The impact of alcohol and its metabolites on the epigenome of astrocytes

University Of Pennsylvania, Philadelphia PA

Investigators

Abstract

PROJECT SUMMARY Alcohol use disorder (AUD) is a global disease burden and while biological mechanisms underlying AUD have largely been examined in neurons, the role of glial cells is historically understudied. One glial cell type potentially important in AUD is astrocytes, which undergo transcriptional and functional changes upon alcohol exposure. Knowledge of how this is regulated is limited. Since astrocytes are the most abundant glial cell type in the central nervous system (CNS) and dynamically modulate neuronal activity and synaptic plasticity, it is conceivable that the impact of ethanol (EtOH) and its metabolite acetate on astrocytes may lead to both pronounced intracellular effects and subsequent downstream effects on the CNS through epigenetic mechanisms. In support of this notion, acetyl-CoA synthetase 2 (ACSS2) converts acetate to acetyl-CoA used in chromatin regulation of gene expression. Acetyl-CoA is used by histone acetyltransferases (HATs) to drive histone acetylation, which is associated with active transcription and is thought to underlie alcohol-related behaviours. However, whether acetate contributes to histone acetylation specifically in astrocytes, and whether this process is mediated by ACSS2, is unknown. Our lab has previously shown that EtOH is metabolized and deposited as acetate in the brain. During my preliminary studies, I found ACSS2 is highly expressed in and localized to the nucleus of astrocytes, suggesting an epigenetic, gene regulatory role. Treating primary astrocytes with acetate for 24 hours induced differential regulation of over 800 genes by RNA-seq. Moreover, an ACSS2 inhibitor reduced certain acetate-induced transcriptional effects. Interestingly, treating astrocytes with acetate for only 1 hour increased immediate early gene (IEG) expression, although this was not identified at 24 hours. This suggests astrocytes induce distinct waves of gene expression, which has never been directly tested in astrocytes but can importantly contribute to neuronal activity. Spatial transcriptomics analysis in vivo agrees with this, as stimulating fear memories in mice led to astrocytes upregulating certain IEGs at an early time point. Strikingly, this upregulation did not occur in full-body ACSS2 knockout mice. Based on the these evidence and models, I hypothesize that alcohol and its metabolites stimulate waves of transcription in astrocytes, where ACSS2 incorporates acetate into histone acetylation to activate genes that promote alcohol-associated behaviours. To address this hypothesis, I propose to focus on two specific aims: (1) to determine the wave-trajectory of astrocyte gene expression and the impact of alcohol and its metabolites, and (2) to determine whether astrocytes in the brain respond to alcohol metabolism by incorporating alcohol-derived acetate into histone acetylation at key DNA regulatory regions. Completion of these aims will not only reveal potential new therapeutic targets for AUD but will also unveil the capability and mechanism of astrocytes undergoing wave-trajectory of gene expression, yet to be studied. Notably, my study is different from my supervisor’s current NIAAA R01 submission under review.