Protease-activated receptor 2 expression in trigeminal neurons innervating the rat nasal mucosa

Neuroimmune communication in allergic rhinitis

The prevalence rate of allergic rhinitis (AR) is high worldwide. The inhalation of allergens induces AR, which is an immunoglobulin E-mediated and type 2 inflammation-driven disease. Recently, the role of neuroimmune communication in AR pathogenesis has piqued the interest of the scientific community. Various neuropeptides, such as substance P (SP), vasoactive intestinal peptide (VIP), calcitonin gene-related peptide (CGRP), nerve growth factor (NGF), and neuromedin U (NMU), released via "axon reflexes" or "central sensitization" exert regulatory effects on immune cells to elicit "neurogenic inflammation," which contributes to nasal hyperresponsiveness (NHR) in AR. Additionally, neuropeptides can be produced in immune cells. The frequent colocalization of immune and neuronal cells at certain anatomical regions promotes the establishment of neuroimmune cell units, such as nerve-mast cells, nerve-type 2 innate lymphoid cells (ILC2s), nerve-eosinophils and nerve-basophils units. Receptors expressed both on immune cells and neurons, such as TRPV1, TRPA1, and Mas-related G protein-coupled receptor X2 (MRGPRX2) mediate AR pathogenesis. This review focused on elucidating the mechanisms underlying neuroimmune communication in AR.

[Neuroimmunology of allergic rhinitis part 2 : Interactions of neurons and immune cells and neuroimmunological units]

Allergic rhinitis is an IgE-mediated, type‑2 inflammatory disease. neuropeptides are released by neurons and interact with immune cells. Via colocalization, neuroimmune cell units such as nerve-mast cell units, nerve-type 2 innate lymphoid cell (ILC2) units, nerve-eosinophil units, and nerve-basophil units are formed. Markedly elevated tryptase levels were found in nasal lavage fluid and were strongly associated with neuropeptide levels. A close anatomical connection allows bidirectional communication between immune and neuronal cells. Transient receptor potential vanilloid 1 (TRPV1) and transient receptor potential ankyrin repeat 1 (TRPA1) are critically involved in immunological reactions in the setting of allergic rhinitis. Neuroimmunological communication plays an important role in the inflammatory process, so that allergic rhinitis can no longer be considered a purely immunological disease, but rather a combined neuroimmunological disease.

Protease-activated receptors in health and disease

Proteases are signaling molecules that specifically control cellular functions by cleaving protease-activated receptors (PARs). The four known PARs are members of the large family of G protein-coupled receptors. These transmembrane receptors control most physiological and pathological processes and are the target of a large proportion of therapeutic drugs. Signaling proteases include enzymes from the circulation; from immune, inflammatory epithelial, and cancer cells; as well as from commensal and pathogenic bacteria. Advances in our understanding of the structure and function of PARs provide insights into how diverse proteases activate these receptors to regulate physiological and pathological processes in most tissues and organ systems. The realization that proteases and PARs are key mediators of disease, coupled with advances in understanding the atomic level structure of PARs and their mechanisms of signaling in subcellular microdomains, has spurred the development of antagonists, some of which have advanced to the clinic. Herein we review the discovery, structure, and function of this receptor system, highlight the contribution of PARs to homeostatic control, and discuss the potential of PAR antagonists for the treatment of major diseases.

Characterization and preclinical evaluation of a protease activated receptor 2 (PAR2) monoclonal antibody as a preventive therapy for migraine

AIM

Migraine pain is thought to result from activation of meningeal nociceptors that might involve dural mast cell degranulation and release of proteases and pronociceptive mediators. Tryptase, the most abundant dural mast cell protease, has been demonstrated to stimulate dural mast cells, as well as trigeminal nociceptors by activating the protease activated receptor 2. Mast cell or neuronal protease activated receptors 2 may therefore represent a novel target for migraine treatment. In this study, we characterized and evaluated a novel protease activated receptor 2 monoclonal antibody as a preventive anti-migraine pain therapy in preclinical models.

