Maintained expression of von Willebrand Factor during endothelial apoptosis

Introduction:

Von Willebrand Factor (VWF) plays an important role in haemostasis by binding platelets, stabilizing factor VØ and focusing fibrin formation to sites platelet adhesion. During apoptosis, endothelial cells detached from their underlying matrix, and shed into the circulation. These apoptosis particles have the potential to act as micro-emboli and sites for the formation of micro-thrombi. increased tissue factors and hence pro-coagulation activity has been reported for apoptotic endothelium, and this has been suggested as potentially important for atherosclerosis (1-3).separately, our group has demonstrated anti-coagulant activity for apoptotic endothelial cells in the form of maintained urokinase plasminogen activator (5),and anti-platelet aggregatory activity (4-6).recognizing that micro-thrombotic potential results from a balanced between pro- and anti- thrombotic activities, this study investigates antigen levels and activity of VWF in apoptotic human umbilical vein endothelium (HUVEC).

Methods:

HUVEC were treated by serum and serum and matrix deprivation and also serum deprivation in detached form to: serum deprived non-apoptotic endothelial cells, serum and matrix deprive apoptotic endothelial cells .VWF antigen levels as well as VWF collagen binding activity were determined by ELISA. The effect of PMA stimulation on VWF secretion was also studied for these populations.

Results:

VWF was detected in all HUVEC populations studied, while levels were similar for apoptotic and non-apoptotic population. VWF activity was confirmed on the basis of collagen binding, and paralleled levels for antigen level. When cells were treated with PMA, secretion of VWF and this appeared to be bi-phasic, with an early response within 10 minutes, followed by a delayed prolonged and greater response one to two hours after stimulation. Apoptotic cells also appeared response to PMA.

Conclusion:

VWF is maintained during endothelial apoptotis, so that this pro-coagulation molecule may facilitate micro-thrombosis around apoptosis particles. the antigen appears to be primarily intracellular with limited potential for secretion.