Directed Differentiation of Human Pluripotent Stem Cells to Cytotrophoblast and Syncytiotrophoblast

Human pluripotent stem cells (hPSCs) form an ideal system to study the formation of placental cells, from an undifferentiated human embryonic stem cell state. The conventional human in vitro model systems to study the human placenta cannot be employed for understanding placental dysfunctions or the development of specialized placental cell types. Hence, human PSCs make an ideal model system to study human placental development and disorders. Here, we describe an efficient and validated protocol to reproducibly study the formation of human cytotrophoblasts (CTBs) and syncytiotrophoblast (STBs) from undifferentiated hPSCs. CTBs are the trophoblast stem cells that can differentiate into specialized placental cell types such as STBs. The multinucleated STB plays vital role in the exchange of nutrients and gases across the placenta and secretes several hormones during pregnancy, such as human chorionic gonadotropin β (hCGβ). Here we describe two methods of seeding the hPSCs: chemical (clumps method) and enzymatic methods (single cells) to differentiate them to CTB and STB, activating BMP (B) signaling and inhibiting ACTIVIN/NODAL and FGF signaling pathways (2i), thus naming our protocol as "B2i" (Sudheer et al., Stem Cells Dev 21:2987-3000, 2012). This protocol forms the perfect model system for understanding in vitro placentation, modeling diseases arising from abnormal placentation that cause complications such as miscarriage, preeclampsia or intrauterine growth restriction (IUGR), and drug discovery for placental disorders.