The cardiovascular actions of protease-activated receptors

Acetaminophen Overdose Reveals Protease-Activated Receptor 4 as a Low-Expressing but Potent Receptor on the Hepatic Endothelium

Background & Aims

Hepatic endothelial cell (EC) dysfunction and centrilobular hepatocyte necrosis occur with acetaminophen (APAP) overdose. The protease thrombin, which is acutely generated during APAP overdose, can signal through protease-activated receptors 1 and 4 (PAR1/PAR4). PAR1 is a high-affinity thrombin receptor that is known to signal on ECs, whereas PAR4 is a low-affinity thrombin receptor, and evidence for its expression and function on ECs is mixed. This study aims to exploit the high levels of thrombin generated during APAP overdose to determine (1) if hepatic endothelial PAR4 is a functional receptor, and (2) endothelial-specific functions for PAR1 and PAR4 in a high thrombin setting.

Methods

We generated mice with conditional deletion(s) of Par1/Par4 in ECs and overdosed them with APAP. Hepatic vascular permeability, erythrocyte congestion/bleeding, and liver function were assessed following overdose. Additionally, we investigated the expression levels of endothelial PARs and how they influence transcription in APAP-overdosed liver ECs using endothelial Translating Ribosome Affinity Purification followed by next-generation sequencing (TRAPseq).

Results

We found that mice deficient in high-expressing endothelial Par1 or low-expressing Par4 had equivalent reductions in APAP-induced hepatic vascular instability but no effect on hepatocyte necrosis. Additionally, mice with loss of endothelial Par1 and Par4 had reduced permeability at an earlier time point after APAP overdose when compared to mice singly deficient in either receptor in ECs. We also found that endothelial PAR1-but not PAR4-can regulate transcription in hepatic ECs.

Conclusions

Low-expressing PAR4 can react similarly to high-expressing PAR1 in APAP-overdosed hepatic ECs, demonstrating that PAR4 is a potent thrombin receptor. Additionally, these receptors are functionally redundant but act divergently in their expression and ability to influence transcription in hepatic ECs.

NOMENCLATURE

F2r and F2rl3 are the gene names for PAR1 and PAR4, respectively. For simplicity, we hereafter refer to these genes as Par1 and Par4 .

Mechanism of Hirudin-Mediated Inhibition of Proliferation in Ovarian Cancer Cells

To investigate the inhibitory effect of hirudin on the cell proliferation of human ovarian cancer A2780 cells by preventing thrombin and its underlying molecular mechanism. Cell Counting Kit-8 (CCK-8) method was used to detect the effect of different concentrations of hirudin and thrombin on the cell proliferation of A2780 cells. PAR-1 wild-type overexpression plasmid was constructed utilizing enzyme digestion identification, and it was transferred to A2780 cells. Sequencing and Western blot were used to detect the changes in PAR-1 protein expression. Western blot detection of PKCα protein phosphorylation in A2780 cells was performed. We also implemented quantitative PCR to detect the mRNA expression levels of epithelial-mesenchymal transition (EMT)-related genes, CDH2, Snail, and Vimentin, in A2780 cells. 1 μg/ml hirudin treatment maximally inhibited the promotion of A2780 cell proliferation by thrombin. Hirudin inhibited the binding of thrombin to the N-terminus of PAR-1, hindered PKCα protein phosphorylation in A2780 cells, and downregulated the mRNA expression levels of CDH2, Snail, and Vimentin. In conclusion, hirudin inhibits the cell proliferation of ovarian cancer A2780 cells, and the underlying mechanism may be through downregulating the transcription level of EMT genes, CDH2, Snail, and Vimentin. This study indicates that hirudin may have a therapeutic potential as an anti-cancer agent for ovarian cancer.

Coagulation Factor Xa Has No Effects on the Expression of PAR1, PAR2, and PAR4 and No Proinflammatory Effects on HL-1 Cells

Atrial fibrillation (AF), characterised by irregular high-frequency contractions of the atria of the heart, is of increasing clinical importance. The reasons are the increasing prevalence and thromboembolic complications caused by AF. So-called atrial remodelling is characterised, among other things, by atrial dilatation and fibrotic remodelling. As a result, AF is self-sustaining and forms a procoagulant state. But hypercoagulation not only appears to be the consequence of AF. Coagulation factors can exert influence on cells via protease-activated receptors (PAR) and thereby the procoagulation state could contribute to the development and maintenance of AF. In this work, the influence of FXa on Heart Like-1 (HL-1) cells, which are murine adult atrial cardiomyocytes (immortalized), was investigated. PAR1, PAR2, and PAR4 expression was detected. After incubations with FXa (5-50 nM; 4-24 h) or PAR1- and PAR2-agonists (20 µM; 4-24 h), no changes occurred in PAR expression or in the inflammatory signalling cascade. There were no time- or concentration-dependent changes in the phosphorylation of the MAP kinases ERK1/2 or the p65 subunit of NF-κB. In addition, there was no change in the mRNA expression of the cell adhesion molecules (ICAM-1, VCAM-1, fibronectin). Thus, FXa has no direct PAR-dependent effects on HL-1 cells. Future studies should investigate the influence of FXa on human cardiomyocytes or on other cardiac cell types like fibroblasts.

Prophylactic rivaroxaban in the early post-discharge period reduces the rates of hospitalization for atrial fibrillation and incidence of sudden cardiac death during long-term follow-up in hospitalized COVID-19 survivors

Introduction: While acute Coronavirus disease 2019 (COVID-19) affects the cardiovascular (CV) system according to recent data, an increased CV risk has been reported also during long-term follow-up (FU). In addition to other CV pathologies in COVID-19 survivors, an enhanced risk for arrhythmic events and sudden cardiac death (SCD) has been observed. While recommendations on post-discharge thromboprophylaxis are conflicting in this population, prophylactic short-term rivaroxaban therapy after hospital discharge showed promising results. However, the impact of this regimen on the incidence of cardiac arrhythmias has not been evaluated to date. Methods: To investigate the efficacy of this therapy, we conducted a single center, retrospective analysis of 1804 consecutive, hospitalized COVID-19 survivors between April and December 2020. Patients received either a 30-day post-discharge thromboprophylaxis treatment regimen using rivaroxaban 10 mg every day (QD) (Rivaroxaban group (Riva); n = 996) or no thromboprophylaxis (Control group (Ctrl); n = 808). Hospitalization for new atrial fibrillation (AF), new higher-degree Atrioventricular-block (AVB) as well as incidence of SCD were investigated in 12-month FU [FU: 347 (310/449) days]. Results: No differences in baseline characteristics (Ctrl vs Riva: age: 59.0 (48.9/66.8) vs 57 (46.5/64.9) years, p = n.s.; male: 41.5% vs 43.7%, p = n.s.) and in the history of relevant CV-disease were observed between the two groups. While hospitalizations for AVB were not reported in either group, relevant rates of hospitalizations for new AF (0.99%, n = 8/808) as well as a high rate of SCD events (2.35%, n = 19/808) were seen in the Ctrl. These cardiac events were attenuated by early post-discharge prophylactic rivaroxaban therapy (AF: n = 2/996, 0.20%, p = 0.026 and SCD: n = 3/996, 0.30%, p < 0.001) which was also observed after applying a logistic regression model for propensity score matching (AF: χ ²-statistics = 6.45, p = 0.013 and SCD: χ ²-statistics = 9.33, p = 0.002). Of note, no major bleeding complications were observed in either group. Conclusion: Atrial arrhythmic and SCD events are present during the first 12 months after hospitalization for COVID-19. Extended prophylactic Rivaroxaban therapy after hospital discharge could reduce new onset of AF and SCD in hospitalized COVID-19 survivors.

Beneficial Effect of Edoxaban on Preventing Atrial Fibrillation and Coagulation by Reducing Inflammation via HBG1/HBD Biomarkers

Background: Atrial fibrillation (AF) is the most common cardiac arrhythmia. The effectiveness and mechanism of edoxaban in preventing stroke after atrial fibrillation remain unclear.

Methods: The expressions of HBG1 and HBD in red blood cells were tested in AF. Sixty C57B/6J mice were randomly divided into the following groups: the control (CON) group, atrial fibrillation (AF) group, AF + edoxaban group, and AF + rivaroxaban group. H&E staining assay and reticular fiber staining were performed. Myocardial fibrosis was evaluated by the Masson staining assay, Sirius red staining assay, and immunohistochemical assay for the expressions of α-SMA and COL1A1. ELISA and RT-PCR assay were performed for the detection of inflammatory parameters (TNF-α, IL-1β, IL-6, and IL-10). Blood lipids were detected by using the Beckman automatic biochemical analyzer. Furthermore, four items of coagulation were detected, and molecular docking among HBG1, HBD, and MASP1 (Xa) was performed by PyMOL 2.1 software. The BP neural network model, cubic spline interpolation, and support vector machine model were constructed to predict prothrombin time based on HBG1 and HBD expressions. COIP assay was performed to construct the interaction between HBG1 and HBD. The functional enrichment analysis was performed by DAVID and Metascape tools.

