Structure, function and pathophysiology of protease activated receptors

Effect of Protease-Activated Receptor-2-Activating Peptide on Guinea Pig Airway Resistance and Isolated Tracheal Strips

Purpose:

Protease-activated receptors (PARs) are a family of G-protein-coupled receptors distributed in a number of tissues. PAR-2 is expressed on airway epithelium and smooth muscles and overexpressed under pathological conditions, such as asthma and chronic obstructive pulmonary disease. However, the role of PAR-2 in airways has not yet been defined. In this study, we investigated the role of PAR-2-activating peptide (SLIGRL) on histamine-induced bronchoconstriction and the mechanisms underlying the bronchoprotective effect both in vivo and in vitro.

Materials and Methods:

The effect of SLIGRL was tested in vivo using histamine-induced bronchoconstriction in the guinea pig and in vitro using isolated tracheal spiral strips.

Results:

In vivo pretreatment with SLIGRL significantly reduced the histamine-induced increased bronchoconstriction. Neither propranolol nor vagotomy abolished the inhibitory effect of SLIGRL. Furthermore, indomethacin or glibenclamide did not antagonize the inhibitory response to SLIGRL. In isolated tracheal spiral strips in vitro, SLIGRL did not affect the contractile response to acetylcholine or potassium chloride; however, histamine-induced contraction was inhibited in a dose-dependent manner.

Conclusion:

Our data demonstrate the protective effect of SLIGRL in airways; however, this effect appears to be mediated independently of prostanoids, nitric oxide, circulating adrenaline, ATP-sensitive K + channels, and vagal stimulation.

CETSA beyond Soluble Targets: a Broad Application to Multipass Transmembrane Proteins

Demonstration of target binding is a key requirement for understanding the mode of action of new therapeutics. The cellular thermal shift assay (CETSA) has been introduced as a powerful label-free method to assess target engagement in physiological environments. Here, we present the application of live-cell CETSA to different classes of integral multipass transmembrane proteins using three case studies, the first showing a large and robust stabilization of the outer mitochondrial five-pass transmembrane protein TSPO, the second being a modest stabilization of SERCA2, and the last describing an atypical compound-driven stabilization of the GPCR PAR2. Our data demonstrated that using modified protocols with detergent extraction after the heating step, CETSA can reliably be applied to several membrane proteins of different complexity. By showing examples with distinct CETSA behaviors, we aim to provide the scientific community with an overview of different scenarios to expect during CETSA experiments, especially for challenging, membrane bound targets.

The parmodulin NRD-21 is an allosteric inhibitor of PAR1 Gq signaling with improved anti-inflammatory activity and stability

Novel analogs of the allosteric, biased PAR1 ligand ML161 (parmodulin 2, PM2) were prepared in order to identify potential anti-thrombotic and anti-inflammatory compounds of the parmodulin class with improved properties. Investigations of structure-activity relationships of the western portion of the 1,3-diaminobenzene scaffold were performed using an intracellular calcium mobilization assay with endothelial cells, and several heterocycles were identified that inhibited PAR1 at sub-micromolar concentrations. The oxazole NRD-21 was profiled in additional detail, and it was confirmed to act as a selective, reversible, negative allosteric modulator of PAR1. In addition to inhibiting human platelet aggregation, it showed superior anti-inflammatory activity to ML161 in a qPCR assay measuring the expression of tissue factor in response to the cytokine TNF-alpha in endothelial cells. Additionally, NRD-21 is much more plasma stable than ML161, and is a promising lead compound for the parmodulin class for anti-thrombotic and anti-inflammatory indications.

Proteinase-activated receptor-2 enhances Bcl2-like protein-12 expression in lung cancer cells to suppress p53 expression

INTRODUCTION

The pathogenesis of lung cancer is unclear. Less expression of p53 or p53 mutation was identified in lung cancer cells, which plays a role in the development of lung cancer. Recent reports indicate that Bcl2-like protein-12 (Bcl2L12) can inhibit the expression of p53. Lung cancer cells express proteinase-activated receptor-2 (PAR2). This study tests the hypothesis that activation of PAR2 inhibits the expression of p53 in lung cancer cells.

MATERIAL AND METHODS

Lung cancer cells were collected from patients with non-small cell lung cancer (NSCLC). The cells were exposed to active peptides or trypsin in the culture for 48 h. The expression of p53 was assessed by RT-qPCR and Western blotting.

RESULTS

We observed that lung cancer cells express Bcl2L12. Activation of PAR2 increases expression of Bcl2L12 in lung cancer cells. Bcl2L12 mediates PAR2-suppressed p53 expression in lung cancer cells. IgE-activated mast cell suppression of p53 expression in lung cancer cells can be prevented by knocking down Bcl2L12. The Bcl2L12 bound Mdm2, the transcription factor of p53, to prevent the Mdm2 from binding to the promoter of p53 and thus inhibited p53 expression in lung cancer cells. PAR2 could attenuate lung cancer cell apoptosis via inducing Bcl2L12.

CONCLUSIONS

Lung cancer cells express Bcl2L12, which mediates the effects of activation of PAR2 on suppressing the expression of p53 in lung cancer cells, implying that Bcl2L12 may be a novel therapeutic target for the treatment of lung cancer.

Proteinase‑activated receptor 2 deficiency is a protective factor against cardiomyocyte apoptosis during myocardial ischemia/reperfusion injury

Previous studies have established that proteinase‑​activated receptor 2 (PAR2) activation protects against myocardial ischemia/reperfusion injury (MI/RI). However, the role of PAR2 deficiency in MI/RI remains unclear. The aim of the present study was to examine the effect of PAR2 deficiency on cardiomyocyte apoptosis and to clarify the potential molecular mechanisms for its protective effect against MI/RI. Using a mouse model of MI/RI, cardiac function was evaluated by echocardiography, infarct size was assessed by triphenyltetrazolium chloride staining, and myocardial cell apoptosis was measured by terminal deoxynucleotide transferase‑mediated dUTP nick end‑labeling staining. Annexin V/propidium iodide staining, and expression of Bcl‑2 and cleaved PARP were determined to assess apoptosis in myocardial H9c2 cells exposed to hypoxia/reoxygenation (H/R) injury‑simulating MI/RI. Phosphorylated ERK1/2, JNK, and p38 MAPK protein expression levels were analyzed by western blotting. The findings indicated that PAR2 deficiency markedly reduced cardiomyocyte apoptosis in the MI/RI mouse model, as well as in myocardial H9c2 cells exposed to H/R. Furthermore, PAR2 knockdown clearly prevented phosphorylation of ERK1/2 and JNK in myocardial H9c2 cells. The results revealed that PAR2 deficiency alleviated MI/RI‑associated apoptosis by inhibiting phosphorylation of ERK1/2 and JNK. Therefore, targeted PAR2 silencing may be a potential therapeutic approach for alleviation of MI/RI.

Conformational Plasticity of Human Protease-Activated Receptor 1 upon Antagonist- and Agonist-Binding

G protein-coupled receptors (GPCRs) show complex relationships between functional states and conformational plasticity that can be qualitatively and quantitatively described by contouring their free energy landscape. However, how ligands modulate the free energy landscape to direct conformation and function of GPCRs is not entirely understood. Here, we employ single-molecule force spectroscopy to parametrize the free energy landscape of the human protease-activated receptor 1 (PAR1), and delineate the mechanical, kinetic, and energetic properties of PAR1 being set into different functional states. Whereas in the inactive unliganded state PAR1 adopts mechanically rigid and stiff conformations, upon agonist or antagonist binding the receptor mechanically softens, while increasing its conformational flexibility, and kinetic and energetic stability. By mapping the free energy landscape to the PAR1 structure, we observe key structural regions putting this conformational plasticity into effect. Our insight, complemented with previously acquired knowledge on other GPCRs, outlines a more general framework to understand how GPCRs stabilize certain functional states.

