Geographic ancestry and markers of preterm birth

Inflammatory factors, genetic variants, and predisposition for preterm birth

Preterm birth is a major clinical and public health challenge, with a prevalence of 11% worldwide. It is the leading cause of death in children younger than 5 years old and represents 70% of neonatal deaths and 75% of neonatal morbidity. Despite the clinical and public health significance, this condition's etiology is still unclear, and most of the cases are spontaneous. There are several known preterm birth risk factors, including inflammatory diseases and the genetic background, although the underlying molecular mechanisms are far from understood. The present review highlights the research advances on the association between inflammatory-related genes and the increased risk for preterm delivery. The most associated genetic variants are the TNFα rs1800629, the IL1α rs17561, and the IL1RN rs2234663. Moreover, many of the genes discussed in this review are also implicated in pathologies involving inflammatory or autoimmune systems, such as periodontal disease, bowel inflammatory disease, and autoimmune rheumatic diseases. This review presents evidence suggesting a common genetic background to preterm birth, autoimmune and inflammatory diseases susceptibility.

Concepts in preterm birth research: Interview with a stakeholder

Preterm birth continues to be a clinical problem of vast significance all over the world [1,2]. The complexities of the biology of preterm birth suggest a syndrome with multiple factors that synchronize rupture of membranes, uterine contraction, cervical dilation, and labor. Multiple genetic, environmental, and basic biological factors are associated with preterm birth. Despite many years of effort, we still do not completely understand preterm birth, the basic mechanisms underlying parturition, or the relationship(s) between the two. My position has always been that breakthroughs in this area will come from an inclusive, integrative, and interdisciplinary approach that hears the voices of multiple stakeholders, encompasses "outside the box" thinking and utilizes novel methodologies. To document the voices of stakeholders, alternative thinking and the seeds of development of novel methodologies, I have begun to interview stakeholders in preterm birth. This is an interview with Ramkumar Menon, MS, PhD, Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine & Perinatal Research, The University of Texas Medical Branch at Galveston. Dr. Menon is past president and current Executive Director of PREBIC Global. He has surmounted considerable challenges to not only produce outstanding science from his own laboratory, but also to bring together collaborators and support from all over the world to bear upon the problem of preterm birth. What follows is an interview I did with him in 2014.

Oxidative stress damage-associated molecular signaling pathways differentiate spontaneous preterm birth and preterm premature rupture of the membranes

STUDY HYPOTHESIS

In women with preterm premature rupture of the membranes (PPROM), increased oxidative stress may accelerate premature cellular senescence, senescence-associated inflammation and proteolysis, which may predispose them to rupture.

STUDY FINDING

We demonstrate mechanistic differences between preterm birth (PTB) and PPROM by revealing differences in fetal membrane redox status, oxidative stress-induced damage, distinct signaling pathways and senescence activation.

WHAT IS KNOWN ALREADY

Oxidative stress-associated fetal membrane damage and cell cycle arrest determine adverse pregnancy outcomes, such as spontaneous PTB and PPROM.

STUDY DESIGN, SAMPLES/MATERIALS, METHODS

Fetal membranes and amniotic fluid samples were collected from women with PTB and PPROM. Molecular, biochemical and histologic markers were used to document differences in oxidative stress and antioxidant enzyme status, DNA damage, secondary signaling activation by Ras-GTPase and mitogen-activated protein kinases, and activation of senescence between membranes from the two groups.

MAIN RESULTS AND THE ROLE OF CHANCE

Oxidative stress was higher and antioxidant enzymes were lower in PPROM compared with PTB. PTB membranes had minimal DNA damage and showed activation of Ras-GTPase and ERK/JNK signaling pathway with minimal signs of senescence. PPROM had higher numbers of cells with DNA damage, prosenescence stress kinase (p38 MAPK) activation and signs of senescence.

LIMITATIONS, REASONS FOR CAUTION

Samples were obtained retrospectively after delivery. The markers of senescence that we tested are specific but are not sufficient to confirm senescence as the pathology in PPROM.

WIDER IMPLICATIONS OF THE FINDINGS

Oxidative stress-induced DNA damage and senescence are characteristics of fetal membranes from PPROM, compared with PTB with intact membranes. PTB and PPROM arise from distinct pathophysiologic pathways. Oxidative stress and oxidative stress-induced cellular damages are likely determinants of the mechanistic signaling pathways and phenotypic outcome.

STUDY FUNDING AND COMPETING INTERESTS

This study is supported by developmental funds to Dr R. Menon from the Department of Obstetrics and Gynecology at The University of Texas Medical Branch at Galveston and funds to Dr M. Kacerovský from the Ministry of Health Czech Republic (UHHK, 001799906). The authors report no conflict of interest.

