Aquaporins in the female reproductive system of mammals

Water and ion accumulation is the driving force for rapid expansion of the amnion and allantois of mammalian placentae during early gestation, and, therefore, essential for embryonic/fetal growth and survival. Aquaporins (AQP) are a family of small integral plasma membrane proteins that primarily transport water across the plasma membrane. To date, thirteen AQP isoforms (AQP 0-12) have been identified in mammals. AQP 1, 2, 3, 4, 5, 6, 7, 8, 9, and 11 are expressed in the female reproductive tract. Based on their structural and functional properties, AQPs are divided into three subgroups: classical aquaporins (AQP 0, 1, 2, 4, 5, 6, and 8), aquaglyceroporins (AQP 3, 7, 9, and 10), and superaquaporins (AQP 11 and 12). Expression of AQPs in the uterus and placenta is regulated by hormones and nutrients to maintain fluid homeostasis in the conceptus. The underlying mechanisms may involve signal transduction pathways mediated by cAMP, MAPK, PKC, and PI3K/Akt/mTOR. Such new knowledge will advance basic understanding of mammalian reproductive biology to enhance embryonic/fetal survival, growth and development in women and livestock.