Telomere Restriction Fragment Research Articles

The association between age and telomere length is age-dependent: Evidence for a threshold model of telomere length maintenance.

Telomere length and dynamics are commonly used biomarkers of somatic state, yet the role of telomeres underlying the aging process is still debated. Indeed, to date, empirical evidence for an association between age and telomere length is mixed. Here, we test if the age-dependency of the association between age and telomere length can provide a potential explanation for the reported inconsistencies across studies. To this end, we quantified telomere length by telomere restriction fragment analysis in two groups of Japanese quail (Coturnix japonica) that differed in their age distribution. One group consisted of young adults only, whereas the second group consisted of adults across a wide range of ages. In the young adults group, there was a highly significant negative association between telomere length and age, whereas no association between age and telomere length was found in the all-ages adults group. This difference between groups was not due to telomere length-dependent selective disappearance. Our results shows that the association between telomere length and age is age-dependent and suggest that the costs and benefits associated with telomere maintenance are dynamic across an individual's life course.

Optimization of Performance Parameters of the TAGGG Telomere Length Assay.

Telomeres are repetitive sequences which are present at chromosomal ends; their shortening is a characteristic feature of human somatic cells. Shortening occurs due to a problem with end replication and the absence of the telomerase enzyme, which is responsible for maintaining telomere length. Interestingly, telomeres also shorten in response to various internal physiological processes, like oxidative stress and inflammation, which may be impacted due to extracellular agents like pollutants, infectious agents, nutrients, or radiation. Thus, telomere length serves as an excellent biomarker of aging and various physiological health parameters. The TAGGG telomere length assay kit is used to quantify average telomere lengths using the telomere restriction fragment (TRF) assay and is highly reproducible. However, it is an expensive method, and because of this, it is not employed routinely for large sample numbers. Here, we describe a detailed protocol for an optimized and cost-effective measurement of telomere length using Southern blots or TRF analysis and non-radioactive chemiluminescence-based detection.

TRF2 rescues telomere attrition and prolongs cell survival in Duchenne muscular dystrophy cardiomyocytes derived fromhuman iPSCs.

Duchenne muscular dystrophy (DMD) is a severe muscle wasting disease caused by the lack of dystrophin. Heart failure, driven by cardiomyocyte death, fibrosis, and the development of dilated cardiomyopathy, is the leading cause of death in DMD patients. Current treatments decrease the mechanical load on the heart but do not address the root cause of dilated cardiomyopathy: cardiomyocyte death. Previously, we showed that telomere shortening is a hallmark of DMD cardiomyocytes. Here, we test whether prevention of telomere attrition is possible in cardiomyocytes differentiated from patient-derived induced pluripotent stem cells (iPSC-CMs) and if preventing telomere shortening impacts cardiomyocyte function. We observe reduced cell size, nuclear size, and sarcomere density in DMD iPSC-CMs compared with healthy isogenic controls. We find that expression of just one telomere-binding protein, telomeric repeat-binding factor 2 (TRF2), a core component of the shelterin complex, prevents telomere attrition and rescues deficiencies in cell size as well as sarcomere density. We employ a bioengineered platform to micropattern cardiomyocytes for calcium imaging and perform Southern blots of telomere restriction fragments, the gold standard for telomere length assessments. Importantly, preservation of telomere lengths in DMD cardiomyocytes improves their viability. These data provide evidence that preventing telomere attrition ameliorates deficits in cell morphology, activation of the DNA damage response, and premature cell death, suggesting that TRF2 is a key player in DMD-associated cardiac failure.

