Genetics of vasopressin receptors

A Review of Oxytocin and Arginine-Vasopressin Receptors and Their Modulation of Autism Spectrum Disorder

Oxytocin (OXT) and arginine-vasopressin (AVP) play a key regulatory part in social and affiliative behaviors; two aspects highly compromised in Autism Spectrum Disorder (ASD). Furthermore, variants in the adjacent oxytocin-vasopressin gene regions have been found to be associated with ASD diagnosis and endophenotypes. This review focuses mainly on common OXTr single nucleotide polymorphisms (SNPs), AVPR1a microsatellites and AVPR1b polymorphisms in relation to the development of autism. Although these genes did not surface in genome-wide association studies, evidence supports the hypothesis that these receptors and their polymorphisms are widely involved in the regulation of social behavior, and in modulating neural and physiological pathways contributing to the etiology of ASD. With a specific focus on variants considered to be among the most prevalent in the development of ASD, these issues will be discussed in-depth and suggestions to approach inconsistencies in the present literature will be provided. Translational implications and future directions are deliberated from a short-term and a forward-looking perspective. While the scientific community has made significant progress in enhancing our understanding of ASD, more research is required for the ontology of this disorder to be fully elucidated. By supplementing information related to genetics, highlighting the differences across male and female sexes, this review provides a wider view of the current state of knowledge of OXTr and AVPr mechanisms of functioning, eventually addressing future research in the identification of further risk factors, to build new strategies for early interventions.

Pharmacological characterization of FE 201874, the first selective high affinity rat V1A vasopressin receptor agonist

BACKGROUND AND PURPOSE

Distinct vasopressin receptors are involved in different physiological and behavioural functions. Presently, no selective agonist is available to specifically elucidate the functional roles of the V1A receptor in the rat, one of the most widely used animal models. FE 201874 is a new derivative of the human selective V1A receptor agonist F180. In this study, we performed a multi-approach pharmacological and functional characterization of FE 201874 to determine whether it is selective for V1A receptors.

EXPERIMENTAL APPROACH

We modified an available human selective V1A receptor agonist (F180) and determined its pharmacological properties in cell lines expressing vasopressin/oxytocin receptors (affinity and coupling to second messenger cascades), in an ex vivo model (aorta ring contraction) and in vivo in rats (proliferation of adrenal cortex glomerulosa cells and lactation).

KEY RESULTS

FE 201874 exhibited nanomolar affinity for the rat V1A receptor; it was highly selective towards the rat V1B and V2 vasopressin receptors and behaved as a full V1A agonist in all the pharmacological tests performed. FE 201874 bound to the oxytocin receptor, but with moderate affinity, and behaved as an oxytocin antagonist in vitro, but not in vivo.

CONCLUSIONS AND IMPLICATIONS

On functional grounds, all the data demonstrate that FE 201874 is the first selective agonist of the rat V1A receptor isoform available. Hence, FE 201874 may have potential as a treatment for the vasodilator-induced hypotension occurring in conditions such as septic shock and could be the most suitable compound for discriminating between the behavioural effects of arginine vasopressin and oxytocin.

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.

The challenge of translation in social neuroscience: a review of oxytocin, vasopressin, and affiliative behavior

Social neuroscience is rapidly exploring the complex territory between perception and action where recognition, value, and meaning are instantiated. This review follows the trail of research on oxytocin and vasopressin as an exemplar of one path for exploring the "dark matter" of social neuroscience. Studies across vertebrate species suggest that these neuropeptides are important for social cognition, with gender- and steroid-dependent effects. Comparative research in voles yields a model based on interspecies and intraspecies variation of the geography of oxytocin receptors and vasopressin V1a receptors in the forebrain. Highly affiliative species have receptors in brain circuits related to reward or reinforcement. The neuroanatomical distribution of these receptors may be guided by variations in the regulatory regions of their respective genes. This review describes the promises and problems of extrapolating these findings to human social cognition, with specific reference to the social deficits of autism.

Effects of the renal medullary pH and ionic environment on vasopressin binding and signaling

The kidney has a cortico-medullary interstitial gradient of decreasing pH and increasing concentrations of sodium chloride and urea, but the influence of these gradients on receptor signaling is largely unknown. Here, we measured G-protein coupled receptor function in LLC-PK1 cells acutely exposed to conditions mimicking different kidney regions. Signaling through the parathyroid hormone receptor, normally expressed in the cortex, was greatly reduced at an acidic pH similar to that of the inner medulla. Parathyroid hormone receptor, tagged with green fluorescent protein, showed no ligand-induced internalization. In contrast, under both acidic and hyperosmotic conditions, vasopressin increased intracellular cAMP, and upon binding to its type 2 receptor (V2R) was internalized and degraded. Dose-displacement binding assays with selective vasopressin/oxytocin receptor ligands under inner medullary conditions indicated a shift in the V2R pharmacological profile. Oxytocin did not bind to the V2R, as it does under normal conditions and the vasopressin type 1 receptor (V1R) had reduced affinity for vasopressin compared to the V2R in low pH and high osmolality. We suggest that the cortico-medullary gradient causes a receptor-specific selectivity in ligand binding that is of functional significance to the kidney. While the gradient is important for urinary concentration, it may also play a substantial role in fine-tuning of the vasopressin response through the V2R.

