Cloning and functional characterization of a third pituitary adenylate cyclase-activating polypeptide receptor subtype expressed in insulin-secreting cells

Development of a New Enzyme-Linked Immunosorbent Assay (ELISA) for Measuring the Content of PACAP in Mammalian Tissue and Plasma

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a naturally occurring neuropeptide found in both the central and peripheral nervous systems of vertebrates. Recent studies have revealed the presence of PACAP and its corresponding receptors, namely, the pituitary adenylate cyclase-activating polypeptide type I receptor (PAC1R), vasoactive intestinal peptide receptor 1 (VIPR1), and vasoactive intestinal peptide receptor 2 (VIPR2), in various structures implicated in migraine pathophysiology, including sensory trigeminal neurons. Human studies have demonstrated that when infused, PACAP can cause dilation of cranial vessels and result in delayed migraine-like attacks. In light of this, we present a novel ELISA assay that has been validated for quantifying PACAP in tissue extracts and human plasma. Using two well characterized antibodies specifically targeting PACAP, we successfully developed a sandwich ELISA assay, capable of detecting and accurately quantifying PACAP without any cross-reactivity to closely related peptides. The quantification range was between 5.2 pmol/L and 400 pmol/L. The recovery in plasma ranged from 98.2% to 100%. The increasing evidence pointing to the crucial role of PACAP in migraine pathophysiology necessitates the availability of tools capable of detecting changes in the circulatory levels of PACAP and its potential application as a reliable biomarker.

Targeting VIP and PACAP Receptor Signaling: New Insights into Designing Drugs for the PACAP Subfamily of Receptors

Pituitary Adenylate Cyclase-Activating Peptide (PACAP) and Vasoactive Intestinal Peptide (VIP) are neuropeptides involved in a diverse array of physiological and pathological processes through activating the PACAP subfamily of class B1 G protein-coupled receptors (GPCRs): VIP receptor 1 (VPAC1R), VIP receptor 2 (VPAC2R), and PACAP type I receptor (PAC1R). VIP and PACAP share nearly 70% amino acid sequence identity, while their receptors PAC1R, VPAC1R, and VPAC2R share 60% homology in the transmembrane regions of the receptor. PACAP binds with high affinity to all three receptors, while VIP binds with high affinity to VPAC1R and VPAC2R, and has a thousand-fold lower affinity for PAC1R compared to PACAP. Due to the wide distribution of VIP and PACAP receptors in the body, potential therapeutic applications of drugs targeting these receptors, as well as expected undesired side effects, are numerous. Designing selective therapeutics targeting these receptors remains challenging due to their structural similarities. This review discusses recent discoveries on the molecular mechanisms involved in the selectivity and signaling of the PACAP subfamily of receptors, and future considerations for therapeutic targeting.

Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) in Physiological and Pathological Processes within the Gastrointestinal Tract: A Review

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide widely distributed in the central nervous system (CNS) and many peripheral organs, such as the digestive tract, endocrine, reproductive and respiratory systems, where it plays different regulatory functions and exerts a cytoprotective effect. The multifarious physiological effects of PACAP are mediated through binding to different G protein-coupled receptors, including PAC1 (PAC1-R), VPAC1 (VPAC1-R) and VPAC2 (VPAC2-R) receptors. In the gastrointestinal (GI) tract, PACAP plays an important regulatory function. PACAP stimulates the secretion of digestive juices and hormone release, regulates smooth muscle contraction, local blood flow, cell migration and proliferation. Additionally, there are many reports confirming the involvement of PACAP in pathological processes within the GI tract, including inflammatory states, neuronal injury, diabetes, intoxication and neoplastic processes. The purpose of this review is to summarize the distribution and pleiotropic action of PACAP in the control of GI tract function and its cytoprotective effect in the course of GI tract disorders.

A Clinical Approach for the Use of VIP Axis in Inflammatory and Autoimmune Diseases

The neuroendocrine and immune systems are coordinated to maintain the homeostasis of the organism, generating bidirectional communication through shared mediators and receptors. Vasoactive intestinal peptide (VIP) is the paradigm of an endogenous neuropeptide produced by neurons and endocrine and immune cells, involved in the control of both innate and adaptive immune responses. Exogenous administration of VIP exerts therapeutic effects in models of autoimmune/inflammatory diseases mediated by G-protein-coupled receptors (VPAC1 and VPAC2). Currently, there are no curative therapies for inflammatory and autoimmune diseases, and patients present complex diagnostic, therapeutic, and prognostic problems in daily clinical practice due to their heterogeneous nature. This review focuses on the biology of VIP and VIP receptor signaling, as well as its protective effects as an immunomodulatory factor. Recent progress in improving the stability, selectivity, and effectiveness of VIP/receptors analogues and new routes of administration are highlighted, as well as important advances in their use as biomarkers, contributing to their potential application in precision medicine. On the 50th anniversary of VIP's discovery, this review presents a spectrum of potential clinical benefits applied to inflammatory and autoimmune diseases.

Recent advances in vasoactive intestinal peptide physiology and pathophysiology: focus on the gastrointestinal system

Vasoactive intestinal peptide (VIP), a gut peptide hormone originally reported as a vasodilator in 1970, has multiple physiological and pathological effects on development, growth, and the control of neuronal, epithelial, and endocrine cell functions that in turn regulate ion secretion, nutrient absorption, gut motility, glycemic control, carcinogenesis, immune responses, and circadian rhythms. Genetic ablation of this peptide and its receptors in mice also provides new insights into the contribution of VIP towards physiological signaling and the pathogenesis of related diseases. Here, we discuss the impact of VIP on gastrointestinal function and diseases based on recent findings, also providing insight into its possible therapeutic application to diabetes, autoimmune diseases and cancer.

PACAP/PAC1 Expression and Function in Micturition Pathways

Neural injury, inflammation, or diseases commonly and adversely affect micturition reflex function that is organized by neural circuits in the CNS and PNS. One neuropeptide receptor system, pituitary adenylate cyclase-activating polypeptide (PACAP; Adcyap1), and its cognate receptor, PAC1 (Adcyap1r1), have tissue-specific distributions in the lower urinary tract. PACAP and associated receptors are expressed in the LUT and exhibit changes in expression, distribution, and function in preclinical animal models of bladder pain syndrome (BPS)/interstitial cystitis (IC), a chronic, visceral pain syndrome characterized by pain, and LUT dysfunction. Blockade of the PACAP/PAC1 receptor system reduces voiding frequency and somatic (e.g., hindpaw, pelvic) sensitivity in preclinical animal models and a transgenic mouse model that mirrors some clinical symptoms of BPS/IC. The PACAP/receptor system in micturition pathways may represent a potential target for therapeutic intervention to reduce LUT dysfunction following urinary bladder inflammation.

Discovery of PACAP and its receptors in the brain

Pituitary adenylate-cyclase-activating polypeptide (PACAP) is a 27- or 38-amino acid neuropeptide, which belongs to the vasoactive intestinal polypeptide (VIP)/glucagon/secretin family. PACAP shows particularly high homology (~ 68%) to VIP. Because of the high homology of the amino acid sequences of PACAP and VIP, these peptides share three class B-G-protein coupled receptors: the PAC1-Receptor (PAC1-R), the VPAC1-Receptor (VPAC1-R) and VPAC2-Receptor (VPAC2-R). These receptors have high homology to each other, and their high homology is utilized for these discoveries. This review provides mainly an overview of the history of the discovery of PACAP and its three receptors.

