Tachykinins and tachykinin receptors: a growing family

Distribution of the neurokinin-1 receptor in equine intestinal smooth muscle

REASON FOR PERFORMING STUDY

Tachykinins have profound effects on equine intestinal motility, but the distribution of the neurokinin receptors (NKRs) through which they act is unknown. This study reports the distribution of one of these receptors, the neurokinin-1 receptor (NK1R), in smooth muscle throughout the equine intestinal tract.

OBJECTIVES

To quantify the distribution of the NK1R, based upon mRNA expression, in smooth muscle of different regions of the equine intestinal tract.

METHODS

Nine regions of the intestinal tract were sampled in 5 mature horses. Total RNA was isolated from smooth muscle and reverse transcribed; NK1R mRNA was then quantified using real-time PCR.

RESULTS

NK1R mRNA was found at all levels of the sampled intestinal tract. The smooth muscle of the proximal small intestine and the ventral colon exhibited the highest level of NK1R mRNA expression in the equine intestinal tract.

CONCLUSIONS

Tachykinins probably affect intestinal contractility and propulsion in the proximal small intestine and in the ventral colon.

Anxiolytic-like effects of substance P administration into the dorsal, but not ventral, hippocampus and its influence on serotonin

Substance P (SP) is known to be involved in processes related to learning and memory, fear, anxiety and stress. SP and NK1 receptors are localized in the hippocampus, a brain structure involved in learning and memory as well as emotional processes. As there is evidence for differential functions of the ventral (VH) and dorsal (DH) hippocampus in a variety of behaviors, we here evaluated the effects of injections of SP into the VH and DH in rats submitted to the elevated plus-maze (EPM) and open field (OF) tests. The results obtained showed that infusions of 100 and 1000 ng of SP into the DH, but not VH, increased open arm activity in the EPM and in the central zone of the OF, indicative of anxiolytic-like action. These effects were observed in the absence of significant changes in general motor activity. In an additional experiment to examine whether these effects of SP are mediated by local serotoninergic mechanisms, extracellular concentrations of this monoamine were assessed by use of in vivo microdialysis. Infusions of SP into the DH did not influence the extracellular concentration of serotonin. These data indicate that neurokinins in the DH, but not VH, are involved in mechanisms associated with anxiety and that the mediation of SP in anxiety-related behaviors is independent of local serotonergic mechanisms.

Role of substance P and bradykinin in acute pancreatitis induced by secretory phospholipase A2

OBJECTIVES

Secretory phospholipases A2 (sPLA2s) induce acute pancreatitis when injected into the common bile duct of rats. Substance P via neurokinin 1 (NK-1) receptors and bradykinin via B2 receptors are described to play important roles in the pathophysiology of acute pancreatitis. This study was undertaken to evaluate the role of substance P and bradykinin in the sPLA2-induced pancreatitis.

METHODS

Rats were submitted to the common bile duct injection of sPLA2 obtained from Naja mocambique mocambique venom at 300 microg/kg. At 4 hours thereafter, measurement of pancreatic plasma extravasation, pancreatic and lung myeloperoxidase (MPO), serum amylase, and serum tumor necrosis factor alpha levels were evaluated.

RESULTS

Injection of sPLA2 significantly increased all parameters evaluated. Pretreatment with either the NK-1 receptor antagonist SR140333 or the B2 receptor antagonist icatibant largely reduced the increased pancreatic plasma extravasation and circulating levels of tumor necrosis factor alpha. Both treatments partly reduced the MPO levels in the pancreas, whereas in the lungs, icatibant was more efficient to reduce the increased MPO levels. In addition, icatibant largely reduced the serum levels of amylase, whereas SR140333 had no significant effect.

CONCLUSIONS

We concluded that NK-1 and B2 receptors can regulate important steps in the local and remote inflammation during acute pancreatitis induced by sPLA2.

Detection of stable N-terminal protachykinin A immunoreactivity in human plasma and cerebrospinal fluid

Substance P (SP) is a neuropeptide that is released from sensory nerves and several types of immune cells. It is involved in the transmission of pain and has a number of pro-inflammatory effects. Like other neuropeptides, SP is derived from a large precursor peptide, protachykinin A (PTA). Alternative splicing results in the production of four distinct PTA molecules that all contain the sequence of SP and a common N-terminal region consisting of 37 amino acids. We have developed a sandwich immunoassay using antibodies against the N-terminal part of PTA. Here we demonstrate that N-terminal PTA immunoreactivity is present in human circulation and cerebrospinal fluid (CSF). The concentration was about 90 times higher in CSF than in EDTA-plasma. Analytical reversed phase HPLC revealed that NT-PTA 1-37 is the main immunoreactivity in human circulation and CSF. Moreover, compared to the low in vitro stability of SP of less than 12 min, NT-PTA immunoreactivity is absolutely stable in EDTA-plasma and CSF for more than 48 h. As NT-PTA 1-37 is produced in stoichiometric amounts and is theoretically co-released with SP, we suggest the measurement of NT-PTA immunoreactivity as surrogate molecule for the release of bioactive SP.

Early vertebrate chromosome duplications and the evolution of the neuropeptide Y receptor gene regions

Background

One of the many gene families that expanded in early vertebrate evolution is the neuropeptide (NPY) receptor family of G-protein coupled receptors. Earlier work by our lab suggested that several of the NPY receptor genes found in extant vertebrates resulted from two genome duplications before the origin of jawed vertebrates (gnathostomes) and one additional genome duplication in the actinopterygian lineage, based on their location on chromosomes sharing several gene families. In this study we have investigated, in five vertebrate genomes, 45 gene families with members close to the NPY receptor genes in the compact genomes of the teleost fishes Tetraodon nigroviridis and Takifugu rubripes. These correspond to Homo sapiens chromosomes 4, 5, 8 and 10.

Results

Chromosome regions with conserved synteny were identified and confirmed by phylogenetic analyses in H. sapiens, M. musculus, D. rerio, T. rubripes and T. nigroviridis. 26 gene families, including the NPY receptor genes, (plus 3 described recently by other labs) showed a tree topology consistent with duplications in early vertebrate evolution and in the actinopterygian lineage, thereby supporting expansion through block duplications. Eight gene families had complications that precluded analysis (such as short sequence length or variable number of repeated domains) and another eight families did not support block duplications (because the paralogs in these families seem to have originated in another time window than the proposed genome duplication events). RT-PCR carried out with several tissues in T. rubripes revealed that all five NPY receptors were expressed in the brain and subtypes Y2, Y4 and Y8 were also expressed in peripheral organs.

Conclusion

We conclude that the phylogenetic analyses and chromosomal locations of these gene families support duplications of large blocks of genes or even entire chromosomes. Thus, these results are consistent with two early vertebrate tetraploidizations forming a paralogon comprising human chromosomes 4, 5, 8 and 10 and one teleost tetraploidization. The combination of positional and phylogenetic data further strengthens the identification of orthologs and paralogs in the NPY receptor family.

Cardiovascular responses to intravenous administration of human hemokinin-1 and its truncated form hemokinin-1(4-11) in anesthetized rats

Human hemokinin-1 and its carboxy-terminal fragment human hemokinin-1(4-11) have been recently identified as the members of the tachykinin family. The peripheral cardiovascular effects of these two tachykinin peptides were investigated in anesthetized rats. Lower doses of human hemokinin-1 (0.1-3 nmol/kg) injected intravenously (i.v.) induced depressor response, whereas higher doses (10 and 30 nmol/kg) caused biphasic (depressor and pressor) responses. The depressor response is primarily due to the action on endothelial tachykinin NK(1) receptor to release endothelium-derived relaxing factor (NO) and vagal reflex was absent in this modulation. The pressor response is mediated through the activation of tachykinin NK(1) receptor to release catecholamines from sympathetic ganglia and adrenal medulla. Moreover, human hemokinin-1 injected i.v. produced a dose-dependent tachycardia response along with blood pressure responses and the activation of sympathetic ganglia and adrenal medulla are involved in the tachycardia response. Human hemokinin-1(4-11) only lowered mean arterial pressure dose-dependently (0.1-30 nmol/kg) and the mechanisms involved in the depressor response are similar to that of human hemokinin-1. Additionally, human hemokinin-1(4-11) could also produce tachycardia response dose-dependently and the mechanisms involved in the tachycardia response are similar to that of human hemokinin-1 except that bilateral adrenalectomy could not affect the tachycardia markedly, indicating that the tachycardia induced by human hemokinin-1(4-11) is primarily due to the stimulation of sympathetic ganglia. In a word, to a certain extent, human hemokinin-1(4-11) is the active fragment of human hemokinin-1, however, the differences between human hemokinin-1 and hemokinin-1(4-11) involved in the effects of cardiovascular system suggest that the divergent amino acid residues at the N-terminus of human hemokinin-1 produced different activation properties for tachykinin NK(1) receptor.

