Presynaptic targets for acute ethanol sensitivity

JNK Signaling Positively Regulates Acute Ethanol Tolerance in C. elegans

Alcohol use disorder (AUD) is a chronic neurobehavioral condition characterized by a cycle of tolerance development, increased consumption, and reinstated craving and seeking behaviors during withdrawal. Understanding the intricate mechanisms of AUD necessitates reliable animal models reflecting its key features. Caenorhabditis elegans (C. elegans), with its conserved nervous system and genetic tractability, has emerged as a valuable model organism to study AUD. Here, we employ an ethanol vapor exposure model in Caenorhabditis elegans, recapitulating AUD features while maintaining high-throughput scalability. We demonstrate that ethanol vapor exposure induces intoxication-like behaviors, acute tolerance, and ethanol preference, akin to mammalian AUD traits. Leveraging this model, we elucidate the conserved role of c-jun N-terminal kinase (JNK) signaling in mediating acute ethanol tolerance. Mutants lacking JNK signaling components exhibit impaired tolerance development, highlighting JNK's positive regulation. Furthermore, we detect ethanol-induced JNK activation in C. elegans. Our findings underscore the utility of C. elegans with ethanol vapor exposure for studying AUD and offer novel insights into the molecular mechanisms underlying acute ethanol tolerance through JNK signaling.

Data-driven learning of narcosis mode of action identifies a CNS transcriptional signature shared between whole organism Caenorhabditis elegans and a fish gill cell line

With the large numbers of man-made chemicals produced and released in the environment, there is a need to provide assessments on their potential effects on environmental safety and human health. Current regulatory frameworks rely on a mix of both hazard and risk-based approaches to make safety decisions, but the large number of chemicals in commerce combined with an increased need to conduct assessments in the absence of animal testing makes this increasingly challenging. This challenge is catalysing the use of more mechanistic knowledge in safety assessment from both in silico and in vitro approaches in the hope that this will increase confidence in being able to identify modes of action (MoA) for the chemicals in question. Here we approach this challenge by testing whether a functional genomics approach in C. elegans and in a fish cell line can identify molecular mechanisms underlying the effects of narcotics, and the effects of more specific acting toxicants. We show that narcosis affects the expression of neuronal genes associated with CNS function in C. elegans and in a fish cell line. Overall, we believe that our study provides an important step in developing mechanistically relevant biomarkers which can be used to screen for hazards, and which prevent the need for repeated animal or cross-species comparisons for each new chemical.

Drunken lipid membranes, not drunken SNARE proteins, promote fusion in a model of neurotransmitter release

Alcohol affects many neuronal proteins that are upstream or down-stream of synaptic vesicle fusion and neurotransmitter release. Less well studied is alcohol's effect on the fusion machinery including SNARE proteins and lipid membranes. Using a SNARE-driven fusion assay we show that fusion probability is significantly increased at 0.4% v/v (68 mM) ethanol; but not with methanol up to 10%. Ethanol appears to act directly on membrane lipids since experiments focused on protein properties [circular dichroism spectrometry, site-directed fluorescence interference contrast (sdFLIC) microscopy, and vesicle docking results] showed no significant changes up to 5% ethanol, but a protein-free fusion assay also showed increased lipid membrane fusion rates with 0.4% ethanol. These data show that the effects of high physiological doses of ethanol on SNARE-driven fusion are mediated through ethanol's interaction with the lipid bilayer of membranes and not SNARE proteins, and that methanol affects lipid membranes and SNARE proteins only at high doses.

Differential Expression of Presynaptic Munc13-1 and Munc13-2 in Mouse Hippocampus Following Ethanol Drinking

