Endopolyploid and proliferating trophoblast cells express different patterns of intracellular cytokeratin and glycogen localization in the rat placenta.

The presence of keratin intermediate filaments is a characteristic of trophoblast differentiation. Meantime, their intracellular localization in the functionally different subtypes of placental trophoblast is poorly investigated in rodent, whereas their placentae are being broadly investigated in recent years as a model of the feto-maternal interaction. The purpose was to study the intracellular distribution of cytokeratin filaments in correlation with glycogen deposits, both being important constituents of the trophoblast cells in rat placenta. Different rat trophoblast cell populations exhibited different patterns of cytokeratin immunolocalization. The most intensive immunostaining was observed in the highly endopolyploid SGTCs (secondary giant trophoblast cells) at the border with decidua basalis. The most prominent cytokeratin-positive threads were found at the periphery of cytoplasm and in the extensive system of cytoplasmic sprouts by which the SGTC connect each other. Similar cytokeratin intensity and distribution was detected in the TSC (trabecular spongiotrophoblast cells) of the junctional zone of placenta that line the lacunae with the maternal blood. Clusters of highly proliferative pre-glycogen as well as glycogen cells showed some weaker cytokeratin signals mostly in the perinuclear and peripheral zones of cytoplasm. At the 11.5th to the 13.5th day of gestation, the interstitial and endovascular invasive endopolyploid TGTCs (tertiary giant trophoblast cells) prove the intensive cytokeratin staining throughout the cytoplasm and its sprouts. Meantime, the TGTCs were glycogen negative. By contrast, glycogen was heavily accumulated in the glycogen cells that belong both to the junctional zone of placenta and the cuff of the central arterial channel underlying the monolayer of endovascularly invading TGTCs. Thus, the TGTCs that are first to penetrate into the depth of the uterine wall do not contain glycogen but are accompanied by the glycogen-rich cells. The SGTC also contained the prominent deposits of glycogen at the periphery of cytoplasm and in the cytoplasmic sprouts. At the 16th day of gestation, an extensive interstitial invasion of the cytokeratin-positive glycogen trophoblast cells from the junctional zone was observed. The patterns of cytokeratin and glycogen intracellular localization are specific for each subtype of the rat trophoblast; that is, most probably, accounted for by the functional diversity of different trophoblast populations, i.e. patterns of invasion/phagocytosis and their involvement in a barrier at the feto-maternal interface.