Perinatal depression and DNA methylation of oxytocin-related genes: a study of mothers and their children

The present study investigated the association of perinatal depression (PD) with differential methylation of 3 genomic regions among mother and child dyads: exon 3 within the oxytocin receptor (OXTR) gene and 2 intergenic regions (IGR) between the oxytocin (OXT) and vasopressin (AVP) genes. Maternal PD was assessed at 5 time-points during pregnancy and postpartum. Four groups were established based on Edinburgh Postnatal Depression Scale (EPDS) cut-off scores: no PD, prenatal or postpartum depressive symptoms only and persistent PD (depressive symptoms both prenatally and postpartum). Salivary DNA was collected from mothers and children at the final time-point, 2.9 years postpartum. Mothers with persistent PD had significantly higher overall OXTR methylation than the other groups and this pattern extended to 16/22 individual CpG sites. For the IGR, only the region closer to the AVP gene (AVP IGR) showed significant differential methylation, with the persistent PD group displaying the lowest levels of methylation overall, but not for individual CpG sites. These results suggest that transient episodes of depression may not be associated with OXTR hypermethylation. Validation studies need to confirm the downstream biological effects of AVP IGR hypomethylation as it relates to persistent PD. Differential methylation of the OXTR and IGR regions was not observed among children exposed to maternal PD. The consequences of OXTR hypermethylation and AVP IGR hypomethylation found in mothers with persistent PDS may not only impact the OXT system, but may also compromise maternal behavior, potentially resulting in negative outcomes for the developing child.     

The contributions of oxytocin and vasopressin pathway genes to human behavior

Arginine vasopressin (AVP) and oxytocin (OXT) are social hormones and mediate affiliative behaviors in mammals and as recently demonstrated, also in humans. There is intense interest in how these simple nonapeptides mediate normal and abnormal behavior, especially regarding disorders of the social brain such as autism that are characterized by deficits in social communication and social skills. The current review examines in detail the behavioral genetics of the first level of human AVP-OXT pathway genes including arginine vasopressin 1a receptor (AVPR1a), oxytocin receptor (OXTR), AVP (AVP-neurophysin II [NPII]) and OXT (OXT neurophysin I [NPI]), oxytocinase/vasopressinase (LNPEP), ADP-ribosyl cyclase (CD38) and arginine vasopressin 1b receptor (AVPR1b). Wherever possible we discuss evidence from a variety of research tracks including molecular genetics, imaging genomics, pharmacology and endocrinology that support the conclusions drawn from association studies of social phenotypes and detail how common polymorphisms in AVP-OXT pathway genes contribute to the behavioral hard wiring that enables individual Homo sapiens to interact successfully with conspecifics. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.     

AVPR1b variation and the emergence of adaptive phenotypes in Platyrrhini primates

Platyrrhini (New World monkeys, NWm) are a group of primates characterized by behavioral and reproductive traits that are otherwise uncommon among primates, including social monogamy, direct paternal care, and twin births. As a consequence, the study of Platyrrhine primates is an invaluable tool for the discovery of the genetic repertoire underlying these taxon‐specific traits. Recently, high conservation of vasopressin (AVP) sequence, in contrast with high variability of oxytocin (OXT), has been described in NWm. AVP and OXT functions are possible due to interaction with their receptors: AVPR1a, AVPR1b, AVPR2, and OXTR; and the variability in this system is associated with the traits mentioned above. Understanding the variability in the receptors is thus fundamental to understand the function and evolution of the system as a whole. Here we describe the variability of AVPR1b coding region in 20 NWm species, which is well‐known to influence behavioral traits such as aggression, anxiety, and stress control in placental mammals. Our results indicate that 4% of AVPR1b sites may be under positive selection and a significant number of sites under relaxed selective constraint. Considering the known role of AVPR1b, we suggest that some of the changes described here for the Platyrrhini may be a part of the genetic repertoire connected with the complex network of neuroendocrine mechanisms of AVP–OXT system in the modulation of the HPA axis. Thus, these changes may have promoted the emergence of social behaviors such as direct paternal care in socially monogamous species that are also characterized by small body size and twin births.     

