Energy intake and leukocyte telomere length in young adults

Increase in the Inflammatory Marker GlycA over 13 Years in Young Adults Is Associated with Poorer Cognitive Function in Midlife

Background

Inflammatory markers are elevated in patients with dementia. Evidence for an association between inflammation and cognitive function in dementia-free individuals is sparse, inconsistent, and predominantly restricted to the elderly. Assessment of inflammatory markers in young adults as predictors of cognitive function in midlife, well before the onset of overt dementia, is lacking. Furthermore, rarely has the relation with longitudinal change in inflammatory markers been examined.

Objective

To examine the association of the inflammatory markers C-reactive protein (CRP), fibrinogen, white blood cell count (WBC) and GlycA, a novel NMR-determined biomarker of systemic inflammation, measured in young adulthood and of GlycA change over 13 years follow-up with cognitive function in midlife.

Methods

507 participants of the Jerusalem Lipid Research Clinic (LRC) study were assessed at 3 time points over 18–22 years. First, the inflammatory variables GlycA, CRP, fibrinogen, and WBC were measured in blood samples drawn at ages 28–32. Then, in blood samples drawn a mean 13 years later (range, 12–16 years) at ages 41–46, GlycA was again measured (in 484 individuals). Subsequently at ages 48–52, on average 7 years later, global cognitive function and its five specific component domains were assessed with a NeuroTrax computerized test battery. Multiple regression and multivariable logistic models were applied.

Results

Inverse unadjusted associations were shown for baseline levels and longitudinal change in inflammatory markers and measures of cognition. Multiple regression models were adjusted for age at cognitive assessment, sex, socio-demographic characteristics, baseline measures of leisure-time vigorous activity, smoking status and body mass index (BMI) at ages 28–32, change in smoking status and BMI between ages 28–32 and 41–46, and depression assessed at the time of cognitive testing. The highest quintile of GlycA change, but not the baseline inflammation measures, was inversely related to global cognition (standardized β = -.109, p = .011) as well as to the information processing speed and memory domains (standardized β = -.124, p = .008 and-.117, p = .014, respectively). The multivariable-adjusted odds ratio for low ranked global cognitive function (lowest fifth) comparing the extreme quintiles of GlycA change was 4.8 (95%CI, 1.7–13.5, p = .003; p for trend = .031).

Conclusions

In this longitudinal study of a novel systemic inflammatory marker in a population-based cohort of young adults, GlycA increase over 13 years, but not baseline measures of inflammation, was associated with poorer cognitive function in midlife.

Leukocyte telomere length dynamics in women and men: menopause vs age effects

Background: A longer leukocyte telomere length (LTL) in women than men has been attributed to a slow rate of LTL attrition in women, perhaps due to high estrogen exposure during the premenopausal period.

Methods: To test this premise we performed a longitudinal study (an average follow-up of 12 years) in a subset of the population-based Danish National Twin Registry. Participants consisted of 405 women, aged 37.5 (range 18.0–64.3) years, and 329 men, aged 38.8 (range 18.0–58.5) years, at baseline examination.

Results: Women showed a longer LTL [kb ± standard error(SE)] than men (baseline: 7.01 ± 0.03 vs 6.87 ± 0.04; follow-up: 6.79 ± 0.03 vs 6.65 ± 0.03; both P = 0.005). Women displayed deceleration of LTL attrition (bp/years ± SE), as they transitioned from the premenopausal period (20.6 ± 1.0) through the perimenopausal period (16.5 ± 1.3) to the postmenopausal period (15.1 ± 1.7). Age was not associated with LTL attrition in women after statistical control for menopausal status. Men, in contrast, displayed a trend for age-dependent increase in the rate of LTL attrition, which differed significantly from the pattern in women (P for interaction = 0.01).

Conclusions: Results indicate that the premenopausal period is expressed in a higher rate of LTL attrition than the postmenopausal period. They further suggest that the sex gap in LTL stems from earlier ages—the period of growth and development. The higher rate of LTL attrition in premenopausal women, we propose, might relate to estrogen-mediated increased turnover of erythrocytes, menstrual bleeding or both.

