Extending the lifespan of long-lived mice

A critical analysis of the role of growth hormone and IGF-1 in aging and lifespan

Studies in Caenorhabditis elegans demonstrate that disruption of the daf-2 signaling pathways extends lifespan. Similarities among the daf-2 pathway, insulin-like signaling in flies and yeast, and the mammalian insulin-like growth factor 1 (IGF-1) signaling cascade raise the possibility that modifications to IGF-1 signaling could also extend lifespan in mammals. In fact, growth hormone (GH)/IGF-1-deficient dwarf mice do live significantly longer than their wild-type counterparts. However, multiple endocrine deficiencies and developmental anomalies inherent in these models confound this interpretation. Here, we critique the current mammalian models of GH/IGF-1 deficiency and discuss the actions of GH/IGF-1 on biological aging and lifespan.

Implications for the insulin signaling pathway in Snell dwarf mouse longevity: a similarity with the C. elegans longevity paradigm

Mutation analyses in the nematode, Caenorhabditis elegans, and mice have identified genes that increase their life-span via hormonal signal transduction, i.e. the insulin/insulin-like growth factor-1 (IGF-1) pathway in nematodes, and the growth hormone (GH)-thyriod stimulating hormone (TSH)-prolactin system in Snell dwarf mouse mutants. We have shown that the GH deficiency due to Pit1 mutation in the long-lived Snell dwarf mice may decrease circulating insulin levels, thereby resulting in a decreased activity of the insulin/IGF-1 signaling pathway. The data presented are consistent with our hypothesis that the decreased circulating insulin levels resulting from the Pit1 mutation mimics a physiological state similar to that proposed to occur in the long-lived C. elegans, daf-2 mutant. Our studies demonstrate a series of changes in components of the insulin/IGF-1-signaling pathway that suggest a reduction-of-function of this pathway in the aged dwarf. These include a decreased IRS-2 pool level, a decrease in PI3K activity and its association with IRS-2 and decreased docking of p85alpha to IRS-2. Our data also suggest a preferential docking of IRS-2-p85 alpha -p110 alpha in the aged dwarf liver and IRS-2-p85 alpha -p110 beta in the aged control. We speculate that the preference for the p110 alpha-containing complex may be a specific characteristic of a downstream segment of the longevity-signaling cascade. We conclude that the Pit1 mutation may result in physiological homeostasis that favors longevity, and that the Snell dwarf mutant conforms to the nematode longevity paradigm.

Stem cells from birth to death: The history and the future

The concept that adult stem cells, despite their impressive proliferative potential, are immortal has been challenged by experimental studies of hematopoietic stem cells. In this review, we discuss the properties that characterize a stem cell, the growing list of tissues in which stem cells are found, how they can be identified and isolated, how stem cells may transdifferentiate, and the findings that illustrate how age affects the hematopoietic stem cell population. We propose that an aging stem cell population affects tissue and organ homeostasis, particularly in response to environmental stresses, and we hypothesize that through this mechanism the functional status of stem cells affects the longevity of the organism.

Mechanisms of ageing: public or private?

Ageing--the decline in survival and fecundity with advancing age is caused by damage to macromolecules and tissues. Ageing is not a programmed process, in the sense that no genes are known to have evolved specifically to cause damage and ageing. Mechanisms of ageing might therefore not be expected to be as highly conserved between distantly related organisms as are mechanisms of development and metabolism. However, evidence is mounting that modulators of the rate of ageing are conserved over large evolutionary distances. As we discuss in this review, this conservation might stem from mechanisms that match reproductive rate to nutrient supply.