Interactions between Endothelial Cells and Blood Platelets

Whole Blood Based Multiparameter Assessment of Thrombus Formation in Standard Microfluidic Devices to Proxy In Vivo Haemostasis and Thrombosis

Microfluidic assays are versatile tests which, using only small amounts of blood, enable high throughput analyses of platelet function in several minutes. In combination with fluorescence microscopy, these flow tests allow real-time visualisation of platelet activation with the possibility of examining combinatorial effects of wall shear rate, coagulation and modulation by endothelial cells. In particular, the ability to use blood and blood cells from healthy subjects or patients makes this technology promising, both for research and (pre)clinical diagnostic purposes. In the present review, we describe how microfluidic devices are used to assess the roles of platelets in thrombosis and haemostasis. We place emphasis on technical aspects and on experimental designs that make the concept of "blood-vessel-component-on-a-chip" an attractive, rapidly developing technology for the study of the complex biological processes of blood coagulability in the presence of flow.

Platelet-endothelial interactions in atherosclerosis

The pathogenesis of atherosclerosis, the leading cause of morbidity and mortality in the United States, is multifactorial. Many factors that have been shown to influence the development of atherosclerosis also affect the function of the endothelium through soluble or cell-cell interactions. Among these, interactions between platelets and endothelial cells have only recently begun to receive systematic study. This article reviews recent evidence showing how the interaction between platelets and endothelial cells may play a important role in the pathogenesis of atherosclerosis, suggesting an underappreciated potential locus for pharmacologic intervention.

Platelets induce alterations of chemotactic and adhesive properties of endothelial cells mediated through an interleukin-1-dependent mechanism. Implications for atherogenesis

Platelets and alterations of chemotactic and adhesive properties of endothelium play an important role in the pathophysiology of atherosclerosis. We investigated the effect of platelets on secretion of monocyte chemotactic protein-1 (MCP-1) and on surface expression of intercellular adhesion molecule-1 (ICAM-1) of cultured endothelium. Pretreatment of cultured monolayers of endothelial cells with alpha-thrombin-activated platelets significantly enhanced secretion of MCP-1 and ICAM-1 surface expression (P<0.01) that could be inhibited by interleukin-1 (IL-1) antagonists by approximately 40%. Activation of transcription factor nuclear factor-kappaB (NF-kappaB) which regulates transcription of early inflammatory response genes such as MCP-1, was significantly increased in endothelial cells treated with activated platelets via an IL-1 mediated mechanism as determined by electrophoretic mobility shift assay (EMSA) and kappaB-dependent transcriptional activity. In trans-well experiments, alpha-thrombin-activated platelets enhanced IL-1-dependent surface expression of vitronectin receptor (alpha(v)beta(3)) on the luminal aspect of endothelial monolayers and promoted alpha(v)beta(3)-mediated platelet/endothelium adhesion that could be inhibited by the antiadhesive peptides GRGDSP and c(RGDfV). We conclude that activated platelets induce significant changes in chemotactic (secretion of MCP-1) and adhesive (surface expression of ICAM-1 and alpha(v)beta(3)) properties of cultured endothelium. These findings imply a potential pathophysiological mechanism of platelets in an early stage of atherogenesis.

Activated platelets induce monocyte chemotactic protein-1 secretion and surface expression of intercellular adhesion molecule-1 on endothelial cells

BACKGROUND

Platelet/endothelium interaction plays an important role in the pathophysiology of inflammation and atherosclerosis. The role of platelets for monocyte chemotactic protein-1 (MCP-1) secretion and surface expression of intercellular adhesion molecule-1 (ICAM-1) on endothelial cells has been assessed.

