Validation of Minimally-Invasive Sample Collection Methods for Measurement of Telomere Length

Cross-tissue comparison of telomere length and quality metrics of DNA among individuals aged 8 to 70 years

Telomere length (TL) is an important biomarker of cellular aging, yet its links with health outcomes may be complicated by use of different tissues. We evaluated within- and between-individual variability in TL and quality metrics of DNA across five tissues using a cross-sectional dataset ranging from 8 to 70 years (N = 197). DNA was extracted from all tissue cells using the Gentra Puregene DNA Extraction Kit. Absolute TL (aTL) in kilobase pairs was measured in buccal epithelial cells, saliva, dried blood spots (DBS), buffy coat, and peripheral blood mononuclear cells (PBMCs) using qPCR. aTL significantly shortened with age for all tissues except saliva and buffy coat, although buffy coat was available for a restricted age range (8 to 15 years). aTL did not significantly differ across blood-based tissues (DBS, buffy coat, PBMC), which had significantly longer aTL than buccal cells and saliva. Additionally, aTL was significantly correlated for the majority of tissue pairs, with partial Spearman's correlations controlling for age and sex ranging from ⍴ = 0.18 to 0.51. We also measured quality metrics of DNA including integrity, purity, and quantity of extracted DNA from all tissues and explored whether controlling for DNA metrics improved predictions of aTL. We found significant tissue variation: DNA from blood-based tissues had high DNA integrity, more acceptable A260/280 and A260/230 values, and greater extracted DNA concentrations compared to buccal cells and saliva. Longer aTL was associated with lower DNA integrity, higher extracted DNA concentrations, and higher A260/230, particularly for saliva. Model comparisons suggested that incorporation of quality DNA metrics improves models of TL, although relevant metrics vary by tissue. These findings highlight the merits of using blood-based tissues and suggest that incorporation of quality DNA metrics as control variables in population-based studies can improve TL predictions, especially for more variable tissues like buccal and saliva.

Associations between telomere length, glucocorticoid receptor gene DNA methylation, volume of stress-related brain structures, and academic performance in middle-school-age children

Background

The biological embedding theory posits that early life experiences can lead to enduring physiological and molecular changes impacting various life outcomes, notably academic performance. Studying previously revealed and objective biomarkers of early life stress exposure, such as telomere length (TL), glucocorticoid receptor gene DNA methylation (DNAme), and the volume of brain structures involved in the regulation of HPA axis functioning (the hippocampus, the amygdala, and the medial prefrontal cortex), in relation to academic performance is crucial. This approach provides an objective measure that surpasses the limitations of self-reported early life adversity and reveals potential molecular and neurological targets for interventions to enhance academic outcomes.

Methods

The participants were 52 children of Mexican or Central American origin aged 11.6-15.6 years. DNA methylation levels and TL were analyzed in three cell sources: saliva, whole blood, and T cells derived from whole blood.

Results

Overall, the concordance across three systems of stress-related biomarkers (TL, DNAme, and the brain) was observed to some extent, although it was less pronounced than we expected; no consistency in different cell sources was revealed. Each of the academic domains that we studied was characterized by a unique and distinct complex of associations with biomarkers, both in terms of the type of biomarker, the directionality of the observed effects, and the cell source of biomarkers. Furthermore, there were biomarker-by-sex interaction effects in predicting academic performance measures.

Conclusions

Assessed in an understudied youth sample, these preliminary data present new essential evidence for a deepened understanding of the biological mechanisms behind associations between exposure to early life stress and academic performance.

Intergenerational effects of maternal lifetime stressor exposure on offspring telomere length in Black and White women

BACKGROUND

Although maternal stressor exposure has been associated with shorter telomere length (TL) in offspring, this literature is based largely on White samples. Furthermore, timing of maternal stressors has rarely been examined. Here, we examined how maternal stressors occurring during adolescence, pregnancy, and across the lifespan related to child TL in Black and White mothers.

METHOD

Mothers (112 Black; 110 White; Mage = 39) and their youngest offspring (n = 222; Mage = 8) were part of a larger prospective cohort study, wherein mothers reported their stressors during adolescence (assessed twice during adolescence for the past year), pregnancy (assessed in midlife for most recent pregnancy), and across their lifespan (assessed in midlife). Mother and child provided saliva for TL measurement. Multiple linear regression models examined the interaction of maternal stressor exposure and race in relation to child TL, controlling for maternal TL and child gender and age. Race-stratified analyses were also conducted.

RESULTS

Neither maternal adolescence nor lifespan stressors interacted with race in relation to child TL. In contrast, greater maternal pregnancy stressors were associated with shorter child TL, but this effect was present for children of White but not Black mothers. Moreover, this effect was significant for financial but not social pregnancy stressors. Race-stratified models revealed that greater financial pregnancy stressors predicted shorter telomeres in offspring of White, but not Black mothers.

CONCLUSIONS

Race and maternal stressors interact and are related to biological aging across generations, but these effects are specific to certain races, stressors, and exposure time periods.

Relative Telomere Length Is Associated with the Risk of Development and Severity of the Course of Age-Related Macular Degeneration in the Russian Population

One of the most significant factors for age-related macular degeneration (AMD) development is considered to be aging, the processes of which are closely associated with telomere shortening. The different forms, indicators of aggressiveness, and intensities of AMD can be observed in the same age group, confirming the need to find a biomarker for early diagnosis and be capable of monitoring the progression of the pathological process. Therefore, we investigated whether the relative telomere length (RTL) has any connection with the risk of development of disease and its progression. RTL was measured using RT-PCR in 166 people, including 96 patients with AMD. RTL was significantly lower in patients with AMD. Women were more likely to develop AMD than men (odds ratio (OR) = 9.53 × 10⁶ vs. OR = 1.04 × 10⁸, respectively). The decrease in RTL in patients reliably correlated with the progression of AMD, and the smallest RTL was observed in late-stage patients. RTL < 0.8 is a significant risk factor for disease progression. The results of our research showed that RTL may be considered as a potential biomarker and a promising predictor of disease progression in patients with early AMD.

