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The Brain Epigenome Goes Drunk: Alcohol Consumption Alters Histone Acetylation and Transcriptome
Please cite this article in press as: de Diego et al., The Brain Epigenome Goes Drunk: Alcohol Consumption Alters Histone Acetylation and Transcriptome, Trends in Biochemical Sciences (2019), https://doi.org/10.1016/j.tibs.2019.11.002
Spotlight
The Brain Epigenome Goes Drunk: Alcohol Consumption Alters Histone Acetylation and Transcriptome Irene de Diego,1 Annika Mu¨ller-Eigner,1 and Shahaf Peleg1,2,* Recent studies demonstrated that alcohol consumption can induce epigenetic changes in the brain, although the exact mechanism underlying such changes remained unclear. Now, a report by Mews et al. shows a direct link between alcohol consumption and histone acetylation changes in the brain, which are mediated by the neuronal acetyl-CoA synthase, ACSS2. Alcohol addiction is a behavioral disorder involving both genetic and environmental factors. Although genetic predisposition may underlie individual differences in vulnerability, it is still unclear how alcohol triggers an addictive phenotype. Changes in neuronal activity, memory processing, and synaptic plasticity during alcohol consumption are key for the process of drug rewarding and for learning the environmental cues that will cause drug seeking and relapse [1]. However, the exact molecular and genetic mechanisms underlying this process are only starting to be revealed. Recent studies demonstrated that alcohol could affect gene expression partially by altering the epigenetic landscape, which in turn impacts behavior and learning [2]. Such epigenetic changes, particularly histone modifications, are closely linked to metabolic activity [3,4]. It has been shown that mitochondrial-derived citrate supports the
acetyl-CoA pool, which is utilized for histone acetylation [3,5]. Furthermore, previous work established another connection between local metabolic activity on the chromatin area and the fueling of the acetylation of histones [6]. In particular, the levels of histone acetylation were impacted by conversion of acetate to acetyl-CoA by the acetyl-CoA synthetase (ACSS2), which was crucial for proper hippocampal memory formation. While the metabolism–epigenetic connectivity has been shown to have a role in various diseases, such as cancer, as well as in memory formation and during aging [3–6], it remained unclear to what extent such connectivity could underlie addictive behavior, including alcoholism. Nonetheless, because ethanol is metabolized into acetate in the liver [2,7], alcohol consumption is likely to cause increased circulating acetate levels and opens the question of how such increased levels may cause histone acetylation alteration in various tissues across the body. Now, a new study by Mews et al. [8] has demonstrated a direct link between acetate metabolism in the liver and histone acetylation in the brain in mice (Figure 1). To establish this causal relation, the authors performed isotope labeling of protein acetylation in vivo, monitored by mass spectrometry (MS). Deuterated ethanol (d6-EtOH) was intraperitoneally injected in mice, and deuterium labeling of acetylated histones was measured after injection. The data showed that labeled EtOH was rapidly metabolized by the liver, resulting in increased labeled acetate in the blood. The label was then rapidly incorporated and detected on histone acetylation in hippocampus and prefrontal cortex. Interestingly, the labeling was rapidly removed from the histones.
