VPAC and PAC receptors: From ligands to function

Revisiting the evolution of Family B1 GPCRs and ligands: Insights from mollusca

Family B1 G protein-coupled receptors (GPCRs) are one of the most well studied neuropeptide receptor families since they play a central role in many biological processes including endocrine, gastrointestinal, cardiovascular and reproduction in animals. The genes for these receptors emerged from a common ancestral gene in bilaterian genomes and evolved via gene/genome duplications and deletions in vertebrate and invertebrate genomes. Their existence and function have mostly been characterized in vertebrates and few studies exist in invertebrate species. Recently, an increased interest in molluscs, means a series of genomes have become available, and since they are less modified than insect and nematode genomes, they are ideal to explore the origin and evolution of neuropeptide gene families. This review provides an overview of Family B1 GPCRs and their peptide ligands and incorporates new data obtained from Mollusca genomes and taking a comparative approach challenges existing models on their origin and evolution.

Pleural mesothelioma from fluoro-edenite exposure: PACAP and PAC1 receptor. A preliminary report

Pleural mesothelioma is a devastating malignancy primarily associated with asbestos exposure. However, emerging evidence suggests that exposure to fluoro-edenite fibers, a naturally occurring mineral fiber, can also lead to the development of pleural mesothelioma. In this study, based on the hypothesis that pituitary adenylate cyclase-activating polypeptide (PACAP) and PACAP-preferring receptor (PAC1R) expressions could be dysregulated in pleural mesothelioma samples and that they could potentially act as diagnostic or prognostic biomarkers, we aimed to investigate the immunohistochemical expression of PACAP and PAC1R in pleural biopsies from patients with pleural mesothelioma exposed to fluoro-edenite fibers. A total of 12 patients were included in this study, and their biopsies were processed for immunohistochemical analysis to evaluate the expression of PACAP and its receptor. The study revealed a correlation between the overexpression of PACAP and PAC1R and shorter overall survival in patients with malignant mesothelioma. These findings suggest that PACAP and PAC1R expression levels could serve as potential prognostic biomarkers for malignant mesothelioma. Furthermore, the immunohistochemical analysis of PACAP and PAC1R may provide valuable information for clinicians to guide therapeutic decisions and identify patients with poorer prognosis.

Blood serum levels of PACAP and migraine onset: A systematic review and meta-analysis of observational studies

OBJECTIVE

We conducted a systematic review and meta-analysis to explore the relationship between blood pituitary adenylate cyclase-activating polypeptide (PACAP) levels and migraine.

BACKGROUND

PACAP is involved in the onset of migraine, but the results from clinical studies on PACAP level variations across different periods of migraine are conflicting.

METHODS

We systematically searched for observational studies that reported PACAP levels in people with migraine and non-migraine controls published in English from the PubMed, Web of Science, and Ovid electronic databases, or in Chinese from the Chinese National Knowledge Infrastructure and the WanFang Med database. The Newcastle-Ottawa Quality Assessment Scale was used to assess the quality of the included studies. The quality of evidence for each outcome was assessed according to the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) guidelines.

RESULTS

Of the 514 identified studies, 8 were eligible for inclusion. There was a "very low" level of evidence suggesting that the PACAP level is negatively correlated with migraine disease duration in adults with migraine (summaryr = -0.35, 95% confidence interval [CI] -0.49 to -0.22) and that the PACAP is higher in people with migraine during the ictal period than in the interictal period (standardized mean difference = 0.41, 95% CI 0.17 to 0.66) for both adults and children with migraine. Adult patients with episodic migraine (weighted mean difference [WMD] = -9.58 pg/mL, 95% CI -13.41 to -5.75 pg/mL) or chronic migraine (WMD = -10.93 pg/mL, 95% CI -15.57 to -6.29 pg/mL) had lower blood PACAP levels than non-migraine controls during the interictal period, supported by a "low" or "very low" quality of evidence, respectively, according to the GRADE rules.

CONCLUSION

There is a very low certainty of evidence suggesting that the PACAP level is negatively correlated with migraine disease duration of adults with migraine and it varies greatly among different periods of migraine of both adults and children with migraine.

Cluster headache: an update on clinical features, epidemiology, pathophysiology, diagnosis, and treatment

Cluster headache (CH) is one of the worst primary headaches that remain underdiagnosed and inappropriately treated. There are recent advances in the understanding of this disease and available treatments. This paper aims to review CH's recent clinical and pathophysiological findings, diagnosis, and treatment. We performed a narrative literature review on the socio-demographics, clinical presentations, pathophysiological findings, and diagnosis and treatment of CH. CH affects 0.1% of the population with an incidence of 2.07-9.8/100,00 person-years-habitants, a mean prevalence of 53/100,000 inhabitants (3-150/100,000 inhabitants). The male-to-female ratio remains inconclusive, as the ratio of 4.3:1 has recently been modified to 1.3-2.6, possibly due to previous misdiagnosis in women. Episodic presentation is the most frequent (80%). It is a polygenetic and multifactorial entity that involves dysfunction of the trigeminovascular system, the trigeminal autonomic reflex, and the hypothalamic networks. An MRI of the brain is mandatory to exclude secondary etiologies. There are effective and safe pharmacological treatments oxygen, sphenopalatine, and great occipital nerve block, with the heterogeneity of clinical trial designs for patients with CH divided into acute, transitional, or bridge treatment (prednisone) and preventive interventions. In conclusion, CH remains underdiagnosed, mainly due to a lack of awareness within the medical community, frequently causing a long delay in reaching a final diagnosis. Recent advances in understanding the principal risk factors and underlying pathophysiology exist. There are new therapeutic possibilities that are effective for CH. Indeed, a better understanding of this challenging pathology will continue to be a subject of research, study, and discoveries in its diagnostic and therapeutic approach.

Protective effect of pituitary adenylate cyclase activating polypeptide in diabetic keratopathy

Diabetic keratopathy (DK) is the major complication of the cornea characterizing diabetes-affected patients. This ocular pathology is correlated with the hyperglycemic state leading to delayed corneal wound healing and recurrent corneal ulcers. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide with widespread distribution throughout the body, and exerting cytoprotective effects in the neural and non-neuronal parts of the eye, including the cornea. The purpose of the present study was to investigate whether changes in PACAP expression can concur for delayed epithelial wound healing in diabetic cornea and whether the protective effect of the peptide could be mediated through the activation of the EGFR signaling pathway, which has been reported to be impaired in DK. Expression and distribution of PACAP, PAC1R, and EGFR were investigated through immunohistochemistry analysis in the cornea of normal and diabetic rats. The role of the peptide on wound healing during DK was evaluated in an in vitro model represented by rabbit corneal epithelial cells grown in high glucose conditions. Western blotting and immunofluorescence analysis were used to examine the ability of PACAP to induce the activation of the EGFR/ERK1/2 signaling pathway. Our results showed that in diabetic cornea the expression of PACAP, PAC1R, and EGFR is drastically reduced. The treatment with PACAP via PAC1R activation enhanced cell viability and corneal epithelium wound healing in cells grown under high glucose conditions. Furthermore, both EGFR and ERK1/2 signaling was induced upon the peptide treatment. Overall, our results showed the trophic efficiency of PACAP for enhancing the corneal epithelium re-epithelialization suggesting that the peptide could be beneficially valuable as a treatment for DK.

Long-term Effects of the pituitary-adenylate cyclase-activating Polypeptide (PACAP38) in the Adult Mouse Retina: Microglial Activation and Induction of Neural Proliferation

The degenerative retinal disorders characterized by progressive cell death and exacerbating inflammation lead ultimately to blindness. The ubiquitous neuropeptide, PACAP38 is a promising therapeutic agent as its proliferative potential and suppressive effect on microglia might enable cell replacement and attenuate inflammation, respectively. Our previous finding that PACAP38 caused a marked increase of the amacrine cells in the adult (1-year-old) mouse retina, served as a rationale of the current study. We aimed to determine the proliferating elements and the inflammatory status of the PACAP38-treated retina. Three months old mice were intravitreally injected with 100 pmol PACAP38 at 3 months intervals (3X). Retinas of 1-year-old animals were dissected and effects on cell proliferation, and expression of inflammatory regulators were analyzed. Interestingly, both mitogenic and anti-mitogenic actions were detected after PACAP38-treatment. Further analysis of the mitogenic effect revealed that proliferating cells include microglia, endothelial cells, and neurons of the ganglion cell layer but not amacrine cells. Furthermore, PACAP38 stimulated retinal microglia to polarize dominantly into M2-phenotype but also might cause subsequent angiogenesis. According to our results, PACAP38 might dampen pro-inflammatory responses and help tissue repair by reprogramming microglia into an M2 phenotype, nonetheless, with angiogenesis as a warning side effect.

