A role for proteinase-activated receptor-1 in inflammatory bowel diseases

PAR-1 Antagonism to Promote Gut Mucosa Healing in Crohn's Disease Patients: A New Avenue for CVT120165

A new paradigm has been added for the treatment of inflammatory bowel diseases such as Crohn's disease and ulcerative colitis. In addition to resolving symptoms and inflammatory cell activation, the objective of tissue repair and mucosal healing is also now considered a primary goal. In the search of mediators that would be responsible for delayed mucosal healing, protease-activated receptor-1 (PAR-1) has emerged as a most interesting target. Indeed, in Crohn's disease, the endogenous PAR-1 agonist thrombin is drastically activated. Activation of PAR-1 is known to be associated with epithelial dysfunctions that hamper mucosal homeostasis. This review gathers the scientific evidences of a potential role for PAR-1 in mucosal damage and mucosal dysfunctions associated with chronic intestinal inflammation. The potential clinical benefits of PAR-1 antagonism to promote mucosal repair in CD patients are discussed. Targeted local delivery of a PAR-1 antagonist molecule such as CVT120165, a formulated version of the FDA-approved PAR-1 antagonist vorapaxar, at the mucosa of Crohn's disease patients could be proposed as a new indication for IBD that could be rapidly tested in clinical trials.

The thrombin receptor modulates astroglia-neuron trophic coupling and neural repair after spinal cord injury

Excessive activation of the thrombin receptor, protease activated receptor 1 (PAR1) is implicated in diverse neuropathologies from neurodegenerative conditions to neurotrauma. PAR1 knockout mice show improved outcomes after experimental spinal cord injury (SCI), however information regarding the underpinning cellular and molecular mechanisms is lacking. Here we demonstrate that genetic blockade of PAR1 in female mice results in improvements in sensorimotor co-ordination after thoracic spinal cord lateral compression injury. We document improved neuron preservation with increases in Synapsin-1 presynaptic proteins and GAP43, a growth cone marker, after a 30 days recovery period. These improvements were coupled to signs of enhanced myelin resiliency and repair, including increases in the number of mature oligodendrocytes, their progenitors and the abundance of myelin basic protein. These significant increases in substrates for neural recovery were accompanied by reduced astrocyte (Serp1) and microglial/monocyte (CD68 and iNOS) pro-inflammatory markers, with coordinate increases in astrocyte (S100A10 and Emp1) and microglial (Arg1) markers reflective of pro-repair activities. Complementary astrocyte-neuron co-culture bioassays suggest astrocytes with PAR1 loss-of-function promote both neuron survival and neurite outgrowth. Additionally, the pro-neurite outgrowth effects of switching off astrocyte PAR1 were blocked by inhibiting TrkB, the high affinity receptor for brain derived neurotrophic factor. Altogether, these studies demonstrate unique modulatory roles for PAR1 in regulating glial-neuron interactions, including the capacity for neurotrophic factor signaling, and underscore its position at neurobiological intersections critical for the response of the CNS to injury and the capacity for regenerative repair and restoration of function.

The thrombin receptor links brain derived neurotrophic factor to neuron cholesterol production, resiliency and repair after spinal cord injury

Despite concerted efforts to identify CNS regeneration strategies, an incomplete understanding of how the needed molecular machinery is regulated limits progress. Here we use models of lateral compression and FEJOTA clip contusion-compression spinal cord injury (SCI) to identify the thrombin receptor (Protease Activated Receptor 1 (PAR1)) as an integral facet of this machine with roles in regulating neurite growth through a growth factor- and cholesterol-dependent mechanism. Functional recovery and signs of neural repair, including expression of cholesterol biosynthesis machinery and markers of axonal and synaptic integrity, were all increased after SCI in PAR1 knockout female mice, while PTEN was decreased. Notably, PAR1 differentially regulated HMGCS1, a gene encoding a rate-limiting enzyme in cholesterol production, across the neuronal and astroglial compartments of the intact versus injured spinal cord. Pharmacologic inhibition of cortical neuron PAR1 using vorapaxar in vitro also decreased PTEN and promoted neurite outgrowth in a cholesterol dependent manner, including that driven by suboptimal brain derived neurotrophic factor (BDNF). Pharmacologic inhibition of PAR1 also augmented BDNF-driven HMGCS1 and cholesterol production by murine cortical neurons and by human SH-SY5Y and iPSC-derived neurons. The link between PAR1, cholesterol and BDNF was further highlighted by demonstrating that the deleterious effects of PAR1 over-activation are overcome by supplementing cultures with BDNF, cholesterol or by blocking an inhibitor of adenylate cyclase, Gαi. These findings document PAR1-linked neurotrophic coupling mechanisms that regulate neuronal cholesterol metabolism as an important component of the machinery regulating CNS repair and point to new strategies to enhance neural resiliency after injury.

Cell type-specific mechanisms coupling protease-activated receptor-1 to infectious colitis pathogenesis

BACKGROUND

Protease-activated receptor-1 (PAR-1) plays a major role in multiple disease processes, including colitis. Understanding the mechanisms coupling PAR-1 to disease pathogenesis is complicated by the fact that PAR-1 is broadly expressed across multiple cell types.

OBJECTIVE

Determine the specific contributions of PAR-1 expressed by macrophages and colonic enterocytes to infectious colitis.

METHODS

Mice carrying a conditional PAR-1 allele were generated and bred to mice expressing Cre recombinase in a myeloid- (PAR-1ΔM ) or enterocyte-specific (PAR-1ΔEPI ) fashion. Citrobacter rodentium colitis pathogenesis was analyzed in mice with global PAR-1 deletion (PAR-1-/- ) and cell type-specific deletions.

RESULTS

Constitutive deletion of PAR-1 had no significant impact on weight loss, crypt hypertrophy, crypt abscess formation, or leukocyte infiltration in Citrobacter colitis. However, colonic shortening was significantly blunted in infected PAR-1-/- mice, and these animals exhibited decreased local levels of IL-1β, IL-22, IL-6, and IL-17A. In contrast, infected PAR-1ΔM mice lost less weight and had fewer crypt abscesses relative to controls. PAR-1ΔM mice had diminished CD3+ T cell infiltration into colonic tissue, but macrophage and CD4+ T cell infiltration were similar to controls. Also contrasting results in global knockouts, PAR-1ΔM mice exhibited lower levels of IL-1β, but not Th17-related cytokines (ie, IL-22, IL-6, IL-17A). Infected PAR-1ΔEPI mice exhibited increased crypt hypertrophy and crypt abscess formation, but local cytokine elaboration was similar to controls.

CONCLUSIONS

These studies reveal complex, cell type-specific roles for PAR-1 in modulating the immune response to Citrobacter colitis that are not readily apparent in analyses limited to mice with global PAR-1 deficiency.

Protease Activated Receptor 4 as a Novel Modulator of Regulatory T Cell Function

Regulatory T cells (Tregs) are a subpopulation of T cells that maintain immunological tolerance. In inflammatory responses the function of Tregs is tightly controlled by several factors including signaling through innate receptors such as Toll like receptors and anaphylatoxin receptors allowing an effective immune response to be generated. Protease-activated receptors (PARs) are another family of innate receptors expressed on multiple cell types and involved in the pathogenesis of autoimmune disorders. Whether proteases are able to directly modulate Treg function is unknown. Here, we show using two complimentary approaches that signaling through PAR-4 influences the expression of CD25, CD62L, and CD73, the suppressive capacity, and the stability of Tregs, via phosphorylation of FoxO1 and negative regulation of PTEN and FoxP3. Taken together, our results demonstrate an important role of PAR4 in tuning the function of Tregs and open the possibility of targeting PAR4 to modulate immune responses.

Expression and Clinical Significance of Elafin in Inflammatory Bowel Disease

BACKGROUND

The expression of elafin in inflammatory bowel disease (IBD) is controversial. Here, we detected the expression of elafin in the peripheral blood and colonic mucosa of patient with IBD and then explored its role and value in assessing the activity and severity of IBD.

