title: Hemoglobin directs macrophage differentiation and prevents foam cell formation in human atherosclerotic plaques.
abstract: OBJECTIVE
  The purpose of this study was to examine selective macrophage differentiation occurring in areas of intraplaque hemorrhage in human atherosclerosis.
  
  
  BACKGROUND
  Macrophage subsets are recognized in atherosclerosis, but the stimulus for and importance of differentiation programs remain unknown.
  
  
  METHODS
  We used freshly isolated human monocytes, a rabbit model, and human atherosclerotic plaques to analyze macrophage differentiation in response to hemorrhage.
  
  
  RESULTS
  Macrophages characterized by high expression of both mannose and CD163 receptors preferentially exist in atherosclerotic lesions at sites of intraplaque hemorrhage. These hemoglobin (Hb)-stimulated macrophages, M(Hb), are devoid of neutral lipids typical of foam cells. In vivo modeling of hemorrhage in the rabbit model demonstrated that sponges exposed to red cells showed an increase in mannose receptor-positive macrophages only when these cells contained Hb. Cultured human monocytes exposed to Hb:haptoglobin complexes, but not interleukin-4, expressed the M(Hb) phenotype and were characterized by their resistance to cholesterol loading and up-regulation of ATP-binding cassette (ABC) transporters. M(Hb) demonstrated increased ferroportin expression, reduced intracellular iron, and reactive oxygen species (ROS). Degradation of ferroportin using hepcidin increased ROS and inhibited ABCA1 expression and cholesterol efflux to apolipoprotein A-I, suggesting reduced ROS triggers these effects. Knockdown of liver X receptor alpha (LXRα) inhibited ABC transporter expression in M(Hb) and macrophages differentiated in the antioxidant superoxide dismutase. Last, LXRα luciferase reporter activity was increased in M(Hb) and significantly reduced by overnight treatment with hepcidin. Collectively, these data suggest that reduced ROS triggers LXRα activation and macrophage reverse cholesterol transport.
  
  
  CONCLUSIONS
  Hb is a stimulus for macrophage differentiation in human atherosclerotic plaques. A decrease in macrophage intracellular iron plays an important role in this nonfoam cell phenotype by reducing ROS, which drives transcription of ABC transporters through activation of LXRα. Reduction of macrophage intracellular iron may be a promising avenue to increase macrophage reverse cholesterol transport.
authors.affiliation: Department of Internal Medicine, Emory University School of Medicine, Atlanta, Georgia, USA. avfinn@emory.edu
authors.forename: Aloke V
authors.initials: AV
authors.lastname: Finn
authors.forename: Masataka
authors.initials: M
authors.lastname: Nakano
authors.forename: Rohini
authors.initials: R
authors.lastname: Polavarapu
authors.forename: Vinit
authors.initials: V
authors.lastname: Karmali
authors.forename: Omar
authors.initials: O
authors.lastname: Saeed
authors.forename: XiaoQing
authors.initials: X
authors.lastname: Zhao
authors.forename: Saami
authors.initials: S
authors.lastname: Yazdani
authors.forename: Fumiyuki
authors.initials: F
authors.lastname: Otsuka
authors.forename: Talina
authors.initials: T
authors.lastname: Davis
authors.forename: Anwer
authors.initials: A
authors.lastname: Habib
authors.forename: Jagat
authors.initials: J
authors.lastname: Narula
authors.forename: Frank D
authors.initials: FD
authors.lastname: Kolodgie
authors.forename: Renu
authors.initials: R
authors.lastname: Virmani
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D000818:Animals; D015703:Antigens, CD / Q000378:metabolism; D015214:Antigens, Differentiation, Myelomonocytic / Q000378:metabolism; D050197:Atherosclerosis / Q000276:immunology* / Q000473:pathology; D002454:Cell Differentiation; D015536:Down-Regulation; D006454:Hemoglobins / Q000502:physiology*; D006470:Hemorrhage / Q000276:immunology*; D006801:Humans; D016753:Interleukin-10 / Q000378:metabolism; D015847:Interleukin-4 / Q000378:metabolism; D007501:Iron / Q000378:metabolism; D037181:Lectins, C-Type / Q000378:metabolism; D000071518:Liver X Receptors; D008264:Macrophages / Q000166:cytology / Q000502:physiology*; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins / Q000378:metabolism; D009000:Monocytes / Q000166:cytology / Q000502:physiology; D009389:Neovascularization, Pathologic; D057093:Orphan Nuclear Receptors / Q000378:metabolism; D058226:Plaque, Atherosclerotic / Q000276:immunology* / Q000473:pathology; D011817:Rabbits; D017382:Reactive Oxygen Species / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism; D051116:Receptors, Scavenger / Q000378:metabolism; D000098902:CD163 Antigen
chemical_list: D018528:ATP-Binding Cassette Transporters; D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D000098902:CD163 Antigen; D006454:Hemoglobins; C508609:IL10 protein, human; C508598:IL4 protein, human; D037181:Lectins, C-Type; D000071518:Liver X Receptors; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins; C000605213:NR1H3 protein, human; D057093:Orphan Nuclear Receptors; D017382:Reactive Oxygen Species; D011956:Receptors, Cell Surface; D051116:Receptors, Scavenger; D016753:Interleukin-10; D015847:Interleukin-4; D007501:Iron