Regulation by nicotine of Gpr51 and Ntrk2 expression in various rat brain regions

The Impact of Cigarette Quitting during Pregnancy on Other Prenatal Health Behaviors

Several economic studies have evaluated the effects of cigarette smoking and quitting on other health behaviors such as alcohol use and weight gain. However, there is little research that evaluates the effects of cigarette quitting during pregnancy on other health behaviors such as caloric intake, alcohol consumption, multivitamin use, and caffeine intake. In this paper, we evaluate these effects and employ a genetic variant that predicts cigarette quitting to aid in identification. We find some evidence that cigarette quitting during pregnancy may increase multivitamin use and caloric intake and reduce caffeine consumption.

Transcriptome sequencing of gene expression in the brain of the HIV-1 transgenic rat

The noninfectious HIV-1 transgenic (HIV-1Tg) rat was developed as a model of AIDs-related pathology and immune dysfunction by manipulation of a noninfectious HIV-1^gag-pol virus with a deleted 3-kb SphI-MscI fragment containing the 3′ -region of gag and the 5′ region of pol into F344 rats. Our previous studies revealed significant behavioral differences between HIV-1Tg and F344 control rats in their performance in the Morris water maze and responses to psychostimulants. However, the molecular mechanisms underlying these behavioral differences remain largely unknown. The primary goal of this study was to identify differentially expressed genes and enriched pathways affected by the gag-pol-deleted HIV-1 genome. Using RNA deep sequencing, we sequenced RNA transcripts in the prefrontal cortex, hippocampus, and striatum of HIV-1Tg and F344 rats. A total of 72 RNA samples were analyzed (i.e., 12 animals per group × 2 strains × 3 brain regions). Following deep-sequencing analysis of 50-bp paired-end reads of RNA-Seq, we used Bowtie/Tophat/Cufflinks suites to align these reads into transcripts based on the Rn4 rat reference genome and to measure the relative abundance of each transcript. Statistical analyses on each brain region in the two strains revealed that immune response- and neurotransmission-related pathways were altered in the HIV-1Tg rats, with brain region differences. Other neuronal survival-related pathways, including those encoding myelin proteins, growth factors, and translation regulators, were altered in the HIV-1Tg rats in a brain region-dependent manner. This study is the first deep-sequencing analysis of RNA transcripts associated the HIV-1Tg rat. Considering the functions of the pathways and brain regions examined in this study, our findings of abnormal gene expression patterns in HIV-1Tg rats suggest mechanisms underlying the deficits in learning and memory and vulnerability to drug addiction and other psychiatric disorders observed in HIV-positive patients.

Brain-derived neurotrophic factor and neuropsychiatric disorders

Brain derived neurotrophic factor (BDNF) is the most prevalent growth factor in the central nervous system (CNS). It is essential for the development of the CNS and for neuronal plasticity. Because BDNF plays a crucial role in development and plasticity of the brain, it is widely implicated in psychiatric diseases. This review provides a summary of clinical and preclinical evidence for the involvement of this ubiquitous growth factor in major depressive disorder, schizophrenia, addiction, Rett syndrome, as well as other psychiatric and neurodevelopmental diseases. In addition, the review includes a discussion of the role of BDNF in the mechanism of action of pharmacological therapies currently used to treat these diseases, such antidepressants and antipsychotics. The review also covers a critique of experimental therapies such as BDNF mimetics and discusses the value of BDNF as a target for future drug development.

Smoking and body weight: evidence using genetic instruments

Several studies have evaluated whether the high and rising obesity rates over the past three decades may be due to the declining smoking rates. There is mixed evidence across studies - some find negative smoking effects and positive cigarette cost effects on body weight, while others find opposite effects. This study applies a unique approach to identify the smoking effects on body weight and to evaluate the heterogeneity in these effects across the body mass index (BMI) distribution by utilizing genetic instruments for smoking. Using a data sample of 1057 mothers from Norway, the study finds heterogeneous effects of cigarette smoking on BMI - smoking increases BMI at low/moderate BMI levels and decreases BMI at high BMI levels. The study highlights the potential advantages and challenges of employing genetic instrumental variables to identify behavior effects including the importance of qualifying the instruments and the need for large samples.