Neurokinin receptor modulation of respiratory activity in the rabbit

The respiratory role of neurokinin (NK) receptors was investigated in alpha-chloralose-urethane-anaesthetized, vagotomized, paralysed and artificially ventilated rabbits by using bilateral microinjections (30-50 nL) of NK receptor agonists and antagonists. Microinjections were performed in a region located just caudal to the rostral expiratory neurons. This region displayed features similar to those of the pre-Bötzinger complex (pre-BötC) of adult cats and rats, and proved to produce excitatory respiratory effects in response to microinjections of D,L-homocysteic acid. We used as agonists (0.1, 0.5 and 5 mM) substance P (SP), the NK1 receptor agonists [Sar(9), Met(O2)(11)]-SP and GR 73632, the NK2 receptor agonist NKA, the NK3 receptor agonist senktide, and as antagonists (5 mM) the NK1 receptor antagonist CP-99,994 and the NK2 receptor antagonist MEN 10376. SP always increased respiratory frequency, but NK1 receptor agonists did not change respiratory variables. NKA and senktide at 5 mm increased respiratory frequency. CP-99,994 caused increases in respiratory frequency and did not antagonize the effects of SP. MEN 10376 prevented the respiratory responses induced by NKA and reduced those provoked by SP. SP or the NK1 receptor agonists (5 mM) injected (1 microL) into the IV ventricle caused marked excitatory effects on respiration. The results suggest that NK2 and NK3, but not NK1, receptors are involved in the excitatory modulation of inspiratory activity within the investigated region and are consistent with the notion that the pre-BötC neurons are important components of the inspiratory rhythm-generating mechanisms.

Tac1 regulation by RNA-binding protein and miRNA in bone marrow stroma: Implication for hematopoietic activity

Hematopoiesis is the process by which immune and blood cells are produced from a finite number of relatively few hematopoietic stem cells (HSCs). In adults, hematopoiesis occurs in the adult bone marrow (BM), with the support of stromal cells. This support partly occurs through the production of hematopoietic regulators belonging to the families of cytokines and neuropeptides/neurotransmitters, which mediate their actions through specific receptors. Thus, stromal cells could be central to the neural-hematopoietic-immune axis. This study focuses on Tac1, which encodes hematopoietic regulators belonging to the tachykinin family of neuropeptides. We examined post-transcriptional regulation of Tac1 in BM stroma. Since this gene is inducible in stroma, we selected cytokines with varying hematopoietic effects: stimulator Stem Cell Factor (SCF), broad-acting IL-11 and suppressive TGF-beta1. RNA shift with Tac1 mRNA and cytoplasmic extracts from IL-11 and SCF-stimulated stroma showed RNA shift after 15min at 37 degrees C, whereas a shift was detected with extracts from TGF-beta1-stimulated stroma after 5min at room temperature. Another level of post-transcriptional regulation was observed by the detection of miRNAs that interact with the 3' untranslated region of Tac1 mRNA. In summary, this study showed that cytokine induced miRNA downregulation and RNA-binding protein(s) are involved in post-transcriptional regulation of Tac1 in BM stroma. The broad categories of cytokines as hematopoietic stimulators or inhibitors might depend on the avidity of RNA-binding protein(s) for Tac1 mRNA, as well as the ability to degrade or stabilize the specific miRNAs.

Metalloelastase in lungs and alveolar macrophages is modulated by extracellular substance P in mice

Metalloelastase (MMP-12), mainly produced by macrophages, has been shown to play a key role in the pathogenesis of emphysema in animal models. Chronic cigarette smoke increases pulmonary MMP-12, which is closely correlated with an elevation of pulmonary substance P (SP). Because alveolar macrophages (AMs) contain the neurokinin-1 receptor (NK1R), we tested whether SP was able to trigger the upregulation of MMP-12 synthesis in AMs by acting on the NK1R. AMs isolated from bronchoalveolar lavage cells in C3H/HeN mice were cultured with control medium or SP that was coupled without or with NK1R antagonists (CP-99,994 or aprepitant) for 24 h. We found that SP significantly increased the mRNA of MMP-12 and NK1R by 11-fold and 82%, respectively, in AMs (P<0.05), and these responses were abolished by NK1R antagonists with little change in the cells' viability. Because pulmonary SP is primarily released by bronchopulmonary C-fibers (PCFs), we further asked whether destruction of PCFs would reduce SP and MMP-12. Two groups of mice were pretreated with vehicle and neonatal capsaicin (NCAP) to degenerate PCFs, respectively. Our results show that NCAP treatment significantly decreased mRNA and protein levels of SP associated with a reduction NK1R and MMP-12 in the lungs and AMs. These findings suggest that SP has a modulatory effect on pulmonary MMP-12 by acting on NK1R to trigger MMP-12 syntheses in the AMs.

D1 receptor regulation of preprotachykinin-A gene by extracellular signal-regulated kinase pathway in striatal cultures

In animal models of Parkinson's disease, a supersensitive response to dopamine (DA) is associated with a switch in the coupling of striatal DA D1 receptors from a cyclic AMP/protein kinase A signaling pathway to one involving extracellular signal-regulated kinase/mitogen-associated protein kinase. In this study, we found that generation of organotypic striatal cultures, with concomitant loss of DA innervation, led to a downregulation in preprotachykinin-A gene expression, which was reinstated by D1 receptor activation in an extracellular signal-regulated kinase/mitogen-associated protein kinase-dependent manner. These data demonstrate that acute organotypic slice cultures recapitulate important changes in D1 receptor-mediated signal transduction seen in DA-denervated animals, providing a valuable model system to study denervation effects on DA signaling and striatal gene expression.

Neurokinins robustly activate the majority of septohippocampal cholinergic neurons

In the brain, tachykinins acting via the three cloned neurokinin (NK) receptors are implicated in stress-related affective disorders. Hemokinin-1 is a novel tachykinin that reportedly prefers NK1 to NK2 or NK3 receptors. Although NK1 and NK3 receptors are abundantly expressed in the brain, NK2-receptor-mediated electrophysiological effects have rarely been described as NK2 receptors are expressed only in a few brain regions such as the nucleus of the medial septum/diagonal band. Medial septal/diagonal band neurons that control hippocampal mnemonic functions also colocalize NK1 and NK3 receptors. Functionally, intraseptal activation of all three NK receptors increases hippocampal acetylcholine release and NK2 receptors have specifically been implicated in stress-induced hippocampal acetylcholine release. Electrophysiological studies on the effects of NKs on septohippocampal cholinergic neurons are lacking and electrophysiological effects of hemokinin-1 have thus far not been reported in brain neurons. In the present study we examined the electrophysiological and pharmacological effects of multiple NKs on fluorescently tagged septohippocampal cholinergic neurons using whole-cell patch-clamp recordings in a rat brain slice preparation. We demonstrate that a vast majority of septohippocampal cholinergic cells are activated by NK1, NK2 and NK3 receptor agonists as well as by hemokinin-1 via direct post-synaptic mechanisms. Pharmacologically, hemokinin-1 recruits not only NK1 but also NK2 and NK3 receptors to activate septohippocampal cholinergic neurons that are the primary source of acetylcholine for the hippocampus.

Contractile properties of the pig bladder mucosa in response to neurokinin A: a role for myofibroblasts?

