Mapping of multiple subunits of the neuronal nicotinic acetylcholine receptor to chromosome 15 in man and chromosome 9 in mouse

Novel CHRNA3 variants identified in a patient with bladder dysfunction, dysautonomia, and gastrointestinal dysmotility

Congenital anomalies of the kidney and urinary tract (CAKUT) are estimated to be responsible for 20%-50% of congenital anomalies and are also a leading etiology of early-onset renal disease. Primary CAKUT are caused by genetic factors that impair proper in-utero genitourinary tract development and secondary CAKUT result from the influence of environmental factors. The CHRNA3 gene, which encodes the Alpha-3 subunit of the nicotinic acetylcholine receptor, is hypothesized to be associated with Megacystis-microcolon-intestinal hyperperistalsis syndrome. More recently, pathogenic variants in CHRNA3 have been identified in individuals with CAKUT as well as individuals with panautonomic failure. Here we present a patient with neurogenic bladder, vesicoureteral reflux, mydriasis, and gastrointestinal dysmotility found to have novel compound heterozygous variants in CHRNA3. These findings support the consideration of CHRNA3 disruption in the differential for CAKUT with dysautonomia and gastrointestinal dysmotility.

The CHRNA5 Polymorphism (rs16969968) and its Association with Waterpipe Smoking Addiction among Jordanians

Waterpipe smoking is a form of tobacco use that causes nicotine/tobacco dependence and has become a global health problem. In the current study, the association of rs16969968 SNP in the CHRNA5 gene with waterpipe dependence was investigated. A total of 386 men and women who used a waterpipe to smoke tobacco were recruited and divided into less dependent and more dependent smokers based on their score on the Lebanon Waterpipe Dependence Scale (LWDS). Results showed a significant difference in the distribution of GG, GA, and AA genotypes by waterpipe dependence status (P<0.001). The more dependent group showed a higher frequency of the AA genotype than the less dependent smokers' group (38% versus 23% respectively). In addition, the more dependent smokers exhibited more A allele than less dependent smokers (53% versus 37% respectively, P<0.001). In conclusion, there is an association between the rs16969968 SNP and waterpipe dependence as assessed by the LWDS.

Acute nicotine administration stimulates ciliary activity via α3β4 nAChR in the mouse trachea

Mucociliary clearance, the continuous removal of mucus-trapped particles by cilia-driven directed transport of the airway lining fluid, is the primary innate defense mechanism of the airways. It is potently activated by acetylcholine (ACh) addressing muscarinic receptors with a currently less defined role of nicotinic ACh receptors (nAChR). We here set out to determine their contribution in driving ciliary activity in an explanted mouse trachea preparation utilizing selected agonists and antagonists and nAChR-subunit deficient mice. Nicotine (100 µM) induced an increase in ciliary beat frequency, accompanied by a sharp, but not long lasting increase in particle transport speed (PTS) on the mucosal surface showing marked desensitization within the next 30 min. Nicotine-induced PTS acceleration was sensitive to the general nAChR inhibitors mecamylamine and d-tubocurarine as well as to the α3β4-nAChR antagonist α-conotoxin AulB, but not to other antagonists primarily addressing α3β2-nAChR or α4-, α7- and α9-containing nAChR. Agonists at α3β*-nAChR (epibatidine, cytisine), but not cotinine mimicked the effect. Tracheas from mice with genetic deletion of nAChR subunits α5, α7, α9, α10, α9/10, and β2 retained full PTS response to nicotine, whereas this was entirely lost in tracheas from mice lacking the β4-subunit. Collectively, our data show that nicotinic stimulation of α3β4-nAChR acutely increases PTS to the same extent as the established strong activator ATP. In view of the marked desensitization observed in the present setting, the physiological relevance of these receptors in adapting mucociliary clearance to rapidly changing endogenous or environmental stimuli remains open.

