Future targets for migraine treatment beyond CGRP

BACKGROUND

Migraine is a disabling and chronic neurovascular headache disorder. Trigeminal vascular activation and release of calcitonin gene-related peptide (CGRP) play a pivotal role in the pathogenesis of migraine. This knowledge has led to the development of CGRP(-receptor) therapies. Yet, a substantial proportion of patients do not respond to these treatments. Therefore, alternative targets for future therapies are warranted. The current narrative review provides a comprehensive overview of the pathophysiological role of these possible non-CGRP targets in migraine.

FINDINGS

We covered targets of the metabotropic receptors (pituitary adenylate cyclase-activating polypeptide (PACAP), vasoactive intestinal peptide (VIP), amylin, and adrenomedullin), intracellular targets (nitric oxide (NO), phosphodiesterase-3 (PDE3) and -5 (PDE5)), and ion channels (potassium, calcium, transient receptor potential (TRP), and acid-sensing ion channels (ASIC)). The majority of non-CGRP targets were able to induce migraine-like attacks, except for (i) calcium channels, as it is not yet possible to directly target channels to elucidate their precise involvement in migraine; (ii) TRP channels, activation of which can induce non-migraine headache; and (iii) ASICs, as their potential in inducing migraine attacks has not been investigated thus far. Drugs that target its receptors exist for PACAP, NO, and the potassium, TRP, and ASIC channels. No selective drugs exist for the other targets, however, some existing (migraine) treatments appear to indirectly antagonize responses to amylin, adrenomedullin, and calcium channels. Drugs against PACAP, NO, potassium channels, TRP channels, and only a PAC₁ antibody have been tested for migraine treatment, albeit with ambiguous results.

CONCLUSION

While current research on these non-CGRP drug targets has not yet led to the development of efficacious therapies, human provocation studies using these targets have provided valuable insight into underlying mechanisms of migraine headaches and auras. Further studies are needed on these alternative therapies in non-responders of CGRP(-receptor) targeted therapies with the ultimate aim to pave the way towards a headache-free future for all migraine patients.

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.

The Heterogeneity of Response of PC12 Cells from Different Laboratories to Nerve Growth Factor and Pituitary Adenylate Cyclase-Activating Polypeptide Questions the Reproducibility of Studies Carried Out with Tumor Cell Lines

BACKGROUND

PC12 pheochromocytoma tumor cell lines are widely used to decipher the intracellular signaling mechanisms mediating the effects of some growth factors. Nevertheless, the disparity in appearance of some PC12 cell lines used in the different publications questions our ability to compare the results obtained by the numerous laboratories which use them. This led us to analyze the phenotypic aspect and transcriptomic expression of 5 PC12 cell lines from different origins under control conditions and after treatment with nerve growth factor (NGF) or pituitary adenylate cyclase-activating polypeptide (PACAP).

METHODS

Characterization of the 5 PC12 cell lines was conducted using imaging techniques and high-throughput real-time PCR combined with bioinformatics analysis.

RESULTS

The results show that the 5 cell lines are very variable in terms of shape, proliferation rate, motility, adhesion to the substrate, and gene expression. This high heterogeneity of the cell lines is also found when looking at their response to NGF or PACAP on gene expression or differentiation, with even in some cases opposite effects, as, for example, on cell proliferation. Actually, only 2 of the cell lines tested exhibited some phenotypic similarities with each other, even though the transcriptomic analyses show that they are far from identical.

DISCUSSION/CONCLUSION

As this issue of cell heterogenicity is not restricted to PC12 cells, the present results highlight the need to facilitate the supply of cell lines at low cost, the necessity to standardize practices regarding the use of cell lines, and the requirement to define precise markers of established cell lines which should be monitored in every publication. Regarding this latter point, the present data show that transcriptomic analysis by real-time PCR using a panel of genes of interest is easy to implement and provides a reliable method to control the possible drift of the cells over time in culture. Transcriptomic phenotyping combined with bioinformatics analysis can also be a useful approach to predict the response of the cells to treatments in terms of cell signaling activation, which can help to choose among several cell lines the most appropriate one for the investigation of a particular mechanism. Taken together, the results from this study highlight the need to use well-characterized cell lines with standardized protocols to generate reproducible results from 1 laboratory to the other.

Neuronal control of the vagina in vertebrates: A review

BACKGROUND

At present, there is an increased interest in the vaginal microbiome. It is believed that microbes play equally important roles in the vagina, including the modulation of neuronal pathways, as in the gut. However, in man as well as in animals, the vagina is the least well-studied part of the female reproductive system. The vagina, a fibromuscular tract, having two main functions, i.e., childbirth and sexual intercourse, is mainly innervated by the pudendal nerve and the pelvic splanchnic nerves (the uterovaginal nerve plexus) containing sympathetic, parasympathetic and nociceptive nerve fibers. Innervation density in the vaginal wall undergoes significant remodeling due to hormonally mediated physiological activity. Knowledge about expression and function of neuropeptides and neurotransmitters in the vaginal fibers is incomplete or not established. Most research concerning the neuroregulation of the vagina and the function and expression of neuropeptides and neurotransmitters, is performed in several vertebrate species, including large farm animals, rodents, domestic fowl and lizards.

