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Jordan CJ, Xi ZX. Identification of the Risk Genes Associated With Vulnerability to Addiction: Major Findings From Transgenic Animals. Front Neurosci 2022; 15:811192. [PMID: 35095405 PMCID: PMC8789752 DOI: 10.3389/fnins.2021.811192] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2021] [Accepted: 12/14/2021] [Indexed: 12/21/2022] Open
Abstract
Understanding risk factors for substance use disorders (SUD) can facilitate medication development for SUD treatment. While a rich literature exists discussing environmental factors that influence SUD, fewer articles have focused on genetic factors that convey vulnerability to drug use. Methods to identify SUD risk genes include Genome-Wide Association Studies (GWAS) and transgenic approaches. GWAS have identified hundreds of gene variants or single nucleotide polymorphisms (SNPs). However, few genes identified by GWAS have been verified by clinical or preclinical studies. In contrast, significant progress has been made in transgenic approaches to identify risk genes for SUD. In this article, we review recent progress in identifying candidate genes contributing to drug use and addiction using transgenic approaches. A central hypothesis is if a particular gene variant (e.g., resulting in reduction or deletion of a protein) is associated with increases in drug self-administration or relapse to drug seeking, this gene variant may be considered a risk factor for drug use and addiction. Accordingly, we identified several candidate genes such as those that encode dopamine D2 and D3 receptors, mGluR2, M4 muscarinic acetylcholine receptors, and α5 nicotinic acetylcholine receptors, which appear to meet the risk-gene criteria when their expression is decreased. Here, we describe the role of these receptors in drug reward and addiction, and then summarize major findings from the gene-knockout mice or rats in animal models of addiction. Lastly, we briefly discuss future research directions in identifying addiction-related risk genes and in risk gene-based medication development for the treatment of addiction.
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Affiliation(s)
- Chloe J. Jordan
- Division of Alcohol, Drugs and Addiction, Department of Psychiatry, McLean Hospital, Harvard Medical School, Belmont, MA, United States
- *Correspondence: Chloe J. Jordan,
| | - Zheng-Xiong Xi
- Molecular Targets and Medications Discovery Branch, National Institute on Drug Abuse, Intramural Research Program, Baltimore, MD, United States
- Zheng-Xiong Xi,
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Busceti CL, Ginerete RP, Di Menna L, D'Errico G, Cisani F, Di Pietro P, Imbriglio T, Bruno V, Battaglia G, Fornai F, Monn JA, Pittaluga A, Nicoletti F. Behavioural and biochemical responses to methamphetamine are differentially regulated by mGlu2 and mGlu3 metabotropic glutamate receptors in male mice. Neuropharmacology 2021; 196:108692. [PMID: 34217776 DOI: 10.1016/j.neuropharm.2021.108692] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2021] [Revised: 06/04/2021] [Accepted: 06/27/2021] [Indexed: 01/09/2023]
Abstract
Group II metabotropic glutamate receptors (mGlu2 and mGlu3 receptors) shape mechanisms of methamphetamine addiction, but the individual role played by the two subtypes is unclear. We measured methamphetamine-induced conditioned place preference (CPP) and motor responses to single or repeated injections of methamphetamine in wild-type, mGlu2-/-, and mGlu3-/-mice. Only mGlu3-/-mice showed methamphetamine preference in the CPP test. Motor response to the first methamphetamine injection was dramatically reduced in mGlu2-/-mice, unless these mice were treated with the mGlu5 receptor antagonist, MTEP. In contrast, methamphetamine-induced sensitization was increased in mGlu3-/-mice compared to wild-type mice. Only mGlu3-/-mice sensitized to methamphetamine showed increases in phospho-ERK1/2 levels in the nucleus accumbens (NAc) and free radical formation in the NAc and medial prefrontal cortex. These changes were not detected in mGlu2-/-mice. We also measured a series of biochemical parameters related to the mechanism of action of methamphetamine in naïve mice to disclose the nature of the differential behavioural responses of the three genotypes. We found a reduced expression and activity of dopamine transporter (DAT) and vesicular monoamine transporter-2 in the NAc and striatum of mGlu2-/-and mGlu3-/-mice, whereas expression of the DAT adaptor, syntaxin 1A, was selectively increased in the striatum of mGlu3-/-mice. Methamphetamine-stimulated dopamine release in striatal slices was largely reduced in mGlu2-/-, but not in mGlu3-/-, mice. These findings suggest that drugs that selectively enhance mGlu3 receptor activity or negatively modulate mGlu2 receptors might be beneficial in the treatment of methamphetamine addiction and associated brain damage.
