Single-cell transcriptomics reveals cytotrophoblast subtypes and senescence in recurrent spontaneous abortion

Recurrent spontaneous abortion (RSA), defined as the loss of two or more pregnancies before 20 weeks of gestation, remains a challenging clinical problem with largely unknown pathogenesis. In this study, we performed single-cell RNA sequencing analysis of control and RSA villous tissues and identified three subtypes of cytotrophoblasts (CTBs): CTB1, which is mainly involved in protein synthesis; CTB2, a highly proliferative progenitor population; and CTB3, an adhesive and invasive subtype that serves as the precursor of extravillous trophoblasts. We also characterized syncytiotrophoblasts, which are responsible for hormone production. In RSA villi, the functions of both CTBs and syncytiotrophoblasts were impaired. Notably, CTB2 and CTB3 exhibited pronounced features of cellular senescence, potentially contributing to reduced proliferative and differentiation capacity. These findings suggest that aberrant trophoblast senescence may underlie defective placentation in RSA and highlight potential therapeutic targets for restoring trophoblast function and improving pregnancy outcomes.