Nature vs nurture: interplay between the genetic control of telomere length and environmental factors

Influence of EE2 exposure, age and sex on telomere length in European long-snouted seahorse (Hippocampus guttulatus)

After a Telomere Lengthening in juvenile stage, a progressive telomere shortening occurs with age despite higher telomerase level. Telomere Length (TL) may also reflect past physiological state such as a chronic chemical stress. Several studies have revealed a correlation between TL, ageing and/or sex in vertebrates, including teleosts; however, the patterns of telomere dynamics with telomerase mRNA expression, sex, lifespan or chemical stress in teleosts are unclear. The first aim of this study is to verify if telomere length is age and sex-dependent. The second aim is to consider if TL is a useful indicator of stress response in European long-snouted seahorse, Hippocampus guttulatus, an ectothermic and non-model system. We showed that after telomere lengthening during the juvenile stage, a telomeric attrition became significant in sexually mature individuals (p = 0.042). TL decreased in older seahorses despite the presence of somatic telomerase mRNA expression at all life stages studied. There was no difference in TL between males and females, but telomerase mRNA expression was consistently higher in females than males. Exposure to EE2 had no effect on TL in young seahorses, but was correlated with a significant increase in telomerase mRNA expression and various physiological disruptions. Here, a growth retardation of -10 % for body length (p = 0.016) and approximately -45 % for mass (p = 0.001) compared to healthy juvenile seahorses was observed. Our data suggest that telomere dynamics alone should not be used as a marker of EE2 exposure in juvenile seahorses.

Control of telomere length in yeast by SUMOylated PCNA and the Elg1 PCNA unloader

Telomeres cap and protect the linear eukaryotic chromosomes. Telomere length is determined by an equilibrium between positive and negative regulators of telomerase activity. A systematic screen for yeast mutants that affect telomere length maintenance in the yeast Saccharomyces cerevisiae revealed that mutations in any of ~500 genes affects telomere length. One of the genes that, when mutated, causes telomere elongation is ELG1, which encodes an unloader of PCNA, the processivity factor for replicative DNA polymerases. PCNA can undergo SUMOylation on two conserved residues, K164 and K127, or ubiquitination at lysine 164. These modifications have already been implicated in genome stability processes. We report that SUMOylated PCNA acts as a signal that positively regulates telomerase activity. We also uncovered physical interactions between Elg1 and the CST (Cdc13-Stn1-Ten) complex and addressed the mechanism by which Elg1 and Stn1 negatively regulates telomere elongation, coordinated by SUMO. We discuss these results with respect to how chromosomal replication and telomere elongation are coordinated.

Telomeres are shorter in wild Saccharomyces cerevisiae isolates than in domesticated ones

Telomeres are ribonucleoproteins that cap chromosome-ends and their DNA length is controlled by counteracting elongation and shortening processes. The budding yeast Saccharomyces cerevisiae has been a leading model to study telomere DNA length control and dynamics. Its telomeric DNA is maintained at a length that slightly varies between laboratory strains, but little is known about its variation at the species level. The recent publication of the genomes of over 1,000 S. cerevisiae strains enabled us to explore telomere DNA length variation at an unprecedented scale. Here, we developed a bioinformatic pipeline (YeaISTY) to estimate telomere DNA length from whole-genome sequences and applied it to the sequenced S. cerevisiae collection. Our results revealed broad natural telomere DNA length variation among the isolates. Notably, telomere DNA length is shorter in those derived from wild rather than domesticated environments. Moreover, telomere DNA length variation is associated with mitochondrial metabolism, and this association is driven by wild strains. Overall, these findings reveal broad variation in budding yeast's telomere DNA length regulation, which might be shaped by its different ecological life-styles.

Relative Telomere Length Is Associated With Age-Related Macular Degeneration in Women

Purpose

Relative telomere length (RTL) is a biomarker for physiological aging. Premature shortening of telomeres is associated with oxidative stress, which is one possible pathway that might contribute to age-related macular degeneration (AMD). We therefore aimed to investigate the association between RTL and AMD in a well-characterized group of elderly individuals.

Methods

We measured RTL in participants of the AugUR study using a multiplex quantitative PCR-based assay determining the ratio between the telomere product and a single-copy gene product (T/S ratio). AMD was assessed by manual grading of color fundus images using the Three Continent AMD Consortium Severity Scale.

