Scribble (Scrib) is highly conserved epithelial polarity protein. Also endothelial cells express Scrib, but its function in the vascular system is elusive. Given that Scrib controls the polarized phenotype of epithelial cells, we hypothesize that also in endothelial cells Scrib contributes to mechanotransduction and phenotype maintenance in the vasculature.

Unidirectional laminar flow generated by the ibidi-flow system induced an alignment of HUVEC and resulted in a translocation of Scrib to the leading part of the cell diametric to the flow direction. Upon shear stress exposure, HUVEC treated with Scrib siRNA showed an increased cell length and size and a changed F-actin pattern from circular to stress fibre morphology compared to scrambled siRNA transfected cells. Analyzing the role of Scrib in shear stress-induced signalling and gene expression, we found that Scrib knockdown leads to a six fold increase in the mRNA of the transcription factor KLF2. As KLF2 is known to mediate the shear stress-induced expression of eNOS, we determined the effect of Scrib in this setting. Scrib siRNA indeed increased eNOS protein level in HUVEC, suggestive of a vasoprotective effect of Scrib downregulation. To test this aspect, HUVEC were exposed to TNFa to induce inflammatory activation as determined by the expression of the adhesion molecule VCAM1. Indeed, Scrib knockdown attenuated the TNFa-induced VCAM-1 protein expression.

Taken together, these observations identify Scrib as a negative regulator of endothelial shear stress signalling. Inhibition of Scrib could be a strategy to enhance the beneficial effects of laminar flow on endothelial cell function.