Results: The expressions of HBG1 and HBD in red blood cells of the patients with atrial fibrillation were decreased. The results showed a lower level of hemoglobin in red blood cells with HBG1-siRNA and HBG1-siRNA. Compared with the AF group, the collagen fiber percentage in the AF + edoxaban group was decreased (p < 0.05). After using edoxaban, the expressions of TNF-α, IL-1β, IL-6, and IL-10 were significantly decreased (p < 0.05). The LDL-C, TC, and TG levels were downregulated in the AF + edoxaban group. The PT and APTT levels in the AF + edoxaban group were more increasing than in the AF mice (p < 0.05). Compared with the AF group, the expressions of HBG1 and HBD were downregulated in the AF + edoxaban group (p < 0.05). HBG1 protein matched well with HBD and MASP1(Xa) protein surfaces. There exists a significant interaction between HBG1, HBD, and PT via the BP neural network and support vector machine. Enrichment analysis showed that HBG1 and HBD were mainly enriched in blood coagulation.

Conclusion: Edoxaban could prevent atrial fibrillation and coagulation by reducing inflammation, lipids, and fibrosis via HBG1/HBD biomarkers effectively, and the effect was superior to that of rivaroxaban.

Rivaroxaban attenuates cardiac hypertrophy by inhibiting protease-activated receptor-2 signaling in renin-overexpressing hypertensive mice

Rivaroxaban (Riv), a direct factor Xa (FXa) inhibitor, exerts anti-inflammatory effects in addition to anticoagulation. However, its role in cardiovascular remodeling is largely unknown. We tested the hypothesis that Riv attenuates the progression of cardiac hypertrophy and fibrosis induced by continuous activation of the renin-angiotensin system (RAS) in renin-overexpressing hypertensive transgenic (Ren-Tg) mice. We treated 12-week-old male Ren-Tg and wild-type (WT) mice with a diet containing Riv (12 mg/kg/day) or a regular diet for 4 weeks. After this, FXa in plasma significantly increased in Ren-Tg mice compared with WT mice, and Riv inhibited this increase. Left ventricular wall thickness (LVWT) and the area of cardiac fibrosis evaluated by Masson's trichrome staining were greater in Ren-Tg mice than in WT mice, and Riv decreased them. Cardiac expression levels of the protease-activated receptor (PAR)-2, tumor necrosis factor-α, transforming growth factor (TGF)-β1, and collagen type 3 α1 (COL3A1) genes were all greater in Ren-Tg mice than in WT mice, and Riv attenuated these increases. To investigate the possible involvement of PAR-2, we treated Ren-Tg mice with a continuous subcutaneous infusion of 10 μg/kg/day of the PAR-2 antagonist FSLLRY for 4 weeks. FSLLRY significantly decreased LVWT and cardiac expression of PAR-2, TGF-β1, and COL3A1. In isolated cardiac fibroblasts (CFs), Riv or FSLLRY pretreatment inhibited the FXa-induced increase in the phosphorylation of extracellular signal-regulated kinases. In addition, Riv or FSLLRY inhibited FXa-stimulated wound closure in CFs. Riv exerts a protective effect against cardiac hypertrophy and fibrosis development induced by continuous activation of the RAS, partly by inhibiting PAR-2.

Novel Targets for Hypertension Drug Discovery

PURPOSE OF REVIEW

Despite the availability of various medications and prescribing combination therapies, uncontrolled blood pressure and resistance are observed in more than 40% of patients. The purpose of this review is to discuss emerging novel approaches for the treatment of hypertension and propose future research and clinical directions.

RECENT FINDINGS

Hypertension is a common disease of the cardiovascular system which may arise solely or as a comorbidity of other disorders. It is a crucial risk factor for cardiovascular diseases such as coronary artery disease, myocardial infarction, congestive heart failure, renal failure, and stroke. The results from current literature regarding the novel approaches showed several targets that could be explored as potential therapeutic options. These include toll-like receptor 4, a critical regulator of angiotensin II-induced hypertension; protease-activated receptor 2, which promotes collagen deposition and inflammatory responses; chemerin, which causes metabolic and obesity-associated hypertension; apelin receptor; transient receptor potential melastatin; urotensin-II; and Tie2 receptor. This review discusses various targets and pathways that could be emerging pharmacological therapies for hypertension.

Comparison of Inflammatory Mediators in Patients With Atrial Fibrillation Using Warfarin or Rivaroxaban

Background: Atrial fibrillation (AF) is the most common arrhythmia associated with high risk of venous thromboembolism. Inflammatory mechanisms may be involved in the pathophysiology of AF and in the AF-related thrombogenesis, and patients with AF might benefit from the use of anticoagulants with anti-inflammatory properties. However, the evidence is still scarce, and it points out the need of trials seeking to investigate the levels of inflammatory mediators in patients with AF under different anticoagulant therapies. Therefore, this study was designed to define whether patients with AF treated either with an activated coagulation factor X (FXa) inhibitor (rivaroxaban) or with a vitamin K inhibitor (warfarin) present changes in peripheral levels of inflammatory mediators, mainly cytokines and chemokines. Methods: A total of 127 subjects were included in this study, divided into three groups: patients with non-valvular atrial fibrillation (NVAF) using warfarin (N = 42), patients with NVAF using rivaroxaban (N = 29), and controls (N = 56). Plasma levels of inflammatory mediators were quantified by immunoassays. Results: Patients with AF (both warfarin and rivaroxaban groups) presented increased levels of inflammatory cytokines in comparison with controls. The use of rivaroxaban was associated with decreased levels of inflammatory cytokines in comparison with warfarin. On the other hand, patients with AF using rivaroxaban presented increased levels of the chemokines (MCP-1 in comparison with warfarin users; MIG and IP-10 in comparison with controls). Conclusions: AF is associated with an inflammatory profile that was less pronounced in patients on rivaroxaban in comparison with warfarin users. Further studies are necessary to assess the clinical implications of our results and whether patients with AF would benefit from rivaroxaban anti-inflammatory effects.

Rivaroxaban, a Direct Factor Xa Inhibitor, Ameliorates Hypertensive Renal Damage Through Inhibition of the Inflammatory Response Mediated by Protease-Activated Receptor Pathway

Background

An enhanced renin‐angiotensin system causes hypertensive renal damage. Factor Xa not only functions in the coagulation cascade but also activates intracellular signaling through protease‐activated receptors (PAR). We investigated the effects of rivaroxaban, a factor Xa inhibitor, on hypertensive renal damage in hypertensive mice overexpressing renin (Ren‐TG).

Methods and Results

The 12‐ to 16‐week‐old Ren‐TG and wild‐type mice were orally administered with or without 6 or 12 mg/kg of rivaroxaban for 1 or 4 months. Plasma factor Xa was significantly increased in the Ren‐TG compared with the wild‐type mice and was reduced by 12 mg/kg of rivaroxaban (P<0.05). Urinary albumin excretion (UAE) was higher in the nontreated 8‐month‐old Ren‐TG than in the wild‐type mice (69.6±29 versus 20.1±8.2 μg/day; P<0.01). Treatment with 12 mg/kg of rivaroxaban for 4 months decreased the UAE to 38.1±13.2 μg/day (P<0.01). Moreover, rivaroxaban treatment attenuated histologic changes of glomerular hypertrophy, mesangial matrix expansion, effacement of the podocyte foot process, and thickened glomerular basement membrane in the Ren‐TG. The renal expression of PAR‐2 was increased in the Ren‐TG, but was inhibited with rivaroxaban treatment. In vitro study using the human podocytes showed that the expressions of PAR‐2 and inflammatory genes and nuclear factor–‐κB activation were induced by angiotensin II stimulation, but were inhibited by rivaroxaban. PAR‐2 knockdown by small interfering RNA also attenuated the PAR‐2‐related inflammatory gene expressions.

Conclusions

These findings indicate that rivaroxaban exerts protective effects against angiotensin II–induced renal damage, partly through inhibition of the PAR‐2 signaling‐mediated inflammatory response.

Proteinase-activated receptor 1 antagonism ameliorates experimental pulmonary hypertension

AIMS

Pulmonary hypertension (PH) is characterized by progressive increases in pulmonary vascular resistance (PVR). Thrombotic lesions are common pathological findings. The pulmonary artery has a unique property regarding the vasoconstrictive response to thrombin, which is mediated by proteinase-activated receptor 1 (PAR1). We aim to elucidate the role of PAR1 in the development and progression of PH.

METHODS AND RESULTS

A rat model of monocrotaline-induced PH and a mouse model of hypoxia (Hx)-induced PH were used to investigate the effects of atopaxar (a PAR1 antagonist) and PAR1 knockout on haemodynamic parameters, right ventricular hypertrophy (RVH), vascular remodelling and survival. In perfused lung preparations, the pressor response to PAR1 agonist was significantly augmented in monocrotaline-induced PH. Both the preventive and therapeutic administration of atopaxar significantly inhibited the increase in PVR and the development of RVH and prolonged survival. A real-time PCR revealed that the level of PAR1 mRNA in the pulmonary artery was significantly higher than that in any of the systemic arteries examined in control rats, and the level was significantly up-regulated in monocrotaline-induced PH. PAR1 gene knockout significantly attenuated the haemodynamic and histological findings in the mouse model of Hx-induced PH.