Genetics and preterm birth

Although the etiology of preterm birth is incompletely understood, phenotype classifications combined with recent technologies such as genome-wide association studies and next-generation sequencing could lead to discovering genotypes associated with preterm birth. Identifying genetic contributions will allow for genetic screening tests to predict or detect pregnancies with potential for preterm birth. In this article we discuss current knowledge regarding phenotype classifications, genotypes, and their associations with preterm birth.

The PhenX Toolkit pregnancy and birth collections

PURPOSE

Pregnancy and childbirth are normal conditions, but complications and adverse outcomes are common. Both genetic and environmental factors influence the course of pregnancy. Genetic epidemiologic research into pregnancy outcomes could be strengthened by the use of common measures, which would allow data from different studies to be combined or compared. Here, we introduce perinatal researchers to the PhenX Toolkit and the Collections related to pregnancy and childbirth.

METHODS

The Pregnancy and Birth Collections were drawn from measures in the PhenX Tooklit. The lead author selected a list of measures for each Collection, which was reviewed by the remaining authors and revised on the basis of their comments. We chose the measures we thought were most relevant for perinatal research and had been linked most strongly to perinatal outcomes.

RESULTS

The Pregnancy and Birth Health Conditions Collection includes 24 measures related to pregnancy and fertility history, maternal complications, and infant complications. The Pregnancy and Birth Outcome Risk Factors Collection includes 43 measures of chemical, medical, psychosocial, and personal factors associated with pregnancy outcomes.

CONCLUSIONS

The biological complexity of pregnancy and its sensitivity to environmental and genomic influences suggest that multidisciplinary approaches are needed to generate new insights or practical interventions. To fully exploit new research methods and resources, we encourage the biomedical research community to adopt standard measures to facilitate pooled or meta-analyses.

DNA methylation: an epigenetic risk factor in preterm birth

Spontaneous preterm birth (PTB; birth prior to 37 weeks of gestation) is a complex phenotype with multiple risk factors that complicate our understanding of its etiology. A number of recent studies have supported the hypothesis that epigenetic modifications such as DNA methylation induced by pregnancy-related risk factors may influence the risk of PTB or result in changes that predispose a neonate to adult-onset diseases. The critical role of timing of gene expression in the etiology of PTB makes it a highly relevant disorder in which to examine the potential role of epigenetic changes. Because changes in DNA methylation patterns can result in long-term consequences, it is of critical interest to identify the epigenetic patterns associated with adverse pregnancy outcomes. This review examines the potential role of DNA methylation as a risk factor for PTB and discusses several issues and limitations that should be considered when planning DNA methylation studies.

An overview of racial disparities in preterm birth rates: caused by infection or inflammatory response?

Infection has been hypothesized to be one of the factors associated with spontaneous preterm birth (PTB) and with the racial disparity in rates of PTB between African American and Caucasian women. However, recent findings refute the generalizability of the role of infection and inflammation. African Americans have an increased incidence of PTB in the setting of intraamniotic infection, periodontal disease, and bacterial vaginosis compared to Caucasians. Herein we report variability in infection- and inflammation-related factors based on race/ethnicity. For African American women, an imbalance in the host proinflammatory response seems to contribute to infection-associated PTB, as evidenced by a greater presence of inflammatory mediators with limited or reduced presence of immune balancing factors. This may be attributed to differences in the genetic variants associated with PTB between African Americans and Caucasians. We argue that infection may not be a cause of racial disparity but in association with other risk factors such as stress, nutritional deficiency, and differences in genetic variations in PTB, pathways and their complex interactions may produce differential inflammatory responses that may contribute to racial disparity.

Interaction between interleukin-1 receptor 2 and Toll-like receptor 4, and cervical cytokines

The objective was to assess the impact of genetic variation on cervical cytokine concentrations of interleukin (IL)-1α, IL-1β, IL-6, IL-8 and tumor necrosis factor alpha (TNF-α), and first, to determine if these variants interact with polymorphisms in Toll-like receptor 4 (TLR4) that were previously shown to associate with pro-inflammatory cervical cytokine concentrations, and second, to determine if findings are affected by bacterial vaginosis (BV). We examined 183 single nucleotide polymorphisms (SNPs) in 13 cytokine genes and receptors for associations with cervical cytokine levels in 188 African American and European American women. We tested for associations of gene-gene interactions between SNPs in TLR4 and cytokine gene and receptor polymorphisms with cervical pro-inflammatory cytokines. None of the single locus associations were significant after correction for multiple testing in either European Americans or African Americans. However, there were significant gene-gene interactions between IL-1R2 rs485127 and two SNPs in TLR4 (rs1554973 and rs7856729) with IL-1β after correction for multiple testing. Our study demonstrates that interactions between TLR4 and IL-1R2 are associated with cervical pro-inflammatory cytokine concentrations. These results provide important insights into the possible regulatory mechanisms of the inflammatory response in the presence and absence of microbial disorders such as BV. Additionally, the observed differences in allele frequencies between African Americans and those of European descent may partially explain population disparity in pregnancy-related phenotypes that are cytokine concentration-dependent.