High Affinity Fluorescent Probe for Proteinase-Activated Receptor 2 (PAR2)

PAR2 is a proteolytically activated G protein-coupled receptor (GPCR) that is implicated in various cancers and inflammatory diseases. Ligands with low nanomolar affinity for PAR2 have been developed, but there is a paucity of research on the development of PAR2-targeting imaging probes. Here, we report the development of seven novel PAR2-targeting compounds. Four of these compounds are highly potent and selective PAR2-targeting peptides (EC₅₀ = 10 to 23 nM) that have a primary amine handle available for facile conjugation to various imaging components. We describe a peptide of the sequence Isox-Cha-Chg-ARK(Sulfo-Cy5)-NH₂ as the most potent and highest affinity PAR2-selective fluorescent probe reported to date (EC₅₀ = 16 nM, K _D = 38 nM). This compound has a greater than 10-fold increase in potency and binding affinity for PAR2 compared to the leading previously reported probe and is conjugated to a red-shifted fluorophore, enabling in vitro and in vivo studies.

Microenvironment proteinases, proteinase-activated receptor regulation, cancer and inflammation

We propose that in the microenvironment of inflammatory tissues, including tumours, extracellular proteinases can modulate cell signalling in part by regulating proteinase-activated receptors (PARs). We have been exploring this mechanism in a variety of inflammation and tumour-related settings that include tumour-derived cultured cells from prostate and bladder cancer, as well as immune inflammatory cells that are involved in the pathology of inflammatory diseases including multiple sclerosis. Our work showed that proteinase signalling via the PARs affects prostate and bladder cancer-derived tumour cell behaviour and can regulate calcium signalling in human T-cell and macrophage-related inflammatory cells as well as in murine splenocytes. Further, we found that the tumour-derived prostate cancer cells and immune-related cells (Jurkat, THP1, mouse splenocytes) can produce PAR-regulating proteinases (including kallikreins: kallikrein-related peptidases), that can control tissue function by both a paracrine and autocrine mechanism. We suggest that this PAR-driven signalling process involving secreted microenvironment proteinases can play a key role in cancer and inflammatory diseases including multiple sclerosis.

PRSS21/testisin inhibits ovarian tumor metastasis and antagonizes proangiogenic angiopoietins ANG2 and ANGPTL4

Ovarian cancer is the leading cause of death among all the gynecological cancers in the USA. Ovarian cancer employs a unique mode of metastasis, as exfoliated tumor cells disseminate within the peritoneal cavity, colonizing in several sites as well as accumulating ascites. Tumor recurrence and widespread metastasis are significant factors contributing to poor prognosis. PRSS21 is a metastasis-associated ovarian cancer gene that encodes the glycosyl-phosphatidylinositol-linked serine protease, testisin. Testisin expression is increased in multiple ovarian tumor types, with relatively little expression in normal tissues, but is differentially decreased in metastatic ovarian serous carcinomas compared to primary tumors. Here we explored the function of testisin in late-stage ovarian cancer progression using a murine xenograft model of ovarian intraperitoneal tumor metastasis. Increased tumor testisin expression inhibited intra-peritoneal tumor seeding and colonization, ascites accumulation, and metastatic tumor burden that was dependent on catalytically active testisin. The known testisin substrate, protease-activated receptor-2 (PAR-2), is a target of testisin activity. Gene profiling and mechanistic studies demonstrate that testisin activity suppresses the synthesis and secretion of pro-angiogenic angiopoietins, ANG2 and ANGPTL4, which normally promote vascular leak and edema. These observations support a model wherein testisin activates PAR-2 to antagonize proangiogenic angiopoietins that modulate vascular permeability and ascites accumulation associated with ovarian tumor metastasis. KEY MESSAGES: Testisin inhibits metastatic ovarian tumor burden and ascites production. Testisin activity antagonizes ANG2 and ANGPTL4 synthesis and secretion. PAR-2 is a proteolytic target of testisin on the surface of ovarian cancer cells.

Nonhemostatic Activities of Factor Xa: Are There Pleiotropic Effects of Anti-FXa Direct Oral Anticoagulants?

Factor Xa (FXa) is the key serine protease of the coagulation cascade as it is the point of convergence of the intrinsic and extrinsic pathways, leading to the formation of thrombin. Factor Xa is an established target of anticoagulation therapy, due to its central role in coagulation. Over the past years, several direct oral anticoagulants (DOACs) targeting FXa have been developed. Rivaroxaban, apixaban, and edoxaban are used in clinical practice for prevention and treatment of thrombotic diseases. Increasing evidence suggests that FXa exerts nonhemostatic cellular effects that are mediated mainly through protease-activated receptors-1 and -2 and are involved in pathophysiological conditions, such as atherosclerosis, inflammation, and fibrosis. Direct inhibition of FXa by DOACs could be beneficial in these conditions. This is a narrative review that focuses on the cellular effects of FXa in various cell types and conditions, as well as on the possible pleiotropic effects of FXa-targeting DOACs.

HIV-induced neuroinflammation: impact of PAR1 and PAR2 processing by Furin

HIV-associated neurocognitive disorders (HAND) is a syndrome defined by neurocognitive deficits that are driven by viral neurotoxins, cytokines, free radicals, and proteases expressed in the brain. This neurological disease has also been linked to activation of Protease-Activated Receptors 1 and 2 (PAR1,2). These receptors are highly expressed in the central nervous system and are upregulated in HAND. Secretory basic-amino-acid-specific Proprotein Convertases (PCs), which cleave precursor proteins at basic residues, are also induced in HAND. They are vital for many biological processes including HIV-1 entry into cells. The cytoprotective role of Furin, PC5, and PACE4 has been linked to the presence of a potential PC-cleavage site R₄₁XXXXR₄₆↓ in PAR1. Furthermore, Furin binds PAR1 and both are trapped in the trans-Golgi-network (TGN) as inactive proteins, likely due to the intermediary trafficking role of phospho-Furin acidic cluster sorting protein 1 (PACS1). Nothing is known about PAR2 and its possible recognition by PCs at its putative R₃₁XXXXR₃₆↓ processing site. The present study implicates PACS1 in the retrograde trafficking of PAR1 to the TGN and demonstrates that the cytosolic extreme C-terminal tail of PAR1 contains an acidic phosphorylatable PACS1-sensitive domain. We further show the requirement of Asn₄₇ in PAR1 for its Furin-dependent TGN localization. Our data revealed that Furin is the only convertase that efficiently cleaves PAR2 at Arg₃₆↓. N-glycosylation of PAR2 at Asn₃₀ reduces the efficacy, but enhances selectivity of the Furin cleavage. Finally, in co-cultures comprised of human neuroblastoma SK-N-SH cells (stably expressing PAR1/2 and/or Furin) and HIV-1-infected primary macrophages, we demonstrate that the expression of Furin enhances neuronal cell viability in the context of PAR1- or PAR2-induced neuronal cytotoxicity. The present study provides insights into early stages of HIV-1 induced neuronal injury and the protective role of Furin in neurons co-expressing PAR1 and/or PAR2, as observed in HAND.

