Aquaporins and placenta.

Water is the major component of cells and tissues. The fetal body consists of about 70-90% water and its fluid balance is dependent on the mother. In fact, abortion, premature birth, amniotic fluid volume abnormality, malformation and fetal growth restrictions might result when the homeostasis of the maternal-fetal fluid exchange is disrupted. Thus, maternal-fetal fluid balance is critical during pregnancy. In this sense, several mechanisms, including aquaporins (AQPs) have been reported to play important roles in maternal-fetal fluid balance. AQPs are small membrane proteins (about 30kDa), present in different organs, that increase the permeability of water, as well as other small uncharged molecules to be transported across the bilayer cell membranes. Several aquaporins are expressed in placenta, and aquaporins play key roles in the placental function. Even though aquaporins have a proven crucial role in water homeostasis, the physiological and pathological importance of aquaporins as glycerol channels is not fully understood. This review focuses on advances in our knowledge of the roles of aquaporins in placental cells, particularly the roles of AQP3 and AQP9 in placental metabolism and points to the pathophysiological importance of glycerol channels in placenta, as well as the signal transduction pathways activated by them. Moreover, the regulation of aquaporins expression by different placental hormones, such as leptin and the mechanisms involved will be discussed.