Telomere length in different tissues of elderly patients

Association between leukocyte telomere length and the risk of pancreatic cancer: Findings from a prospective study

INTRODUCTION

Telomeres and telomerase play important role in maintaining chromosome integrity and genomic stability. Recent epidemiologic data showed inconsistent findings which suggested that both short and long leukocyte telomeres could be associated with increased risk of pancreatic cancer. We prospectively examined the association between telomere length and pancreatic cancer risk in a population-based cohort study.

METHODS

The Singapore Chinese Health Study recruited 63,257 Chinese aged 45 to 74 years from 1993 to 1998 in Singapore. Relative telomere length in peripheral blood leukocytes was quantified using a validated monochrome multiplex quantitative polymerase chain reaction method in 26,540 participants, including 116 participants who later developed pancreatic cancer after an average of 13 years of follow-up. Cox proportional hazard regression method was used to calculate hazard ratio (HR) and its 95% confidence interval (CI) of pancreatic cancer risk associated with telomere length, with adjustment for confounding factors.

RESULTS

Longer telomeres were significantly associated with higher risk of pancreatic cancer (Ptrend = 0.02). Compared with lowest quartile, subjects with highest quartile of telomere length had an HR of 2.18 (95% CI: 1.25-3.80) for developing pancreatic cancer. In stratified analysis, this association remained among pancreatic adenocarcinoma patients but not among pancreatic non-adenocarcinoma patients. In continuous scale, the HRs and 95% CIs were 3.08 (1.17-8.11) for adenocarcinoma patients and 1.47 (0.43-5.06) for non-adenocarcinoma patients. The HRs and 95% CIs of the highest quartile of telomere length, compared with the lowest quartile, for adenocarcinoma and non-adenocarcinoma were 2.50 (1.22-5.13) and 1.63 (0.66-4.03), respectively. The length of follow-up from the collection of blood for the measurement of telomere length to the diagnosis of cancer (median = 8.0, range: from 5.0 months to 16.2 years) had no significant impact on the association between telomere length and pancreatic cancer risk.

CONCLUSIONS

The present study demonstrates that longer telomeres are associated with increased risk of overall pancreatic cancer.

Prenatal and Childhood Traffic-Related Air Pollution Exposure and Telomere Length in European Children: The HELIX Project

BACKGROUND

Telomere length is a molecular marker of biological aging.

OBJECTIVE

Here we investigated whether early-life exposure to residential air pollution was associated with leukocyte telomere length (LTL) at 8 y of age.

METHODS

In a multicenter European birth cohort study, HELIX (Human Early Life Exposome) ([Formula: see text]), we estimated prenatal and 1-y childhood exposure to nitrogen dioxide ([Formula: see text]), particulate matter with aerodynamic diameter [Formula: see text] ([Formula: see text]), and proximity to major roads. Average relative LTL was measured using quantitative real-time polymerase chain reaction (qPCR). Effect estimates of the association between LTL and prenatal, 1-y childhood air pollution, and proximity to major roads were calculated using multiple linear mixed models with a random cohort effect and adjusted for relevant covariates.

RESULTS

LTL was inversely associated with prenatal and 1-y childhood [Formula: see text] and [Formula: see text] exposures levels. Each standard deviation (SD) increase in prenatal [Formula: see text] was associated with a [Formula: see text] (95% CI: [Formula: see text], [Formula: see text]) change in LTL. Prenatal [Formula: see text] was nonsignificantly associated with LTL ([Formula: see text] per SD increase; 95% CI: [Formula: see text], 0.6). For each SD increment in 1-y childhood [Formula: see text] and [Formula: see text] exposure, LTL shortened by [Formula: see text] (95% CI: [Formula: see text], [Formula: see text]) and [Formula: see text] (95% CI: [Formula: see text], 0.1), respectively. Each doubling in residential distance to nearest major road during childhood was associated with a 1.6% (95% CI: 0.02, 3.1) lengthening in LTL.

CONCLUSION

Lower exposures to air pollution during pregnancy and childhood were associated with longer telomeres in European children at 8 y of age. These results suggest that reductions in traffic-related air pollution may promote molecular longevity, as exemplified by telomere length, from early life onward. https://doi.org/10.1289/EHP4148.

Telomeres, Telomerase and Ageing

Telomeres are specialised structures at the end of linear chromosomes. They consist of tandem repeats of the hexanucleotide sequence TTAGGG, as well as a protein complex called shelterin. Together, they form a protective loop structure against chromosome fusion and degradation. Shortening or damage to telomeres and opening of the loop induce an uncapped state that triggers a DNA damage response resulting in senescence or apoptosis.Average telomere length, usually measured in human blood lymphocytes, was thought to be a biomarker for ageing, survival and mortality. However, it becomes obvious that regulation of telomere length is very complex and involves multiple processes. For example, the "end replication problem" during DNA replication as well as oxidative stress are responsible for the shortening of telomeres. In contrast, telomerase activity can potentially counteract telomere shortening when it is able to access and interact with telomeres. However, while highly active during development and in cancer cells, the enzyme is down-regulated in most human somatic cells with a few exceptions such as human lymphocytes. In addition, telomeres can be transcribed, and the transcription products called TERRA are involved in telomere length regulation.Thus, telomere length and their integrity are regulated at many different levels, and we only start to understand this process under conditions of increased oxidative stress, inflammation and during diseases as well as the ageing process.This chapter aims to describe our current state of knowledge on telomeres and telomerase and their regulation in order to better understand their role for the ageing process.

Sex- And tissue-specific differences in telomere length in a reptile

The usage of telomere length (TL) in blood as a proxy for the TL of other tissues relies on the assumption that telomere dynamics across all tissues are similar. However, telomere attrition can be caused by reactive oxygen species (ROS) which may vary with metabolic rate, which itself varies across organs depending upon the life history strategy of an organism. Thus, we chose to measure the telomeres of various cell types in juvenile painted dragon lizards, Ctenophorus pictus, given their unusual life history strategy. Individuals typically only experience a single mating season. We measured the TL of male and female dragons using qPCR and observed that TL varied with tissue type and sex. Telomeres of blood cells were longer than those of liver, heart, brain, and spleen, and females had longer telomeres than males. Brain telomeres in males were approximately half the length of those in females. Telomeric attrition in the male brain may be due to the need for rapid learning of reproductive tactics (territory patrol and defense, mate-finding). Significant correlations between the TL of tissue types suggest that blood TL may be a useful proxy for the TL of other tissues. Our comparison of organ-specific telomere dynamics, the first in a reptile, suggests that the usage of blood TL as a proxy requires careful consideration of the life history strategy of the organism.

Mendelian Randomization and mediation analysis of leukocyte telomere length and risk of lung and head and neck cancers

BACKGROUND

Evidence from observational studies of telomere length (TL) has been conflicting regarding its direction of association with cancer risk. We investigated the causal relevance of TL for lung and head and neck cancers using Mendelian Randomization (MR) and mediation analyses.

METHODS

We developed a novel genetic instrument for TL in chromosome 5p15.33, using variants identified through deep-sequencing, that were genotyped in 2051 cancer-free subjects. Next, we conducted an MR analysis of lung (16 396 cases, 13 013 controls) and head and neck cancer (4415 cases, 5013 controls) using eight genetic instruments for TL. Lastly, the 5p15.33 instrument and distinct 5p15.33 lung cancer risk loci were evaluated using two-sample mediation analysis, to quantify their direct and indirect, telomere-mediated, effects.

RESULTS

The multi-allelic 5p15.33 instrument explained 1.49-2.00% of TL variation in our data (p = 2.6 × 10-9). The MR analysis estimated that a 1000 base-pair increase in TL increases risk of lung cancer [odds ratio (OR) = 1.41, 95% confidence interval (CI): 1.20-1.65] and lung adenocarcinoma (OR = 1.92, 95% CI: 1.51-2.22), but not squamous lung carcinoma (OR = 1.04, 95% CI: 0.83-1.29) or head and neck cancers (OR = 0.90, 95% CI: 0.70-1.05). Mediation analysis of the 5p15.33 instrument indicated an absence of direct effects on lung cancer risk (OR = 1.00, 95% CI: 0.95-1.04). Analysis of distinct 5p15.33 susceptibility variants estimated that TL mediates up to 40% of the observed associations with lung cancer risk.

