TPH2 polymorphisms across the spectrum of psychiatric morbidity: A systematic review and meta-analysis

Sex differences in offspring risk and resilience following 11β-hydroxylase antagonism in a rodent model of maternal immune activation

Maternal immune activation (MIA) puts offspring at greater risk for neurodevelopmental disorders associated with impaired social behavior. While it is known that immune signaling through maternal, placental, and fetal compartments contributes to these phenotypical changes, it is unknown to what extent the stress response to illness is involved and how it can be harnessed for potential interventions. To this end, on gestational day 15, pregnant rat dams were administered the bacterial mimetic lipopolysaccharide (LPS; to induce MIA) alongside metyrapone, a clinically available 11β-hydroxylase (11βHSD) inhibitor used to treat hypercortisolism in pregnant, lactating, and neonatal populations. Maternal, placental, and fetal brain levels of corticosterone and placental 11βHSD enzymes type 1 and 2 were measured 3-hrs post treatment. Offspring social behaviors were evaluated across critical phases of development. MIA was associated with increased maternal, placental, and fetal brain corticosterone concentrations that were diminished with metyrapone exposure. Metyrapone protected against reductions in placental 11βHSD2 in males only, suggesting that less corticosterone was inactivated in female placentas. Behaviorally, metyrapone-exposure attenuated MIA-induced social disruptions in juvenile, adolescent, and adult males, while females were unaffected or performed worse. Metyrapone-exposure reversed MIA-induced transcriptional changes in monoamine-, glutamate-, and GABA-related genes in adult male ventral hippocampus, but not in females. Taken together, these findings illustrate that MIA-induced HPA responses act alongside the immune system to produce behavioral deficits. As a clinically available drug, the sex-specific benefits and constraints of metyrapone should be investigated further as a potential means of reducing neurodevelopmental risks due to gestational MIA.

Leveraging DNA methylation to predict treatment response in major depressive disorder: A critical review

Major depressive disorder (MDD) is a debilitating and prevalent mental disorder with a high disease burden. Despite a wide array of different treatment options, many patients do not respond to initial treatment attempts. Selection of the most appropriate treatment remains a significant clinical challenge in psychiatry, highlighting the need for the development of biomarkers with predictive utility. Recently, the epigenetic modification DNA methylation (DNAm) has emerged to be of great interest as a potential predictor of MDD treatment outcomes. Here, we review efforts to date that seek to identify DNAm signatures associated with treatment response in individuals with MDD. Searches were conducted in the databases PubMed, Scopus, and Web of Science with the concepts and keywords MDD, DNAm, antidepressants, psychotherapy, cognitive behavior therapy, electroconvulsive therapy, transcranial magnetic stimulation, and brain stimulation therapies. We identified 32 studies implicating DNAm patterns associated with MDD treatment outcomes. The majority of studies (N = 25) are focused on selected target genes exploring treatment outcomes in pharmacological treatments (N = 22) with a few studies assessing treatment response to electroconvulsive therapy (N = 3). Additionally, there are few genome-scale efforts (N = 7) to characterize DNAm patterns associated with treatment outcomes. There is a relative dearth of studies investigating DNAm patterns in relation to psychotherapy, electroconvulsive therapy, or transcranial magnetic stimulation; importantly, most existing studies have limited sample sizes. Given the heterogeneity in both methods and results of studies to date, there is a need for additional studies before existing findings can inform clinical decisions.

Interaction between childhood trauma experience and TPH2 rs7305115 gene polymorphism in brain gray matter volume

BACKGROUND

Childhood trauma is one of the most extensively studied and well-supported environmental risk factors for the development of mental health problems. The human tryptophan hydroxylase 2 (TPH2) gene is one of the most promising candidate genes in numerous psychiatric disorders. However, it is now widely acknowledged that neither genetic variation nor environmental exposure alone can fully explain all the phenotypic variance observed in psychiatric disorders. Therefore, it is necessary to consider the interaction between the two factors in psychiatric research.

METHODS

We enrolled a sizable nonclinical cohort of 786 young, healthy adults who underwent structural MRI scans and completed genotyping, the Childhood Trauma Questionnaire (CTQ) and behavioural scores. We identified the interaction between childhood trauma and the TPH2 rs7305115 gene polymorphism in the gray matter volume (GMV) of specific brain subregions and the behaviour in our sample using a multiple linear regression framework. We utilized mediation effect analysis to identify environment /gene-brain-behaviour relationships.

RESULTS

We found that childhood trauma and TPH2 rs7305115 interacted in both behaviour and the GMV of brain subregions. Our findings indicated that the GMV of the right posterior parietal thalamus served as a significant mediator supporting relationship between childhood trauma (measured by CTQ score) and anxiety scores in our study population, and the process was partly modulated by the TPH2 rs7305115 gene polymorphism. Moreover, we found only a main effect of childhood trauma in the GMV of the right parahippocampal gyrus area, supporting the relationship between childhood trauma and anxiety scores as a significant mediator.

CONCLUSIONS

Our findings suggest that early-life trauma may have a specific and long-term structural effect on brain GMV, potentially leading to altered cognitive and emotional processes involving the parahippocampal gyrus and thalamus that may also be modulated by the TPH2 gene polymorphism. This finding highlights the importance of considering genetic factors when examining the impact of early-life experiences on brain structure and function. Gene‒environment studies can be regarded as a powerful objective supplement for targeted therapy, early diagnosis and treatment evaluation in the future.

A central serotonin regulating gene polymorphism (TPH2) determines vulnerability to acute tryptophan depletion-induced anxiety and ventromedial prefrontal threat reactivity in healthy young men

Serotonin (5-HT) has long been implicated in adaptive emotion regulation as well as the development and treatment of emotional dysregulations in mental disorders. Accumulating evidence suggests a genetic vulnerability may render some individuals at a greater risk for the detrimental effects of transient variations in 5-HT signaling. The present study aimed to investigate whether individual variations in the Tryptophan hydroxylase 2 (TPH2) genetics influence susceptibility for behavioral and neural threat reactivity dysregulations during transiently decreased 5-HT signaling. To this end, interactive effects between TPH2 (rs4570625) genotype and acute tryptophan depletion (ATD) on threat reactivity were examined in a within-subject placebo-controlled pharmacological fMRI trial (n = 51). A priori genotype stratification of extreme groups (GG vs. TT) allowed balanced sampling. While no main effects of ATD on neural reactivity to threat-related stimuli and mood state were observed in the entire sample, accounting for TPH2 genotype revealed an ATD-induced increase in subjective anxious arousal in the GG but not the TT carriers. The effects were mirrored on the neural level, such that ATD specifically reduced ventromedial prefrontal cortex reactivity towards threat-related stimuli in the GG carriers. Furthermore, the ATD-induced increase in subjective anxiety positively associated with the extent of ATD-induced changes in ventromedial prefrontal cortex activity in response to threat-related stimuli in GG carriers. Together the present findings suggest for the first time that individual variations in TPH2 genetics render individuals susceptible to the anxiogenic and neural effects of a transient decrease in 5-HT signaling.

Serotonergic multilocus genetic variation moderates the association between interpersonal relationship and adolescent depressive symptoms

BACKGROUND

Research suggests that genetic variants linked to serotonin functioning moderate the association between environmental stressors and depressive symptoms, but examining gene-environment interactions with single polymorphisms limits power.

METHODS

A multilocus genetic profile score (MGPS) approach to measuring serotonergic multilocus genetic variation and examined interactions with interpersonal relationship, insomnia with depressive symptoms as outcomes in an adolescent sample (average age = 14.15 ± 0.63 years since first measurement; range: 13 to 15).