Cholinergic Receptors and Addiction

Human behavior can be controlled by physical or psychological dependencies associated with addiction. One of the most insidious addictions in our society is the use of tobacco products which contain nicotine. This addiction can be associated with specific receptors in the brain that respond to the natural neurotransmitter acetylcholine. These nicotinic acetylcholine receptors (nAChR) are ligand-gated ion channels formed by the assembly of one or multiple types of nAChR receptor subunits. In this paper, we review the structure and diversity of nAChR subunits and our understanding for how different nAChR subtypes play specific roles in the phenomenon of nicotine addiction. We focus on receptors containing β2 and/or α6 subunits and the special significance of α5-containing receptors. These subtypes all have roles in regulating dopamine-mediated neurotransmission in the mesolimbic reward pathways of the brain. We also discuss the unique roles of homomeric α7 nAChR in behavioral responses to nicotine and how our knowledge of nAChR functional diversity may help guide pharmacotherapeutic approaches for treating nicotine addiction. While nicotine addiction is a truly global problem, the use of areca nut (betel) products is also a serious addiction associated with public health issues across most of South Asia, impacting as many as 600 million people. We discuss how cholinergic receptors of the brain are also involved with areca addiction and the unique challenges for dealing with addiction to this substance.

Effects of L-theanine on posttraumatic stress disorder induced changes in rat brain gene expression

Posttraumatic stress disorder (PTSD) is characterized by the occurrence of a traumatic event that is beyond the normal range of human experience. The future of PTSD treatment may specifically target the molecular mechanisms of PTSD. In the US, approximately 20% of adults report taking herbal products to treat medical illnesses. L-theanine is the amino acid in green tea primarily responsible for relaxation effects. No studies have evaluated the potential therapeutic properties of herbal medications on gene expression in PTSD. We evaluated gene expression in PTSD-induced changes in the amygdala and hippocampus of Sprague-Dawley rats. The rats were assigned to PTSD-stressed and nonstressed groups that received either saline, midazolam, L-theanine, or L-theanine + midazolam. Amygdala and hippocampus tissue samples were analyzed for changes in gene expression. One-way ANOVA was used to detect significant difference between groups in the amygdala and hippocampus. Of 88 genes examined, 17 had a large effect size greater than 0.138. Of these, 3 genes in the hippocampus and 5 genes in the amygdala were considered significant (P < 0.05) between the groups. RT-PCR analysis revealed significant changes between groups in several genes implicated in a variety of disorders ranging from PTSD, anxiety, mood disorders, and substance dependence.

Alternative CHRNB4 3'-UTRs mediate the allelic effects of SNP rs1948 on gene expression

Common genetic factors strongly contribute to both nicotine, the main addictive component of tobacco, and alcohol use. Several lines of evidence suggest nicotinic acetylcholine receptors as common sites of action for nicotine and alcohol. Specifically, rs1948, a single-nucleotide polymorphism (SNP) located in the CHRNB4 3′-untranslated region (UTR), has been associated to early age of initiation for both alcohol and tobacco use. To determine the allelic effects of rs1948 on gene expression, two rs1948-containing sequences of different lengths corresponding to the CHRNB4 3′-UTR were cloned into pGL3-promoter luciferase reporter vectors. Data obtained showed that the allelic effects of SNP rs1948 on luciferase expression are mediated by the length and species of transcripts generated. In addition, it was found that miR-3157 increased the overall luciferase expression while miR-138, a microRNA known to play a role in neuroadaptation to drug abuse, decreased luciferase expression when compared to basal conditions. These findings demonstrate the importance of SNP rs1948 on the regulation of CHRNB4 expression and provide the first evidence of CHRNB4 down-regulation by miR-138.

Linkage analyses of stimulant dependence, craving, and heavy use in American Indians

