Alpha2-adrenergic-agonist brimonidine stimulates negative feedback and attenuates injury-induced phospho-ERK and dedifferentiation of chicken müller cells

Abstract

PURPOSE. Retinal injury induces Müller cell dedifferentiation by activating extracellular signalregulated kinase (ERK) signaling. Stimulation of α2-adrenergic receptors protects against injury but also activates ERK in Müller cells. The purpose of this work was to study the effect of α2-adrenergic signaling on injury-induced ERK and Müller cell dedifferentiation. We tested the hypothesis that α2-stimulation triggers negative feedback regulation of the injury-induced ERK pathway that attenuates Müller cell dedifferentiation. METHODS. Chicken retina injured by N-methyl-D-aspartate and cultured primary Müller cells were stimulated by the α2-adrenergic agonist brimonidine. Immunostaining, quantitative RTPCR, and Western blot techniques in combination with receptor blockers were used for analysis of the cellular responses. RESULTS. Alpha2-adrenergic receptor stimulation attenuated injury-induced ERK activation and dedifferentiation of Müller cells as seen by decreased phospho-ERK, expression of transitin, and retinal progenitor cell genes. The attenuation was concomitant with a synergistic upregulation of several negative ERK-signal feedback regulators including ERK-phosphatases, Raf1-, and growth factor receptor-binding proteins. The results were also seen in cultures of primary Müller cells. CONCLUSIONS. Alpha2-adrenergic signaling on Müller cells elicits an intracellular attenuation of the injury response that comprises negative ERK-signaling feedback leading to attenuated Müller cell dedifferentiation. The implications of this study are that adrenergic stress signals may directly modulate glial function in retina and that α2-adrenergic receptor pharmacology may be used to control glial injury response.