Human airway trypsin-like protease enhances interleukin-8 synthesis in bronchial epithelial cells by activating protease-activated receptor 2

Human airway trypsin-like protease (HAT) localizes at human bronchial epithelial cells (HBECs). HAT enhanced release of interleukin-8 (IL-8) from HBECs at 10-100 mU/mL and the enhanced release was almost completely abolished by 50 μM leupeptin, a serine protease inhibitor. Previous reports suggested that HAT displays its physiological functions via protease-activated receptor 2 (PAR2). In the present study, we examined the mechanism whereby HAT upregulates IL-8 synthesis in HBECs with a focus on PAR2. Northern blot analysis revealed that HAT enhanced IL-8 mRNA expression at concentrations of 10-100 mU/mL. PAR2 activating peptide (PAR2 AP) also enhanced IL-8 release and IL-8 mRNA expression in HBECs at 50-1,000 μM at similar levels as HAT. Knockdown of PAR2 mRNA by siRNA methods showed that PAR2 mRNA expression was significantly depressed in primary HBECs, and both HAT- and PAR2 AP-induced IL-8 mRNA elevation was significantly depressed in PAR2 siRNA-transfected HBECs. Additionally, HAT cleaved the PAR2 activating site (R³⁶-S³⁷ bond) of synthetic PAR2 N-terminal peptide. These results indicate that HAT stimulates IL-8 synthesis in airway epithelial cells via PAR2 and could help to amplify inflammation in chronic respiratory tract disease.

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.

Membrane-Anchored Serine Proteases and Protease-Activated Receptor-2-Mediated Signaling: Co-Conspirators in Cancer Progression

Pericellular proteolysis provides a significant advantage to developing tumors through the ability to remodel the extracellular matrix, promote cell invasion and migration, and facilitate angiogenesis. Recent advances demonstrate that pericellular proteases can also communicate directly to cells by activation of a unique group of transmembrane G-protein-coupled receptors (GPCR) known as protease-activated receptors (PAR). In this review, we discuss the specific roles of one of four mammalian PARs, namely PAR-2, which is overexpressed in advanced stage tumors and is activated by trypsin-like serine proteases that are highly expressed or otherwise dysregulated in many cancers. We highlight recent insights into the ability of different protease agonists to bias PAR-2 signaling and the newly emerging evidence for an interplay between PAR-2 and membrane-anchored serine proteases, which may co-conspire to promote tumor progression and metastasis. Interfering with these pathways might provide unique opportunities for the development of new mechanism-based strategies for the treatment of advanced and metastatic cancers.

Protease activated receptor 2 (PAR2) activation causes migraine-like pain behaviors in mice

BACKGROUND

Pain is the most debilitating symptom of migraine. The cause of migraine pain likely requires activation of meningeal nociceptors. Mast cell degranulation, with subsequent meningeal nociceptor activation, has been implicated in migraine pathophysiology. Degranulating mast cells release serine proteases that can cleave and activate protease activated receptors. The purpose of these studies was to investigate whether protease activated receptor 2 is a potential generator of nociceptive input from the meninges by using selective pharmacological agents and knockout mice.

METHODS

Ratiometric Ca++ imaging was performed on primary trigeminal and dural cell cultures after application of 2at-LIGRL-NH2, a specific protease activated receptor 2 agonist. Cutaneous hypersensitivity and facial grimace was measured in wild-type and protease activated receptor 2-/- mice after dural application of 2at-LIGRL-NH2 or compound 48-80, a mast cell degranulator. Behavioral experiments were also conducted in mice after dural application of 2at-LIGRL-NH2 (2AT) in the presence of either C391, a selective protease activated receptor 2 antagonist, or sumatriptan.

RESULTS

2at-LIGRL-NH2 evoked Ca2+ signaling in mouse trigeminal neurons, dural fibroblasts and in meningeal afferents. Dural application of 2at-LIGRL-NH2 or 48-80 caused dose-dependent grimace behavior and mechanical allodynia that were attenuated by either local or systemic application of C391 as well as in protease activated receptor 2-/- mice. Nociceptive behavior after dural injection of 2at-LIGRL-NH2 was also attenuated by sumatriptan.

CONCLUSIONS

Functional protease activated receptor 2 receptors are expressed on both dural afferents and fibroblasts and activation of dural protease activated receptor 2 produces migraine-like behavioral responses. Protease activated receptor 2 may link resident immune cells to meningeal nociceptor activation, driving migraine-like pain and implicating protease activated receptor 2 as a therapeutic target for migraine in humans.

Protease-activated receptor-2 signaling through β-arrestin-2 mediates Alternaria alkaline serine protease-induced airway inflammation

Alternaria alternata is a fungal allergen associated with severe asthma and asthma exacerbations. Similarly to other asthma-associated allergens, Alternaria secretes a serine-like trypsin protease(s) that is thought to act through the G protein-coupled receptor protease-activated receptor-2 (PAR2) to induce asthma symptoms. However, specific mechanisms underlying Alternaria-induced PAR2 activation and signaling remain ill-defined. We sought to determine whether Alternaria-induced PAR2 signaling contributed to asthma symptoms via a PAR2/β-arrestin signaling axis, identify the protease activity responsible for PAR2 signaling, and determine whether protease activity was sufficient for Alternaria-induced asthma symptoms in animal models. We initially used in vitro models to demonstrate Alternaria-induced PAR2/β-arrestin-2 signaling. Alternaria filtrates were then used to sensitize and challenge wild-type, PAR2-/- and β-arrestin-2-/- mice in vivo. Intranasal administration of Alternaria filtrate resulted in a protease-dependent increase of airway inflammation and mucin production in wild-type but not PAR2-/- or β-arrestin-2-/- mice. Protease was isolated from Alternaria preparations, and select in vitro and in vivo experiments were repeated to evaluate sufficiency of the isolated Alternaria protease to induce asthma phenotype. Administration of a single isolated serine protease from Alternaria, Alternaria alkaline serine protease (AASP), was sufficient to fully activate PAR2 signaling and induce β-arrestin-2-/--dependent eosinophil and lymphocyte recruitment in vivo. In conclusion, Alternaria filtrates induce airway inflammation and mucus hyperplasia largely via AASP using the PAR2/β-arrestin signaling axis. Thus, β-arrestin-biased PAR2 antagonists represent novel therapeutic targets for treating aeroallergen-induced asthma.

Protease-activated receptor-1 impedes prostate and intestinal tumor progression in mice

Essentials Protease activated receptor-1 (PAR-1) has been proposed to drive cancer progression. Surprisingly, PAR-1 deletion accelerated tumor progression in two distinct experimental settings. PAR-1 deletion was shown to limit the apoptosis of transformed epithelial cells. Thrombin- and activated protein C-mediated PAR-1 activation have unique effects on tumor cell biology. SUMMARY: Background Multiple studies have implicated protease-activated receptor-1 (PAR-1), a G-protein-coupled receptor activated by proteolytic cleavage of its N-terminus, as one target coupling thrombin-mediated proteolysis to tumor progression. Objective To analyze the role of PAR-1 in the setting of two distinct spontaneously developing tumor models in mice. Methods We interbred PAR-1-deficient mice with Transgenic Adenocarcinoma of the Mouse Prostate (TRAMP) mice, which spontaneously develop prostate tumors, and adenomatous polyposis coli Min (APCMin/+ ) mice, which spontaneously develop intestinal adenomas. Results Analyses of TRAMP mice with advanced disease (30 weeks) revealed that PAR-1 deficiency resulted in significantly larger and more aggressive prostate tumors. Prostates collected at an earlier time point (12 weeks of age) revealed that PAR-1 promotes apoptosis in transformed epithelia. In vitro analyses of TRAMP-derived cells revealed that activated protein C-mediated PAR-1 cleavage can induce tumor cell apoptosis, suggesting that tumor cell-intrinsic PAR-1 functions can limit tumor progression. Paralleling results in TRAMP mice, PAR-1-deficient APCMin/+ mice developed three-fold more adenomas than PAR-1-expressing mice, and the adenomas that formed were significantly larger. Moreover, loss of PAR-1 expression was shown to limit apoptosis in transformed intestinal epithelial cells. Conclusions Together, these results demonstrate a previously unrecognized role for PAR-1 in impeding tumor progression in vivo. These results also offer a cautionary note suggesting that long-term PAR-1 inhibition could increase malignancy risk in some contexts.