Amphetamine-type substances are the second most widely used illicit drugs in the United States. There is evidence to suggest that stimulant use (cocaine and methamphetamine) has a heritable component, yet the areas of the genome underlying these use disorders are yet to be identified. This study's aims were to map loci linked to stimulant dependence, heavy use, and craving in an American Indian community at high risk for substance dependence. DSM diagnosis of stimulant dependence, as well as indices of stimulant "craving," and "heavy use," were obtained using the Semi-Structured Assessment for the Genetics of Alcoholism (SSAGA). Genotypes were determined for a panel of 791 microsatellite polymorphisms in 381 members of multiplex families using SOLAR. Stimulant dependence, stimulant "craving," and "heavy stimulant use," were all found to be heritable. Analyses of multipoint variance component LOD scores, failed to yield evidence of linkage for stimulant dependence. For the stimulant "craving" phenotype, linkage analysis revealed a locus that had a LOD score of 3.02 on chromosome 15q25.3-26.1 near the nicotinic receptor gene cluster. A LOD score of 2.05 was found at this same site for "heavy stimulant use." Additional loci with LOD scores above 2.00 were found for stimulant "craving" on chromosomes 12p13.33-13.32 and 18q22.3. These results corroborate the importance of "craving" as an important phenotype that is associated with regions on chromosome 12, 15, and 18, that have been highlighted in prior segregation studies in this and other populations for substance dependence-related phenotypes.

Nicotinic acetylcholine receptor subunits and associated proteins in human sperm

We demonstrated previously the involvement of a nicotinic acetylcholine receptor containing an alpha7 subunit in the human sperm acrosome reaction (a modified exocytotic event essential to fertilization). Here we report the presence in human sperm of alpha7, alpha9, alpha3, alpha5, and beta4 nicotinic acetylcholine receptor subunits and the following proteins known to be associated with the receptor in the somatic cell: rapsyn and the tyrosine kinases c-SRC and FYN. The alpha7 subunit appears to exist as a homomer in the posterior post-acrosomal and neck regions of sperm and is probably linked to the cytoskeleton via rapsyn. The alpha3, alpha5, and beta4 subunits are present in the sperm flagellar mid-piece of sperm and possibly exist as alpha3alpha5beta4 and/or alpha3beta4 channels. The alpha9 subunit is present in the sperm mid-piece. We detected the FYN and c-SRC tyrosine kinases in the flagellar mid-piece region. Both co-precipitated only with the nicotinic acetylcholine receptor beta4 subunit. Immunolocalization with a C-terminal SRC kinase antibody, which recognizes several members of SRC kinase family, detected a SRC kinase co-localized with the alpha7 subunit in the neck region of sperm. Immunoprecipitation studies with that antibody demonstrated that the alpha7 subunit is associated with a SRC kinase. Antagonists of tyrosine phosphorylation inhibited the acetylcholine-initiated acrosome reaction, suggesting the involvement of a SRC kinase in the acrosome reaction.

Mice lacking neuronal nicotinic acetylcholine receptor β4-subunit and mice lacking both α5- and β4-subunits are highly resistant to nicotine-induced seizures

Nicotine, the main addictive component of tobacco, evokes a wide range of dose-dependent behaviors in rodents, and when administrated in high doses, it can induce clonic-tonic seizures. Nicotine acts through the nicotinic acetylcholine receptors (nAChRs). Mutations in the human α4- and the β2-nAChR subunit genes cause autosomal dominant nocturnal frontal lobe epilepsy. Using transgenic mice with mutations in nAChR subunits, it was demonstrated previously that the α4-, α5-, and α7-subunits are involved in nicotine-induced seizures. To examine the possibility that the β4-subunit is also involved in this phenotype, we tested mice with homozygous β4-subunit deficiency. The β4 null mice were remarkably resistant to nicotine-induced seizures compared with wild-type and α5 null mice. We also generated mice with double deficiency of both α5- and β4-nAChR subunits and demonstrated that they were more resistant to nicotine’s convulsant effect than either the α5 or the β4 single mutant mice. In addition, the single α5 mutants and the double α5β4-deficient mice exhibited a significantly shorter latency time to seizure than that of the wild-type mice. Our results thus show that β4-containing nAChRs have a crucial role in the pathogenesis of nicotine-induced seizures. Furthermore, by comparing multiple mutant mice with single and double subunit deficiency, we suggest that nicotinic receptors containing either α5- or β4-subunits are involved in nicotine-induced seizures and that receptors containing both subunits are likely to contribute to this phenomena as well. However, the α5-subunit, but not the β4-subunit, regulates the rate of response to high doses of nicotine.

