Physiological and pathobiological significance of ocular glycoproteins. I. Studies using fluorescein labelled glycine max

Lectin receptors of normal and dystrophic corneas

In recent years, our laboratory has used lectins to detect carbohydrate-related abnormalities in dystrophic corneas and species-specific differences in the carbohydrates of normal corneas. These studies have: 1) demonstrated that abnormal glycoconjugates are present in corneas with macular and lattice dystrophy, 2) provided additional means of differentiating corneas with macular, lattice and granular dystrophy, 3) demonstrated that distinct species-specific differences are present in the glycoconjugates of normal corneas and 4) provided guidelines for the selection of an animal model for the study of corneal glycoconjugates.

Delay in migration of the corneal epithelium after incorporation of [3H]-mannose in organ cultures

PURPOSE

Corneal epithelial cell surface carbohydrate moieties influence migration during wound healing. The purpose of the present study was to investigate the incorporation of galactose and mannose sugar during corneal epithelial migration and their effect on the rate of wound healing.

METHODS

Organ cultures of non-migrating (n = 6) and migrating (n = 30) corneal epithelia were prepared. The incorporation of [3H]-galactose and [3H]-mannose was followed in the migrating samples after 18, 24, 48 and 72h incubation and at 18h in the non-migrating samples. Wound size was documented at the same intervals and the rate of healing was established.

RESULTS

The migrating corneal epithelium of the galactose and mannose treated samples incorporated more radioactive sugar than the non-migrating samples. Mannose incorporation decreased with time whereas the rate of healing was significantly delayed (41 +/- 0.01 microm/h) compared to galactose treated samples (63 +/- 0.01 microm/h) and controls (61 +/- 0.01 microm/h) during the active healing phase (18-48h). Galactose incorporation increased with time.

CONCLUSIONS

Incorporation of mannose sugar has an inhibitory effect on the rate of migration during the linear healing phase of the corneal epithelium.

Localization of a corneal basement membrane glycoconjugate in bovine eye

Lectin histochemistry was used to analyze the ocular surface basement membrane in order to identify novel, tissue-specific glycoconjugates. Soybean agglutinin (SBA), a lectin marker for N-acetylgalactosamine residues, recognized a 130 kDa glycoconjugate in corneal but not conjunctival basement membrane. Following corneal epithelial cell wounding in vitro, the glycoconjugate was not expressed at the epithelial cell-stromal interface until 72-96 h in culture, much later than the expression of other basement membrane molecules. In epithelial cells maintained on various extracellular matrix substrates (laminin, collagen type IV, or a mixture of laminin, collagen type IV and heparan sulfate proteoglycan), the glycoconjugate localization patterns changed with time in culture from a diffuse cellular or perinuclear ring to an extensive extracellular filament network. The presence of SBA in the culture medium did not affect migration or adhesion in either the wound healing model or in culture cells. However, the presence of SBA did delay the deposition of laminin at the zone of basement membrane reformation in the wound healing model. The 130 kDa glycoconjugate is a candidate for molecules which impart a tissue-specificity to the corneal basement membrane, and which may be involved in cell-matrix interaction.

Characterization of galactose-containing glycoconjugates in the human retina: a lectin histochemical study

Seven specimens of morphologically normal formalin-fixed and paraffin-embedded human retina were studied using a panel of fourteen biotinylated lectins, all of which react with glycoconjugates containing galactose and N-acetylgalactosamine residues. Agaricus bisporus (ABA), Bauhinia purpurea (BPA), Phaseolus vulgaris (PHA-E), peanut (PNA) and Ricinus communis (RCA-I) agglutinins labeled photoreceptor cells prior to enzymatic predigestion. BPA and PNA bound specifically to cones. The plexiform layers reacted with ABA, BPA and PHA-E, while only ABA and PHA-E labeled the nuclear layers. After pretreatment with neuraminidase to remove terminal sialic acid, all five lectins, as well as Erythrina cristagalli (ECA), Helix pomatia (HPA) and Maclura pomifera (MPA) agglutinins labeled both rods and cones. Furthermore, the plexiform layers additionally reacted with ECA, PNA and RCA-I, and the nuclear layers with BPA and RCA-I after neuraminidase pretreatment. Retinal vascular endothelial cells consistently bound ABA, ECA, PHA-E and RCA-I, but they could also bind BPA, HPA, Bandeiraea simplicifolia (BSA-I), Dolichos biflorus (DBA) and Euonymus europaeus (EEA) agglutinins in unpretreated sections, as well as MPA, PNA, soybean (SBA) and Sophora japonica (SJA) agglutinins subsequent to predigestion with neuraminidase. The nonpigmented ciliary epithelium reacted with the same lectins as photoreceptor cells, but it was also labeled by DBA. Sambucus nigra agglutinin (SNA) did not specifically bind to any intraocular structure. These findings favor the theory that, in unpretreated specimens, Gal(beta 1----3)GalNAc (BPA and PNA) is mainly responsible for labeling of cones, while Gal(beta 1----3/4)GlcNAc units, partly substituted with terminal sialic acid (PHA-E and RCA-I), explain labeling of rods. Following pretreatment with neuraminidase, further Gal(beta 1----3)GalNAc (BPA and PNA) and, especially, Gal(beta 1----3/4)GlcNAc (BPA, ECA, PHA-E, PNA and RCA-I) and alpha GalNAc units (BPA, HPA and MPA), the latter partly linked to the protein backbone, contribute to labeling of photoreceptor cells. Gal(beta 1----3/4)GlcNAc units may be mainly responsible for labeling of nuclear and plexiform layers. Finally, other related receptor sites (SBA and SJA), some of which are blood-group specific (BSA-I, DBA, EEA and HPA) are restricted to retinal vascular endothelia.

