title: Human monocytes and macrophages differ in their mechanisms of adaptation to hypoxia.
abstract: BACKGROUND
  Inflammatory arthritis is a progressive disease with chronic inflammation of joints, which is mainly characterized by the infiltration of immune cells and synovial hyperproliferation. Monocytes migrate towards inflamed areas and differentiate into macrophages. In inflamed tissues, much lower oxygen levels (hypoxia) are present in comparison to the peripheral blood. Hence, a metabolic adaptation process must take place. Other studies suggest that Hypoxia Inducible Factor 1-alpha (HIF-1α) may regulate this process, but the mechanism involved for human monocytes is not yet clear. To address this issue, we analyzed the expression and function of HIF-1α in monocytes and macrophages, but also considered alternative pathways involving nuclear factor of kappa light polypeptide gene enhancer in B-cells (NFκB).
  
  
  METHODS
  Isolated human CD14⁺ monocytes were incubated under normoxia and hypoxia conditions with or without phorbol 12-myristate 13-acetate (PMA) stimulation, respectively. Nuclear and cytosolic fractions were prepared in order to detect HIF-1α and NFκB by immunoblot. For the experiments with macrophages, primary human monocytes were differentiated into human monocyte derived macrophages (hMDM) using human macrophage colony-stimulating factor (hM-CSF). The effects of normoxia and hypoxia on gene expression were compared between monocytes and hMDMs using quantitative PCR (quantitative polymerase chain reaction).
  
  
  RESULTS
  We demonstrate, using primary human monocytes and hMDM, that the localization of transcription factor HIF-1α during the differentiation process is shifted from the cytosol (in monocytes) into the nucleus (in macrophages), apparently as an adaptation to a low oxygen environment. For this localization change, protein kinase C alpha/beta 1 (PKC-α/β₁) plays an important role. In monocytes, it is NFκB1, and not HIF-1α, which is of central importance for the expression of hypoxia-adjusted genes.
  
  
  CONCLUSIONS
  These data demonstrate that during differentiation of monocytes into macrophages, crucial cellular adaptation mechanisms are decisively changed.
authors.forename: Monique
authors.initials: M
authors.lastname: Fangradt
authors.forename: Martin
authors.initials: M
authors.lastname: Hahne
authors.forename: Timo
authors.initials: T
authors.lastname: Gaber
authors.forename: Cindy
authors.initials: C
authors.lastname: Strehl
authors.forename: Roman
authors.initials: R
authors.lastname: Rauch
authors.forename: Paula
authors.initials: P
authors.lastname: Hoff
authors.forename: Max
authors.initials: M
authors.lastname: Löhning
authors.forename: Gerd-Rüdiger
authors.initials: GR
authors.lastname: Burmester
authors.forename: Frank
authors.initials: F
authors.lastname: Buttgereit
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D015687:Cell Hypoxia / Q000502:physiology; D002478:Cells, Cultured; D018922:HL-60 Cells; D006801:Humans; D008264:Macrophages / Q000378:metabolism*; D009000:Monocytes / Q000378:metabolism*; D020298:U937 Cells