Epigenetics, microRNA, and addiction

Research progress of DNA methylation on the regulation of substance use disorders and the mechanisms

Drug abuse can damage the central nervous system and lead to substance use disorder (SUD). SUD is influenced by both genetic and environmental factors. Genes determine an individual's susceptibility to drug, while the dysregulation of epigenome drives the abnormal transcription processes, promoting the development of SUD. One of the most widely studied epigenetic mechanisms is DNA methylation, which can be inherited stably. In ontogeny, DNA methylation pattern is dynamic. DNA dysmethylation is prevalent in drug-related psychiatric disorders, resulting in local hypermethylation and transcriptional silencing of related genes. In this review, we summarize the role and regulatory mechanisms of DNA methylation in cocaine, opioids, and methamphetamine in terms of drug exposure, addiction memory, withdrawal relapse, intergenerational inheritance, and focus on cell-specific aspects of the studies with a view to suggesting possible therapeutic regimens for targeting methylation in both human and animal research.

Unveiling the Complexities of Medications, Substance Abuse, and Plants for Recreational and Narcotic Purposes: An In-Depth Analysis

The complexities surrounding the use of medications, substance abuse, and the recreational use of plants are multifaceted and warrant a comprehensive examination. This review highlights the complexities surrounding the consumption of chemical substances in excess or for non-medical purposes, obtained through legal prescriptions, over-the-counter purchases, or illicit means, with an emphasis on the predictive role of stressors and individual-level variables in the development of substance use disorders, as well as the influence of the regulatory environment on patterns of consumption. Additionally, the alarming escalation in the mortality rate associated with illicit drug and opioid overdoses is also underscored. The recreational use of prescription medications can lead to significant health risks, particularly when combined with other substances; therefore, the need for interventions and preventive measures to address substance abuse among various populations is imperative. Furthermore, novel insights on substance abuse addiction, exploring the neurobiological mechanisms underlying addiction, and discussing treatment approaches and interventions are elucidated. Advancements in technology for detecting substance abuse are also highlighted, displaying innovative tools for more effective identification and monitoring. In conclusion, the complexities of medications, substance abuse, and the recreational use of plants reveal a landscape marked by overlapping motivations and health implications. The distinction between medical and recreational use is critical for understanding user behavior and addressing public health concerns.

Molecular and Environmental Determinants of Addictive Substances

Knowledge about determinants of addiction in people taking addictive substances is poor and needs to be supplemented. The novelty of this paper consists in the analysis of innovative aspects of current research about relationships between determinants of addiction in Polish patients taking addictive substances and rare available data regarding the relationships between these factors from studies from recent years from other environments, mainly in Europe, and on the development of genetic determinants of physiological responses. We try to explain the role of the microelements Mn, Fe, Cu, Co, Zn, Cr, Ni, Tl, Se, Al, B, Mo, V, Sn, Sb, Ag, Sr, and Ba, the toxic metals Cd, Hg, As, and Pb, and the rare earth elements Sc, La, Ce, Pr, Eu, Gd, and Nd as factors that may shape the development of addiction to addictive substances or drugs. The interactions between factors (gene polymorphism, especially ANKK1 (TaqI A), ANKK1 (Taq1 A-CT), DRD2 (TaqI B, DRD2 Taq1 B-GA, DRD2 Taq1 B-AA, DRD2-141C Ins/Del), and OPRM1 (A118G)) in patients addicted to addictive substances and consumption of vegetables, consumption of dairy products, exposure to harmful factors, and their relationships with physiological responses, which confirm the importance of internal factors as determinants of addiction, are analyzed, taking into account gender and region. The innovation of this review is to show that the homozygous TT mutant of the ANKK1 TaqI A polymorphism rs 1800497 may be a factor in increased risk of opioid dependence. We identify a variation in the functioning of the immune system in addicted patients from different environments as a result of the interaction of polymorphisms.

How life events may confer vulnerability to addiction: the role of epigenetics

Substance use disorder (SUD) represents a large and growing global health problem. Despite the strong addictive potency of drugs of abuse, only a minority of those exposed develop SUDs. While certain life experiences (e.g., childhood trauma) may increase subsequent vulnerability to SUDs, mechanisms underlying these effects are not yet well understood. Given the chronic and relapsing nature of SUDs, and the length of time that can elapse between prior life events and subsequent drug exposure, changes in SUD vulnerability almost certainly involve long-term epigenetic dysregulation. To validate this idea, functional effects of specific epigenetic modifications in brain regions mediating reinforcement learning (e.g., nucleus accumbens, prefrontal cortex) have been investigated in a variety of animal models of SUDs. In addition, the effects of epigenetic modifications produced by prior life experiences on subsequent SUD vulnerability have been studied, but mostly in a correlational manner. Here, we review how epigenetic mechanisms impact SUD-related behavior in animal models and summarize our understanding of the relationships among life experiences, epigenetic regulation, and future vulnerability to SUDs. Despite variations in study design, epigenetic modifications that most consistently affect SUD-related behavior are those that produce predominantly unidirectional effects on gene regulation, such as DNA methylation and histone phosphorylation. Evidence explicitly linking environmentally induced epigenetic modifications to subsequent SUD-related behavior is surprisingly sparse. We conclude by offering several directions for future research to begin to address this critical research gap.

Epigenetic mechanisms of nicotine dependence

Smoking continues to be a leading cause of preventable disease and death worldwide. Nicotine dependence generates a lifelong propensity towards cravings and relapse, presenting an ongoing challenge for the development of treatments. Accumulating evidence supports a role for epigenetics in the development and maintenance of addiction to many drugs of abuse, however, the involvement of epigenetics in nicotine dependence is less clear. Here we review evidence that nicotine interacts with epigenetic mechanisms to enable the maintenance of nicotine-seeking across time. Research across species suggests that nicotine increases permissive histone acetylation, decreases repressive histone methylation, and modulates levels of DNA methylation and noncoding RNA expression throughout the brain. These changes are linked to the promoter regions of genes critical for learning and memory, reward processing and addiction. Pharmacological manipulation of enzymes that catalyze core epigenetic modifications regulate nicotine reward and associative learning, demonstrating a functional role of epigenetic modifications in nicotine dependence. These findings are consistent with nicotine promoting an overall permissive chromatin state at genes important for learning, memory and reward. By exploring these links through next-generation sequencing technologies, epigenetics provides a promising avenue for future interventions to treat nicotine dependence.

Neurogenetics and Epigenetics of Loneliness

Loneliness, an established risk factor for both, mental and physical morbidity, is a mounting public health concern. However, the neurobiological mechanisms underlying loneliness-related morbidity are not yet well defined. Here we examined the role of genes and associated DNA risk polymorphic variants that are implicated in loneliness via genetic and epigenetic mechanisms and may thus point to specific therapeutic targets. Searches were conducted on PubMed, Medline, and EMBASE databases using specific Medical Subject Headings terms such as loneliness and genes, neuro- and epigenetics, addiction, affective disorders, alcohol, anti-reward, anxiety, depression, dopamine, cancer, cardiovascular, cognitive, hypodopaminergia, medical, motivation, (neuro)psychopathology, social isolation, and reward deficiency. The narrative literature review yielded recursive collections of scientific and clinical evidence, which were subsequently condensed and summarized in the following key areas: (1) Genetic Antecedents: Exploration of multiple genes mediating reward, stress, immunity and other important vital functions; (2) Genes and Mental Health: Examination of genes linked to personality traits and mental illnesses providing insights into the intricate network of interaction converging on the experience of loneliness; (3) Epigenetic Effects: Inquiry into instances of loneliness and social isolation that are driven by epigenetic methylations associated with negative childhood experiences; and (4) Neural Correlates: Analysis of loneliness-related affective states and cognitions with a focus on hypodopaminergic reward deficiency arising in the context of early life stress, eg, maternal separation, underscoring the importance of parental support early in life. Identification of the individual contributions by various (epi)genetic factors presents opportunities for the creation of innovative preventive, diagnostic, and therapeutic approaches for individuals who cope with persistent feelings of loneliness. The clinical facets and therapeutic prospects associated with the current understanding of loneliness, are discussed emphasizing the relevance of genes and DNA risk polymorphic variants in the context of loneliness-related morbidity.

The role of miRNA-144-3p/Oprk1/KOR in nicotine dependence and nicotine withdrawal in male rats

INTRODUCTION

The kappa-opioid receptor (KOR) has been implicated in mediating the behavioral and biochemical effects associated with nicotine reward and withdrawal; however, its underlying mechanisms remain to be further explored.

