Telomeres are shorter in placental trophoblasts of pregnancies complicated with intrauterine growth restriction (IUGR)

Evidence of Placental Aging in Late SGA, Fetal Growth Restriction and Stillbirth-A Systematic Review

During pregnancy, the placenta undergoes a natural aging process, which is considered normal. However, it has been hypothesized that an abnormally accelerated and premature aging of the placenta may contribute to placenta-related health issues. Placental senescence has been linked to several obstetric complications, including abnormal fetal growth, preeclampsia, preterm birth, and stillbirth, with stillbirth being the most challenging. A systematic search was conducted on Pubmed, Embase, and Scopus databases. Twenty-two full-text articles were identified for the final synthesis. Of these, 15 presented original research and 7 presented narrative reviews. There is a paucity of evidence in the literature on the role of placental aging in late small for gestational age (SGA), fetal growth restriction (FGR), and stillbirth. For future research, guidelines for both planning and reporting research must be implemented. The inclusion criteria should include clear differentiation between early and late SGA and FGR. As for stillbirths, only those with no other known cause of stillbirth should be included in the studies. This means excluding stillbirths due to congenital defects, infections, placental abruption, and maternal conditions affecting feto-maternal hemodynamics.

Role of Inflammaging on the Reproductive Function and Pregnancy

During female lifetime and pregnancy, inflammation and cellular senescence are implicated in physiological processes, from ovulation and menstruation, to placental homeostasis and delivery. Several lifestyles, nutritional, and environmental insults, as well as long-lasting pregestational inflammatory diseases may lead to detrimental effects in promoting and sustaining a chronic excessive inflammatory response and inflammaging, which finally contribute to the decay of fertility and pregnancy outcome, with a negative effect on placental function, fetal development, and future health risk profile in the offspring. Maladaptation to pregnancy and obstetric disease may in turn increase maternal inflammaging in a feedback loop, speeding up aging processes and outbreak of chronic diseases. Maternal inflammaging may also impact, through transgenerational effects, on future adult health. Hence, efficacious interventions should be implemented by physicians and healthcare professionals involved in prevention activities to reduce the modifiable factors contributing to the inflammaging process in order to improve public health.

Cellular senescence in normal and adverse pregnancy

Cellular senescence (CS) is defined as a state of terminal proliferation arrest accompanied by morphological alterations, pro-inflammatory phenotype, and metabolic changes. In recent years, the implications of senescence in numerous physiological and pathological conditions such as development, tissue repair, aging, or cancer have been evident. Some inductors of senescence are tissue repair pathways, telomere shortening, DNA damage, degenerative disorders, and wound healing. Lately, it has been demonstrated that CS plays a decisive role in the development and progression of healthy pregnancy and labor. Premature maternal-fetal tissues senescence (placenta, choriamniotic membranes, and endothelium) is implicated in many adverse pregnancy outcomes, including fetal growth restriction, preeclampsia, preterm birth, and intrauterine fetal death. Here we discuss cellular senescence and its association with normal pregnancy development and adverse pregnancy outcomes. Current evidence allows us to establish the relevance of CS in processes associated with the appropriate development of placentation, the progression of pregnancy, and the onset of labor; likewise, it allows us to understand the undeniable participation of CS deregulation in pathological processes associated with pregnancy.

Heterogenous Differences in Cellular Senescent Phenotypes in Pre-Eclampsia and IUGR following Quantitative Assessment of Multiple Biomarkers of Senescence

Premature ageing of the placenta in pregnancy outcomes is associated with the persistent presence of oxidative stress and placental insufficiency reducing its functional capacity. In this study, we investigated cellular senescence phenotypes of pre-eclampsia and IUGR pregnancies by simultaneously measuring several biomarkers of senescence. Maternal plasma and placental samples were collected at term gestation from nulliparous women undergoing pre-labour elective caesarean section with pre-eclampsia without intrauterine growth restriction (PE; n = 5), pre-eclampsia associated with intrauterine growth restriction (n = 8), intrauterine growth restriction (IUGR < 10th centile; n = 6), and age-matched controls (n = 20). Placental absolute telomere length and senescence gene analysis was performed by RTqPCR. The expression of cyclin-dependent kinase inhibitors (p21 and p16) was determined by Western blot. Senescence-associated secretory phenotypes (SASPs) were evaluated in maternal plasma by multiplex ELISA assay. Placental expression of senescence-associated genes showed significant increases in CHEK1, PCNA, PTEN, CDKN2A, and CCNB-1 (p < 0.05) in pre-eclampsia, while TBX-2, PCNA, ATM, and CCNB-1 expression were evident (p < 0.05) and were significantly decreased in IUGR compared with controls. Placental p16 protein expression was significantly decreased in pre-eclampsia only compared with controls (p = 0.028). IL-6 was significantly increased in pre-eclampsia (0.54 pg/mL ± 0.271 vs. 0.3 pg/mL ± 0.102; p = 0.017) while IFN-γ was significantly increased in IUGR (4.6 pg/mL ± 2.2 vs. 2.17 pg/mL ± 0.8; p = 0.002) compared with controls. These results provide evidence of premature senescence in IUGR pregnancies, and while cell cycle checkpoint regulators are activated in pre-eclampsia, the cellular phenotype is one of cell repair and subsequent proliferation rather than progression to senescence. The heterogeneity of these cellular phenotypes highlights the complexity of characterising cellular senescence and may equally be indicative of the differing pathophysiological insults unique to each obstetric complication.

The epigenetic aging, obesity, and lifestyle

The prevalence of obesity has dramatically increased worldwide over the past decades. Aging-related chronic conditions, such as type 2 diabetes and cardiovascular disease, are more prevalent in individuals with obesity, thus reducing their lifespan. Epigenetic clocks, the new metrics of biological age based on DNA methylation patterns, could be considered a reflection of the state of one’s health. Several environmental exposures and lifestyle factors can induce epigenetic aging accelerations, including obesity, thus leading to an increased risk of age-related diseases. The insight into the complex link between obesity and aging might have significant implications for the promotion of health and the mitigation of future disease risk. The present narrative review takes into account the interaction between epigenetic aging and obesity, suggesting that epigenome may be an intriguing target for age-related physiological changes and that its modification could influence aging and prolong a healthy lifespan. Therefore, we have focused on DNA methylation age as a clinical biomarker, as well as on the potential reversal of epigenetic age using a personalized diet- and lifestyle-based intervention.

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.

Symptoms of Prenatal Depression Associated with Shorter Telomeres in Female Placenta

BACKGROUND

Depression is a common mood disorder during pregnancy impacting one in every seven women. Children exposed to prenatal depression are more likely to be born at a low birth weight and develop chronic diseases later in life. A proposed hypothesis for this relationship between early exposure to adversity and poor outcomes is accelerated aging. Telomere length has been used as a biomarker of cellular aging. We used high-resolution telomere length analysis to examine the relationship between placental telomere length distributions and maternal mood symptoms in pregnancy.

