Targeting the intracellular signaling "STOP" and "GO" pathways for the treatment of alcohol use disorders

BDNF in Ventrolateral Orbitofrontal Cortex to Dorsolateral Striatum Circuit Moderates Alcohol Consumption and Gates Alcohol Habit

BDNF plays a crucial role in shaping the structure and function of neurons. BDNF signaling in the dorsolateral striatum (DLS) is part of an endogenous pathway that protects against the development of alcohol use disorder (AUD). Dysregulation of BDNF levels in the cortex or dysfunction of BDNF/TrkB signaling in the DLS results in the escalation of alcohol drinking and compulsive alcohol use. The major source of BDNF in the striatum is the prefrontal cortex. We identified a small ensemble of BDNF-positive neurons in the ventrolateral orbitofrontal cortex (vlOFC), a region involved in AUD, that extend axonal projections to the DLS. We speculated that BDNF in vlOFC-to-DLS circuit may play a role in limiting alcohol drinking and that heavy alcohol use disrupts this protective pathway. We found that BDNF expression is reduced in the vlOFC of male but not female mice after long-term cycles of binge alcohol drinking and withdrawal. We discovered that overexpression of BDNF in vlOFC-to-DLS but not in vlOFC-to-dorsomedial striatum (DMS) or M2 motor cortex-to-DLS circuit reduces alcohol but not sucrose intake and preference. The DLS plays a major role in habitual behaviors. We hypothesized that BDNF in vlOFC-to-DLS circuitry controls alcohol intake by gating habitual alcohol seeking. We found that BDNF over-expression in vlOFC-to-DLS circuit and systemic administration of BDNF receptor TrkB agonist, LM22A-4, biases habitually trained mice towards goal-directed alcohol seeking. Together, our data suggest that BDNF in a small ensemble of vlOFC-to-DLS neurons gates alcohol intake by attenuating habitual alcohol seeking.

Inhibition of ERK1/2 or CRMP2 Disrupts Alcohol Memory Reconsolidation and Prevents Relapse in Rats

Relapse to alcohol abuse, often caused by cue-induced alcohol craving, is a major challenge in alcohol addiction treatment. Therefore, disrupting the cue-alcohol memories can suppress relapse. Upon retrieval, memories transiently destabilize before they reconsolidate in a process that requires protein synthesis. Evidence suggests that the mammalian target of rapamycin complex 1 (mTORC1), governing the translation of a subset of dendritic proteins, is crucial for memory reconsolidation. Here, we explored the involvement of two regulatory pathways of mTORC1, phosphoinositide 3-kinase (PI3K)-AKT and extracellular regulated kinase 1/2 (ERK1/2), in the reconsolidation process in a rat (Wistar) model of alcohol self-administration. We found that retrieval of alcohol memories using an odor-taste cue increased ERK1/2 activation in the amygdala, while the PI3K-AKT pathway remained unaffected. Importantly, ERK1/2 inhibition after alcohol memory retrieval impaired alcohol-memory reconsolidation and led to long-lasting relapse suppression. Attenuation of relapse was also induced by post-retrieval administration of lacosamide, an inhibitor of collapsin response mediator protein-2 (CRMP2)-a translational product of mTORC1. Together, our findings indicate the crucial role of ERK1/2 and CRMP2 in the reconsolidation of alcohol memories, with their inhibition as potential treatment targets for relapse prevention.

Participation of cAMP-Mediated Signaling Transduction in the Regulation of the Secretory Function of Neuroglia during Ethanol-Induced Neurodegeneration

We studied the involvement of cAMP and PKA in the regulation of the secretion of neurotrophic growth factors by macro-and microglial cells in the model of ethanol-induced neurodegeneration in vitro and in vivo. The stimulating role of cAMP in the secretion of neurotrophins by intact astrocytes and oligodendrocytes was shown, while PKA does not participate in this process. On the contrary, the inhibitory role of cAMP (implemented via PKA activation) in the production of neurogenesis stimulators by microglial cells under conditions of optimal vital activity was found. Under the influence of ethanol, the role of cAMP and PKA in the production of growth factors by macroglial cells was considerably changed. The involvement of PKA in the cAMP-dependent signaling pathways and inversion of the role of this signaling pathway in the implementation of the neurotrophic secretory function of astrocytes and oligodendrocytes, respectively, directly exposed to ethanol in vitro were noted. Long-term exposure of the nervous tissue to ethanol in vivo led to the loss of the stimulating role of cAMP/PKA signaling on neurotrophin secretion by macroglial cells without affecting its inhibitory role in the regulation of this function in microglial cells.