RESULTS

(1) interpersonal relationship predicted adolescent depressive symptoms; (2) insomnia mediated the effect of interpersonal relationships on adolescent depressive symptoms; (3) the THP2 gene rs4570625 polymorphism G allele was a key risk factor for depressive symptom, and the MGPS moderated the effects of teacher-student relationship and insomnia on adolescent depressive symptom. Specifically, as the MGPS increased, the effects of insomnia on adolescent depressive symptom were enhanced; further, when the MGPS score increased, the effect of teacher-student relationship on depression showed a similar phenomenon with an increased slope and enhanced prediction; and (4) the results of sensitivity analysis showed that multilocus genetic interaction with the environment had a better explanatory power and stability for depression than single polymorphism studies.

CONCLUSION

MGPS provides substantial power to examine gene-environmental interactions linked to affective outcomes among adolescents.

TPH2-703 G/T polymorphism is associated with stress, depression, and psychosocial symptoms in mentally healthy Mexicans

Tryptophan hydroxylase (TPH) catalyzes the rate-limiting step of serotonin synthesis. TPH2 is the brain-specific isoform of this enzyme, and genetic variations in the TPH2 gene have been shown to impact its transcription and enzymatic activity and are associated with mood disorders. In this study we focused on the rs4570625 (-703G/T) single nucleotide polymorphism of TPH2 gene. By using conventional polymerase chain reaction (PCR), we examined the effect of this polymorphism on stress, anxiety, and depression symptoms as well as quality of life, evaluated based on the Holmes-Rahe Inventory, the Beck Anxiety Inventory, the Beck Depression Inventory, and the World Health Organization Quality of Life - Short Version, respectively. We found that individuals with the homozygous recessive T/T genotype had lower stress and depression scores. In addition, the quality of life in the psychological health domain was better in males with the T/T genotype. These results suggest that T/T genotype could decrease the susceptibility to developing stress and depression in the Mexican population without a diagnosis for an emotional disorder.

Effect of Prolonged Exposure to Short Daylight and a Tryptophan Hydroxylase Inhibitor on the Behavior and Brain Serotonin System in Danio rerio

We studied the effect of reduced tryptophan hydroxylase (TPH) activity and short daylight exposure on the behavior and the 5-HT system of the brain in D. rerio. Male and female D. rerio were exposed for 30 days to standard (12:12 h light:dark) and short (4:20 h light:dark) photoperiods in the presence or absence of TPH inhibitor (p-chlorophenylalanine, pCPA, 5 mg/liter). On day 31, the fish behavior in the "novel tank diving" test, their sex and body weight were determined, and the levels of pCPA, 5-HT, and its metabolite 5-HIAA were measured by HPLC; the levels of the key genes encoding metabolism enzymes (Tph1a, Tph1b, Tph2, and Mao) and receptors of 5-HT (Htr1aa, Htr2aa) were assessed by real-time PCR with reverse transcription. The short daylight exposure caused masculinization of females, reduced body weight, and motor activity in the "novel tank diving" test, but did not affect the 5-HT system of the brain. Long-term pCPA treatment had no effect on sex and body weight, significantly reduced the 5-HIAA level, but increased Tph1a and Tph2 gene expression in the brain. No effects of the interaction of short daylight and pCPA exposure on the sex, body weight, behavior, and 5-HT system of the brain were found. Thus, a moderate decrease in TPH activity cannot potentiate the negative effects of short daylight exposure on the sex, body weight, behavior, and 5-HT system of D. rerio.

In Vitro and In Vivo Chaperone Effect of (R)-2-amino-6-(1R, 2S)-1,2-dihydroxypropyl)-5,6,7,8-tetrahydropterin-4(3H)-one on the C1473G Mutant Tryptophan Hydroxylase 2

Tryptophan hydroxylase 2 (TPH2) is the key and rate-limiting enzyme of serotonin (5-HT) synthesis in the mammalian brain. The 1473G mutation in the Tph2 gene decreases TPH2 activity in the mouse brain by twofold. (R)-2-amino-6-(1R, 2S)-1,2-dihydroxypropyl)-5,6,7,8-tetrahydropterin-4(3H)-one (BH4) is a pharmacological chaperone for aromatic amino acid hydroxylases. In the present study, chaperone effects of BH4 on the mutant C1473G TPH2 were investigated in vitro and in vivo. In vitro BH4 increased the thermal stability (T50 value) of mutant and wild-type TPH2 molecules. At the same time, neither chronic (twice per day for 7 days) intraperitoneal injection of 48.3 mg/kg of BH4 nor a single intraventricular administration of 60 μg of the drug altered the mutant TPH2 activity in the brain of Balb/c mice. This result indicates that although BH4 shows a chaperone effect in vitro, it is unable to increase the activity of mutant TPH2 in vivo.

Molecular signature of excessive female aggression: study of stressed mice with genetic inactivation of neuronal serotonin synthesis

Aggression is a complex social behavior, critically involving brain serotonin (5-HT) function. The neurobiology of female aggression remains elusive, while the incidence of its manifestations has been increasing. Yet, animal models of female aggression are scarce. We previously proposed a paradigm of female aggression in the context of gene x environment interaction where mice with partial genetic inactivation of tryptophan hydroxylase-2 (Tph2+/- mice), a key enzyme of neuronal 5-HT synthesis, are subjected to predation stress resulting in pathological aggression. Using deep sequencing and the EBSeq method, we studied the transcriptomic signature of excessive aggression in the prefrontal cortex of female Tph2+/- mice subjected to rat exposure stress and food deprivation. Challenged mutants, but not other groups, displayed marked aggressive behaviors. We found 26 genes with altered expression in the opposite direction between stressed groups of both Tph2 genotypes. We identified several molecular markers, including Dgkh, Arfgef3, Kcnh7, Grin2a, Tenm1 and Epha6, implicated in neurodevelopmental deficits and psychiatric conditions featuring impaired cognition and emotional dysregulation. Moreover, while 17 regulons, including several relevant to neural plasticity and function, were significantly altered in stressed mutants, no alteration in regulons was detected in stressed wildtype mice. An interplay of the uncovered pathways likely mediates partial Tph2 inactivation in interaction with severe stress experience, thus resulting in excessive female aggression.

Measuring tryptophan dynamics using fast scan cyclic voltammetry at carbon fiber microelectrodes with improved sensitivity and selectivity

Despite the fact that tryptophan (Trp) is an essential amino acid that humans typically obtain through diet, there are several interesting tryptophan dynamics at play in the body. Quantifying and understanding these dynamics are crucial in studies of depression, autism spectrum disorder, and other disorders that involve neurotransmitters directly synthesized from tryptophan. Here we detail the optimization of waveform parameters in fast scan cyclic voltammetry at carbon fiber microelectrodes to yield four-fold higher sensitivity and six-fold higher selectivity compared to previously reported methods. We demonstrate the utility of our method in measuring (1) exogenous Trp dynamics from administration of Trp to PC-12 cells with and without overexpression of tryptophan hydroxylase-2 and (2) endogenous Trp dynamics in pinealocyte cultures with and without stimulation via norepinephrine. We observed interesting differences in Trp dynamics in both model systems, which demonstrate that our method is indeed sensitive to Trp dynamics in different applications.

