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

Signaling pathways and promoter regions that mediate pituitary adenylate cyclase activating polypeptide (PACAP) self-regulation in gonadotrophs

Pituitary adenylate cyclase-activating polypeptide (PACAP) is thought to play a role in the development and regulation of gonadotrophs. PACAP levels are very high in the rodent fetal pituitary, and decline substantially and rapidly at birth, followed by a significant rise in FSHβ and GnRH-R expression. Because there is evidence that PACAP stimulates its own transcription, we propose that this self-regulation is interrupted around the time of birth. To begin to examine the mechanisms for PACAP self-regulation, we used two well-established gonadotroph cell lines, αT3-1 cells and the more mature LβT2 cells which were transfected with a PACAP promoter-reporter construct As in vivo, the basal PACAP transcription level is significantly lower in the more mature LβT2 cells in which basal cAMP signaling is also much reduced. The PACAP promoter was stimulated by PACAP in both cell lines. Treatment with inhibitors of second messenger pathways implicated PKA, PKC and MAPK in PACAP transcription. Three regions of the PACAP promoter were found to confer inhibition or stimulation of PACAP transcription. By inhibiting cAMP response element binding (CREB) activity and mutating a proximal CREB binding site, we found that CREB is essential for promoter activation. Finally, overexpression of PACAP receptor HOP1 isoform, to increase the level in LβT2 cells to that of αT3-1 cells and simulate the E19 pituitary, increased PACAP- stimulated sensitivity and significantly altered downstream gene transcription. These results provide novel insight into the feed-forward regulation of PACAP expression that may help initiate gonadotroph function at birth.

PAC1 receptor blockade reduces central nociceptive activity: new approach for primary headache?

Pituitary adenylate cyclase activating polypeptide-38 (PACAP38) may play an important role in primary headaches. Preclinical evidence suggests that PACAP38 modulates trigeminal nociceptive activity mainly through PAC1 receptors while clinical studies report that plasma concentrations of PACAP38 are elevated in spontaneous attacks of cluster headache and migraine and normalize after treatment with sumatriptan. Intravenous infusion of PACAP38 induces migraine-like attacks in migraineurs and cluster-like attacks in cluster headache patients. A rodent-specific PAC1 receptor antibody Ab181 was developed, and its effect on nociceptive neuronal activity in the trigeminocervical complex was investigated in vivo in an electrophysiological model relevant to primary headaches. Ab181 is potent and selective at the rat PAC1 receptor and provides near-maximum target coverage at 10 mg/kg for more than 48 hours. Without affecting spontaneous neuronal activity, Ab181 effectively inhibits stimulus-evoked activity in the trigeminocervical complex. Immunohistochemical analysis revealed its binding in the trigeminal ganglion and sphenopalatine ganglion but not within the central nervous system suggesting a peripheral site of action. The pharmacological approach using a specific PAC1 receptor antibody could provide a novel mechanism with a potential clinical efficacy in the treatment of primary headaches.

Current knowledge of pituitary adenylate cyclase activating polypeptide (PACAP) in articular cartilage

Pituitary adenylate cyclase activating polypeptide (PACAP) is an evolutionally well conserved neuropeptide, mainly expressed by neuronal and peripheral cells. It proves to be an interesting object of study both for its trophic functions during the development of several tissues and for its protective effects against oxidative stress, hypoxia, inflammation and apoptosis in different degenerative diseases. This brief review summarises the recent findings concerning the role of PACAP in the articular cartilage. PACAP and its receptors are expressed during chondrogenesis and are shown to activate the pathways involved in regulating cartilage development. Moreover, this neuropeptide proves to be chondroprotective against those stressors that determine cartilage degeneration and contribute to the onset of osteoarthritis (OA), the most common form of degenerative joint disease. Indeed, the degenerated cartilage exhibits low levels of PACAP, suggesting that its endogenous levels in adult cartilage may play an essential role in maintaining physiological properties. Thanks to its peculiar characteristics, exogenous administration of PACAP could be suggested as a potential tool to slow down the progression of OA and for cartilage regeneration approaches.

VIP Modulation of Hippocampal Synaptic Plasticity: A Role for VIP Receptors as Therapeutic Targets in Cognitive Decline and Mesial Temporal Lobe Epilepsy

Vasoactive intestinal peptide (VIP) is an important modulatory peptide throughout the CNS acting as a neurotransmitter, neurotrophic or neuroprotective factor. In the hippocampus, a brain area implicated in learning and memory processes, VIP has a crucial role in the control of GABAergic transmission and pyramidal cell activity in response to specific network activity by either VIP-containing basket cells or interneuron-selective (IS) interneurons and this appears to have a differential impact in hippocampal-dependent cognition. At the cellular level, VIP regulates synaptic transmission by either promoting disinhibition, through activation of VPAC₁ receptors, or enhancing pyramidal cell excitability, through activation of VPAC₂ receptors. These actions also control several important synaptic plasticity phenomena such as long-term potentiation (LTP) and long-term depression (LTD). This paper reviews the current knowledge on the activation and multiple functions of VIP expressing cells in the hippocampus and their role in controlling synaptic transmission, synaptic plasticity and learning and memory processes, discussing also the role of VPAC₁ and VPAC₂ VIP receptors in the regulation of these different processes. Furthermore, we address the current knowledge regarding changes in VIP mediated neurotransmission in epileptogenesis and mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS), and discuss the therapeutic opportunities of using selective VIP receptor ligands to prevent epileptogenesis and cognitive decline in MTLE-HS.

Tracing the Origins of the Pituitary Adenylate-Cyclase Activating Polypeptide (PACAP)

Pituitary adenylate cyclase activating polypeptide (PACAP) is a well-conserved neuropeptide characteristic of vertebrates. This pluripotent hypothalamic neuropeptide regulates neurotransmitter release, intestinal motility, metabolism, cell division/differentiation, and immunity. In vertebrates, PACAP has a specific receptor (PAC₁) but it can also activate the Vasoactive Intestinal Peptide receptors (VPAC₁ and VPAC₂). The evolution of the vertebrate PACAP ligand - receptor pair has been well-described. In contrast, the situation in invertebrates is much less clear. The PACAP ligand - receptor pair in invertebrates has mainly been studied using heterologous antibodies raised against mammalian peptides. A few partial PACAP cDNA clones sharing >87% aa identity with vertebrate PACAP have been isolated from a cnidarian, several protostomes and tunicates but no gene has been reported. Moreover, current evolutionary models of the peptide and receptors using molecular data from phylogenetically distinct invertebrate species (mostly nematodes and arthropods) suggests the PACAP ligand and receptors are exclusive to vertebrate genomes. A basal deuterostome, the cephalochordate amphioxus (Branchiostoma floridae), is the only invertebrate in which elements of a PACAP-like system exists but the peptides and receptor share relatively low sequence conservation with the vertebrate homolog system and are a hybrid with the vertebrate glucagon system. In this study, the evolution of the PACAP system is revisited taking advantage of the burgeoning sequence data (genome and transcriptomes) available for invertebrates to uncover clues about when it first appeared. The results suggest that elements of the PACAP system are absent from protozoans, non-bilaterians, and protostomes and they only emerged after the protostome-deuterostome divergence. PACAP and its receptors appeared in vertebrate genomes and they probably shared a common ancestral origin with the cephalochordate PACAP/GCG-like system which after the genome tetraploidization events that preceded the vertebrate radiation generated the PACAP ligand and receptor pair and also the other members of the Secretin family peptides and their receptors.

