Sex- and Genotype-Dependent Nicotine-Induced Behaviors in Adolescent Rats with a Human Polymorphism (rs2304297) in the 3'-UTR of the CHRNA6 Gene

Striatal Cholinergic Interneurons Control Physical Nicotine Withdrawal via Muscarinic Receptor Signaling

Striatal cholinergic interneurons (ChIs) provide acetylcholine tone to the striatum and govern motor functions. Nicotine withdrawal elicits physical symptoms that dysregulate motor behavior. Here, the role of striatal ChIs in physical nicotine withdrawal is investigated. Mice under RNAi-dependent genetic inhibition of striatal ChIs (ChIGI) by suppressing the sodium channel subunit NaV1.1, lessening action potential generation and activity-dependent acetylcholine release is first generated. ChIGI markedly reduced the somatic signs of nicotine withdrawal without affecting other nicotine-dependent or striatum-associated behaviors. Multielectrode array (MEA) recording revealed that ChIGI reversed ex vivo nicotine-induced alterations in the number of neural population spikes in the dorsal striatum. Notably, the drug repurposing strategy revealed that a clinically-approved antimuscarinic drug, procyclidine, fully mimicked the therapeutic electrophysiological effects of ChIGI. Furthermore, both ChIGI and procyclidine prevented the nicotine withdrawal-induced reduction in striatal dopamine release in vivo. Lastly, therapeutic intervention with procyclidine dose-dependently diminished the physical signs of nicotine withdrawal. The data demonstrated that the striatal ChIs are a critical substrate of physical nicotine withdrawal and that muscarinic antagonism holds therapeutic potential against nicotine withdrawal.

Potential immunologic and prognostic roles of CHRNA6 in SCLC and pan-cancer

Background

Small cell lung cancer (SCLC) is considered the most malignant subtype of lung cancer, and it has a restricted range of therapeutic choices. The emergence of immunotherapy has offered new possibilities for patients with SCLC. However, the scarcity of clinical specimens has hampered the progress of clinical studies and we still face a shortage of dependable indicators to forecast the effectiveness of immunotherapy for SCLC.

Methods

In our study, we assessed the ImmuneScore and StromalScore of 81 SCLC samples obtained from the cBioPortal database. By comparing gene expression differences between the high and low immune scores groups, we identified 24 differentially expressed genes. Subsequently, an intersection was performed with genes that exhibited differential expression between normal and SCLC tissues, leading us to isolate the gene CHRNA6. To gain a deeper insight into the possible significance of CHRNA6 in SCLC, we singled out 50 genes that showed the most pronounced positive and negative associations with its expression. We then pinpointed hub genes for subsequent functional enrichment analyses by establishing a protein-protein interactions network. We additionally assessed the link between CHRNA6 expression in SCLC and characteristics of the immune microenvironment, along with the efficacy of immunotherapy, using the CIBERSORT, immunophenoscores (IPS), and tumor immune dysfunction and exclusion (TIDE) algorithms. Furthermore, we confirmed the prognostic impact of CHRNA6 expression in SCLC patients undergoing immunotherapy within a clinical cohort. Lastly, we obtained data from The Cancer Genome Atlas (TCGA) to investigate CHRNA6 expression in various tumors and its associations with genetic alterations, DNA methylation, copy number variation, clinicopathological characteristics, biological processes, immune microenvironment, prognosis, and drug sensitivity.

Results

In SCLC, we found that CHRNA6 function was associated with immune activation pathways such as antigen presentation processing and positive regulation of adaptive immune response, and that CHRNA6 demonstrated a strong correlation with immune cells infiltration. In addition, analysis of the clinical cohort revealed that patients with SCLC who exhibited elevated expression of CHRNA6 experienced better responses to immunotherapy. Our pan-cancer analysis disclosed that the expression of CHRNA6 is dysregulated in a multitude of cancers, potentially due to genetic mutations, copy number gains, and DNA demethylation. The gene set enrichment analysis (GSEA) outcomes indicated that CHRNA6 participates in immune responses and may play a positive immune regulatory role in most cancers. Furthermore, CHRNA6 has been observed to have a notable relationship with immune checkpoints, immunomodulators, immune cell infiltration, patient outcomes, and drug sensitivity across various cancers.