MATERIALS AND METHODS

Sixty-eight patients with IBD were selected as an experimental group. The control group included 38 healthy individuals. The expression of elafin mRNA in peripheral blood leukocytes and in serum was detected by qRT-PCR and enzyme-linked immunosorbent assay, respectively. The inflamed and noninflamed tissues were collected by colonoscopy. The expression of elafin in the intestinal mucosa was determined by immunohistochemistry staining and qRT-PCR. The expression of elafin between groups and among each stage of IBD was compared. The correlations of elafin expression with erythrocyte sedimentation rate and C-reactive protein were determined by Spearman's correlation analysis and with clinical disease activity indices (Best Crohn's Disease Activity Index and modified Mayo scores) by Pearson's correlation analysis.

RESULTS

Elafin mRNA levels decreased significantly in active ulcerative colitis (UC) but increased in remission UC. However, in Crohn's disease (CD), we did not detect the aforementioned significant differences. Although serum IL-8 levels increased, serum elafin concentrations decreased both in UC and in CD, but the differences among stages were not significant. The expression of elafin in the inflamed colonic mucosa in both CD and UC was lower than that in the normal mucosa in controls and lower than that in the noninflamed mucosa in IBD. Moreover, the relative expression of elafin mRNA in peripheral blood leukocytes in UC was negatively correlated with erythrocyte sedimentation rate, C-reactive protein, and modified Mayo scores, and in CD, it was negatively correlated with Best Crohn's Disease Activity Index scores.

CONCLUSIONS

Elafin decreased in active patients with IBD and was negatively correlated with disease activity, suggesting that elafin may play a protective role and could be used as an index to evaluate disease activity in IBD.

Targeting PAR1: Now What?

Protease-activated receptors (PARs) are a ubiquitously expressed class of G-protein-coupled receptors (GPCRs) that enable cells to respond to proteases in the extracellular environment in a nuanced and dynamic manner. PAR1 is the archetypal family member and has been the object of large-scale drug development programs since the 1990s. Vorapaxar and drotrecogin-alfa are approved PAR1-targeted therapeutics, but safety concerns have limited the clinical use of vorapaxar and questions regarding the efficacy of drotrecogin-alfa led to its withdrawal from the market. New understanding of mechanisms of PAR1 function, discovery of improved strategies for modifying PAR1 function, and identification of novel indications for PAR1 modulators have provided new opportunities for therapies targeting PAR1. In this review, we critically evaluate prospects for the next generation of PAR1-targeted therapeutics.

G Protein-Coupled Receptors in Macrophages

As the largest receptor gene family in the human genome, with >800 members, the signal-transducing G protein-coupled receptors (GPCRs) play critical roles in nearly all conceivable physiological processes, ranging from the sensing of photons and odorants to metabolic homeostasis and migration of leukocytes. Unfortunately, an exhaustive review of the several hundred GPCRs expressed by myeloid cells/macrophages (P.J. Groot-Kormelink, L .Fawcett, P.D. Wright, M. Gosling, and T.C. Kent, BMC Immunol 12:57, 2012, doi:10.1186/1471-2172-13-57) is beyond the scope of this chapter; however, we will endeavor to cover the GPCRs that contribute to the major facets of macrophage biology, i.e., those whose expression is restricted to macrophages and the GPCRs involved in macrophage differentiation/polarization, microbial elimination, inflammation and resolution, and macrophage-mediated pathology. The chemokine receptors, a major group of myeloid GPCRs, will not be extensively covered as they are comprehensively reviewed elsewhere.

Phosphotidylserine exposure and neutrophil extracellular traps enhance procoagulant activity in patients with inflammatory bowel disease

Inflammatory bowel disease (IBD)-associated thromboembolic event often lacks precise aetiology. The aim of this study was to investigate the contribution of phosphatidylserine (PS) exposure and neutrophil extracellular traps (NETs) towards the hypercoagulable state in IBD. We demonstrated that the levels of PS exposed MPs and the sources of MP-origin, platelets, erythrocytes, leukocytes and cultured endothelial cells (ECs) were higher in IBD groups than in healthy controls using flow cytometry and confocal microscopy. Wright-Giemsa and immunofluorescence staining demonstrated that the elevated NETs were released by activated IBD neutrophils or by control neutrophils treated with IBD sera obtained from patients with the active disease. MPs and MP-origin cells in IBD groups, especially in active stage, markedly shortened coagulation time and had increased levels of fibrin, thrombin and FXa production as assessed by coagulation function assays. Importantly, we found that on stimulated ECs, PS rich membranes provided binding sites for FXa and FVa, promoting fibrin formation while TNF blockage or IgG depletion attenuated this effect. Treatment of control neutrophils with TNF and isolated IgG from PR3-ANCA-positive active IBD patients also resulted in the release of NETs. Blockade of PS with lactadherin prolonged coagulation time, decreased fibrin formation to control levels, and inhibited the procoagulant enzymes production in the MPs and MP-origin cells. NET cleavage by DNase I partly decreased PCA in IBD or stimulated neutrophils. Our study reveals a previously unrecognised link between hypercoagulable state and PS exposure or NETs, and may further explain the epidemiological association of thrombosis within IBD patients.

Genetic targeting of protease activated receptor 2 reduces inflammatory astrogliosis and improves recovery of function after spinal cord injury

Inflammatory-astrogliosis exacerbates damage in the injured spinal cord and limits repair. Here we identify Protease Activated Receptor 2 (PAR2) as an essential regulator of these events with mice lacking the PAR2 gene showing greater improvements in motor coordination and strength after compression-spinal cord injury (SCI) compared to wild type littermates. Molecular profiling of the injury epicenter, and spinal segments above and below, demonstrated that mice lacking PAR2 had significantly attenuated elevations in key hallmarks of astrogliosis (glial fibrillary acidic protein (GFAP), vimentin and neurocan) and in expression of pro-inflammatory cytokines (interleukin-6 (IL-6), tumor necrosis factor (TNF) and interleukin-1 beta (IL-1β)). SCI in PAR2-/- mice was also accompanied by improved preservation of protein kinase C gamma (PKCγ)-immunopositive corticospinal axons and reductions in GFAP-immunoreactivity, expression of the pro-apoptotic marker BCL2-interacting mediator of cell death (BIM), and in signal transducer and activator of transcription 3 (STAT3). The potential mechanistic link between PAR2, STAT3 and astrogliosis was further investigated in primary astrocytes to reveal that the SCI-related serine protease, neurosin (kallikrein 6) promotes IL-6 secretion in a PAR2 and STAT3-dependent manner. Data point to a signaling circuit in primary astrocytes in which neurosin signaling at PAR2 promotes IL-6 secretion and canonical STAT3 signaling. IL-6 promotes expression of GFAP, vimentin, additional IL-6 and robust increases in both neurosin and PAR2, thereby driving the PAR2-signaling circuit forward. Given the significant reductions in astrogliosis and inflammation as well as superior neuromotor recovery observed in PAR2 knockout mice after SCI, we suggest that this receptor and its agonists represent new drug targets to foster neuromotor recovery.

Enterococcus faecalis Gelatinase Mediates Intestinal Permeability via Protease-Activated Receptor 2

Microbial protease-mediated disruption of the intestinal epithelium is a potential mechanism whereby a dysbiotic enteric microbiota can lead to disease. This mechanism was investigated using the colitogenic, protease-secreting enteric microbe Enterococcus faecalis. Caco-2 and T-84 epithelial cell monolayers and the mouse colonic epithelium were exposed to concentrated conditioned media (CCM) from E. faecalis V583 and E. faecalis lacking the gelatinase gene (gelE). The flux of fluorescein isothiocyanate (FITC)-labeled dextran across monolayers or the mouse epithelium following exposure to CCM from parental or mutant E. faecalis strains indicated paracellular permeability. A protease-activated receptor 2 (PAR2) antagonist and PAR2-deficient (PAR2(-/-)) mice were used to investigate the role of this receptor in E. faecalis-induced permeability. Gelatinase (GelE) purified from E. faecalis V583 was used to confirm the ability of this protease to induce epithelial cell permeability and activate PAR2. The protease-mediated permeability of colonic epithelia from wild-type (WT) and PAR2(-/-) mice by fecal supernatants from ulcerative colitis patients was assessed. Secreted E. faecalis proteins induced permeability in epithelial cell monolayers, which was reduced in the absence of gelE or by blocking PAR2 activity. Secreted E. faecalis proteins induced permeability in the colonic epithelia of WT mice that was absent in tissues from PAR2(-/-) mice. Purified GelE confirmed the ability of this protease to induce epithelial cell permeability via PAR2 activation. Fecal supernatants from ulcerative colitis patients induced permeability in the colonic epithelia of WT mice that was reduced in tissues from PAR2(-/-) mice. Our investigations demonstrate that GelE from E. faecalis can regulate enteric epithelial permeability via PAR2.

