title: Oxygen tension plays a critical role in the hematopoietic microenvironment in vitro.
abstract: BACKGROUND
  In the bone marrow mesenchymal stromal cells and osteoblasts form functional niches for hematopoietic stem and progenitor cells. This microenvironment can be partially mimicked using in vitro co-culture systems. In this study, we examined the oxygen tension in three distinct compartments in a co-culture system of purified CD34(+) cells and mesenchymal stromal cells with regard to different spatial localizations.
  
  
  METHODS
  Hypoxic cells in the co-culture were visualized by pimonidazole staining. Hematopoietic cell distribution, and functional and phenotypic characteristics were analyzed by flow cytometry. The secretion of vascular endothelial growth factor and stromal-derived factor-1 by mesenchymal stromal cells in low oxygen co-cultures was determined by an enzyme-linked immunosorbent assay. The effect of co-culture medium on the hematopoietic cell migration potential was tested in a transwell assay.
  
  
  RESULTS
  In co-cultures under atmospheric oxygen tension, regions of low oxygen tension could be detected beneath the feeder layer in which a reservoir of phenotypically more primitive hematopoietic cells is located in vitro. In low oxygen co-culture, the adhesion of hematopoietic cells to the feeder layer was decreased, whereas hematopoietic cell transmigration beneath mesenchymal stromal cells was favored. Increased vascular endothelial growth factor-A secretion by mesenchymal stromal cells under low oxygen conditions, which increased the permeability of the monolayer, was responsible for this effect. Furthermore, vascular endothelial growth factor-A expression in low oxygen mesenchymal stromal cells was induced via hypoxia-inducible factor signaling. However, stromal cell-derived factor-1 secretion by mesenchymal stromal cells was down-regulated under low oxygen conditions in a hypoxia-inducible factor-independent manner.
  
  
  CONCLUSIONS
  We demonstrate for the first time that differences in oxygen tension cause selective modification of hematopoietic cell and mesenchymal stromal cell interactions in a co-culture system, thus confirming that oxygen tension plays a critical role in the interaction between hematopoietic cells and the niche environment.
authors: Medical Clinic and Polyclinic I, University Hospital Dresden, 01307 Dresden, Germany.
authors: Duohui
authors: D
authors: Jing
authors: Manja
authors: M
authors: Wobus
authors: David M
authors: DM
authors: Poitz
authors: Martin
authors: M
authors: Bornhäuser
authors: Gerhard
authors: G
authors: Ehninger
authors: Rainer
authors: R
authors: Ordemann
mesh_terms: D018952:Antigens, CD34 / Q000378:metabolism; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism; D002448:Cell Adhesion / Q000235:genetics; D002465:Cell Movement / Q000235:genetics; D054377:Chemokine CXCL12 / Q000235:genetics / Q000378:metabolism; D018920:Coculture Techniques; D005786:Gene Expression Regulation; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D000860:Hypoxia; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism; D016130:Immunophenotyping; D016023:Integrins / Q000235:genetics / Q000378:metabolism; D059630:Mesenchymal Stem Cells / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism*; D011485:Protein Binding; D019718:Receptors, CXCR4 / Q000235:genetics / Q000378:metabolism; D055153:Stem Cell Niche / Q000502:physiology*; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics / Q000378:metabolism; D000099162:Endothelial PAS Domain-Containing Protein 1
chemical_list: D018952:Antigens, CD34; D051792:Basic Helix-Loop-Helix Proteins; D054377:Chemokine CXCL12; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D016023:Integrins; D010100:Oxygen; D019718:Receptors, CXCR4; D042461:Vascular Endothelial Growth Factor A; D000099162:Endothelial PAS Domain-Containing Protein 1