Maternal cadmium exposure during late pregnancy causes fetal growth restriction via inhibiting placental progesterone synthesis

Cadmium (Cd) is a major environmental pollutant. Maternal Cd exposure throughout pregnancy caused fetal growth restriction (FGR). However, the pivotal time window of Cd-evoked FGR and its mechanism are unknown. Here, we will establish a murine model to explore the effects of maternal Cd exposure at different stages of gestation on fetal growth and placental progesterone biosynthesis. Pregnant mice were randomly divided into four groups. For Cd groups, mice were given with CdCl2 (150 mg/L) through drinking water at early (GDO-GD6), middle (GD7-GD12) and late (GD13-GD17) gestation, respectively. The controls received reverses osmosis (RO) water. Results showed that maternal cadmium exposure only in late gestation lowered fetal weight and length. Correspondingly, placental Cd level in late gestational Cd exposure is the highest among three different gestational stages. Although gestational Cd exposure had few adverse effects in the weight and diameter of mouse placenta, placental vascular development, as determined by H&E staining and cluster of differentiation-34 (CD-34) immunostaining, was impaired in mice exposed to Cd during late pregnancy. Additionally, late gestational exposure to cadmium markedly reduced progesterone level in maternal serum and placenta. In line, the expression of key progesterone synthetases, including steroidogenic acute regulatory protein (StAR) and 3 beta-hydroxyl steroid dehydrogenase (3 beta-HSD), was obviously downregulated in placenta from mice was exposed Cd during late pregnancy. These data suggest that maternal Cd exposure during late pregnancy, but not early and middle pregnancy, induces fetal growth restriction partially via inhibiting placental progesterone synthesis.