Pituitary adenylate cyclase-activating polypeptide deficient mice show length abnormalities of the axon initial segment

We previously found that pituitary adenylate cyclase-activating polypeptide (PACAP)-deficient (PACAP-/-) mice exhibit dendritic spine morphology impairment and neurodevelopmental disorder (NDD)-like behaviors such as hyperactivity, increased novelty-seeking behavior, and deficient pre-pulse inhibition. Recent studies have indicated that rodent models of NDDs (e.g., attention-deficit hyperactivity disorder (ADHD) and autism spectrum disorder) show abnormalities in the axon initial segment (AIS). Here, we revealed that PACAP-/- mice exhibited a longer AIS length in layer 2/3 pyramidal neurons of the primary somatosensory barrel field compared with wild-type control mice. Further, we previously showed that a single injection of atomoxetine, an ADHD drug, improved hyperactivity in PACAP-/- mice. In this study, we found that repeated treatments of atomoxetine significantly improved AIS abnormality along with hyperactivity in PACAP-/- mice. These results suggest that AIS abnormalities are associated with NDDs-like behaviors in PACAP-/- mice. Thus, improvement in AIS abnormalities will be a novel drug therapy for NDDs.

Gene deletion of the PACAP/VIP receptor, VPAC2R, alters glycemic responses during metabolic and psychogenic stress in adult female mice

Pituitary adenylate cyclase-activating polypeptide (PACAP) and the homologous peptide, vasoactive intestinal peptide (VIP), participate in glucose homeostasis using insulinotropic and counterregulatory processes. The role of VIP receptor 2 (VPAC2R) in these opposing actions needs further characterization. In this study, we examined the participation of VPAC2R on basal glycemia, fasted levels of glucoregulatory hormones and on glycemia responses during metabolic and psychogenic stress using gene-deleted (Vipr2-/- ) female mice. The mean basal glycemia was significantly greater in Vipr2-/- in the fed state and after an 8-h overnight fast as compared to wild-type (WT) mice. Insulin tolerance testing following a 5-h fast (morning fast, 0.38 U/kg insulin) indicated no effect of genotype. However, during a more intense metabolic challenge (8 h, ON fast, 0.25 U/kg insulin), Vipr2-/- females displayed significantly impaired insulin hypoglycemia. During immobilization stress, the hyperglycemic response and plasma epinephrine levels were significantly elevated above basal in Vipr2-/- , but not WT mice, in spite of similar stress levels of plasma corticosterone. Together, these results implicate participation of VPAC2R in upregulated counterregulatory processes influenced by enhanced sympathoexcitation. Moreover, the suppression of plasma GLP-1 levels in Vipr2-/- mice may have removed the inhibition on hepatic glucose production and the promotion of glucose disposal by GLP-1. qPCR analysis indicated deregulation of central gene markers of PACAP/VIP signaling in Vipr2-/- , upregulated medulla tyrosine hydroxylase (Th) and downregulated hypothalamic Vip transcripts. These results demonstrate a physiological role for VPAC2R in glucose metabolism, especially during insulin challenge and psychogenic stress, likely involving the participation of sympathoadrenal activity and/or metabolic hormones.

Heme and Cu2+-induced vasoactive intestinal peptide (VIP) tyrosine nitration: A possible molecular mechanism for the attenuated anti-inflammatory effect of VIP in inflammatory diseases

Vasoactive intestinal peptide (VIP) is a neuropeptide that play an important role in immunoregulation and anti-inflammation. Numerous inflammatory/autoimmune disorders are associated with decreased VIP binding ability to receptors and diminished VIP activation of cAMP generation in immune cells. However, the mechanisms linking oxidative/nitrative stress to VIP immune dysfunction remain unknown. It has been reported that the elevated heme or Cu2+ in inflammatory diseases can cause oxidative and nitrative damage to nearby biological targets under high oxidative stress conditions, which affects the structure and activity of linked peptides or proteins. Thus, the VIP down-regulated immune response may be interfered by redox metal catalyzed VIP tyrosine nitration. To explore this, we systematically investigated the possibility of heme or Cu2+ to catalyze VIP tyrosine nitration. The results showed that Tyr10 and Tyr22 of VIP can both be nitrated in heme/H2O2/NO2- system as well as in Cu2+/H2O2/NO2- system. Then, we used synthetic mutant VIPs with tyrosine residues substituted by 3-nitrotyrosine to study the impact of tyrosine nitration on VIP activity in SHSY-5Y cells. Our findings demonstrated that VIP nitration dramatically decreased the content of its α-helix and random coil, suggesting that VIP nitration might reduce its affinity to the receptor. This was further confirmed in the cAMP assay. The results showed that 10 nM of these tyrosine nitrated VIPs could significantly (p < 0.01) decrease cAMP secretion compared to the wild type VIP. Our data reveal that the attenuation of the neuroprotective effect of VIP in inflammation-related diseases might be attributed to metal-catalyzed VIP tyrosine nitration.

PACAP regulates VPAC1 expression, inflammatory processes and lipid homeostasis in M1- and M2-macrophages

Background

Pituitary adenylate cyclase-activating polypeptide (PACAP) acts as an anti-atherogenic neuropeptide and plays an important role in cytoprotective, as well as inflammatory processes, and cardiovascular regulation. Therefore, the aim of this study is to investigate the regulatory effects of PACAP and its receptor VPAC1 in relation to inflammatory processes and lipid homeostasis in different macrophage (MΦ) subtypes.

Methods

To investigate the role of PACAP deficiency in the pathogenesis of atherosclerosis under standard chow (SC) or cholesterol-enriched diet (CED) in vivo, PACAP-/- mice were crossbred with ApoE-/- to generate PACAP-/-/ApoE-/- mice. Lumen stenosis in the aortic arch and different MΦ-subtypes were analyzed in atherosclerotic plaques by quantitative immunohistochemistry. Undifferentiated bone marrow-derived cells (BMDC) from 30-weeks-old ApoE-/- and PACAP-/-/ApoE-/- mice were isolated, differentiated into BMDM1- and BMDM2-MΦ, and incubated with oxidized low-density lipoprotein (oxLDL). In addition, PMA-differentiated human THP-1 MΦ were further differentiated into M1-/M2-MΦ and subsequently treated with PACAP38, the VPAC1 agonist [(Ala11,22,28)VIP], the antagonist (PG 97-269), and/or oxLDL. Uptake/accumulation of oxLDL was analyzed by oxLDL-DyLight™488 and Bodipy™ 493/503. The mRNA expression was analyzed by qRT-PCR, protein levels by Western blot, and cytokine release by ELISA.

Results

In vivo, after 30 weeks of SC, PACAP-/-/ApoE-/- mice showed increased lumen stenosis compared with ApoE-/- mice. In atherosclerotic plaques of PACAP-/-/ApoE-/- mice under CED, immunoreactive areas of VPAC1, CD86, and CD163 were increased compared with ApoE-/- mice. In vitro, VPAC1 protein levels were increased in PACAP-/-/ApoE-/- BMDM compared with ApoE-/- BMDM, resulting in increased TNF-α mRNA expression in BMDM1-MΦ and decreased TNF-α release in BMDM2-MΦ. Concerning lipid homeostasis, PACAP deficiency decreased the area of lipid droplets in BMDM1-/M2-MΦ with concomitant increasing adipose differentiation-related protein level. In THP-1 M1-/M2-MΦ, the VPAC1 antagonist increased the uptake of oxLDL, whereas the VPAC1 agonist decreased the oxLDL-induced intracellular triglyceride content.

Conclusion

Our data suggest that PACAP via VPAC1 signaling plays an important regulatory role in inflammatory processes in atherosclerotic plaques and in lipid homeostasis in different MΦ-subtypes, thereby affecting foam cell formation. Therefore, VPAC1 agonists or PACAP may represent a new class of anti-atherogenic therapeutics.

