Regulation of cardiomyocyte full-length tissue factor expression and microparticle release under inflammatory conditions in vitro

Summary.  Background:  Myocardial inflammation is associated with an increase in circulating microparticles (MPs) and procoagulability. Objectives:  We determined whether acute inflammation was associated with altered full-length tissue factor (flTF) expression and increased procoagulability in cardiomyocytic cells. Methods:  This study examined the transcriptional regulation of flTF expression in murine cardiomyocytic (HL-1) cells. Also, the generation of MPs by HL-1 cells and their ability to diffuse through an artificial endothelium was evaluated. Results:  Constitutive and tumor necrosis factor-α (TNF-α)-induced flTF expression of HL-1 was reduced when c-Jun N-terminal kinase (JNK) was inhibited. Tissue factor (TF)-positive procoagulant MPs were released from HL-1 cells in response to TNF-α. JNK inhibition potentiated the release of MPs from HL-1 cells without affecting MP-associated TF activity. MP generation was dependent on RhoA activation and associated with a reorganization of the actin cytoskeleton. Increased diffusion of HL-1-derived MPs through an endothelial monolayer was found after TNF-α treatment. The increased diffusion was dependent not only on TNF-α but also on HL-1-released mediators. Conclusions:  Full-length TF expression in HL-1 cells was regulated through JNK. The TNF-α-induced increase in procoagulability was mediated through RhoA-dependent release of flTF-bearing MPs. These MPs were able to diffuse through an endothelial barrier adjacent to HL-1 cells and increased the procoagulability of the extracellular endothelial space. Cardiomyocytes seem to be a likely source of flTF-bearing procoagulant MPs.