BACKGROUND AND PURPOSE

The bladder urothelium is now known to have active properties. Our aim was to investigate the contractile properties of the urinary mucosa in response to the tachykinin neurokinin A (NKA) and carbachol.

EXPERIMENTAL APPROACH

Discrete concentration-response curves for carbachol and NKA were obtained in matched strips of porcine detrusor, mucosa and intact bladder, suspended in organ baths. The effects of inhibitors and tachykinin receptor antagonists were studied on NKA-mediated contractions in mucosal strips. Intact sections of bladder and experimental strips were processed for histology and immunohistochemistry.

KEY RESULTS

All types of strips contracted to both carbachol and NKA. Mucosal responses to NKA (pD2 7.2) were higher than those in intact strips and were inhibited by the NK2 receptor antagonist SR48968 (pKB 9.85) but not the NK1 receptor antagonist SR140333, tetrodotoxin or indomethacin. Immunostaining for smooth muscle actin and vimentin occurred under the urothelium and on blood vessels. Desmin immunostaining and histological studies showed only sparse smooth muscle to be present in the mucosal strips. Removal of smooth muscle remnants from mucosal strips did not alter the responses to NKA.

CONCLUSIONS AND IMPLICATIONS

This study has shown both functional and histological evidence for contractile properties of the mucosa, distinct from the detrusor. Mucosal contractions to NKA appear to be directly mediated via NK2 receptors. The main cell type mediating mucosal contractions is suggested to be suburothelial myofibroblasts. Mucosal contractions may be important in vivo for matching the luminal surface area to bladder volume.

Pain and stress in a systems perspective: reciprocal neural, endocrine, and immune interactions

This paper advances a psychophysiological systems view of pain in which physical injury, or wounding, generates a complex stress response that extends beyond the nervous system and contributes to the experience of pain. Through a common chemical language comprising neurotransmitters, peptides, endocannabinoids, cytokines, and hormones, an ensemble of interdependent nervous, endocrine, and immune processes operates in concert to cope with the injury. These processes act as a single agent and comprise a supersystem. Acute pain in its multiple dimensions, and the related symptoms that commonly occur with it, are products of the supersystem. Chronic pain can develop as a result of unusual stress. Social stressors can compound the stress resulting from a wound or act alone to dysregulate the supersystem. When the supersystem suffers dysregulation, health, function, and sense of well-being suffer. Some chronic pain conditions are the product of supersystem dysregulation. Individuals vary and are vulnerable to dysregulation and dysfunction in particular organ systems due to the unique interactions of genetic, epigenetic and environmental factors, as well as the past experiences that characterize each person.

PERSPECTIVE

Acute tissue injury activates an ensemble of interdependent nervous, endocrine, and immune processes that operate in concert and comprise a supersystem. Some chronic pain conditions result from supersystem dysregulation. Individuals vary and are vulnerable to dysregulation due to the unique interactions of genetic, epigenetic, and environmental factors and past experiences that characterize each person. This perspective can potentially assist clinicians in assessing and managing chronic pain patients.

Expression of preprotachykinin-A mRNA isoforms and substance P production in T lymphocytes of human healthy subjects

The influence of sex and age on the expression pattern of preprotachykinin-A (PPT-A) mRNA isoforms encoding substance P and other tackykinins such as neurokinin A (NKA), neuropeptide K (NPK) and neuropeptide gamma (NPgamma) in human immunocompetent cells and the role of this pattern on SP production are unknown. To investigate these questions, we assessed PPT-A isoform expression and SP production in CD3+ lymphocytes of normal healthy subjects. There were no significant differences in PPT-A isoforms in relation to sex or age. The most frequently expressed isoforms were beta and gamma: after lymphocyte stimulation with phytohemagglutinin (PHA), there was a significant increase in their frequency (p<0.0001). Significantly higher SP levels were found in subjects expressing beta and gamma PPT-A than in those with beta PPT-A only (p=0.001). These findings provide evidence of a heterogeneous expression of PPT-A isoforms in CD3+ lymphocytes of normal healthy subjects.

Hypermethylation of tachykinin-1 is a potential biomarker in human esophageal cancer

PURPOSE

Our aim was to investigate whether and at what stage hypermethylation of the tachykinin-1 (TAC1) gene is associated with human esophageal neoplastic transformation.

EXPERIMENTAL DESIGN

TAC1 promoter hypermethylation was examined by real-time methylation-specific PCR in 258 human esophageal specimens and 126 plasma samples from patients or tissues at various stages of neoplastic evolution.

RESULTS

TAC1 hypermethylation in tissue samples showed highly discriminative receiver-operator characteristic curve profiles, clearly distinguishing esophageal squamous cell carcinoma (ESCC) and esophageal adenocarcinoma (EAC) from normal esophagus (P < 0.0001). Both frequencies and normalized methylation values of TAC1 tissue methylation were significantly higher in Barrett's metaplasia (BE), dysplastic Barrett's esophagus, EAC, and ESCC than in normal esophagus (P < 0.01). The frequency of TAC1 hypermethylation increased dramatically and early during neoplastic progression, from 7.5% in normal esophagus to 55.6% in BE from patients with Barrett's metaplasia alone, 57.5% in dysplastic Barrett's esophagus, and 61.2% in EAC. There was a significant relationship between TAC1 hypermethylation and BE segment length, a known clinical risk factor for neoplastic progression. Twelve (50%) of 24 ESCC exhibited TAC1 hypermethylation. Overall patient survival correlated significantly with TAC1 methylation status in ESCC patients (mean survival, 22 versus 110 months; P = 0.0102, log-rank test), but not in EAC patients. Both mean normalized methylation values and frequency of TAC1 hypermethylation in plasma samples were significantly higher in EAC patients than in control subjects. Treatment of KYSE220 ESCC and BIC EAC cells with 5-aza-2'-deoxycytidine reduced TAC1 methylation and increased TAC1 mRNA expression.

CONCLUSIONS

TAC1 promoter hypermethylation is a common event in both major histologic types of human esophageal carcinoma, occurs early, correlates with other progression risk factors in esophageal adenocarcinogenesis, and is a tissue biomarker of a poor prognosis in ESCC. Circulating methylated TAC1 promoter DNA also offers potential as a biomarker for the diagnosis of EAC.

In vitro substance P-dependent induction of bone marrow cells in common (CD10) acute lymphoblastic leukaemia

The aim of the present research was to investigate the possible in vitro stimulatory effect of substance P (SP) on blasts induction in childhood common acute lymphoblastic leukaemia (ALL). Bone marrow aspirates were incubated with SP receptor agonist or antagonist (spantide) and subsequently assayed for the presence of human interleukin (IL)-1b using ELISA kit. Blast cells incubated with SP receptor agonist were found to result in a significant increase of IL-1b concentration while incubated with spantide resulted in control levels of IL-1b. These findings suggest the novel possible role of SP in blasts proliferation in childhood ALL of common (CD10) origin.

Tachykinins and Hematopoiesis

Originally discovered in the 1930s, tachykinins have been a subject of renewed interest. Antagonists to the tachykinin receptors have shown potential in the treatment of a variety of maladies including neurodegenerative disorders, heart disease, pain perception and malignancies. Tachykinins have been the subject of intense studies due to their impact on hematopoiesis that has significant effects on endothelial tissue and vascular conditions. Hematopoiesis relies on a relatively small subset of bone marrow-resident hematopoietic stem cells. This review discusses the network developed by cytokines and the tachykinins to regulate hematopoiesis. An understanding of tachykinin effect on normal hematopoietic functions and their involvement in hematological disorders could lead to new treatments for bone marrow disorders such as fibrosis, leukemia and anemia.

