Abstract
Purpose:
Many studies have tried to characterize corneal epithelial stem cell markers, based on their restricted expression pattern in the basal cell layer of the limbal epithelium. This study focused on markers identified by a functional approach. ABCG2/BCRP, an ATP-transporter protein, identifies a population of human limbal epithelial cells with a high colony-forming efficiency in vitro. C/EBPδ and Bmi-1 identify quiescent stem cells in the limbus and are responsible for mitotic quiescence and self-renewal properties while p63α sustain the stem cell proliferation potential. In order to validate these experimental markers in the normal human cornea, we studied their expression pattern in a large series of surgical specimens using immunohistochemistry. These data were further compared with the cytokeratin profile of the corneal and limbal epithelium.
Methods:
Histologically normal human corneas were obtained from surgical specimens of 30 patients (age 7 m to 84 y) enucleated for uveal melanoma (16/36) or retinoblastoma (14/36) at the Hôpital Ophtalmique Jules-Gonin. Clinical charts were reviewed for corneal disease. Paraffin sections were immunostained with antibodies against C/EBPδ, Bmi-1, BCRP/ABCG2, p63α, CK3, CK5, CK15, CK19 and Ki67.
Results:
In all specimens, C/EBPδ and p63α were diffusely expressed in the nucleus of basal epithelial cells in the limbus but also in the central and peripheral cornea. By contrast, Bmi-1 expression was weak and restricted to the basal layer of the limbus. ABCG2/BCRP was demonstrated in basal cells of limbus, but also in central cornea,
Conclusions:
We studied the expression of functional stem cell markers ABCG2/BCRP, Bmi-1, p63α and C/EBPδ in the normal human cornea and found that only Bmi-1 was always restricted to limbus while ABCG2/BCRP, p63α and C/EBPδ were diffusely expressed in the corneal epithelium. These data show that caution should be exerted when extrapolating experimental data to normal human cornea.
Keywords: 482 cornea: epithelium •
554 immunohistochemistry •
721 stem cells