Comparative proteomic analysis revealed complex responses to classical/novel duck reovirus infections in the spleen tissue of Cairna moschata

Duck reovirus (DRV), a member of the genus Orthoreovirus in the family Reoviridae, was first isolated from Muscovy ducks. The disease associated with DRV causes great economic losses to the duck industry. However, the responses of duck (Cairna moschata) to the classical/novel DRV (C/NDRV) infections are largely unknown. To reveal the relationship of pathogenesis and immune response, the proteomes of duck spleen cells under the control and C/NDRV infections were compared. In total, 5986 proteins were identified, of which 5389 proteins were quantified. The different accumulated proteins (DAPs) under the C/NDRV infections showed displayed various biological functions and diverse subcellular localizations. The proteins related to the serine protease system were siginificantly changed, suggesting that the activated serine protease system may play an important role under the C/NDRV infections. Furthermore, the differences in the responses to the C/NRDV infections between the duck liver and spleen tissues were compared. Only a small number of common DAPs were identified in both liver and spleen tissues, suggesting diversified pattern involved in the responses to the C/NRDV infections. However, the changes in the proteins involved in the serine protease systems were similar in both liver and spleen cells. Our data may give a comprehensive resource for investigating the responses to C/NDRV infections in ducks. SIGNIFICANCE: A newly developed MS/MS-based method involving isotopomer labels and 'tandem mass' has been applied to protein accurate quantification in current years. However, no studies on the responses of duck (Cairna moschata) spleen tissue to the classical/novel DRV (C/NDRV) infections have been performed. As a continued study of our previous report on the responses of duck liver tissue to the C/NDRV infections, the current study further compared the differences in the responses to the C/NRDV infections between the duck liver and spleen tissues. Our results will provide an opportunity to reveal the relationship of pathogenesis and immune response and basic information on the pathogenicity of C/NDRV in ducks.

Protease-activated receptor 2 induces migration and promotes Slug-mediated epithelial-mesenchymal transition in lung adenocarcinoma cells

Protease-activated receptor 2 (PAR2), a G protein-coupled receptor for trypsin, contributes to growth, anti-apoptosis, and migration in lung cancer. Given that PAR2 activation in airway epithelial cells compromises the airway epithelium barrier by disruption of E-cadherin adhesion, PAR2 may be involved in epithelial-mesenchymal transition (EMT) in lung adenocarcinoma cells. Although PAR2 is known to promote the migration of lung cancer cells, the detailed mechanism of this event is still not clear. Here, we found that PAR2 is highly expressed in several lung adenocarcinoma cell lines. In two lung adenocarcinoma cell lines, CL1-5 and H1299 cells, activation of PAR2 induces migration and Slug-mediated EMT. The underlying mechanisms involved in PAR2-induced migration and EMT in CL1-5 cells were further investigated. We showed that PAR2-induced migration of CL1-5 cells is mediated by the Src/p38 mitogen-activated protein kinase (p38 MAPK) signaling pathway. β-arrestin 1, not G protein, is involved in this PAR2-mediated Src/p38 MAPK signaling pathway. PAR2-induced EMT in CL1-5 cells is dependent on the activation of extracellular-signal-regulated kinase 2 (ERK2). The activation of ERK2 further mediates Slug stabilization through suppressing the activity of glycogen synthase kinase 3β. In addition, a poor prognosis was observed in lung adenocarcinoma patients with a high expression of PAR2. Thus, PAR2 regulates migration through β-arrestin 1-dependent activation of p38 MAPK and EMT through ERK2-mediated stabilization of Slug in lung adenocarcinoma cells. Our finding also suggests that PAR2 might serve as a therapeutic target for metastatic lung adenocarcinoma and a potential biomarker for predicting the prognosis of lung adenocarcinoma.

Role of the blood coagulation cascade in hepatic fibrosis

Liver is the primary source of numerous proteins that are critical for normal function of the blood coagulation cascade. Because of this, diseases of the liver, particularly when affiliated with severe complications like cirrhosis, are associated with abnormalities of blood clotting. Although conventional interpretation has inferred cirrhosis as a disorder of uniform bleeding risk, it is now increasingly appreciated as a disease wherein the coagulation cascade is precariously rebalanced. Moreover, prothrombotic risk factors are also associated with a more rapid progression of fibrosis in humans, suggesting that coagulation proteases participate in disease pathogenesis. Indeed, strong evidence drawn from experimental animal studies indicates that components of the coagulation cascade, particularly coagulation factor Xa and thrombin, drive profibrogenic events, leading to hepatic fibrosis. Here, we concisely review the evidence supporting a pathologic role for coagulation in the development of liver fibrosis and the potential mechanisms involved. Further, we highlight how studies in experimental animals may shed light on emerging clinical evidence, suggesting that beneficial effects of anticoagulation could extend beyond preventing thrombotic complications to include reducing pathologies like fibrosis.

Keratinocyte-specific ablation of protease-activated receptor 2 prevents gingival inflammation and bone loss in a mouse model of periodontal disease

Chronic periodontitis is characterised by gingival inflammation and alveolar bone loss. A major aetiological agent is Porphyromonas gingivalis, which secretes proteases that activate protease-activated receptor 2 (PAR₂ ). PAR₂ expressed on oral keratinocytes is activated by proteases released by P. gingivalis, inducing secretion of interleukin 6 (IL-6), and global knockout of PAR₂ prevents bone loss and inflammation in a periodontal disease model in mice. To test the hypothesis that PAR₂ expressed on gingival keratinocytes is required for periodontal disease pathology, keratinocyte-specific PAR₂ -null mice were generated using K14-Cre targeted deletion of the PAR₂ gene (F2rl1). These mice were subjected to a model of periodontitis involving placement of a ligature around a tooth, combined with P. gingivalis infection ("Lig + Inf"). The intervention caused a significant 44% decrease in alveolar bone volume (assessed by microcomputed tomography) in wildtype (K14-Cre:F2rl1^wt/wt ), but not littermate keratinocyte-specific PAR₂ -null (K14-Cre:F2rl1^fl/fl ) mice. Keratinocyte-specific ablation of PAR₂ prevented the significant Lig + Inf-induced increase (2.8-fold) in the number of osteoclasts in alveolar bone and the significant up-regulation (2.4-4-fold) of the inflammatory markers IL-6, IL-1β, interferon-γ, myeloperoxidase, and CD11b in gingival tissue. These data suggest that PAR₂ expressed on oral epithelial cells is a critical regulator of periodontitis-induced bone loss and will help in designing novel therapies with which to treat the disease.

