Leukocyte telomere length and hippocampus volume: a meta-analysis

Genetically predicted telomere length and Alzheimer’s disease endophenotypes: a Mendelian randomization study

Telomere length (TL) is associated with biological aging, consequently influencing the risk of age-related diseases such as Alzheimer’s disease (AD). We aimed to evaluate the potential causal role of TL in AD endophenotypes (i.e., cognitive performance, N = 2233; brain age and AD-related signatures, N = 1134; and cerebrospinal fluid biomarkers (CSF) of AD and neurodegeneration, N = 304) through a Mendelian randomization (MR) analysis. Our analysis was conducted in the context of the ALFA (ALzheimer and FAmilies) study, a population of cognitively healthy individuals at risk of AD. A total of 20 single nucleotide polymorphisms associated with TL were used to determine the effect of TL on AD endophenotypes. Analyses were adjusted by age, sex, and years of education. Stratified analyses by APOE-ɛ4 status and polygenic risk score of AD were conducted. MR analysis revealed significant associations between genetically predicted longer TL and lower levels of CSF Aβ and higher levels of CSF NfL only in APOE-ɛ4 non-carriers. Moreover, inheriting longer TL was associated with greater cortical thickness in age and AD-related brain signatures and lower levels of CSF p-tau among individuals at a high genetic predisposition to AD. Further observational analyses are warranted to better understand these associations.

Telomere length and brain aging: A systematic review and meta-analysis

The current evidence on the association of leukocyte telomere length (LTL) with age-related structural and cognitive changes in the brain is mixed. Herein conforming to PRISMA 2020 guidelines, we performed a systematic review and meta-analysis using data from 27 observational studies in non-demented individuals. We used effect size and p-value based meta-analysis methods considering marked heterogeneity among studies. We found that the longer LTL was associated with higher brain volume (β = 0.43, 95%CI: 0.36-0.50%, p = 0.008, N = 1102) and with higher global cognition (β = 0.01; 95%CI: 0.00-0.02, p = 0.03, N = 19609) by effect size based meta-analysis and with brain volume, hippocampal volume, global cognition, cognitive domains of attention/speed as well as executive functions by p-value based meta-analysis. No significant association of LTL with brain white matter hyperintensities was detected. Furthermore, the evidence strongly suggests a subgroup-specific canonical effect of telomeres, notably in older individuals and females. In conclusion, we provide meta-analytic evidence on the beneficial effect of telomeres on brain structure as well as cognition and advocate for a beneficial subgroup-specific effect that warrants further attention.

Correlation between reduced telomere length and behavioural and emotional problems in left-behind children in a rural area in China

Evidence shows that being left behind experience (LBE) during childhood may increase the risks of poor psychopathological outcomes. However, it is unclear to what extent the mental health is affected by the LBE. Telomere length (TL), one of the most extensively studied biological markers of cellular ageing, provides a valuable tool for exploring the potential effects of parent-child separation on psychological problems by integrating genetic and environmental factors. In this study, a total of 613 children (mean age = 10.77, SD = 1.92) were recruited from the rural area of Deyang, Sichuan Province, China. We used a self-designed questionnaire to assess LBE, and collected psychopathological outcomes by using the Piers-Harris Children's Self-concept Scale, the Teacher's Report Form 6/18 and the Youth Self-Report 11/18. Terminal restriction fragment analysis was used to measure TL in peripheral blood leukocytes. Analyses revealed that 342 out of 613 participants (55.79%) were Left-behind children. LBE was observed to associated with shorter TL, lower self-esteem, and increased behavioural and emotional problems. The cumulative effects of LBE may be reflected by greater altered telomere homeostasis, decreased self-esteem, and worsened behavioural and emotional problems. The association of the total time of being left behind with self-esteem and behavioural and emotional problems was significantly mediated by altered telomere homeostasis, with estimated effects of 14.19%, 47.95% and 45.13%, respectively. The LBE in childhood, especially prolonged parent-child separation, increases the risk of mental health problems in childhood and adolescence.

