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PubMed2000

[Pressure influence on mRNA expression and protein synthesis of inducible nitric oxide synthetase in bovine trabecular meshwork cell].

OBJECTIVE: To investigate the inducible nitric oxide synthetase (iNOS) mRNA expression and protein synthesis in bovine trabecular meshwork cell and discuss the possible effects of nitric oxide (NO) in the development of glaucoma. METHODS: 20 mm Hg, 40 mm Hg, 60 mm Hg and 80 mm Hg pressure were respectively added on cultured trabecular cells of new born bovine. No pressure group was set as the control. The changes of iNOS mRNA and protein in trabecular meshwork cells under different pressures were demonstrated qualitatively and quantitatively by in situ hybridization and nicotinamide-adenine dinucleotide phosphate diaphorase (NADPH-d) histochemical assay. RESULTS: The expression of iNOS mRNA and its protein synthesis became higher and higher as the pressure was increased. There was weak iNOS mRNA expression in the control and 20 mm Hg groups, and no significant difference between them. 40 mm Hg and 60 mm Hg groups had a statistical difference from the control group. And 80 mm Hg group had a very significant difference from the control group. There was no difference between 40 mm Hg and 60 mm Hg groups, but they had significant difference from 80 mm Hg group. NADPH-d histochemical assay showed almost the same results except that there was significant difference between 40 mm Hg and 60 mm Hg groups. CONCLUSIONS: Pressure can evoke the expression of iNOS mRNA, and the nitric oxide thus produced can be one of the causes of trabecular meshwork destruction, that may induce or aggravate glaucoma.

Animals↗
PubMed1987

Beta-adrenergic receptors in human trabecular meshwork. Identification and autoradiographic localization.

Beta-adrenergic receptors were identified in slide-mounted sections of human trabecular meshwork by in-vitro labeling, light microscopic autoradiography. Autoradiograms were generated after incubation of slide-mounted tissue sections with 125I-cyanopindolol, a selective high-affinity probe for beta-adrenergic receptors. Experiments in which an excess of either unlabeled Practolol (beta 1 selective ligand) or Zinterol (beta 2 selective ligand) were included suggested that most of the receptors were of the beta 2 subtype. Data from displacement studies using increasing concentrations of the highly specific beta 1- and beta 2-adrenergic receptor antagonists, ICI-89,406 and ICI-118,551, respectively, confirmed the predominance of the beta 2-adrenergic receptors. Similar results obtained with cultured trabecular endothelial cells suggest that the beta-adrenergic receptors may be associated with the endothelial cells of the trabecular meshwork in vivo. These results provide anatomic evidence for the hypothesis that beta-adrenergic agents improve outflow by direct action on the trabecular meshwork and provide a rationale for the development of more selective beta 2-adrenergic agents to increase outflow facility.

Autoradiography↗
PubMed2001

Beta-adrenergic blocker therapy and the trabecular meshwork.

PURPOSE: To determine whether beta-adrenergic blocker (beta-blocker) therapy for glaucoma causes changes in the trabecular meshwork due to underperfusion. METHODS: Thirty-five eyes from 19 donors with primary open-angle glaucoma (POAG) were divided into three groups: eyes receiving beta-blocker therapy along with standard medications, eyes receiving standard medications but no beta-blockers, and eyes with elevated intraocular pressure but receiving no therapy. Transmission electron microscopy was used to assess the extracellular material of the cribriform region, the structure of the trabecular lamellae, and pigmentation of the trabecular cells. Six eyes from four normal donors were used as controls. RESULTS: No specific changes in the trabecular meshwork were found in eyes receiving beta-blocker therapy. The amount and composition of the extracellular matrix of the cribriform region and the morphology of the lamellae were similar among the three groups of eyes with POAG. Pigmentation of trabecular cells appeared to be a marker for aqueous flow, as significantly more cells contained pigment in regions of the meshwork with thin or normal lamellae than in regions with thickened and fused lamellae. These regions were variable around the circumference of the eye, and were similar between eyes with and without beta-Blocker therapy. CONCLUSION: beta-Blocker therapy could not be proven to cause underperfusion changes in the trabecular meshwork or other discernible effects. Preferential pathways for aqueous flow probably exist within regions of the trabecular meshwork, as evidenced by lamellar appearance and pigmentation of the adjacent trabecular cells.

