Regulation of anterior chamber drainage by bicarbonate-sensitive soluble adenylyl cyclase in the ciliary body

Glaucoma is a leading cause of blindness affecting as many as 2.2 million Americans. All current glaucoma treatment strategies aim to reduce intraocular pressure (IOP). IOP results from the resistance to drainage of aqueous humor (AH) produced by the ciliary body in a process requiring bicarbonate. Once secreted into the anterior chamber, AH drains from the eye via two pathways: uveoscleral and pressure-dependent or conventional outflow (C(t)). Modulation of "inflow" and "outflow" pathways is thought to occur via distinct, local mechanisms. Mice deficient in the bicarbonate channel bestrophin-2 (Best2), however, exhibit a lower IOP despite an increase in AH production. Best2 is expressed uniquely in nonpigmented ciliary epithelial (NPE) cells providing evidence for a bicarbonate-dependent communicative pathway linking inflow and outflow. Here, we show that bicarbonate-sensitive soluble adenylyl cyclase (sAC) is highly expressed in the ciliary body in NPE cells, but appears to be absent from drainage tissues. Pharmacologic inhibition of sAC in mice causes a significant increase in IOP due to a decrease in C(t) with no effect on inflow. In mice deficient in sAC IOP is elevated, and C(t) is decreased relative to wild-type mice. Pharmacologic inhibition of sAC did not alter IOP or C(t) in sAC-deficient mice. Based on these data we propose that the ciliary body can regulate C(t) and that sAC serves as a critical sensor of bicarbonate in the ciliary body regulating the secretion of substances into the AH that govern outflow facility independent of pressure.     

兔先天性青光眼的临床研究

目的 总结兔先天性青光眼的临床特点。方法 对先天性青光眼兔和正常兔进行临床观察,研究其在眼压、眼球结构、视功能方面的变化。结果 青光眼兔的眼压明显升高,角膜直径变大,前房变深,眼轴变长,房角变宽,眼底视乳头损害明显,视觉诱发电位明显异常。结论 兔先天性青光眼的房水排泄障碍部位可能在小梁,兔眼球壁对高眼压的耐受力弱,在高眼压下容易出现眼球扩张,视功能损害。     

Mechanisms of ATP release, the enabling step in purinergic dynamics

The only effective intervention to slow onset and progression of glaucomatous blindness is to lower intraocular pressure (IOP). Among other modulators, adenosine receptors (ARs) exert complex regulation of IOP. Agonists of A(3)ARs in the ciliary epithelium activate Cl(-) channels, favoring increased formation of aqueous humor and elevated IOP. In contrast, stimulating A(1)ARs in the trabecular outflow pathway enhances release of matrix metalloproteinases (MMPs) from trabecular meshwork (TM) cells, reducing resistance to outflow of aqueous humor to lower IOP. These opposing actions are thought to be initiated by cellular release of ATP and its ectoenzymatic conversion to adenosine. This view is now supported by our identification of six ectoATPases in trabecular meshwork (TM) cells and by our observation that external ATP enhances TM-cell secretion of MMPs through ectoenzymatic formation of adenosine. ATP release is enhanced by cell swelling and stretch. Also, enhanced ATP release and downstream MMP secretion is one mediator of the action of actin depolymerization to reduce outflow resistance. Inflow and outflow cells share pannexin-1 and connexin hemichannel pathways for ATP release. However, vesicular release and P2X(7) release pathways were functionally limited to inflow and outflow cells, respectively, suggesting that blocking exocytosis might selectively inhibit inflow, lowering IOP.     

