Single-cell transcriptome analyses reveal disturbed decidual microenvironment in women of advanced maternal age

Background: Advanced maternal age (AMA) increases pregnancy risk. However, uterine-specific mechanisms independent of oocyte and embryo quality remain poorly defined. This study aimed to characterise the decidual microenvironment in women of AMA to identify key pathological changes and regulatory pathways. Methods and Results: Through integrated histology, organoid modelling, and high-resolution scRNA-seq of first-trimester decidua from women of AMA and controlled reproductive age, we uncovered a pathologically remodelled decidual microenvironment characterised by fibroblast expansion, immune depletion, and disrupted intercellular communication in the AMA decidua. Central to this pathology was hyperactivated TGF-ß signalling, driving fibroblast-to-myofibroblast transition (FMT) and extracellular matrix overproduction, thereby fuelling fibrosis. Aberrant TGF-ß further impaired decidual stromal cell (DSC) differentiation, causing failure of the essential mesenchymal-to-epithelial transition (EMT). We identified PRR15 as a novel DSC-specific regulator that is markedly suppressed in AMA. PRR15 deficiency unleashed hyperactive TGF-ß/SMAD signalling, directly causing decidualization failure, enhanced fibrosis, and aborted DSC differentiation. Epithelial-mesenchymal transition and immune cell reprogramming towards profibrotic phenotypes further amplify the fibrotic pathology. Conclusion: This study established the aged decidual microenvironment, orchestrated by dysregulated TGF-ß signalling and PRR15 loss, as a critical independent determinant of reproductive failure in AMA. Thus, it unveils novel diagnostic and therapeutic targets and strategies. Overall design: This study investigated the impact of advanced maternal age (AMA) on the cellular and molecular composition of the human decidua during early pregnancy. Decidual tissue samples were collected from six women undergoing elective first-trimester surgical termination. The participants were stratified into two cohorts based on maternal age: the AMA group (35–49 years, n = 3) and a control (CTR) group of women of optimal reproductive age (22–30 years, n = 3). Women aged 31–34 years were excluded to avoid overlap between groups. All participants were clinically healthy, with no history of hormonal treatment, genetic abnormalities, reproductive disorders, or chronic systemic disease. Single-cell RNA sequencing (scRNA-seq) was performed on freshly isolated decidual tissue from each individual to characterize the cellular composition and transcriptional changes associated with AMA. The primary experimental variable under investigation was maternal age. The CTR group served as the baseline reference for identifying age-related alterations in cell populations, differentiation states, and intercellular communication. Each sample represents an independent biological replicate. The design enabled comparative analysis of decidual stromal cells, fibroblasts, and immune cells between the two age-defined groups.