Ultrastructural localization of sulfated and unsulfated keratan sulfate in normal and macular corneal dystrophy type I

Abstract

Keratan sulfate (KS) proteoglycans are of importance for the maintenance of corneal transparency as evidenced in the condition macular corneal dystrophy type I (MCD I), a disorder involving the absence of KS sulfation, in which the cornea becomes opaque. In this transmission electron microscope study quantitative immuno- and histochemical methods have been used to examine a normal and MCD I cornea. The monoclonal antibody, 5-D-4, has been used to localize sulfated KS and the lectin Erythrina cristagalli agglutinin (ECA) to localize poly N -acetyllactosamine (unsulfated KS). In normal cornea high levels of sulfated KS were detected in the stroma, Bowman's layer, and Descemet's membrane and low levels in the keratocytes, epithelium and endothelium. Furthermore, in normal cornea, negligible levels of labeling were found for N -acetyllactosamine (unsulfated KS). In the MCD I cornea sulfated KS was not detected anywhere, but a specific distribution of N -acetyllactosamine (unsulfated KS) was evident: deposits found in the stroma, keratocytes, and endothelium labeled heavily as did the disrupted posterior region of Descemet's membrane. However, the actual cytoplasm of cells and the undisrupted regions of stroma revealed low levels of labeling. In conclusion, little or no unsulfated KS is present in normal cornea, but in MCD I cornea the abnormal unsulfated KS was localized in deposits and did not associate with the collagen fibrils of the corneal stroma. This study has also shown that ECA is an effective probe for unsulfated KS.

Altered Fine Structures of Corneal and Skeletal Keratan Sulfate and Chondroitin/Dermatan Sulfate in Macular Corneal Dystrophy

“…This tight control of proteoglycan composition and content undoubtedly underlines the necessity of these molecular components for maintenance of tissue matrix organization and corneal transparency. On the other hand, sulfation, chain length, and contents of each glycosaminoglycan type were altered in each one of the eight diseased corneas analyzed here, and such alterations are likely involved in the consequential disruption of matrix organization and the impaired corneal transparency (32,38).…”

Structural and biochemical aspects of keratan sulphate in the cornea

“…It is also of interest to note that, even though collagen intermolecular spacing within the fibril is not altered in MCD [179], occasional pockets of large diameter collagen fibrils are seen in the stroma in MCD type I and type II [180][181][182]. The molecular mechanisms which lead to the clinical presentation of MCD are yet to be fully elucidated, but work is ongoing using various KS-GAG markers to help our understanding of this disease [47, 183,184].…”

Immunohistochemical Classification of Primary and Recurrent Macular Corneal Dystrophy in Germany: Subclassification of Immunophenotype I A Using a Novel Keratan Sulfate Antibody

“…This and the focally accentuated deposition of under-or non-sulfated KS would then cause the cloudy stroma with discrete white opacities superimposed. By Erythrina cristagalli agglutinin (ECA)-labeling it was shown that the typical deposits seen histopathologically in MCD corneas in type I mainly consist of unsulfated KS (Lewis et al, 2000). Deposition of under-or non-sulfated KS is lacking or only minimally present in normal corneas (Lewis et al, 2000).…”

“…By Erythrina cristagalli agglutinin (ECA)-labeling it was shown that the typical deposits seen histopathologically in MCD corneas in type I mainly consist of unsulfated KS (Lewis et al, 2000). Deposition of under-or non-sulfated KS is lacking or only minimally present in normal corneas (Lewis et al, 2000). In patients with MCD type I and I A the changed KS metabolism with reduced or absent KS in cartilage (e.g.…”

“…However, besides corneal clouding, no other clinically relevant consequences of the undersulfation of KS have yet been described. The normal human cornea contains sulfated KS (as detected with mAb 5-D-4) in the corneal stroma, keratocytes, Bowman's layer, corneal endothelial cells, Descemet's membrane and the epithelium (Lewis et al, 2000).…”