Organoids have emerged as revolutionary biomimetic systems that offer a physiologically relevant in vitro model to study the specific tissue or organ of origin. In the field of female reproductive biology, endometrial organoids have proven their high value in the exploration of intricate physiological processes of the endometrium such as hormonal differentiation (decidualization) and embryo-receptivity, as well as to understand the pathophysiology of diseases associated with endometrial deficits. Moreover, organoid-based adhesion models have emerged as appropriate in vitro platform that faithfully reproduces the receptive endometrium. These in vitro models offer new tools to explore the molecular mechanisms of the early embryo-endometrium interaction and to bypass the barrier of ethical restrictions. This review highlights recent advances in the endometrial research domain, focusing on endometrial epithelial organoid models that closely replicate the cellular, transcriptomic and functional characteristics of the native tissue. A comprehensive overview of the transcriptomic changes during the menstrual cycle is provided, as well as of the detailed comparison between the different cell populations of the endometrium and the endometrial organoid model. Here, we provide evidence that endometrial organoids mimic the native endometrial tissue and offer relevant tools to advance our understanding of endometrial (patho)biology, enabling us to gain insights into molecular pathways.

Endometriosis-associated pain has debilitating effects on the quality of life of patients. Despite its high prevalence in reproductive-aged women, the pathophysiology is still unknown, impeding the development of targeted treatment approaches. The prospective ExPAND study proposes the neurosteroids pregnenolone sulphate (PS) and dehydroepiandrosterone sulphate (DHEAS) as potential contributors to endometriosis-associated pain, due to their agonistic action at the pain-related ion channel TRPM3. To this end, endometrium, deep endometriosis lesions, and peritoneal fluid were prospectively collected in four demarcated patient groups, which were characterised based on their pain symptoms, as scored via the WERF-EPHect questionnaire, i.e., (1) control (n = 44), (2) endometriosis patients with no pain symptoms (n = 24), (3) with only severe dysmenorrhea (n = 54), or (4) with both severe dysmenorrhea and non-cyclic pelvic pain (n = 78). Tissue mRNA expression levels of steroidogenic enzymes were investigated and showed significantly increased levels of CYP17A1 in the endometrium of patients with severe pain symptoms compared to control tissue. In addition, liquid chromatography with tandem mass spectrometry (LC-MS/MS) was performed to investigate neurosteroid concentrations in the peritoneal fluid. Both neurosteroids PS and DHEAS were present in the peritoneal fluid at concentrations that are known to stimulate TRPM3 activity in vitro. Finally, using microfluorimetric Ca²⁺ imaging, we demonstrate that both DHEAS and PS stimulate human stem-cell-derived sensory neurons in a TRPM3-dependent manner. Taken together, these data indicate a potential contribution of steroidogenesis and TRPM3 in endometriosis-associated pain.