Molecular markers of DNA repair and brain metabolism correlate with cognition in centenarians

Abstract

Oxidative stress is an important factor in age-associated neurodegeneration. Accordingly, mitochondrial dysfunction and genomic instability have been considered as key hallmarks of aging and have important roles in age-associated cognitive decline and neurodegenerative disorders. In order to evaluate whether maintenance of cognitive abilities at very old age is associated with key hallmarks of aging, we measured mitochondrial bioenergetics, mitochondrial DNA copy number and DNA repair capacity in peripheral blood mononuclear cells from centenarians in a Danish 1915 birth cohort (n = 120). Also, the circulating levels of brain-derived neurotrophic factor, NAD⁺ /NADH and carbonylated proteins were measured in plasma of the centenarians and correlated to cognitive capacity. Mitochondrial respiration was well preserved in the centenarian cohort when compared to young individuals (21-35 years of age, n = 33). When correlating cognitive performance of the centenarians with mitochondrial function such as basal respiration, ATP production, reserve capacity and maximal respiration, no overall correlations were observed, but when stratifying by sex, inverse associations were observed in the males (p < 0.05). Centenarians with the most severe cognitive impairment displayed the lowest activity of the central DNA repair enzyme, APE1 (p < 0.05). A positive correlation between cognitive capacity and levels of NAD⁺ /NADH was observed (p < 0.05), which may be because NAD⁺ /NADH consuming enzyme activities strive to reduce the oxidative DNA damage load. Also, circulating protein carbonylation was lowest in centenarians with highest cognitive capacity (p < 0.05). An opposite trend was observed for levels of brain-derived neurotrophic factor (p = 0.17). Our results suggest that maintenance of cognitive capacity at very old age may be associated with cellular mechanisms related to oxidative stress and DNA metabolism.

Keywords: Centenarians; Cognition; DNA maintenance; Mitochondria; Oxidative stress.

Fig. 1

Mitochondrial function is preserved in centenarians. Group-wise comparison of mitochondrial function in PBMCs from centenarians (n = 120) and young individuals (n = 33). Each value represents the mean of 2–5 replicates. Median ± IQR (interquartile range) is shown

Fig. 2

PBMC mitochondrial respiration correlates negatively with the cognitive scores in centenarian men. A) The association between the CCS and the mitochondrial parameters in women (n = 47) and men (n = 15) has been tested using a linear regression and a Spearman rank correlation in case of non-normal distribution. B) The association between the MMSE and the mitochondrial parameters in women (n = 88) and men (n = 25) has been tested using a linear regression and a Spearman rank correlation in case of non-normal distribution. A tendency line is plotted when the correlation analysis is significant in normal distributed data. Each value represents the mean of 2–5 replicates. For a description of the statistical analyses performed, see Supplementary Table 3. CCS cognitive composite score, MMSE mini-mental state examination

Fig. 3

PBMC mitochondrial respiration is lower in centenarians that achieve a CCS in comparison to the centenarians that do not achieve a CCS. Group-wise comparison of mitochondrial respiration in PBMCs from centenarians that achieved a cognitive composite score (Yes; n = 62) and centenarians that did not achieve a cognitive composite score (No; n = 58). Each value represents the mean of 2–5 replicates. Median ± IQR is shown. For a description of the statistical analyses performed, see Supplementary Table 5. *p < 0.05; ** p < 0.01

Fig. 4

Comparison of APE1 protein expression and incision activity in PBMCs from centenarians and young individuals. A) Group-wise comparison of APE1 protein expression in PBMCs from centenarians (n = 89) and young individuals (n = 30). Median ± IQR is shown. B) APE1 incision activity (amol/ng/min) in young individuals (n = 31) compared to centenarians (n = 95). Mean ± SD is shown. *** p < 0.001

Fig. 5

High APE1 protein expression and activity in PBMCs from centenarians are associated with a high MMSE score. The association between the MMSE and A) the relative APE1 protein expression (n = 84) has been tested using a Spearman rank correlation and B) APE1 incision activity (n = 90) using a linear regression (r = 0.16; p value = 0.13). C) Relative APE1 protein expression and D) APE1 incision activity in PBMCs from centenarians classified with MMSE scores below 17, MMSE scores between 18 and 23 and MMSE scores above 24. Median ± IQR is shown in C), and mean ± SD is shown in D). Differences were assessed by Kruskal–Wallis test followed by Dunn’s multiple comparison test with Bonferroni correction in C) and one-way ANOVA in D)

Fig. 6

High NAD⁺ /NADH in plasma from centenarians is associated with high cognitive scores. A) Comparison of NAD⁺/NADH in plasma from centenarians (n = 120) and young individuals (n = 31). Median ± IQR is shown. B) and C) Association between the levels of NAD⁺/NADH in plasma of centenarians and cognitive measurements. B) CCS (n = 59) and C) MMSE (n = 96) (rho = 0.38; p value = 0.085). The associations between cognitive scores and NAD⁺/NADH have been tested using a Spearman rank correlation

Fig. 7

Protein carbonylation is higher in PBMCs from centenarians in comparison to young individuals and is negatively associated with cognition. A) Comparison of carbonylated proteins in plasma from centenarians (n = 120) and young individuals (n = 31). Mean ± SD is shown. *p < 0.05. B) Association between the carbonylated proteins in plasma of centenarians and CCS (n = 59). C) Association between the carbonylated proteins in plasma of centenarians and MMSE (n = 96) (r =  − 0.11; p value = 0.27). The associations have been tested using linear regression

Fig. 8

BDNF levels in plasma from centenarians are higher than in young individuals and are associated positively with cognition. A) Comparison of BDNF levels in plasma from centenarians (n = 120) and young individuals (n = 31). ***p < 0.001. Median ± IQR is shown. B) Association between the BDNF levels in plasma of centenarians and MMSE (n = 83). The association between cognitive scores and BDNF levels has been tested using a Spearman rank correlation (rho = 0.13; p value = 0.17)

Fig. 9

Overview. A) Graphical illustration of cellular mechanisms correlating with maintenance of cognitive capacity in centenarians. Unbalanced mitochondrial metabolism may lead to oxidative stress, with an increase of protein and DNA oxidation. Higher levels of NAD⁺/NADH and BDNF may stimulate the DNA damage response (PARylation) and DNA repair activity (APE1), respectively. Altogether, this may lead to less oxidative damage and better maintenance of cognitive capacity. B) Summary of findings