METHODS

Flow cytometry, immunocytochemistry, calcium imaging, Homogeneous Time Resolved Technology (HTRF) epitope competition assay and serum pharmacokinetic (PK) assay in rats were performed to confirm the activity, specificity and in vivo stability of PAR650097, a novel anti- protease activated receptor 2 monoclonal antibody. In vivo assessment was performed in female C57BL/6J mice by evaluation of PAR650097 in preventing cutaneous allodynia elicited by (a) supradural injection of the protease activated receptor 2 agonist, Ser-Leu-Ile-Gly-Arg-Leu-amide trifluoroacetate (SLIGRL), or calcitonin gene-related (CGRP) peptide, and (b) induction of latent sensitization by priming with three daily episodes of restraint stress followed by challenge with a subthreshold inhalational exposure to umbellulone (UMB), a transient receptor potential ankyrin 1 (TRPA1) agonist. PAR650097 was administered as a pretreatment prior to the first restraint stress, umbellulone exposure, SLIGRL or calcitonin gene-related peptide injection. Additionally, fremanezumab, a calcitonin gene-related peptide antibody was administered as pre-treatment prior to supradural administration of calcitonin gene-related peptide or SLIGRL.

RESULTS

In vitro, PAR650097 demonstrated rapid interaction with protease activated receptor 2, enabling it to fully inhibit protease-induced protease activated receptor 2 activation, in human and mouse cells, with high potency. Furthermore, PAR650097 was highly selective for protease activated receptor 2, demonstrating no affinity for protease activated receptor 1 protein and no functional effect on the activation of cellular protease activated receptor 1 with thrombin. In addition, PAR650097 had an acceptable PK profile, compatible with testing the effects of selective protease activated receptor 2 inhibition in vivo. In vivo, PAR650097 blocked cutaneous allodynia induced by either supradural SLIGRL or calcitonin gene-related peptide. Fremanezumab abolished cutaneous allodynia induced by supradural CGRP, and partially attenuated cutaneous allodynia induced by SLIGRL. Administration of PAR650097, before the first restraint stress episode, did not prevent the acute stress-induced cutaneous allodynia or restraint stress priming revealed by cutaneous allodynia induced by inhalational umbellulone. In contrast, PAR650097 prevented expression of cutaneous allodynia when given before the umbellulone challenge in restraint stress-primed animals.

CONCLUSION

PAR650097 specifically inhibits endogenously expressed protease activated receptor 2 in human and mouse cells with high potency. This antibody has an acceptable PK profile in rodents and effectively blocked SLIGR-induced cutaneous allodynia. PAR650097 additionally prevented cutaneous allodynia induced by supradural calcitonin gene-related peptide, indicating that the protease activated receptor 2 receptor is a downstream consequence of calcitonin gene-related peptide actions. Fremanezumab effectively blocked calcitonin gene-related peptide-induced cutaneous allodynia and only partially reduced cutaneous allodynia induced by a protease activated receptor 2 activator, suggesting both calcitonin gene-related peptide-dependent and -independent mechanisms in promoting migraine pain. While PAR650097 did not prevent stress-induced cutaneous allodynia or priming, it effectively prevented cutaneous allodynia induced by a TRPA1 agonist in animals with latent sensitization. Activation of protease activated receptor 2, therefore, contributes to both calcitonin gene-related peptide-dependent and -independent mechanisms in promoting migraine-like pain. Therapeutic targeting of protease activated receptor 2 receptors may represent an anti-migraine pain strategy with a potentially broad efficacy profile.

