An X-ray scattering investigation of corneal structure in keratocan-deficient mice

The transparency of the cornea has been closely linked with the characteristic size and arrangement of its constituent collagen fibrils. This arrangement, in turn, is thought to depend on interactions with intervening matrix proteoglycans. The purpose of this investigation was to examine fibrillar collagen organisation in the corneas of mice homozygous for a null mutation in keratocan, a keratan sulfate-containing proteoglycan. Low-angle synchrotron X-ray scattering techniques were used. We found that keratocan-deficient mice had corneal collagen fibrils with significantly larger diameters than those in wild-type littermates. Furthermore, there was an increase in the centre-to-centre spacing of the collagen fibrils that was accompanied by a decrease in nearest-neighbour fibrillar order. We hypothesise that a lack of keratocan might lower the number of keratan sulfate proteoglycans that associate with collagen, leading to alterations in their diameters and spatial arrangements. Alternatively, it might change the osmotic balance between the inside and outside of fibrils, causing them to swell and move further apart.