PAR-1 Activation Research Articles

PAR2, not PAR1, regulates endothelium‐dependent vascular tone in resistance arteries

Protease activated receptors (PARs), a subfamily of G‐protein‐coupled receptors, are activated by cleavage of its extracellular domains. Four mammalian PAR members have been identified (PAR1‐4). PAR1 is the thrombin receptor, while PAR2 is activated physiologically by peptides or N‐terminal proteolytic cleavage. The resulting cleaved N‐termini acts as a tethered ligand that initiates receptor signaling. PARs may regulate vascular tone, cell permeability and cell proliferation. However, the precise roles of PAR1 and PAR2 in regulating vascular tone via the endothelium, and how PAR‐evoked signals transmit extracellularly and intracellularly, are incompletely understood.To explore the physiological functions, and the underlying signalling pathways in native endothelium, PAR1 (TFLLR‐NH2) and PAR2 (2‐Furoyl‐LIGRLO‐amide; 2fLI) activating peptides were used, and changes in intracellular Ca2+ and contractility measured in en face rat mesenteric arteries. Surprisingly, PAR1 activation (TFLLR‐NH2or trypsin) neither triggered Ca2+ signals in endothelial cells or alter vascular tone. On the other hand, PAR2 activation (2fLI) evoked large global propagating Ca2+ waves in endothelial cells and endothelium‐dependent dilation of mesenteric arteries. The Ca2+ signals evoked by PAR2 activation were kinetically distinctive when compared to those of muscarinic receptor activation. PAR2 activation (2fLI) also evoked responses in different clusters of endothelial cells from those of muscarinic receptor (acetylcholine) activation. PAR2 activation with 2fLI or trypsin failed to evoke Ca2+ signals after depletion of the internal store with the Ca2+‐ATPase (SERCA) inhibitor, CPA. This result suggests that PAR2 evokes Ca2+ release from internal stores. Pharmacological block of inositol 1,4,5‐trisphosphate (IP3) with either 2‐APB or caffeine, also blocked PAR2‐evoked Ca2+ signals. Phospholipase C inhibition (U73122) also blocked the Ca2+ signals evoked by PAR2 activation. Therefore, PAR2 is a PLC linked G protein coupled receptor which evokes Ca2+ release from the internal store via IP3 receptors in endothelial cells. The TRPC3 blocker, PYR3 and store‐operated Ca2+ entry (SOCE) blocker, YM58483 each significantly supressed PAR2 mediated Ca2+ signals, suggesting internal store was replenished via TRPC3 channel and SOCE.In conclusion, PAR2 rather than PAR1, regulates vascular tone in mesenteric arteries by evoking Ca2+ release from the internal store via IP3 receptors to generate propagating Ca2+ waves in distinct sub‐populations of endothelial cells.

Excitation of Vagal Afferent Neurons by Fecal Supernatant from Inflammatory Bowel Disease Patients

BackgroundThe gut‐ microbiota‐brain axis has received increasing attention recently due to evidence that colonic microbes can affect brain function and behavior. Recent studies have demonstrated that vagal afferent neurons may be an important conduit between the gut microbiota and the brain, as it is capable of detecting mediators released from the gut microbiota. However, it is unknown whether i) the gut microbiota from healthy human stool donors affects nodose ganglion (NG) neurophysiology or ii) gut microbial dysbiosis during inflammatory bowel disease (IBD) impacts the function of vagal afferent neurons.HypothesisRemodeling of gut microbiota during IBD increases secretion of mediators that change the excitability of vagal afferent neurons.MethodsTo examine the effect of IBD patients’ fecal supernatant (FS; 1:20 dilution) on the excitability of mouse vagal afferent neurons, NG neurons from C57/Bl6 mice were collected, dissociated, and incubated overnight with FS from 5 active Crohn’s disease (CD) patients, 7 active ulcerative colitis (UC) patients, and 5 healthy volunteers (HV). Current and voltage‐clamp recordings were used to assess changes in neuronal excitability and ion channel function.ResultsCD and UC FS significantly increased the excitability of NG neurons through a reduction in the rheobase of 40% (CD:60 cells vs. control: 54 cells), P<0.0001, Mann‐Whitney test) and 23% (n= 50 cells vs. control: 46 cells, P= 0.0038, Mann‐Whitney test) compared to their individual vehicle control neurons, respectively. This decrease in rheobase was accompanied by a two‐fold increase in the number of action potentials elicited at twice rheobase (P <0.01, Mann‐Whitney test). However, neither resting membrane potential, nor input resistance was altered in NG neurons treated with IBD FS compared with vehicle control neurons. HV FS had no effect on NG excitability. CD and UC FS significantly reduced voltage‐gated K+ currents (P= 0.0075 and P <0.0001, two‐way ANOVA followed by Sidak's multiple comparison test, respectively), but had no effect on voltage‐gated Na+ currents. The excitatory effect of CD and UC FS of NG neurons was blocked by the cysteine protease inhibitor (E64) (30 nM), but not the serine protease inhibitor (FUT175) (10 μM). In all CD patients, pre‐incubation of E64 blocked the increase in excitability by CD patient FS (CD rheobase:40.6 ± 3.6 pA vs.CD+ E64 rheobase: 73.9 ± 4.5 pA) (P<0.0001, one‐way ANOVA followed by Tukey's multiple comparison). However, E64 was only able to block the excitatory effect of FS from 5 out of 7 UC patients FS (UC rheobase:43.8 ± 4.7 pA vs. UC+ E64 rheobase: 83.5 ± 4.3 pA) (P=0.0092, one‐way ANOVA followed by Tukey's multiple comparison). The protease‐activated receptor 2 (PAR2) antagonist GB83 (10 μM) also blocked the effect of the CD and UC patient supernatant on NG neurons (P=0.0081and P=0.0116, Kruskal‐Wallis test, respectively).ConclusionFS from active IBD patients contain mediators that can excite NG neurons. Cysteine proteases directly mediates the effect of IBD FS on NG neurons by activation of PAR‐2. Signaling pathways downstream of PAR‐2 activation lead to inhibition of voltage‐gated K+ currents.

