Pituitary adenylate cyclase-activating polypeptide (PACAP) ameliorates experimental autoimmune encephalomyelitis by suppressing the functions of antigen presenting cells

Lipids shape brain function through ion channel and receptor modulations: physiological mechanisms and clinical perspectives

Lipids represent the most abundant molecular type in the brain, with a fat content of ∼60% of the dry brain weight in humans. Despite this fact, little attention has been paid to circumscribe the dynamic role of lipids in brain function and disease. Membrane lipids such as cholesterol, phosphoinositide, sphingolipids, arachidonic acid, and endocannabinoids finely regulate both synaptic receptors and ion channels that ensure critical neural functions. After a brief introduction on brain lipids and their respective properties, we review here their role in regulating synaptic function and ion channel activity, action potential propagation, neuronal development, and functional plasticity and their contribution in the development of neurological and neuropsychiatric diseases. We also provide possible directions for future research on lipid function in brain plasticity and diseases.

Targeting the PAC1 receptor mitigates degradation of myelin and synaptic markers and diminishes locomotor deficits in the cuprizone demyelination model

Multiple sclerosis (MS) is a demyelinating disease of the central nervous system with a strong neuroinflammatory component. Current treatments principally target the immune system but fail to preserve long-term myelin health and do not prevent neurological decline. Studies over the past two decades have shown that the structurally related neuropeptides VIP and PACAP (vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide, respectively) exhibit pronounced anti-inflammatory activities and reduce clinical symptoms in MS disease models, largely via actions on their bivalent VIP receptor type 1 and 2. Here, using the cuprizone demyelination model, we demonstrate that PACAP and VIP, and strikingly the PACAP-selective receptor PAC1 agonist maxadilan, prevented locomotor deficits in the horizontal ladder and open field tests. Moreover, only PACAP and maxadilan were able to prevent myelin deterioration, as assessed by a reduction in the expression of the myelin markers proteolipid protein 1, oligodendrocyte transcription factor 2, quaking-7 (APC) and Luxol Fast Blue staining. Furthermore, PACAP and maxadilan (but not VIP), prevented striatal synaptic loss and diminished astrocyte and microglial activation in the corpus callosum of cuprizone-fed mice. In vitro, PACAP or maxadilan prevented lipopolysaccharide (LPS)-induced polarisation of primary astrocytes at 12-24 h, an effect that was not seen with maxadilan in LPS-stimulated microglia. Taken together, our data demonstrates for the first time that PAC1 agonists provide distinctive protective effects against white matter deterioration, neuroinflammation and consequent locomotor dysfunctions in the cuprizone model. The results indicate that targeting the PAC1 receptor may provide a path to treat myelin-related diseases in humans.

Differential Expression of PACAP/VIP Receptors in the Post-Mortem CNS White Matter of Multiple Sclerosis Donors

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) are two neuroprotective and anti-inflammatory molecules of the central nervous system (CNS). Both bind to three G protein-coupled receptors, namely PAC1, VPAC1 and VPAC2, to elicit their beneficial effects in various CNS diseases, including multiple sclerosis (MS). In this study, we assessed the expression and distribution of PACAP/VIP receptors in the normal-appearing white matter (NAWM) of MS donors with a clinical history of either relapsing-remitting MS (RRMS), primary MS (PPMS), secondary progressive MS (SPMS) or in aged-matched non-MS controls. Gene expression studies revealed MS-subtype specific changes in PACAP and VIP and in the receptors' levels in the NAWM, which were partly corroborated by immunohistochemical analyses. Most PAC1 immunoreactivity was restricted to myelin-producing cells, whereas VPAC1 reactivity was diffused within the neuropil and in axonal bundles, and VPAC2 in small vessel walls. Within and around lesioned areas, glial cells were the predominant populations showing reactivity for the different PACAP/VIP receptors, with distinctive patterns across MS subtypes. Together, these data identify the differential expression patterns of PACAP/VIP receptors among the different MS clinical entities. These results may offer opportunities for the development of personalized therapeutic approaches to treating MS and/or other demyelinating disorders.

Potential Crosstalk between the PACAP/VIP Neuropeptide System and Endoplasmic Reticulum Stress-Relevance to Multiple Sclerosis Pathophysiology

Multiple sclerosis (MS) is an immune-mediated disorder characterized by focal demyelination and chronic inflammation of the central nervous system (CNS). Although the exact etiology is unclear, mounting evidence indicates that endoplasmic reticulum (ER) stress represents a key event in disease pathogenesis. Pituitary adenylate cyclase-activating peptide (PACAP) and vasoactive intestinal peptide (VIP) are two structurally related neuropeptides that are abundant in the CNS and are known to exert neuroprotective and immune modulatory roles. Activation of this endogenous neuropeptide system may interfere with ER stress processes to promote glial cell survival and myelin self-repair. However, the potential crosstalk between the PACAP/VIP system and ER stress remains elusive. In this review, we aim to discuss how these peptides ameliorate ER stress in the CNS, with a focus on MS pathology. Our goal is to emphasize the importance of this potential interaction to aid in the identification of novel therapeutic targets for the treatment of MS and other demyelinating disorders.

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.

Multiple Sclerosis: Inflammatory and Neuroglial Aspects

Multiple sclerosis (MS) represents the most common acquired demyelinating disorder of the central nervous system (CNS). Its pathogenesis, in parallel with the well-established role of mechanisms pertaining to autoimmunity, involves several key functions of immune, glial and nerve cells. The disease's natural history is complex, heterogeneous and may evolve over a relapsing-remitting (RRMS) or progressive (PPMS/SPMS) course. Acute inflammation, driven by infiltration of peripheral cells in the CNS, is thought to be the most relevant process during the earliest phases and in RRMS, while disruption in glial and neural cells of pathways pertaining to energy metabolism, survival cascades, synaptic and ionic homeostasis are thought to be mostly relevant in long-standing disease, such as in progressive forms. In this complex scenario, many mechanisms originally thought to be distinctive of neurodegenerative disorders are being increasingly recognized as crucial from the beginning of the disease. The present review aims at highlighting mechanisms in common between MS, autoimmune diseases and biology of neurodegenerative disorders. In fact, there is an unmet need to explore new targets that might be involved as master regulators of autoimmunity, inflammation and survival of nerve cells.

