A 5-HT1Areceptor promoter polymorphism influences fronto-limbic functional connectivity and depression severity in bipolar disorder

Effects of serotonin transporter and receptor polymorphisms on depression

INTRODUCTION

Serotonin is highly implicated in the regulation of emotional state and the execution of cognitive tasks, so much so that the serotonin transporter genes (5-HTT, SLC6A4) and the serotonin receptor genes (HTR1A, HTR1B, HTR2A) have become the perfect candidates when studying the effects that these genes and their polymorphic variations have on depression characteristics.

OBJECTIVE

A review of research reports that have studied the effects of variations in the serotonin transporter and receptor genes on different clinical features of depression.

METHODS

A search of the Scopus, Web of Science and PubMed databases was conducted using the keywords ("depression" AND "polymorphism").

CONCLUSIONS

According to the review of 54 articles, the short allele of the 5-HTTLPR polymorphism was found to be the most reported risk factor related to the development of depression and its severity. Variations in the genes studied (SLC6A4, HTR1A, HTR2A) can generate morphological alterations of brain structures.

Catechol-O-methyltransferase activity does not influence emotional processing in men

BACKGROUND

Catechol-O-methyltransferase (COMT) regulates cortical dopaminergic transmission and prefrontal-dependent cognitive function. However, its role in other cognitive processes, including emotional processing, is relatively unexplored. We therefore investigated the separate and interactive influences of COMT inhibition and Val¹⁵⁸Met (rs4680) genotype on performance on an emotional test battery.

METHODS

We recruited 74 healthy men homozygous for the functional COMT Val¹⁵⁸Met polymorphism. Volunteers were administered either a single 200 mg dose of the brain-penetrant COMT inhibitor tolcapone or placebo in a double-blind, randomised manner. Emotional processing was assessed using the emotional test battery, and mood was rated using visual analogue scales and the Profile of Mood States (POMS) questionnaire across the test day.

RESULTS

There were no main or interactive effects of Val¹⁵⁸Met genotype or tolcapone on any of the emotional processing measures or mood ratings.

CONCLUSIONS

Our findings suggest that, at least in healthy adult men, COMT has little or no effect on emotional processing or mood. These findings contrast with several neuroimaging studies that suggest that COMT modulates neural activity during emotional processing. Thus, further studies are required to understand how COMT impacts on the relationship between behavioural output and neural activity during emotional processing. Nevertheless, our data suggest that novel COMT inhibitors under development for treating cognitive dysfunction are unlikely to have acute off target effects on emotional behaviours.

Effects of Serotonin Transporter and Receptor Polymorphisms on Depression

INTRODUCTION

Serotonin is highly implicated in the regulation of emotional state and the execution of cognitive tasks, so much so that the serotonin transporter genes (5-HTT, SLC6A4) and the serotonin receptor genes (HTR1A, HTR1B, HTR2A) have become the perfect candidates when studying the effects that these genes and their polymorphic variations have on depression characteristics.

OBJECTIVE

A review of research reports that have studied the effects of variations in the serotonin transporter and receptor genes on different clinical features of depression.

METHODS

A search of the Scopus, Web of Science and PubMed databases was conducted using the keywords ("depression" AND "polymorphism").

CONCLUSIONS

According to the review of 54 articles, the short allele of the 5-HTTLPR polymorphism was found to be the most reported risk factor related to the development of depression and its severity. Variations in the genes studied (SLC6A4, HTR1A, HTR2A) can generate morphological alterations of brain structures.

Genetic neuroimaging of bipolar disorder: a systematic 2017-2020 update

There is evidence of genetic polymorphism influences on brain structure and function, genetic risk in bipolar disorder (BD), and neuroimaging correlates of BD. How genetic influences related to BD could be reflected on brain changes in BD has been efficiently reviewed in a 2017 systematic review. We aimed to confirm and extend these findings through a Preferred Reporting Items for Systematic reviews and Meta-Analyses-based systematic review. Our study allowed us to conclude that there is no replicated finding in the timeframe considered. We were also unable to further confirm prior results of the BDNF gene polymorphisms to affect brain structure and function in BD. The most consistent finding is an influence of the CACNA1C rs1006737 polymorphism in brain connectivity and grey matter structure and function. There was a tendency of undersized studies to obtain positive results and large, genome-wide polygenic risk studies to find negative results in BD. The neuroimaging genetics in BD field is rapidly expanding.