Drastic decline in vasoactive intestinal peptide expression in the suprachiasmatic nucleus in obese mice on a long-term high-fat diet

The suprachiasmatic nucleus (SCN) is the main region for the regulation of circadian rhythms. Although the SCN contains a heterogeneous neurochemical phenotype with a wide variety of neuropeptides, a key role has been suggested for the vasoactive intestinal neuropeptide (VIP) as a modulator circadian, reproductive, and seasonal rhythms. VIP is a 28-amino acid polypeptide hormone that belongs to the secretin-glucagon peptide superfamily and shares 68 % homology with the pituitary adenylate cyclase-activating polypeptide (PACAP). VIP acts as an endogenous appetite inhibitor in the central nervous system, where it participates in the control of appetite and energy homeostasis. In recent years, significant efforts have been made to better understand the role of VIP in the regulation of appetite/satiety and energy balance. This study aimed to elucidate the long-term effect of an obesogenic diet on the distribution and expression pattern of VIP in the SCN and nucleus accumbens (NAc) of C57BL/6 mice. A total of 15 female C57BL/6J mice were used in this study. Female mice were fed ad libitum with water and, either a standard diet (SD) or a high-fat diet (HFD) to induce obesity. There were 7 female mice on the SD and 8 on the HFD. The duration of the experiment was 365 days. The morphological study was performed using immunohistochemistry and double immunofluorescence techniques to study the neurochemical profile of VIP neurons of the SCN of C57BL/6 mice. Our data show that HFD-fed mice gained weight and showed reduced VIP expression in neurons of the SCN and also in fibres located in the NAc. Moreover, we observed a loss of neuropeptide Y (NPY) expression in fibres surrounding the SCN. Our findings on VIP may contribute to the understanding of the pathophysiological mechanisms underlying obesity in regions associated with uncontrolled intake of high-fat foods and the reward system, thus facilitating the identification of novel therapeutic targets.

Reference gene recommendations and PACAP receptor expression in murine sympathetic ganglia of the autonomic nervous system that innervate adipose tissues after chronic cold exposure

Pituitary adenylate cyclase-activating polypeptide (PACAP) is an important regulator of the stress response in mammals, influencing both the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous system (SNS). PACAP has been reported to influence energy homeostasis, including adaptive thermogenesis, an energy burning process in adipose tissue regulated by the SNS in response to cold stress and overfeeding. While research suggests PACAP acts centrally at the level of the hypothalamus, knowledge of PACAP's role within the sympathetic nerves innervating adipose tissues in response to metabolic stressors is limited. This work shows, for the first time, gene expression of PACAP receptors in stellate ganglia and highlights some differential expression with housing temperature. Additionally, we present our dissection protocol, analysis of tyrosine hydroxylase gene expression as a molecular biomarker for catecholamine producing tissue and recommend three stable reference genes for the normalization of quantitative real time-polymerase chain reaction (qRT-PCR) data when working with this tissue. This study adds to information about neuropeptide receptor expression in peripheral ganglia of the sympathetic nervous system innervating adipose tissue and provides insight into PACAP's role in the regulation of energy metabolism.

Migraine Treatment: Towards New Pharmacological Targets

Migraine is a debilitating neurological condition affecting millions of people worldwide. Until a few years ago, preventive migraine treatments were based on molecules with pleiotropic targets, developed for other indications, and discovered by serendipity to be effective in migraine prevention, although often burdened by tolerability issues leading to low adherence. However, the progresses in unravelling the migraine pathophysiology allowed identifying novel putative targets as calcitonin gene-related peptide (CGRP). Nevertheless, despite the revolution brought by CGRP monoclonal antibodies and gepants, a significant percentage of patients still remains burdened by an unsatisfactory response, suggesting that other pathways may play a critical role, with an extent of involvement varying among different migraine patients. Specifically, neuropeptides of the CGRP family, such as adrenomedullin and amylin; molecules of the secretin family, such as pituitary adenylate cyclase-activating peptide (PACAP) and vasoactive intestinal peptide (VIP); receptors, such as transient receptor potential (TRP) channels; intracellular downstream determinants, such as potassium channels, but also the opioid system and the purinergic pathway, have been suggested to be involved in migraine pathophysiology. The present review provides an overview of these pathways, highlighting, based on preclinical and clinical evidence, as well as provocative studies, their potential role as future targets for migraine preventive treatment.

Gene Expression Analysis Links Autocrine Vasoactive Intestinal Peptide and ZEB1 in Gastrointestinal Cancers

VIP (vasoactive intestinal peptide) is a 28-amino acid peptide hormone expressed by cancer and the healthy nervous system, digestive tract, cardiovascular, and immune cell tissues. Many cancers express VIP and its surface receptors VPAC1 and VPAC2, but the role of autocrine VIP signaling in cancer as a targetable prognostic and predictive biomarker remains poorly understood. Therefore, we conducted an in silico gene expression analysis to study the mechanisms of autocrine VIP signaling in cancer. VIP expression from TCGA PANCAN tissue samples was analyzed against the expression levels of 760 cancer-associated genes. Of the 760 genes, 10 (MAPK3, ZEB1, TEK, NOS2, PTCH1 EIF4G1, GMPS, CDK2, RUVBL1, and TIMELESS) showed statistically meaningful associations with the VIP (Pearson's R-coefficient > |0.3|; p < 0.05) across all cancer histologies. The strongest association with the VIP was for the epithelial-mesenchymal transition regulator ZEB1 in gastrointestinal malignancies. Similar positive correlations between the VIP and ZEB1 expression were also observed in healthy gastrointestinal tissues. Gene set analysis indicates the VIP is involved in the EMT and cell cycle pathways, and a high VIP and ZEB1 expression is associated with higher median estimate and stromal scores These findings uncover novel mechanisms for VIP- signaling in cancer and specifically suggest a role for VIP as a biomarker of ZEB1-mediated EMT. Further studies are warranted to characterize the specific mechanism of this interaction.

PACAP6-38 improves nitroglycerin-induced central sensitization by modulating synaptic plasticity at the trigeminal nucleus caudalis in a male rat model of chronic migraine

AIMS

Chronic migraine (CM) is a common neurological disorder with complex pathogenesis. Evidence suggests that pituitary adenylate cyclase-activating peptide (PACAP) induces migraine-like attacks and may be potential a new target for migraine treatment, but the therapeutic results of targeting PACAP and its receptors are not uniform. Therefore, the aim of this study was to investigate the regulatory effect of PACAP type I receptor (PAC1R) antagonist, PACAP6-38, on nitroglycerin (NTG)-induced central sensitization in a CM model.

METHODS

Sprague-Dawley (SD) rats received repeated injections of NTG to construct a CM model. Mechanical and thermal thresholds were measured using Von Frey filaments and hot plate tests. C-Fos expression was measured by western blotting and immunofluorescence staining to assess the central sensitization. PACAP6-38 was intracerebrally injected into the trigeminal nucleus caudalis (TNC), and then the changes in c-Fos, the synaptic-associated proteins, phospho-ERK1/2 (p-ERK1/2), phosphorylation of cyclic adenosine monophosphate response element-binding protein (p-CREB) and brain-derived neurotrophic factor (BDNF) were detected. Transmission electron microscopy (TEM) and Golgi-Cox staining were used to observe the ultrastructure of synapses and dendritic structures of TNC neurons.

RESULTS

The results showed that PACAP and PAC1R expression were significantly raised in the TNC after repeated NTG injections. Additionally, PACAP6-38 treatment alleviated nociceptive sensitization, inhibited NTG-induced overexpression of c-Fos and synaptic-associated proteins in the TNC of CM rat, restored aberrant synaptic structures. Furthermore, the expression of ERK/CREB/BDNF pathway was depressed by PACAP6-38.

CONCLUSIONS

Our results demonstrated that abnormal synaptic structure in the TNC of CM, which could be reversed by inhibition of PAC1R via down-regulating the ERK/CREB/BDNF signaling pathway. PACAP6-38 improves NTG-induced central sensitization by regulating synaptic plasticity in the TNC of CM rat, which may provide new insights into the treatments targeting PACAP/PAC1R in migraine.

The effect of Lu AG09222 on PACAP38- and VIP-induced vasodilation, heart rate increase, and headache in healthy subjects: an interventional, randomized, double-blind, parallel-group, placebo-controlled study

BACKGROUND

Pituitary adenylate cyclase-activating polypeptide (PACAP), structurally related to vasoactive intestinal peptide (VIP), is one of the important mediators in the pathogenesis of migraine and is known to dilate cranial arteries and induce headache and migraine. Our objective was to determine whether Lu AG09222-an investigational humanized monoclonal antibody directed against PACAP ligand-would inhibit the PACAP-signaling cascade by abolishing its vasodilatory and headache-inducing abilities.

METHODS

In a randomized, double-blind, parallel-group, single-dose, placebo-controlled study of Lu AG09222, healthy volunteers aged 18-45 years without history of headache disorders were randomly allocated to three treatment sequences (1:2:2) on two experimental infusion visits with 9 ± 3 days' interval: placebo + saline + saline (n = 5), placebo + PACAP38 + VIP (n = 10), and Lu AG09222 + PACAP38 + VIP (n = 10). The primary outcome measure was area under the curve (AUC) of the change in superficial temporal artery (STA) diameter from 0 to 120 min after start of infusion of PACAP38. The study was conducted at the Danish Headache Center in Copenhagen, Denmark.

RESULTS

In participants who received Lu AG09222 + PACAP38 infusion, there was a significantly lower STA diameter (mean (SE) [95% CI] AUC ‒35.4 (4.32) [‒44.6, ‒26.3] mm × min; P < 0.0001) compared to participants who received placebo + PACAP38 infusion. Secondary and explorative analysis revealed that PACAP38 infusion induced an increase in facial blood flow, heart rate and mild headache, and indicated that these PACAP38-induced responses were inhibited by Lu AG09222.

