Isolation of a novel 38 residue-hypothalamic polypeptide which stimulates adenylate cyclase in pituitary cells

Design and biological assessment of membrane-tethering neuroprotective peptides derived from the pituitary adenylate cyclase-activating polypeptide type 1 receptor

BACKGROUND

The pituitary adenylate cyclase-activating polypeptide (PACAP) type 1 receptor (PAC1), a class B G protein-coupled receptor (GPCR), has emerged as a promising target for treating neurodegenerative conditions. Unfortunately, despite years of research, no PAC1-specific agonist has been discovered, as activity on two other GPCRs, VPAC1 and VPAC2, is retained with current analogs. Cell signaling is related to structural modifications in the intracellular loops (ICLs) of GPCRs. Thus, we hypothesized that peptides derived from the ICLs (called pepducins) of PAC1 might initiate, as allosteric ligands, signaling cascades after recognition of the parent receptor and modulation of its conformational landscape.

METHODS

Three pepducins were synthesized and evaluated for their ability to 1) promote cell survival; 2) stimulate various signaling pathways associated with PAC1 activation; 3) modulate selectively PAC1, VPAC1 or VPAC2 activation; and 4) sustain mobility and prevent death of dopaminergic neurons in a zebrafish model of neurodegeneration.

RESULTS

Assays demonstrated that these molecules promote SH-SY5Y cell survival, a human neuroblastoma cell line expressing PAC1, and activate signaling via Gα_s and Gα_q, with distinct potencies and efficacies. Also, PAC1-Pep1 and PAC1-Pep2 activated selectively PAC1-mediated Gα_s stimulation. Finally, experiments, using a zebrafish neurodegeneration model, showed a neuroprotective action with all three pepducins and in particular, revealed the ability of PAC1-Pep1 and PAC1-Pep3 to preserve fish mobility and tyrosine hydroxylase expression in the brain.

CONCLUSION

We have developed the first neuroprotective pepducins derived from PAC1, a class B GPCR.

GENERAL SIGNIFICANCE

PAC1-derived pepducins represent attractive templates for the development of innovative neuroprotecting molecules.

PACAP27 induces migraine-like attacks in migraine patients

Introduction

Pituitary adenylate cyclase-activating polypeptide (PACAP) is found in two functional isoforms, namely PACAP38 and PACAP27. The migraine-inducing properties of PACAP38 are well studied. However, it is not known whether the lesser-known and under-studied protein isoform, PACAP27, can also induce migraine attacks. Here, we studied the effect of human PACAP27 infusion on induction of migraine in a provocation model.

Methods

In a crossover study, 20 migraine without aura patients were randomly assigned to receive human PACAP27 (10 picomol/kg/min) or saline (placebo) infusion over 20 min. We recorded the migraine and associated symptoms.

Results

All patients completed the study. PACAP27 provoked migraine-like attacks in 11 patients (55%) and two developed attacks after placebo (10%) ( p = 0.022). The headache intensity and duration after PACAP27 was significantly greater compared to placebo ( p = 0.003).

Conclusion

PACAP27 triggers migraine attacks without aura. These novel data strengthen the role of PACAP and its receptors in migraine pathogenesis.

PACAP/PAC1 Regulation of Inflammation via Catecholaminergic Neurons in a Model of Multiple Sclerosis

The sympathetic nervous system (SNS) serves to maintain homeostasis of vital organ systems throughout the body, and its dysfunction plays a major role in human disease. The SNS also links the central nervous system to the immune system during different types of stress via innervation of the lymph nodes, spleen, thymus, and bone marrow. Previous studies have shown that pituitary adenylate cyclase-activating polypeptide (PACAP, gene name adcyap1) exhibits anti-inflammatory properties in the experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis. Because PACAP is known to regulate SNS function, we hypothesized that part of the immunoprotective action of PACAP is due to its neuromodulatory effects on sympathetic neurons. To examine this, we used an inducible, targeted approach to conditionally disrupt not only the PACAP-preferring PAC1 receptor gene (adcyap1r1) in dopamine β-hydroxylase-expressing cells, which includes postganglionic sympathetic neurons, but also catecholaminergic neurons in the brain and adrenomedullary chromaffin cells. In contrast to our previous EAE studies using PACAP global knockout mice which developed severe and prolonged EAE, we found that mice with conditional loss of PAC1 receptors in catecholaminergic cells developed a delayed time course of EAE with reduced helper T cell type 1 (Th1) and Th17 and enhanced Th2 cell polarization. At later time points, similar to mice with global PACAP loss, mice with conditional loss of PAC1 exhibited more severe clinical disease than controls. The latter was associated with a reduction in the abundance of thymic regulatory T cells (Tregs). These studies indicate that PAC1 receptor signaling acts in catecholaminergic cells in a time-dependent manner. At early stages of disease development, it enhances the ability of the SNS to polarize the Th response towards a more inflammatory state. Then, after disease is established, it enhances the ability of the SNS to dampen the inflammatory response via Tregs. The lack of concordance in results between global PACAP KO mice and mice with the PAC1 deletion targeted to catecholaminergic cells during early EAE may be explained by the fact that PACAP acts to regulate inflammation via multiple receptor subtypes and multiple targets, including inflammatory cells.

Melatonin mediates monochromatic green light-induced satellite cell proliferation and muscle growth in chick embryo

Background

Green light penetrates the skull and has directly affected on the secretion of melatonin in plasma, which regulates the endocrine activities to influence the muscle growth, satellite cell mitotic activity and quality properties of meat from the embryonic period to posthatch in chick. Pituitary adenylate cyclase-activating polypeptide 6–38 (PACAP6-38) could inhibit the synthesis and secretion of pineal melatonin. Finding a new way for exploring the mechanism of light-regulated muscle growth in ovo is essential for promoting the productive performance in poultry.

Methods

Chick embryos were exposed to darkness (D-group) and green light (G-group) throughout the embryonic period, and injected with PACAP6-38 or saline at embryonic day 8. Plasma hormone, skeletal muscle fiber areas, satellite cell proliferation activity, paired domain homeobox transcription factor 7 and myogenic regulatory factors were observed.

Results

By saline treatment, the percentage of proliferating cell nuclear antigen immunoreactive cells and mitotic activity of satellite cells in skeletal muscle were higher in G-group than those of in D-group at post-hatching day 0. With the increase of plasma melatonin, green light promoted the secretion of growth hormone (GH) and insulin like factor 1 (IGF-1) in plasma, the satellite cell proliferation, the size of muscle fiber, as well as the mRNA expressions of Pax7, myogenic regulatory factors and IGF-1R. After PACAP6-38 treatment to inhibit the secretion of melatonin in ovo, aforementioned parameters were remarkably decreased and the difference of these parameters was disappeared between D-group and G-group.

Conclusion

These data indicated that stimulation with monochromatic green light during incubation enhanced the secretion of melatonin and up-regulation of GH-IGF-1 axis to activate the satellite cells proliferation and myofiber formation, involving the expression of Pax7 and myogenic regulatory factors.

PACAP Is Lethal to Flavobacterium psychrophilum Through Either Direct Membrane Permeabilization or Indirectly, by Priming the Immune Response in Rainbow Trout Macrophages

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a multifunctional neuropeptide that is widely distributed in mammals and is capable of performing roles as a neurotransmitter, neuromodulator, and vasodilator. This polypeptide belongs to the glucagon/secretin superfamily, of which some members have been shown to act as antimicrobial peptides in both mammalian and aquatic organisms. In teleosts, PACAP has been demonstrated to have direct antimicrobial activity against several aquatic pathogens, yet this phenomenon has never been studied throughout a live bacterial challenge. The present study focuses on the influence of synthetic Clarias gariepinus 38 amino acid PACAP on the rainbow trout monocyte/macrophage-like cell line, RTS11, when exposed to the coldwater bacterial pathogen Flavobacterium psychrophilum. PACAP was shown to have direct antimicrobial activity on F. psychrophilum when grown in both cytophaga broth and cell culture media (L-15). Further, the ability of teleostean PACAP to permeabilize the membrane of an aquatic pathogen, F. psychrophilum, was demonstrated for the first time. The viability of RTS11 when exposed to PACAP was also observed using a trypan blue exclusion assay to determine optimal experimental doses of the antimicrobial peptide. This displayed that only concentrations higher than 0.1 μM negatively impacted RTS11 survival. Interestingly, when RTS11 was pre-treated with PACAP for 24 h before experiencing infection with live F. psychrophilum, growth of the pathogen was severely inhibited in a dose-dependent manner when compared to cells receiving no pre-treatment with the polypeptide. Relative expression of pro-inflammatory cytokines (IL-1β, TNFα, and IL-6) and PACAP receptors (VPAC1 and PAC1) was also analyzed in RTS11 following PACAP exposure alone and in conjunction with live F. psychrophilum challenge. These qRT-PCR findings revealed that PACAP may have a synergistic effect on RTS11 immune function. The results of this study provide evidence that PACAP has immunostimulatory activity on rainbow trout immune cells as well as antimicrobial activity against aquatic bacterial pathogens such as F. psychrophilum. As there are numerous pathogens that plague the aquaculture industry, PACAP may stimulate the teleost immune system while also providing an efficacious alternative to antibiotic use.

