Expression of tissue factor in the rabbit aorta after balloon injury
Introduction
Tissue factor (TF), which behaves as a high-affinity cell surface receptor and a specific cofactor for plasma coagulation factors VII/VIIa, is a primary initiator of the blood coagulation cascade 1, 2. TF is distributed in the adventitia and variably in the media in normal vessels 3, 4. Overexpression of TF protein and mRNA, and its procoagulant activity have been found in human atherosclerotic plaques 5, 6, 7, 8, and TF-expressing cells are identified as macrophages and smooth muscle cells (SMCs) in the intima. TF expressed in the intima is thought to play an important role in thrombus formation after plaque rupture and in the thrombotic complications after angioplasty 5, 6, 7, 8, 9. Medial SMCs also expressed high levels of TF mRNA and activity after balloon injury in rat aortas [10]. Furthermore, recent studies have demonstrated other roles of TF beyond coagulation 11, 12, 13, 14. However, there is no data on the expression and changes of TF with progression of arterial intimal lesions.
In the present study, we examined the expression, distribution and activity of TF, and their changes with time in rabbit aortas in response to balloon injury. Our results indicate that TF protein, mRNA and activity are rapidly induced in vivo in the medial SMCs and continuously expressed in the neointima. The TF expressed in SMCs may contribute to hypercoagulable properties of injured arteries.
Section snippets
Animals
A total of 80 male Japanese white rabbits (2.0–2.3 kg) was used in this study. All surgical procedures were performed under aseptic technique and general anesthesia by intravenous injection of pentobarbital (25 mg/kg). The endothelium of the descending thoracic aortas was denuded by two passages of an inflated 4F Fogarty catheter (Baxter Healthcare, McGaw Parl, IL) as described previously [15]. Animals were killed by over-dose of pentobarbital (50 mg/kg, i.v.) 2 min after administration of
Immunohistochemistry
TF protein was found in some medial SMCs (HHF35-positive cells), which were scattered throughout the media but preferentially located just beneath the internal elastic lamina at 2–72 h after balloon injury (Fig. 1A). The number of TF-positive SMCs in the inner layer of the media increased at 72 h (Fig. 1B). TF-positive SMCs were predominantly found in the neointima as well as in the inner layer of the media at 2–8 weeks after balloon injury. Almost all of neointimal SMCs at 4 weeks after injury
Discussion
In the present report, we demonstrated that TF protein and mRNA were rapidly induced in the medial SMCs, mainly in the inner layer after balloon injury, and were subsequently detected in the newly formed intimal SMCs. In addition, TF expressed in these SMCs showed procoagulant activity.
It has been reported that significant TF mRNA and protein were expressed in human atherosclerotic plaques of carotid endarterectomy specimens, and TF expression was noted in macrophages, mesenchymal-appearing
Acknowledgements
We thank Dr Josiah N. Wilcox, Department of Medicine, Emory University, for helpful discussion and Dr Yuichi Kamikubo, The Chemo-Sero-Therapeutic Research Institute, Kumamoto, Japan, for giving us guinea-pig anti-TF antibody. This work was supported by a Grant-in-Aid for Scientific Research on Priority Areas from the Ministry of Education, Science, Sports and Culture of Japan (Nos. 06670236 and 09670194) and a Grant-in-Aid for Research Project from Miyazaki Medical College.
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