Oxidative stress and potential applications of free radical scavengers in glaucoma

Abstract

Glaucoma is the leading cause of irreversible blindness in industrialized countries and comprises a group of diseases characterized by progressive optic nerve degeneration. Glaucoma is commonly associated with elevated intraocular pressure due to impaired outflow of aqueous humor resulting from abnormalities within the drainage system of the anterior chamber angle (open-angle glaucoma) or impaired access of aqueous humor to the drainage system (angle-closure glaucoma). Oxidative injury and altered antioxidant defense mechanisms in glaucoma appear to play a role in the pathophysiology of glaucomatous neurodegeneration that is characterized by death of retinal ganglion cells. Oxidative protein modifications occurring in glaucoma serve as immunostimulatory signals and alter neurosupportive and immunoregulatory functions of glial cells. Initiation of the apoptotic cascade observed in glaucomatous retinopathy can involve oxidant mechanisms and different agents have been shown to be neuroprotective. This review focuses on the molecular mechanisms of oxidant injury and summarizes studies that have investigated novel free radical scavengers in the treatment of glaucomatous neurodegeneration.     

Analytical model for managing hypotony after implantation surgery of a glaucoma drainage device

The main aim of glaucoma treatment is to reduce the intraocular pressure (IOP). One of the most common surgical treatments of glaucoma is the implantation of a glaucoma drainage device to drain the aqueous humor from the anterior chamber to a filtration bleb, where the aqueous humor is absorbed. In some cases, the excess of drainage causes ocular hypotony, which constitutes a sight-threatening complication. To prevent hypotony after this intervention, surgeons frequently introduce a suture into the device tube, which increases the hydraulic resistance of the tube and, therefore, the IOP. This study aims to provide an analytical model to correct hypotony following implantation surgery of a glaucoma drainage device, which may help glaucoma surgeons decide on hypotony treatment. The results indicate that the IOP after implanting a cylindrical tube around 300 μm in diameter is essentially the same as that built up in the filtering bleb and can hardly be controlled by introducing a straight suture unless the suture diameter is slightly lower than that of the tube. On the contrary, when the tube diameter is smaller than, for example, 100 μm, significant reductions of the IOP can be obtained by introducing a thin suture into the tube.

     

Mapping Molecular Differences and Extracellular Matrix Gene Expression in Segmental Outflow Pathways of the Human Ocular Trabecular Meshwork

Elevated intraocular pressure (IOP) is the primary risk factor for glaucoma, and lowering IOP remains the only effective treatment for glaucoma. The trabecular meshwork (TM) in the anterior chamber of the eye regulates IOP by generating resistance to aqueous humor outflow. Aqueous humor outflow is segmental, but molecular differences between high and low outflow regions of the TM are poorly understood. In this study, flow regions of the TM were characterized using fluorescent tracers and PCR arrays. Anterior segments from human donor eyes were perfused at physiological pressure in an ex vivo organ culture system. Fluorescently-labeled microspheres of various sizes were perfused into anterior segments to label flow regions. Actively perfused microspheres were segmentally distributed, whereas microspheres soaked passively into anterior segments uniformly labeled the TM and surrounding tissues with no apparent segmentation. Cell-tracker quantum dots (20 nm) were localized to the outer uveal and corneoscleral TM, whereas larger, modified microspheres (200 nm) localized throughout the TM layers and Schlemm’s canal. Distribution of fluorescent tracers demonstrated a variable labeling pattern on both a macro- and micro-scale. Quantitative PCR arrays allowed identification of a variety of extracellular matrix genes differentially expressed in high and low flow regions of the TM. Several collagen genes (COL16A1, COL4A2, COL6A1 and 2) and MMPs (1, 2, 3) were enriched in high, whereas COL15A1, and MMP16 were enriched in low flow regions. Matrix metalloproteinase activity was similar in high and low regions using a quantitative FRET peptide assay, whereas protein levels in tissues showed modest regional differences. These gene and protein differences across regions of the TM provide further evidence for a molecular basis of segmental flow routes within the aqueous outflow pathway. New insight into the molecular mechanisms of segmental aqueous outflow may aid in the design and delivery of improved treatments for glaucoma patients.     