The Munc13 family of proteins is critically involved in synaptic vesicle priming and release in glutamatergic neurons in the brain. Munc13-1 binds to alcohol and, in Drosophila, modulates sedation sensitivity and self-administration. We examined the effect of alcohol consumption on the expression of Munc13-1 and Munc13-2, NMDA receptor subunits GluN1, GluN2A and GluN2B in the hippocampus-derived HT22 cells, hippocampal primary neuron culture, and wild-type and Munc13-1+/- male mouse hippocampus after ethanol consumption (Drinking in the Dark (DID) paradigm). In HT22 cells, Munc13-1 was upregulated following 25 mM ethanol treatment for 24 h. In the primary neuronal culture, however, the expression of both Munc13-1 and Munc13-2 increased after ethanol exposure. While Munc13-1 was upregulated in the hippocampus, Munc13-2 was downregulated following DID. This differential effect was found in the CA1 subfield of the hippocampus. Although Munc13-1+/- mice had approximately 50% Munc13-1 expression compared to wild-type, it was nonetheless significantly increased following DID. Munc13-1 and Munc13-2 were expressed in vesicular glutamate transporter1 (VGLUT1) immunoreactive neurons in the hippocampus, but ethanol did not alter the expression of VGLUT1. The NMDA receptor subunits, GluN1, GluN2A and GluN2B were upregulated in the hippocampal primary culture and in the CA1. Ethanol exerts a differential effect on the expression of Munc13-1 and Munc13-2 in the CA1 in male mice. Our study also found that ethanol's effect on Munc13 expression is dependent on the experimental paradigm, and both Munc13-1 and Munc13-2 could contribute to the ethanol-induced augmentation of glutamatergic neurotransmission.

Neuropeptidergic regulation of compulsive ethanol seeking in C. elegans

Despite the catastrophic consequences of alcohol abuse, alcohol use disorders (AUD) and comorbidities continue to strain the healthcare system, largely due to the effects of alcohol-seeking behavior. An improved understanding of the molecular basis of alcohol seeking will lead to enriched treatments for these disorders. Compulsive alcohol seeking is characterized by an imbalance between the superior drive to consume alcohol and the disruption or erosion in control of alcohol use. To model the development of compulsive engagement in alcohol seeking, we simultaneously exploited two distinct and conflicting Caenorhabditis elegans behavioral programs, ethanol preference and avoidance of aversive stimulus. We demonstrate that the C. elegans model recapitulated the pivotal features of compulsive alcohol seeking in mammals, specifically repeated attempts, endurance, and finally aversion-resistant alcohol seeking. We found that neuropeptide signaling via SEB-3, a CRF receptor-like GPCR, facilitates the development of ethanol preference and compels animals to seek ethanol compulsively. Furthermore, our functional genomic approach and behavioral elucidation suggest that the SEB-3 regulates another neuropeptidergic signaling, the neurokinin receptor orthologue TKR-1, to facilitate compulsive ethanol-seeking behavior.

Effect of ethanol on Munc13-1 C1 in Membrane: A Molecular Dynamics Simulation Study

BACKGROUND

EtOH has a significant effect on synaptic plasticity. Munc13-1 is an essential presynaptic active zone protein involved in priming the synaptic vesicle and releasing neurotransmitter in the brain. It is a peripheral membrane protein and binds to the activator, diacylglycerol (DAG)/phorbol ester at its membrane-targeting C1 domain. Our previous studies identified Glu-582 of C1 domain as the alcohol-binding residue (Das, J. et al, J. Neurochem., 126, 715-726, 2013).

METHODS

Here, we describe a 250 ns molecular dynamics (MD) simulation study on the interaction of EtOH and the activator-bound Munc13-1 C1 in the presence of varying concentrations of phosphatidylserine (PS).

RESULTS

In this study, Munc13-1 C1 shows higher conformational stability in EtOH than in water. It forms fewer hydrogen bonds with phorbol 13-acetate in the presence of EtOH than in water. EtOH also affected the interaction between the protein and the membrane and between the activator and the membrane. Similar studies in a E582A mutant suggest that these effects of EtOH are mostly mediated through Glu-582.

CONCLUSIONS

EtOH forms hydrogen bonds with Glu-582. While occupancy of the EtOH molecules at the vicinity (4Å) of Glu-582 is 34.4%, the occupancy in the E582A mutant is 26.5% of the simulation time. In addition, the amount of PS in the membrane influences the conformational stability of the C1 domain and interactions in the ternary complex. This study is important in providing the structural basis of EtOH's effects on synaptic plasticity.

Functional validity, role, and implications of heavy alcohol consumption genetic loci

High alcohol consumption is a risk factor for morbidity and mortality, yet few genetic loci have been robustly associated with alcohol intake. Here, we use U.K. Biobank (n = 125,249) and GERA (n = 47,967) datasets to determine genetic factors associated with extreme population-level alcohol consumption and examine the functional validity of outcomes using model organisms and in silico techniques. We identified six loci attaining genome-wide significant association with alcohol consumption after meta-analysis and meeting our criteria for replication: ADH1B (lead SNP: rs1229984), KLB (rs13130794), BTF3P13 (rs144198753), GCKR (rs1260326), SLC39A8 (rs13107325), and DRD2 (rs11214609). A conserved role in phenotypic responses to alcohol was observed for all genetic targets available for investigation (ADH1B, GCKR, SLC39A8, and KLB) in Caenorhabditis elegans. Evidence of causal links to lung cancer, and shared genetic architecture with gout and hypertension was also found. These findings offer insight into genes, pathways, and relationships for disease risk associated with high alcohol consumption.

