Expression of aquaporin 8 and its up-regulation by cyclic adenosine monophosphate in human WISH cells

Objective: Water absorption across the fetal chorioamniotic membranes is a critical regulatory pathway for amniotic fluid volume homeostasis. Aquaporins are cell membrane proteins that significantly enhance membrane permeability to water by acting as water channels. We recently demonstrated that aquaporin 8 is expressed in human amnion, chorion, and placenta. Thus, aquaporin 8 expression represents a molecular mechanism of amniotic water absorption through intramembranous pathways. The current study sought to determine whether aquaporin 8 is expressed in human amnion-derived cell culture and to explore its regulation by second messenger cyclic adenosine monophosphate. Study Design: Human amnion–derived WISH cells were cultured. Total RNA was isolated and reverse transcriptase-polymerase chain reaction was used to determine aquaporin 8 gene expression. To determine the effect of cyclic adenosine monophosphate on aquaporin 8 expression, WISH cells were cultured in the presence of either monobutyryl cyclic adenosine monophosphate or the cyclic adenosine monophosphate–elevating agent forskolin. Multiplex semiquantitative reverse transcriptase–polymerase chain reaction was carried out to quantify aquaporin 8 messenger RNA levels. Results: Reverse transcriptase–polymerase chain reaction detected aquaporin 8 expression in WISH cells. After forskolin treatment for 2 hours, aquaporin 8 messenger RNA expression in WISH cells increased 4-fold (P< .001). Stimulation of aquaporin 8 gene expression by colforsin was observed throughout the study period of 20 hours. Incubation of WISH cells with monobutyryl cyclic adenosine monophosphate resulted in a 2-fold increase in aquaporin 8 messenger RNA level (P< .001). However, stimulation of aquaporin 8 gene expression by monobutyryl cyclic adenosine monophosphate attenuated to baseline level after 20 hours of monobutyryl cyclic adenosine monophosphate treatment. Conclusion: The current study demonstrates the expression of aquaporin 8 water channel in human amnion–derived WISH cells and aquaporin 8 expression up-regulation by second messenger cyclic adenosine monophosphate. Aquaporin 8 messenger RNA demonstrates a relatively short biologic half-life in vitro, which renders its rapid responsiveness to regulation (Am J Obstet Gynecol 2003;188:997-1001.)