Synergistic regulation of fibroblast phenotype by high-dose estrogen and matrix stiffness: implications for intrauterine adhesion therapy

Intrauterine adhesion (IUA) is a leading cause of uterine infertility and often recurs post surgery due to limited treatments. Although estrogen is widely used to prevent recurrence, its efficacy remains unclear. A key characteristic of IUA is the excessive production of extracellular matrix (ECM) by activated myofibroblasts, which disrupts normal endometrial mechanics. Whether estrogen and ECM stiffness synergistically promote fibroblast to myofibroblast transition remains unknown. This study investigates why estrogen shows unsatisfactory efficacy in preventing IUA recurrence. We cultured cells on substrates with different stiffness levels to mimic the mechanical properties of healthy and fibrotic endometrial tissues. We treated immortalized human endometrial stromal fibroblast cell lines, as well as fibroblasts isolated from normal and fibrotic tissues, with varying estrogen concentrations. Additionally, we used transforming growth factor (TGF)-beta 1 to induce fibroblast activation, creating a cellular model of intrauterine adhesion. Our results showed that high-dose estrogen promotes fibroblast-to-myofibroblast transition in normal endometrial tissue but reverses this process in fibrotic tissue. Analysis of human endometrial stromal fibroblast cell lines and TGF-β1-induced human endometrial stromal fibroblast cells further indicated that high-dose estrogen inhibits myofibroblast activation. Notably, the opposing effects of estrogen on fibroblasts from normal versus fibrotic tissues are influenced by tissue stiffness. Furthermore, estrogen receptor alpha partially mediates the response of endometrial stromal cells to high-dose estrogen. These data suggest high-dose estrogen and ECM stiffness collaboratively regulate the fibroblast phenotype. Targeting myofibroblasts with high-dose estrogen in the adhesion region represents a promising antifibrotic strategy.