Endothelin–1 Via Endothelin Receptor B (ETB) Activation Contributes To Apoptosis Of Rat Retinal Ganglion Cells

Abstract

Abstract: : Purpose:Endothelin–1 (ET–1) administration to the retrobulbar region of the retina has been shown to produce optic nerve axonal damage similar to that seen in glaucoma. The purpose of this study was to determine if ET–1 treatment could directly contribute to cell death of retinal ganglion cells both in culture and in vivo in rats. Methods:Brown Norway rats, intravitreally injected with 2 nmole ET–1, were sacrificed 48 h post–injection and retinas were isolated and processed for TUNEL assay to detect apoptosis. Virally transformed rat retinal ganglion cells (RGC–5 cells) were treated with 100 nM ET–1 for 96 h either with or without pretreatment with endothelin receptor antagonists and apoptotic changes were monitored using TUNEL assay. ET_B receptor expression was studied in RGC–5 cells treated with different doses of ET–1 for 24 hr, by immunoblotting. Results:Intravitreal ET–1 treatment could produced a 20 % increase in apoptotic cell death of retinal ganglion cells, compared to vehicle–injected control eyes . ET–1 (100 nM) treatment for 4 days produced a modest increase in number of cells undergoing cell death which was appreciably blocked by pretreatment with the ET_B receptor antagonist. ET–1 treatment for 24 hr produced a dose–dependent increase in ET_B receptor expression in RGC–5 cells. Conclusions: Elevations in ocular endothelin concentrations (as seen in primary open angle glaucoma) acting throgh ET_B receptors, could contribute to apoptosis of retinal ganglion cells. The current study suggests possibilities for developing endothelin receptor antagonists as potential neuroprotective agents in attenuating retinal ganglion cell death seen in glaucoma.

Keywords: ganglion cells • apoptosis/cell death • neuroprotection