Variations in the vesicular monoamine transporter 1 gene (VMAT1/SLC18A1) are associated with bipolar i disorder

Structural mechanisms for VMAT2 inhibition by tetrabenazine

The vesicular monoamine transporter 2 (VMAT2) is a proton-dependent antiporter responsible for loading monoamine neurotransmitters into synaptic vesicles. Dysregulation of VMAT2 can lead to several neuropsychiatric disorders including Parkinson's disease and schizophrenia. Furthermore, drugs such as amphetamine and MDMA are known to act on VMAT2, exemplifying its role in the mechanisms of actions for drugs of abuse. Despite VMAT2's importance, there remains a critical lack of mechanistic understanding, largely driven by a lack of structural information. Here, we report a 3.1 Å resolution cryo-electron microscopy (cryo-EM) structure of VMAT2 complexed with tetrabenazine (TBZ), a non-competitive inhibitor used in the treatment of Huntington's chorea. We find TBZ interacts with residues in a central binding site, locking VMAT2 in an occluded conformation and providing a mechanistic basis for non-competitive inhibition. We further identify residues critical for cytosolic and lumenal gating, including a cluster of hydrophobic residues which are involved in a lumenal gating strategy. Our structure also highlights three distinct polar networks that may determine VMAT2 conformational dynamics and play a role in proton transduction. The structure elucidates mechanisms of VMAT2 inhibition and transport, providing insights into VMAT2 architecture, function, and the design of small-molecule therapeutics.

Structural mechanisms for VMAT2 inhibition by tetrabenazine

The vesicular monoamine transporter 2 (VMAT2) is a proton-dependent antiporter responsible for loading monoamine neurotransmitters into synaptic vesicles. Dysregulation of VMAT2 can lead to several neuropsychiatric disorders including Parkinson's disease and schizophrenia. Furthermore, drugs such as amphetamine and MDMA are known to act on VMAT2, exemplifying its role in the mechanisms of actions for drugs of abuse. Despite VMAT2's importance, there remains a critical lack of mechanistic understanding, largely driven by a lack of structural information. Here we report a 3.1 Å resolution cryo-EM structure of VMAT2 complexed with tetrabenazine (TBZ), a non-competitive inhibitor used in the treatment of Huntington's chorea. We find TBZ interacts with residues in a central binding site, locking VMAT2 in an occluded conformation and providing a mechanistic basis for non-competitive inhibition. We further identify residues critical for cytosolic and lumenal gating, including a cluster of hydrophobic residues which are involved in a lumenal gating strategy. Our structure also highlights three distinct polar networks that may determine VMAT2 conformational dynamics and play a role in proton transduction. The structure elucidates mechanisms of VMAT2 inhibition and transport, providing insights into VMAT2 architecture, function, and the design of small-molecule therapeutics.

Vesicular monoamine transporter (VMAT) regional expression and roles in pathological conditions

Vesicular monoamine transporters (VMATs) are key regulators of neurotransmitter release responsible for controlling numerous physiological, cognitive, emotional, and behavioral functions. They represent important therapeutic targets for numerous pathological conditions. There are two isoforms of VMAT transporter proteins that function as secondary active transporters into the vesicle for storage and release via exocytosis: VMAT1 (SLC18A1) and VMAT2 (SLC18A2) which differ in their function, quantity, and regional expression. VMAT2 has gained considerable interest as a therapeutic target and diagnostic marker. Inhibitors of VMAT2 have been used as an effective therapy for a range of pathological conditions. Additionally, the functionality and phenotypic classification of classical and nonclassical catecholaminergic neurons are identified by the presence of VMAT2 in catecholaminergic neurons. Dysregulation of VMAT2 is also implicated in many neuropsychiatric diseases. Despite the complex role of VMAT2, many aspects of its function remain unclear. Therefore, our aim is to expand our knowledge of the role of VMAT with a special focus on VMAT2 in different systems and cellular pathways which may potentially facilitate development of novel, more specific therapeutic targets. The current review provides a summary demonstrating the mechanism of action of VMAT, its functional role, and its contribution to disease progression and utilization as therapeutic targets.

Autoantibody profiling of monoamine oxidase A knockout mice, an autism spectrum disorder model

Monoamine oxidase A (MAO A) is the critical enzyme to degrade serotonin in the brain and the knockout mouse exhibits hyperserotonemia and abnormalities that are observed in autism spectrum disorder (ASD). Thus, the MAO A knockout mouse is a valuable model for studying neurological and behavioral impairments in ASD. Based on the immune dysfunction hypothesis, dysregulated humoral immunity may cause neurological impairments. To address this hypothesis, we use high-density proteome microarray to profile the serum antibodies in both wild-type and MAO A knockout mice. The distingue autoantibody signatures were observed in the MAO A knockout and wild-type controls and showed 165 up-regulated and 232 down-regulated autoantibodies. The up-regulated autoantibodies were prone to target brain tissues while down-regulated ones were enriched in sex organs. The identified autoantibodies help bridge the gap between ASD mouse models and humoral immunity, not only yielding insights into the pathological mechanisms but also providing potential biomarkers for translational research in ASD.

3D biocomposite culture enhances differentiation of dopamine-like neurons from SH-SY5Y cells: A model for studying Parkinson's disease phenotypes

Studies of underlying neurodegenerative processes in Parkinson's Disease (PD) have traditionally utilized cell cultures grown on two-dimensional (2D) surfaces. Biomimetic three-dimensional (3D) cell culture platforms have been developed to better emulate features of the brain's natural microenvironment. We here use our bioengineered brain-like tissue model, composed of a silk-hydrogel composite, to study the 3D microenvironment's contributions on the development and performance of dopaminergic-like neurons (DLNs). Compared with 2D culture, SH-SY5Y cells differentiated in 3D microenvironments were enriched for DLNs concomitant with a reduction in proliferative capacity during the neurodevelopmental process. Additionally, the 3D DLN cultures were more sensitive to oxidative stresses elicited by the PD-related neurotoxin 1-methyl-4-phenylpyridinium (MPP). MPP induced transcriptomic profile changes specific to 3D-differentiated DLN cultures, replicating the dysfunction of neuronal signaling pathways and mitochondrial dynamics implicated in PD. Overall, this physiologically-relevant 3D platform resembles a useful tool for studying dopamine neuron biology and interrogating molecular mechanisms underlying neurodegeneration in PD.

Functional and Biochemical Consequences of Disease Variants in Neurotransmitter Transporters: A Special Emphasis on Folding and Trafficking Deficits

Neurotransmitters, such as γ-aminobutyric acid, glutamate, acetyl choline, glycine and the monoamines, facilitate the crosstalk within the central nervous system. The designated neurotransmitter transporters (NTTs) both release and take up neurotransmitters to and from the synaptic cleft. NTT dysfunction can lead to severe pathophysiological consequences, e.g. epilepsy, intellectual disability, or Parkinson’s disease. Genetic point mutations in NTTs have recently been associated with the onset of various neurological disorders. Some of these mutations trigger folding defects in the NTT proteins. Correct folding is a prerequisite for the export of NTTs from the endoplasmic reticulum (ER) and the subsequent trafficking to their pertinent site of action, typically at the plasma membrane. Recent studies have uncovered some of the key features in the molecular machinery responsible for transporter protein folding, e.g., the role of heat shock proteins in fine-tuning the ER quality control mechanisms in cells. The therapeutic significance of understanding these events is apparent from the rising number of reports, which directly link different pathological conditions to NTT misfolding. For instance, folding-deficient variants of the human transporters for dopamine or GABA lead to infantile parkinsonism/dystonia and epilepsy, respectively. From a therapeutic point of view, some folding-deficient NTTs are amenable to functional rescue by small molecules, known as chemical and pharmacological chaperones.