CONCLUSION

The specific expression of PAR1 in the pulmonary artery and its up-regulation were suggested to play a critical role in the development and progression of experimental PH in murine models. PAR1 is a potential therapeutic target for the treatment of PH.

Factor Xa Inhibition by Rivaroxaban Modified Mitochondrial-Associated Proteins in Human Abdominal Aortic Aneurysms

BACKGROUND

The presence of intraluminal thrombus and mitochondrial dysfunction in human abdominal aortic aneurysms (AAAs) have been associated with aneurysmal growth and rupture. The objective of the study was to study if endogenous factor Xa (FXa) may modulate mitochondrial functionality and expression of proteins associated with mitophagy in human AAAs.

METHODS

AAA sites with intraluminal thrombus were obtained from 6 patients undergoing elective AAA surgery repair. Control samples were collected from 6 organ donors. The effect of FXa was analyzed by in vitro incubation of AAA with 50 nmol/L rivaroxaban, an oral FXa inhibitor.

RESULTS

The enzymatic activities of citrate synthase, a biomarker of mitochondrial density, and cytochrome C oxidase, a biomarker of mitochondrial respiratory chain functionality, were significantly reduced in the AAA sites with respect to the healthy aorta (citrate synthase activity in μU/min/μg protein: control: 3.51 ± 0.22 vs. AAA: 0.37 ± 0.15.; P < 0.01; cytochrome C oxidase activity in μOD/min/μg protein: control: 8.05 ± 1.57 vs. AAA: 3.29 ± 1.05; P < 0.05). The addition of rivaroxaban to AAA reverted the activity of both citrate synthase and cytochrome C oxidase to similar values to control. Mitochondrial Drp-1 expression was higher in AAA sites than in either control aortas or rivaroxaban-incubated AAA sites. Cytosolic content of Drp-1 phosphorylated at Ser637, mitochondrial Parkin, and mitochondrial PINK1-Parkin interaction were significantly reduced in the AAA sites with respect to control aortas. For all these parameters, rivaroxaban-incubated AAA showed similar values compared with control aortas.

CONCLUSIONS

In human AAA, rivaroxaban improved mitochondrial functionality that was associated with changes in proteins related to mitophagy. Its opens possible new effects of endogenous FXa on the mitochondria in the human AAA site.

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.

Tissue kallikrein-related peptidase8 protects rat heart against acute ischemia reperfusion injury

Tissue kallikrein-related peptidases (KLKs) play important roles in acute cardiac injury and cardiac remodeling. However, the exact cardiac actions of KLK8 have not been determined. Transgenic rat overexpressing KLK8 was established to examine the role of KLK8 in the heart. Cardiac injury was induced by ischemia/reperfusion (I/R) and examined by infarct size measurement and TUNEL staining. The molecular mechanisms were investigated in cultured neonatal rat cardiomyocytes (CMs). Western blot analysis was used to determine the protein levels. KLK8 protein level was significantly increased in the cardiac ischemic risk area. KLK8 overexpression mitigated I/R-induced cardiac injury, as evidenced by decreased infarct size and apoptosis in cardiac ischemic risk area in vivo. Via in vitro studies, it was found that KLK8 overexpression attenuated the Hypoxia/Reoxygenation (H/R) injury in CMs; both B2R and PAR2 antagonist significantly attenuated KLK8-induced protective actions under H/R injury. Moreover, KLK8 overexpressed CMs showed significant higher phosphorylation levels of Akt, ERK1/2 and PKA under H/R stimulation; B2R antagonist attenuated the phosphorylation levels of Akt and ERK1/2, while PAR2 antagonist attenuated the phosphorylation levels of PKA and ERK1/2. KLK8 protects the heart against I/R-induced cardiac injury, which may represent a new therapeutic target in cardiac medicine.

Coagulation factor XI induces Ca2+ response and accelerates cell migration in vascular smooth muscle cells via proteinase-activated receptor 1

Activated coagulation factor XI (FXIa) is a serine proteinase that plays a key role in the intrinsic coagulation pathway. The analysis of FXI-knockout mice has indicated the contribution of FXI to the pathogenesis of atherosclerosis. However, the underlying mechanism remains unknown. We hypothesized that FXIa exerts vascular smooth muscle effects via proteinase-activated receptor 1 (PAR₁). Fura-2 fluorometry revealed that FXIa elicited intracellular Ca²⁺ signal in rat embryo aorta smooth muscle A7r5 cells. The influx of extracellular Ca²⁺ played a greater role in generating Ca²⁺ signal than the Ca²⁺ release from intracellular stores. The FXIa-induced Ca²⁺ signal was abolished by the pretreatment with atopaxar, an antagonist of PAR₁, or 4-amidinophenylmethanesulfonyl fluoride (p-APMSF), an inhibitor of proteinase, while it was also lost in embryonic fibroblasts derived from PAR₁^-/- mice. FXIa cleaved the recombinant protein containing the extracellular region of PAR₁ at the same site (R45/S46) as that of thrombin, a canonical PAR₁ agonist. The FXIa-induced Ca²⁺ influx was inhibited by diltiazem, an L-type Ca²⁺ channel blocker, and by siRNA targeted to Ca_V1.2. The FXIa-induced Ca²⁺ influx was also inhibited by GF109203X and rottlerin, inhibitors of protein kinase C. In a wound healing assay, FXIa increased the rate of cell migration by 2.46-fold of control, which was partly inhibited by atopaxar or diltiazem. In conclusion, FXIa mainly elicits the Ca²⁺ signal via the PAR₁/Ca_V1.2-mediated Ca²⁺ influx and accelerates the migration in vascular smooth muscle cells. The present study provides the first evidence that FXIa exerts a direct cellular effect on vascular smooth muscle.

Are anticoagulants still indicated in pulmonary arterial hypertension?

Pulmonary arterial hypertension (PAH) is a type of pulmonary hypertension that is a progressive, fatal disease. Multiple underlying mechanisms for PAH have been identified, including vasoconstriction, intimal proliferation, medial hypertrophy, inflammation, mitochondrial dysfunction, and in situ thrombosis. Because it is an uncommon disease, it has been challenging to identify a specific treatment that targets the dominant disease mechanism in a given patient. Early success demonstrating that some patients (approximately 10%) possess pulmonary vasoreactivity at diagnosis has driven the development of pulmonary vasodilators as the mainstay of treatment. However, while they improve exercise tolerance in clinical trials, their effect on survival is limited. Therapies that target underlying disease mechanisms that affect a majority of patients are clearly needed if we are to significantly improve overall survival.

In the actual guidelines, chronic anticoagulation is no longer recommended in patients with idiopathic, hereditary, and drug-induced PAH although there is much indirect evidence for this.

There are data from over 40 years which include: (1) pathology studies showing the presence of thrombotic lesions in a majority of patients with PAH, both idiopathic and associated with many other conditions; (2) a similar frequency of thrombotic lesions in patients treated with pulmonary vasodilators as was seen in the years before their use; (3) mechanistic studies showing that procoagulant conditions predispose to the development of intraluminal thrombosis that contributes to vascular remodeling and the progressive nature of the pathologic changes; and (4) observational studies that, with one exception, have demonstrated a substantial survival advantage in patients with PAH treated with oral anticoagulation.

Acknowledging that no prospective randomized trial with anticoagulants has ever been done, we recommend a pragmatic approach to the use of anticoagulants in PAH. We suggest that the risks and benefits of chronic anticoagulation be considered in individual patients, and that warfarin be prescribed in patients with PAH, unless they have an increased risk of bleeding.

The question of whether direct oral anticoagulants (DOACs) would provide the same benefit as vitamin K antagonists is valid, but presently there are no data at all regarding their use in PAH. However, in patients with PAH in whom warfarin anticoagulation management proves problematic, it is reasonable to switch the patient to a DOAC as is current practice for other conditions.

Protease-activated receptor 1 activation enhances doxorubicin-induced cardiotoxicity

OBJECTIVE

The anti-cancer anthracycline drug Doxorubicin (Dox) causes cardiotoxicity. We investigated the role of protease-activated receptor 1 (PAR-1) in Dox-induced cardiotoxicity.

METHODS AND RESULTS

In vitro experiments revealed that PAR-1 enhanced Dox-induced mitochondrial dysfunction, reactive oxygen species and cell death of cardiac myocytes and cardiac fibroblasts. The contribution of PAR-1 to Dox-induced cardiotoxicity was investigated by subjecting PAR-1^-/- mice and PAR-1^+/+ mice to acute and chronic exposure to Dox. Heart function was measured by echocardiography. PAR-1^-/- mice exhibited significant less cardiac injury and dysfunction compared to PAR-1^+/+ mice after acute and chronic Dox administration. PAR-1^-/- mice had reduced levels of nitrotyrosine, apoptosis and inflammation in their heart compared to PAR-1^+/+ mice. Furthermore, inhibition of PAR-1 in wild-type mice with vorapaxar significantly reduced the acute Dox-induced cardiotoxicity.

