Cystic fibrosis transmembrane conductance regulator dysfunction in VIP knockout mice.

Vasoactive intestinal peptide (VIP), a neuropeptide, controls multiple functions in exocrine tissues, including inflammation, and relaxation of airway and vascular smooth muscles, and regulates CFTR-dependent secretion, which contributes to mucus hydration and local innate defense of the lung. We had previously reported that VIP stimulates the VPAC1 receptor, PKCϵ signaling cascade, and increases CFTR stability and function at the apical membrane of airway epithelial cells by reducing its internalization rate. Moreover, prolonged VIP stimulation corrects the molecular defects associated with F508del, the most common CFTR mutation responsible for the genetic disease cystic fibrosis. In the present study, we have examined the impact of the absence of VIP on CFTR maturation, cellular localization, and function in vivo using VIP knockout mice. We have conducted pathological assessments and detected signs of lung and intestinal disease. Immunodetection methods have shown that the absence of VIP results in CFTR intracellular retention despite normal expression and maturation levels. A subsequent loss of CFTR-dependent chloride current was measured in functional assays with Ussing chamber analysis of the small intestine ex vivo, creating a cystic fibrosis-like condition. Interestingly, intraperitoneal administration of VIP corrected tissue abnormalities, close to the wild-type phenotype, as well as associated defects in the vital CFTR protein. The results show in vivo a primary role for VIP chronic exposure in CFTR membrane stability and function and confirm in vitro data.

Pharmacology and functions of receptors for vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide: IUPHAR review 1.

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are members of a superfamily of structurally related peptide hormones that includes glucagon, glucagon-like peptides, secretin, gastric inhibitory peptide (GIP) and growth hormone-releasing hormone (GHRH). VIP and PACAP exert their actions through three GPCRs - PAC(1) , VPAC(1) and VPAC(2) - belonging to class B (also referred to as class II, or secretin receptor-like GPCRs). This family comprises receptors for all peptides structurally related to VIP and PACAP, and also receptors for parathyroid hormone, corticotropin-releasing factor, calcitonin and related peptides. PAC(1) receptors are selective for PACAP, whereas VPAC(1) and VPAC(2) respond to both VIP and PACAP with high affinity. VIP and PACAP play diverse and important roles in the CNS, with functions in the control of circadian rhythms, learning and memory, anxiety and responses to stress and brain injury. Recent genetic studies also implicate the VPAC(2) receptor in susceptibility to schizophrenia and the PAC(1) receptor in post-traumatic stress disorder. In the periphery, VIP and PACAP play important roles in the control of immunity and inflammation, the control of pancreatic insulin secretion, the release of catecholamines from the adrenal medulla and as co-transmitters in autonomic and sensory neurons. This article, written by members of the International Union of Basic and Clinical Pharmacology Committee on Receptor Nomenclature and Drug Classification (NC-IUPHAR) subcommittee on receptors for VIP and PACAP, confirms the existing nomenclature for these receptors and reviews our current understanding of their structure, pharmacology and functions and their likely physiological roles in health and disease. More detailed information has been incorporated into newly revised pages in the IUPHAR database (http://www.iuphar-db.org/DATABASE/FamilyMenuForward?familyId=67).

Pharmacogenomics in pulmonary arterial hypertension: Toward a mechanistic, target-based approach to therapy.