Acetazolamide↗
PubMed1989

Characterization of beta-adrenergic receptors in cultured human trabecular cells and in human trabecular meshwork.

The characterization of beta-adrenergic receptors on cultured human trabecular cells and trabecular meshwork from human autopsy eyes was carried out by radioligand binding utilizing (125I)-iodopindolol. In cultured cells, the observed binding of (125I)-iodopindolol was of high affinity (Kd = 43 pM) and saturable. Scatchard plots were linear and revealed a Bmax of 33 +/- 7 fmol/mg of protein. Competition studies with a series of agonists and antagonists revealed that human trabecular cells contain a single class of beta-adrenergic receptors of the beta 2 subtype. Similarly, the IC50 of ICI 89,406 (176 nM) in human trabecular meshwork from autopsy eyes supports the presence of beta 2-adrenergic receptors in this tissue.

Adult↗
PubMed1995

In vivo gene transfer into murine corneal endothelial and trabecular meshwork cells.

PURPOSE: To determine whether a reporter gene can be introduced into adult mammalian corneal endothelial and trabecular meshwork cells in vivo using a recombinant replication-deficient adenovirus. METHODS: Purified replication-deficient adenovirus containing the cytomegalovirus-promoted Escherichia coli reporter gene, lacZ, was injected into the vitreous cavities or anterior chambers of 30 adult CD-1 mice using the contralateral eyes as controls. LacZ expression was assessed histochemically in enucleated eyes from 2 to 21 days after injection using the beta-Galactosidase (beta-Gal) assay. RESULTS: LacZ expression was demonstrated in corneal endothelial and trabecular meshwork cells for as long as 14 days after injection. beta-Gal activity was also observed in lens and iris epithelial cells. There was no toxicity of the adenoviral vector demonstrated histologically, and no nonocular tissues expressed lacZ as measured by beta-Gal assay. CONCLUSIONS: A functional gene can be transferred in vivo into adult mammalian corneal endothelial and trabecular meshwork cells using a replication-defective adenoviral vector. Gene expression is relatively short-lived compared to that demonstrated previously in other ocular tissues (photoreceptors and retinal pigment epithelium). Adenoviral vectors may be a viable means for short-term delivery of therapeutic genes in vivo to cells in the anterior segment of the eye.

Adenoviruses, Human↗
PubMed2000

Ultrastructural localization of myocilin in human trabecular meshwork cells and tissues.

We examined ultrastructurally the localization of myocilin (formerly called trabecular meshwork inducible glucocorticoid response, or TIGR) protein in cultured human trabecular meshwork (TM) cells and in normal human TM tissues. The TM, a specialized tissue located at the chamber angle of the eye, is believed to be responsible for the development of glaucoma. The myocilin gene has been directly linked to both juvenile and primary open-angle glaucomas, and multiple mutations have been identified. Human TM cells were treated with 0.1 mM of dexamethasone (DEX) to induce myocilin expression. This protein was immunolocalized by colloidal gold electron microscopy using an anti-human myocilin polyclonal antibody. Double labeling with different sizes of gold particles was also performed with additional monoclonal antibodies specific for cell organelles and structures. In both DEX-treated and untreated cultured cells, myocilin was associated with mitochondria, cytoplasmic filaments, and vesicles. In TM tissues, myocilin was localized to mitochondria and cytoplasmic filaments of TM cells, elastic-like fibers in trabecular beams, and extracellular matrices in the juxtacanalicular region. These results indicate that myocilin is localized both intracellularly and extracellularly at multiple sites. This protein may exert diverse biological functions at different sites.