Lectin-binding sites in the anterior segment of the human eye

The anterior segment of the human eye was screened for differences in the lectin-binding patterns of Con A, PNA, GS-I, WGA, SBA, DBA, and UEA-I to enable cell typing for cell-culture purposes. An immunohistochemical technique combining an indirect antibody-lectin method with the avidin-biotin system was used. Con A and WGA were bound by all cells except the conjunctival goblet cells. UEA-I was exclusively bound by both vascular endothelial cells and some corneal and conjunctival epithelial cells. The binding of GS-I, PNA, SBA, and DBA showed an uneven pattern and differed among the cases investigated. The reasons for these differences are not clear. Our results indicate that the usefulness of lectins for cell-typing purposes is restricted and must be determined for every case.

Cellular carbohydrate components in human, rabbit and rat lacrimal gland. Studies using fluorescein and peroxidase labelled lectins

Orbital lacrimal glands from adult male and female rabbits, rats and humans were examined for the presence of intracellular receptors of four lectins: concanavalin-A agglutinin, lutus tetragonolobus agglutinin, ricinus comunis-60 agglutinin and wheat-germ agglutinin using fluorescein-conjugated lectin and peroxidase labelling methods for fluorescence and electron microscopy, respectively. Lectins were used as specific probes to detect carbohydrate moiety of the lacrimal gland. The pattern of labelling with the lectins suggests that N-acetyl-glucosamine, N-acetyl-D-galactosamine, D-galactose, D-mannose, sialic acid and L-fucose are contained in the lacrimal gland of the three species. The significance of these findings is discussed.

A histochemical comparison of human corneal stromal glycoconjugates with eight other species. Distinct species-dictated differences in binding sites of Griffonia simplicifolia I

Frozen sections of human, calf, rabbit, rat, cat, dog, goat, lamb, and hog corneas were stained with various lectins using an avidin-biotin-peroxidase complex to study glycoconjugates of stromal matrix. Staining of the stromal matrix and keratocytes with an alpha-galactose-specific lectin, Griffonia simplicifolia I (GSA-I) was species-dependent. The stromal matrices of cat, dog, and hog corneas invariably reacted intensely with this lectin, whereas those of the human, calf, rabbit, rat, and lamb did not react. A positive reaction with GSA-I could be abolished in each instance by preincubation of the sections with alpha-galactosidase. The stromal matrices and keratocytes of all nine species reacted positively with wheat germ agglutinin, concanavalin A, and Ricinus communis agglutinin but did not react with soybean agglutinin. Results of this study may help select an appropriate animal model for further investigate human corneal stromal glycoconjugates.

Lectin binding in retinoblastoma

Lectins were used as cytochemical probes to examine the relationship between normal retina and retinoblastoma. Cases of retinoblastoma in which there were either Flexner-Wintersteiner rosettes or fleurettes accompanied by nontumorous retina were studied with ten biotinylated lectins. Pineal and ocular tumors from cases of trilateral retinoblastoma were also studied. Con-A, LCA, PNA, WGA and RCA-I labeled tissue of each type to varying degrees, while BS-I, DBA, SBA, S-WGA and UEA-I bound neither tumor nor retina. The high degree of binding homology suggests biochemical as well as structural similarities between these tissues.