title: FIH-1/c-kit signaling: a novel contributor to corneal epithelial glycogen metabolism.
abstract: OBJECTIVE
  Corneal epithelial cells have large stores of glycogen, which serve as their primary energy source. Recently, we demonstrated that factor-inhibiting hypoxia-inducible factor 1 (FIH-1) diminished glycogen stores in vitro and in vivo, working through the Akt/Glycogen Synthase Kinase (GSK)-3β pathway. In this study we investigated the relationship between FIH-1 and c-kit as it pertains to limbal and corneal epithelial glycogen stores.
  
  
  METHODS
  Limbal and corneal epithelia from wild-type FIH-1(-/-) and Kit(W/Wv) mice were stained with periodic acid Schiff (PAS) to detect glycogen. RNA samples prepared from laser-capture microdissected populations of limbal epithelium were subjected to real-time quantitative PCR to determine c-kit ligand expression. Submerged cultures of primary human corneal epithelial keratinocytes (HCEKs) transduced with FIH-1 were treated with c-kit ligand to establish further a FIH-1/c-kit interaction via Western analysis. Akt phosphorylation was assessed by Western blotting.
  
  
  RESULTS
  The limbal epithelial cells of FIH-1 null mice had an increase in glycogen levels as well as increased c-kit ligand mRNA compared with wild-type controls. Consistent with a FIH-1/c-kit association, the diminished Akt signaling observed in FIH-1-overexpressing HCEKs could be restored by the addition of c-kit ligand. Interestingly, Akt signaling and glycogen content of the corneal epithelium were significantly decreased in c-kit mutant mice.
  
  
  CONCLUSIONS
  c-Kit signaling has been shown to affect glucose metabolism via the Akt/GSK-3β pathway. An inverse relationship between FIH-1 and c-kit signaling pathways accounts, in part, for differences in glycogen content between corneal and limbal epithelial cells.
authors.affiliation: Department of Dermatology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611, USA.
authors.forename: Han
authors.initials: H
authors.lastname: Peng
authors.forename: Julia
authors.initials: J
authors.lastname: Katsnelson
authors.forename: Wending
authors.initials: W
authors.lastname: Yang
authors.forename: Melissa A
authors.initials: MA
authors.lastname: Brown
authors.forename: Robert M
authors.initials: RM
authors.lastname: Lavker
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D004734:Energy Metabolism; D019573:Epithelium, Corneal / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D018014:Gene Transfer Techniques; D006003:Glycogen / Q000378:metabolism*; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D016850:Limbus Corneae / Q000166:cytology; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D019009:Proto-Oncogene Proteins c-kit / Q000378:metabolism* / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology*; D019089:Stem Cell Factor / Q000235:genetics
chemical_list: D012333:RNA, Messenger; D019089:Stem Cell Factor; D006003:Glycogen; D006899:Mixed Function Oxygenases; C551240:factor inhibiting hypoxia-inducible factor 1, mouse; D019009:Proto-Oncogene Proteins c-kit; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D051057:Proto-Oncogene Proteins c-akt; D038362:Glycogen Synthase Kinase 3
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