Monoclonal antibodies and lectins as probes for investigation of the cell biology of human trabecular meshwork: a preliminary report

Histochemical Analysis of Glaucoma Caused by a Myocilin Mutation in a Human Donor Eye

OBJECTIVE

Mutations in myocilin (MYOC) may cause either juvenile open angle glaucoma (JOAG) or adult-onset primary open angle glaucoma (POAG). MYOC encodes a glycoprotein that is normally secreted from trabecular meshwork cells that regulate intraocular pressure. Prior in vitro, transgenic rodent, and organ culture experiments have suggested that abnormal accumulation of MYOC protein within trabecular meshwork cells is a key step in glaucoma pathophysiology. We investigated the pathogenesis of MYOC glaucoma by examining a donor eye from a patient with JOAG caused by a Tyr437His MYOC mutation.

DESIGN

Case-control, immunohistochemical study of a donor eye from a patient with JOAG caused by a Tyr437His MYOC mutation and age-matched control donor eyes.

SUBJECTS

An eye from a 59-year-old male with JOAG caused by a Tyr437His MYOC mutation and eyes from five donors (ages 51-66) with no known ocular disease were examined.

METHODS

Frozen fixed sections of the iridocorneal angle were prepared from the donor eyes of the MYOC glaucoma patient and control eyes. We used antibodies directed against MYOC, collagen IV, and BiP/GRP78 as well as wheat germ agglutinin and concanavalin A lectins to localize MYOC protein in the trabecular meshwork.

MAIN OUTCOME MEASURE

Qualitative comparison of MYOC protein labeling and localization in the trabecular meshwork of donor eyes from a glaucoma patient with a MYOC mutation and from control subjects.

RESULTS

Using immunohistochemistry, we detected more abundant MYOC protein within the trabecular meshwork of the MYOC glaucoma patient's eye than in control eyes. We further localized MYOC protein within the trabecular meshwork cells of the MYOC glaucoma patient's eye by co-labeling with the endoplasmic reticulum (ER) marker GRP78 (BiP). Little to no MYOC was identified within the trabecular meshwork cells of control eyes. Minimal extracellular MYOC was detected in both MYOC glaucoma eyes and control eyes.

CONCLUSIONS

This is the first histopathological analysis of an eye from a glaucoma patient with a MYOC mutation. Furthermore, this analysis supports our model of MYOC-associated glaucoma, in which MYOC mutations cause abnormal intracellular retention of MYOC within the ER of trabecular meshwork cells as a key step towards development of glaucoma.

Glycoconjugates of the rat ciliary body epithelium: a lectin histochemical and protein blotting study

The present study sought to identify and partially characterize the glycoconjugates specific to the double-layered ciliary body epithelium of the rat eye by lectin histochemistry and lectin blottings. Hydrated paraffin sections of Carnoy-fixed Sprague-Dawley rat eyes were stained with a panel of 21 different biotinylated lectins, followed by streptavidin-peroxidase and the glucose oxidase-diaminobenzidine-nickel staining procedure. The results of lectin histochemistry revealed that the inner epithelial layer was rich in GlcNAc(beta1,4)GlcNAc, alpha-Gal, Gal(beta1,3)GalNAc, GalNAc(alpha1,3)GalNAc/Gal, GalNAc(alpha1,6)Gal, Fuc(alpha1,2)Gal(beta1,4)GlcNAc and Gal(beta1,4)GlcNAc(beta1,2)Man(alpha1,6) sugar residues as shown by its positive reactivities with S-WGA, PWA, DSA, GS-I-B4, PNA, DBA, SBA, WFA, UEA-I, LTA and PHA-E. The reactivities of GS-I-B4, PNA, DBA and SBA were restricted to the inner layer at the tips of the ciliary processes. On the other hand, the outer epithelial layer was stained evenly by DSA and Jacalin, and partly by MAA, showing that this epithelial layer was rich in GlcNAc(beta1,4)GlcNAc, Gal(beta1,3)GalNAc and NeuAc(alpha2,3)Gal disaccharides. These lectin binding patterns of the ciliary body epithelium suggest a topographical and functional difference in this double cell-layered epithelium. Their possible roles in the secretion of aqueous humour and production of ciliary zonule are discussed. Some identified lectin markers specific to these two cell layers may be useful for further experimental studies. Glycoproteins extracted from the dissected ciliary body were separated by SDS-PAGE electrophoresis and analyzed by protein blottings with 8 different lectins. The results showed that at least 10 major membrane-bound glycoproteins, with molecular weights ranging from 30 to 150 kD, rich in beta-GlcNAc, beta-Gal, alpha/beta-GalNAc and NeuAc(alpha2,6)Gal residues, were present in the microsomal fraction.

