An inappropriate response to progestogens in the human endometrium can result in fertility issues and jeopardize progestin-based treatments against pathologies such as endometriosis. PGRMC1 can mediate progesterone response in the breast and ovaries but its endometrial functions remain unknown. AG-205 is an alleged PGRMC1 inhibitor but its specificity was recently questioned. We added AG-205 in the cultures of two endometrial cell lines and performed a transcriptomic comparison. AG-205 significantly increased expression of genes coding enzymes of the cholesterol biosynthetic pathway or of steroidogenesis. However, these observations were not reproduced with cells transfected with siRNA against PGRMC1 or its related proteins (MAPRs). Furthermore, AG-205 retained its ability to increase expression of selected target genes even when expression of PGRMC1 or all MAPRs was concomitantly downregulated, indicating that neither PGRMC1 nor any MAPR is required to mediate AG-205 effect. In conclusion, although AG-205 has attractive effects encouraging its use to develop therapeutic strategies, for instance against breast cancer, our study delivers two important warning messages. First, AG-205 is not specific for PGRMC1 or other MAPRs and its mechanisms of action remain unclear. Second, due to its effects on genes involved in steroidogenesis, its use may increase the risk for endometrial pathologies resulting from imbalanced hormones concentrations.

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Study question What is the role of PGRMC1 in the human endometrium (especially in tissue remodeling) and its potential contribution to the development of endometrial diseases? Summary answer In primary endometrial stromal cell culture, PGRMC1 downregulation modifies expression of genes implicated in extracellular matrix remodeling as well as in cell migration and invasion. What is known already It has been suggested that Progesterone Receptor Membrane Component-1 (PGRMC1) is involved in gynecological pathologies. In particular, Pgrmc1 conditional KO in the mouse female reproductive tract induced subfertility and spontaneous development of endometrial cysts. Moreover, siRNA-mediated downregulation of PGRMC1 expression influenced TNF-α-induced activity of matrix metalloproteinase-9 (MMP-9) in cytotrophoblast cells, suggesting that PGRMC1 is a regulator of MMPs. In addition to playing a major role in the physiological breakdown of the human endometrium at menstruation, MMPs are strongly suspected to favor the pathogenesis of endometriosis lesions. Study design, size, duration Not applicable Participants/materials, setting, methods We compared transcriptomes obtained by RNA-sequencing from distinct primary endometrial stromal cell (ESC) cultures transfected with one of two specific siRNA targeting PGRMC1 mRNA or with a control siRNA. Expression changes for selected genes were confirmed by RT-qPCR. Migration and invasion capacities of the cells were also studied using Transwell assay. Finally, immunocytochemistry was performed on these primary cultures to localize the presence of PGRMC1 as well as the canonical progesterone receptor (PR). Main results and the role of chance RNA-sequencing data converged to show that the reduction of PGRMC1 expression by the specific siRNA significantly increased (up to 3-fold) the expression of several genes involved in the extracellular matrix (ECM) remodeling, as well as in the processes of migration and invasion. These changes were reproduced by RT-qPCR on other distinct primary endometrial stromal cultures isolated from other patients. In parallel, Transwell assays showed no significant changes in the migration and invasion capacities of the primary endometrial stromal cell cultures previously invalidated for PGRMC1 by transfection of the cells with a specific siRNA by comparison with a control siRNA. However, immunocytochemistry studies on these primary endometrial stromal cells showed that progesterone receptor (PR) labeling was restricted to cell nuclei, suggesting a constitutively activated PR in these cultures. Limitations, reasons for caution The absence of changes in migration and invasion properties of primary ESC cultures observed by Transwell assay could be due to the fact that the progesterone receptor seems to be constitutively activated in these cultures potentially causing a repressive effect on the migration and invasion capacity of the cells. Wider implications of the findings The modification of expression of genes implicated in ECM remodeling, and cell migration and invasion after PGRMC1 downregulation in primary ESC cultures is interesting in the context of endometriosis in which reduction of PGRMC1 expression could improve the migration and invasion capacities of lesions to implant into the host tissue. Trial registration number Not applicable