METHODS

Adult male Sprague-Dawley rats were used to establish a nicotine dependence and withdrawal model by injecting nicotine (3 mg/kg/day, s.c.) or vehicle for 14 days, followed by the termination of nicotine for 7 days. Body weight gain, pain behaviors, and withdrawal scores were assessed in succession. MicroRNA (miRNA) sequencing was performed, and quantitative real-time PCR was used to detect the expression of candidate miRNAs and Oprk1. Western blotting was performed to examine KOR protein expression of KOR. Luciferase assay was conducted to validate the relationship of certain miRNAs/Oprk1.

RESULTS

The behavioral results showed that nicotine dependence and withdrawal induced behavioral changes. Biochemical analyses demonstrated that miR-144-3p expression decreased and Oprk1/KOR expression increased in the prefrontal cortex, nucleus accumben, and hippocampus. Further investigation suggested that miR-144-3p exerted an inhibitory effect on Oprk1 expression in PC12 cells.

CONCLUSIONS

This study revealed that miR-144-3p/Oprk1/KOR might be a potential pathway underlying the adverse effects induced by nicotine dependence and withdrawal, and might provide a novel therapeutic target for smoking cessation.

IMPLICATIONS

This study demonstrates an impact of nicotine dependence and nicotine withdrawal on behavioral outcomes and the expressions of miR-144-3p/Oprk1/KOR in male rats. These findings have important translational implications given the continued use of nicotine and the difficulty in smoking cessation worldwide, which can be applied to alleviated the adverse effects induced by nicotine dependence and withdrawal, thus assist smokers to quit smoking.

Abstinence from Escalation of Cocaine Intake Changes the microRNA Landscape in the Cortico-Accumbal Pathway

Cocaine administration alters the microRNA (miRNA) landscape in the cortico-accumbal pathway. These changes in miRNA can play a major role in the posttranscriptional regulation of gene expression during withdrawal. This study aimed to investigate the changes in microRNA expression in the cortico-accumbal pathway during acute withdrawal and protracted abstinence following escalated cocaine intake. Small RNA sequencing (sRNA-seq) was used to profile miRNA transcriptomic changes in the cortico-accumbal pathway [infralimbic- and prelimbic-prefrontal cortex (IL and PL) and nucleus accumbens (NAc)] of rats with extended access to cocaine self-administration followed by an 18-h withdrawal or a 4-week abstinence. An 18-h withdrawal led to differential expression (fold-change > 1.5 and p < 0.05) of 21 miRNAs in the IL, 18 miRNAs in the PL, and two miRNAs in the NAc. The mRNAs potentially targeted by these miRNAs were enriched in the following pathways: gap junctions, neurotrophin signaling, MAPK signaling, and cocaine addiction. Moreover, a 4-week abstinence led to differential expression (fold-change > 1.5 and p < 0.05) of 23 miRNAs in the IL, seven in the PL, and five miRNAs in the NAc. The mRNAs potentially targeted by these miRNAs were enriched in pathways including gap junctions, cocaine addiction, MAPK signaling, glutamatergic synapse, morphine addiction, and amphetamine addiction. Additionally, the expression levels of several miRNAs differentially expressed in either the IL or the NAc were significantly correlated with addiction behaviors. Our findings highlight the impact of acute and protracted abstinence from escalated cocaine intake on miRNA expression in the cortico-accumbal pathway, a key circuit in addiction, and suggest developing novel biomarkers and therapeutic approaches to prevent relapse by targeting abstinence-associated miRNAs and their regulated mRNAs.

MicroRNA-423-5p Mediates Cocaine-Induced Smooth Muscle Cell Contraction by Targeting Cacna2d2

Cocaine abuse increases the risk of atherosclerotic cardiovascular disease (CVD) and causes acute coronary syndromes (ACS) and hypertension (HTN). Significant research has explored the role of the sympathetic nervous system mediating the cocaine effects on the cardiovascular (CV) system. However, the response of the sympathetic nervous system alone is insufficient to completely account for the CV consequences seen in cocaine users. In this study, we examined the role of microRNAs (miRNAs) in mediating the effect of cocaine on the CV system. MiRNAs regulate many important biological processes and have been associated with both response to cocaine and CV disease development. Multiple miRNAs have altered expression in the CV system (CVS) upon cocaine exposure. To understand the molecular mechanisms underlying the cocaine response in the CV system, we studied the role of miRNA-423-5p and its target Cacna2d2 in the regulation of intracellular calcium concentration and SMC contractility, a critical factor in the modulation of blood pressure (BP). We used in vivo models to evaluate BP and aortic stiffness. In vitro, cocaine treatment decreased miR-423-5p expression and increased Cacna2d2 expression, which led to elevated intracellular calcium concentrations and increased SMC contractility. Overexpression of miR-423-5p, silencing of its target Cacna2d2, and treatment with a calcium channel blocker reversed the elevated SMC contractility caused by cocaine. In contrast, suppression of miR-423-5p increased the intracellular calcium concentration and SMC contractibility. In vivo, smooth muscle-specific overexpression of miR-423-5p ameliorated the increase in BP and aortic stiffness associated with cocaine use. Thus, miR-423-5p regulates SMC contraction by modulating Cacna2d2 expression increasing intracellular calcium concentrations. Modulation of the miR-423-5p-Cacna2d2-Calcium transport pathway may represent a novel therapeutic strategy to improve cocaine-induced HTN and aortic stiffness.

The Effects of Transcranial Focused Ultrasound Stimulation of Nucleus Accumbens on Neuronal Gene Expression and Brain Tissue in High Alcohol-Preferring Rats

We investigated the effect of low-intensity focused ultrasound (LIFU) on gene expression related to alcohol dependence and histological effects on brain tissue. We also aimed at determining the miRNA-mRNA relationship and their pathways in alcohol dependence-induced expression changes after focused ultrasound therapy. We designed a case-control study for 100 days of observation to investigate differences in gene expression in the short-term stimulation group (STS) and long-term stimulation group (LTS) compared with the control sham group (SG). The study was performed in our Experimental Research Laboratory. 24 male high alcohol-preferring rats 63 to 79 days old, weighing 270 to 300 g, were included in the experiment. LTS received 50-day LIFU and STS received 10-day LIFU and 40-day sham stimulation, while the SG received 50-day sham stimulation. In miRNA expression analysis, it was found that LIFU caused gene expression differences in NAc. Significant differences were found between the groups for gene expression. Compared to the SG, the expression of 454 genes in the NAc region was changed in the STS while the expression of 382 genes was changed in the LTS. In the LTS, the expression of 32 genes was changed in total compared to STS. Our data suggest that LIFU targeted on NAc may assist in the treatment of alcohol dependence, especially in the long term possibly through altering gene expression. Our immunohistochemical studies verified that LIFU does not cause any tissue damage. These findings may lead to new studies in investigating the efficacy of LIFU for the treatment of alcohol dependence and also for other psychiatric disorders.

Molecular pattern of a decrease in the rewarding effect of cocaine after an escalating-dose drug regimen

BACKGROUND

Long-term cocaine exposure leads to dysregulation of the reward system and initiates processes that ultimately weaken its rewarding effects. Here, we studied the influence of an escalating-dose cocaine regimen on drug-associated appetitive behavior after a withdrawal period, along with corresponding molecular changes in plasma and the prefrontal cortex (PFC).

METHODS

We applied a 5 day escalating-dose cocaine regimen in rats. We assessed anxiety-like behavior at the beginning of the withdrawal period in the elevated plus maze (EPM) test. The reinforcement properties of cocaine were evaluated in the Conditioned Place Preference (CPP) test along with ultrasonic vocalization (USV) in the appetitive range in a drug-associated context. We assessed corticosterone, proopiomelanocortin (POMC), β-endorphin, CART 55-102 levels in plasma (by ELISA), along with mRNA levels for D2 dopaminergic receptor (D2R), κ-receptor (KOR), orexin 1 receptor (OX1R), CART 55-102, and potential markers of cocaine abuse: miRNA-124 and miRNA-137 levels in the PFC (by PCR).

RESULTS

Rats subjected to the escalating-dose cocaine binge regimen spent less time in the cocaine-paired compartment, and presented a lower number of appetitive USV episodes. These changes were accompanied by a decrease in corticosterone and CART levels, an increase in POMC and β-endorphin levels in plasma, and an increase in the mRNA for D2R and miRNA-124 levels, but a decrease in the mRNA levels for KOR, OX1R, and CART 55-102 in the PFC.