The role of the Thrombin/PAR axis in modulating CD8+ T cell anti-tumor immunity

Abstract CD8+ tumor infiltrating lymphocytes (TIL) are critical for tumor clearance following immune checkpoint inhibitor (ICI) therapy. Thrombin, the central hemostatic protease, is activated in the tumor microenvironment and CD8+ T cells express the thrombin-cleavable protease activated receptors (PAR-1, -2, -3, -4). Recent studies showed that thrombin can enhance CD8+ T cell effector functions, but the role of thrombin in ICI is unknown. We hypothesized that thrombin enhances CD8+ TIL anti-tumor effector functions (αTEF) during ICI therapy. Consistent with this hypothesis, we found that reducing circulating prothrombin to ~10% of normal completely abrogated the efficacy of PD-1 blockade therapy to reduce tumor growth, reduced CD8+ TIL infiltration into tumor tissue, and limited αTEF. Mechanistic in vitro studies showed that thrombin stimulation of isolated murine or human CD8+ T cells resulted in a dose-dependent increase in survival, proliferation and cytokine production (activation profile). Surprisingly, when we stimulated CD8+ T cells lacking PAR-1 or PAR-2, we observed an increase in their activation profile relative to WT CD8+T cells in the absence of thrombin, which was further enhanced with thrombin. Moreover, stimulation of PAR-2 deficient CD8+ T cells with a specific PAR-1 activating peptide resulted in an increased activation profile compared to WT CD8+ T cells stimulated with the same peptide. Together these data suggest that 1) thrombin promotes adaptive tumor immunity in the context of ICI therapy, 2) thrombin promotes αTEF through PAR-1 dependent and independent mechanisms and 3) PAR-2 suppresses CD8+ T cell functions independently of thrombin and limits the capacity of PAR-1 activation to enhance effector functions. Supported by grants from NIH T32 (5T32AI118697-04)

PAR4 Primarily Mediates Thrombin‐induced Morphological Changes in MEG‐01 Cells through PI3K/Akt and RhoA/ROCK Signaling Pathways

Platelet activation is critical in hemostasis and thrombosis. Thrombin most potently activates platelets via two protease‐activated receptors (PARs): PAR1 and PAR4. While PAR1 activation results in a rapid and transient signal required for the initiation phase of platelet aggregation, PAR4 activation induces a sustained signal associated with later phases responsible for stable thrombus formation. The present study focused on the differential signaling pathways by PAR1 and PAR4 involved in thrombin‐induced intracellular events in human megakaryoblastic leukemia cell line, MEG‐01. Interestingly, we found that thrombin triggers not only Gq/PLC‐mediated calcium signaling, but also G12/13/RhoA/ROCK‐mediated morphological changes in MEG‐01 cells via PAR1 and PAR4, which showed close similarity to those observed in platelets. We developed a new image‐based assay to quantify the morphological changes in living cells and extensively investigated on the underlying mechanism for thrombin‐induced morphological changes in MEG‐01 cells. Selective blockade of PAR1 and PAR4 by vorapaxar and BMS‐986120, respectively, indicated that PAR4 activation primarily mediates thrombin‐induced morphological changes in MEG‐01 cells. Moreover, treatment of a set of kinase inhibitors showed that the PAR4‐mediated morphological changes were predominantly mediated via PI3K/Akt and RhoA/ROCK signaling pathways. As in the platelets, PAR4‐mediated signaling pathways are significant in thrombin‐induced morphological changes in MEG‐01 cells. Based on the close similarity to thrombin‐induced signaling in platelets, MEG‐01 cell line is a useful complementary in vitro model that can be used in research on platelets and thrombosis.

