Evidence of an association between the vasopressin V1b receptor gene (AVPR1B) and childhood-onset mood disorders

A complex selection signature at the human AVPR1B gene

BACKGROUND

The vasopressin receptor type 1b (AVPR1B) is mainly expressed by pituitary corticotropes and it mediates the stimulatory effects of AVP on ACTH release; common AVPR1B haplotypes have been involved in mood and anxiety disorders in humans, while rodents lacking a functional receptor gene display behavioral defects and altered stress responses.

RESULTS

Here we have analyzed the two exons of the gene and the data we present suggest that AVPR1B has been subjected to natural selection in humans. In particular, analysis of exon 2 strongly suggests the action of balancing selection in African populations and Europeans: the region displays high nucleotide diversity, an excess of intermediate-frequency alleles, a higher level of within-species diversity compared to interspecific divergence and a genealogy with common haplotypes separated by deep branches. This relatively unambiguous situation coexists with unusual features across exon 1, raising the possibility that a nonsynonymous variant (Gly191Arg) in this region has been subjected to directional selection.

CONCLUSION

Although the underlying selective pressure(s) remains to be identified, we consider this to be among the first documented examples of a gene involved in mood disorders and subjected to natural selection in humans; this observation might add support to the long-debated idea that depression/low mood might have played an adaptive role during human evolution.

Next generation tools for the annotation of human SNPs

Computational biology has the opportunity to play an important role in the identification of functional single nucleotide polymorphisms (SNPs) discovered in large-scale genotyping studies, ultimately yielding new drug targets and biomarkers. The medical genetics and molecular biology communities are increasingly turning to computational biology methods to prioritize interesting SNPs found in linkage and association studies. Many such methods are now available through web interfaces, but the interested user is confronted with an array of predictive results that are often in disagreement with each other. Many tools today produce results that are difficult to understand without bioinformatics expertise, are biased towards non-synonymous SNPs, and do not necessarily reflect up-to-date versions of their source bioinformatics resources, such as public SNP repositories. Here, I assess the utility of the current generation of webservers; and suggest improvements for the next generation of webservers to better deliver value to medical geneticists and molecular biologists.

Non-human primates: model animals for developmental psychopathology

Non-human primates have been used to model psychiatric disease for several decades. The success of this paradigm has issued from comparable cognitive skills, brain morphology, and social complexity in adult monkeys and humans. Recently, interest in biological psychiatry has focused on similar brain, social, and emotional developmental processes in monkeys. In part, this is related to evidence that early postnatal experiences in human development may have profound implications for subsequent mental health. Non-human primate studies of postnatal phenomenon have generally fallen into three basic categories: experiential manipulation (largely manipulations of rearing), pharmacological manipulation (eg drug-induced psychosis), and anatomical localization (defined by strategic surgical damage). Although these efforts have been very informative each of them has certain limitations. In this review we highlight general findings from the non-human primate postnatal developmental literature and their implications for primate models in psychiatry. We argue that primates are uniquely capable of uncovering interactions between genes, environmental challenges, and development resulting in altered risk for psychopathology.

Association study of the estrogen receptor alpha gene (ESR1) and childhood-onset mood disorders

Depressive disorders are heterogeneous psychiatric disorders involving deficits in cognitive, psychomotor, and emotional processing. Depressive disorders have a significant genetic component, with severe, recurrent and early-onset forms demonstrating elevated heritability. In this study we genotyped eleven single nucleotide polymorphisms (SNPs) spanning the estrogen receptor alpha gene (ESR1) in a large family-based childhood-onset mood disorder (COMD) sample. None of the individual SNP or global haplotype analyses was significant in the entire COMD sample, but haplotype analysis of three SNPs in strong linkage disequilibrium (rs746432, rs2077647, and rs532010) uncovered an association with COMD, specifically in females. Our data are consistent with previous studies demonstrating a female-specific association between ESR1 and neurobehavioral phenotypes. These results suggest the existence of sex-specific etiological factors in depressive disorders, related to estrogen, with onset in childhood.

The role of the arginine vasopressin Avp1b receptor in the acute neuroendocrine action of antidepressants

In times of stress the hypothalamic-pituitary-adrenal (HPA) axis is activated and releases two neurohormones, corticotropin-releasing hormone (Crh) and arginine vasopressin (Avp), to synergistically stimulate the secretion of adrenocorticotropin hormone (ACTH) from the anterior pituitary, culminating in a rise in circulating glucocorticoids. Avp mediates its actions at the Avp V1b receptor (Avpr1b) present on pituitary corticotropes. Dysregulation of the stress response is associated with the pathophysiology of depression and a major treatment involves increasing the availability of monamines at the synaptic cleft. Acute administration of selective serotonin reuptake inhibitors (SSRI) and tricyclic antidepressants (TCA) has previously been shown to activate the HPA axis. The present study was undertaken to evaluate the involvement of the Avpr1b in the HPA axis response to acute SC administration of an SSRI (fluoxetine 10mg/kg) and a TCA (desipramine 10mg/kg). We measured plasma ACTH and corticosterone (CORT) levels and neuropeptide mRNA expression in the hypothalamic paraventricular nucleus (PVN) of Avpr1b knockout (KO) mice and wild-type controls. Fluoxetine and desipramine administration significantly attenuated plasma ACTH and CORT levels in male and female Avpr1b KO mice when compared to their wild-type counterparts. Avp, oxytocin (Oxt) and Crh mRNA expression in the PVN did not change in fluoxetine-treated male Avpr1b KO or wild-type mice. In contrast, fluoxetine treatment increased PVN Avp mRNA levels in female Avpr1b wild type but not KO animals. PVN Oxt mRNA levels increased in fluoxetine-treated female mice of both genotypes. The data suggests that the Avpr1b is required to drive the HPA axis response to acute antidepressant treatment and provides further evidence of a sexual dichotomy in the regulation of PVN Avp/Oxt gene expression following antidepressant administration.