Implantation of the mammalian embryo requires profound endometrial changes for successful pregnancy, including epithelial-mesenchymal transition of the luminal epithelium and stromal-epithelial transition of the stromal cells resulting in decidualization. Claudins (Cldn) determine the variability in tight junction paracellular permeability and may play a role during these epithelial and decidual changes. We here localized Cldn3, Cldn7 and Cldn10 proteins in the different compartments of murine endometrium up to day 8.5 of pregnancy (dpc) as well as in human endometrium and first trimester decidua. In murine estrous endometrium, luminal and glandular epithelium exhibited Cldn3 and Cldn7, whereas Cldn10 was only detectable in glandular epithelium. At 4.5 dpc, Cldn3 protein shifted to an apical localization, whereas Cldn7 vanished in the epithelium of the implantation chamber. At this stage, there was no stromal signal for Cldn3 and Cldn7, but a strong induction of Cldn10 in the primary decidual zone. Cldn3 proteins emerged at 5.5 dpc spreading considerably from 6.5 dpc onward in the endothelial cells of the decidual blood sinusoids and in the decidual cells of the compact antimesometrial region. In addition to Cldn3, Cldn10 was identified in human endometrial epithelia. Both proteins were not detected in human first trimester decidual cells. Cldn3 was shown in murine trophoblast giant cells as well as in human extravillous trophoblast cells and thus may have an impact on trophoblast invasion in both species. We here showed a specific claudin signature during early decidualization pointing to a role in decidual angiogenesis and regulation of trophoblast invasion.
Keywords: Angiogenesis; Claudins; Decidualization; Tight junctions; Trophoblast invasion.