Reliable assessment of telomere maintenance mechanisms in neuroblastoma

BackgroundTelomere maintenance mechanisms (TMM) are a hallmark of high-risk neuroblastoma, and are conferred by activation of telomerase or alternative lengthening of telomeres (ALT). However, detection of TMM is not yet part of the clinical routine, and consensus on TMM detection, especially on ALT assessment, remains to be achieved.MethodsWhole genome sequencing (WGS) data of 68 primary neuroblastoma samples were analyzed. Telomere length was calculated from WGS data or by telomere restriction fragment analysis (n = 39). ALT was assessed by C-circle assay (CCA, n = 67) and detection of ALT-associated PML nuclear bodies (APB) by combined fluorescence in situ hybridization and immunofluorescence staining (n = 68). RNA sequencing was performed (n = 64) to determine expression of TERT and telomeric long non-coding RNA (TERRA). Telomerase activity was examined by telomerase repeat amplification protocol (TRAP, n = 15).ResultsTumors were considered as telomerase-positive if they harbored a TERT rearrangement, MYCN amplification or high TERT expression (45.6%, 31/68), and ALT-positive if they were positive for APB and CCA (19.1%, 13/68). If all these markers were absent, tumors were considered TMM-negative (25.0%, 17/68). According to these criteria, the majority of samples were classified unambiguously (89.7%, 61/68). Assessment of additional ALT-associated parameters clarified the TMM status of the remaining seven cases with high likelihood: ALT-positive tumors had higher TERRA expression, longer telomeres, more telomere insertions, a characteristic pattern of telomere variant repeats, and were associated with ATRX mutations.ConclusionsWe here propose a workflow to reliably detect TMM in neuroblastoma. We show that unambiguous classification is feasible following a stepwise approach that determines both, activation of telomerase and ALT. The workflow proposed in this study can be used in clinical routine and provides a framework to systematically and reliably determine telomere maintenance mechanisms for risk stratification and treatment allocation of neuroblastoma patients.

Increase in short telomeres during the third trimester in human placenta.

An increase in telomere shortening in gestational tissues has been proposed as a mechanism involved in the timing for the initiation of parturition. An increase in very short telomeres with increasing gestational age has been observed in mice; this study sought to explore this phenomenon in human pregnancies. Specifically, this study addressed the hypothesis that prior to labor, the quantity of very short telomeres (<3 kilobase (kb) lengths) increases in human placental tissue as term gestation approaches. The primary outcome was the quantity of very short telomeres present in placental tissue. Quantitative measurements of very short telomeres were performed using real-time polymerase chain reaction (qPCR) adaptation of the telomere restriction fragment technique. Placental tissue from 69 pregnant individuals were included. Mean gestational age was 39.1 weeks (term) and 36.2 weeks (preterm). For term versus preterm placentas, the observed increase in very short telomeres were as follows: 500 bp telomeres increased by 1.67-fold (p < 0.03); 1 kb telomeres increased 1.67-fold (p < 0.08); and 3 kb telomeres increased 5.20-fold (p < 0.001). This study confirms a significant increase in very short telomeres in human placental tissue at term; thereby supporting the hypothesis that telomere shortening at term contributes to the mechanism that determine the length of pregnancy thereby leading to onset of parturition.

G-quadruplex stabilizer Tetra-Pt(bpy) disrupts telomere maintenance and impairs FAK-mediated migration of telomerase-positive cells

G-quadruplex regulates a wide spectrum of biological processes, including telomere maintenance, DNA replication and transcription. The development of small molecules to selectively target G-quadruplex and their application remain hotspots in cancer therapy. Here, we explored the biological effect of G-quadruplexes stabilizer Tetra-Pt(bpy) in telomerase-positive cancer cells. Telomere maintenance was evaluated by telomerase repeat amplification protocol, chromosome orientation fluorescence in situ hybridization and telomere restriction fragment assays. We found that Tetra-Pt(bpy) accelerates telomere shortening through dual inhibition of telomerase activity and telomere sister chromatin exchanges mediated by telomeric G-quadruplexes. Consequently, Tetra-Pt(bpy)-treated cancer cells became enriched with extremely short telomeres and produced a strong telomeric DNA damage response following long-term treatment, leading to cell proliferation inhibition and senescence. Experimental evidence from RNA seq and cell migration-related assays showed that Tetra-Pt(bpy) decreased cell-matrix adhesion and inhibited the migration of non-senescent tumor cells. Mechanistically, Tetra-Pt(bpy) induced the formation of G-quadruplexes in focal adhesion kinase (FAK)-encoding gene PTK2, resulting in FAK transcription inhibition. Tetra-Pt(bpy) reduced xenograft tumor formation and inhibited tumor cell growth and migration in mice. This study further elucidates the function of G-quadruplexes in the human genome and reveals the potential of Tetra-Pt(bpy) as a novel chemotherapeutic agent for targeting telomerase-positive cancer cells.