Effects of the Combination of the C1473G Mutation in the Tph2 Gene and Lethal Yellow Mutations in the Raly-Agouti Locus on Behavior, Brain 5-HT and Melanocortin Systems in Mice

Tryptophan hydroxylase 2 (TPH2) is the key and rate-limited enzyme of serotonin (5-HT) synthesis in the brain. The C1473G mutation in the Tph2 gene results in a two-fold decrease in enzyme activity in the mouse brain. The lethal yellow (A^Y) mutation in the Raly-Agouti locus results in the overexpression of the Agouti gene in the brain and causes obesity and depressive-like behavior in mice. Herein, the possible influences of these mutations and their combination on body mass, behavior, brain 5-HT and melanocortin systems in mice of the B6-1473CC/aa. B6-1473CC/A^Ya, B6-1473GG/aa are investigated. B6-1473GG/A^Ya genotypes were studied. The 1473G and A^Y alleles increase the activity of TPH2 and the expression of the Agouti gene, respectively, but they do not alter 5-HT and 5-HIAA levels or the expression of the genes Tph2, Maoa, Slc6a4, Htr1a, Htr2a, Mc3r and Mc4r in the brain. The 1473G allele attenuates weight gain and depressive-like immobility in the forced swim test, while the A^Y allele increases body weight gain and depressive-like immobility. The combination of these alleles results in hind limb dystonia in the B6-1473GG/A^Ya mice. This is the first evidence for the interaction between the C1473G and A^Y mutations.

Early antidepressant treatment response prediction in major depression using clinical and TPH2 DNA methylation features based on machine learning approaches

OBJECTIVE

To identify DNA methylation and clinical features, and to construct machine learning classifiers to assign the patients with major depressive disorder (MDD) into responders and non-responders after a 2-week treatment into responders and non-responders.

METHOD

Han Chinese patients (291 in total) with MDD comprised the study population. Datasets contained demographic information, environment stress factors, and the methylation levels of 38 methylated sites of tryptophan hydroxylase 2 (TPH2) genes in peripheral blood samples. Recursive Feature Elimination (RFE) was employed to select features. Five classification algorithms (logistic regression, classification and regression trees, support vector machine, logitboost and random forests) were used to establish the models. Performance metrics (AUC, F-Measure, G-Mean, accuracy, sensitivity, specificity, positive predictive value and negative predictive value) were computed with 5-fold-cross-validation. Variable importance was evaluated by random forest algorithm.

RESULT

RF with RFE outperformed the other models in our samples based on the demographic information and clinical features (AUC = 61.2%, 95%CI: 60.1-62.4%) / TPH2 CpGs features (AUC = 66.6%, 95%CI: 65.4-67.8%) / both clinical and TPH2 CpGs features (AUC = 72.9%, 95%CI: 71.8-74.0%).

CONCLUSION

The effects of TPH2 on the early-stage antidepressant response were explored by machine learning algorithms. On the basis of the baseline depression severity and TPH2 CpG sites, machine learning approaches can enhance our ability to predict the early-stage antidepressant response. Some potentially important predictors (e.g., TPH2-10-60 (rs2129575), TPH2-2-163 (rs11178998), age of first onset, age) in early-stage treatment response could be utilized in future fundamental research, drug development and clinical practice.

Association of Functional Polymorphism in TPH2 Gene with Alcohol Dependence and Personality Traits: Study in Cloninger's Type I and Type II Alcohol-Dependent Inpatients

Alcohol dependence (AD) is a complex disorder with a poorly understood etiology. In this study, we investigated the relationship between genetic variation in the TPH2 gene, which encodes the enzyme responsible for serotonin synthesis in the brain, and both AD and personality traits, with attention to Cloninger's types of AD. The study included 373 healthy control subjects, 206 inpatients with type I AD, and 110 inpatients with type II AD. All subjects were genotyped for the functional polymorphism rs4290270 in the TPH2 gene, and AD patients completed the Tridimensional Personality Questionnaire (TPQ). The AA genotype and the A allele of the rs4290270 polymorphism were more frequent in both patient groups compared with the control group. In addition, a negative association was found between the number of A alleles and TPQ scores for harm avoidance in patients with type II, but not type I, AD. These results support the involvement of genetic variations of the serotonergic system in the pathogenesis of AD, especially type II AD. They also suggest that in a subset of patients, genetic variation of TPH2 could potentially influence the development of AD by affecting the personality trait of harm avoidance.

Comparison of Fluorometric and Chromatographic Methods of In Vitro Assay of Tryptophan Hydroxylase 2, the Key Enzyme of Serotonin Synthesis in the Brain

We present rapid and sensitive assay of tryptophan hydroxylase 2 enzyme activity based on the fluorescence of the complex of 5-hydroxytryptophan (5-HTP) with o-phthalic aldehyde. This method was compared with the standard method based on chromatographic isolation of 5-HTP followed by its quantification using an electrochemical detector. High sensitivity of the developed fluorometric method and similarity of the results obtained by fluorometric and chromatographic methods were demonstrated. The use of this rapid, cheap, and effective fluorometric method can simplify and facilitate measurements of tryptophan hydroxylase 2 activity and can make this assay available for a wide range of neurochemical and pharmacological laboratories.

Investigation of Genetic Variants Associated with Tryptophan Metabolite Levels via Serotonin and Kynurenine Pathways in Patients with Bipolar Disorder

The kynurenine pathway (KP) may play a role in the pathophysiology of bipolar disorder (BD). We conducted a genome-wide association study (GWAS) to identify genetic variants associated with the plasma levels of the metabolites of tryptophan (TRP) via the serotonin (5-HT) and kynurenine (KYN) pathways in 44 patients with BD and 45 healthy controls. We assessed whether variants that were differentially associated with metabolite levels based on the diagnostic status improved the prediction accuracy of BD using penalized regression approaches. We identified several genetic variants that were significantly associated with metabolites (5-HT, 5-hydroxytryptophan (5-HTP), TRP, and quinolinic acid (QA) or metabolite ratios (5-HTP/TRP and KYN/TRP) and for which the diagnostic status exerted a significant effect. The inclusion of genetic variants led to increased accuracy in the prediction of the BD diagnostic status. Specifically, we obtained an accuracy of 0.77 using Least Absolute Shrinkage and Selection Operator (LASSO) regression. The predictors retained as informative in this model included body mass index (BMI), the levels of TRP, QA, and 5-HT, the 5-HTP/TRP ratio, and genetic variants associated with the levels of QA (rs6827515, rs715692, rs425094, rs4645874, and rs77048355) and TRP (rs292212) or the 5-HTP/TRP ratio (rs7902231). In conclusion, our study identified statistically significant associations between metabolites of TRP via the 5-HT and KYN pathways and genetic variants at the genome-wide level. The discriminative performance of penalized regression models incorporating clinical, genetic, and metabolic predictors warrants a follow-up analysis of this panel of determinants.

Acute treatment with 5-hydroxytryptophan increases social approach behaviour but does not activate serotonergic neurons in the dorsal raphe nucleus in juvenile male BALB/c mice: A model of human disorders with deficits of sociability

BACKGROUND

The BALB/c mouse has been proposed as a model of human psychiatric disorders characterised by elevated anxiety and altered sociability. Juvenile BALB/c mice show decreased social exploratory behaviour, increased anxiety, and reduced brain serotonin synthesis compared to other strains including C57BL/6J mice.

AIM

To determine whether supplementation of brain serotonin synthesis alters social behaviour and activation of serotonergic neurons across subregions of the dorsal raphe nucleus (DR) in BALB/c mice.

METHODS

Juvenile male BALB/c mice were assigned to one of four treatment conditions: vehicle/vehicle, carbidopa (25 mg/kg)/vehicle, vehicle/5-HTP (10 mg/kg), carbidopa (25 mg/kg)/5-HTP (10 mg/kg). Social behaviour was measured using the three-chamber social approach test, followed by immunohistochemical staining for TPH2 and c-Fos to measure activation of serotonergic neurons across subregions of the DR.

RESULTS

Mice treated with carbidopa/5-HTP spent more time in the social cage zone and covered more distance in the social approach test compared to other treatment groups. There was no difference between treatment groups in the activation of serotonergic neurons across subregions of the DR. However, the DRD was associated with increased social approach behaviour in carbidopa/5-HTP treated animals.

