Protease-activated receptor-4 inhibition protects from multiorgan failure in a murine model of systemic inflammation

Elevated protease-activated receptor 4 (PAR4) gene expression in Alzheimer's disease predicts cognitive decline

Platelet activation of protease-activated receptor 4 (PAR4) and thrombin are at the top of a chain of events leading to fibrin deposition, microinfarcts, blood-brain barrier disruption, and inflammation. We evaluated mRNA expression of the PAR4 gene F2RL3 in human brain and global cognitive performance in participants with and without cognitive impairment or dementia. Data were acquired from the Religious Orders Study (ROS) and the Rush Memory and Aging Project (MAP). F2RL3 mRNA was elevated in AD cases and was associated with worse retrospective longitudinal cognitive performance. Moreover, F2RL3 expression interacted with clinical AD diagnosis on longitudinal cognition whereas this relationship was attenuated in individuals without cognitive impairment. Additionally, when adjusting for the effects of AD neuropathology, F2RL3 expression remained a significant predictor of cognitive decline. F2RL3 expression correlated positively with transcript levels of proinflammatory markers including TNFα, IL-1β, NFκB, and fibrinogen α/β/γ. Together, these results reveal that F2RL3 mRNA expression is associated with multiple AD-relevant outcomes and its encoded product, PAR4, may play a role in disease pathogenesis.

Pepducin-mediated G Protein-Coupled Receptor Signaling in the Cardiovascular System

ABSTRACT

Pepducins are small-lipidated peptides designed from the intracellular loops of G protein-coupled receptors (GPCRs) that act in an allosteric manner to modulate the activity of GPCRs. Over the past 2 decades, pepducins have progressed initially from pharmacologic tools used to manipulate GPCR activity in an orthosteric site-independent manner to compounds with therapeutic potential that have even been used safely in phase 1 and 2 clinical trials in human subjects. The effect of pepducins at their cognate receptors has been shown to vary between antagonist, partial agonist, and biased agonist outcomes in various primary and clonal cell systems, with even small changes in amino acid sequence altering these properties and their receptor selectivity. To date, pepducins designed from numerous GPCRs have been studied for their impact on pathologic conditions, including cardiovascular diseases such as thrombosis, myocardial infarction, and atherosclerosis. This review will focus in particular on pepducins designed from protease-activated receptors, C-X-C motif chemokine receptors, formyl peptide receptors, and the β2-adrenergic receptor. We will discuss the historic context of pepducin development for each receptor, as well as the structural, signaling, pathophysiologic consequences, and therapeutic potential for each pepducin class.

Discovery of 7, 4'-dimethoxy-3-hydroxyflavone as a protease-activated receptor 4 antagonist with antithrombotic activity and less bleeding tendency in mice

There is growing evidence of the importance of protease-activated receptor 4 (PAR4), one of thrombin receptors, as a therapeutic target in thrombotic cardiovascular diseases. In the present study, we utilized ligand-based virtual screening, bioassay, and structure-activity relationship study to discover PAR4 antagonists with new chemical scaffolds from natural origin, and examined their application as antiplatelet agents. By using these approaches, we have identified a flavonoid, 7, 4'-dimethoxy-3-hydroxyflavone, that exhibits anti-PAR4 activity. 7, 4'-Dimethoxy-3-hydroxyflavone inhibited PAR4-mediated human platelet aggregation, GPIIb/IIIa activation, and P-selectin secretion. Also, it inhibited PAR4 downstream signaling pathways, including Ca2+/protein kinase C, Akt, and MAP kinases ERK and p38, in human platelets, and suppressed PAR4-mediated β-arrestin recruitment in CHO-K1 cells exogenously expressed human PAR4. In a microfluidic system, 7, 4'-dimethoxy-3-hydroxyflavone reduced thrombus formation on collagen-coated chambers at an arterial shear rate in recalcified whole blood. Furthermore, mice treated with 7, 4'-dimethoxy-3-hydroxyflavone were significantly protected from FeCl3-induced carotid arterial occlusions, without significantly affecting tail bleeding time. In conclusion, 7, 4'-dimethoxy-3-hydroxyflavone represents a new class of nature-based PAR4 antagonist, it shows effective in vivo antithrombotic properties with less bleeding tendency, and could be a potential candidate for developing new antiplatelet agents.

[The role of thrombin in the pathogenesis of atherosclerosis and its complications]

Thrombin is a key regulator of the homeostasis system. Also, it actively participates in progression of various systemic diseases, including atherosclerosis. There is a large amount of experimental and clinical data on the involvement of thrombin in the pathogenesis of ischemic heart disease (IHD). Thus, studying thrombin activity regulation is promising. Also, the question whether it is possible to use biomarkers of thrombin activity as predictors of cardiovascular complications in IHD patients is relevant. The present review focuses on major mechanisms of thrombin functioning, its role in development and progression of atherosclerosis, and available tests for evaluation of thrombin functional activity. Major clinical studies are discussed that evaluated the efficacy of thrombin inhibitors and protease-activated receptor antagonists.

Pulmonary histopathology in fatal paraquat poisoning

Paraquat is a potent herbicide widely used in the Indian agriculture industry. Human fatality due to paraquat poisoning is not uncommon in this country. The primary effect of paraquat is on the lungs, and the resultant pulmonary damage leads to the patient's demise. There is a high mortality rate in paraquat poisoning as the treatment is usually supportive with no known antidote. There are limited human studies that have observed the histopathological changes in lungs in paraquat poisoning. The authors have discussed the time-related histopathological changes in lungs in paraquat poisoning on autopsy subjects. The role of anticoagulants and fibrinolytic agents in the treatment of this poisoning has also been discussed.

Platelet-Mediated NET Release Amplifies Coagulopathy and Drives Lung Pathology During Severe Influenza Infection

The influenza A virus (IAV) causes a respiratory tract infection with approximately 10% of the population infected by the virus each year. Severe IAV infection is characterized by excessive inflammation and tissue pathology in the lungs. Platelet and neutrophil recruitment to the lung are involved in the pathogenesis of IAV, but the specific mechanisms involved have not been clarified. Using confocal intravital microscopy in a mouse model of IAV infection, we observed profound neutrophil recruitment, platelet aggregation, neutrophil extracellular trap (NET) production and thrombin activation within the lung microvasculature in vivo. Importantly, deficiency or antagonism of the protease-activated receptor 4 (PAR4) reduced platelet aggregation, NET production, and neutrophil recruitment. Critically, inhibition of thrombin or PAR4 protected mice from virus-induced lung tissue damage and edema. Together, these data imply thrombin-stimulated platelets play a critical role in the activation/recruitment of neutrophils, NET release and directly contribute to IAV pathogenesis in the lung.

