A major role for proteolytic activity and proteinase-activated receptor-2 in the pathogenesis of infectious colitis

Cathepsin S causes inflammatory pain via biased agonism of PAR2 and TRPV4

Serine proteases such as trypsin and mast cell tryptase cleave protease-activated receptor-2 (PAR2) at R(36)↓S(37) and reveal a tethered ligand that excites nociceptors, causing neurogenic inflammation and pain. Whether proteases that cleave PAR2 at distinct sites are biased agonists that also induce inflammation and pain is unexplored. Cathepsin S (Cat-S) is a lysosomal cysteine protease of antigen-presenting cells that is secreted during inflammation and which retains activity at extracellular pH. We observed that Cat-S cleaved PAR2 at E(56)↓T(57), which removed the canonical tethered ligand and prevented trypsin activation. In HEK and KNRK cell lines and in nociceptive neurons of mouse dorsal root ganglia, Cat-S and a decapeptide mimicking the Cat-S-revealed tethered ligand-stimulated PAR2 coupling to Gαs and formation of cAMP. In contrast to trypsin, Cat-S did not mobilize intracellular Ca(2+), activate ERK1/2, recruit β-arrestins, or induce PAR2 endocytosis. Cat-S caused PAR2-dependent activation of transient receptor potential vanilloid 4 (TRPV4) in Xenopus laevis oocytes, HEK cells and nociceptive neurons, and stimulated neuronal hyperexcitability by adenylyl cyclase and protein kinase A-dependent mechanisms. Intraplantar injection of Cat-S caused inflammation and hyperalgesia in mice that was attenuated by PAR2 or TRPV4 deletion and adenylyl cyclase inhibition. Cat-S and PAR2 antagonists suppressed formalin-induced inflammation and pain, which implicates endogenous Cat-S and PAR2 in inflammatory pain. Our results identify Cat-S as a biased agonist of PAR2 that causes PAR2- and TRPV4-dependent inflammation and pain. They expand the role of PAR2 as a mediator of protease-driven inflammatory pain.

Structure and putative signaling mechanism of Protease activated receptor 2 (PAR2) - a promising target for breast cancer

Experimental evidences have observed enhanced expression of protease activated receptor 2 (PAR2) in breast cancer consistently. However, it is not yet recognized as an important therapeutic target for breast cancer as the primary molecular mechanisms of its activation are not yet well-defined. Nevertheless, recent reports on the mechanism of GPCR activation and signaling have given new insights to GPCR functioning. In the light of these details, we attempted to understand PAR2 structure & function using molecular modeling techniques. In this work, we generated averaged representative stable models of PAR2, using protease activated receptor 1 (PAR1) as a template and selected conformation based on their binding affinity with PAR2 specific agonist, GB110. Further, the selected model was used for studying the binding affinity of putative ligands. The selected ligands were based on a recent publication on phylogenetic analysis of Class A rhodopsin family of GPCRs. This study reports putative ligands, their interacting residues, binding affinity and molecular dynamics simulation studies on PAR2-ligand complexes. The results reported from this study would be useful for researchers and academicians to investigate PAR2 function as its physiological role is still hypothetical. Further, this information may provide a novel therapeutic scheme to manage breast cancer.

A Role of a Lymphocyte Tryptase, Granzyme A, in Experimental Ulcerative Colitis

In the large-intestinal mucosae of rats orally administered dextran sulfate sodium, which induces an enteritis resembling ulcerative colitis (UC), the activity for granzyme A, a lymphocyte tryptase, increased at an earlier stage than that at which UC markers (growth-regulated gene product/cytokine-induced neutrophil chemoattractant-1 and caspase-3) increased. This suggests involvement of the enzyme in the exacerbation and perpetuation of enteritis.

Intestinal protease-activated receptor-2 and fecal serine protease activity are increased in canine inflammatory bowel disease and may contribute to intestinal cytokine expression

Serine proteases elicit cellular responses via protease-activated receptor-2 (PAR-2) which is known to regulate inflammation and the immune response. Although the gastrointestinal tract is exposed to large amounts of proteolytic enzymes, the role of PAR-2 in canine inflammatory bowel disease (IBD) remains unclear. The objective of this study was to investigate the effects of PAR-2 activation on inflammatory cytokine/chemokine gene expression in canine intestine and the expression of intestinal PAR-2 and fecal serine protease activity in dogs with IBD. Duodenal biopsies from healthy dogs were cultured and treated ex vivo with trypsin or PAR-2 agonist peptide, and inflammatory cytokine/chemokine gene expression in the tissues was then quantified by real-time PCR. PAR-2 mRNA and protein expression levels in the duodenal mucosa were examined by real-time PCR and immunohistochemistry, respectively. Fecal serine protease activity was determined by azocasein assay. In ex vivo-cultured duodenum, trypsin and PAR-2 agonist peptide induced significant up-regulation of mRNA expression levels of interleukin-1 β (IL-1β), IL-8, mucosae-associated epithelial chemokine (MEC) and fractalkine, and this up-regulation was inhibited by a serine protease inhibitor. Duodenal PAR-2 mRNA and protein expression levels were higher in dogs with IBD than in healthy control dogs. Fecal serine protease activity was significantly elevated in dogs with IBD, and the level of activity correlated positively with the clinical severity score. These results suggest that PAR-2 may contribute to the pathogenesis of canine IBD by inducing expression of inflammatory mediators in response to luminal serine proteases.

Luminal trypsin induces enteric nerve-mediated anion secretion in the mouse cecum

Proteases play a diverse role in health and disease. An excessive concentration of proteases has been found in the feces of patients with inflammatory bowel disease or irritable bowel syndrome and been implicated in the pathogenesis of such disorders. This study examined the effect of the serine protease, trypsin, on intestinal epithelial anion secretion when added to the luminal side. A mucosal-submucosal sheet of the mouse cecum was mounted in Ussing chambers, and the short-circuit current (I sc) was measured. Trypsin added to the mucosal (luminal) side increased I sc with an ED50 value of approximately 10 μM. This I sc increase was suppressed by removing Cl(-) from the bathing solution. The I sc increase induced by 10-100 μM trypsin was substantially suppressed by tetrodotoxin, and partially inhibited by a neurokinin-1 receptor antagonist, but not by a muscarinic or nicotinic ACh-receptor antagonist. The trypsin-induced I sc increase was also significantly inhibited by a 5-hydroxytryptamine-3 receptor (5-HT3) antagonist and substantially suppressed by the simultaneous addition of both 5-HT3 and 5-HT4 receptor antagonists. We conclude that luminal trypsin activates the enteric reflex to induce anion secretion, 5-HT and substance P playing important mediating roles in this secreto-motor reflex. Luminal proteases may contribute to the cause of diarrhea occurring with some intestinal disorders.

Enteric bacterial proteases in inflammatory bowel disease- pathophysiology and clinical implications

Numerous reports have identified a dysbiosis in the intestinal microbiota in patients suffering from inflammatory bowel diseases (IBD), yet the mechanism(s) in which this complex microbial community initiates or perpetuates inflammation remains unclear. The purpose of this review is to present evidence for one such mechanism that implicates enteric microbial derived proteases in the pathogenesis of IBD. We highlight and discuss studies demonstrating that proteases and protease receptors are abundant in the digestive system. Additionally, we investigate studies demonstrating an association between increased luminal protease activity and activation of protease receptors, ultimately resulting in increased intestinal permeability and exacerbation of colitis in animal models as well as in human IBD. Proteases are essential for the normal functioning of bacteria and in some cases can serve as virulence factors for pathogenic bacteria. Although not classified as traditional virulence factors, proteases originating from commensal enteric bacteria also have a potential association with intestinal inflammation via increased enteric permeability. Reports of increased protease activity in stools from IBD patients support a possible mechanism for a dysbiotic enteric microbiota in IBD. A better understanding of these pathways and characterization of the enteric bacteria involved, their proteases, and protease receptors may pave the way for new therapeutic approaches for these diseases.