To gain more mechanistic insight, the authors revealed that histone acetylation, driven by alcohol metabolism, is ACSS2 dependent. By using a approach similar to that used in their previous study [6], the authors locally knocked down ACSS2 in the hippocampus. Interestingly, the incorporation of labeled acetyl groups into histone acetylation was abolished following the reduction of ACCS2, thus demonstrating the role of the enzyme in integrating liver acetate metabolism into epigenetic alterations [6,8]. Furthermore, Mews et al. also examined the transcriptional changes mediated by alcohol-derived histone acetylation in the brain. Increased levels of H3K9ac and H3K27ac mediated by alcohol consumption were correlated with increased mRNA levels and transcriptome reprogramming. Those increased histone acetylation levels at key neuronal genes were ACSS2 dependent, supporting the notion that ACSS2 is a suitable drug target for attenuating drug-induced transcriptional dysregulation. By using a cell culture model, the authors further demonstrated that acetate supplementation to primary hippocampal neurons ex vivo induced transcriptional regulation of various genes, which was blocked in the presence of an ACSS2 inhibitor. Interestingly, a large number of genes were downregulated upon acetate treatment [8]. It is possible that an increase in certain histone acetylation marks may induce a global redistribution of histone modifications that may cause not only gene upregulation, but also downregulation [9]. Taken together, the data reported by Mews et al. support the notion that alcohol consumption activates learning programs of addiction by changing the
Trends in Biochemical Sciences, -- 2019, Vol. --, No. --
1
Please cite this article in press as: de Diego et al., The Brain Epigenome Goes Drunk: Alcohol Consumption Alters Histone Acetylation and Transcriptome, Trends in Biochemical Sciences (2019), https://doi.org/10.1016/j.tibs.2019.11.002
Trends in Biochemical Sciences
Figure 1. Alcohol Consumption Impacts Hippocampal Histone Acetylation via Acetate Metabolism. (A) After alcohol consumption, ethanol is metabolized into acetate in the liver. (B) This increases acetate levels in the blood and, thus, acetate supply to the brain (i.e., hippocampus). (C) Increased levels of acetate in the hippocampus boost the acetylation of histones in an acetyl-co-enzyme A (CoA) synthetase 2 (ACSS2)dependent manner, (D) changing the epigenetic landscape, deregulating gene expression, and affecting gene behavior. Abbreviation: HAT, histone acetyltransferase.
epigenetic landscape, in particular histone acetylation [2,7]. Indeed, mice conditioned to ethanol chose to spend more time on a rewarding ethanol-associated chamber compared with unconditioned mice, a behavior that was abolished in ACSS2-knockout mice [8]. Of particular interest, the epigenetic dysregulation following alcohol exposure is not exclusive to the adult brain, because it also occurs in the gestating fetus. This study shows that maternal alcohol consumption affects histone acetylation in the fetal brain, a mechanism that may underlie the epigenetic changes implicated in numerous alcohol-associated postnatal disorders [10]. In summary, this study demonstrates a direct link between alcohol consumption and epigenetic changes in the brain and, thus, cognitive function [8]. Such observations could have relevant implications for the treatment of drug addiction, because inhibiting the metabolism–epigenetic connectivity may be used to prevent the conditioning and rewarding effects of ethanol. Targeting ACSS2 indeed holds promise 2
for future epigenetic interventions, especially in preventing relapses. However, there are other sources of acetate, such as the gut microbiome, which may boost histone acetylation and affect brain function [11,12]. This nexus between an external influence on metabolism and brain epigenome may underlie not only drug addiction, but also the etiology of other metabolic syndromes. For example, gut microbes communicate with the brain, and dysfunctional microbiomes correlate with disorders such as depression, anxiety, or metabolic syndrome [11]. It has been hypothesized that such microbe–brain crosstalk is mediated by metabolites that change the brain epigenetic patterns. Indeed, a more recent study demonstrated that the gut microbiome can affect histone acetylation and methylation in multiple host tissues and that it depends on host diet [12]. Nevertheless, direct evidence of how external stimuli triggers epigenetic changes remains scarce. The new study
Trends in Biochemical Sciences, -- 2019, Vol. --, No. --
by Mews et al. [8] represents an important step to understand the link between metabolism and epigenetics in alcohol addiction, but more research is needed to develop novel therapies. For example, it remains unclear how other prolonged alcohol consumption patterns, such as binge drinking or chronic consumption, would impact histone acetylation levels because they may have different effects in gene expression and addictive behavior. Furthermore, it would be interesting to study the impact on other relevant brain areas, such as the amygdala. Future work should address more specifically how alcohol-associated changes in the epigenome are responsible for the addictive phenotype. In addition, because acquisition of ethanol-conditioned behaviors requires ACSS2, an interesting question is whether ACSS2 is also required for maintaining the learned addictive phenotype. Testing how ACSS2 inhibition impacts behavior once addiction has been established, would help determine whether such a therapy would be useful for treating alcohol addicts or as a preventative measure. 1Epigenetics,
Metabolism, and Longevity, Independent Research Group, Leibniz Institute for Farm Animal Biology (FBN), 18196, Dummerstorf, Germany
2Laboratory
for Metabolism and Epigenetics in Brain Aging, Institute of Neuroregeneration and Neurorehabilitation, Qingdao University, Qingdao, China *Correspondence: [email protected], [email protected] https://doi.org/10.1016/j.tibs.2019.11.002 ª 2019 Elsevier Ltd. All rights reserved.