CONCLUSION

Our results indicate that activation of PAR-1 contributes to Dox-induced cardiotoxicity. Inhibition of PAR-1 may be a new approach to reduce Dox-induced cardiotoxicity in cancer patients.

Thrombin-Induced Responses via Protease-Activated Receptor 1 Blocked by the Endothelium on Isolated Porcine Retinal Arterioles

PURPOSE

Thrombin, a serine protease, causes organ-specific responses to vessels. However, the mechanism by which thrombin affects the retinal microcirculation remains unclear. We examined the effects of thrombin on the retinal microvasculature and signaling mechanisms.

METHODS

Porcine retinal arterioles were isolated, cannulated, and pressurized (55 cmH₂O) without flow in this in vitro study. Videomicroscopy techniques recorded changes in diameter in the retinal arterioles in response to thrombin at concentrations ranging from 0.001 to 20 mU/ml.

RESULTS

Extraluminal administration of thrombin induced concentration-dependent vascular responses, that is, vasoconstriction at low concentrations less than 5 mU/ml and vasorelaxation with high concentrations greater than 5 mU/ml. However, intraluminal administration of thrombin (5 mU/m) did not constrict the retinal arterioles; in denuded vessels, intraluminal administration constricted the retinal arterioles. Thrombin-induced vasoconstriction was significantly (p < 0.01) suppressed by pretreatment with a protein kinase C (PKC) inhibitor and a protease-activated receptor (PAR)-1 inhibitor but not by PAR-2 and PAR-4 inhibitors or denudation. A rho kinase (ROCK) inhibitor also suppressed thrombin-induced vasoconstriction (5 mU/ml) compared with sodium nitroprusside. Endothelial denudation and pretreatment with an endothelial nitric oxide (NO) synthase inhibitor suppressed vasorelaxation caused by a high concentration of thrombin.

CONCLUSIONS

A low concentration of thrombin causes vasoconstriction of smooth muscles via PAR-1, PKC, and ROCK, and a high concentration of thrombin possibly causes vasorelaxation of the retinal arterioles via nitric oxide synthase activation in the endothelium. The vascular endothelium might block signaling of thrombin-induced vasoconstriction in the retinal arterioles when administered intraluminally.

Pleiotropic effects of the hemostatic system

Atherothrombosis is characterized by the inflammatory process of atherosclerosis combined with a hypercoagulable state leading to superimposed thrombus formation. In atherosclerotic plaques, cell signaling can occur via protease-activated receptors (PARs), four of which have been identified so far (PAR1-PAR4). Proteases that are able to activate PARs can be produced systemically, but also at the sites of lesions, and they include thrombin and activated factor X. After PAR activation, downstream signaling can lead to both proinflammatory effects and a hypercoagulable state. Which specific effect occurs depends on the type of protease and activated PAR, and the site of activation. Hypercoagulable effects are mainly exerted through PAR1 and PAR4, whereas proinflammatory responses are mostly seen after PAR1 and PAR2 activation. PAR signaling pathways contribute to atherothrombosis, suggesting that inhibition of these pathways possibly prevents cardiovascular events based on this pathophysiological mechanism. In this review, we highlight the pathways by which PAR activation leads to proinflammatory responses and a hypercoagulable state. Furthermore, we give an overview of potential pharmacological treatment targets that promote vascular protection.

Thrombin induces protease-activated receptor 1 signaling and activation of human atrial fibroblasts and dabigatran prevents these effects

BACKGROUND

Data with animal cells and models suggest that thrombin activates cardiac fibroblasts (Fib) to myofibroblasts (myoFib) via protease-activated receptor 1 (PAR1) cleavage, and in this way promotes adverse atrial remodeling and, thereby, atrial fibrillation (AF).

OBJECTIVE

Here, we explored the effects of thrombin on human atrial Fib and whether they are antagonized by the clinically available direct thrombin inhibitor, dabigatran.

METHODS

Fib isolated from atrial appendages of patients without AF undergoing elective cardiac surgery were evaluated for PAR expression and treated with thrombin with or without dabigatran. PAR1 cleavage, downstream signaling and myoFib markers were investigated by immunofluorescence and Western blot. Collagen synthesis, activity of matrix metalloprotease (MMP)-2 and proliferation were assessed by Picro-Sirius red staining, gelatinolytic zymography and BrdU incorporation, respectively. Fib function was studied as capability to contract a collagen gel and stimulate the chemotaxis of peripheral blood monocytes from healthy volunteers.

RESULTS

Primary human atrial Fib expressed PAR1, while levels of the other PARs were very low. Thrombin triggered PAR1 cleavage and phosphorylation of ERK1/2, p38 and Akt, elicited a switch to myoFib enriched for αSMA, fibronectin and type I collagen, and induced paracrine/autocrine transforming growth factor beta-1, cyclooxygenase-2, endothelin-1 and chemokine (C-C motif) ligand 2 (CCL2); conversely, MMP-2 activity decreased. Thrombin-primed cells displayed enhanced proliferation, formed discrete collagen-containing cellular nodules, and stimulated the contraction of a collagen gel. Furthermore, their conditioned medium caused monocytes to migrate. All these effects were prevented by dabigatran.

CONCLUSION

These results with human cells complete the knowledge about thrombin actions on cardiac Fib and strengthen the translational potential of the emerging paradigm that pharmacological blockade of thrombin may counteract molecular and cellular events underlying AF.

Why we should not skip aspirin in cardiovascular prevention

Since more than 20 years, aspirin is an approved and established first-line antiplatelet medication in cardiovascular prevention. This is partially due to ist unique mode of action which is not shared with any other antiplatelet agent as well by the reliability of its pharmacological efficacy: inhibition of platelet COX-1 and subsequent thromboxane formation in almost every patient. Aspirin acts synergistic with ADP-antagonists in dual antiplatelet therapy of acute coronary syndroms (ACS) and percutaneous coronary interventions (PCI) and is also approved for long-term secondary prevention. Patients with atrial fibrillation are an exception and benefit more from anticoagulants. After the introduction of the new oral anticoagulants (NOACs), i.e. direct inhibitors of factor Xa or thrombin formation, there is a renewed discussion about the role of antiplatelet agents, specifically if additional dual antiplatelet treatment is still necessary for an optimum clinical effect or whether one component, such as aspirin might be skipped in favor of other classes of oral antiplatelet agents, such as ADP-antagonists. The available data are insufficient to recommend this because of a low number of studies and a still uncertain benefit/ risk (bleeding) ratio. More research on aspirin as a chemopreventive appears also to be necessary and is going on, in particular in individuals at high-risk for vascular thrombotic diseases (diabetics, preeclampsia, venous thrombembolism).

Cyclic Nucleotide-Directed Protein Kinases in Cardiovascular Inflammation and Growth

Cardiovascular disease (CVD), including myocardial infarction (MI) and peripheral or coronary artery disease (PAD, CAD), remains the number one killer of individuals in the United States and worldwide, accounting for nearly 18 million (>30%) global deaths annually. Despite considerable basic science and clinical investigation aimed at identifying key etiologic components of and potential therapeutic targets for CVD, the number of individuals afflicted with these dreaded diseases continues to rise. Of the many biochemical, molecular, and cellular elements and processes characterized to date that have potential to control foundational facets of CVD, the multifaceted cyclic nucleotide pathways continue to be of primary basic science and clinical interest. Cyclic adenosine monophosphate (cyclic AMP) and cyclic guanosine monophosphate (cyclic GMP) and their plethora of downstream protein kinase effectors serve ubiquitous roles not only in cardiovascular homeostasis but also in the pathogenesis of CVD. Already a major target for clinical pharmacotherapy for CVD as well as other pathologies, novel and potentially clinically appealing actions of cyclic nucleotides and their downstream targets are still being discovered. With this in mind, this review article focuses on our current state of knowledge of the cyclic nucleotide-driven serine (Ser)/threonine (Thr) protein kinases in CVD with particular emphasis on cyclic AMP-dependent protein kinase (PKA) and cyclic GMP-dependent protein kinase (PKG). Attention is given to the regulatory interactions of these kinases with inflammatory components including interleukin 6 signals, with G protein-coupled receptor and growth factor signals, and with growth and synthetic transcriptional platforms underlying CVD pathogenesis. This article concludes with a brief discussion of potential future directions and highlights the importance for continued basic science and clinical study of cyclic nucleotide-directed protein kinases as emerging and crucial controllers of cardiac and vascular disease pathologies.

