title: Effect of oxygen on cardiac differentiation in mouse iPS cells: role of hypoxia inducible factor-1 and Wnt/beta-catenin signaling.
abstract: BACKGROUND
  Disturbances in oxygen levels have been found to impair cardiac organogenesis. It is known that stem cells and differentiating cells may respond variably to hypoxic conditions, whereby hypoxia may enhance stem cell pluripotency, while differentiation of multiple cell types can be restricted or enhanced under hypoxia. Here we examined whether HIF-1alpha modulated Wnt signaling affected differentiation of iPS cells into beating cardiomyocytes.
  
  
  OBJECTIVE
  We investigated whether transient and sustained hypoxia affects differentiation of cardiomyocytes derived from murine induced pluripotent stem (iPS) cells, assessed the involvement of HIF-1alpha (hypoxia-inducible factor-1alpha) and the canonical Wnt pathway in this process.
  
  
  METHODS
  Embryoid bodies (EBs) derived from iPS cells were differentiated into cardiomyocytes and were exposed either to 24 h normoxia or transient hypoxia followed by a further 13 days of normoxic culture.
  
  
  RESULTS
  At 14 days of differentiation, 59 ± 2% of normoxic EBs were beating, whilst transient hypoxia abolished beating at 14 days and EBs appeared immature. Hypoxia induced a significant increase in Brachyury and islet-1 mRNA expression, together with reduced troponin C expression. Collectively, these data suggest that transient and sustained hypoxia inhibits maturation of differentiating cardiomyocytes. Compared to normoxia, hypoxia increased HIF-1alpha, Wnt target and ligand genes in EBs, as well as accumulation of HIF-1alpha and beta-catenin in nuclear protein extracts, suggesting involvement of the Wnt/beta-catenin pathway.
  
  
  CONCLUSIONS
  Hypoxia impairs cardiomyocyte differentiation and activates Wnt signaling in undifferentiated iPS cells. Taken together the study suggests that oxygenation levels play a critical role in cardiomyocyte differentiation and suggest that hypoxia may play a role in early cardiogenesis.
authors.affiliation: Heart Failure Research Group, Baker IDI Heart and Diabetes Institute, Melbourne, Australia.
authors.forename: Tanya L
authors.initials: TL
authors.lastname: Medley
authors.forename: Milena
authors.initials: M
authors.lastname: Furtado
authors.forename: Nicholas T
authors.initials: NT
authors.lastname: Lam
authors.forename: Rejhan
authors.initials: R
authors.lastname: Idrizi
authors.forename: David
authors.initials: D
authors.lastname: Williams
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Verma
authors.forename: Mauro
authors.initials: M
authors.lastname: Costa
authors.forename: David M
authors.initials: DM
authors.lastname: Kaye
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D015687:Cell Hypoxia; D002460:Cell Line; D005786:Gene Expression Regulation; D051793:Hypoxia-Inducible Factor 1 / Q000235:genetics / Q000378:metabolism; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism; D057026:Induced Pluripotent Stem Cells / Q000166:cytology* / Q000378:metabolism*; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000166:cytology* / Q000378:metabolism*; D010101:Oxygen Consumption; D015398:Signal Transduction; D051153:Wnt Proteins / Q000235:genetics / Q000378:metabolism; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism
chemical_list: D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D051153:Wnt Proteins; D051176:beta Catenin