Centrally administered hemokinin-1 (HK-1), a neurokinin NK1 receptor agonist, produces substance P-like behavioral effects in mice and gerbils

Hemokinin-1 is a mediator of chronic restraint stress-induced pain

The Tac4 gene-derived hemokinin-1 (HK-1) binds to the NK1 receptor, similarly to Substance P, and plays a role in acute stress reactions and pain transmission in mice. Here we investigated Tac4 mRNA expression in stress and pain-related regions and its involvement in chronic restraint stress-evoked behavioral changes and pain using Tac4 gene-deleted (Tac4-/-) mice compared to C57Bl/6 wildtypes (WT). Tac4 mRNA was detected by in situ hybridization RNAscope technique. Touch sensitivity was assessed by esthesiometry, cold tolerance by paw withdrawal latency from 0°C water. Anxiety was evaluated in the light-dark box (LDB) and open field test (OFT), depression-like behavior in the tail suspension test (TST). Adrenal and thymus weights were measured at the end of the experiment. We found abundant Tac4 expression in the hypothalamic-pituitary-adrenal axis, but Tac4 mRNA was also detected in the hippocampus, amygdala, somatosensory and piriform cortices in mice, and in the frontal regions and the amygdala in humans. In Tac4-/- mice of both sexes, stress-induced mechanical, but not cold hyperalgesia was significantly decreased compared to WTs. Stress-induced behavioral alterations were mild or absent in male WT animals, while significant changes of these parameters could be detected in females. Thymus weight decrease can be observed in both sexes. Higher baseline anxiety and depression-like behaviors were detected in male but not in female HK-1-deficient mice, highlighting the importance of investigating both sexes in preclinical studies. We provided the first evidence for the potent nociceptive and stress regulating effects of HK-1 in chronic restraint stress paradigm. Identification of its targets might open new perspectives for therapy of stress-induced pain.

Hemokinin-1 induces transcriptomic alterations in pain-related signaling processes in rat primary sensory neurons independent of NK1 tachykinin receptor activation

The tachykinin hemokinin-1 (HK-1) is involved in immunological processes, inflammation, and pain. Although the neurokinin 1 receptor (NK1R) is described as its main target, several effects are mediated by currently unidentified receptor(s). The role of HK-1 in pain is controversial, depending on the involvement of peripheral and central sensitization mechanisms in different models. We earlier showed the ability of HK-1 to activate the trigeminovascular system, but the mechanisms need to be clarified. Therefore, in this study, we investigated HK-1-induced transcriptomic alterations in cultured rat trigeminal ganglion (TRG) primary sensory neurons. HK-1 was applied for 6 or 24 h in 1 μM causing calcium-influx in these neurons, 500 nM not inducing calcium-entry was used for comparison. Next-generation sequencing was performed on the isolated RNA, and transcriptomic changes were analyzed to identify differentially expressed (DE) genes. Functional analysis was performed for gene annotation using the Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and Reactome databases. NK1R and Neurokinin receptor 2 (NK2R) were not detected. Neurokinin receptor 3 (NK3R) was around the detection limit, which suggests the involvement of other NKR isoforms or other receptors in HK-1-induced sensory neuronal activation. We found protease-activated receptor 1 (PAR1) and epidermal growth factor receptor (EGFR) as DE genes in calcium signaling. The transmembrane protein anthrax toxin receptor 2 (ANTXR2), a potential novel pain-related target, was upregulated. Acid-sensing ion channel 1; 3 (Asic1,3), N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptors decreased, myelin production and maintenance related genes (Mbp, Pmp2, Myef2, Mpz) and GNDF changed by HK-1 treatment. Our data showed time and dose-dependent effects of HK-1 in TRG cell culture. Result showed calcium signaling as altered event, however, we did not detect any of NK receptors. Presumably, the activation of TRG neurons is independent of NK receptors. ANTXR2 is a potential new target, PAR-1 has also important role in pain, however their connection to HK-1 is unknown. These findings might highlight new targets or key mediators to solve how HK-1 acts on TRG.

Novel Pituitary Actions of TAC4 Gene Products in Teleost

Tachykinin 4 (TAC4) is the latest member of the tachykinin family involved in several physiological functions in mammals. However, little information is available about TAC4 in teleost. In the present study, we firstly isolated TAC4 and six neurokinin receptors (NKRs) from grass carp brain and pituitary. Sequence analysis showed that grass carp TAC4 could encode two mature peptides (namely hemokinin 1 (HK1) and hemokinin 2 (HK2)), in which HK2 retained the typical FXGLM motif in C-terminal of tachyinin, while HK1 contained a mutant VFGLM motif. The ligand-receptor selectivity showed that HK2 could activate all 6 NKRs but with the highest activity for the neurokinin receptor 2 (NK2R). Interestingly, HK1 displayed a very weak activation for each NKR isoform. In grass carp pituitary cells, HK2 could induce prolactin (PRL), somatolactin α (SLα), urotensin 1 (UTS1), neuromedin-B 1 (NMB1), cocaine- and amphetamine-regulated transcript 2 (CART2) mRNA expression mediated by NK2R and neurokinin receptor 3 (NK3R) via activation cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA), phospholipase C (PLC)/inositol 1,4,5-triphosphate (IP3)/protein kinase C (PKC) and calcium²⁺ (Ca²⁺)/calmodulin (CaM)/calmodulin kinase-II (CaMK II) cascades. However, the corresponding stimulatory effects triggered by HK1 were found to be notably weaker. Furthermore, based on the structural base for HK1, our data suggested that a phenylalanine (F) to valine (V) substitution in the signature motif of HK1 might have contributed to its weak agonistic actions on NKRs and pituitary genes regulation.

Hemokinin-1 Gene Expression Is Upregulated in Trigeminal Ganglia in an Inflammatory Orofacial Pain Model: Potential Role in Peripheral Sensitization

A large percentage of primary sensory neurons in the trigeminal ganglia (TG) contain neuropeptides such as tachykinins or calcitonin gene-related peptide. Neuropeptides released from the central terminals of primary afferents sensitize the secondary nociceptive neurons in the trigeminal nucleus caudalis (TNC), but also activate glial cells contributing to neuroinflammation and consequent sensitization in chronic orofacial pain and migraine. In the present study, we investigated the newest member of the tachykinin family, hemokinin-1 (HK-1) encoded by the Tac4 gene in the trigeminal system. HK-1 had been shown to participate in inflammation and hyperalgesia in various models, but its role has not been investigated in orofacial pain or headache. In the complete Freund’s adjuvant (CFA)-induced inflammatory orofacial pain model, we showed that Tac4 expression increased in the TG in response to inflammation. Duration-dependent Tac4 upregulation was associated with the extent of the facial allodynia. Tac4 was detected in both TG neurons and satellite glial cells (SGC) by the ultrasensitive RNAscope in situ hybridization. We also compared gene expression changes of selected neuronal and glial sensitization and neuroinflammation markers between wild-type and Tac4-deficient (Tac4^-/-) mice. Expression of the SGC/astrocyte marker in the TG and TNC was significantly lower in intact and saline/CFA-treated Tac4^-/- mice. The procedural stress-related increase of the SGC/astrocyte marker was also strongly attenuated in Tac4^-/- mice. Analysis of TG samples with a mouse neuroinflammation panel of 770 genes revealed that regulation of microglia and cytotoxic cell-related genes were significantly different in saline-treated Tac4^-/- mice compared to their wild-types. It is concluded that HK-1 may participate in neuron-glia interactions both under physiological and inflammatory conditions and mediate pain in the trigeminal system.

