Abstract
Abstract: :
Purpose: The administration of steroids carries a risk for generating posterior subcapsular cateracts (PSC). PSC formation appears to be associated with the migration of lens epithelial cells (LEC) to the posterior of the lens. Thus the normal transition from LEC into lens fiber cells (LFC) that occurs at the lens equator is likely being perturbed. This normal process involves cessation of proliferation and activation of cellular differentiation which is accompanied by changes in protein expression and activity and, ultimately, induction of an apoptosis–like process that removes the cell nuclei and organelles. PSC development is specific to glucocorticoid (GC) steroids, and together with the recent identification of a transcriptionally active alpha glucocorticoid receptor (GR) in LEC, a GR–mediated mechanism for PSC induction is suggested. The purpose of this investigation was to examine LEC cultures for potential changes in proliferation and differentiation following GC administration. Methods: Cultured human B3 LEC, treated with dexamethasone (Dex), were assayed for viability and proliferation using Alamar blue and Cyquant and by BrdU incorporation. Transcription of specific mRNAs was analyzed by quantitative real–time PCR (Q–PCR) and protein expression by Western blotting. Assays for caspase activities were performed using commercial kits. Results: Dex–treated LEC exhibited enhanced rates of proliferation relative to untreated controls. Dex treatment induced a downregulation of γ–crystallin and an increase in αB–crystallin expressions. Expression levels of several proteins involved in apoptosis pathways were modified by Dex treatment and the levels of caspase activation were reduced. Dex–treated LEC were less susceptible to the compounds staurosporine and actinomycin D and to UV light. Conclusions: Steroid (Dex) administration appears to enhance proliferation of LEC and to modulate or inhibit differentiation into LFC. Concomitantly, Dex–treated LEC also appeared to be less susceptible to triggers of apoptosis. The data support a role for steroid–induced perturbation of the LEC–LFC transition in PSC development.
Keywords: receptors: pharmacology/physiology • cataract • cell death/apoptosis