Comparison qPCR study for selecting a valid single copy gene for measuring absolute telomere length

Telomere shortening is a well-known biomarker for biological aging. A previous review of the methods used to measure telomere length (TL) noted how challenging it is to compare results from different studies using diverse methodological techniques. The most commonly used high throughput method for measuring average TL is the quantitative PCR (qPCR) method, where there are two protocols available; the relative TL and the absolute TL (aTL) method. All qPCR methods have similarities in that they use two different primer sets to measure the telomere repeat sequence (TTAGGG)_n and a single copy gene region to calculate the average TL, (T/S) ratio. The difference between the relative TL and the aTL assay lies with the introduction of duplex oligomer standards to identify TL in kilobase pairs rather than using the traditional relative TL, T/S ratio method. Problems were noted using 36B4 (RPLP0), which was originally used as a suitable single copy gene qPCR assay. A previous aTL publication attempted to replace the 36B4 (RPLP0) single copy gene using the Interferon beta 1 gene (IFNB1) but results showed a lack of agreement with the TL results when compared to the DNAmTL assay. Here, we compare the two single copy gene assays previously used for the aTL assay and offer an alternative IFNB1 single copy gene assay without non-specific priming amplification to provide more consistent diploid copy number determination and a more robust and reproducible assay for measuring absolute TL.

Salivary telomere length and the risks of prediabetes and diabetes among middle-aged and older adults: findings from the Health and Retirement Study

AIM

To assess the association of telomere length (TL) with prediabetes/diabetes and to explore the potential factors affecting TL among individuals with prediabetes/diabetes by weight status.

METHODS

This study included 3,379 eligible adults (aged 45-85 years, males: 42%) from the US Health and Retirement Study in 2008. TL was assayed using quantitative PCR of saliva (T/S ratio). Linear and nonlinear associations between TL and prediabetes/diabetes were assessed using the logistic regression and restricted cubic spline model, respectively, adjusting for TL-plate numbers, age, sex, race, body mass index, lifestyles, diabetes medications, and cardiometabolic parameters (blood pressure, C-reactive protein, and total cholesterol). Multiple linear regression was used for testing any factors associated with TL.

RESULTS

Among 3,379 participants, 868 (25.7%) had prediabetes with a mean TL of 1.34 ± 0.37 (T/S ratio) and 858 (25.4%) had diabetes with a mean TL of 1.36 ± 0.43 (T/S ratio). Neither linear nor nonlinear association of TL with prediabetes/diabetes was significant by weight status. Age was negatively associated with TL in both normal-weight (β = - 0.002, p = 0.025) and overweight/obese (β = - 0.002, p = 0.006) prediabetes, but non-significant in normal-weight and overweight/obese diabetes. BMI and cardiometabolic parameters were not associated with TL in prediabetes/diabetes by weight status.

CONCLUSIONS

Salivary TL was not associated with prediabetes/diabetes among the US middle-aged and older adults. Further longitudinal studies are required to establish the link between TL and diabetes development and to identify potential factors affecting TL shortening, particularly in normal-weight diabetic patients.

The association between sleep quality and telomere length: A systematic literature review

Several sleep parameters present an elevated risk for processes that contribute to cellular aging. Short sleep duration, sleep apnoea, and insomnia are significantly associated with shorter telomeres, a biological marker of cellular aging. However, there has been no review or analysis of studies that have examined the association between the psychological construct of sleep quality and telomere length. The present study aimed to provide a systematic review of the association between sleep quality and telomere length. A systematic review of English articles was conducted using MEDLINE/PubMed, PsycINFO, Google Scholar, and Web of Science electronic databases, with the final search conducted on 3rd September 2021. Search terms included sleep quality, poor sleep, insomnia, sleep difficulties, sleep issue*, non-restorative sleep, telomere*, cellular aging, and immune cell telomere length. Study eligibility criteria included human participants aged 18 years or older and a reproducible methodology. Study appraisal and synthesis were completed using a systematic search in line with a PICOS approach (P = Patient, problem, or population; I = Intervention, prognostic factor, exposure; C = Comparison, control, or comparator; O = Outcomes; S = Study designs). Twenty-two studies met review inclusion criteria. Qualitative synthesis of the literature indicated insufficient evidence overall to support a significant association between sleep quality and telomere length. Limitations across studies were addressed, such as the assessment of examined constructs. Findings highlight important targets for future research, including the standardised operationalisation of the sleep quality construct and experimental study designs. Research in this area has clinical significance by identifying possible mechanisms that increase the risk for age-related disease and mortality. PROSPERO Registration No.: CRD 42021233139.

Evaluation of clonal hematopoiesis in pediatric ADA-SCID gene therapy participants

Autologous stem cell transplant with gene therapy (ASCT-GT) provides curative therapy while reducing pretransplant immune-suppressive conditioning and eliminating posttransplant immune suppression. Clonal hematopoiesis of indeterminate potential (CHIP)-associated mutations increase and telomere lengths (TLs) shorten with natural aging and DNA damaging processes. It is possible that, if CHIP is present before ASCT-GT or mutagenesis occurs after busulfan exposure, the hematopoietic stem cells carrying these somatic variants may survive the conditioning chemotherapy and have a selective reconstitution advantage, increasing the risk of hematologic malignancy and overall mortality. Seventy-four peripheral blood samples (ranging from baseline to 120 months after ASCT-GT) from 10 pediatric participants who underwent ASCT-GT for adenosine deaminase-deficient severe combined immune deficiency (ADA-SCID) after reduced-intensity conditioning with busulfan and 16 healthy controls were analyzed for TL and CHIP. One participant had a significant decrease in TL. There were no CHIP-associated mutations identified by the next-generation sequencing in any of the ADA-SCID participants. This suggests that further studies are needed to determine the utility of germline analyses in revealing the underlying genetic risk of malignancy in participants who undergo gene therapy. Although these results are promising, larger scale studies are needed to corroborate the effect of ASCT-GT on TL and CHIP. This trial was registered at www.clinicaltrials.gov as #NCT00794508.

Minimally invasive biomarkers in human and non-human primate evolutionary biology: Tools for understanding variation and adaptation

BACKGROUND

The use of minimally invasive biomarkers (MIBs - physiological biomarkers obtained from minimally invasive sample types) has expanded rapidly in science and medicine over the past several decades. The MIB approach is a methodological strength in the field of human and non-human primate evolutionary biology (HEB). Among humans and our closest relatives, MIBs provide unique opportunities to document phenotypic variation and to operationalize evolutionary hypotheses.

AIMS

This paper overviews the use of MIBs in HEB. Our objectives are to (1) highlight key research topics which successfully implement MIBs, (2) identify promising yet under-investigated areas of MIB application, and (3) discuss current challenges in MIB research, with suggestions for advancing the field.