METHODS

This study utilised samples from the longitudinal Grown in Wales (GiW) study. Women participating in this study were recruited at their presurgical appointment prior to a term elective caesarean section (ELCS). Women completed the Edinburgh Postnatal Depression Scale (EPDS) and trait subscale of the State-Trait Anxiety Inventory (STAI). Telomere length distributions were generated using single telomere length analysis (STELA) in 109 term placenta (37-42 weeks). Multiple linear regression was performed to examine the relationship between maternally reported symptoms of depression and anxiety at term and mean placental telomere length.

RESULTS

Prenatal depression symptoms were significantly negatively associated with XpYp telomere length in female placenta (B = -0.098, p = 0.026, 95% CI -0.184, -0.012). There was no association between maternal depression symptoms and telomere length in male placenta (B = 0.022, p = 0.586, 95% CI -0.059, 0.103). There was no association with anxiety symptoms and telomere length for either sex.

CONCLUSION

Maternal prenatal depression is associated with sex-specific differences in term placental telomeres. Telomere shortening in female placenta may indicate accelerated placental aging.

Telomeres and replicative cellular aging of the human placenta and chorioamniotic membranes

Recent hypotheses propose that the human placenta and chorioamniotic membranes (CAMs) experience telomere length (TL)-mediated senescence. These hypotheses are based on mean TL (mTL) measurements, but replicative senescence is triggered by short and dysfunctional telomeres, not mTL. We measured short telomeres by a vanguard method, the Telomere shortest length assay, and telomere-dysfunction-induced DNA damage foci (TIF) in placentas and CAMs between 18-week gestation and at full-term. Both the placenta and CAMs showed a buildup of short telomeres and TIFs, but not shortening of mTL from 18-weeks to full-term. In the placenta, TIFs correlated with short telomeres but not mTL. CAMs of preterm birth pregnancies with intra-amniotic infection showed shorter mTL and increased proportions of short telomeres. We conclude that the placenta and probably the CAMs undergo TL-mediated replicative aging. Further research is warranted whether TL-mediated replicative aging plays a role in all preterm births.

Telomere erosion as a placental clock: From placental pathologies to adverse pregnancy outcomes

The placenta provides nutritional and gas exchange between fetus and mother. Early in pregnancy, placental trophoblasts proliferate rapidly and invade aggressively. As pregnancy progresses, placental cells begin to age. Indeed, pregnancy itself has a tightly regulated duration, determined in large part by placental lifespan. Late in pregnancy, placental cells reach a senescent apoptotic state, activated by a number of intrinsic and extrinsic factors, including oxidative stress (OS), and DNA damage. Pregnancy complications, stillbirths and neonatal deaths have been related to OS and abnormal placental aging. Telomeres, the protective nucleoprotein structures at the ends of linear chromosomes, shorten both from cell replication and from exposure to OS. When telomeres become critically short they trigger cell cycle arrest and eventually cell death. Telomere attrition thus provide an intrinsic mechanism to explain tissue senescence and aging. Mounting evidence suggests that senescence of placental and fetal membrane cells results from telomere attrition. We review the studies that have addressed the role of telomere length (TL) in placentas from normal and complicated pregnancies, including pre-eclampsia, intrauterine growth restriction, gestational diabetes, and stillbirth. To date studies have uncovered associations between TL and a number of obstetrical complications. Future research is needed to determine whether these associations are causative, i.e. whether these clinical conditions result from telomere dysfunction, and whether particular features of telomeres, e.g. mean or shortest length, etc. could serve as clinically useful biomarkers of placental health.

The placenta in fetal growth restriction: What is going wrong?

The placenta is essential for the efficient delivery of nutrients and oxygen from mother to fetus to maintain normal fetal growth. Dysfunctional placental development underpins many pregnancy complications, including fetal growth restriction (FGR) a condition in which the fetus does not reach its growth potential. The FGR placenta is smaller than normal placentae throughout gestation and displays maldevelopment of both the placental villi and the fetal vasculature within these villi. Specialized epithelial cells called trophoblasts exhibit abnormal function and development in FGR placentae. This includes an altered balance between proliferation and apoptotic death, premature cellular senescence, and reduced colonisation of the maternal decidual tissue. Thus, the placenta undergoes aberrant changes at the macroscopic to cellular level in FGR, which can limit exchange capacity and downstream fetal growth. This review aims to compile stereological, in vitro, and imaging data to create a holistic overview of the FGR placenta and its pathophysiology, with a focus on the contribution of trophoblasts.

A review of maternal prenatal exposures to environmental chemicals and psychosocial stressors-implications for research on perinatal outcomes in the ECHO program

Exposures to environmental chemicals and psychosocial stressors during pregnancy have been individually associated with adverse perinatal outcomes related to birthweight and gestational age, but are not often considered in combination. We review types of psychosocial stressors and instruments used to assess them and classes of environmental chemical exposures that are known to adversely impact perinatal outcomes, and identify studies relevant studies. We discuss the National Institutes of Health's Environmental influences on Child Health Outcomes (ECHO) program that has combined existing longitudinal cohorts that include more than 50,000 children across the U.S. We describe future opportunities for investigators to use this important new resource for addressing relevant and critical research questions to maternal health. Of the 84 cohorts in ECHO, 38 collected data on environmental chemicals and psychosocial stressors and perinatal outcomes. The diverse ECHO pregnancy cohorts provide capacity to compare regions with distinct place-based environmental and social stressors.

Obesity is associated with shorter telomeres in 8 year-old children

Telomere length is considered a biomarker of biological aging. Shorter telomeres and obesity have both been associated with age-related diseases. To evaluate the association between various indices of obesity with leukocyte telomere length (LTL) in childhood, data from 1,396 mother-child pairs of the multi-centre European birth cohort study HELIX were used. Maternal pre-pregnancy body mass index (BMI) and 4 adiposity markers in children at age 8 (6–11) years were assessed: BMI, fat mass, waist circumference, and skinfold thickness. Relative LTL was obtained. Associations of LTL with each adiposity marker were calculated using linear mixed models with a random cohort effect. For each 1 kg/m² increment in maternal pre-pregnancy BMI, the child’s LTL was 0.23% shorter (95%CI: 0.01,0.46%). Each unit increase in child BMI z-score was associated with 1.21% (95%CI: 0.30,2.11%) shorter LTL. Inverse associations were observed between waist circumference and LTL (−0.96% per z-score unit; 95%CI: −2.06,0.16%), and skinfold thickness and LTL (−0.10% per z-score unit; 95%CI: −0.23,0.02%). In conclusion, this large multicentric study suggests that higher child adiposity indicators are associated with short telomeres in children, and that associations are stronger for child BMI than for maternal pre-pregnancy BMI.