CONCLUSIONS

Our findings support a causal role for long telomeres in lung cancer aetiology, particularly for adenocarcinoma, and demonstrate that telomere maintenance partially mediates the lung cancer susceptibility conferred by 5p15.33 loci.

Telomere biology and age-related diseases

Telomeres are the protective end caps of chromosomes and shorten with every cell division. Telomere length has been proposed as a biomarker of biological age and a risk factor for age-related diseases. Epidemiologic studies show an association between leukocyte telomere length (LTL) and mortality. There is solid evidence that links LTL with cardiovascular disease. Short telomeres promote atherosclerosis and impair the repair of vascular lesions. Alzheimer's disease patients have also a reduced LTL. Telomeres measured in tumor tissue from breast, colon and prostate are shorter than in healthy tissue from the same organ and the same patient. In healthy tissue directly adjacent to these tumors, telomeres are also shorter than in cells that are more distant from the cancerous lesion. A reduced telomere length in cancer tissue from breast, colon and prostate is associated with an advanced disease state at diagnosis, faster disease progression and poorer survival. By contrast, results regarding LTL and cancer are inconsistent. Furthermore, the majority of studies did not find significant associations between LTL, bone mineral density (BMD) and osteoporosis. The present manuscript gives an overview about our current understanding of telomere biology and reviews existing knowledge regarding the relationship between telomere length and age-related diseases.

Cross-sectional associations of sex hormones with leucocyte telomere length, a marker of biological age, in a community-based cohort of older men

CONTEXT

Telomeres protect chromosomes from damage, and shorter leucocyte telomere length (LTL) is a marker of advancing biological age. The association between testosterone (T) and its bioactive metabolites, dihydrotestosterone (DHT) and oestradiol (E2) with telomere length, particularly in older men, is uncertain. The study aimed to clarify associations of sex hormones with LTL in older men.

PARTICIPANTS AND METHODS

We used cross-sectional data from 2913 men aged 76.7 ± 3.2 years with morning blood samples assayed for T, DHT, E2 (mass spectrometry), and sex hormone-binding globulin (SHBG, immunoassay), to correlate sex hormones with LTL measured using PCR and expressed as T/S ratio in multivariable linear regression models adjusted for age, cardiometabolic risk factors and cardiovascular disease history.

RESULTS

Average difference per decade of age was T -0.46 nmol/L, DHT -0.11 nmol/L, E2 -7.5 pmol/L, SHBG +10.2 nmol/L and LTL (T/S ratio) -0.065. E2 correlated with T/S ratio (r = 0.038, P = 0.039) and SHBG was inversely correlated (r = -0.053, P = 0.004). After multivariable adjustment, E2 was associated with T/S ratio (per 1 SD increase E2: coefficient 0.011, P = 0.043), T and DHT were not associated. When E2 and SHBG were simultaneously included, E2 remained positively (coefficient 0.014, P = 0.014) and SHBG inversely (coefficient -0.013, P = 0.037) associated with T/S ratio.

CONCLUSIONS

In older men, neither T nor DHT is associated with LTL while E2 is independently associated with LTL and SHBG is inversely associated, thus relating sex hormone exposure to lower biological age. Further research is needed to determine causality and clarify the role of sex hormones in male ageing.

Maternal cortisol output in pregnancy and newborn telomere length: Evidence for sex-specific effects

Newborn telomere length is a potential biomarker of the effects of maternal-fetal processes on offspring long-term health. A number of maternal psychosocial and environmental factors in pregnancy (e.g., stress, health, socioeconomic status) have been associated with shortened telomere length at birth. The physiological mechanisms responsible for potential effects of maternal factors on newborn telomere length have yet to be identified. Indirect evidence suggests that disruptions in maternal hypothalamic-pituitary-adrenal (HPA) axis functioning in pregnancy may be involved. Studies are needed that test whether maternal HPA axis functioning in pregnancy is associated with newborn telomere length. This study examined whether maternal HPA axis functioning across pregnancy, reflected in hair cortisol collected within one week after delivery, predicted newborn telomere length assessed from leukocyte cord blood collected at birth among 93 sociodemographically diverse mother-infant dyads. We further tested whether associations between maternal hair cortisol and newborn telomere length differed by infant sex, given documented sex differences in prenatal environmental exposure effects on offspring health, patterns of cortisol exposure during gestation, and telomere biology across the lifespan. In a multi-group structural equation modeling analysis that accounted for cortisol exposures across trimesters, maternal cortisol levels in pregnancy were not associated with newborn telomere length in the sample as a whole. However, significant sex differences emerged, with a significant positive association among females and a lack of a significant association among males. In addition, analyses revealed that cortisol levels were higher across trimesters among mothers of male infants than mothers of female infants. The results suggest that functioning of the maternal HPA axis in pregnancy may differ by fetal sex and have sex-specific effects on newborn telomere biology. These findings have implications for understanding the mechanisms by which maternal psychosocial and environmental exposures influence newborn telomere length and for elucidating mechanisms contributing to sex disparities in health.

Telomeres in neurological disorders

Ever since their discovery, the telomeres and the telomerase have been topics of intensive research, first as a mechanism of cellular aging and later as an indicator of health and diseases in humans. By protecting the chromosome ends, the telomeres play a vital role in preserving the information in our genome. Telomeres shorten with age and the rate of telomere erosion provides insight into the proliferation history of cells. The pace of telomere attrition is known to increase at the onset of several pathological conditions. Telomere shortening has been emerging as a potential contributor in the pathogenesis of several neurological disorders including autism spectrum disorders (ASD), schizophrenia, Alzheimer's disease (AD), Parkinson's disease (PD) and depression. The rate of telomere attrition in the brain is slower than that of other tissues owing to the low rate of cell proliferation in brain. Telomere maintenance is crucial for the functioning of stem cells in brain. Taking together the studies on telomere attrition in various neurological disorders, an association between telomere shortening and disease status has been demonstrated in schizophrenia, AD and depression, in spite of a few negative reports. But, studies in ASD and PD have failed to produce conclusive results. The cause-effect relationship between TL and neurological disorders is yet to be elucidated. The factors responsible for telomere erosion, which have also been implicated in the pathogenesis of neurological disorders, need to be explored in detail. Telomerase activation is now being considered as a potential therapeutic strategy for neurological disorders.

Alcohol consumption and leukocyte telomere length

The relationship between alcohol consumption and mortality generally exhibits a U-shaped curve. The longevity observed with moderate alcohol consumption may be explained by other confounding factors, and, if such a relationship is present, the mechanism is not well understood. Indeed, the optimal amount of alcohol consumption for health has yet to be determined. Leukocyte telomere length is an emerging quantifiable marker of biological age and health, and a shorter telomere length is a predictor of increased mortality. Because leukocyte telomere length is a quantifiable and objectively measurable biomarker of aging, we sought to identify the amount of alcohol consumption associated with the longest telomere length and least telomere length attrition. Among over 2,000 participants from two distinct cohort studies, we found no pattern of alcohol consumption that was associated with longer telomere length or less telomere length attrition over time. Binge drinking may reduce telomere length. Using telomere length as a marker of age and health, these data fail to demonstrate any benefits of alcohol consumption, even when consumed in moderation.

Novel biomolecules of ageing, sex differences and potential underlying mechanisms of telomere shortening in coronary artery disease

Telomere length (TL), growth differentiate factor (GDF)11, insulin growth factor (IGF)1, sirtuin (SIRT)1 and inflammatory processes have been related to ageing and age-related diseases, like coronary artery disease (CAD). We aimed to investigate the associations between leukocyte TLs (LTLs), chronological age, sex and comorbidities in CAD patients. Any covariations between LTL, GDF11, IGF1, SIRT-1 and pro-inflammatory cytokines were further assessed.

METHODS

In 300 patients with stable CAD (age 36-81 years, 20% females), DNA and RNA were isolated from whole blood for PCR analysis and relative quantification of LTLs and gene-expression of GDF11, IGF1,SIRT1, IL-12, IL-18 and IFNƴ, respectively. Serum was prepared for the analyses of circulating IL-18, IL-12, IL-6 and TNFα.