Results

Among the 2262 individuals 70 to 95 years old (627 with AMD and 1635 without AMD), RTL was significantly shorter in individuals with AMD compared to AMD-free participants. In age- and sex-adjusted logistic regression analyses, we observed an 8% higher odds for AMD per 0.1 unit shorter RTL (odds ratio [OR] = 1.08; 95% confidence interval [CI], 1.02–1.14; P = 0.005). The estimates remained stable when adjusted for smoking, high-density lipoprotein cholesterol, cardiovascular disease, diabetes, and hypertension. Interestingly, this association was only present in women (OR = 1.14; 95% CI, 1.06–1.23; P < 0.001), but not in men (OR = 1.01; 95% CI, 0.93–1.10; P = 0.76). A significant sex-by-RTL interaction on AMD was detected (P = 0.043).

Conclusions

Our results show an association of RTL with AMD that was restricted to women. This is in line with altered reactive oxygen species levels and higher telomerase activity in women and provides an indication for a sex-differential pathway for oxidative stress and AMD.

Plasticity, pleiotropy and fitness trade-offs in Arabidopsis genotypes with different telomere lengths

Telomere length has been implicated in the organismal response to stress, but the underlying mechanisms are unknown. Here we examine the impact of telomere length changes on the responses to three contrasting abiotic environments in Arabidopsis, and measure 32 fitness, developmental, physiological and leaf-level anatomical traits. We report that telomere length in wild-type and short-telomere mutants is resistant to abiotic stress, while the elongated telomeres in ku70 mutants are more plastic. We detected significant pleiotropic effects of telomere length on flowering time and key leaf physiological and anatomical traits. Furthermore, our data reveal a significant genotype by environment (G × E) interaction for reproductive fitness, with the benefits and costs to performance depending on the growth conditions. These results imply that life-history trade-offs between flowering time and reproductive fitness are impacted by telomere length variation. We postulate that telomere length in plants is subject to natural selection imposed by different environments.

Urinary arsenic and relative telomere length in 5-7 year old children in Bangladesh

BACKGROUND

Telomere length has been associated with the occurrence and progression of common chronic and age-related diseases, and in younger populations, may represent a biomarker of disease susceptibility. Early childhood is a critical period for telomere biology as this period is characterized by a rapid decline in telomere length due to a large turnover of highly proliferative cells and may represent a period of unique sensitivity to environmental insults. Arsenic (As) exposure has been associated with both telomere lengthening and shortening in adults and children and some evidence suggests the effects may differ by level and timing of exposure.

OBJECTIVES

Given the lack of clarity across studies, we investigated the association between urinary As and leukocyte telomere length among 476 five- to seven-year-old children enrolled in the Bangladesh Environmental Research in Children's Health (BiRCH) cohort.

METHODS

In a series of multivariable models, adjusted for key covariates, we examined associations between urinary As and relative telomere length (RTL) of whole blood DNA.

RESULTS

We observed small but consistent, negative associations between urinary As and RTL, such that a doubling of urinary As was associated with a -0.017 (95% CI: -0.030, -0.005; p = 0.0056) decrease in RTL, in fully adjusted models. We also observed a somewhat stronger inverse relationship between urinary As concentration and RTL among children born to fathers ≥ 30 years of age at the time of birth, than those < 30 years; however, we did not observe a statistically significant interaction.

DISCUSSION

Our study suggests that As influences RTL, with detectable associations in early to mid-childhood. Further studies are needed to confirm our findings and investigate the potential long-term impacts of telomere shortening in childhood on later life health outcomes. Additional studies exploring how dose and timing of exposure may relate to RTL are critical to understanding As's relationship to telomere length.

Telomere attrition: metabolic regulation and signalling function?

Stress exposure can leave long-term footprints within the organism, like in telomeres (TLs), protective chromosome caps that shorten during cell replication and following exposure to stressors. Short TLs are considered to indicate lower fitness prospects, but why TLs shorten under stressful conditions is not understood. Glucocorticoid hormones (GCs) increase upon stress exposure and are thought to promote TL shortening by increasing oxidative damage. However, evidence that GCs are pro-oxidants and oxidative stress is causally linked to TL attrition is mixed . Based on new biochemical findings, we propose the metabolic telomere attrition hypothesis: during times of substantially increased energy demands, TLs are shortened as part of the transition into an organismal 'emergency state', which prioritizes immediate survival functions over processes with longer-term benefits. TL attrition during energy shortages could serve multiple roles including amplified signalling of cellular energy debt to re-direct critical resources to immediately important processes. This new view of TL shortening as a strategy to resolve major energetic trade-offs can improve our understanding of TL dynamics. We suggest that TLs are master regulators of cell homeostasis and propose future research avenues to understand the interactions between energy homeostasis, metabolic regulators and TL.

