Thrombin induces proteinase-activated receptor-1 gene expression in endothelial cells via activation of Gi-linked Ras/mitogen-activated protein kinase pathway

Inflammation and coagulation abnormalities via the activation of the HMGB1‑RAGE/NF‑κB and F2/Rho pathways in lung injury induced by acute hypoxia

High‑altitude acute hypoxia is commonly associated with respiratory cardiovascular diseases. The inability to adapt to acute hypoxia may lead to cardiovascular dysfunction, lung injury and even death. Therefore, understanding the molecular basis of the adaptation to high‑altitude acute hypoxia may reveal novel therapeutic approaches with which to counteract the detrimental consequences of hypoxia. In the present study, a high‑altitude environment was simulated in a rat model in order to investigate the role of the high mobility group protein‑1 (HMGB1)/receptor for advanced glycation end products (RAGE)/NF‑κB and F2/Rho signaling pathways in lung injury induced by acute hypoxia. It was found that acute hypoxia caused inflammation through the HMGB1/RAGE/NF‑κB pathway and coagulation dysfunction through the F2/Rho pathway, both of which may be key processes in acute hypoxia‑induced lung injury. The present study provides new insight into the molecular basis of lung injury induced by acute hypoxia. The simultaneous activation of the HMGB1/RAGE/NF‑κB and F2/Rho signaling pathways plays a critical role in hypoxia‑induced inflammatory responses and coagulation abnormalities, and provides a theoretical basis for the development of potential therapeutic strategies.

TRAP-induced PAR1 expression with its mechanism during AMI in a rat model

BACKGROUND AND OBJECTIVE

Protease-activated receptor 1 (PAR1) is crucial in individuals with acute myocardial infarction (AMI). The continuous and prompt PAR1 activation mainly dependent on PAR1 trafficking is essential for the role of PAR1 during AMI in which cardiomyocytes are in hypoxia. However, the PAR1 trafficking in cardiomyocytes specially during the hypoxia is still unclear.

METHODS AND RESULT

A rat AMI model was created. PAR1 activation with thrombin-receptor activated peptide (TRAP) had a transient effect on cardiac function in normal rats but persistent improvement in rats with AMI. Cardiomyocytes from neonatal rats were cultured in a normal CO2 incubator and a hypoxic modular incubator chamber. The cells were then subjected to western blot for the total protein expression and staining with fluorescent reagent and antibody for PAR1 localization. No change in total PAR1 expression following TRAP stimulation was observed; however, it led to increased PAR1 expression in the early endosomes in normoxic cells and decreased expression in the early endosomes in hypoxic cells. Under hypoxic conditions, TRAP restored the PAR1 expression on both cell and endosomal surfaces within an hour by decreasing Rab11A (8.5-fold; 179.93 ± 9.82% of the normoxic control group, n = 5) and increasing Rab11B (15.5-fold) expression after 4 h of hypoxia. Similarly, Rab11A knockdown upregulated PAR1 expression under normoxia, and Rab11B knockdown downregulated PAR1 expression under both normoxic and hypoxic conditions. Cardiomyocytes knocked out of both Rab11A, and Rad11B lost the TRAP-induced PAR1 expression but still exhibited the early endosomal TRAP-induced PAR1 expression under hypoxia.

CONCLUSIONS

TRAP-mediated activation of PAR1 in cardiomyocytes did not alter the total PAR1 expression under normoxic conditions. Instead, it triggers a redistribution of PAR1 levels under normoxic and hypoxic conditions. TRAP reverses the hypoxia-inhibited PAR1 expression in cardiomyocytes by downregulating Rab11A expression and upregulating Rab11B expression.

The serine protease plasmin plays detrimental roles in epithelial sodium channel activation and podocyte injury in Dahl salt-sensitive rats

Salt-sensitive hypertension is associated with poor clinical outcomes. The epithelial sodium channel (ENaC) in the kidney plays pivotal roles in sodium reabsorption and blood pressure regulation, in which its γ subunit is activated by extracellular serine proteases. In proteinuric nephropathies, plasmin filtered through injured glomeruli reportedly activates γENaC in the distal nephron and causes podocyte injury. We previously reported that Dahl salt-sensitive (DS) rats fed a high-salt (HS) diet developed hypertension and proteinuria along with γENaC activation and that a synthetic serine protease inhibitor, camostat mesilate, mitigated these changes. However, the role of plasmin in DS rats remained unclear. In this study, we evaluated the relationship between plasmin and hypertension as well as podocyte injury and the effects of plasmin inhibitors in DS rats. Five-week-old DS rats were divided into normal-salt diet, HS diet, and HS+plasmin inhibitor (either tranexamic acid [TA] or synthetic plasmin inhibitor YO-2) groups. After blood pressure measurement and 24 h urine collection over 5 weeks, rats were sacrificed for biochemical analyses. The HS group displayed severe hypertension and proteinuria together with activation of plasmin in urine and γENaC in the kidney, which was significantly attenuated by YO-2 but not TA. YO-2 inhibited the attachment of plasmin(ogen) to podocytes and alleviated podocyte injury by inhibiting apoptosis and inflammatory/profibrotic cytokines. YO-2 also suppressed upregulation of protease-activated receptor-1 and phosphorylated ERK1/2. These results indicate an important role of plasmin in the development of salt-sensitive hypertension and related podocyte injury, suggesting plasmin inhibition as a potential therapeutic strategy.

Complement and Coagulation System Crosstalk in Synaptic and Neural Conduction in the Central and Peripheral Nervous Systems

Complement and coagulation are both key systems that defend the body from harm. They share multiple features and are similarly activated. They each play individual roles in the systemic circulation in physiology and pathophysiology, with significant crosstalk between them. Components from both systems are mapped to important structures in the central nervous system (CNS) and peripheral nervous system (PNS). Complement and coagulation participate in critical functions in neuronal development and synaptic plasticity. During pathophysiological states, complement and coagulation factors are upregulated and can modulate synaptic transmission and neuronal conduction. This review summarizes the current evidence regarding the roles of the complement system and the coagulation cascade in the CNS and PNS. Possible crosstalk between the two systems regarding neuroinflammatory-related effects on synaptic transmission and neuronal conduction is explored. Novel treatment based on the modulation of crosstalk between complement and coagulation may perhaps help to alleviate neuroinflammatory effects in diseased states of the CNS and PNS.

Molecular Dambusters: What Is Behind Hyperpermeability in Bradykinin-Mediated Angioedema?

In the last few decades, a substantial body of evidence underlined the pivotal role of bradykinin in certain types of angioedema. The formation and breakdown of bradykinin has been studied thoroughly; however, numerous questions remained open regarding the triggering, course, and termination of angioedema attacks. Recently, it became clear that vascular endothelial cells have an integrative role in the regulation of vessel permeability. Apart from bradykinin, a great number of factors of different origin, structure, and mechanism of action are capable of modifying the integrity of vascular endothelium, and thus, may participate in the regulation of angioedema formation. Our aim in this review is to describe the most important permeability factors and the molecular mechanisms how they act on endothelial cells. Based on endothelial cell function, we also attempt to explain some of the challenging findings regarding bradykinin-mediated angioedema, where the function of bradykinin itself cannot account for the pathophysiology. By deciphering the complex scenario of vascular permeability regulation and edema formation, we may gain better scientific tools to be able to predict and treat not only bradykinin-mediated but other types of angioedema as well.

Brain Protease Activated Receptor 1 Pathway: A Therapeutic Target in the Superoxide Dismutase 1 (SOD1) Mouse Model of Amyotrophic Lateral Sclerosis

Glia cells are involved in upper motor neuron degeneration in amyotrophic lateral sclerosis (ALS). Protease activated receptor 1 (PAR1) pathway is related to brain pathologies. Brain PAR1 is located on peri-synaptic astrocytes, adjacent to pyramidal motor neurons, suggesting possible involvement in ALS. Brain thrombin activity in superoxide dismutase 1 (SOD1) mice was measured using a fluorometric assay, and PAR1 levels by western blot. PAR1 was localized using immunohistochemistry staining. Treatment targeted PAR1 pathway on three levels; thrombin inhibitor TLCK (N-Tosyl-Lys-chloromethylketone), PAR1 antagonist SCH-79797 and the Ras intracellular inhibitor FTS (S-trans-trans-farnesylthiosalicylic acid). Mice were weighed and assessed for motor function and survival. SOD1 brain thrombin activity was increased (p < 0.001) particularly in the posterior frontal lobe (p = 0.027) and hindbrain (p < 0.01). PAR1 levels were decreased (p < 0.001, brain, spinal cord, p < 0.05). PAR1 and glial fibrillary acidic protein (GFAP) staining decreased in the cerebellum and cortex. SOD1 mice lost weight (≥17 weeks, p = 0.047), and showed shorter rotarod time (≥14 weeks, p < 0.01). FTS 40mg/kg significantly improved rotarod scores (p < 0.001). Survival improved with all treatments (p < 0.01 for all treatments). PAR1 antagonism was the most efficient, with a median survival improvement of 10 days (p < 0.0001). Our results support PAR1 pathway involvement in ALS.