Linking the Triad of Telomere Length, Inflammation, and Gut Dysbiosis in the Manifestation of Depression

Telomere length is an indispensable marker for cellular and biological aging, and it also represents an individual's physical and mental health status. Telomere shortening has been observed in chronic inflammatory conditions, which in turn accelerates aging and risk for psychiatric disorders, including depression. Considering the influence of inflammation and telomere shortening on the gut-brain axis, herein we describe a plausible interplay between telomere attrition, inflammation, and gut dysbiosis in the neurobiology of depression. Telomere shortening and hyperinflammation are well reported in depression. A negative impact of augmented inflammation has been noted on the intestinal permeability and microbial consortia and their byproducts in depressive patients. Moreover, gut dysbiosis provokes host-immune responses. As the gut microbiome is gaining importance in the manifestation and management of depression, herein we discuss whether telomere attrition is connected with the perturbation of commensal microflora. We also describe a pathological connection of cortisol with hyperinflammation, telomere shortening, and gut dysbiosis occurring in depression. This review summarizes how the triad of telomere attrition, inflammation, and gut dysbiosis is interconnected and modulates the risk for depression by regulating the systemic cortisol levels.

In vivo biomarkers of structural and functional brain development and aging in humans

Brain aging is a major determinant of aging. Along with the aging population, prevalence of neurodegenerative diseases is increasing, therewith placing economic and social burden on individuals and society. Individual rates of brain aging are shaped by genetics, epigenetics, and prenatal environmental. Biomarkers of biological brain aging are needed to predict individual trajectories of aging and the risk for age-associated neurological impairments for developing early preventive and interventional measures. We review current advances of in vivo biomarkers predicting individual brain age. Telomere length and epigenetic clock, two important biomarkers that are closely related to the mechanistic aging process, have only poor deterministic and predictive accuracy regarding individual brain aging due to their high intra- and interindividual variability. Phenotype-related biomarkers of global cognitive function and brain structure provide a much closer correlation to age at the individual level. During fetal and perinatal life, autonomic activity is a unique functional marker of brain development. The cognitive and structural biomarkers also boast high diagnostic specificity for determining individual risks for neurodegenerative diseases.

Telomere length and human hippocampal neurogenesis

Short telomere length is a risk factor for age-related disease, but it is also associated with reduced hippocampal volumes, age-related cognitive decline and psychiatric disorder risk. The current study explored whether telomere shortening might have an influence on cognitive function and psychiatric disorder pathophysiology, via its hypothesised effects on adult hippocampal neurogenesis. We modelled telomere shortening in human hippocampal progenitor cells in vitro using a serial passaging protocol that mimics the end-replication problem. Serially passaged progenitors demonstrated shorter telomeres (P ≤ 0.05), and reduced rates of cell proliferation (P ≤ 0.001), with no changes in the ability of cells to differentiate into neurons or glia. RNA-sequencing and gene-set enrichment analyses revealed an effect of cell ageing on gene networks related to neurogenesis, telomere maintenance, cell senescence and cytokine production. Downregulated transcripts in our model showed a significant overlap with genes regulating cognitive function (P ≤ 1 × 10^-5), and risk for schizophrenia (P ≤ 1 × 10^-10) and bipolar disorder (P ≤ 0.005). Collectively, our results suggest that telomere shortening could represent a mechanism that moderates the proliferative capacity of human hippocampal progenitors, which may subsequently impact on human cognitive function and psychiatric disorder pathophysiology.