RESULTS

Patients with previous myocardial infarction (MI) presented with 20% shorter LTLs vs. patients without (p = 0.019) indicating LTLs to be of importance for CAD severity. The observation however, was only observed in men (p = 0.009, n = 115), in which the upper LTL quartile associated with 64% lower frequency of previous MI compared to quartile 1-3 (p = 0.005, adjusted). LTLs were not differently distributed according to sex or comorbidities such as hypertension, diabetes type 2 and metabolic syndrome. LTLs and GDF11 were inversely correlated to age (r = -0.17; p = 0.007 and r = -0.16; p = 0.010, respectively), however, separated in gender, LTL only in women (r = -0.37) and GDF11 only in men (r = -0.19) (p = 0.006, both). GDF11 and SIRT1 were strongly inter-correlated (r = 0.56, p ≤ 0.001), suggesting common upstream regulators. LTLs were moderately correlated to GDF11 and SIRT1 in overweight women (BMI ≥ 25 kg/m²) (r = 0.41; p = 0.027 and 0.43; p = 0.020, respectively), which may reflect common life-style influences on LTLs and these markers. In all women, we observed further that the highest LTL quartile associated with higher GDF11 and SIRT expression and lower circulating levels of IL-12, IL-18 and TNFα, as compared to quartile 1, which may indicate lifestyle influences on female LTLs. In men, the highest LTL quartile associated with lower IFNƴ expression and lower circulating TNFα. Overall, the results indicate an association between chronic low-grade inflammation and LTLs.

CONCLUSIONS

Shorter LTLs in CAD patients with previously suffered MI may indicate telomere attrition as part of its pathophysiology in men. The inverse association between LTLs and age exclusively in women underpins the previously reported decline in attrition rate in men with increasing age. As elevated GDF11 and SIRT1 along with attenuated pro-inflammatory cytokines seem to positively affect LTL in women, we hypothesize a potential sex-dimorphism in LTL regulation, which may implicate sex- adjusted health-preventive therapies.

Telomere Biology and Human Phenotype

Telomeres are nucleoprotein structures that cap the end of each chromosome arm and function to maintain genome stability. The length of telomeres is known to shorten with each cell division and it is well-established that telomere attrition is related to replicative capacity in vitro. Moreover, telomere loss is also correlated with the process of aging in vivo. In this review, we discuss the mechanisms that lead to telomere shortening and summarise telomere homeostasis in humans throughout a lifetime. In addition, we discuss the available evidence that shows that telomere shortening is related to human aging and the onset of age-related disease.

Telomere length measurement by qPCR - Summary of critical factors and recommendations for assay design

Research in the last decade has explored the length of telomeres, the protective ends of eukaryotic chromosomes, as a biomarker for the cumulative effects of environmental exposures and life experiences as well as a risk factor for major diseases. With a growing interest in telomere biology across biomedical, epidemiological and public health research, it is critical to ensure that the measurement of telomere length is performed with high precision and accuracy. Of the several major methods utilized to determine telomere length, quantitative PCR (qPCR) remains the most cost-effective and suitable method for large-scale epidemiological and population studies. However, inconsistencies in recent reports utilizing the qPCR method highlight the need for a careful methodological analysis of each step of this process. In this review, we summarize each critical step in qPCR telomere length assay, including sample type selection, sample collection, storage, processing issues and assay procedures. We provide guidance and recommendations for each step based on current knowledge. It is clear that a collaborative and rigorous effort is needed to characterize and resolve existing issues related to sample storage, both before and after DNA extraction, as well as the impact of different extraction protocols, reagents and post extraction processing across all tissue types (e.g. blood, saliva, buccal swabs, etc.) to provide the needed data upon which best practices for TL analyses can be agreed upon. Additionally, we suggest that the whole telomere research community be invited to collaborate on the development and implementation of standardized protocols for the assay itself as well as for reporting in scientific journals. The existing evidence provides substantial support for the continuation of telomere research across a range of different exposures and health outcomes. However, as with any technological or methodologic advance in science, reproducibility, reliability and rigor need to be established to ensure the highest quality research.

The association between longer relative leukocyte telomere length and risk of glioma is independent of the potentially confounding factors allergy, BMI, and smoking

PURPOSE

Previous studies have suggested an association between relative leukocyte telomere length (rLTL) and glioma risk. This association may be influenced by several factors, including allergies, BMI, and smoking. Previous studies have shown that individuals with asthma and allergy have shortened relative telomere length, and decreased risk of glioma. Though, the details and the interplay between rLTL, asthma and allergies, and glioma molecular phenotype is largely unknown.

METHODS

rLTL was measured by qPCR in a Swedish population-based glioma case-control cohort (421 cases and 671 controls). rLTL was related to glioma risk and health parameters associated with asthma and allergy, as well as molecular events in glioma including IDH1 mutation, 1p/19q co-deletion, and EGFR amplification.

RESULTS

Longer rLTL was associated with increased risk of glioma (OR = 1.16; 95% CI 1.02-1.31). Similar to previous reports, there was an inverse association between allergy and glioma risk. Specific, allergy symptoms including watery eyes was most strongly associated with glioma risk. High body mass index (BMI) a year prior diagnosis was significantly protective against glioma in our population. Adjusting for allergy, asthma, BMI, and smoking did not markedly change the association between longer rLTL and glioma risk. rLTL among cases was not associated with IDH1 mutation, 1p/19q co-deletion, or EGFR amplification, after adjusting for age at diagnosis and sex.

CONCLUSIONS

In this Swedish glioma case-control cohort, we identified that long rLTL increases the risk of glioma, an association not confounded by allergy, BMI, or smoking. This highlights the complex interplay of the immune system, rLTL and cancer risk.

Telomere length as a predictor of emotional processing in the brain

Shorter telomere length (TL) has been associated with the development of mood disorders as well as abnormalities in brain morphology. However, so far, no studies have considered the role TL may have on brain function during tasks relevant to mood disorders. In this study, we examine the relationship between TL and functional brain activation and connectivity, while participants (n = 112) perform a functional magnetic resonance imaging (fMRI) facial affect recognition task. Additionally, because variation in TL has a substantial genetic component we calculated polygenic risk scores for TL to test if they predict face‐related functional brain activation. First, our results showed that TL was positively associated with increased activation in the amygdala and cuneus, as well as increased connectivity from posterior regions of the face network to the ventral prefrontal cortex. Second, polygenic risk scores for TL show a positive association with medial prefrontal cortex activation. The data support the view that TL and genetic loading for shorter telomeres, influence the function of brain regions known to be involved in emotional processing.

Sex differences in effects of maternal risk and protective factors in childhood and pregnancy on newborn telomere length

Little research has examined determinants of newborn telomere length, a potential biomarker of lifetime disease risk impacted by prenatal exposures. No study has examined whether maternal exposures in childhood influence newborn telomere length or whether there are sex differences in the maternal factors that influence newborn telomere length. We tested whether a range of maternal risk and protective factors in childhood and pregnancy were associated with newborn telomere length among 151 sociodemographically diverse mother-infant dyads. We further examined whether the pattern of associations differed by infant sex. Newborn telomere length was assessed from cord blood collected at birth. Risk/protective factors included maternal health (smoking, body mass index), socioeconomic status (education, income), stress exposures, and mental health (depressive and posttraumatic stress disorder symptoms) in pregnancy as well as maternal experiences of abuse (physical, emotional, sexual) and familial emotional support in childhood. When examined within the whole sample, only maternal smoking in pregnancy and familial emotional support in childhood emerged as significant predictors of newborn telomere length. Male and female newborns differed in their pattern of associations between the predictors and telomere length. Among males, maternal smoking, higher body mass index, and elevated depressive symptoms in pregnancy and maternal sexual abuse in childhood were associated with shorter newborn telomere length; higher maternal educational attainment and household income in pregnancy and greater maternal familial emotional support in childhood were associated with longer newborn telomere length. Together, these factors accounted for 34% of the variance in male newborn telomere length. None of the risk/protective factors were associated with female newborn telomere length. The results suggest that male fetuses are particularly susceptible to maternal exposure effects on newborn telomere length. These findings have implications for elucidating mechanisms contributing to sex disparities in health.