The heritability of leucocyte telomere length dynamics

Background

Leucocyte telomere length (LTL) is a complex trait associated with ageing and longevity. LTL dynamics are defined by LTL and its age-dependent attrition. Strong, but indirect evidence suggests that LTL at birth and its attrition during childhood largely explains interindividual LTL variation among adults. A number of studies have estimated the heritability of LTL, but none has assessed the heritability of age-dependent LTL attrition.

Methods

We examined the heritability of LTL dynamics based on a longitudinal evaluation (an average follow-up of 12 years) in 355 monozygotic and 297 dizygotic same-sex twins (aged 19–64 years at baseline).

Results

Heritability of LTL at baseline was estimated at 64% (95% CI 39% to 83%) with 22% (95% CI 6% to 49%) of shared environmental effects. Heritability of age-dependent LTL attrition rate was estimated at 28% (95% CI 16% to 44%). Individually unique environmental factors, estimated at 72% (95% CI 56% to 84%) affected LTL attrition rate with no indication of shared environmental effects.

Conclusions

This is the first study that estimated heritability of LTL and also its age-dependent attrition. As LTL attrition is much slower in adults than in children and given that having a long or a short LTL is largely determined before adulthood, our findings suggest that heritability and early life environment are the main determinants of LTL throughout the human life course. Thus, insights into factors that influence LTL at birth and its dynamics during childhood are crucial for understanding the role of telomere genetics in human ageing and longevity.

DCAF4, a novel gene associated with leucocyte telomere length

BACKGROUND

Leucocyte telomere length (LTL), which is fashioned by multiple genes, has been linked to a host of human diseases, including sporadic melanoma. A number of genes associated with LTL have already been identified through genome-wide association studies. The main aim of this study was to establish whether DCAF4 (DDB1 and CUL4-associated factor 4) is associated with LTL. In addition, using ingenuity pathway analysis (IPA), we examined whether LTL-associated genes in the general population might partially explain the inherently longer LTL in patients with sporadic melanoma, the risk for which is increased with ultraviolet radiation (UVR).

RESULTS

Genome-wide association (GWA) meta-analysis and de novo genotyping of 20 022 individuals revealed a novel association (p=6.4×10(-10)) between LTL and rs2535913, which lies within DCAF4. Notably, eQTL analysis showed that rs2535913 is associated with decline in DCAF4 expressions in both lymphoblastoid cells and sun-exposed skin (p=4.1×10(-3) and 2×10(-3), respectively). Moreover, IPA revealed that LTL-associated genes, derived from GWA meta-analysis (N=9190), are over-represented among genes engaged in melanoma pathways. Meeting increasingly stringent p value thresholds (p<0.05, <0.01, <0.005, <0.001) in the LTL-GWA meta-analysis, these genes were jointly over-represented for melanoma at p values ranging from 1.97×10(-169) to 3.42×10(-24).

CONCLUSIONS

We uncovered a new locus associated with LTL in the general population. We also provided preliminary findings that suggest a link of LTL through genetic mechanisms with UVR and melanoma in the general population.

Plasma irisin levels predict telomere length in healthy adults

The ageing process is strongly influenced by nutrient balance, such that modest calorie restriction (CR) extends lifespan in mammals. Irisin, a newly described hormone released from skeletal muscles after exercise, may induce CR-like effects by increasing adipose tissue energy expenditure. Using telomere length as a marker of ageing, this study investigates associations between body composition, plasma irisin levels and peripheral blood mononuclear cell telomere length in healthy, non-obese individuals. Segmental body composition (by bioimpedance), telomere length and plasma irisin levels were assessed in 81 healthy individuals (age 43 ± 15.8 years, BMI 24.3 ± 2.9 kg/m(2)). Data showed significant correlations between log-transformed relative telomere length and the following: age (p < 0.001), height (p = 0.045), total body fat percentage (p = 0.031), abdominal fat percentage (p = 0.038), visceral fat level (p < 0.001), plasma leptin (p = 0.029) and plasma irisin (p = 0.011), respectively. Multiple regression analysis using backward elimination revealed that relative telomere length can be predicted by age (b = -0.00735, p = 0.001) and plasma irisin levels (b = 0.04527, p = 0.021). These data support the view that irisin may have a role in the modulation of both energy balance and the ageing process.