The transgenerational transmission of maternal adverse childhood experiences (ACEs): Insights from placental aging and infant autonomic nervous system reactivity

OBJECTIVE

To test alterations in placental cellular aging as one pathway by which maternal early adversity influences physiologic development in her offspring.

METHODS

Maternal report of her adverse childhood experiences (ACE) was obtained prenatally along with measures of prenatal stress and demographic information. Placentas (N = 67) were collected at birth and telomere length (TL) was measured in four separate fetally-derived placental tissues: amnion, chorion, villus, and umbilical cord. At four months of age, infants completed the still-face paradigm (SFP) during which respiratory sinus arrhythmia (RSA) data were collected; RSA reactivity and RSA recovery was available from 44 and 41 infants respectively. Multi-level mixed effects models examined the impact of maternal ACE score on placental TL. Generalized linear models tested the relation between composite placental TL and infant RSA, as well as the moderation of maternal ACE score and infant RSA by composite placental TL.

RESULTS

Higher maternal ACE score significantly predicted shorter placental TL across tissues (β = -0.015; P = 0.036) and infant RSA across the SFP. No direct relation was found between placental TL and RSA, however composite placental TL moderated the relation between ACE score and both infant RSA reactivity (β = 0.025; P = 0.005) and RSA recovery (β = -0.028; P = 0.032). In infants with shorter composite placental TL, higher ACE score predicted greater RSA suppression during the still-face epoch relative to play period 1 and greater RSA augmentation during play period 2 relative to the still-face epoch.

CONCLUSIONS

These data are the first, to our knowledge, to report that changes in placental TL influence the transgenerational impact of maternal early life adversity on the development of her offspring's autonomic nervous system.

The Role of Epigenetics in Placental Development and the Etiology of Preeclampsia

In this review, we comprehensively present the function of epigenetic regulations in normal placental development as well as in a prominent disease of placental origin, preeclampsia (PE). We describe current progress concerning the impact of DNA methylation, non-coding RNA (with a special emphasis on long non-coding RNA (lncRNA) and microRNA (miRNA)) and more marginally histone post-translational modifications, in the processes leading to normal and abnormal placental function. We also explore the potential use of epigenetic marks circulating in the maternal blood flow as putative biomarkers able to prognosticate the onset of PE, as well as classifying it according to its severity. The correlation between epigenetic marks and impacts on gene expression is systematically evaluated for the different epigenetic marks analyzed.

The effect of maternal body mass index (BMI) and telomere function on in vitro fertilization (IVF) outcome: a preliminary cohort study

Telomeres are a specific base sequence of DNA, responsible for chromosome stability and DNA protection. We aimed to investigate the association between telomere systems and IVF outcomes according to patients' BMI. For all telomere characteristics, there was a distinct trend towards shorter telomeres and activation of telomere shortening compensatory mechanisms in the BMI group >25 kg/m², reaching statistical significance for senescence only (r = 0.7, p value <0.01). There was a trend towards a relationship between telomere length and number of oocytes between telomere length and fertilization rate, but these did not reach a statistical significance. For pregnancy outcome, all telomere characteristics were better for the patients who achieved a pregnancy. While there is paucity of data in the literature concerning the association between telomere characteristics and infertility, telomeres might contribute to the association between obesity and sub-optimal IVF results.

Children Born Small for Gestational Age: Differential Diagnosis, Molecular Genetic Evaluation, and Implications

Children born small for gestational age (SGA), defined as a birth weight and/or length below -2 SD score (SDS), comprise a heterogeneous group. The causes of SGA are multifactorial and include maternal lifestyle and obstetric factors, placental dysfunction, and numerous fetal (epi)genetic abnormalities. Short-term consequences of SGA include increased risks of hypothermia, polycythemia, and hypoglycemia. Although most SGA infants show catch-up growth by 2 years of age, ∼10% remain short. Short children born SGA are amenable to GH treatment, which increases their adult height by on average 1.25 SD. Add-on treatment with a gonadotropin-releasing hormone agonist may be considered in early pubertal children with an expected adult height below -2.5 SDS. A small birth size increases the risk of later neurodevelopmental problems and cardiometabolic diseases. GH treatment does not pose an additional risk.

Telomere Homeostasis and Senescence Markers Are Differently Expressed in Placentas From Pregnancies With Early- Versus Late-Onset Preeclampsia

BACKGROUND

Early-onset preeclampsia (EOPE; <34 weeks' gestation) usually has more severe morbidity for the mother and fetus compared to late-onset preeclampsia (LOPE). Telomere homeostasis is disrupted in preeclampsia (PE) and senescence markers are increased. The pathophysiologic differences between early and LOPE are not fully unraveled yet.

METHODS

We studied placental biopsies from 7 pregnancies with EOPE, 6 pregnancies with LOPE, and 13 healthy gestational age-matched controls. Telomere length and aggregate formation were assessed using qualitative fluorescence in situ hybridization and electronic quantitative methods. Senescence markers were evaluated including senescence-associated heterochromatin foci, β-galactosidase (SAβ-Gal), and P16 staining, as was the expression of P16 complementary DNA (cDNA) using real-time quantitative polymerase chain reaction (RT-qPCR).

RESULTS

There were no differences in maternal age, gravidity, parity, body mass index, and mode of conception between the study and the control groups. The percentage of trophoblasts with short telomeres was higher in placental samples from EOPE (52.61% [12.27%]) versus LOPE (28.72% [10.14%]); both were higher compared to controls (7.53% [5.14%], P = .03). Aggregate formation was enhanced in EOPE (8.72% [2.49%]) compared to LOPE (4.54% [1.45%]); both were higher than in healthy controls (2.72% [1.08%], P = .03). Trophoblasts from EOPE versus LOPE were more likely to stain positive for SAβ-Gal and P16 compared to controls (P < .001). P16 cDNA expression assayed by RT-qPCR was 7.51 times higher in EOPE compared to controls and 5.86 times higher than in LOPE.

CONCLUSIONS

Impaired telomere homeostasis and senescence markers are more prominent in EOPE versus LOPE. These findings may contribute to our understanding of the pathophysiology and explain their different clinical presentations and outcomes.

