Telomere Length and Preterm Birth in Pregnant Mexican-Origin Women

Accelerated epigenetic clock aging in maternal peripheral blood and preterm birth

BACKGROUND

Epigenetic clocks use CpG DNA methylation to estimate biological age. Acceleration is associated with cancer, heart disease, and shorter life span. Few studies evaluate DNA methylation age and pregnancy outcomes. AgeAccelGrim is a novel epigenetic clock that combines 7 DNA methylation components.

OBJECTIVE

This study aimed to determine whether maternal biological aging (via AgeAccelGrim) is associated with early preterm birth.

STUDY DESIGN

A prospective cohort of patients with singleton pregnancies and at high risk of spontaneous preterm birth delivering at a tertiary university hospital were included in this study. Genome-wide CpG methylation was measured using the Illumina EPIC BeadChip (Illumina, Inc, San Diego, CA) from maternal blood samples obtained at <28 weeks of gestation. AgeAccelGrim and its 7 DNA methylation components were estimated by the Horvath DNA methylation age online tool. Positive values are associated with accelerated biological aging, whereas negative values are associated with slower biological aging relative to each subject's age. The primary outcome was preterm birth at <34 weeks of gestation (any indication). The secondary outcomes were preterm birth at <37 and <28 weeks of gestation. AgeAccelGrim was analyzed as a continuous variable and in quartiles. Exploratory analyses evaluated each of the 7 DNA methylation components included in the composite AgeAccelGrim. Data were analyzed by chi-square test, t test, rank-sum test, logistic regression (controlling a priori for maternal age, cell counts, low socioeconomic status, and gestational age at the time of sample collection), and Kaplan-Meier survival analyses. The log-rank test was used to test the equality of the survival functions.

RESULTS

Overall, 163 patients met the inclusion criteria. Of the patients, 48%, 39%, and 21% delivered at <37, <34, and <28 weeks of gestation, respectively. The median AgeAccelGrim was -0.35 years (interquartile range, -2.24 to 1.31) for those delivering at term. Those delivering preterm had higher AgeAccelGrim values that were inversely proportional to delivery gestational age (preterm birth at <37 weeks of gestation: +0.40 years [interquartile range: -1.21 to +2.28]; preterm birth at <34 weeks of gestation: +0.51 years [interquartile range: -1.05 to +2.67]; preterm birth at <28 weeks of gestation: +1.05 years [interquartile range: -0.72 to +2.72]). Estimated DNA methylation of the 7 epigenetic clock component values was increased among those with preterm birth at <34 weeks of gestation, although the differences were only significant for DNA methylation of plasminogen activation inhibitor 1. In regression models, AgeAcccelGrim was associated with an elevated risk of preterm birth with increasing magnitude for increasing severity of preterm birth. For each 1-year increase in the AgeAccelGrim value (ie, each 1-year increase in biological age compared with chronologic age), the adjusted odds of preterm birth were 11% (adjusted odds ratio, 1.11; 95% confidence interval, 1.00-1.24), 13% (adjusted odds ratio, 1.13; 95% confidence interval, 1.01-1.26), and 18% (adjusted odds ratio, 1.18; 95% confidence interval, 1.04-1.35) higher for preterm birth at <37, <34, and <28 weeks of gestation, respectively. Similarly, individuals with accelerated biological aging (≥75th percentile AgeAccelGrim) had more than double the odds of preterm birth at <34 weeks of gestation (adjusted odds ratio, 2.36; 95% confidence interval, 1.10-5.08) and more than triple the odds of preterm birth at <28 weeks of gestation (adjusted odds ratio, 3.89; 95% confidence interval, 1.61-9.38). The adjusted odds ratio for preterm birth at <37 weeks of gestation was 1.73 but spanned the null (adjusted odds ratio, 1.73; 95% confidence interval, 0.81-3.69). In Kaplan-Meier survival analyses, those in the highest AgeAccelGrim quartile delivered the earliest (log-rank P value of <.001).

CONCLUSION

Accelerated biological aging was associated with preterm birth among high-risk patients. Future research confirming these findings and elucidating factors that slow biological aging may improve birth outcomes.

U-shaped relationship between ozone exposure and preterm birth risk associated with preconception telomere length