METHODS AND RESULTS

Monolayers of human umbilical vein endothelial cells were incubated with nonstimulated or ADP-activated platelets for 6 hours, and secretion of MCP-1 and surface expression of ICAM-1 were determined by ELISA and flow cytometry, respectively. In the presence of ADP-activated platelets, both MCP-1 secretion and ICAM-1 surface expression were significantly increased compared with nonstimulated platelets (P<0.02). Activation of the transcription factor nuclear factor-kappaB (NF-kappaB) determined by electrophoretic mobility shift assay and kappaB-dependent transcriptional activity was enhanced in the presence of activated platelets. In addition, ADP-activated platelets induced MCP-1 and ICAM-1 promoter-dependent transcription. Liposomal transfection of a double-stranded kappaB phosphorothioate oligonucleotide, but not of the mutated form, inhibited MCP-1 secretion and surface expression of ICAM-1 on activated endothelium (P<0.05).

CONCLUSIONS

The present study indicates that activated platelets modulate chemotactic (MCP-1) and adhesive (ICAM-1) properties of endothelial cells via an NF-kappaB-dependent mechanism. Platelet-induced activation of the NF-kappaB system might contribute to early inflammatory events in atherogenesis.

Vitronectin receptor (alpha(v)beta3) mediates platelet adhesion to the luminal aspect of endothelial cells: implications for reperfusion in acute myocardial infarction

BACKGROUND

Platelet interaction with endothelium plays an important role in the pathophysiology of coronary microcirculation. We assessed the role of the vitronectin receptor (integrin alpha(v)beta3) in platelet/endothelium adhesion.

METHODS AND RESULTS

We investigated the effect on platelet/endothelium adhesion of plasma obtained from patients with acute myocardial infarction during reperfusion (before and 8, 24, 48, and 72 hours and 5 to 7 days after direct angioplasty) and with pretreatment with alpha-thrombin (2 U/mL) and recombinant human interleukin-1beta. Platelet/endothelium adhesion was significantly enhanced by approximately 20% after pretreatment of endothelium with patient plasma for 4 hours (P<.05) compared with endothelium treated with pooled control plasma. Plasma-induced platelet/endothelium adhesion was, in part, RGD peptide dependent. Pretreatment of endothelial cells with alpha-thrombin or recombinant human interleukin-1beta enhanced platelet/endothelium adhesion and surface expression of alpha(v)beta3 on the luminal aspect of endothelium (P<.05). The adhesion of platelets, isolated platelet microparticles, and Chinese hamster ovary cells bearing human recombinant alpha(IIb)beta3 (platelet glycoprotein IIb-IIIa) to activated endothelial cells was inhibited by antiadhesive peptides GRGDSP and c(RGDfV) and monoclonal antibodies 4F10, LM609, and 7E3.

CONCLUSIONS

The expression of vitronectin receptor exposed on the luminal aspect of activated endothelium is enhanced and mediates platelet/endothelium adhesion. Vitronectin receptor-mediated platelet attachment to activated endothelium during reperfusion may contribute to reperfusion injury and could be a target for antiadhesive therapy.

Unstimulated platelets evoke calcium responses in human umbilical vein endothelial cells

Interactions between human platelets and human umbilical vein endothelial cells (HUVEC) were studied by monitoring changes in cytosolic [Ca2+]i in both cell types. Confluent monolayers of Fura-2-loaded HUVEC, grown on gelatin-coated coverslips, responded to repeated addition of a suspension of unstimulated platelets by transient increases in cytosolic [Ca2+]i. These platelet-evoked Ca2+ responses were not caused by products secreted from the platelets and were insensitive to inhibitors of platelet activation and/or platelet aggregation. The platelet-evoked rises in [Ca2+]i in endothelial cells, similarly as the thrombin-evoked rises, were blocked by preincubation of HUVEC with the phospholipase C inhibitor U73122 or the Ca2+ influx blocker Ni2+. In contrast, treatment with the protein tyrosine kinase inhibitor genistein was without effect. Video imaging experiments, in which the fluorescence signal was analysed from the individual cells of an endothelial monolayer, showed that only 2-20% of the cells, scattered over the monolayer, responded to the addition of platelets by a transient increase in [Ca2+]i, whereas most of the cells responded to thrombin. This leads to the conclusion that unstimulated platelets can activate HUVEC putatively by mechanical interaction with individual endothelial cells in the monolayer.