title: Hypoxia-inducible angiopoietin-2 expression is mimicked by iodonium compounds and occurs in the rat brain and skin in response to systemic hypoxia and tissue ischemia.
abstract: Angiopoietins are ligands for the endothelial cell tyrosine kinase receptor Tie-2. Ang-1, the major physiological activator of Tie-2, promotes blood vessel maturation and stability. Ang-2 counteracts this effect by competitively inhibiting the binding of Ang-1 to Tie-2. Using a combined RNase protection/semiquantitative reverse transcriptase-polymerase chain reaction approach, we demonstrate that hypoxia up-regulates Ang-2 mRNA levels by up to 3.3-fold in two human endothelial cell lines. In bovine microvascular endothelial (BME) cells, the flavoprotein oxidoreductase inhibitor diphenylene iodonium (DPI) and the related compound iodonium diphenyl mimic induction of Ang-2 but not vascular endothelial growth factor (VEGF) by hypoxia; in combination with hypoxia, DPI further increases Ang-2 expression but has no effect on the induction of VEGF by hypoxia. Neither Ang-2 or VEGF was increased by cyanide or rotenone, suggesting that failure in mitochondrial electron transport is not involved in the oxygen-sensing system that controls their expression. In ischemic rat dorsal skin flaps or in the brain of rats maintained for 12 hours under conditions of hypoxia, Ang-2 mRNA was up-regulated 7.5- or 17.6- fold, respectively. VEGF was concomitantly increased, whereas expression of Ang-1, Tie-2, and the related receptor Tie-1 was unaltered. In situ hybridization localized Ang-2 mRNA to endothelial cells in hypoxic skin. These findings 1) show that up-regulation of Ang-2 by hypoxia occurs widely in endothelial cells in vitro and in vivo; 2) suggest that induction of Ang-2, but not VEGF, by hypoxia in BME cells is controlled by a flavoprotein oxidoreductase that is sensitive to iodonium compounds; and 3) point to Ang-2 and VEGF as independently regulated and selective effectors of hypoxia-induced vascular sprouting.
authors.affiliation: Department of Morphology, University Medical Center, and Plastic and Reconstructive Surgery Unit, University Hospital, Geneva, Switzerland.
authors.forename: S J
authors.initials: SJ
authors.lastname: Mandriota
authors.forename: C
authors.initials: C
authors.lastname: Pyke
authors.forename: C
authors.initials: C
authors.lastname: Di Sanza
authors.forename: P
authors.initials: P
authors.lastname: Quinodoz
authors.forename: B
authors.initials: B
authors.lastname: Pittet
authors.forename: M S
authors.initials: MS
authors.lastname: Pepper
mesh_terms: D042702:Angiopoietin-2; D000818:Animals; D001713:Biphenyl Compounds / Q000494:pharmacology; D001921:Brain / Q000378:metabolism*; D002417:Cattle; D002460:Cell Line; D016228:Endothelial Growth Factors / Q000378:metabolism; D006801:Humans; D000860:Hypoxia / Q000378:metabolism*; D007511:Ischemia / Q000378:metabolism*; D008222:Lymphokines / Q000378:metabolism; D008297:Male; D009861:Onium Compounds / Q000494:pharmacology; D011506:Proteins / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D012867:Skin / Q000098:blood supply / Q000378:metabolism*; D015854:Up-Regulation; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors
chemical_list: D042702:Angiopoietin-2; D001713:Biphenyl Compounds; D016228:Endothelial Growth Factors; D008222:Lymphokines; D009861:Onium Compounds; D011506:Proteins; D012333:RNA, Messenger; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; C031291:diphenyliodonium; C007517:diphenyleneiodonium