Protease-activated receptor 4 plays a role in lipopolysaccharide-induced inflammatory mechanisms in murine macrophages

The role of protease-activated receptor (PAR)4 in thrombin-induced platelet aggregation has been studied, and PAR4 blockade is thought to be useful as a new and promising approach in antiplatelet therapy in humans. In recent years, studies have been conducted to clarify the role of PAR4 in the host defense against invading microorganisms and pathogen-induced inflammation; however, to date, the role of PAR4 in mediating the LPS-induced inflammatory repertoire in macrophages remains to be elucidated. Here, we investigated the effects of the synthetic PAR4 agonist peptide (PAR4-AP) AYPGKF-NH₂ on the phagocytosis of zymosan-FITC particles; NO, ROS, and iNOS expression; and cytokine production in C57/BL6 macrophages cocultured with PAR4-AP/LPS. The PAR4-AP impaired LPS-induced and basal phagocytosis, which was restored by pharmacological PAR4 blockade. Coincubation with the PAR4-AP/LPS enhanced NO and ROS production and iNOS expression; decreased IL-10, but not TNF-α, in the culture supernatant; and increased translocation of the p65 subunit of the proinflammatory gene transcription factor NF-κ-B. Our results provide evidence for a complex mechanism and new approach by which PAR4 mediates the macrophage response triggered by LPS through counter-regulating the phagocytic activity of macrophages and innate response mechanisms implicated in the killing of invading pathogens.

Thromboinflammation: challenges of therapeutically targeting coagulation and other host defense mechanisms

Thrombosis with associated inflammation (thromboinflammation) occurs commonly in a broad range of human disorders. It is well recognized clinically in the context of superficial thrombophlebitis (thrombosis and inflammation of superficial veins); however, it is more dangerous when it develops in the microvasculature of injured tissues and organs. Microvascular thrombosis with associated inflammation is well recognized in the context of sepsis and ischemia-reperfusion injury; however, it also occurs in organ transplant rejection, major trauma, severe burns, the antiphospholipid syndrome, preeclampsia, sickle cell disease, and biomaterial-induced thromboinflammation. Central to thromboinflammation is the loss of the normal antithrombotic and anti-inflammatory functions of endothelial cells, leading to dysregulation of coagulation, complement, platelet activation, and leukocyte recruitment in the microvasculature. α-Thrombin plays a critical role in coordinating thrombotic and inflammatory responses and has long been considered an attractive therapeutic target to reduce thromboinflammatory complications. This review focuses on the role of basic aspects of coagulation and α-thrombin in promoting thromboinflammatory responses and discusses insights gained from clinical trials on the effects of various inhibitors of coagulation on thromboinflammatory disorders. Studies in sepsis patients have been particularly informative because, despite using anticoagulant approaches with different pharmacological profiles, which act at distinct points in the coagulation cascade, bleeding complications continue to undermine clinical benefit. Future advances may require the development of therapeutics with primary anti-inflammatory and cytoprotective properties, which have less impact on hemostasis. This may be possible with the growing recognition that components of blood coagulation and platelets have prothrombotic and proinflammatory functions independent of their hemostatic effects.

Protease activated receptor 4 limits bacterial growth and lung pathology during late stage Streptococcus pneumoniae induced pneumonia in mice

Streptococcus pneumoniae is a common causative pathogen of pneumonia and sepsis. Pneumonia and sepsis are associated with enhanced activation of coagulation, resulting in the production of several host-derived proteases at the primary site of infection and in the circulation. Serine proteases cleave protease activated receptors (PARs), which form a molecular link between coagulation and inflammation. PAR4 is one of four subtypes of PARs and is widely expressed by multiple cell types in the respiratory tract implicated in pulmonary inflammation, by immune cells and by platelets. In mice, mouse (m)PAR4 is the only thrombin receptor expressed by platelets. We here sought to determine the contribution of mPAR4 to the host response during pneumococcal pneumonia. Pneumonia was induced by intranasal inoculation with S. pneumoniae in mPAR4-deficient (par4-/- ) and wild-type mice. Mice were sacrificed after 6, 24 or 48 hours (h). Blood, lungs, liver and spleen were collected for analyses. Ex vivo stimulation assays were performed with S. pneumoniae and mPAR4 activating peptides. At 48 h after infection, higher bacterial loads were found in the lungs and blood of par4-/- mice (p < 0.05), accompanied by higher histopathology scores and increased cytokine levels (p < 0.05) in the lungs. Ex vivo, co-stimulation with mPAR4 activating peptide enhanced the whole blood cytokine response to S. pneumoniae. Thrombin inhibition resulted in decreased cytokine release after S. pneumoniae stimulation in human whole blood. Our findings suggest that mPAR4 contributes to antibacterial defence during murine pneumococcal pneumonia.

The Kallikrein-Kinin System: A Novel Mediator of IL-17-Driven Anti-Candida Immunity in the Kidney

The incidence of life-threatening disseminated Candida albicans infections is increasing in hospitalized patients, with fatalities as high as 60%. Death from disseminated candidiasis in a significant percentage of cases is due to fungal invasion of the kidney, leading to renal failure. Treatment of candidiasis is hampered by drug toxicity, the emergence of antifungal drug resistance and lack of vaccines against fungal pathogens. IL-17 is a key mediator of defense against candidiasis. The underlying mechanisms of IL-17-mediated renal immunity have so far been assumed to occur solely through the regulation of antimicrobial mechanisms, particularly activation of neutrophils. Here, we identify an unexpected role for IL-17 in inducing the Kallikrein (Klk)-Kinin System (KKS) in C. albicans-infected kidney, and we show that the KKS provides significant renal protection in candidiasis. Microarray data indicated that Klk1 was upregulated in infected kidney in an IL-17-dependent manner. Overexpression of Klk1 or treatment with bradykinin rescued IL-17RA-/- mice from candidiasis. Therapeutic manipulation of IL-17-KKS pathways restored renal function and prolonged survival by preventing apoptosis of renal cells following C. albicans infection. Furthermore, combining a minimally effective dose of fluconazole with bradykinin markedly improved survival compared to either drug alone. These results indicate that IL-17 not only limits fungal growth in the kidney, but also prevents renal tissue damage and preserves kidney function during disseminated candidiasis through the KKS. Since drugs targeting the KKS are approved clinically, these findings offer potential avenues for the treatment of this fatal nosocomial infection.

