Browsing by Subject "primary open angle glaucoma"
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Item Endothelin-1 Mediated Regulation of Extracellular Matrix Collagens- A Role in Pathology of Primary Open Angle Glaucoma(2007-11-01) Rao, Vidhya Ramachandiran; Thomas Yoroi; Neeraj Agarwal; Raghu KrishnamoorthyEndothelin -1 Mediated Regulation of Extracellular Matrix Collagens –A role in Pathology of Primary Open Angle Glaucoma. Vidhya R. Rao, Doctor of Philosophy. (Pharmacology and Neuroscience), November, 2007, 157 pp., 3 tables, 18 figures. Summary. Primary Open Angle Glaucoma (POAG) is a progressive optic neuropathy characterized by loss of retinal ganglion cells, optic nerve degeneration and characteristic extracellular matrix (ECM) remodeling of the optic nerve head. An increase in collagen type I and VI is observed at the level of lamina cribosa (LC), a distinct connective tissue region of optic nerve in POAG subjects. Extensive ECM remodeling with enhanced collagen deposition observed in POAG is consistent with the pathology of fibrosis. Mechanisms contributing to ECM remodeling in POAG is not known. Endothelin-1(ET-1), a potent vaso-active peptide plays a key role in glaucoma pathology. Intra-vitreal administration of ET-1 in animal models results in optic neuropathy, RGC apoptosis, axonal transport block and ONA activation. An upregulation of ET-1 and ETB receptors is observed in glaucomatous LC and animal models of glaucoma and ET-1 mediated detrimental effects in POAG appears to be mediated by ETB receptors. ET-1 initiatives and maintains enhanced collagen synthesis and deposition in various tissues under pathological conditions and is recognized as a potent profibrotic factor. In the present study we hypothesized that ET-1 increases extracellular matrix collagen deposition in lamina cribrosa and this change in ECM contributes to optic nerve fibrosis. We have demonstrated that cells of lamina cribrose (LC) cells, express functional ETA and ETB receptors. ET-1 increases intracellular calcium mobilization via ETA receptors and increases NO release by mechanisms involving both ETA and ETB receptors. Consistent with POAG pathology we have observed an upregulation ETB receptors in LC cells in response to chronic treatment with ET-1. LC cells also express prepro-ET-1, the primary gene transcript of ET-1. We have demonstrated for the first time that ET-1 exerts its profibrotic effects by enhancing collagen type I and type VI mRNA, protein synthesis, deposition and secretion in LC cells. ET-1 enhanced collagen deposition in LC cells appears to involve both ETA and ETB receptors, as both of the receptor antagonist, individually inhibit ET-1 mediated collagen synthesis. We have demonstrated that ET-1 also exerts its profibrotic effects in vivo by enhancing collagen deposition in rat optic nerve head. We have also observed an apparent decrease in ET-1 mediated collagen VI deposition in optic nerve heads of ETB deficient transgenic rats suggesting that ET-1 mediated collagen VI synthesis involves ETB receptor activation. In conclusion, endothlein-1 stimulates collagen synthesis and deposition both in vitro in LC cells as well as in vivo at the level of rat optic nerve head. ET-1 mediated increase in collage synthesis at the level of optic nerve head could render a fibrotic mechanism that contributes to the progression of POAG.Item Extracellular PACE4 is increased following transient oxygen glucose deprivation in Optic Nerve Astrocytes(2008-05-01) Fuller, John Anthony; Wordinger, Robert J.; Clark, Abbot F.; Krishnamoorthy, Raghu R.Fuller, John Anthony Extracellular PACE4 is increased following transient oxygen glucose deprivation in Optic Nerve Astrocytes. Doctor of Philosophy (Biomedical Sciences), May, 2008, 140 pp., 2 tables, 25 illustrations, bibliography, 218 titles. Primary Open Angle Glaucoma (POAG) is a family of heterogeneous optic neuropathies characterized by progressive retinal ganglion cell (RGC) death that leads to peripheral vision loss and eventually blindness. Various risk factors are associated with glaucoma, however the molecular mechanisms leading to RGC cell death remain unknown. The optic nerve serves as the conduit for the transmission of retinal ganglion action potentials to the brain. The cells that compromise the optic nerve form a scaffold that forms a physical support for the RGC axons. One cell type found throughout the optic nerve and associated with the RGC axon is the optic nerve astrocyte (ONA). Astrocytes are a predominant cell throughout the CNS and are believed to play crucial roles in metabolic, growth factor, and structural support, and respond to protect neurons during injury. The neuronal-glial interface in the optic nerve is poorly understood and believed to plan an important role in POAG pathophysiology, as unmyelenated RGC axons have direct contact with astrocyte processes. IN this study, the subtilisin-like Proprotein Convertases, (SPC) a family of proteases responsible for cleaving a wide variety of protein substrates, were examined in the retina and optic nerve head. PACE4, an SPC found to be secreted and active in the extracellular matrix was found to be highly expressed in the optic nerve, and colocalized to Mϋller cells in the retina and astrocytes in the optic nerve. Exposure of primary optic nerve astrocytes to oxygen-glucose deprivation (OGD) induces