Myricetin reverses epithelial-endothelial transition and inhibits vasculogenic mimicry and angiogenesis of hepatocellular carcinoma by directly targeting PAR1.

Most antiangiogenic inhibitors targeting endothelium-dependent vessels cannot inhibit tumor growth but promote tumor invasion and metastasis in some patients. Vasculogenic mimicry (VM) employs mechanisms that differ from those used to construct endothelium-dependent vessels. Inhibiting VM may be a novel antiangiogenic strategy against alternative tumor vascularization. In this paper, myricetin was selected from among several flavonoid compounds as an effective PAR1 antagonist. In two different hepatocellular carcinoma (HCC) cell lines high-expressed PAR1, myricetin inhibited cell migration, invasion and VM formation and reversed the expression of epithelial-endothelial transition (EET) markers by inhibiting PAR1 activation. Knockout of PAR1 inhibited HCC cell invasion and metastasis and weakened the inhibitory effect of myricetin on HCC cells. The migration, invasion and tube formation ability of PLC-PRF-5 cells were enhanced after PAR1 overexpression, and the inhibitory effect of myricetin was enhanced. A docking assay revealed that myricetin binds to Leu258 and Thr261 in the PAR1 activity pocket. Mutation of Leu258 and Thr261 inhibited the antitumor effect of myricetin in vitro and in vivo. In summary, myricetin reverses PAR1-mediated EET and inhibits HCC cell invasion, metastasis, VM formation and angiogenesis by targeting PAR1, and Leu258 and Thr261 of PAR1 participate in VM and angiogenesis in HCC tissues.

A62 PROTEASE-ACTIVATED RECEPTOR-2 ACTIVATION ENHANCES EPITHELIAL WOUND HEALING THROUGH SRC PATHWAY-DEPENDENT CELL MIGRATION

BackgroundProtease-activated receptors (PARs) and their activating enzymes play a role in inflammatory bowel disease (IBD) pathogenesis, but the specific roles of PAR2 in disease initiation and progression remain unclear. Interestingly, PAR2 activation has both pro-proliferative and pro-migratory effects and could be involved with restoration of the epithelial barrier following injury. We previously showed that the PAR2 activation increase the epithelial wound healing through ERK, PI3K and JNK pathways. However, the role of Src kinase, which is also activated by PAR2, is not known.AimsWe hypothesized that PAR-2 activation induces a wound healing response in intestinal epithelial cells through Src activity.MethodsCircular wounds were made in T84 colonic epithelial cells monolayers. Wounded monolayers were treated with the PAR2 activating peptide, 2-furoyl-LIGRLO (2fLI, 5 μM), or the inactive control reverse-sequence peptide, 2-furoyl-OLRGIL (2fO, 5 μM), and live cell imaging was used to record wound closure over a 12 or 24-hr period. The specificity of PAR2 was assessed with a PAR2 inhibitor (GB88). Proliferation and cytotoxicity were measured using EdU and TUNEL assays. The mechanism of action was evaluated using inhibitors of FAK (PF57328 and FAK14) and Src (PP2) and western blot (WB) was used to confirm the protein levels [p-FAK (Y397; Y576/577) and p-Src (Y416)]. For immunofluorescence, images of E-cadherin and F-actin or p-FAK were taken to capture the entire wound border and surrounding cells.ResultsPAR2 activation by 2fLI promoted wound closure compared to 2fO or vehicle control at the 12 and 24 hr timepoints ( p<0.05). PAR2’s ability to enhance wound closure was blocked with the PAR2 inhibitor, GB88 ( p<0.01). PAR2 activation had no effect on proliferation at the wound-edge and did not cause apoptosis, but enhanced lamellipodia/filopodia formation ( p<0.001), indicating that PAR2 might program the cells toward a migratory phenotype rather than a proliferative phenotype. When we investigated the mechanisms of action, PAR2 activation did not induce focal adhesion kinase (FAK) expression in T84 cells and inhibition of FAK by selective inhibitors (PF573288 and FAK14) did not alter PAR2-induced wound healing. The immunofluorescence for p-FAK (Y397) and WB (Y937 and Y576/577) confirmed these results. However, the Src tyrosine kinase inhibitor (PP2, p<0.0001) inhibited PAR2-induced wound healing. PAR2 activation increased Src phosphorylation (Y416, p<0.05).ConclusionsPAR2 activation drives wound healing in part via Src tyrosine kinase activity, but independently of FAK activity. These findings provide a further mechanism whereby PAR2 can participate in the resolution of intestinal wounds in gastrointestinal inflammatory diseases.Funding AgenciesCAG, CIHR

Neurocoagulation from a Mechanistic Point of View in the Central Nervous System.

