A polymorphic region in the human transcription factor AP-2beta gene is associated with specific personality traits

The regulatory role of AP-2β in monoaminergic neurotransmitter systems: insights on its signalling pathway, linked disorders and theragnostic potential

Monoaminergic neurotransmitter systems play a central role in neuronal function and behaviour. Dysregulation of these systems gives rise to neuropsychiatric and neurodegenerative disorders with high prevalence and societal burden, collectively termed monoamine neurotransmitter disorders (MNDs). Despite extensive research, the transcriptional regulation of monoaminergic neurotransmitter systems is not fully explored. Interestingly, certain drugs that act on these systems have been shown to modulate central levels of the transcription factor AP-2 beta (AP-2β, gene: TFAP2Β). AP-2β regulates multiple key genes within these systems and thereby its levels correlate with monoamine neurotransmitters measures; yet, its signalling pathways are not well understood. Moreover, although dysregulation of TFAP2Β has been associated with MNDs, the underlying mechanisms for these associations remain elusive. In this context, this review addresses AP-2β, considering its basic structural aspects, regulation and signalling pathways in the controlling of monoaminergic neurotransmitter systems, and possible mechanisms underpinning associated MNDS. It also underscores the significance of AP-2β as a potential diagnostic biomarker and its potential and limitations as a therapeutic target for specific MNDs as well as possible pharmaceutical interventions for targeting it. In essence, this review emphasizes the role of AP-2β as a key regulator of the monoaminergic neurotransmitter systems and its importance for understanding the pathogenesis and improving the management of MNDs.

The role of reward sensitivity in obesity and its association with Transcription Factor AP-2B: A longitudinal birth cohort study

OBJECTIVE

One factor potentially contributing to obesity is reward sensitivity. We investigated the association between reward sensitivity and measures of obesity from 9-33 years of age, paying attention to the inner structure of reward sensitivity.

METHODS

The sample included both birth cohorts (originally n = 1176) of the Estonian Children Personality Behaviour and Health Study. The association between reward sensitivity and measures of obesity was assessed using mixed-effects regression models. Associations at ages 9 (younger cohort only), 15, 18, 25 and 33 (older cohort) years were analyzed by one-way ANOVA. The indirect effect of the gene encoding transcription factor 2 beta (TFAP2B) on obesity through reward sensitivity was tested using mediation analysis.

RESULTS

According to linear mixed effects regression models, an increase in scores of Insatiability by Reward and both of its components, Excessive Spending and Giving in to Cravings, significantly increased body weight, body mass index, sum of five skinfolds, waist circumference, hip circumference and waist-to-height ratio from 15 to 25 years of age. Findings were similar at age 9 and 33 years. In contrast, no association between obesity and Openness to Rewards or its facets was observed. The TFAP2B genotype was also associated with fixation to rewards in females, but not with striving towards reward multiplicity.

CONCLUSION

Our results suggest that reward sensitivity is associated with obesity by its reward fixation component. The heterogeneity of the reward sensitivity construct should be taken into account in studies on body composition.

Influence of TFAP2B and KCTD15 genetic variability on personality dimensions in anorexia and bulimia nervosa

INTRODUCTION

TFAP2B and KCTD15 are obesity-related genes that interact to regulate feeding behavior. We hypothesize that variability in these loci, isolated or in combination, could also be related to the risk of eating disorders (ED) and/or associated psychological traits.

METHODS

We screened 425 participants (169 ED patients, 75 obese subjects, and 181 controls) for 10 clinically relevant and tag single-nucleotide polymorphisms (SNPs) in KCTD15 and TFAP2B by the Sequenom MassARRAY platform and direct sequencing. Psychometric evaluation was performed with EDI-2 and SCL-90R inventories.

RESULTS

The KCTD15 rs287103 T variant allele was associated with increased risk of bulimia nervosa (BN) (OR = 4.34 [1.47-29.52]; p = .003) and with scores of psychopathological scales of these patients. Haplotype *6 in KCTD15 was more frequent in controls (OR = 0.40 [0.20-0.80], p = .009 for anorexia nervosa), while haplotype *4 in TFAP2B affected all three scales of the SCL-90R inventory in BN patients (p ≤ .01). Epistasis analyses revealed relevant interactions with body mass index of BN patients (p < .001). Genetic profiles in obese patients did not significantly differ from those found in ED patients.