Endothelial dysfunction in cirrhosis: Role of inflammation and oxidative stress

This review describes the recent developments in the pathobiology of endothelial dysfunction (ED) in the context of cirrhosis with portal hypertension and defines novel strategies and potential targets for therapy. ED has prognostic implications by predicting unfavourable early hepatic events and mortality in patients with portal hypertension and advanced liver diseases. ED characterised by an impaired bioactivity of nitric oxide (NO) within the hepatic circulation and is mainly due to decreased bioavailability of NO and accelerated degradation of NO with reactive oxygen species. Furthermore, elevated inflammatory markers also inhibit NO synthesis and causes ED in cirrhotic liver. Therefore, improvement of NO availability in the hepatic circulation can be beneficial for the improvement of endothelial dysfunction and associated portal hypertension in patients with cirrhosis. Furthermore, therapeutic agents that are identified in increasing NO bioavailability through improvement of hepatic endothelial nitric oxide synthase (eNOS) activity and reduction in hepatic asymmetric dimethylarginine, an endogenous modulator of eNOS and a key mediator of elevated intrahepatic vascular tone in cirrhosis would be interesting therapeutic approaches in patients with endothelial dysfunction and portal hypertension in advanced liver diseases.

Main ion channels and receptors associated with visceral hypersensitivity in irritable bowel syndrome

Irritable bowel syndrome (IBS) is a very frequent functional gastrointestinal disorder characterized by recurrent abdominal pain or discomfort and alteration of bowel habits. The IBS physiopathology is extremely complex. Visceral hypersensitivity plays an important role in the pathogenesis of abdominal pain in both in vitro and in vivo models of this functional disorder. In order to obtain a general view of the participation of the main ion channels and receptors regarding the visceral hypersensitivity in the IBS and to describe their chemical structure, a literature review was carried out. A bibliographical research in the following electronic databases: Pubmed and Virtual Library in Health (BVS) was fulfilled by using the search terms "ion channels" "or" "receptors" "and" "visceral hypersensitivity" "or" "visceral nociception" "and" "irritable bowel syndrome". Original and review articles were considered for data acquisition. The activation of the ATP ion-gated channels, voltage-gated sodium (Na_v) and calcium (Ca_v) channels, as well as the activation of protease-activated receptors (PAR2), transient receptor potential vanilloide-1, serotonin, cannabinoids and cholecystokinin are involved in the genesis of visceral hypersensitivity in IBS. The involvement of ion channels and receptors concerning visceral hypersensitivity is noteworthy in IBS models.

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.

Protease-activated receptor (PAR)2, but not PAR1, is involved in collateral formation and anti-inflammatory monocyte polarization in a mouse hind limb ischemia model

AIMS

In collateral development (i.e. arteriogenesis), mononuclear cells are important and exist as a heterogeneous population consisting of pro-inflammatory and anti-inflammatory/repair-associated cells. Protease-activated receptor (PAR)1 and PAR2 are G-protein-coupled receptors that are both expressed by mononuclear cells and are involved in pro-inflammatory reactions, while PAR2 also plays a role in repair-associated responses. Here, we investigated the physiological role of PAR1 and PAR2 in arteriogenesis in a murine hind limb ischemia model.

METHODS AND RESULTS

PAR1-deficient (PAR1-/-), PAR2-deficient (PAR2-/-) and wild-type (WT) mice underwent femoral artery ligation. Laser Doppler measurements revealed reduced post-ischemic blood flow recovery in PAR2-/- hind limbs when compared to WT, while PAR1-/- mice were not affected. Upon ischemia, reduced numbers of smooth muscle actin (SMA)-positive collaterals and CD31-positive capillaries were found in PAR2-/- mice when compared to WT mice, whereas these parameters in PAR1-/- mice did not differ from WT mice. The pool of circulating repair-associated (Ly6C-low) monocytes and the number of repair-associated (CD206-positive) macrophages surrounding collaterals in the hind limbs were increased in WT and PAR1-/- mice, but unaffected in PAR2-/- mice. The number of repair-associated macrophages in PAR2-/- hind limbs correlated with CD11b- and CD115-expression on the circulating monocytes in these animals, suggesting that monocyte extravasation and M-CSF-dependent differentiation into repair-associated cells are hampered.

CONCLUSION

PAR2, but not PAR1, is involved in arteriogenesis and promotes the repair-associated response in ischemic tissues. Therefore, PAR2 potentially forms a new pro-arteriogenic target in coronary artery disease (CAD) patients.

The Role of Mitogen-Activated Protein Kinase-Activated Protein Kinases (MAPKAPKs) in Inflammation

Mitogen-activated protein kinase (MAPK) pathways are implicated in several cellular processes including proliferation, differentiation, apoptosis, cell survival, cell motility, metabolism, stress response and inflammation. MAPK pathways transmit and convert a plethora of extracellular signals by three consecutive phosphorylation events involving a MAPK kinase kinase, a MAPK kinase, and a MAPK. In turn MAPKs phosphorylate substrates, including other protein kinases referred to as MAPK-activated protein kinases (MAPKAPKs). Eleven mammalian MAPKAPKs have been identified: ribosomal-S6-kinases (RSK1-4), mitogen- and stress-activated kinases (MSK1-2), MAPK-interacting kinases (MNK1-2), MAPKAPK-2 (MK2), MAPKAPK-3 (MK3), and MAPKAPK-5 (MK5). The role of these MAPKAPKs in inflammation will be reviewed.

Inhibition of protease-activated receptor 1 ameliorates intestinal radiation mucositis in a preclinical rat model

PURPOSE

To determine, using a specific small-molecule inhibitor of protease-activated receptor 1 (PAR1) signaling, whether the beneficial effect of thrombin inhibition on radiation enteropathy development is due to inhibition of blood clotting or to cellular (PAR1-mediated) thrombin effects.

METHODS AND MATERIALS

Rats underwent fractionated X-irradiation (5 Gy×9) of a 4-cm small-bowel segment. Early radiation toxicity was evaluated in rats receiving PAR1 inhibitor (SCH602539, 0, 10, or 15 mg/kg/d) from 1 day before to 2 weeks after the end of irradiation. The effect of PAR1 inhibition on development of chronic intestinal radiation fibrosis was evaluated in animals receiving SCH602539 (0, 15, or 30 mg/kg/d) until 2 weeks after irradiation, or continuously until termination of the experiment 26 weeks after irradiation.

RESULTS

Blockade of PAR1 ameliorated early intestinal toxicity, with reduced overall intestinal radiation injury (P=.002), number of myeloperoxidase-positive (P=.03) and proliferating cell nuclear antigen-positive (P=.04) cells, and collagen III accumulation (P=.005). In contrast, there was no difference in delayed radiation enteropathy in either the 2- or 26-week administration groups.

CONCLUSION

Pharmacological blockade of PAR1 seems to reduce early radiation mucositis but does not affect the level of delayed intestinal radiation fibrosis. Early radiation enteropathy is related to activation of cellular thrombin receptors, whereas platelet activation or fibrin formation may play a greater role in the development of delayed toxicity. Because of the favorable side-effect profile, PAR1 blockade should be further explored as a method to ameliorate acute intestinal radiation toxicity in patients undergoing radiotherapy for cancer and to protect first responders and rescue personnel in radiologic/nuclear emergencies.