Coagulation mechanisms are critical for maintaining homeostasis in the central nervous system (CNS). Thrombin, an important player of the coagulation cascade, activates protease activator receptors (PARs), members of the G-protein coupled receptor family. PAR1 is located on neurons and glia. Following thrombin activation, PAR1 signals through the extracellular signal-regulated kinase pathway, causing alterations in neuronal glutamate release and astrocytic morphological changes. Similarly, the anticoagulation factor activated protein C (aPC) can cleave PAR1, following interaction with the endothelial protein C receptor. Both thrombin and aPC are expressed on endothelial cells and pericytes in the blood-brain barrier (BBB). Thrombin-induced PAR1 activation increases cytosolic Ca2+ concentration in brain vessels, resulting in nitric oxide release and increasing F-actin stress fibers, damaging BBB integrity. aPC also induces PAR1 activation and preserves BBB vascular integrity via coupling to sphingosine 1 phosphate receptors. Thrombin-induced PAR1 overactivation and BBB disruption are evident in CNS pathologies. During epileptic seizures, BBB disruption promotes thrombin penetration. Thrombin induces PAR1 activation and potentiates N-methyl-D-aspartate receptors, inducing glutamate-mediated hyperexcitability. Specific PAR1 inhibition decreases status epilepticus severity in vivo. In stroke, the elevation of brain thrombin levels further compromises BBB integrity, with direct parenchymal damage, while systemic factor Xa inhibition improves neurological outcomes. In multiple sclerosis (MS), brain thrombin inhibitory capacity correlates with clinical presentation. Both thrombin inhibition by hirudin and the use of recombinant aPC improve disease severity in an MS animal model. This review presents the mechanisms underlying the effects of coagulation on the physiology and pathophysiology of the CNS.

PAR4-Mediated PI3K/Akt and RhoA/ROCK Signaling Pathways Are Essential for Thrombin-Induced Morphological Changes in MEG-01 Cells.

Thrombin stimulates platelets via a dual receptor system of protease-activated receptors (PARs): PAR1 and PAR4. PAR1 activation induces a rapid and transient signal associated with the initiation of platelet aggregation, whereas PAR4 activation results in a prolonged signal, required for later phases, that regulates the stable formation of thrombus. In this study, we observed differential signaling pathways for thrombin-induced PAR1 and PAR4 activation in a human megakaryoblastic leukemia cell line, MEG-01. Interestingly, thrombin induced both calcium signaling and morphological changes in MEG-01 cells via the activation of PAR1 and PAR4, and these intracellular events were very similar to those observed in platelets shown in previous studies. We developed a novel image-based assay to quantitatively measure the morphological changes in living cells, and observed the underlying mechanism for PAR1- and PAR4-mediated morphological changes in MEG-01 cells. Selective inhibition of PAR1 and PAR4 by vorapaxar and BMS-986120, respectively, showed that thrombin-induced morphological changes were primarily mediated by PAR4 activation. Treatment of a set of kinase inhibitors and 2-aminoethoxydiphenyl borate (2-APB) revealed that thrombin-mediated morphological changes were primarily regulated by calcium-independent pathways and PAR4 activation-induced PI3K/Akt and RhoA/ROCK signaling pathways in MEG-01 cells. These results indicate the importance of PAR4-mediated signaling pathways in thrombin-induced morphological changes in MEG-01 cells and provide a useful in vitro cellular model for platelet research.

PARP inhibitor BMN-673 induced apoptosis by trapping PARP-1 and inhibiting base excision repair via modulation of pol-β in chromatin of breast cancer cells

PARP inhibitors emerged as clinically effective anti-tumor agents in combination with DNA damaging agents but the toxicity of DNA damaging agents and their off-target effects caused serious problems in cancer therapy. They confer cytotoxicity in cancer cells both by catalytic inhibition and trapping of PARP-1 at the DNA damage site. There is a lack of direct evidence to quantitatively determine the trapped PARP-1 in cellular DNA. Here, we have precisely evaluated the mechanism of PARP trapping mediated anti-cancer action of Quinacrine (QC), BMN-673, and their combination (QC + BMN-673) in breast cancer cells. We introduced a strategy to measure the cellular PARP trapping potentiality of BMN-673 in QC pretreated cells using a fluorescence-based assay system. It was found that QC+ BMN-673 induced apoptosis by triggering DNA damage in breast cancer cells. Treatment with QC + BMN-673 stimulated the expression of PARP-1 in the chromatin compared to that of PARP-2 and PARP-3. QC + BMN-673 treatment also caused a dose-dependent and time-dependent accumulation of PARP-1 and inhibition of PARylation in the chromatin. Upregulation of BER components (pol-β and FEN-1), an unchanged HR and NHEJ pathway proteins, and reduction of luciferase activity of the cells transfected with R-p21-P (LP-BER) were noted in combined drug-treated cells. Interestingly, silencing of pol-β resulted in unchanged PARP-1 trapping and PAR activity in the chromatin with increasing time after QC + BMN-673 treatment without altering APC and FEN-1 expression. Thus, our data suggested that the QC + BMN-673 augmented breast cancer cell death by pol-β mediated repair inhibition primarily through trapping of PARP-1 besides PARP-1 catalytic inhibition.