CONCLUSIONS

The presented data reflect a part of a bigger picture of a multilevel interplay between neurotransmitter systems and neuromodulators underlying processes associated with cocaine abuse.

Orexin Reserve: A Mechanistic Framework for the Role of Orexins (Hypocretins) in Addiction

In 2014, we proposed that orexin signaling transformed motivationally relevant states into adaptive behavior directed toward exploiting an opportunity or managing a threat, a process we referred to as motivational activation. Advancements in animal models since then have permitted higher-resolution measurements of motivational states; in particular, the behavioral economics approach for studying drug demand characterizes conditions that lead to the enhanced motivation that underlies addiction. This motivational plasticity is paralleled by persistently increased orexin expression in a topographically specific manner-a finding confirmed across species, including in humans. Normalization of orexin levels also reduces drug motivation in addiction models. These new advancements lead us to update our proposed framework for the orexin function. We now propose that the capacity of orexin neurons to exhibit dynamic shifts in peptide production contributes to their role in adaptive motivational regulation and that this is achieved via a pool of reserve orexin neurons. This reserve is normally bidirectionally recruited to permit motivational plasticity that promotes flexible, adaptive behavior. In pathological states such as addiction, however, we propose that the orexin system loses capacity to adaptively adjust peptide production, resulting in focused hypermotivation for drug, driven by aberrantly and persistently high expression in the orexin reserve pool. This mechanistic framework has implications for the understanding and treatment of several psychiatric disorders beyond addiction, particularly those characterized by motivational dysfunction.

Epigenetic Effects of Addictive Drugs in the Nucleus Accumbens

Substance use induces long-lasting behavioral changes and drug craving. Increasing evidence suggests that epigenetic gene regulation contributes to the development and expression of these long-lasting behavioral alterations. Here we systematically review extensive evidence from rodent models of drug-induced changes in epigenetic regulation and epigenetic regulator proteins. We focus on histone acetylation and histone methylation in a brain region important for drug-related behaviors: the nucleus accumbens. We also discuss how experimentally altering these epigenetic regulators via systemically administered compounds or nucleus accumbens-specific manipulations demonstrate the importance of these proteins in the behavioral effects of drugs and suggest potential therapeutic value to treat people with substance use disorder. Finally, we discuss limitations and future directions for the field of epigenetic studies in the behavioral effects of addictive drugs and suggest how to use these insights to develop efficacious treatments.

Roles of miR-592-3p and Its Target Gene, TMEFF1, in the Nucleus Accumbens During Incubation of Morphine Craving

BACKGROUND

Prolonged forced abstinence from morphine can increase cue-induced cravings for the drug, contributing to a persistent vulnerability to relapse. Previous studies have identified the implications of aberrant microRNA (miRNA) regulation in the pathogenesis of morphine addiction, but the changes in miRNA expression during the incubation of morphine craving are still unknown.

METHODS

Nucleus accumbens (NAc)-specific altered miRNA transcriptomics was determined in a mouse model of cue-induced incubation of morphine craving following a next-generation sequencing method and verified by RT-qPCR. Bioinformatics analysis was performed to predict the target gene of selected miRNA, and the protein expression of the target gene was detected by western blot. A dual-luciferase assay was performed to confirm the binding sites, and gain- and loss-of-function strategy was applied to understand the mechanism of miRNA and its target gene.

RESULTS

The miR-592-3p observed to be downregulated in the NAc core was linked to the incubation of morphine craving, and a dual-luciferase assay was performed to confirm the binding sites of miR-592-3p in its target gene, tomoregulin-1 (TMEFF1). Also, gain- and loss-of-function analyses revealed that the inhibition of miR-592-3p expression in the NAc core negatively regulated TMEFF1 expression, thereby enhancing the incubation of morphine craving; however, the overexpression of miR-592-3p in the NAc core resulted in a decreased expression of TMEFF1, thereby reducing the incubation of morphine craving.

CONCLUSION

Our findings demonstrated that miR-592-3p can improve the incubation of morphine craving by targeting TMEFF1, and thus, it holds a therapeutic potential to inhibit opioid craving.

Key transcription factors mediating cocaine-induced plasticity in the nucleus accumbens

Repeated cocaine use induces coordinated changes in gene expression that drive plasticity in the nucleus accumbens (NAc), an important component of the brain's reward circuitry, and promote the development of maladaptive, addiction-like behaviors. Studies on the molecular basis of cocaine action identify transcription factors, a class of proteins that bind to specific DNA sequences and regulate transcription, as critical mediators of this cocaine-induced plasticity. Early methods to identify and study transcription factors involved in addiction pathophysiology primarily relied on quantifying the expression of candidate genes in bulk brain tissue after chronic cocaine treatment, as well as conventional overexpression and knockdown techniques. More recently, advances in next generation sequencing, bioinformatics, cell-type-specific targeting, and locus-specific neuroepigenomic editing offer a more powerful, unbiased toolbox to identify the most important transcription factors that drive drug-induced plasticity and to causally define their downstream molecular mechanisms. Here, we synthesize the literature on transcription factors mediating cocaine action in the NAc, discuss the advancements and remaining limitations of current experimental approaches, and emphasize recent work leveraging bioinformatic tools and neuroepigenomic editing to study transcription factors involved in cocaine addiction.

Alcohol induced impairment/abnormalities in brain: Role of MicroRNAs

Alcohol is a highly toxic substance and has teratogenic properties that can lead to a wide range of developmental disorders. Excessive use of alcohol can change the structural and functional aspects of developed brain and other organs. Which can further lead to significant health, social and economic implications in many countries of the world. Convincing evidence support the involvement of microRNAs (miRNAs) as important post-transcriptional regulators of gene expression in neurodevelopment and maintenance. They also show differential expression following an injury. MiRNAs are the special class of small non coding RNAs that can modify the gene by targeting the mRNA and fine tune the development of cells to organs. Numerous pieces of evidences have shown the relationship between miRNA, alcohol and brain damage. These studies also show how miRNA controls different cellular mechanisms involved in the development of alcohol use disorder. With the increasing number of research studies, the roles of miRNAs following alcohol-induced injury could help researchers to recognize alternative therapeutic methods to treat/cure alcohol-induced brain damage. The present review summarizes the available data and brings together the important miRNAs, that play a crucial role in alcohol-induced brain damage, which will help in better understanding complex mechanisms. Identifying these miRNAs will not only expand the current knowledge but can lead to the identification of better targets for the development of novel therapeutic interventions.

HIV-1 Tat and cocaine impact astrocytic energy reservoir influence on miRNA epigenetic regulation

Astrocytes are the primary regulator of energy metabolism in the central nervous system (CNS), and impairment of astrocyte's energy resource may trigger neurodegeneration. HIV infections and cocaine use are known to alter epigenetic modification, including miRNAs, which can target gene expression post-transcriptionally. However, miRNA-mediated astrocyte energy metabolism has not been delineated in HIV infection and cocaine abuse. Using next-generation sequencing (NGS), we identified a total of 1900 miRNAs, 64 were upregulated and 68 miRNAs were downregulated in the astrocytes by HIV-1 Tat with cocaine exposure. Moreover, miR-4727-3p, miR-5189-5p, miR-5090, and miR-6810-5p expressions were significantly impacted, and their gene targets were identified as VAMP2, NFIB, PPM1H, MEIS1, and PSD93 through the bioinformatic approach. In addition, the astrocytes treated with the nootropic drug piracetam protects these miRNAs. These findings provide evidence that the miRNAs in the astrocytes may be a potential biomarker and therapeutic target for HIV and cocaine abuse-induced neurodegeneration.

Epigenetic Regulation of Circadian Clocks and Its Involvement in Drug Addiction

Based on studies describing an increased prevalence of addictive behaviours in several rare sleep disorders and shift workers, a relationship between circadian rhythms and addiction has been hinted for more than a decade. Although circadian rhythm alterations and molecular mechanisms associated with neuropsychiatric conditions are an area of active investigation, success is limited so far, and further investigations are required. Thus, even though compelling evidence connects the circadian clock to addictive behaviour and vice-versa, yet the functional mechanism behind this interaction remains largely unknown. At the molecular level, multiple mechanisms have been proposed to link the circadian timing system to addiction. The molecular mechanism of the circadian clock consists of a transcriptional/translational feedback system, with several regulatory loops, that are also intricately regulated at the epigenetic level. Interestingly, the epigenetic landscape shows profound changes in the addictive brain, with significant alterations in histone modification, DNA methylation, and small regulatory RNAs. The combination of these two observations raises the possibility that epigenetic regulation is a common plot linking the circadian clocks with addiction, though very little evidence has been reported to date. This review provides an elaborate overview of the circadian system and its involvement in addiction, and we hypothesise a possible connection at the epigenetic level that could further link them. Therefore, we think this review may further improve our understanding of the etiology or/and pathology of psychiatric disorders related to drug addiction.

