Human ganglion cells express the alpha-2 adrenergic receptor: Relevance to neuroprotection

Abstract

Background/aim: Alpha-2α adrenergic receptor (α2-AR) agonists are thought to be neuroprotective, preventing retinal ganglion cell death independent of pressure reduction. Previous studies have identified α2-ARs in rat retina. The authors aimed to demonstrate the presence and localisation of α2-ARs in human and rat retina and on the rat retinal ganglion cell line, RGC-5. Methods: Seven postmortem human and three postmortem rat eyes were paraformaldehyde fixed and frozen. RGC-5 cells were also paraformaldehyde fixed. The expression of α2A- ARs was determined by antibody immunofluorescence. Results: α 2A-AR expression was identified in the human retina, on ganglion cells, and cells in the inner and outer nuclear layers (INL, ONL). Differential α2A-AR staining patterns in the INL and ONL suggest a further restriction to as yet unidentified neuronal subclasses. The RGC-5 cell line also expressed α2A-ARs in undifferentiated cells and an increased expression upon fully differentiated cells. Conclusion: α2-AR agonists in addition to their pressure lowering effects in the eye, may act directly upon retinal neurons, including retinal ganglion cells. The presence of α2-ARs on the RGC-5 cell line allows future investigation of these possible direct effects using in vitro glaucoma model systems.