Endometriotic Organoids as an In Vitro Model of Endometriotic Lesion Development

The development and progression of endometriotic lesions are poorly understood, but immune cell dysfunction and inflammation are closely associated with the pathophysiology of the disease. A lack of suitable 3D in vitro models permitting the study of interactions between cell types and the microenvironment is a contributing factor. To address this limitation, we developed endometriotic organoids (EO) to explore the role of epithelial-stromal interactions and model cell invasion associated with lesion development. Using a non-adherent microwell culture system, spherical organoids were generated with endometriotic epithelial cells (12Z) combined with immortalized endometriotic stromal cells (iEc-ESC) or immortalized uterine stromal cells (iHUF). Cell compartmentalization was observed in organoids with epithelial cells lining the periphery of a stromal cell core. Organoids with iEc-ESC (EO) stimulated the growth of a stratified epithelial cell layer compared to those with iHUF which developed a single layer. Transcriptome analysis found 4,522 differentially expressed genes (DEG) between organoid types and the top DEG included increased expression of interleukins and prostaglandin synthase enzymes. An overlap of the EO DEG with baboon endometriotic lesions was highly significant. Finally, to mimic invasion of endometrial tissue into the peritoneum, a model was developed using EO and an extracellular matrix containing human peritoneal mesothelial cells (LP9). Invasion of EO into the extracellular matrix-LP9 layer was increased in presence of estrogen or THP1-derived proinflammatory macrophages. Taken together, our results strongly support the concept that endometriotic organoids are an appropriate model for dissecting the mechanisms that contribute to endometriotic lesion development. One Sentence Summary Endometriotic organoids are an appropriate model to study epithelial-stromal interactions and model cell invasion associated with lesion development. ### Competing Interest Statement The authors have declared no competing interest.