Tunable Surface Charge Enables the Electrostatic Adsorption-Controlled Release of Neuroprotective Peptides from a Hydrogel-Nanoparticle Drug Delivery System

We exploit the electrostatic interactions between the positively charged neuroprotective peptide, pituitary adenylate cyclase-activating polypeptide (PACAP), and negatively charged poly(lactic-co-glycolic acid) (PLGA) nanoparticles to control PACAP release from the surface of nanoparticles dispersed in a hyaluronan-methylcellulose (HAMC) hydrogel composite. PACAP is a promising therapeutic for the treatment of neurological disorders, yet it has been difficult to deliver in vivo. Herein, the PACAP release rate was tuned by manipulating peptide adsorption onto the surface of blank nanoparticles by modifying either nanoparticle loading in the hydrogel or nanoparticle surface charge. This peptide-nanoparticle interaction was controlled by the pH-responsive carboxylic acid end terminal groups of PLGA. We further validated this system with the controlled release of a novel stabilized PACAP analog: Ac-[Ala¹⁵, Ala²⁰]PACAP-propylamide, which masks its recognition to peptidases in circulation. Both wild-type and stabilized PACAP released from the vehicle increased the production of neuroprotective Interleukin-6 from cultured primary astrocytes. Using computational fluid dynamics methods, PACAP release from the composite was predicted based on experimentally derived adsorption isotherms, which exhibited similar release profiles to experimental data. This versatile adsorption-based system was used to deliver PACAP locally to the brains of stroke-injured mice over a 10 day period in vivo, highlighting its effectiveness for the controlled release of PACAP to the central nervous system.

Significance of serum VIP and PACAP in multiple sclerosis: an exploratory case-control study

BACKGROUND

Multiple sclerosis (MS) is a chronic inflammatory neurodegenerative disease of the central nervous system. Vasoactive and intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP) are neuropeptides that play roles in anti-inflammation and neuroprotection in MS. In this study, we aimed to determine the serum levels of VIP and PACAP in MS patients versus healthy controls and to correlate them with demographics and clinical characteristics.

METHODS

Serum samples were collected from MS patients (n = 145) and healthy controls (n = 73) to measure serum levels VIP and PACAP.

RESULTS

VIP serum levels were lower in MS patients than healthy controls (p < 0.001). Serum PACAP levels were the same among the two groups. Gender-based analysis showed that VIP levels were lower in healthy females (1238.840 pg/ml) than healthy males (3300.105 pg/ml; p < 0.001), and PACAP serum levels were significantly lower in male MS patients (48,516.214 fg/ml) than female MS patients (62,466.400 fg/ml; p = 0.029). ROC curve suggested that serum VIP level can discriminate patients with MS from healthy controls. Relapsing-remitting MS, progressive-MS, and clinically isolated syndrome groups were different in age, MS disease duration, EDSS score, and VIP levels (p < 0.05). MS disease type and history of previous relapses in the preceding 24 months predicted serum VIP levels, while gender predicted PACAP levels.

CONCLUSION

VIP serum levels are decreased in MS patients and can be used to differentiate between MS patients and healthy controls. Further studies with larger sample sizes are required to investigate VIP as a marker to reflect MS disease progression.

Pituitary Adenylate Cyclase-Activating Polypeptide Alleviates Intestinal, Extra-Intestinal and Systemic Inflammatory Responses during Acute Campylobacter jejuni-induced Enterocolitis in Mice

Human Campylobacter jejuni infections are emerging, and constitute a significant health burden worldwide. The ubiquitously expressed pituitary adenylate cyclase-activating polypeptide (PACAP) is well-known for its cell-protective and immunomodulatory effects. In our actual intervention study, we used an acute campylobacteriosis model and assessed the potential disease-alleviating effects of exogenous PACAP. Therefore, secondary abiotic IL-10^-/- mice were perorally infected with C. jejuni and treated with synthetic PACAP38 intraperitoneally from day 2 until day 5 post-infection. Whereas PACAP did not interfere with the gastrointestinal colonization of the pathogen, mice from the PACAP group exhibited less severe clinical signs of C. jejuni-induced disease, as compared to mock controls, which were paralleled by alleviated apoptotic, but enhanced cell proliferative responses in colonic epithelia on day 6 post-infection. Furthermore, PACAP dampened the accumulation of macrophages and monocytes, but enhanced regulatory T cell responses in the colon, which were accompanied by less IFN-γ secretion in intestinal compartments in PACAP versus mock-treated mice. Remarkably, the inflammation-dampening properties of PACAP could also be observed in extra-intestinal organs, and strikingly, even the systemic circulation on day 6 post-infection. For the first time, we provide evidence that synthetic PACAP might be a promising candidate to combat acute campylobacteriosis and post-infectious sequelae.

Protective Effects of Pituitary Adenylate Cyclase-Activating Polypeptide and Vasoactive Intestinal Peptide Against Cognitive Decline in Neurodegenerative Diseases

Cognitive impairment is one of the major symptoms in most neurodegenerative disorders such as Alzheimer’s (AD), Parkinson (PD), and Huntington diseases (HD), affecting millions of people worldwide. Unfortunately, there is no treatment to cure or prevent the progression of those diseases. Cognitive impairment has been related to neuronal cell death and/or synaptic plasticity alteration in important brain regions, such as the cerebral cortex, substantia nigra, striatum, and hippocampus. Therefore, compounds that can act to protect the neuronal loss and/or to reestablish the synaptic activity are needed to prevent cognitive decline in neurodegenerative diseases. Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) are two highly related multifunctional neuropeptides widely distributed in the central nervous system (CNS). PACAP and VIP exert their action through two common receptors, VPAC1 and VPAC2, while PACAP has an additional specific receptor, PAC1. In this review article, we first presented evidence showing the therapeutic potential of PACAP and VIP to fight the cognitive decline observed in models of AD, PD, and HD. We also reviewed the main transduction pathways activated by PACAP and VIP receptors to reduce cognitive dysfunction. Furthermore, we identified the therapeutic targets of PACAP and VIP, and finally, we evaluated different novel synthetic PACAP and VIP analogs as promising pharmacological tools.

The Effects of Carbenoxolone against Experimental Autoimmune Encephalomyelitis in a Mouse Model

INTRODUCTION

Multiple sclerosis (MS) is a complex demyelinating disease involving central nervous system (CNS). It is still a challenge to secure an effective therapeutic strategy against this disease. Carbenoxolone (CBX) is a derivative of glycyrrhetinic acid, which is widely used in brain research for its gap-junction inhibition effects. Many researchers have observed CBX-mediated suppression of CNS inflammation in their studies.

OBJECTIVE

We want to further examine its anti-inflammation effects in CNS demyelinating disease like MS.

METHODS

Thus, our study applied an experimental autoimmune encephalomyelitis (EAE) mouse model and examined the effects of CBX on it.

RESULTS AND CONCLUSIONS

We found that CBX significantly reversed the EAE severity and pathology in EAE. IL-17-secreting and IFN-γ-secreting CD4+ T lymphocytes were remarkably lower in the spleen of CBX-treated mice. Production of IL-23 and IL-17 from cortex in EAE animals was markedly reduced by CBX. Furthermore, CBX treatment increased the expression of brain-derived neurotrophic factor. This study provides evidence for the protective role of CBX against EAE.