Pharmacogenomics is the study of how genetic variations influence the response to drugs, by correlating gene expression with the drug's efficacy and toxicity. This concept has recently been successfully applied in oncology. To test its applicability to PAH, we examined two experimental models of the disease: mice with deletion of the Vasoactive Intestinal Peptide gene (VIP(- /-)); and rats injected with monocrotaline (MCT). Since the two models express comparable phenotypic features, we analyzed their particular gene alterations, with special reference to genes related to pulmonary vasoconstriction, vascular remodeling, and inflammation. We then compared the phenotypic and genotypic responses in each model to treatment with the same drug, VIP. In untreated VIP(-/-) mice there was over-expression of almost all genes promoting vasoconstriction/ proliferation, as well as inflammation, and under-expression of all vasodilator/anti-proliferative genes. As expected, treatment with VIP fully corrected both the key PAH features, and all gene expression alterations. MCT-treated rats showed two distinct sets of alterations. One, similar to that in VIP(- /-) mice, i.e., tended to promote vascular remodeling and inflammation, e.g., up-regulation of myosin polypeptides, procollagen, and some inflammatory genes. The other was a set of opposite alterations that suggested an effort to modulate the PAH, e.g., up-regulation of the VIP and NOS3 genes. In this model, VIP treatment failed to correct many of the genotypic abnormalities, and, in parallel, incompletely corrected the phenotypic changes as well. This preliminary proof-of-concept study demonstrates the importance of genomic information in determining therapeutic outcome, and thus in selecting personalized therapy. Full validation of the merits of pharmacogenomics must await studies of lungs from patients with different forms of PAH.

VIP and endothelin receptor antagonist: an effective combination against experimental pulmonary arterial hypertension.

BACKGROUND: Pulmonary Arterial Hypertension (PAH) remains a therapeutic challenge, and the search continues for more effective drugs and drug combinations. We recently reported that deletion of the vasoactive intestinal peptide (VIP) gene caused the spontaneous expression of a PH phenotype that was fully corrected by VIP. The objectives of this investigation were to answer the questions: 1) Can VIP protect against PH in other experimental models? and 2) Does combining VIP with an endothelin (ET) receptor antagonist bosentan enhance its efficacy? METHODS: Within 3 weeks of a single injection of monocrotaline (MCT, s.c.) in Sprague Dawley rats, PAH developed, manifested by pulmonary vascular remodeling, lung inflammation, RV hypertrophy, and death within the next 2 weeks. MCT-injected animals were either untreated, treated with bosentan (p.o.) alone, with VIP (i.p.) alone, or with both together. We selected this particular combination upon finding that VIP down-regulates endothelin receptor expression which is further suppressed by bosentan. Therapeutic outcomes were compared as to hemodynamics, pulmonary vascular pathology, and survival. RESULTS: Treatment with VIP, every other day for 3 weeks, begun on the same day as MCT, almost totally prevented PAH pathology, and eliminated mortality for 45 days. Begun 3 weeks after MCT, however, VIP only partially reversed PAH pathology, though more effectively than bosentan. Combined therapy with both drugs fully reversed the pathology, while preventing mortality for at least 45 days. CONCLUSIONS: 1) VIP completely prevented and significantly reversed MCT-induced PAH; 2) VIP was more effective than bosentan, probably because it targets a wider range of pro-remodeling pathways; and 3) combination therapy with VIP plus bosentan was more effective than either drug alone, probably because both drugs synergistically suppressed ET-ET receptor pathway.

17ß-estradiol protects the lung against acute injury: possible mediation by vasoactive intestinal polypeptide.

Beyond their classical role as a class of female sex hormones, estrogens (e.g. 17ß-estradiol) exert important biological actions, both protective and undesirable. We have investigated the ability of estradiol to protect the lung in three models of acute injury induced by 1) oxidant stress due to the herbicide paraquat; 2) excitotoxicity, caused by glutamate agonist N-methyl-d-aspartate; and 3) acute alveolar anoxia. We also assessed the role of estrogen receptors (ER) ERα and ERß and the neuropeptide vasoactive intestinal peptide (VIP) in mediating this protection. Isolated guinea pig or rat lungs were perfused in situ at constant flow and mechanically ventilated. The onset and severity of lung injury were monitored by increases in pulmonary arterial and airway pressures, wet/dry lung weight ratio, and bronchoalveolar lavage fluid protein content. Estradiol was infused into the pulmonary circulation, beginning 10 min before induction of injury and continued for 60-90 min. Lung injury was marked by significant increases in the above measurements, with paraquat producing the most severe, and excitotoxicity the least severe, injury. Estradiol significantly attenuated the injury in each model. Both ER were constitutively expressed and immunohistochemically demonstrable in normal lung, and their selective agonists reduced anoxic injury, the only model in which they were tested. As it protected against injury, estradiol rapidly and significantly stimulated VIP mRNA expression in rat lung. Estradiol attenuated acute lung injury in three experimental models while stimulating VIP gene expression, a known mechanism of lung protection. The up-regulated VIP expression could have partially mediated the protection by estrogen.

