© 2001 by European Society of Cardiology
Copyright © 2001, European Society of Cardiology
Platelet-released phospholipids link haemostasis and angiogenesis
aExperimental Cell Research Program, Methodist Research Institute, 1701 N. Senate, Rm. 1417 MPC, Indianapolis, IN 46202, USA
bDepartment of Physiology and Biophysics, Indiana University School of Medicine, Indianapolis, IN, USA
cDivision of Pulmonary and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
dDepartment of Biochemistry (Signal Transduction Research Group), University of Alberta, Edmonton, Alberta, Canada
* Corresponding author. Tel.: +1-317-929-2663; fax: +1-317-929-2021 dkenglish{at}msn.com
Considerable attention has focused on identifying mediators of neovascularization at sites of growth and abnormal tissue development. By contrast, mediators of angiogenesis at sites of injury and wound repair are not well defined but factors generated during blood coagulation (haemostasis) are attractive candidates. In addition to proteins generated, activated and released during the activation of clotting cascades, platelet-derived lipid mediators are now known to play a key role in many aspects of the angiogenic response. The first indication of lipid mediator involvement in angiogenesis was the discovery that lysophosphatidate (LPA), phosphatidic acid (PA) and sphingosine 1-phosphate (SPP) are high affinity agonists for G-protein coupled EDG (endothelial differentiation gene) receptors. The prototype for this family, EDG-1, was cloned from genes expressed when endothelial cells were activated to assume an angiogenic phenotype in vitro. The subsequent finding that SPP is a high affinity ligand for EDG-1 led Spiegel, Hla and associates (Lee et al., Science 1998;279:1552–1555) to hypothesize that platelet-released phospholipids play an important role in angiogenesis. These investigators and others demonstrated that SPP, LPA and phosphatidate (PA) induce many important endothelial cell responses associated with angiogenesis, including liberation of endothelial cells from established monolayers, chemotactic migration, proliferation, adherens junction assembly and morphogenesis into capillary-like structures. Although these studies indicated the potential involvement of platelet-derived phospholipids in angiogenesis, their physiological importance was not established. However, recent work demonstrates that <80% of the potent endothelial cell chemoattractive activity generated in human serum during clotting — an activity necessary for optimal angiogenesis — results from platelet-derived SPP. Other factors released from platelets during clotting, including LPA and PA, exert profound effects on endothelial cells that contribute unique aspects to the angiogenic response. These combined studies establish that SPP and other platelet-derived lipid mediators provide a novel link between haemostasis and angiogenesis.
KEYWORDS Angiogenesis; Hemostasis; Platelets; Endothelial receptors