Ephrin-B2 Induces Migration of Endothelial Cells Through the Phosphatidylinositol-3 Kinase Pathway and Promotes Angiogenesis in Adult Vasculature

A bone-derived mixture of TGFβ-superfamily members forms a more mature vascular network than bFGF or TGF-β2 in vivo

Clinical trials of therapeutic angiogenesis for the treatment of cardiovascular ischemia have failed to meet the expectations with the use of single growth factors, namely VEGF and bFGF. We show here that a bovine bone-derived growth factor mixture (GFM) of TGFbetas, BMPs, and no more than 0.1% aFGF can initiate a dose-dependent angiogenic response in subcutaneously implanted Growth Factor Reduced Matrigel plugs that includes abundant smooth muscle actin positive (SMA+) tubes and functional CD31+, red blood cell filled, capillaries. Tube forming activity of the single factors, recombinant bFGF and bone-derived TGF-beta2, were comparable to GFM, but only the bone-derived factors were able to create a larger fraction of SMA+ tubes than Matrigel alone at an equal dose. Basic FGF formed a greater number of RBC-filled capillaries within the plugs than GFM or TGF-beta2 at the highest doses, although GFM created RBC-filled capillaries that penetrated deeper into the plugs than bFGF. However, bFGF showed the greatest number of non-cell-lined, RBC-filled pools, suggestive of vessel rupture, and the largest number of plugs showing signs of fluid accumulation in the form of large, cell-lined clefts in the implants. TGF-beta2 showed less RBC-filled pools, but a significant number of implants with signs of fluid accumulation. At high doses of GFM penetration by blood vessels and mesenchymal cells was obstructed by cartilage development within the plugs accompanied by a prominent band of SMA+ granulation tissue with abundant RBC-filled capillaries encapsulating the implants. Thus, GFM is also capable of dramatically remodeling the vascular system in the interstitial space surrounding the plug. These results show that GFM is capable of inducing the formation of a more mature vascular system than that formed by the single factors bFGF and TGFbeta-2. Natural mixtures of TGFbetas, BMPs, and FGFs may have superior clinical utility in therapeutic angiogenesis applications.

Role of the ephrin and Eph receptor tyrosine kinase families in angiogenesis and development of the cardiovascular system

Angiogenesis is a highly complex orchestrated process that plays a critical role in normal development and in the pathophysiology of multiple disease processes, including tumour neovascularization, ischaemic recovery, and wound healing. In recent years there has been a resurgence of interest in Eph receptors and their ligands, ephrins, as their participation in vasculogenesis and angiogenesis has become apparent. The Eph receptor family is the largest family of receptor tyrosine kinases identified to date. The Eph receptors and their membrane-anchored ligands, ephrins, are unique in that they mediate bi-directional signalling. This is concomitant with activation of the Eph receptor tyrosine kinase domain and transduction of the typical forward signal into the receptor-bearing cell. The ligand-receptor interaction also leads to transduction of a reverse signal into the ephrin-bearing cell. The Eph/ephrin signalling mechanism is responsible for diverse and complex biological functions mediated by Eph receptors and ephrin ligands. These include vascular development, tissue-border formation, cell migration, axon guidance, and synaptic plasticity. The role of Eph receptors and ephrins in the processes of development of the cardiovascular system, angiogenesis, and vascular remodelling has been the subject of intense investigation since they were first identified in 1987. This review addresses the role of this new growth factor receptor tyrosine kinase family in those processes and provides new insights into the way in which Eph receptors and ephrin ligands modulate the angiogenic response and participate in vascular remodelling and vascular boundary formation during development of the cardiovascular system and vascularization of cancer.

