Injury-induced alterations in newly synthesized sulphated proteoglycans from rabbit arterial neointima covered by regenerated endothelium

Vascular PG-M/versican variants promote platelet adhesion at low shear rates and cooperate with collagens to induce aggregation

We have identified a novel von Willebrand factor/fibrinogen/selectin-independent, platelet adhesion-promoting function of vascular PG-M/versicans that may be relevant in normal venous thrombosis and critical in atherosclerotic conditions. A purification scheme was devised to obtain vascular versicans, which by biochemical, immunochemical, and ultrastructural means were asserted to be 1) composed primarily of isoforms V1 and V2; 2) free of contaminants; 3) prevalently substituted with chondroitin-4-sulfate and dermatan sulfate (DS) chains; and 4) capable of binding hyaluronan to form link protein-stabilized ternary complexes. Real-time analysis of human platelet perfused under diverse shear forces showed that they largely failed to bind to several vascular and nonvascular proteoglycans (PGs). In contrast, they bound in a dose- and shear rate-dependent manner to vascular versicans, exhibiting a unique attachment-detachment kinetics and establishing a firm substrate tethering characterized with no significant aggregation. Digestion of these PGs with lyases and competition experiments with purified glycosaminoglycans revealed that platelet adhesion to vascular versicans was primarily mediated by their DS chains. Incorporation of the versicans into fibrillar collagen substrates augmented their adhesive activity and strongly promoted platelet aggregation at low and high shear rates. Affinity chromatography of platelet surfaces on DS columns identified a 120-140 kDa polypeptide complex that behaved as a specific vascular versican binding membrane ligand in solid-phase binding assays. These findings indicate that selective versican variants of the subendothelium may serve as ancillary GPIbalpha/integrin/selectin-independent platelet ligands in healthy and diseased vascular beds and may be directly responsible for the platelet accruing after rupture of atherosclerotic plaques.

The mechanisms of coronary restenosis: insights from experimental models

Since its introduction into clinical practice, more than 20 years ago, percutaneous transluminal coronary angioplasty (PTCA) has proven to be an effective, minimally invasive alternative to coronary artery bypass grafting (CABG). During this time there have been great improvements in the design of balloon catheters, operative procedures and adjuvant drug therapy, and this has resulted in low rates of primary failure and short-term complications. However, the potential benefits of angioplasty are diminished by the high rate of recurrent disease. Up to 40% of patients undergoing angioplasty develop clinically significant restenosis within a year of the procedure. Although the deployment of endovascular stents at the time of angioplasty improves the short-term outcome, 'in-stent' stenosis remains an enduring problem. In order to gain an insight into the mechanisms of restenosis, several experimental models of angioplasty have been developed. These have been used together with the tools provided by recent advances in molecular biology and catheter design to investigate restenosis in detail. It is now possible to deliver highly specific molecular antagonists, such as antisense gene sequences, to the site of injury. The knowledge provided by these studies may ultimately lead to novel forms of intervention. The present review is a synopsis of our current understanding of the pathological mechanisms of restenosis.