Non-coding RNA in alcohol use disorder by affecting synaptic plasticity

Circulating microRNA profiling identifies microRNAs linked to prediabetes associated with alcohol dependence syndrome

BACKGROUND

MicroRNAs are abundant in serum and have emerged as important regulators of gene expression, implicating them in a wide range of diseases. The purpose of this study was to discover and validate serum miRNAs in prediabetes associated with alcohol dependence syndrome (ADS).

METHOD

Serum samples from ADS patients with or without prediabetes and normoglycemic controls were subjected to microarray. Validation of identified candidate miRNAs was performed by RT-qPCR. Additionally, GO and KEGG pathway analyses were carried out to uncover target genes anticipated to be controlled by the candidate miRNAs.

RESULTS

Notably, 198, and 172 miRNAs were differentially expressed in ADS-patients with or without prediabetes compared to healthy controls, and 7 miRNAs in ADS-patients with prediabetes compared to ADS-normoglycemic patients, respectively. Furthermore, hsa-miR-320b and hsa-miR-3135b were differentially expressed exclusively in ADS-patients with prediabetes, and this was further validated. Interestingly, GO and KEGG pathway analysis revealed that genes predicted to be modulated by the candidates were considerably enriched in numerous diabetes-related biological processes and pathways.

CONCLUSION

Our findings revealed that ADS-patients with or without prediabetes have different sets of miRNAs compared to normoglycemic healthy subjects. We propose serum hsa-miR-320b and hsa-miR-3135b as potential biomarkers for the diagnosis of prediabetes in ADS-patients.

Polygenic influences on the behavioral effects of alcohol withdrawal in a mixed-ancestry population from the collaborative study on the genetics of alcoholism (COGA)

Alcohol withdrawal (AW) is a feature of alcohol use disorder that may occur in up to half of individuals with chronic, heavy alcohol consumption whenever alcohol use is abruptly stopped or significantly reduced. To date, few genes have been robustly associated with AW; this may be partly due to most studies defining AW as a binary construct despite the multiple symptoms and their range in severity from mild to severe. The current study examined the effects of genome-wide loci on a factor score for AW in high risk and community family samples in the Collaborative Study for the Genetics of Alcoholism (COGA). In addition, we tested whether differentially expressed genes associated with alcohol withdrawal in model organisms are enriched in human genome-wide association study (GWAS) effects. Analyses employed roughly equal numbers of males and females (mean age 35, standard deviation = 15; total N = 8009) and included individuals from multiple ancestral backgrounds. Genomic data were imputed to the HRC reference panel and underwent strict quality control procedures using Plink2. Analyses controlled for age, sex, and population stratification effects using ancestral principal components. We found support that AW is a polygenic disease (SNP-heritability = 0.08 [95 % CI = 0.01, 0.15; pedigree-based heritability = 0.12 [0.08,0.16]. We identified five single nucleotide variants that met genomewide significance, some of which have previously been associated with alcohol phenotypes. Gene-level analyses suggest a role for COL19A1 in AW; H-MAGMA analyses implicated 12 genes associated with AW. Cross-species enrichment analyses indicated that variation within genes identified in model organism studies explained <1 % of the phenotypic variability in human AW. Notably, the surrounding regulatory regions of model organism genes explained more variance than expected by chance, indicating that these regulatory regions and gene sets may be important for human AW. Lastly, when comparing the overlap in genes identified from the human GWAS and H-MAGMA analyses with the genes identified from the animal studies, there was modest overlap, indicating some convergence between the methods and organisms.

Alcohol reverses the effects of KCNJ6 (GIRK2) noncoding variants on excitability of human glutamatergic neurons

Synonymous and noncoding single nucleotide polymorphisms (SNPs) in the KCNJ6 gene, encoding G protein-gated inwardly rectifying potassium channel subunit 2 (GIRK2), have been linked with increased electroencephalographic frontal theta event-related oscillations (ERO) in subjects diagnosed with alcohol use disorder (AUD). To identify molecular and cellular mechanisms while retaining the appropriate genetic background, we generated induced excitatory glutamatergic neurons (iN) from iPSCs derived from four AUD-diagnosed subjects with KCNJ6 variants ("Affected: AF") and four control subjects without variants ("Unaffected: UN"). Neurons were analyzed for changes in gene expression, morphology, excitability and physiological properties. Single-cell RNA sequencing suggests that KCNJ6 AF variant neurons have altered patterns of synaptic transmission and cell projection morphogenesis. Results confirm that AF neurons express lower levels of GIRK2, have greater neurite area, and elevated excitability. Interestingly, exposure to intoxicating concentrations of ethanol induces GIRK2 expression and reverses functional effects in AF neurons. Ectopic overexpression of GIRK2 alone mimics the effect of ethanol to normalize induced excitability. We conclude that KCNJ6 variants decrease GIRK2 expression and increase excitability and that this effect can be minimized or reduced with ethanol.

