Single-cell characterization of trophoblast-epithelial interactions at the human maternal-fetal interface during early implantation

Abstract Human embryo implantation is crucial for successful pregnancy, yet its molecular mechanisms remain poorly understood due to ethical and technological limitations. In this study, we constructed an embryo implantation model using single-cell RNA sequencing (scRNA-seq) data from the implantation sites (ISs) of patients with tubal ectopic pregnancy (TEP) to infer the embryo implantation mechanisms at the maternal-fetal interface during early human pregnancy. Based on scRNA-seq data from normal intrauterine pregnancies (IUP) in the public database (GSE214607), we identified and validated marker genes for trophoblast cells and their subtypes. We applied CellPhoneDB and CellChat to map intercellular communication networks at the maternal-fetal interface in the TEP model. By validating the predicted ligand-receptor interacting pairs against IUP data, we assessed the utility of the TEP model as a reference for studying implantation mechanisms. Results revealed similar gene expression patterns at the transcriptional level between trophoblast cells in TEP and IUP, and Immunofluorescence staining further supported the conserved expression of key marker genes in the two types of pregnancy tissues. Cell–cell interaction analysis suggested bidirectional ligand-receptor communications between extravillous trophoblasts (EVTs) and non-ciliated secretory epithelial cells, involving extracellular matrix remodeling, angiogenesis, and immune regulation. Meanwhile, macrophages may participate in trophoblast-immune interactions through the IL-1 signaling pathway. These signaling pathways showed a certain degree of conservation between TEP and IUP. The TEP model provides a complementary tool for studying early implantation, offering new perspectives for elucidating molecular mechanisms at the maternal-fetal interface and for preventing and treating infertility.