In vitro effects of combining Mim8 with factor VIII, FVIIa, and activated prothrombin complex concentrates in thrombin generation assays.

Background: Mim8 is a novel antifactor IXa/antifactor X bispecific antibody in clinical development for prophylactic treatment of hemophilia A with and without inhibitors. Patients treated with Mim8 may need supplementary bleed treatment under certain conditions such as surgery or major trauma.

Objectives: This study aimed to better understand the response of Mim8 in thrombin generation assays (TGAs) alone or in combination with other hemostatic proteins.

Platelet protein S limits venous but not arterial thrombosis propensity by controlling coagulation in the thrombus.

Anticoagulant protein S (PS) in platelets (PSplt) resembles plasma PS and is released on platelet activation, but its role in thrombosis has not been elucidated. Here we report that inactivation of PSplt expression using the Platelet factor 4 (Pf4)-Cre transgene (Pros1lox/loxPf4-Cre+) in mice promotes thrombus propensity in the vena cava, where shear rates are low, but not in the carotid artery, where shear rates are high. At a low shear rate, PSplt functions as a cofactor for both activated protein C and tissue factor pathway inhibitor, thereby limiting factor X activation and thrombin generation within the growing thrombus and ensuring that highly activated platelets and fibrin remain localized at the injury site.

RhoA, Rac1, and Cdc42 differentially regulate αSMA and collagen I expression in mesenchymal stem cells.

Mesenchymal stem cells (MSC) are suggested to be important progenitors of myofibroblasts in fibrosis. To understand the role of Rho GTPase signaling in TGFβ-induced myofibroblast differentiation of MSC, we generated a novel MSC line and its descendants lacking functional Rho GTPases and Rho GTPase signaling components. Unexpectedly, our data revealed that Rho GTPase signaling is required for TGFβ-induced expression of α-smooth muscle actin (αSMA) but not of collagen I α1 ().

PAR1 biased signaling is required for activated protein C in vivo benefits in sepsis and stroke.

Activated protein C (APC) cleaves protease-activated receptor 1 (PAR1) in vitro at R46 to initiate beneficial cell signaling; however, thrombin and APC can cleave at R41. To elucidate PAR1-dependent aspects of the pharmacologic in vivo mechanisms of APC, we generated C57BL/6 mouse strains carrying QQ41 or QQ46 point mutations in PAR1 ( gene). Using these strains, we determined whether or not recombinant murine signaling-selective APC mutants would reduce septic death or provide neuroprotection against ischemic stroke when mice carried PAR1-homozygous mutations that prevent cleavage at either R41 or R46.