Sensory neuropeptides are required for bone and cartilage homeostasis in a murine destabilization-induced osteoarthritis model

Numerous studies identified a role for the sensory neuropeptides substance P (SP) and alpha calcitonin gene-related peptide (αCGRP) in osteoarthritis (OA) pain behavior. Surprisingly, little attention has been paid on how their trophic effects on cartilage and bone cells might affect structural changes of bone and cartilage in OA pathology. Here, we sought to elucidate sensory neuropeptides influence on structural alterations of bone and cartilage during murine OA pathophysiology. OA was induced by destabilization of the medial meniscus (DMM) in the right knee joint of 12 weeks old male C57Bl/6J wildtype (WT) mice and mice either deficient for SP (tachykinin 1 (Tac1)-/-) or αCGRP. By OARSI histopathological grading we observed significant cartilage matrix degradation after DMM surgery in αCGRP-deficient mice after 4 weeks whereas Tac1-/- scores were not different to sham mice before 12 weeks after surgery. Indentation-type atomic force microscopy (IT-AFM) identified a strong superficial zone (SZ) cartilage phenotype in Tac1-/- Sham mice. Opposed to WT and αCGRP-/- mice, SZ cartilage of Tac1-/- mice softened 2 weeks after OA induction. In Tac1-/- DMM mice, bone volume to total volume ratio (BV/TV) increased significantly compared to the Tac1-/- Sham group, 2 weeks after surgery. WT mice had reduced BV/TV compared to αCGRP-/- and Tac1-/- mice after 12 weeks. Increased calcified cartilage thickness and medial condyle diameter were detected in the medial tibia of all groups 8 weeks after OA induction by nanoCT analysis. Meniscal ossification occurred in all OA groups, but was significantly stronger in the absence of neuropeptides. Increased serum concentration of the respective non-deleted neuropeptide was observed in both neuropeptide-deficient mice strains. Both neuropeptides protect from age-related bone structural changes under physiological conditions and SP additionally demonstrates an anabolic effect on bone structure preservation in a pathophysiological situation. Both neuropeptide deficient mice display an intrinsic structural cartilage matrix phenotype that might alter progression of cartilage degeneration in OA.

Hemokinin-1 is an important mediator of pain in mouse models of neuropathic and inflammatory mechanisms

The Tac4 gene-derived hemokinin-1 (HK-1) is present in pain-related regions and activates the tachykinin NK1 receptor, but with binding site and signaling pathways different from Substance P (SP). NK1 receptor is involved in nociception, but our earlier data showed that it has no role in chronic neuropathic hyperalgesia, similarly to SP. Furthermore, NK1 antagonists failed in clinical trials as analgesics due to still unknown reasons. Therefore, we investigated the role of HK-1 in pain conditions of distinct mechanisms using genetically modified mice. Chronic neuropathic mechanical and cold hyperalgesia after partial sciatic nerve ligation (PSL) were determined by dynamic plantar aesthesiometry and withdrawal latency from icy water, motor coordination on the accelerating Rotarod. Peripheral nerve growth factor (NGF) production was measured by ELISA, neuronal and glia cell activation by immunohistochemistry in pain-related regions. Acute somatic and visceral chemonocifensive behaviors were assessed after intraplantar formalin or intraperitoneal acetic-acid injection, respectively. Resiniferatoxin-induced inflammatory mechanical and thermal hyperalgesia by aesthesiometry and increasing temperature hot plate. Chronic neuropathic mechanical and cold hypersensitivity were significantly decreased in HK-1 deficient mice. NGF level in the paw homogenates of intact mice were significantly lower in case of HK-1 deletion. However, it significantly increased under neuropathic condition in contrast to wildtype mice, where the higher basal concentration did not show any changes. Microglia, but not astrocyte activation was observed 14 days after PSL in the ipsilateral spinal dorsal horn of wildtype, but not HK-1-deficient mice. However, under neuropathic conditions, the number of GFAP-positive astrocytes was significantly smaller in case of HK-1 deletion. Acute visceral, but not somatic nocifensive behavior, as well as neurogenic inflammatory mechanical and thermal hypersensitivity were significantly reduced by HK-1 deficiency similarly to NK1, but not to SP deletion. We provide evidence for pro-nociceptive role of HK-1, via NK1 receptor activation in acute inflammation models, but differently from SP-mediated actions. Identification of its targets and signaling can open new directions in pain research.

Mouse Hemokinin-1 Decapeptide Subjected to a Brain-specific Post-translational Modification

BACKGROUND/AIM

The tachykinin mouse hemokinin-1, expressed by the mouse Tac4 gene, produces either analgesia or nociception, interacting with the neurokinin 1 receptor. TAC4 precursor processing is not identical to the processing of the TAC1 precursor, for the release of substance P (amidated undecapeptide). The characterization of the mouse hemokinin-1 sequence was required.

MATERIALS AND METHODS

We developed anti-tachykinin-specific antibodies for the immunoaffinity purification of tachykinins.

RESULTS

Using MALDI-ToF, we identified mouse hemokinin-1 as an amidated decapeptide expressed in murine brain and periphery. Furthermore, we interestingly observed an additional mass peak corresponding to acetylated mouse hemokinin-1 and this post-translational modification is brain-specific, not detected in the periphery.

CONCLUSION

We suggest that the N-terminal acetylation of the peptide provides greater potency for ligand-receptor interactions during neural cell signaling.

Role of hemokinin-1 in health and disease

Hemokinin-1 (HK-1), the newest tachykinin encoded by the Tac4 gene was discovered in 2000. Its name differs from that of the other members of this peptide family due to its first demonstration in B lymphocytes. Since tachykinins are classically found in the nervous system, the significant expression of HK-1 in blood cells is a unique feature of this peptide. Due to its widespread distribution in the whole body, HK-1 is involved in different physiological and pathophysiological functions involving pain inflammation modulation, immune regulation, respiratory and endocrine functions, as well as tumor genesis. Furthermore, despite the great structural and immunological similarities to substance P (SP), the functions of HK-1 are often different or the opposite. They both have the highest affinity to the tachykinin NK1 receptor, but HK-1 is likely to have a distinct binding site and signalling pathways. Moreover, several actions of HK-1 different from SP have been suggested to be mediated via a presently not identified own receptor/target molecule. Therefore, it is very important to explore its effects at different levels and compare its characteristics with SP to get a deeper insight in the different cellular mechanisms. Since HK-1 has recently been in the focus of intensive research, in the present review we summarize the few clinical data and experimental results regarding HK-1 expression and function in different model systems obtained throughout the 16years of its history. Synthesizing these findings help to understand the complexity of HK-1 actions and determine its biomarker values and/or drug development potentials.

Distribution of hemokinin-1 in the rat trigeminal ganglion and trigeminal sensory nuclear complex

OBJECTIVE

A new mammalian tachykinin peptide encoded in a TAC4 gene was identified and designated as hemokinin-1 (HK-1). A representative of the tachykinin peptide family is substance P (SP), and the function of SP has been well characterized as a pain transmitter or modulator, while it is possible that HK-1 is involved in pruriceptive processing, but, as yet, the distribution of HK-1 peptide in the trigeminal sensory system is still unknown. Thus, the aim of the present study was to elucidate the distribution of HK-1, while comparing the expression of SP, in the trigeminal ganglion and trigeminal sensory nuclear complex.