Evidence for a role of caveolin-1 in neurokinin-1 receptor plasma-membrane localization, efficient signaling, and interaction with beta-arrestin 2

This study was focused on the relationship between the plasma-membrane localization of neurokinin-1 receptor (NK1-R) and its endocytic and signaling properties. First, we employed electron paramagnetic resonance (EPR) to study the domain structure of HEK-293 cells and NK1-R microlocalization. EPR spectra and the GHOST condensation routine demonstrated that NK1-R was distributed in a well-ordered domain of HEK-293 cells possibly representing lipid raft/caveolae microdomains, whereas the impairment of caveolae changed the NK1-R plasma-membrane distribution. Internalization and second messenger assays combined with bioluminescence resonance energy transfer were employed subsequently to evaluate the functional importance of the NK1-R microlocalization in lipid raft/caveolae microdomains. The internalization pattern was delineated through the use of dominant-negative mutants (DNM) of caveolin-1 S80E (Cav1 S80E), dynamin-1 K44A (Dyn K44A), and beta-arrestin (beta-arr 319-418) and by means of cell lines that expressed various endogenous levels of beta-arrestins. NK1-R displayed rapid internalization that was substantially reduced by DNMs of dynamin-1 and beta-arrestin and even more profoundly in cells lacking both beta-arrestin1 and beta-arrestin2. These internalization data were highly suggestive of the predominant use of the clathrin-mediated pathway by NK1-R, even though NK1-R tended to reside constitutively in lipid raft/caveolae microdomains. Evidence was also obtained that the proper clustering of the receptor in these microdomains was important for effective agonist-induced NK1-R signaling and for its interaction with beta-arrestin2.

The significance of substance P in physiological and malignant haematopoiesis

The role of substance P (SP) in physiological haematopoiesis is well established. However, it also seems to be important in the neoplastic transformation of bone marrow, leading to the development of acute leukaemia in children, and also metastases to bone marrow of solid tumours (particularly neuroblastoma and breast cancer) in early stages of these diseases. This review summarises the available data on SP involvement in both processes. In the future, SP antagonists may be used as anti-neoplastic drugs, for example by direct or indirect blocking of tumour cell proliferation through inhibition of growth factor production and interleukin-1b synthesis.

Cardiovascular responses to rat/mouse hemokinin-1, a mammalian tachykinin peptide: systemic study in anesthetized rats

Rat/mouse hemokinin-1 is a mammalian tachykinin peptide whose biological functions have not been well characterized. In the present study, an attempt has been made to investigate the effect and mechanism of action of rat/mouse hemokinin-1 on systemic arterial pressure after intravenous (i.v.) injections in anesthetized rats by comparing it with that of substance P. Our data showed that injection of rat/mouse hemokinin-1 (0.1, 0.3, 1, 3 and 10 nmol/kg) lowered systemic arterial pressure dose-dependently. This effect was significantly blocked by pretreatment with SR140333 (a selective tachykinin NK1 receptor antagonist) and the NO synthase inhibitor L-NAME (Nomega-nitro-L-arginine methyl ester hydrochloride), respectively, but was not affected by bilateral vagotomy or the muscarinic receptor blocker atropine. Compared to rat/mouse hemokinin-1, a dose of 3 nmol/kg of substance P caused biphasic changes in systemic arterial pressure (depressor and pressor responses). The results suggest that the mechanism of the depressor response caused by substance P was similar to rat/mouse hemokinin-1 in that it was inhibited by SR140333 and L-NAME, respectively, but that there was a component of the cardiovascular change induced by rat/mouse hemokinin-1 (but not substance P) that was attenuated by SR48968 (a selective tachykinin NK2 receptor antagonist). The depressor response induced by rat/mouse hemokinin-1 (i.v.) might be explained primarily by the action on endothelial tachykinin NK1 receptors to release endothelium-derived relaxing factor (NO) and this effect was not affected by vagal components. In addition, rat/mouse hemokinin-1 could not induce the pressor response through stimulation of sympathetic ganglion like substance P in anesthetized rats.

Neurokinin 1 Receptor Antagonists: Correlation between in Vitro Receptor Interaction and in Vivo Efficacy

We compared the neurokinin 1 receptor (NK(1)R) antagonists aprepitant, CP-99994 [(2S,3S)-3-(2-methoxybenzylamino)-2-phenylpiperidine], and ZD6021 [3-cyano-N-((2S)-2-(3,4-dichlorophenyl)-4-[4-[2-(methyl-(S)-sulfinyl)phenyl]piperidino]butyl)-N-methyl]napthamide]] with respect to receptor interactions and duration of efficacy in vivo. In Ca(2+) mobilization assays (fluorometric imaging plate reader), antagonists were applied to human U373MG cells simultaneously with or 2.5 min before substance P (SP). In reversibility studies, antagonists were present for 30 min before washing, and responses to SP were repeatedly measured afterward. The compounds were administered i.p. to gerbils, and the gerbil foot tap (GFT) response was monitored at various time points. The NK(1)R receptor occupancy for aprepitant was determined in striatal regions. Levels of compound in brain and plasma were measured. Antagonists were equipotent at human NK(1)R and acted competitively with SP. After preincubation, aprepitant and ZD6021 attenuated the maximal responses, whereas CP-99994 only shifted the SP concentration-response curve to the right. The inhibitory effect of CP-99994 was over within 30 min, whereas for ZD6021, 50% inhibition still persisted after 60 min. Aprepitant produced maximal inhibition lasting at least 60 min. CP-99994 (3 micromol/kg) inhibited GFT by 100% 15 min after administration, but the effect declined rapidly together with brain levels thereafter. The efficacy of ZD6021 (10 micromol/kg) lasted 4 h and correlated well with brain levels. Aprepitant (3 micromol/kg) inhibited GFT and occupied striatal NK(1)R by 100% for >48 h despite that brain levels of compound were below the limit of detection after 24 h. Slow functional reversibility is associated with long-lasting in vivo efficacy of NK(1)R antagonists, whereas the efficacy of compounds with rapid reversibility is reflected by their pharmacokinetics.

Bladder inflammatory transcriptome in response to tachykinins: neurokinin 1 receptor-dependent genes and transcription regulatory elements

BACKGROUND

Tachykinins (TK), such as substance P, and their neurokinin receptors which are ubiquitously expressed in the human urinary tract, represent an endogenous system regulating bladder inflammatory, immune responses, and visceral hypersensitivity. Increasing evidence correlates alterations in the TK system with urinary tract diseases such as neurogenic bladders, outflow obstruction, idiopathic detrusor instability, and interstitial cystitis. However, despite promising effects in animal models, there seems to be no published clinical study showing that NK-receptor antagonists are an effective treatment of pain in general or urinary tract disorders, such as detrusor overactivity. In order to search for therapeutic targets that could block the tachykinin system, we set forth to determine the regulatory network downstream of NK1 receptor activation. First, NK1R-dependent transcripts were determined and used to query known databases for their respective transcription regulatory elements (TREs).

METHODS

An expression analysis was performed using urinary bladders isolated from sensitized wild type (WT) and NK1R-/- mice that were stimulated with saline, LPS, or antigen to provoke inflammation. Based on cDNA array results, NK1R-dependent genes were selected. PAINT software was used to query TRANSFAC database and to retrieve upstream TREs that were confirmed by electrophoretic mobility shift assays.

RESULTS

The regulatory network of TREs driving NK1R-dependent genes presented cRel in a central position driving 22% of all genes, followed by AP-1, NF-kappaB, v-Myb, CRE-BP1/c-Jun, USF, Pax-6, Efr-1, Egr-3, and AREB6. A comparison between NK1R-dependent and NK1R-independent genes revealed Nkx-2.5 as a unique discriminator. In the presence of NK1R, Nkx2-5 _01 was significantly correlated with 36 transcripts which included several candidates for mediating bladder development (FGF) and inflammation (PAR-3, IL-1R, IL-6, alpha-NGF, TSP2). In the absence of NK1R, the matrix Nkx2-5_02 had a predominant participation driving 8 transcripts, which includes those involved in cancer (EYA1, Trail, HSF1, and ELK-1), smooth-to-skeletal muscle trans-differentiation, and Z01, a tight-junction protein, expression. Electrophoretic mobility shift assays confirmed that, in the mouse urinary bladder, activation of NK1R by substance P (SP) induces both NKx-2.5 and NF-kappaB translocations.