CONCLUSIONS

This proof-of-mechanism study demonstrated that Lu AG09222 inhibited PACAP38-induced cephalic vasodilation and increases in heart rate, and reduced concomitant headache. Lu AG09222 may be a potential therapy against migraine and other PACAP-mediated diseases.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT04976309. Registration date: July 19, 2021.

PACAP-mediated gating of anxiety-controlling circuits

Combining the use of ex vivo and in vivo optogenetics, viral tracing, electrophysiology and behavioral testing, we show that the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) gates anxiety-controlling circuits by differentially affecting synaptic efficacy at projections from the basolateral amygdala (BLA) to two different subdivisions of the dorsal subdivision of the bed nucleus of the stria terminalis (BNST), modifying the signal flow in BLA-ovBNST-adBNST circuits in such a way that adBNST is inhibited. Inhibition of adBNST is translated into the reduced firing probability of adBNST neurons during afferent activation, explaining the anxiety-triggering actions of PACAP in BNST, as inhibition of adBNST is anxiogenic. Our results reveal how innate, fear-related behavioral mechanisms may be controlled by neuropeptides, PACAP specifically, at the level of underlying neural circuits by inducing long-lasting plastic changes in functional interactions between their different structural components.

Shared and independent roles of CGRP and PACAP in migraine pathophysiology

The neuropeptides calcitonin gene-related peptide (CGRP) and pituitary adenylate cyclase-activating polypeptide (PACAP) have emerged as mediators of migraine pathogenesis. Both are vasodilatory peptides that can cause migraine-like attacks when infused into people and migraine-like symptoms when injected into rodents. In this narrative review, we compare the similarities and differences between the peptides in both their clinical and preclinical migraine actions. A notable clinical difference is that PACAP, but not CGRP, causes premonitory-like symptoms in patients. Both peptides are found in distinct, but overlapping areas relevant to migraine, most notably with the prevalence of CGRP in trigeminal ganglia and PACAP in sphenopalatine ganglia. In rodents, the two peptides share activities, including vasodilation, neurogenic inflammation, and nociception. Most strikingly, CGRP and PACAP cause similar migraine-like symptoms in rodents that are manifested as light aversion and tactile allodynia. Yet, the peptides appear to act by independent mechanisms possibly by distinct intracellular signaling pathways. The complexity of these signaling pathways is magnified by the existence of multiple CGRP and PACAP receptors that may contribute to migraine pathogenesis. Based on these differences, we suggest PACAP and its receptors provide a rich set of targets to complement and augment the current CGRP-based migraine therapeutics.

Control of myeloid cell functions by nociceptors

The immune system has evolved to protect the host from infectious agents, parasites, and tumor growth, and to ensure the maintenance of homeostasis. Similarly, the primary function of the somatosensory branch of the peripheral nervous system is to collect and interpret sensory information about the environment, allowing the organism to react to or avoid situations that could otherwise have deleterious effects. Consequently, a teleological argument can be made that it is of advantage for the two systems to cooperate and form an “integrated defense system” that benefits from the unique strengths of both subsystems. Indeed, nociceptors, sensory neurons that detect noxious stimuli and elicit the sensation of pain or itch, exhibit potent immunomodulatory capabilities. Depending on the context and the cellular identity of their communication partners, nociceptors can play both pro- or anti-inflammatory roles, promote tissue repair or aggravate inflammatory damage, improve resistance to pathogens or impair their clearance. In light of such variability, it is not surprising that the full extent of interactions between nociceptors and the immune system remains to be established. Nonetheless, the field of peripheral neuroimmunology is advancing at a rapid pace, and general rules that appear to govern the outcomes of such neuroimmune interactions are beginning to emerge. Thus, in this review, we summarize our current understanding of the interaction between nociceptors and, specifically, the myeloid cells of the innate immune system, while pointing out some of the outstanding questions and unresolved controversies in the field. We focus on such interactions within the densely innervated barrier tissues, which can serve as points of entry for infectious agents and, where known, highlight the molecular mechanisms underlying these interactions.

PACAP and acetylcholine cause distinct Ca2+ signals and secretory responses in chromaffin cells

The adrenomedullary chromaffin cell transduces chemical messages into outputs that regulate end organ function throughout the periphery. At least two important neurotransmitters are released by innervating preganglionic neurons to stimulate exocytosis in the chromaffin cell-acetylcholine (ACh) and pituitary adenylate cyclase activating polypeptide (PACAP). Although PACAP is widely acknowledged as an important secretagogue in this system, the pathway coupling PACAP stimulation to chromaffin cell secretion is poorly understood. The goal of this study is to address this knowledge gap. Here, it is shown that PACAP activates a Gαs-coupled pathway that must signal through phospholipase C ε (PLCε) to drive Ca2+ entry and exocytosis. PACAP stimulation causes a complex pattern of Ca2+ signals in chromaffin cells, leading to a sustained secretory response that is kinetically distinct from the form stimulated by ACh. Exocytosis caused by PACAP is associated with slower release of peptide cargo than exocytosis stimulated by ACh. Importantly, only the secretory response to PACAP, not ACh, is eliminated in cells lacking PLCε expression. The data show that ACh and PACAP, acting through distinct signaling pathways, enable nuanced and variable secretory outputs from chromaffin cells.

Temporal alterations of pituitary adenylate cyclase activating polypeptide and its receptors in a rat model induced by recurrent chemical stimulations: Relevant to chronic migraine

Background: Migraine is a common type of primary headache with disabling brain dysfunction. It has been found that pituitary adenylate cyclase activating polypeptide (PACAP) is involved in the pathogenesis of migraine, however, the role of PACAP and its receptors in chronic migraine remains unclear. Therefore, the present study aimed to explore the changes of PACAP and its receptors in different duration after recurrent dural inflammation soup stimulations and to investigate the co-expression between PACAP and calcitonin gene-related peptide (CGRP). Methods: Adult male rats were implanted with cannula surrounding superior sagittal sinus, which was followed by dural infusion of inflammatory soup (IS) or normal saline (NS). The rats were randomly divided into 4 groups (n = 8 for each group): IS stimulation for seven days (IS-7 group), IS stimulation for 14 days (IS-14 group), IS stimulation for 21 days (IS-21 group), and NS control for 21 days (CON group). The facial mechanical withdrawal threshold was daily measured during the whole experiment. The behavioral changes (ipsilateral and bilateral face grooming behavior) in a plastic cage of rats were observed and recorded. The expression of PACAP, its receptors (PAC1, VPAC1, VPAC2), and CGRP in the trigeminal ganglia (TG) and the trigeminal nucleus caudalis (TNC) was examined by immunohistochemistry. Immunofluorescence was used to explore the co-expression of PACAP, PAC1 receptor, and CGRP after repeated IS administration in the TG. Results: The ipsilateral facial grooming time of IS-21 group displayed an apparent increase than CON group after repeated stimulation on day 2, while significant differences were observed on day 14. No differences were found between the IS-21 and CON group in bilateral facial grooming. Dural IS stimulation induced a significantly decrease in facial mechanical withdrawal thresholds. PACAP positive cells in the regions of TNC were gradually decreased with the IS days increasing. PACAP and PAC1 receptor expression in the TG had a trend of increasing first and then decreasing. There was no significant difference in expression of VPAC1 and VPAC2 in the TG and the TNC. Immunofluorescence showed that PACAP was mainly expressed in TG neurons. PACAP and PAC1 receptor co-expression decreased gradually after repetitive IS stimulation. While the co-expression between PACAP and CGRP reached the peak in IS-7 group after repetitive IS stimulation, and then decreased. Conclusions: This study demonstrated that repetitive chemical stimulations induced a gradual decrease of PACAP in the TNC, while the PACAP and PAC1 receptor expression in TG showed dynamical changes of increasing first and then decreasing after repeated IS administration. These results suggested exhaustion of PACAP could be involved in the duration of chronic migraine and implied PACAP may contribute to the pathology of migraine through the PAC1 receptor, which was associated with CGRP.

Role of PACAP in migraine: An alternative to CGRP?

