A single-cell atlas of uterosacral ligaments reveals progressive cellular remodeling in pelvic organ prolapse

Background Pelvic organ prolapse (POP) is a common disorder of pelvic support tissues, but its cellular basis in the uterosacral ligament (USL) remains poorly defined. Most existing single-cell studies, have failed to characterize stage-specific cellular changes across different POP severities, lacking a stage-resolved perspective across disease severity stages. Methods We profiled USL samples from 10 women with POP (4 moderate, 6 severe) and 4 controls by single-cell RNA sequencing, and analyzed 167,609 high-quality cells using clustering, trajectory inference, differential expression, cell–cell communication, and transcription factor analyses to systematically decode progressive USL cellular alterations. Results Ten major cell populations were identified. Fibroblasts, smooth muscle cells (SMCs), and endothelial cells formed the structural core of the USL, while macrophages, neutrophils, mast cells, and T cells showed progressive inflammatory activation with increasing disease severity. Fibroblasts were highly heterogeneous and shifted from progenitor-like and perivascular states toward inflammatory, matrix-remodeling, and myofibroblast-like phenotypes. SMCs moved from a contractile program to stress-responsive and ECM-remodeling states, and endothelial cells underwent functional reprogramming rather than major compositional change. Cell–cell communication between stromal cells declined, whereas fibroblast–immune interactions increased. Collagen-related signaling decreased, while immune-associated ligand–receptor programs became more prominent as disease advanced. Conclusion Distinct from previous cross-sectional single-cell studies on POP, this work provides a unique stage-resolved transcriptomic landscape covering moderate-to-severe POP stages. POP is marked by coordinated stromal remodeling, immune activation, and disrupted intercellular signaling in the USL. This single-cell transcriptomic atlas provides a refined framework for interpreting stage-specific molecular alterations across graded POP severities and may facilitate the development of targeted therapeutic strategies for pelvic floor dysfunction.