SNARE Complex-Associated Proteins and Alcohol

Alcohol addiction causes major health problems throughout the world, causing numerous deaths and incurring a huge economic burden to society. To develop an intervention for alcohol addiction, it is necessary to identify molecular target(s) of alcohol and associated molecular mechanisms of alcohol action. The functions of many central and peripheral synapses are impacted by low concentrations of ethanol (EtOH). While the postsynaptic targets and mechanisms are studied extensively, there are limited studies on the presynaptic targets and mechanisms. This article is an endeavor in this direction, focusing on the effect of EtOH on the presynaptic proteins associated with the neurotransmitter release machinery. Studies on the effects of EtOH at the levels of gene, protein, and behavior are highlighted in this article.

Ethanol Stimulates Locomotion via a Gαs-Signaling Pathway in IL2 Neurons in Caenorhabditis elegans

Alcohol abuse is among the top causes of preventable death, generating considerable financial, health, and societal burdens. Paradoxically, alcohol...

Alcohol is a potent pharmacological agent when consumed acutely at sufficient quantities and repeated overuse can lead to addiction and deleterious effects on health. Alcohol is thought to modulate neuronal function through low-affinity interactions with proteins, in particular with membrane channels and receptors. Paradoxically, alcohol acts as both a stimulant and a sedative. The exact molecular mechanisms for the acute effects of ethanol on neurons, as either a stimulant or a sedative, however remain unclear. We investigated the role that the heat shock transcription factor HSF-1 played in determining a stimulatory phenotype of Caenorhabditis elegans in response to physiologically relevant concentrations of ethanol (17 mM; 0.1% v/v). Using genetic techniques, we demonstrate that either RNA interference of hsf-1 or use of an hsf-1(sy441) mutant lacked the enhancement of locomotion in response to acute ethanol exposure evident in wild-type animals. We identify that the requirement for HSF-1 in this phenotype was IL2 neuron-specific and required the downstream expression of the α-crystallin ortholog HSP-16.48. Using a combination of pharmacology, optogenetics, and phenotypic analyses we determine that ethanol activates a G_αs-cAMP-protein kinase A signaling pathway in IL2 neurons to stimulate nematode locomotion. We further implicate the phosphorylation of a specific serine residue (Ser322) on the synaptic protein UNC-18 as an end point for the G_αs-dependent signaling pathway. These findings establish and characterize a distinct neurosensory cell signaling pathway that determines the stimulatory action of ethanol and identifies HSP-16.48 and HSF-1 as novel regulators of this pathway.

Small Heat Shock Proteins Are Novel Common Determinants of Alcohol and Nicotine Sensitivity in Caenorhabditis elegans

Addiction to drugs is strongly determined by multiple genetic factors. Alcohol and nicotine produce distinct pharmacological effects within the nervous system through discrete molecular targets; yet, data from family and twin analyses support the existence of common genetic factors for addiction in general. The mechanisms underlying addiction, however, are poorly described and common genetic factors for alcohol and nicotine remain unidentified. We investigated the role that the heat shock transcription factor, HSF-1, and its downstream effectors played as common genetic modulators of sensitivity to addictive substances. Using Caenorhabditis elegans, an exemplary model organism with substance dose-dependent responses similar to mammals, we demonstrate that HSF-1 altered sensitivity to both alcohol and nicotine. Using a combination of a targeted RNAi screen of downstream factors and transgenic approaches we identified that these effects were contingent upon the constitutive neuronal expression of HSP-16.48, a small heat shock protein (HSP) homolog of human α-crystallin. Furthermore we demonstrated that the function of HSP-16.48 in drug sensitivity surprisingly was independent of chaperone activity during the heat shock stress response. Instead we identified a distinct domain within the N-terminal region of the HSP-16.48 protein that specified its function in comparison to related small HSPs. Our findings establish and characterize a novel genetic determinant underlying sensitivity to diverse addictive substances.

