Our lab previously showed that N-myc downstream-regulated gene 1 (NDRG1) enhances trophoblast differentiation, and that lentivirus-mediated knockdown of NDRG1 in primary human trophoblasts (PHTs) increases susceptibility to hypoxic injury, while over-expression of NDRG1 promotes cellular viability and differentiation. NDRG1 localizes to syncytiotrophoblasts, with increased expression in placentas of pregnancies affected by fetal growth restriction (FGR). We sought to advance our studies, and test the hypothesis that NDRG1 mitigates hypoxia-induced placental injury in vivo.
We performed expression analysis in mouse placenta using immunohistochemistry, in situ hybridization and western blot. We crossbred NDRG1 heterozygous mice and placed pregnant dams in 12% oxygen at E12.5, while controls remained in ambient air. At E18.5 we sacrificed the dams, collected embryos and placentas, and analyzed their phenotype, stratified by fetal NDRG1 genotype and sex.
We initially confirmed placental hypoxia using intraperitoneal injection of pimonidazole to pregnant dams and immunohistochemical detection. Using in-situ hybridization and immunohistochemistry we demonstrated NDRG1 expression adjacent to the chorionic plate in the placental labyrinth. The weight of NDRG1-null embryos and placentas was reduced compared to wild type (embryos 0.950+/−0.14 gm vs. 1.130+/−0.15 gm, p<0.001, placentas 0.0810+/−0.002 vs. 0.0940+/−0.002, p<0.001). Importantly, although weight reduction was not exacerbated by hypoxia, we found markedly reduced survival of hypoxic NDRG1-null female embryos (frequency of 11.6% in hypoxia vs. 30.9% in control, p=0.006), with no effect in NDRG1-null male embryos (frequency of 26.6% in hypoxia vs. 24.1% in control, p=NS).
Placental expression of NDRG1 in the mouse is analogous to that of humans. Deletion of NDRG1 causes FGR, establishing the role of this protein in feto-placental defense. The susceptibility of NDRG1-null females to hypoxic injury suggests that the NDRG1-mediated adaptive response to intrauterine hypoxia is influenced by fetal sex.
© 2012 Mosby, Inc. Published by Elsevier Inc. All rights reserved.