Preconception leukocyte telomere length and pregnancy outcomes among women with demonstrated fecundity

Telomere length and telomerase activity in men and non-pregnant women with and without metabolic syndrome: a systematic review and bootstrapped meta-analysis

Purpose

We performed a systematic review and meta-analysis to examine the associations between telomere length and telomerase activity in subjects with and without metabolic syndrome (MetS).

Methods

The meta-analysis protocol was registered in the PROSPERO database. The PubMed, Embase, Cochrane Library, and LILACS databases were searched for studies reporting telomere length or telomerase activity in adult men and non-pregnant women with and without MetS. The risk of bias was assessed with the Newcastle-Ottawa Scale. Random effects and inverse variance methods were used to meta-analyze associations. We conducted a bootstrapped analysis to test the accuracy of clinical results.

Results

Five studies reported telomere length and two studies telomerase activity. There was no significant difference in telomere length (standardized mean difference [SMD]: 0.10, 95% confidence interval [CI]: -0.07, 0.28, I 2: 54%), between subjects of similar age (mean difference: 2.68, 95%CI: -0.04, 5.40 years) with and without the MetS. Subjects with MetS displayed significantly higher body mass index, triglycerides, and blood pressure, and lower HDL-cholesterol values than subjects without the syndrome. A bootstrapping mediation analysis of telomere length confirmed the clinical results. There was no significant difference in telomerase activity (SMD: 1.19, 95% CI -0.17, 2.55, I 2: 93%) between subjects with and without the MetS.

Conclusion

There were no significant differences of telomere length and telomerase activity in patients with MetS and subjects of similar age without the syndrome.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40200-024-01513-4.

Univariable and multivariable Mendelian randomization investigating the effects of telomere length on the risk of adverse pregnancy outcomes

Background

Numerous observational studies have revealed a correlation between telomere length (TL) and adverse pregnancy outcomes (APOs). However, the impacts of TL on APOs are still unclear.

Methods

Mendelian randomization (MR) was carried out using summary data from genome-wide association studies (GWAS). Inverse variance weighted (IVW) was employed as the primary analysis to explore the causal relationship between TL and APOs. The exposure data came from a GWAS dataset of IEU analysis of the United Kingdom Biobank phenotypes consisting of 472,174 European participants. Summary-level data for five APOs were obtained from the GWAS datasets of the FinnGen consortium. We also performed multivariate MR (MVMR), adjusting for smoking, alcohol intake, body mass index (BMI), and number of live births. In addition, we conducted a series of rigorous analyses to further examine the validity of our MR findings.

Results

After Bonferroni correction and rigorous quality control, univariable MR (UVMR) demonstrated that a shorter TL was significantly associated with an increased risk of spontaneous abortion (SA) (odds ratio [OR]: 0.815; 95% confidence interval [CI]: 0.714-0.930; P = 0.002) and preterm birth (PTB) (OR: 0.758; 95% CI: 0.632-0.908; P = 0.003) in the IVW model. There was a nominally significant relationship between TL and preeclampsia (PE) in the IVW model (OR: 0.799; 95% CI: 0.651-0.979; P = 0.031). However, no significant association was found between TL and gestational diabetes mellitus (GDM) (OR: 0.950; 95% CI: 0.804-1.122; P = 0.543) or fetal growth restriction (FGR) (OR: 1.187; 95% CI: 0.901-1.565; P = 0.223) among the five statistical models. Furthermore, we did not find a significant causal effect of APOs on TL in the reverse MR analysis. MVMR analysis showed that the causal effects of TL on SA remained significant after accounting for smoking, alcohol intake, BMI, and number of live births.

Conclusion

Our MR study provides robust evidence that shorter telomeres were associated with an increased risk of SA. Further work is necessary to investigate the potential mechanisms. UVMR and MVMR findings showed limited evidence that TL affects the risk of PTB, PE, GDM, and FGR, illustrating that the outcomes of previous observational studies may have been confounded.

Potential effects of assisted reproductive technology on telomere length and telomerase activity in human oocytes and early embryos

Telomeres are repetitive DNA sequences at eukaryotic chromosome ends and function in maintaining genome integrity and stability. These unique structures undergo shortening due to various factors including biological aging, consecutive DNA replication, oxidative stress, and genotoxic agents. Shortened telomeres can be lengthened by the enzyme telomerase and alternative lengthening of telomeres in germ cells, early embryos, stem cells, and activated lymphocytes. If telomeres reach to critical length, it may lead to genomic instability, chromosome segregation defects, aneuploidy, and apoptosis. These phenotypes also occur in the oocytes and early embryos, produced using assisted reproductive technologies (ARTs). Thus, a number of studies have examined the potential effects of ART applications such as ovarian stimulation, culture conditions, and cryopreservation procedures on telomeres. Herein, we comprehensively reviewed impacts of these applications on telomere length and telomerase activity in ART-derived oocytes and embryos. Further, we discussed use of these parameters in ART centers as a biomarker in determining oocyte and embryo quality.