Assessing the impact of nicotine dependence genes on the risk of facial clefts: An example of the use of national registry and biobank data

BACKGROUND

Maternal smoking during pregnancy has been associated with risk of facial clefts in offspring, but causation has not yet been established. It is possible that the effect of maternal smoking on facial clefts is mediated through genes that are involved in nicotine dependence. Gamma-aminobutyric acid B receptor 2 (GABBR2), dopa decarboxylase (DDC), and cholinergic receptor nicotinic alpha 4 (CHRNA4) are three examples of genes that have previously shown strong associations with nicotine dependence.

METHODS

We used a population-based sample of 377 case-parent trios of cleft lip with or without cleft palate (CL/P) and 762 control-parent trios from Norway (1996-2001) to investigate whether variants in GABBR2, DDC and CHRNA4 are associated with maternal first-trimester smoking and with clefting risk. We used HAPLIN (Gjessing et al. 2006), a statistical software tailored for family-based association tests, to perform haplotype-based analyses on 12 SNPs in these genes (rs10985765, rs1435252, rs3780422, rs2779562, and rs3750344 in GABBR2; rs2060762, rs3757472, rs1451371, rs3735273, and rs921451 in DDC; rs4522666 and rs1044393 in CHRNA4).

RESULTS

When analyzed one at a time, there was little evidence of association between any of the 12 SNPs and maternal first-trimester smoking. In haplotype analyses, however, one copy of the maternal G-G-c-G-c haplotype in DDC was linked with smoking prevalence (odds ratio: 1.5; 95% confidence interval: 1.0-2.1). This same haplotype also increased the risk of isolated CL/P in offspring by 1.5-fold with one copy and 2.4-fold with two copies (P_trend = 0.06). No statistically significant associations were detected with GABBR2 and CHRNA4.

CONCLUSIONS

Despite strong associations previously reported between nicotine dependence and variants in GABBR2, DDC and CHRNA4, these genes were poor predictors of maternal first-trimester smoking in our data. The direct association of the DDC haplotype with CL/P suggests that this haplotype may either have direct effects on clefts or it may influence clefting risks through other yet unexplored risk behavior(s).

17A, a novel non-coding RNA, regulates GABA B alternative splicing and signaling in response to inflammatory stimuli and in Alzheimer disease

Alternative splicing is a central component of human brain complexity; nonetheless, its regulatory mechanisms are still largely unclear. In this work, we describe a novel non-coding (nc) RNA (named 17A) RNA polymerase (pol) III-dependent embedded in the human G-protein-coupled receptor 51 gene (GPR51, GABA B2 receptor). The stable expression of 17A in SHSY5Y neuroblastoma cells induces the synthesis of an alternative splicing isoform that abolish GABA B2 intracellular signaling (i.e., inhibition of cAMP accumulation and activation of K(+) channels). Indeed, 17A is expressed in human brain, and we report that it is upregulated in cerebral tissues derived from Alzheimer disease patients. We demonstrate that 17A expression in neuroblastoma cells enhances the secretion of amyloid β peptide (Aβ) and the Aβ x-42/Αβ x-40 peptide ratio and that its synthesis is induced in response to inflammatory stimuli. These data correlate, for the first time, the activity of a novel pol III-dependent ncRNA to alternative splicing events and, possibly, to neurodegeneration induced by abnormal GABA B function. We anticipate that further analysis of pol III-dependent regulation of alternative splicing will disclose novel regulatory pathways associated to brain physiology and/or pathology.