Labor and inflammation increase the expression of oxytocin receptor in human amnion

The oxytocin/oxytocin receptor (OXT/OXTR) system plays an important role in the regulation of parturition. The amnion is a major source of prostaglandins and inflammatory cytokine synthesis, which increase both before and during labor. Amnion is a noncontractile tissue; therefore, the role played by OXT/OXTR in this tissue will be fundamentally different from the role played in myometrial contractions. In the present study, we demonstrate increased OXTR mRNA and protein concentrations in human amnion epithelial cells associated with the onset of labor. We show that incubation of primary human amnion epithelial cells with IL1B results in a rapid, transient up-regulation of OXTR mRNA expression, which peaks in prelabor samples after 6 h. Incubation of prelabor amnion epithelial cells with OXT results in a marked increase of prostaglandin E(2) synthesis, and we demonstrate that OXT activates the extracellular signal-regulated protein kinase signal transduction pathway to stimulate up-regulation of cyclo-oxygenase 2 in human amnion epithelial cells. The increased ability of human amnion to produce prostaglandins in response to OXT treatment suggests a complementary role for the OXT/OXTR system in the activation of human amnion and the onset of labor.     

Oxytocin Prevents the Development of 3-NP-Induced Anxiety and Depression in Male and Female Rats: Possible Interaction of OXTR and mGluR2

Huntington disease (HD) is a progressive neurological disorder with dominant motor symptoms. It also has psychiatric manifestations, like anxiety and depression, that can emerge themselves before motor symptoms and impose a major burden on patients. Oxytocin (OXT) is a newly emerged treatment for disorders like autism and schizophrenia and recently is using to alleviate depression and anxiety. In the current study, we investigated the behavioral and molecular effects of OXT on the development of anxiety and depression in 3-nitropropionic acid (3-NP)-induced model of HD. Anxiety- and depression-like behaviors as well as the levels of oxytocin receptor (OXTR), metabotropic glutamate receptor (mGluR) 2, mGluR5, and glutathione (GSH) were measured in striatum, hippocampus, prefrontal cortex, and amygdala. Also, we questioned if sex had any modulatory effect. We found that 3-NP increased anxiety and depression compared to controls. It also reduced the levels of OXTR and mGluR2, increased mGluR5, and reduced GSH in studied brain regions. Pretreatment with OXT before the injection of 3-NP ameliorated anxiety and depression. Additionally, it protected the brain from developing low levels of OXTR, mGluR2, and GSH and high levels of mGluR5 in studied regions. The protective effects of OXT were similar between male and female animals. These data suggest that OXTR, mGluR2, mGluR5, and GSH may contribute to psychiatric manifestations of HD. In addition, pretreatment with OXT could prevent the mood changes in male and female rats.

     

GIP-dependent expression of hypothalamic genes

GIP (glucose dependent insulinotrophic polypeptide), originally identified as an incretin peptide synthesized in the gut, has recently been identified, along with its receptors (GIPR), in the brain. Our objective was to investigate the role of GIP in hypothalamic gene expression of biomarkers linked to regulating energy balance and feeding behavior related neurocircuitry. Rats with lateral cerebroventricular cannulas were administered 10 μg GIP or 10 microl artificial cerebrospinal fluid (aCSF) daily for 4 days, after which whole hypothalami were collected. Real time Taqman? RT-PCR was used to quantitatively compare the mRNA expression levels of a set of genes in the hypothalamus. Administration of GIP resulted in up-regulation of hypothalamic mRNA levels of AVP (46.9±4.5 %), CART (25.9±2.7 %), CREB1 (38.5±4.5 %), GABRD (67.1±11 %), JAK2 (22.1±3.6 %), MAPK1 (33.8±7.8 %), NPY (25.3±5.3 %), OXT (49.1±5.1 %), STAT3 (21.6±3.8 %), and TH (33.9±8.5 %). In a second experiment the same set of genes was evaluated in GIPR(-/-) and GIPR(+/?) mice to determine the effect of lack of GIP stimulation on gene expression. In GIPR(-/-) mice expressions of the following genes were down-regulated: AVP (27.1±7.5 %), CART (28.3±3.7 %), OXT (25.2±5.8 %), PTGES (23.9±4.5 %), and STAT3 (8.8±2.3 %). These results suggest that AVP, CART, OXT and STAT3 may be involved in energy balance-related hypothalamic circuits affected by GIP.     

