Factor VIIa stimulates endothelin-1 synthesis in TNF-primed endothelial cells by activation of protease-activated receptor 2

Re-evaluation of mouse tissue factor pathway inhibitor and comparison of mouse and human tissue factor pathway inhibitor physiology

Essentials Mouse models are often used to define roles of tissue factor pathway inhibitor (TFPI) in man. TFPI isoform-specific KOs reveal unexpected differences between mouse and human TFPI physiology. Mouse plasma contains 20 times more TFPI than man, derived from TFPIγ, a form not found in man. TFPIγ null mice, expressing only TFPI isoforms α and β, may better reflect the human situation. SUMMARY: Background Mouse models can provide insight into the pathophysiology of human thrombosis and hemostasis. Tissue factor pathway inhibitor (TFPI) regulates coagulation through protein S (PS)-enhanced factor (F) Xa inhibition and FXa-dependent inhibition of FVIIa/tissue factor (TF) activity. TFPI is expressed as isoforms α and β in man, and α, β and γ in the mouse. Objective Assess the reliability of extending TFPI-related studies in mice to humans. Method Compare mouse and human TFPI physiology using a variety of methods. Results Mouse TFPI and human TFPI are similar in regard to: (i) the mechanisms for FVIIa/TF and FXa inhibition; (ii) TFPIα is a soluble form and TFPIβ is glycosyl phosphatidyl inositol (GPI) membrane anchored; (iii) the predominant circulating form of TFPI in plasma is lipoprotein-associated; (iv) low levels of TFPIα circulate in plasma and increase following heparin treatment; and (v) TFPIα is the isoform in platelets. They differ in that: (i) mouse TFPI circulates at a ~20-fold higher concentration; (ii) mouse lines with isolated isoform deletions show this circulating mouse TFPI is derived from TFPIγ; (iii) sequences homologous to the mouse TFPIγ exon are present in many species, including man, but in primates are unfavorable for splicing; and (iv) tandem mass spectrometry (MS/MS) detects sequences for TFPI isoforms α and β in human plasma and α and γ in mouse plasma. Conclusion To dissect the pathophysiological roles of human TFPIα and TFPIβ, studies in TFPIγ null mice, expressing only α and β, only α or only β should better reflect the human situation.

Characterisation of preproendothelin-1 derived peptides identifies Endothelin-Like Domain Peptide as a modulator of Endothelin-1

Endothelin-1 (ET-1) is involved in the pathogenesis of cardiac and renal diseases, and in the progression of tumour growth in cancer, but current diagnosis and treatment remain inadequate. Peptides derived from the 212 amino acid precursor preproendothelin-1 (ppET-1) may have utility as biomarkers, or cause biological effects that are unaffected by endothelin receptor antagonists. Here, we used specific immunoassays and LC-MS/MS to identify NT-proET-1 (ppET-1_[18–50]), Endothelin-Like Domain Peptide (ELDP, ppET-1_[93–166]) and CT-proET-1 (ppET-1_[169–212]) in conditioned media from cultured endothelial cells. Synthesis of these peptides correlated with ET-1, and plasma ELDP and CT-proET-1 were elevated in patients with chronic heart failure. Clearance rates of NT-proET-1, ELDP and CT-proET-1 were determined after i.v. injection in anaesthetised rats. CT-proET-1 had the slowest systemic clearance, hence providing a biological basis for it being a better biomarker of ET-1 synthesis. ELDP contains the evolutionary conserved endothelin-like domain sequence, which potentially confers biological activity. On isolated arteries ELDP lacked direct vasoconstrictor effects. However, it enhanced ET-1 vasoconstriction and prolonged the increase in blood pressure in anaesthetised rats. ELDP may therefore contribute to disease pathogenesis by augmenting ET-1 responses.

Tissue Factor-Factor VIIa complex induces cytokine expression in coronary artery smooth muscle cells

OBJECTIVE

Within atherosclerotic lesions Tissue Factor (TF)-Factor VIIa (FVIIa) not only contributes to thrombotic events but also alters vascular remodeling through enhancement of migration. Moreover, the TF-FVIIa-FXa complex activates protease-activated receptors (PAR). TF/FVIIa/PAR-2 signaling has also been shown to promote proliferation and metastasis of tumor cells. Since coagulation factors promote inflammation which plays a major role during atherosclerosis as well as tumor metastasis this study sought to investigate the effects of FVIIa on the inflammatory response in vascular cells.