Leukocyte telomere length associates with nasopharyngeal carcinoma risk and survival in Hong Kong Chinese

Telomere shortening occurs as an early event in tumorigenesis. The TERT-CLPTM1L locus associates with nasopharyngeal carcinoma (NPC) risk. It remains unknown if leukocyte telomere length (LTL) associates with NPC risk and survival. The relative LTL (rLTL) was measured by quantitative-PCR in 2,996 individuals comprised of 1,284 NPC cases and 1712 matched controls. The odds ratio (OR) and 95% confidence intervals (CI) were calculated by logistic regression. The hazard ratio (HR) and 95% CI were calculated by Cox regression for survival analysis with rLTL and other clinical parameters in 1,243 NPC with a minimum follow-up period of 25 months. NPC patients had significantly shorter telomere length than controls. Shorter rLTL significantly associated with increased NPC risk, when the individuals were dichotomized into long and short telomeres based on median-split rLTL in the control group (OR = 2.317; 95% CI = 1.989-2.700, p = 4.10 × 10^-27 ). We observed a significant dose-response association (p_trend  = 3.26 × 10^-34 ) between rLTL and NPC risk with OR being 3.555 (95% CI = 2.853-4.429) for the individuals in the first quartile (shortest) compared with normal individuals in the fourth quartile (longest). A multivariate Cox regression analysis adjusted by age demonstrated an independent effect of rLTL on NPC survival for late-stage NPC patients, when the individuals were categorized into suboptimal rLTL versus the medium rLTL based on a threshold set from normal (HR = 1.471, 95% CI = 1.056-2.048, p = 0.022). Shorter blood telomeres may be markers for higher susceptibility for NPC risk. Suboptimal rLTL may be a poor prognostic factor for advanced NPC patients, as it associates independently with poor survival.

Shorter telomeres associated with high doses of glucocorticoids: the link to increased mortality?

OBJECTIVE

Patients with non-functioning pituitary adenomas exhibit high morbidity and mortality rates. Growth hormone deficiency and high doses of glucocorticoid substitution therapy have been identified as corresponding risk factors. Interestingly, high levels of endogenous cortisol in, e.g., patients with post-traumatic stress disorder or patients with Cushing's disease have been linked to shorter telomere length. Telomeres are noncoding DNA regions located at the end of chromosomes consisting of repetitive DNA sequences which shorten with ageing and hereby determine cell survival. Therefore, telomere length can serve as a predictor for the onset of disease and mortality in some endocrine disorders (e.g., Cushing's disease).

DESIGN/METHODS

We examine telomere length from blood in patients (n = 115) with non-functioning pituitary adenomas (NFPA) in a cross-sectional case control (n = 106, age-, gender- matched) study using qPCR. Linear regression models were used to identify independent predictors of telomere length.

RESULTS

We show that patients with NFPA exhibited shorter telomeres than controls. No significant association of indices of growth hormone deficiency (IGF-1-level-SDS, years of unsubstituted growth hormone deficiency etc.) with telomere length was detected. Interestingly, linear regression analysis showed that hydrocortisone replacement dosage in patients with adrenal insufficiency (n = 52) was a significant predictor for shorter telomere length (β = 0.377; p = 0.018) independent of potential confounders. Median split analysis revealed that higher hydrocortisone intake (> 20 mg) was associated with significantly shorter telomeres.

CONCLUSION

These observations strengthen the importance of adjusted glucocorticoid treatment in NFPA patients with respect to morbidity and mortality rates.

A review of telomere length in sarcopenia and frailty

Sarcopenia and frailty are associated with several important health-related adverse events, including disability, loss of independence, institutionalization and mortality. Sarcopenia can be considered a biological substrate of frailty, and the prevalence of both these conditions progressively increases with age. Telomeres are nucleoprotein structures located at the end of linear chromosomes and implicated in cellular ageing, shorten with age, and are associated with various age-related diseases. In addition, telomere length (TL) is widely considered a molecular/cellular hallmark of the ageing process. This narrative review summarizes the knowledge about telomeres and analyzes for the first time a possible association of TL with sarcopenia and frailty. The overview provided by the present review suggests that leukocyte TL as single measurement, calculated by quantitative real-time polymerase chain reaction (qRT-PCR), cannot be considered a meaningful biological marker for complex, multidimensional age-related conditions, such as sarcopenia and frailty. Panels of biomarkers, including TL, may provide more accurate assessment and prediction of outcomes in these geriatric syndromes in elderly people.

Leukocyte telomere length throughout the continuum of colorectal carcinogenesis

Considering the high prevalence of colorectal cancer (CRC) and relatively high mortality there is strong interest in identification of clinically relevant biomarkers. Telomere shortening is supposed to contribute to genomic instability and crucially involved in process of carcinogenesis. Peripheral blood leukocyte (PBL) telomere length was previously investigated in several studies as potential biomarker for CRC but with controversial results. This prompted us to investigate relative PBL telomere length in association with different histological findings throughout the continuum of colorectal carcinogenesis in order to reflect the whole spectrum of putative CRC development in a large study involving 2011 individuals. The study based on the Colorectal Cancer Study of Austria (CORSA), including 384 CRC cases as well as age- and gender-matched 544 high-risk adenomas, 537 low-risk adenoma patients and 546 colonoscopy-negative controls. Relative expression of telomeric repeats and the single copy reference gene, albumin (T/S ratio) was determined using monochrome multiplex quantitative PCR (MMQPCR). Telomeres were found to be significantly longer in CRC patients compared to control subjects (P = 3.61x10^-6). Yet, no significant differences in telomere length could be detected for high-risk (P = 0.05956) and low-risk colorectal adenoma patients (P = 0.05224). In addition, results presented in this manuscript highlight the impact of various epidemiological factors on PBL telomere length and its involvement in CRC. However, further large studies also including colorectal adenomas are necessary to confirm these results.

Leukocyte telomere length in relation to risk of lung adenocarcinoma incidence: Findings from the Singapore Chinese Health Study

Telomeres are crucial in the maintenance of chromosome integrity and genomic stability. Critically short telomeres can trigger programed cell death while cells with longer telomeres may have increased likelihood of replicative errors, resulting in genetic mutations and chromosomal alterations, and ultimately promoting oncogenesis. Data on telomere length and lung cancer risk from large prospective cohort studies are spare. Relative telomere length in peripheral blood leukocytes was quantified using a validated monochrome multiplex quantitative polymerase chain reaction (qPCR) method in 26,540 participants of the Singapore Chinese Health Study. After a follow-up of 12 years, 654 participants developed lung cancer including 288 adenocarcinoma, 113 squamous cell carcinoma and 253 other/unknown histological type. The Cox proportional hazard regression was used to estimate hazard ratio (HR) and 95% confidence interval (CI). HR of lung adenocarcinoma for individuals in the highest comparing the lowest 20 percentile of telomere length was 2.84 (95% CI 1.94-4.14, p_trend  < 0.0001). This positive association was present in never smokers (p_trend  < 0.0001), ever smokers (p_trend  = 0.0010), men (p_trend  = 0.0003), women (p_trend  < 0.0001), and in shorter (p_trend  = 0.0002) and longer (p_trend  = 0.0001) duration of follow-up. There was no association between telomere length and risk of squamous cell carcinoma or other histological type of lung cancer in all or subgroups of individuals. The agreement of results from this prospective cohort study with those of previous prospective studies and Mendelian randomization studies suggest a possible etiological role of telomere length in the development of lung adenocarcinoma.

Telomere Length and Bipolar Disorder

Variation in telomere length is heritable and is currently considered a promising biomarker of susceptibility for neuropsychiatric disorders, particularly because of its association with memory function and hippocampal morphology. Here, we investigate telomere length in connection to familial risk and disease expression in bipolar disorder (BD). We used quantitative PCRs and a telomere-sequence to single-copy-gene-sequence ratio method to determine telomere length in genomic DNA extracted from buccal smears from 63 patients with BD, 74 first-degree relatives (49 relatives had no lifetime psychopathology and 25 had a non-BD mood disorder), and 80 unrelated healthy individuals. Participants also underwent magnetic resonance imaging to determine hippocampal volumes and cognitive assessment to evaluate episodic memory using the verbal paired associates test. Telomere length was shorter in psychiatrically well relatives (p=0.007) compared with unrelated healthy participants. Telomere length was also shorter in relatives (regardless of psychiatric status; p<0.01) and patients with BD not on lithium (p=0.02) compared with lithium-treated patients with BD. In the entire sample, telomere length was positively associated with left and right hippocampal volume and with delayed recall. This study provides evidence that shortened telomere length is associated with familial risk for BD. Lithium may have neuroprotective properties that require further investigation using prospective designs.

Telomeres, Aging and Exercise: Guilty by Association?

