Differential DNA synthesis in response to activation of protease-activated receptors on cultured guinea-pig tracheal smooth muscle cells

Proteinase-activated receptor-2 agonist activates anti-influenza mechanisms and modulates IFNγ-induced antiviral pathways in human neutrophils

Proteinase-activated receptor-2 (PAR₂) is expressed by human leukocytes and participates in the development of inflammatory diseases. Recent studies demonstrated an ability of PAR₂ agonist to enhance IFNγ-induced antiviral responses of human leukocytes. However, the precise cellular antiviral defense mechanisms triggered in leukocytes after stimulation with IFNγ and/or PAR₂ agonist remain elusive. Therefore, we aimed to identify neutrophil defense mechanisms involved in antiviral resistance. Here we demonstrated that PAR₂ agonist enhanced IFNγ-related reduction of influenza A virus (IAV) replication in human neutrophils. PAR₂-mediated decrease in IAV replication was associated with reduced NS-1 transcription. Moreover, PAR₂-dependent neutrophil activation resulted in enhanced myeloperoxidase degranulation and extracellular myeloperoxidase disrupted IAV. The production of ROS was elevated in response to PAR₂ activation. Interestingly, IFNγ did not influence both effects: PAR₂ agonist-triggered myeloperoxidase (MPO) release and reactive oxygen species (ROS) production, which are known to limit IAV infections. In contrast, orthomyxovirus resistance gene A (MxA) protein expression was synergistically elevated through PAR₂ agonist and IFNγ in neutrophils. Altogether, these findings emphasize two PAR₂-controlled antiviral mechanisms that are independent of or modulated by IFNγ.

Role of proteinase-activated receptor-2 in anti-bacterial and immunomodulatory effects of interferon-γ on human neutrophils and monocytes

Recent studies show that proteinase-activated receptor-2 (PAR(2)) contributes to the development of inflammatory responses. However, investigations into the precise role of PAR(2) activation in the anti-microbial defence of human leucocytes are just beginning. We therefore evaluated the contribution of PAR(2) to the anti-microbial response of isolated human innate immune cells. We found that PAR(2) agonist, acting alone, enhances phagocytosis of Staphylococcus aureus and killing of Escherichia coli by human leucocytes, and that the magnitude of the effect is similar to that of interferon-γ (IFN-γ). However, co-application of PAR(2) -cAP and IFN-γ did not enhance the phagocytic and bacteria-killing activity of leucocytes beyond that triggered by either agonist alone. On the other hand, IFN-γ enhances PAR(2) agonist-induced monocyte chemoattractant protein 1 (MCP-1) secretion by human neutrophils and monocytes. Furthermore, phosphoinositide-3 kinase and janus kinase molecules are involved in the synergistic effect of PAR(2) agonist and IFN-γ on MCP-1 secretion. Our findings suggest a potentially protective role of PAR(2) agonists in the anti-microbial defence established by human monocytes and neutrophils.

Nafamostat mesilate, a potent tryptase inhibitor, modulates periodontitis in rats

Previous reports have demonstrated increased tryptase-like proteolytic activity in the crevicular fluid of patients with periodontal disease. In the present study, we have investigated the effect of tryptase inhibition with nafamostat mesilate (NM, 6-amino-2-naphtlyl p-guanidinobenzoate dimethansulfonate) on the development of experimental periodontitis in rats. Eighty (80) male Wistar rats were randomly separated into four groups: Control group, NM group (daily 0.1 mg/kg body weight of NM, i.p.), Ligature group (ligature placed at lower right first molars), and NM+Ligature group. The amount of alveolar bone loss (ABL) around the mesial root surface of the first mandibulary molar, as well as the myeloperoxidase (MPO) activity, and total proteolytic activity [N-benzoyl-L: -arginine-p-nitroanilide (BApNA) substrate] were determined at 7 and 14 days. NM led to significantly (p < 0.05) decreased ABL in animals subjected to ligature-induced periodontitis. Tryptase inhibition prevented the onset of significant ABL at 7 days of experiment (0.44 ± 0.16 and 0.60 ± 0.22, p > 0.05, NM+Ligature and Control, respectively) and significantly decreased the ABL at 14 days (0.97 ± 0.17 versus 1.82 ± 0.26, p < 0.001, NM+Ligature versus Ligature, respectively). In addition, NM significantly decreased MPO and total proteolytic activity at 14 days (p < 0.05). These data provided evidence that tryptase inhibition with NM attenuates gingival granulocyte infiltration and ABL in an experimental model of periodontitis in rats.

