Effects of exposure to an EDC mixture on the pubertal timing through a maternal behavioral epigenetic multigenerational transmission

Endocrine disrupting chemicals (EDCs) are today a rising public health challenge because of their ubiquity and presence in complex mixtures and their effects on the developing body throughout generations. We aim at studying the effect of a mixture of EDCs on female sexual development during 3 generations of females after exposure and determine whether an epigenetic hypothalamic mechanism is involved in those effects.
Female rats were orally exposed from 2 weeks before gestation until weaning to corn oil or a mixture of 14 anti-androgenic and estrogenic EDCs at low doses (F0 generation). Sexual development (vaginal opening, GnRH interpulse interval and estrous cyclicity) as well as maternal behavior were measured from F1 to F3 generation. An RNAseq was carry out using mediobasal hypothalamus from females at P21 from the F1 and F3 generation to decipher targets of the exposure, then validated by RT-PCR and studied for epigenetic modifications by ChIP.
F2 and F3 females showed a delayed puberty (delayed VO) and a decrease in the percentage of females having regular estrous cycles, characterized by a significant increase in the time spent in estrus and decreased time spent in diestrus. A hypothalamic epigenetic mechanism is known to be involved in the onset of puberty. We have observed both transcriptional and histone epigenetic alterations in genes involved in estrogen (ESR1), glutamtergic (GRIN2Dà and dopamine (TH and DRD1) signaling as well as in glucocorticoid activity (NR3C1 and CRH), kisspeptin (KISS1) and oxytocin (OXT). We have as well observed that F1 females, exposed in utero, which shows a decrease in TH mRNA expression spent less time licking and more time resting alone. Those modifications on maternal behavior are known to be transmitted through generations.
Overall, data shows that gestational exposure to an EDCs mixture can affect maternal behavior and sexual development during several generations. The F1 alteration of maternal behavior caused by in utero exposure to the mixture of EDCs trigger a multigenerational transmission of the phenotype and an induces an altered epigenetic reprogramming if the hypothalamus.