A floating endometrial organoid model recapitulates epithelial-stromal cell interactions in vitro.

Organoids are 3D structures in which stem, progenitor and differentiated cells spontaneously assemble into structures resembling the original tissue. Endometrial organoids, developed from tissue fragments, are genetically stable and responsive to hormone stimulation acquiring a hallow lumen, secretory activity and apico-basal polarity. However, they show some limitations in mimicking the midluteal endometrium since they lack endothelial, immune, and stromal cells, thus providing limited information about epithelial-stromal interactions. We developed a 3D-model to generate endometrial organoids in floating Matrigel™ droplets using standard medium. Floating organoids form gland-like structures constituted by epithelial cells organized around a central lumen, and contain stromal cells grown in close contact, either outside or inside the organoid structure. Similarly to conventional endometrial organoids, floating organoids retain the expression of endometrial and decidual genes, assessed by qRT-PCR for a panel of fifteen genes, although with a pattern of expression resembling, in most cases, what observed in hormonally differentiated organoids. In conclusion, we describe a simple and rapid model to generate 3D endometrial organoids, ensuring the persistence of epithelial-stromal cell interaction, which fosters the development of differentiated organoids, thereby enabling the study of the reciprocal modulation between epithelium and stroma.