Modulation of protease activated receptor 1 influences human metapneumovirus disease severity in a mouse model

Human metapneumovirus (hMPV) infection causes acute respiratory tract infections (RTI) which can result in hospitalization of both children and adults. To date, no antiviral or vaccine is available for this common viral infection. Immunomodulators could represent an interesting strategy for the treatment of severe viral infection. Recently, the role of protease-activated receptors (PAR) in inflammation, coagulation and infection processes has been of growing interest. Herein, the effects of a PAR1 agonist and a PAR1 antagonist on hMPV infection were investigated in BALB/c mice. Intranasal administration of the PAR1 agonist resulted in increased weight loss and mortality of infected mice. Conversely, the PAR1 antagonist was beneficial to hMPV infection by decreasing weight loss and clinical signs and by significantly reducing pulmonary inflammation, pro-inflammatory cytokine levels (including IL-6, KC and MCP-1) and recruitment of immune cells to the lungs. In addition, a significant reduction in pulmonary viral titers was also observed in the lungs of PAR1 antagonist-treated mice. Despite no apparent direct effect on virus replication during in vitro experiments, an important role for PAR1 in the regulation of furin expression in the lungs was shown for the first time. Further experiments indicated that the hMPV fusion protein can be cleaved by furin thus suggesting that PAR1 could have an effect on viral infectivity in addition to its immunomodulatory properties. Thus, inhibition of PAR1 by selected antagonists could represent an interesting strategy for decreasing the severity of paramyxovirus infections.

Applications of small molecule probes in dissecting mechanisms of bacterial virulence and host responses

Elucidating the molecular and biochemical details of bacterial infections can be challenging because of the many complex interactions that exist between a pathogen and its host. Consequently, many tools have been developed to aid the study of bacterial pathogenesis. Small molecules are a valuable complement to traditional genetic techniques because they can be used to rapidly perturb genetically intractable systems and to monitor post-translationally regulated processes. Activity-based probes are a subset of small molecules that covalently label an enzyme of interest based on its catalytic mechanism. These tools allow monitoring of enzyme activation within the context of a native biological system and can be used to dissect the biochemical details of enzyme function. This review describes the development and application of activity-based probes for examining aspects of bacterial infection on both sides of the host-pathogen interface.

Toward drugs for protease-activated receptor 2 (PAR2)

PAR2 has a distinctive functional phenotype among an unusual group of GPCRs called protease activated receptors, which self-activate after cleavage of their N-termini by mainly serine proteases. PAR2 is the most highly expressed PAR on certain immune cells, and it is activated by multiple proteases (but not thrombin) in inflammation. PAR2 is expressed on many types of primary human cells and cancer cells. PAR2 knockout mice and PAR2 agonists and antagonists have implicated PAR2 as a promising target in inflammatory conditions; respiratory, gastrointestinal, metabolic, cardiovascular, and neurological dysfunction; and cancers. This article summarizes salient features of PAR2 structure, activation, and function; opportunities for disease intervention via PAR2; pharmacological properties of published or patented PAR2 modulators (small molecule agonists and antagonists, pepducins, antibodies); and some personal perspectives on limitations of assessing their properties and on promising new directions for PAR2 modulation.

Cross-talk between toll-like receptor 4 (TLR4) and proteinase-activated receptor 2 (PAR(2) ) is involved in vascular function

BACKGROUND AND PURPOSE

Proteinase-activated receptors (PARs) and toll-like receptors (TLRs) are involved in innate immune responses. The aim of this study was to evaluate the possible cross-talk between PAR(2) and TLR4 in vessels in physiological condition and how it varies following stimulation of TLR4 by using in vivo and ex vivo models.

EXPERIMENTAL APPROACH

Thoracic aortas were harvested from both naïve and endotoxaemic rats for in vitro studies. Arterial blood pressure was monitored in anaesthetized rats in vivo. LPS was used as a TLR4 agonist while PAR(2) activating peptide (AP) was used as a PAR(2) agonist. Aortas harvested from TLR4(-/-) mice were also used to characterize the PAR(2) response.

KEY RESULTS

PAR(2) , but not TLR4, expression was enhanced in aortas of endotoxaemic rats. PAR(2) AP-induced vasorelaxation was increased in aortic rings of LPS-treated rats. TLR4 inhibitors, curcumine and resveratrol, reduced PAR(2) AP-induced vasorelaxation and PAR(2) AP-induced hypotension in both naïve and endotoxaemic rats. Finally, in aortic rings from TLR4(-/-) mice, the expression of PAR(2) was reduced and the PAR(2) AP-induced vasodilatation impaired compared with those from wild-type mice and both resveratrol and curcumine were ineffective.

CONCLUSIONS AND IMPLICATIONS

Cross-talk between PAR(2) and TLR4 contributes to vascular homeostasis.

Genetic risk factors for pancreatic disorders

A combination of genetic, environmental, and metabolic factors contribute to the development and recurrence of acute and chronic pancreatitis; information on all of these is required to manage patients effectively. For example, variants that affect regulation of the protease, serine (PRSS)1-PRSS2, and claudin (CLDN)2 loci, rather than their coding sequences, interact with other genetic and environmental factors to affect disease development. New strategies are needed to use these data and determine their contribution to pathogenesis, because these variants differ from previously studied, rare variants in exons (coding regions) of genes such as PRSS1, SPINK1, cystic fibrosis transmembrane conductance regulator (CFTR), chymotrypsin (CTR)C, and calcium-sensing receptor (CASR). Learning how various genetic factors affect pancreatic cells and systems could lead to etiology-based therapies rather than treatment of symptoms.

Activation of PAR(2) receptors sensitizes primary afferents and causes leukocyte rolling and adherence in the rat knee joint

BACKGROUND AND PURPOSE

The PAR(2) receptors are involved in chronic arthritis by mechanisms that are as yet unclear. Here, we examined PAR(2) activation in the rat knee joint.

EXPERIMENTAL APPROACH

PAR(2) in rat knee joint dorsal root ganglia (DRG) cells at L3-L5, retrogradely labelled with Fluoro-gold (FG) were demonstrated immunohistochemically. Electrophysiological recordings from knee joint nerve fibres in urethane anaesthetized Wistar rats assessed the effects of stimulating joint PAR(2) with its activating peptide, 2-furoyl-LIGRLO-NH(2) (1-100 nmol·100 μL(-1) , via close intra-arterial injection). Fibre firing rate was recorded during joint rotations before and 15 min after administration of PAR(2) activating peptide or control peptide. Leukocyte kinetics in the synovial vasculature upon PAR(2) activation were followed by intravital microscopy for 60 min after perfusion of 2-furoyl-LIGRLO-NH(2) or control peptide. Roles for transient receptor potential vanilloid-1 (TRPV1) or neurokinin-1 (NK(1) ) receptors in the PAR(2) responses were assessed using the selective antagonists, SB366791 and RP67580 respectively.

KEY RESULTS

PAR(2) were expressed in 59 ± 5% of FG-positive DRG cells; 100 nmol 2-furoyl-LIGRLO-NH(2) increased joint fibre firing rate during normal and noxious rotation, maximal at 3 min (normal; 110 ± 43%, noxious; 90 ± 31%). 2-Furoyl-LIGRLO-NH(2) also significantly increased leukocyte rolling and adhesion over 60 min. All these effects were blocked by pre-treatment with SB366791 and RP67580 (P < 0.05 compared with 2-furoyl-LIGRLO-NH(2) alone).

CONCLUSIONS AND IMPLICATIONS

PAR(2) receptors play an acute inflammatory role in the knee joint via TRPV1- and NK(1) -dependent mechanisms involving both PAR(2) -mediated neuronal sensitization and leukocyte trafficking.

