title: Early macrophage recruitment and alternative activation are critical for the later development of hypoxia-induced pulmonary hypertension.
abstract: BACKGROUND
  Lung inflammation precedes the development of hypoxia-induced pulmonary hypertension (HPH); however, its role in the pathogenesis of HPH is poorly understood. We sought to characterize the hypoxic inflammatory response and to elucidate its role in the development of HPH. We also aimed to investigate the mechanisms by which heme oxygenase-1, an anti-inflammatory enzyme, is protective in HPH.
  
  
  RESULTS
  We generated bitransgenic mice that overexpress human heme oxygenase-1 under doxycycline control in an inducible, lung-specific manner. Hypoxic exposure of mice in the absence of doxycycline resulted in early transient accumulation of monocytes/macrophages in the bronchoalveolar lavage. Alveolar macrophages acquired an alternatively activated phenotype (M2) in response to hypoxia, characterized by the expression of found in inflammatory zone-1, arginase-1, and chitinase-3-like-3. A brief 2-day pulse of doxycycline delayed, but did not prevent, the peak of hypoxic inflammation, and could not protect against HPH. In contrast, a 7-day doxycycline treatment sustained high heme oxygenase-1 levels during the entire period of hypoxic inflammation, inhibited macrophage accumulation and activation, induced macrophage interleukin-10 expression, and prevented the development of HPH. Supernatants from hypoxic M2 macrophages promoted the proliferation of pulmonary artery smooth muscle cells, whereas treatment with carbon monoxide, a heme oxygenase-1 enzymatic product, abrogated this effect.
  
  
  CONCLUSIONS
  Early recruitment and alternative activation of macrophages in hypoxic lungs are critical for the later development of HPH. Heme oxygenase-1 may confer protection from HPH by effectively modifying the macrophage activation state in hypoxia.
authors.affiliation: Division of Newborn Medicine, Children's Hospital Boston, Harvard Medical School, MA 02115, USA.
authors.forename: Eleni
authors.initials: E
authors.lastname: Vergadi
authors.forename: Mun Seog
authors.initials: MS
authors.lastname: Chang
authors.forename: Changjin
authors.initials: C
authors.lastname: Lee
authors.forename: Olin D
authors.initials: OD
authors.lastname: Liang
authors.forename: Xianlan
authors.initials: X
authors.lastname: Liu
authors.forename: Angeles
authors.initials: A
authors.lastname: Fernandez-Gonzalez
authors.forename: S Alex
authors.initials: SA
authors.lastname: Mitsialis
authors.forename: Stella
authors.initials: S
authors.lastname: Kourembanas
mesh_terms: D000818:Animals; D002245:Carbon Dioxide / Q000378:metabolism; D002455:Cell Division / Q000276:immunology; D051547:Heme Oxygenase-1 / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D006801:Humans; D006976:Hypertension, Pulmonary / Q000276:immunology* / Q000473:pathology; D000860:Hypoxia / Q000276:immunology* / Q000473:pathology; D016753:Interleukin-10 / Q000378:metabolism; D008262:Macrophage Activation / Q000276:immunology*; D016676:Macrophages, Alveolar / Q000276:immunology* / Q000473:pathology; D051379:Mice; D008822:Mice, Transgenic; D009000:Monocytes / Q000276:immunology / Q000473:pathology; D009131:Muscle, Smooth, Vascular / Q000276:immunology / Q000473:pathology; D011014:Pneumonia / Q000276:immunology / Q000473:pathology; D011651:Pulmonary Artery / Q000276:immunology / Q000473:pathology; D015533:Transcriptional Activation / Q000276:immunology
chemical_list: C556062:IL10 protein, mouse; D016753:Interleukin-10; D002245:Carbon Dioxide; D051547:Heme Oxygenase-1