CONCLUSIONS

Supplementation of serotonin synthesis can increase social approach behaviour in juvenile BALB/c mice. An increase in locomotor behaviour was also observed suggesting that increasing central serotonin synthesis may have led to a reduction in state anxiety, manifesting in increased exploratory behaviour. As no effect on serotonergic activation within the DR was found, alternative mechanisms are likely important for the effects of 5-HTP on social behaviour.

Genetics of social anxiety disorder: a systematic review

Social anxiety disorder (SAD) is a common psychiatric disorder, often associated with avoidant temperament. Research studies have implicated a strong genetic architecture of SAD. We have conducted a systematic review on the genetics of SAD and yielded 66 articles. In general, prior research studies have focused on the serotonin transporter, oxytocin receptor, brain-derived neurotrophic factor and catechol-O-methyltransferase genes. Mixed and inconsistent results have been reported. Additional approaches and phenotypes have also been investigated, including pharmacogenetics of treatment response, imaging genetics and gene-environment interactions. Future directions warrant further international collaborative efforts, deep-phenotyping of clinical characteristics including consistent and reliable measurement-based symptom severity, and larger sample sizes to ensure sufficient power for stratification due to the heterogeneity of this chronic and often debilitating condition.

Meta-analysis of association between TPH2 single nucleotide poiymorphism and depression

Tryptophan hydroxylase 2 (TPH2) plays a crucial role in the human brain. Although the association between the TPH2 gene and depression has been suggested in previous meta-analyses, studies based on Chinese subjects are often neglected. Therefore, we included some previous studies based on Chinese subjects to explore the relationship between TPH2 polymorphisms and depression via conducting an extensive meta-analysis. We reviewed 40 research papers that included data on TPH2 gene single nucleotide polymorphisms (SNPs) from 5766 patients with depression and 5988 healthy subjects. The analysis showed an association between polymorphisms in the TPH2 gene and depression, and some results were significant in 24 studies that included Chinese Han study participants. The results of our meta-analysis showed that rs4570625, rs17110747, rs120074175, rs4290270, rs120074175, and rs4290270 may be significantly associated with depression, and that rs11178997 (A/A genotype) may be a significant risk factor for depression in the Chinese subjects. Based on the results of this study, biological experiments should be performed in the future to explore how different SNPs affect depression.

Serotonin and early life stress interact to shape brain architecture and anxious avoidant behavior - a TPH2 imaging genetics approach

BACKGROUND

Early life stress has been associated with emotional dysregulations and altered architecture of limbic-prefrontal brain systems engaged in emotional processing. Serotonin regulates both, developmental and experience-dependent neuroplasticity in these circuits. Central serotonergic biosynthesis rates are regulated by Tryptophan hydroxylase 2 (TPH2) and transgenic animal models suggest that TPH2-gene associated differences in serotonergic signaling mediate the impact of aversive early life experiences on a phenotype characterized by anxious avoidance.

METHODS

The present study employed an imaging genetics approach that capitalized on individual differences in a TPH2 polymorphism (703G/T; rs4570625) to determine whether differences in serotonergic signaling modulate the effects of early life stress on brain structure and function and punishment sensitivity in humans (n = 252).

RESULTS

Higher maltreatment exposure before the age of 16 was associated with increased gray matter volumes in a circuitry spanning thalamic-limbic-prefrontal regions and decreased intrinsic communication in limbic-prefrontal circuits selectively in TT carriers. In an independent replication sample, associations between higher early life stress and increased frontal volumes in TT carriers were confirmed. On the phenotype level, the genotype moderated the association between higher early life stress exposure and higher punishment sensitivity. In TT carriers, the association between higher early life stress exposure and punishment sensitivity was critically mediated by increased thalamic-limbic-prefrontal volumes.

CONCLUSIONS

The present findings suggest that early life stress shapes the neural organization of the limbic-prefrontal circuits in interaction with individual variations in the TPH2 gene to promote a phenotype characterized by facilitated threat avoidance, thus promoting early adaptation to an adverse environment.

Sex-dependent complex association of TPH2 with multiple dimensions of ADHD

BACKGROUND

Tryptophan hydroxylase 2 (TPH2) is a key enzyme in the biosynthesis of serotonin in the brain. This study aims to investigate the role of a functional variant in TPH2 (rs17110747) in the pathophysiology of ADHD. This variant has been implicated in mood disorders in recent meta-analysis. This study uses a comprehensive approach that combines association testing and pharmaco-dynamic evaluation of behaviour, in a large sample of children with ADHD (n = 570).

METHODS

The association between various ADHD relevant traits and rs17110747 was analyzed using family-based association tests (FBAT). Children were assessed by parents, teachers and research staff under three experimental conditions (EC): baseline, placebo, and methylphenidate using a double-blind placebo-controlled crossover trial.

OUTCOMES

FBAT analysis conducted in a sample stratified based on sex of the proband, showed that there was a highly significant overtransmission of the G allele from parents to affected girls. In addition, significant association with several behavioral and cognitive dimensions of ADHD was observed only when the proband was female. Further, girls with the G/G genotype (rs17110747) had greater response to placebo when evaluated by parents.

INTERPRETATION

These results suggest that there may be a complex association of TPH2 in the etiology of ADHD, with a sex-specific effect.

A Rhesus Monkey Model of Non-suicidal Self-Injury

Non-suicidal self-injury (NSSI) is a type of behavioral pathology seen not only in a variety of clinical conditions but also among non-clinical populations, particularly adolescents and young adults. With the exception of rare genetic conditions that give rise to self-harming behaviors, the etiology of NSSI and the events that trigger specific episodes of this behavior remain poorly understood. This review presents the features of an important, extensively studied animal model of NSSI, namely spontaneously occurring self-injurious behavior (SIB) in rhesus macaque monkeys. We compare and contrast rhesus monkey SIB with NSSI with respect to form, prevalence rates, environmental and biological risk factors, behavioral correlates, proposed functions, and treatment modalities. Many parallels between rhesus monkey SIB and NSSI are demonstrated, which supports the validity of this animal model across several domains. Determining the etiology of spontaneously occurring SIB in monkeys, its underlying biological mechanisms, and which pharmacological agents are most effective for treating the disorder may aid in identifying potential risk factors for the occurrence of NSSI in humans and developing medications for severe cases that are resistant to conventional psychotherapeutic approaches.

Alexithymia is associated with reduced vitamin D levels, but not polymorphisms of the vitamin D binding-protein gene

OBJECTIVE

Alexithymia is a personality trait characterized by difficulties in identifying and describing emotions, which is associated with various psychiatric disorders, including depression and posttraumatic stress disorder (PTSD). Its pathogenesis is incompletely understood but previous studies suggested that genetic as well as metabolic factors, are involved. However, no results on the role of vitamin D and the polymorphisms rs4588 and rs7041 of the vitamin D binding protein (VDBP) have been published so far.

METHODS

Serum levels of total 25(OH)D were measured in two general-population samples (total n = 5733) of the Study of Health in Pomerania (SHIP). The Toronto Alexithymia Scale-20 (TAS-20) was applied to measure alexithymia. Study participants were genotyped for rs4588 and rs7041. Linear and logistic regression analyses adjusted for sex, age, waist circumference, physical activity, season and study and, when applicable, for the batch of genotyping and the first three genetic principal components, were performed. In sensitivity analyses, the models were additionally adjusted for depressive symptoms.

RESULTS

25(OH)D levels were negatively associated with TAS-20 scores (β = -0.002; P < 0.001) and alexithymia according to the common cutoff of TAS-20>60 (β = -0.103; P < 0.001). These results remained stable after adjusting for depressive symptoms. The tested genetic polymorphisms were not significantly associated with alexithymia.

CONCLUSIONS

Our results suggest that low vitamin D levels may be involved in the pathophysiology of alexithymia. Given that no associations between alexithymia and rs4588 as well as rs7041 were observed, indicates that behavioral or nutritional features of alexithymic subjects could also explain this association.

