Developmental Dioxin Exposure Negatively Affects Fertility and Pregnancy Outcomes in Mice for Multiple Generations.

Abstract

TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) is an ubiquitous environmental contaminant and known endocrine disruptor, capable of interfering with multiple aspects of mammalian reproduction. Mammals are most sensitive to toxicant exposure during early development; thus we developed a mouse model of in utero TCDD exposure in order to examine the impact of this toxicant on adult reproductive function. For our study, pregnant C57bl/6 mice were provided a single dose of TCDD (10 μg/kg) by gavage on gestation day 15.5 (E15.5) and the dams were observed until normal delivery. Female offspring (F1) of TCDD exposed dams and several subsequent generations (F2-F4) were examined at sexual maturity for fertility, uterine decidualization capacity and pregnancy outcomes. Our initial studies of F1 animals revealed diminished uterine progesterone receptor (PR) expression and the majority of mice were infertile or exhibited a poor decidualization response leading to early pregnancy failure. Among mice which were able to achieve pregnancy, preterm birth (PTB) was common. Examination of surviving F3/F4 mice also revealed a significant number of infertile animals, and this transgenerational effect of TCDD was also correlated with diminished uterine PR and impaired decidualization. In F3/F4 mice which were able to become pregnant, ancestral toxicant exposure was associated with a significant increased risk of PTB. In order to further evaluate pregnancy failure in toxicant-exposed mice, in a subsequent study, we euthanized both control and F1 mice during late pregnancy (E18.5) for qRT-PCR analysis of selected genes at the maternal-fetal interface. These studies revealed that a history of developmental toxicant exposure was associated with a premature placental loss of PR mRNA expression and a concomitant increase in expression of toll-like receptor-4 mRNA, a mediator of inflammation. Since immunosuppression is a major function of progesterone related to the timing of birth, we speculated that a loss of PR in our toxicant-exposed mice may lead to PTB as a consequence of a heightened inflammatory response. To test this theory, we examined the ability of pregnant F1 and F3 mice to resist an inflammatory challenge mediated by intraperitoneal injection of lipopolysaccharide (LPS). Following the identification of a dose of LPS that did not induce PTB in control mice (200 μg/kg), F1 and F3 mice were subjected to an identical LPS challenge on E15.5 of pregnancy. In contrast to control animals, which were resistant to the LPS challenge, 100% of mice with a history of TCDD exposure (F1) or their descendants (F3) delivered within 16 hrs of treatment. Our data suggest that TCDD exposure during early development affects multiple aspects of reproductive tract function in adult animals. Significantly, following early life TCDD exposure, we observed a multigenerational incidence of PTB associated with increased sensitivity to non-microbial inflammation at the maternal-fetal interface. The rate of PTB in women in industrialized countries continues to increase despite better health care and patient awareness. Our experimental model in mice supports the possibility that ancestral, early life TCDD exposure may lead to heritable epigenetic alterations affecting fertility and birth outcomes. In humans, the risk of PTB may be yet another adult condition with its origins in the fetal environment. Support: NIEHS ES014942, NCCAM AT006245 and The Endometriosis Association (platform)