Single-cell transcriptomic landscape of the mid-secretory eutopic endometrium reveals receptivity defects in adenomyosis

Adenomyosis (AM) is a common gynecological disorder in reproductive-age women, with impaired endometrial receptivity as a key contributor to infertility. However, a comprehensive single-cell atlas of the eutopic endometrium during the implantation window remains lacking, particularly regarding the roles of specific subpopulations in shaping the implantation microenvironment. This gap has limited mechanistic insights into AM-associated implantation failure. We performed 10x Genomics single-cell RNA sequencing of mid-secretory eutopic endometrium from three primary infertile AM patients and three parous controls, validated by qRT-PCR, immunohistochemistry, and immunofluorescence. AM-derived cells accounted for a higher proportion of epithelial, perivascular, and proliferative populations, whereas stromal and immune cell fractions remained largely unchanged. Notably, an expanded epithelial subpopulation characterized by the stem cell markers LGR5 and SOX9 exhibited excessive proliferative activity and strengthened tight junctions, collectively disrupting the establishment of a receptive epithelial phenotype. In the stroma, a DIO2+ decidual subpopulation with senescence-associated secretory phenotype (SASP) features was markedly reduced in AM, accompanied by downregulation of inflammatory mediators and key decidualization markers, indicative of impaired decidualization. Cell–cell communication analysis revealed marked remodeling of epithelial–stromal crosstalk in AM. Hyperactive epithelial PTN and loss of ncWNT could be linked to aberrant proliferative activity and polarity alterations, while reduced epithelial DKK1 and IGF2 signaling, together with stromal ncWNT loss, may partially explain deficient decidualization. In summary, our findings indicate that excessive proliferation and impaired differentiation of epithelial cells, along with insufficient inflammatory activation and decidualization defects in stromal cells, jointly underlie reduced endometrial receptivity in AM. Moreover, altered epithelial signaling may further compromise stromal decidualization.