Altered behaviour, dopamine and norepinephrine regulation in stressed mice heterozygous in TPH2 gene

Gene-environment interaction (GxE) determines the vulnerability of an individual to a spectrum of stress-related neuropsychiatric disorders. Increased impulsivity, excessive aggression, and other behavioural characteristics are associated with variants within the tryptophan hydroxylase-2 (Tph2) gene, a key enzyme in brain serotonin synthesis. This phenotype is recapitulated in naïve mice with complete, but not with partial Tph2 inactivation. Tph2 haploinsufficiency in animals reflects allelic variation of Tph2 facilitating the elucidation of respective GxE mechanisms. Recently, we showed excessive aggression and altered serotonin brain metabolism in heterozygous Tph2-deficient male mice (Tph2^+/-) after predator stress exposure. Here, we sought to extend these studies by investigating aggressive and anxiety-like behaviours, sociability, and the brain metabolism of dopamine and noradrenaline. Separately, Tph2^+/- mice were examined for exploration activity in a novel environment and for the potentiation of helplessness in the modified swim test (ModFST). Predation stress procedure increased measures of aggression, dominancy, and suppressed sociability in Tph2^+/- mice, which was the opposite of that observed in control mice. Anxiety-like behaviour was unaltered in the mutants and elevated in controls. Tph2^+/- mice exposed to environmental novelty or to the ModFST exhibited increased novelty exploration and no increase in floating behaviour compared to controls, which is suggestive of resilience to stress and despair. High-performance liquid chromatography (HPLC) revealed significant genotype-dependent differences in the metabolism of dopamine, and norepinephrine within the brain tissue. In conclusion, environmentally challenged Tph2^+/- mice exhibit behaviours that resemble the behaviour of non-stressed null mutants, which reveals how GxE interaction studies can unmask latent genetically determined predispositions.

Amino Acid Trp: The Far Out Impacts of Host and Commensal Tryptophan Metabolism

Tryptophan (Trp) is an essential amino acid primarily derived from the diet for use by the host for protein synthesis. The intestinal tract is lined with cells, both host and microbial, that uptake and metabolize Trp to also generate important signaling molecules. Serotonin (5-HT), kynurenine and its downstream metabolites, and to a lesser extent other neurotransmitters are generated by the host to signal onto host receptors and elicit physiological effects. 5-HT production by neurons in the CNS regulates sleep, mood, and appetite; 5-HT production in the intestinal tract by enterochromaffin cells regulates gastric motility and inflammation in the periphery. Kynurenine can signal onto the aryl hydrocarbon receptor (AHR) to elicit pleiotropic responses from several cell types including epithelial and immune cells, or can be further metabolized into bioactive molecules to influence neurodegenerative disease. There is a remarkable amount of cross-talk with the microbiome with regard to tryptophan metabolites as well. The gut microbiome can regulate the production of host tryptophan metabolites and can use dietary or recycled trp to generate bioactive metabolites themselves. Trp derivatives like indole are able to signal onto xenobiotic receptors, including AHR, to elicit tolerogenic effects. Here, we review studies that demonstrate that tryptophan represents a key intra-kingdom signaling molecule.

REVERSE phenotyping-Can the phenotype following constitutive Tph2 gene inactivation in mice be transferred to children and adolescents with and without adhd?

INTRODUCTION

Experimental models of neuropsychiatric disorders, for example, ADHD, are used to mimic specific phenotypic traits of a complex human disorder. However, it remains unresolved to what extent the animal phenotype reflects the specific human trait. The null mutant mouse of the serotonin-synthesizing tryptophan hydroxylase-2 (Tph2^-/- ) gene has been proposed as experimental model for ADHD with high face validity for impulsive, aggressive, and anxious behaviors. To validate this ADHD-like model, we examined the Tph2^-/- phenotype in humans when considering allelic variation of TPH2 function ("reverse phenotyping").

METHODS

58 participants (6 females, 8-18 years) were examined, of whom 32 were diagnosed with ADHD. All participants were phenotyped for impulsivity, aggression, and anxiety using questionnaires, behavioral tests, and MRI scanning while performing the 4-choice serial reaction time task. Additionally, participants were genotyped for the TPH2 G-703T (rs4570625) polymorphism. To analyze the relation between TPH2 G-703T variants and the impulsive/aggressive/anxious phenotype, mediation analyses were performed using behavioral and MRI data as potential mediators.

RESULTS

We found that the relation between TPH2 G-703T and aggression as part of the reverse Tph2^- /^- phenotype was mediated by structure and function of the right middle and inferior frontal gyrus.

CONCLUSION

At the example of trait aggression, our results support the assumption that the Tph2 null mutant mouse reflects the TPH2 G-703T-dependent phenotype in humans. Additionally, we conclude that "reverse phenotyping" is a promising method to validate experimental models and human findings for refined analysis of disease mechanisms.

Risks of Major Mental Disorders and Irritable Bowel Syndrome among the Offspring of Parents with Irritable Bowel Syndrome: A Nationwide Study

Irritable bowel syndrome (IBS) is a functional bowel disorder that is highly comorbid with mental disorders. However, few studies have examined the risk of attention-deficit/hyperactivity disorder (ADHD), autism spectrum disorder (ASD), bipolar disorder, major depressive disorder (MDD), and schizophrenia in the offspring of parents with IBS. We used nationally representative cross-sectional survey data to analyze cross-generational transmission patterns of both IBS and major mental disorders. Odds ratio (OR) was calculated by using logistic regression models with adjustment for potential confounding factors. Offspring of parents with IBS were more likely to develop IBS themselves (OR = 2.41, 95% confidence interval (CI), 2.09–2.78), ADHD (OR = 1.33, 95% CI, 1.08–1.62), and MDD (OR = 1.32, 95% CI, 1.04–1.68) than the controls. Data stratification by parental sex revealed that paternal IBS increased risk of ADHD (OR = 1.34, 95% CI, 1.01–1.77) in the offspring, while maternal IBS increased the risk of MDD (OR = 1.51, 95% CI, 1.11–2.06). This is the first study to reveal parental IBS is associated with IBS, ADHD, and MDD among offspring, suggesting the necessity for early implementation of prevention strategies for at-risk children.

Serotonin deficiency induced after brain maturation rescues consequences of early life adversity

Brain serotonin (5-HT) system dysfunction is implicated in depressive disorders and acute depletion of 5-HT precursor tryptophan has frequently been used to model the influence of 5-HT deficiency on emotion regulation. Tamoxifen (TAM)-induced Cre/loxP-mediated inactivation of the tryptophan hydroxylase-2 gene (Tph2) was used to investigate the effects of provoked 5-HT deficiency in adult mice (Tph2 icKO) previously subjected to maternal separation (MS). The efficiency of Tph2 inactivation was validated by immunohistochemistry and HPLC. The impact of Tph2 icKO in interaction with MS stress (Tph2 icKO × MS) on physiological parameters, emotional behavior and expression of 5-HT system-related marker genes were assessed. Tph2 icKO mice displayed a significant reduction in 5-HT immunoreactive cells and 5-HT concentrations in the rostral raphe region within four weeks following TAM treatment. Tph2 icKO and MS differentially affected food and water intake, locomotor activity as well as panic-like escape behavior. Tph2 icKO prevented the adverse effects of MS stress and altered the expression of the genes previously linked to stress and emotionality. In conclusion, an experimental model was established to study the behavioral and neurobiological consequences of 5-HT deficiency in adulthood in interaction with early-life adversity potentially affecting brain development and the pathogenesis of depressive disorders.

