Ultrastructural localization of collagen IV, fibronectin, and laminin in the trabecular meshwork of normal and glaucomatous eyes

Purpose: To determine whether differences in the ultrastructural characteristics or composition of the basement membranes of the trabecular lamellae and Schlemm's canal exist in normal eyes and eyes with primary open-angle glaucoma (POAG). Basement membranes play key roles in the attachment of the overlying trabecular cells and Schlemm's canal cells. Methods: Electron microscopy used in conjunction with immunogold labeling was used to examine the ultrastructure of the basement membranes in the trabecular meshwork and to determine the presence of collagen IV, laminin, and fibronectin in 6 normal eyes and 6 eyes with POAG. To determine which cells in the meshwork synthesized these molecules in situ hybridization was studied in an additional 8 normal eyes. Results: No distinctive ultrastructural changes were found in the basement membranes of glaucomatous eyes, whether early or advanced disease, when compared with normal eyes. Label for all three proteins was present in the basement membranes of the trabecular lamellae, Schlemm's canal, and in scattered patches within the juxtacanalicular tissue. Laminin and fibronectin were most abundant in the periphery of the sheath material surrounding the elastic tendons in the juxtacanalicular tissue. In contrast to previously published light microscopic studies, no increase in fibronectin was found in glaucoma. Regions of the basement membrane of the canal underlying giant vacuoles were similar to regions without giant vacuoles in both appearance and labeling. In situ hybridization revealed that mRNA for all three proteins was present in most trabecular cells throughout the meshwork; no regional differences in cellular labeling within were observed. Conclusion:The ultrastructural characteristics and immunogold labeling of basement membranes were similar in normal and glaucomatous eyes; no additional structures were labeled in POAG eyes that were not also labeled in normal eyes. Label of the patches of amorphous fibrogranular material within the juxtacanalicular tissue suggests it is basement membrane in origin, while the sheath material which is known to accumulate in POAG was not heavily labeled and does not appear to be basement membrane in origin. Copyright (C) 2001 S. Karger AG, Basel.