New insights into protease-activated receptor 4 signaling pathways in the pathogenesis of inflammation and neuropathic pain: a literature review

Pain is an unpleasant sensory and emotional experience that is commonly associated with actual or potential tissue damage. Despite decades of pain research, many patients continue to suffer from chronic pain that is refractory to current treatments. Accumulating evidence has indicated an important role of protease-activated receptor 4 (PAR4) in the pathogenesis of inflammation and neuropathic pain. Here we reviewed PAR4 expression and activation via intracellular signaling pathways and the role of PAR4 signaling pathways in the development and maintenance of pain. Understanding PAR4 and its corresponding signaling pathways will provide insight to further explore the molecular basis of pain, which will also help to identify new targets for pharmacological intervention for pain relief.

Dysregulated protease activated receptor 1 (PAR1) promotes metastatic phenotype in breast cancer through HMGA2

As the majority of patients with basal-like breast carcinoma present with invasive, metastatic disease that do not respond to available therapies, it is essential to identify new therapeutic targets that impact invasion and metastasis. Protease-activated receptor 1 (PAR1), a G-protein coupled receptor has been shown to act as an oncogene, but underlying mechanisms are not well understood. Here, we show that ectopic expression of functionally active PAR1 in MCF-7 cells induced a hormone-refractory, invasive phenotype representative of advanced basal-like breast carcinoma that readily formed metastatic lesions in lungs of mice. PAR1 was found to globally upregulate mesenchymal markers, including vimentin, a direct target of PAR1, and downregulate the epithelial markers including E-cadherin, as well as estrogen receptor. In contrast, non-signaling PAR1 mutant receptor did not lead to an invasive, hormone refractory phenotype. PAR1 expression increased spheroid formation and the level of stemness markers and self-renewal capacity in human breast cancer cells. We identified HMGA2 (high mobility group A2) as an important regulator of PAR1-mediated invasion. Inhibition of PAR1 signaling suppresses HMGA2-driven invasion in breast cancer cells. HMGA2 gene and protein are highly expressed in metastatic breast cancer cells. Overall, our results show that PAR1/HMGA2 pathway may present a novel therapeutic target.

CCAAT/enhancer-binding protein δ (C/EBPδ) aggravates inflammation and bacterial dissemination during pneumococcal meningitis

Background

The prognosis of bacterial meningitis largely depends on the severity of the inflammatory response. The transcription factor CAAT/enhancer-binding protein δ (C/EBPδ) plays a key role in the regulation of the inflammatory response during bacterial infections. Consequently, we assessed the role of C/EBPδ during experimental meningitis.

Methods

Wild-type and C/EBPδ-deficient mice (C/EBPδ^−/−) were intracisternally infected with Streptococcus pneumoniae and sacrificed after 6 or 30 h, or followed in a survival study.

Results

In comparison to wild-type mice, C/EBPδ^−/− mice showed decreased bacterial loads at the primary site of infection and decreased bacterial dissemination to lung and spleen 30 h after inoculation. Expression levels of the inflammatory mediators IL-10 and KC were lower in C/EBPδ^−/− brain homogenates, whereas IL-6, TNF-α, IL-1β, and MIP-2 levels were not significantly different between the two genotypes. Moreover, C/EBPδ^−/− mice demonstrated an attenuated systemic response as reflected by lower IL-10, IL-6, KC, and MIP-2 plasma levels. No differences in clinical symptoms or in survival were observed between wild-type and C/EBPδ^−/− mice.

Conclusion

C/EBPδ in the brain drives the inflammatory response and contributes to bacterial dissemination during pneumococcal meningitis. C/EBPδ does, however, not affect clinical parameters of the disease and does not confer a survival benefit.

Blockade of proteinase-activated receptor 4 inhibits neutrophil recruitment in experimental inflammation in mice

OBJECTIVE AND DESIGN

The activation of proteinase-activated receptors (PARs) has been implicated in the development of important hallmarks of inflammation, including in vivo leukocyte recruitment; however, its role in the regulation of leukocyte migration in response to inflammatory stimuli has not been elucidated until now. Here, we examined the effects of the PAR4 antagonist YPGKF-NH 2 (tcY-NH2) on neutrophil recruitment in experimentally induced inflammation.

METHODS

BALB/c mice were intrapleurally injected with tcY-NH2 (40 ng/kg) prior to intrapleural injection of carrageenan (Cg) or neutrophil chemoattractant CXCL8; the number of infiltrating neutrophils was evaluated after 4 h, and KC production was assessed at different times after Cg injection. Neutrophil adhesion and rolling cells were studied using a brain circulation preparation 4 h after the Cg or CXCL8 challenge in tcY-NH2-treated mice.

RESULTS

PAR4 blockade inhibited CXCL8- and Cg-induced neutrophil migration into the pleural cavity of BALB/c mice and reduced neutrophil rolling and adherence. Surprisingly, PAR4 blockade increased the level of KC in response to carrageenan.

CONCLUSION

These results demonstrated that PAR4 blockade impairs neutrophil migration in vivo, suggesting that PAR4 plays an important role in the regulation of inflammation, at least in part because of its ability to inhibit the actions of the neutrophil chemoattractant CXCL8.

Protease-activated receptor signalling by coagulation proteases in endothelial cells

Endothelial cells express several types of integral membrane protein receptors, which upon interaction and activation by their specific ligands, initiate a signalling network that links extracellular cues in circulation to various biological processes within a plethora of cells in the vascular system. A small family of G-protein coupled receptors, termed protease-activated receptors (PAR1-4), can be specifically activated by coagulation proteases, thereby modulating a diverse array of cellular activities under various pathophysiological conditions. Thrombin and all vitamin K-dependent coagulation proteases, with the exception of factor IXa for which no PAR signalling has been attributed, can selectively activate cell surface PARs on the vasculature. Thrombin can activate PAR1, PAR3 and PAR4, but not PAR2 which can be specifically activated by factors VIIa and Xa. The mechanistic details of the specificity of PAR signalling by coagulation proteases are the subject of extensive investigation by many research groups worldwide. However, analysis of PAR signalling data in the literature has proved to be challenging since a single coagulation protease can elicit different signalling responses through activation of the same PAR receptor in endothelial cells. This article is focused on briefly reviewing the literature with respect to determinants of the specificity of PAR signalling by coagulation proteases with special emphasis on the mechanism of PAR1 signalling by thrombin and activated protein C in endothelial cells.