CONCLUSION

This is the first report describing a role for Nkx2.5 in the urinary tract. As Nkx2.5 is the unique discriminator of NK1R-modulated inflammation, it can be imagined that in the near future, new based therapies selective for controlling Nkx2.5 activity in the urinary tract may be used in the treatment in a number of bladder disorders.

Substance P provides neuroprotection in cerebellar granule cells through Akt and MAPK/Erk activation: Evidence for the involvement of the delayed rectifier potassium current

In the current study, we have evaluated the ability of substance P (SP) and other neurokinin 1 receptor (NK1) agonists to protect, in a dose- and time-dependent manner, primary cultures of rat cerebellar granule cells (CGCs) from serum and potassium deprivation-induced cell death (S-K5). We also established the presence of SP high affinity NK1 transcripts and the NK1 protein localization in the membrane of a sub-population of CGCs. Moreover, SP significantly and dose-dependently reduced the Akt 1/2 and Erk1/2 dephosphorylation induced by S-K5 conditions, as demonstrated by Western blot analysis. Surprisingly, in SP-treated CGCs caspase-3 activity was not inhibited, while the calpain-1 activity was moderately reduced. Corroborating this result, SP blocked calpain-mediated cleavage of tau protein, as demonstrated by the reduced appearance of a diagnostic fragment of 17 kDa by Western blot analysis. In addition, SP induced a significant reduction of the delayed rectifier K+ currents (Ik) in about 42% of the patched neurons, when these were evoked with depolarizing potential steps. Taken together, the present results demonstrate that the activation of NK1 receptors expressed in CGCs promote the neuronal survival via pathways involving Akt and Erk activation and by inhibition of Ik which can contribute to the neuroprotective effect of the peptide.

Neurokinin-1 enables measles virus trans-synaptic spread in neurons

Measles virus (MV), a morbillivirus that remains a significant human pathogen, can infect the central nervous system, resulting in rare but often fatal diseases, such as subacute sclerosing panencephalitis. Previous work demonstrated that MV was transmitted trans-synaptically and that, while a cellular receptor for the hemagglutinin (H) protein was required for MV entry, it was dispensable for subsequent cell-to-cell spread. Here, we explored what role the other envelope protein, fusion (F), played in trans-synaptic transport. We made the following observations: (1) MV-F expression in infected neurons was similar to that seen in infected fibroblasts; (2) fusion inhibitory peptide (FIP), an inhibitor of MV fusion, prevented both infection and spread in primary neurons; (3) Substance P, a neurotransmitter with the same active site as FIP, also blocked neuronal MV spread; and (4) both genetic deletion and pharmacological inhibition of the Substance P receptor, neurokinin-1 (NK-1), reduced infection of susceptible mice. Together, these data implicate a role for NK-1 in MV CNS infection and spread, perhaps serving as an MV-F receptor or co-receptor on neurons.

A role for tachykinins in the regulation of human sperm motility

BACKGROUND

Tachykinins and tachykinin receptors are widely distributed in the male reproductive tract and appear to be involved in reproduction. However, the function and expression of tachykinins and their receptors in human spermatozoa remain poorly studied. We analysed the effects of tachykinins on sperm motility and characterized the population of tachykinin receptors in human spermatozoa.

METHODS AND RESULTS

Motility analysis was performed following World Health Organization guidelines and we found that substance P (SP), human hemokinin-1 (hHK-1), neurokinin A (NKA) and neurokinin B (NKB) produced concentration-dependent increases in sperm progressive motility. The effects of tachykinins were antagonized by the NK(1) receptor-selective antagonist SR 140333, the NK(2) receptor-selective antagonist, SR 48968 and, to a lesser extent, also by the NK(3) receptor-selective antagonist SR 142801. Immunocytochemistry studies showed expression of the NK(1), NK(2) and NK(3) tachykinin receptor proteins in spermatozoa with different major sites of localization for each receptor. Western blot analysis confirmed the presence of tachykinin receptors in sperm cell homogenates. RT-PCR demonstrated expression of the genes that encode SP/NKA (TAC1), NKB (TAC3) and hHK-1 (TAC4) but not the genes TACR1, TACR2 and TACR3 encoding NK(1), NK(2) and NK(3) receptors, respectively.

CONCLUSIONS

These results show for the first time that the NK(1), NK(2) and NK(3) tachykinin receptor proteins are present in human spermatozoa. Our findings suggest that tachykinins, probably acting through these three tachykinin receptors, play a role in the regulation of human sperm motility.

Polyethylene particle-induced bone resorption in substance P-deficient mice

Aseptic loosening is the major cause of total joint replacement failure. Substance P (SP) is a neurotransmitter richly distributed in sensory nerve fibers, bone, and bone-related tissue. The purpose of this study was to investigate the potential impact of SP on bone metabolism in polyethylene particle-induced osteolysis. We utilized the murine calvarial osteolysis model based on ultrahigh molecular weight polyethylene (UHMWPE) particles in 14 wild-type mice (C57BL/J6) and 14 SP-deficient mice. Group 1 (C57BL/J 6) and group 3 (SP-knockout) received sham surgery, and group 2 (C57BL/J6) and group 4 (SP-knockout) were treated with polyethylene particles. Analytical methods included three-dimensional micro-computed tomographic (micro-CT) analysis and histomorphometry. Bone resorption was measured within the midline suture. The number of osteoclasts was determined by counting the tartrate-resistant acid phosphatase-positive cells. UHMWPE-particle treated SP-deficient mice showed significantly reduced osteolysis compared to wild-type mice, as confirmed by histomorphometry (P < 0.001) and micro-CT (P = 0.035). Osteoclast numbers were significantly reduced in groups 3 and 4 compared to groups 1 and 2 (P < 0.001). Unexpectedly, SP-deficient mice (group 3) showed a significantly increased absolute bone mass compared to wild-type mice (group 1) (P = 0.02). The findings of our murine calvaria model lead to the assumption that SP is a promoter in particle-induced osteolysis. The pathophysiology of aseptic loosening is complex, and neuropeptides are not solely responsible for the progress of implant loosening; however, we conclude that there could be coherence between neurotransmitters and particle-induced osteolysis in patients with aseptic loosening.

Contributions to the field of neurotransmitters by Japanese scientists, and reflections on my own research

PART I DESCRIBES IMPORTANT CONTRIBUTIONS MADE BY SOME JAPANESE PIONEERS IN THE FIELD OF NEUROTRANSMITTERS: (their achievements in parentheses) J. Takamine (isolation and crystallization of adrenaline); K. Shimidzu (early hint for acetylcholine as a neurotransmitter); F. Kanematsu (donation of the Kanematsu Memorial Institute in Sydney); T. Hayashi (discovery of the excitatory action of glutamate and the inhibitory action of GABA); and I. Sano (discovery of a high concentration of dopamine in striatum, its reduction in a patient with Parkinson's disease and the treatment with DOPA). In Part II, I present some of my reflections on my research on neurotransmitters. The work of my colleagues and myself has made some significant contributions to the establishment of neurotransmitter roles played by GABA and substance P, the first amino acid and the first peptide neurotransmitters, respectively. By the early 1960s, 3 substances, i.e., acetylcholine, noradrenaline, and adrenaline, had been established as neurotransmitters. Now the number of neurotransmitters is believed to be as many as 50 or even more mainly due to the inclusion of several amino acids and a large number of peptide transmitters.

Determination of substance P in rat spinal cord by high-performance liquid chromatography electrospray quadrupole ion trap mass spectrometry

Substance P is a neuropeptide that belongs to the tachykinin neuropeptide family. It is an 11-amino acid polypeptide with the amino acid sequence: Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met. It is synthesized as a larger protein and then enzymatically converted into the active undecapeptide. Substance P is widely distributed in the central and peripheral nervous systems. In the central nervous system, substance P participates in various behavioral responses and in regulating neuronal survival and degeneration. In the spinal cord, substance P participates in neurotransmission of pain and modulates autonomic reflexes. A rapid and selective method was developed for the determination of substance P concentration in rat spinal cord. The method consisted of a tissue homogenization, dilution, centrifugation and analysis by full-scan liquid chromatography electrospray quadrupole ion trap mass spectrometry (LC-ESI-QIT). The separation was achieved using a 50 x 2.1 mm C(18) analytical column combined with a gradient mobile phase composed of methanol: 0.1% formic acid in water set at a flow rate of 0.2 mL/min. An analytical range of 10-500 pmol/g was tested to analyze rat spinal cord. The LOD observed was 10 fmol injected on column. The novel method met all requirements of specificity, sensitivity, linearity, precision, accuracy and stability. In conclusion, a rapid and sensitive LC-ESI/MS/MS method was developed to identify and quantify substance P in rat spinal cord.