A polymorphic genomic duplication on human chromosome 15 is a susceptibility factor for panic and phobic disorders

Anxiety disorders are complex and common psychiatric illnesses associated with considerable morbidity and social cost. We have studied the molecular basis of the cooccurrence of panic and phobic disorders with joint laxity. We have identified an interstitial duplication of human chromosome 15q24-26 (named DUP25), which is significantly associated with panic/agoraphobia/social phobia/joint laxity in families, and with panic disorder in nonfamilial cases. Mosaicism, different forms of DUP25 within the same family, and absence of segregation of 15q24-26 markers with DUP25 and the psychiatric phenotypes suggest a non-Mendelian mechanism of disease-causing mutation. We propose that DUP25, which is present in 7% control subjects, is a susceptibility factor for a clinical phenotype that includes panic and phobic disorders and joint laxity.

Radiation hybrid mapping of 11 alpha and beta nicotinic acetylcholine receptor genes in Rattus norvegicus

Acetylcholine is the main neurotransmitter of the vestibular efferents and a wide variety of muscarinic and nicotinic acetylcholine receptors are expressed in the vestibular periphery. To date, 11 nicotinic subunits (alpha and beta) have been reported in mammals. Previously, our group [Brain Res. 778 (1997) 409] reported that these nicotinic acetylcholine receptor alpha and beta subunits were differentially expressed in the vestibular periphery of the rat. To begin an understanding of the molecular genetics of these vestibular efferents, this study examined the chromosomal locations of these nicotinic acetylcholine receptor genes in the rat (Rattus norvegicus). Using radiation hybrid mapping and a rat radiation hybrid map server (www.rgd.mcw.edu/RHMAP SERVER/), we determined the chromosomal position for each of these genes. The alpha2-7, alpha9, alpha10, and beta2-4 nicotinic subunits mapped to the following chromosomes: alpha2, chr. 15; alpha3, chr. 8; alpha4, chr. 3; alpha5, chr. 8; alpha6, chr. 16; alpha7, chr. 1; alpha9, chr. 14; alpha10, chr. 7; beta2, chr. 2; beta3, chr. 16; and beta4, chr. 8. With the location for each of these nicotinic subunits known, it is now possible to develop consomic and/or congenic strains of rats that can be used to study the functional genomics of each of these subunits.

Selected contribution: variation in acute hypoxic ventilatory response is linked to mouse chromosome 9

Genetic determinants confer variation among inbred mouse strains with respect to the magnitude and pattern of breathing during acute hypoxic challenge. Specifically, inheritance patterns derived from C3H/HeJ (C3) and C57BL/6J (B6) parental strains suggest that differences in hypoxic ventilatory response (HVR) are controlled by as few as two genes. The present study demonstrates that at least one genetic determinant is located on mouse chromosome 9. This genotype-phenotype association was established by phenotyping 52 B6C3F2 (F2) offspring for HVR characteristics. A genome-wide screen was performed using microsatellite DNA markers (n = 176) polymorphic between C3 and B6 mice. By computing log-likelihood values (LOD scores), linkage analysis compared marker genotypes with minute ventilation (&Vdot;E), tidal volume (VT), and mean inspiratory flow (VT/TI, where TI is inspiratory time) during acute hypoxic challenge (inspired O2 fraction = 0.10, inspired CO2 fraction = 0.03 in N2). A putative quantitative trait locus (QTL) positioned in the vicinity of D9Mit207 was significantly associated with hypoxic VE (LOD = 4.5), VT (LOD = 4.0), and VT/TI (LOD = 5.1). For each of the three HVR characteristics, the putative QTL explained more than 30% of the phenotypic variation among F(2) offspring. In conclusion, this genetic model of differential HVR characteristics demonstrates that a locus approximately 33 centimorgans from the centromere on mouse chromosome 9 confers a substantial proportion of the variance in VE, VT, and VT/TI during acute hypoxic challenge.