The vasoactive intestinal peptide gene is a key modulator of pulmonary vascular remodeling and inflammation.

Pulmonary vascular remodeling and inflammation often coexist in clinical and experimentally induced pulmonary arterial hypertension (PAH). In some instances, the pulmonary hypertension may be the primary, or at least the initial, problem, while inflammatory or autoimmune responses appear to initiate or dominate the picture in other cases. Based on studies in a model of PAH resulting from targeted deletion of the neuropeptide vasoactive intestinal peptide (VIP) gene, we propose that, at least in this experimental model, but possibly also in other situations, both vascular remodeling and inflammation may be mediated by one and the same mechanism: uncontrolled activation of calcineurin-NFAT (nuclear factor of activated T cells) signaling. If this hypothesis is validated, VIP would emerge as an endogenous modulator of pulmonary vascular remodeling and inflammation, through its suppression of NFAT activation.

Moderate pulmonary arterial hypertension in male mice lacking the vasoactive intestinal peptide gene.

BACKGROUND: Vasoactive intestinal peptide (VIP), a pulmonary vasodilator and inhibitor of vascular smooth muscle proliferation, has been reported absent in pulmonary arteries from patients with idiopathic pulmonary arterial hypertension (PAH). We have tested the hypothesis that targeted deletion of the VIP gene may lead to PAH with pulmonary vascular remodeling. METHODS AND RESULTS: We examined VIP knockout (VIP-/-) mice for evidence of PAH, right ventricular (RV) hypertrophy, and pulmonary vascular remodeling. Relative to wild-type control mice, VIP-/- mice showed moderate RV hypertension, RV hypertrophy confirmed by increased ratio of RV to left ventricle plus septum weight, and enlarged, thickened pulmonary artery and smaller branches with increased muscularization and narrowed lumen. Lung sections also showed perivascular inflammatory cell infiltrates. No systemic hypertension and no arterial hypoxemia existed to explain the PAH. The condition was associated with increased mortality. Both the vascular remodeling and RV remodeling were attenuated after a 4-week treatment with VIP. CONCLUSIONS: Deletion of the VIP gene leads to spontaneous expression of moderately severe PAH in mice during air breathing. Although not an exact model of idiopathic PAH, the VIP-/- mouse should be useful for studying molecular mechanisms of PAH and evaluating potential therapeutic agents. VIP replacement therapy holds promise for the treatment of PAH, and mutations of the VIP gene may be a factor in the pathogenesis of idiopathic PAH.

Mice lacking the VIP gene show airway hyperresponsiveness and airway inflammation, partially reversible by VIP.

The mechanisms leading to asthma, and those guarding against it, are yet to be fully defined. The neuropeptide VIP is a cotransmitter, together with nitric oxide (NO), of airway relaxation, and a modulator of immune and inflammatory responses. NO-storing molecules in the lung were recently shown to modulate airway reactivity and were proposed to have a protective role against the disease. We report here that mice with targeted deletion of the VIP gene spontaneously exhibit airway hyperresponsiveness to the cholinergic agonist methacholine as well as peribronchiolar and perivascular cellular infiltrates and increased levels of inflammatory cytokines in bronchoalveolar lavage fluid. Immunologic sensitization and challenge with ovalbumin generally enhanced the airway hyperresponsiveness and airway inflammation in all mice. Intraperitoneal administration of VIP over a 2-wk period in knockout mice virtually eliminated the airway hyperresponsiveness and reduced the airway inflammation in previously sensitized and challenged mice. The findings suggest that 1) VIP may be an important component of endogenous anti-asthma mechanisms, 2) deficiency of the VIP gene may predispose to asthma pathogenesis, and 3) treatment with VIP or a suitable agonist may offer potentially effective replacement therapy for this disease.