Neutrophil cathepsin G proteolysis of protease-activated receptor 4 generates a novel, functional tethered ligand

AbstractPlatelet-neutrophil interactions regulate ischemic vascular injury. Platelets are activated by serine proteases that cleave protease-activated receptor (PAR) amino termini, resulting in an activating tethered ligand. Neutrophils release cathepsin G (CatG) at sites of injury and inflammation, which activates PAR4 but not PAR1, although the molecular mechanism of CatG-induced PAR4 activation is unknown. We show that blockade of the canonical PAR4 thrombin cleavage site did not alter CatG-induced platelet aggregation, suggesting CatG cleaves a different site than thrombin. Mass spectrometry analysis using PAR4 N-terminus peptides revealed CatG cleavage at Ser67-Arg68. A synthetic peptide, RALLLGWVPTR, representing the tethered ligand resulting from CatG proteolyzed PAR4, induced PAR4-dependent calcium flux and greater platelet aggregation than the thrombin-generated GYPGQV peptide. Mutating PAR4 Ser67or Arg68 reduced CatG-induced calcium flux without affecting thrombin-induced calcium flux. Dog platelets, which contain a conserved CatG PAR4 Ser-Arg cleavage site, aggregated in response to human CatG and RALLLGWVPTR, while mouse (Ser-Gln) and rat (Ser-Glu) platelets were unresponsive. Thus, CatG amputates the PAR4 thrombin cleavage site by cleavage at Ser67-Arg68 and activates PAR4 by generating a new functional tethered ligand. These findings support PAR4 as an important CatG signaling receptor and suggest a novel therapeutic approach for blocking platelet-neutrophil-mediated pathophysiologies.

Coagulation Factor Xa Induces Proinflammatory Responses in Cardiac Fibroblasts via Activation of Protease-Activated Receptor-1.

Coagulation factor (F) Xa induces proinflammatory responses through activation of protease-activated receptors (PARs). However, the effect of FXa on cardiac fibroblasts (CFs) and the contribution of PARs in FXa-induced cellular signalling in CF has not been fully characterised. To answer these questions, human and rat CFs were incubated with FXa (or TRAP-14, PAR-1 agonist). Gene expression of pro-fibrotic and proinflammatory markers was determined by qRT-PCR after 4 and 24 h. Gene silencing of F2R (PAR-1) and F2RL1 (PAR-2) was achieved using siRNA. MCP-1 protein levels were measured by ELISA of FXa-conditioned media at 24 h. Cell proliferation was assessed after 24 h of incubation with FXa ± SCH79797 (PAR-1 antagonist). In rat CFs, FXa induced upregulation of Ccl2 (MCP-1; >30-fold at 4 h in atrial and ventricular CF) and Il6 (IL-6; ±7-fold at 4 h in ventricular CF). Increased MCP-1 protein levels were detected in FXa-conditioned media at 24 h. In human CF, FXa upregulated the gene expression of CCL2 (>3-fold) and IL6 (>4-fold) at 4 h. Silencing of F2R (PAR-1 gene), but not F2RL1 (PAR-2 gene), downregulated this effect. Selective activation of PAR-1 by TRAP-14 increased CCL2 and IL6 gene expression; this was prevented by F2R (PAR-1 gene) knockdown. Moreover, SCH79797 decreased FXa-induced proliferation after 24 h. In conclusion, our study shows that FXa induces overexpression of proinflammatory genes in human CFs via PAR-1, which was found to be the most abundant PARs isoform in this cell type.

Expression/Activation of PAR-1 in Airway Epithelial Cells of COPD Patients: Ex Vivo/In Vitro Study.

The role of PAR-1 expression and activation was described in epithelial cells from the central and distal airways of COPD patients using an ex vivo/in vitro model. PAR-1 immunoreactivity was studied in epithelial cells from surgical specimens of the central and distal airways of COPD patients and healthy control (HC). Furthermore, PAR-1 expression and activation were measured in both the human bronchial epithelial cell line (16HBE) and normal human bronchial epithelial cells (NHBEs) exposed to cigarette smoke extract (CSE) (10%) or thrombin. Finally, cell proliferation, apoptosis, and IL-8 release were detected in stimulated NHBEs. We identified higher levels of PAR-1 expression/activation in epithelial cells from the central airways of COPD patients than in HC. Active PAR-1 increased in epithelial cells from central and distal airways of COPD, with higher levels in COPD smokers (correlated with pack-years) than in COPD ex-smokers. 16HBE and NHBEs exposed to CSE or thrombin showed increased levels of active PAR-1 (localized in the cytoplasm) than baseline conditions, while NHBEs treated with thrombin or CSE showed increased levels of IL-8 proteins, with an additional effect when used in combination. Smoking habits generate the upregulation of PAR-1 expression/activation in airway epithelial cells, and promoting IL-8 release might affect the recruitment of infiltrating cells in the airways of COPD patients.

