Induction of vascular smooth muscle cell growth by selective activation of the thrombin receptor Effect of heparin

Abstract

The synthetic peptide, SFLLRNPNDKYEPF, has been recently described as a peptide mimicking the new amino-terminus created by cleavage of the thrombin receptor, therefore acting as an agonist of the thrombin receptor. This peptide was a porect mitogen for rdbbit arterial smooth muscle -ells (SMC) and exhibited the same activity as that of native a-thrombin. Both compounds stimulated the proliferation of growth-arrested SMCs with half-maximum mitogenic responses at I nM. NAPAP. a synthetic inhibitor of the enzymatic activity of thrombin, specifically inhibitad thrombin-induced SMC growth (I& = 0.35 + 0.04pM) but was without effect on the mitogenic effect of the agonist peptide. These results therefore demonstrate that the mitogenic effect of a-thrombin for SMCs is intimately linked to its esterolytic activity. Heparin, which inhibited fetal calf serum-induced SMC growth, was without effect or. thrombin-induced SMC growth but strongly reduced the mitogenic effect of the agonist peptide (ICS = 32 5 5 rf@ml). This effect wa:: not relatd to the anti-coagulant activity of heparin but was highly dependent on molecular mass and on the global charge of the molecule and WGE alsc observed for other sulphated polysaccharides such as pentosan polysulphate.

Urokinase and Tissue-type Plasminogen Activator Are Required for the Mitogenic and Chemotactic Effects of Bovine Fibroblast Growth Factor and Platelet-derived Growth Factor-BB for Vascular Smooth Muscle Cells

“…While in vitro studies with vascular SMCs have identified several agents that stimulate their proliferation in culture, growth factors responsible for vascular injury-induced intimal SMC replication have only begun to be identified. Along with PDGF (28 -30) and bFGF (31), several enzymes of the coagulation cascade and fibrinolytic system are now considered to be likely candidates (3,5,(32)(33)(34)(35)(36). The first evidence for the involvement of fibrinolytic enzymes in such a process came from data by Clowes et al (7) showing that u-PA was expressed by vascular SMC during mitogenesis and t-PA during migration in an injured rat carotid artery.…”

Stimulation of activin A expression in rat aortic smooth muscle cells by thrombin and angiotensin II correlates with neointimal formation in vivo.

“…1 Although the key molecules involved in these processes are not known, several vasoactive agonists including angiotensin II (AII) and ␣ -thrombin have been implicated. These G-protein-coupled receptor (GPCR) agonists are potent mitogens for rat aortic smooth muscle (RASM) cells in vitro (1)(2)(3)(4)(5)(6) and also induce extracellular matrix formation (7)(8)(9)(10). AII acts by direct activation of the AII type 1 (AT 1 ) receptor (11), whereas ␣ -thrombin binds to its receptor and by enzymatic cleavage, generates a new amino terminus tethered ligand that activates the receptor (for review see ref- erence 12).…”

Thrombin induces endothelial cell growth via both a proteolytic and a non-proteolytic pathway

“…It is a potent cloned thrombin receptor and to induce platelet activation, Ca2+ activator of platelets [2] and presents a variety of functions upon fluxes in endothelial cells and platelets, or smooth muscle cell inflammatory and vascular cells. Thrombin is chemotactic for proliferation [16][17][18]. Since this ligand can only be generated by monocytes and mitogenic for lymphocytes [3,4].…”

“…mechanism of thrombin-induced mitogenesis. We therefore Thrombin has a direct mitogenic effect on rat neonatal and investigated the possibility that thrombin might induce mitobovine aortic smooth muscle cells, quiescent fibroblasts and genicity in endothelial cells via both thrombin cell receptorvascular endothelial cells [8,[11][12][13][14][15][16]. The enzymic activity of dependent and -independent pathways.…”