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 characteri stics or composition of the basement membranes of the trabecular lamellae a nd Schlemm's canal exist in normal eyes and eyes with primary open-angle gl aucoma (POAG). Basement membranes play key roles in the attachment of the o verlying trabecular cells and Schlemm's canal cells. Methods: Electron micr oscopy 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 norma l eyes and 6 eyes with POAG. To determine which cells in the meshwork synth esized 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 dis ease, when compared with normal eyes. Label for all three proteins was pres ent in the basement membranes of the trabecular lamellae, Schlemm's canal, and in scattered patches within the juxtacanalicular tissue. Laminin and fi bronectin were most abundant in the periphery of the sheath material surrou nding the elastic tendons in the juxtacanalicular tissue. In contrast to pr eviously published light microscopic studies, no increase in fibronectin wa s found in glaucoma. Regions of the basement membrane of the canal underlyi ng giant vacuoles were similar to regions without giant vacuoles in both ap pearance and labeling. In situ hybridization revealed that mRNA for all thr ee proteins was present in most trabecular cells throughout the meshwork; n o regional differences in cellular labeling within were observed. Conclusio n:The ultrastructural characteristics and immunogold labeling of basement m embranes were similar in normal and glaucomatous eyes; no additional struct ures were labeled in POAG eyes that were not also labeled in normal eyes. L abel of the patches of amorphous fibrogranular material within the juxtacan alicular tissue suggests it is basement membrane in origin, while the sheat h 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. K arger AG, Basel.