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Snapshot Science: Does In Utero BPA Exposure Affect Genes Related to Development of Diabetes and Obesity in Amniocytes?
Using samples from a unique repository of human amniocytes exposed to bisphenol A (BPA) in utero, collaborators from Children’s Hospital of Philadelphia and the University of Pennsylvania performed sex-specific analyses to identify gene expression changes in pathways associated with diabetes and obesity, such as fatty liver disease and type 2 diabetes, and novel differentially methylated regions (DMRs) with potential distal regulatory functions. Additionally, the team found that amniotic fluid BPA concentrations in the second trimester of pregnancy was associated with change in gene expression for genes important to the development obesity and diabetes, with the largest changes seen in male amniocytes.
Researchers found 101 genes with altered expression in male amniocytes exposed to BPA in utero with enrichment of pathways critical to hepatic dysfunction, collagen signaling, and adipogenesis. They identified 36 DMRs in male BPA-exposed amniocytes and 14 in female amniocyte analysis. Surprisingly, most of the DMRs were not linked with changes in gene expression at the nearest gene. Using in silico Hi-C analysis, a tool to investigate 3D chromatin interactions, researchers identified interactions between DMRs and 24 distal genes with significant expression changes in male amniocytes and 12 genes with significant changes in expression in female amniocytes.
Why it matters:
Sara Pinney, MD, MS, senior author and physician-scientist in CHOP’s Division of Endocrinology and Diabetes, noted that any exposure that disrupts epigenetic reprogramming during development could potentially affect the individual’s health status decades later. In studies with animal models, exposure to BPA in utero during critical periods of fetal development is linked to alterations in deoxyribonucleic acid (DNA) methylation and the later onset of obesity and diabetes, but the molecular mechanisms driving these phenomena are not known. A comprehensive understanding of how an adverse intrauterine environment could lead to a disruption in epigenetic mechanisms and disease later in life in humans is necessary for the development of preventive strategies or treatments.
Who conducted the study:
The study team included first author Amita Bansal, PhD, former post-doctoral fellow at the Penn Center of Excellence in Environmental Toxicology and Center for Research on Reproduction, and current faculty member at Australian National University; senior author Dr. Pinney, assistant professor of Pediatrics at Perelman School of Medicine at the University of Pennsylvania and attending physician in the Division of Endocrinology and Diabetes at CHOP; Aporva Joshi, research technician in the Division of Endocrinology and Diabetes at CHOP; and investigators from the Penn Center of Excellence in Environmental Toxicology, Center for Research on Reproduction and Women’s Health, Epigenetics Program, and Bioinformatics Core.
How they did it:
The study team obtained amniocytes, a human fetal stem cell, collected at gestational ages 16 to 18 weeks from women who underwent clinically indicated amniocentesis between 2002 and 2006. The amniocytes studied were from women who had healthy singleton full term pregnancies. The scientists used a nested case-control study design matching for maternal age, gestational age at amniocentesis, gestational age at birth, and distribution of offspring sex.
BPA amniotic fluid concentrations reported in a prior study determined BPA exposure. Researchers performed gene expression analysis with RNA sequencing, confirmation studies with QPCR analysis, and used enhanced reduced representation bisulfite sequencing (ERRBS) to determine significant changes in DNA methylation. Investigators identified DMRs based on weighted Welch expansion using the DEFIANT (DMRs: easy, fast, identification and annotation) program and determined potential distal gene interactions via in silico Hi-C analysis based on data generated from human embryonic stem cells.
Novel aspects of this study include the use of amniocytes as human stem cells to profile novel changes in the transcriptome and methylome after in utero BPA exposure, which may begin explain how in utero BPA exposure leads to the development of diabetes and obesity in later life; the sex-specific analyses, made possible based on the nested case control study design, identified a greater number of genes with significant changes in gene expression in male amniocytes compared to females; and the use of in silico Hi-C analysis to demonstrate how DMRs may interact with distal genes through 3D chromatin looping.
“Changes in DNA methylation, which can impact gene expression, may also be an important marker of in utero environmental exposure affecting fetal development,” Dr. Pinney said.
While the underlying message is for humans to reduce their exposure to environmental chemicals including BPA, this can be extremely difficult for an individual since exposure to BPA is ubiquitous. “The real message is a public health message that, as a community and society, we need to work on decreasing these environmental exposures, especially based on our findings and others suggesting that exposures during gestation may affect health status much later in life,” Dr. Pinney said.
Where the study was published:
The study appears in the February 2020 issue of The Journal of Clinical Endocrinology and Metabolism.
Where to learn more:
Find out more about Dr. Pinney’s study in the CHOP press release.