Venous thrombosis, including deep vein thrombosis (DVT) and pulmonary embolism, is a major source of morbidity and mortality worldwide 1]. Although it is accepted that the combination of so-called virchow triad, namely 1) vascular abnormalities and endothelial dysfunction, 2) hypercoagulability and 3) stasis, may play a pivotal role in the pathogenesis of venous thrombosis, the underlying mechanisms are not fully elucidated.
The pathogenesis of thrombosis involves a variety of factors among which platelet adhesion to endothelial cells is one element of importance 2, 3]. The data that adhesion can occur in the mice who lack fibrinogen and VWF suggests that some pivotal mechanisms, for example, the platelet-endothelial interaction, may be involved in this process and the concomitant thrombosis 4]. We have known that the rougher the membrane surfaces are, the more the platelets adhere and the poorer the hemocompatibility is, and vice versa 5]. The above data suggested that the dynamic regulation of endothelial membrane shape may affect the process of platelet adhesion. In fact, the morphology of endothelial membrane changed with environment frequently. For example, when the transmural pressure elevated or cells were exposed to E2, projections, such as membrane ruffles, pseudopodia and microvilli, will appear on the outer surface of endothelium and stretch into the vessel lumen 6, 7].
Kadandale et al. 8] identified that autophagy plays a pivotal role in blood cell cortical remodeling, with involvement in the extension of cell protrusions, such as lamellipodia and filopodia. Rapamycin is a kind of autophagy agonist, which was reported to be associated with regulation of endothelial cytoskeleton 9]. Every year, rapamycin-eluting stents are implanted in millions of patients with coronary artery disease who undergo percutaneous coronary intervention. However, evidence indicated that rapamycin-eluting stents may be associated with an increased risk for stent thrombosis when compared with bare-metal stents 4, 10]. For example, Camici et al. 10] reported that rapamycin promoted arterial thrombosis in vivo. In endothelial cells, rapamycin can enhance the activity of tissue factor (TF) which is a key trigger of coagulation cascade. In addition, the effects that rapamycin inhibits tissue plasminogen activator (t-PA) and induces plasminogen activator inhibitor 1 (PAI-1) in human umbilical vein endothelial cells (HUVECs) may contribute to thrombosis associated with rapamycin-eluting stents 11]. On the contrary, Daemen et al. and others 12, 13] found that rapamycin-eluting stents were safe and effective compared with bare-metal ones. Thus, it is necessary to elucidate the effect of rapamycin on thrombosis.
In this study, we found that rapamycin (500 ng/kg) promoted formation of microvilli-like structure in endothelium and thrombotic occlusion in the modified DVT rat model. HUVECs treated with rapamycin demonstrated that both dorsal ruffling and platelets-endothelial adhesion were promoted. Suppressing dorsal ruffling by cytochalasin B led to inhibited platelet-endothelial adhesion. Further analysis suggested that rapamycin-mediated autophagy activation may contribute to the formation of the dorsal ruffling in endothelial cells.