We’ve all been warned — from our teachers, our parents, or from outrageous college movies — if you overindulge with booze you may not remember much the next morning. Now, exciting new research shows that an alcohol metabolite can alter our brain’s histone acetylation and can mix up memories at the molecular level.
Neurons make use of acetate, that’s normally found circulating in our systems, to generate the acetyl-CoA that drives histone acetylation. When alcohol is consumed and metabolised by the liver, it causes a surge in circulating acetate, and members Shelley Berger’s lab (University of Pennsylvania, USA) asked whether this metabolite spike could impact the neural epigenome.
The researchers injected mice with heavy-isotope labelled ethanol and found that:
- Alcohol-derived acetate is incorporated into acetylated histones in the hippocampus and the prefrontal cortex, up to 4 hours after injection as measured by mass spectrometry
- shRNA knockdown of the brain-enriched enzyme acetyl-CoA synthetase 2 (ACSS2) prevents alcohol metabolites from becoming acetylated histones
- Labelled carbon incorporated into other molecules, like glutamine, doesn’t make it to histones, which suggests that ACSS2 is the most important molecule here
- H3K9ac and H3K27ac peaks increase genome-wide 1 hour after alcohol injection, as measured by ChIP-seq, except in ACSS2 knockdown mice
- Genes that are induced (RNA-seq) by alcohol injection and overlap with acetylation peaks are enriched for functions like protein binding, postsynaptic density, and drug response
Since alcohol has many known, and potentially confounding, effects on brain circuitry and cell signalling, the talented team isolated primary neurons from the mouse hippocampus to examine the epigenome more closely. They added acetate to the neurons, to mimic an alcohol binge, and then performed RNA-seq to find that:
- 3613 genes are upregulated by acetate, including some that are related to signal transduction and learning and memory, but most of them are unchanged when ACSS2 is inactivated by a small molecule inhibitor
- Upregulated genes that are sensitive to ACSS2 inhibition are related to plasticity, behavior, and memory
- Genes that are induced by acetate, and are sensitive to ACSS2 inhibition, contain binding motifs for neuronal transcription factors
- The upregulated genes in cell culture largely overlap with those that are induced by alcohol in vivo
To explore whether ACSS2-mediated histone acetylation has an impact on alcohol-related behavior, the talented team exposed wildtype and ACSS2 knockdown (KD) mice to an ethanol conditioned place preference study where they received either alcohol or saline injections in one of two contextually distinct environments. Then, when the animals could freely move between the environments, wildtype mice spent more time in the alcohol-associated box while the KD animals showed no preference.
Co-first author Phillip Mews shares, “This is significant because in alcohol use disorders, memory of alcohol-associated cues is a primary driver of craving and relapse, even after prolonged periods of abstinence. Our findings establish a direct link between alcohol metabolism and histone acetylation in the hippocampus, indicating that translational treatment strategies that target this metabolic-epigenetic nexus may pave the way for novel therapeutic interventions for alcohol use and other neuropsychiatric disorders.”
The researchers also found that exposure to alcohol in utero leads to labelled histones in the embryonic mouse brain, which could have important implications for fetal alcohol spectrum disorders (FASD).
Take a sip of the original article in Nature, October 2019.