Baicalin Protects against Thrombin-Induced Cell Injury in Human Umbilical Vein Endothelial Cells

Thrombin plays a pivotal role in the pathogenesis of atherosclerosis. Baicalin, an active flavonoid compound, was shown to attenuate the development of atherosclerosis, but the mechanism remains elusive. In the present study, the role and mechanism of baicalin in thrombin-induced cell injury was investigated in human umbilical vein endothelial cells (HUVECs). Our results showed that baicalin significantly reduced thrombin-induced apoptosis of HUVECs. Additional experiments showed that baicalin inhibited thrombin-induced NF-κB activation and PAR-1 expression. In addition, baicalin decreased thrombin-induced PAR-1 expression by inhibiting ERK pathway. These results indicated that baicalin has protective effects on thrombin-induced cell injury in HUVECs possibly through inhibition of PAR-1 expression and its downstream NF-κB activation, which was mediated by ERK1/2 activation.

Thrombin Signaling Promotes Pancreatic Adenocarcinoma through PAR-1-Dependent Immune Evasion

Pancreatic ductal adenocarcinoma (PDAC) is associated with robust activity of the coagulation system. To determine mechanisms by which clotting factors influence PDAC tumor progression, we generated and characterized C57Bl/6-derived KPC (KRas^G12D, TRP53^R172H ) cell lines. Tissue factor (TF) and protease-activated receptor-1 (PAR-1) were highly expressed in primary KPC pancreatic lesions and KPC cell lines similar to expression profiles observed in biopsies of patients with PDAC. In allograft studies, tumor growth and metastatic potential were significantly diminished by depletion of TF or Par-1 in cancer cells or by genetic or pharmacologic reduction of the coagulation zymogen prothrombin in mice. Notably, PAR-1-deleted KPC cells (KPC-Par-1^KO) failed to generate sizable tumors, a phenotype completely rescued by restoration of Par-1 expression. Expression profiling of KPC and KPC-Par-1^KO cells indicated that thrombin-PAR-1 signaling significantly altered immune regulation pathways. Accordingly, KPC-Par-1^KO cells failed to form tumors in immune-competent mice but displayed robust tumor growth comparable to that observed with control KPC cells in immune-compromised NSG mice. Immune cell depletion studies indicated that CD8 T cells, but not CD4 cells or natural killer cells, mediated elimination of KPC-Par-1^KO tumor cells in C57Bl/6 mice. These results demonstrate that PDAC is driven by activation of the coagulation system through tumor cell-derived TF, circulating prothrombin, and tumor cell-derived PAR-1 and further indicate that one key mechanism of thrombin/PAR-1-mediated tumor growth is suppression of antitumor immunity in the tumor microenvironment. SIGNIFICANCE: The tissue factor-thrombin-PAR-1 signaling axis in tumor cells promotes PDAC growth and disease progression with one key mechanism being suppression of antitumor immunity in the microenvironment.

The podocyte protease web: uncovering the gatekeepers of glomerular disease

Proteases regulate glomerular physiology. The last decade has revealed a multitude of podocyte proteases that govern the glomerular response to numerous chemical, mechanical, and metabolic cues. These proteases form a protein signaling web that integrates stress stimuli and serves as a key controller of the glomerular microenvironment. Both the extracellular and intracellular proteolytic networks are perturbed in focal segmental glomerulosclerosis, as well as hypertensive and diabetic nephropathy. Accordingly, the highly intertwined podocyte protease web is an integrative part of the podocyte's damage response. Novel mass spectrometry-based technologies will help to untangle this proteolytic network: functional readouts acquired from deep podocyte proteomics, single glomerular proteomics, and degradomics have exposed unanticipated protease activity in podocytes. Future efforts should characterize the interdependency and upstream regulation of key proteases, along with their role in promoting tissue heterogeneity in glomerular diseases. These efforts will not only illuminate the machinery of podocyte proteostasis but also reveal avenues for therapeutic intervention in the podocyte protease web.

Protease-activated receptors in kidney disease progression

Protease-activated receptors (PARs) are members of a well-known family of transmembrane G protein-coupled receptors (GPCRs). Four PARs have been identified to date, of which PAR1 and PAR2 are the most abundant receptors, and have been shown to be expressed in the kidney vascular and tubular cells. PAR signaling is mediated by an N-terminus tethered ligand that can be unmasked by serine protease cleavage. The receptors are activated by endogenous serine proteases, such as thrombin (acts on PARs 1, 3, and 4) and trypsin (PAR2). PARs can be involved in glomerular, microvascular, and inflammatory regulation of renal function in both normal and pathological conditions. As an example, it was shown that human glomerular epithelial and mesangial cells express PARs, and these receptors are involved in the pathogenesis of crescentic glomerulonephritis, glomerular fibrin deposition, and macrophage infiltration. Activation of these receptors in the kidney also modulates renal hemodynamics and glomerular filtration rate. Clinical studies further demonstrated that the concentration of urinary thrombin is associated with glomerulonephritis and type 2 diabetic nephropathy; thus, molecular and functional mechanisms of PARs activation can be directly involved in renal disease progression. We briefly discuss here the recent literature related to activation of PAR signaling in glomeruli and the kidney in general and provide some examples of PAR1 signaling in glomeruli podocytes.

Thrombin Enhanced Matrix Metalloproteinase-9 Expression and Migration of SK-N-SH Cells via PAR-1, c-Src, PYK2, EGFR, Erk1/2 and AP-1

Neuroinflammation is a hallmark of neurodegenerative disorders in the central nerve system (CNS). Thrombin has been known as one of the factors in pathological processes including migration, blood-brain barrier breakdown, brain edema formation, neuroinflammation, and neuronal death. Thrombin has been shown to be a regulator of matrix metalloproteinase (MMPs) expression leading to cell migration. Among MMPs, the elevated expression of MMP-9 has been observed in patients with brain diseases, which may contribute to the pathology of neuroinflammatory and neurodegenerative diseases. However, the mechanisms underlying thrombin-induced MMP-9 expression in SK-N-SH cells were not completely understood. Here, we used gelatin zymography, Western blot, real-time PCR, promoter activity assay, and cell migration assay to demonstrate that thrombin induced the expression of pro-form MMP-9 protein and messenger RNA (mRNA), and promoter activity in SK-N-SH cells, which were attenuated by pretreatment with the pharmacological inhibitor of protease-activated receptor-1 (PAR-1, SCH79797), Gi-coupled receptor (GPA2), c-Src (PP1), Pyk2 (PF431396), EGFR (AG1478), PI3K (LY294002), Akt (SH-5), MEK1/2 (U0126), or AP-1 (TanshinoneIIA) and transfection with small interfering RNA (siRNA) of PAR-1, Gi, c-Src, Pyk2, EGFR, Akt, p44, p42, or c-Jun. Moreover, thrombin-stimulated c-Src, Pyk2, EGFR, Akt, p42/p44 MAPK, or c-Jun phosphorylation was attenuated by their respective inhibitor of PP1, PF431396, AG1478, SH-5, U0126, or TanshinoneIIA. Finally, pretreatment with these inhibitors also blocked thrombin-induced SK-N-SH cell migration. Our results concluded that thrombin binding to PAR-1 receptor activated Gi-protein/c-Src/Pyk2/EGFR/PI3K/Akt/p42/p44 MAPK cascade, which in turn elicited AP-1 activation and ultimately evoked MMP-9 expression and cell migration in SK-N-SH cells.

Expression of protease activated receptor-1 in chronic periodontitis

BACKGROUND

Protease activated receptor-1 (PAR1) activation by thrombin may play a role in repair and homeostasis of periodontal tissues. The main objective of this study is to investigate PAR1 expression in patients with periodontitis, before and after non-surgical periodontal treatment, and to associate its expression with the presence of inflammatory biomarkers and PAR2 expression.

