The Water Channel Aquaporin 1 Is a Novel Molecular Target of Polychlorinated Biphenyls for in Utero Anomalies

Despite serious health risks in humans and wild life, the underlying mechanisms that explain the gene-environment effects of chemical toxicants are largely unknown. Polychlorinated biphenyls (PCBs) are one of the most ubiquitous environmental toxicants worldwide, with reported epidemiological evidence for reproductive and neurocognitive anomalies in humans. Here, we show that Aroclor 1254, a mixture of structurally distinct PCBs, causes preterm birth in interleukin (IL)-10^-/- mice at a dose that does not show any adverse effects in wild type mice, highlighting the significance of IL-10 as an anti-toxicant cytokine. Aroclor 1254-treated IL-10^-/- mice demonstrated increased amniotic fluid, intrauterine growth restriction, and reduced litter size with postnatal neuromotor defects. Further, our results identify aquaporin 1 (AQP1), a potent effector of fluid volume regulation and angiogenic activity, as a novel placental target of PCBs. In vivo or in vitro exposure to Aroclor 1254 coupled with IL-10 deficiency significantly reduced the protein content of AQP1. Reduced uterine AQP1 levels were associated with defective spiral artery transformation. Importantly, recombinant IL-10 reversed PCB-induced in vivo and in vitro effects. These data demonstrate for the first time that the IL-10-AQP1 axis is a novel regulator of PCB-induced in utero effects.The health consequences of environmental toxicants are likely to have critical effects during in utero fetal development because of the complex signaling cascades, high cellular proliferation rates, and differentiation events. Mammalian reproduction involves a complex but highly choreographed sequence of molecular processes. These processes include interactions between the hormonally stimulated uterus and the developing blastocyst, implantation, placental and fetal development, and parturition (1, 2). Although the hormonal milieu, metabolic changes, and placental microenvironment are programmed in a pregnancy compatible manner, pregnancy presents itself as an immunological and hormonal paradox (3, 4). The role of steroid hormones is well known in uterine receptivity, implantation, local immune modulation, and pregnancy success (5). If not temporally produced and regulated, their dysfunction lead to infertility or pregnancy loss. Man-made chemicals like polychlorinated biphenyls (PCBs)² act like hormones and interfere with their cognate receptor functions impacting normal biological processes (6, 7). Although the genotoxic effects of PCBs have been investigated intensively and epidemiological studies have highlighted their health risks (6, 7), the mechanisms responsible for reproductive and neurodevelopmental effects still remain enigmatic. The overarching goal of our studies is to identify unknown pathways and targets that impart adverse effects on pregnancy. In this study, we directed our efforts toward establishing an experimental system to evaluate the in utero gene-environment effects of PCBs using wild type mice and their counterparts deficient in pregnancy compatible anti-inflammatory cytokines such as interleukin 10 (IL-10).IL-10 is a potent anti-inflammatory cytokine that controls inflammatory insult in most organs, particularly at the maternal-fetal interface. IL-10 is produced by gestational tissue and maternal immune cells in the intrauterine microenvironment in humans (8, 9) and in mice (10). We and others have reported that IL-10^-/- mice experience preterm birth and resorptions in response to low doses of inflammatory triggers such as lipopolysaccharide (LPS) (11, 12) or poly(I-C) (13). Importantly, the pregnancy outcome in treated IL-10^-/- mice can be rescued by giving an exogenous dose of IL-10 (11, 14). We have also demonstrated poor IL-10 production in placental and decidual tissues from preterm labor deliveries and missed abortions (15, 16). These data suggest that an inflammatory environment coupled with genetic stress (IL-10 deficiency) may lead to adverse pregnancy outcomes. In consideration of these observations, we hypothesize that exposure to toxicants such as PCBs mimics the physiological counterpart of inflammation that predisposes to adverse pregnancy outcomes when combined with genetic deficiency in loci crucial for pregnancy success such as IL-10.PCBs are chlorinated aromatic hydrocarbon compounds consisting of a group of 209 structurally diverse congeners, identified based on the position of chlorine atoms (7). Since the start of their manufacture in the 1920s until their ban in late 1970s, PCBs were globally valued for their noninflammability and high heat and chemical stability and thus were used widely in a multitude of commercial and industrial applications (7, 17). Improper disposal and accidental release of these compounds led to their introduction into the environment, placing them in the list of widespread environmental contaminants. Subsequently, their lipophilicity facilitated their bioaccumulation in the food chain and bio-concentration at successively higher levels (6, 18-21). PCBs have now been detected globally, in different environmental matrices, wild life, food, and humans (6, 18, 20). Convincing evidence exist for their toxicity, both in humans as well as in laboratory animals (7). From epidemiological studies in humans it has been observed that exposure to PCBs causes various reproductive anomalies that include irregular and shorter menstrual cycles, delayed conception, miscarriage, reduced lactating time, low birth weight, preterm birth, small for gestational age infants, and higher incidence of still-births and mortality among children (22-27). PCB congeners may work in an aryl hydrocarbon receptor-dependent or -independent pathway (6, 7, 28). Despite the knowledge that PCBs affect either aryl hydrocarbon receptor or estrogen receptor signaling, there is a paucity of molecular mechanisms underlying the most sensitive developmental effects of PCBs, and thus new pathways and targets need to be identified.Aroclor 1254 is a mixture of more than one hundred different PCB congeners and may impart cumulative adverse effects on female reproductive health (29, 30). In this study, we show that Aroclor 1254 exposure induces preterm birth in IL-10^-/- mice with reduced litter size and birth weight, increased amniotic fluid, and postnatal neurocognitive defects. Importantly, we have identified aquaporin 1 (AQP1) as a novel target of PCB action at the maternal-fetal interface. Our findings for the first time provide direct experimental evidence for a protective role of IL-10 against PCB exposure. These findings may have implications for the understanding and management of environmental toxicant-induced female reproductive anomalies in humans.