METHODS

This review summarizes, on a bibliographic basis, the current knowledge on vaginal innervation and function of neuropeptides and neurotransmitters expressed in vaginal nerve fibers in several vertebrate species, including humans. The presence and role played by the local microbioma is also explored.

CONCLUSION

A thorough knowledge of the vaginal innervation is necessary to unravel the putative communication of the vaginal microbiome and vaginal nerve fibers, but also to understand the effects of vaginal pathologies and of administered drugs on the neuroregulation of the vagina.

Pituitary adenylate cyclase-activating polypeptide attenuates mitochondria-mediated oxidative stress and neuronal apoptosis after subarachnoid hemorrhage in rats

Mitochondria-mediated oxidative stress and neuronal apoptosis play an important role in early brain injury following subarachnoid hemorrhage (SAH). Pituitary adenylate cyclase-activating polypeptide (PACAP) has been shown to reduce oxidative stress and cellular apoptosis by maintaining mitochondrial function under stress. The objective of this study is to investigate the effects of PACAP on mitochondria dysfunction - induced oxidative stress and neuronal apoptosis in both vivo and vitro models of SAH. PACAP Knockout CRISPR and exogenous PACAP38 were used to verify the neuroprotective effects of PACAP in rats after endovascular perforation - induced SAH as well as in primary neuron culture after hemoglobin stimulation. The results showed that endogenous PACAP knockout aggravated mitochondria dysfunction - mediated ATP reduction, reactive oxygen species accumulation and neuronal apoptosis in ipsilateral hemisphere at 24 h after SAH in rats. The exogenous PACAP38 treatment provided both short- and long-term neurological benefits by attenuating mitochondria - mediated oxidative stress and neuronal apoptosis after SAH in rats. Consistently, the exogenous PACAP38 treatment presented similar neuroprotection in the primary neuron culture after hemoglobin stimulation. Pharmacological inhibition of adenylyl cyclase (AC) or extracellular signal-regulated kinase (ERK) partly abolished the anti-oxidative stress and anti-apoptotic effects provided by PACAP38 treatment after the experimental SAH both in vivo and in vitro, suggesting the involvement of the AC-cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA) and ERK pathway. Collectively, PACAP38 may serve as a promising treatment strategy for alleviating early brain injury after SAH.

The pivotal role of pituitary adenylate cyclase-activating polypeptide for lactate production and secretion in astrocytes during fear memory

BACKGROUND

Pituitary adenylate cyclase-activating polypeptide (PACAP) plays an essential role in the modulation of astrocyte functions. Although lactate secretion from astrocytes contributes to many forms of neuronal plasticity in the central nervous system, including fear learning and memory, the role of PACAP in lactate secretion from astrocytes is unclear.

METHODS

The amygdala and hippocampus of PACAP (+ / +) and PACAP (-/-) mice were acquired 1 h after memory acquisition and recall in the passive avoidance test. The concentration of glycogen and lactate in these regions was measured. The concentration of lactate in the hippocampus's extracellular fluid was also measured by microdialysis during memory acquisition or intracerebroventricular administration of PACAP.

RESULTS

We observed that memory acquisition caused a significant decrease in glycogen concentration and increased lactate concentration in the PACAP (+ / +) mice's hippocampus. However, memory acquisition did not increase in the lactate concentration in PACAP (-/-) mice's hippocampus. Further, memory retrieval evoked lactate production in the amygdala and the hippocampus of PACAP (+ / +) mice. Still, there was no significant increase in lactate concentration in the same regions of PACAP (-/-) mice. In vivo microdialysis in rats revealed that the hippocampus's extracellular lactate concentration increased after a single PACAP intracerebroventricular injection. Additionally, the hippocampus's extracellular lactate concentration increased with the memory acquisition in PACAP (+ / +) mice, but not in PACAP (-/-) mice.

CONCLUSIONS

PACAP may enhance lactate production and secretion in astrocytes during the acquisition and recall of fear memories.

Chemoarchitecture of the bed nucleus of the stria terminalis: Neurophenotypic diversity and function

The bed nucleus of the stria terminalis (BNST) is a compact but neurophenotypically complex structure in the ventral forebrain that is structurally and functionally linked to other limbic structures, including the amygdala nuclear complex, hypothalamic nuclei, hippocampus, and related midbrain structures, to participate in a wide range of functions, especially emotion, emotional learning, stress-related responses, and sexual behaviors. From a variety of sensory inputs, the BNST acts as a node for signal integration and coordination for information relay to downstream central neuroendocrine and autonomic centers for appropriate homeostatic physiological and behavioral responses. In contrast to the role of the amygdala in fear, the BNST has gained wide interest from work suggesting that it has main roles in mediating sustained responses to diffuse, unpredictable and/or long-duration threats that are typically associated with anxiety-related responses. Further, some BNST subregions are highly sexually dimorphic which appear contributory to the differential stress and social interactive behaviors, including reproductive responses, between males and females. Notably, maladaptive BNST neuroplasticity and function have been implicated in chronic pain, depression, anxiety-related abnormalities, and other psychopathologies including posttraumatic stress disorders. The BNST circuits are predominantly GABAergic-the glutaminergic neurons represent a minor population-but the complexity of the system results from an overlay of diverse neuropeptide coexpression in these neurons. More than a dozen neuropeptides may be differentially coexpressed in BNST neurons, and from variable G protein-coupled receptor signaling, may inhibit or activate downstream circuit activities. The mechanisms and roles of these peptides in modulating intrinsic BNST neurocircuit signaling and BNST long-distance target cell projections are still not well understood. Nevertheless, an understanding of some of the principal players may allow assembly of the circuit interactions.