The role of pituitary adenylyl cyclase activating polypeptide in affective signs of nicotine withdrawal

Recent evidence implicates endogenous pituitary adenylyl cyclase activating polypeptide (PACAP) in the aversive effect of nicotine. In the present study, we assessed if nicotine-induced conditioned place preference (CPP) or affective signs of nicotine withdrawal would be altered in the absence of PACAP and if there were any sex-related differences in these responses. Male and female mice lacking PACAP and their wild-type controls were tested for baseline place preference on day 1, received conditioning with saline or nicotine (1 mg/kg) on alternate days for 6 days and were then tested for CPP the next day. Mice were then exposed to four additional conditioning and were tested again for nicotine-induced CPP 24 hr later. Controls were conditioned with saline in both chambers and tested similarly. All mice were then, 96 hr later, challenged with mecamylamine (3 mg/kg), and tested for anxiety-like behaviors 30 min later. Mice were then, 2 hr later, forced to swim for 15 min and then tested for depression-like behaviors 24 hr later. Our results showed that male but not female mice lacking PACAP expressed a significant CPP that was comparable to their wild-type controls. In contrast, male but not female mice lacking PACAP exhibited reduced anxiety- and depression-like behaviors compared to their wild-type controls following the mecamylamine challenge. These results suggest that endogenous PACAP is involved in affective signs of nicotine withdrawal, but there is a sex-related difference in this response.

PAC1 deficiency attenuates progression of atherosclerosis in ApoE deficient mice under cholesterol-enriched diet

The neuropeptide, pituitary adenylate cyclase-activating polypeptide (PACAP) is vasoactive and cytoprotective and exerts immunoregulatory functions throughout the nervous, neuroendocrine cardiovascular and immune systems in health and disease. PACAP mainly acts through PAC1 receptor signaling in neuronal communication, but the role of PAC1 in immune regulation of atherosclerosis is not known. Here, we generated PAC1^-/-/ApoE^-/- mice to test, whether PAC1^-/- influences plasma cholesterol-/triglyceride levels and/or atherogenesis in the brachiocephalic trunk (BT) seen in ApoE^-/- mice, under standard chow (SC) or cholesterol-enriched diet (CED). Furthermore, the effect of PAC1^-/-, on inflammatory, autophagy-, apoptosis- and necroptosis-relevant proteins in atherosclerotic plaques was determined. In plaques of PAC1^-/-/ApoE^-/- mice fed a SC, the immunoreactivity for apoptotic, autophagic, necroptotic and proinflammatory proteins was increased, however, proliferation was unaffected. Interestingly, without affecting hyperlipidemia, PAC1^-/- in ApoE^-/- mice remarkably reduced CED-induced lumen stenosis seen in ApoE^-/- mice. Thus, PAC1^-/- allows unchecked inflammation, necroptosis and decreased proliferation during SC, apparently priming the BT to develop reduced atheroma under subsequent CED. Remarkably, no differences in inflammation/necroptosis signatures in the atheroma under CED between PAC1^-/-/ApoE^-/- and ApoE^-/- mice were observed. These data indicate that selective PAC1 antagonists should offer potential as a novel class of atheroprotective therapeutics, especially during hypercholesterolemia.

Novelty in Inflammation and Immunomodulation in Migraine

BACKGROUND

Migraine is a diffuse and disabling disease. Its pathophysiology is complex and involves both central and peripheral dysfunctions.

OBJECTIVE

This review will discuss the pathogenesis of migraine from the origin of the neuro-inflammatory theory, to the modern pathophysiological model and the latest therapies.

METHODS

PUBMED and EMBASE (up to May 2019) were searched for: migraine, inflammation, immunomodulation. An additional search was carried out from the bibliography of previous review articles.

RESULTS

Migraine was thought to be mainly a vascular disorder, according to the so-called "vascular theory". Based on animal models, a new hypothesis called "the neuro-inflammatory" was conceived at the end of the 20th century. The growing knowledge about the trigeminovascular system and its role in the inflammatory-pain pathway, allowed to identify other specific neurotransmitters, such as the Calcitonin Gene-Related Peptide and Pituitary Adenylate Cyclase-Activating Peptide. Evidence was provided that the inflammatory-pain system could become sensitised and, due to this sensitisation, the pain could also perpetuate, even in the absence of any triggers of the migraine attack. At last, brain immune cells modification during cortical spreading depression in migraine was demonstrated, along with the existence and function of the glymphatic system. The better comprehension of the immune system abnormalities allowed the development of new immunomodulating drugs: the monoclonal antibodies against the CGRP or the CGRP receptor. Moreover, new insights into the molecular mechanism of CGRP, and the function of C-fibres and Aδ-fibres, highlighted the mechanism of action of Botulinum Toxin type A in the treatment of chronic migraine.

The role of pituitary adenylyl cyclase-activating polypeptide in the motivational effects of addictive drugs

Pituitary adenylyl cyclase activating polypeptide (PACAP) was originally isolated from the hypothalamus and found to stimulate adenylyl cyclase in the pituitary. Later studies showed that this peptide and its receptors (PAC1, VPAC1, and VPAC2) are widely expressed in the central nervous system (CNS). Consistent with its distribution in the CNS, the PACAP/PAC1 receptor system is involved in several physiological responses, such as mediation of the stress response, modulation of nociception, regulation of prolactin release, food intake, etc. This system is also implicated in different pathological states, e.g., affective component of nociceptive processing, anxiety, depression, schizophrenia, and post-traumatic stress disorders. A review of the literature on PubMed revealed that PACAP and its receptors also play a significant role in the actions of addictive drugs. The goal of this review is to discuss the literature regarding the involvements of PACAP and its receptors in the motivational effects of addictive drugs. We particularly focus on the role of this peptide in the motivational effects of morphine, alcohol, nicotine, amphetamine, methamphetamine, and cocaine. This article is part of the special issue on Neuropeptides.

Drosophila Middle-Term Memory: Amnesiac is Required for PKA Activation in the Mushroom Bodies, a Function Modulated by Neprilysin 1

In Drosophila, the mushroom bodies (MB) constitute the central brain structure for olfactory associative memory. As in mammals, the cAMP/PKA pathway plays a key role in memory formation. In the MB, Rutabaga (Rut) adenylate cyclase acts as a coincidence detector during associative conditioning to integrate calcium influx resulting from acetylcholine stimulation and G-protein activation resulting from dopaminergic stimulation. Amnesiac encodes a secreted neuropeptide required in the MB for two phases of aversive olfactory memory. Previous sequence analysis has revealed strong homology with the mammalian pituitary adenylate cyclase-activating peptide (PACAP). Here, we examined whether amnesiac is involved in cAMP/PKA dynamics in response to dopamine and acetylcholine co-stimulation in living flies. Experiments were conducted with both sexes, or with either sex. Our data show that amnesiac is necessary for the PKA activation process that results from coincidence detection in the MB. Since PACAP peptide is cleaved by the human membrane neprilysin hNEP, we searched for an interaction between Amnesiac and Neprilysin 1 (Nep1), a fly neprilysin involved in memory. We show that when Nep1 expression is acutely knocked down in adult MB, memory deficits displayed by amn hypomorphic mutants are rescued. Consistently, Nep1 inhibition also restores normal PKA activation in amn mutant flies. Taken together, the results suggest that Nep1 targets Amnesiac degradation to terminate its signaling function. Our work thus highlights a key role for Amnesiac in establishing within the MB the PKA dynamics that sustain middle-term memory (MTM) formation, a function modulated by Nep1.SIGNIFICANCE STATEMENT The Drosophila amnesiac gene encodes a secreted neuropeptide whose expression is required for specific memory phases in the mushroom bodies (MB), the olfactory memory center. Here, we show that Amnesiac is required for PKA activation resulting from coincidence detection, a mechanism by which the MB integrate two spatially distinct stimuli to encode associative memory. Furthermore, our results uncover a functional relationship between Amnesiac and Neprilysin 1 (Nep1), a membrane peptidase involved in memory and expressed in the MB. These results suggest that Nep1 modulates Amnesiac levels. We propose that on conditioning, Amnesiac release from the MB allows, via an autocrine process, the sustaining of PKA activation-mediating memory, which subsequently is inactivated by Nep1 degradation.