Association between Oxytocin Receptor Gene Polymorphisms and Self-Rated ‘Empathic Concern’ in Schizophrenia

The nonapeptide oxytocin (OXT) and its receptor (OXTR) have been implicated in social cognition, empathy, emotion and stress regulation in humans. Previous studies reported associations between OXT and OXTR genetic polymorphisms and risk for disorders characterized by impaired socio-emotional functioning, such as schizophrenia and autism. Here we investigate the influence of two single nucleotide polymorphisms (SNPs) within the OXTR gene on a measure of socio-emotional functioning in schizophrenic patients. OXTR SNPs that were previously investigated in other studies were genotyped in 145 patients diagnosed with schizophrenia according to DSM-IV and 145 healthy controls matched for age and gender. The Interpersonal Reactivity Index (IRI) was used to assess cognitive (‘perspective taking’), affective (‘empathic concern’) and self-related (‘personal distress’) dimensions of empathy. No group differences in genotype frequencies were observed. MANCOVA revealed a significant main (F [1,282] = 10.464; p<0.01) and interaction effect (genotype by diagnosis: F [1,282] = 4.329; p<0.05) of OXTR SNP rs2254298(A>GG) with ‘empathic concern’. Within the schizophrenia group, linear regression analysis determined OXTR rs2254298 genotype, PANSS negative and general symptom score, and age of disease onset as being significantly associated with ‘empathic concern’. OXTR rs2254298 significantly impacted PANSS general psychopathology scores. No associations were found for OXTR rs53576, IRI ‘perspective taking’ or ‘personal distress’ ratings. Our preliminary findings support hypotheses about an involvement of OXTR rs2254298 in emotional empathy in schizophrenic and healthy individuals, warranting independent replication.     

Vasopressin regulation of the proestrous luteinizing hormone surge in wild-type and Clock mutant mice

In the female mouse, ovulation and estrous cyclicity are under both hormonal and circadian control. We have shown that mice with a mutation in the core circadian gene Clock have abnormal estrous cycles and do not have a luteinizing hormone (LH) surge on the afternoon of proestrus due to a defect at the hypothalamic level. In the present study, we tested the hypotheses that vasopressin (AVP) can act as a circadian signal to regulate the proestrous release of LH, and that this signal is deficient in the Clock mutant. We found that Avp expression in the suprachiasmatic nucleus (SCN) and AVP 1a receptor (Avpr1a) expression in the hypothalamus is reduced in Clock mutant mice compared to wild-type mice. Intracerebroventricular (i.c.v.) injection of AVP on the afternoon of proestrus is sufficient to induce LH secretion, which reaches surge levels in 50% of Clock mutant mice. The effect of AVP on the Clock mutant LH surge is mediated by AVPR1A, as co-infusion of AVP and an AVPR1A-specific antagonist prevents AVP induction of LH release, although infusion of an AVPR1A antagonist into wild-type mice failed to prevent a proestrous LH surge. These results suggest that reduced hypothalamic AVP signaling plays a role in the absence of the proestrous LH surge in Clock mutant mice. The results also support the hypothesis that AVP produced by the SCN may be a circadian signal that regulates LH release.     

Deficiency of sterol regulatory element‐binding protein‐1c induces schizophrenia‐like behavior in mice

Schizophrenia is a hereditary disease that approximately 1% of the worldwide population develops. Many studies have investigated possible underlying genes related to schizophrenia. Recently, clinical studies suggested sterol regulatory element‐binding protein (SREBP) as a susceptibility gene in patients with schizophrenia. SREBP controls cellular lipid homeostasis by three isoforms: SREBP‐1a, SREBP‐1c and SREBP‐2. This study used SREBP‐1c knockout (KO) mice to examine whether a deficiency in SREBP‐1c would affect their emotional and psychiatric behaviors. Altered mRNA expression in genes downstream from SREBP‐1c was confirmed in the brains of SREBP‐1c KO mice. Schizophrenia‐like behavior, including hyperactivity during the dark phase, depressive‐like behavior, aggressive behavior and deficits in social interaction and prepulse inhibition, was observed in SREBP‐1c KO mice. Furthermore, increased volume of the lateral ventricle was detected in SREBP‐1c KO mice. The mRNA levels of several γ‐aminobutyric acid (GABA)‐receptor subtypes and/or glutamic acid decarboxylase 65/67 decreased in the hippocampus and medial prefrontal cortex of SREBP‐1c KO mice. Thus, SREBP‐1c deficiency may contribute to enlargement of the lateral ventricle and development of schizophrenia‐like behaviors and be associated with altered GABAergic transmission.     

Clock Gene Modulates Roles of OXTR and AVPR1b Genes in Prosociality

Background

The arginine vasopressin receptor (AVPR) and oxytocin receptor (OXTR) genes have been demonstrated to contribute to prosocial behavior. Recent research has focused on the manner by which these simple receptor genes influence prosociality, particularly with regard to the AVP system, which is modulated by the clock gene. The clock gene is responsible for regulating the human biological clock, affecting sleep, emotion and behavior. The current study examined in detail whether the influences of the OXTR and AVPR1b genes on prosociality are dependent on the clock gene.