The effect of intrauterine growth on leukocyte telomere length at birth

Objective: Telomeres are specialized nucleoprotein structures located at the ends of chromosomes, which play a crucial role in genomic stability. Telomere shortening has been proposed as a biomarker for the onset of age-related diseases. This study aimed to determine whether restricted or increased intrauterine growth affects leukocyte telomere length (LTL) at birth. Materials and methods: One hundred sixty-five (n = 165) full-term neonates participated in the study. Fetuses were classified as intrauterine growth restriction (IUGR, n = 21), large-for-gestational-age (LGA, n = 15), or appropriate-for-gestational-age (AGA, n = 129), based on customized birth-weight standards. Mixed arteriovenous cord blood samples were collected for isolation of leukocyte DNA. The LTL was measured using multiplex monochrome quantitative real-time PCR and telomeric restriction fragments through Southern blot analysis (terminal restriction fragment [TRF]). Results: Despite differences among groups in birth weight, length and head circumference, LTL did not differ among AGA (6.78 ± 0.58), IUGR (10.54 ± 1.80), and LGA (11.95 ± 2.42) neonates (p = .098). Cord blood IGF-1 and IGFBP-3 concentrations were higher in the LGA group. LTL positively correlated with birth length (r = 0.176, p = .032). Conclusions: Intrauterine growth does not seem to affect LTL at birth. Further studies, comprising a larger sample size of IUGR, LGA, and AGA neonates, are required to determine whether growth at birth influences LTL.

Maternal human telomerase reverse transcriptase variants are associated with preterm labor and preterm premature rupture of membranes

Objective

Premature aging and short telomere lengths of fetal tissues are associated with spontaneous preterm labor (PTL) and preterm premature rupture of membranes (pPROM). Maintenance of telomere length is performed by the enzyme telomerase. Human telomerase reverse transcriptase (hTERT) is a subunit of telomerase, and its dysfunction affects telomere shortening. This study assessed whether maternal or fetal genetic variations in the hTERT gene are associated with PTL or pPROM.

Methods

A case (PTL or pPROM) control (term birth) genetic association study was conducted in 654 non-Hispanic white mothers (438 term, 162 PTL, 54 pPROM) and 502 non-Hispanic white newborns (346 term, 116 PTB, 40 pPROM). Maternal and fetal DNA samples were genotyped for 23 single nucleotide polymorphisms (SNPs) within the hTERT gene. Allele frequencies were compared between cases and controls, stratified by PTL and pPROM. Maternal and fetal data were analyzed separately.

Results

Allelic differences in one SNP of hTERT (rs2853690) were significantly associated with both PTL (adjusted OR 2.24, 95%CI 1.64–3.06, p = 2.32e-05) and with pPROM (adjusted OR 7.54, 95%CI 3.96–14.33, p = 2.39e-07) in maternal DNA. There was no significant association between the hTERT SNPs analyzed and PTL or pPROM in the fetal samples.

Conclusion

hTERT polymorphisms in fetal DNA do not associate with PTL or pPROM risk; however, maternal genetic variations in hTERT may play a contributory role in risk of PTL and PPROM.

Maternal-fetal cross talk through cell-free fetal DNA, telomere shortening, microchimerism, and inflammation

There exists a strong correlation between unscheduled inflammation at the maternal-fetal interface and the continuum of pregnancy complications. In normal pregnancy, immunological tolerance is established to protect the semi-allogeneic fetus. There has been extensive research on how the immunity, endovascular trophoblast migration, and hormonal nexus are orchestrated during pregnancy at the maternal-fetal interface to program a normal pregnancy outcome. It is not clear what contributes to the plasticity of uterine immune tolerance, fetal survial, and long-term post-partum health of the mother and the offspring. Old and new concepts have reemerged and emerged that include cell-free fetal DNA (cffDNA), telomere shortening, microchimerism involving bidirectional migration of maternal and fetal cells, and pregnancy as a stress factor. The question is how these pathways converge in a gestational age-dependent manner to contribute to the health of the mother and the offspring later in life and respond to an array of inflammatory challenges. In this Review, we provide pertinent discussion on maternal-fetal cross talk through cffDNA, telomere shortening, and microchimerism in the context of inflammatory and anti-inflammatory settings, particularly how these pathways lead to normal and adverse pregnancy outcomes.

The fetal programming of telomere biology hypothesis: an update

Research on mechanisms underlying fetal programming of health and disease risk has focused primarily on processes that are specific to cell types, organs or phenotypes of interest. However, the observation that developmental conditions concomitantly influence a diverse set of phenotypes, the majority of which are implicated in age-related disorders, raises the possibility that such developmental conditions may additionally exert effects via a common underlying mechanism that involves cellular/molecular ageing-related processes. In this context, we submit that telomere biology represents a process of particular interest in humans because, firstly, this system represents among the most salient antecedent cellular phenotypes for common age-related disorders; secondly, its initial (newborn) setting appears to be particularly important for its long-term effects; and thirdly, its initial setting appears to be plastic and under developmental regulation. We propose that the effects of suboptimal intrauterine conditions on the initial setting of telomere length and telomerase expression/activity capacity may be mediated by the programming actions of stress-related maternal-placental-fetal oxidative, immune, endocrine and metabolic pathways in a manner that may ultimately accelerate cellular dysfunction, ageing and disease susceptibility over the lifespan. This perspectives paper provides an overview of each of the elements underlying this hypothesis, with an emphasis on recent developments, findings and future directions.This article is part of the theme issue 'Understanding diversity in telomere dynamics'.

Is there a role for placental senescence in the genesis of obstetric complications and fetal growth restriction?

The placenta ages as pregnancy advances, yet its continued function is required for a successful pregnancy outcome. Placental aging is a physiological phenomenon; however, there are some placentas that show signs of aging earlier than others. Premature placental senescence and aging are implicated in a number of adverse pregnancy outcomes, including fetal growth restriction, preeclampsia, spontaneous preterm birth, and intrauterine fetal death. Here we discuss cellular senescence, a state of terminal proliferation arrest, and how senescence is regulated. We also explore the role of physiological placental senescence and how aberrant placental senescence alters placental function, contributing to the pathophysiology of fetal growth restriction, preeclampsia, spontaneous preterm labor/birth, and unexplained fetal death.

Telomere length heterogeneity in placenta revealed with high-resolution telomere length analysis

INTRODUCTION

Telomeres, are composed of tandem repeat sequences located at the ends of chromosomes and are required to maintain genomic stability. Telomeres can become shorter due to cell division and specific lifestyle factors. Critically shortened telomeres are linked to cellular dysfunction, senescence and aging. A number of studies have used low resolution techniques to assess telomere length in the placenta. In this study, we applied Single Telomere Length Analysis (STELA) which provides high-resolution chromosome specific telomere length profiles to ask whether we could obtain more detailed information on the length of individual telomeres in the placenta.

METHODS

Term placentas (37-42 weeks) were collected from women delivering at University Hospital of Wales or Royal Gwent Hospital within 2 h of delivery. Multiple telomere-length distributions were determined using STELA. Intraplacental variation of telomere length was analysed (N = 5). Telomere length distributions were compared between labouring (N = 10) and non-labouring (N = 11) participants. Finally, telomere length was compared between female (N = 17) and male (N = 20) placenta.