miR-409 and miR-411 Modulation in the Adult Brain of a Rat Model of Depression and After Fluoxetine Treatment

Depression is a chronic debilitating disorder predicted to affect around 20% of the world population. Both brain and peripheral changes, including neuroplastic changes have been shown to occur in the brains of depressed individuals and animal models of depression. Over the past few decades, growing evidence has supported the role of miRNAs as regulators of critical aspects of brain plasticity and function, namely in the context of depression. These molecules are not only highly expressed in the brain, but are also relatively stable in bodily fluids, including blood. Previous microarray analysis from our group has disclosed molecular players in the hippocampal dentate gyrus (DG), in the context of depression and antidepressant treatment. Two miRNAs in particular-miR-409-5p and miR-411-5p-were significantly up-regulated in the DG of an unpredictable chronic mild stress (CMS) rat model of depression and reversed by antidepressant treatment. Here, we further analyzed the levels of these miRNAs along the DG longitudinal axis and in other brain regions involved in the pathophysiology of depression, as well as in peripheral blood of CMS-exposed rats and after fluoxetine treatment. The effects of CMS and fluoxetine treatment on miR-409-5p and miR-411-5p levels varied across brain regions, and miR-411-5p was significantly decreased in the blood of fluoxetine-treated rats. Additional bioinformatic analyses revealed target genes and pathways of these miRNAs related to neurotransmitter signaling and neuroplasticity functions; an implication of the two miRNAs in the regulation of the cellular and molecular changes observed in these brain regions in depression is worth further examination.

High-Resolution mRNA and Secretome Atlas of Human Enteroendocrine Cells

Enteroendocrine cells (EECs) sense intestinal content and release hormones to regulate gastrointestinal activity, systemic metabolism, and food intake. Little is known about the molecular make-up of human EEC subtypes and the regulated secretion of individual hormones. Here, we describe an organoid-based platform for functional studies of human EECs. EEC formation is induced in vitro by transient expression of NEUROG3. A set of gut organoids was engineered in which the major hormones are fluorescently tagged. A single-cell mRNA atlas was generated for the different EEC subtypes, and their secreted products were recorded by mass-spectrometry. We note key differences to murine EECs, including hormones, sensory receptors, and transcription factors. Notably, several hormone-like molecules were identified. Inter-EEC communication is exemplified by secretin-induced GLP-1 secretion. Indeed, individual EEC subtypes carry receptors for various EEC hormones. This study provides a rich resource to study human EEC development and function.

Human-specific mutations in VMAT1 confer functional changes and multi-directional evolution in the regulation of monoamine circuits

BACKGROUND

Neurochemicals like serotonin and dopamine play crucial roles in human cognitive and emotional functions. Vesicular monoamine transporter 1 (VMAT1) transports monoamine neurotransmitters, and its variant (136Thr) is associated with various psychopathological symptoms and reduced monoamine uptake relative to 136Ile. We previously showed that two human-specific amino acid substitutions (Glu130Gly and Asn136Thr/Ile) of VMAT1 were subject to positive natural selection. However, the potential functional alterations caused by these substitutions (Glu130Gly and Asn136Thr) remain unclear. To assess functional changes in VMAT1 from an evolutionary perspective, we reconstructed ancestral residues and examined the role of these substitutions in monoamine uptake in vitro using fluorescent false neurotransmitters (FFN), which are newly developed substances used to quantitatively assay VMATs.

RESULTS

Immunoblotting confirmed that all the transfected YFP-VMAT1 variants are properly expressed in HEK293T cells at comparable levels, and no significant difference was seen in the density and the size of vesicles among them. Our fluorescent assays revealed a significant difference in FFN206 uptake among VMAT1 variants: 130Glu/136Asn, 130Glu/136Thr, and 130Gly/136Ile showed significantly higher levels of FFN206 uptake than 130Gly/136Asn and 130Gly/136Thr, indicating that both 130Glu and 136Ile led to increased neurotransmitter uptake, for which 136Thr and 136Asn were comparable by contrast.

CONCLUSIONS

These findings suggest that monoamine uptake by VMAT1 initially declined (from 130Glu/136Asn to 130Gly/136Thr) in human evolution, possibly resulting in higher susceptibility to the external environment of our ancestors.

Conserved regulation of neurodevelopmental processes and behavior by FoxP in Drosophila

FOXP proteins form a subfamily of evolutionarily conserved transcription factors involved in the development and functioning of several tissues, including the central nervous system. In humans, mutations in FOXP1 and FOXP2 have been implicated in cognitive deficits including intellectual disability and speech disorders. Drosophila exhibits a single ortholog, called FoxP, but due to a lack of characterized mutants, our understanding of the gene remains poor. Here we show that the dimerization property required for mammalian FOXP function is conserved in Drosophila. In flies, FoxP is enriched in the adult brain, showing strong expression in ~1000 neurons of cholinergic, glutamatergic and GABAergic nature. We generate Drosophila loss-of-function mutants and UAS-FoxP transgenic lines for ectopic expression, and use them to characterize FoxP function in the nervous system. At the cellular level, we demonstrate that Drosophila FoxP is required in larvae for synaptic morphogenesis at axonal terminals of the neuromuscular junction and for dendrite development of dorsal multidendritic sensory neurons. In the developing brain, we find that FoxP plays important roles in α-lobe mushroom body formation. Finally, at a behavioral level, we show that Drosophila FoxP is important for locomotion, habituation learning and social space behavior of adult flies. Our work shows that Drosophila FoxP is important for regulating several neurodevelopmental processes and behaviors that are related to human disease or vertebrate disease model phenotypes. This suggests a high degree of functional conservation with vertebrate FOXP orthologues and established flies as a model system for understanding FOXP related pathologies.

Deletion of the vesicular monoamine transporter 1 (vmat1/slc18a1) gene affects dopamine signaling

The vesicular monoamine transporter is involved in presynaptic catecholamine storage and neurotransmission. Two isoforms of the transporter exist, VMAT1 and VMAT2, and both are expressed in the brain, though VMAT2 expression is more robust and has been more widely studied. In this study we investigated the role of VMAT1 KO on markers of dopaminergic function and neurotransmission, and dopamine-related behaviors. Null-mutant VMAT1 mice were studied behaviorally using the tail suspension test, elevated zero maze and locomotor activity assessments. Tissue monoamines were measured both ex vivo and by using in vivo microdialysis. Protein expression of tyrosine hydroxylase and D2 dopamine receptors was measured using western blot analysis. Results show that VMAT1 KO mice have decreased dopamine levels in the frontal cortex, increased postsynaptic D2 expression, and lower frontal cortex tyrosine hydroxylase expression compared to WT mice. VMAT1 KO mice also show an exaggerated behavioral locomotor response to acute amphetamine treatment. We conclude that dopaminergic signaling is robustly altered in the frontal cortex of VMAT1 null-mutant mice and suggest that VMAT1 may be relevant to the pathogenesis and/or treatment of psychiatric illnesses including schizophrenia and bipolar disease.

Expression of the Vesicular Monoamine Transporter Gene Solute Carrier Family 18 Member 1 (SLC18A1) in Lung Cancer

BACKGROUND

One aspect of smoking and lung cancer that has not been closely examined, is that regarding genes that may predispose to tobacco dependence. Smoking and mental illness are tightly linked, apparently the result of smokers using cigarettes to self-medicate for mental problems. The gene for solute carrier family 18 member A1 (vesicular monoamine transporter; SLC18A1) is of particular interest in this regard because of its association with schizophrenia, autism and bipolar illness as well as with cancer. In the current study, the relationship of SLC18A1 expression with smoking and lung cancer was analyzed.