Brazilian Psychiatric Association guidelines for the management of suicidal behavior. Part 1. Risk factors, protective factors, and assessment

Suicide is a global public health problem that causes the loss of more than 800,000 lives each year, principally among young people. In Brazil, the average mortality rate attributable to suicide is approximately 5.23 per 100,000 population. Although many guidelines have been published for the management of suicidal behavior, to date, there are no recent guidelines based on the principles of evidence-based medicine that apply to the reality of suicide in Brazil. The objective of this work is to provide key guidelines for managing patients with suicidal behavior in Brazil. This project involved 11 Brazilian psychiatry professionals selected by the Psychiatric Emergencies Committee (Comissão de Emergências Psiquiátricas) of the Brazilian Psychiatric Association for their experience and knowledge in psychiatry and psychiatric emergencies. For the development of these guidelines, 79 articles were reviewed (from 5,362 initially collected and 755 abstracts). In this review, we present definitions, risk and protective factors, assessments, and an introduction to the Safety Plan.

Systematic review registry number: CRD42020206517

Reward sensitivity, affective neuroscience personality, symptoms of attention-deficit/hyperactivity disorder, and TPH2-703G/T (rs4570625) genotype

OBJECTIVE

Reward sensitivity is an increasingly used construct in psychiatry, yet its possible inner structure and relationship with other affective variables are not well known.

METHODS

A reward sensitivity measurement scale was constructed on the basis of large item pool collected from birth cohort representative samples (the Estonian Children Personality Behaviour and Health Study; original n = 1238). Affective Neuroscience Personality Scale (ANPS) and the Adult Attention deficit hyperactivity disorder (ADHD) Self-Report Scale (ASRS) were administered in young adulthood. A variant (rs4570625) of the gene encoding tryptophan hydroxylase 2 (TPH2) that is responsible for the synthesis of central serotonin was genotyped.

RESULTS

Reward sensitivity consisted of two orthogonal components, operationally defined as Openness to Rewards and Insatiability by Reward, that respectively characterise the striving towards multiple rewards and the strong pursuit and fixation to a particular reward. While SEEKING and PLAY (and to lower extent CARE) of the ANPS co-varied with Openness to Rewards, FEAR, SADNESS, and ANGER were related to Insatiability by Reward. The total score of ASRS was moderately correlated with Insatiability by Reward, while the association with Openness to Rewards was negligible. However, ASRS Inattention had some negative relationship with the Social Experience facet of Openness to Rewards. The T/T homozygotes for the TPH2 promoter polymorphism had lower Insatiability by Reward but not Openness to Rewards.

CONCLUSIONS

Behaviours sensitive to rewards are separable to the components of variability and fixation, and these components are differentially related to affective aspects of personality, attention, and hyperactivity as well as to TPH2 genotype.

Application of antidepressants in depression: A systematic review and meta-analysis

BACKGROUND

The type and quantities of antidepressants are increasing, but the efficacy and safety of first-line and emerging drugs vary between studies. In this article, we estimated the efficacy and safety of first-line and emerging antidepressants (anti-inflammatory drugs and ketamine).

METHOD

ystematic search of EMBASE, ERIC, MEDLINE, psycARTICLES, and psycINFO without language restriction for studies on the depression, depressive symptoms, antidepressants, fluoxetine (Prozac), paroxetine, escitalopram, sertraline, fluvoxamine, venlafaxine, duloxetine, NSAIDs, anti-cytokine drugs or pioglitazone published before May 1st, 2019. Information on study characteristics, depression or depressive symptoms, antidepressants and the descriptive statistics (including efficacy and safety of antidepressants) was extracted independently by 2 investigators. Estimates were pooled using random-effects meta-analysis. Differences by study-level characteristics were estimated using stratified meta-analysis and meta-regression. The response and remission of antidepressants were used as clinical evaluation indicators, and the evaluation criteria were clinical depression scales. OR value of antidepressants as assessed by meta-analysis.

RESULTS

The literature search retrieved 5529 potentially relevant articles of which 49 studies were finally included. We compared the efficacy of antidepressants (seven first-line antidepressants (fluoxetine, paroxetine, escitalopram, sertraline, fluvoxamine, venlafaxine, duloxetine), there kinds of anti-inflammatory drugs(NASIDs, cytokine-inhibitor, pioglitazone) and ketamine) by comparing the OR values.

CONCLUSION

The three drugs with the highest OR value in response were NASID (OR = 3.62(1.58, 8.32)), venlafaxin (OR = 3.50(1.83, 6.70)) and ketamine (OR = 3.28(1.89, 5.68)), while the highest OR value in remission were NASID (OR = 3.17(1.60, 6.29)), ketamine (OR = 2.99(1.58, 5.67)) and venlafaxin (OR = 2.55(1.72, 3.78)). Through reading the literature, we found 69 SNPs associated with depression. Major depression was a debilitating disorder that could ultimately lead to enormous societal and economical challenge [1]. The number of person which affected by depression was up to 16% of the population worldwide. More than 300 million individuals were estimated to suffer depression these days [1,2]. Therefore, it is apparent that safety and effective treatments for depression are necessary. In the 1930 s, the first drug for schizophrenia was discovered. This finding was a landmark for the emerging of biological psychiatry. In the 1950 s, pharmacologists had stumbled upon the antidepressant effect of imipramine. Since then, every 30 years, the use of antidepressants had made a pulsatile leap. Selective serotonin reuptake inhibitors (SSRIs) are the most widely-prescribed psychiatric drugs for the treatment of depression. However, the efficacy was variable and incomplete: 60%-70% of the patients do not experience remission, while 30%-40% do not show a significant response [3,4]. Nevertheless, SSRIs, SNRIs (selective serotonin-norepinephrine reuptake inhibitors, which can block norepinephrine at the same time) and NaSSAs (norepinephrine and selective serotonin receptor agonist), constituted the first-line clinical drugs. Nearly 30 years after the outbreak of SSRIs, antidepressants have ushered in a new chapter. It has been found that anti-inflammatory drugs could also have the small and moderate antidepressant effect and it's widely discussed [5]. More than 40 anti-inflammatory drugs have been certificated to have antidepressant effects in preclinical and clinical studies [6]. The antidepressant that has been approved for use recently is ketamine. There is no comprehensive comparison of the efficacy of all these drugs. In this review, we tried to estimate the efficacy and safety of first-line antidepressants, anti-inflammatory drugs and ketamine. On the other hand, with the development of GWAS, SNPs related to depression have been reported, and the corresponding mechanisms have been elaborated, respectively. However, patients with these SNPs have not been treated with individualized drugs according to the mechanisms. We hope to push this process forward through the summary of this article.

METHODS

Search Strategy and Study Eligibility.

The role of TPH2 variant rs4570625 in shaping infant attention to social signals

TPH2, the rate-limiting enzyme in the synthesis of serotonin, has been connected to several psychiatric outcomes. Its allelic variant, rs4570625, has been found to relate to individual differences in cognitive and emotion regulation during infancy with T-carriers of rs4570625 showing a relatively heightened attention bias for fearful faces. A significant gene-environment interaction was also reported with the T-carriers of mothers with depressive symptoms showing the highest fear bias. We investigated these associations in a sample of 8-month old infants (N = 330), whose mothers were prescreened for low/high levels of prenatal depressive and/or anxiety symptoms. Attention disengagement from emotional faces (neutral, happy, fearful, and phase-scrambled control faces) to distractors was assessed with eye tracking and an overlap paradigm. Maternal depressive symptoms were assessed at several time points during pregnancy and postpartum. The mean levels of symptoms at six months postpartum and the trajectories of symptoms from early pregnancy until six months postpartum were used in the analyses (N = 274). No main effect of the rs4570625 genotype on attention disengagement was found. The difference in fear bias between the genotypes was significant but in an opposite direction compared to a previous study. The results regarding the interaction of the genotype and maternal depression were not in accordance with the previous studies. These results show inconsistencies in the effects of the rs4570625 genotype on attention biases in separate samples of infants from the same population with only slight differences in age.