PAR-2-mediated control of barrier function and motility differs between early and late phases of postinfectious gut dysfunction in the rat

Proteinase-activated receptor-2 (PAR-2) and mast cell (MC) mediators contribute to inflammatory and functional gastrointestinal disorders. We aimed to characterize jejunal PAR-2-mediated responses and the potential MC involvement in the early and late phases of a rat model of postinfectious gut dysfunction. Jejunal tissues of control and Trichinella spiralis-infected (14 and 30 days postinfection) rats, treated or not with the MC stabilizer, ketotifen, were used. Histopathology and immunostaining were used to characterize inflammation, PAR-2 expression, and mucosal and connective tissue MCs. Epithelial barrier function (hydroelectrolytic transport and permeability) and motility were assessed in vitro in basal conditions and after PAR-2 activation. Intestinal inflammation on day 14 postinfection (early phase) was significantly resolved by day 30 (late phase) although MC counts and epithelial permeability remained increased. PAR-2-mediated ion transport (Ussing chambers, in vitro) and epithelial surface PAR-2 expression were reduced in the early phase, with a trend toward normalization during the late phase. In control conditions, PAR-2 activation (organ bath) induced biphasic motor responses (relaxation followed by excitation). At 14 days postinfection, spontaneous contractility and PAR-2-mediated relaxations were enhanced; motor responses were normalized on day 30. Postinfectious changes in PAR-2 functions were not affected by ketotifen treatment. We concluded that, in the rat model of Trichinella spiralis infection, alterations of intestinal PAR-2 function and expression depend on the inflammatory phase considered. A lack of a ketotifen effect suggests no interplay between MCs and PAR-2-mediated motility and ion transport alterations. These observations question the role of MC mediators in PAR-2-modulating postinfectious gut dysfunction.

Novel animal models of acute and chronic cancer pain: a pivotal role for PAR2

Targeted therapy to prevent the progression from acute to chronic pain in cancer patients remains elusive. We developed three novel cancer models in mice that together recapitulate the anatomical, temporal, and functional characteristics of acute and chronic head and neck cancer pain in humans. Using pharmacologic and genetic approaches in these novel cancer models, we identified the interaction between protease-activated receptor 2 (PAR2) and serine proteases to be of central importance. We show that serine proteases such as trypsin induce acute cancer pain in a PAR2-dependent manner. Chronic cancer pain is associated with elevated serine proteases in the cancer microenvironment and PAR2 upregulation in peripheral nerves. Serine protease inhibition greatly reduces the severity of persistent cancer pain in wild-type mice, but most strikingly, the development of chronic cancer pain is prevented in PAR2-deficient mice. Our results demonstrate a direct role for PAR2 in acute cancer pain and suggest that PAR2 upregulation may favor the development and maintenance of chronic cancer pain. Targeting the PAR2-serine protease interaction is a promising approach to the treatment of acute cancer pain and prevention of chronic cancer pain.

PAR2-induced inflammatory responses in human kidney tubular epithelial cells

Protease-activated receptor-2 (PAR2) is a G protein-coupled receptor abundantly expressed in the kidney. The aim of this study was to profile inflammatory gene and protein expression induced by PAR2 activation in human kidney tubular epithelial cells (HTEC). A novel PAR2 antagonist, GB88, was used to confirm agonist specificity. Intracellular Ca(2+) (iCa(2+)) mobilization, confocal microscopy, gene expression profiling, qRTPCR, and protein expression were used to characterize PAR2 activation. PAR2 induced a pronounced increase in iCa(2+) concentration that was blocked by the PAR2 antagonist. Treatment with SLIGKV-NH2 at the apical or basolateral cell surface for 5 h induced expression of a range of inflammatory genes by greater than fourfold, including IL-1β, TRAF1, IL-6, and MMP-1, as assessed by cDNA microarray and qRTPCR analysis. Using antibody arrays, GM-CSF, ICAM-1, TNF-α, MMP-1, and MMP-10 were among the induced proteins secreted. Cytokine-specific ELISAs identified three- to sixfold increases in GM-CSF, IL-6, IL-8, and TNF-α, which were blocked by GB88 and protein kinase C inhibitors. Treatment of cells at the basolateral surface induced more potent inflammatory responses, with release of MCP-1 and fibronectin to the apical and basolateral compartments; apical treatment only increased secretion of these factors to the apical compartment. PAR2 activation at the basolateral surface dramatically reduced transepithelial electrical resistance (TEER) whereas apical treatment had no effect. There was very little leakage (<5%) of peptides across the cell monolayer (liquid chromatography-mass spectrometry). In summary, SLIGKV-NH2 induced robust proinflammatory responses in HTEC that were antagonized by GB88. These results suggest that PAR2 antagonists could be useful disease-modifying, anti-inflammatory agents in kidney disease.

[Roles of Pseudomonas aeruginosa-derived proteases as a virulence factor]

The major virulence factors produced by Pseudomonas aeruginosa include secreted proteases that damage host tissues. Of the proteases analyzed, alkaline protease (AprA) and elastase B (LasB) have been characterized extensively. Although P. aeruginosa protein database predicts the presence of several other potential proteases, little has been known about the proteases involving in the pathogenicity of this organism. In this study, we found that P. aeruginosa produces a novel large extracellular protease (LepA) distinct from known proteases such as AprA and LasB. Sequence analysis of LepA showed a molecular future of the proteins transported by the two-partner secretion pathway. We demonstrated that LepA can activate NF-kB-driven promoter through protease-activated receptor-1, -2 or -4. On the other hand, one of the functions of proteases is to hydrolyze proteins and peptides for nutrient acquisition either by degrading host enzymes or even by causing tissue damage to further the survival of the bacterium. Therefore, to investigate the role of LepA in in vivo virulence and growth of P. aeruginosa, we compared the virulence and growth of a wild-type strain and its mutant using a mouse model of acute systemic infection by P. aeruginosa. Our results suggest that LepA contributes to the in vivo virulence and growth of P. aeruginosa.

Modulating human proteinase activated receptor 2 with a novel antagonist (GB88) and agonist (GB110)

BACKGROUND AND PURPOSE

Many cells express proteinase activated receptor 2 (PAR2) on their plasma membrane. PAR2 is activated by proteolytic enzymes, such as trypsin and tryptase that cleave the receptor N-terminus, inititating signalling to intracellular G proteins. Studies on PAR2 have relied heavily upon activating effects of proteases and peptide agonists that lack stability and bioavailability in vivo.

EXPERIMENTAL APPROACH

A novel small molecule agonist GB110 and an antagonist GB88 were characterized in vitro against trypsin, peptide agonists, PAR2 antibody, PAR1 agonists and flow cytometry,in seven cell lines using intracellular Ca(2+) mobilization and examined in vivo against PAR2- and PAR1-induced rat paw oedema.

KEY RESULTS

GB110 is a potent non-peptidic agonist activating PAR2-mediated Ca(2+) release in HT29 cells (EC(50) ∼200 nM) and six other human cell lines, inducing PAR2 internalization. GB88 is a unique PAR2 antagonist, inhibiting PAR2 activated Ca(2+) release (IC(50) ∼2 µM) induced by native (trypsin) or synthetic peptide and non-peptide agonists. GB88 was a competitive and surmountable antagonist of agonist 2f-LIGRLO-NH(2), a competitive but insurmountable antagonist of agonist GB110, and a non-competitive insurmountable antagonist of trypsin. GB88 was orally active and anti-inflammatory in vivo, inhibiting acute rat paw oedema elicited by agonist GB110 and proteolytic or peptide agonists of PAR2 but not by corresponding agonists of PAR1 or PAR4.

CONCLUSIONS AND IMPLICATIONS

The novel PAR2 agonist and antagonist modulate intracellular Ca(2+) and rat paw oedema, providing novel molecular tools for examining PAR2-mediated diseases.