Mechanisms underlying a critical period of respiratory development in the rat

Twenty-five years ago, Filiano and Kinney (1994) proposed that a critical period of postnatal development constitutes one of the three risk factors for sudden infant death syndrome (SIDS). The underlying mechanism was poorly understood. In the last 17 years, much has been uncovered on this period in the rat. Against several expected trends of development, abrupt neurochemical, metabolic, ventilatory, and electrophysiological changes occur in the respiratory system at P12-13. This results in a transient synaptic imbalance with suppressed excitation and enhanced inhibition, and the response to acute hypoxia is the weakest at this time, both at the cellular and system's levels. The basis for the synaptic imbalance is likely to be contributed by a reduced expression of brain-derived neurotrophic factor (BDNF) and its TrkB receptors in multiple brain stem respiratory-related nuclei during the critical period. Exogenous BDNF or a TrkB agonist partially reverses the synaptic imbalance, whereas a TrkB antagonist accentuates the imbalance. A transient down-regulation of pituitary adenylate cyclase-activating polypeptide (PACAP) at P12 in respiratory-related nuclei also contributes to the vulnerability of this period. Carotid body denervation during this time or perinatal hyperoxia merely delays and sometimes prolongs, but not eliminate the critical period. The rationale for the necessity of the critical period in postnatal development is discussed.

Neurovascular mechanisms of migraine and cluster headache

Vascular theories of migraine and cluster headache have dominated for many years the pathobiological concept of these disorders. This view is supported by observations that trigeminal activation induces a vascular response and that several vasodilating molecules trigger acute attacks of migraine and cluster headache in susceptible individuals. Over the past 30 years, this rationale has been questioned as it became clear that the actions of some of these molecules, in particular, calcitonin gene-related peptide and pituitary adenylate cyclase-activating peptide, extend far beyond the vasoactive effects, as they possess the ability to modulate nociceptive neuronal activity in several key regions of the trigeminovascular system. These findings have shifted our understanding of these disorders to a primarily neuronal origin with the vascular manifestations being the consequence rather than the origin of trigeminal activation. Nevertheless, the neurovascular component, or coupling, seems to be far more complex than initially thought, being involved in several accompanying features. The review will discuss in detail the anatomical basis and the functional role of the neurovascular mechanisms relevant to migraine and cluster headache.

Perivascular neurotransmitters: Regulation of cerebral blood flow and role in primary headaches

In order to understand the nature of the relationship between cerebral blood flow (CBF) and primary headaches, we have conducted a literature review with particular emphasis on the role of perivascular neurotransmitters. Primary headaches are in general considered complex polygenic disorders (genetic and environmental influence) with pathophysiological neurovascular alterations. Identified candidate headache genes are associated with neuro- and gliogenesis, vascular development and diseases, and regulation of vascular tone. These findings support a role for the vasculature in primary headache disorders. Moreover, neuronal hyperexcitability and other abnormalities have been observed in primary headaches and related to changes in hemodynamic factors. In particular, this relates to migraine aura and spreading depression. During headache attacks, ganglia such as trigeminal and sphenopalatine (located outside the blood-brain barrier) are variably activated and sensitized which gives rise to vasoactive neurotransmitter release. Sympathetic, parasympathetic and sensory nerves to the cerebral vasculature are activated. During migraine attacks, altered CBF has been observed in brain regions such as the somatosensory cortex, brainstem and thalamus. In regulation of CBF, the individual roles of neurotransmitters are partly known, but much needs to be unraveled with respect to headache disorders.

PACAP-38 and PACAP(6-38) Degranulate Rat Meningeal Mast Cells via the Orphan MrgB3-Receptor

Infusion of pituitary adenylate cyclase activating peptide-38 (PACAP-38) provokes migraine attacks in migraineurs and headache in non-migraineurs. Adverse events like long-lasting flushing and heat sensation can be terminated with oral antihistamine treatment, indicating the involvement of mast cell activation after PACAP-infusion. Degranulation of rat peritoneal mast cells was provoked by several isoforms of PACAP via previously unknown receptor pharmacology. The effect might thus be mediated either via specific splice variants of the PAC₁-receptor or via an unknown receptor for PACAP-38. In the present study, we characterize degranulation of rat meningeal mast cells in response to PACAP-receptor ligands. Furthermore, we investigate if PACAP-38-induced mast cell degranulation is mediated via PAC₁-receptor splice variants and/or via the orphan Mas-related G-protein coupled member B3 (MrgB₃)-receptor. To address this, the pharmacological effect of different PACAP isoforms on meningeal mast cell degranulation was investigated in the hemisected skull model after toluidine blue staining followed by microscopic quantification. Presence of mRNA encoding PAC₁-receptor splice variants and the MrgB₃-receptor in rat mast cells was investigated by Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR) analysis. The effect of PACAP isoforms on PAC₁- and MrgB₃-receptor-expressing Xenopus laevis oocytes were performed by two-electrode voltage-clamp (TEVC) electrophysiology. PACAP-38 is a more potent mast cell degranulating agent than Pituitary Adenylate Cyclase Activating Peptide-27 (PACAP-27) in the meninges. Presence of mRNA encoding the PAC₁-receptor and its different splice variants could not be detected in peritoneal mast cells by RT-PCR, whereas the orphan MrgB₃-receptor, recently suggested to be a mediator of basic secretagogues-induced mast cell degranulation, was widely present. In PAC₁-receptor-expressing Xenopus laevis oocytes both PACAP-38, PACAP-27 and the specific PAC₁-receptor agonist maxadilan were equipotent, however, only PACAP-38 showed a significant degranulatory effect on mast cells. We confirmed Pituitary Adenylate Cyclase Activating Peptide(6–38) [PACAP(6–38)] to be a PAC₁-receptor antagonist, and we demonstrated that it is a potent mast cell degranulator and have an agonistic effect on MrgB₃-receptors expressed in oocytes. The present study provides evidence that PACAP-induced mast cell degranulation in rat is mediated through a putative new PACAP-receptor with the order of potency being: PACAP-38 = PACAP(6–38) > > PACAP-27 = maxadilan. The results suggest that the observed responses are mediated via the orphan MrgB₃-receptor.

Exploration of attractor modules for sporadic amyotrophic lateral sclerosis via systemic module inference and attract method

Sporadic amyotrophic lateral sclerosis (SALS) is a devastating neurodegenerative disorder. However, the understanding of SALS is still poor. This research aimed to excavate attractor modules for SALS by integrating the systemic module inference and attract method. To achieve this, gene expression data and protein-protein data were recruited and preprocessed. Then, based on the Spearman's correlation coefficient (SCC) of the interactions under these two conditions, two PPI networks separately with 870 nodes (979 interactions) in normal control group and 601 nodes (777 interactions) in SALS group were built. Systemic module inference method was performed to identify the modules, and attract method was used to identify attractor modules. Finally, pathway enrichment analysis was performed to disclose the functional enrichment of these attractor modules. In total 44 and 118 modules were identified for normal control and SALS groups, respectively. Among them, 6 modules were with similar gene composition between the two groups, and all 6 modules were considered as the attractor module via attract method. These attractor modules might be potential biomarkers for early diagnosis and therapy of SALS, which could provide insight into the disease biology and suggest possible directions for drug screening programs.

