Induction of Endothelial Cell Chemotaxis by Sphingosine 1-Phosphate and Stabilization of Endothelial Monolayer Barrier Function by Lysophosphatidic Acid, Potential Mediators of Hematopoietic Angiogenesis

Abstract

Angiogenesis, the formation of new blood vessels, is an important component of restoration of hematopoiesis after BMT, but the mediators involved in hematopoietic angiogenesis have not been identified. We examined the influence of the lipid growth factors, phosphatidic acid (PA), lysophosphatidic acid (LPA), and sphingosine 1-phosphate (S1P), on several angiogenic properties of endothelial cells, including migration and stabilization of vascular barrier integrity. In a previous study, PA was found to disrupt the permeability of established endothelial monolayers, an early event in the angiogenic response that liberates cells for subsequent mobilization. In the present study, both PA and LPA weakly induced the chemotactic migration of endothelial cells from an established monolayer. The chemotactic response induced by PA and LPA was similar in intensity to that observed with optimal levels of the known protein endothelial cell chemoattractants, basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF). A markedly greater chemotactic response was effected by nanomolar concentrations of S1P, indicating that this platelet-derived factor plays an important role in a key aspect of angiogenesis, chemotactic migration of endothelial cells. The chemotactic response to S1P was completely inhibited by preincubation of endothelial cells with antisense oligonucleotides to the high-affinity S1P receptor, Edg-1. In addition, chemotaxis of endothelial cells to S1P was inhibited by preincubation of cells with specific inhibitors of tyrosine kinases, but inhibitors of phosphatidylinositol 3' kinase had little effect. Finally, LPA effectively stabilized endothelial monolayer barrier function, a late event in angiogenesis. Thus, the phospholipid growth factors, PA, S1P, and LPA, display divergent and potent effects on angiogenic properties of endothelial cells and angiogenic differentiation of endothelial cells potentially act in tandem to effectively induce neovascularization. These mediators may thus exert important roles in restoration of hematopoiesis, as they facilitate blood vessel formation at sites of transplanted stem cells, allowing the progeny of engrafted progenitors to move from marrow sinusoids to the peripheral vasculature.

Phosphatidylinositol 3-Kinase and NF-κB Regulate Motility of Invasive MDA-MB-231 Human Breast Cancer Cells by the Secretion of Urokinase-type Plasminogen Activator

“…nase (50). The data of the present report demonstrate that the regulatory p85␣ subunit of PI 3-kinase is required for enhanced migration of metastatic tumor cells because overexpression of a dominant negative regulatory (p85DN) subunit markedly decreased cell migration.…”

Role of G protein-coupled receptors in inflammation

“…Acta Pharmacologica Sinica npg trast to thrombin, another GPCR ligand sphingosine 1-phosphate (S1P) promotes stabilization of the endothelial barrier [69] . This effect of S1P is mediated through its receptor S1P1, which promotes adherens junction assembly in endothelial cells, thus fortifying vascular endothelial barrier [70,71] .…”

Pulmonary phosphatidic acid phosphatase and lipid phosphate phosphohydrolase

“…S1P was identified as a potent mitogen arising from the phosphorylation of sphingosine (88). This lipid phosphate was later recognized as the polar agent in serum that promoted EDG-1-overexpressing HEK 293 cells to form tubular, capillary-like networks (88) and was subsequently found to act as a chemotactic factor in angiogenesis (59,196). LPA and sphingosylphosphorylcholine were also shown to bind EDG-1 but with low affinity.…”

“…Part of the remaining "excess" LPP activity in whole lung tissue could arise from endothelial cells, which have high phosphatidate phosphohydrolase activity in other tissues (59). Whether pulmonary endothelial cells function in transcytosis and/or potocytosis as do endothelial cells in other organs is not presently known.…”

“…Gaseous exchange, the major physiological function of the lung, requires a sufficient alveolar surface area, appropriate surface tension as influenced by pulmonary surfactant, and a capillary bed positioned to deliver CO 2 and accept O 2 . S1P is known to influence angiogenesis through action via S1P 1 receptors on smooth muscle and endothelial cells (59,145). Although the S1P 1 receptor clearly plays a role in angiogenesis, the functions of the remaining S1P and LPA receptors are less defined, and the importance of these receptors in lung must still be examined in further detail.…”