Platelet interactions with subendothelial surfaces under physiological shear conditions: Response to type VI collagen and an endothelial cell wound model

[摘要] The elucidation of the molecular mechanisms of platelet adhesion and aggregation in response to naturally occurring subendothelial surfaces under flow conditions is important medically in atherosclerosis and mural thrombosis. Type VI collagen is a subendothelial constituent that binds vWF and platelets. The interaction of platelets with type VI collagen and the roles of platelet glycoprotein receptors and vWF were studied under flow conditions using epi-fluorescent video microscopy coupled with digital image processing. We found that surface coverage was less than 6% on collagen VI at a high wall shear rate (1000s$sp{-1}$), and approximately 60% at a low wall shear rate (100s$sp{-1}$). The molecular mechanisms involved in low shear platelet binding were studied using monoclonal antibodies to platelet GPIb and GPIIb-IIIa, and polymeric ATA. Anti-GPIIb-IIIa was the most effective in eliminating adhesion (surface coverage, 0.8%), followed by anti-GPIb (4.3%), and ATA (12.6%). Experiments with vWD blood indicated that vWF is involved in platelet adhesion to collagen VI at 100s$sp{-1}$. Our results suggest a possible role for collagen VI and vWF in platelet adhesion and aggregation in vascular regions with low shear rates.The endothelial cells lining the vasculature present the ultimate biocompatible surface to flowing blood. Upon blood vessel injury the endothelial cells exhibit an acute response by releasing compounds that mediate the local tissue response. Endothelial derived PGI$sb2$ and NO act as local modulators of platelet function. To incorporate this aspect of a vascular wound into our model of a damaged blood vessel, monolayers of human umbilical vein endothelial cells were cultured on collagen I coated coverslips and subjected to microinjury prior to exposure to flowing blood. To determine the effect of PGI$sb2$ on platelet function, monolayers of HUVECs were incubated with aspirin to inhibit PGI$sb2$ formation. The effect of NO on platelet function was also investigated by using L-NMMA to block NO production. Treatment with aspirin resulted in increased platelet adhesion within the wound site, while treatment with L-NMMA did not. This indicates that endothelial PGI$sb2$ but not NO may act to reduce platelet reactivity within a wound.

[发布机构] Rice University

[效力级别] engineering