Sexually dimorphic role for insular perineuronal nets in aversion-resistant alcohol consumption

Compulsive alcohol drinking is a key symptom of alcohol use disorder (AUD) that is particularly resistant to treatment. An understanding of the biological factors that underly compulsive drinking will allow for the development of new therapeutic targets for AUD. One animal model of compulsive alcohol drinking involves the addition of bitter-tasting quinine to an ethanol solution and measuring the willingness of the animal to consume ethanol despite the aversive taste. Previous studies have demonstrated that this type of aversion-resistant drinking is modulated in the insular cortex of male mice by specialized condensed extracellular matrix known as perineuronal nets (PNNs), which form a lattice-like structure around parvalbumin-expressing neurons in the cortex. Several laboratories have shown that female mice exhibit higher levels of aversion-resistant ethanol intake, but the role of PNNs in females in this behavior has not been examined. Here we compared PNNs in the insula of male and female mice and determined if disrupting PNNs in female mice would alter aversion-resistant ethanol intake. PNNs were visualized in the insula by fluorescent labeling with Wisteria floribunda agglutinin (WFA) and disrupted in the insula by microinjecting chondroitinase ABC, an enzyme that digests the chondroitin sulfate glycosaminoglycan component of PNNs. Mice were tested for aversion-resistant ethanol consumption by the addition of sequentially increasing concentrations of quinine to the ethanol in a two-bottle choice drinking in the dark procedure. PNN staining intensity was higher in the insula of female compared to male mice, suggesting that PNNs in females might contribute to elevated aversion-resistant drinking. However, disruption of PNNs had limited effect on aversion-resistant drinking in females. In addition, activation of the insula during aversion-resistant drinking, as measured by c-fos immunohistochemistry, was lower in female mice than in males. Taken together, these results suggest that neural mechanisms underlying aversion-resistant ethanol consumption differ in males and females.

Sexually Dimorphic Role for Insular Perineuronal Nets in Aversion-Resistant Ethanol Consumption

Compulsive alcohol drinking is a key symptom of alcohol use disorder (AUD) that is particularly resistant to treatment. An understanding of the biological factors that underly compulsive drinking will allow for the development of new therapeutic targets for AUD. One animal model of compulsive alcohol drinking involves the addition of bitter-tasting quinine to an ethanol solution and measuring the willingness of the animal to consume ethanol despite the aversive taste. Previous studies have demonstrated that this type of aversion-resistant drinking is modulated in the insular cortex of male mice by specialized condensed extracellular matrix known as perineuronal nets (PNNs), which form a lattice-like structure around parvalbumin-expressing neurons in the cortex. Several laboratories have shown that female mice exhibit higher levels of aversion-resistant ethanol intake but the role of PNNs in females in this behavior has not been examined. Here we compared PNNs in the insula of male and female mice and determined if disrupting PNNs in female mice would alter aversion-resistant ethanol intake. PNNs were visualized in the insula by fluorescent labeling with Wisteria floribunda agglutinin (WFA) and disrupted in the insula by microinjecting chondroitinase ABC, an enzyme that digests the chondroitin sulfate glycosaminoglycan component of PNNs. Mice were tested for aversion-resistant ethanol consumption by the addition of sequentially increasing concentrations of quinine to the ethanol in a two-bottle choice drinking in the dark procedure. PNN staining intensity was higher in the insula of female compared to male mice, suggesting that PNNs in females might contribute to elevated aversion-resistant drinking. However, disruption of PNNs had limited effect on aversion-resistant drinking in females. In addition, activation of the insula during aversion-resistant drinking, as measured by c-fos immunohistochemistry, was lower in female mice than in males. Taken together, these results suggest that neural mechanisms underlying aversion-resistant ethanol consumption differ in males and females.

Alcohol use disorder is associated with DNA methylation-based shortening of telomere length and regulated by TESPA1: implications for aging