PACAP neuropeptide promotes Hepatocellular Protection via CREB-KLF4 dependent autophagy in mouse liver Ischemia Reperfusion Injury

Organ ischemia reperfusion injury (IRI), associated with acute hepatocyte death, remains an unresolved problem in clinical orthotopic liver transplantation (OLT). Autophagy, an intracellular self-digesting progress, is responsible for cell reprograming required to regain post-stress homeostasis.

Methods: Here, we analyzed the cytoprotective mechanism of pituitary adenylate cyclase-activating polypeptide (PACAP)-promoted hepatocellular autophagy in a clinically relevant mouse model of extended hepatic cold storage (4 °C UW solution for 20 h) followed by syngeneic OLT.

Results: In contrast to 41.7% of liver graft failure by day 7 post-transplant in control group, PACAP treatment significantly improved graft survival (91.7% by day 14), and promoted autophagy-associated regeneration programs in OLT. In parallel in vitro studies, PACAP-enhanced autophagy ameliorated cellular damage (LDH/ALT levels), and diminished necrosis in H₂O₂-stressed primary hepatocytes. Interestingly, PACAP not only induced nuclear cAMP response element-binding protein (CREB), but also triggered reprogramming factor Kruppel-like factor 4 (KLF4) expression in IR-stressed OLT. Indeed, CREB inhibition attenuated hepatic autophagy and recreated hepatocellular injury in otherwise PACAP-protected livers. Furthermore, CREB inhibition suppressed PACAP-induced KLF4 expression, whereas KLF4 blockade abolished PACAP-promoted autophagy and neutralized PACAP-mediated hepatoprotection both in vivo and in vitro.

Conclusion: Current study documents the essential neural regulation of PACAP-promoted autophagy in hepatocellular homeostasis in OLT, which provides the emerging therapeutic principle to combat hepatic IRI in OLT.

Cryo-EM structure of the human PAC1 receptor coupled to an engineered heterotrimeric G protein

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a pleiotropic neuropeptide hormone. The PACAP receptor PAC1R, which belongs to the class B G-protein-coupled receptors (GPCRs), is a drug target for mental disorders and dry eye syndrome. Here, we present a cryo-EM structure of human PAC1R bound to PACAP and an engineered G_s heterotrimer. The structure revealed that transmembrane helix TM1 plays an essential role in PACAP recognition. The extracellular domain (ECD) of PAC1R tilts by ~40° compared with that of the glucagon-like peptide-1 receptor (GLP-1R) and thus does not cover the peptide ligand. A functional analysis demonstrated that the PAC1R ECD functions as an affinity trap and is not required for receptor activation, whereas the GLP-1R ECD plays an indispensable role in receptor activation, illuminating the functional diversity of the ECDs in class B GPCRs. Our structural information will facilitate the design and improvement of better PAC1R agonists for clinical applications.

Current State of Understanding of the Role of PACAP in the Hypothalamo-Hypophyseal Gonadotropin Functions of Mammals

PACAP was discovered 30 years ago in Dr. Akira Arimura's laboratory. In the past three decades since then, it has become evident that this peptide plays numerous crucial roles in mammalian organisms. The most important functions of PACAP are the following: 1. neurotransmitter, 2. neuromodulator, 3. hypophysiotropic hormone, 4. neuroprotector. This paper reviews the accumulated data regarding the distribution of PACAP and its receptors in the mammalian hypothalamus and pituitary gland, the role of PACAP in the gonadotropin hormone secretion of females and males. The review also summarizes the interaction between PACAP, GnRH, and sex steroids as well as hypothalamic peptides including kisspeptin. The possible role of PACAP in reproductive functions through the biological clock is also discussed. Finally, the significance of PACAP in the hypothalamo-hypophysial system is considered and the facts missing, that would help better understand the function of PACAP in this system, are also highlighted.

Investigation of sumatriptan and ketorolac trometamol in the human experimental model of headache

BACKGROUND

Pituitary adenylate cyclase-activating polypeptide-38 (PACAP38) induces headache in healthy volunteers but the precise mechanisms by which PACAP38 leads to headache are unclear. We investigated the headache preventive effect of sumatriptan and ketorolac on PACAP38-induced headache in healthy volunteers. In addition, we explored contribution of vascular mechanisms to PACAP38-induced headache using high resolution magnetic resonance angiography.

METHODS

Thirty-four healthy volunteers were divided in two groups (A and B) and received infusion of PACAP38 (10 picomol/kg/min) over 20 min. Group A was pretreated with intravenous sumatriptan (4 mg) or ketorolac (30 mg) 20 min before infusion of PACAP38. Group B received infusion of sumatriptan or ketorolac as post-treatment 90 min after infusion of PACAP38. In both experiments, we used a randomized, double-blind, cross-over design. We recorded headache characteristics and circumference of extra-intracerebral arteries.

RESULTS

We found no difference in AUC _{(0-6 h)} of PACAP38-induced headache in group A, pretreated with sumatriptan or ketorolac (p = 0.297). There was no difference between sumatriptan and ketorolac in PACAP38-induced circumference change (AUC_{Baseline-110 min}) of MMA (p = 0.227), STA (p = 0.795) and MCA (p = 0.356). In group B, post-treatment with ketorolac reduced PACAP38-headache compared to sumatriptan (p < 0.001). Post-treatment with sumatriptan significantly reduced the circumference of STA (p = 0.039) and MMA (p = 0.015) but not of MCA (p = 0.981) compared to ketorolac. In an explorative analysis, we found that pre-treatment with sumatriptan reduced PACAP38-induced headache compared to no treatment (AUC_0-90min).

CONCLUSIONS

Post-treatment with ketorolac was more effective in attenuating PACAP38-induced headache compared to sumatriptan. Ketorolac exerted its effect without affecting PACAP38-induced arterial dilation, whereas sumatriptan post-treatment attenuated PACAP38-induced dilation of MMA and STA. Pre-treatment with sumatriptan attenuated PACAP38-induced headache without affecting PACAP38-induced arterial dilation. Our findings suggest that ketorolac and sumatriptan attenuated PACAP38-induced headache in healthy volunteers without vascular effects.

TRIAL REGISTRATION

Clinicaltrials.gov (NCT03585894). Registered 13 July 2018.

Cryo-EM structures of PAC1 receptor reveal ligand binding mechanism

The pituitary adenylate cyclase-activating polypeptide type I receptor (PAC1R) belongs to the secretin receptor family and is widely distributed in the central neural system and peripheral organs. Abnormal activation of the receptor mediates trigeminovascular activation and sensitization, which is highly related to migraine, making PAC1R a potential therapeutic target. Elucidation of PAC1R activation mechanism would benefit discovery of therapeutic drugs for neuronal disorders. PAC1R activity is governed by pituitary adenylate cyclase-activating polypeptide (PACAP), known as a major vasodilator neuropeptide, and maxadilan, a native peptide from the sand fly, which is also capable of activating the receptor with similar potency. These peptide ligands have divergent sequences yet initiate convergent PAC1R activity. It is of interest to understand the mechanism of PAC1R ligand recognition and receptor activity regulation through structural biology. Here we report two near-atomic resolution cryo-EM structures of PAC1R activated by PACAP38 or maxadilan, providing structural insights into two distinct ligand binding modes. The structures illustrate flexibility of the extracellular domain (ECD) for ligands with distinct conformations, where ECD accommodates ligands in different orientations while extracellular loop 1 (ECL1) protrudes to further anchor the ligand bound in the orthosteric site. By structure-guided molecular modeling and mutagenesis, we tested residues in the ligand-binding pockets and identified clusters of residues that are critical for receptor activity. The structures reported here for the first time elucidate the mechanism of specificity and flexibility of ligand recognition and binding for PAC1R, and provide insights toward the design of therapeutic molecules targeting PAC1R.