Mediators and modulators of pulmonary arterial hypertension.

Pulmonary hypertension (PH), defined as a mean pulmonary arterial (PA) pressure of >25 mmHg at rest or >30 mmHg during exercise, is characterized by a progressive and sustained increase in pulmonary vascular resistance that eventually leads to right ventricular failure. Clinically, PH may result from a variety of underlying diseases (Table 1 and Refs. 50, 113, 124). Pulmonary arterial hypertension (PAH) may be familial (FPAH) or sporadic (idiopathic, IPAH), formerly known as primary pulmonary hypertension, i.e., for which there is no demonstrable cause. More often, PAH is due to a variety of identifiable diseases including scleroderma and other collagen disorders, liver disease, human immunodeficiency virus, and the intake of appetite-suppressant drugs such as phentermine and fenfluramine (72). Other, more common, causes of PAH include left ventricular failure (perhaps the most common cause), valvular lesions, chronic pulmonary diseases, sleep-disordered breathing, and prolonged residence at high altitude. This classification, now widely accepted, was first proposed at a meeting in Evian, France, in 1998, and modified in Venice, Italy, in 2003 (124).

The multiple mediators of neurogenic smooth muscle relaxation.

The regulation of smooth muscle relaxation is vitally important for normal functioning of respiratory airways, gastrointestinal organs and the circulatory system. Since the recognition that such relaxation is not under adrenergic or cholinergic control, there has been an active search for the nonadrenergic, noncholinergic (NANC) mediators. A recent paper highlights the complex but coordinated control of the internal anal sphincter by three neurotransmitters.

Ionotropic glutamate receptors in lungs and airways: molecular basis for glutamate toxicity.

We earlier showed that the ionotropic glutamate receptor agonist N-methyl D-aspartate (NMDA) induces excitotoxic pulmonary edema, and that endogenous activation of NMDA receptors (NMDAR) could mediate lung injury caused by oxidative stress. In this study, we searched for evidence of NMDAR expression in the rat lung and in the alveolar macrophage (AM) cell line NR8383, and for possible regulation of receptor expression by NMDA. The presence of mRNA for NMDAR 1 and the four known NMDAR 2 subtypes (A, B, C, and D) was examined by reverse transcriptase-polymerase chain reaction using isoform-specific primers. NMDAR 1 was expressed in all lung regions examined (peripheral, midlung, and mainstem), as well as in trachea and the AMs. Expression of NMDAR 2A and 2B subtypes was not detected, whereas NMDAR 2C was present only in peripheral and mid-lung samples. NMDAR 2D was the dominant subtype expressed in the peripheral, gas-exchange zone of lung and in alveolar macrophages, and this expression was upregulated in lungs treated with NMDA. Western blot confirmed the presence of NMDAR 1 protein in all lung regions and in AMs. These findings provide a molecular-biological basis for the excitotoxic actions of glutamate in rat lungs and airways, and raise the question of a possible physiologic role for NMDAR in lung and airway function.

Nitric oxide and vasoactive intestinal peptide as co-transmitters of airway smooth-muscle relaxation: analysis in neuronal nitric oxide synthase knockout mice.