Deciphering Conformational Changes Associated with the Maturation of Thrombin Anion Binding Exosite I

Thrombin participates in procoagulation, anticoagulation, and platelet activation. This enzyme contains anion binding exosites, ABE I and ABE II, which attract regulatory biomolecules. As prothrombin is activated to thrombin, pro-ABE I is converted into mature ABE I. Unexpectedly, certain ligands can bind to pro-ABE I specifically. Moreover, knowledge of changes in conformation and affinity that occur at the individual residue level as pro-ABE I is converted to ABE I is lacking. Such changes are transient and were not captured by crystallography. Therefore, we employed nuclear magnetic resonance (NMR) titrations to monitor development of ABE I using peptides based on protease-activated receptor 3 (PAR3). Proton line broadening NMR revealed that PAR3 (44-56) and more weakly binding PAR3G (44-56) could already interact with pro-ABE I on prothrombin. ¹H-¹⁵N heteronuclear single-quantum coherence NMR titrations were then used to probe binding of individual ¹⁵N-labeled PAR3G residues (F47, E48, L52, and D54). PAR3G E48 and D54 could interact electrostatically with prothrombin and tightened upon thrombin maturation. The higher affinity for PAR3G D54 suggests the region surrounding thrombin R77a is better oriented to bind D54 than the interaction between PAR3G E48 and thrombin R75. Aromatic PAR3G F47 and aliphatic L52 both reported on significant changes in the chemical environment upon conversion of prothrombin to thrombin. The ABE I region surrounding the 30s loop was more affected than the hydrophobic pocket (F34, L65, and I82). Our NMR titrations demonstrate that PAR3 residues document structural rearrangements occurring during exosite maturation that are missed by reported X-ray crystal structures.

FXa inhibition by rivaroxaban modifies mechanisms associated with the pathogenesis of human abdominal aortic aneurysms

AIMS

To evaluate if rivaroxaban, an oral factor Xa (FXa) inhibitor, could modify the expression in vitro of inflammatory and oxidative stress biomarkers in abdominal aortic aneurysmal (AAA) sites showing intraluminal thrombus.

METHODS

AAA sites with intraluminal mural thrombus were obtained from six patients undergoing elective AAA repair. In addition, control abdominal aortic samples were obtained from six organ donors. AAA sites were incubated in the presence and absence of 50 nmol l^-1 rivaroxaban.

RESULTS

AAA sites showing thrombus demonstrated higher content of FXa than control. Interleukin-6 levels released from AAA [Control: median: 23.45 (interquartile range: 16.17-37.15) vs. AAA: median: 153.07 (interquartile range: 100.80-210.69) pg ml^-1  mg tissue^-1 , P < 0.05] and the expression levels of nitric oxide synthase 2 were significantly higher in AAA than in control. The protein expression level of NADPH oxidase subunits gp67-and gp91-phox, but did not gp47-phox, were also significantly higher in the AAA sites than in control. Addition of rivaroxaban to AAA sites explants significantly reduced the release of interleukin-6 [median: 51.61 (interquartile range: 30.87-74.03) pg ml^-1  mg tissue^-1 , P < 0.05 with respect to AAA alone] and the content of nitric oxide synthase 2, gp67 and gp91-phox NADPH subunits. The content of matrix metallopeptidase 9 was significantly higher in the AAA sites as compared to control. Rivaroxaban also reduced matrix metallopeptidase 9 content in AAA sites to similar levels to control.

CONCLUSIONS

FXa inhibition by rivaroxaban exerted anti-inflammatory and antioxidative stress properties in human AAA sites, suggesting a role of FXa in these mechanisms associated with the pathogenesis of AAA.

Metalloproteinase-9 contributes to endothelial dysfunction in atherosclerosis via protease activated receptor-1

The atherosclerotic process begins when vascular endothelial cells undergo pro-inflammatory changes such as aberrant activation to dysfunctional phenotypes and apoptosis, leading to loss of vascular integrity. Our laboratory has demonstrated that exposure of mice to second hand smoke triggers an increase in expression of metalloproteinase-9. Further, metalloproteinase-9 released by second hand smoke-activated leukocytes may propagate pro-atherogenic alterations in endothelial cells. We have shown that levels of metalloproteinase-9 were increased in the plasma from apolipoprotein E deficient (ApoE-/-) mice exposed to second hand smoke relative to non-exposed controls. Moreover, we have collected data from two different, but complementary, treatments of second hand smoke exposed atherosclerotic mice. Animals received either cell specific metalloproteinase-9 directed siRNA to minimize metalloproteinase-9 expression in neutrophils and endothelial cells, or a pharmacological inhibitor of Bruton's tyrosine kinase which indirectly limits metalloproteinase-9 production in neutrophils. These treatments reduced atherosclerotic changes in mice and improved overall vascular health. We also demonstrated that metalloproteinase-9 could activate endothelial cells and induce their apoptosis via cleavage of protease activated receptor-1. In summary, better understanding of metalloproteinase-9's pathogenic capabilities as well as novel signaling pathways involved may lead to development of treatments which may provide additional benefits to atherosclerosis patients with a history of second hand smoke exposure.

Protease-Activated Receptor 1 Contributes to Angiotensin II-Induced Cardiovascular Remodeling and Inflammation

BACKGROUND

Angiotensin II (Ang II) plays an important role in cardiovascular disease. It also leads to the activation of coagulation. The coagulation protease thrombin induces cellular responses by activating protease-activated receptor 1 (PAR-1). We investigated whether PAR-1 contributes to Ang II-induced cardiovascular remodeling and inflammation.

METHODS AND RESULTS

PAR-1+/+ (wild-type; WT) and PAR-1-/- mice were infused with Ang II (600 ng/kg/min) for up to 4 weeks. In WT mice, this dose of Ang II did not cause a significant increase in blood pressure but it did cause pathological changes in both the aorta and the heart. Ang II infusion resulted in vascular remodeling of the aorta, demonstrated by a significant increase in medial wall thickening and perivascular fibrosis. Importantly, both parameters were significantly attenuated by PAR-1 deficiency. Furthermore, perivascular fibrosis around coronary vessels was reduced in Ang II-treated PAR-1-/- mice compared to WT mice. In addition, PAR-1 deficiency significantly attenuated Ang II induction of inflammatory cytokines and profibrotic genes in the aortas compared to WT mice. Finally, PAR-1 deficiency had no effect on Ang II-induced heart hypertrophy. However, the heart function measured by fractional shortening was less impaired in PAR-1-/- mice than in WT mice.

CONCLUSION

Our data indicate that PAR-1 plays a significant role in cardiovascular remodeling mediated by a blood pressure-independent action of Ang II.

Direct Thrombin Inhibitors Prevent Left Atrial Remodeling Associated With Heart Failure in Rats

The present study tested the hypothesis that thrombin participates in formation of left atrial remodeling and that direct oral anticoagulants, such as direct thrombin inhibitors (DTIs), can prevent its progression. In a rat model of heart failure associated with left atrial dilation, we found that chronic treatment with DTIs reduces the atrial remodeling and the duration of atrial fibrillation (AF) episodes induced by burst pacing by inhibiting myocardial hypertrophy and fibrosis. In addition to the prevention of thromboembolism complicating AF, DTIs may be of interest to slow down the progression of the arrhythmogenic substrate.

Hypercoagulability causes atrial fibrosis and promotes atrial fibrillation

AIMS

Atrial fibrillation (AF) produces a hypercoagulable state. Stimulation of protease-activated receptors by coagulation factors provokes pro-fibrotic, pro-hypertrophic, and pro-inflammatory responses in a variety of tissues. We studied the effects of thrombin on atrial fibroblasts and tested the hypothesis that hypercoagulability contributes to the development of a substrate for AF.

METHODS AND RESULTS

In isolated rat atrial fibroblasts, thrombin enhanced the phosphorylation of the pro-fibrotic signalling molecules Akt and Erk and increased the expression of transforming growth factor β1 (2.7-fold) and the pro-inflammatory factor monocyte chemoattractant protein-1 (6.1-fold). Thrombin also increased the incorporation of ³H-proline, suggesting enhanced collagen synthesis by fibroblasts (2.5-fold). All effects could be attenuated by the thrombin inhibitor dabigatran. In transgenic mice with a pro-coagulant phenotype (TM^pro/pro), the inducibility of AF episodes lasting >1 s was higher (7 out of 12 vs. 1 out of 10 in wild type) and duration of AF episodes was longer compared with wild type mice (maximum episode duration 42.8 ± 68.4 vs. 0.23 ± 0.39 s). In six goats with persistent AF treated with nadroparin, targeting Factor Xa-mediated thrombin generation, the complexity of the AF substrate was less pronounced than in control animals (LA maximal activation time differences 23.3 ± 3.1 ms in control vs. 15.7 ± 2.1 ms in nadroparin, P < 0.05). In the treated animals, AF-induced α-smooth muscle actin expression was lower and endomysial fibrosis was less pronounced.

CONCLUSION

The hypercoagulable state during AF causes pro-fibrotic and pro-inflammatory responses in adult atrial fibroblasts. Hypercoagulability promotes the development of a substrate for AF in transgenic mice and in goats with persistent AF. In AF goats, nadroparin attenuates atrial fibrosis and the complexity of the AF substrate. Inhibition of coagulation may not only prevent strokes but also inhibit the development of a substrate for AF.