DESIGN

The trigeminal ganglion and the brain stem of male SD rats were used in the immunohistochemical study. Since the amino acid sequence in the carboxyl-terminal regions of HK-1 and SP is common, polyclonal antibodies of HK-1 and SP derived from 6 amino acids consisting of amino-terminal regions of these peptides were produced in guinea pig and rabbit, respectively. The immunohistochemical staining of HK-1 and SP was conducted using frozen sections of the trigeminal ganglion and brain stem in rats.

RESULTS

Immunohistochemical studies revealed the expression of HK-1 in small- and medium-sized trigeminal ganglion neurons, in the paratrigeminal nucleus, and in lamina I of the trigeminal nucleus caudalis, while there was no immunoreactivity of HK-1 in the trigeminal nucleus principalis, trigeminal nucleus oralis, and trigeminal nucleus interpolaris.

CONCLUSION

These findings indicate that HK-1 is a target molecule for treatment of itch in the orofaicial regions.

Hemokinin-1 mediates anxiolytic and anti-depressant-like actions in mice

The tachykinin NK1 receptor was suggested to be involved in psychiatric disorders, but its antagonists have failed to be effective as antidepressants in clinical trials. Hemokinin-1 (HK-1), the newest tachykinin, is present in several brain regions and activates the NK1 receptor similarly to substance P (SP), but acts also through other mechanisms. Therefore, we investigated the roles of the Tac4 gene-derived HK-1 in comparison with SP and neurokinin A (NKA) encoded by the Tac1 gene, as well as the NK1 receptor in anxiety and depression-like behaviors in mice. Mice lacking SP/NKA, HK-1 or the NK1 receptor (Tac1^-/-, Tac4^-/-, Tacr1^-/-, respectively) compared to C57Bl/6 wildtypes (WT), and treatment with the NK1 antagonist CP99994 were used in the experiments. Anxiety was evaluated in the light-dark box (LDB) and the elevated plus maze (EPM), locomotor activity in the open field (OFT) tests. Hedonic behavior was assessed in the sucrose preference test (SPT), depression-like behavior in the tail suspension (TST) and forced swim (FST) tests. FST-induced neuronal responsiveness was evaluated with Fos immunohistochemistry in several stress-related brain regions. In the LDB, Tac4^-/- mice spent significantly less, while Tacr1^-/- and CP99994-treated mice spent significantly more time in the lit compartment. In the EPM only Tac4^-/- showed reduced time in the open arms, but no difference was observed in any other groups. In the OFT Tac4^-/- mice showed significantly reduced, while Tac1^-/- and Tacr1^-/- animals increased motility than the WTs, but CP99994 had no effect. NK1^-/- consumed markedly more, while Tac4^-/- less sucrose solution compared to WTs. In the TST and FST, Tac4^-/- mice showed significantly increased immobility. However, depression-like behavior was decreased both in cases of genetic deletion and pharmacological blockade of the NK1 receptor. FST-induced neuronal activation in different nuclei involved in behavioral and neuroendocrine stress responses was significantly reduced in the brain of Tac4 ^-/- mice. Our results provide the first evidence for an anxiolytic and anti-depressant-like actions of HK-1 through a presently unknown target-mediated mechanism. Identification of its receptor and/or signaling pathways might open new perspectives for anxiolytic and anti-depressant therapies.

Changes in the disposition of substance P in the rostral ventromedial medulla after inflammatory injury in the rat

This study examined whether peripheral inflammatory injury increases the levels or changes the disposition of substance P (SubP) in the rostral ventromedial medulla (RVM), which serves as a central relay in bulbospinal pathways of pain modulation. Enzyme immunoassay and reverse transcriptase quantitative polymerase chain reaction were used to measure SubP protein and transcript, respectively, in tissue homogenates prepared from the RVM and the periaqueductal gray (PAG) and cuneiform nuclei of rats that had received an intraplantar injection of saline or complete Freund's adjuvant (CFA). Matrix-Assisted Laser Desorption/Ionization Time of Flight analysis confirmed that the RVM does not contain hemokinin-1 (HK-1), which can confound measurements of SubP because it is recognized equally well by commercial antibodies for SubP. Levels of SubP protein in the RVM were unchanged four hours, four days and two weeks after injection of CFA. Tac1 transcripts were similarly unchanged in the RVM four days or two weeks after CFA. In contrast, the density of SubP immunoreactive processes in the RVM increased 2-fold within four hours and 2.7-fold four days after CFA injection; it was unchanged at two weeks. SubP-immunoreactive processes in the RVM include axon terminals of neurons located in the PAG and cuneiform nucleus. SubP content in homogenates of the PAG and cuneiform nucleus was significantly increased four days after CFA, but not at four hours or two weeks. Tac1 transcripts in homogenates of these nuclei were unchanged four days and two weeks after CFA. These findings suggest that there is an increased mobilization of SubP within processes in the RVM shortly after injury accompanied by an increased synthesis of SubP in neurons that project to the RVM. These findings are consonant with the hypothesis that an increase in SubP release in the RVM contributes to the hyperalgesia that develops after peripheral inflammatory injury.

Neuropeptide receptors as potential drug targets in the treatment of inflammatory conditions

Cross-talk between the nervous, endocrine and immune systems exists via regulator molecules, such as neuropeptides, hormones and cytokines. A number of neuropeptides have been implicated in the genesis of inflammation, such as tachykinins and calcitonin gene-related peptide. Development of their receptor antagonists could be a promising approach to anti-inflammatory pharmacotherapy. Anti-inflammatory neuropeptides, such as vasoactive intestinal peptide, pituitary adenylate cyclase-activating polypeptide, α-melanocyte-stimulating hormone, urocortin, adrenomedullin, somatostatin, cortistatin, ghrelin, galanin and opioid peptides, are also released and act on their own receptors on the neurons as well as on different inflammatory and immune cells. The aim of the present review is to summarize the most prominent data of preclinical animal studies concerning the main pharmacological effects of ligands acting on the neuropeptide receptors. Promising therapeutic impacts of these compounds as potential candidates for the development of novel types of anti-inflammatory drugs are also discussed.

Hemokinin-1 is an important mediator of endotoxin-induced acute airway inflammation in the mouse

OBJECTIVE

Hemokinin-1, the newest tachykinin encoded by the preprotachykinin C (Tac4) gene, is predominatly produced by immune cells. Similarly to substance P, it has the greatest affinity to the tachykinin NK1 receptor, but has different binding site and signaling mechanisms. Furthermore, several recent data indicate the existence of a not yet identified own receptor and divergent non-NK1-mediated actions. Since there is no information on its functions in the airways, we investigated its role in endotoxin-induced pulmonary inflammation.

METHODS

Acute pneumonitis was induced in Tac4 gene-deleted (Tac4(-/-)) mice compared to C57Bl/6 wildtypes by intranasal E. coli lipopolysaccharide (LPS). Airway responsiveness to inhaled carbachol was measured with unrestrained whole body plethysmography 24h later. Semiquantitative histopathological scoring was performed; reactive oxygen species (ROS) production was measured with luminol bioluminescence, myeloperoxidase activity with spectrophotometry, and inflammatory cytokines with Luminex.

RESULTS

All inflammatory parameters, such as histopathological alterations (perivascular edema, neutrophil/macrophage accumulation, goblet cell hyperplasia), myeloperoxidase activity, ROS production, as well as interleukin-1beta, interleukin-6, tumor necrosis factor alpha, monocyte chemoattractant protein-1 and keratinocyte chemoattractant concentrations were significantly diminished in the lung of Tac4(-/-) mice. However, bronchial hyperreactivity similarly developed in both groups. Interestingly, in LPS-treated Tac4(-/-) mouse lungs, bronchus-associated, large, follicle-like lymphoid structures developed.