METHODS/RESULTS

FVIIa induces interleukin-8 (IL-8) and IL-6 in primary smooth muscle cells (SMC), which was correlated to the expression of TF and PAR-2 as shown by immunoassay and qRT-PCR. The effect was dose-dependent and required TF, the proteolytic activity of FVIIa and PAR-2. Secondary effects of downstream coagulation factors were excluded. No proinflammatory FVIIa effect was observed in endothelial cells (EC) and mononuclear cells (MNC), expressing either TF or PAR-2. In atherosclerotic lesions mRNA expression of PAR-1, PAR-2 and IL-8 was elevated compared to healthy vessels indicating a role for PAR-1 and PAR-2 signaling in atherosclerosis.

CONCLUSION

In addition to the procoagulant and promigratory role of the TF-FVIIa complex we identify a proinflammatory role of FVIIa in human SMC dependent on expression of TF and PAR-2 that provides yet another link between coagulation and inflammation.

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

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

LIGR, a protease-activated receptor-2-derived peptide, enhances skin pigmentation without inducing inflammatory processes

The protease-activated receptor-2 (PAR-2) is a seven transmembrane G-protein-coupled receptor that could be activated by serine protease cleavage or by synthetic peptide agonists. We showed earlier that activation of PAR-2 with Ser-Leu-Ile-Gly-Arg-Leu-NH(2) (SLIGRL), a known PAR-2 activating peptide, induces keratinocyte phagocytosis and increases skin pigmentation, indicating that PAR-2 regulates pigmentation by controlling phagocytosis of melanosomes. Here, we show that Leu-Ile-Gly-Arg-NH(2) (LIGR) can also induce skin pigmentation. Both SLIGRL and LIGR increased melanin deposition in vitro and in vivo, and visibly darkened human skins grafted onto severe combined immuno-deficient (SCID) mice. Both SLIGRL and LIGR stimulated Rho-GTP activation resulting in keratinocyte phagocytosis. Interestingly, LIGR activates only a subset of the PAR-2 signaling pathways, and unlike SLIGRL, it does not induce inflammatory processes. LIGR did not affect many PAR-2 signaling pathways, including [Ca(2+)] mobilization, cAMP induction, the induction of cyclooxgenase-2 (COX-2) expression and the secretion of prostaglandin E2, interleukin-6 and -8. PAR-2 siRNA inhibited LIGR-induced phagocytosis, indicating that LIGR signals via PAR-2. Our data suggest that LIGR is a more specific regulator of PAR-2-induced pigmentation relative to SLIGRL. Therefore, enhancing skin pigmentation by topical applications of LIGR may result in a desired tanned-like skin color, without enhancing inflammatory processes, and without the need of UV exposure.

Induction of inflammatory cytokine release from human umbilical vein endothelial cells by agonists of proteinase-activated receptor-2

1. Human endothelial cells express proteinase-activated receptor-2 (PAR-2), inflammatory cytokines and trypsin (EC 3.4.21.4). However, little is known about the mechanism through which trypsin induces cytokine release from endothelial cells. 2. In the present study, we investigated the effect of trypsin on cytokine release from primary cultures of human umbilical vein endothelial cells (HUVEC) using an antibody based protein microarray and ELISA. 3. The results showed that 1 microg/mL trypsin induced release of 32 different inflammatory factors, whereas 100 micromol/L Ser-Leu-Ile-Gly-Lys-Val-NH2 (SLIGKV-NH2) only stimulated secretion of 16 inflammatory factors from HUVEC, as assessed by an antibody based protein microarray. Because the release of interleukin (IL)-1a, IL-8, IL-10 and IL-12 was markedly increased following PAR-2 activation, their release was investigated further using ELISA. Increases in release of up to approximately 4.8-, 4.3-, 4.1- and 1.8-fold were observed for IL-1a, IL-10, IL-12 and IL-8, respectively, when HUVEC were challenged with trypsin for 16 h. Agonist peptides of PAR-2, namely SLIGKV-NH2 and trans-cinnamoyl-Leu-Ile-Gly-Arg-Leu-Orn-NH2 (tc-LIGRLO-NH2), also provoked significant release of IL-8. Trypsin-induced cytokine release was inhibited by its inhibitors soybean trypsin inhibitor, alpha1-antitrypsin and the inhibitor peptide of PAR-2 Phe-Ser-Leu-Leu-Arg-Tyr-NH2 (FSLLRY-NH2). 4. These data indicate the action of trypsin on HUVEC is most likely through activation of PAR-2, suggesting that PAR-2-related mechanisms are involved in the inflammatory process in humans.

