Abstract
Purpose: :
Optic nerve (ON) injury results in the selective death of retinal ganglion cells (RGCs). Although the earliest detection of RGC death is at about 48 hrs post injury, there have been no studies of the early cell events in the retina soon after damage to the axons of the RGCs. Therefore, we investigated cellular signaling in the retina during the 6 hr period immediately following ON injury in mice.
Methods: :
Early signaling responses were detected through differences in phosphoproteins at 30, 60 and 360 min post ON crush using highly sensitive proteome technology. Both tyrosine- and serine/threonine- phosphorylated proteins were followed. To detect gene expression at the 360 min time point, microarray data were generated from mRNA laser-captured from the ganglion cell layer (GCL) of control and ON injury groups. Immunohistochemistry was used to localize the detected changes.
Results: :
Our studies revealed that many cells in the retina were highly active within 60 min following ON crush and that gene expression was occurring in the GCL by 360 min. ERK1/MAPK1 cascades were active within 30 min, suggesting signaling throughout the retina. Phosphorylation of the GluR1 ionotrophic glutamate receptor occurred by 60 min, suggesting activation of Ca2+ mediated signaling and increased sensitivity to glutamate. Proteins associated with cytokine signaling were activated and there were postranslational modifications to histones within 360 min. Some of the phosphorylated proteins were localized to cell types such as Muller cells and photoreceptors within 30 min, indicating that all layers of the retina were making responses to the ON crush. Analysis of differential gene expression in the GCL at 360 min post crush revealed that genes associated with apoptosis (e.g. Bax), calcium homeostasis (Ca2+ channels), and cytokine signaling (e.g. Socs3) were differentially expressed at this early time point.
Conclusions: :
Our data demonstrate that throughout the retina, neurons and glia respond rapidly post injury with changes in protein phosphorylation and gene expression. These early changes in cell signaling and cell survival pathways, glutamate and Ca2+ homoeostasis, and gene expression set up RGC death very soon after axonal injury.
Keywords: optic nerve • ganglion cells • signal transduction