MATERIALS AND METHODS

The association between smoking, SLC18A1 expression and overall survival in the lung cancer dataset in The Cancer Genome Atlas was evaluated using the Genomic Data Commons Data Portal (https://portal.gdc.cancer.gov), as well as CbioPortal for Cancer Genomics (http://www.cbioportal.org) and the University of California Santa Cruz Xena browser (https://xenabrowser.net).

RESULTS

Increased expression of SLC18A1 was found to be associated with a significantly increased survival in patients with adenocarcinoma (p=0.0058), but not those with squamous carcinoma (p=0.96). Lifelong never-smokers had the highest SLC18A1 expression. In the Pan Cancer Atlas, increased expression of SLC18A1 places such a tumor in group C5, among immunologically-quiet tumors.

CONCLUSION

Most never-smokers with lung cancer do not respond to immune checkpoint inhibitors (ICIs). But for unknown reasons, a small proportion do show clinical benefit from the ICI pembrolizumab. Because of the good response of this group, it may be worthwhile assessing their SLC18A1 expression pre-treatment as a marker for potential clinical benefit. If SLC18A1 expression is low, a never-smoker may respond well to ICIs. High levels of expression would indicate a C5 tumor less likely to respond to ICIs. SLC18A1 might complement other biomarkers currently under study in relation to programmed cell death protein 1/programmed cell death protein ligand 1 inhibition.

Positive and balancing selection on SLC18A1 gene associated with psychiatric disorders and human-unique personality traits

Maintenance of genetic variants susceptible to psychiatric disorders is one of the intriguing evolutionary enigmas. The present study detects three psychiatric disorder‐relevant genes (CLSTN2, FAT1, and SLC18A1) that have been under positive selection during the human evolution. In particular, SLC18A1 (vesicular monoamine transporter 1; VMAT1) gene has a human‐unique variant (rs1390938, Thr136Ile), which is associated with bipolar disorders and/or the anxiety‐related personality traits. 136Ile shows relatively high (20–61%) frequency in non‐African populations, and Tajima's D reports a significant peak around the Thr136Ile site, suggesting that this polymorphism has been positively maintained by balancing selection in non‐African populations. Moreover, Coalescent simulations predict that 136Ile originated around 100,000 years ago, the time being generally associated with the Out‐of‐Africa migration of modern humans. Our study sheds new light on a gene in monoamine pathway as a strong candidate contributing to human‐unique psychological traits.

Association Study of VMAT1 Polymorphisms and Suicide Behavior

Genetic association studies have linked suicide behavior with genes encoding transporters of monoamine. Variants in the vesicular monoamine transporter 1 (VMAT1) have been previously shown to be associated with several psychiatric disorders including schizophrenia and bipolar disorder. However, their association with suicide behavior has not been explored. In the present study, we genotyped three single-nucleotide polymorphisms (rs2270637, rs1390938, and rs2279709) within this gene in 100 individuals who attempted suicide, 236 suicide victims, and 300 control subjects without any history of psychiatric disorders or suicide ideation. We demonstrated no difference in genotype, allele, or haplotype frequencies of theses single-nucleotide polymorphisms between the study groups. Consequently, contribution of VMAT1 in risk of psychiatric disorders might be independent of suicide behavior. Future studies with larger sample sizes are needed to confirm our results.

Deletions at SLC18A1 increased the risk of CRC and lower SLC18A1 expression associated with poor CRC outcome

Copy number variations (CNVs) contribute to the development of colorectal cancer (CRC). We conducted a two-stage association study to identify CNV risk loci for CRC. We performed a gene-based rare CNV study on 694 sporadic CRC and 1641 controls using Illumina Human-OmniExpress-12v1.0 BeadChips, and further replicated in 934 CRC cases and 2680 controls for risk CNVs by using TaqMan Copy Number Assay. Tumor buddings, cancer cells in the center of primary tumor and normal intestinal epithelial cells were captured using laser capture microdissection (LCM) and were assayed using AffymetrixGeneChip® Human Genome U133 Plus 2.0 Array. In addition, The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus data were assessed for the effects of risk CNVs. We found that germline deletions affecting the last six exons of SLC18A1 significantly associated with CRC with a combined P value of 6.4 × 10-5 by a two-stage analysis. Both in TCGA CRC RNA seq dataset and GDS4382, SLC18A1 was significantly down regulated in CRC tissues than in paired normal tissues (N = 32 and 17 pairs, P = 0.004 and 0.009, respectively). In LCM samples, similar observations were obtained that the expression levels of SLC18A1 in the tumor buddings, cancer cells in the center of primary tumor, and stroma of both tumor budding and cancer cells were lower than normal intestinal epithelial and stromal cells (fold change = 0.17-0.62, 0.12-0.57 and 0.37-0.68, respectively). In summary, the germline deletions at SLC18A1 contributed to the development of CRC. The role of SLC18A1 required further exploration.

Vesicular monoamine transporter 1 gene polymorphism and white matter integrity in major depressive disorder

The genetic variant of the vesicular monoamine transporter 1 gene (VMAT1) has been suggested to be associated with monoaminergic signaling and neural circuit activity related to emotion processing. We aimed to investigate microstructural changes in white matter tracts of patients with major depressive disorder (MDD), and examined the interaction effect between VMAT1 Thr136Ile (rs1390938) polymorphism and MDD on white matter integrity. Diffusion tensor imaging (DTI) and VMAT1 Thr136Ile (rs1390938) genotyping were performed on 103 patients diagnosed with MDD and 83 healthy control participants. DTI was used to investigate microstructural changes in white matter tracts in patients compared to healthy controls. The possible interaction effect between rs1390938 and MDD on white matter integrity was also assessed. Patients with MDD exhibited lower fractional anisotropy (FA) values of the forceps major (p<0.001), forceps minor (p=0.001), inferior longitudinal fasciculus (left: p=0.001; right: p<0.001), parietal endings of the superior longitudinal fasciculus (left: p<0.001; right: p=0.002), left temporal endings of the superior longitudinal fasciculus (p=0.001), and right uncinate fasciculus (p=0.001). Significant genotype-by-diagnosis interaction effects were observed on FA values of the right uncinate fasciculus (p=0.001), with A-allele carrier patients exhibiting lower FA values compared to G-allele homozygous patients (p=0.003). No significant differences in FA values were observed between genotype subgroups among healthy controls. Our results may contribute to the evidence indicating an association between the VMAT1 gene and structural brain alterations in depression.

Association study of the vesicular monoamine transporter 1 (VMAT1) gene with autism in an Iranian population

Autism Spectrum Disorders (ASD) (MIM 209850) are a group of neurodevelopmental disorders distinguished by destructed social interaction and communication abilities along with peculiar repetitive behavior. Several genetic loci have been linked to this disorder. Vesicular monoamine transporter 1 (VMAT1/SLC18A1) is an attractive candidate gene for psychiatric disorders because of its participation in regulation monoamines. In the present case-control study, we evaluated the link between three non-synonymous single nucleotide polymorphisms (SNPs) (rs2270641 [Pro4Thr], rs2270637 [Thr98Ser] and rs1390938 [Thr136Ile]) and one intronic SNP (rs2279709) across the VMAT1 gene and ASD in a group of Iranian patients. Allele frequency analyses showed significant over-presentation of rs1390938-G allele in cases compared with controls (P<0.001). The analysis under different genetic models showed that the AA genotype of the rs1390938 was protective against ASD under dominant and recessive models. The rs2270641 SNP was associated with ASD risk only in over-dominant model. Other SNPs showed no significant difference in allele or genotype frequencies between two groups. Haplotype analysis revealed that C A T T and C A T G haplotypes (rs2270637, rs1390938, rs2279709 and rs2270641 respectively) have a protective effect against ASD. Consequently, the functional rs1390938 SNP in VMAT1 is associated with ASD in Iranian population. Considering the role of VMAT1 in regulation of monoamines, the dysregulated expression of this protein during early stages of brain development might be implicated in ASD.

