Changes in histone modifications in hypoosmolar-stressed astrocytes: new insights in tissue response to edema after brain injury

VILLARREAL A

Capital Federal

Congreso; Primer Encuentro del Club de la Glia Cono Sur; 2022

Reactive astrogliosis involves transcriptional, phenotypic and functional changes. Astrocyte functional changes have high impact on brain injury outcome; however the epigenetic mechanisms regulating gene expression, such as histone modifications, remain obscure. We have recently shown that astrocytes exposed to pro-inflammatory signals promote changes in histone acetylation, which resembles a situation of advanced injury progression. However, to date, there is no available description on early epigenetic changes in injury-affected astrocytes. Such early changes might “condition” the acquisition of reactive and stable astrocyte phenotype during injury progression while being exposed to other damage and/or pro-inflammatory signals. We hypothesize that hypo-osmolar stress promoted by early edema, prime astrocyte to become reactive during injury progression.In a model of brain cortical injury by pial disruption in adult male Wistar rats we observed, using immunofluorescence, a higher number of astrocytes with lower levels of H3K9ac at 3.5 hours in the injured hemisphere when compared to non-injured hemisphere. Also, the injury promoted an increase in GFAP and AQP4 immunoreactivity, which radially decreased at higher distances from the injury core, probably indicating astrocyte swelling in response to edema. In vitro, primary cultures of astrocytes respond to hypotonic stress with a significant decrease in histone acetylation (H3K9ac and H3K27ac). The levels of both histone acetylation marks are restored after 24 h recovery in isotonic medium. Inhibition of histone deacetylases with Trichostatin A prevented the decrease of H3K9ac after hypotonic stress.We are currently analyzing changes in astrocyte phenotype and chromatin configuration after hypoosmolar stress and recovery in pro-inflammatory medium. However, so far our results strongly suggest that, astrocytes exposed to edema-like microenvironment are able to dramatically change the global levels of histone acetylation. During the recovery in histone acetylation levels, chromatin might be re-decorated but in a “reactive epigenome”. Funding: PICT2018, ISN-CAEN2019