Pharmacological and physiological characterization of d[Leu4, Lys8]vasopressin, the first V1b-selective agonist for rat vasopressin/oxytocin receptors

Recently, we synthesized and characterized the first selective V(1b) vasopressin (VP)/oxytocin receptor agonist, d[Cha(4)]arginine vasopressin. However, this agonist was only selective for the human receptors. We thus decided to design a selective V(1b) agonist for the rodent species. We started from previous observations showing that modifying [deamino(1),Arg(8)]VP in positions 4 and 8 altered the rat VP/oxytocin receptor selectivity. We synthesized a series of 13 [deamino(1),Arg(8)]VP analogs modified in positions 4 and 8. Among them, one seemed very promising, d[Leu(4), Lys(8)]VP. In this paper, we describe its pharmacological and physiological properties. This analog exhibited a nanomolar affinity for the rat, human, and mouse V(1b) VP receptors and a strong V(1b) selectivity for the rat species. On AtT20 cells stably transfected with the rat V(1b) receptor, d[Leu(4), Lys(8)]VP behaved as a full agonist on both phospholipase C and MAPK assays. Additional experiments revealed its ability to induce the internalization of enhanced green fluorescent protein-tagged human and mouse V(1b) receptors as expected for a full agonist. Additional physiological experiments were performed to further confirm the selectivity of this peptide. Its antidiuretic, vasopressor, and in vitro oxytocic activities were weak compared with those of VP. In contrast, used at low doses, its efficiency to stimulate adrenocorticotropin or insulin release from mouse pituitary or perfused rat pancreas, respectively, was similar to that obtained with VP. In conclusion, d[Leu(4), Lys(8)]VP is the first selective agonist available for the rat V(1b) VP receptor. It will allow a better understanding of V(1b) receptor-mediated effects in rodents.

Management of Hyponatremia and Clinical Use of Vasopressin Antagonists

Hyponatremia, the most common electrolyte disorder in hospitalized patients, has been associated with high rate of mortality among both this population and nonhospitalized patients. This review describes briefly the classification and pathogenesis of hyponatremia, and, in greater detail, the management of hyponatremia with a particular emphasis on the clinical pharmacology of arginine vasopressin (AVP) antagonists. This review includes more in-depth discussion on the pharmacology of conivaptan, an AVP antagonist recently approved by the United States Food and Drug Administration.

Association between the arginine vasopressin 1a receptor (AVPR1a) gene and autism in a family-based study: mediation by socialization skills

We examined three microsatellites in the arginine vasopressin 1a receptor gene (AVPR1a), two in the promoter region (RS1 and RS3) and an intronic microsatellite (AVR), for association with autism as well as scores on the Vineland Adaptive Behavior Scale (VABS), the Autism Diagnostic Interview-Revised (ADI-R) and the Autism Diagnostic Observation Scale-Generic (ADOS-G), measures that are widely used to diagnose autism spectrum disorders. We tested for association between the AVPR1a microsatellites and autism in 116 families (128 probands diagnosed with the ADI-R and ADOS-G using a family-based association test (UNPHASED)). Testing each individual microsatellite showed significant transmission disequilibrium in these families with the AVR intronic microsatellite (UNPHASED: LRS=11.46, global P-value=0.009, df=3). Haplotype analysis of three microsatellites also showed significant association (LRS=144.94, df=103, global P=0.004). Additionally, significant association is observed between these three microsatellite haplotypes and the VABS scores (P=0.009), with the ADI-R (P=0.009) and the ADOS-G (P=0.0000765) diagnoses of autistic disorder versus pervasive developmental disorder-not otherwise specified (PDD-NOS) that were available for 47 of these probands. This is the third consecutive report of an association between the AVPR1a gene and autism spectrum disorders and in the current study a third microsatellite is shown to be associated with autism spectrum disorders as well as haplotypes consisting of all three markers. Importantly, the association appears to be mainly mediated by the role of the AVPR1a gene in shaping socialization skills, similar to its role in lower vertebrates.Molecular Psychiatry (2006) 11, 488-494. doi:10.1038/sj.mp.4001812; published online 7 March 2006.