title: Development of congenital stromal corneal dystrophy is dependent on export and extracellular deposition of truncated decorin.
abstract: OBJECTIVE
  Congenital stromal corneal dystrophy (CSCD) is an autosomal dominant condition with clouding of the cornea due to stromal opacities. It is caused by mutations in the decorin gene (DCN) leading to the expression of a truncated form of decorin. In an attempt to replicate this condition in mice, a knock-in mouse strain, 952delT Dcn, was created.
  
  
  METHODS
  Mice were constructed by targeted mutation. Sequencing of genomic DNA confirmed correct genotype. Mouse and human corneas, including corneas from patients with CSCD, and primary keratocyte cultures were subjected to Western blot analysis, transmission electron microscopy, and immunofluorescence microscopy.
  
  
  RESULTS
  Histologically, the mice did not show any organ pathology. Corneas were clear, and the electron-lucent deposits observed in CSCD were not present. Furthermore, while nearly equivalent amounts of normal and truncated decorin are present in CSCD corneas, truncated decorin was hardly detectable in the mouse corneas. By immunofluorescence analysis of corneas from 952delT Dcn homozygous mice, decorin was found only in keratocytes. In primary cultures of mouse corneal explants, truncated decorin was retained intracellularly in contrast with human corneal explants where truncated decorin was exported into the culture medium. Immunofluorescence analysis revealed that native mouse decorin localized to the Golgi complex, whereas the truncated decorin accumulated in the endoplasmic reticulum (ER).
  
  
  CONCLUSIONS
  The ER retention of truncated decorin may explain why the mouse corneas remained clear. The consequences of the decorin mutation are different in mice and humans, and 952delT Dcn knock-in mice are therefore not a suitable model for CSCD.
authors.affiliation: Department of Clinical Medicine, University of Bergen, Bergen, Norway 2Department of Ophthalmology, Haukeland University Hospital, Bergen, Norway.
authors.forename: Anne Elisabeth Christensen
authors.initials: AE
authors.lastname: Mellgren
authors.affiliation: Center for Medical Genetics and Molecular Medicine, Haukeland University Hospital, Bergen, Norway.
authors.forename: Ove
authors.initials: O
authors.lastname: Bruland
authors.affiliation: Department of Biomedicine, University of Bergen, Bergen, Norway.
authors.forename: Anni
authors.initials: A
authors.lastname: Vedeler
authors.affiliation: Department of Biomedicine, University of Bergen, Bergen, Norway.
authors.forename: Jaakko
authors.initials: J
authors.lastname: Saraste
authors.affiliation: Norwegian Veterinary Institute, Bergen, Norway.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Schönheit
authors.affiliation: Department of Ophthalmology, Haukeland University Hospital, Bergen, Norway.
authors.forename: Cecilie
authors.initials: C
authors.lastname: Bredrup
authors.affiliation: Center for Medical Genetics and Molecular Medicine, Haukeland University Hospital, Bergen, Norway 6Department of Clinical Science, University of Bergen, Bergen, Norway.
authors.forename: Per Morten
authors.initials: PM
authors.lastname: Knappskog
authors.affiliation: Department of Clinical Medicine, University of Bergen, Bergen, Norway 2Department of Ophthalmology, Haukeland University Hospital, Bergen, Norway.
authors.forename: Eyvind
authors.initials: E
authors.lastname: Rødahl
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D003315:Cornea / Q000378:metabolism / Q000648:ultrastructure; D003317:Corneal Dystrophies, Hereditary / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D060527:Corneal Keratocytes / Q000378:metabolism; D058575:Decorin / Q000235:genetics / Q000378:metabolism*; D004195:Disease Models, Animal; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism*; D006801:Humans; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D008854:Microscopy, Electron; D009154:Mutation
chemical_list: C546879:Dcn protein, mouse; D058575:Decorin