Regenerative potential of the zebrafish corneal endothelium

Corneal transparency, critical for clear vision, is maintained in part by the pump function of the corneal endothelial cells that are arrested in G(1) phase of the cell cycle in adult humans. Thus loss of endothelial cells leads to a decrease in endothelial cell density. A decrease below a critical threshold results in corneal edema and subsequent vision loss. Corneal edema due to endothelial dysfunction is a common indication for transplantation in developed countries. The zebrafish has emerged as a model for vertebrate regeneration due to its ease of genetic manipulation and remarkable regenerative capacity. The purpose of this study was to investigate the response and regenerative potential of the zebrafish corneal endothelium to pharmacological and mechanical injury. Similar to the human cornea, Na(+)/K(+) ATPase activity is necessary to maintain the pump function as intracameral injection of ouabain resulted in an increase in central corneal thickness. Surgical removal of the majority of the central corneal endothelium resulted in a similar increase in corneal thickness. Remarkably, by just one week post-injury the central corneal endothelium had largely re-formed. Immunofluorescence of phosphorylated histone H3 indicated that this recovery correlated with corneal endothelial cells re-entering the cell cycle. In conclusion, our results establish zebrafish as a useful model of corneal injury and repair that may offer insights into the mechanism of cell cycle arrest in human corneal endothelial cells.