Pituitary Adenylate Cyclase-Activating Polypeptide-A Neuropeptide as Novel Treatment Option for Subacute Ileitis in Mice Harboring a Human Gut Microbiota

The neuropeptide Pituitary adenylate cyclase-activating polypeptide (PACAP) is well-known for its important functions in immunity and inflammation. Data regarding anti-inflammatory properties of PACAP in the intestinal tract are limited, however. In our present preclinical intervention study we addressed whether PACAP treatment could alleviate experimental subacute ileitis mimicking human gut microbiota conditions. Therefore, secondary abioitic mice were subjected to human fecal microbiota transplantation (FMT) and perorally infected with low-dose Toxoplasma gondii to induce subacute ileitis on day 0. From day 3 until day 8 post-infection, mice were either treated with synthetic PACAP38 or placebo. At day 9 post-infection, placebo, but not PACAP treated mice exhibited overt macroscopic sequelae of intestinal immunopathology. PACAP treatment further resulted in less distinct apoptotic responses in ileal and colonic epithelia that were accompanied by lower T cell numbers in the mucosa and lamina propria and less secretion of pro-inflammatory cytokines in intestinal ex vivo biopsies. Notably, ileitis-associated gut microbiota shifts were less distinct in PACAP as compared to placebo treated mice. Inflammation-ameliorating effects of PACAP were not restricted to the intestines, but could also be observed in extra-intestinal including systemic compartments as indicated by lower apoptotic cell counts and less pro-inflammatory cytokine secretion in liver and lungs taken from PACAP treated as compared to placebo control mice, which also held true for markedly lower serum TNF and IL-6 concentrations in the former as compared to the latter. Our preclinical intervention study provides strong evidence that synthetic PACAP alleviates subacute ileitis and extra-intestinal including systemic sequelae of T cell-driven immunopathology. These findings further support PACAP as a novel treatment option for intestinal inflammation including inflammatory bowel diseases (IBD).

Immunoregulatory Effects of Neuropeptides on Endothelial Cells: Relevance to Dermatological Disorders

Many skin diseases, including psoriasis and atopic dermatitis, have a neurogenic component. In this regard, bidirectional interactions between components of the nervous system and multiple target cells in the skin and elsewhere have been receiving increasing attention. Neuropeptides released by sensory nerves that innervate the skin can directly modulate functions of keratinocytes, Langerhans cells, dermal dendritic cells, mast cells, dermal microvascular endothelial cells and infiltrating immune cells. As a result, neuropeptides and neuropeptide receptors participate in a complex, interdependent network of mediators that modulate the skin immune system, skin inflammation, and wound healing. In this review, we will focus on recent studies demonstrating the roles of α-melanocyte-stimulating hormone, calcitonin gene-related peptide, substance P, somatostatin, vasoactive intestinal peptide, pituitary adenylate cyclase-activating peptide, and nerve growth factor in modulating inflammation and immunity in the skin through their effects on dermal microvascular endothelial cells.

Pituitary adenylate cyclase-activating polypeptide in the testis of the quail Coturnix coturnix: Expression, localization, and phylogenetic analysis

To evaluate the involvement of pituitary adenylate cyclase-activating polypeptide (PACAP)/receptors system in the control of testis activity, we have investigated the expression and localization of PACAP and the distribution of its receptors in the testis of mature samples of quail Coturnix coturnix, and we have performed a phylogenetic analysis of PACAP in birds. Using histological, molecular, and bioinformatics tools, we demonstrated that (a) PACAP messenger RNA shows a high sequence identity with that reported in other birds studied so far and in other vertebrates. Furthermore, we showed that purifying selection acts on PACAP; (b) the PACAP peptide is present only in Leydig cells, whereas its receptors are localized within both Leydig and germ cells; (c) the synthesis of PACAP does not take place in seminiferous tubules. The role of PACAP in the control of spermatogenesis and steroidogenesis in birds is discussed. Finally, we talk about the phylogenetic and evolutionary relationships between PACAP in birds and in other vertebrates.

Impaired neonatal cardiorespiratory responses to hypoxia in mice lacking PAC1 or VPAC2 receptors

The stress peptide pituitary adenylate cyclase activating polypeptide (PACAP) and its specific receptor PACAP type 1 receptor (PAC1) have been implicated in sudden infant death syndrome (SIDS). PACAP is also critical to the neonatal cardiorespiratory response to homeostatic stressors identified in SIDS, including hypoxia. However, which of PACAP's three receptors, PAC1, vasoactive intestinal peptide receptor type 1 (VPAC1), and/or vasoactive intestinal peptide receptor type 2 (VPAC2), are involved is unknown. In this study, we hypothesized that PAC1, but not VPAC2, is involved in mediating the cardiorespiratory response to hypoxia during neonatal development. To test this hypothesis, head-out plethysmography and surface ECG electrodes were used to assess the cardiorespiratory variables of unanesthetized postnatal day 4 PAC1 and VPAC2-knockout (KO) and wild-type (WT) mice in response to a 10% hypoxic challenge. Our results demonstrate that compared with WT pups, the early and late hypoxic rate of expired CO₂ (V̇co₂), V̇co₂ and ventilatory responses were blunted in PAC1-KO neonates, and during the posthypoxic period, minute ventilation (V̇e), V̇co₂ and heart rate were increased, while the increase in apneas normally associated with the posthypoxic period was reduced. Consistent with impaired cardiorespiratory control in these animals, the V̇e/V̇co₂ slope was reduced in PAC1-KO pups, suggesting that breathing was inappropriately matched to metabolism. In contrast, VPAC2-KO pups exhibited elevated heart rate variability during hypoxia compared with WT littermates, but the effects of the VPAC2-KO genotype on breathing were minimal. These findings suggest that PAC1 plays the principal role in mediating the cardiorespiratory effects of PACAP in response to hypoxic stress during neonatal development and that defective PACAP signaling via PAC1 may contribute to the pathogenesis of SIDS.

Therapeutic potential of PACAP in alcohol toxicity

Alcohol addiction is a worldwide concern as its detrimental effects go far beyond the addicted individual and can affect the entire family as well as the community. Considerable effort is being expended in understanding the neurobiological basis of such addiction in hope of developing effective prevention and/or intervention strategies. In addition, organ damage and neurotoxicological effects of alcohol are intensely investigated. Pharmacological approaches, so far, have only provided partial success in prevention or treatment of alcohol use disorder (AUD) including the neurotoxicological consequences of heavy drinking. Pituitary adenylate cyclase-activating polypeptide (PACAP) is an endogenous 38 amino-acid neuropeptide with demonstrated protection against neuronal injury, trauma as well as various endogenous and exogenous toxic agents including alcohol. In this mini-review, following a brief presentation of alcohol addiction and its neurotoxicity, the potential of PACAP as a therapeutic intervention in toxicological consequences of this devastating disorder is discussed.

Neuropeptides Exert Neuroprotective Effects in Alzheimer's Disease

Alzheimer's disease (AD) is an age-related neurodegenerative disorder characterized by cognitive deficits and neuronal loss. Deposition of beta-amyloid peptide (Aβ) causes neurotoxicity through the formation of plaques in brains of Alzheimer's disease. Numerous studies have indicated that the neuropeptides including ghrelin, neurotensin, pituitary adenylate cyclase-activating polypeptide (PACAP), neuropeptide Y, substance P and orexin are closely related to the pathophysiology of Alzheimer's disease. The levels of neuropeptides and their receptors change in Alzheimer's disease. These neuropeptides exert neuroprotective roles mainly through preventing Aβ accumulation, increasing neuronal glucose transport, increasing the production of neurotrophins, inhibiting endoplasmic reticulum stress and autophagy, modulating potassium channel activity and hippocampal long-term potentiation. Therefore, the neuropeptides may function as potential drug targets in the prevention and cure of Alzheimer's disease.

Pituitary Adenylate Cyclase Activating Polypeptide (PACAP) Reduces Oxidative and Mechanical Stress-Evoked Matrix Degradation in Chondrifying Cell Cultures

Pituitary adenylate cyclase activating polypeptide (PACAP) is an endogenous neuropeptide also secreted by non-neural cells, including chondrocytes. PACAP signaling is involved in the regulation of chondrogenesis, but little is known about its connection to matrix turnover during cartilage formation and under cellular stress in developing cartilage. We found that the expression and activity of hyaluronidases (Hyals), matrix metalloproteinases (MMP), and aggrecanase were permanent during the course of chondrogenesis in primary chicken micromass cell cultures, although protein levels changed daily, along with moderate and relatively constant enzymatic activity. Next, we investigated whether PACAP influences matrix destructing enzyme activity during oxidative and mechanical stress in chondrogenic cells. Exogenous PACAP lowered Hyals and aggrecanase expression and activity during cellular stress. Expression and activation of the majority of cartilage matrix specific MMPs such as MMP1, MMP7, MMP8, and MMP13, were also decreased by PACAP addition upon oxidative and mechanical stress, while the activity of MMP9 seemed not to be influenced by the neuropeptide. These results suggest that application of PACAP can help to preserve the integrity of the newly synthetized cartilage matrix via signaling mechanisms, which ultimately inhibit the activity of matrix destroying enzymes under cellular stress. It implies the prospect that application of PACAP can ameliorate articular cartilage destruction in joint diseases.