Effects of Heparin and Bivalirudin on Thrombin-Induced Platelet Activation: Differential Modulation of PAR Signaling Drives Divergent Prothrombotic Responses.

Heparin and bivalirudin are widely used as anticoagulants in the setting of acute thrombosis. In this study, we investigated how these drugs affect the ability of thrombin to generate a prothrombotic platelet response via activation of the protease-activated receptors (PARs) 1 and 4. We examined the effects of heparin/antithrombin and bivalirudin on PAR1- and PAR4-mediated intracellular calcium mobilization, aggregation, α-granule release, and procoagulant membrane exposure in platelets exposed to thrombin concentrations likely to be encountered in the thrombus microenvironment during thrombosis. At physiological antithrombin levels, heparin treatment resulted in complete and sustained inhibition of thrombin-induced PAR4-mediated platelet activation, but transient PAR1 signaling was sufficient to elicit significant α-granule release and platelet aggregation. In contrast, bivalirudin treatment resulted in rapid and profound inhibition of signaling from both PAR receptors, followed by a delayed phase of PAR4-mediated platelet activation, resulting in a robust prothrombotic response. Combination treatment with bivalirudin and subtherapeutic concentrations of heparin completely inhibited the residual platelet activation observed with single drug treatment at all time-points. Our results show that heparin and bivalirudin have different and complementary inhibitory effects on the activation of PAR1 and PAR4 by thrombin.

Poly(ADP-ribose) polymerase inhibitor PJ34 protects against UVA-induced oxidative damage in corneal endothelium

Fuchs endothelial corneal dystrophy (FECD) is one of the main causes for corneal endothelial blindness, which is characterized by the progressive decline of corneal endothelial cells. Poly (ADP-ribose) polymerase (PARP) was reported to be involved in cell death and apoptosis of several diseases. However, the role of PARP1 in the progression of FECD remains elusive. In the present study, we reported that UVA irradiation caused the corneal endothelial damage and corneal edema in mice, which was accompanied with the elevated activity of PARP1 and PAR. The PARP1 inhibitor PJ34 resolved the corneal edema and protected corneal endothelium from UVA-induced oxidative damage, mitochondrial dysfunction, and cell apoptosis. Mechanistically, PARP1 inhibition exerted its anti-apoptotic effects through downregulation of the phosphorylation levels of JNK1/2 and p38 MAPK and subsequentlythe increase of MKP-1. Our results suggest that PARP1 inhibition protects corneal endothelium from UVA-induced oxidative damage, which provides a potential alternative strategy for the therapy of FECD.

Protease-activated receptor-2 activation enhances epithelial wound healing via epidermal growth factor receptor

ABSTRACT The intestinal barrier function relies on the presence of a single layer of epithelial cells. Barrier dysfunction is associated with the inflammatory bowel diseases (IBD). Understanding the mechanisms involved in intestinal wound healing in order to sustain the barrier function has a great therapeutic potential. Activation of protease-activated receptor-2 (PAR2) induces COX-2 expression in intestinal epithelial cells via EGFR transactivation. COX-2 is well known for its protective effects in the gastrointestinal tract. Therefore, we hypothesized that PAR-2 activation induces a wound healing response in intestinal epithelial cells through COX-2-derived lipid mediators and EGFR transactivation. Immunofluorescence and calcium assay were used to characterize CMT-93 mouse colonic epithelial cell line for PAR2 expression and its activity, respectively. Treatment with PAR2 activating peptide 2-furoyl-LIGRLO-NH2 (2fLI), but not by its inactive reverse-sequence peptide (2fO) enhanced wound closure in scratch wounded monolayers. The EGFR tyrosine kinase inhibitor (PD153035), broad-spectrum matrix metalloproteinase inhibitor (GM6001) and Src tyrosine kinase inhibitor (PP2) inhibited PAR2-induced wound healing. However, PAR2 activation did not induce COX-2 expression in CMT-93 cells and inhibition of COX-2 by COX-2 selective inhibitor (NS-398) did not alter PAR2-induced wound healing. In conclusion, PAR2 activation drives wound healing in CMT-93 cells via EGFR transactivation. Matrix metalloproteinases and Src tyrosine kinase activity may involve in EGFR transactivation and PAR2-induced wound healing is independent of COX-2 activity. These findings provide a mechanism whereby PAR2 can participate in the resolution of intestinal wounds in gastrointestinal inflammatory diseases.