Telomere Length and the Risk of Alzheimer's Disease: The Rotterdam Study

There is a wide interest in biomarkers that capture the burden of detrimental factors as these accumulate with the passage of time, i.e., increasing age. Telomere length has received considerable attention as such a marker, because it is easily quantified and it may aid in disentangling the etiology of dementia or serve as predictive marker. We determined the association of telomere length with risk of Alzheimer’s disease and all-cause dementia in a population-based setting. Within the Rotterdam Study, we performed quantitative PCR to measure mean leukocyte telomere length in blood. We determined the association of telomere length with risk of Alzheimer’s disease until 2016, using Cox regression models. Of 1,961 participants (mean age 71.4±9.3 years, 57.1% women) with a median follow-up of 8.3 years, 237 individuals were diagnosed with Alzheimer’s disease. We found a U-shaped association between telomere length and risk of Alzheimer’s disease: compared to the middle tertile the adjusted hazard ratio was 1.59 (95% confidence interval (CI), 1.13–2.23) for the lowest tertile and 1.47 (1.03–2.10) for the highest tertile. Results were similarly U-shaped but slightly attenuated for all-cause dementia. In conclusion, shorter and longer telomere length are both associated with an increased risk of Alzheimer’s disease in the general population.

Association of Short-term Change in Leukocyte Telomere Length With Cortical Thickness and Outcomes of Mental Training Among Healthy Adults: A Randomized Clinical Trial

Importance

Telomere length is associated with the development of age-related diseases and structural differences in multiple brain regions. It remains unclear, however, whether change in telomere length is linked to brain structure change, and to what extent telomere length can be influenced through mental training.

Objectives

To assess the dynamic associations between leukocyte telomere length (LTL) and cortical thickness (CT), and to determine whether LTL is affected by a longitudinal contemplative mental training intervention.

Design, Setting, and Participants

An open-label efficacy trial of three 3-month mental training modules with healthy, meditation-naive adults was conducted. Data on LTL and CT were collected 4 times over 9 months between April 22, 2013, and March 31, 2015, as part of the ReSource Project. Data analysis was performed between September 23, 2016, and June 21, 2019. Of 1582 eligible individuals, 943 declined to participate; 362 were randomly selected for participation and assigned to training or retest control cohorts, with demographic characteristics matched. The retest control cohorts underwent all testing but no training. Intention-to-treat analysis was performed.

Interventions

Training cohort participants completed 3 modules cultivating interoception and attention (Presence), compassion (Affect), or perspective taking (Perspective).

Main Outcomes and Measures

Change in LTL and CT.

Results

Of the 362 individuals randomized, 30 participants dropped out before study initiation (initial sample, 332). Data were available for analysis of the training intervention in 298 participants (n = 222 training; n = 76 retest control) (175 women [58.7%]; mean [SD] age, 40.5 [9.3] years). The training modules had no effect on LTL. In 699 observations from all 298 participants, mean estimated changes in the relative ratios of telomere repeat copy number to single-copy gene (T/S) were for no training, 0.004 (95% CI, -0.010 to 0.018); Presence, -0.007 (95% CI, -0.025 to 0.011); Affect, -0.005 (95% CI, -0.019 to 0.010); and Perspective, -0.001 (95% CI, -0.017 to 0.016). Cortical thickness change data were analyzed in 167 observations from 67 retest control participants (37 women [55.2%], mean [SD] age, 39.6 [9.0] years). In this retest control cohort subsample, naturally occurring LTL change was related to CT change in the left precuneus extending to the posterior cingulate cortex (mean t161 = 3.22; P < .001; r = 0.246). At the individual participant level, leukocyte telomere shortening as well as lengthening were observed. Leukocyte telomere shortening was related to cortical thinning (t77 = 2.38; P = .01; r = 0.262), and leukocyte telomere lengthening was related to cortical thickening (t77 = 2.42; P = .009; r = 0.266). All analyses controlled for age, sex, and body mass index.

Conclusions and Relevance

The findings of this trial indicate an association between short-term change in LTL and concomitant change in plasticity of the left precuneus extending to the posterior cingulate cortex. This result contributes to the evidence that LTL changes more dynamically on the individual level than previously thought. Further studies are needed to determine potential long-term implications of such change in relation to cellular aging and the development of neurodegenerative disorders. No effect of contemplative mental training was noted in what may be, to date, the longest intervention with healthy adults.

Trial Registration

ClinicalTrials.gov identifier: NCT01833104.