METHODS

Gingival crevicular fluid (GCF) samples and clinical parameters, including probing depth, clinical attachment level, bleeding on probing, and gingival and plaque indices, were collected from periodontally healthy individuals and patients with moderate chronic periodontitis (CP) before and 6 weeks after periodontal non-surgical treatment. PAR1 and PAR2 messenger RNA (mRNA) at the GCF were evaluated by quantitative polymerase chain reaction (qPCR). Flow cytometry analysis identified the GCF PAR1-expressing cells. GCF inflammatory biomarkers were also determined.

RESULTS

Clinical parameters were significantly improved after therapy (P <0.01). The qPCR analysis showed that, before therapy, PAR1 mRNA levels in CP were similar to controls. Periodontal treatment led to increased PAR1 expression in CP (P <0.05). PAR1 expression was inversely correlated to PAR2 expression and with interleukins 6 and 8, tumor necrosis factor-α, interferon-γ, and matrix metalloproteinase-2 levels.

CONCLUSIONS

Periodontal treatment results in PAR1 overexpression in the GCF, and PAR1 expression is associated with decreased expression of inflammatory biomarkers and inversely correlated to PAR2 expression in the GCF. Therefore, the data suggest the importance of PAR1 mediating the known anabolic actions of thrombin in the periodontium.

Long-circulating self-assembled cholesteryl albumin nanoparticles enhance tumor accumulation of hydrophobic anticancer drug

The objective of this study was to develop an albumin nanoparticle with improved stability and drug loading capacity. Generation of nanomaterials having physiologically stable and high potential for drug delivery is still challenging. Herein we synthesized cholesteryl albumin conjugate using N,N-disuccinimidyl carbonate coupling reagent and prepared paclitaxel-loaded cholesteryl albumin nanoparticle (PTX-Chol-BSA) by self-assembly with the mean hydrodynamic diameter of 147.6±1.6nm and with high loading capacity. PTX-Chol-BSA nanoparticle showed much higher colloidal stability than a simple complex of PTX and BSA (PTX-BSA) and sustained release profile. PTX-Chol-BSA nanoparticles exhibited greater cellular uptake and cytotoxicity in B16F10 and MCF-7 cancer cell lines, as compared with PTX in Cremophor EL/ethanol (PTX-Cre/EtOH) and PTX-BSA formulations. A pharmacokinetic study in tumor-bearing mice showed that the area under the concentration-time curve (AUC0-8 h) following the administration of PTX-Chol-BSA was 1.6-2-fold higher than those following the administration of PTX-Cre/EtOH and PTX-BSA. In addition, the tumor AUC0-8 h of PTX-Chol-BSA was around 2-fold higher than that of PTX-BSA. Furthermore, in vivo antitumor efficacy results revealed that PTX-Chol-BSA nanoparticles have greater antitumor efficacy. In conclusion, we demonstrated the potential of PTX-Chol-BSA nanoparticles for anti-tumor chemotherapy, with enhanced in vitro and in vivo behaviors, as compared to PTX-BSA and PTX-Cre/EtOH.

Mechanotransduction of shear stress occurs through changes in VE-cadherin and PECAM-1 tension: implications for cell migration

Recent work has shown that cadherins at cell-cell junctions bear tensile forces. Using novel FRET-based tension sensors, we showed first that in response to shear stress, endothelial cells rapidly reduce mechanical tension on vascular endothelial (VE)-cadherin. Second, we observed a simultaneous increase in tension on platelet endothelial cell adhesion molecule (PECAM)-1, induced by an interaction with vimentin. In this commentary, we discuss how our results fit with existing data on cadherins as important mediators of mechanotransduction, in particular, in cell migration where mechanical tension across cadherins may communicate the direction of movement. The ability of PECAM-1 to bear mechanical tension may also be important in other PECAM-1 functions, such as leukocyte transmigration through the endothelium. Additionally, our observation that vimentin expression was required for PECAM-1 tension and mechanotransduction of fluid flow suggests that intermediate filaments are capable of transmitting tension. Overall, our results argue against models where an external force is passively transferred across the cytoskeleton, and instead suggest that cells actively respond to extracellular forces by modulating tension across junctional proteins.

Pathologies at the nexus of blood coagulation and inflammation: thrombin in hemostasis, cancer, and beyond

Thrombin is the protease involved in blood coagulation. Its deregulation can lead to hemostatic abnormalities, which range from subtle subclinical to serious life-threatening coagulopathies, i.e., during septicemia. Additionally, thrombin plays important roles in many (patho)physiological conditions that reach far beyond its well-established role in stemming blood loss and thrombosis, including embryonic development and angiogenesis but also extending to inflammatory processes, complement activation, and even tumor biology. In this review, we will address thrombin's broad roles in diverse (patho)physiological processes in an integrative way. We will also discuss thrombin as an emerging major target for novel therapies.

Protective effects of transgenic human endothelial protein C receptor expression in murine models of transplantation

Thrombosis and inflammation are major obstacles to successful pig-to-human solid organ xenotransplantation. A potential solution is genetic modification of the donor pig to overexpress molecules such as the endothelial protein C receptor (EPCR), which has anticoagulant, anti-inflammatory and cytoprotective signaling properties. Transgenic mice expressing human EPCR (hEPCR) were generated and characterized to test this approach. hEPCR was expressed widely and its compatibility with the mouse protein C pathway was evident from the anticoagulant phenotype of the transgenic mice, which exhibited a prolonged tail bleeding time and resistance to collagen-induced thrombosis. hEPCR mice were protected in a model of warm renal ischemia reperfusion injury compared to wild type (WT) littermates (mean serum creatinine 39.0 ± 2.3 μmol/L vs. 78.5 ± 10.0 μmol/L, p < 0.05; mean injury score 31 ± 7% vs. 56 ± 5%, p < 0.05). Heterotopic cardiac xenografts from hEPCR mice showed a small but significant prolongation of survival in C6-deficient PVG rat recipients compared to WT grafts (median graft survival 6 vs. 5 days, p < 0.05), with less hemorrhage and edema in rejected transgenic grafts. These data indicate that it is possible to overexpress EPCR at a sufficient level to provide protection against transplant-related thrombotic and inflammatory injury, without detrimental effects in the donor animal.

Angiostatic factors in the pulmonary endarterectomy material from chronic thromboembolic pulmonary hypertension patients cause endothelial dysfunction

Chronic thromboembolic pulmonary hypertension (CTEPH) is a rare disease with persistent thrombotic occlusion or stenosis of the large pulmonary arteries resulting in pulmonary hypertension. Surgical removal of the neointimal layer of these vessels together with the non-resolved thrombus consisting of organized collagen-rich fibrotic areas with partly recanalized regions is the treatment of choice (pulmonary endarterectomy, PEA). The present study investigates endothelial cells isolated from such material as well as factors present in the surgical PEA material, which may contribute to impairment of recanalization and thrombus non-resolution. We observed muscularized vessels and non-muscularized vessels in the PEA material. The isolated endothelial cells from the PEA material showed significantly different calcium homeostasis as compared to pulmonary artery endothelial cells (hPAECs) from normal controls. In the supernatant (ELISA) as well as on the tissue level (histochemical staining) of the PEA material, platelet factor 4 (PF4), collagen type I and interferon-gamma-inducible 10 kD protein (IP-10) were detected. CXCR3, the receptor for PF4 and IP-10, was particularly elevated in the distal parts of the PEA material as compared to human control lung (RT-PCR). PF4, collagen type I and IP-10 caused significant changes in calcium homeostasis and affected the cell proliferation, migration and vessel formation in hPAECs. The presence of angiostatic factors like PF4, collagen type I and IP-10, as recovered from the surgical PEA material from CTEPH patients, may lead to changes in calcium homeostasis and endothelial dysfunction.

