Abstract
Purpose: :
The cornea is the most transplanted tissue world-wide and with the current shortage of donors, alternative strategies are required to supplement tissue donation for transplantation. Over the past two decades there has been substantial research into adult corneolimbal epithelial stem cells (SC) and their therapeutic application. However, few studies have investigated when and how these SC and their niche develop in humans.
Methods: :
To characterize this development, human fetal corneas were obtained from 8-22 weeks' gestation (n=173) as well as neonatal (n=2) and adult (n=10) specimens. Histological and immunohistochemical assessments were conducted to determine changes in corneal architecture and in the expression of developmental and SC-associated genes. Fresh fetal corneas were explanted in tissue culture to propagate and characterize ocular surface progenitors using flow cytometry, RT-PCR, immunohistochemistry and colony forming assays.
Results: :
Histological analysis and confirmation by scanning electron microscopy identified a novel ridge-like structure that circumscribed the peripheral cornea, which we hypothesize represents the rudimentary SC niche. Fetal corneas from different gestational ages were stained with putative adult SC (CK-15, p63-alpha, ABCG2), proliferation (Ki-67) and differentiation (CK-3/12) markers to disclose SC activity across the entire cornea which became confined to the limbal ridge prior to eye-lid opening, a phenomena analogous to SC activity in the developing epidermis. For the first time, pure long-term cultures of fetal ocular surface epithelium were established using a murine 3T3 feeder-free system where cells displayed typical morphological, phenotypical and functional properties of adult corneolimbal epithelial SC.
Conclusions: :
These novel investigations have identified SC activity in vivo and in vitro in the developing human fetal cornea. Optimization of culture conditions and purification of this SC population may provide an alternative epithelial SC source for clinical applications.
Keywords: development • cornea: epithelium • gene/expression