Regulator of G protein signalling 4 controls secretion of von Willebrand factor to the subendothelial matrix

Abstract

The haemostatic protein von Willebrand Factor (VWF) exists in plasma and subendothelial pools; the former secreted from endothelial storage granules, Weibel-Palade bodies (WPBs), by basal secretion with a contribution from agonist-stimulated secretion, the latter secreted into the subendothelial matrix by a constitutive pathway, not involving WPBs. We set out to determine if the constitutive release of subendothelial VWF is actually regulated and if so, what functional consequences this might have. Constitutive VWF secretion can be increased by a range of factors; changes in VWF expression, levels of TNF-alpha or other environmental cues. An RNAseq analysis revealed that expression of RGS4 (Regulator of G protein signalling 4) was reduced in endothelial cells (HUVECs) grown under these conditions. si-RGS4 treatment of HUVECs increased constitutive basolateral secretion of VWF, probably by affecting the anterograde secretory pathway. In a simple model of endothelial damage we show that RGS4-silenced cells increased platelet recruitment onto the subendothelial matrix under flow. These results show that changes in RGS4 expression alter levels of subendothelial VWF, affecting platelet recruitment. This introduces a novel control over VWF function.