TRP Channels in the Focus of Trigeminal Nociceptor Sensitization Contributing to Primary Headaches

Pain in trigeminal areas is driven by nociceptive trigeminal afferents. Transduction molecules, among them the nonspecific cation channels transient receptor potential vanilloid 1 (TRPV1) and ankyrin 1 (TRPA1), which are activated by endogenous and exogenous ligands, are expressed by a significant population of trigeminal nociceptors innervating meningeal tissues. Many of these nociceptors also contain vasoactive neuropeptides such as calcitonin gene-related peptide (CGRP) and substance P. Release of neuropeptides and other functional properties are frequently examined using the cell bodies of trigeminal neurons as models of their sensory endings. Pathophysiological conditions cause phosphorylation, increased expression and trafficking of transient receptor potential (TRP) channels, neuropeptides and other mediators, which accelerate activation of nociceptive pathways. Since nociceptor activation may be a significant pathophysiological mechanism involved in both peripheral and central sensitization of the trigeminal nociceptive pathway, its contribution to the pathophysiology of primary headaches is more than likely. Metabolic disorders and medication-induced painful states are frequently associated with TRP receptor activation and may increase the risk for primary headaches.

Trypsin-protease activated receptor-2 signaling contributes to pancreatic cancer pain

Pain treatment is a critical aspect of pancreatic cancer patient clinical care. This study investigated the role of trypsin-protease activated receptor-2 (PAR-2) in pancreatic cancer pain. Pancreatic tissue samples were collected from pancreatic cancer (n=22) and control patients (n=22). Immunofluorescence analyses confirmed colocalization of PAR-2 and neuronal markers in pancreatic cancer tissues. Trypsin levels and protease activities were higher in pancreatic cancer tissue specimens than in the controls. Supernatants from cultured human pancreatic cancer tissues (PC supernatants) induced substance P and calcitonin gene-related peptide release in dorsal root ganglia (DRG) neurons, and FS-NH₂, a selective PAR-2 antagonist, inhibited this effect. A BALB/c nude mouse orthotopic tumor model was used to confirm the role of PAR-2 signaling in pancreatic cancer visceral pain, and male Sprague-Dawley rats were used to assess ambulatory pain. FS-NH₂ treatment decreased hunch scores, mechanical hyperalgesia, and visceromotor reflex responses in tumor-bearing mice. In rats, subcutaneous injection of PC supernatant induced pain behavior, which was alleviated by treatment with FS-NH₂ or FUT-175, a broad-spectrum serine protease inhibitor. Our findings suggest that trypsin-PAR-2 signaling contributes to pancreatic cancer pain in vivo. Treatment strategies targeting PAR-2 or its downstream signaling molecules might effectively relieve pancreatic cancer pain.

Steroid Treatment Reduces Allergic Airway Inflammation and Does Not Alter the Increased Numbers of Dendritic Cells and Calcitonin Gene-Related Peptide-Expressing Neurons in Airway Sensory Ganglia

OBJECTIVES

Our previous data demonstrated that allergic airway inflammation induces migration of dendritic cells (DC) into airway sensory jugular and nodose ganglia (jugular-nodose ganglion complex; JNC). Here we investigated the effects of steroid treatment regarding the expression and migration of DC and calcitonin gene-related peptide (CGRP)-immunoreactive neurons of vagal sensory ganglia during allergic airway inflammation.

METHODS

A house dust mite (HDM) model for allergic airway inflammation was used. The mice received 0.3 mg fluticasone propionate per kilogram of body weight in the last 9 days. JNC slices were analyzed on MHC II, the neuronal marker PGP9.5, and the neuropeptide CGRP.

RESULTS

Allergic airway inflammation increased the numbers of DC and CGRP-expressing neurons in the JNC significantly in comparison to the controls (DC/neurons: HDM 44.58 ± 1.6% vs. saline 33.29 ± 1.6%, p < 0.05; CGRP-positive neurons/total neurons: HDM 30.65 ± 1.9% vs. saline 19.49 ± 2.3%, p < 0.05). Steroid treatment did not have any effect on the numbers of DC and CGRP-expressing neurons in the JNC compared to HDM-treated mice.