Serine protease inhibition reduces post-ischemic granulocyte recruitment in mouse intestine

Proteases and proteinase-activated receptor (PAR) activation are involved in several intestinal inflammatory conditions. We hypothesized that serine proteases and PAR activation could also modulate the intestinal injury induced by ischemia-reperfusion (I-R). C57Bl/6 mice were subjected to 90 minutes of intestinal ischemia followed or not by reperfusion. Sham-operated animals served as controls. After ischemia, plasma and tissue serine protease activity levels were increased compared to the activity measured in plasma and tissues from sham-operated mice. This increase was maintained or further enhanced after 2 and 5 hours of reperfusion, respectively. Trypsin (25 kDa) was detected in tissues both after ischemia and 2 hours of reperfusion. Treatment with FUT-175 (10 mg/kg), a potent serine protease inhibitor, increased survival after I-R, inhibited tissue protease activity, and significantly decreased intestinal myeloperoxidase (MPO) activity and chemokine and adhesion molecule expression. We investigated whether serine proteases modulate granulocyte recruitment by a PAR-dependent mechanism. MPO levels and adhesion molecule expression were significantly reduced in I-R groups pre-treated with the PAR(1) antagonist SCH-79797 (5 mg/kg) and in Par(2)(-/-)mice, compared, respectively, to vehicle-treated group and wild-type littermates. Thus, increased proteolytic activity and PAR activation play a pathogenic role in intestinal I-R injury. Inhibition of PAR-activating serine proteases could be beneficial to reduce post-ischemic intestinal inflammation.

Intracolonic infusion of fecal supernatants from ulcerative colitis patients triggers altered permeability and inflammation in mice: role of cathepsin G and protease-activated receptor-4

BACKGROUND

Cathepsin G (Cat-G) is a neutrophil serine-protease found in the colonic lumen of ulcerative colitis (UC) patients. Cat-G is able to activate protease-activated receptor-4 (PAR(4) ) located at the apical side of enterocytes, leading to epithelial barrier disruption. However, the mechanisms through which Cat-G triggers inflammation are not fully elucidated. The aims of our study were to evaluate in vivo the effects of UC fecal supernatants and Cat-G on epithelial barrier function and inflammation, and the connection between these two parameters.

METHODS

Male balb/c mice were used in this study. We evaluated the effect of a 2-hour intracolonic infusion of 1) fecal supernatants from UC patients pretreated or not with specific Cat-G inhibitor (SCGI); 2) PAR(4) -activating peptide (PAR(4) -AP); and 3) Cat-G on colonic myeloperoxidase (MPO) activity and paracellular permeability (CPP). The involvement of PAR(4) was assessed by pretreating animals with pepducin P4pal-10, which blocks PAR(4) signaling. We investigated the role of myosin light chain (MLC) kinase by using its inhibitor, ML-7, and we determined phosphorylated MLC (pMLC) levels in mice colonic mucosa.

RESULTS

UC fecal supernatants, Cat-G, and PAR(4) agonist increased both CPP and MPO activity in comparison with healthy subjects fecal supernatants. ML-7 inhibited the CPP increase triggered by Cat-G by 92.3%, and the enhanced MPO activity by 43.8%. Intracolonic infusion of UC fecal supernatant determined an increased phosphorylation level of MLC.

CONCLUSIONS

These observations support that luminal factors such as Cat-G play an important proinflammatory role in the pathogenesis of colitis, mainly depending on CPP increase by MLC phosphorylation.

Functional role of kallikrein 6 in regulating immune cell survival

BACKGROUND

Kallikrein 6 (KLK6) is a newly identified member of the kallikrein family of secreted serine proteases that prior studies indicate is elevated at sites of central nervous system (CNS) inflammation and which shows regulated expression with T cell activation. Notably, KLK6 is also elevated in the serum of multiple sclerosis (MS) patients however its potential roles in immune function are unknown. Herein we specifically examine whether KLK6 alters immune cell survival and the possible mechanism by which this may occur.

METHODOLOGY/PRINCIPAL FINDINGS

Using murine whole splenocyte preparations and the human Jurkat T cell line we demonstrate that KLK6 robustly supports cell survival across a range of cell death paradigms. Recombinant KLK6 was shown to significantly reduce cell death under resting conditions and in response to camptothecin, dexamethasone, staurosporine and Fas-ligand. Moreover, KLK6-over expression in Jurkat T cells was shown to generate parallel pro-survival effects. In mixed splenocyte populations the vigorous immune cell survival promoting effects of KLK6 were shown to include both T and B lymphocytes, to occur with as little as 5 minutes of treatment, and to involve up regulation of the pro-survival protein B-cell lymphoma-extra large (Bcl-XL), and inhibition of the pro-apoptotic protein Bcl-2-interacting mediator of cell death (Bim). The ability of KLK6 to promote survival of splenic T cells was also shown to be absent in cell preparations derived from PAR1 deficient mice.

CONCLUSION/SIGNIFICANCE

KLK6 promotes lymphocyte survival by a mechanism that depends in part on activation of PAR1. These findings point to a novel molecular mechanism regulating lymphocyte survival that is likely to have relevance to a range of immunological responses that depend on apoptosis for immune clearance and maintenance of homeostasis.

Haemostatic system in inflammatory bowel diseases: New players in gut inflammation

Inflammation and coagulation constantly influence each other and are constantly in balance. Emerging evidence supports this statement in acute inflammatory diseases, such as sepsis, but it also seems to be very important in chronic inflammatory settings, such as inflammatory bowel disease (IBD). Patients with Crohn’s disease and ulcerative colitis have an increased risk of thromboembolic events, and several abnormalities concerning coagulation components occur in the endothelial cells of intestinal vessels, where most severe inflammatory abnormalities occur. The aims of this review are to update and classify the type of coagulation system abnormalities in IBD, and analyze the strict and delicate balance between coagulation and inflammation at the mucosal level. Recent studies on possible therapeutic applications arising from investigations on coagulation abnormalities associated with IBD pathogenesis will also be briefly presented and critically reviewed.

Insulin-like growth factor-1 receptor transactivation modulates the inflammatory and proliferative responses of neurotensin in human colonic epithelial cells

Neurotensin (NT) is a gastrointestinal neuropeptide that modulates intestinal inflammation and healing by binding to its high-affinity receptor NTR1. The dual role of NT in inflammation and healing is demonstrated in models of colitis induced by Clostridium difficile toxin A and dextran sulfate sodium, respectively, and involves NF-κB-dependent IL-8 expression and EGF receptor-mediated MAPK activation in human colonocytes. However, the detailed signaling pathways involved in these responses remain to be elucidated. We report here that NT/NTR1 coupling in human colonic epithelial NCM460 cells activates tyrosine phosphorylation of the insulin-like growth factor-1 receptor (IGF-1R) in a time- and dose-dependent manner. NT also rapidly induces Src tyrosine phosphorylation, whereas pretreatment of cells with the Src inhibitor PP2 before NT exposure decreases NT-induced IGF-1R phosphorylation. In addition, inhibition of IGF-1R activation by either its specific antagonist AG1024 or siRNA against IGF-1 significantly reduces NT-induced IL-8 expression and NF-κB-dependent reporter gene expression. Pretreatment with AG1024 also inhibits Akt activation and apoptosis induced by NT. Silencing of Akt expression by siRNA also substantially attenuates NT-induced IL-8 promoter activity and NF-κB-dependent reporter gene expression. This is the first report to indicate that NT transactivates IGF-1R and that this response is linked to Akt phosphorylation and NF-κB activation, contributing to both pro-inflammatory and tissue repair signaling pathways in response to NT in colonic epithelial cells. We propose that IGF-1R activation represents a previously unrecognized key pathway involved in the mechanisms by which NT and NTR1 modulate colonic inflammation and inflammatory bowel disease.