an increase in PACE4 mRNA. Furthermore, protein levels of extracellular, processed PACE4 increase following transient ODG, whereas the pro form of the molecule is degraded, and is believed to be chaperoned by the cleaved cysteine rich domain, a product found at high levels in the optic nerve in situ and the ONA in vitro. Due to the extracellular activity of PACE4, we hypothesized that it may regulate the bioactivity of TGF-β2, a growth factor believed to be involved in glaucoma-associated ONH remodeling by inducing the production of extracellular matrix (ECM). When PACE4 is inhibited via siRNA-mediated knockdown, as well as extracellular inactivation, TGF-β2 levels decrease. In addition, fibronectin, a major component of the ECM, is decreased. Furthermore, there is an increase in latent TGF-β2 secreted from the cell. It is therefore possible that PACE4 plays an active role in extracellular growth factor maturation, and may be a central mediator for growth factor bioactivity in the glaucomatous ONA.Item The Role of Wnt/β-catenin Signaling in the Trabecular Meshwork Relating to Ocular Hypertensive Primary Open Angle Glaucoma(2017-05-01) Webber, Hannah C.; Mao, Weiming; Clark, Abbot F.; Pang, Iok-HouOcular hypertension is the greatest causative risk factor of primary open angle glaucoma (POAG), the most prevalent subset of age-related glaucoma. Wnt signaling antagonist sFRP1 is increased in the trabecular meshwork (TM) of patients with POAG and induces ocular hypertension in human ex vivo eyes and in mice, which is resolved upon downstream Wnt/β-catenin signaling activation. The molecular mechanisms behind this remain unknown. β-catenin plays a role as an accessory protein to classical cadherin cytosolic domains, connecting these cell-cell adhesion proteins to the actin cytoskeleton. In other cell types, Wnt/β-catenin signaling crosstalks with the TGFβ/SMAD pathway, which is overactive in the POAG TM and is implicated in ocular hypertension. Our hypothesis is that the Wnt/β-catenin signaling pathway maintains TM cell adhesion and intraocular pressure by stabilizing cadherins junctions on the TM cell membrane and by inhibiting the POAG-related TGFβ/SMAD pathway. We used primary or transformed human non-glaucomatous TM (NTM) cells for all molecular and cell-based studies. NTM cells were treated with reporter viruses to study DNA binding element activity, recombinant protein to modulate Wnt/β-catenin or TGFβ/SMAD pathways, or siRNA to knockdown pathway mediators or cadherins. After treatment, NTM nucleic acid or protein was isolated or probed for Wnt/β-catenin or TGFβ signaling markers or cadherins. Some NTM cells were also plated for Real Time Cell Analysis (RTCA) cell impedance assays. Ad5.CMV recombinant adenoviruses encoding K-cadherin and/or sFRP1 were injected into BALB/cJ mouse eyes. Conscious IOP was assessed for up to 35 days. We found that Wnt/β-catenin signaling cross-inhibits TGFβ signaling in a β-catenin and Smad4-dependent manner. This cross-inhibition resulted in a decreased K-cadherin and fibronectin expression. Wnt/β-catenin signaling also enhanced mRNA, protein, and membrane-bound levels of K-cadherin, the most highly expressed cadherin isoform in the TM. In vivo, K-cadherin reduced the ocular hypertensive effects of sFRP1. RTCA assays showed that Wnt/β-catenin signaling and K-cadherin are responsible for maintenance of TM cell adhesion. Wnt/β-catenin signaling is responsible for intraocular pressure maintenance through increased expression of K-cadherin-mediated TM cell adhesion and through inhibition of TGFβ/SMAD signaling.Item Tissue Transglutaminase in Glaucoma(2008-08-01) Tovar-Vidales, Tara; Clark, Abbot F.; Reeves, Rustin E.; Sheedlo, HaroldTovar-Vidales, Tara, Tissue Transglutaminase in Glaucoma. Doctor of Philosophy (Cell Biology and Genetics), August 2008; 113pp; 0 tables, 23 illustrations, 165 bibliography, 25 titles. Primary open-angle glaucoma (POAG) is the second leading cause of irreversible blindness worldwide. Elevated intraocular pressure (IOP) is the major risk factor for POAG and is due to resistance of aqueous humor (AH) outflow through the trabecular meshwork ™ and Schlemm’s canal. Transforming growth factor-beta2 (TGF-β2) is elevated in the aqueous humor of glaucomatous eyes compared to normal eyes. Thus, TGF-β2 may play a role in regulating IOP. Tissue transglutaminase (TGM2) is a member of the transglutaminase family involved in cross-linking ECM proteins. In POAG, there are increased cross-linked extracellular matrix proteins (ECM) in the TM, and therefore, may result in elevated AH outflow resistance and elevated IOP. In this study, we examined the differences in both protein expression and enzyme activity of TGM2 between normal and glaucomatous TM cells and tissues. The findings demonstrated the presence of TGM2 in normal and glaucomatous cultured TM cells. We also showed that glaucomatous cultured TM cells and tissues have elevated levels of TGM2. Thus, this data suggest that TGM2 may have a pathogenic role in elevated outflow resistance and elevated IOP. Second, we observed the induction of TGM2 by TGF-β1, β2, and β3 in cultured TM cells, suggesting TGF-β isoforms regulate TGM2 protein levels. Finally, we observed that R-Smads and O38 regulated TGM2 protein levels, suggesting TGF-β2 acts through both its canonical and non-canonical signaling pathway to regulate TGM2.