BALKAN ENDEMIC NEPHROPATHY, PULSE WAVE VELOCITY AND INCREASED TELOMERE LENGTH-ASSOCIATED CARDIOVASCULAR MORTALITY IN PATIENTS UNDERGOING CHRONIC HEMODIALYSIS

Objective: Balkan endemic nephropathy (BEN) is characterized with later onset, milder forms of hypertension and lower pulse wave velocity (PWV)). We hypothesized that telomere length (TL) would be longer in BEN patients and associated with lower PWV and less cardiovascular (CV) mortality. Design and method: On total 124 hemodialysed (HD) patients (68 BEN, 56 non-BEN; 48.4% men; 65 ± 14 years) were enrolled and followed-up for 25 months. Blood pressure and PWV were determined before mid-week dialysis. TL was determined by telomere restriction fragment analysis. Results: Age-sex adjusted TL was significantly longer in the BEN group (7.19 vs 6.79; p &lt; 0.001) despite being significantly older. In the BEN group TL was associated with PWV (beta = -0.373, p &lt; 0.05), and in the non-BEN group with age (beta = -0.680, p &lt; 0.01). In the full-adjusted model of multivariate linear regression analyses significant predictors of TL were systolic BP/PWV, and age in the BEN and the non-BEN group, respectively. BEN patients died significantly less frequently from CV events than non-BEN patients (p &lt; 0.001) and lived significantly longer (log-rank p = 0.04). Patients who died had significantly shorter TL than survivors (p &lt; 0.001). In the Cox Regression analysis older age, diagnosis of non-BEN and shorter TL were determinants of shorter survival in the entire cohort. In the BEN group shorter TL was the only determinant of shorter survival (HR 0.11 [95% CI 0.03, 0.35]). To analyze the diagnostic value of TL for CV mortality we used ROC analysis that revealed TL &lt; 6.21 Kb to be useful for prediction of CV mortality in patients undergoing chronic HD. Conclusions: Shorter TL is associated with CV mortality in patients undergoing chronic HD. BEN patients had longer TL and longer survival than other ESKD patients. PWV was significant predictor of TL in BEN patients. This study confirmed our hypothesis that BEN is associated with slower vascular aging.

Monitoring Telomere Maintenance During Regeneration of Annelids.

Telomere shortening is a hallmark of aging and eventually constrains the proliferative capacity of cells. The protocols discussed here are used for monitoring telomeres comprehensively in Aeolosoma viride, a model system for regeneration studies. We present methods for analyzing the activity of telomerase enzyme in regenerating tissue by telomeric repeat amplification protocol (TRAP) assay, for comparing telomere length between existing tissue and newly regenerated tissue by telomere restriction fragment (TRF) assay, as well as for visualizing telomeres by fluorescence in situ hybridization (FISH).

High heritability of telomere length and low heritability of telomere shortening in wild birds.

Telomere length and telomere shortening predict survival in many organisms. This raises the question of the contribution of genetic and environmental effects to variation in these traits, which is still poorly known, particularly for telomere shortening. We used experimental (cross-fostering) and statistical (quantitative genetic "animal models") means to disentangle and estimate genetic and environmental contributions to telomere length variation in pedigreed free-living jackdaws (Corvus monedula). Telomere length was measured twice in nestlings, at ages 4 (n=715) and 29days (n=474), using telomere restriction fragment (TRF) analysis, adapted to exclude interstitial telomeric sequences. Telomere length shortened significantly over the nestling period (10.4±0.3bpday-1 ) and was highly phenotypically (rP =0.95±0.01) and genetically (rG >0.99±0.01) correlated within individuals. Additive genetic effects explained a major part of telomere length variation among individuals, with its heritability estimated at h2 =0.74 on average. We note that TRF-based studies reported higher heritabilities than qPCR-based studies, and we discuss possible explanations. Parent-offspring regressions yielded similar heritability estimates for mothers and fathers when accounting for changes in paternal telomere length over life. Year effects explained a small but significant part of telomere length variation. Heritable variation for telomere shortening was low (h2 =0.09±0.11). The difference in heritability between telomere length (high) and telomere shortening (low) agrees with evolutionary theory, in that telomere shortening has stronger fitness consequences in this population. Despite the high heritability of telomere length, its evolvability, which scales the additive genetic variance by mean telomere length, was on average 0.48%. Hence, evolutionary change of telomere length due to selection is likely to be slow.

The influence of phylogeny and life history on telomere lengths and telomere rate of change among bird species: A meta-analysis.