Is DNA methylation in the brain a mechanism of alcohol use disorder?

Alcohol use disorder (AUD) is a worldwide problem. Unfortunately, the molecular mechanisms of alcohol misuse are still poorly understood, therefore successful therapeutic approaches are limited. Accumulating data indicate that the tendency for compulsive alcohol use is inherited, suggesting a genetic background as an important factor. However, the probability to develop AUD is also affected by life experience and environmental factors. Therefore, the epigenetic modifications that are altered over lifetime likely contribute to increased risk of alcohol misuse. Here, we review the literature looking for the link between DNA methylation in the brain, a common epigenetic modification, and AUD-related behaviors in humans, mice and rats. We sum up the main findings, identify the existing gaps in our knowledge and indicate future directions of the research.

Long Non-Coding RNAs: The New Frontier into Understanding the Etiology of Alcohol Use Disorder

Alcohol use disorder (AUD) is a complex, chronic, debilitating condition impacting millions worldwide. Genetic, environmental, and epigenetic factors are known to contribute to the development of AUD. Long non-coding RNAs (lncRNAs) are a class of regulatory RNAs, commonly referred to as the “dark matter” of the genome, with little to no protein-coding potential. LncRNAs have been implicated in numerous processes critical for cell survival, suggesting that they play important functional roles in regulating different cell processes. LncRNAs were also shown to display higher tissue specificity than protein-coding genes and have a higher abundance in the brain and central nervous system, demonstrating a possible role in the etiology of psychiatric disorders. Indeed, genetic (e.g., genome-wide association studies (GWAS)), molecular (e.g., expression quantitative trait loci (eQTL)) and epigenetic studies from postmortem brain tissues have identified a growing list of lncRNAs associated with neuropsychiatric and substance use disorders. Given that the expression patterns of lncRNAs have been associated with widespread changes in the transcriptome, including methylation, chromatin architecture, and activation or suppression of translational activity, the regulatory nature of lncRNAs may be ubiquitous and an innate component of gene regulation. In this review, we present a synopsis of the functional impact that lncRNAs may play in the etiology of AUD. We also discuss the classifications of lncRNAs, their known functional roles, and therapeutic advancements in the field of lncRNAs to further clarify the functional relationship between lncRNAs and AUD.

MicroRNA Regulation of the Environmental Impact on Adolescent Neurobehavioral Development: A Systematic Review

Adolescence is a late developmental period marked by pronounced reorganization of brain networks in which epigenetic mechanisms play a fundamental role. This brain remodeling is associated with a peculiar behavior characterized by novelty seeking and risky activities such as alcohol and drug abuse, which is associated with increased susceptibility to stress. Hence, adolescence is a vulnerable postnatal period since short- and long-term deleterious effects of alcohol drinking and drug abuse are a serious worldwide public health concern. Among several other consequences, it has been proposed that exposure to stress, alcohol, or other drugs disrupts epigenetic mechanisms mediated by small non-coding microRNAs (miRNAs). During adolescence, this modifies the expression of a variety of genes involved in neurodevelopmental processes such as proliferation, differentiation, synaptogenesis, neural plasticity, and apoptosis. Hence, the effect of miRNAs dysregulation during adolescence might contribute to a long-term impact on brain function. This systematic review focuses on the miRNA expression patterns in the adolescent rodent brain with special interest in the impact of stress and drugs such as amphetamine, cocaine, nicotine, cannabis, and ketamine. The results point to a relevant and complex role of miRNAs in the regulation of the molecular processes involved in adolescent brain development as part of a dynamic epigenetic network sensitive to environmental events with distinctive changes across adolescence. Several miRNAs have been assessed evidencing changing expression profiles during the adolescent transition which are altered by exposure to stress and drug abuse. Since this is an emerging rapidly growing field, updating the present knowledge will contribute to improving our understanding of the epigenetic regulation mechanisms involved in the neurodevelopmental changes responsible for adolescent behavior. It can be expected that increased knowledge of the molecular mechanisms mediating the effect of environmental threats during the adolescent critical developmental period will improve understanding of psychiatric and addictive disorders emerging at this stage.