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X. Zhang, A.F. Clark, T. Yorio; Differential Expression of Glucocorticoid Receptor Beta between Normal and Glaucomatous Trabecular Meshwork Cell Lines-Potential Role in Regulating Glucocorticoid Responsiveness in Glaucoma . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2086.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Glucocorticoid (GC) responsivness is a risk factor for glaucoma. GCs increase the deposition of extracellular matrix materials in trabecular meshwork (TM)and hence increase intraocular pressure (IOP). Approximately 35% of the general population are steroid responders, while almost all the primary open angle glaucoma patients are GC responders. The mechanism underlying GC responsiveness in ocular hypertension is unknown. Glucocorticoid receptor beta (GRß) is reported to regulate GC resistance in other diseases, especially in asthma. Currently we are investigating the potential role of GRß in regulating GC sensitivity in glaucoma. Methods: Normal TM cell lines (3 primary and 1 transformed) and glaucomatous TM cell lines (3 primary and 1 transformed) were treated with dexamethasone (Dex) for 72 hours. Western blotting analysis for cytosolic and nuclear fractions and immunofluorescence microscopy were performed to measure GRß expression, subcellular distribution, and regulation by Dex. Co-immunoprecipitation, double immunofluorescence microscopy, and confocal immunofluorescence microscopy were used to determine whether GRß is closely associated with heat shock protein 90 (hsp90) and the cytoskeleton. Results: Both western blot and immunofluorescence microscopy showed that GRß was expressed not only in the nucleus but also in the cytoplasm. Most normal TM cell lines expressed a high amount of GRß which was more concentrated in the nuclear region. In contrast, all the glaucomatous TM cell lines expressed relatively lower amounts of GRß which was evenly distributed in the cytoplasm and the nucleus. Three days of Dex treatment appeared to up-regulate the nuclear GRß in normal TM cell lines but not in glaucomatous TM cell lines. Co-immunoprecipitation demonstrated that GRß can complex with hsp90 in both normal and glaucomatous TM cell lines. Immunofluorescence Microscopy showed that in normal TM cells, cytoplasmic staining of GRß was apparently fibrous in nature, suggesting a cytoskeletaal localization of GRß; however, the cytoplasmic distribution pattern of GRß was punctuate in glaucomatous TM cells. Conclusions: It has been reported that GRß exerts a negative effect on GRα's action in the nuclear region. The low amount of nuclear GRß in glaucomatous TM cells may account for the high sensitivity to GCs in glaucoma subjects. An apparent decrease in transport of GRß from the cytoplasm to the nucleus may be a mechanism responsible for the less nuclear accumulation of GRß in glaucomatous TM cells.
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