Molecular Toxicology and Pathophysiology of Comorbid Alcohol Use Disorder and Post-Traumatic Stress Disorder Associated with Traumatic Brain Injury

The increasing comorbidity of alcohol use disorder (AUD) and post-traumatic stress disorder (PTSD) associated with traumatic brain injury (TBI) is a serious medical, economic, and social issue. However, the molecular toxicology and pathophysiological mechanisms of comorbid AUD and PTSD are not well understood and the identification of the comorbidity state markers is significantly challenging. This review summarizes the main characteristics of comorbidity between AUD and PTSD (AUD/PTSD) and highlights the significance of a comprehensive understanding of the molecular toxicology and pathophysiological mechanisms of AUD/PTSD, particularly following TBI, with a focus on the role of metabolomics, inflammation, neuroendocrine, signal transduction pathways, and genetic regulation. Instead of a separate disease state, a comprehensive examination of comorbid AUD and PTSD is emphasized by considering additive and synergistic interactions between the two diseases. Finally, we propose several hypotheses of molecular mechanisms for AUD/PTSD and discuss potential future research directions that may provide new insights and translational application opportunities.

Implication of the PTN/RPTPβ/ζ Signaling Pathway in Acute Ethanol Neuroinflammation in Both Sexes: A Comparative Study with LPS

Binge drinking during adolescence increases the risk of alcohol use disorder, possibly by involving alterations of neuroimmune responses. Pleiotrophin (PTN) is a cytokine that inhibits Receptor Protein Tyrosine Phosphatase (RPTP) β/ζ. PTN and MY10, an RPTPβ/ζ pharmacological inhibitor, modulate ethanol behavioral and microglial responses in adult mice. Now, to study the contribution of endogenous PTN and the implication of its receptor RPTPβ/ζ in the neuroinflammatory response in the prefrontal cortex (PFC) after acute ethanol exposure in adolescence, we used MY10 (60 mg/kg) treatment and mice with transgenic PTN overexpression in the brain. Cytokine levels by X-MAP technology and gene expression of neuroinflammatory markers were determined 18 h after ethanol administration (6 g/kg) and compared with determinations performed 18 h after LPS administration (5 g/kg). Our data indicate that Ccl2, Il6, and Tnfa play important roles as mediators of PTN modulatory actions on the effects of ethanol in the adolescent PFC. The data suggest PTN and RPTPβ/ζ as targets to differentially modulate neuroinflammation in different contexts. In this regard, we identified for the first time important sex differences that affect the ability of the PTN/RPTPβ/ζ signaling pathway to modulate ethanol and LPS actions in the adolescent mouse brain.

Inhibition of RPTPβ/ζ reduces chronic ethanol intake in adolescent mice and modulates ethanol effects on hippocampal neurogenesis and glial responses in a sex-dependent manner

Pleiotrophin (PTN) is a cytokine that modulates ethanol drinking and reward and regulates glial responses in different contexts. PTN is an inhibitor of Receptor Protein Tyrosine Phosphatase (RPTP) β/ζ. Inhibition of RPTPβ/ζ reduces binge-like drinking in adult male mice. Whether inhibition of RPTPβ/ζ is effective in reducing ethanol consumption during adolescence and in both sexes remained to be studied. In this work, male and female adolescent mice underwent an intermittent access to ethanol (IAE) 2-bottle choice protocol. Treatment with MY10 (60 mg/kg, i.g.), a small-molecule RPTPβ/ζ inhibitor, reduced chronic 3-week ethanol consumption only in male mice. We detected an ethanol-induced overall decrease in hippocampal GFAPir and Iba1ir, independently of the treatment received, suggesting that RPTPβ/ζ is not key in the regulation of IAE-induced glial responses. However, we found a significant negative correlation between the size of microglial cells and the number of hippocampal neuronal progenitors only in male mice after IAE. This correlation was disrupted by treatment with MY10 before each drinking session, which may be related to the ability of MY10 to regulate the intensity of the perineuronal nets (PNNs) in the hippocampus in a sex-dependent manner. The data show for the first time that inhibition of RPTPβ/ζ reduces chronic voluntary ethanol consumption in adolescent mice in a sex-dependent manner. In addition, we show evidence for sex-specific differences in the effects of IAE on glial responses and hippocampal neurogenesis, which may be related to different actions of the RPTPβ/ζ signalling pathway in the brains of male and female mice.