Gene expression changes in the nucleus accumbens of alcohol-preferring rats following chronic ethanol consumption

The objective of this study was to determine the effects of binge-like alcohol drinking on gene expression changes in the nucleus accumbens (ACB) of alcohol-preferring (P) rats. Adult male P rats were given ethanol under multiple scheduled access (MSA; three 1-h dark cycle sessions/day) conditions for 8 weeks. For comparison purposes, a second ethanol drinking group was given continuous/daily alcohol access (CA; 24h/day). A third group was ethanol-naïve (W group). Average ethanol intakes for the CA and MSA groups were approximately 9.5 and 6.5 g/kg/day, respectively. Fifteen hours after the last drinking episode, rats were euthanized, the brains extracted, and the ACB dissected. RNA was extracted and purified for microarray analysis. The only significant differences were between the CA and W groups (p<0.01; Storey false discovery rate=0.15); there were 374 differences in named genes between these 2 groups. There were 20 significant Gene Ontology (GO) categories, which included negative regulation of protein kinase activity, anti-apoptosis, and regulation of G-protein coupled receptor signaling. Ingenuity analysis indicated a network of transcription factors, involving oncogenes (Fos, Jun, Junb had higher expression in the ACB of the CA group), suggesting increased neuronal activity. There were 43 genes located within rat QTLs for alcohol consumption and preference; 4 of these genes (Tgfa, Hspa5, Mtus1 and Creb3l2) are involved in anti-apoptosis and increased transcription, suggesting that they may be contributing to cellular protection and maintaining high alcohol intakes. Overall, these findings suggest that chronic CA drinking results in genomic changes that can be observed during the early acute phase of ethanol withdrawal. Conversely, chronic MSA drinking, with its associated protracted withdrawal periods, results in genomic changes that may be masked by tight regulation of these genes following repeated experiences of ethanol withdrawal.

Association and interaction analyses of GABBR1 and GABBR2 with nicotine dependence in European- and African-American populations

Previous studies have demonstrated that the gamma-aminobutyric acid type B (GABA(B)) receptor plays an essential role in modulating neurotransmitter release and regulating the activity of ion channels and adenyl cyclase. However, whether the naturally occurring polymorphisms in the two GABA(B) receptor subunit genes interact with each other to alter susceptibility to nicotine dependence (ND) remains largely unknown. In this study, we genotyped 5 and 33 single nucleotide polymorphisms (SNPs) for GABA(B) receptor subunit 1 and 2 genes (GABBR1, GABBR2), respectively, in a sample of 2037 individuals from 602 nuclear families of African- American (AA) or European-American (EA) origin. We conducted association analyses to determine (1) the association of each subunit gene with ND at both the individual SNP and haplotype levels and (2) the collective effect(s) of SNPs in both GABA(B) subunits on the development of ND. Several individual SNPs and haplotypes in GABBR2 were significantly associated with ND in both ethnic samples. Two haplotypes in AAs and one haplotype in EAs showed a protective effect against ND, whilst two other haplotypes in AAs and three haplotypes in EAs showed a risk effect for developing ND. Interestingly, these significant haplotypes were confined to two regions of GABBR2 in the AA and EA samples. Additionally, we found two minor haplotypes in GABBR1 to be positively associated with Heaviness of Smoking Index (HSI) in the EA sample. Finally, we demonstrated the presence of epistasis between GABBR1 and GABBR2 for developing ND. The variants of GABBR1 and GABBR2 are significantly associated with ND, and the involvement of GABBR1 is most likely through its interaction with GABBR2, whereas GABBR2 polymorphisms directly alter susceptibility to ND. Future studies are needed with more dense SNP coverage of GABBR1 and GABBR2 to verify the epistatic effects of the two subunit genes.