Rif1 Binding and Control of Chromosome-Internal DNA Replication Origins Is Limited by Telomere Sequestration

The Saccharomyces cerevisiae telomere-binding protein Rif1 plays an evolutionarily conserved role in control of DNA replication timing by promoting PP1-dependent dephosphorylation of replication initiation factors. However, ScRif1 binding outside of telomeres has never been detected, and it has thus been unclear whether Rif1 acts directly on the replication origins that it controls. Here, we show that, in unperturbed yeast cells, Rif1 primarily regulates late-replicating origins within 100 kb of a telomere. Using the chromatin endogenous cleavage ChEC-seq technique, we robustly detect Rif1 at late-replicating origins that we show are targets of its inhibitory action. Interestingly, abrogation of Rif1 telomere association by mutation of its Rap1-binding module increases Rif1 binding and origin inhibition elsewhere in the genome. Our results indicate that Rif1 inhibits replication initiation by interacting directly with origins and suggest that Rap1-dependent sequestration of Rif1 increases its effective concentration near telomeres, while limiting its action at chromosome-internal sites.

In medio stat virtus: unanticipated consequences of telomere dysequilibrium

The integrity of chromosome ends, or telomeres, depends on myriad processes that must balance the need to compact and protect the telomeric, G-rich DNA from detection as a double-stranded DNA break, and yet still permit access to enzymes that process, replicate and maintain a sufficient reserve of telomeric DNA. When unable to maintain this equilibrium, erosion of telomeres leads to perturbations at or near the telomeres themselves, including loss of binding by the telomere protective complex, shelterin, and alterations in transcription and post-translational modifications of histones. Although the catastrophic consequences of full telomere de-protection are well described, recent evidence points to other, less obvious perturbations that arise when telomere length equilibrium is altered. For example, critically short telomeres also perturb DNA methylation and histone post-translational modifications at distal sites throughout the genome. In murine stem cells for example, this dysregulated chromatin leads to inappropriate suppression of pluripotency regulator factors such as Nanog. This review summarizes these recent findings, with an emphasis on how these genome-wide, telomere-induced perturbations can have profound consequences on cell function and fate.

This article is part of the theme issue ‘Understanding diversity in telomere dynamics’.

Association between Body Iron Status and Leukocyte Telomere Length, a Biomarker of Biological Aging, in a Nationally Representative Sample of US Adults

BACKGROUND

Excess iron levels can induce oxidative stress and could therefore affect telomere attrition. However, little is known about the impact of body iron status on telomere length.

OBJECTIVE

Our aim was to examine the association between serum ferritin concentrations, an indicator of body iron status, and leukocyte telomere length in US adults.

DESIGN

We conducted a nationwide, population-based, cross-sectional study.

PARTICIPANTS/SETTING

We used data from the National Health and Nutrition Examination Survey (NHANES) 1999-2002. We included 7,336 adults aged 20 years or older who had available data on serum ferritin levels and telomere length. High ferritin levels were defined as a serum ferritin level >200 ng/mL (449.4 pmol/L) in women and >300 ng/mL (674.1 pmol/L) in men. Low ferritin levels were defined as a serum ferritin level <30 ng/mL (67.4 pmol/L).

MAIN OUTCOME MEASURES

Leukocyte telomere length was assayed using the quantitative polymerase chain reaction method.

STATISTICAL ANALYSES

Linear regression with survey weights was performed to estimate the association between serum ferritin levels and telomere length.

RESULTS

The prevalence of adults with high and low serum ferritin levels was 10.9% and 17.6%, respectively. High ferritin levels were inversely associated with telomere length compared to normal ferritin levels. After adjustment for demographic, socioeconomic and lifestyle factors, body mass index, C-reactive protein, and leukocyte cell type composition, the β coefficient for log-transformed telomere length was -0.020 (standard error [SE]=0.009; P=0.047). The association was stronger in adults aged 65 years or older (β coefficient -0.081, SE=0.017; P<0.001) than in adults 20 to 44 years old (β coefficient -0.023, SE=0.019; P=0.24) or adults aged 45 to 64 years old (β coefficient 0.024, SE=0.015; P=0.10) (P for interaction 0.003). Low ferritin levels were not significantly associated with telomere length compared with normal ferritin levels.

CONCLUSIONS

In a US nationally representative population, high body iron status was associated with shorter telomeres, especially in adults aged 65 years or older.

