Factor VIIa bound to endothelial cell protein C receptor activates protease activated receptor-1 and mediates cell signaling and barrier protection

Center for Biomedical Research, The University of Texas Health Science Center at Tyler, Tyler, TX, USA.
Blood (Impact Factor: 10.45). 03/2011; 117(11):3199-208. DOI: 10.1182/blood-2010-09-310706
Source: PubMed


Recent studies have shown that factor VIIa (FVIIa) binds to the endothelial cell protein C receptor (EPCR), a cellular receptor for protein C and activated protein C, but the physiologic significance of this interaction is unclear. In the present study, we show that FVIIa, upon binding to EPCR on endothelial cells, activates endogenous protease activated receptor-1 (PAR1) and induces PAR1-mediated p44/42 mitogen-activated protein kinase (MAPK) activation. Pretreatment of endothelial cells with FVIIa protected against thrombin-induced barrier disruption. This FVIIa-induced, barrier-protective effect was EPCR dependent and did not involve PAR2. Pretreatment of confluent endothelial monolayers with FVIIa before thrombin reduced the development of thrombin-induced transcellular actin stress fibers, cellular contractions, and paracellular gap formation. FVIIa-induced p44/42 MAPK activation and the barrier-protective effect are mediated via Rac1 activation. Consistent with in vitro findings, in vivo studies using mice showed that administration of FVIIa before lipopolysaccharide (LPS) treatment attenuated LPS-induced vascular leakage in the lung and kidney. Overall, our present data provide evidence that FVIIa bound to EPCR on endothelial cells activates PAR1-mediated cell signaling and provides a barrier-protective effect. These findings are novel and of great clinical significance, because FVIIa is used clinically for the prevention of bleeding in hemophilia and other bleeding disorders.

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Available from: Ramakrishnan Gopalakrishnan, Mar 05, 2014
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    • "Nevertheless, it will be of interest to directly examine the role of platelet EPCR on rFVIIa-mediated thrombin generation of the activated platelet. An additional effect of the FVIIa–EPCR interaction regards signaling effects via the activation of endothelial protease activated receptor 1 (PAR-1) [62] [63]. These signaling events result in endothelial cell barrier protection, similar to the effects of APC–EPCR [64]. "
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    ABSTRACT: Recombinant factor VIIa (rFVIIa) has been developed to treat bleeding episodes in patients with inhibitor-complicated hemophilia. More recently, it has become apparent that rFVIIa is also useful in a prophylactic setting, although its prophylactic effect with a once-daily administration is difficult to explain given its half life of ~ 2 hours. The prohemostatic effects of rFVIIa have been ascribed to enhancement of thrombin generation and various downstream effects thereof. There is an ongoing debate on the tissue factor-dependency of rFVIIa, but accumulating evidence is in favor of a TF-independent mechanism. rFVIIa interacts with cellular surfaces and with various receptors on vascular cells. These interactions may contribute significantly to its mode of action in patients with hemophilia. In this review we will summarize laboratory and clinical evidence on the mode of action of rFVIIa in hemophilia with an emphasis on recent insights regarding the interactions of rFVIIa with cellular receptors.
    Preview · Article · Dec 2014 · Blood Reviews
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    • "Studies from our laboratory [19] and others [20], [21] have established that FVIIa binds endothelial protein C receptor (EPCR) in a true ligand manner. The interaction between FVIIa and EPCR is capable of not only eliciting protease activated receptor-1 (PAR1)-mediated barrier protective signaling [22], [23], but also promotes internalization of the receptor–ligand complex [24]. At present, it is unknown whether FVIIa binding to EPCR influences AT inactivation of FVIIa. "
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    ABSTRACT: Recent studies have suggested that antithrombin (AT) could act as a significant physiologic regulator of FVIIa. However, in vitro studies showed that AT could inhibit FVIIa effectively only when it was bound to tissue factor (TF). Circulating blood is known to contain only traces of TF, at best. FVIIa also binds endothelial cell protein C receptor (EPCR), but the role of EPCR on FVIIa inactivation by AT is unknown. The present study was designed to investigate the role of TF and EPCR in inactivation of FVIIa by AT in vivo. Low human TF mice (low TF, ∼1% expression of the mouse TF level) and high human TF mice (HTF, ∼100% of the mouse TF level) were injected with human rFVIIa (120 µg kg-1 body weight) via the tail vein. At varying time intervals following rFVIIa administration, blood was collected to measure FVIIa-AT complex and rFVIIa antigen levels in the plasma. Despite the large difference in TF expression in the mice, HTF mice generated only 40-50% more of FVIIa-AT complex as compared to low TF mice. Increasing the concentration of TF in vivo in HTF mice by LPS injection increased the levels of FVIIa-AT complexes by about 25%. No significant differences were found in FVIIa-AT levels among wild-type, EPCR-deficient, and EPCR-overexpressing mice. The levels of FVIIa-AT complex formed in vitro and ex vivo were much lower than that was found in vivo. In summary, our results suggest that traces of TF that may be present in circulating blood or extravascular TF that is transiently exposed during normal vessel damage contributes to inactivation of FVIIa by AT in circulation. However, TF's role in AT inactivation of FVIIa appears to be minor and other factor(s) present in plasma, on blood cells or vascular endothelium may play a predominant role in this process.
    Full-text · Article · Aug 2014 · PLoS ONE
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    • "In particular, PARs 1 and 2 can be involved in both inflammatory and anti-inflammatory processes [19]. Enzymes that regulate PAR1 in such tissues range from the coagulation proteinases, such as thrombin and factor VIIa/Xa [21, 22], to the kallikrein-related peptidase family (KLKs) [23]. The prostate is recognized as an important source of proteinases and KLKs, for which the most widely recognized KLK family member, KLK3/prostate-specific antigen (PSA), is used as a prognostic indicator of prostate cancer [24, 25]. "
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    ABSTRACT: Background: Nonbacterial prostatitis has no established etiology. We hypothesized that proteinase-activated receptor-1 (PAR1) can play a role in prostatitis. We therefore investigated the effects of PAR1 stimulation in the context of a new model of murine nonbacterial prostatitis. Methods: Using a hapten (ethanol-dinitrobenzene sulfonic acid- (DNBS-)) induced prostatitis model with both wild-type and PAR1-null mice, we examined (1) the location of PAR1 in the mouse prostate and (2) the impact of a PAR1-activating peptide (TFLLR-NH2: PAR1-TF) on ethanol-DNBS-induced inflammation. Results: Ethanol-DNBS-induced inflammation was maximal at 2 days. In the tissue, PAR1 was expressed predominantly along the apical acini of prostatic epithelium. Although PAR1-TF on its own did not cause inflammation, its coadministration with ethanol-DNBS reduced all indices of acute prostatitis. Further, PAR1-TF administration doubled the prostatic production of interleukin-10 (IL-10) compared with ethanol-DNBS treatment alone. This enhanced IL-10 was not observed in PAR1-null mice and was not caused by the reverse-sequence receptor-inactive peptide, RLLFT-NH2. Surprisingly, PAR1-TF, also diminished ethanol-DNBS-induced inflammation in PAR1-null mice. Conclusions: PAR1 is expressed in the mouse prostate and its activation by PAR1-TF elicits immunomodulatory effects during ethanol-DNBS-induced prostatitis. However, PAR1-TF also diminishes ethanol-DNBS-induced inflammation via a non-PAR1 mechanism by activating an as-yet unknown receptor.
    Full-text · Article · Dec 2013 · Mediators of Inflammation
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