STRUCTURAL BASIS OF SUGAR TRANSPORT ACROSS THE PLACENTAL BARRIER

摘要

Placenta is an organ specialized for the maternofetal exchange of various substances during the mammalian embryonic development. Glucose is one of the most important substances used as a source for ATP synthesis and biosynthesis of a variety of macromolecules. It is supplied from the maternal blood via placenta during the fetal development. Maternal blood and fetal blood are separated by syncytial cell layer(s) called syncytiotrophoblast layer(s). Specialized transport systems allow hydrophilic molecules such as glucose efficiently to pass through the lipid bilayers of plasma membranes of this layer. Facilitated-diffusion glucose transporters of Glut family are integral membrane proteins serving for the specific transport of glucose (and related sugars) across cellular membranes depending on its concentration gradient. We showed that an isoform Glutl is abundant in the cells of blood-tissue barriers such as blood-brain barrier, blood-retinal barrier, and blood-aqueous barrier (Takata et al., 1990,1993,1997; Takata, 1996). Glutl is localized at the critical plasma membranes of the cells forming the barrier and plays a pivotal role in the transfer of glucose across the barrier. In the placenta, abundant Glutl was observed in the rat (Takata et al.,1990; 1994) and human placentas (Takata et al., 1992). Glutl seems to be important in the maternofetal transfer of glucose across the placental barrier.