Intraovarian thrombin and activated protein C signaling system regulates steroidogenesis during the periovulatory period

In addition to its role in blood coagulation, thrombin directly stimulates protease-activated receptors (PAR) or interacts with thrombomodulin (THBD) to activate membrane-bound protein C which stimulates PAR1 and PAR4 receptors to promote downstream pleiotropic effects. Our DNA microarray, RT-PCR, and immunostaining analyses demonstrated ovarian expression of THBD, activated protein C (APC) receptor [endothelial protein C receptor (EPCR)], as well as PAR1 and PAR4 receptors in mice. After treatment of gonadotropin-primed immature mice with an ovulatory dose of human chorionic gonadotropin (hCG) (a LH surrogate), major increases in the expression of THBD, EPCR, PAR1, and PAR4 were detected in granulosa and cumulus cells of preovulatory follicles. Immunoassay analyses demonstrated sustained increases in ovarian prothrombin and APC levels after hCG stimulation. We obtained luteinizing granulosa cells from mice treated sequentially with equine CG and hCG. Treatment of these cells with thrombin or agonists for PAR1 or PAR4 decreased basal and forskolin-induced cAMP biosynthesis and suppressed hCG-stimulated progesterone production. In cultured preovulatory follicles, treatment with hirudin (a thrombin antagonist) and SCH79797 (a PAR1 antagonist) augmented hCG-stimulated progesterone biosynthesis, suggesting a suppressive role of endogenous thrombin in steroidogenesis. Furthermore, intrabursal injection with hirudin or SCH79797 led to ipsilateral increases in ovarian progesterone content. Our findings demonstrated increased ovarian expression of key components of the thrombin-APC-PAR1/4 signaling system after LH/hCG stimulation, and this signaling pathway may allow optimal luteinization of preovulatory follicles. In addition to assessing the role of thrombin and associated genes in progesterone production by the periovulatory ovary, these findings provide a model with which to study molecular mechanisms underlying thrombin-APC-PAR1/4 signaling.

Heterotrimeric G proteins, focal adhesion kinase, and endothelial barrier function

Ligands by binding to G protein coupled receptors (GPCRs) stimulate dissociation of heterotrimeric G proteins into Gα and Gβγ subunits. Released Gα and Gβγ subunits induce discrete signaling cues that differentially regulate focal adhesion kinase (FAK) activity and endothelial barrier function. Activation of G proteins downstream of receptors such as protease activated receptor 1 (PAR1) and histamine receptors rapidly increases endothelial permeability which reverses naturally within the following 1-2 h. However, activation of G proteins coupled to the sphingosine-1-phosphate receptor 1 (S1P1) signal cues that enhance basal barrier endothelial function and restore endothelial barrier function following the increase in endothelial permeability by edemagenic agents. Intriguingly, both PAR1 and S1P1 activation stimulates FAK activity, which associates with alteration in endothelial barrier function by these agonists. In this review, we focus on the role of the G protein subunits downstream of PAR1 and S1P1 in regulating FAK activity and endothelial barrier function.

Role of protein kinase Czeta in thrombin-induced RhoA activation and inter-endothelial gap formation of human dermal microvessel endothelial cell monolayers

We studied the potential involvement of the Ca(2+)-independent atypical protein kinase C isoform PKCzeta in mediating the thrombin-induced increase in endothelial permeability. Studies were done using human dermal microvessel endothelial cells (HMEC), which we showed constitutively expressed PKCzeta. We quantified the patency of inter-endothelial junctions (IEJs) and endothelial barrier function by measuring transendothelial electrical resistance (TER) in confluent HMEC monolayers. In control monolayers, thrombin decreased TER by approximately 50%, indicating thrombin-dependent opening of IEJs. Thrombin also elicited increases in cytosolic Ca(2+) concentration [Ca(2+)](i), actin stress fiber formation, and myosin light chain (MLC) phosphorylation. Pan-PKC inhibitors, calphostin C and chelerythrine, abrogated these responses. Thrombin also decreased TER after depletion of conventional and novel Ca(2+)-dependent PKC isoforms using phorbol 12-myristate 13-acetate (PMA). In these PMA-treated cells, thrombin induced inter-endothelial gap formation, MLC phosphorylation, and actin stress fiber formation, but failed to increase [Ca(2+)](i). Inhibition of PKCzeta activation using the PKCzeta pseudosubstrate peptide (PSI), depletion of PKCzeta protein with siRNA, and competitive inhibition of PKCzeta activity using dominant-negative (dn) PKCzeta mutant all prevented the thrombin-induced decrease in TER and MLC phosphorylation. Expression of dn-PKCzeta also inhibited thrombin-induced RhoA activation. These findings reveal a novel Ca(2+)-independent, PKCzeta-dependent mechanism of thrombin-induced increase in endothelial permeability. The results raise the possibility that inhibition of PKCzeta may be a novel drug target for thrombin-induced inflammatory hyperpermeability.

Ca2+ influx via TRPC channels induces NF-kappaB-dependent A20 expression to prevent thrombin-induced apoptosis in endothelial cells

NF-kappaB signaling is known to induce the expression of antiapoptotic and proinflammatory genes in endothelial cells (ECs). We have shown recently that Ca(2+) influx through canonical transient receptor potential (TRPC) channels activates NF-kappaB in ECs. Here we show that Ca(2+) influx signal prevents thrombin-induced apoptosis by inducing NF-kappaB-dependent A20 expression in ECs. Knockdown of TRPC1 expressed in human umbilical vein ECs with small interfering RNA (siRNA) suppressed thrombin-induced Ca(2+) influx and NF-kappaB activation in ECs. Interestingly, we observed that thrombin induced >25% of cell death (apoptosis) in TRPC1-knockdown ECs whereas thrombin had no effect on control or control siRNA-transfected ECs. To understand the basis of EC survival, we performed gene microarray analysis using ECs. Thrombin stimulation increased only a set of NF-kappaB-regulated genes 3- to 14-fold over basal levels in ECs. Expression of the antiapoptotic gene A20 was the highest among these upregulated genes. Like TRPC1 knockdown, thrombin induced apoptosis in A20-knockdown ECs. To address the importance of Ca(2+) influx signal, we measured thrombin-induced A20 expression in control and TRPC1-knockdown ECs. Thrombin-induced p65/RelA binding to A20 promoter-specific NF-kappaB sequence and A20 protein expression were suppressed in TRPC1-knockdown ECs compared with control ECs. Furthermore, in TRPC1-knockdown ECs, thrombin induced the expression of proapoptotic proteins caspase-3 and BAX. Importantly, thrombin-induced apoptosis in TRPC1-knockdown ECs was prevented by adenovirus-mediated expression of A20. These results suggest that Ca(2+) influx via TRPC channels plays a critical role in the mechanism of cell survival signaling through A20 expression in ECs.

Is thrombin a key player in the 'coagulation-atherogenesis' maze?

In addition to its established roles in the haemostatic system, thrombin is an intriguing coagulation protease demonstrating an array of effects on endothelial cells, vascular smooth muscle cells (VSMC), monocytes, and platelets, all of which are involved in the pathophysiology of atherosclerosis. There is mounting evidence that thrombin acts as a powerful modulator of many processes like regulation of vascular tone, permeability, migration and proliferation of VSMC, recruitment of monocytes into the atherosclerotic lesions, induction of diverse pro-inflammatory markers, and all of these are related to the progression of cardiovascular disease. Recent studies in transgenic mice models indicate that the deletion of the natural thrombin inhibitor heparin cofactor II promotes an accelerated atherogenic state. Moreover, the reduction of thrombin activity levels in apolipoprotein E-deficient mice, because of the administration of the direct thrombin inhibitor melagatran, attenuates plaque progression and promotes stability in advanced atherosclerotic lesions. The combined evidence points to thrombin as a pivotal contributor to vascular pathophysiology. Considering the clinical development of selective anticoagulants including direct thrombin inhibitors, it is a relevant moment to review the different thrombin-induced mechanisms that contribute to the initiation, formation, progression, and destabilization of atherosclerotic plaques.

