The subendothelium of the HMEC-1 cell line supports thrombus formation in the absence of von Willebrand factor and collagen types I, III and VI

The macromolecular composition of the extracellular matrix (ECM) produced b y the human microvascular endothelial cell line (HMEC-1) was determined by ELISA and its thrombogenicity was studied in blood perfusion assays. Result s were compared with those obtained with the ECM produced by human umbilica l vein endothelial cells (HUVEC). The HMEC-1's ECM contains collagen type I V, fibronectin, laminin and thrombospondin, but no detectable levels of col lagen types I, III and VI, or von Willebrand factor (vWF), whereas all thes e components were found in the ECM synthesized by HUVEC. HMEC-1's ECM was p erfused with low-molecular-weight heparin-anticoagulated blood at two wall shear rates (650/s and 2600/s), representative of moderate and high arteria l wall shear rates, in parallel plate flow chambers for 5 min. This resulte d in the formation of large platelet aggregates, compared to essentially a monolayer of adherent platelets on HUVEC's ECM. Interestingly, large thromb i were formed at 2600/s when HMEC-1's ECM was perfused with the blood of a patient with severe type III von Willebrand disease lacking both plasma and platelet vWF, indicating that vWF was not absolutely required for thrombus formation on this matrix. Thrombin generated on the HMEC-1's ECM contribut ed importantly to the large platelet thrombi formed, shown by performing bl ood perfusion experiments in the presence of thrombin inhibitors. Our resul ts indicate that 1) platelet adhesion and aggregate formation on a subendot helium may occur at a high shear rate (2600/s) without the participation of collagen types I, III and VI, and vWF; and 2) the HMEC-1 cell line may pro ve useful for in vitro studies of the thrombogenic properties of microvascu lar subendothelium which in most cases does not contain fibrillar collagens and vWF.