Identifying effects of genetic obesity exposure on leukocyte telomere length using Mendelian randomization

Background

Observational studies have shown that obesity is closely associated with leukocyte telomere length (LTL). However, the causal relationship between obesity and LTL remains unclear. This study investigated the causal relationship between obesity and LTL through the Mendelian randomization approach.

Materials and Methods

The genome-wide association study (GWAS) summary data of several studies on obesity-related traits with a sample size of more than 600,000 individuals were extracted from the UK Biobank cohort. The summary-level data of LTL-related GWAS (45 6,717 individuals) was obtained from the IEU Open GWAS database. An inverse-variance-weighted (IVW) algorithm was utilized as the primary MR analysis method. Sensitivity analyses were conducted via MR-Egger regression, IVW regression, leave-one-out test, MR-pleiotropy residual sum, and outlier methods.

Results

High body mass index was correlated with a short LTL, and the odds ratio (OR) was 0.957 (95% confidence interval [CI] 0.942-0.973, p = 1.17E-07). The six body fat indexes (whole body fat mass, right leg fat mass, left leg fat mass, right arm fat mass, left arm fat mass, and trunk fat mass) were consistently inversely associated with LTL. Multiple statistical sensitive analysis approaches showed that the adverse effect of obesity on LTL was steady and dependable.

Conclusion

The current study provided robust evidence supporting the causal assumption that genetically caused obesity is negatively associated with LTL. The findings may facilitate the formulation of persistent strategies for maintaining LTL.

OXIDATIVE STRESS AND REPRODUCTIVE FUNCTION: Sperm telomeres, oxidative stress, and infertility

In brief

Oxidative stress is recognized as an underlying driving factor of both telomere dysfunction and human subfertility/infertility. This review briefly reassesses telomere integrity as a fertility biomarker before proposing a novel, mechanistic rationale for the role of oxidative stress in the seemingly paradoxical lengthening of sperm telomeres with aging.

Abstract

The maintenance of redox balance in the male reproductive tract is critical to sperm health and function. Physiological levels of reactive oxygen species (ROS) promote sperm capacitation, while excess ROS exposure, or depleted antioxidant defenses, yields a state of oxidative stress which disrupts their fertilizing capacity and DNA structural integrity. The guanine moiety is the most readily oxidized of the four DNA bases and gets converted to the mutagenic lesion 8-hydroxy-deoxyguanosine (8-OHdG). Numerous studies have also confirmed oxidative stress as a driving factor behind accelerated telomere shortening and dysfunction. Although a clear consensus has not been reached, clinical studies also appear to associate telomere integrity with fertility outcomes in the assisted reproductive technology setting. Intriguingly, while sperm cellular and molecular characteristics make them more susceptible to oxidative insult than any other cell type, they are also the only cell type in which telomere lengthening accompanies aging. This article focuses on the oxidative stress response pathways to propose a mechanism for the explanation of this apparent paradox.

Telomeres, aging and reproduction

PURPOSE OF REVIEW

Women's fertility decay starts at the mid 30 s. However, the current delay of childbearing leads to ovarian aging and the need of assisted reproduction technologies (ART). Telomere biology is one of the main pathways involved in organismal aging. Thus, this review will focus on the knowledge acquired during the last 2 years about the telomere pathway and its influence on female fertility and the consequences for the newborn.

RECENT FINDINGS

New research on telomere biology reaffirms the relationship of telomere attrition and female infertility. Shorter maternal telomeres, which could be aggravated by external factors, underly premature ovarian aging and other complications including preeclampsia, preterm birth and idiopathic pregnancy loss. Finally, the telomere length of the fetus or the newborn is also affected by external factors, such as stress and nutrition.

SUMMARY

Recent evidence shows that telomeres are implicated in most processes related to female fertility, embryo development and the newborn's health. Thus, telomere length and telomerase activity may be good biomarkers for early detection of ovarian and pregnancy failures, opening the possibility to use telomere therapies to try to solve the infertility situation.