Endothelin–1 Acts Through Endothelin B (ETB) Receptors to Mediate Apoptosis of Rat Retinal Ganglion Cells

Abstract

Abstract: : Purpose: Endothelin–1 administration to the retrobulbar portion of rodent retinas has been shown to produce a diffuse loss of axons and promote apoptotic cell death of retinal ganglion cells. The purpose of this study was to determine if the endothelin B (ET_B) receptor was involved in mediating retinal ganglion cell death by ET–1 treatment in rat retinas Methods: Brown Norway rats were intravitreally injected with 2 nmole ET–1 in HEPES buffer or were injected with HEPES buffer alone (vehicle). Rats were sacrificed 48 hr. post injection and TUNEL assays were performed to detect apoptosis in the retina. In a different set of experiments, wild–type and ET_B–deficient rats were injected with 2 nmole ET–1 and processed for TUNEL assay to detect apoptosis. Virally transformed RGC–5 cells in culture were treated with 1, 10 or 100 nM ET–1 and immunoblot analysis of ET_B receptor protein was performed in plasma membrane fractions obtained from these cells. Results: Intravitreal injection of ET–1 in Brown Norway rats produced an appreciable increase in apoptotic cell death of retinal ganglion cells, compared to vehicle–injected rats. ET–1 mediated apoptosis of retinal ganglion cells was attenuated in ET_B–deficient rats. ET–1 treatment produced an increase in ET_B protein expression in the wild–type cultured rat retinal ganglion cells. Conclusions: Apoptosis of retinal ganglion cells by ET–1 treatment is mediated through ET_B receptors. An upregulation of ET_B receptor expression by ET–1 treatment could contribute to ET–1 mediated apoptosis of retinal ganglion cells.

Keywords: apoptosis/cell death • ganglion cells • neuroprotection