Adult↗
PubMed1989

Trabecular meshwork recovery after phagocytic challenge.

The short and long term response of the trabecular meshwork to a phagocytic challenge and the response of the meshwork to different types of foreign particles was studied by injecting one eye of 25 adult cats with a phagocytic agent (zymosan, blood, or latex microspheres) while the fellow eye received a control solution. Eyes were examined histologically at various intervals from one day to five months after infusion. Active trabecular cell phagocytosis and changes in cell shape were found with all agents. The extent of these changes varied with the agent used. Zymosan caused marked changes and inflammation, with numerous macrophages found throughout the meshwork. Trabecular cell migration and cell loss occurred, although it was often difficult to distinguish macrophages from rounded trabecular cells. The meshwork eventually recovered from this inflammatory insult, as trabecular lamellae became less edematous and once again acquired a lining of trabecular cells. Blood and latex microspheres caused less disruption, with microspheres often found in otherwise normal appearing cells. Trabecular cellularity was quantitated after the blood and the zymosan infusions. No cell loss was observed after the blood infusion, while zymosan-infused eyes had an initial 15% cell loss (p less than .04) when compared with fellow control eyes. This zymosan-associated trabecular cell loss may have been due to phagocytosis, inflammation, or a combination of both. The cell loss had recovered by the end of 150 days (p less than .02), as trabecular cell numbers in experimental eyes became comparable to fellow control eyes.

Animals↗
PubMed1989

[Cytochemical localization of actin filaments in endothelial cells of rabbit trabecular meshwork].

Localization of actin filaments in the endothelial cells of rabbit trabecular meshwork was studied by the nitrobenzoxadiazole-phallacidin (NBD-ph) staining method for fluorescence microscopy and modified heavy meromyosin (HMM) decoration method for electron microscopy. Endothelial cells stained with NBD-ph exhibited intense fluorescence which was apparently associated with the basal plasma membrane area. By the modified HMM decoration method, labeled actin filaments were readily detected in the prefixed endothelial cells, because of the distinctive arrowhead-like appearance, observed beneath the basal plasma membrane facing the trabecular collagen sheet. The actin filaments were arranged with dual directionality within the bundle. In contrast, intermediate (10nm) filaments in the deeper region of endothelial cells were always unlabeled with HMM. The function of the actin filament bundles in endothelial cells may be to maintain the cell shape and provide contractility of the trabecular meshwork resulting in an alteration of the outflow resistance of aqueous humor drainage.

Actins↗
PubMed1987

Localization of extracellular proteins of the human trabecular meshwork by indirect immunofluorescence.

We used monospecific antibodies on semithin frozen sections to identify and localize the major tissue constituents of the nonglaucomatous human trabecular meshwork. The trabecular beams (sheets and cords) consist of a basement membrane (subendothelial extracellular matrix) surrounding an interstitial central core of connective tissue (substantia propria). The basement membrane contains collagen types III, IV, and V, the glycoproteins laminin and fibronectin, and the basement membrane-associated heparan sulfate proteoglycan. The trabecular basement membrane is unlike most subendothelial basement membranes because it contains collagen type III and a relatively disorganized structure. The central core contains collagen types I and III, and elastin. The closely linked juxtacanalicular meshwork contains collagen type III, but no collagen type I or elastin. The connective tissue composition of the trabecular meshwork appears similar to other highly compliant and resilient tissues, such as lung, blood vessels, and conjunctiva.

Adult↗
PubMed1978

[The glaucoma in heterochromic cyclitis Fuchs. Gonioscopic studies and electron microscopic investigations of the trabecular meshwork (author's transl)].