Leukocyte telomere length and age at menopause

BACKGROUND

Telomere length is a marker of cellular aging that varies with the individual, is inherited, and is highly correlated across somatic cell types within persons. Interindividual variability of telomere length may partly explain differences in reproductive aging rates. We examined whether leukocyte telomere length was associated with menopausal age.

METHODS

We evaluated the relationship between leukocyte telomere length and age at natural menopause in 486 white women ≥65 years of age. We fit linear regression models adjusted for age, income, education, body mass index, physical activity, smoking, and alcohol intake. We repeated the analysis in women with surgical menopause. We also performed sensitivity analyses excluding women (1) with unilateral oophorectomy, (2) who were nulliparous, or (3) reporting menopausal age <40 years, among other exclusions.

RESULTS

For every 1-kb increase in leukocyte telomere length, average age at natural menopause increased by 10.2 months (95% confidence interval = 1.3 to 19.0). There was no association among 179 women reporting surgical menopause. In all but one sensitivity analysis, the association between leukocyte telomere length and age at menopause became stronger. However, when excluding women with menopausal age <40 years, the association decreased to 7.5 months (-0.4 to 15.5).

CONCLUSIONS

Women with the longest leukocyte telomere length underwent menopause 3 years later than those with the shortest leukocyte telomere length. If an artifact, an association would likely also have been observed in women with surgical menopause. If these results are replicated, leukocyte telomere length may prove to be a useful predictor of age at menopause.

Telomeres shorten at equivalent rates in somatic tissues of adults

Telomere shortening in somatic tissues largely reflects stem cell replication. Previous human studies of telomere attrition were predominantly conducted on leukocytes. However, findings in leukocytes cannot be generalized to other tissues. Here we measure telomere length in leukocytes, skeletal muscle, skin and subcutaneous fat of 87 adults (aged 19–77 years). Telomeres are longest in muscle and shortest in leukocytes, yet are strongly correlated between tissues. Notably, the rates of telomere shortening are similar in the four tissues. We infer from these findings that differences in telomere length between proliferative (blood and skin) and minimally proliferative tissues (muscle and fat) are established during early life, and that in adulthood, stem cells of the four tissues replicate at a similar rate.

Telomere shortening as a result of cell proliferation has been implicated in human ageing. Here, Daniali and colleagues show that telomere length and the rate of age-dependent shortening vary between adults but are similar within tissues of the same individual.

Comparison between southern blots and qPCR analysis of leukocyte telomere length in the health ABC study

Only a few studies, primarily limited to small samples, have examined the relationship between leukocyte telomere length (LTL) data generated by Southern blots, expressed in kilobases, versus quantitative PCR data, expressed in the telomere product/a single gene product (T/S). In the present study, we compared LTL data generated by the two methods in 681 elderly participants (50% African Americans, 50% of European origin, 49.2% women, mean age 73.7±2.9 years) in the Health Aging and Body Composition Study. The correlation between the data generated by the two methods was modest (R (2) = .27). Both methods captured the age effect on LTL and the longer LTL in women than in men. However, only the Southern blot method showed a significantly longer LTL in African Americans than in European decent individuals, which might be attributed to the larger measurement error of the quantitative PCR-based method than the Southern blots.