References 1. Robison, A.J. and Nestler, E.J. (2011) Transcriptional and epigenetic mechanisms of addiction. Nat. Rev. Neurosci. 12, 623–637 2. Ponomarev, I. (2013) Epigenetic control of gene expression in the alcoholic brain. Alcohol Res. 35, 69–76
Please cite this article in press as: de Diego et al., The Brain Epigenome Goes Drunk: Alcohol Consumption Alters Histone Acetylation and Transcriptome, Trends in Biochemical Sciences (2019), https://doi.org/10.1016/j.tibs.2019.11.002
3. Peleg, S. et al. (2016) The metabolic impact on histone acetylation and transcription in ageing. Trends Biochem. Sci. 41, 700–711 4. Suganuma, T. and Workman, J.L. (2018) Chromatin and metabolism. Annu. Rev. Biochem. 87, 27–49 5. Wellen, K.E. et al. (2009) ATP-citrate lyase links cellular metabolism to histone acetylation. Science 324, 1076–1080 6. Mews, P. et al. (2017) Acetyl-CoA synthetase regulates histone acetylation and hippocampal memory. Nature 546, 381–386
7. Zakhari, S. (2013) Alcohol metabolism and epigenetics changes. Alcohol Res. 35, 6–16 8. Mews, P. et al. (2019) Alcohol metabolism contributes to brain histone acetylation. Nature 574, 717–721 9. Feller, C. et al. (2015) Global and specific responses of the histone acetylome to systematic perturbation. Mol. Cell 57, 559–571 10. Murray, J. et al. (2016) Moderate alcohol drinking in pregnancy increases risk for
children’s persistent conduct problems: causal effects in a Mendelian randomisation study. J. Child Psychol. Psychiatry 57, 575–584 11. Stilling, R.M. et al. (2016) The neuropharmacology of butyrate: the bread and butter of the microbiota-gut-brain axis? Neurochem. Int. 99, 110–132 12. Krautkramer, K.A. et al. (2016) Dietmicrobiota interactions mediate global epigenetic programming in multiple host tissues. Mol. Cell 64, 982–992
Trends in Biochemical Sciences, -- 2019, Vol. --, No. --
3
Spotlight
The Brain Epigenome Goes Drunk: Alcohol Consumption Alters Histone Acetylation and Transcriptome Irene de Diego,1 Annika Mu¨ller-Eigner,1 and Shahaf Peleg1,2,* Recent studies demonstrated that alcohol consumption can induce epigenetic changes in the brain, although the exact mechanism underlying such changes remained unclear. Now, a report by Mews et al. shows a direct link between alcohol consumption and histone acetylation changes in the brain, which are mediated by the neuronal acetyl-CoA synthase, ACSS2. Alcohol addiction is a behavioral disorder involving both genetic and environmental factors. Although genetic predisposition may underlie individual differences in vulnerability, it is still unclear how alcohol triggers an addictive phenotype. Changes in neuronal activity, memory processing, and synaptic plasticity during alcohol consumption are key for the process of drug rewarding and for learning the environmental cues that will cause drug seeking and relapse [1]. However, the exact molecular and genetic mechanisms underlying this process are only starting to be revealed. Recent studies demonstrated that alcohol could affect gene expression partially by altering the epigenetic landscape, which in turn impacts behavior and learning [2]. Such epigenetic changes, particularly histone modifications, are closely linked to metabolic activity [3,4]. It has been shown that mitochondrial-derived citrate supports the
acetyl-CoA pool, which is utilized for histone acetylation [3,5]. Furthermore, previous work established another connection between local metabolic activity on the chromatin area and the fueling of the acetylation of histones [6]. In particular, the levels of histone acetylation were impacted by conversion of acetate to acetyl-CoA by the acetyl-CoA synthetase (ACSS2), which was crucial for proper hippocampal memory formation. While the metabolism–epigenetic connectivity has been shown to have a role in various diseases, such as cancer, as well as in memory formation and during aging [3–6], it remained unclear to what extent such connectivity could underlie addictive behavior, including alcoholism. Nonetheless, because ethanol is metabolized into acetate in the liver [2,7], alcohol consumption is likely to cause increased circulating acetate levels and opens the question of how such increased levels may cause histone acetylation alteration in various tissues across the body. Now, a new study by Mews et al. [8] has demonstrated a direct link between acetate metabolism in the liver and histone acetylation in the brain in mice (Figure 1). To establish this causal relation, the authors performed isotope labeling of protein acetylation in vivo, monitored by mass spectrometry (MS). Deuterated ethanol (d6-EtOH) was intraperitoneally injected in mice, and deuterium labeling of acetylated histones was measured after injection. The data showed that labeled EtOH was rapidly metabolized by the liver, resulting in increased labeled acetate in the blood. The label was then rapidly incorporated and detected on histone acetylation in hippocampus and prefrontal cortex. Interestingly, the labeling was rapidly removed from the histones.
