The placenta is made up of a branching network of villi trees, composed of specialised cells called trophoblast. Placental villi consist of a dual layer of trophoblast subsets; an underlying layer of cytotrophoblasts (CTB) supply the overlying syncytiotrophoblast (STB) layer, which encompasses the villi surface. Studying aspects of trophoblast development is necessary to understand the mechanisms that may lead to pathophysiological outcomes. Because the placenta is only present during pregnancy, three-dimensional (3D) in vitro organoid culture models are beneficial to study first-trimester placental development on a cellular level.
Existing 3D trophoblast models have been developed in a range of morphological structures, from various trophoblasts or substitute cell types. However, these models lack the ability to recapture the complete trophoblast lifecycle and architectural resemblance to authentic villi tissue.
We have developed an in vitro 3D model to produce anatomically accurate placental villi organoids. This ‘placentoid’ method utilises human embryonic stem cells (hESC), cultured in media containing growth factors and inhibitors to direct the differentiation of trophoblast populations. Cells are grown on an inverted PDMS villi scaffold to encourage trophoblast bilayers to assemble in the same orientation as de novo tissue.
Over a 14-day culture, we observed the differentiation of hESC into trophoblast populations, confirmed by the presence of Ki67 CTB marker, and the STB marker, hCG. The presence of trophoblast cells was further validated with qPCR for specific marker genes. The trophoblasts migrate to cover the villi bumps, forming an outer layer of STBs, capable of shedding syncytial nuclear aggregates.
The placentoid model is capable of recapturing morphological features and characteristics of genuine placental villi, currently lacking in existing villi models. Recreating villi with the correct orientation of the trophoblast bilayers provides an accurate and reliable method to study factors that may impact placental villi development.