Progesterone-driven stabilization of hybrid E/M states in amniotic epithelial cells enhances regeneration and immune modulatory capacities.

Epithelial-mesenchymal plasticity (EMP) plays a pivotal role in development, regeneration, and disease progression. In this study, we demonstrate that progesterone (P4) delays EMP in amniotic epithelial cells (AECs), promoting the emergence of hybrid epithelial/mesenchymal (E/M) phenotypes. These hybrid cells co-express E and M traits and exhibit distinct surface markers. Compared to fully M, hybrid AECs display enhanced collective migration, upregulation of stemness transcription factors, and enhanced immunomodulatory properties in vitro and in vivo. Their regenerative potential was validated by in vitro tendon differentiation on PLGA-fleeces and in an ovine tendon injury model, where the transplantation of hybrid AECs accelerated early regeneration. This effect was associated with a timely transition from inflammation to proliferation, mediated by macrophage polarization and extracellular matrix remodeling. Our findings reveal that P4 maintains AECs in a functionally hybrid E/M state, conferring regenerative and immunomodulatory advantages. These results offer insights into the physiological regulation of EMP and support the therapeutic relevance of hybrid AECs as promising candidates for cell-based regenerative medicine therapy.