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

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

Tissue kallikrein mediates pro-inflammatory pathways and activation of protease-activated receptor-4 in proximal tubular epithelial cells

Tissue kallikrein (KLK1) expression is up-regulated in human diabetic kidney tissue and induced by high glucose (HG) in human proximal tubular epithelial cells (PTEC). Since the kallikrein-kinin system (KKS) has been linked to cellular inflammatory process in many diseases, it is likely that KLK1 expression may mediate the inflammatory process during the development of diabetic nephropathy. In this study, we explored the role of KLK1 in tubular pro-inflammatory responses under the diabetic milieu. Recombinant KLK1 stimulated the production of inflammatory cytokines in PTEC via the activation of p42/44 and p38 MAPK signaling pathways. Molecular knockdown of endogenous KLK1 expression by siRNA transfection in PTEC attenuated advanced glycation end-products (AGE)-induced IL-8 and ICAM-1 productions in vitro. Interestingly, exposure of PTEC to KLK1 induced the expression of protease-activated receptors (PARs). There was a 2.9-fold increase in PAR-4, 1.4-fold increase in PAR-1 and 1.2-fold increase in PAR-2 mRNA levels. Activation of PAR-4 by a selective agonist was found to elicit the pro-inflammatory and pro-fibrotic phenotypes in PTEC while blockade of the receptor by specific antagonist attenuated high glucose-induced IL-6, CCL-2, CTGF and collagen IV expression. Calcium mobilization by the PAR-4 agonist in PTEC was desensitized by pretreatment with KLK1. Consistent with these in vitro findings, there was a markedly up-regulation of tubular PAR-4 expression in human diabetic renal cortical tissues. Together, these results suggest that up-regulation of KLK1 in tubular epithelial cells may mediate pro-inflammatory pathway and PAR activation during diabetic nephropathy and provide a new therapeutic target for further investigation.

Protease-activated receptor-2 induces migration of pancreatic cancer cells in an extracellular ATP-dependent manner

BACKGROUND

Protease-activated receptor 2 (PAR-2) is a G protein-coupled receptor suggested to play an important role in the proliferation and migration of tumor cells of epithelial origin. However, the role of PAR-2 in the setting of pancreatic cancer remains largely unexplored.

OBJECTIVES

To understand the importance of PAR-2 in pancreatic cancer cell migration.

METHODS AND RESULTS

The present study shows that PAR-2 does not affect pancreatic cancer cell proliferation but significantly induces the migration of pancreatic cancer cells in scratch assays. Interestingly, PAR-2 does not affect migration in a trans-well setting. This apparent discrepancy depends on extracellular ATP release in the scratch assays and the addition of exogenous (ATP)-induced PAR-2-dependent migration in trans-well assays, whereas a specific P2Y11 receptor antagonist prevents PAR-2-driven migration in scratch assays. In the scratch assays, inhibitors of Src, Rac, protein kinase C, mitogen-activated protein kinase kinase, p38, and epidermal growth factor (EGF) receptor blocked PAR-2-driven migration, whereas they did not affect fetal calf serum-driven wound closure.

CONCLUSION

Taken together, PAR-2 activation drives pancreatic cancer cell migration via an EGF-Src-Rac-p38/mitogen-activated protein kinase kinase/EGF1/2 signaling pathway, which is facilitated by extracellular ATP. Targeting the PAR-2/ATP-driven signaling pathway may therefore limit cell migration, which could inhibit pancreatic cancer metastasis.

Recombinant thrombomodulin protects mice against histone-induced lethal thromboembolism

Introduction

Recent studies have shown that histones, the chief protein component of chromatin, are released into the extracellular space during sepsis, trauma, and ischemia-reperfusion injury, and act as major mediators of the death of an organism. This study was designed to elucidate the cellular and molecular basis of histone-induced lethality and to assess the protective effects of recombinant thrombomodulin (rTM). rTM has been approved for the treatment of disseminated intravascular coagulation (DIC) in Japan, and is currently undergoing a phase III clinical trial in the United States.

Methods

Histone H3 levels in plasma of healthy volunteers and patients with sepsis and DIC were measured using enzyme-linked immunosorbent assay. Male C57BL/6 mice were injected intravenously with purified histones, and pathological examinations were performed. The protective effects of rTM against histone toxicity were analyzed both in vitro and in mice.

Results

Histone H3 was not detectable in plasma of healthy volunteers, but significant levels were observed in patients with sepsis and DIC. These levels were higher in non-survivors than in survivors. Extracellular histones triggered platelet aggregation, leading to thrombotic occlusion of pulmonary capillaries and subsequent right-sided heart failure in mice. These mice displayed symptoms of DIC, including thrombocytopenia, prolonged prothrombin time, decreased fibrinogen, fibrin deposition in capillaries, and bleeding. Platelet depletion protected mice from histone-induced death in the first 30 minutes, suggesting that vessel occlusion by platelet-rich thrombi might be responsible for death during the early phase. Furthermore, rTM bound to extracellular histones, suppressed histone-induced platelet aggregation, thrombotic occlusion of pulmonary capillaries, and dilatation of the right ventricle, and rescued mice from lethal thromboembolism.

Conclusions

Extracellular histones cause massive thromboembolism associated with consumptive coagulopathy, which is diagnostically indistinguishable from DIC. rTM binds to histones and neutralizes the prothrombotic action of histones. This may contribute to the effectiveness of rTM against DIC.

CCAAT-enhancer binding protein delta (C/EBPδ) protects against Klebsiella pneumoniae-induced pulmonary infection: potential role for macrophage migration

Mounting evidence suggests an important role for CCAAT-enhancer binding protein delta (C/EBPδ) in the acute-phase response after bacterial infection. However, whether C/EBPδ limits pneumonia remains elusive and is the aim of this study. Therefore, bacterial outgrowth, inflammatory responses, inflammatory cell influx, and survival were assessed in wild-type and C/EBPδ(-/-) mice infected with Klebsiella pneumoniae via the airways. We showed that C/EBPδ expression is highly induced in the lung during pulmonary infection and that Klebsiella-induced mortality was significantly increased among C/EBPδ(-/-) mice. Bacterial loads and inflammatory responses were similar in wild-type and C/EBPδ(-/-) mice early during infection, whereas bacterial loads were increased in C/EBPδ(-/-) mice later during infection. Moreover, macrophage numbers were reduced in lungs of C/EBPδ(-/-) mice. In vitro experiments showed that C/EBPδ only slightly affects macrophage function. Our data thus show that C/EBPδ contributes to host defense against Klebsiella-induced pneumonia and suggests that C/EBPδ-dependent macrophage mobilization is a key mechanism.