To gain more mechanistic insight, the authors revealed that histone acetylation, driven by alcohol metabolism, is ACSS2 dependent. By using a approach similar to that used in their previous study [6], the authors locally knocked down ACSS2 in the hippocampus. Interestingly, the incorporation of labeled acetyl groups into histone acetylation was abolished following the reduction of ACCS2, thus demonstrating the role of the enzyme in integrating liver acetate metabolism into epigenetic alterations [6,8]. Furthermore, Mews et al. also examined the transcriptional changes mediated by alcohol-derived histone acetylation in the brain. Increased levels of H3K9ac and H3K27ac mediated by alcohol consumption were correlated with increased mRNA levels and transcriptome reprogramming. Those increased histone acetylation levels at key neuronal genes were ACSS2 dependent, supporting the notion that ACSS2 is a suitable drug target for attenuating drug-induced transcriptional dysregulation. By using a cell culture model, the authors further demonstrated that acetate supplementation to primary hippocampal neurons ex vivo induced transcriptional regulation of various genes, which was blocked in the presence of an ACSS2 inhibitor. Interestingly, a large number of genes were downregulated upon acetate treatment [8]. It is possible that an increase in certain histone acetylation marks may induce a global redistribution of histone modifications that may cause not only gene upregulation, but also downregulation [9]. Taken together, the data reported by Mews et al. support the notion that alcohol consumption activates learning programs of addiction by changing the
Trends in Biochemical Sciences, -- 2019, Vol. --, No. --
1
Please cite this article in press as: de Diego et al., The Brain Epigenome Goes Drunk: Alcohol Consumption Alters Histone Acetylation and Transcriptome, Trends in Biochemical Sciences (2019), https://doi.org/10.1016/j.tibs.2019.11.002
Trends in Biochemical Sciences
Figure 1. Alcohol Consumption Impacts Hippocampal Histone Acetylation via Acetate Metabolism. (A) After alcohol consumption, ethanol is metabolized into acetate in the liver. (B) This increases acetate levels in the blood and, thus, acetate supply to the brain (i.e., hippocampus). (C) Increased levels of acetate in the hippocampus boost the acetylation of histones in an acetyl-co-enzyme A (CoA) synthetase 2 (ACSS2)dependent manner, (D) changing the epigenetic landscape, deregulating gene expression, and affecting gene behavior. Abbreviation: HAT, histone acetyltransferase.
