title: A reduced oxygen tension (5%) is not beneficial for maintaining human embryonic stem cells in the undifferentiated state with short splitting intervals.
abstract: BACKGROUND
  Human embryos grow naturally in vivo in lower oxygen (O(2)) tension environments than atmospheric O(2) tension. Therefore, human embryonic stem cells (hESC), a derivative of embryos, will likely grow more favorably in a reduced O(2) tension. This study aimed to compare the behavior of hESC under reduced O(2) tension (5%) versus normoxia (21%).
  
  
  METHODS
  hESC lines were cultured in different O(2) tensions and then examined for morphology, apoptosis and gene expression profiles.
  
  
  RESULTS
  hESC grown in 5% O(2) tension were not morphologically different from hESC grown in normoxia on day 7 of the first and fourth passages. However, after prolonged culture without splitting (10-14 days), hESC colonies were thinner and looked better morphologically in 5% O(2), but the cells proliferated more slowly and their sizes were larger. At most time points, the gene expression profiles in both O(2) tensions showed no major difference in representative stemness genes (Oct-3/4, Nanog and Cripto), differentiation genes (Desmin, Nestin, alpha-fetoprotein and GDF-9) and hypoxia-related genes (HIF-1alpha and VEGF). A lower level of cyclin-D1 mRNA (suggestive of less Wnt pathway signaling on day 7 of the fourth passage) and a higher level of Desmin (suggestive of more differentiation to mesoderm, at day 7 of the first passage) were detected in 5% O(2).
  
  
  CONCLUSIONS
  This study suggests that for routine culture of hESC with a short splitting interval (7 days), a low O(2) tension (5% O(2)) probably does not provide significant advantages over the standard 21% O(2) tension for the maintenance of an undifferentiated state by the criteria used in this study.
authors.affiliation: Division of Reproductive Endocrinology and Infertility, Department of Obstetrics and Gynecology, College of Medicine and the Hospital, National Taiwan University, No. 7 Chung-Shan S. Rd, Taipei 100, Taiwan.
authors.forename: Hsin-Fu
authors.initials: HF
authors.lastname: Chen
authors.forename: Hung-Chih
authors.initials: HC
authors.lastname: Kuo
authors.forename: Wannhsin
authors.initials: W
authors.lastname: Chen
authors.forename: Fang-Chun
authors.initials: FC
authors.lastname: Wu
authors.forename: Yu-Shih
authors.initials: YS
authors.lastname: Yang
authors.forename: Hong-Nerng
authors.initials: HN
authors.lastname: Ho
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D000954:Antigens, Surface / Q000235:genetics / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects; D018929:Cell Culture Techniques; D002454:Cell Differentiation / Q000187:drug effects / Q000235:genetics; D015687:Cell Hypoxia / Q000187:drug effects / Q000235:genetics; D002460:Cell Line; D049109:Cell Proliferation; D053595:Embryonic Stem Cells / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D020869:Gene Expression Profiling; D006801:Humans; D050814:Octamer Transcription Factor-3 / Q000235:genetics / Q000378:metabolism; D010100:Oxygen / Q000494:pharmacology*; D011509:Proteoglycans / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D051153:Wnt Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D000954:Antigens, Surface; D050814:Octamer Transcription Factor-3; D011509:Proteoglycans; C107064:TRA-1-60 antigen, human; D051153:Wnt Proteins; D000469:Alkaline Phosphatase; D010100:Oxygen