Comparative proteomic analysis revealed complex responses to classical/novel duck reovirus infections in Cairna moschata

Duck reovirus (DRV) is an typical aquatic bird pathogen belonging to the Orthoreovirus genus of the Reoviridae family. Reovirus causes huge economic losses to the duck industry. Although DRV has been identified and isolated long ago, the responses of Cairna moschata to classical/novel duck reovirus (CDRV/NDRV) infections are largely unknown. To investigate the relationship of pathogenesis and immune response, proteomes of C. moschata liver cells under the C/NDRV infections were analyzed, respectively. In total, 5571 proteins were identified, among which 5015 proteins were quantified. The differential expressed proteins (DEPs) between the control and infected liver cells displayed diverse biological functions and subcellular localizations. Among the DEPs, most of the metabolism-related proteins were down-regulated, suggesting a decrease in the basal metabolisms under C/NDRV infections. Several important factors in the complement, coagulation and fibrinolytic systems were significantly up-regulated by the C/NDRV infections, indicating that the serine protease-mediated innate immune system might play roles in the responses to the C/NDRV infections. Moreover, a number of molecular chaperones were identified, and no significantly changes in their abundances were observed in the liver cells. Our data may give a comprehensive resource for investigating the regulation mechanism involved in the responses of C. moschata to the C/NDRV infections.

Characterization of Protease-Activated Receptor (PAR) ligands: Parmodulins are reversible allosteric inhibitors of PAR1-driven calcium mobilization in endothelial cells

Several classes of ligands for Protease-Activated Receptors (PARs) have shown impressive anti-inflammatory and cytoprotective activities, including PAR2 antagonists and the PAR1-targeting parmodulins. In order to support medicinal chemistry studies with hundreds of compounds and to perform detailed mode-of-action studies, it became important to develop a reliable PAR assay that is operational with endothelial cells, which mediate the cytoprotective effects of interest. We report a detailed protocol for an intracellular calcium mobilization assay with adherent endothelial cells in multiwell plates that was used to study a number of known and new PAR1 and PAR2 ligands, including an alkynylated version of the PAR1 antagonist RWJ-58259 that is suitable for the preparation of tagged or conjugate compounds. Using the cell line EA.hy926, it was necessary to perform media exchanges with automated liquid handling equipment in order to obtain optimal and reproducible antagonist concentration-response curves. The assay is also suitable for study of PAR2 ligands; a peptide antagonist reported by Fairlie was synthesized and found to inhibit PAR2 in a manner consistent with reports using epithelial cells. The assay was used to confirm that vorapaxar acts as an irreversible antagonist of PAR1 in endothelium, and parmodulin 2 (ML161) and the related parmodulin RR-90 were found to inhibit PAR1 reversibly, in a manner consistent with negative allosteric modulation.

Protease-Activated Receptor 4 (PAR4): A Promising Target for Antiplatelet Therapy

Cardiovascular diseases (CVDs) are currently among the leading causes of death worldwide. Platelet aggregation is a key cellular component of arterial thrombi and major cause of CVDs. Protease-activated receptors (PARs), including PAR1, PAR2, PAR3 and PAR4, fall within a subfamily of seven-transmembrane G-protein-coupled receptors (GPCR). Human platelets express PAR1 and PAR4, which contribute to the signaling transduction processes. In association with CVDs, PAR4 not only contributes to platelet activation but also is a modulator of cellular responses that serve as hallmarks of inflammation. Although several antiplatelet drugs are available on the market, they have many side effects that limit their use. Emerging evidence shows that PAR4 targeting is a safer strategy for preventing thrombosis and consequently may improve the overall cardiac safety profile. Our present review summarizes the PAR4 structural characteristics, activation mechanism, role in the pathophysiology of diseases and understanding the association of PAR4 targeting for improved cardiac protection. Conclusively, this review highlights the importance of PAR4 antagonists and its potential utility in different CVDs.

Proteinases and their receptors in inflammatory arthritis: an overview

Proteinases are enzymes with established roles in physiological and pathological processes such as digestion and the homeostasis, destruction and repair of tissues. Over the past few years, the hormone-like properties of circulating proteinases have become increasingly appreciated. Some proteolytic enzymes trigger cell signalling via proteinase-activated receptors, a family of G protein-coupled receptors that have been implicated in inflammation and pain in inflammatory arthritis. Proteinases can also regulate ion flux owing to the cross-sensitization of transient receptor potential cation channel subfamily V members 1 and 4, which are associated with mechanosensing and pain. In this Review, the idea that proteinases have the potential to orchestrate inflammatory signals by interacting with receptors on cells within the synovial microenvironment of an inflamed joint is revisited in three arthritic diseases: osteoarthritis, spondyloarthritis and rheumatoid arthritis. Unanswered questions are highlighted and the therapeutic potential of modulating this proteinase-receptor axis for the management of disease in patients with these types of arthritis is also discussed.

Exogenous cathepsin G upregulates cell surface MHC class I molecules on immune and glioblastoma cells

Major histocompatibility complex (MHC) class I molecules present antigenic peptides to cytotoxic T cells. During an adaptive immune response, MHC molecules are regulated by several mechanisms including lipopolysaccharide (LPS) and interferon gamma (IFN-g). However, it is unclear whether the serine protease cathepsin G (CatG), which is generally secreted by neutrophils at the site of inflammation, might regulate MHC I molecules. We identified CatG, and to a higher extend CatG and lactoferrin (LF), as an exogenous regulator of cell surface MHC I expression of immune cells and glioblastoma stem cells. In addition, levels of MHC I molecules are reduced on dendritic cells from CatG deficient mice compared to their wild type counterparts. Furthermore, cell surface CatG on immune cells, including T cells, B cells, and NK cells triggers MHC I on THP-1 monocytes suggesting a novel mechanism for CatG to facilitate intercellular communication between infiltrating cells and the respective target cell. Subsequently, our findings highlight the pivotal role of CatG as a checkpoint protease which might force target cells to display their intracellular MHC I:antigen repertoire.

Proteinase-activated receptor 2 promotes TGF-β-dependent cell motility in pancreatic cancer cells by sustaining expression of the TGF-β type I receptor ALK5

Pancreatic ductal adenocarcinoma (PDAC) is characterized by high expression of transforming growth factor (TGF)-β and the G protein-coupled receptor proteinase-activated receptor 2 (PAR2), the latter of which functions as a cell-surface sensor for serine proteinases asscociated with the tumour microenvironment. Since TGF-β and PAR2 affect tumourigenesis by regulating migration, invasion and metastasis, we hypothesized that there is signalling crosstalk between them. Depleting PDAC and non-PDAC cells of PAR2 by RNA interference strongly decreased TGF-β1-induced activation of Smad2/3 and p38 mitogen-activated protein kinase, Smad dependent transcriptional activity, expression of invasion associated genes, and cell migration/invasion in vitro. Likewise, the plasminogen activator-inhibitor 1 gene in primary cultures of aortic smooth muscle cells from PAR2-/- mice displayed a greatly attenuated sensitivity to TGF-β1 stimulation. PAR2 depletion in PDAC cells resulted in reduced protein and mRNA levels of the TGF-β type I receptor activin receptor-like kinase 5 (ALK5). Forced expression of wild-type ALK5 or a kinase-active ALK5 mutant, but not a kinase-active but Smad-binding defective ALK5 mutant, was able to rescue TGF-β1-induced Smad3 activation, Smad dependent transcription, and cell migration in PAR2-depleted cells. Together, our data show that PAR2 is crucial for TGF-β1-induced cell motility by its ability to sustain expression of ALK5. Therapeutically targeting PAR2 may thus be a promising approach in preventing TGF-β-dependent driven metastatic dissemination in PDAC and possibly other stroma-rich tumour types.

