Astrocytes of the optic nerve exhibit a region-specific and temporally distinct response to elevated intraocular pressure
The optic nerve is an important tissue in glaucoma and the unmyelinated nerve head region remains an important site of many early neurodegenerative changes.  In humans and mice, astrocytes constitute the major glial cell type in the region, and in glaucoma they become reactive, influencing the optic nerve head (ONH) microenvironment and disease outcome. To determine the response of ONH astrocytes in glaucoma, we studied their transcriptional response to an elevation in intraocular pressure (IOP) induced by the microbead occlusion model. We also assessed the response of astrocytes in the more distal myelinated optic nerve proper (ONP). In this experimental model, astrocytes of the optic nerve exhibited a region-specific and temporally distinct response: ONH astrocytes showed very few early transcriptional changes and ONP astrocytes demonstrated substantially larger changes over the course of the experiment. Overall design: We studied the transcriptional response of ONH and ONP astrocytes to an elevation in IOP induced by the microbead occlusion model. Mice were sacrificed at day 0 (untreated), day 7 or day 30 post-injection. To specifically isolate astrocyte mRNA from the dissected tissues, we used the ribotag method to genetically tag ribosomes in astrocytes, which enabled purification of astrocyte-associated mRNA throughout the entire cell, including the fine processes, for bulk RNA-sequencing.