Mesenchymal-epithelial transition serves to rapidly, yet transiently, restore the endometrial epithelium during postpartum uterine regeneration

The uterus is a remarkable organ in its ability to undergo extensive tissue damage during menstruation and parturition, yet achieves efficient, scar-free repair. Coordinated regulation of this regenerative process is essential for uterine homeostasis and fertility; however, the underlying mechanisms remain incompletely understood. Here, we demonstrate that mesenchymal-to-epithelial transition (MET) is a critical contributor to postpartum endometrial regeneration using PdgfraCreERT2/+; Rosa26-tdTomatofl/+ lineage tracing mice. Flow cytometry revealed a marked increase in mesenchymal-derived (MD) epithelial cells during active tissue repair. Notably, these cells are transient, undergoing clearance primarily via apoptosis following epithelial restoration. We also identified a migratory population of transitional cells of mesenchymal origin within the mesometrial stroma that incorporate into the luminal epithelium, consistent with an active MET program. Single-nucleus RNA sequencing (snRNA-seq) revealed that MD epithelial cells exhibit gene expression profiles associated with cell adhesion and cytoskeletal remodeling, while transitional cells were enriched for genes involved in junctional assembly and actin dynamics. MET-associated genes were significantly upregulated in both transitional and MD epithelial populations. Cell-cell communication analysis highlighted WNT, BMP, and EPHA signaling as candidate regulators of MET during regeneration. Together, these findings provide confirmation of MET as a physiologic mechanism of postpartum endometrial repair and uncover a coordinated signaling network that drives this process. Disruption of MET may contribute to pathologies such as endometriosis or endometrial cancer, underscoring the importance of understanding mesenchymal-epithelial plasticity in both normal and disease states.