Local Regulation of Thrombin Activity by Factor Xa in Peripheral Nerve Schwann Cells

Thrombin through its receptor plays an important role in the peripheral nervous system (PNS) but the pathways leading to its generation there are not known. In the blood, activated factor X (FXa) which is formed from factor X (FX) by tissue factor (TF) and factor VII (FVII), cleaves prothrombin into thrombin. We here studied these factors in vivo in mouse sciatic nerve and in vitro in a Schwannoma cell line and provide mRNA, immunoblot and immunohistochemistry evidence that FX and FXa are expressed in the normal and injured peripheral nerve and in Schwannoma cells. Furthermore, TF and FVII were localized histologically to the node of Ranvier in the sciatic nerve. Adding exogenous FXa increased the thrombin levels in sciatic nerve (11.6 ± 1.6 mU/ml compared to 35.2 ± 6 mU/ml p = 0.02) and in Schwannoma cell line (4.5 ± 0.2 mU/ml compared to 18.1 ± 0.5 mU/ml p < 0.001), indicating a large reserve of prothrombin. In the injured nerve, FX mRNA was upregulated 1 day after injury compared to normal nerve (103 ± 38 versus 1 ± 0.3 FOI p < 0.001). FXa protein levels increased 1 h after the injury and then decreased significantly at 1 and 2 days following injury despite an increase in its precursor, FX. Injecting the selective FXa inhibitor apixaban immediately upon injury decreased thrombin activation and improved motor function after nerve injury. The results localize the extrinsic coagulation pathway and FXa to the PNS, suggesting a critical role for FXa in PNS thrombin formation and the possible therapeutic use of selective FXa inhibitors in nerve injuries.

The Role of PAR2 in TGF-β1-Induced ERK Activation and Cell Motility

Background: Recently, the expression of proteinase-activated receptor 2 (PAR2) has been shown to be essential for activin receptor-like kinase 5 (ALK5)/SMAD-mediated signaling and cell migration by transforming growth factor (TGF)-β1. However, it is not known whether activation of non-SMAD TGF-β signaling (e.g., RAS–RAF–MEK–extracellular signal-regulated kinase (ERK) signaling) is required for cell migration and whether it is also dependent on PAR2. Methods: RNA interference was used to deplete cells of PAR2, followed by xCELLigence technology to measure cell migration, phospho-immunoblotting to assess ERK1/2 activation, and co-immunoprecipitation to detect a PAR2–ALK5 physical interaction. Results: Inhibition of ERK signaling with the MEK inhibitor U0126 blunted the ability of TGF-β1 to induce migration in pancreatic cancer Panc1 cells. ERK activation in response to PAR2 agonistic peptide (PAR2–AP) was strong and rapid, while it was moderate and delayed in response to TGF-β1. Basal and TGF-β1-dependent ERK, but not SMAD activation, was blocked by U0126 in Panc1 and other cell types indicating that ERK activation is downstream or independent of SMAD signaling. Moreover, cellular depletion of PAR2 in HaCaT cells strongly inhibited TGF-β1-induced ERK activation, while the biased PAR2 agonist GB88 at 10 and 100 µM potentiated TGF-β1-dependent ERK activation and cell migration. Finally, we provide evidence for a physical interaction between PAR2 and ALK5. Our data show that both PAR2–AP- and TGF-β1-induced cell migration depend on ERK activation, that PAR2 expression is crucial for TGF-β1-induced ERK activation, and that the functional cooperation of PAR2 and TGF-β1 involves a physical interaction between PAR2 and ALK5.

Transforming Growth Factor-β1/Activin Receptor-like Kinase 5-Mediated Cell Migration is Dependent on the Protein Proteinase-Activated Receptor 2 but not on Proteinase-Activated Receptor 2-Stimulated Gq-Calcium Signaling

Transforming growth factor-β (TGF-β), serine proteinases such as trypsin, and proteinase-activated receptor 2 (PAR2) promote tumor development by stimulating invasion and metastasis. Previously, we found that in cancer cells derived from pancreatic ductal adenocarcinoma (PDAC) PAR2 protein is necessary for TGF-β1-dependent cell motility. Here, we show in the same cells that, conversely, the type I TGF-β receptor activin receptor-like kinase 5 is dispensable for trypsin and PAR2 activating peptide (PAR2-AP)-induced migration. To reveal whether Gq-calcium signaling is a prerequisite for PAR2 to enhance TGF-β signaling, we investigated the effects of PAR2-APs, PAR2 mutation and PAR2 inhibitors on TGF-β1-induced migration, reporter gene activity, and Smad activation. Stimulation of cells with PAR2-AP alone failed to enhance basal or TGF-β1-induced C-terminal phosphorylation of Smad3, Smad-dependent activity of a luciferase reporter gene, and cell migration. Consistently, in complementary loss of function studies, abrogation of the PAR2-Gq-calcium signaling arm failed to suppress TGF-β1-induced cell migration, reporter gene activity, and Smad3 activation. Together, our findings suggest that the calcium-regulating motif is not required for PAR2 to synergize with TGF-β1 to promote cell motility. Additional experiments in PDAC cells revealed that PAR2 and TGF-β1 synergy may involve TGF-β1 induction of enzymes that cause autocrine cleavage/activation of PAR2, possibly through a biased signaling function. Our results suggest that although reducing PAR2 protein expression may potentially block TGF-β's prooncogenic function, inhibiting PAR2-Gq-calcium signaling alone would not be sufficient to achieve this effect.

MicroRNA-205 Mediates Proteinase-Activated Receptor 2 (PAR2) -Promoted Cancer Cell Migration

Activation of proteinase-activated receptor 2 (PAR₂) promotes cell migration in cancers, but the exact mechanism underlying this process remains largely unknown. Here we report that activation of PAR₂ reduced miR-205 expression, whereas inhibition of miR-205 promoted cell migration in cancer cells. Overexpression of miR-205 blocked PAR₂-mediated stimulation of cell migration. BMPR1B was identified as a downstream target gene of miR-205. In colorectal carcinoma specimens from patients, the level of PAR₂ was negatively correlated with that of miR-205, but it was positively associated with BMPR1B expression. Taken together, our findings indicate that PAR₂ signaling promotes cancer cell migration through miR-205/BMPR1B pathway in human colorectal carcinoma.

Neural tube closure: cellular, molecular and biomechanical mechanisms

Neural tube closure has been studied for many decades, across a range of vertebrates, as a paradigm of embryonic morphogenesis. Neurulation is of particular interest in view of the severe congenital malformations - 'neural tube defects' - that result when closure fails. The process of neural tube closure is complex and involves cellular events such as convergent extension, apical constriction and interkinetic nuclear migration, as well as precise molecular control via the non-canonical Wnt/planar cell polarity pathway, Shh/BMP signalling, and the transcription factors Grhl2/3, Pax3, Cdx2 and Zic2. More recently, biomechanical inputs into neural tube morphogenesis have also been identified. Here, we review these cellular, molecular and biomechanical mechanisms involved in neural tube closure, based on studies of various vertebrate species, focusing on the most recent advances in the field.

