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

MONTEVERDE BM; VIDOS C; RAMOS AJ; VILLARREAL A

Mar del Plata

Congreso; Reunión anual de sociedades de biociencias 2022. Sociedad Argentina de Investigaciones Clínicas; 2022

Sociedad Argentina de Investigación Clínica (SAIC)

Astrocytes respond to brain injury through a mechanism known as reactive astrogliosis involving 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 increase the level of histone acetylation. However, to date, there is no available description on early epigenetic changes in injury-affected astrocytes. 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 (Villarreal et al., 2011), we addressed the levels of H3K9ac in astrocyte nuclei at 1.5 and 3.5 hours post injury. We observed, using immunofluorescence, a significative higher number of astrocytes with lower levels of H3K9ac at 3.5 hours 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, we exposed primary culture of astrocytes to hypotonic (20, 30 and 40% osm) culture medium to promote hypo-osmolar stress. We observed a statistically significant decrease in the levels of H3K9ac after 1 and 3 hours which were restored to control values 24h- after recovery in complete isotonic medium. A similar pattern was observed for H3K27ac suggesting a phenomenon of global histone deacetylation in response to stress.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