DISCUSSION AND CONCLUSIONS

A range of MIBs are used to investigate focal topics in HEB, including energetics and life history variation/evolution, developmental plasticity, and social status and dominance relationships. Nonetheless, we identify gaps in existing MIB research on traits such as physical growth and gut function that are central to the field. Several challenges remain for HEB research using MIBs, including the need for additional biomarkers and methods of assessment, robust validations, and approaches that are standardized across labs and research groups. Importantly, researchers must provide better support for adaptation and fitness effects in hypothesis testing (e.g., by obtaining complementary measures of energy expenditure, demonstrating redundancy of function, and performing lifetime/longitudinal analyses). We point to continued progress in the use of MIBs in HEB to better understand the past, present, and future of humans and our closest primate relatives.

No Mediation Effect of Telomere Length or Mitochondrial DNA Copy Number on the Association Between Adverse Childhood Experiences (ACEs) and Central Arterial Stiffness

Background

Adverse childhood experiences (ACEs) have been linked to increased cardiovascular disease (CVD) risk. Previous reports have suggested that accelerated biological aging—indexed by telomere length (TL) and mitochondrial DNA copy number (mtDNAcn)—may contribute to associations between ACEs and cardiovascular health outcomes. Here, we examine the potential mediating effects of TL and mtDNAcn on the association between ACEs and central arterial stiffness—an intermediate cardiovascular health outcome—as a novel pathway linking ACEs to CVD risk among young adults.

Methods and Results

One hundred and eighty‐five (n=102 women; mean age, 22.5±1.5 years) individuals provided information on ACEs. TL (kb per diploid cell) and mtDNAcn (copies per diploid cell) were quantified using quantitative polymerase chain reaction techniques. Central arterial stiffness was measured as carotid‐femoral pulse wave velocity (cfPWV; m/s). Multiple linear regression analyses were used to examine the associations between ACEs, TL, mtDNAcn, and cfPWV. ACEs were positively associated with cfPWV ( β =0.147, P =0.035). TL ( β =−0.170, P =0.011) and mtDNAcn ( β =−0.159, P =0.019) were inversely associated with cfPWV. Neither TL ( β =−0.027, P =0.726) nor mtDNAcn ( β =0.038, P =0.620) was associated with ACEs. Neither marker mediated the association between ACEs and cfPWV.

Conclusions

An increasing number of ACEs were associated with a faster cfPWV and thus, a greater degree of central arterial stiffness. ACEs were not associated with either TL or mtDNAcn, suggesting that these markers do not represent a mediating pathway linking ACEs to central arterial stiffness.

Perinatal and early childhood biomarkers of psychosocial stress and adverse experiences

The human brain develops through a complex interplay of genetic and environmental influences. During critical periods of development, experiences shape brain architecture, often with long-lasting effects. If experiences are adverse, the effects may include the risk of mental and physical disease, whereas positive environments may increase the likelihood of healthy outcomes. Understanding how psychosocial stress and adverse experiences are embedded in biological systems and how we can identify markers of risk may lead to discovering new approaches to improve patient care and outcomes. Biomarkers can be used to identify specific intervention targets and at-risk children early when physiological system malleability increases the likelihood of intervention success. However, identifying reliable biomarkers has been challenging, particularly in the perinatal period and the first years of life, including in preterm infants. This review explores the landscape of psychosocial stress and adverse experience biomarkers. We highlight potential benefits and challenges of identifying risk clinically and different sub-signatures of stress, and in their ability to inform targeted interventions. Finally, we propose that the combination of preterm birth and adversity amplifies the risk for abnormal development and calls for a focus on this group of infants within the field of psychosocial stress and adverse experience biomarkers. IMPACT: Reviews the landscape of biomarkers of psychosocial stress and adverse experiences in the perinatal period and early childhood and highlights the potential benefits and challenges of their clinical utility in identifying risk status in children, and in developing targeted interventions. Explores associations between psychosocial stress and adverse experiences in childhood with prematurity and identifies potential areas of assessment and intervention to improve outcomes in this at-risk group.

Comparison of Telomere Length between Buccal Cells and Blood Cells

Telomere length (TL) in blood cells is commonly used as a proxy for TL in other tissue types. The source of DNA of adequate quality and quantity is important for TL analysis. Compared to blood cells, buccal cells easy for genomic DNA preparation would facilitate the rapid and reliable TL analysis. However, the feasibility of buccal cells for TL analysis remains yet unestablished. We characterized TL of buccal cells and blood cells collected from 52 individuals using buccal cell swabs and fingertip sticks. Relative TL (RTL) determined by quantitative PCR showed that there is a strong correlation between buccal RTL and blood RTL (r=0.877, p<0.001), suggesting that buccal cells are adequate sources of DNA for TL analysis. The validity of sampling using buccal cell swabs provides simple operation and good reproducibility for TL analysis, that overcomes the discomfort and risk of infection caused by blood sampling.

Telomere Length as a marker of biological aging: A critical review of recent literature

INTRODUCTION

Aging is characterized as a syndrome of deleterious, progressive, universal, and irreversible function changes affecting every structural and functional aspect of the organism and accompanied by a generalized increase in mortality. Although a substantial number of candidates for biomarkers of aging have been proposed, none has been validated or universally accepted. Human telomeres constitute hexameric repetitive DNA sequence nucleoprotein complexes that cap chromosome ends, regulating gene expression and modulating stress-related pathways. Telomere length (TL) shortening is observed both in cellular senescence and advanced age, leading to the investigation of TL as a biomarker for aging and a risk factor indicator for the development and progression of the most common age-related diseases.

OBJECTIVE

The present review underlines the connection between TL and the pathophysiology of the diseases associated with telomere attrition.

METHODS

We performed a structured search of the PubMed database for peer-reviewed research of the literature regarding leukocyte TL and cardiovascular diseases (CVD), more specifically stroke and heart disease, and focused on the relevant articles published during the last 5 years. We also applied Hill's criteria of causation to strengthen this association.

RESULTS

We analyzed the recent literature regarding TL length, stroke, and CVD. Although approximately one-third of the available studies support the connection, the results of different studies seem to be rather conflicting as a result of different study designs, divergent methods of TL determination, small study samples, and patient population heterogeneity. After applying Hill's criteria, we can observe that the literature conforms to them weakly, with chronology being the only Hill criterion of causality that probably cannot be contested.

