Heparanase and platelet factor-4 induce smooth muscle cell proliferation and migration via basic fibroblast growth factor release from the extracellular matrix: Implications in the restenosis process
Myler, Heather Ann
West, Jennifer L.
Doctor of Philosophy
Basic fibroblast growth factor (bFGF) plays an instrumental role in the cascade of events leading to restenosis, vascular re-occlusion due to excessive smooth muscle cell (SMC) proliferation, migration and extracellular matrix (ECM) deposition following arterial intervention procedures such as balloon angioplasty. The mechanism of bFGF activation following vascular injury has remained elusive. bFGF is stored bound to heparan sulfate proteoglycans in the ECM of the arterial media; release from extracellular sequestration may activate bFGF and initiate SMC proliferation and migration. bFGF mobilization at injured sites may be induced by platelet degranulation products. We have carried out in vitro studies demonstrating that platelet-derived heparanase and platelet factor-4 (PF4) liberate bFGF from the ECM of vascular SMCs, resulting in the induction of SMC proliferation and migration. Increases in proliferation and migration were inhibited by treatment with a bFGF-neutralizing antibody, suggesting that proliferation and migration in response to heparanase or PF4 are mediated by bFGF activation. When platelets were seeded on top of SMCs, degranulation products were found to release bFGF from the ECM, increasing cell proliferation and cell migration. These increases in SMC proliferation and migration were completely inhibited by the addition of a bFGF-neutralizing antibody. In order to investigate the role of heparanase and PF4 in vivo, each was delivered to the uninjured rat carotid artery. Heparanase and PF4 were both found to release bFGF, induce substantial SMC proliferation and increase the expression of several growth factor receptors thought to promote restenosis. An antibody that neutralizes platelet-derived heparanase was developed and evaluated in a rat carotid balloon injury model. Perivascular delivery of anti-heparanase IgG was found to inhibit bFGF depletion from the arterial wall by approximately 60% (p < 0.001) at 4 days. This correlated with the reduction in intimal thickening observed at 14 days. Platelet degranulation products, such as heparanase and PF4, may liberate bFGF from extracellular sequestration, activating the growth factor and inducing the SMC proliferation and migration that contribute to luminal narrowing following vascular injury. In addition, platelet-derived heparanase is likely to play a key role in initiating events leading to restenosis via bFGF mobilization.
Molecular biology; Cell biology; Physiology