Thrombin receptors and their antagonists: an update on the patent literature

IMPORTANCE OF THE FIELD

Thrombin plays a central role in cardiovascular inflammation. Most of the cellular responses to thrombin are mediated by cell surface protease-activated receptors (PARs). Several preclinical studies indicate that PARs are potential targets for treating cardiovascular diseases such as thrombosis, atherosclerosis and restenosis. Among PARs, PAR-1 has emerged as an important therapeutic target.

AREAS COVERED IN THIS REVIEW

This review covers recent advances in the development of thrombin receptors antagonists. It is focused on the search for PAR-1 antagonists as this is at the moment the most promising and attractive target. However, some early promising studies on PAR-3 and -4 antagonists are also reported.

WHAT THE READER WILL GAIN

The review has been written in order to give to the reader hints and references that cover, in our opinion, the most interesting and/or promising approaches in this research field.

TAKE HOME MESSAGE

Research on PAR-1 antagonists has finally led to good clinical candidates such as SCH-530348 (Schering-Plough) and E-5555 (Eisai Co.). Clinical trials clearly demonstrate that development of PAR1 antagonists is not only possible but most likely will lead to development of antiplatelet drugs as well as of drugs useful for the treatment of inflammatory, proliferative and neurodegenerative diseases.

Proteinase-activated receptors induce interleukin-8 expression by intestinal epithelial cells through ERK/RSK90 activation and histone acetylation

Proteinase-activated receptors (PARs) are involved in both inflammation and tumorigenesis in epithelial cells. Interleukin (IL)-8 is a potent chemoattractant and is also involved in angiogenesis. The molecular mechanism whereby PARs induce epithelial IL-8 expression is not known. In HT-29 colonic epithelial cells, PAR(1) or PAR(2) agonists stimulated the expression of IL-8 through a NF-kappaB-dependent pathway without inducing IkappaB degradation and disassociation of IkappaB from NF-kappaB. Further studies revealed that PAR activation induced the phosphorylation of p65 at Ser-276 in the nucleus, which increased the recruitment of histone acetyltransferase (HAT) p300 to p50. Inhibition of ERK activation completely blocked PAR-induced IL-8 expression, phosphorylation of p65 and HAT activity. We also demonstrated that RSK p90 was the downstream kinase that mediated ERK-induced nuclear p65 phosphorylation. In conclusion, activation of either PAR(1) or PAR(2) stimulated the transcriptional up-regulation of IL-8 in HT-29 colonic epithelial cells through a pathway that involved ERK/RSK p90, NF-kappaB phosphorylation, and HAT activity. These studies provide evidence of a new role for serine proteinases and PARs in the regulation of gene expression in colonic inflammation and tumorigenesis.

Matrix metalloproteinase-10 is upregulated by thrombin in endothelial cells and increased in patients with enhanced thrombin generation

OBJECTIVE

Thrombin is a multifunctional serine protease that promotes vascular proinflammatory responses whose effect on endothelial MMP-10 expression has not previously been evaluated.

METHODS AND RESULTS

Thrombin induced endothelial MMP-10 mRNA and protein levels, through a protease-activated receptor-1 (PAR-1)-dependent mechanism, in a dose- and time-dependent manner. This effect was mimicked by a PAR-1 agonist peptide (TRAP-1) and antagonized by an anti-PAR-1 blocking antibody. MMP-10 induction was dependent on extracellular regulated kinase1/2 (ERK1/2) and c-jun N-terminal kinase (JNK) pathways. By serial deletion analysis, site-directed mutagenesis and electrophoretic mobility shift assay an AP-1 site in the proximal region of MMP-10 promoter was found to be critical for thrombin-induced MMP-10 transcriptional activity. Thrombin and TRAP-1 upregulated MMP-10 in murine endothelial cells in culture and in vivo in mouse aorta. This effect of thrombin was not observed in PAR-1-deficient mice. Interestingly, circulating MMP-10 levels (P<0.01) were augmented in patients with endothelial activation associated with high (disseminated intravascular coagulation) and moderate (previous acute myocardial infarction) systemic thrombin generation.

CONCLUSIONS

Thrombin induces MMP-10 through a PAR-1-dependent mechanism mediated by ERK1/2, JNK, and AP-1 activation. Endothelial MMP-10 upregulation could be regarded as a new proinflammatory effect of thrombin whose pathological consequences in thrombin-related disorders and plaque stability deserve further investigation.

The protein C pathway and pathologic processes

Alterations in expression of protein C (PC) pathway components have been identified in patients with active inflammatory disease states. While the PC pathway plays a pivotal role in regulating coagulation and fibrinolysis, activated PC (aPC) also exhibits cytoprotective properties. For example, PC-deficient mice challenged in septic/endotoxemic models exhibit phenotypes that include hypotension, disseminated intravascular coagulation, elevated inflammatory mediators, neutrophil adhesion to the microvascular endothelium, and loss of protective endothelial and epithelial cell barriers. Further, inflammatory bowel disease has been correlated with diminished endothelial PC receptor and thrombomodulin levels in the intestinal mucosa. Downregulated expression of the cofactor, protein S, as well as PC, is also associated with ischemic stroke. Studies to elucidate further the structural elements that differentiate the various functions of PC will serve to identify novel therapeutic approaches toward regulating these and other diseases.

Protection of vascular barrier integrity by activated protein C in murine models depends on protease-activated receptor-1

Protease activated receptor-1 (PAR1) mediates barrier protective signalling of activated protein C (APC) in human endothelial cells in vitro and may contribute to APC's beneficial effects in patients with severe sepsis. Mouse models are of key importance for translational research but species differences may limit conclusions for the human system. We analysed whether mouse APC can cleave, activate and induce signalling through murine PAR1 and tested in newly established mouse models if long-term infusion of APC prevents from vascular leakage. Cell surface immunoassays demonstrated efficient cleavage of endogenous murine endothelial PAR1 by either murine or human APC. Pharmacological concentrations of APC of either species had powerful barrier protective effects on cultured murine endothelial cells that required PAR1 cleavage. Vascular endothelial growth factor-mediated hyperpermeability in the skin was reduced by either endogenously generated as well as directly infused recombinant mouse APC in wild-type mice. However APC did not significantly alter the vascular barrier function in PAR1-deficient mice. In endotoxin-challenged mice, infused APC significantly prevented from pulmonary fluid accumulation in the wild-type mice but not in mice lacking PAR1. Our results directly show that murine APC cleaves and signals through PAR1 in mouse endothelial cells. APC reduces vascular permeability in mouse models and PAR1 plays a major role in mediating these effects. Our data in vitro and in vivo support the paradigm that PAR1 contributes to protective effects of APC on vascular barrier integrity in sepsis.

Thrombin bound to a fibrin clot confers angiogenic and haemostatic properties on endothelial progenitor cells

Recent data suggest that endothelial progenitor cells (EPCs) are involved in recanalizing venous thrombi. We examined the impact of a fibrin network, and particularly of adsorbed thrombin, on EPCs derived from cord blood CD34(+) cells. Fibrin networks generated in microplates by adding CaCl(2) to platelet-depleted plasma retained adsorbed thrombin at the average concentration of 4.2 nM per well. EPCs expressed high levels of endothelial cell protein C receptor and thrombomodulin, allowing the generation of activated protein C on the fibrin matrix in the presence of exogenous human protein C. The fibrin matrix induced significant EPC proliferation and, when placed in the lower chamber of a Boyden device, strongly enhanced EPC migration. These effects were partly inhibited by hirudin by 41% and 66%, respectively), which suggests that fibrin-adsorbed thrombin interacts with EPCs via the thrombin receptor PAR-1. Finally, spontaneous lysis of the fibrin network, studied by measuring D-dimer release into the supernatant, was inhibited by EPCs but not by control mononuclear cells. Such an effect was associated with a 10-fold increase in plasminogen activator inhibitor-1 (PAI-1) secretion by EPCs cultivated in fibrin matrix. Overall, our data show that EPCs, in addition to their angiogenic potential, have both anticoagulant and antifibrinolytic properties. Thrombin may modulate these properties and contribute to thrombus recanalization by EPCs.

