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Xinbo Li, Kevin Phan, Ted S Acott, Mary J Kelley; Involvement of ATP binding cassette transporter 1 (ABCA1) in the regulation of outflow facility. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):3282.
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Obstruction of aqueous humor in flow through trabecular meshwork (TM) results in elevated intraocular pressure, a key risk factor for primary open angle glaucoma (POAG). The ATP binding cassette transporter 1 (ABCA1), recently reported to be involved in POAG, also binds with the PDZ-domain containing Rho Guanine-nucleotide exchange factor (PDZ-RhoGEF). Here, we investigated ABCA1 expression in human TM cells and tissues, as well as the effect of ABCA1 inhibition on outflow facility.
Single immunofluorescence (IF) labeling of ABCA1, Cx43 or ZO-1 was carried out in 8 µm frozen sections from perfused human anterior segments. Double immunofluorescence labeling of ABCA1/ZO-1, ZO-1/Cx43, ABCA1/Cx43 was performed in cultured human TM cells and tissues. ABCA1 inhibitor Glyburide (100 µM) was used to inhibit ABCA1 for 3 days, and its effect on outflow facility was monitored using the ex-vivo anterior segment perfusion system.
IF combined with confocal microscopy showed that ABCA1 is highly expressed in cultured TM cells and tissues, and in perfused human TM, but its expression in sclera is weak and absent in cornea. Double IF showed partial co-localization of ABCA1/ZO-1, ABCA1/Cx43 and Cx43/ZO-1 in cultured TM cells and tissue. Glyburide-treated TM cells demonstrated changes in ABCA1 cellular localization. Glyburide treatment reduced outflow, which was restored to pre-treatment levels after withdrawal of the inhibitor (n=4). This reduction was approximately 40%, as determined by one-way ANOVA, with Dunnett’s Multiple Comparison Test. The DMSO-treated control, however, showed no change in outflow.
ABCA1 is highly expressed in cultured TM cells and tissues, and it may be involved in outflow facility regulation. The evidence suggests that ABCA1, Cx43, and ZO-1 may associate in a tripartite complex in human TM affecting outflow facility.
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