CONCLUSIONS

This is the first study that evaluates the combined role of TFAP2B and KCTD15 genes in ED. Our preliminary findings suggest that the interaction of genetic variability in these loci could influence the risk for ED and/or anthropometric and psychological parameters.

Microsatellite polymorphisms associated with human behavioural and psychological phenotypes including a gene-environment interaction

Background

The genetic and environmental influences on human personality and behaviour are a complex matter of ongoing debate. Accumulating evidence indicates that short tandem repeats (STRs) in regulatory regions are good candidates to explain heritability not accessed by genome-wide association studies.

Methods

We tested for associations between the genotypes of four selected repeats and 18 traits relating to personality, behaviour, cognitive ability and mental health in a well-studied longitudinal birth cohort (n = 458-589) using one way analysis of variance. The repeats were a highly conserved poly-AC microsatellite in the upstream promoter region of the T-box brain 1 (TBR1) gene and three previously studied STRs in the activating enhancer-binding protein 2-beta (AP2-β) and androgen receptor (AR) genes. Where significance was found we used multiple regression to assess the influence of confounding factors.

Results

Carriers of the shorter, most common, allele of the AR gene’s GGN microsatellite polymorphism had fewer anxiety-related symptoms, which was consistent with previous studies, but in our study this was not significant following Bonferroni correction. No associations with two repeats in the AP2-β gene withstood this correction. A novel finding was that carriers of the minor allele of the TBR1 AC microsatellite were at higher risk of conduct problems in childhood at age 7-9 (p = 0.0007, which did pass Bonferroni correction). Including maternal smoking during pregnancy (MSDP) in models controlling for potentially confounding influences showed that an interaction between TBR1 genotype and MSDP was a significant predictor of conduct problems in childhood and adolescence (p < 0.001), and of self-reported criminal behaviour up to age 25 years (p ≤ 0.02). This interaction remained significant after controlling for possible confounders including maternal age at birth, socio-economic status and education, and offspring birth weight.

Conclusions

The potential functional importance of the TBR1 gene’s promoter microsatellite deserves further investigation. Our results suggest that it participates in a gene-environment interaction with MDSP and antisocial behaviour. However, previous evidence that mothers who smoke during pregnancy carry genes for antisocial behaviour suggests that epistasis may influence the interaction.

Electronic supplementary material

The online version of this article (doi:10.1186/s12881-017-0374-y) contains supplementary material, which is available to authorized users.

Aggressive behavior in humans: Genes and pathways identified through association studies

Aggressive behavior has both genetic and environmental components. Many association studies have been performed to identify genetic factors underlying aggressive behaviors in humans. In this review we summarize the previous work performed in this field, considering both candidate gene (CGAS) and genome-wide association studies (GWAS), excluding those performed in samples where the primary diagnosis is a psychiatric or neurological disorder other than an aggression-related phenotype. Subsequently, we have studied the enrichment of pathways and functions in GWAS data. The results of our searches show that most CGAS have identified associations with genes involved in dopaminergic and serotonergic neurotransmission and in hormone regulation. On the other hand, GWAS have not yet identified genome-wide significant associations, but top nominal findings are related to several signaling pathways, such as axon guidance or estrogen receptor signaling, and also to neurodevelopmental processes and synaptic plasticity. Future studies should use larger samples, homogeneous phenotypes and standardized measurements to identify genes that underlie aggressive behaviors in humans. © 2016 Wiley Periodicals, Inc.

Discussing the putative role of obesity-associated genes in the etiopathogenesis of eating disorders

In addition to the identification of mutations clearly related to Mendelian forms of obesity; genome-wide association studies and follow-up studies have in the last years pinpointed several loci associated with BMI. These genetic alterations are located in or near genes expressed in the hypothalamus that are involved in the regulation of eating behavior. Accordingly, it seems plausible that these SNPs, or others located in related genes, could also help develop aberrant conduct patterns that favor the establishment of eating disorders should other susceptibility factors or personality dimensions be present. However, and somewhat surprisingly, with few exceptions such as BDNF, the great majority of the genes governing these pathways remain untested in patients with anorexia nervosa, bulimia nervosa or binge-eating disorder. In the present work, we review the few existing studies, but also indications and biological concepts that point to these genes in the CNS as good candidates for association studies with eating disorder patients.

Neuropsychological correlates of transcription factor AP-2Beta, and its interaction with COMT and MAOA in healthy females

BACKGROUND

The transcription factor AP-2β has been shown to impact clinical and neuropsychological properties. Apparently, it regulates the transcription of genes that code for molecules which are part of the catecholaminergic transmission system. This investigation focuses on possible effects of the transcription factor AP-2β intron 2 polymorphism on cognitive performance parameters.