Hypothalamic- and pituitary-derived growth and reproductive hormones and the control of energy balance in fish

Most endocrine systems in the body are influenced by the hypothalamic-pituitary axis. Within this axis, the hypothalamus delivers precise signals to the pituitary gland, which in turn releases hormones that directly affect target tissues including the liver, thyroid gland, adrenal glands and gonads. This action modulates the release of additional hormones from the sites of action, regulating key physiological processes, including growth, metabolism, stress and reproduction. Pituitary hormones are released by five distinct hormone-producing cell types: somatotropes (which produce growth hormone), thyrotropes (thyrotropin), corticotropes (adrenocorticotropin), lactotropes (prolactin) and gonadotropes (follicle stimulating hormone and luteinizing hormone), each modulated by specific hypothalamic signals. This careful and distinct organization of the hypothalamo-pituitary axis has been classically associated with the existence of many lineal axes (e.g., the hypothalamic-pituitary-gonadal axis) in charge of the control of the different physiological processes. While this traditional concept is valid, it is becoming apparent that hormones produced by the hypothalamo-pituitary axis have diverse effects. For instance, gonadotropin-releasing hormone II has been associated with a suppressive effect on food intake in fish. Likewise, growth hormone has been shown to influence appetite, swimming activity and aggressive behavior in fish. This review will focus on the hypothalamic and pituitary hormones classically involved in regulating growth and reproduction, and will attempt to provide a general overview of the current knowledge on their actions on energy balance and appetite in fish. It will also give a brief perspective of the role of some of these peptides in integrating feeding, metabolism, growth and reproduction.

The Neuroprotective and Biomarker Potential of PACAP in Human Traumatic Brain Injury

Traumatic brain injury remains a growing public health concern and represents the greatest contributor to death and disability globally among all trauma-related injuries. There are limited clinical data regarding biomarkers in the diagnosis and outcome prediction of TBI. The lack of real effective treatment for recovery calls for research of TBI to be shifted into the area of prevention, treatment of secondary brain injury and neurorehabilitation. The neuropeptide pituitary adenylate cyclase activating polypeptide (PACAP) has been reported to act as a hormone, a neuromodulator, a neurotransmitter and a trophic factor, and has been implicated in a variety of developmental and regenerative processes. The importance of PACAP in neuronal regeneration lies in the upregulation of endogenous PACAP and its receptors and the protective effect of exogenous PACAP after different central nervous system injury. The aim of this minireview is to summarize both the therapeutic and biomarker potential of the neuropeptide PACAP, as a novel possible target molecule presently being investigated in several human conditions including TBI, and with encouraging results in animal models of TBI.

Possible effects of pituitary adenylate cyclase activating polypeptide (PACAP) on early embryo implantation marker HB-EGF in mouse

Pituitary adenylate cyclase activating polypeptide (PACAP) was originally isolated as a hypothalamic neuropeptide stimulating adenylate cyclase activity. Besides its neuroprotective effects, numerous data proved its role in reproductive processes. However, there are limited data on its role in preimplantation embryo development and implantation. Our aim was to analyse the mRNA expression of Adcyap1 (coding region of PACAP) and Hbegf [coding region of HB-EGF (Heparin-binding EGF-like growth factor)] in embryos and pregnant uterus to investigate the possible correlation between them. Eight-week-old BDF1 mice were superovulated and subsequently mated overnight or left in their cage after hCG treatment. Day4 embryos were flushed from mated females. After morphological analysis, Adcyap1 and Hbegf gene expression of embryos and uterine tissues was assessed with qPCR. Our results showed significantly higher Adcyap1 and Hbegf mRNA levels in females producing embryos compared to non-mated ones. Robust elevation of Adcyap1 and slight elevation of Hbegf were detected in females with blastocyst embryos compared with non-blastocysts. We found low rate of Hbegf mRNA expression in uncompacted embryos, whereas morulae and blastocysts expressed high amounts of Hbegf. However, we did not find detectable Adcyap1 mRNA in embryos. Strong correlation was found between uterine tissue and embryonic Hbegf levels, slight correlation between uterine Adcyap1 and Hbegf levels. Uterine tissue Adcyap1 and embryonic Hbegf showed no correlation. In summary, our present data show, for the first time, the correlation between PACAP and HB-EGF mRNA expression suggesting that PACAP might play a role during the peri-implantation period of early mouse embryo development.

Pituitary adenylate cyclase-activating peptide (PACAP) and its receptors in Mus musculus testis

To enlighten the involvement of PACAP/receptors system in the control of mammal testis, we investigated the expression of PACAP and the localization of PACAP and its receptors PAC1, VPAC1, and VPAC2 in the testis of Mus musculus. By molecular and immunohistochemical investigations, we highlighted that PACAP and its receptors are widely represented in germ cells of Mus testis, particularly in spermatocytes I, spermatids, and spermatozoa, strongly suggesting their involvement in spermatogenesis process. Moreover, for the first time in the adult mouse testis we highlighted that PACAP is present within Leydig cells, as PACAP receptors, confirming its involvement in the control of steroidogenesis in mouse.

Protective Effects of PACAP in Peripheral Organs

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide widely distributed in the nervous system, where it exerts strong neuroprotective effects. PACAP is also expressed in peripheral organs but its peripheral protective effects have not been summarized so far. Therefore, the aim of the present paper is to review the existing literature regarding the cytoprotective effects of PACAP in non-neuronal cell types, peripheral tissues, and organs. Among others, PACAP has widespread expression in the digestive system, where it shows protective effects in various intestinal pathologies, such as duodenal ulcer, small bowel ischemia, and intestinal inflammation. PACAP is present in both the exocrine and endocrine pancreas as well as liver where it reduces inflammation and steatosis by interfering with hepatic pathology related to obesity. It is found in several exocrine glands and also in urinary organs, where, with its protective effects being mainly published regarding renal pathologies, PACAP is protective in numerous conditions. PACAP displays anti-inflammatory effects in upper and lower airways of the respiratory system. In the skin, it is involved in the development of inflammatory pathology such as psoriasis and also has anti-allergic effects in a model of contact dermatitis. In the non-neuronal part of the visual system, PACAP showed protective effects in pathological conditions of the cornea and retinal pigment epithelial cells. The positive role of PACAP has been demonstrated on the formation and healing processes of cartilage and bone where it also prevents osteoarthritis and rheumatoid arthritis development. The protective role of PACAP was also demonstrated in the cardiovascular system in different pathological processes including hyperglycaemia-induced endothelial dysfunction and age-related vascular changes. In the heart, PACAP protects against ischemia, oxidative stress, and cardiomyopathies. PACAP is also involved in the protection against the development of pre-senile systemic amyloidosis, which is presented in various peripheral organs in PACAP-deficient mice. The studies summarized here provide strong evidence for the cytoprotective effects of the peptide. The survival-promoting effects of PACAP depend on a number of factors which are also shortly discussed in the present review.

A Comparative Update on the Neuroendocrine Regulation of Growth Hormone in Vertebrates

Growth hormone (GH), mainly produced from the pituitary somatotrophs is a key endocrine regulator of somatic growth. GH, a pleiotropic hormone, is also involved in regulating vital processes, including nutrition, reproduction, physical activity, neuroprotection, immunity, and osmotic pressure in vertebrates. The dysregulation of the pituitary GH and hepatic insulin-like growth factors (IGFs) affects many cellular processes associated with growth promotion, including protein synthesis, cell proliferation and metabolism, leading to growth disorders. The metabolic and growth effects of GH have interesting applications in different fields, including the livestock industry and aquaculture. The latest discoveries on new regulators of pituitary GH synthesis and secretion deserve our attention. These novel regulators include the stimulators adropin, klotho, and the fibroblast growth factors, as well as the inhibitors, nucleobindin-encoded peptides (nesfatin-1 and nesfatin-1-like peptide) and irisin. This review aims for a comparative analysis of our current understanding of the endocrine regulation of GH from the pituitary of vertebrates. In addition, we will consider useful pharmacological molecules (i.e. stimulators and inhibitors of the GH signaling pathways) that are important in studying GH and somatotroph biology. The main goal of this review is to provide an overview and update on GH regulators in 2020. While an extensive review of each of the GH regulators and an in-depth analysis of specifics are beyond its scope, we have compiled information on the main endogenous and pharmacological regulators to facilitate an easy access. Overall, this review aims to serve as a resource on GH endocrinology for a beginner to intermediate level knowledge seeker on this topic.