Role of BDNF in Neuroplasticity Associated with Alcohol Dependence

Abstract

Chronic alcohol consumption is characterized by disturbances of neuroplasticity. Brain-derived neurotrophic factor (BDNF) is believed to be critically involved in this process. Here we aimed to review actual experimental and clinical data related to BDNF participation in neuroplasticity in the context of alcohol dependence. As has been shown in experiments with rodents, alcohol consumption is accompanied by the brain region-specific changes of BDNF expression and by structural and behavioral impairments. BDNF reverses aberrant neuroplasticity observed during alcohol intoxication. According to the clinical data parameters associated with BDNF demonstrate close correlation with neuroplastic changes accompanying alcohol dependence. In particular, the rs6265 polymorphism within the BDNF gene is associated with macrostructural changes in the brain, while peripheral BDNF concentration may be associated with anxiety, depression, and cognitive impairment. Thus, BDNF is involved in the mechanisms of alcohol-induced changes of neuroplasticity, and polymorphisms within the BDNF gene and peripheral BDNF concentration may serve as biomarkers, diagnostic or prognostic factors in treatment of alcohol abuse.

Receptor protein tyrosine phosphatase β/ζ regulates loss of neurogenesis in the mouse hippocampus following adolescent acute ethanol exposure

Adolescence is a critical period for brain maturation in which this organ is more vulnerable to the damaging effects of ethanol. Administration of ethanol in mice induces a rapid cerebral upregulation of pleiotrophin (PTN), a cytokine that regulates the neuroinflammatory processes induced by different insults and the behavioral effects of ethanol. PTN binds Receptor Protein Tyrosine Phosphatase (RPTP) β/ζ and inhibits its phosphatase activity, suggesting that RPTPβ/ζ may be involved in the regulation of ethanol effects. To test this hypothesis, we have treated adolescent mice with the RPTPβ/ζ inhibitor MY10 (60 mg/kg) before an acute ethanol (6 g/kg) administration. Treatment with MY10 completely prevented the ethanol-induced neurogenic loss in the hippocampus of both male and female mice. In flow cytometry studies, ethanol tended to increase the number of NeuN+/activated Caspase-3+ cells particularly in female mice, but no significant effects were found. Ethanol increased Iba1+ cell area and the total marked area in the hippocampus of female mice, suggesting sex differences in ethanol-induced microgliosis. In addition, ethanol reduced the circulating levels of IL-6 and IL-10 in both sexes, although this reduction was only found significant in males and not affected by MY10 treatment. Interestingly, MY10 alone increased the total marked area and the number of Iba1+ cells only in the female hippocampus, but tended to reduce the circulating levels of TNF-α only in male mice. In summary, the data identify a novel modulatory role of RPTPβ/ζ on ethanol-induced loss of hippocampal neurogenesis, which seems unrelated to glial and inflammatory responses. The data also suggest sex differences in RPTPβ/ζ function that may be relevant to immune responses and ethanol-induced microglial responses.

[Contents of BDNF, miR-30a-5p and miR-122 during alcohol withdrawal syndrome]

Some BDNF (brain-derived neurotrophic factor)-targeted microRNAs such as miR-30a-5p associate with alcohol dependence phenomenon however their relationship with AWS is not described. We aimed to measure serum BDNF concentration and relative content of miR-30a-5p over the course of alcohol abstinence and compare obtained results with clinics of AWS. Additionally, we studied relative serum content of miR-30a-5p, a microRNA which does not target BDNF but relates to alcohol use disorder. Serum BDNF concentration increased over the course of alcohol abstinence, contrary relative content of miR-122 but not miR-30a-5p decreased. Moreover, during AWS miR-122 but miR-30a-5p negatively correlated with serum BDNF concentrations. Relative content of miR-122 negatively correlated with depression and state anxiety levels on 8th day of abstinence. According to multiple regressions on 21st day of abstinence alcohol craving and cognitive disturbances may be predictors of serum BDNF concentration, and vice versa. Thus, serum BDNF concentration and relative content of miR-122 associate with some aspects of AWS clinics and may dynamically reflect AWS severity.