Migraine is a widespread and debilitating neurological condition affecting more than a billion people worldwide. Thus, more effective migraine therapies are highly needed. In the last decade, two endogenous neuropeptides, calcitonin gene-related peptide (CGRP) and pituitary adenylate cyclase-activating peptide (PACAP), were identified to be implicated in migraine. Recently, introduction of monoclonal antibodies (mAbs) blocking the CGRP is the most important advance in migraine therapy for decades. However, 40% of patients are unresponsive to these new drugs. We believe that PACAP may be involved in these patients. Like CGRP, PACAP is located to sensory nerve fibers, it dilates cranial arteries, it causes migraine when infused into patients and it is a peptide that lends itself to antibody therapy. Also, recent studies suggest that the PACAP pathway is independent of the CGRP pathway. Understanding the signaling pathways of PACAP may therefore lead to identification of novel therapeutic targets of particular interest in patients unresponsive to anti-CGRP therapy. Accordingly, neutralizing mAb to PACAP is currently in clinical phase II development. The aim of the present review is, therefore, to give a thorough account of the existing data on PACAP, its receptors and its relation to migraine.

Evaluation of serum VIP and aCGRP during pulmonary exacerbation in cystic fibrosis: A longitudinal pilot study of patients undergoing antibiotic therapy

BACKGROUND

Objective monitoring of improvement during treatment of pulmonary exacerbation can be difficulty in children when pulmonary function testing cannot be obtained. Thus, the identification of predictive biomarkers to determine the efficacy of drug treatments is of high priority. The major aim of the current study was to investigate the serum levels of vasoactive intestinal peptide (VIP) and alpha calcitonin gene related peptide (aCGRP) of cystic fibrosis pediatric patients during pulmonary exacerbation and post-antibiotic therapy, and possible associations of their levels with different clinicopathological parameters.

METHODS

21 patients with cystic fibrosis were recruited at onset of pulmonary exacerbation. Serum was collected at time of admission, three days post-antibiotic therapy, and two weeks post-antibiotic therapy (end of antibiotic therapy). Serum VIP and aCGRP levels were measured using ELISA.

RESULTS

Overall least square means of serum aCGRP level but not VIP changed from time of exacerbation to completion of antibiotic therapy (p = 0.005). Serum VIP was significantly associated with the presence of diabetes mellitus (p = 0.026) and other comorbidities (p = 0.013), and with type of antibiotic therapy (p = 0.019). Serum aCGRP level was significantly associated with type of antibiotic therapy (p = 0.012) and positive Staphylococcus aureus microbiology test (p = 0.046).

CONCLUSION

This study could only show significant changes in serum aCGRP levels following treatment of pulmonary exacerbations. Future studies with larger sample size are required to investigate the clinical importance of VIP and aCGRP in cystic fibrosis patients.

PACAP signaling is not involved in GTN- and levcromakalim-induced hypersensitivity in mouse models of migraine

BACKGROUND

Calcitonin gene-related peptide (CGRP) antagonizing drugs represents the most important advance in migraine therapy for decades. However, these new drugs are only effective in 50-60% of patients. Recent studies have shown that the pituitary adenylate cyclase-activating peptide (PACAP38) pathway is independent from the CGRP signaling pathway. Here, we investigate PACAP38 signaling pathways in relation to glyceryl trinitrate (GTN), levcromakalim and sumatriptan.

METHODS

In vivo mouse models of PACAP38-, GTN-, and levcromakalim-induced migraine were applied using tactile sensitivity to von Frey filaments as measuring readout. Signaling pathways involved in the three models were dissected using PACAP-inhibiting antibodies (mAbs) and sumatriptan.

RESULTS

We showed that PACAP mAbs block PACAP38 induced hypersensitivity, but not via signaling pathways involved in GTN and levcromakalim. Also, sumatriptan has no effect on PACAP38-induced hypersensitivity relevant to migraine. This is the first study testing the effect of a PACAP-inhibiting drug on GTN- and levcromakalim-induced hypersensitivity.

CONCLUSIONS

Based on the findings in our mouse model of migraine using migraine-inducing compounds and anti-migraine drugs, we suggest that PACAP acts via a distinct pathway. Using PACAP38 antagonism may be a novel therapeutic target of interest in a subgroup of migraine patients who do not respond to existing therapies.

Neurotransmitter phenotype and axonal projection patterns of VIP-expressing neurons in the inferior colliculus

Neurons in the inferior colliculus (IC), the midbrain hub of the central auditory pathway, send ascending and descending projections to other auditory brain regions, as well as projections to other sensory and non-sensory brain regions. However, the axonal projection patterns of individual classes of IC neurons remain largely unknown. Vasoactive intestinal polypeptide (VIP) is a neuropeptide expressed by subsets of neurons in many brain regions. We recently identified a class of IC stellate neurons that we called VIP neurons because they are labeled by tdTomato (tdT) expression in VIP-IRES-Cre x Ai14 mice. Here, using fluorescence in situ hybridization, we found that tdT+ neurons in VIP-IRES-Cre x Ai14 mice express Vglut2, a marker of glutamatergic neurons, and VIP, suggesting that VIP neurons use both glutamatergic and VIPergic signaling to influence their postsynaptic targets. Next, using viral transfections with a Cre-dependent eGFP construct, we labeled the axonal projections of VIP neurons. As a group, VIP neurons project intrinsically, within the ipsilateral and contralateral IC, and extrinsically to all the major targets of the IC. Within the auditory system, VIP neurons sent axons and formed axonal boutons in higher centers, including the medial geniculate nucleus and the nucleus of the brachium of the IC. Less dense projections terminated in lower centers, including the nuclei of the lateral lemniscus, superior olivary complex, and dorsal cochlear nucleus. VIP neurons also project to several non-auditory brain regions, including the superior colliculus, periaqueductal gray, and cuneiform nucleus. The diversity of VIP projections compared to the homogeneity of VIP neuron intrinsic properties suggests that VIP neurons play a conserved role at the microcircuit level, likely involving neuromodulation through glutamatergic and VIPergic signaling, but support diverse functions at the systems level through their participation in different projection pathways.

Understanding VPAC receptor family peptide binding and selectivity

The vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) receptors are key regulators of neurological processes. Despite recent structural data, a comprehensive understanding of peptide binding and selectivity among different subfamily receptors is lacking. Here, we determine structures of active, Gs-coupled, VIP-VPAC1R, PACAP27-VPAC1R, and PACAP27-PAC1R complexes. Cryo-EM structural analyses and molecular dynamics simulations (MDSs) reveal fewer stable interactions between VPAC1R and VIP than for PACAP27, more extensive dynamics of VIP interaction with extracellular loop 3, and receptor-dependent differences in interactions of conserved N-terminal peptide residues with the receptor core. MD of VIP modelled into PAC1R predicts more transient VIP-PAC1R interactions in the receptor core, compared to VIP-VPAC1R, which may underlie the selectivity of VIP for VPAC1R over PAC1R. Collectively, our work improves molecular understanding of peptide engagement with the PAC1R and VPAC1R that may benefit the development of novel selective agonists.

Immunomodulatory Role of Neuropeptides in the Cornea

The transparency of the cornea along with its dense sensory innervation and resident leukocyte populations make it an ideal tissue to study interactions between the nervous and immune systems. The cornea is the most densely innervated tissue of the body and possesses both immune and vascular privilege, in part due to its unique repertoire of resident immune cells. Corneal nerves produce various neuropeptides that have a wide range of functions on immune cells. As research in this area expands, further insights are made into the role of neuropeptides and their immunomodulatory functions in the healthy and diseased cornea. Much remains to be known regarding the details of neuropeptide signaling and how it contributes to pathophysiology, which is likely due to complex interactions among neuropeptides, receptor isoform-specific signaling events, and the inflammatory microenvironment in disease. However, progress in this area has led to an increase in studies that have begun modulating neuropeptide activity for the treatment of corneal diseases with promising results, necessitating the need for a comprehensive review of the literature. This review focuses on the role of neuropeptides in maintaining the homeostasis of the ocular surface, alterations in disease settings, and the possible therapeutic potential of targeting these systems.

Effects of Pituitary Adenylate Cyclase Activating Polypeptide on Cell Death

Pituitary adenylate cyclase activating polypeptide (PACAP) was first isolated as a hypothalamic peptide based on its efficacy to increase adenylate cyclase (AC) activity. It has a widespread distribution throughout the body including the nervous system and peripheral organs, where PACAP exerts protective effects both in vivo and in vitro through its anti-apoptotic, anti-inflammatory, and antioxidant functions. The aim of the present paper was to review the currently available literature regarding the effects of PACAP on cell death in vitro in neural and non-neural cells. Among others, its effect on apoptosis can be detected in cerebellar granule cells against different toxic stimuli. Different neural cell types from the cerebral cortex are also prevented from cell death. PACAP also shows effects on cell death in cells belonging to the peripheral nervous system and protects both neural and non-neural cells of sensory organs. In addition, cell survival-promoting effect can be observed in different peripheral organ systems including cardiovascular, immune, respiratory, gastrointestinal, urinary, and reproductive systems. The studies summarized here indicate its noteworthy effect on cell death in different in vitro models, suggesting PACAP’s potential therapeutic usage in several pathological conditions.