Telomeres are repetitive tandem DNA sequences that cap chromosomal ends protecting genomic DNA from enzymatic degradation. Telomeres progressively shorten with cellular replication and are therefore assumed to correlate with biological and chronological age. An expanding body of evidence suggests (i) a predictable inverse association between telomere length, aging and age-related diseases and (ii) a positive association between physical activity and telomere length. Both hypotheses have garnered tremendous research attention and broad consensus; however, the evidence for each proposition is inconsistent and equivocal at best. Telomere length does not meet the basic criteria for an aging biomarker and at least 50% of key studies fail to find associations with physical activity. In this review, we address the evidence in support and refutation of the putative associations between telomere length, aging and physical activity. We finish with a brief review of plausible mechanisms and potential future research directions.

Translating Measures of Biological Aging to Test Effectiveness of Geroprotective Interventions: What Can We Learn from Research on Telomeres?

Intervention studies in animals suggest molecular changes underlying age-related disease and disability can be slowed or reversed. To speed translation of these so-called "geroprotective" therapies to prevent age-related disease and disability in humans, biomarkers are needed that can track changes in the rate of human aging over the course of intervention trials. Algorithm methods that measure biological processes of aging from combinations of DNA methylation marks or clinical biomarkers show promise. To identify next steps for establishing utility of these algorithm-based measures of biological aging for geroprotector trials, we considered the history a candidate biomarker of aging that has received substantial research attention, telomere length. Although telomere length possesses compelling biology to recommend it as a biomarker of aging, mixed research findings have impeded clinical and epidemiologic translation. Strengths of telomeres that should be established for algorithm biomarkers of aging are correlation with chronological age across the lifespan, prediction of disease, disability, and early death, and responsiveness to risk and protective exposures. Key challenges in telomere research that algorithm biomarkers of aging must address are measurement precision and reliability, establishing links between longitudinal rates of change across repeated measurements and aging outcomes, and clarity over whether the biomarker is a causal mechanism of aging. These strengths and challenges suggest a research agenda to advance translation of algorithm-based aging biomarkers: establish validity in young-adult and midlife individuals; test responsiveness to exposures that shorten or extend healthy lifespan; and conduct repeated-measures longitudinal studies to test differential rates of change.

Molecular Mechanisms Determining Lifespan in Short- and Long-Lived Species

Aging is a global decline of physiological functions, leading to an increased susceptibility to diseases and ultimately death. Maximum lifespans differ up to 200-fold between mammalian species. Although considerable progress has been achieved in identifying conserved pathways that regulate individual lifespan within model organisms, whether the same pathways are responsible for the interspecies differences in longevity remains to be determined. Recent cross-species studies have begun to identify pathways responsible for interspecies differences in lifespan. Here, we review the evidence supporting the role of anticancer mechanisms, DNA repair machinery, insulin/insulin-like growth factor 1 signaling, and proteostasis in defining species lifespans. Understanding the mechanisms responsible for the dramatic differences in lifespan between species will have a transformative effect on developing interventions to improve human health and longevity.

Cigarette smoking and telomere length: A systematic review of 84 studies and meta-analysis

BACKGROUND

Cigarette smoking is a risk factor for ageing-related disease, but its association with biological ageing, indicated by telomere length, is unclear.

METHODS

We systematically reviewed evidence evaluating association between smoking status and telomere length. Searches were performed in MEDLINE (Ovid) and EMBASE (Ovid) databases, combining variation of keywords "smoking" and "telomere". Data was extracted for study characteristics and estimates for association between smoking and telomere length. Quality of studies was assessed with a risk of bias score, and publication bias was assessed with a funnel plot. I2 test was used to observe heterogeneity. Meta-analysis was carried out to compare mean difference in telomere length by smoking status, and a dose-response approach was carried out for pack-years of smoking and telomere length. A sensitivity analysis was carried out to examine sources of heterogeneity.

RESULTS

A total of 84 studies were included in the review, and 30 among them were included in our meta-analysis. Potential bias was addressed in half of included studies, and there was little evidence of small study bias. Telomere length was shorter among ever smokers compared to never smokers (summary standard mean difference [SMD]: -0.11 (95% CI -0.16 to -0.07)). Similarly, shorter telomere length was found among smokers compared to non-smokers, and among current smokers compared to never or former smokers. Dose-response meta-analysis suggested an inverse trend between pack-years of smoking and telomere length. However, heterogeneity among some analyses was observed.

CONCLUSION

Shorter telomeres among ever smokers compared to those who never smoked may imply mechanisms linking tobacco smoke exposure to ageing-related disease.

Physiological mechanisms of adaptive developmental plasticity in Rana temporaria island populations

BACKGROUND

Adaptive plasticity is essential for many species to cope with environmental heterogeneity. In particular, developmental plasticity allows organisms with complex life cycles to adaptively adjust the timing of ontogenetic switch points. Size at and time to metamorphosis are reliable fitness indicators in organisms with complex cycles. The physiological machinery of developmental plasticity commonly involves the activation of alternative neuroendocrine pathways, causing metabolic alterations. Nevertheless, we have still incomplete knowledge about how these mechanisms evolve under environments that select for differences in adaptive plasticity. In this study, we investigate the physiological mechanisms underlying divergent degrees of developmental plasticity across Rana temporaria island populations inhabiting different types of pools in northern Sweden.

METHODS

In a laboratory experiment we estimated developmental plasticity of amphibian larvae from six populations coming from three different island habitats: islands with only permanent pools, islands with only ephemeral pools, and islands with a mixture of both types of pools. We exposed larvae of each population to either constant water level or simulated pool drying, and estimated their physiological responses in terms of corticosterone levels, oxidative stress, and telomere length.

RESULTS

We found that populations from islands with only temporary pools had a higher degree of developmental plasticity than those from the other two types of habitats. All populations increased their corticosterone levels to a similar extent when subjected to simulated pool drying, and therefore variation in secretion of this hormone does not explain the observed differences among populations. However, tadpoles from islands with temporary pools showed lower constitutive activities of catalase and glutathione reductase, and also showed overall shorter telomeres.

CONCLUSIONS

The observed differences are indicative of physiological costs of increased developmental plasticity, suggesting that the potential for plasticity is constrained by its costs. Thus, high levels of responsiveness in the developmental rate of tadpoles have evolved in islands with pools at high but variable risk of desiccation. Moreover, the physiological alterations observed may have important consequences for both short-term odds of survival and long term effects on lifespan.

Regular exercise participation improves genomic stability in diabetic patients: an exploratory study to analyse telomere length and DNA damage

Physical activity has been demonstrated to be effective in the prevention and treatment of different chronic conditions, including type 2 diabetes (T2D). In particular, several studies highlighted how the beneficial effects of physical activity may be related to the stability of the DNA molecule, such as longer telomeric ends. Here we analyze the effect of exercise training on telomere length, spontaneous and H₂O₂-induced DNA damage, as well as the apoptosis level in leukocytes from untrained or trained T2D patients vs. age-matched control subjects (CS) (57–66 years). Moreover, expression analysis of selected genes belonging to DNA repair systems, cell cycle control, antioxidant and defence systems was performed. Subjects that participated in a regular exercise program showed a longer telomere sequence than untrained counterparts. Moreover, ex vivo treatment of leukocytes with H₂O₂ highlighted that: (1) oxidative DNA damage induced similar telomere attrition in all groups; (2) in T2D subjects, physical activity seemed to prevent a significant increase of genomic oxidative DNA damage induced by chronic exposure to pro-oxidant stimulus, and (3) decreased the sensitivity of leukocytes to apoptosis. Finally, the gene expression analysis in T2D subjects suggested an adaptive response to prolonged exercise training that improved the response of specific genes.

Differences in placental telomere length suggest a link between racial disparities in birth outcomes and cellular aging

BACKGROUND

Health disparities begin early in life and persist across the life course. Despite current efforts, black women exhibit greater risk for pregnancy complications and negative perinatal outcomes compared with white women. The placenta, which is a complex multi-tissue organ, serves as the primary transducer of bidirectional information between the mother and fetus. Altered placental function is linked to multiple racially disparate pregnancy complications; however, little is known about racial differences in molecular factors within the placenta. Several pregnancy complications, which include preeclampsia and fetal growth restriction, exhibit racial disparities and are associated with shorter placental telomere length, which is an indicator of cellular stress and aging. Cellular senescence and telomere dynamics are linked to the molecular mechanisms that are associated with the onset of labor and parturition. Further, racial differences in telomere length are found in a range of different peripheral tissues. Together these factors suggest that exploration of racial differences in telomere length of the placenta may provide novel mechanistic insight into racial disparities in birth outcomes.

