Diana van Heemst

Telomere length in white blood cells is not associated with morbidity or mortality in the oldest old: a population‐based study

Cross‐sectional studies have repeatedly suggested peripheral blood monocyte telomere length as a biomarker of aging. To test this suggestion in a large population‐based follow‐up study of the oldest old, we measured telomere length at baseline in 598 participants of the Leiden 85‐plus Study (mean age at baseline 89.8 years). We also obtained second telomere measurements from 81 participants after an average time span of between 3.9 and 12.9 years. Telomere length at baseline was not predictive for mortality (P > 0.40 for all‐cause, cardiovascular causes, cancer or infectious diseases, Cox regression for gender‐adjusted tertiles of telomere length) or for the incidence of dementia (P = 0.78). Longitudinally, telomere length was highly unstable in a large fraction of participants. We conclude that blood monocyte telomere length is not a predictive indicator for age‐related morbidity and mortality at ages over 85 years, possibly because of a high degree of telomere length instability in this group.

Reduced insulin/IGF-1 signalling and human longevity

Evidence is accumulating that aging is hormonally regulated by an evolutionarily conserved insulin/IGF‐1 signalling (IIS) pathway. Mutations in IIS components affect lifespan in Caenorhabditis elegans, Drosophila melanogaster and mice. Most long‐lived IIS mutants also show increased resistance to oxidative stress. In D. melanogaster and mice, the long‐lived phenotype of several IIS mutants is restricted to females. Here, we analysed the relationship between IIS signalling, body height and longevity in humans in a prospective follow‐up study. Based on the expected effects (increased or decreased signalling) of the selected variants in IIS pathway components (GHRHR, GH1, IGF1, INS, IRS1), we calculated composite IIS scores to estimate IIS pathway activity. In addition, we analysed the relative impact on lifespan and body size of the separate variants in multivariate models. In women, lower IIS scores are significantly associated with lower body height and improved old age survival. Multivariate analyses showed that these results were most pronounced for the GH1 SNP, IGF1 CA repeat and IRS1 SNP. In females, for variant allele carriers of the GH1 SNP, body height was 2 cm lower (P = 0.007) and mortality 0.80‐fold reduced (P = 0.019) when compared with wild‐type allele carriers. Thus, in females, genetic variation causing reduced IIS activation is beneficial for old age survival. This effect was stronger for the GH1 SNP than for variation in the conserved IIS genes that were found to affect longevity in model organisms.

Variation in the human TP53 gene affects old age survival and cancer mortality

Longevity may depend on a balance between tumor suppression and tissue renewal mechanisms [Campisi, J., 2003. Cancer and ageing: rival demons? Nat. Rev. Cancer 3 (5), 339-349]. Mice with constitutively activated p53 are almost cancer free but their life span is reduced and accompanied by early tissue atrophy [Tyner et al., 2002. p53 mutant mice that display early ageing-associated phenotypes. Nature 415 (6867) 45-53]. Replacement of arginine (Arg) by proline (Pro) at position 72 of human p53 decreases its apoptotic potential [Dumont et al., 2003. The codon 72 polymorphic variants of p53 have markedly different apoptotic potential. Nat. Genet. 33 (3), 357-365] providing a tool to test for a similar trade-off in humans. Using a formal meta-analysis of the published literature we show that carriers of the TP53 codon 72 Pro/Pro genotype have an increased cancer risk compared to Arg/Arg carriers (p<0.05). Next, in a prospective study of 1226 people aged 85 years and over we show that carriers of the Pro/Pro genotype have a 41% increased survival (p = 0.032) despite a 2.54 fold increased (p = 0.007) proportional mortality from cancer. It is suggested that human p53 protect against cancer but at a cost of longevity.

Genome-wide association meta-analysis of human longevity identifies a novel locus conferring survival beyond 90 years of age

The genetic contribution to the variation in human lifespan is ∼25%. Despite the large number of identified disease-susceptibility loci, it is not known which loci influence population mortality. We performed a genome-wide association meta-analysis of 7729 long-lived individuals of European descent (≥85 years) and 16 121 younger controls (<65 years) followed by replication in an additional set of 13 060 long-lived individuals and 61 156 controls. In addition, we performed a subset analysis in cases aged ≥90 years. We observed genome-wide significant association with longevity, as reflected by survival to ages beyond 90 years, at a novel locus, rs2149954, on chromosome 5q33.3 (OR = 1.10, P = 1.74 × 10−8). We also confirmed association of rs4420638 on chromosome 19q13.32 (OR = 0.72, P = 3.40 × 10−36), representing the TOMM40/APOE/APOC1 locus. In a prospective meta-analysis (n = 34 103), the minor allele of rs2149954 (T) on chromosome 5q33.3 associates with increased survival (HR = 0.95, P = 0.003). This allele has previously been reported to associate with low blood pressure in middle age. Interestingly, the minor allele (T) associates with decreased cardiovascular mortality risk, independent of blood pressure. We report on the first GWAS-identified longevity locus on chromosome 5q33.3 influencing survival in the general European population. The minor allele of this locus associates with low blood pressure in middle age, although the contribution of this allele to survival may be less dependent on blood pressure. Hence, the pleiotropic mechanisms by which this intragenic variation contributes to lifespan regulation have to be elucidated.