Proteinase-activated receptor-4 plays a major role in the recruitment of neutrophils induced by trypsin or carrageenan during pleurisy in mice

BACKGROUND/AIMS

The activation of proteinase-activated receptors (PARs) has been implicated in the development of important hallmarks of inflammation, including in vivo leukocyte recruitment. Here, we examined the effects of aprotinin, a potent inhibitor of trypsin proteinase and the kallikrein-kinin system, and the PAR-4 antagonist YPGKF-NH(2) (tcY-NH(2)) on neutrophil recruitment in response to carrageenan and trypsin in the pleural cavity of mice.

METHODS

BALB/c mice were intrapleurally injected with trypsin or PAR-4-activating peptide AY-NH(2), pretreated with aprotinin or tcY-NH(2) (1 μg/cavity) prior to an intrapleural injection of trypsin or carrageenan, or pretreated with leukotriene B(4) antagonist U-75302 (3 μg/cavity) prior to a trypsin injection. The number of infiltrating neutrophils was evaluated after 4 h.

RESULTS

PAR-4-activating peptide AY-NH(2) and trypsin-induced neutrophil recruitment was inhibited by aprotinin, tcY-NH(2) or U-75302. Aprotinin and tcY-NH(2) also inhibited neutrophil recruitment induced by carrageenan.

CONCLUSION

These data suggest a key role for PAR-4 in mediating neutrophil recruitment in a mouse model of pleurisy induced by the activity of trypsin or trypsin-like enzymes.

Turning receptors on and off with intracellular pepducins: new insights into G-protein-coupled receptor drug development

G-protein-coupled receptors (GPCRs) are a large family of remarkably versatile membrane proteins that are attractive therapeutic targets because of their involvement in a vast range of normal physiological processes and pathological diseases. Upon activation, intracellular domains of GPCRs mediate signaling to G-proteins, but these domains have yet to be effectively exploited as drug targets. Cell-penetrating lipidated peptides called pepducins target specific intracellular loops of GPCRs and have recently emerged as effective allosteric modulators of GPCR activity. The lipid moiety facilitates translocation across the plasma membrane, where pepducins then specifically modulate signaling of their cognate receptor. To date, pepducins and related lipopeptides have been shown to specifically modulate the activity of diverse GPCRs and other membrane proteins, including protease-activated receptors (PAR1, PAR2, and PAR4), chemokine receptors (CXCR1, CXCR2, and CXCR4), sphingosine 1-phosphate receptor-3 (S1P3), the melanocortin-4 receptor, the Smoothened receptor, formyl peptide receptor-2 (FPR2), the relaxin receptor (LGR7), G-proteins (Gα(q/11/o/13)), muscarinic acetylcholine receptor and vanilloid (TRPV1) channels, and the GPIIb integrin. This minireview describes recent advances made using pepducin technology in targeting diverse GPCRs and the use of pepducins in identifying potential novel drug targets.

Tissue factor, blood coagulation, and beyond: an overview

Emerging evidence shows a broad spectrum of biological functions of tissue factor (TF). TF classical role in initiating the extrinsic blood coagulation and its direct thrombotic action in close relation to cardiovascular risks have long been established. TF overexpression/hypercoagulability often observed in many clinical conditions certainly expands its role in proinflammation, diabetes, obesity, cardiovascular diseases, angiogenesis, tumor metastasis, wound repairs, embryonic development, cell adhesion/migration, innate immunity, infection, pregnancy loss, and many others. This paper broadly covers seminal observations to discuss TF pathogenic roles in relation to diverse disease development or manifestation. Biochemically, extracellular TF signaling interfaced through protease-activated receptors (PARs) elicits cellular activation and inflammatory responses. TF diverse biological roles are associated with either coagulation-dependent or noncoagulation-mediated actions. Apparently, TF hypercoagulability refuels a coagulation-inflammation-thrombosis circuit in “autocrine” or “paracrine” fashions, which triggers a wide spectrum of pathophysiology. Accordingly, TF suppression, anticoagulation, PAR blockade, or general anti-inflammation offers an array of therapeutical benefits for easing diverse pathological conditions.

Correlation of protease-activated receptor-2 expression and synovitis in rheumatoid and osteoarthritis

Protease-activated receptor-2 (PAR-2) is known to be pro-inflammatory and increasing evidence points to an inflammatory component in osteoarthritis. This investigation examined the relationship between synovitis and PAR-2 expression, histological and immunohistochemical analysis being performed on synovial samples obtained from OA and RA patients, along with non-arthritic samples obtained by post mortem (PM). Samples were also analysed for PAR-4 expression, this receptor also having putative pro-inflammatory roles. Analysis involved comparison of inflammatory indices (synovial thickness and monocyte infiltration) with expression of PAR-2 and PAR-4. Synovial explants were also analysed for TNFα generation in the presence of a PAR-2 antagonist (ENMD-1068) or vehicle. OA synovia showed heterogeneity of inflammatory indicators, some samples overlapping with those from the RA cohort whilst others appeared similar to the PM cohort. PAR-2 expression, both in the lining layer and the interstitium, correlated strongly and significantly with synovial thickness (r = 0.91) and monocyte infiltration (r = 0.83), respectively (P < 0.001 in both cases), and this remains significant on individual cohort analysis. PAR-2 was co-localised to CD3 and CD68 cells in RA and OA synovium as well as fibroblasts derived from these synovia. PAR-4 was also expressed, but the relationship with inflammatory indicators was substantially weaker. Inflammatory indicators in OA synovia showed considerable variability, but correlated strongly with PAR-2 expression, suggesting PAR-2 upregulation in synovitis. Heterogeneity of inflammatory indicators was paralleled by wide variation in TNFα generation between samples. Secretion of this cytokine was dose-dependently inhibited by ENMD-1068, providing evidence of a functional role for PAR-2 in promoting synovitis.

Signal protein-derived peptides as functional probes and regulators of intracellular signaling

The functionally important regions of signal proteins participating in their specific interaction and responsible for transduction of hormonal signal into cell are rather short in length, having, as a rule, 8 to 20 amino acid residues. Synthetic peptides corresponding to these regions are able to mimic the activated form of full-size signal protein and to trigger signaling cascades in the absence of hormonal stimulus. They modulate protein-protein interaction and influence the activity of signal proteins followed by changes in their regulatory and catalytic sites. The present review is devoted to the achievements and perspectives of the study of signal protein-derived peptides and to their application as selective and effective regulators of hormonal signaling systems in vitro and in vivo. Attention is focused on the structure, biological activity, and molecular mechanisms of action of peptides, derivatives of the receptors, G protein α subunits, and the enzymes generating second messengers.

