Distribution and quantitative changes in amounts of aquaporin 1, 5 and 9 in the pig uterus during the estrous cycle and early pregnancy

Mariusz T Skowronski

doi:10.1186/1477-7827-8-109

Abstract

BackgroundAquaporins (AQPs) are a family of membrane channel proteins that facilitate bulk water transport. To date, 11 isoforms of AQPs have been reported to be expressed in the female and male reproductive systems. The purpose of our study was to determine the localization and quantitative changes in the expression of AQP1, 5 and 9 within the pig uterus during different stages of the estrous cycle and early pregnancy.MethodsImmunoperoxidase and semi-quantitative immunoblotting techniques were used to examine the distribution and changes in amounts of AQP1, AQP5 and AQP9 in uteral cells of pigs at the early (Days 2-4), middle (10-12), late (14-16) stage of the luteal phase and late (18-20) stage of the follicular phase of the estrous cycle as well as on Days 14-16 and 30-32 of gestation (the onset and the end of implantation process).ResultsThe results demonstrated that AQP1, 5, and 9 were clearly detected in all studied stages of the estrous cycle and pregnancy. AQP1 was localized within uterine blood vessels. In cyclic gilts, endometrial and myometrial expression of AQP1 protein did not change significantly but increased during gestation. AQP5 was localized in smooth muscle cells and uterine epithelial cells. Endometrial expression of AQP5 protein did not change significantly between Days 2-4 and 10-12 of the estrous cycle but increased on Days 14-16 and 18-20 as well as during early pregnancy. Myometrial expression of AQP5 did not differ significantly during the estrous cycle but increased in the pregnancy. The anti-AQP9 antibody labeled uterine epithelial cells of uterus. Endometrial expression of AQP9 did not change significantly between Days 2-4 and 10-12 of the estrous cycle but increased on Days 14-16 and 18-20 as well as during early pregnancy.ConclusionsThe results suggest that a functional and distinctive collaboration exists among diverse AQPs in water handling during the different uterine phases in the estrous cycle and early pregnancy.

Highlights

Aquaporins (AQPs) are a family of membrane channel proteins that facilitate bulk water transport
Skowronski et al [11] showed the expression of AQP1 in the endothelial cells of the uterine blood vessels, AQP5 in the myometrium, as well as AQP5 and AQP9 in luminal and glandular epithelium
Using immunoblotting with the AQP1 antibody, AQP1 was detected in a protein fraction isolated from the porcine kidney, which served as a positive control for AQP1 protein expression

Summary

Introduction

Aquaporins (AQPs) are a family of membrane channel proteins that facilitate bulk water transport. Aquaporins (AQPs) are integral plasma membrane proteins that primarily transport water across the plasma membrane. These proteins were identified more than a decade ago [1]. Lindsay & Murphy [16] reported AQP1 expression in endothelial cells of the endometrium and in the inner circular layer of the rat myometrium. Lindsay & Murphy [17] showed AQP9 expression in the apical plasma membrane of the glandular epithelium of the rat uterus. Skowronski et al [11] showed the expression of AQP1 in the endothelial cells of the uterine blood vessels, AQP5 in the myometrium, as well as AQP5 and AQP9 in luminal and glandular epithelium.

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