Telomere shortening triggers a feedback loop to enhance end protection

Telomere homeostasis is controlled by both telomerase machinery and end protection. Telomere shortening induces DNA damage sensing kinases ATM/ATR for telomerase recruitment. Yet, whether telomere shortening also governs end protection is poorly understood. Here we discover that yeast ATM/ATR controls end protection. Rap1 is phosphorylated by Tel1 and Mec1 kinases at serine 731, and this regulation is stimulated by DNA damage and telomere shortening. Compromised Rap1 phosphorylation hampers the interaction between Rap1 and its interacting partner Rif1, which thereby disturbs the end protection. As expected, reduction of Rap1–Rif1 association impairs telomere length regulation and increases telomere–telomere recombination. These results indicate that ATM/ATR DNA damage checkpoint signal contributes to telomere protection by strengthening the Rap1–Rif1 interaction at short telomeres, and the checkpoint signal oversees both telomerase recruitment and end capping pathways to maintain telomere homeostasis.

Long Telomeres Do Not Affect Cellular Fitness in Yeast

Telomeres, the ends of the eukaryotic chromosomes, help to maintain the genome’s integrity and thus play important roles in aging and cancer. Telomere length is strictly controlled in all organisms. In humans, telomeres shorten with age, and it has been proposed that telomere shortening may play a causal role in aging. We took advantage of the availability of yeast strains with genetically or physiologically generated differences in telomere length to measure the effect that telomere length may have on cellular growth. By comparing the growth rates affecting telomere length of various yeast mutants we show that there is no correlation between their telomere length and cellular fitness. We also show that wild-type yeast cells carrying extremely long telomeres (~5 times longer than the average) showed no signs of mitotic or meiotic defects, and competition experiments found no differences in growth between strains with normal telomeres and strains with long telomeres. No advantage or disadvantage of cells with long telomeres was detected under stress conditions either. Finally, telomere length had no effect in a chronological life span assay, which measures survival of post-mitotic-stage cells. We conclude that extreme telomere length has no effects (positive or negative) on the fitness of yeast cells.

Telomeres protect the chromosomal ends from fusion, degradation, and unwanted repair. Therefore, telomeres preserve genome stability and cell viability. In humans, telomeres shorten with each cell duplication event and with age. It has thus been proposed that telomere shortening may be responsible for human aging and that elongation of telomeres may be a way to rejuvenate cells and to combat aging. However, it is difficult to prove this hypothesis in human cells. Yeasts are easy to manipulate and have telomeres whose length is strictly maintained. Here we show that yeast cells manipulated to have extremely long telomeres (~5-fold those of normal cells) did not show any improvement or reduction in fitness compared to otherwise identical cells with telomeres of normal length under all the conditions tested. Moreover, an assay that measures cell aging showed no effect of the presence of extremely long telomeres. We thus conclude that extreme telomere length, at least in yeast cells, does not affect cellular fitness, aging, or senescence.

Association between Long Interspersed Nuclear Element-1 Methylation and Relative Telomere Length in Wilms Tumor

Background:

DNA hypomethylation of long interspersed nuclear elements-1 (LINEs-1) occurs during carcinogenesis, whereas information addressing LINE-1 methylation in Wilms tumor (WT) is limited. The main purpose of our study was to quantify LINE-1 methylation levels and evaluate their relationship with relative telomere length (TL) in WT.

Methods:

We investigated LINE-1 methylation and relative TL using bisulfite-polymerase chain reaction (PCR) pyrosequencing and quantitative PCR, respectively, in 20 WT tissues, 10 normal kidney tissues and a WT cell line. Significant changes were analyzed by t-tests.

Results:

LINE-1 methylation levels were significantly lower (P < 0.05) and relative TLs were significantly shorter (P < 0.05) in WT compared with normal kidney. There was a significant positive relationship between LINE-1 methylation and relative TL in WT (r = 0.671, P = 0.001). LINE-1 Methylation levels were significantly associated with global DNA methylation (r = 0.332, P < 0.01). In addition, relative TL was shortened and LINE-1 methylation was decreased in a WT cell line treated with the hypomethylating agent 5-aza-2′-deoxycytidine compared with untreated WT cell line.

Conclusion:

These results suggest that LINE-1 hypomethylation is common and may be linked to telomere shortening in WT.

Impaired telomere maintenance in Alazami syndrome patients with LARP7 deficiency

BACKGROUND

Loss of function in genes required for telomere maintenance result in disorders known as telomeropathies, which are characterized by a pattern of symptoms including generalized and specific lymphocytopenias as well as very short telomere length and disease anticipation.

METHODS

Because human LARP7 is the most likely ortholog of the Tetrahymena p65 protein, which is required for telomerase activity in that organism, we investigated the effects of LARP7 silencing in human cells as well as in two distinct families with Alazami syndrome (loss of function of LARP7).