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

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

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

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

Immunomodulatory Effects of the Neuropeptide Pituitary Adenylate Cyclase-Activating Polypeptide in Acute Toxoplasmosis

Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) is an endogenous neuropeptide with distinct functions including the regulation of inflammatory processes. PACAP is able to modify the immune response by directly regulating macrophages and monocytes inhibiting the production of inflammatory cytokines, chemokines and free radicals. Here, we analyzed the effect of exogenous PACAP on peripheral immune cell subsets upon acute infection with the parasite Toxoplasma gondii (T. gondii). PACAP administration was followed by diminished innate immune cell recruitment to the peritoneal cavity of T. gondii-infected mice. PACAP did not directly interfere with parasite replication, instead, indirectly reduced parasite burden in mononuclear cell populations by enhancing their phagocytic capacity. Although proinflammatory cytokine levels were attenuated in the periphery upon PACAP treatment, interleukin (IL)-10 and Transforming growth factor beta (TGF-β) remained stable. While PACAP modulated VPAC1 and VPAC2 receptors in immune cells upon binding, it also increased their expression of brain-derived neurotrophic factor (BDNF). In addition, the expression of p75 neurotrophin receptor (p75^NTR) on Ly6C^hi inflammatory monocytes was diminished upon PACAP administration. Our findings highlight the immunomodulatory effect of PACAP on peripheral immune cell subsets during acute Toxoplasmosis, providing new insights about host-pathogen interaction and the effects of neuropeptides during inflammation.

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

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

Immunomodulatory Roles of PACAP and VIP: Lessons from Knockout Mice

A bidirectional cross-talk is established between the nervous and immune systems through common mediators including neuropeptides, neurotransmitters, and cytokines. Among these, PACAP and VIP are two highly related neuropeptides widely distributed in the organism with purported immunomodulatory actions. Due to their well-known anti-inflammatory properties, administration of these peptides has proven to be beneficial in models of acute and chronic inflammatory diseases. Nevertheless, the relevance of the endogenous source of these peptides in the modulation of immune responses remains to be elucidated. The development of transgenic mice with specific deletions in the genes coding for these neuropeptides (Vip and Adcyap1) or for their G-protein-coupled receptors VPAC1, VPAC2, and PAC1 (Vipr1, Vipr2, Adcyap1r1) has allowed to address this question, underscoring the complexity of the immunoregulatory properties of PACAP and VIP. The goal of this review is to integrate the existing information on the immune phenotypes of mice deficient for PACAP, VIP, or their receptors, to provide a global view on the roles of these endogenous neuropeptides during immunological health and disease.

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.

Neuropeptides and Microglial Activation in Inflammation, Pain, and Neurodegenerative Diseases

Microglial cells are responsible for immune surveillance within the CNS. They respond to noxious stimuli by releasing inflammatory mediators and mounting an effective inflammatory response. This is followed by release of anti-inflammatory mediators and resolution of the inflammatory response. Alterations to this delicate process may lead to tissue damage, neuroinflammation, and neurodegeneration. Chronic pain, such as inflammatory or neuropathic pain, is accompanied by neuroimmune activation, and the role of glial cells in the initiation and maintenance of chronic pain has been the subject of increasing research over the last two decades. Neuropeptides are small amino acidic molecules with the ability to regulate neuronal activity and thereby affect various functions such as thermoregulation, reproductive behavior, food and water intake, and circadian rhythms. Neuropeptides can also affect inflammatory responses and pain sensitivity by modulating the activity of glial cells. The last decade has witnessed growing interest in the study of microglial activation and its modulation by neuropeptides in the hope of developing new therapeutics for treating neurodegenerative diseases and chronic pain. This review summarizes the current literature on the way in which several neuropeptides modulate microglial activity and response to tissue damage and how this modulation may affect pain sensitivity.

VPAC2 (vasoactive intestinal peptide receptor type 2) receptor deficient mice develop exacerbated experimental autoimmune encephalomyelitis with increased Th1/Th17 and reduced Th2/Treg responses

Vasoactive intestinal peptide (VIP) and pituitary adenylyl cyclase-activating polypeptide (PACAP) are two structurally-related neuropeptides with widespread expression in the central and peripheral nervous systems. Although these peptides have been repeatedly shown to exert potent anti-inflammatory actions when administered in animal models of inflammatory disease, mice deficient in VIP and PACAP were recently shown to exhibit different phenotypes (ameliorated and exacerbated, respectively) in response to experimental autoimmune encephalomyelitis (EAE). Therefore, elucidating what are the specific immunoregulatory roles played by each of their receptor subtypes (VPAC1, VPAC2, and PAC1) is critical. In this study, we found that mice with a genetic deletion of VIPR2, encoding the VPAC2 receptor, exhibited exacerbated (MOG35-55)-induced EAE compared to wild type mice, characterized by enhanced clinical and histopathological features, increased proinflammatory cytokines (TNF-α, IL-6, IFN-γ (Th1), and IL-17 (Th17)) and reduced anti-inflammatory cytokines (IL-10, TGFβ, and IL-4 (Th2)) in the CNS and lymph nodes. Moreover, the abundance and proliferative index of lymph node, thymus and CNS CD4(+)CD25(+)FoxP3(+) Tregs were strikingly reduced in VPAC2-deficient mice with EAE. Finally, the in vitro suppressive activity of lymph node and splenic Tregs from VPAC2-deficient mice was impaired. Overall, our results demonstrate critical protective roles for PACAP and the VPAC2 receptor against autoimmunity, promoting the expansion and maintenance of the Treg pool.

Pituitary adenylate cyclase-activating polypeptide ameliorates experimental acute ileitis and extra-intestinal sequelae

Background

The neuropeptide Pituitary adenylate cyclase-activating polypeptide (PACAP) plays pivotal roles in immunity and inflammation. So far, potential immune-modulatory properties of PACAP have not been investigated in experimental ileitis.

Methodology/Principal Findings

Mice were perorally infected with Toxoplasma (T.) gondii to induce acute ileitis (day 0) and treated daily with synthetic PACAP38 from day 1 to 6 post infection (p.i.; prophylaxis) or from day 4 to 6 p.i. (therapy). Whereas placebo-treated control mice suffered from acute ileitis at day 7 p.i. and succumbed to infection, intestinal immunopathology was ameliorated following PACAP prophylaxis. PACAP-treated mice exhibited increased abundance of small intestinal FOXP3+ cells, but lower numbers of ileal T lymphocytes, neutrophils, monocytes and macrophages, which was accompanied by less ileal expression of pro-inflammatory cytokines such as IL-23p19, IL-22, IFN-γ, and MCP-1. Furthermore, PACAP-treated mice displayed higher anti-inflammatory IL-4 concentrations in mesenteric lymph nodes and liver and higher systemic anti-inflammatory IL-10 levels in spleen and serum as compared to control animals at day 7 p.i. Remarkably, PACAP-mediated anti-inflammatory effects could also be observed in extra-intestinal compartments as indicated by reduced pro-inflammatory mediator levels in spleen (TNF-α, nitric oxide) and liver (TNF-α, IFN-γ, MCP-1, IL-6) and less severe histopathological sequelae in lungs and kidneys following prophylactic PACAP treatment. Strikingly, PACAP prolonged survival of T. gondii infected mice in a time-of-treatment dependent manner.

