Epigenetic responses following maternal dietary exposure to physiologically relevant levels of bisphenol A

Abstract

Animal studies have linked perinatal bisphenol A (BPA) exposure to altered DNA methylation, but little attention is given to analyzing multiple physiologically relevant doses. Utilizing the viable yellow agouti (A(vy)) mouse, we examine the effects of developmental exposure through maternal diet to 50 ng BPA/kg (n = 14 litters), 50 μg BPA/kg (n = 9 litters), or 50 mg BPA/kg (n = 13 litters) on global and candidate gene methylation at postnatal day 22. Global methylation analysis reveals hypermethylation in tail tissue of a/a and A(vy)/a offspring across all dose groups compared with controls (n = 11 litters; P < 0.02). Analysis of coat color phenotype replicates previous work showing that the distribution of 50 mg BPA/kg A(vy)/a offspring shifts toward yellow (P = 0.006) by decreasing DNA methylation in the retrotransposon upstream of the Agouti gene (P = 0.03). Maternal exposure to 50 μg or 50 ng BPA/kg, however, results in altered coat color distributions in comparison with control (P = 0.04 and 0.02), but no DNA methylation effects at the Agouti gene are noted. DNA methylation at the CDK5 activator-binding protein (Cabp(IAP)) metastable epiallele shows hypermethylation in the 50 μg BPA/kg offspring, compared with controls (P = 0.02). Comparison of exposed mouse liver BPA levels to human fetal liver BPA levels indicates that the three experimental exposures are physiologically relevant. Thus, perinatal BPA exposure affects offspring phenotype and epigenetic regulation across multiple doses, indicating the need to evaluate dose effects in human clinical and population studies.

Fig. 1

A^vy and Cabp^IAP loci (A) The A^vy allele contains a contra-oriented IAP insertion within pseudoexon 1A (PS1A) of the Agouti gene. A cryptic promoter (short arrowhead labeled A^vy ectopic) drives constitutive ectopic Agouti expression. Transcription of the Agouti gene normally initiates from a developmentally regulated hair-cycle specific promoter in exon 2 (short arrowhead labeled A, a wildtype). The location of the bisulfite-converted genomic reverse primer for amplifying the A^vy IAP is underlined. (B) The Cabp^IAP metastable epiallele contains a contra-oriented IAP insertion within intron 6 of the murine CDK5 activator-binding protein (Cabp) gene, resulting in short aberrant transcripts originating from the 5′-LTR of the IAP (short arrowhead labeled Cabp AT1a,b). Aberrant transcripts also originate at the normal transcription start site (short arrowhead labeled Cabp wildtype) and truncate 5′ of the IAP insertion (Cabp AT2 and AT3). Normal Cabp transcription covers 14 exons, resulting in a 2-kb transcript. The location of the bisulfite-converted genomic reverse primer for amplifying the Cabp^IAP locus is underlined.

Fig. 2

Coat color distribution (A) Coat color phenotype distribution among 50 mg/kg BPA exposed offspring (n = 45) versus corn oil control offspring (n = 38). 50 mg/kg BPA maternal intake demonstrates a shift in offspring coat color toward yellow (P = 0.006). (B) Coat color phenotype distribution among 50 μ*g/kg BPA offspring (n = 32) and versus corn oil control offspring. 50 μ*g/kg BPA maternal intake demonstrates a shift in coat color toward pseudoagouti (P = 0.04). (C) Coat color phenotype distribution among 50 ng/kg BPA offspring (n = 48) versus corn oil control offspring. 50 ng/kg BPA maternal intake demonstrates a shift in offspring coat color toward heavily mottled/pseudoagouti (P = 0.02). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]