RESULTS

Depletion of LARP7 caused a reduction in telomerase enzymatic activity and progressively shorter telomeres in human cancer cell lines. Alazami syndrome patients from two separate cohorts exhibited very short lymphocyte telomeres. Further, wild-type offspring of LARP7 mutant individuals also had very short telomeres, comparable to what is observed in telomerase (hTERT) mutant cohorts.

CONCLUSIONS

Together, these experiments demonstrate that in addition to the readily apparent developmental disorder associated with LARP7 deficiency, an underlying telomeropathy exists even in unaffected siblings of these individuals.

Baseline biopsychosocial determinants of telomere length and 6-year attrition rate

BACKGROUND

Short leukocyte telomere length (TL) and accelerated telomere attrition have been associated with various deleterious health outcomes, although their determinants have not been explored collectively in a large-scale study.

MATERIAL AND METHODS

Leukocyte TL was measured (baseline N=2936; 6-year follow-up N=1860) in participants (18-65 years) from the NESDA study. Baseline determinants of TL included sociodemographics, lifestyle, chronic diseases, psychosocial stressors, and metabolic and physiological stress markers. Multivariate linear regression models were used to examine the associations between these determinants and (1) baseline TL, and (2) 6-year TL change. Multinomial logistic regression analyses were used to examine the predictors of telomere attrition and lengthening, as compared to stable TL.

RESULTS

Short baseline TL was associated with older age, male sex, non-European ethnicity, cigarette smoking, recent life events, and higher triglycerides, glucose and pre-ejection period (R(2)=11.3%). The 6-year telomere attrition was inversely associated with baseline TL (R(2)=51.6%); also older age, long sleep, not having a partner, high childhood trauma index, and gastrointestinal disease were associated with 6-year TL attrition (additional R(2)=3.7%). Telomere attrition seemed to have slightly more predictors than lengthening.

CONCLUSIONS

Sociodemographic, lifestyle, psychosocial stress and metabolic and physiological stress factors are cross-sectionally linked with TL. Telomere attrition over six years was strongly associated with baseline TL, suggesting an internal homeostatic influence. Modulation of the identified determinants may become target of future studies to promote telomere maintenance and healthy aging.

Estimating Telomere Length Heritability in an Unrelated Sample of Adults: Is Heritability of Telomere Length Modified by Life Course Socioeconomic Status?

Telomere length (TL) is a widely used marker of biological aging and is associated with an increased risk of morbidity and mortality. Recently, there has been evidence for an association between TL and socioeconomic status (SES), particularly for measures of education and childhood SES. Individual differences in TL are also influenced by genetic factors, with heritability estimates from twin and sibling studies ranging from 34 to 82 percent. Yet the additive heritability of TL as a result of measured genetic variations and the extent to which heritability is modified by SES is still unknown. Data from the Health and Retirement Study, a nationally representative cohort of older adults (mean age 69 years), were used to provide the first estimates of molecular-based heritability of TL using genome-wide complex trait analysis (GCTA). We found that additive genetic variance contributed 28 percent (p = .012) of total phenotypic variance of TL in the European American sample (n = 3,290). Estimation using the GCTA and KING Robust relationship inference methods did not differ significantly in this sample. None of the variance from the gene-by-SES interactions examined contributed significantly to the total TL variance. Estimation of heritability and genetic interaction with SES in the African American sample (n = 442) was too unstable to provide reliable estimates.

Rapamycin induces pluripotent genes associated with avoidance of replicative senescence

Primary rodent cells undergo replicative senescence, independent from telomere shortening. We have recently shown that treatment with rapamycin during passages 3-7 suppressed replicative senescence in rat embryonic fibroblasts (REFs), which otherwise occurred by 10-14 passages. Here, we further investigated rapamycin-primed cells for an extended number of passages. Rapamycin-primed cells continued to proliferate without accumulation of senescent markers. Importantly, these cells retained the ability to undergo serum starvation- and etoposide-induced cell cycle arrest. The p53/p21 pathway was functional. This indicates that rapamycin did not cause either transformation or loss of cell cycle checkpoints. We found that rapamycin activated transcription of pluripotent genes, oct-4, sox-2, nanog, as well as further upregulated telomerase (tert) gene. The rapamycin-derived cells have mostly non-rearranged, near-normal karyotype. Still, when cultivated for a higher number of passages, these cells acquired a chromosomal marker within the chromosome 3. We conclude that suppression mTORC1 activity may prevent replicative senescence without transformation of rodent cells.