Very preterm birth is associated with PLAGL1 gene hypomethylation at birth and discharge

Scoping Review of Early Toxic Stress and Epigenetic Alterations in the Neonatal Intensive Care Unit

BACKGROUND

Preterm infants are uniquely vulnerable to early toxic stress exposure while in the neonatal intensive care unit (NICU) and also being at risk for suboptimal neurodevelopmental outcomes. However, the complex biological mechanisms responsible for variations in preterm infants' neurodevelopmental outcomes because of early toxic stress exposure in the NICU remain unknown. Innovative preterm behavioral epigenetics research offers a possible mechanism and describes how early toxic stress exposure may lead to epigenetic alterations, potentially affecting short- and long-term outcomes.

OBJECTIVE

The aim of this study was to review the relationships between early toxic stress exposures in the NICU and epigenetic alterations in preterm infants. The measurement of early toxic stress exposure in the NICU and effect of epigenetic alterations on neurodevelopmental outcomes in preterm infants were also examined.

METHODS

We conducted a scoping review of the literature published between January 2011 and December 2021 using databases PubMed, CINAHL, Cochrance Library, PsycINFO, and Web of Science. Primary data-based research that examined epigenetics, stress, and preterm infants or NICU were included.

RESULTS

A total of 13 articles from nine studies were included. DNA methylations of six specific genes were studied in relation to early toxic stress exposure in the NICU: SLC6A4, SLC6A3, OPRMI, NR3C1, HSD11B2, and PLAGL1. These genes are responsible for regulating serotonin, dopamine, and cortisol. Poorer neurodevelopmental outcomes were associated with alterations in DNA methylation of SLC6A4, NR3C1, and HSD11B2. Measurements of early toxic stress exposure in the NICU were inconsistent among the studies.

DISCUSSION

Epigenetic alterations secondary to early toxic stress exposures in the NICU may be associated with future neurodevelopmental outcomes in preterm infants. Common data elements of toxic stress exposure in preterm infants are needed. Identification of the epigenome and mechanisms by which early toxic stress exposure leads to epigenetic alterations in this vulnerable population will provide evidence to design and test individualized intervention.

Causes of preterm birth: Genetic factors in preterm birth and preterm infant phenotypes

AIM

The aim is to provide an overview of recent research on genetic factors that influence preterm birth in the context of neonatal phenotypic assessment.

METHODS

This is a nonsystematic review of the recent scientific literature.

RESULTS

Maternal and fetal genetic diversity and rare genome variants are linked with crucial immune response sites. In addition, more frequent in preterm neonates, de novo variants may lead to attention deficits, hyperactivity, autism spectrum disorders, and infertility of both sexes later in life. Environmental factors may also greatly burden fetal, and consequently, neonatal development and neurodevelopment through a failure in the fetal epigenome reprogramming process and even influence the initiation of spontaneous preterm pregnancy termination. Minimally invasive analysis of the transcription factors associated with preterm birth helps elucidate labor mechanisms and predict its timing. We also provide valuable summaries of genomic and transcriptomic factors that contribute to preterm birth.

CONCLUSIONS

Investigation of the human genome, epigenome, and transcriptome helps to identify molecular mechanisms linked with preterm delivery and premature newborn clinical appearance in early and late neonatal life and even predict developmental outcomes. Further studies are needed to fully understand the implications of genetic changes in preterm births. These data could be used to develop targeted interventions aimed at selecting the most effective individual treatment and rehabilitation plan.

NR3C1 gene methylation and cortisol levels in preterm and healthy full-term infants in the first 3 months of life

Aim: To describe NR3C1 exon-1F methylation and cortisol levels in newborns. Materials & methods: Preterm ≤1500 g and full-term infants were included. Samples were collected at birth and at days 5, 30 and 90 (or at discharge). Results: 46 preterm and 49 full-term infants were included. Methylation was stable over time in full-term infants (p = 0.3116) but decreased in preterm infants (p = 0.0241). Preterm infants had higher cortisol levels on the fifth day, while full-term infants showed increasing levels (p = 0.0177) over time. Conclusion: Hypermethylated sites in NR3C1 at birth and higher cortisol levels on day 5 suggest that prematurity, reflecting prenatal stress, affects the epigenome. Methylation decrease over time in preterm infants suggests that postnatal factors may modify the epigenome, but their role needs to be clarified.

