Vasopressin and oxytocin: molecular biology and evolution of the peptide hormones and their receptors

Akt-mediated mitochondrial metabolism regulates proplatelet formation and platelet shedding post vasopressin exposure

BACKGROUND

Platelet shedding from mature megakaryocytes (MKs) in thrombopoiesis is the critical step for elevating circulating platelets fast and efficiently, however, the underlying mechanism is still not well-illustrated, and the therapeutic targets and candidates are even less.

OBJECTIVES

In order to investigate the mechanisms for platelet shedding after vasopressin treatment and find new therapeutic targets for thrombocytopenia.

METHODS

Platelet production was evaluated both in vivo and in vitro after arginine vasopressin (AVP) administration. The underlying biological mechanism of AVP-triggered thrombopoiesis were then investigated by a series of molecular and bioinformatics techniques.

RESULTS

it is observed that proplatelet formation and platelet shedding in the final stages of thrombopoiesis promoted by AVP, an endogenous hormone, can quickly increases peripheral platelets. This rapid elevation is thus able to speed up platelet recovery after radiation as expected. The mechanism analysis reveal that proplatelet formation and platelet release from mature MKs facilitated by AVP is mainly mediated by Akt-regulated mitochondrial metabolism. In particular, phosphorylated Akt regulates mitochondrial metabolism through driving the association of hexokinase-2 with mitochondrial voltage dependent anion channel-1 in AVP-mediated thrombopoiesis. Further studies suggest that this interaction is stabilized by IκBα, the expression of which is controlled by insulin-regulated membrane aminopeptidase.

CONCLUSION

these data demonstrate that phosphorylated Akt-mediated mitochondrial metabolism regulates platelet shedding from MKs in response to AVP, which will provide new therapeutic targets and further drug discovery clues for thrombocytopenia treatment.

Insulin-Regulated Aminopeptidase in Women with Breast Cancer: A Role beyond the Regulation of Oxytocin and Vasopressin

Simple Summary

Insulin-regulated aminopeptidase (IRAP) is a well-known enzyme involved mainly in the regulation of the peptide hormones, oxytocin and vasopressin. However, this enzyme activity has hardly been analyzed in breast cancer patients. Additionally, the influence of both the hormonal status (pre or postmenopause) and the administration of neoadjuvant chemotherapy have rarely been studied. We show that there is a weak association between IRAP activity and the circulating levels of peptide hormones with variations depending on the hormonal status and the neoadjuvant treatment, and propose a role beyond oxytocin and vasopressin regulation that is related to the local mammary renin-angiotensin system and glucose transportation to the cells.

Abstract

Insulin-regulated aminopeptidase (IRAP) is the only enzyme known to cleave oxytocin and vasopressin; however, it is also the high-affinity binding site for angiotensin IV (AngIV) receptor type 4 (AT4) ligands and it is related to insulin-dependent glucose transporters through the translocation of the glucose transporter type 4 (GLUT4). Previous studies have demonstrated an association between IRAP activity and the number and size of mammary tumors in an animal model of breast cancer (BC). Also, a highly significant increase in IRAP activity has been found in BC tissue from women patients. Here, we found no changes in circulating IRAP in premenopausal (preMP) women, but it increased significantly in postmenopausal (postMP) women not treated with neoadjuvant chemotherapy (NACH). However, in women treated with NACH, IRAP activity increased in both preMP and postMP women. Two years of follow-up indicated lower levels of IRAP activity in untreated preMP women, but a return to control levels in untreated postMP women, while IRAP activity returned to control levels in women treated with NACH. Circulating oxytocin decreased in both preMP and postMP women during the follow-up period. Differences in Oxytocin appeared between preMP and postMP women treated with NACH, but not in women who were not treated with NACH. On the contrary, circulating vasopressin increased in untreated and treated preMP and postMP women, with most of the differences related to the hormonal status as well as the neoadjuvant treatment during the two year follow-up We propose that IRAP is involved in mechanisms related not only to oxytocin and/or vasopressin regulation, but also to the local mammary RAS through AngIV and its role in glucose transportation through the IRAP/GLUT4 system.