Secreted key regulators (Fgf1, Bmp4, Gdf3) are expressed by PAC1-immunopositive retinal ganglion cells in the postnatal rat retina

Identified as a member of the secretin/glucagon/VIP superfamily, pituitary adenylate cyclase-activating polypeptide (PACAP1-38) has been recognized as a hormone, neurohormone, transmitter, trophic factor, and known to be involved in diverse and multiple developmental processes. PACAP1-38 was reported to regulate the production of important morphogens (Fgf1, Bmp4, Gdf3) through PAC1-receptor in the newborn rat retina. To follow up, we aimed to reveal the identity of retinal cells responsible for the production and secretion of Fgf1, Bmp4, and Gdf3 in response to PACAP1-38 treatment. Newborn (P1) rats were treated with 100 pmol PACAP1-38 intravitreally. After 24 h, retinas were dissected and processed for immunohistochemistry performed either on flat-mounted retinas or cryosections. Brn3a and PAC1-R double labeling revealed that 90% of retinal ganglion cells (RGCs) expressed PAC1-receptor. We showed that RGCs were Fgf1, Bmp4, and Gdf3- immunopositive and PAC1-R was co-expressed with each protein. To elucidate if RGCs release these secreted regulators, the key components for vesicle release were examined. No labeling was detected for synaptophysin, Exo70, or NESP55 in RGCs but an intense Rab3a-immunoreactivity was detected in their cell bodies. We found that the vast majority of RGCs are responsive to PACAP, which in turn could have a significant impact on their development or/and physiology. Although Fgf1, Bmp4, and Gdf3 were abundantly expressed in PAC1-positive RGCs, the cells lack synaptophysin and Exo70 in the newborn retina thus unable to release these proteins. These proteins could regulate postnatal RGC development acting through intracrine pathways.

Current overview of the role of neuropeptides in ILC2s and future directions

The neural and immune systems are closely connected, and recently, their molecular mechanisms and relationships with diseases have attracted substantial attention. Particularly, it has been increasingly reported that ILC2s, which produce type 2 cytokines independent of acquired immunity, are regulated by neuropeptides such as catecholamines, acetylcholine, vasoactive intestinal peptide, neuromedins, and calcitonin gene-related peptide. However, the regulatory mechanisms in this regard are only partially understood, implying that further studies are still needed to clarify the complete mechanisms and processes. In this review, we summarize current reports on the regulatory effect of neuropeptides on ILC2s, some of which have conflicting results, possibly owing to the complexity of G-protein coupled receptors. By summarizing the current evidence, we hope to be able to identify what is currently unknown as well as what needs to be clarified in the future.

VIP plasma levels associate with survival in severe COVID-19 patients, correlating with protective effects in SARS-CoV-2-infected cells

Infection by SARS‐CoV‐2 may elicit uncontrolled and damaging inflammatory responses. Thus, it is critical to identify compounds able to inhibit virus replication and thwart the inflammatory reaction. Here, we show that the plasma levels of the immunoregulatory neuropeptide VIP are elevated in patients with severe COVID‐19, correlating with reduced inflammatory mediators and with survival on those patients. In vitro, vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase‐activating polypeptide (PACAP), highly similar neuropeptides, decreased the SARS‐CoV‐2 RNA content in human monocytes and viral production in lung epithelial cells, also reducing cell death. Both neuropeptides inhibited the production of proinflammatory mediators in lung epithelial cells and in monocytes. VIP and PACAP prevented in monocytes the SARS‐CoV‐2‐induced activation of NF‐kB and SREBP1 and SREBP2, transcriptions factors involved in proinflammatory reactions and lipid metabolism, respectively. They also promoted CREB activation, a transcription factor with antiapoptotic activity and negative regulator of NF‐kB. Specific inhibition of NF‐kB and SREBP1/2 reproduced the anti‐inflammatory, antiviral, and cell death protection effects of VIP and PACAP. Our results support further clinical investigations of these neuropeptides against COVID‐19.

New Insights on Metabolic and Genetic Basis of Migraine: Novel Impact on Management and Therapeutical Approach

Migraine is a hereditary disease, usually one-sided, sometimes bilateral. It is characterized by moderate to severe pain, which worsens with physical activity and may be associated with nausea and vomiting, may be accompanied by photophobia and phonophobia. The disorder can occur at any time of the day and can last from 4 to 72 h, with and without aura. The pathogenic mechanism is unclear, but extensive preclinical and clinical studies are ongoing. According to electrophysiology and imaging studies, many brain areas are involved, such as cerebral cortex, thalamus, hypothalamus, and brainstem. The activation of the trigeminovascular system has a key role in the headache phase. There also appears to be a genetic basis behind the development of migraine. Numerous alterations have been identified, and in addition to the genetic cause, there is also a close association with the surrounding environment, as if on the one hand, the genetic alterations may be responsible for the onset of migraine, on the other, the environmental factors seem to be more strongly associated with exacerbations. This review is an analysis of neurophysiological mechanisms, neuropeptide activity, and genetic alterations that play a fundamental role in choosing the best therapeutic strategy. To date, the goal is to create a therapy that is as personalized as possible, and for this reason, steps forward have been made in the pharmacological field in order to identify new therapeutic strategies for both acute treatment and prophylaxis.

Pituitary adenylate cyclase-activating polypeptide receptor activation in the hypothalamus recruits unique signaling pathways involved in energy homeostasis

Pituitary adenylate cyclase activating polypeptide (PACAP) exerts pleiotropic effects on ventromedial nuclei (VMN) of the hypothalamus and its control of feeding and energy expenditure through the type I PAC1 receptor (PAC1R). However, the endogenous role of PAC1Rs in the VMN and the downstream signaling responsible for PACAP's effects on energy balance are unknown. Numerous studies have revealed that PAC1Rs are coupled to both Gαs/adenylyl cyclase/protein kinase A (Gαs/AC/PKA) and Gαq/phospholipase C/protein kinase C (Gαq/PLC/PKC), while also undergoing trafficking following stimulation. To determine the endogenous role of PAC1Rs and downstream signaling that may explain PACAP's pleiotropic effects, we used RNA interference to knockdown VMN PAC1Rs and pharmacologically inhibited PKA, PKC, and PAC1R trafficking. Knocking down PAC1Rs increased meal sizes, reduced total number of meals, and induced body weight gain. Inhibition of either PKA or PKC alone in awake male Sprague-Dawley rats, attenuated PACAP's hypophagic and anorectic effects during the dark phase. However, PKA or PKC inhibition potentiated PACAP's thermogenic effects during the light phase. Analysis of locomotor activity revealed that PKA inhibition augmented PACAP's locomotor effects, whereas PKC inhibition had no effect. Finally, PACAP administration in the VMN induces surface PAC1R trafficking into the cytosol which was blocked by endocytosis inhibitors. Subsequently, inhibition of PAC1R trafficking into the cytosol attenuated PACAP-induced hypophagia. These results revealed that endogenous PAC1Rs uniquely engage PKA, PKC, and receptor trafficking to mediate PACAP's pleiotropic effects in VMN control of feeding and metabolism.NEW & NOTEWORTHY Endogenous PAC1 receptors, integral to VMN management of feeding behavior and body weight regulation, uniquely engage PKA, PKC, and receptor trafficking to mediate the hypothalamic ventromedial nuclei control of feeding and metabolism. PACAP appears to use different signaling mechanisms to regulate feeding behavior from its effects on metabolism.

Vasoactive intestinal peptide exerts an excitatory effect on hypothalamic kisspeptin neurons during estrogen negative feedback

Hypothalamic kisspeptin neurons are the primary modulators of gonadotropin-releasing hormone (GnRH) neurons. It has been shown that circadian rhythms driven by the suprachiasmatic nucleus (SCN) contribute to GnRH secretion. Kisspeptin neurons are potential targets of SCN neurons due to reciprocal connections with the anteroventral periventricular and rostral periventricular nuclei (AVPV/PeN) and the arcuate nucleus of the hypothalamus (ARH). Vasoactive intestinal peptide (VIP), a notable SCN neurotransmitter, modulates GnRH secretion depending on serum estradiol levels, aging or time of the day. Considering that kisspeptin neurons may act as interneurons and mediate VIP's effects on the reproductive axis, we investigated the effects of VIP on hypothalamic kisspeptin neurons in female mice during estrogen negative feedback. Our findings indicate that VIP induces a TTX-independent depolarization of approximately 30% of AVPV/PeN kisspeptin neurons in gonad-intact (diestrus) and ovariectomized (OVX) mice. In the ARH, the percentage of kisspeptin neurons that were depolarized by VIP was even higher (approximately 90%). An intracerebroventricular infusion of VIP leds to an increased percentage of kisspeptin neurons expressing the phospho^Ser133 cAMP-response-element-binding protein (pCREB) in the AVPV/PeN. On the other hand, pCREB expression in ARH kisspeptin neurons was similar between saline- and VIP-injected mice. Thus, VIP can recruit different signaling pathways to modulate AVPV/PeN or ARH kisspeptin neurons, resulting in distinct cellular responses. The expression of VIP receptors (VPACR) was upregulated in the AVPV/PeN, but not in the ARH, of OVX mice compared to mice on diestrus and estradiol-primed OVX mice. Our findings indicate that VIP directly influences distinct cellular aspects of the AVPV/PeN and ARH kisspeptin neurons during estrogen negative feedback, possibly to influence pulsatile LH secretion.