PKC isoenzymes differentially modulate the effect of thrombin on MAPK-dependent RPE proliferation

Thrombin signalling through PAR (protease-activated receptor)-1 is involved in cellular processes, such as proliferation, differentiation and cell survival. Following traumatic injury to the eye, thrombin signalling may participate in disorders, such as PVR (proliferative vitreoretinopathy), a human eye disease characterized by the uncontrolled proliferation, transdifferentiation and migration of otherwise quiescent RPE (retinal pigment epithelium) cells. PARs activate the Ras/Raf/MEK/ERK MAPK pathway (where ERK is extracellular-signal-regulated kinase, MAPK is mitogen-activated protein kinase and MEK is MAPK/ERK kinase) through the activation of G(alpha) and G(betagamma) heterotrimeric G-proteins, and the downstream stimulation of the PLC (phospholipase C)-beta/PKC (protein kinase C) and PI3K (phosphoinositide 3-kinase) signalling axis. In the present study, we examined the molecular signalling involved in thrombin-induced RPE cell proliferation, using rat RPE cells in culture as a model system for PVR pathogenesis. Our results showed that thrombin activation of PAR-1 induces RPE cell proliferation through Ras-independent activation of the Raf/MEK/ERK1/2 MAPK signalling cascade. Pharmacological analysis revealed that the activation of 'conventional' PKC isoforms is essential for proliferation, although thrombin-induced phosphorylation of ERK1/2 requires the activation of atypical PKCzeta by PI3K. Consistently, thrombin-induced ERK1/2 activation and RPE cell proliferation were prevented completely by PI3K or PKCzeta inhibition. These results suggest that thrombin induces RPE cell proliferation by joint activation of PLC-dependent and atypical PKC isoforms and the Ras-independent downstream stimulation of the Raf/MEK/ERK1/2 MAPK cascade. The present study is the first report demonstrating directly thrombin-induced ERK phosphorylation in the RPE, and the involvement of atypical PKCzeta in this process.

Matrix metalloproteinase-1 and thrombin differentially activate gene expression in endothelial cells via PAR-1 and promote angiogenesis

Many tumor types express matrix metalloproteinase-1 (MMP-1); its collagenase activity facilitates both tumor cell invasion and metastasis. MMP-1 expression is also associated with increased angiogenesis; however, the exact mechanism by which this occurs is not clear. MMP-1 proteolytically activates protease activated receptor-1 (PAR-1), a thrombin receptor that is highly expressed in endothelial cells. Thrombin is also present in the tumor microenvironment, and its activation of PAR-1 is pro-angiogenic. It is currently unknown whether MMP-1 activation of PAR-1 induces angiogenesis in a similar or different manner compared with thrombin. We sought to determine the mechanism by which MMP-1 promotes angiogenesis and to compare the effects of MMP-1 with those of thrombin. Our results demonstrate that via PAR-1, MMP-1 activates mitogen-activated protein kinase signaling cascades in microvessel endothelial cells. Although thrombin activation of PAR-1 also induces signaling through these pathways, the time-course of activation appears to vary. Gene expression analysis revealed a possible consequence of these signaling differences as MMP-1 and thrombin induce expression of different subsets of pro-angiogenic genes. Furthermore, the combination of thrombin and MMP-1 is more angiogenic than either protease alone. These data demonstrate that MMP-1 acts directly on endothelial cells as a pro-angiogenic signaling molecule and also suggest that the effects of MMP-1 may complement the activity of thrombin to better facilitate angiogenesis and promote tumor progression.

Parstatin, the cleaved peptide on proteinase-activated receptor 1 activation, is a potent inhibitor of angiogenesis

The proteolytic activation by thrombin of the proteinase-activated receptor 1 unveils the tethered peptide ligand and cleaves a 41-amino acid peptide. In this report, we show that this peptide, which we have designated as "parstatin," is a potent inhibitor of angiogenesis. Synthesized parstatin suppressed both the basic angiogenesis and that stimulated by basic fibroblast growth factor and vascular endothelial growth factor in the chick embryo model in vivo and in the rat aortic ring assay. Parstatin also abrogated endothelial cell migration and capillary-like network formation on the Matrigel and fibrin angiogenesis models in vitro. Treatment of endothelial cells with parstatin resulted in inhibition of cell growth by inhibiting the phosphorylation of extracellular signal-regulated kinases in a specific and reversible fashion and by promoting cell cycle arrest and apoptosis through a mechanism involving activation of caspases. We have shown that parstatin acts as a cell-penetrating peptide, exerting its biological effects intracellularly. The uptake into cells and the inhibitory activity were dependent on parstatin hydrophobic region. These results support the notion that parstatin may represent an important negative regulator of angiogenesis with possible therapeutic applications.

Over-expression of the thrombin receptor (PAR-1) in the placenta in preeclampsia: a mechanism for the intersection of coagulation and inflammation

OBJECTIVE

Preeclampsia (PE) is characterized by excessive thrombin generation, which has been implicated in the multiple organ damage associated with the disease. The biological effects of thrombin on coagulation and inflammation are mediated by protease-activated receptor-1 (PAR-1), a G protein-coupled receptor. The aim of this study was to determine whether preterm PE is associated with changes in placental expression of PAR-1.

STUDY DESIGN

This cross-sectional study included two groups matched for gestational age at delivery: (1) patients with preterm PE (<37 weeks of gestation; n = 26) and (2) a control group of patients with preterm labor without intra-amniotic infection (n = 26). Placental tissue microarrays were immunostained for PAR-1. Immunoreactivity of PAR-1 in the villous trophoblasts was graded as negative, weak-positive, or strong-positive.

RESULTS

(1) The proportion of cases with strong PAR-1 immunoreactivity was significantly higher in placentas of patients with PE than in placentas from the control group (37.5% (9/24) vs. 8.7% (2/23); p = 0.036, respectively). (2) PAR-1 immunoreactivity was found in the cellular compartments of the placental villous tree, mainly in villous trophoblasts and stromal endothelial cells. (3) PAR-1 was detected in 92.3% (24/26) of the placentas of women with PE and in 88.5% (23/26) of the placentas from the control group.

CONCLUSION

Placentas from pregnancies complicated by preterm PE had a significantly higher frequency of strong PAR-1 expression than placentas from women with spontaneous preterm labor. This observation is consistent with a role for PAR-1 as a mediator of the effect of thrombin on coagulation and inflammation in PE. We propose that the effects of thrombin in PE are due to increased thrombin generation and higher expression of PAR-1, the major receptor for this enzyme.

Thrombin-mediated increases in cytosolic [Ca2+] involve different mechanisms in human pulmonary artery smooth muscle and endothelial cells

Thrombin is a procoagulant inflammatory agonist that can disrupt the endothelium-lumen barrier in the lung by causing contraction of endothelial cells and promote pulmonary cell proliferation. Both contraction and proliferation require increases in cytosolic Ca(2+) concentration ([Ca(2+)](cyt)). In this study, we compared the effect of thrombin on Ca(2+) signaling in human pulmonary artery smooth muscle (PASMC) and endothelial (PAEC) cells. Thrombin increased the [Ca(2+)](cyt) in both cell types; however, the transient response was significantly higher and recovered quicker in the PASMC, suggesting different mechanisms may contribute to thrombin-mediated increases in [Ca(2+)](cyt) in these cell types. Depletion of intracellular stores with cyclopiazonic acid (CPA) in the absence of extracellular Ca(2+) induced calcium transients representative of those observed in response to thrombin in both cell types. Interestingly, CPA pretreatment significantly attenuated thrombin-induced Ca(2+) release in PASMC; this attenuation was not apparent in PAEC, indicating that a PAEC-specific mechanism was targeted by thrombin. Treatment with a combination of CPA, caffeine, and ryanodine also failed to abolish the thrombin-induced Ca(2+) transient in PAEC. Notably, thrombin-induced receptor-mediated calcium influx was still observed in PASMC after CPA pretreatment in the presence of extracellular Ca(2+). Ca(2+) oscillations were triggered by thrombin in PASMC resulting from a balance of extracellular Ca(2+) influx and Ca(2+) reuptake by the sarcoplasmic reticulum. The data show that thrombin induces increases in intracellular calcium in PASMC and PAEC with a distinct CPA-, caffeine-, and ryanodine-insensitive release existing only in PAEC. Furthermore, a dynamic balance between Ca(2+) influx, intracellular Ca(2+) release, and reuptake underlie the Ca(2+) transients evoked by thrombin in some PASMC. Understanding of such mechanisms will provide an important insight into thrombin-mediated vascular injury during hypertension.