Conclusion/Significance

Synthetic PACAP ameliorates acute small intestinal inflammation and extra-intestinal sequelae by down-regulating Th1-type immunopathology, reducing oxidative stress and up-regulating anti-inflammatory cytokine responses. These findings provide novel potential treatment options of inflammatory bowel diseases.

VIP and PACAP: neuropeptide modulators of CNS inflammation, injury, and repair

Inflammatory processes play both regenerative and destructive roles in multiple sclerosis, stroke, CNS trauma, amyotrophic lateral sclerosis and aging-related neurodegenerative diseases such as Alzheimer's, Parkinson's and Huntington's. Endogenous defence mechanisms against these pathologies include those that are directly neuroprotective, and those that modulate the expression of inflammatory mediators in microglia, astrocytes, and invading inflammatory cells. While a number of mechanisms and molecules have been identified that can directly promote neuronal survival, less is known about how the brain protects itself from harmful inflammation, and further, how it co-opts the healing function of the immune system to promote CNS repair. The two closely related neuroprotective peptides, vasoactive intestinal peptide (VIP) and pituitary adenylyl cyclase-activating peptide (PACAP), which are up-regulated in neurons and immune cells after injury and/or inflammation, are known to protect neurons, but also exert powerful in vivo immunomodulatory actions, which are primarily anti-inflammatory. These peptide actions are mediated by high-affinity receptors expressed not only on neurons, but also astrocytes, microglia and peripheral inflammatory cells. Well-established immunomodulatory actions of these peptides are to inhibit macrophage and microglia production and release of inflammatory mediators such as TNF-α and IFN-γ, and polarization of T-cell responses away from Th1 and Th17, and towards a Th2 phenotype. More recent studies have revealed that these peptides can also promote the production of both natural and inducible subsets of regulatory T-cells. The neuroprotective and immunomodulatory actions of VIP and PACAP suggest that receptors for these peptides may be therapeutic targets for neurodegenerative and neuroinflammatory diseases and other forms of CNS injury.

Effects of pituitary adenylate cyclase activating polypeptide on CD4(+)/CD8(+) T cell levels after traumatic brain injury in a rat model

BACKGROUND

The effect of pituitary adenylate cyclase activating polypeptide (PACAP) during traumatic brain injury (TBI) and whether it can modulate secondary injury has not been reported previously. The present study evaluated the potential protective effects of ventricular infusion of PACAP in a rat model of TBI.

METHODS

Male Sprague Dawley rats were randomly divided into 3 treatment groups (n=6, each): sham-operated, vehicle (normal saline)+TBI, and PACAP+TBI. Normal saline or PACAP (1 μg/5 μL) was administered intracerebroventricularly 20 minutes before TBI. Right parietal cortical contusion was produced via a weight-dropping method. Brains were extracted 24 hours after trauma. Histological changes in brains were examined by HE staining. The numbers of CD4(+) and CD8(+) T cells in blood and the spleen were detected via flow cytometry.

RESULTS

In injured brain regions, edema, hemorrhage, inflammatory cell infiltration, and swollen and degenerated neurons were observed under a light microscope, and the neurons were disorderly arrayed in the hippocampi. Compared to the sham group, average CD4(+) CD8(-) lymphocyte counts in blood and the spleen were significantly decreased in rats that received TBI+vehicle, and CD4(-) CD8(+) were increased. In rats administered PACAP prior to TBI, damage was attenuated as evidenced by significantly increased CD4(+), and decreased CD8(+), T lymphocytes in blood and the spleen.

CONCLUSION

Pretreatment with PACAP may protect against TBI by influencing periphery T cellular immune function.

Prolonged acetylsalicylic-acid-supplementation-induced gastritis affects the chemical coding of the stomach innervating vagal efferent neurons in the porcine dorsal motor vagal nucleus (DMX)

The main goal of our research was to study the possible alterations of the chemical coding of the dorsal motor vagal nucleus (DMX) neurons projecting to the porcine stomach prepyloric region following prolonged acetylsalicylic acid supplementation. Fast Blue (FB) was injected into the studied area of the stomach. Since the seventh day following the FB injection, acetylsalicylic acid (ASA) was given orally to the experimental gilts. All animals were euthanized on the 28th day after FB injection. Medulla oblongata sections were then processed for double-labeling immunofluorescence for choline acetyltransferase (ChAT), pituitary adenylate cyclase-activating peptide (PACAP), vasoactive intestinal polypeptide (VIP), nitric oxide synthase (NOS), galanin (GAL), substance P (SP), leu enkephalin (LENK), and cocaine- and amphetamine-regulated transcript (CART). In the control DMX, only PACAP was observed in 30.08 ± 1.97 % of the FB-positive neurons, while VIP, NOS, GAL, SP, LENK, and CART were found exclusively in neuronal processes running between FB-labeled perikarya. In the ASA DMX, PACAP was revealed in 49.53 ± 5.73 % of traced vagal perikarya. Moreover, we found de novo expression of VIP in 40.32 ± 7.84 %, NOS in 25.02 ± 6.08 %, and GAL in 3.37 ± 0.85 % of the FB-labeled neurons. Our results suggest that neuronal PACAP, VIP, NOS, and GAL are mediators of neural response to aspirin-induced stomach inflammatory state.

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase activating polypeptide (PACAP) in humans with multiple sclerosis

Multiple sclerosis (MS) is a chronic neuroinflammatory disease of the central nervous system that leads to demyelination and neurodegeneration. VIP and PACAP are structurally related neuropeptides with neuroprotective and anti-inflammatory activities. To evaluate VIP and PACAP-38 in plasma and CSF in humans in correlation with IL-6, IL-10 and TNFα, we compared 20 MS individuals with 27 healthy controls. In MS, a decrease in PACAP-38 in CSF and a decrease in plasma IL-6 concentration were seen. A positive correlation between plasma VIP and plasma IL-6 was identified. We conclude that VIP and PACAP may influence the course of MS.