The Role of JAK and STAT3 in Regulation of Secretory Function of Neuroglial Cells of Different Types in Ethanol-Induced Neurodegenerationt

The effects of JAK and STAT3 inhibitors on the production of neurotrophic growth factors by different types of neuroglial cells were studied under conditions of in vitro and in vivo models of ethanol-induced neurodegeneration. It was shown that these signaling molecules do not participate in the secretion of neurotrophins by intact astrocytes and oligodendrocytes. The inhibitory role of JAK in the regulation of this function of microglial cells was revealed. We also revealed significant changes in the role of JAK and the presence of STAT3 specifics within the framework of JAK/STAT signaling in the production of growth factors by various glial elements under the influence of ethanol. Neurodegeneration modeled in vitro led to the appearance of a "negative" effect of STAT3 on the production of neurogenesis stimulants by all types of glial cells. Moreover, the role of STAT3 in oligodendrocytes and microglial cells generally corresponded to that of JAK/STAT signaling. In astrocytes, only selective blockade of STAT3 (but not JAK) led to stimulation of their function. In mice subjected to prolonged peroral alcoholization, the neuroglial responses to the pharmacological regulation of JAK/STAT signaling were different. An inversion of the role of JAK and STAT3 in the production of neurotrophins by oligodendrocytes was noted. In addition, JAK inhibitor did not stimulate secretory function of microglial cells under conditions of prolonged exposure to ethanol in vivo.

Alcohol and the brain: from genes to circuits

Alcohol use produces wide-ranging and diverse effects on the central nervous system. It influences intracellular signaling mechanisms, leading to changes in gene expression, chromatin remodeling, and translation. As a result of these molecular alterations, alcohol affects the activity of neuronal circuits. Together, these mechanisms produce long-lasting cellular adaptations in the brain that in turn can drive the development and maintenance of alcohol use disorder (AUD). We provide an update on alcohol research, focusing on multiple levels of alcohol-induced adaptations, from intracellular changes to changes in neural circuits. A better understanding of how alcohol affects these diverse and interlinked mechanisms may lead to the identification of novel therapeutic targets and to the development of much-needed novel and efficacious treatment options.

Trends in kinase drug discovery: targets, indications and inhibitor design

The FDA approval of imatinib in 2001 was a breakthrough in molecularly targeted cancer therapy and heralded the emergence of kinase inhibitors as a key drug class in the oncology area and beyond. Twenty years on, this article analyses the landscape of approved and investigational therapies that target kinases and trends within it, including the most popular targets of kinase inhibitors and their expanding range of indications. There are currently 71 small-molecule kinase inhibitors (SMKIs) approved by the FDA and an additional 16 SMKIs approved by other regulatory agencies. Although oncology is still the predominant area for their application, there have been important approvals for indications such as rheumatoid arthritis, and one-third of the SMKIs in clinical development address disorders beyond oncology. Information on clinical trials of SMKIs reveals that approximately 110 novel kinases are currently being explored as targets, which together with the approximately 45 targets of approved kinase inhibitors represent only about 30% of the human kinome, indicating that there are still substantial unexplored opportunities for this drug class. We also discuss trends in kinase inhibitor design, including the development of allosteric and covalent inhibitors, bifunctional inhibitors and chemical degraders.