Mature dendritic cells express functional thrombin receptors triggering chemotaxis and CCL18/pulmonary and activation-regulated chemokine induction

Protease-activated receptors (PARs) are a family of G protein-coupled receptors that are activated by serine protease-mediated proteolytic cleavage of their extracellular domain. We have previously characterized the expression and function of PARs in human monocytes and macrophages, yet information about PARs in dendritic cells (DC) is scarce. Monocyte-derived immature DC do not express PARs. Upon maturation with LPS, but not with TNF-alpha or CD40 ligand, DC express PAR1 and PAR3, but not PAR2 or PAR4. Stimulation of DC with the serine protease thrombin or PAR1-activating peptide elicits actin polymerization and concentration-dependent chemotactic responses in LPS-, but not in TNF-alpha-matured DC. The thrombin-induced migration is a true chemotaxis with only negligible chemokinesis. Stimulation of PARs with thrombin or the respective receptor-activating peptides activates ERK1/2 and Rho kinase as well as subsequent phosphorylation of the regulatory myosin L chain 2. The ERK1/2- and Rho kinase 1-mediated phosphorylation of myosin L chain 2 was indispensable for the PAR-mediated chemotaxis as shown by pharmacological inhibitors. Additionally, thrombin stimulated the Rho-dependent release of the CC chemokine CCL18/pulmonary and activation-regulated chemokine, which induces chemotaxis of lymphocytes and immature DC as well as fibroblast proliferation. The colocalization of CD83(+) DC with CCL18 in human atherosclerotic plaques revealed by immunofluorescence microscopy combined with the presence of functionally active thrombin receptors on mature DC point to a previously unrecognized functional role of thrombin in DC biology. The thrombin-induced stimulation of mature DC may be of particular relevance in atherosclerotic lesions, which harbor all components of this novel mechanism.

Thrombin receptor and ventricular arrhythmias after acute myocardial infarction

The mechanism mediating the development of ventricular arrhythmia (VA) after acute myocardial infarction (AMI) is still uncertain. Thrombin receptor (TR) activation has been proven to be arrhythmogenic in many other situations, and we hypothesize that it may participate in the genesis of post-AMI VA. Using a left coronary artery ligation rat model of AMI, we found that a local injection of hirudin into the left ventricle (LV) significantly reduced the ratio of VA durations to infarction sizing, whereas injection of thrombin receptor-activating peptide (TRAP) increased the ratios of VA duration to infarction sizing. The effects of TR activation on whole-cell currents were investigated in isolated myocytes. TRAP increased a glibenclamide-sensitive outward current. Pretreatment of rats with glibenclamide (4 mg/kg intraperitoneally) eliminated the effects of a local injection of TRAP on the ratios of VA durations to infarction sizing. TR mRNA and protein expression in the ischemic left ventricle had reached its peak by 20 min postligation in the rat AMI model (P < 0.05). TR-immunoreactive myocytes were observed in infarcted LV but were seldom seen in the right ventricle or in the normal heart. By 60 min, TR transcript levels had returned to control levels. We conclude that increased TR activation and expression in the infarcted LV after AMI may contribute to VA through a mechanism involving glibenclamide-sensitive potassium channels.

Thrombin-promoted release of UDP-glucose from human astrocytoma cells

BACKGROUND AND PURPOSE

The P2Y14 receptor is activated by UDP-sugars, most potently by UDP-glucose, but not by free nucleotides, suggesting that UDP-glucose is the cognate agonist for this receptor. However, evidence for regulated release of UDP-glucose is scarce. In the present study, the occurrence of receptor-promoted release of UDP-glucose was investigated, using 1321N1 human astrocytoma cells.

EXPERIMENTAL APPROACH

UDP-glucose release and hydrolysis were measured using HPLC-based techniques. Phospholipase C activation and actin cytoskeleton reorganization were assessed by measuring inositol phosphate formation and fluorescence confocal microscopy, respectively.

KEY RESULTS

Thrombin and the protease-activating receptor-1 (PAR1) peptide TFLLRNPNDK (PAR1-AP) evoked the release of UDP-glucose and ATP, which was accompanied by enhanced inositol phosphate formation. Although carbachol promoted fourfold greater inositol phosphate formation than thrombin, it failed to promote nucleotide release. Thrombin-promoted nucleotide release was inhibited by BAPTA-AM, brefeldin A and cytochalasin D, and was insensitive to Pertussis toxin and PI3-kinase inhibitors. Thrombin, but not carbachol, induced actin cytoskeleton reorganization, a hallmark of Rho activation in 1321N1 cells. However, PAR-promoted UDP-glucose release was not affected by Rho kinase inhibition.

CONCLUSIONS AND IMPLICATIONS

PAR1-evoked UDP-glucose release reflected a Ca2+-dependent mechanism, engaging additional signalling independently of G(i) and Rho kinase activation and requiring a functional actin cytoskeleton and Golgi structures. Our study demonstrates the occurrence of Ca2+ -dependent release of UDP-glucose from astrocytoma cells in response to a physiologically relevant stimulus, that is, a G-protein-coupled receptor agonist. Given the presence of P2Y14 receptors in astrocytes, UDP-glucose may have important autocrine/paracrine functions in the brain.

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

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

Prevention of the hypercontractile response to thrombin by proteinase-activated receptor-1 antagonist in subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Cerebral vasospasm is one of the major complications of subarachnoid hemorrhage (SAH). Its pathogenesis still remains elusive, and effective therapeutic strategies are yet to be established. We investigated the role of proteinase-activated receptor-1 (PAR1) in the hypercontractile state in SAH.

METHODS

Rabbit double hemorrhage model was used as a model of SAH. The contractile response to thrombin and the PAR1 expression were evaluated in the isolated rings of basilar artery.

RESULTS

Thrombin exhibited only a minor contractile effect in the control, whereas it induced augmented contractions in SAH. The expression of PAR1 was upregulated in SAH. Intracisternal injection of PAR1 antagonist E5555 prevented the enhancement of the contractile responses to thrombin in SAH. The maximal prevention was obtained with 2 microg/kg weight/injection. The contractile responses to K(+) depolarization or endothelin-1 remained unaffected. The upregulation of PAR1 was also prevented by E5555 (2 microg/kg weight/injection) to a level similar to that seen in the control. Ex vivo treatment with E5555 (1 micromol/L) inhibited the contraction induced by thrombin, whereas it had little effect on the contraction induced by K(+) depolarization or endothelin-1, in the basilar artery of SAH. E5555 also inhibited the [Ca(2+)](i) elevation induced by thrombin, but not trypsin, in cultured smooth muscle cells.

CONCLUSIONS

PAR1 plays a critical role in upregulating PAR1 itself, thereby enhancing the contractile response to thrombin in SAH. PAR1 could thus be a therapeutic target. However, the usefulness of PAR1 antagonist remains to be investigated in vivo.

Up-regulation of proteinase-activated receptor 1 and increased contractile responses to thrombin after subarachnoid haemorrhage

BACKGROUND AND PURPOSE

The mechanism for the development of post-haemorrhagic cerebral vasospasm after subarachnoid haemorrhage (SAH) still remains unknown.

EXPERIMENTAL APPROACH

We investigated the role of thrombin and its receptor PAR1 in the development of hyper-contractility of the basilar artery in a rabbit double haemorrhage model, which received two injections of autologous blood into the cisterna magna.

KEY RESULTS

In the basilar artery isolated from the control rabbits, thrombin, only at 10 units ml(-1), induced a transient endothelium-dependent relaxation and a slight smooth muscle contraction. In SAH, the contractile response to thrombin was markedly enhanced, while the endothelium-dependent relaxant effect of thrombin remained unchanged. The enhancement of the contractile responses was also observed in the absence of endothelium and thrombin induced an enhanced contraction at concentrations higher than 0.3 units ml(-1). The contractile response to PAR1-activating peptide was also enhanced after SAH. However, the contractile responses to high K+ and endothelin-1, and the myofilament Ca2+-sensitivity remained unchanged after SAH. An immunoblot analysis suggested the up-regulation of PAR1 in the smooth muscle of the basilar artery. The heparinization of blood before injection prevented the enhancement of the contractile responses to thrombin and PAR1-activating peptide.