Animal models of DIC and their relevance to human DIC: a systematic review

Disseminated intravascular coagulation (DIC) is a severe clinical condition with activation of coagulation and fibrinolysis. Its diagnosis is based on the International Society of Thrombosis and Haemostasis (ISTH) scoring system of DIC. Animal models of DIC, used to investigate pathophysiology and evaluate treatments, have not been developed in a standardized way, which impedes comparison between models and translation to the human setting. In the current review of animal models of DIC an overview of species, inducers, and dosing regimens is provided. Diagnostic approaches are compared in the light of the ISTH score and treatments tested in animal models of DIC are summarized. Systematic analysis revealed that the rat is by far the preferred species amongst animal models of DIC and lipopolysaccharides (LPS) the preferred inducer of DIC. An overview of the reporting of ISTH DIC score parameters elucidated that only about 25% of the studies measure all of the four parameters necessary for the implementation the ISTH scoring system. Furthermore, most therapeutic interventions tested in animal models of DIC are administered prophylactically, which may be irrelevant to the clinical setting and could explain why compounds effective in preclinical animal models often fail in clinical trials. It is concluded that Implementation of a scoring system in animal models of DIC may increase the ability to compare DIC amongst animal models and improve the translational aspect of treatment effect.

Systemic versus localized coagulation activation contributing to organ failure in critically ill patients

In the pathogenesis of sepsis, inflammation and coagulation play a pivotal role. Increasing evidence points to an extensive cross-talk between these two systems, whereby inflammation not only leads to activation of coagulation but coagulation also considerably affects inflammatory activity. The intricate relationship between inflammation and coagulation may not only be relevant for vascular atherothrombotic disease in general but has in certain clinical settings considerable consequences, for example in the pathogenesis of microvascular failure and subsequent multiple organ failure, as a result of severe infection and the associated systemic inflammatory response. Molecular pathways that contribute to inflammation-induced activation of coagulation have been precisely identified. Pro-inflammatory cytokines and other mediators are capable of activating the coagulation system and downregulating important physiological anticoagulant pathways. Activation of the coagulation system and ensuing thrombin generation is dependent on an interleukin-6-induced expression of tissue factor on activated mononuclear cells and endothelial cells and is insufficiently counteracted by physiological anticoagulant mechanisms and endogenous fibrinolysis. Interestingly, apart from the overall systemic responses, a differential local response in various vascular beds related to specific organs may occur.

Targeting protease-activated receptor-1 with cell-penetrating pepducins in lung cancer

Protease-activated receptors (PARs) are G-protein-coupled receptors that are activated by proteolytic cleavage and generation of a tethered ligand. High PAR1 expression has been documented in a variety of invasive cancers of epithelial origin. In the present study, we investigated the contribution of the four PAR family members to motility of lung carcinomas and primary tumor samples from patients. We found that of the four PARs, only PAR1 expression was highly increased in the lung cancer cell lines. Primary lung cancer cells isolated from patient lung tumors migrated at a 10- to 40-fold higher rate than epithelial cells isolated from nonmalignant lung tissue. Cell-penetrating pepducin inhibitors were generated against the first (i1) and third (i3) intracellular loops of PAR1 and tested for their ability to inhibit PAR1-driven migration and extracellular regulated kinase (ERK)1/2 activity. The PAR1 pepducins showed significant inhibition of cell migration in both primary and established cell lines similar to silencing of PAR1 expression with short hairpin RNA (shRNA). Unlike i1 pepducins, the i3 loop pepducins were effective inhibitors of PAR1-mediated ERK activation and tumor growth. Comparable in efficacy with Bevacizumab, monotherapy with the PAR1 i3 loop pepducin P1pal-7 provided significant 75% inhibition of lung tumor growth in nude mice. We identify the PAR1-ERK1/2 pathway as a feasible target for therapy in lung cancer.

Protease-activated receptors and myocardial infarction

Protease-activated receptors (PARs) are widely expressed within the heart. They are activated by a myriad of proteases, including coagulation proteases. In vitro studies showed that activation of PAR-1 and PAR-2 on cardiomyocytes induced hypertrophy. In addition, PAR-1 stimulation on cardiac fibroblasts induced proliferation. Genetic and pharmacologic approaches have been used to investigate the role of the different PARs in cardiac ischemia/reperfusion (I/R) injury. In mice and rats, PAR-1 is reported to play a role in inflammation, infarct size, and remodeling after cardiac I/R injury. However, there are notable differences between the effect of a deficiency in PAR-1 and inhibition of PAR-1. For instance, inhibition of PAR-1 reduced infarct size whereas there was no effect of a deficiency of PAR-1. These differences maybe due to off-target effects of the inhibitor or PAR-4 compensation of PAR-1 deficiency. Similarly, a deficiency of PAR-2 was associated with reduced cardiac inflammation and improved heart function after I/R injury, whereas pharmacologic activation of PAR-2 was found to be protective due to increased vasodilatation. These differences maybe due to different signaling responses induced by an endogenous protease versus an exogenous agonist peptide. Surprisingly, PAR-4 deficiency resulted in increased cardiac injury and increased mortality after I/R injury. In contrast, a pharmacological study indicated that inhibition of PAR-4 was cardioprotective. It is possible that the major cellular target of the PAR-4 inhibitor is platelets, which have been shown to contribute to inflammation in the injured heart, whereas PAR-4 signaling in cardiomyocytes may be protective. These discrepant results between genetic and pharmacological approaches indicate that further studies are needed to determine the role of different PARs in the injured heart.

Curcumin immune-mediated and anti-apoptotic mechanisms protect against renal ischemia/reperfusion and distant organ induced injuries

Renal ischemia followed by reperfusion results in kidney injury which in turn produces and releases destructive inflammatory cytokines into the circulation causing subsequent distant organ injury. Little data suggest the immune mechanism of curcumin on protection against ischemia/reperfusion induced injury. We investigated the immunomodulatory and anti-apoptotic effects of curcumin on ischemia/reperfusion (I/R) injury in rats. Thirty-six rats were randomly divided into three experimental groups (sham, I/R and curcumin pretreated I/R, n=12 each). Curcumin was administered orally to curcumin pretreated I/R group. Curcumin can significantly decrease both systemic as well as blood levels of cytokines (p<0.05). Treatment with curcumin also resulted in significant reduction in serum and tissue level of TNF-α, IL-1β, IL-12, IL-18 and INF-γ that were increased by renal I/R injury (p<0.05). Curcumin pretreatment reduce pulmonary apoptotic pathway via significant inhibition of TGF-β and caspase-3 in kidney and lung tissues. Given that pulmonary apoptosis is an important complication of acute renal injury, we identified curcumin protective effect against distant organ I/R induced injury. Based on our results, we concluded that curcumin protects the kidneys and other vital organs against I/R injury via immune-mediated and the new identified anti-apoptotic mechanisms.