Inhibitory Effect of FXa on Secretory Group IIA Phospholipase A2

It is well known that the expression level of secretory group IIA phospholipase A2 (sPLA2-IIA) is elevated in inflammatory diseases and lipopolysaccharide (LPS) upregulates the expression of sPLA2-IIA in human umbilical vein endothelial cells (HUVECs). Activated factor X (FXa) is an important enzyme in the coagulation cascade responsible for thrombin generation, and it influences cell signaling in various cell types by activating protease-activated receptors (PARs). Here, FX or FXa was examined for its effects on the expression and activity of sPLA2-IIA in HUVECs and mouse. Prior treatment of cells or mouse with FXa inhibited LPS-induced expression and activity of sPLA2-IIA via interacting with FXa receptor (effective cell protease receptor-1, EPR-1). And FXa suppressed the activation of cytosolic phospholipase A2 (cPLA2) and extracellular signal-regulated kinase (ERK) 1/2 by LPS. Therefore, these results suggest that FXa may inhibit LPS-mediated expression of sPLA2-IIA by suppression of cPLA2 and ERK 1/2.

Kallikrein-related peptidase 8 is expressed in myocardium and induces cardiac hypertrophy

The tissue kallikrein-related peptidase family (KLK) is a group of trypsin- and chymotrypsin-like serine proteases that share a similar homology to parent tissue kallikrein (KLK1). KLK1 is identified in heart and has anti-hypertrophic effects. However, whether other KLK family members play a role in regulating cardiac function remains unknown. In the present study, we demonstrated for the first time that KLK8 was expressed in myocardium. KLK8 expression was upregulated in left ventricle of cardiac hypertrophy models. Both intra-cardiac adenovirus-mediated and transgenic-mediated KLK8 overexpression led to cardiac hypertrophy in vivo. In primary neonatal rat cardiomyocytes, KLK8 knockdown inhibited phenylephrine (PE)-induced cardiomyocyte hypertrophy, whereas KLK8 overexpression promoted cardiomyocyte hypertrophy via a serine protease activity-dependent but kinin receptor-independent pathway. KLK8 overexpression increased epidermal growth factor (EGF) production, which was blocked by the inhibitors of serine protease. EGF receptor (EGFR) antagonist and EGFR knockdown reversed the hypertrophy induced by KLK8 overexpression. KLK8-induced cardiomyocyte hypertrophy was also significantly decreased by blocking the protease-activated receptor 1 (PAR1) or PAR2 pathway. Our data suggest that KLK8 may promote cardiomyocyte hypertrophy through EGF signaling- and PARs-dependent but a kinin receptor-independent pathway. It is implied that different KLK family members can subtly regulate cardiac function and remodeling.

Protease-activated receptor 4 deficiency offers cardioprotection after acute ischemia reperfusion injury

Protease-activated receptor (PAR)4 is a low affinity thrombin receptor with less understood function relative to PAR1. PAR4 is involved in platelet activation and hemostasis, but its specific actions on myocyte growth and cardiac function remain unknown. This study examined the role of PAR4 deficiency on cardioprotection after myocardial ischemia-reperfusion (IR) injury in mice. When challenged by in vivo or ex vivo IR, PAR4 knockout (KO) mice exhibited increased tolerance to injury, which was manifest as reduced infarct size and a more robust functional recovery compared to wild-type mice. PAR4 KO mice also showed reduced cardiomyocyte apoptosis and putative signaling shifts in survival pathways in response to IR. Inhibition of PAR4 expression in isolated cardiomyocytes by shRNA offered protection against thrombin and PAR4-agonist peptide-induced apoptosis, while overexpression of wild-type PAR4 significantly enhanced the susceptibility of cardiomyocytes to apoptosis, even under low thrombin concentrations. Further studies implicate Src- and epidermal growth factor receptor-dependent activation of JNK on the proapoptotic effect of PAR4 in cardiomyocytes. These findings reveal a pivotal role for PAR4 as a regulator of cardiomyocyte survival and point to PAR4 inhibition as a therapeutic target offering cardioprotection after acute IR injury.

Protease-activated receptor 4: a critical participator in inflammatory response

Protease-activated receptors (PARs) are G protein-coupled receptors of which four members PAR1, PAR2, PAR3, and PAR4 have been identified, characterized by a typical mechanism of activation involving various related proteases. The amino-terminal sequence of PARs is cleaved by a broad array of proteases, leading to specific proteolytic cleavage which forms endogenous tethered ligands to induce agonist-biased PAR activation. The biological effect of PARs activated by coagulation proteases to regulate hemostasis and thrombosis plays an enormous role in the cardiovascular system, while PAR4 can also be activated by trypsin, cathepsin G, the activated factor X of the coagulation cascade, and trypsin IV. Irrespective of its role in thrombin-induced platelet aggregation, PAR4 activation is believed to be involved in inflammatory lesions, as show by investigations that have unmasked the effects of PAR4 on neutrophil recruitment, the regulation of edema, and plasma extravasation. This review summarizes the roles of PAR4 in coagulation and other extracellular protease pathways, which activate PAR4 to participate in normal regulation and disease.

Multiple Signaling Pathways Contribute to the Thrombin-induced Secretory Phenotype in Vascular Smooth Muscle Cells

We attempted to investigate molecular mechanisms underlying phenotypic change of vascular smooth muscle cells (VSMCs) by determining signaling molecules involved in chemokine production. Treatment of human aortic smooth muscle cells (HAoSMCs) with thrombin resulted not only in elevated transcription of the (C-C motif) ligand 11 (CCL11) gene but also in enhanced secretion of CCL11 protein. Co-treatment of HAoSMCs with GF109230X, an inhibitor of protein kinase C, or GW5074, an inhibitor of Raf-1 kinase, caused inhibition of ERK1/2 phosphorylation and significantly attenuated expression of CCL11 at transcriptional and protein levels induced by thrombin. Both Akt phosphorylation and CCL11 expression induced by thrombin were attenuated in the presence of pertussis toxin (PTX), an inhibitor of Gi protein-coupled receptor, or LY294002, a PI3K inhibitor. In addition, thrombin-induced production of CCL11 was significantly attenuated by pharmacological inhibition of Akt or MEK which phosphorylates ERK1/2. These results indicate that thrombin is likely to promote expression of CCL11 via PKC/Raf-1/ERK1/2 and PTX-sensitive protease-activated receptors/PI3K/Akt pathways in HAoSMCs. We propose that multiple signaling pathways are involved in change of VSMCs to a secretory phenotype.

c-Src/Pyk2/EGFR/PI3K/Akt/CREB-activated pathway contributes to human cardiomyocyte hypertrophy: Role of COX-2 induction

Thrombin and COX-2 regulating cardiac hypertrophy are via various signaling cascades. Several transcriptional factors including CREB involve in COX-2 expression. However, the interplay among thrombin, CREB, and COX-2 in primary human neonatal ventricular cardiomyocytes remains unclear. In this study, thrombin-induced COX-2 promoter activity, mRNA and protein expression, and PGE2 synthesis were attenuated by pretreatment with the inhibitors of c-Src (PP1), Pyk2 (PF431396), EGFR (AG1478), PI3K/Akt (LY294002/SH-5), and p300 (GR343), or transfection with siRNAs of c-Src, Pyk2, EGFR, p110, Akt, CREB, and p300. Moreover, thrombin-stimulated phosphorylation of c-Src, Pyk2, EGFR, Akt, CREB and p300 was attenuated by their respective inhibitors. These results indicate that thrombin-induced COX-2 expression is mediated through PAR-1/c-Src/Pyk2/EGFR/PI3K/Akt linking to CREB and p300 cascades. Functionally, thrombin-induced hypertrophy and ANF/BNP release were, at least in part, mediated through a PAR-1/COX-2-dependent pathway. We uncover the importance of COX-2 regarding human cardiomyocyte hypertrophy that will provide a therapeutic intervention in cardiovascular diseases.

Protective role of Kalpaamruthaa in type II diabetes mellitus-induced cardiovascular disease through the modulation of protease-activated receptor-1

Background:

Kalpaamruthaa (KA) is a formulatory herbal preparation has beneficial antioxidant, anti-apoptotic and anti-inflammatory properties against cardiovascular damage (CVD).

Objective:

The present study was undertaken to investigate the protective role of KA in type II diabetes mellitus-induced CVD through the modulation of protease-activated receptor-1 (PAR1).

Materials and Methods:

CVD was developed in 8 weeks after type II diabetes mellitus induction with high fat diet (2 weeks) and low dose of streptozotocin (2 × 35 mg/kg b.w. i.p. in 24 h interval). CVD-induced rats treated with KA (200 mg/kg b.w. in 0.5 ml of olive oil) orally for 4 weeks.

Results:

KA increased the activities of enzymatic antioxidants and the levels of non-enzymatic antioxidants in pancreas of CVD-induced rats. KA effectively reduced the lipid peroxides and carbonyl content in the pancreas of CVD-induced rats. KA reduced cellular damage by ameliorating the activities of marker enzymes in plasma, heart and liver. The protective nature of KA was further evidenced by histological observation in pancreas. Further, KA reduced CVD by decreasing the expression of PAR1 in heart.

Conclusion:

This study exhibits the defending role of KA in type II diabetes mellitus-induced CVD through altering PAR1.

