title: Notch signaling promotes the corneal epithelium wound healing.
abstract: OBJECTIVE
  The Notch signaling pathway plays crucial roles in regulation of cell proliferation, differentiation and cell fate decision in multiple tissues and cell types. This study was designed to test the effects of enhanced Notch activity on corneal epithelium homeostasis and wound healing using the transgenic mice that overexpressed an activated Notch1 (NICD) in cornea epithelium.
  
  
  METHODS
  The studies were performed on R26(fN1-ICD) transgenic mice that carry a NICD cDNA (cDNA) whose expression is prevented by a "Lox-STOP-Lox" cassette. When this transgenic mouse is bred to a mouse strain carrying a Cre recombinase expression cassette driven by a tissue-specific keratin 14 (K14) promoter, the floxed "STOP" cassette is excised and NICD is expressed in the cornea epithelium. The expression level of NICD and its downstream target genes, hairy and enhancer of split 1 (Hes1) and hairy/enhancer-of-split related with YRPW motif 1 (Hey1), in the transgenic corneal epithelium was examined by quantitative PCR (qPCR). The phenotypes and morphology of the transgenic corneal epithelium were compared with that of wild type (WT) controls. The proliferation rate of the epithelial cells was assessed by 5-bromo-2'-deoxyuridine (BrdU) incorporation and the differentiation statues were examined by K14, tumor protein p63 (p63), K12, and zona occludens 1 (ZO-1) immunoreactivity at either normal developmental condition or after corneal epithelial debridement. The corneal epithelial response to wound healing was studied by fluorescent staining and Richardson's staining macroscopically and by H&E staining at microscope level at 0, 6, 12, 18, and 24 h post injury.
  
  
  RESULTS
  Although overexpression of NICD in cornea epithelium led to upregulation of its downstream targets, i.e., Hes1 and Hey1, this did not alter corneal epithelial cell proliferation and differentiation. However, wound healing induced Notch activity and overexpression of NICD promoted corneal epithelial wound healing, which was in agreement with more rapid early proliferation response in NICD transgenic mice than in the wild type control mice.
  
  
  CONCLUSIONS
  These findings further demonstrate the functional role of Notch signaling in corneal epithelium wound healing response.
authors.affiliation: Department of Ophthalmology and Visual Sciences, James Graham Brown Cancer Center, University of Louisville School of Medicine, Louisville, KY, USA.
authors.forename: Huayi
authors.initials: H
authors.lastname: Lu
authors.forename: Qingxian
authors.initials: Q
authors.lastname: Lu
authors.forename: Yajuan
authors.initials: Y
authors.lastname: Zheng
authors.forename: Qiutang
authors.initials: Q
authors.lastname: Li
mesh_terms: D000818:Animals; D001483:Base Sequence; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics; D018797:Cell Cycle Proteins / Q000235:genetics; D002454:Cell Differentiation / Q000235:genetics / Q000502:physiology; D049109:Cell Proliferation; D017931:DNA Primers / Q000235:genetics; D019573:Epithelium, Corneal / Q000293:injuries* / Q000473:pathology / Q000503:physiopathology*; D015870:Gene Expression; D018398:Homeodomain Proteins / Q000235:genetics; D006706:Homeostasis; D051379:Mice; D008822:Mice, Transgenic; D051881:Receptor, Notch1 / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction; D000072056:Transcription Factor HES-1; D014945:Wound Healing / Q000235:genetics / Q000502:physiology*
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D018797:Cell Cycle Proteins; D017931:DNA Primers; D018398:Homeodomain Proteins; D051881:Receptor, Notch1; D000072056:Transcription Factor HES-1; C489734:Hes1 protein, mouse; C120420:Hey1 protein, mouse; C497762:Notch1 protein, mouse