Dexamethasone regulates endothelin-1 and endothelin receptors in human non-pigmented ciliary epithelial (HNPE) cells

Endothelin-1 (ET- 1) lowers intraocular pressure (IOP) in animal models by regulating aqueous humour dynamics through both inflow and outflow mechanisms. Moreover, ET's concentration is elevated in glaucoma patients and in animal models of glaucoma. Glucocorticoid therapy often can lead to increase IOP in susceptible individuals including patients with primary open angle glaucoma (POAG). In this study, we examined the effects of dexamethasone (Dex), a frequently used anti-inflammatory glucocorticoid, on the synthesis and release of endothelin-1 and on the expression of endothelin receptors in human non-pigmented ciliary epithelial (HNPE) cells, an established source for ET-1 in the anterior chamber. As measured by ET-1 immunoreactivity, ET-1 was concentration-dependently increased following 24 hr Dex treatment, with a maximum concentration (100 nM) causing a threefold increase of ET-1 release. Western blot analysis of HNPE cells showed the expression of endothelin receptor A (ETA) and endothelin receptor B (ETB) with approximate molecular weights of 40 kDa. Dex treatment decreased ETA receptor expression at all Dex doses, but up-regulated ETB receptors with 10 nM Dex having the greatest effect. Quantitative PCR demonstrated that Dex also increased the mRNA of pre-pro-ET-1 (ppET-1) and ETB but decreased the mRNA of ETA. RU486, a glucocorticoid receptor antagonist, was able to block Dex's actions on ET release and ETB receptor expression, but did not block its action on ETA receptor expression. Endothelin receptors were minimally expressed in HNPE cells as determined in binding experiments (B-max: ETA 17, ETB 25 fmol mg(-1) membrane protein). However Dex treatment stimulated a dramatic increase in ETB receptor density while decreasing ETA receptors (Bmax: ETA 11, ETB 116 fmol mg(-1) membrane protein). The regulation of endothelin and its receptors could be a novel mechanism associated with glucocorticoid's effects on intraocular pressure. The increase in ET-1 and disproportionate regulation in ET receptor expression by Dex could promote dysregulation in ET's mechanism on both inflow and outflow, thus affecting aqueous humour dynamics in the anterior chamber of the eye. (C) 2003 Elsevier Science Ltd. All rights reserved.