Enhanced protein repair and recycling are not correlated with longevity in 15 vertebrate endotherm species

Abstract

Previous studies have shown that longevity is associated with enhanced cellular stress resistance. This observation supports the disposable soma theory of aging, which suggests that the investment made in cellular maintenance will be proportional to selective pressures to extend lifespan. Maintenance of protein homeostasis is a critical component of cellular maintenance and stress resistance. To test the hypothesis that enhanced protein repair and recycling activities underlie longevity, we measured the activities of the 20S/26S proteasome and two protein repair enzymes in liver, heart and brain tissues of 15 different mammalian and avian species with maximum lifespans (MLSP) ranging from 3 to 30 years. The data set included Snell dwarf mice, in which lifespan is increased by ∼50% compared to their normal littermates. None of these activities in any of the three tissues correlated positively with MLSP. In liver, 20S/26S proteasome and thioredoxin reductase (TrxR) activities correlated negatively with body mass. In brain tissue, TrxR was also negatively correlated with body mass. Glutaredoxin (Grx) activity in brain was negatively correlated with MLSP and this correlation remained after residual analysis to remove the effects of body mass, but was lost when the data were analysed using Felsenstein's independent contrasts. Snell dwarf mice had marginally lower 20S proteasome, TrxR and Grx activities than normal controls in brain, but not heart tissue. Thus, increased longevity is not associated with increased protein repair or proteasomal degradation capacities in vertebrate endotherms.

Fig. 1

Correlation between 20S proteasome activity and MLSP. a 20S proteasome activity is negatively correlated with MLSP in liver, but not in heart (b) or brain (c). Analysis of the residuals of 20S proteasome activity plotted against residual of MLSP (d) shows the absence of a statistically significant correlation. e Statistically significant correlation of liver 20S proteasome activity with body mass (p < 0.05). All values are natural log-transformed and each data point represents the mean from duplicate measurement from three to eight individuals of a given species

Fig. 2

Correlation between 26S proteasome activity and MLSP. 26S proteasome activity correlates negatively with MLSP (p < 0.025) in liver (a) but not brain (b). The trend in (a) is driven by the correlation of liver 26S proteasome activity with body mass (c). All values are natural log-transformed and each data point represents the mean from duplicate measurement from three to eight individuals of a given species

Fig. 3

Ubiquitin protein levels do not correlate with MLSP. a The amino acid sequence of ubiquitin is conserved in the seven species analysed. b A representative western detection of ubiquitin in electrophoresed rabbit liver homogenate proteins of four individuals. Sizes in kilodalton represent protein marker sizes. Lanes represent ubiquitin protein levels in liver of different species. c, d No correlation between extent of protein ubiquitylation and MLSP in c liver and d brain tissue. All values are natural log-transformed and each data point represents the mean from duplicate measurement from three to eight individuals of a given species

Fig. 4

Correlation between thioredoxin reductase (TrxR) activity and MLSP or body mass. TrxR activity is negatively correlated with MLSP a in liver (p < 0.025), but not in b heart or c brain tissue. d–f Correlation of TrxR activity with the species’ body mass. TrxR is negatively correlated with body mass in d liver (p < 0.05), and f brain tissue, but not in e heart tissue. All values are natural log-transformed and each data point represents the mean from duplicate measurement from three to eight individuals of a given species

Fig. 5

Correlation between glutaredoxin (Grx) activity and MLSP. Grx activity in a liver and b heart does not correlate with MLSP. Brain Grx does correlate negatively with MLSP (c) (p < 0.025). All values are natural log-transformed and each data point represents the mean from duplicate measurement from three to eight individuals of a given species

Fig. 6

Protein degradation and protein repair enzymes are not upregulated in long-lived Snell dwarf mice compared to normal controls. a 20S proteasome activity is significantly lower in Snell normal mice in brain tissue but no significance is found in heart tissue. b 26S proteasome activity and c ubiquitin protein levels are not different between Snell dwarf and Snell normal mice in brain tissue. d Thioredoxin reductase and e glutaredoxin activity levels are significantly higher in Snell normal mice compared to Snell dwarf mice in brain tissue but not in heart tissue. White bars represent Snell normal mice and black bars represent Snell dwarf mice. Values are means ± SEM of duplicate measurements made in each of five individuals per genotype. *p < 0.05, significantly different using a two-tailed t test