Pituitary adenylate cyclase-activating polypeptide: Protective effects in stroke and dementia

Evidence shows that pituitary adenylate cyclase-activating polypeptide (PACAP) improves stroke outcomes and dementia. The blood-brain barrier (BBB) controls the peptide and regulatory protein exchange between the central nervous system and the blood; the transport of these regulatory substances across the BBB has been altered in animal models of stroke and Alzheimer's disease (AD). PACAP is a powerful neurotrophin that can cross the BBB, which may aid in the therapy of neurodegenerative diseases, including stroke and AD. PACAP may function as a potential drug in the treatment, prevention, or management of stroke and AD and other neurodegenerative conditions. Here, we review the effects of PACAP in studies on stroke and dementias.

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.

The globus pallidus as a target for neuropeptides and endocannabinoids participating in central activities

The globus pallidus in the basal ganglia plays an important role in movement regulation. Neuropeptides and endocannabinoids are neuronal signalling molecules that influence the functions of the whole brain. Endocannabinoids, enkephalin, substance P, neurotensin, orexin, somatostatin and pituitary adenylate cyclase-activating polypeptides are richly concentrated in the globus pallidus. Neuropeptides and endocannabinoids exert excitatory or inhibitory effects in the globus pallidus mainly by modulating GABAergic, glutamatergic and dopaminergic neurotransmission, as well as many ionic mechanisms. Pallidal neuropeptides and endocannabinoids are associated with the pathophysiology of a number of neurological disorders, such as Parkinson's disease, Huntington's disease, schizophrenia, and depression. The levels of neuropeptides and endocannabinoids and their receptors in the globus pallidus change in neurological diseases. It has been demonstrated that spontaneous firing activity of globus pallidus neurons is closely related to the manifestations of Parkinson's disease. Therefore, the neuropeptides and endocannabinoids in the globus pallidus may function as potential targets for treatment in some neurological diseases. In this review, we highlight the morphology and function of neuropeptides and endocannabinoids in the globus pallidus and their involvement in neurological diseases.

PACAP regulation of central amygdala GABAergic synapses is altered by restraint stress

The pituitary adenylate cyclase-activating polypeptide (PACAP) system plays a central role in the brain's emotional response to psychological stress by activating cellular processes and circuits associated with threat exposure. The neuropeptide PACAP and its main receptor PAC1 are expressed in the rodent central amygdala (CeA), a brain region critical in negative emotional processing, and CeA PACAPergic signaling drives anxiogenic and stress coping behaviors. Despite this behavioral evidence, PACAP's effects on neuronal activity within the medial subdivision of the CeA (CeM, the major output nucleus for the entire amygdala complex) during basal conditions and after psychological stress remain unknown. Therefore, in the present study, male Wistar rats were subjected to either restraint stress or control conditions, and PACAPergic regulation of CeM cellular function was assessed using immunohistochemistry and whole-cell patch-clamp electrophysiology. Our results demonstrate that PACAP-38 potentiates GABA release in the CeM of naïve rats, via its actions at presynaptic PAC1. Basal PAC1 activity also enhances GABA release in an action potential-dependent manner. Notably, PACAP-38's facilitation of CeM GABA release was attenuated after a single restraint stress session, but after repeated sessions returned to the level observed in naïve animals. A single restraint session also significantly decreased PAC1 levels in the CeM, with repeated restraint sessions producing a slight recovery. Collectively our data reveal that PACAP/PAC1 signaling enhances inhibitory control of the CeM and that psychological stress can modulate this influence to potentially disinhibit downstream effector regions that mediate anxiety and stress-related behaviors. This article is part of the special issue on 'Neuropeptides'.

Decreased synovial fluid pituitary adenylate cyclase-activating polypeptide (PACAP) levels may reflect disease severity in post-traumatic knee osteoarthritis after anterior cruciate ligament injury

BACKGROUND

It has been demonstrated that anterior cruciate ligament (ACL) injury-induced cartilage degeneration is the key risk factor for post-traumatic knee osteoarthritis (PTKOA).Pituitary adenylate cyclase-activating polypeptide (PACAP), a common neuropeptide exerting a wide spectrum of functions, has been proved to inhibit inflammation and prevent cartilage degeneration.

