Quantitative analysis of collagen from normal developing corneas and corneal scars

We measured the relative solubility of collagen in acetic acid after pepsin digestion and tentatively identified the types of collagen present in corneas of rabbits of various ages and in corneal scar tissue, using hydroxyproline assays and polyacrylamide gel electrophoretic analyses. More than 80% of the collagen in normal developing rabbit cornea was soluble after pepsin treatment; no more than 45% of that in two-week-old corneal scars was soluble. The predominant collagens in normal cornea and healing tissue were types I and AB. Type AB increased from 6% of the total collagen in fetal cornea to 11% in cornea from young adults. Collagen from two-week-old corneal wounds contained 16% type AB. Corneal type AB collagen was less soluble and more resistant to degradation by mammalian collagenase than was type I collagen. Unlike the normal cornea, in healing tissue the relative rate of synthesis of type I to type AB collagens did not correspond to their deposition. These results suggest a basic alteration in the molecular structure of the corneal scar, which may be instrumental in preventing the healing tissue from producing a normal, functioning organ.