Dexamethasone alters F-actin architecture and promotes cross-linked actin network formation in human trabecular meshwork tissue

Elevated intraocular pressure is an important risk factor for the development of glaucoma, a leading cause of irreversible blindness. This ocular hypertension is due to increased hydrodynamic resistance to the drainage of aqueous humor through specialized outflow tissues, including the trabecular meshwork (TM) and the endothelial lining of Schlemm's canal. We know that glucocorticoid therapy can cause increased outflow resistance and glaucoma in susceptible individuals, that the cytoskeleton helps regulate aqueous outflow resistance, and that glucocorticoid treatment alters the actin cytoskeleton of cultured TM cells. Our purpose was to characterize the actin cytoskeleton of cells in outflow pathway tissues in situ, to characterize changes in the cytoskeleton due to dexamethasone treatment in situ, and to compare these with changes observed in cell culture. Human ocular anterior segments were perfused with or without 10(-7) M dexamethasone, and F-actin architecture was investigated by confocal laser scanning microscopy. We found that outflow pathway cells contained stress fibers, peripheral actin staining, and occasional actin "tangles." Dexamethasone treatment caused elevated IOP in several eyes and increased overall actin staining, with more actin tangles and the formation of cross-linked actin networks (CLANs). The actin architecture in TM tissues was remarkably similar to that seen in cultured TM cells. Although CLANs have been reported previously in cultured cells, this is the first report of CLANs in tissue. These cytoskeletal changes may be associated with increased aqueous humor outflow resistance after ocular glucocorticoid treatment.     

The role of TGF-β in the pathogenesis of primary open-angle glaucoma

Transforming growth factor-β2 (TGF-β2) is found in increasing amounts in aqueous humor and reactive optic nerve astrocytes of patients with primary open-angle glaucoma (POAG), a major cause of blindness worldwide. The available data strongly indicate that TGF-β2 is a key player contributing to the structural changes in the extracellular matrix (ECM) of the trabecular meshwork and optic nerve head as characteristically seen in POAG. The changes involve an induction in the expression of various ECM molecules and are remarkably similar in trabecular meshwork cells and optic nerve head astrocytes. The ECM changes in the trabecular meshwork most probably play a role in the increase of aqueous humor outflow resistance causing higher intraocular pressure (IOP). In the optic nerve head, TGF-β2-induced changes might contribute to deformation of the optic nerve axons causing impairment of axonal transport and neurotrophic supply and leading to their continuous degeneration. The increase in IOP further adds mechanical stress and strain to optic nerve axons and accelerates degenerative changes. In addition, high IOP might induce the expression of activated TGF-β1 in trabecular meshwork cells and optic nerve head astrocytes; this again might significantly lead to the progress of axonal degeneration. The action of TGF-β2 in POAG is largely mediated through the connective tissue growth factor, whereas the activities of TGF-β1 and -β2 are modulated by the blocking effects of bone morphogenetic protein-4 (BMP-4) and BMP-7, by gremlin that inhibits BMP signaling and by several species of microRNAs.     

The role of matricellular proteins in glaucoma

Glaucoma is an optic neuropathy affecting approximately 60 million people worldwide and is the second most common cause of irreversible blindness. Elevated intraocular pressure (IOP) is the main risk factor for developing glaucoma and is caused by impaired aqueous humor drainage through the trabecular meshwork (TM) and Schlemm's canal (SC). In primary open angle glaucoma (POAG), this elevation in IOP in turn leads to deformation at the optic nerve head (ONH) specifically at the lamina cribrosa (LC) region where there is also a deposition of extracellular matrix (ECM) molecules such as collagen and fibronectin.Matricellular proteins are non-structural secreted glycoproteins that help cells communicate with their surrounding ECM. This family of proteins includes connective tissue growth factor (CTGF), also known as CCN2, thrombospondins (TSPs), secreted protein acidic and rich in cysteine (SPARC), periostin, osteonectin, and Tenascin-C and -X and other ECM proteins. All members appear to play a role in fibrosis and increased ECM deposition. Most are widely expressed in tissues particularly in the TM and ONH and deficiency of TSP1 and SPARC have been shown to lower IOP in mouse models of glaucoma through enhanced outflow facility. The role of these proteins in glaucoma is emerging as some have an association with the pathophysiology of the TM and LC regions and might therefore be potential targets for therapeutic intervention in glaucoma.     

