Browsing by Subject "POAG"
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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 The Role of Mechanosensory TRPV4 Channels and Nitric Oxide Signaling in Intraocular Pressure Homeostasis and its Impairment in Glaucoma(2020-08) Patel, Pinkal D.; Zode, Gulab S.; Clark, Abbot F.; Pang, Iok-Hou; Krishnamoorthy, Raghu R.; Rickards, Caroline A.Several population-based studies have identified elevated intraocular pressure (IOP) as a major causative risk factor associated with primary open angle glaucoma (POAG), the most common form of glaucoma that affects millions of people worldwide. Moreover, multi-ethnic clinical trials in several different countries over the last few decades have provided overwhelming evidence showing correlation between lowering of IOP and reduced progression of vision loss. As a result, IOP reducing therapeutic interventions are the gold standard in glaucoma therapy. Although the role of IOP is evident in pathology of POAG, very few studies have delved into the complex physiological mechanisms that regulate IOP homeostasis. From continuous telemetry recordings in nonhuman primates, we now know that IOP is a dynamic variable that fluctuates throughout the day. However, despite the fluctuations, the mean IOP is still maintained within a narrow physiological range. The level of IOP elevation at any given time depends on the resistance to aqueous humor outflow encountered in the conventional outflow pathway consisting of the trabecular meshwork (TM), Schlemm's canal (SC), and the distal episcleral vessels. Recent studies have suggested that the cells of the outflow pathway have intrinsic ability to detect biomechanical stimuli in their environment (like shear stress) and convert these stimuli into biochemical signals to elicit specific cellular responses. Although mechanotransduction at the TM is deemed critical for IOP homeostasis, we are yet to conclusively identify the exact signaling pathway involved. In this study, we identify the role of transient receptor potential vanilloid IV channels (TRPV4) in sensing mechanical stress on the TM. We show that shear stress activates TRPV4 channels in human primary TM cells, which leads to endothelial nitric oxide synthase (eNOS)-dependent nitric oxide (NO) production. NO, itself has been identified as a key regulator of IOP. Exogenous NO delivery to the eye has been shown to reduce IOP in humans. However, the underlying mechanism that regulates endogenous levels of NO still remains unknown. To this end, we demonstrate that TRPV4 channels regulate eNOS-dependent NO production in primary human TM cells and ex vivo cultured human TM tissues. We show that TRPV4 activation by mechanical shear leads to activation of eNOS signaling and NO production. Furthermore, pharmacological activation of TRPV4 channels via a selective agonist GSK1016790A (GSK101) leads to eNOS phosphorylation and NO production. In animal models, we demonstrate a role of TRPV4 channels in regulating physiological IOP. Treatment of C57BL/6J mouse eyes with TRPV4 agonist GSK101 leads to reduction in baseline night-time IOP and nominal improvement in outflow facility. We also show that conditional knockout of TRPV4 channels in Ad5-Cre injected TRPV4f/f mice leads to increase in IOP. We use the NOS3-/- (eNOS) to further show that TRPV4 mediated lowering of IOP is eNOS dependent. Dysregulation of the TM cells leads to increase in resistance and IOP elevation. Furthermore, glaucomatous human TM cells show impaired activity of TRPV4 channels and disrupted TRPV4-eNOS signaling. Flow/shear stress activation of TRPV4 channels and subsequent NO release were also impaired in glaucomatous primary human TM cells. Together, our studies demonstrate a central role for TRPV4-eNOS signaling in lowering the resting IOP. Our results also provide evidence that impaired TRPV4 channel activity in TM cells contributes to TM dysfunction and elevated IOP in glaucoma.