CONCLUSION

The present review attempted to examine the purported relation between leukocyte TL and age-related diseases such as CVD and more specific stroke and heart disease in view of the best established, comprehensive, medical and epidemiological criteria that have characterized the focused recent relevant research. Although several recommendations have been made that may contribute significantly to the field, a call for novel technical approaches and studies is mandatory to further elucidate the possible association.

The prevalence of nurse burnout and its association with telomere length pre and during the COVID-19 pandemic

Background

Burnout is a work-related stress syndrome characterized by emotional exhaustion, depersonalization, and reduced personal accomplishment. Nurse burnout is related to nurses’ deteriorating mental health and poorer patient care quality and thus, is a significant concern in healthcare. The Coronavirus Disease 2019 (COVID-19) pandemic has swept the world and distressed the healthcare systems. Because of the body’s stress mechanism, it is vital to examine the current prevalence of nurse burnout and understand it at a biological level, using an epigenetic biomarker, telomere length.

Purpose

To determine the prevalence of burnout among nurses in the Peri-Operative and Labor & Delivery settings pre and during the COVID-19 pandemic and to examine the effects of burnout on absolute telomere length.

Methods

This is a cross-sectional study assessing the prevalence of nurses’ burnout and the relationships between nurses’ burnout and telomere length. Due to the COVID-19 pandemic, we had to stop the study during the mid of data collection. Even though the study was not designed to capture changes before and during the pandemic, we analyzed two groups’ data before and during the pandemic. The study took place in a US hospital. Nurses in the hospital’s Operating Room, Post-Anesthesia Care Unit, and Labor & Delivery Unit participated in the study. Maslach Burnout Inventory survey and nurses’ demographics were administered online. Telomere length was measured via finger-prick blood.

Results

146 nurses participated in the study, with 120 participants’ blood samples collected. The high-level burnout rate was 70.5%. Correlation analysis did not reveal a direct correlation between nurse burnout and telomere length. However, in a multiple regression analysis, the final model contained the burnout subscale of emotional exhaustion, years as an RN, and work unit’s nursing care quality. There was a low degree of departure from normality of the mean absolute telomere length in the pre-pandemic group and a substantial degree of departure in the during-pandemic group.

Conclusions

Nurse burnout is a prevalent phenomenon in healthcare, and this study indicates that nurses currently experience high levels of burnout. Nurses’ cellular biomarker, telomere length, is shorter in the group of nurses during the COVID-19 pandemic than before. Appropriate measures should be implemented to decrease nurses’ burnout symptoms and improve nurses’ psychological and physical health. Nurses, especially those younger than 60, report higher burnout symptoms, particularly emotional exhaustion. This study indicates the need for intervention to promote nurses’ health during the pandemic and beyond. If not appropriately managed, nurse burnout may continue to be a significant issue facing the healthcare system.

Prenatal exposure to maternal psychological distress and telomere length in childhood

Telomere length (TL) is a biological marker of cellular aging, and shorter TL in adulthood is associated with increased morbidity and mortality risk. It is likely that these differences in TL are established long before adulthood, and there is growing evidence that TL can reflect prenatal experiences. Although maternal prenatal distress predicts newborn TL, it is unknown whether the relation between prenatal exposure to maternal distress and child TL persists through childhood. The purpose of the current longitudinal, prospective study is to examine the relation between prenatal exposure to maternal distress (perceived stress, depressive symptoms, pregnancy-related anxiety) and TL in childhood. Participants included 102 children (54 girls) and their mothers. Mothers' distress was assessed five times during pregnancy, at 12 weeks postpartum, and at the time of child telomere measurement between 6 and 16 years of age. Maternal distress during pregnancy predicted shorter offspring TL in childhood, even after accounting for postnatal exposure to maternal distress and other covariates. These findings indicate that maternal mental health predicts offspring TL biology later in childhood than previously observed. This study bolsters claims that telomere biology is subject to fetal programming and highlights the importance of supporting maternal mental health during pregnancy.

Longitudinal Follow-Up of Blood Telomere Length in HIV-Exposed Uninfected Children Having Received One Year of Lopinavir/Ritonavir or Lamivudine as Prophylaxis

Telomere shortening can be enhanced upon human immunodeficiency virus (HIV) infection and by antiretroviral (ARV) exposures. The aim of this study was to evaluate the acute and long-term effect on telomere shortening of two ARV prophylaxes, lopinavir/ritonavir (LPV/r) and lamivudine (3TC), administered to children who are HIV-exposed uninfected (CHEU) to prevent HIV acquisition through breastfeeding during the first year of life, and to investigate the relationship between telomere shortening and health outcomes at six years of age. We included 198 CHEU and measured telomere length at seven days of life, at week-50 and at six years (year-6) using quantitative polymerase chain reaction. At week-50, telomere shortening was observed among 44.3% of CHEU, irrespective of the prophylactic treatment. Furthermore, this telomere shortening was neither associated with poor growth indicators nor neuropsychological outcomes at year-6, except for motor abilities (MABC test n = 127, β = -3.61, 95%CI: -7.08, -0.14; p = 0.04). Safety data on telomere shortening for infant HIV prophylaxis are scarce. Its association with reduced motor abilities deserves further attention among CHEU but also HIV-infected children receiving ARV treatment.

Coming up short: Comparing venous blood, dried blood spots & saliva samples for measuring telomere length in health equity research

BACKGROUND

Telomere length (TL) in peripheral blood mononuclear cells (PBMC) from fresh venous blood is increasingly used to estimate molecular impacts of accumulated social adversity on population health. Sometimes, TL extracted from saliva or dried blood spots (DBS) are substituted as less invasive and more scalable specimen collection methods; yet, are they interchangeable with fresh blood? Studies find TL is correlated across tissues, but have not addressed the critical question for social epidemiological applications: Do different specimen types show the same association between TL and social constructs?

METHODS

We integrate expertise in social epidemiology, molecular biology, and the statistical impact of measurement error on parameter estimates. Recruiting a diverse sample of 132 Metro-Detroit women, we measure TL for each woman from fresh blood PBMC, DBS, and saliva. Using regression methods, we estimate associations between social characteristics and TL, comparing estimates across specimen types for each woman.

RESULTS

Associations between TL and social characteristics vary by specimen type collected from the same woman, sometimes qualitatively altering estimates of the magnitude or direction of a theorized relationship. Being Black is associated with shorter TL in PBMC, but longer TL in saliva or DBS. Education is positively associated with TL in fresh blood, but negatively associated with TL using DBS.