Novel molecular insights into RhoA GTPase-induced resistance to aqueous humor outflow through the trabecular meshwork

Impaired drainage of aqueous humor through the trabecular meshwork (TM) culminating in increased intraocular pressure is a major risk factor for glaucoma, a leading cause of blindness worldwide. Regulation of aqueous humor drainage through the TM, however, is poorly understood. The role of RhoA GTPase-mediated actomyosin organization, cell adhesive interactions, and gene expression in regulation of aqueous humor outflow was investigated using adenoviral vector-driven expression of constitutively active mutant of RhoA (RhoAV14). Organ-cultured anterior segments from porcine eyes expressing RhoAV14 exhibited significant reduction of aqueous humor outflow. Cultured TM cells expressing RhoAV14 exhibited a pronounced contractile morphology, increased actin stress fibers, and focal adhesions and increased levels of phosphorylated myosin light chain (MLC), collagen IV, fibronectin, and laminin. cDNA microarray analysis of RNA extracted from RhoAV14-expressing human TM cells revealed a significant increase in the expression of genes encoding extracellular matrix (ECM) proteins, cytokines, integrins, cytoskeletal proteins, and signaling proteins. Conversely, various ECM proteins stimulated robust increases in phosphorylation of MLC, paxillin, and focal adhesion kinase and activated Rho GTPase and actin stress fiber formation in TM cells, indicating a potential regulatory feedback interaction between ECM-induced mechanical strain and Rho GTPase-induced isometric tension in TM cells. Collectively, these data demonstrate that sustained activation of Rho GTPase signaling in the aqueous humor outflow pathway increases resistance to aqueous humor outflow through the trabecular pathway by influencing the actomyosin assembly, cell adhesive interactions, and the expression of ECM proteins and cytokines in TM cells.     

Antithrombin III, a serpin family protease inhibitor, is a major heparin binding protein in porcine aqueous humor

Our hypothesis is that the proteins in aqueous humor may be involved in the regulation of outflow facility through the trabecular meshwork and uveoscleral meshwork. In this study, we analyzed the profile of heparin-binding proteins present in porcine aqueous humor to identify and characterize secretory proteins with a binding affinity for heparin. A single step involving heparin-sepharose affinity chromatography of porcine aqueous humor yielded a approximately 60 kDa protein as the major heparin-binding species. This protein was specifically eluted from the column by heparin. The N-terminal sequence and immunological cross reactivity of this protein confirmed its identity as antithrombin III. Aqueous humor from different species, as well as cells from human trabecular meshwork, Schlemm's canal, and lens epithelium, contained detectable amounts of antithrombin III. Based on its known anticoagulative function in endothelial cells and effects on the production of prostacyclin, it is reasonable to speculate that antithrombin III present in aqueous humor might influence the physiology of the trabecular and uveoscleral meshwork and thereby regulate intraocular pressure.     

Pro-fibrotic pathway activation in trabecular meshwork and lamina cribrosa is the main driving force of glaucoma

While primary open-angle glaucoma (POAG) is a leading cause of blindness worldwide, it still does not have a clear mechanism that can explain all clinical cases of the disease. Elevated IOP is associated with increased accumulation of extracellular matrix (ECM) proteins in the trabecular meshwork (TM) that prevents normal outflow of aqueous humor (AH) and has damaging effects on the fine mesh-like lamina cribrosa (LC) through which the optic nerve fibers pass. Applying a pathway analysis algorithm, we discovered that an elevated level of TGFβ observed in glaucoma-affected tissues could lead to pro-fibrotic pathway activation in TM and in LC. In turn, activated pro-fibrotic pathways lead to ECM remodeling in TM and LC, making TM less efficient in AH drainage and making LC more susceptible to damage from elevated IOP via ECM transformation in LC. We propose pathway targets for potential therapeutic interventions to delay or avoid fibrosis initiation in TM and LC tissues.     

