Myocilin Gene Expression in the Trabecular Meshwork of Rats in a Steroid-Induced Ocular Hypertension Model

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Abstract
To investigate the expression pattern of myocilin in the trabecular meshwork of normal and dexamethasone-induced ocular hypertensive rat eyes. An ocular hypertension model was generated by application of topical dexamethasone to rat eyes 4 times daily for 1, 2, and 4 weeks. Age-matched untreated eyes served as controls. The intraocular pressure (IOP) was monitored by electronic Tono-pen under anesthesia. The protein and mRNA levels of myocilin in the trabecular meshwork and endothelial lining of Schlemm's canal were investigated by immunohistochemistry and in situ hybridization, respectively. For semiquantitative evaluation, areas with positive staining were analyzed by a computer-assisted image-processing system with NIH software. The IOP in rat eyes was elevated after 2 weeks of topical dexamethasone treatment. Despite the IOP elevation, the protein and mRNA levels of myocilin in the trabecular meshwork and around Schlemm's canal in the steroid-treated eyes were not different from those of controls. No discernible changes in myocilin expression in the chamber angle indicate that myocilin may not be directly linked to ocular hypertension, at least not in rat eyes after relatively short-term steroid application.