CONCLUSIONS

We provide the first evidence that hemokinin-1 plays a crucial pro-inflammatory role in the lung by increasing inflammatory cell activities, and might also be a specific regulator of lymphocyte functions.

Tachykinin peptide, substance P, and its receptor NK-1R play an important role in alimentary tract mucosal inflammation during cytotoxic therapy

The alimentary tract mucosal inflammation has been a topic of concern in oncology; though many modalities of treatment have been proposed for mucosal inflammation, the contributing adverse effects have severely affected the quality of life of patients. This review focuses on the importance of neurogenic peptide, Substance P and its receptor NK-1R in modulating the cascades of events in mucosal inflammation during cytotoxic therapy. There are various preclinical and clinical models showing increased expression of Substance P/NK-1R in ionizing radiation and chemotherapy, but only very few preclinical studies to our knowledge have highlighted or examined its role in mucosal inflammation. Hence, the importance of neuropeptide involved in the inflammatory events in mucosal inflammation in cytotoxic therapy could be a major breakthrough for future research purposes and treatment. The factors contributing to the severity of tissue reactions have been multietiogenic; thus, resultant treatment also has to be directed toward multiple contributing factors. This review also focuses on the significance of care strategy to be adopted in alimentary tract mucositis when multietiogenic factors are taken into consideration.

Neuropeptides in learning and memory

Dementia conditions and memory deficits of different origins (vascular, metabolic and primary neurodegenerative such as Alzheimer's and Parkinson's diseases) are getting more common and greater clinical problems recently in the aging population. Since the presently available cognitive enhancers have very limited therapeutical applications, there is an emerging need to elucidate the complex pathophysiological mechanisms, identify key mediators and novel targets for future drug development. Neuropeptides are widely distributed in brain regions responsible for learning and memory processes with special emphasis on the hippocampus, amygdala and the basal forebrain. They form networks with each other, and also have complex interactions with the cholinergic, glutamatergic, dopaminergic and GABA-ergic pathways. This review summarizes the extensive experimental data in the well-established rat and mouse models, as well as the few clinical results regarding the expression and the roles of the tachykinin system, somatostatin and the closely related cortistatin, vasoactive intestinal polypeptide (VIP) and pituitary adenylate-cyclase activating polypeptide (PACAP), calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY), opioid peptides and galanin. Furthermore, the main receptorial targets, mechanisms and interactions are described in order to highlight the possible therapeutical potentials. Agents not only symptomatically improving the functional impairments, but also inhibiting the progression of the neurodegenerative processes would be breakthroughs in this area. The most promising mechanisms determined at the level of exploratory investigations in animal models of cognitive disfunctions are somatostatin sst4, NPY Y2, PACAP-VIP VPAC1, tachykinin NK3 and galanin GALR2 receptor agonisms, as well as delta opioid receptor antagonism. Potent and selective non-peptide ligands with good CNS penetration are needed for further characterization of these molecular pathways to complete the preclinical studies and decide if any of the above described targets could be appropriate for clinical investigations.

Hemokinin-1 competitively inhibits substance P-induced stimulation of osteoclast formation and function

Hemokinin-1 (HK-1) is a novel member of the tachykinin family that is encoded by preprotachykinin 4 (TAC4) and shares the neurokinin-1 receptor (NK1-R) with substance P (SP). Although HK-1 is thought to be an endogenous peripheral SP-like endocrine or paracrine molecule in locations where SP is not expressed, neither the distribution of HK-1 in the maxillofacial area nor the role HK-1 in bone tissue have been examined. In this study, we investigated the distribution of HK-1 in trigeminal ganglion (TG) and maxillary bone, and assessed the expression of HK-1 during osteoclast differentiation. In vivo, rat molars were loaded for 5 days using the Waldo method. In vitro, rat osteoclast-like cells were induced from bone marrow cells. HK-1 distribution and expression were examined by immunofluorescence staining and reverse transcription polymerase chain reaction (RT-PCR). In vivo, HK-1 was localized in rat TG neurons; however, the number of HK-1-positive neurons was less than that of SP-positive neurons. In the maxillary bone, nerve fibers, blood vessels, and osteocytes were immunopositive for HK-1. Furthermore, HK-1-positive immunoreactivity was found in osteoclasts on the pressure side. In vitro, PCR showed that TAC4 and NK1-R mRNA was expressed in osteoclasts as well as in bone marrow cells. Although SP (10⁻⁷ M) treatment led to an increased number of osteoclasts, HK-1 (10⁻⁷ M) treatment did not. The numbers of biotin-labeled HK-1 peptides bound osteoclasts significantly decreased upon incubation with unlabeled SP and biotin-labeled HK-1 compared with biotin-labeled HK-1 alone. These results suggest that HK-1 may not stimulate the differentiation and function of osteoclasts. SP-stimulated osteoclast formation is competitively regulated by peripheral HK-1 through NK1-Rs.

Study on the distribution sites and the molecular mechanism of analgesia after intracerebroventricular injection of rat/mouse hemokinin-1 in mice

Hemokinin-1 is a peptide encoded by Pptc, which belongs to the family of mammalian tachykinins. Our previous results showed that rat/mouse hemokinin-1 (r/m HK-1) produced striking analgesia after intracerebroventricular (i.c.v.) injection in mice, and the analgesia could be blocked by the NK1 receptor antagonist and the opioid receptor antagonist, respectively. However, the precise distribution sites and the molecular mechanism involved in the analgesic effect after i.c.v. administration of r/m HK-1 are needed to be further investigated deeply. Using the fluorescence labeling method, our present results directly showed that r/m HK-1 peptides were mainly distributed at the ventricular walls and several juxta-ventricular structures for the first time. Our results showed that the mRNA expressions of NK1 receptor, PPT-A, PPT-C, KOR, PDYN, DOR and PENK were not changed markedly, as well as the protein expression of NK1 receptor was hardly changed. However, both the transcripts and proteins of MOR and POMC were up-regulated significantly, indicating that the analgesic effect induced by i.c.v. administration of r/m HK-1 is related to the activation of NK1 receptor first, then it is related to the release of endogenous proopiomelanocortin, as well as the increased expression level of μ opioid receptor. These results should facilitate further the analysis of the analgesia of r/m HK-1 in the central nerval system in acute pain and may open novel pharmacological interventions.

Role of tachykinin 1 and 4 gene-derived neuropeptides and the neurokinin 1 receptor in adjuvant-induced chronic arthritis of the mouse

Objective

Substance P, encoded by the Tac1 gene, is involved in neurogenic inflammation and hyperalgesia via neurokinin 1 (NK1) receptor activation. Its non-neuronal counterpart, hemokinin-1, which is derived from the Tac4 gene, is also a potent NK1 agonist. Although hemokinin-1 has been described as a tachykinin of distinct origin and function compared to SP, its role in inflammatory and pain processes has not yet been elucidated in such detail. In this study, we analysed the involvement of tachykinins derived from the Tac1 and Tac4 genes, as well as the NK1 receptor in chronic arthritis of the mouse.

Methods

Complete Freund’s Adjuvant was injected intraplantarly and into the tail of Tac1^−/−, Tac4^−/−, Tacr1^−/− (NK1 receptor deficient) and Tac1^−/−/Tac4^−/− mice. Paw volume was measured by plethysmometry and mechanosensitivity using dynamic plantar aesthesiometry over a time period of 21 days. Semiquantitative histopathological scoring and ELISA measurement of IL-1β concentrations of the tibiotarsal joints were performed.

