EphrinB reverse signaling contributes to endothelial and mural cell assembly into vascular structures

Abstract

EphrinB transmembrane ligands and their cognate EphB receptor tyrosine kinases regulate vascular development through bidirectional cell-to-cell signaling, but little is known about the role of EphrinB during postnatal vascular remodeling. We report that EphrinB is a critical mediator of postnatal pericyte-to-endothelial cell assembly into vascular structures. This function is dependent upon extracellular matrixsupported cell-to-cell contact, engagement of EphrinB by EphB receptors expressed on another cell, and Srcdependent phosphorylation of the intracytoplasmic domain of EphrinB. Phosphorylated EphrinB marks angiogenic blood vessels in the developing and hypoxic retina, the wounded skin, and tumor tissue, and is detected at contact points between endothelial cells and pericytes. Furthermore, inhibition of EphrinB activity prevents proper assembly of pericytes and endothelial cells into vascular structures. These results reveal a role for EphrinB signaling in orchestrating pericyte/endothelial cell assembly, and suggest that therapeutic targeting of EphrinB may prove useful for disrupting angiogenesis when it contributes to disease. (Blood. 2009;114:1707-1716) IntroductionBlood vessels are composed of endothelial cells that form the inner lining of vessels and pericytes, also known as mural cells, that envelope the endothelium. Pericytes are embedded into the vascular basement membrane and make direct contact with endothelial cells through extensions that reach deeply into the endothelial cells, without an intervening basal membrane. 1,2 Endothelial cells are better characterized, but pericytes are emerging as critical regulators of vascular function because they are thought to stabilize the vessel wall and to regulate endothelial cell survival, growth, maturation, and permeability. 2 Pericytes have multilineage progenitor potential and are developmentally close to mesenchymal stem cells (MSCs). 3 Genetic mouse models have implicated several receptor-ligand systems as mediators of endothelial-pericyte interactions, including Ang-1/Tie2, transforming growth factor-␤ and its receptors, plateletderived growth factor (PDGF)/PDGF receptor-1, the sphingosine-1-phosphate (S1P)/S1P 1 , and Dll4/Notch. 2 The family of EphB (erythropoietin-producing hepatoma) receptors tyrosine kinases and their surface-bound EphrinB (erythropoietin-producing hepatoma interactor B) ligands have recently emerged as critical regulators of cardiovascular development and pathologic angiogenesis, modulating both endothelial cells and pericyte function. 4 Upon cell-to-cell contact, EphrinB ligands both activate the cognate EphB receptors (forward signaling) and undergo phosphorylation at the C terminus initiating signaling (reverse signaling). 5,6 Genetic experiments have shown that the global knockout of EphB4, EphrinB2, or the endothelial-specific inactivation of EphrinB2 produced a very similar phenotype of embryonic death with prominent remodeling defects of the vascular system. [7][8][9] The role of EphrinB2 reverse signaling in vascular ...

The role of pericytes in angiogenesis

“…More recently, Salvucci et al (2009) reported that Eph-B is a critical mediator of postnatal pericyte to endothelial cell assembly into vascular tubes. Furthermore, inhibition of Eph-B activity prevents assembly of pericytes and endothelial cells.…”

Ephrin-B2 regulates endothelial cell morphology and motility independently of Eph-receptor binding

“…7B). Additionally, recent data have implicated a role for EphB-ephrin-B signaling in the assembly of endothelial and mural cells into vascular structures (Salvucci et al, 2009) and also in the adhesion and migration of monocytes on endothelial cells (Pfaff et al, 2008).…”

EphrinB2 Reverse Signaling Protects against Capillary Rarefaction and Fibrosis after Kidney Injury

“…In adult mice, ephrinB has been reported to be phosphorylated and activated in ECs and pericytes in wounded skin of mice. 17 However, there are no studies investigating the role of ephrinB2 reverse signaling in angiogenesis and fibrosis after tissue injury in adults. We therefore investigated the role of ephrinB2 signaling in the kidney after injury.…”