title: The non-canonical NOTCH ligand DLK1 exhibits a novel vascular role as a strong inhibitor of angiogenesis.
abstract: OBJECTIVE
  The epidermal growth factor-like protein Delta-like 1 (DLK1) regulates multiple differentiation processes. It resembles NOTCH ligands structurally and is considered a non-canonical ligand. Given the crucial role of the NOTCH pathway in angiogenesis, we hypothesized that DLK1 could regulate angiogenesis by interfering with NOTCH. We therefore investigated the expression and function of DLK1 in the vascular endothelium and its role in the regulation of angiogenesis.
  
  
  RESULTS
  We report DLK1 expression in the endothelium of different species, including human, cow, pig, and mouse. Angiogenesis was studied by using in vitro and in vivo models of angiotube formation in endothelial cells, retinal phenotypes in Dlk1-null mice, and vessel development in zebrafish. DLK1 overexpression strongly inhibited angiotube formation, whereas lung endothelial cells from Dlk1-null mice were highly angiogenic. In vivo studies demonstrated DLK1-mediated inhibition of neovessel formation and revealed an altered pattern of angiogenesis in the retinas of Dlk1-null mice. The expression of human DLK1 in zebrafish embryos severely altered the formation of intersegmental vessels, while knockdown of the orthologous gene was associated with ectopic and increased tumour-induced angiogenesis. NOTCH-dependent signalling as determined by gene expression reporters was inhibited by the presence of DLK1 in vascular endothelial cells. In contrast, Dlk1-null mice showed increased levels of NOTCH downstream targets, such as Snail and Slug.
  
  
  CONCLUSIONS
  Our results unveil a novel inhibitory role for DLK1 in the regulation of angiogenesis, mediated by antagonism of the NOTCH pathway, and establish the basis for investigating its action in pathological settings.
authors: Laboratorio Mixto Consejo Superior de Investigaciones Científicas-Fundación Renal Iñigo Alvarez de Toledo, Centro de Biología Molecular Severo Ochoa, Nicolás Cabrera 1, 28029 Madrid, Spain.
authors: Patricia
authors: P
authors: Rodríguez
authors: María Angeles
authors: MA
authors: Higueras
authors: Alvaro
authors: A
authors: González-Rajal
authors: Arántzazu
authors: A
authors: Alfranca
authors: Marta
authors: M
authors: Fierro-Fernández
authors: Rosa Ana
authors: RA
authors: García-Fernández
authors: Maria José
authors: MJ
authors: Ruiz-Hidalgo
authors: María
authors: M
authors: Monsalve
authors: Fernando
authors: F
authors: Rodríguez-Pascual
authors: Juan Miguel
authors: JM
authors: Redondo
authors: Jose Luis
authors: JL
authors: de la Pompa
authors: Jorge
authors: J
authors: Laborda
authors: Santiago
authors: S
authors: Lamas
mesh_terms: D000818:Animals; D002135:Calcium-Binding Proteins; D002417:Cattle; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins / Q000502:physiology*; D051379:Mice; D009389:Neovascularization, Pathologic / Q000209:etiology; D018919:Neovascularization, Physiologic; D051880:Receptors, Notch / Q000037:antagonists & inhibitors; D015861:Retinal Neovascularization / Q000209:etiology; D015398:Signal Transduction; D014945:Wound Healing; D015027:Zebrafish
chemical_list: D002135:Calcium-Binding Proteins; C512925:Dlk1 protein, mouse; D036341:Intercellular Signaling Peptides and Proteins; D051880:Receptors, Notch