Platelet angiogenic activities and their regulation on EPC functions

Platelets are essential for haemostasis and thrombosis but also play a major role in angiogenesis. Activated platelets recruit progenitor cells and induce differentiation into endothelial progenitor cells (EPCs) which contribute importantly to vascular regeneration and endothelium reparation. However the interactions between platelets and EPCs are poorly understood. The present book provides new evidence supporting that platelets are an important player in angiogenesis. We have shown that platelets store pro-angiogenic and anti-angiogenic regulators in separate α–granules and may release them distinctly upon different platelet stimuli. PAR1-PR which is rich in pro-angiogenic regulators promotes angiogenesis more profoundly both in vitro and in vivo as compared to PAR4-PR which is prone anti-angiogenic regulator release. Apart from platelet-released mediators we have also identified that platelet membrane components tetraspanin CD151 and α6β1 integrin as well as EPC α6β1 integrin are important for platelet-enhanced EPC tube formation. Furthermore our results indicate that platelets undergo de novo protein synthesis of SDF-1α upon activation.