epigenetic landscape, in particular histone acetylation [2,7]. Indeed, mice conditioned to ethanol chose to spend more time on a rewarding ethanol-associated chamber compared with unconditioned mice, a behavior that was abolished in ACSS2-knockout mice [8]. Of particular interest, the epigenetic dysregulation following alcohol exposure is not exclusive to the adult brain, because it also occurs in the gestating fetus. This study shows that maternal alcohol consumption affects histone acetylation in the fetal brain, a mechanism that may underlie the epigenetic changes implicated in numerous alcohol-associated postnatal disorders [10]. In summary, this study demonstrates a direct link between alcohol consumption and epigenetic changes in the brain and, thus, cognitive function [8]. Such observations could have relevant implications for the treatment of drug addiction, because inhibiting the metabolism–epigenetic connectivity may be used to prevent the conditioning and rewarding effects of ethanol. Targeting ACSS2 indeed holds promise 2
for future epigenetic interventions, especially in preventing relapses. However, there are other sources of acetate, such as the gut microbiome, which may boost histone acetylation and affect brain function [11,12]. This nexus between an external influence on metabolism and brain epigenome may underlie not only drug addiction, but also the etiology of other metabolic syndromes. For example, gut microbes communicate with the brain, and dysfunctional microbiomes correlate with disorders such as depression, anxiety, or metabolic syndrome [11]. It has been hypothesized that such microbe–brain crosstalk is mediated by metabolites that change the brain epigenetic patterns. Indeed, a more recent study demonstrated that the gut microbiome can affect histone acetylation and methylation in multiple host tissues and that it depends on host diet [12]. Nevertheless, direct evidence of how external stimuli triggers epigenetic changes remains scarce. The new study
Trends in Biochemical Sciences, -- 2019, Vol. --, No. --
by Mews et al. [8] represents an important step to understand the link between metabolism and epigenetics in alcohol addiction, but more research is needed to develop novel therapies. For example, it remains unclear how other prolonged alcohol consumption patterns, such as binge drinking or chronic consumption, would impact histone acetylation levels because they may have different effects in gene expression and addictive behavior. Furthermore, it would be interesting to study the impact on other relevant brain areas, such as the amygdala. Future work should address more specifically how alcohol-associated changes in the epigenome are responsible for the addictive phenotype. In addition, because acquisition of ethanol-conditioned behaviors requires ACSS2, an interesting question is whether ACSS2 is also required for maintaining the learned addictive phenotype. Testing how ACSS2 inhibition impacts behavior once addiction has been established, would help determine whether such a therapy would be useful for treating alcohol addicts or as a preventative measure. 1Epigenetics,
Metabolism, and Longevity, Independent Research Group, Leibniz Institute for Farm Animal Biology (FBN), 18196, Dummerstorf, Germany
2Laboratory
for Metabolism and Epigenetics in Brain Aging, Institute of Neuroregeneration and Neurorehabilitation, Qingdao University, Qingdao, China *Correspondence: [email protected], [email protected] https://doi.org/10.1016/j.tibs.2019.11.002 ª 2019 Elsevier Ltd. All rights reserved.
References 1. Robison, A.J. and Nestler, E.J. (2011) Transcriptional and epigenetic mechanisms of addiction. Nat. Rev. Neurosci. 12, 623–637 2. Ponomarev, I. (2013) Epigenetic control of gene expression in the alcoholic brain. Alcohol Res. 35, 69–76
Please cite this article in press as: de Diego et al., The Brain Epigenome Goes Drunk: Alcohol Consumption Alters Histone Acetylation and Transcriptome, Trends in Biochemical Sciences (2019), https://doi.org/10.1016/j.tibs.2019.11.002
3. Peleg, S. et al. (2016) The metabolic impact on histone acetylation and transcription in ageing. Trends Biochem. Sci. 41, 700–711 4. Suganuma, T. and Workman, J.L. (2018) Chromatin and metabolism. Annu. Rev. Biochem. 87, 27–49 5. Wellen, K.E. et al. (2009) ATP-citrate lyase links cellular metabolism to histone acetylation. Science 324, 1076–1080 6. Mews, P. et al. (2017) Acetyl-CoA synthetase regulates histone acetylation and hippocampal memory. Nature 546, 381–386
7. Zakhari, S. (2013) Alcohol metabolism and epigenetics changes. Alcohol Res. 35, 6–16 8. Mews, P. et al. (2019) Alcohol metabolism contributes to brain histone acetylation. Nature 574, 717–721 9. Feller, C. et al. (2015) Global and specific responses of the histone acetylome to systematic perturbation. Mol. Cell 57, 559–571 10. Murray, J. et al. (2016) Moderate alcohol drinking in pregnancy increases risk for
children’s persistent conduct problems: causal effects in a Mendelian randomisation study. J. Child Psychol. Psychiatry 57, 575–584 11. Stilling, R.M. et al. (2016) The neuropharmacology of butyrate: the bread and butter of the microbiota-gut-brain axis? Neurochem. Int. 99, 110–132 12. Krautkramer, K.A. et al. (2016) Dietmicrobiota interactions mediate global epigenetic programming in multiple host tissues. Mol. Cell 64, 982–992
Trends in Biochemical Sciences, -- 2019, Vol. --, No. --
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