Longevity is highly variable among animal species and has coevolved with other life‐history traits, such as body size and rates of reproduction. Telomeres, through their erosion over time, are one of the cell mechanisms that produce senescence at the cell level and might even have an influence on the rate of aging in whole organisms. However, uneroded telomeres are also risk factors of cell immortalization. The associations of telomere lengths, their rate of change, and life‐history traits independent of body size are largely underexplored for birds. To test associations of life‐history traits and telomere dynamics, we conducted a phylogenetic meta‐analysis using studies of 53 species of birds. We restricted analyses to studies that applied the telomere restriction fragment length (TRF) method, and examined relationships between mean telomere length at the chick (Chick TL) and adult (Adult TL) stages, the mean rate of change in telomere length during life (TROC), and life‐history traits. We examined 3 principal components of 12 life‐history variables that represented: body size (PC1), the slow–fast continuum of pace of life (PC2), and postfledging parental care (PC3). Phylogeny had at best a small‐to‐medium influence on Adult and Chick TL (r 2 = .190 and .138, respectively), but a substantial influence on TROC (r 2 = .688). Phylogeny strongly influenced life histories: PC1 (r 2 = .828), PC2 (.838), and PC3 (.613). Adult TL and Chick TL were poorly associated with the life‐history variables. TROC, however, was negatively and moderate‐to‐strongly associated with PC2 (unadjusted r = −.340; with phylogenetic correction, r = −.490). Independent of body size, long‐lived species with smaller clutches, and slower embryonic rate of growth may exhibit less change in telomere length over their lifetimes. We suggest that telomere lengths may have diverged, even among closely avian‐related species, yet telomere dynamics are strongly linked to the pace of life.

MicroRNA-340-5p increases telomere length by targeting telomere protein POT1 to improve Alzheimer's disease in mice.

Alzheimer's disease (AD) is a chronic neurodegenerative disorder which is the primary cause of dementia in the elderly. Telomere attrition has been proposed as a hallmark of aging. Our study aimed to explore the mechanism of the protection of telomere 1 (POT1) in regulating telomere length and affecting cellular senescence in AD. The AD mouse model was established by d-galactose and aluminum chloride,and the water maze test and dark avoidance test were used to detect the behaviors of mice and confirm the success of AD mouse model. AD cell model was established with HT22 cells induced by Aβ42 oligomers. POT1 expression in the AD model was detected by quantitative real-time polymerase chain reaction. Cellular telomere length in hippocampal tissue was analyzed by telomere restriction fragment. Localization of intracellular POT1, telomerase, and telomeres was analyzed by immunofluorescence and fluorescence in situ hybridization. Dual-luciferase assay was used to validate the targeted binding relationship between microRNA-340-5p(miR-340-5p) and POT1. After inhibiting POT1 expression, the symptoms of AD in mice were improved. Aβ1-42 deposition was reduced, whereas telomere length and telomerase activity was increased. Dual-luciferase assay verified the binding relationship between miR-340-5p and POT1. An increase in miR-340-5p expression could alleviate cellular senescence and AD symptoms. miR-340-5p increased cellular telomere length and delayed cell senescence by inhibiting POT1 expression to improve AD symptoms. This study made a conclusion that miR-340-5p increased cellular telomere length and delayed cell senescence by inhibiting POT1 expression to improve AD symptoms in mice.

Telomere Length in Valve Tissue Is Shorter in Individuals With Aortic Stenosis and in Calcified Valve Areas

BackgroundShort telomere length (TL) is associated with age-related diseases, in particular cardiovascular diseases. However, whether the onset and course of aortic stenosis (AS) is linked to TL in aortic valves remains unknown.ObjectivesTo assess telomere dynamics (TL and telomerase activity) in aortic valves and the possible implication of TL in onset and course of AS.MethodsDNA was extracted from aortic valves obtained from 55 patients (78.2% men; age, 37–79 years), who had undergone replacement surgery due to AS (AS group, n = 32), aortic valve regurgitation and aortic dilation (Non-AS group, n = 23). TL was measured by telomere restriction fragment analysis (TRF) in calcified and non-calcified aortic valve areas. Telomerase activity was evaluated using telomerase repeat amplification protocol (TRAP) in protein extracts from non-calcified and calcified areas of valves obtained from 4 additional patients (50% men; age, 27–70 years).ResultsTL was shorter in calcified aortic valve areas in comparison to non-calcified areas (n = 31, 8.58 ± 0.73 kb vs. 8.12 ± 0.75 kb, p < 0.0001), whereas telomerase activity was not detected in any of those areas. Moreover, patients from AS group displayed shorter telomeres in non-calcified areas than those from the Non-AS group (8.40 ± 0.64 kb vs. 8.85 ± 0.65, p = 0.01).ConclusionsShort telomeres in aortic valves may participate in the development of AS, while concurrently the calcification process seems to promote further local decrease of TL in calcified areas of valves.

