The Regulation of Cellular Stress Resistance and DNA Repair in a Long-Lived Mutant Mouse.

Abstract

Mutations that extend lifespan in invertebrates often lead to resistance to multiple forms of stress, suggesting that stress resistance might also be important in lifespan determination in mammals. Work in this thesis supports this idea from several perspectives. Snell dwarf mice have a mutation in the gene Pit1 which extends their lifespan approximately 40% relative to controls and delays the progression of multiple age-related pathologies. We found that skin-derived fibroblast cultures grown from Snell dwarf mice are resistant to cell death induced by both oxidative stresses and stresses that are, in part, oxidation-independent, like heat, heavy metals, and DNA damaging agents. We also found that fibroblast resistance to the oxidative stressor peroxide is correlated with resistance to other stressors, both oxidative and non-oxidative, suggesting regulation of these properties by an overlapping set of mechanisms. We found similar patterns of resistance in fibroblasts grown from mice with other lifespan-extending mutations. An additional set of experiments showed that Snell dwarf fibroblasts have an enhanced ability to repair UV-induced DNA lesions, providing a possible explanation for their resistance to death cause by UV irradiation. Snell dwarf fibroblasts express higher levels of two nucleotide excision proteins than control, which may contribute to their enhanced DNA repair and to delayed aging and diminished neoplasia in these mice. Extending these approaches to comparative biology, we found that resistance to some cellular stressors is correlated with maximum lifespan across mammalian species. Fibroblasts from long-lived species of rodents are significantly resistant to heavy metals and some oxidative stressors, and show similar trends for death caused by heat or DNA alkylation. For other agents however, such as UV light, there was no association between lifespan and cellular stress resistance. These results suggest that as rodent species evolved longer lifespan, there was also a coordinate increase in the cellular resistance to many, but not all, cellular stressors. Overall, these results support the idea that mechanisms that regulate lifespan in mammals also tend to increase cellular stress resistance. The further study of the mechanisms of stress resistance in mammals may then help us better understand the molecular regulation of aging.