Collagen Fibril Disorganisation in the Corneas of Keratocan-deficient Mice as Revealed by Synchrotron X-ray Diffraction

Abstract

Abstract: : Purpose: To examine collagen fibril diameter, spacing and organisation in the corneal stromas of keratocan-null Kera^-/- mice. Methods: Immediately after enucleation, the corneas from 4-month-old Kera^-/- mice and their age-matched, wild-type littermates were either fixed in 2.5% formalin (n=8) or frozen (n=12) and transported to the synchrotron radiation source at Daresbury, UK. Low-angle synchrotron X-ray patterns were obtained from which the average fibril diameter, interfibrillar spacing and the degree of order in the nearest neighbour fibril packing were assessed. Results:In corneas that were stored frozen, a small but significant increase in the average diameter of the collagen fibrils was found between wild-type and Kera^-/- corneas (32.2 nm to 35.3 nm) together with an increase in the average interfibrillar spacing (44.6 nm to 50.7 nm). Kera^-/- mice showed a significant decrease in local fibril order. Similar effects were found in the frozen and fixed corneas. Conclusions: Kera^-/- corneas showed an increased diameter and interfibrillar spacing suggesting that these corneas were more hydrated. The constituent fibrils were more disordered, an effect also observed in Lum^-/- mice (Invest. Ophthalmol. Vis. Sci. 42:1750-1756) although, unlike in Lum^-/- mice, it has been previously noted that there is no increase in light scattering in Kera^-/- corneas.

Keywords: cornea: stroma and keratocytes • proteoglycans/glycosaminoglycans • cornea: basic science