Effect of pituitary adenylate cyclase-activating polypeptide (PACAP) in the regulation of hypothalamic kisspeptin expression

Pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptor are broadly distributed in the brain, and PACAP is known to work as a multifunctional peptide. However, it is still largely unknown how PACAP affects the hypothalamic-pituitary-gonadal (HPG) axis. In this study, we examined the effect of PACAP on hypothalamic kisspeptin expression, a known regulator of gonadotropin-releasing hormone. We used two hypothalamic cell models, mHypoA-50 and mHypoA-55, which were originated from kisspeptin-expressing neuron in anterioventral periventricular nucleus and arcuate nucleus regions in the hypothalamus, respectively. Expression of Kiss-1 gene, which encodes kisspeptin, was significantly increased by PACAP stimulation in both mHypoA-50 and mHypoA-55 cells, by up to 2.69 ± 0.93-fold and 4.89 ± 1.13-fold, respectively. PACAP6-38, a PACAP receptor antagonist did not antagonize the action of PACAP on Kiss-1 gene expression but increased Kiss-1 gene by itself in these cells. PACAP-induced Kiss-1 gene expression in both mHypoA-50 and mHypoA-55 cells was almost completely prevented in the presence of H89, a protein kinase A inhibitor. PACAP was expressed in both these hypothalamic cell models and its expression was up-regulated by estradiol in mHypoA-50 cells but not in mHypoA-55 cells. Stimulation of mHypoA-50 and mHypoA-55 cells with PACAP increased the expression levels of corticotropin-releasing hormone and neurotensin, both of which could modulate HPG axis. Our present observations suggest that hypothalamic PACAP might modulate the HPG axis by directly or indirectly modulating Kiss-1 gene expression.

Role of kisspeptin and Kiss1R in the regulation of prolactin gene expression in rat somatolactotroph GH3 cells

Hypothalamic kisspeptin is a known principal activator of gonadotropin-releasing hormone neurons and governs the hypothalamic-pituitary-gonadal axis. Previous reports have shown that kisspeptin is also released into the hypophyseal portal circulation and directly affects the anterior pituitary. In this study, we examined the direct effect of kisspeptin on pituitary prolactin-producing cells. The rat pituitary somatolactotroph cell line GH3 expresses the kisspeptin receptor (Kiss1R); however, in these cells, kisspeptin failed to stimulate prolactin-promoter activity. When GH3 cells overexpressed Kiss1R, kisspeptin clearly increased prolactin-promoter activity, with a concomitant increase in extracellular signal-regulated kinase (ERK) and cAMP/protein kinase A (PKA) signaling pathways. In the experiments using GH3 cells overexpressing Kiss1R, kisspeptin did not potentiate thyrotropin-releasing hormone (TRH)-induced prolactin-promoter activity, but it potentiated the pituitary adenylate cyclase-activating polypeptide-induced prolactin-promoter activity, with a concomitant enhancement of ERK and PKA signaling pathways. Although the basal and TRH-induced prolactin-promoter activities were not modulated by increasing amounts of Kiss1R expression in GH3 cells, kisspeptin-stimulated prolactin-promoter activity was increased by the amount of Kiss1R overexpression. Endogenous Kiss1r mRNA expression in GH3 cells was significantly increased by treatment with estradiol (E2) but not by TRH. In addition, kisspeptin's ability to stimulate prolactin-promoter activity was restored after E2 treatment in non-transfected GH3 cells. Our current observations suggest that kisspeptin might have a direct effect on prolactin expression in the anterior pituitary prolactin-producing cells under the influence of E2, which may regulate Kiss1R expression and function.

Intranasal application of PACAP and β-cyclodextrin before the "critical period of proestrous stage" can block ovulation

INTRODUCTION

It was previously shown that intracerebroventricular administration of pituitary adenylate cyclase-activating polypeptide (PACAP) prior to GnRH mobilization in proestrus prevents ovulation in rats. In this study, we examined whether PACAP given intranasally could influence luteinizing hormone (LH) and prolactin (PRL) surges and ovulation.

METHODS

On the day of proestrus PACAP, p-cyclodextrin (modifier of blood-brain barrier) or PACAP + p-cyclodextrin was applied intranasally between 12:30 and 13:00. Blood samples were taken at 16:00, 18:00, and 20:00 for measuring plasma hormone levels. In the next morning, the expelled ova were counted. p-Cyclodextrin was also administered to male and diestrous female rats between 12:30 and 13:00 and blood was taken at 18:00.

RESULTS

PACAP prevented LH and PRL surges and ovulation in about half of the rats, p-cyclodextrin alone more effectively prevented ovulation. When PACAP and p-cyclodextrin were administered together, more rats ovulated like when PACAP given alone. p-Cyclodextrin did not influence LH and PRL levels in diestrous females; however, in males, it significantly enhanced PRL level.

DISCUSSION

Not only the intracerebroventricular, but the intranasal application of PACAP prevented ovulation. p-Cyclodextrin alone is more effective than PACAP and enhances PRL levels in male rats. PACAP and p-cyclodextrin given together weaken each other's effect. p-Cyclodextrin, as excipient of various drugs, has to be used carefully in human medications.

The novel small-molecule antagonist of PAC1 receptor attenuates formalin-induced inflammatory pain behaviors in mice

We recently developed PA-8, a novel small-molecule antagonist of PACAP type 1 (PAC1) receptor. In the present study, we examined whether PA-8 was effective against formalin-induced inflammatory pain in mice. Both intrathecal and oral administration of PA-8 resulted in the dose-dependent attenuation of the second phase of formalin-induced nociceptive responses. PA-8 also inhibited c-fos upregulation in the ipsilateral dorsal horn of the spinal cord. The results suggested that PACAP-PAC1 receptor signaling system in the spinal cord were primarily involved in the transmission of inflammatory pain, and PA-8 could be useful for the development of novel analgesics for treating inflammatory pain.

Spatiotemporal Expression Changes of PACAP and Its Receptors in Retinal Ganglion Cells After Optic Nerve Crush

Pituitary adenylate cyclase-activating polypeptide (PACAP) has been demonstrated to play a crucial part in protecting retinal ganglion cells (RGCs) from apoptosis in various retinal injury animal models. PACAP has two basic groups of receptors: PACAP receptor type 1 (PAC1R) and vasoactive intestinal polypeptide/PACAP receptors (VPAC1R and VPAC2R). However, few studies illustrated the spatial and temporal expression changes of endogenous PACAP and its receptors in a rodent optic nerve crush (ONC) model. In this study, a significant upregulation of PACAP and PAC1R in the retina after ONC was observed in both protein and RNA levels. The peak level of PACAP and PAC1R expression could be found on the fifth day following ONC. In addition, immunofluorescent labeling indicated that PACAP and PAC1R were localized mainly in RGCs. On the contrary, VPAC1R and VPAC2R were hardly detected in the retina. Collectively, the spatiotemporal expression of PACAP and its high-affinity receptor PAC1R were remarkably changed after ONC, and mainly expressed in the ganglion cell layer of the retina. This suggested that the upregulation of PACAP and PAC1R may play a vital role in RGC death after ONC.