METHODS

This hypothesis-driven investigation examined the effects and interactions of the transcription factor AP-2β intron 2 polymorphism, the Val158Met catechol-O-methyltransferase (COMT) polymorphism, and the variable number of tandem repeat polymorphism of monoamine oxidase A (MAOA) on cognitive performance parameters within a group of 200 healthy women (age: mean ± SD, 23.93 ± 3.33 years).

RESULTS

The AP-2β polymorphism significantly influenced cognitive performance (in particular, the Trail Making Test part B), whereas the MAOA and COMT polymorphisms did not. However, there was an interaction effect of the AP-2β × MAOA × COMT genotypes on the decision bias β of the degraded-stimulus version of the continuous performance task. Only the Val158Met COMT polymorphism showed an influence on personality questionnaires (openness and self-transcendence; NEO Five-Factor Inventory, Temperament and Character Inventory).

CONCLUSION

The transcription factor AP-2β intron 2 polymorphism had more influence on cognition than the MAOA and COMT polymorphisms. Possibly, the AP-2β genotype might influence cognition through pathways other than those that regulate MAOA and COMT transcription. Interactions of transcription factor AP-2β, COMT, and MAOA polymorphisms suggest higher leverage effects of transcription factor AP-2β in subjects with high dopamine availability.

Association between neonatal temperament, SLC6A4, DRD4 and a functional polymorphism located in TFAP2B

Genetic studies on human personality have provided little satisfactory results to date mainly because of the complexity of this trait. Neonatal temperament using observational measures is an alternative phenotype to approach genetics to human behavior. An association study was conducted on 117 Caucasian newborns. Their temperament was evaluated using the Neonatal Behavior Assessment Scale 48 h after birth. Thirteen polymorphisms in the SLC6A4, DRD4 and TFAP2B genes were genotyped. Linear regression was performed to analyze data, and Bonferroni correction was applied. To check the functional effect of the TFAP2B Indel Intron 2 polymorphism, reporter gene luciferase assays using a mouse cortical neural progenitor cell line and quantitative polymerase chain reaction (qPCR) studies in human post-mortem brain samples were performed. A significant association was found between 5-HTTLPR, 5-HTTLPR + rs25531 and TFAP2B Indel Intron 2 with Range of State cluster as well as an interaction between rs25531 and TFAP2B Indel Intron 2 with Range of State. DRD4 variable number tandem repeat exon 3 was associated with orientation. A 30% increase in the luciferase levels of the TFAP2B 5-repeat alleles compared with the 6-repeat alleles (P-value = 0.03) was found using the pGL3 promoter vector. The qPCR experiments showed the same trend as the in vitro studies, although no significant results were obtained. This study supports a role of the SLC6A4, DRD4 and TFAP2B genes in the temperament, including a gene-gene interaction between SLC6A4 and TFAP2B. It also provides evidence about an effect of the TFAP2B polymorphism in TFAP2B gene transcription.

Does the transcription factor AP-2beta have an impact on the genetic and early environmental influence on ethanol consumption?

Genes involved in alcoholism have consensus sites for the transcription factor activator protein (TFAP) 2β. In the present study, we investigated TFAP-2β protein levels in the ethanol-preferring alko, alcohol (AA) and the ethanol-avoiding alko, non-alcohol (ANA) rat lines. Furthermore, basal and ethanol-induced TFAP-2β levels were examined in Wistar rats exposed to different early postnatal environments that are known to affect later ethanol consumption. Taken together, we found differences in brainstem TFAP-2β protein between the AA and ANA rats.

Transcription factor AP-2 beta genotype and psychosocial adversity in relation to adolescent depressive symptomatology

The aim of this study was to investigate possible interactions between the gene coding for activating protein-2 beta (AP-2 beta) and psychosocial factors to predict depressive symptoms in adolescents. Two-hundred 16- and 19-year-old adolescents from the county of Västmanland, Sweden, were asked to complete a questionnaire, interviewed about psychosocial risk factors, and genotyped with regard to the transcription factor AP-2 beta intron 2 polymorphism. AP-2 beta genotype interacted significantly both with type of housing and parental separation to predict depressive symptoms. Individuals who were homozygous for the short AP-2 beta allele displayed higher depression scores when psychosocial adversity was taken into account. Amongst carriers of one or two copies of the long allele, there was no difference in depressive symptoms despite differences in psychosocial environments.