Telomere length and signal joint T-cell receptor rearrangement excision circles as biomarkers for chronological age estimation

Background Chronological age estimation is a challenging marker in the field of forensic medicine. The current study aimed to investigate the accuracy of signal joint T-cell receptor rearrangement excision circles (sjTRECs) quantification and telomere length measurement as methods for estimating chronological age. Methods Telomere length was estimated in the DNA derived from the buccal cells through estimating the telomeric restriction fragment (TRF) length using TeloTTAGGG Telomere Length Assay while the sjTRECs quantification was carried out on DNA isolated from the blood samples using qPCR. Results The TRF length was shortened with increased age (r = −0.722, p < 0.001). The sjTRECs were also decreased with increased age (r = −0.831, p < 0.001). Stronger coefficient and lower standard error of the estimate was obtained when multiple regression analysis for age prediction based on the values of both methods was applied (r = −0.876, p < 0.001).

The Association between Antidiabetic Agents and Leukocyte Telomere Length in the Novel Classification of Type 2 Diabetes Mellitus

Aims: This study aimed to explore the new role of telomere length (TL) in the novel classification of type 2 diabetes mellitus (T2DM) patients driven by cluster analysis. Materials and Methods: A total of 541 T2DM patients were divided into 4 subgroups by k-means analysis: mild obesity-related diabetes (MOD), severe insulin-deficient diabetes (SIDD), severe insulin-resistant diabetes (SIRD), and mild age-related diabetes (MARD). After patients with insufficient data were excluded, further analysis was conducted on 246 T2DM patients. The TL was detected using telomere restriction fragment, and the related diabetic indexes were also measured by clinical standard procedures. Results: The MARD group had significantly shorter TLs than the MOD and SIDD groups. Then, we subdivided all T2DM patients into the MARD and NONMARD groups, which included the MOD, SIDD, and SIRD groups. The TLs of the MARD group, associated with age, were discovered to be significantly shorter than those of the NONMARD group (p = 0.0012), and this difference in TL disappeared after metformin (p = 0.880) and acarbose treatment (p = 0.058). The linear analysis showed that metformin can more obviously reduce telomere shortening in the MARD group (r = 0.030, 95% CI 0.010–0.051, p = 0.004), and acarbose can more apparently promote telomere attrition in the SIRD group (r = –0.069, 95% CI –0.100 to –0.039, p< 0.001) compared with other T2DM patients after adjusting for age and gender. Conclusions: The MARD group was found to have shorter TLs and benefit more from the antiaging effect of metformin than other T2DM. Shorter TLs were observed in the SIRD group after acarbose use.

Human shelterin protein POT1 prevents severe telomere instability induced by homology-directed DNA repair.

The evolutionarily conserved POT1 protein binds single-stranded G-rich telomeric DNA and has been implicated in contributing to telomeric DNA maintenance and the suppression of DNA damage checkpoint signaling. Here, we explore human POT1 function through genetics and proteomics, discovering that a complete absence of POT1 leads to severe telomere maintenance defects that had not been anticipated from previous depletion studies in human cells. Conditional deletion of POT1 in HEK293E cells gives rise to rapid telomere elongation and length heterogeneity, branched telomeric DNA structures, telomeric R-loops, and telomere fragility. We determine the telomeric proteome upon POT1-loss, implementing an improved telomeric chromatin isolation protocol. We identify a large set of proteins involved in nucleic acid metabolism that engage with telomeres upon POT1-loss. Inactivation of the homology-directed repair machinery suppresses POT1-loss-mediated telomeric DNA defects. Our results unravel as major function of human POT1 the suppression of telomere instability induced by homology-directed repair.