Mental performance in old age dependent on Cortisol and genetic variance in the mineralocorticoid and glucocorticoid receptors

Depression and cognitive decline have been associated with changes in circulating cortisol concentrations. Cortisol exerts its functions through mineralocorticoid (MR) and glucocorticoid (GR) receptors. However, data on the influence of variations in the MR and GR genes on depressive symptoms and cognitive functioning in older adults are scarce. Therefore, we explored the impact of MR-215G/C, MR-I180V, GR-ER22/23EK, GR-N363S, and GR-BclI polymorphisms on these end points in the population-based Leiden 85-plus Study. This prospective study includes 563 participants aged 85 years and older, with a mean follow-up of 4.2 years. In this study, high morning cortisol levels (per 1 SD cortisol) associated with impairments in global cognitive functioning (p=0.002) at baseline (age 85). These impairments were mainly attributable to lower attention (p=0.057) and slower processing speed (p=0.014). Similar effects were also observed during follow-up (age 85–90), where participants with higher cortisol levels (per 1 SD cortisol) had impaired global cognitive functioning (p=0.003), as well as impairments in attention (p=0.034) and processing speed (p=0.013). Changes in depressive symptoms were observed for the MR-I180V single-nucleotide polymorphism (SNP), where during follow-up the prevalence of depressive symptoms was higher in the 180V-allele carriers (p=0.049) compared to noncarriers. Dependent on these polymorphisms, no differences in overall and in specific domains of cognitive functioning were observed. In conclusion, the MR-I180V SNP has a specific effect on depressive symptoms, independent from cognitive functioning, and other polymorphisms in the MR and GR genes. In contrast, these genetic variants in the MR and GR genes do not influence cognitive functioning in old age.

A Meta-Analysis of Thyroid-Related Traits Reveals Novel Loci and Gender-Specific Differences in the Regulation of Thyroid Function

Thyroid hormone is essential for normal metabolism and development, and overt abnormalities in thyroid function lead to common endocrine disorders affecting approximately 10% of individuals over their life span. In addition, even mild alterations in thyroid function are associated with weight changes, atrial fibrillation, osteoporosis, and psychiatric disorders. To identify novel variants underlying thyroid function, we performed a large meta-analysis of genome-wide association studies for serum levels of the highly heritable thyroid function markers TSH and FT4, in up to 26,420 and 17,520 euthyroid subjects, respectively. Here we report 26 independent associations, including several novel loci for TSH (PDE10A, VEGFA, IGFBP5, NFIA, SOX9, PRDM11, FGF7, INSR, ABO, MIR1179, NRG1, MBIP, ITPK1, SASH1, GLIS3) and FT4 (LHX3, FOXE1, AADAT, NETO1/FBXO15, LPCAT2/CAPNS2). Notably, only limited overlap was detected between TSH and FT4 associated signals, in spite of the feedback regulation of their circulating levels by the hypothalamic-pituitary-thyroid axis. Five of the reported loci (PDE8B, PDE10A, MAF/LOC440389, NETO1/FBXO15, and LPCAT2/CAPNS2) show strong gender-specific differences, which offer clues for the known sexual dimorphism in thyroid function and related pathologies. Importantly, the TSH-associated loci contribute not only to variation within the normal range, but also to TSH values outside the reference range, suggesting that they may be involved in thyroid dysfunction. Overall, our findings explain, respectively, 5.64% and 2.30% of total TSH and FT4 trait variance, and they improve the current knowledge of the regulation of hypothalamic-pituitary-thyroid axis function and the consequences of genetic variation for hypo- or hyperthyroidism.

VDR gene variants associate with cognitive function and depressive symptoms in old age

Vitamin D has been recently implicated in brain function. Our objective was to test whether genetic variance in the vitamin D receptor (VDR) gene is associated with cognitive functioning and depressive symptoms in old age. The study was carried out in the prospective population-based Leiden 85-plus Study. All 563 participants of the study were genotyped for Cdx-2, FokI, BsmI, ApaI and TaqI polymorphisms in the VDR gene. Our data revealed an overall worse performance on tests measuring cognitive functioning for carriers of BsmI (p=0.013) and TaqI (p=0.004) polymorphisms, and of haplotype 2 (BAt) (p=0.004). In contrast, carriers of ApaI variant-allele and of haplotype 1 (baT) had better cognitive functioning together with less depressive symptoms. These associations could not be explained by differences in calcium levels, and by selective survival, since no associations between the VDR gene variants and calcium levels and mortality were observed. In conclusion, our results show that genetic variance in the VDR gene influences the susceptibility to age-related changes in cognitive functioning and in depressive symptoms.

