A novel human placental barrier model based on trophoblast stem cells derived from human iPS cells.

The placenta acts as an interface between the fetus and the expecting mother. Various drugs and environmental pollutants can pass through the human placental barrier and may harm the developing fetus. Currently available in vitro placental barrier models are often inadequate, because they are lacking the functional trophoblast cells. Therefore, we developed and characterized a new human placental model using trophoblast stem cells derived from human induced pluripotent stem (iPS) cells. Umbilical vein endothelial cells, fibroblast, and trophoblast stem cells were co-cultured using micromesh cell culture technique. These cells formed a tight three-layered structure. This co-culture model induced progressive fusion of trophoblast stem cells and formed a syncytialized epithelium that resembles the in vivo syncytiotrophoblast. Our model allowed the cultured trophoblasts to form microvilli and to reconstitute expression and physiological localization of membrane transport proteins, such as transporter for ATP binding cassette subfamily B member 1, ATP binding cassette subfamily C member 3, and glucose transporter-1. Drug permeability assays were performed using five compounds. The results from the permeability assays were comparable to the ones obtained with ex vivo placenta models. In conclusion, we developed a novel co-culture model mimicking human placenta that provides a useful tool for the studies on transfer of substances between the mother and fetus.