OBJECTIVE

The current study was performed to investigate circulating and synovial fluid PACAP concentrations in ACL injury patients to determine their relationship with the disease progression of the severity of post-traumatic knee osteoarthritis (PTKOA).

METHODS

72 ACL injury patients receiving arthroscopical examination and surgery were enrolled in the study. Meanwhile, 60 gender-and-age non-traumatic patellar dislocation patients were enrolled as controls. The VAS score, Lysholm Score and International Knee Documentation Committee (IKDC) score were all recorded to evaluate the clinical severity. Serum and synovial fluid (SF) PACAP levels were investigated by enzyme-linked immunosorbent assay (ELISA).The IL-1β and TNF-α levels were also investigated. The degree of meniscus injury was assessed by MR imaging. The modified Mankin score was recorded to examine the cartilage histopathological alternations. Receiver operating characteristic (ROC) curve was performed to discuss the diagnostic value of PACAP levels for the prediction of the radiographic grading in comparison with IL-1β and TNF-α.

RESULTS

Serum PACAP levels between PTKOA patients and patellar dislocation did not reach significant differences. However, SF PACAP levels were significantly lower in PTKOA patients than controls. In addition, SF PACAP levels were negatively associated with MRI imaging grade for meniscus injury and VAS score, and were positively associated with Lysholm and IKDC scores. In addition, SF PACAP levels were negatively related to Mankin score as well as the expressions of IL-1β and TNF-α. ROC analysis curve showed that attenuated PACAP may serve as a favorable marker for the diagnosis of MRI for meniscus injury.

CONCLUSIONS

SF PACAP concentrations showed an independent and negative association with disease severity in PTKOA following ACL injury. Local treatment with PACAP may act as a possible adjuvant therapy for delaying the process of PTKOA.

The synovial fluid neuropeptide PACAP may act as a protective factor during disease progression of primary knee osteoarthritis and is increased following hyaluronic acid injection

The correlation of serum and synovial fluid (SF) pituitary adenylate cyclase-activating polypeptide (PACAP) levels with disease progression of primary knee osteoarthritis (OA) was explored. Radiographic severity of OA was determined by Kellgren-Lawrence (K-L) grades. PACAP levels were measured by ELISA before treatment, and 4 and 8 wk following hyaluronic acid (HA) injection. Levels of IL-1β and MMP-3 were also detected. The numeric pain scale (NPS), revised Oxford Knee Score (OKS), and American Knee Society Score (AKSS) were employed to evaluate to symptomatic severity. Receiver-operating-characteristic (ROC) curve analysis was carried out to compare the diagnostic value of PACAP, IL-1β, and MMP-3 for the K-L grade. PACAP concentrations in SF but not serum were significantly lower in OA patients compared with controls. SF PACAP levels were negatively associated with K-L grades and higher NPS as well as worse AKSS and OKS. Further analysis demonstrated that PACAP concentration in SF was negatively correlated with expressions of IL-1β as well as MMP-3 and may act as a marker for radiographic progression along with MMP-3. Last, we found SF PACAP levels exhibited an incremental trend after HA injection. These findings confirmed the crucial role of PACAP deficiency in the development of primary knee OA.

PAC1 receptor mRNA and protein distribution in rat and human trigeminal and sphenopalatine ganglia, spinal trigeminal nucleus and in dura mater

BACKGROUND

To further understand the role of pituitary adenylate cyclase-activating polypeptide 1 (PAC1) receptors in headache disorders, we mapped their expression in tissues of the trigemino-autonomic system by immunohistochemistry and in situ hybridization.

METHODS

To optimize screening for monoclonal antibodies suitable for immunohistochemistry on formalin-fixed, paraffin-embedded tissues, we developed a new enzyme-linked immunosorbent assay using formalin-fixed, paraffin-embedded cells overexpressing human PAC1 receptors. 169G4.1 was selected from these studies for analysis of rat and human tissues and chimerized onto a mouse backbone to avoid human-on-human cross-reactivity. Immunoreactivity was compared to PAC1 receptor mRNA by in situ hybridization in both species.

RESULTS

169G4.1 immunoreactivity delineated neuronal cell bodies in the sphenopalatine ganglion in both rat and human, whereas no staining was detected in the trigeminal ganglion. The spinal trigeminal nucleus in both species showed immunoreactivity as especially strong in the upper laminae with both cell bodies and neuropil being labelled. No immunoreactivity was seen in either rat or human dura mater vessels. In situ hybridization in both species revealed mRNA in sphenopalatine ganglion neurons and the spinal trigeminal nucleus, a weak signal in the trigeminal nucleus and no signal in dural vessels.

CONCLUSION

Taken together, these data support a role for PAC1 receptors in the trigemino-autonomic system as it relates to headache pathophysiology.

