Abstract
Purpose :
In glaucoma, the unmyelinated optic nerve head (ONH) region is a preferential site of significant pathophysiological changes such as tissue remodeling, neuroinflammation, axonal transport dysfunction, and axonal damage. This region is densely populated with astrocytes that become "reactive," leading to interest in studying their contribution to the pathology. Previous research on the astrocyte response relied on whole-tissue transcriptomic profiling or immunohistochemistry with a limited number of protein markers. Therefore, we lack a complete picture of how astrocytes react in glaucoma over time. We also don't know whether ONH and optic nerve proper (ONP) astrocytes respond differently. We recently showed that ONH and ONP astrocytes are morphologically and transcriptionally distinct. Here we examine the ONH and ONP astrocyte-specific transcriptional response following a chronic elevation in IOP.
Methods :
We used the Ribotag method to obtain astrocyte-specific mRNA from ONH and ONP of GFAP-Cre x Rpl22 mice. Samples were then sequenced. Experimental glaucoma was induced using a microbead occlusion model and animals sacrificed on days 7 (IOP peaks) and 30 (IOP returns baseline).
Results :
Expecting an early response, it was surprising that ONH astrocytes showed very few significant DEGs (only 62) and no pathway enrichment at day 7 vs 0. ONP astrocytes (310 DEGs) were enriched for cell-cell communication and keratinization. In the later period 30 vs 7 day comparison, ONH astrocytes (441 DEGs) upregulated primarily oxidative phosphorylation and protein metabolism, while downregulating a larger number of diverse processes. ONP astrocytes (30 vs 7 days; 3756 DEGs) also upregulated primarily processes for energy metabolism. Very few A1, A2, or pan-reactive associated genes were upregulated in either astrocyte populations. Additionally, there was no upregulation of well-known signaling pathways associated with astrocyte reactivity.
Conclusions :
ONH and ONP astrocytes respond differently to experimental glaucoma. Surprisingly, the most transcriptional changes were later in injury (30 vs 7 day comparisons) and in both populations energy metabolism was the most significant upregulated process. Transcriptional changes persisted even at day 30, a time when IOP had returned to near pre-injury levels. There was very little neuroinflammatory transcriptional response.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.