Genome-wide significant predictors of metabolites in the one-carbon metabolism pathway

Low plasma B-vitamin levels and elevated homocysteine have been associated with cancer, cardiovascular disease and neurodegenerative disorders. Common variants in FUT2 on chromosome 19q13 were associated with plasma vitamin B12 levels among women in a genome-wide association study in the Nurses' Health Study (NHS) NCI-Cancer Genetic Markers of Susceptibility (CGEMS) project. To identify additional loci associated with plasma vitamin B12, homocysteine, folate and vitamin B6 (active form pyridoxal 5'-phosphate, PLP), we conducted a meta-analysis of three GWA scans (total n = 4763, consisting of 1658 women in NHS-CGEMS, 1647 women in Framingham-SNP-Health Association Resource (SHARe) and 1458 men in SHARe). On chromosome 19q13, we confirm the association of plasma vitamin B12 with rs602662 and rs492602 (P-value = 1.83 x 10(-15) and 1.30 x 10(-14), respectively) in strong linkage disequilibrium (LD) with rs601338 (P = 6.92 x 10(-15)), the FUT2 W143X nonsense mutation. We identified additional genome-wide significant loci for plasma vitamin B12 on chromosomes 6p21 (P = 4.05 x 10(-08)), 10p12 (P-value=2.87 x 10(-9)) and 11q11 (P-value=2.25 x 10(-10)) in genes with biological relevance. We confirm the association of the well-studied functional candidate SNP 5,10-methylene tetrahydrofolate reductase (MTHFR) Ala222Val (dbSNP ID: rs1801133; P-value=1.27 x 10(-8)), on chromosome 1p36 with plasma homocysteine and identify an additional genome-wide significant locus on chromosome 9q22 (P-value=2.06 x 10(-8)) associated with plasma homocysteine. We also identified genome-wide associations with variants on chromosome 1p36 with plasma PLP (P-value=1.40 x 10(-15)). Genome-wide significant loci were not identified for plasma folate. These data reveal new biological candidates and confirm prior candidate genes for plasma homocysteine, plasma vitamin B12 and plasma PLP.

Genome-wide association study of smoking initiation and current smoking

For the identification of genes associated with smoking initiation and current smoking, genome-wide association analyses were carried out in 3497 subjects. Significant genes that replicated in three independent samples (n = 405, 5810, and 1648) were visualized into a biologically meaningful network showing cellular location and direct interaction of their proteins. Several interesting groups of proteins stood out, including glutamate receptors (e.g., GRIN2B, GRIN2A, GRIK2, GRM8), proteins involved in tyrosine kinase receptor signaling (e.g., NTRK2, GRB14), transporters (e.g., SLC1A2, SLC9A9) and cell-adhesion molecules (e.g., CDH23). We conclude that a network-based genome-wide association approach can identify genes influencing smoking behavior.

NMDA receptors regulate nicotine-enhanced brain reward function and intravenous nicotine self-administration: role of the ventral tegmental area and central nucleus of the amygdala

Nicotine is considered an important component of tobacco responsible for the smoking habit in humans. Nicotine increases glutamate-mediated transmission throughout brain reward circuitries. This action of nicotine could potentially contribute to its intrinsic rewarding and reward-enhancing properties, which motivate consumption of the drug. Here we show that the competitive N-methyl-D-aspartate (NMDA) receptor antagonist LY235959 (0.5-2.5 mg per kg) abolished nicotine-enhanced brain reward function, reflected in blockade of the lowering of intracranial self-stimulation (ICSS) thresholds usually observed after experimenter-administered (0.25 mg per kg) or intravenously self-administered (0.03 mg per kg per infusion) nicotine injections. The highest LY235959 dose (5 mg per kg) tested reversed the hedonic valence of nicotine from positive to negative, reflected in nicotine-induced elevations of ICSS thresholds. LY235959 doses that reversed nicotine-induced lowering of ICSS thresholds also markedly decreased nicotine self-administration without altering responding for food reinforcement, whereas the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor antagonist NBQX had no effects on nicotine intake. In addition, nicotine self-administration upregulated NMDA receptor subunit expression in the central nucleus of the amygdala (CeA) and ventral tegmental area (VTA), suggesting important interactions between nicotine and the NMDA receptor. Furthermore, nicotine (1 microM) increased NMDA receptor-mediated excitatory postsynaptic currents in rat CeA slices, similar to its previously described effects in the VTA. Finally, infusion of LY235959 (0.1-10 ng per side) into the CeA or VTA decreased nicotine self-administration. Taken together, these data suggest that NMDA receptors, including those in the CeA and VTA, gate the magnitude and valence of the effects of nicotine on brain reward systems, thereby regulating motivation to consume the drug.