Methodology/Principal Findings

This study assessed interactions between the clock gene (rs1801260, rs6832769) and the OXTR (rs1042778, rs237887) and AVPR1b (rs28373064) genes in association with individual differences in prosociality in healthy male Chinese subjects (n = 436). The Prosocial Tendencies Measure (PTM-R) was used to assess prosociality. Participants carrying both the GG/GA variant of AVPR1b rs28373064 and the AA variant of clock rs6832769 showed the highest scores on the Emotional PTM. Carriers of both the T allele of OXTR rs1042778 and the C allele of clock rs1801260 showed the lowest total PTM scores compared with the other groups.

Conclusions

The observed interaction effects provide converging evidence that the clock gene and OXT/AVP systems are intertwined and contribute to human prosociality.     

Centrally administered adrenomedullin 2 activates hypothalamic oxytocin-secreting neurons, causing elevated plasma oxytocin level in rats

We examined the effects of intracerebroventricular (i.c.v.) administration of adrenomedullin 2 (AM2) on plasma oxytocin (OXT) and arginine vasopressin (AVP) levels in conscious rats. Plasma OXT levels were markedly increased 5 min after i.c.v. administration of AM2 (1 nmol/rat) compared with vehicle and remained elevated in samples taken at 10, 15, 30, and 60 min. By contrast, plasma AVP levels were not significantly elevated in samples taken between 5 and 180 min after i.c.v. administration of AM2 except at the 30-min time point. Fos-like immunoreactivity (Fos-LI) was observed in various brain areas, including the paraventricular (PVN) and the supraoptic nuclei (SON) after i.c.v. administration of AM2 (2 nmol/rat) in conscious rats (measured at 90 min post-AM2 infusion). Dual immunostaining for OXT/Fos and AVP/Fos showed that OXT-LI neurons predominantly exhibited nuclear Fos-LI compared with AVP-LI neurons in the PVN and the SON. In situ hybridization histochemistry showed that i.c.v. administration of AM2 (0.2, 1, and 2 nmol/rat) caused marked induction of the expression of the c-fos gene in the PVN and the SON. This induction was significantly reduced by pretreatment with both the calcitonin gene-related peptide (CGRP) antagonist CGRP-(8-37) (3 nmol/rat) and the AM receptor antagonist AM-(22-52) (27 nmol/rat). These results suggest that centrally administered AM2 mainly activates OXT-secreting neurons in the PVN and the SON, at least in part through the CGRP and/or AM receptors with marked elevation of plasma OXT levels in conscious rats.     

Molecular cloning and characterization of human RAI1, a gene associated with schizophrenia

Schizophrenia is a common neuropsychiatric disorder of uncertain etiology that is believed to result from the interaction of environmental factors and multiple genes. To identify new genes predisposing to schizophrenia, numerous groups have focused on CAG-repeat-containing genes. We previously reported a CAG repeat polymorphism that was shown to be associated with both the severity of the phenotype and the response to medication in schizophrenic patients. In this article, we now report the genomic structure of this gene, the retinoic acid inducible-1 gene (RAI1), and present its characterization. This gene, located on chromosome 17p11.2, comprises six exons coding for a 7.6-kb mRNA. The RAI1 gene is highly homologous to its mouse counterpart and it is expressed at high levels mainly in neuronal tissues.     

Oxytocin and vasopressin in the human brain: social neuropeptides for translational medicine

The neuropeptides oxytocin (OXT) and arginine vasopressin (AVP) are evolutionarily highly conserved mediators in the regulation of complex social cognition and behaviour. Recent studies have investigated the effects of OXT and AVP on human social interaction, the genetic mechanisms of inter-individual variation in social neuropeptide signalling and the actions of OXT and AVP in the human brain as revealed by neuroimaging. These data have advanced our understanding of the mechanisms by which these neuropeptides contribute to human social behaviour. OXT and AVP are emerging as targets for novel treatment approaches--particularly in synergistic combination with psychotherapy--for mental disorders characterized by social dysfunction, such as autism, social anxiety disorder, borderline personality disorder and schizophrenia.     