Cooperative interaction of Angiopoietin-like proteins 1 and 2 in zebrafish vascular development

Angiopoietin-like protein (Angptl) 1 and Angptl2, which are considered orphan ligands, are highly homologous, particularly in the fibrinogen-like domain containing the putative receptor binding site. This similarity suggests potentially cooperative functions between the two proteins. In this report, the function of Angptl1 and Angptl2 is analyzed by using morpholino antisense technology in zebrafish. Knockdown of both Angptl1 and Angptl2 produced severe vascular defects due to increased apoptosis of endothelial cells at the sprouting stage. In vitro studies showed that Angptl1 and Angptl2 have antiapoptotic activities through the phosphatidylinositol 3-kinase/Akt pathway, and coinjection of constitutively active Akt/protein kinase B mRNA rescued impaired vascular development seen in double knockdown embryos. These results provide a physiological demonstration of the cooperative interaction of Angptl1 and Angptl2 in endothelial cells through phosphatidylinositol 3-kinase/Akt mediated antiapoptotic activities.

Anti-angiogenic activity of the mutant Dutch A(beta) peptide on human brain microvascular endothelial cells

Cerebral amyloid angiopathy is a common pathological feature of patients with Alzheimer's disease (AD) and it is also the hallmark of individuals with a rare autosomal dominant disorder known as hereditary cerebral hemorrhage with amyloidosis-Dutch type. We have shown previously that wild type A(beta) peptides are anti-angiogenic both in vitro and in vivo and could contribute to the compromised cerebrovascular architecture observed in AD. In the present study, we investigated the potential anti-angiogenic activity of the Dutch A(beta)(1-40) (E22Q) peptide. We show that compared to wild type A(beta), freshly solubilized Dutch A(beta) peptide more potently inhibits the formation of capillary structures induced by plating human brain microvascular endothelial cells onto a reconstituted basement membrane. Aggregated/fibrillar preparations of wild type A(beta) and Dutch A(beta) do not appear to be anti-angiogenic in this assay. The stronger anti-angiogenic activity of the Dutch A(beta) compared to wild type A(beta) appears to be related to the increased formation of low molecular weight A(beta) oligomers in the culture medium surrounding human brain microvascular endothelial cells. Using oligonucleotide microarray analysis of human brain microvascular endothelial cells, followed by a genome-scale computational analysis with the Ingenuity Pathways Knowledge Base, networks of genes affected by an anti-angiogenic dose of Dutch A(beta) were identified. This analysis highlights that several biological networks involved in angiogenesis, tumorigenesis, atherosclerosis, cellular migration and proliferation are disrupted in human brain microvascular endothelial cells exposed to Dutch A(beta). Altogether, these data provide new molecular clues regarding the pathological activity of Dutch A(beta) peptide in the cerebrovasculature.

Diverse roles of eph receptors and ephrins in the regulation of cell migration and tissue assembly

Eph receptor tyrosine kinases and ephrins have key roles in regulation of the migration and adhesion of cells required to form and stabilize patterns of cell organization during development. Activation of Eph receptors or ephrins can lead either to cell repulsion or to cell adhesion and invasion, and recent work has found that cells can switch between these distinct responses. This review will discuss biochemical mechanisms and developmental roles of the diverse cell responses controlled by Eph receptors and ephrins.

EphB4 signaling is capable of mediating ephrinB2-induced inhibition of cell migration

Signaling between the ligand ephrinB2 and the respective receptors of the EphB class is known to play a vital role during vascular morphogenesis and angiogenesis. The relative contribution of each EphB receptor type present on endothelial cells to these processes remains to be determined. It has been shown that ephrinB2-EphB receptor signal transduction leads to a repulsive migratory behavior of endothelial cells. It remained unclear whether this anti-migratory effect can be mediated by EphB4 signaling alone or whether other EphB receptors are necessary. It also remained unclear whether the kinase activity of EphB4 is pivotal to its action. To answer these questions, we developed a cellular migration system solely dependent on ephrinB2-EphB4 signaling. Using this system, we could show that EphB4 activation leads to the inhibition of cell migration. Furthermore we identified PP2, a known inhibitor of kinases of the Src family, and PD 153035, a known inhibitor of EGF receptor kinase, as inhibitors of EphB4 kinase activity. Using PP2, the inhibition of cell migration by ephrinB2 could be relieved, demonstrating that the kinase function of EphB4 is of prominent importance in this process. These results show that EphB4 activation is not only accompanying ephrinB2 induced repulsive behavior of cells, but is capable of directly mediating this effect.