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Affiliation(s)
| | | | | | | | | | | | | | - Valeria Bruno
- IRCCS Neuromed, Pozzilli, Italy; Department of Physiology and Pharmacology, University Sapienza, Roma, Italy
| | - Giuseppe Battaglia
- IRCCS Neuromed, Pozzilli, Italy; Department of Physiology and Pharmacology, University Sapienza, Roma, Italy
| | - Francesco Fornai
- IRCCS Neuromed, Pozzilli, Italy; Department of Translational Research and New Technologies in Medicine and Surgery, University of Pisa, Pisa, Italy
| | | | - Anna Pittaluga
- Department of Pharmacy, University of Genova, Genova, Italy; IRCCS Ospedale Policlinico San Martino, Genova, Italy
| | - Ferdinando Nicoletti
- IRCCS Neuromed, Pozzilli, Italy; Department of Physiology and Pharmacology, University Sapienza, Roma, Italy.
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Heilig M, Barbier E, Johnstone AL, Tapocik J, Meinhardt MW, Pfarr S, Wahlestedt C, Sommer WH. Reprogramming of mPFC transcriptome and function in alcohol dependence. GENES, BRAIN, AND BEHAVIOR 2017; 16:86-100. [PMID: 27657733 PMCID: PMC5555395 DOI: 10.1111/gbb.12344] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/05/2016] [Revised: 08/30/2016] [Accepted: 09/19/2016] [Indexed: 01/07/2023]
Abstract
Despite its limited immediate reinforcement value, alcohol has a potent ability to induce neuroadaptations that promote its incentive salience, escalation of voluntary alcohol intake and aversion-resistant alcohol seeking. A constellation of these traits, collectively called 'post-dependent', emerges following brain exposure to repeated cycles of intoxication and withdrawal. The medial prefrontal cortex (mPFC) and its subdivisions exert top-down regulation of approach and avoidance behaviors, including those that lead to alcohol intake. Here, we review an emerging literature which indicates that a reprogramming of mPFC function occurs with prolonged exposure of the brain to cycles of alcohol intoxication and withdrawal. This reprogramming results in molecular dysregulations that contribute to the post-dependent syndrome. Convergent evidence has identified neuroadaptations resulting in altered glutamatergic and BDNF-mediated signaling, and for these pathways, direct evidence for a mechanistic role has been obtained. Additional evidence points to a dysregulation of pathways involving calcium homeostasis and neurotransmitter release. Recent findings indicate that global DNA hypermethylation is a key factor in reprogramming the mPFC genome after a history of dependence. As one of the results of this epigenetic remodeling, several histone modifying epigenetic enzymes are repressed. Among these, PR-domain zinc-finger protein 2, a methyltransferase that selectively mono-methylates histone H3 at lysine 9 has been functionally validated to drive several of the molecular and behavioral long-term consequences of alcohol dependence. Information processing within the mPFC involves formation of dynamic neuronal networks, or functional ensembles that are shaped by transcriptional responses. The epigenetic dysregulations identified by our molecular studies are likely to alter this dynamic processing in multiple ways. In summary, epigenetic molecular switches in the mPFC appear to be turned on as alcoholism develops. Strategies to reverse these processes may offer targets for disease-modifying treatments.
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Affiliation(s)
- M. Heilig
- Center for Social and Affective Neuroscience, Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden
| | - E. Barbier
- Center for Social and Affective Neuroscience, Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden
| | - A. L. Johnstone
- Department of Psychiatry and Behavioral Sciences, University of Miami Miller School of Medicine, Miami, FL, USA
| | - J. Tapocik
- Center for Social and Affective Neuroscience, Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden
| | - M. W. Meinhardt
- Department of Psychopharmacology, Central Institute of Mental Health, University of Heidelberg, Mannheim, Germany
| | - S. Pfarr
- Department of Psychopharmacology, Central Institute of Mental Health, University of Heidelberg, Mannheim, Germany
| | - C. Wahlestedt
- Department of Psychiatry and Behavioral Sciences, University of Miami Miller School of Medicine, Miami, FL, USA
| | - W. H. Sommer
- Department of Psychopharmacology, Central Institute of Mental Health, University of Heidelberg, Mannheim, Germany
- Department of Addiction Medicine, Central Institute of Mental Health, University of Heidelberg, Mannheim, Germany
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