Seven patients suffering from heterochromic cyclitis Fuchs had been investigated by gonioscopy after paracentesis of the anterior chamber. Independent to previous intraocular pressure and tonographical results parts or all of the canal of Schlemm were filled with blood, followed by haemorrhage into the trabecular meshwork on several sites and bleeding into the anterior chamber. Three of the patients were operated on because of a chronic secundary glaucoma and the dissected trabecular meshwork was investigated by electron microscopy. Atrophy of the inner--and outer wall of the canal of Schlemm as well as missing of the endothelium of the trabecular meshwork was to be observed. Discussing the gonioscopical observations and electron-microscopical results the glaucoma in heterochromic cyclitis Fuchs seems to be caused by a collapse of the canal of Schlemm and not by increasing resistance in trabecular meshwork by sclerosis or hyaline membranes.

Aged↗
PubMed1984

Hexokinase of calf trabecular meshwork.

Although aqueous outflow is most likely a passive, nonenergy-dependent process, alterations in cellular function in the trabecular meshwork presumably are involved in the development of some types of glaucoma. Accordingly, it seems important to define both the normal and abnormal biochemistry of this tissue. The authors have chosen glycolysis as their starting point, concentrating on the regulatory enzymes, hexokinase, and, in a companion paper, phosphofructokinase. Hexokinase activity has been measured in the 100,000 X g supernatant of homogenates prepared from excised calf trabecular meshwork. Treatment of the homogenate with Triton X-100 before centrifuging caused a twofold increase in measurable activity. Electrophoresis on cellulose acetate revealed types I and II isoenzymes. Electrophoresis on starch gel further resolved type 1 into the adult and fetal subtypes. The principal isoenzyme type released into solution by Triton X-100 was type 1. The kinetic behavior of hexokinase was measured by varying the concentrations of glucose at saturating levels of ATP. Kms calculated from these plots were 7.15 X 10(-2) M, 1.78 X 10(-3) M, and 1.19 X 10(-4) M. Apart from the fetal form of type I hexokinase, the isoenzymes from trabecular meshwork resemble those of other ocular tissues and most extraocular tissues. The special role, if any, of the fetal isoenzyme in regulating glycolysis is not known. Possibly, it is a "kinetically adaptable" isoenzyme.

Animals↗
PubMed1984

Effects of chondroitin sulfate on trabecular meshwork in rabbit eyes: an electron microscopic study.

The intraocular pressure of four New Zealand albino rabbit eyes was elevated when we replaced the aqueous humor of these eyes repeatedly with a chondroitin sulfate solution. Seen by electron microscopy, the trabecular meshwork of these eyes showed moderately increased collagen fibers, elastic fibers, and fine fibrils, and thickening of basement membrane. The amount of extracellular material present was markedly increased when compared with control eyes. Three types of basement membranes were noted. Compact multilaminated basement membrane and placoid accumulations of filamentous material with a granular background were found adjacent to the endothelial cells of the trabecular meshwork, and fine fibrils were observed around the angular aqueous veins. The ultrastructural alterations we observed were similar to those seen in some human glaucoma cases. The metabolism of trabecular meshwork cells may be affected by the long-term chondroitin sulfate treatment. As a result, extracellular matrix material appears to be accumulated in the trabecular meshwork, which may then contribute to an increased outflow resistance and a mild intraocular pressure elevation.

Animals↗
PubMed1987

Cultured trabecular-meshwork cells: immunohistochemical and lectin-binding characteristics.

We examined the extracellular matrix formation and lectin-binding properties of cultured trabecular-meshwork cells established from cynomolgus monkey and bovine eyes. Using an avidin-biotin complex method, we found that the extracellular matrix in both the monkey and bovine cultures stained intensely with antibodies to fibronectin, type IV collagen, and laminin. These materials were especially prominent when the cultured monkey trabecular-meshwork cells aggregated in clusters, manifesting their close anatomic relationship to trabecular beams. Cell-surface and intracellular lectin-binding properties were studied using eight biotinylated lectins: concanavalin A (Con A), peanut agglutinin (PNA), Ricinus communis agglutinin (RCA), Dolichos biflorus agglutinin (DBA), soy bean agglutinin (SBA), Phaseolus vulgaris (PHA), wheat germ agglutinin (WGA), and Ulex europaeus agglutinin I (UEA I). Both monkey and bovine trabecular-meshwork cells showed positive cell surface and intracellular binding to Con A, WGA, and PHA. Only moderate cell-surface staining was observed with RCA, and no visible staining occurred with PNA, DBA, SBA, and UEA-1.