Antagonism of Protease Activated Receptor-2 by GB88 Reduces Inflammation Triggered by Protease Allergen Tyr-p3

The occurrence of allergic diseases induced by aeroallergens has increased in the past decades. Among inhalant allergens, mites remain the important causal agent of allergic diseases. Storage mites- Tyrophagus putrescentiae are found in stored products or domestic environments. Major allergen Tyr-p3 plays a significant role in triggering IgE-mediated hypersensitivity. However, its effects on pulmonary inflammation, internalization, and activation in human epithelium remain elusive. Protease-activated receptors (PARs) are activated upon cleavage by proteases. A549 cells were used as an epithelial model to examine the PAR activation by Tyr-p3 and therapeutic potential of PAR-2 antagonist (GB88) in allergic responses. Enzymatic properties and allergen localization of Tyr-p3 were performed. The release of inflammatory mediators, phosphorylation of mitogen-activated protein kinase (MAPK), and cell junction disruptions were evaluated after Tyr-p3 challenge. Enzymatic properties determined by substrate digestion and protease inhibitors indicated that Tyr-p3 processes a trypsin-like serine protease activity. The PAR-2 mRNA levels were significantly increased by nTyr-p3 but inhibited by protease inhibitors or GB88. Protease allergen of nTyr-p3 significantly increased the levels of pro-inflammatory cytokines (IL-6 and TNF-α), chemokine (IL-8), and IL-1β in epithelial cells. nTyr-p3 markedly increased phosphorylation of extracellular signal-regulated kinase (ERK)1/2 and MAP kinase. When cells were pretreated with GB88 then added nTyr-p3, the phosphorylated ERK1/2 did not inhibit by GB88. GB88 increased ERK1/2 phosphorylation in human epithelium cells. GB88 is able to block PAR-2-mediated calcium signaling which inhibits the nTyr-p3-induced Ca2+ release. Among the pharmacologic inhibitors, the most effective inhibitor of the nTyr-p3 in the induction of IL-8 or IL-1β levels was GB88 followed by SBTI, MAPK/ERK, ERK, and p38 inhibitors. Levels of inflammatory mediators, including GM-CSF, VEGF, COX-2, TSLP, and IL-33 were reduced by treatment of GB88 or SBTI. Further, GB88 treatment down-regulated the nTyr-p3-induced PAR-2 expression in allergic patients with asthma or rhinitis. Tight junction and adherens junction were disrupted in epithelial cells by nTyr-p3 exposure; however, this effect was avoided by GB88. Immunostaining with frozen sections of the mite body showed the presence of Tyr-p3 throughout the intestinal digestive system, especially in the hindgut around the excretion site. In conclusion, our findings suggest that Tyr-p3 from domestic mites leads to disruption of the airway epithelial barrier after inhalation. Proteolytic activity of Tyr-p3 causes the PAR-2 mRNA expression, thus leading to the release of numerous inflammatory mediators. Antagonism of PAR2 activity suggests GB88 as the therapeutic potential for anti-inflammation medicine, especially in allergy development triggered by protease allergens.

Proteinase-activated receptors in GtoPdb v.2021.3

Proteinase-activated receptors (PARs, nomenclature as agreed by the NC-IUPHAR Subcommittee on Proteinase-activated Receptors [39]) are unique members of the GPCR superfamily activated by proteolytic cleavage of their amino terminal exodomains. Agonist proteinase-induced hydrolysis unmasks a tethered ligand (TL) at the exposed amino terminus, which acts intramolecularly at the binding site in the body of the receptor to effect transmembrane signalling. TL sequences at human PAR1-4 are SFLLRN-NH2, SLIGKV-NH2, TFRGAP-NH2 and GYPGQV-NH2, respectively. With the exception of PAR3, synthetic peptides with these sequences (as carboxyl terminal amides) are able to act as agonists at their respective receptors. Several proteinases, including neutrophil elastase, cathepsin G and chymotrypsin can have inhibitory effects at PAR1 and PAR2 such that they cleave the exodomain of the receptor without inducing activation of Gαq-coupled calcium signalling, thereby preventing activation by activating proteinases but not by agonist peptides. Neutrophil elastase (NE) cleavage of PAR1 and PAR2 can however activate MAP kinase signaling by exposing a TL that is different from the one revealed by trypsin [82]. PAR2 activation by NE regulates inflammation and pain responses [111, 72] and triggers mucin secretion from airway epithelial cells [112].

Synergistic activation of thrombin and angiotensin II receptors revealed by bioluminescence resonance energy transfer.

We recently reported a physical interaction between the angiotensin II (AngII) receptor (AT1R) and thrombin receptor (PAR1) in HEK293 cells using bioluminescence resonance energy transfer (BRET) technology. This was characterized by thrombin trans-activating AT1R and the synergistic responses of the AT1R-PAR1 complex. Here, we investigated the other face of the coin by examining the effect of AT1R on PAR1 activity using BRET. AngII/AT1R did not promote PAR1 activation in the absence of thrombin. However, the combination of thrombin and AngII resulted in their synergistic/allosteric action. Moreover, AngII/AT1R potentiated the maximal thrombin responses, suggesting specific conformational changes within the AT1R-PAR1 complex. Overall, our data confirm the functional AT1R-PAR1 interplay and further support the implication of both AT1R and PAR1 protomers in their synergistic interaction as previously reported.