RESULTS

There were no significant influences of sampling site, mode of delivery or foetal sex on the telomere-length distributions obtained. The mean telomere length was 7.7 kb ranging from 5.0 kb to 11.7 kb across all samples (N = 42) and longer compared with other human tissues at birth. STELA also revealed considerable telomere length heterogeneity within samples.

CONCLUSIONS

We have shown that STELA can be used to study telomere length homeostasis in the placenta regardless of sampling site, mode of delivery and foetal sex. Moreover, as each amplicon is derived from a single telomeric molecule, from a single cell, STELA can reveal the full detail of telomere-length distributions, including telomeres within the length ranges observed in senescent cells. STELA thus provides a new tool to interrogate the relationship between telomere length and pregnancy complications linked to placental dysfunction.

Correlation of cord blood telomere length with birth weight

Background

Intrauterine growth restriction affects 3% of newborns; and the lightest 10% of whom are classified as small for gestational age (SGA). These low-birth weight newborns are at increased risk of neonatal morbidity such as hypoxia and hypoglycaemia. In later life, they are at higher risk of several age-related diseases such as cardiovascular and metabolic disorders and dementia. As having short telomeres is also associated with these diseases, we tested if these newborns might already start with shorter telomeres at birth.

Findings

Relative telomere lengths were determined using quantitative real-time PCR in cord blood samples from 195 newborns of Chinese ancestry. Based on the telomere length normalised to a single copy gene and a reference DNA sample as internal control, we found statistically significant correlations between relative telomere length and both unadjusted and gestational age-adjusted birth weight, with the lighter newborns having shorter telomeres. The SGA birth weight group comprising the bottom 10% of the samples also had the shortest telomeres compared to the medium and heaviest birth weight groups.

Conclusions

Our results indicate that there is reduction of cord blood telomere length for newborns with lower birth weight.

Differences in placental telomere length suggest a link between racial disparities in birth outcomes and cellular aging

BACKGROUND

Health disparities begin early in life and persist across the life course. Despite current efforts, black women exhibit greater risk for pregnancy complications and negative perinatal outcomes compared with white women. The placenta, which is a complex multi-tissue organ, serves as the primary transducer of bidirectional information between the mother and fetus. Altered placental function is linked to multiple racially disparate pregnancy complications; however, little is known about racial differences in molecular factors within the placenta. Several pregnancy complications, which include preeclampsia and fetal growth restriction, exhibit racial disparities and are associated with shorter placental telomere length, which is an indicator of cellular stress and aging. Cellular senescence and telomere dynamics are linked to the molecular mechanisms that are associated with the onset of labor and parturition. Further, racial differences in telomere length are found in a range of different peripheral tissues. Together these factors suggest that exploration of racial differences in telomere length of the placenta may provide novel mechanistic insight into racial disparities in birth outcomes.

OBJECTIVE

This study examined whether telomere length measured in 4 distinct fetally derived tissues were significantly different between black and white women. The study had 2 hypotheses: (1) that telomere length that is measured in different placental tissue types would be correlated and (2) that across all sampled tissues telomere length would differ by race.

STUDY DESIGN

In a prospective study, placental tissue samples were collected from the amnion, chorion, villus, and umbilical cord from black and white singleton pregnancies (N=46). Telomere length was determined with the use of monochrome multiplex quantitative real-time polymerase chain reaction in each placental tissue. Demographic and pregnancy-related data were also collected. Descriptive statistics characterized the sample overall and among black and white women separately. The overall impact of race was assessed by multilevel mixed-effects linear regression models that included empirically relevant covariates.

RESULTS

Telomere length was correlated significantly across all placental tissues. Pairwise analyses of placental tissue telomere length revealed significantly longer telomere length in the amnion compared with the chorion (t=-2.06; P=.043). Overall telomere length measured in placenta samples from black mothers were significantly shorter than those from white mothers (β=-0.09; P=.04). Controlling for relevant maternal and infant characteristics strengthened the significance of the observed racial differences (β=-0.12; P=.02). Within tissue analyses revealed that the greatest difference by race was found in chorionic telomere length (t=-2.81; P=.007).

CONCLUSION

These findings provide the first evidence of racial differences in placental telomere length. Telomere length was significantly shorter in placental samples from black mothers compared with white mothers. Given previous studies that have reported that telomere length, cellular senescence, and telomere dynamics are molecular factors that contribute to the rupture of the amniotic sac, onset of labor, and parturition, our findings of shorter telomere length in placentas from black mothers suggest that accelerated cellular aging across placental tissues may be relevant to the increased risk of preterm delivery in black pregnancies. Our results suggest that racial differences in cellular aging in the placenta contribute to the earliest roots of health disparities.

Telomerase activity in pregnancy complications (Review)

Telomeres are specific DNA regions positioned at the ends of chromosomes and composed of functional non-coding repeats. Upon cell division, the telomeres decrease in length by a preordained amount. When the telomeres become critically short, cells lose the ability to divide and enter a specific functioning mode designated as 'cellular senescence'. However, human tissues express an enzyme that deters the shrinking of the telomeres, the telomerase. Due to its ability to maintain telomere length, the telomerase slows down and possibly suspends the aging of the cells. In regard to this, solid evidence demonstrates that female human fertility decreases with increased maternal age and that various adverse factors, including alterations in telomerase activity, can contribute to age-associated infertility in women. The fact that telomerase activity is regulated in a time- and location-dependent manner in both embryo and placental tissues, highlights it potential importance to the successful completion of pregnancy. Since maternal age is a crucial determining factor for the success of in vitro and in vivo fertilization, numerous studies have focused on telomerase activity and its correlation with mammalian fertilization, as well as the following cleavage and pre-implantation developmental processes. Associations between telomerase activity and pregnancy complications have been previously observed. Our aim in this review was to summarize and critically discuss evidence correlating telomerase activity with pregnancy complications.

Reflections on the role of senescence during development and aging

New and stimulating results have challenged the concept that cellular senescence might not be synonymous with aging. It is indisputable that during aging, senescent cell accumulation has an impact on organismal health. Nevertheless, senescent cells are now known to display physiological roles during embryonic development, during wound healing repair and as a cellular response to stress. The fact that senescence has been found in cells that did not attain their maximal round of replications, nor have metabolic alterations or DNA damage, also challenges the paradigm that senescence is cellular aging, and it is in favor of the idea that cellular senescence is a phenomenon that has a function by itself. Therefore, in order to understand this phenomenon it is important to analyze the relationship between senescence and other cellular responses that have many features in common, such as apoptosis, cancer and autophagy, particularly highlighting their role during development and adulthood.