Animals↗
PubMed1998

Endothelin receptor A is expressed and mediates the [Ca2+]i mobilization of cells in human ciliary smooth muscle, ciliary nonpigmented epithelium, and trabecular meshwork.

PURPOSE: To identify which endothelin receptor subtype is expressed and is functional in the human ciliary body and trabecular meshwork, tissues that regulate aqueous humor dynamics. METHODS: Immunocytochemistry was used to characterize the primary culture cells of normal human ocular cells. Endothelin receptor gene expression was probed with reverse transcription of polymerase chain reaction (RT-PCR). Intracellular calcium ([Ca2+]i) mobilization was measured with video image microscopy using Fura-2AM as a fluorescent probe. RESULTS: Identities of primary cultures, human ciliary smooth muscle (HCSM), ciliary nonpigmented epithelial (HCE), and trabecular meshwork (HTM) cells were confirmed by immunocytochemistry, using cell-specific markers and observing typical cell morphologies. The presence of endothelin receptor A (ETA) was detected with RT-PCR in all three types of cells. The mRNA phenotype was verified with restriction enzyme BamHI digestion. No ETB receptor subtype expression was detected with RT-PCR under the cell culture conditions used. The [Ca2+]i of HCSM cells was increased from 57 +/- 7 nM to 328 +/- 108 nM (n = 23; mean +/- SE; P < 0.05) by 1 nM endothelin-1 (ET-1). In HCE cells, [Ca2+]i increased from 40 +/- 3 nM to 90 +/- 10 nM (n = 55) (P < 0.001) with the same concentration of ET-1. Similarly, ET-1 (1 nM) increased the [Ca2+]i from 51 +/- 6 nM to 185 +/- 47 nM (n = 19) (P < 0.001) in the HTM cells. The agonist for ETB, S6c, had no effect on [Ca2+]i transients in all three cell types. No ETB receptor expression was detected in these cell types under the experimental and culture conditions. CONCLUSION: ETA receptor is expressed and is possibly responsible for mediating the signal for [Ca2+]i mobilization by ET-1 in human ciliary smooth muscle, ciliary nonpigmented epithelial cells, and trabecular meshwork cells.

Calcium↗
PubMed2005

Extracellular trafficking of myocilin in human trabecular meshwork cells.

Myocilin (MYOC) is a protein with a broad expression pattern, but unknown function. MYOC associates with intracellular structures that are consistent with secretory vesicles, however, in most cell types studied, MYOC is limited to the intracellular compartment. In the trabecular meshwork, MYOC associates with intracellular vesicles, but is also found in the extracellular space. The purpose of the present study was to better understand the mechanism of extracellular transport of MYOC in trabecular meshwork cells. Using a biochemical approach, we found that MYOC localizes intracellularly to both the cytosolic and particulate fractions. When intracellular membranes were separated over a linear sucrose gradient, MYOC equilibrated in a fraction less dense than traditional secretory vesicles and lysosomes. In pulse-labeling experiments that followed nascent MYOC over time, the characteristic doublet observed for MYOC by SDS-PAGE did not change, even in the presence of brefeldin A; indicating that MYOC is not glycosylated and is not released via a traditional secretory mechanism. When conditioned media from human trabecular meshwork cells were examined, both native and recombinant MYOC associated with an extracellular membrane population having biochemical characteristics of exosomes, and containing the major histocompatibility complex class II antigen, HLA-DR. The association of MYOC with exosome-like membranes appeared to be specific, on the extracellular face, and reversible. Taken together, data suggest that MYOC appears in the extracellular space of trabecular meshwork cells by an unconventional mechanism, likely associated with exosome-like vesicles.

