A human-relevant mixture of endocrine disrupting chemicals induces changes in hippocampal DNA methylation correlating with hyperactive behavior in male mice

Humans are ubiquitously exposed to endocrine disrupting chemicals (EDCs), substances that interfere with endogenous hormonal signaling. Exposure during early development is of particular concern due to the programming role of hormones during this period. A previous epidemiological study has shown association between prenatal co-exposure to 8 EDCs (Mixture N1) and language delay in children, suggesting an effect of this mixture on neurodevelopment. Furthermore, in utero exposure to Mixture N1 altered gene expression and behavior in adult mice. In this study, we investigated whether epigenetic mechanisms could underlie the long term effects of Mixture N1 on gene expression and behavior. To this end, we analyzed DNA methylation at regulatory regions of genes whose expression was affected by Mixture N1 in the hippocampus of in utero exposed mice using bisulfite-pyrosequencing. We show that Mixture N1 decreases DNA methylation in males at three genes that are part of the hypothalamus-pituitary-adrenal (HPA) axis: Nr3c1, Nr3c2, and Crhr1, coding for the glucocorticoid receptor, the mineralocorticoid receptor, and the corticotropin releasing hormone receptor 1, respectively. Furthermore, we show that the decrease in Nr3c1 methylation correlates with increased gene expression, and that Nr3c1, Nr3c2, and Crhr1 methylation correlates with hyperactivity and reduction in social behavior. These findings indicate that an EDC mixture corresponding to a human exposure scenario induces epigenetic changes, and thus programming effects, on the HPA axis that are reflected in the behavioral phenotypes of the adult male offspring.