Triggers in everyday life such as running into a former drinking buddy, walking by a once-familiar bar, and attending social gatherings can all cause recovering alcoholics to “fall off the wagon.” About 40 to 60 percent of people who have gone through treatment for substance abuse will experience some kind of relapse, according to the National Institute on Drug Abuse. But what drives the biology behind these cravings has remained largely unknown.
Now, a team led by researchers from the Perelman School of Medicine at the University of Pennsylvania, have shown, in mouse models, how acetate—a byproduct of the alcohol breakdown produced mostly in the liver—travels to the brain’s learning system and directly alters proteins that regulate DNA function. This impacts how some genes are expressed and ultimately affects how mice behave when given environmental cues to consume alcohol. Their findings were published today in Nature.
“It was a huge surprise to us that metabolized alcohol is directly used by the body to add chemicals called acetyl groups to the proteins that package DNA, called histones,” said the study’s senior author Shelley Berger, PhD, the Daniel S. Och University Professor in the departments Cell and Developmental Biology and Biology, and director of the Penn Epigenetics Institute. “To our knowledge, this data provides the first empirical evidence indicating that a portion of acetate derived from alcohol metabolism directly influences epigenetic regulation in the brain.”
It has been known that a major source of acetate in the body comes from the breakdown of alcohol in the liver, which leads to rapidly increased blood acetate. In this study, the team, co-led by Philipp Mews, PhD, a former graduate student in the Berger lab who is now a postdoctoral fellow at Mount Sinai, and Gabor Egervari, MD, PhD, a postdoctoral fellow in Berger’s lab, sought to determine whether acetate from alcohol breakdown contributes to rapid histone acetylation in the brain. They did so by using stable-isotope labeling of alcohol to show that alcohol metabolism does, in fact, contribute to this process by directly depositing acetyl groups onto histones via an enzyme called ACSS2.
Authors said that “ACSS2, ‘fuels’ a whole machinery of gene regulators ‘on site’ in the nucleus of nerve cells to turn on key memory genes that are important for learning. In fact, Berger and colleagues published findings on ACSS2 in a 2017 Nature paper. In that paper and previous work, the researchers found that ACSS2 is needed to form spatial memories.
In the current study, to better understand how the alcohol-induced changes in gene expression ultimately effect behavior, Berger and her team employed a behavioral test. Mice were exposed to “neutral” stimuli and alcohol reward in distinct compartments, distinguished by environmental cues. After this conditioning period, the researchers measured the preference of the mice by allowing them free access to either compartment, and recording the time spent in both the neutral and alcohol-paired chamber. They found that, as expected, mice with normal ACSS2 activity spent more time in the alcohol compartment following the training period.
To test the importance of ACSS2 in this behavior, researchers reduced the protein level of ACSS2 in a brain region important for learning and memory, and observed that, with lowered ACSS2, there was no preference shown for the alcohol-paired compartment.”
Read further from Penn Medicine News (October 2019)