Results

Mechanical hyperalgesia was significantly reduced from day 11 in Tac4^−/− and Tacr1^−/− animals, while paw swelling was not altered in any strain. Inflammatory histopathological alterations (synovial swelling, leukocyte infiltration, cartilage destruction, bone damage) and IL-1β concentration in the joint homogenates were significantly smaller in Tac4^−/− and Tac1^−/−/Tac4^−/− mice.

Conclusions

Hemokinin-1, but not substance P increases inflammation and hyperalgesia in the late phase of adjuvant-induced arthritis. While NK1 receptors mediate its antihyperalgesic actions, the involvement of another receptor in histopathological changes and IL-1β production is suggested.

In vitro and in vivo pharmacological characterization of the novel NK₁ receptor selective antagonist Netupitant

The novel NK(1) receptor ligand Netupitant has been characterized in vitro and in vivo. In calcium mobilization studies CHO cells expressing the human NK receptors responded to a panel of agonists with the expected order of potency. In CHO NK(1) cells Netupitant concentration-dependently antagonized the stimulatory effects of substance P (SP) showing insurmountable antagonism (pK(B) 8.87). In cells expressing NK(2) or NK(3) receptors Netupitant was inactive. In the guinea pig ileum Netupitant concentration-dependently depressed the maximal response to SP (pK(B) 7.85) and, in functional washout experiments, displayed persistent (up to 5h) antagonist effects. In mice the intrathecal injection of SP elicited the typical scratching, biting and licking response that was dose-dependently inhibited by Netupitant given intraperitoneally in the 1-10mg/kg dose range. In gerbils, foot tapping behavior evoked by the intracerebroventricular injection of a NK(1) agonist was dose-dependently counteracted by Netupitant given intraperitoneally (ID(50) 1.5mg/kg) or orally (ID(50) 0.5mg/kg). In time course experiments in gerbils Netupitant displayed long lasting effects. In all the assays Aprepitant elicited similar effects as Netupitant. These results suggest that Netupitant behaves as a brain penetrant, orally active, potent and selective NK(1) antagonist. Thus this molecule can be useful for investigating the NK(1) receptor role in the control of central and peripheral functions. Netupitant has clinical potential in conditions such as chemotherapy induced nausea and vomiting, in which the blockade of NK(1) receptors has been demonstrated valuable for patients.

Hemokinins modulate endothelium function and promote angiogenesis through neurokinin-1 receptor

Substance P as a member of tachykinin family plays an important role in angiogenesis. Hemokinins (HKs) have been identified as new members of substance P-like peptides of tachykinin family. However, the effects of HKs on endothelial cells and angiogenesis have not been studied. For the first time, here we demonstrated that r/mHK-1, hHK-1 and hHK(4-11) dose-dependently stimulated the proliferation, migration, adhesion and tube formation of freshly isolated human umbilical vein endothelial cells (HUVECs), and further exhibited in vivo angiogenic effects in chick embryo chorioallantoic membrane model. The angiogenic effects of HKs were inhibited by the selective antagonist of neurokinin-1 rather than neurokinin-2 receptor. Mechanistically, HKs activated ERK1/2 phosphorylation, stimulated nitric oxide production, and upregulated the expression of endothelial nitric oxide synthase (eNOS) and vascular endothelial growth factor (VEGF) in HUVECs. Taken together, our data suggest that HKs emerge as pivotal endogenous regulators of angiogenesis and represent potential targets for the intervention of angiogenesis in different pathological conditions given their specific peripheral distribution.

Hemokinin-1 gene expression is upregulated in microglia activated by lipopolysaccharide through NF-κB and p38 MAPK signaling pathways

The mammalian tachykinins, substance P (SP) and hemokinin-1 (HK-1), are widely distributed throughout the nervous system and/or peripheral organs, and function as neurotransmitters or chemical modulators by activating their cognate receptor NK(1). The TAC1 gene encoding SP is highly expressed in the nervous system, while the TAC4 gene encoding HK-1 is uniformly expressed throughout the body, including a variety of peripheral immune cells. Since TAC4 mRNA is also expressed in microglia, the resident immune cells in the central nervous system, HK-1 may be involved in the inflammatory processes mediated by these cells. In the present study, we found that TAC4, rather than TAC1, was the predominant tachykinin gene expressed in primary cultured microglia. TAC4 mRNA expression was upregulated in the microglia upon their activation by lipopolysaccharide, a well-characterized Toll-like receptor 4 agonist, while TAC1 mRNA expression was downregulated. Furthermore, both nuclear factor-κB and p38 mitogen-activated protein kinase intracellular signaling pathways were required for the upregulation of TAC4 mRNA expression, but not for the downregulation of TAC1 mRNA expression. These findings suggest that HK-1, rather than SP, plays dominant roles in the pathological conditions associated with microglial activation, such as neurodegenerative and neuroinflammatory disorders.

The N-terminal domain of human hemokinin-1 influences functional selectivity property for tachykinin receptor neurokinin-1

Human hemokinin-1 (hHK-1) is a substance P-like tachykinin peptide preferentially expressed in non-neuronal tissues. It is involved in multiple physiological functions such as inflammation, hematopoietic cells development and vasodilatation via the interaction with tachykinin receptor neurokinin-1 (NK1). To further understand the intracellular signal transduction mechanism under such functional multiplicity, current study was focused on the differential activation of Gs and Gq pathways by hHK-1 and its C-terminal fragments, which is termed as functional selectivity. We demonstrated these hHK-1 and related peptide fragments can independently activate Gs and Gq pathways, showing a relative bias toward Gq over Gs pathway. The T1, K3 and Q6 of hHK-1 might play roles in the activation of adenylate cyclase mediated by Gs, while having negligible effect on Gq mediated intracellular calcium release. The stepwise truncation of N-terminal amino acid of hHK-1 caused gradual decrease in ERK1/2 phosphorylation level and NF-κB activity. However, it had little influence on the induction of NK1 receptor desensitization and internalization. Taken together these data support that hHK-1 and its C-terminal fragments are human NK1 receptor agonists with different functional selectivity properties and that such functional selectivity leads to differential activation of downstream signaling and receptor trafficking.

Early B-cell factor regulates the expression of Hemokinin-1 in the olfactory epithelium and differentiating B lymphocytes

Hemokinin-1, encoded by the TAC4 gene, is a tachykinin most closely related to substance P. Previous studies have shown that TAC4 distinguishes itself from other tachykinins by its predominantly non-neuronal expression profile, particularly in cells of the immune system. Here we report for the first time that the highest levels of TAC4 expression are found in the olfactory epithelium. Furthermore, we identify olfactory neuron-specific transcription factor (Olf-1), also known as early B-cell factor (EBF), as a novel regulator of TAC4 expression. EBF present in the olfactory epithelium and in B cells binds to two sites in the TAC4 promoter and modulates expression in developing B cells. Our findings suggest a role for TAC4 in cell differentiation, and represent a regulatory bridge between the nervous system and the immune system.

Expression and function of human hemokinin-1 in human and guinea pig airways

Background

Human hemokinin-1 (hHK-1) and endokinins are peptides of the tachykinin family encoded by the TAC4 gene. TAC4 and hHK-1 expression as well as effects of hHK-1 in the lung and airways remain however unknown and were explored in this study.

Methods

RT-PCR analysis was performed on human bronchi to assess expression of tachykinin and tachykinin receptors genes. Enzyme immunoassay was used to quantify hHK-1, and effects of hHK-1 and endokinins on contraction of human and guinea pig airways were then evaluated, as well as the role of hHK-1 on cytokines production by human lung parenchyma or bronchi explants and by lung macrophages.