Pharmacology, biodistribution, and efficacy of GPCR-based pepducins in disease models

G protein-coupled receptors (GPCR) are a superfamily of receptors that are vital in a wide array of physiological processes. Modulation of GPCR signaling has been an intensive area of therapeutic study, mainly due to the diverse pathophysiological significance of GPCRs. Pepducins are cell-penetrating lipidated peptides designed to target the intracellular loops of the GPCR of interest. Pepducins can function as agonists or antagonists of their cognate receptor, making them highly useful compounds for the study of GPCR signaling. Pepducins have been used to control platelet-dependent hemostasis and thrombosis, tumor growth, invasion, and angiogenesis, as well as to improve sepsis outcomes in mice. Pepducins have been successfully designed against a wide variety of GPCRs including the protease-activated receptors (PAR1, 2, 4), the chemokine receptors (CXCR1, 2, 4), the sphingosine-1-phosphate receptor (S1P3), the adrenergic receptor (ADRA1B), and have the potential to help reveal the functions of intractable GPCRs. Pharmacokinetic, pharmacodynamic, and biodistribution studies have showed that pepducins are widely distributed throughout the body except the brain and possess appropriate drug-like properties for use in vivo. Here, we discuss the delivery, pharmacology, and biodistribution of pepducins, as well as the effects of pepducins in models of inflammation, cardiovascular disease, cancer, and angiogenesis.

Role of fibrinogen and protease-activated receptors in acute xenobiotic-induced cholestatic liver injury

Alpha-naphthylisothiocyanate (ANIT)-induced cholestatic liver injury causes tissue factor (TF)-dependent coagulation in mice, and TF deficiency reduces ANIT-induced liver injury. However, the mechanism whereby TF contributes to hepatotoxicity in this model is not known. Utilizing pharmacological and genetic strategies, we evaluated the contribution of fibrinogen and two distinct receptors for thrombin, protease-activated receptor-1 (PAR-1) and PAR-4, in a model of acute ANIT hepatotoxicity. ANIT administration (60 mg/kg, po) caused a marked induction of the genes encoding the three fibrinogen chains (α, β, and γ) in liver, an increase in plasma fibrinogen, and concurrent deposition of thrombin-cleaved fibrin in liver. Partial depletion of circulating fibrinogen with ancrod did not impact ANIT hepatotoxicity. However, complete fibrin(ogen) deficiency significantly reduced serum alanine aminotransferase activity and hepatocellular necrosis in ANIT-treated mice. ANIT-induced hepatocellular necrosis was similar in PAR-1(-/-) mice compared with PAR-1(+/+) mice. Interestingly, the progression of ANIT-induced hepatocellular necrosis was significantly reduced in PAR-4(-/-) mice and by administration of an inhibitory PAR-4 pepducin (P4Pal-10, 0.5 mg/kg, sc) to wild-type mice 8 h after ANIT treatment. Interestingly, a distinct lesion, parenchymal-type peliosis, was also observed in PAR-4(-/-) mice treated with ANIT and in mice that were given P4Pal-10 prior to ANIT administration. The results suggest that fibrin(ogen), but not PAR-1, contributes to the progression of ANIT hepatotoxicity in mice. Moreover, the data suggest a dual role for PAR-4 in ANIT hepatotoxicity, both mediating an early protection against peliosis and contributing to the progression of hepatocellular necrosis.

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.

Protease-activated receptor 2 blocking peptide counteracts endotoxin-induced inflammation and coagulation and ameliorates renal fibrin deposition in a rat model of acute renal failure

Glomerular and microvascular thrombosis due to the activation of inflammation and coagulation pathway contribute to the occurrence of acute renal failure in sepsis. The protease-activated receptors (PARs) have been shown to play an important role in the interplay between inflammation and coagulation. We hypothesized that PAR-2 blocking would improve glomerular and vascular thrombosis by attenuating inflammation and coagulation, leading to the prevention of acute renal failure, and assessed the effects of the PAR-2 blocking peptide (PAR-2 BP) in a rat model of LPS-induced acute renal failure. Levels of TNF-alpha were significantly expressed 1 h after LPS administration, followed by 1) an increase in levels of tissue factor, factor VIIa, factor Xa, thrombin and plasminogen activator inhibitor 1; 2) unchanged levels of tissue factor pathway inhibitor; and 3) subsequent deposition of fibrin in kidney tissues, which led to the elevation of creatinine and blood urea nitrogen. Time-dependent PAR-2 expression was observed at both the gene and protein levels. Immunoreactivities of PAR-2 and fibrin were observed in the glomerulus and small arteries. Protease-activated receptor blocking peptide suppressed TNF-alpha elevation and attenuated activation of the coagulation, thus leading to a decrease in fibrin formation and its deposition in the glomerulus. However, the levels of creatinine and blood urea nitrogen remained unchanged. These results show that PAR-2 plays a key role in the inflammatory and coagulation process of LPS-induced renal failure; however, PAR-2 inhibition alone does not affect improvement in the renal function.

Inflammation and coagulation

In the pathogenesis of sepsis, inflammation and coagulation play a pivotal role. Increasing evidence points to an extensive cross-talk between these two systems, whereby inflammation leads to activation of coagulation, and coagulation also considerably affects inflammatory activity. Molecular pathways that contribute to inflammation-induced activation of coagulation have been precisely identified. Pro-inflammatory cytokines and other mediators are capable of activating the coagulation system and down-regulating important physiologic anticoagulant pathways. Activation of the coagulation system and ensuing thrombin generation is dependent on expression of tissue factor and the simultaneous down-regulation of endothelial-bound anticoagulant mechanisms and endogenous fibrinolysis. Conversely, activated coagulation proteases may affect specific cellular receptors on inflammatory cells and endothelial cells and thereby modulate the inflammatory response.

