Amniotic fluid (AF) is an essential accompaniment of normal pregnancy, necessary for fetal movement, growth and development. Excess (polyhydramnios) or deficient (oligohydramnios) AF volume is associated with significant perinatal morbidity. Despite the critical importance of AF volume, there is a lack of understanding of mechanism(s), which result in AF volume abnormalities. The intramembranous pathway of AF fluid absorption (across the amniotic membrane) has recently been recognized as a critical regulatory path for AF resorption, contributing importantly to AF volume homeostasis. Yet the underlying molecular and cellular mechanisms for water absorption across the amniotic membranes remain unknown. Aquaporins (AQPs) are cell membrane water channel proteins that greatly enhance cell membrane water permeability. Of the 11 mammalian AQPs identified to date, our studies detected the expression of three AQPs (AQP 3, 8 and 9) in human and ovine chorioamniotic membranes and placenta. In situ hybridization reveals that AQP8 is expressed in epithelial cells of human amnion and chorion, as well as trophoblasts of placenta. In addition, the investigators have demonstrated that AQP8 gene expression is maintained in a human amnion epithelial cell line, and AQP8 gene expression in amnion cells is upregulated by second messenger cAMP. In view of preliminary studies, the investigators hypothesize that AF water absorption occurs via, and is regulated by, select AQP water channels in the chorioamniotic membranes. The investigators propose to: 1) Characterize the temporal and spatial expression of water channels (AQP 3, 8 and 9) in both human and ovine fetal membranes, and correlate its change to known changes in AF volume dynamics throughout pregnancy in sheep; 2) Investigate the endocrine (oxytocin, prolactin) and second messenger camp regulation of AQPs gene expression in human amnion cell line in vitro; and 3) Explore endocrine and cAMP regulation of epithelial AQPs gene expression in vivo and determine the effect on AF volume. Our objective is to determine the regulatory mechanisms of fetal membrane AQP expression and delineate the role of AQPs in AF homeostasis.