Functionalization through Lithiation of (S)-N-(1-Phenylpropyl)-2-phenylquinoline-4-carboxamide. Application to the Labeling with Carbon-11 of NK-3 Receptor Antagonist SB 222200

Lithiation of (S)-N-(1-phenylpropyl)-2-phenylquinoline-4-carboxamide with the complex n-BuLi/TMEDA (1/1 molar ratio) in THF at -60 degrees C for 5 h occurred selectively at the position 3 of the quinoline ring. This selectivity was shown by the absence of racemization of the stereogenic center and the formation of the corresponding functionalized quinolines in 59-74% yield by subsequent reaction with an electrophile at -60 degrees C for 1 h. The 3-trimethylstannyl derivative was subjected to a Stille reaction using methyl, phenyl, or thienyliodide to afford the alkyl or aryl quinolines in moderate to good yields. This methodology was successfully applied to the radiosynthesis of [11C]SB 222200 using methyl iodide labeled with carbon-11 (beta+ emitter, t1/2=20.4 min) for the in vivo study of NK-3 receptor by positron emission tomography (48-58% radiochemical yields from [11C]CH3I, decay corrected, 45 min total synthesis time).

Synthetic non-peptide mimetics of alpha-helices

Proteins in nature fold into native conformations in which combinations of peripherally projected aliphatic, aromatic and ionic functionalities direct a wide range of properties. Alpha-helices, one of the most common protein secondary structures, serve as important recognition regions on protein surfaces for numerous protein-protein, protein-DNA and protein-RNA interactions. These interactions are characterized by conserved structural features within the alpha-helical domain. Rational design of structural mimetics of these domains with synthetic small molecules has proven an effective means to modulate such protein functions. In this tutorial review we discuss strategies that utilize synthetic small-molecule antagonists to selectively target essential protein-protein interactions involved in certain diseases. We also evaluate some of the protein-protein interactions that have been or are potential targets for alpha-helix mimetics.

Herpes simplex virus type-1 latency-associated transcript-induced immunoreactivity of substance P in trigeminal neurons is reversed by bone morphogenetic protein-7

Herpes simplex virus type-1 (HSV-1) primarily infects mucoepithelial tissues of the eye and the orofacial region. Subsequently, the virus is retrogradely transported through the axons of the trigeminal sensory neurons to their nuclei, where the virus establishes a life-long latent infection. During this latency period, the viral genome is transcriptionally silent except for a single region encoding the latency-associated transcript (LAT). To understand how HSV-1 latency might affect the expression of substance P in sensory neurons, we transfected primary cultures of trigeminal neurons obtained from rat embryos, with LAT expressing plasmids. The expression of LAT increased the percentage of substance P-immunoreactive neurons by two thirds. To examine the effect of bone morphogenetic protein-7 (BMP7) on the LAT-induced increase in substance P expression in trigeminal neurons, cultures transfected with LAT were treated with BMP7. Treatment with BMP7 reversed the effects of LAT on substance P expression in trigeminal neurons. Our data show for the first time that LAT increases substance P expression in trigeminal neurons and BMP7 can reverse these effects of LAT.

Tachykinins and excitotoxicity in cerebellar granule cells

The tachykinins represent an important group of neuropeptides that are widely distributed both in the central and peripheral nervous system where they perform several functions connected with neuronal modulation, often in synergy with glutamate excitatory transmission. While a great deal of data is available on their distribution and many studies have been performed by molecular, biochemical, and immunohistochemical techniques, much less is known about their physiological role, in particular in the cerebellum. This review is an attempt to summarize the diverse evidence suggesting a role for tachykinins in cerebellar granule neurons.

Molecular cloning, mutations and effects of NK1 receptor antagonists reveal the human-like pharmacology of gerbil NK1 receptors

The present study investigates the pharmacology of the cloned neurokinin 1 receptor from the gerbil (gNK(1)R), a species claimed to have human-like NK(1)R (hNK(1)R) pharmacology. The amino acid sequence of NK(1)R was cloned. The hNK(1)R, rat NK(1)R (rNK(1)R), gNK(1)R and mutants of the gNK(1)R were expressed in CHO cells. The affinity and potency of NKR agonists and the NK(1)R antagonists CP99994 and RP67580 (NK(1)R-selective) and ZD6021 (NK1/2R) were assessed in vitro by monitoring [(3)H]-SarMet SP binding and substance P-evoked mobilization of intracellular Ca(2+). The gerbil foot tap (GFT) method was used to assess the potency of the antagonists in vivo. The gNK(1)R coding sequence displayed an overall 95% and 97% homology with hNK(1)R and rNK(1)R, respectively. The affinity of the NK(1)R-selective agonist (3)H-SarMet SP for human and gerbil NK(1)R was similar (2.0 and 3.1 nM) but lower for rNK(1)R (12.4 nM). The rank order potency of the agonists for NK(1)R was SP > or = ASMSP > or = NKA >>> pro7NKB in all species. The NK(1)R antagonists, ZD6021 and CP99994, had comparable affinity and potency for gerbil and human NK(1)R, but were 1000-fold less potent for rNK(1)R. In contrast, RP67580 had comparable affinity and potency for all three species. Mutations in positions 116 and 290 did not affect agonist potency at the gNK(1)R while the potency of the antagonists ZD6021 and CP99994 were markedly decreased (10-20-fold). It is concluded that gNK(1)R has similar antagonist pharmacology as the human-like orthologue and that species differences in antagonist function depend on key residues in the coding sequence and antagonist structure.

Effects of neonatal capsaicin treatment in the neutrophil production, and expression of preprotachykinin-I and tachykinin receptors in the rat bone marrow

Bone marrow is richly innervated with both myelinated and non-myelinated nerve fibers, but the role of this innervation on hemopoiesis is poorly understood. Therefore, the aim of this study was to investigate the role of C-fibers on hematopoiesis. Wistar rats were neonatally injected with either capsaicin or its vehicle, and used at adult ages (8-10 weeks). In capsaicin-pretreated rats, the levels of substance P (SP) in bone marrow fluid were markedly reduced in comparison with the vehicle group (13.1+/-4.5 pg/ml versus 47.3+/-5.5 pg/ml, p<0.05). In bone marrow, the number of total leukocytes was 28% higher (p<0.05) in capsaicin-pretreated group, and this accompanied by a higher number of neutrophils, particularly of the immature forms. The mononuclear cell and eosinophils counts did not differ significantly among vehicle and capsaicin groups. In peripheral blood, the number of circulating neutrophils in the capsaicin group increased by 53.8% (p<0.05), whereas the number of mononuclear cells did not change significantly among groups. Eosinophils were virtually absent in the circulating blood in both groups. Semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) showed that both preprotachykinin (PPT)-I mRNA and the tachykinin neurokinin (NK)-1 mRNA expression in bone marrow cells significantly increased in capsaicin group, whereas the NK-2 mRNA expression was unchanged after capsaicin pretreatment. In conclusion, our data show that chronic neuropeptide depletion enhance the neutrophil proliferation and differentiation in the rat bone marrow by mechanisms involving upregulation of PPT-I gene and NK-1 receptors.