Electrophysiological and behavioral correlates of polymorphisms in the transcription factor AP-2beta coding gene

Transcription factor AP-2beta may influence brain monoaminergic systems by regulating target genes. Several monoaminergic genes, including the serotonin transporter gene, have AP-2beta binding sites. Late auditory-evoked potentials (P1, N1/P2) and impulsiveness-related personality traits are correlated, and both are modulated by monoaminergic neurotransmission. The present study assesses the impact of two AP-2beta polymorphisms (VNTRs within intron 1 and 2) together with the serotonin transporter polymorphism 5-HTTLPR on late auditory-evoked potentials and personality for the first time. EEG was recorded from 91 male subjects at central electrode positions while tones of six intensity levels were presented. Additionally, subjects completed personality questionnaires. Both AP-2beta polymorphisms revealed significant main effects on P1, and haplotype analysis confirmed the contribution of both AP-2beta-polymorphisms. Additionally, AP-2beta and 5-HTTLPR showed interactions with respect to P1. 5-HTTLPR revealed a main effect on N1/P2 but not P1. Impulsiveness showed an association with intron 1 VNTR. The results are discussed with respect to differential impact of AP-2beta polymorphisms and 5-HTTLPR on the monoaminergic systems. The findings promote replication in a larger sample and suggest a potential usefulness of AP-2beta polymorphisms in explaining or predicting central nervous diseases, drug effects and side effects.

Association analysis of 15 polymorphisms within 10 candidate genes for antisocial behavioural traits

This study sought to test 15 simple sequence repeat polymorphisms within 10 candidate genes for association with antisocial behavioural traits. Genes included were those known to regulate dopamine synthesis and transmission in the brain (DBH, DRD2, MAOA, TFAP2B, NR4A2, LMX1B) and those involved in the differentiation of social and sexual behaviour in men and women (AR, ESR1, OXTR, AVPR1A). Participants were Caucasians (men=1007, women=1089) aged 20-24 years who were assessed for indicators of antisocial traits such as pseudo-maturity, substance misuse and unstable lifestyle. Significant associations for antisocial traits were found with AR and ESR1 polymorphisms in men, and with polymorphisms within NR4A2 and TFAP2B in women. The association with TFAP2B remained significant after correction for multiple testing. This pattern of associations suggests that genetic variation within transcription factors may in part explain the variation observed in the population for antisocial behavioural phenotypes.

Personality traits of agreeableness and extraversion are associated with ADH4 variation

BACKGROUND

Personality traits are associated with substance dependence (SD); genetic factors may influence both. Strong associations between ADH4 variation and SD have been reported. We aimed to investigate the relationship between ADH4 variation and personality traits in the present study.

METHODS

We assessed dimensions of the five-factor model of personality in 243 subjects with SD (175 European Americans [EAs] and 68 African Americans [AAs]) and 296 healthy control subjects (256 EAs and 40 AAs). We also genotyped 7 ADH4 markers (spanning the locus) and 38 unlinked ancestry-informative markers in these subjects. The relationships between the diplotypes, alleles, and genotypes at ADH4 and personality traits were examined using multivariate analysis of covariance (MANCOVA), controlling for potential confounders.

RESULTS

Generally, SD patients, older individuals, and male subjects scored higher on neuroticism and lower on other personality factors. Personality factors were associated with the diplotypes. The allele A or genotype A/A of single nucleotide polymorphism (SNP)6 (rs1800759 at the gene promoter) was significantly associated with agreeableness scores. There were associations between extraversion and SNP1 (hcv2033010 at the 3' end) and SNP2 (rs1042364 in exon 9) in subjects with higher conscientiousness scores.

CONCLUSIONS

The personality traits of agreeableness and extraversion are related to ADH4 polymorphism. Among the ADH4 markers that appear to predispose to certain personality traits, the functional variant rs1800759 (SNP6) in the promoter region is most important. We conclude that personality traits and SD have a partially overlapping genetic basis.

