Sensibilisation comportementale à l'alcool et mécanismes épigénétiques

La sensibilisation comportementale à l éthanol serait responsable de 2 étapes charnières de l alcoolodépendance : la perte de contrôle de la prise d alcool et la vulnérabilité à la rechute. Le blocage de ce phénomène pourrait ouvrir de nouvelles voies de recherche thérapeutique. On sait que la sensibilisation comportementale à la cocaïne est régulée par des mécanismes épigénétiques car une récente étude de Romieu et al. (2008) rapporte le blocage de cette sensibilisation par la trichostatine A (TSA), un inhibiteur des histones désacétylases (HDAC). Ces HDACs sont en effet des enzymes responsables de l acétylation des histones, un mécanisme épigénétique. Nous avons donc tenté d inhiber la sensibilisation comportementale à l éthanol à l aide de 2 inhibiteurs HDAC (HDACi), le sodium butyrate et la TSA. Cependant, aucun effet de ces HDACi n a été observé sur cette sensibilisation. C est pourquoi nous pensons que le mécanisme épigénétique particulier d acétylation/désacétylation des histones ne serait pas impliqué dans la sensibilisation comportementale à l éthanol.AMIENS-BU Santé (800212102) / SudocSudocFranceF

Sensibilisation comportementale à l'éthanol et mécanismes épigénétiques

L alcoolodépendance est un problème majeur de Santé Publique. C est une maladie chronique hautement récidivante en dépit des pharmaco- et psychothérapies existantes. Depuis plusieurs années, l implication des mécanismes épigénétiques dans les comportements liés à l éthanol se fait de plus en plus concrète. L objectif de cette étude était principalement d évaluer l implication du mécanisme particulier d acétylation/désacétylation des histones dans la sensibilisation comportementale à l éthanol, un modèle de neuroadaptations apparaissant dès les premiers contacts avec l éthanol et perdurant à très long-terme. Dans une première partie, nous avons étudié l effet d un inhibiteur d histone désacétylase (HDAC), le butyrate de sodium (NaB), sur le développement et le maintien de la sensibilisation à l éthanol 1,0 et 2,0 g/kg. Nous avons mis en évidence que le NaB prévient et inverse la sensibilisation à l éthanol 1,0 mais pas 2,0 g/kg. Nous avons ensuite identifié, au niveau génique et protéique, certaines cibles, dont le BDNF, spécifiquement régulées lors du blocage de la sensibilisation. Dans une seconde partie, nous avons caractérisé la réponse épigénétique à l éthanol chez des souris sensibilisées ou résistantes à la sensibilisation à 2,0 g/kg. Nous avons ainsi mis en évidence des différences de réponse à l éthanol entre souris sensibilisées et résistantes au niveau 1/ de l expression striatale de gènes liés aux mécanismes épigénétiques et 2/ de l activité de plusieurs enzymes (HDAC, HAT, DNMT) dans le striatum et des taux d acétylation de l histone H4 dans le core du noyau accumbens. L ensemble de ces résultats confirme l implication des mécanismes épigénétiques, et en particulier la balance HDAC/HAT dans la sensibilisation comportementale à l éthanol, et ce, à plusieurs niveaux. L acétylation des histones serait un mécanisme indispensable dans le développement et le maintien de la sensibilisation à l éthanol 1,0 g/kg ; et la réponse épigénétique à la réexposition à l éthanol est fortement dépendante de la vulnérabilité individuelle à développer une sensibilisation à l éthanol 2,0 g/kg.AMIENS-BU Santé (800212102) / SudocSudocFranceF

Expression of ethanol-induced behavioral sensitization is associated with alteration of chromatin remodeling in mice.

International audienceBACKGROUND: Ethanol-induced behavioral sensitization (EIBS) is proposed to play a role in early and recurring steps of addiction. EIBS does not occur uniformly in all animals even from the same inbred strain. Since recent data demonstrate that epigenetic mechanisms are likely to be involved in the development and the persistence of ethanol-related behaviors, we explored the involvement of epigenetic mechanisms in ethanol response after EIBS development. METHODOLOGY: DBA/2J mice were i.p. injected with saline or ethanol (2 g/kg) once a day for 10 consecutive days. At day 17, ethanol-treated mice were split in resistant and sensitized groups. Brains were then removed 30 min after a saline or 2 g/kg ethanol challenge to assess i) gene expression using PCR array targeting 84 epigenetic-related genes and ii) histone deacetylases (HDAC), histone acetylases (HAT) and DNA methyltransferases (DNMT) activities as well as H4K12 acetylation. PRINCIPAL FINDINGS: Acute ethanol administration decreased dnmt1, esco2 and rps6ka5 genes expression. These genes were similarly altered in sensitized but not in resistant mice after an ethanol challenge, suggesting that resistant mice were tolerant to the transcriptional outcomes of an ethanol challenge. Whereas global HAT or DNMT activity was not affected, global HDAC activity was reduced after an acute ethanol injection. HDAC inhibition occurred in all ethanol-treated mice but with a lesser extent in sensitized animals. As a consequence, H4 acetylation was specifically potentiated in the core of the Nac proportionally to the striatal HDAC activity decrease. CONCLUSIONS/SIGNIFICANCE: The present study highlights that the contrasted behavioral response to an ethanol challenge between resistant and sensitized mice may be mediated by epigenetic mechanisms occurring specifically in the striatum. Here we show that vulnerability to ethanol dependence and relapse could be, at least in part, due to individual variability in acute ethanol-induced epigenetic response

Mécanismes épigénétiques et troubles de l’usage d’alcool : une cible thérapeutique intéressante?