CONCLUSIONS

The present findings indicate an important role of DC and CGRP-containing neurons in the pathogenesis of allergic airway inflammation. However, steroid treatment did not have an effect on the population of DC and neurons displaying CGRP in the JNC, whereas steroid treatment was found to suppress allergic airway inflammation.

Evaluation on potential contributions of protease activated receptors related mediators in allergic inflammation

Protease activated receptors (PARs) have been recognized as a distinctive four-member family of seven transmembrane G protein-coupled receptors (GPCRs) that can be cleaved by certain serine proteases. In recent years, there has been considerable interest in the role of PARs in allergic inflammation, the fundamental pathologic changes of allergy, but the potential roles of PARs in allergy remain obscure. Since many of these proteases are produced and actively involved in the pathologic process of inflammation including exudation of plasma components, inflammatory cell infiltration, and tissue damage and repair, PARs appear to make important contribution to allergy. The aim of the present review is to summarize the expression of PARs in inflammatory and structural cells, the influence of agonists or antagonists of PARs on cell behavior, and the involvement of PARs in allergic disorders, which will help us to better understand the roles of serine proteases and PARs in allergy.

PAR2 and Temporomandibular Joint Inflammation in the Rat

The proteinase-activated receptor 2 (PAR2) is a putative therapeutic target for arthritis. We hypothesized that the early pro-inflammatory effects secondary to its activation in the temporomandibular joint (TMJ) are mediated by neurogenic mechanisms. Immunofluorescence analysis revealed a high degree of neurons expressing PAR2 in retrogradely labeled trigeminal ganglion neurons. Furthermore, PAR2 immunoreactivity was observed in the lining layer of the TMJ, co-localizing with the neuronal marker PGP9.5 and substance-P-containing peripheral sensory nerve fibers. The intra-articular injection of PAR2 agonists into the TMJ triggered a dose-dependent increase in plasma extravasation, neutrophil influx, and induction of mechanical allodynia. The pharmacological blockade of natural killer 1 (NK1) receptors abolished PAR2-induced plasma extravasation and inhibited neutrophil influx and mechanical allodynia. We conclude that PAR2 activation is pro-inflammatory in the TMJ, through a neurogenic mechanism involving NK1 receptors. This suggests that PAR2 is an important component of innate neuro-immune response in the rat TMJ.

Involvement of capsaicin-sensitive afferent nerves in the proteinase-activated receptor 2-mediated vasodilatation in the rat dura mater

Neurogenic inflammation of the dura mater encephali has been suggested to contribute to the mechanisms of meningeal nociception and blood flow regulation. Recent findings demonstrated that the rat dura mater is innervated by trigeminal capsaicin-sensitive peptidergic nociceptive afferent nerves which mediate meningeal vascular responses through activation of the transient receptor potential vanilloid type 1 (TRPV1) receptor. The present work explored the functional significance of the capsaicin-sensitive subpopulation of dural afferent nerves via their contribution to the meningeal vascular responses evoked through activation of the proteinase-activated receptor 2 (PAR-2). The vascular responses of the dura mater were studied by laser Doppler flowmetry in a rat open cranial window preparation. Topical applications of trypsin, a PAR-2-activator, or Ser-Leu-Ile-Gly-Arg-Leu-amide (SLIGRL-NH(2)), a selective PAR-2 agonist peptide, resulted in dose-dependent increases in meningeal blood flow. The SLIGRL-NH(2)-induced vasodilatation was significantly reduced following capsaicin-sensitive afferent nerve defunctionalization by prior systemic capsaicin treatment and by pretreatment of the dura mater with the calcitonin gene-related peptide (CGRP) receptor antagonist CGRP(8-37). Nomega-nitro-L-arginine methyl ester hydrochloride (L-NAME) an unspecific inhibitor of nitric oxide (NO) production, but not 1-(2-trifluoromethylphenyl) imidazole (TRIM), a neuronal NO synthase inhibitor, also inhibited the vasodilator response to SLIGRL-NH(2). The vasodilator responses elicited by very low concentrations of capsaicin (10 nM) were significantly enhanced by prior application of SLIGRL-NH(2). The present findings demonstrate that activation of the PAR-2 localized on capsaicin-sensitive trigeminal nociceptive afferent nerves induces vasodilatation in the dural vascular bed by mechanisms involving NO and CGRP release. The results indicate that the PAR-2-mediated activation and sensitization of meningeal capsaicin-sensitive C-fiber nociceptors may be significantly implicated in the pathophysiology of headaches.