Pituitary adenylate cyclase-activating polypeptide is a potent broad-spectrum antimicrobial peptide: Structure-activity relationships

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a naturally occurring cationic peptide with potent immunosuppressant and cytoprotective activities. We now show that full length PACAP38 and to a lesser extent, the truncated form PACAP27, and the closely related vasoactive intestinal peptide (VIP) and secretin had antimicrobial activity against the Gram-negative bacteria Escherichia coli in the radial diffusion assay. PACAP38 was more potent than either the bovine neutrophil antimicrobial peptide indolicidin or the synthetic antimicrobial peptide ARVA against E. coli. PACAP38 also had activity against the Gram-positive bacteria Staphylococcus aureus in the same assay with comparable potency to indolicidin and ARVA. In the more stringent broth dilution assay, PACAP38 had moderate sterilizing activity against E. coli, and potent sterilizing activity against the Gram-negative bacteria Pseudomonas aeruginosa. PACAP27, VIP and secretin were much less active than PACAP38 in this assay. PACAP38 also had some activity against the Gram-positive bacteria Bacillus cereus in the broth dilution assay. Many exopeptidase-resistant analogs of PACAP38, including both receptor agonists and antagonists, had antimicrobial activities equal to, or better than PACAP38, in both assays. PACAP38 made the membranes of E. coli permeable to SYTOX Green, suggesting a classical membrane lytic mechanism. These data suggest that analogs of PACPAP38 with a wide range of useful biological activities can be made by judicious substitutions in the sequence.

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

Background

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

Methods

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

Results

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

Conclusions

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

IL-6 knockout mice are protected from cocaine-induced kindling behaviors; possible involvement of JAK2/STAT3 and PACAP signalings

IL-6 has been recognized as an anticonvulsant against certain neuroexcitotoxicities. We aimed to investigate on the interactive role between IL-6 and PACAP in cocaine-induced kindling behaviors. Although we found that cocaine (45 mg/kg, i.p./day x 5) significantly increased IL-6 and TNF-α expression, it resulted in a decrease in IFN-γ expression. We observed that the cocaine-induced increase in IL-6 expression was more pronounced than that in TNF-α expression. Genetic depletion of IL-6 significantly activated cocaine kindling behaviors. This phenomenon was also consistently observed in WT mice that received a neutralizing IL-6 receptor antibody. Cocaine-treated IL-6 knockout mice exhibited significantly decreased PACAP and PACAP receptor (PAC1R) mRNA levels and significantly increased TNF-α gene expression. TNF-α knockout mice were protected from cocaine kindling via an up-regulation of IL-6, phospho-JAK2/STAT3, PACAP, and PAC1R levels, which produced anti-apoptotic effects. Recombinant IL-6 protein (rIL-6, 2 μg, i.v./mouse/day x 5) also up-regulated phospho-JAK2/STAT3, PACAP, and PAC1R mRNA levels, leading to anti-apoptotic effects in IL-6 knockout mice. Consistently, AG490, a JAK2/STAT3 inhibitor, and PACAP 6-38, a PAC1 receptor antagonist, counteracted rIL-6-mediated protection. Combined, our results suggest that IL-6 gene requires up-regulation of phospho-JAK2/STAT3, PACAP, and PAC1R and down-regulation of the TNF-α gene to modulate its anticonvulsive/neuroprotective potential.

Role of light and the circadian clock in the rhythmic oscillation of intraocular pressure: Studies in VPAC2 receptor and PACAP deficient mice

The intraocular pressure of mice displays a daily rhythmicity being highest during the dark period. The present study was performed to elucidate the role of the circadian clock and light in the diurnal and the circadian variations in intraocular pressure in mice, by using animals with disrupted clock function (VPAC2 receptor knockout mice) or impaired light information to the clock (PACAP knockout mice). In wildtype mice, intraocular pressure measured under light/dark conditions showed a statistically significant 24 h sinusoidal rhythm with nadir during the light phase and peak during the dark phase. After transfer of the wildtype mice into constant darkness, the intraocular pressure increased, but the rhythmic changes in intraocular pressure continued with a pattern identical to that obtained during the light/dark cycle. The intraocular pressure in VPAC2 receptor deficient mice during light/dark conditions also showed a sinusoidal pattern with significant changes as a function of a 24 h cycle. However, transfer of the VPAC2 receptor knockout mice into constant darkness completely abolished the rhythmic changes in intraocular pressure. The intraocular pressure in PACAP deficient mice oscillated significantly during both 24 h light and darkness and during constant darkness. During LD conditions, the amplitude of PACAP deficient was significantly lower compared to wildtype mice, resulting in higher daytime and lower nighttime values. In conclusion, by studying the VPAC2 receptor knockout mouse which lacks circadian control and the PACAP knockout mouse which displays impaired light signaling, we provided evidence that the daily intraocular pressure rhythms are primarily generated by the circadian master clock and to a lesser extent by environmental light and darkness.