Candidate l-methionine target piRNA regulatory networks analysis response to cocaine-conditioned place preference in mice

BACKGROUND

Methionine has been proven to inhibit addictive behaviors of cocaine dependence. However, the mechanism of methionine response to cocaine CPP is unknown. Recent evidence highlights piRNAs to regulate genes via a miRNA-like mechanism. Here, next-generation sequencing is used to study mechanism on methionine response to drug-induced behaviors though piRNA.

METHODS

l-methionine treatment cocaine CPP animal model was used to do non-coding RNA sequencing. There were four groups to sequence: saline+saline (SS), MET+saline (MS), MET+cocaine (MC), and cocaine+saline. Combining mRNA sequencing data, the network and regulation of piRNA were analyzed with their corresponding mRNA and miRNA.

RESULTS

Analysis of the piRNAome reveals that piRNAs inversely regulated their target mRNA genes. KEGG analysis of DE-piRNA target mRNA genes were enriched in Morphine addiction, GABAergic synapse and Cholinergic synapse pathway. Furthermore, four significantly differential expressed genes Cacna2d3, Epha6, Nedd4l, and Vav2 were identified and regulated by piRNAs in the process of l-methionine inhibits cocaine CPP. Thereinto, Vav2 was regulated by multiple DE piRNAs by sharing the common sequence: GTCTCTCCAGCCACCTT. Meanwhile, it was found that piRNA positively regulates miRNA and three genes Bcl3, Il20ra, and Insrr were identified and regulated by piRNA through miRNA.

CONCLUSION

The results showed that piRNA negatively regulated target mRNA genes and positively regulated target miRNA genes. Genes located in substance dependence, signal transduction and also nervous functions pathways were identified. When taken together, these data may explain the roles of l-methionine in counteracting the effects of cocaine CPP via piRNAs.

Evaluation of miRNA as Biomarkers of Emotional Valence in Pigs

Simple Summary

It is widely recognized that the assessment of animal welfare should include measures of positive emotional (affective) state. Existing behavioral and physiological indicators of a positive affective state frequently lack sensitivity, objectivity or are unsuitable in a production environment. Therefore, there is a need to develop new approaches to accurately and objectively measure a positive emotional state in animals, including novel molecular markers such a miRNA. These biomarkers must be measurable in the peripheral circulation and provide an accurate account of the physiological and molecular activity in regions of the brain associated with emotional processing. Further, such markers require validation against established behavioral and physiological indices. Here we investigated the efficacy of circulating miRNA as biomarkers of emotional state in the pig.

Abstract

The ability to assess the welfare of animals is dependent on our ability to accurately determine their emotional (affective) state, with particular emphasis being placed on the identification of positive emotions. The challenge remains that current physiological and behavioral indices are either unable to distinguish between positive and negative emotional states, or they are simply not suitable for a production environment. Therefore, the development of novel measures of animal emotion is a necessity. Here we investigated the efficacy of microRNA (miRNA) in the brain and blood as biomarkers of emotional state in the pig. Female Large White × Landrace pigs (n = 24) were selected at weaning and trained to perform a judgment bias test (JBT), before being exposed for 5 weeks to either enriched (n = 12) or barren housing (n = 12) conditions. Pigs were tested on the JBT once prior to treatment, and immediately following treatment. MiRNA and neurotransmitters were analyzed in blood and brain tissue after euthanasia. Treatment had no effect on the outcomes of the JBT. There was also no effect of treatment on miRNA expression in blood or the brain (FDR p > 0.05). However, pigs exposed to enriched housing had elevated dopamine within the striatum compared to pigs in barren housing (p = 0.02). The results imply that either (a) miRNAs are not likely to be valid biomarkers of a positive affective state, at least under the type of conditions employed in this study, or (b) that the study design used to modify affective state was not able to create differential affective states, and therefore establish the validity of miRNA as biomarkers.

Genomics and epigenomics of addiction

Recent progress in the genomics and epigenomics of addiction has contributed to improving our understanding of this complex mental disorder's etiology, filling the gap between genes, environment, and behavior. We review the behavioral genetic studies reporting gene and environment interactions that explain the polygenetic contribution to the resilience and vulnerability to develop addiction. We discuss the evidence of polymorphic candidate genes that confer susceptibility to develop addiction as well as the studies of specific epigenetic marks that contribute to vulnerability and resilience to addictive-like behavior. A particular emphasis has been devoted to the miRNA changes that are considered potential biomarkers. The increasing knowledge about the technology required to alter miRNA expression may provide promising novel therapeutic tools. Finally, we give future directions for the field's progress in disentangling the connection between genes, environment, and behavior.

microRNA regulation related to the protective effects of environmental enrichment against cocaine-seeking behavior

BACKGROUND

MicroRNAs (miRNAs) are "master post-transcriptional regulators" of gene expression. Here we investigate miRNAs involved in the incentive motivation for cocaine elicited by exposure to cocaine-associated cues.

METHODS

We conducted NanoString nCounter analyses of microRNA expression in the nucleus accumbens shell of male rats that had been tested for cue reactivity in a previous study. These rats had been trained to self-administer cocaine while living in isolate housing, then during a subsequent 21-day forced abstinence period they either stayed under isolate housing or switched to environmental enrichment (EE), as this EE intervention is known to decrease cocaine seeking. This allowed us to create groups of "high" and "low" cocaine seekers using a median split of cocaine-seeking behavior.

RESULTS

Differential expression analysis across high- and low-seekers identified 33 microRNAs that were differentially expressed in the nucleus accumbens shell. Predicted mRNA targets of these microRNAs are implicated in synaptic plasticity, neuronal signaling, and neuroinflammation signaling, and many are known addiction-related genes. Of the 33 differentially-expressed microRNAs, 8 were specifically downregulated in the low-seeking group and another set of 8 had expression levels that were significantly correlated with cocaine-seeking behavior.

CONCLUSION

These findings not only confirm the involvement of previously identified microRNAs (e.g., miR-212, miR-495) but also reveal novel microRNAs (e.g., miR-3557, miR-377) that alter, or are altered by, processes associated with cocaine-seeking behavior. Further research examining the mechanisms involved in these microRNA changes and their effects on signaling may reveal novel therapeutic targets for attenuating drug craving.

Epigenetic Mechanisms in Drug Relapse

A growing body of evidence from the past 15 years implicates epigenetic mechanisms in the behavioral effects of addictive drugs. The main focus of these studies has been epigenetic mechanisms of psychomotor sensitization and drug reinforcement, as assessed by the conditioned place preference and drug self-administration procedures. Some of these studies have documented long-lasting changes in the expression of epigenetic enzymes and molecules that persist for weeks after the last drug exposure. These observations have inspired more recent investigations on the epigenetic mechanisms of relapse to drug seeking after prolonged abstinence. Here, we review studies that have examined epigenetic mechanisms (e.g., histone modifications, chromatin remodeler-associated modifications, and DNA methylation) that contribute to relapse to cocaine, amphetamine, methamphetamine, morphine, heroin, nicotine, or alcohol seeking, as assessed in rodent models. We first provide a brief overview of studies that have examined persistent epigenetic changes in the brain after prolonged abstinence from noncontingent drug exposure or drug self-administration. Next, we review studies on the effect of either systemic or brain site-specific epigenetic manipulations on the reinstatement of drug-conditioned place preference after extinction of the learned preference, the reinstatement of drug seeking after operant drug self-administration and extinction of the drug-reinforced responding, and the incubation of drug craving (the time-dependent increase in drug seeking after cessation of drug self-administration). We conclude by discussing the implications of these studies for understanding mechanisms contributing to persistent relapse vulnerability after prolonged abstinence. We also discuss the implications of these results for translational research on the potential use of systemically administered epigenetic enzyme inhibitors for relapse prevention in human drug users.