Chronic heavy alcohol consumption is associated with increased mortality and morbidity and often leads to premature aging; however, the mechanisms of alcohol-associated cellular aging are not well understood. In this study, we used DNA methylation derived telomere length (DNAmTL) as a novel approach to investigate the role of alcohol use on the aging process. DNAmTL was estimated by 140 cytosine phosphate guanines (CpG) sites in 372 individuals with alcohol use disorder (AUD) and 243 healthy controls (HC) and assessed using various endophenotypes and clinical biomarkers. Validation in an independent sample of DNAmTL on alcohol consumption was performed (N = 4219). Exploratory genome-wide association studies (GWAS) on DNAmTL were also performed to identify genetic variants contributing to DNAmTL shortening. Top GWAS findings were analyzed using in-silico expression quantitative trait loci analyses and related to structural MRI hippocampus volumes of individuals with AUD. DNAmTL was 0.11-kilobases shorter per year in AUD compared to HC after adjustment for age, sex, race, and blood cell composition (p = 4.0 × 10-12). This association was partially attenuated but remained significant after additionally adjusting for BMI, and smoking status (0.06 kilobases shorter per year, p = 0.002). DNAmTL shortening was strongly associated with chronic heavy alcohol use (ps < 0.001), elevated gamma-glutamyl transferase (GGT), and aspartate aminotransferase (AST) (ps < 0.004). Comparison of DNAmTL with PCR-based methods of assessing TL revealed positive correlations (R = 0.3, p = 2.2 × 10-5), highlighting the accuracy of DNAmTL as a biomarker. The GWAS meta-analysis identified a single nucleotide polymorphism (SNP), rs4374022 and 18 imputed ones in Thymocyte Expressed, Positive Selection Associated 1(TESPA1), at the genome-wide level (p = 3.75 × 10-8). The allele C of rs4374022 was associated with DNAmTL shortening, lower hippocampus volume (p < 0.01), and decreased mRNA expression in hippocampus tissue (p = 0.04). Our study demonstrates DNAmTL-related aging acceleration in AUD and suggests a functional role for TESPA1 in regulating DNAmTL length, possibly via the immune system with subsequent biological effects on brain regions negatively affected by alcohol and implicated in aging.

Diet-induced obesity leads to alterations in behavior and gut microbiota composition in mice

The high prevalence of obesity and associated metabolic disorders are one of the major public health problems worldwide. Among the main causal factors of obesity, excessive consumption of food rich in sugar and fat stands out due to its high energy density. The regulation of food intake relies on hypothalamic control by the action of several neuropeptides. Excessive consumption of hypercaloric diets has impact in the behavior and in the gut microbiota. In the present study, we used a high-sugar and fat (HSB) diet for 12 weeks to induce obesity in C57BL/6 mice and to investigate its effects on the gut microbiota, hypothalamic peptides, and behavior. We hypothesize that chronic consumption of HSB diet can change the behavior. Additionally, we also hypothesize that changes in gut microbiota can be associated with changes in the transcriptional regulation of hypothalamic peptides and behavior. To evaluate the gut microbiota, we performed the sequencing of 16S rRNA gene, which demonstrate that HSB diet modulates the gut microbiota with an increase in the Firmicutes and Actinobacteria phylum and a decrease of Bacteroidetes phylum. The real time qPCR revealed that HSB-fed mice presented changes in the transcriptional regulation of hypothalamic neuropeptides genes such as Npy, Gal and Galr1. The Marble-burying and Light/dark box tests also showed an alteration in anxiety and impulsive behaviors for the HSB-fed mice. Our data provides evidence that obesity induced by HSB diet consumption is associated with alterations in gut microbiota and behavior, highlighting the multifactorial characteristics of this disease.

LRRK2 Gene Variants Associated With a Higher Risk for Alcohol Dependence in Multiethnic Populations

Background: Genetics influence the vulnerability to alcohol use disorders, and among the implicated genes, three previous studies have provided evidences for the involvement of LRRK2 in alcohol dependence (AD). LRRK2 expression is broadly dysregulated in postmortem brain from AD humans, as well as in the brain of mice with alcohol dependent-like behaviors and in a zebrafish model of alcohol preference. The aim of the present study was to evaluate the association of variants in the LRRK2 gene with AD in multiethnic populations from South and North America. Methods: Alcohol-screening questionnaires [such as CAGE and Alcohol Use Disorders Identification Test (AUDIT)] were used to determine individual risk of AD. Multivariate logistic regression analyses were done in three independent populations (898 individuals from Bambuí, Brazil; 3,015 individuals from Pelotas, Brazil; and 1,316 from the United States). Linkage disequilibrium and conditional analyses, as well as in silico functional analyses, were also conducted. Results: Four LRRK2 variants were significantly associated with AD in our discovery cohort (Bambuí): rs4768231, rs4767971, rs7307310, and rs1465527. Two of these variants (rs4768231 and rs4767971) were replicated in both Pelotas and US cohorts. The consistent association signal (at the LRRK2 locus) found in populations with different genetic backgrounds reinforces the relevance of our findings. Conclusion: Taken together, these results support the notion that genetic variants in the LRRK2 locus are risk factors for AD in humans.

