Induction of Oxidative Stress and Alteration of Synaptic Gene Expression in Newborn Hippocampal Granule Cells after Developmental Exposure to Aroclor 1254.

INTRODUCTION: Hippocampal newborn neurons integrate into functional circuits where they play an important role in learning and memory. We previously showed that perinatal exposure to Aroclor 1254, a commercial mixture of polychlorinated biphenyls (PCBs) associated with alterations of cognitive function in children, disrupted the normal maturation of excitatory synapses in the dentate gyrus. We hypothesized that hippocampal immature neurons underlie some of the cognitive effects of PCBs. METHODS: We used newly generated neurons to examine the effects of PCBs in mice following maternal exposure. Newborn dentate granule cells were tagged with enhanced green fluorescent protein using a transgenic mouse line. The transcriptome of the newly generated granule cells was assessed using RNA sequencing. RESULTS: Gestational and lactational exposure to 6 mg/kg/day of Aroclor 1254 disrupted the mRNA expression of 1,308 genes in newborn granule cells. Genes involved in mitochondrial functions were highly enriched with 154 genes significantly increased in exposed compared to control mice. The upregulation of genes involved in oxidative phosphorylation was accompanied by signs of endoplasmic reticulum stress and an increase in lipid peroxidation, a marker of oxidative stress, in the subgranular zone of the dentate gyrus but not in mature granule cells in the granular zone. Aroclor 1254 exposure also disrupted the expression of synaptic genes. Using laser-captured subgranular and granular zones, this effect was restricted to the subgranular zone, where newborn neurons are located. CONCLUSION: Our data suggest that gene expression in newborn granule cells is disrupted by Aroclor 1254 and provide clues to the effects of endocrine-disrupting chemicals on the brain.

Multi- and Transgenerational Outcomes of an Exposure to a Mixture of Endocrine-Disrupting Chemicals (EDCs) on Puberty and Maternal Behavior in the Female Rat.

BACKGROUND: The effects of endocrine-disrupting chemicals (EDCs) on fertility and reproductive development represent a rising concern in modern societies. Although the neuroendocrine control of sexual maturation is a major target of EDCs, little is known about the potential role of the hypothalamus in puberty and ovulation disruption transmitted across generations. OBJECTIVES: We hypothesized that developmental exposure to an environmentally relevant dose of EDC mixture could induce multi- and/or transgenerational alterations of sexual maturation and maternal care in female rats through epigenetic reprograming of the hypothalamus. We investigated the transmission of a disrupted reproductive phenotype via the maternal germline or via nongenomic mechanisms involving maternal care. METHODS: Adult female Wistar rats were exposed prior to and during gestation and until the end of lactation to a mixture of the following 13 EDCs: di-n-butyl phthalate (DnBP), di(2-ethylhexyl) phthalate (DEHP), bisphenol A (BPA), vinclozolin, prochloraz, procymidone, linuron, epoxynaxole, dichlorodiphenyldichloroethylene, octyl methoxynimmate, 4-methylbenzylidene camphor (4-MBC), butylparaben, and acetaminophen. Perinatally exposed offspring (F1) were mated with unexposed males to generate germ cell (F2) and transgenerationally exposed (F3 and F4) females. Sexual maturation, maternal behavior, and hypothalamic targets of exposure were studied across generations. RESULTS: Germ cell (F2) and transgenerationally (F3) EDC-exposed females, but not F1, displayed delayed pubertal onset and altered folliculogenesis. We reported a transgenerational alteration of key hypothalamic genes controlling puberty and ovulation (Kiss1, Esr1, and Oxt), and we identified the hypothalamic polycomb group of epigenetic repressors as actors of this mechanism. Furthermore, we found a multigenerational reduction of maternal behavior (F1-F3) induced by a loss in hypothalamic dopaminergic signaling. Using a cross-fostering paradigm, we identified that the reduction in maternal phenotype was normalized in EDC-exposed pups raised by unexposed dams, but no reversal of the pubertal phenotype was achieved. DISCUSSION: Rats developmentally exposed to an EDC mixture exhibited multi- and transgenerational disruption of sexual maturation and maternal care via hypothalamic epigenetic reprogramming. These results raise concerns about the impact of EDC mixtures on future generations. https://doi.org/10.1289/EHP8795.

Persistent vs Transient Alteration of Folliculogenesis and Estrous Cycle After Neonatal vs Adult Exposure to Bisphenol A.

Exposure to bisphenol A (BPA), a ubiquitous endocrine-disrupting chemical (EDC), is known to produce variable effects on female puberty and ovulation. This variability of effects is possibly due to differences in dose and period of exposure. Little is known about the effects of adult exposure to environmentally relevant doses of this EDC and the differences in effect after neonatal exposure. This study sought to compare the effects of neonatal vs adult exposure to a very low dose or a high dose of BPA for 2 weeks on ovulation and folliculogenesis and to explore the hypothalamic mechanisms involved in such disruption by BPA. One-day-old and 90-day-old female rats received daily subcutaneous injections of corn oil (vehicle) or BPA (25 ng/kg/d or 5 mg/kg/d) for 15 days. Neonatal exposure to both BPA doses significantly disrupted the estrous cycle and induced a decrease in primordial follicles. Effects on estrous cyclicity and folliculogenesis persisted into adulthood, consistent with a disruption of organizational mechanisms. During adult exposure, both doses caused a reversible decrease in antral follicles and corpora lutea. A reversible disruption of the estrous cycle associated with a delay and a decrease in the amplitude of the LH surge was also observed. Alterations of the hypothalamic expression of the clock gene Per1 and the reproductive peptide phoenixin indicated a disruption of the hypothalamic control of the preovulatory LH surge by BPA.