Telomere homeostasis in trophoblasts and in cord blood cells from pregnancies complicated with preeclampsia

BACKGROUND

Telomeres are nucleoprotein structures, essential for chromosome stability and cell survival. Telomeres are progressively shortened with each cell division and by environmental factors. Telomere loss has been linked to age and stress-induced premature senescence. Dysfunctional telomeres tend to form aggregates, which consist of the end-to-end fusion of telomeres. Telomere elongation is carried out by telomerase, which is a specific reverse transcriptase capable of adding telomeric repeats to chromosome termini. The TERC gene encodes the RNA template of the telomerase. Another compensatory mechanism that is enhanced in response to telomere shortening and senescence is the telomere capture (TC). Telomere shortening and elevated aggregate formation have been observed in trophoblasts from pregnancies complicated with preeclampsia (PE).

OBJECTIVE

We opted to study mechanisms of telomere shortening in trophoblasts from pregnancies complicated with PE and to assess telomere length and homeostasis in fetal cord blood cells from PE pregnancies.

STUDY DESIGN

Placental specimens and cord blood samples from uncomplicated pregnancies and from pregnancies complicated with PE were collected. Staining with 4',6-diamidino-2-phenylindole was used to assess nuclear fragmentation: senescence-associated heterochromatin foci (SAHF). Fluorescence in situ hybridization was used to evaluate TERC gene copy number and TC. Telomere length and aggregate formation were assessed in cord blood using quantitative fluorescence in situ hybridization. Nonparametric Kruskal-Wallis and Mann-Whitney U tests were applied to test the differences between the study groups.

RESULTS

Nine samples from pregnant patients with PE without intrauterine growth restriction and 14 samples from uncomplicated pregnancies that served as controls were collected. In cord blood cells, no differences were observed in telomere length, aggregate formation, TERC copy number, TC, or SAHF between PE and controls. In PE trophoblasts the percentage of cells with SAHF was higher in PE trophoblasts compared to controls (56.8 SD = 10.5% vs 35.2 SD = 10.7%, P = .028). The percentage of cells with abnormal TERC copy number was increased in PE trophoblasts compared to controls (31 ± 3.6% vs 12.97 SD = 5%, P = .004) as well as the percentage of cells with TC (27.4 SD = 9.4% vs 16 SD = 4.67%, P = .028).

CONCLUSION

We suggest that telomere shortening in PE trophoblasts is linked to cellular increased senescence. Alterations in telomere homeostasis mechanisms are present in such cases. These findings support the role of telomeres in the pathogenesis of trophoblastic dysfunction in PE. The lack of telomere shortening, modified telomere homeostasis mechanisms, and increased senescence in cord blood from pregnancies complicated with PE suggests that these processes are probably restricted primarily to the placenta.

The role of telomeres and telomerase reverse transcriptase isoforms in pluripotency induction and maintenance

Telomeres are linear guanine-rich DNA structures at the ends of chromosomes. The length of telomeric DNA is actively regulated by a number of mechanisms in highly proliferative cells such as germ cells, cancer cells, and pluripotent stem cells. Telomeric DNA is synthesized by way of the ribonucleoprotein called telomerase containing a reverse transcriptase (TERT) subunit and RNA component (TERC). TERT is highly conserved across species and ubiquitously present in their respective pluripotent cells. Recent studies have uncovered intricate associations between telomeres and the self-renewal and differentiation properties of pluripotent stem cells. Interestingly, the past decade's work indicates that the TERT subunit also has the capacity to modulate mitochondrial function, to remodel chromatin structure, and to participate in key signaling pathways such as the Wnt/β-catenin pathway. Many of these non-canonical functions do not require TERT's catalytic activity, which hints at possible functions for the extensive number of alternatively spliced TERT isoforms that are highly expressed in pluripotent stem cells. In this review, some of the established and potential routes of pluripotency induction and maintenance are highlighted from the perspectives of telomere maintenance, known TERT isoform functions and their complex regulation.

Telomere homeostasis in IUGR placentas - A review

Telomeres are nucleoprotein structures located at the termini of chromosomes. They are essential for chromosome stability. Telomeres become shorter due to mitotic cycles and environmental factors. When telomeres are shortened and therefore dysfunctional, cellular senescence occurs and organ dysfunction might develop. During pregnancy, fetal growth restriction secondary to placental insufficiency has been linked to impaired telomere homeostasis in which telomeres are shorter, telomerase is decreased, and compensatory mechanisms of telomere capture are enhanced. These characteristics, along with increased signs of senescence, indicate telomere dysfunction in trophoblasts from placentas affected by intrauterine growth restriction (IUGR). This review summarizes the information currently available regarding telomere homeostasis in trophoblasts from human pregnancies affected by IUGR. Improved understanding of placental physiology might help in the development of treatment options for fetuses with IUGR.

Lower placental telomere length may be attributed to maternal residential traffic exposure; a twin study

BACKGROUND

High variation in telomere length between individuals is already present before birth and is as wide among newborns as in adults. Environmental exposures likely have an impact on this observation, but remain largely unidentified. We hypothesize that placental telomere length in twins is associated with residential traffic exposure, an important environmental source of free radicals that might accelerate aging. Next, we intend to unravel the nature-nurture contribution to placental telomere length by estimating the heritability of placental telomere length.

METHODS

We measured the telomere length in placental tissues of 211 twins in the East Flanders Prospective Twin Survey. Maternal traffic exposure was determined using a geographic information system. Additionally, we estimated the relative importance of genetic and environmental sources of variance.

RESULTS

In this twin study, a variation in telomere length in the placental tissue was mainly determined by the common environment. Maternal residential proximity to a major road was associated with placental telomere length: a doubling in the distance to the nearest major road was associated with a 5.32% (95% CI: 1.90 to 8.86%; p=0.003) longer placental telomere length at birth. In addition, an interquartile increase (22%) in maternal residential surrounding greenness (5 km buffer) was associated with an increase of 3.62% (95% CI: 0.20 to 7.15%; p=0.04) in placental telomere length.

CONCLUSIONS

In conclusion, we showed that maternal residential proximity to traffic and lower residential surrounding greenness is associated with shorter placental telomere length at birth. This may explain a significant proportion of air pollution-related adverse health outcomes starting from early life, since shortened telomeres accelerate the progression of many diseases.

Placental telomere shortening in stillbirth: a sign of premature senescence?

OBJECTIVE

The objective of this study is to investigate placental telomere shortening in unexplained stillbirths (SBs) as an indication of premature senescence.

METHODS

Placentas were collected from 42 unexplained SB (>22 weeks), 43 term and 15 preterm live births, at the Policlinico Hospital of Modena (Italy). DNA extracted from placentae was studied for telomere length by real time PCR. Standard curves were generated for telomere lengths from single copy gene amplifications using a reference DNA. The telomere length for each sample was derived based on the ratio of telomere length between the sample and single copy gene standard (T/S ratio). The mean ratio of placental telomere in term live births was 5.181 ± 3.841.

