New insights about the peculiar role of the 28–38 C-terminal segment and some selected residues in PACAP for signaling and neuroprotection

Novel Small Molecule Positive Allosteric Modulator SPAM1 Triggers the Nuclear Translocation of PAC1-R to Exert Neuroprotective Effects through Neuron-Restrictive Silencer Factor

The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) exerts effective neuroprotective activity through its specific receptor, PAC1-R. We accidentally discovered that as a positive allosteric modulator (PAM) of PAC1-R, the small-molecule PAM (SPAM1) has a hydrazide-like structure, but different binding characteristics, from hydrazide for the N-terminal extracellular domain of PAC1-R (PAC1-R-EC1). SPAM1 had a significant neuroprotective effect against oxidative stress, both in a cell model treated with hydrogen peroxide (H₂O₂) and an aging mouse model induced by D-galactose (D-gal). SPAM1 was found to block the decrease in PACAP levels in brain tissues induced by D-gal and significantly induced the nuclear translocation of PAC1-R in PAC1R-CHO cells and mouse retinal ganglion cells. Nuclear PAC1-R was subjected to fragmentation and the nuclear 35 kDa, but not the 15 kDa fragments, of PAC1-R interacted with SP1 to upregulate the expression of Huntingtin (Htt), which then exerted a neuroprotective effect by attenuating the binding availability of the neuron-restrictive silencer factor (NRSF) to the neuron-restrictive silencer element (NRSE). This resulted in an upregulation of the expression of NRSF-related neuropeptides, including PACAP, the brain-derived neurotrophic factor (BDNF), tyrosine hydroxylase (TH), and synapsin-1 (SYN1). The novel mechanism reported in this study indicates that SPAM1 has potential use as a drug, as it exerts a neuroprotective effect by regulating NRSF.

A novel small positive allosteric modulator of neuropeptide receptor PAC1-R exerts neuroprotective effects in MPTP mouse Parkinson's disease model

As a neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP)-preferring receptor, PAC1-R mediates effective neuroprotective activity. Based on the finding that the antibiotic doxycycline (DOX) with clinical neuroprotective activity functions as a positive allosteric modulator (PAM) of neuropeptide PACAP receptor 1 (PAC1-R), we use virtual and laboratory screening to search for novel small molecule PAMs of PAC1-R. Virtual screening is carried out using a small-molecule library TargetMol. After two-level precision screening with Glide, the top five compounds with the best predicted affinities for PAC1-R are selected and named small positive allosteric modulator 1‒5 (SPAM1‒5). Our results show that only 4-{[4-(4-Oxo-3,4-2-yl)butanamido]methyl}benzoic acid (SPAM1) has stronger neuroprotective activity than DOX in the MPP+ PD cell model and MPTP PD mouse model. SPAM1 has a higher affinity for PAC1-R than DOX, but has no antibiotic activity. Moreover, both SPAM1 and DOX block the decrease of PAC1-R level in mouse brain tissues induced by MPTP. The successful screening of SPAM1 offers a novel drug for the treatment of neurodegenerative disease targeting the PAC1-R.

TAT-tagging of VIP exerts positive allosteric modulation of the PAC1 receptor and enhances VIP neuroprotective effect in the MPTP mouse model of Parkinson's disease

BACKGROUND

The cationic Arginine-rich peptide (CARP) TAT had been tagged at the C-terminal end of the vasoactive intestinal peptide (VIP) to construct VIP-TAT in order to improve traversing ability. Interestingly, it was found that TAT may bind the positive allosteric modulation (PAM) site of the N-terminal extracellular domain of neuropeptide receptor PAC1 (PAC1-EC1), imitating the C-terminus part of pituitary adenylate cyclase-activating polypeptide (PACAP) PACAP(28-38) fragment.

METHODS

To test this hypothesis, we addressed the neuroprotective effects of VIP, VIP-TAT and PACAP38 in Parkinson's Disease (PD) cellular and mouse models. We also analyzed the peptides affinity for PAC1 and their ability to activate it.

RESULTS

VIP-TAT had in vitro and in vivo neuroprotective effects much efficient than VIP in PD cellular and mouse models. The isothermal titration calorimetry (ITC) and competition binding bioassays confirmed that TAT binds PAC1-EC1 at the same site as PACAP(28-38). The cAMP experiments showed TAT-VIP results in a higher activation potency of PAC1 than VIP alone.

