The Role of Decidualization in Regulating Endometrial Hemostasis during the Menstrual Cycle, Gestation, and in Pathological States

Progesterone-induced decidualized human endometrial stromal cells form a hemostatic envelope that protects against hemorrhage during invasion of endometrial capillaries by implanting blastocyst-derived cytotrophoblasts (CTs). This hemostatic milieu reflects co-upregulated expression of tissue factor (TF), the primary initiator of hemostasis via thrombin generation and plasminogen activator inhibitor type 1, which inactivates tissue-type plasminogen activator, the primary fibrinolytic agent. During deep invasion of the decidua, CTs breach and remodel spiral arteries and arterioles to produce high-conductance vessels. Shallow invasion results in incomplete vascular transformation and an underperfused fetal - placental unit associated with preeclampsia and intrauterine growth restriction. Decidual hemorrhage and severe thrombophilias elicit aberrant thrombin generation from decidual cell-expressed TF. Such thrombin induces decidual cells to synthesize and secrete soluble fms-like tyrosine kinase-1 (sFlt-1), the matrix metalloproteinases MMP-1 and MMP-3, and the neutrophil chemoattractant interleukin-8. Excess sFlt-1 at the implantation site may inhibit CT invasion by altering the angiogenic factor balance. During abruptions, thrombin-enhanced MMP-1, MMP-3 by decidual cells and neutrophil-derived proteases degrade the decidual and fetal membrane extracellular matrix to promote preterm premature rupture of the membranes. In association with long-term progestin-only contraception, overexpression of decidual cell-derived thrombin promotes aberrant angiogenesis and vessel maintenance to contribute to abnormal uterine bleeding.