title: Hypoxia promotes osteogenesis but suppresses adipogenesis of human mesenchymal stromal cells in a hypoxia-inducible factor-1 dependent manner.
abstract: BACKGROUND
  Bone fracture initiates a series of cellular and molecular events including the expression of hypoxia-inducible factor (HIF)-1. HIF-1 is known to facilitate recruitment and differentiation of multipotent human mesenchymal stromal cells (hMSC). Therefore, we analyzed the impact of hypoxia and HIF-1 on the competitive differentiation potential of hMSCs towards adipogenic and osteogenic lineages.
  
  
  RESULTS
  Bone marrow derived primary hMSCs cultured for 2 weeks either under normoxic (app. 18% O(2)) or hypoxic (less than 2% O(2)) conditions were analyzed for the expression of MSC surface markers and for expression of the genes HIF1A, VEGFA, LDHA, PGK1, and GLUT1. Using conditioned medium, adipogenic or osteogenic differentiation as verified by Oil-Red-O or von-Kossa staining was induced in hMSCs under either normoxic or hypoxic conditions. The expression of HIF1A and VEGFA was measured by qPCR. A knockdown of HIF-1α by lentiviral transduction was performed, and the ability of the transduced hMSCs to differentiate into adipogenic and osteogenic lineages was analyzed. Hypoxia induced HIF-1α and HIF-1 target gene expression, but did not alter MSC phenotype or surface marker expression. Hypoxia (i) suppressed adipogenesis and associated HIF1A and PPARG gene expression in hMSCs and (ii) enhanced osteogenesis and associated HIF1A and RUNX2 gene expression. shRNA-mediated knockdown of HIF-1α enhanced adipogenesis under both normoxia and hypoxia, and suppressed hypoxia-induced osteogenesis.
  
  
  CONCLUSIONS
  Hypoxia promotes osteogenesis but suppresses adipogenesis of human MSCs in a competitive and HIF-1-dependent manner. We therefore conclude that the effects of hypoxia are crucial for effective bone healing, which may potentially lead to the development of novel therapeutic approaches.
authors.affiliation: Department of Rheumatology and Clinical Immunology, Charité University Hospital, Berlin, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Wagegg
authors.forename: Timo
authors.initials: T
authors.lastname: Gaber
authors.forename: Ferenz L
authors.initials: FL
authors.lastname: Lohanatha
authors.forename: Martin
authors.initials: M
authors.lastname: Hahne
authors.forename: Cindy
authors.initials: C
authors.lastname: Strehl
authors.forename: Monique
authors.initials: M
authors.lastname: Fangradt
authors.forename: Cam Loan
authors.initials: CL
authors.lastname: Tran
authors.forename: Kerstin
authors.initials: K
authors.lastname: Schönbeck
authors.forename: Paula
authors.initials: P
authors.lastname: Hoff
authors.forename: Andrea
authors.initials: A
authors.lastname: Ode
authors.forename: Carsten
authors.initials: C
authors.lastname: Perka
authors.forename: Georg N
authors.initials: GN
authors.lastname: Duda
authors.forename: Frank
authors.initials: F
authors.lastname: Buttgereit
mesh_terms: D050156:Adipogenesis; D015703:Antigens, CD / Q000378:metabolism; D015687:Cell Hypoxia; D002478:Cells, Cultured; D050659:Core Binding Factor Alpha 1 Subunit / Q000235:genetics / Q000378:metabolism; D055785:Gene Knockdown Techniques; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D059630:Mesenchymal Stem Cells / Q000378:metabolism / Q000502:physiology*; D010012:Osteogenesis; D047495:PPAR gamma / Q000235:genetics / Q000378:metabolism; D010641:Phenotype; D034622:RNA Interference; D015533:Transcriptional Activation; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics / Q000378:metabolism
chemical_list: D015703:Antigens, CD; D050659:Core Binding Factor Alpha 1 Subunit; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D047495:PPAR gamma; C493709:RUNX2 protein, human; C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A