Adverse Birth Outcomes and Birth Telomere Length: A Systematic Review and Meta-analysis

Objectives To synthesize previous findings on the difference in birth telomere length between newborns with and without intrauterine growth restriction (IUGR) or with and without preterm birth. Study design We systematically searched 3 databases (PubMed, Embase, and Web of Science) for publications that examined the relationships of IUGR or preterm birth with birth telomere length. We conducted meta-analysis to pool the estimated difference in birth telomere length either between IUGR and non-IUGR or between preterm birth and full-term birth. Subgroup analyses were conducted by tissues (newborn blood vs placenta) and techniques used for telomere length measurement (quantitative polymerase chain reaction [qPCR] vs telomere restriction fragment). Results We included 11 articles on comparing birth telomere length between IUGR (combined n = 227) and non-IUGR (n = 1897) and 7 articles on comparing birth telomere length between preterm birth (n = 182) and full-term birth (n = 1320). We found IUGR was associated with shorter birth telomere length only when birth telomere length was measured in placenta (pooled standardized mean difference [SMD] = −0.85; 95% CI −1.13 to −0.57; IUGR/non-IUGR n = 87/173), but not in newborn blood (pooled SMD = 0.00, 95% CI −0.18 to 0.19; IUGR/non-IUGR n = 148/1733). Birth telomere length was significantly longer in preterm birth than in full-term birth when birth telomere length was measured by qPCR (pooled SMD = 0.40, 95% CI 0.18-0.63; preterm birth/full-term birth n = 137/682) but not by telomere restriction fragment (pooled SMD = 0.05, 95% CI −0.29 to 0.38; preterm birth/full-term birth n = 44/444). Conclusions IUGR is associated with shorter placental telomere length and preterm birth is associated with longer birth telomere length measured by qPCR.

Antioxidant supplementation slows telomere shortening in free-living white stork chicks.

Telomere length (TL) and shortening is increasingly shown to predict variation in survival and lifespan, raising the question of what causes variation in these traits. Oxidative stress is well known to accelerate telomere attrition in vitro, but its importance in vivo is largely hypothetical. We tested this hypothesis experimentally by supplementing white stork (Ciconia ciconia) chicks with antioxidants. Individuals received either a control treatment, or a supply of tocopherol (vitamin E) and selenium, which both have antioxidant properties. The antioxidant treatment increased the concentration of tocopherol for up to two weeks after treatment but did not affect growth. Using the telomere restriction fragment technique, we evaluated erythrocyte TL and its dynamics. Telomeres shortened significantly over the 21 days between the baseline and final sample, independent of sex, mass, size and hatching order. The antioxidant treatment significantly mitigated shortening rate of average TL (-31% in shorter telomeres; percentiles 10th, 20th and 30th). Thus, our results support the hypothesis that oxidative stress shortens telomeres in vivo.

Quantitative Proteomics Reveal Peroxiredoxin Perturbation Upon Persistent Lymphocytic Choriomeningitis Virus Infection in Human Cells.

Experimental data indicate that during persistent infection, lymphocytic choriomeningitis virus (LCMV) may both directly or indirectly modulate regulatory cellular processes and alter cellular functions that are not critical for survival, but are essential for cell homeostasis. In order to shed more light on these processes, two-dimensional differential in-gel electrophoresis (2D-DIGE) and MALDI-TOF tandem mass spectrometry were used to determine the proteome response of the HeLa cell line to persistent LCMV infection. Quantitative analysis revealed 24 differentially abundant proteins. Functional analysis showed that LCMV-responsive proteins were primarily involved in metabolism, stress, and the defense response. Among identified proteins, we discovered significant changes for peroxiredoxins, a family of antioxidant enzymes. Decreased amount of these antioxidant proteins correlated with elevation of reactive oxygen species (ROS) in infected cells. Increased levels of ROS were accompanied by changes in the pattern of telomere restriction fragments (TRFs) in infected cells and mediated activation of hypoxia-inducible transcription factor-1 (HIF-1) and phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathways. Moreover, treatment with antioxidants resulted in reduced levels of viral nucleoprotein, indicating a connection between ROS-dependent signaling and viral replication.

