Abstract

Human endometrium undergoes cyclic regeneration involving stem/progenitor cells, but the role of resident endometrial mesenchymal stem cells (eMSC) as progenitors of endometrial stromal fibroblasts (eSF) has not been definitively demonstrated. In endometriosis, eSF display progesterone (P₄) resistance with impaired decidualization in vivo and in vitro. To investigate eMSC as precursors of eSF and whether endometriosis P₄ resistance is inherited from eMSC, we analyzed transcriptomes of eutopic endometrium eMSC and eSF isolated by fluorescence-activated cell sorting (FACS) from endometriosis (eMSC_endo, eSF_endo) and controls (eMSC_control, eSF_control) and their derived primary cultures. Differentially expressed lineage-associated genes (LG) of FACS-isolated eMSC and eSF were largely conserved in endometriosis. In culture, eSF_control maintained in vitro expression of a subset of eSF LG and decidualized in vitro with P₄. The eMSC_control cultures differentiated in vitro to eSF lineage, down-regulating eMSC LG and up-regulating eSF LG, showing minimal transcriptome differences versus eSF_control cultures and decidualizing in vitro. Cultured eSF_endo displayed less in vitro LG stability and did not decidualize in vitro. In vitro, eMSC_endo differentiated to eSF lineage but showed more differentially expressed genes versus eSF_endo cultures, and did not decidualize in vitro, demonstrating P₄ resistance inherited from eMSC_endo. Compared to controls, cultures from tissue-derived eSF_endo uniquely had a pro-inflammatory phenotype not present in eMSC_endo differentiated to eSF in vitro, suggesting divergent niche effects for in vivo versus in vitro lineage differentiation. These findings substantiate eMSC as progenitors of eSF and reveal eSF in endometriosis as having P₄ resistance inherited from eMSC and a pro-inflammatory phenotype acquired within the endometrial niche.