CONCLUSIONS AND IMPLICATIONS

The present study demonstrated, for the first time, that the contractile response of the basilar artery to thrombin was markedly enhanced after SAH. Mechanistically, our findings suggested that the activation of thrombin following hemorrhage up-regulated the expression of PAR1, thereby inducing the hyper-responsiveness to thrombin.

c-Src interacts with and phosphorylates RelA/p65 to promote thrombin-induced ICAM-1 expression in endothelial cells

The procoagulant thrombin promotes polymorphonuclear leukocyte (PMN) adhesion to endothelial cells by a mechanism involving expression of intercellular adhesion molecule-1 (ICAM-1) via an NF-kappaB-dependent pathway. We now provide evidence that activation of c-Src is crucial in signaling thrombin-induced ICAM-1 expression via tyrosine phosphorylation of RelA/p65. Stimulation of human umbilical vein endothelial cells with thrombin resulted in a time-dependent activation of c-Src, with maximal activation occurring at 30 min after thrombin challenge. Inhibition of c-Src by pharmacological and genetic approaches impaired thrombin-induced NF-kappaB-dependent reporter activity and ICAM-1 expression. Analysis of the NF-kappaB pathway revealed that the effect of c-Src inhibition occurred independently of IkappaBalpha degradation and NF-kappaB DNA binding function and was not associated with exchange of NF-kappaB dimers. Phosphorylation of RelA/p65 at Ser(536), an event mediating the transcriptional activity of DNA-bound RelA/p65, was also insensitive to c-Src inhibition. Interestingly, thrombin induced association of c-Src with RelA/p65, and inhibition of c-Src prevented this response, indicating that this interaction is contingent on activation of c-Src. We also observed that thrombin induced tyrosine phosphorylation of RelA/p65, and this phosphorylation was lost upon inhibition of c-Src, consistent with the requirement of activated c-Src for interaction with RelA/p65. These data implicate an important role of c-Src in phosphorylating RelA/p65 to promote the transcriptional activity of NF-kappaB and thereby ICAM-1 expression in endothelial cells.

Prevention of stroke and dementia by statin therapy: Experimental and clinical evidence of their pleiotropic effects

Stroke and dementia are major causes of disability in most countries. Epidemiological studies have demonstrated that statins (3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors) are likely to reduce the risk for developing these formidable disorders. The favorable outcomes in statin users may be attributable to not only cholesterol-dependent actions, but also various cholesterol-independent actions called "pleiotropic effects." Several clinical trials have suggested that statins decrease the incidence of stroke, especially ischemic stroke. Statins improve endothelial function, inhibit platelet activation, reduce blood coagulability, and suppress inflammatory reactions, all of which may contribute to the beneficial effects of the therapy. Statins also reduce the risk of vasospasm caused by subarachnoid hemorrhage (SAH). In addition, statins might inhibit the development and progression of Alzheimer's disease (AD), the dominant type of dementia in most industrialized countries, upstream of the amyloid cascade. In vitro studies have shown that statins modulate the metabolism of the beta-amyloid precursor protein (APP) and reduce the extracellular level of its proteolytic product, amyloid-beta (Abeta). The aggregated Abeta is cytotoxic, leading to formation of neurofibrillary tangles and neuronal loss in the brain. Inflammatory processes are active in AD and may contribute significantly to AD pathology. We review the experimental background regarding the pleiotropic effects of statins and summarize clinical trials that examined the preventative effects of statin therapy on stroke and dementia. We include current trials in which statin therapy is initiated within 24 hr of onset of acute ischemic stroke.

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

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

Upregulation of proteinase-activated receptors and hypercontractile responses precede development of arterial lesions after balloon injury

Thrombin and other proteinases exert vascular effects by activating the proteinase-activated receptors (PARs). The expression of PARs has been shown to be upregulated after balloon injury and in human arteriosclerosis. However, the relationship between the receptor upregulation and the alteration of vasomotor function remains to be elucidated. We herein demonstrated that the contractile responses to the PAR-1 and PAR-2 agonist were markedly enhanced in the rabbit femoral arteries after balloon injury. Neointimal thickening was established 4 wk after the injury. No histological change was observed in the sham operation, where the saphenous artery was ligated without any balloon injury. The contractile response to K+depolarization was significantly attenuated 1 wk after the injury and then partly recovered after 4 wk. Thrombin, PAR-1-activating peptide, trypsin, and PAR-2-activating peptide induced no significant contraction in the control. All these stimulants induced enhanced responses 1 wk after balloon injury. Such enhanced responses were seen 4 wk after the injury, except for thrombin. There was no change in the Ca2+sensitivity of the contractile apparatus as evaluated in the permeabilized preparations. PAR-1-activating peptide (100 μmol/l), but no other stimulants, induced an enhanced contraction in the sham operation. The expression of PAR-1 and PAR-2 slightly increased after the sham operation, whereas it markedly and significantly increased after balloon injury. Our observations suggest that balloon injury induced the receptor upregulation, thereby enhancing the contractile response before the establishment of vascular lesions. The local inflammation associated with the sham operation may also contribute to the receptor upregulation.

Caveolin-1 regulates store-operated Ca2+ influx by binding of its scaffolding domain to transient receptor potential channel-1 in endothelial cells

Caveolin-1 associates with store-operated cation channels (SOC) in endothelial cells. We examined the role of the caveolin-1 scaffolding domain (CSD) in regulating the SOC [i.e., transient receptor potential channel-1 (TRPC1)] in human pulmonary artery endothelial cells (HPAECs). We used the cell-permeant antennapedia (AP)-conjugated CSD peptide, which competes for protein binding partners with caveolin-1, to assess the interactions of caveolin-1 with TRPC1 and its consequences on thrombin-induced Ca2+ influx. We observed that AP-CSD peptide markedly reduced thrombin-induced Ca2+ influx via SOC in HPAECs in contrast to control peptide. AP-CSD also suppressed thapsigargin-induced Ca2+ influx. Streptavidin-bead pull-down assay indicated strong binding of biotin-labeled AP-CSD peptide to TRPC1. Immunoprecipitation studies demonstrated an interaction between endogenous TRPC1 and ectopically expressed hemagglutinin-tagged CSD. Analysis of the deduced TRPC1 amino acid sequence revealed the presence of CSD binding consensus sequence in the TRPC1 C terminus. We also observed that an AP-TRPC1 peptide containing the CSD binding sequence markedly reduced the thrombin-induced Ca2+ influx. We identified the interaction between biotin-labeled AP-TRPC1 C terminus peptide and caveolin-1. Thus, these results demonstrate a crucial role of caveolin-1 scaffolding domain interaction with TRPC1 in regulating Ca2+ influx via SOC.

Integration of P2Y receptor-activated signal transduction pathways in G protein-dependent signalling networks

The role of nucleotides in intracellular energy provision and nucleic acid synthesis has been known for a long time. In the past decade, evidence has been presented that, in addition to these functions, nucleotides are also autocrine and paracrine messenger molecules that initiate and regulate a large number of biological processes. The actions of extracellular nucleotides are mediated by ionotropic P2X and metabotropic P2Y receptors, while hydrolysis by ecto-enzymes modulates the initial signal. An increasing number of studies have been performed to obtain information on the signal transduction pathways activated by nucleotide receptors. The development of specific and stable purinergic receptor agonists and antagonists with therapeutical potential largely contributed to the identification of receptors responsible for nucleotide-activated pathways. This article reviews the signal transduction pathways activated by P2Y receptors, the involved second messenger systems, GTPases and protein kinases, as well as recent findings concerning P2Y receptor signalling in C6 glioma cells. Besides vertical signal transduction, lateral cross-talks with pathways activated by other G protein-coupled receptors and growth factor receptors are discussed.

Ca2+ influx induced by protease-activated receptor-1 activates a feed-forward mechanism of TRPC1 expression via nuclear factor-kappaB activation in endothelial cells

Thrombin activation of protease-activated receptor-1 induces Ca(2+) influx through store-operated cation channel TRPC1 in endothelial cells. We examined the role of Ca(2+) influx induced by the depletion of Ca(2+) stores in signaling TRPC1 expression in endothelial cells. Both thrombin and a protease-activated receptor-1-specific agonist peptide induced TRPC1 expression in human umbilical vein endothelial cells, which was coupled to an augmented store-operated Ca(2+) influx and increase in endothelial permeability. To delineate the mechanisms of thrombin-induced TRPC1 expression, we transfected in endothelial cells TRPC1-promoter-luciferase (TRPC1-Pro-Luc) construct containing multiple nuclear factor-kappaB (NF-kappaB) binding sites. Co-expression of dominant negative IkappaBalpha mutant prevented the thrombin-induced increase in TRPC1 expression, indicating the key role of NF-kappaB activation in mediating the response. Using TRPC1 promoter-deletion mutant constructs, we showed that NF-kappaB binding sites located between -1623 and -871 in the TRPC1 5'-regulatory region were required for thrombin-induced TRPC1 expression. Electrophoretic mobility shift assay utilizing TRPC1 promoter-specific oligonucleotides identified that the DNA binding activities of NF-kappaB to NF-kappaB consensus sites were located in this domain. Supershift assays using NF-kappaB protein-specific antibodies demonstrated the binding of p65 homodimer to the TRPC1 promoter. Inhibition of store Ca(2+) depletion, buffering of intracellular Ca(2+), or down-regulation of protein kinase Calpha downstream of Ca(2+) influx all blocked thrombin-induced NF-kappaB activation and the resultant TRPC1 expression in endothelial cells. Thus, Ca(2+) influx via TRPC1 is a critical feed-forward pathway responsible for TRPC1 expression. The NF-kappaB-regulated TRPC1 expression may be an essential mechanism of vascular inflammation and, hence, a novel therapeutic target.