Glycans of the trabecular meshwork in primary open angle glaucoma

AIMS

Glycan expression was compared in glaucomatous trabecular meshwork (TM) and normal TM in order to determine any differences which may reflect pathological changes underlying primary open angle glaucoma (POAG).

METHODS

Resin embedded TM from trabeculectomy specimens from 15 eyes with POAG and from 12 eyes with normal anterior segments were probed with a panel of biotinylated lectins and an avidin-peroxidase revealing system at the light microscope level. Statistical analyses were performed on the comparative staining results.

RESULTS

The lectins ConA and ePHA showed strong staining in all areas of both glaucomatous and normal TM; ePHA staining of Schlemm's canal (SC) from POAG TM was significantly less than that from normal TM (ePHA-SC p = 0.04). The lectins PSA, LCA, and SNA bound moderately strongly to SC endothelium and weakly to the endothelium of the corneoscleral meshwork (CSM); glaucomatous SC endothelial binding was significantly less than that of normal SC endothelium for PSA and LCA (PSA-SC p = 0.002, LCA-SC p = 0.002). STA and DSA showed moderately strong binding while WGA, ECA, AHA, and MPA bound weakly throughout the TM; for DSA and MPA this staining was significantly greater in POAG than in normal TM (DSA-SC p = 0.001, DSA-CSM p = 0.002, MPA-SC p = 0.01, MPA-CSM p = 0.02). Jac stained strongly throughout the TM and showed no significant difference in POAG compared with normal TM (Jac-SC p = 0.6, Jac-CSM p = 1). 1PHA, SBA, DBA, CTA, UEA-1 and LTA did not bind to glaucomatous TM or normal TM. There were no age-related changes seen.

CONCLUSIONS

The expression of some complex and hybrid, bisected and non-bisected N-linked glycans is significantly diminished in glaucomatous TM compared with normal TM. Some glycans with multiple N-acetylglucosamine residues and O-linked glycans with terminal and subterminal galactosyl groups are significantly increased in POAG TM. Glycan expression does not change significantly with age in POAG or normal TM.

Qualitative and quantitative analyses of sialic acid in the human trabecular meshwork

By using colloidal iron and polycationic ferritin at low pH (1.8 and 1.9, respectively) as electron histochemical stains, we localized sialic acid moieties in the trabecular meshwork of normal human eyes. The markers were distributed continuously over the entire surface of the trabecular cells, but were localized linearly as well as randomly in the basal lamina. Within the beams, the markers were located irregularly in the collagen core, but were absent from the elastic tissue and from the 100 nm banded structures in the cortical zone. Pretreatment of the tissue with neuraminidase abolished this staining which indicates that sialated moieties are present in the stained structures. Biochemical analysis with the lectin Limax flavus agglutinin revealed that the major sialated polypeptides in individual samples of human trabecular meshwork migrated at apparent molecular weights of 56, 75, 95, 128, 140, 180 and 220 kDa under reducing conditions. The fractions at approximate molecular weights of 180 and 220 kDa include the sialoglycoproteins thrombospondin and fibronectin, respectively. The total content of sialic acid in the human trabecular meshwork (patient age range, 27-57 yr) was 3.6 +/- 0.6 mumol g-1 wet weight, as determined by a colorimetric assay. We conclude that significant quantities of sialic acid are present in the normal human trabecular meshwork as neuraminidase-sensitive alpha-ketosidically linked terminal residues of the polypeptides.