Role of MAPK ERK1/2 and p38 in the Regulation of Secretory Functions of Different Populations of Neuroglia in Ethanol-Induced Neurodegeneration

We studied the participation of ERK1/2 and p38 in secretion of neurotrophic growth factors by various types of neuroglia under conditions of in vitro and in vivo modeled ethanol-induced neurodegeneration. The inhibitory role of these protein kinases in the production of neurotrophins by intact astrocytes and the absence of their participation in the regulation of functions of oligodendrocytes and microglial cells were shown. Under conditions of ethanol neurotoxicity, the role of ERK1/2 and p38 in the production of growth factors by glial elements was significantly changed. Neurodegeneration modeled in vitro led to inversion of the role of both protein kinases in the secretion of neurotrophins by astroglia and inhibition of the cytokine-synthesizing function of oligodendrocytes and microglial cells by ERK1/2 and p38. In mice receiving ethanol per os for a long time (as well as in cells in vitro exposed to ethanol), mitogen-activated kinases stimulated the function of astrocytes and inhibited the production of growth factors by microglial cells. At the same time, chronic alcoholization was accompanied by the appearance of the stimulating role of ERK1/2 and p38 in the implementation of the secretory function by oligodendrocytes.

Brain-specific inhibition of mTORC1 eliminates side effects resulting from mTORC1 blockade in the periphery and reduces alcohol intake in mice

Alcohol Use Disorder (AUD) affects a large portion of the population. Unfortunately, efficacious medications to treat the disease are limited. Studies in rodents suggest that mTORC1 plays a crucial role in mechanisms underlying phenotypes such as heavy alcohol intake, habit, and relapse. Thus, mTORC1 inhibitors, which are used in the clinic, are promising therapeutic agents to treat AUD. However, chronic inhibition of mTORC1 in the periphery produces undesirable side effects, which limit their potential use for the treatment of AUD. To overcome these limitations, we designed a binary drug strategy in which male mice were treated with the mTORC1 inhibitor RapaLink-1 together with a small molecule (RapaBlock) to protect mTORC1 activity in the periphery. We show that whereas RapaLink-1 administration blocked mTORC1 activation in the liver, RapaBlock abolished the inhibitory action of Rapalink-1. RapaBlock also prevented the adverse side effects produced by chronic inhibition of mTORC1. Importantly, co-administration of RapaLink-1 and RapaBlock inhibited alcohol-dependent mTORC1 activation in the nucleus accumbens and attenuated alcohol seeking and drinking.

Differential correlation of serum BDNF and microRNA content in rats with rapid or late onset of heavy alcohol use

Heavy alcohol use reduces the levels of the brain-derived neurotrophic factor (BDNF) in the prefrontal cortex of rodents through the upregulation of microRNAs (miRs) targeting BDNF mRNA. In humans, an inverse correlation exists between circulating blood levels of BDNF and the severity of psychiatric disorders including alcohol abuse. Here, we set out to determine whether a history of heavy alcohol use produces comparable alterations in the blood of rats. We used an intermittent access to 20% alcohol using the two-bottle choice paradigm (IA20%2BC) and measured circulating levels of BDNF protein and miRs targeting BDNF in the serum of Long-Evans rats before and after 8 weeks of excessive alcohol intake. We observed that the drinking profile of heavy alcohol users is not unified, whereas 70% of the rats gradually escalate their alcohol intake (late onset), and 30% of alcohol users exhibit a very rapid onset of drinking (rapid onset). We found that serum BDNF levels are negatively correlated with alcohol intake in both rapid onset and late onset rats. In contrast, increased expression of the miRs targeting BDNF, miR30a-5p, miR-195-5p, miR191-5p and miR206-3p, was detected only in the rapid onset rats. Finally, we report that the alcohol-dependent molecular changes are not due to alterations in platelet number. Together, these data suggest that rats exhibit both late and rapid onset of alcohol intake. We further show that heavy alcohol use produces comparable changes in BDNF protein levels in both groups. However, circulating microRNAs are responsive to alcohol only in the rapid onset rats.