Tracking and fixed ranking of leukocyte telomere length across the adult life course

Short leukocyte telomere length (LTL) is associated with atherosclerosis in adults and diminished survival in the elderly. LTL dynamics are defined by LTL at birth, which is highly variable, and its age-dependent attrition thereafter, which is rapid during the first 20 years of life. We examined whether age-dependent LTL attrition during adulthood can substantially affect individuals’ LTL ranking (e.g., longer or shorter LTL) in relation to their peers. We measured LTL in samples donated 12 years apart on average by 1156 participants in four longitudinal studies. We observed correlations of 0.91–0.96 between baseline and follow-up LTLs. Ranking individuals by deciles revealed that 94.1% (95% confidence interval of 92.6–95.4%) showed no rank change or a 1 decile change over time. We conclude that in adults, LTL is virtually anchored to a given rank with the passage of time. Accordingly, the links of LTL with atherosclerosis and longevity appear to be established early in life. It is unlikely that lifestyle and its modification during adulthood exert a major impact on LTL ranking.

Leukocyte telomere length and coronary artery calcification in Palestinians

OBJECTIVE

Shorter leukocyte telomere length (LTL) is associated with higher incidence of coronary heart disease (CHD) and increased mortality. We examined the association of LTL with coronary artery calcification (CAC), which reflects the cumulative burden of coronary atherosclerosis, in an urban Arab sample of Palestinians, a population at high risk of CHD.

METHODS

Using a cross-sectional design, a random sample of East Jerusalem residents, comprising 250 men aged 45-77 and women aged 55-76 and free of CHD or past stroke, was drawn from the Israel national population register. LTL was measured by Southern blots. CAC was determined by 16-slice multidetector helical CT scanning using Agatston scoring. We applied multivariable logistic modeling to examine the association between sex-specific tertiles of LTL and CAC (comparing scores >100 vs. <100, and the upper third vs. the lower 2 thirds), controlling for age, sex, education and coronary risk factors.

RESULTS

CAC, evident in 65% of men and 52% of women, was strongly associated with age (sex-adjusted Spearman's rho 0.495). The multivariable-adjusted odds ratios for CAC >100 (found in 30% of men and 29% of women) were 2.92 (95% CI 1.28-6.68) and 2.29 (0.99-5.30) for the lower and mid-tertiles of LTL vs. the upper tertile, respectively (Ptrend = 0.008). Findings were similar for CAC scores in the upper tertile (Ptrend = 0.006), and persisted after the exclusion of patients with diabetes or receiving statins.

CONCLUSIONS

Shorter LTL was associated with a greater prevalence of asymptomatic coronary atherosclerosis in an urban Arab population-based sample. Mechanisms underlying this association should be sought.

Intake of small-to-medium-chain saturated fatty acids is associated with peripheral leukocyte telomere length in postmenopausal women

Dietary factors, including dietary fat, may affect the biological aging process, as reflected by the shortening of telomere length (TL), by affecting levels of oxidative stress and inflammatory responses. We examined the direct relations of total and types of dietary fats and fat-rich foods to peripheral leukocyte TL. In 4029 apparently healthy postmenopausal women who participated in the Women's Health Initiative, intakes of total fat, individual fatty acids, and fat-rich foods were assessed by a questionnaire. TL was measured by quantitative polymerase chain reaction. Intake of short-to-medium-chain saturated fatty acids (SMSFAs; aliphatic tails of ≤ 12 carbons) was inversely associated with TL. Compared with participants in other quartiles of SMSFA intake, women who were in the highest quartile (median: 1.29% of energy) had shorter TLs [mean: 4.00 kb (95% CI: 3.89, 4.11 kb)], whereas women in the lowest quartile of intake (median: 0.29% of energy) had longer TLs [mean: 4.13 kb (95% CI: 4.03, 4.24 kb); P-trend = 0.046]. Except for lauric acid, all other individual SMSFAs were inversely associated with TL (P < 0.05). In isoenergetic substitution models, the substitution of 1% of energy from SMSFAs with any other energy source was associated with 119 bp longer TLs (95% CI: 21, 216 bp). Intakes of nonskim milk, butter, and whole-milk cheese (major sources of SMSFAs) were all inversely associated with TL. No significant associations were found with long-chain saturated fatty acids, monounsaturated fatty acids, and polyunsaturated fatty acids. In conclusion, we found that higher intakes of SMSFAs and SMSFA-rich foods were associated with shorter peripheral leukocyte TL among postmenopausal women. These findings suggest the potential roles of SMSFAs in the rate of biological aging.