The role of proteases in pain

Proteinase-activated receptors (PARs) are a family of G protein-coupled receptor that are activated by extracellular cleavage of the receptor in the N-terminal domain. This slicing of the receptor exposes a tethered ligand which binds to a specific docking point on the receptor surface to initiate intracellular signalling. PARs are expressed by numerous tissues in the body, and they are involved in various physiological and pathological processes such as food digestion, tissue remodelling and blood coagulation. This chapter will summarise how serine proteinases activate PARs leading to the development of pain in several chronic pain conditions. The potential of PARs as a drug target for pain relief is also discussed.

Protective and pathological roles of tissue factor in the heart

Tissue factor (TF) is expressed in the heart where it is required for haemostasis. High levels of TF are also expressed in atherosclerotic plaques and likely contribute to atherothrombosis after plaque rupture. Indeed, risk factors for atherothrombosis, such as diabetes, hypercholesterolaemia, smoking and hypertension, are associated with increased TF expression in circulating monocytes, microparticles and plasma. Several therapies that reduce atherothrombosis, such as statins, ACE inhibitors, beta-blockers and anti-platelet drugs, are associated with reduced TF expression. In addition to its haemostatic and pro-thrombotic functions, the TF : FVIIa complex and downstream coagulation proteases activate cells by cleavage of protease-activated receptors (PARs). In mice, deficiencies in either PAR-1 or PAR-2 reduce cardiac remodelling and heart failure after ischaemia-reperfusion injury. This suggests that inhibition of coagulation proteases and PARs may be protective in heart attack patients. In contrast, the TF/thrombin/PAR-1 pathway is beneficial in a mouse model of Coxsackievirus B3-induced viral myocarditis. We found that stimulation of PAR-1 increases the innate immune response by enhancing TLR3-dependent IFN-β expression. Therefore, inhibition of the TF/thrombin/PAR-1 pathway in patients with viral myocarditis could have detrimental effects.

CONCLUSION

The TF : FVIIa complex has both protective and pathological roles in the heart.

Tissue factor, protease activated receptors and pathologic heart remodelling

Tissue factor is the primary initiator of coagulation cascade and plays an essential role in haemostasis and thrombosis. In addition, tissue factor and coagulation proteases contribute to many cellular responses via activation of protease activated receptors. The heart is an organ with high levels of constitutive tissue factor expression. This review focuses on the role of tissue factor, coagulation proteases and protease activated receptors in heart haemostasis and the pathological heart remodelling associated with myocardial infarction, viral myocarditis and hypertension.

Plasmin-dependent modulation of the blood-brain barrier: a major consideration during tPA-induced thrombolysis?

Plasmin, the principal downstream product of tissue-type plasminogen activator (tPA), is known for its potent fibrin-degrading capacity but is also recognized for many non-fibrinolytic activities. Curiously, plasmin has not been conclusively linked to blood-brain barrier (BBB) disruption during recombinant tPA (rtPA)-induced thrombolysis in ischemic stroke. This is surprising given the substantial involvement of tPA in the modulation of BBB permeability and the co-existence of tPA and plasminogen in both blood and brain throughout the ischemic event. Here, we review the work that argues a role for plasmin together with endogenous tPA or rtPA in BBB alteration, presenting the overall controversy around the topic yet creating a rational case for an involvement of plasmin in this process.

Factor Xa inhibits HMGB1-induced septic responses in human umbilical vein endothelial cells and in mice

Nuclear DNA-binding protein high mobility group box 1 (HMGB1) acts as a late mediator of severe vascular inflammatory conditions, such as sepsis. Activated factor X (FXa) is an important player in the coagulation cascade responsible for thrombin generation, and it influences cell signalling in various cell types by activating protease-activated receptors (PARs). However, the effect of FXa on HMGB1-induced inflammatory response has not been studied. First, we addressed this issue by monitoring the effects of post-treatment with FXa on lipopolysaccharide (LPS)- and cecal ligation and puncture (CLP)-mediated release of HMGB1 and HMGB1-mediated regulation of pro-inflammatory responses in human umbilical vein endothelial cells (HUVECs) and septic mice. Post-treatment with FXa was found to suppress LPS-mediated release of HMGB1 and HMGB1-mediated cytoskeletal rearrangements. FXa also inhibited HMGB1-mediated hyperpermeability and leukocyte migration in septic mice. In addition, FXa inhibited the production of tumour necrosis factor-α and interleukin (IL)-1β. FXa also facilitated the downregulation of CLP-induced release of HMGB1, production of IL-6, and mortality. Collectively, these results suggest that FXa may be regarded as a candidate therapeutic agent for treating vascular inflammatory diseases by inhibiting the HMGB1 signalling pathway.

Multiple roles of the coagulation protease cascade during virus infection

The coagulation cascade is activated during viral infections. This response may be part of the host defense system to limit spread of the pathogen. However, excessive activation of the coagulation cascade can be deleterious. In fact, inhibition of the tissue factor/factor VIIa complex reduced mortality in a monkey model of Ebola hemorrhagic fever. Other studies showed that incorporation of tissue factor into the envelope of herpes simplex virus increases infection of endothelial cells and mice. Furthermore, binding of factor X to adenovirus serotype 5 enhances infection of hepatocytes but also increases the activation of the innate immune response to the virus. Coagulation proteases activate protease-activated receptors (PARs). Interestingly, we and others found that PAR1 and PAR2 modulate the immune response to viral infection. For instance, PAR1 positively regulates TLR3-dependent expression of the antiviral protein interferon β, whereas PAR2 negatively regulates expression during coxsackievirus group B infection. These studies indicate that the coagulation cascade plays multiple roles during viral infections.

Protease activated receptor-2 contributes to heart failure

Heart failure is a major clinical problem worldwide. Previous studies have demonstrated an important role for G protein-coupled receptors, including protease-activated receptors (PARs), in the pathology of heart hypertrophy and failure. Activation of PAR-2 on cardiomyocytes has been shown to induce hypertrophic growth in vitro. PAR-2 also contributes to myocardial infarction and heart remodeling after ischemia/reperfusion injury. In this study, we found that PAR-2 induced hypertrophic growth of cultured rat neonatal cardiomyocytes in a MEK1/2 and p38 dependent manner. In addition, PAR-2 activation on mouse cardiomyocytes increased expression of the pro-fibrotic chemokine MCP-1. Furthermore, cardiomyocyte-specific overexpression of PAR-2 in mice induced heart hypertrophy, cardiac fibrosis, inflammation and heart failure. Finally, in a mouse model of myocardial infarction induced by permanent ligation of the left anterior descending coronary artery, PAR-2 deficiency attenuated heart remodeling and improved heart function independently of its contribution to the size of the initial infarct. Taken together, our data indicate that PAR-2 signaling contributes to the pathogenesis of hypertrophy and heart failure.

Coagulation factor Xa induces an inflammatory signalling by activation of protease-activated receptors in human atrial tissue

Activated factor X (FXa) is an important player in the coagulation cascade responsible for thrombin generation, which is activated during atrial fibrillation. Increasing evidence suggests that FXa influences cell signalling in various cell types by activating protease-activated receptors (PARs). It is so far not known if molecular effects of FXa affect atrial signal transduction. To study the effects of FXa, human atrial tissue slices were cultivated with FXa up to 24h. Additionally, rapid pacing was applied at 4Hz to resemble atrial fibrillation. The inhibitory impact of FXa antagonist (Rivaroxaban), protease-activated receptor 1 antagonist (SCH79797), and protease-activated receptor 2 antagonist (GB83) were analysed under experimental conditions. The exposure of atrial tissue to FXa resulted in the 1.7 fold upregulation of PAR2-mRNA, activation of MAP kinases (ERK1/2) and NF-κB signalling. Furthermore FXa increased the expression of adhesion molecule ICAM-1 (1.82 ± 0.20), chemokine IL-8 (1.94 ± 0.20), as well as prothrombotic molecule PAI-1 (1.52 ± 0.17). The combination of rapid pacing and FXa caused significant upregulation of PAR1 (2.82 ± 0.22), PAR2 (2.66 ± 0.40), ICAM-1 (2.13 ± 0.25), IL-8 (2.22 ± 0.24), LOX-1 (2.59 ± 0.35), and PAI-1 (2.65 ± 0.52) at the mRNA level. Rivaroxaban and GB83 prevented upregulation of PARs, ICAM-1, LOX-1, IL-8, and activation of MAP kinases. The elevation in the expression of PAI-1 was hindered in the presence of SCH79797, or Rivaroxaban. The present study indicates that FXa mediates inflammatory signalling in atrial tissue. Importantly, FXa and tachyarrhythmia act synergistically to increase expression of protease-activated receptors and inflammatory mediators. Rivaroxaban prevented effectively FXa-induced molecular effects in human atrial tissue particularly during rapid pacing.

Potent cardioprotection from ischemia-reperfusion injury by a two-domain fusion protein comprising annexin V and Kunitz protease inhibitor

BACKGROUND

Considerable evidence suggests that coagulation proteases (tissue factor [TF]/activated factor VII [FVIIa]/FXa/thrombin) and their target protease activated receptors (PAR-1/PAR-2) play important roles in myocardial ischemia-reperfusion (I-R) injury. We hypothesized that localized inhibition of TF/FVIIa on the membrane surfaces of ischemic cells could effectively block coagulation cascade and subsequent PAR-1/PAR-2 cell signaling, thereby protecting the myocardium from I-R injury.