Negative regulation of protease-activated receptor 1-induced Src kinase activity by the association of phosphocaveolin-1 with Csk

Protease-activated receptor 1 (PAR1), a G protein-coupled receptor (GPCR) for thrombin, has been correlated with cell proliferation. PAR1 is activated by the irreversibly proteolytic cleavage, internalized via clathrin-coated pits, and then sorted to lysosomes for degradation. Caveolae play important roles in both signaling transduction and internalization of several GPCRs. However, the role of caveolae in cellular signaling and trafficking of PAR1 is still unclear. In this study, we show that PAR1 was partially localized in caveolae. Disruption of caveolae by cholesterol depletion did not inhibit PAR1 internalization, indicating that internalization of PAR1 was not via caveolae. Of interest, activation of PAR1 resulted in the phosphorylation of caveolin-1, a principal component of caveolae, on tyrosine 14 by a Gi-linked Src kinase pathway and p38 mitogen-activated protein kinase. Analysis of immunoprecipitates from cells stimulated by PAR1 showed that phosphocaveolin-1 but not caveolin-1 with mutation at tyrosine 14 could bind to Csk. In addition, phosphocaveolin-1 could not bind to CskS109C mutant with the defective SH2 domain. These results indicated that phosphocaveolin-1 was associated with the SH2 domain of Csk in response to PAR1 activation. The association further resulted in a rapid decrease in Src kinase activity. Thus, PAR1-induced Src activation is negatively regulated by recruiting Csk through phosphocaveolin-1. Our results also reveal that phosphocaveolin-1 represents a novel effector of PAR1 to downregulate Src kinase activity. The downregulation of PAR1-induced Src activation mediated by phosphocaveolin-1 provides an additional mechanism for the termination of PAR1 signaling at its downstream molecules.

Involvement of Gi/o in the PAR-4-induced NO production in endothelial cells

We investigated the involvement of G(i/o) protein in NO production following the activation of proteinase-activated receptor-4 (PAR-4) in cultured bovine aortic endothelial cells. AYPGKF-NH(2) (PAR-4 activating peptide), thrombin, and ionomycin induced a concentration-dependent NO production, with the maximal production seen at 30 microM, 0.1U/ml, and 1 microM, respectively. Ionomycin elevated [Ca(2+)](i) in a concentration-dependent manner. However, AYPGKF-NH(2) and thrombin induced no [Ca(2+)](i) elevation. The loading of cells with BAPTA almost completely inhibited both the NO production and [Ca(2+)](i) elevation induced by 1 microM ionomycin, while it had no significant effect on the AYPGKF-NH(2)-induced NO production. Treatment with pertussis toxin inhibited the AYPGKF-NH(2)-induced NO production, while it had no effect on the ionomycin-induced NO production. Our findings thus demonstrate, for the first time, that PAR-4 activation induced NO production in a manner mostly independent of the Ca(2+) signal and also that G(i/o) is involved in such NO production in vascular endothelial cells.

Contribution of extracellular proteolysis and microglia to intracerebral hemorrhage

Proteases, such as tissue plasminogen activator, thrombin, metalloproteinases, and cathepsins, have complex functions in the mammalian brain under both normal and pathological conditions. Some of these proteases are expressed by neuronal cells, whereas others are made by the immunocompetent, macrophage-like cells of the brain: the microglia. This article reviews the physiological and pathological functions of these proteinases in the brain as well as recent findings linking extracellular proteases with neuronal cell death in ischemic or hemorrhagic stroke. Better understanding of protease expression and signaling, microglial activation, and their relationship with neuronal cell death during stroke injury could contribute to the development of relevant inhibitors as novel neuroprotective agents for treating ischemic stroke and intracerebral hemorrhage.

Transport across the endothelium: regulation of endothelial permeability

An important function of the endothelium is to regulate the transport of liquid and solutes across the semi-permeable vascular endothelial barrier. Two cellular pathways controlling endothelial barrier function have been identified. The transcellular pathway transports plasma proteins of the size of albumin or greater via the process of transcytosis in vesicle carriers originating from cell surface caveolae. Specific signalling cues are able to induce the internalisation of caveolae and their movement to the basal side of the endothelium. Caveolin-1, the primary structural protein required for the formation of caveolae, is also important in regulating vesicle trafficking through the cell by controlling the activity and localisation of signalling molecules that mediate vesicle fission, endocytosis, fusion and finally exocytosis. An important function of the transcytotic pathways is to regulate the delivery of albumin and immunoglobulins, thereby controlling tissue oncotic pressure and host-defence. The paracellular pathway induced during inflammation is formed by gaps between endothelial cells at the level of adherens and tight junctional complexes. Paracellular permeability is increased by second messenger signalling pathways involving Ca2+ influx via activation of store-operated channels, protein kinase Calpha (PKCalpha), and Rho kinase that together participate in the stimulation of myosin light chain phosphorylation, actin-myosin contraction, and disruption of the junctions. In this review of the field, we discuss the current understanding of the signalling pathways regulating paracellular and transcellular endothelial permeability.

Chemokine receptor 7 activates phosphoinositide-3 kinase-mediated invasive and prosurvival pathways in head and neck cancer cells independent of EGFR

Chemokine receptor 7 (CCR7) upregulation, which mediates immune cell survival and migration to lymph nodes, has recently been associated with nodal metastasis of squamous cell carcinoma of the head and neck (SCCHN). However, the mechanism of CCR7 in tumor progression, its downstream signaling mediators, and interactions with other pathways contributing to metastasis of SCCHN have not been determined. We hypothesized that inflammatory chemokine-mediated signals could also promote tumor proliferation and mitogenic effects. Functional assays showed that chemotaxis and invasion of metastatic SCCHN cells were dependent on phosphoinositide-3 kinase (PI3K) and its substrate, activated phospholipase Cgamma-1. In addition, treatment of CCR7(+) metastatic SCCHN cells with CCL19 (MIP-3beta) showed rapid activation of the prosurvival, PI3K/Akt pathway. Transactivation of EGFR-mediated and mitogen-activated protein kinase signaling pathways, which can promote migration and survival in parallel, did not appear to contribute to the functional or biochemical effects of CCR7 stimulation. Thus, proinflammatory chemokine signals that mediate activation, trafficking and survival of tumor-infiltrating immune cells in the tumor microenvironment actually appear to induce signals for progression of cancer cells. The CCR7-mediated pathway in metastatic SCCHN cells functions independently of EGFR signal transduction and therefore may represent an additional target for therapeutic intervention to prevent tumor progression and metastasis.

Functional role of TRPC channels in the regulation of endothelial permeability

The endothelial cells (ECs) form a semipermeable barrier between the blood and the tissue. An important function of the endothelium is to maintain the integrity of the barrier function of the vessel wall. Ca(2+) signaling in ECs plays a key role in maintaining the barrier integrity. Transient receptor potential canonical (TRPC) channels are mammalian homologs of Drosophila TRP Ca(2+)-permeable channels expressed in EC. TRPC channels are thought to function as a Ca(2+) entry channel operated by store-depletion as well as receptor-activated channels in a variety of cell types, including ECs. Inflammatory mediators such as thrombin, histamine, bradykinin, and others increase endothelial permeability by actin polymerization-dependent EC rounding and formation of inter-endothelial gaps, a process critically dependent on the increase in EC cytosolic [Ca(2+)] ([Ca(2+)](i)). Increase in endothelial permeability depends on both intracellular Ca(2+) release and extracellular Ca(2+) entry through TRPC channels. This review summarizes recent findings on the role of TRPC channels in the mechanism of Ca(2+) entry in ECs, and, in particular, the role of TRPC channels in regulating endothelial barrier function.