Surface Topology of Collagen Fibrils Associated with Proteoglycans in Mouse Cornea and Sclera

Abstract

Purpose: To clarify the histological basis for the optical difference in the cornea and sclera, we investigated the surface ultrastructure of D-periodic collagen fibrils. Methods: The fibril arrangement and topology of D-periodic collagen fibrils from corneas and scleras of mice were examined by transmission and scanning electron microscopy, as well as by atomic force microscopy (AFM). The banding patterns were estimated by densitometry and compared with the profile made by computer simulation from the protein sequence of amino acids. Results: Considerable association of proteoglycans/glycosaminoglycanson XI bands of corneal D-periodic collagen fibrils was seen with ruthenium red staining. Atomic force microscopy imaging showed that the depth of the groove in the D-periodicity of corneal collagen fibrils was shallow compared with that of the sclera. Conclusions: Corneal collagen fibrils are associated with many extracellular matrix components on both elevated and depressed surfaces of D-periodic bands, which may serve to maintain interfibrillar spaces, resulting in corneal transparency.