CONCLUSION

Findings raise concerns about the use of TL measures derived from different tissues in social epidemiological research. Investigators need to consider the possibility that associations between social variables and TL may be systematically related to specimen type, rather than be valid indicators of socially-patterned biopsychosocial processes.

Association between ideal cardiovascular health and telomere length in participants older than 55 years old from the SUN cohort

INTRODUCTION AND OBJECTIVES

Telomeres are noncoding regions located at the end of chromosomes and their shortening has been associated with risk factors and cardiovascular disease. The aim of this study was to evaluate the association between ideal cardiovascular health (Life's simple 7) and the odds of having short telomeres in a subsample of participants older than 55 years from the Seguimiento Universidad de Navarra (SUN) study.

METHODS

We included 886 participants older than 55 years (645 men and 241 women). Telomere length was measured using a real-time quantitative polymerase chain reaction. Cardiovascular health score was defined by the American Heart Association as a composite score of 7 key risk factors (smoking status, physical activity, diet, body mass index, blood pressure, total cholesterol, and fasting blood glucose) with 0 to 2 points for each factor. We categorized this score in tertiles as poor (0-9 points), intermediate (10-11 points) and ideal (12-14 points). The odds of having short telomeres was defined as telomere length below the 20th percentile.

RESULTS

Individuals with higher ideal cardiovascular health had a lower prevalence of having short telomeres (adjusted OR, 0.60; 95%CI, 0.34-1.05; P trend=.052). This association was statistically significant in men (adjusted OR, 0.37; 95%CI, 0.17-0.83; P trend=.025) but not in women.

CONCLUSIONS

An inverse association between cardiovascular health score and short telomeres was found especially for men older than 55 years in the SUN population. The SUN project was registered at ClinicalTrials.gov (Identifier: NCT02669602).

Telomere length and epigenetic age acceleration in adolescents with anxiety disorders

Evidence on the relationship between genetics and mental health are flourishing. However, few studies are evaluating early biomarkers that might link genes, environment, and psychopathology. We aimed to study telomere length (TL) and epigenetic age acceleration (AA) in a cohort of adolescents with and without anxiety disorders (N = 234). We evaluated a representative subsample of participants at baseline and after 5 years (n = 76) and categorized them according to their anxiety disorder diagnosis at both time points: (1) control group (no anxiety disorder, n = 18), (2) variable group (anxiety disorder in one evaluation, n = 38), and (3) persistent group (anxiety disorder at both time points, n = 20). We assessed relative mean TL by real-time quantitative PCR and DNA methylation by Infinium HumanMethylation450 BeadChip. We calculated AA using the Horvath age estimation algorithm and analyzed differences among groups using generalized linear mixed models. The persistent group of anxiety disorder did not change TL over time (p = 0.495). The variable group had higher baseline TL (p = 0.003) but no accelerated TL erosion in comparison to the non-anxiety control group (p = 0.053). Furthermore, there were no differences in AA among groups over time. Our findings suggest that adolescents with chronic anxiety did not change telomere length over time, which could be related to a delay in neuronal development in this period of life.

Child buccal telomere length and mitochondrial DNA content as biomolecular markers of ageing in association with air pollution

BACKGROUND

Pro-inflammatory conditions such as air pollution might induce biological ageing. However, the available evidence on such an impact in children is still very scarce. We studied in primary schoolchildren the association of ambient residential air pollution exposure with telomere length (TL) and mitochondrial DNA content (mtDNAc), two important targets of the core axis of ageing.

METHODS

Between 2012 and 2014, buccal TL and mtDNAc were repeatedly assessed using qPCR in 197 Belgian primary schoolchildren (mean age 10.3 years) as part of the COGNAC study. At the child's residence, recent (week), sub-chronic (month) and chronic (year) exposure to nitrogen dioxide (NO₂), particulate matter ≤ 2.5 µm (PM_2.5) and black carbon (BC) were estimated using a high resolution spatiotemporal model. A mixed-effects model with school and subject as random effect was used while adjusting for a priori chosen covariates.

RESULTS

An interquartile range (IQR) increment (1.9 µg/m³) in chronic PM_2.5 exposure was associated with a 8.9% (95% CI: -15.4 to -1.9%) shorter TL. In contrast to PM_2.5, chronic exposure to BC and NO₂ was not associated with TL but recent exposure to BC and NO₂ showed significant inverse associations with TL: an IQR increment in recent exposure to BC (0.9 µg/m³) and NO₂ (10.2 µg/m³) was associated with a 6.2% (95% CI: -10.6 to -1.6%) and 6.4% (95% CI: -11.8 to -0.7%) shorter TL, respectively. Finally, an IQR increment in chronic PM_2.5 exposure was associated with a 12.7% (95% CI: -21.7 to -2.6%) lower mtDNAc. However, no significant associations were seen for NO₂ and BC or for other exposure windows.

CONCLUSION

Chronic exposure to PM_2.5 below the EU threshold was associated with child's shorter buccal TL and lower mtDNAc, while traffic-related pollutants (BC and NO₂) showed recent effects on telomere biology. Our data add to the literature on air pollution-induced effects of TL and mtDNAc, two measures part of the core axis of cellular ageing, from early life onwards.

Educational mobility and telomere length in middle-aged and older adults: testing three alternative hypotheses

Critical period, social mobility, and social accumulation are three hypotheses that may explain how educational mobility impacts health. Thus far, there is little evidence on how these processes are associated with biological aging as measured by telomere length. Using cross-sectional data from the 2008 Health and Retirement Study, we examined the association between educational mobility (parental education and contemporaneous education) and telomere length. The final model is adjusted for sociodemographic factors and socioeconomic status, childhood adversity, and health behaviors/risk factors, as well as depressive symptoms. A total of 1,894 participants were included in the main analyses. High parental education was associated with longer telomere length in a fully adjusted model (B = 0.03, CI [0.002,0.07]). Downwardly mobile individuals (high parental education and low contemporaneous education) had longer telomere length compared to stably low individuals in a fully adjusted model (B = 0.05, CI [0.004,0.09]). There was support for the critical period hypothesis and partial support for the change hypothesis. There was no evidence to support the social accumulation hypothesis. Prospective studies are needed to understand the mechanism that can help further explain the association between educational mobility and telomere length.