Anti-Inflammatory mechanisms of enteric Heligmosomoides polygyrus infection against trinitrobenzene sulfonic acid-induced colitis in a murine model

Recent studies showed that enteric helminth infection improved symptoms in patients with inflammatory bowel disease as well as in experimental models of colitis. The aim of this study was to determine the mechanism of the protective effect of helminth infection on colitis-induced changes in immune and epithelial cell function. BALB/c mice received an oral infection of Heligmosomoides polygyrus third-stage larvae, were given intrarectal saline or trinitrobenzene sulfonic acid (TNBS) on day 10 postinfection, and were studied 4 days later. Separate groups of mice received intrarectal saline or TNBS on day 10 and were studied on day 14. Muscle-free colonic mucosae were mounted in Ussing chambers to measure mucosal permeability and secretion. Expression of cytokines was assessed by quantitative real-time PCR, and mast cells were visualized by immunohistochemistry. TNBS-induced colitis induced mucosal damage, upregulated Th1 cytokines, and depressed secretory responses. Heligmosomoides polygyrus elevated Th2 cytokine expression, increased mast cell infiltration and mucosal resistance, and also reduced some secretory responses. Prior H. polygyrus infection prevented TNBS-induced upregulation of Th1 cytokines and normalized secretory responses to specific agonists. TNBS-induced colitis did not alter H. polygyrus-induced mast cell infiltration or upregulation of Th2 cytokine expression. The results indicate that the protective mechanism of enteric nematode infection against TNBS-induced colitis involves prevention of Th1 cytokine expression and improved colonic function by a mechanism that may involve mast cell-mediated protection of neural control of secretory function. Similar response patterns could account for the clinical improvement seen in inflammatory bowel disease with helminthic therapy.

Thrombin induces fibroblast CCL2/JE production and release via coupling of PAR1 to Galphaq and cooperation between ERK1/2 and Rho kinase signaling pathways

Uncontrolled activation of the coagulation cascade after tissue injury has been implicated in both inflammation and tissue fibrosis. Thrombin exerts pluripotent cellular effects via its high-affinity receptor, proteinase-activated receptor-1 (PAR(1)) and signaling via Galpha(i/o), Galpha(q), or Galpha(12/13). Activation of PAR(1) on fibroblasts, a key effector cell in fibrosis, results in the induction of several mediators, including the potent monocyte and fibrocyte chemoattractant CCL2. The aim of this study was to identify the G protein and signaling pathway involved in PAR(1)-mediated CCL2 production and release. Using a novel PAR(1) antagonist that blocks the interaction between PAR(1) and Galpha(q), we report for the first time that PAR(1) coupling to Galpha(q) is essential for thrombin-induced CCL2 gene expression and protein release in murine lung fibroblasts. We further demonstrate that these effects are mediated via the cooperation between ERK1/2 and Rho kinase signaling pathways: a calcium-independent protein kinase C (PKC), c-Raf, and ERK1/2 pathway was found to mediate PAR(1)-induced CCL2 gene transcription, whereas a phospholipase C, calcium-dependent PKC, and Rho kinase pathway influences CCL2 protein release. We propose that targeting the interaction between PAR(1) and Galpha(q) may allow us to selectively interfere with PAR(1) proinflammatory and profibrotic signaling, while preserving the essential role of other PAR(1)-mediated cellular responses.

Functional GI disorders: from animal models to drug development

Despite considerable efforts by academic researchers and by the pharmaceutical industry, the development of novel pharmacological treatments for irritable bowel syndrome (IBS) and other functional gastrointestinal (GI) disorders has been slow and disappointing. The traditional approach to identifying and evaluating novel drugs for these symptom-based syndromes has relied on a fairly standard algorithm using animal models, experimental medicine models and clinical trials. In the current article, the empirical basis for this process is reviewed, focusing on the utility of the assessment of visceral hypersensitivity and GI transit, in both animals and humans, as well as the predictive validity of preclinical and clinical models of IBS for identifying successful treatments for IBS symptoms and IBS-related quality of life impairment. A review of published evidence suggests that abdominal pain, defecation-related symptoms (urgency, straining) and psychological factors all contribute to overall symptom severity and to health-related quality of life. Correlations between readouts obtained in preclinical and clinical models and respective symptoms are small, and the ability to predict drug effectiveness for specific as well as for global IBS symptoms is limited. One possible drug development algorithm is proposed which focuses on pharmacological imaging approaches in both preclinical and clinical models, with decreased emphasis on evaluating compounds in symptom-related animal models, and more rapid screening of promising candidate compounds in man.

The contribution of PARs to inflammation and immunity to fungi

During inflammation, host- and microbial-derived proteases trigger the activation of protease-activated receptors (PARs), a family of G-protein-coupled receptors. We report here that activation of Toll-like receptors (TLRs) by fungi unmasks an essential and divergent role for PAR(1) and PAR(2) in downstream signaling and inflammation. TLRs activated PARs and triggered distinct signal transduction pathways involved in inflammation and immunity to Candida albicans and Aspergillus fumigatus. Inflammation was promoted by PAR(1) and PAR(2) activation in response to Candida and by PAR(2) inhibition in response to Aspergillus. This occurred by TLR regulation of PAR signaling, with TLR2 promoting PAR(1) activity, and TLR4 suppressing PAR(2) activity. Thus, tissue injury and pathogens induce signals that are integrated at the level of distinct TLR/PAR-dependent pathways, the exploitation or subversion of which contributes to divergence in microbial promotion of inflammatory response.

Activated protein C-cleaved protease activated receptor-1 is retained on the endothelial cell surface even in the presence of thrombin

Activated protein C (APC) signals in endothelial cells ex vivo through protease activated receptor-1 (PAR1). However, it is controversial whether PAR1 can mediate APC's protective effects in sepsis because the inflammatory response results in thrombin generation and thrombin proteolytically activates PAR1 much more efficiently than APC. Here we show that APC can induce powerful barrier protective responses in an endothelial cell monolayer in the presence of thrombin. Using cell surface immunoassays with conformation sensitive monoclonal anti-PAR1 antibodies we analyzed cleavage of endogenous PAR1 on the endothelial cell surface by APC in the absence and presence of thrombin. Incubation with APC caused efficient PAR1 cleavage and upon coincubation with thrombin APC supported additional PAR1 cleavage. Thrombin-cleaved PAR1 rapidly disappeared from the cell surface whereas, unexpectedly, the APC-cleaved PAR1 remained and could be detected on the cell surface, even when thrombin at concentrations of up to 1 nM was also present. Our findings demonstrate for the first time directly that APC can generate a distinct PAR1 population on endothelial cells in the presence of thrombin. The data suggest that different trafficking of activated PAR1 might explain how PAR1 signaling by APC can be relevant when thrombin is present.

Proteinases and signalling: pathophysiological and therapeutic implications via PARs and more

Proteinases like thrombin, trypsin and tissue kallikreins are now known to regulate cell signaling by cleaving and activating a novel family of G-protein-coupled proteinase-activated receptors (PARs 1-4) via exposure of a tethered receptor-triggering ligand. On their own, short synthetic PAR-selective PAR-activating peptides (PAR-APs) mimicking the tethered ligand sequences can activate PARs 1, 2 and 4 and cause physiological responses both in vitro and in vivo. Using the PAR-APs as sentinel probes in vivo, it has been found that PAR activation can affect the vascular, renal, respiratory, gastrointestinal, musculoskeletal and nervous systems (both central and peripheral nervous system) and can promote cancer metastasis and invasion. In general, responses triggered by PARs 1, 2 and 4 are in keeping with an innate immune inflammatory response, ranging from vasodilatation to intestinal inflammation, increased cytokine production and increased or decreased nociception. Further, PARs have been implicated in a number of disease states, including cancer and inflammation of the cardiovascular, respiratory, musculoskeletal, gastrointestinal and nervous systems. In addition to activating PARs, proteinases can cause hormone-like effects by other signalling mechanisms, like growth factor receptor activation, that may be as important as the activation of PARs. We, therefore, propose that the PARs themselves, their activating serine proteinases and their associated signalling pathways can be considered as attractive targets for therapeutic drug development. Thus, proteinases in general must now be considered as 'hormone-like' messengers that can signal either via PARs or other mechanisms.

