Human Decidual RUNX1 Promotes Angiogenesis and Trophoblast Differentiation by Regulating Extracellular Vesicle Signaling

During early pregnancy, human endometrial stromal cells differentiate into secretory decidual cells via a process regulated by ovarian steroid hormones. Decidual cells play a crucial role by secreting various factors that support essential events in forming a functional placenta, including uterine angiogenesis and the differentiation and development of trophoblasts. We previously reported that the conditional ablation of the transcription factor RUNX1 in the mouse uterus leads to subfertility due to insufficient maternal angiogenesis and impaired trophoblast differentiation. In this study, we examined the role of RUNX1 in facilitating communication mechanisms among human decidual cells and other cell types present in the pregnant uterus. We demonstrated that RUNX1 regulates the conserved HIF2α-RAB27B pathway in primary human endometrial stromal cells (HESC) during decidualization, which promotes the secretion of extracellular vesicles (EVs) by these cells. Consequently, the depletion of RUNX1 in HESC led to reduced EV secretion. Mass spectrometry identified several cargo proteins in decidual EVs, including ANGPTL2 and IGF2, which could regulate angiogenesis or trophoblast differentiation. We found that RUNX1 directly regulates their expression, resulting in partial changes to these cargoes when it is absent. We observed that delivering EVs lacking ANGPTL2 or IGF2 to human endothelial cells significantly decreased the formation of vascular networks compared to introducing control EVs carrying these factors. Furthermore, adding IGF2-depleted EVs to human trophoblast cells inhibited their differentiation into the extravillous trophoblast lineage. These findings collectively highlight the crucial role of decidual RUNX1 in promoting essential cell-cell interactions for angiogenesis and trophoblast differentiation during placenta formation.