Early Puberty and Telomere Length in Preadolescent Girls and Mothers

OBJECTIVE

To test the association between early puberty and telomere length in preadolescent girls and mothers from a large representative sample of US females.

STUDY DESIGN

We analyzed data from 1194 preadolescent girls and 2421 mothers from the Fragile Families and Child Wellbeing Study. Participants were from a population-based birth cohort (1998-2000) born in large US cities. Telomere length was assessed by quantitative polymerase chain reaction from saliva samples provided by preadolescent girls and mothers of preadolescent youth. Mothers completed a questionnaire about their child's pubertal development to determine concurrent Tanner stages and provided self-reports of her own age at menarche. Linear regression models were used to estimate the association between pubertal development (status and timing) and telomere length.

RESULTS

Early pubertal timing but not pubertal status was associated with shorter telomere length in preadolescent girls (P < .01). Early age at menarche was associated with shorter telomere length in a sample of mothers of preadolescent youth (P < .05).

CONCLUSIONS

Results provide evidence for the association between early puberty and shorter telomeres evidenced by associations in both preadolescent girls and mothers. Future research should address the limitations of this study by using longitudinal measurements of pubertal development assessed through medical examinations and repeated assessments of telomere length to capture telomere attrition.

Ultra-processed food consumption and the risk of short telomeres in an elderly population of the Seguimiento Universidad de Navarra (SUN) Project

BACKGROUND

Telomere length (TL) is a marker of biological age that may be affected by dietary factors through oxidation and inflammation mechanisms. In addition, ultra-processed food (UPF) consumption has increased worldwide and it has been associated with the risk of developing several diseases.

OBJECTIVES

We aimed to evaluate the association between UPF consumption and the risk of having short telomeres in an elderly population of the Seguimiento Universidad de Navarra (SUN) Project.

METHODS

This is a cross-sectional study of 886 participants (645 men and 241 women) aged 57-91 y recruited from the SUN Project (Spain, 1999-2018). TL was measured from saliva samples by real-time qPCR at baseline and UPF consumption was collected using a validated 136-item FFQ and classified according to the NOVA system. We evaluated the association between consumption of energy-adjusted UPF categorized into quartiles (low, medium-low, medium-high, and high consumption) and the risk of having short telomeres (<20th percentile) using logistic regression models.

RESULTS

Those participants with the highest UPF consumption had almost twice the odds of having short telomeres compared with those with the lowest consumption (adjusted OR: 1.82; 95% CI: 1.05, 3.22; P-trend = 0.03).

CONCLUSIONS

A higher consumption of UPF (>3 servings/d) was associated with higher risk of having shorter telomeres in an elderly Spanish population of the SUN Project.This trial was registered at clinicaltrials.gov as NCT02669602.

Psychosocial Stressors and Telomere Length: A Current Review of the Science

A growing literature suggests that exposure to adverse social conditions may accelerate biological aging, offering one mechanism through which adversity may increase risk for age-related disease. As one of the most extensively studied biological markers of aging, telomere length (TL) provides a valuable tool to understand potential influences of social adversity on the aging process. Indeed, a sizeable literature now links a wide range of stressors to TL across the life span. The aim of this article is to review and evaluate this extant literature with a focus on studies that investigate psychosocial stress exposures and experiences in early life and adulthood. We conclude by outlining potential biological and behavioral mechanisms through which psychosocial stress may influence TL, and we discuss directions for future research in this area.

Standard guidelines for the publication of telomere qPCR results in evolutionary ecology

Telomere length has been used as a proxy of fitness, aging and lifespan in vertebrates. In the last decade, dozens of articles reporting on telomere dynamics in the fields of ecology and evolution have been published for a wide range of taxa. With this growing interest, it is necessary to ensure the accuracy and reproducibility of telomere length measurement techniques. Real-time quantitative PCR (qPCR) is routinely applied to measure relative telomere length. However, this technique is highly sensitive to several methodological variables and the optimization of qPCR telomere assays remains highly variable between studies. Therefore, standardized guidelines are required to enable the optimization of robust protocols, and to help in judging the validity of the presented results. This review provides an overview of preanalytical and analytical factors that can lead to qPCR inconsistencies and biases, including: (a) sample type, collection and storage; (b) DNA extraction, storage and quality; (c) qPCR primers, laboratory reagents, and assay conditions; and (d) data analysis. We propose a minimum level of information for publication of qPCR telomere assays in evolutionary ecology considering the methodological pitfalls and sources of error. This review highlights the complexity of the optimization and validation of qPCR for telomere measurement per se, demonstrating the importance of transparency and clarity of reporting methodological details required for reliable, reproducible and comparable qPCR telomere assays. We encourage efforts to implement standardized protocols that ensure the rigour and quality of telomere dynamics studies.

Telomere length analysis from minimally-invasively collected samples: Methods development and meta-analysis of the validity of different sampling techniques: American Journal of Human Biology

OBJECTIVES

Telomeres are the protective caps of chromosomes. They shorten with cell replication, age, and possibly environmental stimuli (eg, infection and stress). Short telomere length (TL) predicts subsequent worse health. Although venous whole blood (VWB) is most commonly used for TL measurement, other, more minimally invasive, sampling techniques are becoming increasingly common due to their field-friendliness, allowing for feasible measurement in low-resource contexts. We conducted statistical validation work for measuring TL in dried blood spots (DBS) and incorporated our results into a meta-analysis evaluating minimally invasive sampling techniques to measure TL.

METHODS

We isolated DNA extracts from DBS using a modified extraction protocol and tested how they endured different shipping conditions and long-term cryostorage. We then included our in-house DBS TL validation statistics (correlation values with VWB TL and age) in a series of meta-analyses of results from 24 other studies that published similar associations for values between TL measured in DBS, saliva, and buccal cells.

RESULTS

Our modified DBS extraction technique produced DNA yields that were roughly twice as large as previously recorded. Partially extracted DBS DNA was stable for 7 days at room temperature, and still provided reliable TL measurements, as determined by external validation statistics. In our meta-analysis, DBS TL had the highest external validity, followed by saliva, and then buccal cells-possibly reflecting similarities/differences in cellular composition vs VWB.

CONCLUSIONS

DBS DNA is the best proxy for VWB from the three minimally-invasively specimen types evaluated and can be used to expand TL research to diverse settings and populations.