There are conflicting findings regarding the association of ozone (O3) exposure with preterm birth (PTB) occurrence. In the present study, two cohorts were combined to explore the relationship between maternal O3 exposure during pregnancy and PTB risk, and analyze the underlying mechanisms of this relationship in terms of alterations in the preconception telomere length. Cohort 1 included mothers who participated in the National Free Preconception Health Examination Project in Henan Province from 2014 to 2018 along with their newborns (n = 1,066,696). Cohort 2 comprised mothers who conceived between 2016 and 2018 and their newborns (n = 1871) from six areas in Henan Province. The telomere length was assessed in the peripheral blood of mothers at the preconception stage. Data on air pollutant concentrations were collected from environmental monitoring stations and individual exposures were assessed using an inverse distance-weighted model. O3 concentrations (100.60 ± 14.13 μg/m3) were lower in Cohort 1 than in Cohort 2 (114.09 ± 15.17 μg/m3). Linear analyses showed that PTB risk decreased with increasing O3 exposure concentrations in Cohort 1 but increased with increasing O3 exposure concentrations in Cohort 2. Nonlinear analyses revealed that PTB risk tended to decrease and then increase with increasing O3 exposure concentrations in both cohorts. Besides, PTB risk was reduced by 88% for each-unit increase in telomere length in those exposed to moderate O3 concentrations (92.4-123.7 μg/m3, P < 0.05). While no significant association was observed between telomere length and PTB at extreme O3 concentration exposure during entire pregnancy (<92.4 or >123.7 μg/m3, P > 0.05) in Cohort 2. These findings reveal a nonlinear (U-shaped) relationship between O3 exposure and PTB risk. Furthermore, telomere with elevated length was associated with decreased risk of PTB only when exposed to moderate concentrations of O3, but not when exposed to extreme concentrations of O3 during pregnancy.

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.

Genetic variants associated with spontaneous preterm birth in women from India: a prospective cohort study

Background

Despite having the highest number of preterm births globally, no genomic study on preterm birth was previously published from India or other South-Asian countries.

Methods

We conducted a genome-wide association (GWA) study of spontaneous preterm birth (sPTB) on 6211 women from India. We used a novel resampling procedure to identify the associated single nucleotide polymorphisms (SNPs) followed by haplotype association analysis and imputation.

Findings

We found that 512 maternal SNPs were associated with sPTB (p < 2.51e-3), of which minor allele at 19 SNPs (after Bonferroni correction) had increased genotype relative risk. Haplotypes containing six of the 19 SNPs (rs13011430, rs8179838, rs2327290, rs4798499, rs7629800, and rs13180906) were associated with sPTB (p < 9.9e-4; Bonferroni adjusted p-value <0.05). After imputation in regions around the 19 SNPs, 15 imputed SNPs were found to be associated with sPTB (Bonferroni adjusted p-value <0.05). One of these imputed SNPs, rs35760881, and three other SNPs (rs17307697, rs4308815, and rs10983507) were also reported to be associated with sPTB in women belonging to European ancestry. Moreover, we found that GG genotype at rs1152954, one of the associated SNPs, enhanced risk of sPTB and reduced telomere length.

Interpretation

This is the first study from South Asia on the genome-wide identification of maternal SNPs associated with sPTB. These SNPs are known to alter the expression of genes associated with major pathways in sPTB viz. inflammation, apoptosis, cervical ripening, telomere maintenance, selenocysteine biosynthesis, myometrial contraction, and innate immunity. From a public health perspective, the trans-ethnic association of four SNPs identified in our study may help to stratify women with risk of sPTB in most populations.

Funding

Department of Biotechnology (India), Grand Challenges India - All Children Thriving Program and Biotechnology Industry Research Assistance Council (BIRAC).

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.

Telomeres, oxidative stress, and timing for spontaneous term and preterm labor

Telomeres are nucleoprotein complexes located at the distal ends of chromosomes. In adults, progressive telomere shortening occurs throughout the lifetime and is thought to contribute to progressive aging, physiological senescence, multiorgan dysfunction, and ultimately, death. As discussed in this review, multiple lines of evidence provide support for the biological plausibility that a telomere-based clock mechanism also determines the length of gestation, leading to the onset of labor (parturition). After telomere expansion at the beginning of pregnancy, the telomere lengths in the gestational tissues (ie, the placenta and fetal membranes) progressively shorten throughout the remainder of pregnancy. The rate of telomere shortening can be accelerated by conditions that affect the mother and result in oxidative stress. Preterm births in the United States are associated with multiple risk factors that are linked with increased oxidative stress. Antioxidant vitamins (ie, vitamins E and C) mitigate the effects of oxidative stress and delay or prevent telomere shortening. Clinical trials with vitamins E and C and with multivitamins started during the periconception period have been associated with reduced rates of preterm births. In the United States, African-American women have a 2-3-fold higher rate of preterm birth. African-American women have multiple risk factors for premature birth, all of which are distinct and potentially additive with regard to epigenetic telomere shortening. The "weathering effect" is the hypothesis to explain the increased rates of chronic illness, disabilities, and early death observed in African-Americans. With regard to pregnancy, accelerated weathering with the associated telomere shortening in the gestational tissues would not only explain the preterm birth disparity but could also explain why highly educated, affluent African-American women continue to have an increased rate of preterm birth. These studies suggest that the racial disparities in preterm birth are potentially mediated by telomere shortening produced by lifetime or even generational exposure to the effects of systemic racism and socioeconomic marginalization. In conclusion, this review presents multiple lines of evidence supporting a novel hypothesis regarding the biological clock mechanism that determines the length of pregnancy, and it opens the possibility of new approaches to prevent or reduce the rate of spontaneous preterm birth.