A review and meta-analysis: Cross-tissue telomere length correlations in healthy humans

Inflammatory age and its impact on age-related health in older Chinese adults

INTRODUCTION

A standardized measure for inflammaging is lacking. We introduced the inflammatory age (iAge) as a quantification method and explored its associations with age-related traits and diseases in an older Chinese cohort.

METHODS

Inflammatory markers including white blood cell count (WBC), neutrophils, lymphocytes, monocytes, C-reactive protein, platelets and albumin were measured. Quantitative real-time polymerase chain reaction was used to measure telomere length. Traditional multivariable linear, partial least squares, and logistic regression were used.

RESULTS

iAge was constructed based on WBC, neutrophils, monocytes and albumin, which were associated with telomere length independently. A higher iAge indicated a heavier aging-related inflammation burden. Per 1-year increase in iAge was associated with higher body mass index (β 0.86 (95 % CI 0.67, 1.05) kg/m2), waist circumference (β 2.37 (95 % CI 1.85, 2.90) cm), glycosylated hemoglobin A1c (β 0.06 (95 % CI 0.02, 0.10) %), systolic blood pressure (β 1.06 (95 % CI 0.10, 2.03) mmHg), triglycerides (β 0.05 (95 % CI 0.01, 0.08) mmol/L), 10-year cardiovascular diseases risk (β 0.05 (95 % CI 0.02, 0.08) %), diabetes (OR 1.22 (95 % CI 1.02, 1.46)), hypertension (OR 1.21 (95 % CI 1.04, 1.42)) and metabolic syndrome risks (OR 1.25 (95 % CI 1.04, 1.51)), and lower fasting plasma glucose (β -0.016 (95 % CI -0.024, -0.007) mmol/L), total cholesterol (β -0.06 (95 % CI -0.12, -0.01) mmol/L) and high-density lipoprotein cholesterol (β -0.05 (95 % CI -0.07, -0.03) mmol/L).

CONCLUSION

The newly introduced iAge, derived from inflammatory markers and telomere length, aligns with various metabolic dysfunctions and age-related disease risks, underscoring its potential ability in identifying aging-related phenotypes.

Cross-Tissue Comparison of Epigenetic Aging Clocks in Humans

Epigenetic clocks are a common group of tools used to measure biological aging - the progressive deterioration of cells, tissues and organs. Epigenetic clocks have been trained almost exclusively using blood-based tissues but there is growing interest in estimating epigenetic age using less-invasive oral-based tissues (i.e., buccal or saliva) in both research and commercial settings. However, differentiated cell types across body tissues exhibit unique DNA methylation landscapes and age-related alterations to the DNA methylome. Applying epigenetic clocks derived from blood-based tissues to estimate epigenetic age of oral-based tissues may introduce biases. We tested the within-person comparability of common epigenetic clocks across five tissue types: buccal epithelial, saliva, dry blood spots, buffy coat (i.e., leukocytes), and peripheral blood mononuclear cells. We tested 284 distinct tissue samples from 83 individuals aged 9-70 years. Overall, there were significant within-person differences in epigenetic clock estimates from oral-based versus blood-based tissues, with average differences of almost 30 years observed in some age clocks. In addition, most epigenetic clock estimates of blood-based tissues exhibited low correlation with estimates from oral-based tissues despite controlling for cellular proportions and other technical factors. Our findings indicate that application of blood-derived epigenetic clocks in oral-based tissues may not yield comparable estimates of epigenetic age, highlighting the need for careful consideration of tissue type when estimating epigenetic age.

Leukocyte telomere length is associated with MRI-thigh fat-free muscle volume: data from 16 356 UK Biobank adults

BACKGROUND

Telomere attrition may share common biological mechanisms with bone and muscle loss with aging. Here, we investigated the association between these hallmarks of aging using data from UK Biobank, a large observational study.

METHODS

Leukocyte telomere length (LTL as T/S ratio) was measured using a multiplex qPCR assay at baseline (2006-2010). Bone mineral density (whole body and regional; via dual-energy X-ray absorptiometry), trabecular bone score (via lumbar-spine dual-energy X-ray absorptiometry images), fat-free muscle volume (thighs; via magnetic resonance imaging), and muscle fat infiltration (thighs; via magnetic resonance imaging) were measured during the imaging visit (2014-2018). Regression models were used to model LTL against a muscle or bone outcome, unadjusted and adjusted for covariates.

RESULTS

A total of 16 356 adults (mean age: 62.8 ± 7.5 years, 50.5% women) were included. In the fully adjusted model, thigh fat-free muscle volume was associated with LTL in the overall sample (adjusted standardized β (aβ) = 0.017, 95% CI 0.009 to 0.026, P < 0.001, per SD increase in LTL), with stronger associations in men (aβ = 0.022, 95% CI 0.010 to 0.034, P < 0.001) than in women (aβ = 0.013, 95% CI 0.000 to 0.025, P = 0.041) (sex-LTL P = 0.028). The adjusted odds ratio (aOR) for low thigh fat-free muscle volume (body mass index-adjusted, sex-specific bottom 20%) was 0.93 per SD increase in LTL (95% CI 0.89 to 0.96, P < 0.001) in the overall sample, with stronger associations in men (aOR = 0.92, 95% CI 0.87 to 0.99, P = 0.008) than women (aOR = 0.93, 95% CI 0.88 to 0.98, P = 0.009), although the sex difference was not statistically significant in this model (sex-LTL P = 0.37). LTL was not associated with bone mineral density, trabecular bone score, or muscle fat infiltration in the overall or subgroup analyses (P > 0.05).

CONCLUSIONS

LTL was consistently associated with thigh fat-free muscle volume in men and women. Future research should investigate moderating effects of lifestyle factors (e.g., physical activity, nutrition, or chronic diseases) in the association between LTL and muscle volume.

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.

Telomere length is not a useful tool for chronological age estimation in animals

Telomeres are short repetitive DNA sequences capping the ends of chromosomes. Telomere shortening occurs during cell division and may be accelerated by oxidative damage or ameliorated by telomere maintenance mechanisms. Consequently, telomere length changes with age, which was recently confirmed in a large meta-analysis across vertebrates. However, based on the correlation between telomere length and age, it was concluded that telomere length can be used as a tool for chronological age estimation in animals. Correlation should not be confused with predictability, and the current data and studies suggest that telomeres cannot be used to reliably predict individual chronological age. There are biological reasons for why there is large individual variation in telomere dynamics, which is mainly due to high susceptibility to a wide range of environmental, but also genetic factors, rendering telomeres unfeasible as a tool for age estimation. The use of telomeres for chronological age estimation is largely a misguided effort, but its occasional reappearance in the literature raises concerns that it will mislead resources in wildlife conservation.