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Shannon M. Niere, Emely Hoffman, Kristin M. Perkumas, R R. Allingham, Craig E. Crosson, W Daniel Stamer; PEDF Modulation of Schlemm's Canal Barrier Function. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1983.
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Pigment epithelial-derived factor (PEDF) has anti-angiogenic activity, participating in the regulation of retinal endothelial barrier function; however its role in other ocular endothelia are unknown. Since PEDF is a constituent of aqueous humor, the goal of the present study was to measure levels in human aqueous humor and examine PEDF effects on the permeability of Schlemm's canal (SC) endothelia, part of the blood-aqueous barrier.
After informed consent, aqueous humor was obtained from patients with no known ocular disease undergoing routine cataract surgery. Samples were assayed for PEDF using ELISA. In a second assay, primary cultures of SC and aqueous plexus (AP) endothelia were isolated from human donor and porcine eyes, respectively. Cells were plated at confluence on Transwell filters in DMEM containing 10% FBS and after one week, cells were put into serum-free media +/- PEDF (0.3-1 μM) and assayed for transendothelial electrical resistance (TEER) using an ohmmeter.
PEDF levels in aqueous humor were detected in 9/10 patient samples, ranging from 0.4 to >100 ng/ml. At the upper end of the physiological range, PEDF (1 μM for 24 hours) increased net TEER of human SC endothelial monolayers from 14 ± 1 to 17 ± 1 ohm*cm2, while porcine AP cells increased from 21±2 to 30±2 ohm*cm2 (p<0.05). In both cell types, significant changes in TEER were not observed at earlier time points, or using lower concentrations of PEDF.
PEDF is present in normal aqueous humor at a range of concentrations, suggesting a role for PEDF in the regulation of blood-aqueous barrier at the level of Schlemm's canal and consistent with its function in blood-retinal barrier homeostasis. Interestingly, effects of PEDF were not immediate, but required 24 hours; suggesting involvement in long-term control of blood-aqueous barrier.
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