Clomifene and Assisted Reproductive Technology in Humans Are Associated with Sex-Specific Offspring Epigenetic Alterations in Imprinted Control Regions

Children conceived with assisted reproductive technology (ART) have an increased risk of adverse outcomes, including congenital malformations and imprinted gene disorders. In a retrospective North Carolina-based-birth-cohort, we examined the effect of ovulation drugs and ART on CpG methylation in differentially methylated CpGs in known imprint control regions (ICRs). Nine ICRs containing 48 CpGs were assessed for methylation status by pyrosequencing in mixed leukocytes from cord blood. After restricting to non-smoking, college-educated participants who agreed to follow-up, ART-exposed (n = 27), clomifene-only-exposed (n = 22), and non-exposed (n = 516) groups were defined. Associations of clomifene and ART with ICR CpG methylation were assessed with linear regression and stratifying by offspring sex. In males, ART was associated with hypomethylation of the PEG3 ICR [β(95% CI) = -1.46 (-2.81, -0.12)] and hypermethylation of the MEG3 ICR [3.71 (0.01, 7.40)]; clomifene-only was associated with hypomethylation of the NNAT ICR [-5.25 (-10.12, -0.38)]. In female offspring, ART was associated with hypomethylation of the IGF2 ICR [-3.67 (-6.79, -0.55)]. Aberrant methylation of these ICRs has been associated with cardiovascular disease and metabolic and behavioral outcomes in children. The results suggest that the increased risk of adverse outcomes in offspring conceived through ART may be due in part to altered methylation of ICRs. Larger studies utilizing epigenome-wide interrogation are warranted.

Racial and ethnic representation in epigenomic studies of preterm birth: a systematic review

Aim: We conducted a systematic review evaluating race/ethnicity representation in DNA methylomic studies of preterm birth. Data sources: PubMed, EMBASE, CINHAL, Scopus and relevant citations from 1 January 2000 to 30 June 2019. Study appraisal & synthesis methods: Two authors independently identified abstracts comparing DNA methylomic differences between term and preterm births that included race/ethnicity data. Results: 16 studies were included. Black and non-Hispanic Black deliveries were well represented (28%). However, large studies originating from more than 95% White populations were excluded due to unreported race/ethnicity data. Most studies were cross-sectional, allowing for reverse causation. Most studies were also racially/ethnically homogeneous, preventing direct comparison of DNA methylomic differences across race/ethnicities. Conclusion: In DNA methylomic studies, Black women and infants were well represented. However, the literature has limitations and precludes drawing definitive conclusions.

Epigenetic biomarkers and preterm birth

Preterm birth (PTB) is a major public health challenge, and novel, sensitive approaches to predict PTB are still evolving. Epigenomic markers are being explored as biomarkers of PTB because of their molecular stability compared to gene expression. This approach is also relatively new compared to gene-based diagnostics, which relies on mutations or single nucleotide polymorphisms. The fundamental principle of epigenome diagnostics is that epigenetic reprogramming in the target tissue (e.g. placental tissue) might be captured by more accessible surrogate tissue (e.g. blood) using biochemical epigenome assays on circulating DNA that incorporate methylation, histone modifications, nucleosome positioning, and/or chromatin accessibility. Epigenomic-based biomarkers may hold great potential for early identification of the majority of PTBs that are not associated with genetic variants or mutations. In this review, we discuss recent advances made in the development of epigenome assays focusing on its potential exploration for association and prediction of PTB. We also summarize population-level cohort studies conducted in the USA and globally that provide opportunities for genetic and epigenetic marker development for PTB. In addition, we summarize publicly available epigenome resources and published PTB studies. We particularly focus on ongoing genome-wide DNA methylation and epigenome-wide association studies. Finally, we review the limitations of current research, the importance of establishing a comprehensive biobank, and possible directions for future studies in identifying effective epigenome biomarkers to enhance health outcomes for pregnant women at risk of PTB and their infants.