Involvement of some large immunophilins and their ligands in the protection and regeneration of neurons: a hypothetical mode of action

The powerful immunosuppressive drugs such as FK506 and its derivatives induce some regeneration and protection of neurons from ischaemic brain injury and some other neurological disorders. The drugs form complexes with diverse FKBPs but apparently the FKBP52/FK506 complex was shown to be involved in the protection and regeneration of neurons. We used several different sequence attributes in searching diverse genomic databases for similar motifs as those present in the FKBPs. A Fortran library of algorithms (Par_Seq) has been designed and used in searching for the similarity of sequence motifs extracted from the multiple sequence alignments of diverse groups of proteins (query motifs) and the target motifs which are encoded in various genomes. The following sequence attributes were used in the establishment of the degree of convergence between: (A) amino acid (AA) sequence similarity (ID) of the query/target motifs and (B) their: (1) AA composition (AAC); (2) hydrophobicity (HI); (3) Jensen-Shannon entropy; and (4) AA propensity to form a particular secondary structure. The sequence hallmark of two different groups of peptidylprolyl cis/trans isomerases (PPIases), namely tetratricopetide repeat (TPR) motifs, which are present in the heat-shock cyclophilins and in the large FK506-binding proteins (FKBPs) were used to search various genomic databases. The Par_Seq algorithm has revealed that the TPR motifs have similar sequence attributes as a number of hydrophobic sequence segments of functionally unrelated membrane proteins, including some of the TMs from diverse G protein-coupled receptors (GPCRs). It is proposed that binding of the FKBP52/FK506 complex to the membranes via the TPR motifs and its interaction with some membrane proteins could be in part responsible for some neuro-regeneration and neuro-protection of the brain during some ischaemia-induced stresses.

Association of genetic variations in neurokinin-2 receptor with enhanced cough sensitivity to capsaicin in chronic cough

BACKGROUND

Chronic cough is associated with increased sensitivity to inhaled capsaicin, and both tachykinins and their receptors play important roles in the cough reflex. However, associations between polymorphisms of the tachykinin receptor genes and cough sensitivity in patients with non-productive chronic cough have not been reported.

METHODS

Direct sequencing was used to identify single nucleotide polymorphisms (SNPs) in the genes for the neurokinin-1 and neurokinin-2 receptors (NK-1R and NK-2R, respectively). Informative non-synonymous SNPs were scored using the single base extension method for 312 patients with chronic cough and for 100 age matched healthy controls. The cough response to capsaicin was recorded for 312 patients with chronic cough, and the potential genetic association between cough sensitivity to capsaicin and the NK-1R and NK-2R genotypes was evaluated.

RESULTS

Two informative SNPs were identified in NK-2R (Gly231Glu and Arg375His), whereas no informative SNP was found in NK-1R. After adjusting for atopy, sex, age, and smoking, the prevalence of enhanced cough sensitivity to capsaicin was higher in the chronic cough patients with the 231Glu allele (p = 0.004; OR 1.69 (95% CI 1.18 to 2.42)) and the 231Glu_375Arg haplotype (p = 0.003; OR 1.71 (95% CI 1.20 to 2.24)). Moreover, the lowest capsaicin concentration to cause five consecutive coughs (C5) was significantly lower in patients with 231Glu (mean (SD) 44.1 (53.2) v 60.9 (55.8) microM/l, p = 0.04) and those with 231Glu_375Arg (43.2 (52.7) v 69.6 (52.0) microM/l, p = 0.03).

CONCLUSIONS

The results of this study suggest that NK-2R gene polymorphisms are involved in the enhanced cough sensitivity to capsaicin of patients with chronic cough.

Bovine respiratory syncytial virus lacking the virokinin or with a mutation in furin cleavage site RA(R/K)R109 induces less pulmonary inflammation without impeding the induction of protective immunity in calves

The BRSV fusion (F) protein is cleaved at two furin consensus sequence sites, resulting in the generation of disulphide-linked F1 and F2 subunits and the release of an intervening peptide of 27 amino acids (pep27), which is converted into a biologically active tachykinin (virokinin). The role of the virokinin and the importance of one of the furin cleavage sites, FCS-2 [RA(R/K)R109], in the pathogenesis of BRSV infection and in the subsequent development of immunity was studied in gnotobiotic calves infected with a recombinant BRSV (rBRSV) lacking pep27 (rBRSVdelta p27) or with rBRSV108/109, which contains two amino acid substitutions in FCS-2 (RANN109). Although replication of the mutant viruses and the parental wild-type (WT) rBRSV in the lungs was similar, the extent of gross and microscopic lesions induced by the mutant viruses was less than that induced by WT rBRSV. Furthermore, the numbers of eosinophils in the lungs of calves infected with the mutant viruses were significantly less than that in calves infected with WT virus. These observations suggest a role for the virokinin in the pathogenesis of BRSV infection. Following mucosal immunization with rBRSVdelta p27, the levels of BRSV-specific serum antibodies were similar to those induced by WT virus. In contrast, the level of neutralizing antibodies induced by rBRSV108/109 was 10-fold lower than that induced by WT virus. Nevertheless, resistance to BRSV challenge induced by the mutant and WT viruses was similar, suggesting that neither pep27 nor FCS-2 plays a major role in the induction of protective immunity.

Substance P induces expression of the corticotropin-releasing factor receptor 1 by activation of the neurokinin-1 receptor

The neuropeptide substance P (SP) has been found to be possibly involved in the etiology of affective and anxiety disorders. However, the molecular mechanisms underlying this involvement are still poorly understood. In this study, we used macroarrays to investigate the differential gene expression profile induced by SP, particularly of genes which have been shown to be involved in the pathophysiology of affective disorders. As a model system, we used the human astrocytoma cell line U373 MG as well as primary rat astroglial cells, which both are known to express functional neurokinin-1 receptors (NK-1-R) and to secret various cytokines upon stimulation with SP. Among several regulated genes, we found that SP (100 and 1000 nM) induced the expression of the corticotropin-releasing factor receptor 1 (CRF1 receptor). Further analyses revealed that this induction was mediated (a) via NK-1-R, as the selective NK-1-R-antagonist L-733,060 (1 microM) strongly inhibited SP-induced CRF1 receptor expression, and (b) intracellularly, by protein kinase C, p42/44 and p38 mitogen-activated protein kinases (MAPK), as shown by using specific inhibitors of signal transduction pathways. In conclusion, this study demonstrates that SP induces CRF1 receptor expression in cells of the CNS, which may be of potential interest for a better understanding of the interplay between SP and the stress hormone axis and, thus, diseases like affective or anxiety disorders. Further studies are needed to substantiate this link in vivo.

Recognition of GPCRs by Peptide Ligands and Membrane Compartments theory: Structural Studies of Endogenous Peptide Hormones in Membrane Environment

One of the largest family of cell surface proteins, G-protein coupled receptors (GPCRs) regulate virtually all known physiological processes in mammals. With seven transmembrane segments, they respond to diverse range of extracellular stimuli and represent a major class of drug targets. Peptidergic GPCRs use endogenous peptides as ligands. To understand the mechanism of GPCR activation and rational drug design, knowledge of three-dimensional structure of receptor–ligand complex is important. The endogenous peptide hormones are often short, flexible and completely disordered in aqueous solution. According to “Membrane Compartments Theory”, the flexible peptide binds to the membrane in the first step before it recognizes its receptor and the membrane-induced conformation is postulated to bind to the receptor in the second step. Structures of several peptide hormones have been determined in membrane-mimetic medium. In these studies, micelles, reverse micelles and bicelles have been used to mimic the cell membrane environment. Recently, conformations of two peptide hormones have also been studied in receptor-bound form. Membrane environment induces stable secondary structures in flexible peptide ligands and membrane-induced peptide structures have been correlated with their bioactivity. Results of site-directed mutagenesis, spectroscopy and other experimental studies along with the conformations determined in membrane medium have been used to interpret the role of individual residues in the peptide ligand. Structural differences of membrane-bound peptides that belong to the same family but differ in selectivity are likely to explain the mechanism of receptor selectivity and specificity of the ligands. Knowledge of peptide 3D structures in membrane environment has potential applications in rational drug design.