Results

In human bronchi, expression of the genes that encode for hHK-1, tachykinin NK₁-and NK₂-receptors was demonstrated. hHK-1 protein was found in supernatants from explants of human bronchi, lung parenchyma and lung macrophages. Exogenous hHK-1 caused a contractile response in human bronchi mainly through the activation of NK₂-receptors, which blockade unmasked a NK₁-receptor involvement, subject to a rapid desensitization. In the guinea pig trachea, hHK-1 caused a concentration-dependant contraction mainly mediated through the activation of NK₁-receptors. Endokinin A/B exerted similar effects to hHK-1 on both human bronchi and guinea pig trachea, whereas endokinins C and D were inactive. hHK-1 had no impact on the production of cytokines by explants of human bronchi or lung parenchyma, or by human lung macrophages.

Conclusions

We demonstrate endogenous expression of TAC4 in human bronchi, the encoded peptide hHK-1 being expressed and involved in contraction of human and guinea pig airways.

Effects of rat/mouse hemokinin-1, human hemokinin-1 and human hemokinin-1(4-11), mammalian tachykinin peptides, on rate and perfusion pressure in the isolated guinea pig heart

Rat/mouse hemokinin-1 (r/m HK-1), human hemokinin-1 (h HK-1) and human hemokinin-1(4-11) (h HK-1(4-11)) are members of the tachykinin family. In the present study, the coronary vascular activities and cardiac functions of r/m HK-1, h HK-1 and h HK-1(4-11) were investigated in isolated, spontaneously beating guinea pig hearts. Bolus injections of r/m HK-1 caused decrease in perfusion pressure indicative of coronary vasodilation, which was primarily due to the action on tachykinin NK1 receptors on vascular endothelial cells, causing the release of nitric oxide that relaxed the coronary vessels. H HK-1 caused biphasic perfusion pressure changes that were coronary vasodilation followed by coronary vasoconstriction. The mechanisms involved in the vasodilation induced by h HK-1 were similar to that of r/m HK-1 while the mechanisms for coronary vasoconstriction were mediated through the activation of tachykinin NK2 receptors on coronary sympathetic neurons to release catecholamines. H HK-1(4-11) only produced coronary vasoconstriction and the mechanisms involved in this effect were similar to that of h HK-1 in vasoconstriction. Moreover, r/m HK-1 and h HK-1 produced similar decreases in heart rate indicative of negative chronotropic responses and the decreases were mainly mediated through the activation of tachykinin NK1 receptors to release ACh acting on muscarinic receptors. H HK-1(4-11) also produced negative chronotropic response, which was mainly mediated through tachykinin NK2 receptors and muscarinic receptors. Our present results provide evidence that all of the three tachykinins could influence cardiac function and coronary vascular activity in the isolated guinea pig heart.

Characterization of intrathecally administered hemokinin-1-induced nociceptive behaviors in mice

Hemokinin-1 is a novel mammalian tachykinin cloned from mouse bone marrow. At present, pharmacological profile and physiological role of hemokinin-1 are still unclear. In the present study, we found that intrathecal (i.t.) administration of hemokinin-1 (0.00625-1.6 nmol) induced nociceptive responses consisting of scratching, biting and licking, which resemble substance P-induced behavioral responses in mice. The behaviors evoked by low-dose of hemokinin-1 (0.0125 nmol) were dose-dependently inhibited by i.t. co-administration of CP-99,994, a non-peptidic tachykinin NK(1) receptor antagonist, whereas high-dose of hemokinin-1 (0.1 nmol)-induced behaviors were not affected. Moreover, sendide, a peptidic tachykinin NK(1) receptor antagonist, failed to reduce the behavioral responses of both low- and high-dose of hemokinin-1. In contrast, substance P-induced behaviors were completely suppressed by both CP-99,994 and sendide. These results suggest that hemokinin-1 plays an important role in pain transmission at spinal cord. Moreover, the mechanism of hemokinin-1-induced nociceptive behaviors may be dose-dependent, and distinct from substance P-induced nociceptive behaviors.

Targeted deletion of the tachykinin 4 gene (TAC4-/-) influences the early stages of B lymphocyte development

Hemokinin-1 (HK-1), encoded by the TAC4 gene, is a tachykinin peptide that is predominantly expressed in non-neuronal cells, such as immune cells. We have disrupted the mouse TAC4 gene to obtain a better understanding of the actions of HK-1 during hematopoiesis. We demonstrate here that TAC4(-/-) mice exhibit an increase of CD19(+)CD117(+)HSA(+)BP.1(-) "fraction B" pro-B cells in the bone marrow, whereas pre-B, immature, and mature B cells are within the normal range. We show that in vitro cultures derived from TAC4(-/-) bone marrow, sorted "fraction B" pro-B cells or purified long-term reconstituting stem cells, contain significantly higher numbers of pro-B cells compared with controls, suggesting an inhibitory role for HK-1 on developing B cells. Supporting this idea, we show that addition of HK-1 to cultures established from long-term reconstituting stem cells and the newly described intermediate-term reconstituting stem cells leads to a significant decrease of de novo generated pro-B cells. Based on our studies, we postulate that HK-1 plays an inhibitory role in hematopoiesis, and we hypothesize that it may be part of the bone marrow microenvironment that supports and regulates the proliferation and differentiation of hematopoietic cells.

The amino-terminal region of hemokinin-1 regulates the induction of thermal hyperalgesia in rats

It is known that intrathecal administration of substance P (SP) induces thermal hyperalgesia, whereas hemokinin-1 (HK-1), a member of the same tachykinin family as SP, hardly induces thermal hyperalgesia; however, the underlying mechanism remains to be elucidated. Therefore, we aimed to clarify which amino acid of these peptides contributes to the induction of thermal hyperalgesia. When two chimera peptides between the N-terminal region of SP and the C-terminal region of HK-1, and vice versa, SP (1-5)/HK-1 and HK-1 (1-5)/SP, were intrathecally administered, SP (1-5)/HK-1 induced thermal hyperalgesia whereas HK-1 (1-5)/SP had hardly any effect; furthermore, thermal hyperalgesia was induced by only C-terminal fragments of HK-1 and SP. These findings indicate that the N-terminal region of HK-1 is involved in the non-induction of thermal hyperalgesia. Next, we synthesized and intrathecally administered these chimera peptides in which part of the N-terminal region of HK-1 was replaced with that of SP, and vice versa, and all synthesized peptides induced thermal hyperalgesia. Both SP (1-2)/HK-1 and HK-1 (1-4)/SP certainly induced thermal hyperalgesia, although HK-1 and HK-1 (1-5)/SP had hardly any effect; therefore, it is probable that Ser at the 2nd position and Arg at the 5th position of HK-1 may be involved in the non-induction of thermal hyperalgesia. Furthermore, peptides in which amino acid at the 3rd and/or 4th positions of HK-1 was replaced with that of SP were synthesized. Intrathecal administration of HK-1 (1-2,4-5)/SP, but not HK-1 (1-2,5)/SP and HK-1 (1-3,5)/SP, hardly induced thermal hyperalgesia. These findings indicate that three amino acids, Ser, Thr and Arg at the 2nd, 4th and 5th positions of HK-1, respectively, regulate the induction of thermal hyperalgesia by HK-1.