Neuropeptide Regulation of Social Attachment: The Prairie Vole Model

Social attachments are ubiquitous among humans and integral to human health. Although great efforts have been made to elucidate the neural underpinnings regulating social attachments, we still know relatively little about the neuronal and neurochemical regulation of social attachments. As a laboratory animal research model, the socially monogamous prairie vole (Microtus ochrogaster) displays behaviors paralleling human social attachments and thus has provided unique insights into the neural regulation of social behaviors. Research in prairie voles has particularly highlighted the significance of neuropeptidergic regulation of social behaviors, especially of the roles of oxytocin (OT) and vasopressin (AVP). This article aims to review these findings. We begin by discussing the role of the OT and AVP systems in regulating social behaviors relevant to social attachments, and thereafter restrict our discussion to studies in prairie voles. Specifically, we discuss the role of OT and AVP in adult mate attachments, biparental care, social isolation, and social buffering as informed by studies utilizing the prairie vole model. Not only do these studies offer insight into social attachments in humans, but they also point to dysregulated mechanisms in several mental disorders. We conclude by discussing these implications for human health. © 2017 American Physiological Society. Compr Physiol 7:81-104, 2017.

Normolipidic dietary fat modifies circulating Renin-Angiotensin system-regulating aminopeptidase activities in rat with breast cancer

HYPOTHESIS

Renin-angiotensin system (RAS) has been considered not only as a regulator of systemic volume and electrolyte balance but also has been recently involved in various pathological processes such as cancer. In the etiology of breast cancer, dietary factors have been analyzed and especially the influence of dietary fat has been studied, but the underlying mechanisms remain unclear. In this study, we analyzed RAS-regulating enzymes in serum of rats with N-methyl nitrosourea (NMU)-induced breast cancer fed with different diets.

STUDY DESIGN

Four groups of rats were injected intraperitoneally with 3 doses of 50 mg/kg body weight of NMU at different days after birth and were fed with an AIN-93 commercial diet or AIN-93 diets with 4% fat constituted respectively by extra virgin olive oil, refined sunflower oil, and refined sunflower oil enriched to 50% with oleic acid.

METHOD

After sacrifice, blood and tumor samples were collected by spectrophotometric determinations of RAS-regulating enzymes in plasma and histopathology studies.

RESULTS

We show that the type of dietary fat does not influence latency period, incidence of animals with tumors, incidence of mortality, or tumor yield per rat. However, changes were observed in tumor volume and the histopathology. The type of dietary fat also differently modified the enzymes involved in RAS regulation.

CONCLUSIONS

It might suggest that one of the mechanisms by which dietary fat affects breast cancer is the modification of the RAS system, which may be consider as a new target for integrative therapies.

Observations on the evolution of the melanocortin receptor gene family: distinctive features of the melanocortin-2 receptor

The melanocortin receptors (MCRs) are a gene family in the rhodopsin class of G protein-coupled receptors. Based on the analysis of several metazoan genome databases it appears that the MCRs are only found in chordates. The presence of five genes in the family (i.e., mc1r, mc2r, mc3r, mc4r, mc5r) in representatives of the tetrapods indicates that the gene family is the result of two genome duplication events and one local gene duplication event during the evolution of the chordates. The MCRs are activated by melanocortin ligands (i.e., ACTH, α-MSH, β-MSH, γ-MSH, δ-MSH) which are all derived from the polypeptide hormone/neuropeptide precursor, POMC, and as a result the functional evolution of the MCRs is intimately associated with the co-evolution of POMC endocrine and neuronal circuits. This review will consider the origin of the MCRs, and discuss the evolutionary relationship between MC2R, MC5R, and MC4R. In addition, this review will analyze the functional evolution of the mc2r gene in light of the co-evolution of the MRAP (Melanocortin-2 Receptor Accessory Protein) gene family.