Identifying functionally relevant candidate genes for inflexible ethanol intake in mice and humans using a guilt-by-association approach

Gene prioritization approaches are useful tools to explore and select candidate genes in transcriptome studies. Knowing the importance of processes such as neuronal activity, intracellular signal transduction, and synapse plasticity to the development and maintenance of compulsive ethanol drinking, the aim of the present study was to explore and identify functional candidate genes associated with these processes in an animal model of inflexible pattern of ethanol intake. To do this, we applied a guilt-by-association approach, using the GUILDify and ToppGene software, in our previously published microarray data from the prefrontal cortex (PFC) and striatum of inflexible drinker mice. We then tested some of the prioritized genes that showed a tissue-specific pattern in postmortem brain tissue (PFC and nucleus accumbens (NAc)) from humans with alcohol use disorder (AUD). In the mouse brain, we prioritized 44 genes in PFC and 26 in striatum, which showed opposite regulation patterns in PFC and striatum. The most prioritized of them (i.e., Plcb1 and Prkcb in PFC, and Dnm2 and Lrrk2 in striatum) were associated with synaptic neuroplasticity, a neuroadaptation associated with excessive ethanol drinking. The identification of transcription factors among the prioritized genes suggests a crucial role for Irf4 in the pattern of regulation observed between PFC and striatum. Lastly, the differential transcription of IRF4 and LRRK2 in PFC and nucleus accumbens in postmortem brains from AUD compared to control highlights their involvement in compulsive ethanol drinking in humans and mice.

Inhibition of Lrrk2 reduces ethanol preference in a model of acute exposure in zebrafish

Due to its multifactorial and yet to be fully understood origin, ethanol addiction is a field that still requires studies for the elucidation of novel genes and pathways that potentially influence the establishment and maintenance of addiction-like phenotypes. In this context, the present study aimed to evaluate the role of the LRRK2 pathway in the modulation of ethanol preference behavior in Zebrafish (Danio rerio). Using the behavioral Conditioned Place Preference (CPP) paradigm, we accessed the preference of animals for ethanol. Next, we evaluated the transcriptional regulation of the gene lrrk2 and the receptors drd1, drd2, grin1a, gria2a, and gabbr1b in the zebrafish brain. Additionally, we used a selective inhibitor of Lrrk2 (GNE-0877) to assess the role of this gene in the preference behavior. Our results revealed four distinct ethanol preference phenotypes (Light, Heavy, Negative Reinforcement, and Inflexible), each showing different transcriptional regulation patterns of the drd1, drd2, grin1a, gria2a, and gabbr1b receptors. We showed that the lrrk2 gene was hyperregulated only in the brains of the animals with the Inflexible phenotype. Most importantly, we showed, for the first time in the context of preference for ethanol, that treatment with the GNE-0877 inhibitor modulates the transcription of the target receptor genes and reduces the preference for ethanol in the animals of the Inflexible group. This result corroborates the hypothesis that the LRRK2 pathway is involved in the inflexible preference for ethanol behavior. Lastly, we identified a possible pharmacological target for the treatment of abusive preference behavior for ethanol.

Maternal separation affects expression of stress response genes and increases vulnerability to ethanol consumption

INTRODUCTION

Maternal separation is an early life stress event associated with behavioral alterations and ethanol consumption. We aimed to expand the current understanding on the molecular mechanisms mediating the impact of postnatal stress on ethanol consumption.

METHODS

In the first experiment (T1), some of the pups were separated from their mothers for 6 hr daily (Maternal Separation group - MS), whereas the other pups remained in the cage with their respective mothers (Control group - C). In the second experiment (T2), mice from both groups were subjected to the model of free-choice between water and sucrose solution or between water and ethanol solution. Maternal behavior was assessed at the end of T1. At the end of both T1 and T2, pups were subjected to the light/dark box behavioral test and blood corticosterone concentrations were analyzed.

RESULTS

Our maternal separation protocol led to intense maternal care and affected weight gain of the animals. The expression of stress response genes was altered with higher levels of Crh and Pomc being observed in the hypothalamus, and higher levels of Crhr1, Crhr2, Htr2a and lower levels of Nr3c1 and Htr1a being observed in the hippocampus after T1. At the end of T2, we observed higher levels of Avp and Pomc in the hypothalamus, and higher levels of Crhr1, Crhr2, Nr3c1, Slc6a4, Bdnf and lower levels of Htr1a in the hippocampus. Additionally, maternal separation increased vulnerability to ethanol consumption during adolescence and induced changes in anxiety/stress-related behavior after T2. Furthermore, voluntary ethanol consumption attenuated stress response and modified expression of reward system genes: enhancing Drd1 and Drd2, and reducing Gabbr2 in the striatum.

CONCLUSION

Maternal separation induced behavioral changes and alterations in the expression of key genes involved in HPA axis and in the serotonergic and reward systems that are likely to increase vulnerability to ethanol consumption in adolescence. We demonstrated, for the first time, that ethanol consumption masked stress response by reducing the activity of the HPA axis and the serotonergic system, therefore, suggesting that adolescent mice from the MS group probably consumed ethanol for stress relieving purposes.