Abstract
Purpose::
Corn1 mice develop corneal abnormality shortly after birth, such as epithelial hyperplasia and total vascularization, thus serving as a model for ocular surface disorders. To the end of determining the mechanism of pathogenesis, we investigated the homeostasis of corneal epithelium in the corn1 mouse.
Methods::
To track epithelial cell movement in the cornea, corn1 mice were mated with GFPU (ubiquitous GFP) mice to generate a hybrid, corn1-GFPU. Ocular surface whole-mounts were examined for the presence of GFP stripes, which was taken as a sign of directed cell movement. Cell movement was also determined directly by in vivo time-lapse fluorescence microscopy, monitoring epithelial GFP patterns over 50 weeks. Cell division was determined by systemic bromodeoxyuridine (BrdU) which was administered continuously for 24 hours by an osmotic pump. Corneal surface cells were characterized by immunohistochemistry by expression of MUC5AC, keratin 8, and keratin 12. Vascular development in the cornea was monitored by either in vivo fluorescence microscopy or sulforhodamine-101 angiogram.
Results::
Corn1-GFPU mice exhibited properties of both GFPU mice (epithelial GFP expression) and corn1 mice (epithelial hyperplasia and vascularization) in the cornea. GFP expression in the corneal epithelium was ubiquitous in newborns, but the number of highly GFP positive cells decreased gradually as the animal grew. At about two weeks, GFP-positive cell stripes appeared at the limbus toward the central cornea; the radial stripes stopped their centripetal progression in the middle of the cornea between four and six weeks. Thereafter GFP patterns remained generally unchanged, with gradual and random local movements, for the duration of observations. BrdU labeling indexes in the basal epithelium were more than 50% on average, but nearly 100% in some areas inside a hyperplastic zone. Immunohistochemistry showed that some cells were highly positive with keratin 8, some of which were also positive with MUC5AC.
Conclusions::
Epithelial cells of the adult corn1-GFPU cornea are generally statinoary and yet mitotically active, suggesting the local presence of epithelial stem cells within the cornea. Epithelial homeostasis of adult corn1-GFPU corneas is abnormal, mimicking that of a normal conjunctiva or a pathological, conjunctivalized cornea.
Keywords: cornea: epithelium • cornea: basic science • imaging/image analysis: non-clinical