Coagulation factor V mediates inhibition of tissue factor signaling by activated protein C in mice

Abstract

Key Points• Factor V and protein S are required for sepsis mortality reduction and suppression of inflammatory gene expression by activated protein C.• The R506Q mutation (Leiden mutation) abrogates the antiinflammatory cofactor function of factor V for activated protein C.The key effector molecule of the natural protein C pathway, activated protein C (aPC), exerts pleiotropic effects on coagulation, fibrinolysis, and inflammation. Coagulation-independent cell signaling by aPC appears to be the predominant mechanism underlying its highly reproducible therapeutic efficacy in most animal models of injury and infection. In this study, using a mouse model of Staphylococcus aureus sepsis, we demonstrate marked disease stage-specific effects of the anticoagulant and cell signaling functions of aPC. aPC resistance of factor (f)V due to the R506Q Leiden mutation protected against detrimental anticoagulant effects of aPC therapy but also abrogated the anti-inflammatory and mortalityreducing effects of the signaling-selective 5A-aPC variant that has minimal anticoagulant function. We found that procofactor V (cleaved by aPC at R506) and protein S were necessary cofactors for the aPC-mediated inhibition of inflammatory tissue-factor signaling. The antiinflammatory cofactor function of fV involved the same structural features that govern its cofactor function for the anticoagulant effects of aPC, yet its anti-inflammatory activities did not involve proteolysis of activated coagulation factors Va and VIIIa. These findings reveal a novel biological function and mechanism of the protein C pathway in which protein S and the aPC-cleaved form of fV are cofactors for anti-inflammatory cell signaling by aPC in the context of endotoxemia and infection. (Blood. 2015;126(21):2415-2423 Introduction Natural aPC exerts pleiotropic effects on coagulation, fibrinolysis, and inflammation (for review, see Esmon, 1 Mosnier and Griffin,2 and Dahlbäck and Villoutreix 3 ) that are predominantly mediated by 2 mechanistically discernable pathways: (1) aPC degrades activated coagulation factor (f)Va and fVIIIa to curtail the formation of thrombin by the plasma coagulation system and (2) when bound to the endothelial protein C receptor (EPCR, ProcR) or the integrin aMb2 (Mac1)(CD11b/CD18), aPC becomes competent for activating the G protein-coupled protease activated receptor (PAR) 1, 2, or 3. PAR activation and crosstalk with other receptors mediate anti-inflammatory and cytoprotective effects of aPC in innate immune cells, vascular endothelium, and other cells (for review, see Weiler,4 Mosnier et al, 5 and Dahlbäck and Villoutreix 6). In animal models of endotoxemia and sepsis, the cell signaling activity of aPC on vascular endothelium and innate immune cells is the predominant therapeutic mechanism of action, and recombinant variants of aPC that are largely devoid of anticoagulant activity but retain signaling function confer vasoprotection, inhibit inflammation, and reduce mortality. 7-9 Although the incidence of microvascular coagulopathies in p...

Individual clotting factor contributions to mortality following trauma

“…Additionally, the PROWESS trial found heterozygous factor V leiden carriers displayed reduced mortality in the setting of sepsis(22). In subsequent mouse studies, Liang et al identified protein C cleaved factor V as a crucial cofactor inhibiting a novel inflammatory tissue factor signaling pathway mediated by activated protein C(23). Discovery of factor V’s role in a new murine protein C mediated inflammatory pathway is exciting and insinuates factor V may play an even larger function in dictating the balance of hypocoagulability, hypercoagulability, and inflammation after trauma.…”

Targeting clotting proteins in cancer therapy – progress and challenges

“…In the presence of NAPc2, the TF-induced TRIF response was not only preserved, but stabilization of the ternary complex with NAPc2 prevented the suppression of TF signaling by aPC. This signaling role of aPC is, similar to aPC anticoagulant activity, dependent on protein S as well as FV anticoagulant cofactor function that is lost in FV Leiden (90). These data suggest that EPCR ligand occupancy by either FXa or aPC determines TLR4-TRIF activation and indicate a control switch function for EPCR in the hardwiring of innate immune and coagulation signaling.…”

Regulation of long‐term repopulating hematopoietic stem cells by EPCR/PAR1 signaling

“…144–146 Blood coagulation and primary hemostasis evolved as important defense mechanisms to prevent bleeding, 147 and a primary function of the vascular TM/aPC/EPCR pathway is to counterbalance intravascular thrombosis and maintain endothelial quiescence. With new functions emerging in our understanding of EPCR in BM LT-HSCs and the challenge of deciphering the mechanisms of the tight regulation by distinct PAR1 signaling, 6 new questions arise on the relevance of the hemostatic system for human stem cell physiology, and future studies will enhance our understanding of the role of PAR1 and NO signaling in clinical G-CSF– and AMD3100-induced HSPC mobilization.…”

“…Since the first cloning and identification of EPCR as the physiological receptor for the powerful anticoagulant aPC 143 and the discovery of EPCR/aPC/PAR1 anticoagulant signaling, 14 additional evidence emerged for a close interaction between the coagulation systems and inflammation, cellular metabolism, angiogenesis, and innate immunity. [144][145][146] Blood coagulation and primary hemostasis evolved as important defense mechanisms to prevent bleeding, 147 and a primary function of the vascular TM/aPC/EPCR pathway is to counterbalance intravascular thrombosis and maintain endothelial quiescence. With new functions emerging in our understanding of EPCR in BM LT-HSCs and the challenge of deciphering the mechanisms of the tight regulation by distinct PAR1 signaling, 6 new questions arise on the relevance of the hemostatic system for human stem cell physiology, and future studies will enhance our understanding of the role of PAR1 and NO signaling in clinical G-CSF-and AMD3100-induced HSPC mobilization.…”