Temporal and spatial expression of aquaporins 1, 5, 8, and 9: Potential transport of water across the endometrium and chorioallantois of pigs

Introduction: The uterus and placenta transport water during pregnancy recognition signaling, conceptus implantation, and placental development/placentation. This is likely influenced by aquaporins (AQPs) in the reproductive tract. This study determined mRNA and cell-type specific expression of AQP 1, 5, 8, and 9 proteins in the porcine uterus and placenta. Methods: Porcine uteri and Chorioallantois were subjected to real-time PCR and immunofluorescence microscopy. Results: AQP1 mRNA was maximal by Day 25 in endometrium and remained stable thereafter. AQP1 mRNA did not change in chorioallantois. AQP1 protein localized to erythrocytes and endothelium of the endometrium and allantois, and to smooth muscle of the myometrium. AQP5 protein localized to apical and lateral surfaces of the chorionic epithelia of areolae, but mRNA did not change in chorioallantois. AQP8 mRNA was high in the endometrium from Days 15 through 60 of gestation, and protein localized to multiple cell types within the endometrium and chorioallantois. AQP9 mRNA was highest in the endometrium on Days 10, 12 and 25, but did not change in the chorioallantois. AQP9 protein localized to the apical surface of endometrial luminal epithelial cells during early pregnancy, with a shift towards the basal surface later. AQP9 protein was observed in the allantoic epithelium. Discussion: Results reveal pigs can potentially use AQP1, AQP5, AQP8, and AQP9 to transport water from the endometrial bloodstream to the allantoic bloodstream or allantoic fluid. The reverse is also possible and may explain the mechanism for changing volumes of allantoic fluid and hydration of allantoic connective tissues during pregnancy.

Automated summary

This study determined the expression of four aquaporin proteins in the porcine uterus and placenta and found that pigs can potentially use these proteins to transport water between the endometrial bloodstream and allantoic fluid. This finding may explain the mechanism for changing volumes of allantoic fluid and hydration of allantoic connective tissues during pregnancy.