Background: Successful implantation relies on the tightly regulated invasion of extravillous trophoblasts (EVTs). However, little is known about their phenotypic differentiation and relevant motile behaviour. Furthermore, the cell-cell interactions between EVTs and decidual arterioles during physiological transformation are also poorly understood. Methods: A total of 128 decidual specimens from early and late gestations containing components of EVTs and spiral arterioles were investigated using immunohistochemistry and periodic acid-Schiff reaction. Results: Unipolar, tadpole-like EVTs are observed throughout the interstitial area, with a tendency to decrease along the invasive pathway. The stellate differentiation of the EVTs is identified around and inside decidual arterioles or in the third-trimester myometrium. Furthermore, stellate transformation of EVTs precedes its interactions with the decidual arteriole. These specialized stellate trophoblasts invade and infiltrate the tunica media, accompanying lacuna formation inside the vessel wall and perturbation of actin fibre alignment of the tunica media. Conclusion: Stellate transformation of trophoblasts may explain controlled invasion of EVTs and probably plays a key role in initiating cell-cell interaction in decidual vascular remodelling.
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