PACAP deficiency aggravates atherosclerosis in ApoE deficient mice

Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) plays an important role in cytoprotection, inflammation and cardiovascular regulation. Thus, we studied the involvement of PACAP in atherogenesis. Differentiated human THP-1 macrophages (MΦ) were stimulated with oxidized low-density lipoproteins (oxLDL) and the influence of PACAP38 treatment on lipid content and TNF release was determined. To test the effect of PACAP deficiency (PACAP^-/-) on the development of atherosclerosis under standard chow (SC) or cholesterol-enriched diet (CED) in vivo, PACAP^-/- mice were crossbred with ApoE^-/- to generate PACAP^-/-/ApoE^-/- mice. Blood cholesterol and triglyceride levels were quantified. Lumen stenosis in the brachiocephalic trunk, cellularity and amounts of pro-inflammatory as well as autophagy-, apoptosis- and necroptosis-relevant proteins were analysed in atherosclerotic plaques by quantitative immunohistochemistry. In vitro, PACAP38 inhibited oxLDL-induced intracellular lipid storage as well as TNF release in MФ. In vivo, after SC, but not under CED, PACAP^-/-/ApoE^-/- mice showed an increased lumen stenosis compared to ApoE^-/- mice. In atherosclerotic plaques of PACAP^-/-/ApoE^-/- mice, the immunoreactive areas of TNF⁺, IL-1β⁺, autophagic, apoptotic and necroptotic cells were increased. In contrast, the overall cell density was decreased compared to ApoE^-/- under SC, while no differences were seen under CED. Similar plasma cholesterol levels were observed in PACAP^-/-/ApoE^-/- and ApoE^-/- mice under the respective feeding regime. Thus, PACAP^-/-/ApoE^-/- mice represent a novel mouse model of accelerated atherosclerosis where CED is not required. Our data indicate that PACAP acts as an endogenous atheroprotective neuropeptide. Thus, stable PACAP agonists may have potential as anti-atherosclerotic therapeutics. The specific PACAP receptor(s) mediating atheroprotection remain(s) to be identified.

Pituitary adenylate cyclase-activating polypeptide: Postnatal development in multiple brain stem respiratory-related nuclei in the rat

The pituitary adenylate cyclase-activating polypeptide (PACAP) plays an important role in anterior pituitary hormone secretion, neurotransmission, and the control of breathing. Mice lacking PACAP die suddenly mainly in the 2^nd postnatal week, coinciding temporally with a critical period of respiratory development uncovered by our laboratory in the rat. The goal of the current study was to test our hypothesis that PACAP expression is reduced during the critical period in normal rats. We undertook immunohistochemistry and optical densitometry of PACAP (specifically PACAP38) in several brain stem respiratory-related nuclei of postnatal days P2-21 rats, and found that PACAP immunoreactivity was significantly reduced at P12 in the pre-Bötzinger complex, nucleus ambiguus, hypoglossal nucleus, and the ventrolateral subnucleus of the nucleus tractus solitarius. No changes were observed in the control, non-respiratory cuneate nucleus at P12. Results imply that the down-regulation of PACAP during normal postnatal development may contribute to the critical period of vulnerability, when the animals' response to hypoxia is at its weakest.

Comparison of the effects of PACAP-38 and its analog, acetyl-[Ala15, Ala20] PACAP-38-propylamide, on spatial memory, post-learning BDNF expression and oxidative stress in rat

We compared the effects of single intraveinous injection of pituitary adenylate cyclase-activating polypeptide-38 (P38) to those of its analog, acetyl-[Ala¹⁵, Ala²⁰]PACAP-38-propylamide (P38-alg) on spatial memory in the Morris water maze (MWM) using a weak massed-learning procedure, post-training brain derived neurotrophic factor (BDNF) and post-training oxidative stress biomarker assays in male Wistar rats. Acquisition of the MWM task following P38 (30 μg/kg) and P38-alg (30 μg/kg) treatments was similar to control group (Saline: 0.9% NaCl) and there was no interaction between treatments and performance. However, in the probe test, P38-treated group showed a specific interest for the target quadrant whereas the two other groups exhibited less focused place searching behavior. Moreover, P38 had an anxiogenic effect as measured by the distribution of swimming at the periphery of the pool. The swimming test resulted in a decrease in BDNF contents in the hippocampus. P38 but not P38-alg treatment restored BDNF expression. In terms of oxidative stress, both P38 and P38-alg treatments had antioxidative effects. The activity of antioxidative enzymes in the neocortex was increased. However only P38 reduced the levels of carbonylated proteins (CP). These data show that P38 and P38-alg have different behavioral and neurobiological effects. Thus, P38-alg and other analogs with specific functional profiles, inducing beneficial central effects (e.g. neuroprotection) while minimizing undesired peripheral effects may be useful for potential therapeutical use.

Amnesiac Is Required in the Adult Mushroom Body for Memory Formation

It was proposed that the Drosophila amnesiac gene (amn) is required for consolidation of aversive memory in the dorsal paired medial (DPM) neurons, a pair of large neurons that broadly innervate the mushroom bodies (MB), the fly center for olfactory learning and memory (Waddell et al., 2000). Yet, a conditional analysis showed that it was not possible to rescue the memory deficit of amn^X8 null mutant flies when amn expression was restored only in the adult (DeZazzo et al., 1999), which led the authors to suggest that amn might be involved in the development of brain structures that normally promote adult olfactory memory. To further investigate temporal and spatial requirements of Amnesiac (AMN) peptide in memory, we used RNA interference in combination with conditional drivers. Experiments were conducted either in both sexes, or in either sexes. Our data show that acute modulation of amn expression in adult DPM neurons does not impact memory. We further show that amn expression is required for normal development of DPM neurons. Detailed enhancer trap analyses suggest that amn transcription unit contains two distinct enhancers, one specific of DPM neurons, and the other specific of α/β MB neurons. This prompted us to investigate extensively the role of AMN in the adult MB. Together, our results demonstrate that amn is acutely required in adult α/β MB neurons for middle-term and long-term memory. The data thus establish that amn plays two distinct roles. Its expression is required in DPM neurons for their development, and in adult MB for olfactory memory.SIGNIFICANCE STATEMENT The Drosophila amnesiac gene encodes a neuropeptide whose expression was proposed to be required for consolidation of aversive memory in the dorsal paired medial (DPM) neurons, a pair of large neurons that broadly innervate the mushroom bodies (MB), the olfactory memory center. Here, we investigated amnesiac temporal and spatial requirement using conditional tools that allowed us to manipulate its expression in selected neurons. This work leads to a complete reassessment of the role of amnesiac in brain development and memory. We show that amnesiac is required for two distinct processes: for normal development of DPM neurons, and in adult MB for memory.

Signalling Alterations in Bones of Pituitary Adenylate Cyclase Activating Polypeptide (PACAP) Gene Deficient Mice

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide with diverse developmental roles, including differentiation of skeletal elements. It is a positive regulatory factor of chondrogenesis and osteogenic differentiation in vitro, but little is known about its in vivo role in bone formation. In our experiments, diaphyses of long bones from hind limbs of PACAP gene-deficient mice showed changes in thickness and increased staining intensity. Our main goal was to perform a detailed morphological and molecular biological analysis of femurs from PACAP knockout (KO) and wild type (WT) mice. Transverse diameter and anterior cortical bone thickness of KO femurs showed significant alterations with disturbed Ca²⁺ accumulation and collagen type I expression. Higher expression and activity of alkaline phosphatase were also observed, accompanied by increased fragility PACAP KO femurs. Increased expression of the elements of bone morphogenic protein (BMP) and hedgehog signalling was also observed, and are possibly responsible for the compensation mechanism accounting for the slight morphological changes. In summary, our results show that lack of PACAP influences molecular and biomechanical properties of bone matrix, activating various signalling cascade changes in a compensatory fashion. The increased fragility of PACAP KO femur further supports the role of endogenous PACAP in in vivo bone formation.

Altered Notch Signaling in Developing Molar Teeth of Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP)-Deficient Mice

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide with neuroprotective and neurotrophic effects. This suggests its influence on the development of teeth, which are, similarly to the nervous system, ectoderm and neural crest derivatives. Our earlier studies have shown morphological differences between wild-type (WT) and PACAP-deficient mice, with upregulated sonic hedgehog (SHH) signaling in the lack of PACAP. Notch signaling is a key element of proper tooth development by regulating apoptosis and cell proliferation. In this study, our main goal was to evaluate the possible effects of PACAP on Notch signaling pathway. Immunohistochemical staining was performed of Notch receptors (Notch1, 2, 3, 4), their ligands [delta-like protein (DLL)1, 3, 4, Jagged1, 2], and intracellular target molecules [CSL (CBF1 humans/Su (H) Drosophila/LAG1 Caenorhabditis elegans transcription factor); TACE (TNF-α converting enzyme), NUMB] in molar teeth of 5-day-old WT, and homozygous and heterozygous PACAP-deficient mice. We measured immunopositivity in the enamel-producing ameloblasts and dentin-producing odontoblasts. Notch2 receptor and DLL1 expression were elevated in ameloblasts of PACAP-deficient mice compared to those in WT ones. The expression of CSL showed similar results both in the ameloblasts and odontoblasts. Jagged1 ligand expression was elevated in the odontoblasts of homozygous PACAP-deficient mice compared to WT mice. Other Notch pathway elements did not show significant differences between the genotype groups. The lack of PACAP leads to upregulation of Notch pathway elements in the odontoblast and ameloblast cells. The underlying molecular mechanisms are yet to be elucidated; however, we propose SHH-dependent and independent processes. We hypothesize that this compensatory upregulation of Notch signaling by the lack of PACAP could represent a salvage pathway in PACAP-deficient animals.