OBJECTIVE

This study examined whether telomere length measured in 4 distinct fetally derived tissues were significantly different between black and white women. The study had 2 hypotheses: (1) that telomere length that is measured in different placental tissue types would be correlated and (2) that across all sampled tissues telomere length would differ by race.

STUDY DESIGN

In a prospective study, placental tissue samples were collected from the amnion, chorion, villus, and umbilical cord from black and white singleton pregnancies (N=46). Telomere length was determined with the use of monochrome multiplex quantitative real-time polymerase chain reaction in each placental tissue. Demographic and pregnancy-related data were also collected. Descriptive statistics characterized the sample overall and among black and white women separately. The overall impact of race was assessed by multilevel mixed-effects linear regression models that included empirically relevant covariates.

RESULTS

Telomere length was correlated significantly across all placental tissues. Pairwise analyses of placental tissue telomere length revealed significantly longer telomere length in the amnion compared with the chorion (t=-2.06; P=.043). Overall telomere length measured in placenta samples from black mothers were significantly shorter than those from white mothers (β=-0.09; P=.04). Controlling for relevant maternal and infant characteristics strengthened the significance of the observed racial differences (β=-0.12; P=.02). Within tissue analyses revealed that the greatest difference by race was found in chorionic telomere length (t=-2.81; P=.007).

CONCLUSION

These findings provide the first evidence of racial differences in placental telomere length. Telomere length was significantly shorter in placental samples from black mothers compared with white mothers. Given previous studies that have reported that telomere length, cellular senescence, and telomere dynamics are molecular factors that contribute to the rupture of the amniotic sac, onset of labor, and parturition, our findings of shorter telomere length in placentas from black mothers suggest that accelerated cellular aging across placental tissues may be relevant to the increased risk of preterm delivery in black pregnancies. Our results suggest that racial differences in cellular aging in the placenta contribute to the earliest roots of health disparities.

Effects of size at birth, childhood growth patterns and growth hormone treatment on leukocyte telomere length

BACKGROUND

Small size at birth and rapid growth in early life are associated with increased risk of cardiovascular disease in later life. Short children born small for gestational age (SGA) are treated with growth hormone (GH), inducing catch-up in length. Leukocyte telomere length (LTL) is a marker of biological age and shorter LTL is associated with increased risk of cardiovascular disease.

OBJECTIVES

To investigate whether LTL is influenced by birth size, childhood growth and long-term GH treatment.

METHODS

We analyzed LTL in 545 young adults with differences in birth size and childhood growth patterns. Previously GH-treated young adults born SGA (SGA-GH) were compared to untreated short SGA (SGA-S), SGA with spontaneous catch-up to a normal body size (SGA-CU), and appropriate for gestational age with a normal body size (AGA-NS). LTL was measured using a quantitative PCR assay.

RESULTS

We found a positive association between birth length and LTL (p = 0.04), and a trend towards a positive association between birth weight and LTL (p = 0.08), after adjustments for gender, age, gestational age and adult body size. Weight gain during infancy and childhood and fat mass percentage were not associated with LTL. Female gender and gestational age were positively associated with LTL, and smoking negatively. After adjustments for gender, age and gestational age, SGA-GH had a similar LTL as SGA-S (p = 0.11), SGA-CU (p = 0.80), and AGA-NS (p = 0.30).

CONCLUSIONS

Larger size at birth is positively associated with LTL in young adulthood. Growth patterns during infancy and childhood are not associated with LTL. Previously GH-treated young adults born SGA have similar LTL as untreated short SGA, SGA with spontaneous catch-up and AGA born controls, indicating no adverse effects of GH-induced catch-up in height on LTL.

Relative Telomere Repeat Mass in Buccal and Leukocyte-Derived DNA

Telomere length has garnered interest due to the potential role it may play as a biomarker for the cellular aging process. Telomere measurements obtained from blood-derived DNA are often used in epidemiological studies. However, the invasive nature of blood draws severely limits sample collection, particularly with children. Buccal cells are commonly sampled for DNA isolation and thus may present a non-invasive alternative for telomere measurement. Buccal and leukocyte derived DNA obtained from samples collected at the same time period were analyzed for telomere repeat mass (TRM). TRM was measured in buccal-derived DNA samples from individuals for whom previous TRM data from blood samples existed. TRM measurement was performed by qPCR and was normalized to the single copy 36B4 gene relative to a reference DNA sample (K562). Correlations between TRM from blood and buccal DNA were obtained and also between the same blood DNA samples measured in separate laboratories. Using the classical twin design, TRM heritability was estimated (N = 1892, MZ = 1044, DZ = 775). Buccal samples measured for TRM showed a significant correlation with the blood-1 (R = 0.39, p < 0.01) and blood-2 (R = 0.36, p < 0.01) samples. Sex and age effects were observed within the buccal samples as is the norm within blood-derived DNA. The buccal, blood-1, and blood-2 measurements generated heritability estimates of 23.3%, 47.6% and 22.2%, respectively. Buccal derived DNA provides a valid source for the determination of TRM, paving the way for non-invasive projects, such as longitudinal studies in children.

Telomere length and depression: prospective cohort study and Mendelian randomisation study in 67 306 individuals

BACKGROUND

Depression has been cross-sectionally associated with short telomeres as a measure of biological age. However, the direction and nature of the association is currently unclear.

AIMS

We examined whether short telomere length is associated with depression cross-sectionally as well as prospectively and genetically.

METHOD

Telomere length and three polymorphisms, TERT, TERC and OBFC1, were measured in 67 306 individuals aged 20-100 years from the Danish general population and associated with register-based attendance at hospital for depression and purchase of antidepressant medication.

RESULTS

Attendance at hospital for depression was associated with short telomere length cross-sectionally, but not prospectively. Further, purchase of antidepressant medication was not associated with short telomere length cross-sectionally or prospectively. Mean follow-up was 7.6 years (range 0.0-21.5). The genetic analyses suggested that telomere length was not causally associated with attendance at hospital for depression or with purchase of antidepressant medication.

CONCLUSIONS

Short telomeres were not associated with depression in prospective or in causal, genetic analyses.

Resistance training and redox homeostasis: Correlation with age-associated genomic changes

Regular physical activity is effective as prevention and treatment for different chronic conditions related to the ageing processes. In fact, a sedentary lifestyle has been linked to a worsening of cellular ageing biomarkers such as telomere length (TL) and/or specific epigenetic changes (e.g. DNA methylation), with increase of the propensity to aging-related diseases and premature death. Extending our previous findings, we aimed to test the hypothesis that 12 weeks of low frequency, moderate intensity, explosive-type resistance training (EMRT) may attenuate age-associated genomic changes. To this aim, TL, global DNA methylation, TRF2, Ku80, SIRT1, SIRT2 and global protein acetylation, as well as other proteins involved in apoptotic pathway (Bcl-2, Bax and Caspase-3), antioxidant response (TrxR1 and MnSOD) and oxidative damage (myeloperoxidase) were evaluated before and after EMRT in whole blood or peripheral mononuclear cells (PBMCs) of elderly subjects. Our findings confirm the potential of EMRT to induce an adaptive change in the antioxidant protein systems at systemic level and suggest a putative role of resistance training in the reduction of global DNA methylation. Moreover, we observed that EMRT counteracts the telomeres' shortening in a manner that proved to be directly correlated with the amelioration of redox homeostasis and efficacy of training regime, evaluated as improvement of both muscle's power/strength and functional parameters.

