Differential expression of collagen types XVIII/endostatin and XV in normal, keratoconus, and scarred human corneas.
OBJECTIVE
This study was designed to clarify the expression of 2 closely related collagen (Col) types XVIII and XV, and the proteolytically derived endostatin fragment of ColXVIII in normal, keratoconus, and scarred human corneas.


METHODS
Immunohistochemistry, in situ hybridization, immunoelectron microscopy, and Western immunoblotting were used for human corneal samples obtained from penetrating keratoplasty.


RESULTS
In the normal cornea, ColXVIII was immunolocalized to the corneal and conjunctival epithelial basement membrane (EBM), Descemet s membrane, and the limbal and conjunctival capillaries. Immunoreaction for endostatin was otherwise similar, but it also was present in corneal epithelial cells. Western immunoblotting showed that normal cornea contains several endostatin fragments ranging from 20 to 100 kDa. ColXV was present in the EBM of the limbus and conjunctiva, but not in EBM of the clear cornea. In situ hybridization revealed that corneal basal epithelial cells were responsible for the synthesis of ColXVIII mRNA. Keratoconus cases were characterized by an irregular EBM immunoreactivity for ColXVIII and endostatin and patchy immunoreactivity beneath EBM. In scarred corneas, highly increased immunoreactivity for ColXVIII, endostatin, and ColXV was present within stroma.


CONCLUSIONS
The results indicate that ColXVIII and ColXV are differentially expressed in normal human corneas. Constant expression of ColXVIII by corneal EBM suggests that it is an important structural molecule. Aberrant expression of ColXVIII, endostatin, and ColXV in keratoconus and scarred corneas emphasizes the active role these molecules in the wound healing process.
Määttä
Marko
M
Department of Ophthalmology, Helsinki University Central Hospital, Helsinki, Finland. mmaatta@mailcity.com
Heljasvaara
Ritva
R
Sormunen
Raija
R
Pihlajaniemi
Taina
T
Autio-Harmainen
Helena
H
Tervo
Timo
T
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015153:Blotting, Western; D003094:Collagen / Q000378:metabolism*; D043170:Collagen Type XVIII / Q000378:metabolism*; D003315:Cornea / Q000378:metabolism*; D043169:Endostatins / Q000378:metabolism*; D005260:Female; D006801:Humans; D007124:Immunoenzyme Techniques; D017403:In Situ Hybridization; D007634:Keratitis / Q000378:metabolism*; D007640:Keratoconus / Q000378:metabolism*; D008297:Male; D016253:Microscopy, Immunoelectron; D008875:Middle Aged
C085811:COL15A1 protein, human; D043170:Collagen Type XVIII; D043169:Endostatins; D003094:Collagen