Role of T-cell derived prothrombin in septicemia

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The serine protease thrombin is involved in a number of physiological functions beyond hemostasis including angiogenesis, embryogenesis, tumorigenesis and inflammation. Serum levels of prothrombin derive from protein synthesis in the liver, yet expression of the prothrombin (F2) gene in a variety of other tissues has been demonstrated to occur during embryogenesis. While considerable insights have been obtained on how thrombin exerts its crucial function in various pathologies, little is known about the (patho)physiological functions of extrahepatic prothrombin expression. By generating bone marrow chimeric animals in which prothrombin is selectively ablated in the bone marrow compartment, we recently observed a critical function of bone marrow-derived prothrombin in septicemia. Ablation of prothrombin expression specifically in bone marrow-derived cells led to a higher survival rate in septicemia despite unaltered serum levels of prothrombin. To identify cell type(s) expressing prothrombin in the bone marrow compartment, we employed magnetic- (MACS) and fluorescence-activated cell sorting (FACS) followed by luminometry based on purified cells obtained from a newly designed transgenic mouse model (termed ‘D-Insight’) in which endogenous prothrombin expression is tagged by luciferase reporters. Isolating different bone marrow-derived cell populations by MACS and FACS followed by luminometry, we identified antigen-experienced CD4- and CD8- positive T-cells to express prothrombin. We now want to decipher the enigmatic functional role of bone marrow-derived prothrombin expression in the modulation of septicemia. To this end, we will make use of tissue-specific prothrombin knock-out mice and combine this with functional studies in vivo and in vitro, omics and pharmacological approaches to disentangle the role of T-cell derived prothrombin in septicemia. Illuminating non-canonical functions of coagulation components beyond their hemostatic functions is central to elucidate their contribution to the pathophysiologies of very common and most devastating disorders. This may also aid novel avenues to identify rationalized targets for combatting septicemia, an up-to-date fatal condition for a significant proportion of affected patients around the globe.