Epidermal growth factor receptor transactivation is required for proteinase-activated receptor-2-induced COX-2 expression in intestinal epithelial cells

Proteinase-activated receptor (PAR)(2), a G protein-coupled receptor activated by serine proteinases, has been implicated in both intestinal inflammation and epithelial proliferation. Cyclooxygenase (COX)-2 is overexpressed in the gut during inflammation as well as in colon cancer. We hypothesized that PAR(2) drives COX-2 expression in intestinal epithelial cells. Treatment of Caco-2 colon cancer cells with the PAR(2)-activating peptide 2-furoyl-LIGRLO-NH(2) (2fLI), but not by its reverse-sequence PAR(2)-inactive peptide, for 3 h led to an increase in intracellular COX-2 protein expression accompanied by a COX-2-dependent increase in prostaglandin E(2) production. 2fLI treatment for 30 min significantly increased metalloproteinase activity in the culture supernatant. Increased epidermal growth factor receptor (EGFR) phosphorylation was observed in cell lysates following 40 min of treatment with 2fLI. The broad-spectrum metalloproteinase inhibitor marimastat inhibited both COX-2 expression and EGFR phosphorylation. The EGFR tyrosine kinase inhibitor PD153035 also abolished 2fLI-induced COX-2 expression. Although PAR(2) activation increased ERK MAPK phosphorylation, neither ERK pathway inhibitors nor a p38 MAPK inhibitor affected 2fLI-induced COX-2 expression. However, inhibition of either Src tyrosine kinase signaling by PP2, Rho kinase signaling by Y27632, or phosphatidylinositol 3 (PI3) kinase signaling by LY294002 prevented 2fLI-induced COX-2 expression. Trypsin increased COX-2 expression through PAR(2) in Caco-2 cells and in an EGFR-dependent manner in the noncancerous intestinal epithelial cell-6 cell line. In conclusion, PAR(2) activation drives COX-2 expression in Caco-2 cells via metalloproteinase-dependent EGFR transactivation and activation of Src, Rho, and PI3 kinase signaling. Our findings provide a mechanism whereby PAR(2) can participate in the progression from chronic inflammation to cancer in the intestine.

Matrix metalloproteinase 9 contributes to gut microbe homeostasis in a model of infectious colitis

BACKGROUND

Inflammatory bowel diseases are associated with increased expression of zinc-dependent Matrix Metalloproteinase 9 (MMP-9). A stark dysregulation of intestinal mucosal homeostasis has been observed in patients with chronic inflammatory bowel diseases. We therefore sought to determine the contribution of MMP-9 to the pathogenesis of Citrobacter rodentium-induced colitis and its effects on gut microbiome homeostasis.

RESULTS

Wild-type and MMP-9-/- mice aged 5-6 weeks were challenged with C. rodentium by orogastric gavage and sacrificed either 10 or 30 days post-infection. Disease severity was assessed by histological analysis of colonic epithelial hyperplasia and by using an in vivo intestinal permeability assay. Changes in the inflammatory responses were measured by using qPCR, and the composition of the fecal microbiome evaluated with both qPCR and terminal restriction fragment length polymorphism. Activation and localization of MMP-9 to the apical surface of the colonic epithelium in response to C. rodentium infection was demonstrated by both zymography and immunocytochemistry. The pro-inflammatory response to infection, including colonic epithelial cell hyperplasia and barrier dysfunction, was similar, irrespective of genotype. Nonmetric multidimensional scaling of terminal restriction fragments revealed a different fecal microbiome composition and C. rodentium colonization pattern between genotypes, with MMP-9-/- having elevated levels of protective segmented filamentous bacteria and interleukin-17, and lower levels of C. rodentium. MMP-9-/- but not wild-type mice were also protected from reductions in fecal microbial diversity in response to the bacterial enteric infection.

CONCLUSIONS

These results demonstrate that MMP-9 expression in the colon causes alterations in the fecal microbiome and has an impact on the pathogenesis of bacterial-induced colitis in mice.

Targeting proteinase-activated receptors: therapeutic potential and challenges

Proteinase-activated receptors (PARs), a family of four seven-transmembrane G protein-coupled receptors, act as targets for signalling by various proteolytic enzymes. PARs are characterized by a unique activation mechanism involving the proteolytic unmasking of a tethered ligand that stimulates the receptor. Given the emerging roles of these receptors in cancer as well as in disorders of the cardiovascular, musculoskeletal, gastrointestinal, respiratory and central nervous system, PARs have become attractive targets for the development of novel therapeutics. In this Review we summarize the mechanisms by which PARs modulate cell function and the roles they can have in physiology and diseases. Furthermore, we provide an overview of possible strategies for developing PAR antagonists.

The expression of protease-activated receptor 2 and 4 in the colon of irritable bowel syndrome patients

BACKGROUND

Irritable bowel syndrome (IBS) pathophysiology has not been fully understood. Abnormalities of serine proteases have been identified in IBS patients. In addition, protease-activated receptors (PAR) activation interferes with several components of the pathogenesis of IBS, so, evaluating the PAR expression in IBS patients may contribute to understanding the pathogenesis of the disease.

AIMS

This study aimed to investigate whether the expression of PAR4 and PAR2 in the colon was changed in IBS patients and was associated with IBS.

METHODS

Colon mucosal biopsies of 34 IBS patients (16 constipation- and 18 diarrhea-predominant) and 18 control subjects were collected. Gene transcripts of PAR2, PAR4, tryptase, and trypsin were quantified using real-time polymerase chain reaction (PCR) and the expression of PAR2 and PAR4 receptors was also measured by immunohistology and image analysis.

RESULTS

In IBS patients, the mRNA expression of tryptase and trypsin normalized against β-actin gene was higher compared to control subjects (P < 0.001). No difference was observed in the PAR2 mRNA level or protein level between control subjects on the one hand and IBS patients or subgroups on the other. In IBS or IBS subgroups patients, the expression of PAR4 in the mRNA level or protein level was lower than the control subjects.

CONCLUSIONS

This study, for the first time, indicated the PAR4 expression in IBS patients. Decreased PAR4 expression may help us to understand the pathogenesis of IBS.

Brain-gut interactions increase peripheral nociceptive signaling in mice with postinfectious irritable bowel syndrome

BACKGROUND & AIMS

To investigate the peripheral sensory effects of repeated stress in patients with postinfectious irritable bowel syndrome (IBS), we tested whether stress following self-limiting bacterial colitis increases colonic dorsal root ganglia (DRG) nociceptive signaling.

METHODS

C57BL/6 mice were infected with Citrobacter rodentium. Stress was induced using a 9-day water avoidance paradigm (days 21-30 after infection). Colonic DRG neuronal excitability was measured using perforated patch clamp techniques, in vitro multi-unit afferent recordings, and measurements of visceromotor reflexes.

RESULTS

Combined stress and prior infection increased corticosterone and epinephrine levels, compared with infected animals, but did not alter the resolution of colonic inflammation. These changes were associated with increased neuronal excitability and parallel changes in multi-unit afferent recordings and visceromotor reflex thresholds. Protease activity was increased at day 30 following infection with C rodentium. Protease inhibitors markedly reduced the effects of colonic supernatants on neuronal excitability from C rodentium but not stressed animals. Colonic DRG neurons expressed messenger RNAs for the β(2) adrenergic and glucocorticoid receptors; incubation with stress mediators recapitulated the effects on neuronal excitability observed with chronic stress alone. PAR2 activation with concentrations of the activating peptide SLIGRL that had no effect on neuronal excitability in controls caused marked increases in excitability when applied to neurons from chronically stressed animals.

CONCLUSIONS

Stress, combined with prior acute colitis, results in exaggerated peripheral nociceptive signaling. Proteases and stress mediators can signal directly to colonic DRG neurons; further analysis of these pathways could provide new targets for treatment of patients with postinfectious IBS.

