title: Hypoxia induces netrin-1 and Unc5b in atherosclerotic plaques: mechanism for macrophage retention and survival.
abstract: OBJECTIVE
  Hypoxia is intimately linked to atherosclerosis and has become recognized as a primary impetus of inflammation. We recently demonstrated that the neuroimmune guidance cue netrin-1 (Ntn1) inhibits macrophage emigration from atherosclerotic plaques, thereby fostering chronic inflammation. However, the mechanisms governing netrin-1 expression in atherosclerosis are not well understood. In this study, we investigate the role of hypoxia in regulating expression of netrin-1 and its receptor uncoordinated-5-B receptor (Unc5b) in plaque macrophages and its functional consequences on these immune cells.
  
  
  RESULTS
  We show by immunostaining that netrin-1 and Unc5b are expressed in macrophages in hypoxia-rich regions of human and mouse plaques. In vitro, Ntn1 and Unc5b mRNA are upregulated in macrophages treated with oxidized low-density lipoprotein or inducers of oxidative stress (CoCl2, dimethyloxalylglycine, 1% O2). These responses are abrogated by inhibiting hypoxia-inducible transcription factor (HIF)-1α, indicating a causal role for this transcription factor in regulating Ntn1 and Unc5b expression in macrophages. Indeed, using promoter-luciferase reporter genes, we show that Ntn1- and Unc5b-promoter activities are induced by oxidized low-density lipoprotein and require HIF-1α. Correspondingly, J774 macrophages overexpressing active HIF-1α show increased netrin-1 and Unc5b expression and reduced migratory capacity compared with control cells, which was restored by blocking the effects of netrin-1. Finally, we show that netrin-1 protects macrophages from apoptosis under hypoxic conditions in a HIF-1α-dependent manner.
  
  
  CONCLUSIONS
  These findings provide a molecular mechanism by which netrin-1 and its receptor Unc5b are expressed in atherosclerotic plaques and implicate hypoxia and HIF-1α-induced netrin-1/Unc5b in sustaining inflammation by inhibiting the emigration and promoting the survival of lesional macrophages.
authors.affiliation: Department of Medicine, Marc and Ruti Bell Vascular Biology and Disease Program, Leon H. Charney Division of Cardiology, New York University School of Medicine, New York, NY 10016, USA.
authors.forename: Bhama
authors.initials: B
authors.lastname: Ramkhelawon
authors.forename: Yuan
authors.initials: Y
authors.lastname: Yang
authors.forename: Janine M
authors.initials: JM
authors.lastname: van Gils
authors.forename: Bernd
authors.initials: B
authors.lastname: Hewing
authors.forename: Katey J
authors.initials: KJ
authors.lastname: Rayner
authors.forename: Sajesh
authors.initials: S
authors.lastname: Parathath
authors.forename: Liang
authors.initials: L
authors.lastname: Guo
authors.forename: Scott
authors.initials: S
authors.lastname: Oldebeken
authors.forename: Jessica L
authors.initials: JL
authors.lastname: Feig
authors.forename: Edward A
authors.initials: EA
authors.lastname: Fisher
authors.forename: Kathryn J
authors.initials: KJ
authors.lastname: Moore
mesh_terms: D000818:Animals; D050197:Atherosclerosis / Q000378:metabolism* / Q000503:physiopathology; D015687:Cell Hypoxia / Q000235:genetics / Q000502:physiology; D002465:Cell Movement / Q000235:genetics / Q000502:physiology; D002470:Cell Survival / Q000235:genetics / Q000502:physiology; D002478:Cells, Cultured; D006801:Humans; D000860:Hypoxia / Q000235:genetics* / Q000378:metabolism; D007249:Inflammation / Q000378:metabolism / Q000503:physiopathology; D008264:Macrophages / Q000166:cytology* / Q000378:metabolism; D051379:Mice; D000075386:Netrin Receptors; D012333:RNA, Messenger / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000235:genetics* / Q000378:metabolism
chemical_list: D000075386:Netrin Receptors; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; C532445:UNC5B protein, human
keywords: HIF-1; Ntn1; apoptosis; guidance; macrophage; migration