Endothelial cell surface limits coagulation without modulating the antithrombin potency.

Area of Science:

• Coagulation and Anticoagulation Science
• Endothelial Cell Biology
• Thrombosis Research

Background:

• Antithrombin (AT) interacts with endothelial cells via receptors like heparan sulphate glycosaminoglycan (HSPG), potentially modulating its anticoagulant activity.
• Endothelial cells play a role in regulating coagulation and anticoagulation processes.

Purpose of the Study:

• To investigate the role of endothelial cells, particularly HSPG and other receptors, in modulating antithrombin (AT) activity.
• To evaluate the contribution of endothelial cells to anticoagulation, especially in the absence of AT.
• To identify alternative anticoagulant mechanisms present on endothelial cells.

Main Methods:

• Thrombin generation assay (TGA) performed on human umbilical vein endothelial cells (HUVEC) and human microvascular endothelial cells (HMVEC).
• Experiments involved normal and AT-deficient plasma spiked with varying concentrations of recombinant or plasma-derived AT.
• Cells were treated with heparin, heparanase enzymes, or blocking antibodies against EPCR and TFPI to assess receptor involvement.

Main Results:

• Endothelial cells reduced thrombin generation in normal plasma and maintained anticoagulation in AT-deficient plasma.
• Cells did not amplify the anticoagulant activity of added AT, and binding affinity did not correlate with anticoagulant potency.
• Binding of AT to cells was independent of HSPG, and the observed antithrombotic activity in AT-deficient plasma was not inhibited by blocking EPCR or TFPI.

Conclusions:

• Endothelial cells do not appear to provide significant co-factor activity for AT via HSPG.
• Alternative anticoagulant systems on endothelial cells contribute to maintaining antithrombotic activity, particularly in the absence of AT.
• These findings highlight novel endothelial-mediated anticoagulant mechanisms beyond AT function.