Platelets Induce Proliferation of Human Umbilical Vein Endothelial Cells via CD154-CD40 Pathway Independently of VEGF

Background: Platelets take part in repairing the lesions of endothelial damage. To understand the molecular mechanism of this process, we tested the hypothesis that CD154 expressed on activated platelets stimulates proliferation of human endothelial cells. Methods: The expression levels of CD154 and CD40 on platelets and endothelial cells, respectively, were measured by flow cytometry and confocalmicroscopy. Function-blocking monoclonal antibody against CD154 was developed after immunization with CD154- transfected L cells. Results: An anti-CD40 agonist antibody and soluble CD154 both induced significant proliferation ofendothelial cells. In addition, a function-blocking anti-CD154 a ntibody inhibited the platelet-induced proliferation of endothelial cells, indicating that the CD154-CD40 pathway is involved in these cellular interactions. An anti-VEGF antibody failed to inhibit the proliferation. This, in addition to the fact that very small amounts of VEGF are released from platelets or endothelial cells, suggests that VEGF does not play an important role in the platelet-stimulated proliferation of endothelial cells. Conclusion: Our results indicate that platelets induce proliferation of endothelial cells by CD154-CD40 interactions independently of VEGF. Background: Platelets take part in repairing the lesions of endothelial damage. To understand the molecular mechanism of this process, we tested the hypothesis that CD154 expressed on activated platelets stimulates proliferation of human endothelial cells. Methods: The expression levels of CD154 and CD40 on platelets and endothelial cells, respectively, were measured by flow cytometry and confocalmicroscopy. Function-blocking monoclonal antibody against CD154 was developed after immunization with CD154- transfected L cells. Results: An anti-CD40 agonist antibody and soluble CD154 both induced significant proliferation ofendothelial cells. In addition, a function-blocking anti-CD154 a ntibody inhibited the platelet-induced proliferation of endothelial cells, indicating that the CD154-CD40 pathway is involved in these cellular interactions. An anti-VEGF antibody failed to inhibit the proliferation. This, in addition to the fact that very small amounts of VEGF are released from platelets or endothelial cells, suggests that VEGF does not play an important role in the platelet-stimulated proliferation of endothelial cells. Conclusion: Our results indicate that platelets induce proliferation of endothelial cell