AP-1 and C/EBPβ Regulate Endothelin B (ET_B) Receptor in Retinas of Rats in Response to Elevated Intraocular Pressure

Abstract

Purpose: Expression of the endothelin B (ET_B) receptor is increased in retinas of eyes with elevated intraocular pressure (IOP) in a rat model of glaucoma. The aim of this study was to determine if transcription factors AP-1 and C/EBPβ contribute to upregulation of ET_B receptor expression in retinal ganglion cells in rats.

Methods: Real-time PCR were employed to determine ET_A and ET_B gene expression in human non-pigmented ciliary epithelial cells (HNPE) following overexpression or knockdown of c-Jun and C/EBPβ. The Morrison’s ocular hypertension model in rats was developed by injection with hypertonic saline into episcleral veins in the left eye to produce IOP elevation, while the corresponding right right eyes served as the contralateral control. Real-time PCR was used to detect mRNA levels of c-Jun, C/EBPβ, ET_A receptor and ET_B receptor from retinal ganglion cell layers obtained by laser capture microdissection from cryosection of retinas. Immunofluorescent staining was used to determine c-Jun and C/EBPβ expression in retina sections from rats with elevated IOP.

Results: Knock-down of c-Jun and C/EBPβ significantly downregulated mRNA levels of ET_A and ET_B in HNPE cells; on the other hand, overexpression c-Jun and C/EBPβ upregulated mRNA levels of ET_B and ET_A in HNPE cells. In retinal ganglion cell layer obtained from retinas of elevated IOP eyes there was a 2.2-, 3.8- and 4.4-fold increase in mRNA levels of c-Jun, ET_A receptor and ET_B receptor respectively, compared to those from contralateral eyes. Immunostaining of c-Jun and C/EBPβ was significantly increased in retinal ganglion cells in eyes with IOP elevation for two weeks compared to the corresponding contralateral eyes.

Conclusions: c-Jun and C/EBPβ contribute to upregulation of ET_A and ET_B gene expression. Increased immunostaining of c-Jun and C/EBPβ are also correlated with the expression of ET_B at RGC layer in a rat model of glaucoma with elevated IOP. The direct role of c-Jun in controlling ET_B receptor expression is still under investigation, which will shed light on molecular mechanisms underlying glaucomatous changes in rodent eyes with ocular hypertension.

Keywords: 688 retina • 739 transcription factors • 533 gene/expression