Elsevier

Atherosclerosis

Volume 139, Issue 2, 4 August 1998, Pages 265-271
Atherosclerosis

Expression of tissue factor in the rabbit aorta after balloon injury

https://doi.org/10.1016/S0021-9150(98)00077-XGet rights and content

Abstract

Tissue factor (TF) is a primary initiator of the extrinsic pathway of blood coagulation. Recently TF has been shown to be overexpressed in atherosclerotic lesions and it is thought to contribute to the thrombogenicity of the plaques. We studied TF expression in the media and the neointima of rabbit aortas at various intervals after balloon injury. TF protein was immunohistochemically detected in smooth muscle cells (SMCs) of the inner layer of the media at 2 h after injury and was subsequently detected in SMCs in the neointima, whereas no TF expression was detected in the uninjured aortas except for the adventitia. Immunohistochemical and immunoelectron microscopic studies revealed that TF-positive SMCs were of an immature or synthetic phenotype and TF protein was detected in the rough endoplasmic reticulum in SMCs. TF mRNA in the intima and media increased at 2 h after injury and returned to near baseline levels at 12–24 h, whereas TF activity also increased at 2 h and continued at similar levels over the next 72 h. TF mRNA and activity increased markedly at 2–8 weeks after injury. These data suggest that TF is rapidly induced in the medial SMCs and hereafter is constitutively expressed in the neointima. TF expressed in the neointima may contribute to hypercoagulable properties of injured arteries.

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.

References (30)

  • SM Ahern et al.

    Regulation of human tissue factor expression by mRNA turnover

    J Biol Chem

    (1993)
  • AB Mulder et al.

    Association of smooth muscle cell tissue factor with caveolae

    Blood

    (1996)
  • TA Drake et al.

    Selective cellular expression of tissue factor in human tissues

    Am J Pathol

    (1989)
  • JN Wilcox et al.

    Localization of tissue factor in the normal vessel wall and in the atherosclerotic plaque

    Proc Natl Acad Sci USA

    (1989)
  • JD Marmur et al.

    Identification of active tissue factor in human coronary atheroma

    Circulation

    (1996)
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