Type V Collagen Controls Decidual Extracellular Matrix Organization and Angiogenesis During Embryo Implantation.

Extracellular matrix (ECM) remodeling and angiogenesis are essential processes underlying endometrial decidualization during embryo implantation. Fibrillar collagens, the major structural components of the ECM, form the architectural framework of the decidua and undergo dynamic reorganization during this process. However, the functional role of type V collagen-a key regulator of collagen fibrillogenesis-remains undefined. Here, we demonstrate that Col5a1 is highly expressed in decidual stromal and endothelial cells of the mouse uterus. Conditional deletion of Col5a1 leads to progressive uterine hemorrhage beginning at gestation day 8, culminating in complete embryo resorption and pregnancy loss by day 12. Col5a1-deficient decidua exhibits severe structural distortion, marked disorganization of fibrillar collagen, shallow and misdirected embryo invasion, and profound disruption of decidual angiogenesis and vascular network formation. Transcriptomic profiling further reveals distinct gene expression signatures and signaling pathways regulated by COL5A1 in the decidua. Collectively, these findings identify type V collagen as a critical ECM regulator required for maintaining decidual integrity, supporting angiogenesis, and ensuring successful pregnancy.