Rahmana, M. D. R.; Hill, C. J.; Wilm, B.; Hapangama, D. K.

Peritoneal endometriosis causes pelvic pain and infertility, but the underlying mechanisms related to these symptoms are not fully understood. Endometriosis diagnosis is typically delayed; thus, patient samples are unsuitable to study early endometriosis formation in situ. This study aimed to generate a 3D co-culture model of early peritoneal endometriosis using patient-derived primary cells, providing unique opportunities to examine endometriotic lesion initiation and progression. Peritoneal wash fluid, fallopian tube mesentery and endometrial biopsies were collected from patients undergoing laparoscopic surgery to isolate primary cells. A composite 3D hydrogel construct was assembled by embedding human peritoneal fibroblasts (HPFs) in a Matrigel-collagen I matrix and subsequent seeding with a layer of human peritoneal mesothelial cells (HPMCs). Immunohistological investigation of the composite hydrogel construct confirmed the successful assembly of a simple peritoneum layer model comprising a mesothelial monolayer, basement membrane and underlying fibroblasts, while secretion of tissue plasminogen activator demonstrated functional mesothelial physiology. Endometrial epithelial organoids (EEOs) were co-cultured with endometrial stromal cells (ESCs) to form endometrial assembloids mimicking shed endometrial tissue fragments at menstruation. When transplanted onto the peritoneal layer model, endometrial assembloids adhered, thus simulating early endometriotic lesion formation. Histological analysis demonstrated direct cell-cell contacts between HPMC, HPF and ESC at the endometrial-peritoneal interface, suggesting the involvement of those cell types in lesion initiation. Our modifiable superficial endometriosis model allows for further refinement by the addition of hormones, cytokines and/or other cell types to determine the underlying molecular mechanism involved in endometriotic lesion formation.