Disruption of the mouse gene encoding the blood coagulation inhibitor thrombomodulin (Thbd) leads to embryonic lethality caused by an unknown defect in the placenta. We show that the abortion of thrombomodulin-deficient embryos is caused by tissue factor-initiated activation of the blood coagulation cascade at the feto-maternal interface. Activated coagulation factors induce cell death and growth inhibition of placental trophoblast cells by two distinct mechanisms. The death of giant trophoblast cells is caused by conversion of the thrombin substrate fibrinogen to fibrin and subsequent formation of fibrin degradation products. In contrast, the growth arrest of trophoblast cells is not mediated by fibrin, but is a likely result of engagement of protease-activated receptors (PAR)-2 and PAR-4 by coagulation factors. These findings show a new function for the thrombomodulin-protein C system in controlling the growth and survival of trophoblast cells in the placenta. This function is essential for the maintenance of pregnancy.

Activated protein C (aPC) therapy reduces mortality in adult patients with severe sepsis. In mouse endotoxemia and sepsis models, mortality reduction requires the cell signaling function of aPC, mediated through protease-activated receptor-1 (PAR1) and endothelial protein C receptor (EPCR; also known as Procr). Candidate cellular targets of aPC include vascular endothelial cells and leukocytes. Here, we show that expression of EPCR and PAR1 on hematopoietic cells is required in mice for an aPC variant that mediates full cell signaling activity but only minimal anticoagulant function (5A-aPC) to reduce the mortality of endotoxemia. Expression of EPCR in mature murine immune cells was limited to a subset

Infection and inflammation are invariably associated with activation of the blood coagulation mechanism, secondary to the inflammation-induced expression of the coagulation initiator tissue factor (TF) on innate immune cells. By investigating the role of cell-surface receptors for coagulation factors in mouse endotoxemia, we found that the protein C receptor (ProcR; EPCR) was required for the normal in vivo and in vitro induction of lipopolysaccharide (LPS)-regulated gene expression. In cultured bone marrowderived myeloid cells and in monocytic RAW264.7 cells, the LPS-induced expression of functionally active TF, assembly of the ternary TF-VIIa-Xa initiation complex of blood coagulation, and the EPCR-dependent activation of protease-activated receptor 2 (PAR2) by the ternary TF-VIIa-Xa complex were required for the normal LPS induction of messenger RNAs encoding the TLR3/4 signaling adaptor protein Pellino-1 and the transcription factor interferon regulatory factor 8. In response to in vivo challenge with LPS, mice lacking EPCR or PAR2 failed to fully initiate an interferon-regulated gene expression program that included the Irf8 target genes Lif, Iigp1, Gbp2, Gbp3, and Gbp6. The inflammation-induced expression of TF and crosstalk with EPCR, PAR2, and TLR4 therefore appear necessary for the normal evolution of interferon-regulated host responses. (Blood. 2015;125(18):2845-2854

Elevated plasma levels of fibrinogen are associated with the presence of cardiovascular disease, but it is controversial whether elevated fibrinogen causally imparts an increased risk, and as such is a true modifier of cardiovascular disease, or is merely associated with disease. By investigating a transgenic mouse model of hyperfibrinogenemia, we show that elevated plasma fibrinogen concentration IntroductionNumerous epidemiological studies have documented the association of elevated plasma fibrinogen levels with cardiovascular disease. [1][2][3][4][5][6][7] Cross-sectional prospective studies imply that elevated plasma fibrinogen levels are an independent and predictive parameter for increased risk of coronary artery disease, stroke, and peripheral vascular disease. The magnitude of the increase in fibrinogen levels correlates with the presence and severity of peripheral arterial disease, the extent of myocardial necrosis in infarcted patients, and cerebrovascular accidents. The disease risk associated with hyperfibrinogenemia is disproportionally augmented in those individuals with the highest fibrinogen levels, indicating a threshold effect. Notwithstanding its recognized value as a marker for the presence of cardiovascular disease, it remains controversial whether an elevated fibrinogen level itself imparts an increased risk, and therefore represents a true modifier of vascular disease, or is merely associated with disease. Fibrinogen production in the liver is regulated by cytokines and is greatly enhanced in the acute phase response to infection and other inflammatory processes. [8][9][10][11] It is therefore possible that moderately elevated fibrinogen levels simply report a state of inflammation associated with vascular disease. On the other hand, augmented fibrinogen levels, per se, could alter the hemodynamic properties of blood or enhance concentration driven enzyme-substrate interactions between thrombin, fibrinogen, and platelets, and thus lead to increased intravascular fibrin deposition and thrombosis. These views are not mutually exclusive, as augmentation of fibrinogen levels secondary to an inflammatory challenge could nevertheless amplify or accelerate the disease process. Moreover, fibrinogen and fibrin degradation products might in turn enhance the inflammatory aspect of vascular lesions by regulating cytokine production and leukocyte-endothelial interactions. [12][13][14][15][16][17] Recently described genetically altered mice with chronically increased plasma fibrinogen levels in the absence of underlying inflammation provide a novel experimental tool to investigate the cause-effect relationship between hyperfibrinogenemia and vascular disease. 18 The mutant mouse strain (hereafter referred to as Hifib mice) was derived by pronuclear oocyte microinjection of the entire mouse fibrinogen locus, including all 3 fibrinogen chains as well as several kilobases of flanking sequence. The added transgenic fibrinogen allele is inherited in a Mendelian fashion, and the mice were reported to exhibit...