LAUSR

Decidualization is an essential process for embryo implantation and maintenance of pregnancy, and abnormal decidualization contributed to several pregnancy disorders like a miscarriage. The objective of this study was to explore the regulation and function of CD55 in human decidualization. By immunohistochemical staining, it was found that CD55 expression was higher in first‐trimester decidua than in the endometrium. In both primary endometrial stromal cells and immortalized cell line T‐hESCs, CD55 was upregulated by induction of in vitro decidualization with medroxyprogesterone acetate (MPA) and 8‐Br‐cAMP. During decidualization in vitro, CD55 was stimulated by 8‐Br‐cAMP in a time‐ and concentration‐dependent manner, which was reversed by a PKA inhibitor H89 and partially by an AKT activator SC79. Knocking down CD55 expression diminished the expression of decidualization markers prolactin (PRL) and insulin‐like growth factor‐binding protein 1 (IGFBP1), accompanied by inhibition of Src, aberrant activation of ERK and decreased expression of several decidualization‐related genes, including FOXO1, EGFR, and STAT3. Furthermore, the decidua of unexplained miscarriage women and the endometrium of unexplained infertile women both exhibited decreased CD55 expression. Collectively, these findings revealed that 8‐Br‐cAMP promotes CD55 expression via PKA activation and AKT dephosphorylation, and decreased CD55 impairs decidualization by inactivation of Src, aberrant activation of ERK pathway, and compromised expression of decidualization‐related genes, indicating that CD55 deficiency may contribute to the pathogenesis of spontaneous miscarriage and infertility.