OBJECTIVES

We recently developed an annexin V-Kunitz inhibitor fusion protein (ANV-6L15) that could specifically bind to anionic phospholipids on the membrane surfaces of apoptotic cells and efficiently inhibit the membrane-anchored TF/FVIIa. In this study, we investigated the cardioprotective effect of ANV-6L15 in a rat cardiac I-R model in comparison with that of hirudin.

METHODS

Left coronary artery occlusion was maintained for 45 min followed by 4 h of reperfusion in anesthetized Sprague-Dawley rats. One minute before or 2 min after coronary ligation, rats received an intravenous bolus injection of ANV-6L15 (2.5-250 μg kg(-1) ), vehicle, or hirudin via bolus injection and continuous infusion.

RESULTS AND CONCLUSIONS

ANV-6L15 dose-dependently reduced infarct size by up to 87% and decreased plasma levels of cardiac troponin I, tumor necrosis factor-α, and soluble intercellular adhesion molecule-1, by up to 97%, 96%, and 66%, respectively, with little impact on the coagulation parameters. ANV-6L15 also ameliorated hemodynamic derangements, attenuated neutrophil infiltration and reduced Terminal deoxynucleotidyl transferase dUTP nick end labeling-positive apoptotic cardiomyocytes. Hirudin was less efficacious even at supraclinical dose. ANV-6L15 confers exceptionally potent cardioprotection and is a promising drug candidate for the prevention of myocardial I-R injury.

PAR-1 contributes to the innate immune response during viral infection

Coagulation is a host defense system that limits the spread of pathogens. Coagulation proteases, such as thrombin, also activate cells by cleaving PARs. In this study, we analyzed the role of PAR-1 in coxsackievirus B3-induced (CVB3-induced) myocarditis and influenza A infection. CVB3-infected Par1(-/-) mice expressed reduced levels of IFN-β and CXCL10 during the early phase of infection compared with Par1(+/+) mice that resulted in higher viral loads and cardiac injury at day 8 after infection. Inhibition of either tissue factor or thrombin in WT mice also significantly increased CVB3 levels in the heart and cardiac injury compared with controls. BM transplantation experiments demonstrated that PAR-1 in nonhematopoietic cells protected mice from CVB3 infection. Transgenic mice overexpressing PAR-1 in cardiomyocytes had reduced CVB3-induced myocarditis. We found that cooperative signaling between PAR-1 and TLR3 in mouse cardiac fibroblasts enhanced activation of p38 and induction of IFN-β and CXCL10 expression. Par1(-/-) mice also had decreased CXCL10 expression and increased viral levels in the lung after influenza A infection compared with Par1(+/+) mice. Our results indicate that the tissue factor/thrombin/PAR-1 pathway enhances IFN-β expression and contributes to the innate immune response during single-stranded RNA viral infection.

Coagulation and coagulation signalling in fibrosis

Following tissue injury, a complex and coordinated wound healing response comprising coagulation, inflammation, fibroproliferation and tissue remodelling has evolved to nullify the impact of the original insult and reinstate the normal physiological function of the affected organ. Tissue fibrosis is thought to result from a dysregulated wound healing response as a result of continual local injury or impaired control mechanisms. Although the initial insult is highly variable for different organs, in most cases, uncontrolled or sustained activation of mesenchymal cells into highly synthetic myofibroblasts leads to the excessive deposition of extracellular matrix proteins and eventually loss of tissue function. Coagulation was originally thought to be an acute and transient response to tissue injury, responsible primarily for promoting haemostasis by initiating the formation of fibrin plugs to enmesh activated platelets within the walls of damaged blood vessels. However, the last 20years has seen a major re-evaluation of the role of the coagulation cascade following tissue injury and there is now mounting evidence that coagulation plays a critical role in orchestrating subsequent inflammatory and fibroproliferative responses during normal wound healing, as well as in a range of pathological contexts across all major organ systems. This review summarises our current understanding of the role of coagulation and coagulation initiated signalling in the response to tissue injury, as well as the contribution of uncontrolled coagulation to fibrosis of the lung, liver, kidney and heart. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.

Neuroprotective effect of protease-activated receptor-2 in the hypoxia-induced apoptosis of rat RGC-5 cells

Hypoxia-induced apoptosis of retinal ganglion cells (RGCs) is regarded as a pivotal pathological process in various ocular diseases. Protease-activated receptor-2 (PAR-2) is involved in the regulation of cell inflammation, differentiation, and apoptosis in many cell types and tissues, but the role of PAR-2 in RGCs under pathological conditions remains unknown. The purpose of this study was to investigate the role of PAR-2 in the apoptosis of RGCs under hypoxic stress. An immortalized rat RGC line (RGC-5) was exposed to hypoxia (5 % O₂). The expression and location of PAR-2 in RGC-5 cells under hypoxia stress were investigated using real-time PCR, western blotting and immunocytochemistry. Cell viability was determined using the Cell Counting Kit-8 assay. Apoptosis was detected using Hoechst 33342 staining and AnnexinV-FITC/PI assays. The role of Bcl-2, Bax, and the active subunit of caspase-3 was also investigated. The results showed that PAR-2 was functionally expressed in RGC-5 cells and up-regulated at both mRNA and protein levels under hypoxic stress. The PAR-2 selective agonist, SLIGRL, rescued RGC-5 cells from hypoxia-induced apoptosis through up-regulation of the Bcl-2/Bax ratio and down-regulation of caspase-3 activation. This study provides the first evidence that PAR-2 has a protective effect against the hypoxia-induced apoptosis of RGC-5 cells.

Defining the cellular repertoire of GPCRs identifies a profibrotic role for the most highly expressed receptor, protease-activated receptor 1, in cardiac fibroblasts

G-protein-coupled receptors (GPCRs) have many roles in cell regulation and are commonly used as drug targets, but the repertoire of GPCRs expressed by individual cell types has not been defined. Here we use an unbiased approach, GPCR RT-PCR array, to define the expression of nonchemosensory GPCRs by cardiac fibroblasts (CFs) isolated from Rattus norvegicus. CFs were selected because of their importance for cardiac structure and function and their contribution to cardiac fibrosis, which occurs with advanced age, after acute injury (e.g., myocardial infarction), and in disease states (e.g., diabetes mellitus, hypertension). We discovered that adult rat CFs express 190 GPCRs and that activation of protease-activated receptor 1 (PAR1), the most highly expressed receptor, raises the expression of profibrotic markers in rat CFs, resulting in a 60% increase in collagen synthesis and conversion to a profibrogenic myofibroblast phenotype. We use siRNA knockdown of PAR1 (90% decrease in mRNA) to show that the profibrotic effects of thrombin are PAR1-dependent. These findings, which define the expression of GPCRs in CFs, provide a proof of principle of an approach to discover previously unappreciated, functionally relevant GPCRs and reveal a potential role for thrombin and PAR1 in wound repair and pathophysiology of the adult heart.

Thrombin induced connective tissue growth factor expression in rat vascular smooth muscle cells via the PAR-1/JNK/AP-1 pathway

AIM

To investigate the signaling pathways involved in thrombin-induced connective tissue growth factor (CTGF) expression in rat vascular smooth muscle cells (VSMCs).

METHODS

Experiments were preformed on primary rat aortic smooth muscle cells (RASMCs) and a rat VSMC line (A10). CTGF protein levels were measured using Western blotting. Luciferase reporter genes and dominant negative mutants (DNs) were used to investigate the signaling pathways mediating the induction of CTGF expression by thrombin.

RESULTS

Thrombin (0.3-3.0 U/mL) caused a concentration- and time-dependent increase in CTGF expression in both RASMCs and A10 cells. Pretreating A10 cells with the protease-activated receptor 1 (PAR-1) antagonist SCH79797 (0.1 μmol/L) significantly blocked thrombin-induced CTGF expression, while the PAR-4 antagonist tcY-NH(2) (30 μmol/L) had no effect. The PAR-1 agonist SFLLRN-NH(2) (300 μmol/L) induced CTGF expression, while the PAR-4 agonist GYPGQV-NH(2) (300 μmol/L) had no effect. Thrombin (1 U/mL) caused time-dependent phosphorylation of c-Jun N-terminal kinase (JNK). Pretreating with the JNK inhibitor SP600125 (3-30 μmol/L) or transfection with DNs of JNK1/2 significantly attenuated thrombin-induced CTGF expression. Thrombin (0.3-3.0 U/mL) increased activator protein-1 (AP-1)-luciferase activity, which was inhibited by the JNK inhibitor SP600125. The AP-1 inhibitor curcumin (1-10 μmol/L) concentration-dependently attenuated thrombin-induced CTGF expression.

CONCLUSION

Thrombin acts on PAR-1 to activate the JNK signaling pathway, which in turn initiates AP-1 activation and ultimately induces CTGF expression in VSMCs.