PACAP/Receptor System in Urinary Bladder Dysfunction and Pelvic Pain Following Urinary Bladder Inflammation or Stress

Complex organization of CNS and PNS pathways is necessary for the coordinated and reciprocal functions of the urinary bladder, urethra and urethral sphincters. Injury, inflammation, psychogenic stress or diseases that affect these nerve pathways and target organs can produce lower urinary tract (LUT) dysfunction. Numerous neuropeptide/receptor systems are expressed in the neural pathways of the LUT and non-neural components of the LUT (e.g., urothelium) also express peptides. One such neuropeptide receptor system, pituitary adenylate cyclase-activating polypeptide (PACAP; Adcyap1) and its cognate receptor, PAC1 (Adcyap1r1), have tissue-specific distributions in the LUT. Mice with a genetic deletion of PACAP exhibit bladder dysfunction and altered somatic sensation. PACAP and associated receptors are expressed in the LUT and exhibit neuroplastic changes with neural injury, inflammation, and diseases of the LUT as well as psychogenic stress. Blockade of the PACAP/PAC1 receptor system reduces voiding frequency in preclinical animal models and transgenic mouse models that mirror some clinical symptoms of bladder dysfunction. A change in the balance of the expression and resulting function of the PACAP/receptor system in CNS and PNS bladder reflex pathways may underlie LUT dysfunction including symptoms of urinary urgency, increased voiding frequency, and visceral pain. The PACAP/receptor system in micturition pathways may represent a potential target for therapeutic intervention to reduce LUT dysfunction.

Immunization against full-length protein and peptides from the Lutzomyia longipalpis sand fly salivary component maxadilan protects against Leishmania major infection in a murine model

Leishmaniasis is an arthropod vectored disease causing considerable human morbidity and mortality. Vaccination remains the most realistic and practical means to interrupt the growing number and diversity of sand fly vectors and reservoirs of Leishmania. Since transmission of Leishmania is achieved exclusively by sand fly vectors via immune-modulating salivary substances, conventional vaccination requiring an unmodified host immune response for success are potentially destined to fail unless immunomodulatory factors are somehow neutralized. Using cationic liposome DNA complexes (CLDC) as an adjuvant system along with Lu. longipalpis sand fly salivary component maxadilan (MAX) as antigen (Ag), we show that mice are protected from the MAX-induced exacerbation of infection with Leishmania major (Lm). The CLDC adjuvant and alum were comparable in terms of lesion induration and decreased parasite burden, however the alum adjuvant imposed more inflammation at the injection site. BALB/c, C3H and C57BL/6 mice vaccinated with MAX-CLDC containing either the full-length MAX or peptides spanning the N- and C-terminal regions of MAX are protected against footpad challenges with Lm co-injected with MAX. When compared to unvaccinated controls, all strains of mice immunized with CLDC containing either peptides encompassing the first 20 N-terminal AA or those spanning the last 15 AA of the C-terminal domain of MAX demonstrated decreased parasite burden after 9 or 18 weeks post challenge with Lm + MAX. MAX-CLDC immunized mice showed increased IFNγ-secreting and decreased IL-4-secreting CD4⁺ cells in footpad-draining lymph nodes. Antisera from C-terminal peptide (P11) MAX-CLDC-vaccinated animals was capable of recognizing FL-MAX and its C-terminal domain and also blocked MAX-mediated reprogramming of bone marrow-derived dendritic cells (BM-DC) in vitro. This peptide vaccine targeting sand fly MAX, improves host immunity against MAX-mediated immunomodulation.

[Liposome modified with VIP-lipopeptide as a new drug delivery system]

We have designed a novel lipid analog (lipopeptide) that mimics the structural features of modified phospholipids. This lipopeptide is easily synthesized using a peptide synthesizer and has been shown to be useful for the modification of liposomes, which are used as an active targeted drug delivery system (DDS). Vasoactive intestinal peptide (VIP) has high homology with pituitary adenylate cyclase activating peptide (PACAP). There are three major PACAP receptors: PAC1R, VPAC1R, and VPAC2R. PAC1R has affinity only for PACAP, whereas VPAC1R and VPAC2R have the same affinity for both VIP and PACAP. In the present study, we synthesized several lipopeptides conjugated with VIP through different linkers and found that liposomes modified with these lipopeptides (VIP-Lips) selectively recognized the PACAP/VIP receptors. The anti-cancer activity of these VIP-Lips was evaluated by encapsulation of an antitumor drug, doxorubicin (DOX), into the modified liposomes (VIP-Lips-DOX) against the human osteosarcoma cell line, Saos-2, which highly expresses the VIP receptor. cAMP production was then measured to determine how well the VIP-Lips were able to recognize VPAC2R. The results clearly indicate that the proposed lipopeptide methodology holds promise as a DDS for cancer therapy.

Emerging Role of PACAP as a New Potential Therapeutic Target in Major Diabetes Complications

Enduring diabetes increases the probability of developing secondary damage to numerous systems, and these complications represent a cause of morbidity and mortality. Establishing the causes of diabetes remains the key step to eradicate the disease, but prevention as well as finding therapies to ameliorate some of the major diabetic complications is an equally important step to increase life expectancy and quality for the millions of individuals already affected by the disease or who are likely to develop it before cures become routinely available. In this review, we will firstly summarize some of the major complications of diabetes, including endothelial and pancreatic islets dysfunction, retinopathy, and nephropathy, and then discuss the emerging roles exerted by the neuropeptide pituitary adenylate cyclase activating polypeptide (PACAP) to counteract these ranges of pathologies that are precipitated by the prolonged hyperglycemic state. Finally, we will describe the main signalling routes activated by the peptide and propose possible future directions to focus on developing more effective peptide-based therapies to treat the major complications associated with longstanding diabetes.

Stapled Vasoactive Intestinal Peptide (VIP) Derivatives Improve VPAC2 Agonism and Glucose-Dependent Insulin Secretion

Agonists of vasoactive intestinal peptide receptor 2 (VPAC2) stimulate glucose-dependent insulin secretion, making them attractive candidates for the treatment of hyperglycaemia and type-II diabetes. Vasoactive intestinal peptide (VIP) is an endogenous peptide hormone that potently agonizes VPAC2. However, VIP has a short serum half-life and poor pharmacokinetics in vivo and is susceptible to proteolytic degradation, making its development as a therapeutic agent challenging. Here, we investigated two peptide cyclization strategies, lactamisation and olefin-metathesis stapling, and their effects on VPAC2 agonism, peptide secondary structure, protease stability, and cell membrane permeability. VIP analogues showing significantly enhanced VPAC2 agonist potency, glucose-dependent insulin secretion activity, and increased helical content were discovered; however, neither cyclization strategy appeared to effect proteolytic stability or cell permeability of the resulting peptides.

The PACAP-regulated gene selenoprotein T is abundantly expressed in mouse and human β-cells and its targeted inactivation impairs glucose tolerance

Selenoproteins are involved in the regulation of redox status, which affects several cellular processes, including cell survival and homeostasis. Considerable interest has arisen recently concerning the role of selenoproteins in the regulation of glucose metabolism. Here, we found that selenoprotein T (SelT), a new thioredoxin-like protein of the endoplasmic reticulum, is present at high levels in human and mouse pancreas as revealed by immunofluorescence and quantitative PCR. Confocal immunohistochemistry studies revealed that SelT is mostly confined to insulin- and somatostatin-producing cells in mouse and human islets. To elucidate the role of SelT in β-cells, we generated, using a Cre-Lox strategy, a conditional pancreatic β-cell SelT-knockout C57BL/6J mice (SelT-insKO) in which SelT gene disruption is under the control of the rat insulin promoter Cre gene. Glucose administration revealed that male SelT-insKO mice display impaired glucose tolerance. Although insulin sensitivity was not modified in the mutant mice, the ratio of glucose to insulin was significantly higher in the SelT-insKO mice compared with wild-type littermates, pointing to a deficit in insulin production/secretion in mutant mice. In addition, morphometric analysis showed that islets from SelT-insKO mice were smaller and that their number was significantly increased compared with islets from their wild-type littermates. Finally, we found that SelT is up-regulated by pituitary adenylate cyclase-activating polypeptide (PACAP) in β-pancreatic cells and that SelT could act by facilitating a feed-forward mechanism to potentiate insulin secretion induced by the neuropeptide. Our findings are the first to show that the PACAP-regulated SelT is localized in pancreatic β- and δ-cells and is involved in the control of glucose homeostasis.