CONCLUSIONS

The correlation of the peptides cationic properties with their affinity for PAC1 and their ability to activate the receptor, indicated that electrostatic interactions mediate the binding of TAT to the PAM domain of the PAC1-EC1, which induces the conformational changes of PAC1-EC1 required to promote the subsequent structural interaction and activation of the receptor with VIP.

GENERAL SIGNIFICANCE

VIP-TAT has some potency for the development of a novel drug targeting neurodegenerative diseases.

Targeting the PAC1 Receptor for Neurological and Metabolic Disorders

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

The amidated PACAP1-23 fragment is a potent reduced-size neuroprotective agent

BACKGROUND

Neurodegenerative disorders, such as Parkinson's disease (PD), are characterized by neuronal death involving, among other events, mitochondrial dysfunction and excitotoxicity. Along these lines, several attempts have been made to slow this pathology but none have been yet discovered. Based on its capacity to cross the blood-brain barrier and provide neuronal protection in vitro and in vivo, the pituitary adenylate cyclase-activating polypeptide (PACAP) represents a promising lead molecule. Pharmacological studies showed that PACAP interacts with three different G protein-coupled receptors, i.e. PAC1, VPAC1 and VPAC2. However, only PAC1 is associated with neuronal anti-apoptotic actions, whilst VPAC activation might cause adverse effects. In the context of the development of PAC1-selective agonists, PACAP(1-23) (PACAP23) appears as the shortest known PACAP bioactive fragment.

METHODS

Hence, the capacity of this peptide to bind PACAP receptors and protect neuroblastoma cells was evaluated under conditions of mitochondrial dysfunction and glutamate excitotoxicity. In addition, its ability to activate downstream signaling events involving G proteins (Gα_s and Gα_q), EPAC, and calcium was also assessed.

RESULTS

Compared to the endogenous peptide, PACAP23 showed a reduced affinity towards PAC1, although this fragment exerted potent neuroprotection. However, surprisingly, some disparities were observed for PACAP23 signaling compared to full length PACAP, suggesting that downstream signaling related to neuroprotection is distinctly regulated following subtle differences in their PAC1 interactions.

CONCLUSIONS

Altogether, this study demonstrates the potent neuroprotective action of amidated PACAP23.

GENERAL SIGNIFICANCE

PACAP23 represents an attractive template for development of shorter PACAP-derived neuroprotective molecules.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

GENERAL SIGNIFICANCE

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

PACAP27 induces migraine-like attacks in migraine patients

Introduction

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

Methods

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

Results

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

Conclusion

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

Neuroprotective Effects of Brain-Gut Peptides: A Potential Therapy for Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disease and is typically associated with progressive motor and non-motor dysfunctions. Currently, dopamine replacement therapy is mainly used to relieve the motor symptoms, while its long-term application can lead to various complications and does not cure the disease. Numerous studies have demonstrated that many brain-gut peptides have neuroprotective effects in vivo and in vitro, and may be a promising treatment for PD. In recent years, some progress has been made in studies on the neuroprotective effects of some newly-discovered brain-gut peptides, such as glucagon-like peptide 1, pituitary adenylate cyclase activating polypeptide, nesfatin-1, and ghrelin. However, there is still no systematic review on the neuroprotective effects common to these peptides. Thus, here we review the neuroprotective effects and the associated mechanisms of these four peptides, as well as other brain-gut peptides related to PD, in the hope of providing new ideas for the treatment of PD and related clinical research.

Antibacterial properties of the pituitary adenylate cyclase-activating polypeptide: A new human antimicrobial peptide

The Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP), a polycationic, amphiphilic and helical neuropeptide, is well known for its neuroprotective actions and cell penetrating properties. In the present study, we evaluated the potent antibacterial property of PACAP38 and related analogs against various bacterial strains. Interestingly, PACAP38 and related analogs can inhibit the growth of various bacteria including Escherichia coli (JM109), Bacillus subtilis (PY79), and the pathogenic Burkholderia cenocepacia (J2315). Investigation of the mechanism of action suggested that a PACAP metabolite, identified as PACAP(9–38), might indeed be responsible for the observed PACAP38 antibacterial action. Surprisingly, PACAP(9–38), which does not induce haemolysis, exhibits an increased specificity toward Burkholderia cenocepacia J2315 compared to other tested bacteria. Finally, the predisposition of PACAP(9–38) to adopt a π-helix conformation rather than an α-helical conformation like PACAP38 could explain this gain in specificity. Overall, this study has revealed a new function for PACAP38 and related derivatives that can be added to its pleiotropic biological activities. This innovative study could therefore pave the way toward the development of new therapeutic agents against multiresistant bacteria, and more specifically the Burkholderia cenocepacia complex.