Hemokinin-1 activates the MAPK pathway and enhances B cell proliferation and antibody production

Hemokinin 1 (HK-1) is a substance P-like tachykinin peptide predominantly expressed in non-neuronal tissues. In addition to a prominent function in lymphoid development, recent studies indicate a potential role for HK-1 in immunoregulation. The current study was focused on its action on mature B cells. Despite the negligible effect on its own, HK-1 exhibited a profound influence on B cell activation elicited by several classical signals, including LPS stimulation, BCR cross-linking, and CD40 ligation. Cells therefore showed enhanced proliferation, survival, and CD80/86 expression, and produced more IgM with a higher frequency of Ab-forming cells. Biochemical analysis revealed that HK-1 alone was sufficient to induce the activation of MAPKs and the expression of Blimp-1 and Xbp-1 in B cells. Nevertheless, costimulation with a known B cell activator resulted in much enhanced phosphorylation of MAPKs and transcriptional activation of Blimp-1 and Xbp-1. Overall, these data support that HK-1 provides an important costimulatory signal for B cell activation, possibly through synergistic activation of the MAPK pathway and induction of transcription factors critical for plasmacytic differentiation.

Differential effects of substance P or hemokinin-1 on transient receptor potential channels, TRPV1, TRPA1 and TRPM8, in the rat

Two tachykinin peptides, substance P (SP) and hemokinin-1 (HK-1), and three transient receptor potential (TRP) channels, TRPV1, TRPA1 and TRPM8, are similarly localized in the spinal dorsal horn and dorsal root ganglion, suggesting that TRP channels may be related or modulated by these tachykinin peptides. Thus, to clarify whether the responses of TRP channels are modulated by SP or HK-1, the effects of pretreatment with SP or HK-1 on the induction of scratching behavior by TRP channel agonists were examined. Pretreatment with SP or HK-1 enhanced the induction of scratching behavior by resiniferatoxin, a TRPV1 agonist, whereas scratching behavior induced by menthol, a TRPM8 agonist, was suppressed by pretreatment with these peptides. On the other hand, pretreatment with SP, but not HK-1, suppressed the induction of scratching behavior by cinnamaldehyde, a TRPA1 agonist. Taken together, the present results indicate that SP or HK-1 differentially modulated the response of TRPV1, TRPA1 or TRPM8 channel.

Antimicrobial properties of hemokinin-1 against strains of Pseudomonas aeruginosa

AIMS

In this study, we examined whether hemokinin-1, the newest member of the tachykinin family and a close relative of substance P, has antimicrobial properties which have been attributed to other neuropeptides including substance P.

MAIN METHODS

Top agar assays were performed to determine the antimicrobial activity of hemokinin-1 and substance P against various microorganisms.

KEY FINDINGS

Here we provide evidence that hemokinin-1 peptide possesses antimicrobial properties against some strains of Pseudomonas aeruginosa, while substance P was only marginally effective.

SIGNIFICANCE

Our study is the first to link hemokinin-1 to the essential role of defending the body against microbial challenges and adds hemokinin-1 to the list of potential drugs that could help in the fight against P. aeruginosa, an opportunistic human pathogen.

In vitro characterization of the effects of rat/mouse hemokinin-1 on mouse colonic contractile activity: a comparison with substance P

Rat/mouse hemokinin-1 (r/m HK-1) has been identified as a member of the tachykinin family and its effect in colonic contractile activity remains unknown. We investigated the effects and mechanisms of actions of r/m HK-1 on the mouse colonic contractile activity in vitro by comparing it with that of substance P (SP). R/m HK-1 induced substantial contractions on the circular muscle of mouse colon. The maximal contractile responses to r/m HK-1 varied significantly among proximal-, mid- and distal-colon, suggesting that the action of r/m HK-1 was region-specific in mouse colon. The contractile response induced by r/m HK-1 is primarily via activation of tachykinin NK(1) receptors leading to activation of cholinergic excitatory pathways and with a minor contribution of NK(2) receptors, which may be on the smooth muscle itself. A direct action on colonic smooth muscles may be also involved. In contrast, SP induced biphasic colonic responses (contractile and relaxant responses) on the circular muscle, in which the contractile action of SP was equieffective with r/m HK-1. SP exerted its contractile effect predominantly through neural and muscular tachykinin NK(1) receptors, but unlike r/m HK-1 did not appear to act via NK(2) receptors. The relaxation induced by SP was largely due to release of nitric oxide (NO) produced via an action on neural NK(1) receptors. These results indicate that the receptors and the activation properties involved in r/m HK-1-induced mouse colonic contractile activity are different from those of SP.

Regulatory mechanisms in the differential expression of Hemokinin-1

Hemokinin-1, encoded by the TAC4 gene, is the most recent addition to the tachykinin family. Although most closely related to the neuropeptide Substance P, Hemokinin-1 distinguishes itself from other tachykinins by its predominantly non-neuronal expression pattern. Its expression in T and B lymphocytes, macrophages, and dendritic cells points to an important role for Hemokinin-1 in the immune system. To seek reasons for its preferential expression in the immune system and ultimately to provide clues to its function, we investigated the molecular mechanisms driving the differential expression pattern of this unique tachykinin. Our study provides the first analysis of the promoter region of the TAC4 gene, which reveals regulatory mechanism different from the Substance P promoter. We demonstrate for the first time that Hemokinin-1 initiates transcription from multiple start sites through a TATA-less promoter. Conservation of the 5' non-coding region indicates the importance of the upstream regulatory region in directing expression of Hemokinin-1 in specific cell types, during cell differentiation and activation. Furthermore, NFkappaB, a transcription factor important in the activation of immune cells was shown to be involved in promoting increased TAC4 transcription during PMA induction of a T cell line. Our studies reveal that Hemokinin-1 is regulated by a unique transcription regulation system that likely governs its differential expression pattern and suggests a role for Hemokinin-1 distinct from Substance P.

Increase in hemokinin-1 mRNA in the spinal cord during the early phase of a neuropathic pain state

BACKGROUND AND PURPOSE

Substance P (SP), a representative member of the tachykinin family, is involved in nociception under physiological and pathological conditions. Recently, hemokinin-1 (HK-1) was identified as a new member of this family. Although HK-1 acts on NK(1) tachykinin receptors that are thought to be innate for SP, the roles of HK-1 in neuropathic pain are still unknown.

EXPERIMENTAL APPROACH

Using rats that had been subjected to chronic constrictive injury (CCI) of the sciatic nerve as a neuropathic pain model, we examined the changes in expression of SP- and HK-1-encoding genes (TAC1 and TAC4, respectively) in the L4/L5 spinal cord and L4/L5 dorsal root ganglia (DRGs) in association with changes in pain-related behaviours in this neuropathic pain state.

KEY RESULTS

The TAC4 mRNA level was increased on the ipsilateral side of the dorsal spinal cord, but not in DRGs, at day 3 after CCI. In contrast, the TAC1 mRNA level was significantly increased in the DRGs at day 3 after CCI without any changes in the dorsal spinal cord. Analysis of a cultured microglial cell line revealed the presence of TAC4 mRNA in microglial cells. Minocycline, an inhibitor of microglial activation, blocked the increased expression of TAC4 mRNA after CCI and inhibited the associated pain-related behaviours and microglial activation in the spinal cord.

CONCLUSIONS AND IMPLICATIONS

The present results suggest that HK-1 expression is increased at least partly in activated microglial cells after nerve injury and is clearly involved in the early phase of neuropathic pain.