Growth Factors and Alcohol Use Disorder

Neurotrophic growth factors were originally characterized for their support in neuronal differentiation, outgrowth, and survival during development. However, it has been acknowledged that they also play a vital role in the adult brain. Abnormalities in growth factors have been implicated in a variety of neurological and psychiatric disorders, including alcohol use disorder (AUD). This work focuses on the interaction between alcohol and growth factors. We review literature suggesting that several growth factors play a unique role in the regulation of alcohol consumption, and that breakdown in these growth factor systems is linked to the development of AUD. Specifically, we focus on the brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), fibroblast growth factor 2 (FGF2), and insulin growth factor 1 (IGF-1). We also review the literature on the potential role of midkine (MDK) and pleiotrophin (PTN) and their receptor, anaplastic lymphoma kinase (ALK), in AUD. We show that alcohol alters the expression of these growth factors or their receptors in brain regions previously implicated in addiction, and that manipulations on these growth factors and their downstream signaling can affect alcohol-drinking behaviors in animal models. We conclude that there is a need for translational and clinical research to assess the therapeutic potential of new pharmacotherapies targeting these systems.

Investigating the link between serum concentrations of brain-derived neurotrophic factor and behavioral measures in anxious alcohol-dependent individuals

Brain-derived neurotrophic factor (BDNF) plays a role in different neurophysiological processes, including those involved in alcohol- and anxiety-related behaviors. Preclinical and clinical studies indicate that chronic excessive alcohol use leads to a downregulation of BDNF production in the periphery and in the brain. In addition, a decrease in BDNF concentrations in the blood has been reported to be associated with increased anxiety levels. Non-treatment-seeking alcohol-dependent individuals with high trait anxiety were studied to assess whether serum BDNF concentrations may be linked to self-reported levels of alcohol drinking, anxiety, and other behavioral measures. Participants had a current diagnosis of alcohol dependence, high trait anxiety score, and were not seeking treatment for alcohol dependence or anxiety. A fasting blood sample was collected from each participant and serum BDNF was measured using an enzyme-linked immunosorbent assay (ELISA). Behavioral data were collected on the same day, including measures of alcohol drinking, craving, dependence severity, and anxiety. Bivariate correlations were run between BDNF levels and behavioral measures. Serum BDNF concentrations were negatively correlated with average drinks per drinking days (r = -0.41, p = 0.02) and positively correlated with obsessive-compulsive drinking scale (r = 0.48, p = 0.007) and state-trait anxiety inventory (r = 0.52, p = 0.003) scores. These findings shed light on the possible role of the BDNF system in the neurobiology of alcohol- and anxiety-related behaviors.

Evolution of BDNF serum levels during the first six months after alcohol withdrawal

OBJECTIVES

Brain-Derived Neurotrophic Factor (BDNF) has been associated with alcohol dependence and appear to vary after withdrawal, although the link with the withdrawal outcome on the long term is unknown. We aimed to assess the evolution of BDNF levels during the six months following withdrawal and determine the association with the status of alcohol consumption.

METHODS

Serum BDNF levels of alcohol-dependent patients (n = 248) and biological and clinical parameters were determined at the time of alcohol cessation (D0), 14 days (D14), 28 days (D28), and 2, 4, and 6 months after (M2, M4, M6).

RESULTS

Abstinence decreased during follow-up and was 31.9% after six months. BDNF levels increased by 14 days after withdrawal and remained elevated throughout the six-month period, independently of alcohol consumption. Serum BDNF levels evolved over time (p < 0.0001), with a correlation between BDNF and GGT levels. The prescription of baclofen at the time of withdrawal was associated with higher serum BDNF levels throughout the follow-up and that of anti-inflammatory drugs with lower BDNF levels.

CONCLUSIONS

A link between BDNF levels, liver function, and the inflammatory state in the context of alcohol abuse and not only with alcohol dependence itself is proposed.

BDNF levels and liver stiffness in subjects with alcohol use disorder: Evaluation after alcohol withdrawal

Background: Brain-derived neurotrophic factor (BDNF) plays a key role in the processes of withdrawal and addiction in alcohol use disorder (AUD), and is also involved in liver homeostasis. The role of BDNF in liver damage and its link with liver stiffness are not known. We hypothesize that serum BDNF levels are linked to changes in hepatic elasticity, both of which depend on variations in alcohol consumption.Objectives: We aimed to study the evolution of BDNF levels and changes in the liver stiffness (LS) of AUD subjects, within two months following withdrawal.Methods: We measured LS by FibroScan® (as an indicator of the degree of liver fibrosis), gamma glutamyl transferase (GGT) levels (as a nonspecific but sensitive marker of liver status) and serum BDNF levels of 62 alcohol-dependent subjects without previously identified liver complications. Measures were obtained at the time of withdrawal (M0) and two months later (M2). Results: BDNF levels increased after alcohol withdrawal and small variations of LS were observed. BDNF values increased significantly according to fibrosis stages measured by LS (p = .028 at M0), and were predicted by GGT levels in a regression model (p = .007 at M0 and p = .003 at M2).Conclusion: In AUD, BDNF levels were associated with measured LS when divided into fibrosis risk categories. Changes in LS and BDNF levels after alcohol withdrawal may be related to changes in homeostatic mechanisms, in addition to those of liver status.

