title: Xanthine oxidase-derived ROS upregulate Egr-1 via ERK1/2 in PA smooth muscle cells; model to test impact of extracellular ROS in chronic hypoxia.
abstract: Exposure of newborn calves to chronic hypoxia causes pulmonary artery (PA) hypertension and remodeling. Previous studies showed that the redox-sensitive transcription factor, early growth response-1 (Egr-1), is upregulated in the PA of chronically hypoxic calves and regulates cell proliferation. Furthermore, we established in mice a correlation between hypoxic induction of Egr-1 and reduced activity of extracellular superoxide dismutase (EC-SOD), an antioxidant that scavenges extracellular superoxide. We now hypothesize that loss of EC-SOD in chronically hypoxic calves leads to extracellular superoxide-mediated upregulation of Egr-1. To validate our hypothesis and identify the signaling pathways involved, we utilized PA tissue from normoxic and chronically hypoxic calves and cultured calf and human PA smooth muscle cells (PASMC). Total SOD activity was low in the PA tissue, and only the extracellular SOD component decreased with hypoxia. PA tissue of hypoxic calves showed increased oxidative stress and increased Egr-1 mRNA. To mimic the in vivo hypoxia-induced extracellular oxidant imbalance, cultured calf PASMC were treated with xanthine oxidase (XO), which generates extracellular superoxide and hydrogen peroxide. We found that 1) XO increased Egr-1 mRNA and protein, 2) XO induced the phosphorylation of ERK1/2 and, 3) pretreatment with an ERK1/2 inhibitor prevented induction of Egr-1 by XO. siRNA knock-down of EC-SOD in human PASMC also upregulated Egr-1 mRNA and protein, activated ERK1/2, and enhanced SMC proliferation and reduced apoptosis. We conclude that an oxidant/antioxidant imbalance arising from loss of EC-SOD in the PA with chronic hypoxia induces Egr-1 via activation of ERK1/2 and contributes to pulmonary vascular remodeling.
authors.affiliation: Department of Pediatrics, University of Colorado Denver, Aurora, Colorado, United States of America.
authors.forename: Tanya
authors.initials: T
authors.lastname: Hartney
authors.forename: Rahul
authors.initials: R
authors.lastname: Birari
authors.forename: Sujatha
authors.initials: S
authors.lastname: Venkataraman
authors.forename: Leah
authors.initials: L
authors.lastname: Villegas
authors.forename: Maylyn
authors.initials: M
authors.lastname: Martinez
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Black
authors.forename: Kurt R
authors.initials: KR
authors.lastname: Stenmark
authors.forename: Eva
authors.initials: E
authors.lastname: Nozik-Grayck
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis; D002417:Cattle; D049109:Cell Proliferation; D002908:Chronic Disease; D004195:Disease Models, Animal; D051766:Early Growth Response Protein 1 / Q000235:genetics / Q000378:metabolism*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D005110:Extracellular Space / Q000201:enzymology; D006801:Humans; D000860:Hypoxia / Q000201:enzymology* / Q000473:pathology; D020935:MAP Kinase Signaling System; D008297:Male; D051379:Mice; D032389:Myocytes, Smooth Muscle / Q000201:enzymology* / Q000473:pathology; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D011651:Pulmonary Artery / Q000473:pathology; D034741:RNA, Small Interfering / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000378:metabolism; D015854:Up-Regulation; D014969:Xanthine Oxidase / Q000378:metabolism*
chemical_list: D051766:Early Growth Response Protein 1; D034741:RNA, Small Interfering; D017382:Reactive Oxygen Species; D013482:Superoxide Dismutase; D014969:Xanthine Oxidase; D048049:Extracellular Signal-Regulated MAP Kinases