Genes encoding for AP-2β and the Serotonin Transporter are associated with the Personality Character Spiritual Acceptance

In several twin studies the relative contribution of genetic factors for personality traits has amounted to figures between 40 and 60%. In the present study we investigated to which degree polymorphisms in the 5-HTT and AP-2beta genes are implicated in the neural processes involved in the formation of Temperament and Character traits, as estimated by Cloninger's TCI. Considering the background of previous reports, associations with the character Self-Transcendence and its sub-scale Spiritual Acceptance in particular, were of interest. A stratified random sample of 200 individuals (total population=5173), matched for age, gender and risk behaviors, from volunteering 16- and 19-year-old adolescents students in Sweden was investigated. Cloninger's TCI inventory was used for investigation of temperament and character traits. Blood samples were used for analyses of a promoter serotonin transporter polymorphism (5-HTTLPR) and an intron 2 polymorphism in the transcription factor AP-2beta gene. Among boys individuals with presence of the short 5-HTTLPR genotype showed lower scores, whereas individuals with presence of the short AP-2beta genotype showed higher scores of personality character Self-Transcendence and its sub-scale Spiritual Acceptance. Among girls no effect of either genotype was found. Both among boys and girls, significant interactive effects were found between 5-HTTLPR and AP-2beta genotypes, with regard to Self-Transcendence and Spiritual acceptance. Boys and girls with the combination of presence of the short 5-HTTLPR, and homozygosity for the long AP-2beta genotype scored significantly lower on Self-Transcendence and Spiritual Acceptance.

The lack of association between monoamine oxidase (MAO) intron 13 polymorphism and platelet MAO-B activity among men

Monoamine oxidase (MAO), a mitochondrial flavine containing enzyme, exists in two isoenzymes, MAO-A and MAO-B. Platelets contain MAO-B subtype, proposed to be a biomarker for different personality characteristics and vulnerability for substance abuse. The most common polymorphism of MAO-B gene, a single base change (A or G) occurs in intron 13. It has been proposed to be a functional polymorphism, controlling the activity of MAO-B in platelets. The aim of the study was to determine the association between platelet MAO-B activity and MAO-B intron 13 polymorphism in 225 racially and ethnically uniform healthy Caucasian men of the Croatian origin. Our results showed that platelet MAO-B activity did not differ between subjects subdivided into those with <<A-allele>> or <<G-allele>>. This polymorphism of the MAO-B gene did not control the activity of the MAO-B in platelets. Platelet MAO-B activity was associated only with the smoking status, and it was significantly decreased in smokers when compared to nonsmokers. No significant association was found between MAO-B polymorphism and smoking status. In healthy individuals of the Croatian origin, the studied MAO-B polymorphism showed a lack of functional importance in regulating MAO-B activity in platelets. Since different populations may vary in the association between functional polymorphism and the MAO-B activity, and the genotype of transcription factor AP-2 beta was reported to be associated with altered platelet MAO-B activity, and with specific personality traits, further studies on different populations should be conducted to elucidate the molecular mechanism/s regulating platelet MAO-B activity.

Transcription factor AP-2 and monoaminergic functions in the central nervous system

In the central nervous system, transcription factor AP-2 family is one of the critical regulatory factors for neural gene expression and neuronal development. Several genes in the monoaminergic systems display AP-2 binding sites in regulatory regions. In addition, brainstem levels of transcription factor AP-2alpha and AP-2beta are positively correlated to monoamine measures in rat forebrain, suggesting a regulatory role of AP-2 also in the adult brain. Great changes in psychiatric phenotypes due to genetic factors are seldom the result of a single gene polymorphism. Recently, identification of combinations of candidate genes that are all linked to one disease or psychiatric phenotype has been discussed. The expression of these candidate genes might be regulated by the same transcription factors, e.g. AP-2. Recent data on transcription factor AP-2 family in relation to monoaminergic functions are described in this paper. Transcription factor AP-2beta genotype has been studied in relation to personality, platelet monoamine oxidase (MAO) activity, CSF-levels of monoamine metabolites, binge-eating disorder, premenstrual dysphoric disorder, and schizophrenia. Furthermore, the involvement of AP-2 in the molecular mechanism of antidepressant drugs is discussed. Altogether, this paper discusses data supporting a notion that the transcription factor AP-2 family is involved in the regulation of the monoaminergic systems both pre- and postnatally, and, therefore, might be involved in the pathophysiology of neuropsychiatric disorders.