mTORC1 pathway is involved in the kappa opioid receptor activation-induced increase in excessive alcohol drinking in mice

KOP-r agonist U50,488H produces strong aversion and anxiety/depression-like behaviors that enhance alcohol intake and promote alcohol seeking and relapse-like drinking in rodents. Mammalian target of rapamycin complex 1 (mTORC1) pathway in mouse striatum is highly involved in excessive alcohol intake and seeking, and in the U50,488H-induced conditioned place aversion. Therefore, we hypothesized that KOP-r activation increases alcohol consumption through the mTORC1 activation. This study focuses on: (1) how chronic excessive alcohol drinking (4-day drinking-in-the-dark paradigm followed by 3-week chronic intermittent access drinking paradigm [two-bottle choice, 24-h access every other day]) affected nuclear transcript levels of the mTORC1 pathway genes in mouse nucleus accumbens shell (NAcs), using transcriptome-wide RNA sequencing analysis; and (2) whether selective mTORC1 inhibitor rapamycin could alter excessive alcohol drinking and prevent U50,488H-promoted alcohol intake. Thirteen nuclear transcripts of mTORC1 pathway genes showed significant up-regulation in the NAcs, with two genes down-regulated, after excessive alcohol drinking, suggesting the mTORC1 pathway was profoundly disrupted. Single administration of rapamycin decreased alcohol drinking in a dose-dependent manner. U50,488H increased alcohol drinking, and pretreatment with rapamycin, at a dose lower than effective doses, blocked the U50,488H-promoted alcohol intake in a dose-dependent manner, indicating a mTORC1-mediated mechanism. Our results provide supportive and direct evidence relevant to the transcriptional profiling of the critical mTORC1 genes in mouse NAc shell: with functional and pharmacological effects of rapamycin, altered nuclear transcripts in the mTORC1 signaling pathway after excessive alcohol drinking may contribute to increased alcohol intake triggered by KOP-r activation.

Inhibition of Receptor Protein Tyrosine Phosphatase β/ζ Reduces Alcohol Intake in Rats

BACKGROUND

Pleiotrophin (PTN) and midkine (MK) are cytokines that are up-regulated in the prefrontal cortex (PFC) after alcohol administration and have been shown to reduce alcohol intake and reward. Both cytokines are endogenous inhibitors of receptor protein tyrosine phosphatase (RPTP) β/ζ (a.k.a. PTPRZ1). Recently, a new compound named MY10 was designed with the aim of mimicking the activity of PTN and MK. MY10 has already shown promising results regulating alcohol-related behaviors in mice.

METHODS

We have now tested the effects of MY10 on alcohol operant self-administration and Drinking In the Dark-Multiple Scheduled Access (DID-MSA) paradigms in rats. Gene expression of relevant genes in the PTN/MK signaling pathway in the PFC was analyzed by real-time PCR.

RESULTS

MY10, at the highest dose tested (100 mg/kg), reduced alcohol consumption in the alcohol operant self-administration paradigm (p = 0.040). In the DID-MSA paradigm, rats drank significantly less alcohol (p = 0.019) and showed a significant decrease in alcohol preference (p = 0.002). We observed that the longer the exposure to alcohol, the greater the suppressing effects of MY10 on alcohol consumption. It was demonstrated that the effects of MY10 were specific to alcohol since saccharin intake was not affected by MY10 (p = 0.804). MY10 prevented the alcohol-induced down-regulation of Ptprz1 (p = 0.004) and anaplastic lymphoma kinase (Alk; p = 0.013) expression.

