Thrombospondin mediates migration and potentiates platelet‐derived growth factor‐dependent migration of calf pulmonary artery smooth muscle cells

Abstract

A precipitating factor in the development of atherosclerotic lesions is the inappropriate migration and proliferation of vascular smooth muscle cells (SMC) within the intima of the vessel wall. Focusing on the role of extracellular matrix proteins in SMC migration, we have demonstrated that thrombospondin (TSP) itself is a potent modulator of SMC motility and acts to potentiate platelet-derived growth factor (PDGF)-mediated SMC migration as well. Migration of SMC to TSP was dose dependent. Interestingly, maximal SMC migration to TSP exceeded that to either PDGF or basic fibroblast growth factor (bFGF). The distal COOH terminus of TSP was shown to mediate SMC migration as demonstrated by complete inhibition of the response by monoclonal antibody (mAb) C6.7. Nevertheless, proteolytic fragments of TSP were not as potent as intact TSP in mediating SMC migration. Only by combining the heparin-binding domain (HBD) with the 140 kD COOH terminal fragment was SMC migration restored to levels seen with intact TSP. Based on antibody inhibition studies, an alpha v-containing integrin receptor, but not alpha v beta 1 or alpha v beta 3, appeared to be involved in SMC migration to TSP. The coincidental expression of PDGF and TSP at sites of vascular injury and inflammation led us to evaluate the effect of suboptimal levels of TSP on SMC responsiveness to PDGF. SMC migration in response to PDGF was enhanced nearly 60% in the presence of suboptimal concentrations of TSP. This effect was specific for PDGF and dependent on the concentration of TSP with maximal potentiation obtained between 50-100 nM TSP, concentrations tenfold lower than those necessary for SMC migration to TSP itself. mAb C6.7 completely inhibited enhancement but, as with SMC migration to TSP alone, TSP proteolytic fragments did not possess the effectiveness of the intact molecule. Additional experiments assessing SMC migration to PDGF demonstrated that PDGF stimulated SMC motility indirectly by inducing TSP synthesis. These studies suggested that TSP functions as an autocrine motility factor to modulate SMC migration, which in conjunction with PDGF could serve to aggravate and accelerate development of atherosclerotic lesions at sites of vascular injury or inflammation.

Versican-thrombospondin-1 binding in vitro and colocalization in microfibrils induced by inflammation on vascular smooth muscle cells

“…The conformation of TSP1, therefore, may influence neointima formation through altering its interactions with versican and potentially other ECM components. However, TSP1 also interacts with several receptors on VSMC and thereby has direct effects on HASMC proliferation and migration (Isenberg et al, 2005;Lee et al, 2003;Lymn et al, 2002;Yabkowitz et al, 1993). Thus, TSP1 bound to versican on microfibrils may alter VSMC responses by providing prolonged stimulation of TSP1 receptors on these VSMC.…”

Extracellular Matrix Molecules: Potential Targets in Pharmacotherapy

“…Involved in cell adhesion, migration and growth (Chiquet-Ehrismann and Chiquet, 2003), wound healing, and neovascularization (Hsia and Schwarzbauer, 2005;Trebaul et al, 2007) Ehlers-Danlos syndrome (Burch et al, 1997;Mao and Bristow, 2001) Fibrotic diseases, inflammation, tumorigenesis (Chiquet-Ehrismann and Chiquet, 2003) Thrombospondins (1-5) Involved in cell migration (Yabkowitz et al, 1993), platelet aggregation, inflammatory response, and wound healing (Adams and Lawler, 2004) Thrombospondin-5; pseudoachondroplasia and multiple epiphyseal dysplasia (Posey et al, 2008) Tumor progression (Lawler and Detmar, 2004;Kazerounian et al, 2008); atherosclerosis (Roth et al, 1998;Takahashi et al, 2008) Nidogen/entactin (nidogen 1 and nidogen 2) Involved in cell adhesion (Yi et al, 1998;Grimpe et al, 1999), wound healing (Sephel et al, 1996) and basement membrane stabilization (Ho et al, 2008) Osteoarthritis (Kruegel et al, 2008); cancer and tumor progression (Oivula et al, 1999;Ulazzi et al, 2007;…”

Thrombospondin-1, -2 and -5 have differential effects on vascular smooth muscle cell physiology

“…Functions such as inducing EC apoptosis are experimentally attributed to CD36 binding of Type 1 repeats, while others, such as CD47 and integrin binding are attributed to the relatively conserved C-terminal domain [6]. Previous experiments indicate hyperglycemia, dyslipidemia, leptin, inflammatory mediators, such as TGFβ1, and statins drugs all regulate TSP-1 expression and function [7][8][9][10], implying TSP-1's importance to vascular pathologies such as atherosclerosis and intimal hyperplasia. While TSP-1 is well characterized in the literature, less is known about the effects of other TSPs on VSMCs and their contributions to vascular disease progression.…”