Protease-activated receptor-2 regulates vascular endothelial growth factor expression in MDA-MB-231 cells via MAPK pathways

Protease-activated receptor 2 (PAR2) is a G-protein coupled receptor that is cleaved and activated by serine proteases including the coagulation protease factor VIIa (FVIIa). There is evidence that PAR2 function contributes to angiogenesis, but the mechanisms involved are poorly defined. Here we show that PAR2 activation in human breast cancer cells leads to the upregulation of vascular endothelial growth factor (VEGF). Activation of PAR2 with agonist peptide (AP), trypsin or FVIIa results in a robust increase of VEGF message and protein. Incubation of cells with PAR1-AP, PAR3-AP, PAR4-AP, or thrombin has only a modest effect on VEGF production. Cleavage blocking antibodies show that FVIIa-mediated VEGF production is PAR2 mediated. Mitogen-activated protein kinase (MAPK) pathway inhibitors U0126 and SB203580 inhibit PAR2-mediated VEGF production. Incubation of cells with PAR2-AP leads to significant extracellular regulated kinase1/2 (ERK1/2) and p38 MAPK phosphorylation and activation. Collectively, these data suggest that PAR2 signaling through MAPK pathways leads to the production of proangiogenic VEGF in breast cancer cells.

Differential expression of tissue factor (TF) in calcineurin inhibitor-induced nephrotoxicity and rejection—implications for development of a possible diagnostic marker

Deposition of fibrin in the form of fibrinoid necrosis is a common feature of severe acute renal allograft rejection. The role of the coagulation system and its initiator tissue factor (TF) during this process is, however, still poorly understood. In this study, we analyzed the expression of TF in 88 renal transplants afflicted with different forms of rejection and calcineurin inhibitor-induced nephrotoxicity, to see whether there was differential expression of this protein. TF immunoreactivity was evaluated semiquantitatively in six different renal structures: the podocytes, Bowman epithelium, the endothelium of the glomeruli, the brush border of tubular cells, the thin ascending loop of Henle, and small arteries/arterioles. The TF expression of normal renal tissue (n=6) was restricted to the glomerular podocytes and Bowman epithelium, and to some extent the ascending loop of Henle. Renal allografts undergoing acute rejection (AR) of grades I-III, (n=13, n=17 and n=12, respectively) did not show any altered TF expression in the glomeruli or vascular endothelium. In the ascending loop of Henle, a reduced expression could be seen (ARI, p=0.015; and ARII, p=0.043). TF staining of the brush border of renal transplants undergoing acute cyclosporin A (CsA) nephrotoxicity (n=18) was significantly higher than in normal kidneys (p=0.0003), as well as in transplants undergoing various degrees of acute rejection (ARI, p=0.027; ARII, p=0.0012; and ARIII, p=0.0001). Tubular brush border-expressed TF was also evident in 10 of 15 allografts suffering from chronic CsA nephrotoxicity, compared to 4 out of 13 cases with chronic allograft vasculopathy (CAV), but the increase was not statistically significant relative to normal kidneys. The majority of the grafts afflicted with either of the two chronic conditions displayed a TF-positive arterial endothelium (CAV, p=0.0034; and chronic CsA nephrotoxicity, p=0.0026) relative to controls. In conclusion, these results indicate that vascular TF expression is not altered during acute rejection, but may be of importance in chronic allograft nephropathy. Furthermore, TF immunoreactivity in the tubular brush border may be specific to acute CsA nephrotoxicity and might be used as a biomarker for this condition. Further studies are required to evaluate the possible role of brush border-expressed TF in the pathogenesis of CsA nephrotoxicity.