Epigenetic effects of prenatal stress on 11β-hydroxysteroid dehydrogenase-2 in the placenta and fetal brain

Abstract

Maternal exposure to stress during pregnancy is associated with significant alterations in offspring neurodevelopment and elevated maternal glucocorticoids likely play a central role in mediating these effects. Placental 11β-hydroxysteroid dehydrogenase type 2 (HSD11B2) buffers the impact of maternal glucocorticoid exposure by converting cortisol/corticosterone into inactive metabolites. However, previous studies indicate that maternal adversity during the prenatal period can lead to a down-regulation of this enzyme. In the current study, we examined the impact of prenatal stress (chronic restraint stress during gestational days 14-20) in Long Evans rats on HSD11B2 mRNA in the placenta and fetal brain (E20) and assessed the role of epigenetic mechanisms in these stress-induced effects. In the placenta, prenatal stress was associated with a significant decrease in HSD11B2 mRNA, increased mRNA levels of the DNA methyltransferase DNMT3a, and increased DNA methylation at specific CpG sites within the HSD11B2 gene promoter. Within the fetal hypothalamus, though we find no stress-induced effects on HSD11B2 mRNA levels, prenatal stress induced decreased CpG methylation within the HSD11B2 promoter and increased methylation at sites within exon 1. Within the fetal cortex, HSD11B2 mRNA and DNA methylation levels were not altered by prenatal stress, though we did find stress-induced elevations in DNMT1 mRNA in this brain region. Within individuals, we identified CpG sites within the HSD11B2 gene promoter and exon 1 at which DNA methylation levels were highly correlated between the placenta and fetal cortex. Overall, our findings implicate DNA methylation as a mechanism by which prenatal stress alters HSD11B2 gene expression. These findings highlight the tissue specificity of epigenetic effects, but also raise the intriguing possibility of using the epigenetic status of placenta to predict corresponding changes in the brain.

Figure 1. Gene schematic of HSD11B2 and CpG sites analyzed.

The rat HSD11B2 gene contains a promoter and five exons. The promoter (lowercase letters) and first part of exon 1 (capital letters) are indicated and the ATG site is bolded. 38 CpG sites from −378 to +56 were analyzed for methylation levels and are indicated in bold and numbered.

Figure 2. Tissue-specific expression of HSD11B2 and DNMTs in offspring exposed to prenatal stress.

Average (mean ± SEM) mRNA levels of (A) HSD11B2, (B) DNMT1, and (C) DNMT3a in hypothalamus (HYPO), cortex, and placenta in control offspring and offspring exposed to prenatal stress. Relative gene expression levels were determined by the 2ddCT method using cyclophilin-A and beta-actin as internal standards. Relative expression was normalized to control (non-stress) cortex samples. (n = 8/group; † p<0.1; *p<0.05, **p<0.01).

Figure 3. Tissue-specific effects of prenatal stress on DNA methylation of the HSD11B2 promoter and exon 1.

Average (mean ± SEM) % DNA methylation at 38 CpG sites in the HSD11B2 promoter and exon 1 in (A) fetal hypothalamus, (B) fetal cortex, and (C) placenta of control offspring and offspring exposed to prenatal stress. Location of Sp1 and NF-κB transcription factor binding sites indicated, as well as the transcription start site (TSS) and ATG start codon. (n = 4/group run in duplicate; *p<0.05).