Brainstem levels of transcription factor AP-2 in rat are changed after treatment with phenelzine, but not with citalopram

BACKGROUND

Before therapeutic effect is obtained after treatment with antidepressant drugs, like serotonin selective reuptake inhibitors (SSRIs), tricyclic antidepressants (TCAs) and monoamine oxidase inhibitors (MAO-Is) there is an initial lag-period of a few weeks. Neuronal adaptations on a molecular level are supposed to be involved in the initiation of the antidepressant effect. Transcription factor AP-2 is essential for neuronal development and many genes involved in the brainstem monoaminergic systems have binding sites for AP-2 in their regulatory regions. The genotype of the AP-2beta isoform has been associated with e.g. anxiety-related personality traits and with platelet MAO activity. In addition, previous studies have shown that the levels of AP-2alpha and AP-2beta in rat whole brain were decreased after 10 days of treatment with citalopram (SSRI) and imipramine (TCA), and were increased with phenelzine (MAO-I).

RESULTS

In the present study, we report that treatment with citalopram for 1, 7 or 21 days did not have effect on the AP-2 levels in rat brainstem. However, after treatment with phenelzine for 1, 7 or 21 days the levels of AP-2alpha and AP-2beta had increased after 7 days, but had returned to control levels at day 21.

CONCLUSION

The decrease in AP-2 levels in rat whole brain previously seen after treatment with citalopram does not seem to be localised to the brainstem, it may rather occur in the monoaminergic terminal projection areas. The present data suggest that the increase in AP-2 levels previously seen in rat whole brain after subchronic treatment with phenelzine is located in the brainstem. It cannot, however, be excluded that other brain regions are involved.

Investigation of transcription factor AP-2 beta genotype in women with premenstrual dysphoric disorder

It has repeatedly been shown that the serotonergic system is involved in the symptomatology of premenstrual dysphoric disorder (PMDD). Women with PMDD are reported to differ from symptom-free controls with regard to serotonin-related biological markers. Evidence from family and twin studies suggests a genetic contribution to the aetiology of PMDD. The expression of human transcription factor AP-2beta in neural crest cell lineages and neuroectodermal cells suggests that this protein may be of importance for functional characteristics of neurons by regulating the expression of target genes. Within the monoaminergic systems, several genes have binding sites for AP-2beta in regulatory regions, suggesting an involvement of AP-2beta in these systems. The gene encoding AP-2beta is located on chromosome 6p12-p21.1 and includes a polymorphic region consisting of a variable number of [CAAA] repeats located in the second intron. We have earlier shown that AP-2beta genotype is associated with serotonergic phenotypes and that brainstem levels of AP-2beta correlate positively to serotonin metabolism in rat frontal cortex. The aim of this study was to investigate the relationship between PMDD and transcription factor AP-2beta genotype. The participants included 176 women with PMDD and 91 healthy controls. Genotyping was performed by polymerase chain reactions. We did not observe any differences in AP-2beta genotype frequencies between PMDD subjects and controls. Our results suggest that AP-2beta genotype is not a risk factor for PMDD. To our knowledge, this is the first study investigating transcription factor AP-2beta genotype in women with PMDD. Hence, these results should be considered preliminary until replicated.

Genetics of personality: are we making progress?

For centuries, scientists are intrigued by the differences in personality between individuals. As early as in the ancient Greek civilization, people tried to formulate theories to systematize this diversity. With the increased interest in behavior genetics, personality was also considered a challenging phenotype. From the early start, studies suggested a heritable component in personality. After the successes of molecular genetic studies in unraveling the genetic basis of (mostly) monogenic diseases, the focus shifted towards complex traits, including psychiatric disorders. It was observed in several studies that personality measures differed between patients with psychiatric disorders and healthy controls. Therefore, normal personality was considered a viable endophenotype in the search for genes involved in psychiatric disorders such as affective disorders, ADHD and substance dependence. Genes that were to be found in studies on personality could be candidate genes for particular psychiatric disorders. In the course of time, however the study of genes for personality turned out to be at least as hard as the search for genes involved in other complex disorders. In this review, past studies, present problems and future directions concerning the study of personality genetics are discussed.

Phenelzine treatment increases transcription factor AP-2 levels in rat brain

BACKGROUND

The elevations of noradrenaline (NA) and serotonin (5-HT) levels in response to acute serotonin reuptake inhibitor (SSRI) or tricyclic antidepressant (TCA) exposure are not consistent with the time course for the therapeutic action of these antidepressants. Thus, neuronal adaptations are needed for the therapeutic effect to arise. Transcription factor Activating Protein -2 (AP-2) is critical for mammalian neural gene expression. Several genes involved in brainstem CNS transmitter systems, especially the monoamines, have AP-2 binding sites in their regulatory regions. We have previously shown that treatment with citalopram and imipramin resulted in a decrease in AP-2alpha and AP-2beta levels in rat brain. We have also reported an association between a specific genotype of AP-2beta to personality traits, binge-eating disorder and platelet monoamine oxidase (MAO) activity.

