Aberrant epithelial differentiation may contribute to endometrial polyp formation: insights from single-cell analysis

Endometrial polyps (EPs) are benign overgrowths of the endometrium causing abnormal uterine bleeding and infertility. Despite their clinical significance, the molecular mechanisms underlying their development and recurrence remain poorly understood, warranting comprehensive transcriptomic investigation. We hypothesized that transcriptomic differences, particularly at the single-cell level as revealed through cellular trajectory analysis, distinguish EPs from adjacent endometrium. To investigate this, paired EP and adjacent endometrium (adEN) samples were collected from 12 women undergoing hysteroscopic polypectomy (proliferative phase, n = 9; secretory phase, n = 3) and analyzed using bulk and single-cell RNA sequencing (scRNA-seq). Bulk RNA-seq revealed high transcriptional similarity between EPs and adENs, with only a few differentially expressed genes (FDR < 0.05) in proliferative-phase EPs, including upregulation of KMT2B and DLEC1 and downregulation of COL9A1 and RAB3C, potentially reflecting epigenetic regulation and protective mechanisms against tumorigenesis. scRNA-seq identified eight major cell clusters namely stromal, epithelial, endothelial, immune, perivascular, macrophage, B cell, and ciliated populations in both tissues. Pseudotime analysis revealed a mid-transcriptional arrest and enrichment of MECOM/EYA2-positive intermediate epithelial states in EPs, in contrast to the late, mature epithelial stage seen in the adENs. This aberrant epithelial maturation may be associated with impaired perivascular and endothelial differentiation, potentially contributing to defective vascular remodeling and polyp persistence. In conclusion, while EPs exhibit global transcriptomic similarity to adENs, single-cell and pseudotime analyses suggest subtle but significant disruptions in epithelial differentiation and vascular remodeling that might be involved in EPs development. Study limitations include scRNA-seq restricted to the proliferative phase, which may limit generalizability. Nevertheless, future functional studies using primary epithelial organoids derived from EPs may provide a physiologically relevant model to evaluate targeted therapeutic strategies including hormonal interventions with potential applications in infertility management.