Pituitary adenylate cyclase activating peptide deficient mice exhibit impaired thymic and extrathymic regulatory T cell proliferation during EAE

We have shown that mice deficient in pituitary adenylate cyclase-activating polypeptide (PACAP, gene name ADCYAP1) manifest enhanced sensitivity to experimental autoimmune encephalomyelitis (EAE), supporting the anti-inflammatory actions described for this neuropeptide. In addition to an increased proinflammatory cytokine response in these mice, a reduction in regulatory T cell (Treg) abundance in the lymph nodes (LN) was observed, suggesting altered Treg kinetics. In the present study, we compared in PACAP deficient (KO) vs. wild type mice the abundances and rates of proliferation FoxP3⁺ Tregs in three sites, the LN, central nervous system (CNS) and thymus and the relative proportions of Th1, Th2, and Th17 effector subsets in the LN and CNS. Flow cytometry analyses revealed a decrease in Treg proliferation and an increased T effector/Tregs ratio in the LN and CNS of PACAP KO mice. In the thymus, the primary site of do novo natural Treg production, the total numbers and proliferative rates of FoxP3⁺ Tregs were significantly reduced. Moreover, the expression of IL-7, a cytokine implicated in thymic Treg expansion during EAE, failed to increase at the peak of the disease in the thymus and LN of PACAP KO mice. In addition to these Treg alterations, a specific reduction of Th2 cells (about 4-fold) was observed in the lymph nodes in PACAP KO mice, with no effects on Th1 and Th17 subsets, whereas in the CNS, Th1 and Th17 cells were increased and Th2 decreased. Our results suggest that endogenous production of the neuropeptide PACAP protects against EAE by modulating Treg expansion and Th subsets at multiple sites.

The gap-junction inhibitor carbenoxolone suppresses the differentiation of Th17 cells through inhibition of IL-23 expression in antigen presenting cells

Carbenoxolone (CBX) is a widely used gap-junction inhibitor. We have previously shown that treatment with CBX significantly delayed the onset of experimental autoimmune encephalomyelitis (EAE). However, the mechanism by which CBX delays the onset of EAE remains to be elucidated. Here, we show that CBX specifically inhibits the production of IL-23 by dendritic cells (DCs) and microglia in vitro. CBX treatment significantly reduced the population of Th17 cells in EAE mice. Furthermore, CBX downregulated the expression of IL-23 p19 via increased production of protein phosphatase 2A (PP2A). Thus, CBX may be an effective therapeutic strategy against Th17-mediated autoimmune diseases, such as multiple sclerosis.

Targeting VIP and PACAP receptor signalling: new therapeutic strategies in multiple sclerosis

MS (multiple sclerosis) is a chronic autoimmune and neurodegenerative pathology of the CNS (central nervous system) affecting approx. 2.5 million people worldwide. Current and emerging DMDs (disease-modifying drugs) predominantly target the immune system. These therapeutic agents slow progression and reduce severity at early stages of MS, but show little activity on the neurodegenerative component of the disease. As the latter determines permanent disability, there is a critical need to pursue alternative modalities. VIP (vasoactive intestinal peptide) and PACAP (pituitary adenylate cyclase-activating peptide) have potent anti-inflammatory and neuroprotective actions, and have shown significant activity in animal inflammatory disease models including the EAE (experimental autoimmune encephalomyelitis) MS model. Thus, their receptors have become candidate targets for inflammatory diseases. Here, we will discuss the immunomodulatory and neuroprotective actions of VIP and PACAP and their signalling pathways, and then extensively review the structure–activity relationship data and biophysical interaction studies of these peptides with their cognate receptors.

Pituitary adenylate cyclase-activating polypeptide plays an anti-inflammatory role in endotoxin-induced airway inflammation: in vivo study with gene-deleted mice

The presence of pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptors in capsaicin-sensitive peptidergic sensory nerves, inflammatory and immune cells suggest its involvement in inflammation. However, data on its role in different inflammatory processes are contradictory and there is little known about its functions in the airways. Therefore, our aim was to examine intranasal endotoxin-induced subacute airway inflammation in PACAP gene-deficient (PACAP⁻/⁻) and wild-type (PACAP⁺/⁺) mice. Airway responsiveness to inhaled carbachol was determined in unrestrained mice with whole body plethysmography 6 h and 24 h after LPS. Myeloperoxidase (MPO) activity referring to the number of accumulated neutrophils and macrophages was measured with spectrophotometry and interleukin-1β (IL-1β) concentration with ELISA from the lung homogenates. Histological evaluation and semiquantitative scoring were also performed. Bronchial responsiveness, as well as IL-1β concentration and MPO activity markedly increased at both timepoints. Perivascular edema dominated the histological picture at 6 h, while remarkable peribronchial granulocyte accumulation, macrophage infiltration and goblet cell hyperplasia were seen at 24h. In PACAP⁻/⁻ mice, airway hyperreactivity was significantly higher 24 h after LPS and inflammatory histopathological changes were more severe at both timepoints. MPO increase was almost double in PACAP⁻/⁻ mice compared to the wild-types at 6 h. In contrast, there was no difference between the IL-1β concentrations of the PACAP⁺/⁺ and PACAP⁻/⁻ mice. These results provide evidence for a protective role for PACAP in endotoxin-induced airway inflammation and hyperreactivity.

Production and functions of IL-33 in the central nervous system

Interleukin-33 (IL-33) is a novel multifunctional IL-1 family cytokine. IL-33 signals via a heterodimer composed of IL-1 receptor-related protein ST2 and IL-1 receptor accessory protein (IL-1RAcP). IL-33 has been shown to activate T helper 2 cells (Th2), mast cells and basophils to produce a variety of Th2 cytokines and mediate allergic-type immune responses. Recent studies have revealed that glial cells are induced to express IL-33 mRNA and protein. However, the functions of IL-33 and its producing cells in the central nervous system (CNS) are still uncertain. In this study, we investigated the expression and function of IL-33 in the CNS. IL-33 is produced by endothelial cells and astrocytes but not by microglia or neurons. The IL-33 receptors are expressed mainly in microglia and astrocytes. IL-33 dose-dependently induces the proliferation of microglia and enhances the production of pro-inflammatory cytokines, such as IL-1β and TNFα, as well as the anti-inflammatory cytokine IL-10. It also enhances chemokines and nitric oxide production and phagocytosis by microglia. Thus, IL-33 produced in the CNS activates microglia and may function as a pro-inflammatory mediator in the pathophysiology of the CNS.

Small but powerful: short peptide hormones and their role in autoimmune inflammation

In the recent years, it has become increasingly clear that the immune response is also influenced by mediators which were first discovered as regulators in the nervous or also cardiovascular system. Here, small peptide hormones may play an important role. Kinins like bradykinins act on the endothelium and play a role for trafficking of lymphocytes over the blood-brain barrier. Neuropeptides like vasoactive intestinal peptide or neuropeptide Y also directly act on T cells and favour the differentiation of Th2 cells or regulatory T cell populations. Recently, the renin-angiotensin system (RAS) came into the focus of interest. Inhibition of the RAS at different levels may influence autoimmune responses and involve T cells as well as antigen-presenting cells, probably via different signalling pathways. Inhibitors of angiotensin converting enzyme and antagonists of the angiotensin 1 receptors are used in the treatment of hypertension, kidney disease or stroke by millions of people worldwide. These inexpensive and safe pharmaceuticals may also represent an interesting and innovative approach for the (combination) treatment of autoimmune diseases like multiple sclerosis.