Anterior segment development relevant to glaucoma

Development of the ocular anterior segment involves a series of inductive interactions between neural ectoderm, surface ectoderm and periocular mesenchyme. The timing of these events is well established but less is known about the molecular mechanisms involved. Various genes that participate in these processes have been identified. As the roles of more genes are determined, developmental pathways and networks will emerge. Here, we focus on recent advances made using mouse models. We summarize key morphological events in formation of anterior chamber structures, including the aqueous humor drainage structures that are involved in intraocular pressure (IOP) regulation and glaucoma. We discuss the developmental roles of genes that associate with abnormal anterior segment development and elevated IOP or glaucoma (including Bmp4, Cyp1b1, Foxc1, Foxc2, Pitx2, Lmx1b and Tyr ) and how some of these genes may fit into developmental networks.     

Treatment of post-traumatic trabecular mashwork thrombosis and secondary glaucoma with intracameral tissue plasminogen activator in previously unrecognized sickle cell anemia

Intracameral tissue plasminogen activator (t-PA) application in a child with previously unrecognized sickle cell anemia, post-traumatic hyphema, thrombosis in trabecular mashwork and consecutive acute glaucoma showed positive results. Thirteen year-old boy, son of African father and Caucasian mother, was admitted to hospital, with symptoms of acute glaucoma and partial hyphema after right eye trauma. Visual acuity of affected eye was 0.5 and intraocular pressure (IOP) 46 mm Hg. Despite a common therapy three days later clinical condition of patient's right eye was getting worst. Visual acuity was only hand motion (HM) and IOP 53 mmHg. At this point rose suspicion of sickle cell disease (SCD) and decision about injecting t-PA (20 microg) into anterior chamber was made. Cytological examination of aqueous humor revealed 10% sickled erythrocytes. Hemoglobin electrophoresis discovered hemoglobin S so that diagnosis of SCD was confirmed. Intraocular application of t-PA showed excellent results in post-traumatic hyphema with trabecular mashwork thrombosis in the patient with sickle cell anemia. Two-years follow up confirmed permanent normalisation of IOP and visual acuity. Successful outcome with anterior chamber paracentesis and intracameral injection of t-PA is promising novel approach, which we recommend in treatment of post-traumatic hyphema in SCD.     

Adenovirus conducted connective tissue growth factor on extracellular matrix in trabecular meshwork and its role on aqueous humor outflow facility

Deposition of extracellular matrix (ECM) in trabecular meshwork, such as fibronectin, collagen IV, elastin. leads to increased resistance of trabecular meshwork in primary open angle glaucoma (POAG). Connective tissue growth factor (CTGF) is known to regulate the ECM deposits. In this study, we detect the effect of adenovirus conducted CTGF (Adv-CTGF) transfection on either the expression of ECM components or aqueous humor outflow facility. Adv-CTGF was used to transfect rat trabecular meshwork cells in vivo and in vitro. Aqueous humor outflow facility was test by microbeads perfusion. Protein expression of CTGF, fibronectin, and collagen IV was determined using Western blot. In the Adv-CTGF group, the outflow facility displayed a significant decrease from baseline. It appears as though the transfection with Adv-CTGF significantly affects the aqueous humor outflow pattern. A negative correlation between IOP and PEFL indicated that a decrease in the area of bead deposition corresponded to an overall decrease of outflow, leading to an elevated IOP. Adv-CTGF can enhance the expression of CTGF, fibronectin and collagen IV. CTGF is the novel target for treatment of POAG. It is necessary to further study to test inhibition of CTGF expression for treatment of POAG.     

