humanin levels in offspring of centenarians (n=18), who have a higher chance of becoming centenarians themselves, are significantly higher than age-matched control levels (n=19)(C). * indicates p<.05, columns with different numbers are significantly different from each other.