RESULTS

A twofold decrease in telomere length was seen in SBs (over all 2.455 ± 1.239; p < 0.001). For early SBs (above 34 weeks), the T/S was 2.8884 ± 1.224 and for late SBs, the T/S was 2.207 ± 1.201, both lower than term live births (both p < 0.01). T/S remained lower both in small for gestational age-SB (2.639 ± 1.619) and appropriate for gestational age-SB (2.653 ± 1.335) with no difference between these subgroups (p = ns). T/S was lower in SB compared with spontaneous preterm births (PTBs) (6.382 ± 5.525; p < 0.01), whereas SBs telomere length were similar to those of preterm premature rupture of membranes (pPROM) (3.296 ± 3.599; p = ns).

CONCLUSIONS

Substantial reduction in telomere length in SBs is indicative of placental senescence. These data provide mechanistic insights that premature aging may lead to placental dysfunction as an initiator of fetal demise in unexplained SBs.

Setting the trajectory: racial disparities in newborn telomere length

OBJECTIVE

To explore racial differences in newborn telomere length (TL) and the effect moderation of the sex of the infant while establishing the methodology for the use of newborn blood spots for TL analyses.

STUDY DESIGN

Pregnant mothers were recruited from the Greater New Orleans area. TL was determined via monochrome multiplex quantitative real-time polymerase chain reaction on DNA extracted from infant blood spots. Demographic data and other covariates were obtained via maternal report before the infant's birth. Birth outcome data were obtained from medical records and maternal report.

RESULTS

Black infants weighed significantly less than white infants at birth and had significantly longer TL than white infants (P=.0134), with the strongest effect observed in black female infants. No significant differences in gestational age were present.

CONCLUSIONS

Significant racial differences in TL were present at birth in this sample, even after we controlled for a range of birth outcomes and demographic factors. Because longer initial TL is predictive of more rapid TL attrition across the life course, these findings provide evidence that, even at birth, biological vulnerability to early life stress may differ by race and sex.

Perinatal complications and aging indicators by midlife

BACKGROUND

Perinatal complications predict increased risk for morbidity and early mortality. Evidence of perinatal programming of adult mortality raises the question of what mechanisms embed this long-term effect. We tested a hypothesis related to the theory of developmental origins of health and disease: that perinatal complications assessed at birth predict indicators of accelerated aging by midlife.

METHODS

Perinatal complications, including both maternal and neonatal complications, were assessed in the Dunedin Multidisciplinary Health and Development Study cohort (N = 1037), a 38-year, prospective longitudinal study of a representative birth cohort. Two aging indicators were assessed at age 38 years, objectively by leukocyte telomere length (TL) and subjectively by perceived facial age.

RESULTS

Perinatal complications predicted both leukocyte TL (β = -0.101; 95% confidence interval, -0.169 to -0.033; P = .004) and perceived age (β = 0.097; 95% confidence interval, 0.029 to 0.165; P = .005) by midlife. We repeated analyses with controls for measures of family history and social risk that could predispose to perinatal complications and accelerated aging, and for measures of poor health taken in between birth and the age-38 follow-up. These covariates attenuated, but did not fully explain the associations observed between perinatal complications and aging indicators.

CONCLUSIONS

Our findings provide support for early-life developmental programming by linking newborns' perinatal complications to accelerated aging at midlife. We observed indications of accelerated aging "inside," as measured by leukocyte TL, an indicator of cellular aging, and "outside," as measured by perceived age, an indicator of declining tissue integrity. A better understanding of mechanisms underlying perinatal programming of adult aging is needed.

Telomere shortening in intra uterine growth restriction placentas

INTRODUCTION

Placentas from pregnancies complicated with IUGR (intrauterine growth restriction) express altered telomere homeostasis. In the current study, we examined mechanisms of telomere shortening in these placentas.

METHODS

Placental biopsies from 15 IUGR and 15 healthy control pregnancies were examined. The percentage of trophoblasts with fragmented nuclei: senescence-associated heterochromatin foci (SAHF), was calculated using DAPI staining. The amount of human telomerase reverse transcriptase (hTERT) mRNA was evaluated using RtPCR levels of telomere capture using FISH in those samples were estimated.

RESULTS

The percentage of trophoblasts with SAHF was higher in IUGR compared to control samples, (25±13.4% vs. 1.6±1.6%, P<0.0001), hTERT mRNA was decreased (0.5±0.2 vs. 0.9±0.1, P<0.0001) and telomere capture was increased (13.2±9.7% vs.1.3±2.5%, P<0.001).

CONCLUSIONS

We suggest that IUGR placentas express increased signs of senescence as part of the impaired telomere homeostasis. One factor that mediates telomere shortening in these placentas is decreased hTERT mRNA, leading to decreased protein expression and therefore, reduced telomere elongation. Telomere capture, which is a healing process, is increased in IUGR trophoblasts as a compensatory mechanism.

Placental telomere length decreases with gestational age and is influenced by parity: a study of third trimester live-born twins

BACKGROUND

In contrast to the postnatal period, little is known about telomere length (TL) during prenatal life. The decrease in placental TL remains unknown, although intra uterine growth retardation and preeclampsia are associated with shorter placental TL. The aim of this study is to assess the decrease of placental TL during the third trimester of gestation and to explore the role of potential "growth influencing factors".

METHODS

The study sample consisted of 329 live-born twins from the East Flanders Prospective Twin Survey. TL was determined using a multiplex quantitative PCR method. Gestational age, sex, birth order, placental characteristics, parity, maternal and paternal age, diabetes, hypertension, smoking, alcohol use, and socio economic status (SES) were considered "growth influencing factors". Bivariable multilevel regression analysis with "growth influencing factors" was performed.

RESULTS

Placental TL ranged from 4.3 kbp to 84.4 kbp with a median of 10.8 kbp. Ln(TL) decreased in a linear fashion with an estimated TL decreasing from 13.98 kbp at 28 weeks to 10.56 kbp at 42 weeks. The regression coefficient of gestational age became smaller if considered together with SES (b = -0.017; p = 0.08) or diabetes (b = -0.018; p = 0.07) and bigger if considered together with parity (b = -0.022; p = 0.02), indicating that part of the association between gestational age and telomere length is explained by these three confounding factors.

CONCLUSION

Placental TL decreases during the third trimester of gestation of live-born twins with approximately 25% indicating that telomere shortening may play a role in aging of the placenta.

Unexplained antepartum stillbirth: a consequence of placental aging?

Unexplained antepartum stillbirth is a major obstetric health problem. Data demonstrate a rapid rise in risk per 1000 continuing pregnancies as gestation advances beyond 40 weeks. We review the evidence that such stillbirths are a consequence of aging related changes in the late gestation placenta. We suggest that the relatively small number of continuing pregnancies after 40 completed weeks means that negative effects of genes that produce aging affect so few pregnancies that polymorphisms in genes that produce these effects are retained in the population. Aging related changes likely represent a consequence of the damaging effects of oxidative stress, increased by cigarette smoking counteracted by the mitigating effects of oxidative defence pathways. The aging related changes are likely downstream from nutrient sensing units such as mTOR and include effects on production of telomerase and consequent shortening of telomere length. The late gestation changes occur in the context of increasing fetal growth and nutrient supply demands that can produce the rapid development of a mismatch between placental supply and fetal need resulting in fetal demise. Premature aging may also play an important role in antepartum stillbirth occurring earlier in pregnancy, especially in the context of growth restriction.