Flt1 and Flk1 mediate regulation of intraocular pressure and their double heterozygosity causes the buphthalmia in mice

Flt1 and Flk1 are receptor tyrosine kinases for vascular endothelial growth factor-A which play a crucial role in physiological and pathological angiogenesis. To study genetic interaction between the Flt1 and Flk1 genes, we crossed between Flt1 and Flk1 heterozygous (Flt1(+/-) and Flk1(+/-)) mice. We found that Flt1; Flk1 double heterozygous (Flt1(+/-); Flk1(+/-)) mice showed enlarged eyes similar to the buphthalmia detected in human congenital glaucoma with elevation of intraocular pressure (IOP). Actually, IOP was elevated in Flt1(+/-); Flk1(+/-) mice and also in Flt1 or Flk1 single heterozygous mice. However, none of these mutants showed hallmarks of glaucoma such as ganglion cell death and excavation of optic disc. To clarify the pathological causes for enlarged eyes and elevated IOP, we investigate the mice from matings between Flt1(+/-) and Flk1(+/-) mice. Flt1(+/-) mice showed enlarged Schlemm's canal and disordered collagen fibers in the sclera, whereas Flk1(+/-) mice showed atrophied choriocapillaris in the choroid. These tissues are a part of the main outflow and alternative uveoscleral outflow pathway of the aqueous humor, suggesting that these pathological changes found in Flt1(+/-) and Flk1(+/-) mice are associated with the buphthalmia in Flt1(+/-); Flk1(+/-) mice.     

Senescent phenotype of trabecular meshwork cells displays biomarkers in primary open-angle glaucoma

Glaucoma is a major cause of irreversible blindness, affecting more than 70 million individuals worldwide. Elevated intraocular pressure (IOP) is a major risk factor in the development of glaucoma and in the progression of glaucomatous damage. High IOP usually occurs as a result of an increase in aqueous humor outflow resistance in trabecular meshwork (TM). Primary open angle glaucoma (POAG) is characterized by quantifiable parameters including the IOP, the aqueous outflow facility, and geometric measurements of the optic disc and visual defects. Morphological and biochemical analyses of the TM of POAG patients revealed loss of cells, increased accumulation of extracellular matrix (ECM), changes in the cytoskeleton, cellular senescence and the process of subclinical inflammation. Various biochemical and molecular biology biomarkers of TM cells senescence are considered in the article. Oxidative stress is becoming an important factor more likely to be involved in the pathogenesis of POAG. Treatment of TM cells with oxidative stress induced POAG-typical changes like ECM accumulation, cell death, disarrangement of the cytoskeleton, advanced senescence and the release of inflammatory markers. Oxidative stress is able to induce characteristic glaucomatous TM changes and these oxidative stress-induced TM changes can be minimized by the use of antioxidants, such as carnosine-related analogues and IOP-lowering substances. There is evidence demonstrating that carnosine related analogues may have antioxidative capacities, can prevent cellular senescence and the attrition of telomeres during the action of oxidative stress. Prevention of oxidative stress exposure to the TM with N-acetylcarnosine ophthalmic prodrug of carnosine and oral formulation of non-hydrolized carnosine may help to reduce the progression of POAG. The previous work has demonstrated that carnosine is able to reach the TM directly via the transcorneal and systemic pathways of administration with N-acetylcarnosine ophthalmic prodrug and oral formulation of non-hydrolized carnosine. We suggest in this article that dual therapy with N-acetylcarnosine lubricant eye drops, oral formulation of non-hydrolized carnosine combined with anti-glaucoma adrenergic drug may become the first-line therapy in glaucoma due to their efficiency in reducing IOP, prevention and reversal of oxidative stress-induced damages in TM and the low rate of severe side effects during combined treatment.     