Therapeutic potential of VIP vs PACAP in diabetes

Type 2 diabetes (T2D) is characterized by chronic insulin resistance and a progressive decline in beta-cell function. Although rigorous glucose control can reduce morbidity and mortality associated with diabetes, achieving optimal long-term glycemic control remains to be accomplished in many diabetic patients. As beta-cell mass and function inevitably decline in T2D, exogenous insulin administration is almost unavoidable as a final outcome despite the use of oral antihyperglycemic agents in many diabetic patients. Pancreatic islet cell death, but not the defect in new islet formation or beta-cell replication, has been blamed for the decrease in beta-cell mass observed in T2D patients. Thus, therapeutic approaches designed to protect islet cells from apoptosis could significantly improve the management of T2D, because of its potential to reverse diabetes not just ameliorate glycemia. Therefore, an ideal beta-cell-preserving agent is expected to protect beta cells from apoptosis and stimulate postprandial insulin secretion along with increasing beta-cell replication and/or islet neogenesis. One such potential agent, the islet endocrine neuropeptide vasoactive intestinal peptide (VIP) strongly stimulates postprandial insulin secretion. Because of its broad spectrum of biological functions such as acting as a potent anti-inflammatory factor through suppression of Th1 immune response, and induction of immune tolerance via regulatory T cells, VIP has emerged as a promising therapeutic agent for the treatment of many autoimmune diseases including diabetes.

Agnathan VIP, PACAP and their receptors: ancestral origins of today's highly diversified forms

VIP and PACAP are pleiotropic peptides belonging to the secretin superfamily of brain-gut peptides and interact specifically with three receptors (VPAC₁, PAC₁ and VPAC₂) from the class II B G protein-coupled receptor family. There is immense interest regarding their molecular evolution which is often described closely alongside gene and/or genome duplications. Despite the wide array of information available in various vertebrates and one invertebrate the tunicate, their evolutionary origins remain unresolved. Through searches of genome databases and molecular cloning techniques, the first lamprey VIP/PACAP ligands and VPAC receptors are identified from the Japanese lamprey. In addition, two VPAC receptors (VPACa/b) are identified from inshore hagfish and ligands predicted for sea lamprey. Phylogenetic analyses group these molecules into their respective PHI/VIP, PRP/PACAP and VPAC receptor families and show they resemble ancestral forms. Japanese lamprey VIP/PACAP peptides synthesized were tested with the hagfish VPAC receptors. hfVPACa transduces signal via both adenylyl cylase and phospholipase C pathways, whilst hfVPACb was only able to transduce through the calcium pathway. In contrast to the widespread distribution of VIP/PACAP ligands and receptors in many species, the agnathan PACAP and VPAC receptors were found almost exclusively in the brain. In situ hybridisation further showed their abundance throughout the brain. The range of VIP/PACAP ligands and receptors found are highly useful, providing a glimpse into the evolutionary events both at the structural and functional levels. Though representative of ancestral forms, the VIP/PACAP ligands in particular have retained high sequence conservation indicating the importance of their functions even early in vertebrate evolution. During these nascent stages, only two VPAC receptors are likely responsible for eliciting functions before evolving later into specific subtypes post-Agnatha. We also propose VIP and PACAP's first functions to predominate in the brain, evolving alongside the central nervous system, subsequently establishing peripheral functions.

Pharmacology and functions of receptors for vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide: IUPHAR review 1

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are members of a superfamily of structurally related peptide hormones that includes glucagon, glucagon-like peptides, secretin, gastric inhibitory peptide (GIP) and growth hormone-releasing hormone (GHRH). VIP and PACAP exert their actions through three GPCRs - PAC(1) , VPAC(1) and VPAC(2) - belonging to class B (also referred to as class II, or secretin receptor-like GPCRs). This family comprises receptors for all peptides structurally related to VIP and PACAP, and also receptors for parathyroid hormone, corticotropin-releasing factor, calcitonin and related peptides. PAC(1) receptors are selective for PACAP, whereas VPAC(1) and VPAC(2) respond to both VIP and PACAP with high affinity. VIP and PACAP play diverse and important roles in the CNS, with functions in the control of circadian rhythms, learning and memory, anxiety and responses to stress and brain injury. Recent genetic studies also implicate the VPAC(2) receptor in susceptibility to schizophrenia and the PAC(1) receptor in post-traumatic stress disorder. In the periphery, VIP and PACAP play important roles in the control of immunity and inflammation, the control of pancreatic insulin secretion, the release of catecholamines from the adrenal medulla and as co-transmitters in autonomic and sensory neurons. This article, written by members of the International Union of Basic and Clinical Pharmacology Committee on Receptor Nomenclature and Drug Classification (NC-IUPHAR) subcommittee on receptors for VIP and PACAP, confirms the existing nomenclature for these receptors and reviews our current understanding of their structure, pharmacology and functions and their likely physiological roles in health and disease. More detailed information has been incorporated into newly revised pages in the IUPHAR database (http://www.iuphar-db.org/DATABASE/FamilyMenuForward?familyId=67).

Trophic effects of PACAP on pancreatic islets: a mini-review

Progressive beta-cell insufficiency in the pancreas is a hallmark of both types I and II diabetes, and agents that protect against beta-cell dysfunction are potential drug targets for diabetes mellitus. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a strong secretagogue of insulin from pancreatic islets and is suggested to be involved in physiological blood glucose homeostasis and the pathology of diabetes. Recent studies in genetically engineered animal models have shown that PACAP stimulates pancreatic functions, especially in cooperation with other regulatory factors including glucose. Furthermore, chronic activation of PACAP signaling regulates pancreatic islet mass in a context-dependent manner. Accumulating in vivo and in vitro evidence suggest that PACAP has trophic effects and regulates both proliferation and cell viability of beta-cells and thereby contributes to protection against diabetes. This review focuses on such trophic actions of PACAP on pancreatic beta-cells and discusses the pathophysiological significance of pancreatic PACAP, with the aim to provide information for future development of treatment for diabetes.

Expression analysis of PAC1-R and PACAP genes in zebrafish embryos

This study describes the expression of the pituitary adenylate cyclase-activating polypeptide (PACAP1 and PACAP2) and PAC1 receptor genes (PAC1a-R and PAC1b-R) in the brain of zebrafish (Danio rerio) during development. In situ hybridization of the 24- and 48-hpf embryos revealed that PACAP genes were expressed in the telencephalon, the diencephalon, the rhombencephalon, and the neurons in the dorsal part of the spinal cord. PACAP2 mRNA appears to be the most abundant form during brain development. The two PAC1-R subtypes showed a similar expression pattern: mRNAs were detected in the forebrain, the thalamus, and the rhombencephalon. However, in the tectum, only PAC1b-R gene was detected. These results suggest that, in fish, PACAP may play a role in brain development.