The Therapeutic Impact of New Migraine Discoveries

BACKGROUND

Migraine is one of the most disabling neurological conditions and associated with high socio-economic costs. Though certain aspects of the pathomechanism of migraine are still incompletely understood, the leading hypothesis implicates the role of the activation of the trigeminovascular system. Triptans are considered to be the current gold standard therapy for migraine attacks; however, their use in clinical practice is limited. Prophylactic treatment includes non-specific approaches for migraine prevention. All these support the need for future studies in order to develop innovative anti-migraine drugs.

OBJECTIVE

The present study is a review of the current literature regarding new therapeutic lines in migraine research.

METHODS

A systematic literature search in the database of PUBMED was conducted concerning therapeutic strategies in a migraine published until July 2017.

RESULTS

Ongoing clinical trials with 5-HT1F receptor agonists and glutamate receptor antagonists offer promising new aspects for acute migraine treatment. Monoclonal antibodies against CGRP and the CGRP receptor are revolutionary in preventive treatment; however, further long-term studies are needed to test their tolerability. Preclinical studies show positive results with PACAP- and kynurenic acid-related treatments. Other promising therapeutic strategies (such as those targeting TRPV1, substance P, NOS, or orexin) have failed to show efficacy in clinical trials.

CONCLUSION

Due to their side-effects, current therapeutic approaches are not suitable for all migraine patients. Especially frequent episodic and chronic migraine represents a therapeutic challenge for researchers. Clinical and preclinical studies are needed to untangle the pathophysiology of migraine in order to develop new and migraine-specific therapies.

Pleiotropic pituitary adenylate cyclase-activating polypeptide (PACAP): Novel insights into the role of PACAP in eating and drug intake

Pituitary adenylate cyclase-activating polypeptide (PACAP) was discovered thirty years ago, but its role in eating and drug use disorders has only recently begun to be investigated. The present review develops the hypothesis that, although PACAP normally functions to tightly regulate intake, inhibiting it through negative feedback, this relationship can become dysregulated with the development of dependence, such that PACAP instead acts through positive feedback to promote excessive intake. We propose that repeated exposure to palatable food and drugs of abuse can alter the downstream responses of specific populations of neurons to stimulation by PACAP, leading to the perpetuation of the addiction cycle. Thus, this review will first describe published literature on homeostatic food intake, which shows that PACAP suppresses food intake, while its levels are themselves increased by overfeeding. Next, it will present literature on palatable food, cocaine, alcohol, and nicotine, which overall demonstrates that PACAP in specific limbic brain regions can promote their seeking and intake and itself is stimulated by their intake. Then, it will present literature on affective behavior, which shows that chronic stress increases levels of PACAP, which then promotes anxiety and depression, factors that can trigger substance seeking. Finally, the review will address mechanisms through which chronic substance exposure may dysregulate the PACAP system, proposing that it alters expression of PACAP receptor splice variants. While many questions remain to be addressed, the current evidence suggests that PACAP could be a viable medication target for the treatment of binge eating and drug and alcohol use disorders.

[Recent advances in the elucidation of migraine pathophysiology]

Three hypotheses have been proposed so far regarding the pathophysiology of migraine: one is the "vascular theory", which posits cerebral vascular dysfunction as the etiological factor. The second is the "neuronal theory", which suggests that migraine is triggered by cortical spreading depression. The third is the "trigemino-vascular theory", which postulates that migraine is triggered by inflammation of trigeminal nerves and vessels around trigeminal ganglion cells. Nowadays, the "trigemino-vascular theory" is widely accepted. However, recent advances in imaging analysis indicate that the origin of migraine lies in a premonitory phase which precedes the aura phase. Modern imaging techniques such as functional MRI and PET reveal high activity of the hypothalamic area during the premonitory phase of migraine. These findings suggest that hypothalamic activation might be a generator of a migraine attack. On the other hand, current analyses show that the photosensitivity of migraine (photophobia) could be caused by dysfunction of the newly discovered intrinsically photosensitive retinal ganglion cells (ipRGCs). In the absence of visual signaling from rods and cones, light activation of ipRGCs expressing melanopsin photopigment is sufficient to produce photophobia during migraine. The ipRGCs project to the hypothalamus; their activation might be the trigger for migraine attacks. Significant advances in molecular biology and imaging in recent years have clarified the previous hypotheses of migraine pathophysiology.

Distinct VIP and PACAP Functions in the Distal Nerve Stump During Peripheral Nerve Regeneration

Vasoactive Intestinal Peptide (VIP) and Pituitary Adenylyl Cyclase Activating Peptide (PACAP) are regeneration-associated neuropeptides, which are up-regulated by neurons following peripheral nerve injury. So far, they have only been studied for their roles as autocrine signals for both neuronal survival and axon outgrowth during peripheral nerve regeneration. In this report, we examined VIP and PACAP's paracrine effects on Schwann cells and macrophages in the distal nerve stump during peripheral nerve regeneration. We show that VPAC1, VPAC2, and PAC1 are all up-regulated in the mouse distal nerve following peripheral nerve injury and are highly expressed in Schwann cells and macrophages within the distal sciatic nerve. We further investigated the effect of VIP and PACAP on cultured rat Schwann cells, and found that VIP and PACAP can not only promote myelin gene expression in Schwann cells but can also inhibit the release of pro-inflammatory cytokines by Schwann cells. Furthermore, we show that VIP and PACAP inhibit the release of pro-inflammatory cytokines and enhance anti-inflammatory cytokine expression in sciatic nerve explants. Our results provide evidence that VIP and PACAP could have important functions in the distal nerve stump following injury to promote remyelination and regulate the inflammatory response. Thus, VIP and PACAP receptors appear as important targets to promote peripheral nerve repair following injury.

Pituitary Adenylate Cyclase-Activating Peptide (PACAP)-Glutamate Co-transmission Drives Circadian Phase-Advancing Responses to Intrinsically Photosensitive Retinal Ganglion Cell Projections by Suprachiasmatic Nucleus

Results from a variety of sources indicate a role for pituitary adenylate cyclase-activating polypeptide (PACAP) in light/glutamate-induced phase resetting of the circadian clock mediated by the retinohypothalamic tract (RHT). Attempts to block or remove PACAP’s contribution to clock-resetting have generated phenotypes that differ in their responses to light or glutamate. For example, previous studies of circadian behaviors found that period-maintenance and early-night phase delays are intact in PACAP-null mice, yet there is a consistent deficit in behavioral phase-resetting to light stimulation in the late night. Here we report rodent stimulus–response characteristics of PACAP release from the RHT, and map these to responses of the suprachiasmatic nucleus (SCN) in intact and PACAP-deficient mouse hypothalamus with regard to phase-resetting. SCN of PACAP-null mice exhibit normal circadian rhythms in neuronal activity, but are “blind” to glutamate stimulating phase-advance responses in late night, although not in early night, consistent with previously reported selective lack of late-night light behavioral responsiveness of these mice. Induction of CREB phosphorylation, a hallmark of the light/glutamate response of the SCN, also is absent in SCN-containing ex vivo slices from PACAP-deficient mouse hypothalamus. PACAP replacement to the SCN of PACAP-null mice restored wild-type phase-shifting of firing-rate patterns in response to glutamate applied to the SCN in late night. Likewise, ex vivo SCN of wild-type mice post-orbital enucleation are unresponsive to glutamate unless PACAP also is restored. Furthermore, we demonstrate that the period of efficacy of PACAP at SCN nerve terminals corresponds to waxing of PACAP mRNA expression in ipRGCs during the night, and waning during the day. These results validate the use of PACAP-deficient mice in defining the role and specificity of PACAP as a co-transmitter with glutamate in ipRGC-RHT projections to SCN in phase advancing the SCN circadian rhythm in late night.