Conclusions

Our findings indicate that the CHRNA6 may act as a predictive indicator for SCLC patients receiving immunotherapy. The study also uncovers the aberrant expression of CHRNA6 in a range of human cancers and its potential roles in immunology and prognosis, offering novel perspectives for tailored cancer therapies.

Sub-chronic nicotine exposure influences methamphetamine self-administration and dopamine overflow in a sex-and genotype-dependent manner in humanized CHRNA6 3'-UTR SNP (rs2304297) adolescent rats

Introduction: The rewarding effects of drugs of abuse are associated with the dopaminergic system in the limbic circuitry. Nicotine exposure during adolescence is linked to increased use of drugs of abuse with nicotine and methamphetamine (METH) commonly used together. Nicotine acts on neuronal nicotinic acetylcholine receptor (nAChR) systems, critical for reward processing and drug reinforcement, while METH leads to a higher dopamine (DA) efflux in brain reward regions. A human single nucleotide polymorphism (SNP) in the 3'-untranslated region (UTR) of the α6 nicotinic receptor subunit gene (CHRNA6, rs2304297), has been linked with tobacco/nicotine and general substance use during adolescence. Using CRISPR-Cas9 genomic engineering, our lab recapitulated the CHRNA6 3'UTRC123G SNP, generating α6CC and α6GG allele carriers in Sprague Dawley rats. We hypothesized the CHRNA6 3'UTRC123G SNP would sex- and genotype-dependently enhance nicotine-induced METH self-administration as well as nicotine-induced DA overflow in the nucleus accumbens shell of adolescent α6GG and α6CC carriers. Methods: Adolescent male and female rats underwent a 4-day sub-chronic, low-dose (0.03 mg/kg/0.1 mL, x2) nicotine pretreatment paradigm to assess intravenous METH (0.02 mg/kg/0.1 mL) self-administration as well as nicotine- and METH (0.02 mg/kg/0.1 mL)-induced DA overflow in the nucleus accumbens shell (NAcS) using in vivo microdialysis coupled with high-performance liquid-chromatography-electrochemical detection (HPLC-ECD). Results: Nicotine pretreatment sex- and genotype-dependently enhanced subsequent METH self-administration in adolescent CHRNA6 3'UTRC123G SNP rats. Further nicotine and METH-induced DA overflow is observed in α6CC females as compared to α6GG females, with METH-induced DA overflow enhanced in α6GG males when compared to α6CC males. Conclusion: These findings demonstrate that the CHRNA6 3'-UTRC123G SNP can sex- and genotype-dependently impact adolescent nicotine-induced effects on METH self-administration and stimulant-induced DA overflow in reward regions of the brain.

Dopamine and Norepinephrine Tissue Levels in the Developing Limbic Brain Are Impacted by the Human CHRNA6 3'-UTR Single-Nucleotide Polymorphism (rs2304297) in Rats

We previously demonstrated that a genetic single-nucleotide polymorphism (SNP, rs2304297) in the 3' untranslated region (UTR) of the human CHRNA6 gene has sex- and genotype-dependent effects on nicotine-induced locomotion, anxiety, and nicotine + cue-induced reinstatement in adolescent rats. This study aims to investigate how the CHRNA6 3'-UTR SNP influences dopaminergic and noradrenergic tissue levels in brain reward regions during baseline and after the reinstatement of drug-seeking behavior. Naïve adolescent and adult rats, along with those undergoing nicotine + cue reinstatement and carrying the CHRNA6 3'-UTR SNP, were assessed for dopamine (DA), norepinephrine (NE), and metabolites in reward pathway regions. The results reveal age-, sex-, and genotype-dependent baseline DA, NE, and DA turnover levels. Post-reinstatement, male α6GG rats show suppressed DA levels in the Nucleus Accumbens (NAc) Shell compared to the baseline, while nicotine+ cue-induced reinstatement behavior correlates with neurotransmitter levels in specific brain regions. This study emphasizes the role of CHRNA6 3'-UTR SNP in the developmental maturation of the dopaminergic and noradrenergic system in the adolescent rat brain, with tissue levels acting as predictors of nicotine + cue-induced reinstatement.