Roles for pituitary adenylate cyclase-activating peptide (PACAP) expression and signaling in the bed nucleus of the stria terminalis (BNST) in mediating the behavioral consequences of chronic stress

Anxiety disorders are frequently long-lasting and debilitating for more than 40 million American adults. Although stressor exposure plays an important role in the etiology of some anxiety disorders, the mechanisms by which exposure to stressful stimuli alters central circuits that mediate anxiety-like emotional behavior are still unknown. Substantial evidence has implicated regions of the central extended amygdala, including the bed nucleus of the stria terminalis (BNST) and the central nucleus of the amygdala as critical structures mediating fear- and anxiety-like behavior in both humans and animals. These areas organize coordinated fear- and anxiety-like behavioral responses as well as peripheral stress responding to threats via direct and indirect projections to the paraventricular nucleus of the hypothalamus and brainstem regions (Walker et al. Eur J Pharmacol 463:199-216, 2003, Prog Neuropsychopharmacol Biol Psychiatry 33(8):1291-1308, 2009; Ulrich-Lai and Herman Nat Rev Neurosci 10:397-409, 2009). In particular, the BNST has been argued to mediate these central and peripheral responses when the perceived threat is of long duration (Waddell et al. Behav Neurosci 120:324-336, 2006) and/or when the anxiety-like response is sustained (Walker and Davis Brain Struct Funct 213:29-42, 2008); hence, the BNST may mediate pathological anxiety-like states that result from exposure to chronic stress. Indeed, chronic stress paradigms result in enhanced BNST neuroplasticity that has been associated with pathological anxiety-like states (Vyas et al. Brain Res 965:290-294, 2003; Pego et al. Eur J Neurosci 27:1503-1516, 2008). Here we review evidence that suggests that pituitary adenylate cyclase-activating polypeptide (PACAP) and corticotropin-releasing hormone (CRH) work together to modulate BNST function and increase anxiety-like behavior. Moreover, we have shown that BNST PACAP as well as its cognate PAC1 receptor is substantially upregulated following chronic stress, particularly in the BNST oval nucleus where PACAP-containing neurons closely interact with CRH-containing neurons (Kozicz et al. Brain Res 767:109-119, 1997; Hammack et al. Psychoneuroendocrinology 34:833-843, 2009). We describe how interactions between PACAP and CRH in the BNST may mediate stress-associated behaviors, including anorexia and anxiety-like behavior. These studies have the potential to define specific mechanisms underlying anxiety disorders, and may provide important therapeutic strategies for stress and anxiety management.

Association between pituitary adenylate cyclase-activating polypeptide and reproduction in the blue gourami

In order to gain a better understanding of the roles of pituitary adenylate cyclase-activating polypeptide (PACAP) in reproduction and growth, the expression of the PACAP gene during the reproduction cycle and its potential role in regulating gonadotropin and growth hormone (GH) gene transcription in blue gourami were investigated. The cDNA sequences of the full-length blue gourami brain PACAP and that of its related peptide (PRP) were acquired. PACAP cDNA had two variants, obtainable by alternative splicing: a long form encoding for both PRP and PACAP and a short form encoding only for PACAP. In females, mRNA levels of PACAP were very high only in individuals with oocytes in the maturation stage, as compared to levels in unpaired vitellogenic and non-vitellogenic fish. The PACAP mRNA levels in males were high only in nest builders, as opposed to in non-nest building males and juveniles. In pituitary culture cells from high vitellogenic females, PACAP38 (the 38 amino acid form) only brought about an increase in betaFSH levels, without altering GH and betaLH mRNA levels. On the other hand, in adult non-reproductive male pituitary cells, PACAP38 decreased the GH mRNA level. Based on these results, we propose that in the blue gourami, PACAP is involved in the final oocyte maturation stage in females, whereas in males, it is associated with sexual behavior. In addition, the effect of PACAP38 on pituitary hormone gene expression is different in females and males, indicating that PACAP38 is potentially a hypophysiotropic regulator of reproduction, which mediates pituitary hormone expression.

Pituitary adenylate cyclase-activating polypeptide (PACAP)/PAC1HOP1 receptor activation coordinates multiple neurotrophic signaling pathways: Akt activation through phosphatidylinositol 3-kinase gamma and vesicle endocytosis for neuronal survival

MAPK and Akt pathways are predominant mediators of trophic signaling for many neuronal systems. Among the vasoactive intestinal peptide/secretin/glucagon family of related peptides, pituitary adenylate cyclase-activating polypeptide (PACAP) binding to specific PAC(1) receptor isoforms can engage multiple signaling pathways and promote neuroprotection through mechanisms that are not well understood. Using a primary sympathetic neuronal system, the current studies demonstrate that PACAP activation of PAC(1)HOP1 receptors engages both MAPK and Akt neurotrophic pathways in an integrated program to facilitate neuronal survival after growth factor withdrawal. PACAP not only stimulated prosurvival ERK1/2 and ERK5 activation but also abrogated SAPK/JNK and p38 MAPK signaling in parallel. In contrast to the potent and rapid effects of PACAP in ERK1/2 phosphorylation, PACAP stimulated Akt phosphorylation in a late phase of PAC(1)HOP1 receptor signaling. From inhibitor and immunoprecipitation analyses, the PACAP/PAC(1)HOP1 receptor-mediated Akt responses did not represent transactivation mechanisms but appeared to depend on G alpha(q)/phosphatidylinositol 3-kinase gamma activity and vesicular internalization pathways. Phosphatidylinositol 3-kinase gamma-selective inhibitors blocked PACAP-stimulated Akt phosphorylation in primary neuronal cultures and in PAC(1)HOP1-overexpressing cell lines; RNA interference-mediated knockdown of the receptor effectors attenuated PACAP-mediated Akt activation. Similarly, perturbation of endocytic pathways also blocked Akt phosphorylation. Between ERK and Akt pathways, PACAP-stimulated Akt signaling was the primary cascade that attenuated cultured neuron apoptosis after growth factor withdrawal. The partitioning of PACAP-mediated Akt signaling in endosomes may be a key mechanism contributing to the high spatial and temporal specificity in signal transduction necessary for survival pathways.

Role of pituitary adenylate cyclase-activating polypeptide in the pancreatic endocrine system

In the pancreatic islets, pituitary adenylate cyclase-activating polypeptide (PACAP) is expressed in beta cells and autonomic nerve terminals; the majority of these nerve terminals are parasympathetic. PACAP binds to three types of G protein-coupled receptors (GPCRs): VPAC1 receptors, VPAC2 receptors, and PAC1 receptors. All these receptor types are expressed in pancreatic islets. PACAP stimulates insulin and glucagon secretion. These actions are achieved in part through increased formation of cAMP after activation of adenylate cyclase and in part through increase in cytosolic calcium, achieved through increase in calcium uptake and release from intracellular calcium stores. Deletion of PAC1 receptors or VPAC2 receptors results in impaired insulin secretion and glucose intolerance. Studies in PAC1 receptor gene deleted mice have suggested that PACAP may be of physiological importance in mediating prandial insulin secretion and in contributing to the glucagon response to hypoglycemia. Animal studies have also suggested that activation of the receptors, in particular VPAC2 receptors, may be used as a therapeutic approach for the treatment of type 2 diabetes. Hence, PACAP is an islet neuropeptide with a potential role in islet physiology and as a basis for development of islet-promoting therapy in type 2 diabetes.

VPAC and PAC receptors: From ligands to function

Vasoactive intestinal peptide (VIP) and the pituitary adenylate cyclase activating polypeptides (PACAPs) share 68% identity at the amino acid level and belong to the secretin peptide family. Following the initial discovery of VIP almost four decades ago a substantial amount of knowledge has been presented describing the mechanisms of action, distribution and pleiotropic functions of these related peptides. It is now known that the physiological actions of these widely distributed peptides are produced through activation of three common G-protein coupled receptors (VPAC(1), VPAC(2) and PAC(1)R) which preferentially stimulate adenylate cyclase and increase intracellular cAMP, although stimulation of other intracellular messengers, including calcium and phospholipase D, has been reported. Using a range of in vitro and in vivo approaches, including cell-based functional assays, transgenic animals and rodent models of disease, VPAC/PAC receptor activation has been associated with numerous physiological processes (e.g. control of circadian rhythms) and clinical conditions (e.g. pulmonary hypertension), which underlies on-going research efforts and makes these peptides and their cognate receptors attractive targets for the pharmaceutical industry. However, despite the considerable interest in VPAC/PAC receptors and the processes which they mediate, there is still a paucity of selective and available, non-peptide ligands, which has hindered further advances in this field both at the basic research and clinical level. This review summarises the current knowledge of VIP/PACAP and the VPAC/PAC receptors with regard to their distribution, pharmacology, signalling pathways, splice variants and finally, the utility of animal models in exploring their physiological roles.

