GRα and GRβ expression levels in trabecular meshwork determines steroid responsiveness upon glucocorticoid treatment

Purpose Glucocorticoid (GC) induced ocular hypertension (OHT) is a serious side effect of prolonged GC therapy with patients showing elevated intraocular pressure (IOP). Two major isoforms of glucocorticoid receptor (GRα and GRβ) regulate GCs sensitivity and specificity in various tissues. GRβ acts as a dominant negative regulator of GC activities and has been shown to regulate GC responsiveness in trabecular meshwork (TM). We evaluated GRα and GRβ expression levels in two mouse strains and studied how expression levels regulate GC and GC-induced OHT. Methods TM cells from C57BL/6J and BALB/cJ mice strains were isolated and characterized. RNA was isolated from TM cells and evaluated for GRα and GRβ expression levels using quantitative (Q)-PCR. To study how both TM cell lines respond to Dexamethasone (DEX) they were treated with DEX (100nM) and myocilin (MYOC) expression in TM cells was determined by Q-PCR analysis. Three month old C57BL/6J and BALB/cJ mice strains were used to evaluate changes in IOP upon DEX treatment. Mice were peri-ocularly injected with DEX-Acetate (100ug/eye) in both eyes. Conscious IOP measurements were taken using a TonoLab tonometer. Two-tailed Student’s t-test and One-way ANOVA were used for statistical analysis. Results MTM cells from both strains (C57BL/6J and BALB/cJ) expressed TM markers, including collagen IV, laminin and α-smooth muscle actin. GRα expression levels between both strains were similar. TM cells from BALB/cJ mice expressed significantly higher levels of GRβ compared to TM cells from C57BL/6J. When TM cells were treated with 100nM DEX, TM cells from C57BL/6J showed induction of myocilin expression compared to untreated controls whereas; TM cells from BALB/cJ did not show myocilin induction. IOP measurements upon DEX-Acetate treatment showed significant IOP elevation in C57BL/6J mice (ΔIOP of 3.5mmHg, p Conclusions In mouse, GRα and GRβ expression levels determines GC responsiveness. Higher GRβ expression levels leads to GC resistance. The current findings provide an important foundation for comparisons of GRα and GRβ expression levels in the TM among different strains. Also, manipulating GRα to GRβ expression levels holds a promise for desensitizing cells and tissues to GCs effects.