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Abstract

The widely accepted oxidative stress theory of aging postulates that aging results from accumulation of oxidative damage. Surprisingly, data from the longest-living rodent known, naked mole-rats [MRs; mass 35 g; maximum lifespan (MLSP) > 28.3 years], when compared with mice (MLSP 3.5 years) exhibit higher levels of lipid peroxidation, protein carbonylation, and DNA oxidative damage even at a young age. We hypothesize that age-related changes in protein structural stability, oxidation, and degradation are abrogated over the lifespan of the MR. We performed a comprehensive study of oxidation states of protein cysteines [both reversible (sulfenic, disulfide) and indirectly irreversible (sulfinic/sulfonic acids)] in liver from young and old C57BL/6 mice (6 and 28 months) and MRs (2 and >24 years). Furthermore, we compared interspecific differences in urea-induced protein unfolding and ubiquitination and proteasomal activity. Compared with data from young mice, young MRs have 1.6 times as much free protein thiol groups and similar amounts of reversible oxidative damage to cysteine. In addition, they show less urea-induced protein unfolding, less protein ubiquitination, and higher proteasome activity. Mice show a significant age-related increase in cysteine oxidation and higher levels of ubiquitination. In contrast, none of these parameters were significantly altered over 2 decades in MRs. Clearly MRs have markedly attenuated age-related accrual of oxidation damage to thiol groups and age-associated up-regulation of homeostatic proteolytic activity. These pivotal mechanistic interspecies differences may contribute to the divergent aging profiles and strongly implicate maintenance of protein stability and integrity in successful aging.

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Physiological functions of thioredoxin and thioredoxin reductase

Elias Arnér, Arne Holmgren (2000)

Thioredoxin, thioredoxin reductase and NADPH, the thioredoxin system, is ubiquitous from Archea to man. Thioredoxins, with a dithiol/disulfide active site (CGPC) are the major cellular protein disulfide reductases; they therefore also serve as electron donors for enzymes such as ribonucleotide reductases, thioredoxin peroxidases (peroxiredoxins) and methionine sulfoxide reductases. Glutaredoxins catalyze glutathione-disulfide oxidoreductions overlapping the functions of thioredoxins and using electrons from NADPH via glutathione reductase. Thioredoxin isoforms are present in most organisms and mitochondria have a separate thioredoxin system. Plants have chloroplast thioredoxins, which via ferredoxin-thioredoxin reductase regulates photosynthetic enzymes by light. Thioredoxins are critical for redox regulation of protein function and signaling via thiol redox control. A growing number of transcription factors including NF-kappaB or the Ref-1-dependent AP1 require thioredoxin reduction for DNA binding. The cytosolic mammalian thioredoxin, lack of which is embryonically lethal, has numerous functions in defense against oxidative stress, control of growth and apoptosis, but is also secreted and has co-cytokine and chemokine activities. Thioredoxin reductase is a specific dimeric 70-kDa flavoprotein in bacteria, fungi and plants with a redox active site disulfide/dithiol. In contrast, thioredoxin reductases of higher eukaryotes are larger (112-130 kDa), selenium-dependent dimeric flavoproteins with a broad substrate specificity that also reduce nondisulfide substrates such as hydroperoxides, vitamin C or selenite. All mammalian thioredoxin reductase isozymes are homologous to glutathione reductase and contain a conserved C-terminal elongation with a cysteine-selenocysteine sequence forming a redox-active selenenylsulfide/selenolthiol active site and are inhibited by goldthioglucose (aurothioglucose) and other clinically used drugs.

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Negligible senescence in the longest living rodent, the naked mole-rat: insights from a successfully aging species.

Rochelle Buffenstein (2008)

Aging refers to a gradual deterioration in function that, over time, leads to increased mortality risk, and declining fertility. This pervasive process occurs in almost all organisms, although some long-lived trees and cold water inhabitants reportedly show insignificant aging. Negligible senescence is characterized by attenuated age-related change in reproductive and physiological functions, as well as no observable age-related gradual increase in mortality rate. It was questioned whether the longest living rodent, the naked mole-rat, met these three strict criteria. Naked mole-rats live in captivity for more than 28.3 years, approximately 9 times longer than similar-sized mice. They maintain body composition from 2 to 24 years, and show only slight age-related changes in all physiological and morphological characteristics studied to date. Surprisingly breeding females show no decline in fertility even when well into their third decade of life. Moreover, these animals have never been observed to develop any spontaneous neoplasm. As such they do not show the typical age-associated acceleration in mortality risk that characterizes every other known mammalian species and may therefore be the first reported mammal showing negligible senescence over the majority of their long lifespan. Clearly physiological and biochemical processes in this species have evolved to dramatically extend healthy lifespan. The challenge that lies ahead is to understand what these mechanisms are.

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Life-long reduction in MnSOD activity results in increased DNA damage and higher incidence of cancer but does not accelerate aging.

Arthur Epstein, Michelle Hamilton-Page, Holly Van Houten … (2003)

Mice heterozygous for the Sod2 gene (Sod2+/- mice) have been used to study the phenotype of life-long reduced Mn-superoxide dismutase (MnSOD) activity. The Sod2+/- mice have reduced MnSOD activity (50%) in all tissues throughout life. The Sod2+/- mice have increased oxidative damage as demonstrated by significantly elevated levels of 8-oxo-2-deoxyguanosine (8oxodG) in nuclear DNA in all tissues of Sod2+/- mice studied. The levels of 8oxodG in nuclear DNA increased with age in all tissues of Sod2+/- and wild-type (WT) mice, and at 26 mo of age, the levels of 8oxodG in nuclear DNA were significantly higher (from 15% in heart to over 60% in liver) in the Sod2+/- mice compared with WT mice. The level of 8oxodG was also higher in mitochondrial DNA isolated from liver and brain in Sod2+/- mice compared with WT mice. The increased oxidative damage to DNA in the Sod2+/- mice is associated with a 100% increase in tumor incidence (the number of mice with tumors) in old Sod2+/- mice compared with the old WT mice. However, the life spans (mean and maximum survival) of the Sod2+/- and WT mice were identical. In addition, biomarkers of aging, such as cataract formation, immune response, and formation of glycoxidation products carboxymethyl lysine and pentosidine in skin collagen changed with age to the same extent in both WT and Sod2+/- mice. Thus life-long reduction of MnSOD activity leads to increased levels of oxidative damage to DNA and increased cancer incidence but does not appear to affect aging.

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PubMed ID:: 19223593

PMC ID:: 2651236

DOI:: 10.1073/pnas.0809620106

ScienceOpen disciplines: Chemistry

Keywords: Animals,Cysteine,metabolism,Longevity,physiology,Mice,Mole Rats,Oxidation-Reduction,Oxidative Stress,Protein Folding,Protein Stability,Rats,Ubiquitination

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ScienceOpen disciplines: Chemistry

Keywords: Animals, Cysteine, metabolism, Longevity, physiology, Mice, Mole Rats, Oxidation-Reduction, Oxidative Stress, Protein Folding, Protein Stability, Rats, Ubiquitination

Protein stability and resistance to oxidative stress are determinants of longevity in the longest-living rodent, the naked mole-rat.

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Journal of Circulating Biomarkers

Most cited references 35

Physiological functions of thioredoxin and thioredoxin reductase

Negligible senescence in the longest living rodent, the naked mole-rat: insights from a successfully aging species.

Life-long reduction in MnSOD activity results in increased DNA damage and higher incidence of cancer but does not accelerate aging.

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