PACAP, VIP and their receptors in the metazoa: insights about the origin and evolution of the ligand-receptor pair

The evolution, function and interaction of ligand-receptor pairs are of major pharmaceutical interest. Comparative sequence analysis approaches using data from phylogenetically distant organisms can provide insights into their origin and possible physiological roles. The present review focuses on the pituitary adenylate cyclase-activating polypeptide (PACAP), vasoactive intestinal polypeptide (VIP) and their receptors in the metazoa. A PACAP-like peptide is present in tunicates and chordates while VIP- and PACAP/VIP-specific receptors have only been isolated in the latter phyla. The apparently disparate evolution of the ligands and their specific receptors raises questions about their evolution during the metazoan radiation and also about how the ligands may have acquired new functions.

Role of VIP and PACAP in islet function

Vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are two closely related neuropeptides that are expressed in islets and in islet parasympathetic nerves. Both peptides bind to their common G-protein-coupled receptors, VPAC1 and VPAC2, and PACAP, in addition to the specific receptor PAC1, all three of which are expressed in islets. VIP and PACAP stimulate insulin secretion in a glucose-dependent manner and they both also stimulate glucagon secretion. This action is achieved through increased formation of cAMP after activation of adenylate cyclase and stimulation of extracellular calcium uptake. Deletion of PAC1 receptors or VPAC2 receptors results in glucose intolerance. These peptides may be of importance in mediating prandial insulin secretion and the glucagon response to hypoglycemia. Animal studies have also suggested that activation of the receptors, in particular VPAC2 receptors, may be used as a therapeutic approach for the treatment of type 2 diabetes. This review summarizes the current knowledge of the potential role of VIP and PACAP in islet function.

Molecular, cellular, and functional characterizations of pituitary adenylate cyclase-activating polypeptide and its receptors in the cerebellum of New and Old World monkeys

The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) exerts trophic activities during cerebellar development, and a neuroprotective effect of PACAP has been demonstrated in pathological conditions such as stroke. However, all these data have been obtained in rodents, and neuroprotective effects of PACAP in primates remain unknown. Because of their evolutionary relationships with humans, monkeys represent powerful models for validating the therapeutic interest in PACAP. The objective of the present study was to characterize PACAP and its receptors in the cerebellum of two nonhuman primates. RT-PCR and in situ hybridization experiments revealed that PACAP is expressed in the cerebellum by Purkinje cells. Via immunohistochemistry, PACAP was detected in Purkinje cells and radial glial fibers. With regard to PACAP receptors, PAC1-R and VPAC1-R were detected by RT-PCR. In situ hybridization revealed a strong expression of PAC1-R and VPAC1-R in the granule cell layer (GCL), and VPAC1-R was also expressed in the Purkinje cell layer. A high density of PACAP binding sites was visualized in the GCL and the Purkinje cell layer. Competition studies indicated that, in the GCL, PACAP induced complete displacement of [(125)I]PACAP27 binding, whereas vasoactive intestinal polypeptide (VIP) was a weak competitor. In contrast, in the Purkinje cell layer, both PACAP and VIP displaced [(125)I]PACAP27 binding. Measurement of cAMP levels showed that PACAP is a powerful activator of adenylyl cyclase, whereas VIP is about 100-fold less potent. Altogether, these observations constitute the first demonstration of a functional PACAPergic system in monkey cerebellum. They strongly suggest that neuroprotective effects of PACAP can be transposed to primates, including human.

A novel recombinant, VPAC2-selective agonist enhancing insulin release and glucose disposal

AIM

To obtain the recombinant, VPAC2-selective ( VPAC2: type 3 receptor of pituitary adenylate cyclase activating polypeptide which shared by vasoactive intestinal peptide) agonist with effects on glucose disposal by intein-mediated, single column purification.

METHODS

A gene encoding 32-amino acid peptide named rMBAY was designed and synthesized and cloned into Escherichia coli expression vector, pKYB (NEB, USA). The recombinant vector was transferred into E coli ER2566 strain and the target protein was overexpressed as a fusion to the N-terminus of a self-cleavable affinity tag. After the fusion protein was purified by chitin-affinity chromatography, the self-cleavage activity of the intein was induced by beta-mercaptoethanol and the target peptide, rMBAY, was released from the chitin-bound intein tag.

RESULTS

Approximately 53 mg rMBAY with the purity over 95% was obtained by single column purification from 1 L induced culture fermented in 5 L fermenter. The results of the competitive binding assay and cAMP accumulation assay indicated that the recombinant rMBAY had special binding selectivity and potency for VPAC2. The recombinant peptide, rMBAY, enhanced insulin release and decreased the plasma glucose level after intraperitoneal injection (50 ng/kg) with a high concentration of glucose (1.8 mmol/kg) in the NIH mice.

CONCLUSION

An efficient production procedure of a recombinant VPAC2-selective agonist with corresponding effects on glucose disposal was established.

Characterisation of the mouse vasoactive intestinal peptide receptor type 2 gene, Vipr2, and identification of a polymorphic LINE-1-like sequence that confers altered promoter activity

The VPAC(2) receptor is a seven transmembrane spanning G protein-coupled receptor for two neuropeptides, vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP). It has a distinct tissue-specific, developmental and inducible expression that underlies an important neuroendocrine role. Here, we report the characterisation of the gene that encodes the mouse VPAC(2) receptor (Vipr2), localisation of the transcriptional start site and functional analysis of the promoter region. The Vipr2 gene contains 12 introns within its protein-coding region and spans 68.6 kb. Comparison of the 5' untranslated region sequences for cloned 5'-RACE products amplified from different tissues showed they all were contained within the same exon, with the longest extending 111 bp upstream of the ATG start site. Functional analysis of the 3.2-kb 5'-flanking region using sequentially deleted sequences cloned into a luciferase gene reporter vector revealed that this region is active as a promoter in mouse AtT20 D16:16 and rat GH4C1 cell lines. The core promoter is located within a 180-bp GC-rich region proximal to the ATG start codon and contains potential binding sites for Sp1 and AP2, but no TATA-box. Further upstream, in two out of three mice strains examined, we have discovered a 496-bp polymorphic DNA sequence that bears a significant identity to mouse LINE-1 DNA. Comparison of the promoter activity between luciferase reporter gene constructs derived from the BALB/c (which contains this sequence) and C57BL/6J (which lacks this sequence) Vipr2 promoter regions has shown three-fold difference in luciferase gene activity when expressed in mouse AtT20 D16:16 and alphaT3-1 cells, but not when expressed in the rat GH4C1 cells or in COS 7 cells. Our results suggest that the mouse Vipr2 gene may be differentially active in different mouse strains, depending on the presence of this LINE-1-like sequence in the promoter region.