Trophic effect of PACAP on human corneal endothelium

Cornea's posterior surface includes endothelium maintaining stromal hydration and clarity. Due to their limited proliferative capability, the loss of endothelial cells can outcome in permanent opacity. In the last years, different studies have demonstrated the protective effect of pituitary adenylate cyclase-activating polypeptide (PACAP) in different ocular diseases. However, its role on human corneal endothelial cells (HCECs) has not been investigated, yet. Here, we have developed a culture protocol to differentiate HCECs from donor's cornea. PACAP treatment prevented damage induced by growth factors deprivation of cells grown on transwell supports as revealed by TERR measurements. Moreover, this peptide significantly increased tight junction proteins expression by conferring resistance to endothelial barrier. This effect is also related to promotion of cell viability as demonstrated by MTT assay. Furthermore, PACAP stimulated repairing of corneal endothelium lesion as shown by wound healing analysis. In conclusion, our data suggest that this peptide could represent an important trophic factor in maintaining functionality of human corneal endothelium.

Pituitary adenylate cyclase-activating polypeptide (PACAP) protects against mitoxantrone-induced cardiac injury in mice

Mitoxantrone (MXT) is an androstenedione that is used to treat cancers and progressive forms of multiple sclerosis; however, its use is limited by its cardiotoxicity. Pituitary adenylate cyclase activating polypeptide (PACAP) is a member of the secretin/growth hormone-releasing hormone/vasoactive intestinal peptide family and has many functions, including cytoprotection and immunosuppression. We tested the hypothesis that PACAP can protect against MXT-induced cardiotoxicity in mice. Female BALB/c mice were treated once weekly for 4 weeks with saline (n=14) or MXT (3mg/kg, i.p.; n=14). Half of the mice in each group received PACAP (10μg, i.p.) 1h before and 24 and 48h after MXT, while the remaining mice received injections of saline on the same schedule. Echocardiography was used to assess cardiac structure and function. In mice treated with MXT and saline, body weight was significantly reduced after the third dose of MXT. PACAP significantly attenuated the reduction in body weight; however, the weights did not return to control level. Compared to controls, MXT-treated mice had significantly increased left ventricular (LV) diameter and LV volume and decreased LV posterior wall thickness. Fractional shortening (FS) and ejection fraction (EF) were also significantly decreased. Treatment with PACAP prevented MXT-induced LV dilation and significantly attenuated the reductions in FS and EF, although FS and EF did not return to control level. PACAP38 did not prevent MXT-induced decreases in LV posterior wall thickness. MXT dose-dependently decreased the viability of cultured U937 (human leukemia) cells; PACAP did not protect cultured U937 cells from MXT-mediated cell death. In conclusion, PACAP can attenuate MXT-mediated LV dilation and dysfunction in mice.

Backup Mechanisms Maintain PACAP/VIP-Induced Arterial Relaxations in Pituitary Adenylate Cyclase-Activating Polypeptide-Deficient Mice

BACKGROUND

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a multifunctional neuropeptide in the VIP/secretin/glucagon peptide superfamily. Two active forms, PACAP1-38 and PACAP1-27, act through G protein-coupled receptors, the PAC1 and VPAC1/2 receptors. Effects of PACAP include potent vasomotor activity. Vasomotor activity and organ-specific vasomotor effects of PACAP-deficient mice have not yet been investigated; thus, the assessment of its physiological importance in vasomotor functions is still missing. We hypothesized that backup mechanisms exist to maintain PACAP pathway activity in PACAP knockout (KO) mice. Thus, we investigated the vasomotor effects of exogenous vasoactive intestinal peptide (VIP) and PACAP polypeptides in PACAP wild-type (WT) and PACAP-deficient (KO) male mice.

METHODS

Carotid and femoral arteries were isolated from 8- to 12-week-old male WT and PACAP-KO mice. Vasomotor responses were measured with isometric myography.

RESULTS

In the arteries of WT mice the peptides induced relaxations, which were significantly greater to PACAP1-38 than to PACAP1-27 and VIP. In KO mice, PACAP1-38 did not elicit relaxation, whereas PACAP1-27 and VIP elicited significantly greater relaxation in KO mice than in WT mice. The specific PAC1R and VPAC1R antagonist completely blocked the PACAP-induced relaxations.

CONCLUSION

Our data suggest that in PACAP deficiency, backup mechanisms maintain arterial relaxations to polypeptides, indicating an important physiological role for the PACAP pathway in the regulation of vascular tone.

Daily rhythms of the expression of genes from the somatotropic axis: The influence on tilapia (Oreochromis niloticus) of feeding and growth hormone administration at different times

The aim of this research was to investigate the presence of daily rhythms in the somatotropic axis of tilapia fed at two times (mid-light, ML or mid-dark, MD) and the influence of the time of day of growth hormone (GH) administration on the response of this axis. Two different GH injection times were tested: ZT 3 (3h after lights on) and ZT 15 (3h after lights off). In both experiments, the mRNA expression levels of hypothalamic pituitary adenylate cyclase-activating polypeptide (pacap), pituitary growth hormone (gh), liver insulin-like growth factors (igf1 and igf2a), and liver and muscle growth hormone receptors (ghr1 and ghr2) and IGF receptors (igf1ra and igf2r) were evaluated by means of qPCR. Daily rhythms were observed in the liver for ghr1, ghr2 and igf2r but only in fish fed at ML, with the acrophases located in the light phase (ZT 3:30, 3:31 and 7:38 h, respectively). In the muscle, ghr1 displayed a significant rhythm in both groups and ghr2 in ML fed fish (acrophases at ZT 5:29, 7:14 and 9:23h). The time of both GH administration and feeding influenced the response to GH injection: ML fed fish injected with GH at ZT 15 h showed a significant increase in liver igf1, igf2a and ghr2; and muscle ghr2 expression. This is the first report that describes the existence of daily rhythms in the somatotropic axis of tilapia and its time-dependent responses of GH administration. Our results should be considered when investigating the elements of the somatotropic axis in tilapia and GH administration.

Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) Is Involved in Adult Mouse Hippocampal Neurogenesis After Stroke

In the subgranular zone (SGZ) of the hippocampus, neurogenesis persists throughout life and is upregulated following ischemia. Accumulating evidence suggests that enhanced neurogenesis stimulated by ischemic injury contributes to recovery after stroke. However, the mechanisms underlying the upregulation of neurogenesis are unclear. We have demonstrated that a neuropeptide, pituitary adenylate cyclase-activating polypeptide (PACAP), exerts a wide range of effects on neural stem cells (NSCs) during neural development. Here, we examined the effects of endogenous and exogenous PACAP in adult NSCs of the SGZ. Immunostaining showed expression of the PACAP receptor PAC1R in nestin-positive NSCs of adult naive mice. PACAP injection into the lateral ventricle increased bromodeoxyuridine (BrdU)-positive proliferative cells in the SGZ. These data suggest that PACAP promoted the proliferation of NSCs. In global ischemia model mice, the number of BrdU-positive cells was increased in wild-type mice but not in PACAP heterozygous knockout mice. The BrdU-positive cells that increased in number after ischemia were immunopositive for SOX2, a marker of NSCs, and differentiated into NeuN-positive mature neurons at 4 weeks after ischemia. These findings suggest that PACAP contributes to the proliferation of NSCs and may be associated with recovery after brain injury.

Interictal plasma pituitary adenylate cyclase-activating polypeptide levels are decreased in migraineurs but remain unchanged in patients with tension-type headache

BACKGROUND

Pituitary adenylate cyclase-activating polypeptide (PACAP) is associated with migraine phase; however, whether PACAP levels could be used to distinguish between migraine and tension-type headache (TTH) remains unknown. We compared interictal plasma PACAP levels among healthy controls, migraineurs, and patients with TTH.

METHODS

Interictal plasma levels of PACAP were measured in 133 migraineurs, 106 patients with TTH, and 50 controls using enzyme-linked immunoassays. We further evaluated the relationships between interictal PACAP plasma concentrations and clinical parameters, such as headache severity, attack frequency, and duration.

RESULTS

We found that migraineurs had significantly lower interictal plasma PACAP levels than patients with TTH and healthy controls. However, there were no significant differences between patients with TTH and healthy controls. Plasma PACAP levels were significantly lower in patients with episodic migraine (EM) than in patients with episodic tension-type headache (ETTH) and in patients with chronic migraine (CM) than in patients with chronic tension-type headache (CTTH). Interictal PACAP levels were negatively correlated with duration in the CM group.

CONCLUSIONS

The results of this study demonstrated differences in interictal PACAP levels in migraine and TTH, suggesting that PACAP is involved in the pathogenesis of migraine rather than TTH.

Central administration of chicken growth hormone-releasing hormone decreases food intake in chicks

Growth hormone-releasing hormone (GHRH) is well known as a stimulator of growth hormone (GH) secretion. GHRH not only stimulates GH release but also modifies feeding behavior and energy homeostasis in rodents. In chickens (Gallus gallus domesticus), on the other hand, two types of GHRH, namely, chicken GHRH (cGHRH) and cGHRH-like peptide (cGHRH-LP), have been identified. The purpose of the present study was to investigate the effect of central injection of cGHRH and cGHRH-LP on feeding behavior in chicks. Intracerebroventricular (ICV) injection of both cGHRH and cGHRH-LP (0.04 to 1 nmol) significantly decreased food intake without any abnormal behavior in chicks. Furthermore, the feeding-inhibitory effect was not abolished by co-injection of the antagonist for pituitary adenylate cyclase-activating polypeptide (PACAP) or corticotropin-releasing hormone (CRH) receptors, suggesting that the anorexigenic effect of cGHRH and cGHRH-LP might not be related to the PACAP and CRH systems in the brain of chicks. Finally, 24-h food deprivation increased mRNA expression of cGHRH but not cGHRH-LP in the diencephalon. These results suggest that central cGHRH is related to inhibiting feeding behavior and energy homeostasis in chicks.