Vasopressin-like peptide and its receptor function in an indirect diuretic signaling pathway in the red flour beetle

The insect arginine vasopressin-like (AVPL) peptide is of special interest because of its potential function in the regulation of diuresis. Genome sequences of the red flour beetle Tribolium castaneum yielded the genes encoding AVPL and AVPL receptor, whereas the homologous sequences are absent in the genomes of the fruitfly, malaria mosquito, silkworm, and honeybee, although a recent genome sequence of the jewel wasp revealed an AVPL sequence. The Tribolium receptor for the AVPL, the first such receptor identified in any insect, was expressed in a reporter system, and showed a strong response (EC(50)=1.5 nM) to AVPL F1, the monomeric form having an intramolecular disulfide bond. In addition to identifying the AVPL receptor, we have demonstrated that it has in vivo diuretic activity, but that it has no direct effect on Malpighian tubules. However, when the central nervous system plus corpora cardiaca and corpora allata are incubated along with the peptide and Malpighian tubules, the latter are stimulated by the AVPL peptide, suggesting it acts indirectly. Summing up all the results from this study, we conclude that AVPL functions as a monomer in Tribolium, indirectly stimulating the Malpighian tubules through the central nervous system including the endocrine organs corpora cardiaca and corpora allata. RNA interference in the late larval stages successfully suppressed mRNA levels of avpl and avpl receptor, but with no mortality or abnormal phenotype, implying that the AVPL signaling pathway may have been near-dispensable in the early lineage of holometabolous insects.

Vasopressin is a physiological substrate for the insulin-regulated aminopeptidase IRAP

Insulin-regulated aminopeptidase (IRAP) is a membrane aminopeptidase and is homologous to the placental leucine aminopeptidase, P-LAP. IRAP has a wide distribution but has been best characterized in adipocytes and myocytes. In these cells, IRAP colocalizes with the glucose transporter GLUT4 to intracellular vesicles and, like GLUT4, translocates from these vesicles to the cell surface in response to insulin. Earlier studies demonstrated that purified IRAP cleaves several peptide hormones and that, concomitant with the appearance of IRAP at the surface of insulin-stimulated adipocytes, aminopeptidase activity toward extracellular substrates increases. In the present study, to identify in vivo substrates for IRAP, we tested potential substrates for cleavage by IRAP-deficient (IRAP(-/-)) and control mice. We found that vasopressin and oxytocin were not processed from the NH(2) terminus by isolated IRAP(-/-) adipocytes and skeletal muscles. Vasopressin was not cleaved from the NH(2) terminus after injection into IRAP(-/-) mice and exhibited a threefold increased half-life in the circulation of IRAP(-/-) mice. Consistent with this finding, endogenous plasma vasopressin levels were elevated twofold in IRAP(-/-) mice, and vasopressin levels in IRAP(-/-) brains, where plasma vasopressin originates, showed a compensatory decrease. We further established that insulin increased the clearance of vasopressin from control but not from IRAP(-/-) mice. In conclusion, we have identified vasopressin as the first physiological substrate for IRAP. Changes in plasma and brain vasopressin levels in IRAP(-/-) mice suggest a significant role for IRAP in regulating vasopressin. We have also uncovered a novel IRAP-dependent insulin effect: to acutely modify vasopressin.

An intron-based real-time PCR method for measuring vasopressin gene transcription

The hypothalamus contains distinct neuronal populations that express distinguishing neuropeptides. The supraoptic nucleus contains magnocellular neurons that predominantly express either vasopressin or oxytocin. Transcriptional activators of vasopressin and other neuropeptides have been the subject of much research. Here we present a method of measuring neuropeptide transcription by tailoring one-step quantitative real-time PCR (qRT-PCR) for the analysis of processed and pre-mRNA (heteronuclear RNA). Using moderate and strong hyperosmotic stimuli to induce transcription, we report an increase in vasopressin transcription (pre-mRNA) of 141% and 406% over control levels in response to a 2% injection of 900 mOsm saline or a 1% body weight i.p. injection of 2 M NaCl, respectively. These results agree with a host of studies employing the more labor-intensive method of in situ hybridization histochemistry by which investigators also measured intron-containing heteronuclear RNAs. Furthermore, these results confirm that qRT-PCR with intron-specific primers can be used to rapidly analyze transcription, and suggest an important further benefit of a real-time PCR analysis, such as the ability of measuring transcription of multiple neuropeptides along with other genes from a single sample.