PACAP38 and PAC1 receptor blockade: a new target for headache?

Pituitary adenylate cyclase activating polypeptide-38 (PACAP38) is a widely distributed neuropeptide involved in neuroprotection, neurodevelopment, nociception and inflammation. Moreover, PACAP38 is a potent inducer of migraine-like attacks, but the mechanism behind this has not been fully elucidated.

Migraine is a neurovascular disorder, recognized as the second most disabling disease. Nevertheless, the antibodies targeting calcitonin gene-related peptide (CGRP) or its receptor are the only prophylactic treatment developed specifically for migraine. These antibodies have displayed positive results in clinical trials, but are not effective for all patients; therefore, new pharmacological targets need to be identified.

Due to the ability of PACAP38 to induce migraine-like attacks, its location in structures previously associated with migraine pathophysiology and the 100-fold selectivity for the PAC₁ receptor when compared to VIP, new attention has been drawn to this pathway and its potential role as a novel target for migraine treatment. In accordance with this, antibodies against PACAP38 (ALD 1910) and PAC₁ receptor (AMG 301) are being developed, with AMG 301 already in Phase II clinical trials. No results have been published so far, but in preclinical studies, AMG 301 has shown responses comparable to those observed with triptans. If these antibodies prove to be effective for the treatment of migraine, several considerations should be addressed, for instance, the potential side effects of long-term blockade of the PACAP (receptor) pathway. Moreover, it is important to investigate whether these antibodies will indeed represent a therapeutic advantage for the patients that do not respond the CGRP (receptor)-antibodies.

In conclusion, the data presented in this review indicate that PACAP38 and PAC₁ receptor blockade are promising antimigraine therapies, but results from clinical trials are needed in order to confirm their efficacy and side effect profile.

PAC1 Receptors: Shapeshifters in Motion

Shapeshifters, in common mythology, are entities that can undergo multiple physical transformations. As our understanding of G protein-coupled receptors (GPCRs) has accelerated and been refined over the last two decades, we now understand that GPCRs are not static proteins, but rather dynamic structures capable of moving from one posture to the next, and adopting unique functional characteristics at each transition. This model of GPCR dynamics underlies our current understanding of biased agonism-how different ligands to the same receptor can generate different intracellular signals-and constitutive receptor activity, or the level of unbound basal receptor signaling that can be attenuated by inverse agonists. From information derived from related class B receptors, we have recently modeled the structure and molecular dynamics of the full-length pituitary adenylate cyclase activating polypeptide (PACAP, Adcyap1)-selective PAC1 receptor (PAC1R, Adcyap1r1). The class B receptors are different from the class A GPCRs in part from the presence of a large extracellular domain (ECD); the transitions of the ECD along with the dynamics of the transmembrane domains (TMD or 7TM) of the PAC1R describes a series of open- and closed-state conformations that appear to identify the mechanisms for receptor activation. The PAC1R shapeshifts also have the ability of delineating the mechanisms and the design of reagents that may direct biased agonism (or antagonism) for potential therapeutics.

Pituitary Adenylate Cyclase-Activating Peptide (PACAP) Signaling and the Dark Side of Addiction

While addiction to drugs of abuse represents a significant health problem worldwide, the behavioral and neural mechanisms that underlie addiction and relapse are largely unclear. The concept of the dark side of addiction, developed and explored by George Koob and colleagues, describes a systematic decrease in reward-related processing following drug self-administration and subsequent recruitment of anti-reward (i.e., stress) systems. Indeed, the activation of central nervous system (CNS) stress-response systems by drugs of abuse is contributory not only to mood and anxiety-related disorders but critical to both the maintenance of addiction and relapse following abstinence. In both human and animal studies, compounds that activate the bed nucleus of the stria terminalis (BNST) have roles in stress-related behaviors and addiction processes. The activation of pituitary adenylate cyclase-activating peptide (PACAP) systems in the BNST mediates many consequences of chronic stressor exposure that may engage in part downstream corticotropin-releasing hormone (CRH) signaling. Similar to footshock stress, the BNST administration of PACAP or the PAC1 receptor-specific agonist maxadilan can facilitate relapse following extinction of cocaine-seeking behavior. Further, in the same paradigm, the footshock-induced relapse could be attenuated following BNST pretreatment with PAC1 receptor antagonist PACAP6-38, implicating PACAP systems as critical components underlying stress-induced reinstatement. In congruence with previous work, the PAC1 receptor internalization and endosomal MEK/ERK signaling appear contributory mechanisms to the addiction processes. The studies offer new insights and approaches to addiction and relapse therapeutics.

Pituitary Adenylate Cyclase-Activating Polypeptide-27 (PACAP-27) in the Thalamic Paraventricular Nucleus Is Stimulated by Ethanol Drinking

BACKGROUND

The paraventricular nucleus of the thalamus (PVT) is a limbic brain structure that affects ethanol (EtOH) drinking, but the neurochemicals transcribed in this nucleus that may participate in this behavior have yet to be fully characterized. The neuropeptide, pituitary adenylate cyclase-activating polypeptide (PACAP), is known to be transcribed in other limbic areas and to be involved in many of the same behaviors as the PVT itself, possibly including EtOH drinking. It exists in 2 isoforms, PACAP-38 and PACAP-27, with the former expressed at higher levels in most brain regions. The purpose of this study was to characterize PACAP in the PVT and to assess its response to EtOH drinking.

METHODS

First, EtOH-naïve, Sprague Dawley rats were examined using quantitative real-time polymerase chain reaction (qPCR) and immunohistochemistry, to characterize PACAP mRNA and peptide throughout the rostrocaudal axis of the PVT. Next, EtOH-naïve, vGLUT2-GFP transgenic mice were examined using immunohistochemistry, to identify the neurochemical phenotype of the PACAPergic cells in the PVT. Finally, Long Evans rats were trained to drink 20% EtOH under the intermittent-access paradigm and then examined with PCR and immunohistochemistry, to determine the effects of EtOH on endogenous PACAP in the PVT.

RESULTS

Gene expression of PACAP was detected across the entire PVT, denser in the posterior than the anterior portion of this nucleus. The protein isoform, PACAP-27, was present in a high percentage of cell bodies in the PVT, again particularly in the posterior portion, while PACAP-38 was instead dense in fibers. All PACAP-27⁺ cells colabeled with glutamate, which itself was identified in the majority of PVT cells. EtOH drinking led to an increase in PACAP gene expression and in levels of PACAP-27 in individual cells of the PVT.

CONCLUSIONS

This study characterizes the PVT neuropeptide, PACAP, and its understudied protein isoform, PACAP-27, and demonstrates that it is involved in pharmacologically relevant EtOH drinking. This indicates that PACAP-27 should be further investigated for its possible role in EtOH drinking.

Pituitary adenylate cyclase-activating polypeptide ameliorates vascular dysfunction induced by hyperglycaemia

BACKGROUND

Short-lasting hyperglycaemia occurs frequently in prediabetes and poorly controlled diabetes mellitus leading to vascular damage. Pituitary adenylate cyclase-activating polypeptide (PACAP) has been shown to play a protective role in vascular complications of diabetes; moreover, antioxidant effects of PACAP were also described. Therefore, we hypothesized that PACAP exerts protective effects in short-term hyperglycaemia-induced vascular dysfunctions.

METHODS

After short-term hyperglycaemia, acetylcholine-induced and sodium nitroprusside-induced vascular relaxation of mouse carotid arteries were tested with a myograph with or without the presence of PACAP or superoxide dismutase. Potential direct antioxidant superoxide-scavenging action of pituitary adenylate cyclase-activating peptide was tested with pyrogallol autoxidation assay; furthermore, the effect of pituitary adenylate cyclase-activating peptide or superoxide dismutase was investigated on hyperglycaemia-associated vascular markers.