Assessment of Telomere Length in Archived Formalin-Fixed, Paraffinized Human Tissue Is Confounded by Chronological Age and Storage Duration

Telomeres shorten with physiological aging but undergo substantial restoration during cancer immortalization. Increasingly, cancer studies utilize the archive of formalin-fixed, paraffin-embedded (FFPE) tissues in diagnostic pathology departments. Conceptually, such studies would be confounded by physiological telomere attrition and loss of DNA integrity from prolonged tissue storage. Our study aimed to investigate these two confounding factors. 145 FFPE tissues of surgically-resected, non-diseased appendixes were retrieved from our pathology archive, from years 2008 to 2014. Cases from 2013 to 2014 were categorized by patient chronological age (0–20 years, 21–40 years, 41–60 years, > 60 years). Telomere lengths of age categories were depicted by telomere/chromosome 2 centromere intensity ratio (TCR) revealed by quantitative fluorescence in situ hybridization. Material from individuals aged 0–20 years from years 2013/2014, 2011/2012, 2009/2010, and 2008 were compared for storage effect. Telomere integrity was assessed by telomere fluorescence intensity (TFI). Epithelial TCRs (mean ± SD) for the respective age groups were 4.84 ± 2.08, 3.64 ± 1.21, 2.03 ± 0.37, and 1.93 ± 0.45, whereas corresponding stromal TCRs were 5.16 ± 2.55, 3.84 ± 1.36, 2.49 ± 1.20, and 2.93 ± 1.24. A trend of inverse correlation with age in both epithelial and stromal tissues is supported by r = -0.69, p < 0.001 and r = -0.42, p < 0.001 respectively. Epithelial TFIs (mean ± SD) of years 2013/2014, 2011/2012, 2009/2010 and 2008 were 852.60 ± 432.46, 353.04 ± 127.12, 209.24 ± 55.57 and 429.22 ± 188.75 respectively. Generally, TFIs reduced with storage duration (r = -0.42, p < 0.001). Our findings agree that age-related telomere attrition occurs in normal somatic tissues, and suggest that an age-based reference can be established for telomere studies on FFPE tissues. We also showed that FFPE tissues archived beyond 2 years are suboptimal for telomere analysis.

The Telomere/Telomerase System in Chronic Inflammatory Diseases. Cause or Effect?

Telomeres are specialized nucleoprotein structures located at the end of linear chromosomes and telomerase is the enzyme responsible for telomere elongation. Telomerase activity is a key component of many cancer cells responsible for rapid cell division but it has also been found by many laboratories around the world that telomere/telomerase biology is dysfunctional in many other chronic conditions as well. These conditions are characterized by chronic inflammation, a situation mostly overlooked by physicians regarding patient treatment. Among others, these conditions include diabetes, renal failure, chronic obstructive pulmonary disease, etc. Since researchers have in many cases identified the association between telomerase and inflammation but there are still many missing links regarding this correlation, the latest findings about this phenomenon will be discussed by reviewing the literature. Our focus will be describing telomere/telomerase status in chronic diseases under the prism of inflammation, reporting molecular findings where available and proposing possible future approaches.

Genome-wide landscape of DNA methylomes and their relationship with mRNA and miRNA transcriptomes in oxidative and glycolytic skeletal muscles

The physiological, biochemical and functional differences between oxidative and glycolytic muscles play important roles in human metabolic health and in animal meat quality. To explore these differences, we determined the genome-wide landscape of DNA methylomes and their relationship with the mRNA and miRNA transcriptomes of the oxidative muscle psoas major (PMM) and the glycolytic muscle longissimus dorsi (LDM). We observed the hypo-methylation of sub-telomeric regions. A high mitochondrial content contributed to fast replicative senescence in PMM. The differentially methylated regions (DMRs) in promoters (478) and gene bodies (5,718) were mainly enriched in GTPase regulator activity and signaling cascade-mediated pathways. Integration analysis revealed that the methylation status within gene promoters (or gene bodies) and miRNA promoters was negatively correlated with mRNA and miRNA expression, respectively. Numerous genes were closely related to distinct phenotypic traits between LDM and PMM. For example, the hyper-methylation and down-regulation of HK-2 and PFKFB4 were related to decrease glycolytic potential in PMM. In addition, promoter hypo-methylation and the up-regulation of miR-378 silenced the expression of the target genes and promoted capillary biosynthesis in PMM. Together, these results improve understanding of muscle metabolism and development from genomic and epigenetic perspectives.

Racial and Socioeconomic Variation in Genetic Markers of Telomere Length: A Cross-Sectional Study of U.S. Older Adults

Background

Shorter telomere length (TL) has been associated with stress and adverse socioeconomic conditions, yet U.S. blacks have longer TL than whites. The role of genetic versus environmental factors in explaining TL by race and socioeconomic position (SEP) remains unclear.

Methods

We used data from the U.S. Health and Retirement Study (N = 11,934) to test the hypothesis that there are differences in TL-associated SNPs by race and SEP. We constructed a TL polygenic risk score (PRS) and examined its association with race/ethnicity, educational attainment, assets, gender, and age.

Results

U.S. blacks were more likely to have a lower PRS for TL, as were older individuals and men. Racial differences in TL were statistically accounted for when controlling for population structure using genetic principal components. The GWAS-derived SNPs for TL, however, may not have consistent associations with TL across different racial/ethnic groups.

Conclusions

This study showed that associations of race/ethnicity with TL differed when accounting for population stratification. The role of race/ethnicity for TL remains uncertain, however, as the genetic determinants of TL may differ by race/ethnicity. Future GWAS samples should include racially diverse participants to allow for better characterization of the determinants of TL in human populations.

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Blacks, older individuals, and men are more likely to have a polygenic risk score predisposing them to longer telomeres.

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There is no association between telomere length and race/ethnicity after controlling for population structure.

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GWAS studies have not included diverse samples, and genetic associations with telomere length may differ by race/ethnicity.

Telomeres are structures that protect the ends of chromosomes from damage. Shorter telomeres may be a marker of human aging. Shorter telomeres have been associated with higher stress and lower levels of education, but U.S. blacks have longer telomeres than whites. We show that blacks, older individuals, and men have genetic markers that may predispose them to longer telomeres. After accounting for genetic population structure, there is no longer an association between telomere length and self-reported race/ethnicity. Because genetic determinants of telomere length may differ by race/ethnicity, it is critical that future genetic studies include racially/ethnically diverse populations.

Aneuploidy and asynchronous replication in non-alcholic fatty liver disease and cryptogenic cirrhosis

BACKGROUND/AIMS

Non-alcoholic fatty liver disease (NAFLD) and cryptogenic cirrhosis (CC), which is largely a late sequela of NAFLD, are considered pre-neoplastic conditions that might progress to hepatocellular carcinoma. Aneuploidy, telomere aggregates and synchronization of replication were evaluated as markers of genetic instability in these patients.

METHODOLOGY

Peripheral blood lymphocytes from 22 patients with NAFLD, 20 patients with CC and 20 age-matched healthy controls were analyzed. To determine random aneuploidy, we used the fluorescence in situ hybridization (FISH) with probes for chromosomes 9 and 18. The rate of aneuploidy was inferred from the fraction of cells revealing one, three or more hybridization signals per cell. Aggregate size was divided into three fusion groups of 2-5, 6-10 and 11-15 telomeres, relative to the size of a single telomere. The replication pattern was determined by FISH in two pairs of alleles, 15qter and 13qter. Asynchrony was determined by the presence of one single and one set of double dots in the same cell.

RESULTS

Significantly higher random aneuploidy rate was found in the CC patients than in the control group, and to a lesser degree in NAFLD patients. Telomere aggregates were insignificantly higher in both groups. Only patients with CC showed significantly higher rate of asynchronous replication with proportionately more cells with two single dots among the normal cells (p<0.001).

CONCLUSIONS

These results likely reflect changes in gene replication and cell cycle progression in these conditions, possibly correlating with their malignant potential.

Long telomeres and cancer risk among 95 568 individuals from the general population

BACKGROUND

Results regarding telomere length and cancer risk are conflicting. We tested the hypothesis that long telomeres are associated with increased risk of any cancer and specific cancer types in genetic and observational analyses.

METHODS

Individuals (N = 95 568) from the Copenhagen City Heart Study and the Copenhagen General Population Study had the telomere length-associated genotypes rs7726159 (TERT), rs1317082 (TERC), and rs2487999 (OBFC1) determined, and 65 176 had telomere length measured. A total of 10 895 individuals had had a cancer diagnosis. Endpoints were any cancer and 25 specific cancer types. We conducted Cox regression analyses and logistic regression analyses. The three genotypes were combined as an allele sum.

