CHOP researchers find chemical’s impact on metabolic genes most pronounced in male offspring
Previous research has linked exposure to bisphenol A (BPA) in the womb with higher rates of obesity and diabetes later in life, but the biological mechanisms driving those changes have largely remained a mystery. In a new study, researchers at Children’s Hospital of Philadelphia (CHOP) and the Center for Excellence in Environmental Toxicology (CEET) at the University of Pennsylvania (Penn) have for the first time identified changes in gene expression associated with BPA exposure in utero and have found those effects are most pronounced in cells from male offspring.
The study was published in the February 2020 issue of The Journal of Clinical Endocrinology and Metabolism.
“These changes provide insight into possible mechanisms responsible for the onset of metabolic disease including diabetes, obesity, fatty liver disease, and thyroid disease later in life,” said Sara Pinney, M.D., M.S., a physician scientist in CHOP’s Division of Endocrinology and Diabetes and Penn’s CEET. “The results add to the body of existing evidence identifying a strong association between developmental BPA exposure with later metabolic dysfunction.”
BPA, a synthetic chemical commonly used in plastics manufacturing, is ubiquitous in the food supply and environment and can be both ingested and absorbed through the skin. Human and animal studies have linked the chemical to a variety of health effects, including reproductive and metabolic abnormalities.
To drill down on the molecular mechanisms driving those changes, Pinney and her team looked at human amniocyte cells, which are human fetal stem cells, collected from pregnant women who underwent amniocentesis during their second-trimester of pregnancy. As stem cells, amniocytes have unique properties that make them a rich resource for studies on gestational exposures. The amniocytes were collected between 2002 and 2006, a time period when amniocentesis was a fairly common procedure in pregnant women over 35 years of age to look for fetal chromosomal abnormalities.
In a prior study, the researchers measured BPA concentration in the amniotic fluid and therefore could identify samples that had been exposed to BPA during gestation. In the amniocytes exposed to BPA in utero, researchers performed RNA sequencing to determine if BPA exposure lead to significant changes in gene expression.
In male cells, the team found 101 genes whose expression had been altered. In female cells researchers found only one gene with altered expression. When analyzed, the genes with significant changes in expression were key members of metabolic pathways associated with fatty liver disease, type 2 diabetes, and fat tissue development, among others.
The team also analyzed the DNA of the amniocytes for changes in methylation, which is essentially an on/off switch for gene expression, depending on whether a gene has a methyl group attached (“off”) or not (“on”). In both male and female amniocytes that had been exposed to BPA, the researchers found changes in methylation patterns in specific regions within the genome. As in the gene expression analysis, Pinney and her team found that the sex of the offspring had a large effect on the number of differentially methylated regions.
Taking the research a step further, the team then sought to identify whether changes in DNA methylation in the BPA-exposed amniocytes affected gene expression. In their initial analysis, researchers did not find a strong relationship between changes in DNA methylation and expression of the nearest gene. However, recent advances in the field suggest that due to the 3D structure of DNA, regions of DNA that are otherwise far apart might come close together and interact in 3D space. Therefore, the researchers plugged the differentially methylated regions into an existing 3D model of DNA interactions.
What they found surprised them: whereas many of the differentially methylated regions were far from metabolic genes in a linear sequence of the genome, in 3D space, those regions were in close proximity. So although DNA methylation changes didn’t always correlate with the expression levels of the nearest gene, the loops of DNA in 3D space put those regions close to otherwise far-away genes and may have affected their expression.
“Using powerful genome-wide techniques, we were able to identify novel changes in human amniocytes associated with gestational BPA exposure,” Pinney said. “Given the sex-specific effects we observed, it will be very important to take the biological sex of the offspring into account in future research when trying to understand the impacts of environmental exposures.”
The research was supported by the National Institute of Environmental Health Science, the National Institute of Diabetes and Digestive and Kidney Diseases, and the National Center for Advancing Translational Sciences of the National Institutes of Health.
Bansal A, Robles-Matos N, Wang PZ, Condon DE, Joshi A, Pinney SE. “In utero Bisphenol A Exposure Is Linked with Sex Specific Changes in the Transcriptome and Methylome of Human Amniocytes,” The Journal of Clinical Endocrinology and Metabolism, February 2020. https://doi.org/10.1210/clinem/dgz037
Contact: Kaila Revello, The Children’s Hospital of Philadelphia, 267-426-6054 or firstname.lastname@example.org