RESULTS

PACAP administration resulted in reduced endothelial dysfunction after a 1-h hyperglycaemic episode. PACAP was able to restore acetylcholine-induced relaxation of the vessels and improved sodium nitroprusside-induced relaxation. This effect was comparable to the protective effect of superoxide dismutase, but PACAP was unable to directly scavenge superoxide produced by autoxidation of pyrogallol. Endothelial dysfunction was associated with elevated levels of fibroblast growth factor basic, matrix metalloproteinase 9 and nephroblastoma overexpressed gene proteins. Their release was reduced by PACAP administration.

CONCLUSION

These results suggest a strong protective role of PACAP in the vascular complications of diabetes.

Role of pituitary adenylate cyclase-activating polypeptide in modulating hypothalamic-pituitary system

BACKGROUND

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a multifunctional peptide that is isolated and identified from the ovine hypothalamus, whose effects and mechanisms have been elucidated in numerous studies. The PACAP and its receptor are widely expressed, not only in the hypothalamus but also in peripheral organs.

METHODS

The studies on the role of PACAP in the hypothalamic-pituitary system, including those by the authors, were summarized.

RESULTS

In the pituitary gonadotrophs, PACAP increases the gonadotrophin α-, luteinizing hormoneβ-, and follicle-stimulating hormone β-subunit expression and the expression of gonadotropin-releasing hormone (GnRH) receptor and its own receptor, PAC1R. Moreover, a low-frequency GnRH pulse increases the expression of PACAP and PAC1R more than a high-frequency GnRH pulse in the gonadotrophs. The PACAP stimulates prolactin synthesis and secretion and increases PAC1R in the lactotrophs. In the hypothalamus, PACAP increases the expression of the GnRH receptors, although it is unable to increase the expression of GnRH in the GnRH-producing neurons.

CONCLUSION

The PACAP not only acts directly in each hormone-producing cell, it possibly might regulate hormone synthesis via the expression of its own receptors or those of other hormones.

Effects of PACAP on Dry Eye Symptoms, and Possible Use for Therapeutic Application

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a 27- or 38-amino acid neuropeptide, which belongs to the vasoactive intestinal polypeptide/glucagon/secretin family of peptides. PACAP and its three receptor subtypes are expressed in neural tissues and in the eye, including the retina, cornea, and lacrimal gland. PACAP is known to exert pleiotropic effects on the central nervous system and in eye tissues where it plays important roles in protecting against dry eye. This review provides an overview of current knowledge regarding dry eye symptoms in aged animals and humans and the protective effects, mechanisms of action. In addition, we also refer to the development of a new preventive/therapeutic method by PACAP of dry eye patients.

Signaling pathways activated by PACAP in MCF-7 breast cancer cells

PACAP has opposing roles ranging from activation to inhibition of tumor growth and PACAP agonists/antagonists could be used in tumor therapy. In this study, the effect of PACAP stimulation on signaling pathways was investigated in MCF-7 human adenocarcinoma breast cancer cells. Results showed that MCF-7 cells express VPAC1 and VPAC2, but not PAC1, receptors. In addition, PACAP increased the phosphorylation levels of STAT1, Src and Raf within seconds, confirming their involvement in early stages of PACAP signaling whereas maximal phosphorylation of AKT, ERK and p38 was reached 10 to 20 min later. Moreover, selective inhibition of Src or PI3K resulted in a significant decrease in the phosphorylation of ERK and AKT, but not p38, demonstrating that PACAP signaling follows Src/Raf/ERK and PI3K/AKT pathways. On the other hand, selective inhibition of PLC or PKA resulted in a significant decrease in the phosphorylation of p38, but not AKT or ERK, indicating that PACAP signaling also follows the PLC and PKA/cAMP pathways. Furthermore, PACAP induced ROS through H₂O₂ production whereas pretreatment with NAC inhibitor decreased AKT and ERK phosphorylation, but not p38. Selective NOX2 inhibition affected Src/Raf/Erk and PI3K/Akt pathways, without affecting the p38/PLC/PKA pathway whereas other inhibitors (ML171, VAS2870) had no effect on PACAP induced ROS generation. On the other hand, PACAP induced calcium release, which was decreased by pretreatment with PLC inhibitor. Finally, PACAP stimulation promoted apoptosis by increasing Bax and decreasing Bcl2 expression. In conclusion, we demonstrated that PACAP signaling in MCF-7 cells follows the Src/Raf/ERK and PI3K/AKT pathways and is VPAC1 dependent in a ROS dependent manner, whereas it follows PLC and PKA/cAMP pathways and is VPAC2 dependent through p38 MAP kinase activation involving calcium.

Interaction between kisspeptin and adenylate cyclase-activating polypeptide 1 on the expression of pituitary gonadotropin subunits: a study using mouse pituitary lbetaT2 cells

We examined direct effect of kisspeptin on pituitary gonadotrophs. Kisspeptin-10 (KP10) significantly increased the promoter activities of the gonadotropin subunits, common alpha-glycoprotein (Cga), luteinizing hormone beta (Lhb), and follicle-stimulatinghormone beta (Fshb) in LbetaT2 cells overexpressing kisspeptin receptor (Kiss1r). KP10 and gonadotropin-releasing hormone (GnRH) increased gonadotropin subunit levels to similar degrees and combined treatment with GnRH and KP10 did not potentiate their individual effects. Adenylate cyclase-activating polypeptide 1 (ADCYAP1) also stimulates all three gonadotropin subunits. When cells were stimulated with both KP10 and ADCYAP1, expression of gonadotropin subunits was further increased compared to KP10 or ADCYAP1 alone. KP10 and GnRH dramatically increased serum response element (Sre) promoter levels but only slightly increased cAMP response element (Cre) promoter levels. Combined stimulation with KP10 and GnRH further increased Sre promoter levels. In contrast, ADCYAP1 slightly increased Sre promoter expression but did not modify the effect of KP10. However, ADCYAP1 increased Cre promoter to greater levels than KP10 alone, and combined treatment with KP10 and ADCYAP1 further increased Cre promoter expression. KP10 increased the expression of ADCYAP1 type I receptor (Adcyap1r) and the basal activity of the Cga promoter was increased at a higher Adcyap1r transfection level. The KP10-induced fold increase in all three gonadotropin subunit promoters was not altered by transfection with a higher amount of Adcyap1r vector. Our findings using model cells show that distinct signaling activation by ADCYAP1 potentiates the action of KP10. We also found that KP10 increases Adcyap1r expression.

Distribution of pituitary adenylate cyclase-activating polypeptide 2 in zebrafish brain

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a multipotent neuropeptide with an amino acid sequence that is well conserved among vertebrates. In teleosts, including zebrafish, the PACAP gene (adcyap1) has been duplicated to yield adcyap1a (coding PACAP1) and adcyap1b (coding PACAP2). This study aims to determine the distribution of these PACAPs and their mRNAs in zebrafish. We generated a zebrafish PACAP2-specific antibody. Using real-time PCR, we observed that adcyap1b mRNA was primarily localized in the brain, with the highest level in the telencephalon, followed by the diencephalon. Using immunostaining of brain tissue samples, PACAP2 immunoreactivity was observed mainly in the telencephalon, hypothalamus, and cerebellum, and the immunopositive fibers formed a line to the habenula. PACAP2-immunopositive cells were observed in the ventral and dorsal regions of the telencephalon and in the hypothalamic nucleus of the diencephalon in the colchicine-injected brain. This distribution of PACAP2 suggests its involvement in higher brain functions in teleosts, such as learning and cognition, as well as instinctive behaviors such as feeding and emotional regulation.

Chronic changes in pituitary adenylate cyclase-activating polypeptide and related receptors in response to repeated chemical dural stimulation in rats

Background

Preclinical experimental studies revealed an acute alteration of pituitary adenylate cyclase-activating polypeptide in response to a single activation of the trigeminovascular system, which suggests a potential role of pituitary adenylate cyclase-activating polypeptide in the pathogenesis of migraine. However, changes in pituitary adenylate cyclase-activating polypeptide after repeated migraine-like attacks in chronic migraine are not clear. Therefore, the present study investigated chronic changes in pituitary adenylate cyclase-activating polypeptide and related receptors in response to repeated chemical dural stimulations in the rat.