The genetic overlap between mood disorders and cardiometabolic diseases: a systematic review of genome wide and candidate gene studies

Meta-analyses of genome-wide association studies (meta-GWASs) and candidate gene studies have identified genetic variants associated with cardiovascular diseases, metabolic diseases and mood disorders. Although previous efforts were successful for individual disease conditions (single disease), limited information exists on shared genetic risk between these disorders. This article presents a detailed review and analysis of cardiometabolic diseases risk (CMD-R) genes that are also associated with mood disorders. First, we reviewed meta-GWASs published until January 2016, for the diseases 'type 2 diabetes, coronary artery disease, hypertension' and/or for the risk factors 'blood pressure, obesity, plasma lipid levels, insulin and glucose related traits'. We then searched the literature for published associations of these CMD-R genes with mood disorders. We considered studies that reported a significant association of at least one of the CMD-R genes and 'depression' or 'depressive disorder' or 'depressive symptoms' or 'bipolar disorder' or 'lithium treatment response in bipolar disorder', or 'serotonin reuptake inhibitors treatment response in major depression'. Our review revealed 24 potential pleiotropic genes that are likely to be shared between mood disorders and CMD-Rs. These genes include MTHFR, CACNA1D, CACNB2, GNAS, ADRB1, NCAN, REST, FTO, POMC, BDNF, CREB, ITIH4, LEP, GSK3B, SLC18A1, TLR4, PPP1R1B, APOE, CRY2, HTR1A, ADRA2A, TCF7L2, MTNR1B and IGF1. A pathway analysis of these genes revealed significant pathways: corticotrophin-releasing hormone signaling, AMPK signaling, cAMP-mediated or G-protein coupled receptor signaling, axonal guidance signaling, serotonin or dopamine receptors signaling, dopamine-DARPP32 feedback in cAMP signaling, circadian rhythm signaling and leptin signaling. Our review provides insights into the shared biological mechanisms of mood disorders and cardiometabolic diseases.

Immunomodulatory Effects Mediated by Dopamine

Dopamine (DA), a neurotransmitter in the central nervous system (CNS), has modulatory functions at the systemic level. The peripheral and central nervous systems have independent dopaminergic system (DAS) that share mechanisms and molecular machinery. In the past century, experimental evidence has accumulated on the proteins knowledge that is involved in the synthesis, reuptake, and transportation of DA in leukocytes and the differential expression of the D1-like (D1R and D5R) and D2-like receptors (D2R, D3R, and D4R). The expression of these components depends on the state of cellular activation and the concentration and time of exposure to DA. Receptors that are expressed in leukocytes are linked to signaling pathways that are mediated by changes in cAMP concentration, which in turn triggers changes in phenotype and cellular function. According to the leukocyte lineage, the effects of DA are associated with such processes as respiratory burst, cytokine and antibody secretion, chemotaxis, apoptosis, and cytotoxicity. In clinical conditions such as schizophrenia, Parkinson disease, Tourette syndrome, and multiple sclerosis (MS), there are evident alterations during immune responses in leukocytes, in which changes in DA receptor density have been observed. Several groups have proposed that these findings are useful in establishing clinical status and clinical markers.

Association between genetic variants of serotonergic and glutamatergic pathways and the concentration of neurometabolites of the anterior cingulate cortex in paediatric patients with obsessive-compulsive disorder

OBJECTIVES

The present study aimed to assess the relationship between variability in genes related to the pathophysiology of obsessive-compulsive disorder (OCD) and the concentration of different neurometabolites in the anterior cingulate cortex (ACC).

METHODS

We concomitantly assessed neurometabolite concentrations using 3-T (1)H-MRS and 262 single nucleotide polymorphism (SNPs) in 35 genes in 41 paediatric OCD patients.

RESULTS

There were significant associations, after Bonferroni correction, between the concentration of inositol, glutamate and glutamine, and total choline and five polymorphisms located in genes related to serotonin and glutamate (i.e., the vesicular monoamine transporter 1 gene, SLC18A1 [rs6586896]; the serotonin receptor 1B gene, HTR1B [rs6296 and rs6298]; and the glutamate receptor, ionotropic, AMPA1 gene, GRIA1 [rs707176 and rs2963944]).

CONCLUSIONS

The association observed between these polymorphisms and the neurometabolite concentrations could indicate the presence of a biological interaction between the serotonin and the glutamate pathways that could be involved in the pathophysiology of OCD. More studies with this methodology could increase our understanding of the aetiology and pathophysiology of OCD in children.

A Functional Vesicular Monoamine Transporter 1 (VMAT1) Gene Variant Is Associated with Affect and the Prevalence of Anxiety, Affective, and Alcohol Use Disorders in a Longitudinal Population-Representative Birth Cohort Study

BACKGROUND

Inter-individual differences in the monoaminergic systems have been shown to moderate the risk for a lifetime history of anxiety, affective, and alcohol use disorders. A common single nucleotide polymorphism in the vesicular monoamine transporter 1 gene (VMAT1 rs1390938 G/A; Thr136Ile) has been reported as functional in vitro and associated with bipolar disorder and anxiety. We aimed at assessing the association between the VMAT1 genotype, affect, and affect-related psychiatric disorders in a longitudinal population-representative study.

METHODS

We used the database of the Estonian Children Personality Behaviour and Health Study (beginning in 1998). Cohorts of initially 9- (recalled at ages 15 and 18 years, n=579) and 15- (recalled at ages 18 and 25 years; n=654) year-old children provided self-reports on impulsivity, anxiety, depressiveness, neuroticism, and alcohol use. In addition, psychiatric assessment based on DSM-IV was carried out in the older cohort at age 25 years.

RESULTS

Subjects homozygous for the less prevalent A (136Ile) allele reported lower maladaptive impulsivity, state and trait anxiety, depressiveness, and neuroticism and were less likely to have been diagnosed with an affective, anxiety, and/or alcohol use disorder by young adulthood. While in the younger cohort alcohol use started at younger age, this birth cohort effect was dependent on genotype: only G allele carriers and in particular the GG homozygotes started alcohol use earlier.

CONCLUSIONS

VMAT1 rs1390938/Thr136Ile is associated with mood, personality, and alcohol use in the general population. Subjects homozygous for the "hyperfunction" allele (AA; Ile/Ile) appear to be more resilient to these disorders.

Assessment of individual differences in the rat nucleus accumbens transcriptome following taste-heroin extended access

Heroin addiction is a disease of chronic relapse that harms the individual through devaluation of personal responsibilities in favor of finding and using drugs. Only some recreational heroin users devolve into addiction but the basis of these individual differences is not known. We have shown in rats that avoidance of a heroin-paired taste cue reliably identifies individual animals with greater addiction-like behavior for heroin. Here rats received 5min access to a 0.15% saccharin solution followed by the opportunity to self-administer either saline or heroin for 6h. Large Suppressors of the heroin-paired taste cue displayed increased drug escalation, motivation for drug, and drug loading behavior compared with Small Suppressors. Little is known about the molecular mechanisms of these individual differences in addiction-like behavior. We examined the individual differences in mRNA expression in the nucleus accumbens (NAc) of rats that were behaviorally stratified by addiction-like behavior using next-generation sequencing. We hypothesized that based on the avoidance of the drug-paired cue there will be a unique mRNA profile in the NAc. Analysis of strand-specific whole genome RNA-Seq data revealed a number of genes differentially regulated in NAc based on the suppression of the natural saccharine reward. Large Suppressors exhibited a unique mRNA prolife compared to Saline controls and Small Suppressors. Genes related to immunity, neuronal activity, and behavior were differentially expressed among the 3 groups. In total, individual differences in avoidance of a heroin-paired taste cue are associated with addiction-like behavior along with differential NAc gene expression.