Telomere length and health outcomes: An umbrella review of systematic reviews and meta-analyses of observational studies

The aim of the present study was to map and grade evidence for the relationships between telomere length with a diverse range of health outcomes, using an umbrella review of systematic reviews with meta-analyses. We searched for meta-analyses of observational studies reporting on the association of telomere length with any health outcome (clinical disease outcomes and intermediate traits). For each association, random-effects summary effect size, 95% confidence interval (CI), and 95% prediction interval were calculated. To evaluate the credibility of the identified evidence, we assessed also heterogeneity, evidence for small-study effect and evidence for excess significance bias. Twenty-one relevant meta-analyses were identified reporting on 50 different outcomes. The level of evidence was high only for the association of short telomeres with higher risk of gastric cancer in the general population (relative risk, RR = 1.95, 95%CI: 1.68-2.26), and moderate for the association of shorter telomeres with diabetes or with Alzheimer's disease, even if limited to meta-analyses of case-control studies. There was weak evidence for twenty outcomes and not significant association for 27 health outcomes. The present umbrella review demonstrates that shorter telomere length may have an important role in incidence gastric cancer and, probably, diabetes and Alzheimer's disease. At the same time, conversely to general assumptions, it does not find strong evidence supporting the notion that shorter telomere length plays an important role in many health outcomes that have been studied thus far.

Telomere shortening in blood leukocytes of patients with posttraumatic stress disorder

Telomeres are protective fragments on chromosome ends involved in maintaining genome stability, preventing chromosomal fusions, regulation of cell division. It was shown that telomere attrition rate is accelerated in age-related diseases, as well as in response to physiological and psychosocial stress. The aim of this study was to evaluate relative leukocyte telomere length (LTL) in patients with post traumatic stress disorder (PTSD), as well as to investigate association of functional SNPs of telomerase TERC and TERT genes with LTL and PTSD. The relative LTL was measured by multiplex quantitative PCR method; genotyping of TERC rs12696304, TERT rs7726159 and rs2736100 was performed by PCR with sequence specific primers. Comparison of LTL in diseased and healthy subjects showed that PTSD patients had shorter average LTL than controls. Also, the frequency and the carriage rate of the TERT rs2736100*T allele was higher in PTSD patients compared to controls. Overall our results are in line with previous research in different populations. Furthermore, we have demonstrated that rs2736100 of TERT gene was significantly associated with PTSD and the minor allele of this polymorphism may be considered as a risk factor for PTSD in the Armenian population.

Brain age and other bodily 'ages': implications for neuropsychiatry

As our brains age, we tend to experience cognitive decline and are at greater risk of neurodegenerative disease and dementia. Symptoms of chronic neuropsychiatric diseases are also exacerbated during ageing. However, the ageing process does not affect people uniformly; nor, in fact, does the ageing process appear to be uniform even within an individual. Here, we outline recent neuroimaging research into brain ageing and the use of other bodily ageing biomarkers, including telomere length, the epigenetic clock, and grip strength. Some of these techniques, using statistical approaches, have the ability to predict chronological age in healthy people. Moreover, they are now being applied to neurological and psychiatric disease groups to provide insights into how these diseases interact with the ageing process and to deliver individualised predictions about future brain and body health. We discuss the importance of integrating different types of biological measurements, from both the brain and the rest of the body, to build more comprehensive models of the biological ageing process. Finally, we propose seven steps for the field of brain-ageing research to take in coming years. This will help us reach the long-term goal of developing clinically applicable statistical models of biological processes to measure, track and predict brain and body health in ageing and disease.