Genome-wide association study identifies TPH2 variant as a novel locus for severe CV-A6-associated hand, foot, and mouth disease in Han Chinese

BACKGROUND

Little is known about the association between genetic susceptibility and the severity of hand, foot, and mouth disease (HFMD) infected with coxsackievirus A6 (CV-A6).

METHODS

Three hundred and sixty-four CV-A6 HFMD patients were enrolled, including 115 severe and 249 mild patients. A genome-wide association study (GWAS) was performed involving eight DNA pools of 115 severe and 115 mild CV-A6 HFMD patients pair-matched by age and gender. Differences in relative allele signal scores of SNPs in Illumina Human OmniZhongHua-8 BeadChips were compared between the two groups. The tag SNPS for potentially functional SNPs or their high linked SNPs were selected for individual genotyping in all 364 patients and assessed for their associations with severe CV-A6 HFMD using multivariable logistic regression analyses.

RESULTS

The top 30 significant SNPs obtained from pooled DNA GWAS analysis were checked for biological functions and their high linkage disequilibrium (LD) SNPs. Four tag SNPs (rs1558206, rs6927647, rs9375728 and rs10879355) were selected for further individual genotyping in 364 CV-A6 patients. Only SNP rs10879355 was associated with severe CV-A6 HFMD, with CC genotype having a greater risk of severe illness than TT+TC genotypes (OR=2.48, 95%CI: 1.34, 4.56). SNP rs4290270 is in complete LD with rs10879355 in Chinese Han children.

CONCLUSIONS

This is the first report that one potentially functional SNP rs4290270 in the TPH2 gene may be associated with the risk of severe CV-A6 HFMD.

The Absence of Serotonin in the Brain Alters Acute Stress Responsiveness by Interfering With the Genomic Function of the Glucocorticoid Receptors

Alterations in serotonergic transmission have been related to a major predisposition to develop psychiatric pathologies, such as depression. We took advantage of tryptophan hydroxylase (TPH) 2 deficient rats, characterized by a complete absence of serotonin in the brain, to evaluate whether a vulnerable genotype may influence the reaction to an acute stressor. In this context, we investigated if the glucocorticoid receptor (GR) genomic pathway activation was altered by the lack of serotonin in the central nervous system. Moreover, we analyzed the transcription pattern of the clock genes that can be affected by acute stressors. Adult wild type (TPH2^+/+) and TPH2-deficient (TPH2^-/-) male rats were sacrificed after exposure to one single session of acute restraint stress. Protein and gene expression analyses were conducted in the prefrontal cortex (PFC). The acute stress enhanced the translocation of GRs in the nucleus of TPH2^+/+ animals. This effect was blunted in TPH2^-/- rats, suggesting an impairment of the GR genomic mechanism. This alteration was mirrored in the expression of GR-responsive genes: acute stress led to the up-regulation of GR-target gene expression in TPH2^+/+, but not in TPH2^-/- animals. Finally, clock genes were differently modulated in the two genotypes after the acute restraint stress. Overall our findings suggest that the absence of serotonin within the brain interferes with the ability of the HPA axis to correctly modulate the response to acute stress, by altering the nuclear mechanisms of the GR and modulation of clock genes expression.

The neuroscience of sadness: A multidisciplinary synthesis and collaborative review

Sadness is typically characterized by raised inner eyebrows, lowered corners of the mouth, reduced walking speed, and slumped posture. Ancient subcortical circuitry provides a neuroanatomical foundation, extending from dorsal periaqueductal grey to subgenual anterior cingulate, the latter of which is now a treatment target in disorders of sadness. Electrophysiological studies further emphasize a role for reduced left relative to right frontal asymmetry in sadness, underpinning interest in the transcranial stimulation of left dorsolateral prefrontal cortex as an antidepressant target. Neuroimaging studies - including meta-analyses - indicate that sadness is associated with reduced cortical activation, which may contribute to reduced parasympathetic inhibitory control over medullary cardioacceleratory circuits. Reduced cardiac control may - in part - contribute to epidemiological reports of reduced life expectancy in affective disorders, effects equivalent to heavy smoking. We suggest that the field may be moving toward a theoretical consensus, in which different models relating to basic emotion theory and psychological constructionism may be considered as complementary, working at different levels of the phylogenetic hierarchy.

Suicide: Genetics and Heritability

Nature vs nurture is, and has been, a never stopping debate since Lamarck and Darwin exposed their corresponding theories on evolution, and even before them, such discussion already existed. Is suicide a heritable conduct? Is it learnt? Maybe the answer is both and none, at the same time. From genetic twin studies to epigenetic and environmental influence on development, this chapter aims to take a look at different points of view and most relevant theories in one of the worlds leading causes of death, specially for young individuals. We explore different studies aiming to find biomarkers for suicide, as well as other traits frequently encountered in individuals who engage in suicidal behavior, such as impulsivity, aggressivity, and hopelessness. Finally, this chapter also looks at some of the most recent approaches in treatment and prevention of suicidal behavior, in order to highlight what they have in common and try to explain (at least partially) why they could be effective.

Genetic Advance in Depressive Disorder

Major depressive disorder (MDD) and bipolar disorder (BPD) are both chronic, severe mood disorder with high misdiagnosis rate, leading to substantial health and economic burdens to patients around the world. There is a high misdiagnosis rate of bipolar depression (BD) just based on symptomology in depressed patients whose previous manic or mixed episodes have not been well recognized. Therefore, it is important for psychiatrists to identify these two major psychiatric disorders. Recently, with the accumulation of clinical sample sizes and the advances of methodology and technology, certain progress in the genetics of major depression and bipolar disorder has been made. This article reviews the candidate genes for MDD and BD, genetic variation loci, chromosome structural variation, new technologies, and new methods.

Genomewide Gene-by-Sex Interaction Scans Identify ADGRV1 for Sex Differences in Opioid Dependent African Americans

Sex differences in opioid dependence (OD) are genetically influenced. We conducted genomewide gene-by-sex interaction scans for the DSM-IV diagnosis of OD in 8,387 African-American (AA) or European-American subjects (43.6% women; 4,715 OD subjects). Among AAs, 9 SNPs were genome-wide significant at ADGRV1 (adhesion G-protein-coupled receptor V1, lead-SNP rs2366929*(C/T), p = 1.5 × 10-9) for sex-different risk of OD, with the rs2366929*C-allele increasing OD risk only for men. The top co-expressions in brain were between ADGRV1 and GRIK2 in substantia nigra and medullary inferior olivary nucleus, and between ADGRV1 and EFHC2 in frontal cortex and putamen. Significant sex-differential ADGRV1 expression from GTEx was detected in breast (Bonferroni-corrected-p < 0.002) and in heart (p < 0.0125), with nominal significance identified in brain, thyroid, lung, and stomach (p < 0.05). ADGRV1 co-expression and disease-enrichment analysis identifying the top 10 diseases showed strikingly sexually dimorphic risks. The enrichment and transcriptome analyses provided convergent support that ADGRV1 exerts a sex-different effect on OD risk. This is the first study to identify genetic variants contributing to sex differences in OD. It shows that ADGRV1 contributes to OD risk only in AA men, a finding that warrants further study.

Alternative splicing in serotonergic system: Implications in neuropsychiatric disorders

BACKGROUND

The serotonergic system is a key component of physiological brain function and is essential for proper neurological activity. Numerous neuropsychiatric disorders are associated with deregulation of the serotonergic system. Accordingly, many pharmacological treatments are focused on modulation of this system. While providing a promising line of therapeutic moderation, these approaches may be complicated due to the presence of alternative splicing events for key genes in this pathway. Alternative splicing is a co-transcriptional process by which different mRNA transcripts can be produced from the same gene. These different isoforms may have diverse activities and functions, and their relative balance is often critical for the maintenance of homeostasis. Alternative splicing greatly increases the production of proteins, augmenting cell plasticity, and provides an important control point for regulation of gene expression.