Modulation of meningeal nociceptors mechanosensitivity by peripheral proteinase-activated receptor-2: the role of mast cells

Inflammatory-related activation and sensitization of meningeal nociceptors is believed to play a key role in promoting the intracranial throbbing pain of migraine. We have shown recently that mast cell activation and various mast cell-derived inflammatory mediators can promote activation and sensitization of meningeal nociceptors. Mast cell tryptase has also been proposed to promote pain hypersensitivity by activating the proteinase-activated receptor 2 (PAR2) that is expressed on nociceptive neurons. In this study using in vivo single-unit recording in the trigeminal ganglion of anaesthetized rats, we found that local meningeal activation of PAR2 using the specific agonist SLIGRL-NH2 promoted sensitization of the threshold response while provoking desensitization of the suprathreshold responses. SLIGRL-NH2 also excited a subpopulation of meningeal nociceptors. Chronic mast cell depletion enhanced the sensitizing effects of PAR2 activation while curbing its desensitizing effects. Mast cell depletion did not change the PAR2-mediated excitatory effect. We propose that by enhancing the mechanical sensitivity of meningeal nociceptors local PAR2 activation could play a role in promoting the throbbing pain of migraine and that local mast cell degranulation may modulate such an effect.

Intrathecal administration of proteinase-activated receptor-2 agonists produces hyperalgesia by exciting the cell bodies of primary sensory neurons

Proteinase-activated receptors (PARs) are a family of G-protein-coupled receptors that are activated by endogenous serine proteinases that cleave the N-terminal domain of the receptor unmasking a "tethered ligand" sequence. Trypsin and other agonists at PAR(2) act on peripheral nerves to augment the transfer of nociceptive information. We tested whether PAR(2) agonists also exert a spinal pronociceptive effect by i.t. administering the selective ligand, Ser-Leu-Ile-Gly-Arg-Leu-NH(2) (SLI-GRL). This produced thermal and mechanical hyperalgesia in rats and mice and augmented mechanical and thermal hyperalgesia seen in the formalin inflammatory pain test. Effects of SLIGRL were abrogated in PAR(2)-deficient mice and were not seen with the inactive control peptide, Leu-Arg-Gly-Ile-Leu-Ser-NH(2). Surprisingly, electrophysiological studies, using whole-cell recording from rat substantia gelatinosa neurons, failed to demonstrate an increase in excitatory transmission or neuronal excitability following treatment with SLIGRL or trypsin. In fact, the actions of trypsin were consistent with a decrease in dorsal horn excitability. SLIGRL and trypsin did, however, depolarize and increase the excitability of large, medium and small primary afferent, dorsal root ganglion neurons. The effects were associated with an increase in conductance at hyperpolarized potentials and a decrease in conductance at depolarized potentials. PAR(2)-like immunoreactivity was found in DRG but not in spinal dorsal horn. These results suggest that activation of DRG neuron cell bodies may account for the pronociceptive actions of i.t. applied PAR(2) agonists. They also imply that pathophysiological release of PAR(2)-activating proteases in the vicinity of DRG neurons may produce profound effects on nociceptive processing in vivo.