PACAP-38 Induces Transcriptomic Changes in Rat Trigeminal Ganglion Cells Related to Neuroinflammation and Altered Mitochondrial Function Presumably via PAC1/VPAC2 Receptor-Independent Mechanism

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a broadly expressed neuropeptide which has diverse effects in both the peripheral and central nervous systems. While its neuroprotective effects have been shown in a variety of disease models, both animal and human data support the role of PACAP in migraine generation. Both PACAP and its truncated derivative PACAP(6-38) increased calcium influx in rat trigeminal ganglia (TG) primary sensory neurons in most experimental settings. PACAP(6-38), however, has been described as an antagonist for PACAP type I (known as PAC1), and Vasoactive Intestinal Polypeptide Receptor 2 (also known as VPAC2) receptors. Here, we aimed to compare the signaling pathways induced by the two peptides using transcriptomic analysis. Rat trigeminal ganglion cell cultures were incubated with 1 µM PACAP-38 or PACAP(6-38). Six hours later RNA was isolated, next-generation RNA sequencing was performed and transcriptomic changes were analyzed to identify differentially expressed genes. Functional analysis was performed for gene annotation using the Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and Reactome databases. We found 200 common differentially expressed (DE) genes for these two neuropeptides. Both PACAP-38 and PACAP(6-38) treatments caused significant downregulation of NADH: ubiquinone oxidoreductase subunit B6 and upregulation of transient receptor potential cation channel, subfamily M, member 8. The common signaling pathways induced by both peptides indicate that they act on the same target, suggesting that PACAP activates trigeminal primary sensory neurons via a mechanism independent of the identified and cloned PAC1/VPAC2 receptor, either via another target structure or a different splice variant of PAC1/VPAC2 receptors. Identification of the target could help to understand key mechanisms of migraine.

Signal Transduction by VIP and PACAP Receptors

Homeostasis of the human immune system is regulated by many cellular components, including two neuropeptides, VIP and PACAP, primary stimuli for three class B G protein-coupled receptors, VPAC1, VPAC2, and PAC1. Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) regulate intestinal motility and secretion and influence the functioning of the endocrine and immune systems. Inhibition of VIP and PACAP receptors is an emerging concept for new pharmacotherapies for chronic inflammation and cancer, while activation of their receptors provides neuroprotection. A small number of known active compounds for these receptors still impose limitations on their use in therapeutics. Recent cryo-EM structures of VPAC1 and PAC1 receptors in their agonist-bound active state have provided insights regarding their mechanism of activation. Here, we describe major molecular switches of VPAC1, VPAC2, and PAC1 that may act as triggers for receptor activation and compare them with similar non-covalent interactions changing upon activation that were observed for other GPCRs. Interhelical interactions in VIP and PACAP receptors that are important for agonist binding and/or activation provide a molecular basis for the design of novel selective drugs demonstrating anti-inflammatory, anti-cancer, and neuroprotective effects. The impact of genetic variants of VIP, PACAP, and their receptors on signalling mediated by endogenous agonists is also described. This sequence diversity resulting from gene splicing has a significant impact on agonist selectivity and potency as well as on the signalling properties of VIP and PACAP receptors.

Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) Protects Striatal Cells and Improves Motor Function in Huntington’s Disease Models: Role of PAC1 Receptor

Huntington’s disease (HD) is a hereditary neurodegenerative disorder caused by the expression of mutant huntingtin (mHtt). One of the main features of HD is the degeneration of the striatum that leads to motor discoordination. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide that acts through three receptors named PAC1R, VPAC1R, and VPAC2R. In the present study, we first investigated the effect of PACAP on STHdhQ7/Q7 and STHdhQ111/Q111 cells that express wild-type Htt with 7 and mHtt with 111 glutamines, respectively. Then we explored the capacity of PACAP to rescue motor symptoms in the R6/1, a murine model of HD. We found that PACAP treatment (10^–7 M) for 24 h protects STHdhQ111/Q111 cells from mHtt-induced apoptosis. This effect is associated with an increase in PAC1R transcription, phosphorylation of ERK and Akt, and an increase of intracellular c-fos, egr1, CBP, and BDNF protein content. Moreover, the use of pharmacological inhibitors revealed that activation of ERK and Akt mediates these antiapoptotic and neurotrophic effects of PACAP. To find out PAC1R implication, we treated STHdh cells with vasoactive intestinal peptide (VIP), which exhibits equal affinity for VPAC1R and VPAC2R, but lower affinity for PAC1R, in contrast to PACAP which has same affinity for the three receptors. VIP reduced cleaved caspase-3 protein level, without promoting the expression of c-fos, egr1, CBP, and the neurotrophin BDNF. We next measured the protein level of PACAP receptors in the striatum and cortex of R6/1 mice. We observed a specific reduction of PAC1R at the onset of motor symptoms. Importantly, the intranasal administration of PACAP to R6/1 animals restored the motor function and increased the striatal levels of PAC1R, CBP, and BDNF. In conclusion, PACAP exerts antiapoptotic and neurotrophic effects in striatal neurons mainly through PAC1R. This effect in HD striatum allows the recovery of motor function and point out PAC1R as a therapeutic target for treatment of HD.

A Broad Overview on Pituitary Adenylate Cyclase-Activating Polypeptide Role in the Eye: Focus on Its Repairing Effect in Cornea

Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) is a neuropeptide with widespread distribution throughout the central and peripheral nervous system as well as in many other peripheral organs. It plays cytoprotective effects mediated mainly through the activation of specific receptors. PACAP is known to play pleiotropic effects on the eye, including the cornea, protecting it against different types of insult. This review firstly provides an overview of the anatomy of the cornea and summarizes data present in literature about PACAP’s role in the eye and, in particular, in the cornea, either in physiological or pathological conditions.

A Review on the Role of Endogenous Neurotrophins and Schwann Cells in Axonal Regeneration

Injury to the peripheral nerve is traditionally referred to acquired nerve injury as they are the result of physical trauma due to laceration, stretch, crush and compression of nerves. However, peripheral nerve injury may not be completely limited to acquired physical trauma. Peripheral nerve injury equally implies clinical conditions like Guillain-Barré syndrome (GBS), Carpal tunnel syndrome, rheumatoid arthritis and diabetes. Physical trauma is commonly mono-neuropathic as it engages a single nerve and produces focal damage, while in the context of pathological conditions the damage is divergent involving a group of the nerve causing polyneuropathy. Damage to the peripheral nerve can cause a diverse range of manifestations from sensory impairment to loss of function with unpredictable recovery patterns. Presently no treatment option provides complete or functional recovery in nerve injury, as nerve cells are highly differentiated and inert to regeneration. However, the regenerative phenotypes in Schwann cells get expressed when a signalling cascade is triggered by neurotrophins. Neurotrophins are one of the promising biomolecules that are released naturally post-injury with the potential to exhibit better functional recovery. Pharmacological intervention modulating the expression of these neurotrophins such as brain-derived neurotrophic factor (BDNF) and pituitary adenylyl cyclase-activating peptide (PACAP) can prove to be a significant treatment option as endogenous compounds which may have remarkable innate advantage showing maximum 'biological relevance'.

Design and Synthesis of Brain Penetrant Glycopeptide Analogues of PACAP With Neuroprotective Potential for Traumatic Brain Injury and Parkinsonism

There is an unmet clinical need for curative therapies to treat neurodegenerative disorders. Most mainstay treatments currently on the market only alleviate specific symptoms and do not reverse disease progression. The Pituitary adenylate cyclase-activating polypeptide (PACAP), an endogenous neuropeptide hormone, has been extensively studied as a potential regenerative therapeutic. PACAP is widely distributed in the central nervous system (CNS) and exerts its neuroprotective and neurotrophic effects via the related Class B GPCRs PAC1, VPAC1, and VPAC2, at which the hormone shows roughly equal activity. Vasoactive intestinal peptide (VIP) also activates these receptors, and this close analogue of PACAP has also shown to promote neuronal survival in various animal models of acute and progressive neurodegenerative diseases. However, PACAP's poor pharmacokinetic profile (non-linear PK/PD), and more importantly its limited blood-brain barrier (BBB) permeability has hampered development of this peptide as a therapeutic. We have demonstrated that glycosylation of PACAP and related peptides promotes penetration of the BBB and improves PK properties while retaining efficacy and potency in the low nanomolar range at its target receptors. Furthermore, judicious structure-activity relationship (SAR) studies revealed key motifs that can be modulated to afford compounds with diverse selectivity profiles. Most importantly, we have demonstrated that select PACAP glycopeptide analogues (2LS80Mel and 2LS98Lac) exert potent neuroprotective effects and anti-inflammatory activity in animal models of traumatic brain injury and in a mild-toxin lesion model of Parkinson's disease, highlighting glycosylation as a viable strategy for converting endogenous peptides into robust and efficacious drug candidates.