AIM

The objective of this narrative review is to discuss the potential impact of alternative splicing of different components of the serotonergic system and speculate on their involvement in several neuropsychiatric disorders.

CONCLUSIONS

The specific role of each isoform in disease and their relative activities in the signalling pathways involved are yet to be determined. We need to gain a better understanding of the basis of alternative isoforms of the serotonergic system in order to fully understand their impact and be able to develop new effective pharmacological isoform-specific targets.

Tryptophan hydroxylase 2 as a therapeutic target for psychiatric disorders: focus on animal models

Introduction: Tryptophan hydroxylase 2 (TPH2) is the key, rate-limiting enzyme of serotonin (5-HT) synthesis in the brain. Some polymorphic variants of the human Tph2 gene are associated with psychiatric disorders. Area covered: This review focuses on the mechanisms underlying the association between the TPH2 activity and behavioral disturbances in models of psychiatric disorders. Specifically, it discusses: 1) genetic and posttranslational mechanisms defining the TPH2 activity, 2) behavioral effects of knockout and loss-of-function mutations in the mouse Tph2 gene, 3) pharmacological inhibition and the activation of the TPH2 activity and 4) alterations in the brain TPH2 activity in animal models of psychiatric disorders. We show the dual role of the TPH2 activity: both deficit and excess of the TPH2 activity cause significant behavioral disturbances in animal models of depression, anxiety, aggression, obsessive-compulsive disorders, schizophrenia, and catalepsy. Expert opinion: Pharmacological chaperones correcting the structure of the TPH2 molecule are promising tools for treatment of some hereditary psychiatric disorders caused by loss-of-function mutations in the human Tph2 gene; while some stress-induced affective disorders, associated with the elevated TPH2 activity, may be effectively treated by TPH2 inhibitors. This dual role of TPH2 should be taken into consideration during therapy of psychiatric disorders.

Identification of Cholecystokinin by Genome-Wide Profiling as Potential Mediator of Serotonin-Dependent Behavioral Effects of Maternal Separation in the Amygdala

Converging evidence suggests a role of serotonin (5-hydroxytryptamine, 5-HT) and tryptophan hydroxylase 2 (TPH2), the rate-limiting enzyme of 5-HT synthesis in the brain, in modulating long-term, neurobiological effects of early-life adversity. Here, we aimed at further elucidating the molecular mechanisms underlying this interaction, and its consequences for socio-emotional behaviors, with a focus on anxiety and social interaction. In this study, adult, male Tph2 null mutant (Tph2 -/-) and heterozygous (Tph2 +/-) mice, and their wildtype littermates (Tph2 +/+) were exposed to neonatal, maternal separation (MS) and screened for behavioral changes, followed by genome-wide RNA expression and DNA methylation profiling. In Tph2 -/- mice, brain 5-HT deficiency profoundly affected socio-emotional behaviors, i.e., decreased avoidance of the aversive open arms in the elevated plus-maze (EPM) as well as decreased prosocial and increased rule breaking behavior in the resident-intruder test when compared to their wildtype littermates. Tph2 +/- mice showed an ambiguous profile with context-dependent, behavioral responses. In the EPM they showed similar avoidance of the open arm but decreased prosocial and increased rule breaking behavior in the resident-intruder test when compared to their wildtype littermates. Notably, MS effects on behavior were subtle and depended on the Tph2 genotype, in particular increasing the observed avoidance of EPM open arms in wildtype and Tph2 +/- mice when compared to their Tph2 -/- littermates. On the genomic level, the interaction of Tph2 genotype with MS differentially affected the expression of numerous genes, of which a subset showed an overlap with DNA methylation profiles at corresponding loci. Remarkably, changes in methylation nearby and expression of the gene encoding cholecystokinin, which were inversely correlated to each other, were associated with variations in anxiety-related phenotypes. In conclusion, next to various behavioral alterations, we identified gene expression and DNA methylation profiles to be associated with TPH2 inactivation and its interaction with MS, suggesting a gene-by-environment interaction-dependent, modulatory function of brain 5-HT availability.

TPH-2 Gene Polymorphism in Major Depressive Disorder Patients With Early-Wakening Symptom

Background: Sleep disturbances, such as early wakening, are frequently observed in patients with major depressive disorder (MDD). The suprachiasmatic nuclei (SCN), which controls circadian rhythm, is innervated by the raphe nucleus, a region where Tryptophan hydroxylase-2 (TPH-2) gene is primarily expressed. Although TPH-2 is often implicated in the pathophysiology of depression, few studies have applied a genetic and imaging technique to investigate the mechanism of early wakening symptom in MDD. We hypothesized that TPH-2 variants could influence the function of SCN in MDD patients with early wakening symptom. Methods: One hundred and eighty five MDD patients (62 patients without early wakening and 123 patients with early wakening) and 64 healthy controls participated in this study. Blood samples were collected and genotyping of rs4290270, rs4570625, rs11178998, rs7305115, rs41317118, and rs17110747 were performed by next-generation sequencing (NGS) technology. Logistic regression model was employed for genetic data analysis using the PLINK software. Based on the allele type, rs4290270, which was significant in the early wakening MDD group, participants were categorized into two groups (A allele and T carrier). All patients underwent whole brain resting-state functional magnetic resonance imaging (rs-fMRI) scanning and a voxel-wise functional connectivity comparison was performed between the groups. Results: rs4290270 was significantly linked to MDD patients who exhibited early wakening symptom. The functional connectivities of the right SCN with the right fusiform gyrus and right middle frontal gyrus were increased in the T carrier group compared to the A allele group. In addition, the functional connectivities of the left SCN with the right lingual gyrus and left calcarine sulcus were decreased in the T carrier group compared to the A allele group. Conclusion: These findings suggested that the TPH-2 gene variant, rs4290270, affected the circadian regulating function of SCN. The altered functional connectivities, observed between the SCN and right fusiform gyrus, right middle frontal gyrus, the right lingual gyrus and left calcarine sulcus, could highlight the neural mechanism by which SCN induces sleep-related circadian disruption in T carrier MDD patients. Hence, rs4290270 could potentially serve as a reliable biomarker to identify MDD patients with early wakening symptom.

Unraveling the Molecular Determinants of Manual Therapy: An Approach to Integrative Therapeutics for the Treatment of Fibromyalgia and Chronic Fatigue Syndrome/Myalgic Encephalomyelitis

Application of protocols without parameter standardization and appropriate controls has led manual therapy (MT) and other physiotherapy-based approaches to controversial outcomes. Thus, there is an urgency to carefully define standard protocols that elevate physiotherapy treatments to rigorous scientific demands. One way in which this can be achieved is by studying gene expression and physiological changes that associate to particular, parameter-controlled, treatments in animal models, and translating this knowledge to properly designed, objective, quantitatively-monitored clinical trials (CTs). Here, we propose a molecular physiotherapy approach (MPTA) requiring multidisciplinary teams, to uncover the scientific reasons behind the numerous reports that historically attribute health benefits to MT-treatments. The review focuses on the identification of MT-induced physiological and molecular responses that could be used for the treatment of fibromyalgia (FM) and chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME). The systemic effects associated to mechanical-load responses are considered of particular relevance, as they suggest that defined, low-pain anatomic areas can be selected for MT treatment and yet yield overall benefits, an aspect that might result in it being essential to treat FM. Additionally, MT can provide muscle conditioning to sedentary patients without demanding strenuous physical effort, which is particularly detrimental for CFS/ME patients, placing MT as a real option for integrative medicine programs to improve FM and CFS/ME.