Antagonism of protease-activated receptor 2 protects against experimental colitis

Many trypsin-like serine proteases such as β-tryptase are involved in the pathogenesis of colitis and inflammatory bowel diseases. Inhibitors of individual proteases show limited efficacy in treating such conditions, but also probably disrupt digestive and defensive functions of proteases. Here, we investigate whether masking their common target, protease-activated receptor 2 (PAR2), is an effective therapeutic strategy for treating acute and chronic experimental colitis in rats. A novel PAR2 antagonist (5-isoxazoyl-Cha-Ile-spiro[indene-1,4'-piperidine]; GB88) was evaluated for the blockade of intracellular calcium release in colonocytes and anti-inflammatory activity in acute (PAR2 agonist-induced) versus chronic [2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced] models of colitis in Wistar rats. Disease progression (disease activity index, weight loss, and mortality) and postmortem colonic histopathology (inflammation, bowel wall thickness, and myeloperoxidase) were measured. PAR2 and tryptase colocalization were investigated by using immunohistochemistry. GB88 was a more potent antagonist of PAR2 activation in colonocytes than another reported compound, N¹-3-methylbutyryl-N⁴-6-aminohexanoyl-piperazine (ENMD-1068) (IC₅₀ 8 μM versus 5 mM). Acute colonic inflammation induced in rats by the PAR2 agonist SLIGRL-NH₂ was inhibited by oral administration of GB88 (10 mg/kg) with markedly reduced edema, mucin depletion, PAR2 receptor internalization, and mastocytosis. Chronic TNBS-induced colitis in rats was ameliorated by GB88 (10 mg/kg/day p.o.), which reduced mortality and pathology (including colon obstruction, ulceration, wall thickness, and myeloperoxidase release) more effectively than the clinically used drug sulfasalazine (100 mg/kg/day p.o.). These disease-modifying properties for the PAR2 antagonist in both acute and chronic experimental colitis strongly support a pathogenic role for PAR2 and PAR2-activating proteases and therapeutic potential for PAR2 antagonism in inflammatory diseases of the colon.

Protease-activated receptor 2 signaling in inflammation

Protease-activated receptors (PARs) are G protein-coupled receptors that are activated by proteolytical cleavage of the amino-terminus and thereby act as sensors for extracellular proteases. While coagulation proteases activate PARs to regulate hemostasis, thrombosis, and cardiovascular function, PAR2 is also activated in extravascular locations by a broad array of serine proteases, including trypsin, tissue kallikreins, coagulation factors VIIa and Xa, mast cell tryptase, and transmembrane serine proteases. Administration of PAR2-specific agonistic and antagonistic peptides, as well as studies in PAR2 knockout mice, identified critical functions of PAR2 in development, inflammation, immunity, and angiogenesis. Here, we review these roles of PAR2 with an emphasis on the role of coagulation and other extracellular protease pathways that cleave PAR2 in epithelial, immune, and neuronal cells to regulate physiological and pathophysiological processes.

PAR2 promotes vaccine-induced protection against Helicobacter infection in mice

BACKGROUND & AIMS

Protective immunization limits Helicobacter infection of mice by undetermined mechanisms. Protease-activated receptor 2 (PAR2) signaling is believed to regulate immune and inflammatory responses. We investigated the role of PAR2 in vaccine-induced immunity against Helicobacter infection.

METHODS

Immune responses against Helicobacter infection were compared between vaccinated PAR2-/- and wild-type (WT) mice. Bacterial persistence, gastric pathology, and inflammatory and cellular responses were assessed using the rapid urease test (RUT), histologic analyses, quantitative polymerase chain reaction, and flow cytometry, respectively.

RESULTS

Following vaccination, PAR2-/- mice did not have reductions in Helicobacter felis infection (RUT values were 0.01±0.01 for WT mice and 0.11±0.13 for PAR2-/- mice; P<.05). The vaccinated PAR2-/- mice had reduced inflammation-induced stomach tissue damage (tissue damage scores were 8.83±1.47 for WT mice and 4.86±1.35 for PAR2-/- mice; P<.002) and reduced T-helper (Th)17 responses, based on reduced urease-induced interleukin (IL)-17 secretion by stomach mononuclear cells (5182 ± 1265 pg/mL for WT mice and 350±436 pg/mL for PAR2-/- mice; P<.03) and reduced recruitment of CD4+ IL-17+ T cells into the gastric mucosa of PAR2-/- mice following bacterial challenge (3.7%±1.5% for WT mice and 2.6%±1.1% for PAR2-/- mice; P<.05). In vitro, H felis-stimulated dendritic cells (DCs) from WT mice induced greater secretion of IL-17 by ovalbumin-stimulated OT-II transgenic CD4+ T cells compared with DCs from PAR2-/- mice (4298±347 and 3230±779; P<.04), indicating that PAR2-/- DCs are impaired in priming of Th17 cells. Adoptive transfer of PAR2+/+ DCs into vaccinated PAR2-/- mice increased vaccine-induced protection (RUT values were 0.11±0.10 and 0.26±0.15 for injected and noninjected mice, respectively; P<.03).

CONCLUSIONS

PAR2 activates DCs to mediate vaccine-induced protection against Helicobacter infection in mice.

Mesalazine (5-aminosalicylic acid) alters faecal bacterial profiles, but not mucosal proteolytic activity in diarrhoea-predominant irritable bowel syndrome

BACKGROUND

Imbalances in gut luminal bacteria may contribute to the pathogenesis of irritable bowel syndrome (IBS).

AIM

To explore select bacteriological and anti-inflammatory effects of mesalazine (mesalamine; 5-aminosalicylic acid or 5ASA) and their relation to potential therapeutic effects in IBS.

METHODS

Prospective pilot study of 12 women with diarrhoea-predominant IBS. Patients received oral mesalazine (1.5 g b.d.) for 4 weeks followed by a 4-week washout phase. Molecular profiling of stool bacterial communities and IBS symptoms were assessed before, during and after mesalazine treatment. Colonic mucosal biopsies were assessed for proteolytic activity. Qualitative and quantitative effects of mesalazine on stool microbiota, mucosal proteolytic activity and IBS symptoms were assessed.

RESULTS

Faecal bacteria decreased by 46% on mesalazine treatment (P = 0.014), but returned to baseline during washout. Firmicutes and Bacteroidetes represented 95% of identified phylotypes, with a trend towards an increase in the proportion of Firmicutes at week 4 in symptomatic responders [median (IQR) 14% (49) increase] compared with nonresponders [median 5% (11) decrease, P = 0.088]. Rectosigmoid mucosal proteolytic activity did not change between baseline and treatment [median 23.2 (17.9) vs. 19.5 (46.7) mU activity/mg tissue, P = 0.433]. Eight of 12 (67%) patients responded favourably to mesalazine based on a global relief questionnaire, with significant decreases in days with discomfort and increases in bowel movement satisfaction.

CONCLUSIONS

Mesalazine treatment is associated with a decrease in faecal bacteria abundance and rebalancing of the major constituents of the microbiota. Further study of the bacteriological and anti-inflammatory properties of mesalazine in IBS is warranted.

Neutrophil elastase acts as a biased agonist for proteinase-activated receptor-2 (PAR2)

Human neutrophil proteinases (elastase, proteinase-3, and cathepsin-G) are released at sites of acute inflammation. We hypothesized that these inflammation-associated proteinases can affect cell signaling by targeting proteinase-activated receptor-2 (PAR(2)). The PAR family of G protein-coupled receptors is triggered by a unique mechanism involving the proteolytic unmasking of an N-terminal self-activating tethered ligand (TL). Proteinases can either activate PAR signaling by unmasking the TL sequence or disarm the receptor for subsequent enzyme activation by cleaving downstream from the TL sequence. We found that none of neutrophil elastase, cathepsin-G, and proteinase-3 can activate G(q)-coupled PAR(2) calcium signaling; but all of these proteinases can disarm PAR(2), releasing the N-terminal TL sequence, thereby preventing G(q)-coupled PAR(2) signaling by trypsin. Interestingly, elastase (but neither cathepsin-G nor proteinase-3) causes a TL-independent PAR(2)-mediated activation of MAPK that, unlike the canonical trypsin activation, does not involve either receptor internalization or recruitment of β-arrestin. Cleavage of synthetic peptides derived from the extracellular N terminus of PAR(2), downstream of the TL sequence, demonstrated distinct proteolytic sites for all three neutrophil-derived enzymes. We conclude that in inflammation, neutrophil proteinases can modulate PAR(2) signaling by preventing/disarming the G(q)/calcium signal pathway and, via elastase, can selectively activate the p44/42 MAPK pathway. Our data illustrate a new mode of PAR regulation that involves biased PAR(2) signaling by neutrophil elastase and a disarming/silencing effect of cathepsin-G and proteinase-3.