Resting-state functional connectivity and presynaptic monoamine signaling in Alcohol Dependence

Alcohol Dependence (AD) is a chronic relapsing disorder with high degrees of morbidity and mortality. While multiple neurotransmitter systems are involved in the complex symptomatology of AD, monoamine dysregulation and subsequent neuroadaptations have been long postulated to play an important role. Presynaptic monoamine transporters, such as the vesicular monoamine transporter 1 (VMAT1), are likely critical as they represent a key common entry point for monoamine regulation and may represent a shared pathway for susceptibility to AD. Excessive monoaminergic signaling as mediated by genetic variation in VMAT1 might affect functional brain connectivity in particular in alcoholics compared to controls. We conducted resting-state fMRI functional connectivity (FC) analysis using the independent component analysis (ICA) approach in 68 AD subjects and 72 controls. All subjects were genotyped for the Thr136Ile (rs1390938) variant in VMAT1. Functional connectivity analyses showed a significant increase of resting-state FC in 4 networks in alcoholics compared to controls (P < 0.05, corrected). The FC was significantly positively correlated with Alcohol Dependence Scale (ADS). The hyperfunction allele 136Ile was associated with a significantly decreased FC in the Default Mode Network, Prefrontal Cortex Network, and Executive Control Network in alcohol dependent participants (P < 0.05, corrected), but not in controls. Our data suggest that increased FC might represent a neuroadaptive mechanism relevant to AD that is furthermore mediated by genetic variation in VMAT1. The hyperfunction allele Thr136Ile might have a protective effect that is, in particular, relevant in AD by mechanism of increased monoamine transport into presynaptic storage vesicles.

Reconstruction of the gene regulatory network involved in the sonic hedgehog pathway with a potential role in early development of the mouse brain

The Sonic hedgehog (Shh) signaling pathway is crucial for pattern formation in early central nervous system development. By systematically analyzing high-throughput in situ hybridization data of E11.5 mouse brain, we found that Shh and its receptor Ptch1 define two adjacent mutually exclusive gene expression domains: Shh⁺Ptch1⁻ and Shh⁻Ptch1⁺. These two domains are associated respectively with Foxa2 and Gata3, two transcription factors that play key roles in specifying them. Gata3 ChIP-seq experiments and RNA-seq assays on Gata3-knockdown cells revealed that Gata3 up-regulates the genes that are enriched in the Shh⁻Ptch1⁺ domain. Important Gata3 targets include Slit2 and Slit3, which are involved in the process of axon guidance, as well as Slc18a1, Th and Qdpr, which are associated with neurotransmitter synthesis and release. By contrast, Foxa2 both up-regulates the genes expressed in the Shh⁺Ptch1⁻ domain and down-regulates the genes characteristic of the Shh⁻Ptch1⁺ domain. From these and other data, we were able to reconstruct a gene regulatory network governing both domains. Our work provides the first genome-wide characterization of the gene regulatory network involved in the Shh pathway that underlies pattern formation in the early mouse brain.

Recent large-scale projects of high-throughput in situ hybridization (ISH) have generated a wealth of spatiotemporal information on gene expression patterns in the early mouse brain. We have developed a computational approach that combines publicly available high-throughput ISH data with our own experimental data to investigate gene regulation, involving signal molecules and transcription factors (TFs), during early brain development. The analysis indicates that two key TFs, Foxa2 and Gata3, play antagonizing roles in the formation of two mutually exclusive domains established by the Sonic hedgehog signaling pathway in the developing mouse brain. Further ChIP-seq and RNA-seq experiments support this hypothesis and have identified novel target genes of Gata3, including the axon guidance regulators Slit2 and Slit3 as well as three neurotransmitter-associated genes, Slc18a1, Th and Qdpr. The findings have allowed us to reconstruct the gene regulatory network brought into play by the Sonic hedgehog pathway that mediates early mouse brain development.

Functional genetic variants in the vesicular monoamine transporter 1 modulate emotion processing

Emotional behavior is in part heritable and often disrupted in psychopathology. Identification of specific genetic variants that drive this heritability may provide important new insight into molecular and neurobiological mechanisms involved in emotionality. Our results demonstrate that the presynaptic vesicular monoamine transporter 1 (VMAT1) Thr136Ile (rs1390938) polymorphism is functional in vitro, with the Ile allele leading to increased monoamine transport into presynaptic vesicles. Moreover, we show that the Thr136Ile variant predicts differential responses in emotional brain circuits consistent with its effects in vitro. Lastly, deep sequencing of bipolar disorder (BPD) patients and controls identified several rare novel VMAT1 variants. The variant Phe84Ser was only present in individuals with BPD and leads to marked increase monoamine transport in vitro. Taken together, our data show that VMAT1 polymorphisms influence monoamine signaling, the functional response of emotional brain circuits and risk for psychopathology.

VMAT1 deletion causes neuronal loss in the hippocampus and neurocognitive deficits in spatial discrimination

Vesicular monoamine transporters (VMAT) are involved in presynaptic storage and release of neurotransmitters. While it was thought initially that only VMAT2 is brain expressed and VMAT1 is present only in the periphery, recent data have challenged the exclusive expression of VMAT2 in the brain. To further elucidate the role of VMAT1 brain expression and its potential role in neuropsychiatric disorders, we have investigated mice lacking VMAT1. Comparison of wildtype and knock-out (KO) mice using qPCR and immunohistochemistry documents the expression of VMAT1 in the brain. Deletion of VMAT1 leads to increased hippocampal apoptosis and reduced neurogenesis as assessed by caspase-3-labeling and 5-bromo-deoxy-uridine-labeling. Behavioral data show that mice lacking VMAT1 have neurocognitive deficits. VMAT2 expression is not altered in VMAT1 KO mice, suggesting a distinct role of VMAT1. Our data support VMAT1 brain expression and suggest that VMAT1 plays a key role in survival of hippocampal neurons and thus might contribute to neurocognitive deficits observed in neuropsychiatric disorders.