Intein-mediated rapid purification and characterization of a novel recombinant agonist for VPAC2

In order to obtain the recombinant VPAC2 agonist efficiently by intein-mediated single column purification, a gene encoding 32-amino acids peptide was designed, synthesized and cloned into Escherichia coli expression vector pKYB. The recombinant vector pKY-ROM was transferred into E. coli ER2566 cells and the target protein was over-expressed as a fusion to the N-terminus of a self-cleavable affinity tag. After the rMROM-intein-CBD fusion protein was purified by chitin-affinity chromatography, the self-cleavage activity of the intein was induced by beta-mercaptoethanol and the rMROM with the homogeneity over 95% was released from the chitin-bound intein tag. The recombinant linear rMROM competitively displaced [125I] PACAP38 on VPAC2 with a half-maximal inhibitory concentration (IC50) of 60 +/- 5 nM, whereas the IC50 of rMROM at human VPAC1 was observed up to 10 microM and no binding was detected at PAC1. rMROM stimulated the cAMP accumulation in Chinese hamster ovary (CHO) cells expressing the human VPAC2 with a half-maximal stimulatory concentration (EC50) of 0.6 nM, which was 500-fold less potent at VPAC1and had no activity on PAC1. An efficient production procedure of a novel recombinant VPAC2-selective agonist was established.

Pharmacological characterization of endothelin receptors-mediated contraction in the mouse isolated proximal and distal colon

The study investigated the role of endothelin (ET) and the ET receptor subtypes ET(A) and ET(B) in mediating longitudinal contraction in the mouse proximal and distal colon. Cumulative concentration-response curves to a range of ET agonists (ET-1, ET-2, ET-3, (Ala(1,3,11,13)) ET and IRL 1620) were established by administering concentrations ranging from 0.01 nM to 0.3 microM. Concentration-response curves to ET-1, which exhibits a high affinity for both ET(A) and ET(B) receptor subtypes, were also established in the presence of the ET(A) antagonist BMS 182874 and the ET(B) antagonist IRL1038. The addition of the selective ET(A) receptor antagonist BMS 182874 caused a rightward shift of the concentration-response curve to ET-1 in both sections of the colon. The ET(B) receptor antagonist IRL1038 (0.3-1 microM) did not significantly effect the response to ET-1 in the proximal colon but caused a significant decrease in response towards higher concentrations ranges (>or=3 nM) in the distal colon. A comparison of the concentration-response curves to ET-1, ET-2 and ET-3 showed a rank order of potency ET-1>or=ET-2>>ET-3 in the proximal colon and ET-1>or=ET-2>or=ET-3 in the distal colon. The selective ET(B) receptor agonists, (Ala(1,3,11,13)) ET and IRL 1620 did not produce any response in the proximal sections of the colon but produced a smaller contraction in the distal segments. The data indicate that ET can contract the proximal tissues of the mouse colon predominantly via ET(A) receptors and in the distal tissues via ET(A) and ET(B) receptors.

Novel concepts of neuropeptide-based drug therapy: vasoactive intestinal polypeptide and its receptors

Chronic inflammatory airway diseases such as bronchial asthma or chronic obstructive pulmonary disease (COPD) are major contributors to the global burden of disease. Although inflammatory cells play the central role in the pathogenesis of the diseases, recent observations indicate that also resident respiratory cells represent important targets for pulmonary drug development. Especially targeting airway neuromediators offers a possible mechanism by which respiratory diseases may be treated in the future. Among numerous peptide mediators such as tachykinins, calcitonin gene-related peptide, neurotrophins or opioids, vasoactive intestinal polypeptide (VIP) is one of the most abundant molecules found in the respiratory tract. In human airways, it influences many respiratory functions via the receptors VPAC1, VPAC2 and PAC1. VIP-expressing nerve fibers are present in the tracheobronchial smooth muscle layer, submucosal glands and in the walls of pulmonary and bronchial arteries and veins. Next to its strong bronchodilator effects, VIP potently relaxes pulmonary vessels, and plays a pivotal role in the mediation of immune mechanisms. A therapy utilizing the respiratory effects of VIP would offer potential benefits in the treatment of obstructive and inflammatory diseases and long acting VIP-based synthetic non-peptide compounds may represent a novel target for drug development.

Down-regulation of vasoactive intestinal peptide and altered expression of its receptors in rat diabetic cardiomyopathy

Vasoactive intestinal peptide (VIP) is a vasorelaxant peptide that addresses two receptor subtypes, VPAC1 and VPAC2. It stimulates insulin secretion and mediates anti-inflammatory effects and has been proposed for treatment of type 2 and autoimmune diabetes. In the heart, VIP is produced and released primarily by intrinsic neurons and improves cardiac perfusion and function. Here, we investigated the involvement of this system in the events underlying development of experimentally induced diabetic cardiomyopathy. Rats received a single streptozotocin injection, and cardiac VIP content [radioimmune assay (RIA)], expression of the VIP precursors VPAC1 and VPAC2 [real-time reverse transcription-polymerase chain reaction (RT-PCR)], and VPAC1 and VPAC2 tissue distribution (immunohistochemistry) were assessed 4, 8, and 16 weeks thereafter and compared with corresponding vehicle-treated controls. Cardiac neuropathy manifests progressively during the first 4 months of diabetes at the preproVIP mRNA and VIP peptide level and is accompanied by initial down-regulation of VPAC2 at one prime target of VIP-containing axons, i.e., smooth muscle cells of coronary arterioles. VPAC1 is expressed by macrophages. After initial changes that are specific for atria and ventricles, respectively, VPAC1 and VPAC2 expression return to control levels at 16 weeks despite ongoing loss of VIP. Given the cardioprotective role of the VIP signaling system, the persistence of receptors has therapeutic implications since it is the prerequisite for trials with VPAC2 agonists.

PKA-dependent and PKA-independent pathways for cAMP-regulated exocytosis

Stimulus-secretion coupling is an essential process in secretory cells in which regulated exocytosis occurs, including neuronal, neuroendocrine, endocrine, and exocrine cells. While an increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) is the principal signal, other intracellular signals also are important in regulated exocytosis. In particular, the cAMP signaling system is well known to regulate and modulate exocytosis in a variety of secretory cells. Until recently, it was generally thought that the effects of cAMP in regulated exocytosis are mediated by activation of cAMP-dependent protein kinase (PKA), a major cAMP target, followed by phosphorylation of the relevant proteins. Although the involvement of PKA-independent mechanisms has been suggested in cAMP-regulated exocytosis by pharmacological approaches, the molecular mechanisms are unknown. Newly discovered cAMP-GEF/Epac, which belongs to the cAMP-binding protein family, exhibits guanine nucleotide exchange factor activities and exerts diverse effects on cellular functions including hormone/transmitter secretion, cell adhesion, and intracellular Ca(2+) mobilization. cAMP-GEF/Epac mediates the PKA-independent effects on cAMP-regulated exocytosis. Thus cAMP regulates and modulates exocytosis by coordinating both PKA-dependent and PKA-independent mechanisms. Localization of cAMP within intracellular compartments (cAMP compartmentation or compartmentalization) may be a key mechanism underlying the distinct effects of cAMP in different domains of the cell.

Cytosolic Ca2+ responses to sub-picomolar and nanomolar PACAP in pancreatic beta-cells are mediated by VPAC2 and PAC1 receptors

Pituitary adenylate cyclase-activating polypeptide (PACAP) potentiates glucose-induced insulin release and increases cytosolic Ca2+ concentration ([Ca2+]i) in islet beta-cells in a concentration-dependent manner with two peaks at 10(-13) and 10(-9) M. PAC1 receptor (PAC1-R) and VPAC2 receptor (VPAC2-R) are expressed in pancreatic beta-cells and thought to be involved in insulin release. We aimed to determine the receptor types involved in the [Ca2+]i responses to 10(-13) and 10(-9) M PACAP. We measured [Ca2+]i in beta-cells and examined comparative effects of PAC1-R-selective agonist maxadilan, its antagonist M65, VPAC2-R-selective agonist Ro25-1553, and native ligands of PACAP and VIP. In the presence of 8.3 mM glucose, maxadilan, Ro25-1553, PACAP, and VIP at 10(-13) and 10(-9) M all increased [Ca2+]i. PACAP and maxadilan elicited greater effects at 10(-9) M than at 10(-13) M both in the incidence and amplitude of [Ca2+]i responses. For VIP and Ro25-1553, in contrast, the effects at 10(-9) and 10(-13) M were comparable. Furthermore, the amplitude of [Ca2+]i responses to 10(-9) M PACAP, but not 10(-13) M PACAP, was suppressed by M65. The results suggest that VPAC2-R and PAC1-R contribute equally to [Ca2+]i responses to sub-picomolar concentrations of PACAP, while PAC1-R has greater contribution to [Ca2+]i responses to nanomolar concentrations of this peptide.

