Existence of Corneal Endothelial Slow-Cycling Cells

PURPOSE. To demonstrate the presence and location of corneal endothelial progenitor cells. METHODS. Progenitor cell markers nestin, leucine-rich repeat-containing G-protein-coupled receptor 5, Sox9, and nerve growth factor receptor p75, as well as proliferation marker Ki-67, were examined on postnatal day (P)3, P30, and P90 corneas using immunofluorescence microscopy. Mice (P3) were pulsed with 5-bromo-2'-deoxyuridine (BrdU) and chased. RESULTS. Cell proliferation was observed in all layers of P3 corneas. No posterior stromal cell proliferation was noted in P30 corneas. Progenitor cell markers were expressed in the P3 cornea, but were downregulated during maturation with minimal or no expression in P90 central corneas. In contrast, cells expressing progenitor markers were located exclusively at the corneal periphery at P90. Clusters of cells reactive for progenitor markers were in the endothelial and subendothelial space in the P90 peripheral cornea. Reactivity against BrdU was localized to the central and peripheral cornea at 1 week, and to the extreme periphery 3 weeks following a BrdU pulse. Cells reactive for both BrdU and progenitor markers were localized to the peripheral endothelium. At 3 weeks, cells reactive for BrdU and the progenitor markers were localized in the peripheral endothelium. Approximately, 20% to 45% of the progenitor marker positive cells also were labeled with BrdU. CONCLUSIONS. During development, the murine corneal endothelium is composed of proliferating cells expressing progenitor markers. In contrast, in the mature endothelium slow-cycling cells, cells expressing progenitor markers and a subpopulation of slow-cycling cells expressing progenitor makers are restricted to the endothelial periphery.