RESULTS

Subchronic administration (10 days) of phenelzine (PLZ) increased the levels of AP-2alpha, AP-2beta and the DNA binding activity of AP-2 in nuclear extracts prepared from rat whole brain when compared with sham treated animals.

CONCLUSION

These data suggest that AP-2 is not involved in the therapeutic effect of antidepressants. Rather, the effects of antidepressants seen on the levels of AP-2 might be involved in the expression of side-effects during the lag-period.

Genetic polymorphisms and personality in healthy adults: a systematic review and meta-analysis

A meta-analysis was conducted on studies reporting data on associations between candidate genes and human personality. Studies reporting data for psychiatric populations (including organic disease and substance abuse) were excluded. A total of 46 studies contributed to the analysis. Pooled data using a fixed-effects model suggested significant associations between the 5HTT LPR, DRD4 c>t, DRD4 length, DRD2 A1/A2, DRD3 A1/A2 polymorphisms and personality traits. A multivariate analysis using a mixed-effects model and including age, sex and predominant ethnicity as covariates was applied to the analyses of 5HTT LPR and DRD4 length polymorphism data. Only the association between the 5HTT LPR polymorphism and avoidance traits remained significant (P=0.038). However, sensitivity analyses excluding data from studies reporting allele frequencies not in Hardy-Weinberg equilibrium and unpublished data resulted in this association no longer being significant. Implications for the design of future association studies of human personality are discussed, including the likely sample sizes that will be required to achieve sufficient power and the potential role of moderating variables such as sex.

Toward a molecular architecture of personality

Epidemiological studies provided a large body of evidence that personality dimensions are influenced by genetic factors and that the genetic component is highly complex, polygenic, and epistatic. However, consistent findings on the genetic basis of personality have yet remained sparse. In recent years, molecular genetics has begun to identify specific genes coding in particular for components of the serotonergic and dopaminergic neurotransmitter systems representing quantitative trait loci (QTLs) for behavioral traits. The QTL concept suggests that complex traits are not attributable to single genes. According to this polygenic model, the genetic basis of personality and behavior and its pathological variations thus results from additive or nonadditive interactions of various genes. As the number of suitable candidate genes constantly increases, the QTL model provides a reasonable explanation for the genetic basis of personality and its disorders. In this review, the current knowledge on the impact of a large number of candidate gene polymorphisms (e.g. variations in serotonin and dopamine receptor and serotonin transporter genes) on personality and temperament is summarized. Additionally, investigations of gene-gene and gene-environment interactions in humans and animals, which currently intensify the identification of genes that underlie behavioral variations, are examined. The findings converge on the notion that a probabilistic rather than deterministic impact of genes on the expression of behavior will contribute to the demystification of behavioral disorders.

No association between a transcription factor Activating Protein 2beta (AP-2beta) gene variant and schizophrenia

Genetic components are involved in the aetiology of schizophrenia. Activating Protein 2 (AP-2) transcription factors are essential for neural gene expression and neural development. Transcription factor AP-2beta has also been connected with monoaminergic genes and monoamine levels in various brain regions. Thus, the AP-2beta gene is a suitable candidate taking both the neurodevelopmental and dopamine hypotheses of schizophrenia into account. We investigated 135 schizophrenic patients and 382 control subjects with regard to an intronic AP-2beta variant without evidence of any association. We conclude that the investigated AP-2beta variant is not of major importance to schizophrenia in the investigated Swedish population.

Risk factors for the neurohumoral alterations underlying personality disturbances

Numerous studies have shown that MAO-B activity in platelets correlates with specific personality characteristics such as sensation seeking and impulsiveness. Low levels of platelet MAO as well as the personality traits associated with these low levels have been associated with type 2 alcoholism, recurrent criminality and antisocial violent behavior. Platelet MAO has a high degree of heritability and regulation of MAOB gene expression seems to explain most of the inter-individual differences in activity. The transcription factor family AP-2 is an important regulatory factor for neural gene expression and neural development, especially in midbrain structures, including the monoaminergic nuclei. In man, the gene encoding AP-2beta contains a polymorphic region in the second intron, consisting of a variable number of tandem repeats [CAAA](4-5). The long AP-2beta allele has previously been associated with specific personality traits as well as with binge-eating disorder characterized by an impulsive temperament. We have shown that males and females homozygous for the long AP-2beta allele display significantly lower platelet MAO activity compared to subjects with one or two short alleles. Thus, we find it likely that the personality disturbances previously linked to low platelet MAO activity could be associated with the presence of two long alleles of the AP-2beta gene. We suggest that the molecular mechanisms underlying the association between platelet MAO and vulnerability, e.g. substance abuse, may involve specific transcription factors that regulate the expression of midbrain monoamine structures as well as that of platelet MAO.

