Differential expression and regional distribution of aquaporins in amnion of normal and gestational diabetic pregnancies

The region of the amnion overlying the placenta plays an active role in fluid exchange between amniotic fluid and fetal blood perfusing the surface of the placenta, whereas little transfer occurs across the reflected amnion that contacts the membranous chorion. Because aquaporins (AQPs) facilitate rapid movement of water across cells, we hypothesized that AQP gene expression in placental amnion is higher than in reflected amnion. Furthermore, because gestational diabetes mellitus (GDM) is often associated with polyhydramnios, we hypothesized that amnion AQP gene expression is reduced when amniotic fluid volume is elevated. Human placental and reflected amnion were obtained at cesarean delivery and subjected to relative quantitation of AQP mRNA by real-time RT-qPCR and proteins by western immunoblot. Amnion mRNA levels of five AQPs differed by up to 400-fold (P < 0.001), with AQP1 and AQP3 most abundant, AQP8 least and AQP9 and AQP11 intermediately expressed. Aquaporin proteins showed a similar profile. Aquaporin mRNA abundance was higher (P < 0.001) in placental than reflected amnion, whereas protein levels were lower (P < 0.01). In GDM pregnancies, neither AQP mRNA nor protein levels were different from normal. There was no correlation between AQP mRNA or protein levels with the amniotic fluid index in normal or GDM subjects. We conclude that there is a strong differential expression profile among individual AQPs and between regions of the amnion. These findings suggest differences in contribution of individual AQPs to water transport in the two regions of the amnion. Furthermore, AQP expression in the amnion is not altered in patients with GDM.