Genomics and pharmacogenomics of schizophrenia

Schizophrenia (SCZ) is among the most disabling of mental disorders. Several neurobiological hypotheses have been postulated as responsible for SCZ pathogenesis: polygenic/multifactorial genomic defects, intrauterine and perinatal environment-genome interactions, neurodevelopmental defects, dopaminergic, cholinergic, serotonergic, gamma-aminobutiric acid (GABAergic), neuropeptidergic and glutamatergic/N-Methyl-D-Aspartate (NMDA) dysfunctions, seasonal infection, neuroimmune dysfunction, and epigenetic dysregulation. SCZ has a heritability estimated at 60-90%. Genetic studies in SCZ have revealed the presence of chromosome anomalies, copy number variants, multiple single-nucleotide polymorphisms of susceptibility distributed across the human genome, aberrant single nucleotide polymorphisms (SNPs) in microRNA genes, mitochondrial DNA mutations, and epigenetic phenomena. Pharmacogenetic studies of psychotropic drug response have focused on determining the relationship between variation in specific candidate genes and the positive and adverse effects of drug treatment. Approximately, 18% of neuroleptics are major substrates of CYP1A2 enzymes, 40% of CYP2D6, and 23% of CYP3A4; 24% of antidepressants are major substrates of CYP1A2 enzymes, 5% of CYP2B6, 38% of CYP2C19, 85% of CYP2D6, and 38% of CYP3A4; 7% of benzodiazepines are major substrates of CYP2C19 enzymes, 20% of CYP2D6, and 95% of CYP3A4. About 10-20% of Western populations are defective in genes of the CYP superfamily. Only 26% of Southern Europeans are pure extensive metabolizers for the trigenic cluster integrated by the CYP2D6+CYP2C19+CYP2C9 genes. The pharmacogenomic response of SCZ patients to conventional psychotropic drugs also depends on genetic variants associated with SCZ-related genes. Consequently, the incorporation of pharmacogenomic procedures both to drugs in development and drugs on the market would help to optimize therapeutics in SCZ and other central nervous system (CNS) disorders.

Design, synthesis and interaction at the vesicular monoamine transporter-2 of lobeline analogs: potential pharmacotherapies for the treatment of psychostimulant abuse

The vesicular monoamine transporter-2 (VMAT2) is considered as a new target for the development of novel therapeutics to treat psychostimulant abuse. Current information on the structure, function and role of VMAT2 in psychostimulant abuse are presented. Lobeline, the major alkaloidal constituent of Lobelia inflata, interacts with nicotinic receptors and with VMAT2. Numerous studies have shown that lobeline inhibits both the neurochemical and behavioral effects of amphetamine in rodents, and behavioral studies demonstrate that lobeline has potential as a pharmacotherapy for psychostimulant abuse. Systematic structural modification of the lobeline molecule is described with the aim of improving selectivity and affinity for VMAT2 over neuronal nicotinic acetylcholine receptors and other neurotransmitter transporters. This has led to the discovery of more potent and selective ligands for VMAT2. In addition, a computational neural network analysis of the affinity of these lobeline analogs for VMAT2 has been carried out, which provides computational models that have predictive value in the rational design of VMAT2 ligands and is also useful in identifying drug candidates from virtual libraries for subsequent synthesis and evaluation.

Incomplete coverage of candidate genes: a poorly considered bias

Current genetic investigations are performed both on the basis of a rational and biologically based choice of candidate genes and through genome wide scans. Nonetheless, lack of replication is a common problem in psychiatric genetics as well as in other genetic fields. There are a number of reasons for this inconsistency, among them a well known but poorly considered issue is gene coverage. The aim of the present paper is to focus on this well known and defectively deemed bias, especially when a candidate gene approach is chosen. The rational and the technical feasibility of this proposal are discussed as well as a survey of current investigations. The known consistent methodology to fix this bias is also discussed.

Vesicular monoamine transporters: structure-function, pharmacology, and medicinal chemistry

Vesicular monoamine transporters (VMAT) are responsible for the uptake of cytosolic monoamines into synaptic vesicles in monoaminergic neurons. Two closely related VMATs with distinct pharmacological properties and tissue distributions have been characterized. VMAT1 is preferentially expressed in neuroendocrine cells and VMAT2 is primarily expressed in the CNS. The neurotoxicity and addictive properties of various psychostimulants have been attributed, at least partly, to their interference with VMAT2 functions. The quantitative assessment of the VMAT2 density by PET scanning has been clinically useful for early diagnosis and monitoring of the progression of Parkinson's and Alzheimer's diseases and drug addiction. The classical VMAT2 inhibitor, tetrabenazine, has long been used for the treatment of chorea associated with Huntington's disease in the United Kingdom, Canada, and Australia, and recently approved in the United States. The VMAT2 imaging may also be useful for exploiting the onset of diabetes mellitus, as VMAT2 is also expressed in the β-cells of the pancreas. VMAT1 gene SLC18A1 is a locus with strong evidence of linkage with schizophrenia and, thus, the polymorphic forms of the VMAT1 gene may confer susceptibility to schizophrenia. This review summarizes the current understanding of the structure-function relationships of VMAT2, and the role of VMAT2 on addiction and psychostimulant-induced neurotoxicity, and the therapeutic and diagnostic applications of specific VMAT2 ligands. The evidence for the linkage of VMAT1 gene with schizophrenia and bipolar disorder I is also discussed.

VMAT2: a dynamic regulator of brain monoaminergic neuronal function interacting with drugs of abuse

The monoaminergic neuron, in particular the dopaminergic neuron, is central to mediating the hedonic and addictive properties of drugs of abuse. The effects of amphetamine (AMPH) and cocaine (COC), for example, depend on the ability to increase dopamine in the synapse, by effects on either the plasma membrane transporter DAT or the vesicular transporter for monoamine storage, VMAT2. The potential role of DAT as a target for AMPH and COC has been reviewed extensively. Here, we present VMAT2 as a target that enables the rewarding and addictive actions of these drugs, based on imaging, neurochemical, biochemical, cell biological, genetic, and immunohistochemical evidence. The presence of VMAT2 in noradrenergic, serotoninergic, histaminergic, and potentially trace aminergic neurons invites consideration of a wider role for aminergic neurotransmission in AMPH and COC abuse and addiction.

Novel loci for major depression identified by genome-wide association study of Sequenced Treatment Alternatives to Relieve Depression and meta-analysis of three studies

We report a genome-wide association study (GWAS) of major depressive disorder (MDD) in 1221 cases from the Sequenced Treatment Alternatives to Relieve Depression (STAR*D) study and 1636 screened controls. No genome-wide evidence for association was detected. We also carried out a meta-analysis of three European-ancestry MDD GWAS data sets: STAR*D, Genetics of Recurrent Early-onset Depression and the publicly available Genetic Association Information Network-MDD data set. These data sets, totaling 3957 cases and 3428 controls, were genotyped using four different platforms (Affymetrix 6.0, 5.0 and 500 K, and Perlegen). For each of 2.4 million HapMap II single-nucleotide polymorphisms (SNPs), using genotyped data where available and imputed data otherwise, single-SNP association tests were carried out in each sample with correction for ancestry-informative principal components. The strongest evidence for association in the meta-analysis was observed for intronic SNPs in ATP6V1B2 (P=6.78 x 10⁻⁷), SP4 (P=7.68 x 10⁻⁷) and GRM7 (P=1.11 x 10⁻⁶). Additional exploratory analyses were carried out for a narrower phenotype (recurrent MDD with onset before age 31, N=2191 cases), and separately for males and females. Several of the best findings were supported primarily by evidence from narrow cases or from either males or females. On the basis of previous biological evidence, we consider GRM7 a strong MDD candidate gene. Larger samples will be required to determine whether any common SNPs are significantly associated with MDD.

Monoamine transporters: vulnerable and vital doorkeepers

Transporters of dopamine, serotonin, and norepinephrine have been empirically used as medication targets for several mental illnesses in the last decades. These protein-targeted medications are effective only for subpopulations of patients with transporter-related brain disorders. Since the cDNA clonings in early 1990s, molecular studies of these transporters have revealed a wealth of information about the transporters' structure-activity relationship (SAR), neuropharmacology, cell biology, biochemistry, pharmacogenetics, and the diseases related to the human genes encoding these transporters among related regulators. Such new information creates a unique opportunity to develop transporter-specific medications based on SAR, mRNA, DNA, and perhaps transporter trafficking regulation for a number of highly relevant diseases including substance abuse, depression, schizophrenia, and Parkinson's disease.