Levels of transcription factors AP-2alpha and AP-2beta in the brainstem are correlated to monoamine turnover in the rat forebrain

The transcription factors AP-2alpha and AP-2beta are implicated to play an important role during embryonic development of different parts of the brain, and in targeted regulation of gene expression in the adult brain. Several monoaminergic genes have binding sites for AP-2 in regulatory regions. We have in the present study, analysed the association between AP-2 levels in the brainstem of rats (n=9) and monoamine levels in the frontal cortex, septum and hippocampus. Several regionally specific correlations were found between AP-2alpha and AP-2beta and specific monoamines in the rat forebrain. The data support our notion that the transcription factor AP-2 family is involved in the regulation of the monoaminergic systems and, therefore, might be involved in the pathophysiology of neuropsychiatric disorders.

Genetic mechanisms of behavior--don't forget about the transcription factors

Major changes in psychiatric phenotypes due to genetic factors are seldom the result of single gene polymorphisms, but more often the result of several genetic mechanisms. In this millennium article we discuss the notion that the expression of numerous candidate genes could be regulated by the same transcription factors, and that polymorphisms in transcription factor genes might explain some phenotypes. We describe recent results of studies on the biological marker thrombocyte monoamine oxidase (trbc MAO) and the transcription factor AP-2beta. Low levels of trbc MAO is associated with temperamental characteristics such as sensation seeking and impulsiveness, and the enzyme is genetically regulated by specific transcriptional mechanisms. Transcription factor AP-2beta is important for the development of midbrain structures and AP-2beta has several binding sites in the regulatory regions of genes encoding key proteins in the monoamine transmitter systems. We have recently shown AP-2beta to be linked to personality, binge-eating disorder, treatment with antidepressant drugs, and also to trbc MAO. Regardless of whether transcriptions factors, such as AP-2beta, regulate the expression of eg, the number of monoamine neurons or a variety of candidate genes within the monoamine systems, or both, we would like to emphasize the role of transcription factors, besides polymorphisms in monoaminergic candidate genes, when explaining inter-individual differences in temperament and psychiatric vulnerability.

Personality and polymorphisms of genes involved in aminergic neurotransmission

Genetic factors significantly contribute to the determination of human personality traits assessed by self-report questionnaires. However, only in the past few years have common genetic polymorphisms especially the dopamine D4 receptor and the serotonin transporter promoter region been associated with specific personality traits such as novelty seeking and harm avoidance, respectively. The effects of these genes are modest and several genes are likely accounting for individual differences in personality dimensions that can be attributed to genetic factors. Molecular genetic studies of adult personality have also been extended to investigations of early human temperament and some of the genes associated with adult personality traits are also contributing to the earliest developmental expressions of human behavior. Additionally, some of these same genes have also been implicated in various types of abnormal behavior including addiction, obsessive-compulsive disorder, attention deficit, depression, aggression and psychosis. Future research directions will no doubt take advantage of the bioinformatics revolution coinciding with the completion of the first phase of the human genome project. It should soon be possible to identify many of the genes contributing to specific personality traits and to better define their role in determining normal and abnormal behavior from early development through adulthood.

The genotype of human transcription factor AP-2beta is associated with platelet monoamine oxidase B activity

Platelet monoamine oxidase B (MAO; EC 1.4.3.4.) activity is stable in the individual and is mainly genetically regulated. Levels of MAO-B in platelets have repeatedly been shown to be associated with personality traits. We have recently also demonstrated an association between the genotype of AP-2beta to a variety of personality traits as well as binge-eating disorder. In the present study we have analysed blood samples from 158 males and 64 females with regard to platelet MAO activity and genotype of transcription factor AP-2beta. In both sexes homozygotes for the long allele [CAAA](5) were significantly associated with low platelet MAO activity P<0.0001 (males) and P=0.0158 (females). This study represents a novel approach to increase the understanding about the molecular mechanisms for how the MAOB gene is regulated in blood cells and how this regulation is linked to personality traits.