Neuroimmune regulation of alcohol consumption: behavioral validation of genes obtained from genomic studies

Abstract

Analysis of mouse brain gene expression, using strains that differ in alcohol consumption, provided a number of novel candidate genes that potentially regulate alcohol consumption. We selected six genes [beta-2-microglobulin (B2m), cathepsin S (Ctss), cathepsin F (Ctsf), interleukin 1 receptor antagonist (Il1rn), CD14 molecule (Cd14) and interleukin 6 (Il6)] for behavioral validation using null mutant mice. These genes are known to be important for immune responses but were not specifically linked to alcohol consumption by previous research. Null mutant mice were tested for ethanol intake in three tests: 24 hr two-bottle choice, limited access two-bottle choice and limited access to one bottle of ethanol. Ethanol consumption and preference were reduced in all the null mutant mice in the 24 hr two-bottle choice test, the test that was the basis for selection of these genes. No major differences were observed in consumption of saccharin in the null mutant mice. Deletion of B2m, Ctss, Il1rn, Cd14 and Il6 also reduced ethanol consumption in the limited access two bottle choice test for ethanol intake; with the Il1rn and Ctss null mutants showing reduced intake in all three tests (with some variation between males and females). These results provide the most compelling evidence to date that global gene expression analysis can identify novel genetic determinants of complex behavioral traits. Specifically, they suggest a novel role for neuroimmune signaling in regulation of alcohol consumption.

Glial and Neuroimmune Mechanisms as Critical Modulators of Drug Use and Abuse

“…Validating several candidate genes from these studies (including Cd14, Il1ra, and Il6) through single-gene null mutations in mice confirmed that knockout of each gene resulted in decreased alcohol consumption on a two-bottle choice test (Blednov et al, 2012). In humans, polymorphisms with genes encoding for IL-1β, IL-1RN, IL-10, and other immune-related genes have been associated with alcohol dependence, the functional impact of these allelic variants generally supporting a link between increased pro-inflammatory signaling and increased susceptibility to alcoholism (Marcos et al, 2008;Pastor et al, 2005).…”

CRF-Amplified Neuronal TLR4/MCP-1 Signaling Regulates Alcohol Self-Administration

“…A large body of evidence supports the role of GABAergic transmission and its interaction with neuroimmune mechanisms that include TLR4, in alcohol dependence and its effects (Alfonso-Loeches et al, 2010;Pascual et al, 2011;Blednov et al, 2012;Crews and Vetreno, 2014;Bajo et al, 2014). Alcohol releases endogenous ligands for TLR4 in the brain (Crews et al, 2013) and knockout of the TLR4 accessory protein CD14 interferes with the ability of LPS to increase alcohol drinking in wild-type mice (Blednov et al, 2011).…”

“…In the ventral pallidum (VP), which is implicated in drug abuse decisions, voluntary excessive drinking is regulated by the a1 subunits Yang et al, 2011), but human clinical linkage studies support a role for the a2 subunits in alcohol dependence (Edenberg, 2012). A large body of evidence indicates that neuroimmune (including Toll-like receptor 4 (TLR)) signaling contributes to reward-system activity and is associated with alcohol dependence and the effects of alcohol, and postmortem human studies correlate neuroimmune gene expression with lifetime alcohol consumption (Crews et al, 2011;Pascual et al, 2011;Blednov et al, 2012;Crews and Vetreno, 2014). However, the relationship of the neuroimmune signals to the GABA A subunits and the initiation of binge drinking by previously naive individuals is still unclear.…”

Promising Pharmacogenetic Targets for Treating Alcohol Use Disorder: Evidence from Preclinical Models

“…Metaanalyses of gene expression studies in alcohol preferring strains of mice and postmortem tissue from human alcoholics revealed dysregulation of neuroimmune and neuroinflammatory signaling pathways [151]. Null mutant mice for six of these dys regulated immune candidate genes (B2m, Ctsf, Ctss, Il1rn, Cd14 and Il6 ) showed reduced voluntary alco hol intake and preference [151]. The findings from this study validate the use of genomic analysis for identi fying functional groups of genes that regulate alcohol consumption and, in doing so, indicated a novel role for neuroimmune signaling in controlling drinking.…”