Introduction: VWF strings can form within the vascular lumen following endothelial activation and have been implicated in platelet adhesion and worsened outcome following stroke. However, the molecular interactions facilitating VWF string anchorage to the endothelial surface are currently unknown. Here we examined the novel role of endothelial vimentin in mediating the anchorage of VWF strings within the cerebrovasculature. We hypothesize that VWF released from activated endothelium remains anchored at the luminal surface (i.e. VWF strings) through direct interaction with extracellular vimentin.
Methods: Cultured endothelial cell (EC) experiments were performed with human umbilical vein EC (HUVECs) and human brain microvascular EC (HBMVECs). EC were stimulated with histamine (10 uM) under flow conditions. Specific protein interactions were probed with recombinant vimentin and A2 domain of VWF. Mouse middle cerebral and superior cerebellar arteries from WT and vimentin KO mice were set up in a pressurized artery chamber, stimulated with histamine, and then processed for VWF immunofluorescence to quantify VWF strings. VWF string formation was further evaluated by cranial window preparation using labeled platelets to detect real-time in vivo string formation.
Results: In cultured EC, histamine stimulation promoted the production of long VWF strings that were significantly attenuated in the presence of recombinant vimentin or A2 domain of VWF. In pressurized cerebral arteries, histamine stimulation promoted VWF strings that aligned along the luminal endothelial surface. VWF string formation was reduced 2.9 fold in arteries from vimentin knockout mice (P=0.02). Histamine stimulation in the cranial window produced platelet-adherent strings in the pial microvasculature.
Conclusions: These studies provide in vitro and in vivo evidence for a novel interaction between vimentin and the A2 domain of VWF at the endothelial surface which contributes to the anchorage of VWF strings in the microvasculature. This vimentin/VWF interaction critically regulates VWF-mediated platelet adhesion at the surface of activated endothelium and could thus provide a novel therapeutic target in the treatment of acute ischemic stroke.