Adverse Birth Outcomes and Birth Telomere Length: A Systematic Review and Meta-Analysis

To synthesize previous findings on the difference in birth telomere length between newborns with and without intrauterine growth restriction (IUGR) or with and without preterm birth. We systematically searched 3 databases (PubMed, Embase, and Web of Science) for publications that examined the relationships of IUGR or preterm birth with birth telomere length. We conducted meta-analysis to pool the estimated difference in birth telomere length either between IUGR and non-IUGR or between preterm birth and full-term birth. Subgroup analyses were conducted by tissues (newborn blood vs placenta) and techniques used for telomere length measurement (quantitative polymerase chain reaction [qPCR] vs telomere restriction fragment). We included 11 articles on comparing birth telomere length between IUGR (combined n=227) and non-IUGR (n=1897) and 7 articles on comparing birth telomere length between preterm birth (n=182) and full-term birth (n=1320). We found IUGR was associated with shorter birth telomere length only when birth telomere length was measured in placenta (pooled standardized mean difference [SMD]=-0.85; 95% CI -1.13 to -0.57; IUGR/non-IUGR n=87/173), but not in newborn blood (pooled SMD=0.00, 95% CI -0.18 to 0.19; IUGR/non-IUGR n=148/1733). Birth telomere length was significantly longer in preterm birth than in full-term birth when birth telomere length was measured by qPCR (pooled SMD=0.40, 95% CI 0.18-0.63; preterm birth/full-term birth n=137/682) but not by telomere restriction fragment (pooled SMD=0.05, 95% CI -0.29 to 0.38; preterm birth/full-term birth n=44/444). IUGR is associated with shorter placental telomere length and preterm birth is associated with longer birth telomere length measured by qPCR.

The telomere gestational clock: increasing short telomeres at term in the mouse

The biologic mechanism(s) regulating the length of gestation are currently poorly understood. After peaking at the blastocyst stage, the average telomere lengths have been reported to shorten during the remainder of gestation in the placenta and fetal membranes in both human and mouse pregnancies, thereby providing a potential countdown biologic clock. These previous studies have reported changes in the average telomere lengths, whereas it has now been shown that the shortest telomeres, not the average telomere lengths, are the mediators of telomere dysfunction which limits cellular survival and results in aging. These studies sought to assess for the first time a significant increase in short telomeres in the fetal membrane and placental tissue near the end of pregnancy in the mouse. Placental and fetal membrane tissues were harvested from timed-pregnant CD-1 mice on gestational days 14-18 prior to the onset of parturition. Telomere lengths were determined for 30 DNA samples (5 each forgestational days 14, 16, and 18 from placentas and fetal membranes) using acommercial high-throughput quantitative fluorescence in situ hybridization technique. Quantitative measurements of representative short telomeres (ie, 3kband 5 kb telomere fragments) were performed for 29-30 DNA samples (4-7 each for gestational days 14, 15, 16, 17, and 18 from placentas, fetal membranes, and maternal liver) using a real-time quantitative polymerase chain reaction modification of the classic telomere restriction fragment technique. The median telomere lengths of fetal membrane tissue decreased from gestational days 14-18 (18,705-16,364 kb) and were significantly shorter than telomeres in placental tissue (P < .05). Representative histograms for the distribution of telomere lengths in mouse fetal membranes (as shown in the Figure) confirm a curve skewed to the left (toward shorter telomere lengths).The relative quantity of the representative short telomeres (ie, 3 kb and 5 kb fragments) increased significantly as gestation progressed in both placenta and fetal membrane tissue. In gestational day 18 fetal membranes, the relative quantity of 3 kb and 5 kb telomeres increased 5.5-fold and 9.3-fold compared with gestational day 14 tissues (P < .05). In placental tissue the relative quantity of 3 kb and 5 kb telomeres increased 9.3-fold and 7.8-fold compared with gestational day 14 tissues (P < .05). Studies performed using adult liver tissue demonstrated little variation of the representative short telomeres and no significant difference between the nonpregnant and pregnant samples. These mouse studies have demonstrated that the distribution of telomere lengths in fetal membrane and placental tissues are skewed toward shorter lengths and that the quantity of representative short telomeres increase significantly prior to parturition. The telomere gestational clock is a novel hypothesis supported by several preliminary mouse studies and interesting associations in human pregnancies between maternal conditions and telomere lengths. (eg, stress, education, pollution, neighborhood quality, and race). As such, the current hypothesis generating study provides a foundation for future research regarding the potential role for a telomere-based biologic clock that determines gestational length in human and other mammalian pregnancies.