Modifying the protease, antiprotease pattern by elafin overexpression protects mice from colitis

BACKGROUND & AIMS

Colonic tissues of patients with inflammatory bowel disease have been reported to have increased proteolytic activity, but no studies have clearly addressed the role of the balance between proteases and antiproteases in the pathogenesis of colitis. We investigated the role of Elafin, a serine protease inhibitor expressed by skin and mucosal surfaces in human inflammatory conditions, and the proteases neutrophil elastase (NE) and proteinase-3 (PR-3) in mice with colitis.

METHODS

We studied mice with heterozygous disruptions in NE and PR-3, mice that express human elafin (an inhibitor of NE and PR-3), and naïve mice that received intracolonic adenoviral vectors that express elafin. Trinitrobenzene sulfonic acid (TNBS) or dextran sodium sulphate (DSS) was used to induce colitis. Protease, cytokine levels, and NF-κB activity were measured in colons of mice. Caco-2 and HT29 cells were studied in assays for cytokine expression, permeability, and NF-κB activity.

RESULTS

Elafin expression or delivery re-equilibrated the proteolytic balance in inflamed colons of mice. In mice given TNBS or DSS, transgenic expression of elafin or disruption of NE and PR-3 protected against the development of colitis. Similarly, adenoviral delivery of Elafin significantly inhibited inflammatory parameters. Elafin modulated a variety of inflammatory mediators in vitro and in vivo and strengthened intestinal epithelial barrier functions.

CONCLUSIONS

The protease inhibitor Elafin prevents intestinal inflammation in mouse models of colitis and might be developed as a therapeutic agent for inflammatory bowel disease.

Cleavage and activation of a Toll-like receptor by microbial proteases

Toll-like receptors (TLRs) are innate receptors that show high conservation throughout the animal kingdom. Most TLRs can be clustered into phylogenetic groups that respond to similar types of ligands. One exception is avian TLR15. This receptor does not categorize into one of the existing groups of TLRs and its ligand is still unknown. Here we report that TLR15 is a sensor for secreted virulence-associated fungal and bacterial proteases. Activation of TLR15 involves proteolytic cleavage of the receptor ectodomain and stimulation of NF-κB-dependent gene transcription. Receptor activation can be mimicked by the expression of a truncated TLR15 of which the entire ectodomain is removed, suggesting that receptor cleavage alleviates receptor inhibition by the leucine-rich repeat domain. Our results indicate TLR15 as a unique type of innate immune receptor that combines TLR characteristics with an activation mechanism typical for the evolutionary distinct protease-activated receptors.

Structure, function and pathophysiology of protease activated receptors

Discovered in the 1990s, protease activated receptors(1) (PARs) are membrane-spanning cell surface proteins that belong to the G protein coupled receptor (GPCR) family. A defining feature of these receptors is their irreversible activation by proteases; mainly serine. Proteolytic agonists remove the PAR extracellular amino terminal pro-domain to expose a new amino terminus, or tethered ligand, that binds intramolecularly to induce intracellular signal transduction via a number of molecular pathways that regulate a variety of cellular responses. By these mechanisms PARs function as cell surface sensors of extracellular and cell surface associated proteases, contributing extensively to regulation of homeostasis, as well as to dysfunctional responses required for progression of a number of diseases. This review examines common and distinguishing structural features of PARs, mechanisms of receptor activation, trafficking and signal termination, and discusses the physiological and pathological roles of these receptors and emerging approaches for modulating PAR-mediated signaling in disease.

Mucosal allergic sensitization to cockroach allergens is dependent on proteinase activity and proteinase-activated receptor-2 activation

We have shown that proteinase-activated receptor-2 (PAR(2)) activation in the airways leads to allergic sensitization to concomitantly inhaled Ags, thus implicating PAR(2) in the pathogenesis of asthma. Many aeroallergens with proteinase activity activate PAR(2). To study the role of PAR(2) in allergic sensitization to aeroallergens, we developed a murine model of mucosal sensitization to cockroach proteins. We hypothesized that PAR(2) activation in the airways by natural allergens with serine proteinase activity plays an important role in allergic sensitization. Cockroach extract (CE) was administered to BALB/c mice intranasally on five consecutive days (sensitization phase) and a week later for four more days (challenge phase). Airway hyperresponsiveness (AHR) and allergic airway inflammation were assessed after the last challenge. To study the role of PAR(2), mice were exposed intranasally to a receptor-blocking anti-PAR(2) Ab before each administration of CE during the sensitization phase. Mucosal exposure to CE induced eosinophilic airway inflammation, AHR, and cockroach-specific IgG1. Heat-inactivated or soybean trypsin inhibitor-treated CE failed to induce these effects, indicating that proteinase activity plays an important role. The use of an anti-PAR(2) blocking Ab during the sensitization phase completely inhibited airway inflammation and also decreased AHR and the production of cockroach-specific IgG1. PAR(2) activation by CE acts as an adjuvant for allergic sensitization even in the absence of functional TLR4. We conclude that CE induces PAR(2)-dependent allergic airway sensitization in a mouse model of allergic airway inflammation. PAR(2) activation may be a general mechanism used by aeroallergens to induce allergic sensitization.

Proteinase-activated receptor 2 activation promotes an anti-inflammatory and alternatively activated phenotype in LPS-stimulated murine macrophages

Proteinase-activated receptor 2 (PAR(2)), a 7-transmembrane G protein-coupled receptor, contributes to inflammation either positively or negatively in different experimental systems. Previously, we reported that concurrent activation of PAR(2) and TLRs in human lung and colonic epithelial cells resulted in a synergistic increase in NF-κB-mediated gene expression, but a down-regulation of IRF-3-mediated gene expression. In this study, the effect of PAR(2) activation on LPS-induced TLR4 signaling was examined in primary murine macrophages. The PAR(2) activation of wild-type macrophages enhanced LPS-induced expression of the anti-inflammatory cytokine, IL-10, while suppressing gene expression of pro-inflammatory cytokines, TNF-α, IL-6, and IL-12. Similar PAR(2)-mediated effects on LPS-stimulated IL-10 and IL-12 mRNA were also observed in vivo. In contrast, PAR 2-/- macrophages exhibited diminished LPS-induced IL-10 mRNA and protein expression and downstream STAT3 activation, but increased KC mRNA and protein. PAR(2) activation also enhanced both rIL-4- and LPS-induced secretion of IL-4 and IL-13, and mRNA expression of alternatively activated macrophage (AA-M) markers, e.g. arginase-1, mannose receptor, Ym-1. Thus, in the context of a potent inflammatory stimulus like LPS, PAR(2) activation acts to re-establish tissue homeostasis by dampening the production of inflammatory mediators and causing the differentiation of macrophages that may contribute to the development of a Th2 response.