Alteration of cytoskeletal structure, integrin distribution, and migratory activity by phagocytic challenge in cells from an ocular tissue—The trabecular meshwork

Summary The trabecular meshwork is a specialized tissue in the anterior chamber of the eye that regulates the aqueous humor outflow and controls the intraocular pressure. Cells in the trabecular meshwork are believed to be essential for maintenance of the outflow system, and their malfunctioning may lead to elevation of intraocular pressure and development of glaucoma. These cells are avid phagocytes. Using an in vitro tissue culture system, we have previously shown that bovine trabecular meshwork cells exhibited a short-term loss of cell-matrix adhesiveness after exposure to latex microspheres. The current study showed that 4 h after phagocytosis, the cytoskeletal structure in trabecular meshwork cells was disrupted, the formation of focal contact formation was limited, and the cellular migratory activity was increased. These in vitro responses paralleled those that occur in vivo. By 24 h, all the changes demonstrated returned to normal. Our data suggest that the short-term loss in cell-matrix cohesiveness observed after phagocytic challenge may be related to the reorganization of cytoskeletal structures and the decline of focal contact formation. The altered cell migration may also be interlinked.     

Guanylate cyclase activators, cell volume changes and IOP reduction

Glaucoma afflicts millions of people worldwide and is a major cause of blindness. The risk to develop glaucoma is enhanced by increases in IOP, which result from deranged flow of aqueous humor. Aqueous humor is a fluid located in the front of the eye that gives the eye its buoyancy and supplies nutrients to other eye tissues. Aqueous humor is secreted by a tissue called ciliary processes and exits the eye via two tissues; the trabecular meshwork (TM) and Schlemm's canal. Because the spaces through which the fluid flows get smaller as the TM joins the area of the Schlemm's canal, there is resistance to aqueous humor outflow and this resistance creates IOP. There is a correlation between changes in TM and Schlemm's canal cell volume and rates of aqueous humor outflow; agents that decrease TM and Schlemm's canal cell volume, increase the rate of aqueous humor outflow, thus decreasing IOP. IOP is regulated by guanylate cyclase activators as shown in humans, rabbits and monkeys. There are two distinct groups of guanylate cyclases, membrane guanylate cyclase and soluble guanylate cyclase (sGC); activation of both have been shown to decrease IOP. Members of the membrane guanylate cyclase family of receptors bind to peptide ligands, while the sGC responds to gases (such as NO and CO(2)) and compounds (such as YC1, [3-(5'-hydroxymethyl-2'furyl)-1-benzyl indazole), a benzyl indazole derivative, and BAY-58-2667); activation of either results in formation of cyclic GMP (cGMP) and activation of protein kinase G (PKG) and subsequent phosphorylation of target proteins, including the high conductance calcium activated potassium channel (BKca channel). While activators of both membrane guanylate cyclase and sGC have the ability to lower IOP, the IOP lowering effects of sGC are noteworthy because sGC activators can be topically applied to the eye to achieve an effect. We have demonstrated that activators of sGC increase the rate at which aqueous humor exits the eye in a time course that correlates with the time course for sGC-induced decreases in TM and Schlemm's canal cell volume. Additionally, sGC-induced decrease in cell volume is accompanied by both K(+) and Cl(-) efflux induced by activation of K(+) and Cl(-) channels, including the BKca channel and/or K(+)Cl(-) symport. This suggests that parallel K(+)Cl(-) efflux, and resultant H(2)O efflux result in decreases in cell volume. These observations suggest a functional role for sGC activators, and suggest that the sGC/cGMP/PKG systems are potential therapeutic targets in the treatment of glaucoma.     

Potential role of lysosomal dysfunction in the pathogenesis of primary open angle glaucoma

Primary open angle glaucoma (POAG) is a late onset disease usually accompanied by elevated intraocular pressure (IOP) that results from the failure of the trabecular meshwork (TM) to maintain normal levels of aqueous humor outflow resistance. Cells in the TM are subjected to chronic oxidative stress through reactive oxygen species (ROS) present in the aqueous humor (AH) and generated by normal metabolism. Exposure to ROS is thought to contribute to the morphological and physiological alterations of the outflow pathway in aging and POAG. Our results indicate that chronic exposure of TM cells to oxidative stress causes the accumulation of nondegradable material within the lysosomal compartment leading to diminished lysosomal activity and increased SA-β-Gal expression. Because the lysosomal compartment is responsible for maintaining general cellular turnover, such impaired activity may lead to a progressive cellular decline in the TM cell function and thus contribute to the progression of POAG.