Recently published studies suggest that the procoagulant receptor protein tissue factor (TF) is involved in vitro in cell adhesion and migration, via an interaction of its cytoplasmic domain with cytoskeletal proteins, Interestingly, TF is abundantly expressed in myocardium, but not in skeletal muscle. To elucidate the possible roles of TF in the myocardium, this study examined the cellular distribution of TF in relation to cytoskeletal proteins, as well as its relative amounts in different segments of premature, mature, and pathologically altered cardiac muscle. In juvenile and adult hearts, TF was predominantly detectable in the transverse part of the intercalated discs, where it co-localized with cytoskeletal proteins such as desmin and vinculin, The lowest amount of TF was observed in right atrial and the highest in left ventricular myocardium, which correlated with the number of contact sites of cardiomyocytes in these segments of the cardiac muscle. Lower levels of TF were present in structurally altered myocardium from patients with hypertension or ventricular hypertrophy. In addition, TF expression was decreased in human heart during sepsis and transiently decreased in rabbit heart in an endotoxaemia model, which indicates that a reduction in TF may contribute to cardiac failure in sepsis. The microtopography of TF at cardiomyocyte contact sites indicates that TF may play a structural role in the maintenance of cardiac muscle. Copyright (C) 2000 John Wiley & Sons, Ltd.

We employed a novel mouse line that expresses low levels of human tissue factor (TF) in the absence of murine TF to analyze the role of TF in gestation. Low-TF female mice had a 14-18% incidence of fatal postpartum uterine hemorrhage, suggesting that TF plays an important role in uterine hemostasis. Low-TF female mice mated with low-TF male mice had a 42% incidence of fatal midgestational hemorrhage (n = 41), whereas no fatal midgestational hemorrhages were observed in low-TF female mice mated with wild-type male mice (n = 43). Placentas of low-TF embryos from both low-TF and normal (+/-) TF females were abnormal and contained numerous maternal blood pools in the labyrinth. Placentas of TF null embryos surviving beyond embryonic day 10.5 exhibited similar defects. The mouse maternal-embryonic placental barrier consists of four cellular layers (layers I, II, and III and endothelial cells), where layer I lines the maternal lacunae. Comparison of TF-deficient placentas with control placentas by immunohistochemical and ultrastructural analyses revealed thinning of layer I and a reduction in the number of cellular contacts of layer I trophoblasts spanning the maternal blood space between adjacent trabeculae. These structural changes in low-TF and TF null placentas result in enlarged maternal lacunae, as determined by morphometric analysis, and placental hemorrhage, which leads to midgestational death of low-TF female mice. This study demonstrated that TF is required for uterine hemostasis and revealed an unexpected role of TF in the maintenance of the placental labyrinth.

Whereas tissue factor, a high-affinity cell-surface receptor and essential cofactor for the serine protease factor VII is constitutively present in certain tissues such as epithelial tissue, brain and placenta, it is not normally expressed by cells within the vasculature. However, the stimulation of monocytes and endothelial cells by a variety of inflammatory and immunological reactions results in the induction of cell surface tissue factor (TF) expression. TF is also expressed on tumour cells, and may play a role in tumour growth and metastasis formation. To examine the role of TF in these processes we developed monoclonal antibodies to human tissue factor apoprotein. The antibodies were characterized by neutralization of the procoagulant activity and by immunoblotting. With two of these monoclonal antibodies a sandwich ELISA was developed for the rapid quantitation of TF. The sensitivity of the assay permits extensive studies involving the modulation of TF expression on small numbers of cells. The results are comparable to the functional clotting assay as evaluated with unpurified TF and with the tumour cell line MCF-7. For certain applications, monitoring of cellular TF expression by ELISA using anti-TF monoclonal antibodies is preferable because it is not influenced by other coagulation factors or by inhibitors of procoagulant activity on the cells.