title: Heme induces heme oxygenase 1 via Nrf2: role in the homeostatic macrophage response to intraplaque hemorrhage.
abstract: OBJECTIVE
  Intraplaque hemorrhage (IPH) is an important progression event in advanced atherosclerosis, in large part because of the delivery of prooxidant hemoglobin in erythrocytes. We have previously defined a novel macrophage phenotype (hemorrhage-associated-mac) in human advanced plaques with IPH. These may be atheroprotective in view of raised heme oxygenase 1 (HO-1), CD163, and interleukin-10 expression and suppressed oxidative stress.
  
  
  RESULTS
  We have used a combination of small interfering RNA and pharmacological reagents, protein analysis, and oxidative stress measurements to dissect the pathway leading to the development of this phenotype. We found that erythrocytes, hemoglobin, or purified heme similarly induced CD163 and suppressed human leukocyte antigen and reactive oxygen species. HO-1 was required for the development of each of these features. Challenge of macrophages with purified heme provoked nuclear translocation of Nrf2, and Nrf2 small interfering RNA resulted in significant inhibition of the ability of heme to induce HO-1 protein. Furthermore, tert-butyl-hydroquinone, which activates Nrf2, upregulated CD163, suppressed human leukocyte antigen, and induced interleukin-10, further supporting a role for Nrf2-mediated signaling. However, an inducible protein transactivator is also probably necessary, as heme-induced HO-1 mRNA expression was fully inhibited by the protein synthesis inhibitor cycloheximide.
  
  
  CONCLUSIONS
  Our experiments define an Nrf2-mediated pathway by which heme induces a homeostatic macrophage response following IPH.
authors.affiliation: Cardiovascular Sciences, National Heart and Lung Institute, Imperial College London, London, United Kingdom. joseph.boyle@imperial.ac.uk
authors.forename: Joseph J
authors.initials: JJ
authors.lastname: Boyle
authors.forename: Michael
authors.initials: M
authors.lastname: Johns
authors.forename: Jonathan
authors.initials: J
authors.lastname: Lo
authors.forename: Alessandra
authors.initials: A
authors.lastname: Chiodini
authors.forename: Nicola
authors.initials: N
authors.lastname: Ambrose
authors.forename: Paul C
authors.initials: PC
authors.lastname: Evans
authors.forename: Justin C
authors.initials: JC
authors.lastname: Mason
authors.forename: Dorian O
authors.initials: DO
authors.lastname: Haskard
mesh_terms: D015703:Antigens, CD / Q000378:metabolism; D015214:Antigens, Differentiation, Myelomonocytic / Q000378:metabolism; D002478:Cells, Cultured; D004912:Erythrocytes / Q000473:pathology; D006418:Heme / Q000378:metabolism*; D051547:Heme Oxygenase-1 / Q000378:metabolism*; D006470:Hemorrhage / Q000473:pathology / Q000503:physiopathology*; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D016753:Interleukin-10 / Q000378:metabolism; D008264:Macrophages / Q000187:drug effects / Q000473:pathology / Q000502:physiology*; D009000:Monocytes / Q000473:pathology; D051267:NF-E2-Related Factor 2 / Q000378:metabolism*; D058226:Plaque, Atherosclerotic / Q000473:pathology / Q000503:physiopathology*; D034741:RNA, Small Interfering / Q000494:pharmacology; D011956:Receptors, Cell Surface / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D000098902:CD163 Antigen
chemical_list: D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D000098902:CD163 Antigen; D051267:NF-E2-Related Factor 2; C495635:NFE2L2 protein, human; D034741:RNA, Small Interfering; D011956:Receptors, Cell Surface; D016753:Interleukin-10; D006418:Heme; D051547:Heme Oxygenase-1