Neuronal nicotinic acetylcholine receptors: from the gene to the disease

The neuronal nicotinic acetylcholine receptors are excitatory ligand-gated channels. Widely expressed throughout the peripheral and central nervous system, their properties depend upon their subunit composition. Furthermore, genetic studies have revealed a high degree of variation at the genomic level and alternative splicing of the mRNAs coding for these integral membrane proteins. In particular, genes coding for alpha4 and alpha7 subunits harbour a high degree of polymorphisms. Although well characterised at their molecular and functional level, the role of these receptors in the central nervous system remains obscure. Despite accumulating evidence for the participation of nicotinic receptors in disorders of the central nervous system including nicotinic addiction, Parkinson's disease, Alzheimer's disease and Tourette's syndrome, the exact role of these receptors is still speculative. Because most of these phenotypes are complex and genetically heterogeneous, the investigation is difficult. However, in the past few years, significant progress has been made in understanding the contribution of nicotinic acetylcholine receptors to the origin of epilepsies and schizophrenia. By concentrating on the latest results gained for these diseases, we discuss in this review the possible relationships between neuronal nicotinic receptors and neurological and psychiatric disorders.

Autosomal dominant nocturnal frontal-lobe epilepsy: genetic heterogeneity and evidence for a second locus at 15q24

Autosomal dominant nocturnal frontal-lobe epilepsy (ADNFLE) is a recently identified partial epilepsy in which two different mutations have been described in the alpha4 subunit of the neuronal nicotinic acetylcholine receptor (CHRNA4). An additional seven families are presented in which ADNFLE is unlinked to the CHRNA4 region on chromosome 20q13.2. Seven additional sporadic cases showed no evidence of defective CHRNA4. One of the families showed evidence of linkage to 15q24, close to the CHRNA3/CHRNA5/CHRNB4 cluster (maximum LOD score of 3.01 with D15S152). Recombination between ADNFLE and CHRNA4, linkage to 15q24 in one family, and exclusion from 15q24 and 20q13.2 in others demonstrate genetic heterogeneity with at least three different genes for ADNFLE. The CHRNA4 gene and the two known CHRNA4 mutations are responsible for only a minority of ADNFLE. Although the ADNFLE phenotype is clinically homogeneous, there appear to be a variety of molecular defects responsible for this disorder, which will provide a challenge to the understanding of the basic mechanism of epileptogenesis.

Human neuronal nicotinic receptors

Nicotine is a very widely used drug of abuse, which exerts a number of neurovegetative, behavioural and psychological effects by interacting with neuronal nicotinic acetylcholine receptors (NAChRs). These receptors are distributed widely in human brain and ganglia, and form a family of ACh-gated ion channels of different subtypes, each of which has a specific pharmacology and physiology. As human NAChRs have been implicated in a number of human central nervous system disorders (including the neurodegenerative Alzheimer's disease, schizophrenia and epilepsy), they are suitable potential targets for rational drug therapy. Much of our current knowledge about the structure and function of NAChRs comes from studies carried out in other species, such as rodents and chicks, and information concerning human nicotinic receptors is still incomplete and scattered in the literature. Nevertheless, it is already evident that there are a number of differences in the anatomical distribution, physiology, pharmacology, and expression regulation of certain subtypes between the nicotinic systems of humans and other species. This review will attempt to survey the major achievements reached in the study of the structure and function of NAChRs by examining the molecular basis of their functional diversity viewed mainly from pharmacological and biochemical perspectives. It will also summarize our current knowledge concerning the structure and function of the NAChRs expressed by other species, and the newly discovered drugs used to classify their numerous subtypes. Finally, the role of NAChRs in behaviour and pathology will be considered.

The molecular biology of neuronal nicotinic acetylcholine receptors

The molecular cloning of genes encoding neuronal nicotinic acetylcholine receptors (nAChRs) has made possible a better understanding of the pharmacology and toxicology of cholinergic compounds. Neuronal nAChRs are related in structure to the nAChRs present at the neuromuscular junction. They are composed of multiple subunits designated either alpha and beta. Eight alpha and three beta subunit genes have been cloned. The alpha subunits contain the ligand binding sites, whereas beta subunits are structural subunits that contribute to the function of the receptor. A large number of nAChRs can be formed from different combinations of alpha and beta subunits. Different combinations of alpha and beta subunits can produce receptors in vitro with distinct ion conducting properties. Each subunit gene is expressed in a distinct pattern in the nervous system. The expression of at least some of the nAChR subunit genes is regulated during development and by cell-cell interactions. Each neuronal nAChR subtype has a distinct pharmacology. Both alpha and beta subunits contribute to the pharmacological properties of each subtype. The expression of multiple nAChR subtypes may allow for precise control of neurotransmission mediated by acetylcholine in diverse populations of neurons.