Lack of Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) Disturbs Callus Formation

Pituitary adenylate cyclase–activating polypeptide (PACAP) is a naturally secreted signaling peptide and has important regulatory roles in the differentiation of the central nervous system and its absence results in disorders in femur development. PACAP has an important function in prevention of oxidative stress or mechanical stress in chondrogenesis but little is known about its function in bone regeneration. A new callus formation model was set to investigate its role in bone remodeling. Fracturing was 5 mm distal from the proximal articular surface of the tibia and the depth was 0.5 mm. Reproducibility of callus formation was investigated with CT 3, 7, and 21 days after the operation. Absence of PACAP did not alter the alkaline phosphatase (ALP) activation in PACAP KO healing process. In developing callus, the expression of collagen type I increased in wild-type (WT) and PACAP KO mice decreased to the end of healing process. Expression of the elements of BMP signaling was disturbed in the callus formation of PACAP KO mice, as bone morphogenic protein 4 (BMP4) and 6 showed an early reduction in bone regeneration. However, elevated Smad1 expression was demonstrated in PACAP KO mice. Our results indicate that PACAP KO mice show various signs of disturbed bone healing and suggest PACAP compensatory and fine tuning effects in proper bone regeneration.

Vasoactive Intestinal Peptide Deficiency Is Associated With Altered Gut Microbiota Communities in Male and Female C57BL/6 Mice

Vasoactive intestinal peptide (VIP) is crucial for gastrointestinal tract (GIT) health. VIP sustains GIT homeostasis through maintenance of the intestinal epithelial barrier and acts as a potent anti-inflammatory mediator that contributes to gut bacterial tolerance. Based on these biological functions by VIP, we hypothesized that its deficiency would alter gut microbial ecology. To this end, fecal samples from male and female VIP+/+, VIP+/-, and VIP-/- littermates (n = 47) were collected and 16S rRNA sequencing was conducted. Our data revealed significant changes in bacterial composition, biodiversity, and weight loss from VIP-/- mice compared to VIP+/+ and VIP+/- littermates, irrespective of sex. The gut bacteria compositional changes observed in VIP-/- mice was consistent with gut microbial structure changes reported for certain inflammatory and autoimmune disorders. Moreover, predicted functional changes by PICRUSt software suggested an energy surplus within the altered microbiota from VIP-/- mice. These data support that VIP plays an important role in maintaining microbiota balance, biodiversity, and GIT function, and its genetic removal results in significant gut microbiota restructuring and weight loss.

Pituitary Adenylate Cyclase-Activating Polypeptide Modulates Hippocampal Synaptic Transmission and Plasticity: New Therapeutic Suggestions for Fragile X Syndrome

Pituitary adenylate cyclase-activating polypeptide (PACAP) modulates glutamatergic synaptic transmission and plasticity in the hippocampus, a brain area with a key role in learning and memory. In agreement, several studies have demonstrated that PACAP modulates learning in physiological conditions. Recent publications show reduced PACAP levels and/or alterations in PACAP receptor expression in different conditions associated with cognitive disability. It is noteworthy that PACAP administration rescued impaired synaptic plasticity and learning in animal models of aging, Alzheimer's disease, Parkinson's disease, and Huntington's chorea. In this context, results from our laboratory demonstrate that PACAP rescued metabotropic glutamate receptor-mediated synaptic plasticity in the hippocampus of a mouse model of fragile X syndrome (FXS), a genetic form of intellectual disability. PACAP is actively transported through the blood-brain barrier and reaches the brain following intranasal or intravenous administration. Besides, new studies have identified synthetic PACAP analog peptides with improved selectivity and pharmacokinetic properties with respect to the native peptide. Our review supports the shared idea that pharmacological activation of PACAP receptors might be beneficial for brain pathologies with cognitive disability. In addition, we suggest that the effects of PACAP treatment might be further studied as a possible therapy in FXS.

Effect of pituitary adenylate cyclase-activating polypeptide-27 on cerebral hemodynamics in healthy volunteers: A 3T MRI study

Pituitary adenylate cyclase-activating polypeptide (PACAP) has emerged as an important signaling peptide in migraine pathogenesis. Recently, we have shown that the less-abundant PACAP isoform, PACAP27, induced migraine and headache in patients equipotently to PACAP38. The present study examined the effect of PACAP27 on cerebral hemodynamics in healthy volunteers using high resolution magnetic resonance angiography (MRA). Eighteen healthy volunteers received infusion of PACAP27 (10 pmol/kg/min) or placebo over 20 min and were scanned repeatedly in fixed intervals for 5 h in a double-blind, randomized, placebo-controlled study. The circumference of extra-intracerebral arteries was measured and compared with PACAP38 data. We found significant dilation of middle meningeal artery (MMA) (p = 0.019), superficial temporal artery (p = 0.001) and external carotid artery (p = 0.039) after PACAP27 infusion compared to placebo. Whereas the middle cerebral artery (MCA) (p = 0.011) and internal carotid artery (ICA) (p_ICAcervical = 0.015, p_ICAcerebral = 0.019) were constricted. No effects on basilar artery (p = 0.708) and cavernous portion of ICA were found. Post hoc analyses revealed significant larger area under the curve for MMA after PACAP38 compared to PACAP27 (p = 0.033). We also found that PACAP27 induced headache in nine out of twelve (75%) volunteers and one (17%) after placebo. In conclusion, PACAP27 induced headache and dilated extracerebral arteries (>5 h) and slightly constricted MCA in healthy volunteers. Post hoc analysis of PACAP38 data compared with PACAP27 showed that PACAP isoforms dilates MMA with significantly different magnitude.

Targeting the PAC1 Receptor for Neurological and Metabolic Disorders

The pituitary adenylate cyclase-activating polypeptide (PACAP)-selective PAC1 receptor (PAC1R, ADCYAP1R1) is a member of the vasoactive intestinal peptide (VIP)/secretin/glucagon family of G protein-coupled receptors (GPCRs). PAC1R has been shown to play crucial roles in the central and peripheral nervous systems. The activation of PAC1R initiates diverse downstream signal transduction pathways, including adenylyl cyclase, phospholipase C, MEK/ERK, and Akt pathways that regulate a number of physiological systems to maintain functional homeostasis. Accordingly, at times of tissue injury or insult, PACAP/PAC1R activation of these pathways can be trophic to blunt or delay apoptotic events and enhance cell survival. Enhancing PAC1R signaling under these conditions has the potential to mitigate cellular damages associated with cerebrovascular trauma (including stroke), neurodegeneration (such as Parkinson's and Alzheimer's disease), or peripheral organ insults. Conversely, maladaptive PACAP/PAC1R signaling has been implicated in a number of disorders, including stressrelated psychopathologies (i.e., depression, posttraumatic stress disorder, and related abnormalities), chronic pain and migraine, and metabolic diseases; abrogating PAC1R signaling under these pathological conditions represent opportunities for therapeutic intervention. Given the diverse PAC1R-mediated biological activities, the receptor has emerged as a relevant pharmaceutical target. In this review, we first describe the current knowledge regarding the molecular structure, dynamics, and function of PAC1R. Then, we discuss the roles of PACAP and PAC1R in the activation of a variety of signaling cascades related to the physiology and diseases of the nervous system. Lastly, we examine current drug design and development of peptides and small molecules targeting PAC1R based on a number of structure- activity relationship studies and key pharmacophore elements. At present, the rational design of PAC1R-selective peptide or small-molecule therapeutics is largely hindered by the lack of structural information regarding PAC1R activation mechanisms, the PACAP-PAC1R interface, and the core segments involved in receptor activation. Understanding the molecular basis governing the PACAP interactions with its different cognate receptors will undoubtedly provide a basis for the development and/or refinement of receptor-selective therapeutics.