Overview of the genetics of major depressive disorder

Major depressive disorder (MDD) is a common psychiatric illness with high levels of morbidity and mortality. Despite intensive research during the past several decades, the neurobiological basis and pathophysiology of depressive disorders remain unknown. Genetic factors play important roles in the development of MDD, as indicated by family, twin, and adoption studies, and may reveal important information about disease mechanisms. This article describes recent developments in the field of psychiatric genetics, with a focus on MDD. Early twin studies, linkage studies, and association studies are discussed. Recent findings from genome-wide association studies are reviewed and future directions discussed. Despite all efforts, thus far, no single genetic variation has been identified to increase the risk of depression substantially. Genetic variants are expected to have only small effects on overall disease risk, and multiple genetic factors in conjunction with environmental factors are likely necessary for the development of MDD. Future large-scale studies are needed to dissect this complex phenotype and to identify pathways involved in the etiology of MDD.

Genetic variants in the vesicular monoamine transporter 1 (VMAT1/SLC18A1) and neuropsychiatric disorders

Vesicular monoamine transporters (VMATs) are involved in the presynaptic packaging of monoaminergic neurotransmitters into storage granules. Upon an action potential, vesicles release their contents into the synaptic cleft via exocytosis. Since insufficient or excess release of neurotransmitter might alter neurochemical function and neurotransmission, VMATs are an important target for biological research in neuropsychiatric disorders. Two structurally related but pharmacologically distinct VMATs have been identified, encoded by separate genes, VMAT1 (SLC18A1) and VMAT2 (SLC18A2). Although it was reported initially that only VMAT2 is expressed in brain, recent studies indicate that VMAT1 is also expressed in brain, thus making both transporters plausible candidate genes for neuropsychiatric disorders. The gene encoding VMAT1 is located on chromosome 8p21, a region implicated in linkage studies of schizophrenia, bipolar disorder, and anxiety-related phenotypes. Furthermore, several recent genetic case-control studies have documented an association between common missense variations in the VMAT1 gene and susceptibility to bipolar disorder and schizophrenia. Variations in the VMAT1 gene might affect transporter function and might be involved in the etiology of neuropsychiatric disorders. This chapter describes methods for genotyping three missense polymorphisms implicated in neuropsychiatric disorders (Thr4Pro, Thr98Ser, Thr136Ile) using TaqMan-based PCR and standard PCR approaches.

Genetic regulation of catecholamine synthesis, storage and secretion in the spontaneously hypertensive rat

Understanding catecholamine metabolism is crucial for elucidating the pathogenesis of hereditary hypertension. Here we integrated transcriptional and biochemical profiling with physiologic quantitative trait locus (eQTL and pQTL) mapping in adrenal glands of the HXB/BXH recombinant inbred (RI) strains, derived from the spontaneously hypertensive rat (SHR) and normotensive Brown Norway (BN.Lx). We found simultaneous down-regulation of five heritable transcripts in the catecholaminergic pathway in young (6 weeks) SHRs. We identified cis-acting eQTLs for Dbh, Pnmt (catecholamine biosynthesis) and Vamp1 (catecholamine secretion); enzymatic activities of Dbh and Pnmt paralleled transcripts, with pQTLs for activities mirroring eQTLs. We also detected trans-regulated expression of Vmat1 and Chga (both involved in catecholamine storage), with co-localization of these trans-eQTLs to the Pnmt locus. Pnmt re-sequencing revealed promoter polymorphisms that result in decreased response of the transfected SHR promoter to glucocorticoid, compared with BN.Lx. Of physiological pertinence, Dbh activity negatively correlated with systolic blood pressure in RI strains, whereas Pnmt activity was negatively correlated with heart rate. The finding of such cis- and trans-QTLs at an age before the onset of frank hypertension suggests that these heritable changes in biosynthetic enzyme expression represent primary genetic mechanisms for regulation of catecholamine action and blood pressure control in this widely studied model of hypertension.

Dissociable brain structural changes associated with predisposition, resilience, and disease expression in bipolar disorder

Genetic factors are important in the etiology of bipolar disorder (BD). However, first-degree relatives of BD patients are at risk for a number of psychiatric conditions, most commonly major depressive disorder (MDD), although the majority remain well. The purpose of the present study was to identify potential brain structural correlates for risk and resilience to mood disorders in patients with BD, type I (BD-I) and their relatives. Structural magnetic resonance imaging scans were acquired from 30 patients with BD-I, 50 of their first-degree relatives (28 had no Axis I disorder, while 14 had MDD) and 52 controls. We used voxel-based morphometry, implemented in SPM5 to identify group differences in regional gray matter volume. From the identified clusters, potential differences were further examined based on diagnostic status (BD-I patients, MDD relatives, healthy relatives, controls). Whole-brain voxel-based analysis identified group differences in the left hemisphere in the insula, cerebellum, and substantia nigra. Increased left insula volume was associated with genetic preposition to BD-I independent of clinical phenotype. In contrast, increased left substantia nigra volume was observed in those with the clinical phenotype of BD-I. Changes uniquely associated with the absence of a clinical diagnosis in BD relatives were observed in the left cerebellum. Our data suggest that in BD, genetic and phenotype-related influences on brain structure are dissociable; if replicated, these findings may help with early identification of high-risk individuals who are more likely to transition to syndromal states.

Case-control association study of 65 candidate genes revealed a possible association of a SNP of HTR5A to be a factor susceptible to bipolar disease in Bulgarian population

BACKGROUND

Bipolar affective disorder (BAD) is a psychiatric illness characterized by episodes of mania and depression. Although the etiology is not clear, epidemiological studies suggest it is a result of an interaction of genetic and environmental factors. Despite of enormous efforts and abundant studies conducted, none has yet been identified definitively a gene susceptible to bipolar disorder.

METHODS

Ninety-four Bulgarian patients diagnosed with bipolar disorder and 184 Bulgarian healthy individuals, were used for genotyping of 191 single nucleotide polymorphisms (SNPs) by TaqMan and/or Invader assays. Seventeen SNPs that revealed P value less than 0.05 in the first screening were genotyped using an additional independent set of samples, consisting of 78 BAD cases and 372 controls.

RESULTS

After applying the Bonferonni correction on genotyping results of 172 cases and 556 controls, only one SNP, rs1800883, in the HTR5A gene revealed a significant level of P value (P=0.000097; odds ratio=1.80 (95%CI, 1.27-2.54); corrected P=0.017).

CONCLUSIONS

Our findings suggest that HTR5A gene could play an important role in the pathogenesis of bipolar disorder in our population. However these findings should be viewed with caution and replication studies in other populations are necessary in support of these findings.

Chromosome 8p as a potential hub for developmental neuropsychiatric disorders: implications for schizophrenia, autism and cancer

Defects in genetic and developmental processes are thought to contribute susceptibility to autism and schizophrenia. Presumably, owing to etiological complexity identifying susceptibility genes and abnormalities in the development has been difficult. However, the importance of genes within chromosomal 8p region for neuropsychiatric disorders and cancer is well established. There are 484 annotated genes located on 8p; many are most likely oncogenes and tumor-suppressor genes. Molecular genetics and developmental studies have identified 21 genes in this region (ADRA1A, ARHGEF10, CHRNA2, CHRNA6, CHRNB3, DKK4, DPYSL2, EGR3, FGF17, FGF20, FGFR1, FZD3, LDL, NAT2, NEF3, NRG1, PCM1, PLAT, PPP3CC, SFRP1 and VMAT1/SLC18A1) that are most likely to contribute to neuropsychiatric disorders (schizophrenia, autism, bipolar disorder and depression), neurodegenerative disorders (Parkinson's and Alzheimer's disease) and cancer. Furthermore, at least seven nonprotein-coding RNAs (microRNAs) are located at 8p. Structural variants on 8p, such as copy number variants, microdeletions or microduplications, might also contribute to autism, schizophrenia and other human diseases including cancer. In this review, we consider the current state of evidence from cytogenetic, linkage, association, gene expression and endophenotyping studies for the role of these 8p genes in neuropsychiatric disease. We also describe how a mutation in an 8p gene (Fgf17) results in a mouse with deficits in specific components of social behavior and a reduction in its dorsomedial prefrontal cortex. We finish by discussing the biological connections of 8p with respect to neuropsychiatric disorders and cancer, despite the shortcomings of this evidence.

