The cellular basis of corneal transparency: evidence for 'corneal crystallins'

In vivo corneal light scattering measurements using a novel confocal micros cope demonstrated greatly increased backscatter from corneal stromal fibroc ytes (keratocytes) in opaque compared to transparent corneal tissue in both humans and rabbits. Additionally, two water-soluble proteins, transketolas e (TKT) and aldehyde dehydrogenase class 1 (ALDHI), isolated from rabbit ke ratocytes showed unexpectedly abundant expression (similar to 30% of the so luble protein) in transparent corneas and markedly reduced levels in opaque scleral fibroblasts or keratocytes from hazy, freeze injured regions of th e cornea, Together these data suggest that the relatively high expressions of TKT and ALDH1 contribute to corneal transparency in the rabbit at the ce llular level, reminiscent of enzyme-crystallins in the lens. We also note t hat ALDH1 accumulates in the rabbit corneal epithelial cells, rather than A LDH3 as seen in other mammals, consistent with the taxon-specificity observ ed among lens enzyme-crystallins, Our results suggest that corneal cells, l ike lens cells, may preferentially express water-soluble proteins, often en zymes, for controlling their optical properties.