Effect of SMOC1 on thrombin-induced changes in endothelial cell barrier function. (A) Fluorescein isothiocyanate–labeled dextran (70 kDa; arbitrary units [AU]) permeability in confluent cultures of human endothelial cells treated with a control siRNA (siCTL) or siRNA against SMOC1 (siSMOC1); n = 6 independent cell batches. **P < .01, ***P < .001, 2-way ANOVA and Bonferroni test. (B) CD144, CD31, and DAPI (gray) in endothelial cells under basal conditions (Control) and following the addition of thrombin (0.3 U/mL, 20 minutes). Experiments were performed in the absence and presence of recombinant SMOC1 (rSMOC1). Scale bars, 20 μm. The red boxes denote the area highlighted in the lower images. Comparable results were obtained in 4 additional experiments.