Latent Epigenetic Programs in Muller Glia Contribute to Stress, Injury, and Disease Response in the Retina

Abstract

Previous studies have demonstrated the dynamic changes in chromatin structure during retinal development that correlate with changes in gene expression. However, a major limitation of those prior studies was the lack of cellular resolution. Here, we integrate single-cell (sc) RNA-seq and scATAC-seq with bulk retinal data sets to identify cell type-specific changes in the chromatin structure during development. Although most genes promoter activity is strongly correlated with chromatin accessibility, we discovered several hundred genes that were transcriptionally silent but had accessible chromatin at their promoters. Most of those silent/accessible gene promoters were in the Muller glial cells. The Muller cells are radial glia of the retina and perform a variety of essential functions to maintain retinal homeostasis and respond to stress, injury, or disease. The silent/accessible genes in Muller glia are enriched in pathways related to inflammation, angiogenesis, and other types of cell-cell signaling and were rapidly activated when we tested 15 different physiologically relevant conditions to mimic retinal stress, injury, or disease in human and murine retinae. We refer to these as "pliancy genes" because they allow the Muller glia to rapidly change their gene expression and cellular state in response to different types of retinal insults. The Muller glial cell pliancy program is established during development, and we demonstrate that pliancy genes are necessary and sufficient for regulating inflammation in the murine retina in vivo. In zebrafish, Muller glia can de-differentiate and form retinal progenitor cells that replace lost neurons. The pro-inflammatory pliancy gene cascade is not activated in zebrafish Muller glia following injury, and we propose a model in which species-specific pliancy programs underly the differential response to retinal damage in species that can regenerate retinal neurons (zebrafish) versus those that cannot (humans and mice).