Agonists of proteinase-activated receptor-2 enhance IFN-gamma-inducible effects on human monocytes: role in influenza A infection

Proteinase-activated receptor-2 (PAR(2)) is expressed by different types of human leukocytes and involved in the development of inflammatory and infectious diseases. However, its precise role in the regulation of human monocyte and macrophage function during viral infection remains unclear. Also, the ability of PAR(2) agonists to enhance the effects induced by immune mediators during infection or inflammation is still poorly investigated. Therefore, we investigated the ability of a PAR(2) agonist to enhance IFN-gamma-induced suppression of influenza A virus replication in human monocytes. We found that this effect correlates with an increased abundance of IkappaBalpha after costimulation of cells with PAR(2) agonist and IFN-gamma. Remarkably, coapplication of PAR(2) agonist and IFN-gamma also enhances the effects of IFN-gamma on IFN-gamma-inducible protein 10 kDa release, and CD64 and alphaVbeta3 surface expression by human monocytes. Together, these findings indicate a potentially protective role of PAR(2) activation during the progression of influenza A virus infection. This effect could be associated with the ability of PAR(2) agonists to enhance IFN-gamma-induced protective effects on human monocytes.

Beta-tryptase regulates IL-8 expression in airway smooth muscle cells by a PAR-2-independent mechanism

Mast cells are central in the development of several allergic diseases and contain a number of pre-formed mediators. beta-tryptase, the most abundant mast cell product, is increasingly recognized as a key inflammatory mediator, as it causes the release of cytokines, particularly the chemokine IL-8, from both inflammatory and structural cells. The molecular mechanisms, however, remain largely unknown. In this study we sought to investigate whether beta-tryptase could induce IL-8 expression in human airway smooth muscle (ASM) cells and to explore the molecular mechanisms involved. We found that purified human beta-tryptase stimulated IL-8 production in a time- and concentration-dependent manner, which was inhibited by protease inhibitors and mimicked by recombinant human beta-tryptase, but not by the protease-activated receptor-2 (PAR-2) agonist SLIGKV-NH(2), consistent with the low-level expression of PAR-2 protein in these cells. beta-tryptase also up-regulated IL-8 mRNA expression, as analyzed by RT-PCR and real-time PCR, which was abolished by the transcription inhibitor actinomycin D. Reporter gene assay showed that beta-tryptase-induced IL-8 transcription was mediated by the transcription factors activator protein-1, CCAAT/enhancer binding protein, and NF-kappaB, and chromatin immunoprecipitation assay demonstrated that beta-tryptase induced in vivo binding of these transcription factors to the IL-8 gene promoter. Furthermore, beta-tryptase stabilized IL-8 mRNA, suggesting additional post-transcriptional regulation. Collectively these findings show that beta-tryptase up-regulates IL-8 expression in ASM cells through a PAR-2-independent proteolytic mechanism and coordinated transcriptional and post-transcriptional regulation, which may be of particular importance in understanding the role and the mechanisms of action of beta-tryptase in regulating chemokine expression in mast cell-related disorders.

Protease-activated receptors: novel PARtners in innate immunity

Protease-activated receptors (PARs) belong to a family of G protein-coupled receptors activated by serine proteases via proteolytic cleavage. PARs are expressed on epithelial cells, endothelial cells, and leukocytes, indicating a role in controlling barrier function against external danger. During inflammation, microorganisms as well as host immune cells release various proteases activating PARs. Thus, PARs can be viewed as an integral component of the host antimicrobial alarm system. When stimulated, PARs regulate various functions of leukocytes in vivo and in vitro, revealing a novel pathway by which proteases affect innate immune responses. Understanding protease-immune interactions could lead to novel strategies for the treatment of infectious and immune-related diseases.

The protease-activated receptor2 (PAR2)-prostaglandin E2-prostanoid EP receptor axis: a potential bronchoprotective unit in the respiratory tract?

Protease-activated receptor2 (PAR2) is a subtype of G protein-coupled receptor that is widely expressed within the respiratory tract. Stimulation of PAR2 by proteases such as trypsin and tryptase, or by small peptidic activators induces a complex array of effects within the airways. One such PAR2-mediated effect by basal airway epithelial cells is the generation of prostaglandin E2. Prostaglandin E2 produces a raft of anti-inflammatory effects within the airways, principally through the activation of the prostanoid EP2 and EP3 receptor subtypes. This article reviews the PAR2-prostaglandin E2-prostanoid EP receptor axis and discusses approaches through which its activation may provide beneficial effects in respiratory disease.