Increased Expression of Plasma miRNA-320a and let-7b-5p in Heroin-Dependent Patients and Its Clinical Significance

Heroin use disorder is a chronic and relapsing disease that induces persistent changes in the brain. The diagnoses of heroin use disorders are mainly based on subjective reports and no valid biomarkers available. Recent researches have revealed that circulating miRNAs are useful non-invasive biomarkers for diagnosing brain diseases such as Alzheimer's disease, multiple sclerosis, schizophrenia, and bipolar disorder. However, studies on circulating miRNAs for the diagnosis of heroin use disorders are rarely reported. In this study, we investigated the differential expression of plasma miRNAs in 57 heroin-dependent patients. Based on literature research and microarray analysis, two candidate miRNAs, miR-320a and let-7b-5p, were selected and analyzed by quantitative real-time RT-PCR. The results showed miR-320a and let-7b were significantly upregulated in plasma of the heroin-dependent patients compared to that in healthy controls. The area under curves (AUCs) of receiver operating characteristic (ROC) curves of miR-320a and let-7b-5p were 0.748 and 0.758, respectively. The sensitivities of miR-320a and let-7b-5p were 71.9 and 70.2%, while the specificities of miR-320a and let-7b-5p were 76.1 and 78.3%, respectively. The combination of these two miRNAs predicted heron dependence with an AUC of 0.782 (95% CI 0.687-0.876), with 73.7% sensitivity and 82.6% specificity. Our findings suggest a potential use for circulating miRNAs as biomarkers for the diagnosis of heroin abuse.

Cocaine Administration and Its Abstinence Conditions Modulate Neuroglia

Cocaine induces neuronal changes as well as non-neuronal (astrocytes, microglia, oligodendroglia) mechanisms, but these changes can also be modulated by various types of drug abstinence. Due to the very complex and still incompletely understood nature of cocaine use disorder, understanding of the mechanisms involved in addictive behavior is necessary to further search for effective pharmacotherapy of this disease. The aim of this study was to investigate changes at the gene and protein levels associated with glial cell activity after cocaine exposure, as well as during early cocaine abstinence (3 days) with extinction training or in home cage isolation. Cocaine self-administration significantly decreased myelin regulatory factor (MYRF) and cyclic nucleotide phosphodiesterase (CNP) expression in the hippocampus as well as pleckstrin (PLEK) and T-lymphocyte activation antigen (CD86) in the rat striatum. Depending on cocaine abstinence conditions, microglial PLEK expression was increased through extinction training but did not change in the home cage isolation. In addition, downregulation of gene expression associated with oligodendrocytes (CNP, MYRF) and microglia regulator of G protein signaling 1 (RGS1) was observed in the hippocampus, regardless of the type of drug abstinence, while downregulation of myelin and lymphocyte protein (MAL) expression was found only in rats exposed to abstinence in the home cage. Taken together, the presented results strongly suggest that cocaine abstinence evokes significant changes in gene expression associated with the proper functioning of glial cells, suggesting their significant involvement in adaptive changes in the brain associated with cocaine exposure. Interestingly, drug abstinence conditions are important factors influencing observed changes at the transcript levels of selected genes, which may be of clinical interest.

Cocaine-regulated microRNA miR-124 controls poly (ADP-ribose) polymerase-1 expression in neuronal cells

MiR-124 is a highly expressed miRNA in the brain and regulates genes involved in neuronal function. We report that miR-124 post-transcriptionally regulates PARP-1. We have identified a highly conserved binding site of miR-124 in the 3'-untranslated region (3'UTR) of Parp-1 mRNA. We demonstrate that miR-124 directly binds to the Parp-1 3'UTR and mutations in the seed sequences abrogate binding between the two RNA molecules. Luciferase reporter assay revealed that miR-124 post-transcriptionally regulates Parp-1 3'UTR activity in a dopaminergic neuronal cell model. Interestingly, the binding region of miR-124 in Parp-1 3'UTR overlapped with the target sequence of miR-125b, another post-transcriptional regulator of Parp-1. Our results from titration and pull-down studies revealed that miR-124 binds to Parp-1 3'UTR with greater affinity and confers a dominant post-transcriptional inhibition compared to miR-125b. Interestingly, acute or chronic cocaine exposure downregulated miR-124 levels concomitant with upregulation of PARP-1 protein in dopaminergic-like neuronal cells in culture. Levels of miR-124 were also downregulated upon acute or chronic cocaine exposure in the mouse nucleus accumbens (NAc)-a key reward region of brain. Time-course studies revealed that cocaine treatment persistently downregulated miR-124 in NAc. Consistent with this finding, miR-124 expression was also significantly reduced in the NAc of animals conditioned for cocaine place preference. Collectively, these studies identify Parp-1 as a direct target of miR-124 in neuronal cells, establish miR-124 as a cocaine-regulated miRNA in the mouse NAc, and highlight a novel pathway underlying the molecular effects of cocaine.

Genomics and the future of psychopharmacology: MicroRNAs offer novel therapeutics

MicroRNAs (miRNAs) are short, noncoding RNAs functioning as regulators of the transcription of protein-coding genes in eukaryotes. During the last two decades, studies on miRNAs indicate that they have potential as diagnostic and prognostic biomarkers for a wide range of cancers. Research interest in miRNAs has moved to embrace further medical disciplines, including neuropsychiatric disorders, comparing miRNA expression and mRNA targets between patient and control blood samples and postmortem brain tissues, as well as in animal models of neuropsychiatric disorders. This manuscript reviews recent findings on miRNAs implicated in the pathology of mood disorders, schizophrenia, and autism, as well as their diagnostic potential, and their potential as tentative targets for future therapeutics. The plausible contribution of X chromosome miRNAs to the larger prevalence of major depression among women is also evaluated.


Altered serum microRNA expression profile in subjects with heroin and methamphetamine use disorder

OBJECTIVES

Drug abuse is one of the most severe global social and public health problems, especially in China. However, objective blood biomarkers that are easy to detect are still in great need. This study was aim to explore the expression pattern of circulating microRNAs (miRNAs) in subjects with drug addiction and test the potential of altered serum miRNAs as noninvasive diagnostic tools for drug abuse.

METHODS

Serum samples were obtained from 42 heroin abusers, 42 methamphetamine (MA) abusers and 42 controls. Microarray-based miRNA analysis was first applied to screen unique serum miRNA profiles in drug abusers on a training set of serum samples from 12 heroin abusers, 12 MA abusers and 12 control subjects. The expression levels of selected candidate miRNAs were subsequently verified in individual samples of the training set and further confirmed independently in a validation set of samples from 30 heroin abusers, 30 MA abusers and 30 controls using real-time quantitative polymerase chain reaction (RT-qPCR).

RESULTS

Microarray analysis identified 116 and 109 significantly altered miRNAs in heroin abusers and MA abusers, respectively. Three miRNAs, including let-7b-5p, miR-206 and miR-486-5p, were verified to be significantly and steadily increased in heroin abusers, and miR-9-3p was significantly increased in MA abusers compared with normal controls. The areas under the curve (AUCs) of the ROC curve of these miRNAs ranged from 0.718 to 0.867.

CONCLUSIONS

Our study raises the possibility that the altered serum miRNAs could potentially be used as an auxiliary tool to identify individuals in drug abuse and addiction.

Epigenetic Mechanisms of Opioid Addiction

Opioid use kills tens of thousands of Americans each year, devastates families and entire communities, and cripples the health care system. Exposure to opioids causes long-term changes to brain regions involved in reward processing and motivation, leading vulnerable individuals to engage in pathological drug seeking and drug taking that can remain a lifelong struggle. The persistence of these neuroadaptations is mediated in part by epigenetic remodeling of gene expression programs in discrete brain regions. Although the majority of work examining how epigenetic modifications contribute to addiction has focused on psychostimulants such as cocaine, research into opioid-induced changes to the epigenetic landscape is emerging. This review summarizes our knowledge of opioid-induced epigenetic modifications and their consequential changes to gene expression. Current evidence points toward opioids promoting higher levels of permissive histone acetylation and lower levels of repressive histone methylation as well as alterations to DNA methylation patterns and noncoding RNA expression throughout the brain's reward circuitry. Additionally, studies manipulating epigenetic enzymes in specific brain regions are beginning to build causal links between these epigenetic modifications and changes in addiction-related behavior. Moving forward, studies must leverage advanced chromatin analysis and next-generation sequencing approaches combined with bioinformatics pipelines to identify novel gene networks regulated by particular epigenetic modifications. Improved translational relevance also requires increased focus on volitional drug-intake models and standardization of opioid exposure paradigms. Such work will significantly advance our understanding of how opioids cause persistent changes to brain function and will provide a platform on which to develop interventions for treating opioid addiction.