CONCLUSIONS

Our results support and provide further evidence regarding the efficacy of MY10 on alcohol-related behaviors and suggest the consideration of the blockade of RPTPβ/ζ as a target for reducing excessive alcohol consumption.

Inhibition of FGF Receptor-1 Suppresses Alcohol Consumption: Role of PI3 Kinase Signaling in Dorsomedial Striatum

Excessive alcohol intake leads to mesostriatal neuroadaptations, and to addiction phenotypes. We recently found in rodents that alcohol increases fibroblast growth factor 2 (FGF2) expression in the dorsomedial striatum (DMS), which promotes alcohol consumption. Here, we show that systemic or intra-DMS blockade of the FGF2 receptor, FGF receptor-1 (FGFR1), suppresses alcohol consumption, and that the effects of FGF2-FGFR1 on alcohol drinking are mediated via the phosphoinositide 3 kinase (PI3K) signaling pathway. Specifically, we found that sub-chronic alcohol treatment (7 d × 2.5 g/kg, i.p.) increased Fgfr1 mRNA expression in the dorsal hippocampus and dorsal striatum. However, prolonged and excessive voluntary alcohol consumption in a two-bottle choice procedure increased Fgfr1 expression selectively in DMS. Importantly, systemic administration of the FGFR1 inhibitor PD173074 to mice, as well as its infusion into the DMS of rats, decreased alcohol consumption and preference, with no effects on natural reward consumption. Finally, inhibition of the PI3K, but not of the mitogen-activated protein kinase (MAPK) signaling pathway, blocked the effects of FGF2 on alcohol intake and preference. Our results suggest that activation of FGFR1 by FGF2 in the DMS leads to activation of the PI3K signaling pathway, which promotes excessive alcohol consumption, and that inhibition of FGFR1 may provide a novel therapeutic target for alcohol use disorder.SIGNIFICANCE STATEMENT Long-term alcohol consumption causes neuroadaptations in the mesostriatal reward system, leading to addiction-related behaviors. We recently showed that alcohol upregulates the expression of fibroblast growth factor 2 (FGF2) in dorsomedial striatum (DMS) or rats and mice, and in turn, FGF2 increases alcohol consumption. Here, we show that long-term alcohol intake also increases the expression of the FGF2 receptor, FGFR1 in the DMS. Importantly, inhibition of FGFR1 activity by a selective receptor antagonist reduces alcohol drinking, when given systemically or directly into the DMS. We further show that the effects of FGF2-FGFR1 on alcohol drinking are mediated via activation of the PI3K intracellular signaling pathway, providing an insight on the mechanism for this effect.

Brain Regional and Temporal Changes in BDNF mRNA and microRNA-206 Expression in Mice Exposed to Repeated Cycles of Chronic Intermittent Ethanol and Forced Swim Stress

Brain-derived neurotrophic factor (BDNF) expression and signaling activity in brain are influenced by chronic ethanol and stress. We previously demonstrated reduced Bdnf mRNA levels in the medial prefrontal cortex (mPFC) following chronic ethanol treatment and forced swim stress (FSS) enhanced escalated drinking associated with chronic ethanol exposure. The present study examined the effects of chronic ethanol and FSS exposure, alone and in combination, on Bdnf mRNA expression in different brain regions, including mPFC, central amygdala (CeA), and hippocampus (HPC). Additionally, since microRNA-206 has been shown to negatively regulate BDNF expression, the effects of chronic ethanol and FSS on its expression in the target brain regions were examined. Mice received four weekly cycles of chronic intermittent ethanol (CIE) vapor or air exposure and then starting 72-h later, the mice received either a single or 5 daily 10-min FSS sessions (or left undisturbed). Brain tissue samples were collected 4-h following final FSS testing and Bdnf mRNA and miR-206 levels were determined by qPCR assay. Results indicated dynamic brain regional and time-dependent changes in Bdnf mRNA and miR-206 expression. In general, CIE and FSS exposure reduced Bdnf mRNA expression while miR-206 levels were increased in the mPFC, CeA, and HPC. Further, in many instances, these effects were more robust in mice that experienced both CIE and FSS treatments. These results have important implications for the potential link between BDNF signaling in the brain and ethanol consumption related to stress interactions with chronic ethanol experience.