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Rachel S Chong, Li Fong Seet, Stephanie Chu, Li Zhen Toh, Tina T Wong; Increased aquaporin-1 expression in the iris is associated with raised intraocular pressure. Invest. Ophthalmol. Vis. Sci. 2016;57(12):6000.
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© ARVO (1962-2015); The Authors (2016-present)
Aquaporins are important transmembrane proteins that act as passive conduits for water transport, of which aquaporin-1 (AQP-1) has the highest expression in the eye. Deletion of AQP-1 in transgenic mice results in a significant decrease in intraocular pressure (IOP) suggesting that AQP-1 down-regulation may lead to decreased aqueous humour secretion resulting in IOP reduction. We hypothesised that higher expression of aquaporin-1 (AQP-1) in ocular tissues may be associated with elevated IOP.
Iris tissues were obtained intra-operatively from glaucoma patients undergoing trabeculectomies between 55 and 85 years old and age-matched normal cadaveric controls with no history of ocular disease. Hospital charts were reviewed for records of previous glaucoma medication and IOP at the time of surgery. Glaucoma severity was graded using the Hodapp-Parrish-Anderson score. Tissues from glaucoma patients (n = 54; POAG = 29, PACG = 25) were subjected to real-time polymerase chain reaction (qPCR) for AQP-1. Western blot was also performed to compare AQP-1 protein expression in glaucomatous and normal iris tissues. Pearson correlation coefficient was used to determine the association between AQP-1 expression and IOP using qPCR. One-way ANOVA was used for statistical analysis of AQP-1 expression with ocular medication or glaucoma severity.
A significant and positive correlation was found between increased IOP (17.46±0.50 mmHg) and AQP-1 expression (4.21±0.33 fold change/GAPDH) in the iris tissues of glaucoma patients (r = 0.30, p = 0.03). No significant association was found between ocular medication or glaucoma severity with AQP-1 expression. Western blot of iris tissues also showed greater AQP-1 expression in glaucoma than control eyes.
Our results are consistent with the hypothesis that increased expression of AQP-1 is associated with elevated IOP in glaucoma eyes. Further studies are needed to determine if targeting AQP-1 receptor may be a potential therapeutic approach for lowering IOP.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
QPCR of AQP-1 in the iris is positively correlated with IOP.
Protein levels of AQP-1 appear higher in iris tissues from glaucoma eyes in comparison with normal eyes.
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