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 mast cell integrates the splanchnic and systemic inflammatory response in portal hypertension

Portal hypertension is a clinical syndrome that is difficult to study in an isolated manner since it is always associated with a greater or lesser degree of liver functional impairment. The aim of this review is to integrate the complications related to chronic liver disease by using both, the array of mast cell functions and mediators, since they possibly are involved in the pathophysiological mechanisms of these complications. The portal vein ligated rat is the experimental model most widely used to study this syndrome and it has been considered that a systemic inflammatory response is produced. This response is mediated among other inflammatory cells by mast cells and it evolves in three linked pathological functional systems. The nervous functional system presents ischemia-reperfusion and edema (oxidative stress) and would be responsible for hyperdynamic circulation; the immune functional system causes tissue infiltration by inflammatory cells, particularly mast cells and bacteria (enzymatic stress) and the endocrine functional system presents endothelial proliferation (antioxidative and antienzymatic stress) and angiogenesis. Mast cells could develop a key role in the expression of these three phenotypes because their mediators have the ability to produce all the aforementioned alterations, both at the splanchnic level (portal hypertensive enteropathy, mesenteric adenitis, liver steatosis) and the systemic level (portal hypertensive encephalopathy). This hypothetical splanchnic and systemic inflammatory response would be aggravated during the progression of the chronic liver disease, since the antioxidant ability of the body decreases. Thus, a critical state is produced, in which the appearance of noxious factors would favor the development of a dedifferentiation process protagonized by the nervous functional system. This system rapidly induces an ischemia-reperfusion phenotype with hydration and salinization of the body (hepatorenal syndrome, ascites) which, in turn would reduce the metabolic needs of the body and facilitate its temporary survival.

Transcription factor network downstream of protease activated receptors (PARs) modulating mouse bladder inflammation

BACKGROUND

All four PARs are present in the urinary bladder, and their expression is altered during inflammation. In order to search for therapeutic targets other than the receptors themselves, we set forth to determine TFs downstream of PAR activation in the C57BL/6 urinary bladders.

METHODS

For this purpose, we used a protein/DNA combo array containing 345 different TF consensus sequences. Next, the TF selected was validated by EMSA and IHC. As mast cells seem to play a fundamental role in bladder inflammation, we determined whether c-kit receptor deficient (Kit w/Kit w-v) mice have an abrogated response to PAR stimulation. Finally, TFEB antibody was used for CHIP/Q-PCR assay and revealed up-regulation of genes known to be downstream of TFEB.

RESULTS

TFEB, a member of the MiTF family of basic helix-loop-helix leucine zipper, was the only TF commonly up-regulated by all PAR-APs. IHC results confirm a correlation between inflammation and TFEB expression in C57BL/6 mice. In contrast, Kit w/Kit w-v mice did not exhibit inflammation in response to PAR activation. EMSA results confirmed the increased TFEB binding activity in C57BL/6 but not in Kit w/Kit w-v mice.

CONCLUSION

This is the first report describing the increased expression of TFEB in bladder inflammation in response to PAR activation. As TFEB belongs to a family of TFs essential for mast cell survival, our findings suggest that this molecule may influence the participation of mast cells in PAR-mediated inflammation and that targeting TFEB/MiTF activity may be a novel approach for the treatment of bladder inflammatory disorders.

Tissue factor: a mediator of inflammatory cell recruitment, tissue injury, and thrombus formation in experimental colitis

There is growing evidence for an interplay between inflammatory and coagulation pathways in acute and chronic inflammatory diseases. However, it remains unclear whether components of the coagulation pathway, such as tissue factor (TF), contribute to intestinal inflammation, and whether targeting TF will blunt the inflammatory cell recruitment, tissue injury, and enhanced thrombus formation that occur in experimental colitis. Mice were fed 3% dextran sodium sulfate (DSS) to induce colonic inflammation, with some mice receiving a mouse TF-blocking antibody (muTF-Ab). The adhesion of leukocytes and platelets in colonic venules, light/dye-induced thrombus formation in cremaster muscle microvessels, as well as disease activity index, thrombin-antithrombin (TAT) complexes in plasma, and histopathologic changes in the colonic mucosa were monitored in untreated and muTF-Ab-treated colitic mice. In untreated mice, DSS elicited the recruitment of adherent leukocytes and platelets in colonic venules, caused gross and histologic injury, increased plasma TAT complexes, and enhanced thrombus formation in muscle arterioles. muTF-Ab prevented elevation in TAT complexes, reduced blood cell recruitment and tissue injury, and blunted thrombus formation in DSS colitic mice. These findings implicate TF in intestinal inflammation and support an interaction between inflammation and coagulation in experimental colitis.

Regulatory network of inflammation downstream of proteinase-activated receptors

Background

Protease-activated receptors (PAR) are present in the urinary bladder, and their expression is altered in response to inflammation. PARs are a unique class of G protein-coupled that carry their own ligands, which remain cryptic until unmasked by proteolytic cleavage. Although the canonical signal transduction pathway downstream of PAR activation and coupling with various G proteins is known and leads to the rapid transcription of genes involved in inflammation, the effect of PAR activation on the downstream transcriptome is unknown.

We have shown that intravesical administration of PAR-activating peptides leads to an inflammatory reaction characterized by edema and granulocyte infiltration. Moreover, the inflammatory response to intravesical instillation of known pro-inflammatory stimuli such as E. coli lipopolysaccharide (LPS), substance P (SP), and antigen was strongly attenuated by PAR1- and to a lesser extent by PAR2-deficiency.

Results

Here, cDNA array experiments determined inflammatory genes whose expression is dependent on PAR1 activation. For this purpose, we compared the alteration in gene expression in wild type and PAR1^-/- mice induced by classical pro-inflammatory stimuli (LPS, SP, and antigen). 75 transcripts were considered to be dependent on PAR-1 activation and further annotated in silico by Ingenuity Pathways Analysis (IPA) and gene ontology (GO). Selected transcripts were target validated by quantitative PCR (Q-PCR). Among PAR1-dependent transcripts, the following have been implicated in the inflammatory process: b2m, ccl7, cd200, cd63, cdbpd, cfl1, dusp1, fkbp1a, fth1, hspb1, marcksl1, mmp2, myo5a, nfkbia, pax1, plaur, ppia, ptpn1, ptprcap, s100a10, sim2, and tnfaip2. However, a balanced response to signals of injury requires a transient cellular activation of a panel of genes together with inhibitory systems that temper the overwhelming inflammation. In this context, the activation of genes such as dusp1 and nfkbia seems to counter-balance the inflammatory response to PAR activation by limiting prolonged activation of p38 MAPK and increased cytokine production. In contrast, transcripts such as arf6 and dcnt1 that are involved in the mechanism of PAR re-sensitization would tend to perpetuate the inflammatory reaction in response to common pro-inflammatory stimuli.

Conclusion

The combination of cDNA array results and genomic networks reveals an overriding participation of PAR1 in bladder inflammation, provides a working model for the involvement of downstream signaling, and evokes testable hypotheses regarding the transcriptome downstream of PAR1 activation.

It remains to be determined whether or not mechanisms targeting PAR1 gene silencing or PAR1 blockade will ameliorate the clinical manifestation of cystitis.

Mandatory role of proteinase-activated receptor 1 in experimental bladder inflammation

Background

In general, inflammation plays a role in most bladder pathologies and represents a defense reaction to injury that often times is two edged. In particular, bladder neurogenic inflammation involves the participation of mast cells and sensory nerves. Increased mast cell numbers and tryptase release represent one of the prevalent etiologic theories for interstitial cystitis and other urinary bladder inflammatory conditions. The activity of mast cell-derived tryptase as well as thrombin is significantly increased during inflammation. Those enzymes activate specific G-protein coupled proteinase-activated receptors (PAR)s.

Four PARs have been cloned so far, and not only are all four receptors highly expressed in different cell types of the mouse urinary bladder, but their expression is altered during experimental bladder inflammation. We hypothesize that PARs may link mast cell-derived proteases to bladder inflammation and, therefore, play a fundamental role in the pathogenesis of cystitis.