A missense mutation in the neuronal nicotinic acetylcholine receptor alpha 4 subunit is associated with autosomal dominant nocturnal frontal lobe epilepsy

Epilepsy affects at least 2% of the population at some time in their lives. The epilepsies are a heterogeneous group of disorders, many with an inherited component. Although specific genes have been identified in a few rare diseases causing seizures as part of a more diffuse brain disorder, the molecular pathology of the common idiopathic epilepsies is still unknown. Linkage has been reported for some generalised epilepsy syndromes, but only very recently for familial partial epilepsy syndromes. Autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) is a partial epilepsy causing frequent, violent, brief seizures at night, usually beginning in childhood. The gene for ADNFLE maps to chromosome 20q13.2-q13.3 in one large Australian kindred. The neuronal nicotinic acetylcholine receptor alpha 4 subunit (CHRNA4) maps to the same region of 20q (ref. 12) and the gene is expressed in all layers of the frontal cortex. We screened affected family members for mutations within CHRNA4 and found a missense mutation that replaces serine with phenylalanine at codon 248, a strongly conserved amino acid residue in the second transmembrane domain. The mutation is present in all 21 available affected family members and in four obligate carriers, but not in 333 healthy control subjects.

The CEPH consortium linkage map of human chromosome 15q

The CEPH consortium map of chromosome 15q is presented. The map contains 41 loci defined by genotypes generated from CEPH family DNAs with 45 different probe and restriction enzyme combinations contributed by 10 laboratories. A total of 29 loci have been placed on the map with likelihood support of at least 1000:1. The map extends from 15q13 to 15q25-qter. Multipoint linkage analyses provided estimates that the male, female, and sex-averaged maps extend for 127, 190, and 158 cM, respectively. The largest interval is 21 cM and is between D15S37 and D15S74. The on-average locus spacing is 5.6 cM and the mean genetic distance between the 21 uniquely placed loci is 8 cM.

Isolation, mapping, and characterization of two cDNA clones expressed in the cerebellum

In an effort to characterize genes expressed in the cerebellum, we have isolated two cDNA clones, H11B (D16S286) and 507 (D5S344), that hybridized to a cerebellar cDNA probe. Using a panel of human-rodent somatic cell hybrids, cDNA clone H11B was mapped to human chromosome 16, and clone 507 was mapped to human chromosome 5. TaqI RFLPs were identified with both clones and were used for linkage analysis in the CEPH families. D16S286 was tightly linked to several markers near chromosome 16p13, and D5S344 was tightly linked to several markers on chromosome 5q. Sequence tagged sites or expressed sequence tags were generated from the 3' untranslated regions of both cDNA clones.

Chromosomal localization of seven neuronal nicotinic acetylcholine receptor subunit genes in humans

We have determined the chromosomal location of seven human neuronal nicotinic acetylcholine receptor subunit genes by genomic Southern analysis of hamster/human somatic cell hybrid DNAs. The beta 2 subunit gene was localized to human chromosome 1, the alpha 2 and beta 3 subunit genes were localized to human chromosome 8, the alpha 3, alpha 5, and beta 4 subunit genes were localized to human chromosome 15, and the alpha 4 subunit gene was localized to human chromosome 20. Mapping of the beta 2 subunit gene to chromosome 1 establishes a syntenic group with the amylase gene locus on human chromosome 1 and mouse chromosome 3, while mapping of the alpha 3 subunit gene to chromosome 15 confirms the existence of a syntenic group with the mannose phosphate isomerase gene locus on human chromosome 15 and mouse chromosome 9.