Luminal cathepsin g and protease-activated receptor 4: a duet involved in alterations of the colonic epithelial barrier in ulcerative colitis

Impairment of the colonic epithelial barrier and neutrophil infiltration are common features of inflammatory bowel disease. Luminal proteases affect colonic permeability through protease-activated receptors (PARs). We evaluated: (i) whether fecal supernatants from patients with ulcerative colitis (UC) trigger alterations of colonic paracellular permeability and inflammation, and (ii) the roles of cathepsin G (Cat-G), a neutrophil serine protease, and its selective receptor, PAR(4), in these processes. Expression levels of both PAR(4) and Cat-G were determined in colonic biopsies from UC and healthy subjects. The effects of UC fecal supernatants on colonic paracellular permeability were measured in murine colonic strips. Involvement of Cat-G and PAR(4) was evaluated using pepducin P4pal-10 and specific Cat-G inhibitor (SCGI), respectively. In addition, the effect of PAR(4)-activating peptide was assessed. UC fecal supernatants, either untreated or pretreated with SCGI, were infused into mice, and myeloperoxidase activity was determined. PAR(4) was found to be overexpressed in UC colonic biopsies. Increased colonic paracellular permeability that was triggered by UC fecal supernatants was blocked by both SCGI (77%) and P4pal-10 (85%). Intracolonic infusion of UC fecal supernatants into mice increased myeloperoxidase activity. This effect was abolished by SCGI. These observations support that both Cat-G and PAR(4) play key roles in generating and/or amplifying relapses in UC and provide a rationale for the development of new therapeutic agents in the treatment of this disease.

The urokinase receptor (uPAR) facilitates clearance of Borrelia burgdorferi

The causative agent of Lyme borreliosis, the spirochete Borrelia burgdorferi, has been shown to induce expression of the urokinase receptor (uPAR); however, the role of uPAR in the immune response against Borrelia has never been investigated. uPAR not only acts as a proteinase receptor, but can also, dependently or independently of ligation to uPA, directly affect leukocyte function. We here demonstrate that uPAR is upregulated on murine and human leukocytes upon exposure to B. burgdorferi both in vitro as well as in vivo. Notably, B. burgdorferi-inoculated C57BL/6 uPAR knock-out mice harbored significantly higher Borrelia numbers compared to WT controls. This was associated with impaired phagocytotic capacity of B. burgdorferi by uPAR knock-out leukocytes in vitro. B. burgdorferi numbers in vivo, and phagocytotic capacity in vitro, were unaltered in uPA, tPA (low fibrinolytic activity) and PAI-1 (high fibrinolytic activity) knock-out mice compared to WT controls. Strikingly, in uPAR knock-out mice partially backcrossed to a B. burgdorferi susceptible C3H/HeN background, higher B. burgdorferi numbers were associated with more severe carditis and increased local TLR2 and IL-1β mRNA expression. In conclusion, in B. burgdorferi infection, uPAR is required for phagocytosis and adequate eradication of the spirochete from the heart by a mechanism that is independent of binding of uPAR to uPA or its role in the fibrinolytic system.

Lyme borreliosis is caused by the spirochete Borrelia burgdorferi and is transmitted through ticks. Since its discovery approximately 30 years ago it has become the most important vector-borne disease in the Western world. The pathogenesis of this complex zoonosis is still not entirely understood. We here demonstrate that the urokinase receptor (uPAR) is upregulated in mice and humans upon exposure to B. burgdorferi in vitro and in vivo. Importantly, we describe the function of uPAR in the immune response against the spirochete; using uPAR knock-out mice, we show that uPAR plays an important role in phagocytosis of B. burgdorferi by leukocytes both in vitro as well as in vivo. In addition, we show that the mechanism by which uPAR is involved in the phagocytosis of B. burgdorferi is independent of ligation to its natural ligand uPA or uPAR's role in fibrinolysis. Our study contributes to the understanding of the pathogenesis of Lyme borreliosis and might contribute to the development of innovative novel treatment strategies for Lyme borreliosis.

Activated protein C protects against myocardial ischemia/ reperfusion injury via inhibition of apoptosis and inflammation

OBJECTIVE

In spite of major advances in reperfusion therapy for patients presenting with acute coronary syndrome, long-term morbidity is still substantial. A limitation of initial treatment of myocardial ischemia is the lack of prevention of ischemia/reperfusion (I/R) injury. Activated protein C (APC), a crucial mediator in the coagulation process, plays a prominent role in the crosstalk between coagulation and inflammation and provides cytoprotective effects via inhibition of apoptosis and inflammation in several human and animal studies.

METHODS AND RESULTS

APC was administered in an animal model for myocardial I/R. APC largely inhibited early myocardial I/R injury after varying reperfusion times, an effect that was absent on administration of heparin, a nonspecific anticoagulant agent. The protective effects of APC were absent in case of absence or blockade of protease activated receptor-1 (PAR-1), indicating a critical role for PAR-1 in this process. Furthermore, we showed a strong antiapoptotic effect of APC in the early phase of reperfusion combined with an antiinflammatory effect at an early stage (IL-6), as well as at a later stage (leukocyte infiltration).

CONCLUSIONS

APC exerts strong protective effects on early myocardial I/R injury, primarily via inhibition of apoptosis and inflammation, which are regulated via PAR-1.

Protease-activated receptor 4 uses anionic residues to interact with alpha-thrombin in the absence or presence of protease-activated receptor 1

Thrombin activates protease-activated receptor 1 (PAR1) faster than protease-activated receptor 4 (PAR4) due to a hirudin-like sequence in the exodomain of PAR1 that binds thrombin's exosite I. However, recombinant exodomain studies indicate that PAR4 does have extended contacts with alpha-thrombin that influence PAR4's kinetics of cleavage. In this report, the role of an anionic cluster (Asp(57), Asp(59), Glu(62), and Asp(65)) in the exodomain of PAR4 is examined for its influence on cleavage and activation of PAR4 on cells in the absence or presence of PAR1. Alpha-thrombin induces wild-type PAR4 (PAR4-wt) calcium flux with an EC(50) of 110 nM, whereas mutation of the four anionic residues (PAR4-AAAA) increases the EC(50) to 641 nM. In contrast, PAR4-wt and PAR4-AAAA are activated by gamma-thrombin with similar EC(50) values (588 and 449 nM, respectively; p = 0.48), suggesting a role for alpha-thrombin's exosite I in PAR4 activation. Coexpression of PAR1 lowered the EC(50) of cleavage for PAR4-wt from 321 to 26 nM and for PAR4-AAAA from 1.5 microM to 360 nM. Individual point mutations at Asp(57), Asp(59), Glu(62), and Asp(65) show that PAR4-D57A is activated by alpha-thrombin with the same EC(50) as PAR4-wt (140 nM) whereas PAR4-D59A is the same as PAR4-AAAA (699 nM). Glu(62) and Asp(65) contribute to alpha-thrombin recognition, but to a lesser extent. This report shows that PAR4 uses its anionic cluster to interact with alpha-thrombin and that this interaction is important even in the presence of PAR1.

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.