Pregnancy hormones reversibly dampen single cell vascular smooth muscle traction force and f-actin alignment

During normal pregnancy, cardiac output and blood volume increase to support the developing fetus. In tandem, systemic vascular resistance decreases to prevent adverse cardiovascular outcomes and maintain blood pressure. In addition to this altered vessel mechanical loading, hormones, including estrogen and progesterone, progressively rise. Postpartum, hormone levels drop concurrently with hemodynamic unloading. Despite known changes in tissue-scale cardiovascular function during pregnancy, the direct effects and memory of pregnancy hormones on vascular smooth muscle cell contractility and intracellular cytoskeletal structure remain elusive. Therefore, we characterize single human umbilical artery smooth muscle cell mechanics in response to hormonal stimuli independent of hemodynamic loading, extracellular matrix remodeling, and cell geometry. Using micropatterned traction force microscopy and fluorescent actin fiber imaging, we determined the roles of increased estrogen and progesterone on human umbilical artery smooth muscle cells. Cells were treated with third-trimester levels of estrogen and progesterone for 24 h, then traction force, actin fiber alignment, and nuclear morphology were evaluated before and after hormone removal. Combined estrogen and progesterone significantly dampened cell traction force compared to control, yet this relaxation was absent in groups subsequently deprived of hormone-treated media for 24 h. We observed similar trends in fiber alignment, where both estrogen- and progesterone-treated cells exhibited more disorganized fibers than controls, with complete reversal to aligned fibers after hormone removal. Our results suggest that pregnancy hormones may be flexible drivers of arterial mechanoadaptation during early pregnancy and postpartum, with cell relaxation caused by disorganized actin fibers consistent with a synthetic cell phenotype.