Activation of the vasoactive intestinal peptide 2 receptor modulates normal and atrophying skeletal muscle mass and force

Of the two known vasoactive intestinal peptide receptors (VPAC1R and VPAC2R), the VPAC2R is expressed in skeletal muscle. To evaluate the function of the VPAC2R in the physiological control of skeletal muscle mass, we utilized the VPAC1R selective agonist [K15,R16,L27]VIP(1-7) GRF(8-27)-NH2 and the VPAC2R selective agonist Ro-25-1553 to treat mice and rats undergoing either nerve damage-, corticosteroid-, or disuse-induced skeletal muscle atrophy. These analyses demonstrated that activation of VPAC2R, but not VPAC1R, reduced the loss of skeletal muscle mass and force during conditions of skeletal muscle atrophy resulting from corticosteroid administration, denervation, casting-induced disuse, increased skeletal muscle mass, and force of nonatrophying muscles. These studies indicate that VPAC2R agonists may have utility for the treatment of skeletal muscle-wasting diseases.

VIP enhances both pre- and postsynaptic GABAergic transmission to hippocampal interneurones leading to increased excitatory synaptic transmission to CA1 pyramidal cells

Vasoactive intestinal peptide (VIP) is present in the hippocampus in three subtypes of GABAergic interneurones, two of which innervate preferentially other interneurones, responsible for pyramidal cell inhibition. We investigated how pre- and postsynaptic modulation of GABAergic transmission (to both pyramidal cells and interneurones) by VIP could influence excitatory synaptic transmission in the CA1 area of the hippocampus. VIP (0.1-100 nM) increased [(3)H]GABA release from hippocampal synaptosomes (maximum effect at 1 nM VIP; 63.8 +/- 4.0%) but did not change [(3)H]glutamate release. VIP (0.3-30 nM) enhanced synaptic transmission in hippocampal slices (maximum effect at 1 nM VIP; field excitatory postsynaptic potentials (epsp) slope: 23.7 +/- 1.1%; population spike amplitude: 20.3 +/- 1.7%). The action on field epsp slope was fully dependent on GABAergic transmission since it was absent in the presence of picrotoxin (50 microM) plus CGP55845 (1 microM). VIP (1 nM) did not change paired-pulse facilitation but increased paired-pulse inhibition in CA1 pyramidal cells (16.0 +/- 0.9%), reinforcing the involvement of GABAergic transmission in the action of VIP. VIP (1 nM) increased muscimol-evoked inhibitory currents by 36.4 +/- 8.7% in eight out of ten CA1 interneurones in the stratum radiatum. This suggests that VIP promotes increased inhibition of interneurones that control pyramidal cells, leading to disinhibition of synaptic transmission to pyramidal cell dendrites. In conclusion, concerted pre- and postsynaptic actions of VIP lead to disinhibition of pyramidal cell dendrites causing an enhancement of synaptic transmission.

Modulation of voltage-dependent calcium channels by neurotransmitters and neuropeptides in parasympathetic submandibular ganglion neurons

The control of saliva secretion is mainly under parasympathetic control, although there also could be a sympathetic component. Sympathetic nerves are held to have a limited action in secretion in submandibular glands because, on electrical stimulation, only a very small increase to the normal background, basal secretion occurs. Parasympathetic stimulation, on the other hand, caused a good flow of saliva with moderate secretion of acinar mucin, plus an extensive secretion of granules from the granular tubules. The submandibular ganglion (SMG) is a parasympathetic ganglion which receives inputs from preganglionic cholinergic neurons, and innervates the submandibular salivary gland to control saliva secretion. Neurotransmitters and neuropeptides acting via G-protein coupled receptors (GPCRs) change the electrical excitability of neurons. In these neurons, many neurotransmitters and neuropeptides modulate voltage-dependent calcium channels (VDCCs). The modulation is mediated by a family of GPCRs acting either directly through the membrane delimited G-proteins or through second messengers. However, the mechanism of modulation and the signal transduction pathway linked to an individual GPCRs depend on the animal species. This review reports how neurotransmitters and neuropeptides modulate VDCCs and how these modulatory actions are integrated in SMG systems. The action of neurotransmitters and neuropeptides on VDCCs may provide a mechanism for regulating SMG excitability and also provide a cellular mechanism of a variety of neuronal Ca(2+)-dependent processes.

VIP and PACAP induce selective neuronal differentiation of mouse embryonic stem cells

The capacity of embryonic stem cells (ES cells) to differentiate into neuronal cells represents a potential source for neuronal replacement and a model for studying factors controlling early stages of neuronal differentiation. Various molecules have been used to induce such differentiation but so far neuropeptides acting via functional G-protein-coupled receptors (GPCRs) have not been investigated. Vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are neuropeptides expressed in early development which affect neuronal precursor proliferation and neuronal differentiation. VIP and PACAP share two common receptors (VPAC1 and VPAC2 receptors) while only PACAP binds with high affinity to PAC1 receptors. The aim of the study was to determine whether VIP and PACAP could produce functional neuronal differentiation of ES cells. Mouse ES cells were allowed to aggregate in embryoid bodies (EBs) in the presence or not of VIP and PACAP for 1 week. VIP and PACAP potently increased the proportion of EB-derived cells expressing specifically a neuronal phenotype shown by immunocytochemistry and neurite outgrowth without altering glial cell number. Binding and RT-PCR analyses demonstrated the presence of VPAC2 and PAC1 receptors on ES cells. Accordingly, both peptides increased cyclic AMP and intracellular calcium. In contrast, EB-derived cells only expressed a functional PAC1 receptor, suggesting a switch in GPCR phenotype during ES cell differentiation. These original data demonstrate that functional GPCRs for VIP and PACAP are present on ES cells and that these neuropeptides may induce their differentiation into a neuronal phenotype. It opens an exciting new field for neuropeptide regulation of tissue ontogenesis.

[Transgenic mice overexpressing PACAP in pancreatic beta-cells: acute and chronic effects on insulin and glucose homeostasis]

PACAP belongs to the vasoactive intestinal polypeptide (VIP)/secretin/glucagon superfamily, which also includes glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP). PACAP shares an insulinotropic property with the latter two peptides; for instance, it stimulates insulin secretion from islets in a glucose-dependent manner at femtomolar concentrations. However, the pathophysiological significance of PACAP in diabetes remains largely unknown, for several reasons, including a lack of low-molecular weight PACAP ligands and a lack of suitable animal models. As an approach to understanding PACAP's pancreatic function in vivo, we have recently generated transgenic mice overexpressing PACAP in islet beta cells under the control of human insulin promoter (Tg mice). As a consequence, it has been demonstrated that in addition to stimulating insulin secretion, PACAP has long-term effects on pancreatic endocrine cells, including proliferation of beta cells during streptozotocin-induced diabetes development as well as aging. These observations provide additional information to support the possibility that drugs associated with PACAP-signaling pathways might be of therapeutic value for the treatment of diabetes. In this review, we briefly summarize these previous studies using Tg mice and also focus on the physiological and pathophysiological roles mediated by PACAP during diabetes development.