Shortened telomere length is associated with unfair treatment attributed to race in African Americans living in Tallahassee, Florida

OBJECTIVES

Experiences of interpersonal discrimination are pervasive stressors in the lives of African Americans. Increased discrimination stress may cause premature aging. Telomere length (TL) is a plastic genetic trait that is an emerging indicator of cellular health and aging. Short TL is a risk factor for the earlier onset of disease. TL shortens with age, a process that may be accelerated by psychosocial stress. Our study explores the relationship between TL and experiences of discrimination in the form of self-reported unfair treatment (UT).

METHODS

Using a qPCR-based method, we measured TL in DNA from saliva samples provided by 135 African American adults from Tallahassee, FL. We developed discrimination measures using a modified survey that explores nine social domains of self-reported unfair treatment experienced both directly and indirectly. We used multiple regression to examine associations between UT and TL.

RESULTS

We found that racial discrimination in the form of self-reported unfair treatment attributed to race (UT-Race-Self) is inversely associated with TL.

CONCLUSIONS

The significant association between increased UT-Race-Self and shorter telomeres supports the hypothesis that psychosocial stress stemming from racial discrimination may affect TL. The potential impact of discrimination on TL may contribute to premature biological aging and racial health inequalities seen in African Americans.

Association between diet quality indexes and the risk of short telomeres in an elderly population of the SUN project

BACKGROUND

Shorter telomeres are associated with several age-related diseases, and lifestyle factors could influence this relationship. The aim of this study was to examine associations between salivary telomere length (TL) and diet quality using 5 evidence-based dietary indexes in an elderly (>55 years old) Spanish population of the SUN project (n = 886).

METHOD

TL was measured using the quantitative real-time polymerase chain reaction. Age-adjusted TL variable through residuals methods was used for all analysis. Diet quality was assessed by the Prime Diet Quality Score (PDQS), Fat Quality Index (FQI), Mediterranean Diet Adherence Screener (MEDAS), Dietary Approaches to Stop Hypertension (DASH) index and the Alternative Healthy Eating Index (AHEI-2010).

RESULTS

TL did differ according to sex, smoking status, and dyslipidemia in elderly subjects of the SUN study. In addition, subjects with dyslipidemia (compared to absence of dyslipidemia) had a significantly higher risk (27% vs. 18%, p = 0.015) of short telomeres (<percentile 20th). Interestingly, a lower risk of having short telomeres was observed among participants in the top tertiles of the following diet quality score PDQS, MEDAS and DASH compared to the bottom tertiles in crude and adjusted models. Moreover, FQI and AHEI-2010 scores showed an inverse association with the risk of having short telomeres after adjustment for potential confounders (model adjusted for dyslipidemia interaction, p for trend = 0.025 and 0.021, respectively; and model additionally adjusted for sex and smoking status, p for trend = 0.033 and 0.029, respectively).

CONCLUSION

Adherence to high quality diet is associated to longer salivary TL in our elderly Spanish population of the SUN study.

Physician-Training Stress and Accelerated Cellular Aging

BACKGROUND

Stress is a key precipitant for many common diseases, but established biological markers to track stress and guide investigations into mechanisms linking stress and disease are lacking. Cross-sectional studies have identified correlations between stress and telomere attrition, but no large, longitudinal studies examining the impacts of chronic stress on telomere length exist. Residency training for physicians is a well-established stressful experience and can be used as a prospective stress model.

METHODS

In a longitudinal cohort study of 250 interns (first-year residents) at 55 United States hospital systems serving during the 2015-2016 academic year, we examined associations between measures of the residency experience and saliva-measured telomere attrition.

RESULTS

Telomere length shortened significantly over the course of internship year, from mean ± SD of 6465.1 ± 876.8 base pairs before internship to 6321.5 ± 630.6 base pairs at the end of internship (t₂₄₆ = 2.69; p = .008). Stressful early family environments and neuroticism were significantly associated with shorter preinternship telomere length. Longer work hours were associated with greater telomere intern telomere loss over the year (p = .002). Of note, the mean telomere attrition during internship year was six times greater than the typical annual attrition rate identified in a recent meta-analysis.

CONCLUSIONS

This work implicates telomere attrition as a biologically measurable consequence of physician training, with the magnitude of attrition associated with workload. Identification of an objective, biological sequela of residency stress may help to facilitate the development of effective interventions. Further, the findings implicate telomere attrition as an objective biomarker to follow the pathologic effects of stress, in general.

How and when to use dried blood spots in psychoneuroendocrinological research

OBJECTIVE

The term "dried blood spot" (DBS) refers to a sampling technique in which capillary whole blood is spotted on filter paper. Given the possibility to determine a wide range of hormones and related biomarkers in DBS, the method should be of interest to researchers in psychoneuroendocrinology. So far, however, the how and when of using DBS in this context have not been outlined.

METHODS

A review of the literature was conducted in order to describe the materials and procedures necessary to determine relevant biological markers from DBS (how to use DBS). In addition, a comparison of the DBS method with other sampling techniques was undertaken and examples of its previous use in psychoneuroendocrinology were provided (when to use DBS).

RESULTS

Both dyadic and DBS self-sampling are feasible, and a number of protocols are available to determine endocrine and immune, genetic and epigenetic markers. Decisions to use DBS instead of venous blood or saliva sampling should mainly be guided by whether it is sensible and feasible to determine the parameter of interest in whole blood obtained from DBS. In addition, DBS are well suited for large study populations with specific vulnerabilities, and for remotely located studies with budgetary constraints.

CONCLUSION

Dried blood spots are a promising material as well as a simple sampling technique for psychoneuroendocrinological research. Future efforts should be directed at continuing to adapt existing serum and plasma analysis protocols for use with DBS, and at testing the feasibility of DBS self-sampling in field studies.

Does Salivary Telomere Length Explain Race/Ethnic Differences in Aging?

Telomere length (TL) is a biomarker that can be used to characterize variability in aging and may explain race/ethnic differences in aging. Yet, it remains unclear if TL is related to aging-associated health risks in multi-ethnic populations or if it explains race/ethnic differences in health. We examine whether salivary TL (STL) explains any of the race/ethnic variability in 15 indicators of high-risk biological, physical and cognitive health among 4,074 white, black, and Latinx older adults ages 54+ in the 2008 Health and Retirement Study. TL was assayed from saliva using quantitative PCR (T/S ratio). Decomposition analyses from logistic regression models show variation in STL does not account for any of the observed race/ethnic differences health. In age-adjusted, race-stratified models, STL was associated with HDL, total cholesterol, and lung function among whites, but was not associated with any markers of health among black or Latinx groups. In this diverse national sample of older adults, STL does not account for race/ethnic differences in late life health, is associated with relatively few indicators of health among whites, and is not associated with indicators of health among black or Latinx groups. STL may not be a useful biomarker for understanding racial/ethnic differences in population aging among older adults.

