Thrombospondin-1 Mediates Smooth Muscle Cell Proliferation Induced by Interaction With Human Platelets

Abstract

Objectives-Platelet adherence and activation are associated with smooth muscle cell (SMC) proliferation and arterial restenosis. This study examined platelet-SMC interaction on fibrillar type I collagen and analyzed the role of thrombospondin (TSP)-1 in platelet-induced SMC proliferation. Methods and Results-When SMCs cultured on fibrillar collagen were treated with human platelets (5 preparations), 7.45Ϯ2.94% of the cells passed through S phase within 24 hours, as determined by bromodeoxyuridine nuclear labeling. The addition of platelets markedly induced SMC TSP-1 mRNA expression and cell surface protein accumulation, which colocalized with adhered platelets, as determined by ␣ IIb integrin immunostaining. Direct interaction of platelets with SMCs was necessary for its effect on proliferation and TSP-1 accumulation, as determined in the transwell culture system. The anti-TSP-1 blocking antibody strongly inhibited platelet-induced SMC proliferation by Ϸ60%. Analysis of the receptors for TSP-1 accumulation on the SMC surface revealed that ␤ 1 integrins are mainly involved. The anti-␤ 1 integrin blocking antibody, which potently suppressed TSP-1 accumulation on SMCs, also markedly inhibited platelet-stimulated SMC proliferation. Conclusions-TSP-1 and ␤ 1 integrin interaction is involved in platelet-stimulated SMC proliferation. This in vitro coculture system could prove useful for examining the molecular mechanism underlying platelet-induced vascular remodeling and for studying the mechanism of a tested drug for restenosis. Key Words: atherosclerosis Ⅲ platelet-derived factors Ⅲ integrins Ⅲ collagen (type I) Ⅲ vascular injury T he vascular endothelium plays a fundamental role in the local regulation of vascular tone and homeostasis. 1 Injury of a vascular segment elicits a complex sequence of events characterized by platelet adhesion and aggregation, leukocyte infiltration, and smooth muscle cell (SMC) migration and proliferation. 2,3 In experimental models, platelet aggregation and adhesion to the wall of injured vessels have been demonstrated in the early phase after balloon injury. 4 Even though platelets disappeared from the arterial surface within a few days after injury, initial platelet adhesions appear to play important roles in intimal lesion formation. 5 Platelet adherence and activation are associated with the local release of potent vasoactive factors, such as thrombin, platelet-derived growth factor (PDGF), transforming growth factor (TGF)-␤, insulin-like growth factor-I, and thromboxane A 2 . 6 These factors are known to stimulate the migration, proliferation, and synthesis of extracellular matrix molecules by SMCs that may lead to the development of an intimal lesion. However, the molecular mechanism behind the role of platelets in lesion formation is still not entirely clear. See coverThe matricellular protein thrombospondin (TSP)-1 is a 450-kDa homotrimeric glycoprotein that influences cell function by modulating cell-matrix interaction (see recent reviews 7,8 ). It is well known that TSP-1 is se...

Endogenous thrombospondin-1 is not necessary for proliferation but is permissive for vascular smooth muscle cell responses to platelet-derived growth factor

“…N-terminal domains of TSP1 and TSP2 also stimulate chemotaxis in a h1 integrin-dependent manner, but in the case of TSP2, this probably involves a4h1 or a6h1. These data are also consistent with the report that both TSP1 and h1 integrin blocking antibodies inhibit platelet-stimulated SMC proliferation (Ichii et al, 2002).…”

Thrombospondins: from structure to therapeutics

“…Recent studies support a PDGF-independent role for TSP1 in SMC proliferation, implicating a 3 b 1 [137], a v b 3 [138] and CD47 [139] in signaling pathways involving ERK1/2 and S6 kinase. The interaction of TSP1 with platelet integrins further mediates plateletinduced SMC proliferation [140]. TSP1 also affects SMC migration in Boyden chamber and transwell assays, identifying it as a chemoattractant for SMCs, a property probably located in the TSP1 G domain [141], interacting with a v b 3 , a 2 b 1 and CD47.…”

Platelets are necessary for airway wall remodeling in a murine model of chronic allergic inflammation

“…9 Likewise, inhibition of platelet contact to smooth-muscle cells effectively suppressed proliferation in vitro, with implications for restenosis. 10 Evidence points to an involvement of platelets in asthma, since large numbers of pulmonary megakaryocytes have been noted in the lungs obtained at autopsy from patients who have died from status asthmaticus. 11 Additionally, aggregates of platelets with "fibrillary" material (fibrin) have been observed on the damaged airway lumenal surface in patients with asthma.…”