Blockade of glutamate release from microglia attenuates experimental autoimmune encephalomyelitis in mice

Multiple sclerosis (MS) is a chronic inflammatory demyelinating and neurodegenerative disease of the central nervous system. Despite a variety of anti-inflammatory or immunomodulation drugs including interferon-beta are effective to reduce relapse risk, most patients have progressive neurological deterioration due to axonal degeneration. Accumulation of activated microglia is a pathological hallmark of active MS lesion. Microglia can act as not only antigen-presenting cells but also effector cells to damage other cells in the central nervous system. Especially, glutamate released by activated microglia induces excito-neurotoxicity and may contribute to neurodegeneration in MS. Gap junction is a major cell-to-cell channel and is composed of paired hemichannels on coupled cells. Recent studies showed that cells release various small molecules (including ions, ATP, and amino acids) from unpaired hemichannel of gap junction that is openly exposed to the extracellular space. We have previously revealed that activated microglia produce glutamate via glutaminase and release it through hemichannels of gap junctions. Thus, in this study, we examined whether the glutaminase inhibitor and the gap junction blocker relieved experimental autoimmune encephalomyelitis (EAE) that is an animal model of MS. Here we show that the gap junction blocker carbenoxolone (CBX) and the glutaminase inhibitor 6-diazo-5-oxo-L-norleucine (DON) decreased glutamate release from activated microglia and rescued neuronal death in a dose-dependent manner in vitro. In EAE mice, treatment with CBX or DON also attenuated EAE clinical symptoms. Thus, blockade of glutamate release from activated microglia with CBX or DON may be an effective therapeutic strategy against neurodegeneration in MS.

Pituitary adenylyl cyclase-activating polypeptide is an intrinsic regulator of Treg abundance and protects against experimental autoimmune encephalomyelitis

Pituitary adenylyl cyclase-activating polypeptide (PACAP) is a widely expressed neuropeptide originally discovered in the hypothalamus. It closely resembles vasoactive intestinal peptide (VIP), a neuropeptide well known to inhibit macrophage activity, promote Th2-type responses, and enhance regulatory T cell (Treg) production. Recent studies have shown that administration of PACAP, like VIP, can attenuate dramatically the clinical and pathological features of murine models of autoimmune diseases such as experimental autoimmune encephalomyelitis (EAE) and collagen-induced arthritis. However, specific roles (if any) of endogenous VIP and PACAP in the protection against autoimmune diseases have not been explored. Here, we subjected PACAP-deficient mice to myelin oligodendrocyte glycoprotein (MOG(35-55))-induced EAE. MOG immunization of PACAP-deficient mice triggered heightened clinical and pathological manifestations of EAE compared to wild-type mice. The increased sensitivity was accompanied by enhanced mRNA expression of proinflammatory cytokines (TNFalpha, IL-6, IFN-gamma, IL-12p35, IL-23p19, and IL-17), chemokines (MCP-1/CCL2, MIP-1alpha/CCL3, and RANTES/CCL5), and chemotactic factor receptors (CCR1, CCR2, and CCR5), but downregulation of the anti-inflammatory cytokines (IL-4, IL-10, and TGF-beta) in the spinal cord. Moreover, the abundance of CD4(+)CD25(+)FoxP3(+) Tregs in lymph nodes and levels of FoxP3 mRNA in the spinal cord were also diminished. The reduction in Tregs was associated with increased proliferation and decreased TGF-beta secretion in lymph node cultures stimulated with MOG. These results demonstrate that endogenous PACAP provides protection in EAE and identify PACAP as an intrinsic regulator of Treg abundance after inflammation.

Intravenous tolerance modulates macrophage classical activation and antigen presentation in experimental autoimmune encephalomyelitis

Macrophages act as the first line of self defense by mounting an inflammatory response to antigen and as antigen presenting cells to initiate the adaptive immune response. Inhibition of macrophage activation is one of the possible approaches to modulate inflammation. Intravenous (i.v.) tolerance has proved to be an effective method for ameliorating experimental autoimmune diseases. Whether macrophages are involved in tolerance induction is still largely undefined. In the present study we found that i.v. tolerance induction resulted in lower B7.1, B7.2 and MHC class II molecules, and reduced phagocytosis by both peritoneal macrophages and adherent splenocytes. Macrophages from tolerized mice were associated with a significantly impaired response of MOG-sensitized T cells to MOG. Macrophages from tolerized mice produced low levels of pro-inflammatory molecules IL-12, TNF-alpha, IL-1beta, RANTES and MCP-1 and high levels of IL-10 and TGF-beta. Administration of anti-TGF-beta led to a reduction of IL-10 in tolerized mice. Thus, i.v. tolerance inhibits macrophage classical activation and APC function, increases macrophage alternative activation and IL-10 and TGF-beta production. These cytokines, in turn, induce enhanced production of IL-10 in macrophages in MOG i.v. mice.

Gamma-aminobutyric acid transporter 1 negatively regulates T cell-mediated immune responses and ameliorates autoimmune inflammation in the CNS

gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter of the CNS, and GABA transporter 1 (GAT-1) is critical in maintaining a GABA reservoir and associated functions. The wide expression of GAT-1 in the CNS prompted us to explore its role in neuroimmunological disorders. In mice induced with experimental autoimmune encephalomyelitis (EAE), the animal model of multiple sclerosis, we found that the expression levels of GAT-1 mRNA and protein in spinal cord were greatly suppressed as compared with those in naive mice and irrelevant Ag-immunized mice. Therefore, we induced EAE in GAT-1(-/-) mice and found that the disease was significantly aggravated and was accompanied by some nonclassic EAE signs. Mononuclear cells from GAT-1(-/-) mice with EAE showed much higher Ag-specific proliferative responses. Proinflammatory cytokine production in these mice was also greatly up-regulated. Further studies revealed that GAT-1 deficiency induced vigorous immune responses by enhancing IkappaB kinase phosphorylation and NF-kappaB-DNA binding activity, as well as strengthening the T-bet-STAT1 circuit signaling pathway. Finally, we found that GAT-1 was expressed only on activated T cells primed with Ags, but not on B cells or macrophages. These findings indicate that GAT-1 is a critical modulator in T cell-mediated immune responses and in EAE pathogenesis.

Chronological changes of CD4(+) and CD8(+) T cell subsets in the experimental autoimmune encephalomyelitis, a mouse model of multiple sclerosis

Multiple sclerosis (MS) is an inflammatory disease of the central nervous system (CNS). The etiology of MS remains unclear, but T cells specific for myelin components, such as myelin oligodendrocyte glycoprotein (MOG), are thought to play a critical role in the onset of MS. Experimental autoimmune encephalomyelitis (EAE) has been used as an animal model of MS, and T helper type 1 (Th1) cells play an essential role for the pathogenesis of EAE through the production of Th1 cytokines, interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha). We examined CD4(+) and CD8(+) T cell responses in the spleen and CNS of EAE mice, generated by immunization with a peptide (35-55 amino acid residues) of MOG. The number of both CD4(+) and CD8(+) T cells and their MOG-reactivity in the CNS were associated with increasing disease severity but not those in the spleen, suggesting that the MOG-specific CD4(+) and CD8(+) T cells in the CNS are involved in the development of EAE. Polymerase chain reaction analysis suggested that both CD4(+) and CD8(+) T cells produced IFN-gamma and TNF-alpha, while CD4(+) T cells also produced interleukin-17 (IL-17), an important factor in the development of EAE. Thus, CD4(+) T cells may contribute to the induction of EAE by producing IL-17. Furthermore, CD8(+) T cells express higher levels of a suppressive cytokine, IL-10. Taking together, our data suggest that CD4(+) T cells are involved in the early phase of EAE, whereas CD8(+) T cells have a regulatory role in the later stage of EAE.

Induction of colitis and rapid development of colorectal tumors in mice deficient in the neuropeptide PACAP

Pituitary adenylyl cyclase activating peptide (PACAP) is expressed in central, sensory, autonomic, and enteric neurons. Although it classically acts as a neurotransmitter/neuromodulator, recent studies indicate that PACAP can also regulate immune function. To this effect, PACAP has been shown to reduce clinical symptoms and inflammation in mouse models of human immune-based diseases such as rheumatoid arthritis, Crohn's Disease, septic shock and multiple sclerosis. Despite these findings, the role of the endogenous peptide in regulating immune function is unknown. To determine if endogenous PACAP plays a protective role in inflammatory bowel disease (IBD) and IBD-associated colorectal cancer in mice, PACAP-deficient (KO) mice were subjected to 3 cycles of dextran sulfate sodium (DSS) in drinking water over 2 months, an established mouse model for colitis. Compared to wild type (WT) controls, PACAP KO mice exhibited more severe clinical symptoms of colitis and had significantly higher colonic inflammation on pathological examination. Moreover, 60% of the PACAP KO mice developed colorectal tumors with an aggressive-appearing pathology. Consistent with published data, DSS-treated WT mice did not develop such tumors. The results demonstrate a new mouse model which rapidly develops inflammation-associated colorectal cancer in the absence of a carcinogen.

Inhibition of midkine alleviates experimental autoimmune encephalomyelitis through the expansion of regulatory T cell population

CD4(+)CD25(+) regulatory T (Treg) cells are crucial mediators of autoimmune tolerance. The factors that regulate Treg cells, however, are largely unknown. Here, we show that deficiency in midkine (MK), a heparin-binding growth factor involved in oncogenesis, inflammation, and tissue repair, attenuated experimental autoimmune encephalomyelitis (EAE) because of an expansion of the Treg cell population in peripheral lymph nodes and decreased numbers of autoreactive T-helper type 1 (T(H)1) and T(H)17 cells. MK decreased the Treg cell population ex vivo in a dose-dependent manner by suppression of STAT5 phosphorylation that is essential for Foxp3 expression. Moreover, administration of anti-MK RNA aptamers significantly expanded the Treg cell population and alleviated EAE symptoms. These observations indicate that MK serves as a critical suppressor of Treg cell expansion, and inhibition of MK using RNA aptamers may provide an effective therapeutic strategy against autoimmune diseases, including multiple sclerosis.

Impaired nerve regeneration and enhanced neuroinflammatory response in mice lacking pituitary adenylyl cyclase activating peptide

Peripheral nerve injury models are used to investigate processes that can potentially be exploited in CNS injury. A consistent change that occurs in injured peripheral neurons is an induction in expression of pituitary adenylyl cyclase activating peptide (PACAP), a neuropeptide with putative neuroprotective and neuritogenic actions. PACAP-deficient mice were used here to investigate actions of endogenous PACAP after facial nerve injury. Although motor neuron survival after axotomy was not significantly different in PACAP deficient vs. wild type mice, recovery of axon regeneration after crush injury was significantly delayed. The impaired regeneration was associated with 8- to 12-fold increases in gene expression of proinflammatory cytokines tumor necrosis factor-alpha, interferon-gamma, interleukin (IL) -6, and a 90% decrease in the anti-inflammatory cytokine IL-4 at the injury site. Similar cytokine changes and an increased microglial response were observed in the brainstem facial motor nucleus. Because immunocompromised animals such as SCID mice are known to exhibit peripheral nerve regeneration defects, the observations raise the novel hypothesis that PACAP is critically involved in a carefully controlled immune response that is necessary for proper nerve regeneration after injury.

Inhibitory effect of PACAP-38 on acute neurogenic and non-neurogenic inflammatory processes in the rat

Inhibitory actions of pituitary adenylate cyclase activating polypeptide (PACAP) have been described on cellular/vascular inflammatory components, but there are few data concerning its role in neurogenic inflammation. In this study we measured PACAP-like immunoreactivity with radioimmunoassay in the rat plasma and showed a two-fold elevation in response to systemic stimulation of capsaicin-sensitive sensory nerves by resiniferatoxin, but not after local excitation of cutaneous afferents. Neurogenic plasma extravasation in the plantar skin induced by intraplantar capsaicin or resiniferatoxin, as well as carrageenan-induced paw edema were significantly diminished by intraperitoneal PACAP-38. In summary, these results demonstrate that PACAP is released from activated capsaicin-sensitive afferents into the systemic circulation. It diminishes acute pure neurogenic and mixed-type inflammatory reactions via inhibiting pro-inflammatory mediator release and/or by acting at post-junctional targets on the vascular endothelium.

Solution structure and mutational analysis of pituitary adenylate cyclase-activating polypeptide binding to the extracellular domain of PAC1-RS

The pituitary adenylate cyclase-activating polypeptide (PACAP) receptor is a class II G protein-coupled receptor that contributes to many different cellular functions including neurotransmission, neuronal survival, and synaptic plasticity. The solution structure of the potent antagonist PACAP (residues 6'-38') complexed to the N-terminal extracellular (EC) domain of the human splice variant hPAC1-R-short (hPAC1-R(S)) was determined by NMR. The PACAP peptide adopts a helical conformation when bound to hPAC1-R(S) with a bend at residue A18' and makes extensive hydrophobic and electrostatic interactions along the exposed beta-sheet and interconnecting loops of the N-terminal EC domain. Mutagenesis data on both the peptide and the receptor delineate the critical interactions between the C terminus of the peptide and the C terminus of the EC domain that define the high affinity and specificity of hormone binding to hPAC1-R(S). These results present a structural basis for hPAC1-R(S) selectivity for PACAP versus the vasoactive intestinal peptide and also differentiate PACAP residues involved in binding to the N-terminal extracellular domain versus other parts of the full-length hPAC1-R(S) receptor. The structural, mutational, and binding data are consistent with a model for peptide binding in which the C terminus of the peptide hormone interacts almost exclusively with the N-terminal EC domain, whereas the central region makes contacts to both the N-terminal and other extracellular parts of the receptor, ultimately positioning the N terminus of the peptide to contact the transmembrane region and result in receptor activation.

The neuropeptide genes TAC1, TAC3, TAC4, VIP and PACAP(ADCYAP1), and susceptibility to multiple sclerosis

The related immunomodulatory neuropeptides vasoactive intestinal peptide (VIP) and pituitary adenylyl cyclase activating peptide (PACAP; gene symbol ADCYAP1) have recently been proposed as novel therapeutics for the treatment of multiple sclerosis (MS). These neuropeptides, as well as those belonging to the tachykinin family exert pleiotropic effects, many of which are of relevance to central nervous system inflammation. In the present study, we have analysed 14 single nucleotide polymorphisms (SNPs) and 4 microsatellite markers in the VIP, ADCYAP1, TAC3 and TAC4 genes for susceptibility to MS in a case-control collection from Northern Ireland. Following correction for multiple comparisons, we did not find any significant associations between single polymorphic markers or multiple-marker haplotypes and susceptibility to MS. Furthermore, we analysed 2 SNPs in the TAC1 gene in a set of Sardinian trio MS families, based on our previous observation of association of these SNPs with MS in the Northern Irish (Genes Immun. 2005, 6, 265-270). Analysis of these SNPs in the Sardinians was not significant though a similar trend to that originally observed in the Northern Irish was present. Meta-analysis of the Sardinian and Northern Irish TAC1 SNP genotype data revealed a Mantel-Haenszel Common OR Estimate for the TAC1 intron 1 SNP rs2072100 of 0.76 (95% CI 0.63-0.92; P=0.005; A allele) and for the TAC1 promoter SNP rs7793277 of 0.76 (95% CI 0.615-0.95; P=0.014; C allele). Our data advocate a need for further exploration of the TAC1 gene region in MS.

Effect of pituitary adenylate cyclase activating polypeptide-38 on sensory neuropeptide release and neurogenic inflammation in rats and mice

Substance P (SP) and calcitonin gene-related peptide (CGRP), released from capsaicin-sensitive sensory nerves induce local neurogenic inflammation, while somatostatin exerts systemic anti-inflammatory actions. The aim of the present study was to investigate the release of pituitary adenylate cyclase activating polypeptide-38 (PACAP-38) and its effects on sensory neuropeptide release in vitro and acute neurogenic ear swelling in vivo. Capsaicin (10(-6) M) or electrical field stimulation (EFS; 40 V, 0.1 ms, 10 Hz, 120 s; 1200 impulses)-induced release of PACAP-38, SP, CGRP and somatostatin from isolated rat tracheae was measured with radioimmunoassay. Mustard oil-induced neurogenic inflammation in the mouse ear was determined with a micrometer and in the rat hind paw skin by the Evans Blue leakage technique. Capsaicin and EFS evoked 27% and more than twofold elevation of PACAP-38 release respectively, compared with the prestimulated basal values from isolated trachea preparation. Exogenously administered PACAP-38 (20-2000 nM) diminished both capsaicin- and EFS-evoked sensory neuropeptide release in a concentration-dependent manner. The maximal inhibitory effects of PACAP on capsaicin-induced substance P, CGRP and somatostatin release amounted to 75.4%, 73.3% and 90.0%, while EFS-evoked release of these peptides was 80.03%, 87.7% and 67.7%. In case of capsaicin stimulation the EC50 values for substance P, CGRP and somatostatin were 82.9 nM, 60.1 nM and 66.9 nM, respectively. When EFS was performed, these corresponding EC50 data were 92.1 nM, 67.8 nM and 20.9 nM. PACAP-38 (10, 100 and 1000 microg/kg i.p. in 200 microl volume) inhibited neurogenic ear swelling in the mouse. Furthermore, 100 microg/kg i.p. PACAP also significantly diminished mustard oil-evoked plasma protein extravasation in the rat skin. These results suggest that PACAP-38 is released from the stimulated peripheral terminals of capsaicin-sensitive afferents and it is able to inhibit the outflow of sensory neuropeptides. Based on this mechanism of action PACAP is also able to effectively diminish/abolish neurogenic inflammatory response in vivo after systemic administration.

Postulated vasoactive neuropeptide autoimmunity in fatigue-related conditions: a brief review and hypothesis

Disorders such as chronic fatigue syndrome (CFS) and gulf war syndrome (GWS) are characterised by prolonged fatigue and a range of debilitating symptoms of pain, intellectual and emotional impairment, chemical sensitivities and immunological dysfunction. Sudden infant death syndrome (SIDS) surprisingly may have certain features in common with these conditions. Post-infection sequelae may be possible contributing factors although ongoing infection is unproven. Immunological aberration may prove to be associated with certain vasoactive neuropeptides (VN) in the context of molecular mimicry, inappropriate immunological memory and autoimmunity. Adenylate cyclase-activating VNs including pituitary adenylate cyclase-activating polypeptide (PACAP), vasoactive intestinal peptide (VIP) and calcitonin gene-related peptide (CGRP) act as hormones, neurotransmitters, neuroregulators, immune modulators and neurotrophic substances. They and their receptors are potentially immunogenic. VNs are widely distributed in the body particularly in the central and peripheral nervous systems and have been identified in the gut, adrenal gland, blood cells, reproductive system, lung, heart and other tissues. They have a vital role in maintaining cardio-respiratory function, thermoregulation, memory, concentration and executive functions such as emotional responses including social cues and appropriate behaviour. They are co-transmitters for a number of neurotransmitters including acetylcholine and gaseous transmitters, are potent immune regulators with primarily anti-inflammatory activity, and have a significant role in protection of the nervous system against toxic assault as well as being important in the maintenance of homeostasis. This paper describes a biologically plausible mechanism for the development of certain fatigue-related syndromes based on loss of immunological tolerance to these VNs or their receptors following infection, other events or de novo resulting in significant pathophysiology possibly mediated via CpG fragments and heat shock (stress) proteins. These conditions extend the public health context of autoimmunity and VN dysregulation and have implications for military medicine where radiological, biological and chemical agents may have a role in pathogenesis. Possible treatment and prevention options are considered.