Sensing the air around us: the voltage-gated-like ion channel family

Ion channels are a complex set of proteins having many important physiologic and potentially pathologic roles. The flow of ions through these channels and the subsequent cellular depolarization can trigger complex mechanisms such as cardiac rhythm, hormone secretion, and numerous sensory experiences. The transient receptor potential (TRP) channels are an important means for multiple organ systems to interact with their environment. The various TRP channel subfamilies respond to voltage or to ligands such as G-protein coupled receptors. Their ability to sense temperature, pain, stretch, and osmolarity among others enables them to mediate responses such as smooth muscle contraction, cough, or sensation of pain.

Gene and protein expression of protease-activated receptor 2 in structural and inflammatory cells in the nasal mucosa in seasonal allergic rhinitis

BACKGROUND

Protease-activated receptor 2 (PAR 2) has been shown to be responsible for trypsin and mast cell tryptase-induced airway inflammation. Here, the present study aimed to explore the expression of PAR 2 in the nasal mucosa of seasonal allergic rhinitis (SAR).

METHODS

Study subjects were recruited for the study by medical history, physical examination and laboratory screening tests. Using immunohistochemistry, laser-assisted cell picking and subsequently real-time PCR, nasal mucosa biopsies of SAR patients were investigated for PAR 2 gene and protein expression in complex tissues of the nasal mucosa.

RESULTS

Gene and protein expression of PAR 2 was firstly detected in nasal mucosa of SAR patients. The relative gene expression level of PAR 2 was significantly increased in complex tissues of the nasal mucosa of SAR (6.21+/-4.02 vs. controls: 1.38+/-0.86, P=0.004). Moreover, PAR 2 mRNA expression in epithelial cells (SAR: 4.78+/-4.64 vs. controls: 0.84+/-0.61, P=0.003) but not in mucus (SAR: 1.51+/-1.15 vs. controls: 1.35+/-1.02, P=0.78) and endothelial cells (SAR: 1.20+/-0.57 vs. controls: 1.73+/-1.30, P=0.5) was found to be significantly changed in the nasal mucosa in SAR. Using double immunohistochemistry the present study demonstrated that the total numbers of mast cells (P=0.0003) and eosinophils (P=0.03) and the numbers of eosinophils expressing PAR 2 (P=0.006) were significantly elevated in the nasal mucosa of SAR compared with the controls.

CONCLUSION

The abundant presence and distribution of gene and protein expression of PAR 2 in different cell types in the nasal mucosa under normal situation, the increased expression of PAR 2 in epithelial cells and the increased number of eosinophils with PAR 2 suggest that PAR 2 may contribute to the pathogenesis of allergic diseases such as SAR.

Rhodamine backfilling and confocal microscopy as a tool for the unambiguous identification of neuronal cell types: a study of the neurones of the rat cochlear nucleus

Adequate interpretation of the functional data characterising the projection neurones of the cochlear nucleus (CN) is impossible without the unequivocal classification of these cell types at the end of the experiments. In this study, morphological criteria applicable for unambiguous identification of CN neurones have been sought. The neurones were labelled with rhodamine from incisions severing the projection pathways of the individual cell types, allowing their selective labelling and morphological characterisation. Confocal microscopy was employed for the investigation of the rhodamine-filled cells whose morphology was assessed after reconstructing the three-dimensional images of the cell bodies and proximal processes. The diameters of the somata and the number of processes originating from the cell bodies were also determined. In most of the cases, unambiguous identification of the bushy, octopus and Purkinje-like cells was relatively straightforward. On the other hand, precise classification of the pyramidal cells was often difficult, especially because giant cells could easily possess morphological features resembling pyramidal neurones. Occasionally, giant cells also mimicked the appearance of octopus neurones, which may be another important source of identification error, especially as these two cell types are often situated close to each other in the CN. It is concluded that morphological criteria defined in the present work may be effectively applied for the unambiguous identification of the projection neurones of the CN, even following functional measurements, when the correct cell classification is essential for the interpretation of the experimental data. Moreover, the present study also confirmed that Purkinje-like cells project to the cerebellum.