ApoE plasma levels and risk of cardiovascular mortality in old age

Background The ɛ2, ɛ3, and ɛ4 alleles of the apolipoprotein E gene (APOE) encode three isoforms, apoE2, E3, and E4, respectively. The apoE isoforms circulate in different plasma concentrations, but plasma concentrations of the same isoform also differ between individuals. Whereas the isoforms have been associated with cardiovascular disease, the relation between plasma apoE levels and cardiovascular disease is unknown. Methods and Findings We assessed APOE genotypes, plasma levels of apoE, cardiovascular risk factors, and mortality in a population-based sample of 546 individuals aged 85 y who participated in the Leiden 85-plus Study and were prospectively followed for specific causes of death for 5 y. Participants in the highest tertile of apoE levels suffered a twofold-increased risk of cardiovascular mortality (hazard ratio compared to lowest tertile, 2.08; 95% confidence interval [CI], 1.30 to 3.33). Among the 324 participants with the ɛ3ɛ3 genotype, the hazard from cardiovascular disease was threefold increased (highest versus lowest tertile 3.01; 95% CI 1.60 to 5.66), with similar estimates for men and women. Other causes of death were not increased significantly. Plasma levels of apoE in ɛ3ɛ3 participants were positively correlated with total cholesterol ( p < 0.001), low-density lipoprotein cholesterol ( p < 0.001) and triglycerides ( p < 0.001) and negatively with high-density lipoprotein cholesterol levels ( p = 0.010). Adjustment for plasma lipids did not change the hazard ratios, whereas interaction was absent. The risk associated with high levels of apoE, however, was strongest in participants from the lowest tertile of C-reactive protein (CRP) levels and absent in those from the highest tertile ( p interaction < 0.001). Among participants from the lowest tertile of CRP levels, those with a high apoE levels had a significantly steeper increase in CRP than those with low apoE levels ( p = 0.020). Similar cardiovascular mortality risks as in ɛ3ɛ3 participants were found in ɛ2 and ɛ4 carriers. Conclusions In old age, high plasma apoE levels precede an increase of circulating CRP and strongly associates with cardiovascular mortality, independent of APOE genotype and plasma lipids.

Haplotypes in the human Foxo1a and Foxo3a genes; impact on disease and mortality at old age

Recently, the Daf-16 gene has been shown to regulate the lifespan of nematodes and flies. In mammals, the Daf-16 homologues are forkhead (FOXO) transcription factors, of which specific functions have been identified for Foxo1a and Foxo3a. Despite that, their influence on human age-related trajectories and lifespan is unknown. Here, we analysed the effect of genetic variance in Foxo1a and Foxo3a on metabolic profile, age-related diseases, fertility, fecundity and mortality. This study was carried out in the prospective population-based Leiden 85-plus Study, which includes 1245 participants, aged 85 years or more. The mean follow-up time was 4.4 years. Haplotype analyses of Foxo1a revealed that carriers of haplotype 3 ‘TCA’ have higher HbA1c levels (P=0.025) and a 1.14-fold higher all-cause mortality risk (P=0.021). This increase in mortality was attributable to death from diabetes, for which a 2.43-fold increase was observed (P=0.025). The analyses with Foxo3a haplotypes revealed no differences in metabolic profile, fertility or fecundity. However, increased risks of stroke were observed for Foxo3a block-A haplotype 2 ‘GAGC’ (P=0.007) and haplotype 4 ‘AAAT’ (P=0.014) carriers. In addition, the haplotype 2 ’GAGC’ carriers had a 1.13-fold increased risk for all-cause mortality (P=0.036) and 1.19-fold increased risk for cardiovascular mortality (P=0.052). In conclusion, this study shows that genetic variation in evolutionarily conserved Foxo1a and Foxo3a genes influences lifespan in our study population.

Genes encoding longevity: from model organisms to humans

Ample evidence from model organisms has indicated that subtle variation in genes can dramatically influence lifespan. The key genes and molecular pathways that have been identified so far encode for metabolism, maintenance and repair mechanisms that minimize age‐related accumulation of permanent damage. Here, we describe the evolutionary conserved genes that are involved in lifespan regulation of model organisms and humans, and explore the reasons of discrepancies that exist between the results found in the various species. In general, the accumulated data have revealed that when moving up the evolutionary ladder, together with an increase of genome complexity, the impact of candidate genes on lifespan becomes smaller. The presence of genetic networks makes it more likely to expect impact of variation in several interacting genes to affect lifespan in humans. Extrapolation of findings from experimental models to humans is further complicated as phenotypes are critically dependent on the setting in which genes are expressed, while laboratory conditions and modern environments are markedly dissimilar. Finally, currently used methodologies may have only little power and validity to reveal genetic variation in the population. In conclusion, although the study of model organisms has revealed potential candidate genetic mechanisms determining aging and lifespan, to what extent they explain variation in human populations is still uncertain.