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Shaoqing He, Alena Z. Minton, Dorota Stankowska, Raghu R. Krishnamoorthy; Transcriptional Regulation of Endothelin B (ETB) Receptor in Retinas of Rats in Response to Elevated Intraocular Pressure. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5388.
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Expression of the endothelin B (ETB) 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 study transcription factors contributing to upregulation of ETB receptor expression in retinal ganglion cells in rats.
Luciferase assays were employed to identify promoter elements involved ETB gene expression in human non-pigmented ciliary epithelial cells, following analysis of binding site using the software Promo 3. 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. Untreated right eye served as the contralateral control. Immunofluorescent staining was used to determine c-Jun and C/EBPβ expression in retina sections from rats with elevated IOP. Real-time PCR was used to detect mRNA levels of c-Jun, C/EBPβ, ETA receptor and ETB receptor from retinal ganglion cell layers obtained by laser capture microdissection from cryosection of retinas.
The -300 to -1 and -1200- to -600 bp upstream promoter regions of the ETB receptor were found to be key elements that produced increased luciferase expression. Using the Promo3 software, the 1200 bp promoter construct was found to have six AP-1 binding sites. 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. mRNA levels of c-Jun, ETA receptor and ETB receptor were upregulated by 2.2-, 3.8- and 4.4-fold respectively in retinal ganglion cell layer obtained from retinas of elevated IOP eyes, compared to those from contralateral eyes.
The 1200 bp upstream promoter region is important for expression of the human ETB gene. Increased expression and activation of c-Jun may contribute to expression of ETB receptor retinas in response to elevated IOP. Six binding sites of AP-1 in ETB receptor promoter may be important for inducible ETB expression following IOP elevation. The direct role of c-Jun in controlling ETB receptor expression is still under investigation, which will shed light on molecular mechanisms underlying glaucomatous changes in rodent eyes with ocular hypertension.
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