title: Reference gene selection for real-time polymerase chain reaction in human lung cells subjected to cyclic mechanical strain.
abstract: OBJECTIVE
  The respiratory system is constantly exposed to mechanical forces that influence cellular phenotype in health and disease. Quantitative real-time PCR (qPCR) is widely used to determine gene expression. The validity of qPCR depends on using stable reference genes for normalization. The effect of cyclic mechanical strain on reference gene expression by lung epithelial, fibroblast and endothelial cells has not been studied systematically.
  
  
  METHODS
  The stability of expression of fourteen potential reference genes in response to six different regimens of cyclic mechanical strain was ranked using the geNorm tool in human lung epithelial cell lines (A549 and H441), human fetal lung fibroblasts (HFL-1), human lung microvascular endothelial cells, primary human lung fibroblasts and primary human alveolar type 2 (hAT2) cells. The expression variation of these reference genes was also screened in unstimulated whole human lung.
  
  
  RESULTS
  The stability of the selected reference genes varied within and between cell types, the variation in expression being greatest in primary cultures of hAT2. Correspondingly, the effect of expressing message for the stretch responsive gene IL-8 normalized to the 14 reference genes was greatest in the hAT2 cells, there being an almost fivefold difference in mRNA relative change comparing different reference genes in the same samples. The minimum number of genes required to derive a reliable normalization factor for experiments on single lung cell types undergoing mechanical strain was two and for whole human lung it was four.
  
  
  CONCLUSIONS
  These results demonstrate that the optimal reference genes for lung cells subjected to CMS are cell type specific.
authors.affiliation: Unit of Critical Care, National Heart and Lung Institute, Imperial College London, London, UK.
authors.forename: Liao
authors.initials: L
authors.lastname: Pinhu
authors.forename: John E S
authors.initials: JE
authors.lastname: Park
authors.forename: Weixue
authors.initials: W
authors.lastname: Yao
authors.forename: Mark J  D
authors.initials: MJ
authors.lastname: Griffiths
mesh_terms: D002460:Cell Line; D042783:Endothelial Cells / Q000166:cytology / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D015870:Gene Expression / Q000502:physiology*; D006801:Humans; D016209:Interleukin-8 / Q000235:genetics* / Q000378:metabolism; D008168:Lung / Q000166:cytology / Q000378:metabolism*; D016133:Polymerase Chain Reaction / Q000379:methods*; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics*; D015203:Reproducibility of Results; D020545:Respiratory Mucosa / Q000166:cytology / Q000378:metabolism; D013314:Stress, Mechanical
chemical_list: D016209:Interleukin-8; D012333:RNA, Messenger