Age-related alterations of articular cartilage in pituitary adenylate cyclase-activating polypeptide (PACAP) gene-deficient mice

Pituitary adenylate cyclase activating polypeptide (PACAP) is an evolutionarly conserved neuropeptide which is produced by various neuronal and non-neuronal cells, including cartilage and bone cells. PACAP has trophic functions in tissue development, and it also plays a role in cellular and tissue aging. PACAP takes part in the regulation of chondrogenesis, which prevents insufficient cartilage formation caused by oxidative and mechanical stress. PACAP knockout (KO) mice have been shown to display early aging signs affecting several organs. In the present work, we investigated articular cartilage of knee joints in young and aged wild-type (WT) and PACAP KO mice. A significant increase in the thickness of articular cartilage was detected in aged PACAP gene-deficient mice. Amongst PACAP receptors, dominantly PAC1 receptor was expressed in WT knee joints and a remarkable decrease was found in aged PACAP KO mice. Expression of PKA-regulated transcription factors, Sox5, Sox9 and CREB, decreased both in young and aged gene deficient mice, while Sox6, collagen type II and aggrecan expressions were elevated in young but were reduced in aged PACAP KO animals. Increased expression of hyaluronan (HA) synthases and HA-binding proteins was detected parallel with an elevated presence of HA in aged PACAP KO mice. Expression of bone related collagens (I and X) was augmented in young and aged animals. These results suggest that loss of PACAP signaling results in dysregulation of cartilage matrix composition and may transform articular cartilage in a way that it becomes more prone to degenerate.

Progress in regulatory peptide research

The field of regulatory peptide research has developed significant momentum owing to several recent converging trends. Dozens of peptide-based drugs have been approved by the U.S. Food and Drug Administration in the past decade, the majority for the treatment of metabolic disorders, including diabetes. These are the "tip of the spear" for peptide therapeutics, revealing that impediments of delivery, stability, and bioavailability inherent in peptide drugs have in many cases been overcome. While most are orally available, and directed at peripheral targets, pharmaceutical delivery of peptides to the central nervous system through nasal mucosal routes has also seen much progress. Cell-based high-throughput drug discovery methods, the X-ray crystallographic structural definition of G protein-coupled receptors, and deorphanization of peptide-liganded receptors have contributed to the emergence of new targets for pharmacological intervention and accelerated the development of peptide-based as well as nonpeptide congeners for existing ones. Finally, the recognition that peptides act at their receptors, in a cellular context, in conjunction with other peptides and other first messengers, including neurotransmitters, hormones, and autocrine and paracrine factors, has led to an increased appreciation for the combinatorial possibilities of regulatory peptide action, now penetrating to drug design and discovery efforts. The fifteen reviews, reports, and perspectives collected in this special issue of Annals of the New York Academy of Sciences provide a snapshot of the frontiers of the field of regulatory peptide research as they expand physiologically, pharmacologically, and therapeutically.

Neuroprotective Potential of Pituitary Adenylate Cyclase Activating Polypeptide in Retinal Degenerations of Metabolic Origin

Pituitary adenylate cyclase-activating polypeptide (PACAP1-38) is a highly conserved member of the secretin/glucagon/VIP family. The repressive effect of PACAP1-38 on the apoptotic machinery has been an area of active research conferring a significant neuroprotective potential onto this peptide. A remarkable number of studies suggest its importance in the etiology of neurodegenerative disorders, particularly in relation to retinal metabolic disorders. In our review, we provide short descriptions of various pathological conditions (diabetic retinopathy, excitotoxic retinal injury and ischemic retinal lesion) in which the remedial effect of PACAP has been well demonstrated in various animal models. Of all the pathological conditions, diabetic retinopathy seems to be the most intriguing as it develops in 75% of patients with type 1 and 50% of patients with type 2 diabetes, with concomitant progression to legal blindness in about 5%. Several animal models have been developed in recent years to study retinal degenerations and out of these glaucoma and age-related retina degeneration models bear human recapitulations. PACAP neuroprotection is thought to operate through enhanced cAMP production upon binding to PAC1-R. However, the underlying signaling network that leads to neuroprotection is not fully understood. We observed that (i) PACAP is not equally efficient in the above conditions; (ii) in some cases more than one signaling pathways are activated; (iii) the coupling of PAC1-R and signaling is stage dependent; and (iv) PAC1-R is not the only receptor that must be considered to interpret the effects in our experiments. These observations point to a complex signaling mechanism, that involves alternative routes besides the classical cAMP/protein kinase A pathway to evoke the outstanding neuroprotective action. Consequently, the possible contribution of the other two main receptors (VPAC1-R and VPAC2-R) will also be discussed. Finally, the potential medical use of PACAP in some retinal and ocular disorders will also be reviewed. By taking advantage of, low-cost synthesis technologies today, PACAP may serve as an alternative to the expensive treatment modelities currently available in ocular or retinal conditions.

PACAP and PAC1 receptor expression in pancreatic ductal carcinoma

Pancreatic carcinoma is one of the most malignant diseases and is associated with a poor survival rate. Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide that acts on three different G protein-coupled receptors: the specific PAC1 and the VPAC1/2 that also bind vasoactive intestinal peptide. PACAP is widely distributed in the body and has diverse physiological effects. Among other things, it acts as a trophic factor and influences proliferation and differentiation of several different cells both under normal circumstances and tumourous transformation. Changes of PACAP and its receptors have been shown in various tumour types. However, it is not known whether PACAP and its specific receptor are altered in pancreatic cancer. Perioperative data of patients with pancreas carcinoma was investigated over a five-year period. Histological results showed Grade 2 or Grade 3 adenocarcinoma in most cases. PACAP and PAC1 receptor expression were investigated by immunohistochemistry. Staining intensity of PAC1 receptor was strong in normal tissues both in the exocrine and endocrine parts of the pancreas, the receptor staining was markedly weaker in the adenocarcinoma. PACAP immunostaining was weak in the exocrine part and very strong in the islets and nerve elements in non-tumourous tissues. The PACAP immunostaining almost disappeared in the adenocarcinoma samples. Based on these findings a decrease or lack of the PAC1 receptor/PACAP signalling might have an influence on tumour growth and/or differentiation.

The Neuropeptide Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) is Protective in Inflammation and Oxidative Stress-Induced Damage in the Kidney

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a pleiotropic neuropeptide with a widespread distribution throughout the entire body including the urinary system. PACAP exerts protective actions in different injury models related to several organ systems. Its protective effect is mainly based on its antiapoptotic, anti-inflammatory and antioxidant effects. The present review aims to summarize the effects of PACAP in pathologies associated with inflammation and oxidative stress-induced damage in the kidney. Both in vitro and in vivo data are available proving its protective actions against oxidative stress, hypoxia, renal ischemia/reperfusion, diabetic nephropathy, myeloma kidney injury, amyloidosis and different types of drug-induced nephropathies. Data showing the nephroprotection by PACAP emphasize the potential of PACAP’s therapeutic use in various renal pathologies.

PAC1 regulates receptor tyrosine kinase transactivation in a reactive oxygen species-dependent manner

Pituitary adenylate cyclase activating polypeptide (PACAP) is a growth factor for lung cancer cells. PACAP-27 or PACAP-38 binds with high affinity to non-small cell lung cancer (NSCLC) cells, causing elevated cytosolic Ca²⁺, increased proliferation and increased phosphorylation of extracellular regulated kinase (ERK) and the epidermal growth factor receptor (EGFR). The role of reactive oxygen species (ROS) was investigated in these processes. Addition of PACAP-38 to NCI-H838 or A549 cells increased the tyrosine phosphorylation of the EGFR, HER2 and ERK significantly by 4-, 3-, and 2-fold, respectively. The transactivation of the EGFR and HER2 was inhibited by gefitinib or lapatinib (tyrosine kinase inhibitors), PACAP (6-38) (PAC1 antagonist), N-acetylcysteine (NAC is an anti-oxidant) or dipheyleneiodonium (DPI is an inhibitor of Nox and Duox enzymes). PACAP-38 addition to NSCLC cells increased ROS which was inhibited by PACAP (6-38), NAC or DPI. Nox1, Nox2, Nox3, Nox4, Nox5, Duox1 and Duox2 mRNA was present in many NSCLC cell lines. PACAP-38 stimulated the growth of NSCLC cells whereas PACAP (6-38), gefitinib or DPI inhibited proliferation. The results show that ROS are essential for PAC1 to regulate EGFR and HER2 transactivation as well as proliferation of NSCLC cells.