BACKGROUND: Both vasoactive intestinal peptide (VIP) and nitric oxide (NO) relax airway smooth muscle and are potential co-transmitters of neurogenic airway relaxation. The availability of neuronal NO synthase (nNOS) knockout mice (nNOS-/-) provides a unique opportunity for evaluating NO. OBJECTIVE: To evaluate the relative importance of NO, especially that generated by nNOS, and VIP as transmitters of the inhibitory nonadrenergic, noncholinergic (NANC) system. STUDY DESIGN: In this study, we compared the neurogenic (tetrodotoxin-sensitive) NANC relaxation of tracheal segments from nNOS-/- mice and control wild-type mice (nNOS(+/+)), induced by electrical field stimulation (EFS). We also examined the tracheal contractile response to methacholine and its relaxant response to VIP. RESULTS: EFS (at 60 V for 2 ms, at 10, 15, or 20 Hz) dose-dependently reduced tracheal tension, and the relaxations were consistently smaller (approximately 40%) in trachea from nNOS-/- mice than from control wild-type mice (p < 0.001). VIP (10(- 8) to 10(-6) mol/L) induced concentration-dependent relaxations that were approximately 50% smaller in nNOS-/- tracheas than in control tracheas. Methacholine induced concentration-dependent contractions that were consistently higher in the nNOS-/- tracheas relative to wild-type mice tracheas (p > 0.05). CONCLUSION: Our data suggest that, in mouse trachea, NO is probably responsible for mediating a large (approximately 60%) component of neurogenic NANC relaxation, and a similar (approximately 50%) component of the relaxant effect of VIP. The results imply that NO contributes significantly to neurogenic relaxation of mouse airway smooth muscle, whether due to neurogenic stimulation or to the neuropeptide VIP.

New evidence for transmitter role of VIP in the airways: impaired relaxation by a catalytic antibody.

The identity of the transmitter(s) of nonadrenergic, noncholinergic airway smooth muscle relaxation has long been investigated. Recently, nitric oxide (NO) has been proposed as the main, if not the only transmitter. We earlier suggested vasoactive intestinal peptide (VIP) as a candidate transmitter and target for pathogenic catalytic autoantibodies (VIPases) found in certain humans. To re-examine the role of VIP, we studied the airway transport and effects of a model monoclonal antibody (Ab) capable of binding and cleaving VIP. In vitro receptor binding assays indicated the catalytic light chain subunit of the VIPase Ab to inhibit the saturable binding of (Tyr(10-125)I) VIP by guinea pig lung membranes, whereas a catalytically deficient mutant of the Ab light chain was without significant inhibitory activity. Systemically administered IgG preparations of the VIPase Ab accumulated in the airway lavage fluid of guinea pigs at levels close to those in blood, suggesting that the Ab reaches the airways freely. Electrical field stimulation (EFS)-induced relaxations of tracheal strips were weaker and shorter in VIPase-treated animals than in control nonimmune IgG-treated animals. The inhibitory effect of the VIPase was dose-dependent. VIPase-mediated inhibition of EFS-induced relaxation was evident both in the absence and presence of blockade of beta-adrenergic and cholinergic receptors. Thus, circulating VIP binding and cleaving antibodies can reach the airways and attenuate the neurogenic relaxation of guinea pig tracheal smooth muscle, probably by neutralizing endogenously released VIP. The findings support a role for VIP as a major mediator of neurogenic relaxation of guinea pig tracheal smooth muscle. Lack of complete abrogation of relaxation is consistent with a co-transmitter role for NO.

Vasoactive intestinal peptide attenuates cytochrome c translocation, and apoptosis, in rat hippocampal stem cells.

While widely distributed in the brain, one area with concentrated levels of vasoactive intestinal peptide (VIP) is the hippocampus. In this study, rat hippocampal stem cells were used to examine VIP's effects on apoptotic cell death induced by withdrawal of trophic support. In the apoptotic cascade, the translocation of cytochrome c from the mitochondria to the cytoplasm activates caspases, resulting in cell death. VIP decreased this translocation of cytochrome c in a dose-dependent manner, and reduced apoptosis. This demonstrates that VIP regulates neuronal apoptosis and may contribute to stem cell homeostasis.