Therapeutic potential of vasoactive intestinal peptide and its receptor VPAC2 in type 2 diabetes

Owing to the increasing prevalence of type 2 diabetes, the development of novel hypoglycemic drugs has become a research hotspot, with the ultimate goal of developing therapeutic drugs that stimulate glucose-induced insulin secretion without inducing hypoglycemia. Vasoactive intestinal peptide (VIP), a 28-amino-acid peptide, can stimulate glucose-dependent insulin secretion, particularly by binding to VPAC2 receptors. VIP also promotes islet β-cell proliferation through the forkhead box M1 pathway, but the specific molecular mechanism remains to be studied. The clinical application of VIP is limited because of its short half-life and wide distribution in the human body. Based on the binding properties of VIP and VPAC2 receptors, VPAC2-selective agonists have been developed to serve as novel hypoglycemic drugs. This review summarizes the physiological significance of VIP in glucose homeostasis and the potential therapeutic value of VPAC2-selective agonists in type 2 diabetes.

Transcriptome comparative analysis of ovarian follicles reveals the key genes and signaling pathways implicated in hen egg production

Background

Ovarian follicle development plays an important role in determination of poultry egg production. The follicles at the various developmental stages possess their own distinct molecular genetic characteristics and have different biological roles in chicken ovary development and function. In the each stage, several genes of follicle-specific expression and biological pathways are involved in the vary-sized follicular development and physiological events. Identification of the pivotal genes and signaling pathways that control the follicular development is helpful for understanding their exact regulatory functions and molecular mechanisms underlying egg-laying traits of laying hens.

Results

The comparative mRNA transcriptomic analysis of ovarian follicles at three key developmental stages including slow growing white follicles (GWF), small yellow follicles (SYF) of recruitment into the hierarchy, and differentiated large yellow follicles (LYF), was accomplished in the layers with lower and higher egg production. Totally, 137, 447, and 229 of up-regulated differentially expressed genes (DEGs), and 99, 97, and 157 of down-regulated DEGs in the GWF, SYF and LYF follicles, including VIPR1, VIPR2, ADRB2, and HSD17B1 were identified, respectively. Moreover, NDUFAB1 and GABRA1 genes, two most promising candidates potentially associated with egg-laying performance were screened out from the 13 co-expressed DEGs in the GWF, SYF and LYF samples. We further investigated the biological effects of NDUFAB1 and GABRA1 on ovarian follicular development and found that NDUFAB1 promotes follicle development by stimulating granulosa cell (GC) proliferation and decreasing cell apoptosis, increases the expression of CCND1 and BCL-2 but attenuates the expression of caspase-3, and facilitates steroidogenesis by enhancing the expression of STAR and CYP11A1. In contrast, GABRA1 inhibits GC proliferation and stimulates cell apoptosis, decreases the expression of CCND1, BCL-2, STAR, and CYP11A1 but elevates the expression of caspase-3. Furthermore, the three crucial signaling pathways such as PPAR signaling pathway, cAMP signaling pathway and neuroactive ligand-receptor interaction were significantly enriched, which may play essential roles in ovarian follicle growth, differentiation, follicle selection, and maturation.

Conclusions

The current study provided new molecular data for insight into the regulatory mechanism underlying ovarian follicle development associated with egg production in chicken.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08213-w.

Modulatory role of PACAP and VIP on HIFs expression in lung adenocarcinoma

Lung adenocarcinoma is the most frequent form of non-small cell lung cancer. Inside the tumor mass, uncontrolled cell proliferation generates hypoxic areas leading to activation of hypoxia-inducible factors (HIFs) responsible for neovascularization and tumor metastasis. Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) are two neuropeptides widely distributed in respiratory organs. Previous studies have demonstrated that these peptides interfere with hypoxic pathways in various diseases, including tumors. However, their modulatory role in HIFs expression in lung adenocarcinomas has not yet been evaluated. In the present paper, we detected the expression profile of PACAP, VIP and related receptors in healthy and adenocarcinoma human lung tissue. To characterize peptides' modulatory effects on HIFs expression, we also exposed A549 lung adenocarcinoma cells and human normal bronchial epithelial BEAS-2B cells to microenvironmental hypoxia by treating them with deferoxamine (DFX). The results showed that PACAP and VIP significantly reduced HIF-1α and HIF-2α levels in both cell lines following hypoxic stress. The HIF-3α expression profile was related to cellular phenotype as it was lower in BEAS-2B and higher in A549 cells under low oxygen tension. In lung adenocarcinoma cells, peptide treatment restored HIF-3 α expression to control levels. These results suggest that endogenous PACAP and VIP exert controversial roles in cellular hypoxic microenvironments depending on the pathophysiological conditions of the lung tissue.

Emerging drugs for the prevention of migraine

INTRODUCTION

Migraine is a common and disabling neurological disorder. A greater understanding of the pathophysiological mechanisms underlying migraine has led to the availability of specific new drugs targeting calcitonin gene-related peptide (CGRP). The success of the CGRP inhibitors validates research efforts into migraine-specific therapies.

AREAS COVERED

There are additional promising therapeutic targets that will be covered in this paper, focusing on the pain phase. They include pituitary adenylate cyclase-activating polypeptide (PACAP), the orexinergic system, the nitric oxide signaling pathway specifically neuronal nitric oxide synthase inhibitors (nNOSi), and metabotropic glutamate receptor 5 (mGluR5).

EXPERT OPINION

Based on currently available research; the targets discussed in this paper are all on equal footing with each other in terms of their potential as effective novel migraine therapies. There is a need for more clinical trials to pinpoint which of these potential drug targets will be effective for migraine preventio.

Pituitary Adenylate Cyclase-Activating Polypeptide in Learning and Memory

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a highly conserved neuropeptide that regulates neuronal physiology and transcription through Gs/Gq-coupled receptors. Its actions within hypothalamic, limbic, and mnemonic systems underlie its roles in stress regulation, affective processing, neuroprotection, and cognition. Recently, elevated PACAP levels and genetic disruption of PAC1 receptor signaling in humans has been linked to maladaptive threat learning and pathological stress and fear in post-traumatic stress disorder (PTSD). PACAP is positioned to integrate stress and memory in PTSD for which memory of the traumatic experience is central to the disorder. However, PACAP's role in memory has received comparatively less attention than its role in stress. In this review, we consider the evidence for PACAP-PAC1 receptor signaling in learning and plasticity, discuss emerging data on sex differences in PACAP signaling, and raise key questions for further study toward elucidating the contribution of PACAP to adaptive and maladaptive fear learning.

Implications of VIP and PACAP in Parkinson's Disease: What do we Know So Far?

BACKGROUND

Parkinson's disease is one of the most common neurodegenerative disorders and although its aetiology is not yet fully understood, neuroinflammation has been identified as a key factor in the progression of the disease. Vasoactive intestinal peptide and pituitary adenylate-cyclase activating polypeptide are two neuropeptides that exhibit anti-inflammatory and neuroprotective properties, modulating the production of cytokines and chemokines and the behaviour of immune cells. However, the role of chemokines and cytokines modulated by the endogenous receptors of the peptides varies according to the stage of the disease.

METHODS

We present an overview of the relationship between some cytokines and chemokines with vasoactive intestinal peptide, pituitary adenylate cyclase activating polypeptide and their endogenous receptors in the context of Parkinson's disease neuroinflammation and oxidative stress, as well as the modulation of microglial cells by the peptides in this context.

RESULTS

The two peptides exhibit neuroprotective and anti-inflammatory properties in models of Parkinson's disease, as they ameliorate cognitive functions, decrease the level of neuroinflammation and promote dopaminergic neuronal survival. The peptides have been tested in a variety of in vivo and in vitro models of Parkinson's disease, demonstrating the potential for therapeutic application.

CONCLUSION

More studies are needed to establish the clinical use of vasoactive intestinal peptide and pituitary adenylate cyclase activating polypeptide as safe candidates for treating Parkinson's disease, as the use of the peptides in different stages of the disease could produce different results concerning effectiveness.