Gene-gene interactions among CHRNA4, CHRNB2, BDNF, and NTRK2 in nicotine dependence

BACKGROUND

Epidemiological data indicate that nicotine dependence (ND) are influenced by genes, environmental factors, and their interactions. Although it has been documented from molecular experiments that brain-derived neurotrophic factor (BDNF) exerts its functions via neurotrophic tyrosine kinase receptor 2 (NTRK2) and both alpha 4 (CHRNA4) and beta 2 (CHRNB2) subunits are required to form functional alpha 4 beta 2-containing nicotinic receptors (nAChRs), no study is reported demonstrating that there exist gene-gene interactions among the four genes in affecting ND.

METHODS

To determine if gene-gene interactions exist among the four genes, we genotyped six single nucleotide polymorphisms (SNPs) for CHRNA4 and BDNF, nine SNPs for NTRK2, and four SNPs for CHRNB2 in a case-control sample containing 275 unrelated smokers with a Fagerström Test for Nicotine Dependence score of 4.0 or more and 348 unrelated nonsmokers.

RESULTS

By using a generalized multifactor dimensionality reduction algorithm recently developed by us, we found highly significant gene-gene interactions for the gene pairs of CHRNA4 and CHRNB2, CHRNA4 and NTRK2, CHRNB2 and NTRK2, and BDNF and NTRK2 (p < .01 for all four gene pairs) and significant gene-gene interaction between CHRNA4 and BDNF (p = .031) on ND. No significant interaction was detected for CHRNB2 and BDNF (p = .068).

CONCLUSIONS

Our study provides first evidence on the presence of gene-gene interaction among the four genes in affecting ND. Although CHRNB2 alone was not significantly associated with ND in several previously reported association studies on ND, we found it affects ND through interactions with CHRNA4 and NTRK2.

Linkage and association studies in African- and Caucasian-American populations demonstrate that SHC3 is a novel susceptibility locus for nicotine dependence

Our previous linkage study demonstrated that the 9q22-q23 chromosome region showed a 'suggestive' linkage to nicotine dependence (ND) in the Framingham Heart Study population. In this study, we provide further evidence for the linkage of this region to ND in an independent sample. Within this region, the gene encoding Src homology 2 domain-containing transforming protein C3 (SHC3) represents a plausible candidate for association with ND, assessed by smoking quantity (SQ), the Heaviness of Smoking Index (HSI) and the Fagerström Test for ND (FTND). We utilized 11 single-nucleotide polymorphisms within SHC3 to examine the association with ND in 602 nuclear families of either African-American (AA) or European-American (EA) origin. Individual SNP-based analysis indicated three SNPs for AAs and one for EAs were significantly associated with at least one ND measure. Haplotype analysis revealed that the haplotypes A-C-T-A-T-A of rs12519-rs3750399-rs4877042-rs2297313-rs1547696-rs1331188, with a frequency of 27.8 and 17.6%, and C-T-A-G-T of rs3750399-rs4877042-rs2297313-rs3818668-rs1547696, at a frequency of 44.7 and 30.6% in the AA and Combined samples, respectively, were significantly inversely associated with the ND measures. In the EA sample, another haplotype with a frequency of 10.6%, A-G-T-G of rs1331188-rs1556384-rs4534195-rs1411836, showed a significant inverse association with ND measures. These associations remained significant after Bonferroni correction. We further demonstrated the SHC3 contributed 40.1-59.2% (depending on the ND measures) of the linkage signals detected on chromosome 9. As further support, we found that nicotine administered through infusion increased the Shc3 mRNA level by 60% in the rat striatum, and decreased it by 22% in the nucleus accumbens (NA). At the protein level, Shc3 was decreased by 38.0% in the NA and showed no change in the striatum. Together, these findings strongly implicate SHC3 in the etiology of ND, which represents an important biological candidate for further investigation.