Butanol isomers exert distinct effects on voltage-gated calcium channel currents and thus catecholamine secretion in adrenal chromaffin cells

Butanol (C₄H₁₀OH) has been used both to dissect the molecular targets of alcohols/general anesthetics and to implicate phospholipase D (PLD) signaling in a variety of cellular functions including neurotransmitter and hormone exocytosis. Like other primary alcohols, 1-butanol is a substrate for PLD and thereby disrupts formation of the intracellular signaling lipid phosphatidic acid. Because secondary and tertiary butanols do not undergo this transphosphatidylation, they have been used as controls for 1-butanol to implicate PLD signaling. Recently, selective pharmacological inhibitors of PLD have been developed and, in some cases, fail to block cellular functions previously ascribed to PLD using primary alcohols. For example, exocytosis of insulin and degranulation of mast cells are blocked by primary alcohols, but not by the PLD inhibitor FIPI. In this study we show that 1-butanol reduces catecholamine secretion from adrenal chromaffin cells to a much greater extent than tert-butanol, and that the PLD inhibitor VU0155056 has no effect. Using fluorescent imaging we show the effect of these drugs on depolarization-evoked calcium entry parallel those on secretion. Patch-clamp electrophysiology confirmed the peak amplitude of voltage-gated calcium channel currents (I_Ca) is inhibited by 1-butanol, with little or no block by secondary or tert-butanol. Detailed comparison shows for the first time that the different butanol isomers exert distinct, and sometimes opposing, effects on the voltage-dependence and gating kinetics of I_Ca. We discuss these data with regard to PLD signaling in cellular physiology and the molecular targets of general anesthetics.

Nematodes feel a craving--using Caenorhabditis elegans as a model to study alcohol addiction

Alcohol is the most frequently-used addictive drug. However, the mechanism by which its consumption leads to addiction remains largely elusive. Given the conservation of behavioral reactions to alcohol, Caenorhabitis elegans (C. elegans) has been effectively used as a model system to investigate the relevant molecular targets and pathways mediating these responses. In this article, we review the roles of BK channels (also called SLO-1), the lipid microenvironment, receptors, the synaptic machinery, and neurotransmitters in both the acute and chronic effects of alcohol. We provide an overview of the genes and mechanisms involved in alcoholismrelated behaviors in C. elegans.

Rab-3 and unc-18 interactions in alcohol sensitivity are distinct from synaptic transmission

The molecular mechanisms underlying sensitivity to alcohol are incompletely understood. Recent research has highlighted the involvement of two presynaptic proteins, Munc18 and Rab3. We have previously characterised biochemically a number of specific Munc18 point mutations including an E466K mutation that augments a direct Rab3 interaction. Here the phenotypes of this and other Munc18 mutations were assessed in alcohol sensitivity and exocytosis using Caenorhabditis elegans. We found that expressing the orthologous E466K mutation (unc-18 E465K) enhanced alcohol sensitivity. This enhancement in sensitivity was surprisingly independent of rab-3. In contrast unc-18 R39C, which decreases syntaxin binding, enhanced sensitivity to alcohol in a manner requiring rab-3. Finally, overexpression of R39C could suppress partially the reduction in neurotransmitter release in rab-3 mutant worms, whereas wild-type or E465K mutants showed no rescue. These data indicate that the epistatic interactions between unc-18 and rab-3 in modulating sensitivity to alcohol are distinct from interactions affecting neurotransmitter release.

Caenorhabditis elegans battling starvation stress: low levels of ethanol prolong lifespan in L1 larvae

The nematode Caenorhabditis elegans arrests development at the first larval stage if food is not present upon hatching. Larvae in this stage provide an excellent model for studying stress responses during development. We found that supplementing starved larvae with ethanol markedly extends their lifespan within this L1 diapause. The effects of ethanol-induced lifespan extension can be observed when the ethanol is added to the medium at any time between 0 and 10 days after hatching. The lowest ethanol concentration that extended lifespan was 1 mM (0.005%); higher concentrations to 68 mM (0.4%) did not result in increased survival. In spite of their extended survival, larvae did not progress to the L2 stage. Supplementing starved cultures with n-propanol and n-butanol also extended lifespan, but methanol and isopropanol had no measurable effect. Mass spectrometry analysis of nematode fatty acids and amino acids revealed that L1 larvae can incorporate atoms from ethanol into both types of molecules. Based on these data, we suggest that ethanol supplementation may extend the lifespan of L1 larvae by either serving as a carbon and energy source and/or by inducing a stress response.