Maternal Fenvalerate Exposure Induces Fetal Intrauterine Growth Restriction Through Disrupting Placental Thyroid Hormone Receptor Signaling

Fenvalerate is an environmental endocrine disruptor that disrupts testosterone and estradiol synthesis. Nevertheless, whether fenvalerate disturbs placental TR signaling remains unclear. The aim of this study was to investigate whether maternal fenvalerate exposure causes fetal intrauterine growth restriction (IUGR) and to explore the role of placental thyroid hormone receptor (TR) signaling. Pregnant mice except controls were orally administered to fenvalerate (0.2, 2.0, or 20 mg/kg) daily throughout pregnancy. As expected, fetal weight was lowered in dams that were administered with 20.0 mg/kg of fenvalerate. Moreover, the rate of IUGR was elevated not only in male fetuses but also in female fetuses of dams exposed to 20.0 mg/kg of fenvalerate. Histopathology showed that the internal space of blood vessels in the labyrinth layer was smaller in placentas of mice exposed to fenvalerate. Mechanistic study found no significant difference on TT4 level in maternal serum, although TT3 level in maternal serum was slightly reduced in dams exposed to 2.0 mg/kg of fenvalerate. Interestingly, placental TRα1 and TRβ1 mRNAs were reduced in mice exposed to fenvalerate. Moreover, nuclear translocation of placental TRβ1 was suppressed in fenvalerate-exposed mice. Further analysis showed that placental Vegfα and Igf2, several target genes of TR signaling, were down-regulated in fenvalerate-exposed mice. In addition, mRNA level of placental CD36, Snat1, and Snat2, 3 nutrient transporters, were reduced in fenvalerate-exposed mice. These results suggest that maternal fenvalerate exposure induces fetal IUGR through disrupting placental TR signaling. These results provide a novel mechanistic explanation for fenvalerate-induced fetal IUGR.