Brain-Derived Extracellular Vesicle microRNA Signatures Associated with In Utero and Postnatal Oxycodone Exposure

Oxycodone (oxy) is a semi-synthetic opioid commonly used as a pain medication that is also a widely abused prescription drug. While very limited studies have examined the effect of in utero oxy (IUO) exposure on neurodevelopment, a significant gap in knowledge is the effect of IUO compared with postnatal oxy (PNO) exposure on synaptogenesis—a key process in the formation of synapses during brain development—in the exposed offspring. One relatively unexplored form of cell–cell communication associated with brain development in response to IUO and PNO exposure are extracellular vesicles (EVs). EVs are membrane-bound vesicles that serve as carriers of cargo, such as microRNAs (miRNAs). Using RNA-Seq analysis, we identified distinct brain-derived extracellular vesicle (BDEs) miRNA signatures associated with IUO and PNO exposure, including their gene targets, regulating key functional pathways associated with brain development to be more impacted in the IUO offspring. Further treatment of primary 14-day in vitro (DIV) neurons with IUO BDEs caused a significant reduction in spine density compared to treatment with BDEs from PNO and saline groups. In summary, our studies identified for the first time, key BDE miRNA signatures in IUO- and PNO-exposed offspring, which could impact their brain development as well as synaptic function.

Long non-coding RNA MEG3 attends to morphine-mediated autophagy of HT22 cells through modulating ERK pathway

Context: Morphine is an alkaloid isolated from the poppy plants. The addiction of morphine is a very serious social issue. Some long non-coding RNAs (lncRNAs) have been proposed to engage in drug addiction. Objective: Whether lncRNA maternally expressed gene 3 (MEG3) attended to morphine-mediated autophagy of mouse hippocampal neuronal HT22 cells was probed. Materials and methods: HT22 cells were subjected to 10 µM morphine for 24 h. Cell autophagy was assessed by measuring LC3-II/LC3-I and Beclin-1 expression. qRT-PCR was carried out to measure MEG3 expression. SiRNA oligoribonucleotides targeting MEG3 (si-MEG3) was transfected to silence MEG3. The orexin1 receptor (OX1R), c-fos, p/t-ERK and p/t-PKC expressions were tested by western blotting. SCH772984 was used as an inhibitor of ERK pathway. Results: Morphine elevated OX1R (2.92 times), c-fos (2.06 times), p/t-ERK (2.04 times) and p/t-PKC (2.4 times), Beclin-1 (3.2 times) and LC3-II/LC3-I (3.96 times) expression in HT22 cells. Moreover, followed by morphine exposure, the MEG3 expression was also elevated in HT22 cells (3.03 times). The silence of MEG3 lowered the Beclin-1 (1.85 times), LC3-II/LC3-I (2.12 times), c-fos (1.39 times) and p/t-ERK (1.44 times) expressions in morphine-treated HT22 cells. Inhibitor of ERK pathway SCH772984 further promoted the influence of MEG3 silence on morphine-caused Beclin-1 (1.97 times) and LC3-II/LC3-I (1.92 times) expressions decreases. Conclusions: Up-regulation of MEG3 attended to the morphine-caused autophagy of HT22 cells might be through elevating c-fos expression and promoting ERK pathway activation. More experiments are also needed in the future to analyse the influence of other lncRNAs in drug addiction.

Vapor Cannabis Exposure Promotes Genetic Plasticity in the Rat Hypothalamus

It is well established that cannabis use promotes appetite. However, how cannabis interacts with the brain’s appetite center, the hypothalamus, to stimulate feeding behavior is unknown. A growing body of evidence indicates that the hypothalamic transcriptome programs energy balance. Here, we tested the hypothesis that cannabis targets alternative polyadenylation (APA) sites within hypothalamic transcripts to regulate transcriptomic function. To do this, we used a novel cannabis vapor exposure model to characterize feeding in adult male Long Evans rats and aligned this behavioral response with APA events using a Whole Transcriptome Termini Sequencing (WTTS-Seq) approach as well as functional RNA abundance measurements with real-time quantitative polymerase chain reactions. We found that vapor cannabis exposure promoted food intake in free-feeding and behaviorally sated rats, validating the appetite stimulating properties of cannabis. Our WTTS-Seq analysis mapped 59 unique cannabis-induced hypothalamic APAs that occurred primarily within exons on transcripts that regulate synaptic function, excitatory synaptic transmission, and dopamine signaling. Importantly, APA insertions regulated RNA abundance of Slc6a3, the dopamine transporter, suggesting a novel genetic link for cannabis regulation of brain monoamine function. Collectively, these novel data indicate that a single cannabis exposure rapidly targets a key RNA processing mechanism linked to brain transcriptome function.

It is a complex issue: emerging connections between epigenetic regulators in drug addiction

Drug use leads to addiction in some individuals, but the underlying brain mechanisms that control the transition from casual drug use to an intractable substance use disorder (SUD) are not well understood. Gene x environment interactions such as the frequency of drug use and the type of substance used likely to promote maladaptive plastic changes in brain regions that are critical for controlling addiction-related behavior. Epigenetics encompasses a broad spectrum of mechanisms important for regulating gene transcription that are not dependent on changes in DNA base pair sequences. This review focuses on the proteins and complexes contributing to epigenetic modifications in the nucleus accumbens (NAc) following drug experience. We discuss in detail the three major mechanisms: histone acetylation and deacetylation, histone methylation, and DNA methylation. We discuss how drug use alters the regulation of the associated proteins regulating these processes and highlight how experimental manipulations of these proteins in the NAc can alter drug-related behaviors. Finally, we discuss the ways that histone modifications and DNA methylation coordinate actions by recruiting large epigenetic enzyme complexes to aid in transcriptional repression. Targeting these multiprotein epigenetic enzyme complexes - and the individual proteins that comprise them - might lead to effective therapeutics to reverse or treat SUDs in patients.

Decreased Level of Blood MicroRNA-133b in Men with Opioid Use Disorder on Methadone Maintenance Therapy

Although previous animal studies have indicated that certain micro ribonucleic acids (microRNAs) play a part in the pathway of opioid addiction, whether such findings extend to human models is yet unknown. This study aims to investigate the important microRNA expressions in patients with opioid use disorder (OUD) on methadone maintenance treatment (MMT) compared to healthy controls and analyze the correlation between microRNAs and opioid characteristics among the patients. We recruited 50 patients and 25 controls, and both groups were matched regarding gender, age, and body mass index. Serum microRNAs (miR-133b, miR-23b, miR-190, miR-206, miR-210, and miR-21) were measured. The age of OUD onset, duration of MMT participation, and recent daily methadone dosage were considered the opioid characteristics. We adopted the t-test to compare the difference between patients and controls and Pearson's correlation to evaluate the association between microRNAs and opioid profiles. Only the level of miR-133b in OUD patients on MMT was significantly lower than that in healthy controls. We did not detect differences of any other microRNA expressions between the two groups. Furthermore, we found no evidence to support the association between microRNAs and opioid characteristics. This study indicates that miR-133b values may be decreased in OUD patients on MMT.

Opportunities and challenges in psychopharmacology

This review addresses novel approaches for influencing the transcriptome, the epigenome, the microbiome, the proteome, and the energy metabolome. These innovations help develop psychotropic medications which will directly reach the molecular targets, leading to beneficial effects, and which will be individually adapted to provide more efficacy and less toxicity. The series of advances described here show that these once utopian goals for psychiatric treatment are now real themes of research, indicating that the future path for psychopharmacology might not be as narrow and grim as considered during the last few decades.


