title: Redox-mediated angiogenesis in the hypoxic joint of inflammatory arthritis.
abstract: OBJECTIVE
  Inflammatory arthritis is associated with joint inflammation, synovial tissue proliferation, and degradation of articular cartilage and bone. Angiogenesis is an early and fundamental component of synovial inflammation. Oxygen metabolism is recognized as an important mediator of joint vascular remodeling. The aim of this study was to determine whether in vivo synovial hypoxia (tissue PO2 [tPO2 ]) and tumor necrosis factor (TNF) blocking therapy alter synovial vascular expression of NADPH oxidase (NOX) and how this action regulates angiogenic mechanisms.
  
  
  METHODS
  NOX-2 protein and messenger RNA expression was examined in patients with inflammatory arthritis before and after receiving TNF inhibitor (TNFi) therapy and in mice with collagen-induced arthritis (CIA). Proangiogenic processes were assessed in human microvascular endothelial cells (HMVECs) following culture with NOX-2 activators (TNFα and 4-hydroxynonenal), small interfering RNA (siRNA) for NOX, and the inhibitor diphenyleneiodonium (DPI) under conditions of normoxia or 3% hypoxia.
  
  
  RESULTS
  We demonstrated significantly increased NOX-2 expression in the joints of patients with inflammatory arthritis and the joints of mice with CIA as compared to controls. NOX-2 expression was higher in patients with synovial tPO2 levels <3% than in those with tPO2 levels >3% (P < 0.05), and correlated with in vivo macroscopic/microscopic measures of angiogenesis, such as vascularity and levels of vascular endothelial growth factor, angiopoietin 2, factor VIII, neural cell adhesion molecule, and α-smooth muscle actin (P < 0.05 for all). A decrease in NOX-2 expression was paralleled by an increase in in vivo tPO2 levels only in those patients who were defined as TNFi responders. In vitro NOX-2 activators and 3% hypoxia significantly promoted HMVEC migration, angiogenic tube formation, and secretion of proangiogenic mediators, effects that were blocked by siRNA for NOX-2 or the NOX-2 inhibitor DPI.
  
  
  CONCLUSIONS
  We demonstrated that hypoxia activates NOX-2 protein expression, and NOX-2-induced oxidative stress may be an initiating factor in driving angiogenesis.
authors.affiliation: Dublin Academic Medical Centre and St. Vincent's University Hospital, Dublin, Ireland.
authors.forename: Monika
authors.initials: M
authors.lastname: Biniecka
authors.forename: Mary
authors.initials: M
authors.lastname: Connolly
authors.forename: Wei
authors.initials: W
authors.lastname: Gao
authors.forename: Chin T
authors.initials: CT
authors.lastname: Ng
authors.forename: Emese
authors.initials: E
authors.lastname: Balogh
authors.forename: Martina
authors.initials: M
authors.lastname: Gogarty
authors.forename: Lelani
authors.initials: L
authors.lastname: Santos
authors.forename: Evelyn
authors.initials: E
authors.lastname: Murphy
authors.forename: David
authors.initials: D
authors.lastname: Brayden
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: Veale
authors.forename: Ursula
authors.initials: U
authors.lastname: Fearon
mesh_terms: D000818:Animals; D001169:Arthritis, Experimental / Q000235:genetics / Q000378:metabolism; D015535:Arthritis, Psoriatic / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism; D001172:Arthritis, Rheumatoid / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism; D016022:Case-Control Studies; D042783:Endothelial Cells / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D000860:Hypoxia / Q000235:genetics* / Q000378:metabolism; D007719:Knee Joint; D008562:Membrane Glycoproteins / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D008811:Mice, Inbred DBA; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases / Q000235:genetics* / Q000378:metabolism; D009389:Neovascularization, Pathologic / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis*; D017382:Reactive Oxygen Species; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013583:Synovial Membrane / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors*
chemical_list: D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; D014409:Tumor Necrosis Factor-alpha; C056558:CYBB protein, human; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases