VPAC1 (vasoactive intestinal peptide (VIP) receptor type 1) G protein-coupled receptor mediation of VIP enhancement of murine experimental colitis

Podophyllotoxin-mediated neurotoxicity via the microbiota-gut-brain axis in SD rats based on the toxicological evidence chain (TEC) concept

Podophyllotoxin (PPT) is a naturally occurring aryltetralin lignan. However, its clinical application has been limited due to its neurotoxicity, the mechanism of which remains unclear. This study aimed to investigate the potential involvement of the microbiota-gut-brain (MGB) axis in PPT-induced neurotoxicity using the toxicological evidence chain concept. Our approach included behavioral testing in rats, evaluation of colon and hippocampal pathological changes, examination of proinflammatory factors, brain-gut peptides, and an in-depth analysis of gut microbiome and metabolic profiles. Our results demonstrated that PPT exposure compromised cognitive functions, induced damage to the colon and hippocampus, and increased intestinal permeability in rats. Furthermore, it elevated proinflammatory factors, particularly TNF-α and IL-6, while causing disruptions in the gut microbiota, favoring Escherichia-Shigella over Lactobacillus. Significant alterations in metabolic profiles in feces, serum, and hippocampus, particularly in tryptophan metabolism with a correlation to inflammatory factors and Escherichia-Shigella, were also observed. Our findings suggest that PPT promotes the enrichment of Escherichia-Shigella leading to inflammatory factor production and alterations in kynurenine metabolism in the hippocampus, potentially contributing to neurotoxicity. The study provides novel insights into the mechanistic pathways of PPT-induced neurotoxicity, emphasizing the role of the MGB axis and offering avenues for therapeutic interventions.

VPAC1 and VPAC2 receptor deficiencies negatively influence pregnancy outcome through distinct and overlapping modulations of immune, trophoblast and vascular functions

Pregnancy outcome relies on the maintenance of immune and metabolic homeostasis at the maternal fetal interface. Maternal and perinatal morbidity and mortality is associated with impaired placental development. Multiple regulatory effects of the endogenous-produced vasoactive intestinal peptide (VIP) on vascular, metabolic and immune functions at the maternal-fetal interface have been reported. Here we studied the involvement of the two primary high affinity receptors for VIP (VPAC1 and VPAC2) on maternal immune response, placental homeostasis and pregnancy outcome. Targeted disruption of each receptor gene led to altered placental structure, vascular and trophoblast functional markers and shaped the functional profiles of macrophages and neutrophils towards a proinflammatory state. Several changes in pregnant mice were receptor specific: ROS production elicited by VIP on neutrophils was selectively dependent on the presence of VPAC1 whereas apoptosis rate was associated with the VPAC2 deletion. In peritoneal macrophages from pregnant mice, levels of MHC-II, TLR2, and IL-10 were selectively altered in VPAC2 receptor-deficient mice, whereas IL-6 gene expression was reduced only in mice lacking VPAC1 receptors. Additionally, MMP9 mRNA in isolated TGCs was reduced in VPAC2 receptor deleted mice, while the percentage of IL-12 cells in post-phagocytosis macrophage cultures was selectively reduced in VPAC2 receptor deficient mice. The results indicate that manipulation of VPAC1 and VPAC2 receptor affects immune, vascular and metabolic environment at the maternal fetal interface. These mouse models offer new approaches to study pregnancy complications adding new perspectives to the development of VPAC receptor-selective drugs.

Alterations in Gut Microbiota and Upregulations of VPAC2 and Intestinal Tight Junctions Correlate with Anti-Inflammatory Effects of Electroacupuncture in Colitis Mice with Sleep Fragmentation

The relationship between inflammatory bowel disease and sleep disturbances is complicated and of increasing interest. We investigated the inflammatory and immunological consequences of EA in sleep-deprived colitis and found that dextran sulfate sodium (DSS)-induced colitis in sleep-fragmented (SF) mice was more severe than that in mice with normal sleep. This increase in the severity of colitis was accompanied by reduced body weight, shortened colon length, and deteriorated disease activity index. DSS with SF mice presented obvious diminished intestinal tight junction proteins (claudin-1 and occludin), elevated proinflammatory cytokines (CRP, IFN-γ, IL-6), lowered melatonin and adiponectin levels, downregulated vasoactive intestinal peptide (VIP) type 1 and 2 receptor (VPAC1, VPAC2) expression, and decreased diversity of gut bacteria. EA ameliorated colitis severity and preserved the performance of the epithelial tight junction proteins and VIP receptors, especially VPAC2. Meanwhile, the innate lymphoid cells-derived cytokines in both group 2 (IL-4, IL5, IL-9, IL-13) and group 3 (IL-22, GM-CSF) were elevated in mice colon tissue. Furthermore, dysbiosis was confirmed in the DSS group with and without SF, and EA could maintain the species diversity. Firmicutes could be restored, such as Lachnospiraceae, and Proteobacteria become rebalanced, mainly Enterobacteriaceae, after EA intervention. On the other hand, SF plays different roles in physiological and pathological conditions. In normal mice, interrupted sleep did not affect the expression of claudin-1 and occludin. But VPAC1, VPAC2, and gut microbiota diversity, including Burkholderiaceae and Rhodococcus, were opposite to mice in an inflamed state.

The Role of Vasoactive Intestinal Peptide and Mast Cells in the Regulatory Effect of Lactobacillus casei ATCC 393 on Intestinal Mucosal Immune Barrier

Vasoactive intestinal peptide (VIP) plays an important role in the neuro-endocrine-immune system. Mast cells (MCs) are important immune effector cells. This study was conducted to investigate the protective effect of L. casei ATCC 393 on Enterotoxigenic Escherichia coli (ETEC) K88-induced intestinal mucosal immune barrier injury and its association with VIP/MC signaling by in vitro experiments in cultures of porcine mucosal mast cells (PMMCs) and in vivo experiments using VIP receptor antagonist (aVIP) drug. The results showed that compared with the ETEC K88 and lipopolysaccharides (LPS)-induced model groups, VIP pretreatment significantly inhibited the activation of MCs and the release of β-hexosaminidase (β-hex), histamine and tryptase. Pretreatment with aVIP abolished the protective effect of L. casei ATCC 393 on ETEC K88-induced intestinal mucosal immune barrier dysfunction in C57BL/6 mice. Also, with the blocking of VIP signal transduction, the ETEC K88 infection increased serum inflammatory cytokines, and the numbers of degranulated MCs in ileum, which were decreased by administration of L. casei ATCC 393. In addition, VIP mediated the regulatory effect of L. casei ATCC 393 on intestinal microbiota in mice. These findings suggested that VIP may mediate the protective effect of L.casei ATCC 393 on intestinal mucosal immune barrier dysfunction via MCs.

An Integrated View on Neuronal Subsets in the Peripheral Nervous System and Their Role in Immunoregulation

The peripheral nervous system consists of sensory circuits that respond to external and internal stimuli and effector circuits that adapt physiologic functions to environmental challenges. Identifying neurotransmitters and neuropeptides and the corresponding receptors on immune cells implies an essential role for the nervous system in regulating immune reactions. Vice versa, neurons express functional cytokine receptors to respond to inflammatory signals directly. Recent advances in single-cell and single-nuclei sequencing have provided an unprecedented depth in neuronal analysis and allowed to refine the classification of distinct neuronal subsets of the peripheral nervous system. Delineating the sensory and immunoregulatory capacity of different neuronal subsets could inform a better understanding of the response happening in tissues that coordinate physiologic functions, tissue homeostasis and immunity. Here, we summarize current subsets of peripheral neurons and discuss neuronal regulation of immune responses, focusing on neuro-immune interactions in the gastrointestinal tract. The nervous system as a central coordinator of immune reactions and tissue homeostasis may predispose for novel promising therapeutic approaches for a large variety of diseases including but not limited to chronic inflammation.

Neuroimmune Pathophysiology in Asthma

Asthma is a chronic inflammation of lower airway disease, characterized by bronchial hyperresponsiveness. Type I hypersensitivity underlies all atopic diseases including allergic asthma. However, the role of neurotransmitters (NT) and neuropeptides (NP) in this disease has been less explored in comparison with inflammatory mechanisms. Indeed, the airway epithelium contains pulmonary neuroendocrine cells filled with neurotransmitters (serotonin and GABA) and neuropeptides (substance P[SP], neurokinin A [NKA], vasoactive intestinal peptide [VIP], Calcitonin-gene related peptide [CGRP], and orphanins-[N/OFQ]), which are released after allergen exposure. Likewise, the autonomic airway fibers produce acetylcholine (ACh) and the neuropeptide Y(NPY). These NT/NP differ in their effects; SP, NKA, and serotonin exert pro-inflammatory effects, whereas VIP, N/OFQ, and GABA show anti-inflammatory activity. However, CGPR and ACh have dual effects. For example, the ACh-M3 axis induces goblet cell metaplasia, extracellular matrix deposition, and bronchoconstriction; the CGRP-RAMP1 axis enhances Th2 and Th9 responses; and the SP-NK1R axis promotes the synthesis of chemokines in eosinophils, mast cells, and neutrophils. In contrast, the ACh-α7nAChR axis in ILC2 diminishes the synthesis of TNF-α, IL-1, and IL-6, attenuating lung inflammation whereas, VIP-VPAC1, N/OFQ-NOP axes cause bronchodilation and anti-inflammatory effects. Some NT/NP as 5-HT and NKA could be used as biomarkers to monitor asthma patients. In fact, the asthma treatment based on inhaled corticosteroids and anticholinergics blocks M3 and TRPV1 receptors. Moreover, the administration of experimental agents such as NK1R/NK2R antagonists and exogenous VIP decrease inflammatory mediators, suggesting that regulating the effects of NT/NP represents a potential novel approach for the treatment of asthma.

A Clinical Approach for the Use of VIP Axis in Inflammatory and Autoimmune Diseases

The neuroendocrine and immune systems are coordinated to maintain the homeostasis of the organism, generating bidirectional communication through shared mediators and receptors. Vasoactive intestinal peptide (VIP) is the paradigm of an endogenous neuropeptide produced by neurons and endocrine and immune cells, involved in the control of both innate and adaptive immune responses. Exogenous administration of VIP exerts therapeutic effects in models of autoimmune/inflammatory diseases mediated by G-protein-coupled receptors (VPAC1 and VPAC2). Currently, there are no curative therapies for inflammatory and autoimmune diseases, and patients present complex diagnostic, therapeutic, and prognostic problems in daily clinical practice due to their heterogeneous nature. This review focuses on the biology of VIP and VIP receptor signaling, as well as its protective effects as an immunomodulatory factor. Recent progress in improving the stability, selectivity, and effectiveness of VIP/receptors analogues and new routes of administration are highlighted, as well as important advances in their use as biomarkers, contributing to their potential application in precision medicine. On the 50th anniversary of VIP's discovery, this review presents a spectrum of potential clinical benefits applied to inflammatory and autoimmune diseases.

A Synthetic Agonist to Vasoactive Intestinal Peptide Receptor-2 Induces Regulatory T Cell Neuroprotective Activities in Models of Parkinson's Disease

A paradigm shift has emerged in Parkinson’s disease (PD) highlighting the prominent role of CD4⁺ Tregs in pathogenesis and treatment. Bench to bedside research, conducted by others and our own laboratories, advanced a neuroprotective role for Tregs making pharmacologic transformation of immediate need. Herein, a vasoactive intestinal peptide receptor-2 (VIPR2) peptide agonist, LBT-3627, was developed as a neuroprotectant for PD-associated dopaminergic neurodegeneration. Employing both 6-hydroxydopamine (6-OHDA) and α-synuclein (α-Syn) overexpression models in rats, the sequential administration of LBT-3627 increased Treg activity without altering cell numbers both in naïve animals and during progressive nigrostriatal degeneration. LBT-3627 administration was linked to reductions of inflammatory microglia, increased survival of dopaminergic neurons, and improved striatal densities. While α-Syn overexpression resulted in reduced Treg activity, LBT-3627 rescued these functional deficits. This occurred in a dose-dependent manner closely mimicking neuroprotection. Taken together, these data provide the basis for the use of VIPR2 agonists as potent therapeutic immune modulating agents to restore Treg activity, attenuate neuroinflammation, and interdict dopaminergic neurodegeneration in PD. The data underscore an important role of immunity in PD pathogenesis.

Recent advances in vasoactive intestinal peptide physiology and pathophysiology: focus on the gastrointestinal system

Vasoactive intestinal peptide (VIP), a gut peptide hormone originally reported as a vasodilator in 1970, has multiple physiological and pathological effects on development, growth, and the control of neuronal, epithelial, and endocrine cell functions that in turn regulate ion secretion, nutrient absorption, gut motility, glycemic control, carcinogenesis, immune responses, and circadian rhythms. Genetic ablation of this peptide and its receptors in mice also provides new insights into the contribution of VIP towards physiological signaling and the pathogenesis of related diseases. Here, we discuss the impact of VIP on gastrointestinal function and diseases based on recent findings, also providing insight into its possible therapeutic application to diabetes, autoimmune diseases and cancer.

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.

Role of Transient Receptor Potential Ankyrin 1 Ion Channel and Somatostatin sst4 Receptor in the Antinociceptive and Anti-inflammatory Effects of Sodium Polysulfide and Dimethyl Trisulfide

Transient receptor potential ankyrin 1 (TRPA1) non-selective ligand-gated cation channels are mostly expressed in primary sensory neurons. Polysulfides (POLYs) are Janus-faced substances interacting with numerous target proteins and associated with both protective and detrimental processes. Activation of TRPA1 in sensory neurons, consequent somatostatin (SOM) liberation and action on sst4 receptors have recently emerged as mediators of the antinociceptive effect of organic trisulfide dimethyl trisulfide (DMTS). In the frame of the present study, we set out to compare the participation of this mechanism in antinociceptive and anti-inflammatory effects of inorganic sodium POLY and DMTS in carrageenan-evoked hind-paw inflammation. Inflammation of murine hind paws was induced by intraplantar injection of carrageenan (3% in 30 µL saline). Animals were treated intraperitoneally with POLY (17 µmol/kg) or DMTS (250 µmol/kg) or their respective vehicles 30 min prior paw challenge and six times afterward every 60 min. Mechanical pain threshold and swelling of the paws were measured by dynamic plantar aesthesiometry and plethysmometry at 2, 4, and 6 h after initiation of inflammation. Myeloperoxidase (MPO) activity in the hind paws were detected 6 h after challenge by luminescent imaging. Mice genetically lacking TRPA1 ion channels, sst4 receptors and their wild-type counterparts were used to examine the participation of these proteins in POLY and DMTS effects. POLY counteracted carrageenan-evoked mechanical hyperalgesia in a TRPA1 and sst4 receptor-dependent manner. POLY did not influence paw swelling and MPO activity. DMTS ameliorated all examined inflammatory parameters. Mitigation of mechanical hyperalgesia and paw swelling by DMTS were mediated through sst4 receptors. These effects were present in TRPA1 knockout animals, too. DMTS inhibited MPO activity with no participation of the sensory neuron-SOM axis. While antinociceptive effects of POLY are transmitted by activation of peptidergic nerves via TRPA1, release of SOM and its effect on sst4 receptors, those of DMTS partially rely on SOM release triggered by other routes. SOM is responsible for the inhibition of paw swelling by DMTS, but TRPA1 does not contribute to its release. Modulation of MPO activity by DMTS is independent of TRPA1 and sst4.

Sensory neuron regulation of gastrointestinal inflammation and bacterial host defence

Sensory neurons in the gastrointestinal tract have multifaceted roles in maintaining homeostasis, detecting danger and initiating protective responses. The gastrointestinal tract is innervated by three types of sensory neurons: dorsal root ganglia, nodose/jugular ganglia and intrinsic primary afferent neurons. Here, we examine how these distinct sensory neurons and their signal transducers participate in regulating gastrointestinal inflammation and host defence. Sensory neurons are equipped with molecular sensors that enable neuronal detection of diverse environmental signals including thermal and mechanical stimuli, inflammatory mediators and tissue damage. Emerging evidence shows that sensory neurons participate in host-microbe interactions. Sensory neurons are able to detect pathogenic and commensal bacteria through specific metabolites, cell-wall components, and toxins. Here, we review recent work on the mechanisms of bacterial detection by distinct subtypes of gut-innervating sensory neurons. Upon activation, sensory neurons communicate to the immune system to modulate tissue inflammation through antidromic signalling and efferent neural circuits. We discuss how this neuro-immune regulation is orchestrated through transient receptor potential ion channels and sensory neuropeptides including substance P, calcitonin gene-related peptide, vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide. Recent studies also highlight a role for sensory neurons in regulating host defence against enteric bacterial pathogens including Salmonella typhimurium, Citrobacter rodentium and enterotoxigenic Escherichia coli. Understanding how sensory neurons respond to gastrointestinal flora and communicate with immune cells to regulate host defence enhances our knowledge of host physiology and may form the basis for new approaches to treat gastrointestinal diseases.

In situ proximity of CX3CR1-positive mononuclear phagocytes and VIP-ergic nerve fibers suggests VIP-ergic immunomodulation in the mouse ileum

Being continuously exposed to a plethora of antigens ranging from food antigens to potential pathogenic organisms, the gastrointestinal (GI) tract harbors the largest collection of immune cells in the mammalian body. This immune system has to maintain a delicate balance between mounting an active immune response and maintaining tolerance. The GI tract is also home to an elaborate intrinsic nervous system, the enteric nervous system (ENS). Various in vitro studies of neuro-immune communication have suggested that vasoactive intestinal peptide (VIP), an important GI neurotransmitter, modulates mononuclear phagocytes (MNPs), i.e., dendritic cells and macrophages. Using a combined approach of reverse transcription plus the polymerase chain reaction, immunofluorescence, three-dimensional maximum intensity projections and immunoelectron microscopy, we investigate the interaction between the enteric innervation and MNPs in the ileal lamina propria (LP). We demonstrate that VIP-ergic fibers of the ENS lie adjacent to CX3CR1⁺ MNPs and that VPAC1 is constitutively expressed on ileal CX3CR1+ cells in the LP of the mouse. We also identify, for the first time, CX3CR1⁺ immune cells in the LP at the ultrastructural level. Our data thus reveal the in situ presence of the molecular components that are necessary for a VIP-mediated neuro-immune interaction between the ENS and CX3CR1-expressing immune cells in the LP of the ileum.

VPAC1 receptor (Vipr1)-deficient mice exhibit ameliorated experimental autoimmune encephalomyelitis, with specific deficits in the effector stage

BACKGROUND

Vasoactive intestinal peptide (VIP) and pituitary adenylyl cyclase-activating polypeptide (PACAP) are two highly homologous neuropeptides. In vitro and ex vivo experiments repeatedly demonstrate that these peptides exert pronounced immunomodulatory (primarily anti-inflammatory) actions which are mediated by common VPAC1 and VPAC2 G protein-coupled receptors. In agreement, we have shown that mice deficient in PACAP ligand or VPAC2 receptors exhibit exacerbated experimental autoimmune encephalomyelitis (EAE). However, we observed that VIP-deficient mice are unexpectedly resistant to EAE, suggesting a requirement for this peptide at some stage of disease development. Here, we investigated the involvement of VPAC1 in the development of EAE using a VPAC1-deficient mouse model.

METHODS

EAE was induced in wild-type (WT) and VPAC1 knockout (KO) mice using myelin oligodendrocyte glycoprotein 35-55 (MOG35-55), and clinical scores were assessed continuously over 30 days. Immune responses in the spinal cords were determined by histology, real-time PCR and immunofluorescence, and in the draining lymph nodes by antigen-recall assays. The contribution of VPAC1 expression in the immune system to the development of EAE was evaluated by means of adoptive transfer and bone marrow chimera experiments. In other experiments, VPAC1 receptor analogs were given to WT mice.

RESULTS

MOG35-55-induced EAE was ameliorated in VPAC1 KO mice compared to WT mice. The EAE-resistant phenotype of VPAC1 KO mice correlated with reduced central nervous system (CNS) histopathology and cytokine expression in the spinal cord. The immunization phase of EAE appeared to be unimpaired because lymph node cells from EAE-induced VPAC1 KO mice stimulated in vitro with MOG exhibited robust proliferative and Th1/Th17 responses. Moreover, lymph node and spleen cells from KO mice were fully capable of inducing EAE upon transfer to WT recipients. In contrast, WT cells from MOG-immunized mice did not transfer the disease when administered to VPAC1 KO recipients, implicating a defect in the effector phase of the disease. Bone marrow chimera studies suggested that the resistance of VPAC1-deficient mice was only minimally dependent on the expression of this receptor in the immunogenic/hematopoietic compartment. Consistent with this, impaired spinal cord inductions of several chemokine mRNAs were observed in VPAC1 KO mice. Finally, treatment of WT mice with the VPAC1 receptor antagonist PG97-269 before, but not after, EAE induction mimicked the clinical phenotype of VPAC1 KO mice.

CONCLUSIONS

VPAC1 gene loss impairs the development of EAE in part by preventing an upregulation of CNS chemokines and invasion of inflammatory cells into the CNS. Use of VPAC1 antagonists in WT mice prior to EAE induction also support a critical role for VPAC1 signaling for the development of EAE.

The Role of Neuropeptides in Mouse Models of Colitis

Inflammatory bowel disease (IBD) constitutes an important clinically significant condition that results in morbidity and mortality. IBD can be generally classified into either ulcerative colitis (UC) or Crohn's disease (CD) that differs in the clinical and histopathology. The role of neuropeptides in the pathogenesis of these conditions is becoming increasingly recognized for their importance in modulating the inflammatory state. Animal models provide the greatest insight to better understand the pathophysiology of both disorders which will hopefully allow for improved treatment strategies. This review will provide a better understanding of the role of murine models for studying colitis.

Selective VIP Receptor Agonists Facilitate Immune Transformation for Dopaminergic Neuroprotection in MPTP-Intoxicated Mice

Vasoactive intestinal peptide (VIP) mediates a broad range of biological responses by activating two related receptors, VIP receptor 1 and 2 (VIPR1 and VIPR2). Although the use of native VIP facilitates neuroprotection, clinical application of the hormone is limited due to VIP's rapid metabolism and inability to distinguish between VIPR1 and VIPR2 receptors. In addition, activation of both receptors by therapeutics may increase adverse secondary toxicities. Therefore, we developed metabolically stable and receptor-selective agonists for VIPR1 and VIPR2 to improve pharmacokinetic and pharmacodynamic therapeutic end points. Selective agonists were investigated for their abilities to protect mice against MPTP-induced neurodegeneration used to model Parkinson's disease (PD). Survival of tyrosine hydroxylase neurons in the substantia nigra was determined by stereological tests after MPTP intoxication in mice pretreated with either VIPR1 or VIPR2 agonist or after adoptive transfer of splenic cell populations from agonist-treated mice administered to MPTP-intoxicated animals. Treatment with VIPR2 agonist or splenocytes from agonist-treated mice resulted in increased neuronal sparing. Immunohistochemical tests showed that agonist-treated mice displayed reductions in microglial responses, with the most pronounced effects in VIPR2 agonist-treated, MPTP-intoxicated mice. In parallel studies, we observed reductions in proinflammatory cytokine release that included IL-17A, IL-6, and IFN-γ and increases in GM-CSF transcripts in CD4(+) T cells recovered from VIPR2 agonist-treated animals. Moreover, a phenotypic shift of effector to regulatory T cells was observed. These results support the use of VIPR2-selective agonists as neuroprotective agents for PD treatment.

SIGNIFICANCE STATEMENT

Vasoactive intestinal peptide receptor 2 can elicit immune transformation in a model of Parkinson's disease (PD). Such immunomodulatory capabilities can lead to neuroprotection by attenuating microglial activation and by slowing degradation of neuronal cell bodies and termini in MPTP-intoxicated mice. The protective mechanism arises from altering a Th1/Th2 immune cytokine response into an anti-inflammatory and neuronal sparing profile. These results are directly applicable for the development of novel PD therapies.

Vasoactive intestinal polypeptide promotes intestinal barrier homeostasis and protection against colitis in mice

Inflammatory bowel disease is a chronic gastrointestinal inflammatory disorder associated with changes in neuropeptide expression and function, including vasoactive intestinal peptide (VIP). VIP regulates intestinal vasomotor and secretomotor function and motility; however, VIP's role in development and maintenance of colonic epithelial barrier homeostasis is unclear. Using VIP deficient (VIPKO) mice, we investigated VIP's role in epithelial barrier homeostasis, and susceptibility to colitis. Colonic crypt morphology and epithelial barrier homeostasis were assessed in wildtype (WT) and VIPKO mice, at baseline. Colitic responses were evaluated following dinitrobenzene sulfonic acid (DNBS) or dextran-sodium sulfate (DSS) exposure. Mice were also treated with exogenous VIP. At baseline, VIPKO mice exhibited distorted colonic crypts, defects in epithelial cell proliferation and migration, increased apoptosis, and altered permeability. VIPKO mice also displayed reduced goblet cell numbers, and reduced expression of secreted goblet cell factors mucin 2 and trefoil factor 3. These changes were associated with reduced expression of caudal type homeobox 2 (Cdx2), a master regulator of intestinal function and homeostasis. DNBS and DSS-induced colitis were more severe in VIPKO than WT mice. VIP treatment rescued the phenotype, protecting VIPKO mice against DSS colitis, with results comparable to WT mice. In conclusion, VIP plays a crucial role in the development and maintenance of colonic epithelial barrier integrity under physiological conditions and promotes epithelial repair and homeostasis during colitis.

Matrix metalloproteinases in inflammatory bowel disease: an update

Matrix metalloproteinases (MMPs) are known to be upregulated in inflammatory bowel disease (IBD) and other inflammatory conditions, but while their involvement is clear, their role in many settings has yet to be determined. Studies of the involvement of MMPs in IBD since 2006 have revealed an array of immune and stromal cells which release the proteases in response to inflammatory cytokines and growth factors. Through digestion of the extracellular matrix and cleavage of bioactive proteins, a huge diversity of roles have been revealed for the MMPs in IBD, where they have been shown to regulate epithelial barrier function, immune response, angiogenesis, fibrosis, and wound healing. For this reason, MMPs have been recognised as potential biomarkers for disease activity in IBD and inhibition remains a huge area of interest. This review describes new roles of MMPs in the pathophysiology of IBD and suggests future directions for the development of treatment strategies in this condition.

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.

The neuropeptide vasoactive intestinal peptide: direct effects on immune cells and involvement in inflammatory and autoimmune diseases

Neuropeptides represent an important category of endogenous contributors to the establishment and maintenance of immune deviation in the immune-privileged organs such as the CNS and in the control of acute inflammation in the peripheral immune organs. Vasoactive intestinal peptide (VIP) is a major immunoregulatory neuropeptide widely distributed in the central and peripheral nervous system. In addition to neurones, VIP is synthesized by immune cells which also express VIP receptors. Here, we review the current information on VIP production and VIP-receptor-mediated effects in the immune system, the role of endogenous and exogenous VIP in inflammatory and autoimmune disorders and the present and future VIP therapeutic approaches.

Vasoactive intestinal peptide-deficient mice exhibit reduced pathology in trinitrobenzene sulfonic acid-induced colitis

OBJECTIVES

Vasoactive intestinal peptide (VIP) is an immunomodulatory neuropeptide with therapeutic properties in multiple murine models of inflammatory disease including the trinitrobenzene-sulfonic acid (TNBS)-colitis model of Crohn's disease. Understanding the spectrum of biological actions of endogenously produced VIP may help us dissect the complex and multifactorial pathogenesis of such inflammatory diseases. Our goal was to determine the contribution of endogenously produced VIP to TNBS-colitis by using VIP knockout (KO) mice.

METHODS

TNBS was intracolonically administered to wild-type (WT) and VIP KO mice, and weight loss and colitis were assessed over time. Colon histopathological changes and myeloperoxidase activities were analyzed and the levels of tumor necrosis factor (TNF)-α and interleukin (IL)-6 in colon and serum quantified. The proliferative response in vitro of splenocytes from TNBS WT and VIP KO administered mice to anti-CD3 and anti-CD28 was determined.

RESULTS

VIP KO mice did not exhibit the predicted exacerbated response to TNBS. Instead, they developed a milder clinical profile than WT mice, with lower TNF-α and IL-6 levels. Such potential defects seem selective, because other parameters such as the histopathological scores and the cytokine levels in the colon did not differ between the two strains of mice. Moreover, splenocytes from TNBS-treated VIP KO mice exhibited an enhanced proliferative response to anti-CD3/CD28 stimulation in vitro.

CONCLUSION

Chronic loss of VIP in mice leads to a disruption of certain but not all immunological compartments, corroborating recent findings that VIP KO mice exhibit reduced mortality in the lipopolysaccharide-induced endotoxemia model and attenuated clinical development of experimental autoimmune encephalomyelitis while developing robust T-cell responses.

Upregulation of the transient receptor potential ankyrin 1 ion channel in the inflamed human and mouse colon and its protective roles

Transient Receptor Potential Ankyrin 1 (TRPA1) channels are localized on sensory nerves and several non-neural cells, but data on their functional significance are contradictory. We analysed the presence and alterations of TRPA1 in comparison with TRP Vanilloid 1 (TRPV1) at mRNA and protein levels in human and mouse intact and inflamed colons. The role of TRPA1 in a colitis model was investigated using gene-deficient mice. TRPA1 and TRPV1 expressions were investigated in human colon biopsies of healthy subjects and patients with inflammatory bowel diseases (IBD: ulcerative colitis, Crohn's disease) with quantitative PCR and immunohistochemistry. Mouse colitis was induced by oral 2% dextran-sulphate (DSS) for 10 days. For investigating the functions of TRPA1, Disease Activity Index (weight loss, stool consistency, blood content) was determined in C57BL/6-based Trpa1-deficient (knockout: KO) and wildtype (WT) mice. Sensory neuropeptides, their receptors, and inflammatory cytokines/chemokines were determined with qPCR or Luminex. In human and mouse colons TRPA1 and TRPV1 are located on epithelial cells, macrophages, enteric ganglia. Significant upregulation of TRPA1 mRNA was detected in inflamed samples. In Trpa1 KO mice, Disease Activity Index was significantly higher compared to WTs. It could be explained by the greater levels of substance P, neurokinins A and B, neurokinin 1 receptor, pituitary adenylate-cyclase activating polypeptide, vasoactive intestinal polypeptide, and also interleukin-1beta, macrophage chemoattractant protein-1, monokine induced by gamma interferon-1, tumor necrosis factor-alpha and B-lymphocyte chemoattractant in the distal colon. TRPA1 is upregulated in colitis and its activation exerts protective roles by decreasing the expressions of several proinflammatory neuropeptides, cytokines and chemokines.

Special role of Foxp3 for the specifically altered microRNAs in Regulatory T cells of HCC patients

Background

Regulatory T cells (Tregs) exhibit functional abnormalities in the context of hepatocellular carcinoma (HCC). The microRNAs (miRNAs) are identified as the key modulators in Tregs. This study was to explore whether the expression profiles of miRNAs of Tregs were different in HCC-activated Tregs and whether Foxp3 had special effects on them.

Methods

We isolated HCC-activated Tregs from mice bearing HCC and compared the expression profiles of miRNAs between HCC-activated Tregs and control Tregs by microarray. RNA interference against Foxp3 was also performed through transfection of synthetic siRNAs to Tregs for analyzing the effect of Foxp3 on the expression of miRNAs. Tregs isolated from HCC patients (n = 12) and healthy controls (n = 7) were used for validation of the differentially expressed miRNAs. Finally, bioinformatic analysis was applied to infer their possible roles.

Results

We found nine specifically altered miRNAs in HCC-activated Tregs from the murine model. After transfection with siRNAs against Foxp3, control Tregs showed obvious reduction of Foxp3 and five miRNAs were significantly changed; HCC-activated Tregs exhibited a slight reduction of Foxp3 with three miRNAs significantly changed. Tregs from HCC patients and healthy controls finally confirmed the up-regulation of four miRNAs (hsa-miR-182-5p, hsa-miR-214-3p, hsa-miR-129-5p and hsa-miR-30b-5p). Following bioinformatic analysis suggested these altered miRNAs would target eight important signaling pathways that could affect the functions of Tregs.

Conclusions

Our studies provided the first evidence that Tregs in HCC had the specifically altered expression of miRNAs, which was affected by Foxp3. These results are useful both in finding new biomarkers and in further exploring the functions of Tregs in HCC patients.

Role of VPAC2 receptor in monocrotaline-induced pulmonary hypertension in rats

Pulmonary hypertension (PH) is associated with significant morbidity and mortality. Vasoactive intestinal peptide (VIP) and pituitary adenylyl cyclase activating peptide (PACAP) have pulmonary vasodilatory and positive inotropic effects via receptors VPAC1 and VPAC2, which possess a similar affinity for both peptides, and PAC1, a PACAP-preferring receptor. VIP is a promising option for PH treatment; however, various physiological effects of VIP have limited its clinical use. We investigated the effects of VPAC1 and VPAC2 selective agonists VIP and PACAP to explore more appropriate means of treatment for PH. We examined hemodynamic changes in right ventricular systolic pressure (RVSP), systemic blood pressure (SBP), total pulmonary resistance index (TPRI), total systemic resistance index, and cardiac index (CI) in response to their agonists with monocrotaline (MCT)-induced PH and explored involvement of VIP/PACAP expression and receptors in PH. Sprague-Dawley rats were divided into the MCT group (administered MCT 60 mg/kg) and control group. In MCT-induced PH, decreased VIP and PACAP were associated with upregulation of VPAC1, VPAC2, and PAC1 in lung tissues. Intravenous injection of VPAC2-selective agonist BAY 55-9837 and VIP, but not [Ala(11,22,28)]VIP, improved the CI. The decrease in SBP with VPAC2 agonist was significantly less than that in the control. Although they decreased SBP, these agonists hardly affected RVSP in the control. Activation of VPAC2 receptor with BAY 55-9837 effectively improved RVSP, TPRI, and CI in MCT-induced PH, suggesting a VPAC2 agonist as a possible promising treatment for PH.

VPAC1 overexpression is associated with poor differentiation in colon cancer

Vasoactive intestinal peptide (VIP) is a neurotransmitter that primarily functions as a vasodilator. VIP plays its role through binding to its receptors known as VIP/pituitary adenylate cyclase-activating peptide receptors (VPACs). In this study, we examined the expression of VPAC1 in human colon cancer tissues, analyzed the relationship between VPAC1 expression and cancer malignancy, and explored the possible mechanisms using immunohistochemistry and immunofluorescence double staining. The results showed that (1) poorly differentiated colon cancers have significantly higher VPAC1 expression than well-differentiated colon cancers do (p < 0.01); (2) phospho-epithelial growth factor receptor (EGFR) overexpression/activation in the cytoplasm of cancer cells is related to VPAC1 overexpression; (3) blood vessels surrounding colon cancer have significantly more VPAC1-positive than normal colon mucosa does; (4) tumor-associated macrophages (TAMs) of colon cancer have a higher level of VPAC1 expression than macrophages in normal colon mucosa do. These data suggest that VPAC1 overexpression is associated with poorer differentiation of colon cancer, which is likely caused by subsequent EGFR activation in cancer cells. In addition, VPAC1 overexpression in both blood vessels and macrophages in tumors may also play an important role in the development of aggressive cancer.

Inhibition of vasoactive intestinal polypeptide (VIP) induces resistance to dextran sodium sulfate (DSS)-induced colitis in mice

VIP is highly expressed in the colon and regulates motility, vasodilatation, and sphincter relaxation. However, its role in the development and progress of colitis is still controversial. Our aim was to determine the participation of VIP on dextran sodium sulfate (DSS)-induced colonic mucosal inflammation using VIP(-/-) and WT mice treated with VIP antagonists. Colitis was induced in 32 adult VIP(-/-) and 14 age-matched WT litter-mates by giving 2.5 % DSS in the drinking water. DSS-treated WT mice were injected daily with VIP antagonists, VIPHyb (n = 22), PG 97-269 (n = 9), or vehicle (n = 31). After euthanasia, colons were examined; colonic cytokines mRNA were quantified. VIP(-/-) mice were remarkably resistant to DSS-induced colitis compared to WT. Similarly, DSS-treated WT mice injected with VIPHyb (1 μM) or PG 97-269 (1 nM) had significantly reduced clinical signs of colitis. Furthermore, colonic expression of IL-1ϐ, TNF-α, and IL-6 was significantly lower in VIP(-/-) and VIPHyb or PG 97-269 compared to vehicle-treated WT. Genetic deletion of VIP or pharmacological inhibition of VIP receptors resulted in resistance to colitis. These data demonstrate a pro-inflammatory role for VIP in murine colitis and suggest that VIP antagonists may be an effective clinical treatment for human inflammatory bowel diseases.

Intestinotrophic glucagon-like peptide-2 (GLP-2) activates intestinal gene expression and growth factor-dependent pathways independent of the vasoactive intestinal peptide gene in mice

The enteroendocrine and enteric nervous systems convey signals through an overlapping network of regulatory peptides that act either as circulating hormones or as localized neurotransmitters within the gastrointestinal tract. Because recent studies invoke an important role for vasoactive intestinal peptide (VIP) as a downstream mediator of glucagon-like peptide-2 (GLP-2) action in the gut, we examined the importance of the VIP-GLP-2 interaction through analysis of Vip(-/-) mice. Unexpectedly, we detected abnormal villous architecture, expansion of the crypt compartment, increased crypt cell proliferation, enhanced Igf1 and Kgf gene expression, and reduced expression of Paneth cell products in the Vip(-/-) small bowel. These abnormalities were not reproduced by antagonizing VIP action in wild-type mice, and VIP administration did not reverse the intestinal phenotype of Vip(-/-) mice. Exogenous administration of GLP-2 induced the expression of ErbB ligands and immediate-early genes to similar levels in Vip(+/+) vs. Vip(-/-) mice. Moreover, GLP-2 significantly increased crypt cell proliferation and small bowel growth to comparable levels in Vip(+/+) vs. Vip(-/-) mice. Unexpectedly, exogenous GLP-2 administration had no therapeutic effect in mice with dextran sulfate-induced colitis; the severity of colonic injury and weight loss was modestly reduced in female but not male Vip(-/-) mice. Taken together, these findings extend our understanding of the complex intestinal phenotype arising from loss of the Vip gene. Furthermore, although VIP action may be important for the antiinflammatory actions of GLP-2, the Vip gene is not required for induction of a gene expression program linked to small bowel growth after enhancement of GLP-2 receptor signaling.

VPAC receptors: structure, molecular pharmacology and interaction with accessory proteins

The vasoactive intestinal peptide (VIP) is a neuropeptide with wide distribution in both central and peripheral nervous systems, where it plays important regulatory role in many physiological processes. VIP displays a large biological functions including regulation of exocrine secretions, hormone release, fetal development, immune responses, etc. VIP appears to exert beneficial effect in neuro-degenerative and inflammatory diseases. The mechanism of action of VIP implicates two subtypes of receptors (VPAC1 and VPAC2), which are members of class B receptors belonging to the super-family of GPCR. This article reviews the current knowledge regarding the structure and molecular pharmacology of VPAC receptors. The structure-function relationship of VPAC1 receptor has been extensively studied, allowing to understand the molecular basis for receptor affinity, specificity, desensitization and coupling to adenylyl cyclase. Those studies have clearly demonstrated the crucial role of the N-terminal ectodomain (N-ted) of VPAC1 receptor in VIP recognition. By using different approaches including directed mutagenesis, photoaffinity labelling, NMR, molecular modelling and molecular dynamic simulation, it has been shown that the VIP molecule interacts with the N-ted of VPAC1 receptor, which is itself structured as a 'Sushi' domain. VPAC1 receptor also interacts with a few accessory proteins that play a role in cell signalling of receptors. Recent advances in the structural characterization of VPAC receptor and more generally of class B GPCRs will lead to the design of new molecules, which could have considerable interest for the treatment of inflammatory and neuro-degenerative diseases.

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.

Dysfunction of neurogenic VIP-mediated relaxation in mouse distal colon with dextran sulfate sodium-induced colitis

Vasoactive intestinal peptide (VIP) regulates various functions including motility and immune homeostasis in colon. The VIP system including its receptors has been established to control the development of ulcerative colitis, but the functional changes of the system-regulated motility in colon with ulcerative colitis are not well understood. In this study, we investigated VIP-related contractile responses in distal colon from mice with dextran sulfate sodium (DSS)-induced acute colitis. Electrical stimulation (ES) under our conditions caused relaxation during ES and contraction after withdrawal of ES in a tetrodotoxin-sensitive manner. Pharmacological analyses showed two phases of ES-induced relaxation: a transient neuronal nitric oxide (NO) synthase-dependent phase (I), and a continued VIP receptor-mediated phase (II). Inhibition of VIP receptors and protein kinase A decreased both phases. In colon from DSS-treated mice, ES-induced phase II (also phase I) and VIP-induced, but not cyclic AMP analog-induced, relaxation were decreased. Stimulation with VIP significantly increased cyclic AMP formation in colon preparations from control but not DSS-treated mice. In colon from DSS-treated mice, the basal cyclic AMP level was markedly greater without changes in the level of VIP receptor VPAC(2). Isoprenaline- and forskolin-induced relaxation and cyclic AMP formation were not changed by DSS treatment. These findings suggest that dysfunction of VIP receptors in muscles, in addition to loss of the neuronal VIP and NO pathways, are involved in abnormal motility in mouse colon with DSS-induced colitis.