Role of keratan sulphate (sulphated poly -N-acetyllactosamine repeats) in keratoconic cornea, histochemical, and ultrastructural analysis

Keratan sulphate (KS) is the predominant glycosaminoglycan (GAG) present in the corneal stroma where it is thought to regulate collagen fibril diameter. In this study we investigated the distribution of KS in normal and keratoconic corneas. Four normal, one mild, and four severe keratoconic corneas were used for the study. Distribution of keratan sulphate proteoglycans (KS-PG) was investigated using a primary monoclonal antibody (5-D-4) that recognizes disulphated disaccharides in the poly-N-acetyllactosamine repeats of KS. The immuno-reactivity of 5-D-4 was analyzed by immunohistochemistry and immuno-electron microscopy. Immuno-histochemistry showed diffuse 5-D-4 staining in keratoconic cornea compared to the punctuate staining in normal corneas. In the single cornea with mild keratoconus, immunogold microscopy revealed a very high density of KS-PG staining, especially in the posterior stroma, compared to severe keratoconic and normal cornea. The amount of KS-PG in the stroma in severe keratoconus was slightly less compared to the normal cornea. In the mild keratoconic cornea, a higher quantity of KS-PG was present around the keratocytes. In severe keratoconic corneas, a higher quantity of KS-PG was present within the keratocytes compared to normal cornea. The finding of an altered expression of KS in our keratoconic corneas, in particular the strong expression of KS in keratocytes, is in keeping with reports of an altered expression of proteoglycan metabolism in keratoconus. KS-PG plays an important role in stromal collagen fibril assembly and a dysregulation of KS-PG synthesis or catabolism could explain changes in collagen fibril spacing and diameter, which we have reported elsewhere.