Methods

A rat model of chronic migraine was established by repeated chemical dural stimulations using an inflammatory soup for a different numbers of days. The pituitary adenylate cyclase-activating polypeptide levels were quantified in plasma, the trigeminal ganglia, and the trigeminal nucleus caudalis using radioimmunoassay and Western blotting in trigeminal ganglia and trigeminal nucleus caudalis tissues. Western blot analysis and real-time polymerase chain reaction were used to measure the protein and mRNA expression of pituitary adenylate cyclase-activating polypeptide-related receptors (PAC1, VPAC1, and VPAC2) in the trigeminal ganglia and trigeminal nucleus caudalis to identify changes associated with repetitive applications of chemical dural stimulations.

Results

All rats exhibited significantly decreased periorbital nociceptive thresholds to repeated inflammatory soup stimulations. Radioimmunoassay and Western blot analysis demonstrated significantly decreased pituitary adenylate cyclase-activating polypeptide levels in plasma and trigeminal ganglia after repetitive chronic inflammatory soup stimulation. Protein and mRNA analyses of pituitary adenylate cyclase-activating polypeptide-related receptors demonstrated significantly increased PAC1 receptor protein and mRNA expression in the trigeminal ganglia, but not in the trigeminal nucleus caudalis, and no significant differences were found in the expression of the VPAC1 and VPAC2 receptors.

Conclusions

This study demonstrated the chronic alteration of pituitary adenylate cyclase-activating polypeptide and related receptors in response to repeated chemical dural stimulation in the rat, which suggests the crucial involvement of pituitary adenylate cyclase-activating polypeptide in the development of migraine. The selective increase in pituitary adenylate cyclase-activating polypeptide-related receptors suggests that the PAC1 receptor pathway is a novel target for the treatment of migraine.

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.

Intracellular cAMP Sensor EPAC: Physiology, Pathophysiology, and Therapeutics Development

This review focuses on one family of the known cAMP receptors, the exchange proteins directly activated by cAMP (EPACs), also known as the cAMP-regulated guanine nucleotide exchange factors (cAMP-GEFs). Although EPAC proteins are fairly new additions to the growing list of cAMP effectors, and relatively "young" in the cAMP discovery timeline, the significance of an EPAC presence in different cell systems is extraordinary. The study of EPACs has considerably expanded the diversity and adaptive nature of cAMP signaling associated with numerous physiological and pathophysiological responses. This review comprehensively covers EPAC protein functions at the molecular, cellular, physiological, and pathophysiological levels; and in turn, the applications of employing EPAC-based biosensors as detection tools for dissecting cAMP signaling and the implications for targeting EPAC proteins for therapeutic development are also discussed.

Targeted Orexin and Hypothalamic Neuropeptides for Migraine

The hypothalamus is involved in the regulation of homeostatic mechanisms and migraine-related trigeminal nociception and as such has been hypothesized to play a central role in the migraine syndrome from the earliest stages of the attack. The hypothalamus hosts many key neuropeptide systems that have been postulated to play a role in this pathophysiology. Such neuropeptides include but are not exclusive too orexins, oxytocin, neuropeptide Y, and pituitary adenylate cyclase activating protein, which will be the focus of this review. Each of these peptides has its own unique physiological role and as such many preclinical studies have been conducted targeting these peptide systems with evidence supporting their role in migraine pathophysiology. Preclinical studies have also begun to explore potential therapeutic compounds targeting these systems with some success in all cases. Clinical efficacy of dual orexin receptor antagonists and intranasal oxytocin have been tested; however, both have yet to demonstrate clinical effect. Despite this, there were limitations in these cases and strong arguments can be made for the further development of intranasal oxytocin for migraine prophylaxis. Regarding neuropeptide Y, work has yet to begun in a clinical setting, and clinical trials for pituitary adenylate cyclase activating protein are just beginning to be established with much optimism. Regardless, it is becoming increasingly clear the prominent role that the hypothalamus and its peptide systems have in migraine pathophysiology. Much work is required to better understand this system and the early stages of the attack to develop more targeted and effective therapies aimed at reducing attack susceptibility with the potential to prevent the attack all together.

Therapeutic Approaches for the Management of Trigeminal Autonomic Cephalalgias

Trigeminal autonomic cephalalgia (TAC) encompasses 4 unique primary headache types: cluster headache, paroxysmal hemicrania, hemicrania continua, and short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing and short-lasting unilateral neuralgiform headache attacks with cranial autonomic symptoms. They are grouped on the basis of their shared clinical features of unilateral headache of varying durations and ipsilateral cranial autonomic symptoms. The shared clinical features reflect the underlying activation of the trigeminal-autonomic reflex. The treatment for TACs has been limited and not specific to the underlying pathogenesis. There is a proportion of patients who are refractory or intolerant to the current standard medical treatment. From instrumental bench work research and neuroimaging studies, there are new therapeutic targets identified in TACs. Treatment has become more targeted and aimed towards the pathogenesis of the conditions. The therapeutic targets range from the macroscopic and structural level down to the molecular and receptor level. The structural targets for surgical and noninvasive neuromodulation include central neuromodulation targets: posterior hypothalamus and, high cervical nerves, and peripheral neuromodulation targets: occipital nerves, sphenopalatine ganglion, and vagus nerve. In this review, we will also discuss the neuropeptide and molecular targets, in particular, calcitonin gene-related peptide, somatostatin, transient receptor potential vanilloid-1 receptor, nitric oxide, melatonin, orexin, pituitary adenylate cyclase-activating polypeptide, and glutamate.

In Silico Screening Identified Novel Small-molecule Antagonists of PAC1 Receptor

Pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptors are present in the spinal dorsal horn and dorsal root ganglia, suggesting an important role of PACAP signaling systems in the modulation of spinal nociceptive transmission. Previously, we found that intrathecal injection of PACAP or maxadilan, a selective PACAP type I (PAC1) receptor agonist, induced transient aversive responses followed by a long-lasting mechanical allodynia in mice, suggesting that PACAP-PAC1 receptor systems are involved in chronic pain and that selective PAC1 antagonists may become a new class of analgesics. Although several PAC1 antagonists, such as PACAP 6-38, have been reported, all of them are peptide compounds. In the present study, we identified new small-molecule antagonists of the PAC1 receptor using in silico screening and in vitro/vivo pharmacological assays. The identified small-molecule compounds, named PA-8 and PA-9, dose dependently inhibited the phosphorylation of CREB induced by PACAP in PAC1-, but not VPAC1- or VPAC2-receptor-expressing CHO cells. PA-8 and PA-9 also dose dependently inhibited PACAP-induced cAMP elevation with an IC50 of 2.0 and 5.6 nM, respectively. In vivo pharmacological assays showed that intrathecal injection of these compounds blocked the induction of PACAP-induced aversive responses and mechanical allodynia in mice. In contrast, the compounds when administered alone exerted neither agonistic nor algesic actions in the in vitro/vivo assays. The compounds identified in the present study are new and the first small-molecule antagonists of the PAC1 receptor; they may become seed compounds for developing novel analgesics.

PACAP and its role in primary headaches

Pituitary adenylate cyclase-activating peptide (PACAP) is a neuropeptide implicated in a wide range of functions, such as nociception and in primary headaches. Regarding its localization, PACAP has been observed in the sensory trigeminal ganglion (TG), in the parasympathetic sphenopalatine (SPG) and otic ganglia (OTG), and in the brainstem trigeminocervical complex. Immunohistochemistry has shown PACAP-38 in numerous cell bodies of SPG/OTG, co-stored with vasoactive intestinal peptide (VIP), nitric oxide synthase (NOS) and, to a minor degree, with choline acetyltransferase. PACAP has in addition been found in a subpopulation of calcitonin gene-related peptide (CGRP)-immunoreactive cells in the trigeminal system. The PACAP/VIP receptors (PAC₁, VPAC₁, and VPAC₂) are present in sensory neurons and in vascular smooth muscle related to the trigeminovascular system. It is postulated that PACAP is involved in nociception. In support, abolishment of PACAP synthesis or reception leads to diminished pain responses, whereas systemic PACAP-38 infusion triggers pain behavior in animals and delayed migraine-like attacks in migraine patients without marked vasodilatory effects. In addition, increased plasma levels have been documented in acute migraine attacks and in cluster headache, in accordance with findings in experimental models of trigeminal activation. This suggest that the activation of the trigeminal system may result in elevated venous levels of PACAP, a change that can be reduced when headache is treated. The data presented in this review indicate that PACAP and its receptors may be promising targets for migraine therapeutics.