Regulation of the stimulant actions of neurokinin a and human hemokinin-1 on the human uterus: a comparison with histamine

Regulation of the contractile effects of tachykinins and histamine on the human uterus was investigated with biopsy sections of the outer myometrial layer. The effects of neurokinin A (NKA) and human hemokinin-1 (hHK-1) in tissues from pregnant but not from nonpregnant women were enhanced by the inhibition of neprilysin. The effects of NKA and eledoisin were blocked by the NK2 receptor antagonist SR 48968 but not by the NK1 receptor antagonist SR 140333 in tissues from both groups of women. Human HK-1 acted as a partial agonist blocked by SR 48968 and, to a lesser extent, by SR 140333; endokinin D was inactive. In tissues from pregnant women, responses to high potassium-containing Krebs solution were 2-3-fold higher than those from nonpregnant women. Mepyramine-sensitive maximal responses to histamine were similarly enhanced. The absolute maximum responses to NKA and its stable NK2 receptor-selective analogue, [Lys5MeLeu9Nle10]NKA(4-10), were increased in pregnancy, but their efficacies relative to potassium responses were decreased. Tachykinin potencies were lower in tissues from pregnant women than in those from nonpregnant women. These data 1) show for the first time that hHK-1 is a uterine stimulant in the human, 2) confirm that the NK2 receptor is predominant in mediating tachykinin actions on the human myometrium, and 3) indicate that mammalian tachykinin effects are tightly regulated during pregnancy in a manner that would negate an inappropriate uterotonic effect. The potencies of these peptides in tissues from nonpregnant women undergoing hysterectomy are consistent with their possible role in menstrual and menopausal disorders.

Nuclear localization of SP, CGRP, and NK1R in a subpopulation of dorsal root ganglia subpopulation cells in rats

Signals generated by renal pelvic afferent nerves in response to stimulation are transmitted from peripheral processes of dorsal root ganglia neurons to their central terminals in the dorsal horn of the spinal cord to cause the release of neuropeptides, including SP and CGRP. All of the cellular activities of SP are considered to be mediated through interaction with NK(1)R located on the cell surface. We have investigated the colocalization and subcellular distribution of NK(1)R, SP, and CGRP in different subpopulations of neurons that innervate renal tissue. Our findings therefore provide the first evidence for the presence of NK(1)R, SP, and CGRP in the nuclei of DGR neural cells. The physiological significance of this localization remains unknown. One possibility is that pelvic sensory neurons may regulate their responses to different stimuli by modulating the ratio of CGRP and SP release and/or nuclear NK(1)R expression.

Tachykinins and tachykinin receptors in the gut, with special reference to NK2 receptors in human

Tachykinins (TKs), substance P (SP), neurokinin A (NKA) and B (NKB) are important peptide modulators of intestinal motility in animal species studied so far, including humans. Modulation of motility by TKs can occur at various levels, since these peptides are expressed in cholinergic excitatory motor neurons projecting to both circular and longitudinal muscle, interneurons, and intramural and extramural sensory neurons. The effects of SP, NKA and NKB are preferentially mediated through the stimulation of NK1, NK2 and NK3 receptors, respectively; however, the selectivity of natural TKs for their preferred receptors is relative. In addition, SP and NKA are expressed in similar quantities in the human intestine and adequate stimuli can release similar amount of these TKs from enteric nerves. Furthermore, a single anatomical substrate can express more than one TK receptor type, so that the blockade of a single receptor type may not reveal functional effects in integrated models of motility. In isolated human small intestine and colon circular muscle strips, both NK1 and NK2 receptors mediate contractile effects. Indeed, in the human small intestine, smooth muscle electrical and motor events induced by electrical field stimulation (EFS) can involve either or both NK1 and NK2 receptors or these latter receptors predominantly, depending on the experimental conditions. In contrast, in the human colonic smooth muscle, only the NK2 receptor-mediated component of the response to EFS is prominent and some evidence would suggest that this component is the main excitatory motor mechanism at this level. Furthermore, a NK2 receptor-mediated secretory component in the human colonic mucosa has been recently demonstrated. Thus, it could be speculated that the blockade of both NK1 and NK2 receptors will be necessary to antagonise motor effects induced by exogenous administration or endogenous release of TKs in the small intestine, whereas the blockade of the NK2 receptors would be sufficient to disrupt physiological motor and, possibly, secretory activity at the colonic level. Available evidence indicates that, in healthy volunteers, the infusion of NKA (25 pmol/kg/min i.v.) stimulated small intestine motility and precipitated a series of intestinal and non-intestinal adverse events. Nepadutant (8 mg i.v.), a selective NK2 receptor antagonist, antagonised small intestine motility induced by NKA and prevented associated intestinal adverse events. In another study, the same dose of nepadutant increased colo-rectal compliance during isobaric balloon distension in healthy volunteers pretreated with a glycerol enema, disclosing a NK2 receptor-mediated component in the regulation of colonic smooth muscle tone. However, the prolonged blockade of NK2 receptors by nepadutant (16 mg i.v. b.i.d. for 8 days) did not affect bowel habits, neither in term of movements nor of stool consistency. Altogether, these results indicate that, even when there is a significant redundance in the effects of TKs and in the role of their receptors, the selective blockade of tachykinin NK2 receptors can have functional consequences on human intestinal motility and perception, but this can occur without the disruption of the physiological functions.

Differential expression of NK1 and GABAB receptors in spinal neurones projecting to antinociceptive or pronociceptive medullary centres

The balance between excitatory and inhibitory input exerted upon spinal cord neurones that belong to spinofugal pathways determines the ultimate type of information transmitted to the brain. We compared the relative expression of NK1 and GABAB receptors in two spinomedullary pathways targeting an antinociceptive area and a pronociceptive centre, respectively, the lateral part of the caudal ventrolateral medulla (VLMlat) and the dorsal reticular nucleus (DRt). Spinal cord sections of rats injected in the VLMlat or DRt with the retrograde tracer cholera toxin subunit B were triple-immunoreacted for the tracer, NK1 receptors and GABAB receptors. The dorsal horn neurones labelled from the VLMlat mainly co-localized the two receptors while those labelled from the DRt mainly expressed GABAB receptors, which was particularly evident in neurones of laminae IV-V. The morphological classification of lamina I neurones projecting to the VLMlat showed that fusiform, flattened and pyramidal cells mainly co-localized NK1 and GABAB receptors. As to lamina I neurones projecting to the DRt, multipolar neurones mainly expressed GABAB receptors while the majority of flattened and pyramidal neurones co-localized NK1 and GABAB receptors. The present results suggest that the expression of NK1 and GABAB receptors varies in neurones participating to different spinofugal pathways. The importance of the present findings in the knowledge of the endogenous supraspinal pain control system is discussed.

Regulation of the preprotachykinin-I gene promoter through a protein kinase A-dependent, cyclic AMP response element-binding protein-independent mechanism

Preprotachykinin-I (PPT) gene expression is regulated by a number of stimuli that signal through cyclic AMP (cAMP)-mediated pathways. In the present study, forskolin, an adenylyl cyclase stimulator, significantly increased PPT mRNA levels in PPT-expressing RINm5F cells, an effect paralleled by an increase in PPT promoter-luciferase reporter construct activity. The forskolin-induced stimulation of PPT transcription was protein kinase A dependent (PKA), as shown by blockade with the PKA inhibitor N-[2-(p-bromocinnamylamino) ethyl]-5-isoquinolinesulfonamide. We found that the activation protein 1/cAMP response element (AP1/CRE) site centered at -196 relative to the transcription start site was important for basal and forskolin-induced PPT promoter activity. Because of the involvement of PKA and the similarity of the AP1/CRE element to consensus CRE sequences, we investigated the role of CRE-binding protein (CREB) in the regulation of the PPT promoter. Surprisingly, overexpression of a dominant-negative CREB (i.e. CREB-A) did not affect basal or forskolin-induced PPT promoter activity. Furthermore, binding of CREB to the PPT promoter AP1/CRE site was not demonstrable in electrophoretic mobility shift assays. Rather, our experiments suggested that c-Jun is a member of the complex that binds to this site. We conclude that, at least in RINm5F cells, cAMP-mediated up-regulation of PPT gene expression does not involve CREB or CREB-related transcription factor recruitment to the AP1/CRE site.