Telomere erosion in Sjögren's syndrome: A multi-tissue comparative analysis

BACKGROUND

Acinar progenitor cells within salivary glands have decreased regenerative capacity and exhibit shorter telomeres in primary Sjögren's syndrome (pSS) patients. We investigated whether DNA of saliva, PBMCs, and labial salivary gland (LSG) biopsy tissue have shorter telomeres in pSS compared to controls. mRNA expression of genes associated with pSS pathogenesis (ETS1, LEF1, and MMP9), telomere DNA damage response (ATM), senescence (CDKN2A), telomerase inhibition (IFN-y, TGFβ1), and the shelterin complex (TPP1, POT1) were assessed in LSG tissue by qRT-PCR to examine potential defects in telomere maintenance.

METHODS

Relative telomere length in DNA of saliva, PBMCs, and LSGs from non-pSS sicca and pSS patients was measured using qPCR. Saliva DNA telomere length was further compared to healthy controls. Expression of genes affecting telomere maintenance was analyzed in LSGs using qRT-PCR.

RESULTS

Primary Sjögren's syndrome patients have shorter telomeres in saliva DNA (n = 21) than healthy controls (n = 27) (P = .0035). ATM mRNA expression was higher in pSS LSG tissue (n = 16) vs non-pSS sicca patients (n = 13) (P = .0283) and strongly correlated with LEF1, TPP1, and POT1 (P < .01, r > 0.6).

CONCLUSIONS

Patients with pSS exhibited significant telomere erosion in saliva DNA. Overexpression of ATM in LSGs could represent a compensatory response to telomere shortening. The role of LEF1 in telomere erosion remains to be elucidated.

Sex differences in the association between salivary telomere length and multimorbidity within the US Health & Retirement Study

Background

Telomere length is associated with several physical and mental health conditions, but whether it is a marker of multimorbidity is unclear. We investigated associations between telomere length and multimorbidity by sex.

Methods

Data from adults (N = 5,495) aged ≥50 years were taken from the US Health and Retirement Study (2008–14). Telomere length was measured in 2008 from salivary samples. The cross-sectional associations between telomere length and eight chronic health conditions were explored using logistic regression, adjusting for confounders and stratified by sex. Logistic, ordinal and multinomial regression models were calculated to explore relationships between telomere length and multimorbidity (using a binary variable and a sum of the number of health conditions) and the type of multimorbidity (no multimorbidity, physical multimorbidity, or multimorbidity including psychiatric problems). Using multilevel logistic regression, prospective relationships between telomere length and incident multimorbidity were also explored.

Results

In cross-sectional analyses, longer telomeres were associated with reduced likelihood of lung disease and psychiatric problems among men, but not women. Longer telomeres were associated with lower risk of multimorbidity that included psychiatric problems among men (OR=0.521, 95% CI: 0.284 to 0.957), but not women (OR=1.188, 95% CI: 0.771 to 1.831). Prospective analyses suggested little association between telomere length and the onset of multimorbidity in men (OR=1.378, 95% CI: 0.931 to 2.038) nor women (OR=1.224, 95% CI: 0.825 to 1.815).

Conclusions

Although telomere length does not appear to be a biomarker of overall multimorbidity, further exploration of the relationships is merited particularly for multimorbidity including psychiatric conditions among men.

The telomere world and aging: Analytical challenges and future perspectives

Telomeres, the terminal nucleoprotein structures of eukaryotic chromosomes, play pleiotropic functions in cellular and organismal aging. Telomere length (TL) varies throughout life due to the influence of genetic factors and to a complex balancing between "shortening" and "elongation" signals. Telomerase, the only enzyme that can elongate a telomeric DNA chain, and telomeric repeat-containing RNA (TERRA), a long non-coding RNA involved in looping maintenance, play key roles in TL during life. Despite recent advances in the knowledge of TL, TERRA and telomerase activity (TA) biology and their measurement techniques, the experimental and theoretical issues involved raise a number of problems that should carefully be considered by researchers approaching the "telomere world". The increasing use of such parameters - hailed as promising clinically relevant biomarkers - has failed to be paralleled by the development of automated and standardized measurement technology. Consequently, associating given TL values to specific pathological conditions involves on the one hand technological issues and on the other clinical-biological issues related to the planning of clinically relevant association studies. Addressing these issues would help avoid major biases in association studies involving TL and a number of outcomes, especially those focusing on psychological and bio-behavioral variables. The main challenge in telomere research is the development of accurate and reliable measurement methods to achieve simple and sensitive TL, TERRA, and TA detection. The discovery of the localization of telomeres and TERRA in cellular and extracellular compartments had added an additional layer of complexity to the measurement of these age-related biomarkers. Since combined analysis of TL, TERRA and TA may well provide more exhaustive clinical information than a single parameter, we feel it is important for researchers in the various fields to become familiar with their most common measurement techniques and to be aware of the respective merits and drawbacks of these approaches.

Stress and Salivary Telomere Length in the Second Half of Life: A Comparison of Life-course Models

Background

Previous research has explored the relationship between childhood and adulthood stressful life events (SLEs) and adult salivary telomere length (TL), but no research to date has tested different life-course models in which stress in adulthood may fully, partly, or not mediate the relationship between childhood stress and adult TL.

Methods

To fill this gap, we elaborate over previous work by Puterman et al. (2016) and other standard models that do not account for the temporal order of stressors in childhood and adulthood, by using structural equation modeling (SEM) for a sample of 5,754 Health and Retirement Study (HRS) participants to compare the fit of three nested life-course models-social trajectory, early critical period, and cumulative risk.

Results

Results indicated that the social trajectory model, in which the association between childhood SLEs and TL in later adulthood is fully mediated by adulthood SLEs, fit the data better than the early critical period (no mediation) and cumulative risk (partial mediation) models.

Conclusion

In the social trajectory model, childhood SLEs are related to TL in later life only through adulthood SLEs. The direct physiological effect of childhood SLEs on TL in later life would be overestimated if adulthood SLEs are overlooked.

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.