Activated protein C protects from GvHD via PAR2/PAR3 signalling in regulatory T-cells

Graft-vs.-host disease (GvHD) is a major complication of allogenic hematopoietic stem-cell(HSC) transplantation. GvHD is associated with loss of endothelial thrombomodulin, but the relevance of this for the adaptive immune response to transplanted HSCs remains unknown. Here we show that the protease-activated protein C (aPC), which is generated by thrombomodulin, ameliorates GvHD aPC restricts allogenic T-cell activation via the protease activated receptor (PAR)2/PAR3 heterodimer on regulatory T-cells (Tregs, CD4+FOXP3+). Preincubation of pan T-cells with aPC prior to transplantation increases the frequency of Tregs and protects from GvHD. Preincubation of human T-cells (HLA-DR4-CD4+) with aPC prior to transplantation into humanized (NSG-AB°DR4) mice ameliorates graft-vs.-host disease. The protective effect of aPC on GvHD does not compromise the graft vs. leukaemia effect in two independent tumor cell models. Ex vivo preincubation of T-cells with aPC, aPC-based therapies, or targeting PAR2/PAR3 on T-cells may provide a safe and effective approach to mitigate GvHD.Graft-vs.-host disease is a complication of allogenic hematopoietic stem cell transplantation, and is associated with endothelial dysfunction. Here the authors show that activated protein C signals via PAR2/PAR3 to expand Treg cells, mitigating the disease in mice.

Sensitization of ASIC3 by proteinase-activated receptor 2 signaling contributes to acidosis-induced nociception

Background

Tissue acidosis and inflammatory mediators play critical roles in pain. Pro-inflammatory agents trypsin and tryptase cleave and activate proteinase-activated receptor 2 (PAR₂) expressed on sensory nerves, which is involved in peripheral mechanisms of inflammation and pain. Extracellular acidosis activates acid-sensing ion channel 3 (ASIC3) to trigger pain sensation. Here, we show that a functional interaction of PAR₂ and ASIC3 could contribute to acidosis-induced nociception.

Methods

Electrophysiological experiments were performed on both rat DRG neurons and Chinese hamster ovary (CHO) cells expressing ASIC3 and PAR₂. Nociceptive behavior was induced by acetic acid in rats.

Results

PAR₂-AP, PAR₂-activating peptide, concentration-dependently increased the ASIC3 currents in CHO cells transfected with ASIC3 and PAR₂. The proton concentration–response relationship was not changed, but that the maximal response increased 58.7 ± 3.8% after pretreatment of PAR₂-AP. PAR₂ mediated the potentiation of ASIC3 currents via an intracellular cascade. PAR₂-AP potentiation of ASIC3 currents disappeared after inhibition of intracellular G protein, PLC, PKC, or PKA signaling. Moreover, PAR₂ activation increased proton-evoked currents and spikes mediated by ASIC3 in rat dorsal root ganglion neurons. Finally, peripheral administration of PAR₂-AP dose-dependently exacerbated acidosis-induced nocifensive behaviors in rats.

Conclusions

These results indicated that PAR₂ signaling sensitized ASIC3, which may contribute to acidosis-induced nociception. These represent a novel peripheral mechanism underlying PAR₂ involvement in hyperalgesia by sensitizing ASIC3 in primary sensory neurons.

ENMD-1068 inhibits liver fibrosis through attenuation of TGF-β1/Smad2/3 signaling in mice

Protease-activated receptor 2 (PAR-2) plays an important role in the pathogenesis of liver fibrosis. We studied the effect of N1-3-methylbutyryl-N4-6-aminohexanoyl-piperazine (ENMD-1068), a PAR-2 antagonist, on the development of CCl₄-induced liver fibrosis in mice and activation of hepatic stellate cells (HSCs) isolated from the mice. Before CCl₄ injection, the mice were injected intraperitoneally with either 25 mg/kg or 50 mg/kg ENMD-1068 or with 200 μL of the vehicle control twice per week for 4 weeks. The isolated HSCs were stimulated by TGF-β1 with or without ENMD-1068 to evaluate the role of PAR-2 in TGF-β1 induced HSCs activation and collagen production. We showed that the levels of ALT/AST, collagen content, and α-smooth muscle actin (α-SMA) were significantly reduced by treatment with ENMD-1068 in CCl₄-induced fibrotic mice. Interestingly, we found TGF-β1 signaling-related expression levels of α-SMA, type I and III collagen, and C-terminal phosphorylation of Smad2/3 were significantly decreased in the ENMD-1068 treated HSCs. Moreover, we showed ENMD-1068 treatment inhibited trypsin or SLIGRL-NH₂ stimulated calcium release and TGF-β1 induced Smad transcriptional activity in HSCs. We demonstrated that ENMD-1068 reduces HSCs activation and collagen expression through the inhibiton of TGF-β1/Smad signal transduction.

Homeostatic effects of coagulation protease-dependent signaling and protease activated receptors

A homeostatic function of the coagulation system in regard to hemostasis is well established. Homeostasis of blood coagulation depends partially on protease activated receptor (PAR)-signaling. Beyond coagulation proteases, numerous other soluble and cell-bound proteases convey cellular effects via PAR signaling. As we learn more about the mechanisms underlying cell-, tissue-, and context-specific PAR signaling, we concurrently gain new insights into physiological and pathophysiological functions of PARs. In this regard, regulation of cell and tissue homeostasis by PAR signaling is an evolving scheme. Akin to the control of blood clotting per se (the fibrin-platelet interaction) coagulation proteases coordinately regulate cell- and tissue-specific functions. This review summarizes recent insights into homeostatic regulation through PAR signaling, focusing on blood coagulation proteases. Considering the common use of drugs altering coagulation protease activity through either broad or targeted inhibitory activities, and the advent of PAR modulating drugs, an in-depth understanding of the mechanisms through which coagulation proteases and PAR signaling regulate not only hemostasis, but also cell and tissue homeostasis is required.

Biased Signaling by Agonists of Protease Activated Receptor 2

Protease activated receptor 2 (PAR2) is associated with metabolism, obesity, inflammatory, respiratory and gastrointestinal disorders, pain, cancer, and other diseases. The extracellular N-terminus of PAR2 is a common target for multiple proteases, which cleave it at different sites to generate different N-termini that activate different PAR2-mediated intracellular signaling pathways. There are no synthetic PAR2 ligands that reproduce the same signaling profiles and potencies as proteases. Structure-activity relationships here for 26 compounds spanned a signaling bias over 3 log units, culminating in three small ligands as biased agonist tools for interrogating PAR2 functions. DF253 (2f-LAAAAI-NH₂) triggered PAR2-mediated calcium release (EC₅₀ 2 μM) but not ERK1/2 phosphorylation (EC₅₀ > 100 μM) in CHO cells transfected with hPAR2. AY77 (Isox-Cha-Chg-NH₂) was a more potent calcium-biased agonist (EC₅₀ 40 nM, Ca²⁺; EC₅₀ 2 μM, ERK1/2), while its analogue AY254 (Isox-Cha-Chg-A-R-NH₂) was an ERK-biased agonist (EC₅₀ 2 nM, ERK1/2; EC₅₀ 80 nM, Ca²⁺). Signaling bias led to different functional responses in human colorectal carcinoma cells (HT29). AY254, but not AY77 or DF253, attenuated cytokine-induced caspase 3/8 activation, promoted scratch-wound healing, and induced IL-8 secretion, all via PAR2-ERK1/2 signaling. Different ligand components were responsible for different PAR2 signaling and functions, clues that can potentially lead to drugs that modulate different pathway-selective cellular and physiological responses.