Adenoviridae↗
PubMed2005

The identification of myocilin-associated proteins in the human trabecular meshwork.

Myocilin forms high molecular weight complexes in vivo presumably due to interaction with itself and other myocilin binding proteins. To identify myocilin interacting proteins, yeast 2-hybrid analysis was performed on >1x10(6) human trabecular meshwork cDNA clones. Coimmunoprecipitation and Far Western analysis were also performed on cell lysates obtained from fresh human trabecular meshworks or cultured human monolayer trabecular cell lines. Among the different methods, 46 candidate myocilin-associated proteins were identified, including molecules associated with the extracellular matrix, cytoskeleton, signaling, and metabolism. The most consistent interaction was myocilin-myocilin binding. Yeast-2 hybrid and Far Western analysis also found an association between myocilin and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). None of the other candidate myocilin interacting proteins were identified in more than one method. Characterization of these potential interacting proteins may help to better understand the function of myocilin in the trabecular meshwork and aqueous outflow pathway.

Aged↗
PubMedDate not supplied

In vitro cultures of trabecular meshwork cells of the human eye as a model system for the study of cellular aging.

Cells from the human trabecular meshwork providing a drainage system for the outflow of aqueous humour in the eye were isolated and propagated in monolayer culture. Following serial subcultivation of the primary cultures, there was a gradual decline in the fraction of dividing cells with increasing population doubling level (PDL) resulting finally in growth cessation and disintegration of these 'senescent' cultures. The number of population doublings was at most 20. Senescent cultures revealed reduced glycosaminoglycan synthesis rates (as measured by [14C]glucosamine incorporation) with a relative decrease of hyaluronic acid and increase of heparan sulfate. Medium-supplied (exogenous) hyaluronic acid enhanced hyaluronic acid synthesis of trabecular meshwork cells cultured in a defined, serum-free medium. Ascorbic acid (25-200 micrograms/ml), which is found in very high concentration in the ocular aqueous humour, stimulated hyaluronic acid synthesis of confluent cultures, also. The functional significance of decreased hyaluronic acid (and elevated heparan sulfate) synthesis in the process of cellular aging in vitro (and in vivo?), as well as the importance of hyaluronic acid for the structural integrity and functional activity of the trabecular meshwork were discussed.

Aging↗
PubMed2000

The myocilin (MYOC) gene expression in the human trabecular meshwork.

PURPOSE: We previously reported a novel cytoskeletal protein with a myosin-like domain which is localized in the ciliary rootlet and basal body of connecting cilium of photoreceptor and hence we named it 'myocilin'. It was soon realized that myocilin is identical to a protein called TIGR (trabecular meshwork inducible glucocorticoid response protein) which was found to be responsible for the pathogenesis of juvenile open angle glaucoma. In this study, we employed in situ RNA hybridization to examine the myocilin (MYOC)/ TIGR gene expression in the trabecular meshworks of glaucomatous and nonglaucomatous eyes. METHODS: The glaucomatous specimens were obtained by trabeculectomy from the patients with primary open angle glaucoma (POAG), chronic angle closure glaucoma (CACG) and steroid glaucoma, respectively, and the nonglaucomatous specimens were obtained from a victim of traffic accident at autopsy and from a patient with maxillary sinus carcinoma at enucleation for the operation. The in situ RNA hybridization was carried out with digoxigenin-labeled sense and antisense RNA probes. RESULTS: In all cases, hybridization signals were detected primarily in the trabecular meshwork cells and secondarily in the fibroblast-like cells of corneoscleral wall. CONCLUSIONS: Myocilin gene is expressed clearly in the trabecular meshwork cells of both glaucomatous and nonglaucomatous eyes.

Aged↗