Pharmacogenetics of antipsychotic response in the CATIE trial: a candidate gene analysis

The Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) Phase 1 Schizophrenia trial compared the effectiveness of one typical and four atypical antipsychotic medications. Although trials such as CATIE present important opportunities for pharmacogenetics research, the very richness of the clinical data presents challenges for statistical interpretation, and in particular the risk that data mining will lead to false-positive discoveries. For this reason, it is both misleading and unhelpful to perpetuate the current practice of reporting association results for these trials one gene at a time, ignoring the fact that multiple gene-by-phenotype tests are being carried out on the same data set. On the other hand, suggestive associations in such trials may lead to new hypotheses that can be tested through both replication efforts and biological experimentation. The appropriate handling of these forms of data therefore requires dissemination of association statistics without undue emphasis on select findings. Here we attempt to illustrate this approach by presenting association statistics for 2769 polymorphisms in 118 candidate genes evaluated for 21 pharmacogenetic phenotypes. On current evidence it is impossible to know which of these associations may be real, although in total they form a valuable resource that is immediately available to the scientific community.

The genetics of psychotic bipolar disorder

Psychotic features, defined as delusions or hallucinations, commonly occur in bipolar disorder (BP) and may be indicative of a more homogeneous form of the illness, with possible etiologic ties to schizophrenia. Several studies have shown that psychotic features aggregate in bipolar families, and increased interest in the molecular genetics of psychotic BP is emerging. Although preliminary, linkage studies of psychotic BP show replicated evidence for suggestive genome-wide linkage to chromosomes 8p and 13q, which have been implicated in prior linkage studies of schizophrenia and BP. Association studies of psychotic BP and subtypes such as mood-incongruent psychotic BP have uncovered modest positive results for several candidate schizophrenia susceptibility genes, including dysbindin, DAOA/G30, Disrupted-in-Schizophrenia-1, and neuregulin 1. These tentative results are consistent with the hypothesis that the subphenotype of psychotic BP may represent a clinical manifestation of "overlap" genes between schizophrenia and mood disorder syndromes.

Association between variation in the vesicular monoamine transporter 1 gene on chromosome 8p and anxiety-related personality traits

Vesicular monoamine transporters are involved in the presynaptic packaging of norepinephrine, dopamine and serotonin into storage vesicles. The vesicles release their content upon arrival of an action potential into the synaptic cleft. Dysregulation of monoaminergic neurotransmission has been long postulated to play a relevant role in the etiology of neuropsychiatric disorders. The gene encoding the vesicular monoamine transporter 1 (VMAT1/SLC18A1) maps to chromosome 8p21, a region where several linkage peaks overlap between schizophrenia, bipolar disorder and anxiety-related personality traits. In this study, we tested the hypothesis that the missence variation Thr136Ile in the VMAT1/SLC18A1 gene is associated with anxiety-related personality traits. We tested a total of 337 unrelated subjects of German descent (167 male, 170 female). All participants were carefully screened for psychiatric disorders. The self-report State-Trait Anxiety Inventory (STAI) was completed by all subjects. Genotypes were obtained for the Thr136Ile (rs1390938) variation in the VMAT1 gene for all subjects. Genotype effects on personality variables were computed with MANOVA including age as a co-variant and gender as independent factor (MANCOVA). Results show that STAI scores were significantly affected by genotype (F=3.108; d.f.=4,331; p=0.015) and age (F=7.233; d.f.=2,331; p=0.001) but not by gender. A gender-by-genotype effect was observed for both the STAI state (p=0.052) and trait score (p=0.035). Dissection of the group by gender and subsequent contrast analysis of the genotype effects performed within the female group showed significant results (STAI state: Thr/Ile vs. Ile/Ile: T=4.408, p=0.0004; STAI trait: Thr/Ile vs. Ile/Ile: T=3.074, p=0.009) but not in the male group. Our findings support the hypothesis that anxiety-related personality traits are associated with variation in the VMAT1/SLC18A1 gene.

The histone H3K4 demethylase SMCX links REST target genes to X-linked mental retardation

Gene transcription is critically influenced by chromatin structure and the modification status of histone tails. Methylation of lysine residues in histone tails is dynamically regulated by the opposing activities of histone methyltransferases and histone demethylases. Here we show that JARID1C/SMCX, a JmjC-domain-containing protein implicated in X-linked mental retardation and epilepsy, possesses H3K4 tri-demethylase activity and functions as a transcriptional repressor. An SMCX complex isolated from HeLa cells contains additional chromatin modifiers (the histone deacetylases HDAC1 and HDAC2, and the histone H3K9 methyltransferase G9a) and the transcriptional repressor REST, suggesting a direct role for SMCX in chromatin dynamics and REST-mediated repression. Chromatin immunoprecipitation reveals that SMCX and REST co-occupy the neuron-restrictive silencing elements in the promoters of a subset of REST target genes. RNA-interference-mediated depletion of SMCX derepresses several of these targets and simultaneously increases H3K4 trimethylation at the sodium channel type 2A (SCN2A) and synapsin I (SYN1) promoters. We propose that loss of SMCX activity impairs REST-mediated neuronal gene regulation, thereby contributing to SMCX-associated X-linked mental retardation.

Association study of the vesicular monoamine transporter 1 (VMAT1) gene with schizophrenia in a Japanese population

Background

Vesicular monoamine transporters (VMATs) mediate accumulation of monoamines such as serotonin, dopamine, adrenaline, and noradrenaline from the cytoplasm into storage organelles. The VMAT1 (alternatively solute carrier family 18: SLC18A1) regulates such biogenic amines in neuroendocrine systems. The VMAT1 gene maps to chromosome 8p21.3, a locus with strong evidence of linkage with schizophrenia. A recent study reported that a non-synonymous single nucleotide polymorphism (SNP) of the gene (Pro4Thr) was associated with schizophrenia.

Methods

We attempted to replicate this finding in a Japanese sample of 354 schizophrenics and 365 controls. In addition, we examined 3 other non-synonymous SNPs (Thr98Ser, Thr136Ile, and Val392Leu). Genotyping was performed by the TaqMan allelic discrimination assay.

Results

There was no significant difference in genotype or allele distribution of the three SNPs of Pro4Thr, Thr136Ile, or Val392Leu between patients and controls. There was, however, a significant difference in genotype and allele distributions for the Thr98Ser polymorphism between the two groups (P = 0.01 for genotype and allele). When sexes were examined separately, significant differences were observed in females (P = 0.006 for genotype, P = 0.003 for allele), but not in males. The Thr98 allele was more common in female patients than in female controls (odds ratio 1.69, 95% CI 1.19–2.40, P = 0.003). Haplotype-based analyses also provided evidence for a significant association in females.

Conclusion

We failed to replicate the previously reported association of Pro4Thr of the VMAT1 gene with schizophrenia. However, we obtained evidence for a possible role of the Thr98Ser in giving susceptibility to schizophrenia in women.