The telomere lengthening conundrum--artifact or biology?

Recent longitudinal studies of age-dependent leukocyte telomere length (LTL) attrition have reported that variable proportions of individuals experience LTL lengthening. Often, LTL lengthening has been taken at face value, and authors have speculated about the biological causation of this finding. Based on empirical data and theoretical considerations, we show that regardless of the method used to measure telomere length (Southern blot or quantitative polymerase chain reaction-based methods), measurement error of telomere length and duration of follow-up explain almost entirely the absence of age-dependent LTL attrition in longitudinal studies. We find that LTL lengthening is far less frequent in studies with long follow-up periods and those that used a high-precision Southern blot method (as compared with quantitative polymerase chain reaction determination, which is associated with larger laboratory error). We conclude that the LTL lengthening observed in longitudinal studies is predominantly, if not entirely, an artifact of measurement error, which is exacerbated by short follow-up periods. We offer specific suggestions for design of longitudinal studies of LTL attrition to diminish this artifact.

Leukocyte telomere dynamics in the elderly

Limited data suggest that leukocytes of the elderly display ultra-short telomeres. It was reported that in some elderly persons leukocyte telomere length (LTL) shows age-dependent elongation. Using cross-sectional and longitudinal models, we characterized LTL dynamics in participants of the Longitudinal Study of Aging Danish Twins. We measured LTL by Southern blots of the terminal restriction fragment length (TRFL) in 476 individuals (73–94 years) in a cross-sectional evaluation and in a subset of this cohort comprising 80 individuals (73–81 years at baseline) who were followed–up for approximately 10 years. Based on the mean TRFL, we found that a) the average rate of LTL attrition was respectively, 27 bp/year (P < 0.001) and 31 bp/year (P < 0.001) for the cross-sectional and longitudinal evaluations, and b) mean TRFL was 180 bp (95 % CI 43, 320) longer in females than males (P < 0.010). For the TRFL distribution, which captures telomeres of all lengths in the DNA sample, we observed significant shifts with age toward shorter telomeres. Based on the measurement error of the TRFLs, we computed that in the longitudinal evaluation 10.6 % of individuals would manifest LTL elongation over 10 years, assuming a 340 bp attrition during this period. This was not significantly different from the empirical observation of 7.5 % of individuals showing LTL elongation. We conclude that accumulation of ultra-short telomeres in leukocytes of the elderly reflects a shift toward shorter telomeres in the entire telomere distribution. Measurement error is the probable explanation for LTL elongation in longitudinal studies.

Genome-wide meta-analysis points to CTC1 and ZNF676 as genes regulating telomere homeostasis in humans

Leukocyte telomere length (LTL) is associated with a number of common age-related diseases and is a heritable trait. Previous genome-wide association studies (GWASs) identified two loci on chromosomes 3q26.2 (TERC) and 10q24.33 (OBFC1) that are associated with the inter-individual LTL variation. We performed a meta-analysis of 9190 individuals from six independent GWAS and validated our findings in 2226 individuals from four additional studies. We confirmed previously reported associations with OBFC1 (rs9419958 P = 9.1 × 10⁻¹¹) and with the telomerase RNA component TERC (rs1317082, P = 1.1 × 10⁻⁸). We also identified two novel genomic regions associated with LTL variation that map near a conserved telomere maintenance complex component 1 (CTC1; rs3027234, P = 3.6 × 10⁻⁸) on chromosome17p13.1 and zinc finger protein 676 (ZNF676; rs412658, P = 3.3 × 10⁻⁸) on 19p12. The minor allele of rs3027234 was associated with both shorter LTL and lower expression of CTC1. Our findings are consistent with the recent observations that point mutations in CTC1 cause short telomeres in both Arabidopsis and humans affected by a rare Mendelian syndrome. Overall, our results provide novel insights into the genetic architecture of inter-individual LTL variation in the general population.