Angiopoietin-2 is critical for cytokine-induced vascular leakage.
Genetic experiments (loss-of-function and gain-of-function) have established the role of Angiopoietin/Tie ligand/receptor tyrosine kinase system as a regulator of vessel maturation and quiescence. Angiopoietin-2 (Ang-2) acts on Tie2-expressing resting endothelial cells as an antagonistic ligand to negatively interfere with the vessel stabilizing effects of constitutive Ang-1/Tie-2 signaling. Ang-2 thereby controls the vascular response to inflammation-inducing as well as angiogenesis-inducing cytokines. This study was aimed at assessing the role of Ang-2 as an autocrine (i.e. endothelial-derived) regulator of rapid vascular responses (within minutes) caused by permeability-inducing agents. Employing two independent in vivo assays to quantitatively assess vascular leakage (tracheal microsphere assay, 1-5 min and Miles assay, 20 min), the immediate vascular response to histamine, bradykinin and VEGF was analyzed in Ang-2-deficient (Ang-2(-/-)) mice. In comparison to the wild type control mice, the Ang2(-/-) mice demonstrated a significantly attenuated response. The Ang-2(-/-) phenotype was rescued by systemic administration (paracrine) of an adenovirus encoding Ang-2. Furthermore, cytokine-induced intracellular calcium influx was impaired in Ang-2(-/-) endothelioma cells, consistent with reduced phospholipase activation in vivo. Additionally, recombinant human Ang-2 (rhAng-2) alone was unable to induce vascular leakage. In summary, we report here in a definite genetic setting that Ang-2 is critical for multiple vascular permeability-inducing cytokines.
Division of Vascular Oncology and Metastasis, German Cancer Research Center (DKFZ-ZMBH Alliance), Heidelberg, Germany.
Andrew V
AV
Benest
Karoline
K
Kruse
Soniya
S
Savant
Markus
M
Thomas
Anna M
AM
Laib
Elias K
EK
Loos
Ulrike
U
Fiedler
Hellmut G
HG
Augustin
D042702:Angiopoietin-2 / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D001920:Bradykinin / Q000235:genetics / Q000378:metabolism; D002199:Capillary Permeability / Q000187:drug effects / Q000235:genetics; D002478:Cells, Cultured; D016207:Cytokines / Q000494:pharmacology*; D005260:Female; D061307:Human Umbilical Vein Endothelial Cells; D008168:Lung / Q000166:cytology / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics / Q000378:metabolism
D042702:Angiopoietin-2; D016207:Cytokines; D011993:Recombinant Fusion Proteins; D042461:Vascular Endothelial Growth Factor A; D001920:Bradykinin