PACAP inhibits tumor growth and interferes with clusterin in cervical carcinomas

Secretory clusterin (sCLU), an anti-apoptotic protein, is overexpressed in many tumors and enhances tumorigenesis and chemo-resistance. However, the regulation mechanism controlling the sCLU maturation process or activity remains undetermined. In this study, we found PACAP as a negative regulator of CLU. Overexpression of the PACAP gene in cervical cancer cell lines lacking PACAP expression significantly inhibited cell growth and induced apoptosis. We further demonstrated that interaction of PACAP with CLU significantly downregulated CLU expression and secretion, inhibited the Akt-Raf-ERK pathway, and suppressed the growth of human tumor xenografts in nude mice. This novel inhibitory function of PACAP may be applicable for developing novel molecular therapies for tumors with increased sCLU expression.

Secondary conformational conversion is involved in glycosaminoglycans-mediated cellular uptake of the cationic cell-penetrating peptide PACAP

Glycosaminoglycans (GAGs) contribute to the cellular uptake of cationic cell-penetrating peptides (CPPs). However, molecular details about the contributions of GAGs in CPP internalization remain unclear. In this study, we examined the cellular uptake mechanism of the arginine-rich CPP pituitary adenylate-cyclase-activating polypeptide (PACAP). We observed that the uptake efficacy of PACAP is dependent on the expression of cell surface GAGs. As the binding of PACAP to sulfated GAGs induced a random coil-to-α-helix conformational conversion, we investigated the role of the helical formation in PACAP internalization. Whereas this secondary structure was not crucial for efficient internalization in GAGs-deficient cells, PACAP α-helix was essential for GAGs-dependent uptake.

Inhibition of constitutive TNF production is associated with PACAP-mediated differentiation in PC12 cells

The pituitary adenylate cyclase-activating polypeptide (PACAP) is a trophic neuropeptide that promotes cell survival and neuritogenesis in the central and peripheral nervous system. Our previous transcriptomic studies revealed the down-regulation of the cytokine tumor necrosis factor (TNF) during PACAP-induced PC12 cell differentiation. Here we show that TNF is constitutively expressed in PC12 cells in a manner dependent on NF-κB transcription factor, and that PACAP rapidly inhibits TNF expression and secretion. The inhibition occurs through suppression of RelB subunit of NF-κB, and is likely to prevent the deleterious effects of the cytokine on survival and neurite outgrowth during PC12 cell differentiation.

Peptidergic regulation of plasminogen activator inhibitor-1 gene expression in vivo

BACKGROUND

The mechanisms by which PAI-1 biosynthesis is altered during stress have not been fully elucidated. Studies suggest a major role for neuro-peptidergic modulation of the stress response by PACAP (pituitary adenylate cyclase-activating polypeptide), a member of the VIP/secretin/glucagon family.

OBJECTIVE

We tested the hypothesis that PACAP regulates PAI-1 biosynthesis during stress in vivo.

METHODS

PAI-1 gene expression was monitored by RT-PCR in adrenal glands harvested from C57BL/6J mice that were unstressed, or subjected to restraint stress for 2 h, or treated with PACAP.

RESULTS

PAI-1 mRNA expression was markedly increased in adrenals from stressed mice. Restraint stress resulted in much smaller increments in adrenal tPA mRNA, suggesting that local adrenal tPA/PAI-1 biosynthetic balance is markedly altered by stress. The observed increases in PAI-1mRNA during stress were substantially blunted (55 ± 4%, P < 0.001) by pretreatment with the specific PACAP receptor antagonist, PACAP6-38, compared with pretreatment with vehicle. Administration of the agonist PACAP1-38 alone resulted in a dose-dependent increase in tissue PAI-1 mRNA. PACAP1-38 administration also resulted in substantial increases in plasma PAI-1 antigen and active PAI-1 concentrations that were significantly greater in male mice than in female mice.

CONCLUSIONS

We conclude that adrenal PAI-1 mRNA expression is markedly increased by stress, and that the PACAP peptidergic signaling pathway plays a major role in mediating the stress-induced increase in PAI-1 biosynthesis.

Possible key residues that determine left gastric artery blood flow response to PACAP in dogs

AIM: To determine the effect of pituitary adenylate cyclase-activating polypeptide (PACAP) on left gastric artery (LGA) flow and to unveil the structural or functional important sites that may be critical for discrimination of different receptor subtypes.

METHODS: Peptides, including PACAP-27, PACAP-38, amino acid substituted PACAP-27 and C-terminus truncated analogues PACAP (27-38), were synthesized by a simultaneous multiple solid-phase peptide synthesizer. Flow probes of an ultrasound transit-time blood flowmeter were placed around the LGA of beagle dogs. When peptides were infused intravenously, the blood flow was measured.

RESULTS: [Ala4, Val5]-PACAP-27 caused a concentration-dependent vasodepressor action which was similar to that caused by PACAP-27. The LGA blood flow response to [Ala4, Val5]-PACAP-27 was significantly higher than that to PACAP-27, which was similar to that to vasoactive intestinal polypeptide (VIP) at the same dose. [Ala6]-PACAP-27 did not increase the peak LGA flow. [Gly8]-PACAP-27 showed a similar activity to VIP. [Asn24, Ser25, Ile26]-PACAP-27 did not change the activity of peptides at all doses.

CONCLUSION: NH2 terminus is more important to biological activity of peptides and specific receptor recognition than COOH-terminus.