Regulation of macrophage procoagulant responses by the tissue factor cytoplasmic domain in endotoxemia

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Abstract
Tissue factor (TF) is the primary initiator of coagulation, and the TF pathway mediates signaling through protease-activated receptors (PARs). In sepsis, TF is up-regulated as part of the proinflammatory response in lipopolysaccharide (LPS)–stimulated monocytes leading to systemic coagulation activation. Here we demonstrate that TF cytoplasmic domain–deleted (TFΔCT) mice show enhanced and prolonged systemic coagulation activation relative to wild-type upon LPS challenge. However, TFΔCT mice resolve inflammation earlier and are protected from lethality independent of changes in coagulation. Macrophages from LPS-challenged TFΔCT mice or LPS-stimulated, in vitro–differentiated bone marrow–derived macrophages show increased TF mRNA and functional activity relative to wild-type, identifying up-regulation of macrophage TF expression as a possible cause for the increase in coagulation of TFΔCT mice. Increased TF expression of TFΔCT macrophages does not require PAR2 and is specific for toll-like receptor, but not interferon γ receptor, signaling. The presence of the TF cytoplasmic domain suppresses ERK1/2 phosphorylation that is reversed by p38 inhibition leading to enhanced TF expression specifically in wild-type but not TFΔCT mice. The present study demonstrates a new role of the TF cytoplasmic domain in an autoregulatory pathway that controls LPS-induced TF expression in macrophages and procoagulant responses in endotoxemia.