Telomere length and its association with hippocampal gray matter volume in antipsychotic-naïve/free schizophrenia patients

Accelerated ageing processes are postulated to underlie schizophrenia pathogenesis. This postulate is supported by observations of reduced telomere length in schizophrenia patients. Hippocampus, one of the most important brain regions implicated in schizophrenia, is shown to atrophy at a faster rate in aging. In this study, telomere length (TL) was measured in 30 antipsychotic-naive/free schizophrenia patients and 60 healthy controls using quantitative PCR assay. Hippocampus volume was measured using voxel-based morphometry. Schizophrenia was associated with differential TL between sexes [Status × Sex; F(1,85) = 5.9, p = 0.017, η² = 0.065]. Male schizophrenia patients had significantly lower relative TL than female patients [F(1,85) = 7.38, p = 0.008], while such sex difference was not observed in healthy controls [F(1,85) = 0.16, p = 0.69]. Schizophrenia patients showed a significant sex-by-telomere interaction with both right & left hippocampus, with male patients showing positive association of telomere length with volume, while female patients showed negative association. Telomere shortening and the positive association of telomere length with hippocampus volume was observed only in male patients with schizophrenia. Since correlational observations in this cross-sectional study does not necessarily support definitive causal relationship, further longitudinal studies examining hippocampus volume and telomere in schizophrenia patients are needed.

Telomere length as a predictor of emotional processing in the brain

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

The relationship between naevus count, memory function and telomere length in the Twins UK cohort

The presence of a skin-brain connection whereby alterations in the skin can inform on mechanisms underlying neurodegenerative diseases is increasingly recognized. In this study, we used a discovery (n = 321) and replication (n = 147) sample from the Twins UK population to test the association between naevus count and memory function, and its mediation by telomeres. Memory function was assessed in 1999 and 2009 using the paired associates learning test (PAL), while naevus count and leucocyte telomere length (LTL, assessed by the terminal restriction fragment assay) were measured once. Higher baseline naevus count was significantly associated with fewer errors at the baseline and follow-up PAL, as well as with change in PAL score over 10 years. This association was significantly attenuated after adjustment for LTL. The significant association between naevus count and PAL score was reproduced in the replication sample. These findings suggest that melanocytes might be used as model system to study the biological ageing pathways involved in neurodegeneration.

Stress, Telomeres, and Psychopathology: Toward a Deeper Understanding of a Triad of Early Aging

Telomeres play an important part in aging and show relationships to lifetime adversity, particularly childhood adversity. Meta-analyses demonstrate reliable associations between psychopathology (primarily depression) and shorter telomere length, but the nature of this relationship has not been fully understood. Here, we review and evaluate the evidence for impaired telomere biology as a consequence of psychopathology or as a contributing factor, and the important mediating roles of chronic psychological stress and impaired allostasis. There is evidence for a triadic relationship among stress, telomere shortening, and psychiatric disorders that is positively reinforcing and unfolds across the life course and, possibly, across generations. We review the role of genetics and biobehavioral responses that may contribute to shorter telomere length, as well as the neurobiological impact of impaired levels of telomerase. These complex interrelationships are important to elucidate because they have implications for mental and physical comorbidity and, potentially, for the prevention and treatment of depression.

Telomere Length and Bipolar Disorder

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

Estimating data from figures with a Web-based program: Considerations for a systematic review

BACKGROUND

Systematic reviewers often encounter incomplete or missing data, and the information desired may be difficult to obtain from a study author. Thus, systematic reviewers may have to resort to estimating data from figures with little or no raw data in a study's corresponding text or tables.

METHODS

We discuss a case study in which participants used a publically available Web-based program, called webplotdigitizer, to estimate data from 2 figures. We evaluated and used the intraclass coefficient and the accuracy of the estimates to the true data to inform considerations when using estimated data from figures in systematic reviews.

RESULTS

The estimates for both figures were consistent, although the distribution of estimates in the figure of a continuous outcome was slightly higher. For the continuous outcome, the percent difference ranged from 0.23% to 30.35% while the percent difference of the event rate ranged from 0.22% to 8.92%. For both figures, the intraclass coefficient was excellent (>0.95).

CONCLUSIONS

Systematic reviewers should consider and be transparent when estimating data from figures when the information cannot be obtained from study authors and perform sensitivity analyses of pooled results to reduce bias.