L’épigénétique est un nouveau champ de recherche qui a détrôné la génétique et qui a fait l’objet ces deux dernières décennies d’intenses recherches dans le monde des addictions. L’épigénétique permet de mieux comprendre comment les drogues peuvent modifier à très long terme le fonctionnement cérébral en régulant l’expression de nos gènes. Avec les épidrogues, l’épigénétique propose aussi une piste thérapeutique intéressante dans les troubles de l’usage d’alcool

Striatal-enriched protein tyrosine phosphatase controls responses to aversive stimuli: implication for ethanol drinking.

The STriatal-Enriched protein tyrosine Phosphatase (STEP) is a brain-specific phosphatase whose dysregulation in expression and/or activity is associated with several neuropsychiatric disorders. We recently showed that long-term excessive consumption of ethanol induces a sustained inhibition of STEP activity in the dorsomedial striatum (DMS) of mice. We further showed that down-regulation of STEP expression in the DMS, and not in the adjacent dorsolateral striatum, increases ethanol intake, suggesting that the inactivation of STEP in the DMS contributes to the development of ethanol drinking behaviors. Here, we compared the consequence of global deletion of the STEP gene on voluntary ethanol intake to the consumption of an appetitive rewarding substance (saccharin) or an aversive solution (quinine or denatonium). Whereas saccharin intake was similar in STEP knockout (KO) and wild type (WT) littermate mice, the consumption of ethanol as well as quinine and denatonium was increased in STEP KO mice. These results suggested that the aversive taste of these substances was masked upon deletion of the STEP gene. We therefore hypothesized that STEP contributes to the physiological avoidance towards aversive stimuli. To further test this hypothesis, we measured the responses of STEP KO and WT mice to lithium-induced conditioned place aversion (CPA) and found that whereas WT mice developed lithium place aversion, STEP KO mice did not. In contrast, conditioned place preference (CPP) to ethanol was similar in both genotypes. Together, our results indicate that STEP contributes, at least in part, to the protection against the ingestion of aversive agents

Striatal-enriched protein tyrosine phosphatase controls responses to aversive stimuli: implication for ethanol drinking.

The STriatal-Enriched protein tyrosine Phosphatase (STEP) is a brain-specific phosphatase whose dysregulation in expression and/or activity is associated with several neuropsychiatric disorders. We recently showed that long-term excessive consumption of ethanol induces a sustained inhibition of STEP activity in the dorsomedial striatum (DMS) of mice. We further showed that down-regulation of STEP expression in the DMS, and not in the adjacent dorsolateral striatum, increases ethanol intake, suggesting that the inactivation of STEP in the DMS contributes to the development of ethanol drinking behaviors. Here, we compared the consequence of global deletion of the STEP gene on voluntary ethanol intake to the consumption of an appetitive rewarding substance (saccharin) or an aversive solution (quinine or denatonium). Whereas saccharin intake was similar in STEP knockout (KO) and wild type (WT) littermate mice, the consumption of ethanol as well as quinine and denatonium was increased in STEP KO mice. These results suggested that the aversive taste of these substances was masked upon deletion of the STEP gene. We therefore hypothesized that STEP contributes to the physiological avoidance towards aversive stimuli. To further test this hypothesis, we measured the responses of STEP KO and WT mice to lithium-induced conditioned place aversion (CPA) and found that whereas WT mice developed lithium place aversion, STEP KO mice did not. In contrast, conditioned place preference (CPP) to ethanol was similar in both genotypes. Together, our results indicate that STEP contributes, at least in part, to the protection against the ingestion of aversive agents

Expression of EIBS is not due to changes in global DNMT activity.

<p>During 10 days, mice received daily i.p. injections of saline or ethanol (2 g/kg) solution. DNMT activity was measured in nuclear fractions of striatum, prefrontal cortex, amygdala and hippocampus 30 min after saline or ethanol (2 g/kg) challenge at day 17 (n = 5 per group). Means (± SEM) of DNMT activity are expressed as percentages of control.</p

Individual variability in EIBS development.

<p>On the first day of the experiment (habituation day, H), all mice were injected with saline solution (n = 60). Then, from days 1 to 10, mice received 10 consecutive once-daily i.p. injections of saline (n = 20) or 2 g/kg ethanol (n = 40) solution immediately followed by a 5 min-long locomotor activity recording session. Some mice exhibited EIBS (sensitized mice, n = 29) whereas others failed to sensitize (resistant mice, n = 11). At day 17 (challenge day) mice received a single injection of saline (control group) or 2 g/kg ethanol (acute, resistant and sensitized groups). * indicates an increase <i>vs</i> day 1. † indicates a significant difference between resistant and sensitized mice at the same day. # indicates significant differences between sensitized and acute mice at day 17. @ indicates significant differences between resistant and sensitized groups throughout the induction phase.</p

Expression of EIBS is associated with changes in global HDAC activity in striatum.

<p>During 10 days, mice received daily i.p. injections of saline or ethanol (2 g/kg) solution. HDAC activity was measured in cytosolic and nuclear fractions of striatum (<b>a</b>), prefrontal cortex (<b>b</b>), amygdala (<b>c</b>) and hippocampus (<b>d</b>) 30 min after saline or ethanol (2 g/kg) challenge at day 17 (n = 4–5 per group). Means (± SEM) of HDAC activity are expressed as percentages of control *<i>P<</i>0.05, ***<i>P<</i>0.001 <i>vs</i> control; ^#<i>P<</i>0.05 <i>vs</i> acute; ^†<i>P<</i>0.05, ^†††<i>P<</i>0.001 <i>vs</i> resistant groups.</p