Abstract P245: Activation Of Protease-activated Receptors 1 Leads To Structural Changes In Immortalized Cultured Human Podocytes.

Previous studies have suggested that activation of the protease-activated receptors (PAR) exacerbates the development of diabetic nephropathy. PARs are transmembrane proteins activated by extracellular serine proteases, such as thrombin and trypsin, which are frequently elevated in disease states. We hypothesize that serine protease activation of the PAR1 signaling cascade upregulates calcium channel activity and promotes excessive intracellular Ca 2+ ([Ca 2+ ] i ), leading to podocyte foot retraction, apoptosis, and glomerular filtration barrier (GFB) damage. Immunofluorescent labeling revealed the co-localization of PAR1 and podocyte marker nephrin in freshly isolated human glomeruli. To explore the functional role of PAR1 mediated signaling, we used an immortalized cultured human podocyte (hPod) cell line. Live confocal imaging revealed rapid elevation of [Ca 2+ ] i in response to a PAR1 specific agonist (TFLLR-NH 2 ). Moreover, preincubation with a PAR1 antagonist (RWJ 56100) completely blocked this effect (1616±48 vs. 206±135 a.u., for TFLLR vs. TFLLR+RJW, n&lt;100 cells, p&lt;0.05). Furthermore, we tested potential downstream signaling proteins in hPod cells after PAR1 activation using Western blot analysis. Application of TFLLR-NH 2 led to a decrease in PAR1 expression due to internalization and lysosomal degradation, accompanied by an increase in TRPC6 expression and time-dependent changes in p-ERK1/2 and PLC-γ1 cascades. We further used scanning ion-conductance microscopy (SICM) to detect morphological changes in podocytes, which measures real-time surface topography in hPod cells. This imaging revealed normal protrusion of lamellipodium under control conditions. In contrast, PAR1 activation led to retraction of the lamellipodium, and a significant decrease in surface area (+51±46 vs. -15±8 μm 2 , 30 min after application of vehicle or TFLLR, respectively; n=5, p&lt;0.05). Our studies suggested that PAR1 is involved in GPCR-induced calcium influx in podocytes. Furthermore, these data demonstrate that PAR1-mediated signaling is involved in podocyte structural alterations and may increase [Ca 2+ ] i , potentially leading to loss of GFB integrity and podocyte apoptosis.

Kallikrein 5 Inhibition by the Lympho-Epithelial Kazal-Type Related Inhibitor Hinders Matriptase-Dependent Carcinogenesis.

Simple SummaryHead and neck squamous cell carcinomas (HNSCC) are among the most common cancers worldwide. In contrast to the advances in prevention and treatment of other types of cancer, the five-year survival rate for HNSCC is only about 50% and it has not changed for the past 50 years. This poor prognosis is mainly due to a shortage of suitable markers for early detection, delayed diagnosis and/or referral, and ineffectiveness of chemotherapy. The aim of this study was to explore the inhibitory role of LEKTI in matriptase-dependent squamous cell carcinogenesis and to investigate additional players operating in this pathway. We found that Kallikrein-5 is necessary for PAR-2-mediated IL-8 release, YAP1-TAZ/TEAD activation, and matriptase-mediated oral squamous cell carcinoma migration. This knowledge can contribute for the development of future targeted therapy in HNSCC.Head and neck squamous cell carcinoma remains challenging to treat with no improvement in survival rates over the past 50 years. Thus, there is an urgent need to discover more reliable therapeutic targets and biomarkers for HNSCC. Matriptase, a type-II transmembrane serine protease, induces malignant transformation in epithelial stem cells through proteolytic activation of pro-HGF and PAR-2, triggering PI3K-AKT-mTOR and NFKB signaling. The serine protease inhibitor lympho-epithelial Kazal-type-related inhibitor (LEKTI) inhibits the matriptase-driven proteolytic pathway, directly blocking kallikreins in epithelial differentiation. Hence, we hypothesized LEKTI could inhibit matriptase-dependent squamous cell carcinogenesis, thus implicating kallikreins in this process. Double-transgenic mice with simultaneous expression of matriptase and LEKTI under the keratin-5 promoter showed a prominent rescue of K5-Matriptase+/0 premalignant phenotype. Notably, in DMBA-induced SCC, heterotopic co-expression of LEKTI and matriptase delayed matriptase-driven tumor incidence and progression. Co-expression of LEKTI reverted altered Kallikrein-5 expression observed in the skin of K5-Matriptase+/0 mice, indicating that matriptase-dependent proteolytic pathway inhibition by LEKTI occurs through kallikreins. Moreover, we showed that Kallikrein-5 is necessary for PAR-2-mediated IL-8 release, YAP1-TAZ/TEAD activation, and matriptase-mediated oral squamous cell carcinoma migration. Collectively, our data identify a third signaling pathway for matriptase-dependent carcinogenesis in vivo. These findings are critical for the identification of more reliable biomarkers and effective therapeutic targets in Head and Neck cancer.