Characterization of thrombin receptor expression during vascular lesion formation.

Abstract

Blood vessels respond to injury by initiating cell proliferation and migration that result in vascular lesion formation. To determine the roles of thrombin and the thrombin receptor in this process, we characterized thrombin receptor expression in normal and injured arteries, thrombin receptor-mediated smooth muscle cell mitogenesis, and the regulation of thrombin receptor mRNA expression in vitro. Thrombin receptor mRNA was not detected in normal rat or baboon arteries by in situ hybridization. Immunohistochemistry using an antithrombin receptor antibody (TR-R9), directed against the thrombin cleavage site of the rat aortic smooth muscle cell thrombin receptor, revealed low-level staining for thrombin receptor protein in endothelial cells and smooth muscle cells of normal arteries. In contrast, balloon catheter injury increased thrombin mRNA expression in medial smooth muscle cells within 6 hours. This increased thrombin receptor expression continued within the media and in neointimal cells throughout vascular lesion formation, predominantly in areas of active cell proliferation. In vitro, alpha-thrombin stimulates rat aortic smooth muscle cell proliferation in a concentration-dependent manner. That thrombin receptor activation is required for the mitogenic response was confirmed by demonstrating that the polyclonal antibody TR-R9 inhibits thrombin-induced cell proliferation. Thrombin receptor mRNA synthesis was induced by both basic fibroblast growth factor (maximal stimulation of 1.8-fold at 1 hour) and platelet-derived growth factor (maximal stimulation of 2.4-fold at 8 and 24 hours) in quiesced cultured rat aortic smooth muscle cells. In summary, upregulation of smooth muscle cell thrombin receptor expression occurs very early after vascular injury and continues throughout neointimal development.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered Vascular Injury Responses in Mice Deficient in Protease-Activated Receptor-1

“…and PAR-1 in platelet aggregation, cell proliferation, and matrix synthesis, both thrombin and PAR-1 expression and message appear to be upregulated after vascular injury in animal models 27 and in human atherosclerotic vessels. 28,29 We have shown that PAR-1 is also upregulated in the mouse carotid artery in response to vascular injury.…”

“…25,26 Several of these cellular functions, particularly stimulation of vascular smooth muscle proliferation and collagen synthesis, are integral to vascular wound healing. In addition, PAR-1 mRNA and protein expression is upregulated in response to different forms of vascular injury, such as that induced by balloon angioplasty in the rat and baboon 27 and in human advanced atherosclerotic plaques. 28,29 Thus, elevated thrombin levels at sites of vascular injury can activate the upregulated levels of PAR-1, leading to a number of cellular responses that may participate in the vascular injury response.…”

Up‐regulation of proteinase‐activated receptor 1 and increased contractile responses to thrombin after subarachnoid haemorrhage

“…However, the expression of PAR 1 in smooth muscle has been shown to be upregulated in vascular lesions such as those seen in atherosclerosis (Nelken et al, 1992;Ku and Dai, 1997) and balloon injury models (Wilcox et al, 1994;Fukunaga et al, 2006). Such upregulation of PAR 1 expression in smooth muscle is thus considered to play a critical step in the development of vascular lesions and hyper-contractile state (Hirano, 2007).…”

The Roles of Proteinase-Activated Receptors in the Vascular Physiology and Pathophysiology

“…59 On the other hand, the functional expression of PAR1 and PAR2 in the smooth muscle cells of normal arteries appear to be limited. 60,61 Their effect on smooth muscle may thus play a minor functional role in normal arteries.…”

“…61 PAR1 and PAR2 have been reported to be upregulated in vascular lesions after balloon angioplasty in rats or baboons, and in human advanced atherosclerotic lesions. 60,61,80 As s result, smooth muscle effects such as contraction, migration, proliferation, hypertrophy, and production of the extracellular matrix become dominant in vascular lesions; contributing to an increase in the vascular tone and the development of vascular lesions (Figure).…”