In vivo characterization of the effects of human hemokinin-1 and human hemokinin-1(4-11), mammalian tachykinin peptides, on the modulation of pain in mice

Human hemokinin-1 (h HK-1) and its truncated form h HK-1(4-11) are mammalian tachykinin peptides encoded by the recently identified TAC4 gene in human, and the biological functions of these peptides have not been well investigated. In the present study, an attempt has been made to investigate the effects and mechanisms of action of h HK-1 and h HK-1(4-11) in pain modulation at the supraspinal level in mice using the tail immersion test. Intracerebroventricular (i.c.v.) administration of h HK-1 (0.3, 1, 3 and 6 nmol/mouse) produced a dose- and time-related antinociceptive effect. This effect was significantly antagonized by the NK(1) receptor antagonist SR140333, but not by the NK(2) receptor antagonist SR48968, indicating that the analgesic effect induced by i.c.v. h HK-1 is mediated through the activation of NK(1) receptors. Interestingly, naloxone, beta-funaltrexamine and naloxonazine, but not naltrindole and nor-binaltorphimine, could also block the analgesic effect markedly, suggesting that this effect is related to descending mu opioidergic neurons (primary mu(1) subtype). Human HK-1(4-11) could also induce a dose- and time-dependent analgesic effect after i.c.v. administration, however, the potency of analgesia was less than h HK-1. Surprisingly, SR140333 could not modify this analgesic effect, suggesting that this effect is not mediated through the NK(1) receptors like h HK-1. SR48968 could modestly enhance the analgesic effect induced by h HK-1(4-11), indicating that a small amount of h HK-1(4-11) may bind to NK(2) receptors. Furthermore, none of the opioid receptor (OR) antagonists could markedly block the analgesia of h HK-1(4-11), suggesting that the analgesic effect is not mediated through the descending opioidergic neurons. Blocking of delta ORs significantly enhanced the analgesia, indicating that delta OR is a negatively modulatory factor in the analgesic effect of h HK-1(4-11). It is striking that bicuculline (a competitive antagonist at GABA(A) receptors) effectively blocked the analgesia induced by h HK-1(4-11), suggesting that this analgesic effect is mediated through the descending inhibitory GABAergic neurons. The novel mechanism involved in the analgesic effect of h HK-1(4-11), which is different from that of h HK-1, may pave the way for a new strategy for the investigation and control of pain.

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.

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.

Pharmacological characterization of desensitization in scratching behavior induced by intrathecal administration of hemokinin-1 in the rat

Desensitization is induced by the repeated administration of high doses of substance P (SP) or hemokinin-1 (HK-1). However, little information is available about the mechanisms involved in the induction of desensitization by these peptides. Thus, to characterize this desensitization, we examined the dose-dependent effect of these peptides, the effect of pretreatment with neurokinin 1(NK1) receptor antagonists, and the effect of pretreatment with inhibitors of protein kinases such as protein kinase A (PKA), protein kinase C (PKC), calcium/calmodulin kinase II (CaMKII) and mitogen-activated protein kinase kinase (MEK). The number of scratchings induced by 10(-3)M SP or HK-1 decreased following pretreatment with 10(-11)-10(-3)M SP or HK-1 with a marked reduction at 10(-3) and 10(-6)M SP or HK-1. The effect of NK1 receptor antagonists on desensitization induced by pretreatment with 10(-6)M SP was marked, whereas there was little effect of pretreatment with these antagonists on 10(-6)M HK-1-induced desensitization. Additionally, 10(-6)M SP- and HK-1-induced desensitization was attenuated by pretreatment with PKA, PKC and MEK inhibitors, except a CaMKII inhibitor that inhibited SP-induced desensitization. These results indicate that the receptor and kinases involved in HK-1-induced desensitization are partially different from those of SP.

Co-regulated decrease of Neurokinin-1 receptor and Hemokinin-1 gene expression in monocytes and macrophages after activation with pro-inflammatory cytokines

Hemokinin-1 (HK-1), a potent ligand for the Neurokinin-1 receptor (NK-1) is thought to play a role in the immune system. To investigate the regulation of this receptor-ligand pair, we examined the effects of pro-inflammatory cytokines on their expression in the monocyte/macrophage cell lines Wehi-3 and RAW264.7. We demonstrate co-expression of NK-1 and HK-1 mRNA in both lines, as well as functional NK-1 receptor protein in Wehi-3 cells. Stimulation with IFN-gamma, IL-1beta and TNF-alpha markedly decreased NK-1 and HK-1 mRNA as well as NK-1 receptor protein, which coincided with monocytic differentiation. A co-regulated decrease could also be observed in differentiating primary bone marrow macrophages, suggesting that this receptor-ligand pair may be controlled by cytokine networks and may serve a developmental role in the immune system.

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.

Mechanisms of relaxing response induced by rat/mouse hemokinin-1 in porcine coronary arteries: roles of potassium ion and nitric oxide

Rat and mouse hemokinin-1(r/m hemokinin-1) is a recently described member of the tachykinin family whose cardiovascular functions are not fully understood. In this study, we investigated the mechanisms of the relaxing response induced by r/m hemokinin-1 in isolated porcine coronary arteries by using a specific antagonist of tachykinin NK(1) receptor (SR140333), a nitric oxide synthase inhibitor N(omega)-nitro-L-arginine (L-NNA), and 1H-[1,2,4] Oxadiazolo [4,3-a] quinoxalin-1-one (ODQ), a blocker of cGMP production. r/m Hemokinin-1 (10(-12)-10(-6 )M) evoked a marked endothelium-dependent vasodilatation (E(max)=121.12+/-10.6% and 91.79+/-2.39% in 10(-6) M PGF(2)alpha and 30 mM KCl precontracted arterial rings, respectively) of coronary arteries mediated by activation of endothelial tachykinin NK(1) receptors. Two components contributed to this r/m hemokinin-1-elicited vasodilatation, the first of which was endothelium-derived hyperpolarizing factor (EDHF), which played a major role. This EDHF was identified as a potassium current through certain kinds of potassium channels on the endothelial cell membrane of porcine coronary arteries. Specific antagonists of Ca(2+)-activated K(+) channels (dequalinium and clotrimazole) did not have an inhibitory effect on the r/m hemokinin-1-induced vasodilatation, whereas they did on the substance P-induced vasodilatation. When potassium ion efflux was impaired by a high K(+) concentration (30 mM) or removal of K(+) from the surroundings, NO synthesis was triggered by r/m hemokinin-1 to produce an equivalent EDHF (K(+))-independent vasorelaxation as a compensatory mechanism.

The common carboxyl-terminal region of novel tachykinin peptides contributes to induce desensitization in scratching behavior of rats

Some novel tachykinin peptides exhibiting homology with known members of the tachykinin family have been recently reported; however, little is known about the function of these peptides. Repeated intrathecal administration of substance P (SP) causes desensitization by binding SP to neurokinin 1 (NK1) receptor. Thus, to clarify the characteristics of the receptors involved in these novel peptides, we investigated whether desensitization is induced by intrathecal administration of these peptides in rats since desensitization is induced by binding these peptides to the receptor. Intrathecal administration of 10(-3) M hemokinin-1 (HK-1) and 10(-3) M decapeptide common in the carboxyl-terminal region of endokinin A and endokinin B (EKA/B) as well as SP evoked scratching behavior. When each peptide was administered twice with an interval of 15 min, remarkable desensitization of scratching behavior was produced. Furthermore, the first administration of EKA/B or SP produced clear cross-desensitization to SP, EKA/B and HK-1, whereas the first administration of HK-1 demonstrated weak cross-desensitization to EKA/B and SP. These results suggest that EKA/B and SP may bind to both the NK1 receptor and HK-1-preferred receptor, and HK-1 may preferentially bind to its preferred receptor.