Septin depletion reduces efficiency of VWF string release. HUVECs were depleted of SEPT2, SEPT7, and SEPT9 using siRNA and VWF string secretion under flow assessed by immunofluorescence. (A) Western blotting confirmed effective target protein depletion in HUVECs treated with 300 pM SEPT2/7/ siRNA. MLC2 phosphorylation at ser19 was reduced in SEPT2 KD cells. (B) Depletion of SEPT/7/9 inhibited VWF string formation in HUVECs exposed to 5 dynes/cm². (C) On average, SEPT2/7/9 depletion resulted in shorter VWF strings bound to the endothelial cell surface. Data presented as mean from each independent experiment (n = 3). One-way ANOVA with Tukey multiple comparison test. (D) Confocal microscopy images (0.5 μm Z stacks) were acquired using identical settings. Scale bar, 50 μm. Representative immunofluorescence images of septin and VWF staining in siLUC (top left panel), siSEPT7 (top right panel), siSEPT2 (bottom left panel), and siSEPT9 (bottom right panel) treated HUVECs.