Molecular Variation in AVP and AVPR1a in New World Monkeys (Primates,Platyrrhini): Evolution and Implications for Social Monogamy

The neurohypophysial hormone arginine vasopressin (AVP) plays important roles in fluid regulation and vascular resistance. Differences in AVP receptor expression, particularly mediated through variation in the noncoding promoter region of the primary receptor for AVP (AVPR1a), may play a role in social phenotypes, particularly social monogamy, in rodents and humans. Among primates, social monogamy is rare, but is common among New World monkeys (NWM). AVP is a nonapeptide and generally conserved among eutherian mammals, although a recent paper demonstrated that some NWM species possess a novel form of the related neuropeptide hormone, oxytocin. We therefore characterized variation in the AVP and AVPR1a genes in 22 species representing every genus in the three major platyrrhine families (Cebidae, Atelidae and Pitheciidae). For AVP, a total of 16 synonymous substitutions were detected in 15 NWM species. No non-synonymous substitutions were noted, hence, AVP is conserved in NWM. By contrast, relative to the human AVPR1a, 66 predicted amino acids (AA) substitutions were identified in NWM. The AVPR1a N-terminus (ligand binding domain), third intracellular (G-protein binding domain), and C-terminus were variable among species. Complex evolution of AVPR1a is also apparent in NWM. A molecular phylogenetic tree inferred from AVPR1a coding sequences revealed some consensus taxonomic separation by families, but also a mixed group composed of genera from all three families. The overall dN/dS ratio of AVPR1a was 0.11, but signals of positive selection in distinct AVPR1a regions were observed, including the N-terminus, in which we identified six potential positive selection sites. AA substitutions at positions 241, 319, 399 and 409 occurred uniquely in marmosets and tamarins. Our results enhance the appreciation of genetic diversity in the mammalian AVP/AVPR1a system, and set the stage for molecular modeling of the neurohypophyseal hormones and social behavior in primates.     

Genetic Diversity in Oxytocin Ligands and Receptors in New World Monkeys

Oxytocin (OXT) is an important neurohypophyseal hormone that influences wide spectrum of reproductive and social processes. Eutherian mammals possess a highly conserved sequence of OXT (Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly). However, in this study, we sequenced the coding region for OXT in 22 species covering all New World monkeys (NWM) genera and clades, and characterize five OXT variants, including consensus mammalian Leu⁸-OXT, major variant Pro⁸-OXT, and three previously unreported variants: Ala⁸-OXT, Thr⁸-OXT, and Phe²-OXT. Pro⁸-OXT shows clear structural and physicochemical differences from Leu⁸-OXT. We report multiple predicted amino acid substitutions in the G protein-coupled OXT receptor (OXTR), especially in the critical N-terminus, which is crucial for OXT recognition and binding. Genera with same Pro⁸-OXT tend to cluster together on a phylogenetic tree based on OXTR sequence, and we demonstrate significant coevolution between OXT and OXTR. NWM species are characterized by high incidence of social monogamy, and we document an association between OXTR phylogeny and social monogamy. Our results demonstrate remarkable genetic diversity in the NWM OXT/OXTR system, which can provide a foundation for molecular, pharmacological, and behavioral studies of the role of OXT signaling in regulating complex social phenotypes.     

Association of calnexin with wild type and mutant AVPR2 that causes nephrogenic diabetes insipidus

Over 155 mutations within the V2 vasopressin receptor (AVPR2) gene are responsible for nephrogenic diabetes insipidus (NDI). The expression and subcellular distribution of four of these was investigated in transfected cells. These include a point mutation in the seventh transmembrane domain (S315R), a frameshift mutation in the third intracellular loop (804delG), and two nonsense mutations that code for AVPR2 truncated within the first cytoplasmic loop (W71X) and in the proximal portion of the carboxyl tail (R337X). RT-PCR revealed that mRNA was produced for all mutant receptor constructs. However, no receptor protein, as assessed by Western blot analysis, was detected for 804delG. The S315R was properly processed through the Golgi and targeted to the plasma membrane but lacked any detectable AVP binding or signaling. Thus, this mutation induces a conformational change that is compatible with endoplasmic reticulum (ER) export but dramatically affects hormone recognition. In contrast, the W71X and R337X AVPR2 were retained inside the cell as determined by immunofluorescence. Confocal microscopy revealed that they were both retained in the ER. To determine if calnexin could be involved, its interaction with the AVPR2 was assessed. Sequential coimmunoprecipitation demonstrated that calnexin associated with the precursor forms of both wild-type (WT) and mutant receptors in agreement with its general role in protein folding. Moreover, its association with the ER-retained R337X mutant was found to be longer than with the WT receptor suggesting that this molecular chaperone also plays a role in quality control and ER retention of misfolded G protein-coupled receptors.