Full metadata record
| DC Field | Value | Language |
|---|---|---|
| dc.contributor | School of Optometry | en_US |
| dc.contributor.advisor | Do, Chi-wai (SO) | en_US |
| dc.contributor.advisor | To, Chi-ho (SO) | en_US |
| dc.creator | Chaudhary, Shashi Kant | - |
| dc.identifier.uri | https://theses.lib.polyu.edu.hk/handle/200/13181 | - |
| dc.language | English | en_US |
| dc.publisher | Hong Kong Polytechnic University | en_US |
| dc.rights | All rights reserved | en_US |
| dc.title | Modulation of aqueous humor dynamics by Anoctamin-6 and Na,K-ATPase inhibitors in porcine eyes | en_US |
| dcterms.abstract | Glaucoma is a chronic eye disease characterized by progressive visual field loss resulting from ganglion cell death, leading to blindness if left untreated. Lowering intraocular pressure (IOP) with anti-glaucoma agents remains the primary treatment regimen. However, unwanted ocular side effects and drug resistance are apparent, indicating the importance of identifying novel drug targets for glaucoma treatment. The level of IOP is regulated by a dynamic equilibrium between the aqueous humor (AH) secretion by the ciliary epithelium (CE) and its drainage through the conventional trabecular meshwork (TM) pathway. The clinically-available anti-glaucoma drugs work by either suppressing the AH secretion or facilitating the outflow drainage. None of the existing pharmacologic agents work through both AH secretion and outflow concurrently. In this project, we investigated two cellular targets that may serve dual functions by simultaneously influencing both AH secretion and drainage. | en_US |
| dcterms.abstract | In the first study, we examined the mechanistic actions of anoctamin (Ano) in modulating AH inflow and outflow. The Ano family has 10 isoforms (Ano1 to Ano10), with Ano1 initially reported to function as a Ca2+ -activated Cl-channel (CaCC). Ano6 has also been implicated in regulating the volume-regulated anion channel (VRAC). Recent work has demonstrated that Ano6 acts as a CaCC and VRAC in human TM cells, potentially influencing the AH drainage. On the other hand, AH secretion is primarily driven by transepithelial Cl- transport across the dual-layered CE, which consists of the pigmented ciliary epithelium (PE) and non-pigmented ciliary epithelium (NPE). Cl- efflux by NPE cells likely limits the secretion rate. Despite this, the molecular entities of the Cl- channels remain unclear. | en_US |
| dcterms.abstract | Using excised porcine ciliary body epithelium (CBE) and primary cultured NPE cells, we were able to demonstrate that among all Ano1-10 isoforms, Ano6 was the most abundantly expressed isoform in the porcine CBE and NPE cells, consistent with findings in TM cells. This was confirmed by the localization of Ano6 in NPE, but not PE cells, using immunohistochemistry. Hypotonicity triggered an increase in both the Ano6 gene and protein expressions, whereas the other Ano isoforms demonstrated a reduction in expression upon hypotonic challenge. By means of using various Ano blockers including Tannic acid, CaCCinh-AO1, and T16Ainh-AO1, we demonstrated that Ano6 regulated NPE-cell Cl- efflux. More importantly, Ano6 was found to modulate the hypotonicity-induced and Ca2+ -activated fluid secretion through the combined effects of VRAC and CaCC in porcine CBE. These results were further supported by the inhibitory effects of specific siRNA-Ano6 knockdown on Cl- efflux by NPE cells. Consistent with our hypothesis, Tannic acid was also observed to increase the conventional outflow facility in mouse eyes, supporting the notion that Ano6 may be an important regulator for both AH secretion and outflow drainage and subsequently playing a key role in controlling IOP. | en_US |
| dcterms.abstract | In the second study, we investigated the effects of a selective α2 inhibitor of Na,K-ATPase on both AH inflow and outflow. Active Cl- secretion across the CE is primarily powered by Na,K-ATPase. Various isoforms of Na,K-ATPase are expressed in the CE, with the highest abundance observed in the par plicata region of NPE cells. Recently, DcB, a cyclobutyl derivative of digoxin with strong selectivity for α2 isoform, has been shown to lower IOP in rabbits. However, the precise cellular effects in regulating AH secretion and drainage are elusive. With the aid of simultaneous monitoring of fluid secretion and electrical parameters, we demonstrated that DcB, when added to the aqueous side, triggered a stimulation, rather than an inhibition, of fluid secretion, suggesting that DcB may potentially increase AH secretion. Pretreatment of cAMP stimulated Cl- secretion; however, subsequent addition of DcB failed to alter cAMP-induced response. These results were surprising, as DcB was expected to elicit a direct inhibition of Na,K-ATPase in NPE cells, thereby triggering a reduction instead of a stimulation of AH secretion. By measuring the effect of DcB on the outflow facility, we revealed that the IOP-lowering effect could be primarily due to a facilitation of AH drainage, rather than its effect on AH secretion. | en_US |
| dcterms.abstract | Given the essential roles of Cl- channels and Na,K-ATPase in regulating AH dynamics, our findings have helped us understand the precise functional significance of Ano6 and DcB in modulating AH inflow and outflow. This provides new insight into developing novel targets for achieving better treatment outcomes in glaucoma management. | en_US |
| dcterms.extent | xxi, 177 pages : color illustrations | en_US |
| dcterms.isPartOf | PolyU Electronic Theses | en_US |
| dcterms.issued | 2024 | en_US |
| dcterms.educationalLevel | Ph.D. | en_US |
| dcterms.educationalLevel | All Doctorate | en_US |
| dcterms.LCSH | Glaucoma -- Treatment | en_US |
| dcterms.LCSH | Drug targeting | en_US |
| dcterms.LCSH | Hong Kong Polytechnic University -- Dissertations | en_US |
| dcterms.accessRights | open access | en_US |
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