Corneal endothelial integrity in aging mice lacking superoxide dismutase-1 and/or superoxide dismutase-3

To evaluate the age-induced changes in corneal endothelial morphology in mice lacking the cytosolic copper-zinc superoxide dismutase (SOD-1), the interstitial extracellular superoxide dismutase (SOD-3), or both of these SOD isoenzymes.

The central corneal endothelial morphologies of old C57BL-6J wild type (n=19), SOD-1 null (n=16), SOD-3 null (n=15), and SOD1/3 null (n=11) mice were evaluated using alizarin red staining and light microscope photographs. For comparison, young endothelia from the same genotypes were evaluated similarly. The levels of corneal reactive oxygen species and nitrogen species in all four genotypes were quantified using fluorimetry with 2',7'-dichlorodihydrofluorescein diacetate and OxyBURST.

In accordance with our previous findings, the mean corneal endothelial cell area was larger in the SOD-3 null genotype than in the wild type mice. The SOD-1/3 null genotype had similar cell sizes as the SOD-3 null mice but had a more irregular morphology at an older age. Apparently, these irregularities develop with time as they are not seen in young animals. The SOD-1 null mice did not differ from the wild type mice in corneal endothelial morphology. Elevated levels of reactive oxygen species were seen in SOD-1 null and SOD-3 null corneas, and elevated superoxide levels were seen in all three knockout genotypes.

The increased spontaneous age-related enlargement of corneal endothelial cells seen in the absence of SOD-3 is associated with a more irregular cell pattern when combined with a lack of SOD-1. This indicates more cellular movements and ongoing repair in the SOD-1/3 null genotype and possibly a more vulnerable corneal endothelium. SOD-3 and SOD-1 appear to have functions in preserving corneal endothelial integrity in aging.