Apical and basolateral pools of proteinase-activated receptor-2 direct distinct signaling events in the intestinal epithelium

Studies suggest that there are two distinct pools of proteinase-activated receptor-2 (PAR₂) present in intestinal epithelial cells: an apical pool accessible from the lumen, and a basolateral pool accessible from the interstitial space and blood. Although introduction of PAR₂ agonists such as 2-furoyl-LIGRL-O-NH₂ (2fAP) to the intestinal lumen can activate PAR₂, the presence of accessible apical PAR₂ has not been definitively shown. Furthermore, some studies have suggested that basolateral PAR₂ responses in the intestinal epithelium are mediated indirectly by neuropeptides released from enteric nerve fibers, rather than by intestinal PAR₂ itself. Here we identified accessible pools of both apical and basolateral PAR₂ in cultured Caco2-BBe monolayers and in mouse ileum. Activation of basolateral PAR₂ transiently increased short-circuit current by activating electrogenic Cl⁻ secretion, promoted dephosphorylation of the actin filament-severing protein, cofilin, and activated the transcription factor, AP-1, whereas apical PAR₂ did not. In contrast, both pools of PAR₂ activated extracellular signal-regulated kinase 1/2 (ERK1/2) via temporally and mechanistically distinct pathways. Apical PAR₂ promoted a rapid, biphasic PLCβ/Ca²(+)/PKC-dependent ERK1/2 activation, resulting in nuclear localization, whereas basolateral PAR₂ promoted delayed ERK1/2 activation which was predominantly restricted to the cytosol, involving both PLCβ/Ca²(+) and β-arrestin-dependent pathways. These results suggest that the outcome of PAR₂ activation is dependent on the specific receptor pool that is activated, allowing for fine-tuning of the physiological responses to different agonists.

Profiling gene expression induced by protease-activated receptor 2 (PAR2) activation in human kidney cells

Protease-Activated Receptor-2 (PAR2) has been implicated through genetic knockout mice with cytokine regulation and arthritis development. Many studies have associated PAR2 with inflammatory conditions (arthritis, airways inflammation, IBD) and key events in tumor progression (angiogenesis, metastasis), but they have relied heavily on the use of single agonists to identify physiological roles for PAR2. However such probes are now known not to be highly selective for PAR2, and thus precisely what PAR2 does and what mechanisms of downstream regulation are truly affected remain obscure. Effects of PAR2 activation on gene expression in Human Embryonic Kidney cells (HEK293), a commonly studied cell line in PAR2 research, were investigated here by comparing 19,000 human genes for intersecting up- or down-regulation by both trypsin (an endogenous protease that activates PAR2) and a PAR2 activating hexapeptide (2f-LIGRLO-NH(2)). Among 2,500 human genes regulated similarly by both agonists, there were clear associations between PAR2 activation and cellular metabolism (1,000 genes), the cell cycle, the MAPK pathway, HDAC and sirtuin enzymes, inflammatory cytokines, and anti-complement function. PAR-2 activation up-regulated four genes more than 5 fold (DUSP6, WWOX, AREG, SERPINB2) and down-regulated another six genes more than 3 fold (TXNIP, RARG, ITGB4, CTSD, MSC and TM4SF15). Both PAR2 and PAR1 activation resulted in up-regulated expression of several genes (CD44, FOSL1, TNFRSF12A, RAB3A, COPEB, CORO1C, THBS1, SDC4) known to be important in cancer. This is the first widespread profiling of specific activation of PAR2 and provides a valuable platform for better understanding key mechanistic roles of PAR2 in human physiology. Results clearly support the development of both antagonists and agonists of human PAR2 as potential disease modifying therapeutic agents.

Role of enteric nerves in immune-mediated changes in protease-activated receptor 2 effects on gut function

BACKGROUND

Protease-activated receptors (PARs) are expressed on structural and immune cells. Control of initiation, duration, and magnitude of PAR effects is linked to the level of receptor expression, availability of proteases, and the intracellular signal transduction machinery. We investigated nematode infection-induced changes in PAR(2) expression and the impact on smooth muscle and epithelial responses to PAR(2) agonists.

METHODS

Smooth muscle and epithelial cell function were assessed in wild-type, and IL-4, IL-13 or STAT6 gene-deficient mice following treatment with vehicle, Nippostrongylus brasiliensis or Heligmosomoides polygyrus, or IL-13. The role of enteric nerves was determined using tetrodotoxin to block nerve conduction. Expression of PAR(2) was assessed by real-time PCR, western blot and immunohistochemistry.

KEY RESULTS

Nematode infection induced a STAT6- and IL-13-dependent up-regulation of PAR(2) mRNA expression. The infection-induced hypercontractility to PAR(2) agonists required STAT6/IL-13 and was neurally mediated. In contrast, the infection-induced decrease in epithelial secretion to PAR(2) agonists was partly dependent on STAT6 and independent of enteric nerves. The hyposecretion was correlated with decreased PAR(2) immunofluorescent staining on the apical surface of epithelial cells, but enhanced lamina propria immunostaining for PAR(2).

CONCLUSIONS & INFERENCES

This is the first study to demonstrate an immune regulation of PAR(2) expression that impacts both smooth muscle and epithelial cell responses to PAR(2) agonists. Differences in responses between smooth muscle and epithelial cells are related to the contribution of enteric nerves. These data provide a mechanism by which activation of PAR(2) in immune-based pathologies can induce both transient and long-lasting changes in gut function.

Granzymes in age-related cardiovascular and pulmonary diseases

Chronic inflammation is a hallmark of age-related cardiovascular and pulmonary diseases. Granzymes are a family of serine proteases that have been traditionally viewed as initiators of immune-mediated cell death. However, recent findings suggest that the pathophysiological role of granzymes is complex. Emerging functions for granzymes in extracellular matrix degradation, autoimmunity, and inflammation suggests a multifactorial mechanism by which these enzymes are capable of mediating tissue damage. Recent discoveries showing that granzymes can be produced and secreted by nonimmune cells during disease provide an additional layer of intricacy. This review examines the emerging biochemical and clinical evidence pertaining to intracellular and/or extracellular granzymes in the pathogenesis of aging and cardiopulmonary diseases.

Detergent-resistant microdomains mediate activation of host cell signaling in response to attaching-effacing bacteria

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 causes outbreaks of bloody diarrhea and the hemolytic-uremic syndrome. EHEC intimately adheres to epithelial cells, effaces microvilli and induces attaching-effacing (AE) lesions. Detergent-resistant microdomains (lipid rafts) serve as membrane platforms for the recruitment of signaling complexes to mediate host responses to infection. The aim of this study was to define the role of lipid rafts in activating signal transduction pathways in response to AE bacterial pathogens. Epithelial cell monolayers were infected with EHEC (MOI 100:1, 3 h, 37 degrees C) and lipid rafts isolated by buoyant density ultracentrifugation. Phosphoinositide 3-kinase (PI3K) localization to lipid rafts was confirmed using PI3K and anti-caveolin-1 antibodies. Mice with cholesterol storage disease Niemann-Pick, type C were used as in vivo models to confirm the role of lipid rafts in mediating signaling response to AE organisms. In contrast to uninfected cells, PI3K was recruited to lipid rafts in response to EHEC infection. Metabolically active bacteria and cells with intact cholesterol-rich microdomains were necessary for the recruitment of second messengers to lipid rafts. Recruitment of PI3K to lipid rafts was independent of the intimin (eaeA) gene, type III secretion system, and production of Shiga-like toxins. Colonization of NPC(-/-) colonic mucosa by Citrobacter rodentium and AE lesion formation were both delayed, compared with wild-type mice infected with the murine-specific AE bacterial pathogen. C. rodentium-infected NPC(-/-) mice had reduced colonic epithelial hyperplasia (64+/-8.251 vs 112+/-2.958 microm; P<0.05) and decreased secretion of IFN-gamma (17.6+/-17.6 vs 71+/-26.3 pg/ml, P<0.001). Lipid rafts mediate host cell signal transduction responses to AE bacterial infections both in vitro and in vivo. These findings advance the current understanding of microbial-eukaryotic cell interactions in response to enteric pathogens that hijack signaling responses mediated through lipid rafts.