Results

Here, we demonstrate that in addition to the mouse urinary bladder, all four PA receptors are also expressed in the J82 human urothelial cell line. Intravesical administration of PAR-activating peptides in mice leads to an inflammatory reaction characterized by edema and granulocyte infiltration. Moreover, the inflammatory response to intravesical instillation of known pro-inflammatory stimuli such as E. coli lipopolysaccharide (LPS), substance P, and antigen was strongly attenuated by PAR1-, and to a lesser extent, by PAR2-deficiency.

Conclusion

Our results reveal an overriding participation of PAR1 in bladder inflammation, provide a working model for the involvement of downstream signaling, and evoke testable hypotheses regarding the role of PARs in bladder inflammation. It remains to be determined whether or not mechanisms targeting PAR1 gene silencing or PAR1 blockade will ameliorate the clinical manifestations of cystitis.

Protease-activated receptors: potential therapeutic targets in irritable bowel syndrome?

Protease-activated receptors (PARs) are a family of four G-protein-coupled receptors (PAR-1 to PAR-4) activated by the proteolytic cleavage of their N-terminal extracellular domain. This activation first involves the recognition of the extracellular domain by proteases, such as thrombin, but also trypsin or tryptase which are particularly abundant in the gastrointestinal tract, both under physiological circumstances and in several digestive diseases. Activation of PARs, particularly of PAR-1 and -2, modulates intestinal functions, such as gastrointestinal motility, visceral nociception, mucosal inflammatory response, and epithelial functions (intestinal secretion and permeability). As these physiological properties have been shown to be altered in various extents and combinations in different clinical presentations of irritable bowel syndrome, PARs appear as putative targets for future therapeutic intervention in these patients.

The roles of proteinase-activated receptors in the vascular physiology and pathophysiology

Proteinase-activated receptors (PARs) belong to a family of G protein-coupled receptors, thus mediating the cellular effects of proteinases. In the vascular system, thrombin and other proteinases in the coagulation-fibrinolysis system are considered to be the physiologically relevant agonists, whereas PARs are among the most important mechanisms mediating the interaction between the coagulation-fibrinolysis system and the vascular wall. Under physiological conditions, PARs are mainly expressed in endothelial cells, and participate in the regulation of vascular tone, mostly by inducing endothelium-dependent relaxation. PARs in endothelial cells are also suggested to contribute to a proinflammatory phenotypic conversion and an increase in the permeability of vascular lesions. In smooth muscle cells, PARs mediate contraction, migration, proliferation, hypertrophy, and production of the extracellular matrix, thereby contributing to the development of vascular lesions and the pathophysiology of such vascular diseases as atherosclerosis. However, the expression of PARs in the smooth muscle of normal arteries is limited. The upregulation of PARs in the smooth muscle is thus considered to be a key step for PARs to participate in the pathogenesis of vascular lesions. Elucidating the molecular mechanism regulating the PARs expression is therefore important to develop new strategies for the prevention and treatment of vascular diseases.

Thrombin Inhibits IFN-γProduction in Human Peripheral Blood Mononuclear Cells by Promoting a Th2 Profile

Thrombin, the key enzyme of the coagulation cascade, is involved in inflammation. It was proposed recently that thrombin activity may play an important role in allergic inflammation. Interferon-gamma (IFN-gamma) is a potent Th1-related cytokine secreted by activated T cells and is usually downregulated in allergic inflammation. We recently demonstrated that thrombin enhances interleukin-10 (IL-10) in peripheral blood mononuclear cells (PBMC). Thus, we hypothesized that thrombin may promote a Th2 profile. We here report that human alpha- thrombin downregulates IFN-gamma expression at both protein and mRNA levels in activated PBMCs. The use of proteolytically inactive thrombin and of the specific thrombin receptor agonist peptide, SFLLRN, shows that this downregulation is thrombin specific and requires thrombin proteolytic activity. The addition of an anti- IL-10 monoclonal antibody (mAb) to thrombin-treated PBMCs abolishes IFN-gamma downregulation, suggesting that thrombin exerts its effect through IL-10, a Th2-related cytokine. Furthermore, IFN-gamma reduction was accompanied by increased IL-4 release, as well as by an increase in the proinflammatory cytokine IL-1. In conclusion, the observation that thrombin affects the production of IFN-gamma (Th1 profile) and IL-4 (Th2 profile) provides further evidence for the role played by thrombin in modulating Th1/Th2 cytokine balance, which could be particularly relevant in allergic inflammation.

Protective effect of proteinase-activated receptor 2 activation on motility impairment and tissue damage induced by intestinal ischemia/reperfusion in rodents

We hypothesized that proteinase-activated receptor-2 (PAR(2)) modulates intestinal injuries induced by ischemia/reperfusion. Ischemia (1 hour) plus reperfusion (6 hours) significantly delayed gastrointestinal transit (GIT) compared with sham operation. Intraduodenal injection of PAR(2)-activating peptide SLIGRL-NH(2) significantly accelerated transit in ischemia/reperfusion but not in sham-operated rats. GIT was significantly delayed in ischemia/reperfusion and sham-operated PAR(2)(-/-) mice compared with PAR(2)(+/+). SLIGRL-NH(2) significantly accelerated transit in ischemia/reperfusion in PAR(2)(+/+) but not in PAR(2)(-/-) mice. Prevention of mast cell degranulation with cromolyn, ablation of visceral afferents with capsaicin, and antagonism of calcitonin gene-related peptide (CGRP) and neurokinin-1 receptors with CGRP(8-37) and RP67580, respectively, abolished the SLIGRL-NH(2)-induced stimulatory effect on transit in ischemia/reperfusion. Tissue damage was significantly reduced by SLIGRL-NH(2); this effect was not observed in cromolyn-, capsaicin-, or RP67580-treated rats but was detected following CGRP(8-37). Intestinal PAR(2) mRNA levels were not affected by SLIGRL-NH(2) in ischemia/reperfusion. We propose that PAR(2) modulates GIT and tissue damage in intestinal ischemia/reperfusion by a mechanism dependent on mast cells and visceral afferents. PAR(2) effect on transit might be mediated by CGRP and substance P, whereas the effect on tissue damage appears to involve substance P but not CGRP. PAR(2) might be a signaling system in the neuroimmune communication in intestinal ischemia/reperfusion.

Transgenic mice rich in endogenous omega-3 fatty acids are protected from colitis

Omega-6 (n-6) and omega-3 (n-3) polyunsaturated fatty acids (PUFA) are the precursors of potent lipid mediators and play an important role in regulation of inflammation. Generally, n-6 PUFA promote inflammation whereas n-3 PUFA have antiinflammatory properties, traditionally attributed to their ability to inhibit the formation of n-6 PUFA-derived proinflammatory eicosanoids. Newly discovered resolvins and protectins are potent antiinflammatory lipid mediators derived directly from n-3 PUFA with distinct pathways of action. However, the role of the n-3 PUFA tissue status in the formation of these antiinflammatory mediators has not been addressed. Here we show that an increased n-3 PUFA tissue status in transgenic mice that endogenously biosynthesize n-3 PUFA from n-6 PUFA leads to significant formation of antiinflammatory resolvins and effective reduction in inflammation and tissue injury in colitis. The endogenous increase in n-3 PUFA and related products did not decrease n-6 PUFA-derived lipid mediators such as leukotriene B4 and prostaglandin E2. The observed inflammation protection might result from decreased NF-kappaB activity and expression of TNFalpha, inducible NO synthase, and IL-1beta, with enhanced mucoprotection probably because of the higher expression of trefoil factor 3, Toll-interacting protein, and zonula occludens-1. These results thus establish the fat-1 transgenic mouse as a new experimental model for the study of n-3 PUFA-derived lipid mediators. They add insight into the molecular mechanisms of inflammation protection afforded by n-3 PUFA through formation of resolvins and protectins other than inhibition of n-6 PUFA-derived eicosanoid formation.