Behavioral characterization of early nicotine withdrawal in the mouse: a potential model of acute dependence

BACKGROUND

Clinical and preclinical research have demonstrated that short-term exposure to nicotine during the initial experimentation stage can lead to early manifestation of withdrawal-like signs, indicating the state of "acute dependence". As drug withdrawal is a major factor driving the progression toward regular drug intake, characterizing and understanding the features of early nicotine withdrawal may be important for the prevention and treatment of drug addiction. In this study, we corroborate the previous studies by showing that withdrawal-like signs can be precipitated after short-term nicotine exposure in mice, providing a potential animal model of acute dependence on nicotine.

RESULTS

To model nicotine exposure from light tobacco use during the initial experimentation stage, mice were treated with 0.5 mg/kg (-)-nicotine ditartrate once daily for 3 days. On the following day, the behavioral tests were conducted after implementing spontaneous or mecamylamine-precipitated withdrawal. In the open field test, precipitated nicotine withdrawal reduced locomotor activity and time spent in the center zone. In the elevated plus maze test, the mecamylamine challenge increased the time spent in the closed arm and reduced the number of entries irrespective of nicotine experience. In the examination of the somatic aspect, precipitated nicotine withdrawal enhanced the number of somatic signs. Finally, nicotine withdrawal did not affect cognitive functioning or social behavior in the passive avoidance, spatial object recognition, or social interaction test.

CONCLUSIONS

Collectively, our data demonstrate that early nicotine withdrawal-like signs could be precipitated by the nicotinic antagonist mecamylamine in mice, and that early withdrawal from nicotine primarily causes physical symptoms.

Sex- and genotype-dependent nicotine plus cue-primed reinstatement is enhanced in adolescent Sprague Dawley rats containing the human CHRNA6 3'-UTR polymorphism (rs2304297)

Rationale

Large-scale human candidate gene studies have indicated that a genetic variant (rs2304297) in the alpha(α)6 nicotinic acetylcholine receptor (nAChR) subunit, encoded by the CHRNA6 gene, may play a key role in adolescent nicotine addictive behavior. We hypothesized that the polymorphism selectively enhances nicotine + cue-primed reinstatement, but not nicotine- or cue-reinstatement in α6 GG (risk) vs. α6 CC (non-risk) allele carriers, without having baseline effects on natural rewards.

Methods

Using CRISPR-Cas9 genomic engineering, we developed a humanized rat line with the human gene variant of the CHRNA6 3'-UTR C 123 G polymorphism in Sprague-Dawley rats. Genetically modified adolescent male and female rats were food trained under a fixed-ratio (FR)1 schedule of reinforcement and progressively increased to FR5. Animals were implanted with catheters and began nicotine self-administration (15 μg/kg/infusion) at FR5. Upon reaching stable responding, reinforced behavior was extinguished by removal of drug and cues. Reinstatement testing began for cue only, nicotine only, and nicotine + cue in a Latin Square Design. Animals were returned to extinction conditions for 2 days minimum between testing.

Results

For natural food rewards, nicotine self-administration, progressive ratio, and extinction, adolescent male and female (α6 GG and α6 CC ) rats exhibited equivalent behaviors. Male α6 GG rats show enhanced nicotine + cue-primed reinstatement when compared with male α6 CC rats. This genotype effect on reinstatement was not seen in female rats.

Conclusion

Our findings support the in vivo functional role of the human CHRNA6 3'-UTR SNP genetic variant in sex-dependently enhancing nicotine seeking behavior in adolescent rats. Overall, the findings support clinical and preclinical data highlighting a role of α6 nAChRs mediating sex heterogeneity in substance use and related phenotypes.