Genetic and Epigenetic Consequence of Early-Life Social Stress on Depression: Role of Serotonin-Associated Genes

Early-life adversity caused by poor social bonding and deprived maternal care is known to affect mental wellbeing and physical health. It is a form of chronic social stress that persists because of a negative environment, and the consequences are long-lasting on mental health. The presence of social stress during early life can have an epigenetic effect on the body, possibly resulting in many complex mental disorders, including depression in later life. Here, we review the evidence for early-life social stress-induced epigenetic changes that modulate juvenile and adult social behavior (depression and anxiety). This review has a particular emphasis on the interaction between early-life social stress and genetic variation of serotonin associate genes including the serotonin transporter gene (5-HTT; also known as SLC6A4), which are key molecules involved in depression.

Cortico-limbic functional connectivity mediates the effect of early life stress on suicidality in bipolar depressed 5-HTTLPR*s carriers

BACKGROUND

In bipolar disorder (BD) the risk of suicide in adult life can be influenced by the interaction of adverse childhood experiences with the serotonin transporter polymorphism (5-HTTLPR). The cortico-limbic connectivity is a candidate endophenotype for the disorder, also related to suicidality and affected by the 5-HT system.

METHODS

In 64 (*s carriers = 41; l/l = 23) depressed BD patients, we explored the effect of 5-HTTLPR on corticolimbic functional connectivity (FC) during emotional processing, and the role of FC in moderating/mediating the effect of early stressful events on suicidality among 5-HTTLPR groups, by implementing Generalized Structural Equation Model.

RESULTS

5-HTTLPR affects FC between amygdala (Amy) and anterior cingulate cortex (ACC), temporal pole, putamen/thalamus, and precuneus. The short allele was associated to a more inefficient corticolimbic connectivity. In 5-HTTLPR*s carriers, but not in l/l, the Amy-ACC functional coupling mediated the relationship between stress load and current suicidality.

LIMITATIONS

Patients were not drug-naive, and the recruitment took place in a single center, thus raising the possibility of population stratifications. The sample size is relatively small, but our findings can provide the background for replication study in independent and larger datasets.

CONCLUSIONS

Our results confirm the link between the 5-HTT promoter polymorphism and susceptibility to stress in BD, and suggest that cortico-limbic functional connectivity mediates these effects. This pattern could identify a vulnerability factor for the exacerbation of mood episodes after stressful life events particularly relevant in *s carriers.

Genetic, epigenetic and posttranscriptional mechanisms for treatment of major depression: the 5-HT1A receptor gene as a paradigm

Major depression and anxiety are highly prevalent and involve chronic dysregulation of serotonin, but they remain poorly understood. Here, we review novel transcriptional (genetic, epigenetic) and posttranscriptional (microRNA, alternative splicing) mechanisms implicated in mental illness, focusing on a key serotonin-related regulator, the serotonin 1A (5-HT1A) receptor. Functional single-nucleotide polymorphisms and stress-induced DNA methylation of the 5-HT1A promoter converge to differentially alter pre- and postsynaptic 5-HT1A receptor expression associated with major depression and reduced therapeutic response to serotonergic antidepressants. Major depression is also associated with altered levels of splice factors and microRNA, posttranscriptional mechanisms that regulate RNA stability. The human 5-HT1A 3′-untranslated region is alternatively spliced, removing microRNA sites and increasing 5-HT1A expression, which is reduced in major depression and may be genotype-dependent. Thus, the 5-HT1A receptor gene illustrates the convergence of genetic, epigenetic and posttranscriptional mechanisms in gene expression, neurodevelopment and neuroplasticity, and major depression. Understanding gene regulatory mechanisms could enhance the detection, categorization and personalized treatment of major depression.

Cortico-limbic connectivity as a possible biomarker for bipolar disorder: where are we now?

INTRODUCTION

The fronto-limbic network has been suggested as a key circuitry in the pathophysiology and maintenance of bipolar disorder. In the past decade, a disrupted connectivity within prefrontal-limbic structures was identified as a promising candidate biomarker for the disorder. Areas Covered: In this review, the authors examine current literature in terms of the structural, functional and effective connectivity in bipolar disorder, integrating recent findings of imaging genetics and machine learning. This paper profiles the current knowledge and identifies future perspectives to provide reliable and usable neuroimaging biomarkers for bipolar psychopathology in clinical practice. Expert Opinion: The replication and the translation of acquired knowledge into useful and usable tools represents one of the current greatest challenges in biomarker research applied to psychiatry.