Protective role for protease-activated receptor-2 against influenza virus pathogenesis via an IFN-gamma-dependent pathway

Protease-activated receptor-2 (PAR(2)), a receptor highly expressed in the respiratory tract, can influence inflammation at mucosal surfaces. Although the effects of PAR(2) in the innate immune response to bacterial infection have been documented, knowledge of its role in the context of viral infection is lacking. We thus investigated the role of PAR(2) in influenza pathogenesis in vitro and in vivo. In vitro, stimulation of PAR(2) on epithelial cells inhibited influenza virus type A (IAV) replication through the production of IFN-gamma. In vivo, stimulation of PAR(2) using specific agonists protected mice from IAV-induced acute lung injury and death. This effect correlated with an increased clearance of IAV in the lungs associated with increased IFN- gamma production and a decreased presence of neutrophils and RANTES release in bronchoalveolar fluids. More importantly, the protective effect of the PAR(2) agonist was totally abrogated in IFN- gamma-deficient mice. Finally, compared with wild-type mice, PAR(2)-deficient mice were more susceptible to IAV infection and displayed more severe lung inflammation. In these mice higher neutrophil counts and increased RANTES concentration but decreased IFN- gamma levels were observed in the bronchoalveolar lavages. Collectively, these results showed that PAR(2) plays a protective role during IAV infection through IFN-gamma production and decreased excessive recruitment of inflammatory cells to lung alveoli.

Protease-activated receptor 2 signalling promotes dendritic cell antigen transport and T-cell activation in vivo

Deficiency of protease-activated receptor-2 (PAR2) modulates inflammation in several models of inflammatory and autoimmune disease, although the underlying mechanism(s) are not understood. PAR2 is expressed on endothelial and immune cells, and is implicated in dendritic cell (DC) differentiation. We investigated in vivo the impact of PAR2 activation on DCs and T cells in PAR2 wild-type (WT) and knockout (KO) mice using a specific PAR2 agonist peptide (AP2). PAR2 activation significantly increased the frequency of mature CD11c(high) DCs in draining lymph nodes 24 hr after AP2 administration. Furthermore, these DCs exhibited increased expression of major histocompatibility complex (MHC) class II and CD86. A significant increase in activated (CD44(+) CD62(-)) CD4(+) and CD8(+) T-cell frequencies was also observed in draining lymph nodes 48 hr after AP2 injection. No detectable change in DC or T-cell activation profiles was observed in the spleen. The influence of PAR2 signalling on antigen transport to draining lymph nodes was assessed in the context of delayed-type hypersensitivity. PAR2 WT mice that were sensitized by skin-painting with fluorescein isothiocyanate (FITC) to induce delayed-type hypersensitivity possessed elevated proportion of FITC(+) DCs in draining lymph nodes 24 hr after FITC painting when compared with PAR2 KO mice (0.95% versus 0.47% of total lymph node cells). Collectively, these results demonstrate that PAR2 signalling promotes DC trafficking to the lymph nodes and subsequent T-cell activation, and thus provides an explanation for the pro-inflammatory effect of PAR2 in animal models of inflammation.

Protease-activated receptors as drug targets in inflammation and pain

Proteases have been shown to signal to cells through the activation of a novel class of receptors coupled to G proteins: the protease-activated receptors (PARs). Those receptors are expressed in a wide range of cells, which ultimately are all involved in mechanisms of inflammation and pain. Numerous studies have considered the role of PARs in cells, organ systems or in vivo, highlighting the fact that PAR activation results in signs of inflammation. A growing body of evidences discussed here suggests that these receptors, and the proteases that activate them, interfere with inflammation and pain processes. Whether a role for PARs has been clearly defined in inflammatory and pain pathologies is discussed in this review. Further, the pros and cons for considering PARs as targets for the development of therapeutic options for the treatment of inflammation and pain are discussed.

Citrobacter rodentium colitis evokes post-infectious hyperexcitability of mouse nociceptive colonic dorsal root ganglion neurons

To investigate the possible contribution of peripheral sensory mechanisms to abdominal pain following infectious colitis, we examined whether the Citrobacter rodentium mouse model of human E. coli infection caused hyperexcitability of nociceptive colonic dorsal root ganglion (DRG) neurons and whether these changes persisted following recovery from infection. Mice were gavaged with C. rodentium or distilled water. Perforated patch clamp recordings were obtained from acutely dissociated Fast Blue labelled colonic DRG neurons and afferent nerve recordings were obtained from colonic afferents during ramp colonic distensions. Recordings were obtained on day 10 (acute infection) and day 30 (infection resolved). Following gavage, colonic weights, myeloperoxidase (MPO) activity, stool cultures, and histological scoring established that infection caused colitis at day 10 which resolved by day 30 in most tissues. Electrophysiological recordings at day 10 demonstrated hyperexcitability of colonic DRG neurons (40% mean decrease in rheobase, P = 0.02; 50% mean increase in action potential discharge at twice rheobase, P = 0.02). At day 30, the increase in action potential discharge persisted (approximately 150% increase versus control; P = 0.04). In voltage clamp studies, transient outward (I(A)) and delayed rectifier (I(K)) currents were suppressed at day 10 and I(A) currents remained suppressed at day 30. Colonic afferent nerve recordings during colonic distension demonstrated enhanced firing at day 30 in infected animals. These studies demonstrate that acute infectious colitis evokes hyperexcitability of colonic DRG neurons which persists following resolution of the infection and that suppression of I(A) currents may play a role. Together, these findings suggest that peripheral pain mechanisms could contribute to post-infectious symptoms in conditions such as post-infectious irritable bowel syndrome.

Proteinases as hormones: targets and mechanisms for proteolytic signaling

Proteinases, such as kallikrein-related peptidases, trypsin and thrombin, can play hormone-like 'messenger roles in vivo. They can regulate cell signaling by cleaving and activating a novel family of G-protein-coupled proteinase-activated receptors (PARs 1-4) by unmasking a tethered receptor-triggering ligand. Short synthetic PAR-derived peptide sequences (PAR-APs) can selectively activate PARs 1, 2 and 4, causing physiological responses in vitro and in vivo. Using the PAR-APs to activate the receptors in vivo, it has been found that PARs, like hormone receptors, can affect the vascular, renal, respiratory, gastrointestinal, musculoskeletal and nervous systems (central and peripheral). PARs trigger responses ranging from vasodilatation to intestinal inflammation, increased cytokine production and increased nociception. These PAR-stimulated responses have been implicated in various disease states, including cancer, atherosclerosis, asthma, arthritis, colitis and Alzheimer's disease. In addition to targeting the PARs, proteinases can also cause hormone-like effects by other signaling mechanisms that may be as important as the activation of PARs. Thus, the PARs themselves, their activating serine proteinases and their signaling pathways can be considered as attractive targets for therapeutic drug development. Further, proteinases can be considered as physiologically relevant 'hormone-like' messengers that can convey signals locally or systemically either via PARs or by other mechanisms.

Proteinases as hormones: targets and mechanisms for proteolytic signaling

Proteinases, such as kallikrein-related peptidases, trypsin and thrombin, can play hormone-like 'messenger roles in vivo. They can regulate cell signaling by cleaving and activating a novel family of G-protein-coupled proteinase-activated receptors (PARs 1-4) by unmasking a tethered receptor-triggering ligand. Short synthetic PAR-derived peptide sequences (PAR-APs) can selectively activate PARs 1, 2 and 4, causing physiological responses in vitro and in vivo. Using the PAR-APs to activate the receptors in vivo, it has been found that PARs, like hormone receptors, can affect the vascular, renal, respiratory, gastrointestinal, musculoskeletal and nervous systems (central and peripheral). PARs trigger responses ranging from vasodilatation to intestinal inflammation, increased cytokine production and increased nociception. These PAR-stimulated responses have been implicated in various disease states, including cancer, atherosclerosis, asthma, arthritis, colitis and Alzheimer's disease. In addition to targeting the PARs, proteinases can also cause hormone-like effects by other signaling mechanisms that may be as important as the activation of PARs. Thus, the PARs themselves, their activating serine proteinases and their signaling pathways can be considered as attractive targets for therapeutic drug development. Further, proteinases can be considered as physiologically relevant 'hormone-like' messengers that can convey signals locally or systemically either via PARs or by other mechanisms.