Nrf2 Signaling, a Mechanism for Cellular Stress Resistance in Long-Lived Mice

Abstract

Transcriptional regulation of the antioxidant response element (ARE) by Nrf2 is important for the cellular adaptive response to toxic insults. New data show that primary skin-derived fibroblasts from the long-lived Snell dwarf mutant mouse, previously shown to be resistant to many toxic stresses, have elevated levels of Nrf2 and of multiple Nrf2-sensitive ARE genes. Dwarf-derived fibroblasts exhibit many of the traits associated with enhanced activity of Nrf2/ARE, including higher levels of glutathione and resistance to plasma membrane lipid peroxidation. Treatment of control cells with arsenite, an inducer of Nrf2 activity, increases their resistance to paraquat, hydrogen peroxide, cadmium, and UV light, rendering these cells as stress resistant as untreated cells from dwarf mice. Furthermore, mRNA levels for some Nrf2-sensitive genes are elevated in at least some tissues of Snell dwarf mice, suggesting that the phenotypes observed in culture may be mirrored in vivo. Augmented activity of Nrf2 and ARE-responsive genes may coordinate many of the stress resistance traits seen in cells from these long-lived mutant mice.The discovery of single gene mutations that extend life span, first in invertebrates (43,48,60) and then in mice (9, 14, 19), has provided new momentum for defining the molecular mechanisms that control the aging process. Since Harman first proposed the free radical theory of aging (23), many lines of evidence have suggested that oxidative stress plays an important role in aging. In roundworms (Caenorhabditis elegans) (44, 52) and fruit flies (Drosophila melanogaster) (7, 67, 109), mutations resulting in resistance to toxic stresses, both oxidative and otherwise, tend to result in increases in longevity. The relative importance of oxidation damage as a regulator of life span is more controversial. Longevity is often associated with resistance to oxidative injury within and among species, but most attempts to retard aging by antioxidant treatments have failed to show beneficial effects, and mutations that promote oxidative damage in mice have often had little impact on life span (25,72,81,86,96). Utilizing cells from the Snell dwarf mouse, a model of extended longevity, we are attempting to find the mechanism behind cellular stress resistance in hopes of relating this resistance to the delayed aging of the Snell dwarf animal.Snell dwarf mice are homozygous for a mutation at the Pit-1 locus which causes improper development of the anterior pituitary, leading to low levels of growth hormone, thyroid stimulating hormone, and prolactin in young and adult mice (10, 30). These pituitary defects lead to diminished circulating levels of insulin-like growth factor 1 (IGF-1) and thyroxine, which in turn result in reduced size and hypothermia. Snell dwarf mice, like the closely related Prop1 mutant Ames dwarf (9), live approximately 40% longer than littermate controls on several different background stocks (19,20) and show delay in many forms of aging-related pathologies (1,3,19).Previous work has shown that pr...

p62/SQSTM1 at the interface of aging, autophagy, and disease

“…These features are recapitulated by observations in human fibroblasts and by other studies showing that chronic activation of mTORC1 with IGF-1 reduces proliferative potential and causes accumulation of damaged mitochondria and ROS, leading to cellular senescence (Bitto et al 2010b;Handayaningsih et al 2012). Conversely, long-lived Snell/Dwarf mice show increased basal activation of the NFE2L2 pathway, suggesting that IIS and the antioxidant response cooperate to influence longevity (Leiser and Miller 2010). In fact, Snell/Dwarf mice-derived fibroblasts show lower levels of mTORC1 activity and enhanced autophagy in response to stress (Wang and Miller 2012).…”

“…Continuous, irreparable damage to DNA, proteins, and organelles can be caused by oxidants, radiations, and other insults through free radical reactions (Harman 2003), progressively impairing cellular homeostasis. Living organisms are well equipped with detoxifying, antioxidant, and repair enzymes to cope with this kind of damage (RobidaStubbs et al 2012;Longo 1999;Steinbaugh et al 2012;Leiser and Miller 2010;Salmon et al 2005;Wei et al 2008): this suggests that raising the cellular defenses against stressors would mimic the effects of ageextending interventions. In addition to stress resistance, cellular homeostasis is also influenced by quality control mechanisms that regulate function, structure, and degradation of cellular components, such as the proteinfolding machinery, mitochondrial fission and fusion dynamics, the ubiquitin-proteasome system, and autophagy (Koga et al 2011;Seo et al 2010).…”

Longer lifespan in male mice treated with a weakly estrogenic agonist, an antioxidant, an α‐glucosidase inhibitor or a Nrf2‐inducer

“…Although we cannot rule out effects at other targets by the individual constituents of the mixture of compounds contained in Prot, the increase in expression of xenobiotic response genes in the livers of mice in the present study at the 1200 ppm dose (data not shown) further supports the idea that the effects of Prot on longevity may be at least partly due to Nrf2 activation. For example, Leiser & Miller (2010) reported that primary skin‐derived fibroblasts from the long‐lived Snell dwarf mutant mouse manifest elevated levels of Nrf2, higher levels of glutathione, and increased resistance to plasma membrane lipid peroxidation. Consistent with those findings, mRNA levels for Nrf2‐sensitive genes were reported to be elevated in selected tissues of Snell dwarf mice (Leiser & Miller, 2010).…”

Longevity of insulin receptor substrate1 null mice is not associated with increased basal antioxidant protection or reduced oxidative damage

“…References; 1, Brown-Borg et al 2001;2, Brooks et al 2007;3, Hauck et al 2002 IIS insulin/IGF-1 signalling pathway mutant Irs1 −/− ; insulin receptor substrate-1 knockout GH growth hormone GHRKO growth hormone receptor/binding protein knockout M male and F female a Significant difference at young (3 months) but no difference at old age (24 months) b Significant difference at old age (24 month) but no difference at young age (3 months) c MDA+4-HNE; significant differences at middle-age (12 months) and old age (24 months) but no differences at young age (3 months) levels have previously been shown to be increased in brain, liver, and muscle tissue of Ames dwarf mice (Brown-Borg and Rakoczy 2003), as well as in dermal fibroblasts of Snell dwarf mice (Leiser and Miller 2010). Perhaps surprisingly, we observed no difference in protein (carbonyls) or lipid (4-HNE) oxidative damage in brain, skeletal muscle, or liver between Irs1 −/− and WT mice.…”