Maternal psychosocial stress during pregnancy is associated with newborn leukocyte telomere length

OBJECTIVE

In adults, one of the major determinants of leukocyte telomere length (LTL), a predictor of age-related diseases and mortality, is cumulative psychosocial stress exposure. More recently we reported that exposure to maternal psychosocial stress during intrauterine life is associated with LTL in young adulthood. The objective of the present study was to determine how early in life this effect of stress on LTL is apparent by quantifying the association of maternal psychosocial stress during pregnancy with newborn telomere length.

STUDY DESIGN

In a prospective study of N = 27 mother-newborn dyads maternal pregnancy-specific stress was assessed in early gestation and cord blood peripheral blood mononuclear cells were subsequently collected and analyzed for LTL measurement.

RESULTS

After accounting for the effects of potential determinants of newborn LTL (gestational age at birth, weight, sex, and exposure to antepartum obstetric complications), there was a significant, independent, linear effect of pregnancy-specific stress on newborn LTL that accounted for 25% of the variance in adjusted LTL (β = -0.099; P = .04).

CONCLUSION

Our finding provides the first preliminary evidence in human beings that maternal psychological stress during pregnancy may exert a "programming" effect on the developing telomere biology system that is already apparent at birth, as reflected by the setting of newborn LTL.

Telomeres and human reproduction

Telomeres mediate biologic aging in organisms as diverse as plants, yeast, and mammals. We propose a telomere theory of reproductive aging that posits telomere shortening in the female germ line as the primary driver of reproductive aging in women. Experimental shortening of telomeres in mice, which normally do not exhibit appreciable oocyte aging, and which have exceptionally long telomeres, recapitulates the aging phenotype of human oocytes. Telomere shortening in mice reduces synapsis and chiasmata, increases embryo fragmentation, cell cycle arrest, apoptosis, spindle dysmorphologies, and chromosome abnormalities. Telomeres are shorter in the oocytes from women undergoing in vitro fertilization, who then produce fragmented, aneuploid embryos that fail to implant. In contrast, the testes are replete with spermatogonia that can rejuvenate telomere reserves throughout the life of the man by expressing telomerase. Differences in telomere dynamics across the life span of men and women may have evolved because of the difference in the inherent risks of aging on reproduction between men and women. Additionally, growing evidence links altered telomere biology to endometriosis and gynecologic cancers, thus future studies should examine the role of telomeres in pathologies of the reproductive tract.

An intricate dance: Life experience, multisystem resiliency, and rate of telomere decline throughout the lifespan

Accumulation of life stressors predicts accelerated development and progression of diseases of aging. Telomere length, the DNA-based biomarker indicating cellular aging, is a mechanism of disease development, and is shortened in a dose response fashion by duration and severity of life stressor exposures. Telomere length captures the interplay between genetics, life experiences and psychosocial and behavioral factors. Over the past several years, psychological stress resilience, healthy lifestyle factors, and social connections have been associated with longer telomere length and it appears that these factors can protect individuals from stress-induced telomere shortening. In the current review, we highlight these findings, and illustrate that combining these `multisystem resiliency' factors may strengthen our understanding of aging, as these powerful factors are often neglected in studies of aging. In naturalistic studies, the effects of chronic stress exposure on biological pathways are rarely main effects, but rather a complex interplay between adversity and resiliency factors. We suggest that chronic stress effects can be best understood by directly testing if the deleterious effects of stress on biological aging processes, in this case the cell allostasis measure of telomere shortening, are mitigated in individuals with high levels of multisystem resiliency. Without attending to such interactions, stress effects are often masked and missed. Taking account of the cluster of positive buffering factors that operate across the lifespan will take us a step further in understanding healthy aging. While these ideas are applied to the telomere length literature for illustration, the concept of multisystem resiliency might apply to aging broadly, from cellular to systemic health.

Prenatal stress, telomere biology, and fetal programming of health and disease risk

A substantial body of epidemiological, clinical, cellular, and molecular evidence converges to suggest that conditions during the intrauterine period of life play a critical role in developmental programming to influence subsequent health and susceptibility for common, complex disorders. Elucidation of the biological mechanisms underlying these effects is an area of considerable interest and investigation, and it is important to determine whether these mechanisms are distinct for different health outcomes or whether there are some common underlying pathways that may account for the effects of disparate prenatal and early postnatal conditions on various health and disease risk phenotypes. We propose that telomere biology may represent a common underlying mechanism connecting fetal programming and subsequent health outcomes. It appears that the initial establishment of telomere length and regulation of telomere homeostasis may be plastic and receptive to the influence of intrauterine and other early life conditions. Moreover, telomere homeostasis in various cell types may serve as a fundamental integrator and regulator of processes underlying cell genomic integrity and function, aging, and senescence over the life span. We advance the hypothesis that context- and time-inappropriate exposures to various forms of physiological stress (maternal-placental-fetal endocrine aberrations and immune, inflammatory, and oxidative stresses) during the intrauterine period of development may alter or program the telomere biology system in a manner that accelerates cellular dysfunction, aging, and disease susceptibility over the life span.

Ectopic expression of human telomerase RNA component results in increased telomerase activity and elongated telomeres in bovine blastocysts

Telomeres play an important role in aging, and are critical for the regenerative capacity of mammalian cells. The holoenzyme telomerase rebuilds telomeres and is composed of two components, the catalytic protein telomerase reverse transcriptase (TERT) and the telomerase RNA (TERC). TERC is ubiquitously expressed in somatic cells and is thought to have no regulatory effects on telomerase activity. Transgenic expression of human TERT (hTERT) in bovine somatic and embryonic cells extends telomere length and enhances telomerase activity. To obtain further insight into the regulatory capacity of the two telomerase components, we have studied the ability of hTERC and hTERT to increase telomerase activity and telomere length in bovine embryos. Expression plasmids for the human RNA component (hTERC) and/or the catalytic subunit of human telomerase (hTERT), respectively, were injected into the cytoplasm of in vitro-produced bovine zygotes. Ectopic expression of hTERC increased telomerase activity and telomere length in bovine blastocysts. Coexpression of hTERT and hTERC did not result in further telomere elongation when compared to the hTERC group. These data indicate that TERC is one of the limiting factors of telomerase activity in bovine blastocysts, and further establish bovine preimplantation embryos as a useful model to modulate telomere length with impact for basic embryology and derivation of pluripotent cells.