The cloned avian neurohypophysial hormone receptors

Arginine vasotocin (AVT), a neurohypophysial hormone, has many essential functions in birds including the regulation of salt and fluid balance, blood pressure, the stress response and a variety of behaviors. In addition, AVT controls reproductive functions in birds that are served by oxytocin in mammals. In the following review, we examine the functions of AVT in birds with an emphasis on the present state of knowledge concerning the cloned receptors for this important hormone. Receptor and gene structure, signal transduction mechanisms and expression pattern are all discussed. Finally, we explore the phylogenetic relationships between the cloned avian receptors and other vertebrate and invertebrate neurohypophysial hormone receptors.

Vasotocin and vasopressin stimulation of the chloride secretion in the human bronchial epithelial cell line, 16HBE14o-

1. Effects of neuropeptides of the vasopressin family on Cl(-) secretion have not yet been reported in lung. Using the 16HBE14o- bronchial epithelial cell line, we investigated their action on Cl(-) secretion. 2. In symmetrical Cl(-) solutions, basolateral application of arginine vasotocin (AVT), oxytocin or isotocin induced a transient I(sc) stimulation (I(peak)), whereas arginine vasopressin (AVP) did not. The effects of different Cl(-) channel blockers and of a protein kinase C (PKC) inhibitor suggest that CFTR is involved in I(peak). The calcium-activated K(+) channel (SK4) and the Cl(-)/HCO(-)(3) exchanger favor the driving force for AVT-mediated Cl(-) secretion. The antagonists of V1a (SR49059)- and V1b (SSR149415)-receptors blocked I(peak), while SR121463B, a V2 receptor antagonist, did not. These results point to the stimulation of a V1-like receptor mediating I(peak) and presenting an efficacy order, AVT>oxytocin>isotocin>>AVP. 3. When a serosal to mucosal Cl(-) gradient was applied, AVT and AVP both stimulated I(sc) according to a biphasic profile, I(peak) being followed by a plateau phase (I(plateau)). The pharmacology of I(plateau) suggests that CFTR channels are involved and that Na(+)/K(+)/2Cl(-) is the only transporter associated with I(plateau). dDAVP, a V2 receptor agonist-induced I(plateau) with the same potency as AVP, suggesting the involvement of V2 receptors in the AVP-induced I(plateau). V2 receptors are present on both opposite membranes, while V1-like receptors are mainly expressed on the basolateral membranes. RT-PCR experiments show the expression of V1a, V1b, V2 and vasopressin-activated calcium-mobilizing (VACM) receptors mRNAs.

Vasopressin stimulates ventromedial hypothalamic neurons via oxytocin receptors in oxytocin gene knockout male and female mice

A wealth of neuropharmacological data demonstrates that oxytocin (OT) actions in the mammalian forebrain support a wide variety of affiliative behaviors and repress aggressive behaviors. Based on that literature, it was expected that reproductive and affiliative behaviors would be vastly decreased and aggression markedly increased in OT gene knockout (OTKO) mice. The initial publications reporting the behaviors of these mice did not include such phenotypes. Here, we compared single-unit activities recorded from the ventromedial hypothalamus in tissue slices of male and female OTKO mice and their wild-type littermate to test two hypotheses about OT functional genomics. First, we proposed that in OTKO mice, a very similar 9-amino-acid neuropeptide, arginine vasopressin (a likely gene duplication product), can 'cross over' and compensate for the lack of OT. This hypothesis was confirmed in both males and females. Further, we proposed that because of the lifelong absence of OT in OTKO, OT receptors would be more sensitive to OT in the knockout animals. We tested this idea in males and found that it was correct. Thus, an answer to the 'OTKO paradox' is put forth, with implications for OT-sensitive behaviors in a variety of species.