Tryptase activates phosphatidylinositol 3-kinases proteolytically independently from proteinase-activated receptor-2 in cultured dog airway smooth muscle cells

Mast cell tryptase is a potent mitogen for many cells in the airways and lung, but the cellular mechanisms for its growth stimulatory effects are poorly understood. Our major goal was to determine whether tryptase activates phosphatidylinositol 3-kinases (PI 3-kinases) in cultured dog tracheal smooth muscle cells to induce its mitogenic effects. After exposure to tryptase, cells were lysed. Immunocomplexes prepared from the lysates using an antibody to the p85 subunit of PI 3-kinase, but not using anti-phosphotyrosine antibodies, possessed increased capacity to phosphorylate inositol on its D3 hydroxyl group. Tryptase also increased phosphorylation of Akt, a downstream target of PI 3-kinases. This effect was abolished by one PI 3-kinase inhibitor, wortmannin, and attenuated by another, LY-294004, which also blocked tryptase's mitogenic effects. Treatment of tryptase with p-amidino phenylmethanesulfonyl fluoride, to abolish its proteolytic activity irreversibly, inhibited its stimulatory effects on Akt phosphorylation. Proteinase-activated receptor-2 (PAR-2)-activating peptides failed to increase Akt phosphorylation in cultured dog tracheal smooth muscle cells, but the PAR-2-activating peptides did induce brisk increases in Akt phosphorylation in Madin-Darby canine kidney cells. We concluded that tryptase activates PI 3-kinases in cultured dog tracheal smooth muscle cells to induce its potent mitogenic effects. These effects of tryptase on PI 3-kinases appear to occur via novel proteolytic mechanisms independent from PAR-2. Also, tryptase, although comparable in mitogenic potency to platelet-derived growth factor (PDGF), induces considerably less tyrosine phosphorylation on proteins than occur in response to PDGF.

Physiology and pathophysiology of proteinase-activated receptors (PARs): PARs in the respiratory system: cellular signaling and physiological/pathological roles

Proteinase-activated receptors (PARs), a family of G protein-coupled receptors, are widely distributed in the mammalian body, playing a variety of physiological/pathophysiological roles. In the respiratory systems, PARs, particularly PAR-2 and PAR-1, are expressed in the epithelial and smooth muscle cells. In addition to the G(q/11)-mediated activation of the phospholipase C beta pathway, epithelial PAR activation causes prompt and/or delayed prostanoid formation, leading to airway smooth muscle relaxation and/or modulation of an inflammatory process. PAR-2 present in the epithelium and smooth muscle is considered primarily pro-inflammatory in the respiratory system, although PAR-2 may also be anti-inflammatory under certain conditions. In the lung epithelial cells, PAR-2 can also be activated by exogenous proteinases including house dust mite allergens, in addition to various possible endogenous agonist proteinases. Clinical evidence also suggests possible involvement of PARs, particularly PAR-2, in respiratory diseases. PARs thus appear to play critical roles in the respiratory systems, and the agonists/antagonists for PARs may serve as the novel therapeutic strategy for treatment of certain respiratory diseases including asthma.

Influence of resting tension on protease-activated receptor-mediated relaxation in guinea-pig tracheas

We investigate the role of resting tension on thrombin (THR) induced relaxation of guinea-pig tracheas precontracted with acetylcholine (ACh). Isometric contractions of isolated guinea-pig tracheas were recorded at 4 and 6 g resting tension; and ACh dose-response curves were performed. THR relaxed ACh-precontracted tracheas and this effect was mimicked by the type 2 protease activating receptor agonist peptide (PAR-2 AP) and trypsin. The relaxant effect of 3 U ml(-1) THR and 100 nmol ml(-1) PAR-2 AP was prevented at 4 g by preincubation with the nitric oxide synthase (NOS) inhibitor l-NAME and at 6g resting tension by ibuprofen and diclofenac. However, adenosine trisphospahate (ATP) relaxation was totally prevented by cyclooxygenase (COX) inhibitors but not by NOS inhibitors at both resting tensions. Resting tension influenced the effect of PGE2 on contractile tone of isolated guinea-pig tracheas, the maximal relaxation being -11.1+/-2.97 and -2.0+/-0.4 6 mg mg(-1) tissue wet weight at 6 and 4 g, respectively. Moreover, 30 nmol ml(-1) PGE2 can relax ACh-precontracted tracheas, being the effect up to 91 and 30% at 6 and 4 g, respectively. These data demonstrate that trachea responsiveness is highly dependent on the smooth muscle length, revealing new aspects of stretch-activated receptors that can influence trachea responsiveness in vivo.