Mitochondrial oxidant generation and oxidative damage in Ames dwarf and GH transgenic mice

Abstract

Aging is associated with an accumulation of oxidative damage to proteins, lipids and DNA. Cellular mechanisms designed to prevent oxidative damage decline with aging and in diseases associated with aging. A long-lived mouse, the Ames dwarf, exhibits growth hormone deficiency and heightened antioxidative defenses. In contrast, animals that over express GH have suppressed antioxidative capacity and live half as long as wild type mice. In this study, we examined the generation of H202 from liver mitochondria of Ames dwarf and wild type mice and determined the level of oxidative damage to proteins, lipids and DNA in various tissues of these animals. Dwarf liver mitochondria (24 months) produced less H202 than normal liver in the presence of succinate (p<0.03) andADP (p<0.003). Levels of oxidative DNA damage (8OHdG) were variable and dependent on tissue and age in dwarf and normal mice. Forty-seven percent fewer protein carbonyls were detected in 24-month old dwarf liver tissue compared to controls (p<0.04). Forty percent more (p<0.04) protein carbonyls were detected in liver tissue (3-month old) of GH transgenic mice compared to wild types while 12 month old brain tissue had 53% more protein carbonyls compared to controls (p<0.005). Levels of liver malonaldehyde (lipid peroxidation) were not different at 3 and 12 months of age but were greater in Ames dwarf mice at 24 months compared to normal mice. Previous studies indicate a strong negative correla-

Long-lived Ames dwarf mice: Oxidative damage to mitochondrial DNA in heart and brain

“…This is the first study reporting levels of oxidative damage to mtDNA in long-lived dwarf mice. Previous studies concerning oxidative stress are mainly limited to tissue antioxidant levels (10,11) with some investigations reporting inorganic and lipid peroxides (12) and oxidative damage to proteins and nuclear DNA (13). We show here that 8-oxodG in mtDNA is lower in the brain of dwarfs of both sexes and in the heart of male dwarf mice than in the corresponding organs of wild type mice.…”

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

“…While limited antioxidant parameters were affected by age, we did see age-related changes in oxidative damage (i.e., protein carbonyls and 4-HNE), although the direction of the age-related changes was not consistent between different tissues and different markers (Jacobson et al 2010). Protein carbonyl content increased with advancing age in brains of Ames dwarf mice, whereas age had no effect on hepatic protein carbonyls (Brown-Borg et al 2001). This differs from the age-related effects we observed in the current study using Irs1 −/− mice, with decreased protein carbonyl content within brain and increased content within liver.…”

“…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. In contrast, significant reduction in protein carbonyl content were reported in brain and liver of Ames and Snell dwarf mice compared to WT controls (Brown-Borg et al 2001;Brooks et al 2007). Discrepancies between Irs1 −/− and GH deficient mice may be due to differences in GH signalling, genetic background and/or insulin sensitivity Bartke 2011).…”

“…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.…”

Hormonal regulation of longevity in mammals

“…Interestingly, GH replacement in dwarf mice down-regulates catalase, GPX, and MnSOD proteins and activities in both young and adult animals (Brown- . Metallothionein and glutathione both exhibit ROS scavenging abilities, and levels of these are significantly increased in multiple tissues from the dwarf mouse (Meyer et al, 2003;Brown-Borg et al, 2001). The amino acid methionine, whose metabolic pathway feeds cysteine residues into the GSH pathway, is also highly upregulated in the Ames mouse (Brown-Borg et al, 2005;Uthus and Brown-Borg, 2003;.…”