Social regulation of gonadotropin-releasing hormone

Behavioral interactions among social animals can regulate both reproductive behavior and fertility. A prime example of socially regulated reproduction occurs in the cichlid fish Haplochromis burtoni, in which interactions between males dynamically regulate gonadal function throughout life. This plasticity is mediated by the brain, where neurons that contain the key reproductive regulatory peptide gonadotropin-releasing hormone (GnRH)change size reversibly depending on male social status. To understand how behavior controls the brain, we manipulated the social system of these fish,quantified their behavior and then assessed neural and physiological changes in the reproductive and stress axes. GnRH gene expression was assessed using molecular probes specific for the three GnRH forms in the brain of H. burtoni. We found that perception of social opportunity to increase status by a male leads to heightened aggressiveness, to increased expression of only one of the three GnRH forms and to increases in size of GnRH-containing neurons and of the gonads. The biological changes characteristic of social ascent happen faster than changes following social descent. Interestingly, behavioral changes show the reverse pattern:aggressive behaviors emerge more slowly in ascending animals than they disappear in descending animals. Although the gonads and GnRH neurons undergo similar changes in female H. burtoni, regulation occurs viaendogenous rather than exogenous social signals. Our data show that recognition of social signals by males alters stress levels, which may contribute to the alteration in GnRH gene expression in particular neurons essential for the animal to perform in its new social status.

Effect of forskolin and exogenously administered oxytocin mRNA on oxytocin release by dispersed hypothalamic cultures

Differential vasopressin (VP) gene expression and oxytocin (OT) gene expression were observed in hypothalamic cultures derived from 14-day-old rat fetuses, with VP but not OT being induced by treatment with forskolin and 3-isobutyl-1-methylxanthine. These cultures were used to demonstrate that exogenous VP mRNA could be taken up and translated into releasable VP. In the current studies a similar culture preparation was used to test the hypothesis that, due to the similarity in the mRNA and prohormone structures of VP and OT, the VP-expressing neurons in the cultures would be capable of utilizing exogenous OT mRNA for synthesis of releasable OT. Although OT release was increased by the administration of exogenous OT mRNA, endogenous OT gene expression was also observed. To determine what had induced OT gene expression in the current cultures, the undefined components of the culture preparation, e.g., the glial feeder layer and the serum component of the culture medium, were evaluated. Restraining growth of the glial carpet with cytosine-arabinoside did not alter OT gene expression. Use of a defined medium supplemented with B-27 induced optimal OT gene expression. From this, it is possible to conclude that the components included in B-27 are sufficient for OT gene expression.Factors included in earlier lots of sera may have been responsible for suppression of OT gene expression. Cultures maintained in serum-free, B-27-supplemented medium may provide a useful model system for studying OT gene regulation.

Molecular evolution of the opioid/orphanin gene family

Gene duplication is a recurring theme in the evolution of vertebrate polypeptide hormones and neuropeptides. These duplication events can lead to the formation of gene families in which divergence of function is the usual outcome. In the case of the opioid/orphanin family of genes, duplication events have proceeded along two paths: (a) an apparent duplication of function as seen in the analgesic activity of Proenkephalin and Prodynorphin end-products; and (b) divergence of function as seen in the nociceptic activity of Proorphanin end-products or the melanocortin (color change and chronic stress regulation) activity of Proopiomelanocortin end-products. Although genes coding for Proopiomelanocortin, Proenkephalin, Prodynorphin, and Proorphanin have been extensively studied in mammals, the distribution and radiation of these genes in nonmammalian vertebrates is less well understood. This review will present the hypothesis that the radiation of the opioid/orphanin gene family is the result of the duplication and divergence of the Proenkephalin gene during the radiation of the chordates. To evaluate the Proenkephalin gene duplication hypothesis, a 3'RACE procedure was used to screen for the presence of Prodynorphin-related, Proenkephalin-related, and Proorphanin-related cDNAs expressed in the brains of nonmammalian vertebrates.