Novel biomarkers to assess in utero effects of maternal opioid use: First steps toward understanding short- and long-term neurodevelopmental sequelae

Maternal opioid use disorder is common, resulting in significant neonatal morbidity and cost. Currently, it is not possible to predict which opioid-exposed newborns will require pharmacotherapy for neonatal abstinence syndrome. Further, little is known regarding the effects of maternal opioid use disorder on the developing human brain. We hypothesized that novel methodologies utilizing fetal central nervous system-derived extracellular vesicles isolated from maternal blood can address these gaps in knowledge. Plasma from opioid users and controls between 9 and 21 weeks was precipitated and extracellular vesicles were isolated. Mu opioid and cannabinoid receptor levels were quantified. Label-free proteomics studies and unbiased small RNA next generation sequencing was performed in paired fetal brain tissue. Maternal opioid use disorder increased mu opioid receptor protein levels in extracellular vesicles independent of opioid equivalent dose. Moreover, cannabinoid receptor levels in extracellular vesicles were upregulated with opioid exposure indicating cross talk with endocannabinoids. Maternal opioid use disorder was associated with significant changes in extracellular vesicle protein cargo and fetal brain micro RNA expression, especially in male fetuses. Many of the altered cargo molecules and micro RNAs identified are associated with adverse clinical neurodevelopmental outcomes. Our data suggest that assays relying on extracellular vesicles isolated from maternal blood extracellular vesicles may provide information regarding fetal response to opioids in the setting of maternal opioid use disorder. Prospective clinical studies are needed to evaluate the association between extracellular vesicle biomarkers, risk of neonatal abstinence syndrome and neurodevelopmental outcomes.

Investigating the Effect of Perinatal Nicotine Exposure on Dopaminergic Neurons in the VTA Using miRNA Expression Profiles

Maternal smoking during pregnancy is associated with developmental, cognitive, and behavioral disorders, including low birth weight, attention deficit hyperactivity disorder, learning disabilities, and drug abuse later in life. Nicotine activates the reward-driven behavior characteristic of drug abuse. Dopaminergic (DA) neurons originating from the ventral tegmental area (VTA) of the brain, which are stimulated by nicotine and other stimuli, are widely implicated in the natural reward pathway that is known to contribute to addiction. In recent years, microRNAs have been implicated in disrupting regulatory mechanisms due to their capability of targeting multiple genes and thus inducing downstream effects along many pathways. In order to investigate miRNA expression of dopaminergic neurons from the VTA, we employed patch clamping to identify and harvest both DA and non-DA neurons from rats perinatally exposed to nicotine for use in single-cell RT-qPCR. Our data indicated that miR-140-5p and miR-140-3p were upregulated in DA neurons; while miR-140-3p and miR-212 were differentially expressed in non-DA neurons. A functional enrichment analysis was also performed on our miRNA-gene prediction network and predicted that our miRNAs target genes involved in drug response and neuroplasticity.

Genomics and the future of psychopharmacology: MicroRNAs offer novel therapeutics

MicroRNAs (miRNAs) are short, noncoding RNAs functioning as regulators of the transcription of protein-coding genes in eukaryotes. During the last two decades, studies on miRNAs indicate that they have potential as diagnostic and prognostic biomarkers for a wide range of cancers. Research interest in miRNAs has moved to embrace further medical disciplines, including neuropsychiatric disorders, comparing miRNA expression and mRNA targets between patient and control blood samples and postmortem brain tissues, as well as in animal models of neuropsychiatric disorders. This manuscript reviews recent findings on miRNAs implicated in the pathology of mood disorders, schizophrenia, and autism, as well as their diagnostic potential, and their potential as tentative targets for future therapeutics. The plausible contribution of X chromosome miRNAs to the larger prevalence of major depression among women is also evaluated.
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Opportunities and challenges in psychopharmacology

This review addresses novel approaches for influencing the transcriptome, the epigenome, the microbiome, the proteome, and the energy metabolome. These innovations help develop psychotropic medications which will directly reach the molecular targets, leading to beneficial effects, and which will be individually adapted to provide more efficacy and less toxicity. The series of advances described here show that these once utopian goals for psychiatric treatment are now real themes of research, indicating that the future path for psychopharmacology might not be as narrow and grim as considered during the last few decades.
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MicroRNA cluster miR199a/214 are differentially expressed in female and male rats following nicotine self-administration

Previous research has established sex differences associated with nicotine intake, however a significant gap in knowledge remains regarding the molecular mechanisms that govern these differences at the transcriptional level. One critical regulator of transcription are microRNAs (miRNAs). miRNAs are a family of non-coding RNAs that regulate an array of important biological functions altered in several disease states, including neuroadaptive changes within the brain associated with drug dependence. We examined the prefrontal cortex (PFC) from male and female Sprague-Dawley rats following self-administration (22 days) of nicotine or yoked saline controls using next generation RNA-Sequencing (RNA-Seq) technology and found an array of miRNAs to be significantly and differentially regulated by nicotine self-administration. Of these, we found the expression of miR-199a and 214, which are expressed on the same cluster of chromosome 1, to be upregulated in the female rats exposed to nicotine; upregulation in this group was further validated by real time polymerase chain reaction (RT-PCR). Bioinformatics analysis to assess common targets of miR-199/214 identified Sirtuin 1 (SIRT1), a nicotinamide adenine dinucleotide (NAD)- dependent deacetylase that plays a role in apoptosis, neuron survival, and stress resistance. Using western-blot, we confirmed downregulation of SIRT1 and increased cleaved caspase 3 expression in the brains of nicotine-exposed female rats and no change in expression levels in the other groups. Collectively, our findings highlight a miR-199/214 regulatory network that, through SIRT1, may be associated with nicotine seeking in females which may serve as a potential therapeutic target for sex-specific treatment approaches.

Investigating the genetic profile of dopaminergic neurons in the VTA in response to perinatal nicotine exposure using mRNA-miRNA analyses

Maternal smoking during pregnancy is associated with an increased risk of developmental, behavioral, and cognitive deficits. Nicotine, the primary addictive component in tobacco, has been shown to modulate changes in gene expression when exposure occurs during neurodevelopment. The ventral tegmental area (VTA) is believed to be central to the mechanism of addiction because of its involvement in the reward pathway. The purpose of this study was to build a genetic profile for dopamine (DA) neurons in the VTA and investigate the disruptions to the molecular pathways after perinatal nicotine exposure. Initially, we isolated the VTA from rat pups treated perinatally with either nicotine or saline (control) and collected DA neurons using fluorescent-activated cell sorting. Using microarray analysis, we profiled the differential expression of mRNAs and microRNAs from DA neurons in the VTA in order to explore potential points of regulation and enriched pathways following perinatal nicotine exposure. Furthermore, mechanisms of miRNA-mediated post-transcriptional regulation were investigated using predicted and validated miRNA-gene targets in order to demonstrate the role of miRNAs in the mesocorticolimbic DA pathway. This study provides insight into the genetic profile as well as biological pathways of DA neurons in the VTA of rats following perinatal nicotine exposure.

MiR-9, miR-153 and miR-124 are down-regulated by acute exposure to cocaine in a dopaminergic cell model and may contribute to cocaine dependence

Cocaine is one of the most used psychostimulant drugs worldwide. MicroRNAs are post-transcriptional regulators of gene expression that are highly expressed in brain, and several studies have shown that cocaine can alter their expression. In a previous study, we identified several protein-coding genes that are differentially expressed in a dopaminergic neuron-like model after an acute exposure to cocaine. Now, we used the prediction tool WebGestalt to identify miRNA molecules potentially involved in the regulation of these genes. Using the same cellular model, we found that seven of these miRNAs are down-regulated by cocaine: miR-124-3p, miR-124-5p, miR-137, miR-101-3p, miR-9-5p, miR-369-3p and miR-153-3p, the last three not previously related to cocaine. Furthermore, we found that three of the miRNA genes that are differentially expressed in our model (hsa-miR-9-1, hsa-miR-153-1 and hsa-miR-124-3) are nominally associated with cocaine dependence in a case-control study (2,085 cases and 4,293 controls). In summary, we highlighted novel miRNAs that may be involved in those cocaine-induced changes of gene expression that underlie addiction. Moreover, we identified genetic variants that contribute to cocaine dependence in three of these miRNA genes, supporting the idea that genes differentially expressed under cocaine may play an important role in the susceptibility to cocaine dependence.

Dehydroepiandrosterone and Addiction

Drug addiction has a great negative influence on society, both social and economic burden. It was widely thought that addicts could choose to stop using drugs if only they had some self-control and principles. Nowadays, science has changed this view, defining drug addiction as a complex brain disease that affects behavior in many ways, both biological and psychological. Currently there is no ground-breaking reliable treatment for drug addiction. For more than a decade we are researching an alternative approach for intervention with drug craving and relapse to its usage, using DHEA, a well-being and antiaging food supplement. In this chapter we navigate through the significant therapeutic effect of DHEA on the brain circuits that control addiction and on behavioral performance both in animal models and addicts. We suggest that an integrative program of add-on DHEA treatment may further enable to dynamically evaluate the progress of rehabilitation of an individual patient, in a comprehensive assessment. Such a program may boost and support the detoxification and rehabilitation process, and help patients regain a normal life in a shorter amount of time.