Detailed two-dimensional gel proteomic mapping of the feces of the house dust mite Dermatophagoides pteronyssinus and comparison with D. farinae: Reduced trypsin protease content in D. pteronyssinus and different isoforms

Major domestic mite allergens are present in feces. We present a detailed 2D-E-MS/MS proteomic analysis of the Dermatophagoides pteronyssinus feces. Precise cultivation yielded a pure fecal extract. We detected differences in fecal allergens/digestive enzymes between D. pteronyssinus and D. farinae using 2D-E fingerprinting, including unique information on species-specific protease isoforms. Proteomic analysis was performed by 2D-E coupled with MALDI-TOF/TOF identification. The species-specific differences in the fecal extracts of the mites were attributed to trypsin-like proteases known as group 3 allergens. In D. farinae, Der f 3 exhibited high abundance with a pI similar (acidic) to that of the cysteine protease Der f 1 and the chymotrypsin protease Der f 6, whereas in D. pteronyssinus, Der p 3 was rarely detected and exhibited low abundance only at basic pI. Moreover, Der p 9 was detected at a pI of ~ 10, in contrast to Der p 1 and Der p 6, suggesting different compartmentalization in the body. Overall, in D. pteronyssinus feces, allergens of groups 1, 2, 6, and 15 were quantitatively similar to those of D. farinae with the exception of the group 3 and 9 allergens. This work provides novel insights into mite-defecated proteins/digestive enzymes, which are important allergens.

SIGNIFICANCE

Millions of people are affected by allergy and asthma, and their number is growing. In homes, the major triggers of allergy and asthma are the house dust mites Dermatophagoides farinae and D. pteronyssinus, and a clear understanding of the development of diseases caused by these mites is needed. The major sources of mite allergens are their feces, which are deposited in the environment and are easily inhaled as part of aeroplankton. However, descriptions of and comparisons between the major fecal allergens of these two mites are lacking. This study shows that similar group 1 (cysteine protease), 2 (NPC2 family), 6 (chymotrypsin) and 15 (chitinase-like) allergens are present in the feces of these two mite species, as determined by 2D-E mapping, whereas group 3 (trypsin) and 9 (collagenolytic protease) allergens in the feces of the two species are different. The results provide unique MS/MS mapped fingerprints of mite species-specific isoforms in feces. The presence of ubiquitin in mite feces suggests that these proteins participate in the post-translational modification of fecal proteins. The findings are essential for understanding differences between D. farinae and D. pteronyssinus with respect to immunoreactivity, protease activation mechanisms, association with microbes, and food utilization.

Recent Progress in Research on the Pathogenesis of Pulmonary Thromboembolism: An Old Story with New Perspectives

Pulmonary thromboembolism (PTE) is part of a larger clinicopathological entity, venous thromboembolism. It is also a complex, multifactorial disorder divided into four major disease processes including venous thrombosis, thrombus in transit, acute pulmonary embolism, and pulmonary circulation reconstruction. Even when treated, some patients develop chronic thromboembolic pulmonary hypertension. PTE is also a common fatal type of pulmonary vascular disease worldwide, but earlier studies primarily focused on the pathological changes in the blood component of the disease. With contemporary advances in molecular and cellular biology, people are becoming increasingly aware of coagulation pathways, the function of vascular smooth muscle cells, microparticles, and the inflammatory pathways that play key roles in PTE. Combined hypoxia and immune research has revealed that PTE should be regarded as a class of complex diseases caused by multiple factors involving the vascular microenvironment and vascular cell dysfunction.

Protease-activated Receptor 1 Plays a Proinflammatory Role in Colitis by Promoting Th17-related Immunity

BACKGROUND

Proteolytic cleavage of protease-activated receptor 1 (PAR1) can result in potent downstream regulatory effects on inflammation. Although PAR1 is expressed throughout the gastrointestinal tract and activating proteases are increased in inflammatory bowel disease, the effect of PAR1 activation on colitis remains poorly understood, and has not previously been studied in pediatric disease.

METHODS

Expression of PAR1 and inflammatory cytokines in colonic biopsies from pediatric patients with Crohn's disease exhibiting active moderate to severe colitis was measured by quantitative PCR. The functional relevance of these clinical data was further studied in a mouse model of Citrobacter rodentium-induced colitis.

RESULTS

PAR1 expression was significantly upregulated in the inflamed colons of pediatric patients with Crohn's disease, with expression levels directly correlating to disease severity. In patients with severe colitis, PAR1 expression uniquely correlated with Th17-related (IL17A, IL22, and IL23A) cytokines. Infection of PAR1-deficient (PAR1) and wildtype mice with colitogenic C. rodentium revealed that disease severity and colonic pathology were strongly attenuated in mice lacking PAR1. Furthermore, Th17-type immune response was completely abolished in the colons of infected PAR1 but not wildtype mice. Finally, PAR1 was shown to be essential for secretion of the Th17-driving cytokine IL-23 by C. rodentium-stimulated macrophages.

CONCLUSIONS

This study demonstrates a strong link between PAR1 expression, Th17-type immunity, and disease severity in both pediatric patients with Crohn's disease and C. rodentium-induced colitis in mice. The data presented suggest PAR1 exerts a proinflammatory role in colitis in both humans and mice by promoting a Th17-type immune response, potentially by supporting the production of IL-23.

CALCB splice region pathogenic variants leading to plasma cell neurotropic enrichment in type 1 autoimmune pancreatitis

Recently, we have demonstrated that PRSS1 mutations cause ectopic trypsinogen activation and thereby result in type 1 autoimmune pancreatitis (AIP). However, the molecules involved in inducing obliterative vasculitis and perineural inflammation in the pancreas are not well-described. The present study applied whole-exome sequencing (WES) to determine the underlying etiology and revealed novel missense splice region variants, CALCB c.88T>C (p.Ser30Pro) and IR [1]-mutants, in 2 of the 3 families and 2 of 26 unrelated patients with type 1 AIP. In vitro, both of the mutants displayed decreased βCGRP, ERK1/2 phosphorylation, and co-localized with endoplasmic reticulum and Golgi apparatus. The novel pathogenic variant identified in this case should contribute to our understanding of the expanding spectrum of AIP.

Protease-Activated Receptor-1 Supports Locomotor Recovery by Biased Agonist Activated Protein C after Contusive Spinal Cord Injury

Thrombin-induced secondary injury is mediated through its receptor, protease activated receptor-1 (PAR-1), by "biased agonism." Activated protein C (APC) acts through the same PAR-1 receptor but functions as an anti-coagulant and anti-inflammatory protein, which counteracts many of the effects of thrombin. Although the working mechanism of PAR-1 is becoming clear, the functional role of PAR-1 and its correlation with APC in the injured spinal cord remains to be elucidated. Here we investigated if PAR-1 and APC are determinants of long-term functional recovery after a spinal cord contusive injury using PAR-1 null and wild-type mice. We found that neutrophil infiltration and disruption of the blood-spinal cord barrier were significantly reduced in spinal cord injured PAR-1 null mice relative to the wild-type group. Both locomotor recovery and ability to descend an inclined grid were significantly improved in the PAR-1 null group 42 days after injury and this improvement was associated with greater long-term sparing of white matter and a reduction in glial scarring. Wild-type mice treated with APC acutely after injury showed a similar level of improved locomotor recovery to that of PAR-1 null mice. However, improvement of APC-treated PAR-1 null mice was indistinguishable from that of vehicle-treated PAR-1 null mice, suggesting that APC acts through PAR-1. Collectively, our findings define a detrimental role of thrombin-activated PAR-1 in wound healing and further validate APC, also acting through the PAR-1 by biased agonism, as a promising therapeutic target for spinal cord injury.