title: Endoglin promotes angiogenesis in cell- and animal-based models of retinal neovascularization.
abstract: OBJECTIVE
  We investigated endoglin expression in hypoxic microvascular endothelial cells and retinal endoglin expression in rats that develop experimental oxygen-induced retinopathy (OIR). We also tested neutralizing antibodies (Abs) against endoglin (anti-CD105 Ab) and VEGF (anti-VEGF Ab) either alone or in combination for efficacy against serum-induced retinal microvascular endothelial cell proliferation and retinal neovascularization (NV) in OIR rats. To our knowledge, this marks the first time that a biologic agent has been used to target retinal endoglin and modulate retinal neovascularization.
  
  
  METHODS
  Induction of endoglin by hypoxia was measured by immunohistochemical analysis and ELISA. Proliferation was quantified using a colorimetric 5-bromo-2-deoxyuridine ELISA. Western blots were used to measure endoglin levels in retinas of OIR rats. Immunohistochemical staining was also preformed in OIR rats using anti-CD105 and fluorescein isothiocyanate-conjugated isolectin B4 antibodies.
  
  
  RESULTS
  Anti-CD105 Ab and Anti-VEGF Ab, administered alone or in combination, reduced serum-induced retinal microvascular endothelial cell proliferation. Additionally, in a rat model of oxygen-induced retinopathy, retinal endoglin was significantly increased at 14(2), 14(3), 14(4) and 14(6) compared with retinal levels in control rats. At 14(2), immunohistochemical analysis demonstrated that endoglin was elevated in newly developed vessels at the peripheral extent of major veins, precisely where NV is expected to develop in OIR rats. Neutralizing anti-CD105 reduced retinal NV in OIR rats.
  
  
  CONCLUSIONS
  Our data support other studies showing that reduction of endoglin expression inhibits retinal NV. Our findings demonstrate that retinal endoglin immunolocalization overlaps with nascent neovascular structures in OIR rats. Therefore, endoglin may serve as a useful predictor of incipient neovascular disease.
authors.affiliation: Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, Tennessee, United States.
authors.forename: Joshua M
authors.initials: JM
authors.lastname: Barnett
authors.affiliation: Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, Tennessee, United States.
authors.forename: Sandra
authors.initials: S
authors.lastname: Suarez
authors.affiliation: Department of Ophthalmology and Visual Sciences, Vanderbilt University School of Medicine, Nashville, Tennessee, United States.
authors.forename: Gary W
authors.initials: GW
authors.lastname: McCollum
authors.affiliation: Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, Tennessee, United States.
authors.forename: John S
authors.initials: JS
authors.lastname: Penn
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D015153:Blotting, Western; D049109:Cell Proliferation; D002478:Cells, Cultured; D004195:Disease Models, Animal; D018450:Disease Progression; D000071063:Endoglin; D042783:Endothelial Cells / Q000378:metabolism / Q000473:pathology*; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007150:Immunohistochemistry; D007231:Infant, Newborn; D047908:Intracellular Signaling Peptides and Proteins / Q000096:biosynthesis*; D009389:Neovascularization, Pathologic / Q000378:metabolism* / Q000473:pathology; D051381:Rats; D015861:Retinal Neovascularization / Q000378:metabolism* / Q000473:pathology; D012171:Retinal Vessels / Q000378:metabolism* / Q000473:pathology
chemical_list: D000071063:Endoglin; C501740:Eng protein, rat; D047908:Intracellular Signaling Peptides and Proteins
keywords: angiogenesis; early diagnostic biomarker; retinal neovascularization