MicroRNA Regulation of nAChR Expression and Nicotine-Dependent Behavior in C. elegans

Chronic exposure to nicotine upregulates nicotinic acetylcholine receptors (nAChRs), and such upregulation is critical for the development of nicotine dependence in humans and animal models. However, how nicotine upregulates nAChRs is not well understood. Here, we identify a key role for microRNA in regulating nicotine-dependent behavior by modulating nAChR expression in C. elegans. We show that the nAChR gene acr-19 and alg-1, a key Argonaute-family member in the microRNA machinery, are specifically required for nicotine withdrawal response following chronic nicotine treatment. Chronic exposure to nicotine downregulates alg-1, leading to upregulation of acr-19. This effect is mediated by the microRNA miR-238 that recognizes the 3' UTR of acr-19 transcript. Our results unveil a previously unrecognized role for microRNA in nicotine signaling, providing insights into how chronic nicotine administration leads to upregulation of nAChR and ultimately nicotine dependence.

Cocaine evokes a profile of oxidative stress and impacts innate antiviral response pathways in astrocytes

HIV-1 and Zika virus (ZIKV) represent RNA viruses with neurotropic characteristics. Infected individuals suffer neurocognitive disorders aggravated by environmental toxins, including drugs of abuse such as cocaine, exacerbating HIV-associated neurocognitive disorders through a combination of astrogliosis, oxidative stress and innate immune signaling; however, little is known about how cocaine impacts the progression of ZIKV neural perturbations. Impaired innate immune signaling is characterized by weakened antiviral activation of interferon signaling and alterations in inflammatory signaling, factors contributing to cognitive sequela associated with cocaine in HIV-1/ZIKV infection. We employed cellular/molecular biology techniques to test if cocaine suppresses the efficacy of astrocytes to initiate a Type 1 interferon response to HIV-1/ZIKV, in vitro. We found cocaine activated antiviral signaling pathways and type I interferon in the absence of inflammation. Cocaine pre-exposure suppressed antiviral responses to HIV-1/ZIKV, triggering antiviral signaling and phosphorylation of interferon regulatory transcription factor 3 to stimulate type I interferon gene transcription. Our data indicate that oxidative stress is a major driver of cocaine-mediated astrocyte antiviral immune responses. Although astrocyte antiviral signaling is activated following detection of foreign pathogenic material, oxidative stress and increased cytosolic double-stranded DNA (dsDNA) can drive antiviral signaling via stimulation of pattern recognition receptors. Pretreatment with the glial modulators propentofylline (PPF) or pioglitazone (PIO) reversed cocaine-mediated attenuation of astrocyte responses to HIV-1/ZIKV. Both PPF/PIO protected against cocaine-mediated generation of reactive oxygen species (ROS), increased dsDNA, antiviral signaling pathways and increased type I interferon, indicating that cocaine induces astrocyte type I interferon signaling in the absence of virus and oxidative stress is a major driver of cocaine-mediated astrocyte antiviral immunity. Lastly, PPF and PIO have therapeutic potential to ameliorate cocaine-mediated dysregulation of astrocyte antiviral immunity possibly via a myriad of protective actions including decreases in reactive phenotype and damaging immune factors.

MicroRNAs regulate synaptic plasticity underlying drug addiction

Chronic use of drugs of abuse results in neurochemical, morphological and behavioral plasticity that underlies the emergence of compulsive drug seeking and vulnerability to relapse during periods of attempted abstinence. Identifying and reversing addiction-relevant plasticity is seen as a potential point of pharmacotherapeutic intervention in drug-addicted individuals. Despite considerable advances in our understanding of the actions of drugs of abuse in the brain, this information has thus far yielded few novel treatment options addicted individuals. MicroRNAs are small noncoding RNAs that can each regulate the translation of hundreds to thousands of messenger RNAs. The highly pleiotropic nature of miRNAs has focused attention on their contribution to addiction-relevant structural and functional plasticity in the brain and their potential utility as targets for medications development. In this review, we discuss the roles of miRNAs in synaptic plasticity underlying the development of addiction and then briefly discuss the possibility of using circulating miRNA as biomarkers for addiction.

Cocaine Exposure Increases Blood Pressure and Aortic Stiffness via the miR-30c-5p-Malic Enzyme 1-Reactive Oxygen Species Pathway

Cocaine abuse increases the risk of cardiovascular mortality and morbidity; however, the underlying molecular mechanisms remain elusive. By using a mouse model for cocaine abuse/use, we found that repeated cocaine injection led to increased blood pressure and aortic stiffness in mice associated with elevated levels of reactive oxygen species (ROS) in the aortas, a phenomenon similar to that observed in hypertensive humans. This ROS elevation was correlated with downregulation of Me1 (malic enzyme 1), an important redox molecule that counteracts ROS generation, and upregulation of microRNA (miR)-30c-5p that targets Me1 expression by directly binding to its 3'UTR (untranslated region). Remarkably, lentivirus-mediated overexpression of miR-30c-5p in aortic smooth muscle cells recapitulated the effect of cocaine on Me1 suppression, which in turn led to ROS elevation. Moreover, in vivo silencing of miR-30c-5p in smooth muscle cells resulted in Me1 upregulation, ROS reduction, and significantly suppressed cocaine-induced increases in blood pressure and aortic stiffness-a similar effect to that produced by treatment with the antioxidant N-acetyl cysteine. Discovery of this novel cocaine-↑miR-30c-5p-↓Me1-↑ROS pathway provides a potential new therapeutic avenue for treatment of cocaine abuse-related cardiovascular disease.

Turing Revisited: Decoding the microRNA Messages in Brain Extracellular Vesicles for Early Detection of Neurodevelopmental Disorders

The prevention of neurodevelopmental disorders (NDD) of prenatal origin suffers from the lack of objective tools for early detection of susceptible individuals and the long time lag, usually in years, between the neurotoxic exposure and the diagnosis of mental dysfunction. Human data on the effects of alcohol, lead, and mercury and experimental data from animals on developmental neurotoxins and their long-term behavioral effects have achieved a critical mass, leading to the concept of the Developmental Origin of Health and Disease (DOHaD). However, there is currently no way to evaluate the degree of brain damage early after birth. We propose that extracellular vesicles (EVs) and particularly exosomes, released by brain cells into the fetal blood, may offer us a non-invasive means of assessing brain damage by neurotoxins. We are inspired by the strategy applied by Alan Turing (a cryptanalyst working for the British government), who created a first computer to decrypt German intelligence communications during World War II. Given the growing evidence that microRNAs (miRNAs), which are among the molecules carried by EVs, are involved in cell-cell communication, we propose that decrypting messages from EVs can allow us to detect damage thus offering an opportunity to cure, reverse, or prevent the development of NDD. This review summarizes recent findings on miRNAs associated with selected environmental toxicants known to be involved in the pathophysiology of NDD.

The genetic epidemiology of substance use disorder: A review

BACKGROUND

Substance use disorder (SUD) remains a significant public health issue. A greater understanding of how genes and environment interact to regulate phenotypes comprising SUD will facilitate directed treatments and prevention.

METHODS

The literature studying the neurobiological correlates of SUD with a focus on the genetic and environmental influences underlying these mechanisms was reviewed. Results from twin/family, human genetic association, gene-environment interaction, epigenetic literature, phenome-wide association studies are summarized for alcohol, nicotine, cannabinoids, cocaine, and opioids.

RESULTS

There are substantial genetic influences on SUD that are expected to influence multiple neurotransmission pathways, and these influences are particularly important within the dopaminergic system. Genetic influences involved in other aspects of SUD etiology including drug processing and metabolism are also identified. Studies of gene-environment interaction emphasize the importance of environmental context in SUD. Epigenetic studies indicate drug-specific changes in gene expression as well as differences in gene expression related to the use of multiple substances. Further, gene expression is expected to differ by stage of SUD such as substance initiation versus chronic substance use. While a substantial literature has developed for alcohol and nicotine use disorders, there is comparatively less information for other commonly abused substances.

CONCLUSIONS

A better understanding of genetically-mediated mechanisms involved in the neurobiology of SUD provides increased opportunity to develop behavioral and biologically based treatment and prevention of SUD.