Transgenerational effects of polychlorinated biphenyls: 2. Hypothalamic gene expression in rats†

Abstract

Polychlorinated biphenyls (PCBs) are endocrine-disrupting chemicals (EDCs) with well-established effects on reproduction and behavior in developmentally-exposed (F1) individuals. Because of evidence for transgenerational effects of EDCs on the neuroendocrine control of reproductive physiology, we tested the hypothesis that prenatal PCB exposure leads to unique hypothalamic gene-expression profiles in three generations. Pregnant Sprague-Dawley rats were treated on gestational days 16 and 18 with the PCB mixture Aroclor 1221 (A1221), vehicle (3% DMSO in sesame oil), or estradiol benzoate (EB, 50 μg/kg), the latter a positive control for estrogenic effects of A1221. Maternal- and paternal-lineage F2 and F3 generations were bred using untreated partners. The anteroventral periventricular nucleus (AVPV) and arcuate nucleus (ARC), involved in the hypothalamic control of reproduction, were dissected from F1 to F3 females and males, RNA extracted, and gene expression measured in a qPCR array. We detected unique gene-expression profiles in each generation, which were sex- and lineage-specific. In the AVPV, treatment significantly changed 10, 25, and 11 transcripts in F1, F2, and F3 generations, whereas 10, 1, and 12 transcripts were changed in these generations in the ARC. In the F1 AVPV and ARC, most affected transcripts were decreased by A1221. In the F2 AVPV, most effects of A1221 were observed in females of the maternal lineage, whereas only Pomc expression changed in the F2 ARC (by EB). The F3 AVPV and ARC were mainly affected by EB. It is notable that results in one generation do not predict results in another, and that lineage was a major determinant in results. Thus, transient prenatal exposure of F1 rats to A1221 or EB can alter hypothalamic gene expression across three generations in a sex- and lineage-dependent manner, leading to the conclusion that the legacy of PCBs continues for generations.

Keywords: Aroclor 1221 (A1221); anteroventral periventricular nucleus; arcuate nucleus; endocrine-disrupting chemical; estrogen; hypothalamus; neuroendocrine; polychlorinated biphenyls; sex difference; transgenerational.

Figure 1

Gene-expression profiles are shown in the F1 generation AVPV. Data (mean ± SEM) are normalized to the female DMSO group. Significant main effects of treatment or sex are indicated within panels, and significant interactions of sex and treatment are indicated by brackets. Detailed statistics, including all P-values, are in Supplementary Table S2. Abbreviations: T, treatment; F, female; M, male; D, DMSO; E, EB; A, A1221.

Figure 2

Gene-expression profiles are shown in the F2 generation AVPV. Because of the large number of identified genes, data are presented by category: (A) hormone signaling; (B) neurotransmission; (C) neuropeptides; (D) epigenetic. Data (mean ± SEM) are normalized to the female DMSO group of the maternal lineage. Significant main effects of treatment or sex, and interactions of sex by treatment or treatment by lineage, are indicated within panels. Significant interactions of sex by treatment by lineage are indicated by brackets. Detailed statistics, including all P-values, are in Supplementary Table S2. Abbreviations: T, treatment; S, sex; L, lineage; F, female; M, male; D, DMSO; E, EB; A, A1221; MAT, maternal; PAT, paternal.

Figure 3

Gene expression profiles are shown in the F3 generation AVPV. Data (mean ± SEM) are normalized to the female DMSO group of the maternal lineage. Significant main effects of treatment or sex, and interactions of sex by treatment or treatment by lineage, are indicated within panels. Significant interactions of sex by treatment by lineage are indicated by brackets. Detailed statistics, including all P-values, are in Supplementary Table S2. Abbreviations: T, treatment; S, sex; L, lineage; F, female; M, male; D, DMSO; E, EB; A, A1221; MAT, maternal; PAT, paternal.

Figure 4

Gene-expression profiles are shown in the F1 generation ARC. Data (mean ± SEM) are normalized to the female DMSO group. Significant main effects of treatment or sex are indicated within panels, and significant interactions of sex and treatment are indicated by brackets. Detailed statistics, including all P-values, are in Supplementary Table S2. Abbreviations: T, treatment; F, female; M, male; D, DMSO; E, EB; A, A1221.

Figure 5

Gene-expression profiles are shown in the F2 generation ARC. Data (mean ± SEM) are normalized to the female DMSO group of the maternal lineage. A significant interaction of treatment by lineage is indicated within the panel. A significant interaction of sex by treatment by lineage is indicated by brackets. Detailed statistics, including all P-values, are in Supplementary Table S2. Abbreviations: T, treatment; L, lineage; D, DMSO; E, EB; A, A1221; MAT, maternal; PAT, paternal.

Figure 6

Gene-expression profiles are shown in the F3 generation ARC. Data (mean ± SEM) are normalized to the female DMSO group of the maternal lineage. Significant main effects of treatment or sex, and interactions of sex by treatment or treatment by lineage, are indicated within panels. Significant interactions of sex by treatment by lineage are indicated by brackets. Detailed statistics, including all P-values, are in Supplementary Table S2. Abbreviations: T, treatment; S, sex; L, lineage; F, female; M, male; D, DMSO; E, EB; A, A1221; MAT, maternal; PAT, paternal.