[Altered higher brain function in PACAP-knockout mice]

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide that functions as not only a neurotransmitter/neuromodulator but also a neurotrophic factor. To assess the roles of endogenous PACAP, several groups including ours have independently produced mice with targeted mutations in the PACAP gene. The phenotypes of the mutant mice both confirm and extend our knowledge of the physiological roles of PACAP in the central nervous system as well as many peripheral organs. In this review, we briefly summarize the roles of PACAP in higher brain function, which have been proposed by the studies using the mutant mice as well as histological and pharmacological approaches.

Effect of pituitary adenylate cyclase-activating polypeptide and vasoactive intestinal polypeptide on mouse preantral follicle development in vitro

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a bioactive peptide isolated from ovine hypothalamus. It is transiently expressed in preovulatory follicles and positively affects several parameters correlated with the ovulatory process. It has also been shown to be expressed in the interstitial tissue around primordial and preantral follicles. The aim of the present study was to investigate whether PACAP influences preantral follicle growth and differentiation. Mouse preantral follicles were cultured for 5 d in the presence of FSH and increasing concentrations of PACAP or vasoactive intestinal polypeptide (VIP) (10(-12) to 10(-7) m). In the presence of FSH, follicles increased in diameter and formed an antrum. At the concentrations tested, neither PACAP alone nor VIP alone had any effect on follicle development, but the addition of either peptide to FSH-stimulated follicles caused a dose-dependent inhibition of follicle growth, antrum formation, granulosa cell proliferation, and estradiol production. The effect of PACAP on follicle growth and antrum formation was directly correlated with the length of stimulation and was reversible. Although exposure of follicles to 10(-7) m PACAP and VIP did not affect oocyte growth, it severely impaired completion of meiotic maturation in oocytes isolated from the follicles and cultured for 17 h in medium alone. The cyclic production of PACAP by preovulatory follicles during the estrous cycle in adult rats and its induction by LH in the rat and mouse ovary suggest that this peptide may play a role in the local regulation of preantral follicle growth.

Distribution of the VPAC2 receptor in peripheral tissues of the mouse

The neuropeptide vasoactive intestinal peptide (VIP) exerts its actions through two structurally related G protein-coupled receptors (VPAC(1) and VPAC(2)). Pituitary adenylate cyclase-activating polypeptide (PACAP) is also a potent agonist of VPAC(1) and VPAC(2) receptors as well as of a third, PACAP-specific receptor (PAC(1)). We report here the distribution of the VPAC(2) receptor in peripheral tissues of the mouse, determined by receptor autoradiography using [(125)I]VIP and the selective VPAC(2) receptor agonist [(125)I]Ro25-1553 in wild-type and VPAC(2) receptor-null mice. In addition, displacement experiments with the VPAC(2)-selective agonist Ro25-1553 and the VPAC(1)-selective agonist [K(15),R(16),L(27)]VIP(1-7)/GRF(8-27) were performed using the universal radioligand [(125)I]VIP. The VPAC(2) receptor is found predominantly in smooth muscle (in blood vessels and in the smooth muscle layers of the gastrointestinal and reproductive systems), the basal part of the mucosal epithelium in the colon, lung, the vasculature of the kidney, adrenal medulla, and retina. Unexpectedly, the receptor was also present in thyroid follicular cells and acinar cells of the pancreas, tissues that have not been found to express the receptor in other species, and in very large amounts in the lung. Our data suggest novel functions of the VPAC(2) receptor and additional potential therapeutic uses of drugs acting at the receptor (including the treatment of erectile dysfunction), but our results also indicate that caution should be exercised in using the mouse as an animal model for the evaluation of VIP analogs intended for diagnostic or therapeutic use in man.

Disrupted circadian rhythms in VIP- and PHI-deficient mice

The related neuropeptides vasoactive intestinal peptide (VIP) and peptide histidine isoleucine (PHI) are expressed at high levels in the neurons of the suprachiasmatic nucleus (SCN), but their function in the regulation of circadian rhythms is unknown. To study the role of these peptides on the circadian system in vivo, a new mouse model was developed in which both VIP and PHI genes were disrupted by homologous recombination. In a light-dark cycle, these mice exhibited diurnal rhythms in activity which were largely indistinguishable from wild-type controls. In constant darkness, the VIP/PHI-deficient mice exhibited pronounced abnormalities in their circadian system. The activity patterns started approximately 8 h earlier than predicted by the previous light cycle. In addition, lack of VIP/PHI led to a shortened free-running period and a loss of the coherence and precision of the circadian locomotor activity rhythm. In about one-quarter of VIP/PHI mice examined, the wheel-running rhythm became arrhythmic after several weeks in constant darkness. Another striking example of these deficits is seen in the split-activity patterns expressed by the mutant mice when they were exposed to a skeleton photoperiod. In addition, the VIP/PHI-deficient mice exhibited deficits in the response of their circadian system to light. Electrophysiological analysis indicates that VIP enhances inhibitory synaptic transmission within the SCN of wild-type and VIP/PHI-deficient mice. Together, the observations suggest that VIP/PHI peptides are critically involved in both the generation of circadian oscillations as well as the normal synchronization of these rhythms to light.

Down-regulation of vasoactive intestinal polypeptide receptor expression in atopic dermatitis

BACKGROUND

Receptors for vasoactive intestinal polypeptide (VIP) have recently been suggested to play a key role in immunomodulation with genetically modified mice. However, it is not known whether changes in receptor gene regulation are involved in the pathogenesis of human immune disorders.

OBJECTIVE

We studied the expression of VPAC(2) in acute lesions of the human immune disease atopic dermatitis.

METHODS

By using nonradioactive in situ hybridization, quantitative immunohistochemistry, RT-PCR, and gene array studies, the expression status of VPAC(2) was assessed in atopic dermatitis and control tissues and in the human mast cell line HMC-1.

RESULTS

In situ hybridization and immunohistochemistry demonstrated VPAC(2) mRNA and protein expression in human mast cells surrounded by VIP positive nerve fibers. Gene array experiments and RT-PCR studies showed high levels of VPAC(2) mRNA expression in mast cells that were increased compared to other receptors such as VPAC(1) or VIP in the human mast cell line HMC-1. Stimulation of HMC-1 cells led to a downregulation of VPAC(2). Similarly, quantitative immunohistochemistry for VPAC(2) in acute atopic dermatitis lesions showed a significantly decreased VPAC(2) immunoreactivity in mast cells.

CONCLUSION

The downregulation of VPAC(2) in human mast cells in acute lesions of atopic dermatitis suggests a role of this G-protein;coupled receptor in the pathophysiology of the disease.

VIP as a trophic factor in the CNS and cancer cells

The effects of vasoactive intestinal peptide (VIP) on the proliferation of central nervous system (CNS) and cancer cells were investigated. VIP has important actions during CNS development. During neurogenesis, VIP stimulates the proliferation and differentiation of brain neurons. Addition of VIP to embryonic mouse spinal cord cultures increases neuronal survival and activity dependent neurotrophic factor (ADNF) secretion from astroglial cells. VIP is an integrative regulator of brain growth and development during neurogenesis and embryogenesis. Also, VIP causes increased proliferation of human breast and lung cancer cells in vitro. VIP binds with high affinity to cancer cells, elevates the cAMP and increases gene expression of c-fos, c-jun, c-myc and vascular endothelial cell growth factor. The effects of VIP on cancer cells are reversed by VIPhybrid, a synthetic VPAC(1) receptor antagonist. VIPhyb inhibits the basal growth of lung cancer cells in vitro and tumors in vivo and potentiates the ability of chemotherapeutic drugs to kill cancer cells. Due to the high density of VPAC(1) receptors in cancer cells, VIP has been radiolabeled with 123I, 18F and 99mTc to image tumors. It remains to be determined if radiolabeled VIP analogs will be useful agents for early detection of cancer in patients.