RESULTS

Telomere length increased 67 base-pairs [95% confidence interval (CI) 61-74] per allele. In logistic regression models, the per-allele odds ratio (OR) for cancer was 1.05 (95% CI 1.03-1.07) for the allele sum, 1.05 (1.02-1.09) for rs7726159, 1.05 (1.02-1.08) for rs1317082 and 1.07 (1.02-1.12) for rs2487999. In contrast, the hazard ratio for any cancer was 1.01 (1.00-1.01) per 200-base-pair increase in telomere length in multivariable adjusted observational analysis. In genetic analyses according to specific cancer types, the per-allele odds ratio was 1.19 (1.12-1.27) for melanoma and 1.14 (1.06-1.22) for lung cancer.

CONCLUSIONS

Genetic determinants of long telomeres are associated with increased cancer risk, particularly melanoma and lung cancer. This genetic predisposition to enhanced telomere maintenance may represent a survival advantage for pre-cancerous cells, allowing for multiple cell divisions leading to cancer development.

The impact of hypertension on leukocyte telomere length: a systematic review and meta-analysis of human studies

Shortened leukocyte telomere length (LTL) is a novel biomarker for age and age-related diseases. Several epidemiological studies have examined the association between telomere length in surrogate tissues (for example, blood cells) and hypertension, and meanwhile the majority of studies reported an association some individual studies do not. We carried out a systematic review and meta-analysis to address the hypothesis that, in humans, telomere length is related with hypertension. Searches were conducted in Pubmed by September 2015 and reference lists of retrieved citations were hand searched. Eligible studies measured telomeres for both hypertensive and normotensive subjects. No restrictions were placed on sample size, publication type, age or gender. We calculated summary estimates using fixed and random effects meta-analysis. Publication bias and heterogeneity among studies were further tested. Meta-analyses from 3097 participants (1415 patients with hypertension and 1682 control subjects) showed a significant standardized mean difference between LTL in hypertensive patients and controls, either in the fixed (P<5 × 10^-6) or the random model (P<0.005). Heterogeneity among studies was substantial (Q-statistic P-value <0.001, I² 97.73%). Sensitivity analysis indicated that no single study changed the standardized mean difference qualitatively (0.022> random model P-value >0.002). Egger's test for asymmetry of effect sizes (intercept±s.e.=-7.278±3.574; P=0.072) did not show evidence for strong study publication bias. Leukocyte telomeres may be shorter in hypertensive than in normotensive individuals. Larger studies controlling for confounder effects are needed to confirm these findings and further explore sources of heterogeneity.

Alterations of telomere length and DNA methylation in hairdressers: A cross-sectional study

Working as hairdressers has been associated with increased risk for cancer, particularly bladder cancer. To evaluate if current hairdressers have elevated risks of adverse health effects, we measured several biomarkers related to cancer-related DNA alterations. We enrolled 295 hairdressers and 92 non-hairdressers (all female non-smokers) from Stockholm and southern Sweden. Questionnaire data were collected for each participant, including work tasks for the hairdressers. We measured telomere length in peripheral blood leucocytes using quantitative PCR and DNA methylation status of genes relevant for bladder cancer using methylation sensitive high resolution melting analysis. The hairdressers had shorter telomeres (β = -0.069, P = 0.019) compared with non-hairdressers. Shorter telomeres were found in hairdressers up to 32 years old performing hair waving more than once per week as compared with hairdressers in the same age group performing hair waving less often (β = -0.12, P = 0.037). Hair waving was associated with less frequent CDKN2A methylation (odds ratio, OR = 0.19, P = 0.033). Shorter telomeres in hairdressers may indicate a genotoxic effect. Performing hair waving was associated with short telomere length, although the effect was only observed in young hairdressers. No clear patterns were discerned with regard to DNA methylation of bladder cancer-related genes. The observed changes of methylation were not all in the expected direction and warrant further investigation.

Epidemiological and Mendelian Randomization Studies of Dihydrotestosterone and Estradiol and Leukocyte Telomere Length in Men

CONTEXT

Advancing age is accompanied by an accumulation of ill health and shortening of chromosomal telomeres signifying biological aging. T is metabolized to DHT by 5α-reductase (SRD5A2) and to estradiol (E2) by aromatase (CYP19A1). Telomerase preserves telomeres, and T and E2 regulate telomerase expression and activity in vitro.

OBJECTIVE

The objective of the study was to establish whether circulating T or its metabolites, DHT or E2, and single-nucleotide polymorphisms in SRD5A2 or CYP19A1 associate with leucocyte telomere length (LTL) in men.

PARTICIPANTS AND METHODS

Early-morning serum T, DHT, and E2 were assayed using mass spectrometry, and SRD5A2 and CYP19A1 single-nucleotide polymorphisms and LTL analyzed by PCR in 980 men from the Western Australian Busselton Health Survey who participated in the study. LTL was expressed as the T/S ratio.

RESULTS

Men were aged (mean ± SD) 53.7 ± 15.6 years. LTL decreased linearly with age, from the T/S ratio of 1.89 ± 0.41 at younger than 30 years to 1.50 ± 0.49 at 70 to younger than 80 years (r = -0.225, P < .0001). After adjustment for age, DHT and E2 were positively correlated with LTL (DHT, r = 0.069, P = .030; E2, r = 0.068, P = .034). The SRD5A2 rs9282858 polymorphism was associated with serum DHT but not with LTL. Three dominant alleles of CYP19A1 were each associated with lower serum E2 and shorter LTL: rs2899470 T (E2, 59.3 vs 68.6 pmol/L, P < .0001; T/S ratio, 1.54 vs 1.62, P = .045), rs10046 C (60.5 vs 68.1 pmol/L, P = .0005, 1.54 vs 1.62, P = .035), and rs700518 A (59.9 vs 68.9 pmol/L, P < .0001, 1.54 vs 1.63, P = .020). A single-copy haplotype C/T/I/A/T rs10046/rs2899470/rs11575899/rs700518/rs17703883 (52% prevalence) was associated with both lower E2 and shorter LTL.

CONCLUSIONS

In men, serum DHT and E2 correlate with LTL independently of age. Aromatase gene polymorphisms include three dominant alleles that are associated with both lower serum E2 and shorter LTL. E2 influences telomere length in vivo, thus warranting further studies to examine whether hormonal interventions might slow biological aging in men.

Systematic and Cell Type-Specific Telomere Length Changes in Subsets of Lymphocytes

Telomeres, the protective DNA-protein complexes at the ends of linear chromosomes, are important for genome stability. Leukocyte or peripheral blood mononuclear cell (PBMC) telomere length is a potential biomarker for human aging that integrates genetic, environmental, and lifestyle factors and is associated with mortality and risks for major diseases. However, only a limited number of studies have examined longitudinal changes of telomere length and few have reported data on sorted circulating immune cells. We examined the average telomere length (TL) in CD4+, CD8+CD28+, and CD8+CD28− T cells, B cells, and PBMCs, cross-sectionally and longitudinally, in a cohort of premenopausal women. We report that TL changes over 18 months were correlated among these three T cell types within the same participant. Additionally, PBMC TL change was also correlated with those of all three T cell types, and B cells. The rate of shortening for B cells was significantly greater than for the three T cell types. CD8+CD28− cells, despite having the shortest TL, showed significantly more rapid attrition when compared to CD8+CD28+ T cells. These results suggest systematically coordinated, yet cell type-specific responses to factors and pathways contribute to telomere length regulation.

Comparison of the relative telomere length measured in leukocytes and eleven different human tissues

The relative length of telomeres measured in peripheral blood leukocytes is a commonly used system marker for biological aging and can also be used as a biomarker of cardiovascular aging. However, to what extent the telomere length in peripheral leukocytes reflects telomere length in different organ tissues is still unclear. Therefore, we have measured relative telomere length (rTL) in twelve different human tissues (peripheral blood leukocytes, liver, kidney, heart, spleen, brain, skin, triceps, tongue mucosa, intercostal skeletal muscle, subcutaneous fat, and abdominal fat) from twelve cadavers (age range of 29 week of gestation to 88 years old). The highest rTL variability was observed in peripheral leukocytes, and the lowest variability was found in brain. We found a significant linear correlation between leukocyte rTL and both intercostal muscle (R=0.68, P<0.02) and liver rTL (R=0.60, P<0.05) only. High rTL variability was observed between different organs from one individual. Furthermore, we have shown that even slight DNA degradation (modeled by sonication of genomic DNA) leads to false rTL shortening. We conclude that the rTL in peripheral leukocytes is not strongly correlated with the rTL in different organs.