Chromaffin Cells of the Adrenal Medulla: Physiology, Pharmacology, and Disease

Chromaffin cells (CCs) of the adrenal gland and the sympathetic nervous system produce the catecholamines (epinephrine and norepinephrine; EPI and NE) needed to coordinate the bodily "fight-or-flight" response to fear, stress, exercise, or conflict. EPI and NE release from CCs is regulated both neurogenically by splanchnic nerve fibers and nonneurogenically by hormones (histamine, corticosteroids, angiotensin, and others) and paracrine messengers [EPI, NE, adenosine triphosphate, opioids, γ-aminobutyric acid (GABA), etc.]. The "stimulus-secretion" coupling of CCs is a Ca2+ -dependent process regulated by Ca2+ entry through voltage-gated Ca2+ channels, Ca2+ pumps, and exchangers and intracellular organelles (RE and mitochondria) and diffusible buffers that provide both Ca2+ -homeostasis and Ca2+ -signaling that ultimately trigger exocytosis. CCs also express Na+ and K+ channels and ionotropic (nAChR and GABAA ) and metabotropic receptors (mACh, PACAP, β-AR, 5-HT, histamine, angiotensin, and others) that make CCs excitable and responsive to autocrine and paracrine stimuli. To maintain high rates of E/NE secretion during stressful conditions, CCs possess a large number of secretory chromaffin granules (CGs) and members of the soluble NSF-attachment receptor complex protein family that allow docking, fusion, and exocytosis of CGs at the cell membrane, and their recycling. This article attempts to provide an updated account of well-established features of the molecular processes regulating CC function, and a survey of the as-yet-unsolved but important questions relating to CC function and dysfunction that have been the subject of intense research over the past 15 years. Examples of CCs as a model system to understand the molecular mechanisms associated with neurodegenerative diseases are also provided. Published 2019. Compr Physiol 9:1443-1502, 2019.

Pituitary Adenylate Cyclase-Activating Polypeptide: 30 Years in Research Spotlight and 600 Million Years in Service

Emerging from the depths of evolution, pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptors (i.e., PAC1, VPAC1, VPAC2) are present in multicellular organisms from Tunicates to humans and govern a remarkable number of physiological processes. Consequently, the clinical relevance of PACAP systems spans a multifaceted palette that includes more than 40 disorders. We aimed to present the versatility of PACAP1-38 actions with a focus on three aspects: (1) when PACAP1-38 could be a cause of a malfunction, (2) when PACAP1-38 could be the cure for a malfunction, and (3) when PACAP1-38 could either improve or impair biology. PACAP1-38 is implicated in the pathophysiology of migraine and post-traumatic stress disorder whereas an outstanding protective potential has been established in ischemia and in Alzheimer’s disease. Lastly, PACAP receptors could mediate opposing effects both in cancers and in inflammation. In the light of the above, the duration and concentrations of PACAP agents must be carefully set at any application to avoid unwanted consequences. An enormous amount of data accumulated since its discovery (1989) and the first clinical trials are dated in 2017. Thus in the field of PACAP research: “this is not the end, not even the beginning of the end, but maybe the end of the beginning.”

Strategies for the Identification of Bioactive Neuropeptides in Vertebrates

Neuropeptides exert essential functions in animal physiology by controlling e.g., reproduction, development, growth, energy homeostasis, cardiovascular activity and stress response. Thus, identification of neuropeptides has been a very active field of research over the last decades. This review article presents the various methods used to discover novel bioactive peptides in vertebrates. Initially identified on the basis of their biological activity, some neuropeptides have also been discovered for their ability to bind/activate a specific receptor or based on their biochemical characteristics such as C-terminal amidation which concerns half of the known neuropeptides. More recently, sequencing of the genome of many representative species has facilitated peptidomic approaches using mass spectrometry and in silico screening of genomic libraries. Through these different approaches, more than a hundred of bioactive neuropeptides have already been identified in vertebrates. Nevertheless, researchers continue to find new neuropeptides or to identify novel functions of neuropeptides that had not been detected previously, as it was recently the case for nociceptin.

The Neuroprotective Peptide PACAP1-38 Contributes to Horizontal Cell Development in Postnatal Rat Retina

Purpose

PACAP1-38, a member of the secretin/glucagon superfamily, is expressed in the developing retina with documented neuroprotective effects. However, its function in retinal cell differentiation has yet to be elucidated. Our goals, therefore, were to identify PAC1 expressing cells morphologically, investigate the PACAP1-38 action functionally, and establish PACAP1-38 regulated events developmentally during the first postnatal week in rat retina.

Methods

P1 retinal sections or whole mounts of Wistar rats were used to reveal PAC1 and calbindin immunoreactive structures. P1, P3, or P7 pups were injected intravitreally with 100 pmol PACAP1-38. Tissues were harvested 24 hours post-treatment, then processed for calbindin immunohistochemistry to determine horizontal cell number, or 6, 12, 24 hours post-treatment for real-time PCR and immunoblots to detect PCNA expression. To localize proliferating cells, anti-PCNA antibody was applied.

Results

We showed various PAC1 expressing cells in RPE, NBL, and GCL in P1 retina including calbindin positive horizontal cells. We found that PACAP1-38 induced a marked cell number increase at P3 and P7 and showed upregulated cell proliferation as its mechanism; however, it was ineffective at P1. PACAP1-38 induced proliferative cells localized in the NBL, and double-marker studies demonstrated that the induced proliferative cells were horizontal cells.

Conclusions

PACAP1-38 appears to act in retinal differentiation by inducing mitosis selectively in a time and cell specific manner through PAC1. The control of horizontal cell proliferation raises the novel possibilities that (1) PACAP1-38 may be a major player in retinal patterning and (2) PACAP signaling may be critical in retinoblastoma.

PACAP induces FSHβ gene expression via EPAC

Gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH), are heterodimers of a common α subunit and unique β subunits. Regulation of their levels, primarily by GnRH, is critical for reproductive function. Several other hormones modulate gonadotropin expression, either independently or by modifying the responsiveness to GnRH. Pituitary adenylate cyclase activating peptide (PACAP) is one such hormone. Four-hour treatment of female mouse primary pituitary cells by either GnRH or PACAP induced FSHβ expression, while 24-h treatment repressed FSHβ. Both PACAP and GnRH caused FSH secretion into the medium. In the gonadotropes, PACAP activates primarily Gαs and increases concentration of cAMP, while GnRH primarily functions via Gαq and increases calcium concentration. Herein, we compared PACAP and GnRH signaling pathways that lead to the induction of FSHβ expression. Interestingly, constitutively active Gαs represses LHβ and induces FSHβ expression, while Gαq induces both β-subunits. We determined that FSHβ induction by PACAP requires functional EPAC, a cAMP sensor protein that serves as a guanine exchange factors for small G proteins that then bridges cAMP signaling to MAPK pathway. We further demonstrate that in addition to the prototypical small G protein Ras, two members of the Rho subfamily, Rac and CDC42 are also necessary for PACAP induction of FSHβ, likely via activation of p38 MAPK that leads to induction of cFOS, a critical transcription factor that is necessary and sufficient for FSHβ induction. Therefore, PACAP-induced cAMP pathway leads to MAPK activation that stimulates cFOS induction, to induce the expression of FSHβ subunit and increase FSH concentration.